Cartilage degradation by cocultures of transformed macrophage and fibroblast cell lines. A model of metalloproteinase-mediated connective tissue degradation.

A number of human and mouse macrophage and fibroblast cell lines were examined for their ability to degrade cartilage proteoglycan in an attempt to establish a cell culture model of cartilage degradation. The mouse transformed macrophage cell line J774A.1 alone or in combination with the mouse transformed fibroblast cell line 10ME HD A.5R.1 were the only cell lines capable of extensively degradating cartilage proteoglycan. Incubation of the macrophage cell line J774A.1 on heat-killed cartilage disks resulted in the release of 36% +/- 8 (mean +/- SEM, n = 5) of the radiolabeled cartilage proteoglycan. The fibroblast cell line 10ME HD A.5R.1 alone did not degrade cartilage. However, cocultures of J774A.1 macrophages and 10ME HD A.5R.1 fibroblasts incubated on cartilage discs resulted in the release of 69% +/- 6 (mean +/- SEM, n = 5) of radiolabeled proteoglycan. There was little degradation of cartilage by macrophage/fibroblast cocultures during the first 3 days of culture. Cartilage degradation increased with each subsequent day in culture from 7% +/- 2 on day 4 to 68% +/- 3 (n = 3) by day 7. Supernatants from the macrophage/fibroblast cocultures were incubated with cartilage discs in the presence of general class-specific proteinase inhibitors. The metalloproteinase inhibitors 1,10 phenanthroline, EDTA, and recombinant tissue inhibitor of metalloproteinase were the only inhibitors that significantly blocked cartilage degradation by coculture supernatant. The cartilage degrading metalloproteinase in the macrophage/fibroblast coculture supernatant eluted as a broad peak on Sephacryl S-200HR with an estimated molecular mass between 22 and 55 kDa. These studies suggest that the macrophage/fibroblast coculture model of cartilage degradation may be a useful experimental system for the study of metalloproteinase-mediated connective tissue degradation.