title: Abnormal calcium signaling and sudden cardiac death associated with mutation of calsequestrin.
abstract: Mutations in human cardiac calsequestrin (CASQ2), a high-capacity calcium-binding protein located in the sarcoplasmic reticulum (SR), have recently been linked to effort-induced ventricular arrhythmia and sudden death (catecholaminergic polymorphic ventricular tachycardia). However, the precise mechanisms through which these mutations affect SR function and lead to arrhythmia are presently unknown. In this study, we explored the effect of adenoviral-directed expression of a canine CASQ2 protein carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation D307H (CASQ2(D307H)) on Ca2+ signaling in adult rat myocytes. Total CASQ2 protein levels were consistently elevated approximately 4-fold in cells infected with adenoviruses expressing either wild-type CASQ2 (CASQ2(WT)) or CASQ2(D307H). Expression of CASQ2(D307H) reduced the Ca2+ storing capacity of the SR. In addition, the amplitude, duration, and rise time of macroscopic I(Ca)-induced Ca2+ transients and of spontaneous Ca2+ sparks were reduced significantly in myocytes expressing CASQ2(D307H). Myocytes expressing CASQ2(D307H) also displayed drastic disturbances of rhythmic oscillations in [Ca2+]i and membrane potential, with signs of delayed afterdepolarizations when undergoing periodic pacing and exposed to isoproterenol. Importantly, normal rhythmic activity was restored by loading the SR with the low-affinity Ca2+ buffer, citrate. Our data suggest that the arrhythmogenic CASQ2(D307H) mutation impairs SR Ca2+ storing and release functions and destabilizes the Ca2+-induced Ca2+ release mechanism by reducing the effective Ca2+ buffering inside the SR and/or by altering the responsiveness of the Ca2+ release channel complex to luminal Ca2+. These results establish at the cellular level the pathological link between CASQ2 mutations and the predisposition to adrenergically mediated arrhythmias observed in patients carrying CASQ2 defects.
authors.affiliation: Department of Physiology, Texas Tech University Health Sciences Center, Lubbock, Tex 79430-6551, USA.
authors.forename: Serge
authors.initials: S
authors.lastname: Viatchenko-Karpinski
authors.forename: Dmitry
authors.initials: D
authors.lastname: Terentyev
authors.forename: Inna
authors.initials: I
authors.lastname: Györke
authors.forename: Radmila
authors.initials: R
authors.lastname: Terentyeva
authors.forename: Pompeo
authors.initials: P
authors.lastname: Volpe
authors.forename: Silvia G
authors.initials: SG
authors.lastname: Priori
authors.forename: Carlo
authors.initials: C
authors.lastname: Napolitano
authors.forename: Alessandra
authors.initials: A
authors.lastname: Nori
authors.forename: Simon C
authors.initials: SC
authors.lastname: Williams
authors.forename: Sandor
authors.initials: S
authors.lastname: Györke
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D019943:Amino Acid Substitution; D000818:Animals; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology*; D002155:Calsequestrin / Q000235:genetics* / Q000502:physiology; D016757:Death, Sudden, Cardiac; D004285:Dogs; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D015640:Ion Channel Gating; D046911:Macromolecular Substances; D008297:Male; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000378:metabolism*; D017354:Point Mutation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D017180:Tachycardia, Ventricular / Q000235:genetics* / Q000378:metabolism
chemical_list: C443109:CASQ2 protein, human; D002155:Calsequestrin; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D019837:Ryanodine Receptor Calcium Release Channel