KDR and pulmonary fibrosis: Compared to the room air group, the hyperoxia group exhibited lower expression levels of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2), but had higher protein levels of α-smooth muscle actin (α-SMA), a pulmonary fibrosis biomarker on PN14 (Figures 2A, B).