Long-term Inhibition Of Mitochondrial Permeability Transition Pore Ameliorates Myocardial Remodeling And Dysfunction After Myocardial Infarction In Rat

Heart failure is the final consequence of cardiovascular disease,usually resulting from sustained pressure overload(hypertension),myocardial ischemia or infarction, volume overload(valvular insufficiency),and/or cardiomyopathy.Myocardial infarction(MI) induces scar formation and global changes in the surviving myocardium, also called post-MI ventricular remodeling,which includes ventricular dilation, eccentric myocyte hypertrophy,cardiomyocyte apoptosis,and interstitial fibrosis.Left ventricular(LV) remodeling is now recognized to be a crucial process mediating the progression of chronic heart failure,and heart failure is a leading cause of hospitalization and mortality worldwide.Despite advances in pharmacological treatment,morbidity and mortality in heart failure remain unacceptably high,so it is necessary to find novel therapeutic approaches aimed at attenuating left ventricular remodeling.Mitochondria play critical roles in both the life and death of cardiomyocytes.In healthy cells,their primary functions are to meet the high energy demand of the beating heart by providing ATP through oxidative phosphorylation.However,mitochondria are also important regulators of cell death(apoptosis and necrosis).The switch to a cell death program is mediated by opening of the mitochondrial permeability transition pore (mPTP) in the inner mitochondrial membrane,causing collapse of the membrane potential,mitochondrial swelling,uncoupling of the respiratory chain,and efflux of cytochrome C and other factors that lead to either apoptosis or necrosis.Opening of the mPTP is probably induced by matrix free calcium,increased free fatty acids,reactive oxygen species,depolarization of the mitochondrial membrane potential,and high pH (＞7.0).Increasing evidence suggests that mPTP opening is a crucial event in lethal reperfusion injury,and the protective effects of ischemic preconditioning and postconditioning against ischemia-reperfusion injury are thought to act through inhibition of the mPTP.Recent experiments revealed that enhanced mPTP opening is associated with mitochondrial dysfunction in cardiomyocytes isolated from failing left ventricular myocardium in dogs.But to date,there is no in vivo study on the effect of inhibition of the mPTP on heart failure.We hypothesized that opening of the mPTP is detrimental in heart failure after MI, and that inhibition of the mPTP has a positive effect on myocardial dysfunction. Therefore,in this study,we addressed whether treatment with cyclosporin A(CsA),a powerful potential inhibitor of the mPTP,attenuates LV remodeling and improves myocardial function in rat heart after MI.Objectives1.to observe the role of inhibition of mPTP in post-MI heart failure2.to observe the mPTP opening in Cardiomyocytes isolated from the LV myocardium3.to investigate the role of mPTP inhibitor on mitochondrial ultrastructure4.to investigate the role of mPTP inhibition on myocardium gene expression5.to investigate the role of mPTP inhibition on apoptosis,hypertrophy,fibrosisMethods1.Generation of MI by left coronary ligation.2.Echocardiographic and hemodynamic measurements3.Isolation of cardiomyocytes4.Measurement of mitochondrial permeability transition pore opening Uunder the laser confocal microscope5.Measurement of mitochondrial ultrastructure by electron microscopy 6.Masson's trichrome staining to observe the myocytes hypertrophy and fibrosis7.Detection of serum B-type natriuretic peptide(BNP) using the method of solid phase sandwich enzyme linked immune sorbent assay(ELISA)8.to investigate the myocardium gene expression by Real-time PCR9.to investigate the caspase-3 and calcineurin expression by Western blotResults1.Long-term blocking of the mitochondrial permeability transition pore attenuates LV remolding and dysfunction2.In vivo CsA-treated group had less mPTP opening3.Histomorphometric findings showed that interstitial fibrosis in the noninfarcted LV was significantly increased in the MI alone and MI+FK506 groups,but was attenuated in the MI+CsA group.However,compared with the MI alone group, cardiomyocyte cross-sectional area was reduced by both CsA and FK506 treatment4.Severe myofibril disarray and breakdown was seen in myocytes from the MI alone and MI+FK506 groups,and the mitochondria were damaged.For example,there were large and irregular mitochondria with reduced electron density and abnormal cristae.All of this mitochondrial remodeling was attenuated in the MI+CsA group5.Brain natriuretic peptide(BNP) decreased in CsA-treated group6.Fetal gene expression attenuated by CsA treatment7.We found that the expression of caspase-3 and cleaved caspase-3 was not significantly enhanced in the MI alone group compared with the sham group,and this was the same for the MI+FK506 and MI+CsA groups.Similarly,there were no significant differences among the 4 groups with respect to TUNEL-positive cells(data not shown),and DNA agarose gel electrophoresis revealed no sign of apoptosis.8.Calcineurin maybe involved in the development of myocardial hypertrophy during post-MI heart failure. Conclusion1.We demonstrated that mPTP opening is involved in the process of rat post-MI heart failure2.inhibition of mPTP opening with CsA significantly attenuates myocardial remodeling and dysfunction after MI3.Calcineurin maybe involved in the development of myocardial hypertrophy during post-MI heart failure.Inhibition of calcineurin in the development of LV hypertrophy may,be unfavorable4.Protection by CsA treatment may be independent of apoptosis5.mPTP inhibition may be an important therapeutic target for preventing post-MI heart failure...