Synovial fibroblasts: key players in rheumatoid arthritis

Interleukin-34 produced by human fibroblast-like synovial cells in rheumatoid arthritis supports osteoclastogenesis

Introduction

Interleukin-34 (IL-34) is a recently defined cytokine, showing a functional overlap with macrophage colony stimulating factor (M-CSF). This study was undertaken to address the expression of IL-34 in rheumatoid arthritis (RA) patients and to investigate its regulation and pathogenic role in RA.

Methods

IL-34 levels were determined in the RA synovium, synovial fluid (SF) and fibroblast-like synovial cells (FLS) by immunohistochemistry, real-time PCR, enzyme-linked immunosorbent assay and immunoblotting. RA activity was assessed using Disease Activity Score 28 (DAS28) activity in the plasma collected at baseline and one year after treatment. Conditioned media (CM) were prepared from RA FLS culture with tumor necrosis factor alpha (TNFα) for 24 hours and used for functional assay.

Results

IL-34 was expressed in the synovium, SF, and FLS from RA patients. The production of IL-34 in FLS was up-regulated by TNFα in RA samples compared with osteoarthritis (OA) patients. Importantly, the preferential induction of IL-34 rather than M-CSF by TNFα in RAFLS was mediated by the transcription factor nuclear factor kappa B (NF-κB) and activation of c-Jun N-terminal kinase (JNK). IL-34 elevation in plasma from RA patients was decreased after the administration of disease-modifying anti-rheumatic drugs (DMARDs) in accordance with a decrease in DAS28. CM from RAFLS cultured with TNFα promoted chemotactic migration of human peripheral blood mononuclear cells (PBMCs) and subsequent osteoclast (OC) formation, effects that were attenuated by an anti-IL-34 antibody.

Conclusions

These data provide novel information about the production of IL-34 in RA FLS and indicate that IL-34 is an additional osteoclastogenic factor regulated by TNFα in RA, suggesting a discrete role of IL-34 in inflammatory RA diseases.

Tissue-specific expression of human calcineurin-binding protein 1 in mouse synovial tissue can suppress inflammatory arthritis

Calcineurin (CN) is a calcium- and calmodulin-dependent serine/threonine phosphatase. In immune cells, CN controls the activity of a wide range of transcription factors, including nuclear factor of activated T, nuclear factor-kappa B, c-fos, and Elk-1. CN plays an important role in synoviocyte activation and arthritis progression in vivo and this function is tightly linked to dysregulated intracellular Ca(2+) store and Ca(2+) response triggered by proinflammatory cytokines. In the present study, transgenic mice expressing human calcineurin-binding protein 1 (hCabin1) were generated, driven by type II collagen promoter, and the efficiency of these mice was investigated by experimental arthritis. These transgenic mice successfully expressed hCabin1 in joint tissue as well as other organs such as liver, heart, and brain. The overexpression of hCabin1 reduced the disease severity during collagen-induced arthritis. In fibroblast-like synoviocytes (FLSs) from hCabin1 transgenic mice, the productions of these cytokines, including interleukin (IL)-2, IL-4, and IFN-γ, were decreased and matrix metalloproteinases were also depressed in transgenic mice FLS. In addition, these effects were only found in the joint tissue, which is a major inflammation site. These findings will provide a better knowledge of the pathogenic mechanisms of rheumatoid arthritis and a potential animal model of the chronic inflammatory conditions, including atherosclerosis and transplantation.

The effectiveness of Echinacea extract or composite glucosamine, chondroitin and methyl sulfonyl methane supplements on acute and chronic rheumatoid arthritis rat model

The study aimed to investigate the effect of the oral administration for 15 days of either Echinacea (E) or genuphil (a composite of chondroitin sulphate, glucosamine and methyl sulfonyl methane [GCM]) nutraceutical supplements on female rat model of acute or chronic arthritis induced by bacterial outer membrane protein (OMP) from faecal flora of healthy and rheumatic humans. Anti-cyclic citrullinated peptide (anti-CCP2), C-reactive protein (CRP) and rheumatoid factor (RF) values increased ( p < 0.05) in both arthritic groups as compared to normal values. The rheumatic markers anti-CCP2, CRP and RF values decreased significantly in E- and GCM-treated groups compared to arthritic none-treated acute or chronic groups. The results of RF values of GCM-treated groups in acute and chronic models decreased exhibiting no statistical difference compared with the normal value. Histological examinations of the hind paw sections revealed moderate inflammation, oedema and mild proliferation of synovial cells in acute arthritic rats and more damage to cartilage and bone with severe inflammation in chronic ones. Echinacea acute treated group showed edema with proliferated synovial membrane and partial damage in cartilage and bone. While in the E -chronic treated group, rough edge with destructed cartilage and bone existed. However, the acute GCM group revealed mild cartilage damage. But the chronic GCM group showed mild synovial cells proliferation and revealed no inflammation with mild cartilage damage edge. Results demonstrated the OMP arthropathic property and through promising light on arthritis treatment using E- or GCM, with the advantage of GMC results over that of E -. The composite GCM is needed for further studies over the dose and duration to assess its preventive effects against the bacterial OMP arthrogenicity.

Comparative study of normal and rheumatoid arthritis fibroblast-like synoviocytes proliferation under cyclic mechanical stretch: role of prostaglandin E2

Fibroblast-like synoviocytes (FLSs) are one of the main contributors of prostaglandin E(2) (PGE(2)) in the hyperplastic synovium of rheumatoid arthritis (RA) patients. cyclooxygenase-2 (COX-2)/PGE(2) pathway is involved in the proliferation of several cell types. We have previously shown that mechanical stretch affects COX-2 and PGE(2) production in human RA FLSs; however, its role in cell proliferation remains to be elucidated. In this study, a comparison is drawn between human RA and normal FLSs to understand the role of mechanical stretch and PGE(2) on the proliferation of FLSs. The results showed that physiological level (6%, 1 Hz) of cyclic mechanical stretch significantly decreased the proliferation of RA FLSs but not normal FLSs, while the induction of apoptosis was not observed by stretch in either RA or normal FLSs. IL-1β (5 ng/ml)-induced COX-2/PGE(2) levels are downregulated by stretch in RA FLSs only. Further investigation showed that high concentration (100 and 500 ng/ml) of PGE(2) significantly induced cell proliferation only in RA FLSs, and this induction failed to be suppressed by stretch. In conclusion, this study demonstrated that elevated levels of PGE(2) in the synovial cavity are involved in the proliferation of RA FLSs, and cyclic mechanical stretch regulates the RA synovial hyperplasia.

Enhanced expression of tissue inhibitor of metalloproteinases-4 gene in human osteoarthritic synovial membranes and its differential regulation by cytokines in chondrocytes

Objective:

Tissue inhibitors of metalloproteinases (TIMPs) are multi-functional proteins with matrix metalloproteinases-inhibiting activities. We studied expression of anti-inflammatory, TIMP-4 gene in human joint tissues and its regulation by arthritis-associated cytokines.

Results:

TIMP-4 RNA expression originating from synovial fibroblasts was significantly (2.4 fold; p<0.001) elevated in 8 osteoarthritic (OA) versus 7 non-arthritic synovial membranes. Non-arthritic and OA femoral head and knee chondrocytes displayed substantial but variably constitutive expression of the TIMP-4 mRNA. In articular chondrocytes, transforming growth factor beta (TGF-β1) and oncostatin M (OSM) upregulated TIMP-4 RNA and protein expression while interleukin-1 (IL-1β) and tumor necrosis factor alpha (TNF-α) did not, suggesting differential regulation by arthritis-associated cytokines. Interleukin 17 (IL-17) mildly induced TIMP-4 mRNA. TGF-β1 induction of TIMP-4 expression was partly inhibited by ERK pathway and Sp1 transcription factor inhibitors.

