The spatial and temporal expression of VEGF and its receptors 1 and 2 in post-traumatic bone bridge formation of the growth plate
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Injuries to growth plates may initiate the formation of reversible or irreversible bone-bridges, may leading to bone length discrepancy or axis deviation. As vascular invasion is essential for the formation of bone tissue, the aim of our study was to investigate the kinetic expression of Vascular Endothelial Growth Factor (VEGF) and its receptors R1 and R2 and the ingrowth of vessels in the formation of bone bridges in a rat physeal injury model. Quantitative Real-Time Polymerase Chain Reaction was performed for VEGF and its receptors. Samples from the proximal physis of the tibial bone were immunohistochemically evaluated for the expression of VEGF and its R1 and R2 receptors and Laminin. Morphologically, physeal bone bridge formation was validated by means of Magnetic Resonance Imaging. Kinetic expression of VEGF and VEGF-R1 mRNA documented a tendency towards an increase in expression on day 7. Histological analyses showed a hematoma containing bone debris on day 1 which was replaced with bony trabeculae by day 14, forming a bone bridge by day 28 which was preceded and accompanied by angiogenesis and consistent with MRI data. VEGF and VEGF-R2 was expressed on the debris within the hematoma and bone trabeculae from days 1 to 28. VEGF-R1 expression was only noted until day 14. The findings of our study suggest that physeal bone bridge formation is in part triggered by VEGF expression and associated with angiogenesis, which was shown to precede bone bridge formation and may be further stimulated through VEGF-positive bone debris.
KeywordsGrowth plate injury Bone bridge Vascular endothelial growth factor Laminin
The project S-06-96 W was supported by the AO Research Fund of the AO Foundation. They played no further role in study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication, after the approval of the grant. We would like to acknowledge Maximilian Seles, MD, and Martin Manninger, MD, for their great work in analyzing the immunohistochemical expression of VEGF and its receptors R1 and 2 at the physeal injury site which was object of their doctoral thesis. Furthermore, we would like to thank Ursula Neun, MD, and Elisabeth Wadl, MD, for their contribution to this paper by investigating the immunohistochemical expression of Collagen I and II, and Laminin, respectively, which was also focus of their doctoral thesis. Eventually, we would also like to acknowledge Martina Rupp, DI, for their scientific input and for editing this paper. The monoclonal antibody 2E8/anti-laminin, developed by Eva Engvall, Ph.D., and the antibody CllC1/collagen type II, contributed by Holmdahl F. and Rubin K., were obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by The University of Iowa, Department of Biology, Iowa City, IA 52242. There is no actual or potential conflict of interest including any financial, personal or other relationships with other people or organizations that could inappropriately influence or bias our work.
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