Rho GTPases and leucocyte-induced endothelial remodelling

ICAM-1 nanoclusters regulate hepatic epithelial cell polarity by leukocyte adhesion-independent control of apical actomyosin

Epithelial intercellular adhesion molecule (ICAM)-1 is apically polarized, interacts with, and guides leukocytes across epithelial barriers. Polarized hepatic epithelia organize their apical membrane domain into bile canaliculi and ducts, which are not accessible to circulating immune cells but that nevertheless confine most of ICAM-1. Here, by analyzing ICAM-1_KO human hepatic cells, liver organoids from ICAM-1_KO mice and rescue-of-function experiments, we show that ICAM-1 regulates epithelial apicobasal polarity in a leukocyte adhesion-independent manner. ICAM-1 signals to an actomyosin network at the base of canalicular microvilli, thereby controlling the dynamics and size of bile canalicular-like structures. We identified the scaffolding protein EBP50/NHERF1/SLC9A3R1, which connects membrane proteins with the underlying actin cytoskeleton, in the proximity interactome of ICAM-1. EBP50 and ICAM-1 form nano-scale domains that overlap in microvilli, from which ICAM-1 regulates EBP50 nano-organization. Indeed, EBP50 expression is required for ICAM-1-mediated control of BC morphogenesis and actomyosin. Our findings indicate that ICAM-1 regulates the dynamics of epithelial apical membrane domains beyond its role as a heterotypic cell-cell adhesion molecule and reveal potential therapeutic strategies for preserving epithelial architecture during inflammatory stress.

Protective Effects of Grapefruit Essential Oil against Staphylococcus Aureus-Induced Inflammation and Cell Damage in Human Epidermal Keratinocytes

Staphylococcus aureus (S. aureus) is a common skin pathogenic bacterium, over-colonization can induce skin infections, while its metabolites can also produce irritation to the skin, often accompanied by eczema dermatitis, specific dermatitis and other skin diseases. Grapefruit essential oil is extracted from the fruit of grapefruit (Citrus maxima (Burm) Merr.), a citrus plant that is rich in flavonoids, phenolic acids and high flavanones. Due to its good odor and biological activity such as anti-inflammatory, antibacterial, etc., grapefruit essential oil has been widely used as an additive in food. To evaluate the potential application of grapefruit essential oil as raw materials in cosmetics products and health foods, we developed a cell damage model of skin inflammation stimulated by S. aureus metabolites. Compared to that of lime essential oil, an internal control, we found that grapefruit essential oil could significantly promote HaCaT cells proliferation, reduce reactive oxygen species (ROS) production induced by S. aureus metabolites, inhibit the upregulated expression of IL-1 and COX-2. In the 3D epidermal model, grapefruit essential oil could recover the decreased LOR and FLG contents caused by S. aureus metabolites. These results demonstrated pharmacological evidence for the anti-inflammatory effect of grapefruit essential oil, suggesting a potential application of grapefruit essential oil as cosmetic raw materials for repair and alleviating of skin inflammation caused by S. aureus.

Aqueous humor proteomic analysis of acute angle-closure glaucoma with visual field loss

Background

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency that occurs over the course of hours or days and may cause irreversible blindness if not treated immediately. In most cases, optic nerve damage is the cause of visual field (VF) loss in AACG. There has been no reliable biomarker found to evaluate optic nerve damage to date. Aqueous humor (AH) proteome analysis might reveal the proteomic alterations in AACG and provide helpful clues in the search for an AH biomarker of optic nerve damage and VF loss.

Methods

In this study, we used the AH proteome to explore the functions of differentially expressed proteins (DEPs) during disease progression. The AH proteins from the early-stage group and late-stage group were extracted and analyzed by the data-independent acquisition (DIA) method. The DEPs functions were annotated, and parallel reaction monitoring (PRM) was used to validate the key DEPs.

Results

A total of 87 DEPs were found. Gene Ontology analysis showed that most DEPs were enriched in immunology, hemodynamics, and apoptosis. Ingenuity pathway analysis found that vascular endothelial growth factor (VEGF) signaling, the production of reactive oxygen species (ROS) in macrophages, and the nuclear factor erythroid 2-related factor 2 (NRF2)-mediated oxidative stress response were active pathways in the late stage of AACG. The mechanism of retinal ganglion cell (RGC) death was hypothesized on the basis of DEP functional analysis. A total of 20 DEPs were validated by using PRM, and prostaglandin-H2 D-isomerase was found to have the potential to evaluate optic nerve damage.

Conclusions

This study showed that AH proteomic analysis could reveal the proteomic alterations in the pathogenesis of VF loss in AACG and help to provide objective protein biomarkers to evaluate VF loss. These findings will benefit the application of the AH proteome to clinical research.

