Abstract 1398: A Mutation in Calsequestrin CSQD307H Impairs SR Ca2+ Storage and Release Functions and Causes Polymorphic Ventricular Tachycardia in Mice
Ca2+ storage in the SR lumen is buffered by a high capacity, moderate affinity Ca2+-binding protein named Calsequestrin (CSQ). It was reported that a point mutation in cardiac CSQ, which alters an aspartate at position 307 to a histidine, is associated with Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) in humans. CPVT is a disease that is characterized by a form of ventricular tachycardia that can rapidly progress into ventricular fibrillation and sudden cardiac death. The goal of this study was to investigate in a TG mouse model, whether mutation in CSQ (CSQD307H) is responsible for altered Ca2+ handling and the CPVT phenotype. Three separate TG lines over-expressing the CSQ mutant protein by 2- to 6-fold were generated. Over-expression of CSQD307H did not affect the expression of other SR proteins and did not result in cardiac hypertrophy and or structural changes. Cardiac function was unaffected in TG hearts. On the other hand when challenged with isoproterenol and caffeine, mice developed complex ventricular arrhythmias, including non-sustained ventricular tachycardia, as monitored by continuous ECG recordings. In addition, administration of Isoproterenol and caffeine (100 μM) in myocytes isolated from these TG mice caused profound disturbances in Ca2+ cycling and membrane potential, manifested by extra systolic Ca2+ transients, delayed afterdepolarizations (DADs) and action potentials. The TG myocytes showed a significant decrease in the Ca2+ transient amplitude and no change in SR Ca2+ content, whereas the frequency of spontaneous Ca2+ sparks was significantly increased compared to control. Our data suggest that the CASQ2 (D307H) mutation impairs the Ca2+ storing and release functions of the SR and predisposes the Ca release mechanism to spontaneous activation. In conclusion we propose that CSQ plays a key role in the regulation of SR Ca2+ release and mutations of this protein can cause CPVT.