AHR-mediated m 6 A RNA methylation contributes to PM 2.5 -induced cardiac malformations in zebrafish larvae

A growing body of evidence indicates that ambient fine particle matter (PM 2.5 ) exposure inhibits heart development, but the underlying mechanisms remain elusive. We hypothesized that m 6 A RNA methylation plays an important role in the cardiac developmental toxicity of PM 2.5. In this study, we demonstrated that extractable organic matter (EOM) from PM2.5 significantly decreased global m 6 A RNA methylation levels in the heart of zebrafish larvae, which were restored by the methyl donor, betaine. Betaine also attenuated EOM-induced ROS overgeneration, mitochondrial damage, apoptosis and heart defects. Furthermore, we found that the aryl hydrocarbon receptor (AHR), which was activated by EOM, directly repressed the transcription of methyltransferases mettl14 and mettl3. EOM also induced genome-wide m 6 A RNA methylation changes, which led us to focus more on the aberrant m 6 A methylation changes that were subsequently alleviated by the AHR inhibitor, CH223191. In addition, we found that the expression levels of traf4a and bbc3, two apoptosis related genes, were upregulated by EOM but restored to control levels by the forced expression of mettl14. Moreover, knockdown of either traf4a or bbc3 attenuated EOM-induced ROS overproduction and apoptosis. In conclusion, our results indicate that PM 2.5 induces m 6 A RNA methylation changes via AHR-mediated mettl14 downregulation, which upregulates traf4a and bbc3, leading to apoptosis and cardiac malformations.