Homeostatic role of IRE1a-XBP1-PDI1 in hepatic lipid metabolism

IRE1a-XBP1-PDI1 在肝脂质代谢中的稳态作用

• 批准号: 8888815
• 负责人: RANDAL J. KAUFMAN
• 金额: $ 58.5万
• 依托单位: SANFORD BURNHAM PREBYS MEDICAL DISCOVERY INSTITUTE
• 依托单位国家: 美国
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-01 至 2020-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8888815
• 关键词: Acute; Affect; Animals; Apolipoproteins B; Attenuated; Biochemistry; Cirrhosis; Consumption; Cytosol; Data; Development; Diabetes Mellitus; Diagnostic; Diet; Disease; Dysplasia; Endoplasmic Reticulum; Environment; Epidemic; Etiology; Fatty Liver; Fibrosis; Fructose; Genes; Genetic Models; Genetic Transcription; Grant; Health; Health Care Costs; Hepatic; Hepatocyte; Homeostasis; Human; Hyperlipidemia; Inflammation; Inositol; Insulin Resistance; Intervention; Knockout Mice; Link; Lipids; Lipoproteins; Liver; Liver diseases; Mass Spectrum Analysis; Mediating; Messenger RNA; Metabolic Diseases; Metabolic stress; Mitochondria; Modality; Molecular Chaperones; Molecular Profiling; Mus; Nutrient; Nutritional; Nutritional Study; Obesity; Pathogenesis; Pathway interactions; Physiology; Plasma; Play; Population; Primary carcinoma of the liver cells; Production; Prognostic Marker; Protein Biosynthesis; Protein Disulfide Isomerase; Proteins; Proteomics; RNA Splicing; Reactive Oxygen Species; Research; Role; Signal Transduction; Site; Smooth Endoplasmic Reticulum; Stimulus; Stress; Testing; Therapeutic Intervention; Time; Triglycerides; Very low density lipoprotein; alternative treatment; arm; base; cardiovascular disorder risk; glycosylation; improved; in vivo; insight; intrahepatic; lipid metabolism; lipid transport; mRNA Expression; microsomal triglyceride transfer protein; non-alcoholic fatty liver; nonalcoholic steatohepatitis; novel; novel therapeutic intervention; particle; prevent; protein folding; protein misfolding; public health relevance; response

 DESCRIPTION (provided by applicant): Approximately 20% of the US population suffers from non-alcoholic fatty liver disease (NAFLD) that can progress to hepatosteatosis, fibrosis, cirrhosis and hepatocellular carcinoma. Hepatic secretion of VLDL plays an essential role in regulating intrahepatic and intravascular lipid homeostasis. The overproduction of hepatic VLDL characterizes the pathogenesis of hyperlipidemia in obesity and diabetes and contributes significantly to an increased risk of cardiovascular disease. Despite the significant impact of abnormalities in VLDL secretion on human health, fundamental cellular mechanisms that drive VLDL assembly are yet to be understood. Hepatic VLDL assembly and secretion is significantly reduced by protein misfolding in the endoplasmic reticulum (ER) and increased by the adaptive unfolded protein response (UPR). The proposed research will elucidate the mechanistic role of the UPR in maintaining triglyceride (TG) levels in the ER lumen for VLDL assembly. We will vigorously test the hypothesis that changes in the ER protein-folding environment of the hepatocyte activate inositol-requiring kinase1 (IRE1) to splice Xbp1 mRNA to generate XBP1s in response to a nutritional stimulus are key in the etiology of NAFLD and abnormal lipid secretion and hyperlipidemia. Our hypothesis is based on three recent fundamental findings regarding assembly of VLDL. First, we have demonstrated that nutritional excess alters lipid homeostasis and activates the UPR in hepatocytes. Aim 1 will uncover the mechanism that links metabolic stress with protein misfolding in the ER. Aims 2 and 3 focus on how XBP1s is essential role to maintain ER lipid homeostasis. We have demonstrated that XBP1s provides two independent functions for assembly of TG-rich VLDL. First, XBP1s activates transcription of protein disulfide isomerase (Pdi1) to maintain microsomal TG transfer protein (MTP) in an active form to promote lipid assembly with apolipoprotein B (ApoB). Aim 2 will study how nutritional stress reduces MTP activity in a PDI1-dependent manner. Aim 3 will identify the second mechanism by which XBP1s is essential to promote TG-rich VLDL assembly in an MTP-independent manner using a combination of mRNA-Seq and mass spectrometry approaches. Finally, and significantly, our data show that PDI1 promotes oxidative folding of ApoB, thus for the first time uncovering a protein folding substrate for PDI1 in vivo. Aim 4 will use hepatocyte-specific Pdi1-null mice to study how PDI1 promotes ApoB100 oxidative folding and alters interactions with the protein-folding environment (i.e., molecular chaperones). Results from the proposed studies will elucidate the mechanisms by which IRE1/XBP1 maintains hepatocyte lipid homeostasis by partitioning TG into the ER lumen for VLDL assembly. The findings will provide fundamental understanding of mechanisms that govern VLDL maturation, which will facilitate the development of novel therapeutic approaches to treat hepatosteatosis and hyperlipidemia.

