Influence of genetic predisposition as a mechanism in the development of Arrythmia-induced cardiomyopathy

Aim/Hypothesis:
Arrhythmia-induced cardiomyopathy (AIC) is clinically defined as persistent arrhythmia with dilated cardiomyopathy and left ventricular dysfunction (LVSD), which is reversible with treatment of the underlying arrhythmia. The cause and molecular mechanisms for AIC have been incompletely understood. It remains unclear why some patients develop AIC with a similar burden of atrial fibrillation, and others do not. Thus, we hypothesized that a genetic predisposition contributes to the development of AIC.

Methods and Results:
Using whole-exome sequencing analysis, we analyzed the genetic background of 6 AIC patients with precisely diagnosed AIC and detected a novel truncating mutation in exon 1 of the KCNQ1 gene encoding a potassium channel in the heart. From fibroblasts of this patient, we created an induced pluripotent stem cell (iPSC) line and subsequently generated a KCNQ1 rescue line (TCM3.5_KCNQ1_res) using CRISPR-Cas9. Pluripotency of these iPSCs was analyzed and they were differentiated over 2 months into functional iPSC cardiomyocytes (iPSC-CM). Cell lines were compared to a healthy control and an iPSC cell line from a patient with persistent tachyarrhythmia over several months who did not develop AIC. Immunofluorescence staining of α-actinin and titin revealed a dysregulation in sarcomeric structure of iPSC-CM in the AIC patient as well as in the rescue line compared to healthy control. The introduction of rescue KCNQ1 did not demonstrate any discernible improvement in sarcomere structure. The effect of persistent tachycardia on iPSC-CM was evaluated by chronic culture field pacing of the cells by either tachycardia (Tachy, 120 bpm) or normal frequency/sinus rhythm (SR, 60 bpm) for 24 hours or 7 days. Using whole-cell current clamp, we observed a significant prolongation of action potential duration (APD80) in the AIC patient after 24 hours or 7 days Tachy stimulation compared to SR and basal level with a significant rescue in the KCNQ1 rescue line. The effect of tachycardia on Ca²⁺-transients was assessed via Fura-2 AM epifluorescence measurements. Interestingly, after either SR or Tachy field stimulation, Ca²⁺-transient amplitude was already significantly reduced in AIC patient’s iPSC-CMs compared to control patient under the same conditions. Therefore, tachycardia stimulation had no additional effect in AIC patients. The decreased Ca²⁺-transient amplitude after SR/Tachy stimulation was completely rescued in TCM-KCNQ1-res-CMs. Decreased Ca²⁺-transient amplitude could be molecularly explained by activated CamKII under the same conditions demonstrated by enhanced phosphorylation of CamKII using Western Blot analysis. Visual contraction measurements showed an increased time to bl(80%) and t to peak(90%) in AIC patient CMs compared to healthy control, with the effect also being rescued in iPSC-CM of the KCNQ1 rescue line.

Conclusion:
Our results indicate that KCNQ1 mutations significantly influence the functionality and cellular electrophysiology of iPSC-CM, highlighting the potential impact of genetic predisposition on AIC development. However, this study provides evidence that combinations of cardiomyopathy- as well as ion channel-associated mutations functionally alter cellular electrophysiology and seem to play an important role in the development of AIC. Therefore, examination of the precise mutation via CRISPR-Cas9 genome editing may define a new translational understanding of AIC.