Delayed Onset of Inflammation in Protease-Activated Receptor-2-Deficient Mice

Abstract

Endothelial surface expression of P-selectin and subsequent leukocyte rolling in venules can be induced by mast cell-derived histamine and binding of thrombin to protease-activated receptor-1 (PAR1). We hypothesized that activation of endothelial PAR2 by mast cell tryptase or other proteases also contributes to inflammatory responses. Leukocyte rolling flux and rolling velocity were assessed by intravital microscopy of the cremaster muscles of wild-type mice following perivenular micropipette injections of a control (LSIGRL) or PAR2-activating (SLIGRL) oligopeptide. Injection of SLIGRL increased mean rolling leukocyte flux fraction from 34 ± 11 to 71 ± 24% (p < 0.05) and decreased mean rolling velocity from 63 ± 29 to 32 ± 2 μm/s (p < 0.05). No significant changes occurred with control peptide injection. To further evaluate the role of PAR2 in inflammatory responses, PAR2-deficient mice were generated by gene targeting and homologous recombination. Perivenular injections of SLIGRL resulted in only a small increase in rolling leukocyte flux fraction (from 21 ± 8 to 30 ± 2%) and no change in rolling velocity. Leukocyte rolling after surgical trauma was assessed in 9 PAR2-deficient and 12 wild-type mice. Early (0–15 min) after surgical trauma, the mean leukocyte rolling flux fraction was lower (10 ± 3 vs 30 ± 6%, p < 0.05) and mean rolling velocity was higher (67 ± 46 vs 52 ± 36 μm/s, p < 0.01) in PAR2-deficient compared with control mice. The defect in leukocyte rolling in PAR2-deficient mice did not persist past 30 min following surgical trauma. These results indicate that activation of PAR2 produces microvascular inflammation by rapid induction of P-selectin-mediated leukocyte rolling. In the absence of PAR2, the onset of inflammation is delayed.

Protease-Activated Receptor 2 Mediates Eosinophil Infiltration and Hyperreactivity in Allergic Inflammation of the Airway

“…To our knowledge, our results provide the first evidence that PAR2 plays an important role in mediating the infiltration of leukocytes in the acute phases of allergic inflammation of the airways. In support of our results, perivascular application of PAR2 agonists promotes the rolling and firm adhesion of lymphocytes in rat mesenteric vessels (37), and surgically induced lymphocyte rolling and adhesion is diminished in PAR2ko mice different from those used in the current investigation (38). The intraplantar administration of PAR2 agonists in rats also causes granulocyte infiltration (32).…”

Synergistic induction of tissue factor by coagulation factor Xa and TNF: Evidence for involvement of negative regulatory signaling cascades

“…We also identify the molecular targets whose down-regulation results in this effect. It is also important to note that several recent animal studies have demonstrated that fXa and thrombin, as well as PAR1 and -2, can mediate inflammatory responses in vivo (55)(56)(57). Although this study focuses on a coagulation protease, it is likely that other proteases that are capable of cleaving PAR1 or -2, such as proteases originating from monocytes or neutrophils, when costimulated with inflammatory cytokines could elicit similar endothelial activation (TF and E-selectin induction).…”

Essential role for proteinase-activated receptor-2 in arthritis

“…Furthermore, Lindner and colleagues (19) have reported that although the inflammatory response to surgical trauma was delayed in PAR-2-deficient mice, this inhibition was not long-lasting. The substantial inhibition of adjuvant-induced arthritis we observed in the PAR-2 -/-group, coupled with the failure of NK 1 receptor deletion to inhibit adjuvant arthritis (20), suggests that PAR-2 may mediate chronic joint inflammation by non-neurogenic mediators, perhaps via the cytokine cascade.…”