Impaired methylation alters lipid droplet dynamics in liver and adipose tissue: Role in hepatic steatosis

甲基化受损改变肝脏和脂肪组织中的脂滴动力学：在肝脂肪变性中的作用

• 批准号: 10620687
• 负责人: Kusum K. Kharbanda
• 金额: --
• 依托单位: OMAHA VA MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-01-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10620687
• 关键词: Adipocytes; Adipose tissue; Affect; Alcoholic Hepatitis; Alcoholic Liver Cirrhosis; Alcoholic Liver Diseases; Alcoholism; Alcohols; Animal Model; Benign; Betaine; Biogenesis; Biological Availability; Catabolism; Catalysis; Characteristics; Chronic; Cirrhosis; Consumption; Cytoplasm; Data; Defect; Development; Digestion; Disease Progression; Economic Burden; Enzymes; Ethanol; Fatty Acids; Fatty Liver; Fatty acid glycerol esters; Fibrosis; Generations; Healthcare Systems; Hepatic; Hepatocyte; Hospitalization; Impairment; Lecithin; Lipase; Lipid Binding; Lipids; Lipolysis; Liver; Malignant Neoplasms; Mediating; Metabolic; Metabolism; Methylation; Military Personnel; Modeling; Nonesterified Fatty Acids; Ocular orbit; Organelles; Phosphatidylethanolamine; Phosphatidylethanolamine N-Methyltransferase; Phospholipids; Play; Prevention; Production; Proteins; Reaction; Reporting; Resistance; Risk; Role; Services; Structure; Supplementation; Surface; Testing; Therapeutic Intervention; Triglycerides; Very low density lipoprotein; Veterans; alcohol effect; alcohol misuse; alcohol use initiation; chronic liver disease; experience; fatty liver disease; insight; methyl group; military veteran; monolayer; non-alcoholic fatty liver disease; novel; prevent; problem drinker; targeted treatment; treatment strategy; uptake

The development of fatty liver (steatosis) is an early manifestation of alcoholic liver disease (ALD) that can progress to alcoholic hepatitis and cirrhosis with continued alcohol misuse. Hepatic steatosis is a benign and reversible early stage of ALD. However, fat accumulation is regarded as the “first hit” that leaves the liver more vulnerable to multiple hits leading to ALD progression, and is therefore, a prime target for therapeutic intervention. Our long-term objective is to (i) understand the mechanisms of alcoholic steatosis development and (ii) formulate strategies for treatment/prevention of this and other fatty liver diseases that present with similar histopathological and disease progression characteristics such as non-alcoholic fatty liver disease. We have shown that alcohol-impaired activity of a major liver enzyme, phosphatidylethanolamine methyltransferase (PEMT), inhibits very-low-density lipoprotein (VLDL) secretion, contributing to the development of hepatic steatosis. PEMT catalyzes the methylation of phosphatidylethanolamine (PE) to generate phosphatidylcholine (PC), which is preferentially used in the assembly of VLDL and is necessary for its normal secretion. We have further shown that treatment with betaine, (a methyl donor) increases PC generation by normalizing PEMT activity. This, in turn, normalizes VLDL secretion rate and thus prevents alcoholic steatosis. It has been demonstrated that hepatic cytoplasmic lipid droplets (LDs) play an integral role in VLDL biogenesis. This is because VLDL assembly is regulated by the availability of triglycerides stored in these LDs which must be hydrolyzed to provide substrates for VLDL biogenesis. LDs are surrounded by a monolayer of phospholipids; PC is the most abundant class followed by PE. Further, an orbit of proteins determines the metabolic fate of LD lipid stores. Reduction in LD monolayer PC:PE ratio promotes fusion of these organelles to form supersized structures that are more resistant to lipolysis. Furthermore, a lower PC:PE ratio enhances the binding of the LD-associated proteins known to protect this organelle from lipase digestion. We have evidence that phospholipid and protein composition of hepatic LD changes with the initiation of alcohol-induced hepatic steatosis. Importantly, ethanol-induced hepatic LD accumulation occurs in conjunction with impaired VLDL production and enhanced adipose lipolysis-generated free fatty acid delivery and uptake. However, little is known about why alcohol promotes LD accumulation in hepatocytes but enhances adipocyte LD shrinkage. Based on these considerations, we present a novel hypothesis that alcohol impaired methylation contributes to the development of hepatic steatosis by inhibiting liver LD lipolysis and promoting adipose LD breakdown. We propose that liver phospholipid methylation defect lowers the LD monolayer PC:PE ratio to generate enlarged structures with altered composition of LD-associated proteins. These changes together hinder the lipolysis of the hepatic LD triglyceride stores to disrupt VLDL biogenesis resulting in fat accumulation. Conversely, adipose methylation defects activate lipases that promote LD lipolysis and fatty acid export. We further postulate that betaine supplementation reverses alcoholic steatosis by normalizing hepatic LD monolayer PC:PE ratio and VLDL biogenesis, and by regulating adipose LD lipolysis, hepatic fatty acid uptake and metabolism. To test our hypothesis, we propose the following Specific Aims: Specific Aim 1: To characterize how ethanol alters the phospholipid and protein composition of LDs. Specific Aim 2: To examine the effect of alcohol on LD lipolysis for mobilizing triglyceride stores. Specific Aim 3: To determine the effect of betaine on alcohol-induced alterations in LD dynamics. Completion of these studies will provide insight into the importance of maintaining essential methylation reactions in regulating the dynamics of hepatic and adipose LDs and preventing the development of alcoholic steatosis and other chronic liver diseases including non-alcoholic fatty liver disease.

