Rapid Effects of Stretched Myocardial and Vascular Cells on Gene Expression of Neonatal Rat Cardiomyocytes with Emphasis on Autocrine and Paracrine Mechanisms

Eph receptors constitute the largest family of receptor tyrosine kinases. Multiple transcripts of ephrin-A5, the cognate ligand of the EphA3 receptor, were found in neonatal rat cardiomyocytes. Two cDNA clones encoding the full-length ephrin-A5 (ephrin-A5α) and a 27-amino acid deletion form (ephrin-A5β) were isolated. To examine the role of ephrin-A5 in cardiomyocytes, the cDNAs were inserted into adenoviral vectors, termed Ad.ephrin-A5α and Ad.ephrin-A5β, respectively, and overexpressed in cardiomyocytes. The effect of ephrin-A5 on cardiomyocyte gene expression was investigated using a cDNA expression array and Western blot analysis. The results showed that both ephrin-A5α and ephrin-A5β downregulated cyclin D2, cyclin-dependent kinase-4 proteins, and their cognate receptor EphA3, which were associated with reduced bromodeoxyuridine incorporation in cardiomyocytes. Whereas ephrin-A5α and ephrin-A5β also induced differential gene expression, only ephrin-A5β significantly upregulated the transcription of brain natriuretic peptide and downregulated ras-related protein RAB2, protein kinase C inhibitor protein-1, clusterin, and insulin-like growth factor-binding protein. The results suggest that the two forms of ephrin-A5 share similar function while differ in regulating different sets of genes in cardiomyocytes.

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Abstract 833: MicroRNA-206 Controls Cardiac Myosin Heavy Chain Gene Expression By Targeting RXR-α

Circulation ◽

10.1161/circ.116.suppl_16.ii_162 ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Hitoo Nishi ◽

Koh Ono ◽

Yoshitaka Iwanaga ◽

Takahiro Horie ◽

Minako Kinoshita ◽

...

Keyword(s):

Gene Expression ◽

Mrna Expression ◽

Myosin Heavy Chain ◽

Heavy Chain ◽

Cardiac Contractility ◽

Neonatal Rat ◽

Systemic Hypertension ◽

Expression Ratio ◽

Rat Cardiomyocytes ◽

Neonatal Rat Cardiomyocytes

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.

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