GROWTH-FACTORS FOR BONE-GROWTH AND REPAIR - IGF, TGF-BETA AND BMP

Current research is reviewed regarding the actions of three growth fac tor systems on bone formation: insulin-like growth factors (IGFs), tra nsforming growth factor-beta s (TGF beta s), and bone morphogenetic pr oteins (BMPs). Each growth factor family consists of multiple related growth factor genes. TGF beta s and BMPs 2-7 are subfamilies of a larg er TGF beta superfamily. IGFs, TGF beta s and BMPs are produced by ost eoblasts and other bone cells and affect osteoblast proliferation and differentiation. They are also incorporated into mineralized bone matr ix and retain activity when extracted from bone. Various hormones, gro wth factors, and mechanical stress influence bone cell production of I GFs, TGF beta s, and BMPs. Thus these growth factors may function in l ocal regulation of bone formation. Currently there is much interest in the function of IGF binding proteins, which are also produced by bone cells, in regulating IGF activities in bone. Recently, mechanisms for activation of the TGF beta serine/threonine kinase receptors have bee n investigated, and receptors for BMPs have been identified which are structurally related to TGF beta receptors. In vivo studies are discus sed which demonstrate the applicability of IGFs, TGF beta s and BMPs t o increasing bone formation systemically, promoting fracture healing a nd inducing bone growth around implants.