Former preterm infants are exposed to oxygen (O2) after birth which results in long-term developmental impacts on the lung. Approximately 70% of infants born extremely prematurely (<29 weeks’ gestational age) will have increased pulmonary morbidity and/or early childhood wheezing disorders even though many are not diagnosed with Bronchopulmonary Dysplasia (BPD). These infants are especially vulnerable to airway hyperreactivity (AHR) after respiratory viral infections through poorly understood mechanisms. Herein, we utilize a low-dose hyperoxia mouse model and a unique pediatric human tissue repository grounded on a new discovery that neonatal O2 increases the abundance of lung megakaryocytes (MKs), an understudied myeloid cell biased toward immunomodulatory functions. After respiratory viral infection, lung MKs release profibrotic cytokines such as Thrombospondin-1 (TSP-1), a critical inflammatory regulator and activator of transforming growth factor beta 1 (TGFβ1) that drives fibrosis. We hypothesize that neonatal hyperoxia primes the lung for AHR by increasing the recruitment of lung MKs and predisposing MKs to release pro-fibrotic factors (e.g. TSP-1) after infection. Aim 1 will determine how the hyperoxic lung environment after birth effects lung MK recruitment and seeding including how O2 at different developmental ages and MK depletion affect the lung MK population. Aim 2 will determine how neonatal hyperoxia effects lung MK transcriptome before and after activation using in vitro cytokine assays and RNAseq. Experiments will also determine if AHR is MK or TSP-1 dependent by comparing Influenza infection models of MK-depleted mice to transgenic mice with the TSP-1 gene deleted from MKs. Aim 3 will determine how neonatal O2 effects the bone marrow MK pool, including its effects on platelet production. This proposal is a five-year mentored research award and training plan for Dr. Andrew Dylag, MD to investigate oxygen-induced mechanisms of airway dysfunction in both mice and procured human tissues. Dr. Dylag is an Assistant Professor of Pediatrics (Neonatology) at the University of Rochester Medical Center. The research herein builds on Dr. Dylag’s experience as a clinical neonatologist and a basic scientist interested in O2 injury and post-hyperoxia airway hyperreactivity (AHR). As part of his career development plan, Dr. Dylag will attain expertise through four (4) career aims: 1) Increase knowledge and technical skills in the investigation of lung development and repair after injury using translational in vivo models, 2) Targeted training in bioinformatics analysis including transcriptomics, 3) Develop expertise in applying in vivo laboratory discoveries to human tissues and clinical human disease, and 4) Develop the necessary skills to lead an effective translational research program. Dr. Dylag will attain his stated goals by applying new skills in flow cytometry, immunohistochemistry, transcriptomics, and targeted bioinformatics training...