Nrf2 Inhibits Myocardial Cell Senescence After Myocardial Infarction And Anti-senescence Effect Of Qiliqiangxin On Heart

Background:Cardiac remodeling after myocardial infarction（MI）is a worldwide problem.Cell senescence is a special form of cell cycle arrest,which regulates the pathophysiological processes of many diseases,but the precise role as well as the underlying regulatory mechanism of cardiac cellular senescence in MI remain to be further determined.Nuclear factor erythroid 2-related factor 2（Nrf2）is the core factor of antioxidant stress,which controls the expression of a series of antioxidant genes and cell protective detoxification enzymes.Nrf2 and many downstream genes（HO-1,SOD）have been shown to have protective effects on cardiac resistance to pathological remodeling.we questioned whether Nrf2 plays a role in myocardial senescence of cardiac remodeling after MI,whether the Nrf2-mediated regulation of myocardial senescence has a therapeutic value.Qiliqiangxin（QLQX）is a traditional Chinese medicine,which is composed of 11 herbs.Some animal studies also documented that QLQX could attenuate myocardial remodeling and improve cardiac function in MI.However,the underlying mechanism is not very clear.Objective:to investigate the role and molecular mechanisms of Nrf2 on cardiac cellular senescence after myocardial infarction（MI）and the protective effects of qiliqiangxin（QLQX）on cardiac dysfunction.Methods:Male C57BL/6 and Nrf2 knockout mice aged 8-10 weeks were selected.Left coronary artery ligation was used to establish myocardial infarction model.The mice were randomly divided into 3 groups:sham+saline group（Sham）;Myocardial infarction+saline group（MI+saline）;Myocardial infarction+Qiliqiangxin group（MI+QLQX）.The mice received either QLQX at a dose of 0.25g.kg^-1.d^-1or saline at the same volume for resolving QLQX by oral gavage.From the 2 day after the operation,the medicine was infused continuously for 28 days,and the death of mice was recorded every day.After 28days,cardiac function,apoptosis,oxidative stress and cell senescence were detected.Neonatal rat ventricular myocytes（NRVMs）were isolated and cultured.Cells cultured were transfected with 50 nmol of the control scramble（si NC）,Nrf2 si RNA（si Nrf2）and/or p53 si RNA（sip53）for 48 h with Lipo 3000.Cells were treated with or without H₂O₂(10^-5mol/L)for 3 h in DMEM supplemented with 10%FBS.NRVMs cell senescence and apoptosis were detected by AS-β-Gal staining and Live/dead cell staining.Results:Compared with sham group,the cardiac function of mice decreased significantly after 28 days of MI,and myocardial cell apoptosis,oxidative stress and aging increased significantly.In addition,a downregulated Nrf2 activity was associated with upregulated Keap1 levels and increased phosphorylation of JAK and FYN in the infarcted hearts.Further studies found that the apoptosis and aging of myocardial cells in Nrf2 KO group were more obvious 28 days after MI.Further studies also showed that Nrf2 knockdown promoted H₂O₂-induced senescence and cell death of neonatal rat ventricular myocytes cells.Of interest,these effects of Nrf2 knockdown could be rescued in part by additional p53knockdown.In addition,we also use Qiliqiangxin（QLQX）to intervene and detect its effect on MI-induced myocardial cell apoptosis and aging.It was found that QLQX can not only inhibit MI-induced myocardial senescence,but also improve promote Nrf2 activation.In Nrf2 KO group,myocardial cell senescence did not decrease significantly after QLQX treatment.Conclusion:These results indicate that MI downregulates Nrf2 activity through JAK/Fyn and Keap1 pathways thus promoting oxidative stress to accelerate cellular senescence in the infarcted heart towards cardiac dysfunction;Nrf2 knockout could facilitate on MI-induced myocardial senescence and dysfunction;QLQX protects against MI-induced myocardial senescence and apoptosis as well as dysfunction at least in part via activating Nrf2-mediated anti-senescent signaling in the heart.Nrf2 may be a drug target for suppressing the cellular senescence-associated pathologies in infarcted hearts.