BDNF-TrkB Signaling Maintains AT2 Survival and Is Blocked in Hyperoxia-induced Neonatal Lung Injury

Oxygen supplementation causes an arrest of alveolar formation and a depletion of alveolar epithelial type2 cells (AT2) in preterm infants, both characteristics of bronchopulmonary dysplasia (BPD). BDNF is a key integrator of cell homeostasis and contributes to chronic lung diseases. In this study, (i) wild-type mice were exposed to 85% O2 (HYX) or 21% O2 (NOX) from birth to postnatal day (P)28, followed by spatio-temporal profiling of pulmonary BDNF-signaling on P3-P70. (ii) MLE12 cells, primary murine AT2 (mAT2), and precision-cut ling slices (PCLS) were treated with non-selective Trk inhibitor (K252a), selective TrkB antagonist (Ana12), and TrkB agonist (7,8-dihydroxyflavone). (i) Single cell transcriptomic profiling revealed an expression of Bdnf in mesenchymal cells, but no changes during postnatal development. In contrast, immunofluorescent staining showed a predominant localization of TrkB in AT2 and ACTA2+ cells; its expression and phosphorylation were increased at P7-P21. While hyperoxia induced a 40-fold upregulation of lung Bdnf and a 3-fold elevation of serum BDNF, TrkB abundance and activation decreased by 90%. This was related to a lower Sftpc and increased Acta2 in lungs. (ii) Blockade of Trk(B) reduced survival of MLE12 and mAT2 with a loss of epithelial AT1 and AT2 markers, whereas the TrkB agonist increased survival and regulated AT2 maintenance in PCLS after HYX. Our data identified an important functional role of TrkB signaling in AT2 cells, a mechanism that is blocked in neonatal mouse lungs after hyperoxia and may contribute to a lack of regeneration and to arrest of alveolar growth in infants with BPD.