MDM2 and bronchopulmonary dysplasia: Serpine 1, also known as plasminogen activator inhibitor 1 (PAI-1), can lead to alveolar type II senescence by activating p53-p21 in pulmonary fibrosis (51), while MDM2, the direct ligand of p53, seems to be phosphorylated in BPD, increasing its stability and thereby promoting apoptosis (52).