DYNAMICS OF MICROGLIAL ACTIVATION AND EXPRESSION OF CYTOKINES IN THE SITE OF GLIOBLASTOMA TUMOR RESECTION

Abstract Glioblastoma (GBM) is the most aggressive type of brain cancer. GBM tumors are made up of a large percentage of microgliawhich support the invasive nature of tumor and the resistance to therapy. In the tumor, microglia cells can polarize into M1 and M2 phenotypes. M1 phenotype is distinguished by its ability to eliminate tumor cells, and secrete proinflammatory cytokines, whileM2 phenotype is associated with tumor cell survival and secrete anti-inflammatory cytokines. Tumor resection is one of the primary steps to treat GBM, thus, resulting in tissue damage and causing microglia activation in the surgical area. The activation state of microglia in the site of resection and the impact of microglia on glioma regrowth is unclear. The purpose of this study is to investigate the state of microglia in the tumor resection area and kinetics of microglial activation.C57BL/6/GL261 mouse glioma implantation model was used. 14 days after in-brain implantation of GL261 cells tumors were surgically resected and then re-grown tumors were analyzed at 0 hours,1, 4, 7, 14 and 21 days after tumor resection, together with the originally resected primary tumors. Microglia were purified from tumors with use of magnetic beads. Western blot analysis of microglia, purified from primary and re-grown tumors, demonstrated increase of CD86 (M1) during the first 7 days after resection and then up-regulation of Arginase (M2) in a period from 14thto 21st days after tumor resection. The cytokine expression analysis revealed significant up-regulation of Vascular Endothelial Growth Factor (VEGF) and Monocyte Chemoattractant Protein 1 (MCP1) in microglia purified from re-grown tumors. PCR analysis confirmed these data, indicating increase of VEGF, MCP1 gene expression in tumor infiltrating microglia in re-grown tumor. We can state that microglia infiltrating primary tumor and tumor re-grown after surgical resection, represent significantly different cytokines expression patterns, favorable to increased vascularization and tumor progression.