Role of a 5′-enhancer in the transcriptional regulation of the human endothelial cell protein C receptor gene

Determining Physical Mechanisms of Gene Expression Regulation from Single Cell Gene Expression Data

Many genes are expressed in bursts, which can contribute to cell-to-cell heterogeneity. It is now possible to measure this heterogeneity with high throughput single cell gene expression assays (single cell qPCR and RNA-seq). These experimental approaches generate gene expression distributions which can be used to estimate the kinetic parameters of gene expression bursting, namely the rate that genes turn on, the rate that genes turn off, and the rate of transcription. We construct a complete pipeline for the analysis of single cell qPCR data that uses the mathematics behind bursty expression to develop more accurate and robust algorithms for analyzing the origin of heterogeneity in experimental samples, specifically an algorithm for clustering cells by their bursting behavior (Simulated Annealing for Bursty Expression Clustering, SABEC) and a statistical tool for comparing the kinetic parameters of bursty expression across populations of cells (Estimation of Parameter changes in Kinetics, EPiK). We applied these methods to hematopoiesis, including a new single cell dataset in which transcription factors (TFs) involved in the earliest branchpoint of blood differentiation were individually up- and down-regulated. We could identify two unique sub-populations within a seemingly homogenous group of hematopoietic stem cells. In addition, we could predict regulatory mechanisms controlling the expression levels of eighteen key hematopoietic transcription factors throughout differentiation. Detailed information about gene regulatory mechanisms can therefore be obtained simply from high throughput single cell gene expression data, which should be widely applicable given the rapid expansion of single cell genomics.

The short and long of noncoding sequences in the control of vascular cell phenotypes

The two principal cell types of importance for normal vessel wall physiology are smooth muscle cells and endothelial cells. Much progress has been made over the past 20 years in the discovery and function of transcription factors that coordinate proper differentiation of these cells and the maintenance of vascular homeostasis. More recently, the converging fields of bioinformatics, genomics, and next generation sequencing have accelerated discoveries in a number of classes of noncoding sequences, including transcription factor binding sites (TFBS), microRNA genes, and long noncoding RNA genes, each of which mediates vascular cell differentiation through a variety of mechanisms. Alterations in the nucleotide sequence of key TFBS or deviations in transcription of noncoding RNA genes likely have adverse effects on normal vascular cell phenotype and function. Here, the subject of noncoding sequences that influence smooth muscle cell or endothelial cell phenotype will be summarized as will future directions to further advance our understanding of the increasingly complex molecular circuitry governing normal vascular cell differentiation and how such information might be harnessed to combat vascular diseases.

Endothelial protein C receptor gene variants not associated with severe malaria in ghanaian children

Background

Two recent reports have identified the Endothelial Protein C Receptor (EPCR) as a key molecule implicated in severe malaria pathology. First, it was shown that EPCR in the human microvasculature mediates sequestration of Plasmodium falciparum-infected erythrocytes. Second, microvascular thrombosis, one of the major processes causing cerebral malaria, was linked to a reduction in EPCR expression in cerebral endothelial layers. It was speculated that genetic variation affecting EPCR functionality could influence susceptibility to severe malaria phenotypes, rendering PROCR, the gene encoding EPCR, a promising candidate for an association study.

Methods

Here, we performed an association study including high-resolution variant discovery of rare and frequent genetic variants in the PROCR gene. The study group, which previously has proven to be a valuable tool for studying the genetics of malaria, comprised 1,905 severe malaria cases aged 1–156 months and 1,866 apparently healthy children aged 2–161 months from the Ashanti Region in Ghana, West Africa, where malaria is highly endemic. Association of genetic variation with severe malaria phenotypes was examined on the basis of single variants, reconstructed haplotypes, and rare variant analyses.

Results

A total of 41 genetic variants were detected in regulatory and coding regions of PROCR, 17 of which were previously unknown genetic variants. In association tests, none of the single variants, haplotypes or rare variants showed evidence for an association with severe malaria, cerebral malaria, or severe malaria anemia.

Conclusion

Here we present the first analysis of genetic variation in the PROCR gene in the context of severe malaria in African subjects and show that genetic variation in the PROCR gene in our study population does not influence susceptibility to major severe malaria phenotypes.

