海马齿状回小胶质细胞再殖改善青少年期小鼠创伤性脑损伤成年后的情绪与认知障碍

Microglial repopulation in the hippocampal dentate gyrus and its effect on improving mood and cognitive impairments in adult mice after traumatic brain injury during adolescence

目的:探究小胶质细胞再殖对青少年期小鼠创伤性脑损伤(TBI)成年后情绪与认知障碍的改善效应及分子机制。方法:通过控制性皮质冲击损伤(CCI)建立TBI小鼠模型。将48只5周龄C57BL/6J小鼠随机分为假手术对照组、CCI模型组、CCI模型+小胶质细胞再殖组、CCI模型+小胶质细胞耗竭组,并于青少年期(损伤后4 d)及成年期(损伤后21 d)进行检测。用免疫荧光染色检测PLX5622饲喂对CCI模型组小鼠海马齿状回小胶质细胞的影响;用行为学测试(改良神经损伤严重程度评分、旷场实验、高架O迷宫实验、Y迷宫空间识别实验)检测小胶质细胞再殖对CCI模型小鼠情绪与认知障碍的影响;用RT-qPCR检测小胶质细胞再殖对CCI小鼠海马脑区炎症因子和趋化因子水平的影响。结果:在饲喂PLX56222周后,青少年期小鼠脑内小胶质细胞清除率达99%;在青少年期时海马齿状回再殖小胶质细胞的形态相较于模型组分支增多且变长,成年期也有相应趋势;小胶质细胞再殖能逆转CCI诱导的小鼠在青少年期及成年期后的神经功能和空间工作记忆能力受损、焦虑样行为;小胶质细胞再殖能降低CCI后青少年期及成年期后的小鼠海马脑区的趋化因子(CXCL1、CXCL2)以及炎症因子(IL-6、IL-1β及TNF-α)的表达水平。结论:小胶质细胞再殖能够通过减轻CCI诱导的小鼠海马齿状回小胶质细胞过度激活,并缓解海马脑区神经炎症,进而改善TBI诱导的小鼠青少年期及成年期神经功能受损、焦虑样行为以及空间工作记忆能力受损。

Objective:To explore the effect and molecular mechanism of microglial repopulation on mood and cognitive impairment in adult mice following traumatic brain injury(TBI)during adolescence.Methods:The TBI mouse model was established using controlled cortical impact(CCI).Forty-eight 5-week-old C57BL/6J mice were randomly allocated into sham,CCI model,CCI+microglial repopulation,and CCI+microglial depletion groups,and tested in adolescence[4 days post injury(dpi)]and adulthood(21 dpi).Immunofluorescence staining was used to detect the effects of PLX5622 feeding on the microglia in the dentate gyrus region of hippocampus in the model group.Behavioral tests(modified neurological severity scores,open field test,elevated O maze test,Y maze spatial recognition test)were used to assess the involvement of microglial repopulation in mood and cognitive impairment in the model group.RT-qPCR was used to measure levels of inflammatory factors and chemokines in the hippocampus of TBI mice with microglial repopulation.Result:After two weeks of PLX5622 feeding,the clearance rate of microglia in the brain of adolescent mice reached 99%,and microglia in hippocampal dentate gyrus region of the repopulation group showed increased branching and elongation compared with that of the model control group both in adolescence and adulthood.Microglial repopulation could reverse TBI-induced impaired neural function,spatial working memory and anxietylike behavior in adolescent and adult mice.Microglial repopulation could reduce the expression levels of chemokines(CXCL1,CXCL2)and inflammatory factors(IL-6,IL-1β,TNF-α)in the hippocampus of adolescent and adult mice after TBI.Conclusion:Microglial repopulation can alleviate the neuroinflammation in hippocampal dentate gyrus region by improving the overactivation of microglia after TBI,and then improve the neuro-function impairment,anxiety-like behavior and spatial working memory impairment induced by TBI in adolescent and adult mice.