The Protection Of BDNF Against Myocardial Ischemia/Reperfusion In Rats And Its Mechanism

Background:Brain-derived neurotrophic factor(BDNF)is a growth factor that is widely expressed in the nervous system,which also has positive neuroprotective effects.Studies have shown that BDNF is closely related to the occurrence and development of various diseases such as cerebral ischemic injury,neurodegenerative diseases,and diabetes.In recent years,its important role in the development of the cardiovascular system and related diseases has also attracted much attention.Myocardial ischemia reperfusion injury(MIRI)is the main reason for the high cardiovascular disease-related mortality,which occurs after reperfusion therapy.This study mainly investigated the effect of BDNF on the MIRI and its possible mechanism,and then provided an experimental theoretical basis for clinical treatments.Objective:(1)To observe the effect of BDNF on myocardial ischemia reperfusion injury in rats;(2)To compare the advantages between BDNF pretreatment and BDNF posttreatment and unravel the possible mechanism.(3)To explore the effect of BDNF preconditioning on myocardial cell apoptosis in MIRI rats and its possible mechanism of action and provide a new target for the myocardial protection.Methods:The study was divided into two parts.Part I:(1)The rat models of MIRI were established by ligating the anterior descending branch of the left coronary artery reversibly.90 healthy male SD rats were randomly divided into 5 groups:sham,ischemia(30 min)/reperfusion(2h)(I/R),PBS,BDNF pretreatment and BDNF posttreatment groups;(2)The left ventricular end-diastolic volume(LVEDV),left ventricular end-systolic volume(LVESV),left ventricular ejection fraction(LVEF)and left ventricular short-axis shortening rate(LVFS)were detected by the ultrasonography;(3)The extent of myocardial infarction was determined by the Evans blue/TTC staining;(4)Myocardial fibers and mitochondrial structures were observed under the electron microscope;(5)Lactate Dehydrogenase(LDH)level was measured by LD-L microplate method;(6)Malondialdehyde(MDA)content was determined by the thiobarbituric acid chromogenic method;(7)Superoxide Dismutase(SOD)activity was evaluated by the Xanthine oxidase(hydroxylamine method);(8)Reactive Oxygen Species(ROS)level was measured by the Dihydroethidium staining.Part Ⅱ:(1)The rat models of MIRI were established by ligating the anterior descending branch of the left coronary artery reversibly.50 healthy male SD rats were randomly divided into 5 groups:sham,ischemia(30 min)/reperfusion(2h)(I/R),I/R+BDNF,I/R+BDNF+LY294002(I/R+BDNF+LY)and I/R+LY294002 groups(I/R+LY).(1)LVEDV,LVESV,LVEF and LVFS were detected by the ultrasonography;(2)The apoptosis of cardiomyocytes was determined by TUNEL method;(3)The expressions of apoptosis related proteins Bcl-2,Bax and Caspase-3 were measured by Western blot;(4)The expressions of PI3K downstream related proteins Akt,p-Akt,GSK-3β and p-GSK3βwere detected by Western blot.Results:Part Ⅰ:(1)Compared with the I/R group,the heart function was improved and the size of myocardial infarction was reduced in the BDNF pretreatment group and the BDNF posttreatment group.Meanwhile,the myocardial fiber and mitochondrial structure were both less damaged.The levels of LDH,MDA and ROS were reduced,while the level of SOD increased.(2)Compared with the BDNF posttreatment group,the heart function was improved and the myocardial infarction area decreased in the BDNF pretreatment group.Meanwhile,the myocardial fiber and mitochondrial structure were both less damaged.The levels of LDH,MDA and ROS were reduced,while the level of SOD increased;Part Ⅱ:(1)Compared with the I/R group,the heart function of the I/R+BDNF group was improved and the apoptosis index decreased significantly;(2)Compared with the I/R+BDNF group,the heart function of the I/R+BDNF+LY group was reduced,and the apoptosis index increased significantly;(3)Compared with the I/R group,the expression levels of Bax and Caspase-3 decreased,while the expressions of Bcl-2 and PI3K downstream proteins p-Akt and p-GSK3β increased in the I/R+BDNF group;(4)Compared with the I/R+BDNF group,the expression levels of Bax and Caspase-3 increased,while the expression levels of Bcl-2,p-Akt and p-GSK3β decreased in the I/R+BDNF+LY group.Conclusion:(1)Both BDNF pretreatment and BDNF posttreatment have protective effects on myocardial ischemia reperfusion injury in rats,and BDNF pretreatment performs better.(2)BDNF may reduce the level of ROS and protect the myocardium by relieving oxidative stress.(3)The activation of PI3k/Akt/GSk-3β signaling pathway may be involved in the myocardial protective effect through regulating apoptosis-related proteins,such as Bcl-2,Bax and Caspase-3,etc.