Osteogenic protein-1 with transforming growth factor-β1:: potent inducer of chondrogenesis of synovial mesenchymal stem cells in vitro

Background. Recently, cells derived from synovial mesenchymal stem cells (MSCs) have been regarded as a potential source of cells to induce repair of articular cartilage. To investigate more effective methods for promoting chondrogenesis, we examined the effects of osteogenic protein (OP)-1 with or without transforming growth factor-beta (TGF beta 1) on chondrogenesis of human MSCs in vitro. Methods. MSCs were isolated from the synovial membrane of patients with rheumatoid arthritis undergoing knee replacement surgery. After expansion of the cells, pellet cultures were performed in chondrogenic medium with OP-1 100-200 ng/ml, TGF beta 1 10 ng/ml, or both agents for 3 or 6 weeks. Chondrogenesis was evaluated histologically with safranin O staining, reverse transcription polymerase chain reaction for aggrecan and type II collagen mRNA, and quantification of glycosaminoglycan (GAG) content using a dimethylmethylene blue dye-binding assay. GAG content was normalized by DNA content measured using Hoechst 33258 dye. Results. At 3 weeks of culture, mRNAs for type II collagen and aggrecan were expressed by MSCs treated with either TGF beta 1 or OP-1; however, substantial matrix production was not induced. At 6 weeks, OP-1 increased GAG accumulation dose-dependently in the presence or absence of TGF beta 1, and the GAG content was the highest after combined treatment with 200 ng OP-1 and TGF beta 1. Histological staining for safranin O was poor after treatment with OP-1 or TGF beta 1 alone and slightly increased after combined treatment with TGF beta 1 and OP-1 at 3 weeks. At 6 weeks, OP-1 increased the intensity of staining dose-dependently in the presence or absence of TGF beta 1. However, the histological appearance of the cells treated with OP-1 alone was similar to that of hypertrophic chondrocytes, which was different from that of cells with combined treatment with OP-1 and TGF beta 1. Conclusions. A high dose of OP-1 was useful for enhancing chondrogenesis from synovium-derived MSCs in combined treatment with TGF beta 1.