mTOR Inhibition Primes Chromatin for Epigenetic Resetting During Partial Reprogramming

Hypothesis

Transient mTOR inhibition before cyclic expression of Yamanaka factors enhances chromatin accessibility and TET‑mediated DNA demethylation, thereby increasing the efficiency and durability of epigenetic rejuvenation without compromising cellular identity.

Mechanistic Rationale

mTOR activity drives anabolic programs that favor chromatin condensation through increased histone acetylation and methylation, limiting the plasticity needed for epigenetic resetting. When mTOR is briefly suppressed, cells shift toward a catabolic state marked by upregulated autophagy and NAD+‑dependent sirtuin activity. Autophagy clears damaged histones and chromatin‑associated proteins, while sirtuins deacetylate histones H3K9 and H3K56, creating a more open nucleosome landscape. This metabolic milieu coincides with the early window (days 3‑7) when partial reprogramming initiates steady epigenetic age decline. In this state, TET enzymes gain better access to 5‑mC sites, accelerating hydroxylation and subsequent base‑excision repair–driven demethylation. The result is a deeper, more stable epigenetic reset that retains lineage‑specific transcription factors, avoiding dedifferentiation.

Experimental Design

1. Animal cohorts – Aged (20‑month) C57BL/6 mice divided into four groups (n=20 per group):
   • Control (vehicle)
   • Rapamycin pretreatment (2 mg/kg i.p. 3×/week for 2 weeks) followed by vehicle
   • Cyclic OSK (AAV‑OSK, 2 days on/5 days off) for 8 weeks
   • Rapamycin pretreatment + cyclic OSK (same regimens)
2. Readouts
   • Epigenetic age via multi‑tissue DNA methylation clocks at baseline, week 4, week 8, and week 24
   • Chromatin accessibility (ATAC‑seq) in liver and hippocampus at day 5 of the first OSK cycle
   • TET activity and 5‑hmC levels (dot blot, ELISA)
   • Autophagy flux (LC3‑II/I ratio, p62 degradation) in the same tissues
   • Functional assays: grip strength, gait analysis, visual acuity (optomotor response)
   • Longevity and tumor surveillance up to 30 months
3. Statistical analysis – Two‑way ANOVA with post‑hoc Tukey for interaction effects; Kaplan‑Meier survival curves with log‑rank test.

Predicted Outcomes

• The rapamycin + OSK group will show a significantly greater reduction in epigenetic age (≥15 % additional reversal) compared with OSK alone at week 8, persisting to week 24.
• ATAC‑seq will reveal increased accessibility at promoters of pluripotency‑associated but lineage‑restricted genes (e.g., Klf4 enhancers) only in the combined group.
• 5‑hmC levels and TET activity will peak earlier (day 3) and reach higher amplitude in the rapamycin + OSK condition.
• Autophagy markers will be elevated pretreatment and remain higher during early OSK cycles.
• Functional improvements (strength, vision) will be amplified, and median lifespan will extend beyond the 109 % increase seen with OSK alone.
• No increase in teratoma formation or hyperplasia will be detected, confirming safety.

Falsifiability

If rapamycin pretreatment fails to augment chromatin accessibility, TET activity, or epigenetic age reversal relative to OSK alone, the hypothesis is refuted. Conversely, observing synergistic effects only when mTOR inhibition is temporally misaligned (e.g., given after OSK cycles) would further support the mechanistic window specificity.

References

• Systemic AAV‑OSK extends median lifespan by 109 % in 124‑week‑old mice 1
• Cyclic OSKM extends lifespan and reverses aging hallmarks 2
• Partial reprogramming induces steady epigenetic age decline beginning at days 3‑7 3
• Transient/cyclic OSK protocols show no tumors in mouse lifespan studies 4
• One‑year OSK treatment restores vision via DNAm reversal without pluripotency 5 }