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

Review and update of SPRED1 mutations causing Legius syndrome

Legius syndrome presents as a mild neurofibromatosis type 1 (NF1) phenotype. Multiple café-au-lait spots and macrocephaly are present with or without axillary or inguinal freckling. Other typical NF1-associated features (Lisch nodules, bone abnormalities, neurofibromas, optic pathway gliomas, and malignant peripheral nerve sheath tumors) are systematically absent. Legius syndrome is caused by germline loss-of-function SPRED1 mutations, resulting in overactivation of the RAS-MAPK signal transduction cascade. The first families were identified in 2007. Here, we review all identified SPRED1 mutations and summarize molecular, clinical, and functional data. All mutations have been deposited in a database created using the Leiden Open Variation Database software and accessible at http://www.lovd.nl/SPRED1. At present, the database contains 89 different mutations identified in 146 unrelated probands, including 16 new variants described for the first time. The database contains a spectrum of mutations: 29 missense, 28 frameshift, 19 nonsense, eight copy number changes, two splicing, one silent, one in-frame deletion and a mutation affecting the initiation codon. Sixty-three mutations and deletions are definitely pathogenic or most likely pathogenic, eight SPRED1 mutations are probably benign rare variants, and 17 SPRED1 missense mutations are still unclassified and need further family and functional studies to help with the interpretation.

Downregulation of miR-126 induces angiogenesis and lymphangiogenesis by activation of VEGF-A in oral cancer

Background:

MicroRNA (miRNA)-126 (miR-126) is an endothelial-specific miRNA located within intron 7 of epidermal growth factor-like domain 7 (EGFL7). However, the role of miR-126 in cancer is controversial.

Methods:

We examined the function of miR-126 in oral squamous cell carcinoma (OSCC) cells. Furthermore, a series of 118 cases with OSCC were evaluated for the expression levels of miR-126.

Results:

MicroRNA-126 (miR-126) was associated with cell growth and regulation of vascular endothelial growth factor-A activity, and demethylation treatment increased expression levels of miR-126 and EGFL7 in OSCC cells. A significant association was found between miR-126 expression and tumour progression, nodal metastasis, vessel density, or poor prognosis in OSCC cases. In the multivariate analysis, decreased miR-126 expression was strongly correlated with disease-free survival.

Conclusion:

The present results suggest that miR-126 might be a useful diagnostic and therapeutic target in OSCC.

Role of microRNAs 99b, 181a, and 181b in the differentiation of human embryonic stem cells to vascular endothelial cells

MicroRNAs (miRNAs) are short noncoding RNAs, which post-transcriptionally regulate gene expression. miRNAs are transcribed as precursors and matured to active forms by a series of enzymes, including Dicer. miRNAs are important in governing cell differentiation, development, and disease. We have recently developed a feeder- and serum-free protocol for direct derivation of endothelial cells (ECs) from human embryonic stem cells (hESCs) and provided evidence of increases in angiogenesis-associated miRNAs (miR-126 and -210) during the process. However, the functional role of miRNAs in hESC differentiation to vascular EC remains to be fully interrogated. Here, we show that the reduction of miRNA maturation induced by Dicer knockdown suppressed hES-EC differentiation. A miRNA microarray was performed to quantify hES-EC miRNA profiles during defined stages of endothelial differentiation. miR-99b, -181a, and -181b were identified as increasing in a time- and differentiation-dependent manner to peak in mature hESC-ECs and adult ECs. Augmentation of miR-99b, -181a, and -181b levels by lentiviral-mediated transfer potentiated the mRNA and protein expression of EC-specific markers, Pecam1 and VE Cadherin, increased nitric oxide production, and improved hES-EC-induced therapeutic neovascularization in vivo. Conversely, knockdown did not impact endothelial differentiation. Our results suggest that miR-99b, -181a, and -181b comprise a component of an endothelial-miRNA signature and are capable of potentiating EC differentiation from pluripotent hESCs

MKL1 and MKL2 play redundant and crucial roles in megakaryocyte maturation and platelet formation

Serum response factor and its transcriptional cofactor MKL1 are critical for megakaryocyte maturation and platelet formation. We show that MKL2, a homologue of MKL1, is expressed in megakaryocytes and plays a role in megakaryocyte maturation. Using a megakaryocyte-specific Mkl2 knockout (KO) mouse on the conventional Mkl1 KO background to produce double KO (DKO) megakaryocytes and platelets, a critical role for MKL2 is revealed. The decrease in megakaryocyte ploidy and platelet counts of DKO mice is more severe than in Mkl1 KO mice. Platelet dysfunction in DKO mice is revealed by prolonged bleeding times and ineffective platelet activation in vitro in response to adenosine 5'-diphosphate. Electron microscopy and immunofluorescence of DKO megakaryocytes and platelets indicate abnormal cytoskeletal and membrane organization with decreased granule complexity. Surprisingly, the DKO mice have a more extreme thrombocytopenia than mice lacking serum response factor (SRF) expression in the megakaryocyte compartment. Comparison of gene expression reveals approximately 4400 genes whose expression is differentially affected in DKO compared with megakaryocytes deficient in SRF, strongly suggesting that MKL1 and MKL2 have both SRF-dependent and SRF-independent activity in megakaryocytopoiesis.

miRNAs as potential therapeutic targets for age-related macular degeneration

Since their recent discovery, miRNAs have been shown to play critical roles in a variety of pathophysiological processes. Such processes include pathological angiogenesis, the oxidative stress response, immune response and inflammation, all of which have been shown to have important and interdependent roles in the pathogenesis and progression of age-related macular degeneration (AMD). Here we present a brief review of the pathological processes involved in AMD and review miRNAs and other noncoding RNAs involved in regulating these processes. Specifically, we discuss several candidate miRNAs that show promise as AMD therapeutic targets due to their direct involvement in choroidal neovascularization or retinal pigment epithelium atrophy. We discuss potential miRNA-based therapeutics and delivery methods for AMD and provide future directions for the field of miRNA research with respect to AMD. We believe the future of miRNAs in AMD therapy is promising.

Role of the microRNA-17-92 cluster in the endothelial differentiation of stem cells

MicroRNAs (miRs) are small non-coding RNAs that recently emerged as potent regulators of gene expression. The members of the miR-17-92 cluster have been shown to control endothelial cell functions and neovascularization; however, the regulation and function of the cluster in endothelial cell lineage commitment has not been explored. This project aimed to test the role of the miR-17-92 cluster during endothelial differentiation. We demonstrate that miR-17, miR-18, miR-19 and miR-20 are increased upon the induction of endothelial cell differentiation of murine embryonic stem cells or induced pluripotent stem cells. In contrast, miR-92a and the primary miR-17-92 transcript were downregulated. The inhibition of each individual miR of the cluster by cholesterol-modified antagomirs did not affect endothelial marker gene expression. Moreover, the combination of all antagomirs had no effect. These findings illustrate that although the miR-17-92 cluster regulates vascular integrity and angiogenesis, none of the members has a significant impact on the endothelial differentiation of pluripotent stem cells.

