Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare genetic cardiac disorder triggering syncope or sudden cardiac death, in young individuals under stress conditions, despite normal cardiac structure and ECG at rest. Recently, a novel RyR2 gene mutation leading to CPVT, the RyR2-R169Q, has been identified in a young woman. Yet, its consequences on Ca2+ regulation remains unclear.

This work aims to identify the mechanisms of alteration in CPVT linked to the RyR2-R169Q mutation in a mouse model.

Arrhythmic events have been studied by electrocardiograms (ECGs) recording on Langendorff-perfused hearts from male and female wild-type (WT) and RyR2-R169Q mice. Ventricular cardiomyocytes were enzymatically isolated, loaded with the Ca2+ indicator Fluo-4 AM, to study Ca2+ signaling using confocal microscopy. Cellular proarrhythmogenic Ca2+ events were assessed in quiescent cells, and sarcoplasmic reticulum (SR) Ca2+ content was estimated via rapid perfusion of 10mM caffeine at baseline and under stress condition using isoproterenol (ISO) at 100nM. RyR2 sensitivity to Ca2+ was assessed in permeabilized cardiomycotes with 10% saponin at 10nM, 20nM, 30nM and 50nM of cytosolic Ca2+. Ca2+ transients were triggered by electrical field stimulation at 4Hz. Data analysis was performed using custom scripts on IDL software. The expression levels of RyR2 and its regulatory proteins were analyzed by western blotting and analysed on ImageJ.

Under ISO perfusion, RyR2-R169Q hearts exhibited arrhythmias in both male and female with higher propensity in female. In addition, cardiomyocytes isolated from female RyR2-R169Q showed at baseline, higher proarrhythmogenic events, compared to male as well as reduced SR Ca2+ load, and decreased Ca2+ transients. Morever, the mutation seems to accelerate the delay of appearance of the first arrhythmogenc event. In males, RyR2-R169Q increased automatic Ca2+ transients under stress, SR Ca2+ load, and decay time, while reducing Ca2+ transient amplitude with no change in expression levels of RyR2, SERCA2, PLB, NCX, FKBP12.6, CaM, CSQ, PKA, SPEG, and CaMKII compared to WT at baseline.

The RyR2-R169Q mutation causes gender-specific alterations in Ca2+ handling with an increase RyR2 activity, promoting pro-arrhythmogenic events. Further molecular analysis are needed to clarify the underlying mechanisms.