Hypothesis

Intermittent metabolic hormesis creates a lasting epigenetic mark at autophagy and proteasome gene promoters that sustains cellular cleanup after the stressor ends, and this epigenetic memory—not the transient stress response—is the primary driver of lifespan extension.

Mechanistic Rationale

Hormetic triggers such as periodic fasting activate nutrient‑sensing pathways (AMPK, SIRT1) that recruit histone methyltransferases to deposit H3K4me3 at promoters of genes like LC3B, ATG5 and PSMB5. Recent work shows that CR extends lifespan via TOR inhibition and sirtuin activation [1] [2], yet the persistence of benefits after CR cessation remains unclear [3] [4]. We propose that the same signaling cascades also set a stable chromatin state that keeps these loci poised for transcription, providing a mechanistic bridge between short‑term stress adaptation and long‑term aging suppression.

Testable Predictions

1. Intermittent fasting will increase H3K4me3 at autophagy and proteasome promoters in mouse liver, and this elevation will persist for at least two weeks after the fasting regimen stops.
2. Genetic blockade of the H3K4 methyltransferase SETD1A in hepatocytes will abolish the fasting‑induced H3K4me3 increase and the accompanying rise in LC3B and PSMB5 mRNA, while leaving the acute AMPK/SIRT1 activation intact.
3. Mice with hepatocyte‑specific SETD1A knockout undergoing intermittent fasting will show no improvement in proteasome activity or autophagic flux compared with wild‑type fasted controls, and will not exhibit the lifespan extension seen in wild‑type fasted mice.
4. Pharmacological inhibition of the proteasome during the fasting period will erase the longevity benefit, confirming that the epigenetic mark works through sustained proteolytic capacity.

Experimental Design

Subjects: Male C57BL/6J mice, 8 weeks old. Groups: (i) Wild‑type ad libitum (WT‑AL), (ii) Wild‑type intermittent fasting (WT‑IF, 24 h fast every other day), (iii) Liver‑specific SETD1A KO ad libitum (KO‑AL), (iv) Liver‑specific SETD1A KO intermittent fasting (KO‑IF). Interventions: 3‑month feeding regimen, then return to ad libitum for observation. Readouts: ChIP‑qPCR for H3K4me3 at LC3B, ATG5, PSMB5 promoters (collected at end of IF period and 14 days post‑IF); RT‑qPCR for same genes; proteasome activity assay (fluorogenic substrate); autophagic flux (LC3‑II turnover with bafilomycin); survival monitoring. Controls: Verify AMPK phosphorylation and SIRT1 deacetylation targets to ensure upstream hormetic signaling is intact in KO‑IF mice.

Potential Outcomes and Falsifiability

If the hypothesis is correct, WT‑IF mice will show persistent H3K4me3 elevation, increased gene expression, heightened proteasome/autophagy activity, and a significant lifespan extension relative to WT‑AL. KO‑IF mice will retain normal AMPK/SIRT1 activation but lack the epigenetic mark, fail to up‑regulate target genes, show no boost in proteolytic capacity, and display survival curves indistinguishable from KO‑AL and WT‑AL. This outcome would falsify the idea that hormesis extends life solely via transient stress signaling and instead support an epigenetic memory model.

Conversely, if KO‑IF mice still enjoy lifespan extension despite loss of H3K4me3 at the assayed promoters, the hypothesis would be falsified, indicating that either other epigenetic mechanisms or purely signaling‑based effects dominate the longevity benefit of metabolic hormesis.