Effect And Mechanism Of Endoplasmic Reticulum Stress Preconditioning On Myocardial Ischemia-reperfusion Injury

Objective :(1)To investigate the effect of open heart surgery on endoplasmic reticulum stress(ERS)and whether beating heart surgery can reduce ERS-induced myocardial inflammation and have better myocardial protection.(2)Establish a rat model of myocardial ischemia-reperfusion injury,investigate the expression of endoplasmic reticulum stress(ERS)in rat myocardium after ischemia-reperfusion injury and low-dose tunicamycin(TM)preconditioning against ischemia-reperfusion injury Myocardial effects.Method : Part I: Clinical Research Experiments: In this study,40 patients with rheumatic heart disease who underwent mitral valve replacement(MVR)were randomly divided into two groups: the non-stop group(non-stop group)and the cardiac arrest group(stop group).Two groups of right atrial appendage specimens were taken at the beginning of cardiopulmonary bypass(CPB)and at the end of CPB.The expression of GRP78,NF-κBp65 mRNA and protein were detected.Part II: Animal Model Experiment: A rat model of myocardial ischemia-reperfusion injury was established to simulate myocardial ischemia-reperfusion.30 rats in the laboratory were randomly divided into 3groups: sham operation group(Sham group)and ischemia-reperfusion group(IRgroup).The tunicamycin treatment + IR group(TM + IR group).The Sham group underwent simple thoracotomy without coronary artery ligation;the IR group underwent thoracotomy,the anterior descending branch was ligated for 30 min,and reperfusion was performed for 2h;TM+IR group TM was intraperitoneally injected with 0.6 mg/Kg,30 min after ligation,the anterior descending branch was 30 min,reperfusion 2h.After thoracotomy,the blood was reperfused for 2 hours,and the troponin I(cTnI)content was detected by ELISA.The ultrastructure of myocardial reperfusion was observed by transmission electron microscopy.The hemodynamic index during the modeling process was changed: LVSP,LVDP,±dp/dtmax and other indicators;Real time PCR method was used to measure the expression of GRP78 mRNA and NF-κBp65 mRNA in myocardial specimens after reperfusion for 2 hours;kits were used to detect GRP78 and NF-κBp65 protein contents in myocardial specimens.Result:I.Clinical trial results:(1)General information and operation of the two groups of cases: There were no significant differences in age,weight,cardiothoracic ratio,cardiac function,and CPB flow time between the two groups(P > 0.05).The two groups were comparable.(2)Clinical effects of the two groups: There were no deaths in the two groups,and the recovery was smooth after the operation.The patient was discharged from the hospital.The heart color Doppler examination was performed 1 week after surgery.There was no valve leakage and the valve activity was normal.(3)Comparison of relative expression of GRP78 and NF-κBp65 mRNA in two groups: At the beginning of cardiopulmonary bypass,there was no significant difference in the relative expression of GRP78 and NF-κBp65 mRNA between the two groups.At the end of cardiopulmonary bypass,the expression levels of the two groups weresignificantly increased,and the difference was statistically significant.Compared with the other groups,the expression level of the cardiac arrest group increased more significantly,and the difference was statistically significant.(4)Comparison of GRP78 and NF-κBp65 protein contents in two groups: At the beginning of cardiopulmonary bypass,there was no significant difference in GRP78 and NF-κBp65 protein content between the two groups.At the end of the extracorporeal circulation,the expression levels of the two groups were significantly increased.The difference was statistically significant.In the two groups,the expression level of the cardiac arrest group increased more significantly,and the difference was statistically significant.II.Animal experiment results:(1)Hemodynamic monitoring in rats: The left ventricular systolic pressure(LVSP)and the left ventricle were recorded after the rats were opened thoracic and the coronary artery was threaded(as normal),and reperfused for 30 min,1 h and 2 h(each group at the corresponding time point).End diastolic pressure(LVEDP),maximal rate of increase and decrease in left ventricular pressure(±dp/dt max).The results of hemodynamic test showed that there was no significant difference in the LVSP,LVEDP and ±dp/dt between the two groups(P>0.05).There was no significant difference in the time points of the Sham group(P> >0.05);the other two groups were compared with normal time,LVSP,±dp/dt decreased,LVEDP increased,and I/R group changed more significantly(P<0.05).(2)Rat MIRI degree: In the Sham group,there was no significant difference in cTnI levels between the 2 h reperfusion and the thoracotomy(P>0.05).In the IR group and the TM+IR group,the cTnI level increased significantly at 2 h after reperfusion.Statistical significance(P<0.05),but the IR group was significantly higher than the TM+IR group,the difference was statistically significant(P<0.05).Myocardial ultrastructure showed nosignificant changes in myocardial ultrastructure in the Sham group at 2 h after reperfusion.The IR group had the most severe damage,followed by the TM+IR group.(3)Expression of GRP78 and NF-κBp65 mRNA in rat myocardium:After 2 hours of reperfusion,GRP78 mRNA and NF-κBp65 mRNA were down-regulated in Sham group.Compared with Sham group,IR group and TM+IR group were highly expressed.The difference was statistically significant(P<0.05).Compared with the IR group,the GRP78 mRNA in the TM+IR group was significantly increased(P<0.05).and Compared with the IR group,NF-κBp65 mRNA were down-regulated in TM+IR group.the difference was statistically significant(P<0.05).(4)Expression of GRP78 and NF-κBp65 protein in rat myocardium: After 2 hours of reperfusion,the expression of GRP78 and NF-κBp65 protein in IR and TM+IR groups was significantly higher than that in Sham group.The difference was statistically significant.(P<0.05);Compared with the IR group,the expression of GRP78 protein in the TM+IR group was significantly increased,and the difference was statistically significant(P<0.05).The expression of NF-κBp65 protein in TM+IR group was lower than that in IR group,the difference was statistically significant(P<0.05).In conclusion:1.Intracardiac direct descending valve replacement surgery can activate ERS and induce local myocardial inflammation;compared with stop heart surgery,beating heart surgery can reduce ERS,reduce myocardial inflammatory response and have better Myocardial protection.2.Myocardial ischemia-reperfusion injury(MIRI)induces endoplasmic reticulum stress response(ERS),while low-dose tunicamycin(TM)pretreatment can reduce MIRI.