ABSTRACT Idiopathic Pulmonary Fibrosis (IPF) is a chronic, fatal disease of aging with limited therapeutic options. Despite IPF lungs feature vascular abnormalities, including capillary rarefaction and vascular leak, the impact of vascular endothelial dysfunction in the progression of this disease has remained unexplored. This proposal is designed to fill this knowledge gap. Multi-omics analysis of endothelial cells (ECs) from young and aged mouse lungs performed in our laboratory implicated the transcription factor ERG as an orchestrator of pulmonary vascular repair and inflammation, whose homeostatic function is impaired during fibrosis with aging. Genetic ablation of endothelial ERG in young mice led to increased inflammation, vascular rarefaction, and perpetuated lung fibrosis following bleomycin challenge mirroring the aged lung phenotype. ERG silencing in human lung ECs in vitro led to the increased secretion of fibrogenic mediators that promoted IPF-derived lung fibroblast activation. Whole lung scRNA-seq combined with FACS analysis revealed reduced number of lung progenitor ECs, known as general capillary (gCap) ECs, in ERG deficient mice compared to WT mice; this alteration was also observed in lungs derived from IPF patients. Pharmacologic inhibition of the enhancer-binding protein and epigenetic regulator BRD4 reversed inflammatory responses in ERG-silenced human lung ECs in vitro and restored gCap EC identity in IPF lung explants ex vivo. Moreover, IPF and bleomycin-induced mouse lung fibrosis were associated with overexpression of genes that regulate necroptosis, a form of programmed inflammatory cell death implicated in aging and fibrosis. In addition, inhibition of necroptosis with the specific inhibitor Necrostatin- 1 attenuated inflammation induced by ERG silencing in human lung ECs. Based on these findings we hypothesize that aging-associated epigenetic remodeling impairs ERG transcription in injured lung gCap ECs leading to dysregulated inflammation, capillary rarefaction, and persistent lung fibrosis. Aim 1 of this proposal will characterize the influence of ERG on lung gCap EC regeneration and fibrosis. Aim 2 will define the role of epigenetic mechanisms in lung endothelial ERG chromatin interaction, transcription, and vascular aging. Aim 3 will establish the contribution of endothelial necroptosis to lung vascular abnormalities and fibrosis in aged mice with compromised ERG functions. We will test our hypothesis using in vitro, ex vivo and in vivo models including an organotypic model of human IPF. gCap-enriched ECs and fibroblasts will be isolated from human IPF lungs. Endothelial fibrogenic activity will be evaluated in an endothelial-fibroblast co-culture systems. Conditional knockout and lineage tracing approaches will be used to investigate the role of ERG in endothelial homeostasis and lung fibrosis. Fibrosis, vascular leak, capillary rarefaction, and hypoxia will be evaluated with molecular, biochemical, and histologi...