RESUMO
OBJECTIVE: To explore the role of N~6-methyladenosine(m~6A) catalytic enzymes(methyltransferases and demethylases) in cadmium-induced oxidative damage in human renal epithelial cells(HK-2 cells), and to analyze the correlation between nuclear factor-erythroid 2-related factor 2(NRF2) and m~6A catalytic enzymes. METHODS: i) HK-2 cells in logarithmic growth phase were randomly divided into control group and 6 cadmium sulfate treatment groups, then treated with 0, 2, 4, 8, 16, 32 and 64 μmol/L cadmium sulfate solution for 24 hours. The cell survival rates were detected by CCK-8 assay, and the appropriate doses of cadmium sulfate were selected for subsequent experiments. ii) HK-2 cells in logarithmic growth phase were randomly divided into control group and low-, medium-, and high-dose groups, and treated with 0, 4, 8, and 16 μmol/L cadmium sulfate solution respectively for 24 hours. Subsequently, the levels of reactive oxygen species(ROS) were detected by fluorescence probe. The mRNA expression of NRF2, the m~6A methyltransferases such as methyltransferase like proteins(METTL) 3, METTL14, METTL16 and the m~6A demethylases such as fat mass and obesity associated protein(FTO), AlkB family of nonheme Fe(Ⅱ)/α-ketoglutarate(α-KG)-dependent dioxygenases 5(ALKBH5) were determined by real-time polymerase chain reaction. RESULTS: i) The survival rate of HK-2 cells was more than 60.00% and lower than that of the control group(P<0.05) after the cells were stimulated with 16 μmol/L of cadmium sulfate. Therefore, 4, 8 and 16 μmol/L of cadmium sulfate were selected as the stimulation concentrations in the follow-up experiments. ii) The relative expression of NRF2, METTL3, METTL14 and METTL16 in HK-2 cells in low-dose group increased(all P<0.05), while the levels of ROS and the relative mRNA expression of NRF2, METTL3, METTL14, METTL16 and FTO in HK-2 cells in medium and high-dose groups increased(all P<0.05) when compared with the control group. There was no significant difference in the expression of ALKBH5 mRNA among these 4 groups(P>0.05). In the correlation analysis, NRF2 mRNA expression was positively correlated with the mRNA expression of METTL3 and METTL16 [Pearson correlation coefficient(r) = 0.61 and 0.66, respectively, all P<0.05]. There was no correlation between NRF2 mRNA expression and METTL14, FTO and ALKBH5(r=0.53, 0.48, and 0.01 respectively, all P>0.05). CONCLUSION: Cadmium sulfate may increase intracellular ROS level, up-regulate NRF2 expression and activate NRF2 signaling pathway as well as enhance the expression of METTL3 and METTL16 in HK-2 cells, thus increasing intracellular oxidative damage and decreasing the cell survival rate.