Effects Of Rapamycin On Astrocyte Activation And Glial Scar Formation Following Traumatic Brain Injury

Objective:Rapamycin is a specific inhibitor ofmammalian target of rapamycin(mTOR)pathway,and previous studies have demonstrated that single usage of rapamycincan improve neurological function in the acute phase of traumatic brain injury(TBI),while it has no obvious effects on astrogliosis.However,it is still unclear whether the successive administration of rapamycin could regulate the activation of astrocytes and the formation of glia scar after traumatic brain injury.In the present studywe investigated the effects of successive rapamycin administration on glial fibrillary acidic protein(GFAP,a biomarker of astrogliosis)expression,glia scar formation and motor functional recovery after cryogenic traumatic brain injury.Methods:Adult male ICR mice were randomly divided into control group,TBI model group,and rapamycin treatment gourp The right motor and sensory cortex was exposed to liquid nitrogen to establish the cryogenic TBI model.Mice received daily rapamycin administration(0.5 or 1.5 mg/kg/d,i.p.)and the first inject initiated at 1h post TBI.Rotarod test,vertical beam test and beam walking test were used to evaluate the motor function of mice.Brain infarct volumewas measured by toluidine blue staining.The protein expressions of GFAP,p-mTOR,mTOR,chondroitin sulfate proteoglycans(CSPGs,one type of axon growth inhibitory molecules)and neurofilament-200(NF-200,a biomarker of myelinated axons)in ipsilateralcortex were detected by western blotting and immunohistochemical staining.The area and thickness of glia scar were also measured.Results:The expression of GFAP significantly increased at 3 d and 7 d after TBI(P<0.05).The expression of p-mTOR significantly increased at 1 d after TBI(P<0.05),indicating the activation of mTOR.Rapamycin dose-dependently inhibited TBI-induced GFAP expression,and 1.5 mg/kg/d of rapamycin significantly decreased GFAP(P<0.001)and p-mTOR(P<0.05)expressions after at 3 d after TBI.In the meantime,1.5 mg/kg/d of rapamycin increased infarct volume(P<0.05)and deteriorated motor functional deficts in the acute phase of TBI.0.5 mg/kg/d of rapamycin only showed a descending trendon GFAP expression,and it had no significant effect on infarct volume and neurological function at 3 d after TBI.However,0.5 mg/kg/d of rapamycin ameliorated neurological deficits at both 7 d and 14 d after TBI,and it also significantly decreased the expressions of GFAP and CSPGs(P<0.05),reduced the area and thickness of glia scar(P<0.01),and increased the NF200 expression in the glia scar zone at 14 d after TBI.Conclusion:Successive administration of rapamycin(0.5 mg/kg/d)restrains TBI-induced astrogliosis and formation of glia scar,which may lead to improved neurological function post TBI.In addition,1.5 mg/kg/d rapamycin causes a stronger inhibition on astrogliosis,while it also exacerbates the neurological damage during acute phase post TBI and is not benefit to neurological functional recovery.