Exercise training improves high-density lipoprotein-mediated transcription of proangiogenic microRNA in endothelial cells

BACKGROUND

The functional properties of endothelial cells (ECs) for regulating nitric oxide (NO) bioavailability are important for normal endothelial function. Micro-RNAs (miRs) and especially angiomiRs regulate vascular integrity and angiogenesis. Besides regulation of reverse cholesterol transport, high-density lipoprotein (HDL) also stimulates NO generation by ECs. This function is impaired in patients with chronic heart failure (CHF) and can be attenuated by exercise training. The aim of the present study was to evaluate if HDL-induced miR expression is altered in CHF and if exercise training has an impact.

METHODS

HDL was isolated from CHF patients in NYHA-IIIb (HDLNYHA) and healthy subjects (HDLHealthy) before and after exercise training. Subsequently ECs were incubated for 24 h with the isolated HDL and miR expression was quantified by RT-PCR.

RESULTS

HDL-induced expression of miR-126, miR-21 and miR-222 was significantly reduced in ECs incubated with HDLNYHA when compared to HDLHealthy. Exercise training attenuated this HDL-induced reduction of miR-126 and miR-21. HDL-induced expression of miR-221 and miR-214 was not altered in CHF compared to controls and no impact of exercise training was noted.

CONCLUSION

In conclusion, the present study shows that HDL isolated from CHF patients (NYHA-III) reduces the expression of pro-angiogenic miRs (i.e. miR-126 and miR-21), which may contribute to atherogenesis and endothelial dysfunction. However, exercise training was able to attenuate the HDL-induced reduction in pro-angiogenic miRs expression.

A conditional system to specifically link disruption of protein-coding function with reporter expression in mice

Conditional gene deletion in mice has contributed immensely to our understanding of many biological and biomedical processes. Despite an increasing awareness of nonprotein-coding functional elements within protein-coding transcripts, current gene-targeting approaches typically involve simultaneous ablation of noncoding elements within targeted protein-coding genes. The potential for protein-coding genes to have additional noncoding functions necessitates the development of novel genetic tools capable of precisely interrogating individual functional elements. We present a strategy that couples Cre/loxP-mediated conditional gene disruption with faithful GFP reporter expression in mice in which Cre-mediated stable inversion of a splice acceptor-GFP-splice donor cassette concurrently disrupts protein production and creates a GFP fusion product. Importantly, cassette inversion maintains physiologic transcript structure, thereby ensuring proper microRNA-mediated regulation of the GFP reporter, as well as maintaining expression of nonprotein-coding elements. To test this potentially generalizable strategy, we generated and analyzed mice with this conditional knockin reporter targeted to the Hmga2 locus.

Could microRNAs contribute to the maintenance of β cell identity?

Normal physiology depends on defined functional output of differentiated cells. However, differentiated cells are often surprisingly fragile. As an example, phenotypic collapse and dedifferentiation of β cells were recently discovered in the pathogenesis of type 2 diabetes (T2D). These discoveries necessitate the investigation of mechanisms that function to maintain robust cell type identity. microRNAs (miRNAs), which are small non-coding RNAs, are known to impart robustness to development. miRNAs are interlaced within networks, that include also transcriptional and epigenetic regulators, for continuous control of lineage-specific gene expression. In this Opinion article, we provide a framework for conceptualizing how miRNAs might participate in adult β cell identity and suggest that miRNAs may function as important genetic components in metabolic disorders, including diabetes.

Epidermal growth factor-like domain 7 is a marker of the endothelial lineage and active angiogenesis

Epidermal growth factor-like domain 7 (Egfl7) expression in the developing embryo is largely restricted to sites of mesodermal progenitors of angioblasts/hemangioblasts and the vascular endothelium. We hypothesize that Egfl7 marks the endothelial lineage during embryonic development, and can be used to define the emergence of endothelial progenitor cells, as well as to visualize newly-forming vasculature in the embryo and during the processes of physiologic and pathologic angiogenesis in the adult. We have generated a transgenic mouse strain that expresses enhanced green fluorescent protein (eGFP) under the control of a minimal Egfl7 regulatory sequence (Egfl7:eGFP). Expression of the transgene recapitulated that of endogenous Egfl7 at sites of vasculogenesis and angiogenesis in the allantois, yolk sac, and in the embryo proper. The transgene was not expressed in the quiescent endothelium of most adult organs. However, the uterus and ovary, which undergo vascular growth and remodeling throughout the estrus cycle, expressed high levels of Egfl7:eGFP. Importantly, expression of the Egfl7:eGFP transgene was induced in adult neovasculature. We also found that increased Egfl7 expression contributed to pathologic revascularization in the mouse retina. To our knowledge, this is the first mouse model that enables monitoring of endothelial cells at sites of active vasculogenesis and angiogenesis. This model also facilitated the isolation and characterization of EGFL7(+) endothelial cell populations by fluorescence activated cell sorting (FACS). Together, our results demonstrate that the Egfl7:eGFP reporter mouse is a valuable tool that can be used to elucidate the mechanisms by which blood vessels form during development and under pathologic circumstances.

Concise review: MicroRNA function in multipotent mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSCs) are ideal candidates for different cellular therapies due to their simple isolation, extensive expansion potential, and low immunogenicity. For various therapeutic approaches, such as bone and cartilage repair, MSCs are expected to contribute by direct differentiation to replace the damaged tissue, while many other applications rely on the secretion of paracrine factors which modulate the immune response and promote angiogenesis. MicroRNAs (miRNAs), which target messenger RNA for cleavage or translational repression, have recently been shown to play critical functions in MSC to regulate differentiation, paracrine activity, and other cellular properties such as proliferation, survival, and migration. The global miRNA expression profile of MSC varies according to the tissue of origin, species, and detection methodology, while also certain miRNAs are consistently found in all types of MSC. The function in MSC of more than 60 different miRNAs has been recently described, which is the subject of this review. A special emphasis is given to miRNAs that have demonstrated a function in MSC in vivo. We also present in detail miRNAs with overlapping effects (i.e., common target genes) and discuss future directions to deepen our understanding of miRNA biology in MSC. These recent discoveries have opened the possibility of modulating miRNAs in MSC, in order to enhance their proregenerative, therapeutic potential.

The role of RNA interference in the developmental separation of blood and lymphatic vasculature

Background

Dicer is an RNase III enzyme that cleaves double stranded RNA and generates functional interfering RNAs that act as important regulators of gene and protein expression. Dicer plays an essential role during mouse development because the deletion of the dicer gene leads to embryonic death. In addition, dicer-dependent interfering RNAs regulate postnatal angiogenesis. However, the role of dicer is not yet fully elucidated during vascular development.

Methods

In order to explore the functional roles of the RNA interference in vascular biology, we developed a new constitutive Cre/loxP-mediated inactivation of dicer in tie2 expressing cells.

