Effect Of Endoplasmic Reticulum Stress PERK-eIF2α-ATF4-CHOP Signaling Pathway During Cardioprotection Of Exercise Preconditioning

Objective: Ischemic heart disease has a high mortality rate in cardiovascular disease,and apoptosis caused by myocardial ischemia-reperfusion injury is an important cause of death in ischemic heart disease.PERK-e IF2α-ATF4-CHOP signaling pathway,one of the main signaling pathways of ER stress,is involved in myocardial ischemia-reperfusioninduced apoptosis,which in turn aggravates myocardial injury.Exercise is recognized to improve cardiovascular disease.Although studies have demonstrated that exercise preconditioning can inhibit myocardial ischemia-reperfusion injury and enhance myocardial ischemia and hypoxia tolerance,whether ER stress PERK-e IF2α-ATF4-CHOP pathway is involved in the myocardial protective effect of exercise preconditioning is unclear.Therefore,in this study,we established a mouse model of myocardial ischemia-reperfusion injury to investigate the possible mechanism of ER stress PERK-e IF2α-ATF4-CHOP pathway in the protective effect of exercise preconditioning in myocardial protection.Methods: Thirty-two healthy SPF male C57/B6 mice were randomly divided into sham operation group（Sham）,ischemia-reperfusion group（I/R）,exercise preconditioning + sham operation group（E + Sham）and exercise preconditioning + ischemia-reperfusion group（E+ I/R）.The E + Sham and E + I/R groups performed treadmill exercise for 8 weeks（60-65 %EV,6 days/week,60 min/day,slope 0 °）,and the Sham and I/R groups were routinely reared.Subsequently,the in vivo myocardial ischemia-reperfusion model was established in the I/R and E+I/R groups,ligating the left anterior descending coronary artery after endotracheal intubation,performed ischemia for 45 min,and reperfusion for 120 min before sampling,while the sham and E + Sham groups were only punctured without ligation to establish a sham operation model.Electrocardiogram was used to evaluate the establishment of myocardial ischemia-reperfusion model;myocardial infarction volume was assessed using TTC staining;myocardial tissue injury was observed by HE staining;the expression of apoptosis-related proteins Bcl2,Bax,and caspase3,ER stress-related protein GRP78,and ER stress PERK signaling pathway-related proteins PERK,p-PERK,e IF2α,p-e IF2α,ATF4,and CHOP were detected by Western blotting;and transcriptional level of PERK signaling pathway e IF2α,ATF4,and CHOP m RNA was detected by fluorescence quantitative PCR（q PCR）.Results: The results of ECG showed that the myocardial ischemia-reperfusion model was successfully established.The results of TTC staining showed white infarct areas in the cardiac section in I/R and E + I/R groups,but not in Sham and E + Sham groups,and the myocardial infarct volume in E + I/R group was lower than that in I/R group（P < 0.05）.The q-PCR results showed that the transcriptional level of GRP78 was decreased（P < 0.01）and the protein transcript level on the PERK-e IF2α-ATF4-CHOP pathway was also decreased in mouse myocardium during the ischemia-reperfusion stage after exercise preconditioning.Results of western blotting showed that compared with the sham group,the protein levels of Bcl2 was significantly decreased（P < 0.001）in the I/R group,while the protein levels of Bax（P < 0.001）,caspase3（P < 0.01）,GRP78（P < 0.001）,p-PERK（P < 0.001）,p-e IF2α（P< 0.01）and CHOP（P < 0.05）were significantly increased;compared with the I/R group,the protein levels of Bcl2 was significantly increased（P < 0.01）in E + I/R group,while the protein levels of Bax（P < 0.001）,caspase3（P < 0.001）,GRP78（P < 0.001）,p-PERK/PERK（P < 0.001）,p-e IF2α（P < 0.01）,ATF4（P < 0.05）and CHOP（P < 0.05）were significantly decreased.Conclusion: 1.Exercise preconditioning can reduce myocardial infarction and irreversible injury induced by myocardial ischemia-reperfusion,and improve the tolerance of myocardial cells to ischemia and hypoxia;2.Exercise preconditioning can inhibit apoptosis,and then protect the heart;3.Exercise preconditioning can regulate the expression of PERK-e IF2α-ATF4-CHOP signaling pathway induced by myocardial ischemiareperfusion,and then affect apoptosis,resulting in certain cardioprotective benefits.