Macrophage 3D migration: A potential therapeutic target for inflammation and deleterious progression in diseases

Macrophages are heterogeneous cells that have different physiological functions, such as chemotaxis, phagocytosis, endocytosis, and secretion of various factors. All physiological functions of macrophages are integral to homeostasis, immune defense and tissue repair. However, in several diseases, macrophages are recruited from the blood towards inflammatory sites. This process is called macrophage migration, which promotes deleterious disease progression. Macrophage migration is a key player in many inflammatory diseases, autoimmune diseases and cancers because it contributes to the accumulation of proinflammatory factors, the destruction of tissues and the development of tumors. Therefore, macrophage migration is proposed to be a potential therapeutic target. Macrophages migrate between two-dimensional (2D) and three-dimensional (3D) environments, implying that distinct migratory features and mechanisms are involved. Compared with the 2D migration of macrophages, 3D migration involves more complex variations in cellular morphology and dynamics. The structure of the extracellular matrix, a key factor, is modified in diseases that influence macrophage 3D migration. Macrophage 3D migration relates to disease pathology. Research that focuses on macrophage 3D migration is an emerging field and was reviewed in this article to indicate the molecular and cellular mechanisms of macrophage migration in 3D environments and to provide potential targets for controlling disease progression associated with this migration.

RhoGTPase in Vascular Disease

Ras-homologous (Rho)A/Rho-kinase pathway plays an essential role in many cellular functions, including contraction, motility, proliferation, and apoptosis, inflammation, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Given its role in many physiological and pathological functions, targeting can result in adverse effects and limit its use for therapy. In this review, we have summarized the role of RhoGTPases with an emphasis on RhoA in vascular disease and its impact on endothelial, smooth muscle, and heart and lung fibroblasts. It is clear from the various studies that understanding the regulation of RhoGTPases and their regulators in physiology and pathological conditions is required for effective targeting of Rho.

How leukocytes trigger opening and sealing of gaps in the endothelial barrier

The entry of leukocytes into tissues requires well-coordinated interactions between the immune cells and endothelial cells which form the inner lining of blood vessels. The molecular basis for recognition, capture, and adhesion of leukocytes to the endothelial apical surface is well studied. This review will focus on recent advances in our understanding of events following the firm interaction of leukocytes with the inner surface of the blood vessel wall. We will discuss how leukocytes initiate the transmigration (diapedesis) process, trigger the opening of gaps in the endothelial barrier, and eventually move through this boundary.

Adhesion Molecules: Master Controllers of the Circulatory System

This manuscript will review our current understanding of cellular adhesion molecules (CAMs) relevant to the circulatory system, their physiological role in control of vascular homeostasis, innate and adaptive immune responses, and their importance in pathophysiological (disease) processes such as acute lung injury, atherosclerosis, and pulmonary hypertension. This is a complex and rapidly changing area of research that is incompletely understood. By design, we will begin with a brief overview of the structure and classification of the major groups of adhesion molecules and their physiological functions including cellular adhesion and signaling. The role of specific CAMs in the process of platelet aggregation and hemostasis and leukocyte adhesion and transendothelial migration will be reviewed as examples of the complex and cooperative interplay between CAMs during physiological and pathophysiological processes. The role of the endothelial glycocalyx and the glycobiology of this complex system related to inflammatory states such as sepsis will be reviewed. We will then focus on the role of adhesion molecules in the pathogenesis of specific disease processes involving the lungs and cardiovascular system. The potential of targeting adhesion molecules in the treatment of immune and inflammatory diseases will be highlighted in the relevant sections throughout the manuscript.

Cellular Barriers after Extravasation: Leukocyte Interactions with Polarized Epithelia in the Inflamed Tissue

During the inflammatory response, immune cells egress from the circulation and follow a chemotactic and haptotactic gradient within the tissue, interacting with matrix components in the stroma and with parenchymal cells, which guide them towards the sites of inflammation. Polarized epithelial cells compartmentalize tissue cavities and are often exposed to inflammatory challenges such as toxics or infections in non-lymphoid tissues. Apicobasal polarity is critical to the specialized functions of these epithelia. Indeed, a common feature of epithelial dysfunction is the loss of polarity. Here we review evidence showing that apicobasal polarity regulates the inflammatory response: various polarized epithelia asymmetrically secrete chemotactic mediators and polarize adhesion receptors that dictate the route of leukocyte migration within the parenchyma. We also discuss recent findings showing that the loss of apicobasal polarity increases leukocyte adhesion to epithelial cells and the consequences that this could have for the inflammatory response towards damaged, infected or transformed epithelial cells.

