Transforming growth factor beta 1 and insulin-like growth factor 1 block collagen degradation induced by oncostatin M in combination with tumour necrosis factor alpha from bovine cartilage

Rapamycin insensitive regulation of engineered ligament structure and function by IGF-1

Following rupture, the anterior cruciate ligament (ACL) will not heal and therefore more than 400,000 surgical repairs are performed annually. Ligament engineering is one way to meet the increasing need for donor tissue to replace the native ligament; however, currently these tissues are too weak for this purpose. Treating engineered human ligaments with insulin-like growth factor-1 (IGF-1) improves the structure and function of these grafts. Since the anabolic effects of IGF-1 are largely mediated by rapamycin complex I (mTORC1), we used rapamycin to determine whether mTORC1 was necessary for the improvement in collagen content and mechanics of engineered ligaments. The effect of IGF-1 and rapamycin was determined independently and interactions between the two treatments were tested. Grafts were treated for 6 days before mechanical testing and analysis of collagen content. Following 8 days of treatment, mechanical properties increased 34% with IGF-1 and decreased 24.5% with rapamycin. Similarly, collagen content increased 63% with IGF-1 and decreased 36% with rapamycin. Interestingly, there was no interaction between IGF-1 and rapamycin, suggesting that IGF-1 was working in a largely mTORC1-independent manner. Acute treatment with IGF-1 did not alter procollagen synthesis in growth media, even though rapamycin decreased procollagen 55%. IGF-1 decreased collagen degradation 15%, whereas rapamycin increased collagen degradation 10%. Once again, there was no interaction between IGF-1 and rapamycin on collagen degradation. Together, these data suggest that growth factor-dependent increases in collagen synthesis are dependent on mTORC1 activity; however, IGF-1 improves human-engineered ligament mechanics and collagen content by decreasing collagen degradation in a rapamycin-independent manner. How the anticatabolic effects of IGF-1 are regulated have yet to be determined.NEW & NOTEWORTHY IGF-1 increases and rapamycin decreases mechanical and material properties of engineered human ligaments by regulating collagen content and concentration. There was no interaction between IGF-1 and rapamycin, suggesting that IGF-1 and rapamycin work independently. We found that IGF-1 improves collagen content by decreasing collagen degradation in a rapamycin-independent manner, whereas growth factor-dependent increases in collagen synthesis are blocked by rapamycin. These data may explain why interventions to increase IGF-1 have not helped rehabilitation.

Recent advances in understanding the regulation of metalloproteinases

Metalloproteinases remain important players in arthritic disease, in part because members of this large enzymatic family, namely matrix metalloproteinase-1 (MMP-1) and MMP-13, are responsible for the irreversible degradation of articular cartilage collagen. Although direct inhibition of MMPs fell out of vogue with the initial clinical disappointment of the first generation of compounds, interest in other mechanisms that control these important enzymes has always been maintained. Since these enzymes are critically important for tissue homeostasis, their expression and activity are tightly regulated at many levels, not just by direct inhibition by their endogenous inhibitors the tissue inhibitors of metalloproteinases (TIMPs). Focussing on MMP-13, we discuss recent work that highlights new discoveries in the transcriptional regulation of this enzyme, from defined promoter functional analysis to how more global technologies can provide insight into the enzyme’s regulation, especially by epigenetic mechanisms, including non-coding RNAs. In terms of protein regulation, we highlight recent findings into enzymatic cascades involved in MMP-13 regulation and activation. Importantly, we highlight a series of recent studies that describe how MMP-13 activity, and in fact that of other metalloproteinases, is in part controlled by receptor-mediated endocytosis. Together, these new discoveries provide a plethora of novel regulatory mechanisms, besides direct inhibition, which with renewed vigour could provide further therapeutic opportunities for regulating the activity of this class of important enzymes.

Systems biology reveals how altered TGFβ signalling with age reduces protection against pro-inflammatory stimuli

Osteoarthritis (OA) is a degenerative condition caused by dysregulation of multiple molecular signalling pathways. Such dysregulation results in damage to cartilage, a smooth and protective tissue that enables low friction articulation of synovial joints. Matrix metalloproteinases (MMPs), especially MMP-13, are key enzymes in the cleavage of type II collagen which is a vital component for cartilage integrity. Transforming growth factor beta (TGFβ) can protect against pro-inflammatory cytokine-mediated MMP expression. With age there is a change in the ratio of two TGFβ type I receptors (Alk1/Alk5), a shift that results in TGFβ losing its protective role in cartilage homeostasis. Instead, TGFβ promotes cartilage degradation which correlates with the spontaneous development of OA in murine models. However, the mechanism by which TGFβ protects against pro-inflammatory responses and how this changes with age has not been extensively studied. As TGFβ signalling is complex, we used systems biology to combine experimental and computational outputs to examine how the system changes with age. Experiments showed that the repressive effect of TGFβ on chondrocytes treated with a pro-inflammatory stimulus required Alk5. Computational modelling revealed two independent mechanisms were needed to explain the crosstalk between TGFβ and pro-inflammatory signalling pathways. A novel meta-analysis of microarray data from OA patient tissue was used to create a Cytoscape network representative of human OA and revealed the importance of inflammation. Combining the modelled genes with the microarray network provided a global overview into the crosstalk between the different signalling pathways involved in OA development. Our results provide further insights into the mechanisms that cause TGFβ signalling to change from a protective to a detrimental pathway in cartilage with ageing. Moreover, such a systems biology approach may enable restoration of the protective role of TGFβ as a potential therapy to prevent age-related loss of cartilage and the development of OA.

