Abstract 528: Nogo-B Receptor is Essential for Primitive Blood Vessel Formation and Vasculature Development in Mouse Embryo

Abstract

Nogo-B was previously identified as a protein that is expressed in endothelial cells and vascular smooth muscle cells. Nogo-A/B deficient mice show exaggerated neointimal proliferation and abnormal remodeling. Nogo-B receptor (NgBR) is a type I receptor, which was identified as a receptor specific for Nogo-B. Our previous work has shown that Nogo-B and its receptor (NgBR) are essential for chemotaxis and morphogenesis of endothelial cells in vitro and intersomitic vessel formation via Akt pathway in zebrafish. Our recent work reveals that NgBR is a critic membrane scaffold protein required for Ras translocation and activation, which is essential for VEGF-stimulated Ras-PI3K-Akt signaling pathway. Here, we further demonstrate the roles of NgBR in regulating primitive blood vessel formation in embryoid body culture systems and vasculature development in mouse embryo. Murine NgBR gene-targeting embryonic stem cells (ESC) were generated by homologous recombination approaches. Homozygous knockout of NgBR in ESC results in cell apoptosis. Heterozygous knockout of NgBR does not affect ESC cell survival, but reduces the formation and branching of primitive blood vessels in embryoid body culture systems. In addition, our preliminary results show that NgBR homozygous knockout mice are embryonic lethal happened at E6.5 or earlier, and endothelial cell specific NgBR knockout mice are embryonic lethal happened at E11.5 and have severe blood vessel formation defects in embryo. Mechanistically, NgBR has two potential regulatory roles during embryonic vasculature development. NgBR knockdown not only decreases both Nogo-B and VEGF-stimulated endothelial cell migration by abolishing Akt phosphorylation, but also impairs endothelial cell lineage commitment by delaying BMP4 production during the period of mesoderm formation. These results suggest that NgBR may be one of important genes coordinating the vasculature development.