ATTACHMENT OF ARTICULAR-CARTILAGE CHONDROCYTES TO THE TISSUE FORM OF TYPE-VI COLLAGEN

Type VI collagen is composed of a short triple helix rich in RGD seque nces with globular domains at each extremity of the helix. Disulfide-b onded tetramers of the monomeric molecule associate non-covalently to form networks of microfibrils in connective tissues, including cartila ge. The disulfide-bonded tetramer can be extracted with 6 M guanidine HCl and purified without pepsin digestion and is referred to here as t he tissue form of type VI collagen, Type VI collagen in mature articul ar cartilage appears to be concentrated pericellularly. We undertook a systematic investigation using solid phase assays to establish the na ture of the attachment of bovine articular cartilage chondrocytes to t he intact, tissue form of bovine type VI collagen. The tissue form of type VI collagen was extracted from bovine meniscus cartilage with 6 M guanidine HCl and purified by polyethylene glycol precipitation. When equal molar quantities were coated on microwells, the tissue form of type VI collagen attached more cells than the pepsin-digested form of the molecule that lacked the globular domains. The attachment to the i ntact, tissue form was dose-dependent and saturable and was not inhibi ted by heparin or type II collagen. A linear GRGDSP peptide failed to inhibit attachment of the chondrocytes to the intact, tissue or pepsin -digested forms of type VI collagen, but totally inhibited the interac tion when the intact molecule was;educed and alkylated. In contrast, a cyclic C GRGDSPC* peptide inhibited attachment to the tissue form of type VI collagen, but not to fibronectin. The attachment had a metal ion dependence that could be satisfied by MnCl2, slightly less by MgCl 2, but not at all by CaCl2. A direct interaction between the tissue fo rm of type VI collagen and a chondrocyte cell surface receptor or rece ptors is a structural feature of the pericellular matrix in cartilage.