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新陈代谢的关键整合因素，最近的研究表明，核心时钟基因的遗传破坏会导致糖尿病和肥胖症。相反，高脂肪饮食会扰乱运动活动的昼夜节律，以及24小时的时钟周期和时钟控制的基因表达。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的广泛相互作用，这可能开始解释昼夜节律、脂肪和葡萄糖代谢之间的生理联系。最近，我们的实验室建立了令人兴奋的新证据，表明NAD+的生物合成和NAD+在光-暗周期中发生变化，这导致我们假设NAD+作为一种连接昼夜节律和代谢周期的振荡代谢物发挥作用。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，并在转录水平上受Clock/BMAL1 24小时循环的控制。NAMPT/NAD+的变化调节营养响应脱乙酰酶SIRT1，该酶在肝脏葡萄糖合成和调节生物钟方面都发挥着重要作用。因此，Clock/BMAL1-NAMPT/NAD+-SIRT1途径构成了一个新的代谢反馈环，它整合了日常活动、摄食和葡萄糖动态平衡的循环。这项提议的目的是验证这样的假设，即昼夜节律紊乱通过肝脏中NAMPT-NAD+-SIRT1途径的改变而导致代谢紊乱。随附的AIMS将阐述Clock/BMAL1活性在SIRT1介导的肝脏糖异生控制中的作用，以及NAD+-SIRT1途径在昼夜节律突变小鼠中出现的代谢紊乱的发病机制中的作用。这些研究将进一步加深我们对昼夜节律和新陈代谢之间相互联系的分子机制的理解。 公共卫生相关性：威胁要否定公共卫生最近许多进展的重大危机之一是肥胖症和糖尿病的持续升级。然而，破译这场疫情中的致病因素阻碍了领先的代谢、行为和流行病学研究人员的最大努力。本申请中提出的研究将详细地建立代谢病理生物学和糖尿病的内部生物钟转录网络的基础。

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.