Extractable organic matter from PM2.5 inhibits cardiomyocyte differentiation via AHR-mediated m6A RNA methylation

An ever-increasing body of research has established a link between maternal PM2.5 exposure and congenital heart diseases in the offspring, but the underlying mechanisms remain elusive. We recently reported that activation of the Aryl Hydrocarbon Receptor (AHR) by PM2.5 causes aberrant m⁶A RNA methylation, leading to cardiac malformations in zebrafish embryos. We hypothesized that PM2.5 can disrupt heart development by inducing m⁶A methylation changes through AHR in mammals. In this study, we observed that extractable organic matters (EOM) from PM_2.5 significantly impaired cardiomyocyte differentiation in embryonic rat cardiomyoblasts H9c2. Importantly, EOM exposure reduced global m⁶A methylation levels, which was reversed by AHR inhibition. Moreover, AHR, activated by EOM directly promoted the transcription of the demethylase, FTO, leading to global m⁶A hypomethylation. Specifically, AHR-induced FTO overexpression decreased the m⁶A methylation levels of Nox4 mRNA, resulting in NOX4 overexpression and subsequent oxidative stress in EOM samples. We then demonstrated that oxidative stress contributes to the inhibition of cardiomyocyte differentiation by EOM through suppression of Wnt/β-catenin signaling. In summary, our findings indicate that AHR activation by PM_2.5 directly enhances the expression of the demethylase, FTO, which increases NOX4 expression by reducing its m⁶A methylation. The oxidative stress caused by NOX4 overexpression inhibits Wnt/β-catenin signaling, thereby compromising cardiomyocyte differentiation.

AHR; Cardiomyocyte differentiation; M(6)A RNA methylation; PM2.5; Wnt signaling.