Background & Aims: Junctional adhesion molecule-A (JAM-A) is localized at the tight junctions and controls leukocyte migration into the tissues. However, its functional role in inflammatory bowel disease (IBD) is unexplored. Methods: Control, Crohn's disease (CD), and ulcerative colitis (UC) tissue specimens were studied for JAM-A expression, as well as the colon of mice given dextran sodium sulfate (DSS). Wild-type and JAM-A-/-, Tie-2-Cre-JAM-A-/- (endothelial/hematopoietic-specific JAM inactivation) mice were studied for susceptibility to DSS. Disease activity and colonic inflammation were assessed using a disease activity index histology and endoscopy, and mucosal cytokines were measured by enzyme-linked immunosorbent assay. JAM-A function was investigated by RNA silencing in epithelial cells, and apoptosis was measured. Results: In both CD and UC, as well as in experimental colitis, there is a loss of epithelial but not endothelial JAM-A expression. Deletion of JAM-A results in a dramatic increase in susceptibility to DSS colitis, as assessed by weight loss, disease activity index, histologic and endoscopic severity, and strikingly high mortality rates. This is not caused by the absence of JAM-A in the endothelial or hematopoietic compartments because Tie-2-Cre-JAM-A-/- mice are no more susceptible to DSS colitis than wild-type animals. JAM-A-/- mice displayed increased intestinal permeability and inflammatory cytokine production, and marked epithelial apoptosis. Silencing of JAM-A in intestinal epithelial cells resulted in increased permeability in vitro. Conclusions: Our results show a nonredundant and novel role of JAM-A in controlling mucosal homeostasis by regulating the integrity and permeability of epithelial barrier function.
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