Hypothesis

Aged cells actively suppress autophagy by accumulating oxidized lysosomal phospholipids that directly inhibit mTORC1 and VPS34 complexes, creating a self‑reinforcing loop that is exported via extracellular vesicles.

Mechanistic Basis

• Persistent mTORC1 hyperactivation in aging is not only due to upstream signaling defects but also to lipid‑mediated anchoring of mTORC1 to the lysosomal membrane. Oxidized phosphatidic acid (PA) and bis(monoacylglycero)phosphate (BMP) increase with age, altering lysosomal lipid packing and promoting a conformation of mTORC1 that resists inhibition by amino‑acid starvation.Persistent mTORC1 hyperactivation
• These oxidized lipids also bind the VPS34‑Beclin1 complex, blocking its lipid kinase activity and preventing autophagosome nucleation, independent of transcriptional downregulation of ATG genes.Transcriptional suppressors of autophagy
• Oxidized lysosomal lipids are enriched in extracellular vesicles released by senescent cells. When taken up by neighboring cells, they transfer the inhibitory lipid signature, activating AKT and suppressing autophagy‑related mRNAs, thereby propagating the suppression paracrine.EV‑mediated autophagy inhibition
• The resulting autophagy blockade sustains NLRP3 inflammasome activity, as damaged mitochondria and ubiquitinated proteins are not cleared, reinforcing inflammatory signaling that further stabilizes the oxidized lysosomal lipid environment.

Testable Predictions

1. Lysosomal fractions from old tissues will show a significant increase in oxidized PA and BMP compared with young tissues, and this increase will correlate inversely with LC3‑II levels.
2. Pharmacological reduction of lysosomal lipid oxidation (e.g., using ferrostatin‑1 or overexpressing lysosomal phospholipase A2) will restore mTORC1 sensitivity to starvation and rescue autophagic flux in aged cells.
3. Synthetic liposomes mimicking the aged lysosomal lipid profile will inhibit VPS34 kinase activity in vitro, an effect reversible by adding antioxidants or lipid‑scavenging peptides.
4. Extracellular vesicles isolated from old serum will transfer oxidized lysosomal lipids to recipient cells, leading to rapid mTORC1 reactivation and decreased autophagy; depletion of lipids from EVs will abolish this effect.

Experimental Approach

• Perform lipidomics on purified lysosomes from young and old mouse liver, heart, and immune cells to quantify oxidized PA, BMP, and other phospholipids.[Lipidomics method]
• Treat aged primary fibroblasts with ferrostatin‑1 or overexpress PLA2G15 (lysosomal phospholipase A2) and measure mTORC1 phosphorylation (p‑S6K), VPS34 activity (PI3P production), and autophagic flux (LC3‑II turnover with bafilomycin A1).
• Reconstitute VPS34 activity assays with liposomes of defined lipid composition; add oxidized lipids and assess PI3P synthesis; rescue with Trolox or lipid‑binding peptides.
• Isolate EVs from senescent mesenchymal stem cells, treat young hematopoietic stem cells, and track lysosomal lipid uptake using fluorescent lipid probes; assess autophagy markers and AKT activation.
• Use CRISPR‑KO of lipid‑transfer proteins (e.g., NPC2) to test whether blocking EV lipid transfer prevents paracrine autophagy suppression.

If oxidized lysosomal lipids are necessary and sufficient for the active downregulation of autophagy in aging, then manipulating their levels should break the suppression loop and restore cellular cleanup, directly challenging the view that autophagy decline is merely a passive failure of the machinery.