MAPK3 and diabetes mellitus: As a regulator in the TGF-β1 signaling pathway (Rhyu et al., 2005; He et al., 2015), we examined the phosphorylated ERK1/2 protein levels and found that they were significantly upregulated in the DM group compared with the NC group and obviously down-regulated following 12 weeks of saxagliptin treatment (Figures 5I,J).