Rho kinase as a target for cerebral vascular disorders

The development of novel pharmaceutical treatments for disorders of the cerebral vasculature is a serious unmet medical need. These vascular disorders are typified by a disruption in the delicate Rho signaling equilibrium within the blood vessel wall. In particular, Rho kinase overactivation in the smooth muscle and endothelial layers of the vessel wall results in cytoskeletal modifications that lead to reduced vascular integrity and abnormal vascular growth. Rho kinase is thus a promising target for the treatment of cerebral vascular disorders. Indeed, preclinical studies indicate that Rho kinase inhibition may reduce the formation/growth/rupture of both intracranial aneurysms and cerebral cavernous malformations.

Rho/Rho-associated kinase pathway in glaucoma (Review)

The Rho/ROCK pathway plays important roles in the modulation of the cytoskeletal integrity of cells, the synthesis of extracellular matrix components in the aqueous humor outflow tissue and the permeability of Schlemm's canal endothelial cells. The activation of the Rho/ROCK pathway results in trabecular meshwork (TM) contraction, and the inhibition of this pathway would provoke relaxation of TM with subsequent increase in outflow facility and, thereby, decrease intraocular pressure (IOP). ROCK inhibitors also serve as potent anti‑scarring agents via inhibition of transdifferentiation of tenon fibroblasts into myofibroblasts. Furthermore, the RhoA/ROCK pathway is involved in optic nerve neuroprotection. Inactivation of Rho/ROCK signaling increase ocular blood flow, improve retinal ganglion cell (RGC) survival and promote RGC axon regeneration. Considering the IOP modulation, potent bleb anti-scarring effect and neuroprotective properties of ROCK inhibitors, the Rho/ROCK pathway is an attractive target for anti-glaucoma therapy, and it may be used for human therapy in the near future.

Slit2 prevents neutrophil recruitment and renal ischemia-reperfusion injury

Neutrophils recruited to the postischemic kidney contribute to the pathogenesis of ischemia-reperfusion injury (IRI), which is the most common cause of renal failure among hospitalized patients. The Slit family of secreted proteins inhibits chemotaxis of leukocytes by preventing activation of Rho-family GTPases, suggesting that members of this family might modulate the recruitment of neutrophils and the resulting IRI. Here, in static and microfluidic shear assays, Slit2 inhibited multiple steps required for the infiltration of neutrophils into tissue. Specifically, Slit2 blocked the capture and firm adhesion of human neutrophils to inflamed vascular endothelial barriers as well as their subsequent transmigration. To examine whether these observations were relevant to renal IRI, we administered Slit2 to mice before bilateral clamping of the renal pedicles. Assessed at 18 hours after reperfusion, Slit2 significantly inhibited renal tubular necrosis, neutrophil and macrophage infiltration, and rise in plasma creatinine. In vitro, Slit2 did not impair the protective functions of neutrophils, including phagocytosis and superoxide production, and did not inhibit neutrophils from killing the extracellular pathogen Staphylococcus aureus. In vivo, administration of Slit2 did not attenuate neutrophil recruitment or bacterial clearance in mice with ascending Escherichia coli urinary tract infections and did not increase the bacterial load in the livers of mice infected with the intracellular pathogen Listeria monocytogenes. Collectively, these results suggest that Slit2 may hold promise as a strategy to combat renal IRI without compromising the protective innate immune response.

Exogenous microparticles of iron oxide bind to activated endothelial cells but, unlike monocytes, do not trigger an endothelial response

Targeting particles to sites of inflammation is of considerable interest for applications relating to molecular imaging and drug delivery. We and others have described micron-sized particles of iron oxide (MPIO) that can be directed using specific ligands (e.g. antibodies, peptides and oligosaccharides) to bind to mediators of vascular inflammation in vivo. Since leukocyte binding to these molecules can induce changes in the target cell, an outstanding question has been whether the binding of imaging particles to these mediators induces biologically significant changes in the endothelial cells, potentially initiating or propagating inflammation. Here, we address these questions by looking for changes in endothelial cells following binding of contrast agent. Specifically, we have quantified calcium flux, rearrangement of the actin cytoskeleton, production of reactive oxygen species (ROS), apoptosis and potential secondary changes, such as changes in gene and protein expression follow binding events to primary endothelial cells in vitro. Although leukocytes induced changes to endothelial cell function, we did not see any significant changes to endothelial calcium flux, cytoskeletal organisation, production of ROS or induction of apoptosis in response to antibody-MPIO binding. Furthermore, there were no changes to gene expression monitored via real-time RT-PCR or presentation of protein on the cell surface measured using flow cytometry. Our experiments demonstrate that whilst antibody-targeted microparticles mimic the binding capability of leukocytes to inflamed endothelium, they do not trigger the same cellular responses and do not appear to initiate or compound inflammation. These properties are desirable for targeted therapeutic and diagnostic agents.

