SMAD2 and renal fibrosis: As a pivotal cytokine in diabetic nephropathy pathogenesis, TGF-β mediates apoptosis and transdifferentiating of renal tubular epithelial cells via the TGF-β-Smad2/3 signaling pathway, thereby promoting extracellular matrix (ECM) formation in the kidney and subsequent progression to DN-related renal fibrosis [18].