Fractalkine Attenuates Radiation Induced Brain Injury Through Promoting The M2 Polarization Of Microglia

Objective Radiation induced brain injury(RIBI)is a serious complication in brain cancer patients receiving radiotherapy.And accumulating evidences suggest that activated microglia plays an important role in that pathogenesis,meanwhile,fractalkine(FKN)is a crucial mediator responsible for the biological activity of microglia.In this study,the effect of FKN on activated microglia after radiation and RIBI was explored,and the underlying mechanisms were investigated.Methods(1)In this study,the effect of exogenous FKN on activated microglia phenotypic transformation was detected by Western Blot,cellular immunofluorescence staining and flow cytometry.The inflammatory factor was quantified by quantitative real-time PCR(qRT-PCR).The phagocytosis capacity was investigated using cellular immunofluorescence staining and flow cytometry.(2)Stable knock-down of CX3CR1 in BV2 cells was constructed with lentivirus,then Western Blot and qRT-PCR were used to detect the transfection efficiency.Afterwards we analysed the effect of CX3CR1 receptor on activated BV2 cells phenotypic transformation by Western Blot and qRT-PCR;the phagocytosis capacity of BV2 cells with CX3CR1 knocked down was investigated using flow cytometry.(3)The morris water maze(MWM)was employed to define spatial memory of mice,Western Blot and immunofluorescence were used to detect the microglia phenotypic transformation,the inflammatory factor was quantified by ELISA and the tissue cellular changes were examed by immunohistochemistry and immunofluorescence.Results This study demonstrated that(1)exogenous FKN could promote activated BV2 cells M2 phenotype transformation,diminish radiation induced production of pro-inflammatory factors,and enhance phagocytosis capacity of BV2 cells after radiation.(2)Those effects of exogenous FKN could be partially rescued by knocking down the expression of CX3CR1 recpotor of activated BV2 cells.(3)Furthermore,CX3CR1 gene knock out mice suffered more serious spatial memory injury than normal gene mice after whole brain radiation,and up-regulation of FKN via FKN lentivirus promoted radiation activated microglia M2 transformation and reduced apoptosis in the hippocampus,therefore promoted the recovery of radiation induced brain injury and diminished the spatial memory injury of irradiated mice.Conclusion In conclusion,FKN can reduce the expression of the pro-inflammatory cytokines and enhance the phagocytosis function by regulating the microglia M2 phenotype transformation,therefore attenuate the inflammation damage after radiation and decrease apoptosis in the hippocampus of the mouse after radiation,so the cognitive function of the mouse can be partially improved.Our study unveiled an important role of FKN/CX3CR1 in RIBI,indicating that promotion of FKN/CX3CR1 axis could be a promising strategy for the treatment of RIBI.