Estrogen Receptor-α Agonists Promote Angiogenesis in Human Myometrial Microvascular Endothelial Cells

OBJECTIVE

The relative role of the two estrogen receptors, ERalpha and ERbeta, in mediating angiogenic responses in adult human endothelium is unknown. The aim of this study was to determine whether novel ERalpha-selective agonists, propyl pyrazole triol (PPT) and the tetrahydrochrysene (R,R-THC), up-regulate the expression of vascular endothelial growth factor receptor-2 (VEGFR-2), and promote VEGF-stimulated endothelial cell proliferation in primary cultures of adult female microvascular endothelial cells co-expressing endogenous ERalpha and ERbeta.

METHODS

Confluent primary cultures of microvascular endothelial cells isolated from human myometrium were incubated with 17beta-estradiol (1 and 10 nM), PPT (10 nM to 3 microM), or R,R-THC (10 nM to 3 microM) for 18 hours and VEGFR-2 expression measured by biotin-VEGF165 binding and flow cytometry. Endothelial cell proliferation was assessed in microvascular endothelial cells after incubation with 17beta-estradiol (10 nM), PPT (100 nM), and R,R-THC (100 nM) for 6 days using a tetrazolium-based bioassay.

RESULTS

Both PPT and R,R-THC increased VEGFR-2 expression on myometrial microvascular endothelial cells in a dose-dependent manner, reaching a maximum at 1 microM. Approximately 40% of myometrial microvascular endothelial cell isolates only express ERbeta and do not express ERalpha, and in these neither PPT, R,R-THC, nor 17beta-estradiol increased VEGF binding. PPT- or R,R-THC-stimulated increase in VEGF binding was significantly different between ERalpha+ and ERalpha- microvascular endothelial cell samples (P < .001 and P < .05, respectively). PPT, R,R-THC, and 17beta-estradiol significantly augmented VEGF-stimulated microvascular endothelial cell proliferation in ERalpha+ (P < .05), but not in ERalpha- samples.

CONCLUSIONS

This angiogenic effect of 17beta-estradiol on adult female microvascular endothelial cells is mediated by ERalpha, rather than ERbeta.

Special Edition of Microcirculation Commemorating the 50th Anniversary of the Microcirculatory Society, Inc

This special edition of Microcirculation brings together the proceedings from the Symposium held in the spring of 2004 in the Natcher Auditorium on the campus of the National Institutes of Health to commemorate the 50th Anniversary of the Microcirculatory Society, Inc. Twelve brief reviews are introduced with the goals being to present a collective sense of the history of research in microcirculation, provide insight into where established topics of inquiry stand today, and to define emerging topics of investigation for future research efforts.

Angiogenesis and Microvascular Remodeling: A Brief History and Future Roadmap

Angiogenesis and vessel remodeling determine the integrative control of the architectural structure and functional behaviors of the microcirculation over the lifetime of an organism. Vascular remodeling is the basis of promising therapeutic strategies, including vascularization of ischemic organs. The history of angiogenesis research is long-more than 250 years-and the Microcirculatory Society has been the birthplace of numerous techniques, assays, and scientific concepts that have stimulated massive research endeavors in the pharmaceutical and medical arena. At present, angiogenesis isa dynamic field in which the molecular genetic and proteomic components of the process are still being identified, while integrative systems approaches are once again being recognized as essential to understand microvascular assembly in vivo across multiple scales from cells to whole vessel networks. A short history of people and ideas in this field is presented, followed by discussion of emerging directions receiving intense attention today and major questions that remain unanswered. The primary conclusion is that the need for scientists trained in the integrative approaches nurtured by the Microcirculatory Society over the past 50 years has never been greater, as it is clear that a complete mechanistic understanding of vessel adaptation (based on genomic and proteomic supporting casts) will now require deeper studies of angiogenesis and microvascular remodeling in the exquisite complexity of the native microenvironment-the microcirculation.

Alkaline pH-Induced Extracellular Regulated Protein Kinase Activation in Brain Microvascular Endothelial Cells: Differential Effects of Tris and Lowered CO2

As it was previously reported that Tris-elevated pH acutely activated extracellular regulated protein kinase (ERK) in rat aorta smooth muscle cells, this study tested whether this finding could be extended to endothelial cells and, moreover, the relevance of this finding in brain microvascular endothelial cells with respect to respiratory-induced hypocapnic alkalosis. Exposure of bovine brain microvascular endothelial cells to pH 7.90 due to Tris for 15 and 30 min activated ERK twofold. In contrast, pH elevated to 7.75 and 7.90 by lowered percent CO2 failed to activate ERK (15, 30, and 60 min). These results suggest that respiratory alkalosis due to hypocapnia does not activate ERK in brain microvascular endothelial cells. The ability of Tris to activate ERK suggests a novel pathway, possibly independent of pH elevation, whereby Tris activates ERK.

Blood Substitute Resuscitation as a Treatment Modality for Moderate Hypovolemia

Blood substitute resuscitation as a treatment modality for moderate hypovolemia (approximately 40% blood loss) in a canine model has been evaluated using Oxyglobin (Biopure Hemoglobin Glutamer-200/ Bovine; a hemoglobin-based oxygen-carrier) and Hespan (6% hetastarch; a nonoxygen-carrier) as resuscitants. Autologous (shed) blood served as control. Nine dogs were studied--after splenectomy, each dog was hemorrhaged (32-36 mL/kg; MAP = approximately 50 mmHg) and randomly assigned to the three resuscitation groups. Microvascular, systemic function and oxygenation characteristics were monitored and/or measured simultaneously in prehemorrhagic (baseline), posthemorrhagic and postresuscitation phases for correlation-real-time microvascular changes in the bulbar conjunctiva were noninvasively measured via computer-assisted intravital microscopy and systemic function and oxygenation changes were monitored and/or measured via instrumentation and devices incorporated into our bioengineering station in an operating room setting. Blood chemistry was also studied for relevant measurements. Prehemorrhagic microvascular characteristics were similar in all animals (venular diameter = 41 +/- 12 microm, A:V ratio = approximately 1:2, red-cell velocity = 0.5 +/- 0.3 mm/s). All animals also showed similar prehemorrhagic systemic function and oxygenation measurements comparable to a previous study and were consistent with normal measurements in dogs. At the completion of hemorrhaging to achieve moderate hypovolemia (approximately 40% blood loss with MAP at approximately 50 mmHg), all nine animals showed similar significant (P < 0.01) posthemorrhagic microvascular changes, including approximately 17% decrease in diameter (34 +/- 7 microm), A:V ratio = variable, and approximately 80% increase in velocity (0.9 +/- 0.5 mm/s). All animals also showed similar significant (P < 0.01) posthemorrhagic systemic function and oxygenation changes, with decreases in Hct, aHb(total), MPAP, MAP, SAP, DAP, CO, SVI, CaO2, and CvO2 and increases in HR and lactic acidosis. Shed blood (control) resuscitation restored posthemorrhagic microvascular changes close to prehemorrhagic values (diameter = 39 +/- 6 microm, A:V ratio = approximately 1:2, velocity = 0.6 +/- 0.4 mm/s). Oxyglobin and Hespan restored microvascular changes in similar manner close to prehemorrhagic values (Oxyglobin: diameter = 38 +/- 3 microm, A:V ratio = approximately 1:2, velocity = 0.6 +/- 0.4 mm/s; Hespan: diameter = 38 +/- 7 microm, A:V ratio = 1:2, velocity = 0.5 +/- 0.4 mm/s). After resuscitation, shed blood (control) restored all systemic function and oxygenation changes close to prehemorrhagic values. However, both Oxyglobin and Hespan resuscitation restored systemic function changes, but not oxygenation changes, to prehemorrhagic values. This was an interesting finding because of the different oxygen-carrying capability of Oxyglobin (oxygen-carrying) and Hespan (nonoxygen-carrying). The result suggests that either volume replenishment alone (and not oxygen-carrying capability) is needed to treat moderate hypovolemia or oxygenation measurements obtained by standard methods (oximetry, blood chemistry) may not reflect tissue oxygenation levels.

