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

Background: Pathological cardiac hypertrophy poses a significant threat to human health by leading to ventricular remodeling. CircRNAs play a potential role in the dysregulation of cardiac hypertrophy and recent evidence highlights their translational ability in various diseases. However, it remains unclear if circRNAs have a protein-coding role in myocardial hypertrophy and ventricular remodeling. This study aims to investigate the role of translatable circRNA in the pathogenesis of myocardial hypertrophy. Methods: The Transverse Aortic Constriction (TAC) induced hypertrophy mouse model was constructed. The heart function was evaluated by C57BL/6 mice. The myocardial structure injury and fibrosis were analyzed by HE staining and Masson staining. CircRNAs Microarray assay was used to screen the dysregulated circRNAs. The recombinant adenovirus-associated virus was constructed to over-expression or knockdown FTO or circFTO. Mass spectrometry analysis, Dual-luciferase reporter assay, and Polysome profiling analysis were performed to detect the circFTO encoded protein circFTO-36aa. Results: The study screened for dysregulated circRNAs in sham and transverse aortic constriction (TAC) and found that an up-regulated circular RNA, circFTO is generated from the back-splicing of FTO exon 5 and exon 7. Silencing circFTO by AAV significantly weakened the TAC-induced hypertrophy phenotype. Moreover, the study 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 m6A methylation. It was verified that the m6A reader, IGF2BP2, recognized the circFTO/FTO-36aa elevated m6A methylation and increased mRNA stabilities of m6A methylated hypertrophic genes. Conclusion: Overall, this study sheds 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.