CPVT, a rare genetic cardiac disease, leads to syncope or sudden death following a stress condition in young individuals, despite normal cardiac structure and resting electrocardiograms. A new mutation, R169Q, in the RyR2 gene has been discovered in a young woman with CPVT, but its exact impact on Ca2+ regulation is still unknown.

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

ECG were recorded in langendorff perfused hearts from WT and RyR2-R169Q mice of both sexes. Ventricular cardiomyocytes were isolated using the Langendorf technique, loaded with Fluo-4 AM Ca2+ dye and Ca2+ handling recorded by confocal microscopy. Ca2+ transients were elicited by electrical field stimulation at 1Hz, 2Hz, and 4Hz. Ca2+ sparks were recorded in quiescent cells and sarcoplasmic reticulum (SR) Ca2+ load assessed by rapid caffeine (10mM) perfusion. To mimic stress conditions seen in CPVT, data were collected at baseline and under 100nM Isoproterenol stimulation. Image analysis was performed using custom routines in IDL software, and protein expression of RyR2 and its regulatory proteins was evaluated via western blotting.

Premature ventricular contractions were seen in RyR2-R169Q ECGs under ISO perfusion. In isolated cells, the R169Q mutation led to an increase in pro-arrhythmic events, such as Ca2+ waves and automatic Ca2+ transients, under 100nM Isoproterenol without altering the amplitude of Ca2+ transients. Isoproterenol failed to increase SR Ca2+ load in RyR2-R169Q cardiomyocytes but it increased the Ca2+ sparks frequency normalized by the Ca2+ load. In R169Q male ventricles, RyR2, SERCA2, PLB, NCX, FKBP12.6, CaM, CSQ, PKA, SPEG, and CaMKII protein expression were statistically not different compared to WT male ventricles under basal condition. Expression of SERCA2, NCX, and JPH2 appears consistent between male and female mouse ventricles.

The R169Q mutation likely elevates RyR2 activity, leading to more pro-arrhythmogenic events in CPVT. Future analyses aim to determine the underlying molecular mechanism.