Oxygen differentially affects the hox proteins Hoxb5 and Hoxa5 altering airway branching and lung vascular formation

Hoxb5 and Hoxa5 transcription factor proteins uniquely impact lung morphogenesis at the developmental time point when extremely preterm infants are born. The effect of O 2 exposure (0.4 FiO 2 ) used in preterm infant care on these Hox proteins is unknown. We used ex vivo fetal mouse lung organ cultures to explore the effects of 0.4 FiO 2 on lung airway and vascular formation in the context of Hoxb5 and Hoxa5 expression and regulation. Compared to room air, 48 h (h) 0.4 FiO 2 adversely attenuated airway and microvasculature formation while reducing lung growth and epithelial cell volume, and increasing mesenchymal volume. 0.4 FiO 2 decreased pro-angiogenic Hoxb5 and VEGFR2 while not altering protein levels of angiostatic Hoxa5. Lungs returned to RA after 24 h 0.4FiO 2 had partial structural recovery but remained smaller and less developed. Mesenchymal cell apoptosis increased and proliferation decreased with time in O 2 while epithelial cell proliferation significantly increased. Hoxb5 overexpression led to prominent peri-airway VEGFR2 expression and promoted lung vascular and airway patterning. Hoxa5 overexpression had the opposite effects. We conclude that 0.4 FiO 2 exposure causes a profound loss of airway and lung microvascular development that occurs partially via reduction in pro-angiogenic Hoxb5 while angiostatic Hoxa5 expression is maintained.