Intestinal epithelial barrier dysfunction in colitis.

摘要

The intestinal epithelium acts as a defensive barrier lining the mucosal surface exposed to the external environment. Epithelial dysfunction may lead to numerous inflammatory conditions. Environmental factors have been implicated in initiating and exacerbating intestinal disease, particularly in genetically susceptible individuals. The focus of the present study was to further investigate the role of mediators and epithelial ion transport in inflammatory models to better understand the mechanisms leading to the onset of disease. Nitric oxide (NO) has been shown to affect secretory function during inflammation. Here, we studied the effects of NO on the trafficking of the chloride channel, cystic fibrosis transmembrane conductance regulator (CFTR), to the apical membrane. NO inhibited cAMP-dependent CFTR trafficking in intestinal epithelial cells and correlated temporally with changes in short circuit current in Ussing chamber studies. NO was also shown to selectively disrupt the tight junction protein ZO-1, but this did not lead to changes in epithelial permeability or bacterial translocation. Having assessed the effect of NO on epithelial function, we next explored barrier function in an animal model of intestinal bacterial infection. Citrobacter rodentium caused colitis and NO-independent epithelial dysfunction in mice. The epithelial secretory response to carbachol at 3 and 7 days post-infection was significantly reduced, but these changes were not dependent on inducible nitric oxide synthase (iNOS) or cyclooxygenase (COX)-2 expression. Since luminal pathogens and bacterial translocation have been implicated as possible causative factors in chronic inflammatory disorders, we next assessed the mucosal barrier function of the epithelium in a murine model of radiation enteropathy together with C. rodentium infection. Bacterial translocation leading to systemic infection was significantly increased in infected animals exposed to ionizing radiation. However, these changes occurred without changes to colonic permeability. Taken together, these findings add significantly to our understanding of inflammation at both the cellular and whole animal levels with respect to mediators and functional properties of the intestinal epithelium.