Abstract 17256: Hemangiogenic versus Cardiogenic Mesoderm Development Regulated by ER71 Inhibition of WNT Signaling

Abstract

Background Cardiac linage specification is an important area to explore for regenerative medicine. The circulatory system in developing embryo is speculated to develop from two distinct Flk-1 + mesoderms, hemangiogenic and cardiogenic. However, how Flk-1 + mesoderm commits to hemangiogenic versus cardiogenic fate has not been addressed. We determined if ER71, an Ets transcription factor critical for hematopoietic and endothelial cell development, could modulate the hemangiogenic or cardiogenic outcome of the Flk-1 + mesoderm. Methods and Results Using chimeric mice or in vitro embryonic stem (ES) cell differentiation system, we showed that Er71 -/- ES cells failed to generate hematopoietic or endothelial cells. Unexpectedly, ER71 negatively regulated cardiac development. Er71 -/- ES cells and Er71 deficient Flk-1 + mesoderm generated cardiac and smooth muscle cells more efficiently in culture compared to controls. Enforced Er71 expression reduced cardiomyocyte and smooth muscle cell generation. We further found that PDGFR alpha expression can segregate Flk-1 + mesoderm into hemangiogenic (Flk-1 + PDGFR alpha - ) and cardiogenic (Flk-1 + PDGFR alpha + ) mesoderm. Importantly, ER71 is obligatory for the Flk-1 + PDGFR alpha - hemangiogenic mesoderm development. ER71 deficient embryos and ES cells only produced Flk-1 + PDGFRalpha + cardiogenic mesoderm, which mainly and more efficiently differentiated into smooth muscle cells and cardiomyocytes. Moreover, ER71 could convert committed cardiogenic mesoderm to hemangiogenic mesoderm. Furthermore, ER71 strongly induced VE-cadherin, which formed a complex with beta-catenin and Flk-1. Upon the complex formation, nuclear beta-catenin levels decreased and Wnt signaling reduced. ER71 deficient embryo and Flk-1 + mesoderm displayed enhanced Wnt signaling, which was reduced by ER71 re-introduction. Enhanced cardiac differentiation from Er71 deficient Flk-1 + mesoderm was rescued by Dickkopf-related protein. Conclusions Hemangioblast over cardiac lineage specification is achieved by ER71 inhibition of Wnt signaling. Our findings provide strategies for directing pluripotent stem cell differentiation to hematopoietic, vascular and cardiac cells for future regenerative medicine.