Hypothesis

Aging-related epigenetic drift at the CDKN2A/B locus stems not only from loss of repressive marks but also from a breakdown in the hierarchical selectivity of autophagy that normally removes PRC2 complex components (EZH2, SUZ12, EED) and DNA methyltransferases (DNMT1, DNMT3A/B). When this selective flux falters, epigenetic regulators accumulate, reinforcing a feed‑forward loop that locks the locus in an open, transcriptionally active state.

Mechanistic Rationale

• Autophagy exhibits substrate preference via cargo receptors such as SQSTM1/p62 and NBR1, which can recognize ubiquitinated proteins and specific post‑translational modifications.
• Emerging data show that EZH2 and SUZ12 become phosphorylated and ubiquitinated under oxidative stress, creating potential autophagic "eat‑me" signals.
• In young cells, active autophagy preferentially degrades these phosphorylated PRC2 subunits, limiting their nuclear residence and preserving H3K27me3 at CDKN2A/B promoters.
• With age, mitochondrial dysfunction elevates ROS, impairing autophagosome formation and shifting cargo receptor occupancy toward bulk cytosol, thereby sparing PRC2 components.
• The resulting increase in nuclear EZH2/SUZ12 paradoxically fails to restore repression because concurrent loss of H3K27me3 writers and gain of DNA methylation shift the chromatin state toward a senescent configuration.
• This mirrors the seed idea that autophagy functions as a triage ritual: when the hierarchy collapses, the cell mistakenly spares the very regulators that should be removed first, accelerating senescence.

Testable Predictions

1. In fibroblasts from young donors, immunoprecipitation of SQSTM1/p62 will pull down phosphorylated EZH2 and SUZ12 more efficiently than total EZH2/SUZ12.
2. Pharmacological activation of autophagy (e.g., with spermidine) will reduce nuclear EZH2/SUZ12 levels and increase H3K27me3 at the CDKN2A/B promoter, whereas autophagy inhibition (chloroquine) will have the opposite effect.
3. CRISPR‑mediated mutation of the ubiquitin‑acceptor lysines on EZH2 will block its autophagic degradation and lead to premature p16^INK4a upregulation despite intact autophagic flux.
4. Senescent cells rescued by ectopic expression of a non‑degradable EZH2 mutant will retain high p16^INK4a expression even when autophagy is chemically induced, confirming that loss of PRC2 turnover, not autophagy per se, drives the epigenetic shift.

Experimental Approach

• Isolate primary human fibroblasts from donors aged <30 and >70 years.
• Measure autophagic flux (LC3‑II turnover with bafilomycin A1) and correlate with nuclear EZH2/SUZ12 levels by subcellular fractionation and western blot.
• Perform SQSTM1/p62 pull‑down followed by mass spectrometry to quantify phosphorylated PRC2 subunits.
• Treat cells with spermidine (100 µM) or chloroquine (20 µM) for 24 h, then assess CDKN2A/B promoter methylation (bisulfite sequencing) and H3K27me3 (ChIP‑qPCR).
• Use lentiviral vectors to express wild‑type or lysine‑mutant EZH2 (K→R) in young fibroblasts; monitor p16^INK4a expression and senescence‑associated β‑galactosidase activity.
• Statistical analysis: two‑way ANOVA with age and treatment as factors; significance set at p<0.05.

If the hypothesis holds, enhancing the selective removal of PRC2 components should delay or prevent age‑associated epigenetic drift at the CDKN2A/B locus, uncoupling autophagy flux from senescence outcomes.