Background: Previously, it was shown that the chloride channel ClC-2 modulates intestinal tight junction (TJ) barrier function. The aim of the present study was to investigate the role of ClC-2 in epithelial barrier function and recovery in the event of epithelial injury.
Methods: The role of ClC-2 was investigated in TJ barrier function in dextran sodium sulfate (DSS)-induced colitis in ClC-2 knockout mice and ClC-2 knockdown intestinal Caco-2 cells. Barrier function was measured electrophysiologically and by transepithelial mannitol fluxes. Selected TJ and associated proteins were Western blotted, cytokines were measured using quantitative PCR, and human colonic biopsies were examined with immunohistochemistry.
Results: ClC-2−/− mice had a higher disease activity index, higher histological scores, and increased paracellular permeability compared with wild-type mice when treated with DSS. DSS-treated ClC-2−/− mice had increased claudin-2 expression, greater loss of occludin in the membrane, increased association of occludin with caveolin-1, and significantly increased tumor necrosis factor-α and interleukin-1β messenger RNA. ClC-2 knockdown in human intestinal Caco-2 cells resulted in a greater loss of epithelial resistance in the event of epithelial injury. The restoration of colonic barrier function after DSS colitis was delayed in ClC-2−/− mice. In human colonic biopsies, the protein and messenger RNA expression of ClC-2 was found to be reduced in patients with ulcerative colitis.
Conclusions: ClC-2 plays a critical role in experimental colitis in that its absence increases disease activity, reduces barrier function and recovery, and perturbs TJs. Furthermore, ClC-2 expression is markedly reduced in the colon of human patients with ulcerative colitis.
Article first published online 11 September 2013
*Department of Clinical Sciences, Center for Comparative Medicine and Translational Research, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina;
†Department of Internal Medicine, School of Medicine, University of New Mexico, Albuquerque, New Mexico; and
‡Division of Gastroenterology and Hepatology, Department of Medicine, Center for Gastrointestinal Biology and Disease, and
§Department of Microbiology and Immunology, University of North Carolina School of Medicine, Chapel Hill, North Carolina.
Reprints: Anthony Blikslager, DVM, PhD, Department of Clinical Sciences, Center for Comparative Medicine and Translational Research, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607 (e-mail: email@example.com).
Supported by the Center for Comparative Medicine and Translational Research (P.N., A.B.); R01-DK054452 (S.E.P.); the Center for Gastrointestinal Biology and Disease histology core (P30 DK34987); and a Crohn's and Colitis Foundation of America Research Fellowship Award (N.M.).
The authors have no conflicts of interest to disclose.
Received June 25, 2013
Accepted August 5, 2013