Protein kinase D3 modulates MMP1 and MMP13 expression in human chondrocytes

Many catabolic stimuli, including interleukin-1 (IL-1) in combination with oncostatin M (OSM), promote cartilage breakdown via the induction of collagen-degrading collagenases such as matrix metalloproteinase 1 (MMP1) and MMP13 in human articular chondrocytes. Indeed, joint diseases with an inflammatory component are characterised by excessive extracellular matrix (ECM) catabolism. Importantly, protein kinase C (PKC) signalling has a primary role in cytokine-induced MMP1/13 expression, and is known to regulate cellular functions associated with pathologies involving ECM remodelling. At present, substrates downstream of PKC remain undefined. Herein, we show that both IL-1- and OSM-induced phosphorylation of protein kinase D (PKD) in human chondrocytes is strongly associated with signalling via the atypical PKCι isoform. Consequently, inhibiting PKD activation with a pan-PKD inhibitor significantly reduced the expression of MMP1/13. Specific gene silencing of the PKD isoforms revealed that only PKD3 (PRKD3) depletion mirrored the observed MMP repression, indicative of the pharmacological inhibitor specifically affecting only this isoform. PRKD3 silencing was also shown to reduce serine phosphorylation of signal transducer and activator of transcription 3 (STAT3) as well as phosphorylation of all three mitogen-activated protein kinase groups. This altered signalling following PRKD3 silencing led to a significant reduction in the expression of the activator protein-1 (AP-1) genes FOS and JUN, critical for the induction of many MMPs including MMP1/13. Furthermore, the AP-1 factor activating transcription factor 3 (ATF3) was also reduced concomitant with the observed reduction in MMP13 expression. Taken together, we highlight an important role for PKD3 in the pro-inflammatory signalling that promotes cartilage destruction.

Cytokine-induced MMP13 Expression in Human Chondrocytes Is Dependent on Activating Transcription Factor 3 (ATF3) Regulation

Irreversible breakdown of cartilage extracellular matrix (ECM) by the collagenase matrix metalloproteinase 13 (MMP13) represents a key event in osteoarthritis (OA) progression. Although inflammation is most commonly associated with inflammatory joint diseases, it also occurs in OA and is thus relevant to the prevalent tissue destruction. Here, inflammation generates a cFOS AP-1 early response that indirectly affects MMP13 gene expression. To ascertain a more direct effect on prolonged MMP13 production we examined the potential molecular events occurring between the rapid, transient expression of cFOS and the subsequent MMP13 induction. Importantly, we show MMP13 mRNA expression is mirrored by nascent hnRNA transcription. Employing ChIP assays, cFOS recruitment to the MMP13 promoter occurs at an early stage prior to gene transcription and that recruitment of transcriptional initiation markers also correlated with MMP13 expression. Moreover, protein synthesis inhibition following early FOS expression resulted in a significant decrease in MMP13 expression thus indicating a role for different regulatory factors modulating expression of the gene. Subsequent mRNA transcriptome analyses highlighted several genes induced soon after FOS that could contribute to MMP13 expression. Specific small interfering RNA-mediated silencing highlighted that ATF3 was as highly selective for MMP13 as cFOS. Moreover, ATF3 expression was AP-1(cFOS/cJUN)-dependent and expression levels were maintained after the early transient cFOS response. Furthermore, ATF3 bound the proximal MMP13 AP-1 motif in stimulated chondrocytes at time points that no longer supported binding of FOS Consequently, these findings support roles for both cFOS (indirect) and ATF3 (direct) in effecting MMP13 transcription in human chondrocytes.

Tribbles and arthritis: what are the links?

The pseudo-kinase family of tribbles (TRIB) proteins has been linked to a variety of cell signalling pathways and appears to have functionally divergent roles with respect to intracellular protein degradation and the ability to regulate signal transduction pathways. In the arthritides, inflammation and a wide variety of pro-inflammatory pathways have been implicated to drive the cartilage destruction and consequent disability associated with both rheumatoid arthritis (RA) and osteoarthritis (OA). Despite burgeoning evidence linking the TRIB to inflammation-related pathologies such as diabetes, multiple sclerosis and cancer, very little is known about their roles in arthritis. The present review discusses current knowledge of the impact of TRIB on pro-inflammatory cellular mechanisms and pathways known to be important in the pathogenesis of RA and OA.

Oncostatin M and TLR-4 ligand synergize to induce MCP-1, IL-6, and VEGF in human aortic adventitial fibroblasts and smooth muscle cells

Accumulating evidence suggests that adventitial fibroblasts play a significant role in contributing to inflammation of the arterial wall and pathogenesis of atherosclerosis. The effects of gp130 cytokines on these cells (including oncostatin M-[OSM] and IL-6), some of which have been implicated in atherosclerosis, are currently unknown. Experiments were performed to determine whether gp130 cytokines regulate human aortic adventitial fibroblasts (HAoAFs) or smooth muscle cells (HAoSMCs) alone or in context of TLR-4 ligands (also implicated in atherosclerosis). HAoAFs and HAoSMCs were stimulated with LPS and/or one of OSM, IL-6, IL-11, IL-31, or LIF. ELISAs performed on cell supernatants showed that stimulation with OSM alone caused increased MCP-1, IL-6, and VEGF levels. When combined, LPS and OSM synergized to increase MCP-1, IL-6, VEGF protein, and mRNA expression as assessed by qRT-PCR, in both HAoAFs and HAoSMCs, while LPS-induced IL-8 levels were reduced. Such effects were not observed with other gp130 cytokines. Signalling pathways including STATs, MAPKinases, and NFκB were activated, and LPS induced steady state mRNA levels of the OSM receptor chains OSMRβ and gp130. The results suggest that OSM is able to synergize with TLR-4 ligands to induce proinflammatory responses by HAoAFs and HAoSMCs, supporting the notion that OSM regulation of these cells contributes to the pathogenesis of atherosclerosis.

