[Experimental study on the effect of vascular endothelial growth factor 165 gene on vascularization of dermal substitute].

OBJECTIVE: To investigate the effect of vascular endothelial growth factor 165 (VEGF 165) gene on vascularization of dermal substitute in vivo.

METHODS: Human umbilical vein endothelial cells (HUVECs) were cultured in M199 medium containing FBS in the volume fraction of 10% (briefly called complete medium). (1) HUVECs were divided into non-transfection group (without transfection), empty vector group [transfected with pIRES2-enhanced green fluorescent protein (EGFP) plasmid], and VEGF plasmid group (transfected with pIRES2-EGFP-VEGF plasmid) according to the random number table, with 6 wells in each group. At post transfection hour (PTH) 24, the expression of green fluorescent protein (GFP) in each group was observed under inverted phase contrast fluorescence microscope, and the expression rate of GFP was detected with flow cytometer. Cells in non-transfection group were tested with the same methods as listed above. The cells in stable transfection in empty vector group and VEGF plasmid group were sifted by neomycin. The mRNA and protein expression levels of VEGF 165 in cells and the protein amount of VEGF 165 in the supernatant of cell culture medium in 3 groups were respectively determined by real-time fluorescent quantitation PCR, Western blotting, and enzyme-linked immunosorbent assay. (2) Forty-eight male nude mice were divided into 4 groups according to the random number table, with 12 mice in each group. Mice in saline group were subcutaneously implanted with dermal substitutes which had been cultured in saline for 2 days on both sides of back (the same site below); mice in medium group were subcutaneously implanted with dermal substitutes which had been cultured in complete medium for 2 days; mice in non-transfected cells group were subcutaneously implanted with dermal substitutes that had been cultured in complete medium with non-transfected HUVECs for 2 days; mice in transfected cells group were subcutaneously implanted with dermal substitutes that had been cultured in complete medium with HUVECs stably transfected with VEGF plasmid for 2 days. The dermal substitutes in every group were taken out on post operation day (POD) 3, 7, 14, and 21. Distributions of microvessels and HUVECs in dermal substitutes were observed by immunohistochemical staining, and the microvessel number was counted on POD 14; the expression level of VEGF 165 protein in dermal substitutes was determined by Western blotting. The experiments were all done in triplicate. Data were processed with one-way analysis of variance and LSD method.

RESULTS: (1) Obvious green fluorescence was only observed in the two groups with transfected cells at PTH 24. Expression rates of GFP in the cells of non-transfection group, empty vector group, and VEGF plasmid group were respectively 0, (85.2 ± 3.2) %, and (93.1 ± 2.4) %. In the non-transfection group, empty vector group, and VEGF plasmid group, the relative expression amounts of VEGF 165 mRNA were respectively 1, 1.05 ± 0.09, and 3.02 ± 0.13 (F = 5.28, P < 0.05); the relative expression amounts of VEGF 165 protein were respectively 0.78 ± 0.16, 0.76 ± 0.13, and 1.92 ± 0.18 (F = 7.62, P < 0.05); the protein quantity of VEGF 165 in cell supernatant was respectively (62.4 ± 2.7), (73.1 ± 3.8), (117.5 ± 3.1) pg/mL (F = 15.08, P < 0.05). The mRNA and protein levels of VEGF 165 and VEGF 165 protein amount in supernatant were significantly higher in VEGF plasmid group than in the other two groups, with P values all below 0.05. (2) The number of HUVECs in dermal substitutes of transfected cells group was significantly higher than that of the other three groups on POD 14. The numbers of microvessels of dermal substitutes on POD 14 in saline group, medium group, non-transfected cells group, transfected cells group were respectively 4.2 ± 1.1, 5.2 ± 1.1, 6.6 ± 0.9, 13.8 ± 0.8 per 200 times visual field (F = 17.96, P < 0.01). The microvessel number in transfected cells group was significantly higher than that of the other three groups, with P values all below 0.05. The relative expression ratio of VEGF 165 protein of dermal substitutes in transfected cells group was significantly higher than that in saline group as of POD 7. On POD 14 and 21, the relative expression ratios of VEGF 165 proteins in non-transfected cells group (1.652 ± 0.086, 2.152 ± 0.062) and transfected cells group (2.403 ± 0.091, 2.879 ± 0.047) were significantly higher than those of saline group (1.299 ± 0.027, 1.362 ± 0.103), with P values all below 0.05. And the index level of transfected cells group was significantly higher than that in non-transfected cells group (with P values below 0.05). The VEGF 165 protein content in dermal substitutes increased with time extension in all groups.

CONCLUSIONS: Transfection of VEGF 165 gene in HUVEC could effectively facilitate vascularization of dermal substitutes in vivo by high expression of VEGF 165 protein.