Protease-aktivierte Rezeptoren im Bronchialepithel bei Entzündungsprozessen in der Lunge

Um die Bedeutung von Protease-aktivierte Rezeptoren (PAR) bei Entzündungsprozessen in der Lunge aufzuklären, sollen die zellulären Mechanismen der PAR-Aktivierung und -Deaktivierung auf Lungenepithel, sowie deren Modulation durch pro- bzw. anti-entzündliche Mediatoren (Cytokine, Arachidonsäure und seine Metabolite) und durch extrazelluläre Proteasen untersucht werden. Ziele sind: 1) Identifizierung und Charakterisierung der PAR in humanen bronchialen Epithelzellen 2) Aufklärung der durch PAR-Aktivierung induzierten Zellantworten, wie Freisetzung von Mediatoren oder Proliferation, deren Modulation durch pro- bzw. anti-inflammatorische Mediatoren und Therapeutika (Corticosteroide). 3) Regulation der PAR-Aktivität durch extrazelluläre Proteasen, die durch leukozytäre Zellen sezerniert werden.

Among the four protease-activated receptors (PARs), especially PAR-1 plays an important role in normal lung functioning and in the development of lung diseases, including fibrosis. Here we compared the expression and functional activity of PARs in normal and fibrotic human lung fibroblasts. Both normal and fibrotic cells express PAR-1, -2, and -3 with PAR-2 showing the lowest level. There was no significant difference between normal and fibrotic fibroblasts in the expression levels of PAR-1 and PAR-3, while a 4-fold higher expression level of PAR-2 was observed in fibrotic cells as compared to normal cells. Ca2+ imaging studies revealed apparently only PAR-1 Ca2+ signaling in lung fibroblasts. PAR-1 agonists, thrombin and synthetic activating peptide, induced concentration-dependent Ca2+ mobilization with EC50 values of 5 nM and 1 µM, respectively. The neutrophil protease cathepsin G produced a transient Ca2+ response followed by disabling PAR-1, whereas elastase did not affect the Ca2+ level. PAR-1 activation by thrombin or receptor-activating peptide down-regulated expression of all three PARs in lung fibroblasts with maximal effect at 3 to 6 h, while the expression returned towards basal level after 24-h. Furthermore, PAR-1 agonists dose-dependently increased prostaglandin E2 (PGE2) secretion from lung fibroblasts and induction of cyclooxygenase-2 expression. Then we found that PGE2 down- regulated the expression of all three PARs. The effect of PGE2 was continuously growing with time. Furthermore, PGE2 exerts its effect through the EP2 receptor. This novel autocrine feedback mechanism of PGE2 in lung fibroblasts seems to be an important regulator in lung physiology and pathology.