Axonal guidance and vascular patterning share several guidance cues, including proteins in the netrin family. We demonstrate that netrins stimulate proliferation, migration, and tube formation of human endothelial cells in vitro and that this stimulation is independent of known netrin receptors. Suppression of netrin1a messenger RNA in zebrafish inhibits vascular sprouting, implying a proangiogenic role for netrins during vertebrate development. We also show that netrins accelerate neovascularization in an in vivo model of ischemia and that they reverse neuropathy and vasculopathy in a diabetic murine model. We propose that the attractive vascular and neural guidance functions of netrins offer a unique therapeutic potential.

Blood vessels and nerves often follow parallel trajectories, suggesting that distal targets use common cues that induce vascularization and innervation. Netrins are secreted by the floor plate and attract commissural axons toward the midline of the neural tube. Here, we show that Netrin-1 is also a potent vascular mitogen. Netrin-1 stimulates proliferation, induces migration, and promotes adhesion of endothelial cells and vascular smooth muscle cells with a specific activity comparable to vascular endothelial growth factor and platelet-derived growth factor. Our evidence indicates that the netrin receptor, Neogenin, mediates netrin signaling in vascular smooth muscle cells, but suggests that an unidentified receptor mediates the proangiogenic effects of Netrin-1 on endothelial cells. Netrin-1 also stimulates angiogenesis in vivo and augments the response to vascular endothelial growth factor. Thus, we demonstrate that Netrin-1 is a secreted neural guidance cue with the unique ability to attract both blood vessels and axons, and suggest that other cues may also function as vascular endothelial growth factors.

Stereotypical patterns of vascular and neuronal networks suggest that specific genetic programs tightly control path determination and, consequently, angiogenesis and axon-guidance mechanisms. Our study focuses on one member of the roundabout family of receptors, which traditionally mediate repulsion from the midline. Here, we characterize a fourth member of this family, roundabout4 ( robo4 ), which is the predominant roundabout (robo) that is expressed in embryonic zebrafish vasculature. Gene knockdown and overexpression approaches show that robo4 is essential for coordinated symmetric and directed sprouting of intersomitic vessels and provide mechanistic insights into this process. Also, human robo4 gene functionally compensates for loss of robo4 gene function, suggesting evolutionary conservation. This article reports an endothelial-specific function for a robo gene in vertebrates in vivo .