SMAD3 and bronchopulmonary dysplasia: To investigate the inhibition mechanism of MSCs, EPO and MSCs+EPO on the EMT, TGF-β1 signal pathway-related proteins (TGF-β1, Smad2, p-Smad2, Smad3 p-Smad3 and Smad7) were detected in lung histology in hyperoxia BPD animals.