The human ICAM-2 promoter is endothelial cell-specific in vitro and in vivo and contains critical Sp1 and GATA binding sites

Vascular Perspectives of the Midfacial Superficial Musculoaponeurotic System

Objectives: Presently, data on the vascularization of the superficial musculoaponeurotic system of the face (SMAS) are lacking. Thus, the present study aimed to provide new conclusive data about the topography, density, and relationship of the SMAS blood vessels with other components, namely, the fibrous connective tissue and muscles. Methods: The study included a control lot of 42 cases from the archive of the radiology department. In this group, nuclear magnetic resonance angiography (MRA) was performed in order to identify the main sources of vascular supply. In the second group, tissue samples were collected from the midfacial region of 45 patients from the Oro-Maxillo-Facial and Plastic and Reconstructive Surgery clinics of 'St. Spiridon' County Clinical Emergency Hospital, Iasi. These patients received surgery for excision of tumoral formations that did not involve SMAS components. These samples underwent micro-CT analysis, hematoxylin and eosin (HE) staining, as well as immunohistochemical (IHC) staining for collagen type III, muscle tissue, and the vascular endothelium. Results: We discovered the particular way in which the SMAS components interrelate with vascularization and the regional differences between them. We have discovered a new vascular network specific to the SMAS, highlighted by both the micro-CT technique and microscopy on slides with special IHC staining. Significant differences were observed in the topographic arrangement, density, and relationships of the microscopic vasculature across midfacial regions. IHC staining provided morphological and functional information about the structure and vascularization of SMAS. Conclusions: The MRA technique could not detect the structural blood vessels of the SMAS and other methods for their in vivo visualization must be sought. The blood vessels of the SMAS mainly follow the topography of the muscle fibers. From the SMAS layer where they are found, the distribution branches reach the stroma of the region and the hypoderm. Our data can contribute to the development of surgical techniques tailored to each individual patient, as well as the enhancement of methods for stimulating cutaneous angiogenesis, improving scarring in this region, and advancing biotissue engineering techniques.

Multisite Assembly of Gateway Induced Clones (MAGIC): a flexible cloning toolbox with diverse applications in vertebrate model systems

Here we present the Multisite Assembly of Gateway Induced Clones (MAGIC) system, which harnesses site-specific recombination-based cloning via Gateway technology for rapid, modular assembly of between 1 and 3 "Entry" vector components, all into a fourth, standard high copy "Destination" plasmid backbone. The MAGIC toolkit spans a range of in vitro and in vivo uses, from directing tunable gene expression, to driving simultaneous expression of microRNAs and fluorescent reporters, to enabling site-specific recombinase-dependent gene expression. All MAGIC system components are directly compatible with existing multisite gateway Tol2 systems currently used in zebrafish, as well as existing eukaryotic cell culture expression Destination plasmids, and available mammalian lentiviral and adenoviral Destination vectors, allowing rapid cross-species experimentation. Moreover, herein we describe novel vectors with flanking piggyBac transposon elements for stable genomic integration in vitro or in vivo when used with piggyBac transposase. Collectively, the MAGIC system facilitates transgenesis in cultured mammalian cells, electroporated mouse and chick embryos, as well as in injected zebrafish embryos, enabling the rapid generation of innovative DNA constructs for biological research due to a shared, common plasmid platform.

Role of NLRP3 Inflammasomes in Monocyte and Microglial Recruitments in Choroidal Neovascularization

Although the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice and immunostaining techniques to confirm localization of NLRP3 inflammasomes in the laser-induced CNV (LCNV) lesions. Confocal microscopy was used to image and quantify LCNV volumes. MCC950 was used as NLRP3 inhibitor. ELISA and quantitative RT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that red fluorescent protein (RFP)-positive monocyte-derived macrophages and GFP-positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP-positive macrophages, Cx3cr1GFP-positive microglia, and other cells, resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice showed significantly increased lesion size compared with age-matched controls. Inhibition of NLRP3 resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

Ultrasound-mediated gene delivery specifically targets liver sinusoidal endothelial cells for sustained FVIII expression in hemophilia A mice

The ability to target the native production site of factor VIII (FVIII)-liver sinusoidal endothelial cells (LSECs)-can improve the outcome of hemophilia A (HA) gene therapy. By testing a matrix of ultrasound-mediated gene delivery (UMGD) parameters for delivering a GFP plasmid into the livers of HA mice, we were able to define specific conditions for targeted gene delivery to different cell types in the liver. Subsequently, two conditions were selected for experiments to treat HA mice via UMGD of an endothelial-specific human FVIII plasmid: low energy (LE; 50 W/cm2, 150 μs pulse duration) to predominantly target endothelial cells or high energy (HE; 110 W/cm2, 150 μs pulse duration) to predominantly target hepatocytes. Both groups of UMGD-treated mice achieved persistent FVIII activity levels of ∼10% over 84 days post treatment; however, half of the HE-treated mice developed low-titer inhibitors while none of the LE mice did. Plasma transaminase levels and histological liver examinations revealed minimal transient liver damage that was lower in the LE group than in the HE group. These results indicate that UMGD can safely target LSECs with a lower-energy condition to achieve persistent FVIII gene expression, demonstrating that this novel technology is highly promising for therapeutic correction of HA.

Downregulation of the CD151 protects the cardiac function by the crosstalk between the endothelial cells and cardiomyocytes via exosomes

BACKGROUND

Heart failure (HF) is the last stage in the progression of various cardiovascular diseases. Although it is documented that CD151 contributes to regulate the myocardial infarction, the function of CD151 on HF and involved mechanisms are still unclear.

METHOD AND RESULTS

In the present study, we found that the recombinant adeno-associated virus (rAAV)-mediated endothelial cell-specific knockdown of CD151-transfected mice improved transverse aortic constriction (TAC)-induced cardiac function, attenuated myocardial hypertrophy and fibrosis, and increased coronary perfusion, whereas overexpression of the CD151 protein aggravated cardiac dysfunction and showed the opposite effects. In vitro, the cardiomyocytes hypertrophy induced by PE were significantly improved, while the proliferation and migration of cardiac fibroblasts (CFs) were significantly reduced, when co-cultured with the CD151-silenced endothelial cells (ECs). To further explore the mechanisms, the exosomes from the CD151-silenced ECs were taken by cardiomyocyte (CMs) and CFs, verified the intercellular communication. And the protective effects of CD151-silenced ECs were inhibited when exosome inhibitor (GW4869) was added. Additionally, a quantitative proteomics method was used to identify potential proteins in CD151-silenced EC exosomes. We found that the suppression of CD151 could regulate the PPAR signaling pathway via exosomes.

CONCLUSION

Our observations suggest that the downregulation of CD151 is an important positive regulator of cardiac function of heart failure, which can regulate exosome-stored proteins to play a role in the cellular interaction on the CMs and CFs. Modulating the exosome levels of ECs by reducing CD151 expression may offer novel therapeutic strategies and targets for HF treatment.

Role of NLRP3 inflammasomes in monocyte and microglial recruitments in choroidal neovascularization

Though the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice to characterize migration of Ccr2RFP positive monocytes and Cx3cr1GFP positive microglial cells into CNV lesions after laser-induced rupture of Bruch's membrane. MCC950 was used as NLRP3 inhibitor. Immunostaining was used to confirm localization of NLRP3 inflammasomes in the LCNV lesions. Confocal microscopy was used to image and quantify LCNV volumes. ELISA and qRT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that RFP positive monocyte-derived macrophages and GFP positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP positive macrophages, Cx3cr1GFP positive microglia, and other cells resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice, showed significantly increased lesion size compared to age-matched controls. Inhibition of NLRP3, resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

AGEs promote atherosclerosis by increasing LDL transcytosis across endothelial cells via RAGE/NF-κB/Caveolin-1 pathway

OBJECTIVE

To elucidate the mechanism whereby advanced glycation end products (AGEs) accelerate atherosclerosis (AS) and to explore novel therapeutic strategies for atherosclerotic cardiovascular disease.

