Mechanism of GDNF regulation of Hepatic Steatosis

GDNF调控肝脂肪变性的机制

• 批准号: 9898210
• 负责人: Shanthi K Srinivasan
• 金额: --
• 依托单位: VETERANS HEALTH ADMINISTRATION
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-04-01 至 2021-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9898210
• 关键词: Adrenergic Agents; Autophagocytosis; Cell Line; Centers for Disease Control and Prevention (U.S.); Data; Diabetes Mellitus; Eating; Enteric Nervous System; FDA approved; FRAP1 gene; Fatty Liver; Fatty acid glycerol esters; Functional disorder; Gastrointestinal Motility; Genes; Genetic; Glial Fibrillary Acidic Protein; Goals; Health; Health Care Costs; Healthcare; Healthcare Systems; Hepatic; Hepatocyte; High Fat Diet; Human; In Vitro; Incidence; Indirect Calorimetry; Laboratories; Lead; Lipids; Lipolysis; Liver; Mediating; Metabolic syndrome; Mitochondria; Mus; Neuroglia; Obesity; Obesity Epidemic; Obesity associated liver disease; Overweight; Oxidative Phosphorylation; Palmitates; Pathway interactions; Patients; Pharmacology; Pharmacotherapy; Physical activity; Play; Population; Prevalence; Prevention; Process; Publishing; Regulation; Reporting; Respiration; Role; Signal Pathway; Signal Transduction; Testing; Transgenic Mice; Transgenic Organisms; Triglycerides; Up-Regulation; Veterans; chronic liver disease; cost; established cell line; experimental study; glial cell-line derived neurotrophic factor; improved; in vivo; knock-down; lipid metabolism; liver injury; motility disorder; neurotrophic factor; new therapeutic target; non-alcoholic fatty liver disease; novel; obesity development; overexpression; oxidation; pleiotropism; prevent; promoter; receptor; stellate cell

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease in Veterans and its prevalence continues to increase, with the growing obesity epidemic. Hepatic steatosis is a component of NAFLD, wherein there is accumulation of triglycerides in the liver. Recently we published that GDNF transgenic mice fed a high fat diet are protected from obesity and the development of hepatic steatosis despite similar food intake and physical activity. GDNF transgenic mice over express GDNF in glia under the GFAP promoter (GDNF-tg) GDNF (expressed in glia) and its receptors, cRET and GFR-1 are expressed in human and murine hepatocytes. Thus, GDNF present in the liver can act locally on the hepatocytes. GDNF-tg mice demonstrate enhanced energy utilization assessed by indirect calorimetry. Having established a role for GDNF in preventing hepatic steatosis we recently examined the role of GDNF in preventing liver injury. Our preliminary data demonstrate novel effects of GDNF on the liver that include: (i) GDNF prevents HFD-induced liver injury (ii) GDNF-tg mice fed a HFD have increased hepatic levels of autophagy; and (iii) Hepatocytes treated with GDNF have improved mitochondrial function as seen by increased basal and mitochondrial respiration The mechanisms for these potentially beneficial effects of GDNF have yet to be explored. We hypothesize that the mechanism of GDNF prevention of hepatic injury is through promoting hepatocyte autophagy and by improving mitochondrial function leading to increased hepatocyte survival. GDNF can increase lipid droplet turnover, fat oxidation and oxidative phosphorylation in hepatic cells through the autophagic pathway. In this proposal we will establish the mechanism of GDNF regulation of hepatocyte autophagy and improved mitochondrial function. Currently there are no FDA approved drugs for the treatment of hepatic steatosis. We have identified a novel neurotrophic factor GDNF that decreases both hepatic steatosis and injury through enhancing autophagy and mitochondrial function. Using both genetic and pharmacological approaches we will define the role of GDNF in inducing autophagy to lead to oxidative lipid metabolism, fat reduction and reduced hepatic injury. We propose the following interrelated, but independently achievable aims: Specific Aim 1: To determine if the mechanism by which GDNF decreases hepatocyte lipid accumulation is through enhanced autophagy mediated lipolysis mediated by suppression of mTOR signaling. Preliminary data indicate that GDNF is a potent inducer of autophagy. We will establish whether autophagy mediates the GDNF-induced reduction in cellular lipid stores by studies of overexpression and knockdown of autophagy related genes. Preliminary data indicate that GDNF suppresses pmTOR signaling which is the prime inhibitory pathway of autophagy. We will determine the mechanism of GDNF up regulation of autophagy focusing on the mTOR pathway. WT and GDNF-tg mice will be fed a high fat diet for 8 weeks and genes regulating autophagy in hepatocytes will be assessed. In vitro the mechanism GDNF regulation of palmitate- induced autophagy will be determined focusing on the mTOR/TFEB/PGC1- pathway. Specific Aim 2: To establish that GDNF promotes hepatocyte survival by enhancing mitochondrial respiration by the mechanism of enhanced beta-adrenergic signaling and mitophagy. Our preliminary data demonstrate that GDNF increases mitochondrial function in hepatocytes as seen by increasing basal and maximal mitochondrial respiration as well as improving the mitochondrial respiration in hepatocytes cultured in the presence of palmitate. GDNF also promotes lipolysis through activation of -adrenergic signaling. We will establish the role of GDNF in regulating mitochondrial respiration using the GDNF-tg mice. We will examine the mechanism of GDNF regulation of mitochondrial health focusing on mitophagy and its effects on improving mitochondrial respiration. Taken together our data from this proposal may provide novel targets for the treatment or prevention of hepatic steatosis and injury.

