CTSD and diabetic kidney disease: After comparing the DKD and CT groups, we observed 31 DEPs in both serum and kidney samples, including known diabetes-associated proteins such as Serpina3k, Lpl, C1qb, Lgals3, Ctsd, Pdgfra, Apoc3, Apoc1, Lifr, and Igfbp2, whereas 178 DEPs in both serum and kidney samples were detected between the ANT and DKD groups (Additional file 1: Fig. S1A).