Phosphodiesterase-2 Is Up-Regulated in Human Failing Hearts and Blunts β-Adrenergic Responses in Cardiomyocytes

International audienceObjectives: We investigated whether myocardial phosphodiesterase 2 (PDE2) is altered in heart failure (HF) and determined PDE2-mediated effects on β-adrenoceptor (AR) signaling in healthy and diseased cardiomyocytes.Background: Diminished cAMP- and augmented cGMP-signaling is characteristic for failing hearts. Among the PDE superfamily, PDE2 has the unique property to be stimulated by cGMP, thus leading to a remarkable increase in cAMP hydrolysis mediating a negative cross-talk between cGMP- and cAMP-signaling. However, the role of PDE2 in HF is poorly understood.Methods and Results: Immunoblotting and radioenzymatic assay revealed that myocardial PDE2 expression and activity were ~2-fold higher in advanced human HF. Chronic β-AR stimulation via catecholamine infusions in rats enhanced PDE2 expression 2-fold and cAMP hydrolytic activity 4-fold as determined by FRET-based sensors, which correlated with blunted cardiac β-AR responsiveness. Notably, in diseased cardiomyocytes the higher PDE2 activity could be further enhanced by stimulation of cGMP synthesis via NO donors whereas specific PDE2 inhibition partially restored β-AR responsiveness. Accordingly, PDE2 overexpression in healthy cardiomyocytes reduced the rise in cAMP levels and ICa,L amplitude and abolished the positive inotropic effect following acute β-AR stimulation, without affecting basal contractility. Importantly, PDE2-overexpressing cardiomyocytes showed marked protection from norepinephrine-induced hypertrophic responses.Conclusions: PDE2 is markedly upregulated in failing hearts and desensitizes against acute β-AR stimulation. This may constitute an important defence mechanism during cardiac stress, e.g. by antagonizing excessive β-AR drive. Thus, activating myocardial PDE2 may represent a novel intracellular anti-adrenergic therapeutic strategy in HF

Constitutively active phosphatase inhibitor-1 improves cardiac contractility in young mice but is deleterious after catecholaminergic stress and with aging

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