Stimulation of collagenase 3 expression in synovial fibroblasts of patients with rheumatoid arthritis by contact with a three‐dimensional collagen matrix or with normal cartilage when coimplanted in NOD/SCID mice

Objective

To study the expression of collagenase 3 (matrix metalloproteinase 13 [MMP‐13]) and collagenase 1 (MMP‐1) in synovial fibroblasts from patients with rheumatoid arthritis (RA) when cultured within 3‐dimensional collagen gels or coimplanted with normal cartilage in immunodeficient NOD/SCID mice.

Methods

Messenger RNA (mRNA) and protein expression of collagenase 3 and collagenase 1 were characterized in synovial and skin fibroblasts by Northern blot and Western blot analysis. The mRNA expression of both collagenases in cell–cartilage implants in NOD/SCID mice was investigated by in situ hybridization in combination with immunohistochemistry of human fibroblasts.

Results

Synovial fibroblasts coimplanted with normal cartilage in NOD/SCID mice deeply invaded adjacent cartilage tissue. In this in vivo system of cartilage destruction, collagenase 3 mRNA was induced in synovial fibroblasts at sites of cartilage erosion, while the expression of collagenase 1 mRNA could not be detected. Culture of synovial fibroblasts within 3‐dimensional collagen gels was a ssociated with a marked increase in collagenase 3 mRNA expression and proenzyme production. This stimulatory effect was 1 order of magnitude higher in comparison with a 2–4‐fold increase upon treatment with interleukin‐1 β or tumor necrosis factor α. In contrast, mRNA expression and proenzyme production of collagenase 1 were increased strongly, and to a similar extent, either by contact with 3‐dimensional collagen or by proinflammatory cytokines.

Conclusion

The expression of collagenase 3, in contrast to that of collagenase 1, is preferentially stimulated in synovial fibroblasts by 3‐dimensional collagen rather than by proinflammatory cytokines. The induction of collagenase 3 by cell–matrix interactions represents a potential mechanism contributing to the invasive phenotype of synovial fibroblasts at sites of synovial invasion into cartilage in RA.

     

Functional characterization of adherent synovial fluid cells in rheumatoid arthritis: destructive potential in vitro and in vivo

OBJECTIVE: To characterize the morphologic and immunologic features of adherent synovial fluid cells derived from patients with rheumatoid arthritis (RA), and to explore their potential function in vitro and in vivo by focusing on cartilage destruction. METHODS: Synovial fluid adherent cells obtained from patients with RA and from control subjects were characterized by immunohistochemistry, flow cytometry, and electron microscopy. In vitro, these cells were cultured in the presence of cartilage particles. Cartilage destruction was monitored by the release of sulfated glycosaminoglycans (sGAG) into the medium, and the level of matrix metalloproteinase 1 (MMP-1) in the cell culture supernatant was measured by enzyme-linked immunosorbent assay. To inhibit cartilage destruction in vitro, the MMP inhibitor marimastat was tested in this system. In vivo, in the SCID mouse coimplantation model, RA synovial fluid adherent cells and RA synovial fibroblasts (as positive controls) were coimplanted with human cartilage under the kidney capsule and maintained there for 60 days. RESULTS: In vitro, the synovial fluid adherent cells consisted of 2 subpopulations, large round-shaped macrophage-like cells (CD68+) and spindle-shaped fibroblast-like cells (Thy-1+). When passaged, the latter cells proliferated and organized themselves into 3-dimensional formations. This allowed them to reach collagen particles fixed with agarose. Fibroblasts derived from synovial tissues could not be used in this assay because they grew only in monolayers and not on agarose. The majority (>90%) of passaged RA synovial fluid adherent cells expressed the Thy-1+,CD45-,CD68-,CD86- phenotype. Electron microscopy did not reveal important morphologic differences between the 2 types of fibroblasts, those from synovial tissue or those from synovial fluid. However, synovial fluid adherent cells expressed lower levels of adhesion molecules, including CD54 and galectin 3, as well as the complement-regulatory molecule CD55. The in vitro release of sGAG associated with cell activity was 2.5-fold higher from RA synovial fluid adherent cells in comparison with that from negative control cells. The release of sGAG correlated with the concentration of MMP-1 and was inhibited by the broad-range MMP inhibitor marimastat in a dose-dependent manner. RA synovial fluid adherent cells coimplanted with cartilage in SCID mice showed the same invasive behavior as that displayed by tissue-derived RA synovial fibroblasts. CONCLUSION: Similar to tissue-derived RA synovial fibroblasts, RA synovial fluid adherent cells, which contain "floating" anchorage-independent fibroblast-like cells, mediate cartilage destruction independent of the hyperplastic synovial tissue.     

