Lipid Transport, Bile Acid Synthesis, and Cholesterol Homeostasis

脂质运输、胆汁酸合成和胆固醇稳态

• 批准号: 8195880
• 负责人: WILLIAM M PANDAK
• 金额: --
• 依托单位: VA VETERANS ADMINISTRATION HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8195880
• 关键词: Acetyl-CoA Carboxylase; Affect; American; Animal Model; Atherosclerosis; Attenuated; Bile Acid Biosynthesis Pathway; Bile Acids; Binding; Cells; Cholesterol; Cholesterol Homeostasis; Cirrhosis; Cyclophosphamide; Data; Development; Disease; Endoplasmic Reticulum; Enzymes; Event; Extrahepatic; Fatty Acids; Fatty-acid synthase; Fibrosis; Gene Expression; Genes; Genetic; Hepatic; Hepatocyte; Hereditary Disease; Homeostasis; Hydroxymethylglutaryl-CoA reductase; Hypertriglyceridemia; Impairment; Inflammation; Injury; Intracellular Accumulation of Lipids; Knock-out; Lipids; Liver; Liver cell necrosis; Liver diseases; Mediating; Metabolism; Mitochondria; Modeling; Neurologic; Nuclear Receptors; Pathway interactions; Patient Care; Patients; Peroxisome Proliferator-Activated Receptors; Play; Population; Production; Proteins; Receptor Activation; Regulation; Role; Testing; Time; Tissues; Triglycerides; Variant; Veterans; abstracting; atherogenesis; base; cholesterol biosynthesis; effective therapy; human disease; lipid metabolism; lipid transport; non-alcoholic fatty liver; novel strategies; overexpression; oxidation; prevent; public health relevance; response; sensor; treatment strategy

Proposal Summary/Abstract Disordered regulation of hepatic lipid metabolism is found in a variety of important disorders. In particular, nonalcoholic fatty liver disease (NAFLD) is a disorder of hepatic lipid homeostasis in which both cholesterol and triglycerides accumulate in hepatocytes. A fraction of patients with NAFLD progress to liver cell necrosis, inflammation, and progressive fibrosis. NAFLD is a now recognized as a leading cause of cirrhosis in the U.S. Hepatic lipid accumulation in NAFLD appears to produce injury in part by inducing the unfolded protein response (UPR) in the endoplasmic reticulum; a progression of similar events to those found with the development of atherosclerosis. As with atherogenesis, treatments that reduce intracellular lipid accumulation may attenuate liver injury in NAFLD by repressing the UPR. Recently, we have identified mitochondrial cholesterol delivery and oxidation as crucial steps in the regulation of hepatic lipid metabolism. Increased expression of the mitochondrial cholesterol delivery protein, StARD1, in hepatocytes was found to down-regulate pathways of cholesterol biosynthesis while up-regulating pathways of cholesterol degradation and secretion. Consequences of StARD1 overexpression include markedly decreased intracellular neutral lipids (cholesterol and triglycerides), increased levels of key nuclear receptors important in lipid homeostasis, and reduced expression of HMG CoA reductase, acetyl CoA carboxylase, and fatty acid synthase (rate-determining enzymes in the biosynthesis of cholesterol and fatty acids). We now have shown that hepatic StARD1 overexpression increases cholesterol oxidation via pathways initiated by mitochondrial CYP27A1, and the resulting oxysterol products are regulatory molecules capable of mediating the resulting changes in lipid metabolism. CYP27A1 is a ubiquitous mitochondrial enzyme, and our preliminary data indicate that the StARD1/CYP27A1 pathway may regulate lipid homeostasis in many extrahepatic tissues as well. In the hereditary disorder CTX, caused by genetic deletion of CYP27A1, absence of these regulatory oxysterols is associated with accumulation of lipids in various tissues (inclusive of the liver), accelerated atherosclerosis, and neurologic impairment. The objective of this renewal application is to further elucidate the role of the StARD1/CYP27A1 pathway of cholesterol oxidation in the regulation of hepatic lipid homeostasis. We hypothesize that StARD1 serves as an intracellular sensor of cholesterol availability. When cholesterol is present in excess, mitochondrial cholesterol delivery increases, leading to increased production of CYP27A1 derived oxysterols. The resulting oxysterols then modulate lipid metabolism by binding to nuclear receptors. We further hypothesize that stimulation of this pathway in the liver could represent a useful strategy for treatment of nonalcoholic fatty liver disease. Four specific aims are proposed to study this hypothesis. Specific aim 1 will use selective StARD1 overexpression in intact and knock-out models to determine if StARD1/CYP27A1 pathway derived oxysterols are responsible for activating key nuclear receptors that control the expression of genes involved in the regulation of cholesterol, fatty acid, and bile acid homeostasis; and, subsequently determining how expression of the encoded pathways correlates with respective nuclear receptor activation. In Specific aim 2, we propose to characterize and assess mechanisms of activation of nuclear receptors by StARD1/CYP27A1 pathway derived oxysterols involved in lipid homeostasis. Specific aim 3 will determine the role of the StarD1/CYP27A1 pathway of cholesterol metabolism in attenuating the unfolded protein response (UPR) in hepatocytes. Specific aim 4 will test for the first time the pharmacologic potential of increased StARD1 expression to prevent or reverse disorders of liver lipid accumulation in animal models representative of human disease.