MicroRNAs and stem cells: control of pluripotency, reprogramming, and lineage commitment

Stem cells hold great promise for regenerative medicine and the treatment of cardiovascular diseases. The mechanisms regulating self-renewal, pluripotency, and differentiation are not fully understood. MicroRNAs (miRs) are small noncoding RNAs controlling gene expression, either by inducing mRNA degradation or by blocking mRNA translation. The expression of miRs was shown to regulate various aspects of stem cell functions, including the maintenance and induction of pluripotency for reprogramming. In addition, some miRs control cell fate decisions. This review summarizes the role of miRs in reprogramming and embryonic stem cell self-renewal, and specifically addresses the regulation of cardiovascular cell fate decisions by miRs.

Role of microRNAs in peripheral artery disease (review)

Peripheral arterial disease (PAD) involves a general vascular problem of diffuse atherosclerosis. The key pathological process is characterized by the aberrant proliferation of vascular smooth muscle cells and the formation of neointimal lesions. The molecular mechanisms involved in the regulation of the occurrence and development of PAD remain unclear. microRNAs (miRNAs) are highly conserved 20-25 nt-long non-coding RNAs that negatively regulate gene expression. Recent evidence has demonstrated that specific miRNAs are involved in the pathological processes of PAD, and these miRNAs are found to be critical modulators of vascular cell functions, including cell differentiation, contraction, migration, proliferation and apoptosis. This review summarizes findings of studies regarding the roles of specific miRNAs in PAD.

Primitive erythropoiesis is regulated by miR-126 via nonhematopoietic Vcam-1+ cells

Primitive erythropoiesis defines the onset of hematopoiesis in the yolk sac of the early embryo and is initiated by the emergence of progenitors assayed as colony-forming cells (EryP-CFCs). EryP-CFCs are detected for only a narrow window during embryonic development, suggesting that both their initiation and termination are tightly controlled. Using the embryonic stem differentiation system to model primitive erythropoiesis, we found that miR-126 regulates the termination of EryP-CFC development. Analyses of miR-126 null embryos revealed that this miR also regulates EryP-CFCs in vivo. We identified vascular cell adhesion molecule-1 (Vcam-1) expressed by a mesenchymal cell population as a relevant target of miR-126. Interaction of EryP-CFCs with Vcam-1 accelerated their maturation to ßh1-globin(+) and Ter119(+) cells through a Src family kinase. These findings uncover a cell nonautonomous regulatory pathway for primitive erythropoiesis that may provide insight into the mechanism(s) controlling the developmental switch from primitive to definitive hematopoiesis.

Dre-miR-2188 targets Nrp2a and mediates proper intersegmental vessel development in zebrafish embryos

Background

MicroRNAs (miRNAs) are a class of small RNAs that are implicated in the control of eukaryotic gene expression by binding to the 3′UTR of target mRNAs. Several algorithms have been developed for miRNA target prediction however, experimental validation is still essential for the correct identification of miRNA targets. We have recently predicted that Neuropilin2a (Nrp2a), a vascular endothelial growth factor receptor which is essential for normal developmental angiogenesis in zebrafish, is a dre-miR-2188 target.

Methodology

Here we show that dre-miR-2188 targets the 3′-untranslated region (3′UTR) of Nrp2a mRNA and is implicated in proper intersegmental vessel development in vivo. Over expression of miR-2188 in zebrafish embryos down regulates Nrp2a expression and results in intersegmental vessel disruption, while its silencing increases Nrp2a expression and intersegmental vessel sprouting. An in vivo GFP sensor assay based on a fusion between the GFP coding region and the Nrp2a 3′UTR confirms that miR-2188 binds to the 3′UTR of Nrp2a and inhibits protein translation.

Conclusions

We demonstrate that miR-2188 targets Nrp2a and affects intersegmental vessel development in zebrafish embryos.

MicroRNA-126 contributes to renal microvascular heterogeneity of VCAM-1 protein expression in acute inflammation

Endothelial cells in different microvascular segments of the kidney have diverse functions and exhibit differential responsiveness to disease stimuli. The responsible molecular mechanisms are largely unknown. We previously showed that during hemorrhagic shock, VCAM-1 protein was expressed primarily in extraglomerular compartments of the kidney, while E-selectin protein was highly induced in glomeruli only (van Meurs M, Wulfert FM, Knol AJ, de Haes A, Houwertjes M, Aarts LPHJ, Molema G. Shock 29: 291–299, 2008). Here, we investigated the molecular control of expression of these endothelial cell adhesion molecules in mouse models of renal inflammation. Microvascular segment-specific responses to the induction of anti-glomerular basement membrane (anti-GBM), glomerulonephritis and systemic TNF-α treatment showed that E-selectin expression was transcriptionally regulated, with high E-selectin mRNA and protein levels preferentially expressed in the glomerular compartment. In contrast, VCAM-1 mRNA expression was increased in both arterioles and glomeruli, while VCAM-1 protein expression was limited in the glomeruli. These high VCAM-1 mRNA/low VCAM-1 protein levels were accompanied by high local microRNA (miR)-126 and Egfl7 levels, as well as higher Ets1 levels compared with arteriolar expression levels. Using miR-reporter constructs, the functional activity of miR-126 in glomerular endothelial cells could be demonstrated. Moreover, in vivo knockdown of miR-126 function unleashed VCAM-1 protein expression in the glomeruli upon inflammatory challenge. These data imply that miR-126 has a major role in the segmental, heterogenic response of renal microvascular endothelial cells to systemic inflammatory stimuli.

β2-Glycoprotein I inhibits endothelial cell migration through the nuclear factor κB signalling pathway and endothelial nitric oxide synthase activation

β2-GPI (β2-glycoprotein I) is a plasma glycoprotein ascribed with an anti-angiogenic function; however, the biological role and molecular basis of its action in cell migration remain unknown. The aim of the present study was to assess the contribution of β2-GPI to HAEC (human aortic endothelial cell) migration and the details of its underlying mechanism. Using wound healing and Boyden chamber assays, we found that β2-GPI inhibited endothelial cell migration, which was restored by its neutralizing antibody. NF-κB (nuclear factor κB) inhibitors and lentiviral siRNA (small interfering RNA) silencing of NF-κB significantly attenuated the inhibitory effect of β2-GPI on cell migration. Moreover, β2-GPI was found to induce IκBα (inhibitor of NF-κB) phosphorylation and translocation of p65 and p50. We further demonstrated that mRNA and protein levels of eNOS [endothelial NO (nitric oxide) synthase] and NO production were all increased by β2-GPI and these effects were remarkably inhibited by NF-κB inhibitors and siRNAs of p65 and p50. Furthermore, β2-GPI-mediated inhibition of cell migration was reversed by eNOS inhibitors and eNOS siRNAs. The findings of the present study provide novel insight into the ability of β2-GPI to inhibit endothelial cell migration predominantly through the NF-κB/eNOS/NO signalling pathway, which indicates a potential direction for clinical therapy in vascular diseases.

