Basic fibroblast growth factor inhibits the anabolic activity of insulin-like growth factor 1 and osteogenic protein 1 in adult human articular chondrocytes

Fibroblast growth factor-2 induced chondrocyte cluster formation in experimentally wounded articular cartilage is blocked by soluble Jagged-1

INTRODUCTION

Basic fibroblast growth factor (FGF2) is a mitogen for articular chondrocytes. Cell death frequently occurs upon cartilage wounding and is evident during the progression of osteoarthritis. We hypothesised that incubation of wounded articular cartilage with exogenously added FGF2 would enhance cartilage repair, replacing dead cells through increased cell proliferation.

METHODS

Articular cartilage from the metacarapalphalangeal joint of immature bovine steers was wounded in situ, then incubated in vitro in the continual presence or absence of FGF2. Cellular proliferation was expressed as a ratio of cell density of a fixed area between wounded and adjacent cartilage. Immunolabelling revealed the incorporation of bromodeoxyuridine and localisation of collagen type VI and Notch1 epitopes. gamma-secretase inhibitor N-[N-(3,5-Difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester and soluble Jagged1 ligand (sJ1) were used to analyse the function of Notch signalling in this wound model.

RESULTS

FGF2 induced cellular proliferation at the margins of wounded articular cartilage, where proliferative chondrocytes adopted a cluster configuration. Collagen type VI protein was expressed by chondrocytes in clusters, as was Notch1. Cellular proliferation was not affected by inhibition of gamma-secretase dependent Notch1 signalling. Binding of sJ1 to Notch1 receptors in FGF2 treated cartilage inhibited proliferation.

CONCLUSION

Addition of FGF2 induces rapid chondrocyte proliferation in wounded cartilage, chondrocytes adopt a cluster morphology and also express Notch1. Binding of sJ1 to Notch1 causes apoptosis overriding a proliferative response. This study may shed some light on the significance of increased Notch1 expression and its localisation in chondrocyte clusters in osteoarthritic cartilage.

Cartilage engineering from mesenchymal stem cells

Mesenchymal progenitor cells known as multipotent mesenchymal stromal cells or mesenchymal stem cells (MSC) have been isolated from various tissues. Since they are able to differentiate along the mesenchymal lineages of cartilage and bone, they are regarded as promising sources for the treatment of skeletal defects. Tissue regeneration in the adult organism and in vitro engineering of tissues is hypothesized to follow the principles of embryogenesis. The embryonic development of the skeleton has been studied extensively with respect to the regulatory mechanisms governing morphogenesis, differentiation, and tissue formation. Various concepts have been designed for engineering tissues in vitro based on these developmental principles, most of them involving regulatory molecules such as growth factors or cytokines known to be the key regulators in developmental processes. Growth factors most commonly used for in vitro cultivation of cartilage tissue belong to the fibroblast growth factor (FGF) family, the transforming growth factor-beta (TGF-β) super-family, and the insulin-like growth factor (IGF) family. In this chapter, in vivo actions of members of these growth factors described in the literature are compared with in vitro concepts of cartilage engineering making use of these growth factors.

Basic fibroblast growth factor induces matrix metalloproteinase-13 via ERK MAP kinase-altered phosphorylation and sumoylation of Elk-1 in human adult articular chondrocytes

Degradation of the extracellular matrix (ECM) by matrix metalloproteinases (MMPs) and release of basic fibroblast growth factor (bFGF) are principal aspects of the pathology of osteoarthritis (OA). ECM disruption leads to bFGF release, which activates the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway and its downstream target the Ets-like transcription factor Elk-1. Previously we demonstrated that the bFGF-ERK-Elk-1 signaling axis is responsible for the potent induction of MMP-13 in human primary articular chondrocytes. Here we report that, in addition to phosphorylation of Elk-1, dynamic posttranslational modification of Elk-1 by small ubiquitin-related modifier (SUMO) serves as an important mechanism through which MMP-13 gene expression is regulated. We show that bFGF activates Elk-1 mainly through the ERK pathway and that increased phosphorylation of Elk-1 is accompanied by decreased conjugation of SUMO to Elk-1. Reporter gene assays reveal that phosphorylation renders Elk-1 competent for induction of MMP-13 gene transcription, while sumoylation has the opposite effect. Furthermore, we demonstrate that the SUMO-conjugase Ubc9 acts as a key mediator for Elk-1 sumoylation. Taken together, our results suggest that sumoylation antagonizes the phosphorylation-dependent transactivation capacity of Elk-1. This attenuates transcription of its downstream target gene MMP-13 to maintain the integrity of cartilage ECM homeostasis.

