Expression of G-protein subtypes in cultured cerebral endothelial cells

The Protection of Zinc against Acute Cadmium Exposure: A Morphological and Molecular Study on a BBB In Vitro Model

Cadmium (Cd) is a well-known occupational and environmental pollutant worldwide, and its toxicity is widely recognised. Cd is reported to increase the permeability of the blood–brain barrier (BBB) and to penetrate and accumulate in the brain. Although many lines of evidence show that Cd toxicity is induced by different mechanisms, one of the best known is the Cd-dependent production of reactive oxygen species (ROS). Zinc is a trace element known as coenzyme and cofactor for many antioxidant proteins, such as metallothioneins and superoxide dismutase enzymes. To date, very little is known about the role of Zn in preventing Cd-induced blood–brain barrier (BBB) alterations. The goal of this study was to test the Zn antioxidant capacity against Cd-dependent alterations in a rat brain endothelial cell line (RBE4), as an in vitro model for BBB. In order to mimic acute Cd poisoning, RBE4 cells were treated with CdCl₂ 30 µM for 24 h. The protective role of ZnCl₂ (50 µM) was revealed by evaluating the cell viability, reactive oxygen species (ROS) quantification, cytochrome C distribution, and the superoxide dismutase (SOD) protein activity. Additionally, the effectiveness of Zn in counteracting the Cd-induced damage was investigated by evaluating the expression levels of proteins already known to be involved in the Cd signalling pathway, such as GRP78 (an endoplasmic reticulum (ER) stress protein), caspase3 pro- and cleaved forms, and BAX. Finally, we evaluated if Zn was able to attenuate the alterations of zonula occludens-1 (ZO-1), one of the tight-junction (TJ) proteins involved in the formation of the BBB. Our data clearly demonstrate that Zn, by protecting from the SOD activity impairment induced by Cd, is able to prevent the triggering of the Cd-dependent signalling pathway that leads to ZO-1 dislocation and downregulation, and BBB damage.

Role of pattern recognition receptors of the neurovascular unit in inflamm-aging

Aging is associated with chronic inflammation partly mediated by increased levels of damage-associated molecular patterns, which activate pattern recognition receptors (PRRs) of the innate immune system. Furthermore, many aging-related disorders are associated with inflammation. PRRs, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors (NLRs), are expressed not only in cells of the innate immune system but also in other cells, including cells of the neurovascular unit and cerebral vasculature forming the blood-brain barrier. In this review, we summarize our present knowledge about the relationship between activation of PRRs expressed by cells of the neurovascular unit-blood-brain barrier, chronic inflammation, and aging-related pathologies of the brain. The most important damage-associated molecular pattern-sensing PRRs in the brain are TLR2, TLR4, and NLR family pyrin domain-containing protein-1 and pyrin domain-containing protein-3, which are activated during physiological and pathological aging in microglia, neurons, astrocytes, and possibly endothelial cells and pericytes.

"You Shall Not Pass"-tight junctions of the blood brain barrier

The structure and function of the barrier layers restricting the free diffusion of substances between the central nervous system (brain and spinal cord) and the systemic circulation is of great medical interest as various pathological conditions often lead to their impairment. Excessive leakage of blood-borne molecules into the parenchyma and the concomitant fluctuations in the microenvironment following a transient breakdown of the blood-brain barrier (BBB) during ischemic/hypoxic conditions or because of an autoimmune disease are detrimental to the physiological functioning of nervous tissue. On the other hand, the treatment of neurological disorders is often hampered as only minimal amounts of therapeutic agents are able to penetrate a fully functional BBB or blood cerebrospinal fluid barrier. An in-depth understanding of the molecular machinery governing the establishment and maintenance of these barriers is necessary to develop rational strategies allowing a controlled delivery of appropriate drugs to the CNS. At the basis of such tissue barriers are intimate cell-cell contacts (zonulae occludentes, tight junctions) which are present in all polarized epithelia and endothelia. By creating a paracellular diffusion constraint TJs enable the vectorial transport across cell monolayers. More recent findings indicate that functional barriers are already established during development, protecting the fetal brain. As an understanding of the biogenesis of TJs might reveal the underlying mechanisms of barrier formation during ontogenic development numerous in vitro systems have been developed to study the assembly and disassembly of TJs. In addition, monitoring the stage-specific expression of TJ-associated proteins during development has brought much insight into the “developmental tightening” of tissue barriers. Over the last two decades a detailed molecular map of transmembrane and cytoplasmic TJ-proteins has been identified. These proteins not only form a cell-cell adhesion structure, but integrate various signaling pathways, thereby directly or indirectly impacting upon processes such as cell-cell adhesion, cytoskeletal rearrangement, and transcriptional control. This review will provide a brief overview on the establishment of the BBB during embryonic development in mammals and a detailed description of the ultrastructure, biogenesis, and molecular composition of epithelial and endothelial TJs will be given.

