Hypothesis

During alternate‑day fasting (ADF) the transient rise in mitochondrial ROS activates p62/SQSTM1 and NIX/BNIP3L, which phosphorylate and recruit ubiquitin‑cargo complexes in a defined sequence: damaged mitochondria first, then protein aggregates, followed by ER fragments and lipid droplets. This ROS‑gated receptor cascade creates a temporal hierarchy of autophagic cargo that is absent in constant starvation or fed states. Disrupting the early ROS‑p62/NIX axis (e.g., with mito‑targeted antioxidants or kinase inhibitors) should uncouple mitophagy from downstream aggrephagy, leading to selective accumulation of specific damaged organelles and accelerated age‑related decline.

Mechanistic Basis

• ROS generated during the glycolysis‑to‑fat‑oxidation switch oxidizes cysteine residues on p62, enhancing its affinity for ubiquitin‑tagged mitochondrial outer‑membrane proteins (3).
• Oxidized p62 then scaffolds NIX, promoting its translocation to depolarized mitochondria and initiating mitophagy (1).
• As mitochondrial ROS falls, p62 de‑oxidation reduces its mitochondrial cargo preference, freeing it to bind ubiquitinated protein aggregates and recruit aggrephagy receptors (2).
• Subsequent activation of ER‑phagy receptors (SEC62, FAM134B) occurs only after aggrephagy saturates, reflecting a shift in receptor availability rather than a fixed genetic program (4).
• Thus the hierarchy is a metabolic‑state‑dependent relay, not a rigid timer.

Testable Predictions

1. In liver cells of mice undergoing ADF, mitophagy flux (mt‑Keima) peaks within the first 4 h of the fasting window, preceding aggrephagy (GFP‑LC3‑p62) and ER‑phagy (sec62‑mCherry) peaks by ~2‑h intervals.
2. Acute treatment with mito‑TEMPO (a mitochondrial ROS scavenger) administered at the onset of fasting will blunt the early mitophagy peak without affecting basal autophagy, causing a delay in aggrephagy and ER‑phagy.
3. Mice receiving mito‑TEMPO during ADF will show increased mitochondrial protein carbonylation, elevated p62‑positive aggregates, and impaired ER calcium handling after 4 weeks, correlating with shortened median lifespan compared to ADF‑only controls.
4. Genetic knockout of NIX in hepatocytes will phenocopy the mito‑TEMPO effect, confirming that the ROS‑p62‑NIX axis gates the cargo hierarchy.

Experimental Design (outline)

• Animals: C57BL/6J mice, 8 weeks old, split into ADF, ADF + mito‑TEMPO, ADF + NIX‑LKO, and ad lib fed controls (n=15/group).
• Readouts: Live‑imaging reporters (mt‑Keima, GFP‑LC3‑p62, sec62‑mCherry) via intravital microscopy every 2 h across a 24‑h fasting cycle; biochemical assays (mitochondrial ROS, protein carbonylation, ER stress markers) at 0, 4, 8, 12, 16, 20 h; longitudinal survival and frailty scoring.
• Analysis: Compare timing of peak flux across reporters; test whether ROS scavenging shifts or flattens the mitophagy peak and delays subsequent cargos; assess correlation with aging phenotypes.

If the ROS‑dependent receptor relay dictates the autophagy cargo order, then uncoupling the early step should disrupt the entire sequence and accelerate functional decline. Conversely, if autophagy proceeds in parallel regardless of ROS, mito‑TEMPO will not alter the temporal order, falsifying the hypothesis.