A "Coupled" Subchondral Bone-Articular Cartilage Tissue Culture System for the Study of Cartilage Proteoglycan Metabolism

Current evidence suggests that interactions between the subchondral bone and the articular cartilage of mammalian diarthrodial joints may occur through the action of bone-associated peptide factors. However, there is no suitable organ culture model for studying these interactions. This study defines a long-term tissue culture system where the articular cartilage is coupled to the adjacent subchondral bone obtained from the proximal ends of bovine metacarpals. Autoradiography done over 3 mo., by utilizing$[^{35}S]SO_4$incorporation into cartilage proteoglycan (PG) and a procedure for cutting non-decalcified bone, demonstrated similar numbers of silver grains over chondrocytes in all cartilage zones, including the bone-cartilage interface. Newly synthesized PG (NSPG) from the cartilage of the "coupled" system over a 3-wk period was primarily of large hydrodynamic size (Kav of 0.34). Comparable bovine articular and nasal cartilage slice systems, incubated for short periods of time, yielded similar and somewhat larger NSPG, respectively. Labeled chondroitin sulphate PG accumulating in the medium of primary chondrocyte monolayer cultures, derived from the cartilage of the coupled system at 0, 1, 2, and 3 wk, revealed two polydisperse subpopulations (Kav of 0.30 to 0.38 and 0.51 to 0.68). We conclude that this coupled bone-cartilage system is viable for prolonged periods, is suitable for studies on the metabolism of articular cartilage PGs, and seems to have some advantages over the cultured articular cartilage slice system.