MicroRNA-208a is a regulator of cardiac hypertrophy and conduction in mice

GATA4 regulates ANF expression synergistically with Sp1 in a cardiac hypertrophy model

Cardiac hypertrophy in response to multiple stimuli has important physiological and pathological significances. GATA4 serves as a nuclear integrator of several signalling pathways during cardiac hypertrophy. Sp1 and Sp3 are also reported to be involved in this process. However, the mechanism by which GATA4 acts as a mediator, integrating these ubiquitously expressed transcriptional factors, is poorly understood. We found that the expression of GATA4 and Sp1 was up-regulated in the myocardium of a pressure overload hypertrophy rat model, as well in phenylephrine-induced (PE-induced) hypertrophic growth of neonatal cardiomyocytes. GST pull-down assays demonstrated that GATA4 could interact with Sp1 in vitro. Therefore, we proposed that GATA4 cooperates with Sp1 in regulating ANF expression, as its reactivation is closely linked with hypertrophy. Further studies demonstrated that GATA4 could activate the ANF promoter synergistically with Sp1 through direct interaction. In contrast, Sp3 exhibited antagonistic function, and overexpression of Sp3 repressed the transcriptional synergy between Sp1 and GATA4. We also found that Sp1 alone could activate the ANF promoter in cardiomyocytes, whereas Sp3 exerted negative effects on ANF expression. Bioinformatics analysis revealed novel Sp-binding sites on the ANF promoter. The recruitment of GATA4 and Sp1 on the ANF promoter was enhanced during phenylephrine-mediated hypertrophy, whereas the recruitment of Sp3 was reduced. The phosphorylation of GATA4 by ERK1/2 kinase could enhance the affinity between GATA4 and Sp1. Thus, our findings revealed the critical interaction of GATA4 and Sp1 in modulating ANF expression, indicating their involvement in cardiac hypertrophy.

Regulation of connexin expression by transcription factors and epigenetic mechanisms

Gap junctions are specialized cell-cell junctions that directly link the cytoplasm of neighboring cells. They mediate the direct transfer of metabolites and ions from one cell to another. Discoveries of human genetic disorders due to mutations in gap junction protein (connexin [Cx]) genes and experimental data on connexin knockout mice provide direct evidence that gap junctional intercellular communication is essential for tissue functions and organ development, and that its dysfunction causes diseases. Connexin-related signaling also involves extracellular signaling (hemichannels) and non-channel intracellular signaling. Thus far, 21 human genes and 20 mouse genes for connexins have been identified. Each connexin shows tissue- or cell-type-specific expression, and most organs and many cell types express more than one connexin. Connexin expression can be regulated at many of the steps in the pathway from DNA to RNA to protein. In recent years, it has become clear that epigenetic processes are also essentially involved in connexin gene expression. In this review, we summarize recent knowledge on regulation of connexin expression by transcription factors and epigenetic mechanisms including histone modifications, DNA methylation, and microRNA. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.

Mature and immature microRNA ratios in cultured rat cardiomyocytes during anoxia-reoxygenation

BACKGROUND

The critical role of microRNAs (miRNAs) in the global control of gene expression in the heart has recently been postulated; however, the mechanisms of miRNA regulation in cardiac pathology are not clear.

OBJECTIVE

To evaluate the levels of miR-1, miR-208a and miR-29a expressed in neonatal rat cardiomyocytes during anoxia-reoxygenation (AR).

METHODS

Reverse transcription coupled with real-time polymerase chain reaction was used to evaluate the level of mature and immature miRNAs in cardiomyocyte culture during AR.

RESULTS

THE INITIAL LEVELS OF THE MATURE AND IMMATURE MIRNAS WERE DIFFERENT: mature - miR-1 7.46±4.440, miR-208a 0.02±0.015 and miR-29a 5.60±2.060; immature - miR-1 0.02±0.007, miR-208a 0.05±0.029 and miR-29a 0.01±0.008. The most prominent changes were observed for immature miRNAs during AR, with immature miR-1 and miR-29a expressed at significantly higher levels during remote reoxygenation (AR [0.5 h/24 h]) compared with control, while the level of expressed immature miR-208a was significantly decreased during acute reoxygenation (AR [0.5 h /1 h]) and returned to control levels during remote reoxygenation (AR [0.5h /24 h]). Also, the ratios of mature to immature miRNAs were significantly increased during acute reoxygenation for miR-1 and miR-208a, returning to control levels during remote reoxygenation, while for miR-29a, this ratio had the progressive tendency to decrease under AR.

CONCLUSION

The discordance between the estimated levels of mature and immature miRNA during AR supports the hypothesis that transcriptional and post-transcriptional regulatory mechanisms at the miRNA level play a role in the response of cardiomyocytes to AR, and could be a contributing factor in the differential resistance of cardiomyocytes to AR.

MicroRNAs in heart development

MicroRNAs (miRNAs) are a class of small noncoding RNAs of ~22nt in length which are involved in the regulation of gene expression at the posttranscriptional level by degrading their target mRNAs and/or inhibiting their translation. Expressed ubiquitously or in a tissue-specific manner, miRNAs are involved in the regulation of many biological processes such as cell proliferation, differentiation, apoptosis, and the maintenance of normal cellular physiology. Many miRNAs are expressed in embryonic, postnatal, and adult hearts. Aberrant expression or genetic deletion of miRNAs is associated with abnormal cardiac cell differentiation, disruption of heart development, and cardiac dysfunction. This chapter will summarize the history, biogenesis, and processing of miRNAs as well as their function in heart development, remodeling, and disease.

Regulation of GATA4 transcriptional activity in cardiovascular development and disease

Transcription factors regulate formation and function of the heart, and perturbation of transcription factor expression and regulation disrupts normal heart structure and function. Multiple mechanisms regulate the level and locus-specific activity of transcription factors, including transcription, translation, subcellular localization, posttranslational modifications, and context-dependent interactions with other transcription factors, chromatin remodeling enzymes, and epigenetic regulators. The zinc finger transcription factor GATA4 is among the best-studied cardiac transcriptional factors. This review focuses on molecular mechanisms that regulate GATA4 transcriptional activity in the cardiovascular system, providing a framework to investigate and understand the molecular regulation of cardiac gene transcription by other transcription factors.

