The multifactorial roles of microglia and macrophages in the maintenance and progression of glioblastoma

The functional characteristics of glial cells, in particular microglia, have attained considerable importance in several diseases, including glioblastoma, the most hostile and malignant type of intracranial tumor. Microglia performs a highly significant role in the brain's inflammatory response mechanism. They exhibit anti-tumor properties via phagocytosis and the activation of a number of different cytotoxic substances. Some tumor derived factors, however, transform these microglial cells into immunosuppressive and tumor-supportive, facilitating survival and progression of tumorigenic cells. Glioma-associated microglia and/or macrophages (GAMs) accounts for a large proportion of glioma infiltrating cells. Once within the tumor, GAMs exhibit a distinct phenotype of initiation that subsequently supports the growth and development of tumorigenic cells, angiogenesis and stimulates the infiltration of healthy brain regions. Interventions that suppress or prohibit the induction of GAMs at the tumor site or attenuate their immunological activities accommodating anti-tumor actions are likely to exert positive impact on glioblastoma treatment. In the present paper, we aim to summarize the most recent knowledge of microglia and its physiology, as well as include a very brief description of different molecular factors involved in microglia and glioblastoma interplay. We further address some of the major signaling pathways that regulate the baseline motility of glioblastoma progression. Finally, we discussed a number of therapeutic approaches regarding glioblastoma treatment.