Abstract
Objectives
Nearly 40% of humans have polymorphisms in genes involved in choline metabolism which makes them prone to developing choline deficiency and increased risk for liver damage and liver cancer. Choline is a source of methyl groups needed for many steps in metabolism and epigenetic regulation of gene expression. Although epigenetic aberrations are known to be induced by choline deficiency, it remains unknown how to reverse the changes and attenuate symptoms. Interestingly, certain dietary compounds such as polyphenols have been demonstrated to reverse aberrant epigenetic patterns and exert anti-cancer action. In the present study, we investigate the effects of pterostilbene (PTS) on liver cancer development in rats fed choline-deficient diet and explore mechanisms underlying these effects.
Methods
Fischer 344 rats were fed a choline-sufficient (CSAA, healthy control group), a choline-deficient (CDAA, cancer group) L-amino acid-defined diet or a CDAA diet supplemented with PTS (134 mg/kg BW/day) (n = 6 per group). At the end of 52 weeks, analyses of liver nodules and histopathological features were performed followed by genome-wide investigation of gene expression in livers using RNA sequencing. DNA methylation was assessed by pyrosequencing.
Results
A total of 708 genes were significantly differentially expressed in CDAA + PTS group as compared with CDAA group. Among 351 upregulated genes were Bhmt (4.5-fold), G6pc (3.1-fold), and Aldh1l1 (2.6-fold). These metabolism-related genes were significantly downregulated in CDAA vs. CSAA group and their suppression was associated with liver cancer in previous reports. Among 357 genes found to be significantly downregulated by PTS were strong oncogenes such as Mmp12 (2-fold), Myc (1.9-fold) and Mmp27 (1.8-fold). We found PTS-mediated downregulation of Mmp12, that was a top gene upregulated in CDAA vs. CSAA, coincided with 43% hypermethylation of Mmp12 promoter.
Conclusions
Our findings demonstrate that PTS-mediated changes in gene expression could correspond to changes in DNA methylation of gene regulatory regions and could at least partially explain the observed attenuation of cancer development due to choline deficiency.
Funding Sources
UBC VP Academic Award, CFI John. R. Evans Leaders Fund, and BC Knowledge Development Fund granted to BS.
Genome-Wide Screening of Genes Regulated by DNA Methylation in Colon Cancer Development