The role of microRNAs in muscle development

MicroRNAs play essential roles during animal development, including in developing muscle. Many microRNAs are expressed during muscle development and some, like miR-1 and miR-133, are muscle specific. Muscle microRNAs are integrated into myogenic regulatory networks: their expression is under the transcriptional and posttranscriptional control of myogenic factors, and they in turn have widespread control of muscle gene expression. This review summarizes recent work characterizing the function of microRNAs in muscle biology and specifically focuses on the genetic analysis of muscle microRNAs in a variety of model organisms including worms, flies, zebrafish, and mice.

Isolation of fetal gonads from embryos of timed-pregnant mice for morphological and molecular studies

Gonadal sex differentiation is an important developmental process, in which a bipotential primordial gonad undergoes two distinct pathways, i.e., testicular and ovarian differentiation, dependent on its genetic sex. Techniques of isolating fetal gonads at various developmental stages are valuable for studies on the molecular events involved in cell-fate determination, sex-specific somatic and germ-cell differentiation and structural organization. Here we describe various procedures for isolation of embryonic gonads at different developmental stages from embryos of timed-pregnant mice. The isolated fetal gonads can be used for a variety of studies, such as organ culture, gene and protein expression. As examples of applications, we describe the immunofluorescence detection of SOX9 expression in gonadal tissue sections and microRNAs profiling/expression in fetal gonads at a critical stage for sex determination.

Determination of miRNA targets in skeletal muscle cells

MicroRNAs (miRNAs) are a class of small ∼22 nucleotide noncoding RNAs which regulate gene expression at the posttranscriptional level by either destabilizing and consequently degrading their targeted mRNAs or by repressing their translation. Emerging evidence has demonstrated that miRNAs are essential for normal mammalian development, homeostasis, and many other functions. In addition, deleterious changes in miRNA expression were associated with human diseases. Several muscle-specific miRNAs, including miR-1, miR-133, miR-206, and miR-208, have been shown to be important for normal myoblast differentiation, proliferation, and muscle remodeling in response to stress. They have also been implicated in various cardiac and skeletal muscular diseases. miRNA-based gene therapies hold great potential for the treatment of cardiac and skeletal muscle diseases. Herein, we describe methods commonly applied to study the biological role of miRNAs, as well as techniques utilized to manipulate miRNA expression and to investigate their target regulation.

Circulating microRNAs: novel biomarkers for cardiovascular diseases

MicroRNAs (miRNAs) are a novel class of small, non-coding, single-stranded RNAs that negatively regulate gene expression via translational inhibition or mRNA degradation followed by protein synthesis repression. Many miRNAs are expressed in a tissue- and/or cell-specific manner and their expression patterns are reflective of underlying patho-physiologic processes. miRNAs can be detected in serum or in plasma in a remarkably stable form, making them attractive biomarkers for human diseases. This review describes the progress of identifying circulating miRNAs as novel biomarkers for diverse cardiovascular diseases, including acute myocardial infarction, heart failure, coronary artery disease, diabetes, stroke, essential hypertension, and acute pulmonary embolism. In addition, the origin and function and the different strategies to identify circulating miRNAs as novel biomarkers for cardiovascular diseases are also discussed. Rarely has an opportunity arisen to advance such new biology for the diagnosis of cardiac diseases.

MicroRNA-1 and -133 increase arrhythmogenesis in heart failure by dissociating phosphatase activity from RyR2 complex

In heart failure (HF), arrhythmogenic spontaneous sarcoplasmic reticulum (SR) Ca(2+) release and afterdepolarizations in cardiac myocytes have been linked to abnormally high activity of ryanodine receptors (RyR2s) associated with enhanced phosphorylation of the channel. However, the specific molecular mechanisms underlying RyR2 hyperphosphorylation in HF remain poorly understood. The objective of the current study was to test the hypothesis that the enhanced expression of muscle-specific microRNAs (miRNAs) underlies the HF-related alterations in RyR2 phosphorylation in ventricular myocytes by targeting phosphatase activity localized to the RyR2. We studied hearts isolated from canines with chronic HF exhibiting increased left ventricular (LV) dimensions and decreased LV contractility. qRT-PCR revealed that the levels of miR-1 and miR-133, the most abundant muscle-specific miRNAs, were significantly increased in HF myocytes compared with controls (2- and 1.6-fold, respectively). Western blot analyses demonstrated that expression levels of the protein phosphatase 2A (PP2A) catalytic and regulatory subunits, which are putative targets of miR-133 and miR-1, were decreased in HF cells. PP2A catalytic subunit mRNAs were validated as targets of miR-133 by using luciferase reporter assays. Pharmacological inhibition of phosphatase activity increased the frequency of diastolic Ca(2+) waves and afterdepolarizations in control myocytes. The decreased PP2A activity observed in HF was accompanied by enhanced Ca(2+)/calmodulin-dependent protein kinase (CaMKII)-mediated phosphorylation of RyR2 at sites Ser-2814 and Ser-2030 and increased frequency of diastolic Ca(2+) waves and afterdepolarizations in HF myocytes compared with controls. In HF myocytes, CaMKII inhibitory peptide normalized the frequency of pro-arrhythmic spontaneous diastolic Ca(2+) waves. These findings suggest that altered levels of major muscle-specific miRNAs contribute to abnormal RyR2 function in HF by depressing phosphatase activity localized to the channel, which in turn, leads to the excessive phosphorylation of RyR2s, abnormal Ca(2+) cycling, and increased propensity to arrhythmogenesis.

MiRNAs as regulators of the response to inhaled environmental toxins and airway carcinogenesis

miRNAs are a class of small, noncoding RNAs averaging 22 nucleotides in length that down-regulate gene expression by complimentary binding to the 3' UTR of target genes. A growing body of research suggests that these small RNA species play significant roles in modulating the cellular response to a variety of types of stress. In this review, we summarize the available literature regarding the general response of miRNA to cellular stress, and then specifically focus on the miRNA response to inhaled toxins. These miRNA responses to inhaled toxins appear to be recapitulated in lung carcinogenesis, opening the possibility that modulation of the miRNA response could be a novel strategy for chemoprevention.

