SMAD2 and pulmonary fibrosis: SMAD4 and SMAD7 have a regulating activity to SMAD2/3 and play a significant regulatory role in pathophysiological processes such as skin healing and pulmonary fibrosis; however, NAM showed no obvious effect on the protein expression of SMAD4 and SMAD7 at 28 dpi (Figure 7E,F).