Vascular endothelial cell-specific microRNA-15a inhibits angiogenesis in hindlimb ischemia

The effects and potential mechanisms of the vascular endothelial cell (EC)-enriched microRNA-15a (miR-15a) on angiogenesis remain unclear. Here, we show a novel finding that EC-selective miR-15a transgenic overexpression leads to reduced blood vessel formation and local blood flow perfusion in mouse hindlimbs at 1-3 weeks after hindlimb ischemia. Mechanistically, gain- or loss-of-miR-15a function by lentiviral infection in ECs significantly reduces or increases tube formation, cell migration, and cell differentiation, respectively. By FGF2 and VEGF 3'-UTR luciferase reporter assays, Real-time PCR, and immunoassays, we further identified that the miR-15a directly targets FGF2 and VEGF to facilitate its anti-angiogenic effects. Our data suggest that the miR-15a in ECs can significantly suppress cell-autonomous angiogenesis through direct inhibition of endogenous endothelial FGF2 and VEGF activities. Pharmacological modulation of miR-15a function may provide a new therapeutic strategy to intervene against angiogenesis in a variety of pathological conditions.

Frontiers in preclinical safety biomarkers: microRNAs and messenger RNAs

The measurement of plasma microRNAs (miRNAs) and messenger RNAs (mRNAs) is the most recent effort to identify novel biomarkers in preclinical safety. These genomic markers often display tissue-specific expression, may be released from the tissues into the plasma during toxic events, change early and with high magnitude in tissues and in the blood during specific organ toxicities, and can be measured using multiplex formats. Their validation as biomarkers has been challenged by the technical difficulties. In particular, the concentration of miRNAs in the plasma depends on contamination by miRNAs originating from blood cells and platelets, and the relative fraction of miRNAs in complexes with Argonaute 2, high-density lipoproteins, and in exosomes and microvesicles. In spite of these hurdles, considerable progress has recently been made in assessing the potential value of miRNAs in the clinic, especially in cancer patients and cardiovascular diseases. The future of miRNAs and mRNAs as biomarkers of disease and organ toxicity depends on our ability to characterize their kinetics and to establish robust collection and measurement methods. This review covers the basic biology of miRNAs and the published literature on the use of miRNAs and mRNAs as biomarkers of specific target organ toxicity.

MicroRNAs: molecular features and role in cancer

microRNAs (miRNAs) are small noncoding endogenously produced RNAs that play key roles in controlling the expression of many cellular proteins. Once they are recruited and incorporated into a ribonucleoprotein complex miRISC, they can target specific mRNAs in a miRNA sequence-dependent process and interfere in the translation into proteins of the targeted mRNAs via several mechanisms. Consequently, miRNAs can regulate many cellular pathways and processes. Dysregulation of their physiological roles may largely contribute to disease. In particular, in cancer, miRNAs can be involved in the deregulation of the expression of important genes that play key roles in tumorigenesis, tumor development, and angiogenesis and have oncogenic or tumor suppressor roles. This review focuses on the biogenesis and maturation of miRNAs, their mechanisms of gene regulation, and the way their expression is deregulated in cancer. The involvement of miRNAs in several oncogenic pathways such as angiogenesis and apoptosis, and in the inter-cellular dialog mediated by miRNA-loaded exosomes as well as the development of new therapeutical strategies based on miRNAs will be discussed.

Converging miRNA functions in diverse brain disorders: a case for miR-124 and miR-126

A growing body of information on the biology of miRNAs has revealed new insight into their roles in normal homeostasis and pathology of disease. miRNAs control all steps of the cellular expression machinery acting through a "single miRNA/multiple targets" or "multiple miRNAs/single target" mechanism. They have profound impact on the regulation of signaling pathways, which govern common and specific functions across different cellular phenotypes. There is increasing evidence that various diseases share similar disturbances in gene expression networks. Since miRNAs have both common and varying effects in different cellular contexts, they might also influence overlapping signaling pathways in different organs and disease entities. Here, we review this concept for two miRNAs highly abundant in the brain, miR-124 and miR-126, and their potential role in diseases of the brain.

Combined deep microRNA and mRNA sequencing identifies protective transcriptomal signature of enhanced PI3Kα signaling in cardiac hypertrophy

The perturbation of myocardial transcriptome homeostasis is the hallmark of pathological hypertrophy, underlying the maladaptive myocardial remodeling secondary to pathological stresses. Classic and novel therapeutics that provide beneficial effects against pathological remodeling likely impact myocardial transcriptome architecture, including miRNA and mRNA expression profiles. Microarray and PCR-based technologies, although employed extensively, cannot provide adequate sequence coverage or quantitative accuracy to test this hypothesis directly. The goal of this study was to develop and exploit next-generation sequencing approaches for comprehensive and quantitative analyses of myocardial miRNAs and mRNAs to test the hypothesis that augmented phosphoinositide-3-kinase-p110α (PI3Kα) signaling in the setting of pathological hypertrophy provides beneficial effects through remodeling of the myocardial transcriptome signature. In these studies, a molecular and bioinformatic pipeline permitting comprehensive analysis and quantification of myocardial miRNA and mRNA expression with next-generation sequencing was developed and the impact of enhanced PI3Kα signaling on the myocardial transcriptome signature of pressure overload-induced pathological hypertrophy was explored. These analyses identified multiple miRNAs and mRNAs that were abnormally expressed in pathological hypertrophy and partially or completely normalized with increased PI3Kα signaling. Additionally, several novel miRNAs potentially linked to remodeling in cardiac hypertrophy were identified. Additional experiments revealed that increased PI3Kα signaling reduces cardiac fibrosis in pathological hypertrophy through modulating TGF-β signaling and miR-21 expression. In conclusion, using the approach of combined miRNA and mRNA sequencing, we identify the protective transcriptome signature of enhanced PI3Kα signaling in the context of pathological hypertrophy, and demonstrate the regulation of TGF-β/miR-21 by which enhanced PI3Kα signaling protects against cardiac fibrosis.

MicroRNAs in stress signaling and human disease

Disease is often the result of an aberrant or inadequate response to physiologic and pathophysiologic stress. Studies over the last 10 years have uncovered a recurring paradigm in which microRNAs (miRNAs) regulate cellular behavior under these conditions, suggesting an especially significant role for these small RNAs in pathologic settings. Here, we review emerging principles of miRNA regulation of stress signaling pathways and apply these concepts to our understanding of the roles of miRNAs in disease. These discussions further highlight the unique challenges and opportunities associated with the mechanistic dissection of miRNA functions and the development of miRNA-based therapeutics.

