Mast cell–derived tryptase inhibits apoptosis of human rheumatoid synovial fibroblasts via rho‐mediated signaling

Abstract

Objective. An abundance of mast cells are found in the synovium of patients with rheumatoid arthritis (RA). However, the role of mast cells in the pathogenesis of RA remains unclear. This study was undertaken to elucidate a role for mast cells in RA by investigating the antiapoptotic effects of tryptase, a major product of mast cells, on RA synovial fibroblasts (RASFs).Methods. RA synovial tissue was obtained from RA patients during joint replacement surgery, and histologic changes in the tissue were examined. The expression of cell surface molecules and apoptotic markers on RASFs were detected by flow cytometry. Rho activation was determined using a pull-down assay.Results. Mast cells, bearing both c-Kit and tryptase, accumulated in the sublining area of proliferating synovial tissue from RA patients. Proteaseactivated receptor 2 (PAR-2), a receptor for tryptase, was expressed on RASFs in the lining area, close to tryptase-positive mast cells in the RA synovium. Fasmediated apoptosis of RASFs was significantly inhibited, in a dose-dependent manner, by the addition of tryptase, and this effect correlated with increased activation of Rho kinase. Furthermore, Y27632, a Rho kinase inhibitor, reduced the antiapoptotic effect of tryptase on RASFs, suggesting that Rho was responsible for the antiapoptotic effects of tryptase.Conclusion. These results demonstrate that tryptase has a strong antiapoptotic effect on RASFs through the activation of Rho. Thus, we propose that the release of tryptase by mast cells leads to the binding of tryptase to PAR-2 on RASFs and inhibits the apoptosis of RASFs via the activation of Rho. Such mechanisms could play a pivotal role in the marked proliferation of RASFs and hyperplasia of synovial tissue seen in RA synovium.

Proteinase-activated Receptor 2 (PAR2) Decreases Apoptosis in Colonic Epithelial Cells

“…However, while levels of active caspase-3 and DNA fragmentation were all lowered by tissue factor in serum-starved BHK-21 cells expressing factor VIIa (40,42), these studies did not examine the direct involvement of PAR2 in the anti-apoptotic mechanism, although it is known that BHK-21 cells express PAR2 and the factor VIIa⅐tissue factor complex activates PAR2 to stimulate intracellular Ca 2ϩ release (39,40). In addition to coagulation factors, mast cell-derived tryptase, which can also activate PAR2, has been shown to block Fas-induced apoptosis in rheumatoid synovial fibroblasts, but a role for PAR2 activation was not demonstrated in that study (43). Other proteases, such as the membrane tethered serine protease, matriptase, are expressed by intestinal epithelial cells and regulate barrier function (44), although an anti-apoptotic effect has not been ascribed to them at this point.…”

Mast cells: an expanding pathophysiological role from allergy to other disorders

“…The release of tryptase by mast cells leads to the binding of tryptase to protease-activated receptor 2 (PAR-2) on rheumatoid arthritis synovial fibroblasts (RASFs) and inhibits the apoptosis of RASFs via the activation of Rho. Such mechanisms could play a pivotal role in the marked proliferation of RASFs and hyperplasia of synovial tissue seen in synovium of rheumatoid arthritis (Sawamukai et al 2010). The functional contribution of mast cell-restricted tryptase/heparin complexes is also documented in the K/BxN mouse arthritis model (Shin et al 2009).…”

Interleukin-33 Synergistically Enhances Immune Complex-Induced Tumor Necrosis Factor Alpha and Interleukin-8 Production in Cultured Human Synovium-Derived Mast Cells

“…In humans, the number of degranulated MCs in the synovium is increased in RA patients, and histamine and tryptase levels are increased in the synovial fluid of patients with RA, compared to the levels in samples from patients with OA [9,10,11,12]. MC-derived tryptase suppresses the Fas-mediated apoptosis of synovial fibroblasts through Rho signaling [13]. These reports suggest that MC activation is involved in the pathogenesis of RA.…”