Leptin plays a catabolic role on articular cartilage

Leptin has been shown to play a crucial role in the regulation of body weight. There is also evidence that this adipokine plays a key role in the process of osteoarthritis. However, the precise role of leptin on articular cartilage metabolism is not clear. We investigate the role of leptin on articular cartilage in vivo in this study. Recombinant rat leptin (100 μg) was injected into the knee joints of rats, 48 h later, messenger RNA (mRNA) expression and protein levels of basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), matrix metalloproteinases 2 and 9 (MMP-2, MMP-9), cathepsin D, and collagen II from articular cartilage were analyzed by real-time quantitative polymerase chain reaction (PCR) and western blot. Two important aggrecanases ADAMTS-4 and -5 (a disintegrin and metalloproteinase with thrombospondin motifs 4 and 5) were also analyzed by real-time quantitative PCR. Besides, articular cartilage was also assessed for proteoglycan/GAG content by Safranin O staining. Leptin significantly increased both gene and protein levels of MMP-2, MMP-9, cathepsin D, and collagen II, while decreased bFGF markedly in cartilage. Moreover, the gene expression of ADAMTS-4 and -5 were markedly increased, and histologically assessed depletion of proteoglycan in articular cartilage was observed after treatment with leptin. These results strongly suggest that leptin plays a catabolic role on cartilage metabolism and may be a disadvantage factor involve in the pathological process of OA.

Chondrogenesis, joint formation, and articular cartilage regeneration

The repair of joint surface defects remains a clinical challenge, as articular cartilage has a limited healing response. Despite this, articular cartilage does have the capacity to grow and remodel extensively during pre- and post-natal development. As such, the elucidation of developmental mechanisms, particularly those in post-natal animals, may shed valuable light on processes that could be harnessed to develop novel approaches for articular cartilage tissue engineering and/or regeneration to treat injuries or degeneration in adult joints. Much has been learned through mouse genetics regarding the embryonic development of joints. This knowledge, as well as the less extensive available information regarding post-natal joint development is reviewed here and discussed in relation to their possible relevance to future directions in cartilage tissue repair and regeneration.

rAAV-mediated overexpression of FGF-2 promotes cell proliferation, survival, and alpha-SMA expression in human meniscal lesions

Meniscal tears are a common problem in sports medicine. Direct application of therapeutic vectors derived from the adeno-associated virus might be beneficial to enhance meniscal repair. We tested the hypothesis that overexpression of fibroblast growth factor 2 (FGF-2) through recombinant adeno-associated virus (rAAV) vectors leads to detectable metabolic changes in human meniscal fibrochondrocytes and in human meniscal defects. rAAV-mediated gene transfer was investigated for its ability to promote FGF-2 secretion in human meniscal fibrochondrocytes in vitro, in intact human meniscal explants in situ, and in experimentally created human meniscal lesions. Effects of the treatment on cell proliferation and survival, extracellular matrix synthesis, and expression of the alpha-smooth muscle actin (alpha-SMA) contractile marker were monitored using biochemical, immunohistochemical, histological, and histomorphometric analyses. Efficient production of FGF-2 through rAAV could be achieved in vitro and in situ, both in the intact and injured meniscus. Application of the candidate FGF-2 vector allowed for enhanced cell proliferation and survival compared with control transduction, in particular in areas with poor healing capacity and in sites of injury, consistent with the mitogenic activities of the growth factor. Remarkably, a significant reduction of the amplitude of meniscal tears was noted after FGF-2 treatment, with increased levels of alpha-SMA expression. In contrast, there was no significant stimulation of synthesis of the major extracellular matrix components when the candidate vector was applied and instead, a decrease in the matrix/DNA contents was reported, in good agreement with the properties of FGF-2. Such a direct gene-based approach may have value in options aiming at treating human meniscal defects.

Cartilage homeostasis in health and rheumatic diseases

As the cellular component of articular cartilage, chondrocytes are responsible for maintaining in a low-turnover state the unique composition and organization of the matrix that was determined during embryonic and postnatal development. In joint diseases, cartilage homeostasis is disrupted by mechanisms that are driven by combinations of biological mediators that vary according to the disease process, including contributions from other joint tissues. In osteoarthritis (OA), biomechanical stimuli predominate with up-regulation of both catabolic and anabolic cytokines and recapitulation of developmental phenotypes, whereas in rheumatoid arthritis (RA), inflammation and catabolism drive cartilage loss. In vitro studies in chondrocytes have elucidated signaling pathways and transcription factors that orchestrate specific functions that promote cartilage damage in both OA and RA. Thus, understanding how the adult articular chondrocyte functions within its unique environment will aid in the development of rational strategies to protect cartilage from damage resulting from joint disease. This review will cover current knowledge about the specific cellular and biochemical mechanisms that regulate cartilage homeostasis and pathology.

Joint injury and osteoarthritis: soluble mediators in the course and treatment of cartilage pathology

Osteoarthritis is a disabling disease of the aging generation, which results in loss of quality of life and increased healthcare costs. Cytokines appear to play an important role in the cartilaginous degeneration characterizing the pathological process. Increasing experience is being gained with cytokine-modulating therapies aimed at interfering with effects of chondrodegradative cytokines in the synovial fluid. Although in vitro and in vivo effectiveness of several of these therapies has been demonstrated, clinical effectiveness remains disputable, which may be related to the low levels of inflammatory cytokines found in osteoarthritic joints. By contrast, directly after joint trauma, which has been shown to predipose to early osteoarthritis, synovial fluid cytokine levels are strongly increased. Cytokine-modulating therapies, however, have hardly been considered for this indication. Increased knowledge of intra-articular soluble mediators correlating with cartilage pathology will lead to further development of cytokine-modulating products and, eventually, to effective inhibition of cartilage degeneration, in both the osteoarthritic as well as injured joints.