Effects of Antioxidant and Nitric Oxide on Chemokine Production in TNF-α-stimulated Human Dermal Microvascular Endothelial Cells

Chemokines have been implicated convincingly in the driving of leukocyte emigration in different inflammatory reactions. Multiple signaling mechanisms are reported to be involved in intracellular activation of chemokine expression in vascular endothelial cells by various stimuli. Nevertheless, redox-regulated mechanisms of chemokine expression in human dermal microvascular endothelial cells (HDMEC) remain unclear. This study examined the effects of pyrrolidine dithiocarbamate (PDTC, 0.1 mM) and spermine NONOate (Sper-NO, 1 mM) on the secretion and gene expression of chemokines, interleukin (IL)-8, monocyte chemotactic protein (MCP)-1, regulated upon activation normal T cell expressed and secreted (RANTES), and eotaxin. This study also addresses PDTC and Sper-NO effects on activation of nuclear factor kappa B (NF-kappaB) induced by TNF-alpha (10 ng/ml). Treatment with TNF-alpha for 8 h significantly increased secretion of IL-8, MCP-1, and RANTES, but not of eotaxin, in cultured HDMEC. Up-regulation of these chemokines was suppressed significantly by pretreatment with PDTC or Sper-NO for 1 h, but not by 1 mM 8-bromo-cyclic GMP. The mRNA accumulation of IL-8, MCP-1, RANTES, and eotaxin, and activation of NF-kappaB were induced by TNF-alpha for 2 h; all were suppressed significantly by the above two pretreatments. These findings indicate that both secretion and mRNA accumulation of IL-8, MCP-1, and RANTES in HDMEC induced by TNF-alpha are inhibited significantly by pretreatment with PDTC or Sper-NO, possibly via blocking redox-regulated NF-kappaB activation. These results suggest that restoration of the redox balance using antioxidant agents or nitric oxide pathway modulators may offer new opportunities for therapeutic interventions in inflammatory skin diseases.

Carbon monoxide and nitric oxide mediate cytoskeletal reorganization in microvascular cells via vasodilator-stimulated phosphoprotein phosphorylation: evidence for blunted responsiveness in diabetes

OBJECTIVE

We examined the effect of the vasoactive agents carbon monoxide (CO) and nitric oxide (NO) : n the phosphorylation and intracellular redistribution of vasodilator-stimulated phosphoprotein (VASP), a critical actin motor protein required for cell migration that also controls vasodilation and platelet aggregation.

RESEARCH DESIGN AND METHODS

We examined the effect of donor-released CO and NO in endothelial progenitor cells (EPCs) and platelets from nondiabetic and diabetic subjects and in human microvascular endothelial cells (HMECs) cultured under low (5.5 mmol/l) or high (25 mmol/l) glucose conditions. VASP phosphorylation was evaluated using phosphorylation site-specific antibodies.

RESULTS

In control platelets, CO selectively promotes phosphorylation at VASP Ser-157, whereas NO promotes phosphorylation primarily at Ser-157 and also at Ser-239, with maximal responses at 1 min with both agents on Ser-157 and at 15 min on Ser-239 with NO treatment. In diabetic platelets, neither agent resulted in VASP phosphorylation. In nondiabetic EPCs, NO and CO increased phosphorylation at Ser-239 and Ser-157, respectively, but this response was markedly reduced in diabetic EPCs. In endothelial cells cultured under low glucose conditions, both CO and NO induced phosphorylation at Ser-157 and Ser-239; however, this response was completely lost when cells were cultured under high glucose conditions. In control EPCs and in HMECs exposed to low glucose, VASP was redistributed to filopodia-like structures following CO or NO exposure; however, redistribution was dramatically attenuated under high glucose conditions.

CONCLUSIONS

Vasoactive gases CO and NO promote cytoskeletal changes through site- and cell type-specific VASP phosphorylation, and in diabetes, blunted responses to these agents may lead to reduced vascular repair and tissue perfusion.

In vivo volumetric imaging of vascular perfusion within human retina and choroids with optical micro-angiography

Optical micro-angiography (OMAG), based on Fourier domain optical coherence tomography (OCT), is a recently developed imaging modality that provides dynamic blood flow imaging within microcirculation tissue beds in vivo. This paper presents its first application in imaging the blood circulations in posterior chamber of human eye. To eliminate/minimize the motion artifacts in OMAG flow image caused by the inevitable subject movement, we describe a method to compensate the bulk tissue motion by use of phase changes in sequential OCT A scan signals. By use of a fast OMAG/OCT imaging system at ~840nm wavelength band, we show that OMAG is capable of providing volumetric vasculatural images in retina and choroids, down to capillary level imaging resolution, within approximately 10 s. The depth-resolved volumetric views of the separate retina and choroid vasculatures are also presented. In the end of this paper, we provide a comparison of the OMAG results with those from Doppler OCT and optical coherence angiography.

Speckle variance detection of microvasculature using swept-source optical coherence tomography

We report on imaging of microcirculation by calculating the speckle variance of optical coherence tomography (OCT) structural images acquired using a Fourier domain mode-locked swept-wavelength laser. The algorithm calculates interframe speckle variance in two-dimensional and three-dimensional OCT data sets and shows little dependence to the Doppler angle ranging from 75 degrees to 90 degrees . We demonstrate in vivo detection of blood flow in vessels as small as 25 microm in diameter in a dorsal skinfold window chamber model with direct comparison with intravital fluorescence confocal microscopy. This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.

Cell type-specific aspects in biocompatibility testing: the intercellular contact in vitro as an indicator for endothelial cell compatibility

Endothelial cells cover the inner surface of blood vessels and form the interface between the blood and the tissues. Endothelial cells are involved in regulating barrier function, which is maintained by the interendothelial cell contacts. These interendothelial cell contacts are established by the interaction of different molecules. The maintenance of the barrier requires an appropriate signalling between these molecules. Thus, a number of different signalling pathways are integrated within interendothelial contacts. Since endothelial cells are important in tissue-implant interactions (especially for stent materials) this study examines the expression pattern of different interendothelial contact molecules to determine the usefulness in the analysis of biocompatibility in vitro. The effects of different pro-inflammatory and toxic stimuli and contact of human microvascular endothelial cells to metallic surfaces were examined for their impact on the pattern of interendothelial contact molecules. Striking modifications in the arrangement of these molecules were induced and the mode of modification was dependent on the tested compound. Thus, examining the pattern of expression of specific interendothelial contact molecules in vitro may be useful for testing the endothelial cell compatibility of biomaterials and their corrosion products.

Microvascular endothelial cells exhibit optimal aspect ratio for minimizing flow resistance

A recent analytical solution of the three-dimensional Stokes flow through a bumpy tube predicts that for a given bump area, there exists an optimal circumferential wavenumber which minimizes flow resistance. This study uses measurements of microvessel endothelial cell morphology to test whether this prediction holds in the microvasculature. Endothelial cell (EC) morphology was measured in blood perfused in situ microvessels in anesthetized mice using confocal intravital microscopy. EC borders were identified by immunofluorescently labeling the EC surface molecule ICAM-1 which is expressed on the surface but not in the EC border regions. Comparison of this theory with extensive in situ measurements of microvascular EC geometry in mouse cremaster muscle using intravital microscopy reveals that the spacing of EC nuclei in venules ranging from 27 to 106 microm in diameter indeed lies quite close to this predicted optimal configuration. Interestingly, arteriolar ECs are configured to minimize flow resistance not in the resting state, but at the dilated vessel diameter. These results raise the question of whether less organized circulatory systems, such as that found in newly formed solid tumors or in the developing embryo, may deviate from the optimal bump spacing predicted to minimize flow resistance.

The evolving paradigm for blood cell-endothelial cell interactions in the cerebral microcirculation

Inflammation and microvascular dysfunction have been implicated in a variety of pathologic conditions affecting the brain. Features of the inflammatory response that are common to many of these pathological conditions and that are manifested in the neurovasculature include oxidative stress, diminished endothelial barrier function (increased vascular permeability), increased expression of endothelial cell adhesion molecules, and the recruitment of rolling and adherent leukocytes and platelets. The evidence implicating leukocyte-endothelial cell adhesion in cerebral microvessels as a rate-determining component of the pathophysiology associated with conditions such as ischemia-reperfusion, sickle cell disease, and gamma -irradiation is summarized. Mechanisms that have been proposed to explain the recruitment of adherent leukocytes and platelets in the diseased/injured cerebral microvasculature are also addressed, and a common paradigm for blood cell recruitment induced by seemingly unrelated pathological conditions is outlined. Although there are many structural and functional characteristics of the cerebral microvasculature that distinguish it from other regional vascular beds, the processes that underlie the recruitment of injury-causing inflammatory cells in the brain appear to closely resemble those described for other tissues.

