Lipid Metabolism and Steatosis in Liver

肝脏的脂质代谢和脂肪变性

• 批准号: 8971972
• 负责人: AMRITA KAMAT
• 金额: --
• 依托单位: SOUTH TEXAS VETERANS HEALTH CARE SYSTEM
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8971972
• 关键词: Ablation; Adenylate Cyclase; Adrenergic Agents; Adult; Age; Aging; Animals; Apolipoproteins B; Biological Assay; Body fat; Cardiovascular Diseases; Catecholamines; Cell Fractionation; Cell Nucleus; Characteristics; Chromatography; Co-Immunoprecipitations; Comparative Study; Data; Demographic Aging; Density Gradient Centrifugation; Development; Diagnosis; Elderly; Endoplasmic Reticulum; Exhibits; Fatty Acids; Fatty Liver; Fatty acid glycerol esters; Genetic Transcription; Goals; Health; Hepatic; Hepatocyte; Immunofluorescence Immunologic; In Vitro; Insulin Resistance; Knockout Mice; Label; Laboratories; Lead; Link; Lipids; Liver; Liver Cirrhosis; Liver diseases; Mediating; Membrane; Messenger RNA; Metabolic; Metabolic syndrome; Molecular Target; Non-Insulin-Dependent Diabetes Mellitus; Nuclear; Obesity; Pathogenesis; Peroxisome Proliferator-Activated Receptors; Physiologic pulse; Population; Prevalence; Prevention; Proteins; Receptor Signaling; Risk; Rodent; Role; Signal Transduction; Techniques; Testing; Transcription Coactivator; Triglycerides; Very low density lipoprotein; Veterans; Water; Western Blotting; base; beta-2 Adrenergic Receptors; beta-adrenergic receptor; blood glucose regulation; combat; fatty acid oxidation; in vivo; innovation; lipid metabolism; lipine; mouse model; non-alcoholic fatty liver; nonalcoholic steatohepatitis; novel; overexpression; oxidation; patient population; prevent; synthetic enzyme; transcription factor; very low density lipoprotein triglyceride

DESCRIPTION (provided by applicant): Excessive lipid accumulation in the liver (hepatic steatosis) is a hallmark of nonalcoholic fatty liver disease (NAFLD), which contributes to insulin resistance, type 2 diabetes, and cardiovascular disease. Obesity and aging, demographic characteristics of widespread national prevalence especially in the VA patient population, are two independent drivers of NAFLD. However, the pathogenetic mechanisms involved in the development of NAFLD are not well understood and as such there is an absence of proven therapies. Catecholamines acting via beta-adrenergic receptors ( B-ARs) regulate lipid and glucose homeostasis. In studies from our laboratory and others, obesity and aging have been demonstrated to increase B-AR membrane content and associated adenylyl cyclase responsiveness in liver. In preliminary studies we demonstrated that activation of B-AR signaling, mainly via B2-AR subtype, increases hepatic lipid accumulation in livers of young rodents, whereas inhibition of B-AR signaling in hepatocytes from old rodents reduces cellular lipid accumulation. In comparative studies of wild type (wt) and whole-body B2-AR knockout (ko) mice, we observed that old ko mice exhibited lower levels of liver steatosis and hepatic lipin-1 mRNA levels than the wt animals. Lipin-1 is a key regulator of hepatic lipid metabolism with distinct functions depending on its subcellular localization; in the endoplasmic reticulum (ER) it functions as a triglyceride (TG) synthetic enzyme, whereas in the nucleus it acts as a transcriptional coactivator that enhances fatty acid oxidation. We also observed that in vivo pharmacological activation of B-ARs increases hepatic TG and lipin-1 protein levels while reducing expression of factors (apoB, microsomal transfer protein) involved in secretion of very low density lipoprotein (VLDL)-TGs from the liver. Increased B-AR signaling was also found to reduce expression of PPAR¿, a transcription factor that promotes fatty acid oxidation by mechanisms which may involve interactions with lipin-1 in the nucleus. Based on these findings, we hypothesize that enhanced hepatic B2-AR activation is a major contributor to increased fat accumulation in liver. The overall goal of this study is to elucidate the mechanisms by which hepatic B2-AR signaling promotes lipid accumulation in liver. To test this hypothesis, we propose the following Specific Aims, which will be pursued using the B2-AR ko mouse model and in vivo and in vitro techniques: Aim 1): Determine whether increased hepatic B2-AR signaling augments TG synthesis by inducing lipin-1 transcription and translocation to the endoplasmic reticulum (ER). We hypothesize that in vivo and in vitro overexpression of B2-ARs will increase lipin-1 expression and translocation to the ER, leading to enhanced TG synthesis. We also hypothesize that the increase in lipin-1 transcription and its translocation to the ER will be prevented by inhibiting hepatic B2-AR signaling. Aim 2) Investigate whether increased hepatic B2-AR signaling decreases B-oxidation of fatty acids by inhibiting interaction of lipin-1 with PPAR¿ in the nucleus. We hypothesize that in vivo and in vitro overexpression of B2-ARs will reduce fatty acid B-oxidation by suppressing the interaction of lipin-1 with nuclear PPARa We also hypothesize that the translocation of lipin-1 out of the nucleus and suppression of fatty acid B-oxidation will be prevented by B2-AR ablation. Aim 3) Determine whether B2-AR signaling reduces VLDL assembly and secretion in liver. We hypothesize that in vivo and in vitro overexpression of B2-ARs will reduce assembly and secretion of VLDL-TGs in liver by decreasing factors involved in VLDL secretion such as apoB and microsomal triglycleride transfer protein. We also hypothesize that inhibition of hepatic VLDL secretion will be prevented by B2-AR ablation. With obesity and aging on the rise, especially in the VA patient population, it is vitally important to study the factors responsible fr the development of NAFLD. This study is innovative as the role of B2-AR signaling in development of hepatic steatosis has not yet been investigated. The study is expected to have an important impact by defining new molecular targets for the prevention and/or treatment of NAFLD and its complications.

