The endothelial-specific microRNA miR-126 governs vascular integrity and angiogenesis

Developmental and pathological angiogenesis

The formation of the vascular network is an intricate and complex process that is an obligate requirement during vertebrate development. The cardiovascular system is the first organ to develop and reach a functional state, which underscores the crucial role of the vasculature in the developing embryo. The development of the vasculature into highly branched conduits needs to occur in numerous sites and in precise patterns to supply oxygen and nutrients to the rapidly expanding tissue of the embryo. This process is mediated by the coordinated response of vascular endothelial and mural cells to the heterogeneous angiogenic cues provided by tissues and organs, whereas aberrant regulation and coordination of angiogenic signals during development result in lethality, impaired organ development, or disease states. This article reviews the essential signaling pathways required for establishment of the vertebrate vasculature with a major focus on a key regulatory factor, vascular endothelial growth factor (VEGF). We also discuss current knowledge of physiological angiogenic processes as well as their disruptions in pathological processes, particularly tumorigenesis.

MicroRNAs, diet, and cancer: new mechanistic insights on the epigenetic actions of phytochemicals

There is growing interest in the epigenetic mechanisms that impact human health and disease, including the role of microRNAs (miRNAs). These small (18-25 nucleotide), evolutionarily conserved, non-coding RNA molecules regulate gene expression in a post-transcriptional manner. Several well-orchestered regulatory mechanisms involving miRNAs have been identified, with the potential to target multiple signaling pathways dysregulated in cancer. Since the initial discovery of miRNAs, there has been progress towards therapeutic applications, and several natural and synthetic chemopreventive agents also have been evaluated as modulators of miRNA expression in different cancer types. This review summarizes the most up-to-date information related to miRNA biogenesis, and critically evaluates proposed miRNA regulatory mechanisms in relation to cancer signaling pathways, as well as other epigenetic modifications (DNA methylation patterns, histone marks) and their involvement in drug resistance. We also discuss the mechanisms by which dietary factors regulate miRNA expression, in the context of chemoprevention versus therapy.

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.

Regulation of vascular endothelial growth factor signaling by miR-200b

Vascular endothelial growth factor (VEGF) signaling plays an important role in angiogenesis. In the VEGF signaling pathway, the key components are VEGF and its receptors, Flt-1 and KDR. In this study, we show that transfection of synthetic miR-200b reduced protein levels of VEGF, Flt-1, and KDR. In A549 cells, miR-200b targeted the predicted binding sites in the 3'-untranslated region (3'-UTR) of VEGF, Flt-1, and KDR as revealed by a luciferase reporter assay. When transfected with miR-200b, the ability of HUVECs to form a capillary tube on Matrigel and VEGF-induced phosphorylation of ERK1/2 were significantly reduced. Taken together, these results suggest that miR-200b negatively regulates VEGF signaling by targeting VEGF and its receptors and that miR-200b may have therapeutic potential as an angiogenesis inhibitor.

MicroRNAs and other small silencing RNAs in cancer

Small noncoding RNAs are key controllers of cellular function, and their deregulation can lead to cancer development and metastatic evolution. This review summarizes the most important examples of small RNAs involved in human cancer and discusses their clinical use as biomarkers and drug targets for diagnosis, prognosis, and treatment of cancer. We also describe the possible mechanisms underlying small RNA-mediated transformation and outline the future describing new small RNA families with great potential in cancer biology.

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.

miR126 positively regulates mast cell proliferation and cytokine production through suppressing Spred1

The protein known as Spred1 (Sprouty-related Ena/VASP homology-1 domain-containing protein) has been identified as a negative regulator of growth factor-induced ERK/mitogen-activated protein kinase activation. Spred1 has also been implicated as the target of microRNA-126 (miR126), a miRNA located within the Egfl7 gene, and is involved in the regulation of vessel development through its role in regulating VEGF signaling. In this study, we examined the role of miR126 and Spred1 in the hematopoietic system, as miR126 has been shown to be overexpressed in leukemic cells. miR126 levels were down-regulated during mast cell differentiation from bone marrow cells, whereas Spred1 expression was inversely up-regulated. Overexpression of miR126 suppressed Spred1 expression and enhanced ERK activity in primary bone marrow cells and MC9 mast cells, which were associated with elevated FcεRI-mediated cytokine production. To confirm the effect of Spred1 reduction in vivo, we generated hematopoietic cell-specific Spred1-conditional knockout mice. These mice showed increased numbers of mast cells, and Spred1-deficient bone marrow-derived mast cells were highly activated by cross-linking of Fcε-R stimulation as well as by IL-3 and SCF stimulation. These results suggest that Spred1 negatively regulates mast cell activation, which is modulated by miR126.

Identification of hematopoietic stem cell-specific miRNAs enables gene therapy of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD; also known as Krabbe disease) is an invariably fatal lysosomal storage disorder caused by mutations in the galactocerebrosidase (GALC) gene. Hematopoietic stem cell (HSC)-based gene therapy is being explored for GLD; however, we found that forced GALC expression was toxic to HSCs and early progenitors, highlighting the need for improved regulation of vector expression. We used a genetic reporter strategy based on lentiviral vectors to detect microRNA activity in hematopoietic cells at single-cell resolution. We report that miR-126 and miR-130a were expressed in HSCs and early progenitors from both mice and humans, but not in differentiated progeny. Moreover, repopulating HSCs could be purified solely on the basis of miRNA expression, providing a new method relevant for human HSC isolation. By incorporating miR-126 target sequences into a GALC-expressing vector, we suppressed GALC expression in HSCs while maintaining robust expression in mature hematopoietic cells. This approach protected HSCs from GALC toxicity and allowed successful treatment of a mouse GLD model, providing a rationale to explore HSC-based gene therapy for GLD.

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.