Influence of surface charge and inner composition of porous nanoparticles to cross blood–brain barrier in vitro

The aim of these studies was to evaluate the binding, uptake and transcytosis of 60 nm porous nanoparticles (NPs) that differed in their surface charge and inner composition on the blood-brain barrier (BBB). They were prepared from maltodextrins derived with or without a cationic ligand. In the cationic NPs an anionic lipid was inserted in their core to give DPPG-NPs. The data showed that at 4 degrees C the three NPs bind in different areas on endothelial cells: cationic NPs were found mainly around the paracellular area, while neutral NPs were mainly on the cell surface and DPPG-NPs binding was found at both paracellular areas and on the surface of the cells. At 37 degrees C neutral and cationic NPs had similar degrees of binding and uptake and were transcytosed. Filipin treatment increased their binding and uptake suggesting that sterols are implied in their efflux. Neutral NPs transcytosis was also inhibited by filipin. This inhibition shows that neutral NPs, like LDL in this model, use the caveolae pathway. Neutral and cationic 60 nm porous NPs are potential candidates for drug delivery to the brain.

Human micro- and macrovessel-derived endothelial cells: a comparative study on the effects of adrenaline and a selective adenosine A2-type receptor agonist under normoxic and hypoxic conditions

Adrenaline is a highly effective stimulator of cyclic AMP (cAMP) production in microvascular endothelial cells (ECs)--HMEC-1, showing only a moderate activity in macrovascular ECs--HUVEC. In both EC preparations, adrenaline acts via beta-type receptors. Selective stimulation of adenosine A(2)-type receptors resulted in comparable increases in cAMP formation in ECs lining micro- and macrovessels. Hypoxia largely suppressed the cAMP effects resulting from stimulation of both beta-adrenoceptors and adenosine A(2) type receptors in ECs of microvessels (HMEC-1). In contrast, hypoxia had only slight effect on these responses in ECs of macrovessels (HUVEC). The present data provide further evidence of functional differences between microvessel- and macrovessel-derived ECs.

Characterization of pulmonary cell growth parameters in a continuous perfusion microfluidic environment

In vitro models of the alveolo-pulmonary barrier consist of microvascular endothelial cells and alveolar epithelial cells cultured on opposing sides of synthetic porous membranes. However, these simple models do not reflect the physiological microenvironment of pulmonary cells, wherein cells are exposed to a complex milieu of mechanical and soluble stimuli. In this report, we studied alveolar epithelial (A549) and microvascular endothelial (HMEC-1) cells within varying microfluidic environments as a first step towards building a microfluidic analog of the gas-exchange interface. We fabricated polydimethylsiloxane (PDMS) microdevices for parallel studies of cell growth under multiple flow rates. Cells adhered and proliferated in the microculture chambers for shear stresses up to approximately 2 x 10(-3) dynes/cm(2), corresponding to media turnover rates of approximately 53 seconds. Proliferation of these cells into confluent monolayers and expression of cell-specific markers (SP-A and CD-31) demonstrated successful pulmonary cell culture in microscale devices, a first for alveolar epithelial cells. These results represent the initial steps towards the development of microfluidic analogs of the alveolo-pulmonary barrier and tissue engineering of the lung.

Microvessel-Like Structures from Outgrowth Endothelial Cells from Human Peripheral Blood in 2-Dimensional and 3-Dimensional Co-Cultures with Osteoblastic Lineage Cells

Tissue regeneration involves complex processes in the interaction between different cell types that control the process of neo-vascularization. In bone, osteoblasts and bone marrow stem cells provide cue elements for the proliferation of endothelial cells, differentiation of endothelial precursors, and the maturation of a vascular network. In this study, we investigated outgrowth endothelial cells (OECs), a potential source of autologous endothelial cells derived from human peripheral blood, in direct 2-dimensional (2-D) and 3-D co-culture systems with cells relevant for the regeneration of bone tissue, such as osteoblasts. In the co-cultures, OECs were evaluated in terms of their stability as an endothelial population at the single cell level using flow cytometry and their ability to establish a pre-vascular network at the light-microscopical and ultra-structural level. In co-cultures with the osteoblast cell line MG63 and with human primary osteoblasts (pOBs), OECs, in contrast to human umbilical vein endothelial cells, formed highly organized microvessel-like structures. These microvessel-like structures included the formation of a vascular lumen with tight junctional complexes at intercellular contacts of endothelial cells. In the co-culture, the formation of this vascular network was achieved in the standard growth medium for OECs. Furthermore, using a rotating culture vessel system, 3-D co-cultures consisting of OECs and pOBs were generated. Based on these observations, we conclude that OECs could provide a valuable source of autologous endothelial cells for the generation of complex tissue-engineered tissues.

Oxidative stress and increased eNOS and NADPH oxidase expression in mouse microvessel endothelial cells

Elevated oxidative stress plays a key role in diabetes-associated vascular disease. In this study, we tested the hypothesis that high glucose-induced oxidative stress was associated with changes in the expression of NADPH oxidase, superoxide dismutase (SOD) and endothelial nitric oxide synthase (eNOS). Oxidative stress was assessed in cell cultures of mouse microvessel endothelial cells (MMECs) by fluorescence labelling with dihydroethidium, lucigenin-enhanced chemiluminescence and determining NADPH oxidase subunit and eNOS expression with real-time polymerase chain reaction protocol and Western blotting. Oxidative stress and expression of the NADPH oxidase subunit, p22phox, were both increased, SOD1 and 3 expression lowered and eNOS significantly elevated in MMECs treated with 40 mM glucose for 72 h compared to low glucose medium. Oxidative stress, p22phox mRNA, eNOS mRNA, and protein were lowered by concurrent incubation with sepiapterin. When eNOS protein expression in endothelial cells was significantly decreased by eNOS siRNA treatment, superoxide generation was significantly higher in the MMECs grown in low glucose, but reduced in those grown in high glucose for 72 h. Thus, exposure of MMECs to high glucose results in increased oxidative stress that is associated with increased eNOS and NADPH oxidase subunit expression, notably p22phox, and decreased expression of SOD1 and 3.

Fabrication of a multiple-diameter branched network of microvascular channels with semi-circular cross-sections using xenon difluoride etching

The majority of microfluidic devices employ networks of channels that have rectangular cross-sections. At the microvascular scale of 30 to 300 microm in diameter, however, the distribution of fluid mechanical stresses and the induced shape of cultured cells will be quite different in a rectangular channel from the near-circular cross-sections seen in vivo. While round-cross-section channels have been produced before by wet etching, fine control of feature size has not been demonstrated, and prior work has only produced channels of a single diameter on a given device. In this work, the xenon difluoride process for isotropic etching of silicon was optimized for production of channels with semicircular cross-sections. This process was then used to produce a network of microvessel-scale semicylindrical channels on a silicon chip, the diameter of which was decreased with each level of branching. Additionally, it was demonstrated that endothelial cells will adhere to both the bottom and sides of these channels, indicating that such chips may be useful in the future for culturing in vitro models of the microvasculature.

Pericytes from brain microvessels strengthen the barrier integrity in primary cultures of rat brain endothelial cells

(1) The blood-brain barrier (BBB) characteristics of cerebral endothelial cells are induced by organ-specific local signals. Brain endothelial cells lose their phenotype in cultures without cross-talk with neighboring cells. (2) In contrast to astrocytes, pericytes, another neighboring cell of endothelial cells in brain capillaries, are rarely used in BBB co-culture systems. (3) Seven different types of BBB models, mono-culture, double and triple co-cultures, were constructed from primary rat brain endothelial cells, astrocytes and pericytes on culture inserts. The barrier integrity of the models were compared by measurement of transendothelial electrical resistance and permeability for the small molecular weight marker fluorescein. (4) We could confirm that brain endothelial monolayers in mono-culture do not form tight barrier. Pericytes induced higher electrical resistance and lower permeability for fluorescein than type I astrocytes in co-culture conditions. In triple co-culture models the tightest barrier was observed when endothelial cells and pericytes were positioned on the two sides of the porous filter membrane of the inserts and astrocytes at the bottom of the culture dish. (5) For the first time a rat primary culture based syngeneic triple co-culture BBB model has been constructed using brain pericytes beside brain endothelial cells and astrocytes. This model, mimicking closely the anatomical position of the cells at the BBB in vivo, was superior to the other BBB models tested. (6) The influence of pericytes on the BBB properties of brain endothelial cells may be as important as that of astrocytes and could be exploited in the construction of better BBB models.

