In STZ-induced diabetic mice, Li et al. reported that repeated injection of umbilical cord MSCs could inhibit TGF-β1-triggered myofibroblast differentiation through paracrine action and increase the levels of MMP2 and MMP9, thereby reducing the deposition of fibronectin and collagen I and alleviating proteinuria, glomerular injury, and fibrosis in DKD mouse models [115]. This evidence concerns the gene MMP9 and diabetic kidney disease.