Exogenous synovial stem cells adhere to defect of meniscus and differentiate into cartilage cells

The meniscus is semilunar fibrocartilage, and its injury causes dysfunction of the knee. We previously reported a high chondrogenic potential of synovial mesenchymal stem cells (MSCs). Here, we examined whether intra-articular injected synovial MSCs adhered to the defect of the meniscus, survived there, and differentiated into cartilage cells. MSCs were isolated from the synovium of GFP rats. Cylindrical defects were created in the menisci in wild rats, and GFP-positive synovial MSCs were injected into the knee. In the control group, 100 microl of PBS was injected into the contralateral knee. The menisci were analyzed after day 1, weeks 2, 4, 8, and 12. One day after injecting of 10(7) GFP-positive synovial MSCs, the meniscal defect was filled with the cells. The GFP-positive synovial MSCs expressed type II collagen, exhibited representative characteristics of chondrocytes by electron microscopy at 8 weeks, and could still be observed at 12 weeks. The histological score improved within 12 weeks but there were no statistical difference between the two groups at each period in this model. GFP mRNA expressions were not observed in distant organs at day 1. After intra-articular injection, synovial MSCs attached to the meniscal defect and differentiated into cartilage cells.