Dickkopf-1 perpetuated synovial fibroblast activation and synovial angiogenesis in rheumatoid arthritis

Clinical Rheumatology - Dickkopf-1 (Dkk-1), a regulatory molecule of the Wnt pathway, is elevated and leads to bone resorption in patients with RA. This study is aimed to investigate the...     

Inhibition of fibroblast activation protein and dipeptidylpeptidase 4 increases cartilage invasion by rheumatoid arthritis synovial fibroblasts

Objective

Since fibroblasts in the synovium of patients with rheumatoid arthritis (RA) express the serine proteases fibroblast activation protein (FAP) and dipeptidylpeptidase 4 (DPP‐4)/CD26, we undertook the current study to determine the functional role of both enzymes in the invasion of RA synovial fibroblasts (RASFs) into articular cartilage.

Methods

Expression of FAP and DPP‐4/CD26 by RASFs was analyzed using fluorescence‐activated cell sorting and immunocytochemistry. Serine protease activity was measured by cleavage of fluorogenic substrates and inhibited upon treatment with L‐glutamyl L‐boroproline. The induction and expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in RASFs were detected using real‐time polymerase chain reaction. Densitometric measurements of MMPs using immunoblotting confirmed our findings on the messenger RNA level. Stromal cell–derived factor 1 (SDF‐1 [CXCL12]), MMP‐1, and MMP‐3 protein levels were measured using enzyme‐linked immunosorbent assay. The impact of FAP and DPP‐4/CD26 inhibition on the invasiveness of RASFs was analyzed in the SCID mouse coimplantation model of RA using immunohistochemistry.

Results

Inhibition of serine protease activity of FAP and DPP‐4/CD26 in vitro led to increased levels of SDF‐1 in concert with MMP‐1 and MMP‐3, which are downstream effectors of SDF‐1 signaling. Using the SCID mouse coimplantation model, inhibition of enzymatic activity in vivo significantly promoted invasion of xenotransplanted RASFs into cotransplanted human cartilage. Zones of cartilage resorption were infiltrated by FAP‐expressing RASFs and marked by a significantly higher accumulation of MMP‐1 and MMP‐3, when compared with controls.

Conclusion

Our results indicate a central role for the serine protease activity of FAP and DPP‐4/CD26 in protecting articular cartilage against invasion by synovial fibroblasts in RA.

     

微小RNA-146a对类风湿关节炎患者滑膜成纤维细胞抑制作用的研究

目的 研究微小RNA-146a(miR-146a)对类风湿关节炎(RA)患者滑膜成纤维细胞增殖及细胞因子分泌的影响.方法 体外分离培养RA患者滑膜成纤维细胞,脂质体转染化学合成的miR-146a,~3H掺入法检测滑膜成纤维细胞增殖.酶联免疫吸附试验(ELISA)法检测细胞上清白细胞介素(IL)-8及IL-6水平.实时定量聚合酶链反应(PCR)检测滑膜成纤维细胞中miR-146a靶分子肿瘤坏死因子受体相关因子6(TRAF6)、IL-受体相关激酶(IRAKI)的mRNA水平.应用独立样本t检验进行统计学分析.结果 与阴性对照小RNA相比,miR-146a转染后的滑膜成纤维细胞增殖能力明显下降(2015±545与8799±1922,P<0.01),IL-8及IL-6分泌受到明显抑制[(153±49)pg/ml与(311±123)pg/ml,P<0.01和(295±95)pg/ml与(459±126)pg/ml,P<0.05].定量PCR检测IRAK1的mRNA水平显示,miR-146a转染可明显下调滑膜成纤维细胞IRAK1的表达(0.28±0.07与1,P<0.01).结论 miR-146a可能通过下调IRAKI表达,进而抑制滑膜成纤维细胞增殖及IL-8、IL-6等炎性细胞因子分泌,从而发挥抑制RA滑膜炎症的作用.     

Altered expression of microRNA‐203 in rheumatoid arthritis synovial fibroblasts and its role in fibroblast activation

Objective

MicroRNA (miRNA) are recognized as important regulators of a variety of fundamental biologic processes. Previously, we described increased expression of miR‐155 and miR‐146a in rheumatoid arthritis (RA) and showed a repressive effect of miR‐155 on matrix metalloproteinase (MMP) expression in RA synovial fibroblasts (RASFs). The present study was undertaken to examine alterations in expression of miR‐203 in RASFs and analyze its role in fibroblast activation.

