Epigenetic regulation of vascular endothelial gene expression

Dkk1 and MSX2-Wnt7b signaling reciprocally regulate the endothelial-mesenchymal transition in aortic endothelial cells

OBJECTIVE

Endothelial cells (ECs) can undergo an endothelial-mesenchymal transition with tissue fibrosis. Wnt- and Msx2-regulated signals participate in arteriosclerotic fibrosis and calcification. We studied the impact of Wnt7, Msx2, and Dkk1, a Wnt7 antagonist, on endothelial-mesenchymal transition in primary aortic ECs.

APPROACH AND RESULTS

Transduction of aortic ECs with vectors expressing Dkk1 suppressed EC differentiation and induced a mineralizing myofibroblast phenotype. Dkk1 suppressed claudin 5, PECAM, cadherin 5 (Cdh5), Tie1, and Tie2. Dkk1 converted the cuboidal cell monolayer into a spindle-shaped multilayer and inhibited EC cord formation. Myofibroblast and osteogenic markers, SM22, type I collagen, Osx, Runx2, and alkaline phosphatase, were upregulated by Dkk1 via activin-like kinase/Smad pathways. Dkk1 increased fibrotic mineralization of aortic ECs cultured under osteogenic conditions--the opposite of mesenchymal cell responses. Msx2 and Wnt7b maintained morphology and upregulated markers of differentiated ECs. Deleting EC Wnt7b with the Cdh5-Cre transgene in Wnt7b(fl/fl);LDLR(-/-) mice upregulated aortic osteogenic genes (Osx, Sox9, Runx2, and Msx2) and nuclear phospho-Smad1/5, and increased collagen and calcium accumulation.

CONCLUSIONS

Dkk1 enhances endothelial-mesenchymal transition in aortic ECs, whereas Wnt7b and Msx2 signals preserve EC phenotype. EC responses to Dkk1, Wnt7b, and Msx2 are the opposite of mesenchymal responses, coupling EC phenotypic stability with osteofibrogenic predilection during arteriosclerosis.

The epigenetic feedback loop between DNA methylation and microRNAs in fibrotic disease with an emphasis on DNA methyltransferases

Epigenetic processes play a key regulatory role in many cancers. Recently, it also has been demonstrated to participate in fibrogenesis, especially in fibrotic disease. Fibrotic disease is a pathological response to tissue injury which can occur in any organ. Mechanisms that orchestrate fibrotic disorders in different organs are amazingly generic, involving generation of activated fibroblasts and myofibroblasts by differentiation processes that require extensive alterations in gene expression. Apart from genetic and environmental factors, epigenetic modifications including a combination of microRNAs and DNA methylation are supposed as regulatory mechanisms to control myofibroblast differentiation. It has become obvious that microRNAs, which act as regulators of gene expression at a post-transcriptional level, are differentially expressed in differentiating cells and play important roles in governing DNA methyltransferases (DNMTs) which are enzymes responsible for setting up and maintaining DNA methylation patterns at specific regions of the genome. Some microRNAs targeting DNMT transcripts lead to the demethylation and transcriptional activation of numerous protein coding gene sequences, thereby contributing to gene expression. Moreover, DNMTs also have a critical role in controlling some specific microRNA expression. This cooperative action among DNMTs, microRNAs and DNA methylation indicates that DNMTs may participate in the pathogenesis of myofibroblast differentiation through silencing of certain gene transcription. In this review, we summarize the current knowledge of a potential link between microRNA expression and DNA methylation on how DNMTs work in the process of fibrogenesis.

Systems proteomics of healthy and diseased chromatin

Differences in chromatin-associated proteins allow the same genome to participate in multiple cell types and to respond to an array of stimuli in any given cell. To understand the fundamental properties of chromatin and to reveal its cell- and/or stimulus-specific behaviors, quantitative proteomics is an essential technology. This chapter details the methods for fractionation and quantitative mass spectrometric analysis of chromatin from hearts or isolated adult myocytes, detailing some of the considerations for applications to understanding heart disease. The state-of-the-art methodology for data interpretation and integration through bioinformatics is reviewed.

A mechanistic role for DNA methylation in endothelial cell (EC)-enriched gene expression: relationship with DNA replication timing

Proximal promoter DNA methylation has been shown to be important for regulating gene expression. However, its relative contribution to the cell-specific expression of endothelial cell (EC)-enriched genes has not been defined. We used methyl-DNA immunoprecipitation and bisulfite conversion to analyze the DNA methylation profile of EC-enriched genes in ECs vs nonexpressing cell types, both in vitro and in vivo. We show that prototypic EC-enriched genes exhibit functional differential patterns of DNA methylation in proximal promoter regions of most (eg, CD31, von Willebrand factor [vWF], VE-cadherin, and intercellular adhesion molecule-2), but not all (eg, VEGFR-1 and VEGFR-2), EC-enriched genes. Comparable findings were evident in cultured ECs, human blood origin ECs, and murine aortic ECs. Promoter-reporter episomal transfection assays for endothelial nitric oxide synthase, VE-cadherin, and vWF indicated functional promoter activity in cell types where the native gene was not active. Inhibition of DNA methyltransferase activity indicated important functional relevance. Importantly, profiling DNA replication timing patterns indicated that EC-enriched gene promoters with differentially methylated regions replicate early in S-phase in both expressing and nonexpressing cell types. Collectively, these studies highlight the functional importance of promoter DNA methylation in controlling vascular EC gene expression.

Epigenetics and cardiovascular disease

A commonly-assumed paradigm holds that the primary genetic determinant of cardiovascular disease resides within the DNA sequence of our genes. This paradigm can be challenged. For example, how do sequence changes in the non-coding region of the genome influence phenotype? Why are all diseases not shared between identical twins? Part of the answer lies in the fact that the environment or exogenous stimuli clearly influence disease susceptibility, but it was unclear in the past how these effects were signalled to the static DNA code. Epigenetics is providing a newer perspective on these issues. Epigenetics refers to chromatin-based mechanisms important in the regulation of gene expression that do not involve changes to the DNA sequence per se. The field can be broadly categorized into three areas: DNA base modifications (including cytosine methylation and cytosine hydroxymethylation), post-translational modifications of histone proteins, and RNA-based mechanisms that operate in the nucleus. Cardiovascular disease pathways are now being approached from the epigenetic perspective, including those associated with atherosclerosis, angiogenesis, ischemia-reperfusion damage, and the cardiovascular response to hypoxia and shear stress, among many others. With increasing interest and expanding partnerships in the field, we can expect new insights to emerge from epigenetic perspectives of cardiovascular health. This paper reviews the principles governing epigenetic regulation, discusses their presently-understood importance in cardiovascular disease, and considers the growing significance we are likely to attribute to epigenetic contributions in the future, as they provide new mechanistic insights and a host of novel clinical applications.

