Circular RNA circADAM9 Promotes Inflammation, Oxidative Stress, and Fibrosis of Human Mesangial Cells via the Keap1-Nrf2 Pathway in Diabetic Nephropathy

Circular RNAs (circRNAs) have been discovered as potential biomarkers for diabetic nephropathy (DN). In this study, the potential roles of circADAM9 in high glucose (HG)-induced cell injury of human mesangial cells (HMCs) were investigated, and the underlying mechanism was elucidated.DN cell model in vitro was simulated by HG treatment of HMCs. Endogenous expressions of circADAM9, miR-545-3p, and ubiquitin-specific protease 15 (USP15) were determined by real-time polymerase chain reaction. Cell proliferation and migration were evaluated using Cell Counting Kit-8 and wound healing assays. The inflammatory response was assessed by enzyme-linked immunosorbent assay. Oxidative stress was examined using commercially available kits. Dual-luciferase reporter and RNA pull-down assays were conducted to confirm the interaction among circADAM9, miR-545-3p, and USP15.CircADAM9 was upregulated in DN samples and HG-treated HMCs, while its downregulation inhibited cell proliferation, inflammation, fibrosis, and oxidative stress. Further investigation revealed that circADAM9 exerted this influence by targeting the miR-545-3p/USP15 axis, thereby regulating the KELCH-like ECh-associated protein 1/nuclear factor erythroid 2 related factor 2 (Keap1/Nrf2) pathway. MiR-545-3p knockdown or USP15 overexpression reversed the effect of circADAM9 silencing in HG-induced HMCs.These results indicate that the circADAM9/miR-545-3p/USP15/Keap1/Nrf2 signaling axis is critical for HG-induced cell injury in HMCs and might represent a novel therapeutic target for DN treatment.