Osteogenic protein-1 with transforming growth factor-beta1: 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 (TGFbeta1) 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, TGFbeta1 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 TGFbeta1 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 TGFbeta1, and the GAG content was the highest after combined treatment with 200 ng OP-1 and TGFbeta1. Histological staining for safranin O was poor after treatment with OP-1 or TGFbeta1 alone and slightly increased after combined treatment with TGFbeta1 and OP-1 at 3 weeks. At 6 weeks, OP-1 increased the intensity of staining dose-dependently in the presence or absence of TGFbeta1. 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 TGFbeta1.

CONCLUSIONS: A high dose of OP-1 was useful for enhancing chondrogenesis from synovium-derived MSCs in combined treatment with TGFbeta1.