Suppressed RyR2 Function Represents a Common Cause of Idiopathic Ventricular Fibrillation and Sudden Cardiac Death

Abstract

Cardiac Ryanodine Receptor (RyR2) is the major intracellular calcium release channel located in the sarcoplasmic reticulum. A large number of mutations in RyR2 have been linked to inherited cardiac arrhythmias (CPVT, catecholaminergic polymorphic ventricular tachycardia and IVF, idiopathic ventricular fibrillation) and sudden cardiac death. We previously demonstrated that in contrast to CPVT RyR2 mutations, the IVF RyR2 mutation A4860G suppresses RyR2 function. However, A4860G represents the only IVF RyR2 mutation that has been functionally characterized to date. To determine how common suppression-of-function RyR2 mutations are, we systematically characterized 27 RyR2 mutations that are associated with IVF or sudden cardiac death. Each of these mutations was generated by site-directed mutagenesis and expressed in HEK293 cells. Ca release assays revealed that 7 of these mutations suppress or abolish caffeine-induced Ca release. Single cell Ca imaging studies also indicated that these suppression- or loss-of-function RyR2 mutations reduce or abolish the propensity for store-overload induced Ca release (SOICR) in HEK293 cells. In addition, single channel analysis showed that these mutations significantly reduce the response of the channel to activation by cytosolic and luminal Ca. These observations demonstrate, for the first time, that suppressed or loss of RyR2 function may be a common mechanism underlying idiopathic ventricular fibrillation, which is opposite to the gain-of-function RyR2 mutations associated with CPVT. Thus, understanding the exact molecular defects of disease-causing RyR2 mutations will help to develop novel approaches to the diagnosis and personalized treatment of these lethal cardiac arrhythmias (Supported by CFI, CIHR, AIHS, and LCIA).