Hypothesis

Serial measurement of a defined set of PRC2‑associated CpG sites can serve as a leading indicator of TET‑mediated demethylation dynamics, allowing real‑time adjustment of OSK induction frequency to stay within the therapeutic window between insufficient rejuvenation and epigenetic identity erosion.

Rationale

Recent work shows that OSK‑driven rejuvenation depends on TET1/TET2 activity at PRC2/H3K27me3‑marked loci, and that ribosomal DNA methylation clocks reflect retinal ganglion cell rejuvenation in near‑real time (3). However, clocks have only been used retrospectively. We propose that the rate of methylation change at a subset of these TET‑target CpGs precedes phenotypic outcomes by several days, creating a predictive window. This rate is expected to fluctuate with cellular α‑KG/TET cofactor availability, which is pulsed by OSK expression and subsequently depleted during the off‑doxycycline phase, generating a refractory period that limits further demethylation until metabolites recover.

Predictions

1. In OSK‑cycled mice, the slope of demethylation (Δ% methylation per day) at sentinel CpGs will peak 24–48 h after each doxycycline pulse and decline to baseline before the next pulse if the interval is optimal.
2. Extending the interval beyond the point where the slope reaches zero will lead to a rebound increase in methylation at the same sites, correlating with loss of lineage‑specific markers (e.g., cardiac troponin T, hepatocyte nuclear factor 4α) and emergence of low‑level pluripotency transcripts (e.g., Klf4, Esrrb).
3. Shortening the interval while the slope remains positive will cause cumulative demethylation beyond a threshold (~30 % loss at sentinel CpGs), associated with ectopic OCT4 expression and histological signs of dedifferentiation.
4. Adjusting the OSK pulse frequency to maintain the slope within a predefined target range (e.g., –0.5 % to –1.5 % methylation change per day) will yield a greater increase in functional readouts (e.g., ejection fraction, albumin secretion) and a lower epigenetic age as measured by the LUC clock compared with fixed weekly cycles.

Experimental Design

• Animals: 100‑week‑old C57BL/6J mice, n=10 per group.
• Groups: (A) Fixed weekly OSK (2 days on/5 days off); (B) Adaptive OSK where doxycycline is administered only when the rolling average slope of methylation at 20 sentinel CpGs (selected from PRC2‑marked promoters) falls within –0.5 % to –1.5 %/day, measured via tail‑blood bisulfite sequencing every 48 h; (C) Vehicle control.
• Readouts: (i) Serial blood methylation at sentinel CpGs; (ii) Tissue‑specific epigenetic age (LUC clock) in heart and liver at weeks 4, 8, 12; (iii) Functional assays (echocardiography, serum ALT/AST, glucose tolerance); (iv) Identity markers (immunostaining for cTnT, HNF4α, OCT4) and pluripotency transcript levels (RT‑qPCR).
• Analysis: Compare area under the curve for functional improvement and epigenetic age reduction across groups; test whether adaptive dosing reduces incidence of identity loss (OCT4+ cells) below 5 % while achieving >15 % median lifespan extension relative to controls.

Potential Outcomes

If the hypothesis holds, group B will show superior functional rejuvenation and epigenetic age reset with minimal ectopic pluripotency, demonstrating that methylation kinetics can be used as a prospective dosing controller. Failure to observe a correlation between CpG slope and functional outcomes would falsify the premise that these sites are leading indicators, prompting a search for alternative real‑time biomarkers (e.g., hydroxymethylation flux or circulating metabolites).