Hypothesis

The hierarchical order of selective autophagy—where aggrephagy typically precedes mitophagy under nutrient stress—can be experimentally inverted by combining time‑restricted exercise (TRE) with a transient AMPK‑ULK1 modulation that favors mitophagy initiation. This inversion creates a temporary mismatch between organelle clearance and protein‑aggregate removal, leading to mitochondrial overload and reactive‑oxygen‑species (ROS) spikes in senescent cells that are already reliant on elevated autophagy for survival. The resulting metabolic stress lowers the threshold for senolytic‑induced synthetic lethality, making intermittent senolytic dosing more effective than either intervention alone.

Mechanistic Rationale

1. Autophagy hierarchy is phosphorylation‑driven – ULK1 Ser555 phosphorylation by AMPK promotes phagophore formation that preferentially engages mitophagy receptors (NIX/BNIP3) 2. When ULK1 Ser757 is phosphorylated by mTORC1, the complex shifts toward aggrephagy via p62‑dependent ubiquitinated cargo recognition 1.
2. TRE activates AMPK and transiently inhibits mTORC1 – Exercise bouts increase AMP/ATP ratio, boosting AMPK activity and decreasing mTORC1 signaling for several hours post‑session 4. This creates a window where ULK1 Ser555 is phosphorylated while Ser757 remains relatively dephosphorylated.
3. Pharmacological bias toward mitophagy – A low dose of the AMPK activator AICAR administered immediately after the TRE window further elevates ULK1 Ser555 phosphorylation without affecting Ser757, thereby skewing autophagosome nucleation toward mitochondria 2.
4. Senescent cells depend on balanced autophagy – Many senescent cells upregulate basal autophagy to manage increased protein aggregation and mitochondrial damage; inhibiting either pathway sensitizes them to death 3. Forcing mitophagy first depletes functional mitochondria faster than aggrephagy can clear accumulating aggregates, precipitating ROS‑driven lipid peroxidation and ER stress.
5. Synergy with senolytics – The ROS surge lowers mitochondrial threshold for BCL‑2 family inhibition; senolytics such as navitoclax or dasatinib + quercetin then trigger apoptosis more readily, producing synthetic lethality that exceeds the additive effect of TRE or senolytics alone.

Testable Predictions

• In vitro: Human fibroblasts rendered senescent by irradiation will show increased LC3‑II turnover after TRE‑mimetic serum starvation plus AICAR, with a higher mito‑Keima signal (mitophagy) relative to GFP‑dTomato‑p62 aggregate flux (aggrephagy). ROS (MitoSOX) and γH2AX will peak 4‑6 h post‑treatment. Adding navitoclax at this point will raise Annexin V‑positive cells >2‑fold compared to either treatment alone.
• In vivo: Aged C57BL/6 mice subjected to daily treadmill TRE (12 h active/12 h rest) receive intraperitoneal AICAR (250 mg/kg) at the end of each active phase for 4 weeks, followed by intermittent dasatinib + quercetin (D+Q) weekly. Compared to TRE‑only, D+Q‑only, and vehicle groups, the combined group will demonstrate: (a) reduced SA‑β‑gal‑positive cells in liver and adipose tissue, (b) improved grip strength and treadmill endurance, (c) decreased plasma SASP factors (IL‑6, MMP‑3), and (d) extended median lifespan by ≥15 % over D+Q alone.
• Falsification: If ULK1 Ser555 phosphorylation (measured by phospho‑specific immunoblot) does not increase during the TRE + AICAR window, or if mitophagy flux does not exceed aggrephagy flux, then the predicted ROS surge and senolytic sensitization will not occur, and lifespan benefits will match those of D+Q alone.

Novel Insight

The hypothesis reframes autophagy hierarchy not as a static triage list but as a tunable rheostat controlled by competing kinase inputs on ULK1. By deliberately biasing this rheostat toward mitophagy before aggrephagy, we create a transient metabolic crisis in senescent cells that exploits their reliance on autophagy for survival, thereby converting a housekeeping process into a therapeutic trigger.