Altered Expression of TMEM43 Causes Abnormal Cardiac Structure and Function in Zebrafish

Abstract

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disease caused by heterozygous missense mutations within the gene encoding for the nuclear envelope protein transmembrane protein 43 (TMEM43). The disease is characterized by myocyte loss and fibro-fatty replacement, leading to life-threatening ventricular arrhythmias and sudden cardiac death. However, the role of TMEM43 in the pathogenesis of ACM remains poorly understood. In this study, we generated cardiomyocyte-restricted transgenic zebrafish lines that overexpress eGFP-linked full-length human wild-type (WT) TMEM43 and two genetic variants (c.1073C>T, p.S358L; c.332C>T, p.P111L) using the Tol2-system. Overexpression of WT and p.P111L-mutant TMEM43 was associated with transcriptional activation of the mTOR pathway and ribosome biogenesis, and resulted in enlarged hearts with cardiomyocyte hypertrophy. Intriguingly, mutant p.S358L TMEM43 was found to be unstable and partially redistributed into the cytoplasm in embryonic and adult hearts. Moreover, both TMEM43 variants displayed cardiac morphological defects at juvenile stages and ultrastructural changes within the myocardium, accompanied by dysregulated gene expression profiles in adulthood. Finally, CRISPR/Cas9 mutants demonstrated an age-dependent cardiac phenotype characterized by heart enlargement in adulthood. In conclusion, our findings suggest ultrastructural remodeling and transcriptomic alterations underlying the development of structural and functional cardiac defects in TMEM43-associated cardiomyopathy.

Using Zebrafish Animal Model to Study the Genetic Underpinning and Mechanism of Arrhythmogenic Cardiomyopathy

“…Several rare TMEM43 variants have been sporadically identified in ACM patients [ 53 , 54 , 55 , 58 , 97 ]. To investigate the molecular mechanism underlying TMEM43 mutation-associated ACM, a truncation mutant was generated by using the CRISPR/Cas9-based gene editing technique to shift the reading frame of the zebrafish tmem43 gene [ 94 ]. Interestingly, significantly enlarged ventricular chamber size was observed in the loss-of-function tmem43 mutants in the adult stage, while no obvious cardiac defects or contractile dysfunction were detected during early embryonic stages.…”

“…For the TMEM3 gene, in addition to the aforementioned KO study, transgenic overexpression study on two different ACM-associated TMEM43 variants (P111L and S358L) was also reported [ 94 ]. Transgenic overexpression of TMEM43 gene, either wild-type or mutated (P111L), resulted in cardiac defects such as cardiomyocyte hypertrophy and ventricular chamber enlargement during the early developmental stages in zebrafish.…”

“…Mechanistically, it was proposed that overexpression of TMEM43 variants induced cardiac defects were mediated by hyperactivation of the mammalian target of rapamycin (mTOR) pathway and ribosome biogenesis. This combinatorial study, using both gene KO and transgenic overexpression approaches, indicated that both gain-of-function and loss-of-function of the TMEM43 gene led to cardiac morphology and function defects in zebrafish [ 94 ]. Thus, these findings might imply a potentially unique pathophysiological feature of TMEM43 -associated ACM in human patients.…”

The Many Faces of Arrhythmogenic Cardiomyopathy: An Overview

“… 43 Alterations in cardiac structure and function have also been shown in a transgenic zebrafish model when TMEM43 variants (c.1073C>T, p.S358L; c.332C>T, p.P111L) were expressed. 44 Both variants displayed cardiac morphological defects at juvenile stages and ultrastructural changes within the myocardium, accompanied by dysregulated gene expression profiles in adulthood. 44 These studies emphasize the importance of bedside to bench for further mechanistic elucidation and hopefully translation back to the bedside to improve patient outcomes.…”

“… 44 Both variants displayed cardiac morphological defects at juvenile stages and ultrastructural changes within the myocardium, accompanied by dysregulated gene expression profiles in adulthood. 44 These studies emphasize the importance of bedside to bench for further mechanistic elucidation and hopefully translation back to the bedside to improve patient outcomes.…”