Protease‐activated receptor 2, rather than protease‐activated receptor 1, contributes to the aggressive properties of synovial fibroblasts in rheumatoid arthritis

Abstract

Objective. To investigate whether proteaseactivated receptor 1 (PAR-1) and/or PAR-2 promotes the invasiveness/proliferation of synovial fibroblasts (SFs) and to determine the signaling mechanisms of these pathways.Methods. SFs were isolated from the synovial tissue of patients with rheumatoid arthritis (RA), patients with osteoarthritis (OA), and PAR-1-or PAR-2-knockout (KO) mice. Expression of PAR-1 and PAR-2 was detected by immunofluorescence and Western blotting. The invasion and proliferation of SFs were measured by invasion assay and MTT assay, respectively. Matrix metalloproteinase 2 (MMP-2) and MMP-9 were detected by zymography, and cytokines were measured by enzyme-linked immunosorbent assay.Results. PAR-1 and PAR-2 were colocalized with SFs in RA and OA synovium and, to a considerably lesser extent, in normal synovium. Inhibition of PAR-2 by small interfering RNA (siRNA) inhibited RASF invasion and proliferation, whereas blocking of PAR-1 by siRNA had the reverse effects. SFs from PAR-2-KO mice exhibited slower rates of proliferation and invasion. SFs from PAR-1-KO mice produced less MMP-2 and, in response to tumor necrosis factor ␣ (TNF␣) stimulation, had increased MMP-9 secretion when compared to SFs from wild-type and PAR-2-KO mice. Inhibition of PAR-1, but not PAR-2, stimulated the secretion of interleukin-17 (IL-17) and TNF␣ by RASFs. Furthermore, PAR-1 and PAR-2 had opposing effects on the activation of ERK, p38, and NF-B.Conclusion. Activation of PAR-1 stimulates MMP-2 secretion, inhibits RASF growth and invasion, and decreases production of IL-17 and TNF␣ by RASFs, whereas activation of PAR-2 stimulates RASF growth and invasion and increases production of TNF␣. Thus, although PAR-1 and PAR-2 are coexpressed by RASFs, PAR-2 alone appears to be responsible for the aggressive properties of RASFs and is likely to contribute to the pathologic progression of RA.

The Role of Proteinase-Activated Receptors 1 and 2 in the Regulation of Periodontal Tissue Metabolism and Disease

“…However, in periodontal tissues, PAR 2 seems to be upregulated during inflammation, where it is believed to be activated by bacterial and host proteinases, whereas PAR 1 is upregulated during periodontal tissue repair. This counterregulation of PARs actions was also demonstrated by Xue et al [72] in rheumatoid arthritis synovial fibroblasts, where PAR 2 activation was associated with an elevated TNF-alpha release and PAR 1 activation prevented the release of proinflammatory cytokines. Interestingly, da Silva et al [47] showed that PAR 1 overexpression after periodontal treatment was inversely correlated to PAR 2 expression in gingival crevicular fluid cells.…”

Activated Protein C Inhibits Proliferation and Tumor Necrosis Factor α-Stimulated Activation of p38, c-Jun NH2-Terminal Kinase (JNK) and Akt in Rheumatoid Synovial Fibroblasts

“…In our previous studies, we reported that APC receptors EPCR, PAR-1 and PAR-2 are expressed by RA synovium (63,69) and APC inhibits the migration and activation of RA monocytes via EPCR (63). It is possible that ERK induction and downregulation of TNFα-stimulated p38, JNK and Akt in RSFs by APC will also be mediated by EPCR and PARs.…”

Endothelial protein C receptor-associated invasiveness of rheumatoid synovial fibroblasts is likely driven by group V secretory phospholipase A2

“…Human synovial tissues were fixed in 10% phosphate-buffered saline-buffered formalin. Immunohistochemical and immunofluorescent staining and toluidine blue staining were performed as described previously [26,27]. Isotype IgG for each antibody was used as a negative control.…”