The BMP antagonists follistatin and gremlin in normal and early osteoarthritic cartilage: an immunohistochemical study

OBJECTIVE

Bone morphogenic protein (BMP) activities are controlled in part by antagonists. In human osteoarthritic (OA) cartilage, the BMP antagonists follistatin and gremlin are increased but differentially regulated. Using the OA dog model, we determined if these BMP antagonists were produced at different stages during the disease process by comparing their in situ temporal and spatial distribution.

METHODS

Dogs were sacrificed at 4, 8, 10 and 12 weeks after surgery; normal dogs served as control. Cartilage was removed, differentiating fibrillated and non-fibrillated areas. Immunohistochemistry and morphometric analyses were performed for follistatin, gremlin, BMP-2/4 and IL-1beta. Growth factor-induced gremlin expression was assessed in dog chondrocytes.

RESULTS

Follistatin and gremlin production were very low in normal cartilage. Gremlin was significantly up-regulated in both non-fibrillated and fibrillated areas at 4 weeks, and only slightly increased with disease progression. Follistatin showed a time-dependent increased level in the non-fibrillated areas with significance reached at 8-12 weeks; in the fibrillated areas significant high levels were seen as early as 4 weeks. In the whole cartilage, follistatin and IL-1beta temporal production showed similar patterns; this was also true for gremlin and BMP-2/4, though BMP-2/4 production was already high in the normal dogs. Interestingly, data revealed that basic fibroblast growth factor (bFGF) could be another factor increasing gremlin expression early in the disease process. Comparison between superficial and deep zones revealed similar patterns for follistatin and IL-1beta in the superficial zone only; gremlin and BMP-2/4 had similar patterns in both zones.

CONCLUSION

Data show, for the first time, different spatial and temporal production of gremlin and follistatin in cartilage during OA progression. These findings may reflect different roles for each antagonist in this disease.

Inhibition of histone deacetylases antagonized FGF2 and IL-1beta effects on MMP expression in human articular chondrocytes

Fibroblast growth factor-2 (FGF2) and interleukin-1beta (IL-1beta) stimulate the expression of matrix metalloproteinases (MMPs) in articular chondrocytes, which may contribute to cartilage degradation and development of osteoarthritis. Histone deacetylases (HDACs) have recently been implicated in the regulation of MMP gene expression. To investigate the functional involvement of HDACs in the signaling pathway of FGF2 and IL-1beta, we examined the effects of HDAC inhibition on activities of FGF2 or IL-1beta on gene expression of MMP-1, MMP-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS5), collagen type II, and aggrecan. Human articular chondrocyte cultures were treated with FGF2 or IL-1beta in the presence or absence of HDAC inhibitor (trichostatin A, TSA). Gene expression levels after treatments were assessed using quantitative real time PCR. Results showed that FGF2 and IL-1beta both increased MMP-1 and -13 expression, while IL-1beta also increased MMP-3 mRNA levels. These effects were attenuated in the presence of TSA in a dose dependent manner. In contrast to the effects on MMPs, FGF2 decreased mRNA levels of ADAMTS-5, which was not affected by HDAC inhibition. FGF2, IL-1beta, and TSA inhibited expression of aggrecan, while TSA also decreased mRNA levels of collagen type II. These findings showed that HDAC inhibition antagonized FGF2 and IL-1beta induced MMP expression. Combination of FGF2 and the HDAC inhibitor decreases both anabolic and catabolic genes, which may slow the cartilage turnover and be beneficial for maintaining cartilage integrity.

Growth factor regulation of growth factors in articular chondrocytes

Several lines of evidence indicate that polypeptide growth factors are important in articular cartilage homeostasis and repair. It is not yet clear how these growth factors are regulated. We tested the hypothesis that the growth factors responsible for regulating cartilage are themselves regulated by growth factors. We delivered insulin-like growth factor I (IGF-I), fibroblast growth factor-2 (FGF-2), and/or transforming growth factor-beta1 (TGF-beta1) to adult bovine articular chondrocytes in primary culture and measured the resulting changes in IGF-I, FGF-2, and TGF-beta1 gene expression and protein production. These growth factors differentially regulated their own and each others gene expression and protein production. In concert, they regulated each other in an interactive fashion. Their interactions ranged from inhibitory to synergistic. The time course of the regulatory effects differed among the individual growth factors and combinations. Growth factor-induced changes in growth factor protein production by articular chondrocytes generally corresponded to the changes in gene expression patterns. These studies suggest that interactions among IGF-I, FGF-2, and TGF-beta1 substantially modulate their regulatory functions. The results may help guide the application of growth factors to articular cartilage repair.

The action of resveratrol, a phytoestrogen found in grapes, on the intervertebral disc

STUDY DESIGN

Basic science, biologic study.

OBJECTIVE

To determine the potential benefits of using resveratrol (RSV) for intervertebral disc (IVD) matrix repair and regeneration.