Integration of experimental and computational approaches to sprouting angiogenesis

PURPOSE OF REVIEW

We summarize recent experimental and computational studies that investigate molecular and cellular mechanisms of sprouting angiogenesis. We discuss how experimental tools have unveiled new opportunities for computational modeling by providing detailed phenomenological descriptions and conceptual models of cell-level behaviors underpinned by high-quality molecular data. Using recent examples, we show how new understanding results from bridging computational and experimental approaches.

RECENT FINDINGS

Experimental data extends beyond the tip cell vs. stalk cell paradigm, and involves numerous molecular inputs such as vascular endothelial growth factor and Notch. This data is being used to generate and validate computational models, which can then be used to predict the results of hypothetical experiments that are difficult to perform in the laboratory, and to generate new hypotheses that account for system-wide interactions. As a result of this integration, descriptions of critical gradients of growth factor-receptor complexes have been generated, and new modulators of cell behavior have been described.

SUMMARY

We suggest that the recent emphasis on the different stages of sprouting angiogenesis, and integration of experimental and computational approaches, should provide a way to manage the complexity of this process and help identify new regulatory paradigms and therapeutic targets.

MicroRNAs in hypertension: mechanisms and therapeutic targets

Hypertension is a complex, multifactorial disease, and its development is determined by a combination of genetic susceptibility and environmental factors. Several mechanisms have been implicated in the pathogenesis of hypertension: increased activity of the sympathetic nervous system, overactivation of the renin-angiotensin aldosterone system (RAAS), dysfunction of vascular endothelium, impaired platelet function, thrombogenesis, vascular smooth muscle and cardiac hypertrophy, and altered angiogenesis. MicroRNAs are short, noncoding nucleotides regulating target messenger RNAs at the post-transcriptional level. MicroRNAs are involved in virtually all biologic processes, including cellular proliferation, apoptosis, and differentiation. Thus, microRNA deregulation often results in impaired cellular function and disease development, so microRNAs have potential therapeutic relevance. Many aspects of the development of essential hypertension at the molecular level are still unknown. The elucidation of these processes regulated by microRNAs and the identification of novel microRNA targets in the pathogenesis of hypertension is a highly valuable and exciting strategy that may eventually led to the development of novel treatment approaches for hypertension. This article reviews the potential role of microRNAs in the mechanisms associated with the development and consequences of hypertension and discusses advances in microRNA-based approaches that may be important in treating hypertension.

miR-221 is required for endothelial tip cell behaviors during vascular development

Angiogenesis requires coordination of distinct cell behaviors between tip and stalk cells. Although this process is governed by regulatory interactions between the vascular endothelial growth factor (Vegf) and Notch signaling pathways, little is known about the potential role of microRNAs. Through deep sequencing and functional screening in zebrafish, we find that miR-221 is essential for angiogenesis. miR-221 knockdown phenocopied defects associated with loss of the tip cell-expressed Flt4 receptor. Furthermore, miR-221 was required for tip cell proliferation and migration, as well as tip cell potential in mosaic blood vessels. miR-221 knockdown also prevented "hyper-angiogenesis" defects associated with Notch deficiency and miR-221 expression was inhibited by Notch signaling. Finally, miR-221 promoted tip cell behavior through repression of two targets: cyclin dependent kinase inhibitor 1b (cdkn1b) and phosphoinositide-3-kinase regulatory subunit 1 (pik3r1). These results identify miR-221 as an important regulatory node through which tip cell migration and proliferation are controlled during angiogenesis.

Plexiform vasculopathy of severe pulmonary arterial hypertension and microRNA expression

BACKGROUND

Recent studies have revealed that microRNAs (miRNAs) play a key role in the control of angiogenesis and vascular remodeling. Specific miRNAs in plexiform vasculopathy of severe pulmonary arterial hypertension (PAH) in humans have not yet been investigated.

METHODS

We analyzed expression of miR-143/145 (vascular smooth muscle-specific), miR-126 (endothelial-specific) and related mRNAs in plexiform (PLs) and concentric lesions (CLs), which had been laser-microdissected from specimens of formalin-fixed, paraffin-embedded, explanted lungs of PAH patients (n = 12) and unaffected controls (n = 8). Samples were analyzed by real-time polymerase chain reaction, and protein expression was determined by immunohistochemistry.

RESULTS

Expression levels of miR-143/145 and its target proteins (e.g., myocardin, smooth muscle myosin heavy chain) were found to be significantly higher in CLs than in PLs, whereas miR-126 and VEGF-A were significantly up-regulated in PLs when compared with CLs, indicating a more prominent angiogenic phenotype of PL. This correlates with a down-regulation of miR-204 as well as an up-regulation of miR-21 in PLs, which in turn corresponds to enhanced cell proliferation.

CONCLUSIONS

Our findings show that morphologic changes of plexiform vasculopathy in the end-stage PAH lung are reflected by alterations at the miRNA level.

MicroRNAs in vascular and metabolic disease

Recent findings demonstrated the importance of microRNAs (miRNAs) in the vasculature and the orchestration of lipid metabolism and glucose homeostasis. MiRNA networks represent an additional layer of regulation for gene expression that absorbs perturbations and ensures the robustness of biological systems. This function is very elegantly demonstrated in cholesterol metabolism where miRNAs reducing cellular cholesterol export are embedded in the very same genes that increase cholesterol synthesis. Often their alteration does not affect normal development but changes under stress conditions and in disease. A detailed understanding of the molecular and cellular mechanisms of miRNA-mediated effects on metabolism and vascular pathophysiology could pave the way for the development of novel diagnostic markers and therapeutic approaches. In the first part of this review, we summarize the role of miRNAs in vascular and metabolic diseases and explore potential confounding effects by platelet miRNAs in preclinical models of cardiovascular disease. In the second part, we discuss experimental strategies for miRNA target identification and the challenges in attributing miRNA effects to specific cell types and single targets.

Downregulation of microRNA-126 in endothelial progenitor cells from diabetes patients, impairs their functional properties, via target gene Spred-1

Diabetes mellitus (DM) adversely affects the number and function of circulating endothelial progenitor cells (EPCs). Consequently, there is also a reduction in the repair mechanism of these cells, which is a critical and initiating factor in the development of diabetic vascular disease. The aim of the present study was to analyze miR expression profiles in EPCs from patients with DM and choose the most significantly regulated miR to study its possible role on EPC dysfunction and elucidate its mechanism of action. EPCs were collected from subjects with Type II DM and non-diabetic control subjects. Total RNA was harvested from EPCs, and a total of 5 candidate miRNAs were identified by microarray screening and were quantified by TaqMan real-time PCR. Lentiviral vectors expressing miR-126 and miR-126 inhibitor (anti-miR-126) were transfected into EPCs, and the EPC colony-forming capacity, proliferation activity, migratory activity, differentiation capacity, and apoptotic susceptibility were determined and Western Blotting and mRNA real-time PCR analyses were performed. To study the mechanisms, lentiviral vectors expressing Spred-1 and a short interfering RNA (siRNA) targeting Spred-1 were prepared. Five miRs were aberrantly downregulated in EPCs from DM patients. These miRs included miR-126, miR-21, miR-27a, miR-27b and miR-130a. Anti-miR-126 inhibited EPC proliferation, migration, and enhanced apoptosis. Restored miR-126 expression in EPCs from DM promoted EPC proliferation, migration, and inhibited EPC apoptosis ability. Despite this, miR-126 had no effect on EPC differentiation. miR-126 overexpression significantly downregulated Spred-1 in EPCs. The knockdown of Spred-1 expression in EPCs from DM promoted proliferation, migration, and inhibited apoptosis of the cells. The signal pathway of miR-126 effecting on EPCs is partially mediated through Ras/ERK/VEGF and PI3K/Akt/eNOS regulation. This study provides the first evidence that miR-126 is downregulated in EPCs from diabetic patients, and impairs EPCs-mediated function via its target, Spred-1, and through Ras/ERK/VEGF and PI3K/Akt/eNOS signal pathway.

