SUMMARY Bronchopulmonary dysplasia (BPD) is a chronic lung disease in premature infants, caused by mechanical ventilation and hyperoxia amongst other factors. Thirty percent of infants with moderate to severe BPD develop pulmonary hypertension (PH), characterized by pulmonary vascular remodeling. There are no curative therapies for this disease. Current management is limited to relieving symptoms using pulmonary vasodilators, and minimizing further lung vascular and alveolar insults. My long-term goal is to develop novel targeted therapies to prevent and/or treat BPD associated pulmonary hypertension (BPD-PH). Pulmonary vascular remodeling is characterized by increased smooth muscle cell-specific markers. This results from proliferation and migration of vascular smooth muscle cells, or transdifferentiation from endothelial cells (ECs) to smooth muscle cells (i.e., endothelial-mesenchymal transition, EndoMT). We and others have shown that hyperoxia to newborn mice and mechanical ventilation in preterm lambs cause pulmonary vascular remodeling resulting in PH. This is associated with increased EndoMT, as shown in our recent publication and in preliminary data. We preliminarily show that EndoMT is also observed in the lung of premature infants requiring mechanical ventilation, suggesting that this may be causative in pulmonary vascular remodeling and PH. In mice, we have reported that neonatal hyperoxia causes a persistent reduction of endothelial carnitine palmitoyltransferase 1a (Cpt1a), the rate-limiting enzyme of the carnitine shuttle system responsible for transporting long-chain fatty acids into mitochondria for β-oxidation during fatty acid oxidation. Our preliminary data show that lung Cpt1a gene expression is also reduced in mechanically ventilated preterm lambs and premature human infants. Additionally, endothelial deletion of Cpt1a increased EndoMT and pulmonary vascular remodeling in neonatal mice after exposure to hyperoxia. Furthermore, pharmacological upregulation of Cpt1a attenuated hyperoxia-induced EndoMT in cultured lung ECs. Whether neonatal hyperoxia and mechanical ventilation reduce endothelial Cpt1a, leading to PH is yet to be determined. The central hypothesis is that neonatal hyperoxia and mechanical ventilation cause EndoMT by downregulating endothelial Cpt1a, thereby resulting in pulmonary vascular remodeling and PH. We will test this hypothesis in three Specific Aims. Aim 1 will determine the molecular mechanisms by which Cpt1a regulates hyperoxia-induced EndoMT. In Aim 2, we will define the role of endothelial Cpt1a in neonatal hyperoxia-induced PH and EndoMT. In Aim 3, we will evaluate endothelial Cpt1a and EndoMT as therapeutic targets for BPD-PH using both lamb and mouse models. The combination of clinically relevant lamb and mouse models with our newly generated EC-specific Cpt1a KO mice and newly developed nanoparticle delivery system provides an innovative approach to uncover the mechanisms by which Cpt1a reduction...