Non-coding RNAs as regulators of gene expression and epigenetics

Genome-wide studies have revealed that mammalian genomes are pervasively transcribed. This has led to the identification and isolation of novel classes of non-coding RNAs (ncRNAs) that influence gene expression by a variety of mechanisms. Here we review the characteristics and functions of regulatory ncRNAs in chromatin remodelling and at multiple levels of transcriptional and post-transcriptional regulation. We also describe the potential roles of ncRNAs in vascular biology and in mediating epigenetic modifications that might play roles in cardiovascular disease susceptibility. The emerging recognition of the diverse functions of ncRNAs in regulation of gene expression suggests that they may represent new targets for therapeutic intervention.

MicroRNAs expression in ox-LDL treated HUVECs: MiR-365 modulates apoptosis and Bcl-2 expression

Endothelial cells (ECs) apoptosis induced by oxidized low-density lipoprotein (ox-LDL) is thought to play a critical role in atherosclerosis. MicroRNAs (miRNAs) are a class of noncoding RNAs that posttranscriptionally regulate the expression of genes involved in diverse cell functions, including differentiation, growth, proliferation, and apoptosis. However, whether miRNAs are associated with ox-LDL induced apoptosis and their effect on ECs is still unknown. Therefore, this study evaluated potential miRNAs and their involvement in ECs apoptosis in response to ox-LDL stimulation. Microarray and qRT-PCR analysis performed on human umbilical vein endothelial cells (HUVECs) exposed to ox-LDL identified 15 differentially expressed (4 up- and 11 down-regulated) miRNAs. Web-based query tools were utilized to predict the target genes of the differentially expressed miRNAs, and the potential target genes were classified into different function categories with the gene ontology (GO) term and KEGG pathway annotation. In particular, bioinformatics analysis suggested that anti-apoptotic protein B-cell CLL/lymphoma 2 (Bcl-2) is a target gene of miR-365, an apoptomir up-regulated by ox-LDL stimulation in HUVECs. We further showed that transfection of miR-365 inhibitor partly restored Bcl-2 expression at both mRNA and protein levels, leading to a reduction of ox-LDL-mediated apoptosis in HUVECs. Taken together, our findings indicate that miRNAs participate in ox-LDL-mediated apoptosis in HUVECs. MiR-365 potentiates ox-LDL-induced ECs apoptosis by regulating the expression of Bcl-2, suggesting potential novel therapeutic targets for atherosclerosis.

Targeting miR-375 in gastric cancer

INTRODUCTION

Gastric cancer remains a major cancer burden in the world, with a poor 5-year survival rate. It is necessary to develop new effective therapeutic strategies to improve the long-term clinical outcome. MicroRNA (miRNA), a class of small non-coding RNA, has been identified as a key regulator of gene expression, and is implicated in the pathogenesis of gastric cancer.

AREAS COVERED

This review summarizes the role of miRNAs in gastric carcinogenesis, with an emphasis on the expression and function of miR-375 in gastric cancer and beyond. It also discusses the opportunities and challenges of miR-375 as a potential therapeutic target for gastric cancer. The genes targeted by miR-375, including JAK2 and 3'-phosphoinositide dependent protein kinase-1 (PDK1), are also candidates for gastric cancer therapy.

EXPERT OPINION

Although radical surgery and rational chemotherapy are still the main treatment for gastric cancer, targeting miRNAs, in combination with other conventional therapies, may serve as a promising therapy strategy to improve the clinical outcome.

MicroRNA-126 inhibits ischemia-induced retinal neovascularization via regulating angiogenic growth factors

To investigate the potential transcriptional regulation and signal pathway of a single microRNA in ischemia-induced retinal neovascularization (NV), we used oxygen-induced retinopathy (OIR) in establishing retinal NV model, and quantitative real-time reverse transcriptase PCR analyzing a microRNA (miR-126) alteration. The mice were treated with plasmid pCMV-MIR-126/liposome mixture intravitreal injection, using pCMV-MIR/liposome mixture as control. The expression levels of VEGF, IGF-2 and HIF-1α, and the level changes of total and phosphorylated p38, ERK in retina from OIR mice were determined by western blot analysis. The effects of miR-126 on retinal NV in OIR mice were identified with fluoresecin angiography and H & E staining. No effect of miR-126 intravitreal injection on retinal vessels was performed with CD31 stained retinal sections. Our results showed that miR-126 was significantly decreased in retina from OIR mice. We confirmed that restoration of miR-126 in retina overcame the high levels of VEGF, IGF-2 and HIF-1α through downregulating p38 and ERK signaling molecules in OIR model, and that miR-126 intravitreal injection reduced retinal NV in OIR model. These results suggest that miR-126 might play a potential transcriptional role in the pathogenesis in diabetic retinopathy.

MicroRNAs as biomarkers of disease onset

MicroRNAs (miRNAs) are small, noncoding RNA molecules with the ability to posttranscriptionally regulate gene expression via targeting the 3' untranslated region of messenger RNAs. miRNAs are critical for normal cellular functions such as the regulation of the cell cycle, differentiation, and apoptosis, and they target genes during embryonal and postnatal development, whereas their expression is unbalanced in various pathological states. Importantly, miRNAs are abundantly present in body fluids (e.g., blood), which are routinely examined in patients. These molecules circulate in free and exosome encapsulated forms, and can be efficiently detected and amplified by means of molecular biology tools such as real-time PCR. Together with relative stability, specificity, and reproducibility, they are seen as good candidates for early recognition of the onset of disease. Thus, miRNAs might be considered as biomarkers for many pathological states.

Regulation of angiogenesis and choroidal neovascularization by members of microRNA-23~27~24 clusters

MicroRNAs (miRNAs) modulate complex physiological and pathological processes by repressing expression of multiple components of cellular regulatory networks. Here we demonstrate that miRNAs encoded by the miR-23∼27∼24 gene clusters are enriched in endothelial cells and highly vascularized tissues. Inhibition of miR-23 and miR-27 function by locked nucleic acid-modified anti-miRNAs represses angiogenesis in vitro and postnatal retinal vascular development in vivo. Moreover, miR-23 and miR-27 are required for pathological angiogenesis in a laser-induced choroidal neovascularization mouse model. MiR-23 and miR-27 enhance angiogenesis by promoting angiogenic signaling through targeting Sprouty2 and Sema6A proteins, which exert antiangiogenic activity. Manipulating miR-23/27 levels may have important therapeutic implications in neovascular age-related macular degeneration and other vascular disorders.

