Abstract 18375: A Luminal Calcium Sensing Deficient Mutation of the Cardiac Ryanodine Receptor Diminishes Stress-Induced Ventricular Tachycardias in Calsequestrin Null Mice

Abstract

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease associated with syncope and sudden cardiac death. Naturally occurring mutations in the cardiac ryanodine receptor (RyR2) and calsequestrin (CASQ2) have been linked to CPVT. The sarcoplasmic reticulum (SR) calcium content and the sensitivity of RyR2 to activation by luminal calcium are some of the key factors determining the propensity for Store Overload Induced Calcium Release (SOICR) and SOICR-evoked VTs. We have recently found that the residue E4782 located in the helix bundle crossing (the ion gate) of the RyR2 calcium release channel acts as a SR store calcium sensor responsible for luminal calcium regulation of RyR2 and SOICR. Interestingly, we found that E4782Q mutation completely protected against SOCR-evoked VTs in a CPVT mouse model harboring the disease-causing RyR2 mutation R4496C. In this present study, we determined whether the E4782Q mutation is capable of rescuing the VT phenotype of the CASQ2 null mice, another mouse model of CPVT. We bred E4872Q+/- mice with the CASQ2 null mice to produce CASQ2-/- or CASQ2+/- with or without the heterozygous E4872Q mutation. After the injection of epinephrine (1.6mg/kg) and caffeine (120mg/kg), CASQ2-/- / E4872Q-/- and CASQ2+/- / E4872Q -/- mice showed long lasting VTs during 30-min of ECG recording (83% and 33%, respectively). On the other hand, CASQ2-/- / E4872Q+/- and CASQ2+/- / E4872Q -/- displayed little or no VTs (6.5% and 0.8%, respectively, p < 0.001, when compared with CASQ2-/- / E4872Q -/-, and CASQ2+/- /E4872Q -/-, n=7~9, for each group). Thus, the E4872Q mutation nearly completely rescued the CPVT phenotype in CASQ2 null mice. These observations indicate that targeting the luminal calcium sensor of the RyR2 calcium release channel represents a new and promising therapeutic strategy for treating CPVT and other calcium mediated cardiac arrhythmias.