Activation of proteinase-activated receptor-2 in mesothelial cells induces pleural inflammation

Abstract

Pleural inflammation underlies many pleural diseases, but its pathogenesis remains unclear. Proteinase-activated receptor-2 (PAR2) is a novel seven-transmembrane receptor with immunoregulatory roles. We hypothesized that PAR2is present on mesothelial cells and can induce pleural inflammation. PAR2was detected by immunohistochemistry in all (19 parietal and 11 visceral) human pleural biopsies examined. In cultured murine mesothelial cells, a specific PAR2-activating peptide (SLIGRL-NH2) at 10, 100, and 1,000 μM stimulated a 3-, 42-, and 1,330-fold increase of macrophage inflammatory protein (MIP)-2 release relative to medium control, respectively ( P < 0.05 all) and a 2-, 32-, and 75-fold rise over the control peptide (LSIGRL-NH2, P < 0.05 all). A similar pattern was seen for TNF-α release. Known physiological activators of PAR2, tryptase, trypsin, and coagulation factor Xa, also stimulated dose-dependent MIP-2 release from mesothelial cells in vitro. Dexamethasone inhibited the PAR2-mediated MIP-2 release in a dose-dependent manner. In vivo, pleural fluid MIP-2 levels in C57BL/6 mice injected intrapleurally with SLIGRL-NH2(10 mg/kg) were significantly higher than in mice injected with LSIGRL-NH2or PBS (2,710 ± 165 vs. 880 ± 357 vs. 88 ± 46 pg/ml, respectively; P < 0.001). Pleural fluid neutrophil counts were higher in SLIGRL-NH2group than in the LSIGRL-NH2and PBS groups (by 40- and 26-fold, respectively; P < 0.05). This study establishes that activation of mesothelial cell PAR2potently induces the release of inflammatory cytokines in vitro and neutrophil recruitment into the pleural cavity in vivo.