Omental implantation of BOECs in hemophilia dogs results in circulating FVIII antigen and a complex immune response

Ex vivo gene therapy strategies avoid systemic delivery of viruses thereby mitigating the risk of vector-associated immunogenicity. Previously, we delivered autologous factor VIII (FVIII)-expressing blood outgrowth endothelial cells (BOECs) to hemophilia A mice and showed that these cells remained sequestered within the implanted matrix and provided therapeutic levels of FVIII. Prior to translating this strategy into the canine (c) model of hemophilia A, we increased cFVIII transgene expression by at least 100-fold with the use of the elongation factor 1 alpha (EF1α) promoter and a strong endothelial enhancer element. BOECs isolated from hemophilia A dogs transduced with this lentiviral vector express levels of cFVIII ranging between 1.0 and 1.5 U/mL per 10(6) cells over 24 hours. Autologous BOECs have been implanted into the omentum of 2 normal and 3 hemophilia A dogs. These implanted cells formed new vessels in the omentum. All 3 hemophilia A dogs treated with FVIII-expressing autologous BOECs developed anti-FVIII immunoglobulin G2 antibodies, but in only 2 of the dogs were these antibodies inhibitory. FVIII antigen levels >40% in the absence of FVIII coagulant function were detected in the circulation for up to a year after a single gene therapy treatment, indicating prolonged cellular viability and synthesis of FVIII.

Endothelial mineralocorticoid receptor activation enhances endothelial protein C receptor and decreases vascular thrombosis in mice

Previous studies have shown that aldosterone, which activates the mineralocorticoid receptor (MR), promotes thrombosis in animal models. Our objective was to determine whether MR activation/expression in the vascular endothelium could modify thrombotic risk in vivo and to examine thrombin generation at the surface of aortic endothelial cells (HAECs). MR was conditionally overexpressed in vivo in vascular endothelial cells in mice (MR-EC mice) or stimulated with aldosterone in HAECs. Thrombosis after ferric chloride injury was delayed in MR-EC mice compared with controls as well as in wild-type FVB/NRj mice treated with aldosterone (60 μg/kg/d for 21 d). Thrombin generation in platelet-poor plasma did not differ between MR-EC mice and controls. In MR-EC mice, aortic endothelial cell protein C receptor (EPCR) expression was increased. Aldosterone (10(-8) M) attenuated thrombin generation at the surface of cultured HAECs, and this effect was associated with up-regulation of expression of EPCR, which promotes formation of activated protein C. Aldosterone increases EPCR expression via a transcriptional mechanism involving interaction of MR with the specificity protein 1 site. These findings demonstrate that MR activation acts on endothelial cells to protect against thrombosis in physiological conditions and that MR-mediated EPCR overexpression drives this antithrombotic property through enhancing protein C activation.

The endothelial protein C receptor impairs the antibacterial response in murine pneumococcal pneumonia and sepsis

Pneumococcal pneumonia is a frequent cause of gram-positive sepsis and has a high mortality. The endothelial protein C receptor (EPCR) has been implicated in both the activation of protein C (PC) and the anti-inflammatory actions of activated (A)PC. The aim of this study was to determine the role of the EPCR in murine pneumococcal pneumonia and sepsis. Wild-type (WT), EPCR knockout (KO) and Tie2-EPCR mice, which overexpress EPCR on the endothelium, were infected intranasally (pneumonia) or intravenously (sepsis) with viable Streptococcus pneumoniae and euthanised at 24 or 48 hours after initiation of the infection for analyses. Pneumonia did not alter constitutive EPCR expression on pulmonary endothelium but was associated with an influx of EPCR positive neutrophils into lung tissue. In pneumococcal pneumonia EPCR KO mice demonstrated diminished bacterial growth in the lungs and dissemination to spleen and liver, reduced neutrophil recruitment to the lungs and a mitigated inflammatory response. Moreover, EPCR KO mice displayed enhanced activation of coagulation in the early phase of disease. Correspondingly, in pneumococcal sepsis EPCR KO mice showed reduced bacterial growth in lung and liver and attenuated cytokine release. Conversely, EPCR-overexpressing mice displayed higher bacterial outgrowth in lung, blood, spleen and liver in pneumococcal sepsis. In conclusion, EPCR impairs antibacterial defense in both pneumococcal pneumonia and sepsis, which is associated with an enhanced pro-inflammatory response.

