Checking a set of hypotheses

Mechanism. The absence of enzymes capable of degrading these specific substrates limits catabolic capacity and causes their accumulation.

Prediction. Introduce exogenous catabolic activities, such as soil bacterial enzymes targeted to the lysosome, against a specific substrate; for example, degrade 7-KC in plaque macrophages in vivo with restoration of efferocytosis. The effect should be unattainable through any intervention targeting damage production, including antioxidants and mitochondrial therapy. Substrate clearance without functional restoration would indicate that waste is an epiphenomenon rather than a cause.

Mechanism. Ovarian aging drives systemic aging in women, with the partly PTEN-AKT/mTOR-dependent rate of follicular atresia providing a controllable target.

Prediction. Test low-dose rapamycin or targeted inhibition of primordial follicle activation, measuring AMH, antral follicle count, age at menopause, and systemic endpoints: epigenetic clocks, bone mineral density, PWV, and cognition. Critical controls are comparison with hormone replacement therapy and Mendelian randomization for age at menopause. If estrogen reproduces the entire effect, the driver hypothesis is redundant and the ovary is merely a hormone source.

Mechanism. Reversibly and partially reduce NTRK3/TrkC receptor expression in a small, traceable cohort of stem cells in the aged subventricular zone until the first division, while preserving NTF3/NT-3 production by the vascular niche and its availability to other cells. Restore TrkC before late differentiation of the progeny.

Prediction. Compare transient NTRK3 reduction in the cohort, prolonged reduction, and local NTF3 reduction in the niche. Check receptor responses and NO formation in stem cells, followed by the reserve and mature neuronal progeny. Restoration of suppression-resistant NTRK3 should eliminate the early effect; a division burst followed by depletion or progeny death would not support sustained enhancement of neurogenesis.

Mechanism. Matching activity during REM sleep to the ensemble of new neurons activated by daytime experience supports retention of synaptic inputs and functional participation of these neurons in memory.

Prediction. In old mice, first establish whether the subsequent sleep activity of new granule cells activated by a novel experience is disrupted with age. If confirmed, compare closed-loop control of this ensemble with activation of randomly selected new neurons, matching pulse number, proportion of active cells, sleep phase, and total activity: only the experience-matched condition will improve retention of synaptic inputs and functional participation of new neurons in memory. Controls are the same stimulation during wakefulness and reversible silencing of the new cohort during testing; the precise beneficial activity pattern remains to be established.

Mechanism. Changing selection within the mitochondrial population by preferentially removing dysfunctional mitochondria and restoring healthy ones.

Prediction. Compare clearance, formation of new mitochondria and their combination in terms of respiratory function and the spread of defective mitochondrial DNA.

Mechanism. Prolonged residence of activated oocytes at the secondary follicle stage forms a secondary reserve, with developmental progression regulated in part by FURIN-dependent oocyte signals.

Prediction. Some oocytes labeled after activation at a young age will participate in reproduction substantially later, and altering FURIN will change the rate of secondary follicle development. Track activated oocytes over time, measuring stage duration and reproductive contribution, and compare intervention in Furin with controls for follicle growth and functional outcome. Exclusive derivation of late functional oocytes from recently activated primordial oocytes would not support the secondary reserve; slower growth alone would not demonstrate preserved fertility.

Mechanism. Peripheral tissue circadian clocks diverge from central clocks. Sarcopenia changes myokines, visceral fat changes adipokines, and the aging gut changes metabolites and immune traffic. The brain receives a chronic sickness signal and increases neuroinflammation and sleep disruption, further desynchronizing peripheral tissues.

Prediction. Measure the phase dispersion of circadian transcripts and metabolites between blood and muscle in mice and middle-aged humans, and additionally the liver and hypothalamus in mice. Test whether a strict schedule of eating within a narrow window, morning light, daytime movement, and darkness and cool temperatures at night reduces this dispersion and subsequent functional loss more than the same calories, light and movement distributed without regard to phase. Add heterochronic parabiosis in mice to examine whether desynchronization is transferred, rather than only young factors. Support would be a reduction in intertissue phase dispersion predicting preservation of cognitive, muscular and metabolic function better than chronological age and rejuvenation of any single organ. A benefit fully explained by calories, sleep or physical activity individually would count against the hypothesis.

Mechanism. The inflammatory macrophage state and reduced neuronal BMP signaling are separate defects. The age-related decline in tissue BMP2 and neuronal signaling is not explained by BMP2 production by muscularis macrophages, so restoring an anti-inflammatory macrophage state does not guarantee restoration of the BMP2 source or neuronal BMP response.

Prediction. In old intestinal neuromuscular tissue, compare correction of the inflammatory macrophage state, restoration of BMP signaling in neurons, their combination, and controls. Residual low BMP responsiveness after successful reduction of inflammation should predict incomplete functional recovery, and its correction should add improvement in coordinated propagation of contractions and transport of contents under repeated challenges. Normalization of BMP signaling and motility by macrophage correction alone, or no added function after confirmed neuronal correction, would refute the hypothesis.

Mechanism. Preservation of the adaptive cycle of stress-induced translational inhibition and subsequent recovery supports lasting function during repeated physiological challenges under ISRIB.

Prediction. Compare intermittent and more continuous exposure regimens matched for basal ATF4 reduction and mean translation during control periods, measuring drug exposure separately. If the regimens produce different dynamic reserves, preserved reserve should explain differences in synaptic plasticity and learning in old animals after repeated challenges. Function may deteriorate despite a favorable basal molecular profile and should correlate with recovery of the adaptive cycle rather than maximal ISR suppression. Independent reversible restoration of the adaptive response, with baseline translation and viability controlled, should preserve function.

Mechanism. Age-associated elevation of basal mTORC1 activity in lymphocytes shifts naive T-cells toward terminal effectors and a PD-1-positive phenotype and impairs formation of Tfh-cells and long-lived plasma cells. Brief mTORC1 suppression during antigen presentation and naive T-cell activation should increase the proportion of naive and Tfh-cells and improve response quality, whereas prolonged exposure interferes with mTOR-dependent effector proliferation.

Prediction. In old mice of both sexes (24-26 months), a short rapamycin pulse from 3 days before to 2 days after vaccination with inactivated influenza virus should produce a stronger antigen-specific response than the same cumulative course 2 weeks after vaccination, a prolonged regimen with the same cumulative dose, or control. Measurements on days 7, 14 and 28 include antigen-specific IgG titers, neutralizing activity, antigen-specific Tfh (CXCR5+PD-1+), plasmablasts, CD8 cytotoxic responses, T-cell PD-1 expression and lymphocyte phospho-S6. An effective pulse within the window but an ineffective course outside it supports phase dependence; a weaker prolonged regimen supports the proposed cost of prolonged exposure.

Mechanism. Cells with normal pH may lose function under the same treatment that restores hyperacidic cells. Correcting the pH distribution, rather than achieving a young mean value at any cost, is proposed to preserve function.

Prediction. Measure calibrated pH in individual HSC and compare an untreated aged pool, brief treatment of the entire pool, and treatment restricted to the abnormal fraction, restoring the original cell proportions and normalizing viable HSC numbers. Selective correction should better preserve long-term multilineage repopulation and clonal diversity during serial testing; identical mean pH after treatment may conceal different repopulation outcomes. Shifting pH in young HSC into the observed aged range without changing lysosome abundance or overall cell death should reproduce part of the functional defect, which subsequent normalization should reverse.

Mechanism. ROCK suppression in activated NSC weakens force-bearing adhesions after activation, while preserving the attachment of quiescent NSC.

Prediction. With the same number of early divisions, targeted weakening of force-bearing adhesions will increase the proportion of descendants reaching the olfactory bulb without loss of the initial reserve. Increased movement speed without an increase in correctly positioned functional neurons would not achieve the intervention's goal. Absence of a benefit in reserve preservation would refute the advantage of targeting.

Mechanism. An inhibitory secretory response following microglial phagocytosis limits neurogenesis, making the timing of stimulation relative to clearance consequential.

Prediction. Moderately enhancing MerTK-dependent clearance and then initiating neurogenic stimulation after the inhibitory secretory response subsides will produce more mature neurons than simultaneous treatment. Compare sequential, simultaneous, and individual treatments in the aged mouse dentate gyrus, measuring debris uptake and completed degradation, uncleared apoptotic cells, and effects of the microglial secretome on progenitors, with integrated labeled neurons at 8–12 weeks as the endpoint. Failure to increase neuronal output through temporal separation, or an effect unrelated to the post-phagocytosis secretory response, would reject the hypothesis.

Mechanism. Reduce IL1R1 expression predominantly in endothelial cells near the subgranular zone of the aged hippocampus before a traced wave of neurogenesis and during early descendant survival, preserving other responses to IL-1.

Prediction. Compare endothelial and progenitor IL1R1 suppression at the same baseline inflammatory burden, checking cell specificity, barrier permeability, and local inflammatory signals. Account for movement, nutrition, and signs of general malaise, and track new-neuron origin, survival, and function at 12 weeks. Greater neuronal output after endothelial suppression supports the hypothesis; unchanged output despite reduced endothelial IL1R1 and an attenuated vascular response indicates that this component is not the main age-related constraint.

Mechanism. An experimental RNA-guided editor locally increases METTL3 methyltransferase activity on EZH2 RNA, restoring EZH2 translation to the range of young cells without changing the DNA sequence. Apply the editor during limited precursor amplification and switch it off before terminal maturation.

Prediction. First map altered m6A sites without prespecifying positions, then compare the targeted editor, a catalytically inactive editor, untargeted METTL3, and a control. Check targeting specificity, EZH2 protein, H3K27me3, labeled clone fates, and mature neurons after 12 weeks; EZH2 suppression should abolish the effect. If confirmed targeted correction and EZH2 restoration do not increase mature neurons, this RNA is not a sufficient limiting link.

Mechanism. Loss of sinusoidal endothelial fenestrations during aging restricts insulin access to the liver; fenestrations may act as a separate temporal filter for insulin pulses.

Prediction. In a model of old endothelium with hepatocytes, compare fenestration restoration with control under pulsatile and constant insulin delivery. Measure insulin behind the barrier and match total insulin exposure at hepatocytes, flow and viability; assess suppression of glucose production as the primary outcome and preservation of pulse amplitude as the additional outcome, while checking nonspecific leakage and secretome effects. If there are no differences at equal exposure, the separate temporal-filter hypothesis is rejected.

Mechanism. Increase expression of functional SLC1A3/EAAT1 at the membrane of radial stem cells in the aged dentate gyrus to the young range when self-renewal resumes, stopping the increase in differentiating progeny, to restore their own glutamate uptake and lipogenesis.

Prediction. Compare stem-cell and surrounding-astrocyte interventions at the same extracellular glutamate level, using transport-inactive SLC1A3 with preserved membrane localization as a control. Assess transport, carbon flux into lipids, clonal composition and the reserve, and assess labeled neuronal maturity after 12 weeks. If transporter delivery and transport recover but lipogenesis and long-term neuronal output do not increase, intrinsic glutamate uptake is not a sufficient limiting factor.

Mechanism. An age-related mismatch in post-transcriptional control delays shutdown of translation of the stem-cell program, interfering with the transition of old progenitors into neurons.

Prediction. Compare RNA, ribosome occupancy and proteins across neurogenesis stages in young and old animals, selecting only targets that actually persist. Compare selective reduction of their translation, reduction of their transcription and control, matching the integrated amount of target protein where possible; selective cessation of residual translation should increase the proportion of traced descendants becoming electrophysiologically mature neurons without depleting the reserve, and restoring the protein from an insensitive RNA should abolish the effect. Absence of RNA–protein mismatch, or an outcome determined by the overall rate of protein synthesis, would reject the proposed mechanism.

Mechanism. The capacity to switch metabolic fluxes and replenish metabolites through alternative pathways determines whether aged NSC can compensate for MPC inhibition.

Prediction. Measure the capacity of aged NSC to switch fluxes before intervention using isotopic substrates and a short reversible test. Compare MPC inhibition alone with inhibition combined with restoration of the identified limiting replenishment pathway, for example from glutamine if tracing identifies that pathway, including separate interventions, young cells and control of overall energy availability. At the same MPC level, baseline compensatory reserve is predicted to better predict long-term neuronal output. Restoring weak reserve should restore the intervention's benefit, whereas cells with sufficient reserve should gain almost no additional benefit. Assess functionally mature progeny and NSC preservation over prolonged observation. Failure of reserve to predict the outcome, or failure of its targeted correction to change the response despite confirmed restoration of flux, would refute the hypothesis.

Mechanism. OPTN-dependent selective autophagy removes HIF-1α during prolonged hypoxia, limiting cellular stress and tissue damage.

Prediction. Disrupting this removal will increase HIF-1α and cellular damage. Directing HIF-1α to the autophagic machinery with a small molecule will reproduce part of the protective effect outside the disc and improve measures of aging in mice. Test by jointly measuring oxygen, autophagic flux, HIF-1α and matrix condition, and separately assess targeted protein removal in old mice using functional measures and survival. Preservation of protection despite disrupted HIF-1α removal would weaken the proposed explanation.

Mechanism. Increase GLS1 glutaminase activity to the young range where deficiency is confirmed in neuronally committed precursors of the aged dentate gyrus at the beginning of growth and differentiation, without increasing it in the quiescent reserve.

Prediction. First measure isotope flux rather than relying only on GLS1 RNA. Compare active enzyme, catalytically inactive enzyme and control, and separately compare cells with high and low baseline flux; assess extracellular glutamate, neighboring neuronal death and mature output of labeled progeny. Increased GLS1 activity without restored flux into the cycle and improved mature neuronal output would refute the mechanism; increased neurotoxicity would make the intervention unsuitable.

