MICROGLIAL PHAGOCYTOSIS ACTIVELY REPROGRAMS METABOLISM AND INFLUENCES TUMOR AND NEURONAL CELL SURVIVAL

Microglia are the resident macrophages of the central nervous system (CNS) that maintain brain homeostasis by phagocytosing, for example, apoptotic or necrotic cells (efferocytosis). Recent results in the lab demonstrated that phagocytosis is not only the clearance of debris. Using single-cell RNA sequencing and metabolomics we uncovered an unexpected oxidative stress in post-phagocytic microglia, along with catabolic decline, mitochondrial remodeling, elevated galectin-3 expression, and increased polyamine production. These results suggest that post-phagocytosis events could impact the phagocytes themselves or the surrounding cells. First, we studied whether phagocytosis affects the phagocyte function in a model of glioblastoma, subjected to two consecutive doses of radiotherapy to induce apoptosis of tumor cells. We determined that, despite continued apoptotic challenges, tumor microglia and macrophages cells were able to overcome the stress associated with phagocytosis, suggesting that the changes were adaptive and intended to maintain phagocytic efficacy. Next, we studied the effect of phagocytosis on glioblastoma U251 cells in vitro, and found that the phagocytosis secretome inhibits its survival, an effect that is enhanced when phagocytic microglia are cultured with an inhibitor of the synthesis of the polyamine spermidine. These findings are consistent with those previously obtained in the laboratory where we observed that microglia phagocytosing apoptotic newborn neurons control adult neurogenesis through the phagocytosis secretome. Together, these results reveal that microglial phagocytosis triggers adaptive metabolic and transcriptional changes that preserve their functionality while actively shaping the CNS environment through the secretome, influencing the survival of neighboring cells, including tumor and neuronal populations.