Osteogenic protein-1 differentially regulates the mRNA expression of bone morphogenetic proteins and their receptors in primary cultures of osteoblasts

The mRNA expression patterns of several bone morphogenetic proteins (BMPs) and their receptors (BMPRs) in long-term primary cultures of fetal rat calvaria (FRC) cells were examined by Northern analysis. Their temporal orders of expression were correlated with those of several biochemical markers characteristic of osteoblastic cell differentiation. Distinct temporal patterns of expression of BMPs and BMPRs during osteoblastic cell differentiation were observed. BMP-2 and BMP-7 mRNA levels did not change significantly. BMP-4 mRNA expression increased and reached a peak prior to matrix formation. BMP-5 mRNA expression increased during the mineralization phase and BMP-6 mRNA expression increased throughout all phases of cell differentiation. Effects of BMP-7 (Osteogenic Protein-1; OP-1) on the expression patterns of several other members of the BMP family and the receptors were also studied. OP-1 downregulated the BMP-4, -5, and -6 mRNA levels by a maximal of 2-fold, 1.5-fold, and 6-fold, respectively. OP-1 did not change significantly the OP-1 and BMP-2 mRNA expression. Of the three type I BMPR examined, OP-1 upregulated ActR-I and BMPR-IA mRNA expression slightly but with statistical significance. OP-1 downregulated BMPR-IB mRNA expression slightly. OP-1 upregulated BMPR-II mRNA expression by a maximum of 2-fold. Our findings demonstrate that OP-1 differentially regulates the mRNA expression of several related members of the BMP family and their receptors in osteoblasts. The observations suggest that OP-1 action on osteoblastic cells involves a complex regulation of gene expression of related members of the BMP family and their receptors in a cell differentiation stage dependent manner.     

Differential effects of osteogenic protein-1 (BMP-7) on gene expression of BMP and GDF family members during differentiation of the mouse MC615 chondrocyte cells

The mRNA expression patterns of several bone morphogenetic proteins (BMPs) and growth differentiation factors (GDFs) in long-term cultures of the clonal mouse chondrocyte cell line MC615 were examined. Distinct spatial and temporal patterns of expression of BMPs and GDFs were observed. The temporal orders of expression were correlated with those of several biochemical markers characteristic of chondrocytic cell differentiation. BMP-1, -2, -5, and -6 mRNA expression increased throughout the chondrogenic process and BMP-4 mRNA expression was not changed. GDF-1 and -3 mRNA expression increased throughout the chondrogenic process, and GDF-5, -6, -8, and -9 mRNA expressions were not changed. Effects of osteogenic protein-1 (OP-1, BMP-7) on the expression patterns of several other members of the BMP family and of the GDF family were also examined. OP-1 downregulated the BMP-1, -4, -5, and -6 mRNA expression by a maximal 3-, 5-, 2.5-, and 3-fold, respectively. The BMP-2 mRNA expression was not changed significantly by a low concentration of OP-1, but was increased at 200 ng/ml at day 7 of treatment. In contrast to the BMPs, OP-1 upregulated significantly the six GDF members examined (GDF-1, -3, -5, -6, -8, and -9) by three- to four-fold. Our findings demonstrate that OP-1 differentially regulates the mRNA expression of several related members of the BMP family and upregulates the mRNA expression of several members of the GDF family. The observations suggest that OP-1 action on cartilage differentiation involves a complex regulation of gene expression of several members of the BMP and the GDF family.     

Bone morphogenetic protein (BMP) localization in developing human and rat growth plate, metaphysis, epiphysis, and articular cartilage.

