Induction of immunomodulatory miR-146a and miR-155 in small intestinal epithelium of Vibrio cholerae infected patients at acute stage of cholera

The potential immunomodulatory role of microRNAs in small intestine of patients with acute watery diarrhea caused by Vibrio cholerae O1 or enterotoxigenic Escherichia coli (ETEC) infection was investigated. Duodenal biopsies were obtained from study participants at the acute (day 2) and convalescent (day 21) stages of disease and from healthy individuals. Levels of miR 146a miR 155 and miR 375 and target gene (IRAK1 TRAF6 CARD10) and 11 cytokine mRNAs were determined by qRT PCR. The cellular source of microRNAs in biopsies was analyzed by in situ hybridization. The ability of V. cholerae bacteria and their secreted products to cause changes in microRNA and mRNA levels in polarized tight monolayers of intestinal epithelial cells was investigated. miR 146a and miR 155 were expressed at significantly elevated levels at acute stage of V. cholerae infection and declined to normal at convalescent stage (P< 0.009 versus controls P = 0.03 versus convalescent stage pairwise). Both microRNAs were mainly expressed in the epithelium. Only marginal down regulation of target genes IRAK1 and CARD10 was seen and a weak cytokine profile was identified in the acute infected mucosa. No elevation of microRNA levels was seen in ETEC infection. Challenge of tight monolayers with the wild type V. cholerae O1 strain C6706 and clinical isolates from two study participants caused significant increase in miR 155 and miR 146a by the strain C6706 (P< 0.01). One clinical isolate caused reduction in IRAK1 levels (P< 0.05) and none of the strains induced inflammatory cytokines. In contrast secreted factors from these strains caused markedly increased levels of IL 8 IL 1a and CARD10 (P< 0.001) without inducing microRNA expression. Thus miR 146a and miR155 are expressed in the duodenal epithelium at the acute stage of cholera. The inducer is probably the V. cholerae bacterium. By inducing microRNAs the bacterium can limit the Innate immune response of the host,including inflamation evoked by its own secreted factors,there by decreasing the riskof being eliminated