Fetal bovine bone cells synthesize bone-specific matrix proteins.

Abstract

Cells were isolated from both calvaria and the outer cortices of long bones from 3- to 5-mo. bovine fetuses. The cells were identified as functional osteoblasts by indirect immunofluorescence using antibodies against 3 bone-specific, noncollagenous matrix proteins (osteonectin, the bone proteoglycan and the bone sialoprotein) and against type I collagen. In separate experiments, confluent cultures of the cells were radiolabeled and shown to synthesize and secrete osteonectin, the bone proteoglycan and the bone sialoprotein by immunoprecipitation and fluorography of SDS [sodium dodecyl sulfate] polyacrylamide gels. Analysis of the radiolabeled collagens synthesized by the cultures showed that they produced predominantly (.apprx. 94%) type I collagen, with small amounts of types III and V collagens. This confirmed in bovine bone cells: there was a typical cAMP response to parathyroid hormone; freshly isolated cells possessed high levels of alkaline phosphatase, which diminished during culture but returned to normal levels in mineralizing cultures; and cells grown in the presence of ascorbic acid and .beta.-glycerophosphate rapidly produced and mineralized an extracellular matrix containing largely type I collagen. Antibodies directed against bone-specific, noncollagenous proteins can be used to clearly identify bone cells in vitro.