Circular RNA circFTO promotes pressure overload-induced cardiac hypertrophy by encoding a novel protein FTO-36aa

Pathological cardiac hypertrophy leading to ventricular remodeling poses a significant threat to human health. Circular RNAs (circRNAs) play a potential role in the dysregulation of cardiac hypertrophy, and recent evidence highlights their translational ability in various diseases. However, it is not clear whether circRNAs play a protein-coding role in myocardial hypertrophy and ventricular remodeling. This study aimed to investigate the role of circRNA derived from the fat mass and obesity-associated (FTO) gene (circFTO), a translatable circRNA, and the circFTO-encoded a 36 amino acid protein (FTO-36aa) in the pathogenesis of myocardial hypertrophy.

A transverse aortic constriction (TAC)-induced hypertrophy mouse model was established. The heart function of the C57BL/6 mice was evaluated. Myocardial structure injury and fibrosis were analyzed by hematoxylin and eosin (H&E) staining and Masson staining. CircRNA microarray assays were used to screen the dysregulated circRNAs. The recombinant adenovirus-associated virus (AAV) was constructed to overexpress or knockdown FTO protein or circFTO. Mass spectrometry analyses, dual-luciferase reporter assays, and polysome profiling analyses were performed to detect the FTO-36aa.

The study identified dysregulated circRNAs in sham and TAC models, and found that an upregulated circRNA, circFTO, is generated from the back-splicing of FTO exon 5 and exon 7. The silencing of circFTO by AAV significantly weakened the TAC-induced hypertrophy phenotype. The study also identified a novel protein, FTO-36aa, coded by circFTO, that caused the pro-hypertrophy effect of circFTO. FTO-36aa promoted the ubiquitination-mediated protein degradation of FTO, which suppressed the demethylation of RNA, elevating the global N6-methyladenosine (m⁶A) methylation. Further, the m⁶A reader, IGF2BP2, recognized the circFTO/FTO-36aa elevated m⁶A methylation and increased the messenger RNA (mRNA) stabilities of the m⁶A methylated hypertrophic genes.

Overall, this study shed light on the functional importance of alternative splicing-generated circFTO and its coded FTO-36aa during myocardial hypertrophy. The findings provide fundamental insights into the mechanisms of m⁶A methylation regulation in hypertrophic cardiomyocytes.