Regulatory Roles of the N6-methyladenosine Demethylase FTO in Cardiac Remodeling

Abstract Background The most prevalent internal RNA modification, N6-methyladenosine (m6A), serves as an additional layer of transcriptional and translational regulation. Methyl transferases (like METTL3) and demethylases (e.g., FTO) are the enzymes that catalyze m6A methylations. Our result showed that loss of FTO causes maladaptive cardiac remodeling in rodent hearts, which is consistent with other studies that emphasized the importance of FTO-dependent m6A RNA methylation in maintaining cardiac homeostasis, ventricular hypertrophy, and heart failure. Despite the fact that FTO is essential for stress-induced cardiac hypertrophy, its underlying functional mechanisms in regulating maladaptive cardiac remodeling are not yet known. Purpose In this study, we showed the necessity of FTO dependent m6A methylation in coordinating the molecular and signaling events that are engaged in cardiac hypertrophy, and further identified the detrimental signaling mechanisms that are regulated by FTO during pathological remodeling. Methods Firstly, the control and FTO-cKO (cardiomyocyte specific FTO knockout) group mice were subjected to sham and TAC (transverse aortic constriction) operation. Echocardiography was performed 1 week post-TAC. Secondly, m6A RNA immunoprecipitation (meRIP) sequencing were performed from the isolated mice heart tissue. Additionally, the effect of apoptosis and mTORC1 upon FTO depletion were analysed in both rodents and iPS-CMs. In vitro the interrelation between FTO demethylase, mTORC1 and autophagy in the regulation of cardiac apoptosis were identified by 1. inhibiting mTORC1 pathway with specific inhibitors, and by 2. inhibiting 'late autophagy' in FTO silenced iPS-CMs. Results In contrast to control mice, which exhibit concentric hypertrophy at the beginning of induced pressure overload (PO), echo analysis of one week post-TAC revealed that FTOcKO mice develop a DCM-like phenotype. Further, MeRIP-seq data showed that there is deregulation in the m6A methylation with FTO depletion. Around 114 differently hypermethylated transcripts and 58 differentially hypomethylated transcripts were discovered in FTOcKO sham as compared to Control sham; these transcripts are involved in the control of apoptosis, the mTORC1 signaling pathway, lysosomal biogenesis, and autophagy. In both rodents and iPS-CMs, FTO ablation dramatically enhances cardiac apoptosis and the mTORC1 signaling pathway. Furthermore, inhibition of mTORC1 pathway attenuates cardiac apoptosis in siFTO-iPS-CMs. Moreover, autophagic flux analysis revealed that FTO depletion cause autophagic flux impairment and exacerbate cardiac apoptosis. However, the autophagic flux is ameliorated with mTORC1 inhibition in late-autophagy inhibited siFTO-iPS-CMs. Conclusion Our data unravel the novel roles of FTO demethylase in the course of cardiac remodeling, which opens doors to therapeutic interventions in the treatment of cardiac hypertrophy and heart failure.