Novel mechanisms regulating VLDL secretion and non-alcoholic fatty liver diseases

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Abstract Nonalcoholic fatty liver disease (NAFLD) is currently a highly prevalent form of liver disease. NAFLD is characterized by the accumulation of lipids in hepatocytes that can progress to nonalcoholic steatohepatitis (NASH), which has increased hepatocyte death, inflammation and fibrosis. The molecular basis of the development and progression of NAFLD/NASH are still poorly understood. As a result, no effective therapeutic treatments for this burgeoning health problem are available. Thus, there is a clear unmet research need in this area. Hepatic very-low-density lipoprotein (VLDL) secretion is essential in regulating intrahepatic and intravascular lipid homeostasis, and impaired VLDL secretion leads to steatosis. Vacuole membrane protein 1 (VMP1) is an ER membrane protein that regulates autophagy by promoting the closure of autophagosomes. Recent evidence demonstrates that VMP1 plays a critical role in lipoprotein secretion independent of its autophagy function in cultured hepatoma cells and zebrafish. The major OBJECTIVES of this application are to understand the role and mechanisms by which VMP1 regulates lipid metabolism and NAFLD progression. Our proposal is SIGNIFICANT because it is to investigate a novel pathway in regulating lipid metabolism and development of NAFLD. Work performed under this application will enrich the NAFLD field regarding the critical role of VMP1 as a central regulator of ER-mitochondria and ER-ERGIC-Golgi crosstalk which regulate VLDL secretion at multilayers in the development of NAFLD. Our overall SCIENTIFIC PREMISE is that elucidating pathways whereby loss of VMP1 impairs VLDL secretion and promotes NAFLD/NASH. Our proposal is supported by KEY PRELIMINARY DATA including: 1) Hepatocyte-specific deletion of VMP1 in mice impaired VLDL secretion resulting in hepatic steatosis and NASH; 2) VMP1 is critical to concert ER- mitochondria and ER-Golgi crosstalk to regulate VLDL secretion in NAFLD. Three SPECIFIC AIMS are proposed: 1) Determine the mechanisms by which loss of VMP1 decreases hepatic phosphatidylcholine and phosphatidylethanolamine content resulting in impaired VLDL secretion and NASH; 2) Determine the mechanisms by which loss of VMP1 decreases COPII and ERGIC-53 proteins, impairs VLDL ER-Golgi trafficking and VLDL secretion; and 3) Determine the role of VMP1 in ameliorating diet-induced impaired VLDL secretion and NASH. The LONGTERM GOAL of this work is to identify VMP1-dependent pathways in the pathogenesis of NAFLD/NASH and develop potential strategies by targeting VMP1.