We assessed the distribution and relative staining intensity of bone morphogenetic protein (BMP)-1-7 by immunohistochemistry in tibial growth plates, epiphyses, metaphyses, and articular cartilage in one 21-week and one 22-week human fetus and in five 10-week-old Sprague-Dawley rats. In the rats, articular cartilage was also examined. BMP proteins were mostly cytoplasmic, with negligible matrix staining. Highest BMP levels were seen in (a) hypertrophic and calcifying zone chondrocytes of growth plate (BMP-1-7), (b) osteoblasts and/or osteoprogenitor fibroblasts and vascular cells of the metaphyseal cortex and medulla (BMP-1-6), (c) osteoclasts of the metaphysis and epiphysis (BMP-1,-4,-5, and -6), and (d) mid to deep zone articular chondrocytes of weanling rats (BMP-1-7). BMP staining in osteoclasts, an unexpected finding, was consistently strong with BMP-4, -5, and -6 but was variable and dependent on osteoclast location with BMP-2,-3, and -7. BMP-1-7 were moderately to intensely stained in vascular canals of human fetal epiphyseal cartilage by endothelial cells and pericytes. BMP-1,-3,-5,-6, and -7 were localized in hypertrophic chondrocytes adjacent to cartilage canals. We conclude that BMP expression is associated with maturing chondrocytes of growth plate and articular cartilage, and may play a role in chondrocyte differentiation and/or apoptosis. BMP appears to be expressed by osteoclasts and might be involved in the intercellular "cross-talk" between osteoclasts and neighboring osteoprogenitor cells at sites of bone remodeling.     

Selection and amplification of a bone marrow cell population and its induction to the chondro-osteogenic lineage by rhOP-1: an in vitro and in vivo study.

The differentiation and maturation of osteoprogenitor cells into osteoblasts are processes which are thought to be modulated by transforming growth factors-beta (TGF-beta) as well as by bone morphogenetic proteins (BMPs). Osteogenic protein-1 (OP-1, also known as BMP-7) is a member of the BMP family, and it is considered to have important regulatory roles in skeletal embryogenesis and bone healing. Rat bone marrow cells were cultured in vitro in a collagen-gel medium containing 0.5% fetal bovine serum (FBS) for 10 days in the presence of 40 ng/ml recombinant human OP-1 (rhOP-1). Under these conditions, survival of the bone marrow cell population was dependent on the presence of rhOP-1. Subsequently, the selected cells were cultured-for 6 days in medium containing 40 ng rhOP-1 and 10% FBS. During the last 2 days, dexamethasone (10(-8) M) and beta-glycerophosphate (2 mM) were added to potentiate osteoinduction. Concomitant with an up-regulation of cell proliferation, DNA synthesis levels, colony number and size were determined. Chondro-osteogenic differentiation in vitro was evaluated in terms of the expression of alkaline phosphatase, the production of osteocalcin and the formation of mineralized matrix. After culturing in vitro, cells were placed inside diffusion chambers or inactivated demineralized bone matrix (DBM) cylinders and implanted subdermically into the backs of old rats for 28 days. Biochemical, histological and immunocytochemical analyses provided evidence of cartilage and osteoid tissue inside the diffusion chambers, whereas bone was also observed inside the DBM implants. In conclusion, this experimental procedure is capable of selecting a cell population from bone marrow which, in the presence of rhOP-1, achieves skeletogenic potential under in vitro as well as in vivo environments.     

The bone morphogenetic protein family and osteogenesis.

The BMPs (bone morphogenetic proteins) are a group of related proteins originally identified by their presence in bone-inductive extracts of demineralized bone. By molecular cloning, at least six related members of this family have been identified and are called BMP-2 through BMP-7. These molecules are part of the TGF-beta superfamily, based on primary amino acid sequence homology, including the absolute conservation of seven cysteine residues between the TGF-betas and the BMPs. The BMPs can be divided into subgroups with BMP-2 and BMP-4 being 92% identical, and BMP-5, BMP-6, and BMP-7 being an average of about 90% identical. To examine the individual activities of these molecules, we are producing each BMP in a mammalian expression system. In this system, each BMP is synthesized as a precursor peptide, which is glycosylated, processed to the mature peptide, and secreted as a homodimer. These reagents have been used to demonstrate that single molecules, such as BMP-2, are capable of inducing the formation of new cartilage and bone when implanted ectopically in a rodent assay system. Whether each of the BMPs possesses the same inductive activities in an animal is the subject of ongoing research. Based on the chondrogenic and osteogenic abilities of the BMPs in the adult animal, the expression of the mRNAs for the BMPs has been examined in the development of the embryonic skeleton by in situ hybridization. These studies demonstrate that the BMP mRNAs are spatially and temporally expressed appropriately for the proteins involved in the induction and development of cartilage and bone in the embryonic limb bud.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression, purification and osteogenic bioactivity of recombinant human BMP-4, -9, -10, -11 and -14

