Phenotypic heterogeneity of the endothelium: II. Representative vascular beds

In vivo evaluation of venular glycocalyx during hemorrhagic shock in rats using intravital microscopy

Hemorrhage is responsible for a large percentage of trauma-related deaths but the mechanisms underlying tissue ischemia are complex and not well understood. Despite the evidence linking glycocalyx degradation and hemorrhagic shock, there is no direct data obtained in vivo showing glycocalyx thickness reduction in skeletal muscle venules after hemorrhage. We hypothesize that damage to the endothelial glycocalyx is a key element in hemorrhage pathophysiology and tested the hypothesis that hemorrhage causes glycocalyx degradation in cremaster muscle microvessels. We utilized intravital microscopy to estimate glycocalyx thickness in 48 microvessels while other microvascular parameters were measured using non-invasive techniques. Systemic physiological parameters and blood chemistry were simultaneously collected. We studied 27 post-capillary venules (<16 μm diameter) of 8 anesthetized rats subjected to hemorrhage (40% of total blood volume). Six control rats were equally instrumented but not bled. Dextrans of different molecular weights labeled with FITC or Texas Red were injected. Glycocalyx thickness was estimated from the widths of the fluorescence columns and from anatomical diameter. While control rats did not show remarkable responses, a statistically significant decrease of about 59% in glycocalyx thickness was measured in venules after hemorrhagic shock. Venular glycocalyx thickness and local blood flow changes were correlated: venules with the greatest flow reductions showed the largest decreases in glycocalyx. These changes may have a significant impact in shock pathophysiology. Intravital microscopy and integrated systems such as the one described here may be important tools to identify mechanisms by which resuscitation fluids may improve tissue recovery and outcome following hemorrhage.

α(M)β(2)-integrin-intercellular adhesion molecule-1 interactions drive the flow-dependent trafficking of Guillain-Barré syndrome patient derived mononuclear leukocytes at the blood-nerve barrier in vitro

The mechanisms of hematogenous leukocyte trafficking at the human blood-nerve barrier (BNB) are largely unknown. Intercellular adhesion molecule-1 (ICAM-1) has been implicated in the pathogenesis of Guillain-Barré syndrome (GBS). We developed a cytokine-activated human in vitro BNB model using primary endoneurial endothelial cells. Endothelial treatment with 10 U/ml tissue necrosis factor-α and 20 U/ml interferon-γ resulted in de novo expression of pro-inflammatory chemokines CCL2, CXCL9, CXCL11, and CCL20, with increased expression of CXCL2-3, CXCL8, and CXCL10 relative to basal levels. Cytokine treatment induced/enhanced ICAM-1, E- and P-selectin, vascular cell adhesion molecule-1 and the alternatively spliced pro-adhesive fibronectin variant, fibronectin connecting segment-1 expression in a time-dependent manner, without alterations in junctional adhesion molecule-A expression. Lymphocytes and monocytes from untreated GBS patients express ICAM-1 counterligands, α(M)- and α(L)-integrin, with differential regulation of α(M) -integrin expression compared to healthy controls. Under flow conditions that mimic capillary hemodynamics in vivo, there was a >3-fold increase in total GBS patient and healthy control mononuclear leukocyte adhesion/migration at the BNB following cytokine treatment relative to the untreated state. Function neutralizing monoclonal antibodies against human α(M)-integrin (CD11b) and ICAM-1 reduced untreated GBS patient mononuclear leukocyte trafficking at the BNB by 59% and 64.2%, respectively. Monoclonal antibodies against α(L)-integrin (CD11a) and human intravenous immunoglobulin reduced total leukocyte adhesion/migration by 22.8% and 17.6%, respectively. This study demonstrates differential regulation of α(M)-integrin on circulating mononuclear cells in GBS, as well as an important role for α(M)-integrin-ICAM-1 interactions in pathogenic GBS patient leukocyte trafficking at the human BNB in vitro.

An immortalized human blood-nerve barrier endothelial cell line for in vitro permeability studies

Solute and macromolecular transport studies may elucidate nutritional requirements and drug effects in healthy and diseased peripheral nerves. Endoneurial endothelial cells are specialized microvascular cells that form the restrictive blood-nerve barrier (BNB). Primary human endoneurial endothelial cells (pHEndECs) are difficult to isolate, limiting their widespread availability for biomedical research. We developed a simian virus-40 large T-antigen (SV40-LTA) immortalized human BNB cell line via stable transfection of low passage pHEndECs and observed continuous growth in culture for >45 population doublings. As observed with pHEndECs, the immortalized BNB endothelial cells were Ulex Europaeus agglutinin-1-positive and endocytosed low density lipoprotein, but lost von Willebrand factor expression. Glucose transporter-1, P-glycoprotein (P-gp), γ-glutamyl transpeptidase (γ-GT), large neutral amino acid transporter-1 (LAT-1), creatine transporter (CRT), and monocarboxylate transporter-1 (MCT-1) mRNA expression were retained at all passages with loss of alkaline phosphatase (AP) expression after passages 16-20. Compared with an SV40-LTA immortalized human blood-brain barrier endothelial cell line, there was increased γ-GT protein expression, equivalent expression of organic anion transporting polypeptide-C (OATP-C), organic anion transporter 3 (OAT-3), MCT-1, and LAT-1, and reduced expression of AP, CRT, and P-gp by the BNB cell line at passage 20. Further studies demonstrated lower transendothelial electrical resistance (~181 vs. 191 Ω cm(2)), equivalent permeability to fluoresceinated sodium (4.84 vs. 4.39 %), and lower permeability to fluoresceinated high molecular weight (70 kDa) dextran (0.39 vs. 0.52 %) by the BNB cell line. This cell line retained essential molecular and biophysical properties suitable for in vitro peripheral nerve permeability studies.

Acute and chronic shear stress differently regulate endothelial internalization of nanocarriers targeted to platelet-endothelial cell adhesion molecule-1

Intracellular delivery of nanocarriers (NC) is controlled by their design and target cell phenotype, microenvironment, and functional status. Endothelial cells (EC) lining the vascular lumen represent an important target for drug delivery. Endothelium in vivo is constantly or intermittently (as, for example, during ischemia-reperfusion) exposed to blood flow, which influences NC-EC interactions by changing NC transport properties, and by direct mechanical effects upon EC mechanisms involved in NC binding and uptake. EC do not internalize antibodies to marker glycoprotein PECAM(CD31), yet internalize multivalent NC coated with PECAM antibodies (anti-PECAM/NC) via a noncanonical endocytic pathway distantly related to macropinocytosis. Here we studied the effects of flow on EC uptake of anti-PECAM/NC spheres (~180 nm diameter). EC adaptation to chronic flow, manifested by cellular alignment with flow direction and formation of actin stress fibers, inhibited anti-PECAM/NC endocytosis consistent with lower rates of anti-PECAM/NC endocytosis in vivo in arterial compared to capillary vessels. Acute induction of actin stress fibers by thrombin also inhibited anti-PECAM/NC endocytosis, demonstrating that formation of actin stress fibers impedes EC endocytic machinery. In contrast, acute flow without stress fiber formation, stimulated anti-PECAM/NC endocytosis. Anti-PECAM/NC endocytosis did not correlate with the number of cell-bound particles under flow or static conditions. PECAM cytosolic tail deletion and disruption of cholesterol-rich plasmalemma domains abrogated anti-PECAM/NC endocytosis stimulation by acute flow, suggesting complex regulation of a flow-sensitive endocytic pathway in EC. The studies demonstrate the importance of the local flow microenvironment for NC uptake by the endothelium and suggest that cell culture models of nanoparticle uptake should reflect the microenvironment and phenotype of the target cells.

