Objective. We previously showed that Cyr61 acts to promote fibroblast-like synoviocyte (FLS) proliferation and Th17 cell differentiation, suggesting that Cyr61 plays an important role in mediating the joint inflammation and damage in rheumatoid arthritis (RA). The aim of this study was to investigate whether Cyr61 expression is regulated at the posttranscription level, and if so, how this regulation connects to other etiologic factors in RA.Methods. Expression of microRNA-22 (miR-22) in synovial tissue was detected by real-time polymerase chain reaction (PCR) using miRNA-specific TaqMan MGB probes. MicroRNA-22 promoter activity was analyzed using a Dual-Luciferase Reporter Assay. Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic joint inflammation and variable degrees of bone and cartilage erosion (1). Although the etiology and pathogenesis of RA are still poorly understood, accumulating evidence indicates that fibroblast-like synoviocytes (FLS) are important players in all aspects of the pathogenesis of RA (1-3). We previously demonstrated that the expression of Cyr61, a secreted extracellular matrix (ECM) protein produced by FLS, is stimulated by interleukin-17 (IL-17), and the overexpressed Cyr61 in turn acts to promote FLS proliferation in an autocrine/paracrine manner, thus contributing to the hyperplasia of synovial lining cells (4). Interestingly, Cyr61 can also stimulate FLS to produce IL-6, thus promoting Th17 cell differentiation (5). These results not only revealed for the first time that Cyr61 contributes to hyperplasia of synovial lining cells but also established a novel "feed-forward and malicious cycle" that leads to mutual stimulation of FLS and Th17
IntroductionIt is well known that neutrophils play very important roles in the development of rheumatoid arthritis (RA) and interleukin (IL)-8 is a critical chemokine in promoting neutrophil migration. We previously showed that increased production of Cyr61 by fibroblast-like synoviocytes (FLS) in RA promotes FLS proliferation and Th17 cell differentiation, thus Cyr61 is a pro-inflammatory factor in RA pathogenesis. In this study, we explored the role of Cyr61 in neutrophil migration to the joints of RA patients.MethodsRA FLS were treated with Cyr61 and IL-8 expression was analyzed by real-time PCR and ELISA. The migration of neutrophils recruited by the culture supernatants was determined by the use of a chemotaxis assay. Mice with collagen-induced arthritis (CIA) were treated with anti-Cyr61 monoclonal antibodies (mAb), or IgG1 as a control. Arthritis severity was determined by visual examination of the paws and joint destruction was determined by hematoxylin-eosin (H&E) staining. Signal transduction pathways in Cyr61-induced IL-8 production were investigated by real-time PCR, western blotting, confocal microscopy, luciferase reporter assay or chromatin immunoprecipitation (ChIP) assay.ResultsWe found that Cyr61 induced IL-8 production by RA FLS in an IL-1β and TNF-α independent pathway. Moreover, we identified that Cyr61-induced IL-8-mediated neutrophil migration in vitro. Using a CIA animal model, we found that treatment with anti-Cyr61 mAb led to a reduction in MIP-2 (a counterpart of human IL-8) expression and decrease in neutrophil infiltration, which is consistent with an attenuation of inflammation in vivo. Mechanistically, we showed that Cyr61 induced IL-8 production in FLS via AKT, JNK and ERK1/2-dependent AP-1, C/EBPβ and NF-κB signaling pathways.ConclusionsOur results here reveal a novel role of Cyr61 in the pathogenesis of RA. It promotes neutrophil infiltration via up-regulation of IL-8 production in FLS. Taken together with our previous work, this study provides further evidence that Cyr61 plays a key role in the vicious cycle formed by the interaction between infiltrating neutrophils, proliferated FLS and activated Th17 cells in the development of RA.
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