Hypothesis

Partial, transient reprogramming creates a transient epigenetic state at proteostasis gene enhancers that licenses chaperone‑mediated autophagy (CMA) of β‑sheet‑rich aggregates formed during aging. Rather than indiscriminately dissolving all aggregates, the cell uses this window to selectively target those aggregates that sequester damaged proteostasis components, converting them from inert deposits into processable substrates. If proteostasis capacity is not restored, aggregate dissolution releases toxic intermediates; if it is restored, aggregates are cleared safely.

Mechanistic rationale

1. Epigenetic priming – During days 3‑20 of MPTR, Yamanaka factors deposit H3K27ac at enhancers of HSPA8 (LAMP2A) and other CMA regulators, increasing their transcription without erasing somatic identity [2]. This creates a “proteostasis‑ready” chromatin landscape that persists briefly after factor withdrawal.
2. Aggregate specificity – Aging‑induced β‑sheet aggregates are enriched for proteins with exposed KFERQ‑like motifs, the hallmark of CMA substrates [3]. Sequestration of these motifs within the aggregate core makes them inaccessible to basal CMA, but the transient surge in LAMP2A and chaperone activity during MPTR can extract and unfold them.
3. Safety switch – If CMA activity is experimentally blocked during the MPTR window (e.g., by siRNA against LAMP2A), epigenetic age still declines but aggregates persist and downstream markers of proteotoxic stress rise, predicting that aggregate clearance is uncoupled from epigenetic rejuvenation.
4. Transgenerational memory – Proteostasis enhancer states established by MPTR can be inherited across cell divisions, offering a mechanism for lasting improvement in aggregate handling [6].

Testable predictions

• Prediction 1: Chromatin immunoprecipitation sequencing (ChIP‑seq) for H3K27ac at CMA‑related enhancers will show a peak during days 5‑15 of MPTR that correlates with increased LAMP2A mRNA and enhanced clearance of GFP‑tagged KFERQ reporters fused to known aging aggregates.
• Prediction 2: Knockdown of LAMP2A during the MPTR window will abolish the reduction in aggregate load (measured by filter‑trap assay or Thioflavin‑T fluorescence) despite a comparable decrease in epigenetic age clocks (e.g., GrimAge transcriptomic clock).
• Prediction 3: Cells subjected to MPTR followed by a secondary stress (e.g., proteasome inhibition) will exhibit faster resolubilization of pre‑formed aggregates than naïve cells, demonstrating a durable proteostatic memory.
• Prediction 4: Transient expression of a dCas9‑p300 activator targeted to the HSPA8 enhancer will mimic the MPTR‑induced H3K27ac peak and accelerate aggregate clearance without expressing Yamanaka factors, indicating that epigenetic priming alone is sufficient.

Falsifiability

If aggregate clearance occurs independently of CMA activity (e.g., proceeds normally when LAMP2A is knocked down) or if H3K27ac at proteostasis enhancers does not rise during the safe window, the hypothesis is refuted. Likewise, if forced epigenetic activation of CMA enhancers fails to improve aggregate handling in aged cells, the proposed link between epigenetic priming and aggregate processing would be invalid.

By coupling epigenetic rejuvenation to a selective, chaperone‑mediated disposal pathway, this hypothesis reframes amyloid‑like aggregates not as inert waste but as a timed reservoir that can be safely harvested once the cell’s quality‑control machinery is epigenetically reset.