Experimental acute myocardial infarction: telocytes involvement in neo-angiogenesis

We used rat experimental myocardial infarction to study the ultrastructural recovery, especially neo-angiogenesis in the infarction border zone. We were interested in the possible role(s) of telocytes (TCs), a novel type of interstitial cell very recently discovered in myocardim (see http://www.telocytes.com). Electron microscopy, immunocytochemistry and analysis of several proangiogenic microRNAs provided evidence for TC involvement in neo-angiogenesis after myocardial infarction. Electron microscopy showed the close spatial association of TCs with neoangiogenetic elements. Higher resolution images provided the following information: (a) the intercellular space between the abluminal face of endothelium and its surrounding TCs is frequently less than 50 nm; (b) TCs establish multiple direct nanocontacts with endothelial cells, where the extracellular space seems obliterated; such nanocontacts have a length of 0.4–1.5 μm; (c) the absence of basal membrane on the abluminal face of endothelial cell. Besides the physical contacts (either nanoscopic or microscopic) TCs presumably contribute to neo-angiognesis via paracrine secretion (as shown by immunocytochemistry for VEGF or NOS2). Last but not least, TCs contain measurable quantities of angiogenic microRNAs (e.g. let-7e, 10a, 21, 27b, 100, 126-3p, 130a, 143, 155, 503). Taken together, the direct (physical) contact of TCs with endothelial tubes, as well as the indirect (chemical) positive influence within the ‘angiogenic zones’, suggests an important participation of TCs in neo-angiogenesis during the late stage of myocardial infarction.

Differential expression of microRNAs in different disease states

Disturbances in gene expression as a result of perturbed transcription or posttranscriptional regulation is one of the main causes of cellular dysfunction that underlies different disease states. Approximately a decade ago, the discovery of microRNAs in mammalian cells has renewed our focus on posttranscriptional regulatory mechanisms during pathogenesis. These tiny posttranscriptional regulators are differentially expressed in almost every disease that has been studied to date and can modulate expression of a gene via specifically binding to its messenger RNA. Because of their capacity to simultaneously target multiple functionally related, genes, they are proving to be potentially powerful therapeutic agents/targets. In this review, we focus on the microRNAs that are differentially regulated in the more common cardiovascular pathologies, their targets, and potential function.

MicroRNA-513a-5p mediates TNF-α and LPS induced apoptosis via downregulation of X-linked inhibitor of apoptotic protein in endothelial cells

MicroRNAs (miRNAs) are endogenous non-coding small RNAs that have emerged as one of the central players of gene expression regulation. Endothelial cell apoptosis plays a fundamental role in the development of atherosclerosis. This study was designed to determine the effect of miR-513a-5p on apoptosis of human umbilical vein endothelial cells (HUVECs). HUVECs were treated with tumour necrosis factor-α (TNF-α) and lipopolysaccharide (LPS) and miR-513a-5p expression levels were determined. MiR-513a-5p target gene indentification, validation, and signalling pathways were investigated. Treatment of HUVECs with TNF-α and LPS up-regulated miR-513a-5p expressions more than 2-fold compared to control (P < 0.05). Inhibition of miR-513a-5p by antisense (AS) miR-513a-5p reversed TNF-α and LPS induced apoptosis (P < 0.01). Transfection of HUVECs with miR-513a-5p mimics also induced apoptosis (P < 0.01). Treatment of HUVECs with TNF-α and LPS attenuated X-linked inhibitor of apoptosis (XIAP) while increased caspase-3 expression, poly ADP-ribose polymerase (PARP) cleavage, and p53 expression. These effects were reversed by inhibition of miR-513a-5p. Of those miR-513a-5p candidate target genes, we identified and validated XIAP as a miR-513a-5p target gene. Targeting of the XIAP 3'-untranslated region by miR-513a-5p using luciferase reporter assay resulted in attenuated luciferase activity. Transfection of HUVECs with AS miR-513a-5p increased XIAP protein expression while miR-513a-5p mimics attenuated XIAP expression. These results together suggest that miR-513a-5p mediates TNF-α and LPS induced apoptosis via downregulation of XIAP in HUVECs.

MicroRNA in situ hybridization

In situ hybridization (ISH) is a technology that allows detection of specific nucleic acid sequences in tissue samples at the cellular level. For detection of individual microRNAs (miRNAs) and mRNAs, the ISH technology determines the cellular origin of expression and provides information on expression levels in different tissue compartments and cell populations. This histological expression analysis is of crucial importance for elucidating roles particularly of miRNAs in molecular and biological processes. mRNA expression analyses can partly be replaced by immunohistochemical detection of the protein encoded by the mRNA. Combined with the short sequences of the miRNAs (18-22 bp), this leaves miRNA ISH as an indispensable yet challenging technology in terms of detection and specificity analysis. In this chapter, a simple miRNA ISH protocol using chromogenic detection is presented. I touch upon critical steps in the ISH protocol, different applications on ISH technology platforms, advantageous use of locked nucleic acids (LNA™) in miRNA detection probes, qualification of clinical paraffin samples, and specificity analyses and quantification of the ISH signal.

MicroRNA-214 protects the mouse heart from ischemic injury by controlling Ca²⁺ overload and cell death

Early reperfusion of ischemic cardiac tissue remains the most effective intervention for improving clinical outcome following myocardial infarction. However, abnormal increases in intracellular Ca²⁺ during myocardial reperfusion can cause cardiomyocyte death and consequent loss of cardiac function, referred to as ischemia/reperfusion (IR) injury. Therapeutic modulation of Ca²⁺ handling provides some cardioprotection against the paradoxical effects of restoring blood flow to the heart, highlighting the significance of Ca²⁺ overload to IR injury. Cardiac IR is also accompanied by dynamic changes in the expression of microRNAs (miRNAs); for example, miR-214 is upregulated during ischemic injury and heart failure, but its potential role in these processes is unknown. Here, we show that genetic deletion of miR-214 in mice causes loss of cardiac contractility, increased apoptosis, and excessive fibrosis in response to IR injury. The cardioprotective roles of miR-214 during IR injury were attributed to repression of the mRNA encoding sodium/calcium exchanger 1 (Ncx1), a key regulator of Ca²⁺ influx; and to repression of several downstream effectors of Ca²⁺ signaling that mediate cell death. These findings reveal a pivotal role for miR-214 as a regulator of cardiomyocyte Ca²⁺ homeostasis and survival during cardiac injury.

