IntroductionInterleukin (IL)-27 is a novel member of the IL-6/IL-12 family cytokines that are produced early by antigen-presenting cells in T helper (Th)1-mediated inflammation. Elevated expression of IL-27 has been detected in the synovial membranes and fluid of rheumatoid arthritis (RA).MethodsWe investigated the in vitro effects of IL-27, alone or in combination with inflammatory cytokine tumor necrosis factor (TNF)-α or IL-1 β on the pro-inflammatory activation of human primary fibroblast-like synoviocytes (FLS) from RA patients and normal control subjects, and the underlying intracellular signaling molecules were determined by intracellular staining using flow cytometry.ResultsSignificantly higher plasma concentration of IL-27 was found in RA patients (n = 112) than control subjects (n = 46). Both control and RA-FLS constitutively express functional IL-27 receptor heterodimer, gp130 and WSX-1, with more potent IL-27-mediated activation of signal transducers and activators of transcription (STAT)1 in RA-FLS. IL-27 was found to induce significantly higher cell surface expression of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 and release of inflammatory chemokine IL-6, CCL2, CXCL9, CXCL10 and matrix metalloproteinase-1 of RA-FLS than that of control FLS (all P < 0.05). Moreover, an additive or synergistic effect was observed in the combined treatment of IL-27 and TNF-α or IL-1 β on the surface expression of ICAM-1 and VCAM-1 and the release of CXCL9 and CXCL10 of RA-FLS. Further investigations showed that the expression of ICAM-1, VCAM-1 and chemokines stimulated by IL-27 was differentially regulated by intracellular activation of phosphatidylinositol 3-OH kinase-AKT, c-Jun amino-terminal kinase and Janus kinase pathways.ConclusionsOur results therefore provide a new insight into the IL-27-activated immunopathological mechanisms mediated by distinct intracellular signal transductions in joint inflammation of RA.
Hyperuricemia-mediated uric acid crystal formation may cause joint inflammation and provoke the destruction of joints through the activation of inflammasome-mediated innate immune responses. However, the immunopathological effects and underlying intracellular regulatory mechanisms of uric acid crystal-mediated activation of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) have not been elucidated. Therefore, we investigated the in vitro effects of monosodium urate crystals, alone or in combination with the inflammatory cytokines tumor-necrosis factor (TNF)-a or interleukin (IL)-1b, on the activation of human FLS from RA patients and normal control subjects and the underlying intracellular signaling mechanisms of treatment with these crystals. Monosodium urate crystals were able to significantly increase the release of the inflammatory cytokine IL-6, the chemokine CXCL8 and the matrix metalloproteinase (MMP)-1 from both normal and RA-FLS (all P,0.05). Moreover, the additive or synergistic effect on the release of IL-6, CXCL8 and MMP-1 from both normal and RA-FLS was observed following the combined treatment with monosodium urate crystals and TNF-a or IL-1b. Further experiments showed that the release of the measured inflammatory cytokine, chemokine and MMP-1 stimulated by monosodium urate crystals were differentially regulated by the intracellular activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase pathways but not the p38 mitogen-activated protein kinase pathway. Our results therefore provide a new insight into the uric acid crystal-activated immunopathological mechanisms mediated by distinct intracellular signal transduction pathways leading to joint inflammation in RA. Keywords: cytokines; fibroblast-like synoviocytes; rheumatoid arthritis; signal transduction; uric acid INTRODUCTION Arthritis is the most common cause of joint pain and physical disability in developed countries and worldwide. 1 Gout is an acute inflammatory arthritis whose incidence has increased over the past decade, which is characterized by elevated serum urate concentrations and recurrent attacks by intra-articular uric acid crystal deposition. 2 Rheumatoid arthritis (RA) is a chronic inflammatory polyarthritis with 1% prevalence in industrialized countries, which is characterized by cytokinemediated inflammation of the synovium and destruction of cartilage and bone. 3 Uric acid crystal-mediated gouty attacks have also been observed in patients with RA. 4,5 Fibroblast-like synoviocytes (FLS) are resident mesenchymal cells in synovial joints that play crucial roles in both joint damage and the propagation of inflammation in arthritic diseases. 6 The ability of FLS to erode cartilage is a multistep process that includes the attachment of FLS onto cartilage and the synthesis of matrix metalloproteinases (MMPs) such as MMP-1. 7 Additionally, FLS secrete receptor activator of nuclear factor-kB ligand, which can attract macrophages from the vasculature, stimulate the differentiation of vascular-and tiss...
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