title: BAG3 regulates contractility and Ca(2+) homeostasis in adult mouse ventricular myocytes.
abstract: Bcl2-associated athanogene 3 (BAG3) is a 575 amino acid anti-apoptotic protein that is constitutively expressed in the heart. BAG3 mutations, including mutations leading to loss of protein, are associated with familial cardiomyopathy. Furthermore, BAG3 levels have been found to be reduced in end-stage non-familial failing myocardium. In contrast to neonatal myocytes in which BAG3 is found in the cytoplasm and involved in protein quality control and apoptosis, in adult mouse left ventricular (LV) myocytes BAG3 co-localized with Na(+)-K(+)-ATPase and L-type Ca(2+) channels in the sarcolemma and t-tubules. BAG3 co-immunoprecipitated with β1-adrenergic receptor, L-type Ca(2+) channels and phospholemman. To simulate decreased BAG3 protein levels observed in human heart failure, we targeted BAG3 by shRNA (shBAG3) in adult LV myocytes. Reducing BAG3 by 55% resulted in reduced contraction and [Ca(2+)]i transient amplitudes in LV myocytes stimulated with isoproterenol. L-type Ca(2+) current (ICa) and sarcoplasmic reticulum (SR) Ca(2+) content but not Na(+)/Ca(2+) exchange current (INaCa) or SR Ca(2+) uptake were reduced in isoproterenol-treated shBAG3 myocytes. Forskolin or dibutyryl cAMP restored ICa amplitude in shBAG3 myocytes to that observed in WT myocytes, consistent with BAG3 having effects upstream and at the level of the receptor. Resting membrane potential and action potential amplitude were unaffected but APD50 and APD90 were prolonged in shBAG3 myocytes. Protein levels of Ca(2+) entry molecules and other important excitation-contraction proteins were unchanged in myocytes with lower BAG3. Our findings that BAG3 is localized at the sarcolemma and t-tubules while modulating myocyte contraction and action potential duration through specific interaction with the β1-adrenergic receptor and L-type Ca(2+) channel provide novel insight into the role of BAG3 in cardiomyopathies and increased arrhythmia risks in heart failure.
authors.affiliation: Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA; Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Feldman
authors.affiliation: Comprehensive NeuroAIDS Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Gordon
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: JuFang
authors.initials: J
authors.lastname: Wang
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Jianliang
authors.initials: J
authors.lastname: Song
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Xue-Qian
authors.initials: XQ
authors.lastname: Zhang
authors.affiliation: Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Valerie D
authors.initials: VD
authors.lastname: Myers
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Tilley
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Erhe
authors.initials: E
authors.lastname: Gao
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Hoffman
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Dhanendra
authors.initials: D
authors.lastname: Tomar
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Muniswamy
authors.initials: M
authors.lastname: Madesh
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Rabinowitz
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.affiliation: Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA; Department of Cardiology, Tangdu Hospital, the Fourth Military Medical University, Xi'an, China.
authors.forename: Feifei
authors.initials: F
authors.lastname: Su
authors.affiliation: Comprehensive NeuroAIDS Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Kamel
authors.initials: K
authors.lastname: Khalili
authors.affiliation: Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA; Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA. Electronic address: Joseph.cheung@tuhs.temple.edu.
authors.forename: Joseph Y
authors.initials: JY
authors.lastname: Cheung
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis / Q000235:genetics*; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis / Q000235:genetics*; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002311:Cardiomyopathy, Dilated / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D056966:Excitation Contraction Coupling; D006333:Heart Failure / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology; D006706:Homeostasis; D006801:Humans; D007545:Isoproterenol / Q000008:administration & dosage; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D010750:Phosphoproteins / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C547788:Adrb1 protein, mouse; D051017:Apoptosis Regulatory Proteins; C498806:Bag3 protein, mouse; D020746:Calcium Channels, L-Type; D008565:Membrane Proteins; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D018342:Receptors, Adrenergic, beta-1; C069141:phospholemman; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D002118:Calcium
keywords: BAG3; Calcium channels; Excitation–contraction coupling; Phospholemman; β1-Adrenergic receptor