Role of NPC1L1 in regulating energy metabolism, nutrient utilization & weight gai

描述（由申请人提供）：本研究的目的是了解膳食脂质吸收与整体代谢之间的机制关系。依zetimibe药物通过阻断其在肠道的吸收来降低血浆胆固醇，显然是通过破坏与NPC1L1（尼曼-匹克病，c1型蛋白样蛋白1）相关的途径。对依zetimibe其他生理效应的初步研究表明，经依zetimibe处理的小鼠餐后肠道脂蛋白的大小和组成与对照小鼠不同。我们的研究结果还表明，通过依zetimibe治疗或基因缺失，NPC1L1功能的丧失可以保护小鼠免受饮食诱导的肥胖和胰岛素抵抗。脂肪吸收减少可能是体重增加差异的部分原因，但其他机制，包括能量消耗增加，也可能具有预防糖尿病和肥胖的作用。该建议的重点是确定导致这些不同表型的机制。在具体目标1中，ezetimibe处理的、Npc1l1-/-和对照小鼠将被喂食高脂肪饮食，每组小鼠要么吸收良好（以红花油为基础），要么被Npc1l1-/-和ezetimibe处理的小鼠吸收不良（以可可脂为基础）。将监测体重增加、血浆葡萄糖和能量消耗，以验证除减少脂肪吸收外的机制有助于药物治疗和基因敲除小鼠抵抗肥胖和糖尿病的假设。其他实验将研究这三组小鼠的脂肪、肌肉、心脏和肝脏等高能量组织中膳食脂肪的分配，以验证NPC1L1失活改变这些组织餐后脂质输送和利用的假设。目的1还将确定代谢变化是否源于慢性胆固醇丢失引起的肝细胞中特定受体的激活增加。Specific Aim 2将使用体内方法来确定肌肉、肝脏和脂肪对饮食中甘油三酯利用的差异是由这些组织中npc1l1依赖途径的破坏引起的，还是由胆固醇和脂肪酸吸收减少引起的乳糜微粒组成的改变引起的。NPC1L1和依折替米贝对这些组织葡萄糖代谢的影响也将被专门测试。特异性目的3将确定抑制胆固醇吸收减少饱和脂肪酸吸收而不影响不饱和脂肪酸吸收的机制。体外、细胞培养和体内实验将验证未吸收的胆固醇抑制饱和脂肪酸通过胆汁盐胶束的增溶作用，导致其沉淀和排泄的假设。总之，这些研究将为肥胖和糖尿病的潜在原因提供新的见解，特别是脂肪吸收和代谢与葡萄糖代谢和整体能量平衡的关系。这些研究还将提供有关现有药物作用机制的宝贵信息，具有设计和开发治疗高脂血症、肥胖症和糖尿病等密切相关疾病的新治疗实体的潜力。公共卫生相关性：该研究项目将为肥胖和糖尿病的潜在原因提供重要的新信息，特别是脂肪吸收和代谢与葡萄糖代谢和整体能量平衡的关系。这些研究还将为现有药物的作用机制提供有价值的信息，并将为设计和开发治疗高脂血症、肥胖症和糖尿病等密切相关疾病的新治疗实体确定潜在的新靶点。

DESCRIPTION (provided by applicant): The goal of this research is to understand the mechanistic relationship between dietary lipid absorption and overall metabolism. The drug ezetimibe lowers plasma cholesterol by blocking its absorption in the intestine, apparently by disrupting the pathway associated with NPC1L1 (Nieman-Pick disease, type C1-protein -like protein 1). Preliminary studies into other physiological effects of ezetimibe have revealed that postprandial intestinal lipoproteins from ezetimibe-treated mice are different in size and composition than those from control mice. Our results also show that loss of NPC1L1 function, through ezetimibe treatment or gene deletion, protects mice from diet-induced obesity and insulin resistance. Reduced fat absorption may account for part of the difference in weight gain, but additional mechanisms, including increased energy expenditure, may also confer protection against diabetes and obesity. The focus of this proposal is to determine the mechanism(s) responsible for these different phenotypes. In Specific Aim 1, ezetimibe-treated, Npc1l1-/-, and control mice will be fed high fat diets that are either well absorbed by each group (safflower oil based) or poorly absorbed by Npc1l1-/- and ezetimibe-treated mice (cocoa butter based). Weight gain, plasma glucose, and energy expenditure will be monitored to test the hypothesis that mechanisms in addition to reduced fat absorption contribute resistance to obesity and diabetes of drug-treated and knockout mice. Other experiments will examine the partitioning of dietary fat among high energy tissues such as adipose, muscle, heart and liver in these three groups of mice to test the hypothesis that NPC1L1 inactivation alters postprandial lipid delivery to and utilization by these tissues. Aim 1 will also determine if metabolic changes derive from increased activation of specific receptors in hepatocytes due to chronic cholesterol loss. Specific Aim 2 will use in vivo methods to determine if the difference in dietary triglyceride utilization by muscle, liver and adipose is caused by disruption of NPC1L1-dependent pathways in those tissues or if it is caused by altered chylomicron composition from decreased cholesterol and fatty acid absorption. The effect of NPC1L1 and ezetimibe on glucose metabolism by these tissues will also be specifically tested. Specific Aim 3 will identify the mechanism by which inhibiting cholesterol absorption reduces saturated fatty acid absorption without affecting absorption of unsaturated fatty acids. In vitro, cell culture, and in vivo experiments will test the hypothesis that unabsorbed cholesterol inhibits solubilization of saturated fatty acids by bile salt micelles causing their precipitation and excretion. Together, these studies will provide novel insights about underlying causes of obesity and diabetes, especially the relationship of fat absorption and metabolism with glucose metabolism and overall energy balance. These studies will also provide valuable information about mechanisms of action for existing drugs, with potential for the design and development of new therapeutic entities for treatment of the closely related diseases of hyperlipidemia, obesity and diabetes. PUBLIC HEALTH RELEVANCE: This research project will provide important new information about underlying causes of obesity and diabetes, especially the relationship of fat absorption and metabolism with glucose metabolism and overall energy balance. These studies will also provide valuable information about mechanisms of action for existing drugs, and will identify potential new targets for the design and development of new therapeutic entities for treatment of the closely related diseases of hyperlipidemia, obesity and diabetes.