Results

We show that cell-specific inactivation of dicer in Tie2 expressing cells does not perturb early blood vessel development and patterning. Tie2-Cre; dicer^fl/fl mutant embryos do not show any blood vascular defects until embryonic day (E)12.5, a time at which hemorrhages and edema appear. Then, midgestational lethality occurs at E14.5 in mutant embryos. The developing lymphatic vessels of dicer-mutant embryos are filled with circulating red blood cells, revealing an impaired separation of blood and lymphatic vasculature.

Conclusion

Thus, these results show that RNA interference perturbs neither vasculogenesis and developmental angiogenesis, nor lymphatic specification from venous endothelial cells but actually provides evidence for an epigenetic control of separation of blood and lymphatic vasculature.

EGF-like-domain-7 is required for VEGF-induced Akt/ERK activation and vascular tube formation in an ex vivo angiogenesis assay

EGFL7 is a secreted angiogenic factor, which in contrast to the well-known secreted angiogenic molecules VEGF and FGF-2, is almost exclusively expressed by endothelial cells and may act in an autocrine fashion. Prior studies have shown EGFL7 to mediate its angiogenic effects by interfering with the Notch pathway and/or via the intronic miR126. Less is known about its effects on VEGF signaling. We wanted to investigate the role of epidermal growth factor-like domain 7 (EGFL7) in VEGF-driven angiogenesis using an ex vivo Matrigel-embedded mouse eye cup assay and siRNA mediated knockdown of EGFL7 by siRNA. Our results suggested that VEGF-induced vascular tube formation was significantly impaired after siRNA downregulation of EGFL7. In addition, knockdown of EGFL7 suppressed VEGF upregulation of phospho-Akt and phospho-Erk(1/2) in endothelial cells, but did not alter VEGFR phosphorylation and neuropilin-1 protein expression or miR126 expression. Thus, in conclusion, EGFL7 is required for VEGF upregulation of the Akt/Erk (1/2) pathway during angiogenesis, and may represent a new therapeutic target in diseases of pathological neovascularization.

Egfl7 is differentially expressed in arteries and veins during retinal vascular development

The vasculature of the central nervous system (CNS) is composed of vascular endothelial and mural cells which interact closely with glial cells and neurons. The development of the CNS vascularisation is a unique process which requires the contribution of specific regulators in addition to the classical angiogenic factors. The egfl7 gene is mainly detected in endothelial cells during physiological and pathological angiogenesis. Egfl7 codes for a secreted protein which predominantly accumulates into the extracellular space where it controls vascular elastin deposition or the Notch pathway. Egfl7 is the host gene of the microRNA miR126 which is also expressed in endothelial cells and which plays major functions during blood vessel development. While the expression of egfl7 and that of miR126 were well described in endothelial cells during development, their pattern of expression during the establishment of the CNS vasculature is still unknown. By analysing the expression of egfl7 and miR126 during mouse retina vascularisation, we observed that while expression of miR126 is detected in all endothelia, egfl7 is initially expressed in all endothelial cells and then is progressively restricted to veins and to their neighbouring capillaries. The recruitment of mural cells around retina arteries coincides with the down-regulation of egfl7 in the arterial endothelial cells, suggesting that this recruitment could be involved in the loss of egfl7 expression in arteries. However, the expression pattern of egfl7 is similar when mural cell recruitment is prevented by the injection of a PDGFRβ blocking antibody, suggesting that vessel maturation is not responsible for egfl7 down-regulation in retinal arteries.

MicroRNA-126-5p promotes endothelial proliferation and limits atherosclerosis by suppressing Dlk1

Atherosclerosis, a hyperlipidemia-induced chronic inflammatory process of the arterial wall, develops preferentially at sites where disturbed laminar flow compromises endothelial cell (EC) function. Here we show that endothelial miR-126-5p maintains a proliferative reserve in ECs through suppression of the Notch1 inhibitor delta-like 1 homolog (Dlk1) and thereby prevents atherosclerotic lesion formation. Endothelial recovery after denudation was impaired in Mir126(-/-) mice because lack of miR-126-5p, but not miR-126-3p, reduced EC proliferation by derepressing Dlk1. At nonpredilection sites, high miR-126-5p levels in endothelial cells confer a proliferative reserve that compensates for the antiproliferative effects of hyperlipidemia, such that atherosclerosis was exacerbated in Mir126(-/-) mice. In contrast, downregulation of miR-126-5p by disturbed flow abrogated EC proliferation at predilection sites in response to hyperlipidemic stress through upregulation of Dlk1 expression. Administration of miR-126-5p rescued EC proliferation at predilection sites and limited atherosclerosis, introducing a potential therapeutic approach.

MiRNA-145 is involved in the development of resistin-induced insulin resistance in HepG2 cells

BACKGROUND

Resistin is associated with insulin resistance, and determining its developmental and molecular mechanisms may help the development of novel treatments. MicroRNAs (miRNAs) are involved in many physiological and pathological processes as negative regulators. However, it remains unclear whether miRNAs play a role in resistin-induced insulin resistance. We performed mouse liver miRNA microarrays to analyze the differences in expression between resistin-treated and control mice. Resistin upregulated miR-145 both in vivo and in vitro. Therefore, we aimed to study whether miR-145 played a role in resistin-induced insulin resistance.

METHODS AND RESULTS

We transfected HepG2 cells, and used miR-145 mimics and inhibitors to assess the role of miR-145 in resistin-induced insulin resistance. The overexpression of miR-145 inhibited glucose uptake in HepG2 cells, diminished the phosphorylation of Akt and IRS-1, and induced insulin resistance in hepatocytes. Next, a study of transcriptional regulation revealed that p65 was essential for the upregulation of miR-145 by resistin, and chromatin immunoprecipitation (ChIP) confirmed that p65 could bind to the promoter region of miR-145.

CONCLUSION

miR-145 plays a role in the development of resistin-induced insulin resistance via the p65 pathway.

The therapeutic potential of miRNAs regulated in settings of physiological cardiac hypertrophy

Cardiac hypertrophy is broadly defined as an increase in heart mass. Heart enlargement in a setting of cardiac disease is referred to as pathological hypertrophy and often progresses to heart failure. Physiological hypertrophy refers to heart growth in response to postnatal development, exercise training and pregnancy, and is an adaptive response associated with the activation of cardioprotective signaling cascades. miRNAs have emerged as novel therapeutic targets for numerous pathologies, and miRNA-based therapies have already entered clinical trials. The identification of miRNAs differentially regulated during physiological growth may open up new therapeutic approaches for heart failure. In this review, we present information on miRNAs regulated in models of physiological hypertrophy, describe preclinical cardiac disease studies that have successfully targeted miRNAs regulated in settings of physiological growth (miR-34, miR-15, miR-199b, miR-208a and miR-378), and discuss challenges to overcome for the safe entry of miRNA-based therapies into the clinic for heart failure patients.

Hypoxia-induced deregulation of miR-126 and its regulative effect on VEGF and MMP-9 expression

OBJECTIVE

miR-126, the miRNA considered to be specially expressed in endothelial cells and hematopoietic progenitor cells, is strongly associated with angiogenesis. The purpose is to evaluate the role of miR-126 in hypoxia-induced angiogenesis and the possible mechanisms.

