Cardiac Overexpression of PDE4B Blunts β-Adrenergic Response and Maladaptive Remodeling in Heart Failure.

Background: The cyclic AMP (adenosine monophosphate; cAMP)-hydrolyzing protein PDE4B (phosphodiesterase 4B) is a key negative regulator of cardiac beta-adrenergic receptor stimulation. PDE4B deficiency leads to abnormal Ca(2+)handling and PDE4B is decreased in pressure overload hypertrophy, suggesting that increasing PDE4B in the heart is beneficial in heart failure. Methods: We measured PDE4B expression in human cardiac tissues and developed 2 transgenic mouse lines with cardiomyocyte-specific overexpression of PDE4B and an adeno-associated virus serotype 9 encoding PDE4B. Myocardial structure and function were evaluated by echocardiography, ECG, and in Langendorff-perfused hearts. Also, cAMP and PKA (cAMP dependent protein kinase) activity were monitored by Forster resonance energy transfer, L-type Ca(2+)current by whole-cell patch-clamp, and cardiomyocyte shortening and Ca(2+)transients with an Ionoptix system. Heart failure was induced by 2 weeks infusion of isoproterenol or transverse aortic constriction. Cardiac remodeling was evaluated by serial echocardiography, morphometric analysis, and histology. Results: PDE4B protein was decreased in human failing hearts. The first PDE4B-transgenic mouse line (TG15) had a approximate to 15-fold increase in cardiac cAMP-PDE activity and a approximate to 30% decrease in cAMP content and fractional shortening associated with a mild cardiac hypertrophy that resorbed with age. Basal ex vivo myocardial function was unchanged, but beta-adrenergic receptor stimulation of cardiac inotropy, cAMP, PKA, L-type Ca(2+)current, Ca(2+)transients, and cell contraction were blunted. Endurance capacity and life expectancy were normal. Moreover, these mice were protected from systolic dysfunction, hypertrophy, lung congestion, and fibrosis induced by chronic isoproterenol treatment. In the second PDE4B-transgenic mouse line (TG50), markedly higher PDE4B overexpression, resulting in a approximate to 50-fold increase in cardiac cAMP-PDE activity caused a approximate to 50% decrease in fractional shortening, hypertrophy, dilatation, and premature death. In contrast, mice injected with adeno-associated virus serotype 9 encoding PDE4B (10(12)viral particles/mouse) had a approximate to 50% increase in cardiac cAMP-PDE activity, which did not modify basal cardiac function but efficiently prevented systolic dysfunction, apoptosis, and fibrosis, while attenuating hypertrophy induced by chronic isoproterenol infusion. Similarly, adeno-associated virus serotype 9 encoding PDE4B slowed contractile deterioration, attenuated hypertrophy and lung congestion, and prevented apoptosis and fibrotic remodeling in transverse aortic constriction. Conclusions: Our results indicate that a moderate increase in PDE4B is cardioprotective and suggest that cardiac gene therapy with PDE4B might constitute a new promising approach to treat heart failure.