The retinal vasculature is prone to damages, leading to serious ocular diseases including loss of vision. While angiogenic therapies are being explored as potential treatments, a significant hurdle is our inability to control the three dimensional organization of the vascular network induced by angiogenic factors to ensure proper functioning of pharmacologically induced retinal vasculature. Thus, our long term objective is to unravel mechanisms that control the spatial organization of retinal vascular beds, and in particular to investigate how components of the hypoxia signaling pathway act as spatial cues to determine the direction and position of vascular growth in the retina. These studies will be carried out in three specific aims. Aim 1. Investigate roles of prolyl hydroxylase domain proteins in controlling retinal vascular pattern formation. PHDs negatively regulate the abundance of hypoxia inducible factors (HIFs), the latter of which are essential for angiogenesis. We hypothesize that the level of PHD activity in a tissue microenvironment determines the activity and directionality of vascular growth in its vicinity, and will test this hypothesis by generating chimeric retinas that contain micro tissue domains with PHD deficiency or overexpression. Aim 2. Determine if HIF-la accumulation in a micro tissue domain controls the position and direction of vascular growth in nearby tissues. Aim 3. Explore the role of VEGFR-l in defining vessel to vessel distances. VEGFR-l is produced by endothelial cells and forms tight complex with VEGF-A, a key angiogenic molecule induced by hypoxia. We propose that VEGF-A/VEGFR-1 interaction diminishes bioavailable VEGF-A near the source of VEGFR-l expression and therefore disallows the growth of more microvessels within a certain distance from an existing microvessel. This hypothesis will be tested by creating chimeric retinas that contain micro tissue domains overexpressing VEGFR-1, and assessing vascular density near such tissues. The objective of these studies is to facilitate the development of effective therapies aimed at repairing damaged retinal vascular beds and is highly consistent with the mission of the National Eye Institute (NEI).