Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6.
Cellular and Regenerative Medicine Centre, British Columbia Children's Hospital Research Institute, 938 W 28th Ave, Vancouver, BC, Canada V5Z 4H4.
Cardiovasc Res. 2023 Nov 25;119(15):2522-2535. doi: 10.1093/cvr/cvad155.
Long QT syndrome type 2 (LQTS2) is associated with inherited variants in the cardiac human ether-à-go-go-related gene (hERG) K+ channel. However, the pathogenicity of hERG channel gene variants is often uncertain. Using CRISPR-Cas9 gene-edited hiPSC-derived cardiomyocytes (hiPSC-CMs), we investigated the pathogenic mechanism underlying the LQTS-associated hERG R56Q variant and its phenotypic rescue by using the Type 1 hERG activator, RPR260243.
The above approaches enable characterization of the unclear causative mechanism of arrhythmia in the R56Q variant (an N-terminal PAS domain mutation that primarily accelerates channel deactivation) and translational investigation of the potential for targeted pharmacologic manipulation of hERG deactivation. Using perforated patch clamp electrophysiology of single hiPSC-CMs, programmed electrical stimulation showed that the hERG R56Q variant does not significantly alter the mean action potential duration (APD90). However, the R56Q variant increases the beat-to-beat variability in APD90 during pacing at constant cycle lengths, enhances the variance of APD90 during rate transitions, and increases the incidence of 2:1 block. During paired S1-S2 stimulations measuring electrical restitution properties, the R56Q variant was also found to increase the variability in rise time and duration of the response to premature stimulations. Application of the hERG channel activator, RPR260243, reduces the APD variance in hERG R56Q hiPSC-CMs, reduces the variability in responses to premature stimulations, and increases the post-repolarization refractoriness.
Based on our findings, we propose that the hERG R56Q variant leads to heterogeneous APD dynamics, which could result in spatial dispersion of repolarization and increased risk for re-entry without significantly affecting the average APD90. Furthermore, our data highlight the antiarrhythmic potential of targeted slowing of hERG deactivation gating, which we demonstrate increases protection against premature action potentials and reduces electrical heterogeneity in hiPSC-CMs.
长 QT 综合征 2 型（LQTS2）与心脏人 ether-à-go-go 相关基因（hERG）K+通道的遗传变异有关。然而，hERG 通道基因突变的致病性通常不确定。使用 CRISPR-Cas9 基因编辑 hiPSC 衍生的心肌细胞（hiPSC-CMs），我们研究了与 LQTS 相关的 hERG R56Q 变异的致病机制，以及使用 1 型 hERG 激活剂 RPR260243 进行的表型挽救。
上述方法能够阐明 R56Q 变异（主要加速通道失活的 N 端 PAS 结构域突变）引起心律失常的不明确因果机制，并对靶向药物调节 hERG 失活的潜力进行转化研究。使用单个 hiPSC-CMs 的穿孔膜片钳电生理学，程控电刺激显示 hERG R56Q 变异不会显著改变平均动作电位时程（APD90）。然而，在恒周长起搏时，R56Q 变异会增加 APD90 的逐搏变异性，在率过渡期间增加 APD90 的方差，并增加 2:1 阻滞的发生率。在测量电重构特性的 S1-S2 刺激配对中，还发现 R56Q 变异会增加早期刺激反应的上升时间和持续时间的变异性。应用 hERG 通道激活剂 RPR260243 可降低 hERG R56Q hiPSC-CMs 的 APD 方差，降低对早期刺激的反应变异性，并增加复极化后的不应期。
基于我们的发现，我们提出 hERG R56Q 变异导致 APD 动力学异质性，这可能导致复极的空间离散，并增加折返的风险，而不会显著影响平均 APD90。此外，我们的数据强调了靶向减缓 hERG 失活门控的抗心律失常潜力，我们证明这增加了对早期动作电位的保护，并减少了 hiPSC-CMs 中的电异质性。
