DETECTION OF VITRONECTIN IN MINERALIZED BONE-MATRIX

Adhesive glycoproteins in the bone matrix are of critical importance f or cell anchorage, proliferation, migration, differentiation, and regu lation of bone metabolism. The localization of the adhesive glycoprote in vitronectin (Vn) in murine bone tissue was evaluated by immunohisto chemical staining, Vitronectin was present throughout the mineralized bone matrix of cancellous and cortical bone, whereas cartilage was dev oid of Vn staining, To exclude the possibility that the positive Vn st aining resulted from plasma Vn in blood vessels within the bone sectio ns, adjacent tissue sections were stained with antibodies to fibrinoge n, an abundant plasma protein, Fibrinogen immunoreactivity was confine d to blood vessels in the bone marrow and Haversian system, whereas th e mineralized bone matrix was devoid of staining. The presence of Vn i n murine bones was confirmed by sequential extraction, followed by fra ctionation of the resulting polypeptides by gel electrophoresis and im munoblotting analysis, Hydroxyapatite affinity chromatography raises t he possibility that mineral interactions, at least in parr, mediate th e incorporation of Vn into the bone matrix, These results indicate tha t Vn is a specific component of bone tissue and raise the possibility that Vn is involved in regulation of bone metabolism.