Increased IL-6 receptor expression and signaling in ageing cartilage can be explained by loss of TGF-ß-mediated IL-6 receptor suppression.

OBJECTIVE: Osteoarthritis (OA) development is strongly associated with ageing, possibly due to age-related changes in transforming growth factor-ß (TGF-ß) signaling in cartilage. Recently, we showed that TGF-ß suppresses interleukin (IL)-6 receptor (IL-6R) expression in chondrocytes. As IL-6 is involved in cartilage degeneration, we hypothesized that age-related loss of TGF-ß signaling results in increased IL-6R expression and signaling in ageing cartilage. DESIGN: Bovine articular cartilage was collected and immediately processed to study age-related changes in IL-6R expression using qPCR and IHC (age-range: 0.5-14 years). Moreover, cartilage from young and aged cows was stimulated with rhIL-6 and/or rhTGF-ß1 to measure IL-6-induced p-STAT3 using Western blot. Expression of STAT3-responsive genes was analyzed using qPCR. RESULTS: Expression of IL-6 receptor (bIL-6R) significantly increased in cartilage upon ageing (slope: 0.32, 95%CI: 0.20-0.45), while expression of glycoprotein 130 (bGP130) was unaffected. Cartilage stimulation with IL-6 showed increased induction of p-STAT3 upon ageing (slope: 0.14, 95%CI: 0.08-0.20). Furthermore, IL-6-mediated induction of STAT3-responsive genes like bSOCS3 and bMMP3 was increased in aged compared to young cartilage. Interestingly, the ability of TGF-ß to suppress bIL6R expression in young cartilage was lost upon ageing (slope: 0.21, 95%CI: 0.13-0.30). Concurrently, an age-related loss in TGF-ß-mediated suppression of IL-6-induced p-STAT3 and bSOCS3 expression was observed. CONCLUSIONS: Ageing results in enhanced IL-6R expression and subsequent IL-6-induced p-STAT3 signaling in articular cartilage. This is likely caused by age-related loss of protective TGF-ß signaling, resulting in loss of TGF-ß-mediated IL-6R suppression. Because of the detrimental role of IL-6 in cartilage, this mechanism may be involved in age-related OA development.

TGF-ß dampens IL-6 signaling in articular chondrocytes by decreasing IL-6 receptor expression.

OBJECTIVE: Transforming growth factor-ß (TGF-ß) is an important homeostatic regulator of cartilage. In contrast, interleukin-6 (IL-6) is a pro-inflammatory cytokine implicated in cartilage degeneration. Cross-talk between TGF-ß and IL-6 is reported in tissues other than articular cartilage. Here, we investigated regulation of IL-6 signaling by TGF-ß in articular chondrocytes. DESIGN: Human primary chondrocytes and the human G6 chondrocyte cell line were stimulated with TGF-ß1 or interleukin-1ß (IL-1ß). Expression of IL-6 and IL-6 receptor (IL-6R) was determined on mRNA and protein level. TGF-ß regulation of IL-6 signaling via phosho-STAT3 (p-STAT3) was determined using Western blot, in presence of inhibitors for IL-6R, and Janus kinase(JAK)- and activin receptor-like kinase ALK)5 kinase activity. Furthermore, induction of STAT3-responsive genes was used as a read-out for IL-6 induced gene expression. RESULTS: TGF-ß1 increased IL-6 mRNA and protein expression in both G6 and primary chondrocytes. Moreover, TGF-ß1 stimulation clearly induced p-STAT3), which was abolished by inhibition of either IL-6R, JAK- or ALK5 kinase activity. However, TGF-ß1 did not increase expression of the STAT3-responsive gene SOCS3 and pre-treatment with TGF-ß1 even inhibited induction of p-STAT3 and SOCS3 by rhIL-6. Interestingly, TGF-ß1 potently decreased IL-6R expression. In contrast, IL-1ß did increase IL-6 levels, but did not affect IL-6R expression. Finally, addition of recombinant IL-6R abolished the inhibitory effect of TGF-ß1 on IL-6-induced p-STAT3 and downstream SOCS3, BCL3, SAA1 and MMP1 expression. CONCLUSIONS: In this study we show that TGF-ß decreases IL-6R expression, thereby dampening IL-6 signaling in chondrocytes. This reveals a novel effect of TGF-ß, possibly important to restrict pro-inflammatory IL-6 effects to preserve cartilage homeostasis.