Methods

Differentially expressed miRNA in RASFs versus osteoarthritis synovial fibroblasts (OASFs) were identified by real‐time polymerase chain reaction (PCR)–based screening of 260 individual miRNA. Transfection of miR‐203 precursor was used to analyze the function of miR‐203 in RASFs. Levels of interleukin‐6 (IL‐6) and MMPs were measured by real‐time PCR and enzyme‐linked immunosorbent assay. RASFs were stimulated with IL‐1β, tumor necrosis factor α (TNFα), lipopolysaccharide (LPS), and 5‐azacytidine (5‐azaC). Activity of IκB kinase 2 was inhibited with SC‐514.

Results

Expression of miR‐203 was higher in RASFs than in OASFs or fibroblasts from healthy donors. Levels of miR‐203 did not change upon stimulation with IL‐1β, TNFα, or LPS; however, DNA demethylation with 5‐azaC increased the expression of miR‐203. Enforced expression of miR‐203 led to significantly increased levels of MMP‐1 and IL‐6. Induction of IL‐6 by miR‐203 overexpression was inhibited by blocking of the NF‐κB pathway. Basal expression levels of IL‐6 correlated with basal expression levels of miR‐203.

Conclusion

The current results demonstrate methylation‐dependent regulation of miR‐203 expression in RASFs. Importantly, they also show that elevated levels of miR‐203 lead to increased secretion of MMP‐1 and IL‐6 via the NF‐κB pathway and thereby contribute to the activated phenotype of synovial fibroblasts in RA.

     

Studies of serum immunoglobulin binding to synovial fibroblast cell cultures from patients with rheumatoid arthritis

Using a sensitive 125I-protein A (PrA) binding assay to detect cell surface IgG, we have studied seven different synovial fibroblast cell cultures from patients with rheumatoid arthritis (RA). When these cultures were incubated in the presence of serum from 18 autologous and allogeneic RA patients (all seropositive), we were unable to detect significant IgG binding. Since IgM rheumatoid factor (RF) can block PrA binding, sera were absorbed with aggregated IgG to remove RF without affecting the results. Similar studies on three cell lines with seven rheumatoid sera were performed by antibody-dependent cell-mediated cytotoxicity. No significant cytotoxicity was observed. Since antibodies to collagen are present in rheumatoid sera, several cultures were incubated with ascorbic acid (12.5 microgram/ml) to optimize synthesis of cell surface collagen. These culture conditions did not affect serum immunoglobulin binding by the 125I-PrA assay. Thus, we can find no evidence for a direct humoral immune mediation of synovial proliferation in rheumatoid arthritis. These data do not support the hypothesis that the inflammatory process within the synovium of RA patients is an immunologic response to a fibroblast-associated antigen in the synovial membrane.     

Infected synovial cysts arising as a complication of septic arthritis in a patient with rheumatoid arthritis

An elderly man with rheumatoid arthritis developed a streptococcal septicemia and arthritis following excision of an elbow nodule. His left calf became swollen; thrombophlebitis was initially diagnosed, but pus was aspirated from the calf and elbow and arthrograms showed large synovial cysts in both locations. The importance of aspirating any unusual calf swelling is emphasized.     

The CD69 activation pathway in rheumatoid arthritis synovial fluid t cells

Objective. To study the CD69 activation pathway in synovial fluid (SF) T lymphocytes from patients with rheumatoid arthritis (RA). Methods. Peripheral blood mononuclear cells (PBMC) or SF mononuclear cells (SFMC) were used in proliferation assays with anti-CD69, anti-CD28, anti-CD3, phorbol myristate acetate (PMA), and/or recombinant interleukin-2 (IL-2). CD69+, CD69—, and resting SF T cells were also proliferated. CD25 expression and production of IL-2 after CD69 activation were assessed by flow cytometry and in a bioassay with the IL-2-dependent cell line CTLL-2. Results. RA SFMC did not proliferate either in the presence of anti-CD69 monoclonal antibodies alone or with concomitant PMA activation, when compared with paired or control PBMC. Similar low proliferative responses via the CD3 or CD28 pathway with PMA were observed. This defective proliferation of RA SFMC after stimulation through the CD69 molecule was explained in part by a failure to express CD25 and to produce IL-2. SF CD69- T cells and resting SF T cells had higher rates of proliferation through the alternative costimulatory pathway CD28 than did SF CD69+ T cells or freshly isolated SF T cells. Conclusion. Freshly isolated SF T cells present a profound state of hyporesponsiveness through the CD69 and CD28 costimulatory pathways. This state appears to be dependent on the activation status of SF T cells, since CD69— and resting SF T cells showed recovery of the ability to proliferate through the CD28 activation pathway.     

