Circadian Control of the NAD ⁺ Salvage Pathway by CLOCK-SIRT1

TLDR

Many metabolic and physiological processes display circadian oscillations. Using the specific inhibitor FK866, we demonstrated that NAMPT is required to modulate circadian gene expression. The study demonstrates that CLOCK, a histone acetyltransferase, and its counteracting deacetylase SIRT1 coordinate a circadian NAD⁺ salvage pathway, with CLOCK:BMAL1 driving rhythmic NAMPT expression, SIRT1 binding the Nampt promoter to sustain its own synthesis, and an interlocked transcriptional‑enzymatic feedback loop linking metabolism to circadian rhythms.

Abstract

Many metabolic and physiological processes display circadian oscillations. We have shown that the core circadian regulator, CLOCK, is a histone acetyltransferase whose activity is counterbalanced by the nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase SIRT1. Here we show that intracellular NAD+ levels cycle with a 24-hour rhythm, an oscillation driven by the circadian clock. CLOCK:BMAL1 regulates the circadian expression of NAMPT (nicotinamide phosphoribosyltransferase), an enzyme that provides a rate-limiting step in the NAD+ salvage pathway. SIRT1 is recruited to the Nampt promoter and contributes to the circadian synthesis of its own coenzyme. Using the specific inhibitor FK866, we demonstrated that NAMPT is required to modulate circadian gene expression. Our findings in mouse embryo fibroblasts reveal an interlocked transcriptional-enzymatic feedback loop that governs the molecular interplay between cellular metabolism and circadian rhythms.