Systemic sclerosis: genetics and epigenetics

Systemic sclerosis (SSc) is an autoimmune disease characterized by immune abnormalities, vascular obliteration, excessive extracellular matrix deposition, and fibrosis of the skin and/or internal organs. To date, the exact etiology of this complicated disease remains unknown. Over the past few years, however, the role of genetic susceptibility and epigenetic modifications caused by environmental factors have been intensively studied in relation to the pathogenesis of this disease, and important advances have been made. This review focuses on the recent progress in the field of SSc research, including HLA and non-HLA susceptibility genes identified in genome-wide association studies (GWAS), and aberrant epigenetic modifications of gene loci associated with SSc. HLA genes most closely linked with SSc susceptibility include HLA-A, -B, -C, -DR, -DP and -DQ. A large number of non-HLA genes were also reported. It has also been noted that different genetic variants can be linked to specific clinical patterns. Finally, DNA demethylation of regulatory genes (eNOS, CD40L and CD70), therapeutic effects associated with Trichostatin A (TSA) treatment, and abnormal expression of a large spectrum of microRNAs (miR-21, -31, -146, -503, -145, -29b, etc.) are all observed in SSc. Overall, the findings presented in this review illustrate how both genetic and epigenetic aberrations play important roles in the development of SSc; however, several unanswered questions continue to impede our understanding of this complex disease. Future research should focus on the identification of new biomarkers for early diagnosis and prognosis, which will help improve the clinical outcome of patients with SSc.

Histone deacetylase (HDAC) inhibitors down-regulate endothelial lineage commitment of umbilical cord blood derived endothelial progenitor cells

To test the involvement of histone deacetylases (HDACs) activity in endothelial lineage progression, we investigated the effects of HDAC inhibitors on endothelial progenitors cells (EPCs) derived from umbilical cord blood (UCB). Adherent EPCs, that expressed the endothelial marker proteins (PCAM-1, CD105, CD133, and VEGFR₂) revealed by flow cytometry were treated with three HDAC inhibitors: Butyrate (BuA), Trichostatin A (TSA), and Valproic acid (VPA). RT-PCR assay showed that HDAC inhibitors down-regulated the expression of endothelial genes such as VE-cadherin, CD133, CXCR4 and Tie-2. Furthermore, flow cytometry analysis illustrated that HDAC inhibitors selectively reduce the expression of VEGFR₂, CD117, VE-cadherin, and ICAM-1, whereas the expression of CD34 and CD45 remained unchanged, demonstrating that HDAC is involved in endothelial differentiation of progenitor cells. Real-Time PCR demonstrated that TSA down-regulated telomerase activity probably via suppression of hTERT expression, suggesting that HDAC inhibitor decreased cell proliferation. Cell motility was also decreased after treatment with HDAC inhibitors as shown by wound-healing assay. The balance of acethylation/deacethylation kept in control by the activity of HAT (histone acetyltransferases)/HDAC enzymes play an important role in differentiation of stem cells by regulating proliferation and endothelial lineage commitment.

Nitric oxide: orchestrator of endothelium-dependent responses

The present review first summarizes the complex chain of events, in endothelial and vascular smooth muscle cells, that leads to endothelium-dependent relaxations (vasodilatations) due to the generation of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) and how therapeutic interventions may improve the bioavailability of NO and thus prevent/cure endothelial dysfunction. Then, the role of other endothelium-derived mediators (endothelium-derived hyperpolarizing (EDHF) and contracting (EDCF) factors, endothelin-1) and signals (myoendothelial coupling) is summarized also, with special emphasis on their interaction(s) with the NO pathway, which make the latter not only a major mediator but also a key regulator of endothelium-dependent responses.

Gene regulation in the vascular endothelium: why epigenetics is important for the kidney

We now appreciate that the vascular endothelium plays a crucial role in regulating normal blood vessel physiology in the kidney. The gene products responsible are commonly expressed exclusively, or preferentially, in this cell type. However, despite the importance of regulated gene expression in the vascular endothelium, relatively little is known about the mechanisms that restrict endothelial-specific gene expression to this cell type. Even less is known about how gene expression might be restricted to endothelial cells of discrete regions of the kidney, such as the glomerulus or vasa recta. Although significant progress has been made toward understanding the regulation of endothelial genes through cis/trans paradigms, it has become apparent that additional mechanisms also must be operative. Classic models of transcription in vascular endothelial cells, specifically the cis/trans paradigm, have limitations. For instance, how does the environment have chronic effects on gene expression in endothelial cells after weeks or years? When an endothelial cell divides, how is this information transmitted to daughter cells? Chromatin-based mechanisms, including cell-specific DNA methylation patterns and post-translational histone modifications, recently were shown to play important roles in gene expression. This review investigates the involvement of epigenetic regulatory mechanisms in vascular endothelial cell-specific gene expression using endothelial nitric oxide synthase as a prototypical model.

Epigenetic modifications and diabetic nephropathy

Diabetic nephropathy (DN) is a major complication associated with both type 1 and type 2 diabetes, and a leading cause of end-stage renal disease. Conventional therapeutic strategies are not fully efficacious in the treatment of DN, suggesting an incomplete understanding of the gene regulation mechanisms involved in its pathogenesis. Furthermore, evidence from clinical trials has demonstrated a "metabolic memory" of prior exposure to hyperglycemia that continues to persist despite subsequent glycemic control. This remains a major challenge in the treatment of DN and other vascular complications. Epigenetic mechanisms such as DNA methylation, nucleosomal histone modifications, and noncoding RNAs control gene expression through regulation of chromatin structure and function and post-transcriptional mechanisms without altering the underlying DNA sequence. Emerging evidence indicates that multiple factors involved in the etiology of diabetes can alter epigenetic mechanisms and regulate the susceptibility to diabetes complications. Recent studies have demonstrated the involvement of histone lysine methylation in the regulation of key fibrotic and inflammatory genes related to diabetes complications including DN. Interestingly, histone lysine methylation persisted in vascular cells even after withdrawal from the diabetic milieu, demonstrating a potential role of epigenetic modifications in metabolic memory. Rapid advances in high-throughput technologies in the fields of genomics and epigenomics can lead to the identification of genome-wide alterations in key epigenetic modifications in vascular and renal cells in diabetes. Altogether, these findings can lead to the identification of potential predictive biomarkers and development of novel epigenetic therapies for diabetes and its associated complications.

Nutrition, epigenetics, and metabolic syndrome

SIGNIFICANCE

Epidemiological and animal studies have demonstrated a close link between maternal nutrition and chronic metabolic disease in children and adults. Compelling experimental results also indicate that adverse effects of intrauterine growth restriction on offspring can be carried forward to subsequent generations through covalent modifications of DNA and core histones.

RECENT ADVANCES

DNA methylation is catalyzed by S-adenosylmethionine-dependent DNA methyltransferases. Methylation, demethylation, acetylation, and deacetylation of histone proteins are performed by histone methyltransferase, histone demethylase, histone acetyltransferase, and histone deacetyltransferase, respectively. Histone activities are also influenced by phosphorylation, ubiquitination, ADP-ribosylation, sumoylation, and glycosylation. Metabolism of amino acids (glycine, histidine, methionine, and serine) and vitamins (B6, B12, and folate) plays a key role in provision of methyl donors for DNA and protein methylation.

CRITICAL ISSUES

Disruption of epigenetic mechanisms can result in oxidative stress, obesity, insulin resistance, diabetes, and vascular dysfunction in animals and humans. Despite a recognized role for epigenetics in fetal programming of metabolic syndrome, research on therapies is still in its infancy. Possible interventions include: 1) inhibition of DNA methylation, histone deacetylation, and microRNA expression; 2) targeting epigenetically disturbed metabolic pathways; and 3) dietary supplementation with functional amino acids, vitamins, and phytochemicals.

