title: Impaired local regulation of ryanodine receptor type 2 by protein phosphatase 1 promotes atrial fibrillation.
abstract: OBJECTIVE
  Altered Ca(2+) handling in atrial fibrillation (AF) has been associated with dysregulated protein phosphatase 1 (PP1) and subcellular heterogeneities in protein phosphorylation, but the underlying mechanisms remain unclear. This is due to a lack of investigation into the local, rather than global, regulation of PP1 on different subcellular targets such as ryanodine receptor type 2 (RyR2), especially in AF.
  
  
  RESULTS
  We tested the hypothesis that impaired local regulation of PP1 causes RyR2 hyperphosphorylation thereby promoting AF susceptibility. To specifically disrupt PP1's local regulation of RyR2, we used the spinophilin knockout (Sp(-/-)) mice (Mus musculus) since PP1 is targeted to RyR2 via spinophilin. Without spinophilin, the interaction between PP1 and RyR2 was reduced by 64%, while RyR2 phosphorylation was increased by 43% at serine (S)2814 but unchanged at S2808. Lipid bilayer experiments revealed that single RyR2 channels isolated from Sp(-/-) hearts had an increased open probability. Likewise, Ca(2+) spark frequency normalized to sarcoplasmic reticulum Ca(2+) content was also enhanced in Sp(-/-) atrial myocytes, but normalized by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitors KN-93 and AIP and also by genetic inhibition of RyR2 S2814 phosphorylation. Finally, Sp(-/-) mice exhibited increased atrial ectopy and susceptibility to pacing-induced AF, both of which were also prevented by the RyR2 S2814A mutation.
  
  
  CONCLUSIONS
  PP1 regulates RyR2 locally by counteracting CaMKII phosphorylation of RyR2. Decreased local PP1 regulation of RyR2 contributes to RyR2 hyperactivity and promotes AF susceptibility. This represents a novel mechanism for subcellular modulation of calcium channels and may represent a potential drug target of AF.
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA Interdepartmental Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston, TX, USA.
authors.forename: David Y
authors.initials: DY
authors.lastname: Chiang
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Qiongling
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Katherina M
authors.initials: KM
authors.lastname: Alsina
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Ann P
authors.initials: AP
authors.lastname: Quick
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Julia O
authors.initials: JO
authors.lastname: Reynolds
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Guoliang
authors.initials: G
authors.lastname: Wang
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Darlene
authors.initials: D
authors.lastname: Skapura
authors.affiliation: Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen, Essen, Germany.
authors.forename: Niels
authors.initials: N
authors.lastname: Voigt
authors.affiliation: Institute of Pharmacology, Faculty of Medicine, University Duisburg-Essen, Essen, Germany.
authors.forename: Dobromir
authors.initials: D
authors.lastname: Dobrev
authors.affiliation: Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA Department of Medicine (Cardiology), Baylor College of Medicine, Houston, TX, USA wehrens@bcm.edu.
authors.forename: Xander H T
authors.initials: XH
authors.lastname: Wehrens
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001281:Atrial Fibrillation / Q000209:etiology* / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D004195:Disease Models, Animal; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000099273:Neurabins
chemical_list: D008840:Microfilament Proteins; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D054645:Protein Phosphatase 1; D019837:Ryanodine Receptor Calcium Release Channel; D000099273:Neurabins; C000592748:ryanodine receptor 2. mouse
keywords: Atrial fibrillation; Ca2+/calmodulin-dependent kinase II; Protein phosphatase 1; Ryanodine receptor type 2; Spinophilin