Expression of sentrin, a novel antiapoptotic molecule, at sites of synovial invasion in rheumatoid arthritis

OBJECTIVE: Sentrin, a novel antiapoptotic molecule, has been shown to interact with the signal-competent form of Fas/APO-1 and tumor necrosis factor receptor I (TNFRI), and thereby, to protect cells against anti-Fas/APO-1- and TNF-induced cell death. Since reduced apoptosis in the synovial lining is supposed to contribute to synovial hyperplasia in rheumatoid arthritis (RA), we searched for the expression of sentrin-1 messenger RNA (mRNA) in synovium from patients with RA. METHODS: The expression of sentrin-1 mRNA was examined by in situ hybridization on snap-frozen sections of normal and RA synovial tissues as well as on paraffin-embedded RA synovial specimens, including the interface of cartilage-bone and invading synovium. Immunohistochemical double labeling after in situ hybridization was performed to further characterize sentrin-1 mRNA-expressing cells. In addition, quantitative analysis of sentrin-1 mRNA expression in RA synovial fibroblasts (RASF), osteoarthritis synovial fibroblasts (OASF), and normal fibroblasts was performed by quantitative real-time polymerase chain reaction. Expression levels were standardized to the expression of GAPDH. The in vivo maintenance of sentrin expression in RASF aggressively invading human cartilage was explored in the SCID mouse model of RA. RESULTS: A marked expression of sentrin-1 mRNA could be seen in all RA synovial specimens, predominantly in SF of the lining layer and at sites of invasion of RA synovium into cartilage. In normal synovial tissues, no sentrin-1 mRNA was detectable. RASF showed a maximum 32.5-fold (mean +/- SD 14.9 +/- 11.6) increase of sentrin-1 mRNA expression compared with normal fibroblasts and a maximum 31.4-fold (mean +/-SD 14.3 +/- 10.9) increase compared with OASF. When coimplanted with normal human cartilage in the SCID mouse model, invading RASF maintained their sentrin-1 mRNA expression for at least 60 days in vivo. CONCLUSION: The marked expression of sentrin in rheumatoid synovial tissue, but not in normal or OA synovial tissue, may contribute to the modulation of Fas- and TNFR-mediated apoptosis in RA synovium, and thereby extend the lifespan of invasive, cartilage-destructive SF.     

Expression of interleukin-21 receptor, but not interleukin-21, in synovial fibroblasts and synovial macrophages of patients with rheumatoid arthritis

OBJECTIVE: To determine the role and expression of the cytokine/receptor pair interleukin-21 (IL-21)/IL-21 receptor (IL-21R) in rheumatoid arthritis (RA). METHODS: The expression of IL-21R and IL-21 was analyzed by TaqMan real-time polymerase chain reaction (PCR) and in situ hybridization of synovial biopsy samples from patients with RA and osteoarthritis (OA). Double labeling by immunohistochemistry after in situ hybridization was performed with anti-CD68 antibodies. The expression of IL-21R at the protein level was confirmed by Western blotting. Stimulation experiments were performed with recombinant IL-1beta, tumor necrosis factor alpha (TNFalpha), platelet-derived growth factor (PDGF), and transforming growth factor beta (TGFbeta). The role of IL-21R in cartilage destruction was analyzed in the SCID mouse coimplantation model of RA. RESULTS: IL-21R was found in total RNA extracts and in synovial biopsy samples from RA patients, whereas no expression or only minimal expression was seen in samples from OA patients. Double labeling indicated that both synovial macrophages and synovial fibroblasts expressed IL-21R. Western blotting with anti-IL-21R antibodies confirmed the expression of IL-21R protein in RA synovial fibroblasts (RASFs). Of note, IL-21 was not detectable by real-time PCR and in situ hybridization in the same samples in vivo as in vitro. The level of expression of IL-21R messenger RNA (mRNA) was not altered by stimulation with IL-1beta, TNFalpha, PDGF, or TGFbeta. Interestingly, in the SCID mouse coimplantation model, RASFs did not maintain their expression of IL-21R at sites of invasion into the cartilage. Similarly, IL-21R mRNA was not expressed at sites of invasion into cartilage and bone in RA synovium. CONCLUSION: Our data demonstrate that IL-21R is expressed in RA synovium by RASFs and synovial macrophages. IL-21R is associated with the activated phenotype of RASFs independently of the major proinflammatory cytokines IL-1beta and TNFalpha, but correlates negatively with the destruction of articular cartilage and bone.     