IL-37 diminishes proteoglycan loss in human OA cartilage: donor-specific link between IL-37 and MMP-3.

OBJECTIVE: A hallmark of osteoarthritis (OA) is degradation of articular cartilage proteoglycans. In isolated human OA chondrocytes, the anti-inflammatory cytokine Interleukin-37 (IL-37) lowers the expression of the proteolytic MMP and ADAMTS enzymes, which mediate this degradation. Therefore, we investigated if IL-37 protects against proteoglycan loss in freshly obtained human OA explants. MATERIAL AND METHODS: Human OA cartilage explants were incubated with IL-37. Release of sulphated proteoglycans (sGAGs) was measured with the dimethylmethylene-blue assay. Production and degradation of newly synthesized proteoglycans was measured using 35S-sulphate. Proteoglycan and proteolytic enzyme expression were analyzed by qPCR and Western Blot. Proteolytic activity was determined by measuring MMP- and ADAMTS-generated aggrecan neo-epitopes with ELISA and by using MMP-3-, MMP-13- or ADAMTS-5-inhibitors. RESULTS: Over time, a linear release of sGAGs from OA cartilage was measured. IL-37 reduced this release by 87 µg/ml (24%) 95%CI [21.04-141.4]. IL-37 did not affect 35S-sulphate incorporation or proteoglycan gene expression. In contrast, IL-37 reduced loss of 35S-sulphate labeled GAGs and reduced MMP-3 protein expression, indicating that IL-37 inhibits proteoglycan degradation. Remarkably, we observed two groups of patients; one group in which MMP-3-inhibition lowered sGAG release, and one group in which ADAMTS5-inhibition had this effect. Remarkably, IL-37 was only functional in the group of patients that responded to MMP-3-inhibition. CONCLUSION: We identified a relationship between IL-37 and reduced sGAG loss in OA cartilage. Most likely, this effect is mediated by inhibition of MMP-3 expression. These results suggest that IL-37 could be applied as therapy in a subgroup of OA patients, in which cartilage degradation is mediated by MMP-3.

Osteoarthritis year in review 2016: biology.

This review highlights a selection of literature in the area of osteoarthritis biology published between the 2015 and 2016 Osteoarthritis Research Society International (OARSI) World Congress. Highlights were selected from a pubmed search covering cartilage, bone, inflammation and pain. A personal selection was made based, amongst other things, on topics presented during the 2015 conference. This covers circadian rhythm, TGF-ß signaling, autophagy, SIRT6, exercise, lubricin, TLR's, pain and NGF. Furthermore, in this review we have made an effort to connect these seemingly distant topics into one scheme of connections between them, revealing a theoretical big picture underneath.

Unloading results in rapid loss of TGFß signaling in articular cartilage: role of loading-induced TGFß signaling in maintenance of articular chondrocyte phenotype?

OBJECTIVE: Recently it was shown that loading of articular cartilage explants activates TGFß signaling. Here we investigated if in vivo chondrocytes express permanently high TGFß signaling, and the consequence of the loss of compressive loading-mediated TGFß signaling on chondrocyte function and phenotype. METHOD: Bovine articular cartilage explants were collected within 10 min post mortem and stained immediately and after 30, 60 and 360 min for phosphorylated-Smad2, indicating active TGFß signaling. Explants were unloaded for 48 h and subsequently repeatedly loaded with a compressive load of 3 MPa. In addition, explants were cultured unloaded for 2 weeks and the effect of loading or exogenous TGFß on proteoglycan level and chondrocyte phenotype (Col10a1 mRNA expression) was analyzed. RESULTS: Unloading of articular cartilage results in rapid loss of TGFß signaling while subsequent compressive loading swiftly restored this. Loading and exogenous TGFß enhanced expression of TGFß1 and ALK5. Unloading of explants for 2 weeks resulted in proteoglycan loss and increased Col10a1 expression. Both loading and exogenous TGFß inhibited elevated Col10a1 expression but not proteoglycan loss. CONCLUSION: Our data might imply that in vivo regular physiological loading of articular cartilage leads to enduring TGFß signaling and TGFß-induced gene expression. We propose a hypothetical model in which loading activates a self-perpetuating system that prevents hypertrophic differentiation of chondrocytes and is crucial for cartilage homeostasis.

