Casq2 deletion causes sarcoplasmic reticulum volume increase, premature Ca2+ release, and catecholaminergic polymorphic ventricular tachycardia
Björn C. Knollmann, … , Clara Franzini-Armstrong, Karl Pfeifer
Björn C. Knollmann, … , Clara Franzini-Armstrong, Karl Pfeifer
Published September 1, 2006
Citation Information: J Clin Invest. 2006;116(9):2510-2520. https://doi.org/10.1172/JCI29128.
View: Text | PDF
Research Article Cardiology

Casq2 deletion causes sarcoplasmic reticulum volume increase, premature Ca2+ release, and catecholaminergic polymorphic ventricular tachycardia

Abstract

Cardiac calsequestrin (Casq2) is thought to be the key sarcoplasmic reticulum (SR) Ca2+ storage protein essential for SR Ca2+ release in mammalian heart. Human CASQ2 mutations are associated with catecholaminergic ventricular tachycardia. However, homozygous mutation carriers presumably lacking functional Casq2 display surprisingly normal cardiac contractility. Here we show that Casq2-null mice are viable and display normal SR Ca2+ release and contractile function under basal conditions. The mice exhibited striking increases in SR volume and near absence of the Casq2-binding proteins triadin-1 and junctin; upregulation of other Ca2+-binding proteins was not apparent. Exposure to catecholamines in Casq2-null myocytes caused increased diastolic SR Ca2+ leak, resulting in premature spontaneous SR Ca2+ releases and triggered beats. In vivo, Casq2-null mice phenocopied the human arrhythmias. Thus, while the unique molecular and anatomic adaptive response to Casq2 deletion maintains functional SR Ca2+ storage, lack of Casq2 also causes increased diastolic SR Ca2+ leak, rendering Casq2-null mice susceptible to catecholaminergic ventricular arrhythmias.

Authors

Björn C. Knollmann, Nagesh Chopra, Thinn Hlaing, Brandy Akin, Tao Yang, Kristen Ettensohn, Barbara E.C. Knollmann, Kenneth D. Horton, Neil J. Weissman, Izabela Holinstat, Wei Zhang, Dan M. Roden, Larry R. Jones, Clara Franzini-Armstrong, Karl Pfeifer

×

Figure 2

Casq2–/– hearts lack calsequestrin, display no apparent upregulation of other SR Ca2+-binding proteins, and have decreased triadin 1 and junctin protein levels.

Options: View larger image (or click on image) Download as PowerPoint
Casq2–/– hearts lack calsequestrin, display no apparent upregulation of...
(A) Forty micrograms of homogenate protein from Casq2+/+, Casq2+/–, and Casq2–/– hearts and 30 μg of microsomal protein from control membranes from mouse heart (Casq2) and skeletal muscle (Casq1) were electrophoresed per lane and probed with anti-calsequestrin antibody. Cardiac (Casq2), skeletal muscle (Casq1), and Casq-like proteins are indicated. (B) 45Ca2+ overlay and Stains-all staining of SR membrane proteins obtained from Casq2+/+, Casq2+/–, and Casq2–/– hearts. Seventy-five micrograms of SR membrane protein was loaded per lane in duplicate and subjected to SDS-PAGE, then one-half of the gel was processed for 45Ca2+ overlay (left) and the other half stained with Stains-all (right). One microgram of purified canine Casq2 was also run as an internal standard. (C) Immunoblot detection of SR proteins in microsomes isolated from 10 Casq2+/+, 10 Casq2+/–, and 10 Casq2–/– hearts. Forty micrograms of microsomal protein were electrophoresed per lane, transferred to nitrocellulose paper, and probed with the antibodies indicated on the left. (D) Quantification of protein expression levels. Data represent average values for 4 hearts per genotype expressed relative to Casq2+/+ values. RyR2, cardiac isoform of the RyR; SER, SERCA2a or cardiac isoform of the Ca2+ pump; TRN, triadin 1 or major cardiac isoform of triadin; JCT, junctin; *P < 0.05.