Mechanism. An age-related persistence of the quiescent calcium pattern limits activation; correcting its temporal pattern restores neurogenic capacity.

Prediction. In the aged subventricular zone, reproducing the young temporal pattern will increase the yield of mature olfactory bulb neurons while preserving the stem cell reserve, rather than merely increasing the first wave of divisions. Compare this pattern with a temporally shuffled sequence having the same mean level and amplitudes, and with a control. The hypothesis is rejected if there is no age-related difference in calcium dynamics or if the shuffled sequence is equally effective.

Mechanism. The human Δ133p53α isoform attenuates the senescence response, with tissue preservation potentially accompanied by reduced DNA damage markers.

Prediction. Compared with control progeroid mice, p21, IL-6 and γ-H2AX will decrease, and aortic smooth muscle cells and skin structures will be better preserved. A modest increase in median lifespan is possible. Compare inducible isoform expression with transgene and induction controls, assessing tissues, kyphosis and survival, while evaluating DNA damage and tumor outcomes separately from senescence markers. Reduced p21 without tissue preservation would not confirm functional protection; reduced γ-H2AX would not establish genomic safety, and a result in progeria would not establish lifespan extension during natural aging.

Mechanism. Slow intracellular Cl− replenishment limits the reserve between successive secretory responses. Restoring transport in surviving cells could restore this reserve without first increasing their number, provided the driving ion gradient is maintained.

Prediction. Chloride-store recovery time should predict secretory reserve better than the maximum calcium peak. Compare young and old acini during identical cholinergic stimulus series, directly measuring intracellular Cl− and fluid volume; compare old controls, membrane NKCC1 normalization, and stronger stimulation without transport correction. NKCC1 normalization should restore cumulative secretion normalized to viable acinar mass and recovery after a pause. Partially reducing NKCC1 in young acini to the old functional level should reproduce the decline in repeated responses with comparable first responses and calcium signals; restoring transport should restore the reserve.

Mechanism. C3-dependent inflammation supplies a nutrient environment that sustains dysbiosis. Jointly reducing the biofilm and its inflammatory nutrient supply may durably interrupt this loop through changes in the nutrient environment and microbial function, rather than persistence of the C3 inhibitor in tissue.

Prediction. In a 2×2 comparison of control, standardized biofilm removal, short local C3 blockade, and their combination, the combination should improve long-term attachment and alveolar bone loss outcomes over either intervention alone after matching early microbial load and inflammation. Persistence must be assessed only after local inhibitor disappearance and recovery of functional C3 activity. In an ex vivo tissue–microbial system with equal starting biomass, restoring the nutrient composition characteristic of inflammatory tissue breakdown without returning the drug should re-establish a sustained dysbiotic state, and removing that nutrient supply again should extinguish it.

Mechanism. Sustained regeneration requires both niche softening and restored adhesion that retains hair stem cells in the niche.

Prediction. Compare control, stiffness normalization, adhesion restoration and their combination in old follicles, first confirming that the interventions independently change stiffness and adhesion. Track labeled clones, their exit from the niche, the stem cell reserve and hair growth over two cycles, with random allocation and blinded assessment. The combination should outperform each intervention alone in sustained growth without reserve depletion. Equal benefit from softening without adhesion restoration would refute the proposed necessity of adhesion; retention without renewed growth would separate reserve preservation from function.

Mechanism. The relationship between mechanical loading and the local chondrocyte clock phase determines cartilage resistance to damage through alignment of loading with recovery capacity.

Prediction. In cartilage explants from young and old animals, establish different local phases under the same subsequent conditions and apply identical loading at the same external time, then repeat at the opposite phase, recording the actual phase throughout. The protective window, assessed through mechanical properties, matrix loss and chondrocyte viability after repeated cycles, should follow the local phase shift; weakening adult local clock function should reduce phase dependence. In old animals, optimal external timing should differ with cartilage phase, while a similar phase relationship should predict protection.

Mechanism. The direction of the effect of a proangiogenic intervention depends on the local balance between filling and resorption. Increased vascular support may sustain incomplete remodeling when osteoblast capacity is insufficient to fill resorption cavities.

Prediction. First confirm that a limited endothelial DACH1 pulse changes post-arterial vessels and perfusion in old animals, then compare DACH1 or control with or without prior enhancement of osteoblast reserve in a factorial experiment including both monotherapies. Prior restoration of bone-forming reserve should change the outcome of endothelial DACH1 enhancement, improving work to fracture and closure of resorption cavities. Equal improvement in strength at low and high initial osteoblast reserve, or failure of prior osteoblast support to eliminate incomplete remodeling despite confirmed intervention effects, would refute the hypothesis.

Mechanism. More accurate DNA repair reduces the accumulation of somatic mutations and structural rearrangements, slowing the emergence of functionally defective clones and preserving organ reserve. SIRT6 functions involved in double-strand break repair are a promising starting point, provided they are separated from the protein's metabolic effects.

Prediction. Compare an intervention that increases repair accuracy with a control and a variant that alters the same regulator's non-repair functions in adult animals. Direct measurements of new mutations and structural rearrangements in individual cell clones, rather than γH2AX alone, should show that slower error accumulation precedes preserved function across several tissues and reduced frailty. The early benefit should be slower emergence of functionally defective clones, followed by preservation of organ reserve, and should persist after accounting for changes in cancer risk; existing mutations will not automatically disappear.

Mechanism. Impaired primary-cilium signaling limits the response to SHH, and restoration of ciliary transport restores signal reception.

Prediction. When the defect has been identified beforehand, combining restoration of ciliary transport with limited SHH signaling will produce more functional neurons than either intervention alone, with almost no additional benefit in cells with intact signaling. Measure cilia, localization of signaling components, and the GLI response in young and old dentate gyrus models, without treating cilium absence during mitosis as a pathological defect. In old models with confirmed impairment, compare transport restoration, SHH, and their combination, tracking mature progeny and NSC preservation. Absence of the corresponding defect or persistently weak neuronal output after signaling restoration would reject the mechanism; excessive proliferation without proper maturation does not count as success.

Mechanism. Increasing translational accuracy reduces the formation of newly mistranslated proteins independently of the total rate of protein synthesis. Accumulated persistent protein damage may limit the functional benefit of late induction, and improved clearance is a possible mediator to be measured.

Prediction. In Drosophila, induce a validated high-accuracy variant after development, at midlife or late in life, confirming incorporation of altered RPS23 into active ribosomes and controlling normal protein dosage. A factorial comparison of normal and increased accuracy at normal and moderately reduced translation should show an independent benefit of increased accuracy for motor function and lifespan in both sexes when total translation is matched. Midlife induction should provide greater functional benefit than late induction with the same suppression of new errors; a benefit explained entirely by reduced translation, reduced feeding or the presence of the alteration during development would refute the hypothesis.

Mechanism. The composition of autophagic cargo determines the benefit of clearance for old neurogenesis: preferential removal of damaged material supports neuronal maturation, whereas removal of functionally necessary organelles changes the outcome despite equal total flux.

Prediction. Measure completed lysosomal turnover of several cargo types, then compare states with equal total flux but different aggregate capture while controlling mitochondrial mass, respiration and cell death. Maturation of new neurons should improve only with preferential removal of damaged material; test causality by restoring the relevant cargo adaptor previously established in this system, and separate the autophagic role of FOXO3 from its effects on the cell cycle. If total flux fully explains the outcome regardless of cargo, the hypothesis is rejected.

Mechanism. Neighbors leaving quiescence simultaneously may create excessive mutual inhibition and locally deplete the reserve; staggering their activation is proposed to avoid these effects. Natural age-related synchronization has not yet been demonstrated.

Prediction. Two niches with identical mean ASCL1 expression and identical numbers of cells in each phase will produce different numbers of mature neurons if those phases are arranged differently in space. In a three-dimensional niche of old mouse NSC, impose identical individual ASCL1 pulses and compare neighboring groups of in-phase cells with phases mixed among neighbors, preserving their overall distribution. Control density, nutrition, and contacts, and measure HES1/Notch and each clone's fate; after confirmation, test in the old SVZ with progeny tracing to the olfactory bulb. The criterion is cumulative output of surviving functional neurons and NSC preservation, rather than the first division peak. The hypothesis is rejected if rearranging phases does not change the outcome when individual-cell activation is truly identical.

Mechanism. A delayed miR-124–PTBP splicing switch impairs the production of appropriate isoforms after neuronal gene transcription has begun.

Prediction. Compare young and old descendants at the same stage using long RNA reads and protein isoforms. Restore the physiological miR-124 profile only in previously labeled neuronally committed descendants and test reversal of the effect with miR-124-resistant PTBP1. Input formation, electrical maturation, and survival are predicted to improve with equal numbers of cells born; overall expression changes will explain the result less well than isoform balance.

Mechanism. A correctable prediction error during learning supports integration of new neurons through cortical feedback to the new cohort.

Prediction. In aged mice, compare a gradually changing but learnable odor–outcome relationship with a fully predictable task and a random, unlearnable relationship, matching odors, presentation counts, reward, movement, and overall difficulty using independent control groups. Specifically, learnable prediction error should increase selective remodeling of inputs to new neurons and improve transfer of discrimination to new mixtures; selectively silencing cortical feedback or the new cohort should abolish the advantage. Assess functional integration at comparable new cell numbers and ages; an effect determined only by excitation, reward, or stimulus count refutes the hypothesis.

Mechanism. Alternating periods of reduced activity of mTOR, a regulator of cellular growth, with periods of recovery allows damage clearance and preservation of muscles and regeneration.

Prediction. Compare regimens at comparable exposure, measuring survival, immunity and tissue recovery, to test whether alternating growth and repair is more effective than continuous growth suppression.

Mechanism. Reducing cell growth removes both pathological activation and the compensation needed after neighboring podocytes are lost. Prior unloading should shift the boundary between beneficial suppression of chronic signaling and loss of protective adaptation; unloading may be insufficient when initial coverage is already critically depleted.

Prediction. In old animals of both sexes, compare reduced intraglomerular load, moderate temporary mTOR suppression, their combination, and controls, including unloading before suppression versus simultaneous initiation. Prior unloading should improve podocyte preservation and reduce progression of sclerosis while maintaining filtration function, with confirmed unloading and comparable mTOR suppression. No effect of sequence, or an effect explained entirely by unloading without an interaction with mTOR, would refute the hypothesis.

Mechanism. Circulating factors and senescent vesicles/SASP systemically maintain the old phenotype and transmit senescence between tissues.

Prediction. Dissect heterochronic parabiosis using neutral plasma dilution in old animals, administration of old plasma to young animals, and transfer of labeled EV, tracking organs with p16/p21 reporters. Dilution should produce an effect comparable to parabiosis, indicating that removal of old signals, rather than addition of young ones, is responsible. If dilution does not affect tissue whose cells are already fixed in their state, aging is cell-autonomous after all.

Mechanism. The pathological ovarian state returns and physiological uterine signaling recovers at different rates, allowing uterine recovery before ovarian benefit is lost. The matrix is considered a possible carrier of the longer-lasting ovarian effect, without assuming an exclusive causal role.

Prediction. First confirm ovarian benefit from a reversible neutralizing agent selective for mouse IL-11 and identify a prespecified interval after withdrawal when endometrial IL-11 responses and functional decidualization have recovered while reduced ovarian stiffness and improved output of competent oocytes persist. A limited course followed by mating in this confirmed window should increase live-born offspring per randomized female over a fixed mating period, including zero outcomes, compared with both an age-matched control and continuation of the same initial blockade through implantation. Embryo transfers should show retained improvement in viable embryo output after withdrawal and acceptance of standardized embryos no worse than the age-matched control, whereas continued blockade with confirmed uterine activity should lose part of its advantage at decidualization or implantation.

Mechanism. Temporarily increase local MFGE8 expression in radial stem cells of the aged dentate gyrus that remain after the first neurogenic division and are returning to quiescence, between the first and second experimentally tracked waves of neurogenesis.

Prediction. Compare an increase after the first wave, an increase before it and control. Assess local MFGE8 and mTORC1 in stem cells, tracking the same clones, return to quiescence and mature progeny from both waves, while distinguishing the number of remaining stem cells from their ability to produce neurons again. If MFGE8 increases the quiescent reserve but that reserve does not produce a second productive wave, the hypothesis of preserving a functional reserve is incorrect.

Mechanism. The suppression phase promotes removal of damaged cellular components, while the interval allows protein synthesis and tissue repair.

Prediction. Randomly compare intermittent treatment, continuous treatment and control in naturally old mice of both sexes, using regimens established in a separate pilot to provide comparable total drug exposure and confirmed mTORC1 suppression during treatment and signal recovery during intervals. Intermittent treatment should produce better recovery of specific muscle force after standardized exercise, measured blindly after the same predefined withdrawal period, accounting for baseline force, nutrition, mass, sex, toxicity and tissue drug exposure. No functional advantage with confirmed signal alternation and sufficient precision would limit the central prediction; an advantage explained by lower exposure or toxicity would support regimen optimization but not the specific mechanism of alternating clearance and recovery.

Mechanism. Aging is a programmed reduction in expenditure on repair: the organism evolutionarily stops allocating resources to maintenance after the reproductive window. The mTOR / IGF-1 / AMPK / sirtuin signaling axes constitute a regulatory switch that can be influenced by rapamycin and calorie restriction.

Prediction. Multi-target interventions in mice should produce additive rather than saturating increases in lifespan.

Mechanism. Partially and reversibly reduce TGFBR2 expression in remaining stem cells with an elevated response to TGF-β during cell-cycle entry, restoring the receptor before late differentiation.

