Experimental Confirmation Of Pregnant Myocardial Hypertrophic Preconditioning And The Contribution Of FoxO3a To Cardioprotection Of Hypertrophic Precondioning

Background:Heart failure is a leading cause of death in human,and pathological cardiac hypertrophy is the main pathology of heart failure.So it is of great significance to explore new methods to prevent pathological myocardial hypertrophy.In recent years,the research has been advancing slowly in the pathological cardiac hypertrophy and heart failure,let alone discovery of great importance.We firstly reported a phenomenon termed hypertrophic myocardial preconditiong that short term hypertrophic stimulation protects against subsequent hypertrophic stimulation in heart and slows down the progression of heart failure.However,there were limited studies on the effects of physiological myocardial hypertrophic factors such as excersise or pregnancy-induced phyilogical myocardial hypertrophy on pathological myocardial hypertrophy.Pregnancy induces physiological hypertrophy,manifested as enlarged heart and an increased myocardial cell area,and accompanied with activation of substantial neurohumoral factors,indicating that the heart is under stress during pregnancy.Many lines of evidence have shown that stress with short time and high intensity can induce precondition.However it is unknown whether physiological stress with low intensity and long time by pregnancy can protects against subsequent hypertrophic stimulation in heart and slows down the progression of heart failure.Objective:This study was to verify the phenomenon that myocardial hypertrophic preconditioning with pregnant stimulation obtains antihypertrophic memory factors and renders the heart resistantance to subsequent hypertrophic stimulation as well as slowes progression to heart failure and to explore its inner mechanisms.Methods:The characteristics of cardiac hypertrophy were observed and the plasma Ang? levels were tested in mice during pregnancy.Cardiomyocyte hypertrophy was induced in C57BL/6 mice by either transverse aortic constriction(TAC)or infusion of angiotensin II(Ang II),and in neonatal rat cardiomyocytes(NRCMs)by Ang? exposure.In precondioning group:the mice after 3 weeks postpartum were treated with Ang II or TAC for the same period(4 weeks)as in the control group,and NRMCs were stimulated with Ang? for 12 hours(h),and then the stimuli was removed for 24 h,followed by subsequent re-exposure to Ang II for the same period(48 h)as in the control group.The expression of FoxO3a and p-FoxO3a were evaluated on heart of mice at 3 weeks postpartum and on NRCMs12 hours after Ang II removal.The role of FoxO3a was investigated in antihypertrophic effects of pregnancy by silencing or over expression of myocardial FoxO3a in mice.Results:1.The characteristics of cardiac hypertrophy and Ang? levels in mice during pregnancyPregnancy induced a physiological hypertrophic response in heart of mice.There were increased heart weight/tibia length ratio and cardiomyocyte area as well as plasma Ang ? levels in mice during the middle and late pregnancy.No significant differences were noted between them on myocardial fibrosis and expressions of ANP,P-MHC.The increased cardiomyocyte area and plasma ? levels during the middle and late pregnancy backed to prepregnancy after 3 weeks of delivery.2.Antihypertrophic effect of preconditioning with Ang II in NRCMsCompared to the control group,the cardiomyocyte area and expressions of ANP,?-MHC in NRCMs were all reduced in precondioning group.3.Pregnancy induced cardiac hypertrophy prevented pathological cardiac stimulation in mice treated with Ang ? or TACCompared to the control group,the heart weight/body weight ratio and cardiomyocyte cell surface area were reduced in precondioning group.Expression of ANP,P-MHC levels and the level of myocardial fibrosis were lower in precondioning group than in the control group.4.Expression of FoxO3a and p-FoxO3a in cardiomyocytes after removal of stimulationProtein expression of FoxO3a was significantly increased in heart from 3weeks postpartum mice.To the contrary,protein expression of p-FoxO3a was significantly reduced under this condition as well as in NRCMs after removal of Ang ?stimulation.5.Expression of hypertrophic signal proteins in cardiomyocytesWestern blot analysis showed the significantly reduced p-GSK3,?-Catenin,CyclinD-1,Bax,Cleaved Caspase-3 protein levels,while a significantly increased Bcl-2 in precondioning group,compared to the control group.6.Effects of silencing or overexpression of myocardial FoxO3a on hypertrophic preconditioning in miceSilencing of myocardial FoxO3a attenuated the antihypertrophic effects induced by pregnancy on myocardial hypertrophy in mice with Ang ? stimulation.Compared to scramble+Ang ? group,the cardiomyocyte area,heart weight/body weight ratio,the level of myocardial fibrosis and the expression of ANP,?-MHC in heart from mice with Ang ? stimulation in AAV-FoxO3a+Ang ? group were all increased.Opposite results were obtained in Ang II-infused mice with overexpression of myocardial FoxO3a.Conclusion:Preconditioning with myocardial hypertrophy induced by pregnancy exerts resistance to subsequent myocardial hypertrophic stimulation and slows the progression to heart failure,which indicates the phenomenon of pregant hypertrophic preconditioning.And FoxO3a is involved in pregant hypertrophic preconditioning for cardiac protection.