COL4A1 and diabetes mellitus: To assess the impact of diabetes on the expression of mRNA from genes related to fibrosis, we analyzed the expression of mRNA encoding collagen 1, 3, and 4 (Col1a1, Col3a1, Col4a1), fibronectin (Fn1), matrix metalloproteinases-2 and -9 (Mmp2 and Mmp9), tissue inhibitors of metalloproteinases-1 and -2 (Timp1 and Timp2), as well as the mediator of fibrogenesis TGF-β (Tgfb1) and the mediator of the TGF-β action connective tissue growth factor (Ctgf) (Figure 4A).