Endothelial cell heterogeneity

RNA as a stable polymer to build controllable and defined nanostructures for material and biomedical applications

The value of polymers is manifested in their vital use as building blocks in material and life sciences. Ribonucleic acid (RNA) is a polynucleic acid, but its polymeric nature in materials and technological applications is often overlooked due to an impression that RNA is seemingly unstable. Recent findings that certain modifications can make RNA resistant to RNase degradation while retaining its authentic folding property and biological function, and the discovery of ultra-thermostable RNA motifs have adequately addressed the concerns of RNA unstability. RNA can serve as a unique polymeric material to build varieties of nanostructures including nanoparticles, polygons, arrays, bundles, membrane, and microsponges that have potential applications in biomedical and material sciences. Since 2005, more than a thousand publications on RNA nanostructures have been published in diverse fields, indicating a remarkable increase of interest in the emerging field of RNA nanotechnology. In this review, we aim to: delineate the physical and chemical properties of polymers that can be applied to RNA; introduce the unique properties of RNA as a polymer; review the current methods for the construction of RNA nanostructures; describe its applications in material, biomedical and computer sciences; and, discuss the challenges and future prospects in this field.

Endurance, interval sprint, and resistance exercise training: impact on microvascular dysfunction in type 2 diabetes

Type 2 diabetes (T2D) alters capillary hemodynamics, causes capillary rarefaction in skeletal muscle, and alters endothelial and vascular smooth muscle cell phenotype, resulting in impaired vasodilatory responses. These changes contribute to altered blood flow responses to physiological stimuli, such as exercise and insulin secretion. T2D-induced microvascular dysfunction impairs glucose and insulin delivery to skeletal muscle (and other tissues such as skin and nervous), thereby reducing glucose uptake and perpetuating hyperglycemia and hyperinsulinemia. In patients with T2D, exercise training (EX) improves microvascular vasodilator and insulin signaling and attenuates capillary rarefaction in skeletal muscle. EX-induced changes subsequently augment glucose and insulin delivery as well as glucose uptake. If these adaptions occur in a sufficient amount of tissue, and skeletal muscle in particular, chronic exposure to hyperglycemia and hyperinsulinemia and the risk of microvascular complications in all vascular beds will decrease. We postulate that EX programs that engage as much skeletal muscle mass as possible and recruit as many muscle fibers within each muscle as possible will generate the greatest improvements in microvascular function, providing that the duration of the stimulus is sufficient. Primary improvements in microvascular function occur in tissues (skeletal muscle primarily) engaged during exercise, and secondary improvements in microvascular function throughout the body may result from improved blood glucose control. We propose that the added benefit of combined resistance and aerobic EX programs and of vigorous intensity EX programs is not simply "more is better." Rather, we believe the additional benefit is the result of EX-induced adaptations in and around more muscle fibers, resulting in more muscle mass and the associated microvasculature being changed. Thus, to acquire primary and secondary improvements in microvascular function and improved blood glucose control, EX programs should involve upper and lower body exercise and modulate intensity to augment skeletal muscle fiber recruitment. Under conditions of limited mobility, it may be necessary to train skeletal muscle groups separately to maximize whole body skeletal muscle fiber recruitment.

Understanding and exploiting nanoparticles' intimacy with the blood vessel and blood

While the blood vessel is seldom the target tissue, almost all nanomedicine will interact with blood vessels and blood at some point of time along its life cycle in the human body regardless of their intended destination. Despite its importance, many bionanotechnologists do not feature endothelial cells (ECs), the blood vessel cells, or consider blood effects in their studies. Including blood vessel cells in the study can greatly increase our understanding of the behavior of any given nanomedicine at the tissue of interest or to understand side effects that may occur in vivo. In this review, we will first describe the diversity of EC types found in the human body and their unique behaviors and possibly how these important differences can implicate nanomedicine behavior. Subsequently, we will discuss about the protein corona derived from blood with foci on the physiochemical aspects of nanoparticles (NPs) that dictate the protein corona characteristics. We would also discuss about how NPs characteristics can affect uptake by the endothelium. Subsequently, mechanisms of how NPs could cross the endothelium to access the tissue of interest. Throughout the paper, we will share some novel nanomedicine related ideas and insights that were derived from the understanding of the NPs' interaction with the ECs. This review will inspire more exciting nanotechnologies that had accounted for the complexities of the real human body.

Off-pump CABG surgery reduces systemic inflammation compared with on-pump surgery but does not change systemic endothelial responses: a prospective randomized study

Coronary artery bypass graft (CABG) surgery can result in severe postoperative organ failure. During CABG surgery, cardiopulmonary bypass (CPB) with cardiac arrest is often used (on-pump CABG), which often results in a systemic inflammatory response. To reduce this inflammatory response, off-pump CABG was reintroduced, thereby avoiding CPB. There is increasing evidence that the endothelium plays an important role in the pathophysiology of organ failure after CABG surgery. In this study, 60 patients who were scheduled for elective CABG surgery were randomized to have surgery for on-pump or off-pump CABG. Blood was collected at four time points: start, end, 6 h, and 24 h postoperatively. Levels of inflammatory cytokines, soluble adhesion molecules, and angiogenic factors and their receptors were measured in the plasma. No differences were found in preoperative characteristics between the patient groups. The levels of tumor necrosis factor-α, interleukin 10, and myeloperoxidase, but not interleukin 6, were increased to a greater extent in the on-pump CABG compared with off-pump CABG after sternum closure. The soluble endothelial adhesion molecules E-selectin, vascular cell adhesion molecule 1, and intracellular adhesion molecule 1 were not elevated in the plasma during and after CABG surgery in both on-pump and off-pump CABG. Angiopoietin 2 was only increased 24 h after surgery in both on-pump and off-pump CABG. Higher levels of sFlt-1 were found after sternum closure in off-pump CABG compared with on-pump CABG. Avoiding CPB and aortic cross clamping in CABG surgery reduces the systemic inflammatory response. On-pump CABG does not lead to an increased release of soluble endothelial adhesion molecules in the circulation compared with off-pump CABG.

