Cutting edge: TNF-induced microRNAs regulate TNF-induced expression of E-selectin and intercellular adhesion molecule-1 on human endothelial cells: feedback control of inflammation

Therapeutic gene targeting approaches for the treatment of dyslipidemias and atherosclerosis

PURPOSE OF REVIEW

Despite improved therapies, cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Therefore, new therapeutic approaches are still needed. In the gene therapy field, RNA interference (RNAi) and regulation of microRNAs (miRNAs) have gained a lot of attention in addition to traditional overexpression based strategies. Here, recent findings in therapeutic gene silencing and modulation of small RNA expression related to atherogenesis and dyslipidemia are summarized.

RECENT FINDINGS

Novel gene therapy approaches for the treatment of hyperlipidemia have been addressed. Antisense oligonucleotide and RNAi-based therapies against apolipoprotein B100 and proprotein convertase subtilisin/kexin type 9 have shown already efficacy in preclinical and clinical trials. In addition, several miRNAs dysregulated in atherosclerotic lesions and regulating cholesterol homeostasis have been found, which may represent novel targets for future therapies.

SUMMARY

New therapies for lowering lipid levels are now being tested in clinical trials, and both antisense oligonucleotide and RNAi-based therapies have shown promising results in lowering cholesterol levels. However, the modulation of inflammatory component in atherosclerosis by gene therapy and targeting of the effects to plaques are still difficult challenges.

Control of cholesterol metabolism and plasma high-density lipoprotein levels by microRNA-144

RATIONALE

Foam cell formation because of excessive accumulation of cholesterol by macrophages is a pathological hallmark of atherosclerosis, the major cause of morbidity and mortality in Western societies. Liver X nuclear receptors (LXRs) regulate the expression of the adenosine triphosphate-binding cassette (ABC) transporters, including adenosine triphosphate-binding cassette transporter A1 (ABCA1) and adenosine triphosphate-binding cassette transporter G1 (ABCG1). ABCA1 and ABCG1 facilitate the efflux of cholesterol from macrophages and regulate high-density lipoprotein (HDL) biogenesis. Increasing evidence supports the role of microRNA (miRNAs) in regulating cholesterol metabolism through ABC transporters.

OBJECTIVE

We aimed to identify novel miRNAs that regulate cholesterol metabolism in macrophages stimulated with LXR agonists.

METHODS AND RESULTS

To map the miRNA expression signature of macrophages stimulated with LXR agonists, we performed an miRNA profiling microarray analysis in primary mouse peritoneal macrophages stimulated with LXR ligands. We report that LXR ligands increase miR-144 expression in macrophages and mouse livers. Overexpression of miR-144 reduces ABCA1 expression and attenuates cholesterol efflux to apolipoproteinA1 in macrophages. Delivery of miR-144 oligonucleotides to mice attenuates ABCA1 expression in the liver, reducing HDL levels. Conversely, silencing of miR-144 in mice increases the expression of ABCA1 and plasma HDL levels. Thus, miR-144 seems to regulate both macrophage cholesterol efflux and HDL biogenesis in the liver.

CONCLUSIONS

miR-144 regulates cholesterol metabolism via suppressing ABCA1 expression and modulation of miRNAs may represent a potential therapeutical intervention for treating dyslipidemia and atherosclerotic vascular disease.

Non-Coding RNAs as Potential Neuroprotectants against Ischemic Brain Injury

Over the past decade, scientific discoveries have highlighted new roles for a unique class of non-coding RNAs. Transcribed from the genome, these non-coding RNAs have been implicated in determining the biological complexity seen in mammals by acting as transcriptional and translational regulators. Non-coding RNAs, which can be sub-classified into long non-coding RNAs, microRNAs, PIWI-interacting RNAs and several others, are widely expressed in the nervous system with roles in neurogenesis, development and maintenance of the neuronal phenotype. Perturbations of these non-coding transcripts have been observed in ischemic preconditioning as well as ischemic brain injury with characterization of the mechanisms by which they confer toxicity. Their dysregulation may also confer pathogenic conditions in neurovascular diseases. A better understanding of their expression patterns and functions has uncovered the potential use of these riboregulators as neuroprotectants to antagonize the detrimental molecular events taking place upon ischemic-reperfusion injury. In this review, we discuss the various roles of non-coding RNAs in brain development and their mechanisms of gene regulation in relation to ischemic brain injury. We will also address the future directions and open questions for identifying promising non-coding RNAs that could eventually serve as potential neuroprotectants against ischemic brain injury.

Micro-RNAs in inflammatory diseases and as a link between inflammation and cancer

OBJECTIVE

The objective of this review is to examine the role of miRNA in various inflammatory diseases and in inflammatory diseases progressing to cancer.

INTRODUCTION

MicroRNAs are small, conserved, non-coding RNA molecules which are present in most of the eukaryotes. miRNA have been reported to play a major role in the physiological control of gene expression and in the pathogenesis of various diseases. They regulate the gene expression mainly at the post-transcriptional level. miRNA expression profile is reported to be altered in various inflammatory diseases and subsequently affects the expression of genes, which is important in disease pathogenesis.

METHODS

A Pubmed database search was performed for studies related to miRNA studies in inflammatory disease, cancer and in inflammatory diseases progressing to cancer.

CONCLUSION

The evidence shows very important role of miRNA in inflammatory diseases. Few miRNAs involved in common inflammatory process and suggest miRNA as a link between inflammation and cancer. Future research should be directed to use miRNA therapeutically to target common inflammatory pathway and to develop miRNA as biomarker to detect development of cancer at early stages.

MicroRNAs and Cardiovascular Disease

MicroRNAs (miRNAs) regulate gene expression by binding to their targets and promoting RNA degradation and/or inhibiting protein translation. In recent years, miRNAs have revolutionized our understanding of gene regulatory networks, providing new prospective tools to manage disease. Atherosclerosis and other cardiovascular diseases are a leading cause of disability and death in the US and in other western populations and pose an enormous burden on our healthcare system. Altered lipid homeostasis in liver or in the artery wall, and disruption of endothelial and smooth muscle cell function have been shown to contribute to the onset and progression of cardiovascular disease. This review focuses on recent advances in the field of vascular biology- and lipid metabolism-related miRNomics.

The not-so-neutral role of microRNAs in neutrophil biology

The role of microRNAs (miRNAs) as fine-tuners of gene expression is now well established in most aspects of cellular biology. Critically, it is becoming apparent that characterization of miRNA regulation could further the understanding of elusive cellular processes. Here, I briefly review the current literature assessing the role of miRNAs in the modulation of neutrophil biology and discuss how the definition of such miRNA regulation could help in the better understanding of neutrophil function.