Cardiac hypertrophy is positively regulated by MicroRNA miR-23a

MicroRNAs (miRNAs) are a class of small noncoding RNAs that mediate post-transcriptional gene silencing. Myocardial hypertrophy is frequently associated with the development of heart failure. A variety of miRNAs are involved in the regulation of cardiac hypertrophy, however, the molecular targets of miRNAs in the cardiac hypertrophic cascades remain to be fully identified. We produced miR-23a transgenic mice, and these mice exhibit exaggerated cardiac hypertrophy in response to the stimulation with phenylephrine or pressure overload by transverse aortic banding. The endogenous miR-23a is up-regulated upon treatment with phenylephrine, endothelin-1, or transverse aortic banding. Knockdown of miR-23a attenuates hypertrophic responses. To identify the downstream targets of miR-23a, we found that transcription factor Foxo3a is suppressed by miR-23a. Luciferase assay indicates that miR-23a directly inhibits the translation activity of Foxo3a 3' UTR. Introduction or knockdown of miR-23a leads to the alterations of Foxo3a protein levels. Enforced expression of the constitutively active form of Foxo3a counteracts the provocative effect of miR-23a on hypertrophy. Furthermore, we observed that miR-23a is able to alter the expression levels of manganese superoxide dismutase and the consequent reactive oxygen species, and this effect is mediated by Foxo3a. In addition, our results show that miR-23a and Foxo3a bi-transgenic mice exhibit a reduced hypertrophic response compared with the miR-23a transgenic mice alone. Our present study reveals that miR-23a can mediate the hypertrophic signal through regulating Foxo3a. They form an axis in hypertrophic machinery and can be targets for the development of hypertrophic treatment.

Novel techniques and targets in cardiovascular microRNA research

MicroRNAs (miRNAs) are highly conserved, tiny (∼22 nucleotides) non-coding RNAs that have emerged as potent regulators of mRNA translation. miRNAs exhibit fine-tuning of the control of proteins involved in cell signalling (AE) pathways and in vital cellular and developmental processes. miRNAs are expressed in cardiovascular tissues, and multiple functional aspects of miRNAs underscore their key role in cardiovascular (patho)physiology. The development and increasing use of novel molecular biology tools have contributed to the recent success in miRNA research. In the present review, we discuss current updates on important and novel miRNA techniques, including: (i) miRNA screening tools; (ii) bioanalytical target prediction tools; (iii) target validation tools; and (iv) manipulative miRNA expression tools. We also present an update about recently identified miRNA targets that play a key role in cardiovascular development and disorders.

The MyomiR network in skeletal muscle plasticity

MicroRNA (miRNA) are a class of noncoding RNA involved in regulating gene expression by a posttranscriptional mechanism. Based on work from our laboratory, this review explores the hypothesis that a recently described muscle-specific miRNA, myomiR, network has a central role in the regulation of skeletal muscle plasticity by coordinating changes in fiber type and muscle mass in response to altered contractile activity.

MicroRNAs: new players in cardiac injury and protection

MicroRNAs (miRNAs) have emerged as a novel class of endogenous, small, noncoding RNAs that negatively regulate gene expression via degradation or translational inhibition of their target mRNAs. Over 700 miRNAs have been identified and sequenced in humans, and the number of miRNA genes is estimated at more than 1000. Individual miRNA is functionally important as a transcription factor because it has the ability to regulate the expression of multiple genes through binding to its target with imperfect or perfect complement. In the heart, miRNAs have been involved in several clinical scenarios, such as ischemia/reperfusion (I/R) injury and heart failure suggesting that regulation of their function could be used as a novel cardioprotective strategy. In particular, miRNA-1, miRNA-21, miRNA-24, miRNA-29, miRNA-92a, miRNA-126, miRNA-133, miRNA-320, miRNA-199a, miRNA-208, and miRNA-195 have been shown to be regulated after I/R injury. Because tissue miRNAs can be released into circulating blood, they also offer exciting new opportunities for developing sensitive biomarkers, including miRNA-1, miRNA-126, miR-208, and miRNA-499, for acute myocardial infarction and other cardiac diseases.

Therapeutic inhibition of miR-208a improves cardiac function and survival during heart failure

BACKGROUND

Diastolic dysfunction in response to hypertrophy is a major clinical syndrome with few therapeutic options. MicroRNAs act as negative regulators of gene expression by inhibiting translation or promoting degradation of target mRNAs. Previously, we reported that genetic deletion of the cardiac-specific miR-208a prevents pathological cardiac remodeling and upregulation of Myh7 in response to pressure overload. Whether this miRNA might contribute to diastolic dysfunction or other forms of heart disease is currently unknown.

METHODS AND RESULTS

Here, we show that systemic delivery of an antisense oligonucleotide induces potent and sustained silencing of miR-208a in the heart. Therapeutic inhibition of miR-208a by subcutaneous delivery of antimiR-208a during hypertension-induced heart failure in Dahl hypertensive rats dose-dependently prevents pathological myosin switching and cardiac remodeling while improving cardiac function, overall health, and survival. Transcriptional profiling indicates that antimiR-208a evokes prominent effects on cardiac gene expression; plasma analysis indicates significant changes in circulating levels of miRNAs on antimiR-208a treatment.

CONCLUSIONS

These studies indicate the potential of oligonucleotide-based therapies for modulating cardiac miRNAs and validate miR-208 as a potent therapeutic target for the modulation of cardiac function and remodeling during heart disease progression.

