Sequential appearance of macromolecules in bone induction in the rat.

The appearance of noncollagenous proteins and proteoglycans during induction of cartilage and bone by implanted demineralized bone powder was studied by immunohistochemistry with polyclonal antibodies. Three bone proteins (osteopontin, sialoprotein, and a 62 kDa protein) were present in the bone powder grains before implantation. They appeared to be lost slowly from the granulation tissue but reappeared when bone formation started. The raw powder also contained a cartilage protein, biglycan (S1), chondrocalcin, cartilage oligomeric matrix protein, and the large proteoglycan aggrecan. The amounts of these molecules, however, increased significantly both within and outside the grains on cartilage formation. Cartilage matrix protein (148 kDa protein) appeared sparsely. The 58 kDa protein and fibromodulin (59 kDa protein), particularly the latter, were prevalent in fibrillar bundles. Antibodies against the laminin-staining vessel basement membranes showed an abundant occurrence of capillaries within the matrix grains in the granulation tissue and in the precartilaginous tissue. Bone powder made noninductive by 4 M guanidine HCl did not induce cartilage and did not stain for antibodies against bone proteins or for molecules restricted to cartilage.