MiR-17-3p inhibits angiogenesis by downregulating flk-1 in the cell growth signal pathway

MicroRNAs (miRs) are endogenously expressed small noncoding RNAs that regulate gene expression at the posttranscriptional level. Previous works indicated that the miR-17-92 cluster could regulate endothelial cell (EC) functions involved in angiogenesis. miR-17-3p, a component of the miR-17-92 cluster, could control the angiogenic activity of human umbilical vein ECs in a cell-autonomous manner in vitro. A 21-bp fragment from the Flk-1 3'-untranslated region containing miR-17-3p targeting sites was required for the rapid downregulation of Flk-1 expression by in silico and experimental analysis. Subsequently, the downstream cell growth pathway was inhibited by forced upregulation of miR-17-3p. Based on these data, we conclude that miR-17-3p is a negative regulator of the angiogenic phenotype of ECs through its ability to modulate the expression of Flk-1, which is implicated in the pleiotropic effects of miR-17-92 in angiogenesis.

MicroRNA-31 is overexpressed in psoriasis and modulates inflammatory cytokine and chemokine production in keratinocytes via targeting serine/threonine kinase 40

Psoriasis is characterized by a specific microRNA expression profile, distinct from that of healthy skin. MiR-31 is one of the most highly overexpressed microRNAs in psoriasis skin; however, its biological role in the disease has not been studied. In this study, we show that miR-31 is markedly overexpressed in psoriasis keratinocytes. Specific inhibition of miR-31 suppressed NF-κB-driven promoter luciferase activity and the basal and TNF-α-induced production of IL-1β, CXCL1/growth-related oncogene-α, CXCL5/epithelial-derived neutrophil-activating peptide 78, and CXCL8/IL-8 in human primary keratinocytes. Moreover, interference with endogenous miR-31 decreased the ability of keratinocytes to activate endothelial cells and attract leukocytes. By microarray expression profiling, we identified genes regulated by miR-31 in keratinocytes. Among these genes, we identified serine/threonine kinase 40 (STK40), a negative regulator of NF-κB signaling, as a direct target for miR-31. Silencing of STK40 rescued the suppressive effect of miR-31 inhibition on cytokine/chemokine expression, indicating that miR-31 regulates cytokine/chemokine expression via targeting STK40 in keratinocytes. Finally, we demonstrated that TGF-β1, a cytokine highly expressed in psoriasis epidermis, upregulated miR-31 expression in keratinocytes in vitro and in vivo. Collectively, our findings suggest that overexpression of miR-31 contributes to skin inflammation in psoriasis lesions by regulating the production of inflammatory mediators and leukocyte chemotaxis to the skin. Our data indicate that inhibition of miR-31 may be a potential therapeutic option in psoriasis.

Epigenetic mechanisms in the pathogenesis of diabetic foot ulcers

The incidence of diabetes mellitus, a chronic metabolic disease associated with both predisposing genetic and environmental factors, is increasing globally. As a result, it is expected that there will also be an increasing incidence of diabetic complications which arise as a result of poor glycemic control. Complications include cardiovascular diseases, nephropathy, retinopathy and diabetic foot ulcers. The findings of several major clinical trials have identified that diabetic complications may arise even after many years of proper glycemic control. This has led to the concept of persistent epigenetic changes. Various epigenetic mechanisms have been identified as important contributors to the pathogenesis of diabetes and diabetic complications. The aim of this review is to provide an overview of the pathobiology of type 2 diabetes with an emphasis on complications, particularly diabetic foot ulcers. An overview of epigenetic mechanisms is provided and the focus is on the emerging evidence for aberrant epigenetic mechanisms in diabetic foot ulcers.

TNFα signals through specialized factories where responsive coding and miRNA genes are transcribed

Tumour necrosis factor alpha (TNFα) is a potent cytokine that signals through nuclear factor kappa B (NFκB) to activate a subset of human genes. It is usually assumed that this involves RNA polymerases transcribing responsive genes wherever they might be in the nucleus. Using primary human endothelial cells, variants of chromosome conformation capture (including 4C and chromatin interaction analysis with paired-end tag sequencing), and fluorescence in situ hybridization to detect single nascent transcripts, we show that TNFα induces responsive genes to congregate in discrete 'NFκB factories'. Some factories further specialize in transcribing responsive genes encoding micro-RNAs that target downregulated mRNAs. We expect all signalling pathways to contain this extra leg, where responding genes are transcribed in analogous specialized factories.

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.

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.

IRF-1 and miRNA126 modulate VCAM-1 expression in response to a high-fat meal

RATIONALE

A high-fat diet accompanied by hypertriglyceridemia increases an individual's risk for development of atherosclerosis. An early event in this process is monocyte recruitment through binding to vascular cell adhesion molecule 1 (VCAM-1) upregulated on inflamed arterial endothelium. Diets high in polyunsaturated fatty acids (PUFAs) may provide athero-protection by ameliorating this effect.

OBJECTIVE

We investigated the acute regulation of VCAM-1 expression in human aortic endothelial cells (HAEC) in response to triglyceride-rich lipoproteins (TGRL) isolated from subjects after consumption of a high-fat meal.

METHODS AND RESULTS

Postprandial TGRL isolated from 38 subjects were categorized as proatherogenic or antiatherogenic according to their capacity to alter the inflammatory response of HAEC. Proatherogenic TGRL increased expression of VCAM-1, intercellular adhesion molecule 1 (ICAM-1), and E-selectin by ≈20% compared with stimulation with tumor necrosis factor-α alone, whereas antiatherogenic TGRL decreased VCAM-1 expression by ≈20% while still upregulating ICAM-1. The relative atherogenicity of TGRL positively correlated with particle density of TG, apolipoprotein (Apo)CIII, ApoE, and cholesterol. Ω3-PUFA mimicked the effect of antiatherogenic TGRL by downregulating VCAM-1 expression. TGRL exerted this differential regulation of VCAM-1 by reciprocally modulating expression and activity of the transcription factor interferon regulatory factor 1 (IRF-1) and expression of microRNA 126 (miR-126). Overexpression or silencing of IRF-1 or miR-126 expression recapitulated the proatherogenic or antiatherogenic regulation of VCAM-1.

CONCLUSIONS

In response to a high-fat meal, TGRL bias the inflammatory response of endothelium via transcriptional and posttranscriptional editing of VCAM-1. Subjects with an anti-inflammatory response to a meal produced TGRL that was enriched in nonesterified fatty acids, decreased IRF-1 expression, increased miR-126 activity, and diminished monocyte arrest.

