Proteinase-activated receptor 2 activation promotes an anti-inflammatory and alternatively activated phenotype in LPS-stimulated murine macrophages

Abstract

Proteinase-activated receptor 2 (PAR₂), a 7-transmembrane G protein-coupled receptor, contributes to inflammation either positively or negatively in different experimental systems. Previously, we reported that concurrent activation of PAR₂ and TLRs in human lung and colonic epithelial cells resulted in a synergistic increase in NF-κB-mediated gene expression, but a down-regulation of IRF-3-mediated gene expression. In this study, the effect of PAR₂ activation on LPS-induced TLR4 signaling was examined in primary murine macrophages. The PAR₂ activation of wild-type macrophages enhanced LPS-induced expression of the anti-inflammatory cytokine, IL-10, while suppressing gene expression of pro-inflammatory cytokines, TNF-α, IL-6, and IL-12. Similar PAR₂-mediated effects on LPS-stimulated IL-10 and IL-12 mRNA were also observed in vivo. In contrast, ${\text{PAR}}_2^{-/-}$ macrophages exhibited diminished LPS-induced IL-10 mRNA and protein expression and downstream STAT3 activation, but increased KC mRNA and protein. PAR₂ activation also enhanced both rIL-4- and LPS-induced secretion of IL-4 and IL-13, and mRNA expression of alternatively activated macrophage (AA-Mϕ) markers, e.g. arginase-1, mannose receptor, Ym-1. Thus, in the context of a potent inflammatory stimulus like LPS, PAR₂ activation acts to re-establish tissue homeostasis by dampening the production of inflammatory mediators and causing the differentiation of macrophages that may contribute to the development of a Th2 response.