Hypothesis: Intermittent rapamycin administration aligned with the organism's active phase extends lifespan by strengthening circadian gating of autophagy‑lysosome activity, whereas continuous dosing blunts this rhythm and induces mTORC2‑dependent metabolic toxicity.

Rationale: ’s analysis shows that rapamycin’s longevity effect stems from mimicking nutrient scarcity rather than repairing damage, engaging stress‑response pathways and hormetic autophagy. Circadian regulation of mTORC1 is well documented—CR’s mTOR suppression is BMAL1‑dependent [4] and rapamycin’s effects are phase‑dependent [5]. Yet the downstream link between circadian timing and lysosomal output remains unclear. We propose that rapamycin, when given at the onset of the active phase, transiently inhibits mTORC1, leading to a pulse of TFEB nuclear translocation that drives expression of lysosomal genes. This pulse is reinforced by the circadian repressor REV-ERBα, whose own expression peaks during the active phase and is known to regulate metabolic genes. Rapamycin‑induced TFEB activity upregulates Rev‑erbα transcription (via increased lysosomal degradation of NCOR1 co‑repressor), creating a positive feedback loop that sharpens the autophagic rhythm. Consequently, autophagic flux becomes tightly coupled to feeding‑fasting cycles, enhancing clearance of damaged proteins and organelles without requiring constant mTORC1 suppression.

If this mechanism is correct, then: (1) Mice receiving rapamycin only during the dark (active) phase will exhibit greater lifespan extension than those receiving continuous dosing, despite lower total drug exposure; (2) This benefit will correlate with heightened circadian amplitude of LC3‑II turnover and lysosomal cathepsin activity in liver and muscle; (3) Genetic ablation of Rev‑erbα specifically in hepatocytes will abolish the lifespan advantage of timed rapamycin, while leaving continuous rapamycin’s modest effect intact; (4) Chronic rapamycin will still suppress mTORC2, causing glucose intolerance and hepatic steatosis, whereas timed dosing will preserve mTORC2 activity (p‑AKT‑S473) and metabolic homeostasis.

Testable predictions and experimental design:

• Lifespan study: Cohorts of male and female C57BL/6 mice (n=50 per group) receive (a) vehicle, (b) continuous rapamycin (14 ppm in diet), (c) intermittent rapamycin (same weekly dose administered only during dark phase via timed osmotic pumps or pulsatile feeding), starting at 20 months. Monitor survival, frailty index, and metabolic phenotypes.
• Circadian autophagy readouts: Every 4 h over 48 h at 6‑month intervals, collect liver and muscle for immunoblot of LC3‑I/II, p62, lysosomal LAMP1, and TFEB nuclear/cytosolic ratios; quantify cathepsin B/D activity.
• REV-ERBα dependency: Generate Alb‑Cre;Rev‑erbα^fl/fl mice and repeat intermittent rapamycin regimen; compare lifespan and autophagy rhythms to Rev‑erbα^fl/fl controls.
• mTORC2 signaling: Assess p‑AKT‑S473 and p‑SGK1 levels in liver and adipose tissue after 4 weeks of each regimen; perform glucose tolerance and insulin tolerance tests.
• Metabolic side‑effects: Measure serum lipids, hepatic triglyceride content, and adipocyte size.

Falsification: If intermittent rapamycin fails to outperform continuous dosing in lifespan, or if Rev‑erbα loss does not diminish its benefit while preserving autophagy rhythm, the hypothesis is refuted. Conversely, observing enhanced circadian autophagic flux, preserved mTORC2 signaling, and abolished longevity in liver‑specific Rev‑erbα knockouts would substantiate the model that timed mTOR inhibition leverages circadian lysosomal priming to simulate a harder, yet rhythmic, life state.