Peripheral blood microRNAs: A novel tool for diagnosing disease?

Peripheral blood microRNAs (miRNAs) are endogenous, noncoding small RNAs present in blood. Because of their size, abundance, tissue specificity, and relative stability in peripheral circulation, they offer great promise of becoming a novel noninvasive biomarker. However, the mechanism by which they are secreted, their biological function, and the reason for the existence of extracellular miRNAs are largely unclear. This article describes advances in the study of the mechanism of origin and biological function of extracellular miRNAs along with approaches adopted by research and questions that remain. This work also discusses the potential for peripheral blood miRNAs to serve as a diagnostic tool.

miRNA in wound inflammation and angiogenesis

Chronic wounds represent a rising health and economic burden to our society. Emerging studies indicate that miRNAs play a key role in regulating several hubs that orchestrate the wound inflammation and angiogenesis processes. Of interest to wound inflammation are the regulatory loops where inflammatory mediators elicited following injury are regulated by miRNAs, as well as regulate miRNA expression. Adequate angiogenesis is a key determinant of success in ischemic wound repair. Hypoxia and cellular redox state are among the key factors that drive wound angiogenesis. We provided first evidence demonstrating that miRNAs regulate cellular redox environment via a NADPH oxidase-dependent mechanism in human microvascular endothelial cells (HMECs). We further demonstrated that hypoxia-sensitive miR-200b is involved in induction of angiogenesis by directly targeting Ets-1 in HMECs. These studies point toward a potential role of miRNA in wound angiogenesis. miRNA-based therapeutics represent one of the major commercial hot spots in today's biotechnology market space. Understanding the significance of miRs in wound inflammation and angiogenesis may help design therapeutic strategies for management of chronic nonhealing wounds.

Chromatin state and microRNA determine different gene expression dynamics responsive to TNF stimulation

Gene expression is a dynamic process, and what factors influence gene expression changes upon external stimulus have not been clearly understood. We studied gene expression profiles in human umbilical vein endothelial cells (HUVEC) after the Tumor Necrosis Factor (TNF) stimulus, and found that: the promoters of fast-response up-regulated genes were enriched with several "active" chromatin markers like H3K27ac and H3K4me3, and also preferentially bound by Pol II and c-Myc; the core-promoter regions of slow-response up-regulated genes were frequently occupied by nucleosomes; down-regulated genes were more intensively regulated by microRNAs. Moreover, the Gene Ontology and motif analysis of the promoter regions revealed that gene clusters with different response behaviors had different functions and were regulated by different sets of transcription factors. Our observations suggested that the different gene expression patterns upon external stimulus were regulated by a combination of multi-layer regulators.

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.

Taming endothelial activation with a microRNA

Inflammation plays an essential role in vascular pathologies, including those associated with sepsis and atherosclerosis. Identifying negative regulators of inflammatory signaling pathways may provide novel therapeutic targets for these diseases. In this issue of the JCI, Sun et al. show that in endothelial cells, microRNA-18 1b (miR-18 1b) plays a vital role in controlling inflammation by targeting importin-α3, a regulator of NF-κB nuclear import. These findings provide compelling evidence that modulation of microRNAs may be a useful therapeutic approach for inflammatory vascular diseases.

MicroRNA-181b regulates NF-κB-mediated vascular inflammation

EC activation and dysfunction have been linked to a variety of vascular inflammatory disease states. The function of microRNAs (miRNAs) in vascular EC activation and inflammation remains poorly understood. Herein, we report that microRNA-181b (miR-181b) serves as a potent regulator of downstream NF-κB signaling in the vascular endothelium by targeting importin-α3, a protein that is required for nuclear translocation of NF-κB. Overexpression of miR-181b inhibited importin-α3 expression and an enriched set of NF-κB-responsive genes such as adhesion molecules VCAM-1 and E-selectin in ECs in vitro and in vivo. In addition, treatment of mice with proinflammatory stimuli reduced miR-181b expression. Rescue of miR-181b levels by systemic administration of miR-181b "mimics" reduced downstream NF-κB signaling and leukocyte influx in the vascular endothelium and decreased lung injury and mortality in endotoxemic mice. In contrast, miR-181b inhibition exacerbated endotoxin-induced NF-κB activity, leukocyte influx, and lung injury. Finally, we observed that critically ill patients with sepsis had reduced levels of miR-181b compared with control intensive care unit (ICU) subjects. Collectively, these findings demonstrate that miR-181b regulates NF-κB-mediated EC activation and vascular inflammation in response to proinflammatory stimuli and that rescue of miR-181b expression could provide a new target for antiinflammatory therapy and critical illness.

miR-146a regulates mechanotransduction and pressure-induced inflammation in small airway epithelium

Mechanical ventilation generates biophysical forces, including high transmural pressures, which exacerbate lung inflammation. This study sought to determine whether microRNAs (miRNAs) respond to this mechanical force and play a role in regulating mechanically induced inflammation. Primary human small airway epithelial cells (HSAEpCs) were exposed to 12 h of oscillatory pressure and/or the proinflammatory cytokine TNF-α. Experiments were also conducted after manipulating miRNA expression and silencing the transcription factor NF-κB or toll-like receptor proteins IRAK1 and TRAF6. NF-κB activation, IL-6/IL-8/IL-1β cytokine secretion, miRNA expression, and IRAK1/TRAF6 protein levels were monitored. A total of 12 h of oscillatory pressure and TNF-α resulted in a 5- to 7-fold increase in IL-6/IL-8 cytokine secretion, and oscillatory pressure also resulted in a time-dependent increase in IL-6/IL-8/IL-1β cytokine secretion. Pressure and TNF-α also resulted in distinct patterns of miRNA expression, with miR-146a being the most deregulated miRNA. Manipulating miR-146a expression altered pressure-induced cytokine secretion. Silencing of IRAK1 or TRAF6, confirmed targets of miR-146a, resulted in a 3-fold decrease in pressure-induced cytokine secretion. Cotransfection experiments demonstrate that miR-146a's regulation of pressure-induced cytokine secretion depends on its targeting of both IRAK1 and TRAF6. MiR-146a is a mechanosensitive miRNA that is rapidly up-regulated by oscillatory pressure and plays an important role in regulating mechanically induced inflammation in lung epithelia.

miRNA in systemic lupus erythematosus

Since their recent discovery, the small noncoding RNA known as microRNAs (miRNA) have been reported to play a major role in the physiological control of gene expression and in the pathogenesis of malignant, infectious, and autoimmune disorders. In systemic lupus erythematosus (SLE), an autoimmune disease characterized by the presence of autoantibodies to multiple antigens, the role of miRNA as post-transcriptional regulators of different aspects of the disease process has recently emerged. This article reviews the pertinent literature and mechanisms of action of miRNA that have so far been associated with the pathogenesis of SLE.