METHODS AND RESULTS

The effect of AGEs on low-density lipoprotein (LDL) transcytosis across endothelial cells (ECs) was assessed using an in vitro model of LDL transcytosis. We observed that AGEs activated the receptor for advanced glycation end products (RAGE) on the surface of ECs and consequently upregulated Caveolin-1, which in turn increased caveolae-mediated LDL transcytosis and accelerated AS progression. Our molecular assessment revealed that AGEs activate the RAGE-NF-κB signaling, which then recruits the NF-κB subunit p65 to the RAGE promoter and consequently enhances RAGE transcription, thereby forming a positive feedback loop between the NF-κB signaling and RAGE expression. Increased NF-κB signaling ultimately upregulated Caveolin-1, promoting LDL transcytosis, and inhibition of RAGE suppressed AGE-induced LDL transcytosis. In ApoE-/- mice on a high-fat diet, atherosclerotic plaque formation was accelerated by AGEs but suppressed by EC-specific knockdown of RAGE.

CONCLUSION

AGEs accelerate the development of diabetes-related AS by increasing the LDL transcytosis in ECs through the activation of the RAGE/NF-κB/Caveolin-1 axis, which may be targeted to prevent or treat diabetic macrovascular complications.

Development of a dual hybrid AAV vector for endothelial-targeted expression of von Willebrand factor

Von Willebrand disease (VWD), the most common inherited bleeding disorder in humans, is caused by quantitative or qualitative defects in von Willebrand factor (VWF). VWD represents a potential target for gene therapy applications, as a single treatment could potentially result in a long-term correction of the disease. In recent years, several liver-directed gene therapy approaches have been exploited for VWD, but their efficacy was generally limited by the large size of the VWF transgene and the reduced hemostatic activity of the protein produced from hepatocytes. In this context, we aimed at developing a gene therapy strategy for gene delivery into endothelial cells, the natural site of biosynthesis of VWF. We optimized an endothelial-specific dual hybrid AAV vector, in which the large VWF cDNA was put under the control of an endothelial promoter and correctly reconstituted upon cell transduction by a combination of trans-splicing and homologous recombination mechanisms. In addition, we modified the AAV vector capsid by introducing an endothelial-targeting peptide to improve the efficiency for endothelial-directed gene transfer. This vector platform allowed the reconstitution of full-length VWF transgene both in vitro in human umbilical vein endothelial cells and in vivo in VWD mice, resulting in long-term expression of VWF.

Adeno-Associated Virus Technologies and Methods for Targeted Neuronal Manipulation

Cell-type-specific expression of molecular tools and sensors is critical to construct circuit diagrams and to investigate the activity and function of neurons within the nervous system. Strategies for targeted manipulation include combinations of classical genetic tools such as Cre/loxP and Flp/FRT, use of cis-regulatory elements, targeted knock-in transgenic mice, and gene delivery by AAV and other viral vectors. The combination of these complex technologies with the goal of precise neuronal targeting is a challenge in the lab. This report will discuss the theoretical and practical aspects of combining current technologies and establish best practices for achieving targeted manipulation of specific cell types. Novel applications and tools, as well as areas for development, will be envisioned and discussed.

Identification of a novel distal regulatory element of the human Neuroglobin gene by the chromosome conformation capture approach

Neuroglobin (NGB) is predominantly expressed in the brain and retina. Studies suggest that NGB exerts protective effects to neuronal cells and is implicated in reducing the severity of stroke and Alzheimer's disease. However, little is known about the mechanisms which regulate the cell type-specific expression of the gene. In this study, we hypothesized that distal regulatory elements (DREs) are involved in optimal expression of the NGB gene. By chromosome conformation capture we identified two novel DREs located -70 kb upstream and +100 kb downstream from the NGB gene. ENCODE database showed the presence of DNaseI hypersensitive and transcription factors binding sites in these regions. Further analyses using luciferase reporters and chromatin immunoprecipitation suggested that the -70 kb region upstream of the NGB gene contained a neuronal-specific enhancer and GATA transcription factor binding sites. Knockdown of GATA-2 caused NGB expression to drop dramatically, indicating GATA-2 as an essential transcription factor for the activation of NGB expression. The crucial role of the DRE in NGB expression activation was further confirmed by the drop in NGB level after CRISPR-mediated deletion of the DRE. Taken together, we show that the NGB gene is regulated by a cell type-specific loop formed between its promoter and the novel DRE.

Identification and characterization of a novel porcine endothelial cell-specific Tie1 promoter

BACKGROUND

The use of a transgenic pig for xenotransplantation and as a cardiovascular disease model has caught much attention in the past decades. The vascular endothelial cell is the primary modification target for the application of genetically modified pigs in this field. However, the powerful porcine endothelial cell-specific promoter is still so rare that the mouse and human promoters are commonly used. In the study, the porcine Tie1 (sTie1) promoter was identified and characterized as a potential endothelial cell-specific promoter to generate a cardiovascular disease model.

METHODS

Tie1 promoters with different lengths of 5'-regulatory regions were cloned, and major putative DNA-binding motifs were mutated by site-directed mutagenesis. All fragments were ligated into the luciferase reporter system and were transiently transfected into endothelial cells to identify luciferase activity using a dual luciferase reporter assay.

RESULTS

The luciferase activities of sTie1 promoters with different lengths of the 5'-regulatory region were tested. Results showed that the luciferase activity of the 1234-bp sTie1 fragment was the strongest compared with that of others (P < 0.001). Site-directed mutagenesis in transcription-factor-binding sites, including Ets, GATA, and AP2, verified their key roles in regulating transcription, especially sites Ets (-103), GATA (-211), and AP2 (-3). The activities of Tie1 promoters from pig, human, and mouse were significantly different in pig iliac endothelial cells (PIECs) (P < 0.001), and the sTie1 promoter showed the highest activity. Moreover, sTie1 promoter activity could be detected in porcine embryo fibroblasts and skeletal muscle cells.

CONCLUSIONS

The sTie1 promoter shows a highly conserved sequence compared with the Tie1 promoters in human and mouse, but it has a greater activity in the porcine endothelial cell line than that of human and mouse promoters. Thus, sTie1 will be a valuable tool for generating a pig cardiovascular disease model.

VE-statin/egfl7 expression in endothelial cells is regulated by a distal enhancer and a proximal promoter under the direct control of Erg and GATA-2

Angiogenesis is the process by which new blood vessels arise from existing ones by the budding out of endothelial cell capillaries from the luminal side of blood vessels. Blood vessel formation is essential for organ development during embryogenesis and is associated with several physiological and pathological processes, such as wound healing and tumor development. The VE-statin/egfl7 gene is specifically expressed in endothelial cells during embryonic development and in the adult. We studied here the regulatory mechanisms that control this tissue-specific expression. RT-qPCR analyses showed that the specificity of expression of VE-statin/egfl7 in endothelial cells is not shared with its closest neighbor genes notch1 and agpat2 on the mouse chromosome 2. Chromatin-immunoprecipitation analysis of histone modifications at the VE-statin/egfl7 locus showed that the chromatin is specifically opened in endothelial cells, but not in fibroblasts at the transcription start sites. A 13 kb genomic fragment of promoter was cloned and analyzed by gene reporter assays which showed that two conserved regions are important for the specific expression of VE-statin/egfl7 in endothelial cells; a −8409/−7563 enhancer and the −252/+38 region encompassing the exon-1b transcription start site. The latter contains essential GATA and ETS-binding sites, as assessed by linker-scanning analysis and site-directed mutagenesis. An analysis of expression of the ETS and GATA transcription factors showed that Erg, Fli-1 and GATA-2 are the most highly expressed factors in endothelial cells. Erg and GATA-2 directly control the expression of the endogenous VE-statin/egfl7 while Fli-1 probably exerts an indirect control, as assessed by RNA interference and chromatin immunoprecipitation. This first detailed analysis of the mechanisms that govern the expression of the VE-statin/egfl7 gene in endothelial cells pinpoints the specific importance of ETS and GATA factors in the specific regulation of genes in this cell lineage.