MYADM controls endothelial barrier function through ERM-dependent regulation of ICAM-1 expression

The endothelium maintains a barrier between blood and tissue that becomes more permeable during inflammation. Membrane rafts are ordered assemblies of cholesterol, glycolipids, and proteins that modulate proinflammatory cell signaling and barrier function. In epithelial cells, the MAL family members MAL, MAL2, and myeloid-associated differentiation marker (MYADM) regulate the function and dynamics of ordered membrane domains. We analyzed the expression of these three proteins in human endothelial cells and found that only MYADM is expressed. MYADM was confined in ordered domains at the plasma membrane, where it partially colocalized with filamentous actin and cell-cell junctions. Small interfering RNA (siRNA)-mediated MYADM knockdown increased permeability, ICAM-1 expression, and leukocyte adhesion, all of which are features of an inflammatory response. Barrier function decrease in MYADM-silenced cells was dependent on ICAM-1 expression. Membrane domains and the underlying actin cytoskeleton can regulate each other and are connected by ezrin, radixin, and moesin (ERM) proteins. In endothelial cells, MYADM knockdown induced ERM activation. Triple-ERM knockdown partially inhibited ICAM-1 increase induced by MYADM siRNA. Importantly, ERM knockdown also reduced ICAM-1 expression in response to the proinflammatory cytokine tumor necrosis factor-α. MYADM therefore regulates the connection between the plasma membrane and the cortical cytoskeleton and so can control the endothelial inflammatory response.

Microenvironment and tumor cell plasticity: an easy way out

Cancer cells undergo genetic changes allowing their adaptation to environmental changes, thereby obtaining an advantage during the long metastatic route, disseminated of several changes in the surrounding environment. In particular, plasticity in cell motility, mainly due to epigenetic regulation of cancer cells by environmental insults, engage adaptive strategies aimed essentially to survive in hostile milieu, thereby escaping adverse sites. This review is focused on tumor microenvironment as a collection of structural and cellular elements promoting plasticity and adaptive programs. We analyze the role of extracellular matrix stiffness, hypoxia, nutrient deprivation, acidity, as well as different cell populations of tumor microenvironment.

Flavanone metabolites decrease monocyte adhesion to TNF-α-activated endothelial cells by modulating expression of atherosclerosis-related genes

Flavanones are found specifically and abundantly in citrus fruits. Their beneficial effect on vascular function is well documented. However, little is known about their cellular and molecular mechanisms of action in vascular cells. The goal of the present study was to identify the impact of flavanone metabolites on endothelial cells and decipher the underlying molecular mechanisms of action. We investigated the impact of naringenin and hesperetin metabolites at 0·5, 2 and 10 μm on monocyte adhesion to TNF-α-activated human umbilical vein endothelial cells (HUVEC) and on gene expression. Except hesperetin-7-glucuronide and naringenin-7-glucuronide (N7G), when present at 2 μm, flavanone metabolites (hesperetin-3′-sulphate, hesperetin-3′-glucuronide and naringenin-4′-glucuronide (N4′G)) significantly attenuated monocyte adhesion to TNF-α-activated HUVEC. Exposure of both monocytes and HUVEC to N4′G and N7G at 2 μm resulted in a higher inhibitory effect on monocyte adhesion. Gene expression analysis, using TaqMan Low-Density Array, revealed that flavanone metabolites modulated the expression of genes involved in atherogenesis, such as those involved in inflammation, cell adhesion and cytoskeletal organisation. In conclusion, physiologically relevant concentrations of flavanone metabolites reduce monocyte adhesion to TNF-α-stimulated endothelial cells by affecting the expression of related genes. This provides a potential explanation for the vasculoprotective effects of flavanones.

Endothelial membrane reorganization during leukocyte extravasation

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

p120-Catenin prevents neutrophil transmigration independently of RhoA inhibition by impairing Src dependent VE-cadherin phosphorylation

