Abstract 3200: Attenuation of MicroRNA-1 De-represses the Cytoskeleton Regulatory Protein Twinfilin-1, and This Contributes to Initiation of Cardiac Hypertrophy
Background: MicroRNA (miRNA) is involved in several aspects of cardiac hypertrophy, including cardiac growth, conduction, and fibrosis. However, its effect on the organization and dynamics of the cardiomyocyte cytoskeleton during this pathological process is not known.
Methods and Results: With miRNA microarray and small RNA library sequencing, we identified miRNAs with high expression levels in the human heart. Among them, microRNA-1 (miR-1) was the most abundant miRNA. Northern blot and real-time quantitative PCR analyses verified that miR-1 was highly and specifically expressed in skeletal muscle and heart. Moreover, miR-1 was predominantly expressed in cardiac myocytes, but only presented at low level in other cardiac cell types including cardiac fibroblasts. To investigate the role of miR-1 in cardiac hypertrophy, we generated a rat cardiac hypertrophy model by abdominal aorta constriction. After 1 week’s constriction, miR-1 was substantially down-regulated in the rat hypertrophic left ventricle (n=9) compared to that in the sham-operated controls (n=8; P<0.05). Also, in phenylephrine-induced hypertrophic cardiomyocytes, the level of miR-1 was decreased by 36%. Adenovirus-mediated over-expression of miR-1 in hypertrophic cardiomyocytes reduced the cell size (denoted as cell surface area) and attenuated the expression levels of hypertrophic markers including nppa. Furthermore, by integratively applying bioinformatic target prediction, luciferase reporter assay and Western blot analyses, a cytoskeleton regulatory protein twinfilin-1 was identified as the direct target of miR-1. Accordingly, the protein level of twinfilin-1 was increased in both the hypertrophic hearts and phenylephrine-stimulated cardiomyocytes. In addition, over-expression of twinfilin-1 in cardiomyocytes increased both the cell size and the expression of nppa.
Conclusions: Our results demonstrate that the cytoskeleton regulatory protein twinfilin-1 is a novel target of miR-1, and that reduction of miR-1 by hypertrophic stimuli induces the up-regulation of twinfilin-1, which in turn evokes hypertrophy through the regulation of cardiac cytoskeleton, suggesting a potential new therapeutic target for cardiac hypertrophy.