The Effect Of Brain-derived Microparticles On Neuroinflammation After Traumatic Brain Injury

Background and Objective:Traumatic brain injury（TBI）is a global public health problem with high morbidity and disability.Neuroinflammation play an important role in the secondary brain injury.The previous research of our group found that the increase of brain-derived microparticles（BDMP）in peripheral blood after TBI,which can lead to blood coagulation dysfunction.Subsequent studies have shown that injection of BDMP through the tail vein of the rat can cause cerebral vasospasm.Vasospasm is closely related to changes in the concentration of calcium ions(Ca²⁺)in smooth muscle cells.Microglia are the resident immune cells in the central nervous system and the main effector of the inflammatory response in the central nervous system.Moderately activated microglia have a certain protective effect on neurons,but over-activated microglia will release a large amount of neurotoxic factors.Changes in the concentration of Ca²⁺in microglia can lead to the activation of microglia.However,the relationship between BDMP and neuroinflammation after TBI is currently unclear.This study will explore the relationship between BDMP and neuroinflammation after TBI on the basis of previous work.Method:After culturing microglia in vitro,staining BDMP with PKH26,incubating with BDMP and microglia to find out the specific time when the combination of BDMP and microglia reaches the peak.After BDMP was incubated with microglia,the Ca²⁺blocker nimodipine was used for treatment.Flow cytometry and laser confocal microscopy were used to detect changes in the intracellular Ca²⁺concentration in each group.On this basis,Elisa and PCR were used to detect the changes of inflammatory factors in the culture.The permeability of the blood-brain barrier model of endothelial cells cultured in vitro was tested by scanning ion conductance microscope and transwell experiment.In animal experiments,C56/BL6adult male mice were used to establish a TBI model,and Nimodipine was given immediately after injury.Divided into sham operation group（Sham）,traumatic brain injury group（TBI）and nimodipine group（N）,the changes in the expression of Ca MK II was detected by Western Blot,the activation of microglia in each group was detected by immunofluorescence staining,the changes of inflammatory factors were detected by Elisa,and the changes in blood-brain barrier integrity of each group were detected by Evans Blue,Western Blot and brain tissue water content,and the changes in nerve function of each group were detected by water maze and modified nerve function score.Results:（1）BDMP can be phagocytosed by microglia and reach its peak in 3 hours;（2）BDMP can cause Ca2+influx in microglia,increase the secretion of pro-inflammatory factors,and can be used by the Ca²⁺antagonist nimodipine is partially blocked;（3）The treatment of blocking calcium ions by nimodipine can reduce the activation of microglia and the secretion of inflammatory factors;（4）The treatment of blocking calcium ions by nimodipine can reduce the permeability of the blood-brain barrier in mice after TBI;（5）The treatment of blocking calcium ions by nimodipine can reduce neuronal apoptosis and improve nerve function.Conclusion:BDMP can be phagocytosed by microglia cultured in vitro and reach the peak around 3 hours.BDMP can cause Ca²⁺influx in microglia and increase the secretion of inflammatory factors,which can be partially blocked by nimodipine.After TBI,nimodipine treatment can effectively reduce the activation of microglia,reduce the damage to the integrity of the blood-brain barrier,reduce the apoptosis of neuronal cells,and improve nerve function.