Abstract 14029: Microrna-27a Regulates Beta-Myosin Heavy Chain Gene Expression by Targeting Thyroid Hormone Receptor Beta 1 in Neonatal Rat Ventricular Myocytes
MicroRNAs (miRNAs), small non-coding RNAs, are negative regulators of gene expression and play important roles in gene regulation in the heart. To examine the role of miRNAs in the expression of two isoforms of the cardiac myosin heavy chain (MHC) gene, α- and β-MHC, which regulate cardiac contractility, endogenous miRNAs were down-regulated in neonatal rat ventricular myocytes (NRVMs) using lentivirus-mediated siRNA against Dicer, an essential enzyme for miRNA biosynthesis, and MHC expression levels were examined. As a result, Dicer siRNA could down-regulate endogenous miRNAs simultaneously, including ubiquitous miR-16 and muscle-specific miR-133b and the β-MHC gene but not α-MHC, suggesting that specific miRNAs could up-regulate the β-MHC gene. After screening for β-MHC mRNA expression in NRVMs over-expressing 21 randomly selected miRNAs, miR-27a was found to up-regulate the β-MHC gene but not α-MHC. Moreover, β-MHC protein was down-regulated by silencing endogenous miR-27a. These results suggest that miR-27a could regulate β-MHC gene expression by targeting negative regulators of the β-MHC gene. Bioinformatics screening using TargetScanTM predicted four target genes of miR-27a: thyroid hormone receptor β1 (TRβ1), retinoid × receptor α (RXRα), and thyroid hormone receptor associated protein 1 and 2 (THRAP1 and 2), which might negatively regulate the β-MHC gene in association with the negative thyroid hormone responsive element on the β-MHC promoter. TRβ1 plays a central role in β-MHC gene regulation in association with the other three candidates. While RXRα has already been reported as a target of miR-27a, the present study demonstrated that TRβ1 was a target of miR-27a but not THRAP1 and 2. These findings suggest that TRβ1 and RXRα are involved in β-MHC gene regulation by miR-27a. In addition, miR-27a and TRβ1 siRNA were demonstrated to attenuate the effect of thyroid hormone, a ligand of the thyroid hormone receptor, that down-regulates the β-MHC gene, whereas RXRα siRNA did not cause inhibition, suggesting the predominant role of TRβ1 in this β-MHC gene regulation by miR-27a. In conclusion, miR-27a regulates β-MHC gene expression by targeting TRβ1 in NRVMs.
- © 2010 by American Heart Association, Inc.