The Molecular Mechanism Of MiR-let-7a Regulating Sympathetic Nerve Remodeling After Myocardial Infarction

BackgroundWith the increase in the mortality rate of sudden cardiac death(SCD),more and more people are beginning to pay attention to myocardial infarction,the most severe type of coronary heart disease(CHD).Clinically,unstable plaques in coronary arteries suddenly burst,inflammatory cells and other cytokines continuously accumulate,leading to partial or complete occlusion of blood flow,ischemic necrosis of local myocardial cells,and a series of pathophysiological processes,called myocardial infarction.The occurrence of ventricular arrhythmia(VAs)after MI is one of the main causes of death in patients with this disease.Our previous studies have confirmed that the frequency of VAs after MI is often related to sympathetic nerve activity.Abnormal sympathetic nerve activation and regeneration will cause cardiac electrophysiological instability.Nerve growth factor(NGF)is a key factor in this process.Therefore,how to find an effective upstream target has a very good control effect on the occurrence of VAs,which has a vital role in the clinical sense.miRNA is a non-coding RNA with a relatively short sequence of single-stranded RNA,which is highly expressed in eukaryotes.It is combined with part or all of the 3'UTR region of the target gene by means of complementary base pairing.Therefore,the mRNA of the target gene is decomposed,and the protein translation process cannot be achieved,which further inhibits the role of downstream factors,and finally regulates the release of cytokines,the growth and development of tissues and organs,and the stability of the internal environment.Researchers at home and abroad have found that miRNAs are associated with diseases such as tumors,inflammation,coronary heart disease,and diabetes.MiR-let-7a is one of the earliest discovered miRNAs,which can participate in pathophysiological processes such as cell proliferation and differentiation,angiogenesis,organ development,etc.through a variety of mechanisms.Many documents have also been recorded that miR-let-7a is associated with hypertrophic cardiomyopathy,coronary heart disease,and heart failure and other heart diseases.It can be seen that miR-let-7a plays an important role in cardiovascular disease.There are also articles showing that miR-let-7a can participate in the secretion of pro-inflammatory factors to regulate the inflammatory response.The mechanism of action needs further study.Therefore,we suspect that miR-let-7a is the most critical part of NGF expression and is involved in the pathogenesis of VAsObjectiveMiR-let-7a overexpressed virus was used to intervene in vivo and in vitro experiments,to observe the expression trend of miR-let-7a and NGF,to measure the positive nerve fiber density of GAP43 and TH,as well as the susceptibility to arrhythmia,so as to clarify the mechanism of miR-let-7a in ventricular arrhythmia after myocardial infarctionMethodsThe overall experiment is divided into two parts,vivo experiment and vitro experiment.Firstly,in the vivo experiment,we divided the SD male rats into 4 groups:sham+NC group,sham+Len-let-7a group,MI+NC group,and MI+Len-let-7a group.Rats in the MI+NC group and MI+Len-let-7a group were ligated with the left anterior descending coronary artery to complete the MI model.The sham+NC group and the sham+Len-let-7a group were only threaded and not ligated.After 7 days,all rats were collected from the heart,and the corresponding western blot,qRT-PCR,immunofluorescence,electrical stimulation and other experimental methods were used to detect the corresponding indicators.In vitro experiments,M0 macrophages were firstly induced into M1 macrophages by LPS+IFN-?,and miR-let-7a overexpressed virus was given for intervention to detect the changes of corresponding indicators such as miR-let-7a and NGFResults1.In the MI+NC group and the MI+Len-let-7a group,after the ligation of the left anterior descending branch,the myocardial color of the blood supply area of the ligated artery darkened,and the pulsation weakened or disappeared.,Which indicates that the modeling is successful.2.In vivo experiments,we can conclude that the miR-let-7a expression in the MI+NC group is lower than that in the sham+NC group,but the secretion of NGF has risen.The number of sympathetic nerves also increases with the raise of NGF expression.Increased,miR-let-7a group treated with miR-let-7a overexpressing virus,myocardial miR-let-7a increased,NGF secretion decreased compared with MI+NC group,sympathetic remodeling improved.3.In vitro experiments also showed that the expression of NGF in the M2+Len-let-7a group was significantly less than that in the M1 group without intervention.ConclusionOver-expressed miR-let-7a can effectively inhibit the expression of NGF after myocardial infarction,improve the sympathetic nerve remodeling phenomenon,reduce the general susceptibility to ventricular arrhythmias,and finally achieve the goal of reducing the mortality of myocardial infarction.