Chondroprogenitor cells of synovial tissue

Objective. To assess the chondrogenic potential of cells within the synoviu m, Methods. Explants of synovium taken from various sites in the joint were em bedded in agarose and cultured with transforming growth factor beta 1 (TGF beta 1) to assess their chondrogenic potential. Isolated synovial cells wer e also tested for their chondrogenic potential by culturing them as aggrega tes in a chemically defined medium with TGF beta 1, Cartilage formation was determined with histologic staining and immunohistochemistry. The osteocho ndral potential of the isolated cells was also assessed after subcutaneous implantation of the cells, loaded into porous calcium phosphate ceramic cub es, in athymic mice. Results. A total of 48 synovial explants were cultured in agarose with TGF beta 1, The formation of cartilage was observed in the outer region of 21 e xplants, and type II collagen was localized in that region by immunohistoch emistry. A larger percentage of TGF beta 1+ explants from the inner synoviu m sites formed cartilage compared with those from the outer synovium sites. Chondrogenesis occurred in aggregates incubated with TGF beta 1 as early a s day 7, and by day 14, all TGF beta 1+ aggregates demonstrated chondrogene sis, In contrast with the results of the in vitro aggregate assay for chond rogenesis, no formation of cartilage or bone was evident in any section con taining synovial cell-loaded ceramic cubes that were harvested at either 3 or 6 weeks after implantation subcutaneously in athymic mice. Conclusion. Synovial explants and isolated synovial cells will undergo chon drogenesis when cultured in the presence of TGF beta 1, The data indicate a possible synovial origin for the chondrocytic cells found in rheumatoid pa nnus, Furthermore, these data are consistent with the clinical findings of synovial chondrogenesis leading to synovial chondromatosis.