The impact of insulin treatment on the expression of vascular endothelial cadherin and Beta-catenin in human fetoplacental vessels

Vascular endothelial cadherin and β-catenin play a key role in establishment and maintenance of the endothelial monolayer integrity, regulation of vascular barrier function, and initiation of angiogenesis. The cadherin-catenin complex has been shown to be reduced in type 1 diabetic placenta, but the exact relationship between histopathologic findings and clinical data is not known. Immunohistochemistry of placental tissue from type 1, type 2, and gestational diabetes showed that diabetes per se might be compatible with normal levels of vascular endothelial (VE)-cadherin and β-catenin in fetoplacental vessels as long as the patient has not been treated with insulin. Immunoreactivity of VE-cadherin did correlate poorly with maternal glycemic control, as was investigated in this study, by birth weight, body mass index, and hemoglobin A1c (HbA1c). There was no correlation found between the immunoreactivity of β-catenin and birth weight, body mass index, or HbA1c. However our data did show a strong correlation between immunoreactivity and whether or not the patient had been treated with insulin. Patients diagnosed with gestational diabetes who had not been treated with insulin had similar levels of VE-cadherin and β-catenin to the control group, thus indicating that diabetes per se must not necessarily lead to a reduction. Our study suggests that therapeutic intervention using insulin in pregnancies complicated by diabetes might have potentially harmful effects on placental morphology. Future studies should further investigate these findings.

Endothelium and its alterations in cardiovascular diseases: life style intervention

The endothelium, which forms the inner cellular lining of blood vessels and lymphatics, is a highly metabolically active organ that is involved in many physiopathological processes, including the control of vasomotor tone, barrier function, leukocyte adhesion, and trafficking and inflammation. In this review, we summarized and described the following: (i) endothelial cell function in physiological conditions and (ii) endothelial cell activation and dysfunction in the main cardiovascular diseases (such as atherosclerosis, and hypertension) and to diabetes, cigarette smoking, and aging physiological process. Finally, we presented the currently available evidence that supports the beneficial effects of physical activity and various dietary compounds on endothelial functions.

Tissue factor inflammatory response regulated by promoter genotype and p38 MAPK in neonatal vs. adult microvascular endothelial cells

OBJECTIVE AND DESIGN

Variable tissue factor (TF) expression by human microvascular endothelial cells (HMVEC) may be regulated by two promoter haplotypes, distinguished by an 18-basepair deletion (D) or insertion (I) at -1,208. We sought to determine the relationship between these haplotypes and interleukin-1α (IL-1α)-induced TF expression in neonatal versus adult HMVEC.

RESULTS

IL-1-stimulated TF mRNA, protein, and activity were significantly higher in neonatal compared to adult D/D donors. IL-1-stimulated HMVEC from neonatal D/D donors expressed threefold higher levels of TF mRNA, twofold higher TF protein, and fourfold increased TF activity compared to HMVEC from adult D/D donors. These results indicate that homozygosity for the D haplotype is characterized by increased response to IL-1 in neonates, but not adults. IL-1 induced increased phosphorylation of p38 mitogen-activated protein kinase (MAPK), which was significantly greater in neonatal compared to adult HMVEC. Moreover, inhibition of the p38 MAPK pathway reduced IL-1-stimulated TF mRNA expression in D/D neonatal but not adult HMVEC.

CONCLUSIONS

Upregulation of D/D neonatal HMVEC TF expression by IL-1 is mediated through the p38 MAPK pathway. This heightened response of D/D neonatal HMVEC to inflammatory stimuli may contribute to increased microvascular coagulopathies in susceptible newborn infants.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Nerve-derived transmitters including peptides influence cutaneous immunology

Clinical observations suggest that the nervous and immune systems are closely related. For example, inflammatory skin disorders; such as psoriasis, atopic dermatitis, rosacea and acne; are widely believed to be exacerbated by stress. A growing body of research now suggests that neuropeptides and neurotransmitters serve as a link between these two systems. Neuropeptides and neurotransmitters are released by nerves innervating the skin to influence important actors of the immune system, such as Langerhans cells and mast cells, which are located within close anatomic proximity. Catecholamines and other sympathetic transmitters that are released in response to activation of the sympathetic nervous system are also able to reach the skin and affect immune cells. Neuropeptides appear to direct the outcome of Langerhans cell antigen presentation with regard to the subtypes of Th cells generated and neuropeptides induce the degranulation of mast cells, among other effects. Additionally, endothelial cells, which release many inflammatory mediators and express cell surface molecules that allow leukocytes to exit the bloodstream, appear to be regulated by certain neuropeptides and transmitters. This review focuses on the evidence that products of nerves have important regulatory activities on antigen presentation, mast cell function and endothelial cell biology. These activities are highly likely to have clinical and therapeutic relevance.

Endothelial cell energy metabolism, proliferation, and apoptosis in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by impaired regulation of pulmonary hemodynamics and excessive growth and dysfunction of the endothelial cells that line the arteries in PAH lungs. Establishment of methods for culture of pulmonary artery endothelial cells from PAH lungs has provided the groundwork for mechanistic translational studies that confirm and extend findings from model systems and spontaneous pulmonary hypertension in animals. Endothelial cell hyperproliferation, survival, and alterations of biochemical-metabolic pathways are the unifying endothelial pathobiology of the disease. The hyperproliferative and apoptosis-resistant phenotype of PAH endothelial cells is dependent upon the activation of signal transducer and activator of transcription (STAT) 3, a fundamental regulator of cell survival and angiogenesis. Animal models of PAH, patients with PAH, and human PAH endothelial cells produce low nitric oxide (NO). In association with the low level of NO, endothelial cells have reduced mitochondrial numbers and cellular respiration, which is associated with more than a threefold increase in glycolysis for energy production. The shift to glycolysis is related to low levels of NO and likely to the pathologic expression of the prosurvival and proangiogenic signal transducer, hypoxia-inducible factor (HIF)-1, and the reduced mitochondrial antioxidant manganese superoxide dismutase (MnSOD). In this article, we review the phenotypic changes of the endothelium in PAH and the biochemical mechanisms accounting for the proliferative, glycolytic, and strongly proangiogenic phenotype of these dysfunctional cells, which consequently foster the panvascular progressive pulmonary remodeling in PAH.