Prediction. Compare brief and permanent TGFBR2 reduction, ligand neutralization in the niche, and control; measure stage-specific SMAD responses, vascular condition, clonal output, and mature descendants. Independent receptor restoration should restore sensitivity to niche inhibition. If confirmed reduction of the SMAD response only accelerates division without increasing mature neuron numbers while preserving the reserve, the proposed intervention does not restore neurogenesis.

Mechanism. NL2-dependent fast perisomatic inhibition improves the temporal precision of inhibition and thereby the selectivity of new neuronal responses.

Prediction. First compare inhibitory response latency and variability in tracked new neurons of young and old mice. Then compare NL2 restoration with increased overall inhibitory strength under conditions matched for integrated charge, controlling for maturation stage and the chloride gradient. More precise and sparse responses to similar contexts are predicted without reduced survival of the new cohort, and behavioral improvement should depend on that cohort's activity. The hypothesis is refuted if equal charge produces equal function regardless of inhibition speed.

Mechanism. Somatic clonal evolution allows a few locally competitive clones to populate organs, with DNMT3A/TET2 in blood, NOTCH1 in the esophagus, and mosaicism in the endometrium and liver given as examples.

Prediction. Thin expanding clones in old mice through clonal steering using antibodies against clone-specific surface markers, conditional niche deprivation, or base-editing correction of the driver, measuring lymphoid output, systemic inflammation and survival. The effect of thinning is predicted to exceed any intervention targeting the average cell in the same tissue. If clone removal does not change organ function, clonality is a marker rather than a driver.

Mechanism. Interrupting prolonged VCAM1-dependent contact between surviving proximal tubular epithelial cells and immune cells breaks a failed-repair loop and permits the surviving epithelial cells to redifferentiate.

Prediction. Adult-induced deletion of Vcam1 restricted to proximal epithelium after the established early injury phase should preserve early injury clearance while interrupting prolonged immune interactions around surviving tubules. Lineage tracing should show the same surviving cells recovering mature transport programs, with preservation of measured filtration function at a late time point. Reduced immune contacts without epithelial maturation and improved kidney function, benefit confined to endothelial intervention, or removal of damaged cells instead of their recovery would not support the proposed mechanism.

Mechanism. Preserving the early NKCC1-dependent chloride gradient in new granule neurons maintains the early excitatory action of GABA, followed by a normal transition to the KCC2-dependent mode.

Prediction. Preserving this early gradient with the subsequent normal transition will improve dendritic development and integration compared with uniform early correction of all cells. In old mice, label one cohort of new neurons and compare early, late, and maturity-dependent changes in chloride transport, measuring the GABA reversal potential, incoming synapses, survival, and recruitment during tasks requiring discrimination between similar contexts. Failure to improve integration at a comparable activity level of the mature network would not support the mechanism; prolonged maintenance of an immature state does not count as success.

Mechanism. The ratio of matrix relaxation time to the duration of cellular force has a range favorable to neuronal differentiation.

Prediction. Reversibly changing the speed of the actomyosin cycle should shift the optimal rate of matrix relaxation accordingly, distinguishing this hypothesis from the explanation that making the environment softer is sufficient. Test young and old mouse NSC in three-dimensional gels with identical initial stiffness and ligand density, comparable substance transport, and different relaxation properties; measure cellular forces, spectrin–EGR1, clonal neuron output, and electrical maturation, separating the interaction between the two time parameters from the direct effects of the actomyosin intervention.

Mechanism. The proposed determinant is the balance between mature BDNF and proBDNF resulting from BDNF processing, with a role for the ratio distinct from total trophic factor dose.

Prediction. In the aged subventricular zone, compare CPE correction, increased total BDNF and direct correction of the ratio of forms. Confirm extracellular concentrations of both forms and include a catalytically inactive CPE control. Measure survival, migration, synaptic responses and selectivity of new olfactory bulb neurons. Correction of the ratio is predicted to reproduce the CPE effect, and maintaining a pathological ratio is predicted to abolish it. If the benefit follows only the amount of mature BDNF independently of proBDNF, the hypothesis of an independent role for the ratio is refuted.

Mechanism. Increase expression of the functional RNA-binding protein FMR1/FMRP to the young range when an age-related deficit is detected, in dentate gyrus neural progenitors that retain the ability to divide, during the transition from amplification to neuronal differentiation. GSK3B is proposed as a mediator.

Prediction. First confirm an FMRP deficit at the protein level. Compare functional protein with an RNA-binding-defective variant and a control, accounting for the initial number of divisions; measure GSK3B, neuronal and glial output, and descendant integration. Restoring GSK3B to its elevated initial level will test the proposed mediation. The expected result is an increased neuronal proportion without more divisions; absence of an FMRP deficit limits applicability, and failure to improve the neuronal proportion after correcting the deficit refutes its causal role.

Mechanism. Perineuronal nets composed of chondroitin sulfate proteoglycans stabilize adult circuits and help preserve memory. With age, these nets become excessive and, together with activated microglia and astrocytes, lock in unsuccessful patterns, limiting the ability to rewrite connections.

Prediction. Briefly and locally weaken perineuronal nets in one hippocampal or cortical region in old mice using an enzyme already used in plasticity research or an equivalent, without chronically destroying the nets. Compare with a global anti-inflammatory regimen and stimulation of neurogenesis, measuring region-dependent task learning, retention of old skills, and recovery after minor focal injury. Support would be improved new learning and recovery without erasing old skills or increasing seizure susceptibility, with the plasticity window closing again; failure to close predicts memory chaos rather than benefit. Impaired stable memory after any removal of inhibition, or an effect indistinguishable from general reduction of neuroinflammation, would count against the hypothesis.

Mechanism. Excess surrounding hyaluronan inhibits the macrophage response to renewal signals, whereas cell-surface hyaluronan and its interaction with CD44 support alveolar macrophage survival, and surface hyaluronan participates in alveolar epithelial repair. Spatial separation of these pools should allow relief of the proliferative inhibition while preserving the protective cell coating.

Prediction. In a reconstructed alveolar system containing old macrophages and epithelial cells, independently vary extracellular and surface-bound hyaluronan, with the most discriminating comparison holding total polymer amount constant while changing its location. Preserving the cell coating should support survival, while reducing the surrounding excess should facilitate the renewal response, producing sustained recovery of functional macrophage numbers after a moderate sterile challenge together with preservation of the epithelial barrier. Effects determined solely by total polymer mass or size, or an unavoidable loss of survival and barrier integrity when proliferation is restored, would refute the hypothesis.

Mechanism. Relieving CD22-dependent inhibition restores selective myelin debris clearance, enabling remyelination and restoration of axonal conduction as the key functional mediator. The combination of high CD22 and accumulated myelin debris is proposed to predict response.

Prediction. Stratify old models by CD22 and myelin debris burden and compare a microglia-restricted intervention with a control, separately measuring uptake of debris and synapses, myelin fragment clearance, remyelination, axonal conduction, and cognition. Debris clearance should be followed by restored myelin and conduction; behavioral improvement should not remain fully intact when remyelination is independently prevented. Include a separate control for preventing remyelination without the main intervention and exclude independent tissue damage from that manipulation.

Mechanism. Immobilized CD39 positioned around the signal source, while preserving access to NSC, creates a spatial boundary for ATP degradation. The proposed effect involves limiting ATP exposure of neighboring microglia, with dependence on microglial P2X7 to be tested.

Prediction. At identical temporal ATP exposure directly at NSC, a spatially restricted signal will yield more mature neurons than a diffuse signal. Test this in a three-dimensional niche containing aged mouse NSC, astrocytes and microglia, with inactive-enzyme and equal-enzyme-activity controls lacking a spatial boundary. Measure ATP on both sides and separately control ADP, AMP and adenosine. Supporting results require increased survival and functional maturation of new neurons while preserving the reserve; an effect entirely explained by hydrolysis products would refute the hypothesis.

Mechanism. A selectively smaller initial mitochondrial pool in the future neuron is beneficial only during fate choice; normal expansion of energy capacity is subsequently required.

Prediction. With identical total mitochondrial quantity and quality, asymmetric distribution will produce more progenitor–neuron pairs than equal distribution. Track divisions of young and old mouse NSC while measuring mitochondrial mass, membrane potential, and damage separately, then reversibly reposition organelles to alter their distribution during division without suppressing respiration throughout the cell; compare clonal neuronal output, self-renewal, and subsequent functional maturation, and confirm the result in the neurogenic niche of an old mouse.

Mechanism. Faster measurement using multimodal biological clocks would overcome the time required to test hypotheses through lifespan studies.

Prediction. The ranking of interventions by the clocks after 3 months should predict their ranking by actual lifespan.

Mechanism. Restoration of neuronal competence while retaining original cellular identity serves as the stopping criterion for partial reprogramming.

Prediction. Stopping after neuronal competence is restored will yield more correctly integrated neurons per original clone than a fixed course identical for all cells or continuation until the maximal shift in age markers. Compare exposure durations, functional differentiation, chromatin accessibility, and identity preservation in old NSC; select the stopping criterion on a training set and test it on an independent set. Then test a local intervention in the old SVZ, tracing clones to the olfactory bulb and assessing maturity, integration, pool preservation, and pathological proliferation. The proposed control strategy is not supported if neuronal competence does not predict later neuronal output better than course duration or an age measure.

Mechanism. Selectively reducing NSC sensitivity to PV-dependent ГАМК signaling may release excessive quiescence while retaining the inhibitory network's support for new neurons.

Prediction. First confirm an excessive tonic ГАМК response in old NSC. Compare reversible modification of the corresponding receptors only in NSC with suppression of PV interneurons and a control, achieve comparable early NSC exit from quiescence, and then restore NSC sensitivity. At equal initial activation, the targeted intervention is predicted to yield more surviving, correctly integrated neurons and fewer disturbances of network activity. Check receptor composition and currents at each stage rather than inferring the effect from total ГАМК content.

Mechanism. Endothelial VCAM1 suppression reduces a harmful age-related vascular signal, while preservation of VCAM1 on stem cells maintains their attachment in the SVZ.

Prediction. With an equal reduction in endothelial VCAM1, preserving VCAM1 on NSC will improve retention of the stem cell reserve and late neuronal yield. Compare Vcam1 suppression restricted to endothelium, restricted to NSC, and in both compartments in old mice, analyzing the SVZ and dentate gyrus separately. If suppression in both compartments preserves the reserve and produces equal or better late yield, the need to preserve stem cell VCAM1 in this model is not supported.

Mechanism. An intracrine VEGF signal within old stem cells may support maintenance of the neurogenic reserve independently of extracellular VEGF and vascular changes.

Prediction. Compare restoration of intracellular signaling in old stem cells, increased extracellular VEGF, and control, checking localization and possible construct leakage and measuring vascular permeability, perfusion, and density. Perform the causal comparison only if intracellular signaling can be separated from secretion. Restoration should produce more reactivatable clones and functional neurons without angiogenesis; the proposed mechanism is not supported if improvement occurs only with vascular remodeling or no intracellular deficit is found.

Mechanism. Slow removal of RNAs encoding TGF-β pathway components may prolong the response after the extracellular signal declines.

Prediction. Expose young and old NSC to the same TGF-β pulse, completely remove it, and measure the decay of specific transcripts, m6A, YTHDF2 binding, and the duration of the SMAD response. Compare targeted acceleration of persistent RNA removal with extracellular signal blockade alone, without globally changing m6A metabolism. Restoring the normal decay rate is predicted to shorten the activation delay and increase mature neuron output after a standard stimulus while preserving the ability to re-enter quiescence.

Mechanism. The temporal organization of NO during changes in inflow and opposing pressure determines pump adaptation. Restoring the adaptive range is proposed to provide greater functional benefit than simply increasing resting pump activity.

Prediction. Compare selective iNOS normalization, general NOS blockade, and a control by measuring net volume transported through vessels with intact valves over a complete cycle of variable loading. Selective normalization should improve transport and adaptation; complete NO suppression may increase contraction frequency while impairing adaptation. Reproducing the measured aged persistent NO background in young tissue should produce different transport from pulsed delivery at comparable total exposure, despite the same mean signal, and removing the persistent background should restore adaptation.

Mechanism. Discoordination between soluble and membrane-bound DLK1 may limit the response of the old stem-cell reserve; restoring both components may support self-renewal and sustained neuronal output. Increased self-renewal may delay immediate differentiation.

Prediction. Measure both forms and individual clone responses in the old subventricular zone, then compare restoration of the soluble component, the membrane component, both, and control. Test the protein forms directly and confirm their localization without changing the entire imprinted locus. Joint correction should yield greater cumulative output of functional olfactory bulb neurons over several waves while preserving the reserve; the hypothesis is rejected if the membrane component does not limit the response or soluble DLK1 is sufficient in all cases.

Mechanism. The thymus, where T-cells mature, begins shrinking after puberty, and by 50–60 years its functional tissue has almost disappeared. Loss of thymic output narrows naive T-cell diversity and impairs recognition and removal of senescent cells, accelerating tissue aging early. Thymus restoration would act as a continuously operating “endogenous senolytic” and could be better than periodic courses of senolytic drugs.

Prediction. Old animals with a regenerated thymus should have fewer senescence markers in the liver, kidneys and lungs after several months. Removing T-cells should eliminate the effect.

Mechanism. Antigen-independent conversion of naive CD8⁺ T cells into virtual memory cells, together with thymic involution, depletes the local naive pool available for tumor antigen recognition.

Prediction. Thymic regeneration following suppression of androgen signaling will replenish naive CD8⁺ cells in lymph nodes, strengthen the tumor-specific response and improve the effectiveness of immune checkpoint blockade. Compare sex, age, lymph node cellularity, naive and virtual memory cells, tumor antigen responses and tumor growth in mice, assessing intervention effects together with thymic production of new T cells. An improved response without replenishment of the naive pool would require a different mechanistic explanation.

