title: In vivo inhibition of elevated myocardial beta-adrenergic receptor kinase activity in hybrid transgenic mice restores normal beta-adrenergic signaling and function.
abstract: BACKGROUND
  The clinical syndrome of heart failure (HF) is characterized by an impaired cardiac beta-adrenergic receptor (betaAR) system, which is critical in the regulation of myocardial function. Expression of the betaAR kinase (betaARK1), which phosphorylates and uncouples betaARs, is elevated in human HF; this likely contributes to the abnormal betaAR responsiveness that occurs with beta-agonist administration. We previously showed that transgenic mice with increased myocardial betaARK1 expression had impaired cardiac function in vivo and that inhibiting endogenous betaARK1 activity in the heart led to enhanced myocardial function.
  
  
  RESULTS
  We created hybrid transgenic mice with cardiac-specific concomitant overexpression of both betaARK1 and an inhibitor of betaARK1 activity to study the feasibility and functional consequences of the inhibition of elevated betaARK1 activity similar to that present in human HF. Transgenic mice with myocardial overexpression of betaARK1 (3 to 5-fold) have a blunted in vivo contractile response to isoproterenol when compared with non-transgenic control mice. In the hybrid transgenic mice, although myocardial betaARK1 levels remained elevated due to transgene expression, in vitro betaARK1 activity returned to control levels and the percentage of betaARs in the high-affinity state increased to normal wild-type levels. Furthermore, the in vivo left ventricular contractile response to betaAR stimulation was restored to normal in the hybrid double-transgenic mice.
  
  
  CONCLUSIONS
  Novel hybrid transgenic mice can be created with concomitant cardiac-specific overexpression of 2 independent transgenes with opposing actions. Elevated myocardial betaARK1 in transgenic mouse hearts (to levels seen in human HF) can be inhibited in vivo by a peptide that can prevent agonist-stimulated desensitization of cardiac betaARs. This may represent a novel strategy to improve myocardial function in the setting of compromised heart function.
authors.affiliation: Department of Surgery, Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Akhter
authors.forename: A D
authors.initials: AD
authors.lastname: Eckhart
authors.forename: H A
authors.initials: HA
authors.lastname: Rockman
authors.forename: K
authors.initials: K
authors.lastname: Shotwell
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: W J
authors.initials: WJ
authors.lastname: Koch
mesh_terms: D000262:Adenylyl Cyclases / Q000502:physiology; D000818:Animals; D006328:Cardiac Catheterization; D002316:Cardiotonic Agents / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004790:Enzyme Induction; D005240:Feasibility Studies; D005786:Gene Expression Regulation; D006333:Heart Failure / Q000201:enzymology* / Q000235:genetics / Q000503:physiopathology; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000187:drug effects / Q000235:genetics; D010446:Peptide Fragments / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D011994:Recombinant Proteins; D015290:Second Messenger Systems; D012969:Sodium Fluoride / Q000494:pharmacology; D019076:Transgenes; D016277:Ventricular Function, Left / Q000187:drug effects; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D002316:Cardiotonic Agents; D010446:Peptide Fragments; D011943:Receptors, Adrenergic, beta; D011994:Recombinant Proteins; D012969:Sodium Fluoride; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; C114043:BARKct protein, recombinant; D051552:beta-Adrenergic Receptor Kinases; D000262:Adenylyl Cyclases; D007545:Isoproterenol