METHODS

The expression of miR-126 was detected in hypoxia-treated RF/6A cells and diabetic retinas using real-time PCR. The miR-126 was up- or down-regulated by transfecting miR-126-mimics or inhibitors into RF/6A cells. Cell cycle analysis was performed using flow cytometry. The protein levels of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) were assessed by immunoblotting.

RESULTS

A significantly decreased expression of miR-126 was found in hypoxia-treated RF/6A cells in a time-dependent manner compared with normoxic condition. The expression of miR-126 was also reduced in the retina tissue of streptozotocin-induced diabetic rats. The expression of VEGF and MMP-9 proteins was increased in hypoxia-induced RF/6A cells. In the functional analysis, miR-126-mimic significantly reduced the percentage of RF/6A cells in S phases compared with the negative control under hypoxic conditions. Furthermore, the VEGF and MMP-9 protein levels were sharply decreased in hypoxia-induced RF/6A cells pretreated with miR-126-mimics and increased in the cells pretreated with miR-126-inhibitors.

CONCLUSIONS

miR-126 is down-regulated under hypoxic condition both in vitro and in vivo and may halt the hypoxia-induce neovascularization by suspending the cell cycle progression and inhibiting the expression of VEGF and MMP-9.

microRNA 126 inhibits the transition of endothelial progenitor cells to mesenchymal cells via the PIK3R2-PI3K/Akt signalling pathway

Aims

Endothelial progenitor cells (EPCs) are capable of proliferating and differentiating into mature endothelial cells, and they have been considered as potential candidates for coronary heart disease therapy. However, the transition of EPCs to mesenchymal cells is not fully understood. This study aimed to explore the role of microRNA 126 (miR-126) in the endothelial-to-mesenchymal transition (EndMT) induced by transforming growth factor beta 1 (TGFβ1).

Methods and Results

EndMT of rat bone marrow-derived EPCs was induced by TGFβ1 (5 ng/mL) for 7 days. miR-126 expression was depressed in the process of EPC EndMT. The luciferase reporter assay showed that the PI3K regulatory subunit p85 beta (PIK3R2) was a direct target of miR-126 in EPCs. Overexpression of miR-126 by a lentiviral vector (lenti-miR-126) was found to downregulate the mRNA expression of mesenchymal cell markers (α-SMA, sm22-a, and myocardin) and to maintain the mRNA expression of progenitor cell markers (CD34, CD133). In the cellular process of EndMT, there was an increase in the protein expression of PIK3R2 and the nuclear transcription factors FoxO3 and Smad4; PI3K and phosphor-Akt expression decreased, a change that was reversed markedly by overexpression of miR-126. Furthermore, knockdown of PIK3R2 gene expression level showed reversed morphological changes of the EPCs treated with TGFβ1, thereby giving the evidence that PIK3R2 is the target gene of miR-126 during EndMT process.

Conclusions

These results show that miR-126 targets PIK3R2 to inhibit EPC EndMT and that this process involves regulation of the PI3K/Akt signalling pathway. miR-126 has the potential to be used as a biomarker for the early diagnosis of intimal hyperplasia in cardiovascular disease and can even be a therapeutic tool for treating cardiovascular diseases mediated by the EndMT process.

MicroRNA-223 Antagonizes Angiogenesis by Targeting β1 Integrin and Preventing Growth Factor Signaling in Endothelial Cells

Rationale:

Endothelial cells in situ are largely quiescent, and their isolation and culture are associated with the switch to a proliferative phenotype.

Objective:

To identify antiangiogenic microRNAs expressed by native endothelial cells that are altered after isolation and culture, as well as the protein targets that regulate responses to growth factors.

Methods and Results:

Profiling studies revealed that miR-223 was highly expressed in freshly isolated human, murine, and porcine endothelial cells, but those levels decreased in culture. In primary cultures of endothelial cells, vascular endothelial cell growth factor and basic fibroblast growth factor further decreased miR-223 expression. The overexpression of precursor-miR-223 did not affect basal endothelial cell proliferation but abrogated vascular endothelial cell growth factor–induced and basic fibroblast growth factor–induced proliferation, as well as migration and sprouting. Inhibition of miR-223 in vivo using specific antagomirs potentiated postnatal retinal angiogenesis in wild-type mice, whereas recovery of perfusion after femoral artery ligation and endothelial sprouting from aortic rings from adult miR-223 −/y animals were enhanced. MiR-223 overexpression had no effect on the growth factor–induced activation of ERK1/2 but inhibited the vascular endothelial cell growth factor–induced and basic fibroblast growth factor–induced phosphorylation of their receptors and activation of Akt. β1 integrin was identified as a target of miR-223 and its downregulation reproduced the defects in growth factor receptor phosphorylation and Akt signaling seen after miR-223 overexpression. Reintroduction of β1 integrin into miR-223–ovexpressing cells was sufficient to rescue growth factor signaling and angiogenesis.

Conclusions:

These results indicate that miR-223 is an antiangiogenic microRNA that prevents endothelial cell proliferation at least partly by targeting β1 integrin.

The miR-126-VEGFR2 axis controls the innate response to pathogen-associated nucleic acids

MicroRNA-126 (miR-126) is a microRNA predominately expressed by endothelial cells and controls angiogenesis. We found miR-126 was required for the innate response to pathogen-associated nucleic acids, and that miR-126-deficient mice had increased susceptibility to pseudotyped-HIV infection. miRNA profiling and deep-sequencing indicated that miR-126 was highly and specifically expressed by plasmacytoid dendritic cells (pDCs). miR-126 controlled the survival and function of pDCs, and regulated expression ofinnate response genes, including Tlr7, Tlr9 and Nfkb1, as well as Kdr, which encodes VEGF-receptor 2 (VEGFR2). Deletion of Kdr in DCs resulted in reduced type I interferon production, supporting a role for VEGFR2 in miR-126 regulation of pDCs. These studies identify the miR-126–VEGFR2 axis as an important regulator of the innate response that operates through multiscale control of pDCs.

Microparticles and microRNAs of endothelial progenitor cells ameliorate acute kidney injury

Horizontal information transfer between cells via microparticles is a newly identified communication system. MicroRNAs regulate gene expression and are detected in microparticles. The article by Cantaluppi et al. suggests that microparticles derived from circulating angiogenic cells (“endothelial progenitor cells”, EPC) harbor endothelial-protective miRNAs such as miR-126 and that delivery of EPC-derived microparticles during acute kidney ischemia-reperfusion in rats ameliorates kidney dysfunction and damage. We highlight the importance, future impact and limitations of this study.

