# A pathogenic titin missense mutation in hiPSC-derived cardiomyocytes predisposes to ventricular fibrillation in acute ST-segment elevation myocardial infarction

## TL;DR

A TTN gene mutation in heart cells increases risk of dangerous heart rhythms after heart attacks, according to a study using patient-derived stem cells.

## Contribution

This study identifies a novel TTN missense mutation and its electrophysiological impact on ventricular fibrillation after STEMI using hiPSC-derived cardiomyocytes.

## Key findings

- TTN missense mutation leads to reduced sodium and calcium currents in cardiomyocytes.
- Action potential duration is significantly shortened in patient-derived cardiomyocytes.
- TTN mutation causes localized sarcomeric disruptions despite normal titin striation assembly.

## Abstract

There is growing evidence that genetic factors may play a crucial role in the development of ventricular fibrillation (VF) following acute ST-segment elevation myocardial infarction (STEMI). Previous studies have 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.

The primary objective of this study was to comprehensively determine the role and elucidate the electrophysiological mechanism of TTN missense mutations in VF development after acute STEMI. This was achieved by leveraging the unique capabilities of human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).

Whole-genome sequencing identified TTN mutations 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 carrying a novel TTN variant (c.43803T>A/p.D14601E) and from an unrelated healthy control. Subsequently, a directed differentiation protocol was employed to create iPSC-CMs, followed by rigorous electrophysiological and functional analyses to elucidate the mechanisms underlying the observed phenotypes.

Compared with the control iPSC-CMs, the patient-derived iPSC-CMs with STEMI/VF exhibited a significant shortening of the action potential duration (APD). Specifically, 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. However, the transient outward potassium current remained comparable between the two groups. 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.

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.