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

Objective: 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.

Methods: 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.

Results: 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.

Conclusion: 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.