title: Human G109E-inhibitor-1 impairs cardiac function and promotes arrhythmias.
abstract: A hallmark of human and experimental heart failure is deficient sarcoplasmic reticulum (SR) Ca-uptake reflecting impaired contractile function. This is at least partially attributed to dephosphorylation of phospholamban by increased protein phosphatase 1 (PP1) activity. Indeed inhibition of PP1 by transgenic overexpression or gene-transfer of constitutively active inhibitor-1 improved Ca-cycling, preserved function and decreased fibrosis in small and large animal models of heart failure, suggesting that inhibitor-1 may represent a potential therapeutic target. We recently identified a novel human polymorphism (G109E) in the inhibitor-1 gene with a frequency of 7% in either normal or heart failure patients. Transgenic mice, harboring cardiac-specific expression of G109E inhibitor-1, exhibited decreases in contractility, Ca-kinetics and SR Ca-load. These depressive effects were relieved by isoproterenol stimulation. Furthermore, stress conditions (2Hz +/- Iso) induced increases in Ca-sparks, Ca-waves (60% of G109E versus 20% in wild types) and after-contractions (76% of G109E versus 23% of wild types) in mutant cardiomyocytes. Similar findings were obtained by acute expression of the G109E variant in adult cardiomyocytes in the absence or presence of endogenous inhibitor-1. The underlying mechanisms included reduced binding of mutant inhibitor-1 to PP1, increased PP1 activity, and dephosphorylation of phospholamban at Ser16 and Thr17. However, phosphorylation of the ryanodine receptor at Ser2808 was not altered while phosphorylation at Ser2814 was increased, consistent with increased activation of Ca/calmodulin-dependent protein kinase II (CaMKII), promoting aberrant SR Ca-release. Parallel in vivo studies revealed that mutant mice developed ventricular ectopy and complex ventricular arrhythmias (including bigeminy, trigeminy and ventricular tachycardia), when challenged with isoproterenol. Inhibition of CaMKII activity by KN-93 prevented the increased propensity to arrhythmias. These findings suggest that the human G109E inhibitor-1 variant impairs SR Ca-cycling and promotes arrhythmogenesis under stress conditions, which may present an additional insult in the compromised function of heart failure carriers.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Kobra
authors.initials: K
authors.lastname: Haghighi
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: Pritchard
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Guan-Sheng
authors.initials: GS
authors.lastname: Liu
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Vivek P
authors.initials: VP
authors.lastname: Singh
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Philip
authors.initials: P
authors.lastname: Bidwell
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Chi Keung
authors.initials: CK
authors.lastname: Lam
authors.affiliation: Molecular Biology Division, Biomedical Research Foundation, Academy of Athens, Greece.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Vafiadaki
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Parthib
authors.initials: P
authors.lastname: Das
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Jianyong
authors.initials: J
authors.lastname: Ma
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Swati
authors.initials: S
authors.lastname: Kunduri
authors.affiliation: Molecular Biology Division, Biomedical Research Foundation, Academy of Athens, Greece; 4th Department of Internal Medicine, Medical School, University of Athens and Attikon Hospital, Greece.
authors.forename: Despina
authors.initials: D
authors.lastname: Sanoudou
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Stela
authors.initials: S
authors.lastname: Florea
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Erica
authors.initials: E
authors.lastname: Vanderbilt
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
authors.forename: Hong-Shang
authors.initials: HS
authors.lastname: Wang
authors.affiliation: Division of Cardiology, Internal Medicine, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, United States.
authors.forename: Jack
authors.initials: J
authors.lastname: Rubinstein
authors.affiliation: Cardiovascular Research Center, Ichan School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029, United States.
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Hajjar
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States; Molecular Biology Division, Biomedical Research Foundation, Academy of Athens, Greece. Electronic address: litsa.kranias@uc.edu.
authors.forename: Evangelia G
authors.initials: EG
authors.lastname: Kranias
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics* / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002395:Catecholamines / Q000494:pharmacology; D003971:Diastole / Q000187:drug effects; D006321:Heart / Q000187:drug effects / Q000503:physiopathology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002395:Catecholamines; D007545:Isoproterenol; D011506:Proteins; D019831:Sodium-Calcium Exchanger; D000099211:Phospholamban; C073882:phosphoprotein phosphatase inhibitor 1
keywords: Calcium cycling; Cardiac function; Heart failure; Inhibitor-1; Protein phosphatase 1