CB2 receptor activation inhibits melanoma cell transmigration through the blood-brain barrier

During parenchymal brain metastasis formation tumor cells need to migrate through cerebral endothelial cells, which form the morphological basis of the blood-brain barrier (BBB). The mechanisms of extravasation of tumor cells are highly uncharacterized, but in some aspects recapitulate the diapedesis of leukocytes. Extravasation of leukocytes through the BBB is decreased by the activation of type 2 cannabinoid receptors (CB2); therefore, in the present study we sought to investigate the role of CB2 receptors in the interaction of melanoma cells with the brain endothelium. First, we identified the presence of CB1, CB2(A), GPR18 (transcriptional variant 1) and GPR55 receptors in brain endothelial cells, while melanoma cells expressed CB1, CB2(A), GPR18 (transcriptional variants 1 and 2), GPR55 and GPR119. We observed that activation of CB2 receptors with JWH-133 reduced the adhesion of melanoma cells to the layer of brain endothelial cells. JWH-133 decreased the transendothelial migration rate of melanoma cells as well. Our results suggest that changes induced in endothelial cells are critical in the mediation of the effect of CB2 agonists. Our data identify CB2 as a potential target in reducing the number of brain metastastes originating from melanoma.

In vitro models of the blood-brain barrier for the study of drug delivery to the brain

The most important obstacle to the drug delivery into the brain is the presence of the blood-brain barrier, which limits the traffic of substances between the blood and the nervous tissue. Therefore, adequate in vitro models need to be developed in order to characterize the penetration properties of drug candidates into the central nervous system. This review article summarizes the presently used and the most promising in vitro BBB models based on the culture of brain endothelial cells. Robust models can be obtained using primary porcine brain endothelial cells and rodent coculture models, which have low paracellular permeability and express functional efflux transporters, showing good correlation of drug penetration data with in vivo results. Models mimicking the in vivo anatomophysiological complexity of the BBB are also available, including triple coculture (culture of brain endothelial cells in the presence of pericytes and astrocytes), dynamic, and microfluidic models; however, these are not suitable for rapid, high throughput studies. Potent human cell lines would be needed for easily available and reproducible models which avoid interspecies differences.

Role of the blood-brain barrier in the formation of brain metastases

The majority of brain metastases originate from lung cancer, breast cancer and malignant melanoma. In order to reach the brain, parenchyma metastatic cells have to transmigrate through the endothelial cell layer of brain capillaries, which forms the morphological basis of the blood-brain barrier (BBB). The BBB has a dual role in brain metastasis formation: it forms a tight barrier protecting the central nervous system from entering cancer cells, but it is also actively involved in protecting metastatic cells during extravasation and proliferation in the brain. The mechanisms of interaction of cancer cells and cerebral endothelial cells are largely uncharacterized. Here, we provide a comprehensive review on our current knowledge about the role of junctional and adhesion molecules, soluble factors, proteolytic enzymes and signaling pathways mediating the attachment of tumor cells to brain endothelial cells and the transendothelial migration of metastatic cells. Since brain metastases represent a great therapeutic challenge, it is indispensable to understand the mechanisms of the interaction of tumor cells with the BBB in order to find targets of prevention of brain metastasis formation.