Endothelial protein C receptor 1651C/G polymorphism and soluble endothelial protein C receptor levels in women with idiopathic recurrent miscarriage

High levels of soluble endothelial protein C receptor (EPCR) induce coagulation dysfunction by inhibiting protein C activation, and activated protein C (APC) activity. We tested whether EPCR 1651C/G promoter variant and changes in plasma soluble EPCR levels are risk factors for idiopathic recurrent spontaneous miscarriage (RSM). A case-control study involving 283 RSM cases and 380 age and BMI-matched control women. EPCR 1651C/G genotyping was performed by PCR-RFLP method. Plasma-soluble EPCR levels were measured with ELISA. The 1651G allele frequency and C/G genotype were significantly higher in RSM cases than controls; none of the cases or control participants was a 1651G/G homozygote. Lower soluble EPCR levels were seen in RSM cases compared to controls, and higher soluble EPCR levels were seen in 1651C/G compared to 1651C/C carriers in cases and controls. Lower soluble EPCR levels were seen in cases, both in 1651C/C (P = 0.0046) and 1651C/G (P = 0.0032) genotype carriers. Multivariate analysis demonstrated strong association of EPCR 1651C/G [P = 0.011; adjusted odds ratio (aOR) (95% confidence interval [CI] = 3.13 (1.31-7.60)], but not soluble EPCR plasma levels [P = 0.067; aOR (95% CI) = 1.01 (1.00-1.10)], with increased RSM risk. In addition, smoking was independently associated with increased RSM risk [P = 0.002; aOR (95% CI) = 2.86 (1.48-5.52)]. EPCR 1651C/G polymorphism and elevated soluble EPCR levels but low soluble EPCR levels increase the risk of idiopathic RSM. Replication studies on other racial groups, and other EPCR gene variants, are warranted.

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.

[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.

The angiopoietin-2 gene of endothelial cells is up-regulated in hypoxia by a HIF binding site located in its first intron and by the central factors GATA-2 and Ets-1

Angiopoietins are ligands of the endothelial cell tyrosine kinase receptor Tie2. Angiopoietin-1 (Ang-1) is widely expressed in human normal adult tissues and promotes blood vessel maturation and stabilization by inducing Tie2 receptor phosphorylation. In contrast, the antagonistic ligand Angiopoietin-2 (Ang-2) is up-regulated by hypoxia, expressed only at sites of vascular remodeling and plays a crucial role in destabilizing vessels for normal or pathological angiogenesis. Ang-2 expression is tightly regulated at transcriptional and post-transcriptional levels. To characterize the regulatory sequences of the human Ang-2 gene we cloned a fragment of around 8.5 kb upstream of the Ang-2 coding sequence and analyzed the luciferase reporter activity of constructs of various lengths in endothelial and non-endothelial cells. We isolated a minimal promoter sequence sufficient to promote significant Ang-2 non-cell type specific transcription. Moreover, we identified sequences conferring endothelial specificity. Indeed, sequence analysis of the fragment revealed the presence of several potential binding sites for specific endothelial regulatory factors like GATA or Ets. Using GATA-2 and Ets-1 co-transfection and overexpression assay, we showed that these two factors are able to induce Ang-2 promoter activation. We also show that hypoxic regulation of Ang-2 is HIF-dependent and demonstrate that HIF-1alpha binds in human microvascular endothelial cells (HMVEC) to an evolutionary conserved Hypoxia-Responsive Element (HRE) located in the first intron of the Ang-2 gene. In conclusion, our study provides new elements in favor of HIF involvement in Ang-2 hypoxic regulation and identifies Ets-1 and particularly GATA-2 as central factors in endothelial specific Ang-2 expression.

PROC, PROCR and PROS1 polymorphisms, plasma anticoagulant phenotypes, and risk of cardiovascular disease and mortality in older adults: the Cardiovascular Health Study

BACKGROUND AND OBJECTIVES

Genes encoding protein C anticoagulant pathways are candidates for atherothrombotic and other aging-related disorders.

METHODS

Using a tagSNP approach, and data from the Cardiovascular Health Study (CHS), we assessed associations of common polymorphisms of PROC, PROS1 and PROCR with: (i) plasma protein C, soluble protein C endothelial receptor (sEPCR) and protein S levels measured in a subsample of 336 participants at study entry; and (ii) risk of incident clinical outcomes [coronary heart disease (CHD), stroke, and mortality] in 4547 participants during follow-up. Secondarily, we explored associations between plasma protein C, protein S and sEPCR levels and other candidate genes involved in thrombosis, inflammation, and aging.

RESULTS

The PROCR Ser219Gly polymorphism (rs867186) was strongly associated with higher sEPCR levels, explaining 75% of the phenotypic variation. The PROCR Ser219Gly variant was also associated with higher levels of circulating protein C antigen. An IL10 polymorphism was associated with higher free protein S levels. The minor alleles of PROC rs2069901 and PROS1 rs4857343 were weakly associated with lower protein C and free protein S levels, respectively. There was no association between PROCR Ser219Gly and risk of CHD, stroke, or mortality. The minor allele of another common PROCR tagSNP, rs2069948, was associated with lymphoid PROCR mRNA expression and with increased risk of incident stroke and all-cause mortality, and decreased healthy survival during follow-up.

