Expression of tumor suppressor genes in diet‐induced liver injury: a model of the control of gene expression by gene‐specific CpG island methylation

Abstract

A methyl‐deficient diet (MDD), lacking choline and folate and low in methionine, causes liver injury in rats. We investigated the effects of epigenetic factors on hepatic gene expression in the MDD model. Weanling, male Fisher 344 rats were assigned to receive: 1) control diet for 12 weeks, 2) MDD for 12 weeks, or 3) MDD for 9 weeks followed by methyl repletion with control diet for 3 weeks (MRD). Hepatic RNA and DNA were isolated from 3 rats per dietary group. Gene expression was assessed by microarray and RT‐PCR. Gene‐specific methylation was assessed by pyrosequencing. Microarray analysis revealed ≥4‐fold increase in expression of over 150 genes in the MDD group compared with the controls. Decreased expression toward control levels was observed in the MRD group for most of these genes, and was associated with recovery from liver injury. Among the genes that followed this pattern of expression were the tumor suppressor genes, glutathione‐S‐transferase pi 1 (GSTP1) and metallothionein 2A (MT2A). Methylation patterns of gene specific CpG islands for GSTP1 and MT2A followed inverse trends, with decreased levels of methylation associated with increased gene expression in the MDD group compared with the control and MRD groups. This model of liver injury shows upregulation of tumor suppressor genes associated with diet‐induced suppression of DNA methylation.Funding: American Cancer Society