Tendon healing in vitro: Modification of tenocytes with exogenous vascular endothelial growth factor gene increases expression of transforming growth factor β but minimally affects expression of collagen genes

Abstract

It is not clear how the transfer of exogenous growth factor genes to tenocytes affects collagen production. An increase in collagen production enhances the repair but an increase in growth factors that stimulate tissue fibrosis may cause adhesion. Gene therapy is a new way to regulate tendon healing but it has been explored rarely. We genetically modified tenocytes with the vascular endothelial growth factor (VEGF) gene and investigated the expression of the genes for collagen production in an in vitro model of the proliferating tenocytes. Tenocytes were obtained from cultures of rat intrasynovial tendons and distributed randomly to 25 dishes. The tenocytes in the experimental dishes (n = 9) were treated for 12 hours with plasmid containing the VEGF complementary deoxyribonucleic acid and then were cultured for 5 days; the tenocytes in the control dishes (n = 8) did not receive the exogenous gene. Tenocytes in the other dishes received exogenous platelet-derived growth factor (PDGF) gene for comparison of the effects of VEGF gene therapy. Efficiency of the gene transfer was evaluated by presence of the transgene in the tenocytes which was detected by reverse transcription polymerase chain reactions. Levels of expression of types I and III collagen and transforming growth factor (TGF)-beta genes were determined by quantitative analysis of the products of reverse transcription polymerase chain reactions. Expression of the TGF-beta gene increased significantly in the cells treated with exogenous VEGF cDNA. Expression of type I and III collagen genes by tenocytes was affected minimally by transfer of the VEGF gene to the tenocytes and was significantly weaker than that stimulated by PDGF gene therapy. Efficient gene transfer was confirmed by the presence of the VEGF complementary deoxyribonucleic acid in the tenocytes receiving the transferred gene. Transfer of exogenous VEGF gene has very limited effects on the promotion of collagen production in the proliferating tenocytes. This study suggests that VEGF gene therapy is not as beneficial as PDGF gene therapy to tendon healing and may increase the activities of TGF-beta that are associated with adhesion formations.