Involvement of PAR2 in inflammatory mediator release from human blood eosinophils

Abstract

Proteinase Activated Receptors (PARs) are the members of G-protein-coupled receptor family and can be cleaved by certain serine proteases to expose a tethered ligand domain, which binds and activates the receptors to initiate multiple signaling cascades. There is some evidence that certain proteases may regulate target cells by activating PARs. There are many studies, in which PARs play important roles in inflammation. One study indicated that PAR2 inhibition and deletion significantly suppressed the degree of inflammation due to decreased IL-6 and IL-1 levels. Another study also showed that PARs activation could mediate reactive oxygen species production and MAPK signaling leading to alveolar inflammation. In addition, platelet-derived CAPN1 can trigger the vascular inflammation associated with diabetes via cleavage of PAR1 and the release of TNF from the endothelial cell surface, and sarsasapogenin may alleviate diabetic nephropathy by the downregulation of PAR1. Another Phellodendron amurense bark extract can suppress the particulate matter-induced Ca2+ influx caused by direct action upon PAR2, alleviating inflammation and maintaining homeostatic levels of cell adhesion components. There are also other two antagonists of I-287 and GB88, which can reduce the PAR2-mediated inflammatory reaction. In this study, we tested expression of PARs and IL-5, IL-6, RANTES and ECP release from human blood eosinophils using different enzymes and PAR agonists. The expression of PARs was assessed in human blood eosinophils by flow cytometry and RT-PCR, and the levels of cytokine and eosinophil cationic protein (ECP) in the cultured supernatants were determined with ELISA kits. Flow cytometry shows that human eosinophils express PAR2 protein and do not express PAR1, PAR3 and PAR4 proteins. RT-PCR analysis revealed expression of PAR2 and PAR3 genes in human eosinophils. Tryptase, trypsin and elastase can induce significant IL-5, IL-6 and ECP release. Trypsin and elastase may also stimulate RANTES secretion, but tryptase cannot induce the RANTES secretion. Tryptase, trypsin and elastase-induced cytokine and ECP release from human blood eosinophils most likely occurs via activation of PAR2.