FUTURE DIRECTIONS

Much work is needed with animal models to understand the basic mechanisms responsible for the roles of specific nutrients in fetal and neonatal programming. Such new knowledge is crucial to design effective therapeutic strategies for preventing and treating metabolic abnormalities in offspring born to mothers with a previous experience of malnutrition.

Transcriptional regulation of Nox4 by histone deacetylases in human endothelial cells

Nox4 is a member of the NADPH oxidase family, which represents a major source of reactive oxygen species (ROS) in the vascular wall. Nox4-mediated ROS production mainly depends on the expression levels of the enzyme. The present study was aimed to investigate the mechanisms of Nox4 transcription regulation by histone deacetylases (HDAC). In human umbilical vein endothelial cells (HUVEC) and HUVEC-derived EA.hy 926 cells, treatment with the pan-HDAC inhibitor scriptaid led to a marked decrease in Nox4 mRNA expression. A similar down-regulation of Nox4 mRNA expression was observed by siRNA-mediated knockdown of HDAC3. HDAC inhibition in endothelial cells was associated with enhanced histone acetylation, increased chromatin accessibility in the human Nox4 promoter region, with no significant changes in DNA methylation. In addition, we provided evidence that c-Jun played an important role in controlling Nox4 transcription. Knockdown of c-Jun with siRNA led to a down-regulation of Nox4 mRNA expression. In response to scriptaid treatment, the binding of c-Jun to the Nox4 promoter region was reduced despite the open chromatin structure. In parallel, the binding of RNA polymerase IIa to the Nox4 promoter was significantly inhibited as well, which may explain the reduction in Nox4 transcription. In conclusion, HDAC inhibition decreases Nox4 transcription in human endothelial cells by preventing the binding of transcription factor(s) and polymerase(s) to the Nox4 promoter, most likely because of a hyperacetylation-mediated steric inhibition.

On the epigenetics of vascular regulation and disease

Consolidated knowledge is accumulating as to the role of epigenetic regulatory mechanisms in the physiology of vascular development and vascular tone as well as in the pathogenesis of cardiovascular disease. The modulation of gene expression through modification of the epigenome by structural changes of the chromatin architecture without alterations of the associated genomic DNA sequence is part of the cellular response to environmental changes. Such environmental conditions, which are finally being translated into adaptations of the cardiovascular system, also comprise pathological conditions such as atherosclerosis or myocardial infarction. This review summarizes recent findings on the epigenetics of vascular regulation and disease and presents nutritional and pharmacological approaches as novel epigenetic strategies in the prevention and treatment of cardiovascular disease.

Pulmonary hypertension: chapters of innovation and tribulation

As can be seen by the mounting literature, there has been immense progress in the field of pulmonary hypertension (PH) over the last three decades, illustrated by several important milestones including improved understanding of disease pathogenesis, new classifications of disease, advances in screening and diagnostic techniques, and new rules for staging and follow-up, which have subsequently led to improvements in patient outcomes. The objectives of this manuscript are to not only highlight these very recent advances but also point out areas of deficiencies or gaps in our knowledge that may serve a focal point for future discussion and investigation.

A regulatory role of Kruppel-like factor 4 in endothelial argininosuccinate synthetase 1 expression in response to laminar shear stress

Endothelial argininosuccinate synthetase 1 (ASS1) regulates the provision of l-arginine to nitric oxide synthase 3 (NOS3). Previous studies demonstrated that endothelial ASS1 expression was induced by laminar shear stress (LSS) and that this enzyme plays a role in maintaining anti-inflammatory microenvironments through enhancing NO production. However, differently from the case of NOS3, the regulatory mechanism for the endothelial ASS1 expression in response to LSS is not well understood. This study addressed a specific issue whether endothelial ASS1 expression is regulated by Kruppel-like factors (KLFs) that are presumed to coordinate endothelial gene expressions in response to LSS. The cDNA microarray data indicated that LSS stimulated the expression of numerous KLFs in human umbilical vein endothelial cells. KLF4 showed the highest fold increase and LSS-dependent increases of KLF4 and most other KLFs were similar in young versus senescent endothelial cells. LSS-induced KLF4 expression was verified by RT-PCR and Western blotting. LSS-induced ASS1 expression and NO production were suppressed by a small interfering RNA for KLF4. The ectopic expression of KLF4 led to the increase of ASS1 expression and NO production. The present study demonstrated a key regulatory role of KLF4 in the endothelial ASS1 expression and NO production in response to LSS.

Evidence for a genetic role in varicose veins and chronic venous insufficiency

There is a strong body of circumstantial evidence which implicates genetics in the aetiology and pathology of varicose veins and venous ulcer disease. The aim of this review is to consider the current knowledge of the genetic associations and the ways in which new genetic technologies may be applied to advancing our understanding of the cause and progression of these venous diseases. A number of publications have used a candidate gene approach to identify genes implicated in venous disease. Although these studies have opened up important new insights, there has been a general failure to replicate results in an independent cohort of patients. With our limited knowledge of the biological pathways involved in the pathogenesis of venous disease we are not in a strong position to formulate truly erudite a priori candidate gene hypothesis-directed studies. A genome-wide association study should therefore be considered to help further our understanding of the genetic basis of venous disease. Due to the large sample sizes required for discovery and validation, using the new generations of molecular technologies, it will be necessary to form collaborating groups in order to successfully advance the field of venous disease genetics.

MicroRNA-152 mediates DNMT1-regulated DNA methylation in the estrogen receptor α gene

Background

Estrogen receptor α (ERα) has been shown to protect against atherosclerosis. Methylation of the ERα gene can reduce ERα expression leading to a higher risk for cardiovascular disease. Recently, microRNAs have been found to regulate DNA methyltransferases (DNMTs) and thus control methylation status in several genes. We first searched for microRNAs involved in DNMT-associated DNA methylation in the ERα gene. We also tested whether statin and a traditional Chinese medicine (San-Huang-Xie-Xin-Tang, SHXXT) could exert a therapeutic effect on microRNA, DNMT and ERα methylation.

Methodology/Principal Findings

The ERα expression was decreased and ERα methylation was increased in LPS-treated human aortic smooth muscle cells (HASMCs) and the aorta from rats under a high-fat diet. microRNA-152 was found to be down regulated in the LPS-treated HASMCs. We validated that microRNA-152 can knock down DNMT1 in HASMCs leading to hypermethylation of the ERα gene. Statin had no effect on microRNA-152, DNMT1 or ERα expression. On the contrary, SHXXT could restore microRNA-152, decrease DNMT1 and increase ERα expression in both cellular and animal studies.

Conclusions/Significance

The present study showed that microRNA-152 decreases under the pro-atherosclerotic conditions. The reduced microRNA-152 can lose an inhibitory effect on DNA methyltransferase, which leads to hypermethylation of the ERα gene and a decrease of ERα level. Although statin can not reverse these cascade proatherosclerotic changes, the SHXXT shows a promising effect to inhibit this unwanted signaling pathway.

Expression of Na+-K+ -2Cl- cotransporter 1 is epigenetically regulated during postnatal development of hypertension

BACKGROUND

The expression of Na(+)-K(+)-2Cl(-) cotransporter 1 (NKCC1) is upregulated in spontaneously hypertensive rat (SHR). We investigated whether expression of NKCC1 is epigenetically regulated during postnatal development of hypertension.

