Disrupted tight junctions in the small intestine of cystic fibrosis mice.

The tight junction (TJ) is the major determinant of paracellular permeability, which in the gut protects the body from entry of harmful substances such as microbial components. In cystic fibrosis (CF), there is increased permeability of the small intestine both in humans and in CF mice. To gain insight into the mechanisms of increased intestinal permeability in CF, I analyze the composition of the TJ in a cystic fibrosis transmembrane conductance regulator (Cftr) knockout mouse model. Significant changes in TJ gene expression in the CF intestine were found for Cldn1, Cldn7, Cldn8 and Pmp22, which were expressed at lower levels and Cldn2 that was expressed at a higher level. Protein levels of claudin-2 were increased in the CF intestine as compared to wild-type, while other TJ proteins were not significantly different. In the villus epithelium of the CF intestine, all TJ components analyzed were mislocalized to the basal cytoplasm and showed varying degrees of loss from the TJ and apico-lateral surfaces. The pore-forming claudin-2 in the CF intestine showed more intense staining but was correctly localized to the TJ, principally in the crypts that are enlarged in CF. The cytokine TNFα, known to affect TJ, was elevated to 160% of wild-type in the CF intestine. In summary, there is a dramatic redistribution of claudin proteins from the TJ/lateral membrane to the basal cytoplasm of the villus epithelium in the CF intestine. These changes in TJ protein localization in CF are likely to be involved in the increased permeability of the CF small intestine to macromolecules and TNFα may be a causative factor.