Microbial pattern recognition causes distinct functional micro-RNA signatures in primary human monocytes

Micro-RNAs (miRNAs) are short, non-coding RNAs that regulate gene expression post transcriptionally. Several studies have demonstrated the relevance of miRNAs for a wide range of cellular mechanisms, however, the current knowledge on how miRNAs respond to relevant external stimuli, e.g. in disease scenarios is very limited. To generate a descriptive picture of the miRNA network associated to inflammatory responses, we quantified the levels of 330 miRNAs upon stimulation with a panel of pro-inflammatory components such as microbial pattern molecules (flagellin, diacylated lipopeptide lipopolysaccharide, muramyl dipeptide), infection with Listeria monocytogenes and TNF-α as pro-inflammatory control in primary human monocytes using real time PCR. As a result, we found distinct miRNA response clusters for each stimulus used. Additionally, we identified potential target genes of three selected miRNAs miR-129-5p, miR-146a and miR-378 which were part of PAMP-specific response clusters by transfecting THP1 monocytes with the corresponding pre- or anti-miRNAs and microfluidic PCR arrays. The miRNAs induced distinct transcriptomal signatures, e.g. overexpression of miRNA129-5p, which was selectively upregulated by the NOD2-elicitor MDP, led to an upregulation of DEFB1, IRAK1, FBXW7 and IKK γ (Nemo). Our findings on highly co-regulated clusters of miRNAs support the hypothesis that miRNAs act in functional groups. This study indicates that miRNAs play an important role in fine-tuning inflammatory mechanisms. Further investigation in the field of miRNA responses will help to understand their effects on gene expression and may close the regulatory gap between mRNA and protein expression in inflammatory diseases.

Breast cancer cell-derived matrix supports vascular morphogenesis

The extracellular matrix (ECM), important for maintaining tissue homeostasis, is abnormally expressed in mammary tumors and additionally plays a crucial role in angiogenesis. We hypothesize that breast cancer cells (BCCs) deposit ECM that supports unique patterns of vascular morphogenesis of endothelial cells (ECs). Evaluation of ECM expression revealed that a nontumorigenic cell line (MCF10A), a tumorigenic cell line (MCF7), and a metastatic cell line (MDA-MB-231) express collagens I and IV, fibronectin, and laminin, with tenascin-C limited to MCF10A and MCF7. The amount of ECM deposited by BCCs was found to be higher in MCF10A compared with MCF7 and MDA231, with all ECM differing in their gross structure but similar in mean fiber diameter. Nonetheless, deposition of ECM from BCC lines was overall difficult to detect and insufficient to support capillary-like structure (CLS) formation of ECs. Therefore, a coculture approach was undertaken in which individual BCC lines were cocultured with fibroblasts. Variation in abundance of deposited ECM, deposition of ECM proteins, such as absent collagen I deposition from MDA231-fibroblast cocultures, and fibril organization was found. Deposited ECM from fibroblasts and each coculture supported rapid CLS formation of ECs. Evaluation of capillary properties revealed that CLS grown on ECM deposited from MDA231-fibroblast cocultures possessed significantly larger lumen diameters, occupied the greatest percentage of area, expressed the highest levels of von Willebrand factor, and expressed the greatest amount of E-selectin, which was upregulated independent of exposure to TNF-α. To our knowledge, this is the first study to report tumor cell ECM-mediated differences in vascular capillary features, and thus offers the framework for future investigations interrogating the role of the tumor ECM in supporting vascular morphogenesis.

Heme oxygenase 1 is induced by miR-155 via reduced BACH1 translation in endothelial cells

Heme oxygenase 1 (HO-1) is a stress-inducible enzyme that degrades redox-active heme-producing biliverdin, carbon monoxide, and Fe(2+). It protects cells under various stress conditions and mediates anti-inflammatory and vasodilatory effects in the endothelium. The expression of HMOX1, the HO-1 gene, is highly inducible and its transcriptional regulation is complex. HMOX1 is induced by various proinflammatory stimuli via NF-κB in human endothelial cells, but functional NF-κB-binding elements have not been identified from the human gene. However, the regulation of HMOX1 by the antioxidant-response element is firmly established, with the transcription factor BACH1 serving as a repressor and Nrf2 as an enhancer. miR-155 is one of the TNFα-inducible endothelial microRNAs predicted to bind to the BACH1 mRNA. Oligonucleotides mimicking miR-155 efficiently inhibited BACH1 protein translation, resulting in a concentration-dependent increase in HMOX1 mRNA and protein expression in human umbilical vein endothelial cells. Moreover, endogenous miR-155 was upregulated by TNFα via an NF-κB-dependent mechanism with a subsequent increase in HMOX1 expression. We propose that increased HMOX1 expression in endothelial cells by TNFα results from miR-155-induced repression of BACH1 rather than direct induction of HMOX1 via NF-κB, and that miR-155 is cytoprotective during inflammation by elevating HO-1 expression in endothelial cells.

Shining a light on intestinal traffic

Inflammatory bowel disease (IBD), encompassing Crohn's disease and ulcerative colitis, is associated with enhanced leukocyte infiltration to the gut, which is directly linked to the clinical aspects of these disorders. Thus, leukocyte trafficking is a major target for IBD therapy. Past and emerging techniques to study leukocyte trafficking both in vitro and in vivo have expanded our knowledge of the leukocyte migration process and the role of inhibitors. Various strategies have been employed to target chemokine- and integrin-ligand interactions within the multistep adhesion cascade and the S1P/S1PR1 axis in leukocyte migration. Though there is an abundance of preclinical data demonstrating efficacy of leukocyte trafficking inhibitors, many have yet to be confirmed in clinical studies. Vigilance for toxicity and further research is required into this complex and emerging area of IBD therapy.

MicroRNA epigenetics: a new avenue for wound healing research

A group of small non-coding RNA molecules, termed microRNAs (miRNAs), have generated considerable interest in recent years due to their central role in a growing number of biologic processes. Serving as post-transcriptional regulators of gene expression, miRNAs have also emerged as critical factors in the pathogenesis of many diseases. As a result, they show great potential as accurate diagnostic and prognostic markers, as well as viable therapeutic targets for treating disease. It has been proposed that miRNAs play a significant role in cutaneous wound repair and that aberrant miRNA expression may result in disorganized or poor healing. Specific patterns of miRNA expression have been identified in wound healing models. miRNAs are important regulators of leucocyte function and the cytokine network, and are necessary for endothelial cell migration and capillary formation. These molecules also control proliferation and differentiation of wound-specific cells and can determine extracellular matrix composition. This article reviews the evidence for miRNA regulation of inflammation, angiogenesis, fibroblast function, keratinocyte function, and apoptosis, which are essential components for effective wound repair. The future potential for improving wound healing outcomes using miRNA-based therapies is also discussed.

