B. Eisen

Functional abnormalities in iPSC-derived cardiomyocytes generated from CPVT1 and CPVT2 patients carrying ryanodine or calsequestrin mutations.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia characterized by syncope and sudden death occurring during exercise or acute emotion. CPVT is caused by abnormal intracellular Ca2+ handling resulting from mutations in the RyR2 or CASQ2 genes. Because CASQ2 and RyR2 are involved in different aspects of the excitation‐contraction coupling process, we hypothesized that these mutations are associated with different functional and intracellular Ca²+ abnormalities. To test the hypothesis we generated induced Pluripotent Stem Cell‐derived cardiomyocytes (iPSC‐CM) from CPVT1 and CPVT2 patients carrying the RyR2R420Q and CASQ2D307H mutations, respectively, and investigated in CPVT1 and CPVT2 iPSC‐CM (compared to control): (i) The ultrastructural features; (ii) the effects of isoproterenol, caffeine and ryanodine on the [Ca2+]i transient characteristics. Our major findings were: (i) Ultrastructurally, CASQ2 and RyR2 mutated cardiomyocytes were less developed than control cardiomyocytes. (ii) While in control iPSC‐CM isoproterenol caused positive inotropic and lusitropic effects, in the mutated cardiomyocytes isoproterenol was either ineffective, caused arrhythmias, or markedly increased diastolic [Ca2+]i. Importantly, positive inotropic and lusitropic effects were not induced in mutated cardiomyocytes. (iii) The effects of caffeine and ryanodine in mutated cardiomyocytes differed from control cardiomyocytes. Our results show that iPSC‐CM are useful for investigating the similarities/differences in the pathophysiological consequences of RyR2 versus CASQ2 mutations underlying CPVT1 and CPVT2 syndromes.

Investigating the cardiac pathology of SCO2-mediated hypertrophic cardiomyopathy using patients induced pluripotent stem cell-derived cardiomyocytes

Mutations in SCO2 are among the most common causes of COX deficiency, resulting in reduced mitochondrial oxidative ATP production capacity, often leading to hypertrophic cardiomyopathy (HCM). To date, none of the recent pertaining reports provide deep understanding of the SCO2 disease pathophysiology. To investigate the cardiac pathology of the disease, we were the first to generate induced pluripotent stem cell (iPSC)‐derived cardiomyocytes (iPSC‐CMs) from SCO2‐mutated patients. For iPSC generation, we reprogrammed skin fibroblasts from two SCO2 patients and healthy controls. The first patient was a compound heterozygote to the common E140K mutation, and the second was homozygote for the less common G193S mutation. iPSC were differentiated into cardiomyocytes through embryoid body (EB) formation. To test the hypothesis that the SCO2 mutation is associated with mitochondrial abnormalities, and intracellular Ca2+‐overload resulting in functional derangements and arrhythmias, we investigated in SCO2‐mutated iPSC‐CMs (compared to control cardiomyocytes): (i) the ultrastructural changes; (ii) the inotropic responsiveness to β‐adrenergic stimulation, increased [Ca2+]o and angiotensin‐II (AT‐II); and (iii) the Beat Rate Variability (BRV) characteristics. In support of the hypothesis, we found in the mutated iPSC‐CMs major ultrastructural abnormalities and markedly attenuated response to the inotropic interventions and caffeine, as well as delayed afterdepolarizations (DADs) and increased BRV, suggesting impaired SR Ca2+ handling due to attenuated SERCA activity caused by ATP shortage. Our novel results show that iPSC‐CMs are useful for investigating the pathophysiological mechanisms underlying the SCO2 mutation syndrome.