Glucocorticoids and estrogens modulate the NF-κB pathway differently in the micro- and macrovasculature

Estrogens and glucocorticoids have synergistic effects in the micro and macrovasculature of endothelial cells (ECs), having pro-inflammatory effects in the former and inhibiting the expression of adhesion molecules in the latter. The molecular basis of these effects in the endothelium has not yet been clarified. We postulate that the ECs of the micro- and macrovasculature have different non-genomic mechanisms that regulate levels of preexisting complexes of glucocorticoids and estrogens with their respective receptors. Since these receptors are regulated by NF-κB, their expression could be critical to the activation of a pro- or anti-inflammatory response. In the macrovasculature the synergistic effects of estrogens and glucocorticoids on ECs may be through the inhibition of NF-κB, leading to the inhibition of the expression of inflammatory molecules. It seems likely that glucocorticoid-receptor and estrogen-receptor complexes directly bind to NF-κB proteins in the macrovasculature, resulting in the inhibition of an excessive proinflammatory response. Further insights into these processes may help clarify the role of the endothelial cells of different vascular beds during the inflammatory response and chronic inflammation, and thus contribute to the design of more effective therapeutic strategies for the prevention of diseases related to inflammation, including atherosclerosis, systemic lupus erythematosus and rheumatoid arthritis.

Retargeting of gene expression using endothelium specific hexon modified adenoviral vector

Adenovirus serotype 5 (Ad5) vectors are well suited for gene therapy. However, tissue-selective transduction by systemically administered Ad5-based vectors is confounded by viral particle sequestration in the liver. Hexon-modified Ad5 expressing reporter gene under transcriptional control by the immediate/early cytomegalovirus (CMV) or the Roundabout 4 receptor (Robo4) enhancer/promoter was characterized by growth in cell culture, stability in vitro, gene transfer in the presence of human coagulation factor X, and biodistribution in mice. The obtained data demonstrate the utility of the Robo4 promoter in an Ad5 vector context. Substitution of the hypervariable region 7 (HVR7) of the Ad5 hexon with HVR7 from Ad serotype 3 resulted in decreased liver tropism and dramatically altered biodistribution of gene expression. The results of these studies suggest that the combination of liver detargeting using a genetic modification of hexon with an endothelium-specific transcriptional control element produces an additive effect in the improvement of Ad5 biodistribution.

Alteration of skin perfusion in mottling area during septic shock

BACKGROUND

Mottling score has been reported to be a strong predictive factor during septic shock. However, the pathophysiology of mottling remains unclear.

METHODS

In patients admitted in ICU for septic shock, we measured on the same area the mean skin perfusion by laser Doppler, the mottling score, and variations of both indices between T1 (6 hours after vasopressors were started) and T2 (24 hours later).

RESULTS

Fourteen patients were included, SAPS II was 56 [37-71] and SOFA score at T1 was 10 [7-12]. The mean skin surface area analyzed was 4108 ± 740 mm2; 1184 ± 141 measurements were performed over each defined skin surface area. Skin perfusion was significantly different according to mottling score and decreased from 37 [31-42] perfusion units (PUs) for a mottling score of [0-1] to 22 [20-32] PUs for a mottling score of [2-3] and 23 [16-28] for a score of [4-5] (Kruskal-Wallis test, P = 0.05). We analyzed skin perfusion changes during resuscitation in each patient and together with mottling score variations between T1 and T2 using a Wilcoxon signed-rank test. Among the 14 patients included, mottling score increased (worsened) in 5 patients, decreased (improved) in 5 patients, and remained stable in 4 patients. Baseline skin perfusion at T1 was arbitrarily scored 100%. Mean skin perfusion significantly decreased in all the patients whose mottling score worsened from 100% baseline to 63.2 ± 10.7% (P = 0.001), mean skin perfusion significantly increased in all patients whose mottling score improved from 100% baseline to 172.6 ± 46.8% (P = 0.001), and remained stable in patients whose mottling score did not change (100.5 ± 6.8%, P = 0.95).

CONCLUSIONS

We have shown that mottling score variations and skin perfusion changes during septic shock resuscitation were correlated, providing additional evidence that mottling reflects skin hypoperfusion.

Facing glycosphingolipid-Shiga toxin interaction: dire straits for endothelial cells of the human vasculature

The two major Shiga toxin (Stx) types, Stx1 and Stx2, produced by enterohemorrhagic Escherichia coli (EHEC) in particular injure renal and cerebral microvascular endothelial cells after transfer from the human intestine into the circulation. Stxs are AB(5) toxins composed of an enzymatically active A subunit and the pentameric B subunit, which preferentially binds to the glycosphingolipid globotriaosylceramide (Gb3Cer/CD77). This review summarizes the current knowledge on Stx-caused cellular injury and the structural diversity of Stx receptors as well as the initial molecular interaction of Stxs with the human endothelium of different vascular beds. The varying lipoforms of Stx receptors and their spatial organization in lipid rafts suggest a central role in different modes of receptor-mediated endocytosis and intracellular destiny of the toxins. The design and development of tailored Stx neutralizers targeting the oligosaccharide-toxin recognition event has become a very real prospect to ameliorate or prevent life-threatening renal and neurological complications.

Endothelium under stress: local and systemic messages

Endothelial responses to stressors are nonuniform and follow the rules of stress-induced hormesis. Responses to the same stressor, depending on its intensity, can range from pro-regenerative to pro-lethal. Exposure to sublethal stressors induces a programmed response that results in stress resistance, whereas a lethal level of a stressor accelerates cell demise. Diverse stressors turn on several default programs within the cells; such programs tend to induce anti-oxidative defenses and anti-inflammatory and pro-survival systems, whereas others tend to switch on pro-apoptotic systems. The response of the kidney endothelium to various forms of acute kidney injury follows these general principles. It is characterized by a proinflammatory pattern that includes up-regulation of different adhesion molecules promoting endothelial-leukocyte interactions, generation of reactive oxygen species, with formation of oxidative and nitrosative stress and mitochondrial damage. Simultaneously, a series of adaptive mechanisms, both local and systemic, are ignited. Stressed endothelial cells broadcast distress signals systemically; these signals can be directed toward the restoration of homeostasis or aggravation of the original insult.

Endothelial membrane reorganization during leukocyte extravasation

Leukocyte trafficking from the bloodstream to inflamed tissues across the endothelial barrier is an essential response in innate immunity. Leukocyte adhesion, locomotion, and diapedesis induce signaling in endothelial cells and this is accompanied by a profound reorganization of the endothelial cell surfaces that is only starting to be unveiled. Here we review the current knowledge on the leukocyte-mediated alterations of endothelial membrane dynamics and their role in promoting leukocyte extravasation. The formation of protein- and lipid-mediated cell adhesion nanodomains at the endothelial apical surface, the extension of micrometric apical membrane docking structures, which are derived from microvilli and embrace adhered leukocytes, as well as the vesicle-trafficking pathways that are required for efficient leukocyte diapedesis, are discussed. The coordination between these different endothelial membrane-remodeling events probably provides the road map for transmigrating leukocytes to find exit points in the vessel wall, in a context of severe mechanical and inflammatory stress. A better understanding of how vascular endothelial cells respond to immune cell adhesion should enable new therapeutic strategies to be developed that can abrogate uncontrolled leukocyte extravasation in inflammatory diseases.

