title: Calcium/calmodulin-dependent protein kinase II (CaMKII) inhibition ameliorates arrhythmias elicited by junctin ablation under stress conditions.
abstract: BACKGROUND
  Aberrant calcium signaling is considered one of the key mechanisms contributing to arrhythmias, especially in the context of heart failure. In human heart failure, there is significant down-regulation of the sarcoplasmic reticulum (SR) protein junctin, and junctin deficiency in mice is associated with stress-induced arrhythmias.
  
  
  OBJECTIVE
  The purpose of this study was to determine whether the increased SR Ca(2+) leak and arrhythmias associated with junctin ablation may be associated with increased calcium/calmodulin-dependent protein kinase II (CaMKII) activity and phosphorylation of the cardiac ryanodine receptor (RyR2) and whether pharmacologic inhibition of CaMKII activity may prevent these arrhythmias.
  
  
  METHODS
  Using a combination of biochemical, cellular, and in vivo approaches, we tested the ability of KN-93 to reverse aberrant CaMKII phosphorylation of RyR2. Specifically, we performed protein phosphorylation analysis, in vitro cardiomyocyte contractility and Ca(2+) kinetics, and in vivo ECG analysis in junctin-deficient mice.
  
  
  RESULTS
  In the absence of junctin, RyR2 channels displayed CaMKII-dependent hyperphosphorylation. Notably, CaMKII inhibition by KN-93 reduced the in vivo incidence of stress-induced ventricular tachycardia by 65% in junctin null mice. At the cardiomyocyte level, KN-93 reduced the percentage of junctin null cells exhibiting spontaneous Ca(2+) aftertransients and aftercontractions under stress conditions by 35% and 37%, respectively. At the molecular level, KN-93 blunted the CaMKII-mediated hyperphosphorylation of RyR2 and phospholamban under stress conditions.
  
  
  CONCLUSIONS
  Our data suggest that CaMKII inhibition is effective in preventing arrhythmogenesis in the setting of junctin ablation through modulation of both SR Ca(2+) release and uptake. Thus, it merits further investigation as promising molecular therapy.
authors: Molecular Biology Division, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
authors: Christos
authors: C
authors: Tzimas
authors: 3rd Department of Cardiology, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
authors: John
authors: J
authors: Terrovitis
authors: Clinic of Cardiology & Pulmonology, University Medical Center Goettingen, Goettingen, Germany.
authors: Stephan E
authors: SE
authors: Lehnart
authors: Molecular Biology Division, Biomedical Research Foundation of the Academy of Athens, Athens, Greece; Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati, Cincinnati, Ohio.
authors: Evangelia G
authors: EG
authors: Kranias
authors: Molecular Biology Division, Biomedical Research Foundation of the Academy of Athens, Athens, Greece; Department of Pharmacology, Medical School, National and Kapodistrian University of Athens, Athens, Greece. Electronic address: dsanoudou@med.uoa.gr.
authors: Despina
authors: D
authors: Sanoudou
mesh_terms: D055011:Ablation Techniques; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism / Q000517:prevention & control; D001596:Benzylamines / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D004195:Disease Models, Animal; D006333:Heart Failure / Q000378:metabolism; D051379:Mice; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*; D000099211:Phospholamban; D000096926:Benzenesulfonamides
chemical_list: D001596:Benzylamines; D002118:Calcium; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D047428:Protein Kinase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D013449:Sulfonamides; D000099211:Phospholamban; C072105:KN 93; D000096926:Benzenesulfonamides
keywords: Arrhythmia; Calcium/calmodulin-dependent protein kinase II; Isoproterenol; Junctin; Ryanodine receptor