Contribution of synovial mesenchymal cells to the pathogenesis of rheumatoid arthritis

Modulation of Apoptosis and Differentiation by the Treatment of Sulfasalazine in Rabbit Articular Chondrocytes

This study was conducted to examine the cellular regulatory mechanisms of sulfasalazine (SSZ) in rabbit articular chondrocytes treated with sodium nitroprusside (SNP). Cell phenotype was determined, and the MTT assay, Western blot analysis and immunofluorescence staining of type II collagen was performed in control, SNP-treated and SNP plus SSZ (50~200 μg/mL) rabbit articular chondrocytes. Cellular proliferation was decreased significantly in the SNP-treated group compared with that in the control (p < 0.01). SSZ treatment clearly increased the SNP-reduced proliferation levels in a concentration-dependent manner (p < 0.01). SNP treatment induced significant dedifferentiation and inflammation compared with control chondrocytes (p < 0.01). Type II collagen expression levels increased in a concentration-dependent manner in response to SSZ treatment but were unaltered in SNP-treated chondrocytes (p < 0.05 and < 0.01, respectively). Cylooxygenase-2 (COX-2) expression increased in a concentration-dependent manner in response to SSZ treatment but was unaltered in SNP-treated chondrocytes (p < 0.05). Immunofluorescence staining showed that SSZ treatment increased type II collagen expression compared with that in SNP-treated chondrocytes. Furthermore, phosphorylated extracellular regulated kinase (pERK) expression levels were decreased significantly in the SNP-treated group compared with those in control chondrocytes (p < 0.01). Expression levels of pERK increased in a concentration-dependent manner by SSZ but were unaltered in SNP-treated chondrocytes. pp38 kinase expression levels increased in a concentration-dependent manner by SSZ but were unaltered in control chondrocytes (p < 0.01). In summary, SSZ significantly inhibited nitric oxide-induced cell death and dedifferentiation, and regulated extracellular regulated kinases 1 and 2 and p38 kinase in rabbit articular chondrocytes.

The potential role of angiogenic factors in rheumatoid arthritis

Angiogenesis is an important phenomenon in the pathogenesis of some diseases, such as numerous types of tumors and autoimmunity, and also a number of soluble and cell-bound factors may stimulate neovascularization in inflammatory reaction processes. Here, by highlighting the significance of angiogenesis reaction in rheumatoid arthritis (RA), we will mainly focus on the role of various growth factors, cytokines, enzymes, cells, hypoxic conditions and transcription factors in the angiogenic process and we will then explain some therapeutic strategies based on blockage of angiogenesis and modification of the vascular pathology in RA.

Bone marrow cells carrying the env-pX transgene play a role in the severity but not prolongation of arthritis in human T-cell leukaemia virus type-I transgenic rats: a possible role of articular tissues carrying the transgene in the prolongation of arthritis

Transgenic rats carrying the env-pX gene of human T-cell leukaemia virus type-I (env-pX rats) were immunized with type II collagen (CII), and chronological alterations of arthritis were compared with findings of collagen-induced arthritis (CIA) in wildtype Wistar-King-Aptekman-Hokudai (WKAH) rats. Arthritis induced by CII in env-pX rats was more severe and persisted longer than CIA in WKAH rats. To determine whether the phenomenon is caused mainly by the transgene-carrying lymphocytes or articular tissues, we immunized lethally irradiated env-pX and WKAH rats with reciprocal bone marrow cell (BMC) transplantation. A severe but transient arthritis was induced by CII in WKAH rats reconstituted by env-pX BMC (w/tB/CII rats). On the other hand, in env-pX rats reconstituted by WKAH BMC, arthritis persisted longer than in w/tB/CII rats, although the degree was less at an early phase after CII immunization. These findings suggest that articular tissues rather than the BMCs carrying the env-pX transgene play a role in the prolongation of arthritis in env-pX rats, although BMCs carrying the transgene are associated with the severity of arthritis. When inflammatory cytokines in synovial cells isolated from env-pX rats before they developed arthritis were examined, interleukin-6 (IL-6) was detected at a higher level than in synovial cells from WKAH rats, thus suggesting the critical role of IL-6 in env-pX arthritis.

Active leflunomide metabolite inhibits interleukin 1beta, tumour necrosis factor alpha, nitric oxide, and metalloproteinase-3 production in activated human synovial tissue cultures

BACKGROUND

Leflunomide is now an approved agent for the management of adult rheumatoid arthritis (RA). Its active metabolite A771726 inhibits de novo pyrimidine biosynthesis. Although considered to be an immunosuppressive agent, its mechanism of action remains obscure.

