We found that the intranasal administration of L. reuteri and its tryptophan metabolite indole-3-aldehyde (3-IAld) ameliorated hyperoxia-induced mice lung BPD-like changes, deceased proinflammatory cytokines (IL-1β, IL-6, and TNF-α), and increased the levels of surfactant-associated protein C (SPC), aquaporin 5 (AQP5), and vascular endothelial growth factor receptor 2 (VEGFR2, also known as FLK-1). The gene discussed is AQP5; the disease is bronchopulmonary dysplasia.