Interleukin 37 (IL-37) Reduces High Glucose-Induced Inflammation, Oxidative Stress, and Apoptosis of Podocytes by Inhibiting the STAT3-Cyclophilin A (CypA) Signaling Pathway.

BACKGROUND Diabetic nephropathy (DN), the formation of albuminuria, is one of the most important complications seen in diabetic patients. IL-37, an inhibitor of congenital inflammation and immune response, plays an important role in the occurrence and development of diabetes, but its study in DN has not been previously reported. MATERIAL AND METHODS Podocyte transfection techniques were used to overexpress STAT3 and cyclophilin A (CypA). The expression of IL-37, STAT3, and CypA was detected by RT-qPCR and western blot. Cell survival was detected by CCK-8. The expression of inflammatory factors and molecules related to oxidative stress was detected by ELISA and western blot, and cell apoptosis was detected by flow cytometry and western blot. RESULTS The expression of IL-37 was significantly decreased in high glucose-treated podocytes. IL-37 improved the survival rate of podocytes suffering from high glucose-induced apoptosis. It inhibited the expression of the inflammation-related factors tumor necrosis factor alpha (TNF-alpha), IL-1ß, IL-6, malondialdehyde (MDA), and lactate dehydrogenase (LDH), and promoted the expression of superoxide dismutase (SOD) in high glucose-treated podocytes. In addition, IL-37 inhibited the expression of the inflammation-related proteins MCP-1, NLRP3, ASC, and caspase-1. IL-37 also inhibited high glucose-induced apoptosis of podocytes by inhibiting the expression of the apoptosis-related proteins Bax and cleaved caspase-3/6/9, and by promoting the expression of Bcl-2. At the same time, we found that the STAT3/CypA signaling pathway was activated after induction by high glucose, while it was inhibited after treatment with IL-37. Overexpression of STAT3 and CypA inhibited the effects of IL-37 on the alleviation of inflammation and oxidative stress and on the reduction of apoptosis of high glucose-treated podocytes. CONCLUSIONS IL-37 can significantly reduce podocyte inflammation, oxidative stress, and apoptosis induced by high glucose, and can inhibit the STAT3-CypA signaling pathway. Upregulation of the STAT3-CypA signaling pathway can inhibit the protective effect of IL-37 against podocyte injury induced by high glucose.