Infrapatellar fat pad of patients with end-stage osteoarthritis inhibits catabolic mediators in cartilage

OBJECTIVE

Adipose tissue is known to release inflammatory cytokines and growth factors. In this exploratory study, the authors examined whether the infrapatellar fat pad (IPFP) closely located to cartilage in the knee joint can affect cartilage metabolism. In addition, the authors analysed whether the macrophage types present in IPFP could explain the effect on cartilage.

METHODS

IPFP explants obtained during total knee replacement of 29 patients with osteoarthritis (OA) were used to make fat-conditioned medium (FCM). Explants of bovine cartilage were cultured with or without FCM. Nitric oxide (NO) and glycosaminoglycan release and gene expression of matrix-degrading enzymes in cartilage were analysed. To stimulate catabolic processes in the cartilage, the authors added interleukin 1β, and the effect of six FCMs was evaluated. The presence of different types of macrophages (CD68+, CD86+ and CD206+) in OA IPFPs was compared with subcutaneous adipose tissue samples and IPFP samples from patients with an anterior cruciate ligament rupture.

RESULTS

FCM alone reduced NO and glycosaminoglycan release and matrix metalloproteinase (MMP)1 gene expression by the cartilage. Moreover, when catabolic conditions were enhanced with interleukin 1β, FCM inhibited NO production as well as MMP1 and MMP3 gene expression and increased collagen type II gene expression. Significantly more CD206+ cells were present in OA IPFP samples than in subcutaneous fat or anterior cruciate ligament IPFP samples.

CONCLUSION

In contrast to the authors' expectations, medium conditioned by end-stage OA IPFP inhibited catabolic processes in cartilage. CD206+ cells present in the IPFPs used for making the FCM might have contributed to the inhibition of catabolic processes in the cartilage.

Developmental mechanisms in articular cartilage degradation in osteoarthritis

Osteoarthritis is the most common arthritic condition, which involves progressive degeneration of articular cartilage. The most recent accomplishments have significantly advanced our understanding on the mechanisms of the disease development and progression. The most intriguing is the growing evidence indicating that extracellular matrix destruction in osteoarthritic articular cartilage resembles that in the hypertrophic zone of fetal growth plate during endochondral ossification. This suggests common regulatory mechanisms of matrix degradation in OA and in the development and can provide new approaches for the treatment of the disease by targeting reparation of chondrocyte phenotype.

Protein kinase C isoforms zeta and iota mediate collagenase expression and cartilage destruction via STAT3- and ERK-dependent c-fos induction

The protein kinase C (PKC) signaling pathway is a major regulator of cellular functions and is implicated in pathologies involving extracellular matrix remodeling. Inflammatory joint disease is characterized by excessive extracellular matrix catabolism, and here we assess the role of PKC in the induction of the collagenases, matrix metalloproteinase (MMP)-1 and MMP-13, in human chondrocytes by the potent cytokine stimulus interleukin-1 (IL-1) in combination with oncostatin M (OSM). IL-1 + OSM-stimulated collagenolysis and gelatinase activity were ameliorated by pharmacological PKC inhibition in bovine cartilage, as was collagenase gene induction in human chondrocytes. Small interfering RNA-mediated silencing of PKC gene expression showed that both novel (nPKC delta, nPKC eta) and atypical (aPKC zeta, aPKC iota) isoforms were involved in collagenase induction by IL-1. However, MMP1 and MMP13 induction by IL-1 + OSM was inhibited only by aPKC silencing, suggesting that only atypical isoforms play a significant role in complex inflammatory milieus. Silencing of either aPKC led to diminished IL-1 + OSM-dependent extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription (STAT) 3 phosphorylation, and c-fos expression. STAT3 gene silencing or ERK pathway inhibition also resulted in loss of IL-1 + OSM-stimulated c-fos and collagenase expression. Silencing of c-fos and c-jun expression was sufficient to abrogate IL-1 + OSM-stimulated collagenase gene induction, and overexpression of both c-fos and c-jun was sufficient to drive transcription from the MMP1 promoter in the absence of a stimulus. Our data identify atypical PKC isozymes as STAT and ERK activators that mediate c-fos and collagenase expression during IL-1 + OSM synergy in human chondrocytes. aPKCs may constitute potential therapeutic targets for inflammatory joint diseases involving increased collagenase expression.

Lithium protects cartilage from cytokine-mediated degradation by reducing collagen-degrading MMP production via inhibition of the P38 mitogen-activated protein kinase pathway

OBJECTIVES

To determine the effects and mechanism of action of lithium chloride (LiCl) on cartilage destruction induced by the pro-inflammatory cytokines IL-1, IL-1 + oncostatin M and TNF-α.

METHODS

The release of collagen was assessed in bovine cartilage explant cultures, whereas collagenolytic activities (active and total) in conditioned culture supernatants were determined by bioassay. The expression and production of MMP from chondrocytes were analysed by real-time RT-PCR and ELISA. Signalling pathway analysis was performed using a phospho-antibody array and standard immunoblotting.

RESULTS

LiCl, but not selective glycogen synthase kinase 3 (GSK-3) inhibitor compounds SB-415286 and TDZD-8, significantly decreased pro-inflammatory cytokine-induced collagen release from bovine cartilage via the down-regulation of collagenolytic activity. Furthermore, MMP-1 and MMP-13 expression was reduced in both bovine and human chondrocytes. Pathway analysis revealed that LiCl selectively inhibited activation of the p38 mitogen-activated protein kinase pathway; effects that were recapitulated by specific p38 pathway inhibition.