Critical role for GATA3 in mediating Tie2 expression and function in large vessel endothelial cells

Endothelial phenotypes are highly regulated in space and time by both transcriptional and post-transcriptional mechanisms. There is increasing evidence that the GATA family of transcription factors function as signal transducers, coupling changes in the extracellular environment to changes in downstream target gene expression. Here we show that human primary endothelial cells derived from large blood vessels express GATA2, -3, and -6. Of these factors, GATA3 was expressed at the highest levels. In DNA microarrays of human umbilical vein endothelial cells (HUVEC), small interfering RNA-mediated knockdown of GATA3 resulted in reduced expression of genes associated with angiogenesis, including Tie2. At a functional level, GATA3 knockdown inhibited angiopoietin (Ang)-1-mediated but not vascular endothelial cell growth factor (VEGF)-mediated AKT signaling, cell migration, survival, and tube formation. In electrophoretic gel mobility shift assays and chromatin immunoprecipitation, GATA3 was shown to bind to regulatory regions within the 5'-untranslated region of the Tie2 gene. In co-immunoprecipitation and co-transfection assays, GATA3 and the Ets transcription factor, ELF1, physically interacted and synergized to transactivate the Tie2 promoter. GATA3 knockdown blocked the ability of Ang-1 to attenuate vascular endothelial cell growth factor stimulation of vascular cell adhesion molecule-1 expression and monocytic cell adhesion. Moreover, exposure of human umbilical vein endothelial cells to tumor necrosis factor-alpha resulted in marked down-regulation of GATA3 expression and reduction in Tie2 expression. Together, these findings suggest that GATA3 is indispensable for Ang-1-Tie2-mediated signaling in large vessel endothelial cells.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

[Genes that make the endothelial identity]

The endothelium is a tissue with a distinct identity due to the specific expression of molecular markers by endothelial cells. Further, the endothelium displays a structural heterogeneity illustrated by the expression of specific markers in arteries and in veins. Here, we present a review of the transcriptional and epigenetic mechanisms regulating the expression of the main markers of endothelial cells in man and mouse, demonstrating that there is no common and unique mechanism of specific expression of genes in these cells.

Transcriptional control of endothelial cell development

The transcription factors that regulate endothelial cell development have been a focus of active research for several years, and many players in the endothelial transcriptional program have been identified. This review discusses the function of several major regulators of endothelial transcription, including members of the Sox, Ets, Forkhead, GATA, and Kruppel-like families. This review also highlights recent developments aimed at unraveling the combinatorial mechanisms and transcription factor interactions that regulate endothelial cell specification and differentiation during vasculogenesis and angiogenesis.

Efficient targeted transduction of primary human endothelial cells with dual-targeted lentiviral vectors

Angiogenesis is a rate-limiting factor for numerous human diseases. Angiogenic vessels and also the endothelium of certain organs such as the lung display molecular addresses that can be exploited for the selective delivery of gene therapeutics. Lentiviral vectors (LVs) are powerful tools for stable gene delivery but their integration and expression in undesired cell types poses a serious safety concern. We have developed a dual-targeted LV that can specifically target primary endothelial cells (ECs). Cell selectivity is achieved during entry, using a modified Sindbis virus envelope, and during transcription, with an EC-specific promoter. We evaluated four surface markers for EC targeting and seven promoter sequences from genes preferentially expressed in ECs. The efficiency and specificity of the double targeted vector were assayed in a panel of human primary cultures and tumor cell lines. A vector targeted to CD146, an endothelial adhesion molecule, and carrying a derivative of the EC tyrosine kinase Tie2 promoter, increased specificity of transduction up to 50 times and was also effective at selectively transducing ECs in a mixed coculture with human fibroblasts. The vector presented here is a potentially powerful tool that could be used in a variety of human diseases.

Receptor-mediated tobacco toxicity: acceleration of sequential expression of alpha5 and alpha7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke

Tobacco products and nicotine alter the cell cycle and lead to squamatization of oral keratinocytes (KCs) and squamous cell carcinoma. Activation of nicotinic acetylcholine receptors (nAChRs) elicits Ca(2+) influx that varies in magnitude between different nAChR subtypes. Normal differentiation of KCs is associated with sequential expression of the nAChR subtypes with increasing Ca(2+) permeability, such as alpha5-containing alpha3 nAChR and alpha7 nAChR. Exposure to environmental tobacco smoke (ETS) or an equivalent concentration of nicotine accelerated by severalfold the alpha5 and alpha7 expression in KCs, which could be abolished by mecamylamine and alpha-bungarotoxin with different efficacies, suggesting the following sequence of autoregulation of the expression of nAChR subtypes: alpha3(beta2/beta4) > alpha3(beta2/beta4)alpha5 > alpha7 > alpha7. This conjecture was corroborated by results of quantitative assays of subunit mRNA and protein levels, using nAChR-specific pharmacologic antagonists and small interfering RNAs. The genomic effects of ETS and nicotine involved the transcription factor GATA-2 that showed a multifold increase in quantity and activity in exposed KCs. Using protein kinase inhibitors and dominant negative and constitutively active constructs, we characterized the principal signaling cascades mediating a switch in the nAChR subtype. Cumulative results indicated that the alpha3(beta2/beta4) to alpha3(beta2/beta4)alpha5 nAChR transition predominantly involved protein kinase C, alpha3(beta2/beta4)alpha5 to alpha7 nAChR transition-Ca(2+)/calmodulin-dependent protein kinase II and p38 MAPK, and alpha7 self-up-regulation-the p38 MAPK/Akt pathway, and JAK-2. These results provide a mechanistic insight into the genomic effects of ETS and nicotine on KCs and characterize signaling pathways mediating autoregulation of stepwise overexpression of nAChR subtypes with increasing Ca(2+) permeability in exposed cells. These observations have salient clinical implications, because a switch in the nAChR subunit composition can bring about a corresponding switch in receptor function, leading to profound pathobiologic effects observed in KCs exposed to tobacco products.

Gene expression analysis of embryonic stem cells expressing VE-cadherin (CD144) during endothelial differentiation

Background

Endothelial differentiation occurs during normal vascular development in the developing embryo. This process is recapitulated in the adult when endothelial progenitor cells are generated in the bone marrow and can contribute to vascular repair or angiogenesis at sites of vascular injury or ischemia. The molecular mechanisms of endothelial differentiation remain incompletely understood. Novel approaches are needed to identify the factors that regulate endothelial differentiation.

Methods

Mouse embryonic stem (ES) cells were used to further define the molecular mechanisms of endothelial differentiation. By flow cytometry a population of VEGF-R2 positive cells was identified as early as 2.5 days after differentiation of ES cells, and a subset of VEGF-R2⁺ cells, that were CD41 positive at 3.5 days. A separate population of VEGF-R2⁺ stem cells expressing the endothelial-specific marker CD144 (VE-cadherin) was also identified at this same time point. Channels lined by VE-cadherin positive cells developed within the embryoid bodies (EBs) formed by differentiating ES cells. VE-cadherin and CD41 expressing cells differentiate in close proximity to each other within the EBs, supporting the concept of a common origin for cells of hematopoietic and endothelial lineages.

Results

Microarray analysis of >45,000 transcripts was performed on RNA obtained from cells expressing VEGF-R2⁺, CD41⁺, and CD144⁺ and VEGF-R2^-, CD41^-, and CD144^-. All microarray experiments were performed in duplicate using RNA obtained from independent experiments, for each subset of cells. Expression profiling confirmed the role of several genes involved in hematopoiesis, and identified several putative genes involved in endothelial differentiation.

Conclusion

The isolation of CD144⁺ cells during ES cell differentiation from embryoid bodies provides an excellent model system and method for identifying genes that are expressed during endothelial differentiation and that are distinct from hematopoiesis.

