Modelling arrhythmogenic cardiomyopathy using human iPSCs

Arrhythmogenic Cardiomyopathy (ACM) is a hereditary heart disease characterized by ventricular arrhythmias, sudden cardiac death, and heart failure. Newfoundland and Labrador (NL) hosts one of the world's largest concentrated populations of ACM patients due to a heterozygous, autosomal dominant founder disease-causing variant in the TMEM43 gene (c.1073C>T; p.S358L). My project addresses questions pertaining to 2 less well-known aspects of this disease: 1) Why are there no known individuals with homozygous TMEM43 p.358L variant? 2) Why are females protected from severe disease progression compared to men? For the first question, there is one case of two TMEM43 P.S358L heterozygous patients having children together, with one variant-negative child, and no reported pregnancy losses. Thus, we hypothesize that the homozygous variant might be so severe that it is an early embryonic lethal. We used CRISPR-Cas9 to introduce the homozygous TMEM43-S358L variant into induced pluripotent stem cells (iPSCs) from an affected male ACM patient. These homozygous TMEM43-S358L variant iPSCs can differentiate into functional cardiomyocytes (iPSC-CMs); however, these cardiomyocytes exhibit extreme arrhythmic tendencies and contract approximately twice as fast as heterozygous variant ACM patient iPSC-CMs. Regarding the second question, ACM affects both sexes, but males are more severely affected. We found that iPSC-CMs from a severely affected female patient exhibit clear arrhythmic phenotypes, including calcium alternans, early afterdepolarizations, and oscillations, even at baseline. These abnormalities worsen with β-adrenergic receptor stimulation. This suggests that female carriers may not be fully protected and may exhibit subtler or stress-triggered symptoms. Collectively, these findings suggest that female carriers may not be uniformly protected from disease severity and highlight the importance of considering sex-specific mechanisms in ACM diagnosis and therapeutic approaches. Elucidating these sex-based differences in ACM could help explain why disease presentation varies between males and females and inform the development of more effective, personalized treatments for patients with ACM.