Role of cardiac m6A methyltransferases

Project Summary Human early-onset dilated cardiomyopathy (DCM) is associated with significant morbidity and mortality in utero and after birth. The majority of DCM in fetus is considered to be idiopathic, with a strong association with genetic mutations in sarcomeric genes. Pathogenic sarcomere protein variants often arise from post-transcriptional regulation. However, whether post-transcriptional dysregulation contributes to the pathogenesis of DCM in fetus has not been determined, presenting a significant knowledge gap to understand the etiology of early-onset DCM. In eukaryotic mRNA, N6-methyl-adenosine (m6A) is the most abundant post-transcriptional modification and affects mRNA processing (i.e., stability, splicing) and translation. m6A is deposited by the m6A methyltransferase complex composed of several catalytic subunits including methyltransferase 3 (METTL3) and methyltransferase 14 (METTL14). METTL3 and METTL14 play important roles in adult heart injury and repair, although their potential function during early myocardial development and whether their dysregulation contributes to the pathogenesis of fetal DCM is undetermined. In this proposal, we will address this by leveraging mouse genetics, biochemistry, molecular biology, RNA biology, and histology. First, we will determine the functions of METTL3 and METTL14 in embryonic mouse myocardium, and whether their loss in cardiomyocytes induces fetal DCM in mice. Secondly, we will identify the underlying molecular mechanisms by which METTL3 and METTL14 regulate mRNA fates and early sarcomerogenesis and myofibrillogenesis. Successful completion of the proposed study will reveal key roles for the methyltransferases and post-transcriptomic profile of cardiac mRNAs during early cardiac myogenesis, and uncover the novel pathogenesis of fetal DCM, and thus shed new lights on therapeutic strategies.