The splice variants 120 and 164 of the angiogenic peptide vascular endothelial cell growth factor (VEGF) are expressed during Achilles tendon healing

Background: The Achilles tendon is one of the most common sites of tendon injury and rupture. One of the early events of wound healing is angiogenesis, in which neovascularization prompts delivery of inflammatory cells and fibroblasts to the wound site. Angiogenesis is controlled by a variety of mitogenic, chemotactic, or inhibitory peptides and lipid factors that act on invading endothelial and smooth muscle cells. One of the most important angiogenic factors is the vascular endothelial cell growth factor (VEGF), a glycosylated protein of 46-48 kDa composed of two disulfide-linked subunits. Methods: We therefore investigated the expression of VEGF during healing of artificial lesions of the Achilles tendon in a sheep model by immunohistochemical, biochemical, molecular, and cell biology methods. Two groups were created, the Achilles tendon was tenotomized, and the animals were killed at 3 and 24 weeks. Each group consisted of 6 specimens. Six animals which did not undergo surgery served as controls. Results: VEGF could be immunostained in tenocytes of ruptured but not in normal adult tendons. At microvessels, the receptors VEGFR-1 (flt-1) and VEGFR-2 (KDR) could also be visualized. High VEGF levels in ruptured and negligible levels in normal Achilles tendons could be confirmed and quantified by enzyme-linked immunoassay (ELISA). The highest VEGF concentrations were found in ruptured tendons, whereas the VEGF content in healthy adult tendons was negligible. Interestingly, the VEGF concentration of the original tendon stump was higher after 3 weeks than that of the newly regenerated tendon tissue. However, this difference was not significant (p>0.05). Reverse transcription-polymerase chain reaction (RT-PCR) showed that the splice variants VEGF(120) and VEGF(164) are expressed at 3 weeks and 24 weeks, respectively. Conclusion: These results prove the presence of the splice variants VEGF(120) and VEGF(164) in ruptured tendons during the healing process. The demonstrated up-regulation of VEGF in intrinsic tenocytes suggests a role for VEGF in mechanisms of angiogenesis and Achilles tendon repair. Further research is needed to evaluate if VEGF might be a possible tool to enhance the process of tendon healing.