PROJECT ABSTRACT Retinal neovascular disorders, such as retinopathy of prematurity and diabetic retinopathy, are the most common causes of vision loss of working age adults and infants. Vascular endothelial growth factor (VEGF) inhibitors have transformed the treatment of these disorders and resulted in improved outcomes for millions of patients worldwide. However, regression of neovascularization often leads to deposition of a fibrotic scar on the surface of the retina. These pre-retinal fibrotic scars can contract, resulting in distortion of the retinal surface or detachment of the neurosensory retina. To date, surgery is the only available intervention, often with poor visual outcomes. Despite the importance, very little is known about the molecular mechanisms that regulate the formation of this pathological tissue, and there is debate on the cellular source of fibrotic scar tissue in the retina. One of the main roadblocks for making progress in this field is the lack of a robust and reproducible mouse model to study and manipulate pre- retinal fibrosis, in order to decipher the key cellular and molecular mechanisms that regulate this process. We have developed a novel mouse model of severe retinopathy of prematurity that develops pre-retinal fibrosis subsequent to hypoxia driven neovascularization. Using histology and single cell sequencing, our preliminary data indicates that the pre-retinal fibrotic scar results from pericytes that upregulate collagen I expression following neovascularization. Here, we propose to further understand the mechanism of pre-retinal scar formation by characterizing and manipulating this novel model. First, we will fully characterize this model examining the time course of fibrotic scar formation, vaso- obliteration, neovascularization, retinal inflammation, and visual function. Second, using lineage tracing and single cell sequencing we will determine the identity the critical collagen I producing cells. Third, we propose to test the hypothesis that activation of TGFβ signaling in pericytes is the key driver of pre- retinal fibrosis. Our goal in understanding the cellular and molecular origin of retinal fibrosis is to develop novel therapeutics to prevent blindness from traction in advanced ischemic retinopathies.