Final Activity Report Summary - MSCPA (Mechanisms of Stem Cell Potency in Arthritis) Osteoarthritis is associated with ageing and is the most common musculoskeletal disease, affecting a large proportion of the population. There are no reliably effective treatments for osteoarthritis and current therapeutic approaches have little impact on the associated progressive degeneration of articular cartilage and other joint tissues. Mesenchymal stem cells (MSCs) can differentiate into a variety of cell types in vitro and in vivo, including, chondrocytes, osteoblasts, adipocytes and myocytes. MSCs offer the potential of opening new therapeutic frontiers and the primary focus of this project was to increase our understanding of the way the cells change in a patient with osteoarthritis and how the cells themselves are controlled as they differentiate and become chondrocytes or cartilage cells. Previously we have shown that the proliferation of MSCs isolated from patients with end-stage osteoarthritis was significantly reduced compared to normal controls. We have identified up-regulation of the cyclin-dependent kinase inhibitor p21WAF1 in OA MSCs as a factor that contributes to this decreased growth. Epigenetics provide an element of transcriptional control critical for the regulation of gene expression and for the normal development and growth of cells. Aberrant epigenetic marks have been associated with cancer and aging and individual cells undergo epigenetic changes due to the microenvironment they inhabit. However, there is little or no information on the role of DNA methylation in regulating key genes in differentiation of MSCs to the chondrogenic lineage. The Sox9 transcription factor plays an essential role in promoting chondrogenesis and regulating expression of chondrocyte extracellular-matrix genes including Type ?? collagen and the proteoglycan aggrecan. Analysis of SOX9 promoter regions from multiple species has identified highly conserved regions corresponding to potentially methylated CpG islands. Differences in methylated cytosines in these regions of the SOX9 promoter in MSCs and chondrocytes have been identified and an assay established to test the effect of methylation or demethylation on the ability of MSCs to undergo chondrogenic differentiation. In summary, the results of this project have increased our understanding of the role of MSCs in osteoarthritis and have set a framework in place to assess mechanisms that control differentiation of MSCs to cartilage cells.