MiR-126-3p regulates progesterone receptors and involves development and lactation of mouse mammary gland

MicroRNAs (miRNAs) are small (18-22 nucleotide) non-coding, endogenous regulatory RNA molecules, and they regulate gene expression at the post-transcriptional level through binding to their target mRNAs by base-pairing and subsequently inducing either translational repression or mRNA destabilization by plants, animals, and some viruses. In this study, combining microarray techniques with qRT-PCR, we found that miR-126-3p expression showed significant difference in the mouse mammary cycle during pregnancy, particularly on transition from pregnancy to lactation. Bioinformatics were used to predict target gene of miR-126-3p, and luciferase activity assay to test it, it showed that the progesterone receptor (PGR) 3'UTR is directly targeted by miR-126-3p. In this study, mouse mammary epithelial cells as cell model in vitro were used to study the function of miR-126-3p. Using gene silencing and over-expression for miR-126-3p, the expression of PGR protein and the secretion of casein were detected by western blotting and HPLC, respectively. To determine whether miR-126-3p can affect mouse mammary epithelial cells viability, cells were analyzed by CASY-YY. In conclusion, PGR gene confirmed miR-126-3p target genes through luciferase activity and western blotting. And miR-126-3p could also inhibit proliferation of mouse mammary epithelial cells (P < 0.01) and expression of β-casein (P < 0.01), and down-regulate PGR protein (P < 0.05). Our results suggested that miR-126-3p inhibited expression of PGR protein level as well as the proliferation of mammary epithelial cells, therefore miR-126-3p could play an important role in the process of mammary gland development.

Biological functions of microRNAs

The small regulatory non-coding RNA molecules, known as microRNAs (miRNAs), have been recognized as potential regulator of gene expression and modulate the gene function at the post-transcriptional level. It is now clear that miRNA biogenesis and function are related to the molecular mechanisms of various clinical diseases, which can potentially regulate every aspect of cellular activity, including differentiation and development, metabolism, proliferation, apoptotic cell death viral infection and tumorgenesis. Here, we review recent work and provide insight into the diverse roles of miRNAs.

miR-146a is modulated in human endothelial cell with aging

BACKGROUND

Increasing evidence has demonstrated that the senescence of vascular endothelial cells has critical roles in the pathogenesis of vascular dysfunction such as atherosclerosis and thrombosis. MicroRNA (miR) are small non-coding RNAs that inhibit gene expression by binding to complementary sequences in the 3'UTR of their target mRNAs. MiRs modulate a variety of biological functions such as cell development, cell differentiation, and apoptosis. Moreover, several miRs involved in endothelial cell function have been identified.

METHODS AND RESULTS

Through a microarray approach, we have identified a miR-146a that is progressively modulated in endothelial cells with aging. In young human umbilical vein endothelial cells, this miR is involved in a premature senescence-like phenotype through direct targeting of the NOX4 protein, implicated in cell senescence and aging.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Finding important factors that regulate endothelial cell senescence, like miR-146a, will help provide novel therapeutic strategies for vascular disorders.

MicroRNAs in cardiac disease

MicroRNAs (miRs) are transcriptionally regulated single-strand RNAs that depress protein expression through posttranscriptional mRNA silencing. A host of recent studies have established essential roles for miRs in cardiac development and cardiac health. Regulated myocardial miR expression is observed in a variety of cardiac syndromes, and serum miR levels are being evaluated as disease biomarkers. The manipulation of miR levels in mouse hearts using genetic techniques or engineered miR mimetics and antagonists is elucidating the roles of specific cardiac miRs in cardiac development, and in the cardiac response to injury or stress, and heart disease. The ability to target multiple factors within a single biological response pathway by a given miR has prompted the development of small miR-targeting molecules that can be readily delivered and have sustained in vivo effects. These advances establish a foundation for novel diagnostics and new therapeutic approaches for myocardial infarction, cardiac hypertrophy, and heart failure.

Integrating microRNAs into a system biology approach to acute lung injury

Acute lung injury (ALI), including the ventilator-induced lung injury (VILI) and the more severe acute respiratory distress syndrome (ARDS), are common and complex inflammatory lung diseases potentially affected by various genetic and nongenetic factors. Using the candidate gene approach, genetic variants associated with immune response and inflammatory pathways have been identified and implicated in ALI. Because gene expression is an intermediate phenotype that resides between the DNA sequence variation and the higher level cellular or whole-body phenotypes, the illustration of gene expression regulatory networks potentially could enhance understanding of disease susceptibility and the development of inflammatory lung syndromes. MicroRNAs (miRNAs) have emerged as a novel class of gene regulators that play critical roles in complex diseases including ALI. Comparisons of global miRNA profiles in animal models of ALI and VILI identified several miRNAs (eg, miR-146a and miR-155) previously implicated in immune response and inflammatory pathways. Therefore, via regulation of target genes in these biological processes and pathways, miRNAs potentially contribute to the development of ALI. Although this line of inquiry exists at a nascent stage, miRNAs have the potential to be critical components of a comprehensive model for inflammatory lung disease built by a systems biology approach that integrates genetic, genomic, proteomic, epigenetic as well as environmental stimuli information. Given their particularly recognized role in regulation of immune and inflammatory responses, miRNAs also serve as novel therapeutic targets and biomarkers for ALI/ARDS or VILI, thus facilitating the realization of personalized medicine for individuals with acute inflammatory lung disease.