Modulation of connexin signaling by bacterial pathogens and their toxins

Inherent to their pivotal tasks in the maintenance of cellular homeostasis, gap junctions, connexin hemichannels, and pannexin hemichannels are frequently involved in the dysregulation of this critical balance. The present paper specifically focuses on their roles in bacterial infection and disease. In particular, the reported biological outcome of clinically important bacteria including Escherichia coli, Shigella flexneri, Yersinia enterocolitica, Helicobacter pylori, Bordetella pertussis, Aggregatibacter actinomycetemcomitans, Pseudomonas aeruginosa, Citrobacter rodentium, Clostridium species, Streptococcus pneumoniae, and Staphylococcus aureus and their toxic products on connexin- and pannexin-related signaling in host cells is reviewed. Particular attention is paid to the underlying molecular mechanisms of these effects as well as to the actual biological relevance of these findings.

mir-11 limits the proapoptotic function of its host gene, dE2f1

The E2F family of transcription factors regulates the expression of both genes associated with cell proliferation and genes that regulate cell death. The net outcome is dependent on cellular context and tissue environment. The mir-11 gene is located in the last intron of the Drosophila E2F1 homolog gene dE2f1, and its expression parallels that of dE2f1. Here, we investigated the role of miR-11 and found that miR-11 specifically modulated the proapoptotic function of its host gene, dE2f1. A mir-11 mutant was highly sensitive to dE2F1-dependent, DNA damage-induced apoptosis. Consistently, coexpression of miR-11 in transgenic animals suppressed dE2F1-induced apoptosis in multiple tissues, while exerting no effect on dE2F1-driven cell proliferation. Importantly, miR-11 repressed the expression of the proapoptotic genes reaper (rpr) and head involution defective (hid), which are directly regulated by dE2F1 upon DNA damage. In addition to rpr and hid, we identified a novel set of cell death genes that was also directly regulated by dE2F1 and miR-11. Thus, our data support a model in which the coexpression of miR-11 limits the proapoptotic function of its host gene, dE2f1, upon DNA damage by directly modulating a dE2F1-dependent apoptotic transcriptional program.

Cardiomyocyte overexpression of miR-27b induces cardiac hypertrophy and dysfunction in mice

Recent studies have begun to reveal critical roles of microRNAs (miRNAs) in the pathogenesis of cardiac hypertrophy and dysfunction. In this study, we tested whether a transforming growth factor-β (TGF-β)-regulated miRNA played a pivotal role in the development of cardiac hypertrophy and heart failure (HF). We observed that miR-27b was upregulated in hearts of cardiomyocyte-specific Smad4 knockout mice, which developed cardiac hypertrophy. In vitro experiments showed that the miR-27b expression could be inhibited by TGF-β1 and that its overexpression promoted hypertrophic cell growth, while the miR-27b suppression led to inhibition of the hypertrophic cell growth caused by phenylephrine (PE) treatment. Furthermore, the analysis of transgenic mice with cardiomyocyte-specific overexpression of miR-27b revealed that miR-27b overexpression was sufficient to induce cardiac hypertrophy and dysfunction. We validated the peroxisome proliferator-activated receptor-γ (PPAR-γ) as a direct target of miR-27b in cardiomyocyte. Consistently, the miR-27b transgenic mice displayed significantly lower levels of PPAR-γ than the control mice. Furthermore, in vivo silencing of miR-27b using a specific antagomir in a pressure-overload-induced mouse model of HF increased cardiac PPAR-γ expression, attenuated cardiac hypertrophy and dysfunction. The results of our study demonstrate that TGF-β1-regulated miR-27b is involved in the regulation of cardiac hypertrophy, and validate miR-27b as an efficient therapeutic target for cardiac diseases.

MicroRNAs in the cardiovascular system

PURPOSE OF REVIEW

Reprogramming of gene expression underlies the mechanisms involved in cardiac pathogenesis. MicroRNAs (miRNAs) are unique posttranscriptional regulators of gene expression whose function in cardiac development and disease has recently begun to unravel. In addition, they are potentially highly effective therapeutic tools. In this review, we will summarize the recent advancements in the field.

RECENT FINDINGS

The cardiac-enriched miRNAs, including miR-1, miR-133, and miR-208, as well as the ubiquitous miR-23a and miR-199b, play major roles in the development of cardiac hypertrophy. On the other hand, miR-21, miR-199a, miR-210, and miR-494 have been proven critical for the myocytes' adaptation and survival during hypoxia/ischemia. Using depletion or replacement strategies against some of these miRNAs has proven very effective in preventing or even reversing some disorders. These findings and more will be detailed in this review.

SUMMARY

In general, the discovery of miRNAs has uncovered a new dimension of gene regulation that provides us with unique mechanistic insights into cardiac diseases, in addition to which they can be utilized for new diagnostics and therapeutic strategies.

The therapeutic potential of microRNAs: disease modulators and drug targets

MiRNAs are a class of small, naturally occurring RNA molecules that play critical roles in modulating numerous biological pathways by regulating gene expression. The knowledge that miRNA expression is dysregulated in many pathological disease processes, including cancer, has led to a rapidly expanding body of literature as we try to unveil their mechanism of action. Their putative role as oncogenes or tumour suppressor genes presents a wonderful opportunity to provide targeted cancer treatment strategies. Additionally, their documented function in a host of benign diseases broadens the potential market for miRNA-based therapeutics. The present review outlines the underlying rationales for considering mi(cro)RNAs as therapeutic agents or targets. We highlight the potential of manipulating miRNAs for the treatment of many common diseases, particularly cancers. Finally, we summarize the challenges that need to be overcome to fully harness the potential of miRNA-based therapies so they become the next generation of pharmaceutical products.

Cardiac gene transfer of short hairpin RNA directed against phospholamban effectively knocks down gene expression but causes cellular toxicity in canines

Derangements in calcium cycling have been described in failing hearts, and preclinical studies have suggested that therapies aimed at correcting this defect can lead to improvements in cardiac function and survival. One strategy to improve calcium cycling would be to inhibit phospholamban (PLB), the negative regulator of SERCA2a that is upregulated in failing hearts. The goal of this study was to evaluate the safety and efficacy of using adeno-associated virus (AAV)-mediated cardiac gene transfer of short hairpin RNA (shRNA) to knock down expression of PLB. Six dogs were treated with self-complementary AAV serotype 6 (scAAV6) expressing shRNA against PLB. Three control dogs were treated with empty AAV6 capsid, and two control dogs were treated with scAAV6 expressing dominant negative PLB. Vector was delivered via a percutaneously inserted cardiac injection catheter. PLB mRNA and protein expression were analyzed in three of six shRNA dogs between days 16 and 26. The other three shRNA dogs and five control dogs were monitored long-term to assess cardiac safety. PLB mRNA was reduced 16-fold, and PLB protein was reduced 5-fold, with treatment. Serum troponin elevation and depressed cardiac function were observed in the shRNA group only at 4 weeks. An enzyme-linked immunospot assay failed to detect any T cells reactive to AAV6 capsid in peripheral blood mononuclear cells, heart, or spleen. Microarray analysis revealed alterations in cardiac expression of several microRNAs with shRNA treatment. AAV6-mediated cardiac gene transfer of shRNA effectively knocks down PLB expression but is associated with severe cardiac toxicity. Toxicity may result from dysregulation of endogenous microRNA pathways.

