Hypothesis

Night‑time exposure to blue light disrupts the hepatic circadian clock, preventing BMAL1‑driven transcription of Raptor and thereby uncoupling intermittent rapamycin dosing from autophagy induction. Consequently, the longevity benefit of pulsed mTOR inhibition is lost under chronic circadian misalignment.

Mechanistic rationale

• The core clock heterodimer BMAL1:CLOCK binds E‑box elements in the promoter of Raptor (the regulatory subunit of mTORC1), driving its expression during the active (day) phase [https://doi.org/10.1016/j.cmet.2014.09.012].
• Raptor levels set the basal sensitivity of mTORC1 to amino acids and growth factors; low Raptor at night permits rapamycin‑induced suppression of mTORC1 even when nutrients are present.
• Blue light after dusk suppresses melatonin and shifts the phase of BMAL1 activity, flattening the Raptor oscillation and keeping Raptor high throughout the 24‑h cycle.
• High Raptor maintains mTORC1 activity despite rapamycin, blocking ULK1 dephosphorylation and inhibiting autophagosome formation.
• Without nocturnal autophagy, damaged proteins and organelles accumulate, negating the cellular housekeeping that underlies the healthspan gains of intermittent mTOR inhibition.

Testable predictions

1. Liver‑specific Bmal1 knockout mice will show constitutively low Raptor and will exhibit autophagy induction (LC3‑II accumulation, p62 degradation) after a single daytime rapamycin dose, regardless of lighting conditions.
2. Wild‑type mice subjected to 2 h of blue light (480 nm) starting at ZT12 for two weeks will have flattened hepatic Raptor rhythms (measured by qPCR and Western blot) and will fail to increase LC3‑II after the same rapamycin schedule that elevates autophagy in mice kept in darkness.
3. Pharmacological reinforcement of the clock (e.g., SR9009, a REV‑ERB agonist) in blue‑light‑exposed mice will restore Raptor oscillation and rescue rapamycin‑induced autophagy.
4. Longevity read‑out: In a cohort of middle‑aged mice, intermittent rapamycin (5 mg/kg, i.p., three times weekly) extends median lifespan by ~15 % under dark‑night conditions; this extension disappears when the same regimen is paired with chronic blue‑light exposure.

Experimental outline

• Animals: Male C57BL/6J mice, 8 weeks old, split into four groups (control dark, control blue‑light, Bmal1‑LKO dark, Bmal1‑LKO blue‑light).
• Lighting: Standard 12 h light/12 h dark; blue‑light group receives additional 2 h of 480 nm LED at zeitgeber time 12–14.
• Rapamycin dosing: Intermittent i.p. injections on Monday, Wednesday, Friday for 12 weeks.
• Read‑outs: Hepatic Raptor mRNA (qPCR) and protein (Western) every 4 h over 24 h; LC3‑II/I ratio and p62 levels 4 h post‑rapamycin; serum markers of inflammation; survival monitoring.
• Analysis: Two‑way ANOVA for lighting × genotype effects; Kaplan‑Meier for survival.

Falsifiability

If blue‑light exposure does not attenuate Raptor rhythmicity or autophagy response to rapamycin, or if Bmal1 loss does not abolish the lighting effect, the hypothesis is refuted. Likewise, if lifespan extension persists despite circadian disruption, the proposed mechanistic link between clock‑gated mTORC1 activity and longevity would be invalid.

Broader implication

This hypothesis reframes the mTOR "civilization versus survival" dial as a time‑gated switch: the organism’s ability to toggle between growth and recycling depends not only on nutrient signals but on the integrity of its circadian architecture. Aligning mTOR‑targeted interventions with endogenous clock phases could maximize healthspan gains while minimizing the trade‑off between cellular specialization and survival.