MicroRNA-16 and microRNA-424 regulate cell-autonomous angiogenic functions in endothelial cells via targeting vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1

OBJECTIVE

MicroRNAs play key roles in modulating a variety of cellular processes by posttranscriptional regulation of their target genes. Vascular endothelial growth factor (VEGF), VEGF receptor-2 (VEGFR2), and fibroblast growth factor receptor-1 (FGFR1) were identified by bioinformatic approaches and subsequently validated as targets of microRNA (miR)-16 and miR-424 in endothelial cells (ECs).

METHODS AND RESULTS

Mimetics of these microRNAs reduced VEGF, VEGFR2, and FGFR1 expression, whereas specific antagonists enhanced their expression. Expression of mature miR-16 and miR-424 was upregulated on VEGF or basic fibroblast growth factor (bFGF) treatment. This upregulation was accompanied by a parallel increase in primary transcript (pri-miR)-16-1 and pri-miR-16-2 but not in pri-miR-424 levels, indicating a VEGF/bFGF-dependent transcriptional and posttranscriptional regulation of miR-16 and miR-424, respectively. Reduced expression of VEGFR2 and FGFR1 by miR-16 or miR-424 overexpression regulated VEGF and bFGF signaling through these receptors, thereby affecting the activity of downstream components of the pathways. Functionally, miR-16 or miR-424 overexpression reduced proliferation, migration, and cord formation of ECs in vitro, and lentiviral overexpression of miR-16 reduced the ability of ECs to form blood vessels in vivo.

CONCLUSION

We conclude that these miRNAs fine-tune the expression of selected endothelial angiogenic mediators in response to these growth factors. Altogether, these findings suggest that miR-16 and miR-424 play important roles in regulating cell-intrinsic angiogenic activity of ECs.

MicroRNA-31 regulated by the extracellular regulated kinase is involved in vascular smooth muscle cell growth via large tumor suppressor homolog 2

Aberrant growth of vascular smooth muscle cells (VSMCs) is a major cellular event in the pathogenesis of many proliferative vascular diseases. Recently, microRNA-31 (miR-31) has been found to play a critical role in cancer cell proliferation. However, the biological role of miR-31 in VSMC growth and the mechanisms involved are currently unknown. In the present study, the expression of rat mature miR-31 (rno-miR-31) was determined in cultured VSMCs and in rat carotid arteries. We identified that rno-miR-31 is an abundant miRNA in VSMCs, and its expression was significantly increased in proliferative VSMCs and in vascular walls with neointimal growth. The up-regulation of rno-miR-31 in proliferative VSMCs was inhibited by the inhibitor of mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK). By both gain-of-function and loss-of-function approaches, we demonstrated that rno-miR-31 had a proproliferative effect on VSMCs. We further identified that LATS2 (large tumor suppressor homolog 2) is a downstream target gene product of rno-miR-31 that is involved in rno-miR-31-mediated effect on VSMC proliferation. The LATS2 as a target gene protein of rno-miR-31 is verified in vivo in balloon-injured rat carotid arteries. The results suggest that MAPK/ERK/miR-31/LATS2 may represent a novel signaling pathway in VSMC growth. miR-31 is able to enhance VSMC proliferation via its downstream target gene product, LATS2.

Cholinesterase-Targeting microRNAs Identified in silico Affect Specific Biological Processes

MicroRNAs (miRs) have emerged as important gene silencers affecting many target mRNAs. Here, we report the identification of 244 miRs that target the 3′-untranslated regions of different cholinesterase transcripts: 116 for butyrylcholinesterase (BChE), 47 for the synaptic acetylcholinesterase (AChE-S) splice variant, and 81 for the normally rare splice variant AChE-R. Of these, 11 and 6 miRs target both AChE-S and AChE-R, and AChE-R and BChE transcripts, respectively. BChE and AChE-S showed no overlapping miRs, attesting to their distinct modes of miR regulation. Generally, miRs can suppress a number of targets; thereby controlling an entire battery of functions. To evaluate the importance of the cholinesterase-targeted miRs in other specific biological processes we searched for their other experimentally validated target transcripts and analyzed the gene ontology enriched biological processes these transcripts are involved in. Interestingly, a number of the resulting categories are also related to cholinesterases. They include, for BChE, response to glucocorticoid stimulus, and for AChE, response to wounding and two child terms of neuron development: regulation of axonogenesis and regulation of dendrite morphogenesis. Importantly, all of the AChE-targeting miRs found to be related to these selected processes were directed against the normally rare AChE-R splice variant, with three of them, including the neurogenesis regulator miR-132, also directed against AChE-S. Our findings point at the AChE-R splice variant as particularly susceptible to miR regulation, highlight those biological functions of cholinesterases that are likely to be subject to miR post-transcriptional control, demonstrate the selectivity of miRs in regulating specific biological processes, and open new venues for targeted interference with these specific processes.

Role of microRNAs in endothelial inflammation and senescence

The functionality of endothelial cells is fundamental for the homoeostasis of the vascular system. Increasing evidence shows that endothelial inflammation and senescence contribute greatly to multiple vascular diseases including atherosclerosis. However, little is known regarding the complex upstream regulators of gene expression and translation involved in these responses. MicroRNAs (miRNAs) have emerged as a novel class of endogenous, small, non-coding RNAs that negatively regulate over 30% of genes in a cell via degradation or translational inhibition of their target mRNAs. During the past few years, miRNAs have emerged as key regulators for endothelial biology and function. Endothelial inflammation is critically regulated by miRNAs such as miR-126 and miR-10a in vitro and in vivo. Endothelial aging is additionally controlled by miR-217 and miR-34a. In this review, we summarize the role of miRNAs and their target genes in endothelial inflammation and senescence, and discuss their applicability as drug targets.

