Circadian regulation of lipid metabolism

描述(申请人提供)：我们的长期目标是了解参与每日调节血脂浓度的分子机制，并找出这一调节中的扰动如何导致血脂异常和动脉粥样硬化。我们观察到血浆甘油三酯和胆固醇，主要是与非高密度脂蛋白相关的那些，表现出昼夜节律。在之前的资金周期中，我们表明，当动物受到食物夹带时，血浆脂类的昼夜节律会改变，在时钟突变的小鼠中看不到。机制研究表明，时钟是昼夜节律环路的关键组成部分，控制着微粒体甘油三酯转移蛋白(MTP)的日常调节，MTP是包括SHP在内的含载脂蛋白B的富含甘油三酯的脂蛋白生物合成的必需伴侣。这一调节过程抑制了MTP的表达，并降低了小鼠在光照开始时的血浆甘油三酯。当昼夜节律控制受损时，小鼠会出现持续性高脂血症，因为这种调节机制变得不起作用。因此，我们假设昼夜节律机制可以预防高脂血症和动脉粥样硬化。除了时钟，昼夜节律的正循环还需要BMal1。本研究的目的是明确BMal1在高脂血症和动脉粥样硬化发展中的作用，并揭示控制血脂和动脉粥样硬化的分子、生化和生理机制。我们的方法将是以全局或组织特异性的方式去除BMal1的表达，然后将各种生理、生化和分子方面与它们的野生型兄弟姐妹进行比较。我们的第一个目标是阐明BMal1在昼夜和食物携带的调节血脂和脂蛋白中的作用。第二个目的是确定肝脏和肠道BMal1在调节血脂/脂蛋白中的作用。第三个目标是认识BMal1在动脉粥样硬化进展中的作用。BMal1-/-/Ldlr-/-和BMal1-/-/APOE-/-C57BL/6J背景的小鼠将被随意喂食或西方饮食，并记录动脉粥样硬化的发展。此外，我们还将评估肠道和肝脏BMal1消融对动脉粥样硬化的影响。我们期望证明BMal1在维持血脂和脂蛋白稳态以及预防动脉粥样硬化方面起着至关重要的作用。这些研究的结果将影响生物学的两个领域：脂类代谢和昼夜节律。关于脂代谢的昼夜节律的新的理解将被获得。

DESCRIPTION (provided by applicant): Our long-term goal is to understand molecular mechanisms involved in the diurnal regulation of plasma lipid concentrations and to find out how perturbations in this regulation contribute to dyslipidemia and atherosclerosis. We observed that plasma triglyceride and cholesterol, mainly those associated with non-HDL apoB-lipoproteins, exhibit diurnal rhythms. During the previous funding cycle, we showed that plasma lipid diurnal rhythms are altered when animals are subject to food entrainment and are not seen in Clock mutant mice. Mechanistic studies revealed that Clock, a critical component of the circadian regulatory loop, controls diurnal regulation of microsomal triglyceride transfer protein (MTP), an essential chaperone for the biosynthesis of apoB-containing triglyceride-rich lipoproteins, involving SHP. This regulatory process suppresses MTP expression and lowers plasma triglycerides at the onset of light in mice. When circadian control is impaired mice develop sustained hyperlipidemia because this regulatory mechanism becomes inoperative. Hence, we hypothesize that circadian mechanisms protect against hyperlipidemia and atherosclerosis. Besides Clock, the positive loop of circadian regulation requires Bmal1. The aim of this proposal is to define the role of Bmal1 in the development of hyperlipidemia and atherosclerosis and to uncover molecular, biochemical, and physiological mechanisms that control plasma lipid and atherosclerosis. Our approach will be to ablate Bmal1 expression globally or in tissue-specific manner and then to compare various physiological, biochemical, and molecular aspects with their wild type siblings. Our first aim is to elucidate the role of Bmal1 in diurnal and food entrained regulation of plasma lipids and lipoproteins. The second aim is to ascertain the contribution of hepatic and intestinal Bmal1 in the regulation of plasma lipids/lipoproteins. The third aim is to recognize the role of Bmal1 in the progression of atherosclerosis. Bmal1-/- /Ldlr-/- and Bmal1-/-/Apoe-/- mice on C57BL/6J background will be fed ad libitum chow or western diet and development of atherosclerosis will be documented. Additionally, we will evaluate the effect of intestinal and hepatic Bmal1 ablation on atherosclerosis. We expect to demonstrate that Bmal1 is vital in maintaining plasma lipid and lipoprotein homeostasis, and in the prevention of atherosclerosis. The outcomes from these studies will impact two fields of biology; lipid metabolism and circadian regulation. Novel understanding about the circadian regulation of lipid metabolism will be garnered.