METHODS

The mesenteric arteries from 5-, 10-, and 18-week-old Wistar-Kyoto rats (WKY) and SHRs were subjected to vascular contraction. We determined expression levels of Nkcc1 mRNA and protein, methylation status, and histone modification of Nkcc1 promoter, and DNA methyltransferase (DNMT) activity.

RESULTS

The inhibition of dose-response curves by bumetanide, an inhibitor of NKCC1, as well as the expression of Nkcc1 mRNA and protein was comparable between 5-week-old SHR and age-matched WKY, but greater in 18-week-old SHR than in age-matched WKY. Nkcc1 promoter in WKY was getting methylated with age whereas that in SHR mostly remained hypomethylated after development of hypertension. DNMT3B was highly associated with the promoter of WKY, whereas the CXXC finger protein 1 (Cfp1) was highly bound to the promoter of SHR. At the age of 18 weeks, the DNMT activity in aorta of WKY was about threefold higher than that of SHR. The transcription-activating histone code acetyl H3 was higher in SHR than in WKY, whereas suppressive histone code dimethyl H3K9 was greater in WKY than in SHR.

CONCLUSION

It is concluded that expression of NKCC1 is epigenetically upregulated during postnatal development of hypertension. Our data indicate that maintenance of hypomethylation in Nkcc1 promoter of SHR resulting from low DNMT activity plays an important role in the upregulation of NKCC1 during development of spontaneous hypertension.

Role of activation of 5'-adenosine monophosphate-activated protein kinase in gastric ulcer healing in diabetic rats

BACKGROUND

The potential utility of 5'-adenosine monophosphate-activated protein kinase (AMPK)-activating agents, such as metformin, in inducing angiogenesis, could be a promising approach to promote healing of gastric ulcers complicated by diabetes mellitus. The aim of the present study was to assess the effect of a drug that activates AMPK, namely metformin, in gastric ulcer healing in streptozotocin-induced diabetic rats.

METHODS

Forty male Wistar albino rats were made diabetic by intraperitoneal (i.p.) streptozotocin injection and 10 rats were injected i.p. by a single dose of physiological saline. Six weeks following streptozotocin or saline injection, gastric ulcers were induced by serosal application of acetic acid. Three days after acetic acid application, rats were divided into group 1 (nondiabetic control), group 2 (streptozotocin-injected rats), groups 3-5 (streptozotocin-injected rats treated with metformin or metformin and an inhibitor of AMPK, namely compound C or pioglitazone) for 7 days following acetic acid application.

RESULTS

Administration of metformin, but not pioglitazone, resulted in a significant decrease in the gastric ulcer area, a significant increase in epithelial regeneration assessed histologically, a significant increase in the number of microvessels in the ulcer margin, a significant increase in gastric vascular endothelial growth factor concentration and gastric von Willebrand factor as well as a significant increase in gastric phospho-AMPK. Compound C, an inhibitor of AMPK, blocked metformin-induced changes in assessed parameters suggesting that the effect of metformin was mediated mainly through activation of AMPK.

CONCLUSION

Our results suggest the feasibility of a novel treatment strategy, namely drugs activating AMPK, for patients in whom impairment of ulcer healing constitutes a secondary complication of diabetes mellitus.

Epigenetic regulation of endothelial lineage committed genes in pro-angiogenic hematopoietic and endothelial progenitor cells

RATIONALE

Proangiogenic hematopoietic and endothelial progenitor cells (EPCs) contribute to postnatal neovascularization, but the mechanisms regulating differentiation to the endothelial lineage are unclear.

OBJECTIVE

To elucidate the epigenetic control of endothelial gene expression in proangiogenic cells and EPCs.

METHODS AND RESULTS

Here we demonstrate that the endothelial nitric oxide synthase (eNOS) promoter is epigenetically silenced in proangiogenic cells (early EPCs), CD34(+) cells, and mesoangioblasts by DNA methylation and prominent repressive histone H3K27me3 marks. In order to reverse epigenetic silencing to facilitate endothelial commitment, we used 3-deazaneplanocin A, which inhibits the histone methyltransferase enhancer of zest homolog 2 and, thereby, reduces H3K27me3. 3-Deazaneplanocin A was not sufficient to increase eNOS expression, but the combination of 3-deazaneplanocin A and the histone deacetylase inhibitor Trichostatin A augmented eNOS expression, indicating that the concomitant inhibition of silencing histone modification and enhancement of activating histone modification facilitates eNOS expression. In ischemic tissue, hypoxia plays a role in recruiting progenitor cells. Therefore, we examined the effect of hypoxia on epigenetic modifications. Hypoxia modulated the balance of repressive to active histone marks and increased eNOS mRNA expression. The reduction of repressive H3K27me3 was associated with an increase of the histone demethylase Jmjd3. Silencing of Jmjd3 induced apoptosis and senescence in proangiogenic cells and inhibited hypoxia-mediated up-regulation of eNOS expression in mesoangioblasts.

CONCLUSIONS

These findings provide evidence that histone modifications epigenetically control the eNOS promoter in proangiogenic cells.

Histone demethylase LSD1 deficiency during high-salt diet is associated with enhanced vascular contraction, altered NO-cGMP relaxation pathway, and hypertension

Histone methylation, a determinant of chromatin structure and gene transcription, was thought to be irreversible, but recent evidence suggests that lysine-specific demethylase-1 (LSD1, Kdm1a) induces demethylation of histone H3 lysine 4 (H3K4) or H3K9 and thereby alters gene transcription. We previously demonstrated a human LSD1 phenotype associated with salt-sensitive hypertension. To test the hypothesis that LSD1 plays a role in the regulation of blood pressure (BP) via vascular mechanisms and gene transcription, we measured BP and examined vascular function and endothelial nitric oxide (NO) synthase (eNOS) expression in thoracic aorta of male wild-type (WT) and heterozygous LSD1 knockout mice (LSD1(+/-)) fed either a liberal salt (HS; 4% NaCl) or restricted salt diet (LS; 0.08% NaCl). BP was higher in LSD1(+/-) than WT mice on the HS diet but not different between LSD1(+/-) and WT mice on the LS diet. Further examination of the mechanisms of this salt-sensitive hypertension in LSD1(+/-) mice on the HS diet demonstrated that plasma renin activity and plasma levels and urinary excretion of aldosterone were less in LSD1(+/-) than WT, suggesting suppressed renin-angiotensin-aldosterone system. In contrast, phenylephrine (Phe)-induced aortic contraction was greater in LSD1(+/-) than WT mice on the HS diet. Treatment of aortic rings with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a blocker of guanylate cyclase) enhanced Phe contraction in LSD1(+/-) compared with WT mice on the HS diet. Acetylcholine (Ach)-induced relaxation was less in LSD1(+/-) than WT mice on the HS diet. Endothelium removal or pretreatment with N(ω)-nitro-L-arginine methyl ester (blocker of NOS) or ODQ abolished Ach-induced relaxation in aorta of WT but had minimal effect in LSD1(+/-). Vascular relaxation to sodium nitroprusside, an exogenous NO donor and guanylate cyclase activator, was decreased in LSD1(+/-) vs. WT mice on the HS diet. RT-PCR and Western blots revealed decreased eNOS mRNA expression and eNOS and guanylate cyclase protein in the heart and aorta of LSD1(+/-) compared with WT mice on HS diet. Thus, during the HS diet, LSD1 deficiency is associated with hypertension, enhanced vascular contraction, and reduced relaxation via NO-cGMP pathway. The data support a role for LSD1-mediated histone demethylation in the regulation of NOS/guanylate cyclase gene expression, vascular function, and BP during the HS diet.

