The proinflammatory actions of mast cell tryptase and agonists of protease activated receptor 2 on the human airway epithelium

Abstract

The aims of this study have been to investigate the proinflammatory actions of tryptase on airway epithelial cells and to examine the potential role of PAR-2 in airway inflammation.Tryptase was isolated to high purity and was added to epithelial cells. An increase in 3H-thymidine uptake in 16HBE 14o- cells (maximal at 10 mU/ml) was induced by tryptase without stimulating significant cell proliferation; while at higher concentrations (80 mU/ml), tryptase actually inhibited DNA synthesis and cell growth in an apparently non-cytotoxic manner. Within 3 h of adding tryptase, marked increases in expression of mRNA for IL-6, IL-8 and GM-CSF were detected by RT-PCR. This was followed by increased secretion of IL-6 (maximal at 6h), IL-8 and GM-CSF (both maximal at 24 h and 48 h) into culture supernatants. The actions of tryptase were in all cases inhibited by heat inactivation of the enzyme or by addition of the protease inhibitor leupeptin. The peptide SLIGKV, an agonist for protease activated receptor 2 (PAR - 2), induced responses similar to those elicited with tryptase, suggesting that the proinflammatory actions may be mediated through activation of this receptor.Tryptase induced a progressive decrease in transepithelial resistance (TER) across monolayers of 16HBE 14o- cells at 80 mU/ml though at lower concentrations (10 or 20 uU/ml) could actually increase TER. The peptide agonist of PAR-2 SLIGKV and trypsin were also able to induce a decline in TER. Pretreatment of cells with pertussis toxin, a Gi protein inhibitor, abolished the response to SLIGKV, but not that to tryptase, suggesting that processes other than PAR-2 activation may mediate the decline in TER induced by tryptase.Tryptase and other agonists of PAR-2 activation could play key roles in epithelial inflammation in asthma and in other allergic conditions, and these must represent attractive targets for therapeutic intervention.</p