Role and Mechanisms of E4BP4 over-activation in diet-induced fatty liver disease

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Non-alcoholic liver disease (NAFLD) is the most common liver disease, afflicting 30% of the general population. So far, there has been no effective treatment for NAFDL. Approximately 10% of patients with NAFLD progress from simple steatosis to non-alcoholic steatohepatitis (NASH) and eventually live failure. For patients of NAFLD with liver failure, liver transplant is the only therapeutic option. In spite of a strong correlation between diets rich in fat, cholesterol, and fructose and NAFLD, molecular mechanisms by which high fat, high cholesterol, and high fructose (HFCF) diet promotes liver steatosis, inflammation and fibrosis remains poorly understood. The overall objective of this proposal aims to investigate the role of b-ZIP transcription repressor E4 promoter- binding protein 4 (E4BP4) in driving diet-induced NAFLD in mice. Our preliminary data demonstrated loss of hepatic E4BP4 protects mice against high-fat diet-induced liver steatosis and E4BP4 promotes the expression of Cidea and Fsp27-β, two major lipid droplet binding proteins, in the liver in response to high-fat diet. We also discovered that chronic high-fat diet feeding leads to deSUMOylation of E4BP4 in the liver. Moreover, hepatocytes expressing a non-SUMOylatable E4BP4 show more lipid droplet formation than those of WT- E4BP4. Thus, we hypothesize that E4BP4 deSUMOylation promotes liver steatosis and its progression by increasing lipid biosynthesis and storage during diet-induced fatty liver disease. We will test the central hypothesis by pursuing the following three specific aims: 1. Determine the pathologic role of E4BP4 in promoting HFCF diet-induced NAFLD using liver-specific E4bp4 knockout mice. 2. Uncover molecular pathways of how hepatic E4BP4 promotes lipid accumulation via elevating Cidea and Fsp27-β expression in hepatocytes and the liver during diet-induced NAFLD. 3. Investigate the function and regulation of deSUMOylation of hepatic E4BP4 in the pathogenesis of diet- induced NAFLD. Our study will uncover hepatocyte-specific E4BP4 as a crucial regulator that connects HFCF diet and NAFLD. The completion of the proposed study will gain critical knowledge regarding the molecular pathways driven by E4BP4 to promote the onset and progression of NAFLD. The novel knowledge will shed light on novel preventive or therapeutic measures to treat NAFDL by targeting E4BP4 expression or SUMOylation.