Epigenetics in cardiovascular disease

PURPOSE OF REVIEW

To provide an overview of the biological processes implicated in chromatin-based pathways that control endothelial gene expression patterns in both health and disease and highlight how these processes are relevant to cardiovascular disease.

RECENT FINDINGS

Epigenetics refers to chromatin-based pathways important in the regulation of gene expression and includes three distinct, but highly interrelated, mechanisms: DNA methylation, histone density and posttranslational modifications, and RNA-based mechanisms. It is of great interest that epigenetic regulation of genes enriched in the vascular endothelium is a prominent regulatory pathway. How environmental cues within the vasculature, such as hemodynamic forces or hypoxia, influence these epigenetic mechanisms will be reviewed.

SUMMARY

Although a newer area for study, exciting new evidence identifies that epigenetic processes are highly dynamic and respond to a myriad of environmental stimuli. Integrating chromatin-based pathways into our understanding of gene expression offers newer insight into disease processes.

Repression of P66Shc expression by SIRT1 contributes to the prevention of hyperglycemia-induced endothelial dysfunction

RATIONALE

Inactivation of the p66Shc adaptor protein confers resistance to oxidative stress and protects mice from aging-associated vascular diseases. However, there is limited information about the negative regulating mechanisms of p66Shc expression in the vascular system.

OBJECTIVE

In this study, we investigated the role of SIRT1, a class III histone deacetylase, in the regulation of p66Shc expression and hyperglycemia-induced endothelial dysfunction.

METHODS AND RESULTS

Expressions of p66Shc gene transcript and protein were significantly increased by different kinds of class III histone deacetylase (sirtuin) inhibitors in human umbilical vein endothelial cells and 293A cells. Adenoviral overexpression of SIRT1 inhibited high-glucose-induced p66Shc upregulation in human umbilical vein endothelial cells. Knockdown of SIRT1 increased p66Shc expression and also increased the expression levels of plasminogen activator inhibitor-1 expression, but decreased manganese superoxide dismutase expression in high-glucose conditions. However, knockdown of p66Shc significantly reversed the effects of SIRT1 knockdown. In addition, p66Shc overexpression significantly decreased manganese superoxide dismutase expression and increased plasminogen activator inhibitor-1 expression in high-glucose conditions, which were recovered by SIRT1 overexpression. Moreover, compared to streptozotocin-induced wild-type diabetic mice, endothelium-specific SIRT1 transgenic diabetic mice had decreased p66Shc expression at both the mRNA and the protein levels, improved endothelial function, and reduced accumulation of nitrotyrosine and 8-OHdG (markers of oxidative stress). We further found that SIRT1 was able to bind to the p66Shc promoter (-508 bp to -250 bp), resulting in a decrease in the acetylation of histone H3 bound to the p66Shc promoter region.

CONCLUSION

Our findings indicate that repression of p66Shc expression by SIRT1 contributes to the protection of hyperglycemia-induced endothelial dysfunction.

New molecular mechanisms for cardiovascular disease:blood flow sensing mechanism in vascular endothelial cells

Endothelial cells (ECs) lining blood vessels have a variety of functions and play a critical role in the homeostasis of the circulatory system. It has become clear that biomechanical forces generated by blood flow regulate EC functions. ECs are in direct contact with blood flow and exposed to shear stress, a frictional force generated by flowing blood. A number of recent studies have revealed that ECs recognize changes in shear stress and transmit signals to the interior of the cell, which leads to cell responses that involve changes in cell morphology, cell function, and gene expression. These EC responses to shear stress are thought to play important roles in blood flow-dependent phenomena such as vascular tone control, angiogenesis, vascular remodeling, and atherogenesis. Much research has been done on shear stress sensing and signal transduction, and their molecular mechanisms are gradually becoming understood. However, much remains uncertain, and many candidates have been proposed for shear stress sensors. More extensive studies of vascular mechanobiology should increase our understanding of the molecular basis of the blood flow-mediated control of vascular functions.

Loss of methyl-CpG-binding domain protein 2 enhances endothelial angiogenesis and protects mice against hind-limb ischemic injury

BACKGROUND

Despite intensive investigation, how DNA methylation influences endothelial function remains poorly understood. We used methyl-CpG-binding domain protein 2 (MBD2), an interpreter for DNA methylome-encoded information, to dissect the impact of DNA methylation on endothelial function in both physiological and pathophysiological states.

METHODS AND RESULTS

Human umbilical vein endothelial cells under normal conditions express moderate levels of MBD2, but knockdown of MBD2 by siRNA significantly enhanced angiogenesis and provided protection against H(2)O(2)-induced apoptosis. Remarkably, Mbd2(-/-) mice were protected against hind-limb ischemia evidenced by the significant improvement in perfusion recovery, along with increased capillary and arteriole formation. Loss of MBD2 activated endothelial survival and proangiogenic signals downstream of vascular endothelial growth factor signaling characterized by an increase in endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor receptor 2 expression, along with enhanced extracellular signal-regulated kinase 1/2 activation and BCL-2 expression. Mechanistic studies confirmed the methylation of CpG elements in the eNOS and vascular endothelial growth factor receptor 2 promoter. MBD2 binds to these methylated CpG elements and suppresses eNOS promoter activity. On ischemic insult, key endothelial genes such as eNOS and vascular endothelial growth factor receptor 2 undergo a DNA methylation turnover, and MBD2 interprets the changes of DNA methylation to suppress their expressions. Moreover, MBD2 modulation of eNOS expression is likely confined to endothelial cells because nonendothelial cells such as splenocytes fail to express eNOS after loss of MBD2.

CONCLUSIONS

We provided direct evidence supporting that DNA methylation regulates endothelial function, which forms the molecular basis for understanding how environmental insults (epigenetic factor) affect the genome to modify disease susceptibility. Because MBD2 itself does not affect the methylation of DNA and is dispensable for normal physiology in mice, it could be a viable epigenetic target for modulating endothelial function in disease states.

Uncovering the behaviors of individual cells within a multicellular microvascular community

Although individual cells vary in behavior during the formation of tissues, the nature of such variations are largely uncharacterized. Here, we tracked the morphologies and motilities of ~300 human endothelial cells from an initial dispersed state to the formation of capillary-like structures, distilling the dynamics of tissue morphogenesis into an array of ~36,000 numerical phenotypes. Quantitative analysis of population averages revealed two previously unidentified phases in which the cells spread before forming connections with neighboring cells and where the microvascular plexus stabilized before spatially reorganizing. Analysis at the single-cell level showed that in contrast to the population-averaged behavior, most cells followed distinct temporal patterns that were not reflected in the bulk average. Interestingly, some of these behavioral patterns correlated to the cells' final structural role within the plexus. Knowledge of how individual cells or groups of cells behave enhances our understanding of how native tissues self-organize and could ultimately enable more precise approaches for engineering tissues and synthesizing multicellular communities.