Conclusion:

Enhanced TIMP-4 gene expression in OA synovial membranes and cartilage may be due to induction by TGF-β1, OSM and IL-17, suggesting its pathophysiological role in tissue remodeling in human joints. TGF-β1 induction of TIMP-4 expression is mediated partly by ERK pathway and Sp1 transcription factor.

Synovial fibroblast hyperplasia in rheumatoid arthritis: clinicopathologic correlations and partial reversal by anti-tumor necrosis factor therapy

OBJECTIVE

Synovial fibroblast (SF) hyperplasia contributes to the pathogenesis of rheumatoid arthritis (RA), but quantitative information on this process is scarce. This study was undertaken to evaluate the fibroblast-specific marker Hsp47 as a quantitative marker for SFs and to analyze its clinicopathologic correlates and evolution after anti-tumor necrosis factor α (anti-TNFα) therapy.

METHODS

Synovial biopsy samples were obtained from 48 patients with RA and 20 controls who were healthy or had osteoarthritis (OA). Twenty-five RA patients who had active disease at the time of biopsy underwent a second biopsy after anti-TNFα therapy. Immunolabeling for Hsp47, inflammatory cells, and vascular cell markers was performed. Hsp47-positive lining and sublining fractional areas were quantified, and their correlation with clinicopathologic variables was analyzed.

RESULTS

In normal and diseased synovial tissue, Hsp47 was specifically and uniformly expressed by lining, sublining, and perivascular fibroblasts. Lining SF area was significantly increased in both RA and late OA tissue compared to normal tissue. Sublining SF area was increased in RA tissue but not in late OA tissue compared to normal tissue. Lining SF area was positively correlated with macrophage density, Disease Activity Score in 28 joints, and RA disease duration. In contrast, sublining SF area was negatively correlated with RA disease duration and activity. A significant reduction in lining SF area but not sublining SF area was observed after anti-TNFα therapy.

CONCLUSION

Our findings indicate that Hsp47 is a reliable marker for quantifying SFs in human synovial tissue. Our data suggest that lining and sublining SFs undergo different dynamics during the course of the disease. Lining SF expansion parallels the activity and temporal progression of RA and can be partially reversed by anti-TNFα therapy.

α9β1 integrin-mediated signaling serves as an intrinsic regulator of pathogenic Th17 cell generation

The interaction between matricellular proteins such as tenascin-C (TN-C) and osteopontin (OPN) and integrins has been implicated in the pathology of rheumatoid arthritis in which Th17 cells are recognized as primary pathogenic cells. The differentiation of Th17 cells is tightly regulated by cytokines derived from APCs, receiving various signals including TLR stimuli. In this study, we used a collagen-induced arthritis model and found that increased numbers of α(9) integrin-positive conventional dendritic cells and macrophage were detectable in the draining lymph node (dLN) shortly following first immunization, and these cells produced both TN-C and OPN, ligands for α(9) integrin. α(9) integrin-mediated signaling, induced by TN-C and OPN, promoted the production of Th17-related cytokines by conventional dendritic cells and macrophages in synergy with TLR2 and 4 signaling. This led to the Th17 cell differentiation and arthritis development. Moreover, Th17 cells generated under blocking of α(9) integrin-mediated signaling showed low level of CCR6 expression and impaired migration ability toward CCL20. Thus, we have identified α(9) integrin-mediated signaling by TN-C and OPN as a novel intrinsic regulator of pathogenic Th17 cell generation that contributes to the development of rheumatoid arthritis.

Apoptosis-like cell death induction and aberrant fibroblast properties in human incisional hernia fascia

Incisional hernia often occurs following laparotomy and can be a source of serious problems. Although there is evidence that a biological cause may underlie its development, the mechanistic link between the local tissue microenvironment and tissue rupture is lacking. In this study, we used matched tissue-based and in vitro primary cell culture systems to examine the possible involvement of fascia fibroblasts in incisional hernia pathogenesis. Fascia biopsies were collected at surgery from incisional hernia patients and non-incisional hernia controls. Tissue samples were analyzed by histology and immunoblotting methods. Fascia primary fibroblast cultures were assessed at morphological, ultrastructural, and functional levels. We document tissue and fibroblast loss coupled to caspase-3 activation and induction of apoptosis-like cell-death mechanisms in incisional hernia fascia. Alterations in cytoskeleton organization and solubility were also observed. Incisional hernia fibroblasts showed a consistent phenotype throughout early passages in vitro, which was characterized by significantly enhanced cell proliferation and migration, reduced adhesion, and altered cytoskeleton properties, as compared to non-incisional hernia fibroblasts. Moreover, incisional hernia fibroblasts displayed morphological and ultrastructural alterations compatible with autophagic processes or lysosomal dysfunction, together with enhanced sensitivity to proapoptotic challenges. Overall, these data suggest an ongoing complex interplay of cell death induction, aberrant fibroblast function, and tissue loss in incisional hernia fascia, which may significantly contribute to altered matrix maintenance and tissue rupture in vivo.

Effects of testosterone, estrogen and progesterone on TNF-α mediated cellular damage in rat arthritic synovial fibroblasts

Sexual dimorphism is a well-established phenomenon in rheumatoid arthritis, with women exhibiting higher disease severity. Understanding the role of sex hormones using in vivo animal models is limited due to the systemic effects as well as the difficulty in exploring different dose combinations of the hormones simultaneously. However, cell culture systems pose ideal systems for exploring different combinations and concentrations of the hormones simultaneously. In this study, the procedure for isolation of arthritic fibroblasts was standardized using a combination of collagenase and trypsin based on maximal yield and viability after employing different enzymatic disaggregation procedures. The cultured synovial fibroblasts from arthritic rats did not differ significantly from normal rat fibroblasts in terms of proliferation or secretion of inflammatory mediators. Stimulation of fibroblasts with TNF-α was standardized and TNF-α stimulated rat arthritic synovial fibroblasts exhibited an ideal in vitro system for screening antiinflammatory molecules. The effects of physiological and pharmacological concentrations of testosterone, estrogen and progesterone were studied on TNF-α induced cellular damage in rat arthritic synovial fibroblasts. The results showed that estrogen and testosterone exerted antiinflammatory effects on rat arthritic synovial fibroblasts at physiological and pharmacological concentrations. However, there was no significant difference in the effects between physiological and pharmacological concentrations. Progesterone independently did not show any protective effects. In combination with physiological concentrations of estrogen, progesterone abrogated estrogen's protective effect but it exhibited protection in combination with pharmacological concentrations of estrogen.

Chemerin activates fibroblast-like synoviocytes in patients with rheumatoid arthritis

Introduction

Chemerin is a chemotactic agonist identified as a ligand for ChemR23 that is expressed on macrophages and dendritic cells (DCs). In this study, we analyzed the expression of chemerin and ChemR23 in the synovium of rheumatoid arthritis (RA) patients and the stimulatory effects of chemerin on fibroblast-like synoviocytes (FLSs) from RA patients.