Mechanism. The benefit of reducing microglial tau-containing vesicle release depends on preserving the protective function of PBM, which regulate cerebrospinal fluid flow dynamics and whose function changes with aging.

Prediction. In old mice with tau pathology, use a 2×2 design combining reversible, verified microglia-restricted suppression of the nSMase2/tau-containing vesicle formation pathway with intact or selectively impaired PBM, plus a separate PBM-function rescue. At equal suppression of the microglial mechanism and equal initial tau burden, intact or restored PBM should produce greater reductions in extracellular tau seeding activity and neuronal loss. PBM status should predict functional benefit; an independent benefit of PBM rescue without the predicted interaction would refute the hypothesis.

Mechanism. An early oxidative signal initiates a protective transcriptional program and autophagy. A later antioxidant intervention accelerates the return to a physiological state and reduces damage accumulation between pulses while preserving the already initiated cellular maintenance program. In some aging tissues, protection may still be inducible while recovery after stress is too slow; the antioxidant phase is intended to shorten this late adverse phase.

Prediction. There should be a time window in which an antioxidant is beneficial: administration too early weakens adaptation, whereas administration too late fails to prevent a substantial part of the damage. If the benefits and costs cannot be separated in time, alternation will offer no advantage over a prooxidant pulse alone. The effectiveness of alternation should be predicted better by recovery speed after a standard weak pulse than by the baseline level of oxidative stress, which can be tested by comparing young and middle-aged flies. The initial pharmacological test would use a menadione preparation, such as water-soluble menadione sodium bisulfite, MBS, followed by N-acetylcysteine, NAC, in adult flies of both sexes analyzed separately on a long-lived genetic background, with the key result repeated on another background. The proposed result is increased lifespan causally dependent on the timing of redox exposure, with reduced damage and preserved cellular material processing.

Mechanism. Neurotrypsin degrades the NMJ-specific form of agrin, LRP4/MuSK signaling weakens, and Schwann cells age, producing denervation and NMJ instability. This explains why myostatin inhibitors produce mass without an adequate increase in strength.

Prediction. In a head-to-head test in old mice, compare AAV-DOK7 or a MuSK agonist with a myostatin inhibitor, with a third group receiving the combination. Primary endpoints are specific force (force/CSA) and innervation measures (CMAP, MUNE), rather than mass. The NMJ arm should outperform on strength despite a smaller increase in mass; the combination should be synergistic because the anabolic agent is needed only after innervation is restored.

Mechanism. Reversibly reduce FTO expression during activation only until the first neurogenic division, then restore its baseline level in neuronal descendants before postmitotic maturation.

Prediction. Compare reversible reduction, continuous reduction, and a control with the same early degree of suppression, verifying restoration of the protein and RNA modifications. After 12 weeks, measure labeled mature neurons, their electrophysiology, and the remaining stem cell reserve; independent FTO expression should rescue the late defect. If restoring FTO does not improve maturity and survival relative to continuous suppression at equal early activation, the proposed separation of stages is incorrect.

Mechanism. CCL11 binds CCR3 on microglia, and chronic signaling drives a senescence-like, proinflammatory state that reduces neuronal precursor survival and differentiation in the dentate gyrus, decreasing neurogenesis and memory. Brief blockade during precursor activity should remove this inhibition when neurogenesis is occurring.

Prediction. A short local CCL11/CCR3 antagonist course during two weeks of enriched environment should restore neurogenesis, whereas a chronic course at the same dose should not. Compare these regimens with treatment outside the window and control using DCX- and BrdU-positive cells, ex vivo neurosphere clonogenesis, microglial phenotype, contextual fear conditioning and spatial learning. Microglia-specific CCR3 blockade should reproduce the effect, unlike blockade on precursors, and local CCL11 addition during the window should abolish the benefit.

Mechanism. Restoration of CD40L in the appropriate T-cell–B-cell contact may be sufficient to correct deficient help and improve affinity selection despite persistence of other age-related changes.

Prediction. In old syngeneic recipients given equal numbers of old antigen-specific CD4+ cells, reversible physiological correction of CD40L should improve monoclonal antibody affinity and subsequent memory compared with control treatment, at similar initial numbers of responding B-cells. The additional benefit should depend on CD40 on B-cells in a temporally limited or mosaic control that preserves a measurable baseline response. Increases only in antibody titers or germinal center size, or a requirement for simultaneous BCL6 correction or B-cell replacement, would reject the proposed sufficiency of CD40L.

Mechanism. Candidate actions are improving complete fatty acid oxidation and muscle energy production in the acylcarnitine direction; enhancing kynurenine processing through KAT if this increases fatigue resistance; changing the metabolism of specific phosphocholines to improve membrane composition and muscle cell function; and reducing the formation or action of specific compounds of glutamine with fatty and aromatic acids if their harmful effects on muscles are confirmed. Microbiota enzymes may be targets for some compounds. OR10J5 activators may be included among candidates, but their influence on KAT remains hypothetical.

Prediction. Confirm the molecules' chemical structures and the effects of changing their metabolism in cultured human muscle tissue, then test candidate drugs in tissue from several donors. Test pairs at different concentrations against their individual components, accounting for toxicity and concentrations achievable in the organism, and separately assess whether the combined effect exceeds the expected sum of effects; add a third drug only if it provides an additional benefit. Block proposed mechanisms and remove individual components to determine their contributions. Compare the combination with each component, a control group and exercise in old mice using random allocation and blinded assessment of strength, fatigue, recovery, muscle drug concentrations and side effects, including drug interactions. Success requires a minimal combination that consistently improves muscle function more than individual components with acceptable tolerability; changes in blood markers alone are insufficient.

Mechanism. Dynamic coupling of oxygen release with rapid changes in erythrocyte deformability and passage through capillaries.

Prediction. At matched P50, mechanical correction should improve oxygen delivery during short, repeated demands, particularly in a heterogeneous capillary network. Compare control, hemoglobin-affinity correction, mechanical-response correction and their combination in erythrocytes from old donors, then assess tissue oxygenation in old animals at comparable recorded neuronal activity. No additional benefit from mechanical correction after matching P50, or differences explained by hematocrit, vascular effects of residual drug or reduced brain demand, would refute the hypothesis.

Mechanism. Persistent activity of growth pathways after development continues to drive anabolic signaling, producing hypertrophy, fibrosis, senescence and thrombosis. Changing the cell's operating mode is sufficient without repairing the cell.

Prediction. Test the dose dependence of rapamycin, including intermittent dosing, against reversible phenotypes, left ventricular hypertrophy, fibrosis and SASP, and damage markers, mutations, crosslinks and lipofuscin. Phenotypes are predicted to regress while the damage burden remains unchanged, and geroprotective potency is proportional to the reduction in the signal integral rather than antioxidant activity.

Mechanism. Selective restoration of critically short telomeres in cells with an intact genome and antitumor protection.

Prediction. Test whether selective restoration outperforms nonselective restoration in function and cancer safety.

Mechanism. Insufficient stria vascularis reserve causes a dynamic loss of the cochlea's electrical state during repeated stimulation. Restoring KCNJ10/Kir4.1 in intermediate cells is proposed to restore this electrical reserve and subsequently improve hearing function.

Prediction. After independent phenotyping, randomly assign old animals to Kcnj10 correction or control within predefined groups with preserved or impaired reserve. Use repeated sound stimulation validated as non-damaging at the studied age, with procedural and delivery controls, adult-onset targeting of the required cells and verification of channel localization. The primary outcome is an interaction between the baseline dynamic defect and the intervention's effect on recovery of the auditory response after repeated stimulation. Support requires restoration of measured electrical reserve followed by functional improvement. Absence of the dynamic defect would leave the hypothesis unsupported; restored potential without an improved auditory response would show that the defect was not a sufficient limiting factor; equal responses in animals with preserved and impaired reserve would fail to confirm the proposed selection marker.

Mechanism. Preserved nerve-associated macrophages are required for restored norepinephrine to overcome catecholamine resistance after MAOA blockade.

Prediction. In a 2×2 experiment comparing MAOA blockade or control with preservation or reduction of these macrophages, MAOA blockade should provide less benefit after macrophage loss, measured by glycerol and fatty acid release under identical stimulation with equally restored norepinephrine. Equal benefit would refute the dependence; severe damage producing a functional floor would make the experiment uninformative. Verify removal selectivity, viability and the independent effect of cell loss.

Mechanism. Elevated background membrane conductance in the conducting segment may dissipate the signal, allowing restoration of the local capillary response without delivering a sufficient dilation signal to the arteriole. Excess background SK/IK conductance is the proposed explanation to be tested in the old cerebral network.

Prediction. At equal local hyperpolarization, measure voltage at successive distances toward the feeding arteriole to establish whether old animals have a transmission defect independent of initiation. If confirmed, test capillary PIP2/Kir2.1 restoration together with selective local normalization of excess background SK/IK conductance in the conducting segment. Conduction distance should predict functional hyperemia after equal restoration of the local response, and improving transmission should add benefit where transmission limits the response, assessed by local blood flow and oxygen delivery at comparable neuronal activity.

Mechanism. Temporarily increase KDM6B/JMJD3 H3K27-demethylase activity to the young range in neuronally committed progenitors of the aged subventricular zone, after departure from the stem-cell state and before terminal maturation, to remove the proposed H3K27me3 barrier.

Prediction. Isolate cells with delayed differentiation and map H3K27me3. Compare late and early pulses of equal magnitude, catalytically inactive KDM6B, and a control. Check neuronal gene opening, cell-cycle completion, and mature olfactory bulb neurons; DCX-positive cells alone are not a sufficient result. The late pulse is expected to increase functional descendants while preserving quiescent cells. If removing a confirmed H3K27me3 excess does not restore the transition and mature neuronal output, the proposed epigenetic barrier is not the main one.

Mechanism. With age, macrophages, endothelium, and pericytes become less effective at recognizing and removing apoptotic debris, oxidized LDL-like particles, and collagen fragments. Uncleared material maintains background activation of TLR, RAGE, and complement, creating a vicious circle in which inflammation further impairs clearance.

Prediction. In old mice, compare (1) enhanced phagocytosis through temporary transplantation of young macrophages or activation of merocytic receptors without systemic immunosuppression, (2) local enzymatic clearance of a specific debris class, such as advanced glycation end products or truncated collagen, in skin and a blood vessel, and (3) a vehicle control. Measure intimal thickness, vessel stiffness, wound closure rate, and senescence markers in situ, rather than only blood cytokines. In human plaque and aged dermis samples, test whether local debris burden correlates with senescent cell density after adjustment for chronological age. Support would be local clearance reducing senescence and restoring function in treated tissue while neighboring untreated tissue in the same animal remains old. Evidence against would be clearance removing a marker without changing function or senescence.

Mechanism. Selective suppression of IL-17F reduces its contribution to age-related barrier deterioration while retaining protective IL-17A signaling after injury.

Prediction. Compared with IL-17A blockade, dual blockade and control in old skin, IL-17F blockade should produce barrier recovery comparable to dual blockade, assessed by transepidermal water loss after standardized superficial injury, while better preserving the protective response after injury. Additional epithelial loss of responsiveness to IL-17A should eliminate this protective advantage. Neutralization must be validated separately for A/A, F/F and A/F; an effect from a blocker that also suppresses A/F cannot be attributed exclusively to F/F.

Mechanism. Impaired OTX2 uptake by supporting astrocytes disrupts the extracellular support program for neuroblasts.

Prediction. Separately measure OTX2 secretion by the choroid plexus, its abundance in cerebrospinal fluid and its uptake by astrocytes in young and aged niches. Compare targeted restoration in astrocytes, an equal increase in protein in cerebrospinal fluid, delivery to progenitors and a control. Astrocytic correction is predicted to change the extracellular support program and increase the proportion of neuroblasts that reach the olfactory bulb and functionally integrate, with similar numbers of initial divisions. Uptake must be confirmed independently of surface binding, and the intervention must not change NSC identity. Unimpaired uptake or an effect independent of astrocytes would refute the hypothesis.

Mechanism. A residual spatial defect after regeneration may impair encounters between thymocytes and self-antigens despite normal quantitative markers. Restoring the local distribution of CCL21 should restore movement through medullary selection zones and contacts with medullary epithelial cells and dendritic cells; improved routing cannot compensate for the absence of the relevant antigen.

Prediction. In regenerated old thymic slices or reconstructed tissue with a persistent routing defect, compare restoration of the local CCL21 distribution with uniform addition of the same total amount, controlling epithelial cell number and state, AIRE and antigen expression, viability, and total mature T-cell output. Spatial restoration should improve removal of cells with known self-antigen reactivity while preserving a diverse functional repertoire. If regeneration itself fully restores routing and selection, no additional intervention is needed; if CCL21 distribution does not change selection at equal antigen and cell amounts, or the defect lies exclusively in missing antigens, the hypothesis is refuted.

Mechanism. Uncoordinated ependymal ciliary beating creates changing local flows that destabilize the directional guidance gradient for neuroblast migration.

Prediction. Stabilizing the SLIT gradient while keeping mean concentration and mean flow unchanged will increase the fraction of new neurons reaching and integrating into the olfactory bulb without increasing precursor birth. Compare stable and direction-changing gradients with identical mean parameters in a ventricular-wall model, and separately stabilize the gradient while retaining impaired ciliary beating to test whether the gradient is a causal mediator. Then trace a labeled cohort in aged mice; faster migration with accumulation in incorrect locations does not count as success.

Mechanism. Senescent cells and aging stem cells of the hypothalamus, thymus and bone marrow spread aging through SASP, hormones and immune exhaustion.