Promoter hypomethylation results in increased expression of protein phosphatase 2A in T cells from patients with systemic lupus erythematosus

The catalytic subunit α isoform of protein phosphatase 2A (PP2Acα) activity, protein, and mRNA have been found increased in systemic lupus erythematosus (SLE) T cells and to contribute to decreased IL-2 production. The PP2Acα promoter activity is controlled epigenetically through the methylation of a CpG within a cAMP response element (CRE) motif defined by its promoter. We considered that hypomethylation may account for the increased expression of PP2Acα in patients with SLE. Using bisulfite sequencing, we found that SLE T cells displayed decreased DNA methylation in the promoter region compared with normal T cells. More importantly, we found that the CRE-defined CpG, which binds p-CREB, is significantly less methylated in SLE compared with normal T cells, and the levels of methylation correlated with decreased amounts of DNA methyltransferase 1 transcripts. Methylation intensity correlated inversely with levels of PP2Acα mRNA and SLE disease activity. Chromatin immunoprecipitation assays revealed more binding of p-CREB to the CRE site in SLE T cells, resulting in increased expression of PP2Acα. We propose that PP2Acα represents a new methylation-sensitive gene that, like the previously reported CD70 and CD11a, contributes to the pathogenesis of SLE.

Differential effects of nutritional folic acid deficiency and moderate hyperhomocysteinemia on aortic plaque formation and genome-wide DNA methylation in vascular tissue from ApoE-/- mice

Low folate intake is associated with vascular disease. Causality has been attributed to hyperhomocysteinemia. However, human intervention trials have failed to show the benefit of homocysteine-lowering therapies. Alternatively, low folate may promote vascular disease by deregulating DNA methylation. We investigated whether folate could alter DNA methylation and atherosclerosis in ApoE null mice. Mice were fed one of six diets (n = 20 per group) for 16 weeks. Basal diets were either control (C; 4% lard) or high fat (HF; 21% lard and cholesterol, 0.15%) with different B-vitamin compositions: (1) folic acid and B-vitamin replete, (2) folic acid deficient (-F), (3) folic acid, B6 and B12 deficient (-F-B). -F diets decreased plasma (up to 85%; P < 0.05), whole blood (up to 70%; P < 0.05), and liver folate (up to 65%; P < 0.05) and hepatic SAM/SAH (up to 80%; P < 0.05). -F-B diets reduced plasma (up to 76%; P < 0.05), whole blood (up to 72%; P < 0.05), and liver B12 (up to 39%; P < 0.05) and hepatic SAM/SAH (up to 90%; P < 0.05). -F increased homocysteine 2-fold, while -F-B increased homocysteine 3.6- and 6.8-fold in the C and HF groups (P < 0.05). Plaque formation was increased 2-fold (P < 0.0001) in mice fed a HF diet. Feeding a HF-F diet increased lesion formation by 17% (P < 0.05). There was no change in 5-methyldeoxycytidine in liver or vascular tissue (aorta, periadventitial tissue and heart). These data suggest that atherogenesis is not associated with genome-wide epigenetic changes in this animal model.

DPP4 gene DNA methylation in the omentum is associated with its gene expression and plasma lipid profile in severe obesity

Severely obese subjects with the metabolic syndrome (MS) have higher dipeptidyl peptidase-4 (DPP4) expression in their visceral adipose tissue (VAT) compared to obese individuals without MS. We tested the hypothesis that methylation level of CpG sites in the DPP4 promoter CpG island in VAT was genotype-dependent and associated with DPP4 mRNA abundance and MS-related phenotypes. The VAT DNA was extracted in 92 severely obese premenopausal women undergoing biliopancreatic derivation for the treatment of obesity. Women were nondiabetic and none of them used medication to treat MS features. Cytosine methylation rates (%) of 102 CpG sites in the DPP4 CpG island were assessed by pyrosequencing of sodium bisulfite-treated DNA. Methylation rates were >10% for CpG sites 94-102. Their mean methylation rate (%Meth(94-102)) was different between genotypes for DPP4 polymorphisms rs13015258 (P = 0.001), rs17848915 (P = 0.0004), and c.1926 G>A (P = 0.001). The %Meth(94-102) correlated negatively with DPP4 mRNA abundance (r = -0.25, P < 0.05) and positively with plasma high-density lipoprotein (HDL) cholesterol concentrations (r = 0.22, P < 0.05), whereas DPP4 mRNA abundance correlated positively with plasma total-/HDL-cholesterol ratio (r = 0.25; P < 0.05). In the VAT of nondiabetic severely obese women, genotype-dependent methylation levels of specific CpG sites in the DPP4 promoter CpG island were associated with DPP4 gene expression and variability in the plasma lipid profile. Higher DPP4 gene expression in VAT and its relationship with the plasma lipid profile may be explained by actually unknown DPP4 biological effect or, to another extent, may also be a marker of VAT inflammation known to be associated with metabolic disturbances.

Epigenetic mechanisms in diabetic vascular complications

There has been a rapid increase in the incidence of diabetes as well the associated vascular complications. Both genetic and environmental factors have been implicated in these pathologies. Increasing evidence suggests that epigenetic factors play a key role in the complex interplay between genes and the environment. Actions of major pathological mediators of diabetes and its complications such as hyperglycaemia, oxidant stress, and inflammatory factors can lead to dysregulated epigenetic mechanisms that affect chromatin structure and gene expression. Furthermore, persistence of this altered state of the epigenome may be the underlying mechanism contributing to a 'metabolic memory' that results in chronic inflammation and vascular dysfunction in diabetes even after achieving glycaemic control. Further examination of epigenetic mechanisms by also taking advantage of recently developed next-generation sequencing technologies can provide novel insights into the pathology of diabetes and its complications and lead to the discovery of much needed new drug targets for these diseases. In this review, we highlight the role of epigenetics in diabetes and its vascular complications, and recent technological advances that have significantly accelerated the field.

Nitric oxide: perspectives and emerging studies of a well known cytotoxin

The free radical nitric oxide (NO^•) is known to play a dual role in human physiology and pathophysiology. At low levels, NO^• can protect cells; however, at higher levels, NO^• is a known cytotoxin, having been implicated in tumor angiogenesis and progression. While the majority of research devoted to understanding the role of NO^• in cancer has to date been tissue-specific, we herein review underlying commonalities of NO^• which may well exist among tumors arising from a variety of different sites. We also discuss the role of NO^• in human physiology and pathophysiology, including the very important relationship between NO^• and the glutathione-transferases, a class of protective enzymes involved in cellular protection. The emerging role of NO^• in three main areas of epigenetics—DNA methylation, microRNAs, and histone modifications—is then discussed. Finally, we describe the recent development of a model cell line system in which human tumor cell lines were adapted to high NO^• (HNO) levels. We anticipate that these HNO cell lines will serve as a useful tool in the ongoing efforts to better understand the role of NO^• in cancer.

Glycemic memory associated epigenetic changes

It is evident that metabolic memory, whereby diabetic complications continue to develop and progress in individuals who returned to normal glycemic control after a period of transient hyperglycemia, can have long lasting effects. We have primary findings that transient hyperglycemia causes profound transcriptional changes in vascular endothelial cells. We hypothesized that ambient hyperglycemia triggers gene-activating events of the NFκB p65 promoter that are mediated by changes in epigenetic modifications. In a follow-up study we identified two histone-specific writing and erasing enzymes involved in the underlying regulation of gene expression during transient hyperglycemia and subsequent return to normoglycemia. Experimental evidence indicates that previous hyperglycemia is associated with persistent expression of the NFκB p65 gene, which activates NFκB-dependent proteins, such as MCP-1, which are implicated in diabetes-associated vascular injury. Increased gene transcription is correspondent with H3K4m1, but not H3K4m2 and H3K4m3, on the NFκB p65 gene. In vascular endothelial cells the histone methyltransferase Set7 can write the mono-methylation mark H3K4m1 and this methyl-writing enzyme is recruited as a gene co-activator in response to glucose. Furthermore, Set7 knockdown prevents glucose-induced p65 expression. We hypothesize that these molecular events represent an integrated response of the epigenome that lead to changes in the expression of genes and proteins that regulate the development and progression of diabetic vascular complications. Further characterisation of these glucose-induced epigenetic events and the identification of key enzymes involved will improve our understanding of the pathways implicated in diabetic vascular injury.