Ageing is associated with reduction of mechanically-induced activation of Smad2/3P signaling in articular cartilage.

OBJECTIVE: Mechanical signals control key cellular processes in articular cartilage. Previously we have shown that mechanical compression is an important ALK5/Smad2/3P activator in cartilage explants. However, age-related changes in the cartilage are known to affect tissue mechanosensitivity and also ALK5/Smad2/3P signaling. We have investigated whether ageing of cartilage is associated with an altered response to mechanical compression. DESIGN: Articular cartilage explants of two different age groups (young-6-36 months old, aged-6 - 13 years old) were subjected to dynamic mechanical compression with 3 MPa (physiological) or 12 MPa (excessive) load. Subsequently, essential cartilage extracellular matrix (ECM) components and tissue growth factors gene expression was measured in young and aged cartilage by QPCR. Furthermore, the ability of young and aged cartilage, to activate the Smad2/3P signaling in response to compression was analyzed and compared. This was done by immunohistochemical (IH) Smad2P detection and Smad3-responsive gene expression analysis. RESULTS: Aged cartilage showed a highly reduced capacity for mechanically-mediated activation of Smad2/3P signaling when compared to young cartilage. Compression of aged cartilage, induced collagen type II (Col2a1) and fibronectin (Fn1) expression to a far lesser extent than in young cartilage. Additionally, in aged cartilage no mechanically mediated up-regulation of bone morphogenetic protein 2 (Bmp2) and connective tissue growth factor (Ctgf) was observed. CONCLUSIONS: We identified age-related changes in cellular responses to mechanical stimulation of articular cartilage. We propose that these changes might be associated with age-related alterations in cartilage functioning and can underlie mechanisms for development of age-related cartilage diseases like osteoarthritis (OA).

Expression of TGFß-family signalling components in ageing cartilage: age-related loss of TGFß and BMP receptors.

OBJECTIVE: Ageing is the main risk factor for osteoarthritis (OA). We investigated if expression of transforming growth factor ß (TGFß)-family components, a family which is crucial for the maintenance of healthy articular cartilage, is altered during ageing in cartilage. Moreover, we investigated the functional significance of selected age-related changes. DESIGN: Age-related changes in expression of TGFß-family members were analysed by quantitative PCR in healthy articular cartilage obtained from 42 cows (age: ¾-10 years). To obtain functional insight of selected changes, cartilage explants were stimulated with TGFß1 or bone morphogenetic protein (BMP) 9, and TGFß1 and BMP response genes were measured. RESULTS: Age-related cartilage thinning and loss of collagen type 2a1 expression (∼256-fold) was observed, validating our data set for studying ageing in cartilage. Expression of the TGFß-family type I receptors; bAlk2, bAlk3, bAlk4 and bAlk5 dropped significantly with advancing age, whereas bAlk1 expression did not. Of the type II receptors, expression of bBmpr2 decreased significantly. Type III receptor expression was unaffected by ageing. Expression of the ligands bTgfb1 and bGdf5 also decreased with age. In explants, an age-related decrease in TGFß1-response was observed for the pSmad3-dependent gene bSerpine1 (P = 0.016). In contrast, ageing did not affect BMP9 signalling, an Alk1 ligand, as measured by expression of the pSmad1/5 dependent gene bId1. CONCLUSIONS: Ageing negatively affects both the TGFß-ALK5 and BMP-BMPR signalling routes, and aged chondrocytes display a lowered pSmad3-dependent response to TGFß1. Because pSmad3 signalling is essential for cartilage homeostasis, we propose that this change contributes to OA development.

Inducible chondrocyte-specific overexpression of BMP2 in young mice results in severe aggravation of osteophyte formation in experimental OA without altering cartilage damage.