Insulin-like growth factor 1 blocks collagen release and down regulates matrix metalloproteinase-1, -3, -8, and -13 mRNA expression in bovine nasal cartilage stimulated with oncostatin M in combination with interleukin 1alpha

OBJECTIVE: To investigate the effect of insulin-like growth factor 1 (IGF1) on the release of collagen, and the production and expression of matrix metalloproteinases (MMPs) induced by the proinflammatory cytokine interleukin 1alpha (IL1alpha) in combination with oncostatin M (OSM) from bovine nasal cartilage and primary human articular chondrocytes. METHODS: Human articular chondrocytes and bovine nasal cartilage were cultured with and without IGF1 in the presence of IL1alpha or IL1alpha + OSM. The release of collagen was measured by an assay for hydroxyproline. Collagenase activity was determined with the diffuse fibril assay using 3H acetylated collagen. The expression of MMP-1, MMP-3, MMP-8, MMP-13, and tissue inhibitor of metalloproteinase 1 (TIMP-1) mRNA was analysed by northern blot. RESULTS: IGF1 can partially inhibit the release of collagen induced by IL1alpha or IL1alpha + OSM from bovine nasal cartilage. This was accompanied by a reduced secretion and activation of collagenase by bovine nasal cartilage. IGF1 can also down regulate IL1alpha or IL1alpha + OSM induced MMP-1, MMP-3, MMP-8, and MMP-13 mRNA expression in human articular chondrocytes and bovine chondrocytes. It had no significant effect on the production and expression of TIMP-1 mRNA in chondrocytes. CONCLUSION: This study shows for the first time that IGF1 can partially block the release of collagen from cartilage and suggests that down regulation of collagenases by IGF1 may be an important mechanism in preventing cartilage resorption initiated by proinflammatory cytokines.     

Expression of osteopontin messenger RNA and protein in rheumatoid arthritis: effects of osteopontin on the release of collagenase 1 from articular chondrocytes and synovial fibroblasts

OBJECTIVE: Osteopontin (OPN) is an extracellular matrix protein that has been implicated in the interactions between tumor cells and host matrix, including those involved in invasion and spread of tumor cells. Because joint destruction in rheumatoid arthritis (RA) is mediated by the invasive growth of synovial tissue through its attachment to cartilage, we examined the expression of OPN in the synovia of patients with RA and the effect of OPN on the production of collagenase 1 in rheumatoid synovial fibroblasts and articular chondrocytes. METHODS: The expression of OPN messenger RNA (mRNA) and protein in synovia from 10 RA patients was examined by in situ hybridization and immunohistochemistry. Synovial fibroblasts from RA patients and articular chondrocytes from patients without joint disease were cultured in the presence of various concentrations of OPN, and levels of collagenase 1 in the culture supernatants were measured by enzyme-linked immunosorbent assay. RESULTS: The expression of OPN mRNA and protein was observed in 9 of 10 specimens obtained from patients with RA. OPN was expressed in the synovial lining and sublining layer and at the interface of cartilage and invading synovium. Double labeling revealed that the majority of OPN-expressing cells were positive for the fibroblast-specific enzyme prolyl 4-hydroxylase and negative for the macrophage marker CD68, while only a few, single OPN-expressing cells were positive for CD68 at sites of synovial invasion into cartilage. OPN staining was not observed in lymphocytic infiltrates or leukocyte common antigen (CD45)-positive cells. Three of 3 cultures of human articular chondrocytes secreted detectable basal amounts of collagenase, with a dose-dependent increase upon OPN stimulation, while synovial fibroblast cultures produced much lower levels of collagenase, with only 2 of 4 fibroblast cultures responding in a dose-dependent manner. CONCLUSION: These findings suggest that OPN produced by synovial fibroblasts in the synovial lining layer and at sites of cartilage invasion not only mediates attachment of these cells to cartilage, but also contributes to matrix degradation in RA by stimulating the secretion of collagenase 1 in articular chondrocytes.     