A Slit/miR-218/Robo regulatory loop is required during heart tube formation in zebrafish

Members of the Slit family of secreted ligands interact with Roundabout (Robo) receptors to provide guidance cues for many cell types. For example, Slit/Robo signaling elicits repulsion of axons during neural development, whereas in endothelial cells this pathway inhibits or promotes angiogenesis depending on the cellular context. Here, we show that miR-218 is intronically encoded in slit2 and slit3 and that it suppresses Robo1 and Robo2 expression. Our data indicate that miR-218 and multiple Slit/Robo signaling components are required for heart tube formation in zebrafish and that this network modulates the previously unappreciated function of Vegf signaling in this process. These findings suggest a new paradigm for microRNA-based control of ligand-receptor interactions and provide evidence for a novel signaling pathway regulating vertebrate heart tube assembly.

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.

miRNAs: roles and clinical applications in vascular disease

miRNAs are small, endogenously expressed noncoding RNAs that regulate gene expression, mainly at the post-transcriptional level, via degradation or translational inhibition of their target mRNAs. Functionally, an individual miRNA can regulate the expression of multiple target genes. The study of miRNAs is rapidly growing and recent studies have revealed a significant role of miRNAs in vascular biology and disease. Many miRNAs are highly expressed in the vasculature, and their expression is dysregulated in diseased vessels. Several miRNAs have been found to be critical modulators of vascular pathologies, such as atherosclerosis, lipoprotein metabolism, inflammation, arterial remodeling, angiogenesis, smooth muscle cell regeneration, hypertension, apoptosis, neointimal hyperplasia and signal transduction pathways. Thus, miRNAs may serve as novel biomarkers and/or therapeutic targets for vascular disease. This article summarizes the current studies related to the disease correlations and functional roles of miRNAs in the vascular system and discusses the potential applications of miRNAs in vascular disease.

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.

miR-126 inhibits proliferation of small cell lung cancer cells by targeting SLC7A5

Despite intensive efforts to improve therapies, small cell lung cancer (SCLC) still has a dismal median survival of 18 months. Since miR-126 is under-expressed in the majority of SCLC tumors, we investigated the effect of miR-126 overexpression on the proliferation and cell cycle distribution of H69 cells. Our results demonstrate that miR-126 inhibits proliferation of H69 cells, by delaying the cells in the G1 phase. Short interfering RNA (siRNA) mediated suppression of SLC7A5, a predicted target of mir-126, has the same effect on H69 cells. We also show for the first time that SLC7A5 is a direct target of miR-126.

Conditional deletion of Dicer in vascular smooth muscle cells leads to the developmental delay and embryonic mortality

Dicer is a RNAase III enzyme that cleaves double stranded RNA and generates small interfering RNA (siRNA) and microRNA (miRNA). The goal of this study is to examine the role of Dicer and miRNAs in vascular smooth muscle cells (VSMCs). We deleted Dicer in VSMCs of mice, which caused a developmental delay that manifested as early as embryonic day E12.5, leading to embryonic death between E14.5 and E15.5 due to extensive hemorrhage in the liver, brain, and skin. Dicer KO embryos showed dilated blood vessels and a disarray of vascular architecture between E14.5 and E15.5. VSMC proliferation was significantly inhibited in Dicer KOs. The expression of VSMC marker genes were significantly downregulated in Dicer cKO embryos. The vascular structure of the yolk sac and embryo in Dicer KOs was lost to an extent that no blood vessels could be identified after E15.5. Expression of most miRNAs examined was compromised in VSMCs of Dicer KO. Our results indicate that Dicer is required for vascular development and regulates vascular remodeling by modulating VSMC proliferation and differentiation.

Pervasive roles of microRNAs in cardiovascular biology

First recognized as regulators of development in worms and fruitflies, microRNAs are emerging as pivotal modulators of mammalian cardiovascular development and disease. Individual microRNAs modulate the expression of collections of messenger RNA targets that often have related functions, thereby governing complex biological processes. The wideranging functions of microRNAs in the cardiovascular system have provided new perspectives on disease mechanisms and have revealed intriguing therapeutic targets, as well as diagnostics, for a variety of cardiovascular disorders.

MicroRNA-21 exhibits antiangiogenic function by targeting RhoB expression in endothelial cells

Background

MicroRNAs (miRNAs) are endogenously expressed small non-coding RNAs that regulate gene expression at post-transcriptional level. The recent discovery of the involvement of these RNAs in the control of angiogenesis renders them very attractive in the development of new approaches for restoring the angiogenic balance. Whereas miRNA-21 has been demonstrated to be highly expressed in endothelial cells, the potential function of this miRNA in angiogenesis has never been investigated.

Methodology/Principal Findings

We first observed in endothelial cells a negative regulation of miR-21 expression by serum and bFGF, two pro-angiogenic factors. Then using in vitro angiogenic assays, we observed that miR-21 acts as a negative modulator of angiogenesis. miR-21 overexpression reduced endothelial cell proliferation, migration and the ability of these cells to form tubes whereas miR-21 inhibition using a LNA-anti-miR led to opposite effects. Expression of miR-21 in endothelial cells also led to a reduction in the organization of actin into stress fibers, which may explain the decrease in cell migration. Further mechanistic studies showed that miR-21 targets RhoB, as revealed by a decrease in RhoB expression and activity in miR-21 overexpressing cells. RhoB silencing impairs endothelial cell migration and tubulogenesis, thus providing a possible mechanism for miR-21 to inhibit angiogenesis. Finally, the therapeutic potential of miR-21 as an angiogenesis inhibitor was demonstrated in vivo in a mouse model of choroidal neovascularization.

Conclusions/Significance

Our results identify miR-21 as a new angiogenesis inhibitor and suggest that inhibition of cell migration and tubulogenesis is mediated through repression of RhoB.