SUMMARY OF BACKGROUND DATA

The phytoestrogen RSV is a natural compound found in various plants including grapes and red wines. RSV has been reported to provide a protective effect on articular cartilage in rabbit models for arthritis, but its effect on spine cartilage is unknown. METHODS.: We studied the effect of RSV on bovine IVD cartilage homeostasis by assessing MMP-13 (potent catabolic factor) production, proteoglycan (PG) accumulation and synthesis, and the interaction between RSV and known catabolic factors such as bFGF or IL-1. To understand the molecular mechanisms by which RSV modulates MMP-13 and PG production, we also investigated its downstream target regulatory molecules.

RESULTS

Stimulation of bovine disc cells cultured in monolayer with bFGF or IL-1 augmented the production of MMP-13 and ADAMTS-4 at the transcriptional level and this augmentation was blocked by RSV. Incubation of nucleus pulposus cells with RSV for 21 days significantly increased PG accumulation per cell in a dose-dependent manner, increased PG synthesis, rescued PG losses induced by catabolic reagents bFGF and IL-1, and promoted cell survival to levels seen after incubation with the anabolic protein BMP7 100 ng/mL. Protein-DNA interaction array results suggest that RSV effectively suppresses downstream target molecules of bFGF and IL-1 responsible for oxidative stress, proliferation, and apoptosis.

CONCLUSION

Resveratrol is a potent anabolic mediator of bovine IVD cartilage homeostasis, revealing its potential as a unique biologic treatment to slow the progression of IVD degeneration. These data suggests RSV may have considerable promise in the treatment of disc degeneration.

Effects of exogenous IGF-1 delivery on the early expression of IGF-1 signaling molecules by alginate embedded chondrocytes

Cartilage tissue engineering remains a significant challenge for both researchers and clinicians. Many strategic approaches, such as the delivery of growth factors to an in vitro cultured cartilage construct, continue to receive significant attention. However, the effects of delivering exogenous signaling molecules on endogenous signaling pathways within an engineered tissue are not well understood. In order to address this concern, we have investigated how the delivery of insulin-like growth factor-1 (IGF-1, delivered at concentrations of 0, 10, 50, and 100 ng/mL) affects the endogenous expression of IGF-1, its receptor (IGF-1R), and a well known IGF-1 binding protein (IGFBP-3) by articular chondrocytes embedded in alginate hydrogels over 8 days. To the best of our knowledge, this is the first report of delivery effects upon endogenous signal expression in a three-dimensional system relevant to tissue engineering objectives. Results showed significant differences in mRNA expression of IGF-1, IGF-1R, type II collagen, and type I collagen by day 8 between the induced versus noninduced IGF-1 groups. At day 8, the induced IGF-1 groups expressed IGF-1 mRNA four times lower than the 0 ng/mL IGF-1 group. Further, the IGF-1R mRNA expression was five times higher for the groups exposed to exogenous IGF-1 versus the 0 ng/mL IGF-1 case. Interestingly, the expression of IGFBP-3 decreased for all groups. Type II collagen expression was the highest and type I collagen was the lowest for the IGF-1 delivered samples. Finally, the different concentrations of IGF-1 investigated did not demonstrate significantly different trends in mRNA expression levels. Overall, results indicate that exogenous IGF-1 delivery does affect signaling molecule expression by chondrocytes embedded in alginate hydrogels, particularly downregulating the delivered signal while upregulating its receptor.

Controlled release of growth factors on allograft bone in vitro

Allografts are important alternatives to autografts for treating defects after major bone loss. Bone growth factors have both local autocrine and paracrine effects and regulate the growth, proliferation, and differentiation of osteoprogenitor cells. To study the effects of prolonged, continuous, local delivery of growth factors on bone growth, we developed a new microelectromechanical system (MEMS) drug delivery device. Bone marrow cells from mice were seeded on mouse allograft discs and cultured in osteogenic media with osteogenic protein 1 (OP-1) and/or basic fibroblast growth factor (FGF-2) delivered from MEMS devices for 6 weeks. We monitored bone formation by changes of bone volume using micro-CT scanning and release of osteocalcin using ELISA. The data suggest the MEMS devices delivered constant concentrations of OP-1 and FGF-2 to the media. Bone marrow cells grew on the allografts and increased bone volume. Addition of OP-1 increased bone formation whereas FGF-2 decreased bone formation. Local delivery of growth factors over a prolonged period modulated the differentiation of osteoprogenitor cells on allograft bone.

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.

Molecular network of cartilage homeostasis and osteoarthritis

This review article presents the current understanding of the molecular basis of articular cartilaginous homeostasis, and outlines potential areas to focus on within the developing field of therapeutics for cartilage disorders. Articular cartilage, an integral component of joints in extremities and the vertebral column, is essential for locomotion. Disturbance of joint development or cartilage homeostasis causes congenital osteocartilaginous dysplasia or osteoarthritic diseases, respectively. Symptomatic treatments and surgical replacement of joints are effective but can also be problematic in terms of quality of life over time. Recently, new insights into the molecular biological basis of chondrocyte differentiation and cartilage homeostasis have been reported. While joint formation is regulated by several growth factors such as Wnts (wingless-related MMTV integration site) and Gdfs (growth and differentiation factors), the pathology of osteoarthritis is now interpreted as the disruption of balance between anabolic and catabolic signals. Current findings in molecular biology on joint development are reviewed concisely to aid in the understanding of the molecular network that governs articular cartilage development and homeostasis.

