Abstract 9857: Epicardial Hdac3 Promotes Myocardial Growth Through a Novel MicroRNA Pathway

Abstract

Growth cues from epicardium-derived cells (EPDCs) such as Insulin growth factors (IGFs) and Fibroblast Growth Factors (FGFs) are required for compact myocardial growth, although it is unclear whether/how their expression is regulated by chromatin modifications during this process. To understand the potential function of Histone deacetylase 3 (Hdac3) in the developing epicardium, we conditionally inactivated Hdac3 in the EPDCs. Strikingly, deletion of Hdac3 in the epicardium led to ventricular myocardial wall hypoplasia along with the reduction of EPDCs. To identify disrupted growth signals sending from epicardium to myocardium, we deleted Hdac3 in cultured mouse epicardial cells (MECs) by CRISPR/CAS9 and performed RNA Seq analyses. We found that IGF2 and FGF9 were significantly down regulated in Hdac3 knockout (KO) MECs, which can be rescued by re-expression of intact Hdac3 but not by catalytically dead Hdac3. Importantly, the proliferation of cultured primary embryonic cardiomyocytes was significantly decreased when treated with Hdac3 KO MEC supernatant as compared to those treated with control MEC supernatant, and this proliferation decrease was rescued by supplementation of IGF2 or FGF9. Next, we sought to understand how Hdac3 regulates the expression of IGF2 or FGF9. Interestingly, we found that miR-322/503 was significantly upregulated in Hdac3 KO MECs and Hdac3 epicardial KO hearts. Overexpression of miR-322/503 repressed the expression of IGF2 and FGF9, while knockdown of miR-322/503 restored the expression of IGF2 and FGF9 in Hdac3 KO MECs. Altogether, our findings suggest that Hdac3 in the developing epicardium promotes compact myocardial growth by stimulating IGF2 expression through repressing miR-322/503. Our findings shed light on the potential novel mechanisms of congenital heart defects, and new strategies for myocardial regeneration.