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.