Biological impact of the fibroblast growth factor family on articular cartilage and intervertebral disc homeostasis

Two members of the fibroblast growth factor (FGF) family, basic FGF (bFGF) and FGF-18, have been implicated in the regulation of articular and intervertebral disc (IVD) cartilage homeostasis. Studies on bFGF from a variety of species have yielded contradictory results with regards to its precise role in cartilage matrix synthesis and degradation. In contrast, FGF-18 is a well-known anabolic growth factor involved in chondrogenesis and articular cartilage repair. In this review, we examined the biological actions of bFGF and FGF-18 in articular and IVD cartilage, the specific cell surface receptors bound by each factor, and the unique signaling cascades and molecular pathways utilized to exert their biological effects. Evidence suggests that bFGF selectively activates FGF receptor 1 (FGFR1) to exert degradative effects in both human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme activity, inhibition of matrix production, and increased cell proliferation resulting in clustering of cells seen in arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating FGFR3, increasing matrix formation and cell differentiation while inhibiting cell proliferation, leading to dispersed cells surrounded by abundant matrix. The results from in vitro and in vivo studies suggest the potential usefulness of bFGF and FGFR1 antagonists, as well as FGF-18 and FGFR3 agonists, as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Action of fibroblast growth factor-2 on the intervertebral disc

Introduction

Fibroblast growth factor 2 (FGF2) is a growth factor that is immediately released after cartilage injury and plays a pivotal role in cartilage homeostasis. In human adult articular cartilage, FGF2 mediates anti-anabolic and potentially catabolic effects via the suppression of proteoglycan (PG) production along with the upregulation of matrix-degrading enzyme activity. The aim of the present study was to determine the biological effects of FGF2 in spine disc cells and to elucidate the complex biochemical pathways utilized by FGF2 in bovine intervertebral disc (IVD) cells in an attempt to further understand the pathophysiologic processes involved in disc degeneration.

Methods

We studied the effect of FGF2 on IVD tissue homeostasis by assessing MMP-13 expression (potent matrix-degrading enzyme), PG accumulation, and PG synthesis in the bovine spine IVD, as well as evaluating whether FGF2 counteracts known anabolic factors such as BMP7. To understand the molecular mechanisms by which FGF2 antagonizes BMP7 activity, we also investigated the signaling pathways utilized by FGF2 in bovine disc tissue.

Results

The primary receptor expressed in bovine nucleus pulposus cartilage is FGFR1, and this receptor is upregulated in degenerative human IVD tissue compared with normal IVD tissue. Stimulation of bovine nucleus pulposus cells cultured in monolayer with FGF2 augmented the production of MMP-13 at the transcriptional and translational level in a dose-dependent manner. Stimulation of bovine nucleus pulposus cells cultured in alginate beads for 21 days with FGF2 resulted in a dose-dependent decrease in PG accumulation, due at least in part to the inhibition of PG synthesis. Further studies demonstrate that FGF2 (10 ng/ml) antagonizes BMP7-mediated acceleration of PG production in bovine nucleus pulposus cells via the upregulation of noggin, an inhibitor of the transforming growth factor beta/bone morphogenetic protein signaling pathway. Chemical inhibitor studies showed that FGF2 utilizes the mitogen-activated protein kinase and NF-κB pathways to upregulate noggin, serving as one potential mechanism for its anti-anabolic effects.

Conclusion

FGF2 is anti-anabolic in bovine spine disc cells, revealing the potential of FGF2 antagonists as unique biologic treatments for both prevention and reversal of IVD degeneration.

Basic fibroblast growth factor accelerates matrix degradation via a neuro-endocrine pathway in human adult articular chondrocytes

Pain-related neuropeptides released from synovial fibroblasts, such as substance P, have been implicated in joint destruction. Substance P-induced inflammatory processes are mediated via signaling through a G-protein-coupled receptor, that is, neurokinin-1 tachykinin receptor (NK(1)-R). We determined the pathophysiological link between substance P and its receptor in human adult articular cartilage homeostasis. We further examined if catabolic growth factors such as basic fibroblast growth factor (bFGF or FGF-2) or IL-1beta accelerate matrix degradation via a neural pathway upregulation of substance P and NK(1)-R. We show here that substance P stimulates the production of cartilage-degrading enzymes, such as matrix metalloproteinase-13 (MMP-13), and suppresses proteoglycan deposition in human adult articular chondrocytes via NK(1)-R. Furthermore, we have demonstrated that substance P negates proteoglycan stimulation promoted by bone morphogenetic protein-7, suggesting the dual role of substance P as both a pro-catabolic and anti-anabolic mediator of cartilage homeostasis. We report that bFGF-mediated stimulation of substance P and its receptor NK(1)-R is, in part, through an IL-1beta-dependent pathway.

