Zebra finch chicks received the stress hormone corticosterone for 17 days, and new precision epigenetic clocks showed their biological age nearly 38% above their actual age
Zebra finch chicks received the stress hormone corticosterone for 17 days, and new precision epigenetic clocks showed their biological age nearly 38% above their actual age
Biologists at the Universities of Glasgow and Edinburgh built the first accurate epigenetic clock for zebra finches, calibrating it on birds from one day to nine years old. No such instrument existed for the species before. The age jump in corticosterone-treated chicks traced to a single gene, ZBTB16: its age-associated DNA methylation mark dropped sharply and, unlike another corticosterone target gene, did not recover within four days of treatment withdrawal.
Zebra finches have been used in aging biology for decades: chicks develop in the nest outside the mother's body, so hormones can be administered directly. In a preprint posted October 2, the team selected the best clock from over 2,000 model variants, calibrating it on 99 birds aged one day to nine years and validating it on 96 independent samples. The final model errs by an average of 80 days in a random bird and by only 8 days in chicks of the target age.
They applied this model to 48 chicks that received corticosterone, the avian equivalent of cortisol, in oil solution twice daily from day 12 to day 28 of life; 48 controls received oil alone. On day 29, the clock read the treated chicks as roughly 11 days older than their true age, nearly 38% above the actual 29 days, and the difference persisted four days after treatment ended. A similar tool built for wild wood mice in Edinburgh two weeks earlier yielded the opposite result: supplemental feeding and antiparasitic treatment slowed their clock relative to calendar age, whereas stress in the finch chicks accelerated it sharply.
The strongest response came from the gene ZBTB16: its DNA methylation mark fell by approximately 30 percentage points. Another cortisol target gene, FKBP5, also lost methylation but began recovering within three days of corticosterone withdrawal. ZBTB16 showed no recovery across four days of observation, and its methylation level in treated chicks matched that of birds older than two years while differing from birds under one year.
Before this work, the leading candidate was the cortisol receptor gene GR itself: stress was thought to hypermethylate it, reducing cellular sensitivity to the hormone and triggering metabolic reprogramming. The data did not support this. GR methylation changed weakly and inconsistently, while ZBTB16 appeared on three independent lists simultaneously: as a clock gene, as a top corticosterone responder, and as an age-associated gene. The authors propose that the persistent loss of methylation at ZBTB16, a gene previously linked to metabolism, immunity, and tumor suppression, activates a metabolic survival program through the mTOR/AMPK, insulin, and lipid metabolism pathways that regulate the pace of aging, and that changes at GR are secondary.
The corticosterone dose came from the team's earlier protocol: using that same dose in a different cohort, the laboratory had previously shown that early-life stress shortens adult lifespan by roughly 30%. The 96 chicks in the present experiment were not followed to the end of life. Treatment and other measured factors explained only 15% of the variance in epigenetic age; nest of origin exerted a stronger influence. The same laboratory first demonstrated in 2012 that telomere length in early life predicts total lifespan in zebra finches. The new work adds a molecular pathway from hormone to gene in place of a statistical correlation.