Intravascular pressure and diameter profile of the utero-ovarian resistance artery network: estrous cycle-dependent modulation of resistance artery tone

Blood flow to the ovary varies dramatically in both magnitude and distribution throughout the estrous cycle to meet the hormonal and metabolic demands of the ovarian parenchyma as it cyclically develops and regresses. Several vascular components appear to be critical to vascular regulation of the ovary. As a first step in resolving the role of the resistance arteries and their paired veins in regulating ovarian blood flow and transvascular exchange, we characterized the architecture and intravascular pressure profile of the utero-ovarian resistance artery network in an in vivo preparation of the ovary of the anesthetized Golden hamster. We also investigated estrous cycle-dependent changes in resistance artery tone. The right ovary and the cranial aspect of the uterus in 26 female hamsters were exposed for microcirculatory observations. Estrous-cycle phase was determined in each animal before experimentation. The utero-ovarian vascular architecture was determined and resistance artery diameters were measured in each animal by video microscopy. Servo-null intravascular pressure measurements were made throughout the uteroovarian arterial network in 11 of the animals. Architectural data showed a complex anastomotic network jointly supplying the uterus and ovary. Resistance arteries showed a high degree of coiling and close apposition to veins, maximizing countercurrent-exchange capabilities. Arterial pressure dropped below 60% of systemic arterial pressure before the arteries entered the ovary. Both the ovarian artery and the uterine artery, which jointly feed the ovary, showed cycle day-dependent changes in diameter. Arterial diameters were smallest on the day following ovulation, during the brief luteal phase of the hamster. The data show that resistance arteries comprise a critical part of a complex network designed for intimate local communication and control and suggest that these arteries may play an important role in regulating ovarian blood flow in an estrous cycle-specific manner.

Cerebral angiogenesis after collagenase-induced intracerebral hemorrhage in rats

Spontaneous intracerebral hemorrhage (ICH) is one of the most devastating subtypes of stroke. Since angiogenesis is a fundamental process to brain development and repair by new blood vessel formation from pre-existing ones, mediated by numerous angiogenic factors including vascular endothelial growth factor (VEGF), the goal of the present work is to establish whether there is cerebral angiogenesis in rat brains with collagenase-induced ICH. Investigations were also performed to evaluate whether ICH alters expression of VEGF and its receptors Flt-1 and Flk-1. ICH was induced on adult male Sprague-Dawley rats by stereotactic injection of collagenase type VII into right globus pallidus. Angiogenesis was identified by hematoxylin-eosin stain and double immunolabeling method, and expression of VEGF and the receptors was evaluated by immunohistochemistry and quantitative real time reverse transcription-polymerase chain reaction. New vessels appeared around the hematoma and extended into it from 7 days, and 5-Bromo-2-Deoxyuridine-labeled nuclei in cerebral endothelial cells resided around the hematoma and the labeling peaked from 7 to 14 days. Expression of VEGF, Flt-1 and Flk-1 was observed in cerebral endothelial cells at the hemorrhagic basal ganglion, and increases of their mRNA persisted to 28 days. These findings suggest that ICH can induce cerebral angiogenesis and upregulation of VEGF, Flt-1 and Flk-1 and that modulation of angiogenesis via altering expression of VEGF and its receptors may be a potential strategy for promoting ICH repair.

Edaravone mimics sphingosine-1-phosphate-induced endothelial barrier enhancement in human microvascular endothelial cells

Edaravone is a potent scavenger of hydroxyl radicals and is quite successful in patients with acute cerebral ischemia, and several organ-protective effects have been reported. Treatment of human microvascular endothelial cells with edaravone (1.5 microM) resulted in the enhancement of transmonolayer electrical resistance coincident with cortical actin enhancement and redistribution of focal adhesion proteins and adherens junction proteins to the cell periphery. Edaravone also induced small GTPase Rac activation and focal adhesion kinase (FAK; Tyr(576)) phosphorylation associated with sphingosine-1-phosphate receptor type 1 (S1P(1)) transactivation. S1P(1) protein depletion by the short interfering RNA technique completely abolished edaravone-induced FAK (Tyr(576)) phosphorylation and Rac activation. This is the first report of edaravone-induced endothelial barrier enhancement coincident with focal adhesion remodeling and cytoskeletal rearrangement associated with Rac activation via S1P(1) transactivation. Considering the well-established endothelial barrier-protective effect of S1P, endothelial barrier enhancement as a consequence of S1P(1) transactivation may at least partly be the potent mechanisms for the organ-protective effect of edaravone and is suggestive of edaravone as a therapeutic agent against systemic vascular barrier disorder.

Characteristic quantities of microvascular structures in CLSM volume datasets

A method for fully automated morphological and topological quantification of microvascular structures in confocal laser scanning microscopy (CLSM) volume datasets is presented. Several characteristic morphological and topological quantities are calculated in a series of image-processing steps and can be used to compare single components as well as whole networks of microvascular structures to each other. The effect of the individual image-processing steps is illustrated and characteristic quantities of measured volume datasets are presented and discussed.

Transport of stavudine, delavirdine, and saquinavir across the blood–brain barrier by polybutylcyanoacrylate, methylmethacrylate-sulfopropylmethacrylate, and solid lipid nanoparticles

Permeability of the anti-human immunodeficiency virus (HIV) agents, including stavudine (D4T), delavirdine (DLV), and saquinavir (SQV), across the in vitro blood-brain barrier (BBB) was studied. Here, the anti-HIV agents were incorporated with polybutylcyanoacrylate (PBCA) nanoparticles (NPs), methylmethacrylate-sulfopropylmethacrylate (MMA-SPM) NPs, and solid lipid nanoparticles (SLNs). Transport of the anti-HIV agents across BBB is a key factor in their applications to the therapy of the acquired immunodeficiency syndrome (AIDS). Experimental results revealed that the drug order of the loading efficiency (LE) on PBCA and MMA-SPM was D4T>DLV>SQV. For the entrapment efficiency (EE) in SLNs, this order was reversed. Also, LE of D4T on MMA-SPM was larger than that on PBCA; however, the reverse was true for DLV and SQV. As the particle size increased, LE decreased and EE increased. For a fixed drug carrier, an increase in the particle size yielded a decrease in the BBB permeability coefficient of the anti-HIV agents. Moreover, enhancement in the BBB permeability was on the carrier order of PBCA>MMA-SPM>SLNs for D4T, and for DLV and SQV, the order became PBCA>SLNs>MMA-SPM. PBCA, MMA-SPM, and SLNs were efficacious carriers of D4T, DLV, and SQV to meliorate BBB permeability by 3-16 folds, indicating the clinical potential of the present NP formulations for the AIDS treatment.

Selective control of endothelial cell proliferation with a synthetic dimerizer of FGF receptor-1

Basic fibroblast growth factor (bFGF) is a potent angiogenic molecule, but its therapeutic use is limited by mitogenic effects on multiple cell types. To specifically activate FGF signaling in endothelial cells, a chimeric FGF receptor was generated that contained a modified FK506 drug-binding domain (F36V) fused to the FGF receptor-1 (FGFR1) cytoplasmic domain. Human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells were retrovirally transduced with this chimeric receptor, and the effects of administering synthetic receptor-dimerizing ligands were studied. As expected, both control and transduced cells proliferated in response to bFGF treatment; however, only transduced endothelial cells exhibited dose-dependent proliferative responses to dimerizer treatment. Dimerizer-induced proliferation was MEK-dependent and was accompanied by MAP kinase phosphorylation, indicating that the chimeric receptor utilizes signaling pathways similar to endogenous FGFR1. Although bFGF stimulated wound re-epithelialization in HUVECs (which natively express FGFR1 and FGFR4), chemical dimerization of FGFR1 did not; this suggests FGFR4 may control migration in these cells. The ability to selectively activate receptor subtypes should facilitate the study of signaling pathways in vitro and in vivo beyond what can be accomplished with nonselective natural ligands, and it may eventually permit stimulation of graft cell angiogenesis without driving overgrowth of host cells.

