The involvement of microglial CX3CR1 in heat acclimation-induced amelioration of adult hippocampal neurogenesis impairment in EMF-exposed mice

Microglial CX3C chemokine receptor 1 (CX3CR1) has been implicated in numerous cellular mechanisms, including signalling pathways that regulate brain homoeostasis and adult hippocampal neurogenesis. Specific environmental conditions can impair hippocampal neurogenesis-related cognition, learning and memory. However, the role of CX3CR1 in the neurogenic alterations resulting from the cross-tolerance protection conferred by heat acclimation (HA) against the effects of electromagnetic field (EMF) exposure is less well understood. Here, we investigated the role of microglial CX3CR1 signalling in adult hippocampal neurogenesis induced by HA in EMF-exposed mice. We found that EMF exposure significantly decreased the number of proliferating and differentiating cells in the dentate gyrus (DG) of the hippocampus, resulting in a reduced neurogenesis rate. Moreover, alterations in the phenotypes of activated microglia and decreased expression levels of CX3CR1, but not sirtuin 1 (SIRT1), were observed in the brains of EMF-exposed mice. Remarkably, HA treatment improved microglial phenotypes, restored the expression of CX3CR1, and ameliorated the decrease in the adult hippocampal neurogenesis rate following EMF exposure. Moreover, pharmacological inhibition of CX3CR1 and SIRT1 failed to restore CX3CR1 expression and ameliorate hippocampal neurogenesis impairment following HA plus EMF stimulation. These results indicate that microglial CX3CR1 is involved in the cross-tolerance protective effect of HA on adult hippocampal neurogenesis upon EMF exposure.