miR-29b supplementation decreases expression of matrix proteins and improves alveolarization in mice exposed to maternal inflammation and neonatal hyperoxia.

Even with advances in the care of preterm infants, chronic lung disease or bronchopulmonary dysplasia (BPD) continues to be a significant pulmonary complication. Among those diagnosed with BPD, a subset of infants develop severe BPD with disproportionate pulmonary morbidities. In addition to decreased alveolarization, these infants develop obstructive and/or restrictive lung function due to increases in or dysregulation of extracellular matrix proteins. Analyses of plasma obtained from preterm infants during the first week of life indicate that circulating miR-29b is suppressed in infants that subsequently develop BPD and that decreased circulating miR-29b is inversely correlated with BPD severity. Our mouse model mimics the pathophysiology observed in infants with severe BPD, and we have previously reported decreased pulmonary miR-29b expression in this model. The current studies tested the hypothesis that adeno-associated 9 (AAV9)-mediated restoration of miR-29b in the developing lung will improve lung alveolarization and minimize the deleterious changes in matrix deposition. Pregnant C3H/HeN mice received an intraperitoneal LPS injection on embryonic day 16 and newborn pups were exposed to 85% oxygen from birth to 14 days of life. On postnatal day 3, AAV9-miR-29b or AAV9-control was administered intranasally. Mouse lung tissues were then analyzed for changes in miR-29 expression, alveolarization, and matrix protein levels and localization. Although only modest improvements in alveolarization were detected in the AAV9-miR29b-treated mice at postnatal day 28, treatment completely attenuated defects in matrix protein expression and localization. Our data suggest that miR-29b restoration may be one component of a novel therapeutic strategy to treat or prevent severe BPD in prematurely born infants.