Cardiac insulin resistance and microRNA modulators

Cardiac insulin resistance is a metabolic and functional disorder that is often associated with obesity and/or the cardiorenal metabolic syndrome (CRS), and this disorder may be accentuated by chronic alcohol consumption. In conditions of over-nutrition, increased insulin (INS) and angiotensin II (Ang II) activate mammalian target for rapamycin (mTOR)/p70 S6 kinase (S6K1) signaling, whereas chronic alcohol consumption inhibits mTOR/S6K1 activation in cardiac tissue. Although excessive activation of mTOR/S6K1 induces cardiac INS resistance via serine phosphorylation of INS receptor substrates (IRS-1/2), it also renders cardioprotection via increased Ang II receptor 2 (AT2R) upregulation and adaptive hypertrophy. In the INS-resistant and hyperinsulinemic Zucker obese (ZO) rat, a rodent model for CRS, activation of mTOR/S6K1signaling in cardiac tissue is regulated by protective feed-back mechanisms involving mTOR↔AT2R signaling loop and profile changes of microRNA that target S6K1. Such regulation may play a role in attenuating progressive heart failure. Conversely, alcohol-mediated inhibition of mTOR/S6K1, down-regulation of INS receptor and growth-inhibitory mir-200 family, and upregulation of mir-212 that promotes fetal gene program may exacerbate CRS-related cardiomyopathy.

A phenotypic screen to identify hypertrophy-modulating microRNAs in primary cardiomyocytes

MicroRNAs (miRNAs) are small non-coding RNAs that control expression of complementary target mRNAs. A growing number of miRNAs has been implicated in the pathogenesis of cardiac diseases, mostly based not on functional data, but on the observation that they are dysregulated in diseased myocardium. Consequently, our knowledge regarding a potential cardiac role of the majority of miRNAs is limited. Here, we report the development of an assay format that allows the simultaneous analysis of several hundred molecules with regard to their phenotypic effect on primary rat cardiomyocytes. Using automated microscopy and an edge detection algorithm, this assay achieved high reproducibility and a robust assessment of cardiomyocyte size as a key parameter. Screening a library of synthetic miRNAs revealed several miRNAs previously not recognized as pro- or anti-hypertrophic. Out of these, we selected nine miRNAs and confirmed the pro-hypertrophic potential of miR-22, miR-30c, miR-30d, miR-212, miR-365 and the anti-hypertrophic potential of miR-27a, miR-27b and miR-133a. Quantitative analysis of the expression level of pro-hypertrophic miRNAs in primary cardiomyocytes indicated a rather low level of correlation of the phenotypic effects of individual miRNAs and their expression level. This assay allows the automated determination of cell size in primary cardiomyocytes and permitted the identification of a set of miRNAs capable of regulating cardiomyocyte hypertrophy. Elucidating their mechanism of action should provide insight into mechanisms underlying the cardiomyocyte hypertrophic response. This article is part of a Special Issue entitled 'Possible Editorial'.

Temporal expression of miRNAs and mRNAs in a mouse model of myocardial infarction

Analysis of changes in gene expression is an important means to define molecular differences associated with the phenotypic changes observed in response to myocardial infarction (MI). Several studies in humans or animal models have reported differential miRNA expression in response to MI acutely (animal) or chronically (human). To determine the relative contribution of microRNA (miRNA) and mRNAs to acute and chronic temporal changes in response to MI, mRNA and miRNA expression profiles were performed in three time points post-MI. Changes in mRNA and miRNA expression was analyzed by arrays and confirmed by RT-PCR. Bioinformatic analysis demonstrated that several genes and miRNAs in various pathways are regulated in a temporal or phenotype-specific manner. Furthermore miRNA analyses indicated that miRNAs can target expression of several genes involved in multiple cardiomyopathy-related pathways. Our results suggest that: 1) Differentially regulated miRNAs are predicted to target expression of several genes in multiple biological processes involved in the response to MI; 2) antithetical and compensatory changes in miRNA expression are observed at later disease stages, including antithetical regulation of miR-29, which correlates with the expression of collagen genes, and upregulation of apoptosis-related miRNAs at early stages and antiapoptotic/growth promoting miRNAs at later stages; 3) temporally dependent changes in miRNA and mRNA expression post-MI are generally characterized by dramatic changes acutely postinjury and are normalized as disease progresses; 4) A combinatorial analysis of mRNA and miRNA expression may aid in determining factors involved in compensatory and decompensated responses to cardiac injury.

MicroRNAs in Development and Disease

MicroRNAs (miRNAs) are a class of posttranscriptional regulators that have recently introduced an additional level of intricacy to our understanding of gene regulation. There are currently over 10,000 miRNAs that have been identified in a range of species including metazoa, mycetozoa, viridiplantae, and viruses, of which 940, to date, are found in humans. It is estimated that more than 60% of human protein-coding genes harbor miRNA target sites in their 3′ untranslated region and, thus, are potentially regulated by these molecules in health and disease. This review will first briefly describe the discovery, structure, and mode of function of miRNAs in mammalian cells, before elaborating on their roles and significance during development and pathogenesis in the various mammalian organs, while attempting to reconcile their functions with our existing knowledge of their targets. Finally, we will summarize some of the advances made in utilizing miRNAs in therapeutics.

