Search

Osteoarthritis (OA) is a leading cause of chronic pain and disability, for which there is no cure. Mesenchymal stromal cells (MSCs) have been used in clinical trials for treating OA due to their unique ability to generate paracrine anti-inflammatory and trophic signals. Interestingly, these studies have shown mainly short-term effects of MSCs in improving pain and joint function, rather than sustained and consistent benefits. This may reflect a change or loss in the therapeutic effects of MSCs after intra-articular injection. The present study aimed to unravel the reasons behind the variable efficacy of MSC injections for OA using an in vitro co-culture model. Osteoarthritic human synovial fibroblasts (OA-HSFs) were co-cultured with MSCs to investigate their reciprocal effects on cell responses and whether a short-term exposure of OA cells to MSCs was sufficient for reducing their diseased characteristics in a sustained manner. Gene expression and histological analyses were performed. OA-HSFs exposed to MSCs showed short-term downregulation of inflammatory markers. However, the MSCs showed upregulation of inflammatory markers and impaired ability to undergo osteogenesis and chondrogenesis in the presence of OA-HSFs. Moreover, short-term exposure of OA-HSFs to MSCs was found to be insufficient for inducing sustained changes to their diseased behaviour. These findings suggested that MSCs may not provide long-term effects in correcting the OA joint environment due to them adopting the diseased phenotype of the surrounding tissues, which has important implications for the future development of effective stem-cell-based OA treatments with long-term therapeutic efficacy.

The aim of this study was to immunolocalise type VI collagen and perlecan and determine their interactive properties in the intervertebral disc (IVD). Confocal laser scanning microscopy co-localised perlecan with type VI collagen as pericellular components of IVD cells and translamellar cross-bridges in ovine and murine IVDs. These cross-bridges were significantly less abundant in the heparin sulphate deficient Hspg2 exon 3 null mouse IVD than in wild type. This association of type VI collagen with elastic components provides clues as to its roles in conveying elastic recoil properties to annular tissues. Perlecan and type VI collagen were highly interactive in plasmon resonance studies. Pericellular colocalisation of perlecan and type VI collagen provides matrix stabilisation and cell-matrix communication which allows IVD cells to perceive and respond to perturbations in their biomechanical microenvironment. Perlecan, at the cell surface, provides an adhesive interface between the cell and its surrounding extracellular matrix. Elastic microfibrillar structures regulate tensional connective tissue development and function. The 2010 Global Burden of Disease study examined 291 disorders and identified disc degeneration and associated low back pain as the leading global musculoskeletal disorder emphasising its massive socioeconomic impact and the need for more effective treatment strategies. A greater understanding of how the IVD achieves its unique biomechanical functional properties is of great importance in the development of such therapeutic measures.

Mesenchymal stem cells (MSCs) have been considered as a potential source for cell-based therapies in arthritic diseases for both their chondrogenic and anti-inflammatory properties. Thus, we examined how MSC-based neocartilage responds to tumour necrosis factor alpha (TNF-α) compared to articular chondrocyte (AC)-based neocartilage. Since oxygen tension is altered in arthritic joints, we also examined how increased oxygen tension influences this process. Monolayer-expanded healthy human ACs and bone marrow MSCs were cultured in chondrogenic medium in three-dimensional culture under hypoxia. They were then exposed to TNF-α under hypoxic or increased oxygen tension. We found no inherent anti-inflammatory potential of MSC-derived neocartilage as it pertains to the enzymes studied here: more degradative enzymes were upregulated by TNF-α in MSCs than in ACs, regardless of the oxygen tension. MSCs were also more sensitive to reoxygenation during TNF-α exposure, as indicated by increased proteoglycan loss, increased aggrecanase-generated metabolites, and further upregulation of the major aggrecanases, ADAMTS4 and ADAMTS5. There was also evidence of matrix metalloproteinase (MMP)-mediated aggrecan interglobular domain cleavage and type II collagen loss in response to TNF-α in both MSCs and ACs, but more MMPs were further upregulated by reoxygenation in MSCs than in ACs. Our study provides further evidence that consideration of oxygen tension is essential for studying cartilage degradation; for example, neocartilage produced from MSCs may be more sensitive to the negative effects of repeated hypoxia/reoxygenation events than AC-derived neocartilage. Consideration of the differences in responses may be important for cell-based therapies and selection of adjunctive chondroprotective agents.

Aggrecanases from the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin motifs) family are important therapeutic targets due to their essential role in aggrecan depletion in arthritic diseases. Whether their function is also important for matrix rearrangements during chondrogenesis and thus, cartilage regeneration, is however so far unknown. The aim of this study was to analyse the expression and function of ADAMTS with aggrecanase activity during chondrogenic differentiation of human mesenchymal stem cells (MSCs). Chondrogenic differentiation was induced in bone marrow-derived MSC pellets and expression of COL2A1, aggrecan, ADAMTS1, 4, 5, 9, 16 and furin was followed by quantitative RT-PCR. Formation of the NITEGE (ADAMTS-cleaved) and DIPEN (MMP-cleaved) aggrecan neoepitopes was detected by immunohistochemistry. While the expression of ADAMTS4, 9, 16 and furin was up-regulated during chondrogenesis, ADAMTS1 and 5 were down-regulated. Despite this regulation of ADAMTS, no formation of NITEGE neoepitopes occurred in MSC pellets, indicating no ADAMTS-induced cleavage of aggrecan. In contrast, MMP-induced cleavage of aggrecan appeared at 14 d after induction of chondrogenesis. Submission of differentiated MSC pellets to IL1β treatment for 3 d resulted in strong upregulation of ADAMTS1, 4 and 5, rapid proteoglycan depletion, and stimulation of ADAMTS-induced but not MMP-induced cleavage of aggrecan. Thus, there is no evidence for ADAMTS-induced aggrecan cleavage during chondrogenesis, but proteoglycan turnover is rapidly inducible under inflammatory signals. Therapeutic aggrecanase inhibition for treatment of arthritic disease may thus not impede regenerative self-healing pathways based on chondrogenesis of local progenitor cells in the joint.