OBJECTIVES

Evaluation of the leflunomide active metabolite A771726 (LEF) effect on interleukin 1beta (IL1beta), tumour necrosis factor (TNFalpha), nitric oxide (NO), and stromelysin (metalloproteinase-3 (MMP-3)) production by activated human synovial tissue in culture.

METHODS

Synovial tissue was obtained during surgery from patients undergoing total knee replacement owing to RA or osteoarthritis (OA), cut into small pieces, and cultured in Petri dishes with test materials as previously described. IL1beta, TNFalpha, NO, and MMP-3 were measured in the culture media after 48 hours incubation with different doses of LEF by methods previously described.

RESULTS

LEF (0.3, 3, and 9 micro g/ml) inhibited IL1beta production in the presence of lipopolysaccharide (LPS; 3 micro g/ml) in a dose dependent manner (p<0.01) at LEF 0.3 micro g/ml. TNFalpha production in the presence of IL1beta (1 ng/ml) was also inhibited in a dose dependent manner (p<0.05 at LEF 0.3 micro g/ml). NO and MMP-3 production in the presence of LPS (3 micro g/ml) was inhibited as well (p<0.01 at LEF 1 micro g/ml and at LEF 0.3 micro g/ml, respectively). Synovial cell viability evaluated by the tetrazolium salt XTT was unaffected by the LEF concentration used. There was no qualitative difference in the response of OA and RA synovial tissue.

CONCLUSION

Leflunomide may modulate the rheumatoid articular process by inhibition of local production of IL1beta, TNFalpha, NO, and MMP-3.

Matrix metalloproteinase production by COOH-terminal heparin-binding fibronectin fragment in rheumatoid synovial cells

Fibronectin with IIICS region is present in rheumatoid synovium, and fibronectin fragments are increased in rheumatoid joints. We investigated the ability of COOH-terminal heparin-binding fibronectin fragment (COOH-HBFN-f) containing IIICS to induce matrix metalloproteinase (MMP) production and the role of mitogen-activated protein kinase (MAPK) pathway and CS-1 sequence that can bind alpha4beta1 integrin in MMP induction by COOH-HBFN-f in rheumatoid synovial fibroblasts (RSF). When RSF in monolayer culture were incubated with COOH-HBFN-f, COOH-HBFN-f stimulated the production of MMP-1, MMP-3, and MMP-13 by RSF in association with activation of extracellular signal-regulated kinase, p38 MAPK, and c-Jun NH(2)-terminal kinase. Immunoprecipitation of cell lysates demonstrated the presence of alpha4 integrin in cultured RSF. Similar to COOH-HBFN-f, treatment with CS-1 synthetic peptide derived from IIICS resulted in increased MMP production and activation of the kinases, although the MMP levels were low. Preincubation of RSF with anti-alpha4 integrin antibody resulted in partial suppression of the COOH-HBFN-f-stimulated MMP production. Inhibition studies using protein kinase inhibitors (PD98059 and SB203580) showed that those MAPK pathways contributed to MMP up-regulation by COOH-HBFN-f and CS-1. Thus, the present results have clearly shown that COOH-HBFN-f and CS-1 stimulate MMP production in association with activation of MAPK pathways in RSF. Integrin alpha4beta1 may be partially involved in the MMP induction by COOH-HBFN-f.

A role for angiogenesis in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic debilitating disease characterized by distinct autoimmune, inflammatory and fibrovascular components which lead to synovial proliferation and joint destruction. However, existing treatments specifically target only autoimmune and inflammatory components despite the fact that neovascularization of the inflamed synovium is a hallmark of rheumatoid arthritis. Angiogenesis may contribute to synovial growth, leukocyte recruitment and tissue remodeling, thus potentiating disease progression. Although no therapies currently target angiogenesis, several existing therapies have anti-angiogenic activity. Recent advances in anti-angiogenic strategies in oncology, including the identification of integrin alpha v beta 3 as a crucial effector of angiogenesis, suggest a means to assess the role of angiogenesis in rheumatoid arthritis. Synovial endothelial cells have been shown to express integrin alpha v beta 3, suggesting that these cells may be targeted for angiogenesis inhibition. Prior studies in rat arthritis models have shown benefit after the addition of broad spectrum integrin antagonists. However, formal assessment of integrin-targeted anti-angiogenic activity is now underway. These controlled studies will be important in assessing the efficacy of therapies which target angiogenesis in RA.

Transcriptional regulation of the HOX4C gene by basic fibroblast growth factor on rheumatoid synovial fibroblasts

OBJECTIVE

To examine the expression of genes of the HOX D cluster in the synovial tissue of patients with rheumatoid arthritis (RA), and to determine whether basic fibroblast growth factor (bFGF) influences the expression and transcriptional regulation of the gene.

