| Summary: | Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic cardiac disease characterized by fibrofatty infiltration of the myocardium, life-threatening arrhythmias, and sudden cardiac death. Newfoundland and Labrador is home to a substantial founder population with an autosomal dominant mutation in the transmembrane protein 43 (TMEM43) gene (c.1073C>T; p.S358L), responsible for ARVC type 5. Although we know that this mutation causes ARVC, there is limited information on the TMEM43 protein life cycle, protein-protein interactions, and function. Additionally, it is unknown how the p.S358L mutation affects TMEM43 function, contributes to ARVC, or why it affects only the heart despite being widely expressed. Here I investigate the intracellular trafficking of wild-type TMEM43 in human induced pluripotent stem cells (iPSCs) and iPSC-cardiomyocytes (iPSC-CMs). I find that TMEM43 resides primarily in early endosomes in iPSCs. Interestingly, although TMEM43 remains localized to early endosomes in early contracting iPSC-CMs, it shifts toward the nuclear envelope as iPSC-CMs are cultured in vitro for an extended period of time. CRISPR-Cas9 genetic ablation of the TMEM43 gene has no apparent effects on several intracellular organelles previously shown to be affected by the TMEM43-S358L mutation. However, TMEM43-/- iPSC-CMs exhibit subtle calcium handling aberrations pointing toward a pro-arrhythmic phenotype. Finally, primary ARVC patient dermal fibroblasts show significant changes in the expression of extracellular matrix proteins, which may play a role in the fibrosis seen in ARVC. Together, these studies begin to unravel the basic life cycle and function of the TMEM43 protein in a human-derived cellular model of ARVC.
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