Hypothesis

Oxidative inactivation of autophagy receptors by lipid peroxidation adducts generates spatially restricted autophagy‑incompetent microdomains (“autophagy deserts”) within cells. These deserts prevent selective clearance of the most damaged mitochondria, allowing a vicious cycle of ROS production, further receptor oxidation, and bioenergetic decline. Restoring local redox balance rescues receptor oligomerization, re‑establishes the autophagy hierarchy, and extends healthspan.

Mechanistic basis

1. Redox‑sensitive receptor switch – p62, NBR1 and OPTN contain cysteine residues whose oxidation state controls oligomerization and LC3 binding. Moderate S‑glutathionylation promotes active oligomers, whereas extensive Michael addition of HNE/MDA to the same cysteines blocks disulfide formation and locks receptors in a monomeric, inactive state.[1][4]
2. Microdomain segregation – Mitochondrial subpopulations that generate superoxide (e.g., Complex I‑rich regions) concentrate peroxidizable cardiolipin and iron‑sulfur clusters, creating steep HNE/MDA gradients. In these hotspots, receptor oxidation exceeds the activation threshold, producing autophagy‑incompetent zones where damaged organelles accumulate despite global autophagy induction.[2][3]
3. Feedback loop – Uncleared mitochondria leak more superoxide, amplifying local lipid peroxidation and further oxidizing receptors. Concurrently, HNE/MDA adducts on metabolic enzymes (e.g., citrate synthase, malic enzyme) diminish TCA cycle flux, increasing NADH/NAD+ ratio and impairing SIRT3‑mediated deacetylation of antioxidant enzymes, thereby deepening the oxidative niche.[5]

Testable predictions

• Spatial mapping: Proximity‑labeling (e.g., APEX2‑p62) combined with redox‑sensitive roGFP2‑Orp1 will show that p62 oligomers are depleted precisely in mitochondrial subfractions with the highest HNE/MDA signal in aged tissues.[2]
• Genetic rescue: Knock‑in of cysteine‑to‑serine mutants at p62 Cys105/Cys113 (oxidation‑resistant) should restore oligomerization in high‑ROS mitochondria, reduce HNE‑modified Complex I subunits, and improve respiration in old mice.[1]
• Pharmacological shift: Mitochondria‑targeted catalase (mCAT) or a lipophilic peroxiredoxin mimetic will lower local HNE/MDA without affecting cytosolic redox state, re‑enabling receptor oligomerization and autophagic flux specifically in the desert regions.[3]
• Functional readout: Flux assays using mKeima‑mtDNA will reveal diminished mitophagy in desert regions of aged cells; rescuing redox balance should normalize flux without altering overall LC3‑II levels.

Falsifiable outcomes

If oxidation‑resistant receptor mutants fail to reduce mitochondrial HNE adducts or improve lifespan, or if mitochondrial antioxidants do not restore receptor oligomerization in the predicted microdomains, the hypothesis would be refuted. Conversely, demonstration that localized redox correction re‑engages the autophagy hierarchy and delays age‑related pathology would support the model.

Implications

This reframes autophagy decline not as a global loss of capacity but as a loss of spatial precision. Interventions that preserve the redox‑sensitive switch of autophagy receptors in oxidative microdomains may uncouple ROS signaling from receptor inactivation, offering a targeted strategy to mitigate mitochondrial dysfunction in aging.