CONCLUSIONS

This study demonstrates for the first time that LiCl can protect against cartilage damage induced by pro-inflammatory cytokines, and indicates that LiCl-mediated cartilage protection is not via a GSK-3-dependent mechanism, but potentially via inhibition of the p38 pathway. These data indicate that lithium administration may represent a potential therapy for arthritis.

Muscle cells enhance resistance to pro-inflammatory cytokine-induced cartilage destruction

Pro-inflammatory cytokines IL-1beta and TNFalpha play important roles in the manifestation of arthritis by disrupting the anabolic and catabolic activities of the chondrocytes. We observed a novel mechanism of cartilage regulation by which muscle cells diminish the response of chondrocytes to IL-1beta and TNFalpha. We found that chondrocytes cocultured with muscle cells or cultured in muscle cell-conditioned medium significantly enhanced the expression of cartilage matrix proteins (collagen II and collagen IX) and resisted IL-1beta and TNFalpha-induced cartilage damage. Our data suggest that this effect is achieved by inhibiting the expression of key components of the signaling pathways of pro-inflammatory cytokines (including NFkappaB, ESE-1, Cox-2, and GADD45beta), leading to attenuated expression of cartilage-degrading enzymes (MMPs and ADAMTS4). Therefore, our work unveils a potential role of muscle in regulating cartilage homeostasis and response to pro-inflammatory stimuli, and provides insights on designing treatment strategies for joint degenerative diseases such as arthritis.

Regulation of immature cartilage growth by IGF-I, TGF-beta1, BMP-7, and PDGF-AB: role of metabolic balance between fixed charge and collagen network

Cartilage growth may involve alterations in the balance between the swelling tendency of proteoglycans and the restraining function of the collagen network. Growth factors, including IGF-I, TGF-beta1, BMP-7, and PDGF-AB, regulate chondrocyte metabolism and, consequently, may regulate cartilage growth. Immature bovine articular cartilage explants from the superficial and middle zones were incubated for 13 days in basal medium or medium supplemented with serum, IGF-I, TGF-beta1, BMP-7, or PDGF-AB. Variations in tissue size, accumulation of proteoglycan and collagen, and tensile properties were assessed. The inclusion of serum, IGF-I, or BMP-7 resulted in expansive tissue growth, stimulation of proteoglycan deposition but not of collagen, and a diminution of tensile integrity. The regulation of cartilage metabolism by TGF-beta1 resulted in tissue homeostasis, with maintenance of size, composition, and function. Incubation in basal medium or with PDGF-AB resulted in small volumetric and compositional changes, but a marked decrease in tensile integrity. These results demonstrate that the phenotype of cartilage growth, and the associated balance between proteoglycan content and integrity of the collagen network, is regulated differentially by certain growth factors.

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.

Synergistic collagenase expression and cartilage collagenolysis are phosphatidylinositol 3-kinase/Akt signaling-dependent

The phosphatidylinositol 3-kinase (PI3K) signaling pathway has emerged as a major regulator of cellular functions and has been implicated in several pathologies involving remodeling of extracellular matrix (ECM). The end stage of inflammatory joint diseases is characterized by excessive ECM catabolism, and in this study we assess the role of PI3K signaling in the induction of collagenolytic matrix metalloproteinases (MMPs) in human chondrocytes. We used the most potent cytokine stimulus reported to promote cartilage ECM catabolism, namely interleukin-1 (IL-1) in combination with oncostatin M (OSM). Both OSM and IL-6 (in the presence of its soluble receptor), but not IL-1 nor leukemia inhibitory factor, induced Akt phosphorylation in human chondrocytes. Inhibition of PI3K signaling using LY294002 blocked IL-1+OSM-mediated Akt phosphorylation, induction of MMP-1 and MMP-13, and cartilage collagenolysis. To further explore the role of downstream substrates within the PI3K pathway, complementary use of small molecule inhibitors and specific small interfering RNAs demonstrated that the PI3K subunit p110alpha and Akt1 were required for MMP-1 mRNA induction. MMP-13 induction was also reduced by loss of function of these molecules and by a lack of p110delta, 3-phosphoinositide-dependent kinase-1 or Akt3. We therefore propose that the activities of specific elements of the PI3K signaling pathway, including Akt, are necessary for the synergistic induction of MMP-1 and MMP-13 and the cartilage breakdown stimulated by IL-1+OSM. Our data provide new insight into the mechanism of synergy between IL-1 and OSM and highlight new therapeutic targets for inflammatory joint diseases that aim to repress the expression of collagenases.

Differentially regulated expression of growth differentiation factor 5 and bone morphogenetic protein 7 in articular cartilage and synovium in murine chronic arthritis: potential importance for cartilage breakdown and synovial hypertrophy

OBJECTIVE

To examine whether the endogenous expression of growth differentiation factor 5 (GDF-5) and bone morphogenetic protein 7 (BMP-7) is altered in the cartilage and synovium of human tumor necrosis factor alpha (TNFalpha)-transgenic (hTNFtg) mice with chronic arthritis, and to investigate the response of hTNFtg chondrocytes as well as fibroblast-like synoviocytes (FLS) to these morphogens in vitro.

METHODS

Analyses were performed in hTNFtg mice with chronic destructive arthritis and in wild-type (WT) mice as controls. Expression of GDF-5 and BMP-7 in the articular cartilage and synovium was examined by real-time polymerase chain reaction and immunohistochemistry. Human TNFtg cartilage explants, chondrocytes, and FLS monolayer cultures were assessed for basal matrix biosynthesis as well as growth factor responsiveness, using (35)S-sulfate incorporation assays. In addition, the DNA content/cell proliferation rate was measured.

