Hepatic Epigenomic Changes Associated with Chronic Oxidative Stress in a Mouse Model of Glutathione Deficiency

Purpose Oxidative stress has been shown to be intimately involved in the pathogenesis of fatty liver disease (FLD). A major factor contributing to oxidative stress is the depletion of glutathione (GSH). Our previous studies in glutamate cysteine ligase modifier subunit (Gclm)-null mice demonstrate that ~85% deficiency in hepatic GSH renders mice protected from fatty liver injuries induced by varieties of hepatic insults, including alcohol exposure. It is well-known that epigenetic mechanisms play active roles in modulating gene expression and disease outcome in FLD. The purpose of the current study is to utilize the Gclm-null mouse model to examine in vivo interplay between chronic oxidative stress and DNA methylation at the epigenome level and whether these epigenetic changes are functionally involved in FLD. Methods we performed DNA methylation profiling in the liver and whole blood using the Mouse Promoter Methylation Array. Genes with CpG sites that were significantly affected by GSH deficiency were further investigated for network and functional enrichment. Results Among 22,327 gene promoter regions (from -1300bp to +500bp of the Transcription Start Sites) that were analyzed, in the liver, only 52 and 6 gene promoters were hypo- and hyper-methylated, respectively, in Gclm-null mice relative to wild-type mice, indicating an overall hypo-methylated genome associated with low GSH. Interestingly, the DNA methylation profiles in the liver and blood appeared to be comparable irrespective of the genotype, which leads to the possibility of potential circulating biomarker(s) for hepatic epigenetic fingerprints related to chronic oxidative stress. Ingenuity Pathway Analysis (IPA) revealed that hypo-methylated genes in the KO liver are enriched in canonical pathways of protein phosphorylation, RNA transcription, cytoplasm organization and organismal death. Conclusion our preliminary data indicate that chronic GSH deficiency induces global DNA hypomethylation. The functional significance of observed epigenomic changes is under investigation.