MicroRNA-126 inhibits SOX2 expression and contributes to gastric carcinogenesis

Background

SRY (sex-determining region Y)-box 2 (SOX2) is a crucial transcription factor for the maintenance of embryonic stem cell pluripotency and the determination of cell fate. Previously, we demonstrated that SOX2 plays important roles in growth inhibition through cell cycle arrest and apoptosis, and that SOX2 expression is frequently down-regulated in gastric cancers. However, the mechanisms underlying loss of SOX2 expression and its target genes involved in gastric carcinogenesis remain largely unknown. Here, we assessed whether microRNAs (miRNAs) regulate SOX2 expression in gastric cancers. Furthermore, we attempted to find downstream target genes of SOX2 contributing to gastric carcinogenesis.

Methodology/Principal Findings

We performed in silico analysis and focused on miRNA-126 (miR-126) as a potential SOX2 regulator. Gain- and loss-of function experiments and luciferase assays revealed that miR-126 inhibited SOX2 expression by targeting two binding sites in the 3′-untranslated region (3′-UTR) of SOX2 mRNA in multiple cell lines. In addition, miR-126 was highly expressed in some cultured and primary gastric cancer cells with low SOX2 protein levels. Furthermore, exogenous miR-126 over-expression as well as siRNA-mediated knockdown of SOX2 significantly enhanced the anchorage-dependent and -independent growth of gastric cancer cell lines. We next performed microarray analysis after SOX2 over-expression in a gastric cancer cell line, and found that expression of the placenta-specific 1 (PLAC1) gene was significantly down-regulated by SOX2 over-expression. siRNA- and miR-126-mediated SOX2 knockdown experiments revealed that miR-126 positively regulated PLAC1 expression through suppression of SOX2 expression in gastric cancer cells.

Conclusions

Taken together, our results indicate that miR-126 is a novel miRNA that targets SOX2, and PLAC1 may be a novel downstream target gene of SOX2 in gastric cancer cells. These findings suggest that aberrant over-expression of miR-126 and consequent SOX2 down-regulation may contribute to gastric carcinogenesis.

Independent and tissue-specific prognostic impact of miR-126 in nonsmall cell lung cancer: coexpression with vascular endothelial growth factor-A predicts poor survival

BACKGROUND

Angiogenesis is pivotal in tumor development. Vascular endothelial growth factor-A (VEGF-A) is considered one of the most important angiogenic factors, but lately several microRNAs (miRs) have been associated with vascular development. miR-126 has been related to tumor angiogenesis and in the regulation of VEGF-A. The authors aimed to investigate the prognostic impact of miR-126 and its co-expression with VEGF-A in nonsmall cell lung cancer (NSCLC) patients.

METHODS

Tumor tissue samples from 335 resected stage I to IIIA NSCLC patients were obtained and tissue microarrays (TMAs) were constructed with 4 cores from each tumor specimen. VEGF-A expression was evaluated by immunohistochemistry, and in situ hybridization was used to evaluate the expression of miR-126.

RESULTS

In the total material, miR-126 was a significant negative prognostic factor in both univariate (P = .005) and multivariate analyses (hazard ratio [HR] 1.8, 95% confidence interval [CI] 1.2-2.8, P = .01). Stratified by histology, miR-126 was only significant in squamous cell carcinomas (univariate: P < .001; multivariate: HR 3.1, CI 95% 1.7-5.6, P<.001). Stratified by lymph node status, miR-126 was significant only in the lymph node-positive subgroup (univariate: P<.001; multivariate: HR 4.1, CI 95% 2.0-8.4, P < .001). High miR-126 expression correlated significantly with high VEGF-A expression (P = .037). The co-expression of miR-126 and VEGF-A had a significant prognostic impact (P = .002), with 5-year survival rates of 68%, 51%, and 42% for low/low (n = 150), mixed combinations (n = 129), and high/high (n = 35) expression, respectively.

CONCLUSIONS

miR-126 is a strong and independent negative prognostic factor in NSCLC, and its prognostic impact appears related primarily to histology and nodal status.

Two functional microRNA-126s repress a novel target gene p21-activated kinase 1 to regulate vascular integrity in zebrafish

RATIONALE

MicroRNAs (miRNAs) are key regulators of vascular development and diseases. The function and underlying mechanism of endothelial miRNAs have not been fully defined.

OBJECTIVE

To investigate the role of endothelial miR-126 in zebrafish vascular development.

METHODS AND RESULTS

Two homologs of miR-126, miR-126a (namely miR-126 in previous literature) and miR-126b, with only 1 nucleotide difference in their mature sequences, were identified in zebrafish genome. In vitro analysis showed that both precursors could sufficiently produce mature functional miRNAs. Expression analyses by Northern blot and quantitative RT-PCR showed that both miR-126s accumulated significantly 12 hours after fertilization and were specifically expressed in endothelial cells of zebrafish. Inhibition of miR-126a or miR-126b with specific morpholinos caused cranial hemorrhage, and simultaneous inhibition of both miR-126s resulted in a pronounced hemorrhage in higher percentage of embryos. Bioinformatics prediction showed that the targets of miR-126a/b partially overlapped but essentially differed. p21-activated kinase1 (pak1) was identified as a novel target of miR-126a/b, and pak1 3' untranslated region was differently regulated by these 2 miRNAs. Quantitative RT-PCR, in situ hybridization, and Western blot analyses showed that the level of pak1 was reduced when miR-126a/b were overexpressed. Notably, pak1 expression in endothelial cells was increased when miR-126a/b were knocked down. Furthermore, overexpression of the active form of human pak1 caused cranial hemorrhage, and knockdown pak1 effectively rescued the hemorrhage caused by inhibiting miR-126a/b.

CONCLUSIONS

Two functional endothelial cell-specific miRNAs, miR-126a and miR-126b, synergistically regulate zebrafish vascular integrity, and pak1 is a critical target of miR-126a/b in vascular development.