Prediction. Heterochronic parabiosis and transplantation of young hub tissues into old animals should reproduce most of the effect of “young blood.”

Mechanism. Restoring astrocytic fatty acid oxidation to the young range corrects deficient utilization of lipids already received from neurons.

Prediction. In a coculture of mature neurons and astrocytes from old mice, restoring astrocytic fatty acid oxidation to the young range should preserve repeated neuronal electrical responses after a challenge compared with control at equal neuronal activity, with labeled neuronal lipids traced into oxidation products. Restoration of flux without improved electrical function, or increased oxidative stress, would not support the hypothesis; increased CPT1A without altered flux does not count as correction.

Mechanism. Training is aligned with the appearance of functional inputs and the period of heightened plasticity in the new cohort.

Prediction. With the same amount of training, a regimen aligned with these functional stages will have a greater effect than a fixed interval after cell birth. In old mice, label a neuronal cohort, determine maturation timing in parallel animals, and compare training by biological stage, at a fixed time, and outside the proposed window. Assess cohort survival, reactivation during recall, and whether the behavioral benefit depends on the new neurons through their reversible silencing. An advantage unrelated to cohort maturity or persisting after its silencing cannot be attributed to improved use of neurogenesis.

Mechanism. Keep MEX3A expression low in activated stem cells and increase it only in late neuroblasts to the young range, after the transition to a neuroblast, without increasing it in cells capable of returning to quiescence. This restores the MEX3A protein gradient between the reserve and neuroblasts in the subventricular neurogenic lineage of old mice.

Prediction. Measure protein and RNA binding at each of two separately labelled stages. Compare stage-dependent and uniform expression at comparable total MEX3A production, with an RNA-binding-defective variant previously checked for stability as a separate control. Track stem-cell return to quiescence and mature olfactory bulb neurons after 12 weeks. Restoring the gradient should outperform uniform elevation in reserve preservation and mature descendants; absence of age-related gradient flattening or of this advantage would not support the proposed aging mechanism.

Mechanism. Restored cell adhesion to the basement membrane is required for niche softening to support sustained regeneration through retention of hair stem cells.

Prediction. Compare control, stiffness normalization, adhesion restoration and their combination in old follicles, first confirming that the interventions independently change stiffness and adhesion. Track labeled clones, their exit from the niche, the reserve and hair growth over two cycles with random allocation and blinded assessment. The combination should outperform either intervention alone in sustained growth without reserve depletion. Equal benefit from softening without adhesion restoration would refute the proposed necessity of adhesion; cell retention without renewed growth would distinguish reserve preservation from restoration of its function.

Mechanism. Reduced GLUT4-dependent glucose uptake promotes exit from pathological quiescence, followed by restoration of substrate availability after activation to support a greater yield of mature neurons.

Prediction. Reversible suppression of Slc2a4 only until the first division will increase functional neuron yield per initially labeled stem cell more than permanent suppression. The difference will emerge during maturation even if early activation is identical. In old mice, compare restriction until activation, continuous restriction and controls, including conditions with comparable cumulative exposure; trace clones from the SVZ to the olfactory bulb and assess metabolism, survival and synaptic integration after 8–12 weeks, discrimination of similar odors and preservation of the original stem cell pool. If restoring nutrient availability does not increase mature neuron yield at equal early activation, the proposed need to switch regimes is not supported. This is an untested prediction in mice; effectiveness in humans has not been established.

Mechanism. p38 may support Wnt signaling in proliferating neural precursors, so suppressing it in these cells may compromise neurogenesis despite reducing inflammation in the surrounding niche.

Prediction. In old mice, compare broad p38 suppression with an intervention that reduces the inflammatory response of the surroundings while preserving p38 activity in precursors, including separate interventions in each cell type. Confirm comparable anti-inflammatory effects and measure Wnt antagonists and precursor responses. With equal reductions in inflammation, preserving p38 in the neurogenic lineage is predicted to yield more functional new neurons; restoring downstream Wnt signaling should partially alleviate the deficit caused by p38 suppression.

Mechanism. Temporarily suppressing excess NOTUM restores physiological Wnt sensitivity during regeneration. Restricting the intervention to the recovery phase is proposed to separate regeneration from chronic growth stimulation.

Prediction. Compare brief and prolonged NOTUM suppression, a control and restoration of normal NOTUM levels in aged intestinal organoids and animals, including aged tissue with naturally accumulated mutations. Brief suppression should improve barrier permeability, nutrient absorption, wound closure and tolerance of subsequent injury, with benefits persisting after NOTUM and Wnt normalize and without improvement arising predominantly from expansion of abnormal clones. Follow clones with known driver alterations, dysplasia and normal cell-type proportions; the proposed protective window requires brief and prolonged regimens to differ in preservation of normal clones over sufficient follow-up.

Mechanism. Leaked self-DNA activates cGAS–STING, causing inflammation that produces further damage and DNA leakage. Simultaneously removing the DNA source and suppressing chronic signaling interrupts this self-sustaining loop.

Prediction. Target chronic signaling and a confirmed source of cytosolic DNA separately and together, then assess the return of cytosolic DNA, inflammation and functional deficits in several tissues after withdrawal. Restore the original pathological signal in a model system to test causality. Some old organisms will exhibit a threshold and hysteresis: maintaining improvement will require less intervention than initially achieving it.

Mechanism. Aged epithelium and hematopoietic tissue contain expanded clones with mutations in p53, DNMT3A, TET2 and other genes. A senolytic or growth factor applied to the whole tissue removes competitive pressure and gives these clones an advantage. Selection by quality is required.

Prediction. In mouse models with existing precancerous clones in skin, intestine and hematopoietic tissue, compare a global senolytic, a global mitogen, and a strategy that first marks clones with defective damage control, selectively removes them, and then briefly stimulates regeneration of the remaining cells. Account for the initial clonal landscape and measure mutant clone size, carcinoma incidence and barrier/hematopoietic recovery after 6-12 months. Selective removal before regeneration should reduce cancer and improve function, whereas the same senolytic or mitogen without selection should improve function at the cost of clonal expansion. A linear increase in cancer with every regenerative gain, regardless of which cells divide, would count against the hypothesis.

Mechanism. Locally retained fibrinogen may continue to influence progenitor fate after vascular leakage has been closed; BMP signaling would be measured in lineage-traced progenitors.

Prediction. In the old subventricular zone, first confirm extracellular deposits and their persistence after leakage closure, then compare barrier correction, local deposit removal, their combination, and control at equal perfusion, separating local effects from systemic changes in coagulation. Removing the retained signal should provide additional recovery of neuronal output and integration into the olfactory bulb. The hypothesis is rejected if deposits do not persist or their removal does not alter cell fate under the same barrier conditions.

Mechanism. Preserved epithelial IFNGR is proposed to be necessary for the functional benefit of locally reducing IFN-I, through the IFN-γ-dependent choroid plexus gateway involved in immune surveillance and repair. Reduced microglial signs of inflammation alone would not preserve the benefit when this epithelial component is lost.

Prediction. In naturally old animals, test IFNAR blockade with intact or selectively disrupted IFNGR in the choroid plexus epithelium, using interventions initiated in adulthood. At comparable suppression of IFN-I and comparable microglial inflammation, cognitive recovery should disappear with loss of epithelial IFNGR and return when the physiological epithelial IFNGR response is restored without increasing parenchymal IFN-γ signaling. The blood–cerebrospinal fluid barrier must remain intact; barrier disruption by the epithelial manipulation would prevent isolation of the proposed mechanism.

Mechanism. Distributing Notch2 reduction to a limited fraction of cells leaves an undisturbed reserve available for future neurogenesis.

Prediction. Compare strong reversible Notch2 reduction in a small random fraction of cells with weak reduction in a larger fraction at the same mean niche signal, with an additional comparison matched for the first wave of neuronal output. Measure individual signaling and clonal fates while excluding selection of cells that were already more active. The mosaic regime is predicted to produce a greater cumulative output of functional olfactory bulb neurons after several identical subsequent stimuli. The hypothesis is rejected if outcomes depend only on mean Notch2 or the number of cells activated in the first wave.

Mechanism. Reversibly reduce expression of the secreted Wnt antagonist FRZB/sFRP3 in selected mature granule neurons of the dentate gyrus in aged mice that become active during exploration of a new environment. Restrict the reduction to a limited learning period and subsequently restore FRZB.

Prediction. Compare reduction in the active ensemble, reduction in a random group containing the same number of neurons, and weak uniform reduction. Check FRZB distribution, local Wnt responses, and tracing of new cells. At comparable division counts, assess participation of labeled mature progeny in a repeated task and their electrophysiology; the spatially restricted reduction should improve functional integration at the same overall level of neurogenesis.

Mechanism. Reduce ACTL6A/BAF53A expression only after confirmed cell-cycle exit and simultaneously increase ACTL6B/BAF53B expression to the level in young postmitotic neurons. Apply this coordinated BAF subunit replacement to recently born neurons of the aged dentate gyrus at the early postmitotic stage, without affecting dividing progenitors, to address the proposed limiting competition between subunits.

Prediction. Compare each component separately, their combination, and a control. Verify BAF-complex composition rather than RNA alone, then assess dendrites, synaptic currents, and survival of the labelled cohort after 12 weeks. Independently confirm the absence of division when ACTL6A is reduced. The combined intervention should improve functional maturation more than ACTL6B alone; if it fails to outperform ACTL6B alone despite verified subunit replacement, or worsens survival, the hypothesis of limiting subunit competition is not supported.

Mechanism. Old NK-cells have reduced NKG2D-dependent killing and degranulation, allowing p16-high senescent cells with SASP to accumulate in visceral adipose tissue and skeletal muscle and sustain inflammation and insulin resistance. A senolytic kills the susceptible fraction, but surviving clones and cells with low immunogenicity repopulate the niche; a short NK boost should remove the remainder and make clearance durable.

Prediction. In old mice of both sexes, an IL-15/IL-15Rα course followed by a senolytic such as dasatinib + quercetin or navitoclax should produce synergy greater than the sum of the individual effects, with its magnitude depending on baseline NK function. Compare senolytic alone, IL-15/IL-15Rα alone, the sequence and control, with young mice as a reference, measuring senescent-cell abundance in visceral adipose tissue and skeletal muscle, SASP, NK function, treadmill endurance and glucose tolerance. Failure of the sequence to outperform the senolytic alone would reject the proposed limiting role of immune function.

Mechanism. Temporarily increase SERPINF1/PEDF secretion by endothelial cells near stem cells of the aged subventricular zone before progeny enter neuronal differentiation, then return secretion to baseline after confirmed expansion of the functional reserve.

Prediction. Compare a pulse, continuous elevation and control at comparable total exposure. Measure Notch activity and daughter-cell pair fates, then the proportion of neuronal clones and progeny integration into the olfactory bulb; monitor vascular density and perfusion to distinguish niche changes from vascular effects of PEDF. If reserve cell numbers increase but mature neuronal output does not increase after PEDF withdrawal, the proposed sequence does not restore neurogenesis.

Mechanism. Insufficient mitochondrial delivery leaves growing dendritic regions depleted despite sufficient total mitochondrial mass; restoring distribution supports neuronal integration.

Prediction. Compare transport correction with enhanced biogenesis at comparable mitochondrial mass and respiration, including a separate motor-transport control that does not change the NR2F1 transcriptional program. Filling previously depleted dendritic regions should predict synapse stabilization and mature responses, and equalizing distribution should eliminate the difference between groups. The hypothesis is refuted if improvement follows total АТФ entirely or transport does not affect functional integration.

Mechanism. Continuous PGE2 elevation holds muscle stem cells in a proliferative state during the phase when some descendants should return to quiescence, whereas a short pulse preserves the reserve for subsequent regeneration.

Prediction. At equal area under the tissue PGE2 concentration curve, a short pulse will outperform continuous administration in specific tetanic force after a second injury delivered without treatment after complete cessation of exposure. This advantage will disappear following validated Ptger4 deletion in muscle stem cells and weaken with EP2 blockade. Increased muscle mass or numbers of Pax7-positive cells without improved specific force will not support the hypothesis.

Mechanism. Background activation of NF-kB, cGAS-STING, and the integrated stress response increases with age. Although useful during acute infection and injury, chronic activation suppresses autophagy, mitochondrial biogenesis, and extracellular matrix renewal. Fasting, protein restriction, and rapamycin extend life by temporarily returning the budget to maintenance.

Prediction. In middle-aged mice, compare continuous calorie restriction, intermittent restriction such as 2 days per week or rapamycin cycles, and a continuous low-dose mTOR inhibitor. Measure lifespan, protein synthesis rates in muscle and liver, autophagic flux, mitochondrial respiration, proinflammatory cytokines, and stem cell niche function in hematopoiesis, muscle, and intestine. Separately test whether early shifts in budget markers predict subsequent functional loss better than epigenetic age. Support would be regimens that restore the maintenance/inflammation ratio extending the healthy period more than regimens producing the same weight loss or reduction in mTOR signaling without this shift. Evidence against would be restriction working only through weight loss or a single molecular target, with budget composition adding no predictive power.

Mechanism. Temporarily limiting potentiation in mature granule cells reduces competition with the existing network during integration of new neurons.

Prediction. At the same number of newly born cells, combining neurogenesis stimulation with reversible restriction of potentiation only in mature granule cells during integration will increase survival and the proportion of new cells with functional inputs; silencing the new cohort will eliminate the improvement in discrimination between similar contexts. Control perforant-path input activity and basal transmission separately, and check preservation of memories formed before the intervention; a benefit accompanied by loss of previous memory would not achieve functional rejuvenation.