Rheumatic fever pathogenesis: Approach in research needs change

Despite identifying that rheumatic fever (RF) is the result of an immunological reaction following group-A beta-hemolytic streptococcal infection, the pathogenesis remains elusive. RF has been incorrectly designated as causing pancarditis, since it does not cause myocarditis. Research directed toward myocarditis, targeting myosin to unravel the pathogenesis has not succeeded in more than 60 years. RF causes permanent damage to cardiac valves. The mitral valve (MV), derived from the wall of the left ventricle, is composed of a central core of connective tissue, covered on both sides by endothelium. The left ventricle does not have either myocardial or intermyocardial connective tissue involvement in RF. By exclusion, therefore, the primary site of RF damage appears to be the endothelium. Evaluation of the histopathology and immunopathology indicates that RF is a disease of the valvular and vascular endothelium. It is not a connective tissue disorder. Research to identify pathogenesis needs to be focused toward valvular endothelium.

The glycocalyx and cardiovascular disease in diabetes: should we judge the endothelium by its cover?

Patients with diabetes mellitus are characterized by an extraordinary vascular vulnerability. Traditionally, glucose-induced damage to the vascular endothelium is believed to be one of the first steps in the development of vascular damage. However, in the healthy vessel the endothelium is protected by a matrix layer of highly glycosylated proteins that form a physical barrier between the endothelium and the blood flowing past. Although its presence has been known for half a century, this so-called glycocalyx earned little attention from researchers in the past because of an underestimation of its size. In the last decade it has become clear that its full thickness actually exceeds that of the vascular endothelium. Accumulating research into the functional relevance of the endothelial glycocalyx suggests an important role for this layer in the development of cardiovascular disease in diabetes mellitus. Here we will present an overview of the biochemistry of the intact glycocalyx, current methods to assess the glycocalyx, and its possible role in the pathophysiology of cardiovascular disease in diabetes.

Rho GTPases and cancer cell transendothelial migration

Small Rho GTPases are major regulators of actin cytoskeleton dynamics and influence cell shape and migration. The expression of several Rho GTPases is often up-regulated in tumors and this frequently correlates with a poor prognosis for patients. Migration of cancer cells through endothelial cells that line the blood vessels, called transendothelial migration or extravasation, is a critical step during the metastasis process. The use of siRNA technology to target specifically each Rho family member coupled with imaging techniques allows the roles of individual Rho GTPases to be investigated. In this chapter we describe methods to assess how Rho GTPases affect the different steps of cancer cell transendothelial cell migration in vitro.

Hypoxia induces angiogenic factors in brain microvascular endothelial cells

Hypoxia is increasingly recognized as an important contributing factor to the development of brain diseases such as Alzheimer's disease (AD). In the periphery, hypoxia is a powerful regulator of angiogenesis. However, vascular endothelial cells are remarkably heterogeneous and little is known about how brain endothelial cells respond to hypoxic challenge. The objective of this study is to characterize the effect of hypoxic challenge on the angiogenic response of cultured brain-derived microvascular endothelial cells. Brain endothelial cell cultures were initiated from isolated rat brain microvessels and subjected to hypoxia (1% O(2)) for various time periods. The results showed that hypoxia induced rapid (≤ 0.5h) expression of hypoxia-inducible factor 1α (HIF-1α) and that cell viability, assessed by MTT assay, was unaffected within the first 8h. Examination of brain endothelial cell cultures for pro- and anti-angiogenic proteins by western blot, RT-PCR and ELISA revealed that within 0.5 to 2h of hypoxia levels of vascular endothelial growth factor and endothelin-1 mRNA and protein were elevated. The expression of heme oxygenase-1 also increased but only after 8h of hypoxia. In contrast, similar hypoxia exposure evoked a decrease in endothelial nitric oxide synthase and thrombospondin-2 levels. Exposure of brain endothelial cell cultures to hypoxia resulted in a significant (p<0.001) decrease (94%) in tube length, an in vitro index of angiogenesis, compared to control cultures. The data indicate that, despite a shift toward a pro-angiogenic phenotype, hypoxia inhibited vessel formation in brain endothelial cells. These results suggest that in brain endothelial cells expression of angiogenic factors is not sufficient for the development of new vessels. Further work is needed to determine what factors/conditions prevent hypoxia-induced angiogenic changes from culminating in the formation of new brain blood vessels and what role this may play in the pathologic changes observed in AD and other diseases characterized by cerebral hypoxia.

Hyperthyroidism and pulmonary hypertension: an important association

Pulmonary hypertension is a complex disorder with multiple etiologies. The World Health Organization Group 5 (unclear multifactorial mechanisms) includes patients with thyroid disorders. The authors reviewed the literature on the association between hyperthyroidism and pulmonary hypertension and identified 20 publications reporting 164 patients with treatment outcomes. The systolic pulmonary artery (PA) pressures in these patients ranged from 28 to 78 mm Hg. They were treated with antithyroid medications, radioactive iodine and surgery. The mean pretherapy PA systolic pressure was 39 mm Hg; the mean posttreatment pressure was 30 mm Hg. Pulmonary hypertension should be considered in hyperthyroid patients with dyspnea. All patients with pulmonary hypertension should be screened for hyperthyroidism, because the treatment of hyperthyroidism can reduce PA pressures, potentially avoid the side-effects and costs with current therapies for pulmonary hypertension and limit the consequences of untreated hyperthyroidism. However, the long-term outcome in these patients is uncertain, and this issue needs more study. Changes in the pulmonary circulation and molecular regulators of vascular remodeling likely explain this association.

