Glioma-Associated Microglia Potentiate Neuronal Hyper-Excitability in the Glioma Environment.

Abstract

Background: Hyper-excitable neurons are observed in the glioma brain, contributing to the notorious nature of glioma. It is well established that microglia can modulate neuronal excitability through crosstalk via P2RY12. However, the role of microglia in glioma environments remains poorly understood. Thus, this study aimed to investigate whether loss of microglial P2RY12 could contribute to hyper-excitable neurons within the glioma environment.

Methods: Using two distinct tumor models and normal Thy1-GCaMP6f mice, spontaneous neuronal activity was imaged in the peritumor region with an in vivo 2-photon microscope. Neuronal calcium activity was then compared to expression level of microglial P2RY12. Neuronal activity was further quantified after administering a microglial blocker and compared across different tumor models and cortical regions of a glioma mouse model.

Results: Our findings revealed that hyper-excitable neurons were exclusively observed in cortical regions surrounding glioma tissues. In the glioma environment, microglia exhibited significantly reduced expression of P2RY12, a receptor known to modulate neuronal activity via negative feedback control. In contrast, neuronal excitability and microglial P2RY12 expression relatively remained same to the control in environments of a brain metastasis model. Furthermore, blocking microglial P2RY12 enhanced spontaneous neuronal activity in both the brain metastasis model and distal regions of glioma tumors, effectively replicating the functional loss of P2RY12 observed in glioma conditions.

Conclusions: Results of this study support that neuronal hyper-excitability is a unique observation within a peri-glioma environment driven by loss of microglial P2RY12.