Non-coding RNAs: the "dark matter" of cardiovascular pathophysiology

Large-scale analyses of mammalian transcriptomes have identified a significant number of different RNA molecules that are not translated into protein. In fact, the use of new sequencing technologies has identified that most of the genome is transcribed, producing a heterogeneous population of RNAs which do not encode for proteins (ncRNAs). Emerging data suggest that these transcripts influence the development of cardiovascular disease. The best characterized non-coding RNA family is represented by short highly conserved RNA molecules, termed microRNAs (miRNAs), which mediate a process of mRNA silencing through transcript degradation or translational repression. These microRNAs (miRNAs) are expressed in cardiovascular tissues and play key roles in many cardiovascular pathologies, such as coronary artery disease (CAD) and heart failure (HF). Potential links between other ncRNAs, like long non-coding RNA, and cardiovascular disease are intriguing but the functions of these transcripts are largely unknown. Thus, the functional characterization of ncRNAs is essential to improve the overall understanding of cellular processes involved in cardiovascular diseases in order to define new therapeutic strategies. This review outlines the current knowledge of the different ncRNA classes and summarizes their role in cardiovascular development and disease.

Regulation of immune responses and tolerance: the microRNA perspective

Much has been learned about the molecular and cellular components critical for the control of immune responses and tolerance. It remains a challenge, however, to control the immune response and tolerance at the system level without causing significant toxicity to normal tissues. Recent studies suggest that microRNA (miRNA) genes, an abundant class of non-coding RNA genes that produce characteristic approximately 22 nucleotides small RNAs, play important roles in immune cells. In this article, we discuss emerging knowledge regarding the functions of miRNA genes in the immune system. We delve into the roles of miRNAs in regulating signaling strength and threshold, homeostasis, and the dynamics of the immune response and tolerance during normal and pathogenic immunological conditions. We also present observations based on analyzes of miR-181 family genes that indicate the potential functions of primary and/or precursor miRNAs in target recognition and explore the impact of these findings on target identification. Finally, we illustrate that despite the subtle effects of miRNAs on gene expression, miRNAs have the potential to influence the outcomes of normal and pathogenic immune responses by controlling the quantitative and dynamic aspects of immune responses. Tuning miRNA functions in immune cells, through gain- and loss-of-function approaches in mice, may reveal novel approach to restore immune equilibrium from pathogenic conditions, such as autoimmune disease and leukemia, without significant toxicity.

A Helm model for microRNA regulation in cell fate decision and conversion

microRNAs (miRNAs) constitute a unique class of endogenous small non-coding RNAs that regulate gene expression post-transcriptionally. Studies over the past decade have uncovered a recurring paradigm in which miRNAs are key regulators of cellular behavior under various physiological and pathological conditions. Most surprising is the recent observation that miRNAs have emerged as competent players in somatic cell reprogramming, suggesting an especially significant role for these small RNAs in cell fate settings. Here, we discuss the possible mechanisms underlying miRNA-mediated cell programming (i.e., the development and differentiation of embryonic stem cells) and reprogramming (i.e., turning somatic cells into pluripotent stem cells or other lineages), and provide a "Helm" model of miRNAs in cell fate decision and conversion.

MicroRNA-126 expression is decreased in cultured primary chicken hepatocytes and targets the sprouty-related EVH1 domain containing 1 mRNA

The microRNA-126 (miR-126) is a miRNA expressed in highly vascularized tissues, and it is believed to play a role in angiogenesis by repressing sprouty-related EVH1 domain containing 1 (Spred1). In the current study, we determined the expression pattern of chicken miR-126 (gga-miR-126) and predicted and validated its target genes. The quantitative reverse-transcription (qRT) PCR analysis showed that miR-126 was expressed in various chicken tissues with the highest level in lung. In liver, the expression level of miR-126 increased from 0 to 7 wk of age. The expression of miR-126 in primary chicken hepatocytes decreased with culturing. A miR-126 binding site was predicted in the 3' UTR (untranslated region) of chicken Spred1. Dual-luciferase reporter assays indicated that miR-126 could bind to the predicted site to repress the expression of Spred1. These data validate Spred1 as a target gene of chicken miR-126. These results will help further understand the function and regulation of miR-126 and Spred1 in chickens.

MicroRNA-126 and epidermal growth factor-like domain 7-an angiogenic couple of importance in metastatic colorectal cancer. Results from the Nordic ACT trial

Background:

This study investigated the clinical importance of linked angiogenetic biomarkers to chemotherapy, combined with the anti-vascular endothelial growth factor A (anti-VEGF-A), as a first-line treatment in patients with metastatic colorectal cancer (mCRC).

Methods:

A total of 230 patients from a randomised phase III study were included. The primary microRNA-126 (pri-miRNA-126) A24G single-nucleotide polymorphism and the mature miRNA-126 were analysed by PCR using genomic DNA (full blood) and formalin-fixed paraffin-embedded tissue sections, respectively. The epidermal growth factor-like domain 7 (EGFL7) protein was visualised and quantified using immunohistochemistry.

Results:

High tumour expression of miRNA-126 was significantly related to a longer progression-free survival. The independent prognostic value of miRNA-126 was confirmed using a Cox regression analysis (hazard ratio=0.49, 95% confidence interval=0.29–0.84, P=0.009). Although not significant, a relationship between EGFL7 expression and response rates is suggested, with EGFL7 expression at the invasive front being lower in responding patients than in the non-responders (P=0.063).

Conclusion:

The results validate the previous findings on the prognostic value of miRNA-126 in mCRC and may suggest a relationship between treatment efficacy and EGFL7 expression. As miRNA-126 may target VEGF-A as well as EGFL7, the results may provide predictive information in relation to next-generation anti-angiogenetics.

Circulating microRNAs as novel biomarkers for the early diagnosis of acute coronary syndrome

Small non-coding microRNAs (miRNAs) are important physiological regulators of post-transcriptional gene expression. miRNAs not only reside in the cytoplasm but are also stably present in several extracellular compartments, including the circulation. For that reason, miRNAs are proposed as diagnostic biomarkers for various diseases. Early diagnosis of acute coronary syndrome (ACS), especially non-ST elevated myocardial infarction and unstable angina pectoris, is essential for optimal treatment outcome, and due to the ongoing need for additional identifiers, miRNAs are of special interest as biomarkers for ACS. This review highlights the nature and cellular release mechanisms of circulating miRNAs and therefore their potential role in the diagnosis of myocardial infarction. We will give an update of clinical studies addressing the role of circulating miRNA expression after myocardial infarction and explore the diagnostic value of this potential biomarker.

microRNA control of mouse and human pluripotent stem cell behavior

In the past decade, significant progress has been made in understanding both microRNA function and cellular pluripotency. Here we review the intersection of these two exciting fields. While microRNAs are not required for the establishment and maintenance of pluripotency in early development and cell culture, respectively, they are critically important in the regulation of the cell cycle structure of pluripotent stem cells as well as the silencing of the pluripotency program upon differentiation. Pluripotent cells, both in vivo and in vitro, dominantly express a single family of microRNAs, which can promote the reprogramming of a somatic cell back to a pluripotent state. Here, we review the known mechanisms by which these and other microRNAs regulate the different aspects of the pluripotent stem cell program in both mouse and human.