Importance of endothelial NF-κB signalling in vascular remodelling and aortic aneurysm formation

AIMS

Vascular remodelling and aortic aneurysm formation are induced mainly by inflammatory responses in the adventitia and media. However, relatively little is known about the mechanistic significance of endothelium in the pathogenesis of these vascular disorders. The transcription factor nuclear factor-kappa B (NF-κB) regulates the expressions of numerous genes, including those related to pro-inflammatory responses. Therefore, to investigate the roles of endothelial pro-inflammatory responses, we examined the impact of blocking endothelial NF-κB signalling on intimal hyperplasia and aneurysm formation.

METHODS AND RESULTS

To block endothelial NF-κB signalling, we used transgenic mice expressing dominant-negative IκBα selectively in endothelial cells (E-DNIκB mice). E-DNIκB mice were protected from the development of cuff injury-induced neointimal formation, in association with suppressed arterial expressions of cellular adhesion molecules, a macrophage marker, and inflammatory factors. In addition, the blockade of endothelial NF-κB signalling prevented abdominal aortic aneurysm formation in an experimental model, hypercholesterolaemic apolipoprotein E-deficient mice with angiotensin II infusion. In this aneurysm model as well, aortic expressions of an adhesion molecule, a macrophage marker, and inflammatory factors were suppressed with the inhibited expression and activity of matrix metalloproteinases in the aorta.

CONCLUSION

Endothelial NF-κB activation up-regulates adhesion molecule expression, which may trigger macrophage infiltration and inflammation in the adventitia and media. Thus, the endothelium plays important roles in vascular remodelling and aneurysm formation through its intracellular NF-κB signalling.

Eph/Ephrin signaling in injury and inflammation

The Eph/ephrin receptor-ligand system plays an important role in embryogenesis and adult life, principally by influencing cell behavior through signaling pathways, resulting in modification of the cell cytoskeleton and cell adhesion. There are 10 EphA receptors, and six EphB receptors, distinguished on sequence difference and binding preferences, that interact with the six glycosylphosphatidylinositol-linked ephrin-A ligands and the three transmembrane ephrin-B ligands, respectively. The Eph/ephrin proteins, originally described as developmental regulators that are expressed at low levels postembryonically, are re-expressed after injury to the optic nerve, spinal cord, and brain in fish, amphibians, rodents, and humans. In rodent spinal cord injury, the up-regulation of EphA4 prevents recovery by inhibiting axons from crossing the injury site. Eph/ephrin proteins may be partly responsible for the phenotypic changes to the vascular endothelium in inflammation, which allows fluid and inflammatory cells to pass from the vascular space into the interstitial tissues. Specifically, EphA2/ephrin-A1 signaling in the lung may be responsible for pulmonary inflammation in acute lung injury. A role in T-cell maturation and chronic inflammation (heart failure, inflammatory bowel disease, and rheumatoid arthritis) is also reported. Although there remains much to learn about Eph/ephrin signaling in human disease, and specifically in injury and inflammation, this area of research raises the exciting prospect that novel therapies will be developed that precisely target these pathways.

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

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

Dynamical systems approach to endothelial heterogeneity

Endothelial cells display remarkable phenotypic heterogeneity. An important goal is to elucidate the scope and mechanisms of endothelial heterogeneity and to use this information to develop vascular bed-specific therapies. We reexamine our current understanding of the molecular basis of endothelial heterogeneity. We introduce multistability as a new explanatory framework in vascular biology. We draw on the field of nonlinear dynamics to propose a dynamical systems framework for modeling multistability and its derivative properties, including robustness, memory, and plasticity. Our perspective allows for both a conceptual and quantitative description of system-level features of endothelial regulation.

Role of angiopoietin/tie2 in critical illness: promising biomarker, disease mediator, and therapeutic target?

Critical illness is a descriptive, broad term for a serious clinical condition that can result from enormously heterogeneous etiologies. A common end feature these patients regularly suffer from is the so-called multiple organ dysfunction syndrome (MODS), often a consequence of organ hypoperfusion and ischemia, coagulopathies, overwhelming inflammatory responses, immune paralysis and mitochondrial dysfunction. Mechanistically, endothelial injury and particularly microvascular leakage is a major step in the pathophysiology of MODS and contributes to its mortality. The angiopoietin (Angpt)/Tie2 system consists of the endothelial tyrosine kinase Tie2 and its 4 circulating ligands (Angpt1-4). The balance between the agonistic ligand "Angpt-1" and the antagonistic one "Angpt-2" regulates baseline endothelial barrier function and its response to injury and is therefore considered a gatekeeper of endothelial activation. This paper provides a systematic overview of the Angpt/Tie2 system with respect to (1) its role as a global biomarker of endothelial activation in critical ill patients, (2) its contribution to MODS pathophysiology as a disease mediator, and last but not least (3) putative therapeutic applications to modify the activation state of Tie2 in mice and men.

Impaired cardiac microvascular endothelial cells function induced by Coxsackievirus B3 infection and its potential role in cardiac fibrosis

CVB3 virus tropism and tissue access are modulated by cardiac microvascular endothelial cells (CMVECs) in the context of microvasculature. This study was designed to examine biological behaviors of CMVECs following CVB3 infection and its possible effects on cardiac remodeling. Data demonstrated that CVB3 increased caspase-3 activities, Bax/Bcl-2 protein ratio and TGF-β1 levels in CMVECs, accompanying with elevated microvascular permeability. Double immunofluorescence revealed co-localization of endothelial markers (CD31 and VE-cadherin) and mesenchymal markers (FSP1 and αSMA) in infected CMVECs. Western blot demonstrated that CVB3 significantly decreased the expression of endothelial markers and increased the expression of mesenchymal markers, which were reversed by SB431542 (inhibitor of TGF-β1), indicating that endothelial-to-mesenchymal transition following CVB3 infection was probably induced by CMVECs-derived TGF-β1. Excess extracellular matrix was produced by myocardial cells incubated with supernatants of infected CMVECs. Our results displayed that CVB3 induced notable biological changes of CMVECs, which may contribute to cardiac fibrosis.

Differential susceptibility of human primary aortic and coronary artery vascular cells to RNA interference

BACKGROUND

RNAi technology is a promising tool for gene therapy of vascular disease. However, the biological heterogeneity between endothelial (EC) and vascular smooth muscle cells (SMC) and within different vascular beds make them differentially susceptible to siRNA. This is further complicated by the task of choosing the right transfection reagent that leads to consistent gene silencing across all cell types with minimal toxicity. The goal of this study was to investigate the intrinsic RNAi susceptibility of primary human aortic and coronary artery endothelial and vascular smooth muscle cells (AoEC, CoEC, AoSMC and CoSMC) using adherent cell cytometry.

METHODS

Cells were seeded at a density of 5000cells/well of a 96well plate. Twenty four hours later cells were transfected with either non-targeting unlabeled control siRNA (50nM), or non-targeting red fluorescence labeled siRNA (siGLO Red, 5 or 50nM) using no transfection reagent, HiPerFect or Lipofectamine RNAiMAX. Hoechst nuclei stain was used to label cells for counting. For data analysis an adherent cell cytometer, Celigo was used.

RESULTS

Red fluorescence counts were normalized to the cell count. EC displayed a higher susceptibility towards siRNA delivery than SMC from the corresponding artery. CoSMC were more susceptible than AoSMC. In all cell types RNAiMAX was more potent compared to HiPerFect or no transfection reagent. However, after 24h, RNAiMAX led to a significant cell loss in both AoEC and CoEC. None of the other transfection conditions led to a significant cell loss.

