Synovium-Derived Mesenchymal Stem/Stromal Cells and their Promise for Cartilage Regeneration

Adult tissues are reservoirs of rare populations of cells known as mesenchymal stem/stromal cells (MSCs) that have tissue-regenerating features retained from embryonic development. As well as building up the musculoskeletal system in early life, MSCs also replenish and repair tissues in adult life, such as bone, cartilage, muscle, and adipose tissue. Cells that show regenerative features at least in vitro have been identified from several connective tissues. Bone marrow and adipose tissue are the most well recognized sources of MSCs that are already used widely in clinical practice. Regenerative medicine aims to exploit MSCs and their tissue regeneration even though the underlying mechanisms for their beneficial effects are largely unknown. Despite many studies that have used various tissue-derived MSCs, the most effective tissue source for orthopedic procedures still remains to be identified. Another question that needs to be addressed is how to evaluate autologous MSCs (i.e., patient derived). Previous studies have suggested the features of bone-marrow-derived MSCs can differ widely between individuals, and can be changed in particular in patients suffering from some forms of degenerative disorder, such as osteoarthritis. The synovium is a thin membrane that protects the synovial joints, and it is a rich source of MSCs that show great potential for regenerative medicine. Here, we review synovium-derived MSCs from reports on basic and clinical studies. We discuss their potential to treat cartilage defects caused by either degeneration or trauma, and what needs to be done in further research toward their better exploitation for joint regeneration.