The admiR-able advances in cardiovascular biology through the zebrafish model system

MicroRNAs are small non-coding RNAs endogenously expressed by all tissues during development and adulthood. They regulate gene expression by controlling the stability of targeted messenger RNA. In cardiovascular tissues microRNAs play a role by modulating essential genes involved in heart and blood vessel development and homeostasis. The zebrafish (Danio rerio) system is a recognized vertebrate model system useful to study cardiovascular biology; recently, it has been used to investigate microRNA functions during natural and pathological states. In this review, we will illustrate the advantages of the zebrafish model in the study of microRNAs in heart and vascular cells, providing an update on recent discoveries using the zebrafish to identify new microRNAs and their targeted genes in cardiovascular tissues. Lastly, we will provide evidence that the zebrafish is an optimal model system to undercover new microRNA functions in vertebrates and to improve microRNA-based therapeutic approaches.

CASZ1 promotes vascular assembly and morphogenesis through the direct regulation of an EGFL7/RhoA-mediated pathway

The formation of the vascular system is essential for embryonic development and homeostasis. However, transcriptional control of this process is not fully understood. Here we report an evolutionarily conserved role for the transcription factor CASZ1 (CASTOR) in blood vessel assembly and morphogenesis. In the absence of CASZ1, Xenopus embryos fail to develop a branched and lumenized vascular system, and CASZ1-depleted human endothelial cells display dramatic alterations in adhesion, morphology, and sprouting. Mechanistically, we show that CASZ1 directly regulates Epidermal Growth Factor-Like Domain 7 (Egfl7). We further demonstrate that defects of CASZ1- or EGFL7-depleted cells are in part due to diminished RhoA expression and impaired focal adhesion localization. Moreover, these abnormal endothelial cell behaviors in CASZ1-depleted cells can be rescued by restoration of Egfl7. Collectively, these studies show that CASZ1 is required to directly regulate an EGFL7/RhoA-mediated pathway to promote vertebrate vascular development.

Genome-wide and species-wide in silico screening for intragenic MicroRNAs in human, mouse and chicken

MicroRNAs (miRNAs) are non-coding RNAs (ncRNAs) involved in regulation of gene expression. Intragenic miRNAs, especially those exhibiting a high degree of evolutionary conservation, have been shown to be coordinately regulated and/or expressed with their host genes, either with synergistic or antagonistic correlation patterns. However, the degree of cross-species conservation of miRNA/host gene co-location is not known and co-expression information is incomplete and fragmented among several studies. Using the genomic resources (miRBase and Ensembl) we performed a genome-wide in silico screening (GWISS) for miRNA/host gene pairs in three well-annotated vertebrate species: human, mouse, and chicken. Approximately half of currently annotated miRNA genes resided within host genes: 53.0% (849/1,600) in human, 48.8% (418/855) in mouse, and 42.0% (210/499) in chicken, which we present in a central publicly available Catalog of intragenic miRNAs (http://www.integratomics-time.com/miR-host/catalog). The miRNA genes resided within either protein-coding or ncRNA genes, which include long intergenic ncRNAs (lincRNAs) and small nucleolar RNAs (snoRNAs). Twenty-seven miRNA genes were found to be located within the same host genes in all three species and the data integration from literature and databases showed that most (26/27) have been found to be co-expressed. Particularly interesting are miRNA genes located within genes encoding for miRNA silencing machinery (DGCR8, DICER1, and SND1 in human and Cnot3, Gdcr8, Eif4e, Tnrc6b, and Xpo5 in mouse). We furthermore discuss a potential for phenotype misattribution of miRNA host gene polymorphism or gene modification studies due to possible collateral effects on miRNAs hosted within them. In conclusion, the catalog of intragenic miRNAs and identified 27 miRNA/host gene pairs with cross-species conserved co-location, co-expression, and potential co-regulation, provide excellent candidates for further functional annotation of intragenic miRNAs in health and disease.

Regulation of vascular smooth muscle cell turnover by endothelial cell-secreted microRNA-126: role of shear stress

RATIONALE

Endothelial microRNA-126 (miR-126) modulates vascular development and angiogenesis. However, its role in the regulation of smooth muscle cell (SMC) function is unknown.

OBJECTIVE

To elucidate the role of miR-126 secreted by endothelial cells (ECs) in regulating SMC turnover in vitro and in vivo, as well as the effects of shear stress on the regulation.

METHODS AND RESULTS

Coculture of SMCs with ECs or treatment of SMCs with conditioned media from static EC monoculture (EC-CM) increased SMC miR-126 level and SMC turnover; these effects were abolished by inhibition of endothelial miR-126 and by the application of laminar shear stress to ECs. SMC miR-126 did not increase when treated with EC-CM from ECs subjected to inhibition of miR biogenesis, or with CM from sheared ECs. Depletion of extracellular/secreted vesicles in EC-CM did not affect the increase of SMC miR-126 by EC-CM. Biotinylated miR-126 or FLAG (DYKDDDDK epitope)-tagged Argonaute2 transfected into ECs was detected in the cocultured or EC-CM-treated SMCs, indicating a direct EC-to-SMC transmission of miR-126 and Argonaute2. Endothelial miR-126 represses forkhead box O3, B-cell lymphoma 2, and insulin receptor substrate 1 mRNAs in the cocultured SMCs, suggesting the functional roles of the transmitted miR-126. Systemic depletion of miR-126 in mice inhibited neointimal lesion formation of carotid arteries induced by cessation of blood flow. Administration of EC-CM or miR-126 mitigated the inhibitory effect.

CONCLUSIONS

Endothelial miR-126 acts as a key intercellular mediator to increase SMC turnover, and its release is reduced by atheroprotective laminar shear stress.

MicroRNAs as pharmacological targets in endothelial cell function and dysfunction

Endothelial cell dysfunction is a term which implies the dysregulation of normal endothelial cell functions, including impairment of the barrier functions, control of vascular tone, disturbance of proliferative, migratory and morphogenic capacities of endothelial cells, as well as control of leukocyte trafficking. MicroRNAs are short non-coding RNAs that have emerged as critical regulators of gene expression acting predominantly at the post-transcriptional level. This review summarizes the latest insights in the identification of endothelial-specific microRNAs and their targets, as well as their roles in controlling endothelial cell functions in both autocrine and paracrine manner. In addition, we discuss the therapeutic potential for the treatment of endothelial cell dysfunction and associated vascular pathophysiological conditions.

