Changes of N⁶-methyladenosine modification and unfolded protein response in renal cell injury induced by cadmium

Roles and changes of m⁶A modification and unfolded protein response (UPR) signaling molecules have not been clarified in the renal cell injury induced by cadmium. Our present results indicated that cell apoptosis rate and oxidative stress were both increased in the renal tissue cells of CdSO₄-treated mice when compared with the control group. Detailed analysis further revealed an upward trend in the comprehensive RNA m⁶A modification levels, accompanied by an increase in the expressions of its regulatory proteins, including Mettl3, Mettl16, Alkbh5, Fto, Ythdc2, Ythdf2, etc. as the concentration of cadmium treatment intensified. In addition, the protein expressions of UPR signaling molecules such as Atf4, Atf6, Perk, Xbp1, Grp78, Bax, and Caspase-12 in the cadmium treated group were higher than those in the control group, whereas the expression of the anti-apoptotic protein Bcl-2 was notably reduced. A significant correlation was noted between the levels of m⁶A modification and the protein expressions of UPR signaling molecules. Of particular note, SRAMP predictions suggested that the mRNAs encoding UPR signaling molecules are modified with multiple m⁶A modification sites. Interestingly, immunofluorescence studies illuminated an upsurge in Ythdf2 expression within both the renal medulla and cortex, with a notable translocation from the cytoplasm to the nuclear compartment following cadmium treatment. Concurrently, Xbp1 levels ascended across the entire kidney, predominantly localizing to the cytoplasm. However, the distribution patterns of Ythdf2 and XBP1 throughout the kidney were distinct, with no clear evidence of co-localization between the two. In conclusion, our findings revealed that m⁶A modification and its regulatory proteins as well as UPR signaling molecules are all involved in the cadmium-induced renal tissue cell damage. It appears that the m⁶A modification, orchestrated by a suite of regulatory proteins, may serve as a modulator of UPR signaling molecules. This study furnishes a scientific framework for pinpointing pivotal targets in the etiology of cadmium-induced renal toxicity, offering insights into the realms of RNA epigenetics and UPR signaling responses.