Methods

Chemerin and ChemR23 expression in the RA synovium was ascertained by immunohistochemistry and Western blot analysis. Chemerin expression on cultured FLSs was analyzed by ELISA. ChemR23 expression on FLSs was determined by immunocytochemistry and Western blot analysis. Cytokine production from FLSs was measured by ELISA. FLS cell motility was evaluated by utilizing a scrape motility assay. We also examined the stimulating effect of chemerin on the phosphorylation of mitogen-activated protein kinase (MAPK), p44/42 mitogen-activated protein kinase (ERK1/2), p38MAPK, c-Jun N-terminal kinase (JNK)1/2 and Akt, as well as on the degradation of regulator of NF-κB (IκBα) in FLSs, by Western blot analysis.

Results

Chemerin was expressed on endothelial cells and synovial lining and sublining cells. ChemR23 was expressed on macrophages, immature DCs and FLSs and a few mature DCs in the RA synovium. Chemerin and ChemR23 were highly expressed in the RA synovium compared with osteoarthritis. Chemerin and ChemR23 were expressed on unstimulated FLSs. TNF-α and IFN-γ upregulated chemerin production. Chemerin enhanced the production of IL-6, chemokine (C-C motif) ligand 2 and matrix metalloproteinase 3 by FLSs, as well as increasing FLS motility. The stimulatory effects of chemerin on FLSs were mediated by activation of ERK1/2, p38MAPK and Akt, but not by JNK1/2. Degradation of IκB in FLSs was not promoted by chemerin stimulation. Inhibition of the ERK1/2, p38MAPK and Akt signaling pathways significantly suppressed chemerin-induced IL-6 production. Moreover, blockade of the p38MAPK and Akt pathways, but not the ERK1/2 pathway, inhibited chemerin-enhanced cell motility.

Conclusions

The interaction of chemerin and ChemR23 may play an important role in the pathogenesis of RA through the activation of FLSs.

Low-intensity pulsed ultrasound reduces the inflammatory activity of synovitis

The purpose of this study was to examine the effect of low-intensity pulsed ultrasound (LIPUS) on the cell proliferation and growth of synovial membrane cells stimulated with inflammatory cytokines, and to evaluate the effectiveness of LIPUS treatment of synovitis in the knee joints of animal models for rheumatoid arthritis. The rabbit knee synovial membrane cell line, HIG-82, was cultured in medium with or without IL-1β or TNF-α. Four hours after stimulation with the cytokines, the cells received LIPUS or sham exposure. Cell proliferation and growth were then analyzed. Using MRL/lpr mice, the anti-inflammatory effects of LIPUS were also evaluated in vivo. Stimulation with proinflammatory cytokines significantly up-regulated cell proliferation which was significantly down-regulated by LIPUS exposure. In MRL/lpr mice, exposure of knee joints to LIPUS caused a significant reduction of histological damage compared to the control. Histological lesions were significantly reduced in the joints treated with LIPUS for 3 weeks. Cox-2-positive cells in the knee joints treated with LIPUS were markedly decreased compared to the control joints. Therefore, LIPUS stimulation may be a medical treatment for joint inflammatory diseases, such as synovitis.

Modulation of interleukin-1β-induced inflammatory responses by a synthetic cationic innate defence regulator peptide, IDR-1002, in synovial fibroblasts

Introduction

Innate defence regulator (IDR) peptides are synthetic cationic peptides, variants of naturally occurring innate immune effector molecules known as host defence peptides. IDR peptides were recently demonstrated to limit infection-associated inflammation selectively without compromising host innate immune functions. This study examined the impact of a 12-amino acid IDR peptide, IDR-1002, in pro-inflammatory cytokine interleukin (IL)-1β-induced responses in synovial fibroblasts, a critical cell type in the pathogenesis of inflammatory arthritis.

Methods

Human fibroblast-like synoviocytes (FLS) were stimulated with IL-1β in the presence and absence of IDR-1002. Production of enzyme matrix metalloproteinase-3 (MMP-3) and IL-1-receptor antagonist (IL-1RA) was monitored by enzyme-linked immunosorbent assay (ELISA), and various chemokines were evaluated by using multiplex cytometric bead array. Transcriptional responses were analyzed by quantitative real-time PCR. The impact on IL-1β-induced proteome was investigated by quantitative proteomics by using isobaric tags. IL-1β-induced pathways altered by IDR-1002 implicated by the proteomics analyses were further investigated by using various immunochemical assays. Cellular uptake of the peptide was monitored by using a biotinylated IDR-1002 peptide followed by microscopy probing with streptavidin-Alexa Fluor.

Results

This study demonstrated that IDR-1002 suppressed the production of IL-1β-induced MMP-3 and monocyte chemotactic protein-1 (MCP-1); in contrast, IDR-1002 enhanced the production of IL-1RA, without neutralizing all chemokine responses. IDR-1002 altered the IL-1β-induced proteome primarily by altering the expression of members of nuclear factor kappa-B (NF-κB) and c-Jun N-terminal kinase (JNK) pathways. The proteomics data also suggested that IDR-1002 was altering the transcription factor HNF-4α-mediated responses, known to be critical in metabolic regulation. With various immunochemical assays, it was further demonstrated that IL-1β-induced NF-κB, JNK, and p38 mitogen-activated protein kinase (MAPK) activations were significantly suppressed by IDR-1002.

Conclusions

This study demonstrates the ability of an innate immune-modulatory IDR-peptide to influence the IL-1β-induced regulatory pathways and selectively to suppress inflammatory responses in synovial fibroblasts. The results of this study provide a rationale for examining the use of IDR-peptides as potential therapeutic candidates for chronic inflammatory diseases such as inflammatory arthritis.

Decreases in serum levels of S100A8/9 (calprotectin) correlate with improvements in total swollen joint count in patients with recent-onset rheumatoid arthritis

INTRODUCTION

The aim of this study was to examine the serum levels of S100 proteins and to evaluate their role in patients with recent-onset rheumatoid arthritis (RA).

METHODS

Serum levels of S100A8/9 and S100A12 were analysed in 43 patients with recent-onset RA, both before and three months after the initiation of conventional treatment, as well as in 32 healthy individuals. Disease activity was assessed based on serum levels of C-reactive protein (CRP), the Disease Activity Score for 28 joints (DAS28) and the total number of swollen joints count for 66 joints (SJC).

RESULTS

The levels of serum S100A8/9 and S100A12 were significantly higher in patients with recent-onset RA compared to the levels in healthy individuals (P < 0.0001) and normalised after three months of treatment. Using age- and sex-adjusted analysis, S100A8/9 levels were correlated with CRP (r = 0.439, P < 0.01), DAS28 (r = 0.501, P = 0.002) and SJC (r = 0.443, P = 0.007), while S100A12 was less significantly correlated with these parameters. Higher levels of S100A8/9 at baseline predicted improvement in the levels of CRP and SJC over time. Moreover, decreases in serum S100A8/9 were associated with decreased serum levels of CRP (r = 0.459, P = 0.005) and improvements in SJC (r = 0.459, P = 0.005). In multiple linear regression analyses, decreases in S100A8/9 but not CRP were significant predictors for improvements in SJC (P = 0.001).

CONCLUSIONS

This study is the first to show normalisation of elevated S100 proteins in patients with recent-onset RA after the initiation of conventional treatment. Therefore, S100A8/9 might potentially be a predictive marker for improvement in the total number of swollen joints in patients in the early phase of RA.