Tight junctions at the blood brain barrier: physiological architecture and disease-associated dysregulation

The Blood–brain barrier (BBB), present at the level of the endothelium of cerebral blood vessels, selectively restricts the blood-to-brain paracellular diffusion of compounds; it is mandatory for cerebral homeostasis and proper neuronal function. The barrier properties of these specialized endothelial cells notably depend on tight junctions (TJs) between adjacent cells: TJs are dynamic structures consisting of a number of transmembrane and membrane-associated cytoplasmic proteins, which are assembled in a multimolecular complex and acting as a platform for intracellular signaling. Although the structural composition of these complexes has been well described in the recent years, our knowledge about their functional regulation still remains fragmentary. Importantly, pericytes, embedded in the vascular basement membrane, and perivascular microglial cells, astrocytes and neurons contribute to the regulation of endothelial TJs and BBB function, altogether constituting the so-called neurovascular unit.

The present review summarizes our current understanding of the structure and functional regulation of endothelial TJs at the BBB. Accumulating evidence points to a correlation between BBB dysfunction, alteration of TJ complexes and progression of a variety of CNS diseases, such as stroke, multiple sclerosis and brain tumors, as well as neurodegenerative diseases like Parkinson’s and Alzheimer’s diseases. Understanding how TJ integrity is controlled may thus help improve drug delivery across the BBB and the design of therapeutic strategies for neurological disorders.

Heterotrimeric Gi/Go proteins modulate endothelial TLR signaling independent of the MyD88-dependent pathway

The innate immune recognition of bacterial lipopolysaccharide (LPS) is mediated by Toll-like receptor 4 (TLR4) and results in activation of proinflammatory signaling including NF-κB and MAPK pathways. Heterotrimeric G proteins have been previously implicated in LPS signaling in macrophages and monocytes. In the present study, we show that pertussis toxin sensitive heterotrimeric G proteins (Gα(i/o)) are involved in the activation of MAPK and Akt downstream of TLR2, TLR3, and TLR4 in endothelial cells. Gα(i/o) are also required for full activation of interferon signaling downstream of TLR3 and TLR4 but are not required for the activation of NF-κB. We find that Gα(i/o)-mediated activation of the MAPK is independent of the canonical MyD88, interleukin-1 receptor-associated kinase, and tumor necrosis factor receptor-associated factor 6 signaling cascade in LPS-stimulated cells. Taken together, the data presented here suggest that heterotrimeric G proteins are widely involved in TLR pathways along a signaling cascade that is distinct from MyD88-TRAF6.

Expression and regulation of toll-like receptors in cerebral endothelial cells

Cerebral endothelial cells - the principal components of the blood-brain barrier (BBB) - fulfill several important functions in the central nervous system (CNS). They form an active interface between blood and neuronal tissue and play a key role in the maintenance of the homeostasis of the CNS. Infections caused by different pathogens are often associated with systemic symptoms and may compromise the functional integrity of the BBB as well. In the mediation of the systemic effect of pathogens Toll-like receptors (TLRs) play a significant role. TLRs are a type of pattern recognition receptor and recognize molecules that are broadly shared by pathogens but distinguishable from host molecules. TLRs are broadly distributed on cells of the immune system and function as primary sensors of invading pathogens. There is also growing experimental evidence indicating that Toll-like receptors are expressed on different non-immune cell types as well, like epithelial or endothelial cells. Here we demonstrate the expression of TLR2, TLR3, TLR4 and TLR6 on rat and human cerebral endothelial cells. Oxidative stress significantly upregulated the expression of these receptors whereas TNF-alpha upregulated the expression of TLR2 and TLR3. Furthermore we have shown, that activation of TLR2/6 leads to an increased permeability which is accompanied by a downregulation of occludin and claudin-5 expression and disappearance of these tight junction proteins from the cell membrane. Changes in occludin expression and localization could be inhibited by the ERK1/2 inhibitor U0126. Our results suggest a significant role of the cerebral endothelium in mediation of the neural effects of different inflammatory processes.

