Role of Histone Deacetylase 4 in Alcoholic Liver Disease

项目总结

PROJECT SUMMARY Alcoholic liver disease (ALD) is a major cause of morbidity and mortality worldwide. ALD is the eighth most common cause of mortality in the U.S. and the second leading cause of death among all gastrointestinal diseases. Alcoholic hepatitis (AH) is the progressive form of ALD, which can progress to cirrhosis and hepatocellular carcinoma. Therefore, there is an unmet need for developing effective therapeutic strategies for AH. Evidence suggests histone deacetylases (HDACs) are involved in alcohol-induced cell damages. However, little is known about the role of each HDAC isoform in the pathogenesis of AH. We found that HDAC4 mRNA and protein levels were markedly increased in the human liver with alcoholic cirrhosis and the mouse liver exposed to alcohol. Furthermore, our preliminary data indicate that ethanol increased HDAC4 expression in Huh-7 cells, a human hepatocellular carcinoma cell line. Also, ethanol induced the expression of Hdac4 with concomitant increases in inflammation and oxidative stress in macrophages, which was significantly attenuated when Hdac4 was knocked out or down. Sirtuin 1 (SIRT1) is known to prevent alcohol-related cell damages and liver injury. Consistently, we found that a SIRT1 inhibitor increased interleukin-1b (Il1b) expression, whereas a SIRT1 activator significantly abolished ethanol-induced Hdac4 and Il1b expression in macrophages. It is of interest that Hdac4 deficiency increased Sirt1 expression, while human HDAC4 overexpression elicited the opposite effects in RAW 264.7 macrophages. The preliminary results suggest the HDAC4/SIRT1 axis may play a crucial role in the development of AH. Based on the strong premise described above, we establish the central hypothesis that the deletion of Hdac4 in hepatocytes or macrophages inhibits the development of AH by altering hepatic expression of genes, including SIRT1, that are critically involved in alcohol-induced inflammation and oxidative stress. We will take both targeted (SIRT1 pathway) and untargeted approaches (genome-wide transcriptome analysis) using novel mice that have hepatocyte- or macrophage-specific deletion of Hdac4 under chronic-binge ethanol feeding (the NIAAA model) as in vivo models. We will test the hypothesis by pursuing the following two Specific Aims: 1) to determine the role of hepatocyte and macrophage HDAC4 in the development of AH and to evaluate the HDAC4/SIRT1 axis for the pathogenesis of AH; and 2) to conduct a genome-wide transcriptome analysis to identify HDAC4-regulated genes in hepatocytes and macrophages that mediate the pathogenic processes of AH and to corroborate the findings using human liver specimens and primary human hepatocytes and macrophages. The findings from this exploratory study will produce much-needed information on the role of hepatocyte and macrophage HDAC4 in the pathogenesis of AH. Also, this study will lead to the discovery of new genes/pathways, which can be exploited for future therapies for AH. Therefore, a significant impact on public health is anticipated upon completion of this study.