Roles for microRNAs in the regulation of cell adhesion molecules

Maintenance of appropriate cell adhesion is crucial for normal cellular and organismal homeostasis. Certain microRNAs have recently been found capable of regulating molecules that oversee the fundamental cell biological events that drive cellular adhesion. It is now apparent that microRNAs play crucial roles in the great majority of biochemical pathways that contribute to normal cell adhesion. In this Commentary, we describe the latest advances within this still-emerging field, and highlight connections between the deregulation of microRNAs that affect cell-adhesion-associated molecules and the pathogenesis of several human diseases. Current evidence suggests that the ability of certain microRNAs--notably miR-17, miR-29, miR-31, miR-124 and miR-200--to pleiotropically regulate multiple molecular components of the cell adhesion machinery endows these microRNAs with the capacity to function as key modulators of adhesion-associated processes. This, in turn, holds important implications for our understanding of both the basic biology of cell adhesion and the etiology of multiple pathological conditions.

MicroRNA regulation of innate immune responses in epithelial cells

Mucosal surface epithelial cells are equipped with several defense mechanisms that guard against pathogens. Recent studies indicate that microRNAs (miRNAs) mediate post-transcriptional gene suppression and may be a critical component of the complex regulatory networks in epithelial immune responses. Transcription of miRNA genes in epithelial cells can be elaborately controlled through pathogen recognition receptors, such as Toll-like receptors (TLRs), and associated nuclear factor kappaB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways, and ultimately nuclear transcription factor associated-transactivation and transrepression. Activation of these intracellular signaling pathways may also modulate the process of miRNA maturation. Functionally, miRNAs may modulate epithelial immune responses at every step of the innate immune network, including production and release of cytokines/chemokines, expression of adhesion and costimulatory molecules, shuttling of miRNAs through release of exosomes and feedback regulation of immune homeostasis. Therefore, miRNAs act as critical regulators to the fine-tuning of epithelial immune responses.

The manipulation of miRNA-gene regulatory networks by KSHV induces endothelial cell motility

miRNAs have emerged as master regulators of cancer-related events. miRNA dysregulation also occurs in Kaposi sarcoma (KS). Exploring the roles of KS-associated miRNAs should help to identify novel angiogenesis and lymphangiogenesis pathways. In the present study, we show that Kaposi sarcoma-associated herpesvirus (KSHV), the etiological agent of KS, induces global miRNA changes in lymphatic endothelial cells (LECs). Specifically, the miR-221/miR-222 cluster is down-regulated, whereas miR-31 is up-regulated. Both latent nuclear antigen (LANA) and Kaposin B repress the expression of the miR-221/miR-222 cluster, which results in an increase of endothelial cell (EC) migration. In contrast, miR-31 stimulates EC migration, so depletion of miR-31 in KSHV-transformed ECs reduces cell motility. Analysis of the putative miRNA targets among KSHV-affected genes showed that ETS2 and ETS1 are the downstream targets of miR-221 and miR-222, respectively. FAT4 is one of the direct targets of miR-31. Overexpression of ETS1 or ETS2 alone is sufficient to induce EC migration, whereas a reduction in FAT4 enhances EC motility. Our results show that KSHV regulates multiple miRNA-mRNA networks to enhance EC motility, which eventually contributes to KS progression by promoting the spread of malignant KS progenitor cells. Targeting KSHV-regulated miRNAs or genes might allow the development of novel therapeutic strategies that induce angiogenesis or allow the treatment of pathogenic (lymph)angiogenesis.

MicroRNA-21 targets peroxisome proliferators-activated receptor-alpha in an autoregulatory loop to modulate flow-induced endothelial inflammation

Adhesion of circulating monocytes to vascular endothelial cells (ECs) is a critical event leading to vascular inflammation and, hence, development of atherosclerosis. MicroRNAs (miRs) are a class of endogenous, highly conserved, noncoding small RNAs that play important roles in regulating gene expression and cellular function, as well as pathogenesis of atherosclerosis. Here, we showed that oscillatory shear stress (OSS) induces the expression of miR-21 at the transcriptional level in cultured human umbilical vein ECs via an increased binding of c-Jun, which is a component of transcription factor activator protein-1 (AP-1), to the promoter region of miR-21. OSS induction of miR-21 inhibited the translation, but not transcription, of peroxisome proliferators-activated receptor-α (PPARα) by 3'-UTR targeting. Overexpression of miR-21 up-regulated AP-1 activation, which was attenuated by exogenous expression of PPARα. OSS and overexpression of miR-21 enhanced the expression of adhesion molecules vascular cell adhesion molecule-1 and monocyte chemotactic protein-1 and the consequential adhesion of monocytes to ECs. Overexpression of PPARα significantly attenuated the AP-1-mediated miR-21 expression. These results demonstrate a unique mechanism by which OSS induces AP-1-dependent miR-21 expression, which directly targets PPARα to inhibit its expression, thereby allowing activation of AP-1 and the promotion of monocyte adhesion. Our findings suggest the presence of a positive feedback loop that enables the sustained induction of miR-21, thus contributing to the proinflammatory responses of vascular endothelium under OSS.

Rupture of vulnerable atherosclerotic plaques: microRNAs conducting the orchestra?

MicroRNAs (miRNAs) are tiny, endogenous nucleotides that bind to mRNA and induce translation repression within metazoan cells. Since their discovery in 1993 in Caenorhabditis elegans and the demonstration of miRNAs in Homo sapiens in 2000, research has been fruitful in deciphering the role of these nucleotides in development, tissue homeostasis, and pathologic processes. In humans, around 700 human miRNA nucleotides have been verified, which interfere with 30% of all genes. Recently, the role of miRNA in cardiovascular research gained attention and the involvement of miRNAs in several cardiovascular diseases has been identified. In this review, we focus on the role of miRNAs in atherosclerosis and in particular on the potential role of miRNAs in the development of vulnerable atherosclerotic plaques. The role of miRNA in the main characteristics of these plaques, inflammation, angiogenesis, and apoptosis will be discussed. Finally, the future perspectives and miRNA-based diagnostic and therapeutic potentials will be highlighted.

