Testing the Autophagy Cargo Hierarchy Hypothesis: Mis‑sequencing of Organelle Degradation Drives Inflammasome Activation in Aging

Hypothesis

The autophagic cargo hierarchy is not merely a passive response to stress but an actively regulated triage system whose temporal sequence determines downstream inflammatory signaling. We propose that age‑related decline arises when the normal ordering—ER‑phagy → mitophagy → lipophagy—is disrupted, causing premature or delayed degradation of specific organelles. This mis‑sequencing leads to accumulation of mitochondria‑derived ROS that aberrantly sensitize the p62 receptor, skewing ubiquitin‑dependent cargo selection toward ER‑phagy substrates and triggering inflammasome activation via ER stress‑mediated TXNIP‑NLRP3 signaling.

Mechanistic Model

1. Normal hierarchy – During nutrient stress, ER‑resident receptors (FAM134B, SEC62) are recruited first to clear unfolded protein load, followed by PINK1‑Parkin‑dependent mitophagy mediated by OPTN/NDP52, and finally lipophagy via LC3‑II interaction with perilipin‑2. Each step reduces organelle‑specific danger signals (ER Ca2+ leak, mtROS, lipid peroxidation).
2. Age‑related shift – Chronic low‑grade inflammation elevates basal mtROS, which promotes p62 oligomerization and increases its affinity for ubiquitin‑cargo independent of upstream signals. This causes p62 to outcompete ER‑phagy receptors for limited autophagosomal membranes, delaying ER‑phagy while accelerating mitophagy of already compromised mitochondria.
3. Consequence – Incomplete ER‑phagy leaves misfolded proteins and Ca2+ leak, activating the TXNIP‑NLRP3 inflammasome. Simultaneously, excessive mitophagy depletes functional mitochondria, reducing ATP for autophagosome formation and creating a vicious cycle.

Testable Predictions

• In aged mice, hepatic p62 oligomer levels will be elevated early in fasting, correlating with delayed FAM134B‑positive autophagosome formation and accelerated OPTN‑positive mitophagy.
• Pharmacological inhibition of p62 oligomerization (using a small‑molecule blocker of its PB1 domain) will restore the ER‑phagy → mitophagy sequence and reduce NLRP3 inflammasome activity in aged tissues.
• Wearable‑derived HRV recovery kinetics after a standardized meal will predict the ER‑phagy/mitophagy ratio measured in peripheral blood mononuclear cells, with slower recovery indicating hierarchical inversion in older humans.

Experimental Approach

1. Biochemical fractionation – Isolate liver lysates from young (3 mo) and aged (24 mo) mice at 0, 2, 6, 12 h fasting. Western blot for oligomerized p62 (cross‑linked), FAM134B, OPTN, LC3‑II, and cleaved caspase‑1.
2. Imaging – Confocal colocalization of FAM134B or OPTN with mCherry‑GFP‑LC3 to assess autophagosome formation order; quantify Pearson’s coefficients over time.
3. Intervention – Treat aged mice with the p62 PB1 inhibitor (e.g., GLYX‑13 analog) or vehicle during intermittent fasting; measure serum IL‑1β, hepatic TXNIP expression, and grip strength.
4. Human pilot – Recruit 30 young and 30 older adults; collect fasting‑fed blood draws, assess HRV recovery via chest strap, isolate PBMCs, and flow‑sort for p62 oligomer and organelle‑specific autophagy markers (using organelle‑specific LC3‑associated antibodies). Correlate HRV slope with ER‑phagy/mitophagy ratio.

If the data show that restoring the canonical hierarchy rescues inflammasome activity and improves functional outcomes, the hypothesis will be supported; otherwise, the hierarchy‑disruption model will be falsified.