The overall objective of this 2-year R03 proposal is to prove the hypothesis that the pathogenesis of alcoholic steatohepatitis (ASH) is mediated by epigenetic changes in the methylation of regulatory genes that result from the induction of aberrant hepatic methionine metabolism by exposure to ethanol. The study will use the cystathionine beta synthase (CbS) deficient mouse model of aberrant methionine metabolism in which wildtype (+/+) and heterozygous (+/-) mice with be fed control or ethanol containing diets that will or will not be supplemented with the methyl donor betaine over 4 weeks. Livers will be used for graded histopathology and measurements of methionine metabolites and of transcripts and protein levels of genes relevant to apoptosis and steatosis including those involved in lipogenesis, fatty acid oxidation, and lipid export. Subsequent epigenetic studies will include analyses of individual gene DNA methylation by DNA bisulfite sequencing and by methylation and acetylation of histone residues. Histone studies will include chromatin immunoprecipitation (ChIP) analysis of promoter regions of apoptosis and steatosis genes that have been found to be affected by ethanol feeding, genotype, and betaine supplementation. If the hypothesis is correct, the ethanol fed mouse groups will develop the histopathology of ASH, together with reductions in levels of the methyl donor S- adenosylmethionine (SAM), increase in the methyltransferase inhibitor S-adenosylhomocysteine (SAH), together with activation or suppression of genes involved in steatosis and their epigenetic regulations. The definitive proof of the hypothesis will be demonstration of the prevention of all changes by dietary supplementation with the methyl donor betaine. The significance of the project will be definition and proof of the mechanistic role of altered hepatic methionine metabolism and its epigenetic effects on the pathogenesis of ASH. Furthermore, the studies will point to the potential relevance of the findings to the treatment of ASH, based on correction of the epigenetic mechanisms that regulate its relevant genes. The studies will form the basis for a subsequent R01 application to extend the experimental approach to analysis of the expressions and epigenetic regulation of genes involved in other pathways of alcoholic liver injury and fibrosis in ASH and of relevant DNA and histone methyltransferases, acetylases and de-acetylases that are involved in the epigenetic regulation of these pathways.
The proposed R03 will use ethanol fed and genetically modified mice to study the effects of altered liver methionine metabolism on the genes that contribute to steatosis in alcoholic liver disease and their epigenetic regulation by the methyl donor betaine. The results will form the basis for a more extensive and comprehensive proposal to study mechanisms of epigenetic regulation of other gene pathways for the development of alcoholic liver disease.
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