Leukocyte transendothelial migration (TEM) is regulated by several signaling pathways including Src family kinases (SFK) and the small RhoGTPases. Previous studies have shown that vascular endothelial-cadherin (VE-cad) forms a complex with β-,γ-, and p120-catenins and this complex disassociates to form a transient gap during leukocyte TEM. Additionally, p120-catenin (p120-1A) overexpression in human umbilical vein endothelial cells (HUVEC) stabilizes VE-cad surface expression, prevents tyrosine phosphorylation of VE-cad, and inhibits leukocyte TEM. Based on reports showing that p120 overexpression in fibroblasts or epithelial cells inhibits RhoA and activates Rac and Cdc42 GTPases, and on other reports showing that RhoA activation in endothelial cells is necessary for leukocyte TEM, we reasoned that p120 overexpression inhibited TEM through inhibition of RhoA. To test this idea, we overexpressed a mutant p120 isoform, p120-4A, which does not interact with RhoA. p120-4A colocalized with VE-cad in HUVEC junctions and enhanced VE-cad surface expression, similar to overexpression of p120-1A. Interestingly, overexpression of either p120-4A or p120-1A dramatically blocked TEM, and overexpression of p120-1A in HUVEC did not affect RhoA basal activity or activation of RhoA and Rac induced by thrombin or ICAM-1 crosslinking. In contrast, biochemical studies revealed that overexpression of p120-1A reduced activated pY416-Src association with VE-cad. In summary, p120 overexpression inhibits neutrophil TEM independently of an effect on RhoA or Rac and instead blocks TEM by preventing VE-cad tyrosine phosphorylation and association of active Src with the VE-cad complex.

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

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

On, around, and through: neutrophil-endothelial interactions in innate immunity

This manuscript will review our current understanding of neutrophilic polymorphonuclear leukocyte (neutrophil) interactions with the endothelium during immune and inflammatory responses, focusing on the molecular mechanisms regulating neutrophil adhesion to and migration through the endothelium in response to infection or tissue injury. This is a complex and dynamic area of research and one that has been the topic of several recent comprehensive reviews to which the interested reader is referred (64, 118, 131). By design, this review will begin with a brief review of some basic aspects of neutrophil biology and endothelial adhesion to provide a foundation. The remainder of the review will focus on selected areas of this complex field, specifically the role of the endothelial glycocalyx in regulating neutrophil adhesion and the mechanisms and consequences of migration of neutrophils between (paracellular) and through (transcellular) endothelial cells during egress from the vasculature.

Geranylgeranyl transferase 1 modulates autophagy and apoptosis in human airway smooth muscle

Geranylgeranyl transferase 1 (GGT1) is involved in the posttranslational prenylation of signaling proteins, such as small GTPases. We have shown that blocking the formation of isoprenoids with statins regulates survival of human lung mesenchymal cells; thus, we tested the hypothesis that GGT1 may specifically modulate programmed cell death pathways in these cells. To this end, human airway smooth muscle (HASM) cells were treated with the selective GGT1 inhibitor GGTi-298. Apoptosis was seen using assays for cellular DNA content and caspase activation. Induction of autophagy was observed using transmission electron microscopy, immunoblotting for LC3 lipidation and Atg5-12 complex content, and confocal microscopy to detect formation of lysosome-localized LC3 punctae. Notably, GGT1 inhibition induced expression of p53-dependent proteins, p53 upregulated modulator of apoptosis (Noxa), and damage-regulated autophagy modulator (DRAM), this was inhibited by the p53 transcriptional activation inhibitor cyclic-pifithrin-α. Inhibition of autophagy with bafilomycin-A1 or short-hairpin RNA silencing of Atg7 substantially augmented GGTi-298-induced apoptosis. Overall, we demonstrate for the first time that pharmacological inhibition of GGT1 induces simultaneous p53-dependent apoptosis and autophagy in HASM. Moreover, autophagy regulates apoptosis induction. Thus, our findings identify GGT1 as a key regulator of HASM cell viability.

Quantification of transendothelial migration using three-dimensional confocal microscopy

Migration of cells across endothelial barriers, termed transendothelial migration (TEM), is an important cellular process that underpins the pathology of many disease states including chronic inflammation and cancer metastasis. While this process can be modeled in vitro using cultured cells, many model systems are unable to provide detailed visual information of cell morphologies and distribution of proteins such as junctional markers, as well as quantitative data on the rate of TEM. Improvements in imaging techniques have made microscopy-based assays an invaluable tool for studying this type of detailed cell movement in physiological processes. In this chapter, we describe a confocal microscopy-based method that can be used to assess TEM of both leukocytes and cancer cells across endothelial barriers in response to a chemotactic gradient, as well as providing information on their migration into a subendothelial extracellular matrix, designed to mimic that found in vivo.

The PI3K p110alpha isoform regulates endothelial adherens junctions via Pyk2 and Rac1

Only the p110α isoform of PI3K mediates the association of VE-cadherin with Pyk2, a Rac GEF and the p85 PI3K regulatory subunit, to reduce junctional integrity in response to TNF.

