Glucocorticoids Increase Repair Potential in a Novel in vitro Human Airway Epithelial Wounding Model

Abstract

Airway epithelial damage is a cardinal feature of chronic asthma. Agents which enhance epithelial repair without triggering uncontrolled fibrosis of the mesenchyme would be predicted to be useful in the management of asthma. We have developed a repeat wound model using mucociliated human bronchial epithelial cell (HBEC) cultures to define the key pathways involved in airway epithelial repair, and to study the effects of potential therapeutic agents on epithelial repair in a chronic setting. We show that repair occurs primarily by cell migration to close a defect; this process requires activation of the EGF receptor (EGFR) and subsequent tyrosine kinase signalling. Migration is accompanied by up-regulation of CD44 in motile cells at the wound margins with proliferation of non-migrating cells adjacent to the wound area. In long-term studies beta2 adrenoceptor agonists and phosphodiesterase (PDE) inhibitors have no effect on repair potential, in contrast chronic treatment with the glucocorticoid dexamethasone extends the lifespan of repeatedly wounded differentiated cultures. We suggest part of the beneficial effects of glucocorticoids in asthma is related to this ability to prolong repair potential following repeated episodes of epithelial injury.

IL-13, Asthma and Glycosylation in Airway Epithelial Repair

“…In vitro studies support the hypothesis that epithelial-derived factors are capable of altering the phenotype of adjacent mesenchymal cells [43,44]. The mechanisms involved in initiating and maintaining the epithelial repair response in asthma are largely unknown, however recent studies have demonstrated the airway epithelium in asthmatics is intrinsically altered compared to normals, and that these differences persist for extended periods in culture [45,46].…”

“…Although both secretory and basal cells are involved in epithelial repair, secretory cells play a dominant role in these experiments, consistently demonstrating higher mitosis rates than any other epithelial cell type [35][36][37][38]. In vitro studies using muco-ciliated human bronchial epithelial cells grown in air-liquid interface (ALI) culture, demonstrate that scrape wound repair is achieved by rapid spreading and migration of cells at the wound edge, followed by proliferation of basal cells outside of the wound area [43]. Acute wound repair speeds were inhibited slightly by the steroid dexamethasone, but the same drug potentiated the ability of long-term ALI cultures to repair repeated wounds [43].…”

“…Specific MMP-substrate interactions can be facilitated and regulated at the cell surface via association of MMPs with chaperone molecules. CD44 is strongly upregulated in injured asthmatic airways and at the leading edge of repairing bronchial epithelial cells [43,140], yet its function during airway epithelial repair is unknown. Studies suggest CD44 may co-ordinate MMP-substrate interactions at the plasma membrane by functioning as a docking molecule.…”

“…MMP-7 cleaves pro-HB-EGF into an active soluble form which triggers recruitment and activation of the Erb-B4 receptor (a member of the EGFR family) [141]. The EGF pathway is essential for efficient repair of the bronchial epithelium [43], and a similar mechanism of targeted MMP-7 presentation may occur during lung epithelial repair. Carbohydrate modification of proteins is essential for the creation of such micro-environments at the cell surface; in this case the interaction of MMP-7 (an non-glycosylated protease) with CD44 is dependent on the presence of branched glycosylated side-chains on the extracellular portion of the CD44 molecule.…”

“…Several studies have focused on the role of EGF and its family of receptors on epithelial repair [24,142]. EGF, a well known mitogen for epithelial cells, has been used in to stimulate epithelial wound healing in guinea pigs as well as human airway cell monolayers and differentiated cells in vitro [43,143]. EGFR is known to be up-regulated upon the creation of a wound on airway epithelial monolayers in culture and correlated to the damaged areas of epithelium [24].…”