Noort, R. J.; Salman, W.; Porter, Z. G.; Sadighian, H.; Fuchs, C.; Braun, U.; Pace, D.; Belbin, T.; Hodgkinson, K.; Esseltine, J. L.

Arrhythmogenic Cardiomyopathy (ACM) is clinically characterized by ventricular arrhythmias causing sudden cardiac death and fibrofatty replacement of the myocardium leading to heart failure. One form of ACM is highly prevalent in the Canadian Province of Newfoundland and Labrador (NL) and has earned the moniker, The Newfoundland Curse. This ACM in NL patients is often caused by a fully penetrant heterozygous missense mutation in the TMEM43 gene (TMEM43 c.1073C>T; TMEM43 p.S358L). Although the causative mutation has been identified, little is known about the function of the TMEM43 protein in cardiomyocytes, how the TMEM43 p.S358L mutation contributes to the development of arrhythmias, or why the disease is more severe in males than females. To explore the role of TMEM43 in cardiomyocyte function, we generated induced pluripotent stem cells (iPSCs) from 2 severely affected male Newfoundland ACM (TMEM43 p.S358L) patients. CRISPR-Cas9 was used to genetically repair the heterozygous TMEM43 mutation in ACM patient iPSCs or for TMEM43 gene knockout. ACM patient iPSC-cardiomyocytes with the TMEM43 p.S358L mutation display pro-arrhythmogenic phenotypes in vitro with significantly elevated contraction rates and altered calcium handling, although no obvious gross abnormalities were observed across several major intracellular organelles. TMEM43 protein abundance and half-life appears unchanged in ACM iPSC-CMs where 50% of the TMEM43 protein is WT and 50% is mutant. Gene expression analysis of ACM iPSC-CMs shows an increase in genes related to signaling and metabolism. Importantly, the pro-arrhythmic tendencies of ACM patient iPSC-CMs can be ameliorated with transient GSK3 inhibition.