Abstract EC.01: Endocardial Hdac3 Promotes Myocardial Trabeculation Through A MicroRNA Pathway

Abstract

A key process during early heart development is myocardial trabeculation, which is the formation of bundles of myocardium extending into the chamber. The failure of trabeculation often contributes to many forms of congenital heart defects. Proper trabeculation requires coordination among multiple cell types and signaling communication. For instance, growth signals released from the endocardium are required for trabecular myocardial growth and maturation. However, it is poorly understood how these signaling cascades are initiated and regulated in the endocardium. Recently, our lab demonstrated that epicardial histone deacetylase 3 (HDAC3) is required for myocardial compaction. In this current study, we found that the genetic deletion of Histone deacetylase 3 (Hdac3) in the cardiac endothelial cells in mice resulted in early embryo lethality presenting as a hypotrabeculation cardiac phenotype, suggesting that endocardial Hdac3 deletion disrupted critical signals from the endocardium for trabecular myocardium growth. When cultured with supernatant from Hdac3 knockout (KO) mouse cardiac endothelial cells (MCECs), wild-type (WT) mouse embryonic cardiomyocytes also showed decreased proliferation. Single cell RNA-sequencing identified that transforming growth factor ß3 (Tgfß3) along with their extracellular matrix (ECM) downstream targets was significantly downregulated in Hdac3 deficient endocardial cells. Interestingly, chemical inhibition of deacetylase catalytic activity alone resulted in significant downregulation of Tgfß3 in cultured Hdac3 KO MCECs, suggesting that HDAC3 induces Tgfß3 expression in an enzymatic dependent manner. Mechanistically, we identified that miR-129 was significantly upregulated in Hdac3 KO MCECs and Hdac3 endocardial KO hearts. Overexpression of miR-129 repressed Tgfß3 expression in WT MCECs, whereas knockdown of miR-129 restored Tgfß3 expression in Hdac3 KO MCECs. Our findings reveal a critical signaling pathway in which endocardial HDAC3 promotes trabecular myocardium growth by stimulating Tgfß through repressing miR-129, providing novel insights into elucidating the etiology of congenital heart defects and conceptual strategies to promote myocardial regeneration.