Effect of vascular endothelial growth factor on remodeling of C6 glioma tissue in vivo

Pathological characteristics and biological behaviors of tumor are considered to result from pathological tissue remodeling regulated by the interaction of factors in the tumor microecosystem (TMES). Vascular endothelial growth factor (VEGF) is one of the factors that probably play an important role in the process of tissue remodeling. This study was a comprehensive investigation of the effects of VEGF on remodeling of glioma tissue in vivo. C6 cells with expression vectors containing sense (C6/VEGF+) or antisense (C6/VEGF-) VEGF(164) complementary DNA (cDNA) or an empty vector (C6/vec) were implanted into athymic mice, which served as an in vivo model with different levels of VEGF expression. VEGF expression, water content, and morphological characteristics of these tumor tissues were assayed. Expression of VEGF and water content in C6/VEGF- glioma (C6/VEGF-G) tissues were lower than in C6, C6/VEGF+, and C6/vec glioma (C6G, C6/VEGF+G, C6/vecG) (P < 0.01, P < 0.05); water content correlated with VEGF expression (r = 0.791, P = 0.000). In C6/VEGF-G, tumor cells were not tightly adhered to vascular walls, and the basal lamina surrounded by collagen fibers was monolayer and not continuous. However, in C6G, C6/VEGF+G, and C6/vecG, tumor cells were very close to the vascular walls, with some extending their processes to the wall. Generally, loose basal laminae surrounded by small amounts of collagen fibers were multilayer, integrated, and continuous. Vesicular vacuolar organelle (VVO) structures were observed in plasma of vascular endothelial cells (VECs), and significant correlation was found between VEGF expression level and VVO density (Spearman's r = 0.642, P = 0.007). No correlation was found between VEGF expression and fenestrae formation in VECs (Pearson's correlation r = -0.053, P = 0.846), and fenestrae in neither VECs nor intercellular clefts correlated with water content of tumor tissue (Pearson's correlation r = 0.018, P = 0.947). These results demonstrate that VEGF can aggravate edema in tumor tissues by increasing VVOs and plays critical roles in the stickiness of tumor cells to vessel wall and in the integrity and continuity of the basal lamina of vessels. Our data indicate a possible mechanism of remodeling of glioma tissue and suggest that blocking VEGF might contribute to a therapeutic strategy for glioma.