Hepatic Steatosis Modulation by Apo B Gene Transcription

描述(申请人提供)：超过50%的患有代谢综合征的肥胖患者肝脏甘油三酯(TG)升高(脂肪变性)，这使他们容易患上非酒精性脂肪性肝病(NAFLD)和脂肪性肝炎(NASH)，目前还没有达成共识的治疗方法。人体研究表明，甜菜碱是一种天然存在的微量营养素，可以缓解肝脏脂肪变性，减少NASH，但其作用机制尚不清楚。结果表明，膳食甜菜碱可通过增加载脂蛋白B基因转录促进大鼠肝脏载脂蛋白B的合成，促进肝脏极低密度脂蛋白(VLDL)中甘油三酯的输出，并使肝脏甘油三酯含量降低45%。这表明，在服用甜菜碱的人中观察到的肝脏脂肪变性的减少可能与类似的机制有关。目的1在Zucker(FA/FA)大鼠和果糖喂养的APOBEC-1-/-小鼠(B100)模型上检测甜菜碱逆转肝脏脂肪变性的能力。Zucker大鼠模型和果糖喂养的小鼠模型均增加了果糖的摄入量。B100小鼠作为人类肝脏脂蛋白代谢的模型，因为B100小鼠合成和分泌VLDLB100而不是VLDLB48和VLDLB100。在体内，将测量喂食甜菜碱的啮齿动物的极低密度脂蛋白生成、肝脏脂肪含量、脂肪生成、胆汁酸合成和氧化。目的2通过凝胶漂移试验、染色质免疫沉淀和体外功能丧失与获得研究，确定介导载脂蛋白B基因反式激活的转录因子(Tf)。目的通过对全局和启动子DNA的低甲基化和瞬时转染法的评估，探讨DNA甲基化在调节载脂蛋白B基因表达中的作用，作为甜菜碱作用的一个潜在机制。由于肝脏产生更多的极低密度脂蛋白可导致高甘油三酯血症和低密度脂蛋白胆固醇增加，甜菜碱治疗将与减少热量摄入相结合进行测试。我们认为诱导ApoB转录可能有助于治疗肝脏脂肪变性，减少NASH和肝硬变的发生。然而，从长远来看，对肝脏有利的东西可能不利于心血管风险，然而，了解这种联系使我们能够基于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，并可发展为包括肝硬变在内的肝病。甜菜碱可通过促进肝脏脂肪进入循环脂蛋白来逆转脂肪肝。临床意义是直接的，因为甜菜碱是一种可用的治疗性微量营养素。了解甜菜碱对载脂蛋白B和血清脂蛋白的作用机制，可以通过促进肝脏甘油三酯的输出来进行特定的干预，从而改善治疗。公共卫生相关性：脂肪肝在肥胖人群中越来越常见，并可发展为包括肝硬变在内的肝病。甜菜碱可通过促进肝脏脂肪进入循环脂蛋白来逆转脂肪肝。甜菜碱是一种有效的治疗微量营养素，临床意义是直接的，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促进肝脏甘油三酯的排出来改善治疗。

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.