Prostaglandin F2-alpha receptor (FPr) expression on porcine corpus luteum microvascular endothelial cells (pCL-MVECs)

BACKGROUND

The corpus luteum (CL) is a transient endocrine gland and prostaglandin F2-alpha is considered to be the principal luteolysin in pigs. In this species, the in vivo administration of prostaglandin F2-alpha induces apoptosis in large vessels as early as 6 hours after administration. The presence of the prostaglandin F2-alpha receptor (FPr) on the microvascular endothelial cells (pCL-MVECs) of the porcine corpus luteum has not yet been defined. The aim of the study was to assess FPr expression in pCL-MVECs in the early and mid-luteal phases (EL-p, ML-p), and during pregnancy (P-p). Moreover, the effectiveness of prostaglandin F2-alpha treatment in inducing pCL-MVEC apoptosis was tested.

METHODS

Porcine CLs were collected in the EL and ML phases and during P-p. All CLs from each animal were minced together and the homogenates underwent enzymatic digestion. The pCL-MVECs were then positively selected by an immunomagnetic separation protocol using Dynabeads coated with anti-CD31 monoclonal antibody and seeded in flasks in the presence of EGM 2-MV (Microvascular Endothelial Cell Medium-2). After 4 days of culture, the cells underwent additional immunomagnetic selection and were seeded in flasks until the confluent stage.PCR Real time, western blot and immunodetection assays were utilized to assess the presence of FPr on pCL-MVEC primary cultures. Furthermore, the influence of culture time (freshly isolated, cultured overnight and at confluence) and hormonal treatment (P4 and E2) on FPr expression in pCL-MVECs was also investigated. Apoptosis was detected by TUNEL assay of pCL-MVECs exposed to prostaglandin F2-alpha.

RESULTS

We obtained primary cultures of pCL-MVECs from all animals. FPr mRNA and protein levels showed the highest value (ANOVA) in CL-MVECs derived from the early-luteal phase. Moreover, freshly isolated MVECs showed a higher FPr mRNA value than those cultured overnight and confluent cells (ANOVA). prostaglandin F2-alpha treatment failed to induce an apoptotic response in all the pCL-MVEC cultures.

CONCLUSION

Our data showing the presence of FPr on MVECs and the inability of prostaglandin F2-alpha to evoke an in vitro apoptotic response suggest that other molecules or mechanisms must be considered in order to explain the in vivo direct pro-apoptotic effect of prostaglandin F2-alpha at the endothelial level.

Migration of leukocytes across an endothelium-epithelium bilayer as a model of renal interstitial inflammation

Interstitial inflammation has emerged as a key event in the development of acute renal failure. To gain better insight into the nature of these inflammatory processes, the interplay between tubular epithelial cells, endothelial cells, and neutrophils (PMN) was investigated. A coculture transmigration model was developed, composed of human dermal microvascular endothelial (HDMEC) and human renal proximal tubular cells (HK-2) cultured on opposite sides of Transwell growth supports. Correct formation of an endoepithelial bilayer was verified by light and electron microscopy. The model was used to study the effects of endotoxin (LPS), tumor necrosis factor (TNF)-α, and α-melanocyte-stimulating hormone (α-MSH) by measuring PMN migration and cytokine release. To distinguish between individual roles of microvascular endothelial and epithelial cells in transmigration processes, migration of PMN was investigated separately in HK-2 and HDMEC monolayers. Sequential migration of PMN through endothelium and epithelium could be observed and was significantly increased after proinflammatory stimulation with either TNF-α or LPS (3.5 ± 0.58 and 2.76 ± 0.64-fold vs. control, respectively). Coincubation with α-MSH inhibited the transmigration of PMN through the bilayer after proinflammatory stimulation with LPS but not after TNF-α. The bilayers produced significant amounts of IL-8 and IL-6 mostly released from the epithelial cells. Furthermore, α-MSH decreased LPS-induced IL-6 secretion by 30% but had no significant effect on IL-8 secretion. We established a transmigration model showing sequential migration of PMN across microvascular endothelial and renal tubular epithelial cells stimulated by TNF-α and LPS. Anti-inflammatory effects of α-MSH in this bilayer model are demonstrated by inhibition on PMN transmigration and IL-6 secretion.

Skeletal Muscle Morphology in Patients with Restless Legs Syndrome

AIM

The aim of the study was to assess the cellular and structural properties of skeletal muscle in restless legs syndrome (RLS).

METHOD

Twenty patients and 16 controls were included. Aerobic performance was assessed using a submaximal test. On muscle biopsies taken from the tibialis anterior, fiber distribution and fiber area were analyzed together with parameters surveying the microvascularization, especially the tortuosity, which is expressed as a percent of muscle fiber perimeter in contact with the wall of the microvessel, length of capillary/perimeter of fiber (LC/PF) index.

RESULTS

The RLS group had significantly lower predicted maximal oxygen uptake (p = 0.01) and significantly higher LC/PF index (p = 0.01) compared to the controls.

CONCLUSION

The higher capillary tortuosity in RLS patients indicates the occurrence of significant remodeling in capillary geometry in RLS.

Immune regulation by microvascular endothelial cells: directing innate and adaptive immunity, coagulation, and inflammation

An effective immune response depends not only on the proper activation, regulation, and function of immune cells, but also on their distribution and retention in diverse tissue microenvironments where they encounter a number of stimuli and other cell types. These activities are mediated by endothelial cells, which form specialized microcirculatory networks used by immune cells under both physiological and pathological circumstances. Endothelial cells represent a highly heterogeneous population of cells with the ability to interact with and modulate the function of immune cells. This review is focused on the role of microvascular endothelial cells in innate and adaptive immunity, inflammation, coagulation, angiogenesis, and the therapeutic implications of targeting endothelial cells in selected autoimmune and chronic inflammatory disorders.

Regulation of bovine brain microvascular endothelial tight junction assembly and barrier function by laminar shear stress

Blood-brain barrier (BBB) controls paracellular solute diffusion into the brain microenvironment and is maintained primarily by tight junctions between adjacent microvascular endothelial cells. Studies implicate blood flow-associated shear stress as a pathophysiological mediator of BBB function, although detailed biochemical data are scarce. We hypothesize that shear stress upregulates BBB function via direct modulation of expression and properties of pivotal tight-junction proteins occludin and zonula occludens-1 (ZO-1). Bovine brain microvascular endothelial cells (BBMvECs) were exposed to either steady or pulsatile shear stress (10 and 14 dyn/cm2, respectively) for 24 h. Sheared BBMvECs were monitored for occludin-ZO-1 expression, association, and subcellular localization, and transendothelial permeability of BBMvECs to FITC-dextran and14[C]sucrose was assessed. Actin reorganization and BBMvEC realignment were observed following steady shear stress for 24 h. Substantial increases in occludin mRNA and protein expression (2.73 ± 0.26- and 1.83 ± 0.03-fold) and in occludin-ZO-1 association (2.12 ± 0.15-fold) were also observed. Steady shear stress also induced clear relocalization of both proteins to the cell-cell border in parallel with reduced transendothelial permeability to FITC-dextran (but not sucrose). Following pulsatile shear stress, increased protein levels for both occludin and ZO-1 (2.15 ± 0.02- and 1.67 ± 0.21-fold) and increased occludin-ZO-1 association (2.91 ± 0.14-fold) were observed in parallel with a reduction in transendothelial permeability to14[C]sucrose. Shear stress upregulates BBMvEC barrier function at the molecular level via modulation of expression, association, and localization of occludin and ZO-1. The pulsatile shear model appeared to give the most profound biochemical responses.

