HGF/HGFR Axis and Fatty Liver Disease

HGF/HGFR 轴与脂肪肝疾病

• 批准号: 9077861
• 负责人: Reza Zarnegar
• 金额: $ 34.65万
• 依托单位: UNIVERSITY OF PITTSBURGH AT PITTSBURGH
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-01 至 2020-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9077861
• 关键词: Albumins; Alcoholic Hepatitis; Automobile Driving; Biological; Cell Death; Cell Survival; Cells; Cessation of life; Cirrhosis; Clinical; Coupled; Data; Defect; Disease; Event; Fatty Liver; Fatty acid glycerol esters; Fibrosis; Glucose; Growth Factor Receptors; HGF gene; Hepatic; Hepatocyte; High Fat Diet; Homeostasis; Human; In Vitro; Inflammation; Inflammatory; Insulin; Insulin Receptor; Insulin Resistance; Liver; Liver Failure; Liver diseases; MET gene; Malignant neoplasm of liver; Mediating; Mediator of activation protein; Metabolic; Metabolic syndrome; Metabolism; Modification; Molecular; Mus; Necrosis; Non-Insulin-Dependent Diabetes Mellitus; Pathology; Pathway interactions; Phosphotransferases; Play; Process; Proteasome Inhibition; Protein Kinase; Protein Tyrosine Kinase; Public Health; RIPK1 gene; Regulation; Resistance; Role; Series; Signal Transduction; Site-Directed Mutagenesis; System; Testing; Transgenic Mice; Tyrosine; Up-Regulation; base; cancer type; cell growth; feeding; gain of function; glucose metabolism; hepatic necrosis; in vivo Model; insight; lipid metabolism; liver inflammation; liver injury; loss of function; meetings; mouse model; non-alcoholic; non-alcoholic fatty liver; nonalcoholic steatohepatitis; novel; prevent; public health relevance; receptor function; research study; response; restoration

 DESCRIPTION (provided by applicant): Fatty Liver Disease (FLD) is a leading public health problem in the U.S. and elsewhere. Liver parenchymal cells (hepatocytes) play an essential role in regulating glucose and fat homeostasis which is believed to be achieved by the proper action of the Insulin-Insulin Receptor (I-IR) axis. Dysregulation of this pathway in Type 2 Diabetes (T2D) can result in non-alcoholic FLD (NAFLD) - a disorder showing a spectrum of pathologies from hepatocyte fat accumulation (steatosis), inflammation and necrosis of steatotic hepatocytes (NASH), fibrosis, cirrhosis and liver cancer that are not well understood at the molecular level. Hepatic insulin resistance is believed to be a driver of this process and results from lack of optimum insulin receptor (IR) function in hepatocytes. Recently, we established that the Hepatocyte Growth Factor (HGF)-MET signaling axis controls hepatic glucose and fat metabolism and is essential for optimum hepatic insulin response. Given the fact that the HGF-MET signaling axis not only controls metabolism but also modulates cell growth and survival (i.e. suppression of cell death), we propose that diminished HGF-MET signalling (that is, "HGF Resistance") in the liver acts as a double-edged sword causing a vicious cycle of hepatocyte metabolic derangement coupled with an inability to overcome (or survive) liver damage provoked by insults such as lipotoxicity. RIPK1 (Receptor Interacting Protein Kinase 1) has emerged as the master switch that dictates inflammation and necrosis. Based on our groundbreaking preliminary data examining the impact of the HGF- MET axis on RIPK1 in hepatocytes, we hypothesize that, under normal conditions in hepatocytes, the HGF-MET axis negatively regulates RIPK1 enzymatic activity through directly tyrosine phosphorylating RIPK1 promoting RIPK1 proteosomal degradation in order to protect hepatocytes from RIPK1's pro- inflammatory and pro-necrotic actions, and that, in the setting of hepatocyte lipotoxicity and NAFLD, reduced and defective HGF-MET signaling results in escape of RIPK1 from HGF-MET-mediated negative regulation unleashing RIPK1-dependent hepatocyte inflammation and necrotic cell death. We propose that restoration of HGF-MET signaling will negate this effect. We outline three specific aims to test this novel hypothesis. Aim 1 - we will investigate the functional consequences of tyrosine phoshorylation of RIPK1 by MET using site directed mutagenesis and in vitro hepatocytic cell cuture systems to establish that this modification results in inhibition of RIPK1 enzymatic activity and promotes its proteosomal degradation - hence, RIPK1 mediated inflammation and necrosis are prevented. We will also test the hypothesis that disruption of MET signaling results in uncontrolled RIPK1 activity unleashing RIPK1- mediated hepatocyte death. The molecular mechanisms that regulate RIPK1 are not well understood. We have discovered that MET directly tyrosine phosphorylates RIPK1 on Tyr384 downregulating RIPK1 kinase activity and marking it for proteosomal degradation. Thus, studies under this aim will decipher the molecular regulation of RIPK1 by the tyrosine kinase growth factor receptor MET. Aim 2 - we will directly test our hypothesis that HGF-MET mediated regulation of RIPK1 has biological and pathological implications to liver homeostasis in the setting of fatty liver disease using loss- and gain-of-function mouse models. We believe that HGF-MET insufficiency caused by lipotoxicity exacerbates RIPK1-induced liver inflammation and necrosis and that restoration of HGF-MET signaling will negate this effect. We have discovered that RIPK1 is upregulated and HGF/MET are downregulated in human and mouse fatty liver. The molecular mechanisms that drive progression of fatty liver disease are not well understood. We propose that reduced HGF/MET signaling in fatty hepatocytes causes RIPK1 to escape MET-mediated negative regulation driving RIPK1-induced hepatocyte necrosis. We will induce fatty liver disease (by feeding a high fat diet) in liver specific loss-of function (using LMETKO and LRIPK1 KO) and gain- of-function (Albumin-HGF Transgenic) mouse models. Aim 3 - we will determine the molecular basis of RIPK1 upregulation in hepatocytes by lipotoxicity. We hypothesize that any defect in HGF/MET signaling provoked by lipotoxicity will promote RIPK1 accumulation. Liptoxicity may also stabilizes RIPK1 via direct inhibition of the proteasome. We will perform a series of comprehensive experiments using a hepatocyte culture system and in vivo models to test if one or both of these pathways are active to define the molecular bases of RIPK1 dysregulation in fatty liver disease. The proposed studies will establish a new paradigm by which tyrosine kinase growth factor receptor systems like HGF-Met prevent hepatic inflammation and necrosis by downmodulating the pro-inflammatory and pro- death activity of RIPK1. Our studies will provide rationale for manipulating these key mediators (HGF-MET and RIPK1) in the clinical setting of inflammatory hepatic conditions such as NASH or alcoholic hepatitis.

