Hypothesis

Timed supplementation with NAD+ precursors restores circadian amplitude in senescent cells by enhancing SIRT1‑dependent deacetylation of BMAL1, which weakens the BMAL1‑YAP transcriptional complex, reduces SASP secretion, and lowers senescent cell burden.

Mechanistic Rationale

• The core clock heterodimer CLOCK‑BMAL1 drives expression of DNA‑repair genes and represses p21, thereby opposing senescence (1).
• Senescent cells exhibit low NAD+, high AMP/ATP, AMPK activation, and dampened clock amplitude, accompanied by PER1/2 and CRY1 downregulation (2).
• BMAL1 can cooperate with YAP to hijack enhancers and promote inflammatory gene expression in aged tissue (3).
• SIRT1, an NAD+-dependent deacetylase, modifies BMAL1 at lysine residues, decreasing its transcriptional activity and its affinity for YAP co‑activators (novel mechanistic link).
• Reduced BMAL1‑YAP interaction lowers transcription of SASP components (IL‑6, IL-8, MMPs) while preserving clock‑driven DNA‑repair programs.

Thus, raising NAD+ levels specifically during the active phase should increase SIRT1 activity, deacetylate BMAL1, disrupt the BMAL1‑YAP axis, and re‑synchronize circadian output, leading to diminished inflammaging and senescent cell accumulation.

Experimental Design

1. Animal Model: Use 24‑month-old C57BL/6 mice exhibiting circadian dampening and elevated SASP.
2. Intervention: Administer nicotinamide riboside (NR) at 400 mg/kg/day via drinking water, timed to deliver peak plasma NAD+ at ZT6 (mid‑active phase) versus constant‑delivery control.
3. Groups: (a) Vehicle, (b) Constant NR, (c) Timed NR, (d) Timed NR + SIRT1 inhibitor (EX527) to test specificity.
4. Readouts (collected after 4 weeks):
   • In vivo bioluminescence from Per2::Luc reporter to assess amplitude, period, and phase.
   • NAD+ levels, SIRT1 activity, and BMAL1 acetylation status in liver and adipose tissue (Western blot, immunoprecipitation).
   • BMAL1‑YAP co‑immunoprecipitation and chromatin occupancy at SASP enhancers (ChIP‑qPCR).
   • Plasma and tissue SASP cytokine concentrations (ELISA).
   • Senescent cell burden via p16^Ink4a^‑GFP flow cytometry and SA‑β‑Gal staining.
   • Functional metrics: grip strength, treadmill endurance, and glucose tolerance.

Predicted Outcomes

• Timed NR will increase NAD+ and SIRT1 activity specifically at ZT6, leading to decreased BMAL1 acetylation and reduced BMAL1‑YAP binding.
• This will correlate with heightened circadian amplitude (↑ peak‑trough ratio) and shortened period relative to vehicle.
• SASP IL-6 and IL-8 levels will drop ≥30 % in timed NR mice, accompanied by a ≥25 % reduction in p16^Ink4a^‑positive cells.
• SIRT1 inhibition will abolish these effects, confirming mechanistic dependence.
• Improved physical performance and metabolic homeostasis will follow the molecular rescue.

Falsifiability

If timed NAD+ supplementation fails to enhance circadian amplitude, does not alter BMAL1 acetylation or BMAL1‑YAP interaction, and does not reduce SASP or senescent cell markers compared with controls, the hypothesis is refuted. Conversely, observing the predicted molecular and phenotypic changes supports the claim that reinforcing circadian timing via NAD+/SIRT1 directly mitigates the BMAL1‑YAP‑driven inflammatory arm of senescence.