Galphai2-mediated signaling events in the endothelium are involved in controlling leukocyte extravasation

The trafficking of leukocytes from the blood to sites of inflammation is the cumulative result of receptor-ligand-mediated signaling events associated with the leukocytes themselves as well as with the underlying vascular endothelium. Our data show that Galpha(i) signaling pathways in the vascular endothelium regulate a critical step required for leukocyte diapedesis. In vivo studies using knockout mice demonstrated that a signaling event in a non-lymphohematopoietic compartment of the lung prevented the recruitment of proinflammatory leukocytes. Intravital microscopy showed that blockade was at the capillary endothelial surface and ex vivo studies of leukocyte trafficking demonstrated that a Galpha(i)-signaling event in endothelial cells was required for transmigration. Collectively, these data suggest that specific Galpha(i2)-mediated signaling between endothelial cells and leukocytes is required for the extravasation of leukocytes and for tissue-specific accumulation.

A chemical and genetic approach to the mode of action of fumagillin

Previous mode of action studies identified methionine aminopeptidase 2 (MetAP-2) as the target of the antiangiogenic natural product fumagillin and its drug candidate analog, TNP-470. We report here that TNP-470-mediated MetAP-2 inhibition blocks noncanonical Wnt signaling, which plays a critical role in development, cell differentiation, and tumorigenesis. Consistent with this finding, antisense MetAP-2 morpholino oligonucleotide injection in zebrafish embryos phenocopies gastrulation defects seen in noncanonical Wnt5 loss-of-function zebrafish mutants. MetAP-2 inhibition or depletion blocks signaling downstream of the Wnt receptor Frizzled, but upstream of Calmodulin-dependent Kinase II, RhoA, and c-Jun N-terminal Kinase. Moreover, we demonstrate that TNP-470 does not block the canonical Wnt/beta-catenin pathway. Thus, TNP-470 selectively regulates noncanonical over canonical Wnt signaling and provides a unique means to explore and dissect the biological systems mediated by these pathways.

The blood-brain barrier/neurovascular unit in health and disease

The blood-brain barrier (BBB) is the regulated interface between the peripheral circulation and the central nervous system (CNS). Although originally observed by Paul Ehrlich in 1885, the nature of the BBB was debated well into the 20th century. The anatomical substrate of the BBB is the cerebral microvascular endothelium, which, together with astrocytes, pericytes, neurons, and the extracellular matrix, constitute a "neurovascular unit" that is essential for the health and function of the CNS. Tight junctions (TJ) between endothelial cells of the BBB restrict paracellular diffusion of water-soluble substances from blood to brain. The TJ is an intricate complex of transmembrane (junctional adhesion molecule-1, occludin, and claudins) and cytoplasmic (zonula occludens-1 and -2, cingulin, AF-6, and 7H6) proteins linked to the actin cytoskeleton. The expression and subcellular localization of TJ proteins are modulated by several intrinsic signaling pathways, including those involving calcium, phosphorylation, and G-proteins. Disruption of BBB TJ by disease or drugs can lead to impaired BBB function and thus compromise the CNS. Therefore, understanding how BBB TJ might be affected by various factors holds significant promise for the prevention and treatment of neurological diseases.

Overexpression of bradykinin type 2 receptors on glioma cells enhances bradykinin-mediated blood-brain tumor barrier permeability increase

Variations in the expression levels of bradykinin (BK) type 2 receptors (B2R) in different brain tumors may explain variable increases in BK-mediated blood-brain tumor barrier (BTB) permeability. This study investigated whether elevation of the B2R expression levels on glioma cells enhances BK-mediated BTB permeability increases. Stable transfectants of C6 rat glioma cells overexpressing B2R were established by transfection with recombinant vectors harboring rat B2R cDNA sequence. Elevated B2R expression levels in transfectants were confirmed by quantitative real-time PCR, Western blots, and [3H]-BK binding studies. BTB permeability was quantified with autoradiography and expressed as a unidirectional transport constant, Ki, for [14C]-alpha-aminoisobutyric acid (AIB: Mr 103), using a rat brain tumor model. Baseline Ki values in tumors overexpressing B2R were not significantly higher than in control tumors. Ki values after BK treatment in tumors overexpressing B2R, however, were significantly higher than in control tumors. Western blots confirmed that B2R expression levels in vivo in tumors overexpressing B2R remained higher than in control tumors. These results suggested that alteration of B2R expression levels on tumor cells could modulate BK-mediated BTB permeability. Therefore, B2R expression levels in human glioma could be used to analyze the treatment results of patients undergoing treatment involving BK-modulated BTB permeability.

