The Role Of Receptor For Advanced Glycation End-product(RAGE)in Early Brain Injury After Experimental Subarachnoid Hemorrhage

Background:Subarachnoid hemorrhage(SAH)is a life-threatening disease of central nervous system with high mortality and disability rates.Increasing evidence indicates that early brain injury(EBI)plays a vital role in the pathophysiology of SAH and largely contributes to unfavorable outcome after SAH.The mechanisms of EBI are complex,including mechanical damage due to aneurysm rupture,ischemic injury caused by decreased cerebral blood flow,oxidative stress,brain edema,toxicity of blood components,inflammatory injury,apoptosis and necrosis.It's very difficult to achieve satisfying curative effect for SAH patients by targeting a single mechanism.Hence,it is becoming more and more important to find factors that can regulate multiple mechanisms of EBI.Recently,it was reported that receptor for advanced glycation end-product(RAGE)could promote inflammatory response,mediate apoptosis and autophagy and participate in tissue repair after acute injury.However,it remains obscure that whether RAGE plays a role in the pathogenesis of EBI after SAH.Thus,this study was conduct to explore the expression pattern of RAGE and its potential role in EBI following SAH in both in vivo and in vitro models.Mathods:After the in vivo and in vitro SAH models were established,the expression and cell distribution of RAGE was assessed by quantitative real-time polymerase chain reaction(real-time PCR),Western blotting,immunohistochemistry and immunofluorescent double staining.Based on the expression pattern of RAGE,FPS-ZM1,a specific inhibitor for RAGE,was used to down-regulate the expression of RAGE both in vivo and in vitro.We detected the expression of nuclear factor kappa B(NF-?B)?TNF-? and IL-1?,and the observed the activation of microglia by using Western blotting,enzyme-linked immunosorbent assay,immunohistochemistry and immunofluorescence technology.Then,the neural damage and cell death rate was evaluated by Flouro-Jade B and Nissl staining in vivo and flow cytometry in vitro,respectively.Further,we detected the changes of expressions of apoptosis-associated factors(caspase-3,Bcl-2,Bax)and autophagy-associated factors(LC3,beclin-1).Finally,we measured the brain of water content and neurologic score to assess the impact of RAGE inhibition on neurological function after SAH in rats.Results:Our study indicated that the expression level of RAGE was significantly elevated after SAH and the increased expression of RAGE could be detected in neurons and microglia.Meanwhile,down-regulation of RAGE with its specific inhibitor could induce a significant decrease of NF-?B activity and protein levels of TNF-a and IL-1?.Further,we provided evidences that down-regulation of RAGE could increase neural damage after SAH,which was probably via enhancement of apoptosis and suppression of autophagy.Furthermore,the in vivo experiment demonstrated that inhibition of RAGE significantly attenuated brain edema and improved neurological function at one day after SAH in rats.However,RAGE inhibition failed to reduce brain edema and cannot improve neurological function at day 3 after SAH.Conclusion:Our research provides evidence,for the first time,that RAGE expression could be markedly elevated following SAH and exerts "dual effects" in EBI after SAH(on one hand,RAGE promote inflammatory response causing brain injury;on the other hand,RAGE may confer neuroprotection by mediating apoptosis and autophagy).Our results provide a novel perspective for mechanistic understanding of EBI.Our study also raises the caution that the dual effects of RAGE after SAH may(?)limit therapeutic strategies aimed at reducing RAGE signaling.