Antibodies to kidney endothelial cells contribute to a "leaky" glomerular barrier in patients with chronic kidney diseases

Anti-endothelial cell antibodies (AECA) have been reported to cause endothelial dysfunction, but their clinical importance for tissue-specific endothelial cells is not clear. We hypothesized that AECA reactive with human kidney endothelial cells (HKEC) may cause renal endothelial dysfunction in patients with chronic kidney diseases. We report that a higher fraction (56%) of end-stage renal disease (ESRD) patients than healthy controls (5%) have AECA reactive against kidney endothelial cells (P <0.001). The presence of antibodies was associated with female gender (P < 0.001), systolic hypertension (P < 0.01), and elevated TNF-α (P < 0.05). These antibodies markedly decrease expression of both adherens and tight junction proteins VE-cadherin, claudin-1, and zonula occludens-1 and provoked a rapid increase in cytosolic free Ca(2+) and rearrangement of actin filaments in HKEC compared with controls. This was followed by an enhancement in protein flux and phosphorylation of VE-cadherin, events associated with augmented endothelial cell permeability. Additionally, kidney biopsies from ESRD patients with AECA but not controls demonstrated a marked decrease in adherens and tight junctions in glomerular endothelium, confirming our in vitro data. In summary, our data demonstrate a causal link between AECA and their capacity to induce alterations in glomerular vascular permeability.

Associations between cerebral and systemic endothelial function in migraine patients: a post-hoc study

Background

There is a growing interest in the role of the endothelium in migraine. Recently, our group showed differences in endothelial function between the anterior and posterior cerebral circulation in healthy subjects, reduced vasodilatatory capacity of the posterior cerebral circulation and unimpaired systemic endothelial function in migraine patients without comorbidities. However, the relationship between cerebral and systemic endothelial function and the anterior and posterior cerebral endothelial function in migraine patients is still not clear.

Methods

We compared cerebral and systemic endothelial function through post-hoc linear regression analysis of cerebrovascular reactivity (CVR) to L-arginine between the middle cerebral artery (MCA) and flow-mediated vasodilatation (FMD) of the right brachial artery and the posterior cerebral artery (PCA) and FMD in migraine patients without comorbidities and in healthy subjects. The anterior and posterior cerebral endothelial function was also compared using post-hoc linear regression analysis between CVR to L-arginine in the MCA and the PCA.

Results

No significant correlation was found between CVR to L-arginine in the MCA and FMD and in the PCA and FMD in migraine patients with aura (p = 0.880 vs. p = 0.682), without aura (p = 0.153 vs. p = 0.179) and in healthy subjects (p = 0.869 vs. p = 0.662). On the other hand, we found a significant correlation between CVR to L-arginine in the MCA and PCA in migraine patients with aura (p = 0.004), without aura (p = 0.001) and in healthy subjects (p = 0.002). Detailed analysis of the linear regression between all migraine patients and healthy subjects did not show any difference in the regression coefficient (slope) (p = 0.382). However, a significant difference in curve elevation (intercept) was found (p = 0.002).

Conclusions

Our study suggests that the endothelial function in the cerebral and systemic circulation might be different in migraine patients without comorbidities, while that of the anterior and posterior cerebral circulation might be coupled. These results could improve understanding of endothelial function in migraine patients without comorbidities.

Comparison of choroidal and retinal endothelial cells: characteristics and response to VEGF isoforms and anti-VEGF treatments

Neovascular eye diseases such as wet age-related macular degeneration and proliferative diabetic retinopathy are two of the most common causes of irreversible visual loss. Although mediated by vascular endothelial growth factor (VEGF), the mechanisms of these diseases are not fully understood. Molecular inhibitors of VEGF including pegaptanib, ranibizumab and bevacizumab are used as treatments for these diseases. However, there have been very few direct comparisons between these agents, and as dose and treatment regimes differ their relative efficacies are hard to determine. In vitro comparisons tend to use cells from different sites or species, which show heterogeneity in their responses. The aim of this study was to compare the characteristics of primary cultures of isolated human choroidal endothelial cells (hCEC) and retinal endothelial cells (hREC), and their proliferation responses to stimulation with VEGF 121 and 165, and to compare the anti-proliferative effects of these three drugs. hCEC and hREC were positive for the cell markers VEGFR1, VEGFR2, CD31, CD34 and von Willebrand's factor (vWF), with greater expression of CD34 on the hREC compared to hCEC. Contrary to previous assumptions VEGF isoforms 121 and 165 were found to be equally potent in stimulating endothelial cell proliferation. However, hREC exhibited higher proliferation with either VEGF isoform compared to hCEC. The anti-VEGF treatments ranibizumab and bevacizumab were effective in decreasing proliferation of hCEC induced by the two VEGF isoforms, individually and in combination, with ranibizumab being moderately more effective, particularly in hREC. Pegaptanib was effective in controlling the proliferation of hCEC stimulated by VEGF 165, but was ineffective against the stimulatory effect of VEGF 121. There were found to be significant differences in microvascular endothelial cells from the retina and choroid, both in the expression of cell markers and their behaviour in response to growth factors and currently available anti-VEGF agents, highlighting the importance of targeting treatments to specific intraocular vascular beds and/or diseases.

Bone marrow derived mesenchymal stem cells inhibit inflammation and preserve vascular endothelial integrity in the lungs after hemorrhagic shock

Hemorrhagic shock (HS) and trauma is currently the leading cause of death in young adults worldwide. Morbidity and mortality after HS and trauma is often the result of multi-organ failure such as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), conditions with few therapeutic options. Bone marrow derived mesenchymal stem cells (MSCs) are a multipotent stem cell population that has shown therapeutic promise in numerous pre-clinical and clinical models of disease. In this paper, in vitro studies with pulmonary endothelial cells (PECs) reveal that conditioned media (CM) from MSCs and MSC-PEC co-cultures inhibits PEC permeability by preserving adherens junctions (VE-cadherin and β-catenin). Leukocyte adhesion and adhesion molecule expression (VCAM-1 and ICAM-1) are inhibited in PECs treated with CM from MSC-PEC co-cultures. Further support for the modulatory effects of MSCs on pulmonary endothelial function and inflammation is demonstrated in our in vivo studies on HS in the rat. In a rat “fixed volume” model of mild HS, we show that MSCs administered IV potently inhibit systemic levels of inflammatory cytokines and chemokines in the serum of treated animals. In vivo MSCs also inhibit pulmonary endothelial permeability and lung edema with concurrent preservation of the vascular endothelial barrier proteins: VE-cadherin, Claudin-1, and Occludin-1. Leukocyte infiltrates (CD68 and MPO positive cells) are also decreased in lungs with MSC treatment. Taken together, these data suggest that MSCs, acting directly and through soluble factors, are potent stabilizers of the vascular endothelium and inflammation. These data are the first to demonstrate the therapeutic potential of MSCs in HS and have implications for the potential use of MSCs as a cellular therapy in HS-induced lung injury.