CONCLUSION

This study confirms our prior observation that EC are more susceptible to siRNA than SMC based on intracellular siRNA delivery. RNAiMax treatment led to significant cell loss in AoEC and CoEC, but not in the SMC populations. Additionally, this study is the first to demonstrate that coronary SMC are more susceptible to siRNA than aortic SMC.

Adiponectin diminishes organ-specific microvascular endothelial cell activation associated with sepsis

Experimental sepsis was induced in male C57BL/6j, adiponectin-deficient mice (ADPNKO), and wild-type littermates by i.p. injection of 16 mg/kg lipopolysaccharide or cecal ligation and puncture. Blood and tissue samples were harvested 24 h after model induction. Circulating adiponectin is reduced in mice with endotoxemic challenge and after cecal ligation and puncture compared with healthy control mice. Quantitative reverse transcriptase-polymerase chain reaction for adiponectin reveals a pattern of response that is both model- and organ-specific. When challenged with sepsis, adiponectin deficiency results in increased expression of endothelial adhesion and coagulation molecules in the lung, liver, and kidney as quantified by reverse transcriptase-polymerase chain reaction, increased macrophage and neutrophil infiltration by immunohistochemistry, and vascular leakage in the liver and kidney. Adiponectin-deficient mice have reduced survival following cecal ligation and puncture and increased blood levels of interleukin 6, soluble vascular endothelial growth factor receptor 1, and soluble endothelial adhesion molecules E-selectin and intercellular adhesion molecule 1. Finally, ADPNKO promoted end-organ injury in the liver and kidney, whereas the lungs were not affected. These data suggest a protective role of adiponectin in diminishing microvascular organ-specific endothelial cell activation during sepsis.

Low-grade inflammation, but not endothelial dysfunction, is associated with greater carotid stiffness in the elderly: the Hoorn Study

OBJECTIVE

Biomarkers of low-grade inflammation and endothelial dysfunction are associated with cardiovascular disease. Arterial stiffening may be a mechanism through which low-grade inflammation and (or) endothelial dysfunction lead to cardiovascular disease. Therefore, we investigated whether low-grade inflammation and endothelial dysfunction were associated with greater carotid stiffness in a population-based cohort of elderly individuals.

METHODS

We determined biomarkers of low-grade inflammation (C-reactive protein, serum amyloid A, interleukin 6, interleukin 8, tumour necrosis factor α and soluble intercellular adhesion molecule 1), and of endothelial dysfunction (von Willebrand factor, soluble vascular cell adhesion molecule 1, soluble endothelial selectin, soluble thrombomodulin, soluble intercellular adhesion molecule 1 and flow-mediated dilation), and combined these into mean z-scores (n = 572; women = 286; age 67.5 ± 6.6 years). Additionally, we determined by ultrasonography carotid diameter, distension, pulse pressure and intima-media thickness. Carotid stiffness indices were determined by calculation of the distensibility and compliance coefficient, Young's elastic modulus and β stiffness index.

RESULTS

The study population was characterized by a high prevalence of cardiovascular disease (46%), hypertension (66%) and the use of lipid-lowering (16%) and antihypertensive (34%) medication. After adjustment for the above in addition to sex, age, glucose tolerance status and current smoking, the low-grade inflammation z-score was positively associated with Young's elastic modulus [β (95% confidence interval) 0.080 (0.021-0.139), P = 0.008]. This association was primarily driven through greater diameter. After adjustment for the variables above, the endothelial dysfunction z-score was not associated with carotid stiffness.

CONCLUSION

These data suggest that low-grade inflammation, in the elderly, plays an important role in carotid artery remodelling and stiffening.

Lack of endothelial diaphragms in fenestrae and caveolae of mutant Plvap-deficient mice

Plasmalemmal vesicle-associated protein (PLVAP, PV-1) is specifically expressed in endothelial cells in which it localizes to diaphragms of fenestrae, caveolae, and transendothelial channels. To learn about its function, we generated mutant mice that lack PLVAP. In a C57BL/6N genetic background, homozygous Plvap-deficient embryos die before birth and suffer from subcutaneous edema, hemorrhages, and defects in the vascular wall of subcutaneous capillaries. In addition, hearts of Plvap(-/-) embryos show ventricular septal defects and thinner ventricular walls. In wild-type embryos, PLVAP and caveolae with a stomatal diaphragm are present in endothelial cells of subcutaneous capillaries and endocardium, while a diaphragm is missing in caveolae of Plvap(-/-) littermates. Plvap(-/-) mice in a mixed C57BL/6N/FVB-N genetic background are born and survive at the most for 4 weeks. Capillaries of exocrine and endocrine pancreas and of kidney peritubular interstitium were investigated in more detail as examples of fenestrated capillaries. In these vascular beds, Plvap(-/-) mice show a complete absence of diaphragms in fenestrae, caveolae, and transendothelial channels, findings which are associated with a substantial decrease in the number of endothelial fenestrae. The changes in the capillary phenotype correlate with a considerable retardation of postnatal growth and anemia. Plvap(-/-) mice provide an animal model to clarify the specific functional role of endothelial fenestrae and their contribution to passage of water and solutes in different organs.

Mannose 6-phosphate receptor and sortilin mediated endocytosis of α-galactosidase A in kidney endothelial cells

Prominent vasculopathy in Fabry disease patients is caused by excessive intracellular accumulation of globotriaosylceramide (GL-3) throughout the vascular endothelial cells causing progressive cerebrovascular, cardiac and renal impairments. The vascular lesions lead to myocardial ischemia, atherogenesis, stroke, aneurysm, thrombosis, and nephropathy. Hence, injury to the endothelial cells in the kidney is a key mechanism in human glomerular disease and endothelial cell repair is an important therapeutic target. We investigated the mechanism of uptake of α-galactosidase A (α-Gal A) in renal endothelial cells, in order to clarify if the recombinant enzyme is targeted to the lysosomes via the universal mannose 6-phosphate receptor (M6PR) and possibly other receptors. Immunohistochemical localization of infused recombinant α-Gal A in a renal biopsy from a classic Fabry disease patient showed that recombinant protein localize in the endothelial cells of the kidney. Affinity purification studies using α-Gal A resins identified M6PR and sortilin as α-Gal A receptors in cultured glomerular endothelial cells. Immunohistochemical analyses of normal human kidney with anti-sortilin and anti-M6PR showed that sortilin and M6PR were expressed in the endothelium of smaller and larger vessels. Uptake studies in cultured glomerular endothelial cells of α-Gal A labeled with fluorescence and ¹²⁵I showed by inhibition with RAP and M6P that sortilin and M6PR mediated uptake of α-Gal A. Biacore studies revealed that α-Gal A binds to human M6PR with very high affinity, but M6PR also binds to sortilin in a way that prevents α-Gal A binding to sortilin. Taken together, our data provide evidence that sortilin is a new α-Gal A receptor expressed in renal endothelial cells and that this receptor together with the M6PR is able to internalize circulating α-Gal A during enzyme replacement therapy in patients with Fabry disease.

