Cadmium exposure induces renal fibrosis by inhibiting hsa_circ_0075684/miR-363-3p/KLF4 signaling pathway

To date, no effective chelation therapy exists to remove cadmium (Cd) from the kidneys, a condition that increases the risk of cadmium-induced chronic kidney disease among humans. consequently, it is vital to prevent kidney damage due to cadmium exposure. However, it has been challenging to identify an early diagnostic marker of cadmium-induced kidney damage through mechanism studies. Interestingly, our previous study revealed that the expression of the microRNA miR-363-3p was upregulated in workers who had been diagnosed with chronic occupational cadmium toxicity. Thus, we aimed to investigate the role of miR-363-3p and its potential signaling pathway in cadmium-induced kidney damage. In this study, we identified a novel signaling pathway, hsa_circ_0075684/miR-363-3p/Krüppel-Like Factor 4 (KLF4), through a comprehensive bioinformatics analysis involving six databases. Next, we validated the role of the hsa_circ_0075684/miR-363-3p/KLF4 pathway in human renal tubular epithelial cell line (HK-2) treated with 0, 5, 10 and 15 µM cadmium chloride (CdCl₂). Reverse transcription quantitative PCR (RT-qPCR) and western blot analyses showed that cadmium exposure induced renal fibrosis by regulating the expression of classic renal fibrosis biomarkers, including Fibronectin (Fn), E-cadherin (E-cad) and α-smooth muscle actin (α-SMA) through hsa_circ_0075684/miR-363-3p/KLF4 pathway inhibition. In a mice subchronic model (treated with 0, 5, 10 and 20 mg/kg CdCl₂), Masson's staining revealed obvious renal fibrosis in mice treated with 5, 10 and 20 mg/kg CdCl₂ compared to the control group. The altered expression of hsa_circ_0075684/miR-363-3p/KLF4 pathway components and classic renal fibrosis biomarkers in model mice exposed to cadmium was consistent with that observed in HK-2 cells. In summary, we first report hsa_circ_0075684/miR-363-3p/KLF4 axis in cadmium nephrotoxicity, positioning it as a potential early diagnostic marker for cadmium-induced renal fibrosis.