Background: 

DRA (downregulated in adenoma, Slc26a3) is a member of the Slc26 family of anion transporters which is mutated in congenital chloride diarrhea (CLD). Its genetic ablation interferes with duodenal mucosal HCO3-secretion and Cl-and water absorption. However, CLD patients also have a higher than average incidence of intestinal inflammation.

Aim of the study: 

In order to search for potential explanations for this clinical finding, we measured colonic HCO3-secretion, epithelial surface pH, and mucus release in vivo and in vitro, searched for molecular and histological signs for mucosal inflammation, and investigated the susceptibility for DSS-induced intestinal inflammation, in DRA-deleted mice and WT littermates.

Methods and Results: 

HCO3-secretory rate (JHCO3-), measured by single-pass perfusion in vivo and in isolated mid colonic mucosa in Ussing chambers in vitro, as well as epithelial surface pH, measured by two-photon microscopy in exteriorized mid colon of 1.4% isoflurane-anesthetized DRA-deficient mice in vivo, was significantly reduced. The buildup of a fresh mucus layer, measured by two photon microscopy in vivo, was not different to controls. However, no firm adherent mucus layer was present, implicating that neutral pH may be necessary for optimal mucus gel formation. Proinflammatory cytokine expression was significantly elevated in DRA/-colonic mucosa, which also displayed signs of increased neutrophil infiltration. In addition, DRA-/-mice were more susceptible to the development of DSS colitis.

Conclusions: 

Knockout of DRA results in a severely reduced colonic HCO3-secretory rate, a low epithelial surface pH, a lack of firmly adherent mucus, but a normal speed of overall mucin layer buildup in the colon. The mice also displayed signs of colonic mucosal inflammation and a severely reduced resistance to the development of DSS colitis. The data suggest a relationship between colonic HCO3-secretion, mucus layer stability, mucosal protection, and the development of intestinal inflammation.