Divergent responses of different endothelial cell types to infection with Candida albicans and Staphylococcus aureus

Endothelial cells are important in the pathogenesis of bloodstream infections caused by Candida albicans and Staphylococcus aureus. Numerous investigations have used human umbilical vein endothelial cells (HUVECs) to study microbial-endothelial cell interactions in vitro. However, the use of HUVECs requires a constant supply of umbilical cords, and there are significant donor-to-donor variations in these endothelial cells. The use of an immortalized endothelial cell line would obviate such difficulties. One candidate in this regard is HMEC-1, an immortalized human dermal microvascular endothelial cell line. To determine if HMEC-1 cells are suitable for studying the interactions of C. albicans and S. aureus with endothelial cells in vitro, we compared the interactions of these organisms with HMEC-1 cells and HUVECs. We found that wild-type C. albicans had significantly reduced adherence to and invasion of HMEC-1 cells as compared to HUVECs. Although wild-type S. aureus adhered to and invaded HMEC-1 cells similarly to HUVECs, an agr mutant strain had significantly reduced invasion of HMEC-1 cells, but not HUVECs. Furthermore, HMEC-1 cells were less susceptible to damage induced by C. albicans, but more susceptible to damage caused by S. aureus. In addition, HMEC-1 cells secreted very little IL-8 in response to infection with either organism, whereas infection of HUVECs induced substantial IL-8 secretion. This weak IL-8 response was likely due to the anatomic site from which HMEC-1 cells were obtained because infection of primary human dermal microvascular endothelial cells with C. albicans and S. aureus also induced little increase in IL-8 production above basal levels. Thus, C. albicans and S. aureus interact with HMEC-1 cells in a substantially different manner than with HUVECs, and data obtained with one type of endothelial cell cannot necessarily be extrapolated to other types.

MicroRNA-126 contributes to renal microvascular heterogeneity of VCAM-1 protein expression in acute inflammation

Endothelial cells in different microvascular segments of the kidney have diverse functions and exhibit differential responsiveness to disease stimuli. The responsible molecular mechanisms are largely unknown. We previously showed that during hemorrhagic shock, VCAM-1 protein was expressed primarily in extraglomerular compartments of the kidney, while E-selectin protein was highly induced in glomeruli only (van Meurs M, Wulfert FM, Knol AJ, de Haes A, Houwertjes M, Aarts LPHJ, Molema G. Shock 29: 291–299, 2008). Here, we investigated the molecular control of expression of these endothelial cell adhesion molecules in mouse models of renal inflammation. Microvascular segment-specific responses to the induction of anti-glomerular basement membrane (anti-GBM), glomerulonephritis and systemic TNF-α treatment showed that E-selectin expression was transcriptionally regulated, with high E-selectin mRNA and protein levels preferentially expressed in the glomerular compartment. In contrast, VCAM-1 mRNA expression was increased in both arterioles and glomeruli, while VCAM-1 protein expression was limited in the glomeruli. These high VCAM-1 mRNA/low VCAM-1 protein levels were accompanied by high local microRNA (miR)-126 and Egfl7 levels, as well as higher Ets1 levels compared with arteriolar expression levels. Using miR-reporter constructs, the functional activity of miR-126 in glomerular endothelial cells could be demonstrated. Moreover, in vivo knockdown of miR-126 function unleashed VCAM-1 protein expression in the glomeruli upon inflammatory challenge. These data imply that miR-126 has a major role in the segmental, heterogenic response of renal microvascular endothelial cells to systemic inflammatory stimuli.

Rickettsiae induce microvascular hyperpermeability via phosphorylation of VE-cadherins: evidence from atomic force microscopy and biochemical studies

The most prominent pathophysiological effect of spotted fever group (SFG) rickettsial infection of microvascular endothelial cells (ECs) is an enhanced vascular permeability, promoting vasogenic cerebral edema and non-cardiogenic pulmonary edema, which are responsible for most of the morbidity and mortality in severe cases. To date, the cellular and molecular mechanisms by which SFG Rickettsia increase EC permeability are largely unknown. In the present study we used atomic force microscopy (AFM) to study the interactive forces between vascular endothelial (VE)-cadherin and human cerebral microvascular EC infected with R. montanensis, which is genetically similar to R. rickettsii and R. conorii, and displays a similar ability to invade cells, but is non-pathogenic and can be experimentally manipulated under Biosafety Level 2 (BSL2) conditions. We found that infected ECs show a significant decrease in VE-cadherin-EC interactions. In addition, we applied immunofluorescent staining, immunoprecipitation phosphorylation assay, and an in vitro endothelial permeability assay to study the biochemical mechanisms that may participate in the enhanced vascular permeability as an underlying pathologic alteration of SFG rickettsial infection. A major finding is that infection of R. montanensis significantly activated tyrosine phosphorylation of VE-cadherin beginning at 48 hr and reaching a peak at 72 hr p.i. In vitro permeability assay showed an enhanced microvascular permeability at 72 hr p.i. On the other hand, AFM experiments showed a dramatic reduction in VE-cadherin-EC interactive forces at 48 hr p.i. We conclude that upon infection by SFG rickettsiae, phosphorylation of VE-cadherin directly attenuates homophilic protein-protein interactions at the endothelial adherens junctions, and may lead to endothelial paracellular barrier dysfunction causing microvascular hyperpermeability. These new approaches should prove useful in characterizing the antigenically related SFG rickettsiae R. conorii and R. rickettsii in a BSL3 environment. Future studies may lead to the development of new therapeutic strategies to inhibit the VE-cadherin-associated microvascular hyperpermeability in SFG rickettsioses.

Enhanced endothelial differentiation of adipose-derived stem cells by substrate nanotopography

Adipose-derived stem cells (ADSCs) have great potential as a cell source for tissue engineering and regenerative medicine because they are easier to obtain, have lower donor-site morbidity and are available in larger numbers than stem cells harvested using bone marrow aspiration. Until now, little has been known about how nanotopography affects the proliferation and endothelial differentiation of ADSCs. In the present study, two nanograting substrates with a period (ridge and groove) of about 250 and 500 nm, respectively, were fabricated on quartz and their effect on ADSC fate was investigated. The results showed that proliferation of ADSCs on nanograting substrates decreased while cell attachment was not significantly affected compared to a flat substrate. Endothelial differentiation of ADSCs on both flat and nanograting substrates can be induced with vascular endothelial growth factor, as shown by immunofluorescent staining. Quantitative real-time PCR analysis showed significantly enhanced upregulation of vWF, PECAM-1 and VE-cadherin at the gene level by ADSCs on the nanograting substrates. In vitro angiogenesis assay on Matrigel showed that nanograting substrates enhanced capillary tube formation. This study highlights the beneficial influence of nanotopography on the differentiation of ADSC into endothelial cells which play an important role in vascularization.

The endothelium: influencing vascular smooth muscle in many ways

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Microvascular guidance: a challenge to support the development of vascularised tissue engineering construct

The guidance of endothelial cell organization into a capillary network has been a long-standing challenge in tissue engineering. Some research efforts have been made to develop methods to promote capillary networks inside engineered tissue constructs. Capillary and vascular networks that would mimic blood microvessel function can be used to subsequently facilitate oxygen and nutrient transfer as well as waste removal. Vascularization of engineering tissue construct is one of the most favorable strategies to overpass nutrient and oxygen supply limitation, which is often the major hurdle in developing thick and complex tissue and artificial organ. This paper addresses recent advances and future challenges in developing three-dimensional culture systems to promote tissue construct vascularization allowing mimicking blood microvessel development and function encountered in vivo. Bioreactors systems that have been used to create fully vascularized functional tissue constructs will also be outlined.

O2-filled swimbladder employs monocarboxylate transporters for the generation of O2 by lactate-induced root effect hemoglobin

The swimbladder volume is regulated by O₂ transfer between the luminal space and the blood In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the “Root effect.” While O₂ generation is critical for fish flotation, the molecular mechanism of the secretion and recycling of lactic acid in this critical process is not clear. To clarify molecules that are involved in the blood acidification and visualize the route of lactic acid movement, we analyzed the expression of 17 members of the H⁺/monocarboxylate transporter (MCT) family in the fugu genome and found that only MCT1b and MCT4b are highly expressed in the fugu swimbladder. Electrophysiological analyses demonstrated that MCT1b is a high-affinity lactate transporter whereas MCT4b is a low-affinity/high-conductance lactate transporter. Immunohistochemistry demonstrated that (i) MCT4b expresses in gas gland cells together with the glycolytic enzyme GAPDH at high level and mediate lactic acid secretion by gas gland cells, and (ii) MCT1b expresses in arterial, but not venous, capillary endothelial cells in rete mirabile and mediates recycling of lactic acid in the rete mirabile by solute-specific transcellular transport. These results clarified the mechanism of the blood acidification in the swimbladder by spatially organized two lactic acid transporters MCT4b and MCT1b.

