Introduction: Heterozygous variants are most frequently associated with cardiac arrhythmias, including long QT syndrome, in the general population and within families. Genome-editing of human induced pluripotent stem cells (hiPSC) can be used to model arrhythmias. KCNH2 encodes for the hERG channel which is important for cardiomyocyte repolarization. It was previously reported that a heterozygous point mutation in the PAS domain of hERG was associated with familial long QT type 2 using an overexpression heterologous system. Here, we report that single copy deletion of KCNH2 by targeted gene-editing of the PAS domain displays the long QT phenotype in hiPSC-derived cardiomyocytes (hiPSC-CMs).
Hypothesis: Heterozygous deletion of KCNH2 prolongs repolarization and induces arrhythmias in hiPSC-CMs.
Methods: CRISPR/Cas9 and a highly efficient cloning supplement were used to edit KCNH2 and derive a clonal hiPSC line respectively. Control and edited isogenic hiPSC lines were differentiated to cardiomyocytes using an optimized cardiomyocyte differentiation media and protocol.
Results: A heterozygous four nucleotide deletion in exon 2 of KCNH2 was generated in a hiPSC line using CRISPR/Cas9. The deletion produced an early stop codon in the PAS domain located in the N-terminal region of the hERG channel. Single cell cloning efficiency was 20% for a seeding density of 7 hiPSCs per cm2. The clonal control and edited isogenic hiPSC lines were differentiated to cardiomyocytes. The isogenic hiPSC-CMs expressed >80% cTnT. Electrophysiological characterization was performed on hiPSC-CMs 28 days after differentiation. The hiPSC-CMs with the heterozygous hERG deletion had prolonged field potential durations (FPDs) with an irregular excitability profile and beat period. The control hiPSC-CMs had shorter FPDs and a stable excitability profile.
Conclusions: Single copy deletion of KCNH2 in hiPSC-CMs prolongs repolarization and generates arrhythmias characteristic of long QT syndrome.