Identification of loss-of-function RyR2 mutations associated with idiopathic ventricular fibrillation and sudden death.

Xiaowei Zhong,Yingjie Liu,Ruiwu Wang,Carlo Napolitano,Wenting Guo,Peter P Jones,Yijun Tang,Silvia G Priori,Jinhong Wei,Lin Zhang,S.R Wayne Chen,Joe Z Zhang,Vern Hsen Tan

doi:10.1042/bsr20210209

Abstract

Mutations in cardiac ryanodine receptor (RyR2) are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT). Most CPVT RyR2 mutations characterized are gain-of-function (GOF), indicating enhanced RyR2 function as a major cause of CPVT. Loss-of-function (LOF) RyR2 mutations have also been identified and are linked to a distinct entity of cardiac arrhythmia termed RyR2 Ca2+ release deficiency syndrome (CRDS). Exercise stress testing (EST) is routinely used to diagnose CPVT, but it is ineffective for CRDS. There is currently no effective diagnostic tool for CRDS in humans. An alternative strategy to assess the risk for CRDS is to directly determine the functional impact of the associated RyR2 mutations. To this end, we have functionally screened 18 RyR2 mutations that are associated with idiopathic ventricular fibrillation (IVF) or sudden death. We found two additional RyR2 LOF mutations E4146K and G4935R. The E4146K mutation markedly suppressed caffeine activation of RyR2 and abolished store overload induced Ca2+ release (SOICR) in human embryonic kidney 293 (HEK293) cells. E4146K also severely reduced cytosolic Ca2+ activation and abolished luminal Ca2+ activation of single RyR2 channels. The G4935R mutation completely abolished caffeine activation of and [3H]ryanodine binding to RyR2. Co-expression studies showed that the G4935R mutation exerted dominant negative impact on the RyR2 wildtype (WT) channel. Interestingly, the RyR2-G4935R mutant carrier had a negative EST, and the E4146K carrier had a family history of sudden death during sleep, which are different from phenotypes of typical CPVT. Thus, our data further support the link between RyR2 LOF and a new entity of cardiac arrhythmias distinct from CPVT.

Highlights

The cardiac ryanodine receptor (RyR2) is a sarcoplasmic reticulum (SR) Ca2+ release channel essential for excitation–contraction coupling in the heart [1,2]
Most of these mutations are located in one of the four disease hotspots in RyR2 (Figure 1). All these mutation carriers were labelled as idiopathic ventricular fibrillation (IVF) patients or were associated with sudden unexplained death (SUD). It is unclear whether these mutations are associated with the typical catecholaminergic polymorphic ventricular tachycardia (CPVT) that is caused by GOF RyR2 mutations or with the newly identified RyR2-Ca2+ release deficiency syndrome (CRDS) that is caused by LOF RyR2 mutations [46]
It is generally believed that RyR2-associated ventricular arrhythmias (VAs) and sudden cardiac death (SCD) result from GOF defects of the RyR2 channel [2,3,4,5]

Summary

Introduction

The cardiac ryanodine receptor (RyR2) is a sarcoplasmic reticulum (SR) Ca2+ release channel essential for excitation–contraction coupling in the heart [1,2]. Recent three-dimensional structural studies revealed that a large number of disease-causing RyR2 mutations are clustered at domain interfaces [37,38,39,40,41,42,43,44] These mutations are thought to weaken domain–domain interactions that are important for stabilizing the closed state of the channel, facilitating channel opening and spontaneous SR Ca2+ release [45]. Overall, these observations have led to a general belief that disease-linked RyR2 mutations cause GOF defects, leading to inappropriate activation of the channel and excessive SR Ca2+ release that can precipitate into cardiac arrhythmias, cardiomyopathies, or sudden death [5]

Methods

Results

Conclusion