A Gata2 intronic enhancer confers its pan-endothelia-specific regulation

GATA-2, a transcription factor that has been shown to play important roles in multiple organ systems during embryogenesis, has been ascribed the property of regulating the expression of numerous endothelium-specific genes. However, the transcriptional regulatory hierarchy governing Gata2 activation in endothelial cells has not been fully explored. Here, we document GATA-2 endothelial expression during embryogenesis by following GFP expression in Gata2-GFP knock-in embryos. Using founder transgenic analyses, we identified a Gata2 endothelium enhancer in the fourth intron and found that Gata2 regulation by this enhancer is restricted to the endocardial, lymphatic and vascular endothelium. Whereas disruption of three ETS-binding motifs within the enhancer diminished its activity, the ablation of its single E box extinguished endothelial enhancer-directed expression in transgenic mice. Development of the endothelium is known to require SCL (TAL1), and an SCL-E12 (SCL-Tcfe2a) heterodimer can bind the crucial E box in the enhancer in vitro. Thus, GATA-2 is expressed early in lymphatic, cardiac and blood vascular endothelial cells, and the pan-endothelium-specific expression of Gata2 is controlled by a discrete intronic enhancer.

Action of transcription factors in the control of transferrin receptor expression in human brain endothelium

Brain endothelium has a distinctive phenotype, including high expression of transferrin receptor, p-glycoprotein, claudin-5 and occludin. Dermal endothelium expresses lower levels of the transferrin receptor and it is absent from lung endothelium. All three endothelia were screened for transcription factors that bind the transferrin receptor promoter and show different patterns of binding between the endothelia. The transcription factor YY1 has distinct DNA-binding activities in brain endothelium and non-brain endothelium. The target-sites on the transferrin receptor promotor for YY1 lie in close proximity to those of the transcription initiation complex containing TFIID, so the two transcription factors potentially compete or interfere. Notably, the DNA-binding activity of TFIID was the converse of YY1, in different endothelia. YY1 knockdown reduced transferrin receptor expression in brain endothelium, but not in dermal endothelium, implying that YY1 is involved in tissue-specific regulation of the transferrin receptor. Moreover a distinct YY1 variant is present in brain endothelium and it associates with Sp3. A model is presented, in which expression from the transferrin receptor gene in endothelium requires the activity of both TFIID and Sp3, but whether the gene is transcribed in different endothelia, is related to the balance between activating and suppressive forms of YY1.

Pleiotrophin induces transdifferentiation of monocytes into functional endothelial cells

OBJECTIVE

Pleiotrophin (PTN) is a cytokine that is expressed by monocytes/macrophages in ischemic tissues and that promotes neovascularization, presumably by stimulating proliferation of local endothelial cells. However, the effect of PTN on monocytes/macrophages remains unknown. We investigated the role of PTN in regulating the phenotype of monocytes/macrophages.

METHODS AND RESULTS

RT-PCR, real-time PCR, and fluorescence-activated cell sorter analysis revealed that the expression of PTN by monocytic cells led to a downregulation of CD68, c-fms, and CD14 monocytic cell markers and an upregulation of FLK-1, Tie-2, vascular endothelial-cadherin, platelet endothelial cell adhesion molecule-1, endothelial NO synthase, von Willebrand factor, CD34, GATA-2, and GATA-3 endothelial cell markers. Fibrin gel assays showed that the treatment of mouse and human monocytic cells with PTN led to the formation of tube-like structures. In vivo studies showed that PTN-expressing monocytic cells incorporated into the blood vessels of the quail chorioallantoic membrane. The intracardial injection of PTN-expressing monocytic cells into chicken embryos showed that cells integrated only into the developing vasculature. Finally, the injection of PTN-expressing monocytes into a murine ischemic hindlimb model significantly improved perfusion of the ischemic tissue.

CONCLUSIONS

PTN expression by monocytes/macrophages led to a downregulation of their monocytic cell markers and an upregulation of endothelial cell characteristics, thus inducing the transdifferentiation of monocytes into functional endothelial cells.

Genomic structure, organization and promoter analysis of the human F11R/F11 receptor/junctional adhesion molecule-1/JAM-A

The F11-receptor (F11R) (a.k.a. JAM-1, JAM-A, CD321) is a cell adhesion molecule of the immunoglobulin superfamily involved in platelet adhesion, secretion and aggregation. In addition, the F11R plays a critical role in the function of endothelial cells and in platelet adhesion to inflamed endothelium. In the present study, we used partial sequences of the human F11R gene, F11R cDNAs, and information in unannotated human genome databases, to delineate the F11R gene. We found that the F11R gene is composed of 13 exons (E1a, 1b, 1c, E1-E10) encoding two groups of mRNAs differing in length and sequence at their 5' UTRs, referred to as type 1 and type 2 messages. Type 1 cDNAs are shorter at the 5' end and contain a region not found within type 2 messages. Type 1 mRNAs are present in endothelial cells (EC), platelets, white blood cells and in the cell lines CMK, HeLa, K562, HOG and A549, while type 2 messages are limited to EC. Type 1 messages contain exons E1-E10 whereas type 2 messages usually contain exons E1a, 1c, part of E1 and E2-E10. The translation start site is localized in the 3' end of E1, common for both type 1 and type 2 messages. Expression of these messages is regulated by two alternative promoters, P1 and P2. P1 is a TATA-less promoter containing an initiator element, multiple transcription start sites, several GC and CCAAT boxes, and GATA, NF-kappaB and ets consensus sequences. The cloned P1 drives efficient expression of the luciferase reporter gene. A high level of similarity between human P1 and its rat and mouse counterparts was observed. Promoter P2, located upstream of P1, contains a TATA box, GC boxes, a CCAAT box and GATA and ets consensus sequences. 3' RACE provided evidence for variability in the 3' UTR due to the presence of two polyadenylation signals. The finding of multiple regulatory sites in the promoters supplements the biochemical evidence that the F11R has several different roles in the functional repertoire of endothelial cells, platelets and other cells. In particular, the presence of NF-kappaB provides additional evidence to the significance of the F11R function in the initiation of inflammatory thrombosis.

Identification of endothelial genes up-regulated in vivo

We have used microarrays to identify genes that are selectively expressed in endothelial cells in vivo. Analysis of freshly isolated endothelial cells from the lungs and kidneys reveals that 350 out of the 10,000 genes represented on the microarrays were expressed at higher levels than by the corresponding parenchymal cells. Thirteen of these genes were identified both in the lung and kidney screens from a subset of about 5000 genes. Many of these genes are known to be specifically expressed in endothelial cells, but about 200 genes were potentially novel endothelial genes. The preferential endothelial expression of a selected group of these genes was confirmed by quantitative polymerase chain reaction or in situ mRNA hybridization. Comparison of the genes expressed in lung and kidney endothelia revealed numerous differences. Notably, genes encoding components of an ephrin signaling pathway were highly expressed in lung endothelial cells. In summary, the genes we have identified represent potentially new pan-endothelial and tissue-specific endothelial markers.

The expression of endothelial nitric-oxide synthase is controlled by a cell-specific histone code

Expression of endothelial nitric-oxide synthase (eNOS) mRNA is highly restricted to the endothelial cell layer of medium to large sized arterial blood vessels. Here we assessed the chromatin environment of the eNOS gene in expressing and nonexpressing cell types. Within endothelial cells, but not a variety of nonendothelial cells, the nucleosomes that encompassed the eNOS core promoter and proximal downstream coding regions were highly enriched in acetylated histones H3 and H4 and methylated lysine 4 of histone H3. This differentially modified chromatin domain was selectively associated with functionally competent RNA polymerase II complexes. Endothelial cells were particularly enriched in acetylated histone H3 lysine 9, histone H4 lysine 12, and di- and tri-methylated lysine 4 of histone H3 at the core promoter. Histone modifications at this region, which we have previously demonstrated to exhibit cell-specific DNA methylation, were functionally relevant to eNOS expression. Inhibition of histone deacetylase activity by trichostatin A increased acetylation of histones H3 and H4 at the eNOS proximal promoter in nonexpressing cell types and led to increased steady-state eNOS mRNA transcript levels. H3 lysine 4 methylation was also essential for eNOS expression, since treatment of endothelial cells with methylthioadenosine, a known lysine 4 methylation inhibitor, decreased eNOS RNA levels, H3 lysine 4 methylation, and RNA polymerase II loading at the eNOS proximal promoter. Importantly, methylthioadenosine also prevented the trichostatin A-mediated increase in eNOS mRNA transcript levels in nonendothelial cells. Taken together, these findings provide strong evidence that the endothelial cell-specific expression of eNOS is controlled by cell-specific histone modifications.