非酒精性脂肪性肝病（NAFLD）是退伍军人慢性肝病的常见原因， 随着肥胖症的流行，患病率继续上升。肝脂肪变性是 NAFLD，其中在肝脏中存在甘油三酯的积累。最近我们发表了GDNF 喂食高脂肪饮食的转基因小鼠被保护免于肥胖和肝脂肪变性的发展， 相似的食物摄入量和体力活动。胶质细胞源性神经营养因子转基因小鼠在胶质纤维酸性蛋白诱导下胶质细胞中过表达GDNF 启动子（GDNF-tg）GDNF（在胶质细胞中表达）及其受体cRET和GFR-1 β在人中表达 和鼠肝细胞。因此，存在于肝脏中的GDNF可以局部作用于肝细胞。GDNF-tg小鼠 通过间接量热法评估，证明了增强的能量利用率。在确定了一个角色， GDNF在预防肝脂肪变性中的作用我们最近研究了GDNF在预防肝损伤中的作用。我们 初步数据表明GDNF对肝脏的新作用，包括：（i）GDNF阻止HFD诱导的 肝损伤（ii）喂食HFD的GDNF-tg小鼠具有增加的肝自噬水平;和（iii）肝细胞 用GDNF处理的小鼠具有改善的线粒体功能，如通过增加的基础和线粒体的 GDNF的这些潜在有益作用的机制还有待探索。我们 推测GDNF预防肝损伤的机制可能是通过促进肝细胞增殖， 自噬和通过改善线粒体功能导致肝细胞存活增加。GDNF可以 增加肝细胞中的脂滴周转、脂肪氧化和氧化磷酸化， 自噬途径本研究拟建立GDNF对肝细胞的调控机制 自噬和改善线粒体功能。目前还没有FDA批准的药物用于治疗 肝脏脂肪变性我们已经发现了一种新的神经营养因子GDNF， 脂肪变性和损伤。利用基因和 药理学方法，我们将确定GDNF在诱导自噬导致氧化脂质 代谢，减少脂肪和减少肝损伤。我们提出以下相互关联但又独立的建议： 具体目标1：确定GDNF降低肝细胞脂质的机制 在一些实施方案中，通过抑制mTOR信号传导介导的增强的自噬介导的脂解来促进细胞内的脂质累积。 初步数据表明GDNF是一种有效的自噬诱导剂。我们将确定自噬是否 介导GDNF诱导的细胞脂质储存的减少，通过研究 自噬相关基因初步数据表明GDNF抑制pmTOR信号传导，这是 自噬的主要抑制途径。我们将探讨GDNF上调自噬的机制 专注于mTOR通路。WT和GDNF-tg小鼠将被喂食高脂肪饮食8周，并将基因转染至小鼠。 将评估调节肝细胞中的自噬。在体外GDNF调节棕榈酸的机制- 诱导的自噬将集中在mTOR/TFEB/PGC 1-β通路上确定。具体目标2： 建立GDNF通过增强线粒体呼吸促进肝细胞存活机制 增强的β-肾上腺素信号和线粒体自噬。我们的初步数据表明GDNF增加 通过增加基础和最大线粒体呼吸， 以及改善在棕榈酸存在下培养的肝细胞中的线粒体呼吸。GDNF 还通过激活β-肾上腺素能信号传导促进脂解。我们将确定GDNF在以下方面的作用： 使用GDNF-tg小鼠调节线粒体呼吸。我们将研究GDNF的作用机制 线粒体健康的调节，重点是线粒体自噬及其对改善线粒体呼吸的影响。 总之，我们的数据从这一建议可能提供新的目标，为治疗或预防肝细胞癌。 脂肪变性和损伤。