Bone morphogenetic proteins (BMPs) are cytokines from the TGF-β superfamily, with important roles during embryonic development and in the induction of bone and cartilage tissue differentiation in the adult body. In this contribution, we report the expression of recombinant human BMP-4, BMP-9, BMP-10, BMP-11 (or growth differentiation factor-11, GDF-11) and BMP-14 (GDF-5), using Escherichia coli pET-25b vector. BMPs were overexpressed, purified by affinity his-tag chromatography and shown to induce the expression of early markers of bone differentiation (e.g. smad-1, smad-5, runx2/cbfa1, dlx5, osterix, osteopontin, bone sialoprotein and alkaline phosphatase) in C2C12 cells and in human adipose stem cells. The described approach is a promising method for producing large amounts of different recombinant BMPs that show potential for novel biomedical applications.     

BMP-1及BMP家族在背-腹轴图式形成中的作用

骨形态发生蛋白（bone morphogenetic proteins, BMPs）是一类在发育过程中起重要作用的分子。除BMP-1外,其他BMP分子均属于转化生长因子-β（transforming growth factor-β, TGF-β）/BMP超家族的发育信号分子。在胚胎发育过程中,这些信号分子通过形成浓度梯度对背—腹轴各向异性分化进行调控。它们借助细胞表面受体的识别进行信号传导,参与调控细胞分化、增殖等活动。而BMP-1则属于细胞外基质金属蛋白酶超家族中的Tolloid蛋白酶家族。BMP-1通过水解其他BMP的抑制物（如脊索发生素,Chordin）,达到促进其他BMP信号传导的目的。BMP-1、BMP和Chordin三者通过相互制约与相互促进等一系列作用,在背—腹沿线建立起稳定的BMP信号梯度。本文就BMP浓度梯度的形成及其稳态维持的机制进行回顾与总结。并在此基础上,对各个物种间BMP浓度梯度形成机制的异同,以及可能存在的协同进化进行比较、分析和讨论。     

BMPs are mediators in tissue crosstalk of the regenerating musculoskeletal system

The musculoskeletal system is a tight network of many tissues. Coordinated interplay at a biochemical level between tissues is essential for development and repair. Traumatic injury usually affects several tissues and represents a large challenge in clinical settings. The current demand for potent growth factors in such applications thus accompanies the keen interest in molecular mechanisms and orchestration of tissue formation. Of special interest are multitasking growth factors that act as signals in a variety of cell types, both in a paracrine and in an autocrine manner, thereby inducing cell differentiation and coordinating not only tissue assembly at specific sites but also maturation and homeostasis. We concentrate here on bone morphogenetic proteins (BMPs), which are important crosstalk mediators known for their irreplaceable roles in vertebrate development. The molecular crosstalk during embryonic musculoskeletal tissue formation is recapitulated in adult repair. BMPs act at different levels from the initiation to maturation of newly formed tissue. Interestingly, this is influenced by the spatiotemporal expression of different BMPs, their receptors and co-factors at the site of repair. Thus, the regenerative potential of BMPs needs to be evaluated in the context of highly connected tissues such as muscle and bone and might indeed be different in more poorly connected tissues such as cartilage. This highlights the need for an understanding of BMP signaling across tissues in order to eventually improve BMP regenerative potential in clinical applications. In this review, the distinct members of the BMP family and their individual contribution to musculoskeletal tissue repair are summarized by focusing on their paracrine and autocrine functions.     

