Mechanism Of Excessive Exercise Aggravating Myocardial Remodeling After Myocardial Infarction

Background:Cardiovascular diseases have become one of the leading causes of death worldwide.In China,the incidence of cardiovascular disease is still on the rise,and the load of cardiovascular disease is also ascend ing drastically,and heart failure after myocardial infarction has become one of the main causes of death in patients with coronary heart disease.Cardiac rehabilitation is a multidisciplinary,integrated management approach that can improve the quality of life of patients with heart failure,improve patient exercise performance,and reduce heart failure related hospitalizations.Exercise training is an important part of cardiac rehabilitation in both European and the United States guidelines.Many guidelines recommend that patients with heart failure ngage in moderate intensity exercise training at least five times a week.However,the benefits of the upper limit of moderate exercise duration and prolonged exercise training at moderate intensity for patients with heart failure remain controversial.Epidermal growth factor receptor(EGFR)is the first recognized member of the receptor tyrosine kinase family.Since the epidermal growth factor receptor was first identified in the mid-1970 s,thousands of papers have described its roles in almost every known cellular process and in a variety of disease states,and many studies have shown that EGFR also plays an important role in the pathology of cardiovascular disease s.However,its role in the aggravation of myocardial remodeling by excessive exercise after MI remains unclear.Objective:To determine the effect of excessive exercise on the structure and functions of the heart after myocardial infarction in mice and to elucidate the mechanisms and specific signaling pathway s involved.Methods:Firstly,we constructed the mouse myocardial infarction model by means of coronary artery ligation,and the mice were dispatched to Sham group,MI+0min group,MI+15min group and MI+90min group.Mice were given swimming training for the corresponding length of time according to their groups and their heart ultrasonic examination was conducted every two weeks.Samples were taken after the eight-week training.The changes of heart structure,function and protein expression were detected by Masson staining,WGA staining,immunofluorescence staining,Western blot and PCR.We then used AG1478 to explore the role of EGFR and its phosphorylation in the influence of excessive exercise on cardiac structure and function in myocardial infarction mice.Finally,primary mouse cardiac fibroblasts were extracted and treated with AG1478 and TGF-β,and then the transcription and expression of fibrosis related molecules were detected by Western blot and PCR.Results:Prolonged swimming training after myocardial infarction significantly reduced the survival rate of mice,reduced the fibrosis of infarct area and border area,and increased the incidence of heart rupture.After 8 weeks of swimming training in mice with MI,swimming training for 90 minutes a day significantly reduced the survival rate,increased the incidence of heart rupture,lowered the extent of myocardial fibrosis in the infarcted area as well as the border region,and increased the level of myocardial hypertrophy compared with the MI +0min group.The Left ventricular ejection fraction(LVEF)in MI+90min group was not different from that in MI+0min group.The re was no difference in heart size and LVEF.There was no significant change in Heart weight/body weight(HW/BW).Prolonged swimming training after MI increases EGFR expression and phosphorylation levels.Through proteome sequencing of the samples,we found that compared with the MI group,the expression of EGFR in the heart tissue of mice that underwent swimming training for 90 minutes a day after MI was significantly increased,and it was identified that the phosphorylation level of EGFR was significantly increased through Western blot analysis.AG1478 reduced EGFR phosphorylation,improved survival rate and reduced the incidence of heart rupture in mice.To demonstrate the effect of excessive exercise of EGFR on pathological myocardial remodeling after MI,mice were given the EGFR inhibitor AG1478 by gavage at the beginning of swimming training4 weeks after MI.Compared with the MI+90min+Saline group,the mortality rate,heart rupture rate and fibrosis degree in the infarct area of mice treated with AG1478 were significantly reduced by daily gavage.Cell experiments showed that AG1478 could enhance the differentiation of TGF-β-induced fibroblasts into myofibroblasts.We confirmed it on primary fibroblasts.AG1478 was pretreated with TGF-β and then induced with TGF-β.The results showed that AG1478 significantly increased the transcription and expression of fibrosis related molecules compared with TGF-β treated cells.Conclusions:1.In this study,it was found that moderate exercise(15 min/d swimming training for8 weeks)after MI could improve the cardiac function of mice,whereas excessive exercise(90 min/d swimming training for 8 weeks)after MI could not improve the cardiac function of mice.What’s worse,excessive exercise could even lead to increased cardiac rupture and lower the survival rate of mice by alleviating myocardial fibrosis in the infarct area and border area.2.We also found that excessive swimming training after MI would aggravate the level of pathological myocardial hypertrophy after MI.By using the EGFR inhibitor AG1478,it was found that EGFR phosphorylation plays a key role in reducing myocardial fibrosis in the infarct area and border area and exacerbating pathological myocardial hypertrophy caused by excessive exercise after MI.3.Finally,through in vitro experiments,we found that AG1478 could promote the differentiation of fibroblasts into myofibroblasts induced by TGF-β and increase the expression of fibrosis related molecules.These findings could provide evidence for us to explore the influence of different doses of physical training as a means of cardiac rehabilitation after MI on the structure and function of the heart.Moreover,these results also provided reference for establishing reasonable exercise training program s for patients with myocardial infarction so as to play a role of protecting the heart and avoid the occurrence of adverse events in the meanwhile.