Altered expression of TPP1 in fibroblast-like synovial cells might be involved in the pathogenesis of rheumatoid arthritis

We undertook this study to determine whether the altered expression of telomeric proteins TPP1 and POT1 in fibroblast-like synovial cells (FLS) could provide insights into the pathogenesis of rheumatoid arthritis (RA). FLS were isolated from patients with RA, osteoarthritis (OA) and traumatic joint disease, and cultured in vitro. TPP1 and POT1 mRNA level of FLS were measured using real-time quantitative polymerase chain reaction (RT-qPCR) in 42 RA, 23 OA and 13 healthy cases. Immunofluorescence staining and Western blot were used to detect the expression of TPP1 and POT1 protein. Expression of TPP1 and POT1 mRNA was significantly reduced in RA cases (P < 0.001, respectively), and no significant difference was observed between OA and healthy cases (P > 0.05, respectively). Confocal microscopy images showed TPP1 and POT1 proteins mainly located in nucleus of FLS. Western blot demonstrated that TPP1 protein level was significantly reduced in RA cases (P < 0.001), and POT1 protein expression was not statistical significance among RA, OA patients and healthy cases (P > 0.05). Significant negative correlation was observed between level of TPP1 mRNA and titers of anti-CCP antibody (P < 0.001), RF (P < 0.01). Altered expression of TPP1 might contribute to persistent proliferation of FLS in RA, further study on functions of telomeric proteins in RA would be needed.

Effects of berberine on human rheumatoid arthritis fibroblast-like synoviocytes

Activated rheumatoid arthritis fibroblast-like synoviocytes (RAFLSs) play an important role in the initiation and progression of rheumatoid arthritis (RA). Rapid proliferation and defective apoptosis of RAFLSs are two main mechanisms contributing to synovial hyperplasia. Berberine, the major constituent of Coptidis Rhizoma, has been widely used as an antitumor and anti-inflammation agent. Here we show that berberine significantly inhibited cell proliferation of serum-starved human RAFLSs in a dose-dependent manner. Cell cycle analysis of berberine-treated RAFLSs indicated a cell cycle arrest at the G0/G1 phase. The inhibitory effects of berberine correlated with an induction of cyclin-dependent kinase (CDK) inhibitors Cip1/p21 and Kip1/p27 and a reduction of CDK2, CDK4 and CDK6, and cyclins D1, D2 and E. Furthermore, an apoptosis assay showed that berberine treatment increased apoptotic death of RAFLSs, which was associated with an increased expression of proapoptotic protein Bax and decreased expression of antiapoptotic proteins Bcl-2 and Bcl-xl, disruption of mitochondrial membrane potential, and activation of caspase-3, caspase-9 and poly (ADP-ribose) polymerase. Taken together, these results demonstrate that berberine exerts antiproliferative effects against RAFLSs, likely through deregulation of numerous cell cycle and apoptosis regulators, thus having potential therapeutic implications in the treatment of RA.

Cyclic mechanical stretch downregulates IL-1β-induced COX-2 expression and PGE(2) production in rheumatoid arthritis fibroblast-like synoviocytes

In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) are one of the primary sources of inflammatory cytokines, including prostaglandins (PGs) and matrix metalloproteinases (MMPs) in joints that are detrimental to the bone, cartilage, and the surrounding tissue. Many studies, in recent years, have shown that physiotherapies play a beneficial effect on the maintenance of joint homeostasis in RA; however, the underlying mechanisms involved are still not fully elucidated. This study was performed to investigate cellular mechanism of mechanical strain-mediated actions in RA-FLS. RA-FLS were grown on collagen-coated silicone membranes and were exposed to 6% cyclic mechanical stretch at a frequency of 0.5 Hz for different times in the presence/absence of IL-1β. Real-time PCR and western blotting were used to detect the mRNA and protein level of cyclooxygenase-2 (COX-2) and MMP-1. The production of prostaglandin E(2) (PGE(2)) was quantified by ELISA method. Our results showed that 6% cyclic mechanical stretch significantly inhibited IL-1β-induced MMP-1 (gene) and COX-2 (gene and protein) expression at 15, 40, and 80 min. It also downregulated the IL-1β-induced production of PGE(2). Further investigation of nuclear factor kappa B (NF-κB) signal pathway-related effectors IκB-α and IκB-β revealed that 6% cyclic stretch inhibited their IL-1β-induced degradation in cytoplasm as well as reversed their gene transcription levels. Our data suggest that gentle level of cyclic mechanical stretch exerts a protective effect on RA-FLS as it downregulates the level of MMP-1 protease, COX-2, and proinflammatory PGE(2). The underlying mechanism appears to be, in part, executed through NF-κB and its upstream effectors.

Inflammatory cytokines IL-32 and IL-17 have common signaling intermediates despite differential dependence on TNF-receptor 1

Cytokines IL-32 and IL-17 are emerging as critical players in the pathophysiology of immune-mediated chronic inflammatory diseases. It has been speculated that the molecular mechanisms governing IL-32- and IL-17-mediated cellular responses are differentially dependent on the TNF pathway. In this study, kinome analysis demonstrated that following stimulation with cytokine IL-32, but not IL-17, there was increased phosphorylation of a peptide target corresponding to TNF-R1. Consistent with this observation, blocking TNF-R1 resulted in a suppression of IL-32-induced downstream responses, indicating that IL-32-mediated activity may be dependent on TNF-R1. In contrast, blocking TNF-R1 did not affect IL-17-induced downstream responses. Kinome analysis also implicated p300 (transcriptional coactivator) and death-associated protein kinase-1 (DAPK-1) as signaling intermediates for both IL-32 and IL-17. Phosphorylation of p300 and DAPK-1 upon stimulation with either IL-32 or IL-17 was confirmed by immunoblots. The presence of common targets was supported by results demonstrating similar downstream responses induced in the presence of IL-32 and IL-17, such as transcriptional responses and the direct activation of NF-κB. Furthermore, knockdown of p300 and DAPK-1 altered downstream responses induced by IL-32 and IL-17, and impacted certain cellular responses induced by TNF-α and IL-1β. We hypothesize that p300 and DAPK-1 represent nodes where the inflammatory networks of IL-32 and IL-17 overlap, and that these proteins would affect both TNF-R1-dependent and -independent pathways. Therefore, p300 and DAPK-1 are viable potential therapeutic targets for chronic inflammatory diseases.

Evaluation of SV40-transformed synovial fibroblasts in the study of rheumatoid arthritis pathogenesis

The SV40 T antigen has been used to generate immortalized cells from rheumatoid arthritis (RA) synovial fibroblasts (RASFs) that are commonly used in lieu of primary RASFs. In the current study, we investigated the effect of stimulation by tissue necrosis factor alpha (TNF-α) and interleukin 17 (IL-17) on primary and immortalized RASFs in order to gauge the appropriateness of the use of immortalized RASFs, the MH7A cell line, in the study of RA pathogenesis. Changes in the levels of secretion and expression of 8 proteins associated with RA upon stimulation were assessed by multiplex immunoassay. IL-17 stimulation had a minimal impact on protein secretion and expression for primary and immortalized cells. Basic fibroblast growth factor (FGF-2) was not detectable for the primary cells but was detectable for the immortalized cells. In contrast, monocyte chemoattractant protein 1 (MCP-1) was detectable for primary cells but was undetectable for immortalized cells. In general, protein expression and secretion by cells stimulated with TNF-α were significantly increased. For primary cells, several proteins were below the limit of detection for unstimulated cells and cells stimulated with IL-17, while levels for TNF-α-stimulated cells were within the detectable range. For the same proteins, expression was observed for immortalized cells, regardless of stimulation, suggestive of constitutive activation of the NF-κB signaling pathway. The current study therefore provides strong evidence that immortalized and primary RASFs differ in regard to protein expression and secretion and therefore may not be appropriate for use in the study of RA pathogenesis.

