title: Cardiac-specific ablation of G-protein receptor kinase 2 redefines its roles in heart development and beta-adrenergic signaling.
abstract: G-protein receptor kinase 2 (GRK2) is 1 of 7 mammalian GRKs that phosphorylate ligand-bound 7-transmembrane receptors, causing receptor uncoupling from G proteins and potentially activating non-G-protein signaling pathways. GRK2 is unique among members of the GRK family in that its genetic ablation causes embryonic lethality. Cardiac abnormalities in GRK2 null embryos implicated GRK2 in cardiac development but prevented studies of the knockout phenotype in adult hearts. Here, we created GRK2-loxP-targeted mice and used Cre recombination to generate germline and cardiac-specific GRK2 knockouts. GRK2 deletion in the preimplantation embryo with EIIa-Cre (germline null) resulted in developmental retardation and embryonic lethality between embryonic day 10.5 (E10.5) and E11.5. At E9.5, cardiac myocyte specification and cardiac looping were normal, but ventricular development was delayed. Cardiomyocyte-specific ablation of GRK2 in the embryo with Nkx2.5-driven Cre (cardiac-specific GRK2 knockout) produced viable mice with normal heart structure, function, and cardiac gene expression. Cardiac-specific GRK2 knockout mice exhibited enhanced inotropic sensitivity to the beta-adrenergic receptor agonist isoproterenol, with impairment of normal inotropic and lusitropic tachyphylaxis, and exhibited accelerated development of catecholamine toxicity with chronic isoproterenol treatment. These findings show that cardiomyocyte autonomous GRK2 is not essential for myocardial development after cardiac specification, suggesting that embryonic developmental abnormalities may be attributable to extracardiac effects of GRK2 ablation. In the adult heart, cardiac GRK2 is a major factor regulating inotropic and lusitropic tachyphylaxis to beta-adrenergic agonist, which likely contributes to its protective effects in catecholamine cardiomyopathy.
authors.affiliation: Center for Molecular Cardiovascular Research, University of Cincinnati, Ohio, USA.
authors.forename: Scot J
authors.initials: SJ
authors.lastname: Matkovich
authors.forename: Abhinav
authors.initials: A
authors.lastname: Diwan
authors.forename: Justin L
authors.initials: JL
authors.lastname: Klanke
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Hammer
authors.forename: Yehia
authors.initials: Y
authors.lastname: Marreez
authors.forename: Amy M
authors.initials: AM
authors.lastname: Odley
authors.forename: Eric W
authors.initials: EW
authors.lastname: Brunskill
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schwartz
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Dorn
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology* / Q000633:toxicity; D000818:Animals; D009202:Cardiomyopathies / Q000139:chemically induced; D002316:Cardiotonic Agents / Q000494:pharmacology; D047108:Embryonic Development; D054769:G-Protein-Coupled Receptor Kinase 2; D018390:Gene Targeting; D005804:Genes, Lethal; D006321:Heart / Q000196:embryology*; D007545:Isoproterenol / Q000633:toxicity; D051379:Mice; D032383:Myocytes, Cardiac / Q000201:enzymology*; D015398:Signal Transduction; D013618:Tachyphylaxis; D051552:beta-Adrenergic Receptor Kinases / Q000235:genetics / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D002316:Cardiotonic Agents; C496568:GRK2 protein, mouse; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D007545:Isoproterenol