Native joint-resident mesenchymal stem cells for cartilage repair in osteoarthritis

The role of native (not culture-expanded) joint-resident mesenchymal stem cells (MSCs) in the repair of joint damage in osteoarthritis (OA) is poorly understood. MSCs differ from bone marrow-residing haematopoietic stem cells in that they are present in multiple niches in the joint, including subchondral bone, cartilage, synovial fluid, synovium and adipose tissue. Research in experimental models suggests that the migration of MSCs adjacent to the joint cavity is crucial for chonodrogenesis during embryogenesis, and also shows that synovium-derived MSCs might be the primary drivers of cartilage repair in adulthood. In this Review, the available data is synthesized to produce a proposed model in which joint-resident MSCs with access to superficial cartilage are key cells in adult cartilage repair and represent important targets for manipulation in 'chondrogenic' OA, especially in the context of biomechanical correction of joints in early disease. Growing evidence links the expression of CD271, a nerve growth factor (NGF) receptor by native bone marrow-resident MSCs to a wider role for neurotrophins in OA pathobiology, the implications of which require exploration since anti-NGF therapy might worsen OA. Recognizing that joint-resident MSCs are comparatively abundant in vivo and occupy multiple niches will enable the optimization of single-stage therapeutic interventions for OA.