Immunohistochemical Localization of Bone Morphogenetic Proteins (BMPs) and their Receptors in Solitary and Multiple Human Osteochondromas

The expression of bone morphogenetic proteins (BMPs) and their cognate receptors (BMPRs) in osteochondromas has not been investigated. We determined the immunohistochemical localization and distribution of BMP-2/4, -6 and -7; BMP receptors BMPR-1A, BMPR-1B and BMPR-2; signal transducing proteins phosphorylated Smad1/5/8; and BMP antagonist noggin in the cartilaginous cap of solitary (SO) and multiple (MO) human osteochondromas and compared these with bovine growth plate and articular cartilage. The distribution and localization patterns for BMP-6, BMP-7, BMPR-1A and BMPR-2 were similar between the cartilaginous cap and the growth plate. BMP-2/4 and BMPR-1B were present throughout the growth plate. However, BMP-2/4 and phosphorylated Smad1/5/8 were mainly detected in proliferating chondrocytes of the cartilaginous cap. Also, BMPR-1B was found in hypertrophic chondrocytes of SO and proliferating chondrocytes of MO. Noggin was observed in resting chondrocytes and, to a lesser extent, in clustered proliferating chondrocytes in SO. On the other hand, noggin in MO was observed in proliferating chondrocytes. Since BMPs can stimulate proliferation and hypertrophic differentiation of chondrocytes, these findings suggest that there is an imbalance of BMP-2/4 and noggin interactions that may lead to abnormal regulation of chondrocyte proliferation and differentiation in the cartilaginous cap of human osteochondromas.     

Bone morphogenetic proteins and their receptors in the eye

The human genome encodes at least 42 different members of the transforming growth factor-beta superfamily of growth factors. Bone morphogenetic proteins (BMPs) are the largest subfamily of proteins within the transforming growth factor-beta superfamily and are involved in numerous cellular functions including development, morphogenesis, cell proliferation, apoptosis, and extracellular matrix synthesis. This article first reviews BMPs and BMP receptors, BMP signaling pathways, and mechanisms controlling BMP signaling. Second, we review BMP and BMP receptor expression during embryonic ocular development/ differentiation and in adult ocular tissues. Lastly, future research directions with respect to BMP, BMP receptors, and ocular tissues are suggested.     

The role of chondrocyte-matrix interactions in maintaining and repairing articular cartilage

Throughout life chondrocytes maintain the articular cartilage matrix by replacing degraded macromolecules and respond to focal cartilage injury or degeneration by increasing local synthesis activity. These observations suggest that mechanisms exist within articular cartilage that stimulate chondrocyte anabolic activity in response to matrix degradation or damage. An important cartilage anabolic factor, insulin-like growth factor I (IGF-I), appears to have a role in stimulating chondrocyte anabolic activity. Although IGF-I is ubiquitous, its bioavailability is controlled by a class of secreted proteins, IGF binding proteins (IGFPBs). Of the six known IGFPBs, IGFBP-3 is the most abundant in human articular cartilage. We recently found that with increasing age, articular chondrocytes increase their expression of IGFBP-3. This observation led us to investigate the potential role of IGFBP-3 in chondrocyte-matrix interactions. Using immunofluorescent staining and confocal microscopy we found that IGFBP-3 accumulates with increasing age in the chondrocyte territorial matrix where it co-localizes with fibronectin, but not with tenascin-C or type VI collagen. Using purified proteins we demonstrated that IGFBP-3 binds to fibronectin in a dose dependent manner, but not to tenascin-C. In vitro studies showed that IGFBP-3 alone inhibited chondrocyte synthetic activity while intact fibronectin alone significantly stimulated activity. When fibronectin and IGFBP-3 were combined we found that the inhibitory activity of low concentrations of IGFPB-3 was enhanced. These observations indicate that in mature articular cartilage IGF-I is stored in the chondrocyte territorial matrix through binding to a complex of IGFPB-3 and intact fibronectin. Storage of IGF-I of the territorial matrix may help maintain a relatively constant level of available IGF-I and the local increase in matrix synthesis following matrix damage may result from release of IGF-I. This mechanism may have an important role in maintaining and repairing articular cartilage and failure of this mechanism may lead to progressive articular cartilage degeneration.     

