Circadian regulation of lipid metabolism

描述（由申请人提供）：我们的长期目标是了解参与血浆脂质浓度昼夜调节的分子机制，并找出这种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，主要是那些与非hdl载脂蛋白相关的，表现出昼夜节律。在之前的资助周期中，我们发现当动物受到食物干扰时，血浆脂质昼夜节律会发生改变，而在Clock突变小鼠中没有观察到这一点。机制研究表明，时钟是昼夜节律调节环的关键组成部分，控制微粒体甘油三酯转移蛋白（MTP）的昼夜调节，MTP是含载脂蛋白富含甘油三酯的脂蛋白的生物合成的重要伴侣，涉及SHP。这一调节过程抑制MTP的表达并降低小鼠光照时的血浆甘油三酯。当昼夜节律控制受损时，由于这种调节机制失效，小鼠会发生持续性高脂血症。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Clock外，昼夜节律调节的正环路也需要Bmal1。本研究的目的是明确Bmal1在高脂血症和动脉粥样硬化发生中的作用，揭示控制血脂和动脉粥样硬化的分子、生化和生理机制。我们的方法将是消融Bmal1的全局表达或组织特异性表达，然后将其与野生型兄弟姐妹的各种生理、生化和分子方面进行比较。我们的第一个目标是阐明Bmal1在昼夜和食物携带的血浆脂质和脂蛋白调节中的作用。第二个目的是确定肝脏和肠道Bmal1在调节血浆脂质/脂蛋白中的作用。第三个目的是认识Bmal1在动脉粥样硬化进展中的作用。将C57BL/6J基因背景的Bmal1-/-/ Ldlr-/-和Bmal1-/-/Apoe-/-小鼠随意喂食或西式饮食，记录动脉粥样硬化的发展情况。此外，我们将评估肠道和肝脏Bmal1消融对动脉粥样硬化的影响。我们希望证明Bmal1在维持血浆脂质和脂蛋白稳态以及预防动脉粥样硬化方面至关重要。这些研究的结果将影响生物学的两个领域；脂质代谢和昼夜节律调节。将获得关于脂质代谢昼夜节律调节的新认识。

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.