Background
Glioblastoma (GBM) is a malignant astrocytic tumor and its progression involves the regulation of vascular endothelial growth factor-A (VEGFA). However, the mechanism of VEGFA in regulating GBM progression remains unclear.
Conclusion
VEGFA contributed to tumor property of GBM cells by promoting MDSC differentiation and TGF-β1 secretion by MDSCs, providing potential targets for GBM treatment.
Methods
VEGFA mRNA expression was analyzed by quantitative real-time polymerase chain reaction. Protein expression of VEGFA, cluster of differentiation 9 (CD9), CD81, and transforming growth factor-β1 (TGF-β1) was detected by western blotting assay. Flow cytometry assay was conducted to assess cell proliferation, cell apoptosis and myeloid-derived suppressor cell (MDSC) differentiation. TUNEL cell apoptosis detection kit was utilized to analyze cell apoptosis of tumors. Angiogenic capacity was investigated by tube formation assay. Transwell assay was used to assess cell migration and invasion. The effect of VEGFA on tumor formation was determined by a xenograft mouse model assay. Immunohistochemistry assay was used to analyze positive expression rate of VEGFA in tumor tissues. TGF-β1 level was detected by enzyme-linked immunosorbent assay.
Results
VEGFA expression was upregulated in GBM tissues, GBM cells, and exosomes from GBM patients and GBM cells. VEGFA silencing led to decreased cell proliferation, tube formation, migration and invasion and increased cell apoptosis. Moreover, VEGFA knockdown also delayed tumor formation. VEGFA promoted MDSC differentiation and TGF-β1 secretion by MDSCs by being packaged into exosomes. In addition, TGF-β1 knockdown displayed similar effects with VEGFA silencing on GBM cell phenotypes, and MDSCs attenuated VEGFA knockdown-induced effects by secreting TGF-β1 in A172 and U251 cells.