Heparin potentiates the in vivo ectopic bone formation induced by bone morphogenetic protein-2

Although bone morphogenetic proteins (BMPs) are clinically useful for bone regeneration, large amounts are required to induce new bone formation in monkeys and humans. We found recently that heparin stimulates BMP activity in vitro (Takada, T., Katagiri, T., Ifuku, M., Morimura, N., Kobayashi, M., Hasegawa, K., Ogamo, A., and Kamijo, R. (2003) J. Biol. Chem. 278, 43229-43235). In the present study, we examined whether heparin enhances bone formation induced by BMPs in vivo and attempted to determine the molecular mechanism by which heparin stimulates BMP activity using C2C12 myoblasts. Heparin enhanced BMP-2-induced gene expression and Smad1/5/8 phosphorylation at 24 h and thereafter, although not within 12 h. Heparitinase treatment did not affect the response of cells to BMP-2. In the presence of heparin, degradation of BMP-2 was blocked, and the half-life of BMP-2 in the culture medium was prolonged by nearly 20-fold. Although noggin mRNA was induced by BMP-2 within 1 h regardless of the presence of heparin, noggin failed to inhibit BMP-2 activity in the presence of heparin. Furthermore, simultaneous administration of BMP-2 and heparin in vivo dose-dependently induced larger amounts of mineralized bone tissue compared with BMP-2 alone. These findings clearly indicate that heparin enhances BMP-induced osteoblast differentiation not only in vitro but also in vivo. This study indicates that heparin enhances BMP-induced osteoblast differentiation in vitro and in vivo by protecting BMPs from degradation and inhibition by BMP antagonists.     

IL-1beta, but not BMP-7 leads to a dramatic change in the gene expression pattern of human adult articular chondrocytes--portraying the gene expression pattern in two donors

Anabolic and catabolic cytokines and growth factors such as BMP-7 and IL-1beta play a central role in controlling the balance between degradation and repair of normal and (osteo)arthritic articular cartilage matrix. In this report, we investigated the response of articular chondrocytes to these factors IL-1beta and BMP-7 in terms of changes in gene expression levels. Large scale analysis was performed on primary human adult articular chondrocytes isolated from two human, independent donors cultured in alginate beads (non-stimulated and stimulated with IL-1beta and BMP-7 for 48 h) using Affymetrix gene chips (oligo-arrays). Biostatistical and bioinformatic evaluation of gene expression pattern was performed using the Resolver software (Rosetta). Part of the results were confirmed using real-time PCR. IL-1beta modulated significantly 909 out of 3459 genes detectable, whereas BMP-7 influenced only 36 out of 3440. BMP-7 induced mainly anabolic activation of chondrocytes including classical target genes such as collagen type II and aggrecan, while IL-1beta, both, significantly modulated the gene expression levels of numerous genes; namely, IL-1beta down-regulated the expression of anabolic genes and induced catabolic genes and mediators. Our data indicate that BMP-7 has only a limited effect on differentiated cells, whereas IL-1beta causes a dramatic change in gene expression pattern, i.e. induced or repressed much more genes. This presumably reflects the fact that BMP-7 signaling is effected via one pathway only (i.e. Smad-pathway) whereas IL-1beta is able to signal via a broad variety of intracellular signaling cascades involving the JNK, p38, NFkB and Erk pathways and even influencing BMP signaling.     

Osteogenic protein-1 and interleukin-6 with its soluble receptor synergistically stimulate rat osteoblastic cell differentiation

