LAUSR

Objectives: Circular RNAs (circRNAs) are single-stranded non-coding RNAs that form a covalent closed looped structure and are generated during gene transcription. In our genome-wide analysis of cardiac circRNA expression in both human and mouse hearts we identified a highly abundant circRNA, named here as circHeart and hypothesize an important role for circHeart in cardiomyocyte physiology and homeostasis. Materials and method: We undertook FISH to visualize the localization of circHeart . Online tools have predicted multiple potential miRNA binding sites on circHeart , including the cardiac-enriched microRNA-133a (miR-133a). We assessed the interactions of circHeart with these miRNAs by luciferase and pull-down assays and performed AAV9-mediated RNAi knockdown and overexpression of circHeart in mice in vivo . In vivo phenotype was tracked by echocardiography, electrocardiogram and histological studies. Transverse aortic constriction (TAC) was also performed. Results: FISH imaging showed circHeart localized largely to the cardiomyocyte cytosol. Luciferase and reciprocal pull-down assays suggest circHeart can interact with miR-133a. MiR-133a is a well-known regulator of cardiac hypertrophy and antagomir-133a treatment has been shown to induce cardiac hypertrophy in vivo . In our studies, while AAV9 RNAi-mediated knockdown of circHeart has no apparent baseline effect in the heart it suppresses pathological cardiac hypertrophy post-TAC. More strikingly, AAV9-mediated overexpression of circHeart in vivo resulted in mouse mortality between 3-4 days post-transduction and surviving mice showed evidence of dilated cardiomyopathy. Known targets of miR-133a were concordantly modulated in the knockdown and overexpression mouse model. Conclusion: CircRNAs have huge potential role as therapeutic targets and/or disease biomarkers and represent a new avenue for cardiovascular research. Taken together, our data are consistent with a mechanistic model of circHeart sequestering miR-133a. Inhibiting circHeart abundance presents a potential target for treating cardiac hypertrophy.