RESULTS

The expression of GDF-5 and BMP-7 was decreased in articular cartilage from hTNFtg mice, whereas expression of both morphogens was increased in arthritic synovium from hTNFtg mice, as compared with the levels in WT controls. Isotope incorporation revealed a marked reduction of matrix synthesis in hTNFtg cartilage as well as a decrease in responsiveness to GDF-5 and BMP-7. The DNA content did not change in arthritic cartilage as compared with WT cartilage. In hTNFtg FLS, growth factor stimulation increased the rate of cell proliferation and the production of extracellular matrix.

CONCLUSION

In this murine model of TNFalpha-mediated arthritis, the expression of GDF-5 and BMP-7 is regulated differentially in articular cartilage and synovium. In articular cartilage, the down-regulation of GDF-5 and BMP-7, which function to maintain matrix integrity, could potentially compromise tissue repair, whereas in synovium, the increased expression of GDF-5 and BMP-7 might contribute to synovial hypertrophy.

Synergistic effect of IGF-1 and OP-1 on matrix formation by normal and OA chondrocytes cultured in alginate beads

OBJECTIVE

Growth factor therapy may be useful for stimulation of cartilage matrix synthesis and repair. Thus, the purpose of our study was to further understand the effect of combined insulin-like growth factor-1 (IGF-1) and osteogenic protein-1 (OP-1) treatment on the matrix synthesized by human adult normal and osteoarthritic (OA) chondrocytes.

DESIGN

Chondrocytes were isolated post-mortem from articular cartilage from tali of normal human donors and femoral condyles of OA patients undergoing knee replacement surgery. Cells were cultured in alginate beads for 21 days in four experimental groups: (1) "mini-ITS" control; (2) 100 ng/ml IGF-1; (3) 100 ng/ml OP-1; (4) IGF-1+OP-1, each at 100 ng/ml. Beads were processed for histological (Safranin O and fast green), morphometrical and immunohistochemical (aggrecan, decorin, type I, II, VI, and X collagens, and fibronectin accumulation) analyses.

RESULTS

Histology showed that IGF-1 alone did not induce substantial matrix production. OP-1 alone caused a considerable matrix formation, but the highest matrix accumulation by normal and OA chondrocytes was found when OP-1 and IGF-1 were added together. Morphometrical analysis indicated larger matrices produced by OA chondrocytes than by normal cells under the combined treatment. All tested matrix proteins were more abundant in the combination group. Type X collagen was detected only under the combined OP-1 and IGF-1 treatment and was present at very low levels. Type I collagen was found only in OA chondrocytes.

CONCLUSIONS

The results obtained in the current study suggest that combined therapy with IGF-1 and OP-1 may have a greater potential in treating cartilage defects seen in OA than use of either growth factor alone.

Anabolic and catabolic function of chondrocyte ex vivo is reflected by the metabolic processing of type II collagen

OBJECTIVE

The aim of the present study was to investigate collagen metabolism after anabolic and catabolic stimulation of chondrocytes ex vivo.

DESIGN

Metabolic activities in ex vivo bovine cartilage explants were stimulated with insulin-like growth factor I (IGF-I) or a combination of tumor necrosis factor alpha (TNFalpha) and oncostatin M (OSM). Supernatants were assessed for changes in biochemical markers, N-terminal propeptide of type II (PIINP) collagen and fragments of C-telopeptide of type II collagen (CTX-II). Matrix metalloproteinases (MMP) were added to metabolic inactivated cartilage and evaluated by the two biochemical markers for formation or degradation, respectively. Finally, urinary CTX-II and PIINP were evaluated for assessment of type II collagen turnover in patients with rheumatoid arthritis (RA).

RESULTS

In the bovine articular cartilage explants, IGF-I induced an increase in PIINP level up to 4.8+/-1.1[ng/ml]/mg cartilage whereas CTX-II remained below 0.1+/-0.1[ng/ml]/mg cartilage. In the catabolic stimulated explants both PIINP and CTX-II were released to the supernatant, reaching concentrations of 9.0+/-1.4 and 9.1+/-2.2[ng/ml]/mg cartilage, respectively. RA patients had significantly lower serum concentrations of PIINP (3.4+/-3.7 ng/ml) compared with those healthy individuals (18.7+/-12.41 ng/ml, P<0.001). In contrast, RA patients had significantly higher urinary CTX-II (0.8+/-0.8 mg/mmol) compared to the healthy controls (0.1+/-0.08 mg/mmol, P=0.004).

CONCLUSIONS

This study is the first to demonstrate that precursors and degradation products of type II collagen released into the supernatant can effectively reflect the anabolic and catabolic activities of stimulated cartilage explants.

Matrix metalloproteinase 10 promotion of collagenolysis via procollagenase activation: implications for cartilage degradation in arthritis

OBJECTIVE

We have previously reported the up-regulation of matrix metalloproteinase 10 (MMP-10) following treatment with the procatabolic stimulus of interleukin-1 (IL-1) and oncostatin M (OSM) in chondrocytes. Although MMP-10 is closely related to MMP-3, little is known about the role of MMP-10 in cartilage catabolism. The purpose of this study was to determine whether MMP-10 is expressed in connective tissue cells and to assess how it may contribute to cartilage collagenolysis.

METHODS

MMP gene expression was assessed by real-time polymerase chain reaction using RNA from human articular chondrocytes and synovial fibroblasts stimulated with IL-1 plus OSM or tumor necrosis factor alpha (TNFalpha) plus OSM. Synovial fluid levels of MMP-10 were determined by specific immunoassay. Recombinant procollagenases were used in activation studies. Immunohistochemistry assessed MMP-10 expression in diseased joint tissues.

