Hepatic Steatosis Modulation by Apo B Gene Transcription

描述（由申请人提供）：超过50%的肥胖代谢综合征患者肝脏甘油三酯（TG）（脂肪变性）升高，使他们易患非酒精性脂肪性肝病（NAFLD）和脂肪性肝炎（NASH），目前尚无共识的治疗方法。人体研究表明甜菜碱，一种天然存在的微量营养素，可以减轻肝脂肪变性，减少NASH，然而，这种作用的机制尚不清楚。我们已经证明，大鼠饮食中的甜菜碱通过增加载脂蛋白基因转录来促进肝脏载脂蛋白（apo） B的合成，这有利于肝脏以极低密度脂蛋白（VLDL）的形式输出TG，并使肝脏TG含量降低45%。这表明，在喂食甜菜碱的人身上观察到的肝脂肪变性的减少可能有类似的机制。目的1在两种啮齿动物代谢综合征模型：Zucker （fa/fa）大鼠和果糖喂养的apobec1 -/-小鼠（B100）中测试甜菜碱逆转肝脂肪变性的能力。Zucker大鼠模型过度喂养和果糖喂养小鼠模型果糖摄入量增加。由于B100小鼠合成和分泌VLDL B100而不是VLDL B48和VLDL B100，因此B100小鼠可以作为人肝脏脂蛋白代谢的模型。在喂食甜菜碱的啮齿动物中测量体内VLDL的产生、肝脏脂质含量、脂肪生成、胆汁酸合成和氧化。目的2将定义转录因子（TF），介导载脂蛋白基因的反激活，使用凝胶转移试验，染色质免疫沉淀，和体外功能的丧失和获得研究在啮齿动物肝细胞。目的3通过评估整体和启动子DNA低甲基化和使用甲基化启动子构建的瞬时转染试验，研究DNA甲基化在调节载脂蛋白基因表达中的作用，作为甜菜碱作用的潜在机制。由于肝脏VLDL生成的增加可导致高甘油三酯血症和LDL胆固醇升高，甜菜碱治疗将与减少热量摄入相结合进行试验。我们认为，诱导载脂蛋白转录可能有助于治疗肝脂肪变性，减少NASH和肝硬化的发生。从长远来看，对肝脏有利的可能对心血管风险不利，然而，了解这种联系使我们能够根据每个器官的病理生理来平衡风险。脂肪肝在肥胖人群中越来越常见，并可发展为肝硬化等肝脏疾病。甜菜碱可以通过促进肝脏脂肪卸载到循环脂蛋白中来逆转脂肪肝。临床意义是直接的，因为甜菜碱是一种可用的治疗微量营养素。了解甜菜碱对载脂蛋白B和血清脂蛋白的作用机制，可以通过增强肝脏TG输出的特异性干预来改善治疗。公共卫生相关性：脂肪肝在肥胖人群中越来越常见，并可发展为肝硬化等肝脏疾病。甜菜碱可以通过促进肝脏脂肪卸载到循环脂蛋白中来逆转脂肪肝。临床意义是直接的，因为甜菜碱是一种可用的治疗微量营养素，了解甜菜碱对载脂蛋白B和血清脂蛋白作用的机制可以通过促进TG从肝脏输出来改善治疗。

DESCRIPTION (provided by applicant): Over 50% of obese individuals with metabolic syndrome have increased hepatic triglycerides (TG) (steatosis) that predisposes them to non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) for which there is no consensus treatment. Human studies indicate that betaine, a naturally occurring micronutrient, alleviates hepatic steatosis, and reduces NASH, however, the mechanism responsible for this effect is not known. We have shown that dietary betaine in rats enhances hepatic apolipoprotein (apo) B synthesis through increased apob gene transcription which favors hepatic TG export in very low density lipoproteins (VLDL) and reduces liver TG content by 45%. This suggests a similar mechanism may be responsible for the reduction of hepatic steatosis observed in humans fed betaine. Aim 1 tests the ability of betaine to reverse hepatic steatosis in two rodent metabolic syndrome models: Zucker (fa/fa) rats and fructose-fed apobec-1-/- mice (B100). Zucker rats model overfeeding and fructose-fed mice model increased consumption of fructose. B100 mice serve as a model of human liver lipoprotein metabolism because B100 mice synthesize and secrete VLDL B100 rather than VLDL B48 and VLDL B100. In vivo VLDL production, hepatic lipid content, lipogenesis, bile acid synthesis, and ¿-oxidation will be measured in rodents fed ¿ betaine. Aim 2 will define the transcription factors (TF) that mediate transactivation of the apob gene using gel shift assays, chromatin immunoprecipitation, and in vitro loss and gain of function studies in rodent hepatocytes. Aim 3 examines the role of DNA methylation in regulating apob gene expression as a potential mechanism of betaine action by assessment of global and promoter DNA hypomethylation and transient transfection assays using methylated promoter constructs. As increasing hepatic production of VLDL can lead to hypertriglyceridemia and increased LDL chol, betaine therapy will be tested in combination with reduced caloric intake. We suggest that induction of apob transcription may be beneficial in treating hepatic steatosis, and reducing the development of NASH and cirrhosis. What is favorable for the liver may not be favorable in the long term for cardiovascular risk, however, understanding the association gives us the ability to balance risk based on each organ's pathophysiology. Fatty liver disease is increasingly common in the obese human population, and can progress to liver disease including cirrhosis. Betaine may reverse fatty liver by favoring the unloading of hepatic fat into circulating lipoproteins. Clinical implications are direct as betaine is an available therapeutic micronutrient. Understanding the mechanism responsible for the action of betaine on apo B and serum lipoproteins could improve therapy by specific intervention by enhancing TG export from the liver. PUBLIC HEALTH RELEVANCE: Fatty liver disease is increasingly common in the obese human population, and can progress to liver disease including cirrhosis. Betaine may reverse fatty liver by favoring the unloading of hepatic fat into circulating lipoproteins. Clinical implications are direct as betaine is an available therapeutic micronutrient, and understanding the mechanism responsible for the action of betaine on apo B and serum lipoproteins could improve therapy by enhancing TG export from the liver.