Abstract 3951: Let-7/miR-98 Family Regulates the Expression of GLUT4 by Targeting MEF-2C in Metabolic Control of Cardiomyocytes
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 adipocytes and skeletal muscle. Furthermore, some miRNAs have been implicated in lipid, amino acid, and glucose homeostasis. In order to determine miRNAs, which regulate cardiomyocyte metabolism, we transduced the cardiac-specific microRNA expression library in lenti-viral vector to neonatal cardiomyocytes, and tried to identify miRNAs which affect cellular ATP levels. After screening, we found that forced expression of the let-7/miR-98 family decreased the ATP concentration. These miRNAs have the same seed sequence and the computational miRNA target prediction algorithm showed that the transcription factor, MEF-2C, is one of the targets by let-7/miR-98. We confirmed that overexpression of let-7/miR-98 reduced the protein level of MEF-2C, and reduced its downstream target, GLUT4, a key molecule for glucose uptake. To assess the functional consequences of silencing endogenous let-7/miR-98 in vitro, we used neonatal cardiomyocytes infected with a lentiviral vector in which 3′UTR with tandem sequences complementary to let-7 is linked to the luciferase reporter gene (Lenti-decoy). Cells infected with this Lenti-decoy increased levels of GLUT4. Next we investigated cardiac expression levels of each let-7/miR-98 family member as well as those of GLUT4 in Dahl salt-sensitive rats. Under a high-salt diet, these rats develop compensated concentric left ventricular hypertrophy (LVH) due to systemic hypertension at the age of 11 weeks, followed by global LV hypokinesis (CHF) at 17 weeks. The cardiac expression levels of GLUT4 are reduced at the LVH stage, and further decreased at the CHF stage. While the expression levels of let-7a, b, c, d, e, f, and i were elevated in LVH, those of let-7d, e, f, and i were elevated in CHF. The expression level of miR-98 was slightly elevated in the CHF stage. Thus, let-7/miR-98 regulates the expression of GLUT4 by targeting MEF-2C in cardiomyocytes. Different members of let-7/miR-98 family may be involved in metabolic control of the heart in LVH and CHF.