OBJECTIVES: In osteoarthritis (OA) chondrocytes surrounding lesions express elevated bone morphogenetic protein 2 (BMP2) levels. To investigate the functional consequence of chondrocyte-specific BMP2 expression, we made a collagen type II dependent, doxycycline (dox)-inducible BMP2 transgenic mouse and studied the effect of elevated BMP2 expression on healthy joints and joints with experimental OA. METHODS: We cloned a lentivirus with BMP2 controlled by a tet-responsive element and transfected embryos of mice containing a collagen type II driven cre-recombinase and floxed rtTA to gain a mouse expressing BMP2 solely in chondrocytes and only upon dox exposure (Col2-rtTA-TRE-BMP2). Mice were treated with dox to induce elevated BMP2 expression. In addition, experimental OA was induced (destabilisation of the medial meniscus model) with or without dox supplementation and knee joints were isolated for histology. RESULTS: Dox treatment resulted in chondrocyte-specific upregulation of BMP2 and severely aggravated formation of osteophytes in experimental OA but not in control mice. Moreover, elevated BMP2 levels did not result in alterations in articular cartilage of young healthy mice, although BMP2-exposure did increase VDIPEN expression in the articular cartilage. Strikingly, despite apparent changes in knee joint morphology due to formation of large osteophytes there were no detectible differences in articular cartilage: none with regard to structural damage nor in Safranin O staining intensity when comparing destabilisation of the medial meniscus with or without dox exposure. CONCLUSIONS: Our data show that chondrocyte-specific elevation of BMP2 levels does not alter the course of cartilage damage in an OA model in young mice but results in severe aggravation of osteophyte formation.

The high affinity ALK1-ligand BMP9 induces a hypertrophy-like state in chondrocytes that is antagonized by TGFß1.

OBJECTIVE: In osteoarthritic cartilage, expression of the receptor ALK1 correlates with markers of deleterious chondrocyte hypertrophy. Recently, bone morphogenetic protein 9 (BMP9) was identified as a high affinity ligand for ALK1. Therefore, we studied if BMP9 signaling results in expression of hypertrophy markers in chondrocytes. Furthermore, because transforming growth factorß1 (TGFß1) is a well known anti-hypertrophic factor, the interaction between BMP9 and TGFß1 signaling was also studied. DESIGN: Primary chondrocytes were isolated from bovine cartilage and stimulated with BMP9 and/or TGFß1 to measure intracellular signaling via pSmads with the use of Western blot. Expression of Smad-responsive genes or hypertrophy-marker genes was measured using qPCR. To confirm observations on TGFß/Smad3 responsive genes, a Smad3-dependent CAGA12-luc transcriptional reporter assay was performed in the chondrocyte G6 cell line. RESULTS: In primary chondrocytes, BMP9 potently induced phosphorylation of Smad1/5 and Smad2 to a lesser extent. BMP9-induced Smad1/5 phosphorylation was rapidly (2 h) reflected in gene expression, whereas Smad2 phosphorylation was not. Remarkably, BMP9 and TGFß1 dose-dependently synergized on Smad2 phosphorylation, and showed an additive effect on expression of Smad3-dependent genes like bSerpine1 after 24 h. The activation of the TGFß/Smad3 signaling cascade was confirmed using the CAGA12-luc transcriptional reporter. BMP9 selectively induced bAlpl and bColX expression, which are considered early markers of cellular hypertrophy, but this was potently antagonized by addition of a low dose of TGFß1. CONCLUSIONS: This study shows that in vitro in chondrocytes, BMP9 potently induces pSmad1/5 and a chondrocyte hypertrophy-like state, which is potently blocked by TGFß1. This observation underlines the importance of TGFß1 in maintenance of chondrocyte phenotype.

TGF-ß is a potent inducer of Nerve Growth Factor in articular cartilage via the ALK5-Smad2/3 pathway. Potential role in OA related pain?

OBJECTIVE: Pain is the main problem for patients with osteoarthritis (OA). Pain is linked to inflammation, but in OA a subset of patients suffers from pain without inflammation, indicating an alternative source of pain. Nerve Growth Factor (NGF) inhibition is very efficient in blocking pain during OA, but the source of NGF is unclear. We hypothesize that damaged cartilage in OA releases Transforming Growth Factor-ß (TGF-ß), which in turn stimulates chondrocytes to produce NGF. DESIGN: Murine and human chondrocyte cell lines, primary bovine and human chondrocytes, and cartilage explants from bovine metacarpal joints and human OA joints were stimulated with TGF-ß1 and/or Interleukin-1 (IL-1)ß. We analyzed NGF expression on mRNA level with QPCR and stained human OA cartilage for NGF immunohistochemically. Cultures were additionally pre-incubated with inhibitors for TAK1, Smad2/3 or Smad1/5/8 signaling to identify the TGF-ß pathway inducing NGF. RESULTS: NGF expression was consistently induced in higher levels by TGF-ß than IL-1 in all of our experiments: murine, bovine and human origin, in cell lines, primary chondrocytes and explants cultures. TAK1 inhibition consistently reduced TGF-ß-induced NGF whereas it fully blocked IL-1ß-induced NGF expression. In contrast, ALK5-Smad2/3 inhibition fully blocked TGF-ß-induced NGF expression. Despite the large variation in basal NGF in human OA samples (mRNA and histology), TGF-ß exposure led to a consistent high level of NGF induction. CONCLUSION: We show for the first time that TGF-ß induces NGF expression in chondrocytes, in a ALK5-Smad2/3 dependent manner. This reveals a potential alternative non-inflammatory source of pain in OA.

