Complex aberrant splicing in the induced pluripotent stem cell–derived cardiomyocytes from a patient with long QT syndrome carrying KCNQ1-A344Aspl mutation

Abstract Background Long-QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1 , which encodes the α-subunit of the slow delayed rectifier potassium current (I Ks ) channel. We previously reported that a synonymous mutation, c.1032G>A, p.A344Aspl in KCNQ1 is most commonly identified in the genotyped LQT1 Japanese patients, and the aberrant splicing was analyzed in the lymphocytes isolated from patients' blood samples. However, the mechanisms underlying the observed processes in human cardiomyocytes remains unclear. Objective To establish and analyze patient-specific human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model carrying KCNQ1 -A344Aspl. Methods We generated hiPSCs from the peripheral blood mononuclear cells obtained from an LQT1 patient carrying KCNQ1 -A344Aspl. Using the differentiated cardiomyocytes, we analyzed splicing variants and performed electrophysiological studies. Results We identified seven aberrant RNA variants in A344Aspl-hiPSC-CMs, more complex compared with those in the peripheral lymphocytes. Multi-electrode array analysis revealed that 1 μM isoproterenol significantly prolonged the duration of corrected field potential in A344Aspl-hiPSC-CMs, compared with that in the controls. Additionally, 100 nM E-4031, I Kr blocker, was shown to induce early afterdepolarization-like waveforms in A344Aspl-hiPSC-CMs. Action potential durations (APDs) did not significantly differ between the hiPSC-CM groups. After administrating 500 nM isoproterenol, APDs of A344Aspl-hiPSC-CMs were significantly longer than those of the controls. ML277 and phenylboronic acid, I Ks activators, ameliorated the APDs of hiPSC-CMs. Conclusion We identified complex aberrant mRNA variants in the A344Aspl-hiPSC-CM model, and successfully recapitulated the clinical phenotypes of the patient with concealed LQT1. This model allows the investigation of the underlying mechanisms and development of novel therapies.