Hormesis as a transient epigenetic priming state: testing whether cessation reveals accelerated epigenetic aging

Hormetic stressors such as intermittent fasting, cold exposure, or low-dose radiation trigger a short-lived protective chromatin state that primes stress‑response genes for rapid activation. This state depends on reversible histone acetylation at promoters of FOXO, Nrf2, and autophagy regulators, driven by SIRT1 activation and NAD+ flux. When the stressor is removed, the acetylation marks decay, allowing heterochromatin spreading at those loci and reducing transcriptional resilience. If hormesis merely buys time without repairing damage, then stopping the stimulus should unmask cryptically accumulated aging lesions, visible as an accelerated epigenetic clock. We test this by subjecting C57BL/6 mice to a strict intermittent‑fasting regimen (24 h fasting/24 h refeeding) for six months, then returning them to ad libitum feeding. Cohorts are sampled at baseline, after the intervention, and at 0, 4, and 12 weeks post‑cessation. We measure genome‑wide H3K27ac ChIP‑seq at FOXO3 and NRF2 targets, whole‑blood DNA methylation age (Horvath clock), and functional health‑span metrics (grip strength, glucose tolerance, frailty index). The hypothesis predicts: (1) a significant increase in H3K27ac at stress‑response promoters during fasting, (2) a rapid loss of this mark within two weeks of feeding resumption, (3) a concomitant rise in epigenetic age that exceeds age‑matched controls, and (4) earlier onset of age‑related pathology compared with continuously fed mice. A falsifiable outcome would be no difference in epigenetic age trajectory or health‑span decline between post‑fasting and control groups, indicating that hormetic benefits persist independently of the priming state. This experiment directly probes whether hormesis functions as a transient epigenetic shield rather than a permanent repair mechanism, linking the observed lifespan extension to dynamic chromatin remodeling that collapses when the threat signal disappears.