Oral keratinocytes transduced by BMP induce bone formation in vivo

BMPs are a family of pleiotropic signaling molecules critically involved at various stages in the formation of a variety of tissues and organs including bones and teeth. In addition recombinant BMP proteins can induce bone and dentin regeneration when applied directly to adult tissues. More recently fibroblasts transduced both ex vivo and in vivo by BMP cDNA delivered by recombinant viruses have been shown to induce ectopic and orthotopic bone formation. Fibroblasts transduced ex vivo by BMP-7 convert to osteoblasts upon implantation in vivo. Objectives: To determine if this osteogenic capacity was limited to fibroblasts, we transduced oral keratinocytes ex vivo with a recombinant adenovirus carrying a full length BMP cDNA (AdBMP) or control virus (AdMT). Methods: Nearly confluent cultures of keratinocytes were infected for 24 hrs with a multiplicity of infection of 2 X104 virus particles per cell. The cells were then harvested and resuspended in a thermoset collagen hydrogel at 2 x 106 cells per ml. Equal 200 µl aliquots of the infected cells were injected into the backs of NIH III mice (n=4/virus) and the resultant tissue harvested after 3 weeks. Results: Bone formed in all of the sites implanted with the AdBMP infected cells while none of the AdMT infected cells formed bone. The bone formed by the BMP transduced keratinocytes differed morphologically from that formed by fibroblasts. Immunocytochemical analysis revealed cells expressing keratin and BMP-7 residing within the bony trabeculae. Conclusions:We conclude that BMP transduced keratinocytes secrete BMP and form bony nodules in vivo. Supported by NIH grants DE12466 and AR46254.