Po-01-158 modeling an atrial fibrillation-causing titin mutation using human ipsc-derived atrial cardiomyocytes

Atrial fibrillation (AF) affects more than 33 million people worldwide and, if left untreated, can lead to increased morbidity and mortality. Although AF has been classified as an ‘ion channelopathy’, next-generation sequencing has identified mutations in sarcomeric proteins like TTN, the gene encoding titin, that are associated with AF. Despite progress in understanding the genetic basis of AF, the translation of these discoveries to the bedside care of patients has been limited due to challenges in understanding the myocardial substrate for AF, especially that develops from the mutation in the structural protein. As human atrial tissue is rarely available and animal models are mechanistically limited, our goal is to model AF using mature human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs) by a CRISPR-Cas9-mediated single amino acid substitution of a rare missense ethnic-specific mutation (TTN_T32756I) in an immunoglobulin (Ig)-like domain of the A-band of titin that is enriched in AF-causing pathogenic variants. Isogenic TTN_T32756I hiPSC-aCM mutants were generated using the CRISPR-Cas9 technique. Cells were matured either with metabolic conditioning or co-culturing with atrial fibroblasts in a micropatterned platform. We used confocal microscopy to assess sarcomeric integrity, MuscleMotion to assess contractility, and optical voltage mapping to assess the electrophysiological properties of TTN_T32756I hiPSC-aCMs. T32756I results in a non-conservative amino acid change, which in-silico tools have previously predicted results in an impairment in titin function. Here, we show that TTN_T32756I hiPSC-aCM mutants display aberrant contractility (Fig. 1A-C) and Ca2+ homeostasis (Fig. 1D) leading to abnormal electrophysiology (Fig. 1E-F) at the cellular level without compromising the sarcomeric integrity of the atrial cardiomyocytes (Fig. 1G-H). Our results suggest that a single amino acid change could have a profound effect on titin function, further establishing titin as a major signaling hub for contractility. Ongoing studies will not only identify the key pathways and transcription factors involved in the pathogenesis of TTN_ T32756I mutant but also uncover the impact of the mutation on atrial action potential and cardiac ion channel activity. Our study will shed new light on the mechanisms by which TTN mutation cause AF and identify novel therapeutic targets for patients carrying AF-associated rare variants in the structural genes.