MicroRNAs mediate metabolic stresses and angiogenesis

MicroRNAs are short endogenous RNA molecules that are able to regulate (mainly inhibiting) gene expression at the post-transcriptional level. The MicroRNA expression profile is cell-specific, but it is sensitive to perturbations produced by stresses and diseases. Endothelial cells subjected to metabolic stresses, such as calorie restriction, nutrients excess (glucose, cholesterol, lipids) and hypoxia may alter their functionality. This is predictive for the development of pathologies like atherosclerosis, diabetes, and hypertension. Moreover, cancer cells can activate a resting endothelium by secreting pro-angiogenic factors, in order to promote neoangiogenesis, which is essential for tumor growth. Endothelial altered phenotype is mirrored by altered mRNA, microRNA, and protein expression, with a microRNA being able to control pathways by regulating the expression of multiple mRNAs. In this review we will consider the involvement of microRNAs in modulating the response of endothelial cells to metabolic stresses and their role in promoting or halting angiogenesis.

A New Level of Complexity

The discovery of the regulatory role of noncoding RNAs, and micro (mi)RNAs in particular, has added a new layer of complexity to our understanding of cardiovascular development. miRNAs regulate and modulate various steps of cardiovascular morphogenesis, cell proliferation, differentiation, and phenotype modulation. miRNAs simultaneously regulate multiple targets, and many miRNAs can bind to the same target, allowing for a complex pattern of regulation of gene expression. miRNA families are continuously added during evolution paralleling the increased complexity of the cardiovascular system in vertebrates compared with invertebrates. Several lines of evidence suggest that the appearance of miRNAs is at least in part responsible for the formation of complex organ systems and stable regulatory mechanisms in vertebrates. We review the current understanding of miRNAs during cardiovascular development. Further progress in this area will help to decipher quantitative changes in gene expression that provide robustness to cellular phenotypes and regulatory options to diseases processes. miRNAs might also provide clues to better understand congenital heart defects, which are the most common birth defects in human newborns.

MicroRNAs in Postischemic Vascular Repair

The term angiogenesis describes the growth of endothelial sprouts from preexisting postcapillary venules. More recently, this term has been used to generally indicate the growth and remodeling process of the primitive vascular network into a complex network during development. In adulthood, angiogenesis is activated as a reparative process during wound healing and following ischemia, and it plays a key role in tumor growth and metastasis as well as in inflammatory diseases and diabetic retinopathy. MicroRNAs (miRNAs) are endogenous, small, noncoding RNAs that negatively control gene expression of target mRNAs. In this paper, we aim at describing the role of miRNAs in postischemic angiogenesis. First, we will describe the regulation and the expression of miRNAs in endothelial cells. Then, we will analyze the role of miRNAs in postischemic vascular repair. Finally, we will discuss the role of circulating miRNAs as potential biomarkers in ischemic diseases.

Myc-associated zinc finger protein (MAZ) is regulated by miR-125b and mediates VEGF-induced angiogenesis in glioblastoma

In patients with glioblastomas, vascular endothelial growth factor (VEGF) is a key mediator of tumor-associated angiogenesis. Glioblastomas are notorious for their capacity to induce neovascularization, driving continued tumor growth. Here we report that miR-125b is down-regulated in glioblastoma-associated endothelial cells, resulting in increased expression of its target, myc-associated zinc finger protein (MAZ), a transcription factor that regulates VEGF. The down-regulation of miR-125b was also observed on exposure of endothelial cells to glioblastoma-conditioned medium or VEGF, resulting in increased MAZ expression. Further analysis revealed that inhibition of MAZ accumulation by miR-125b, or by MAZ-specific shRNAs, attenuated primary human brain endothelial cell migration and tubule formation in vitro, phenomena considered to mimick angiogenic processes in vitro. Moreover, MAZ expression was elevated in brain blood vessels of glioblastoma patients. Altogether these results demonstrate a functional feed-forward loop in glioblastoma-related angiogenesis, in which VEGF inhibits the expression of miR-125b, resulting in increased expression of MAZ, which in its turn causes transcriptional activation of VEGF. This loop is functionally impeded by the VEGF receptor inhibitor vandetanib, and our results may contribute to the further development of inhibitors of tumor-angiogenesis.

The predictive value of microRNA-126 in relation to first line treatment with capecitabine and oxaliplatin in patients with metastatic colorectal cancer

Background

MicroRNA-126 is the only microRNA (miRNA) known to be endothelial cell-specific influencing angiogenesis in several ways. The aim of the present study was to analyse the possible predictive value of miRNA-126 in relation to first line capecitabine and oxaliplatin (XELOX) in patients with metastatic colorectal cancer (mCRC).

Methods

The study included 89 patients with mCRC. In situ hybridization (ISH) was performed to detect miRNA-126 in formalin-fixed paraffin embedded tissue from primary tumours. The expression of miRNA-126, area per image (μm²), was measured using image analysis. Clinical response was evaluated according to RECIST. Progression free survival (PFS) was compared using the Kaplan-Meier method and the log rank test. Tumours were classified as low or high miRNA-126 expressing tumours using the median value from the patients with response as cut-off.

Results

The median miRNA-126 expression level was significantly higher in patients responding to XELOX, 3629 μm² (95% CI, 2566-4846), compared to the patients not responding, 1670 μm² (95% CI, 1436-2041), p < 0.0001. The positive predictive value was 90%, and the negative predictive value was 71%. The median PFS of patients with high expressing tumours was 11.5 months (95% CI, 9.0-12.7 months) compared to 6.0 months (95% CI, 4.8-6.9 months) for patients with low expressing tumours, p < 0.0001.

Conclusions

Angiogenesis quantified by ISH of miRNA-126 was related to response to first line XELOX in patients with mCRC, translating to a significant difference in PFS. The predictive value of miRNA-126 remains to be further elucidated in prospective studies.

Regulation of cardiac microRNAs by bone marrow mononuclear cell therapy in myocardial infarction

BACKGROUND

Cell therapy with bone marrow-derived mononuclear cells (BMCs) can improve recovery of cardiac function after ischemia; however, the molecular mechanisms are not yet fully understood. MicroRNAs (miRNAs) are key regulators of gene expression and modulate the pathophysiology of cardiovascular diseases.

