Nonalcoholic fatty liver disease (
NAFLD) is becoming a major etiological risk factor for
hepatocellular carcinoma (HCC) in the United States and other Western countries. In this study, we investigated the role of gene-specific promoter
cytosine DNA methylation and gene expression alterations in the development of
NAFLD-associated HCC in mice using (1) a diet-induced animal model of
NAFLD, (2) a Stelic Animal Model of
nonalcoholic steatohepatitis-derived HCC, and (3) a
choline- and
folate-deficient (CFD) diet (CFD model). We found that the development of
NAFLD and its progression to HCC was characterized by down-regulation of
glycine N-methyltransferase (Gnmt) and this was mediated by progressive Gnmt promoter
cytosine DNA hypermethylation. Using a panel of genetically diverse inbred mice, we observed that Gnmt down-regulation was an early event in the pathogenesis of
NAFLD and correlated with the extent of the
NAFLD-like liver injury. Reduced GNMT expression was also found in human HCC tissue and
liver cancer cell lines. In in vitro experiments, we demonstrated that one of the consequences of GNMT inhibition was an increase in genome methylation facilitated by an elevated level of
S-adenosyl-L-methionine. Overall, our findings suggest that reduced Gnmt expression caused by promoter hypermethylation is one of the key molecular events in the development of
NAFLD-derived HCC and that assessing Gnmt methylation level may be useful for disease stratification.