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). This evidence concerns the gene MDM2 and pulmonary fibrosis.