Endothelial-specific intron-derived miR-126 is down-regulated in human breast cancer and targets both VEGFA and PIK3R2

Endothelial cells are the key components of vascular intima and play pivotal roles in vasculogenesis, angiogenesis, and tumor growth. Using Northern blot and real-time PCR, we confirmed that miR-126 and its host gene EGF-like domain 7 (EGFL7) were widely expressed in rat tissues but strictly expressed in endothelial cells. In mammals, miR-126 gene is embedded in intron7 of EGFL7. To explore the biogenesis of miR-126, plasmid EGFL7(126)-pEGFPc1 containing segment of exon7-intron7-exon8 of EGFL7 was constructed and expressed in 293T. Expression of spliced exon7-8 and excised mature miR-126 was detected by PCR and Northern blot. Knocking-down of endothelial endogenous miR-126 did not affect EGFL7 expression at mRNA or protein level. To investigate the possible roles of miR-126, PicTar, miRBase, miRanda, Bibiserv, and Targetscan were used to screen the targets. VEGFA and PIK3R2 were confirmed as the targets of miR-126 by luciferase reporter assay and Western blot. Interestingly, Northern blot and western blot showed that miR-126 was down-regulated in breast tumors where the VEGF/PI3K/AKT signaling pathway was activated. Introduction of miR-126 mimics into MCF-7 could effectively decrease VEGF/PI3K/AKT signaling activity. In summary, miR-126 was strictly expressed in endothelial cells and excised from EGFL7 pre-mRNA without affecting splicing and expression of its host gene. In addition, miR-126 could target both VEGFA and PIK3R2, and its expression was decreased in human breast cancer, implying that miR-126 may play a role in tumor genesis and growth by regulating the VEGF/PI3K/AKT signaling pathway.

Deregulation of microRNA-503 contributes to diabetes mellitus-induced impairment of endothelial function and reparative angiogenesis after limb ischemia

BACKGROUND

Diabetes mellitus impairs endothelial cell (EC) function and postischemic reparative neovascularization by molecular mechanisms that are not fully understood. microRNAs negatively regulate the expression of target genes mainly by interaction in their 3' untranslated region.

METHODS AND RESULTS

We found that microRNA-503 (miR-503) expression in ECs is upregulated in culture conditions mimicking diabetes mellitus (high D-glucose) and ischemia-associated starvation (low growth factors). Under normal culture conditions, lentivirus-mediated miR-503-forced expression inhibited EC proliferation, migration, and network formation on Matrigel (comparisons versus lentivirus.GFP control). Conversely, blocking miR-503 activity by either adenovirus-mediated transfer of a miR-503 decoy (Ad.decoymiR-503) or by antimiR-503 (antisense oligonucleotide) improved the functional capacities of ECs cultured under high D-glucose/low growth factors. We identified CCNE1 and cdc25A as direct miR-503 targets which are downregulated by high glucose/low growth factors in ECs. Next, we obtained evidence that miR-503 expression is increased in ischemic limb muscles of streptozotocin-diabetic mice and in ECs enriched from these muscles. Moreover, Ad.decoymiR-503 delivery to the ischemic adductor of diabetic mice corrected diabetes mellitus-induced impairment of postischemic angiogenesis and blood flow recovery. We finally investigated miR-503 and target gene expression in muscular specimens from the amputated ischemic legs of diabetic patients. As controls, calf biopsies of nondiabetic and nonischemic patients undergoing saphenous vein stripping were used. In diabetic muscles, miR-503 expression was remarkably higher, and it inversely correlated with cdc25 protein expression. Plasma miR-503 levels were also elevated in the diabetic individuals.

CONCLUSIONS

Our data suggest miR-503 as a possible therapeutic target in diabetic patients with critical limb ischemia.

Control of cardiovascular differentiation by microRNAs

MicroRNAs (miRs) are small non-coding RNAs, which control gene expression either by inducing mRNA degradation or by blocking translation, and play a crucial role in tissue homeostasis. In the cardiovascular system, miRs were shown to control cardiac hypertrophy, fibrosis and apoptosis, angiogenesis, and vessel remodeling. In addition, miRs regulate stem cell maintenance and some miRs induced cell fate decisions. This review summarizes the current insights into the control of stem cells and lineage commitment by miRs focusing specifically to the regulation of endothelial, smooth muscle, and cardiac lineage.

Dysregulation of angiogenesis-related microRNAs in endothelial progenitor cells from patients with coronary artery disease

Endothelial progenitor cells (EPCs) play an important role in vascular repair and maintenance of vascular homeostasis through re-endothelialization and neovascularization. Cardiovascular risk factors that contribute to coronary artery disease (CAD) have been shown to negatively impact EPCs, although the mechanisms are poorly understood. MicroRNAs (miRNAs) which negatively regulate gene expression at the post-transcriptional level have been shown to impact endothelial cell (EC) angiogenic actions, but little is known about their role in modulating EPC function. In this study we first investigated if EPCs expressed EC specific, angiogenesis-related miRNAs; then determined whether the expression of these miRNAs was altered in EPCs from CAD patients as compared with healthy controls. Furthermore, we examined if atorvastatin, known to increase circulating EPC numbers, had any effect on EPC miRNA expression. We found EPCs produced miR-126, miR-130a, miR-221, miR-222 and miR-92a which have thus far been identified as the most important angiogenic miRNAs. Dysregulation of these miRNAs was detected in EPCs from CAD patients and atorvastatin treatment selectively impacted miRNA expression in EPCs. Our data provide evidence that angiogenic miRNAs might play an important role in the control of EPC function, and that their dysregulation might contribute to EPC dysfunction in patients suffering from coronary artery disease. These findings might lead to the development of novel therapeutic modalities for the prevention and treatment of CAD.

