Disruption of NAD/SIRT1-CLOCK Feedback Loop in Diabetes Pathophysiology

描述（申请人提供）：强有力的证据表明，生物钟网络是行为和代谢的关键整合者，最近的研究表明，核心生物钟基因的遗传破坏导致糖尿病和肥胖。相反，高脂肪饮食会破坏运动活动的昼夜节律，以及生物钟和生物钟控制的基因表达的24小时周期。在分子水平上，越来越多的证据揭示了昼夜节律和代谢转录网络之间广泛的相互作用，这可能开始解释昼夜节律、脂质和葡萄糖代谢之间的生理联系。最近，我们的实验室已经建立了令人兴奋的新证据，表明NAD+的生物合成和NAD+在光-暗周期中变化，这使我们假设NAD+作为一种振荡代谢物起着连接昼夜节律和代谢周期的作用。NAD+生物合成的一个主要调节因子是限速酶烟酰胺磷酸核糖基转移酶（Nampt），它在肝脏中从黎明到黄昏变化，并在转录水平上由CLOCK/BMAL1的24小时循环控制。Nampt/NAD+的改变可以调节营养反应性去乙酰化酶SIRT1， SIRT1在肝脏葡萄糖合成和生物钟调节中发挥重要作用。因此，CLOCK/BMAL1-NAMPT/NAD+-SIRT1通路包含一个新的代谢反馈回路，整合了日常活动、摄食和葡萄糖稳态循环。本提案的目的是验证昼夜节律中断通过改变肝脏中NAMPT-NAD+-SIRT1通路导致代谢紊乱的假设。本文的目的是研究CLOCK/BMAL1活性在SIRT1介导的肝脏糖异生控制中的作用，以及NAD+-SIRT1通路在昼夜节律突变小鼠代谢紊乱发病机制中的作用。这些研究将进一步加深我们对昼夜节律和代谢之间相互联系的分子机制的理解。

DESCRIPTION (provided by applicant): Strong evidence has implicated the circadian clock network as a key integrator of behavior and metabolism, and recent studies have shown that genetic disruption of core clock genes leads to diabetes mellitus and obesity. Conversely, high fat diet disrupts circadian rhythms of locomotor activity as well as 24 hr cycles of clock and clock controlled gene expression. At the molecular level, growing evidence has uncovered extensive interactions between circadian and metabolic transcription networks that may begin to explain the physiological connections between circadian rhythms, lipid and glucose metabolism. Recently our lab has established exciting new evidence to show that NAD+ biosynthesis and NAD+ vary across the light-dark cycle, leading us to hypothesisze that NAD+ functions as an oscillating metabolite linking circadian and metabolic cycles. One major regulator of NAD+ biosynthesis is the rate-limiting enzyme nicotinamide phosphoribosyltransferase (Nampt), which varies from dawn to dusk in the liver and is controlled in turn at the transcriptional level by 24 hr cycling of CLOCK/BMAL1. Alterations in Nampt/NAD+ modulate the nutrient-responsive deacetylase SIRT1, which plays an important role in both hepatic glucose synthesis and in the regulation the circadian clock. Thus, the CLOCK/BMAL1-NAMPT/NAD+-SIRT1 pathway comprises a novel metabolic feedback loop that integrates daily cycles of activity, feeding and glucose homeostasis. The goal of this proposal is to test the hypothesis that circadian disruption leads to metabolic disturbances through alterations in the NAMPT-NAD+-SIRT1 pathway in liver. The enclosed aims will address the role of the CLOCK/BMAL1 activity in SIRT1 mediated control of hepatic gluconeogenesis as well as the role of the NAD+-SIRT1 pathway in the pathogenesis of the metabolic disorder seen in circadian mutant mice. These studies will further our understanding of the molecular mechanism underlying the interconnection between circadian rhythm and metabolism. PUBLIC HEALTH RELEVANCE: One of the major crises that threatens to negate many of the recent advances in public health is the unremitting escalation of obesity and diabetes mellitus. However, deciphering the causitive factors in this epidemic has thwarted the best efforts of leading metabolic, behavioral and epidemiologic investigators. The studies proposed in the present application will establish in detail the basis of the internal circadian clock transcription network in metabolic pathobiology and diabetes mellitus.