Biomarkers of endothelial cell activation: candidate markers for drug-induced vasculitis in patients or drug-induced vascular injury in animals

There is a pressing need for vascular biomarkers for studies of drug-induced vasculitis in patients and drug-induced vascular injury (DIVI) in animals. We previously reviewed a variety of candidate biomarkers of endothelial cell (EC) activation (Zhang et al., 2010). Now we update information on EC activation biomarkers from animal data on DIVI and clinical data of vasculitic patients, particularly patients with primary antineutrophil cytoplasmic autoantibody (ANCA)-associated small vessel vasculitis (primary AAVs), including Wegener's granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome and necrotizing crescentic glomerulonephritis. Drug-associated ANCA-positive small vessel vasculitis (drug-AAVs) can closely resemble primary AAVs, suggesting the large overlap between primary idiopathic systemic vasculitis and drug-induced vasculitis. AAVs in patients and DIVI in animals vary considerably; however, there is close resemblance between AAVs and DIVI in some respects: (1) the immunopathogenetic mechanisms (activation of primed neutrophils, ECs and T cells by ANCA in patients and activation of ECs, mast cells, and macrophages by drugs in animals); (2) the morphologic changes (fibrinoid necrosis of the vessel wall and neutrophilic infiltration); (3) the preferable sites (small arteries, arterioles, capillaries and venules); and (4) elevation of vascular biomarkers suggestive of an endothelial origin. The present review discusses soluble and cell component biomarkers and provides a rationale for the potential utility of EC activation biomarkers in nonclinical and clinical studies during new drug development. Further investigation, however, is needed to assess their potential utility.

Influence of the tumor microenvironment on angiogenesis

It is becoming increasingly recognized that the host microenvironment is essential for regulating tumor cell behavior. The cellular stromal compartment can modulate angiogenesis either directly through enhanced secretion of pro-angiogenic factors or reduced secretion of antiangiogenic factors, or indirectly by modulating the surrounding extracellular matrix. Control of angiogenesis represents a critical step in cancer progression and is a potential therapeutic target. This article focuses on the role of the tumor microenvironment in the control of angiogenesis and how dissection of the molecular interactions may enhance prognostic and predictive power and facilitate therapeutic targeting.

Cerebral microvascular endothelium and the pathogenesis of neurodegenerative diseases

Diseases of the central nervous system (CNS) pose a significant health challenge, but despite their diversity, they share many common features and mechanisms. For example, endothelial dysfunction has been implicated as a crucial event in the development of several CNS disorders, such as Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, multiple sclerosis, human immunodeficiency virus (HIV)-1-associated neurocognitive disorder and traumatic brain injury. Breakdown of the blood–brain barrier (BBB) as a result of disruption of tight junctions and transporters, leads to increased leukocyte transmigration and is an early event in the pathology of these disorders. The brain endothelium is highly reactive because it serves as both a source of, and a target for, inflammatory proteins and reactive oxygen species. BBB breakdown thus leads to neuroinflammation and oxidative stress, which are implicated in the pathogenesis of CNS disease. Furthermore, the physiology and pathophysiology of endothelial cells are closely linked to the functioning of their mitochondria, and mitochondrial dysfunction is another important mediator of disease pathology in the brain. The high concentration of mitochondria in cerebrovascular endothelial cells might account for the sensitivity of the BBB to oxidant stressors. Here, we discuss how greater understanding of the role of BBB function could lead to new therapeutic approaches for diseases of the CNS that target the dynamic properties of brain endothelial cells.

Tubulogenesis during blood vessel formation

The ability to form and maintain a functional system of contiguous hollow tubes is a critical feature of vascular endothelial cells (ECs). Lumen formation, or tubulogenesis, occurs in blood vessels during both vasculogenesis and angiogenesis in the embryo. Formation of vascular lumens takes place prior to the establishment of blood flow and to vascular remodeling which results in a characteristic hierarchical vessel organization. While epithelial lumen formation has received intense attention in past decades, more recent work has only just begun to elucidate the mechanisms controlling the initiation and morphogenesis of endothelial lumens. Studies using in vitro and in vivo models, including zebrafish and mammals, are beginning to paint an emerging picture of how blood vessels establish their characteristic morphology and become patent. In this article, we review and discuss the molecular and cellular mechanisms driving the formation of vascular tubes, primarily in vivo, and we compare and contrast proposed models for blood vessel lumen formation.

Plexiform lesions in the lungs of domestic fowl selected for susceptibility to pulmonary arterial hypertension: incidence and histology

Plexiform lesions develop in the pulmonary arteries of humans suffering from idiopathic pulmonary arterial hypertension (IPAH). Plexogenic arteriopathy rarely develops in existing animal models of IPAH. In this study, plexiform lesions developed in the lungs of rapidly growing meat-type chickens (broiler chickens) that had been genetically selected for susceptibility to IPAH. Plexiform lesions developed spontaneously in: 42% of females and 40% of males; 35% of right lungs, and 45% of left lungs; and, at 8, 12, 16, 20, 24, and 52 weeks of age the plexiform lesion incidences averaged 52%, 50%, 51%, 40%, 36%, and 22%, respectively. Plexiform lesions formed distal to branch points in muscular interparabronchial pulmonary arteries exhibiting intimal proliferation. Perivascular mononuclear cell infiltrates consistently surrounded the affected arteries. Proliferating intimal cells fully or partially occluded the arterial lumen adjacent to plexiform lesions. Broilers reared in clean stainless steel cages exhibited a 50% lesion incidence that did not differ from the 64% incidence in flock mates grown on dusty floor litter. Microparticles (30 μm diameter) were injected to determine if physical occlusion and focal inflammation within distal pulmonary arteries might initiate plexiform lesion development. Three months postinjection no plexiform lesions were observed in the vicinity of persisting microparticles. Broiler chickens selected for innate susceptibility to IPAH represent a new animal model for investigating the mechanisms responsible for spontaneous plexogenic arteriopathy.