Influence of hypoxia on the expression of matrix metalloproteinase-1, -3 and tissue inhibitor of metalloproteinase-1 in rheumatoid synovial fibroblasts

OBJECTIVE: The rheumatoid synovium is a hypoxic environment, and hypoxia has been implicated as a factor in the pathogenesis of rheumatoid arthritis (RA). The purpose of this study was to investigate the effect of hypoxia on the expression of matrix metalloproteinase (MMP)-1, -3 and tissue inhibitor of metalloproteinase (TIMP)-1 in rheumatoid synovial fibroblasts. METHODS: Synovial fibroblasts obtained from RA patients were cultured for 48 h under normoxic or hypoxic conditions. Assays included western blot analysis and enzyme-linked immunosorbent assay (ELISA) for MMP-1, -3 and TIMP-1, and northern blot analysis to measure TIMP-1 mRNA levels. RESULTS: Compared with normoxic culture, hypoxia increased MMP-1 and MMP-3 expression in rheumatoid synovial fibroblasts. Hypoxia decreased TIMP-1 expression in rheumatoid synovial fibroblasts, as measured by both protein and mRNA levels. CONCLUSION: These results suggest that microenvironmental conditions, such as hypoxia, may directly contribute to joint destruction in RA by increasing the ratio of MMP-1, -3 to TIMP-1 production in synovial fibroblasts.     

Epigallocatechin-3-gallate suppresses TNF-α -induced production of MMP-1 and -3 in rheumatoid arthritis synovial fibroblasts

Rheumatoid arthritis (RA) synovial fibroblasts produce matrix metaloproteinases (MMPs), which destruct cartilage and bone in RA joint. Tumor necrosis factor-α (TNF-α) is one of the most important mediator leading to MMP production in RA synovial fibroblasts. Here we show that epigallocatechin-3-Gallate (EGCG) suppresses TNF-α-induced production of MMP-1 and MMP-3 in RA synovial fibroblasts, which was accompanied by inhibition of mitogen activated protein kinase (MAPK) and activator protein-1 (AP-1) pathways. EGCG treatment resulted in dose-dependent inhibition of TNF-α-induced production of MMP-1 and MMP-3 at the protein and mRNA levels in RA synovial fibroblast. EGCG treatment also inhibited TNF-α-induced phosphorylation of MAPKs, such as ERK1/2, p38, JNK. Electrophoretic mobility shift assay revealed that EGCG inhibits binding of AP-1 proteins to its response elements in synovial fibroblast treated. Thus, EGCG may play a role in regulating inflammation and bone destruction in RA patients.     

Bacterial peptidoglycans but not CpG oligodeoxynucleotides activate synovial fibroblasts by toll-like receptor signaling

OBJECTIVE: To test the hypothesis that bacterial products acting as adjuvants, such as CpG oligodeoxynucleotides (ODNs) and peptidoglycans (PGs), are able to activate synoviocytes, and to determine the involvement of Toll-like receptors (TLRs) in this activation process. METHODS: Cultured synovial fibroblasts obtained from patients with rheumatoid arthritis (RA) or osteoarthritis (OA) were stimulated with CpG ODNs or PGs. The expression of various integrins was determined by fluorescence-activated cell sorting. TLR and matrix metalloproteinase (MMP) messenger RNA (mRNA) was measured by real-time polymerase chain reaction. Additionally, levels of interleukin-6 (IL-6) and IL-8 in the culture supernatants were assessed by enzyme-linked immunosorbent assay. Blocking experiments were performed by adding anti-TLR-2 and anti-TLR-4 monoclonal antibodies to cultures stimulated with bacterial PGs. RESULTS: Incubation of synovial fibroblasts with CpG ODNs resulted in neither up-regulation of the expression of integrins on the cell surface, up-regulation of MMP mRNA expression, nor IL-6 and IL-8 production. However, incubation of RA synovial fibroblasts as well as OA synovial fibroblasts with staphylococcal PGs led to an up-regulation of CD54 (ICAM-1) surface expression and to increased expression of MMP-1, MMP-3, and MMP-13 mRNA. Furthermore, production of the proinflammatory cytokines IL-6 and IL-8 was increased by treatment with PGs. We demonstrated that cultured synovial fibroblasts express low levels of TLR-2 and TLR-9 mRNA. TLR-2 was up-regulated after stimulation with PGs, whereas TLR-9 mRNA remained at baseline levels after stimulation with CpG ODNs. Anti-TLR-2 monoclonal antibodies significantly inhibited production of IL-6 and IL-8 induced by stimulation with PGs. CONCLUSION: We demonstrate that bacterial PGs activate synovial fibroblasts, at least partially via TLR-2, to express integrins, MMPs, and proinflammatory cytokines. Inhibition of TLR signaling pathways might therefore have a beneficial effect on both joint inflammation and joint destruction.     

