Active Suppression of Autophagy in Aging via Oxidized Phospholipid–PPARγ Signaling

We propose that the age‑dependent inhibition of autophagy isn't only driven by Bcl‑2/Beclin‑1 sequestration, mTORC1 activity, and NRF2 loss, but also by an oxidized phospholipid (oxPL)–activated PPARγ pathway that directly represses core autophagy genes. In aged cells, membrane peroxidation generates oxPLs such as 'POVPC' and 'PGPC', which accumulate in lysosomal membranes and the cytosol. These lipids act as endogenous ligands for PPARγ, promoting its recruitment of the co‑repressor NCoR/SMRT complex to autophagy gene promoters (e.g., ATG5, ATG7, LC3). This transcriptional repression adds a third layer to the existing post‑translational block (Bcl‑2/Beclin‑1) and the NRF2‑dependent decline, creating a synergistic lock on autophagic flux.

Key predictions:

• oxPL levels will correlate inversely with autophagic flux across tissues from young to old mice and humans.
• Pharmacological antagonism of PPARγ (e.g., GW9662) or genetic deletion of PPARγ in myeloid or parenchymal cells will restore ATG gene expression and LC3‑II conversion in aged mice, even when Bcl‑2/Beclin‑1 interaction remains intact.
• Conversely, ectopic overexpression of a constitutively active PPARγ in young cells will mimic the aged autophagy suppression phenotype, increasing p62 accumulation and sensitizing cells to oxidative stress.
• Disrupting the PPARγ–NCoR interaction (using a peptide that blocks the co‑repressor binding site) should rescue autophagy without affecting mTORC1 or NRF2 levels, isolating the lipid‑sensing branch.

Experimental approach:

1. Quantify oxPL species in lysosomal fractions from 3‑month vs 24‑month mouse liver, brain, and aorta using LC‑MS/MS; correlate with ATG5/ATG7 mRNA (qPCR) and LC3‑II/I ratio (Western) 1 2.
2. Treat aged mice with GW9662 or administer a PPARγ‑specific siRNA via lipid nanoparticles; measure autophagic flux using mCherry‑GFP‑LC3 reporter and assess senescence markers (p16, SASP) 5 6.
3. Generate myeloid‑specific PPARγ knockout mice crossed with the Becn1^F121A^ line; test whether combined disruption yields additive lifespan extension beyond either single intervention 4 7.
4. In vitro, expose young fibroblasts to synthetic POVPC; assess PPARγ nuclear translocation (immunofluorescence) and ATG promoter repression (ChIP‑qPCR for NCoR). Rescue with PPARγ antagonist or NCoR‑disrupting peptide.

If oxPL‑PPARγ signaling actively suppresses autophagy, then inhibiting this axis should bypass the need to overcome Bcl‑2/Beclin‑1 binding or NRF2 loss, offering a complementary strategy to rejuvenate cellular cleanup. Failure to observe restored autophagic flux despite PPARγ inhibition would falsify the hypothesis and suggest that lipid‑sensing pathways aren't a dominant brake in aging.