A Pathogenic Titin Missense Mutation in hiPSC-Derived Cardiomyocytes Predisposes to Ventricular Fibrillation in Acute ST-Segment Elevation Myocardial Infarction

Ying-ying JiYang WuJi SunXiao-Xiong LinXu-Miao ChenCheng-Cheng JiLijuan LiuYun-Jiu ChengSUHUA WU^*

• Sun Yat-sen University, Guangzhou, China

Background There is a growing evidence suggesting that the genetic basis may play a crucial role in the development of ventricular fibrillation (VF) subsequent to acute ST-segment elevation myocardial infarction (STEMI). Previous research has demonstrated that both truncating and missense mutations in the TTN gene, which encodes a large cellular structural protein, are linked to arrhythmogenesis. However, the precise role of TTN mutations in the onset of primary VF after acute STEMI remains poorly understood. Objectives The primary objective of the present study was to comprehensively determine the role and elucidate the electrophysiological mechanism of TTN missense mutations in the development of VF after acute STEMI. This was achieved by leveraging the unique capabilities of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Methods Through whole genome sequencing, TTN mutations were detected in four out of six unrelated patients who experienced VF after STEMI (STEMI/VF). Induced pluripotent stem cells were successfully generated from the peripheral blood mononuclear cells obtained from a 47-year - old male harboring a novel TTN variant (c.43803T>A/ p.D14601E) and an unrelated healthy control individual. Subsequently, a well - established protocol of directed differentiation was employed to create iPSC-CMs. Rigorous electrophysiological and functional analyses were then carried out to unearth the underlying mechanisms responsible for the observed phenotypes. Results Compared with the control iPSC-CMs, the iPSC-CMs derived from the patient with STEMI/VF displayed a notable shortening of the action potential duration (APD). Specifically, the peak sodium channel current (INa) and L-type calcium channel current (ICa-L) of the STEMI/VF iPSC-CMs were significantly reduced by 51.64% and 71.56%, respectively. Moreover, the expression of total TTN in STEMI/VF iPSC-CMs was downregulated. Confocal microscopy analysis revealed that although STEMI/VF iPSC-CMs retained the ability to assemble well-aligned titin striations similar to control cells, there were localized disruptions in the sarcomeric patterning. Conclusions The iPSC-CMs obtained from the patient carrying a TTN missense mutation and who suffered from VF after STEMI exhibited a decrease in INa、ICa-L and shortened APD, providing novel insights into the potential electrophysiological mechanisms underlying the development of VF in the context of acute STEMI and TTN mutations.