Osteogenic protein-1 with transforming growth factor-beta1: potent inducer of chondrogenesis of synovial mesenchymal stem cells in vitro

BACKGROUND

Recently, cells derived from synovial mesenchymal stem cells (MSCs) have been regarded as a potential source of cells to induce repair of articular cartilage. To investigate more effective methods for promoting chondrogenesis, we examined the effects of osteogenic protein (OP)-1 with or without transforming growth factor-beta (TGFbeta1) on chondrogenesis of human MSCs in vitro.

METHODS

MSCs were isolated from the synovial membrane of patients with rheumatoid arthritis undergoing knee replacement surgery. After expansion of the cells, pellet cultures were performed in chondrogenic medium with OP-1 100-200 ng/ml, TGFbeta1 10 ng/ml, or both agents for 3 or 6 weeks. Chondrogenesis was evaluated histologically with safranin O staining, reverse transcription polymerase chain reaction for aggrecan and type II collagen mRNA, and quantification of glycosaminoglycan (GAG) content using a dimethylmethylene blue dye-binding assay. GAG content was normalized by DNA content measured using Hoechst 33258 dye.

RESULTS

At 3 weeks of culture, mRNAs for type II collagen and aggrecan were expressed by MSCs treated with either TGFbeta1 or OP-1; however, substantial matrix production was not induced. At 6 weeks, OP-1 increased GAG accumulation dose-dependently in the presence or absence of TGFbeta1, and the GAG content was the highest after combined treatment with 200 ng OP-1 and TGFbeta1. Histological staining for safranin O was poor after treatment with OP-1 or TGFbeta1 alone and slightly increased after combined treatment with TGFbeta1 and OP-1 at 3 weeks. At 6 weeks, OP-1 increased the intensity of staining dose-dependently in the presence or absence of TGFbeta1. However, the histological appearance of the cells treated with OP-1 alone was similar to that of hypertrophic chondrocytes, which was different from that of cells with combined treatment with OP-1 and TGFbeta1.

CONCLUSIONS

A high dose of OP-1 was useful for enhancing chondrogenesis from synovium-derived MSCs in combined treatment with TGFbeta1.

Basic fibroblast growth factor activates the MAPK and NFkappaB pathways that converge on Elk-1 to control production of matrix metalloproteinase-13 by human adult articular chondrocytes

The pathology of joint destruction is associated with elevated production of basic fibroblast growth factor (bFGF) and matrix metalloproteinase-13 (MMP-13). In osteoarthritic joint disease, expression of bFGF and MMP-13 in chondrocytes and their release into the synovial fluid are significantly increased. We have previously found that the capacity for cartilage repair in human adult articular chondrocytes is severely compromised by minimal exposure to bFGF because bFGF reduces responsiveness to bone morphogenetic protein-7 and insulin-like growth factor-1 and induces MMP-13 through protein kinase Cdelta-dependent activation of multiple mitogen-activated protein kinase (MAPK) signaling pathways. Here we show using biochemical and molecular approaches that transcription factor Elk-1, a direct downstream target of MAPK, is a critical transcriptional activator of of MMP-13 by bFGF in human articular chondrocytes. We also provide evidence that Elk-1 is a direct target of NFkappaB and induces MMP-13 expression upon activation of the NFkappaB signaling pathway. Taken together, our results suggest that elevated expression of MMP-13 occurs through Elk-1 activation of both MAPK and NFkappaB signaling pathways, thus revealing a two-pronged biological mechanism by which bFGF controls the production of catabolic enzymes that are associated with excessive degradation of the cartilage matrix in degenerative joint diseases such as osteoarthritis.

OP-1/BMP-7 in cartilage repair

Three years ago we published a book chapter on the role of bone morphogenetic proteins (BMPs) in cartilage repair. Since that time our understanding of the function of osteogenic protein-1 (OP-1) or BMP-7 in cartilage homeostasis and repair has substantially improved and therefore we decided to devote a current review solely to this BMP. Here we summarise the information accumulated on OP-1 from in vitro and ex vivo studies with cartilage cells and tissues as well as from in vivo studies of cartilage repair in various animal models. The primary focus is on articular chondrocytes and cartilage, but data will also be presented on nonarticular cartilage, particularly from the intervertebral disc. The data show that OP-1 is a unique growth factor which, unlike other members of the same BMP family, exhibits in addition to its strong pro-anabolic activity very prominent anti-catabolic properties. Animal studies have demonstrated that OP-1 has the ability to repair cartilage in vivo in various models of articular cartilage degradation, including focal osteochondral and chondral defects and osteoarthritis, as well as models of degeneration in intervertebral disc cartilage. Together our findings indicate a significant promise for OP-1 as therapeutic in cartilage repair.