Oncostatin M in combination with tumor necrosis factor alpha induces cartilage damage and matrix metalloproteinase expression in vitro and in vivo

OBJECTIVE: To determine the effects of the proinflammatory cytokine combination of oncostatin M (OSM) and tumor necrosis factor alpha (TNFalpha) on cartilage destruction in both in vitro and in vivo model systems. METHODS: The release of collagen and proteoglycan was assessed in bovine cartilage explant cultures, while messenger RNA (mRNA) from bovine chondrocytes was analyzed by Northern blotting. Immunohistochemistry was performed on sections prepared from murine joints following injection of adenovirus vectors encoding murine OSM and/or murine TNFalpha. RESULTS: The combination of OSM + TNFalpha induced significant collagen release from bovine cartilage, accompanied by high levels of active collagenolytic activity. Northern blot analysis indicated that this cytokine combination synergistically induced matrix metalloproteinase 1 (MMP-1), MMP-3, and MMP-13 mRNA. The in vivo data clearly indicated that OSM + TNFalpha overexpression increased MMP levels and decreased levels of tissue inhibitor of metalloproteinases 1 (TIMP-1). Specifically, OSM + TNFalpha induced marked synovial hyperplasia, inflammation, and cartilage and bone destruction with a concomitant increase in MMP expression in both cartilage and synovium and decreased TIMP-1 expression in the articular cartilage. These effects were markedly greater than those seen with either cytokine alone. CONCLUSION: This study demonstrates that OSM + TNFalpha represents a potent proinflammatory cytokine combination that markedly induces MMP production in both cartilage and synovium, thus promoting joint destruction.     

Lower expression of histamine H4 receptor in synovial tissues from patients with rheumatoid arthritis compared to those with osteoarthritis

The aim of this study is to compare the expression level of histamine H(4) receptor (H(4)R) mRNA in synovial tissues of rheumatoid arthritis (RA) and osteoarthritis (OA) patients, and to study correlation of results with clinical characteristics of patients with RA. Synovial tissues were obtained from 7 RA and 7 OA patients undergoing artificial arthroplasty. Serum levels of erythrocyte sedimentation rate, C-reactive protein, matrix metalloproteinase-3 (MMP-3), rheumatoid factors, and cyclic citrullinated peptide antibodies were determined. The expression of H(4)R mRNA in synovial tissues was determined by real-time polymerase chain reaction. Expression of H(1)R and H(4)R mRNA were significantly lower in RA compared with OA patients (P < 0.005), while expression of H(2)R mRNA was comparable in both. While a significant negative correlation was found between H(4)R expression and serum MMP-3 concentration (r = -0.70, P < 0.05), no correlation was found between MMP-3 and H(1)R (r = -0.52) or H(2)R (r = 0.23). This study supports the supposition that H(4)R in synovial tissue may play a role in cartilage and bone destruction by influencing the secretion of MMP-3 in patients with RA.     

Quantitation of metalloproteinase gene expression in rheumatoid and psoriatic arthritis synovial tissue distal and proximal to the cartilage-pannus junction

