title: GRK2 blockade with βARKct is essential for cardiac β2-adrenergic receptor signaling towards increased contractility.
abstract: BACKGROUND
  β1- and β2-adrenergic receptors (ARs) play distinct roles in the heart, e.g. β1AR is pro-contractile and pro-apoptotic but β2AR anti-apoptotic and only weakly pro-contractile. G protein coupled receptor kinase (GRK)-2 desensitizes and opposes βAR pro-contractile signaling by phosphorylating the receptor and inducing beta-arrestin (βarr) binding. We posited herein that GRK2 blockade might enhance the pro-contractile signaling of the β2AR subtype in the heart. We tested the effects of cardiac-targeted GRK2 inhibition in vivo exclusively on β2AR signaling under normal conditions and in heart failure (HF).
  
  
  RESULTS
  We crossed β1AR knockout (B1KO) mice with cardiac-specific transgenic mice expressing the βARKct, a known GRK2 inhibitor, and studied the offspring under normal conditions and in post-myocardial infarction (MI). βARKct expression in vivo proved essential for β2AR-dependent contractile function, as β2AR stimulation with isoproterenol fails to increase contractility in either healthy or post-MI B1KO mice and it only does so in the presence of βARKct. The main underlying mechanism for this is blockade of the interaction of phosphodiesterase (PDE) type 4D with the cardiac β2AR, which is normally mediated by the actions of GRK2 and βarrs on the receptor. The molecular "brake" that PDE4D poses on β2AR signaling to contractility stimulation is thus "released". Regarding the other beneficial functions of cardiac β2AR, βARKct increased overall survival of the post-MI B1KO mice progressing to HF, via a decrease in cardiac apoptosis and an increase in wound healing-associated inflammation early (at 24 hrs) post-MI. However, these effects disappear by 4 weeks post-MI, and, in their place, upregulation of the other major GRK in the heart, GRK5, is observed.
  
  
  CONCLUSIONS
  GRK2 inhibition in vivo with βARKct is absolutely essential for cardiac β2AR pro-contractile signaling and function. In addition, β2AR anti-apoptotic signaling in post-MI HF is augmented by βARKct, although this effect is short-lived.
authors.affiliation: Department of Pharmaceutical Sciences, Laboratory for the Study of Neurohormonal Control of the Circulation, Nova Southeastern University College of Pharmacy, Fort Lauderdale, FL 33328, USA. al806@nova.edu.
authors.forename: Norma C
authors.initials: NC
authors.lastname: Salazar
authors.forename: Ximena
authors.initials: X
authors.lastname: Vallejos
authors.forename: Ashley
authors.initials: A
authors.lastname: Siryk
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Rengo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Cannavo
authors.forename: Daniela
authors.initials: D
authors.lastname: Liccardo
authors.forename: Claudio
authors.initials: C
authors.lastname: De Lucia
authors.forename: Erhe
authors.initials: E
authors.lastname: Gao
authors.forename: Dario
authors.initials: D
authors.lastname: Leosco
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Anastasios
authors.initials: A
authors.lastname: Lymperopoulos
mesh_terms: D000818:Animals; D017209:Apoptosis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000378:metabolism; D016207:Cytokines / Q000097:blood; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000037:antagonists & inhibitors* / Q000502:physiology; D054774:G-Protein-Coupled Receptor Kinase 5 / Q000378:metabolism; D006321:Heart / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000502:physiology; D009203:Myocardial Infarction / Q000378:metabolism / Q000503:physiopathology; D016328:NF-kappa B / Q000378:metabolism; D010446:Peptide Fragments / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D018342:Receptors, Adrenergic, beta-1 / Q000235:genetics; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D011994:Recombinant Proteins
chemical_list: D016207:Cytokines; D016328:NF-kappa B; D010446:Peptide Fragments; D019253:Proto-Oncogene Proteins c-bcl-2; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D011994:Recombinant Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; C114043:BARKct protein, recombinant; C496568:GRK2 protein, mouse; D054769:G-Protein-Coupled Receptor Kinase 2; D054774:G-Protein-Coupled Receptor Kinase 5; C517895:Grk5 protein, mouse; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C531980:PDE4D protein, mouse