Macrophage colony-stimulating factor expression in retrovirally transduced cells is dependent upon both the adherence status of the target cells and its 5′ flanking untranslated region

Numerous cell types retrovirally transduced with macrophage colony-stimulating factor (M-CSF) using LXSN-based vectors showed a variable expression of the transgene. Expression of M-CSF correlated with the cells' adherent status. Transduced adherent cells produced the M-CSF, whereas the non-adherent cells synthesized little M-CSF. Studies showed that the 5'-UTR of the M-CSF gene regulated transgenic M-CSF gene expression. Ligation of this 5'-UTR to the enhanced green fluorescent protein gene (EGFP) caused the expression of EGFP to show the same dichotomy as previously seen with the M-CSF. Transgenic M-CSF was expressed within non-adherent cells when the 5'-UTR was removed from the LXSN vector. Quantitative real-time polymerase chain reaction analysis confirmed that lesser production of M-CSF mRNA occurred within the non-adherent cells than in the adherent cells. This difference was eliminated when the 5'-UTR was removed from the retroviral vector. Our work suggests that this 5'-UTR of the M-CSF gene could be an important way to get transgenic expression within adherent cells, but not in non-adherent cells.

Induction of KLF2 by fluid shear stress requires a novel promoter element activated by a phosphatidylinositol 3-kinase-dependent chromatin-remodeling pathway

Fluid shear stress maintains vascular homeostasis by influencing endothelial gene expression. One mechanism by which shear stress achieves this is through the induction of transcription factors including Krüppel-like factor 2(KLF2). We have previously reported that a 62-bp region of the KLF2 promoter is responsible for its shear stress-induced expression via the binding of nuclear factors. In this study, we find that the 62-bp shear stress response region contains a 30-bp tripartite palindrome motif. Electrophoretic mobility supershift and chromatin immunoprecipitation assays demonstrate that PCAF (P-300/cAMP-response element-binding protein-binding protein-associated factor)) and heterogeneous nuclear ribonucleoprotein D bind this region as components of the shear stress regulatory complex. We have also characterized a PI3K-dependent/Akt-independent pathway responsible for shear stress-induced KLF2 nuclear binding, promoter activation, and mRNA expression. Furthermore, the shear stress response region of the KLF2 promoter was specifically immunoprecipitated by antibodies against acetylated histones H3 and H4 in shear-stressed but not static hemangioendothelioma cells. The acetylation of these histones was blocked by PI3K inhibition. Finally, we have found that KLF2 increases endothelial nitric-oxide synthase expression in murine endothelial cultures, an effect that is also blocked by PI3K inhibition. These results define the DNA regulatory element, signal transduction pathway, and molecular mechanism activating the flow-dependent expression of a vital endothelial transcription factor.

Isolation, sequencing, and functional analysis of the TATA-less human ATPase II promoter

Multiple lines of evidence indicate that the P-type Mg(2+)-ATPase, termed ATPase II, could play an important role in apoptosis. With the long-term objective of studying the regulation of this protein during apoptosis, we delineated the exon-intron organization of the human ATPase II gene (within chromosome 4). Subsequently, we used RNA ligase-mediated rapid amplification of cDNA ends to identify a major transcription start site at position -143 with respect to the translation start site. Luciferase reporter analysis of a 1.2-kb 5'-flanking sequence (-1222 to +94 with respect to the transcription start site) revealed strong promoter activity in three human cell lines, human oligodendroglioma (HOG), SHSY5Y (hybrid neuroblastoma), and EA.hy926 (endothelial cell line). Serial deletions from the 5' end of this sequence up to nucleotide -291 yielded some decrease in activity only in the EA.hy926 cells. Further deletion to -217 caused a drastic decrease in activity in all three cell lines, but a -148 fragment showed preferential reduction in activity in the EA.hy926 cells. The promoter activity was nearly equal in two sequence variants of the promoter, one of which (designated as Variant 2) contained a 15-bp direct repeat within a GC-rich region. Additionally, there were several single base-pair changes from the sequence reported by the human genome project. Despite the presence of enhancer/repressor elements, such as Sp1 and NFkappaB, relatively small differences in promoter activity were observed in the three cell lines. However, it is likely that such sequence elements could cause major regulation of promoter activity in cells subjected to conditions that trigger apoptosis. The ATPase II promoter sequence will provide valuable clues to the regulation and role of the ATPase II protein.

Identification of synthetic endothelial cell-specific promoters by use of a high-throughput screen

Transcriptional targeting is a desirable property for many gene transfer applications. Because endothelial cells line most blood vessels, they are attractive candidates for the introduction of therapeutic gene products. As a proof-of-concept study, we attempted to identify a synthetic, endothelial cell-specific promoter by use of a high-throughput screen involving self-inactivating (SIN) human immunodeficiency virus type 1 (HIV-1)-based vectors. Select duplex oligodeoxynucleotides recognized by transcription factors and located 5' of endothelial cell-specific mRNA transcripts were randomly ligated and cloned upstream of a minimal ICAM-2 promoter driving enhanced green fluorescent protein (eGFP) in a SIN HIV-1-based vector. Vesicular stomatitis virus G protein-pseudotyped particles were prepared from a library of >10(6) vector recombinants and used to transduce an endothelial cell line. The highest eGFP expressers were repeatedly sorted, and the synthetic promoters were recovered and retested by a luciferase reporter. Several promoters were active and specific to endothelial cells of varied species, with high selectivity indexes and inducibility under hypoxia-mimetic conditions. One in particular was then introduced back into a SIN HIV-1-based vector to confirm its endothelial cell activity and specificity. This study suggests that SIN vectors may be used in a high-throughput manner to identify tissue-specific promoters of high activity, with potential applications for both transcriptional targeting and gene transfer.

Isolation of a Regulatory Region of Activin Receptor-Like Kinase 1 Gene Sufficient for Arterial Endothelium-Specific Expression

Activin receptor-like kinase 1 (Acvrl1; Alk1) is a type I receptor for transforming growth factor-beta (TGF-beta). ALK1 plays a pivotal role in vascular development and is involved in the development of hereditary hemorrhagic telangiectasia 2 (HHT2), a dominantly inherited vascular disorder, and pulmonary hypertension. We have previously shown that Alk1 is expressed predominantly in arterial endothelial cells (ECs). Despite recent discoveries of a number of artery-specific genes, the regulatory elements of these genes have not been characterized. To investigate the cis-acting elements essential for the artery-specific Alk1 expression, we have generated a series of transgenic constructs with various lengths and regions of Alk1 genomic fragments connected to a LacZ reporter gene, and analyzed the reporter gene expression in transgenic mice. We found that a 9.2-kb genomic fragment, which includes 2.7-kb promoter region and the entire intron 2, is sufficient to drive arterial endothelium-specific expression. The defined regulatory region, as well as the transgenic mouse lines, would be invaluable resources in studying the mechanisms underlying angiogenesis, arteriogenesis, and vascular disorders, such as HHT and pulmonary hypertension. The full text of this article is available online at http://circres.ahajournals.org.

