Isolation, partial purification and in vitro characterization of osteogenic inhibitory protein

A noncollagenous protein has been extracted and partially purified from adult cortical bone. This protein copurifies with another bone matrix protein, bone morphogenetic protein, until treatment with nonionic detergents. Characterization of the biological activity of this new protein has demonstrated it to be a potent osteogenic inhibitor in vitro. The inhibitor antagonizes the chondrogenic activity of devitalized, demineralized bone matrix as well as the activity of soluble bone morphogenetic protein. Bone matrix induced collagen and glycosaminoglycan synthesis are both inhibited in the presence of various concentrations of the osteogenic inhibitory protein. Inhibition of collagen synthesis required the presence of osteogenic inhibitory protein from the initiation of the tissue culture while glycosaminoglycan synthesis could be inhibited at any stage of differentiation. We postulate that this osteogenic inhibitory protein is essential in normal homeostatic bone metabolism, perhaps acting directly on bone morphogenetic protein.