METHODS

The expression of genes of the HOX D cluster, including HOX4C, HOX4D, HOX4H, and HOX4I, was determined in the synovium of 4 patients with RA and 4 with osteoarthritis (OA) by in situ reverse transcription (RT) and RT-polymerase chain reaction (RT-PCR). The induction of HOX4C messenger RNA (mRNA) by bFGF was determined by RT-PCR. The binding activity of a transcriptional regulator of the HOX4C gene, C2, was analyzed by the mobility shift assay. NIH-3T3 cells transfected with a construct containing C2 binding sequence were incubated with bFGF, and the activity of the reporter was measured by luciferase assay.

RESULTS

Using an in situ RT assay, specific expression of HOX4C mRNA was detected in 3 of 4 RA synovial samples, whereas none of the OA synovia expressed HOX4C. HOX4D, HOX4H, and HOX4I genes were expressed in all synovial samples from RA and OA patients. The presence of HOX4C mRNA was also confirmed by RT-PCR and Southern blotting. Treatment with bFGF increased the expression of HOX4C mRNA in RA fibroblasts. The mobility shift assay and luciferase assay showed that bFGF enhanced C2 binding activity and significantly increased the transcriptional activity on RA fibroblasts.

CONCLUSION

Our findings suggest that HOX4C is involved in synovial hyperplasia, and that the transcriptional regulation of HOX4C genes by bFGF may play a crucial role in the pathogenesis of RA.

TGFbeta1 regulates gene expression of its own converting enzyme furin

TGFbeta1 is known for its potent and diverse biological effects, including immune regulation, and cell growth and differentiation. We have recently shown that TGFbeta1 precursor is processed by human furin COOH-terminal to the R-H-R-R278 cleavage site to generate authentic mature TGFbeta1. In the present study, we demonstrate that steady-state furin mRNA levels are increased in rat synovial cells by 2 and 20 ng/ml TGFbeta1. Stimulation with TGFbeta1 results in a significant increase in furin mRNA levels, starting at 3 h with the peak effect observed at 12 h (2.5-fold increase +/-0.4). TGFbeta1 did not increase furin mRNA stability, and treatment of synovial cells with actinomycin D, before TGFbeta1 addition prevented the increase in fur gene expression, suggesting that the observed regulation occurs at the level of gene transcription. Treatment of synovial and NRK-49F fibroblastic cells with exogenous TGFbeta1 (5 ng/ml) or TGFbeta2 (10 ng/ml) translates into an increase in pro-TGFbeta1 processing as evidenced by the appearance of a 40-kD immunoreactive band corresponding to the TGFbeta1 NH2-terminal pro-region. Furin processing activity stimulated by TGFbeta2 correlates with significant increase in extracellular mature and heat-activable TGFbeta1 as determined by an isoform-specific ELISA assay. Taken together, these results demonstrate for the first time that TGFbeta1 upregulates gene expression of its own converting enzyme, and that this expression is translated into augmented processing of the TGFbeta1 precursor form. Such adaptive responsiveness of the TGFbeta1 convertase may represent an important aspect of TGFbeta1 bioavailibility in TGFbeta1-related processes and pathological conditions.

Characterisation of fibroblast-like cells in pannus lesions of patients with rheumatoid arthritis sharing properties of fibroblasts and chondrocytes

OBJECTIVE

To better understand the characteristics of synoviocytes located in the rheumatoid arthritis (RA) pannus.

METHODS

One cell line, termed PSC, was cloned from RA pannus lesions. Phenotypic analysis was done by contrast microscopy, indirect immunostaining, and safranin O staining. Transcription of several protooncogenes and matrix degrading enzymes was evaluated. The expression of mRNA for collagen II was detected by in situ hybridisation. The ability of anchorage independent growth was assessed by soft agarose culture.

RESULTS

PSCs showed a high transcription of protooncogenes c-fos, c-myc and c-jun. They also expressed mRNA for matrix degrading enzymes, such as collagenase, cathepsin B, and cathepsin L. Anchorage independent growth assay demonstrated that PSCs formed colonies in soft agar culture. Phenotypic analysis showed that this fibroblast-like PSC was stained intensely with anti-vimentin and anti-fibroblast antibody. In situ reverse transcriptase assay showed that the cell line expressed type II collagen mRNA.

CONCLUSION

Alternative fibroblast-like cells were identified in the pannus lesion of RA sharing properties of fibroblasts and chondrocytes. These findings suggest that this fibroblast-like cell derived from pannus lesions may contribute to the destruction of the cartilage in RA.