OBJECTIVE: The distinct and different patterns of radiological damage in psoriatic arthritis (PsA) and rheumatoid arthritis (RA) may be a product of the relative balance of proteolytic enzyme and inhibitor gene expression in synovial tissue. This study compared metalloproteinase gene expression in synovium located proximal to the cartilage-pannus junction (CPJ) and distal to the CPJ (non-CPJ) in patients with PsA and RA. METHODS: Synovial biopsies were obtained from CPJ and non-CPJ sites under direct vision at arthroscopy of an inflamed knee in patients with PsA (n = 12) and RA (n = 12) who were not under disease modifying antirheumatic drug treatment. A competitive, quantitative RT-PCR technique was established for synovial RNA using a polycompetitor construct containing mRNA-specific primer sites for collagenase (MMP-1), stromelysin (MMP-3), tissue inhibitor of metalloproteinase-1 (TIMP-1), and GAPDH. cDNA products were separated and quantified by ethidium bromide stained gel electrophoresis and mRNA values were normalized relative to GAPDH expression. RESULTS: MMP-1, MMP-3, and TIMP-1 mRNA were upregulated in RA and PsA synovium with a prodestructive (MMP-1 + MMP-3)/TIMP-1 balance in both diseases. Similar levels of MMP mRNA expression were observed in PsA and RA despite the presence of less radiological erosion in the PsA group. No difference was observed in the degree of upregulation of MMP-1, MMP-3, or TIMP-1 mRNA in paired biopsies from CPJ and non-CPJ sites in either PsA (n = 8) or RA (n = 10). The ratio of TIMP-1 expression in CPJ compared to non-CPJ biopsies was higher in patients with nonerosive disease (10.1 +/- 27.8) than in erosive patients (0.75 +/- 0.27; p = 0.07). CONCLUSION: PsA and RA have similar levels of MMP-1, MMP-3, and TIMP-1 mRNA expression in synovium. There is no evidence of increased metalloproteinase mRNA expression at the CPJ in RA or PsA. The different patterns of radiological progression seen in RA and PsA were not explained by differences in synovial mRNA expression of MMP-1, MMP-3, or TIMP-1.     

Comparative analysis of cathepsin l,cathepsin d,and collagenase messenger rna expression in synovial tissues of patients with rheumatoid arthritis and osteoarthritis,by in situ hybridization

Objective. To compare the expression of cathepsin L, cathepsin D, and collagenase messenger RNA (mRNA) in synovial specimens from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Methods. The expression of cathepsins L and D as well as collagenase mRNA in synovial tissues from 8 patients with RA, 6 patients with OA, and 2 patients with noninflamed joints was evaluated using in situ hybridization with digoxigenin-labeled RNA probes. Results. Both RA and OA synovial tissue expressed cathepsins L and D as well as collagenase mRNA. The expression of the cathepsins was markedly higher in interstitial regions and, to some extent, in perivascular infiltrates of RA synovial tissue compared with OA specimens. Conclusion. Cathepsins L and D mRNA are expressed differently in RA and OA synovial tissues, supporting the concept that these enzymes may contribute to the influx of mononuclear cells into RA synovium. Moreover, the data reveal that the expression of collagenase and cathepsins in RA and OA synovial lining is otherwise largely similar, and suggest that the adhesion of synovial cells to cartilage mediates the invasive destructive process in RA.     

Interleukin 17 induces cartilage collagen breakdown: novel synergistic effects in combination with proinflammatory cytokines

OBJECTIVE: To investigate whether interleukin 17 (IL17), derived specifically from T cells, can promote type II collagen release from cartilage. The ability of IL17 to synergise with other proinflammatory mediators to induce collagen release from cartilage, and what effect anti-inflammatory agents had on this process, was also assessed. METHODS: IL17 alone, or in combination with IL1, IL6, oncostatin M (OSM), or tumour necrosis factor alpha (TNFalpha), was added to bovine nasal cartilage explant cultures. Proteoglycan and collagen release were determined. Collagenolytic activity was determined by bioassay. Chondroprotective effects of IL4, IL13, transforming growth factor beta1 (TGFbeta1) and insulin-like growth factor-1 (IGF1) were assessed by inclusion in the explant cultures. RESULTS: IL17 alone stimulated a dose dependent release of proteoglycan and type II collagen from bovine nasal cartilage explants. Suboptimal doses of IL17 synergised potently with TNFalpha, IL1, OSM, and IL6 to promote collagen degradation. This collagen release was completely inhibited by tissue inhibitor of metalloproteinase-1 and BB-94 (a synthetic metalloproteinase inhibitor), and was significantly reduced by IL4, IL13, TGFbeta1, and IGF1. In IL17 treated chondrocytes, mRNA expression for matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13 was detected. Moreover, a synergistic induction of these MMPs was seen when IL17 was combined with other proinflammatory cytokines. CONCLUSIONS: IL17 can, alone and synergistically in combination with other proinflammatory cytokines, promote chondrocyte mediated MMP dependent type II collagen release from cartilage. Because levels of all these proinflammatory cytokines are raised in rheumatoid synovial fluids, this study suggests that IL17 may act as a potent upstream mediator of cartilage collagen breakdown in inflammatory joint diseases.