Regulated expression of microRNAs-126/126* inhibits erythropoiesis from human embryonic stem cells

MicroRNAs (miRs) play an important role in cell differentiation and maintenance of cell identity, but relatively little is known of their functional role in modulating human hematopoietic lineage differentiation. Human embryonic stem cells (hESCs) provide a model system to study early human hematopoiesis. We differentiated hESCs by embryoid body (EB) formation and compared the miR expression profile of undifferentiated hESCs to CD34(+) EB cells. miRs-126/126* were the most enriched of the 7 miRs that were up-regulated in CD34(+) cells, and their expression paralleled the kinetics of hematopoietic transcription factors RUNX1, SCL, and PU.1. To define the role of miRs-126/126* in hematopoiesis, we created hESCs overexpressing doxycycline-regulated miRs-126/126* and analyzed their hematopoietic differentiation. Induction of miRs-126/126* during both EB differentiation and colony formation reduced the number of erythroid colonies, suggesting an inhibitory role of miRs-126/126* in erythropoiesis. Protein tyrosine phosphatase, nonreceptor type 9 (PTPN9), a protein tyrosine phosphatase that is required for growth and expansion of erythroid cells, is one target of miR-126. PTPN9 restoration partially relieved the suppressed erythropoiesis caused by miRs-126/126*. Our results define an important function of miRs-126/126* in negative regulation of erythropoiesis, providing the first evidence for a role of miR in hematopoietic differentiation of hESCs.

Role of microRNAs in cardiac preconditioning

Preconditioning (PC) of the heart by sublethal ischemia, mild heat shock, or hypoxia has evolved as a powerful experimental tool to discover novel signaling mechanisms in cardioprotection. The ultimate goal is to determine novel therapeutic targets for potential application in humans to protect the heart against ischemia-related injuries. In recent years, there has been a tremendous interest in understanding the role of small noncoding RNAs, microRNAs (miRs), in cardiovascular diseases. miRs have been recognized as regulators of gene expression by destabilization and translational inhibition of target messenger RNAs. Studies have shown that several miRs, including miR-1, miR-133, miR-21, miR-126, miR-320, miR-92a, and miR-199a, are regulated after preconditioning and play an active role in protecting the heart against ischemia/reperfusion injury. These miRs also drive the synthesis of important cardioprotective proteins including heat shock protein (HSP)-70, endothelial nitric oxide synthase, inducible nitric oxide synthase, HSP-20, Sirt1, and hypoxia-inducible factor 1a. We believe that identification and targeted delivery of miR(s) in the heart could have an immense therapeutic potential in reducing myocardial infarction in patients suffering from heart disease.

MicroRNA-218 regulates vascular patterning by modulation of Slit-Robo signaling

RATIONALE

Establishment of a functional vasculature requires the interconnection and remodeling of nascent blood vessels. Precise regulation of factors that influence endothelial cell migration and function is essential for these stereotypical vascular patterning events. The secreted Slit ligands and their Robo receptors constitute a critical signaling pathway controlling the directed migration of both neurons and vascular endothelial cells during embryonic development, but the mechanisms of their regulation are incompletely understood.

OBJECTIVE

To identify microRNAs regulating aspects of the Slit-Robo pathway and vascular patterning.

METHODS AND RESULTS

Here, we provide evidence that microRNA (miR)-218, which is encoded by an intron of the Slit genes, inhibits the expression of Robo1 and Robo2 and multiple components of the heparan sulfate biosynthetic pathway. Using in vitro and in vivo approaches, we demonstrate that miR-218 directly represses the expression of Robo1, Robo2, and glucuronyl C5-epimerase (GLCE), and that an intact miR-218-Slit-Robo regulatory network is essential for normal vascularization of the retina. Knockdown of miR-218 results in aberrant regulation of this signaling axis, abnormal endothelial cell migration, and reduced complexity of the retinal vasculature.

CONCLUSIONS

Our findings link Slit gene expression to the posttranscriptional regulation of Robo receptors and heparan sulfate biosynthetic enzymes, allowing for precise control over vascular guidance cues influencing the organization of blood vessels during development.

MicroRNA-125a/b-5p inhibits endothelin-1 expression in vascular endothelial cells

BACKGROUND

Endothelin-1 (ET-1) is considered to be one of the most potent and long-lasting vasoconstrictive peptides, but the mechanisms on the regulation of ET-1 expression are not fully understood.

METHOD AND RESULTS

In this study, we found that microRNA (miR)-125a-5p and miR-125b-5p are highly expressed in vascular endothelial cells (VECs), which can be regulated by oxidized low-density lipoprotein (oxLDL). To explore the function of miR-125a/b-5p in VECs, we examined the roles of potential targets of miR-125a/b-5p that could influence endothelium function. We found that both miR-125a/b-5p can suppress oxLDL-induced ET-1 expression by directly targeting 3' untranslated region of prepro-endothelin-1 (preproET-1) mRNA determined by luciferase reporter assay, western blot, and enzyme immunometric assay. Consistently, inhibitors of miR-125a/b-5p can directly enhance preproET-1 expression. The decreased expressions of miR-125a-5p and miR-125b-5p are negatively associated with upregulation of preproET-1 expression in aorta of stroke-prone spontaneously hypertensive rats (SHR-SPs).

CONCLUSION

Our finding demonstrated that endothelial miR-125a/b-5p inhibits ET-1 expression in VECs, which revealed a novel miRNA-mediated mechanism in vasomotor homeostasis.

MicroRNAs regulate pituitary development, and microRNA 26b specifically targets lymphoid enhancer factor 1 (Lef-1), which modulates pituitary transcription factor 1 (Pit-1) expression

To understand the role of microRNAs (miRNAs) in pituitary development, a group of pituitary-specific miRNAs were identified, and Dicer1 was then conditionally knocked out using the Pitx2-Cre mouse, resulting in the loss of mature miRNAs in the anterior pituitary. The Pitx2-Cre/Dicer1 mutant mice demonstrate growth retardation, and the pituitaries are hypoplastic with an abnormal branching of the anterior lobe, revealing a role for microRNAs in pituitary development. Growth hormone, prolactin, and thyroid-stimulating hormone β-subunit expression were decreased in the Dicer1 mutant mouse, whereas proopiomelanocortin and luteinizing hormone β-subunit expression were normal in the mutant pituitary. Further analyses revealed decreased Pit-1 and increased Lef-1 expression in the mutant mouse pituitary, consistent with the repression of the Pit-1 promoter by Lef-1. Lef-1 directly targets and represses the Pit-1 promoter. miRNA-26b (miR-26b) was identified as targeting Lef-1 expression, and miR-26b represses Lef-1 in pituitary and non-pituitary cell lines. Furthermore, miR-26b up-regulates Pit-1 and growth hormone expression by attenuating Lef-1 expression in GH3 cells. This study demonstrates that microRNAs are critical for anterior pituitary development and that miR-26b regulates Pit-1 expression by inhibiting Lef-1 expression and may promote Pit-1 lineage differentiation during pituitary development.

