Specialized endothelial tip cells guide neuroretina vascularization and blood-retina-barrier formation

Endothelial tip cells guiding tissue vascularization are primary targets for angiogenic therapies. Whether tip cells require differential signals to develop their complex branching patterns remained unknown. Here we show that diving tip cells invading the neuroretina (D-tip cells) are distinct from tip cells guiding the superficial retinal vascular plexus (S-tip cells). D-tip cells have a unique transcriptional signature, including high TGFß signaling, and acquire blood-retina barrier properties. Endothelial deletion of TGFß receptor I (Alk5) inhibits D-tip cell identity acquisition and deep vascular plexus formation. Loss of endothelial ALK5, but not of the canonical SMAD effectors, leads to aberrant contractile pericyte differentiation, and hemorrhagic vascular malformations. Our data reveal stage-specific tip cell heterogeneity as a requirement for retinal vascular development and suggest that noncanonical-TGFß signaling could improve retinal revascularization and neural function in ischemic retinopathy. Overall design: Retinal single-cell mRNA profiles of WT and Alk5iEKO mice from P6 and P10