RESULTS

MMP-10 expression was confirmed in both chondrocytes and synovial fibroblasts following stimulation with either IL-1 plus OSM or TNFalpha plus OSM, and MMP-10 was detected in synovial fluid samples from patients with various arthropathies. Exogenous MMP-10 significantly enhanced collagenolysis from IL-1 plus OSM-stimulated cartilage, and MMP-10 activated proMMP-1, proMMP-8, and proMMP-13. Immunohistochemistry revealed the presence of MMP-10 in the synovium and cartilage of an IL-1 plus OSM-induced model of arthritis as well as in samples of diseased human tissues.

CONCLUSION

We confirm that both synovial fibroblasts and articular chondrocytes express MMP-10 following treatment with procatabolic stimuli. Furthermore, the detectable levels of synovial fluid MMP-10 and the histologic detection of this proteinase in diseased joint tissues strongly implicate MMP-10 in the cartilage degradome during arthritis. The ability of MMP-10 to superactivate procollagenases that are relevant to cartilage degradation suggests that this activation represents an important mechanism by which this MMP contributes to tissue destruction in arthritis.

Identification of fibronectin neoepitopes present in human osteoarthritic cartilage

OBJECTIVE

Fibronectin fragments are present at high concentrations in the cartilage of patients with rheumatoid arthritis and patients with osteoarthritis (OA) and have been shown to promote cartilage catabolism in human cartilage cultures, suggesting that fibronectin fragments participate in the initiation and progression of arthritic disease. This study was undertaken to 1) identify the major fibronectin fragments in human OA cartilage and confirm their ability to elicit cartilage catabolism, 2) identify the cleavage sites in fibronectin and generate the corresponding neoepitope antibodies, and 3) explore the utility of fibronectin neoepitopes as biomarkers.

METHODS

Fibronectin fragments were purified from human OA cartilage using affinity chromatography; their N-termini were then identified by sequencing. Bovine nasal cartilage was treated with affinity-purified fibronectin fragments and assayed for aggrecan breakdown by monitoring the release of glycosaminoglycans and the aggrecan neoepitope 1771AGEG. Fibronectin neoepitopes were detected by Western blotting in cytokine-treated media of human cartilage explants, and by immunohistochemical analyses of human OA cartilage.

RESULTS

Multiple fibronectin fragments were isolated from human OA cartilage, and all contained the N-terminus 272VYQP. These fragments induced aggrecanase-mediated cartilage catabolism in bovine cartilage explants. Fibronectin fragments with the N-terminus 272VYQP and fragments with the C-terminus VRAA271 were detected following cytokine treatment of human cartilage extracts. These neoepitopes localized with areas of aggrecan loss in OA cartilage.

CONCLUSION

Human OA cartilage contains fibronectin fragments with catabolic activity and a major cleavage site within fibronectin. This study is the first to characterize fibronectin neoepitopes in OA cartilage, suggesting that they may represent a novel biomarker of arthritis.

Effects of ovariectomy and estrogen therapy on type II collagen degradation and structural integrity of articular cartilage in rats: implications of the time of initiation

OBJECTIVE

To investigate how the time of initiation influences the effects of estrogen therapy on type II collagen (CII) turnover and the structural integrity of articular cartilage in ovariectomized rats and to determine whether estrogen exerts direct effects on the catabolic function of chondrocytes ex vivo.

METHODS

A total of 46 Sprague-Dawley rats were distributed into 1 of the following treatment groups: 1) ovariectomy, 2) ovariectomy plus early estrogen therapy, 3) ovariectomy plus delayed estrogen therapy, or 4) sham operation. Cartilage turnover was estimated by measuring the serum levels of C-telopeptide of type II collagen (CTX-II). Cartilage lesions at week 9 were quantified using a published scoring technique. The presence of the CTX-II epitope in articular cartilage was assessed by immunohistochemistry. The effects of estrogen (1-100 nM) on chondrocytes were investigated in bovine cartilage explants subjected to catabolic cytokines (tumor necrosis factor alpha [TNFalpha] and oncostatin M [OSM]).

RESULTS

In ovariectomized rats, estrogen therapy evoked significant decreases in serum CTX-II independently of the time of initiation; yet, delayed initiation resulted in diminished efficacy in terms of preventing cartilage lesions. CTX-II fragments were present in articular cartilage, colocalizing with early lesions at the cartilage surface. In untreated animals, the early relative increases in serum CTX-II were proportional to the severity of cartilage lesions at week 9 (r = 0.73, P < 0.01). Estrogen significantly and dose-dependently countered CTX-II release from TNFalpha plus OSM-stimulated cartilage explants ex vivo.

CONCLUSION

Our results suggest that estrogen counters the acceleration of CII degradation and related structural alterations, and these benefits can be maximized by early initiation after menopause. The protective effect of estrogen seems to involve direct inhibition of the catabolic function of chondrocytes.

Calcitonin directly attenuates collagen type II degradation by inhibition of matrix metalloproteinase expression and activity in articular chondrocytes

OBJECTIVE

Calcitonin was recently reported to counter progression of cartilage degradation in an experimental model of osteoarthritis, and the effects were primarily suggested to be mediated by inhibition of subchondral bone resorption. We investigated direct effects of calcitonin on chondrocytes by assessing expression of the receptor and pharmacological effects on collagen type II degradation under ex vivo and in vivo conditions.

METHODS

Localization of the calcitonin receptor on articular chondrocytes was investigated by immunohistochemistry, and the expression by reverse transcriptase polymerase chain reaction (RT-PCR). In bovine articular cartilage explants, cartilage degradation was investigated by release of C-terminal telopeptides of collagen type II (CTX-II), induced by tumor necrosis factor-alpha (TNF-alpha) [20 ng/ml] and oncostatin M (OSM) [10 ng/ml], with salmon calcitonin [0.0001-1 microM]. In vivo, cartilage degradation was investigated in ovariectomized (OVX) rats administered with oral calcitonin [2 mg/kg calcitonin] for 9 weeks.

