Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

Background: CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear.

Gradient-based parameter optimization method to determine membrane ionic current composition in human induced pluripotent stem cell-derived cardiomyocytes.

Premature cardiac myocytes derived from human induced pluripotent stem cells (hiPSC-CMs) show heterogeneous action potentials (APs), probably due to different expression patterns of membrane ionic currents. We developed a method for determining expression patterns of functional channels in terms of whole-cell ionic conductance (G) using individual spontaneous AP configurations. It has been suggested that apparently identical AP configurations can be obtained using different sets of ionic currents in mathematical models of cardiac membrane excitation.

Disrupted Ca1.2 selectivity causes overlapping long QT and Brugada syndrome phenotypes in the CACNA1C-E1115K iPS cell model.

Background: A missense mutation in the α1c subunit of voltage-gated L-type Ca channel-coding CACNA1C-E1115K, located in the Ca selectivity site, causes a variety of arrhythmogenic phenotypes.

Objective: We aimed to investigate the electrophysiological features and pathophysiological mechanisms of CACNA1C-E1115K in patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs).

Methods: We generated iPSCs from a patient carrying heterozygous CACNA1C-E1115K with overlapping phenotypes of long QT syndrome, Brugada syndrome, and mild cardiac dysfunction.

Loss-of-function mutations in cardiac ryanodine receptor channel cause various types of arrhythmias including long QT syndrome.

Aims: Gain-of-function mutations in RYR2, encoding the cardiac ryanodine receptor channel (RyR2), cause catecholaminergic polymorphic ventricular tachycardia (CPVT). Whereas, genotype-phenotype correlations of loss-of-function mutations remains unknown, due to a small number of analysed mutations. In this study, we aimed to investigate their genotype-phenotype correlations in patients with loss-of-function RYR2 mutations.

Electrophysiological Analysis of hiPSC-Derived Cardiomyocytes Using a Patch-Clamp Technique.

Electrophysiological analysis of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) using a patch-clamp technique enables the most precise evaluation of electrophysiological properties in single cells. Compared to multielectrode array (MEA) and membrane voltage imaging, patch-clamp recordings offer quantitative measurements of action potentials, and the relevant ionic currents which are essential for the research of disease modeling of inherited arrhythmias, safety pharmacology, and drug discovery using hiPSC-CMs. In this chapter, we describe the detail flow of patch-clamp recordings in hiPSC-CMs.

Propranolol Attenuates Late Sodium Current in a Long QT Syndrome Type 3-Human Induced Pluripotent Stem Cell Model.

Background: Long QT syndrome type 3 (LQT3) is caused by gain-of-function mutations in the gene, which encodes the α subunit of the cardiac voltage-gated sodium channel. LQT3 patients present bradycardia and lethal arrhythmias during rest or sleep. Further, the efficacy of β-blockers, the drug used for their treatment, is uncertain.

Phenotype-Based High-Throughput Classification of Long QT Syndrome Subtypes Using Human Induced Pluripotent Stem Cells.

For long QT syndrome (LQTS), recent progress in genome-sequencing technologies enabled the identification of rare genomic variants with diagnostic, prognostic, and therapeutic implications. However, pathogenic stratification of the identified variants remains challenging, especially in variants of uncertain significance. This study aimed to propose a phenotypic cell-based diagnostic assay for identifying LQTS to recognize pathogenic variants in a high-throughput manner suitable for screening.

Gene-Based Risk Stratification for Cardiac Disorders in Mutation Carriers.

Background: Mutations in (), which encodes lamin A and C, typically cause age-dependent cardiac phenotypes, including dilated cardiomyopathy, cardiac conduction disturbance, atrial fibrillation, and malignant ventricular arrhythmias. Although the type of mutations have been reported to be associated with susceptibility to malignant ventricular arrhythmias, the gene-based risk stratification for cardiac complications remains unexplored.

Methods And Results: The multicenter cohort included 77 mutation carriers from 45 families; cardiac disorders were retrospectively analyzed.

Development of a Patient-Derived Induced Pluripotent Stem Cell Model for the Investigation of SCN5A-D1275N-Related Cardiac Sodium Channelopathy.

Background: TheSCN5Agene encodes the α subunit of the cardiac voltage-gated sodium channel, Na1.5. The missense mutation, D1275N, has been associated with a range of unusual phenotypes associated with reduced Na1.

Allele-specific ablation rescues electrophysiological abnormalities in a human iPS cell model of long-QT syndrome with a CALM2 mutation.

Calmodulin is a ubiquitous Ca2+ sensor molecule encoded by three distinct calmodulin genes, CALM1-3. Recently, mutations in CALM1-3 have been reported to be associated with severe early-onset long-QT syndrome (LQTS). However, the underlying mechanism through which heterozygous calmodulin mutations lead to severe LQTS remains unknown, particularly in human cardiomyocytes.

Patient-Specific Human Induced Pluripotent Stem Cell Model Assessed with Electrical Pacing Validates S107 as a Potential Therapeutic Agent for Catecholaminergic Polymorphic Ventricular Tachycardia.

Introduction: Human induced pluripotent stem cells (hiPSCs) offer a unique opportunity for disease modeling. However, it is not invariably successful to recapitulate the disease phenotype because of the immaturity of hiPSC-derived cardiomyocytes (hiPSC-CMs). The purpose of this study was to establish and analyze iPSC-based model of catecholaminergic polymorphic ventricular tachycardia (CPVT), which is characterized by adrenergically mediated lethal arrhythmias, more precisely using electrical pacing that could promote the development of new pharmacotherapies.

Cardiac sodium channel mutation associated with epinephrine-induced QT prolongation and sinus node dysfunction.

Background: Long-QT syndrome (LQTS) is an inherited arrhythmia characterized by prolonged ventricular repolarization and malignant tachyarrhythmias. LQT1, LQT2, and LQT3 are caused by mutations in KCNQ1 (LQT1), KCNH2 (LQT2), and SCN5A (LQT3), which account for approximately 90% of genotyped LQTS patients. Most cardiac events in LQT1 patients occur during exercise, whereas patients with LQT3 tend to have arrhythmic events during rest or asleep.

Ultrastructural maturation of human-induced pluripotent stem cell-derived cardiomyocytes in a long-term culture.

Background: In the short- to mid-term, cardiomyocytes generated from human-induced pluripotent stem cells (hiPSC-CMs) have been reported to be less mature than those of adult hearts. However, the maturation process in a long-term culture remains unknown.

Methods And Results: A hiPSC clone generated from a healthy control was differentiated into CMs through embryoid body (EB) formation.