The effect of synovial fluid from injured knee joints on in vitro chondrogenesis

Various in vivo and in vitro studies suggest that joint homeostasis may have a crucial effect on the quality of regeneration tissue resulting from cartilage tissue engineering techniques. The goal of the current study was to evaluate the effect of synovial fluid (SF) from injured knee joints on in vitro chondrogenesis. Chondrocytes were isolated from a healthy human femoral condyle (post-mortem) and expanded in monolayer for 2 passages. Subsequently, the chondrocytes were redifferentiated for 14 days on collagencoated filters, cultured either in the presence or absence of 10% SF. SF was obtained from 12 injured human knee joints. After 14 days of culture, SF supplementation resulted in a significant downregulation of final proteoglycan (PG) content (7.3 +/- 1.8 mg versus 15.6 +/- 1.3 mg; p = 0.0001), PG content normalized to DNA (0.7 +/- 0.5 mg/microg versus 3.0 +/- 0.6 mg/microg; p < 0.05), relative collagen type II mRNA levels normalized to GAPDH mRNA levels (0.2 +/- 0.3 versus 7.0 +/- 5.6; p < 0.001), and differentiation index (collagen type II/I mRNA ratio; 0.1 +/- 0.2 versus 6.0 +/- 2.9; p < 0.001) as compared to control culture conditions. Additionally, SF-supplemented media resulted in significantly increased cellularity, as reflected by DNA content, compared with control media (1,369 +/- 683 microg versus 514 +/- 72 microg; p < 0.0001). Morphology, and collagen type I, X, and aggrecan mRNA levels were not significantly affected. In conclusion, this study demonstrates that SF from injured human knee joints significantly affects in vitro chondrogenesis and therefore may provide a viable target for future improvement of ACT by refinement of culture techniques, patient selection, or pretreatment of affected joints to restore joint homeostasis.

Basic fibroblast growth factor stimulates matrix metalloproteinase-13 via the molecular cross-talk between the mitogen-activated protein kinases and protein kinase Cdelta pathways in human adult articular chondrocytes

Excessive release of basic fibroblast growth factor (bFGF) during loading and/or injury of the cartilage matrix may contribute to the onset or progression of osteoarthritis. This pathological role may be related to the ability of bFGF to decrease proteoglycan synthesis and to antagonize the activity of anabolic growth factors in cartilage such as insulin-like growth factor-1 and bone morphogenetic protein 7 (BMP7 or OP-1). Matrix metalloproteinase-13 (MMP-13), a catabolic cartilage-degrading enzyme, is dramatically up-regulated by inflammatory cytokines or by fibronectin fragments in articular chondrocytes. In this study, we investigated MMP-13 production by bFGF using human articular chondrocytes. Endogenous concentration of bFGF in synovial fluids collected from arthritis patients and asymptomatic subjects showed a good linear correlation with the endogenous levels of MMP-13. bFGF stimulation of MMP-13 was mediated at the transcriptional level and, at least in part, by stimulation of interleukin-1 production. Also, our findings suggest that bFGF stimulation of MMP-13 required the activation of multiple MAPKs (ERK, p38, and JNK) by bFGF, and more importantly, bFGF activation of protein kinase C (PKC) delta played a key role in the MMP-13 stimulation. Indeed, PKCdelta is the only isoform associated with MMP-13 stimulation among the PKC isoforms tested. PKCdelta controls the bFGF response by regulating multiple MAPK pathways. Our results suggest that PKCdelta activation is a principal rate-limiting event in the bFGF-dependent stimulation of MMP-13 in human adult articular chondrocytes. We propose that deregulation of cross-talk between MAPK and PKCdelta signaling may contribute to the etiology of osteoarthritis in human patients.

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.

Water-soluble C60 fullerene prevents degeneration of articular cartilage in osteoarthritis via down-regulation of chondrocyte catabolic activity and inhibition of cartilage degeneration during disease development

OBJECTIVE

Studies have shown the roles of oxidative stress in the pathogenesis of osteoarthritis (OA) and induction of chondrocyte senescence during OA progression. The aim of this study was to examine the potential of a strong free-radical scavenger, water-soluble fullerene (C60), as a protective agent against catabolic stress-induced degeneration of articular cartilage in OA, both in vitro and in vivo.

METHODS

In the presence or absence of C60 (100 microM), human chondrocytes were incubated with interleukin-1beta (10 ng/ml) or H2O2 (100 microM), and chondrocyte activity was analyzed. An animal model of OA was produced in rabbits by resection of the medial meniscus and medial collateral ligament. Rabbits were divided into 5 subgroups: sham operation or treatment with C60 at 0.1 microM, 1 microM, 10 microM, or 40 microM. The left knee joint was injected intraarticularly with water-soluble C60 (2 ml), while, as a control, the right knee joint received 50% polyethylene glycol (2 ml), once weekly for 4 weeks or 8 weeks. Knee bone and cartilage tissue were prepared for histologic analysis. In addition, in the OA rabbit model, the effect of C60 (10 microM) on degeneration of articular cartilage was compared with that of sodium hyaluronate (HA) (5 mg/ml).

RESULTS

C60 (100 microM) inhibited the catabolic stress-induced production of matrix-degrading enzymes (matrix metalloproteinases 1, 3, and 13), down-regulation of matrix production, and apoptosis and premature senescence in human chondrocytes in vitro. In rabbits with OA, treatment with water-soluble C60 significantly reduced articular cartilage degeneration, whereas control knee joints showed progression of cartilage degeneration with time. This inhibitory effect was dose dependent, and was superior to that of HA. Combined treatment with C60 and HA yielded a significant reduction in cartilage degeneration compared with either treatment alone.

