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Carvedilol induces biased β1 adrenergic receptor-Nitric oxide synthase 3-cyclic guanylyl monophosphate signaling to promote cardiac contractility.

AIMS
β-blockers are widely used in therapy for heart failure and hypertension. β-blockers are also known to evoke additional diversified pharmacological and physiological effects in patients. We aim to characterize the underlying molecular signaling and effects on cardiac inotropy induced by β-blockers in animal hearts.


METHODS AND RESULTS
Wild type mice fed high fat diet (HFD) were treated with carvedilol, metoprolol, or vehicle and echocardiogram analysis was performed. Heart tissues were used for biochemical and histological analyses. Cardiomyocytes were isolated from normal and HFD mice and rats for analysis of adrenergic signaling, calcium handling, contraction, and western blot. Biosensors were used to measure β-blocker-induced cyclic guanosine monophosphate (cGMP) signal and protein kinase A (PKA) activity in myocytes. Acute stimulation of myocytes with carvedilol promotes β1AR- and PKG-dependent inotropic cardiac contractility with minimal increases in calcium amplitude. Carvedilol acts as a biased ligand to promote β1AR coupling to a Gi-PI3K-Akt-nitric oxide synthase 3 (NOS3) cascade and induces robust β1AR-cGMP-PKG signal. Deletion of NOS3 selectively blocks carvedilol, but not isoproterenol induced β1AR-dependent cGMP signal and inotropic contractility. Moreover, therapy with carvedilol restores inotropic contractility and sensitizes cardiac adrenergic reserves in diabetic mice with minimal impact in calcium signal, as well as reduced cell apoptosis and hypertrophy in diabetic hearts.


CONCLUSION
These observations present a novel β1AR-NOS3 signaling pathway to promote cardiac inotropy in the heart, indicating that this signaling paradigm may be targeted in therapy of heart diseases by reduced ejection fraction.


TRANSLATIONAL PERSPECTIVE
Carvedilol transduces β1AR coupling to Gi-PI3K-Akt pathway to promote NOS3-cGMP-PKG signals and evokes cardiac inotropy with minimal elevation of calcium signaling. Chronic therapy with carvedilol not only restores cardiac contractility and adrenergic reserves but also leads to reduction of cardiac remodeling with less cell death than metoprolol. These results may explain at least in part that carvedilol had a significant survival advantage over metoprolol in the treatment of HF in clinical studies. The carvedilol-induced β1AR-NOS3 axis represents a novel regulatory paradigm to increase cardiac inotropy, which can be a promising therapeutic target for treating cardiac diseases with depressed cardiac ejection fraction.