MicroRNAs and tumor vasculature normalization: impact on anti-tumor immune response

Inefficient immune response is a major glitch during tumor growth and progression. Chaotic and leaky blood vessels created in the process of angiogenesis allow tumor cells to escape and extricate anti-cancer immunity. Proangiogenic characteristics of hypoxic tumor microenvironment maintained by low oxygen tension attract endothelial progenitor cells, drive expansion of cancer stem cells, and deviantly differentiate monocyte descendants. Such cellular milieu further boosts immune tolerance and eventually appoint immunity for cancer advantage. Blood vessel normalization strategies that equilibrate oxygen levels within tumor and fix abnormal vasculature bring exciting promises to future anticancer therapies especially when combined with conventional chemotherapy. Recently, a new group of microRNAs (miRs) engaged in angiogenesis, called angiomiRs and hypoxamiRs, emerged as new therapeutic targets in cancer. Some of those miRs were found to efficiently regulate cancer immunity and their dysregulation efficiently programs aberrant angiogenesis and cancer metastasis. The present review highlights new findings in the field of miRs proficiency to normalize aberrant angiogenesis and to restore anti-tumor immune responses.

MicroRNAs in pluripotency, reprogramming and cell fate induction

Pluripotent stem cells display a unique expression pattern of microRNAs (miRNAs). These ~22 nucleotide non-coding RNAs have established a crucial role in controlling gene expression of pluripotent stem cells at the post-transcriptional level. Recent studies made important advances in identifying miRNA regulated processes like de novo DNA methylation, progression of the cell cycle and regulation of cell fate decision. miRNAs have also the ability to reprogram somatic cells to pluripotent stem cells and on the other hand, to induce differentiation of pluripotent stem cells into distinct somatic lineages. Previously it was published that miRNAs can direct reprogramming on its own. Here we provide evidence and critically discuss that the effect of miRNA depends on co-expression of the classical reprogramming factors. During transition between these different cell fates distinct miRNAs adjust the levels of specific transcriptional programs and confer robustness to differentiation processes. This results in a complex network between miRNAs and their targets. The fact that miRNAs itself can also be regulated by its targets establishes complex regulatory loops. Based on bioinformatical predictions, each miRNA theoretically has hundreds of target genes making it even more challenging to understand the complete network between miRNAs and their targets.

MicroRNA control of vascular endothelial growth factor signaling output during vascular development

The regulated response of endothelial cells to signals in their environment is not only critical for the de novo formation of primordial vascular networks during early development (ie, vasculogenesis), but is also required for the subsequent growth and remodeling of new blood vessels from preexisting ones (ie, angiogenesis). Vascular endothelial growth factors (Vegfs) and their endothelial cell-specific receptors play a crucial role in nearly all aspects of blood vessel growth. How the outputs from these pathways affect and coordinate endothelial behavior is an area of intense research. Recently, numerous studies have highlighted roles for microRNAs in modulating Vegf signaling output in several different contexts. In this review, we will provide an overview of how small RNAs regulate multiple aspects of the Vegf signaling pathway. In particular, we highlight areas where identification of microRNAs and their targets has provided new insight into the role of downstream effectors in modulating Vegf output during development. As Vegf plays a broad role in multiple aspects of endothelial biology and has become a target for therapeutic manipulation of pathological blood vessel growth, microRNAs that affect Vegf signaling output will undoubtedly be major targets of clinical value.

Transforming growth factor β-regulated microRNA-29a promotes angiogenesis through targeting the phosphatase and tensin homolog in endothelium

The TGF-β pathway plays an important role in physiological and pathological angiogenesis. MicroRNAs (miRNAs) are a class of 18- to 25-nucleotide, small, noncoding RNAs that function by regulating gene expression. A number of miRNAs have been found to be regulated by the TGF-β pathway. However, the role of endothelial miRNAs in the TGF-β-mediated control of angiogenesis is still largely unknown. Here we investigated the regulation of endothelial microRNA-29a (miR-29a) by TGF-β signaling and the potential role of miR-29a in angiogenesis. MiR-29a was directly up-regulated by TGF-β/Smad4 signaling in human and mice endothelial cells. In a chick chorioallantoic membrane assay, miR-29a overexpression promoted the formation of new blood vessels, and miR-29a suppression completely blocked TGF-β1-stimulated angiogenesis. Consistently, miR-29a overexpression increased tube formation and migration in endothelial cultures. Mechanistically, miR-29a directly targeted the phosphatase and tensin homolog (PTEN) in endothelial cells, leading to activation of the AKT pathway. PTEN knockdown recapitulated the role of miR-29a in endothelial migration, whereas AKT inhibition completely attenuated the stimulating role of miR-29a in angiogenesis. Taken together, these results reveal a crucial role of a TGF-β-regulated miRNA in promoting angiogenesis by targeting PTEN to stimulate AKT activity.

EGFL7 ligates αvβ3 integrin to enhance vessel formation

Angiogenesis, defined as blood vessel formation from a preexisting vasculature, is governed by multiple signal cascades including integrin receptors, in particular integrin αVβ3. Here we identify the endothelial cell (EC)-secreted factor epidermal growth factor-like protein 7 (EGFL7) as a novel specific ligand of integrin αVβ3, thus providing mechanistic insight into its proangiogenic actions in vitro and in vivo. Specifically, EGFL7 attaches to the extracellular matrix and by its interaction with integrin αVβ3 increases the motility of EC, which allows EC to move on a sticky underground during vessel remodeling. We provide evidence that the deregulation of EGFL7 in zebrafish embryos leads to a severe integrin-dependent malformation of the caudal venous plexus, pointing toward the significance of EGFL7 in vessel development. In biopsy specimens of patients with neurologic diseases, vascular EGFL7 expression rose with increasing EC proliferation. Further, EGFL7 became upregulated in vessels of the stroke penumbra using a mouse model of reversible middle cerebral artery occlusion. Our data suggest that EGFL7 expression depends on the remodeling state of the existing vasculature rather than on the phenotype of neurologic disease analyzed. In sum, our work sheds a novel light on the molecular mechanism EGFL7 engages to govern physiological and pathological angiogenesis.

miRNAs as modulators of angiogenesis

MicroRNAs are highly expressed in endothelial cells, and recent data suggest that they regulate aspects of vascular development and angiogenesis. This study highlights the state of the art in this field and potential therapeutic opportunities. MicroRNAs (miRNAs) represent a family of conserved short (≈22 nt) noncoding single-stranded RNAs that have been identified in plants and animals. They are generated by the sequential processing of the RNA template by the enzymes Drosha and Dicer, and mature miRNAs can regulate the levels of gene expression at the posttranscriptional level. miRNAs participate in a diverse range of regulatory events via regulation of genes involved in the control of processes such as development, differentiation, homeostasis, metabolism, growth, proliferation, and apoptosis. However, rather than functioning as regulatory on-off switches, miRNAs often function to modulate or fine-tune cellular phenotypes. So far, more than 1000 mammalian miRNAs have been identified since the discovery of the first two miRNAs (lin-4 and let-7), and bioinformatics predictions indicate that mammalian miRNAs can regulate ∼30% of all protein-coding genes.

MicroRNAs in cardiovascular disease: from pathogenesis to prevention and treatment

The management of cardiovascular risk through lifestyle modification and pharmacotherapy is paramount to the prevention of cardiovascular disease. Epidemiological studies have identified obesity, dyslipidemia, diabetes, and hypertension as interrelated factors that negatively affect cardiovascular health. Recently, genetic and pharmacological evidence in model systems has implicated microRNAs as dynamic modifiers of disease pathogenesis. An expanded understanding of the function of microRNAs in gene regulatory networks associated with cardiovascular risk will enable identification of novel genetic mechanisms of disease and inform the development of innovative therapeutic strategies.

