Neutrophil elastase stimulates human airway epithelial cells to produce PGE₂ through activation of p44/42 MAPK and upregulation of cyclooxygenase-2

The responses of airway epithelium following exposure to neutrophil elastase (NE) were investigated. Human bronchial epithelial cells were explanted on insert surfaces of a modified air-liquid interface culture system to which NE was added to stimulate epithelial cells. PGE₂ release significantly increased within 10 min of incubation with NE and peaked 3 h after NE (20 μg/ml) stimulation. This action required proteolytic activity as α₁-antitrypsin blocked NE-induced PGE₂ release. The production of PGE₂ was also inhibited by indomethacin; a selective cyclooxygenase (COX)-2 inhibitor, celecoxib; and dexamethasone. Moreover, the mRNA expression for COX-2 relative to that for a housekeeping gene was approximately eightfold that of the unstimulated cells. Dexamethasone inhibited COX-2 gene transcription. We further observed that NE-induced PGE ₂ release involved activation of p44/42, but not p38, MAP kinases. Such p44/42 MAP kinases were rapidly phosphorylated, with the concentration of phosphorylated p44/42 MAP kinases peaking at 10 min after stimulation and declining in culture at 90 min. The specific p44/42 MAP kinase inhibitor UO126 completely blocked p44/42 phosphorylation and, subsequently, PGE₂ production. The airway epithelium may play important bronchoprotective and immunomodulatory roles in chronic neutrophilic inflammation.