Calsequestrin 2 (CASQ2) mutations increase expression of calreticulin and ryanodine receptors, causing catecholaminergic polymorphic ventricular tachycardia
Lei Song, … , Christine E. Seidman, J.G. Seidman
Lei Song, … , Christine E. Seidman, J.G. Seidman
Published July 2, 2007
Citation Information: J Clin Invest. 2007;117(7):1814-1823. https://doi.org/10.1172/JCI31080.
View: Text | PDF
Research Article

Calsequestrin 2 (CASQ2) mutations increase expression of calreticulin and ryanodine receptors, causing catecholaminergic polymorphic ventricular tachycardia

Abstract

Catecholamine-induced polymorphic ventricular tachycardia (CPVT) is a familial disorder caused by cardiac ryanodine receptor type 2 (RyR2) or calsequestrin 2 (CASQ2) gene mutations. To define how CASQ2 mutations cause CPVT, we produced and studied mice carrying a human D307H missense mutation (CASQ307/307) or a CASQ2-null mutation (CASQΔE9/ΔE9). Both CASQ2 mutations caused identical consequences. Young mutant mice had structurally normal hearts but stress-induced ventricular arrhythmias; aging produced cardiac hypertrophy and reduced contractile function. Mutant myocytes had reduced CASQ2 and increased calreticulin and RyR2 (with normal phosphorylated proportions) but unchanged calstabin levels, as well as reduced total sarcoplasmic reticulum (SR) Ca2+, prolonged Ca2+ release, and delayed Ca2+ reuptake. Stress further diminished Ca2+ transients, elevated cytosolic Ca2+, and triggered frequent, spontaneous SR Ca2+ release. Treatment with Mg2+, a RyR2 inhibitor, normalized myocyte Ca2+ cycling and decreased CPVT in mutant mice, indicating RyR2 dysfunction was critical to mutant CASQ2 pathophysiology. We conclude that CPVT-causing CASQ2 missense mutations function as null alleles. In the absence of CASQ2, calreticulin, a fetal Ca2+-binding protein normally downregulated at birth, remains a prominent SR component. Adaptive changes to CASQ2 deficiency (increased posttranscriptional expression of calreticulin and RyR2) maintained electrical-mechanical coupling, but increased RyR2 leakiness, a paradoxical response further exacerbated by stress. The central role of RyR2 dysfunction in CASQ2 deficiency unifies the pathophysiologic mechanism underlying CPVT due to RyR2 or CASQ2 mutations and suggests a therapeutic approach for these inherited cardiac arrhythmias.

Authors

Lei Song, Ronny Alcalai, Michael Arad, Cordula M. Wolf, Okan Toka, David A. Conner, Charles I. Berul, Michael Eldar, Christine E. Seidman, J.G. Seidman

×

Figure 1

Introduction of missense mutation D307H and exon 9 deletion into the mouse CASQ2 gene.

Options: View larger image (or click on image) Download as PowerPoint
Introduction of missense mutation D307H and exon 9 deletion into the mou...
(A) The mouse CASQ2 gene is encoded in 11 exons spread over 70 kb. The WT (+), D307H knock-in (307) and exon 9–deletion KO (ΔE9) alleles are contained on a 15-kb XmaI restriction fragment, which encodes exons 9–11. (B) The genotypes of WT (+/+), D307H-knockin heterozygous (307/+) and homozygous (307/307), and exon 9–deletion KO heterozygous (ΔE9/+) and homozygous (ΔE9/ΔE9) mice were determined by size characterization of PCR-amplified DNA fragments. The WT and Neo-excised alleles of D307H-knockin mice were amplified using primers 307F and 307R, which yielded 140-bp and 250-bp fragments, respectively (lanes 1–3). The WT and ΔE9 alleles were amplified with primers F1, F2, and R, producing 250-bp and 400-bp fragments, respectively (lanes 4–6). The D307H allele was amplified by PCR primers 307FB and 307RB, which yielded a 750-bp fragment. After BamHI digestion, the D307H allele produced 500-bp and 250-bp bands (lanes 7–9). M, molecular marker.