RESULTS

The calcitonin receptor was identified in articular chondrocytes by immunohistochemistry and RT-PCR. Calcitonin concentration-dependently increased cAMP levels in isolated chondrocytes. Explants cultured with TNF-alpha and OSM showed a 100-fold increase in CTX-II release compared to vehicle-treated controls (P<0.001). The degradation of type II collagen in these explants was concentration-dependently inhibited by calcitonin, 65% protection at 10 nM calcitonin (P<0.01). TNF-alpha and OSM induced a pronounced increase in matrix metalloproteinase (MMP) activity, which was strongly inhibited by calcitonin. In vivo, administration of salmon calcitonin to OVX rats resulted in significant (P<0.001) decrease in CTX-II levels.

CONCLUSION

These results are the first evidence of calcitonin receptor expression on articular chondrocytes and that the chondroprotective effects of calcitonin might involve the inhibition of MMP expression.

Relative contribution of matrix metalloprotease and cysteine protease activities to cytokine-stimulated articular cartilage degradation

OBJECTIVE

Both matrix metalloprotease (MMP) activity and cathepsin K (CK) activity have been implicated in cartilage turnover. We investigated the relative contribution of MMP activity and CK activity in cartilage degradation using ex vivo and in vivo models.

METHODS

Bovine articular cartilage explants were stimulated with oncostatin M (OSM) 10 ng/ml and tumor necrosis factor-alpha (TNF-alpha) 20 ng/ml in the presence or absence of the broad-spectrum MMP inhibitor GM6001 and the cysteine protease inhibitor, E64. Cartilage degradation was evaluated in the conditioned medium by glycosaminoglycans (GAG), hydroxyproline, and cross-linked C-telopeptide fragments of type II collagen (CTX-II), which were compared to immunohistochemical evaluations of proteoglycans and CTX-II. We assessed MMP expression by gelatine zymography and CK expression by immunohistochemistry. In vivo, CTX-II release was measured from CK-deficient mice.

RESULTS

OSM and TNF-alpha combined induced significant (P<0.01) increase in cartilage degradation products measured by hydroxyproline and CTX-II compared to vehicle control. The cytokines potently induced MMP expression, assessed by zymography, and CK expression investigated by immunohistochemistry. Inhibition of MMP activity completely abrogated hydroxyproline and CTX-II release (P<0.01) and GAG release (P<0.05). In contrast, E64 resulted in increased CTX-II release by 100% (P<0.05) and inhibited GAG release by 30%. Up-regulation of CTX-II fragments was confirmed in vivo in CK null mice.

CONCLUSION

Inhibition of MMP activity reduced both proteoglycan loss and type II collagen degradation. In contrast, inhibition of cysteine proteases resulted in an increase rather than a decrease in MMP derived fragments of collagen type II degradation, CTX-II, suggesting altered collagen metabolism.

Oncostatin M in combination with tumour necrosis factor {alpha} induces a chondrocyte membrane associated aggrecanase that is distinct from ADAMTS aggrecanase-1 or -2

OBJECTIVE

To determine whether oncostatin M (OSM) + tumour necrosis factor alpha (TNFalpha) induces aggrecanase activity in chondrocyte membranes, to determine the effects of transforming growth factor beta1 (TGFbeta1), interleukin 4 (IL4), and tissue inhibitor of metalloproteinases (TIMPs) on this activity, and to determine whether this activity is due to a known ADAMTS aggrecanase.

METHODS

Aggrecanase activity and ability of agents to prevent membrane associated aggrecanase activity were assessed by Western blotting. Expression of known aggrecanases was measured by real time polymerase chain reaction in bovine nasal and human articular chondrocytes.

RESULTS

Chondrocyte membrane associated aggrecanase activity and increased mRNA expression of ADAMTS-1, -4, -5, and -9, but not ADAMTS-4 or -15, were enhanced after stimulation by OSM+TNFalpha in bovine chondrocytes. This activity was inhibited by TIMP-3. In human chondrocytes, OSM+TNFalpha also enhanced ADAMTS-1 and -4 expression, but not that of other ADAMTSs. TNFalpha alone induced ADAMTS-9 expression, whereas OSM addition caused suppression. Both TGFbeta1 and IL4 blocked membrane associated aggrecanase activity and decreased OSM+TNFalpha-induced expression of ADAMTS-9 in bovine and human chondrocytes. IL4 down regulated ADAMTS-4 mRNA, whereas TGFbeta1 increased this expression in both bovine and human chondrocytes.

CONCLUSIONS

OSM+TNFalpha up regulates membrane associated aggrecanase activity and several ADAMTS aggrecanase mRNAs in chondrocytes. The chondroprotective effects of IL4 and TIMP-3 suggest that they may have therapeutic benefit for aggrecanolysis, whereas the differential inhibitory effects of TGFbeta1 may limit its therapeutic potential. Induced membrane associated aggrecanase activity is distinct from known soluble ADAMTS aggrecanases and merits further investigation.

In Vitro, Ex Vivo, andIn VivoMethodological Approaches for Studying Therapeutic Targets of Osteoporosis and Degenerative Joint Diseases: How Biomarkers Can Assist?

