Browsing by Author "Iaccarino, G"

Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen Access
    Alterations in cardiac adrenergic signaling and calcium cycling differentially affect the progression of cardiomyopathy.
    (J Clin Invest, 2001-04) Freeman, K; Lerman, I; Kranias, EG; Bohlmeyer, T; Bristow, MR; Lefkowitz, RJ; Iaccarino, G; Koch, WJ; Leinwand, LA
    The medical treatment of chronic heart failure has undergone a dramatic transition in the past decade. Short-term approaches for altering hemodynamics have given way to long-term, reparative strategies, including beta-adrenergic receptor (betaAR) blockade. This was once viewed as counterintuitive, because acute administration causes myocardial depression. Cardiac myocytes from failing hearts show changes in betaAR signaling and excitation-contraction coupling that can impair cardiac contractility, but the role of these abnormalities in the progression of heart failure is controversial. We therefore tested the impact of different manipulations that increase contractility on the progression of cardiac dysfunction in a mouse model of hypertrophic cardiomyopathy. High-level overexpression of the beta(2)AR caused rapidly progressive cardiac failure in this model. In contrast, phospholamban ablation prevented systolic dysfunction and exercise intolerance, but not hypertrophy, in hypertrophic cardiomyopathy mice. Cardiac expression of a peptide inhibitor of the betaAR kinase 1 not only prevented systolic dysfunction and exercise intolerance but also decreased cardiac remodeling and hypertrophic gene expression. These three manipulations of cardiac contractility had distinct effects on disease progression, suggesting that selective modulation of particular aspects of betaAR signaling or excitation-contraction coupling can provide therapeutic benefit.
  • Thumbnail Image
    ItemOpen Access
    Expression of a beta-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice.
    (Proc Natl Acad Sci U S A, 1998-06-09) Rockman, HA; Chien, KR; Choi, DJ; Iaccarino, G; Hunter, JJ; Ross, J; Lefkowitz, RJ; Koch, WJ
    Heart failure is accompanied by severely impaired beta-adrenergic receptor (betaAR) function, which includes loss of betaAR density and functional uncoupling of remaining receptors. An important mechanism for the rapid desensitization of betaAR function is agonist-stimulated receptor phosphorylation by the betaAR kinase (betaARK1), an enzyme known to be elevated in failing human heart tissue. To investigate whether alterations in betaAR function contribute to the development of myocardial failure, transgenic mice with cardiac-restricted overexpression of either a peptide inhibitor of betaARK1 or the beta2AR were mated into a genetic model of murine heart failure (MLP-/-). In vivo cardiac function was assessed by echocardiography and cardiac catheterization. Both MLP-/- and MLP-/-/beta2AR mice had enlarged left ventricular (LV) chambers with significantly reduced fractional shortening and mean velocity of circumferential fiber shortening. In contrast, MLP-/-/betaARKct mice had normal LV chamber size and function. Basal LV contractility in the MLP-/-/betaARKct mice, as measured by LV dP/dtmax, was increased significantly compared with the MLP-/- mice but less than controls. Importantly, heightened betaAR desensitization in the MLP-/- mice, measured in vivo (responsiveness to isoproterenol) and in vitro (isoproterenol-stimulated membrane adenylyl cyclase activity), was completely reversed with overexpression of the betaARK1 inhibitor. We report here the striking finding that overexpression of this inhibitor prevents the development of cardiomyopathy in this murine model of heart failure. These findings implicate abnormal betaAR-G protein coupling in the pathogenesis of the failing heart and point the way toward development of agents to inhibit betaARK1 as a novel mode of therapy.
  • Thumbnail Image
    ItemOpen Access
    Reciprocal in vivo regulation of myocardial G protein-coupled receptor kinase expression by beta-adrenergic receptor stimulation and blockade.