Characterization of pig intercellular adhesion molecule-2 and its interaction with human LFA-1

Understanding molecular interactions between human leukocytes and porcine endothelium is important for the future success of pig-to-human xenotransplantation. Here we describe the analysis of pig intercellular adhesion molecule-2 (ICAM-2). A 1020-basepair ICAM-2 cDNA generated from pig lung RNA contained an open reading frame (ORF) encoding a 277-amino-acid protein with six potential N-linked glycosylation sites. The mature protein sequence was 55% identical to human ICAM-2, with conservation of five out of six residues critical for binding of the human protein to its ligand LFA-1. Northern blot analysis identified ICAM-2 transcripts of 4.0 and 1.4 kb in cultured pig endothelial cells and mRNA was detected in pig lung, spleen, kidney, liver and heart by RT-PCR. The gene structure and endothelial expression of pig ICAM-2 were strikingly similar to those of its human and mouse counterparts. However, unlike human ICAM-2, expression of pig ICAM-2 on cultured endothelial cells was not down-regulated by treatment with the inflammatory cytokines TNF-alpha and IL-1beta. Pig ICAM-2 expressed on stable transfectants supported firm adhesion of cells expressing human LFA-1. This conservation of function across the species barrier suggests that pig ICAM-2 plays a role in the cellular interactions associated with xenograft rejection.

Retroviral hybrid LTR vector strategy: functional analysis of LTR elements and generation of endothelial cell specificity

Transcriptional targeting is an important aspect of developing gene therapy vectors in order to restrict transgene expression to selected target cells. One approach, when using retroviral vectors, is to replace viral transcriptional control elements within the long terminal repeat (LTR) with sequences imparting the desired specificity. We have developed such hybrid LTR retroviruses, incorporating sequences from each of the human promoters for flt-1, ICAM-2 and KDR, as part of our antivascular cancer gene therapy strategy targeting tumour endothelial cells. The chosen fragments were used to replace the enhancer or combined enhancer and proximal promoter regions of the viral LTR. All showed activity in primary human breast microvascular endothelial cells, with viruses incorporating ICAM-2 sequences exhibiting the greatest specificity versus nonendothelial cells in vitro and a marked alteration of specificity towards endothelial cells in a subcutaneous xenograft model in vivo. Moreover, our study documents the effect of enhancer and/or proximal promoter deletion on LTR activity and reports that differential dependence in different cell lines can give the false impression of specificity if experiments are not adequately controlled. This finding also has implications for other retroviral vector designs seeking to provide transcriptional specificity and for their safety with respect to prevention of gene activation at sites of proviral integration.

Ets motifs are necessary for endothelial cell-specific expression of a 723-bp Tie-2 promoter/enhancer in Hprt targeted transgenic mice

OBJECTIVE

Tie-2 is an endothelial cell-specific receptor tyrosine kinase that is involved in the remodeling of blood vessels and angiogenesis. Our goal was to characterize Tie-2 promoter function as a means of providing insight into the mechanisms of endothelial cell-specific gene regulation.

METHODS AND RESULTS

When targeted to the Hprt locus of mice, a small Tie-2 promoter fragment (containing a 300-bp intronic enhancer coupled upstream to a 423-bp core promoter) (T-short) directed widespread endothelial cell expression in vivo. The T-short promoter contains 2 clusters of Ets sites, one in the first exon, the other in the intronic enhancer. In cultured endothelial cells, a combined mutation of the Ets motifs resulted in a significant reduction in promoter activity. Consistent with these results, the same Ets mutations resulted in a loss of detectable expression of the T-short promoter in all vascular beds with the notable exception of the brain.

CONCLUSIONS

These results suggest that the T-short promoter contains information for widespread expression in the vascular tree, Ets sites are necessary for in vivo promoter activity, and the shorter Tie-2 fragment may be useful as a tool to direct heterologous gene expression within the intact endothelium.

In vivo targeting of tumor endothelial cells by systemic delivery of lentiviral vectors

Tumor angiogenesis is a rate-limiting factor for tumor growth, and the endothelial cells of tumor vessels display specific features that can be exploited for the selective delivery of cancer therapeutics. To specifically target exogenous genes to angiogenic tumor vessels, we generated a panel of vesicular stomatitis virus-pseudotyped lentiviral vectors (LVs) engineered for endothelial cell (EC)-specific expression. We cloned a wide repertoire of transcription regulatory sequences from genes preferentially expressed in ECs (Tie1, Tie2, Flk-1, VE-Cad, and ICAM-2) into self-inactivating LVs to drive expression of the marker gene encoding green fluorescent protein (GFP) or of the conditionally toxic gene encoding nitroreductase, and compared them with the ubiquitously expressing phosphoglycerate kinase (PGK) and cytomegalovirus (CMV) promoters. We evaluated the efficiency and specificity of vector expression in vitro in a panel of human primary cultures, including ECs, fibroblasts, neurons, lymphocytes, and hematopoietic progenitors, and in tumor cell lines. We found that vectors containing promoter and enhancer sequences from the Tie2 gene achieved remarkable specificity of expression in ECs in vitro and in vivo. On intravenous delivery into tumor-bearing mice, the Tie2 vector targeted expression to the ECs of tumor vessels. In contrast, LVs carrying the PGK or CMV promoter gave widespread GFP marking in ECs and non-ECs of tumors and other organs. The previously reported upregulation of the Tie2 gene in ECs activated for angiogenesis may explain the remarkable selectivity of expression of the Tie2 vector in ECs of tumor vessels. The new vector provides the means for selective delivery of gene therapy to tumor sites in vivo.

Targeting gene expression to endothelium in transgenic animals: a comparison of the human ICAM-2, PECAM-1 and endoglin promoters

It is highly likely that successful pig-to-human xenotransplantation of vascularized organs will require genetic modification of the donor pig, and in particular of donor vascular endothelium. Promoters are generally tested in transgenic mice before generating transgenic pigs. Several promoters have been used to drive endothelial cell-specific expression in mice but none have yet been tested in pigs. We compared the promoters of three human genes that are predominantly expressed in vascular endothelium: intercellular adhesion molecule 2 (ICAM-2), platelet endothelial cell adhesion molecule 1 (PECAM-1) and endoglin. Expression of human complement regulatory proteins (hCRPs), directed by each of the promoters in mice, was largely restricted to vascular endothelium and leukocyte subpopulations. However, expression from the PECAM-1 promoter was weak in liver and non-uniform in the small vessels of heart, kidney, and lung. Conversely, expression from the endoglin promoter was consistently strong in the small vessels of these organs but was absent in larger vessels. The ICAM-2 promoter, which produced strong and uniform endothelial expression in all organs examined, was therefore used to generate hCRP transgenic pigs. Leukocytes from 57 pigs containing at least one intact transgene were tested for transgene expression by flow cytometry. Forty-seven of these transgenic pigs were further analyzed by immunohistochemical staining of liver biopsies, and 18 by staining of heart and kidney sections. Only two of the pigs showed expression, which appeared to be restricted to vascular endothelium in heart and kidney but was markedly weaker than in transgenic mice produced with the same batch of DNA. Thus, in this case, promoter performance in mice and pigs was not equivalent. The weak expression driven by the human ICAM-2 promoter in pigs relative to mice suggests the need for additional regulatory elements to achieve species-specific gene expression in pigs.

Outline of a Risk Assessment: The Welfare of Future Xeno-Donor Pigs

The welfare of transgenic animals is often not considered prior to their generation. However, we demonstrate here how a welfare risk assessment can be carried out before transgenic animals are created. We describe a risk assessment identifying potential welfare problems in transgenic pigs generated for future xeno-donation of organs. This assessment is based on currently available information concerning transgenic animal models in which one or more transgenes relevant to future xeno-donation have been inserted. The welfare risk assessment reveals that future xeno-donor pigs may have an increased tendency toward septicaemias, reduced fertility and/or impaired vision. The transgenic animal models used in generating hypotheses about the welfare of xeno-donor pigs can also assist in the testing of these hypotheses. To ensure high levels of welfare of transgenic animals, analogous risk assessments can be used to identify potential welfare problems during the early stages of the generation of new transgenic animals. Such assessments may form part of the basis on which licenses to generate new transgenic animals are granted to research groups.

