PDGFRA and bronchopulmonary dysplasia: In BPD, alveolar septa are thickened with collagen and α-smooth muscle actin -, transforming growth factor (TGF)-β-positive myofibroblasts22–25 and have fewer PDGFR-α-expressing cells in the dysmorphic alveolar septa, suggesting abnormal migration and differentiation of mesenchymal progenitor cells within the interstitia of the terminal air spaces26.