Microvessel scaffold with circular microchannels by photoresist melting

In this research, a new process that integrates the photoresist melting and soft lithography techniques to fabricate microvessel scaffolds with circular microchannels is proposed. The commercial software COMSOL Multiphysics (formerly known as FEMLAB) is the sought after procedure to optimize the structure of the microvessel scaffold. The photolithographic technique is applied to fabricate the negative photoresist THB-120N (JSR Inc.) based microstructure that is followed by melting to the final replica mold with its structure having convex semicircle cross-section. The replica mold is hence used to replicate PDMS to the top and bottom plates of a microvessel scaffold. These two half plates are bonded after having surface treatment by inductive coupled plasma (ICP) to form the complete scaffold with circular microchannels. Finally, the bovine endothelial cells (BEC) are cultured into the scaffold. Encouraging results by semi-dynamic seeding have been observed in this context, depicting the survival of the cells in the scaffold for up to 4 weeks.

An adamantyl-substituted retinoid-derived molecule that inhibits cancer cell growth and angiogenesis by inducing apoptosis and binds to small heterodimer partner nuclear receptor: effects of modifying its carboxylate group on apoptosis, proliferation, and protein-tyrosine phosphatase activity

Apoptotic and antiproliferative activities of small heterodimer partner (SHP) nuclear receptor ligand (E)-4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC), which was derived from 6-[3'-(1-adamantyl)-4'-hydroxyphenyl]-2-naphthalenecarboxylic acid (AHPN), and several carboxyl isosteric or hydrogen bond-accepting analogues were examined. 3-Cl-AHPC continued to be the most effective apoptotic agent, whereas tetrazole, thiazolidine-2,4-dione, methyldinitrile, hydroxamic acid, boronic acid, 2-oxoaldehyde, and ethyl phosphonic acid hydrogen bond-acceptor analogues were inactive or less efficient inducers of KG-1 acute myeloid leukemia and MDA-MB-231 breast, H292 lung, and DU-145 prostate cancer cell apoptosis. Similarly, 3-Cl-AHPC was the most potent inhibitor of cell proliferation. 4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorophenyltetrazole, (2E)-5-{2-[3'-(1-adamantyl)-2-chloro-4'-hydroxy-4-biphenyl]ethenyl}-1H-tetrazole, 5-{4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorobenzylidene}thiazolidine-2,4-dione, and (3E)-4-[3'-(1-adamantyl)-2-chloro-4'-hydroxy-4-biphenyl]-2-oxobut-3-enal were very modest inhibitors of KG-1 proliferation. The other analogues were minimal inhibitors. Fragment-based QSAR analyses relating the polar termini with cancer cell growth inhibition revealed that length and van der Waals electrostatic surface potential were the most influential features on activity. 3-Cl-AHPC and the 3-chlorophenyltetrazole and 3-chlorobenzylidenethiazolidine-2,4-dione analogues were also able to inhibit SHP-2 protein-tyrosine phosphatase, which is elevated in some leukemias. 3-Cl-AHPC at 1.0 microM induced human microvascular endothelial cell apoptosis but did not inhibit cell migration or tube formation.

Actin-dependent regulation of connective tissue growth factor

Expression of connective tissue growth factor (CTGF) in endothelial cells is modulated by shear stress affecting the organization of the cytoskeleton. The molecular connection between alterations of actin and CTGF expression was investigated in human umbilical vein endothelial cells (HUVEC) and a microvascular endothelial cell line. Overexpression of nonpolymerizable monomeric actin R62D interfered with stress fiber formation in HUVEC and concomitantly reduced immunoreactive CTGF. In microvascular endothelial cells, flow-dependent upregulation of CTGF was prevented by this actin mutant. In contrast, overexpression of actin S14C strengthened filamentous actin and increased CTGF expression. These data indicated an inverse relationship between CTGF expression and monomeric actin. Coexpression of the mutant actins and different CTGF promoter constructs revealed an actin-sensitive site between 3 and 4.5 kb of the CTGF promoter. A CArG-like box at −3791 bp was responsible for actin-dependent CTGF induction as shown by mutagenesis. Overexpression of actin S14C activated the nonmutated promoter significantly more strongly than the mutated promoter. Actin polymerization is regulated by the small GTPase RhoA and activation of serum response factor (SRF). Overexpression of constitutively active RhoA or SRF significantly increased CTGF protein synthesis. The 4.5-kb promoter construct, but not the construct with a mutation in the CArG box, was activated by SRF or RhoA, providing evidence for a functional role of this site in CTGF induction. These findings provide novel evidence that monomeric actin is the connecting link between alterations in the cytoskeleton and CTGF gene expression and demonstrate the importance of SRF in regulating CTGF transcription.

N-Acetylchitooligosaccharide is a potent angiogenic inhibitor both in vivo and in vitro

N-acetylchitooligosaccharide (N-acetyl-COs) was prepared by N-acetylation of chitooligosaccharide (COs). In vitro study using human umbilical vein endothelial cells (HUVECs) revealed that both N-acetyl-COs and COs inhibited the proliferation of HUVECs by inducing apoptosis. Treatment of HUVECs by N-acetyl-COs resulted in a significant reduction of density of the migration cells and repressed tubulogenesis process. The antiangiogenic effects of the oligosaccharides were further evaluated using in vivo zebrafish angiogenesis model, and the results showed that both oligosaccharides inhibited the growth of subintestinal vessels (SIV) of zebrafish embryos in a dose-dependent manner, as observed by endogenous alkaline phosphatase (EAP) staining assay. In contrast, no cytotoxicity was found when treating the NIH3T3 and several other cancer cells with the oligosaccharides. Our results also confirmed the antiangiogenic activity of N-acetyl-COs was significantly stronger than the parent oligosaccharide, COs.

Essential role of Src suppressed C kinase substrates in endothelial cell adhesion and spreading

Integrin-mediated substrate adhesion of endothelial cells leads to dynamic rearrangement of the actin cytoskeleton. Protein kinase C (PKC) stimulates reorganization of microfilaments and adhesion, but the mechanism by which this occurs is unknown. Src suppressed C kinase substrate (SSeCKS) is a PKC substrate that may play an important role in regulating actin cytoskeleton. We found that SSeCKS was localized to focal adhesion sites soon after cell adhesion and that SSeCKS translocated from the membrane to the cytosol during the process of cell spreading. Using small interfering RNAs specific to SSeCKS, we show that RPMVEC cells in which SSeCKS expression was inhibited reduce adhesion and spread on LN through blocking the formation of actin stress fibers and focal adhesions. These results demonstrated SSeCKS modulate endothelial cells adhesion and spreading by reorganization of the actin cytoskeleton.

Expression of the ATP-binding cassette membrane transporter, ABCG2, in human and rodent brain microvessel endothelial and glial cell culture systems

PURPOSE

The function of ABCG2 (BCRP), a member of the ATP-binding cassette (ABC) superfamily of membrane-associated drug transporters, at the blood-brain barrier remains highly controversial. This project investigates the functional expression of endogenous ABCG2 in cultures of human and rodent brain cellular compartments.

MATERIALS AND METHODS

RT-PCR, western blot and fluorescent immunocytochemical analyses were performed on ABCG2-overexpressing human breast cancer (MCF-MX100) cells, human and rat brain microvessel endothelial (HBEC and RBE4, respectively), and rat glial cells.

RESULTS

RT-PCR analysis detected ABCG2 mRNA in all the cell culture systems. Western blot analysis with anti-ABCG2 monoclonal BXP-21 antibody detected a robust band at approximately 72 kDa in the ABCG2-overexpressing MCF-MX100 cell line, whereas low expression was found in human and rat brain cell systems. Immunofluorescence microscopy detected predominant plasma membrane localization of ABCG2 in MCF-MX100 cells but weak signal in all brain cellular compartments. In the presence of ABCG2 inhibitors, the accumulation of (3)H-mitoxantrone and pheophorbide A, two established ABCG2 substrates, was significantly increased in MCF-MX100 cells but not in the human and rodent brain cell culture systems.

CONCLUSIONS

Our data show low endogenous ABCG2 protein expression, localization and activity in cultures of human and rat brain microvessel endothelial and glial cells.

Developmental basis of vascular smooth muscle diversity

The origins of vascular smooth muscle are far more diverse than previously thought. Lineage mapping studies show that the segmental organization of early vertebrate embryos leaves footprints on the adult vascular system in the form of a mosaic pattern of different smooth muscle types. Moreover, evolutionarily conserved tissue forming pathways produce vascular smooth muscle from a variety of unanticipated sources. A closer look at the diversity of smooth muscle origins in vascular development provides new perspectives about how blood vessels differ from one another and why they respond in disparate ways to common risk factors associated with vascular disease. The origins of vascular smooth muscle are far more diverse than previously thought. A closer look at the diversity of smooth muscle origins in vascular development provides new perspectives about how blood vessels differ from one another and why they respond in disparate ways to common risk factors associated with vascular disease.

