Anti-MEF2C monoclonal antibody, clone 2E2

In this study, we demonstrate that the lysine methyltransferase G9a inhibits sarcomere organization through regulation of the MEF2C-HDAC5 regulatory axis. Sarcomeres are essential for muscle contractile function. Presently, skeletal muscle disease and dysfunction at the sarcomere level has been associated with mutations of sarcomere proteins. This study provides evidence that G9a represses expression of several sarcomere genes and its over-expression disrupts sarcomere integrity of skeletal muscle cells. G9a inhibits MEF2C transcriptional activity that is essential for expression of sarcomere genes. Through protein interaction assays, we demonstrate that G9a interacts with MEF2C and its corepressor HDAC5. In the presence of G9a, calcium signaling-dependent phosphorylation and export of HDAC5 to the cytoplasm is blocked which likely results in enhanced MEF2C-HDAC5 association. Activation of calcium signaling or expression of constitutively active CaMK rescues G9a-mediated repression of HDAC5 shuttling as well as sarcomere gene expression. Our results demonstrate a novel epigenetic control of sarcomere assembly and identifies new therapeutic avenues to treat skeletal and cardiac myopathies arising from compromised muscle function.

BACKGROUND The genetic basis of atrial fibrillation (AF) and congenital heart disease remains incompletely understood. OBJECTIVE We sought to determine the causative mutation in a family with AF, atrial septal defects, and ventricular septal defects. METHODS We evaluated a pedigree with 16 family members, 1 with an atrial septal defect, 1 with a ventricular septal defect, and 3 with AF; we performed whole exome sequencing in 3 affected family members. Given that early-onset AF was prominent in the family, we then screened individuals with early-onset AF, defined as an age of onset <66 years, for mutations in GATA6. Variants were functionally characterized using reporter assays in a mammalian cell line. RESULTS Exome sequencing in 3 affected individuals identified a conserved mutation, R585L, in the transcription factor gene GATA6. In the Massachusetts General Hospital Atrial Fibrillation (MGH AF) Study, the mean age of AF onset was 47.1 +/- 10.9 years; 79% of the participants were men; and there was no evidence of structural heart disease. We identified 3 GATA6 variants (P91S, A177T, and A543G). Using wild-type and mutant GATA6 constructs driving atrial natriuretic peptide promoter reporter, we found that 3 of the 4 variants had a marked upregulation of luciferase activity (R585L: 4.1-fold, P<.0001; P91S: 2.5-fold, P=.0002; A177T; 1.7-fold, P=.03). In addition, when co-overexpressed with GATA4 and MEF2C, GATA6 variants exhibited upregulation of the alpha myosin heavy chain and atrial natriuretic peptide reporter activity. CONCLUSION Overall, we found gain-of-function mutations in GATA6 in both a family with early-onset AF and atrioventricular septal defects as well as in a family with sporadic, early-onset AF.