METTL3-mediated m6A mRNA modification was involved in cadmium-induced liver injury.

Cadmium is an environmental pollutant that has extensive deleterious effects. However, the mechanisms underlying the hepatotoxicity induced by long-term exposure to cadmium remained undefined. In the present study, we explored the role of m6A methylation in the development of cadmium-induced liver disease. We showed a dynamic change of RNA methylation in liver tissue from mice administrated with cadmium chloride (CdCl2) for 3, 6 and 9 months, respectively. Particularly, the METTL3 expression was declined in a time-dependent manner, associated with the degree of liver injury, indicating the involvement of METTL3 in hepatotoxicity induced by CdCl2. Moreover, we established a mouse model with liver-specific over-expression of Mettl3 and administrated these mice with CdCl2 for 6 months. Notably, METTL3 highly expressed in hepatocytes attenuated CdCl2-induced steatosis and liver fibrosis in mice. In vitro assay also showed METTL3 overexpression ameliorated the CdCl2-induced cytotoxicity and activation of primary hepatic stellate cells. Furthermore, transcriptome analysis identified 268 differentially expressed genes both in mice liver tissue treated with CdCl2 for 3 months and 9 months. Among them, 115 genes were predicted to be regulated by METTL3 determined by m6A2Target database. Further analysis revealed the perturbation of metabolic pathway, glycerophospholipid metabolism, ErbB signaling pathway, Hippo signaling pathway, and choline metabolism in cancer, and circadian rhythm, led to hepatotoxicity induced by CdCl2. Collectively, our findings reveal new insight into the crucial role of epigenetic modifications in hepatic diseases caused by long-term exposure to cadmium.

Identification of miRNAs involved in liver injury induced by chronic exposure to cadmium.

To elaborate the molecular mechanism underlying the hepatotoxicity induced by chronic exposure to cadmium (Cd), a mouse model with hepatocyte-specific deletion of Ppp2r1a (encoding protein phosphatase 2 A Aα subunit, PP2A Aα) gene was used to investigate the effect of cadmium exposure on liver injury. The wild type littermates (WT) and PP2A Aα-/- mice (KO) were treated with cadmium chloride (CdCl2) at concentrations of 0 mg/L, 10 mg/L, 100 mg/L in drinking water for 3, 6 and 9 months (KO mice only for 9 months), respectively. The pathological findings were characterized by progressive inflammation, steatosis, and liver fibrosis upon treatment of CdCl2 in a dose-response and time-dependent manner. Notably, PP2A Aα depletion leads to a more profound liver injury induced by CdCl2 treatment. The transcriptome analysis in livers of KO mice revealed 20 differentially expressed microRNAs (miRNAs) appeared in both 3- and 9-month. Particularly, the alterations of miR-34a-5p, miR-345-5p, and miR-30e-5p expressions were implicated in the development of liver disease and correlated with the degree of liver injury induced by cadmium treatment. Further analysis indicated that miR-34a-5p, miR-345-5p, and miR-30e-5p might be involved in CdCl2-induced liver injury, in part by dysregulation of lipid metabolism and inflammation. The in vitro studies showed that miR-34a-5p was involved in regulation of CdCl2-induced cytotoxicity through directly targeted adiponectin receptor 2 (AdipoR2) mRNA. Taken together, we identified that specific miRNAs were implicated in hepatotoxicity induced by chronic exposure to CdCl2. These findings also provide new insight into the role of PP2A in regulation of miRNAs-mediated liver injury.