提案摘要/摘要 在多种重要疾病中发现了肝脂质代谢的调节无序调节。尤其， 非酒精性脂肪肝病（NAFLD）是肝脂质稳态的疾病 甘油三酸酯积聚在肝细胞中。 NAFLD患者的一小部分发展为肝细胞坏死， 炎症和进行性纤维化。 NAFLD是美国现在被公认为肝硬化的主要原因 NAFLD中的肝脂质积累似乎部分通过诱导展开的蛋白 内质网中的反应（UPR）；与发现的事件相似的事件的进展 动脉粥样硬化的发展。与动脉粥样硬化一样，减少细胞内脂质积累的治疗 可以通过压抑UPR来减轻NAFLD的肝损伤。 最近，我们确定线粒体胆固醇的递送和氧化是至关重要的步骤 调节肝脂质代谢。线粒体胆固醇递送蛋白的表达增加， Stard1，在上调的同时，发现肝细胞中胆固醇生物合成的途径下调途径 胆固醇降解和分泌的途径。 Stard1过表达的后果包括 明显降低了细胞内中性脂质（胆固醇和甘油三酸酯），关键核水平增加 对脂质稳态重要的受体，以及HMG COA还原酶的表达降低，乙酰COA 羧酸和脂肪酸合酶（胆固醇和脂肪的生物合成中的速率确定酶 酸）。我们现在已经表明，肝明星过表达通过 线粒体CYP27A1和产生的氧蛋白酶产物是调节分子的途径 能够介导脂质代谢的结果变化。 CYP27A1是无处不在的线粒体 酶，我们的初步数据表明stard1/cyp27a1途径可能调节脂质稳态 在许多肝外组织中。在遗传性疾病中，CTX是由CYP27A1的遗传缺失引起的 这些调节性氧甲甾醇的不存在与脂质在各种组织中的积累有关（包括 肝脏），加速动脉粥样硬化和神经系统障碍。 此更新应用的目的是进一步阐明stard1/cyp27a1途径的作用 肝脂质稳态调节中的胆固醇氧化。我们假设Stard1用作 胆固醇可用性的细胞内传感器。当胆固醇过量时，线粒体胆固醇 递送增加，导致CYP27A1衍生的氧甲醇的产生增加。产生的氧甲醇 然后通过与核受体结合来调节脂质代谢。我们进一步假设对此的刺激 肝脏中的途径可以代表治疗非酒精性脂肪肝病的有用策略。 提出了四个具体目标来研究这一假设。特定目标1将使用选择性stard1 完整和敲除模型中的过表达，以确定stard1/cyp27a1途径是否衍生氧 负责激活关键的核受体，以控制涉及的基因的表达 调节胆固醇，脂肪酸和胆汁酸稳态；然后，随后确定表达方式 编码的途径与各自的核受体激活相关。在特定目标2中，我们提出 表征和评估Stard1/cyp27a1途径激活核受体的机制 参与脂质稳态的衍生氧蛋白酶。特定目标3将确定stard1/cyp27a1的作用 胆固醇代谢在减弱肝细胞中展开的蛋白质反应（UPR）方面的途径。 具体目标4将首次测试Stard1表达增加的药理潜力以防止 或代表人类疾病的动物模型中肝脂质积累的反向疾病。