Unique cell type-specific junctional complexes in vascular endothelium of human and rat liver sinusoids

Liver sinusoidal endothelium is strategically positioned to control access of fluids, macromolecules and cells to the liver parenchyma and to serve clearance functions upstream of the hepatocytes. While clearance of macromolecular debris from the peripheral blood is performed by liver sinusoidal endothelial cells (LSECs) using a delicate endocytic receptor system featuring stabilin-1 and -2, the mannose receptor and CD32b, vascular permeability and cell trafficking are controlled by transcellular pores, i.e. the fenestrae, and by intercellular junctional complexes. In contrast to blood vascular and lymphatic endothelial cells in other organs, the junctional complexes of LSECs have not yet been consistently characterized in molecular terms. In a comprehensive analysis, we here show that LSECs express the typical proteins found in endothelial adherens junctions (AJ), i.e. VE-cadherin as well as α-, β-, p120-catenin and plakoglobin. Tight junction (TJ) transmembrane proteins typical of endothelial cells, i.e. claudin-5 and occludin, were not expressed by rat LSECs while heterogenous immunreactivity for claudin-5 was detected in human LSECs. In contrast, junctional molecules preferentially associating with TJ such as JAM-A, B and C and zonula occludens proteins ZO-1 and ZO-2 were readily detected in LSECs. Remarkably, among the JAMs JAM-C was considerably over-expressed in LSECs as compared to lung microvascular endothelial cells. In conclusion, we show here that LSECs form a special kind of mixed-type intercellular junctions characterized by co-occurrence of endothelial AJ proteins, and of ZO-1 and -2, and JAMs. The distinct molecular architecture of the intercellular junctional complexes of LSECs corroborates previous ultrastructural findings and provides the molecular basis for further analyses of the endothelial barrier function of liver sinusoids under pathologic conditions ranging from hepatic inflammation to formation of liver metastasis.

Heterogeneity in apoptotic responses of microvascular endothelial cells to oxidative stress

Oxidative stress contributes to disease and can alter endothelial cell (EC) function. EC from different vascular beds are heterogeneous in structure and function, thus we assessed the apoptotic responses of EC from lung and heart to oxidative stress. Since protein kinase Cδ (PKCδ) is activated by oxidative stress and is an important modulator of apoptosis, experiments assessed the level of apoptosis in fixed lung and heart sections of PKCδ wild-type (PKCδ(+/+)) and null (PKCδ(-/-)) mice housed under normoxia (21% O(2)) or hyperoxia (~95% O(2)). We noted a significantly greater number of TUNEL-positive cells in lungs of hyperoxic PKCδ(+/+) mice, compared to matched hearts or normoxic organs. We found that 33% of apoptotic cells identified in hyperoxic lungs of PKCδ(+/+) mice were EC, compared to 7% EC in hyperoxic hearts. We further noted that EC apoptosis was significantly reduced in lungs of PKCδ(-/-) hyperoxic mice, compared to lungs of PKCδ(+/+) hyperoxic mice. In vitro, both hyperoxia and H(2)O(2) promoted apoptosis in EC isolated from microvasculature of lung (LMVEC), but not from the heart (HMVEC). H(2)O(2) treatment significantly increased p38 activity in LMVEC, but not in HMVEC. Inhibition of p38 attenuated H(2)O(2)-induced LMVEC apoptosis. Baseline expression of total PKCδ protein, as well as the caspase-mediated, catalytically active PKCδ cleavage fragment, was higher in LMVEC, compared to HMVEC. PKCδ inhibition significantly attenuated H(2)O(2)-induced LMVEC p38 activation. Conversely, overexpression of wild-type PKCδ or the catalytically active PKCδ cleavage product greatly increased H(2)O(2)-induced HMVEC caspase and p38 activation. We propose that enhanced susceptibility of lung EC to oxidant-induced apoptosis is due to increased PKCδ→p38 signaling, and we describe a PKCδ-centric pathway which dictates the differential response of EC from distinct vascular beds to oxidative stress.

Disruption of Notch1 induces vascular remodeling, intussusceptive angiogenesis, and angiosarcomas in livers of mice

BACKGROUND & AIMS

Notch signaling mediates embryonic vascular development and normal vascular remodeling; Notch1 knockout mice develop nodular regenerative hyperplasia (NRH). The pathogenesis of NRH is unclear, but has been associated with vascular injury in the liver sinusoids in clinical studies. We investigated the role of Notch1 signaling in liver sinusoidal endothelial cells (LSECs).

METHODS

We studied MxCre Notch1(lox/lox) mice (conditional knockout mice without tissue-specific disruption of Notch1); mice with hepatocyte-specific knockout were created by crossing Notch1(lox/lox) with AlbCre(+/-) mice. Portal vein pressure was measured; morphology of the hepatic vasculature was assessed by histologic and scanning electron microscopy analyses. We performed functional and expression analyses of isolated liver cells.

RESULTS

MxCre-induced knockout of Notch1 led to NRH, in the absence of fibrosis, with a persistent increase in proliferation of LSECs. Notch1 deletion led to de-differentiation, vascular remodeling of the hepatic sinusoidal microvasculature, intussusceptive angiogenesis, and dysregulation of ephrinB2/EphB4 and endothelial tyrosine kinase. Time-course experiments revealed that vascular changes preceded node transformation. MxCre Notch1(lox/lox) mice had reduced endothelial fenestrae and developed portal hypertension and hepatic angiosarcoma over time. In contrast, mice with hepatocyte-specific disruption of Notch1 had a normal phenotype.

CONCLUSIONS

Notch1 signaling is required for vascular homeostasis of hepatic sinusoids; it maintains quiescence and differentiation of LSECs in adult mice. Disruption of Notch1 signaling in LSECs leads to spontaneous formation of angiosarcoma, indicating its role as a tumor suppressor in the liver endothelium.

cAMP signaling by anthrax edema toxin induces transendothelial cell tunnels, which are resealed by MIM via Arp2/3-driven actin polymerization

RhoA-inhibitory bacterial toxins, such as Staphylococcus aureus EDIN toxin, induce large transendothelial cell macroaperture (TEM) tunnels that rupture the host endothelium barrier and promote bacterial dissemination. Host cells repair these tunnels by extending actin-rich membrane waves from the TEM edges. We reveal that cyclic-AMP signaling produced by Bacillus anthracis edema toxin (ET) also induces TEM formation, which correlates with increased vascular permeability. We show that ET-induced TEM formation resembles liquid dewetting, a physical process of nucleation and growth of holes within a thin liquid film. We also identify the cellular mechanisms of tunnel closure and reveal that the I-BAR domain protein Missing in Metastasis (MIM) senses de novo membrane curvature generated by the TEM, accumulates at the TEM edge, and triggers Arp2/3-dependent actin polymerization, which induces actin-rich membrane waves that close the TEM. Thus, the balance between ET-induced TEM formation and resealing likely determines the integrity of the host endothelium barrier.