Studies on the contribution of c-fos/AP-1 to arthritic joint destruction

Features characteristic to rheumatoid joint destruction, including synovial overgrowth and bone resorption, are experimentally produced by augmenting c-fos gene expression. We tested here if arthritic joint destruction was inhibited upon inactivation of the c-fos/AP-1 signal by administering short double-stranded AP-1 DNA oligonucleotides into mice with collagen-induced arthritis to compete for the binding of AP-1 in vivo at the promoter binding site. Arthritic joint destruction was inhibited in a sequence-specific and dose-dependent manner by oligonucleotides containing the AP-1 sequence. The oligonucleotides inhibited gene expression at the transcriptional level. Nucleotide sequences besides AP-1 also appeared to be important structurally for binding of AP-1 onto DNA and for the stability of oligonucleotides against nucleases. Immunohistochemical chase experiment administering biotinylated oligonucleotides into arthritic mice showed that AP-1 oligonucleotides reached the inflamed joint. Thus, activation of c-fos/AP-1 appears essentially important in arthritic joint destruction.

Rheumatoid arthritis as a bone marrow disorder

Both the concept of rheumatoid arthritis (RA) as an autoimmune process restricted to joints and the major role of T cells in its pathogenesis have been challenged in the literature. Fibroblastlike and macrophagelike synoviocytes play an important role in RA pannus, and these cells originate in or have their counterpart in bone marrow (BM). Yet the B cell autoimmunity characteristic of RA occurs early, and synovial tissue, like BM, favors the B cell response. Because BM is abnormal in RA, and because germinal centers are unique to RA synovium, RA could be regarded as a disorder of the microenvironments able to sustain B cell response. In fact, RA could even begin in BM, with its onset facilitated by stem cell abnormalities. Moreover, most viruses suspected of playing a role in RA share a BM tropism. This may explain why RA frequently overlaps with other autoimmune disorders and benign lymphoproliferations, such as large granular T lymphocytosis. Because remissions from RA have been reported after BM transplantation, careful studies of the rheumatological outcome of RA patients undergoing such therapeutic procedures are needed. Although RA is a complex process, it can be considered initially as a stem cell disorder requiring treatment similar to that administered to transplant patients. Animal models have provided convincing evidence for these assumptions.

How could infectious agents hide in synovial cells? Possible mechanisms of persistent viral infection in a model for the etiopathogenesis of chronic arthritis

It has been hypothesized that a persistent intra-articular viral infection might play an important part in the pathogenesis of chronic arthritis. However, it remains unclear how such an infection could survive in synovial cells that express large amounts of HLA-DR and intercellular adhesion molecule-1 (ICAM-1) by which they communicate with immunocompetent cells. In an in vitro model of persistent mumps virus infection of synovial cells, results suggested that, in contrast to mock-infected cells, cells containing viral antigen did not express HLA-DR in response to interferon-gamma and that they did not up-regulate ICAM-1 expression under these conditions. Previously it has been shown that infected synovial cells do not express viral surface antigens. By these mechanisms, infected cells, interspersed among a large majority of uninfected cells, might evade recognition and eradication by the immune system. Lack of neoantigen expression on infected cells might be an important viral strategy to maintain a persistent infection and to initiate and perpetuate joint inflammation.

Pathogenic importance of fibronectin in the superficial region of articular cartilage as a local factor for the induction of pannus extension on rheumatoid articular cartilage

To identify the local factors in cartilage that are responsible for the induction of pannus invasion, a 14 day organ culture study in which rheumatoid synovium was grown in contact with cartilage pieces was carried out. Rheumatoid synovium preferentially extended over hyaluronidase treated cartilage pieces, but detached from untreated pieces. Rheumatoid synovium extended over hyaluronidase treated cartilage surfaces containing fibronectin more extensively than over surfaces treated with hyaluronidase only. Extension over hyaluronidase treated cartilage surfaces containing immune complexes was small. The adherence of synovial cells to hyaluronidase treated cartilage slices in vitro was specifically inhibited by the synthetic peptide, Gly-Arg-Gly-Asp-Ser-Pro, which is the adhesive portion of the fibronectin molecule. Furthermore, synovial fibroblast-like cellular extension, morphologically similar to rheumatoid pannus, was observed in the organ culture experiments in which rheumatoid synovium grew over hyaluronidase treated cartilage surfaces containing fibronectin. Synovial tissue extension over fibronectin coated surfaces was inhibited when hyaluronic acid and chondroitin-4-sulphate, major components of cartilage proteoglycans, were present on the cartilage surface. These findings suggest that fibronectin present in the superficial region of cartilage potentiates rheumatoid synovial extension and proteoglycans and immune complexes inhibit rheumatoid synovial extension. It is likely that fibronectin deposited on the eroded surface of articular cartilage induces pannus formation in rheumatoid arthritis.