Hypothesis

In aged organisms, circadian decline converts BMAL1 from a repressor to a co‑activator of YAP‑driven inflammatory enhancers, locking the NLRP3 inflammasome in a constitutively active state. We propose that restoring NAD+ levels at the early active phase (ZT4) will reactivate SIRT3‑mediated deacetylation of mitochondrial proteins, thereby lowering mitochondrial membrane potential and preventing BMAL1‑YAP enhancer retargeting. Simultaneous pharmacologic activation of REV-ERBα at the same circadian window will directly repress NLRP3 and IL-6 transcription. The combined chronotherapeutic intervention should decouple BMAL1 from YAP, reinstate rhythmic NLRP3 suppression, and reduce inflammaging more effectively than either approach alone.

Mechanistic Rationale

NAD+ fuels SIRT3, which deacetylates Complex I subunits and reduces mitochondrial membrane potential—a key checkpoint for NLRP3 activation (see BMAL1‑mitochondria link)[https://pubmed.ncbi.nlm.nih.gov/39686706/]. In aging, NAD+ depletion diminishes SIRT3 activity, permitting hyperpolarized mitochondria that favor NLRP3 assembly. Boosting NAD+ at ZT4, when NAD+ salvage peaks, should restore SIRT3 function and lower the inflammasome trigger.

REV-ERBα directly represses NLRP3 and IL-1β transcription and promotes anti‑inflammatory macrophage polarization[https://pmc.ncbi.nlm.nih.gov/articles/PMC7410924/]. Its activity is ligand‑dependent and enhanced by heme, which itself follows a circadian rhythm. Administering a REV-ERB agonist (e.g., SR9009) concurrently with NAD+ replenishment ensures maximal receptor occupancy during the phase when BMAL1 transcription is rising, preventing the pathological BMAL1‑YAP enhancer hijack observed in aged epidermis[https://doi.org/10.1101/2025.04.22.649967].

By targeting both the metabolic (mitochondrial NAD+/SIRT3) and transcriptional (REV-ERBα) arms, the hypothesis predicts a synergistic break of the inflammasome‑promoting loop.

Testable Predictions

1. Biomarker rhythmicity – Aged mice receiving timed NR (nicotinamide riboside) at ZT4 plus SR9009 will show restored ~24‑h oscillation of Bmal1, Per2, and Nlrp3 mRNA in peritoneal macrophages, whereas monotherapy or mistimed dosing will not.
2. Inflammasome output – NLRP3‑dependent caspase‑1 cleavage and IL‑1β/IL-18 secretion will be reduced by >50 % in the combination group relative to controls, measured by ELISA and Western blot of bone‑marrow‑derived macrophages stimulated with nigericin.
3. Chromatin state – CUT&RUN for BMAL1 and YAP will reveal decreased co‑occupancy at inflammatory enhancers (e.g., Il6, Il1b) only in the combination treatment, confirming enhancer retargeting reversal.
4. Physiological rescue – Frailty index, grip strength, and locomotor activity will improve significantly in aged mice after 8 weeks of combined chronotherapy, outperforming either NR or SR9009 alone.
5. Falsification – If mitochondrial uncoupling (e.g., low‑dose FCCP) abolishes the benefit of NAD+ boosting, or if REV-ERBα knockout eliminates the anti‑inflammatory effect despite NAD+ restoration, the hypothesis is refuted.

Experimental Design

• Use 20‑month‑old C57BL/6 mice, divided into five groups (n=10 per group): vehicle, NR alone (ZT4), SR9009 alone (ZT4), NR+SR9009 (ZT4), and NR+SR9009 administered at ZT16 (anti‑phase control).
• Monitor core body temperature and locomotor activity to confirm circadian entrainment.
• Collect blood and tissues at 4‑hour intervals over 24 h for gene expression, cytokine, and NAD+/NADH assays.
• Perform macrophage isolation for inflammasome assays and chromatin profiling.
• Assess frailty using a validated mouse frailty checklist.

This design directly tests whether timed NAD+ augmentation synergizes with REV-ERBα activation to restore circadian control of the NLRP3 inflammasome and counteract inflammaging.