Increased Heart Failure Development After Pressure Overload-Induced Hypertrophy in Mice with a RyR2-R4496C +/- Knock-In Mutation

Abstract

Elevated spontaneous Ca2+ release from the sarcoplasmic reticulum (SR) Ca2+ release channel (ryanodine receptor-RyR2) due to a gain-of-function of the RyR2 defect contributes to contractile dysfunction and arrhythmias in heart failure (HF). However, whether increased diastolic SR Ca2+ release can promote HF is yet unclear.RyR2R4496C+/- mice associated with an increased SR Ca2+ leak and wild-type (WT) littermates underwent surgery with (TAC) or without (Sham) transverse aortic constriction. Transthoracic echocardiography was performed 1 and 3 weeks post-surgery. Hearts and lungs were dissected, weighed and normalized to tibia length. Gross morphology and collagen content were examined in paraffin-embedded heart slices stained with hematoxylin/eosin and picrosirius red, respectively. Arrhythmias were monitored (24h) with radiotelemetry. Data are presented as mean±S.E.M.RyR2R4496C+/--Sham hearts exhibited no gross baseline changes in ventricular structure and function and fibrosis compared to WT-Sham. 1 week after TAC, WT-TAC mice showed concentric left ventricular (LV) hypertrophy with preserved ejection fraction. In contrast, RyR2R4496C+/--TAC mice exhibited eccentric hypertrophy and significant deterioration of phenotypic changes associated with the transition to HF, such as chamber dilation (LV end-diastolic diameter;WT:-1.4±3%,RyR2R4496C+/-:19.7±3.6%,P<0.05) and reduced ejection fraction (WT:61.7±3.2%,RyR2R4496C+/-:39.4±2.8%,n=14,P<0.05). 3 weeks post-TAC, relative heart weight was increased in RyR2R4496C+/- mice vs. WT-TAC (WT:9.4±0.3mg/mm,RyR2R4496C+/-:11.3±0.7mg/mm,n=13-23,P<0.05). The HF phenotype in RyR2R4496C+/--TAC mice further aggravated 3 weeks after TAC, ultimately resulting in increased relative lung weight (WT:17±8%,RyR2R4496C+/-:101±21%,n=16-20,P<0.05). Hypertrophy continued to increase in RyR2R4496C+/--TAC mice, while it saturated in WT-TAC mice (LV mass;WT:65.2±8.1%,RyR2R4496C+/-:119±13.3%,n=14-21,P<0.05). Strikingly, RyR2R4496C+/--TAC mice did not die for a primary arrhythmic death, but with a progressive electrical deterioration resembling an electromechanical dissociation (mortality rate:60% 4 weeks post-TAC,P<0.05).In summary, HF development was facilitated in RyR2-R4496C+/- mice after pressure overload-induced hypertrophy. Thus, spontaneous SR Ca2+ leak per se may be causally related to the development of HF.