Abstract 841: MicroRNA-133 Regulates the Expression of CPT-1b and GLUT4 by Targeting SRF and KLF15 and Is Involved in Metabolic Control in Cardiac Myocytes
MicroRNAs (miRNAs) are small, non-protein-coding RNAs that recognize target sequences of imperfect complementarity in cognate mRNAs and inhibit protein translation. Growing evidence indicates that miRNAs affect pathways that are fundamental for metabolic control such as adipocyte and skeletal muscle. Furthermore, some miRNAs have been implicated in lipid, amino acid, and glucose homeostasis. In order to determine miRNAs which regulate cardiac myocyte metabolism, we transduced the cardiac-specific microRNA expression library in lenti-viral vector to neonatal cardiac myocytes and tried to identify miRNAs which affect cellular ATP levels. After screening, we found that forced expression of miR-133 decreased the ATP concentration. The computational miRNA target prediction algorithm showed that transcription factors, SRF and KLF-15, are targets of miR-133. We confirmed that overexpression of miR-133 reduced protein levels of SRF and KLF-15, and reduced their downstream targets, CPT-1b and GLUT4, which are key molecules for β-oxidation of fatty acids and glucose uptake. To assess the functional consequences of silencing endogenous miR-133 in vitro, we used neonatal cardiac myocytes infected with a lentiviral vector in which 3′UTR with tandem sequences complementary to miR-133 is linked to the luciferase reporter gene (Lenti-decoy). Cells infected with this Lenti-decoy had decreased functional miR-133 and increased levels of cellular ATP as well as CPT-1b and GLUT4. Next we investigated the expression level of CPT-1b, GLUT4 and miR-133 in a Dahl salt-sensitive rat. In this rat under a high-salt diet, systemic hypertension caused compensated concentric left ventricular hypertrophy (LVH) at the age of 11 weeks, followed by marked LV dilatation and global hypokinesis at 17 weeks. The expression levels of CPT-1b and GLUT4 in the heart are reduced at the LVH stage and further decreased at the congestive heart failure stage. The expression level of miR-133 was parallel to these levels. Thus, miR-133 regulates expression of CPT-1b and GLUT4 by targeting SRF and KLF-15 and is involved metabolic control in cardiac myocytes. The downregulation of miR-133 in failing hearts may contribute to enhancing myocardial energy intake as a compensatory mechanism.