Ets, Ap-1 and GATA factor families regulate the utrophin B promoter: potential regulatory mechanisms for endothelial-specific expression

Duchenne muscular dystrophy is caused by dystrophin deficiency, which can be prevented in the mdx mouse model by over-expression of an autosomal homologue, utrophin. Utrophin has two characterised full-length promoters, A and B. No data are available on the transcriptional regulation of B utrophin, which has been recently localised to the endothelium. Similar to characterised endothelial promoters, Ets and Ap-1 individually trans-activate the human B core promoter. Synergistic activation by GATA-2 and c-jun to the order of 20-fold was observed.

The NFY transcription factor inhibits von Willebrand factor promoter activation in non-endothelial cells through recruitment of histone deacetylases

Human von Willebrand factor (VWF) gene sequences +155 to +247 contain cis-acting elements that contribute toward endothelial specific activation of the VWF promoter. Analyses of this region demonstrated the presence of a GATA-binding site that is necessary for the promoter activation in endothelial cells. We have reported recently the presence of a novel NFY-binding sequence in this region that does not conform to the consensus NFY-binding sequence CCAAT. NFY was shown to function as a repressor of the VWF promoter through interaction with this novel binding site. Here we report that the NFY interacts with histone deacetylases (HDACs) in a cell type-specific manner and recruits them to the VWF promoter to inhibit the promoter activity in non-endothelial cells. Analyses of the acetylation status of histones in the chromatin region containing the VWF promoter sequences demonstrated that these sequences are associated with acetylated histone H4 specifically in endothelial cells. It was also demonstrated that HDACs are specifically recruited to the same chromatin region in non-endothelial cells. We also demonstrated that GATA6 is the GATA family member that interacts with the VWF promoter and that GATA6 is associated with NFY specifically in non-endothelial cells. We propose that NFY recruits HDACs to the VWF promoter, which may result in deacetylation of GATA6 as well as of histones in non-endothelial cells, thus leading to promoter inactivation. In endothelial cells, however, association of HDACs, NFY, and GATA6 is interrupted potentially through endothelial cell-specific signaling/mechanism, thus favoring the balance toward acetylation and activation of the VWF promoter.

Characterization of the human gene encoding the scavenger receptor expressed by endothelial cell and its regulation by a novel transcription factor, endothelial zinc finger protein-2

The scavenger receptor expressed by endothelial cell (SREC), mediates the selective uptake of modified low density lipoprotein (LDL), such as acetylated LDL and oxidized LDL, into endothelial cells. The SREC gene spans 12 kilobase pairs and contains 11 exons. Analysis of full-length cDNA clones of SREC from a peripheral blood leukocyte cDNA library revealed that at least five alternatively spliced cDNAs were present, and two of them encoded soluble forms of SREC. The transcription start site of the SREC gene was mapped, and DNA sequence analysis revealed an Sp1 binding site in its proximal region. Deletion analysis of the 5'-flanking sequence revealed that sequence between base pairs -108 and -98 was critical for the promoter activity. This region contained half of an inverted repeat (IR) sequence with a triple nucleotide spacer (IR-3). A protected sequence between base pairs -268 and +17 was defined by in vitro DNase I footprinting analysis using human umbilical vein endothelial cell (HUVEC) nuclear extract. A novel transcription factor, endothelial zinc finger protein-2 (EZF-2), that binds to the 5'-flanking critical region of the SREC promoter activity was cloned from a HUVEC cDNA library employing a one-hybrid system. Whereas purified recombinant Sp1 alone produced similar protection in in vitro DNase I footprinting analysis, EZF-2 also bound to the 5'-flanking region SREC promoter. Co-transfection of SREC promoter and Sp1 or EZF-2 expression plasmids in HUVEC revealed that EZF-2 but not Sp1 increased SREC promoter activity. On the other hand, the mutation of either the Sp1 motif or IR-3 motif resulted in a decrease in the promoter activity. These results suggest that whereas Sp1 is the major nuclear protein bound to the regulatory region of the promoter, both EZF-2 and Sp1 are responsible for its regulation.

Regulation of alpha1,3galactosyltransferase expression in pig endothelial cells. Implications for xenotransplantation

The disaccharide galactose(alpha)1,3 galactose (the alphaGal epitope) is the major xenoantigen responsible for the hyperacute vascular rejection occurring in pig-to-primates organ transplantation. The synthesis of the alphaGal epitope is catalyzed by the enzyme alpha1,3-galactosyltransferase (alpha1,3GalT). To be able to control porcine alpha1,3GalT gene expression specifically, we have analyzed the upstream portion of the alpha1,3GalT gene, and identified the regulatory sequences. Porcine alpha1,3GalT transcripts were detected by 5' RACE analysis, and the corresponding genomic sequences were isolated from a phage library. The porcine alpha1,3GalT gene consists of at least 10 different exons, four of which contain 5' untranslated sequence. Four distinct promoters, termed A-D, drive alpha1,3GalT gene transcription in porcine cells. A combination of alternative promoter usage and alternative splicing produces a series of transcripts that differ in their 5' portion, but encode the same protein. Promoters A-C have been isolated, and functionally characterized using luciferase reporter gene assays in transfected porcine endothelial cells (PEC-A). Promoter preference in porcine endothelial cells was estimated on the basis of relative transcript levels as determined by real-time quantitative PCR. More than 90% of the alpha1,3GalT transcripts in PEC-A cells originate from promoter B, which has characteristics of a housekeeping gene promoter. While promoter preference remains unchanged, alpha1,3GalT mRNA levels increase by 50% in 12 h upon tumour necrosis factor alpha-activation of PEC-A cells. However, the magnitude of this change induced by inflammatory conditions could be insufficient to affect cell surface alpha1,3-galactosylation.

Cloning and characterization of the human lung endothelial-cell-specific molecule-1 promoter

Endothelial-cell-specific molecule-1 (ESM-1) is a cysteine-rich protein that is expressed primarily in endothelial cells of the lung, kidney and gut. In the present study, we have cloned and sequenced 3,888 bp of the 5' flanking region of the human ESM-1 gene. The full-length promoter directed high-level expression of the luciferase reporter gene in bovine lung microvascular endothelial cells and bovine aortic endothelial cells, but not in nonendothelial cell types. In 5' deletion analyses, a region spanning -81 to +58 was shown to contain information for endothelial-cell-specific expression. Mutational analysis in transient transfection assays uncovered an important role for an Ets-binding motif located between -77 and -74 and a cAMP-response-element (CRE)-like motif located between -68 and -62 in mediating high-level expression in endothelial cells. A second Ets site (-63 to -60) as well as a novel 6-bp palindromic sequence (-58 to -53) were found to inhibit expression. In DNase footprint analyses, both the Ets-binding motifs were protected specifically in endothelial cells, while the CRE-like element and palindrome were protected in endothelial and nonendothelial cells alike. Taken together, these results provide an important foundation for studying endothelial-cell-subtype-specific gene regulation.

The RUNX3 gene--sequence, structure and regulated expression

The RUNX3 gene belongs to the runt domain family of transcription factors that act as master regulators of gene expression in major developmental pathways. In mammals the family includes three genes, RUNX1, RUNX2 and RUNX3. Here, we describe a comparative analysis of the human chromosome 1p36.1 encoded RUNX3 and mouse chromosome 4 encoded Runx3 genomic regions. The analysis revealed high similarities between the two genes in the overall size and organization and showed that RUNX3/Runx3 is the smallest in the family, but nevertheless exhibits all the structural elements characterizing the RUNX family. It also revealed that RUNX3/Runx3 bears a high content of the ancient mammalian repeat MIR. Together, these data delineate RUNX3/Runx3 as the evolutionary founder of the mammalian RUNX family. Detailed sequence analysis placed the two genes at a GC-rich H3 isochore with a sharp transition of GC content between the gene sequence and the downstream intergenic region. Two large conserved CpG islands were found within both genes, one around exon 2 and the other at the beginning of exon 6. RUNX1, RUNX2 and RUNX3 gene products bind to the same DNA motif, hence their temporal and spatial expression during development should be tightly regulated. Structure/function analysis showed that two promoter regions, designated P1 and P2, regulate RUNX3 expression in a cell type-specific manner. Transfection experiments demonstrated that both promoters were highly active in the GM1500 B-cell line, which endogenously expresses RUNX3, but were inactive in the K562 myeloid cell line, which does not express RUNX3.

