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

描述(申请人提供)：本研究的目的是了解膳食脂肪吸收和整体新陈代谢之间的机制关系。药物ezetimibe通过阻断胆固醇在肠道的吸收来降低血浆胆固醇，显然是通过破坏与NPC1L1(Nieman-Pick病，C1型蛋白样蛋白1)相关的途径。对Ezetimibe其他生理作用的初步研究表明，Ezetimibe处理的小鼠的餐后肠道脂蛋白在大小和组成上与对照组小鼠不同。我们的结果还表明，NPC1L1功能的丧失，通过依折麦布治疗或基因缺失，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，包括增加能量消耗，也可能提供对糖尿病和肥胖症的保护。这项建议的重点是确定导致这些不同表型的机制(S)。在具体目标1中，Ezetimibe处理组、NPC1L1-/-组和对照组小鼠将被喂养高脂肪饲料，这些高脂肪饲料要么被每组吸收良好(以红花油为基础)，要么被NPC1L1-/-和Ezetimibe处理组小鼠吸收较差(以可可油为基础)。体重增加、血糖和能量消耗将被监测，以检验这一假设，即除了减少脂肪吸收之外，机制还有助于抵抗药物治疗和基因敲除小鼠的肥胖和糖尿病。其他实验将在这三组小鼠中检查饮食脂肪在脂肪、肌肉、心脏和肝脏等高能组织中的分配，以检验NPC1L1失活改变这些组织的餐后脂肪输送和利用的假设。目标1还将确定代谢变化是否源于慢性胆固醇丢失导致肝细胞中特定受体的激活增加。特定目标2将使用体内方法来确定肌肉、肝脏和脂肪在饮食甘油三酯利用方面的差异是由于这些组织中依赖NPC1L1的途径被破坏所致，还是由于胆固醇和脂肪酸吸收减少而导致的乳糜管成分改变所致。NPC1L1和Ezetimibe对这些组织的葡萄糖代谢的影响也将被具体测试。具体目标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。在体外、细胞培养和体内实验中，将检验这一假设，即未被吸收的胆固醇会抑制饱和脂肪酸被胆盐胶束增溶，导致其沉淀和排泄。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，有可能设计和开发新的治疗实体，用于治疗密切相关的高脂血症、肥胖症和糖尿病等疾病。公共卫生相关性：这项研究项目将提供有关肥胖和糖尿病潜在原因的重要新信息，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。这些研究还将提供有关现有药物作用机制的宝贵信息，并将确定潜在的新目标，以设计和开发新的治疗实体，用于治疗与高脂血症、肥胖症和糖尿病密切相关的疾病。

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.