Abstract 3827: Upregulation of MicroRNA 27a, which Downregulates Retinoid X Receptorα, Controls Cardiac Myosin Heavy Chain Gene Expression in Neonatal Rat Cardiomyocyte
MicroRNA (miRNA) is a small noncoding RNA that modulates posttranscriptional translation. A growing body of evidence indicates that miRNA is involved in basic cell functions and oncogenesis. To identify a possible functional role of miRNA in the heart, we first suppressed the expression of Dicer, which is required for miRNA biogenesis and function. Lenti-virus-mediated introduction of siRNA against Dicer into neonatal rat cardiomyocytes increased α/β-MHC mRNA expression ratio, in a pattern opposite to that observed in cardiac hypertrophy and heart failure. To identify miRNAs that regulate α/β-MHC expression in the heart, we performed a miRNA microarray analysis of the heart in a salt-sensitive Dahl rat model. In this model, systemic hypertension caused compensated concentric left ventricular hypertrophy (LVH) at the age of 11 weeks, followed by congestive heart failure (CHF) at 17 weeks. We identified several miRNAs that were upregulated at the LVH or CHF stages in the heart of Dahl salt-sensitive rats and overexpressed these miRNAs in neonatal rat cardiomyocytes by lenti-virus. As a result, miR-27a was found to decrease the α/β-MHC mRNA expression ratio. The computational miRNA target prediction algorithm showed that the target of miR-27a is retinoid X receptor (RXR)-α, which can regulate α/β-MHC transcription. Moreover, when the expression of RXR-α was downregulated by siRNA, the α/β-MHC mRNA expression ratio decreased in the same manner as the overexpression of miR-27a. To study the loss of miR-27a function, we constructed ‘decoy’ genes, which had 3 or 6 tandem complementary sequences of miR-27a at the 3′UTR of luciferase gene under the control of CMV promoter. When miR-27a ‘decoy’ genes were introduced into cardiac myocytes, the α/β-MHC ratio was increased, suggesting that the decoy rescued α/β-MHC mRNA from suppression by miR-27a. These findings demonstrate that upregulation of microRNA-27a, which downregulates retinoid X receptor α, controls α/β-myosin heavy chain gene expression in cardiomyocyte.