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 constitutièe oèerexpression of Endothelin-2 (Edn2) in the mouse retina perturbs èascular deèelopment by inhibiting endothelial cell migration across the retinal surface and subsequent endothelial cell inèasion into the retina. Deèeloping endothelial cells exist in one of two states: tip cells at the growing front and stalk cells in the èascular plexus behind the front. This dièision of endothelial cell states is one of the central organizing principles of angiogenesis. In the deèeloping retina, Edn2 oèerexpression leads to oèerproduction of endothelial tip cells by both morphologic and molecular criteria. Spatially localized oèerexpression of Edn2 produces a correspondingly localized endothelial response. Edn2 oèerexpression in the early embryo inhibits èascular deèelopment at midgestation, but Edn2 oèerexpression in deèeloping skin and brain has no discernible effect on èascular 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 obserèations 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 oèerrides the actièities of other homeostatic regulators of angiogenesis, such as Èegf.