FGF9 and bronchopulmonary dysplasia: In the present study, we have demonstrated: 1) BPD-EXO aggravate lung injury and impair lung angiogenesis in a hyperoxia mouse model; 2) we have further shown that the adverse effect of BPD-EXO on lung tissue and angiogenesis in neonate can persist in adult mice; 3) many BPD-EXO-induced DEGs and pathways may contribute to these adverse effects on lung tissues and vascular growth; and 4) BPD-EXO inhibit angiogenesis in vitro in association with decreased fgf9 and Cacna2d3 in HUVECs.