Cardiac-restricted overexpression of the Ca 2+ -binding protein S100A1 has been shown to lead to increased myocardial contractile performance in vitro and in vivo. Since decreased cardiac expression of S100A1 is a characteristic of heart failure, we tested the hypothesis that S100A1 gene transfer could restore contractile function of failing myocardium. Adenoviral S100A1 gene delivery normalized S100A1 protein expression in a postinfarction rat heart failure model and reversed contractile dysfunction of failing myocardium in vivo and in vitro. S100A1 gene transfer to failing cardiomyocytes restored diminished intracellular Ca 2+ transients and sarcoplasmic reticulum (SR) Ca 2+ load mechanistically due to increased SR Ca 2+ uptake and reduced SR Ca 2+ leak. Moreover, S100A1 gene transfer decreased elevated intracellular Na + concentrations to levels detected in nonfailing cardiomyocytes, reversed reactivated fetal gene expression, and restored energy supply in failing cardiomyocytes. Intracoronary adenovirus-mediated S100A1 gene delivery in vivo to the postinfarcted failing rat heart normalized myocardial contractile function and Ca 2+ handling, which provided support in a physiological context for results found in myocytes. Thus, the present study demonstrates that restoration of S100A1 protein levels in failing myocardium by gene transfer may be a novel therapeutic strategy for the treatment of heart failure.

S100A1, a Ca2؉ -sensing protein of the EF-hand family, is most highly expressed in myocardial tissue, and cardiac S100A1 overexpression in vitro has been shown to enhance myocyte contractile properties. To study the physiological consequences of S100A1 in vivo, transgenic mice were developed with cardiac-restricted overexpression of S100A1. Characterization of two independent transgenic mouse lines with ϳ4-fold overexpression of S100A1 in the myocardium revealed a marked augmentation of in vivo basal cardiac function that remained elevated after ␤-adrenergic receptor stimulation. Contractile function and Ca 2؉ handling properties were increased in ventricular cardiomyocytes isolated from S100A1 transgenic mice. Enhanced cellular Ca 2؉ cycling by S100A1 was associated both with increased sarcoplasmic reticulum Ca 2؉ content and enhanced sarcoplasmic reticulum Ca 2؉ -induced Ca 2؉ release, and S100A1 was shown to associate with the cardiac ryanodine receptor. No alterations in ␤-adrenergic signal transduction or major cardiac Ca 2؉ -cycling proteins occurred, and there were no signs of hypertrophy with chronic cardiac S100A1 overexpression. Our findings suggest that S100A1 plays an important in vivo role in the regulation of cardiac function perhaps through interacting with the ryanodine receptor. Because S100A1 protein expression is downregulated in heart failure, increasing S100A1 expression in the heart may represent a novel means to augment contractility.

Cardiac-restricted overexpression of the Ca 2+ -binding protein S100A1 has been shown to lead to increased myocardial contractile performance in vitro and in vivo. Since decreased cardiac expression of S100A1 is a characteristic of heart failure, we tested the hypothesis that S100A1 gene transfer could restore contractile function of failing myocardium. Adenoviral S100A1 gene delivery normalized S100A1 protein expression in a postinfarction rat heart failure model and reversed contractile dysfunction of failing myocardium in vivo and in vitro. S100A1 gene transfer to failing cardiomyocytes restored diminished intracellular Ca 2+ transients and sarcoplasmic reticulum (SR) Ca 2+ load mechanistically due to increased SR Ca 2+ uptake and reduced SR Ca 2+ leak. Moreover, S100A1 gene transfer decreased elevated intracellular Na + concentrations to levels detected in nonfailing cardiomyocytes, reversed reactivated fetal gene expression, and restored energy supply in failing cardiomyocytes. Intracoronary adenovirus-mediated S100A1 gene delivery in vivo to the postinfarcted failing rat heart normalized myocardial contractile function and Ca 2+ handling, which provided support in a physiological context for results found in myocytes. Thus, the present study demonstrates that restoration of S100A1 protein levels in failing myocardium by gene transfer may be a novel therapeutic strategy for the treatment of heart failure.

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S100A1 gene transfer in EHT is feasible and augments contractile performance, while characteristic physiological features of EHT remain unchanged. Thus, specific genetic manipulation of tissue constructs prior to implantation should be part of an improved tissue replacement strategy in heart failure.