Subclinical abnormalities in sarcoplasmic reticulum Ca²⁺ release promote eccentric myocardial remodeling and pump failure death in response to pressure overload

Objectives: This study sought to explore whether subclinical alterations of sarcoplasmic reticulum (SR) Ca²⁺ release through cardiac ryanodine receptors (RyR2) aggravate cardiac remodeling in mice carrying a human RyR2 ^R4496C+/- gain-of-function mutation in response to pressure overload. Background: RyR2 dysfunction causes increased diastolic SR Ca²⁺ release associated with arrhythmias and contractile dysfunction in inherited and acquired cardiac diseases, such as catecholaminergic polymorphic ventricular tachycardia and heart failure (HF). Methods: Functional and structural properties of wild-type and catecholaminergic polymorphic ventricular tachycardia-associated RyR2^R4496C+/- hearts were characterized under conditions of pressure overload induced by transverse aortic constriction (TAC). Results: Wild-type and RyR2^R4496C+/- hearts had comparable structural and functional properties at baseline. After TAC, RyR2 ^R4496C+/- hearts responded with eccentric hypertrophy, substantial fibrosis, ventricular dilation, and reduced fractional shortening, ultimately resulting in overt HF. RyR2^R4496C+/--TAC cardiomyocytes showed increased incidence of spontaneous SR Ca²⁺ release events, reduced Ca²⁺ transient peak amplitude, and SR Ca²⁺ content as well as reduced SR Ca²⁺-ATPase 2a and increased Na⁺/Ca ²⁺-exchanger protein expression. HF phenotype in RyR2 ^R4496C+/--TAC mice was associated with increased mortality due to pump failure but not tachyarrhythmic events. RyR2-stabilizer K201 markedly reduced Ca²⁺ spark frequency in RyR2^R4496C+/--TAC cardiomyocytes. Mini-osmotic pump infusion of K201 prevented deleterious remodeling and improved survival in RyR2^R4496C+/--TAC mice. Conclusions: The combination of subclinical congenital alteration of SR Ca ²⁺ release and pressure overload promoted eccentric remodeling and HF death in RyR2^R4496C+/- mice, and pharmacological RyR2 stabilization prevented this deleterious interaction. These findings suggest potential clinical relevance for patients with acquired or inherited gain-of-function of RyR2-mediated SR Ca²⁺ release.