Endothelin-2 signaling in the neural retina promotes the endothelial tip cell state and inhibits angiogenesis

Endothelin signaling is required for neural crest migration and homeostatic regulation of blood pressure. Here, we report that constitutive overexpression of Endothelin-2 (Edn2) in the mouse retina perturbs vascular development by inhibiting endothelial cell migration across the retinal surface and subsequent endothelial cell invasion into the retina. Developing endothelial cells exist in one of two states: tip cells at the growing front and stalk cells in the vascular plexus behind the front. This division of endothelial cell states is one of the central organizing principles of angiogenesis. In the developing retina, Edn2 overexpression leads to overproduction of endothelial tip cells by both morphologic and molecular criteria. Spatially localized overexpression of Edn2 produces a correspondingly localized endothelial response. Edn2 overexpression in the early embryo inhibits vascular development at midgestation, but Edn2 overexpression in developing skin and brain has no discernible effect on vascular structure. Inhibition of retinal angiogenesis by Edn2 requires expression of Endothelin receptor A but not Endothelin receptor B in the neural retina. Taken together, these observations imply that the neural retina responds to Edn2 by synthesizing one or more factors that promote the endothelial tip cell state and inhibit angiogenesis. The response to Edn2 is sufficiently potent that it overrides the activities of other homeostatic regulators of angiogenesis, such as Vegf.