Bronchial airway epithelial cell denudation in the pathogenesis of asthma: The role of IL-4 and IL-13
Asthma is characterized by infiltration and shedding of the bronchial epithelium. The Th2 cytokines IL-4 and IL-13 are involved in the cellular recruitment and infiltration seen in asthma. The effects of IL-4 and IL-13 on cell-matrix interactions, gap formation, increased monolayer permeability and epithelial shedding are unknown. Experiments described in this report test the hypothesis that bronchial airway epithelial cells (BAEC) express paxillin, a structural focal adhesion protein, and down-regulation of paxillin by Th2 cytokines lead to BAEC hyperpermeability. Furthermore, the hypothesis that the Th2 cytokines IL-4 and IL-13 could down-regulate the adherens junction proteins β-catenin and E-cadherin in BAEC, and that this decrease in β-catenin and E-cadherin also may play a role in BAEC hyperpermeability was tested. The presence of paxillin in BAEC was shown by confocal microscopy which also demonstrated gap formation in IL4 and IL-13-stimulated BAEC confluent monolayers that stained positive for β-catenin and E-cadherin. Western blot analysis demonstrated that IL-4 and IL-13 stimulation results in down-regulation of paxillin, β-catenin and E-cadherin production. IL-4 and IL-13 stimulation decreased epithelial cell-matrix attachment as measured by electrical cell-substrate impedance sensing system. IL-4 and IL-13 stimulation increased BAEC monolayer permeability as measured by Evans blue dye/BSA protein leak assay. These results suggest that Th2 cytokines IL-4 and IL-13 down-regulate paxillin production by BAEC, thereby disrupting the cell-matrix interactions. These results also suggest that IL-4 and IL-13 down-regulate β-catenin and E-cadherin production by BAEC, induce gap formation and promote monolayer hyperpermeability. In conclusion, the Th2 cytokines IL-4 and IL-13 appear to disrupt cell-cell and cell-matrix interactions within the bronchial epithelium. This may help explain the epithelial shedding and epithelial membrane hyperpermeability that occurs in asthma.
0307: Molecular biology