title: Colocalization of c-Src (pp60src) and bone morphogenetic protein 2/4 expression during mandibular distraction osteogenesis: in vivo evidence of their role within an integrin-mediated mechanotransduction pathway.
abstract: Craniofacial distraction osteogenesis (DO) is an evolving reconstructive technique with expanding applications for the treatment of bony deficiencies of the facial skeleton. Mechanical force has been known to play a fundamental role in modulating sustained osteogenic response and therefore is believed to function as a critical regulator of DO. We hypothesize that key clustering components of an integrin-mediated signaling pathway, including c-Src (pp60), are necessary for mediating the response to mechanical force. The specific aim of this study is to demonstrate up-regulation of a key focal adhesion molecule, c-Src, selectively in new bone formation subject to the mechanical forces of distraction and to demonstrate a lack of that same up-regulation in new bone formation associated with simple fracture healing. An additional specific aim is to demonstrate colocalization of c-Src expression and bone morphogenetic protein (BMP 2/4) expression during mandibular DO. Using a rat model of mandibular DO, c-Src and BMP 2/4 expression were evaluated in critical size defects, subcritical size defects, and mandibles undergoing gradual distraction. Osseous regeneration was observed in the course of gradual distraction; this process was associated with increased expression of c-Src. Furthermore, the presence of BMP 2/4 closely approximated c-Src expression spatially and temporally, suggesting a link between cytoplasmic focal adhesion activation and the resultant nuclear regulation of osteogenic protein expression. In significant contradistinction, minimal c-Src expression was found in the subcritical-sized defects where the fractures healed secondarily but where no gradual distraction was performed. Instead, the new bone formation inherent in the secondarily healed subcritical-sized defects demonstrated expected BMP 2/4 expression but was devoid of an up-regulation of c-Src. Finally, as expected, minimal expression of both c-Src and BMP was found in fibrous nonunion specimens. C-src expression was observed during gradual distraction; furthermore, minimal c-Src expression was visualized during subacute and critical-size defect fracture healing. C-Src expression also closely approximated BMP expression during DO. These findings that c-Src expression is found primarily only during conditions of cyclic distraction forces strongly implicates that mechanical force during gradual distraction is associated with c-Src expression. These results provide in vivo support for previous in vitro evidence that mechanical force profoundly influences osseous regeneration during distraction osteogenesis by means of a c-Src dependent mechanotransduction pathway, resulting in increased expression of osteogenic proteins, including BMP 2/4.
authors: Section of Plastic Surgery, University of Michigan Medical Center, Ann Arbor, MI, USA.
authors: Samuel T
authors: ST
authors: Rhee
authors: Steven R
authors: SR
authors: Buchman
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000235:genetics*; D001861:Bone Regeneration / Q000502:physiology*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics; D006984:Hypertrophy / Q000473:pathology; D007150:Immunohistochemistry; D016023:Integrins / Q000502:physiology*; D008334:Mandible / Q000473:pathology / Q000502:physiology*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D009434:Neural Pathways / Q000473:pathology*; D019857:Osteogenesis, Distraction; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016212:Transforming Growth Factor beta / Q000235:genetics*
chemical_list: C525720:Bmp2 protein, rat; C525811:Bmp4 protein, rat; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D016023:Integrins; D016212:Transforming Growth Factor beta; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D016392:Proto-Oncogene Proteins pp60(c-src); C496052:Ptk2 protein, rat