Role of arginase-2 and eNOS in the differential vascular reactivity and hypoxia-induced endothelial response in umbilical arteries and veins

The main vasodilator in the placenta is nitric oxide (NO), which is synthesized by endothelial NO synthase (eNOS). Arginase-2 competes with eNOS for l-arginine, and its activity has been related with vascular dysfunction. Recently, we showed that hypoxia induces arginase-2, and decreases eNOS activity in human umbilical vein endothelial cells (HUVEC). However there is evidence that vascular responses to hypoxia are not similar throughout the placental vascular tree. We studied whether arginase-2 plays a role controlling vascular tone in human umbilical vessels, and the changes in the expression of arginase-2 and eNOS proteins by hypoxia in endothelial cells from umbilical arteries (HUAEC) and veins (HUVEC). In isolated umbilical vessels the presence of eNOS and arginase-2 was determined in the endothelium, and the NO-dependent vasoactive responses in the presence and absence of S-(2-boronoethyl)-L-cysteine (BEC, arginase inhibitor) were studied. Additionally, HUAEC and HUVEC were exposed (0-24 h) to hypoxia (2% O2) or normoxia (5% O2), and protein levels of eNOS (total and phosphorylated at serine-1177) and arginase-2 were determined. In umbilical arteries and veins arginase-2 and eNOS were detected mainly at the endothelium. BEC induced a higher concentration-dependent relaxation in umbilical arteries than veins, and these responses were NOS-dependent. In HUAEC exposed to hypoxia there were no changes in eNOS and arginase-2 levels, however there was a significant increase of p-eNOS. In contrast, HUVEC showed an increase in arginase-2 and a reduction of p-eNOS in response to hypoxia. These results show that arginases have a vascular role in placental vessels counteracting the NOS-dependent relaxation, which is differentially regulated in placental artery and vein endothelial cells.

GDNF restores human blood-nerve barrier function via RET tyrosine kinase-mediated cytoskeletal reorganization

Endoneurial microvessels and the perineurium are responsible for maintaining homeostasis in peripheral nerves. Endoneurial endothelial cells form the blood-nerve barrier (BNB). The molecular pathways responsible for endoneurial microvascular barrier formation in humans are not fully understood. We tested the effect of different mitogens on the transendothelial electrical resistance (TEER) of confluent primary human endoneurial endothelial cell (pHEndEC) cultures following serum withdrawal (mimicking diffuse endothelial injury) in vitro. We show that glial-derived neurotrophic factor (GDNF, 1 ng/mL) sufficiently induced a maximal 114.2% recovery in TEER over basal conditions 48 h after serum withdrawal. Solute permeability to high molecular weight dextran was reduced by 52.4% following GDNF treatment. GDNF-mediated increase in TEER was dependent on RET tyrosine-kinase signaling pathways and mildly enhanced by cyclic adenosine monophosphate in combination with maximal concentrations of multiple redundant mitogens. There was no significant increase in adherens or tight junction proteins β-catenin, VE-Cadherin, zona occludens-1 and occludin following GDNF treatment. GDNF induced a small increase in total claudin-5 protein expression without significant increase in messenger RNA or modulation in tyrosine phosphorylation following serum withdrawal. Indirect immunocytochemistry revealed membrane relocation of longitudinal F-actin cytoskeletal filaments in pHEndECs following GDNF treatment, resulting in more continuous intercellular contacts that formed adherens and tight junctions. Together, these results demonstrate a sufficient role for GDNF in human BNB recovery following serum withdrawal in vitro, facilitated primarily by endothelial cell cytoskeletal reorganization. These observations provide insights into the regulation of human BNB function during recovery from peripheral nerve injury.

Insulin entry into muscle involves a saturable process in the vascular endothelium

AIMS/HYPOTHESIS

Insulin's rate of entry into skeletal muscle appears to be the rate-limiting step for muscle insulin action and is slowed by insulin resistance. Despite its obvious importance, uncertainty remains as to whether the transport of insulin from plasma to muscle interstitium is a passive diffusional process or a saturable transport process regulated by the insulin receptor.

METHODS

To address this, here we directly measured the rate of (125)I-labelled insulin uptake by rat hindlimb muscle and examined how that is affected by adding unlabelled insulin at high concentrations. We used mono-iodinated [(125)I]Tyr(A14)-labelled insulin and short (5 min) exposure times, combined with trichloroacetic acid precipitation, to trace intact bioactive insulin.

RESULTS

Compared with saline, high concentrations of unlabelled insulin delivered either continuously (insulin clamp) or as a single bolus, significantly raised plasma (125)I-labelled insulin, slowed the movement of (125)I-labelled insulin from plasma into liver, spleen and heart (p < 0.05, for each) but increased kidney (125)I-labelled insulin uptake. High concentrations of unlabelled insulin delivered either continuously (insulin clamp), or as a single bolus, significantly decreased skeletal muscle (125)I-labelled insulin clearance (p < 0.01 for each). Increasing muscle perfusion by electrical stimulation did not prevent the inhibitory effect of unlabelled insulin on muscle (125)I-labelled insulin clearance.

CONCLUSIONS/INTERPRETATION

These results indicate that insulin's trans-endothelial movement within muscle is a saturable process, which is likely to involve the insulin receptor. Current findings, together with other recent reports, suggest that trans-endothelial insulin transport may be an important site at which muscle insulin action is modulated in clinical and pathological settings.

Action and reaction: the biological response to siRNA and its delivery vehicles

RNA interference (RNAi)-based therapeutics have significant potential for the treatment of human disease. Safe and effective delivery of RNA to target tissues remains a major barrier to realizing its clinical potential. Several factors can affect the in vivo performance of short interfering RNA (siRNA) delivery formulations, including siRNA sequence, structure, chemical modification, and delivery formulation. This review provides an introduction to the principles underlying the pharmacokinetics and pharmacodynamics of systemically administered siRNA and its delivery formulations, including the factors that lead to its degradation, clearance, and tissue uptake, as well as its potential for immunogenicity, toxicity, and off-target effects within the body.

Endothelial cell activation in emergency department patients with sepsis-related and non-sepsis-related hypotension

Previous studies found increased circulating levels of biomarkers related to endothelial cell activation in patients with sepsis, particularly in the most severe sepsis stages of sepsis shock. It remains unclear, however, whether this activation is mainly driven by sepsis-specific mechanisms or occurs as a generalized inflammatory response. The objective of this analysis was to compare patterns of biomarkers of endothelial cell activation in patients with hypotension due to sepsis and nonsepsis etiologies. This is a secondary analysis of a prospective, observational cohort study including emergency department patients older than17 years with an episode of hypotension defined as any systolic blood pressure measurement less than 100 mmHg. Etiology of hypotension episodes was classified as sepsis or nonsepsis (eg, cardiac or hemorrhagic). Endothelial activation biomarkers of cell adhesion (E-selectin, vascular cell adhesion molecule 1 [VCAM-1], and intercellular adhesion molecule 1 [ICAM-1]), coagulation (plasminogen activator inhibitor 1 [PAI-1]), and vascular endothelial growth factor (VEGF) signaling (VEGF, soluble fms-like tyrosine kinase 1 [sFLT-1]) were assayed. A total of 161 patients were analyzed. Hypotension was classified as sepsis (n = 69), nonsepsis (cardiac [n = 35], hemorrhagic [n = 12]), or indeterminate (n = 45). With the exception of PAI-1, median plasma levels of all endothelial markers were significantly higher in patients with sepsis compared with nonsepsis etiology (P < 0.05 for all comparisons). Logistic regression analysis, adjusted for age, sex, mean blood pressure level, and mortality, confirmed a significant association of E-selectin (odds ratio [OR], 3.7; 95% confidence interval [CI], 1.7-7.8, P < 0.001) and sFLT-1 (OR, 2.0; CI, 1.1-3.8; P < 0.03) with sepsis etiology. Biomarkers VCAM-1 (OR, 2.0; CI, 0.88-4.4; P = 0.1), VEGF (OR, 1.5; CI, 0.98-2.2; P = 0.06), ICAM-1 (OR, 1.5; CI, 0.9-2.6; P = 0.2), and PAI-1 (OR, 1.4; CI, 0.8-2.3; P = 0.2) did not reach statistical significance. This study found a sepsis-specific activation of endothelium activation markers, particularly E-selectin and sFLT-1, in emergency department patients with hypotension.