Bone marrow-derived cells and hypertension

Although it is clear that inadequate perfusion underlies most of the organ dysfunction accounting for hypertension-related adverse outcomes, our understanding of the pathophysiologic mechanisms is still evolving. The most important approaches to improving vascular health include reducing injury to the vessel wall and enhancing mechanisms to repair/restore vessel wall function. The main factors responsible for repairing cardiovascular function include vascular progenitor cells and angiogenesis. The purpose of this article is to bring together recent findings indicating that limitations in vascular progenitor cell function seen in hypertension underlie the increased risks for coronary artery disease and other vascular-related adverse outcomes. Improved understanding of systems for vascular repair holds promise for new therapeutic applications in the future, although this subject will not be dealt with in this article. We will focus on a pivotal defense mechanism - bone marrow-derived progenitor cells and their roles in hypertension.

Intracellular delivery strategies for microRNAs and potential therapies for human cardiovascular diseases

MicroRNAs (miRNAs) effectively regulate gene expression in cultured cells and human disease models, and such regulation can be blocked with antibodies against miRNAs if miRNA-associated adverse effects occur. Promising findings using miRNAs to prevent disease progression in animal studies give hope to patients with disorders caused by dysregulated gene expression, such as cardiovascular diseases. Inflammatory cell infiltration, endothelial cell dysfunction, and angiogenesis are common pathologies of cardiovascular diseases. Accumulating data suggest that miRNA-mediated inhibition of gene expression can drive these pathologies in cardiac tissue or vasculature. It is often desirable to deliver exogenously prepared miRNAs or antibodies against miRNAs to target genes or miRNAs in specific cell or tissue types. Because naked miRNAs or antibodies against miRNAs are often unstable in the circulation, investigation has focused on their packaging and efficient delivery to diseased organs.

The prognostic and functional role of microRNAs in acute myeloid leukemia

Expression of microRNAs, a new class of noncoding RNAs that hybridize to target messenger RNA and regulate their translation into proteins, has been recently demonstrated to be altered in acute myeloid leukemia (AML). Distinctive patterns of increased expression and/or silencing of multiple microRNAs (microRNA signatures) have been associated with specific cytogenetic and molecular subsets of AML. Changes in the expression of several microRNAs altered in AML have been shown to have functional relevance in leukemogenesis, with some microRNAs acting as oncogenes and others as tumor suppressors. Both microRNA signatures and a single microRNA (ie, miR-181a) have been shown to supply prognostic information complementing that gained from cytogenetics, gene mutations, and altered gene expression. Moreover, it has been demonstrated experimentally that antileukemic effects can be achieved by modulating microRNA expression by pharmacologic agents and/or increasing low endogenous levels of microRNAs with tumor suppressor function by synthetic microRNA oligonucleotides, or down-regulating high endogenous levels of leukemogenic microRNAs by antisense oligonucleotides (antagomirs). Therefore, it is reasonable to predict the development of novel microRNA-based therapeutic approaches in AML. We review herein results of current studies analyzing changes of microRNA expression in AML and discuss their potential biologic, diagnostic, and prognostic relevance.

Control of autocrine and paracrine myocardial signals: an emerging therapeutic strategy in heart failure

A growing body of evidence supports the hypothesis that autocrine and paracrine mechanisms, mediated by factors released by the resident cardiac cells, could play an essential role in the reparative process of the failing heart. Such signals may influence the function of cardiac stem cells via several mechanisms, among which the most extensively studied are cardiomyocyte survival and angiogenesis. Moreover, besides promoting cytoprotection and angiogenesis, paracrine factors released by resident cardiac cells may alter cardiac metabolism and extracellular matrix turnover, resulting in more favorable post-injury remodeling. It is reasonable to believe that critical intracellular signals are activated and modulated in a temporal and spatial manner exerting different effects, overall depending on the microenvironment changes present in the failing myocardium. The recent demonstration that chemically, mechanically or genetically activated cardiac cells may release peptides to protect tissue against ischemic injury provides a potential route to achieve the delivery of specific proteins produced by these cells for innovative pharmacological regenerative therapy of the heart. It is important to keep in mind that therapies currently used to treat heart failure (HF) and leading to improvement of cardiac function fail to induce tissue repair/regeneration. As a matter of facts, if specific autocrine/paracrine cell-derived factors that improve cardiac function will be identified, pharmacological-based therapy might be more easily translated into clinical benefits than cell-based therapy. This review will focus on the recent development of potential pharmacologic targets to promote and drive at molecular level the cardiac repair/regeneration in HF.

Biological functions of microRNAs: a review

MicroRNAs (miRNAs) are a recently discovered family of endogenous, noncoding RNA molecules approximately 22 nt in length. miRNAs modulate gene expression post-transcriptionally by binding to complementary sequences in the coding or 3' untranslated region of target messenger RNAs (mRNAs). It is now clear that the biogenesis and function of miRNAs are related to the molecular mechanisms of various clinical diseases, and that they can potentially regulate every aspect of cellular activity, including differentiation and development, metabolism, proliferation, apoptotic cell death, viral infection and tumorgenesis. Here, we review recent advances in miRNA research, and discuss the diverse roles of miRNAs in disease.