Osteoprotegerin increases leukocyte adhesion to endothelial cells both in vitro and in vivo

Recombinant osteoprotegerin (OPG) promoted the adhesion of both primary polymorphonuclear neutrophils (PMNs) and leukemic HL60 cells to endothelial cells. Leukocyte/endothelial cell adhesion was promoted by short (peak at 1 hour) preincubation of either endothelial cells or PMNs with OPG, and the peak of proadhesive activity was observed in the same range of OPG concentrations detected in the sera of patients affected by cardiovascular diseases. Although the cognate high-affinity ligands for OPG, membrane receptor activator of nuclear factor-kappaB ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), were detected at significant levels on both PMNs and HL60 cells, they were not expressed on the surface of endothelial cells. However, preincubation of OPG with heparin abrogated its proadhesive activity, whereas pretreatment of endothelial cells with chondroitinase plus heparinases significantly decreased the proadhesive activity of OPG. Taken together, these findings suggest the involvement of both the ligand binding and the N-terminal heparin-binding domains of OPG in mediating its pro-adhesive activity. The relevance of these in vitro findings was underscored by in vivo experiments, in which the topical administration of recombinant OPG increased leukocyte rolling and adhesion to rat mesenteric postcapillary venules. Our data suggest that a pathological increase of OPG serum levels might play an important role in promoting leukocyte/endothelial cell adhesion.

Transglutaminase 1 stabilizes beta-actin in endothelial cells correlating with a stabilization of intercellular junctions

Microvascular endothelial monolayers from mouse myocardium become resistant to various barrier-compromising stimuli correlating with the expression of transglutaminase 1 (TGase1) and its translocation towards cellular junctions. In contrast, endothelial monolayers from mouse lung microvessels do not express TGase1 and remain sensitive to barrier-compromising stimuli corresponding to the known in vivo sensitivity of the lung microvasculature. Using the TGase-substrate 5-(biotinamido)-pentylamine, specific TGase inhibitors and RNAi, one target protein of TGase1 in endothelial cells was found to be beta-actin, suggesting that tissue-specific stabilization of the cortical actin filament network by intracellular TGase1 activity may play a role in controlling barrier properties of endothelial monolayers.

Ghrelin stimulates angiogenesis in human microvascular endothelial cells: Implications beyond GH release

Ghrelin, a peptide hormone isolated from the stomach, releases growth hormone and stimulates appetite. Ghrelin is also expressed in pancreas, kidneys, cardiovascular system and in endothelial cells. The precise role of ghrelin in endothelial cell functions remains unknown. We examined the expression of ghrelin and its receptor (GHSR1) mRNAs and proteins in human microvascular endothelial cells (HMVEC) and determined whether ghrelin affects in these cells proliferation, migration and in vitro angiogenesis; and whether MAPK/ERK2 signaling is important for the latter action. We found that ghrelin and GHSR1 are constitutively expressed in HMVEC. Treatment of HMVEC with exogenous ghrelin significantly increased in these cells proliferation, migration, in vitro angiogenesis and ERK2 phosphorylation. MEK/ERK2 inhibitor, PD 98059 abolished ghrelin-induced in vitro angiogenesis. This is the first demonstration that ghrelin and its receptor are expressed in human microvascular endothelial cells and that ghrelin stimulates HMVEC proliferation, migration, and angiogenesis through activation of ERK2 signaling.

Glutamatergic innervation of the hypothalamic median eminence and posterior pituitary of the rat

Recent studies have localized the glutamatergic cell marker type-2 vesicular glutamate transporter (VGLUT2) to distinct peptidergic neurosecretory systems that regulate hypophysial functions in rats. The present studies were aimed to map the neuronal sources of VGLUT2 in the median eminence and the posterior pituitary, the main terminal fields of hypothalamic neurosecretory neurons. Neurons innervating these regions were identified by the uptake of the retrograde tract-tracer Fluoro-Gold (FG) from the systemic circulation, whereas glutamatergic perikarya of the hypothalamus were visualized via the radioisotopic in situ hybridization detection of VGLUT2 mRNA. The results of dual-labeling studies established that the majority of neurons accumulating FG and also expressing VGLUT2 mRNA were located within the paraventricular, periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area. In contrast, only few FG-accumulating cells exhibited VGLUT2 mRNA signal in the arcuate nucleus. Dual-label immunofluorescent studies of the median eminence and posterior pituitary to determine the subcellular location of VGLUT2, revealed the association of VGLUT2 immunoreactivity with SV2 protein, a marker for small clear vesicles in neurosecretory endings. Electron microscopic studies using pre-embedding colloidal gold labeling confirmed the localization of VGLUT2 in small clear synaptic vesicles. These data suggest that neurosecretory neurons located mainly within the paraventricular, anterior periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area secrete glutamate into the fenestrated vessels of the median eminence and posterior pituitary. The functional aspects of the putative neuropeptide/glutamate co-release from neuroendocrine terminals remain to be elucidated.

Interleukin-1β increases expression and activity of matrix metalloproteinase-2 in cardiac microvascular endothelial cells: role of PKCα/β1and MAPKs

Matrix metalloproteinases (MMPs), a family of extracellular endopeptidases, are implicated in angiogenesis because of their ability to selectively degrade components of the extracellular matrix. Interleukin-1β (IL-1β), increased in the heart post-myocardial infarction (post-MI), plays a protective role in the pathophysiology of left ventricular (LV) remodeling following MI. Here we studied expression of various angiogenic genes affected by IL-1β in cardiac microvascular endothelial cells (CMECs) and investigated the signaling pathways involved in the regulation of MMP-2. cDNA array analysis of 96 angiogenesis-related genes indicated that IL-1β modulates the expression of numerous genes, notably increasing the expression of MMP-2, not MMP-9. RT-PCR and Western blot analyses confirmed increased expression of MMP-2 in response to IL-1β. Gelatin in-gel zymography and Biotrak activity assay demonstrated that IL-1β increases MMP-2 activity in the conditioned media. IL-1β activated ERK1/2, JNKs, and protein kinase C (PKC), specifically PKCα/β1, and inhibition of these cascades partially inhibited IL-1β-stimulated increases in MMP-2. Inhibition of PKCα/β1failed to inhibit ERK1/2. However, concurrent inhibition of PKCα/β1and ERK1/2 almost completely inhibited IL-1β-mediated increases in MMP-2 expression. Inhibition of p38 kinase and nuclear factor-κB (NF-κB) had no effect. Pretreatment with superoxide dismutase (SOD) mimetic, MnTMPyP, increased MMP-2 protein levels, whereas pretreatment with SOD and catalase mimetic, EUK134, partially inhibited IL-1β-stimulated increases in MMP-2 protein levels. Exogenous H2O2significantly increased MMP-2 protein levels, whereas superoxide generation by xanthine/xanthine oxidase had no effect. This in vitro study suggests that IL-1β modulates expression and activity of MMP-2 in CMECs.

