title: The time of metabolism: NAD+, SIRT1, and the circadian clock.
abstract: The mammalian cell contains a molecular clock that contributes, within each organism, to circadian rhythms and variety of physiological and metabolic processes. The clock machinery is constituted by interwined transcriptional-translational feedback loops that, through the action of specific transcription factors, modulate the expression of clock-controlled genes. These oscillations in gene expression necessarily implicate events of chromatin remodeling on a relatively large, global scale, considering that as many 10% of cellular transcripts oscillate in a circadian manner. CLOCK, a transcription factor crucial for circadian function, has intrinsic histone acetyltransferase activity and operates within a large nuclear complex with other chromatin remodelers. CLOCK directs the cyclic acetylation of the histone H3 and of its own partner BMAL1. A search for the histone deacetylase (HDAC) that counterbalanced CLOCK activity revealed that SIRT1, a nicotinamide adenine dinucleotide (NAD(+))-dependent HDAC, functions in a circadian manner. Importantly, SIRT1 is a regulator of several metabolic processes and was found to interact with CLOCK and to be recruited to circadian promoters in a cyclic manner. As many transcripts that oscillate in mammalian peripheral tissues encode proteins that have central roles in metabolic processes, these findings establish a functional and molecular link among energy balance, chromatin remodeling, and circadian physiology.
authors.affiliation: Center for Epigenetics and Metabolism, School of Medicine, University of California, Irvine, Irvine, California 92697, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Bellet
authors.forename: R
authors.initials: R
authors.lastname: Orozco-Solis
authors.forename: S
authors.initials: S
authors.lastname: Sahar
authors.forename: K
authors.initials: K
authors.lastname: Eckel-Mahan
authors.forename: P
authors.initials: P
authors.lastname: Sassone-Corsi
mesh_terms: D000818:Animals; D042002:Chromatin Assembly and Disassembly; D057906:Circadian Clocks / Q000502:physiology*; D006801:Humans; D008660:Metabolism; D008954:Models, Biological; D009243:NAD / Q000378:metabolism*; D056564:Sirtuin 1 / Q000378:metabolism*
chemical_list: D009243:NAD; D056564:Sirtuin 1