Constitutively active phosphatase inhibitor-1 improves cardiac contractility in young mice but is deleterious after catecholaminergic stress and with aging
Katrin Wittköpper, … , Thomas Eschenhagen, Ali El-Armouche
Katrin Wittköpper, … , Thomas Eschenhagen, Ali El-Armouche
Published January 11, 2010
Citation Information: J Clin Invest. 2010;120(2):617-626. https://doi.org/10.1172/JCI40545.
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Constitutively active phosphatase inhibitor-1 improves cardiac contractility in young mice but is deleterious after catecholaminergic stress and with aging

Abstract

Phosphatase inhibitor-1 (I-1) is a distal amplifier element of β-adrenergic signaling that functions by preventing dephosphorylation of downstream targets. I-1 is downregulated in human failing hearts, while overexpression of a constitutively active mutant form (I-1c) reverses contractile dysfunction in mouse failing hearts, suggesting that I-1c may be a candidate for gene therapy. We generated mice with conditional cardiomyocyte-restricted expression of I-1c (referred to herein as dTGI-1c mice) on an I-1–deficient background. Young adult dTGI-1c mice exhibited enhanced cardiac contractility but exaggerated contractile dysfunction and ventricular dilation upon catecholamine infusion. Telemetric ECG recordings revealed typical catecholamine-induced ventricular tachycardia and sudden death. Doxycycline feeding switched off expression of cardiomyocyte-restricted I-1c and reversed all abnormalities. Hearts from dTGI-1c mice showed hyperphosphorylation of phospholamban and the ryanodine receptor, and this was associated with an increased number of catecholamine-induced Ca2+ sparks in isolated myocytes. Aged dTGI-1c mice spontaneously developed a cardiomyopathic phenotype. These data were confirmed in a second independent transgenic mouse line, expressing a full-length I-1 mutant that could not be phosphorylated and thereby inactivated by PKC-α (I-1S67A). In conclusion, conditional expression of I-1c or I-1S67A enhanced steady-state phosphorylation of 2 key Ca2+-regulating sarcoplasmic reticulum enzymes. This was associated with increased contractile function in young animals but also with arrhythmias and cardiomyopathy after adrenergic stress and with aging. These data should be considered in the development of novel therapies for heart failure.

Authors

Katrin Wittköpper, Larissa Fabritz, Stefan Neef, Katharina R. Ort, Clemens Grefe, Bernhard Unsöld, Paulus Kirchhof, Lars S. Maier, Gerd Hasenfuss, Dobromir Dobrev, Thomas Eschenhagen, Ali El-Armouche

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Figure 3

Higher susceptibility to arrhythmia in I-1c double-transgenic mice.

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Higher susceptibility to arrhythmia in I-1c double-transgenic mice. (A) ...
(A) Original telemetric recording of VTs in a dTGI-1c ON mouse (top panel). Number of tTA and double-transgenic mice that developed VTs (black bars) after arrhythmia provocation in freely moving mice. VTs were completely reversible after doxycycline feeding (dTGI-1c OFF). *P < 0.05 by χ2 test. P-waves are denoted by §.(B) Original recordings of ventricular arrhythmias in isolated Langendorff-perfused hearts of dTGI-1c ON and tTA mice, elicited during high-frequency pacing, with 80 or 100 ms cycle length. Shown are left ventricular monophasic action potentials (MAPs) and a bipolar electrogram of the endocardial right ventricular octapolar electrophysiological pacing catheter (EP RV). *P < 0.05 by χ2 test.