Objective. Wnt signaling pathway proteins are involved in embryonic development of cartilage and bone, and, interestingly, developmental processes appear to be recapitulated in osteoarthritic (OA) cartilage. The present study was undertaken to characterize the expression pattern of Wnt and Fz genes during experimental OA and to determine the function of selected genes in experimental and human OA.Methods. Longitudinal expression analysis was performed in 2 models of OA. Levels of messenger RNA for genes from the Wnt/␤-catenin pathway were determined in synovium and cartilage, and the results were validated using immunohistochemistry. Effects of selected genes were assessed in vitro using recombinant protein, and in vivo by adenoviral overexpression.Results. Wnt-induced signaling protein 1 (WISP-1) expression was strongly increased in the synovium and cartilage of mice with experimental OA. Osteoarthritis (OA) results in the destruction of cartilage and bone, ultimately leading to loss of joint function. The cause of the disease is largely unknown, although obesity, genetic factors, and injury have all been associated with increased risk of OA (1,2). Although it is likely that in most cases the initial events leading to OA occur within the cartilage or subchondral bone (3,4), the synovial tissue of many OA patients shows a changed morphology, with a marked inflammatory phenotype (5,6). Wnt-16 andLoss of articular cartilage extracellular matrix is thought to be mediated by matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS-4 and ADAMTS-5), which are likely the most important groups of enzymes in the breakdown of extracellular

Objective. To investigate the development of osteoarthritis (OA) after transection of the medial collateral ligament and partial medial meniscectomy in mice in which genes encoding either interleukin-1␤ (IL-1␤), IL-1␤-converting enzyme (ICE), stromelysin 1, or inducible nitric oxide synthase (iNOS) were deleted.Methods. Sectioning of the medial collateral ligament and partial medial meniscectomy were performed on right knee joints of wild-type and knockout mice. Left joints served as unoperated controls. Serial histologic sections were obtained from throughout the whole joint of both knees 4 days or 1, 2, 3, or 4 weeks after surgery. Sections were graded for OA lesions on a scale of 0-6 and were assessed for breakdown of tibial cartilage matrix proteoglycan (aggrecan) and type II collagen by matrix metalloproteinases (MMPs) and aggrecanases with immunohistochemistry studies using anti-VDIPEN, anti-NITEGE, and Col2-3/4C short neoepitope antibodies. Proteoglycan depletion was assessed by Alcian blue staining and chondrocyte cell death, with the TUNEL technique.Results. All knockout mice showed accelerated development of OA lesions in the medial tibial cartilage after surgery, compared with wild-type mice. ICE-, iNOS-, and particularly IL-1␤-knockout mice developed OA lesions in the lateral cartilage of unoperated limbs. Development of focal histopathologic lesions was accompanied by increased levels of MMP-, aggrecanase-, and collagenase-generated cleavage neoepitopes in areas around lesions, while nonlesional areas showed no change in immunostaining. Extensive cell death was also detected by TUNEL staining in focal areas around lesions.Conclusion. We postulate that deletion of each of these genes, which encode molecules capable of producing degenerative changes in cartilage, leads to changes in the homeostatic controls regulating the balance between anabolism and catabolism, favoring accelerated cartilage degeneration. These observations suggest that these genes may play important regulatory roles in maintaining normal homeostasis in articular cartilage matrix turnover.Osteoarthritis (OA) is a degenerative condition characterized by loss of articular cartilage and joint remodeling. The degradation of cartilage is characterized by increased expression of matrix metalloproteinases (MMPs), cytokines including interleukin-1 (IL-1) and tumor necrosis factor ␣ (TNF␣) and their receptors, and nitric oxide synthase (NOS) (1). Aging mice present Supported by the Arthritis Research Campaign (UK).

Some chondrocytes are much more vulnerable to repetitive mechanical loading than others, suggesting that vigorous activity may lead to cell death in articular cartilage.

The current study clearly demonstrated that marked inflammatory changes in the IPFP occur during the early stage of the MIA model of OA which may contribute to the pain observed at this early stage. The role of the IPFP in later stages of the model needs to be further explored.

Objectives WISP3/CCN6 is mutated in progressive pseudorheumatoid dysplasia and may have effects on cartilage homeostasis. In order to uncover further roles for WISP3/CCN6 its expression was explored in osteoarthritic cartilage. Effects of WISP3/CCN6 on cartilage-relevant metalloproteinase expression were investigated in immortalised (C-28/I2) and primary chondrocytes. Methods Cartilage steady state levels of WISP3/CCN6 mRNA and protein production were determined by quantitative RT-PCR and immunohistochemistry respectively. WISP3/CCN6 was over-expressed in C-28/I2 cells and resultant stable clones analysed by real time RT-PCR for metalloproteinase expression and signalling pathways involved explored with pharmacological inhibition. Effects of WISP3/CCN6 on metalloproteinase expression in primary chondrocytes were investigated by an siRNA approach. Results WISP3/CCN6 was highly expressed in osteoarthritic cartilage compared to undamaged cartilage at RNA and protein levels. WISP3/CCN6 over-expression in C-28/I2 cells resulted in unexpected dual regulation of metalloproteinases: the expression of the potent aggrecanase, ADAMTS5, was down-regulated 9-fold, whilst MMP10 was up-regulated 14-fold, responses accentuated by suspension culture. MMP10 up-regulation was dependent on several MAP kinases but WISP3/CCN6-mediated ADAMTS5 repression was independent of these pathways and partially relieved by activation of β-catenin signalling. WISP3/CCN6 also suppressed ADAMTS5 expression in C-28/I2 cells treated with cytokines. In cytokine-treated primary chondrocytes gene silencing of WISP3/CCN6 resulted in enhanced ADAMTS5 expression whilst MMP10 expression was suppressed. Conclusion WISP3/CCN6 was highly expressed in end-stage osteoarthritic cartilage suggesting a role for this growth factor in cartilage homeostasis. WISP3/CCN6 repression of ADAMTS5 expression and regulation of MMP10 expression suggests complex and context-dependent roles for WISP3/CCN6 in cartilage biology.