METHODS AND RESULTS

We demonstrated that intramyocardial delivery of BMCs in infarcted mice regulates the expression of cardiac miRNAs and significantly downregulates the proapoptotic miR-34a. In vitro studies confirmed that the supernatant of BMC inhibited the expression of H(2)O(2)-induced miR-34a and cardiomyocytes apoptosis. These effects were blocked by neutralizing antibodies directed against insulin-like growth factor-1 (IGF-1). Indeed, IGF-1 significantly inhibited H(2)O(2)-induced miR-34a expression, and miR-34a overexpression abolished the antiapoptotic effect of IGF-1. Likewise, inhibition of IGF-1 signaling in vivo abolished the BMC-mediated inhibition of miR-34 expression and the protective effect on cardiac function and increased apoptosis and cardiac fibrosis. IGF-1 specifically blocked the expression of the precursor and the mature miR-34a, but did not interfere with the transcription of the primary miR-34a demonstrating that IGF-1 blocks the processing of miR-34a.

CONCLUSIONS

Together, our data demonstrate that the paracrine regulation of cardiac miRNAs by transplanted BMCs contributes to the protective effects of cell therapy. BMCs release IGF-1, which inhibits the processing of miR-34a, thereby blocking cardiomyocyte apoptosis.

Hypoxia control to normalize pathologic angiogenesis: potential role for endothelial precursor cells and miRNAs regulation

Tumor microenvironment is a complex and highly dynamic milieu that provides very important clues on tumor development and progression mechanisms. Tumor-associated endothelial cells play a key role in stroma organization. They achieve tumor angiogenesis, a formation of tumor-associated (angiogenic) vessels mainly through sprouting from locally preexisting vessels and/or recruitment of bone marrow-derived endothelial progenitor cells. This process participates to supply nutritional support and oxygen to the growing tumor. Endothelial cells constitute the interface between circulating blood cells, tumor cells and the extracellular matrix, thereby controlling leukocyte recruitment, tumor cell behavior and metastasis formation. Hypoxia, a critical parameter of the tumor microenvironment, controls endothelial/tumor cell interactions and is the key to tumor angiogenesis development. Under hypoxic stress, tumor cells produce factors that promote angiogenesis, vasculogenesis, tumor cell motility, metastasis and cancer stem cell selection. Targeting tumor vessels is a therapeutic strategy that has lately been fast evolving from antiangiogenesis to vessel normalization as discussed in this review. We shall focus on the pivotal role of endothelial cells within the tumor microenvironment, the specific features and the part played by circulating endothelial precursors cells. Attention is stressed on their recruitment to the tumor site and their role in tumor angiogenesis where they are submitted to miRNAs-mediated de/regulation. Here the compensation of the tumor deregulated angiogenic miRNAs - angiomiRs - is emphasized as a potential therapeutic approach. The strategy is to over express anti-angiomiRs in the tumor angiogenesis site upon selective delivery by precursor endothelial cells as miRs carriers.

MicroRNA-182 targets cAMP-responsive element-binding protein 1 and suppresses cell growth in human gastric adenocarcinoma

MicroRNAs (miRNAs) constitute a class of noncoding RNAs that post-transcriptionally regulate gene expression. Recent evidence indicates that many miRNAs function as oncogenes or tumor suppressors by negatively regulating their target genes. In our previous study, using miRNA microarray analysis, we found that miRNA-182 (miR-182) was significantly downregulated in human gastric adenocarcinoma tissue samples. Here, we confirmed the downregulation of miR-182 in a larger sample of gastric tissue samples. Overexpression of miR-182 suppressed the proliferation and colony formation of gastric cancer cells. An oncogene, encoding cAMP-responsive element binding protein 1 (CREB1), serves as a direct target gene of miR-182. A fluorescent reporter assay confirmed that miR-182 binds specifically to the predicted site of the CREB1 mRNA 3'-UTR. When miR-182 was overexpressed in gastric cancer cell lines, both the mRNA and protein levels of CREB1 were depressed. Furthermore, CREB1 was present at a high level in human gastric adenocarcinoma tissues, and this was inversely correlated with miR-182 expression. Ectopic expression of CREB1 overcame the suppressive phenotypes of gastric cancer cells caused by miR-182. These results indicate that miR-182 targets the CREB1 gene and suppresses gastric adenocarcinoma cell growth, suggesting that miR-182 shows tumor-suppressive activity in human gastric cancer.

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.

Regulation of cholesterol homeostasis

Cholesterol homeostasis is among the most intensely regulated processes in biology. Since its isolation from gallstones at the time of the French Revolution, cholesterol has been extensively studied. Insufficient or excessive cellular cholesterol results in pathological processes including atherosclerosis and metabolic syndrome. Mammalian cells obtain cholesterol from the circulation in the form of plasma lipoproteins or intracellularly, through the synthesis of cholesterol from acetyl coenzyme A (acetyl-CoA). This process is tightly regulated at multiple levels. In this review, we provide an overview of the multiple mechanisms by which cellular cholesterol metabolism is regulated. We also discuss the recent advances in the post-transcriptional regulation of cholesterol homeostasis, including the role of small non-coding RNAs (microRNAs). These novel findings may open new avenues for the treatment of dyslipidemias and cardiovascular diseases.

An antagomir to microRNA Let7f promotes neuroprotection in an ischemic stroke model

We previously showed that middle-aged female rats sustain a larger infarct following experimental stroke as compared to younger female rats, and paradoxically, estrogen treatment to the older group is neurotoxic. Plasma and brain insulin-like growth factor-1 (IGF-1) levels decrease with age. However, IGF-1 infusion following stroke, prevents estrogen neurotoxicity in middle-aged female rats. IGF1 is neuroprotective and well tolerated, but also has potentially undesirable side effects. We hypothesized that microRNAs (miRNAs) that target the IGF-1 signaling family for translation repression could be alternatively suppressed to promote IGF-1-like neuroprotection. Here, we report that two conserved IGF pathway regulatory microRNAs, Let7f and miR1, can be inhibited to mimic and even extend the neuroprotection afforded by IGF-1. Anti-mir1 treatment, as late as 4 hours following ischemia, significantly reduced cortical infarct volume in adult female rats, while anti-Let7 robustly reduced both cortical and striatal infarcts, and preserved sensorimotor function and interhemispheric neural integration. No neuroprotection was observed in animals treated with a brain specific miRNA unrelated to IGF-1 (anti-miR124). Remarkably, anti-Let7f was only effective in intact females but not males or ovariectomized females indicating that the gonadal steroid environment critically modifies miRNA action. Let7f is preferentially expressed in microglia in the ischemic hemisphere and confirmed in ex vivo cultures of microglia obtained from the cortex. While IGF-1 was undetectable in microglia harvested from the non-ischemic hemisphere, IGF-1 was expressed by microglia obtained from the ischemic cortex and was further elevated by anti-Let7f treatment. Collectively these data support a novel miRNA-based therapeutic strategy for neuroprotection following stroke.