CONCLUSION

The results indicate that C60 fullerene is a potential therapeutic agent for the protection of articular cartilage against progression of OA.

Biochemical and functional modulation of the cartilage collagen network by IGF1, TGFbeta2 and FGF2

OBJECTIVE

Examine effects of insulin-like growth factor 1 (IGF1), transforming growth factor beta2 (TGFbeta2) and fibroblast growth factor 2 (FGF2) on proteoglycan and collagen network and biomechanical properties of the newly formed cartilage matrix.

METHODS

Bovine articular chondrocytes were cultured in alginate beads for 3 weeks with or without FGF2, TGFbeta2 or IGF1 in the presence of 10% FCS. Proteoglycan content, collagen content, hydroxylysylpyridinoline cross-links and overall matrix metalloproteinase (MMP) activity in the culture medium were measured. Alginate disks cultured for 5 weeks were used to evaluate the effect of growth factors on mechanical properties of the construct by determining the equilibrium aggregate modulus and secant modulus.

RESULTS

IGF1 increased collagen and proteoglycan deposition. FGF2 mainly decreased collagen deposition and TGFbeta2 proteoglycan deposition. A decrease in cross-links was observed in matrix produced by chondrocytes cultured in the presence of TGFbeta2. IGF1 and FGF2 had no influence on the number of cross-links per collagen molecule. Overall MMP activity was significantly higher in culture medium of cells cultured with FGF2. TGFbeta2 and IGF1 had no effect on MMP activity. After 35 days of culture, the matrix produced under influence of IGF1 had a lower permeability and a trend to increase stiffness. FGF2 showed a trend to lower both properties. TGFbeta2 had no effect on these parameters.

CONCLUSION

IGF1, TGFbeta2 and FGF2 had differential effects on collagen network formation. Of the three growth factors tested, IGF1 seems to be best in promoting the formation of a functional collagen network since it increased proteoglycan and collagen deposition and improved the mechanical properties.

Update on the biology of the chondrocyte and new approaches to treating cartilage diseases

Osteoarthritis (OA) is a joint disease that involves degeneration of articular cartilage, limited intraarticular inflammation manifested by synovitis and changes in the subchondral bone. The aetiology of OA is largely unknown, but since it may involve multiple factors, including mechanical, biochemical and genetic factors, it has been difficult to identify unique targets for therapy. Chondrocytes, which are the unique cellular component of adult articular cartilage, are capable of responding to structural changes in the surrounding cartilage matrix. Since the initial stages of OA involve increased cell proliferation and synthesis of matrix proteins, proteinases and cytokines in the cartilage, laboratory investigations have focused on the chondrocyte as a target for therapeutic intervention. The capacity of the adult articular chondrocyte to regenerate the normal cartilage matrix architecture is limited, however, and the damage becomes irreversible unless the destructive process is interrupted. Current pharmacological interventions that address chronic pain are insufficient and no proven disease-modifying therapy is available. Identification of methods for early diagnosis is of key importance, since therapeutic interventions aimed at blocking or reversing structural damage will be more effective when there is the possibility of preserving normal homeostasis. At later stages, cartilage tissue engineering with or without gene therapy with anabolic factors will also require therapy to inhibit inflammation and block damage to newly repaired cartilage. This review will focus on experimental approaches currently under study that may lead to elucidation of effective strategies for therapy in OA, with emphasis on mediators that affect the function of chondrocytes and interactions with surrounding tissues.

Effect of construct properties on encapsulated chondrocyte expression of insulin-like growth factor-1

Hydrogels are a promising type of biomaterial for articular cartilage constructs since they have been shown to enable encapsulated chondrocytes to express their predominant phenotypic marker, type II collagen. Endogenously expressed signaling molecules, such as insulin-like growth factor-1 (IGF-1), are also known to facilitate the retention of this chondrocytic phenotype. Recent investigations have attempted to enhance the ability of encapsulated chondrocytes to regenerate cartilage through delivery of exogenous signaling molecules. However, we hypothesize that by altering construct properties, such as cell density and polymer concentration, we can augment the expression of endogenous IGF-1 in chondrocytes. To this end, bovine articular chondrocytes were encapsulated within alginate hydrogels at two different cell densities (25,000 and 100,000 cells/bead) and various alginate concentrations (0.8%, 1.2%, and 2.0% w/v). These parameters were chosen to simultaneously investigate cell-to-cell distance on paracrine signaling and water content on IGF-1 diffusion by chondrocytes. At 1, 4, and 8d, chondrocytes were analyzed for protein and mRNA expression of IGF-1 as well as type II collagen. Results suggest that cell density and alginate concentration at high cell density can significantly affect the endogenous IGF-1 expression by chondrocytes. Therefore, these results indicate that construct properties can impact chondrocyte gene expression and should be considered in order to create a proper engineered articular cartilage construct.