IL6 - ET1 signaling inhibits alveolar growth through FoxO1-dependent AT2 survival in mechanically ventilated newborn mice

<bold>Rational:</bold> Preterm infants with mechanical ventilation (MV) often evolve bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease. Our group previously showed that lung inflammation of infants with BPD leads to a loss of alveolar epithelial type 2 (AT2) cells and thus of the alveolar epithelium. We now aimed to decipher the molecular mechanisms underlying MV-induced arrest of alveolar growth and to test new therapeutic strategies. <bold>Methods:</bold> (i) Five-day-old mice underwent MV for 8h: wildtype (WT), IL6-/-, and WT with anti IL6 antibody or endothelin-1 receptor inhibitors (ET-1R). (ii) Cell culture: pulmonary microvascular endothelial cells (PMVEC), MLE12, primary AT2 from WT and FoxO1ADA mice with constitutive active FoxO1. <bold>Results:</bold> (i) Transcriptomic profiling, gene expression and protein analyses of lungs after MV revealed activation of IL6-STAT3 signaling and increased Edn1 expression, which was associated with nuclear translocation of the anti-proliferative FoxO1 in AT2. IL6-/- and pharmacologic inhibition of IL6 and ET1-R protected against nuclear trapping of pFoxO1, loss of AT2, and arrest of alveolar formation after MV. (ii) Cell culture studies: cyclic elongation and ET1 increase Il6 mRNA in MLE-12; in contrast, IL-6 induces End1 in PMVEC and MLE-12. Moreover, IL6 reduces cell survival via nuclear pFoxO1. FoxO1 knockdown improved MLE-12 survival, whereas FoxO1 overexpression reversed this effect. Finally, AT2 from FoxO1ADA mice showed reduced survival. <bold>Conclusion:</bold> Pharmacologic inhibition of IL6 and ET-1R prevents FoxO1-mediated loss of AT2 after MV and thereby opens promising therapeutic avenues for preterm infants requiring MV and at risk for BPD.