MicroRNAs involved in the mitogen-activated protein kinase cascades pathway during glucose-induced cardiomyocyte hypertrophy

Cardiac hypertrophy is a key structural feature of diabetic cardiomyopathy in the late stage of diabetes. Recent studies show that microRNAs (miRNAs) are involved in the pathogenesis of cardiac hypertrophy in diabetic mice, but more novel miRNAs remain to be investigated. In this study, diabetic cardiomyopathy, characterized by hypertrophy, was induced in mice by streptozotocin injection. Using microarray analysis of myocardial tissue, we were able to identify changes in expression in 19 miRNA, of which 16 miRNAs were further validated by real-time PCR and a total of 3212 targets mRNA were predicted. Further analysis showed that 31 GO functions and 16 KEGG pathways were enriched in the diabetic heart. Of these, MAPK signaling pathway was prominent. In vivo and in vitro studies have confirmed that three major subgroups of MAPK including ERK1/2, JNK, and p38, are specifically upregulated in cardiomyocyte hypertrophy during hyperglycemia. To further explore the potential involvement of miRNAs in the regulation of glucose-induced cardiomyocyte hypertrophy, neonatal rat cardiomyocytes were exposed to high glucose and transfected with miR-373 mimic. Overexpression of miR-373 decreased the cell size, and also reduced the level of its target gene MEF2C, and miR-373 expression was regulated by p38. Our data highlight an important role of miRNAs in diabetic cardiomyopathy, and implicate the reliability of bioinformatics analysis in shedding light on the mechanisms underlying diabetic cardiomyopathy.

The use of stem cells for the repair of cardiac tissue in ischemic heart disease

Ischemic heart diseases are the leading cause of death in the Western world. With increasing numbers of patients surviving their acute myocardial infarction owing to effective heart catheter techniques and intensive care treatment, congestive heart failure has become an increasing health concern. With therapeutic options for the prevention and treatment of ischemic heart disease being limited at present, huge efforts have been made in the field of stem cell research to try to establish new approaches for myocardial tissue regeneration. Owing to their pronounced differentiation potential, pluripotent stem cells seem to represent the most promising cell source for future engineering of myocardial replacement tissue. However, several crucial hurdles regarding cell yield and purity of the cultured cardiovascular progenitor cells have still not been overcome to facilitate a clinical application today. By contrast, plenty of adult stem and progenitor cells have already been well characterized and investigated in human disease. However, all of these heterogeneous cell lines primarily seem to work in a paracrine manner on ischemic myocardial tissue, rather than transdifferentiating into contractile cardiomyocytes. This article will focus on the production, application and present limitations of stem cells potentially applicable for myocardial repair.

Transcriptional profiling to identify biomarkers of disease and drug response

The discovery, biological qualification and analytical validation of genomic biomarkers requires extensive collaborations between individuals with expertise in biology, statistics, bioinformatics, chemistry, clinical medicine, regulatory science and so on. For clinical utility, blood-borne biomarkers (e.g., mRNA and miRNA) of organ damage, drug toxicity and/or response would be preferred to those that are tissue based. Currently used biomarkers such as serum creatinine (indicating renal dysfunction) denote organ damage whether caused by disease, physical injury or drugs. Therefore, it is anticipated that studies of disease will discover biomarkers that can also be used to identify drug-induced injury and vice versa. This article describes transcriptomic blood-borne biomarkers that have been reported to be connected with disease and drug toxicity. Much more qualification and validation needs to be carried out before many of these biomarkers can prove useful. Discussed here are some of the lessons learned and roadblocks to success.

Therapeutic potential of microRNAs in heart failure

There is an ongoing explosion of information about microRNAs (miRs) in cardiac disease. These small noncoding RNAs regulate protein expression by destabilization and translational inhibition of target mRNAs. Similar to mRNAs, miRs are regulated in cardiac hypertrophy and heart failure, but miR expression profiles appear to be more sensitive than mRNA signatures to changes in clinical status, suggesting that miR levels in myocardium or plasma could enhance clinical diagnostics. Single miRs can target dozens or hundreds of different mRNAs, complicating attempts to determine their individual physiologic effects. However, manipulating individual miRs by overexpression or gene ablation in experimental models has begun to unravel this conundrum: Single miRs tend to regulate numerous effectors within the same functional pathway, producing a coherent physiologic response via multiple parallel perturbations. miRs are attractive nodal therapeutic targets, and stable miR mimetics (agomiRs) and antagonists (antagomiRs) are being evaluated to prevent or reverse heart failure.

Transgenic overexpression of miR-133a in skeletal muscle

Background

MicroRNAs (miRNAs) are a class of non-coding regulatory RNAs of ~22 nucleotides in length. miRNAs regulate gene expression post-transcriptionally, primarily by associating with the 3' untranslated region (UTR) of their regulatory target mRNAs. Recent work has begun to reveal roles for miRNAs in a wide range of biological processes, including cell proliferation, differentiation and apoptosis. Many miRNAs are expressed in cardiac and skeletal muscle, and dysregulated miRNA expression has been correlated with muscle-related disorders. We have previously reported that the expression of muscle-specific miR-1 and miR-133 is induced during skeletal muscle differentiation and miR-1 and miR-133 play central regulatory roles in myoblast proliferation and differentiation in vitro.

Methods

In this study, we measured the expression of miRNAs in the skeletal muscle of mdx mice, an animal model for human muscular dystrophy. We also generated transgenic mice to overexpress miR-133a in skeletal muscle.

Results

We examined the expression of miRNAs in the skeletal muscle of mdx mice. We found that the expression of muscle miRNAs, including miR-1a, miR-133a and miR-206, was up-regulated in the skeletal muscle of mdx mice. In order to further investigate the function of miR-133a in skeletal muscle in vivo, we have created several independent transgenic founder lines. Surprisingly, skeletal muscle development and function appear to be unaffected in miR-133a transgenic mice.

Conclusions

Our results indicate that miR-133a is dispensable for the normal development and function of skeletal muscle.

