SMAD1 and diabetic kidney disease: To explicate the patterns and the molecular mechanism involved in the regulation of SnoN expression in DKD, the expression of Smad1/5 in NRK-52E cells was knocked down by co-transfecting Smad1shRNA and Smad5 shRNA plasmids (sh-Smad1/5) (Supplementary Fig. 3a, b).