Mechanism. Partially and reversibly reduce membrane expression of EFNB2/ephrin-B2 in endothelial cells directly contacting stem cells in the aged subventricular zone, while maintaining baseline membrane expression and contact presentation of JAG1/Jagged1. Apply this during a limited period of stem cell activation, then restore EFNB2, functionally separating the two contact signals.

Prediction. Perform a factorial comparison of partial reduction of EFNB2, JAG1, both proteins, and control. Compare contact preservation, Notch signaling, division counts, and neuronal output of clones; verify that vascular geometry and perfusion remain unchanged. EFNB2 reduction with preserved JAG1 should separate productive activation from reserve loss, and subsequent EFNB2 restoration should preserve the reserve for a second wave.

Mechanism. Targeted modification of a limited set of regulatory regions reproduces the neurogenic benefit of TET2 with less alteration of the remaining epigenome.

Prediction. Select candidate regions from young and aged NSC where DNA modification changes agree with chromatin accessibility and expression, then test them individually and in combinations using a targeted editor, with an inactive catalytic module, nontargeting guides and global TET2 elevation as controls. Fix the set before testing in independent animals. A small combination of regions will reproduce a substantial part of the neuronal output while preserving NSC identity and genome stability, with functional neurons traced from the original cells rather than identified by one marker. Failure of any limited set to reproduce the effect, or a requirement for broad reprogramming, would refute the hypothesis.

Mechanism. Reversibly reduce expression of the type I interferon receptor IFNAR1 in aged dentate-gyrus microglia with an elevated interferon transcriptional program, before activation of the stem-cell cohort.

Prediction. Compare microglial IFNAR1 reduction before stem-cell activation with reduction only after neuron birth, IFNAR1 reduction in progenitors themselves, and control. Confirm cell specificity and the interferon response; separately measure new divisions, death of existing neurons, and survival of new neurons, establishing the mature cohort's origin through genetic tracing. Early reduction should produce more neuronal descendants per initial stem cell than late reduction if the main effect acts through the niche. Preservation of existing neurons without increased traced neuronal output rejects the hypothesis of restored neurogenesis.

Mechanism. The response of old NSC to neurogenic stimulation depends on their local IFNγ response; transient attenuation of IFNγ receptor signaling specifically in highly responsive NSC before activation is proposed to improve their response.

Prediction. A cell's initial IFNγ response will predict the additional benefit from the intervention, and distance from infiltrating T-cells will help explain spatial heterogeneity in the outcome. If the effect is identical in IFNγ-high and IFNγ-low NSC or is explained solely by changes in immune cell numbers, the proposed cell selectivity is not supported.

Mechanism. CHD7-mediated restoration of Sox4/Sox11 accessibility establishes an earlier state required before sustained activation of the late neuronal maturation program.

Prediction. Compare sequential activation of SoxC and a data-selected late neuronal module, the reverse order, simultaneous activation and control in old progenitors, matching the dose and duration of each intervention. The correct-order advantage should persist after matching final expression and cell numbers, assessed through morphology, action potentials and the inputs and outputs of new neurons. If final factor levels suffice regardless of sequence, the hypothesis is refuted.

Mechanism. Repeated phosphate peaks are proposed to leave greater residual endothelial dysfunction when regulatory reserve is low, independently of total daily exposure. The role of Klotho in the response to FGF23 provides a mechanistic basis for investigating phosphate regulatory reserve.

Prediction. In isolated old vessels, reproduce measured phosphate curves with and without peaks while matching area under the curve, mean phosphate, calcium, pH and other medium components. After repeated cycles and washout, smoother exposure should produce less residual impairment of endothelium-dependent relaxation, especially with low regulatory reserve. In old animals, phosphate delivery schedules with measured equal daily exposure should differ in the rate of age-related decline in vascular reactivity and recovery after ordinary loading, without chronic deficiency or impaired bone mineralization.

Mechanism. Loss of sinusoidal endothelial fenestrations during aging restricts insulin access to the liver; fenestrations act as a separate temporal filter for insulin pulses.

Prediction. In a model of old endothelium with hepatocytes, compare fenestration restoration with control under pulsatile and constant insulin delivery. Measure insulin behind the barrier and match total insulin exposure at hepatocytes, flow and viability; assess suppression of glucose production as the primary outcome and preservation of pulse amplitude as the additional outcome, while checking nonspecific leakage and secretome effects. If there are no differences at equal exposure, the separate temporal-filter hypothesis is rejected.

Mechanism. A reversible extracellular step in MUC2 unpacking may limit barrier function even when secretion is preserved. The proposed mechanism applies to a subgroup with a measured disturbance of the ionic environment.

Prediction. Cross freshly secreted young and aged MUC2 with reconstructed young and aged ionic conditions at equal mucin mass. Young mucin in aged ionic conditions should reproduce the defect, whereas aged mucin in young conditions should partially restore the barrier, distinguishing an unpacking defect from irreversible changes in glycosylation. In aged explants, compare restoration of the environment, stimulation of secretion, and a control; correction of the environment should reduce particle penetration, and normalization after transferring aged ionic conditions onto young secretion should restore the barrier.

Mechanism. Aged mechanical properties of the matrix may reimpose a dysfunctional state on cells. Age-related niche stiffness limited the activity of CNS progenitor cells in experiments.

Prediction. Compare interventions targeting cells, interventions targeting their environment, and both orders of combining the interventions.

Mechanism. Selective separation of REST programs permits activation of old precursors while maintaining repression of premature neuronal differentiation.

Prediction. First identify the REST targets actually altered in old precursors. Compare limited correction of the selected module, general REST reduction, and a control, followed by the same differentiation signal and with the first wave of divisions matched. More clones are expected to retain a reserve cell while producing mature neuronal progeny; test integration into the dentate gyrus and a second neurogenic wave. The hypothesis is rejected if the modules cannot be functionally separated or there is no advantage at an equal number of initial divisions.

Mechanism. Senescent cells are heterogeneous and partly evade immunity through increased HLA-E and “don't eat me” signals. With age, the T-cell pool narrows, macrophages complete phagocytosis less effectively and retain an inflammatory phenotype longer. A drug kills the current wave, but the next wave encounters the same immune system unable to recognize it.

Prediction. In old mice, compare a single senolytic treatment, a short course, and a senolytic combined with an intervention that broadens recognition, such as temporary vaccination against a conserved senescent-cell surface marker or transfer of young macrophages with subsequent assessment of clearance after donor cells disappear. Measure p16 after a week, senescent-cell density after 3 and 6 months, tissue inflammation, and kidney, blood vessel and adipose tissue function; check whether healthy quiescent cells are attacked. After intervention ends, clearance should persist only where immune surveillance changed, rather than where initial killing was stronger. An effect duration determined solely by the depth of initial removal would count against the hypothesis.

Mechanism. Glutamine supplies carbon for fatty acid synthesis through IDH2-mediated reductive carboxylation. Age-related weakening of this flux limits lipid provision, cellular biomass production and regeneration.

Prediction. Old cells will show a smaller proportion of reductive flux. Disruption of GLS or IDH2 will impair activation and lipid provision, while restoration of GLS may improve the functional contribution of cells after transplantation. Test using isotope tracing of glutamine carbon and measurements of fatty acid synthesis, activation and regeneration after transplantation, assessing energetics separately from carbon incorporation into biomass. If changing this flux does not affect lipid synthesis and activation, the proposed link is not supported.

Mechanism. NOTUM feedback is restored as the neurogenic niche fills, reinstating limits on growth and fate allocation.

Prediction. Compare a fixed-duration regimen, a regimen stopped according to measured niche occupancy, and a control, with the threshold set in an independent pilot series. Measure the Wnt response, clonal composition, reserve preservation, migration, and descendant types. The predicted result is less variation between animals and a greater cumulative yield of correctly integrated olfactory bulb neurons with the same first wave. If the fixed regimen is equally effective after dose matching, the need for feedback is not supported.

Mechanism. The youthful epigenetic pattern remains present but becomes unreadable; restoring its accessibility restores cellular function.

Prediction. Perform partial reprogramming (OSK) in postmitotic tissues of old animals alongside single-cell sequencing of somatic mutations. Functional restoration with an unchanged mutation burden would indicate that information is unreadable rather than lost. Failure of tissues with a high mutation burden, such as skin and a smoker's bronchial epithelium, to rejuvenate with the same methylome shift would falsify the hypothesis. Recovery capacity is inversely proportional to the fraction of cells with driver mutations and should be measured before therapy.

Mechanism. Derepressed LINE-1 produces immunogenic nucleic acid and, for active copies, new genomic events that amplify damage. Inflammation can occur without completed retrotransposition.

Prediction. Compare LINE-1 RNA suppression, reverse transcription inhibition and suppression of downstream inflammatory signaling, simultaneously measuring LINE-1 RNA, cytosolic reverse transcription products and actual new insertions. If the source indeed sustains damage, suppressing it will reduce recurrence of inflammation after withdrawal of temporary blockade and preserve functional reserve in several tissues.

Mechanism. Spatially localized TIMP2 release supports matrix remodeling along neuroblast migration paths, improving migration and integration while limiting changes to the surrounding matrix.

Prediction. Compare localized and distributed TIMP2 sources with equal total amounts, exposure durations, and confirmed protein activity, mapping matrix remodeling, tracked neuroblast trajectories, final positions, and mature synaptic responses. Localized release is expected to improve correct migration and integration with more restricted changes to the surrounding matrix. Outcomes determined solely by average concentration, or arising from nonspecific increases in the excitability of the existing network, would not support the hypothesis.

Mechanism. The combined intervention may remove a self-sustaining source of oxidation by restoring eNOS coupling. Sufficient endogenous BH4 synthesis and recycling would then maintain the restored state despite the original aged environment.

Prediction. In paired arterial segments from naturally old animals, compare a 2×2 design of vehicle, sepiapterin, reversible reduction of vascular superoxide, and their combination, then repeat the key comparison in available arteries from elderly donors ex vivo. After washout and turnover of the supplied cofactor pool, the combination should sustain endothelium-dependent dilation and NO production, with preserved responses to an independent NO donor, beyond interventions matched for improvement at withdrawal. Persistence should depend on endogenous BH4 metabolic capacity measured before treatment; equal recurrence across groups or failure of sufficient endogenous BH4 synthesis to predict persistence would undermine the proposed switching mechanism.

Mechanism. DNMT3A/B-dependent formation of the neuronal methylome after precursor rejuvenation enables new neurons to mature.

Prediction. In the old dentate gyrus, compare the same initial correction with preserved, temporarily reduced, and restored DNMT3A/B activity in postmitotic descendants. Map enhancer and gene-body methylation rather than substituting mean epigenetic age, and control for the number of newly born cells and changes in fate. Restoring the correct methylation map is predicted to improve dendrites, electrophysiology, and synaptic integration even without a further reduction in estimated age. The hypothesis is rejected if maturation does not depend on this restoration or is explained solely by early cell selection.

Mechanism. OR10J5 activation is proposed to enhance kynurenine processing through KAT enzymes, which convert kynurenine into kynurenic acid. This process is associated with more efficient energy use; the connection between OR10J5 and this process is the proposed hypothesis.

Prediction. Activate the receptor in cultured muscle tissue and compare it with control tissue to determine whether kynurenine processing accelerates and force is maintained longer during repeated contractions. Suppress KAT enzymes and repeat the experiment to determine whether the benefit weakens, accounting for the effect of suppression itself on baseline tissue performance. If the result is positive, compare the intervention with exercise in old mice, including a control group and assessing strength, fatigue and recovery after exertion.

Mechanism. Circulating factors form a self-sustaining secretory feedback circuit across tissues. Temporarily reducing the interacting set below its feedback threshold switches the system out of the pathological state.

Prediction. Identify components whose temporary reduction changes the production of other age-related signals, then compare their selective joint removal with nonspecific exchange and appropriate albumin, volume and procedure controls. Returning a particular combination of removed components should restore the pathological state, whereas individual components should be insufficient; the effect should exhibit a threshold and persist after pharmacokinetics normalize. Functional support requires coordinated improvement in regenerative reserve, resilience to challenge and measures from several organs; proteomic or epigenetic rejuvenation alone is insufficient.

Mechanism. Restoration of transient lysosome–mitochondrion contacts restores lysosomal acidity and clearance through spatial rearrangement of the organelles.

Prediction. Spatial rearrangement will have an effect at an unchanged overall ATP level, whereas increasing organelle biogenesis without restoring contacts will have a weaker effect; permanent rigid tethering may be worse than regulated contacts. In old mouse NSC with confirmed reductions in contacts and impaired acidity, compare a reversible contact linker, a nonfunctional linker, and an increase in lysosome number; measure local pH, autophagic flux, respiration, and mitophagy, distinguishing direct acidification from removal of damaged mitochondria. The main outcome is mature functional neurons per initial NSC with preservation of the reserve, followed by testing in the old SVZ.

Mechanism. Loss of peroxisomal protein import through PRX-5 causes poor lipid droplet mobilization, followed by impaired fatty acid metabolism and mitochondrial dysfunction.

Prediction. Reducing PRX-5 will reproduce age-related disturbances in lipid dynamics; increasing its expression will preserve these dynamics and mitochondrial integrity. Loss of import will eliminate the lifespan benefit of dietary restriction. Compare control, prx-5 suppression and prx-5 enhancement under normal and restricted feeding, sequentially measuring peroxisomal import, lipid reserve utilization, mitochondrial function and survival. Persistence of the dietary restriction effect after confirmed import impairment would contradict the necessary role of this import.

Mechanism. A compartment-specific NAD deficit limits productive activation despite restoration of the total NAD pool.

