The Role And Mechanisms Of Hydrogen Sulfide In Early Brain Injury After Subarachnoid Hemorrhage In Rats

BackgroundAneurysmal subarachnoid hemorrhage(aSAH)is a common and severe subtype of hemorrhagic stroke with high mortality.Early brain injury(EBI),which occurs with the first 72 hours following aneurysm rupture,is considered as the main aspect which contributes to unfavorable outcomes.Among multiple complex mechanisms of EBI after SAH,apoptosis is regarded as one of the most crucial factors that may be associated with delayed neurological deterioration and poor long-term outcomes.Although numerous studies explored the mechanism of apoptosis,none of possible anti-apoptotie agents has been proved ideal in further clinical trials.Mammalian sterile 20-like kinase 1(MST1)is a crucial serine-threonine kinase that belongs to a critical component of the Hippo signaling pathway.MST1 has been proved to have important functions in apoptotic cell death.Hydrogen sulfide(H2S)may be a potential excellent anti-apoptotic agent produced by astrocytes,neurons and microglia,which could rapidly diffuse through cell membrane to exert its effects within seconds due to its high lipophilic property.Previous studies have indicated that H2S could protect blood-brain barrier,inhibit apoptosis,reduce brain edema,and improve neurological function in the ischemic stroke models.However,the underlying anti-apoptotic mechanism of H2S still remains largely unknown.Hence,the present study tested the hypothesis that H2S could inhibit MST1 to reduce neuronal cell apoptosis.Meanwhile,we also aimed to evaluate the clinical values of NaHS in protecting brain injury after aSAH.MethodsIn this study,aSAH models were established by internal carotid artery puncture in male rats.Exogenous NaHS administrated by intraperitoneal injection increased the H2S content in the brain.Chelerythrine,as an MST1 agonist,could enhance caspase-dependent cleavage of MST1.Bleeding score,modified Garcia score,fault foot,and adhesive removal tests were performed to evaluate the neurological functions after aSAH.Brain edema was assessed by measuring brain water content.Western blot was performed to detect the proteins including MST1,cleaved-MST1(cl-MST1),B-cell lymphoma-2(Bcl-2),Bcl-2 related X protein(Bax)and cl-caspase 3.Immunofluorescence was used to detect the expression of MST1 and neuronal apoptosis.ResultsThe expression of MST1 was mainly observed in neurons,but not in astrocytes and microglia.The MST1 expression was rapidly decreased at 3 hours after aSAH,gradually decreased to reach its lowest level at 24 hours and remained at a low level at 72 hours after SAH induction.Exogenous NaHS administration increased the brain H2S content and inhibited the activation of MST1 leading to the inhibition of neuronal apoptosis and the improvement of neurological defect after aSAH.Chelerythrine could reverse the neuroprotective effect of NaHS by promoting the activation of MST1.In addition,delayed NaHS treatment also reduced the neuronal apoptosis and improved neurological recovery.ConclusionExogenous NaHS treatment can significantly increase the brain H2S content and inhibit MST1-induced neuronal apoptosis leading to the reduction of the brain edema and the improvement of neurological function.Delayed NaHS treatment also reduced the neuronal apoptosis and improved neurological recovery,which means that H2S may be an effective agent for those patients with aSAH.