Abstract 16148: Human Cardiac Development and Function Requires Proper Distribution of Transcriptional Complexes

Cell identity and function require accurate transcription factor localization and dysregulation of this process can result in human disease. Heterozygous mutations in GATA4 , a cardiogenic transcription factor, cause congenital heart defects and cardiomyopathy through unknown mechanisms. Here, systems-level analyses of human iPS-derived cardiomyocytes from patients with a GATA4-G296S mutation revealed genome-wide transcription factor occupancy required for human cardiac development and function. We found GATA4 broadly co-occupied thousands of H3K27ac-marked enhancers with another cardiogenic transcription factor, TBX5. The GATA4-G296S mutation disrupted recruitment of TBX5 to MED1-occupied cardiac super-enhancers, and reduced cardiogenic gene activation. This resulted in functional impairments to contractility, calcium handling, sarcomeric organization and metabolic activity, thereby modelling the cardiomyopathy phenotype in vitro . GATA4 and TBX5 were mis-localized at endothelial/endocardial topologically associating domains in G296S mutants, with increased open chromatin at endothelial promoters. These genomic loci were enriched in motifs for ETS family of endothelial regulators and G296S mutant cells failed to properly silence the endothelial/endocardial gene program during cardiogenesis. Furthermore, aberrant expression of Hedgehog signaling and AV canal genes mechanistically explained the clinical ASD and AVSD phenotypes. Topological network analysis discovered novel patterns of cardiac gene regulation and in silico prediction of a GATA4-TBX5 gene network revealed “hubs” centered on PI3K/Akt signaling, supported by experimental validation. This work comprehensively reveals the cooperative mechanisms employed by cardiac transcription factors for human cardiogenesis, elucidates how a single missense mutation leads to congenital heart defects and cardiomyopathy, and illustrates a proof-of-concept in using systems biology to understand human disease.