Neutrophil-mediated epithelial injury during transmigration: role of elastase

Neutrophil-mediated injury to gut epithelium may lead to disruption of the epithelial barrier function with consequent organ dysfunction, but the mech anisms of this are incompletely characterized. Because the epithelial apica l junctional complex, comprised of tight and adherens junctions, is respons ible in part for this barrier function, we investigated the effects of neut rophil transmigration on these structures. Using a colonic epithelial cell line, we observed that neutrophils migrating across cell monolayers formed clusters that were associated with focal epithelial cell loss and the creat ion of circular defects within the monolayer. The loss of epithelial cells was partly attributable to neutrophil-derived proteases, likely elastase, b ecause it was prevented by elastase inhibitors. Spatially delimited disrupt ion of epithelial junctional complexes with focal loss of E-cadherin, beta -catenin, and zonula occludens 1 was observed adjacent to clusters of trans migrating neutrophils. During neutrophil transmigration, fragments of E-cad herin were released into the apical supernatant, and inhibitors of neutroph il elastase prevented this proteolytic degradation. Addition of purified le ukocyte elastase also resulted in release of E-cadherin fragments, but only after opening of tight junctions. Taken together, these data demonstrate t hat neutrophil-derived proteases can mediate spatially delimited disruption of epithelial apical junctions during transmigration. These processes may contribute to epithelial loss and disruption of epithelial barrier function in inflammatory diseases.