MicroRNA-223 Displays a Protective Role Against Cardiomyocyte Hypertrophy by Targeting Cardiac Troponin I-Interacting Kinase

Background/Aims: MicroRNAs play regulatory role in cardiovascular disease. MicroRNA-223 (miR-223) was found to be expressed abundantly in myocardium. TNNI3K, a novel cardiac troponin I (cTnI)-interacting and cardiac hypertrophy related kinase, is computationally predicted as a potential target of miR-223. This study was designed to investigate the cellular and molecular effects of miR-223 on cardiomyoctye hypertrophy, focusing on the role of TNNI3K. Methods: Neonatal rat cardiomyocytes (CMs) were cultured, and CMs hypertrophy was induced by endothelin-1 (ET-1). In vivo cardiac hypertrophy was induced by transverse aorta constriction (TAC) in rats. Expression of miR-223 in CMs and myocardium was detected by real-time PCR (RT-PCR). MiR-223 and TNNI3K were overexpressed in CMs via chemically modifed sense RNA (miR-223 mimic) transfection or recombinant adenovirus infection, respectively. Cell size was measured by surface area calculation using fluorescence microscopy after anti-α-actinin staining. Expression of hypertrophy-related genes was detected by RT-PCR. The protein expression of TNNI3K and cTnI was determined by Western blots. Luciferase assay was employed to confirm the direct binding of miR-223 to the 3'UTR of TNNI3K mRNA. Intracellular calcium was measured by sensitive fluorescent indicator (Furo-2). Video-based edge detection system was employed to measure cardiomyocyte contractility. Results: MiR-223 was downregulated in ET-1 induced hypertrophic CMs and in hypertrophic myocardium compared with respective controls. MiR-223 overexpression in CMs alleviated ET-1 induced hypertrophy, evidenced by smaller cell surface area and downregulated ANP, α-actinin, Myh6 and Myh7 expression. Luciferase reporter gene assay showed that TNNI3K serves as a direct target gene of miR-223. In miR-223-overexpressed CMs, the protein expression of TNNI3K was significantly downregulated. MiR-223 overexpression also rescued the upregulated TNNI3K expression in hypertrophic CMs. Furthermore, cTnI phosphorylation was downregulated post miR-223 overexpression. Ad.rTNNI3K increased intracellular Ca2+ concentrations and cell shortening in CMs, while miR-223 overexpression significantly rescued these hypertrophic effects. Conclusion: By direct targeting TNNI3K, miR-223 could suppress CMs hypertrophy via downregulating cTnI phosphorylation, reducing intracellular Ca2+ and contractility of CMs. miR-223 / TNNI3K axis may thus be major players of CMs hypertrophy.