Idiopathic pulmonary arterial hypertension: an avian model for plexogenic arteriopathy and serotonergic vasoconstriction

Idiopathic pulmonary arterial hypertension (IPAH) is a disease of unknown cause that is characterized by elevated pulmonary arterial pressure and pulmonary vascular resistance attributable to vasoconstriction and vascular remodeling of small pulmonary arteries. Vascular remodeling includes hypertrophy and hyperplasia of smooth muscle (medial hypertrophy) accompanied in up to 80% of the cases by the formation of occlusive plexiform lesions (plexogenic arteriopathy). Patients tend to be unresponsive to vasodilator therapy and have a poor prognosis for survival when plexogenic arteriopathy progressively obstructs their pulmonary arteries. Research is needed to understand and treat plexogenic arteriopathy, but advances have been hindered by the absence of spontaneously developing lesions in existing laboratory animal models. Young domestic fowl bred for meat production (broiler chickens, broilers) spontaneously develop IPAH accompanied by semi-occlusive endothelial proliferation that progresses into fully developed plexiform lesions. Plexiform lesions develop in both female and male broilers, and lesion incidences (lung sections with lesions/lung sections examined) averaged approximately 40% in 8 to 52 week old birds. Plexiform lesions formed distal to branch points in muscular interparabronchial pulmonary arteries, and were associated with perivascular mononuclear cell infiltrates. Serotonin (5-hydroxytryptamine, 5-HT) is a potent vasoconstrictor and mitogen known to stimulate vascular endothelial and smooth muscle cell proliferation. Serotonin has been directly linked to the pathogenesis of IPAH in humans, including IPAH linked to serotonergic anorexigens that trigger the formation of plexiform lesions indistinguishable from those observed in primary IPAH triggered by other causes. Serotonin also plays a major role in the susceptibility of broilers to IPAH. This avian model of spontaneous IPAH constitutes a new animal model for biomedical research focused on the pathogenesis of IPAH and plexogenic arteriopathy.

Effect of sulodexide on endothelial glycocalyx and vascular permeability in patients with type 2 diabetes mellitus

AIMS/HYPOTHESIS

Endothelial glycocalyx perturbation contributes to increased vascular permeability. In the present study we set out to evaluate whether: (1) glycocalyx is perturbed in individuals with type 2 diabetes mellitus, and (2) oral glycocalyx precursor treatment improves glycocalyx properties.

METHODS

Male participants with type 2 diabetes (n = 10) and controls (n = 10) were evaluated before and after 2 months of sulodexide administration (200 mg/day). The glycocalyx dimension was estimated in two different vascular beds using sidestream dark field imaging and combined fluorescein/indocyanine green angiography for sublingual and retinal vessels, respectively. Transcapillary escape rate of albumin (TER(alb)) and hyaluronan catabolism were assessed as measures of vascular permeability.

RESULTS

Both sublingual dimensions (0.64 [0.57-0.75] μm vs 0.78 [0.71-0.85] μm, p < 0.05, medians [interquartile range]) and retinal glycocalyx dimensions (5.38 [4.88-6.59] μm vs 8.89 [4.74-11.84] μm, p < 0.05) were reduced in the type 2 diabetes group compared with the controls whereas TER(alb) was increased (5.6 ± 2.3% vs 3.7 ± 1.7% in the controls, p < 0.05). In line with these findings, markers of hyaluronan catabolism were increased with diabetes (hyaluronan 137 ± 29 vs 81 ± 8 ng/ml and hyaluronidase 78 ± 4 vs 67 ± 2 U/ml, both p < 0.05). Sulodexide increased both the sublingual and retinal glycocalyx dimensions in participants with diabetes (to 0.93 [0.83-0.99] μm and to 5.88 [5.33-6.26] μm, respectively, p < 0.05). In line, a trend towards TER(alb) normalisation (to 4.0 ± 2.3%) and decreases in plasma hyaluronidase (to 72 ± 2 U/ml, p < 0.05) were observed in the diabetes group.

CONCLUSION/INTERPRETATION

Type 2 diabetes is associated with glycocalyx perturbation and increased vascular permeability, which are partially restored following sulodexide administration. Further studies are warranted to determine whether long-term treatment with sulodexide has a beneficial effect on cardiovascular risk.

TRIAL REGISTRATION

www.trialregister.nl NTR780/ http://isrctn.org ISRCTN82695186

FUNDING

An unrestricted Novartis Foundation for Cardiovascular Excellence grant (2006) to M. Nieuwdorp/E. S. G. Stroes, Dutch Heart Foundation (grant number 2005T037).

Shear stress: devil's in the details

In this issue of Blood, Ni et al use an in vivo mouse model of disturbed flow that results in accelerated atherosclerosis to identify novel mechanosensitive genes.

Atrial natriuretic peptide protects against Staphylococcus aureus-induced lung injury and endothelial barrier dysfunction

Lung inflammation and alterations in endothelial cell (EC) permeability are key events to development of acute lung injury (ALI). Protective effects of atrial natriuretic peptide (ANP) have been shown against inflammatory signaling and endothelial barrier dysfunction induced by gram-negative bacterial wall liposaccharide. We hypothesized that ANP may possess more general protective effects and attenuate lung inflammation and EC barrier dysfunction by suppressing inflammatory cascades and barrier-disruptive mechanisms shared by gram-negative and gram-positive pathogens. C57BL/6J wild-type or ANP knockout mice (Nppa-/-) were treated with gram-positive bacterial cell wall compounds, Staphylococcus aureus-derived peptidoglycan (PepG) and/or lipoteichoic acid (LTA) (intratracheal, 2.5 mg/kg each), with or without ANP (intravenous, 2 μg/kg). In vitro, human pulmonary EC barrier properties were assessed by morphological analysis of gap formation and measurements of transendothelial electrical resistance. LTA and PepG markedly increased pulmonary EC permeability and activated p38 and ERK1/2 MAP kinases, NF-κB, and Rho/Rho kinase signaling. EC barrier dysfunction was further elevated upon combined LTA and PepG treatment, but abolished by ANP pretreatment. In vivo, LTA and PepG-induced accumulation of protein and cells in the bronchoalveolar lavage fluid, tissue neutrophil infiltration, and increased Evans blue extravasation in the lungs was significantly attenuated by intravenous injection of ANP. Accumulation of bronchoalveolar lavage markers of LTA/PepG-induced lung inflammation and barrier dysfunction was further augmented in ANP-/- mice and attenuated by exogenous ANP injection. These results strongly suggest a protective role of ANP in the in vitro and in vivo models of ALI associated with gram-positive infection. Thus ANP may have important implications in therapeutic strategies aimed at the treatment of sepsis and ALI-induced gram-positive bacterial pathogens.