 描述（由申请人提供）：脂肪肝病（FLD）是美国和其他地方的一个主要公共卫生问题，肝实质细胞（肝细胞）在调节葡萄糖和脂肪稳态中发挥着重要作用，据信这是通过适当的调节来实现的。胰岛素-胰岛素受体 (I-IR) 轴的作用 2 型糖尿病 (T2D) 中该通路的失调可导致非酒精性症状。 FLD (NAFLD) - 一种表现出肝细胞脂肪堆积（脂肪变性）、脂肪肝细胞炎症和坏死（NASH）、纤维化、肝硬化和肝癌等一系列病理的疾病，这些疾病在分子水平上尚不清楚。据信这是这一过程的驱动因素，并且是肝细胞中缺乏最佳胰岛素受体（IR）功能的结果。最近，我们确定肝细胞生长因子（HGF）-MET 信号轴控制。鉴于 HGF-MET 信号轴不仅控制新陈代谢，而且还调节细胞生长和存活（即抑制细胞死亡），我们建议减少 HGF-MET。肝脏中的信号传导（即“HGF 抵抗”）就像一把双刃剑，导致肝细胞代谢紊乱的恶性循环，以及无法克服（或生存）由诸如此类的侮辱引起的肝损伤。 RIPK1（受体相互作用蛋白激酶 1）已成为决定炎症和坏死的主开关。根据我们检查 HGF-MET 轴对肝细胞中 RIPK1 的影响的开创性初步数据，我们发现，在正常条件下。在肝细胞中，HGF-MET 轴通过直接酪氨酸磷酸化 RIPK1 促进 RIPK1 负向调节 RIPK1 酶活性蛋白体降解以保护肝炎免受 RIPK1 促炎和促坏死作用的影响，并且在肝细胞脂毒性和 NAFLD 的情况下，HGF-MET 信号传导减少和缺陷导致 RIPK1 逃避 HGF-MET 介导的负调节释放 RIPK1 依赖性肝细胞炎症和坏死细胞死亡，我们提出恢复 HGF-MET 信号将消除这种效应。目标 1 - 我们将使用定点诱变和体外肝细胞培养系统研究 MET 对 RIPK1 酪氨酸磷酸化的功能后果，以确定这种修饰会抑制 RIPK1 酶活性并促进其蛋白体。降解 - 因此，RIPK1 介导的炎症和坏死被阻止，我们还将测试 MET 信号传导破坏导致失控的假设。 RIPK1 活性释放 RIPK1 介导的肝细胞死亡 调节 RIPK1 的分子机制尚不清楚。我们发现 MET 直接磷酸化 Tyr384 上的 RIPK1，从而下调 RIPK1 激酶活性并标记其蛋白体降解。酪氨酸激酶生长因子受体 MET 对 RIPK1 的分子调节 目标 2 - 我们将直接测试。我们的假设是，在功能丧失和功能获得的小鼠模型中，HGF-MET 介导的 RIPK1 调节对肝脏稳态具有生物学和病理学意义。我们认为，脂毒性引起的 HGF-MET 不足会恶化 RIPK1。诱导肝脏炎症和坏死，并且 HGF-MET 信号传导的恢复将抵消这种作用。我们发现，在人和小鼠中 RIPK1 上调，而 HGF/MET 下调。脂肪肝疾病进展的分子机制尚不清楚，我们认为脂肪肝细胞中 HGF/MET 信号传导的减少会导致 RIPK1 逃避 MET 介导的负调控，从而导致 RIPK1 诱导的肝细胞坏死。肝脏特定损失的疾病（通过喂养高脂肪饮食） 功能（使用 LMETKO 和 LRIPK1 KO）和功能获得（白蛋白-HGF 转基因）小鼠模型 - 我们将通过脂毒性确定肝细胞中 RIPK1 上调的分子基础。脂毒性引起的脂毒性会促进 RIPK1 积累，脂毒性也可能通过直接抑制蛋白酶体来稳定 RIPK1。肝细胞培养系统和体内模型来测试这些途径中的一个或两个是否活跃，以确定脂肪肝疾病中 RIPK1 失调的分子基础。拟议的研究将建立一个新的范例，通过该范例，酪氨酸激酶生长因子受体系统（如 HGF）。 -Met 通过下调 RIPK1 的促炎和促死亡活性来预防肝脏炎症和坏死，我们的研究将为操纵这些关键介质（HGF-MET 和 RIPK1）提供理论依据。在 NASH 或酒精性肝炎等炎症性肝病的临床环境中。