Prediction. Measure NAD separately in the nucleus, cytosol and mitochondria, checking sensor calibration and pH effects, and compare targeted with untargeted restoration of NAD synthesis at equal total pools and comparable activation. Targeted correction should improve the yield of genetically traced mature neurons without increasing genome damage or depleting the reserve. Reject the hypothesis if there is no local deficit, it cannot be separated from the total pool, or targeted correction provides no advantage; a persistent difference between nuclear and cytosolic pools must be demonstrated rather than assumed.

Mechanism. Peroxisomal ether lipid synthesis limits the lipid supply for new mitochondrial membranes and thereby constrains the benefit of mitochondrial biogenesis.

Prediction. First measure ether lipid synthesis flux and incorporation into mitochondria in aged dentate gyrus precursors. If a deficit is confirmed, compare restoration of GNPAT-dependent synthesis, increased mitochondrial biogenesis, their combination, and a control: the two interventions should show a positive interaction in the yield of functional new neurons, and baseline lipid flux should predict the response better than peroxisome number. The hypothesis is rejected if no deficit is found or if biogenesis is equally beneficial regardless of lipid flux.

Mechanism. Irreversible crosslinks, primarily glucosepane, accumulate in collagen and elastin with age, making tissues stiffer. Cells sense stiffness through YAP/TAZ, whose activity declines in aging stromal cells; loss of YAP/TAZ weakens restraint of cGAS–STING, leading to chronic inflammation, senescence and “inflammaging.” Breaking glucosepane crosslinks, for example with glucosepane-specific enzymes, may restore normal tissue mechanics and YAP/TAZ activity and subsequently reduce inflammation.

Prediction. Cells from a young donor placed on decellularized matrix from an old organism should acquire aging markers faster. Removing crosslinks from the matrix beforehand should weaken this effect. If confirmed, combining matrix therapy with senolytics would be a better strategy than either approach alone.

Mechanism. Removing HLA-E–NKG2A inhibition is insufficient when ligand shedding has impaired NKG2D-mediated recognition. Retaining surface MICA/B restores the activating recognition needed for NK-mediated elimination after NKG2A blockade.

Prediction. A factorial experiment combining NKG2A blockade and prevention of MICA/B shedding with autologous NK-cells from older donors should selectively eliminate persistently senescent cells while preserving recovering tissue cells, particularly in the HLA-E-high, actively shedding subgroup. The MICA/B antibody must preserve NKG2D binding, and an Fc-inactive variant should separate ligand retention from ADCC. Additional NKG2D blockade should abolish specifically the gain from ligand retention. Failure of baseline shedding to predict response, absence of added benefit from MICA/B retention despite confirmed target engagement, or equally effective destruction of recovering cells would refute the hypothesis.

Mechanism. Each cell's mitotic and repair history erases the precise marking of promoters, enhancers, and heterochromatin, leaving the genome intact but losing instructions about which genes to keep active. This explains why epigenetic clocks predict mortality better than many damage markers and why brief induction of Yamanaka factors rejuvenates the transcriptome without turning tissue into a teratoma when dose and duration are limited.

Prediction. In old mice, compare three regimens: (1) partial reprogramming cycles using OSK without c-Myc in short pulses, (2) a senolytic, and (3) their combination. Measure DNA methylation, grip strength, cardiac and renal function, resistance to injury, and tumor frequency, with controls for loss of cell identity using pluripotency markers and histology. In parallel, test whether human skin, muscle, and vascular endothelial organoids from donors aged 70+ years recover barrier function, contractility, and angiogenesis without oncogenic transformation. Support would be a dose window in which epigenetic age and function improve without deterioration in tissue identity or tumor frequency. Evidence against would be function failing to follow epigenetic age, or any substantial rejuvenation being accompanied by loss of identity or cancer.

Mechanism. One senescent cell can impair dozens of neighboring cells through SASP, and one failed stem-cell niche can stop regeneration across an entire tissue domain. Biopsy averages conceal these states, making tissue appear only slightly old even after it has crossed the functional threshold beyond which regeneration does not start.

Prediction. In the same skin, muscle and hematopoietic samples from humans aged 30-80 years, measure distributions of cells with high p16/p21, stem cells capable of producing a complete clone, and matrix regions with abnormal stiffness. Test whether the tails, the upper 1-5%, predict subsequent functional loss, healing rate and mortality better than average epigenetic and clinical markers. In mouse wounds and muscle after injury, compare interventions that specifically reduce the tail, targeted senescent-cell removal or niche replacement, with interventions that shift the mean by the same amount, a systemic antioxidant or NAD precursor. Support would be the tail predicting outcomes and its removal restoring regeneration with an unchanged mean, while shifting the mean without changing the tail does not. The tail adding no information after adjustment for the mean would count against the hypothesis.

Mechanism. S293 improves insulin rhythm through Cx36-mediated intercellular coupling, rather than through increased secretion by individual cells.

Prediction. In islets from elderly donors without diabetes, compare S293 with an inactive peptide, with and without partial GJD2 suppression. During dynamic perfusion, measure insulin pulsations and Cx36 coupling, controlling viability, insulin stores and the secretory response of individual cells and excluding a floor effect after suppression. Rhythm should recover only when Cx36 is preserved; persistence of the effect after its suppression refutes the proposed mechanism. The unit of analysis is the donor.

Mechanism. Neural stem cell-secreted PLA2G7 limits inhibitory synapses through their lipid environment; suppressing PLA2G7 changes this environment and strengthens inhibitory transmission.

Prediction. In old mice, reducing Pla2g7 in the dentate gyrus will strengthen inhibitory transmission and improve spatial learning. In a cellular model, adding phosphatidylcholine will attenuate the PLA2G7-induced deficit of inhibitory synapses. Compare Pla2g7 suppression with a control intervention using electrophysiology, inhibitory contact counts and a memory test; separately test the signal source through conditional gene deletion in stem cells, accounting for locomotor activity and neurogenesis. A cognitive effect without changes in inhibitory transmission would not support the proposed synaptic explanation.

Mechanism. Insufficient local NMDA receptor coagonist support limits the maturation and integration of new neurons despite increased cell production.

Prediction. With equal early numbers of new cells, additional coagonist correction will increase the fraction of mature neurons with functional synapses, and baseline sensitivity of the NMDA response to coagonist addition should predict the benefit. Compare neurogenic stimulation, delayed local coagonist correction, their combination, and control in the aged mouse dentate gyrus; test dependence on NMDA receptors specifically in the new cohort while separately measuring changes in the mature network. Equal effects with and without a coagonist deficit, or effects independent of receptors in new neurons, would not support the mechanism.

Mechanism. A deficit of lipids needed by the brain persists after isolated elimination of leakage. Restoring MFSD2A-mediated lipid transport is proposed to remove this limitation beyond the benefit of closing the blood–brain barrier.

Prediction. Use interventions induced only in adulthood and restricted to brain vascular endothelium to compare old controls, restoration of MFSD2A to the young physiological range, and reduction of CAV1. Also compare transport-active MFSD2A with a validated transport-defective variant under identical CAV1 suppression, with comparable protein expression, localization, and barrier closure. At equal reductions in leakage, transport-active MFSD2A should restore labeled LPC-DHA influx and incorporation into neural tissue lipids and provide additional improvement in a prespecified memory test; increased MFSD2A without restored measured transport should not reproduce this effect. Assess outcomes after sustained barrier restoration, account for plasma tracer content and perfusion, and control for vision, movement, and anxiety.

Mechanism. Partially reduce CX3CR1 expression in microglia of the aged subventricular zone while preserving its expression in dentate-gyrus microglia during one traced wave of neurogenesis.

Prediction. Compare reduction confined to the subventricular zone, confined to the hippocampus, in both niches, and control; confirm spatial specificity and microglial state. In both niches, measure neuroblasts, mature traced descendants, and their integration, accounting for regional differences in migration routes. If regional reduction does not increase mature neuronal output or has the same effect in both niches, the hypothesis of a practically significant opposition between the niches is incorrect.

Mechanism. Age-related loss of AQP4 polarization in astrocytic endfeet, regression of meningeal lymphatic vessels, and reduced arterial pulsation amplitude decrease nighttime clearance. Anti-amyloid antibodies have little effect because they remove the product without restoring drainage.

Prediction. Restore drainage in old mice using VEGF-C for mLV, stabilization of AQP4 polarity, and enhancement of slow-wave sleep; assess tracer clearance, cognitive tests, and tau spread. The key mediation analysis should show that cognitive improvement is not explained by amyloid reduction, distinguishing this hypothesis from the amyloid hypothesis.

Mechanism. Glucosepane cross-links contribute to aortic stiffness, and their enzymatic cleavage reduces it. Pulse pressure is a shared upstream factor affecting the kidney and cerebral microcirculation, so this intervention addresses both chronic kidney disease and vascular dementia.

Prediction. Use PWV (pulse wave velocity) as the primary endpoint, followed by GFR, albuminuria, and white matter hyperintensity volume on MRI. Enzymatic glucosepane cleavage is expected to reduce aortic stiffness. If tissue mass spectrometry confirms glucosepane removal but PWV remains unchanged, the hypothesis is falsified: stiffness is determined by elastin and cellular tone rather than cross-links.

Mechanism. Restore HDAC3 expression to the young range in activated precursors of the aged hippocampus with reduced HDAC3 and without substantial DNA damage, during amplification before the postmitotic state, while preserving physiological CDK1 protein levels.

Prediction. Compare HDAC3 restoration, independent CDK1 restoration and control; measure phase duration, DNA damage, aneuploidy and clonal fate. Test whether returning CDK1 to its low baseline level removes the benefit of HDAC3. The main outcome is normal mature neurons after 12 weeks. If HDAC3 restoration leaves CDK1, division completion and mature neuronal output unchanged, the proposed link does not limit the aged lineage.

Mechanism. An age-related defect in vesicle uptake and functional cargo delivery limits the benefit of choroid plexus extracellular vesicles.

Prediction. Compare uptake and functional cargo release in young and aged cells using a cargo label and a functional reporter. In a factorial experiment, combine identical cargo with different delivery and different cargo with identical delivery, controlling for free contaminants and disrupted vesicles. Restoring delivery at unchanged cargo quantity should increase mature neuronal progeny and their olfactory responses; absence of an age-related delivery defect or an advantage attributable exclusively to young cargo would refute the proposed mechanism.

Mechanism. Separating HDAC2 reduction in mature neurons from preservation of HDAC2 catalytic activity in new neurons maintains the functions needed for their survival and maturation.

Prediction. Compare HDAC2 reduction in the mature network, reduction in all neurons and reduction in all neurons with HDAC2 restored in the new cohort in the old dentate gyrus, including a catalytically inactive control. Targeted preservation of HDAC2 should improve survival and functional maturation of the new cohort without reversing mature-neuron plasticity, assessed through synaptic responses and the new cohort's contribution to distinguishing similar contexts. No additional effect from preserving the cohort would fail to support the proposed separation of functions.

Mechanism. Productive metabolic utilization of lactate after cellular entry, specifically the proposed oxidative limitation, may constrain neuronal maturation independently of lactate transport.

Prediction. Compare old cells with equal transport flux but different confirmed utilization of labeled lactate, separately measuring contributions to energy metabolism, changes in NADH/NAD, and signaling effects. Compare correction of utilization with alternative energy support and pH control, then test the result in the dentate gyrus. Functional new neuron output should follow metabolic flux rather than extracellular concentration; the oxidative-limitation hypothesis is rejected if the effect persists without use of lactate carbon or is fully explained by a redox shift.

Mechanism. Functional young tissue restores functions lost through intrinsic organ damage, and restoring several organ functions increases overall functional reserve.

Prediction. In a naturally old model, compare restoration of two organ functions separately and together using young compatible donor tissues and comparable surgical controls, after stable function of each graft and an acceptable burden of each intervention have been independently demonstrated. Sustained restoration of both functions should provide additional overall functional benefit compared with restoring either alone, assessed through overall functional reserve, duration of maintained function, complications and survival. If the old systemic environment dominates, young grafts will rapidly lose function or overall reserve will not substantially change; no additional benefit despite confirmed function of both grafts would limit the combined-benefit hypothesis.

Mechanism. The functional outcome of selectively increasing muscle KAT depends on renal removal of its product, KYNA. Insufficient OAT1/3–MRP4-mediated tubular secretion permits free KYNA to accumulate and potentially sustain muscle AHR–PDK4, limiting pyruvate utilization.

Prediction. At the same reduction in KYN, the effect should depend on KYNA clearance; adding back only KYNA should abolish rescue, and suppressing muscle AHR should eliminate this dependence. First establish measured free and total KYN/KYNA, albumin and renal KYNA clearance ranges in elderly people, using young people as a reference. Connect contractile muscle microtissues from elderly donors to a polarized human proximal tubule with a separate urinary outlet; compare muscle KYAT1 induction, after confirming KYN→KYNA flux, with a catalytically inactive version at similar expression, crossed with preserved secretion or partial OAT1/3–MRP4 suppression. Match fluid flow, nutrients, albumin and viability, and use labeled KYN to check the source of KYNA and its formation and removal. The primary outcome is force preservation during repeated standard contractions, with randomization within donor blocks, blinded measurement and the donor as the independent biological unit. Restore renal transport to baseline, then reproduce measured metabolic profiles while matching KYN, other measured metabolites and albumin and varying only free KYNA within the observed range; KYNA addition should restore the defect. Separately suppress AHR only in muscle, controlling its own effect on baseline contractility. Absence of a functional defect at KYNA concentrations observed in ordinary aging, failure of KYNA alone to reverse rescue, or persistence of the KYNA-dependent defect after verified AHR suppression would refute the corresponding claims. Changes only in AHR markers or respiration without improved fatigability would not establish the functional basis for geroprotection; effects confined to severe uremia would restrict applicability to kidney disease.

