Comparison between hiPS-CM from RyR2-R420Q CPVT Patients and KI Mice Bearing the Same Mutation

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic arrhythmia that manifests by syncope or sudden death in children and young adults under stress conditions without obvious cardiac structural abnormality. A CPVT mutation located on RyR2 N terminal portion has been identified in two Spanish families (RyR2R420Q). KI mice heterozygous for this mutation presented bradycardia and sino-atrial node dysfunction. Here we generated human induced pluripotent stem cell (hiPSC) from two brothers (one with mutation, the other without mutation as control) of this family and differentiated them into cardiomyocytes (hiPS-CM). In order to verify that the differentiated cells were well cardiomyocytes, we did immunofluorescence labelling for alpha-actinin and RyRs, and compared them with RyR2R420Q KI mice cardiomyocytes with superresolution microscopy. The calcium transient was studied by confocal microscopy as well as the action potential (AP) by micro-electrode technique. The AP duration was longer in RyR2R420Q cells. hiPS-CM are immature cardiomyocytes and contract spontaneously. The beating rate of CPVT hiPS-CM was slower than those of cells derived from the control person. We found all the cells without mutation could follow 1HZ of electrical stimulation while only 55.26% mutation carrying cells could. [Ca2+]i transient was slower both in basal conditions, and after beta-adrenergic stimulation with 100 nM isoproterenol in mutated group. Sarcoplasmic reticulum (SR) Ca2+ load was estimated by rapid caffeine (10mM) application. hiPS-CM from the RyR2R420Q carrier presented smaller SR Ca2+ load than those from the control person. Even if SR Ca2+ load was smaller in RyR2R420Q cells, they often presented proarrythmogenic behavior such as Ca2+ waves. The fact was further enhanced during beta-adrenergic stimulation, pointing to this model as a valuable tool to study the CPVT disease in human cells.