Circadian Clock Feedback Cycle Through NAMPT-Mediated NAD + Biosynthesis

Circadian Oscillations The 24-hour day-night cycle plays an important role in mammalian physiology and behavior and, as most travelers are well aware, there is an intimate link between our in-built circadian clocks and metabolic rhythms. This link is in part forged by the protein deacetylase SIRT1, which regulates the clock's molecular circuitry. SIRT1 uses as a cofactor the cellular metabolite NAD + , which is synthesized through a salvage pathway that includes the enzyme nicotinamide phosphoribosyltransferase (NAMPT) (see the Perspective by Wijnen ). Ramsey et al. (p. 651 ; published online 19 March) and Nakahata et al. (p. 654 , published online 12 March) now show that NAMPT and NAD + levels oscillate during the daily 24-hour cycle and that this oscillation is regulated by the circadian clock. Furthermore, the oscillations in NAD + modulate the activity of SIRT1 feeding back into the circadian clock.