Sex- and estrogen-dependent regulation of a miRNA network in the healthy and hypertrophied heart

BACKGROUND

In pressure overload, profibrotic gene expression and cardiac fibrosis are more pronounced in males than in females. Sex-specific and estrogen-dependent regulation of microRNAs (miRNAs), such as miR-21, may be a potential mechanism leading to sex differences in fibrosis.

OBJECTIVES

To analyze the influence of sex, estrogen, and estrogen receptor beta (ERβ) on the expression of miR-21 and to identify additional miRNAs potentially involved in sex-specific pressure overload-induced cardiac remodeling.

METHODS

The sex-specific regulation of fibrosis-related miRNAs was analyzed in male and female wild type and ERβ-deficient mice after transverse aortic constriction (TAC), in rat fibroblasts, and in a cardiomyocyte-like cell line.

RESULTS

We report the sex-specific expression of functionally-related miR-21, -24, -27a, -27b, 106a, -106b and the regulation of their expression by estrogen in a sex-specific manner. These effects were abolished in ERβ-deficient mice. We demonstrate the presence of common functional target sites for these miRNAs on three repressors of the mitogen-activated protein kinase signaling pathway, i.e. Rasa1, Rasa2 and Spry1, which may all lead to cardiac fibrosis. As expected, transfection with miRNA mimics targeting these repressors induced ERK1/2 phosphorylation.

CONCLUSIONS

Estrogen regulates a network of miRNAs in a sex-specific manner via ERβ. Our data suggest that the sex-specific expression of these miRNAs may be related to sex differences in fibrosis after pressure overload.

Abstract 079: Estrogen Receptor beta Regulation Of miRNA Expression In The Heart - A Hint For Sex Differences In Hypertrophy

Sex differences (SD) in cardiovascular diseases are described and have been attributed to the effects of sex hormones, such as estrogen (E2). Our previous studies in a mouse model of pressure overload revealed SD in fibrosis and apoptosis related genes that were abolished in estrogen receptor β deficient (ERβ-/-) mice. Other studies focus on miRNA regulation by E2, but little is known about sex-specific regulation of miRNAs in heart diseases. We hypothesize that E2 and ERβ are regulators of miRNA expression in the heart potentially contributing to the molecular mechanism of SD observed in cardiovascular diseases.

This project aims to identify SD in the expression of miRNAs in a 9-week transverse aortic constriction (TAC) model and the possible role of E2 and ERβ in their regulation in the heart.

A Targetscan analysis of 80 sex-specific dysregulated genes in hypertrophy allowed identifying 157 different miRNAs that could target them. Based on their expression in the heart we selected 60 miRNAs for quantification by qRT-PCR. In WT mice, 23 miRNAs showed SD in their expression in hypertrophy, all of them showing a higher expression in males than in females. All these significant SD were abolished in ERβ-/- mice. A direct comparison of some of these miRNAs in WT and ERβ-/- female animals identified nine miRNAs significantly higher expressed in the knock-out animals (let-7e, miR-106b, miR-130a, miR-133a, miR-20a, miR-24, miR-27b, miR-29a and miR-378). In vitro studies performed using a female cardiomyocyte cell line (AC16) showed a down-regulation of eight of these miRNAs after a 48h treatment with E2, being the exception miR-133a. The latter showed however a down-regulation after 48h treatment with an ERβ specific agonist, as well as let-7e, miR-106b, miR-130a, miR-20a, miR-24, miR-27b and miR-29a. The effect of treatment with ERα was only visible as a down-regulation of miR-24, miR-29a and miR-378. The potential of these miRNAs having targets in the same pathway and acting in a synergistic way is still under investigation.

ERβ is for the first time identified as a major regulator of miRNA expression in the heart. It may play an important role in determining SD in cardiac hypertrophy, being responsible for the inhibition of miRNA expression in the female heart.

CardioNet: a human metabolic network suited for the study of cardiomyocyte metabolism

Background

Availability of oxygen and nutrients in the coronary circulation is a crucial determinant of cardiac performance. Nutrient composition of coronary blood may significantly vary in specific physiological and pathological conditions, for example, administration of special diets, long-term starvation, physical exercise or diabetes. Quantitative analysis of cardiac metabolism from a systems biology perspective may help to a better understanding of the relationship between nutrient supply and efficiency of metabolic processes required for an adequate cardiac output.

Results

Here we present CardioNet, the first large-scale reconstruction of the metabolic network of the human cardiomyocyte comprising 1793 metabolic reactions, including 560 transport processes in six compartments. We use flux-balance analysis to demonstrate the capability of the network to accomplish a set of 368 metabolic functions required for maintaining the structural and functional integrity of the cell. Taking the maintenance of ATP, biosynthesis of ceramide, cardiolipin and further important phospholipids as examples, we analyse how a changed supply of glucose, lactate, fatty acids and ketone bodies may influence the efficiency of these essential processes.

Conclusions

CardioNet is a functionally validated metabolic network of the human cardiomyocyte that enables theorectical studies of cellular metabolic processes crucial for the accomplishment of an adequate cardiac output.

Activin A stimulates vascular endothelial growth factor gene transcription in human hepatocellular carcinoma cells

BACKGROUND & AIMS

Up-regulation of vascular endothelial growth factor is known to play a critical role in hepatocellular tumor biology. In an attempt to identify factors responsible for vascular endothelial growth factor induction in human hepatocellular carcinoma, we evaluated the effects of activin A, a member of the transforming growth factor-beta cytokine superfamily, on vascular endothelial growth factor gene expression.

METHODS

Expression of vascular endothelial growth factor, activin A, and its receptors was analyzed by immunohistochemistry, polymerase chain reaction, and enzyme-linked immunosorbent assay. Functional vascular endothelial growth factor promoter analysis and gel shift assays were performed to define minimal promoter requirements and potential transcription factors. Nuclear expression and biochemical modifications of Sp1, as well as subcellular distribution, expression, and physical interaction of Smad proteins with Sp1, were assessed with immunoprecipitation and Western blot analysis.

RESULTS

Hepatocellular carcinoma tumors and cell lines expressed activin A and its receptors. Activin A stimulated vascular endothelial growth factor gene transcription through Sp1-dependent induction of vascular endothelial growth factor promoter activity. Furthermore, activin A stimulated the DNA-binding and transactivation potential of Sp1. Immunoprecipitation showed activin A-dependent nuclear translocation of Smad2 and induction of Sp1/Smad2 interaction. The functional relevance of Sp1/Smad2 interaction was confirmed by transient transfection experiments, which showed that overexpression of Smad2 increased vascular endothelial growth factor promoter activity and endogenous vascular endothelial growth factor protein expression, whereas dominant negative Smad2 blocked activin A responsiveness.

CONCLUSIONS

This study identifies activin A as a novel stimulus of vascular endothelial growth factor gene expression in hepatocellular carcinoma and delineates physical and functional cooperation of Sp1 and Smad2 as the underlying mechanism.