The tumour-associated glycoprotein podoplanin is expressed in fibroblast-like synoviocytes of the hyperplastic synovial lining layer in rheumatoid arthritis

Introduction

Activated fibroblast-like synoviocytes (FLSs) in rheumatoid arthritis (RA) share many characteristics with tumour cells and are key mediators of synovial tissue transformation and joint destruction. The glycoprotein podoplanin is upregulated in the invasive front of several human cancers and has been associated with epithelial-mesenchymal transition, increased cell migration and tissue invasion. The aim of this study was to investigate whether podoplanin is expressed in areas of synovial transformation in RA and especially in promigratory RA-FLS.

Methods

Podoplanin expression in human synovial tissue from 18 RA patients and nine osteoarthritis (OA) patients was assessed by immunohistochemistry and confirmed by Western blot analysis. The expression was related to markers of synoviocytes and myofibroblasts detected by using confocal immunofluoresence microscopy. Expression of podoplanin, with or without the addition of proinflammatory cytokines and growth factors, in primary human FLS was evaluated by using flow cytometry.

Results

Podoplanin was highly expressed in cadherin-11-positive cells throughout the synovial lining layer in RA. The expression was most pronounced in areas with lining layer hyperplasia and high matrix metalloproteinase 9 expression, where it coincided with upregulation of α-smooth muscle actin (α-sma). The synovium in OA was predominantly podoplanin-negative. Podoplanin was expressed in 50% of cultured primary FLSs, and the expression was increased by interleukin 1β, tumour necrosis factor α and transforming growth factor β receptor 1.

Conclusions

Here we show that podoplanin is highly expressed in FLSs of the invading synovial tissue in RA. The concomitant upregulation of α-sma and podoplanin in a subpopulation of FLSs indicates a myofibroblast phenotype. Proinflammatory mediators increased the podoplanin expression in cultured RA-FLS. We conclude that podoplanin might be involved in the synovial tissue transformation and increased migratory potential of activated FLSs in RA.

Increased phosphorylation of ezrin/radixin/moesin proteins contributes to proliferation of rheumatoid fibroblast-like synoviocytes

OBJECTIVES

Increasing evidence indicates that ezrin/radixin/moesin (ERM) proteins may play a critical role in cell proliferation. This study examined the role of ERM proteins in proliferation of fibroblast-like synoviocytes (FLS) from patients with RA.

METHODS

Synovial tissues (STs) were obtained from 18 RA and 6 OA patients. The expression of ERM and its phosphorylated proteins in cultured FLS and ST was assessed by western blots or IF staining. Small interference RNA (siRNA)-mediated ERM knockdown was used to inhibit phosphorylation of ERM. Proliferation of FLS was measured by bromodeoxyuridine (BrdU) incorporation into cell DNA and by PCNA immunoblotting.

RESULTS

Our study showed that increased phosphorylation of ERM proteins was found in ST and FLS from patients with RA as compared with OA patients and non-arthritis controls. Treatment with TNF-α, IL-1β or PDGF-induced phosphorylation of ERM proteins in dose- and time-dependent manner by RA FLS, but did not affect the expression of total ERM protein. Rho kinase and p38MAPK signal pathways were involved in TNF-α-induced ERM phosphorylation. We further showed that inhibition of ERM phosphorylation by siRNA-mediated ERM knockdown suppressed TNF-α- or IL-1β-induced BrdU incorporation and PCNA expression in RA FLS.

CONCLUSIONS

This study provides the novel evidence that increased phosphorylation of ERM proteins may contribute to proliferation of RA FLS, suggesting that specific inhibition of ERM phosphorylation may be a new therapeutic approach for RA.

The correlation between increased serum concentrations of interleukin-6 family cytokines and disease activity in rheumatoid arthritis patients

PURPOSE

This study was performed to determine whether the serum concentrations of interleukin (IL)-6 family cytokines are elevated in patients with rheumatoid arthritis (RA) and to investigate the relationship between IL-6 family cytokine levels and disease activity in RA patients.

MATERIALS AND METHODS

We obtained serum samples from 40 patients with RA and 40 age- and sex- matched healthy controls, and we assessed the clinical parameters of disease activity, including the 28-joint disease activity score (DAS28) and C-reactive protein (CRP) levels. Serum samples from five patients with high disease activity (DAS28 > 5.1) were also collected at the eighth week of treatment. Serum concentrations of IL-6, IL-11, and leukemia inhibitory factor (LIF) were measured using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Serum concentrations of IL-6 family cytokines, including IL-6, IL-11, and LIF, were significantly elevated in patients with RA compared to those of healthy controls. Although there was no significant relationship between IL-6 family cytokine levels and DAS28, the IL-6 levels of patients with RA showed a significant correlation with CRP levels. After eight weeks of medical treatment in patients with high disease activity, a decrease in DAS28 was associated with a significant decrease in the serum concentrations of IL-6 and IL-11.

CONCLUSION

The serum concentrations of IL-6 family cytokines were significantly elevated in patients with RA, and they decreased with medical treatment. These findings suggest a possible role for IL-6 family cytokines in the pathogenesis of RA.

Somatic cell plasticity and Niemann-Pick type C2 protein: fibroblast activation

A growing body of evidence points toward activated fibroblasts, also known as myofibroblasts, as one of the leading mediators in several major human pathologies including proliferative fibrotic disorders, invasive tumor growth, rheumatoid arthritis, and atherosclerosis. Niemann-Pick Type C2 (NPC2) protein has been recently identified as a product of the second gene in NPC disease. It encodes ubiquitous, highly conserved, secretory protein with the poorly defined function. Here we show that NPC2 deficiency in human fibroblasts confers their activation. The activation phenomenon was not limited to fibroblasts as it was also observed in aortic smooth muscle cells upon silencing NPC2 gene by siRNA. More importantly, activated synovial fibroblasts isolated from patients with rheumatoid arthritis were also identified as NPC2-deficient at both the NPC2 mRNA and protein levels. The molecular mechanism responsible for activation of NPC2-null cells was shown to be a sustained phosphorylation of ERK 1/2 mitogen-activated protein kinase (MAPK), which fulfills both the sufficient and necessary fibroblast activation criteria. All of these findings highlight a novel mechanism where NPC2 by negatively regulating ERK 1/2 MAPK phosphorylation may efficiently suppress development of maladaptive tissue remodeling and inflammation.

