on November 12, 2007
Published online before print November 12, 2007, doi: 10.1161/CIRCULATIONAHA.107.706515
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Submitted on April 1, 2007
From the Department of Medicine (C.P.), and Department of Surgery (J.N.S., B.L., N.V., J.J.N., C.A.M.), Duke University Medical Center, Durham, NC, and Department of Molecular Cardiology (S.V.N.P.), Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio. Dr Perrino is currently at the Division of Cardiology, Federico II University, Naples, Italy. * To whom correspondence should be addressed. E-mail: prasads2{at}ccf.org.
Background—Downregulation of Methods and Results—To test the role of PI3K on Conclusions—These results suggest a novel paradigm in which human
Accepted on September 21, 2007
Dynamic Regulation of Phosphoinositide 3-Kinase-
Cinzia Perrino MD, PhD, 
Activity and 
-Adrenergic Receptor Trafficking in End-Stage Human Heart Failure
-adrenergic receptors (ARs) under conditions of heart failure requires receptor targeting of phosphoinositide 3-kinase (PI3K)–
and redistribution of ARs into endosomal compartments. Because support with a left ventricular assist device (LVAD) results in significant improvement of cardiac function in humans, we investigated the effects of mechanical unloading on regulation of PI3K activity and intracellular distribution of ARs. Additionally, we tested whether displacement of PI3K from activated ARs would restore agonist responsiveness in failing human cardiomyocytes.AR endocytosis in failing human hearts, we assayed for PI3K activity in human left ventricular samples before and after mechanical unloading (LVAD). Before LVAD, failing human hearts displayed a marked increase in AR kinase 1 (ARK1)–associated PI3K activity that was attributed exclusively to enhanced activity of the PI3K isoform. Increased ARK1-coupled PI3K activity in the failing hearts was associated with downregulation of ARs from the plasma membrane and enhanced sequestration into early and late endosomes compared with unmatched nonfailing controls. Importantly, LVAD support reversed PI3K activation, normalized the levels of agonist-responsive ARs at the plasma membrane, and depleted the ARs from the endosomal compartments without changing the total number of receptors (sum of plasma membrane and early and late endosome receptors). To test whether the competitive displacement of PI3K from the AR complex restored receptor responsiveness, we overexpressed the phosphoinositide kinase domain of PI3K (which disrupts ARK1/PI3K interaction) in primary cultures of failing human cardiomyocytes. Adenoviral-mediated phosphoinositide kinase overexpression significantly increased basal contractility and rapidly reconstituted responsiveness to -agonist.ARs undergo a process of intracellular sequestration that is dynamically reversed after LVAD support. Importantly, mechanical unloading leads to complete reversal in PI3K and ARK1-associated PI3K activation. Furthermore, displacement of active PI3K from ARK1 restores AR responsiveness in failing myocytes.
Key words: heart failure • molecular biology • receptors, adrenergic, beta • signal transduction
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