PROJECT SUMMARY Age-dependent macular degeneration (AMD) is a leading cause of vision loss. Late stage AMD is divided into two types, neovascular or exudative (wet) and atrophic (dry). Wet AMD is increasingly recognized as a group of diseases with differential presentations in patients of different ethnic backgrounds. In patients of European ancestry, it is typically characterized by large drusen and progression to choroidal neovascularization caused by excessive production of vascular endothelial growth factor (VEGF), which is central to disease progression. Wet AMD is therefore treated with intravitreal VEGF inhibitors which have transformed disease prognosis. However, in patients of Asian or African ancestry exudative AMD is most associated with a paucity of drusen and polypoidal choroidal vasculopathy (PCV), a member of the pachychoroid disease spectrum. Despite the prevalence of PCV, this disease remains poorly understood and anti-VEGF therapy is often less effective for these eyes than for those with typical neovascular AMD, leaving a critical need for new therapeutic targets and treatments specifically targeted at this disease. Pachychoroid diseases are characterized by the formation of dilated “pachyvessels” which originate from the choroid and are accompanied by aneurysmal polyps in PCV. Recent genetic studies have linked members of the angiopoietin (Angpt)-TEK endothelial signaling system with PCV and central serous chorioretinopathy, another member of the pachychoroid spectrum. Directly testing this association, we discovered that neural crest specific Angpt1 knockout mice exhibit choriocapillaris attenuation and encroachment of dilated pachyvessels characteristic of pachychoroid and PCV, representing a new genetic model of these poorly understood diseases and a key tool for understanding the role of angiopoietin signaling in disease progression and as a therapeutic target. To further characterize ANGPT1 signaling in the choroidal vasculature, we performed preliminary single cell transcriptomics analysis which revealed that ANGPT1 is essential for maintenance of the differentiated choriocapillaris phenotype. Angpt1 knockout mice exhibited markedly reduced expression of key choriocapillaris functional genes, including the VEGF receptor encoded by Kdr. In contrast, Kdr expression was elevated in other vascular beds, providing a potential mechanism by which ANGPT1 deficiency leads to choriocapillaris dysfunction and pachyvessel formation through dilation of choroidal vessels. In this proposal, we will leverage these findings and our new mouse model to (1) fully characterize the role of angiopoietin signaling in the choriocapillaris and identify unique markers differentiating pachyvessels from the healthy choroid, (2) Understand the respective role(s) of choriocapillaris dysfunction and direct ANGPT1 signaling in pachyvessel formation and (3) investigate the potential of a new ANGPT1 mimetic drug as a targeted therapeutic in pachychoroid d...