Citrullinated fibrinogen detected as a soluble citrullinated autoantigen in rheumatoid arthritis synovial fluids

BACKGROUND: Anti-citrullinated protein antibodies (ACPA) are specifically and frequently detected in sera of patients with rheumatoid arthritis (RA). Citrullinated fibrin or fibrinogen is a candidate autoantigen of such antibodies. OBJECTIVE: To investigate the presence of citrullinated fibrinogen (cFBG) in the plasma or synovial fluid of patients with RA and control patients, and to determine cFBG levels and their relationship with serum markers for RA if it is present. METHODS: A sandwich enzyme linked immunosorbent assay (ELISA) to measure cFBG was established using monoclonal antibodies cF16.1 and cF252.1, generated by immunising mice with R16Cit and R252Cit, the fibrinogen Aalpha chain derived sequences with citrulline at position 16 and 252, respectively, and the presence of cFBG was further investigated with immunoprecipitation-western blotting. RESULTS: Positive signals were detected in 11/15 RA synovial fluids (RASFs), but not in osteoarthritis synovial fluids or RA plasma with sandwich ELISA for cFBG using cF16.1 and an anti-modified citrulline (AMC) antibody. The presence of cFBG in RASFs was confirmed by immunoprecipitation-western blotting. Furthermore, most RA sera strongly reacted against R16Cit. No relationship was seen between RASF cFBG levels and C reactive protein or anti-cyclic citrullinated peptide antibody levels of the paired sera. CONCLUSION: cFBG is detected as a soluble citrullinated autoantigen in RASFs and may therefore be a genuine candidate antigen for ACPA in patients with RA.     

The TNF superfamily member LIGHT contributes to survival and activation of synovial fibroblasts in rheumatoid arthritis

OBJECTIVES: The TNF superfamily member LIGHT has a T-cell co-stimulatory role and has previously been associated with inflammation and autoimmunity. To investigate its role in rheumatoid arthritis (RA), a disease where activated T cells contribute in a prominent way, we have analysed the expression of LIGHT and its receptors in RA and analysed its effects on synovial fibroblasts in vitro. METHODS: The expression of LIGHT was measured in synovial tissues and fluids and the receptors of LIGHT were detected on synovial fibroblasts derived from patients with RA and osteoarthritis (OA). The effects of recombinant LIGHT on the production of proinflammatory cytokines and proteases and on the apoptosis of synovial fibroblasts was assessed. RESULTS: LIGHT mRNA was present in synovial tissues of patients with RA but not with OA. Correspondingly, soluble LIGHT protein could be detected in RA synovial fluid samples at much higher levels than in synovial fluid from patients with OA. Immunohistochemical detection of LIGHT and analysis of synovial fluid cells by flow cytometry revealed CD4 T cells as the major source of LIGHT in the rheumatoid joint. Synovial fibroblasts from RA patients were found to express the LIGHT receptors HVEM and LTbetaR. Recombinant LIGHT induced RA synovial fibroblasts to upregulate MMP-9 mRNA, CD54 and IL-6 in an NF-kappaB-dependent fashion. In vitro, exposure of cultured synovial fibroblasts to LIGHT reduced FAS-mediated apoptosis significantly, without affecting the rate of spontaneous apoptosis. CONCLUSIONS: The results provide evidence for a novel T-cell-dependent activation of synovial fibroblasts by LIGHT in joints of patients with RA, contributing to an inflammatory and destructive phenotype.     

Complement activation in synovial fluid and tissue from patients with juvenile rheumatoid arthritis

Synovial fluid (SF) and synovial tissue from 10 patients with juvenile rheumatoid arthritis were examined. The SFs were heterogeneous with respect to the degree of complement activation. Quantification of C3dg and the terminal complement complex revealed a positive correlation between activation of the early and the late parts of the cascade in all patients. The amount of C-reactive protein and the number of white blood cells in the SF correlated significantly with the degree of complement activation. Weak deposits of C3, C3dg, or terminal complement complex were observed in a few vessels in the synovial tissue from 5 of the patients. There was no correlation between complement activity in SF and in the corresponding tissue. Furthermore, there was no correlation between clinical activity in the joints and the degree of complement activation. It is concluded that there is a discrepancy between synovial tissue and synovial fluid with respect to complement activation. C-reactive protein may, to some extent, be responsible for activation in SF, and the accumulation of white blood cells may be due to complement activation products.     