Activation of TNFR1 ectodomain shedding by mitochondrial Ca2+ determines the severity of inflammation in mouse lung microvessels

Shedding of the extracellular domain of cytokine receptors allows the diffusion of soluble receptors into the extracellular space; these then bind and neutralize their cytokine ligands, thus dampening inflammatory responses. The molecular mechanisms that control this process, and the extent to which shedding regulates cytokine-induced microvascular inflammation, are not well defined. Here, we used real-time confocal microscopy of mouse lung microvascular endothelium to demonstrate that mitochondria are key regulators of this process. The proinflammatory cytokine soluble TNF-α (sTNF-α) increased mitochondrial Ca2+, and the purinergic receptor P2Y2 prolonged the response. Concomitantly, the proinflammatory receptor TNF-α receptor-1 (TNFR1) was shed from the endothelial surface. Inhibiting the mitochondrial Ca2+ increase blocked the shedding and augmented inflammation, as denoted by increases in endothelial expression of the leukocyte adhesion receptor E-selectin and in microvascular leukocyte recruitment. The shedding was also blocked in microvessels after knockdown of a complex III component and after mitochondria-targeted catalase overexpression. Endothelial deletion of the TNF-α converting enzyme (TACE) prevented the TNF-α receptor shedding response, which suggests that exposure of microvascular endothelium to sTNF-α induced a Ca2+-dependent increase of mitochondrial H2O2 that caused TNFR1 shedding through TACE activation. These findings provide what we believe to be the first evidence that endothelial mitochondria regulate TNFR1 shedding and thereby determine the severity of sTNF-α-induced microvascular inflammation.

Differential microRNA expression in experimental cerebral and noncerebral malaria

MicroRNAs (miRNAs) are posttranscriptional regulatory molecules that have been implicated in the regulation of immune responses, but their role in the immune response to Plasmodium infection is unknown. We studied the expression of selected miRNAs following infection of CBA mice with Plasmodium berghei ANKA (PbA), which causes cerebral malaria (CM), or Plasmodium berghei K173 (PbK), which causes severe malaria but without cerebral complications, termed non-CM. The differential expression profiles of selected miRNAs (let-7i, miR-27a, miR-150, miR-126, miR-210, and miR-155) were analyzed in mouse brain and heart tissue by quantitative reverse transcription-PCR (qRT-PCR). We identified three miRNAs that were differentially expressed in the brain of PbA-infected CBA mice: let7i, miR-27a, and miR-150. In contrast, no miRNA changes were detected in the heart, an organ with no known pathology during acute malaria. To investigate the involvement of let-7i, miR-27a, and miR-150 in CM-resistant mice, we assessed the expression levels in gamma interferon knockout (IFN-γ(-/-)) mice on a C57BL/6 genetic background. The expression of let-7i, miR-27a, and miR-150 was unchanged in both wild-type (WT) and IFN-γ(-/-) mice following infection. Overexpression of these three miRNAs during PbA, but not PbK, infection in WT mice may be critical for the triggering of the neurological syndrome via regulation of their potential downstream targets. Our data suggest that in the CBA mouse at least, miRNA may have a regulatory role in the pathogenesis of severe malaria.

MiRNA in innate immune responses: novel players in wound inflammation

Chronic wounds represent a major and rising socioeconomic threat affecting over 6.5 million people in the United States costing in excess of US $25 billion annually. Wound healing is a physiological response to injury that is conserved across tissue systems. In humans, wounding is followed by instant response aimed at hemostasis, which in turn provides the foundation for inflammatory processes that closely follow. Inflammation is helpful and a prerequisite for healing as long as it is mounted and resolved in a timely manner. Chronic inflammation derails the healing cascade resulting in impaired wound closure. Disruption of Dicer, the RNase III enzyme that generates functional miRNAs, has a major impact on the overall immune system. Emerging studies indicate that miRNAs, especially miR-21, miR-146a/b, and miR-155, play a key role in regulating several hubs that orchestrate the inflammatory process. Direct evidence from studies addressing wound inflammation being limited, the current work represents a digest of the relevant literature that is aimed at unveiling the potential significance of miRNAs in the regulation of wound inflammation. Such treatment would help establish new paradigms highlighting a central role of miRs in the understanding and management of dysregulated inflammation as noted in conjunction with chronic wounds.

MicroRNAs in inflammatory lung disease--master regulators or target practice?

MicroRNAs (miRNAs) have emerged as a class of regulatory RNAs with immense significance in numerous biological processes. When aberrantly expressed miRNAs have been shown to play a role in the pathogenesis of several disease states. Extensive research has explored miRNA involvement in the development and fate of immune cells and in both the innate and adaptive immune responses whereby strong evidence links miRNA expression to signalling pathways and receptors with critical roles in the inflammatory response such as NF-κB and the toll-like receptors, respectively. Recent studies have revealed that unique miRNA expression profiles exist in inflammatory lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis and lung cancer. Evaluation of the global expression of miRNAs provides a unique opportunity to identify important target gene sets regulating susceptibility and response to infection and treatment, and control of inflammation in chronic airway disorders. Over 800 human miRNAs have been discovered to date, however the biological function of the majority remains to be uncovered. Understanding the role that miRNAs play in the modulation of gene expression leading to sustained chronic pulmonary inflammation is important for the development of new therapies which focus on prevention of disease progression rather than symptom relief. Here we discuss the current understanding of miRNA involvement in innate immunity, specifically in LPS/TLR4 signalling and in the progression of the chronic inflammatory lung diseases cystic fibrosis, COPD and asthma. miRNA in lung cancer and IPF are also reviewed.

New developments on the TNFα-mediated signalling pathways

TNFα (tumour necrosis factor α) is an extensively studied pleiotropic cytokine associated with the pathogenesis of a variety of inflammatory diseases. It elicits a wide spectrum of cellular responses which mediates and regulates inflammation, immune response, cell survival, proliferation and apoptosis. TNFα initiates its responses by binding to its receptors. TNFα-induced effector responses are mediated by the actions and interactions among the various intracellular signalling mediators in the cell. TNFα induces both survival and apoptotic signal in a TRADD (TNF receptor-associated DD)-dependent and -independent way. The signals are further transduced via a variety of signalling mediators, including caspases, MAPKs (mitogen-activated protein kinases), phospholipid mediators and miRNA/miR (microRNA), whose roles in specific functional responses is not fully understood. Elucidating the complexity and cross talks among signalling mediators involved in the TNFα-mediated responses will certainly aid in the identification of molecular targets, which can potentially lead to the development of novel therapeutics to treat TNFα-associated disorders and in dampening inflammation.

microRNA-222 Controls Neovascularization by Regulating Signal Transducer and Activator of Transcription 5A Expression

Objective— Inflammatory stimuli released into atherosclerotic plaque microenvironment regulate vessel formation by modulating gene expression and translation. microRNAs are a class of short noncoding RNAs, acting as posttranscriptional regulators of protein-coding genes involved in various biological processes, including vascular cell biology. Among them, microRNA-221/222 (miR-221/222) seem to negatively modulate vascular remodeling by targeting different target genes. Here, we investigated their potential contribution to inflammation-mediated neovessel formation.

