Helicobacter pylori (H. pylori) infection causes aberrant DNA methylation of various genes in the gastric mucosa. Cyclooxygenases (COX) play a critical role in peptic ulcer development and healing. Human COX-2 has CpG islands (CGIs) in its promoter region, suggesting a possible epigenetic regulation. Here, we evaluated COX-2 promoter methylation in the gastric mucosa of patients with various gastric diseases and found that COX-2 methylation levels in the gastric mucosa were significantly increased in patients with H. pylori infection. We further investigated the roles of COX-2 during the healing of acetic acid-induced gastric ulcers in H. pylori-infected Mongolian gerbils (MGs). While COX-2 mRNA expression levels on the edges of acetic acid-induced gastric ulcers were significantly increased after ulcer induction in MGs in the absence of H. pylori, no such induction was observed in H. pylori-infected gastric mucosa. Cloning of the MG COX-2 gene revealed abundant CGIs in the promoter region. COX-2 mRNA expression in MG-derived gastric carcinoma MGC2 cells was significantly increased by addition of the demethylating agent 5-Aza-dC. Additionally, COX-2 methylation levels were higher in H. pylori-infected MG gastric mucosa than in control mucosa. These results indicated that epigenetic inhibition of COX-2 mRNA induced by H. pylori impairs gastric ulcer healing.
Part of the book: Chromatin and Epigenetics