Cardiovascular dysregulation of miR-17-92 causes a lethal hypertrophic cardiomyopathy and arrhythmogenesis

MicroRNA cluster miR-17-92 has been implicated in cardiovascular development and function, yet its precise mechanisms of action in these contexts are uncertain. This study aimed to investigate the role of miR-17-92 in morphogenesis and function of cardiac and smooth muscle tissues. To do so, a mouse model of conditional overexpression of miR-17-92 in cardiac and smooth muscle tissues was generated. Extensive cardiac functional studies identified a dose-dependent induction of dilated, hypertrophic cardiomyopathy, and arrhythmia inducibility in transgenic animals, which correlated with premature mortality (98.3 ± 42.5 d, P<0.0001). Expression analyses revealed the abundance of Pten transcript, a known miR-17-92 target, to be inversely correlated with miR-17-92 expression levels and heart size. In addition, we demonstrated through 3'-UTR luciferase assays and expression analyses that Connexin43 (Cx43) is a novel direct target of miR-19a/b and its expression is suppressed in transgenic hearts. Taken together, these data demonstrate that dysregulated expression of miR-17-92 during cardiovascular morphogenesis results in a lethal cardiomyopathy, possibly in part through direct repression of Pten and Cx43. This study highlights the importance of miR-17-92 in both normal and pathological functions of the heart, and provides a model that may serve as a useful platform to test novel antiarrhythmic therapeutics.

miRNAs in endothelial cell signaling: the endomiRNAs

microRNAs (miRNAs) have a pivotal role during the formation and function of the cardiovascular system. More than 300 miRNAs have been currently found within the mammalian genome, however only few specific miRNAs, named endomiRNAs, showed conseved endothelial cell expression and function. In this review we present an overview of the currently known endomiRNAs, focusing on their genome localization, processing and target gene repression during vasculogenesis and angiogenesis.

Synergistic induction of miR-126 by hypoxia and HDAC inhibitors in cardiac myocytes

HDAC inhibitors are under clinical development for the treatment of hypertrophic cardiomyopathy and heart failure although the mechanisms of protection are incompletely understood. Micro-RNA 126, an endothelium-specific miR has been assigned essential developmental roles in the heart by activating survival kinases ERK1/2 and Akt and increasing pro-angiogenic signaling. Here we provide the first evidence that hypoxia and HDAC inhibitors selectively and synergistically stimulate expression of miR-126 in cardiac myocytes. MiR-126 expression was increased 1.7-fold (p<0.05) after 1h of hypoxic exposure and this was further enhanced to 3.0-fold (p<0.01) by simultaneously blocking HDAC with the pan-HDAC inhibitor Tricostatin A (TSA). TSA alone did not increase miR-126. In parallel, hypoxia and TSA synergistically increased p-ERK and p-Akt without effecting VEGF-A level. Knockdown of miR-126 with si-RNA eliminated inductions of p-ERK and p-Akt by hypoxia, whereas miR-126 overexpression mimicked hypoxia and amplified p-ERK and p-Akt in parallel with miR-126. The results suggest that miR-126 is a hypoxia-inducible target of HAT/HDAC and its activation in cardiac myocytes may contribute to cardioprotection by activating cell survival and pro-angiogenic pathways selectively during ischemia.

Functions of microRNAs in cardiovascular biology and disease

In 1993, lin-4 was discovered as a critical modulator of temporal development in Caenorhabditis elegans and, most notably, as the first in the class of small, single-stranded noncoding RNAs now defined as microRNAs (miRNAs). Another eight years elapsed before miRNA expression was detected in mammalian cells. Since then, explosive advancements in the field of miRNA biology have elucidated the basic mechanism of miRNA biogenesis, regulation, and gene-regulatory function. The discovery of this new class of small RNAs has augmented the complexity of gene-regulatory programs as well as the understanding of developmental and pathological processes in the cardiovascular system. Indeed, the contributions of miRNAs in cardiovascular development and function have been widely explored, revealing the extensive role of these small regulatory RNAs in cardiovascular physiology.

Attenuation of miR-126 activity expands HSC in vivo without exhaustion

Lifelong blood cell production is governed through the poorly understood integration of cell-intrinsic and -extrinsic control of hematopoietic stem cell (HSC) quiescence and activation. MicroRNAs (miRNAs) coordinately regulate multiple targets within signaling networks, making them attractive candidate HSC regulators. We report that miR-126, a miRNA expressed in HSC and early progenitors, plays a pivotal role in restraining cell-cycle progression of HSC in vitro and in vivo. miR-126 knockdown by using lentiviral sponges increased HSC proliferation without inducing exhaustion, resulting in expansion of mouse and human long-term repopulating HSC. Conversely, enforced miR-126 expression impaired cell-cycle entry, leading to progressively reduced hematopoietic contribution. In HSC/early progenitors, miR-126 regulates multiple targets within the PI3K/AKT/GSK3β pathway, attenuating signal transduction in response to extrinsic signals. These data establish that miR-126 sets a threshold for HSC activation and thus governs HSC pool size, demonstrating the importance of miRNA in the control of HSC function.

Large impact of low concentration oxidized LDL on angiogenic potential of human endothelial cells: a microarray study

Oxidized LDL (ox-LDL) is a key factor in atherogenesis. It is taken up by endothelial cells primarily by ox-LDL receptor-1 (LOX-1). To elucidate transcriptional responses, we performed microarray analysis on human coronary artery endothelial cells (HCAECs) exposed to small physiologic concentration of ox-LDL- 5 µg/ml for 2 and 12 hours. At 12 hours, cultures treated with ox-LDL exhibited broad shifts in transcriptional activity involving almost 1500 genes (>1.5 fold difference, p<0.05). Resulting transcriptome was enriched for genes associated with cell adhesion (p<0.002), angiogenesis (p<0.0002) and migration (p<0.006). Quantitative PCR analysis revealed that LOX-1 expression in HCAECs is at least an order of magnitude greater than the expression of other major ox-LDL specific receptors CD36 and MSR1. In keeping with the data on LOX-1 expression, pre-treatment of HCAECs with LOX-1 neutralizing antibody resulted in across-the-board inhibition of cellular response to ox-LDL. Ox-LDL upregulated a number of pro-angiogenic genes including multiple receptors, ligands and transcription factors and altered the expression of a number of genes implicated in both stimulation and inhibition of apoptosis. From a functional standpoint, physiologic concentrations of ox-LDL stimulated tube formation and inhibited susceptibility to apoptosis in HCAECs. In addition, ox-LDL exposure resulted in upregulation of miR-1974, miR-1978 and miR-21 accompanied with significant over-presentation of their target genes in the downregulated portion of ox-LDL transcriptome. Our observations indicate that ox-LDL at physiologic concentrations induces broad transcriptional responses which are mediated by LOX-1, and are, in part, shaped by ox-LDL-dependent miRNAs. We also suggest that angiogenic effects of ox-LDL are partially based on upregulation of several receptors that render cells hypersensitive to angiogenic stimuli.

