CLOCK Regulation of Liver Metabolism via Modulation of HNF-4alpha

描述（由申请人提供）： 本提案中提出的目标涉及内源性生物钟在代谢调节中的作用，特别是葡萄糖和脂质稳态。昼夜节律是在一天中发生的内源性振荡。环境信号（zeitgebers）如光和暗有助于内源性昼夜节律的同步和维持，然而，昼夜节律是内在的，在细胞水平上由生物钟基因（包括Clock、Bmall、Period和Cryptochrome）的复杂转录反馈调节控制。虽然昼夜节律系统控制着生物节律，如睡眠-觉醒周期，激素分泌和体温，但越来越多的证据表明昼夜节律和新陈代谢之间存在直接联系。许多对代谢至关重要的转录激活因子（包括核受体超家族成员）似乎在代谢活性组织中经历昼夜振荡。此外，生物钟基因的失调导致脂质和 葡萄糖稳态以及肥胖。CLOCK是一种调节昼夜节律的转录激活因子，最近被发现具有乙酰转移酶活性，可作为一种酶对靶蛋白进行后期修饰。提出的建议提供了初步证据，即CLOCK结合并后修饰HNF-4a，一种对胆汁生成和胆固醇催化转化为胆汁酸起核心作用的蛋白质。 该建议的中心假设是HNF-4a的结合及其随后通过昼夜节律机制的修饰对于正常葡萄糖稳态是至关重要的。HNF-4a是正常的脂质和葡萄糖代谢以及正常的胰腺β细胞功能所必需的。事实上，HNF-4a的突变导致II型糖尿病的早期发作，通常被称为年轻人的成熟型糖尿病（MODY）。昼夜节律的改变会严重干扰脂质和葡萄糖的体内平衡以及体重调节。 这种表型回避了它们在代谢活性组织中究竟如何发挥作用的问题。这一提议表明，CLOCK蛋白可能通过与HNF-4a的直接相互作用和修饰以尚未考虑的方式影响代谢。我们想确定昼夜节律系统如何影响肝脏中的HNF-4a，以便理解为什么昼夜节律紊乱可以在脂质代谢和体重调节中产生如此深刻的变化。这项研究可能会提供深入了解如何生物钟机制可能会在未来作为一个目标的连接或操纵体内葡萄糖稳态

DESCRIPTION (provided by applicant): The goals set forth in this proposal address the role of the endogenous circadian clock in the regulation of metabolism, specifically, glucose and lipid homeostasis. Circadian rhythms are endogenously generated oscillations that take place in the course of a day. Environmental cues (zeitgebers) such as light and dark assist in the synchronization and maintenance of endogenous circadian rhythms, however, circadian rhythms are intrinsic, controlled at the cellular level by complex transcriptional feedback regulation by circadian clock genes including Clock, Bmall, Period and Cryptochrome. While the circadian system is in control of biological rhythms such as the sleep-wake cycle, hormone secretion, and body temperature, evidence is accumulating that there is a direct link between circadian rhythm and metabolism. Numerous transcriptional activators essential for metabolism (including the members of the nuclear receptor superfamily) appear to undergo circadian oscillations in metabolically active tissues. Furthennore, dismptions in circadian clock genes result in aberrations in lipid and glucose homeostasis as well as obesity. CLOCK, best known for its role as a circadian-regulating transcriptional activator, was recently discovered to have acetyltransferase activity, functioning as an enzyme to posttranslationally modify target proteins. The proposal set forth gives preliminary evidence that CLOCK binds to and posttranslationally modifies HNF-4a, a protein central to gluconeogenesis and cholesterol catabolism into bile acids. The central hypothesis of this proposal is that the binding of HNF-4a and its subsequent modification by circadian machinery is critical for nomnal glucose homeostasis. HNF-4a is essential for nomnal lipid and glucose metabolism as well as for normal pancreatic beta cell function. In fact, mutations in HNF-4a cause the early onset of type II diabetes, commonly referred to as maturity-onset diabetes of the young (MODY). Alterations in circadian rhythm produce profound disturbances in lipid and glucose homeostasis as well as body weight regulation. This phenotype begs the question of how exactly they function in metabolically active tissues. This proposal demonstrates ways in which CLOCK protein might impinge on metabolism in a manner which has not yet been considered, through direct interaction with and modification of HNF-4a. We would like to detemiine how the circadian system affects HNF-4a in the liver in order to understand why circadian disturbances can produce such profound changes in lipid metabolism and body weight regulation. This study may provide insight into how circadian clock machinery might be used in the future as a target for the conection or manipulation of glucose homeostasis in the body