Metformin Inhibits Podocyte Damage in Mice with Diabetic Nephropathy by Enhancing Autophagy of Renal Cells

Background: Diabetic kidney disease (DKD) is a systemic microvascular complication of poorly controlled diabetes, caused by chronic hyperglycemia. Metformin, as a first-line drug in oral treatment of patients with type 2 diabetes mellitus (T2DM), has attracted increasing attention because in addition to its significant hypoglycemic effect, it has protective effect on DKD. The purpose of this study was to explore the regulatory role of metformin in DKD. Methods: Twelve 8-week-old male Specific-Pathogen-Free (SPF) C57BL/KsJ-db/db mice were used as animal models of T2DM. Six 8-week-old male C57BL/6 mice were used as control subgroup (NC subgroup); db/db mice were randomly divided into two subgroups: DKD subgroup (n = 6) and metformin (MET) intervention subgroup (DKD + MET subgroup, n = 6). The amount of 24-hour urinary protein and microalbumin, and levels of serum creatinine, and blood urea nitrogen were measured. Hematoxylin-Eosin (HE) staining and Periodic Acid-Schiff (PAS) staining were used to evaluate the morphological and pathological changes of the glomeruli. The expression of glomerular podocyte labeled protein was observed by immunofluorescence. The expressions of podocyte marker protein and autophagy related marker protein were detected by western blot. Results: In contrast with the normal control subgroup, metformin markedly decreased the body weight of DKD mice. Compared with the DKD subgroup, in the DKD + MET subgroup the pathological damage of the renal structure was alleviated, serum creatinine (Scr), blood urea nitrogen (BUN), 24-hour urinary protein and urinary mindin were decreased, while the expressions of microtubule-associated protein light chain 3 (LC3), nephrin, and podocin were increased. Light microscopic evaluation using PAS staining confirmed that the above injuries were alleviated by metformin. The protein of PTEN (phosphatqase and tensin homologue)/Akt (protein kinase B)/mTOR (mechanistic target of rapamycin) pathway in drug group tended to be increased, but did not reach statistical significance. Conclusions: Metformin can improve the pathological damage of DKD, improve the renal functional indicators Scr and BUN, and decrease urinary microalbumin (UMA) and urinary mindin, increase the levels of autophagy proteins LC3 and Beclin-1, and inhibit the podocyte damage in DKD, and then delay the development of DKD.