Silencing the expression of Ras family GTPase homologues decreases inflammation and joint destruction in experimental arthritis

Changes in the expression and activation status of Ras proteins are thought to contribute to the pathological phenotype of stromal fibroblast-like synoviocytes (FLS) in rheumatoid arthritis, a prototypical immune-mediated inflammatory disease. Broad inhibition of Ras and related proteins has shown protective effects in animal models of arthritis, but each of the Ras family homologues (ie, H-, K-, and N-Ras) makes distinct contributions to cellular activation. We examined the expression of each Ras protein in synovial tissue and FLS obtained from patients with rheumatoid arthritis and other forms of inflammatory arthritis. Each Ras protein was expressed in synovial tissue and cultured FLS. Each homolog was also activated following FLS stimulation with tumor necrosis factor-α or interleukin (IL)-1β. Constitutively active mutants of each Ras protein enhanced IL-1β-induced FLS matrix metalloproteinase-3 production, while only active H-Ras enhanced IL-8 production. Gene silencing demonstrated that each Ras protein contributed to IL-1β-dependent IL-6 production, while H-Ras and N-Ras supported IL-1β-dependent matrix metalloproteinase-3 and IL-8 production, respectively. The overlap in contributions of Ras homologues to FLS activation suggests that broad targeting of Ras GTPases in vivo suppresses global inflammation and joint destruction in arthritis. Consistent with this, simultaneous silencing of H-Ras, K-Ras, and N-Ras expression significantly reduces inflammation and joint destruction in murine collagen-induced arthritis, while specific targeting of N-Ras alone is less effective in providing clinical benefits.

Adrenomedullin increases fibroblast-like synoviocyte adhesion to extracellular matrix proteins by upregulating integrin activation

Introduction

Rheumatoid arthritis (RA) is characterized by bone and cartilage invasion by fibroblast-like synoviocytes (FLSs). Adrenomedullin, a peptide with anabolic and antiapoptotic properties, is secreted by rheumatoid FLSs. Adrenomedullin also increases the expression of adhesion molecules in endothelial cells and keratinocytes. Here, we investigated whether adrenomedullin mediated FLS adhesion to extracellular matrix (ECM) proteins.

Methods

FLSs were isolated from synovial tissues from RA and osteoarthritis (OA) patients. Plates were coated overnight with the ECM proteins vitronectin, fibronectin, and type I collagen (Coll.I). Adrenomedullin was used as a soluble FLS ligand before plating. We tested interactions with the adrenomedullin receptor antagonist (22-52)adrenomedullin and with the protein kinase A (PKA) inhibitor H-89, and inhibition of co-receptor RAMP-2 by siRNA. Cell adhesion was measured by using color densitometry. Activation of α₂ and β₁ integrins was evaluated by fluorescent microscopy; integrin inhibition, by RGD peptides; and the talin-integrin interaction, by immunoprecipitation (IP).

Results

Adrenomedullin specifically increased RA-FLS adhesion to vitronectin, fibronectin, and Coll.I; no such effect was found for OA-FLS adhesion. Basal or adrenomedullin-stimulated RA-FLS adhesion was inhibited by (22-52)adrenomedullin, H-89, and RAMP-2 siRNA. Adrenomedullin-stimulated adhesion was inhibited by RGD peptides, and associated with α₂ and β₁ integrin activation. This activation was shown with IP to be related to an integrin-talin interaction and was significantly decreased by (22-52)adrenomedullin.

Conclusions

Adrenomedullin-stimulated RA-FLS adhesion was specific for ECM proteins and mediated by α₂ and β₁ integrins. This effect of adrenomedullin was dependent on adrenomedullin receptors. These results support a new role for adrenomedullin in rheumatoid synovial fibroblast pathobiology.

Arsenic trioxide induces apoptosis of fibroblast-like synoviocytes and represents antiarthritis effect in experimental model of rheumatoid arthritis

OBJECTIVE

recent studies have demonstrated that rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) proliferate as fiercely as tumor cells. Induction of apoptosis in RA FLS therefore provides a new approach for the inhibition of joint destruction. Arsenic trioxide (As(2)O(3)) was reported to be an effective apoptosis inducer in a variety of cell types. We investigated the possible effect of As(2)O(3) on apoptosis induction of RA FLS and the mechanisms involved in this process.

METHODS

apoptosis was determined by flow cytometric analysis, terminal deoxynucleotide transferase-mediated dUTP nick end-labeling, and transmission electron microscopy. The activity and messenger RNA (mRNA) expression of nuclear factor-κB (NF-κB) was then detected by ELISA and real-time polymerase chain reaction, respectively. Activities of caspase-3 and caspase-8 were evaluated using luminogenic substrates. The effect of As(2)O(3) on the morphology of rats with collagen-induced arthritis was evaluated under a light microscope after H&E staining.

RESULTS

as(2)O(3) significantly enhanced the apoptosis of RA FLS. It suppressed the DNA-binding activity and mRNA expression level of NF-κB, probably by inhibiting tumor necrosis factor-α-induced activation of NF-κB. As(2)O(3) treatment significantly increased the activity of both caspase-3 and caspase-8. Morphological analysis revealed histological recovery in the synovial membrane. Synovial hyperplasia and inflammation in the joints were effectively inhibited.

CONCLUSION

as(2)O(3) represents an apoptotic effect on RA FLS through NF-κB signaling pathway, and this process is mediated by the activation of caspase cascade. Treatment with As(2)O(3) significantly improved the pathologic changes of collagen-induced arthritis and may have potential for treatment of RA.

BRAF drives synovial fibroblast transformation in rheumatoid arthritis

Synovial fibroblasts destroy articular cartilage and bone in rheumatoid arthritis, but the mechanism of fibroblast transformation remains elusive. Because gain-of-function mutations of BRAF can transform fibroblasts, we examined BRAF in rheumatoid synovial fibroblasts. The strong gain-of-function mutation, V600R, of BRAF found in melanomas and other cancers was identified in first passage synovial fibroblasts from two of nine rheumatoid arthritis patients and confirmed by restriction site mapping. BRAF-specific siRNA inhibited proliferation of synovial fibroblasts with V600R mutations. A BRAF aberrant splice variant with an intact kinase domain and partial loss of the N-terminal autoinhibitory domain was identified in fibroblasts from an additional patient, and fibroblast proliferation was inhibited by BRAF-specific siRNA. Our finding is the first to establish mechanisms for fibroblast transformation responsible for destruction of articular cartilage and bone in rheumatoid arthritis and establishes a new target for therapeutic intervention.

Ionic currents in intimal cultured synoviocytes from the rabbit

Hyaluronan, a joint lubricant and regulator of synovial fluid content, is secreted by fibroblast-like synoviocytes lining the joint cavity, and secretion is greatly stimulated by Ca²⁺-dependent protein kinase C. This study aimed to define synoviocyte membrane currents and channels that may influence synoviocyte Ca²⁺ dynamics. Resting membrane potential ranged from −30 mV to −66 mV (mean −45 ± 8.60 mV, n = 40). Input resistance ranged from 0.54 GΩ to 2.6 GΩ (mean 1.28 ± 0.57 GΩ; ν = 33). Cell capacitance averaged 97.97 ± 5.93 pF. Voltage clamp using C^s+ pipette solution yielded a transient inward current that disappeared in Ca²⁺-free solutions and was blocked by 1 μM nifedipine, indicating an L-type calcium current. The current was increased fourfold by the calcium channel activator FPL 64176 (300 nM). Using K⁺ pipette solution, depolarizing steps positive to −40 mV evoked an outward current that showed kinetics and voltage dependence of activation and inactivation typical of the delayed rectifier potassium current. This was blocked by the nonspecific delayed rectifier blocker 4-aminopyridine. The synoviocytes expressed mRNA for four Kv1 subtypes (Kv1.1, Kv1.4, Kv1.5, and Kv1.6). Correolide (1 μM), margatoxin (100 nM), and α-dendrotoxin block these Kv1 subtypes, and all of these drugs significantly reduced synoviocyte outward current. The current was blocked most effectively by 50 nM κ-dendrotoxin, which is specific for channels containing a Kv1.1 subunit, indicating that Kv1.1 is critical, either as a homomultimeric channel or as a component of a heteromultimeric Kv1 channel. When 50 nM κ-dendrotoxin was added to current-clamped synoviocytes, the cells depolarized by >20 mV and this was accompanied by an increase in intracellular calcium concentration. Similarly, depolarization of the cells with high external potassium solution caused an increase in intracellular calcium, and this effect was greatly reduced by 1 μM nifedipine. In conclusion, fibroblast-like synoviocytes cultured from the inner synovium of the rabbit exhibit voltage-dependent inward and outward currents, including Ca²⁺ currents. They thus express ion channels regulating membrane Ca²⁺ permeability and electrochemical gradient. Since Ca²⁺-dependent kinases are major regulators of synovial hyaluronan secretion, the synoviocyte ion channels are likely to be important in the regulation of hyaluronan secretion.

