SMAD2 and chronic obstructive pulmonary disease: As shown in Figure 3(c), the protein levels of TGF-βR1, p-Smad2, and p-Smad3 in COPD group were significantly higher than those of normal group, while ginsenoside Rg1 treatment downregulated expressions of TGF-βR1, p-Smad2, and p-Smad3, especially at a high dose.