Comparative transcriptional profiling of regenerating damaged knee joints in two animal models of the newt Notophthalmus viridescens strengthens the role of candidate genes involved in osteoarthritis.

Objectives: To compare joint regeneration in adult newts (N. viridescens) upon both newly established surgical removal and previously reported enzymatic destruction of articular cartilage to identify molecular factors and functionally analyze potentially important regulators involved in osteoarthritis (OA). Methods: Damage of knee cartilage was induced by either intra-articular injection of collagenase or by surgical removal of articular cartilage as a novel additional approach. Changes over time were clinically and histologically analyzed and studied by cDNA microarray analysis, real-time quantitative PCR, immunohistochemistry and functional assays to identify relevant candidate genes and determine their impact on regeneration. Results: Several genes were found to be up-regulated during regeneration, including extracellular matrix components and mediators of cell-matrix interactions, genes encoding for cellular components, for cell and tissue homeostasis and tissue remodelling, for cellular processes as well as signalling molecules. A high activity and diversity of transcription was detected on days 10 and 20, especially in the surgical model. 10 candidate genes were further analyzed. The matricellular protein tenascin C (TN-C) attracted our particular attention due to its prominent up-regulation during regeneration in both models and at different time points. Conclusions: Newts are able to regenerate OA-like articular cartilage damage ad integrum both after enzymatic and mechanical injury. Most of the genes involved in amphibians are also known to be operative in humans and other mammals, especially matricellular factors interfering with optimized matrix remodelling. Our results stress the necessity to elucidate mechanistic differences in different species potentially using identical molecules but with different functional results.

Adipokines and Inflammation Alter the Interaction Between Rheumatoid Arthritis Synovial Fibroblasts and Endothelial Cells.

Objective: The long-distance migration of rheumatoid arthritis synovial fibroblasts (RASFs) in the severe combined immunodeficiency (SCID) mouse model of rheumatoid arthritis (RA) suggests that an interaction between RASFs and endothelial cells (EC) is critical in this process. Our objective was to assess whether immunomodulatory factors such as adipokines and antirheumatic drugs affect the adhesion of RASFs to ECs or the expression of surface molecules. Methods: Primary ECs or human umbilical vein endothelial cell (HUVEC) and primary RASFs were stimulated with adiponectin (10 µg/mL), visfatin (100 ng/mL), and resistin (20 ng/mL) or treated with methotrexate (1.5 and 1,000 µM) and the glucocorticoids prednisolone (1 µM) and dexamethasone (1 µM), respectively. The expression of adhesion molecules was analyzed by real-time polymerase chain reaction. The interaction of both cell types was analyzed under static (cell-to-cell binding assay) and dynamic conditions (flow-adhesion assay). Results: Under static conditions, adipokines increased mostly binding of RASFs to EC (adiponectin: 40%, visfatin: 28%, tumor necrosis factor α: 49%). Under flow conditions, visfatin increased RASF adhesion to HUVEC (e.g., 0.5 dyn/cm2: 75.2%). Reduced adhesion of RASFs to E-selectin was observed after treatment with dexamethasone (e.g., 0.9 dyn/cm2: -40%). In ECs, tumor necrosis factor α (TNF-α) increased expression of intercellular adhesion molecule 1 (20-fold) and vascular cell adhesion molecule 1 (77-fold), whereas P-selectin was downregulated after stimulation with TNF-α (-6-fold). Conclusion: The adhesion of RASFs to EC was increased by visfatin under static and flow conditions, whereas glucocorticoids were able to decrease adhesion to E-selectin. The process of migration and adhesion of RASFs to ECs could be enhanced by adipokines via adhesion molecules and seems to be targeted by therapeutic intervention with glucocorticoids.

Endogenous regeneration after collagenase-induced knee joint damage in the adult newt Notophthalmus viridescens.

OBJECTIVES: To determine whether adult newts (Notophthalmus viridescens) are able to repair experimentally-induced joint damage in order to generate a model system for the study of endogenous joint regeneration. METHODS: Joint instability and articular cartilage lesions of the knee joint of adult newts (N viridescens) were induced by intra-articular injection of collagenase. The changes over time were analysed clinically, by MRI, histologically and by reverse transcription PCR to detect selected relevant markers. RESULTS: After rapid onset of disease with joint luxation, loss of proteoglycans and cartilage volume, the signs ameliorated continuously by regeneration of the affected joint compartments. The majority of joints were morphologically intact and functionally operative after 10 weeks. Upregulation of chondrogenic key genes, homogenous expression levels of factors implicated in cartilage homeostasis and limb regeneration as well as the distribution of the blastemal marker 22/18 in both treated and untreated knees suggest that joint regeneration in adult newts only partially invokes pathways of embryological organogenesis. CONCLUSIONS: Newts are able to regenerate articular cartilage injuries and to restore tissue integrity and function after induction of damage using a procedure known to induce experimental osteoarthritis in murine models. Further analysis of the underlying molecular mechanisms may contribute to the development of novel treatment approaches in joint failure.