P0709 - Assessment of long-term functional outcomes in a murine model of bronchopulmonary dysplasia

Purpose
Bronchopulmonary dysplasia (BPD) affects up to 40% of infants born before 28 weeks’ gestation. Prematurity, hyperoxic toxicity, and barotrauma lead to the deficiency of pulmonary parenchyma and alveolar simplification characteristic of BPD. While many murine models exist for BPD, few have evaluated long-term outcomes such as pulmonary function and exercise tolerance. Here, we assess an established murine hyperoxic lung injury model of BPD for persistent long-term functional outcomes that may mirror those of human BPD.

Methods
Newborn C57Bl/6J mouse littermates were exposed to room air (Normoxia, 21% O2) or hyperoxia (75% O2) for 10 days. On postnatal day 10, one cohort underwent pulmonary function testing (PFT), followed by lung harvest for morphometric analysis. A second cohort of pups were allowed to recover in normoxia until five weeks of age for treadmill exercise tolerance testing (TETT). TETT consists of three acclimation trials on the treadmill apparatus prior to exercise until exhaustion, which is defined as staying on the shock grid at the end of the treadmill for five consecutive shocks. This cohort of mice then continued recovery in normoxia until eight weeks of age prior to repeat TETT and subsequent PFT.

Results
Hyperoxia exposure was associated with significantly increased compliance and inspiratory capacity at postnatal day 10 (Figure1A). On morphometric analysis, this correlated with increased mean linear intercept (the distance between septations) and significantly decreased alveolar count per field, both hallmarks of the alveolar simplification in BPD (Figure1B-C). At postnatal week five, mice exposed to hyperoxia in the neonatal period suffered functional deficits in TETT, as measured by reduced running speed, distance, and time prior to exhaustion compared to controls (Figure2A). At postnatal week eight, there remained persistent functional deficits in TETT (Figure2B). This correlated with increased compliance and inspiratory capacity on PFT, indicative of a continued obstructive lung disease phenotype (Figure2C). Accounting for differences in gender, males exhibited more significant increases in compliance and inspiratory capacity on PFT, while females experienced greater increases in vital capacity and total lung capacity (Figure2D).

Conclusion
Murine postnatal oxygen exposure provokes a reliable obstructive phenotype of bronchopulmonary dysplasia, with increased compliance and inspiratory capacity on pulmonary function testing and alveolar simplification on morphometric analysis. This phenotype lasted into adolescence and adulthood, with a persistent obstructive phenotype on pulmonary function testing and reduced treadmill exercise tolerance. Males and females may experience different degrees of lung injury. Application of this model and its long-term assessments will be crucial in evaluating potential treatments for bronchopulmonary dysplasia.