Calcium and endothelium-mediated vasodilator signaling

Vascular tone refers to the balance between arterial constrictor and dilator activity. The mechanisms that underlie tone are critical for the control of haemodynamics and matching circulatory needs with metabolism, and thus alterations in tone are a primary factor for vascular disease etiology. The dynamic spatiotemporal control of intracellular Ca(2+) levels in arterial endothelial and smooth muscle cells facilitates the modulation of multiple vascular signaling pathways. Thus, control of Ca(2+) levels in these cells is integral for the maintenance of tone and blood flow, and intimately associated with both physiological and pathophysiological states. Hence, understanding the mechanisms that underlie the modulation of vascular Ca(2+) activity is critical for both fundamental knowledge of artery function, and for the development of targeted therapies. This brief review highlights the role of Ca(2+) signaling in vascular endothelial function, with a focus on contact-mediated vasodilator mechanisms associated with endothelium-derived hyperpolarization and the longitudinal conduction of responses over distance.

Uptake of Single-Walled Carbon Nanotubes Conjugated with DNA by Microvascular Endothelial Cells

Single-walled carbon nanotubes (SWCNTs) have been proposed to have great therapeutic potential. SWCNTs conjugated with drugs or genes travel in the systemic circulation to reach target cells or tissues following extravasation from microvessels although the interaction between SWCNT conjugates and the microvascular endothelial cells (ECs) remains unknown. We hypothesized that SWCNT-DNA conjugates would be taken up by microvascular ECs and that this process would be facilitated by SWCNTs compared to facilitation by DNA alone. ECs were treated with various concentrations of SWCNT-DNA-FITC conjugates, and the uptake and intracellular distribution of these conjugates were determined by a confocal microscope imaging system followed by quantitative analysis of fluorescence intensity. The uptake of SWCNT-DNA-FITC conjugates (2 μg/mL) by microvascular ECs was significantly greater than that of DNA-FITC (2 μg/mL), observed at 6 hrs after treatment. For the intracellular distribution, SWCNT-DNA-FITC conjugates were detected in the nucleus of ECs, while DNA-FITC was restricted to the cytoplasm. The fluorescence intensity and distribution of SWCNTs were concentration and time independent. The findings demonstrate that SWCNTs facilitate DNA delivery into microvascular ECs, thus suggesting that SWCNTs serving as drug and gene vehicles have therapeutic potential.

Life is a pattern: vascular assembly within the embryo

The formation of the vascular system is one of the earliest and most important events during organogenesis in the developing embryo because the growing organism needs a transportation system to supply oxygen and nutrients and to remove waste products. Two distinct processes termed vasculogenesis and angiogenesis lead to a complex vasculature covering the entire body. Several cellular mechanisms including migration, proliferation, differentiation and maturation are involved in generating this hierarchical vascular tree. To achieve this aim, a multitude of signaling pathways need to be activated and coordinated in spatio-temporal patterns. Understanding embryonic molecular mechanism in angiogenesis further provides insight for therapeutic approaches in pathological conditions like cancer or ischemic diseases in the adult. In this review, we describe the current understanding of major signaling pathways that are necessary and active during vascular development.

Epithelial protein lost in neoplasm (EPLIN) interacts with α-catenin and actin filaments in endothelial cells and stabilizes vascular capillary network in vitro

Adherens junctions are required for vascular endothelium integrity. These structures are formed by the clustering of the homophilic adhesive protein VE-cadherin, which recruits intracellular partners, such as β- and α-catenins, vinculin, and actin filaments. The dogma according to which α-catenin bridges cadherin·β-catenin complexes to the actin cytoskeleton has been challenged during the past few years, and the link between the VE-cadherin·catenin complex and the actin cytoskeleton remains unclear. Recently, epithelial protein lost in neoplasm (EPLIN) has been proposed as a possible bond between the E-cadherin·catenin complex and actin in epithelial cells. Herein, we show that EPLIN is expressed at similar levels in endothelial and epithelial cells and is located at interendothelial junctions in confluent cells. Co-immunoprecipitation and GST pulldown experiments provided evidence that EPLIN interacts directly with α-catenin and tethers the VE-cadherin·catenin complex to the actin cytoskeleton. In the absence of EPLIN, vinculin was delocalized from the junctions. Furthermore, suppression of actomyosin tension using blebbistatin triggered a similar vinculin delocalization from the junctions. In a Matrigel assay, EPLIN-depleted endothelial cells exhibited a reduced capacity to form pseudocapillary networks because of numerous breakage events. In conclusion, we propose a model in which EPLIN establishes a link between the cadherin·catenin complex and actin that is independent of actomyosin tension. This link acts as a mechanotransmitter, allowing vinculin binding to α-catenin and formation of a secondary molecular bond between the adherens complex and the cytoskeleton through vinculin. In addition, we provide evidence that the EPLIN clutch is necessary for stabilization of capillary structures in an angiogenesis model.

Resident Endothelial Progenitor Cells From Human Placenta Have Greater Vasculogenic Potential Than Circulating Endothelial Progenitor Cells From Umbilical Cord Blood

Endothelial colony-forming cells (ECFCs) isolated from umbilical cord blood (CBECFCs) are highly proliferative and form blood vessels in vivo. The purpose of this investigation was to isolate and characterize a population of resident ECFCs from the chorionic villi of term human placenta and provide a comparative analysis of their proliferative and vasculogenic potential with CBECFCs. ECFCs were isolated from umbilical cord blood and chorionic villi from placentas obtained by caesarean deliveries. Placental ECFCs (PECFCs) expressed CD144, CD31, CD105, and KDR and were negative for CD45 and CD34, consistent with other ECFC phenotypes. PECFCs were capable of 28.6 ± 6.0 population doublings before reaching senescence (vs. 47.4 ± 3.2 for CBECFCs, p < 0.05, n = 4). In single cell assays, 46.5 ± 1.2% underwent at least one division (vs. 51.0 ± 1.8% of CBECFCs, p = 0.07, n = 6), and of those dividing PECFCs, 71.8 ± 0.9% gave rise to colonies of >500 cells (highly proliferative potential clones) over 14 days (vs. 69.4 ± 0.7% of CBECFCs, p = 0.07, n = 9). PECFCs formed 5.2 ± 0.8 vessels/mm(2) in collagen/fibronectin plugs implanted into non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice, whereas CBECFCs formed only 1.7 ± 1.0 vessels/mm(2) (p < 0.05, n = 4). This study demonstrates that circulating CBECFCs and resident PECFCs are identical phenotypically and contain equivalent quantities of high proliferative potential clones. However, PECFCs formed significantly more blood vessels in vivo than CBECFCs, indicating that differences in vasculogenic potential between circulating and resident ECFCs exist.

