c43-4-peptide-apc-cdh1-lifespan-extension
The peptide C43-4 is the first identified activator of the APC/C-Cdh1 complex, the machinery that holds cells in healthy quiescence, and it extended lifespan in both yeast and roundworms
A laboratory at the University of Saskatchewan discovered the short peptide C43-4, which activates the APC/C-Cdh1 complex, a molecular machine that tags surplus cellular proteins for destruction and thereby holds the cell in quiescence instead of letting it slide into senescence. In yeast and in the roundworm C. elegans the peptide extended lifespan through a conserved longevity pathway: in worms, the responsible genes are daf-16 (a FOXO homolog) and aak-2 (an AMPK homolog).
Every cell contains the APC enzyme, which tags surplus proteins with a biochemical label for degradation. Partnered with the protein Cdc20, APC drives cell division. Partnered with the protein Cdh1, it holds the cell in quiescence: not dividing, but alive and functional. It is this second form, APC/Cdh1, that fades with age. In aging quiescent yeast cells, the authors showed that APC targets stop being degraded on schedule and accumulate. This kind of failure is considered a molecular hallmark of aging, after which the cell transitions into irreversible decline.
On September 16 the laboratory published its findings in the journal Genetics. Chemical activators of the APC's Cdc20 branch are already in clinical trials as anticancer agents, so far without success. One such activator did extend the lifespan of dividing yeast cells but had no effect on quiescent ones; for quiescent cells, an agent that works specifically through Cdh1 is needed. The library of short Apc10-binding peptides came from the laboratory's earlier work on reversing drug resistance in breast cancer. In that same study, C43-4 first arrested tumor growth in mice. Out of the entire library, only C43-4 extended yeast lifespan in quiescence, and only through Cdh1.
C43-4 carries its own D-box signal (the RxxL motif), the same tag that natural APC substrates use to mark themselves for recognition through Apc10. Sequence similarity to the cellular stress sensor protein Htz1 pointed the authors to six amino acid positions worth testing by point substitutions. Only one of these, designated D7 and located outside the D-box signal, proved critical: without it, C43-4 lost its ability to bind Apc10 and lost its entire effect on lifespan. This means the peptide acts through precise target recognition, not as a nonspecific foreign protein. Synthetic C43-4 added externally to cells without a membrane carrier extended lifespan even when applied on the seventh day of aging, by which point the cells had already entered the aging process.
To verify that the effect is not limited to yeast, C43-4 was integrated into the genome of the roundworm C. elegans, and those animals lived longer as well. The effect disappeared in worms lacking aak-2 and was markedly reduced in worms lacking daf-16. These are the same AMPK and FOXO gene families that regulate lifespan across many species, including mammals. This indicates that the effect operates through an evolutionarily conserved longevity pathway active in both yeast and worms.
The authors specifically highlight the importance of the Cdh1 branch for the brain: in humans, defects in its function are linked to memory loss, microcephaly, and epilepsy, and amyloid-beta in Alzheimer's disease inactivates Cdh1.
The need for methods to activate APC/Cdh1 in the aging brain cannot be overstated
the authors write.
The precise mechanism by which C43-4 binds Apc10 is, according to the authors, a subject for future work, as are tests in mammals.