Nogo-B receptor is essential for angiogenesis in zebrafish via Akt pathway

Our previous work has shown that axon guidance gene family Nogo-B and its receptor (NgBR) is essential for chemotaxis and morphogenesis of endothelial cells in vitro. To investigate NogoB-NgBR function in vivo, we cloned the zebrafish ortholog of both genes and studied loss of function in vivo using morpholino (MO) antisense technology. Zebrafish ortholog of Nogo-B is expressed in somite while expression of zebrafish NgBR is localized in intersomitic vessel (ISV) and axial dorsal aorta (DA) during embryonic development. NgBR or Nogo-B knockdown embryos show defects in ISV sprouting in the zebrafish trunk. Mechanistically, we found that NgBR knockdown not only abolished its ligand Nogo-B-stimulated endothelial cell migration, but also reduced the VEGF-stimulated phosphorylation of Akt, and VEGF-induced chemotaxis and morphogenesis of human umbilical vein endothelial cells (HUVEC). Further, constitutively activated Akt (myrAkt) or human NgBR mRNA can rescue the NgBR knockdown HUVEC migration defects in vitro or NgBR MO-caused ISV defects in vivo. These data place Akt at the downstream of NgBR in both Nogo-B and VEGF coordinated sprouting of ISVs. In summary, this study identifies the in vivo functional role for Nogo-B and its receptor (NgBR) in angiogenesis in zebrafish.