Mechanism. Insufficient downstream outflow limits transport despite enhanced meningeal lymphatic function. Failure to respond to therapy may reflect a shift of the transport bottleneck farther along the pathway.

Prediction. Baseline measurement of flow through the entire pathway should predict benefit better than vessel morphometry or age. Compare local enhancement of meningeal function with controls in aged models with different baseline outflow efficiencies, measuring inert tracer dynamics throughout the pathway, extracellular macromolecule clearance, neuroinflammation and memory while controlling for motor function and wakefulness. Reversibly reducing downstream outflow should eliminate the benefit even with enlarged meningeal vessels; a separate blockade-only control must exclude independent tissue injury that could mask the benefit.

Mechanism. Temporary BMP suppression permits activation, while subsequent restoration of BMP signaling preserves the stem cell reserve that prolonged suppression may consume.

Prediction. A regimen that ends suppression after a predefined proportion of NSC has been activated will produce a smaller early peak of divisions but a greater cumulative yield of mature neurons over several months than continuous suppression. If continuous suppression preserves the reserve and performs at least as well in late neuronal yield, the advantage of restoring BMP is not supported.

Mechanism. Protective efferent feedback is proposed to preserve restored afferent contacts during repeated acoustic exposure. Medial and lateral efferent systems act on different targets, and α9α10-dependent inhibition primarily tests hair-cell inhibition rather than restoration of the entire efferent innervation.

Prediction. In old mice of both sexes, compare NT-3, support of efferent function, their combination, and controls, first confirming equal early restoration of functional afferent contacts in the comparison groups. Under the same moderate acoustic conditions, efferent support should increase long-term preservation of restored contacts and function, particularly with pronounced initial efferent deficits; a separate quiet environment tests dependence on external load. No improvement in contact preservation, or an apparent benefit explained entirely by altered cochlear amplification, would refute the hypothesis.

Mechanism. The kinetics of FGF-2 binding and release by the matrix determine the duration of factor presentation, potentially maintaining proliferation or permitting the transition to neuronal differentiation.

Prediction. In three-dimensional niches containing aged mouse NSC, vary FGF-2 binding and release kinetics using a perlecan-like matrix while holding stiffness, total dose, contact density and availability of other factors constant. Measure local ERK signal duration and include conditions with equal integrated exposure but different durations. Time-limited presentation is predicted to produce more mature functional neurons than prolonged retention, even with the same early number of divisions, while preserving some NSC in reserve. An effect explained solely by total dose or matrix mechanics would refute the hypothesis; an age-related change in retention must be demonstrated separately.

Mechanism. The limiting factor is functional integration of new myelin sheaths into active neural circuits, rather than only the number of new oligodendrocytes.

Prediction. In old mice, FGF17 exposure aligned with learning should improve retention of the same memory after treatment ends more than exposure shifted relative to learning, at comparable initial acquisition and potentially similar numbers of new oligodendrocytes. Preventing new oligodendrocyte formation through an adult-induced intervention involving Myrf in their precursors should eliminate the additional advantage of the aligned regimen, provided baseline task performance remains intact and there is no general behavioral floor.

Mechanism. Endothelium and pericytes age earlier than many parenchymal cells because they are continually exposed to flow, pressure and inflammatory mediators. Capillaries become sparse, lumen regulation deteriorates, and tissue experiences fluctuating hypoxia. This causes fibrosis and parenchymal senescence that appear to be organ aging despite a vascular initiating defect.

Prediction. In old mice, quantitatively map capillary density, pericyte coverage and reactive hyperemia in the cerebral cortex, muscle and renal cortex. Locally improve one region through gentle restoration of pericyte coverage or brief normalization of capillary membrane stiffness, and compare its function with a symmetrical untreated region in the same animal. In humans, test whether microcirculatory reserve, assessed by skin and muscle reactive hyperemia and cerebrovascular reactivity, predicts subsequent organ decline better than blood pressure and lipids. Local vascular restoration should improve parenchymal function in the same region while systemic aging markers remain unchanged. Parenchymal function failing to follow perfusion, or an effect explained solely by blood pressure and lipids, would count against the hypothesis.

Mechanism. Elevated cytoplasmic calcium leads to extranuclear S100A6 accumulation, CacyBP recruitment and accelerated PARP1 ubiquitination and degradation, followed by DNA damage, cytoplasmic chromatin fragments and cGAS–STING-mediated inflammatory secretion. Mianserin may act through HTR2B/HTR2C antagonism and reduced intracellular calcium.

Prediction. Normalizing calcium signaling or reducing S100A6 will attenuate this cascade in progeroid and aging cells. Combine measurements of calcium, S100A6 localization, PARP1 stability, DNA damage and secretion, with controls distinguishing changes in protein abundance from changes in localization. Then separately assess functional measures and survival in progeroid and naturally aging mouse models. If correcting S100A6 does not preserve PARP1 and reduce DNA damage, the proposed causal chain is not supported.

Mechanism. Periodically replace tissues and organs with those grown from the organism’s own young, reprogrammed cells while preserving continuity of the nervous system.

Prediction. Sequential replacement of the hematopoietic, hepatic and endocrine systems with young autologous cells in animals should produce cumulative gains in healthy lifespan.

Mechanism. An early PGE2–EP4 signal restores the ability of muscle stem cells to participate in regeneration while retaining a functional reserve for subsequent regeneration.

Prediction. In old mice of both sexes, compare identical short early and late pulses with vehicle, verify local exposure and EP4 response, and repeat injury without treatment after recovery and drug clearance. The early pulse should produce greater recovery of specific force after the second injury; equal benefit from early and late pulses would not support the early-window advantage. Test treatment interaction with inducible EP4 deletion in muscle stem cells: a comparable treatment benefit without EP4 in these cells, with informative controls, would contradict the proposed cellular dependence.

Mechanism. Separating the Wnt–NeuroD1 neuronal program from new LINE-1 insertions may preserve neuronal differentiation while reducing the burden of new insertions.

Prediction. Measure LINE-1 transcription separately from actual new insertions in lineage-traced cells of the old hippocampus, then compare the same Wnt pulse with and without selective restriction of retrotransposition while preserving retroelement transcription and checking for direct cell-cycle inhibition. Verify new insertions with an orthogonal method that excludes amplification artifacts. The primary result should be functional neurons with fewer new insertions and an unchanged first wave of neuron birth; the hypothesis is rejected if insertions are not elevated, reducing them does not improve function, or their reduction impairs maturation. Increased LINE-1 RNA alone does not count as genome damage.

Mechanism. Residual matrix stiffness may reactivate surviving fibroblasts through YAP/TAZ–PAI-1, restoring the NOX4-dependent state. Relieving PAI-1-dependent restriction of matrix remodeling during NOX4 suppression may interrupt this recurrence.

Prediction. First cross-recombine old lung cells and decellularized matrices after control or anti-NOX4 treatment: after treatment removal, the old matrix should reactivate previously normalized surviving cells, while the altered matrix should reduce activation of untreated cells, with mechanical effects distinguished from soluble signals. If recurrence is confirmed, compare control, NOX4 blockade, local PAI-1 restriction, and their combination. After complete withdrawal, the combination should provide more sustained recovery of lung compliance and gas exchange without loss of alveolar septa or renewed fibrosis, including when groups are matched for early collagen reduction and surviving cell numbers.

Mechanism. Reduced mTOR activity initiates autophagy, the recycling of cellular components. In experimental systems, subsequent mTOR reactivation is required to complete the cycle and restore the pool of functional lysosomes, so the longest suppression does not necessarily produce the greatest cellular clearance.

Prediction. Compare continuous and pulsed mTORC1 suppression in old mice receiving the same semaglutide treatment, controlling total drug exposure and choosing intervals according to actual recovery of tissue signaling. Pulsed suppression is expected to improve removal of damaged proteins and mitochondria, restoration of functional lysosomes, and preservation of muscle protein synthesis, absolute muscle mass and strength. Deeper mTOR suppression may produce more autophagosomes but less completed recycling of damaged components.

Mechanism. Enhancing high-quality DNA repair while maintaining antitumor barriers and avoiding permanent arrest of cell division.

Prediction. Test for a simultaneous reduction in new mutations and age-related loss of function.

Mechanism. Different hepatocyte lineage trajectories during regeneration may impose different long-term costs through ploidy reduction and adverse genetic events, even when short-term functional recovery is similar. Polyploidy can protect against some scenarios of tumor-suppressor loss, but polyploid cells can divide, change ploidy and give rise to tumors through ploidy reduction.

Prediction. In old animals of both sexes, trace hepatocyte lineages and compare brief regenerative regimens producing similar early functional recovery, accounting for division number, initial genotype and local damage. A regimen with fewer transitions to lower ploidy should produce fewer new adverse genetic events and better preserve function after the next challenge. Establishing causality requires a validated reversible adult intervention that reduces ploidy reduction without suppressing recovery or introducing independent cell-cycle effects; until then, trajectory analysis remains prognostic.

Mechanism. The spatial distribution of Reelin is proposed to guide dendritic orientation toward appropriate inputs in the old neurogenic niche.

Prediction. First compare three-dimensional Reelin maps and young neuron trajectories in young and old tissue. Compare restoration of the young spatial pattern with uniform delivery of the same amount of active protein and a spatially shuffled control, controlling for proteolytic fragments and the total Dab1 response. The correct map is predicted to increase the proportion of correct dendritic orientations and functional inputs without necessarily increasing neuron numbers. Check ectopic processes and network excitability.

Mechanism. Concentrated stimulation preferentially expands responsive clones, limiting neuronal subtype representation. Distributed regional NSC activation restores the diversity and correct positioning of subtypes toward the composition of a young functioning network.

Prediction. In aged mice, compare concentrated activation of the most responsive region with distributed regional activation, using pilot-adjusted parameters to obtain comparable total yields of mature neurons and tracing clonal origins without retrospectively selecting successful clones. Restoration of subtype diversity and correct positioning will predict discrimination of complex odor mixtures better than cell number. Check synaptic integration, maintenance of the stem-cell reserve and absence of differences in the peripheral olfactory epithelium; failure of origin and subtype diversity to improve function at equal neuronal number, maturity and survival would refute the hypothesis.

Mechanism. Precise timing of PGE2–EP4 signaling, rather than simply the average PGE2 level, enables muscle stem cells to support regeneration while preserving a diverse stem cell pool for subsequent injuries.

Prediction. Compare brief interventions during different recovery phases, prolonged stimulation and controls in aged animals of both sexes under the same total load and comparable exposure. Recovery of specific contractile force should persist through several recovery cycles and depend on preservation of a diverse stem cell pool and on EP4 specifically in these cells. Assess repeated-injury recovery, cell-clone fate, fibrosis and functional stem cell reserve; increased mass without increased strength does not support the hypothesis.

Mechanism. Correction of a pathological signaling program downstream of USP16 provides a neurogenic benefit separable from suppression of Cdkn2a/p16 and loss of tumor-suppressive control.

Prediction. Compare partial USP16 reduction, correction of a selected signaling module with unchanged p16, and a control; separately restore p16 to its initial level in the USP16-reduction group. The increase in functional new neurons should persist with the control response preserved, while assessing damage, clonal dominance and arrest of division under stress. The proposed separation is not supported if the benefit disappears whenever p16 and the damage response are preserved; increased dividing-cell numbers without normal neurons do not count as a useful result.

Mechanism. Timely termination of the NOX2-dependent redox signal, with the initial pulse preserved, improves the productivity of old neurogenesis.

Prediction. First measure redox trajectories in tracked cells of young and old mice after the same physiological stimulus, then vary pulse amplitude and the duration of return to baseline separately. Use cell-specific sensors with pH controls, independently measure oxidative damage, and exclude changes in overall physical activity. Correcting recovery duration while preserving the peak is predicted to increase the fraction of descendants that become functional neurons and improve the response to a repeated stimulus. The hypothesis is rejected if there is no age-related slowing, only peak reduction helps, or the effect is fully explained by survival of damaged cells. Assess the reserve and integration after 8–12 weeks.

Mechanism. Contact geometry affects the stability of Cx43-dependent contact signaling. If this explanation is correct, the geometry effect should survive loss of channel conductance and depend on the signaling function of the cytoplasmic tail.

Prediction. Compare continuous and fragmented contacts in three-dimensional niches made from aged mouse NSC and endothelium, matching contact area, oxygen and factor availability, Cx43 amount, stiffness and NSC shape. Measure ERK dynamics, exit from quiescence, neuronal fate and long-term clone maintenance. Compare Cx43 with a nonfunctional channel against a variant with impaired cytoplasmic-tail signaling: the geometry effect should persist after loss of conductance and depend on the tail. An initial increase in division followed by NSC depletion does not count as restored neurogenesis; subsequent confirmation in the aged SVZ is required.

Mechanism. Methylation marks and chromatin structure become blurred with each cell division and each repair cycle. Partial reprogramming would “rewrite the backup” of cellular instructions.

Prediction. If partial reprogramming using OSK Yamanaka factors without c-Myc in old animals restores not only epigenetic clocks but also organ function and lifespan, the hypothesis is correct.

Mechanism. Briefly increase the proteolytic activity of MMP24/MT5-MMP on the surface of selected stem cells in the aged subventricular zone that contact the ependyma, allowing temporary ectodomain cleavage of CDH2/N-cadherin. Use a single window before cell-cycle entry, stop MMP24 activity after activation, and restore the surface amount of CDH2/N-cadherin.

Prediction. Compare brief and continuous increases in activity, catalytically inactive MMP24, and control. Check CDH2 cleavage, contact with the ependyma, cell movement, and neuronal output of clones. Previously validated cleavage-resistant CDH2 should block the effect if it is mediated by this substrate, and the pulse should preserve the functional reserve.