Activation of hypoxia-inducible factors in hyperoxia through prolyl 4-hydroxylase blockade in cells and explants of primate lung

Preterm neonates with respiratory distress syndrome (RDS) often develop a chronic form of lung disease called bronchopulmonary dysplasia (BIRD), characterized by decreased alveolar and vascular development. Ventilator treatment with supraphysiological O-2 concentrations (hyperoxia) contribute to the development of BPD. Hyperoxia down-regulates and hypoxia up-regulates many angiogenic factors in the developing lung. We investigated whether angiogenic responses could be augmented through enhancement of hypoxia-inducible factors 1 alpha and 2 alpha (HIF-1 alpha and -2 alpha, respectively) via blockade of prolyl hydroxylase domain-containing proteins (HIF-PHDs) in human microvascular endothelial cells from developing and adult lung, in epithelial A549 cells, and in fetal baboon explants in relative or absolute hyperoxia. PHD inhibitor (FG-4095) and positive control dimethyloxaloylglycine (DMOG), selective and nonselective HIF-PHD inhibitors, respectively, enhanced HIF-1 alpha and -2 alpha, vascular endothelial growth factor (VEGF), and platelet-endothelial cell adhesion molecule 1 expression in vitro in 95% and 21% O-2. Furthermore, VEGF receptor fms-like tyrosine kinase 1 (Flt-1) was elevated, whereas kinase insert domain-containing receptor/fetal liver kinase 1 (KDR) was diminished in endothelial, but not epithelial, cells. Intracellular Flt- 1 and KDR locations were unchanged by PHD blockade. Like VEGF, FG-4095 and DMOG increased angiogenesis in vitro, both in 95% and 21% 02, an effect that could be blocked through either Flt-1 or KDR. Notably, FG-4095 was effective in stimulating HIFs and VEGF also in fetal baboon lung explants. FG-4095 or DMOG treatment appeared to stimulate the feedback loop promoting HIF degradation in that PHD-2 and/or -3, but not PHD-1, were enhanced. Through actions characterized above, FG-4095 could have desirable effects in enhancing lung growth in BPD.