β-Arrestin-2 mediates the proinflammatory effects of proteinase-activated receptor-2 in the airway

Proteinase-Activated rreceptor-2 (PAR2), a G-protein–coupled Receptor, activated by serine proteinases, is reported to have both protective and proinflammatory effects in the airway. Given these opposing actions, both inhibitors and activators of PAR2 have been proposed for treating asthma. PAR2 can signal through two independent pathways: a β-arrestin–dependent one that promotes leukocyte migration, and a G-protein/Ca2+ one that is required for prostaglandin E2 (PGE2) production and bronchiolar smooth muscle relaxation. We hypothesized that the proinflammatory responses to PAR2 activation are mediated by β-arrestins, whereas the protective effects are not. Using a mouse ovalbumin model for PAR2-modulated airway inflammation, we observed decreased leukocyte recruitment, cytokine production, and mucin production in β-arrestin-2−/− mice. In contrast, PAR2-mediated PGE2 production, smooth muscle relaxation, and decreased baseline airway resistance (measures of putative PAR2 “protective” effects) were independent of β-arrestin-2. Flow cytometry and cytospins reveal that lung eosinophil and CD4 T-cell infiltration, and production of IL-4, IL-6, IL-13, and TNFα, were enhanced in wild-type but not β-arrestin-2−/− mice. Using the forced oscillation technique to measure airway resistance reveals that PAR2 activation protects against airway hyperresponsiveness by an unknown mechanism, possibly involving smooth muscle relaxation. Our data suggest that the PAR2-enhanced inflammatory process is β-arrestin-2 dependent, whereas the protective anticonstrictor effect of bronchial epithelial PAR2 may be β-arrestin independent.