Effect of gene transfection timing on TGF-β1 expression in rabbit mandibular distraction gap

Transforming growth factor-β1 (TGF-β1) is a member of the TGF-β superfamily, and plays an important role in promoting various stages of intramembranous and endochondral bone formation. It is one of the major growth factors that influence new bone formation in the distraction gap during distraction osteogenesis (DO). The major problem of DO is the time required for the treatment. Reports show that gene therapy accelerates osteogenesis, which can significantly benefit patients with DO. However, the optimal timing of gene transfection has not yet been reported. In this study, we used the New Zealand rabbit mandibular DO model for transfecting recombinant plasmid pIRES-hVEGF165-hBMP2 during the latency, distraction, and consolidation periods of DO. The TGF-β1 levels in the distraction gap were detected at different time-points by immunohistochemistry and analyzed semi-quantitatively with the CMIAS-2001A computerized image analyzer. The TGF-β1 levels peaked after 7 days and decreased after 14 days of consolidation in each group. In contrast, the TGF-β1 levels in the transfected distraction period group were significantly higher than those in the other groups. After 28 days of consolidation, TGF-β1 levels decreased and there was no significant difference among the groups. These results indicated that the genes transfected in the distraction period up-regulated the expression of TGF-β1 more than in the latency and consolidation periods, which promoted bone formation in the distraction gap through a series of biological effects. Thus, we obtained a remarkable effect on new bone formation, and showed that the distraction period is optimal for gene therapy.