Myostatin: a novel insight into its role in metabolism, signal pathways, and expression regulation

Myostatin, a member of the transforming growth factor-β (TGF-β) superfamily, is a critical autocrine/paracrine inhibitor of skeletal muscle growth. Since the first observed double-muscling phenotype was reported in myostatin-null animals, a functional role of myostatin has been demonstrated in the control of skeletal muscle development. However, beyond the confines of its traditional role in muscle growth inhibition, myostatin has recently been shown to play an important role in metabolism. During the past several years, it has been well established that Smads are canonical mediators of signals for myostatin from the receptors to the nucleus. However, growing evidence supports the notion that Non-Smad signal pathways also participate in myostatin signaling. Myostatin expression is increased in muscle atrophy and metabolic disorders, suggesting that changes in endogenous expression of myostatin may provide therapeutic benefit for these diseases. MicroRNAs (miRNAs) are a class of non-coding RNAs that negatively regulate gene expression and recent evidence has accumulated supporting a role for miRNAs in the regulation of myostatin expression. This review highlights some of these areas in myostatin research: a novel role in metabolism, signal pathways, and miRNA-mediated expression regulation.

Elevated miR-499 levels blunt the cardiac stress response

Background

The heart responds to myriad stresses by well-described transcriptional responses that involve long-term changes in gene expression as well as more immediate, transient adaptations. MicroRNAs quantitatively regulate mRNAs and thus may affect the cardiac transcriptional output and cardiac function. Here we investigate miR-499, a microRNA embedded within a ventricular-specific myosin heavy chain gene, which is expressed in heart and skeletal muscle.

Methodology/Principal Findings

We assessed miR-499 expression in human tissue to confirm its potential relevance to human cardiac gene regulation. Using a transgenic mouse model, we found that elevated miR-499 levels caused cellular hypertrophy and cardiac dysfunction in a dose-dependent manner. Global gene expression profiling revealed altered levels of the immediate early stress response genes (Egr1, Egr2 and Fos), ß-myosin heavy chain (Myh7), and skeletal muscle actin (Acta1). We verified the effect of miR-499 on the immediate early response genes by miR-499 gain- and loss-of-function in vitro. Consistent with a role for miR-499 in blunting the response to cardiac stress, asymptomatic miR-499-expressing mice had an impaired response to pressure overload and accentuated cardiac dysfunction.

Conclusions

Elevated miR-499 levels affect cardiac gene expression and predispose to cardiac stress-induced dysfunction. miR-499 may titrate the cardiac response to stress in part by regulating the immediate early gene response.

MicroRNAs and cardiovascular diseases

MicroRNAs (miRNAs) are a class of small noncoding RNAs that have gained status as important regulators of gene expression. Recent studies have demonstrated that miRNAs are aberrantly expressed in the cardiovascular system under some pathological conditions. Gain- and loss-of-function studies using in vitro and in vivo models have revealed distinct roles for specific miRNAs in cardiovascular development and physiological function. The implications of miRNAs in cardiovascular disease have recently been recognized, representing the most rapidly evolving research field. In the present minireview, the current relevant findings on the role of miRNAs in cardiac diseases are updated and the target genes of these miRNAs are summarized.

The art of microRNA research

Originally identified as moderate biological modifiers, microRNAs have recently emerged as powerful regulators of diverse cellular processes with especially important roles in disease and tissue remodeling. The rapid pace of studies on microRNA regulation and function necessitates the development of suitable techniques for measuring and modulating microRNAs in different model systems. This review summarizes experimental strategies for microRNA research and highlights the strengths and weaknesses of different approaches. The development of more specific and sensitive assays will further illuminate the biology behind microRNAs and will advance opportunities to safely pursue them as therapeutic modalities.

Gene therapy for ischemic heart disease

INTRODUCTION

Coronary artery disease (CAD) is still the leading cause of death in industrialized nations. Even though revascularization strategies such as percutaneous coronary intervention (PCI) and coronary artery bypass graft surgery (CABG) as well as drug therapy have significantly reduced mortality, about 30% of patients will develop chronic heart failure over time. Ischemic heart disease and heart failure are characterized by an adverse remodeling of the heart, featuring cardiomyocyte hypertrophy, increased fibrosis and capillary rarification.

AREAS COVERED

Beside an assessment of current vector systems, this review focuses on potential target genes affecting angiogenesis/arteriogenesis and contractility. The potential of micro RNA (miRNA) modulation for the de-repression of survival and pro-angiogenic genes is discussed. Since gene therapy of the target region is preferable to avoid systemic contamination, application routes are discussed.

EXPERT OPINION

miRNAs are a promising new development for successful gene therapy, especially for acute myocardial infarction since their miRNA antagonists are easy to apply and appear to be selectively absorbed by the ischemic myocardial tissue. Rapid uptake and prolonged presence of known antimirs and antagomirs support this notion. For ischemic heart disease the most promising gene therapeutic approach seems to be the regional intravenous application of suitable AAV vectors and vascular growth factors, providing the full scope of angiogenesis, vessel maturation and collateral growth optionally combined with genes enhancing contractility.

Role of microRNAs in cardiovascular disease: therapeutic challenges and potentials

MicroRNAs (miRNAs, miRs) are short approximately 22-nucleotide noncoding RNAs that bind to messenger RNA transcripts and in doing so modulate cognate gene expression. In eukaryotes, miRNAs act primarily by causing translational repression although they may also act to destabilize RNA transcripts. During the past few years, a number of studies have demonstrated that miR expression changes as a result of cardiac hypertrophy or heart failure. Additionally, cell-based and transgenic mouse studies have demonstrated that individual miRs can affect a number of aspects of cardiac biology including developmental processes, stem cell differentiation, progression of hypertrophy and failure, ion channel function, as well as angiogenesis, rates of apoptosis, and fibroblast proliferation. In this review, we will summarize several of the miRs known to change in expression in association with heart failure and outline details of what is known about their putative targets. In addition, we will review several aspects of regulation of miR expression that have not been addressed in a cardiovascular context. Finally, as is common to all new and rapidly moving fields, we will highlight some of the gaps and inconsistencies related to miR expression and cardiac phenotypes, particularly those associated with heart failure.