Critical role for apoptosis signal-regulating kinase 1 in the development of inflammatory K/BxN serum-induced arthritis

In this report, we show that apoptosis signal-regulating kinase 1(-/-) (ASK1 KO) mice were resistant to inflammatory arthritis induced in the K/BxN serum transfer model of rheumatoid arthritis (RA). The p38 inhibitor, SD-0006 was administered to wild type (WT) mice as a comparator. Both ASK1 KO and p38 inhibition resulted in marked attenuation of edema, cartilage damage, bone resorption, and general inflammatory responses. Transcriptional profiling of mRNA prepared from paw tissue demonstrated that the production of many proinflammatory genes including cytokines, chemokines, and extracellular matrix degradative enzymes were maintained at basal levels by either ASK1 KO or prophylactic p38 MAPK inhibition. In the mouse whole blood (MWB) assay, tumor necrosis factor-α (TNF-α)-induced KC and CCL2 levels and also LPS-induced interleukin-6 (IL-6), CCL2, and KC levels in MWB from ASK1 KO were significantly lower than those from WT. Furthermore, both p38 and JNK were activated by TNF-α in human synovial fibroblasts isolated from RA patients (RASF). SD-0006 or SP600125, a JNK inhibitor, partially blocked the elevation of IL-6 production in RASF following stimulation with TNF-α. In contrast, dual inhibition with both p38/JNK inhibitors almost completely abolished TNF-α-induced IL-6 production from these cells. Ablation of ASK1 expression in RASF using siRNA for ASK1 resulted in inhibition of TNF-α-induced IL-6 and PGE(2) production. This study is the first to suggest that ASK1 is critical for the development of RA and that ASK1 may be involved in the production of proinflammatory mediators in response to TNF-α stimulation in the RA joint.

Synovial tissue hypoxia and inflammation in vivo

INTRODUCTION

Hypoxia is a microenvironmental feature in the inflamed joint, which promotes survival advantage for cells. The aim of this study was to examine the relationship of partial oxygen pressure in the synovial tissue (tPO(2)) in patients with inflammatory arthritis with macroscopic/microscopic inflammation and local levels of proinflammatory mediators.

METHODS

Patients with inflammatory arthritis underwent full clinical assessment and video arthroscopy to quantify macroscopic synovitis and measure synovial tPO(2) under direct visualisation. Cell specific markers (CD3 (T cells), CD68 (macrophages), Ki67 (cell proliferation) and terminal deoxynucleotidyl transferase dUTP nick end labelling (cell apoptosis)) were quantified by immunohistology. In vitro migration was assessed in primary and normal synoviocytes (synovial fibroblast cells (SFCs)) using a wound repair scratch assay. Levels of tumour necrosis factor alpha (TNFalpha), interleukin 1beta (IL1beta), interferon gamma (IFNgamma), IL6, macrophage inflammatory protein 3alpha (MIP3alpha) and IL8 were quantified, in matched serum and synovial fluid, by multiplex cytokine assay and ELISA.

RESULTS

The tPO(2) was 22.5 (range 3.2-54.1) mm Hg and correlated inversely with macroscopic synovitis (r=-0.421, p=0.02), sublining CD3 cells (-0.611, p<0.01) and sublining CD68 cells (r=-0.615, p<0.001). No relationship with cell proliferation or apoptosis was found. Primary and normal SFCs exposed to 1% and 3% oxygen (reflecting the median tPO(2) in vivo) induced cell migration. This was coupled with significantly higher levels of synovial fluid tumour necrosis factor alpha (TNFalpha), IL1beta, IFNgamma and MIP3alpha in patients with tPO(2) <20 mm Hg (all p values <0.05).

CONCLUSIONS

This is the first study to show a direct in vivo correlation between synovial tPO(2), inflammation and cell migration, thus it is proposed that hypoxia is a possible primary driver of inflammatory processes in the arthritic joint.

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.

Histone deacetylase inhibitors MS-275 and SAHA induced growth arrest and suppressed lipopolysaccharide-stimulated NF-kappaB p65 nuclear accumulation in human rheumatoid arthritis synovial fibroblastic E11 cells

OBJECTIVES

MS-275 and suberoylanilide hydroxamic acid (SAHA) are histone deacetylase (HDAC) inhibitors currently tested in oncology trials. They have also been found to display potent anti-rheumatic activities in rodent models for RA. However, the anti-rheumatic mechanisms of action remain unknown. The study was carried out with the intent of determining the anti-inflammatory and anti-rheumatic mechanisms of the HDAC inhibitors.

METHODS

In this study, the anti-rheumatic mechanisms of MS-275 and SAHA were investigated in several cell culture models.

RESULTS

MS-275 and SAHA inhibited human RA synovial fibroblastic E11 cell proliferation in a non-cytotoxic manner. The anti-proliferative activities were associated with G(0)/G(1) phase arrest and induction of cyclin-dependent kinase inhibitor p21. In addition, MS-275 and SAHA suppressed lipopolysaccharide (LPS)-induced NF-kappaB p65 nuclear accumulation, IL-6, IL-18 and nitric oxide (NO) secretion as well as down-regulated pro-angiogenic VEGF and MMP-2 and MMP-9 production in E11 cells at sub-micromolar levels. At similar concentrations, MS-275 and SAHA suppressed LPS-induced NF-kappaB p65 nuclear accumulation and IL-1beta, IL-6, IL-18 and TNF-alpha secretion in THP-1 monocytic cells. Moreover, NO secretion in RAW264.7 macrophage cells was also inhibited.

CONCLUSIONS

In summary, MS-275 and SAHA exhibited their anti-rheumatic activities by growth arrest in RA synovial fibroblasts, inhibition of pro-inflammatory cytokines and NO, as well as down-regulation in angiogenesis and MMPs. Their anti-rheumatic activities may be mediated through induction of p21 and suppression of NF-kappaB nuclear accumulation.

Slit3 inhibits Robo3-induced invasion of synovial fibroblasts in rheumatoid arthritis

Introduction

The repellent factor family of Slit molecules has been described to have repulsive function in the developing nervous system on growing axons expressing the Robo receptors. However, until today no data are available on whether these repellent factors are involved in the regulation of synovial fibroblast (SF) activity in rheumatoid arthritis (RA).

Methods

mRNA expression in primary synovial fibroblasts was quantified by quantitative reverse transcription PCR and protein expression was measured by fluorescence activated cell sorting (FACS) analysis. Different functional assays were performed with rheumatoid arthritis synovial fibroblasts (RASF): proliferation, migration and a novel in-vitro cartilage destruction assay.

