The different pathways by which bone morphogenetic protein 7 (BMP-7) could exert its osteogenic function in distraction osteogenesis (DO) were investigated. Using immunohistochemistry, the temporal and spatial expression of markers for angiogenesis, cell proliferation, Indian hedgehog pathway, osteogenic growth factors and their receptors were investigated in a rabbit model of DO. Our results showed that local injection of BMP-7 at the lengthened site caused up-regulation of expression of growth factors and their receptors, cell proliferation and vascular markers and Indian hedgehog gene in a temporal fashion. By knowing these pathways, manipulation of DO by pharmaceutical agents may be possible. Based on preliminary data, BMP-7 can accelerate the consolidation of newly formed bone if locally injected early in the distraction phase; however, the exact mechanism remains unknown. The purpose of this study was to investigate the different pathways through which BMP-7 exerts its effects in DO. The right tibia of twenty-four rabbits was lengthened 2.0 cms. The rabbits were divided into three groups : control, placebo and treated groups. The rabbits received no injection (control), buffer (placebo) and 75 micro grams BMP7 (treated) in the distracted zone one week after the start of distraction. The rabbits were sacrificed ten minutes, one day, two days and two weeks following the injections. Using immunohistochemistry, the different pathways of bone formation were assessed by analysing the expression of markers for angiogenesis (VGEF, Vascular Endothelial Growth Factor and PECAM , platelet endothelial cell adhesion molecule) , cell proliferation markers (PCNA, proliferation cell nuclear antigen), osteogenic growth factors (TGFβ, IGF, FGF and their receptors) and Indian hedgehog gene as part of the parathyroid hormone related peptide pathway. BMP-7 may stimulate bone formation through several pathways in a temporal fashion early after local injection, by up-regulating the expression of numerous osteogenic growth factors and their receptors and Indian hedgehog, and late two weeks after the injection, by up-regulating cell proliferation and vascular markers. Our results showed the possible mechanisms of action of BMP-7 in DO and more importantly the various pathways through which pharmacological agents could be used in the manipulation of DO.