Raft.1, a monoclonal antibody raised against the raft microdomain, recognizes G-protein beta1 and 2, which assemble near nucleus after shiga toxin binding to human renal cell line

SUMMARY

Raft microdomains are glycolipid-enriched microdomain scaffolding molecules involved in signal transduction. The binding of Shiga toxin to globotriaosyl ceramide in raft microdomains of the human renal tubular cell line ACHN causes temporal activation of Src-kinase Yes. To study the downstream signaling mechanism proceeding to the activation of Yes, we raised monoclonal antibodies (MAbs) against raft microdomains. The MAbs were screened on the basis of, first, binding to raft microdomains with dot-blot immunostaining, second, intracellular localization of the epitope by flowcytometry after permeabilization, and third, translocation of the antigen molecules after Stx treatment by immunohistochemical staining. Raft.1 MAb bound to the molecules that accumulated to the particular region near the nucleus after Stx treatment. Two-dimensional Western blotting and matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis revealed that the antigen molecule is GTP binding protein beta subunits 1 and 2 (Gbeta1 and 2). That Raft.1 recognized Gbeta1 and 2 was further confirmed by the reactivity to recombinant Gbeta1 and 2 proteins. To our knowledge, this is the first report of production of a MAb recognizing Gbeta1 and 2. Because Gbeta1 and 2 are highly conserved all through organisms and are deeply involved in signal transduction, Raft.1 is expected to be utilized frequently in research.

Lymphocyte trafficking through the blood-brain barrier is dependent on endothelial cell heterotrimeric G-protein signaling

We have previously shown that the engagement of ICAM-1 on brain endothelial cells (EC) results in the propagation of EC signaling pathways that are necessary for efficient lymphocyte migration across the tight vascular barriers of the brain. Signaling via this receptor alone, however, is unlikely to explain the differential recruitment of leukocytes at different vascular beds. In this study, we investigated the role of EC heterotrimeric G-protein-mediated signaling in supporting transendothelial migration of T lymphocytes. Treatment of brain EC monolayers with pertussis toxin (PTX) resulted in ADP-ribosylation of G-protein alpha subunits and inhibition (>80%) of lymphocyte migration without affecting lymphocyte adhesion. Aortic and high endothelial venule EC treated identically resulted in only partial inhibition of lymphocyte migration (<40%). Expression of ribosylation-resistant (PTX-insensitive) G-protein alpha subunits in brain EC restored their ability to support lymphocyte migration after pretreatment with PTX. Treatment of brain EC with PTX did not inhibit ICAM-1-stimulated tyrosine phosphorylation of focal adhesion kinase, suggesting the effects of PTX in inhibiting EC facilitation of lymphocyte migration are distinct from activation of EC through ICAM-1. We conclude that a heterotrimeric G-protein-mediated signaling pathway in brain EC is essential for efficient transendothelial migration of T lymphocytes into the brain.

Chronic morphine-induced changes in mu-opioid receptors and G proteins of different subcellular loci in rat brain

