Mechanism Of MTOR Signaling Pathway Inhibitor Rapamycin On Ischemia-reperfusion Injury In Rats

Objective:Ischemic stroke has become the second leading cause of death in the world.It has the characteristics of high morbidity,high mortality and high disability,which seriously endangers the health of human beings.So far,despite the deepening understanding of the pathophysiology of cerebral ischemia,effective treatment was still lacking.Therefore,it is necessary to search the novel therapeutic targets.Mammalian target of rapamycin(mTOR)signal pathway is a crucial pathway in regulation of cell proliferation and protein synthesis,and plays an important role in neurological diseases such as epilepsy,Parkinson's disease and dementia.Our previous studies have shown that mTOR signaling pathway was abromally activated in the penumbra region after cerebral ischemia-reperfusion in rats.The administration of rapamycin,a specific inhibitor of mTOR,could reverse the activation of mTOR activation induced by cerebral ischemia-reperfusion.It markedly ameliorated the neuronal functional injury,reduced infarct volume and subsequently,plays a protective role.However,the mechanism of the neuroprotection mediated by mTOR inhibitor rapamycin in cerebral ischemia remains unclear.In the present study,we explored the underlying mechanism of rapamycin on neuroprotection by detecting its effect on the changes of neuronal apoptosis,glial cell growth and proinflammatory factor at different stage after ischemia-reperfusion injury.Methods:Rats weighting 250-300g were conducted middle cerebral artery occlusion(MCAO)to build up the focal cerebral ischemia-reperfusion models.Rapamycin was injected ip 1 day or 2 weeks after MCAO at the dose of 3 mg/kg every other day.The changes of neurobehavioral were evaluated at different time points by mNSS score.Neuronal apoptosis was detected by FJB staining.The number and morphology of neuroglial cells and vascular regeneration were observed by immunofluorescent staining.Expression of inflammatory factor was investigated by ELISA.Morris water maze and Y maze were conducted to access the learning and memory of MCAO rats.Results:Cerebral ischemia and reperfusion resulted in neuronal function deficit and a large number of neuron apoptosis.Astrocyte and microglia were proliferated and activated from 3 d to 6 w and peaked at 4w.Oligodendrocytes were significantly decreased from 3d to7d,and gradually increased from 2w.Inflammatory cytokines IL-6 and TNF-? increased and kept at a high level from 3 d to 4 w.The mTOR inhibitor,rapamycin,injected ip 1 day or 2 weeks after MCAO,both can markedly inhibit proliferation and activation of astrocytes and microglia,increase oligodendrocytes,reduce the release of inflammatory factors and upregulate the protein of GLT-1.However,the memory and study of 2w-rapa group was better than 1d-rapa group.Conclusion:Rapamycin may inhibit the activation of astrocytes and microglia,upregulate oligotrocyte and reduce the release of inflammation.The memory of 2w-rapa group was better than 1d-rapa group.The specific mechanism needs further study.