    (Circulation, 1998-10-27) Iaccarino, G; Tomhave, ED; Lefkowitz, RJ; Koch, WJ
    BACKGROUND: Impaired myocardial beta-adrenergic receptor (betaAR) signaling, including desensitization and functional uncoupling, is a characteristic of congestive heart failure. A contributing mechanism for this impairment may involve enhanced myocardial beta-adrenergic receptor kinase (betaARK1) activity because levels of this betaAR-desensitizing G protein-coupled receptor kinase (GRK) are increased in heart failure. An hypothesis has emerged that increased sympathetic nervous system activity associated with heart failure might be the initial stimulus for betaAR signaling alterations, including desensitization. We have chronically treated mice with drugs that either activate or antagonize betaARs to study the dynamic relationship between betaAR activation and myocardial levels of betaARK1. METHODS AND RESULTS: Long-term in vivo stimulation of betaARs results in the impairment of cardiac +betaAR signaling and increases the level of expression (mRNA and protein) and activity of +betaARK1 but not that of GRK5, a second GRK abundantly expressed in the myocardium. Long-term beta-blocker treatment, including the use of carvedilol, improves myocardial betaAR signaling and reduces betaARK1 levels in a specific and dose-dependent manner. Identical results were obtained in vitro in cultured cells, demonstrating that the regulation of GRK expression is directly linked to betaAR signaling. CONCLUSIONS: This report demonstrates, for the first time, that betaAR stimulation can significantly increase the expression of betaARK1 , whereas beta-blockade decreases expression. This reciprocal regulation of betaARK1 documents a novel mechanism of ligand-induced betaAR regulation and provides important insights into the potential mechanisms responsible for the effectiveness of beta-blockers, such as carvedilol, in the treatment of heart failure.
  • Thumbnail Image
    ItemOpen Access
    Targeting Gbeta gamma signaling in arterial vascular smooth muscle proliferation: a novel strategy to limit restenosis.
    (Proc Natl Acad Sci U S A, 1999-03-30) Iaccarino, G; Smithwick, LA; Lefkowitz, RJ; Koch, WJ
    Restenosis continues to be a major problem limiting the effectiveness of revascularization procedures. To date, the roles of heterotrimeric G proteins in the triggering of pathological vascular smooth muscle (VSM) cell proliferation have not been elucidated. betagamma subunits of heterotrimeric G proteins (Gbetagamma) are known to activate mitogen-activated protein (MAP) kinases after stimulation of certain G protein-coupled receptors; however, their relevance in VSM mitogenesis in vitro or in vivo is not known. Using adenoviral-mediated transfer of a transgene encoding a peptide inhibitor of Gbetagamma signaling (betaARKct), we evaluated the role of Gbetagamma in MAP kinase activation and proliferation in response to several mitogens, including serum, in cultured rat VSM cells. Our results include the striking finding that serum-induced proliferation of VSM cells in vitro is mediated largely via Gbetagamma. Furthermore, we studied the effects of in vivo adenoviral-mediated betaARKct gene transfer on VSM intimal hyperplasia in a rat carotid artery restenosis model. Our in vivo results demonstrated that the presence of the betaARKct in injured rat carotid arteries significantly reduced VSM intimal hyperplasia by 70%. Thus, Gbetagamma plays a critical role in physiological VSM proliferation, and targeted Gbetagamma inhibition represents a novel approach for the treatment of pathological conditions such as restenosis.
  • Thumbnail Image
    ItemOpen Access
    β-Adrenergic Receptor Kinase-1 Levels in Catecholamine-Induced Myocardial Hypertrophy
    (1999-01) Iaccarino, G; Dolber, PC; Lefkowitz, RJ; Koch, WJ
    Pressure overload ventricular hypertrophy is accompanied by dysfunctional β-adrenergic receptor signaling due to increased levels of the β-adrenergic receptor kinase-1, which phosphorylates and desensitizes β-adrenergic receptors. In this study, we examined whether increased β-adrenergic receptor kinase 1 expression is associated with myocardial hypertrophy induced by adrenergic stimulation. With use of implanted mini-osmotic pumps, we treated mice with isoproterenol, phenylephrine, or vehicle to distinguish between α1- and β-adrenergic stimulation. Both treatments resulted in cardiac hypertrophy, but only isoproterenol induced significant increases in β-adrenergic receptor kinase-1 protein levels and activity. Similarly, in isolated adult rat cardiac myocytes, 24 hours of isoproterenol stimulation resulted in a significant 2.8-fold increase in β-adrenergic receptor kinase-1 protein levels, whereas 24 hours of phenylephrine treatment did not alter β-adrenergic receptor kinase-1 expression. Our results indicate that increased β-adrenergic receptor kinase-1 is not invariably associated with myocardial hypertrophy but apparently is controlled by the state of β-adrenergic receptor activation.