In vivo, the ratio of MMP2/TIMP2 and MMP9/TIMP1 was also elevated in the skin of diabetes mice by qPCR analysis (Supplementary Figure S1) Therefore, MMP-2 and MMP-9 inhibitors were administered to the STZ-induced diabetic mice to evaluate the changes in skin collagen in vivo. This evidence concerns the gene TIMP1 and diabetes mellitus.