Environment and vascular bed origin influence differences in endothelial transcriptional profiles of coronary and iliac arteries

Atherosclerotic plaques tend to form in the major arteries at certain predictable locations. As these arteries vary in atherosusceptibility, interarterial differences in endothelial cell biology are of considerable interest. To explore the origin of differences observed between typical atheroprone and atheroresistant arteries, we used DNA microarrays to compare gene expression profiles of harvested porcine coronary (CECs) and iliac artery endothelial cells (IECs) grown in static culture out to passage 4. Fewer differences were observed between the transcriptional profiles of CECs and IECs in culture compared with in vivo, suggesting that most differences observed in vivo were due to distinct environmental cues in the two arteries. One-class significance of microarrays revealed that most in vivo interarterial differences disappeared in culture, as fold differences after passaging were not significant for 85% of genes identified as differentially expressed in vivo at 5% false discovery rate. However, the three homeobox genes, HOXA9, HOXA10, and HOXD3, remained underexpressed in coronary endothelium for all passages by at least nine-, eight-, and twofold, respectively. Continued differential expression, despite removal from the in vivo environment, suggests that primarily heritable or epigenetic mechanism(s) influences transcription of these three genes. Quantitative real-time polymerase chain reaction confirmed expression ratios for seven genes associated with atherogenesis and over- or underexpressed by threefold in CECs relative to IECs. The present study provides evidence that both local environment and vascular bed origin modulate gene expression in arterial endothelium. The transcriptional differences observed here may provide new insights into pathways responsible for coronary artery susceptibility.

Epigenetics of the vascular endothelium

Classical models of transcription in vascular endothelial cells, specifically the cis/trans paradigm, have limitations. For instance, how does the environment have chronic effects on gene expression in endothelial cells after weeks or years? When an endothelial cell divides, how is this information transmitted to daughter cells? Epigenetics refers to chromatin-based pathways important in the regulation of gene expression and includes three distinct, but highly interrelated, mechanisms: DNA methylation, histone density and posttranslational modifications, and RNA-based mechanisms. Together they offer a newer perspective on transcriptional control paradigms in vascular endothelial cells and provide a molecular basis for understanding how the environment impacts the genome to modify disease susceptibility. This alternative viewpoint for transcriptional regulation allows a reassessment of the cis/trans model and even helps explain some of its limitations. This review provides an introduction to epigenetic concepts for vascular biologists and uses topical examples in cell biology to provide insight into how cell types or even whole organisms, such as monozygotic human twins with the same DNA sequence, can exhibit heterogeneous patterns of gene expression, phenotype, or diseases prevalence. Using endothelial nitric oxide synthase (NOS3) as an example, we examine the growing body of evidence implicating epigenetic pathways in the control of vascular endothelial gene expression in health and disease.

Genetic and epigenetic mechanisms and their possible role in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease associated with significant cardiovascular morbidity and mortality. The pathogenesis of AAA is poorly defined, making targeting of new therapies problematic. Current evidence favours an interaction of multiple environmental and genetic factors in the initiation and progression of AAA. Epigenetics is the term used to define the properties of the genome that are not explained by the primary sequence, but are due to the modifications of DNA and/or associated proteins. Previous research indicates the association of gene specific promoter DNA hyper-methylation and global DNA hypo-methylation with atherosclerosis. Evidence also suggests an important role for epigenetic processes such as histone acetylation in cardiovascular diseases including atherosclerosis and restenosis. Altered DNA methylation or histone acetylation occur in inflammation, cellular proliferation and remodelling processes and therefore maybe relevant to the pathology of AAA. Important risk factors for AAA, including cigarette smoking, older age, male gender and hypertension, have been linked with epigenetic effects and thus could act in this way to promote AAA. In this review, we discuss the potential role of epigenetic mechanisms in AAA. Since epigenetic alterations are to some extent reversible, further study of this area may identify new treatment targets for AAA.

Epigenetics in atherosclerosis and inflammation

Atherosclerosis is a multifactorial disease with a severe burden on western society. Recent insights into the pathogenesis of atherosclerosis underscore the importance of chronic inflammation in both the initiation and progression of vascular remodelling. Expression of immunoregulatory molecules by vascular wall components within the atherosclerotic lesions is accordingly thought to contribute to the ongoing inflammatory process. Besides gene regulatory proteins (transcription factors), epigenetic mechanisms also play an essential and fundamental role in the transcriptional control of gene expression. These epigenetic mechanisms change the accessibility of chromatin by DNA methylation and histone modifications. Epigenetic modulators are thus critically involved in the regulation of vascular, immune and tissue-specific gene expression within the atherosclerotic lesion. Importantly, epigenetic processes are reversible and may provide an excellent therapeutic target. The concept of epigenetic regulation is gradually being recognized as an important factor in the pathogenesis of atherosclerosis. Recent research provides an essential link between inflammation and reprogramming of the epigenome. In this review we therefore discuss the basis of epigenetic regulation – and the contribution thereof in the regulation of inflammatory processes in general and during atherosclerosis in particular. Moreover we highlight potential therapeutic interventions based on epigenetic mechanisms.

Tumor necrosis factor-alpha decreases sarcoplasmic reticulum Ca2+-ATPase expressions via the promoter methylation in cardiomyocytes

OBJECTIVES

Sarcoplasmic reticulum Ca-ATPases (SERCA2a) plays an essential role in the Ca homeostasis and cardiac functions. Tumor necrosis factor-alpha (TNF-alpha) decreases the SERCA2a, which may underlie cardiac dysfunction during sepsis and heart failure. Because the promoter region of SERCA2a contains CpG islands, gene methylation should be critical in regulating SERCA2a. The present study was to evaluate whether TNF-alpha can modulate SERCA2a via enhancing methylation and to investigate the underlying mechanisms.

DESIGN

Controlled laboratory experiment.

SETTING

University research laboratory.

SUBJECTS

HL-1 cardiomyocytes.

INTERVENTIONS

TNF-alpha (1-50 ng/mL) was administered in HL-1 cardiomyocytes with and without co-administration of an NF-kappaB inhibitor (SN-50, 50 microg/mL), antioxidant agents (ascorbic acid, 100 microM, or coenzyme Q10, 10 microM), or methylation inhibitor (5-aza-2'-deoxycytidine, 0.1, 1 microM).

MEASUREMENTS AND MAIN RESULTS

TNF-alpha (50 ng/mL) decreased the SERCA2a RNA and protein by quantitative polymerase chain reaction and immunoblot. Furthermore, TNF-alpha (50 ng/mL) increased the methylation in the SERCA2a promoter region, which was not influenced by the co-administration of SN-50, ascorbic acid, or coenzyme Q10, but was attenuated by 5-aza-2'-deoxycytidine (0.1 microM). Additionally, TNF-alpha (50 ng/mL) increased the expression of DNA methyltransferase 1.

