Hepatic Steatosis Modulation by Apo B Gene Transcription

Apo B 基因转录调节肝脂肪变性

• 批准号: 7595921
• 负责人: JANET DEHOFF SPARKS
• 金额: $ 26.18万
• 依托单位: UNIVERSITY OF ROCHESTER
• 依托单位国家: 美国
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7595921
• 关键词: Animal Feed; Animals; Antibodies; Apolipoproteins; Apolipoproteins B; Applications Grants; Arts; Betaine; Bile Acid Biosynthesis Pathway; Binding; Biological Assay; Biopsy; Cells; Cholesterol Esters; Cirrhosis; Clinical; Collaborations; Consensus; Consumption; DNA; DNA Methylation; Development; Diet; Dissection; EMSA; Electrophoretic Mobility Shift Assay; Energy Intake; Energy Metabolism; Enhancers; Enzymes; Epigenetic Process; Equilibrium; Event; Fatty Liver; Fatty acid glycerol esters; Fructose; Functional disorder; Funding; Gene Expression; Genes; Genetic; Genetic Transcription; Goals; Hepatic; Hepatocyte; Homocysteine; Homocysteine S-methyltransferase; Homocystine; Human; Hyperphagia; Hypertriglyceridemia; In Vitro; Individual; Inflammation; Institutes; Intervention; Journals; Laboratories; Lead; Ligands; Ligation; Lipids; Lipoprotein (a); Lipoproteins; Liver; Liver diseases; Low-Density Lipoproteins; Measures; Mediating; Messenger RNA; Metabolic; Metabolic syndrome; Metabolism; Methods; Methylation; Micronutrients; Modeling; Modification; Mus; National Heart, Lung, and Blood Institute; National Institute of Diabetes and Digestive and Kidney Diseases; Nonesterified Fatty Acids; Nuclear; Nuclear Extract; Nuclear Orphan Receptor; Obesity; Organ; Oxidative Stress; Patients; Physiology; Pilot Projects; Plasma; Population; Printing; Production; Proteins; Publishing; Rattus; Regulation; Research; Research Personnel; Risk; Rodent; Role; Run-On Assays; Serum; Steatohepatitis; Supplementation; Testing; Therapeutic; Time; Tissues; Transactivation; Transcriptional Regulation; Transfection; Triglycerides; Very low density lipoprotein; Western Blotting; Work; Zucker Rats; base; cardiovascular risk factor; chromatin immunoprecipitation; experience; feeding; foot; gain of function; heart disease risk; hepatoma cell; improved; in vivo; knock-down; lipid biosynthesis; meetings; member; mouse model; non-alcoholic fatty liver; nonalcoholic steatohepatitis; nutrition; oxidation; problem drinker; promoter; protein profiling; public health relevance; response; transcription factor; very low density lipoprotein triglyceride

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.

描述（由申请人提供）：超过 50% 患有代谢综合征的肥胖个体的肝脏甘油三酯 (TG)（脂肪变性）升高，使他们易患非酒精性脂肪肝病 (NAFLD) 和脂肪性肝炎 (NASH)，而目前尚无一致的治疗方法。人体研究表明，甜菜碱是一种天然存在的微量营养素，可以减轻肝脏脂肪变性，并减少 NASH，但造成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可通过增加 apob 基因转录来增强肝脏载脂蛋白 (apo) B 合成，从而有利于极低密度脂蛋白 (VLDL) 中的肝脏 TG 输出，并使肝脏 TG 含量降低 45%。这表明类似的机制可能导致在喂食甜菜碱的人类中观察到的肝脏脂肪变性减少。目标 1 在两种啮齿动物代谢综合征模型中测试甜菜碱逆转肝脂肪变性的能力：Zucker (fa/fa) 大鼠和果糖喂养的 apobec-1-/- 小鼠 (B100)。 Zucker大鼠模型过度喂养和果糖喂养小鼠模型增加了果糖的消耗。 B100小鼠可作为人类肝脏脂蛋白代谢的模型，因为B100小鼠合成和分泌VLDL B100而不是VLDL B48和VLDL B100。将在喂食甜菜碱的啮齿动物中测量体内VLDL产生、肝脂质含量、脂肪生成、胆汁酸合成和β氧化。目标 2 将使用凝胶位移测定、染色质免疫沉淀以及啮齿动物肝细胞的体外功能丧失和获得研究来定义介导 apob 基因反式激活的转录因子 (TF)。目标 3 通过评估整体和启动子 DNA 低甲基化以及使用甲基化启动子构建体的瞬时转染测定，检查 DNA 甲基化在调节 apob 基因表达中的作用作为甜菜碱作用的潜在机制。由于肝脏产生的 VLDL 增加会导致高甘油三酯血症和 LDL 胆固醇增加，因此甜菜碱疗法将与减少热量摄入相结合进行测试。我们认为诱导 apob 转录可能有益于治疗肝脂肪变性，并减少 NASH 和肝硬化的发展。从长远来看，对肝脏有利的因素可能不利于心血管风险，但是，了解这种关联使我们能够根据每个器官的病理生理学来平衡风险。脂肪肝疾病在肥胖人群中越来越常见，并且可以进展为肝病，包括肝硬化。甜菜碱可以通过促进肝脂肪转化为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：脂肪肝病在肥胖人群中越来越常见，并可能发展为肝病，包括肝硬化。甜菜碱可以通过促进肝脂肪转化为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增强肝脏的 TG 输出来改善治疗。