CONCLUSIONS

A common PROCR variant may be associated with decreased healthy survival in older adults. Additional studies are warranted to establish the role of PROCR variants in ischemic and aging-related disorders.

The SCL +40 enhancer targets the midbrain together with primitive and definitive hematopoiesis and is regulated by SCL and GATA proteins

The SCL/Tal-1 gene encodes a basic helix-loop-helix transcription factor with key roles in hematopoietic and neural development. SCL is expressed in, and required for, both primitive and definitive erythropoiesis. Thus far, we have identified only one erythroid SCL enhancer. Located 40 kb downstream of exon 1a, the +40 enhancer displays activity in primitive erythroblasts. We demonstrate here that a 3.7-kb fragment containing this element also targets expression to the midbrain, a known site of endogenous SCL expression. Although the 3.7-kb construct was active in primitive, but not definitive, erythroblasts, a larger 5.0-kb fragment, encompassing the 3.7-kb region, was active in both fetal and adult definitive hematopoietic cells. This included Ter119+ erythroid cells along with fetal liver erythroid and myeloid progenitors. Unlike two other SCL hematopoietic enhancers (+18/19 and -4), +40 enhancer transgenes were inactive in the endothelium. A conserved 400-bp core region, essential for both hematopoietic and midbrain +40 enhancer activity in embryos, relied on two GATA/E-box motifs and was bound in vivo by GATA-1 and SCL in erythroid cells. These results suggest a model in which the SCL +18/19 and/or -4 enhancers initiate SCL expression in early mesodermal derivatives capable of generating blood and endothelium, with subsequent activation of the +40 enhancer via an autoregulatory loop.

Non-hematopoietic EPCR regulates the coagulation and inflammatory responses during endotoxemia

BACKGROUND

Activated protein C (APC) protects the host from severe sepsis. Endothelial protein C receptor (EPCR) is expressed on both hematopoietic leukocytes and non-hematopoietic endothelium, and plays a key role in protein C activation.

OBJECTIVES

We explore the influence of EPCR deletion on the responses to lipopolysaccharide (LPS) and then determine whether the observed differences are due to loss of hematopoietic or non-hematopoietic EPCR.

METHODS AND RESULTS

After LPS challenge, EPCR null (Procr(-/-)) mice exhibited more thrombin and cytokine generation, neutrophil sequestration in the lung and a higher mortality rate than Procr(+/-) mice. Procr(+/-) BM/Procr(-/-) (non-hematopoietic Procr(-/-)) and Procr(-/-) BM/Procr(+/-) (hematopoietic Procr(-/-)) chimeric mice were generated by bone marrow (BM) transplantation. Compared with control Procr(+/-) mice, non-hematopoietic Procr(-/-) mice exhibited reduced protein C activation by thrombin and exaggerated responses to LPS challenge, whereas Procr(+/-) mice and hematopoietic Procr(-/-) mice exhibited similar protein C activation by thrombin and similar responses to LPS challenge.

CONCLUSIONS

EPCR deletion exaggerates the host responses to LPS primarily due to deficiency of EPCR on the non-hematopoietic cells.

The cytoprotective protein C pathway

Protein C is best known for its mild deficiency associated with venous thrombosis risk and severe deficiency associated with neonatal purpura fulminans. Activated protein C (APC) anticoagulant activity involves proteolytic inactivation of factors Va and VIIIa, and APC resistance is often caused by factor V Leiden. Less known is the clinical success of APC in reducing mortality in severe sepsis patients (PROWESS trial) that gave impetus to new directions for basic and preclinical research on APC. This review summarizes insights gleaned from recent in vitro and in vivo studies of the direct cytoprotective effects of APC that include beneficial alterations in gene expression profiles, anti-inflammatory actions, antiapoptotic activities, and stabilization of endothelial barriers. APC's cytoprotection requires its receptor, endothelial cell protein C receptor, and protease-activated receptor-1. Because of its pleiotropic activities, APC has potential roles in the treatment of complex disorders, including sepsis, thrombosis, and ischemic stroke. Although much about molecular mechanisms for APC's effects on cells remains unclear, it is clear that APC's structural features mediating anticoagulant actions and related bleeding risks are distinct from those mediating cytoprotective actions, suggesting the possibility of developing APC variants with an improved profile for the ratio of cytoprotective to anticoagulant actions.