APOE and renal fibrosis: Previous studies have demonstrated that DPP-4 inhibitors not only improve hyperglycemia, but also protect against tissue damage through various stimuli, such as myocardial fibrosis in db/db−/− mice, renal fibrosis in 5/6 nephrectomy rats, renal ischemia-reperfusion injury, cisplatin nephropathy, atherosclerosis in apolipoprotein E-null mice, and non-alcoholic steatohepatitis and renal fibrosis in streptozotocin-induced diabetic mice [26–31].