Inhibition Of The Activating Transcription Factor 6 Branch Of Endoplasmic Reticulum Stress Ameliorates Brain Injury After Deep Hypothermic Circulatory Arrest

ObjectivesDeep hypothermic circulatory arrest(DHCA)is an important procedure in cardiac surgery with the assistance of cardiopulmonary bypass(CPB)in aortic arch surgery and complex congenital heart surgery.Neurological dysfunction is a common complication in patients after DHCA,and the mechanism of brain injury causing neurological dysfunction in DHCA is multifactorial,with intraoperative tissue ischemia and hypoxia and ischemia-reperfusion injury caused by restoration of circulatory rewarming probably being one of the main causes.Endoplasmic reticulum stress(ERS)is considered to be an important factor in neuronal ischemia-reperfusion injury,and its downstream activating transcription factor 6(ATF6)pathway is associated with apoptosis.However,it is not clear whether and how ERS and its downstream ATF6 pathway are involved in DHCA-induced brain injury.In this study,we propose to use a rat DHCA model and a hypothermic oxygen-glucose deprivation reoxygenation(OGD/R)cell model to reveal the role of ERS and its downstream ATF6 pathway in DHCA-related brain injury.MethodsThe experiment was divided into in vitro and in vivo experiments.In the in vitro experiments,rat PC-12 neural cell line was used and divided into control group,hypothermic OGD/R group,ERS blocker 4-phenylbutyrate(4-PBA)group,ERS blocker taurosodeoxycholate(TUDCA)group,ATF6 blocker Ceapin-A7 group,siRNA group,and siRNA-NC group.Hypothermic OGD/R experiments were performed except for the control group.In vivo experiments adult male Sprague-Dawley rats were randomly divided into 4 groups(n=8):CPB group,DHCA group,4-PBA group and Ceapin-A7 group.Only cardiopulmonary bypass was performed in CPB group.the DHCA group,4-PBA group and Ceapin-A7 group were subjected to DHCA.Western blotting was performed to detect ERS and differential expression of apoptosis-related proteins.Cell viability was detected using the CCK-8 kit.The modified neurological severity score(mNSS)was used to evaluate the degree of neurological impairment in rats,and histological staining was used to provide histopathological evidence of brain injury,and ELISA was used to detect blood brain injury markers to assess brain injury.The level of apoptosis was measured using flow cytometry.ResultsIn the in vitro experiment,after the intervention of hypothermic OGD/R,the cell survival rate decreased,ERS and all three UPR branches of ERS were activated,the apoptosis pathway was initiated,and the apoptosis rate was upregulated.In the in vivo experiment,the neurological function of rats was impaired after DHCA.H&E staining suggested hippocampal tissue damage,and the level of brain injury markers in the serum was up-regulated.Similarly,ERS and all three UPR branches of ERS were activated,the apoptosis pathway was also initiated.Inhibition of ERS and ATF6 pathway can effectively inhibit apoptosis and improve cell survival rate.The use of ERS inhibitors and ATF6 inhibitors ameliorated the neurological function of rats after DHCA,inhibited apoptosis,decreased the level of brain injury markers,and reduced the hippocampal tissue damage in rats.ConclusionsIn summary,this study demonstrated that the inhibition of ERS ameliorated brain injury in rats after DHCA surgery.The downregulation of ATF6 ameliorated DHCA-induced brain injury by inhibiting apoptosis.This study provides a new perspective that could aid in improving brain protection strategies after DHCA cycles.Further investigation of the specific mechanisms underlying the role of ERS and the ATF6 pathway in DHCA-related brain injury will help in establishing new therapeutic targets for perioperative brain protection in clinical DHCA.