Endothelial tip cells in ocular angiogenesis: potential target for anti-angiogenesis therapy

Endothelial tip cells are leading cells at the tips of vascular sprouts coordinating multiple processes during angiogenesis. In the developing retina, tip cells play a tightly controlled, timely role in angiogenesis. In contrast, excessive numbers of tip cells are a characteristic of the chaotic pathological blood vessels in proliferative retinopathies. Tip cells control adjacent endothelial cells in a hierarchical manner to form the stalk of the sprouting vessel, using, among others, the VEGF-DLL-Notch signaling pathway, and recruit pericytes. Tip cells are guided toward avascular areas by signals from the local extracellular matrix that are released by cells from the neuroretina such as astrocytes. Recently, tip cells were identified in endothelial cell cultures, enabling identification of novel molecular markers and mechanisms involved in tip cell biology. These mechanisms are relevant for understanding proliferative retinopathies. Agents that primarily target tip cells can block pathological angiogenesis in the retina efficiently and safely without adverse effects. A striking example is platelet-derived growth factor, which was recently shown to be an efficacious additional target in the treatment of retinal neovascularization. Here we discuss these and other tip cell-based strategies with respect to their potential to treat patients with ocular diseases dominated by neovascularization.

MicroRNAs in Vascular Biology

Vascular inflammation is an important component of the pathophysiology of cardiovascular diseases, such as hypertension, atherosclerosis, and aneurysms. All vascular cells, including endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), and infiltrating cells, such as macrophages, orchestrate a series of pathological events. Despite dramatic improvements in the treatment of atherosclerosis, the molecular basis of vascular inflammation is not well understood. In the last decade, microRNAs (miRNAs) have been revealed as novel regulators of vascular inflammation. Each miRNAs suppresses a set of genes, forming complex regulatory network. This paper provides an overview of current advances that have been made in revealing the roles of miRNAs during vascular inflammation. Recent studies show that miRNAs not only exist inside cells but also circulate in blood. These circulating miRNAs are useful biomarkers for diagnosis of cardiovascular diseases. Furthermore, recent studies demonstrate that circulating miRNAs are delivered into certain recipient cells and act as messengers. These studies suggest that miRNAs provide new therapeutic opportunities.

Deep sequencing reveals predominant expression of miR-21 amongst the small non-coding RNAs in retinal microvascular endothelial cells

The retinal vascular endothelium is essential for angiogenesis and is involved in maintaining barrier selectivity and vascular tone. The aim of this study was to identify and quantify microRNAs and other small regulatory non-coding RNAs (ncRNAs) which may regulate these crucial functions. Primary bovine retinal microvascular endothelial cells (RMECs) provide a well-characterized in vitro system for studying angiogenesis. RNA extracted from RMECs was used to prepare a small RNA library for deep sequencing (Illumina Genome Analyzer). A total of 6.8 million reads were mapped to 250 known microRNAs in miRBase (release 16). In many cases, the most frequent isomiR differed from the sequence reported in miRBase. In addition, five novel microRNAs, 13 novel bovine orthologs of known human microRNAs and multiple new members of the miR-2284/2285 family were detected. Several ∼30 nucleotide sno-miRNAs were identified, with the most highly expressed being derived from snoRNA U78. Highly expressed microRNAs previously associated with endothelial cells included miR-126 and miR-378, but the most highly expressed was miR-21, comprising more than one-third of all mapped reads. Inhibition of miR-21 with an LNA inhibitor significantly reduced proliferation, migration, and tube-forming capacity of RMECs. The independence from prior sequence knowledge provided by deep sequencing facilitates analysis of novel microRNAs and other small RNAs. This approach also enables quantitative evaluation of microRNA expression, which has highlighted the predominance of a small number of microRNAs in RMECs. Knockdown of miR-21 suggests a role for this microRNA in regulation of angiogenesis in the retinal microvasculature. J. Cell. Biochem. 113: 2098–2111, 2012. © 2012 Wiley Periodicals, Inc.

A primer on the role of microRNAs in endothelial biology and vascular disease

Endothelial cells are highly proliferative and motile during vascular development. However, as blood vessels mature and stabilize the endothelial lining becomes quiescent, and cell-cell interactions among endothelial cells generate a stable barrier between the blood and tissue. Rather than simply functioning as an inert barrier, endothelial cells constantly sense and respond to environmental cues. Activation of the endothelium can promote the loss of cell-cell adhesion and an increase in the motility and proliferation of the endothelium. This process is requisite for tissue repair, but also plays a role in vascular pathogenesis and is especially relevant to kidney injury. The molecular mechanisms that facilitate these phenotypic alterations are only partially understood. Recent work has shown that microRNAs can modulate endothelial phenotype. These new insights have shed light on the complex mechanisms that endothelial cells use to respond to environmental stimuli. This review addresses the known roles that microRNAs play in controlling angiogenic and inflammatory signals in endothelial cells, and illustrates that microRNAs are important modulators of endothelial function in vascular disease, and therefore represent promising therapeutic targets.

Control by a hair's breadth: the role of microRNAs in the skin

MicroRNAs have continued to attract enormous interest in the scientific community ever since their discovery. Their allure stems from their unique role in posttranscriptional gene expression control as well as their potential application as therapeutic targets in various disease pathologies. While much is known concerning their general biological function, such as their interaction with RNA-induced silencing complexes, many important questions still remain unanswered, especially regarding their functions in the skin. In this review, we summarize our current knowledge of the role of microRNAs in the skin in order to shine new light on our understanding of cutaneous biology and emphasize the significance of these small, single-stranded RNA molecules in the largest organ of the human body. Key events in epidermal and hair follicle biology, including differentiation, proliferation, and pigmentation, all involve microRNAs. We explore the role of microRNAs in several cutaneous processes, such as appendage formation, wound-healing, epithelial-mesenchymal transition, carcinogenesis, immune response, and aging. In addition, we discuss current trends in research and offer suggestions for future studies.

Enemy or partner: relationship between intronic micrornas and their host genes

In the past several years, microRNAs have been identified as a class of important regulators of gene expression. One hot topic in the microRNA field is the location of microRNA genes. Most microRNAs are called intronic microRNAs, which are encoded in the introns of coding or non-coding genes. Some research studies have shown that intronic miRNAs coexpress and act similarly to their host genes; however, other research studies have suggested that their level of expression and function are opposite to that of their host genes. Intronic microRNAs have been reported to play an antagonistic or synergetic role as an enemy or a partner of their host genes. Elucidation of the relationship between intronic microRNAs and their host genes will facilitate a deeper understanding of gene expression and the function of introns. This mini review will discuss recent research addressing intronic microRNAs and their host genes.