Acute tissue-type plasminogen activator release in human microvascular endothelial cells: the roles of Galphaq, PLC-beta, IP3 and 5,6-epoxyeicosatrienoic acid

The acute physiologic release of tissue-type plasminogen activator (t-PA) from the endothelium is critical for vascular homeostasis. This process is prostacyclin- and nitric oxide (NO)-independent in humans. It has been suggested that calcium signaling and endothelial-derived hyperpolarizing factors (EDHF) may play a role in t-PA release. G-protein-coupled receptor-dependent calcium signaling is typically Galphaq-dependent. EDHFs have been functionally defined and in various tissues are believed to be various regioisomers of the epoxyeicosatrienoic acids (EETs). We tested the hypothesis in vitro that thrombin-stimulated t-PA release from human microvascular endothelial cells (HMECs) is both Galphaq- and EDHF-dependent. Conditioned media was harvested following thrombin stimulation, and t-PA antigen was measured by ELISA. Thrombin-induced t-PA release was limited by a membrane-permeable Galphaq inhibitory peptide, the PLC-beta antagonist U73122, and the IP3 receptor antagonist 2-aminoethoxyphenylborane, while the Galphaq agonist Pasteurella toxin modestly induced t-PA release. The cytochrome P450 (CYP450) inhibitor, miconazole, and the arachidonic acid epoxygenase inhibitor MS-PPOH inhibited thrombin-stimulated t-PA release, while 5,6-EET-methyl ester stimulated t-PA release. The 5,6- and 14,15-EET antagonist, 14,15-epoxyeicosa-5(Z)-enoic acid, inhibited t-PA release at the 100 microM concentration. However, thrombin-stimulated t-PA release was unaffected by the prostacyclin and NO inhibitors ASA and L-NAME, as well as the potassium channel inhibitors TEA, apamin and charybdotoxin. These studies suggest that thrombin-stimulated t-PA release is Galphaq-, PLC-beta-, IP3-, and 5,6-EET-dependent while being prostacyclin-, NO- and K+ channel-independent in HMECs.

Immunohistochemical study of the reticular and vascular network of mouse lymph node using vibratome sections

The function of lymph nodes is greatly influenced by their unique microanatomy, in which distinct subpopulations of cells are compartmentalized by a meshwork of reticular cells and fibres, specialized blood and lymphatic vessels and nerves. Using antibodies against extracellular matrix (ECM) proteins (fibronectin, collagen IV and laminin), proteoglycan (perlecan), and a fibroblastic marker (ERTR-7), the distribution and molecular organization of the system of reticular fibres was investigated by three-dimensional (3D) reconstruction methods. Fibronectin, collagen IV and laminin are restricted to reticular fibres and have a similar distribution pattern, whereas perlecan is limited to the vascular system of the lymph node. Various compartments of the lymph node, such as the B-cell follicle, paracortex (including the high endothelial venules and paracortical cord), and medulla have been reconstructed to visualize their vasculature with respect to B and T cells. Since the morphology of lymph nodes may change significantly in pathological conditions, different compartments of reactive lymph node (after low-dose Listeria monocytogenes infection), especially germinal centres, were also investigated. The data presented here should facilitate our understanding of the 3D organization of non-immune cell components of lymph nodes, which is crucial for cell adhesion, migration, activation, and differentiation in normal and pathological conditions.

Angiotensin II type 1 receptor signaling contributes to platelet-leukocyte-endothelial cell interactions in the cerebral microvasculature

Angiotensin II type 1 (AT(1)) receptor signaling has been implicated in cerebral microvascular alterations associated with ischemia, diabetes mellitus, hypercholesterolemia, and atherosclerosis. Platelets, which express AT(1) receptors, also appear to contribute to the thrombogenic and inflammatory responses that are elicited by these pathological conditions. This study assesses the role of AT(1) receptor activation on platelet-leukocyte-endothelial cell interactions elicited in cerebral microvasculature by ischemia and reperfusion. Intravital microscopy was used to monitor the adhesion of platelets and leukocytes that were labeled with different fluorochromes, whereas dihydrorhodamine-123 was used to quantify oxygen radical production in cerebral surface of mice that were either treated with the AT(1) receptor agonist Val-angiotensin II (ANG II) or subjected to bilateral common carotid artery occlusion (BCCAO) followed by reperfusion. ANG II elicited a dose- and time- dependent increase in platelet-leukocyte-endothelial cell interactions in cerebral venules that included rolling platelets, adherent platelets on the leukocytes and the endothelial cells, rolling leukocytes, and adherent leukocytes. All of these interactions were attenuated by treatment with either P-selectin or P-selectin glycoprotein ligand 1 (PSGL-1) antibody. The AT(1) receptor antagonist candesartan and losartan as well as diphenyleneiodonium, an inhibitor of flavoproteins including NAD(P)H oxidase, significantly reduced the platelet-leukocyte-endothelial cell interactions elicited by either ANG II administration or BCCAO/reperfusion. The increased oxygen radical generation elicited by BCCAO/reperfusion was also attenuated by candesartan. These findings are consistent with an AT(1) receptor signaling mechanism, which involves oxygen radical production and ultimately results in P-selectin- and PSGL-1-mediated platelet-leukocyte-endothelial cell interactions in the cerebral microcirculation.

Plasmodium falciparum-infected erythrocytes induce tissue factor expression in endothelial cells and support the assembly of multimolecular coagulation complexes

BACKGROUND

Plasmodium falciparum malaria infects 300-500 million people every year, causing 1-2 million deaths annually. Evidence of a coagulation disorder, activation of endothelial cells (EC) and increase in inflammatory cytokines are often present in malaria.

OBJECTIVES

We have asked whether interaction of parasitized red blood cells (pRBC) with EC induces tissue factor (TF) expression in vitro and in vivo. The role of phosphatidylserine-containing pRBC to support the assembly of blood coagulation complexes was also investigated.

RESULTS

We demonstrate that mature forms of pRBC induce functional expression of TF by EC in vitro with productive assembly of the extrinsic Xnase complex and initiation of the coagulation cascade. Late-stage pRBC also support the prothrombinase and intrinsic Xnase complex formation in vitro, and may function as activated platelets in the amplification phase of the blood coagulation. Notably, post-mortem brain sections obtained from P. falciparum-infected children who died from cerebral malaria and other causes display a consistent staining for TF in the EC.

CONCLUSIONS

These findings place TF expression by endothelium and the amplification of the coagulation cascade by pRBC and/or activated platelets as potentially critical steps in the pathogenesis of malaria. Furthermore, it may allow investigators to test other therapeutic alternatives targeting TF or modulators of EC function in the treatment of malaria and/or its complications.

Photoacoustic imaging of the microvasculature with a high-frequency ultrasound array transducer

Visualization of microvascular networks could provide new information about function and disease. We demonstrate the capabilities of a 30-MHz ultrasound array system for photoacoustic microscopy of small (< or = 300 microm) vessels in a rat. 3D images obtained by translating the array in the elevation direction are compared with photographs of excised skin. The system is shown to have 100-microm lateral resolution, 25-microm axial resolution, and 3-mm imaging depth. To our knowledge this is the first report on photoacoustic microscopy of the microvasculature with a high-frequency array transducer. It is anticipated that the system can be used for studying and diagnosing a number of diseases including cancer, atherosclerosis, dermatological disorders, and peripheral microvascular complications in diabetes.

Isometric contraction of microvascular pericytes from mouse brain parenchyma

Pericytes were isolated and cultured from mouse cerebroparenchymal microvessels. A single pericyte clone was three-dimensionally cultured in a collagen gel by adding tensile stress, resulting in the reconstruction of narrow stringy fibers. When the contractility of these fibers was evaluated isometrically, they contracted in response to acetylcholine (ACh)1 or noradrenaline; this was accompanied by an increase in intracellular calcium concentration ([Ca(2+)]i). The fibers that were pre-contracted by ACh were completely relaxed by papaverine, which is a smooth-muscle relaxant. Moreover, the muscarinic ACh receptor-antagonist atropine depressed the [Ca(2+)]i response that was induced by ACh. This study demonstrates for the first time the quantitative measurement of the contractions produced by cultured microvascular pericytes from mouse brain parenchyma.

Engulfment of apoptotic cells by microvascular endothelial cells induces proinflammatory responses

Circulating endothelial cells (CECs) have been detected in a variety of vascular disorders, but their interactions with healthy endothelium remain unknown. The aim of this study was to evaluate the response of human endothelial cells (ECs) to apoptotic or necrotic ECs in an in vitro model and to delineate pathogenetic pathways. Here we show that incubation of the human microvascular endothelial cell line (HMEC-1) with apoptotic ECs resulted in increased expression of chemokines and enhanced binding of leukocytes to HMEC-1 cells, whereas exposure of HMEC-1 cells to necrotic ECs caused no changes in leukocyte-binding affinity. Both apoptotic and necrotic cells were bound and engulfed by HMEC-1 cells and primary human umbilical vein endothelial cells (HUVECs). We therefore suggest that exposures to apoptotic and necrotic ECs induce different patterns of chemokine synthesis and leukocyte adhesion in healthy ECs. These data indicate that CECs are not only markers of vascular damage but may induce proinflammatory signals in the endothelium.