Objective: Cadmium, a pervasive environmental heavy metal, is a well-established contributor to chronic kidney disease (CKD) following chronic low-level exposure. While the nephrotoxic effects of cadmium are well-documented, the molecular mechanisms underlying its induction of renal fibrosis remain incompletely understood. This study investigates the role of N6-methyladenosine (m6A) methylation in cadmium-induced renal injury and fibrosis. Methods: Population study: A cross-sectional study was conducted in a community-based cohort of middle-aged and elderly individuals. Participants underwent physical examination, and serum TGF-β1, urinary cadmium levels, and whole-blood m6A methylation-related enzymes (METTL3, METTL14, and FTO) were detected. A logistic regression model was established to analyze the association between these factors and CKD. Animal study: Rats were subcutaneously injected with different doses of CdCl2 to establish a model of cadmium-induced nephrotoxicity. Renal histopathological changes were assessed using H&E staining, while the expression levels of TGF-β1, m6A methylation-related enzymes and miR-21 were detected; In vitro experiments: Human renal proximal tubular (HKC) cells were exposed to CdCl2 to evaluate its cytotoxic effects. MeRIP-Seq was performed to identify CdCl₂-induced alternations in m6A methylation patterns and associated signaling pathways. The functional role of METTL3 in regulating TGF-β1 expression and m6A methylation was further validated via METTL3 knockdown experiments. Results: There were significant differences were observed in urinary cadmium levels, TGF-β1 and METTL3 expression between the CKD and non-CKD groups. Multivariate logistic regression analysis showed that age, gender, METTL3 expression, urinary cadmium and TGF-β1 were independent risk factors for CKD. In animal and cellular experiments, cadmium exposure induced dose-dependent renal injury and fibrosis, as evidenced by histopathological analysis. Furthermore, cadmium exposure significantly upregulated m6A methylation levels, METTL3, TGF-β1 and miR-21 expression in both rat kidney tissues and HKC cells. Notably, knockdown of METTL3 attenuated m6A methylation modification, miR-21 maturation and TGF-β1 expression, suggesting a regulatory role of METTL3 in cadmium-induced renal fibrosis. Conclusion: Our findings demonstrate that cadmium exposure upregulated the level of METTL3-mediated m6A methylation modification of pri-miR-21, enhancing the maturation of miR-21, and subsequently promoting the expression of TGF-β1, thereby exacerbating renal injury and renal fibrosis. These results reveal a novel mechanistic link between cadmium toxicity and renal pathology, highlighting METTL3/m6A/miR-21/TGF-β1 as a potential therapeutic target for cadmium-induced nephropathy.

m6A Methylation, Cadmium, TGF-β1, Renal Fibrosis, miR-21