Physiological and excessive mechanical compression of articular cartilage activates Smad2/3P signaling.

OBJECTIVE: Transforming growth factor beta (TGF-ß) in articular cartilage can signal via two routes, the ALK5/Smad2/3P and the ALK1/Smad1/5/8P route, the first being protective and the latter favoring chondrocyte terminal differentiation. Since biomechanical factors are known to play an essential role in osteoarthritis (OA) initiation and progression, we investigated if excessive mechanical compression can alter TGF-ß signaling in cartilage shifting it from ALK5/Smad2/3P to ALK1/Smad1/5/8P pathway, favoring terminal differentiation of chondrocytes. DESIGN: Articular cartilage explants were harvested from bovine metacarpophalangeal joints. After equilibration, explants were subjected to unconfined dynamic mechanical compression (1 Hz) with 3 MPa (physiological) or 12 MPa (excessive) stress. After different time intervals samples were frozen and mRNA levels of selected genes were examined using real-time polymerase chain reaction. RESULTS: In articular cartilage compressed with 3 MPa and also 12 MPa stress the expression of Smad2/3P responsive genes bSerpine1, bSmad7 and bAlk5 was up-regulated, whereas the expression of Smad1/5/8P responsive gene bId1 was down-regulated. Furthermore, the expression of bTgfb1 was significantly up-regulated in both compression groups. When ALK5/Smad2/3P pathway was blocked with a selective ALK4/5/7 inhibitor, the effect of excessive mechanical compression on bSmad7 and bAlk5 expression was prevented. CONCLUSIONS: Here we show that excessive mechanical compression alone is not able to shift TGF-ß signaling toward the ALK1/Smad1/5/8P pathway. In contrast, we show that mechanical compression not only with physiological but also with excessive stress can activate Smad2/3P signaling, which is known to be protective for articular cartilage and to block chondrocyte terminal differentiation.

Patient involvement in basic rheumatology research at Nijmegen: a three year's responsive evaluation of added value, pitfalls and conditions for success.

BACKGROUND: Empirical evidence for effective patient-researcher collaboration in basic research is lacking. This study aims to explore good working models and impact of patient involvement in basic rheumatology research and to identify barriers and facilitators. METHOD: A responsive evaluation of a three years' participatory research project in a basic and translational laboratory research setting. Several working models for patient involvement were piloted and adapted if considered necessary. The study comprised surveys, interviews, training days, meeting reports, Q-sort exercises and field notes, and regular reflective team sessions with participant involvement. A qualitative analysis using thematic coding focused on impact, barriers and facilitators. RESULTS: Thirteen patient research partners (PRPs) and fifteen basic researchers participated. PRPs experienced basic research as fascinating though complex to understand. Their initial role was mostly listening and asking questions. After several meetings equal and more meaningful relationships emerged. Researchers' motivation increased by listening to patient stories. They learned about disease impact on daily life and to speak in understandable language. This enabled PRPs to learn about research and the pathogenesis of their disease. It inspired them to stay involved over a longer period. After three years, both parties preferred 1:1 contacts over collaboration in team meetings. A common language and respectful communication were important facilitators. Limitations were the complexity of disease processes for patients and the time commitment for researchers. Impact was reported as a sincere dialogue with multiple advantages for patients and researchers, and to a lesser extent than expected on the research process and outcomes. CONCLUSION: Patient involvement contributes to motivating young scientists in performing basic research projects. Patients and researchers valued the benefits of long-term one-on-one collaboration. These benefits outweigh the lack of direct impact on basic research goals and performance. A plain language summary of the abstract is available (as) online Additional file 1.

