Homology of bone-inductive proteins from human, monkey, bovine, and rat extracellular matrix

Abstract

Allogeneic implantation of rat extracellular demineralized diaphyseal bone matrix in subcutaneous sites induces a sequence of events resulting in the local differentiation of endochondral bone. However, xenogenic subcutaneous implantation of human, monkey, and bovine extracellular bone matrix into rat showed that bovine matrix had only a weak capacity to induce bone, whereas human and monkey matrix had none at all. This suggested that extracellular matrix-induced bone differentiation is apparently species-specific. We recently reported that the extraction of matrix with 4 M guanidine X HCl resulted in complete removal of the ability to induce endochondral bone differentiation, with the biological activity of the matrix being again restored when the extracted active matrix components (less than 50,000 daltons) were reconstituted with the inactive residue. To define the possible biochemical basis of species specificity, human, monkey, and bovine extracellular bone matrices were extracted with 4 M guanidine X HCl and the extracts were reconstituted with biologically inactive rat residue and bioassayed. The results were similar to those obtained with intact matrices and showed that total extracts of bovine matrix had a weak capacity to induce bone, whereas corresponding extracts of human and monkey matrix did not induce bone. However, partial purification by gel filtration of 4 M guanidine X HCl extracts from each species followed by reconstitution of the different fractions with inactive rat residue resulted in bone induction by all species from fractions containing proteins of less than 50,000 daltons. These observations demonstrate that species specificity of xenogenic extracellular bone matrix is due to immunogenic or inhibitory components (or both) in the guanidine X HCl residue and solubilized extracellular matrix components of greater than 50,000 daltons. These results imply that there is homology in the bone inductive proteins from human, monkey, bovine, and rat extracellular bone matrices.