Prolonged exposure to opioid agonists can induce adaptive changes resulting in tolerance and dependence. Here, rats were rendered tolerant by subcutaneous injections of increasing doses of morphine from 10 to 60 mg/kg for 3, 5, or 10 consecutive days. Binding parameters of the mu-opioid receptor in subcellular fractions were measured with [(3)H]DAMGO ([D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin). Although the density of surface mu-sites did not change after the 5-day morphine treatment, up-regulation of synaptic plasma membrane binding was detected after the 10-day drug administration. In contrast, the number of mu-binding sites in a light vesicle or microsomal fraction (MI) was elevated by 68 and 30% after 5 and 10 days of morphine exposure, respectively. The up-regulated MI mu-sites displayed enhanced coupling to G proteins compared with those detected in saline-treated controls. Pertussis toxin catalyzed ADP ribosylation, and Western blotting with specific antisera was used to quantitate chronic morphine-induced changes in levels of various G protein alpha-subunits. Morphine treatment of 5 days and longer induced significant increases in levels of Galpha(o), Galpha(i1), and Galpha(i2) in MI fractions that are part of an adaptation process. Up-regulation of intracellular mu-sites may be the result of post-translational changes and in part de novo synthesis. The results provide the first evidence that distinct regulation of intracellular mu-opioid receptor G protein coupling and G protein levels may accompany the development of morphine tolerance.

Hydrogen peroxide acts as an EDHF in the piglet pial vasculature in response to bradykinin

We investigated the mechanism of EDHF-mediated dilation to bradykinin (BK) in piglet pial arteries. Topically applied BK (3 micromol/l) induced vasodilation (62 +/- 12%) after the administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) and indomethacin, which was inhibited by endothelial impairment or by the BK(2) receptor antagonist HOE-140 (0.3 micromol/l). Western blotting showed the presence of BK(2) receptors in brain cortex and pial vascular tissue samples. The cytochrome P-450 antagonist miconazole (20 micromol/l) and the lipoxygenase inhibitors baicalein (10 micromol/l) and cinnamyl-3,4-dyhydroxy-alpha-cyanocinnamate (1 micromol/l) failed to reduce the BK-induced dilation. However, the H(2)O(2) scavenger catalase (400 U/ml) abolished the response (from 54 +/- 11 to 0 +/- 2 microm; P < 0.01). The ATP-dependent K(+) (K(ATP)) channel inhibitor glibenclamide (10 micromol/l) had a similar effect as well (from 54 +/- 11 to 16 +/- 5 microm; P < 0.05). Coapplication of the Ca(2+)-dependent K(+) channel inhibitors charybdotoxin (0.1 micromol/l) and apamin (0.5 micromol/l) failed to reduce the response. We conclude that H(2)O(2) mediates the non-nitric oxide-, non-prostanoid-dependent vasorelaxation to BK in the piglet pial vasculature. The response is mediated via BK(2) receptors and the opening of K(ATP) channels.

Tight junctions of the blood-brain barrier: development, composition and regulation

1. The blood-brain barrier is essential for the maintenance and regulation of the neural microenvironment. The main characteristic features of blood-brain barrier endothelial cells are an extremely low rate of transcytotic vesicles and a restrictive paracellular diffusion barrier. 2. Endothelial blood-brain barrier tight junctions differ from epithelial tight junctions, not only by distinct morphological and molecular properties, but also by the fact that endothelial tight junctions are more sensitive to microenvironmental than epithelial factors. 3. Many ubiquitous molecular tight junction components have been identified and characterized including claudins, occludin, ZO-1, ZO-2, ZO-3, cingulin and 7H6. Signaling pathways involved in tight junction regulation include G-proteins, serine-, threonine- and tyrosine-kinases, extra and intracellular calcium levels, cAMP levels, proteases and cytokines. Common to most of these pathways is the modulation of cytoskeletal elements and the connection of tight junction transmembrane molecules to the cytoskeleton. Additionally, crosstalk between components of the tight junction- and the cadherin-catenin system of the adherens junction suggests a close functional interdependence of the two cell-cell contact systems. 4. Important new molecular aspects of tight junction regulation were recently elucidated. This review provides an integration of these new results.

