title: Reduced junctional Na+/Ca2+-exchanger activity contributes to sarcoplasmic reticulum Ca2+ leak in junctophilin-2-deficient mice.
abstract: Expression silencing of junctophilin-2 (JPH2) in mouse heart leads to ryanodine receptor type 2 (RyR2)-mediated sarcoplasmic reticulum (SR) Ca(2+) leak and rapid development of heart failure. The mechanism and physiological significance of JPH2 in regulating RyR2-mediated SR Ca(2+) leak remains elusive. We sought to elucidate the role of JPH2 in regulating RyR2-mediated SR Ca(2+) release in the setting of cardiac failure. Cardiac myocytes isolated from tamoxifen-inducible conditional knockdown mice of JPH2 (MCM-shJPH2) were subjected to confocal Ca(2+) imaging. MCM-shJPH2 cardiomyocytes exhibited an increased spark frequency width with altered spark morphology, which caused increased SR Ca(2+) leakage. Single channel studies identified an increased RyR2 open probability in MCM-shJPH2 mice. The increase in spark frequency and width was observed only in MCM-shJPH2 and not found in mice with increased RyR2 open probability with native JPH2 expression. Na(+)/Ca(2+)-exchanger (NCX) activity was reduced by 50% in MCM-shJPH2 with no detectable change in NCX expression. Additionally, 50% inhibition of NCX through Cd(2+) administration alone was sufficient to increase spark width in myocytes obtained from wild-type mice. Additionally, superresolution analysis of RyR2 and NCX colocalization showed a reduced overlap between RyR2 and NCX in MCM-shJPH2 mice. In conclusion, decreased JPH2 expression causes increased SR Ca(2+) leakage by directly increasing open probability of RyR2 and by indirectly reducing junctional NCX activity through increased dyadic cleft Ca(2+). This demonstrates two novel and independent cellular mechanisms by which JPH2 regulates RyR2-mediated SR Ca(2+) leak and heart failure development.
authors.affiliation: Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas;
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Pediatrics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas;
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Landstrom
authors.affiliation: Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas;
authors.forename: Qiongling
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Physics, University of Exeter and Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Munro
authors.affiliation: Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas;
authors.forename: David
authors.initials: D
authors.lastname: Beavers
authors.affiliation: Windland Smith Rice Sudden Death Genomics Laboratory, Departments of Medicine, Pediatrics, and Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
authors.affiliation: Department of Physics, University of Exeter and Department of Physiology, University of Auckland, Auckland, New Zealand; and.
authors.forename: Christian
authors.initials: C
authors.lastname: Soeller
authors.affiliation: Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; Department of Medicine/Cardiology, Cardiovascular Research Institute, Baylor College of Medicine, Houston, Texas; wehrens@bcm.edu.
authors.forename: Xander H T
authors.initials: XH
authors.lastname: Wehrens
mesh_terms: D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D020013:Calcium Signaling; D002478:Cells, Cultured; D017353:Gene Deletion; D006333:Heart Failure / Q000378:metabolism; D015640:Ion Channel Gating; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002104:Cadmium; D008565:Membrane Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; C000589042:JP2 protein, mouse
keywords: calcium; heart failure; junctophilin; ryanodine receptor; sodium/calcium exchanger