Mineralized tissues contain in their extracellular matrix a protein factor which has the capacity to induce chondrogenesis and osteogenesis in soft tissues that normally do not form cartilage or bone. Urist has called this factor BMP, the bone morphogenetic protein. Efforts to characterize this protein from bone have not been successful because of the small amount and highly interactive nature of BMP, and the complex composition of the bone. Moreover, the assay systems, involving in vivo implantation, have required large amounts of protein. We have approached this problem from two fresh perspectives: 1) an in vitro cell culture assay has been developed; 2) use has been made of the fact that dentin matrix has a higher BMP activity than bone matrix. In our initial studies we have demonstrated the presence of a factor in the rat dentin matrix which is chondrogenic in vitro and osteogenic in vivo, extracted and fractionated the noncollagenous proteins, located the fraction with fractionated the noncollagenous proteins, located the fraction with fractionated the noncollagenous proteins, located the fraction with fractionated the noncollagenous proteins, located the fraction with in vitro chondrogenic activity, and shown that nonmyogenic nionatal rat muscle fibroblasts have receptors for its uptake. We now propose to: 1) purify the CIA to homogeneity and obtain its amino aid sequence; 2) determine its in vivo activity; 3) prepare immunologic and nucleotide probes for its identification; 4) quantitate the receptor binding site and determine the nature of the receptor and the uptake process; 5) examine the role of growth factors and other regulatory agents on its activity in vitro; and 6) explore the use of CIA in vivo in bone defect repair. We believe that these studies can be of immense importance in bringing closer the application of chondrogenic and osteogenic agents to the repair of bone defects.
