Abstract 833: MicroRNA-206 Controls Cardiac Myosin Heavy Chain Gene Expression By Targeting RXR-α
MicroRNA (miRNA) is a small noncoding RNA that modulates posttranscriptional translation. Growing evidence indicates that miRNA is involved in basic cell functions and oncogenesis. In order to find a possible functional role of miRNA in the heart, we first suppressed the expression of Dicer and Ago2, which are required for miRNA biogenesis and function, by lenti-virus-mediated siRNA in neonatal rat cardiomyocytes. Knockdown of Dicer and Ago2 expression significantly increased their beating rate; therefore, we hypothesized that miRNA may regulate the expression of cardiomyocyte contractile protein since cardiac contractility depends on the expression of two myosin heavy chain (MHC) genes, α and β, which are regulated in an antithetical manner by developmental, physiological, and pathological signals. As siRNA against Dicer, which results in the loss of all miRNA function, upregulated α-MHC and downregulated β-MHC mRNA expression, we tried to identify functional miRNAs which have an opposite effect against Dicer siRNA on α/β-MHC expression in the heart. We first performed miRNA microarray analysis in the heart of Dahl salt-sensitive rats in which systemic hypertension caused compensated concentric left ventricular hypertrophy (LVH) at the age of 11 weeks, followed by congestive heart failure (CHF) at the age of 17 weeks. In this model, decreased α/β-MHC ratio is observed at LVH and CHF stages. Next we overexpressed miRNAs which are upregulated in LVH and CHF stages in neonatal rat cardiomyocytes by lenti-virus. After screening these miRNAs, miR-206 was found to decrease the α/β-MHC mRNA expression ratio. The computational miRNA target prediction algorithm showed one of the targets of miR-206 is RXR-α, which regulates α/β-MHC transcription. Forced expression of miR-206 reduced the translation of RXR-α. Moreover, when the expression of RXR-α was downregulated by siRNA, the α/β-MHC mRNA expression ratio decreased in the same manner as miR-206. In conclusion, miR-206 controls the gene expression of MHC isoforms by targeting RXR-α, and these results suggest that miR-206 regulates cardiac contractility.