Differential effects of VEGFR-1 and VEGFR-2 inhibition on tumor metastases based on host organ environment

Tumors induce new blood vessel growth primarily from host organ microvascular endothelial cells (EC), and microvasculature differs significantly between the lung and liver. Vascular endothelial growth factor (VEGF or VEGF-A) promotion of tumor angiogenesis is thought to be mediated primarily by VEGF receptor-2 (VEGFR-2). In this study, VEGFR-2 antibody (DC101) inhibited growth of RenCa renal cell carcinoma lung metastases by 26%, whereas VEGFR-1 antibody (MF-1) had no effect. However, VEGFR-2 neutralization had no effect on RenCa liver metastases, whereas VEGFR-1 neutralization decreased RenCa liver metastases by 31%. For CT26 colon carcinoma liver metastases, inhibition of both VEGFR-1 and VEGFR-2 was required to induce growth delay. VEGFR-1 or VEGFR-2 inhibition decreased tumor burden not by preventing the establishment of micrometastases but rather by preventing vascularization and growth of micrometastases by 55% and 43%, respectively. VEGF induced greater phosphorylation of VEGFR-2 in lung ECs and of VEGFR-1 in liver ECs. EC proliferation, migration, and capillary tube formation in vitro were suppressed more by VEGFR-2 inhibition for lung EC and more by VEGFR-1 inhibition for liver EC. Collectively, our results indicate that liver metastases are more reliant on VEGFR-1 than lung metastases to mediate angiogenesis due to differential activity of VEGFRs on liver EC versus lung EC. Thus, therapies inhibiting specific VEGFRs should consider the targeted sites of metastatic disease.

Endothelial cell heterogeneity of blood-brain barrier gene expression along the cerebral microvasculature

The blood-brain barrier (BBB) refers to the network of microvessels that selectively restricts the passage of substances between the circulation and the central nervous system (CNS). This microvascular network is comprised of arterioles, capillaries and venules, yet the respective contribution of each of these to the BBB awaits clarification. In this regard, it has been postulated that brain microvascular endothelial cells (BMEC) from these different tributaries might exhibit considerable heterogeneity in form and function, with such diversity underlying unique roles in physiological and pathophysiological processes. Means to begin exploring such endothelial differences in situ, free from caveats associated with cell isolation and culturing procedures, are crucial to comprehending the nature and treatment of CNS diseases with vascular involvement. Here, the recently validated approach of immuno-laser capture microdissection (immuno-LCM) coupled to quantitative real-time PCR (qRT-PCR) was used to analyze gene expression patterns of BMEC retrieved in situ from either capillaries or venules. From profiling 87 genes known to play a role in BBB function and/or be enriched in isolated brain microvessels, results imply that most BBB properties reside in both segments, but that capillaries preferentially express some genes related to solute transport, while venules tend toward higher expression of an assortment of genes involved in inflammatory-related tasks. Fuller appreciation of such heterogeneity will be critical for efficient therapeutic targeting of the endothelium and the management of CNS disease.

Effect of high-dose dexamethasone on endothelial haemostatic gene expression and neutrophil adhesion

Glucocorticoid usage especially at high doses is complicated by adverse outcomes such as thrombotic events or acceleration of inflammatory response in conditions like myeloma and osteonecrosis. The mechanism(s) through which high-dose dexamethasone (HDDEXA) causes vascular injury remains unclear. We hypothesized that HDDEXA sensitizes endothelial cells (EC) to the effect of inflammatory mediators and modulates endothelial haemostatic gene expression and leukocyte adhesion. Human umbilical vein endothelial cells (HUVECs) were grown in the absence or presence of HDDEXA and were also tested in the presence or absence of tumor necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS) or thrombin. mRNA and protein expression were measured and the functional consequences of HDDEXA preconditioning on cell adhesion molecules (CAM) were determined by agonist-mediated leukocyte adhesion assay. Treatment with HDDEXA resulted in an increased induction of CAM, tissue factor and von Willebrand factor, while down-regulating thrombomodulin and urokinase. HDDEXA alone had no effect on adhesion but resulted in enhanced TNF-alpha- and LPS-mediated adhesion of neutrophils. Together, these findings suggest that HDDEXA sensitizes HUVEC to the effect of inflammatory mediators and induces a pro-adhesive environment in primary EC. This finding is of importance when glucocorticoid usage is required at therapeutic high doses in patients with or without thrombotic risk factors.

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

A +220 GATA motif mediates basal but not endotoxin-repressible expression of the von Willebrand factor promoter in Hprt-targeted transgenic mice

BACKGROUND

The von Willebrand factor (VWF) gene is a marker for spatial and temporal heterogeneity of the endothelium. A GATA motif at +220 has been implicated in basal VWF expression in vitro. Other studies have shown that GATA3 and VWF are transcriptionally downregulated in response to inflammatory mediators.

OBJECTIVES

Our goal was to determine the importance of the +220 GATA motif in mediating expression of VWF promoter in vivo, and to elucidate whether the GATA element plays a role in spatial and/or temporal regulation of VWF expression.

METHODS

ChIP and electrophoretic mobility shift assays were carried out in human umbilical vein endothelial cells (HUVEC). Reporter gene constructs containing 3.6 kb of the human VWF promoter with and without a mutation of the +220 GATA element were transfected into cultured endothelial cells or targeted to the Hprt locus of mice. The Hprt-targeted mice were subjected to endotoxemia.

RESULTS

In protein-DNA binding assays, the +220 GATA motif bound GATA-2, -3 and -6. Mutation of the GATA site resulted in reduced basal promoter activity in HUVEC. When targeted to the Hprt locus of mice, the GATA mutation resulted in a significant, proportionate reduction of promoter activity in LacZ expressing vascular beds. Systemic administration of lipopolysaccharide (LPS) resulted in a widespread reduction in VWF mRNA expression and promoter activity. LPS-mediated repression of the VWF promoter was unaffected by the GATA mutation.

CONCLUSIONS

A region of the VWF promoter between -2182 and the end of the first intron contains information for LPS-mediated gene repression. The +220 GATA motif is important for basal, but not LPS-repressible expression of the VWF gene.