SMAD4 and chronic kidney disease: Kidney tissues obtained from the CKD group showed a significant up-regulation in TGF-β1, TGF-βRI, TGF-βRII, Smad2, p-Smad2, Smad3, p-Smad3, and Smad4 while it showed a significant down-regulation in Smad7, pointing to activation of TGF-β/Smad signaling pathway.