Inflammation and disruption of the mucosal architecture in claudin-7-deficient mice

Integrity of the intestinal epithelium is required for nutrition absorption and defense against pathogens. Claudins are cell adhesion molecules that localize at tight junctions (TJs); many are expressed in the intestinal tract, but little is known about their functions. Claudin-7 is unique in that it has a stronger basolateral membrane distribution than other claudins, which localize primarily to apical TJs in the intestinal epithelium. We investigated the basolateral functions of claudin-7 and assessed the effects of disruption of Cldn7 in intestines of mice.

We generated Cldn7(-/-) mice and examined their intestines by histology, molecular and cellular biology, and biochemistry approaches. We performed gene silencing experiments in epithelial cell lines using small interfering RNAs (siRNAs).

The Cldn7(-/-) mice had severe intestinal defects that included mucosal ulcerations, epithelial cell sloughing, and inflammation. Intestines of Cldn7(-/-) mice produced significantly higher levels of cytokines, the nuclear factor κB p65 subunit, and cyclooxygenase 2; they also up-regulated expression of matrix metalloproteinases (MMPs)-3 and -7. siRNA in epithelial cell lines showed that the increased expression of MMP-3 resulted directly from claudin-7 depletion, whereas that of MMP-7 resulted from inflammation. Electron microscopy analysis showed that intestines of Cldn7(-/-) mice had intercellular gaps below TJs and cell matrix loosening. Deletion of Cldn7 reduced expression and altered localization of the integrin α2 subunit in addition to disrupting formation of complexes of claudin-7, integrin α2, and claudin-1 that normally form in epithelial basolateral compartments of intestines.

In mice, claudin-7 has non-TJ functions, including maintenance of epithelial cell-matrix interactions and intestinal homeostasis.