Hypothesis

Restoring circadian amplitude through timed NAD+ supplementation and 670 nm light exposure re‑synchronizes the mitochondrial quality‑control clock, specifically the rhythmic activation of PINK1‑Parkin mitophagy, thereby delaying aging more effectively than either intervention alone.

Mechanistic rationale

The core clock transcription factors BMAL1:CLOCK drive daily expression of mitochondrial genes, including Pink1 and Parkin[1]. NAD+ levels oscillate with the clock and feed into SIRT3, which deacetylates PINK1 to promote its activity[2]. 670 nm light enhances cytochrome c oxidase activity, lowering ROS and increasing ATP, which creates a permissive environment for mitophagy[4]. When circadian rhythms are disrupted, the phase relationship between NAD+ peaks and light‑driven mitochondrial activation is lost, leading to mistimed or insufficient mitophagy and accumulation of damaged mitochondria—a driver of inflammaging and tissue decline[3] 5].

Predictions

1. In aged mice under constant light (circadian disruption), combined timed NAD+ precursor (nicotinamide riboside) given at the subjective dawn and 670 nm light delivered at the same circadian time will restore rhythmic mitophagy flux.
2. Restored mitophagy will correlate with improved mitochondrial respiration, reduced IL‑1β inflammasome activation, and extended median lifespan relative to single‑treatment or control groups.
3. If the clock‑mitophagy link is essential, genetic ablation of Bmal1 in myeloid cells will abolish the lifespan benefit of the combined treatment despite NAD+ and light administration.

Experimental design (testable and falsifiable)

• Groups (n=30 per group, male and female, 20‑month‑old C57BL/6J):
  1. Constant light + vehicle (disruption control).
  2. Constant light + timed NAD+ only.
  3. Constant light + timed 670 nm light only.
  4. Constant light + timed NAD+ + timed 670 nm light.
  5. Constant light + timed NAD+ + timed 670 nm light + myeloid‑specific Bmal1 KO.
  6. Standard light‑dark cycle + vehicle (baseline).
• Timing: NAD+ administered via drinking water 2 h before lights‑on (subjective dawn); 670 nm LED panels provide 5 min pulses at the same time daily for 4 weeks.
• Readouts (collected at weeks 0, 2, 4, and at natural death):
  • Mitophagy flux measured by mt‑Keima reporter in liver and muscle.
  • Mitochondrial respiration (Oroboros O2k) and ATP levels.
  • Serum IL‑1β, TNF‑α, and corticosterone melatonin amplitude.
  • Behavioral frailty index and survival curves.
• Falsification: If combined treatment fails to increase mitophagy flux or does not extend lifespan beyond single treatments, the hypothesis is refuted. If myeloid Bmal1 KO does not diminish the benefit, the proposed clock‑mitophagy axis is not necessary.

Expected outcomes and implications

A significant synergistic increase in mitophagy amplitude, coupled with improved bioenergetics and reduced inflammasome activity, would support the view that the circadian system acts as a master timer for mitochondrial quality control. Demonstrating that timed metabolic (NAD+) and photonic (670 nm) cues can rescue this timer offers a concrete, low‑cost geroprotective strategy. Conversely, a lack of effect would suggest that circadian regulation of aging operates through parallel pathways independent of mitophagy, redirecting focus to other clock‑controlled processes such as DNA repair or hormonal cycles.