MicroRNAs in cardiomyocyte development

MicroRNAs (miRNAs) negatively regulate gene expression at the post-transcriptional level, primarily by base-pairing with the 3'-untranslated region (3'-UTR) of their target mRNAs. Many miRNAs are expressed in a tissue/organ-specific manner and are associated with an increasing number of cell proliferation, differentiation, and tissue development events. Cardiac muscle expresses distinct genes encoding structural proteins and a subset of signal molecules that control tissue specification and differentiation. The transcriptional regulation of cardiomyocyte development has been well established, yet only until recently has it been uncovered that miRNAs participate in the regulatory networks. A subset of miRNAs are either specifically or highly expressed in cardiac muscle, providing an opportunity to understand how gene expression is controlled by miRNAs at the post-transcriptional level in this muscle type. miR-1, miR-133, miR-206, and miR-208 have been found to be muscle-specific, and thus have been called myomiRs. The discovery of myomiRs as a previously unrecognized component in the regulation of gene expression adds an entirely new layer of complexity to our understanding of cardiac muscle development. Investigating myomiRs will not only reveal novel molecular mechanisms of the miRNA-mediated regulatory network in cardiomyocyte development, but also raise new opportunities for therapeutic intervention for cardiovascular disease.

Thioredoxin 1 negatively regulates angiotensin II-induced cardiac hypertrophy through upregulation of miR-98/let-7

RATIONALE

Thioredoxin (Trx)1 inhibits pathological cardiac hypertrophy. MicroRNAs (miRNAs) are small noncoding RNAs that downregulate posttranscriptional expression of target molecules.

OBJECTIVES

We investigated the role of miRNAs in mediating the antihypertrophic effect of Trx1 on angiotensin II (Ang II)-induced cardiac hypertrophy.

METHODS AND RESULTS

Microarray analyses of mature rodent microRNAs and quantitative RT-PCR/Northern blot analyses showed that Trx1 upregulates members of the let-7 family, including miR-98, in the heart and the cardiomyocytes therein. Adenovirus-mediated expression of miR-98 in cardiomyocytes reduced cell size both at baseline and in response to Ang II. Knockdown of miR-98, and of other members of the let-7 family, augmented Ang II-induced cardiac hypertrophy, and attenuated Trx1-mediated inhibition of Ang II-induced cardiac hypertrophy, suggesting that endogenous miR-98/let-7 mediates the antihypertrophic effect of Trx1. Cyclin D2 is one of the predicted targets of miR-98. Ang II significantly upregulated cyclin D2, which in turn plays an essential role in mediating Ang II-induced cardiac hypertrophy, whereas overexpression of Trx1 inhibited Ang II-induced upregulation of cyclin D2. miR-98 decreased both expression of cyclin D2 and the activity of a cyclin D2 3'UTR luciferase reporter, suggesting that both Trx1 and miR-98 negatively regulate cyclin D2. Overexpression of cyclin D2 attenuated the suppression of Ang II-induced cardiac hypertrophy by miR-98, suggesting that the antihypertrophic actions of miR-98 are mediated in part by downregulation of cyclin D2.

CONCLUSIONS

These results suggest that Trx1 upregulates expression of the let-7 family, including miR-98, which in turn inhibits cardiac hypertrophy, in part through downregulation of cyclin D2.

Myostatin decreases with aerobic exercise and associates with insulin resistance

PURPOSE

There is mounting evidence that skeletal muscle produces and secretes biologically active proteins or "myokines" that facilitate metabolic cross talk between organ systems. The increased expression of myostatin, a secreted anabolic inhibitor of muscle growth and development, has been associated with obesity and insulin resistance. Despite these intriguing findings, there have been few studies linking myostatin and insulin resistance.

METHODS

To explore this relationship in more detail, we quantified myostatin protein in muscle and plasma from 10 insulin-resistant, middle-aged (53.1 ± 5.5 yr) men before and after 6 months of moderate aerobic exercise training (1200 kcal·wk−¹ at 40%-55% VO2peak). To establish a cause-effect relationship, we also injected C57/Bl6 male mice with high physiological levels of recombinant myostatin protein.

RESULTS

Myostatin protein levels were shown to decrease in muscle (37%, P = 0.042, n = 10) and matching plasma samples (from 28.7 ng·mL−¹ pretraining to 22.8 ng·mL−¹ posttraining, P = 0.003, n = 9) with aerobic exercise. Furthermore, the strong correlation between plasma myostatin levels and insulin sensitivity (R² = 0.82, P < 0.001, n = 9) suggested a cause-effect relationship that was subsequently confirmed by inducing insulin resistance in myostatin-injected mice. A modest increase (44%) in plasma myostatin levels was also associated with significant reductions in the insulin-stimulated phosphorylation of Akt (Thr308) in both muscle and liver of myostatin-treated animals.

CONCLUSIONS

These findings indicate that both muscle and plasma myostatin protein levels are regulated by aerobic exercise and, furthermore, that myostatin is in the causal pathway of acquired insulin resistance with physical inactivity.

MicroRNAs in resolution of acute inflammation: identification of novel resolvin D1-miRNA circuits

Mechanisms controlling resolution of acute inflammation are of wide interest. Here, we investigated microRNAs (miRNAs) in self-limited acute inflammatory exudates and their regulation by resolvin D1 (RvD1). Using real-time PCR analysis, we found in resolving exudates that miR-21, miR-146b, miR-208a, miR-203, miR-142, miR-302d, and miR-219 were selectively regulated (P<0.05) in self-limited murine peritonitis. RvD1 (300 ng/mouse or 15 μg kg(-1)) reduced zymosan-elicited neutrophil infiltration into the peritoneum 25-50% and shortened the resolution interval (R(i)) by ∼4 h. In peritonitis at 12 h, RvD1 up-regulated miR-21, miR-146b, and miR-219 and down-regulated miR-208a in vivo. In human macrophages overexpressing recombinant RvD1 receptors ALX/FPR2 or GPR32, these same miRNAs were significantly regulated (P<0.05) by RvD1 at concentrations as low as 10 nM, recapitulating the in vivo circuit. In addition, RvD1-miRNAs identified herein target cytokines and proteins involved in the immune system, e.g., miR-146b targeted NF-κB signaling, and miR-219 targeted 5-lipoxygenase and reduced leukotriene production. RvD1 also reduced nuclear translocation of NF-κB and SMAD and down-regulated phospho-IκB. Taken together, these results indicate that resolvin-regulated specific miRNAs target genes involved in resolution and establish a novel resolution circuit involving RvD1 receptor-dependent regulation of specific miRNAs.