Rheumatoid arthritis synovial fibroblast and U937 macrophage/monocyte cell line interaction in cartilage degradation

Objective. To examine the interaction between synovial fibroblasts and macrophages in the context of cartilage degradation. Methods. An in vitro model of human cartilage degradation was used, in which purified populations of fibroblasts and macrophages were added to a radio-labeled cartilage disc. Cartilage destruction was measured by the percentage of radiolabel release. Results. Fibroblasts, obtained from either rheumatoid arthritis (RA) or osteoarthritis synovial tissue, could mediate cartilage degradation if cocultured with the U937 macrophage cell line. Skin and RA bone marrow fibroblasts had no degradative effect on cartilage. Fibroblast—macrophage contact was not required for cartilage degradation. Cartilage degradation by synovial fibroblasts was inhibited by antibodies to tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and IL-6. Cartilage degradation was almost completely abrogated by a combination of antibodies to TNFα and IL-1β. Contact between fibroblasts and cartilage was shown to be essential. Antibodies to CD44, but not to intercellular adhesion molecule 1, markedly inhibited cartilage degradation. Conclusion. TNFα, IL-1β, and IL-6 were involved in the activation of synovial fibroblasts to cause cartilage degradation. Cartilage degradation occurred only when fibroblasts were in contact with cartilage. CD44 was demonstrated to be involved in the fibroblast—cartilage interaction.     

类风湿关节炎成纤维样滑膜细胞诱导分化的体外研究

目的 研究类风湿关节炎（RA）成纤维样滑膜细胞（FLS）体外培养时的增生分化特点及细胞分化诱导剂全反式维甲酸（ATRA）、骨化三醇[1，25（OH）2D3]地塞米松（DEX）对RA—FLS增殖分化的影响。方法 关节镜、关节活检针取RA患者滑膜组织或抽取RA患者关节积液分离培养鉴定滑膜细胞．四甲基偶氮唑蓝（MTT）法和流式细胞仪法分别观察ATRA、骨化三醇和地塞米松对FLS细胞存活分数（SF）和细胞周期的影响。结果 RA—FLS在体外无诱导剂作用时呈现良性增殖方式。ATRA、骨化三醇和地塞米松对FLS的细胞标记和免疫染色无明显影响。三种诱导剂对RA—FLS的SF值均有不同程度的抑制（P〈0．05），其中地塞米松抑制作用最明显；骨化三醇和地塞米松对RA—FLS的SF抑制作用呈现剂量依赖性曲线（P〈0．01）。三种诱导剂均促使RA—FLS细胞周期改变即凋亡峰出现、S期缩短。结论 体外培养的RA—FLS生长特性为非恶性无限制增生。ATRA、骨化三醇和地塞米松抑制RA—FLS细胞增殖，促进细胞分化，诱导FLS凋亡，其中地塞米松抗增殖作用最明显；但未发现三者将FLS诱导分化为其他类型细胞。     

Intracellular oxidative activation in synovial fluid neutrophils from patients with rheumatoid arthritis but not from other arthritis patients

OBJECTIVE: To compare total and intracellular oxidative activation of blood and synovial fluid (SF) neutrophils from patients with rheumatoid arthritis (RA) and other arthritides with blood donor neutrophils. METHODS: Peripheral blood and SF samples were obtained from 26 gonarthritis patients (13 RA, 13 non-RA) attending the rheumatology unit for therapeutic joint aspiration. Isolated neutrophils were stimulated by a formylated tripeptide (fMLF) or by microbeads coated with collagen-I. Formation of superoxide-anion-derived reactive oxygen species (ROS) was studied by luminol-enhanced chemiluminescence. Paired samples of blood and SF neutrophils from patients with active arthritis were compared with blood neutrophils from patients in remission and from 47 healthy blood donors. RESULTS: SF neutrophils from patients with RA, but not from non-RA patients, showed high baseline intracellular ROS production. Blood neutrophils from arthritis patients in remission existed in a primed state as revealed by more rapid oxidative response after collagen-bead challenge and a more pronounced response after fMLF stimulation compared to healthy blood donors. Blood neutrophils from RA patients with ongoing gonarthritis, however, did not differ from healthy blood donors concerning oxidative activation, whereas blood neutrophils from non-RA patients with gonarthritis showed a significantly lower peak ROS production. CONCLUSIONS: A novel finding with pathogenetic implications in our study is that SF neutrophils from patients with RA, but not other arthritides, are activated and produce ROS intracellularly. This implies that synovial neutrophils in RA are engaged in the processing of endocytosed material.