Methods and Results— We used quantitative real-time RT-PCR amplification to analyze expression of 7 microRNAs previously linked to vascular biology, such as miR-17-5p, miR-21, miR-126, miR-210, miR-221, miR-222, and miR-296 and found high levels of expression for all of them in quiescent endothelial cells. However, miR-126, miR-221, miR-222, and miR-296 turned out to be down-modulated in endothelial cells exposed to inflammatory stimuli. Applying a gain-of-function approach, we demonstrated that, among them, only miR-222 was involved in inflammation-mediated vascular remodeling. In addition, we identified signal transducer and activator of transcription 5A (STAT5A) as a bona fide target of miR-222 and observed that miR-222 negatively correlated with STAT5A expression in human endothelial cells from advanced neovascularized atherosclerotic lesions.

Conclusion— We identified STAT5A as a novel miR-222 target, and this finding opens up new perspectives for treatment of vascular diseases.

MicroRNA-10a regulation of proinflammatory phenotype in athero-susceptible endothelium in vivo and in vitro

A chronic proinflammatory state precedes pathological change in arterial endothelial cells located within regions of susceptibility to atherosclerosis. The potential contributions of regulatory microRNAs to this disequilibrium were investigated by artery site-specific profiling in normal adult swine. Expression of endothelial microRNA10a (miR-10a) was lower in the athero-susceptible regions of the inner aortic arch and aorto-renal branches than elsewhere. Expression of Homeobox A1 (HOXA1), a known miR-10a target, was up-regulated in the same locations. Endothelial transcriptome microarray analysis of miR-10a knockdown in cultured human aortic endothelial cells (HAEC) identified IkappaB/NF-kappaB-mediated inflammation as the top category of up-regulated biological processes. Phosphorylation of IkappaBalpha, a prerequisite for IkappaBalpha proteolysis and NF-kappaB activation, was significantly up-regulated in miR-10a knockdown HAEC and was accompanied by increased nuclear expression of NF-kappaB p65. The inflammatory biomarkers monocyte chemotactic protein 1 (MCP-1), IL-6, IL-8, vascular cell adhesion molecule 1 (VCAM-1), and E-selectin were elevated following miR-10a knockdown. Conversely, knockin of miR-10a (a conservative 25-fold increase) inhibited the basal expression of VCAM-1 and E-selectin in HAEC. Two key regulators of IkappaBalpha degradation--mitogen-activated kinase kinase kinase 7 (MAP3K7; TAK1) and beta-transducin repeat-containing gene (betaTRC)--contain a highly conserved miR-10a binding site in the 3' UTR. Both molecules were up-regulated by miR-10a knockdown and suppressed by miR-10a knockin, and evidence of direct miR-10a binding to the 3' UTR was demonstrated by luciferase assay. Comparative expression studies of endothelium located in athero-susceptible aortic arch and athero-protected descending thoracic aorta identified significantly up-regulated MAP3K7, betaTRC, phopho-IkappaBalpha, and nuclear p65 expression suggesting that the differential expression of miR-10a contributes to the regulation of proinflammatory endothelial phenotypes in athero-susceptible regions in vivo.

miR-31 functions as a negative regulator of lymphatic vascular lineage-specific differentiation in vitro and vascular development in vivo

The lymphatic vascular system maintains tissue fluid homeostasis, helps mediate afferent immune responses, and promotes cancer metastasis. To address the role microRNAs (miRNAs) play in the development and function of the lymphatic vascular system, we defined the in vitro miRNA expression profiles of primary human lymphatic endothelial cells (LECs) and blood vascular endothelial cells (BVECs) and identified four BVEC signature and two LEC signature miRNAs. Their vascular lineage-specific expression patterns were confirmed in vivo by quantitative real-time PCR and in situ hybridization. Functional characterization of the BVEC signature miRNA miR-31 identified a novel BVEC-specific posttranscriptional regulatory mechanism that inhibits the expression of lymphatic lineage-specific transcripts in vitro. We demonstrate that suppression of lymphatic differentiation is partially mediated via direct repression of PROX1, a transcription factor that functions as a master regulator of lymphatic lineage-specific differentiation. Finally, in vivo studies of Xenopus and zebrafish demonstrated that gain of miR-31 function impaired venous sprouting and lymphatic vascular development, thus highlighting the importance of miR-31 as a negative regulator of lymphatic development. Collectively, our findings identify miR-31 is a potent regulator of vascular lineage-specific differentiation and development in vertebrates.

MicroRNAs distinguish translational from transcriptional silencing during endotoxin tolerance

We reported that gene-selective formation of facultative heterochromatin silences transcription of acute inflammatory genes during endotoxin (LPS) tolerance, according to function. We discovered that reversal of the epigenetically silenced transcription restored mRNA levels but not protein synthesis. Here, we find that translation repression of tumor necrosis factor-alpha (TNFalpha) occurs independent of transcription silencing during LPS tolerance. The process required to disrupt protein synthesis followed Toll-like receptor 4 (TLR4)-dependent induction of microRNA (miR)-221, miR-579, and miR-125b, which coupled with RNA-binding proteins TTP, AUF1, and TIAR at the 3'-untranslated region to arrest protein synthesis. TTP and AUF1 proteins linked to miR-221, whereas TIAR coupled with miR-579 and miR-125b. Functional inhibition of miR-221 prevented TNFalpha mRNA degradation, and blocking miR-579 and miR-125b precluded translation arrest. The functional specificity of the TNFalpha 3'-untranslated region was demonstrated using luciferase reporter with mutations in the three putative miRNA binding sites. Post-transcriptional silencing was gene-specific, because it did not affect production of the IkappaBalpha anti-inflammatory protein. These results suggest that TLR4-dependent reprogramming of inflammatory genes is regulated at two separate and distinct levels. The first level of control is mediated by epigenetic modifications at the promoters that control transcription. The second and previously unrecognized level of control is mediated by TLR4-dependent differential expression of miRNAs that exert post-transcriptional controls. The concept of distinct regulation of transcription and translation was confirmed in murine sepsis. We conclude that transcription- and translation-repressive events combine to tightly regulate pro-inflammatory genes during LPS tolerance, a common feature of severe systemic inflammation.

Gene-specific epigenetic regulation in serious infections with systemic inflammation

Inflammation is a fundamental biologic process that is evolutionally conserved by a germ line code. The interplay between epigenetics and environment directs the code into temporally distinct inflammatory responses, which can be acute or chronic. Here, we discuss the epigenetic processes of innate immune cells during serious infections with systemic inflammation in four stages: homeostasis, incitement, evolution, and resolution. We describe feed-forward loops of serious infections with systemic inflammation that create gene-specific silent facultative heterochromatin and active euchromatin according to gene function, and speculate on the role of epigenetics in survival.