Osteogenic Protein-1 (OP-1, BMP-7), a member of the bone morphogenetic protein family, stimulates synthesis of biochemical markers characteristic of the osteoblastic and chondrocytic phenotypes and induces new bone formation. Interleukin-6 (IL-6), a cytokine produced by a wide variety of cells, appears to interact with other factors producing different biological effects. In the present study, we showed that OP-1 action in fetal rat calvaria (FRC) cells was enhanced by the combination of IL-6 and the soluble receptor IL-6sR. OP-1 alone induced alkaline phosphatase (AP) activity by 4- to 5-fold above the control. Exogenous IL-6 soluble receptor (IL-6sR) synergistically stimulated the OP-1-induced AP activity and mineralized bone nodule formation by an additional 3-fold. The stimulation was IL-6sR concentration-dependent. The combination of IL-6 and IL-6sR synergistically stimulated OP-1 action by an additional 6- to 7-fold. BMPR-II receptor mRNA expression in FRC cells treated with OP-1 and IL-6 plus IL-6sR was stimulated further, while BMPR-IA, -IB, and ActR-I expressions were not affected. The intracellular signaling molecules Smad2 and Smad5 mRNA expressions were not changed under these conditions. The expression of selected BMP family members (BMP-3, -4, and -6) was altered in FRC cells treated with OP-1 in combination with IL-6 and IL-6sR. The combination of IL-6 and IL-6sR reduced the OP-1-stimulated BMP-3 mRNA levels and enhanced the suppressive effect of OP-1 on BMP-4 and -6 mRNA expressions. In conclusion, the present results demonstrate that exogenous IL-6 and IL-6sR synergistically stimulate OP-1 action in primary cultures of rat osteoblastic cells. One possible mechanism of synergy involves differential regulation of the effects of OP-1 on the expression of the type II BMP receptor and several other BMPs.     

Expression of bone morphogenetic protein-7, its receptors and Smad1/5/8 in normal human kidney and renal cell cancer

Bone morphogenetic proteins (BMPs) are cytokines which are important for kidney homeostasis but also have role in the some renal diseases and renal cell carcinoma (RCC). In the last three decades incidence of RCC was constantly increased and the role of different molecular biomarkers in RCC is explored'. We analyzed expression of BMP-7, their receptors (BMPR-IA, BMPR-IB, BMPR-II) and proteins of their signaling pathway (pSmad1/5/8) in sixteen renal cancer samples and paired normal tissue. Tissue samples were analyzed by immunohistochemistry and Western blot. BMP-7, BMP receptors and pSmad1/5/8 were expressed in all structures of normal kidney but dominantly in the proximal tubular cells. In the cancer samples their expression was also noticed. Comparison of BMPs between different tissue showed increased expression of BMPR-IB and pSmad 1/5/8 and decreased expression of BMP-7 and BMPR-II in RCC compared to normal kidney. BMPR-IA was detected with immunohistochemistry but with Western blot attenuated signal was presented. BMP-7, BMP receptors and pSmad1/5/8 were showed in normal kidney and RCC. Detected alterations of BMP-7, BMP receptors and pSmad expression in RCC suggested their possible role in tumorigenesis of kidney cancer.     

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.     

Gene expression profiling of serum- and interleukin-1 beta-stimulated primary human adult articular chondrocytes--a molecular analysis based on chondrocytes isolated from one donor

In order to understand the cellular disease mechanisms of osteoarthritic cartilage degeneration it is of primary importance to understand both the anabolic and the catabolic processes going on in parallel in the diseased tissue. In this study, we have applied cDNA-array technology (Clontech) to study gene expression patterns of primary human normal adult articular chondrocytes isolated from one donor cultured under anabolic (serum) and catabolic (IL-1beta) conditions. Significant differences between the different in vitro cultures tested were detected. Overall, serum and IL-1beta significantly altered gene expression levels of 102 and 79 genes, respectively. IL-1beta stimulated the matrix metalloproteinases-1, -3, and -13 as well as members of its intracellular signaling cascade, whereas serum increased the expression of many cartilage matrix genes. Comparative gene expression analysis with previously published in vivo data (normal and osteoarthritic cartilage) showed significant differences of all in vitro stimulations compared to the changes detected in osteoarthritic cartilage in vivo. This investigation allowed us to characterize gene expression profiles of two classical anabolic and catabolic stimuli of human adult articular chondrocytes in vitro. No in vitro model appeared to be adequate to study overall gene expression alterations in osteoarthritic cartilage. Serum stimulated in vitro cultures largely reflected the results that were only consistent with the anabolic activation seen in osteoarthritic chondrocytes. In contrast, IL-1beta did not appear to be a good model for mimicking catabolic gene alterations in degenerating chondrocytes.