Endothelial cell–cell junctions control efflux of small molecules and leukocyte transendothelial migration (TEM) between blood and tissues. Inhibitors of phosphoinositide 3-kinases (PI3Ks) increase endothelial barrier function, but the roles of different PI3K isoforms have not been addressed. In this study, we determine the contribution of each of the four class I PI3K isoforms (p110α, -β, -γ, and -δ) to endothelial permeability and leukocyte TEM. We find that depletion of p110α but not other p110 isoforms decreases TNF-induced endothelial permeability, Tyr phosphorylation of the adherens junction protein vascular endothelial cadherin (VE-cadherin), and leukocyte TEM. p110α selectively mediates activation of the Tyr kinase Pyk2 and GTPase Rac1 to regulate barrier function. Additionally, p110α mediates the association of VE-cadherin with Pyk2, the Rac guanine nucleotide exchange factor Tiam-1 and the p85 regulatory subunit of PI3K. We propose that p110α regulates endothelial barrier function by inducing the formation of a VE-cadherin–associated protein complex that coordinates changes to adherens junctions with the actin cytoskeleton.

Organizing the cell cortex: the role of ERM proteins

Specialized membrane domains are an important feature of almost all cells. In particular, they are essential to tissues that have a highly organized cell cortex, such as the intestinal brush border epithelium. The ERM proteins (ezrin, radixin and moesin) have a crucial role in organizing membrane domains through their ability to interact with transmembrane proteins and the cytoskeleton. In doing so, they can provide structural links to strengthen the cell cortex and regulate the activities of signal transduction pathways. Recent studies examining the structure and in vivo functions of ERMs have greatly advanced our understanding of the importance of membrane-cytoskeleton interactions.

Mechanical Forces in Endothelial Cells during Firm Adhesion and Early Transmigration of Human Monocytes

Transmigration of leukocytes across the endothelial barrier is a tightly controlled process involving multiple steps, including rolling adhesion, firm adhesion, and then penetration of leukocytes through the endothelial monolayer. While the key molecular signals have been described in great detail, we are only just beginning to unveil the mechanical forces involved in this process. Here, using a microfabricated system that reports traction forces generated by cells, we describe forces generated by endothelial cells during monocyte firm adhesion and transmigration. Average traction force across the endothelial monolayer increased dramatically when monocytes firmly adhered and transmigrated. Interestingly, the endothelial cell that was in direct contact with the monocyte exhibited much larger traction forces relative to its neighbors, and the direction of these traction forces aligned centripetally with respect to the monocyte. The increase in traction force occurred in the local subcellular zone of monocyte adhesion, and dissipated rapidly with distance. To begin to characterize the basis for this mechanical effect, we show that beads coated with anti-ICAM-1 or VCAM-1 antibodies bound to monolayers could reproduce this effect. Taken together, this study provides a new approach to examining the role of cellular mechanics in regulating leukocyte transmigration through the endothelium.

Discriminating between the paracellular and transcellular routes of diapedesis

Leucocyte transendothelial migration (TEM) or diapedesis is pivotal in leucocyte trafficking during the inflammatory and immune responses. The endothelium plays an active role in this process, triggering an array of signalling pathways and reorganizing its cytoskeleton and membrane to facilitate leucocyte TEM. Diapedesis can occur between endothelial cells (paracellular) or through individual endothelial cells (transcellular). This latter route accounts for up to 30% of the total diapedesis in certain endothelial cell types in vitro. Mechanisms underlying both routes of diapedesis have been subjected to intense investigation during recent years. Here we describe a method to discriminate between the paracellular and the transcellular routes of diapedesis in vitro. The method is based on a transmigration assay of human T lymphoblasts through TNF-alpha-stimulated human primary endothelial monolayers, a triple fluorescence labelling of F-actin, the adhesion receptor ICAM-1 and the junctional protein beta-catenin and a subsequent acquisition of z-stacks of high-resolution confocal sections.

Inhibition of leukocyte adhesion by developmental endothelial locus-1 (del-1)

The leukocyte adhesion to endothelium is pivotal in leukocyte recruitment which takes place during inflammatory, autoimmune and infectious conditions. The interaction between leukocytes and endothelium requires an array of adhesion molecules expressed on leukocytes and endothelial cells, thereby promoting leukocyte recruitment into sites of inflammation and tissue injury. Intervention with the adhesion molecules provides a platform for development of anti-inflammatory therapeutics. This review will focus on developmental endothelial locus-1 (Del-1), an endogenous inhibitor of leukocyte adhesion.

Phosphoinositide 3-kinases in cell migration

Cell migration is essential for many biological processes in animals and is a complex highly co-ordinated process that involves cell polarization, actin-driven protrusion and formation and turnover of cell adhesions. The PI3K (phosphoinositide 3-kinase) family of lipid kinases regulate cell migration in many different cell types, both through direct binding of proteins to their lipid products and indirectly through crosstalk with other pathways, such as Rho GTPase signalling. Emerging evidence suggests that the involvement of PI3Ks at different stages of migration varies even within one cell type, and is dependent on the combination of external stimuli, as well as on the signalling status of the cell. In addition, it appears that different PI3K isoforms have distinct roles in cell polarization and migration. This review describes how PI3K signalling is regulated by pro-migratory stimuli, and the diverse ways in which PI3K-mediated signal transduction contributes to different aspects of cell migration.

