Nuclear transcription factor Smad2/3 and fibrosis index Col4a5 were labeled using immunofluorescence double staining in DKD kidney tissue in vivo. The expression of Smad2/3 in myofibroblast nuclei increased, and collagen fibers were deposited in DKD kidney tissues at significantly higher levels relative to those in the control group (Fig. 4C). Here, COL4A5 is linked to diabetic kidney disease.