Lipid Metabolism and Steatosis in Liver

肝脏的脂质代谢和脂肪变性

• 批准号: 8624519
• 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/8624519
• 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; 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; adrenergic; 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; public health relevance; 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）： 肝脏中过度脂质积累（肝脂肪变性）是非酒精性脂肪肝病（NAFLD）的标志，有助于胰岛素抵抗，2型糖尿病和心血管疾病。肥胖和衰老，宽度宽度全国患病率的人口特征，尤其是在VA患者人群中，是NAFLD的两个独立驱动因素。但是，尚不清楚NAFLD发展所涉及的致病机制，因此缺乏可靠的疗法。通过β-肾上腺素能受体（B-ARS）作用的儿茶酚胺调节脂质和葡萄糖稳态。在我们的实验室和其他人的研究中，已证明肥胖和衰老可以增加肝脏中B-AR膜含量和相关的腺苷环酶反应性。在初步研究中，我们证明，B-AR信号的激活主要通过B2-AR亚型增加，增加了幼啮齿动物肝脏中肝脂质的积累，而旧啮齿动物中BAR信号传导的抑制作用减少了细胞脂质的积累。在对野生型（WT）和全身B2-AR敲除（KO）小鼠的比较研究中，我们观察到，与WT动物相比，旧的KO小鼠暴露了较低的肝脏脂肪变性和肝lipin-1 mRNA水平。 Lipin-1是肝脂质代谢的关键调节剂，其功能取决于其亚细胞定位。在内质网（ER）中，它充当甘油三酸酯（TG）合成酶，而在核中，它充当转录共激活因子，可增强脂肪酸氧化。我们还观察到，B-ARS的体内药理激活增加了肝脏TG和Lipin-1蛋白水平，同时减少了涉及非常低密度脂蛋白（VLDL）-TGS-TGS-TGS的因子（APOB，微粒体转移蛋白）的表达。还发现BAR信号传导增加可减少PPAR的表达，这是一种转录因子，通过机制促进脂肪酸氧化，这可能涉及核中与Lipin-1相互作用。基于这些发现，我们假设增强的肝B2-AR激活是肝脏中脂肪积累增加的主要原因。这项研究的总体目标是 阐明肝B2-AR信号传导促进肝脏中脂质积累的机制。为了检验这一假设，我们提出了以下特定目的，该目标将使用B2-AR KO小鼠模型以及体内和体外技术进行追求：AIM 1）：确定是否增加了HEPATITIC B2-AR信号通过诱导的Lipin-1转录和易位到内胞浆式网状网状（ER）（ER）（ER）。我们假设体内和B2-AR的体外过度表达将增加Lipin-1的表达并转移到ER，从而导致TG合成增强。我们还假设Lipin-1转录的增加及其转移到ER的易位将通过抑制肝B2-AR信号传导来预防。 Aim 2) Investigate whether increased hepatitic B2-AR signaling decreases B-oxidation of fatty acids by inhibiting interaction of lipin-1 with PPAR¿ 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 nuclear and suppression of fatty B2-AR消融将预防酸B氧化。目标3）确定B2-AR信号是否会减少肝脏中的VLDL组装和分泌。我们假设体内和体外过度表达B2-ARS将通过减少涉及VLDL分泌的因子（如APOB和微粒细胞甘油酯转移蛋白）来减少肝脏中VLDL-TGS的组装和分泌。我们还假设，B2-AR消融将阻止肝VLDL分泌的抑制作用。随着肥胖和衰老的增长，尤其是在VA患者人群中，研究导致NAFLD发展的因素至关重要。研究具有创新性，因为尚未研究B2-AR信号传导在肝脂肪变性发展中的作用。预计该研究将通过定义用于预防和/或治疗NAFLD及其并发症的新分子靶标的重要影响。