The Rac activator Tiam1 controls efficient T-cell trafficking and route of transendothelial migration

Migration toward chemoattractants is a hallmark of T-cell trafficking and is essential to produce an efficient immune response. Here, we have analyzed the function of the Rac activator Tiam1 in the control of T-cell trafficking and transendothelial migration. We found that Tiam1 is required for chemokine- and S1P-induced Rac activation and subsequent cell migration. As a result, Tiam1-deficient T cells show reduced chemotaxis in vitro, and impaired homing, egress, and contact hypersensitivity in vivo. Analysis of the T-cell transendothelial migration cascade revealed that PKCzeta/Tiam1/Rac signaling is dispensable for T-cell arrest but is essential for the stabilization of polarization and efficient crawling of T cells on endothelial cells. T cells that lack Tiam1 predominantly transmigrate through individual endothelial cells (transcellular migration) rather than at endothelial junctions (paracellular migration), suggesting that T cells are able to change their route of transendothelial migration according to their polarization status and crawling capacity.

Lymphocyte recruitment to the liver: molecular insights into the pathogenesis of liver injury and hepatitis

Recirculation of blood lymphocytes through the liver occurs under normal conditions as part of the process of immune surveillance. In response to injury or infection recruitment from blood increases and the nature and distribution of the infiltrate will determine the type and outcome of the resulting hepatitis. Recruitment from blood occurs via the hepatic sinusoids and is controlled by interactions between circulating lymphocytes and the highly specialised sinusoidal endothelial cells. This is a low flow vascular bed and the molecular basis of recruitment differs from other tissues. In this review we outline the molecular basis of lymphocyte recruitment to the liver and the effect on it of the local tissue microenvironment and how dysregulation of these processes can lead to uncontrolled inflammation and liver damage.

Leukocyte-endothelial cell interactions are linked to vascular permeability via ICAM-1-mediated signaling

Two key characteristics of the inflammatory response are the recruitment of leukocytes to inflamed tissue as well as changes in vessel permeability. We explored the relationship between these two processes using intravital confocal microscopy in cremasters of anesthetized (65 mg/kg Nembutal ip) mice. We provide direct evidence that intercellular adhesion molecule-1 (ICAM-1) links leukocyte-endothelial cell interactions and changes in solute permeability (Ps). Importantly, we show that arterioles, not just venules, respond to proinflammatory stimuli, thus contributing to microvascular exchange. We identified two independent, ICAM-1-mediated pathways regulating Ps. Under control conditions in wild-type (WT) mice, there is a constitutive PKC-dependent pathway (Ps = 1.0 +/- 0.10 and 2.2 +/- 0.46 x 10(-6) cm/s in arterioles and venules, respectively), which was significantly reduced in ICAM-1 knockout (KO) mice (Ps = 0.54 +/- 0.07 and 0.77 +/- 0.11 x 10(-6) cm/s). The PKC inhibitor bisindolylmaleimid l (1 micromol/l in 0.01% DMSO) decreased P(s) in WT mice to levels similar to those in ICAM-1 KO mice. Likewise, a PKC activator (phorbol-12-myristate-acetate; 1 micromol/l in 0.01% DMSO) successfully restored Ps in ICAM-1 KO vessels to be not different from that of the WT controls. On the other hand, during TNF-alpha-induced inflammation, Ps in WT mice was significantly increased (2-fold in venules and 2.5-fold in arterioles) in a Src-dependent and PKC-independent manner. The blockade of Src (PP2; 2 micromol/l in 0.01% DMSO) but not PKC significantly reduced the TNF-alpha-dependent increase in Ps. We conclude that ICAM-1 plays an essential role in the regulation of Ps in microvessels and that there are two separate (constitutive and inducible) signaling pathways that regulate permeability under normal and inflamed conditions.

Reactive oxygen species and endothelial activation

Endothelial activation refers to a specific change in endothelial phenotype, characterized most notably by an increase in endothelial-leukocyte interactions and permeability, which is pivotal to inflammatory responses in both physiologic and pathologic settings. An increasing body of evidence indicates an important role for reactive oxygen species (ROS)-mediated modulation of signal-transduction pathways in many of the processes involved in endothelial activation. ROS generated by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes may be especially important in this regard. We discuss the evidence implicating redox signaling pathways in the molecular and cellular processes underlying endothelial activation and the role in cardiovascular diseases, and also provide a detailed description of NADPH oxidase regulation in endothelial cells, in view of its likely importance in this context.

