Role of Cholesterol in Non Alcoholic Fatty Liver

非酒精性脂肪性肝病(NAFLD)是一种肝脏脂代谢紊乱，其中胆固醇 脂肪会在肝细胞中积聚。相当一部分非酒精性脂肪肝患者进展为肝脏炎症， 坏死和进行性肝纤维化。非酒精性脂肪肝现在被认为是美国肝硬变的主要原因。 在退伍军人群体中；而且，很快就会成为肝脏最常见的适应症 移植。除了进展为终末期肝病外，它还经常与 糖尿病(胰岛素抵抗)和心血管疾病。这些临床表型的聚集现在是 称为新陈代谢综合症。 包括胆固醇和甘油三酯在内的非酒精性脂肪肝的现有治疗方法 降压剂、胰岛素增敏剂、抗氧化剂和生活方式的修饰还没有发现 能有效逆转非酒精性脂肪肝。目前还没有好的治疗方法。更好地理解 肝细胞胆固醇、脂肪、葡萄糖和胆汁酸代谢的相互作用对于形成更多 有效的治疗方法。 肝脏是维持全身脂肪平衡的中心。我们的实验室已经确认了胆固醇在体内的传递 线粒体的氧化作用是调节肝脏脂质代谢的关键步骤。我们发现了 在肝细胞(肝细胞)中增加线粒体胆固醇传递蛋白StARD1的表达， 下调胆固醇生物合成途径，上调胆固醇降解途径 和分泌物。肝脏StARD1表达增加通过以下途径增加胆固醇氧化 线粒体酶，CYP27A1；以及由此产生的氧固醇产物是能够 调节脂类代谢的变化。此外，CYP27A1的最终产物胆汁酸启动了 胆固醇代谢途径本身就是重要的调节分子；能够调节 胆固醇和脂肪通过激活肠道和肝脏核的肠道吸收和代谢 受体，FXR。 本应用的目的是阐明胆固醇的StARD1/CyP27A1途径的作用 氧化在调节肝脏脂肪和血糖动态平衡中的作用。这些研究的完成：1)将 确定是否增加细胞内胆固醇降解为调节性氧化甾醇和FXR激活胆汁 酸能够逆转2个NAFL动物模型的脂肪肝在接近模拟 典型的美国生活方式；2)将被用来分离胆汁酸激活FXR介导的通路 3)寻找未被发现的调节性氧固醇 通过增加StARD1/CYP27A1通路的表达而产生的，这有助于肝脏的深层脂质 在面对西方饮食时注意到的降低；4)寻找控制细胞内的新调控位点 调节氧固醇水平；以及，5)在存在和不存在高脂肪/高胆固醇肠道的情况下确定 天然FXR激动剂(即胆汁酸)与合成FXR激动剂之间的差异 Cyp27a1基因敲除小鼠模型中的肝脏胆固醇、脂肪和葡萄糖代谢；自然发生的 缺乏细胞色素P27A1的脂肪肝的遗传模型产生了氧甾醇。 根据我们的初步发现，我们认为协同使用增加了选择性激活 FXR和调节氧固醇激活的通路可用于逆转NAFL，并可能逆转动脉粥样硬化的形成。 这一提议带来了基础科学发现，导致了新的治疗方法。如中所述 这项提议，这些研究有可能为NAFLD的治疗提供直接的临床前景 不仅是在我们的退伍军人人口中，而且是在整个美国人口中。

Non-alcoholic fatty liver disease (NAFLD) is a disorder of liver lipid metabolism in which both cholesterol and fat accumulate in liver cells. A significant fraction of patients with NAFLD progress to liver inflammation, necrosis, and progressive liver fibrosis. NAFLD is now recognized as a leading cause of cirrhosis in the U.S. and in the Veteran's population; and, is poised to soon represent the most common indication for liver transplantation. In addition to its progression to end-stage liver disease, it is frequently associated with diabetes (insulin resistance) and cardiovascular disease. The clustering of these clinical phenotypes is now known as Metabolic Syndrome. Current therapeutic approaches for the treatment of NAFLD inclusive of cholesterol and triglyceride lowering agents, insulin sensitizing agents, anti-oxidants, and life-style modifications have not been found effective in reversing NAFLD. No good treatment approach currently exists. A better understanding of the interplay of liver cell cholesterol, fat, glucose, and bile acid metabolism is crucial in order to develop more effective therapies. The liver is central to total body lipid homeostasis. Our laboratory has identified delivery of cholesterol into the cell's mitochondria for oxidation as a crucial step in the regulation of liver lipid metabolism. We have found that increased expression of the mitochondrial cholesterol delivery protein, StARD1, in hepatocytes (liver cells), down-regulates pathways of cholesterol biosynthesis while up-regulating pathways of cholesterol degradation and secretion. Increasing liver StARD1 expression increases cholesterol oxidation via pathways initiated by mitochondrial enzyme, CYP27A1; and, the resulting oxysterol products are regulatory molecules capable of mediating changes in lipid metabolism. Furthermore, bile acids, the end product of the CYP27A1 initiated pathway of cholesterol metabolism, are important regulatory molecules in their own right; capable of mediating cholesterol and fat intestinal absorption and metabolism through activation of an intestinal and liver nuclear receptor, FXR. The objective of this application is to elucidate the role of the StARD1/CYP27A1 pathway of cholesterol oxidation in the regulation of hepatic lipid and glucose homeostasis. The completion of these studies: 1) will determine if increasing intracellular cholesterol degradation into regulatory oxysterols and FXR activating bile acids is capable of reversing fatty liver in 2 NAFL animal models under conditions which closely simulate a typical American lifestyle; 2) will be used to pull apart the activation of FXR mediated pathways by bile acids from the effects of increased regulatory oxysterols; 3) to search for undiscovered regulatory oxysterols generated by increasing expression of the StARD1/CYP27A1 pathway that contribute to the profound liver lipid lowering noted in the face of a Western diet; 4) to search for novel sites of regulation which control intracellular regulatory oxysterol levels; and, 5) to determine in the presence and absence of high fat/cholesterol intestinal content how naturally occurring FXR agonists (i.e bile acids) vs. synthetic FXR agonists may differentially alter hepatic cholesterol, fat, and glucose metabolism in a Cyp27a1 knockout mouse model; a naturally occurring genetic model of fatty liver lacking CYP27A1 generated oxysterols. Based on our preliminary findings, we believe that used in concert increased selective activation of the FXR and regulatory oxysterol activated pathways can be utilized to reverse NAFL, and, likely, atherogenesis. This proposal brings forth basic science discoveries that lead to novel treatment approaches. As outlined in the proposal, these studies have the potential to offer immediate clinical promise for treatment of NAFLD not only in our Veterans population, but in the U.S. population as a whole.