脂肪肝（脂肪变性）的发展是酒精性肝病（ALD）的早期表现，可以 继续滥用酒精性肝炎和肝硬化。肝脂肪变性是一种良性， ALD的可逆早期阶段。但是，脂肪的积累被认为是使肝脏更多的“首次命中” 容易受到多次命中的影响，因此是治疗的主要目标。 干涉。我们的长期目标是（i）了解酒精脂肪变性的机制 （ii）制定策略以治疗/预防这种脂肪肝疾病 类似的组织病理学和疾病进展特征，例如非酒精性脂肪肝病。 我们已经表明，主要的肝酶，磷脂酰乙醇胺的饮酒障碍活性 甲基转移酶（PEMT）抑制非常低密度的脂蛋白（VLDL）分泌，有助于 肝脂肪变性的发展。 PEMT催化磷脂酰乙醇胺（PE）的甲基化至 产生磷脂酰胆碱（PC），最好用于VLDL组装，是必要的 它的正常分泌。我们进一步表明，（甲基捐献者）用Betaine的治疗增加了PC 通过标准化PEMT活性产生。反过来，这使VLDL的分泌率正常 酒精脂肪变性。 已经证明肝缸塑料脂质液滴（LDS）在VLDL中起着不可或缺的作用 生物发生。这是因为VLDL组件受这些LDS中存储的甘油三酸酯的可用性调节 必须水解以提供VLDL生物发生的底物。 LD由 磷脂； PC是最丰富的类，其次是PE。此外，蛋白质的轨道决定了 LD脂质商店的代谢命运。 LD单层PC的降低：PE比促进了这些细胞器的融合 形成更大的结构，对脂解具有更耐药性。此外，较低的PC：PE比增强了 LD相关蛋白已知可保护该细胞器免受脂肪酶消化的结合。我们有 肝素LD的磷脂和蛋白质组成随着酒精诱导的主动性而变化的证据 肝脂肪变性。重要的是，乙醇诱导的肝LD积累与受损 VLDL产生和增强的脂肪脂解解产生的游离脂肪酸的递送和摄取。但是，很少 知道为什么酒精会促进肝细胞中的LD积累，但增强了脂肪细胞LD的收缩。 基于这些考虑，我们提出了一个新的假设，即酒精受损的甲基化有助于 通过抑制肝LD脂解和促进脂肪LD分解来发展肝脂肪变性。我们 肝磷脂甲基化缺陷降低LD单层PC：PE比以产生扩大的提案 LD相关蛋白的组成改变的结构。这些变化一起阻碍了 肝LD甘油三酸酯存储以破坏VLDL生物发生，导致脂肪积累。相反，脂肪 甲基化缺陷激活脂肪酶，促进LD脂解和脂肪酸输出。我们进一步假设 Betaine补充剂通过使Hepatitic LD单层PC：PE比率和 VLDL生物发生，并通过调节脂肪LD脂解，肝脂肪酸摄取和代谢。 为了检验我们的假设，我们提出以下特定目的： 特定目标1：表征乙醇如何改变LDS的磷脂和蛋白质组成。 具体目标2：检查酒精对LD脂解对动员甘油三酸酯储存的影响。 特定目的3：确定甜菜碱对酒精诱导的LD动力学改变的影响。 这些研究的完成将洞悉维持基本甲基化的重要性 确定肝和脂肪LDS动力学的反应并防止酒精的发展 脂肪变性和其他慢性肝疾病，包括非酒精性脂肪肝病。