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: 7792592
• 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/7792592
• 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

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: Significance/Relevance to VA Patient Care Misssion Nonalcoholic fatty liver disease (NAFLD) and atherosclerosis are major disorders of lipid metabolism affecting the American, and, more specifically, the Veterans population. NAFLD is now recognized as a leading cause of cirrhosis in the U.S. Hepatic lipid accumulation in NAFLD leads to 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. The studies proposed in this application represent novel approaches based upon our recent findings to more clearly define the regulation of lipid metabolism in hepatocytes. A better understanding of cell cholesterol, fatty acid, and bile acid metabolism is crucial in order to develop more effective therapies for lipid related disorders.

描述（由申请人提供）： 提案摘要/摘要 肝脏脂质代谢调节紊乱存在于多种重要疾病中。具体地，非酒精性脂肪肝病(NAFLD)是一种肝脂质稳态紊乱，其中胆固醇和甘油三酯在肝细胞中积累。一小部分 NAFLD 患者会进展为肝细胞坏死、炎症和进行性纤维化。 NAFLD 现在被认为是美国肝硬化的主要原因。 NAFLD 中的肝脏脂质积累似乎部分通过诱导内质网中的未折叠蛋白反应 (UPR) 来产生损伤；与动脉粥样硬化发展中发现的类似事件的进展。与动脉粥样硬化形成一样，减少细胞内脂质积累的治疗可能通过抑制 UPR 来减轻 NAFLD 中的肝损伤。 最近，我们发现线粒体胆固醇传递和氧化是调节肝脏脂质代谢的关键步骤。研究发现，肝细胞中线粒体胆固醇递送蛋白 StARD1 的表达增加可以下调胆固醇生物合成途径，同时上调胆固醇降解和分泌途径。 StARD1 过度表达的后果包括细胞内中性脂质（胆固醇和甘油三酯）显着降低，对脂质稳态很重要的关键核受体水平增加，以及 HMG CoA 还原酶、乙酰 CoA 羧化酶和脂肪酸合酶（细胞中的速率决定酶）表达减少。胆固醇和脂肪酸的生物合成）。我们现在已经证明，肝脏 StARD1 过度表达通过线粒体 CYP27A1 启动的途径增加胆固醇氧化，并且产生的氧甾醇产物是能够介导脂质代谢变化的调节分子。 CYP27A1 是一种普遍存在的线粒体酶，我们的初步数据表明 StARD1/CYP27A1 通路也可能调节许多肝外组织中的脂质稳态。在由 CYP27A1 基因缺失引起的遗传性疾病 CTX 中，这些调节性氧甾醇的缺失与各种组织（包括肝脏）中脂质的积累、加速动脉粥样硬化和神经功能障碍有关。 此次更新申请的目的是进一步阐明StARD1/CYP27A1胆固醇氧化途径在调节肝脂质稳态中的作用。我们假设 StARD1 作为胆固醇可用性的细胞内传感器。当胆固醇过量时，线粒体胆固醇输送增加，导致 CYP27A1 衍生的氧甾醇的产生增加。产生的氧甾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，刺激肝脏中的这一途径可能是治疗非酒精性脂肪肝的有效策略。 提出了四个具体目标来研究这一假设。具体目标 1 将在完整和敲除模型中使用选择性 StARD1 过表达，以确定 StARD1/CYP27A1 途径衍生的氧甾醇是否负责激活控制胆固醇、脂肪酸和胆汁酸调节相关基因表达的关键核受体体内平衡；然后确定编码途径的表达如何与各自的核受体激活相关。在具体目标 2 中，我们建议表征和评估参与脂质稳态的 StARD1/CYP27A1 途径衍生的氧甾醇激活核受体的机制。具体目标 3 将确定胆固醇代谢的 StarD1/CYP27A1 通路在减弱肝细胞中未折叠蛋白反应 (UPR) 中的作用。具体目标 4 将首次测试 StARD1 表达增加在代表人类疾病的动物模型中预防或逆转肝脏脂质蓄积紊乱的药理学潜力。 公共卫生相关性： 对 VA 患者护理任务的意义/相关性 非酒精性脂肪性肝病 (NAFLD) 和动脉粥样硬化是影响美国人（更具体地说是退伍军人群体）的脂质代谢的主要疾病。 NAFLD 现在被认为是美国肝硬化的主要原因。 NAFLD 中的肝脏脂质积累会导致与动脉粥样硬化发展中发现的类似事件的进展。与动脉粥样硬化一样，减少细胞内脂质积累的治疗可能会减轻 NAFLD 中的肝损伤。本申请中提出的研究代表了基于我们最近发现的新方法，以更清楚地定义肝细胞中脂质代谢的调节。为了开发更有效的脂质相关疾病疗法，更好地了解细胞胆固醇、脂肪酸和胆汁酸代谢至关重要。