TGFß-mediated expression of TGFß-activating integrins in SSc monocytes: disturbed activation of latent TGFß?

INTRODUCTION: The pathophysiology of systemic sclerosis (SSc) is closely linked to overactive TGFß signaling. TGFß is produced and circulates in latent form, making its activation crucial for signaling. This activation can be mediated via integrins. We investigated the balance between active and latent TGFß in serum of SSc patients and investigated if this correlates with integrin expression on monocytes. METHODS: A TGFß/SMAD3- or BMP/SMAD1/5-luciferase reporter construct was expressed in primary human skin fibroblasts. Both acidified and non-acidified sera of ten SSc patients and ten healthy controls were tested on these cells to determine total and active TGFß and BMP levels respectively. A pan-specific TGFß1/2/3 neutralizing antibody was used to confirm TGFß signaling. Monocytes of 20 SSc patients were isolated using CD14+ positive selection, and integrin gene expression was measured using qPCR. Integrin expression was modulated using rhTGFß1 or a small molecule inhibitor of TGFBR1: SB-505124. RESULTS: SSc sera induced 50% less SMAD3-reporter activity than control sera. Serum acidification increased reporter activity, but a difference between healthy control and SSc serum was no longer observed, indicating that total TGFß levels were not different. Addition of a pan-specific TGFß1/2/3 neutralizing antibody fully inhibited SMAD3-reporter activity of both acidified and not-acidified control and SSc sera. Both HC and SSc sera induced similar SMAD1/5-reporter activity, and acidification increased this, but not differently between groups. Interestingly, expression of two integrin alpha subunits ITGA5 and ITGAV was significantly reduced in monocytes obtained from SSc patients. Furthermore, ITGB3, ITGB5, and ITGB8 expression was also reduced in SSc monocytes. Stimulation of monocytes with TGFß1 induced ITGA5 and ITGAV but lowered ITGB8 expression, whereas the use of the TGFß receptor inhibitor SB-505124 had the opposite effect. CONCLUSION: Total TGFß serum levels are not different between SSc patients and controls, but TGFß activity is. This coincides with a reduced expression of TGFß-activating integrins in monocytes of SSc patients. Because TGFß regulates expression of these integrins in monocytes, a negative feedback mechanism possibly underlies these observations.

Expression of TGF-ß Signaling Regulator RBPMS (RNA-Binding Protein With Multiple Splicing) Is Regulated by IL-1ß and TGF-ß Superfamily Members, and Decreased in Aged and Osteoarthritic Cartilage.

OBJECTIVE: RNA-binding protein with multiple splicing (RBPMS) has been shown to physically interact with Smads and enhance transforming growth factor-ß (TGF-ß)-mediated Smad2/3 transcriptional activity in mammalian cells. Objective of this study was to examine whether expression of RBPMS is regulated by interleukin-1ß (IL)-1ß and TGF-ß superfamily growth factors and whether expression of RBPMS is altered during aging and experimental osteoarthritis. METHODS: Expression of RBPMS protein was investigated in chondrocyte cell lines of murine (H4) and human (G6) origin using Western blot analysis. Regulation of RBPMS expression in H4 chondrocytes at mRNA level was done by reverse transcriptase-quantitative polymerase chain reaction. Furthermore, characterization of Smad signaling pathways regulating RBPMS expression was performed by blocking studies using small molecule inhibitors or by transfection studies with adenoviral vector constructs (constitutive-active ALK1 and constitutive-active ALK5). Expression of RBPMS in cartilage of different age groups of C57BL/6N mice (6 months and 20 months) and in a surgically induced osteoarthritis (OA) mouse model was analyzed using immunohistochemistry. RESULTS: RBPMS was shown to be expressed in chondrocytes and cartilage of murine, human, and bovine origin. TGF-ß inhibited RBPMS expression while BMP2 and IL-1ß increased its expression. TGF-ß-induced inhibition was blocked by ALK5 inhibitor. Overexpression of ca-ALK1 stimulated RBPMS expression. Moreover, RBPMS expression was found to be reduced with ageing and in OA pathogenesis. CONCLUSIONS: Expression of RBPMS in chondrocytes is regulated by TGF-ß superfamily members and IL-1ß, indicating a counter-regulatory mechanism. Expression of RBPMS, in cartilage and its reduction during ageing and OA might suggest its potential role in the maintenance of normal articular cartilage.