Delayed onset of inflammation in protease-activated receptor-2-deficient mice

Endothelial surface expression of P-selectin and subsequent leukocyte rolli ng in venules can be induced by mast cell-derived histamine and binding of thrombin to protease-activated receptor-1 (PAR1), We hypothesized that acti vation of endothelial PAR2 by mast cell tryptase or other proteases also co ntributes to inflammatory responses. Leukocyte rolling flux and rolling vel ocity were assessed by intravital microscopy of the cremaster muscles of wi ld-type mice following perivenular micropipette injections of a control (LS IGRL) or PAR2-activating (SLIGRL) oligopeptide. Injection of SLIGRL increas ed 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 <mu>m/s (p < 0.05). No significant changes occurred with control peptide injection . To further evaluate the role of PAR2 in inflammatory responses, PAR2 defi cient mice were generated by gene targeting and homologous recombination. P erivenular injections of SLIGRL resulted in only a small increase in rollin g leukocyte flux fraction (from 21 +/- 8 to 30 +/- 2%) and no change in rol ling velocity. Leukocyte rolling after surgical trauma was assessed in 9 PA R2 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 mum/ s, p < 0.01) in PAR2-deficient compared with control mice. The defect in le ukocyte rolling in PAR2-deficient mice did not persist past 30 min followin g surgical trauma. These results indicate that activation of PAR2 produces microvascular inflammation by rapid induction of P-selectin-mediated leukoc yte rolling. In the absence of PAR2, the onset of inflammation is delayed.