Impaired Right Ventricular Calcium Cycling Is an Early Risk Factor in R14del-Phospholamban Arrhythmias

Abstract

The inherited mutation (R14del) in the calcium regulatory protein phospholamban (PLN) is linked to malignant ventricular arrhythmia with poor prognosis starting at adolescence. However, the underlying early mechanisms that may serve as prognostic factors remain elusive. This study generated humanized mice in which the endogenous gene was replaced with either human wild type or R14del-PLN and addressed the early molecular and cellular pathogenic mechanisms. R14del-PLN mice exhibited stress-induced impairment of atrioventricular conduction, and prolongation of both ventricular activation and repolarization times in association with ventricular tachyarrhythmia, originating from the right ventricle (RV). Most of these distinct electrocardiographic features were remarkably similar to those in R14del-PLN patients. Studies in isolated cardiomyocytes revealed RV-specific calcium defects, including prolonged action potential duration, depressed calcium kinetics and contractile parameters, and elevated diastolic Ca-levels. Ca-sparks were also higher although SR Ca-load was reduced. Accordingly, stress conditions induced after contractions, and inclusion of the CaMKII inhibitor KN93 reversed this proarrhythmic parameter. Compensatory responses included altered expression of key genes associated with Ca-cycling. These data suggest that R14del-PLN cardiomyopathy originates with RV-specific impairment of Ca-cycling and point to the urgent need to improve risk stratification in asymptomatic carriers to prevent fatal arrhythmias and delay cardiomyopathy onset.

Aberrant PLN-R14del Protein Interactions Intensify SERCA2a Inhibition, Driving Impaired Ca2+ Handling and Arrhythmogenesis

“…Consequent aberrations included the prolongation of action potential duration, increased spontaneous aftercontractions, and increased propensity to arrhythmias [16]. In particular, while infrequent premature ventricular contractions were observed under basal conditions, PLN-R14del mice exhibited stress-induced atrioventricular conduction impairment, delayed ventricular activation, prolonged repolarization, and ventricular tachyarrhythmias that originated from the right ventricle [16]. Importantly, most of these electrocardiographic alterations were similar to those seen in PLN-R14del patients [16].…”

“…Emerging evidence from PLN-R14del mouse models, as well as human-derived cardiomyocytes, has established aberrant Ca 2+ cycling as an underlying pathology of the PLN-R14del mutation [13,16,18]. In the recently reported humanized PLN-R14del mouse model, detailed analysis of contractile parameters revealed considerable SR Ca 2+ defects, including depressed Ca 2+ kinetics and contractile parameters, as well as elevated diastolic Ca 2+ levels due to the super-inhibition of SERCA2a activity.…”

“…This was found to trigger increased Ca 2+ -leaks and Ca 2+ sparks, which were associated with increased CaMKII activity. Consequent aberrations included the prolongation of action potential duration, increased spontaneous aftercontractions, and increased propensity to arrhythmias [16]. In particular, while infrequent premature ventricular contractions were observed under basal conditions, PLN-R14del mice exhibited stress-induced atrioventricular conduction impairment, delayed ventricular activation, prolonged repolarization, and ventricular tachyarrhythmias that originated from the right ventricle [16].…”

“…Based on initial findings from PLN-R14del overexpression in a heterologous cell culture system as well as in the mouse heart, PLN-R14del was proposed to exert super-inhibitory effects on SERCA2a activity, leading to cardiac remodeling and early death [5]. Additional evidence has recently emerged from numerous studies on human patients and/or patient-derived cardiomyocytes (iPSC-CMs), and various PLN-R14del animal models [12][13][14][15][16][17][18]. These studies have revealed multiple defects associated with the PLN-R14del mutation, including impaired Ca 2+ homeostasis [12][13][14]16,18], electrical remodeling [19], unfolded protein response (UPR) activation [20], and protein aggregation [15,21,22].…”

“…Additional evidence has recently emerged from numerous studies on human patients and/or patient-derived cardiomyocytes (iPSC-CMs), and various PLN-R14del animal models [12][13][14][15][16][17][18]. These studies have revealed multiple defects associated with the PLN-R14del mutation, including impaired Ca 2+ homeostasis [12][13][14]16,18], electrical remodeling [19], unfolded protein response (UPR) activation [20], and protein aggregation [15,21,22].…”