Adiponectin attenuates lipopolysaccharide-induced acute lung injury through suppression of endothelial cell activation

Adiponectin (APN) is an adipose tissue-derived factor with anti-inflammatory and vascular protective properties whose levels paradoxically decrease with increasing body fat. In this study, APN's role in the early development of ALI to LPS was investigated. Intratracheal LPS elicited an exaggerated systemic inflammatory response in APN-deficient (APN(-/-)) mice compared with wild-type (wt) littermates. Increased lung injury and inflammation were observed in APN(-/-) mice as early as 4 h after delivery of LPS. Targeted gene expression profiling performed on immune and endothelial cells isolated from lung digests 4 h after LPS administration showed increased proinflammatory gene expression (e.g., IL-6) only in endothelial cells of APN(-/-) mice when compared with wt mice. Direct effects on lung endothelium were demonstrated by APN's ability to inhibit LPS-induced IL-6 production in primary human endothelial cells in culture. Furthermore, T-cadherin-deficient mice that have significantly reduced lung airspace APN but high serum APN levels had pulmonary inflammatory responses after intratracheal LPS that were similar to those of wt mice. These findings indicate the importance of serum APN in modulating LPS-induced ALI and suggest that conditions leading to hypoadiponectinemia (e.g., obesity) predispose to development of ALI through exaggerated inflammatory response in pulmonary vascular endothelium.

MicroRNA profiling of diverse endothelial cell types

Background

MicroRNAs are ~22-nt long regulatory RNAs that serve as critical modulators of post-transcriptional gene regulation. The diversity of miRNAs in endothelial cells (ECs) and the relationship of this diversity to epithelial and hematologic cells is unknown. We investigated the baseline miRNA signature of human ECs cultured from the aorta (HAEC), coronary artery (HCEC), umbilical vein (HUVEC), pulmonary artery (HPAEC), pulmonary microvasculature (HPMVEC), dermal microvasculature (HDMVEC), and brain microvasculature (HBMVEC) to understand the diversity of miRNA expression in ECs.

Results

We identified 166 expressed miRNAs, of which 3 miRNAs (miR-99b, miR-20b and let-7b) differed significantly between EC types and predicted EC clustering. We confirmed the significance of these miRNAs by RT-PCR analysis and in a second data set by Sylamer analysis. We found wide diversity of miRNAs between endothelial, epithelial and hematologic cells with 99 miRNAs shared across cell types and 31 miRNAs unique to ECs. We show polycistronic miRNA chromosomal clusters have common expression levels within a given cell type.

Conclusions

EC miRNA expression levels are generally consistent across EC types. Three microRNAs were variable within the dataset indicating potential regulatory changes that could impact on EC phenotypic differences. MiRNA expression in endothelial, epithelial and hematologic cells differentiate these cell types. This data establishes a valuable resource characterizing the diverse miRNA signature of ECs.

Participation of blood vessel cells in human adaptive immune responses

Circulating T cells contact blood vessels either when they extravasate across the walls of microvessels into inflamed tissues or when they enter into the walls of larger vessels in inflammatory diseases such as atherosclerosis. The blood vessel wall is largely composed of three cell types: endothelial cells lining the entire vascular tree; pericytes supporting the endothelium of microvessels; and smooth muscle cells forming the bulk of large vessel walls. Each of these cell types interacts with and alters the behavior of infiltrating T cells in different ways, making these cells active participants in the processes of immune-mediated inflammation. In this review, we compare and contrast what is known about the nature of these interactions in humans.

Direct leukocyte migration across pulmonary arterioles and venules into the perivascular interstitium of murine lungs during bleomycin injury and repair

During acute lung injury and repair, leukocytes are thought to enter the lung primarily across alveolar capillaries and postcapillary venules. We hypothesized that leukocytes also migrate across pulmonary arterioles and venules, which serve as alternative sites for leukocyte influx into the lung during acute lung injury and repair. Lung sections from C57BL/6J mice up to 14 days after intratracheal bleomycin (3.33 U/kg) or saline instillation were assessed by light, fluorescence, confocal, and transmission electron microscopy for evidence of inflammatory cell sequestration and transmigration at these sites. After bleomycin treatment, large numbers of leukocytes (including neutrophils, eosinophils, and monocytes) were present in the vascular lumina and in perivascular interstitia of pulmonary arterioles and venules, as well as within the vascular walls. Leukocytes were observed within well-defined pathways in arteriolar walls and much less structured pathways in venular walls, apparently in the process of transmigration. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were expressed at sites of leukocyte interaction with the luminal surface, especially in arterioles. Leukocytes appeared to exit from the vessels near collagen fibers into the perivascular interstitium. Results indicate that leukocytes can directly migrate across arteriolar and venular walls into the perivascular interstitium, which may represent an important but under-recognized pathway for leukocyte influx into the lung during injury and repair.

Four proteins governing overangiogenic endothelial cell phenotype in patients with multiple myeloma are plausible therapeutic targets

Bone marrow (BM) angiogenesis has an important role in the initiation and progression of multiple myeloma (MM). We looked at novel mechanisms of vessel formation in patients with MM through a comparative proteomic analysis between BM endothelial cells (ECs) of patients with active MM (MMECs) and ECs of patients with monoclonal gammopathy of undetermined significance (MGECs) and of subjects with benign anemia (normal ECs). Four proteins were found overexpressed in MMECs: filamin A, vimentin, α-crystallin B and 14-3-3ζ/δ protein, not yet linked to overangiogenic phenotype. These proteins gave a typical distribution in the BM of MM patients and in MMECs versus MGECs, plausibly according to a different functional state. Their expression was enhanced by vascular endothelial growth factor, fibroblast growth factor 2, hepatocyte growth factor and MM plasma cell conditioned medium in step with enhancement of MMEC angiogenesis. Their silencing RNA knockdown affected critical MMEC angiogenesis-related functions, such as spreading, migration and tubular morphogenesis. A gradual stabilization of 14-3-3ζ/δ protein was observed, with transition from normal ECs to MGECs and MMECs that may be a critical step for the angiogenic switch in MMECs and maintenance of the cell overangiogenic phenotype. These proteins were substantially impacted by anti-MM drugs, such as bortezomib, lenalidomide and panobinostat. Results suggest that these four proteins could be new targets for the antiangiogenic management of MM patients.

Endothelial Dysfunction and Low-Grade Inflammation Are Associated With Greater Arterial Stiffness Over a 6-Year Period

Endothelial dysfunction and low-grade inflammation are associated with cardiovascular disease. Arterial stiffening plays an important role in cardiovascular disease and, thus, may be a mechanism through which endothelial dysfunction and/or low-grade inflammation lead to cardiovascular disease. We investigated the associations between, on the one hand, biomarkers of endothelial dysfunction (soluble endothelial selectin, thrombomodulin, and both vascular and intercellular adhesion molecules 1 and von Willebrand factor) and of low-grade inflammation (C-reactive protein, serum amyloid A, interleukin 6, interleukin 8, tumor necrosis factor-α and, soluble intercellular adhesion molecule 1) and, on the other hand, arterial stiffness over a 6-year period, in 293 healthy adults (155 women). Biomarkers were combined into mean z scores. Carotid, femoral, and brachial arterial stiffness and carotid-femoral pulse wave velocity were determined by ultrasonography. Measurements were obtained when individuals were 36 and 42 years of age. Associations were analyzed with generalized estimating equation and adjusted for sex, height, and mean arterial pressure. The endothelial dysfunction z score was inversely associated with femoral distensibility (β: −0.51 [95% CI: −0.95 to −0.06]) and compliance coefficients (β: −0.041 [95% CI: −0.076 to −0.006]) but not with carotid or brachial stiffness or carotid-femoral pulse wave velocity. The low-grade inflammation z score was inversely associated with femoral distensibility (β: −0.51 [95% CI: −0.95 to −0.07]) and compliance coefficients (β: −0.050 [95% CI: −0.084 to −0.016]) and with carotid distensibility coefficient (β: −0.910 [95% CI: −1.810 to −0.008]) but not with brachial stiffness or carotid-femoral pulse wave velocity. Biomarkers of endothelial dysfunction and low-grade inflammation are associated with greater arterial stiffness. This provides evidence that arterial stiffening may be a mechanism through which endothelial dysfunction and low-grade inflammation lead to cardiovascular disease.