Although our approach to the clinical management of osteoporosis (OP) and degenerative joint diseases (DJD)-major causes of disability and morbidity in the elderly-has greatly advanced in the past decades, curative treatments that could bring ultimate solutions have yet to be found or developed. Effective and timely development of candidate drugs is a critical function of the availability of sensitive and accurate methodological arsenal enabling the recognition and quantification of pharmacodynamic effects. The established concept that both OP and DJD arise from an imbalance in processes of tissue formation and degradation draws attention to need of establishing in vitro, ex vivo, and in vivo experimental settings, which allow obtaining insights into the mechanisms driving increased bone and cartilage degradation at cellular, organ, and organism levels. When addressing changes in bone or cartilage turnover at the organ or organism level, monitoring tools adequately reflecting the outcome of tissue homeostasis become particularly critical. In this context, bioassays targeting the quantification of various degradation and formation products of bone and cartilage matrix elements represent a useful approach. In this review, a comprehensive overview of widely used and recently established in vitro, ex vivo, and in vivo set-ups is provided, which in many cases effectively take advantage of the potentials of biomarkers. In addition to describing and discussing the advantages and limitations of each assay and their methods of evaluation, we added experimental and clinical data illustrating the utility of biomarkers for these methodological approaches.

A model of inflammatory arthritis highlights a role for oncostatin M in pro-inflammatory cytokine-induced bone destruction via RANK/RANKL

Oncostatin M is a pro-inflammatory cytokine previously shown to promote marked cartilage destruction both in vitro and in vivo when in combination with IL-1 or tumour necrosis factor alpha. However, the in vivo effects of these potent cytokine combinations on bone catabolism are unknown. Using adenoviral gene transfer, we have overexpressed oncostatin M in combination with either IL-1 or tumour necrosis factor alpha intra-articularly in the knees of C57BL/6 mice. Both of these combinations induced marked bone damage and markedly increased tartrate-resistant acid phosphatase-positive multinucleate cell staining in the synovium and at the front of bone erosions. Furthermore, there was increased expression of RANK and its ligand RANKL in the inflammatory cells, in inflamed synovium and in articular cartilage of knee joints treated with the cytokine combinations compared with expression in joints treated with the cytokines alone or the control. This model of inflammatory arthritis demonstrates that, in vivo, oncostatin M in combination with either IL-1 or tumour necrosis factor alpha represents cytokine combinations that promote bone destruction. The model also provides further evidence that increased osteoclast-like, tartrate-resistant acid phosphatase-positive staining multinucleate cells and upregulation of RANK/RANKL in joint tissues are key factors in pathological bone destruction.

Differential regulation of chondrocyte metabolism by oncostatin M and interleukin-6

OBJECTIVE

To determine the effects of interleukin (IL)-6 and oncostatin M (OSM) added separately or in combination with IL-1beta on human osteoarthritic (OA) chondrocytes in alginate beads.

DESIGN

Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 12 days, in the absence or in the presence of increasing amounts of IL-6 (20-500ng/ml) with its soluble receptor or OSM (0.1-10ng/ml) and with or without IL-1beta (1.7ng/ml). Aggrecan (AGG), transforming growth factor-beta1 (TGF-beta1), stromelysin-1 [matrix metalloprotease (MMP)-3], tissue inhibitor of metalloproteinases-1 (TIMP-1), macrophage inflammatory protein-1 beta (MIP-1beta), IL-6 and IL-8 productions were assayed by specific enzyme amplified sensitivity immunoassays. Prostaglandin (PG)E(2) was measured by a specific radioimmunoassay and nitrite (NO(2)(-)) by a spectrophotometric method based upon the Griess reaction.

RESULTS

OSM, but not IL-6, decreased basal AGG and TGF-beta1 synthesis. Although IL-6 stimulated basal TIMP-1 production, it did not significantly modify MMP-3/TIMP-1 ratio. In contrast, 10ng/ml OSM highly increased TIMP-1 production, and decreased by half the ratio MMP-3/TIMP-1. IL-1beta highly stimulated *NO, IL-8, IL-6, MIP-1beta and PGE(2) synthesis but decreased AGG and TGF-beta1 production. Neither IL-6 nor OSM modulated IL-1beta-inhibitory effect on AGG production. IL-6, but not OSM, reversed IL-1beta-induced TGF-beta1 inhibition. At 1-10ng/ml, OSM significantly decreased IL-1beta-stimulated IL-8, MIP-1beta, PGE(2) and *NO production but amplified IL-1beta stimulating effect on IL-6 production. IL-6 had no effect on these parameters.

CONCLUSIONS

OSM and IL-6, two glycoprotein 130 binding cytokines, show different activity profiles on OA chondrocytes, indicating that these cytokines could play different roles in the OA disease process.

Oncostatin M in combination with tumor necrosis factor ? 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.

Adenoviral gene transfer of interleukin-1 in combination with oncostatin M induces significant joint damage in a murine model

Oncostatin M (OSM) is an interleukin (IL)-6 family cytokine that we have previously shown can synergize with a number of proinflammatory cytokines to promote the release of collagen from cartilage in explant culture. However, the effects of this potent cytokine combination in vivo are not known. Using adenoviral gene transfer, we have overexpressed murine IL-1 (AdmIL-1) and murine OSM (AdmOSM) intraarticularly in the knees of C57BL/6 mice. Histological analyses indicated marked synovial hyperplasia and inflammatory cell infiltration for both AdmIL-1 and AdmOSM but not in control joints. This inflammation was even more pronounced for the AdmIL-1+AdmOSM combination with evidence of cartilage and bone destruction. Significant loss of both proteoglycan and collagen was also seen for this combination, and immunohistochemistry revealed an increased expression of matrix metalloproteinases (MMPs) with decreased tissue inhibitor of metalloproteinases (TIMPs) in both articular cartilage and synovium. Similar expression profiles for MMPs/TIMPs were found in IL-1+OSM-stimulated human articular chondrocytes. Taken together, these data confirm that, in vivo, OSM can exacerbate the effects of IL-1 resulting in inflammation and tissue destruction characteristic of that seen in rheumatoid arthritis. We provide further evidence to implicate the up-regulation of MMPs as a key factor in joint pathology.