 描述（由适用提供）：大约20％的美国人口患有非酒精性脂肪肝疾病（NAFLD），可以发展为肝瘤病，纤维化，肝硬化 和肝细胞癌。 VLDL的肝分泌在确定血管内和血管内脂质稳态方面起着至关重要的作用。肝VLDL特征过量生产肥胖症和糖尿病中高脂血症的发病机理，并显着促进了心血管疾病的风险增加。尽管异常在VLDL分泌中对人类健康产生了重大影响，但驱动VLDL组装的基本细胞机制尚未肝VLDL组装和分泌显着降低，因为内质网中的蛋白质错误折叠在内质网（ER）中降低，并增加了适应性染色的蛋白质反应（UPR）。拟议的研究将阐明UPR在VLDL组装中维持ER腔内甘油三酸酯（TG）水平的机理作用。我们将大力测试以下假设：肝细胞的ER蛋白折叠环境的变化激活肌醇质子醇的激酶1（IRE1）以剪接XBP1 mRNA，从而产生XBP1，以响应Nafld和Abripidemal和Arbnormal lipidem and Apripidem and Appripidem and Appripidem and Abripidem and afterpiDem和Apripidem and afterpiDem和Apripidem and ripidem and aftripidem and afterpidem and trippidem和afterpy。我们的假设基于有关VLDL组装的三个最新基本发现。首先，我们已经证明了营养过量会改变脂质稳态并激活肝细胞中的UPR。 AIM 1将发现将代谢应激与ER中蛋白质错误折叠联系起来的机制。目标2和3关注XBP1如何保持脂质稳态的重要作用。我们已经证明XBP1提供了两个独立的函数，用于组装富含TG的VLDL。首先，XBP1激活蛋白质二硫化物异构酶（PDI1）的转录，以将微粒体TG转移蛋白（MTP）保持活性形式，以促进用载脂蛋白B（ApoB）促进脂质组装。 AIM 2将研究营养应激如何以PDI1依赖性方式降低MTP活性。 AIM 3将确定XBP1s使用mRNA-SEQ和质谱方法的组合以MTP独立的方式促进富含TG的VLDL组装至关重要的第二种机制。最后，重要的是，我们的数据表明，PDI1促进了APOB的氧化折叠，因此首次发现体内PDI1的蛋白质折叠底物。 AIM 4将使用肝细胞特异性PDI1-NULL小鼠研究PDI1如何促进APOB100氧化折叠并改变与蛋白质折叠环境（即分子伴侣）的相互作用。拟议的研究的结果将阐明IRE1/XBP1通过将TG分隔为VLDL组装的ER管腔来维持肝细胞脂质稳态的机制。这些发现将提供对控制VLDL成熟的机制的基本理解，这将有助于开发新的治疗方法来治疗肝病和高脂血症。