PROJECT SUMMARY Exposure to environmental pollutants or toxins early in life can alter health and fitness as people age. Preterm infants are a prime example because their lungs are exposed too soon and often to excess amounts of oxygen at birth. These individuals are then at risk for growth failure, reduced lung function, impaired host response to respiratory viral infections, and development of cardiovascular disease as they age. We established a unique mouse model wherein exposure to high levels of oxygen (hyperoxia) at birth causes lung and heart disease later in life. Using this model, we now provide new evidence that neonatal hyperoxia also impairs growth by inhibiting fat accumulation. Bone marrow mesenchymal stem cells (BMSCs) isolated from these mice grew slower and were more oxidized. They also displayed reduced capacity to accumulate lipid and differentiate into adipocytes, possibly because they expressed higher levels of 5’-AMP activated protein kinase (AMPK), a master regulator of energy homeostasis that inhibits fatty acid synthesis and cell proliferation. Since the oxidation of stem cells increases with age, we will test the hypothesis that neonatal hyperoxia accelerates the oxidation of mesenchymal stem cells as mice age, thereby altering their ability to differentiate and produce fat. In Aim 1, we will determine how neonatal hyperoxia permanently reprograms the oxidation state and thus differentiation of bone, fat, and lung MSCs. Since growth failure is not seen when transgenic SftpcEC-SOD mice are exposed to hyperoxia, Aim 2 will determine if over-expression of the anti-oxidant extracellular superoxide dismutase by alveolar epithelial type 2 cells restores the oxidation state and adipogenic potential of MSCs. We will also determine whether EC-SOD preserves the differentiation of adjacent lipofibroblasts that support AT2 cell homeostasis. Impact on the Field: Understanding how neonatal hyperoxia disrupts adipogenesis is important because it will increase our understanding of how preterm birth alters health later in life.