The in vitro activity and specificity of human endothelial cell-specific promoters in porcine cells

The chronic shortage of human organs, tissues and cells for transplantation has inspired research on the possibility of using animal donor tissue instead. Transplantation over a species barrier is associated with rejections which are difficult to control. Therefore, it is generally agreed that successful pig to human xenotransplantation requires donor pigs to be genetically modified. Vascular endothelium is the most immediate barrier between the xenogeneic donor organ and host immune and nonimmune defense systems. Thus, these cells are the prime targets for such genetic modifications. Luciferase assays were used to evaluate the activity and specificity of human endothelial-cell specific promoters in porcine aortic-, microvascular- and nonendothelial cells. The promoters for human Flk-1 (fetal liver kinase-1), Flt-1 (fms-like tyrosine kinase), ICAM-2 (intercellular adhesion molecule-2), thrombomodulin and vWf (von Willebrand factor) supported similar levels of luciferase expression in human and porcine aortic endothelial cells, with the Flk-1 promoter being the strongest followed by the thrombomodulin promoter. Relative to the activity of the CMV promoter, the human endothelial cell-specific promoters all showed less activity in porcine kidney microvascular endothelial cells than in liver or brain microvascular endothelial cells. The thrombomodulin and Flk-1 promoters exhibited similar activity in liver and kidney microvascular endothelial cells, whereas the Flk-1 promoter was stronger in aortic and brain microvascular endothelial cells. Human endothelial cell-specific promoters also showed some degree of specificity in pig, because they supported less luciferase activity in porcine nonendothelial cell lines. Based on the in vitro data and previously published in vivo data, the human Flk-1 and thrombomodulin promoters are good candidate promoters for strong endothelial cell-specific gene expression in transgenic pigs.

Analysis of cell-specific promoters for viral gene therapy targeted at the vascular endothelium

The use of viral vectors for vascular gene therapy targeted at the endothelium is limited by the promiscuous tropism of vectors and nonspecificity of viral promoters, resulting in high-level transgene expression in multiple tissues. To evaluate suitable endothelial cell (EC)-specific promoters for vascular gene therapy, we directly compared the ability of the fms-like tyrosine kinase-1 (FLT-1), intercellular adhesion molecule-2 (ICAM-2), and von Willebrand factor (vWF) promoters to drive EC-restricted transcription after cloning into adenoviral vectors upstream of lacZ. Vastly different expression profiles were observed. Whereas both FLT-1 and ICAM-2 promoters generated transgene expression levels similar to cytomegalovirus in ECs in vitro, vWF expression levels were extremely low. Analysis of non-EC types revealed that ICAM-2 but not FLT-1 evoked leaky transgene expression, thus identifying FLT-1 as the most selective promoter. With an ex vivo human gene therapy model, the FLT-1 promoter demonstrated EC-specific transgene expression in intact human vein but no detectable expression from infected exposed smooth muscle cells in EC-denuded vein. Furthermore, when adenoviruses were systemically administered to mice, the FLT-1 promoter demonstrated extremely low-level gene expression in the liver, the major target organ for adenoviral transduction in vivo. This study highlights the potential of using the FLT-1 promoter for local and systemic human gene therapy in hypertension and its complications.

Vascular gene transfer driven by endoglin and ICAM-2 endothelial-specific promoters

The involvement of the vascular endothelium in a large number of diseases supports the importance of vascular-specific gene delivery for their treatment. The hereditary hemorrhagic telangiectasia type 1 is an example of a vascular inherited disease (OMIM 187300). This is an autosomal dominant vascular disorder originated by mutations in the endoglin gene and associated with frequent epistaxis, telangiectases, gastrointestinal bleedings, and arteriovenous malformations in brain, lung and liver. Here, we address for the first time the possibility of using in vivo gene transfer to target endoglin expression to the vasculature. The promoter of the endothelial gene, ICAM-2, was used to generate transgenic animals which demonstrated endothelial expression of endoglin. Next, the promoters of the human endothelial genes, endoglin and ICAM-2, were inserted upstream of the human endoglin cDNA, and the resulting constructs were systemically or locally delivered, demonstrating endoglin expression in the vessel walls of liver, lung and skin. These gene transfer experiments represent an initial step in the treatment of the hereditary hemorrhagic telangiectasia type 1 by gene therapy, and suggest that endoglin and ICAM-2 promoters can be used to deliver other genes to the endothelium specifically.

Molecular regulation of the endothelin-1 gene by hypoxia. Contributions of hypoxia-inducible factor-1, activator protein-1, GATA-2, AND p300/CBP

Endothelin-1 (ET-1) is a peptide hormone with potent vasoconstrictor properties which is synthesized and secreted predominantly by vascular endothelial cells. Its production is regulated by numerous stimuli including ischemia and hypoxia, and the enhanced levels that occur during myocardial ischemia may contribute to the progression of heart failure. We reported previously a preliminary characterization of a hypoxia-inducible factor-1 (HIF-1) binding site in the human ET-1 promoter which contributed to the activation of ET-1 expression in endothelial cells. We report here that the HIF-1 binding site alone is not sufficient for the response to hypoxia but requires an additional 50 base pairs of flanking sequence that includes binding sites for the factors activator protein-1 (AP-1), GATA-2, and CAAT-binding factor (NF-1). Mutation of any one of these sites or the HIF-1 site eliminated induction by hypoxia. Mutations of the AP-1 and GATA-2 sites, but not the HIF-1 site, were complemented by overexpressing AP-1, GATA-2, HIF-1alpha, or the activator protein p300/CBP, restoring the response to hypoxia. Binding studies in vitro confirmed physical associations among GATA-2, AP-1, and HIF-1 factors. Overexpression or depletion of p300/CBP modulated the level of ET-1 promoter expression as well as the endogenous ET-1 transcript but did not change the fold induction by hypoxia in either case. Regulation of the ET-1 promoter by hypoxia in non-endothelial cells required overexpression of GATA-2 and HIF-1alpha. The results support essential roles for AP-1, GATA-2, and NF-1 in stabilizing the binding of HIF-1 and promoting recruitment of p300/CBP to the ET-1 hypoxia response complex.

VEGFR3 gene structure, regulatory region, and sequence polymorphisms

Vascular endothelial growth factor receptor 3 (VEGFR-3) is required for cardiovascular development during embryogenesis. In adults, this receptor is expressed in lymphatic endothelial cells, and mutant VEGFR3 alleles have been implicated in human hereditary lymphedema. To better understand the basis of its specific endothelial lineage-restricted expression, we have characterized the VEGFR3 gene and its regulatory 5' flanking region. The human gene contains 31 exons, of which exons 30a and 30b are alternatively spliced. The VEGFR3 proximal promoter is TATA-less and contains stretches of sequences homologous with the mouse Vegfr3 promoter region. In transfection experiments of cultured cells, the Vegfr3 promoter was shown to control endothelial cell-specific transcription of downstream reporter genes. This result was further confirmed in vivo; in a subset of transgenic mouse embryos, a 1.6 kb Vegfr3 promoter fragment directed weak lymphatic endothelial expression of the LacZ marker gene. This suggests that endothelial cell-specific elements occur in the proximal promoter, although further enhancer elements are probably located elsewhere. The sequence, organization, and variation in the VEGFR3 gene and its regulatory region provide important tools for the molecular genetic analysis of the lymphatic system and its disorders.