Results

First, we found increased expression of Robo3 expression in RASF compared to normal SF. Interestingly, analysis of data from a recently published genome-wide association study suggests a contribution of ROBO3 gene polymorphisms to susceptibility of RA. Functional assays performed with RASF revealed induction of migration and cartilage destruction by Robo3 and increased matrix metalloproteinase (MMP)1 and MMP3 expression. Treatment of RASF in early passages with Slit3 led to inhibition of migration whereas RASF in later passages, having reduced Robo3 expression in cell culture, were not inhibited by Slit3 treatment. Here, reduction of Robo3 expression from passage 3 to 10 might reflect an important step in losing repulsive activity of Slit3.

Conclusions

Taken together, our data showed that deregulation of the Robo3 receptor in synovial fibroblasts in RA correlates with aggressiveness of the fibroblasts. Slit3 reduces the migratory activity of synovial cells from patients with RA, potentially by repulsion of the cells in analogy to the neuronal system. Further studies will be necessary to prove Slit activity in vivo.

Akt activity protects rheumatoid synovial fibroblasts from Fas-induced apoptosis by inhibition of Bid cleavage

Introduction

Synovial hyperplasia is a main feature of rheumatoid arthritis pathology that leads to cartilage and bone damage in the inflamed joints. Impaired apoptosis of resident synoviocytes is pivotal in this process. Apoptosis resistance seems to involve defects in the extrinsic and intrinsic apoptotic pathways. The aim of this study was to investigate the association of PI3Kinase/Akt and the mitochondrial apoptotic pathway in the resistance of rheumatoid arthritis (RA) fibroblast like synovial cells (FLS) to Fas-mediated apoptosis.

Methods

Apoptosis was assessed by ELISA quantification of nucleosomal release, Hoechst staining and activated caspase-3/7 measure in cultured RA FLS stimulated with anti-Fas antibody. Two Phosphoinositol-3-kinase/protein Kinase B (PI3 Kinase) inhibitors, Wortmannine and LY294002, were used before anti-Fas stimulation. Proapoptotic BH3 interacting domain death agonist (Bid) was suppressed in RA FLS by small interfering RNA (siRNA) transfection. Bid was overexpressed by transfection with the pDsRed2-Bid vector. Phosphorylated Akt, caspase-9, and Bid expression were analysed by western blot.

Results

PI3 kinase inhibition sensitizes RA FLS to Fas-induced apoptosis by increasing cleavage of Bid protein. Bid suppression completely abrogated Fas-induced apoptosis and Bid overexpression highly increased apoptotic rate of RA FLS in association with cleavage of caspase-9.

Conclusions

In RA FLS, phosphorylation of Akt protects against Fas-induced apoptosis through inhibition of Bid cleavage. The connection between the extrinsic and the intrinsic apoptotic pathways are critical in this Fas- mediated apoptosis and points to PI3Kinase as potential therapeutic target for RA.

Synovial fibroblasts spread rheumatoid arthritis to unaffected joints

Active rheumatoid arthritis originates from few joints but subsequently affects the majority of joints. Thus far, the pathways of the progression of the disease are largely unknown. As rheumatoid arthritis synovial fibroblasts (RASFs) which can be found in RA synovium are key players in joint destruction and are able to migrate in vitro, we evaluated the potential of RASFs to spread the disease in vivo. To simulate the primary joint of origin, we implanted healthy human cartilage together with RASFs subcutaneously into severe combined immunodeficient (SCID) mice. At the contralateral flank, we implanted healthy cartilage without cells. RASFs showed an active movement to the naive cartilage via the vasculature independent of the site of application of RASFs into the SCID mouse, leading to a marked destruction of the target cartilage. These findings support the hypothesis that the characteristic clinical phenomenon of destructive arthritis spreading between joints is mediated, at least in part, by the transmigration of activated RASFs.

Oral administration of curcumin suppresses production of matrix metalloproteinase (MMP)-1 and MMP-3 to ameliorate collagen-induced arthritis: inhibition of the PKCdelta/JNK/c-Jun pathway

We investigated whether oral administration of curcumin suppressed type II collagen-induced arthritis (CIA) in mice and its effect and mechanism on matrix metalloproteinase (MMP)-1 and MMP-3 production in CIA mice, RA fibroblast-like synoviocytes (FLS), and chondrocytes. CIA in mice was suppressed by oral administration of curcumin in a dose-dependent manner. Macroscopic observations were confirmed by histological examinations. Histological changes including infiltration of immune cells, synovial hyperplasia, cartilage destruction, and bone erosion in the hind paw sections were extensively suppressed by curcumin. The histological scores were consistent with clinical arthritis indexes. Production of MMP-1 and MMP-3 were inhibited by curcumin in CIA hind paw sections and tumor necrosis factor (TNF)-alpha-stimulated FLS and chondrocytes in a dose-dependent manner. As for the mechanism, curcumin inhibited activating phosphorylation of protein kinase Cdelta (PKCdelta) in CIA, FLS, and chondrocytes. Curcumin also suppressed the JNK and c-Jun activation in those cells. This study suggests that the suppression of MMP-1 and MMP-3 production by curcumin in CIA is mediated through the inhibition of PKCdelta and the JNK/c-Jun signaling pathway.

Metastasis-inducing S100A4 protein is associated with the disease activity of rheumatoid arthritis

OBJECTIVES

To evaluate the association between metastasis-inducing protein S100A4 and disease activity in patients with RA, and to demonstrate the effect of TNF-alpha blocking therapy on plasma levels of S100A4 in these patients.

METHODS

Plasma levels of the S100A4 protein were analysed in 40 anti-TNF-alpha naive patients with active RA. Of the 40 patients, 25 were treated with adalimumab and monitored over time. The conformational form of S100A4 was analysed using size-exclusion gel chromatography. TNF-alpha mRNA expression and protein synthesis were analysed by RT-PCR and ELISA, respectively.

RESULTS

Baseline levels of S100A4 were significantly correlated with disease activity in RA patients (r = 0.41; P < 0.01). After 12 weeks of treatment with adalimumab, there was an obvious shift in the conformations of S100A4 from the multimeric to the dimeric forms, whereas the total levels of the S100A4 protein remained unchanged. This suggests that the bioactive (multimer) S100A4 may decline in response to successful treatment with adalimumab. In addition, we showed significant up-regulation of TNF-alpha mRNA (P < 0.01), and protein release to the cell culture medium of monocytes stimulated with the S100A4 multimer compared with those treated with the dimer and to the unstimulated monocytes (P < 0.001).

CONCLUSIONS

This is the first study to show that the levels of the S100A4 protein are correlated with RA disease activity. Furthermore, only the bioactive form, but not the total amount of S100A4, decreases after successful TNF-alpha blocking therapy in patients with RA. These data support an important role for the S100A4 multimer in the pathogenesis of RA.

Different expression levels of TNF receptors on the rheumatoid synovial macrophages derived from surgery and a synovectomy as detected by a new flow cytometric analysis

TNFalpha plays a crucial role in the pathogenesis of rheumatoid arthritis. It is very important to examine the expression of the TNF receptors, the ligand of TNFalpha. In this study, we developed a triple-color flow cytometric analysis using CD45 and CD14 monoclonal antibodies to simply detect the expression of the TNF receptors on the heterogeneous rheumatoid synovial cells. Using this system, we detected a higher population of macrophages and a greater TNF receptor expression on the synovial macrophages derived from a synovectomy in comparison to the findings obtained from knee joint replacement surgery.