Active Autophagy Suppression in Aging Serves to Maintain a Senescence‑Promoting Mitochondrial ROS Reservoir

Active autophagy suppression in aged cells preserves a damaged mitochondrial pool that fuels senescence‑associated secretory phenotype (SASP) through sustained mtROS production. We hypothesize that age‑related lipid remodeling within lysosomes generates a specific phospholipid species that directly binds the ULK1 kinase, blocking its activation irrespective of nutrient status. This lipid‑ULK1 interaction doesn't just block ULK1; it adds a layer to the known mTORC1‑dependent brake (phosphorylation of ULK1‑Ser758) and it's known that autophagy remains resistant to rapamycin or young plasma in certain tissues. Testable predictions: (1) Lysosomal extracts from old mouse liver will contain elevated levels of bis(monoacylglycero)phosphate (BMP) or lysobisphosphatidic acid (LBPA) that co‑immunoprecipitate with ULK1; (2) Chemical depletion of BMP/LBPA using siRNA against the lipid‑synthesizing enzyme PLD3 will restore ULK1 phosphorylation at activating sites and increase LC3‑II flux even when mTORC1 is inhibited; (3) Expressing a ULK1 mutant incapable of binding the lipid will rescue autophagy flux and reduce mtROS, SASP cytokines (IL‑6, IL‑1β) and senescence markers (p16, SA‑β‑gal) in aged fibroblasts; (4) Conversely, augmenting BMP/LBPA in young cells will suppress autophagy and induce a senescence‑like state despite nutrient starvation. Moreover, we'll predict that enhancing lysosomal acidity via V‑ATPase overexpression will reduce BMP/LBPA accumulation, thereby relieving ULK1 inhibition and restoring autophagic clearance of damaged mitochondria. This links the lipid hypothesis to the observed rejuvenation of autophagy by young plasma, which may contain factors that promote lysosomal lipid catabolism. Finally, testing whether pharmacological inhibition of PLD3 (or activation of lipid phosphatases such as PTPIP51) mitigates age‑dependent SASP in vivo will provide a direct readout of the pathway’s contribution to organismal aging. Readouts would include lysosomal lipid mass spectrometry, ULK1 immunoprecipitation followed by lipid blotting, mitochondrial membrane potential assays, and secretory proteome profiling. Targeting this lipid‑ULK1 node could therefore rejuvenate autophagy without globally inhibiting mTORC1, offering a more precise anti‑aging strategy.