Baseline Genome Maintenance, Not Hormetic Stress Response, Sets the Longevity Ceiling

Hypothesis

Exceptional lifespan is determined by a constitutively high fidelity of genome maintenance systems that limit the acquisition of mosaic chromosomal alterations (mCAs). Hormetic interventions activate stress‑response pathways but do not alter this baseline repair capacity; therefore they improve healthspan without extending maximal lifespan unless they also boost intrinsic DNA repair or suppress mutagenic processes.

Rationale

• Centenarians and their offspring show fewer mCAs than age‑matched controls despite greater cumulative stress exposure 1. This inverse relationship indicates that low mCA burden precedes, rather than results from, a long life.
• mCA frequency plateaus around 102 years, suggesting a protective threshold that prevents further genomic instability 2.
• Large deletions (>500 kb) increase mortality risk 3, and total CNV burden negatively correlates with parental lifespan 4. Specific longevity‑associated CNVs affect genes in oxidative‑stress‑induced senescence pathways 5, pointing to constitutive protective genotypes.
• No study demonstrates that repeated hormetic stressors (cold, fasting, exercise, low‑dose radiation) reduce mCA accumulation in humans or model organisms.

Mechanistic Insight

We propose that two distinct molecular layers govern aging:

1. Baseline Layer – comprises high‑fidelity DNA repair (homologous recombination, base excision repair, mismatch repair), robust telomere maintenance, and effective suppression of retrotransposon activity. This layer sets the rate of mCA formation.
2. Stress‑Response Layer – includes HIF‑1α, NRF2, AMPK, and autophagy pathways that are transiently activated by hormetic cues. This layer mitigates damage after it occurs but does not alter the underlying mCA formation rate.

In individuals with a strong Baseline Layer, mCAs accrue slowly, allowing the Stress‑Response Layer to handle occasional insults without tipping into pathology. In contrast, a weak Baseline Layer yields rapid mCA accrual; even frequent hormetic activation cannot keep pace, leading to early onset of clonal hematopoiesis, solid‑tumor risk, or organ failure.

Testable Predictions

1. Genetic augmentation of DNA repair (e.g., overexpressing BRCA1, RAD51, or OGG1) in mice will reduce liver and blood mCA frequency by ≥30 % compared with wild‑type controls and will extend median lifespan, without altering baseline ROS levels or stress‑response gene expression.
2. Pharmacologic hormesis (intermittent fasting, cold exposure) in the same mice will improve glucose tolerance and grip strength but will not further lower mCA burden or increase lifespan beyond the DNA‑repair‑enhanced group.
3. Combined intervention (DNA‑repair enhancement + hormesis) will not produce additive lifespan gains beyond the DNA‑repair alone group, indicating that hormesis acts downstream of mCA formation.
4. In human centenarian offspring, polygenic scores for high‑fidelity DNA repair will correlate inversely with measured mCA burden (Spearman ρ < ‑0.4, p < 0.01), whereas scores for NRF2‑mediated oxidative‑stress response will show no correlation.

Experimental Design

• Model: CRISPR‑activated knock‑in of BRCA1 in C57BL/6J mice; confirm increased homologous‑recombination efficiency via RAD51 foci assay.
• Groups (n = 50 per group): WT control, WT + intermittent fasting, BRCA1‑up, BRCA1‑up + intermittent fasting.
• Readouts (every 6 months): single‑cell sequencing of peripheral blood to quantify mCA burden; clinical frailty index; survival.
• Analysis: Poisson regression for mCA counts; Cox proportional hazards for survival; interaction terms to test additivity.
• Human validation: whole‑genome sequencing of 200 centenarian offspring and 200 age‑matched controls; compute mCA load from sequencing data; correlate with polygenic risk scores for DNA‑repair genes (GWAS catalog) and oxidative‑stress genes.

Falsifiability

If DNA‑repair augmentation fails to reduce mCA frequency or extend lifespan, or if hormetic interventions consistently lower mCA burden across models, the hypothesis would be refuted. Conversely, a clear dissociation—where stress‑response activation improves health markers but leaves mCA accumulation unchanged—would support the claim that constitutive genome maintenance, not hormetic stress perception, determines the ultimate longevity ceiling.