The role of microRNAs in arterial remodelling

Adaptive alterations of the vessel wall architecture, called vascular remodelling, can be found in arterial hypertension, during the formation of aneurysms, in restenosis after vascular interventions, and in atherosclerosis. MicroRNAs (miR) critically affect the main cellular players in arterial remodelling and may either promote or inhibit the structural changes in the vessel wall. They regulate the phenotype of smooth muscle cells (SMCs) and control the inflammatory response in endothelial cells and macrophages. In SMCs, different sets of miRs induce either a synthetic or contractile phenotype, respectively. The conversion into a synthetic SMC phenotype is a crucial event in arterial remodelling. Therefore, reprogramming of the SMC phenotype by miR targeting can modulate the remodelling process. Furthermore, the effects of stimuli that induce remodelling, such as shear stress, angiotensin II, oxidised low-density lipoprotein, or apoptosis, on endothelial cells are mediated by miRs. The endothelial cell-specific miR-126, for example, is transferred in microvesicles from apoptotic endothelial cells and plays a protective role in atherogenesis. The inflammatory response of the innate immune system, especially through macrophages, promotes arterial remodelling. miR-155 induces the expression of inflammatory cytokines, whereas miR-146a and miR-147 are involved in the resolution phase of inflammation. However, in vivo data on the role of miRs in vascular remodelling are still scarce, which are required to test the therapeutic potential of the available, highly effective miR inhibitors.

Development of a probucol-releasing antithrombogenic drug eluting stent

The success of drug eluting stents (DESs) has been challenged by the manifestation of late stent thrombosis after DES implantation. The incomplete regeneration of the endothelial layer poststenting triggers adverse signaling processes precipitating in thrombosis. Various approaches have been attempted to prevent thrombosis, including the delivery of biological agents, such as estradiol, that promote endothelialization, and the use of natural polymers as coating materials. The underlying challenge has been the inability to release the biological agent in synchronization with the temporal sequence of vascular wound healing in vivo. The natural healing process of the endothelium after an injury starts after a week and may take up to a month in humans. This article presents a novel DES formulation using a hemocompatible polyurethane (PU) matrix to sustain the release of probucol (PB), an endothelial agonist, by exploiting the greater difference in the solubility parameters of PB and PU. This results in the formation of crystalline PB aggregates retarding drug release from PU. The physicochemical properties of PB in PU were confirmed using differential scanning calorimetry and X-ray diffraction. Drug-polymer compatibility was examined using infrared spectral analysis. Also, in vitro studies using primary human aortic endothelial cells resulted in the selection of 5% w/w PB as the optimal dose, to be further tested in vitro and in vivo. This work develops and tests a promising new DES formulation to enable faster endothelial cell proliferation poststenting, potentially minimizing the incidence and severity of thrombotic events after DES implantation.

MicroRNA-27a/b controls endothelial cell repulsion and angiogenesis by targeting semaphorin 6A

MicroRNAs (miRs) are small RNAs that regulate gene expression at the posttranscriptional level. miR-27 is expressed in endothelial cells, but the specific functions of miR-27b and its family member miR-27a are largely unknown. Here we demonstrate that overexpression of miR-27a and miR-27b significantly increased endothelial cell sprouting. Inhibition of both miR-27a and miR-27b impaired endothelial cell sprout formation and induced endothelial cell repulsion in vitro. In vivo, inhibition of miR-27a/b decreased the number of perfused vessels in Matrigel plugs and impaired embryonic vessel formation in zebrafish. Mechanistically, miR-27 regulated the expression of the angiogenesis inhibitor semaphorin 6A (SEMA6A) in vitro and in vivo and targeted the 3′-untranslated region of SEMA6A. Silencing of SEMA6A partially reversed the inhibition of endothelial cell sprouting and abrogated the repulsion of endothelial cells mediated by miR-27a/b inhibition, indicating that SEMA6A is a functionally relevant miR-27 downstream target regulating endothelial cell repulsion. In summary, we show that miR-27a/b promotes angiogenesis by targeting the angiogenesis inhibitor SEMA6A, which controls repulsion of neighboring endothelial cells.

Circulating MicroRNAs

In the past few years, the crucial role of different micro-RNAs (miRNAs) in the cardiovascular system has been widely recognized. Recently, it was discovered that extracellular miRNAs circulate in the bloodstream and that such circulating miRNAs are remarkably stable. This has raised the possibility that miRNAs may be probed in the circulation and can serve as novel diagnostic markers. Although the precise cellular release mechanisms of miRNAs remain largely unknown, the first studies revealed that these circulating miRNAs may be delivered to recipient cells, where they can regulate translation of target genes. In this review, we will discuss the nature of the stability of miRNAs that circulate in the bloodstream and discuss the available evidence regarding the possible function of these circulating miRNAs in distant cell-to-cell communication. Furthermore, we summarize and discuss the usefulness of circulating miRNAs as biomarkers for a wide range of cardiovascular diseases such as myocardial infarction, heart failure, atherosclerosis, hypertension, and type 2 diabetes mellitus.

Exercise Training Prevents the Microvascular Rarefaction in Hypertension Balancing Angiogenic and Apoptotic Factors

Aerobic exercise training (ET) lowers hypertension and improves patient outcomes in cardiovascular disease. The mechanisms of these effects are largely unknown. We hypothesized that ET modulates microRNAs (miRNAs) involved in vascularization. miRNA-16 regulates the expression of vascular endothelial growth factor and antiapoptotic protein Bcl-2. miRNA-21 targets Bcl-2. miRNA-126 functions by repressing regulators of the vascular endothelial growth factor pathway. We investigated whether miRNA-16, -21 and -126 are modulated in hypertension and by ET. Twelve-week–old male spontaneously hypertensive rats (SHRs; n=14) and Wistar Kyoto (WKY; n=14) rats were assigned to 4 groups: SHRs, trained SHRs (SHR-T), Wistar Kyoto rats, and trained Wistar Kyoto rats. ET consisted of 10 weeks of swimming. ET reduced blood pressure and heart rate in SHR-Ts. ET repaired the slow-to-fast fiber type transition in soleus muscle and the capillary rarefaction in SHR-Ts. Soleus miRNA-16 and -21 levels increased in SHRs paralleled with a decrease of 48% and 25% in vascular endothelial growth factor and Bcl-2 protein levels, respectively. Hypertension increased Bad and decreased Bcl-x and endothelial NO synthase levels and lowered p-Bad ser112 :Bad ratio. ET in SHR-Ts reduced miRNA-16 and -21 levels and elevated vascular endothelial growth factor and Bcl-2 levels. ET restored soleus endothelial NO synthase levels plus proapoptotic and antiapoptotic mediators in SHR-Ts, indicating that the balance between angiogenic and apoptotic factors may prevent microvascular abnormalities in hypertension. miRNA-126 levels were reduced in SHRs with an increase of 51% in phosphoinositol-3 kinase regulatory subunit 2 expression but normalized in SHR-Ts. Our data show that ET promoted peripheral revascularization in hypertension, which could be associated with regulation of select miRNAs, suggesting a mechanism for its potential therapeutic application in vascular diseases.