The role of guanylyl cyclases in the permeability response to inflammatory mediators in pial venular capillaries in the rat

Inflammatory mediators have a role in the formation of cerebral oedema and there is evidence that cGMP is an important signal in vascular permeability increase. We have investigated the role and the source of cGMP in mediating the permeability response to acutely applied bradykinin and the histamine H(2) agonist dimaprit on single cerebral venular capillaries, by using the single vessel occlusion technique. We found that 8-bromo-cGMP applied acutely resulted in a small and reversible permeability increase with a log EC(50) -7.2 +/- 0.15 M. KT 5823, the inhibitor of cGMP-dependent protein kinase, abolished the permeability responses to both bradykinin and dimaprit, while zaprinast, an inhibitor of type 5 phosphodiesterase, potentiated the response to bradykinin. On the other hand, L-NMMA blocked the response to dimaprit, but not that to bradykinin. Inhibitors of soluble guanylyl cyclase, LY 85353 and methylene blue, also inhibited the permeability response to dimaprit, but not bradykinin. The permeability responses to the natriuretic peptides ANP and CNP were of similar magnitude to that of bradykinin with log EC(50) -10.0 +/- 0.33 M and -8.7 +/- 0.23 M, respectively. The natriuretic peptide receptor antagonist HS-142-1 blocked permeability responses to bradykinin as well as to ANP, and leukotriene D(4) blocked the responses to CNP and bradykinin, but not to dimaprit. In conclusion, the histamine H(2) receptor appears to signal via cGMP that is generated by a NO and soluble guanylyl cyclase, while bradykinin B(2) receptor also signals via cGMP but through particulate guanylyl cyclase.

Hypercapnia stimulates prostaglandin E(2) but not prostaglandin I(2) release in endothelial cells cultured from microvessels of human fetal brain

Hypercapnia-induced cerebral vasodilation involves prostanoids, in newborns. The source of these prostanoids, however, is not yet determined. In the present study we address the hypothesis that microvascular endothelial cells of human fetal cerebrum increase the synthesis of dilator prostanoids in response to high pCO(2). Cells were isolated from a 22-week-old human fetus. Indication of induced abortion was 46 XY-t(3,10) 3q-25 chromosome abnormality. Normocapnia or hypercapnia was performed during normoxic and normothermic conditions in the medium of the cell culture. After normocapnic or hypercapnic stimuli, the amounts of released prostaglandin E(2) and 6-keto-prostaglandin F(1alpha) (the stable metabolite of prostaglandin I(2)) were measured by radioimmunoassay. Endothelial cells cultured from human fetal brain microvessels express PGE(2) and 6-keto-PGF(1alpha) in different degrees. Hypercapnic stimulus induced a significant increase of PGE(2), while expression of 6-keto-PGF(1alpha) was not augmented by the same stimulus. PGE(2) of endothelial origin, therefore, could be a factor in the mediation of the hypercapnia-induced vasodilation in human fetuses.

Pentosan polysulfate regulates scavenger receptor-mediated, but not fluid-phase, endocytosis in immortalized cerebral endothelial cells

1. Effects of pentosan polysulfate (PPS) and the structurally related sulfated polyanions dextran sulfate, fucoidan, and heparin on the scavenger receptor-mediated and fluidphase endocytosis in GP8 immortalized rat brain endothelial cells were investigated. 2. Using 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarboxyamine perchlorate-labeled acetylated low-density lipoprotein (DiI-AcLDL), we found a binding site with high affinity and low binding capacity, and another one with low affinity and high binding capacity. Increasing ligand concentrations could not saturate DiI-AcLDL uptake. DiI-AcLDL uptake, but not binding, was sensitive to pretreatment with filipin, an inhibitor of caveola formation. 3. PPS (20-200 microg/ml) significantly reduced the binding of DiI-AcLDL after coincubation for 3 hr, though this effect was less expressed after 18 hr. Among other polyanions, only fucoidan decreased the DiI-AcLDL binding after 3 hr, whereas dextran sulfate significantly increased it after 18 hr. PPS treatment induced an increase in DiI-AcLDL uptake, whereas other polysulfated compounds caused a significant reduction. 4. Fluid-phase endocytosis determined by the accumulation of Lucifer yellow was concentration and time dependent in GP8 cells. Coincubation with PPS or other sulfated polyanions could not significantly alter the rate of Lucifer yellow uptake. 5. In conclusion. PPS decreased the binding and increased the uptake of DiI-AcLDL in cerebral endothelial cells, an effect not mimicked by the other polyanions investigated.