SMAD2 and chronic obstructive pulmonary disease: (45) combined clinical samples with animal experiments to demonstrate that the expression levels of microRNA-21 (miR-21), phosphorylated Smad2/3 (p-Smad2/3), and T helper 17 (Th17) cell-related cytokines (IL-17A, IL-6) are significantly upregulated in the lung tissue of COPD patients.