Temporal Autophagy Selectivity Determines Senescent Cell Fate

Hypothesis Restoring the ordered sequence of selective autophagy—specifically ensuring that mitophagy precedes aggrephagy during nutrient stress—prevents the re‑accumulation of senescent cells after senolytic clearance.

Mechanistic Rationale Selective autophagy operates through cargo receptors that respond to distinct stressors. Under metabolic stress, mitophagy (mediated by p62/SQSTM1 and NDP52) is activated first to remove damaged mitochondria and limit ROS production [1][2]. Aggrephagy (driven by NBR1 and p62) follows to clear protein aggregates. When this order is inverted—aggrephagy initiates before mitophagy—mitochondrial ROS persists, oxidizing p62 and impairing its oligomerization, which further disrupts the hierarchy [5]. This creates a feed‑forward loop where unresolved mitochondrial damage sustains oxidative stress, activates TP53 nuclear translocation, and promotes a senescent phenotype despite overall autophagic flux [6]. Conversely, enforcing mitophagy‑first timing keeps ROS low, preserves p62 function, and allows TP53 to remain cytosolic, favoring autophagy over apoptosis and suppressing senescence.

Testable Predictions

1. Pharmacologically biasing the autophagy sequence toward mitophagy‑first (using SQ‑1 to potentiate p62‑dependent mitophagy together with a low‑dose NBR1‑binding peptide that transiently inhibits aggrephagy) will extend the senolytic‑induced clearance of senescent cells in aged tissue.
2. Reversing the order (enhancing aggrephagy before mitophagy, e.g., by overexpressing NBR1 while inhibiting p62 oligomerization) will accelerate the return of SA‑β‑gal‑positive cells after senolytic treatment.
3. The protective effect will correlate with restored mitochondrial membrane potential (measured by TMRM) and reduced protein‑aggregate load (measured by filter‑trap assay) without changes in bulk LC3‑II turnover.

Experimental Approach

• Model: 24‑month‑old C57BL/6 mice treated with dasatinib +  quercetin (D+Q) to clear senescent cells.
• Intervention groups (n=8 per group): a) D+Q + vehicle (control) b) D+Q + SQ‑1 (10 mg/kg, i.p., every 48 h) c) D+Q + SQ‑1 + NBR1‑peptide (5 mg/kg, i.p., every 24 h) to bias mitophagy‑first d) D+Q + NBR1‑overexpressing AAV (liver/muscle) to bias aggrephagy‑first e) D+Q + p62‑oligomerization inhibitor (as a positive control for hierarchy disruption)
• Readouts (collected at days 3, 7, 14 post‑treatment):
  • Senescence burden: SA‑β‑gal staining, p16^Ink4a^ mRNA (qPCR)
  • Mitochondrial health: MitoTracker Red intensity, mt‑Keima mitophagy flux
  • Protein aggregates: filter‑trap for ubiquitin‑positive species
  • Autophagy order: tandem mCherry‑GFP‑LC3 coupled with mitochondria‑targeted Keima (mt‑Keima) and aggregate‑sensor (GFP‑NBRI) to quantify relative kinetics.
• Statistical analysis: Two‑way ANOVA with post‑hoc Tukey; significance set at p < 0.05.

Potential Outcomes

• If the hypothesis holds, group c will show a statistically significant delay in senescent‑cell reaccumulation (lower SA‑β‑gal and p16) compared with group a, accompanied by improved mitochondrial metrics and unchanged bulk LC3‑II flux.
• Group d is expected to exhibit the fastest return of senescence markers, confirming that disrupting the mitophagy‑first order exacerbates senescence.
• Lack of difference between groups would falsify the claim that temporal ordering of selective autophagy governs senescent‑cell fate, prompting revision of the model.

Broader Impact Demonstrating that the sequence—not just the magnitude—of autophagic substrate selection dictates cellular fate would shift therapeutic focus from global autophagy activators to precision modulators of cargo‑receptor dynamics. Such strategies could be combined with senolytics to achieve durable tissue rejuvenation.