Hurmach Y. Metabolic polarization of microglial cells in conditions of tumor growth and its correction with agonist of toll-like receptor 3

Gliomas account for more than 70 % of primary brain tumors, and the vast majority of those tumors are highly malignant glioblastomas. Most therapeutic approaches targeting tumor cells have failed. Glioblastomas is heavily infiltrated with myeloid cells, mainly brain-resident microglia and peripheral phagocytes, that are collectively referred to as glioma-associated microglia/macrophages. The growth of malignant gliomas are accompanied with development of local and systemic immunosuppression. The source of such suppression is microglial cells, which are concentrated in hypoxic areas of gliomas and contains 30 % of stromal cells in the tumor tissue. Under the influence of tumor microenvironment, these cells acquire an immunosuppressive, invasive phenotype. This work is dedicated to examine of changes in the functional profile of brain phagocytes and peripheral phagocytes from different locations outside the brain during the development of C6 glioma in rat, as well as to explore the ability of the toll-like receptor 3 agonist (TLR3) to restore antitumor properties of a complex population of microglia in tumor-bearing animals. The purpose of the work was to investigate the functional characteristics of microglial cells and peripheral phagocytes (outside the brain) in C6 glioma-bearing rats and the effect by agonist of TLR3 on microglial cells metabolic profile. In the work, current ideas concerning activation of microglia exposed toTLR and hypoxia. For evaluation of the features of metabolic activation of microglial cells as comparison cells, phagocytes of the outside the brain (peritoneal macrophages) were used. As TLR agonists, bacterial LPS (TLR4 agonist) and Larifan (agonist TLR3) were used. It have been shown that TLR4 and TLR3 agonists cause distinct metabolic activation of microglial cells in vitro: TLR4 agonists cause pro-inflammatory shift of arginine metabolism with increased level of NO production, whereas TLR3 agonists do not affect the metabolism of arginine and increase the expression of CD206. 24-hour exposure to hypoxia causes anti-inflammatory metabolic activation of microglial cells with a possible increase in expression of the CD206 receptor, along with increased arginase and phagocytic activity. For the first time, TLR3 agonist has an ability to induce functional reversion of hypoxic alternatively polarized microglial cells to pro-inflammatory metabolic profile in vitro. New data concerning the metabolic state of microglial cells and phagocytes outside the brain during the growth of C6 glioma in rats were obtained. It has shown that the functional features of the microglia in tumor-bearing animals differ from those characteristic for classical or alternative phagocyte metabolic profile. The non-typical metabolic characteristics of microglial cells detected by us, as well as by other authors, may be the result of the complex composition of the studied phagocyte population, which may include myeloid suppressor cells. The growth of glioma C6 is accompanied by changes in the functional characteristics of phagocytes outside the brain (macrophages within the Mucosal Associated Lymphoid Tissues, and circulating cells) with the acquisition of signs of anti-inflammatory metabolic activation. Alternatively polarized peripheral phagocytes may be the main source of systemic immunosuppression for the development of malignant glioma. It has been shown that the intranasal administration of TLR3 agonist has an ability to inhibite pro-tumoral properties of microglia in C6 glioma-bearing rats, that is accompanied by a decrease in the proliferative potential of tumor cells in vivo. The results of the dissertation are experimentally substantiate the promising use of intranasally delivered TLR3 agonist is capable to abrogate the creation of this pro-tumoral immune infiltrates, probably, through the effect on myeloid-derived suppressor cells, and can be considered as a promising agent for glioma therapy aimed the microglia re-education.