| Background and ObjectiveHeart failure resulted from ischemia heart disease has been the leading threat to human health owing to its high mortality and high morbidity.Autophagy is a major process recycling cellular contents,which is considered protective in ischemic myocardium.Lysosomal degradation is the final step of autophagy while dysfunction is implicated in human heart failure.Altered myocardial expression of cathepsin D?CTSD?,a major lysosomal protease,was observed in human heart failure but the pathophysiological significance of CTSD derangements has not been determined in the heart.This study was aimed to elucidate the change of myocardial CTSD in heart failure induced by myocardial infarction and to investigate its potential role in cardiac remodeling and dysfunction.Methods1.Ctsd homozygous knockout(Ctsd-/-)mice were obtained through breeding Ctsd+/-mice,and subject to echocardiography to detect cardiac morphometric changes;Bafilomycin A1?BFA1?was injected intraperitoneally at 1 hour before tissues were harvested to block the fusion between autophagosomes and lysosomes,the autophagic flux was analyzed by comparing myocardial expression of LC3-II in mice with and without BFA1 treatment.2.The change of myocardial CTSD proteins in myocardial samples from explanted human failing hearts with ischemic heart disease was determined using western blot analyses.3.The myocardial infarction?MI?model was induced by ligating left descending artery on wild type?WT?mice.Serial echocardiography was conducted after surgery to monitor cardiac remodeling process.Western blot analyses,immunofluorescence and RT-PCR were performed to investigate the change of myocardial CTSD.Autophagic flux assays were also carried out in post-MI mice.4.MI model was induced on WT and Ctsd+/-mice.Serial echocardiography was conducted after surgery to monitor cardiac remodeling process.Western blot analyses and immunofluorescence were used to characterize myocardial CTSD;and a catheter-based left ventricular pressure-volume relationship was analyzed.The infarct size was measured using Masson's trichrome staining and autophagic flux assays were also applied.Results1.Mice deficient of Ctsd displayed impaired myocardial autophagosome removal,reduced autophagic flux and restrictive cardiomyopathy evidenced by decreased left ventricular internal dimension and volume with preserved ejection fraction and fraction shortening.2.Western blot analyses revealed an increase in the precursor but not the mature form of CTSD in myocardial samples from explanted human failing hearts with ischemic heart disease,which is recapitulated in chronic MI produced via coronary artery ligation in Ctsd+/+but not Ctsd+/-mice.3.After MI induction,weekly serial echocardiography detected left ventricle chamber dilatation,significant decrease in ejection fraction and fractional shortening throughout the first 4 weeks;an elevated level of CTSD and of autophagic flux were also observed.4.Weekly serial echocardiography detected earlier left ventricle chamber dilatation,greater decreases in ejection fraction and fractional shortening.Pressure-volume relationship analyses at 4 week revealed greater decreases in systolic and diastolic functions,stroke work,stroke volume,and cardiac output;greater increases in the ventricular weight to body weight ratio and the lung weight to body weight ratios,and larger scar size were also detected in Ctsd+/-mice compared with WT mice after MI.Significant increases of myocardial autophagic flux detected at 1 and 4 weeks after induction of myocardial infarction in the WT mice were diminished in the Ctsd+/-mice.ConclusionMyocardial CTSD upregulation induced by myocardial infarction protects against cardiac remodeling and malfunction,which is at least in part through promoting myocardial autophagic flux. |
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