描述（由申请人提供）： 肝脏中过多的脂质积累（肝脂肪变性）是非酒精性脂肪肝病 (NAFLD) 的一个标志，它会导致胰岛素抵抗、2 型糖尿病和心血管疾病，这是全国普遍流行的人口特征，尤其是在退伍军人事务部。患者群体是 NAFLD 的两个独立驱动因素，然而，NAFLD 发生的致病机制尚不清楚，因此缺乏经过验证的儿茶酚胺疗法。我们实验室和其他实验室的研究表明，β-肾上腺素能受体 (B-AR) 调节脂质和葡萄糖稳态，已证明肥胖和衰老会增加肝脏中 B-AR 膜含量和相关的腺苷酸环化酶反应性。在比较研究中，主要通过 B2-AR 亚型激活 B-AR 信号，增加年轻啮齿动物肝脏中的肝脏脂质积累，而抑制年老啮齿动物肝细胞中的 B-AR 信号传导。在野生型 (wt) 和全身 B2-AR 敲除 (ko) 小鼠中，我们观察到老年 ko 小鼠的肝脏脂肪变性水平和肝脏 lipin-1 mRNA 水平低于 wt 动物，Lipin-1 是关键的调节因子。肝脏脂质代谢的功能取决于其亚细胞定位；在内质网 (ER) 中，它充当甘油三酯 (TG) 合成酶，而在细胞核中，它充当转录共激活剂；我们还观察到，B-AR 的体内药理学激活会增加肝脏 TG 和 lipin-1 蛋白水平，同时减少参与极低密度脂蛋白 (VLDL) 分泌的因子（apoB、微粒体转移蛋白）的表达。来自肝脏的 TG 增加也被发现可以减少 PPAR 的表达。 ，一种通过可能涉及细胞核中的 lipin-1 相互作用的机制促进脂肪酸氧化的转录因子，我们发现增强的肝脏 B2-AR 活化是增加肝脏脂肪积累的主要因素。这项研究是为了 阐明肝脏 B2-AR 信号传导促进肝脏脂质积累的机制 为了检验这一假设，我们提出以下具体目标，将使用 B2-AR ko 小鼠模型以及体内和体外技术来实现： 目标 1。 ）：确定增加的肝脏 B2-AR 信号传导是否通过诱导 lipin-1 转录和易位至内质网 (ER) 来增强 TG 合成。我们捕获了体内和体外过表达。 B2-AR 的增加会增加 lipin-1 的表达并易位至 ER，导致 TG 合成增强，我们还发现，抑制肝脏 B2-AR 信号传导可阻止 lipin-1 转录的增加及其易位至 ER。目标 2) 研究肝脏 B2-AR 信号传导增强是否通过抑制 lipin-1 与 PPAR 的相互作用来减少脂肪酸的 B 氧化？我们认为体内和体外 B2-AR 的过度表达会通过抑制 lipin-1 与核 PPARa 的相互作用来减少脂肪酸 B-氧化。我们还认为 lipin-1 转出细胞核并B2-AR 消融可防止脂肪酸 B-氧化的抑制。 目的 3) 确定 B2-AR 信号是否在肝脏中组装和分泌。 B2-AR 将通过减少参与 VLDL 分泌的因子（例如 apoB 和微粒体甘油三酯转移蛋白）来减少肝脏中 VLDL-TG 的组装和分泌。随着年龄的增长，特别是在 VA 患者群体中，研究导致 NAFLD 发生的因素至关重要，因为 B2-AR 信号传导在发生过程中的作用具有创新性。尚未对肝脂肪变性的发生进行研究，预计该研究将通过确定预防和/或治疗 NAFLD 及其并发症的新分子靶点产生重要影响。