Hypothesis

The active suppression of autophagy in aged tissues is not solely cell‑autonomous; it is propagated by senescence‑associated secretory phenotype (SASP) factors that epigenetically silence core autophagy genes in neighboring cells, creating a tissue‑wide blockade.

Mechanistic Model

1. SASP secretion – Senescent cells release IL‑6, IL‑8, and exosomes enriched in miR‑34a (see [4] for EV cargo alteration).
2. Paracrine signaling – IL‑6 binds its receptor on nearby cells, activating JAK/STAT3 signaling, which recruits histone deacetylase 3 (HDAC3) to promoters of autophagy initiators (e.g., ULK1, BECN1).
3. miR‑34a action – Exosomal miR‑34a directly targets the 3′‑UTR of TFEB mRNA, reducing TFEB protein levels and impairing lysosomal biogenesis (linking to [1] where oxidative stress blocks LC3 lipidation).
4. Chromatin remodeling – HDAC3‑mediated deacetylation increases nucleosome density at autophagy gene loci, suppressing transcription despite upstream stress signals.
5. Feedback loop – Reduced autophagy diminishes clearance of damaged mitochondria, raising ROS, which further stabilizes the senescent state and amplifies SASP (connecting [2] and [3] on senescence‑autophagy interplay).

This model extends the cell‑autonomous brakes described in the seed idea (mTORC1 hyperactivity, RUBCN upregulation, disulfide‑crosslinked ATG7/ATG3, PKA‑LC3B phosphorylation) by adding a non‑cell‑autonomous epigenetic layer that can sustain suppression even when those brakes are partially relieved.

Testable Predictions

• Prediction 1: In aged mouse liver, neutralizing IL‑6 with an antibody will increase acetylation of histone H3 at the ULK1 promoter and restore LC3‑II turnover, independent of mTORC1 activity.
• Prediction 2: Pharmacologic inhibition of HDAC3 (e.g., with RGFP966) will rescue TFEB expression and lysosomal acidification in fibroblasts co‑cultured with senescent cells, even when RUBCN is overexpressed.
• Prediction 3: Genetic deletion of miR‑34a in bone‑marrow‑derived macrophages will prevent the spread of autophagy suppression to naïve macrophages exposed to senescent‑cell conditioned media.

Experimental Approach

1. In vivo – Treat 24‑month‑old mice with anti‑IL‑6 antibody or HDAC3 inhibitor for two weeks; assess autophagy flux via tandem mRFP‑GFP‑LC3 reporter and measure senescence markers (p16^INK4a^, SASP cytokines).
2. Ex vivo – Isolate primary hepatocytes from old mice, culture with senescent‑cell conditioned media ± IL‑6 neutralizing antibody or HDAC3 inhibitor; quantify autophagosome formation and TFEB nuclear localization.
3. In vitro – Transfect young fibroblasts with miR‑34a mimic or inhibitor; evaluate TFEB mRNA stability and autophagy readouts under starvation.

Falsifiability

If IL‑6 neutralization or HDAC3 inhibition fails to restore autophagy flux or TFEB activity in aged tissues despite confirmed target engagement, the hypothesis that SASP‑driven epigenetic silencing is a dominant mechanism would be falsified. Conversely, successful rescue would support the model and suggest combinatorial therapies targeting SASP alongside conventional autophagy activators.