CONCLUSIONS

TNF-alpha increased DNA methyltransferase levels, thus enhancing the methylation in the SERCA2a promoter region with a result of reducing SERCA2a. These findings suggest that inhibition of hypermethylation may be a novel treatment strategy for cardiac dysfunction.

Mechanisms of vascular damage in systemic sclerosis

Although being classified as autoimmune connective tissue disease, dominant components of the pathophysiology of systemic sclerosis (SSc) consists of mechanisms of vascular damage, which can occur early in the course of the disease. Amongst them are abnormal vasoreactivity, hypoxia, insufficient neoangiogenesis and direct damage of vascular and perivascular cells. They result in a decreased capillary blood flow, and subsequently in clinically overt symptoms such as Raynaud's syndrome and fingertip ulcers. In addition, in active disease vascular pathology can affect various other organs, predominantly the lung, the kidney, the heart but also the gastrointestinal tract. Vascular pathology contributes also significantly to overall morbidity and mortality in SSc patients and reduces life expectancy by at least a decade. Fortunately, molecular biology has revealed a number of underlying pathways on the cellular and subcellular levels, including key factors of the aberrant function of (peri)vascular cells and autoimmune effector cells, the dysregulation of vasoconstrictive molecules and their receptors, the upregulation of intracellular signaling kinases and the altered balance of hypoxia-induced vascular growth factors. This increasing knowledge of vascular pathology in SSc has also resulted in novel therapeutic approaches ranging from endothelin antagonists to application of progenitor cells to counteract this aberrant vascular pathology and to support the repair of the dysfunctional vasculature.

Deciphering the molecular basis of venous thromboembolism: where are we and where should we go?

Venous thromboembolism (VTE) is a frequent disease that has a major genetic component of risk. However, known identified genetic risk factors account for <30% of idiopathic (without any environmental origin) VTE cases. This article aims to review the lessons learnt during recent decades in the field of the genetics of VTE, describe the present state-of-art methods and discuss promising themes for finding new susceptibility loci.

Hypoxic repression of endothelial nitric-oxide synthase transcription is coupled with eviction of promoter histones

Hypoxia elicits endothelial dysfunction, in part, through reduced expression of endothelial nitric-oxide synthase (eNOS). Here we present evidence that hypoxia causes a rapid decrease in the transcription of the eNOS/NOS3 gene, accompanied by decreased acetylation and lysine 4 (histone H3) methylation of eNOS proximal promoter histones. Surprisingly, we demonstrate that histones are rapidly evicted from the eNOS proximal promoter during hypoxia. We also demonstrate endothelium-specific H2A.Z incorporation at the eNOS promoter and find that H2A.Z is also evicted by hypoxic stimulation. After longer durations of hypoxia, histones are reincorporated at the eNOS promoter, but these histones lack substantial histone acetylation. Additionally, we identify a key role for the chromatin remodeler, BRG1, in re-establishing eNOS expression following reoxygenation of hypoxic cells. We posit that post-translational histone modifications are required to maintain constitutive eNOS transcriptional activity and that histone eviction rapidly resets histone marks and is a proximal event in the hypoxic repression of eNOS. Although nucleosome eviction has been reported in models of transcriptional activation, the observation that eviction can also accompany transcriptional repression in hypoxic mammalian cells argues that eviction may be broadly relevant to both positive and negative changes in transcription.

Increased MAPK activation and impaired insulin signaling in subcutaneous microvascular endothelial cells in type 2 diabetes: the role of endothelin-1

OBJECTIVE

To establish a method for isolation and culture of subcutaneous microvascular endothelial cells (MVEC) from small human tissue biopsies to compare gene and protein expression of insulin signaling molecules in MVEC from insulin-resistant and healthy control subjects.

RESEARCH DESIGN AND METHODS

Stromavascular cells from subcutaneous needle biopsies of type 2 diabetic and control subjects were expanded in culture and the endothelial cells selected with magnetic immune separation. Western blots and RT-PCR were used for protein and gene expression assays.

RESULTS

At least 99% of the expanded primary MVEC could be characterized as endothelial cells. The expression of insulin receptors was low, but insulin increased tyrosine phosphorylation of both the insulin receptor and insulin receptor substrate (IRS)-1 and activated protein kinase B (PKB). The IRS-1 protein expression was reduced and the serine phosphorylation of PKB in response to insulin attenuated whereas basal and insulin-stimulated phosphorylation of extracellular signal-related kinase (ERK)1/2 was increased in type 2 diabetes MVEC. Endothelin (ET)-1 mRNA levels were significantly higher in type 2 diabetes cells. The addition of ET-1 increased the phosphorylation of mitogen-activated protein kinase (MAPK), an effect antagonized by the MEK-1 inhibitor PD98059. Furthermore, the endothelin ET(A) and ET(B) receptor antagonists BQ123 and BQ788 decreased basal MAPK activity in type 2 diabetes MVEC and prevented the ET-1-induced activation.

CONCLUSIONS

We developed a system for isolation and culture of human MVEC from small needle biopsies. Our observations support the concept of "selective" insulin resistance, involving IRS-1 and the PI3kinase pathway, as an underlying factor for a dysregulated microvascular endothelium in type 2 diabetes. Our data also support a role of ET-1 for the increased MAPK activity seen in nonstimulated type 2 diabetes MVEC.

Activation and signaling by the AMP-activated protein kinase in endothelial cells

The AMP-activated protein kinase (AMPK) was initially identified as the kinase that phosphorylates the 3-hydroxy 3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme for cholesterol biosynthesis. As the name suggests, the AMPK is activated by increased intracellular concentrations of AMP, and is generally described as a "metabolite-sensing kinase" and when activated initiates steps to conserve cellular energy. Although there is a strong link between the activity of the AMPK and metabolic control in muscle cells, the activity of the AMPK in endothelial cells can be regulated by stimuli that affect cellular ATP levels, such as hypoxia as well as by fluid shear stress, Ca(2+)-elevating agonists, and hormones such as adiponectin. To date the AMPK in endothelial cells has been implicated in the regulation of fatty acid oxidation, small G protein activity and nitric oxide production as well as inflammation and angiogenesis. Moreover, there is evidence indicating that the activation of the AMPK may help to prevent the vascular complications associated with the metabolic syndrome.

The FOX transcription factors regulate vascular pathology, diabetes and Tregs

A small number of upstream master genes in "higher hierarchy" controls the expression of a large number of downstream genes and integrates the signaling pathways underlying the pathogenesis of cardiovascular diseases with or without autoimmune inflammatory mechanisms. In this brief review, we organize our analysis of recent progress in characterization of forkhead (FOX) transcription factor family members in vascular pathology, diabetes and regulatory T cells into the following sections: (1) Overview of the FOX transcription factor superfamily; (2) Vascular pathology of mice deficient in FOX transcription factors; (3) Roles of FOX transcription factors in endothelial cell pathology; (4) Roles of FOX transcription factors in vascular smooth muscle cells; (5) Roles of FOX transcription factors in the pathogenesis of diabetes; and (6) Immune system phenotypes of mice deficient in FOX transcription factors. Advances in these areas suggest that the FOX transcription factor family plays important roles in vascular development and in the pathogenesis of autoimmune inflammatory cardiovascular diseases.