Estrogen Receptor ? Activation Protects Against Myocardial Infarction Via Notch1 Signalling

BackgroundAccording to the summary of "Chinese Cardiovascular Disease Report 2018",cardiovascular disease has become the most deadly reason among urban and rural residents.Myocardial infarction(MI)is one of the most deadly types of cardiovascular diseases.It has been proved that estrogen and estrogen receptor(ER)have closely relationship with cardiovascular diseases.The effects of estrogen are mediated mainly by ER? and ER?.It has been revealed that ER? plays a protective role in myocardial oxidative damage,vascular endothelial dysfunction,atheromatous plaque formation,blood vessels injury and myocardial ischemic damage.However,the molecular mechanisms behind ER?mediated protection have not yet been completely explained.Notch signalling is an evolutionarily conserved signaling,Notch receptors have been proved to express in many kinds of organs and tissues.Notch1 is highly expressed in embryonic tissues and naive myocardial tissues,but its content significantly reduced after birth.However,it can be activated in various tissues under pathological conditions,such as oxidative stress,myocardial ischemia and vascular injury.This special feature enables Notch1 to perform an important function in a series cellular processes,such as differentiation and proliferation.Many studies have revealed that the Notch1 signalling plays a protective role in damaged tissues.Although the molecular mechanism of Notch1 protection have not yet been completely explained,there is no doubt that Notch1 exerts a positive effect on cardiac regeneration.The purpose of our study is to clarify the role of ER? in myocardial infarction and test the involvement of Notch1 signalling in the cardioprotective effect of ER? activation.PurposeTo determine the cardioprotective effect of ER? on MI injury.To investigate whether ER? manipulates the cardioprotection of Notch1 signalling and elucidate the underlying mechanism.To further explore the role of ER? in Notch1 signaling activation and p-PI3 K and p-Akt expression.MethodsMale C57BL/6-mice were used to establish an MI model through the ligation of the anterior descending branch of the left coronary artery.2,3-Bis(4-hydroxyphenyl)-propionitrile(DPN;a specific agonist of oestrogen receptor ?)and N-[N-(3,5-difluorophenacetyl)-l-alanyl]-s-phenylglycine tbutyl ester(DAPT;a specific inhibitor of Notch1 signalling)were administered via intraperitoneal injection to change ER? and Notch1 activities.Mice were randomly assigned to the following four groups:MI+DPN,MI+DPN+DAPT,MI+DAPT and MI+vehicle.In this study,RTPCR and immunoblotting were used to detect ER? expression;Immunohistochemistry and immunoblotting were used to detect the intracellular domain of Notch(NICD);Immunohistochemistry and enzyme-linked immunosorbent assay(Elisa)were used to assess the myocardial oxidative stress;Use of immunohistochemistry and immunoblotting to detect myocardial apoptosis and collateral circulation;Use TTC staining and immunohistochemical staining to assess myocardial infarct area and scar size after MI;Use echocardiography to analyze the heart function post MI;Immunoblotting was used to detect the levels of phospho-phosphatidylinositol-3-kinase(PI3K)and phospho-protein kinase B(Akt).ResultsDPN-mediated ER? activation effectively protected cardiomyocytes from MI-induced oxidative damage and apoptosis.Furthermore,ER?activation reduced the infarct size and lowered the levels of myocardial enzymes in the serum,thereby leading to greater overall cardiac function improvement.Ischaemic injury-induced myocardial fibrosis was attenuated by ER? activation.Nevertheless,all of these cardioprotective effects of ER? activation were almost abrogated by DAPT administration,i.e.,DAPT attenuated the anti-oxidative and anti-apoptotic effects and the decrease in infarct and fibrotic areas and reversed cardiac functional recovery.The levels of p-PI3 K and p-Akt were increased after DPN administration,and this change was reversed after DAPT administration.ConclusionThis study indicate that ER? stimulation by DPN activates Notch1 signalling and exerts profound cardioprotective effects against MI.Direct activation of ER? protects the heart against cardiomyocyte death and the deterioration of cardiac function post MI and that Notch1 signalling may play a pivotal role in this process.In addition,PI3K/Akt signalling may be a downstream effector of this protective action.