Molecular and cellular basis of microvascular perfusion deficits induced by Clostridium perfringens and Clostridium septicum

Reduced tissue perfusion leading to tissue ischemia is a central component of the pathogenesis of myonecrosis caused by Clostridium perfringens. The C. perfringens α-toxin has been shown capable of inducing these changes, but its potential synergy with perfringolysin O (θ-toxin) is less well understood. Similarly, Clostridium septicum is a highly virulent causative agent of spontaneous gas gangrene, but its effect on the microcirculation has not been examined. Therefore, the aim of this study was to use intravital microscopy to examine the effects of C. perfringens and C. septicum on the functional microcirculation, coupled with the use of isogenic toxin mutants to elucidate the role of particular toxins in the resultant microvascular perfusion deficits. This study represents the first time this integrated approach has been used in the analysis of the pathological response to clostridial toxins. Culture supernatants from wild-type C. perfringens induced extensive cell death within 30 min, as assessed by in vivo uptake of propidium iodide. Furthermore, significant reductions in capillary perfusion were observed within 60 min. Depletion of either platelets or neutrophils reduced the alteration in perfusion, consistent with a role for these blood-borne cells in obstructing perfusion. In addition, mutation of either the α-toxin or perfringolysin O structural genes attenuated the reduction in perfusion, a process that was reversed by genetic complementation. C. septicum also induced a marked reduction in perfusion, with the degree of microvascular compromise correlating with the level of the C. septicum α-toxin. Together, these data indicate that as a result of its ability to produce α-toxin and perfringolysin O, C. perfringens rapidly induces irreversible cellular injury and a marked reduction in microvascular perfusion. Since C. septicum induces a similar reduction in microvascular perfusion, it is postulated that this function is central to the pathogenesis of clostridial myonecrosis, irrespective of the causative bacterium.

Clostridial myonecrosis is a life-threatening process induced by infection with species such as C. perfringens and C. septicum. The associated pathology includes muscle death and a characteristic disruption in tissue perfusion. Exotoxins produced by these species have been implicated in the reduction in perfusion. However, how these toxins function in tandem remains unclear. In this study we used intravital microscopy to study microvascular blood flow in a muscle exposed to products of C. perfringens and C. septicum. C. perfringens supernatants induced cellular injury and a progressive reduction in blood flow. Removal of blood-borne platelets and neutrophils from the circulation reduced the alteration in blood flow. In addition, this response was reduced by genetic deletion of either the α-toxin or perfringolysin O, providing the first indication that each of these exotoxins contributes to the reduction in blood supply to affected tissues. Using a similar approach, we observed that C. septicum supernatant induced a comparable reduction in perfusion, which was mediated in part via the C. septicum α-toxin. These results indicate that platelets, neutrophils and multiple clostridial toxins contribute to reduced blood supply and oxygen delivery associated with clostridial infection and suggest that the dominant component of the pathology is toxin-induced cellular injury and death.

Polarized localization of epithelial CXCL11 in chronic obstructive pulmonary disease and mechanisms of T cell egression

The exit of lymphocytes from the interstitium of the lung, across the bronchial epithelium and into the airway lumen, is known as egression, or luminal clearance. Egression is important for immune surveillance and the resolution of inflammation, but the mechanisms involved are unknown. We show that egression of human T cells across the bronchial epithelium is a multistep process, driven in part by a polarized transepithelial gradient of CXCL11 that is up-regulated in patients with chronic obstructive airways disease. Previous studies have shown that T cells can migrate across a disrupted bronchial epithelium, but we provide evidence that egression does not require epithelial injury, and can take place across an intact epithelial barrier. After negotiating the extracellular matrix, the T cell adheres to the basal surface of the bronchial epithelial cell using alpha(4) and leukocyte function associated-1 integrins before crossing the epithelium in an leukocyte function associated-1-dependent way. We demonstrate an egression-dependent decrease in transepithelial resistance across the epithelium without gross alteration in tight-junction proteins. The process of egression has been relatively overlooked when considering the control of leukocyte trafficking in the lung and other epithelial organs. This study highlights the role of the respiratory epithelium in the trafficking of T lymphocytes from the pulmonary interstitium and into the large airways, during the onset and resolution of pulmonary inflammation.

Regulation of T-cell migration by co-stimulatory molecules

Migration of primed T-cells to the antigenic site is an essential event in the development of effective immunity. This process is tightly regulated in order to ensure efficient and specific responses. Most studies have focused on non-specific mediators of T-cell migration, including integrins and chemokines. However, recent studies have highlighted the key role of the T-cell receptor and co-stimulatory molecules in guiding T-cell access to antigenic tissue. Here, we review the experimental evidence for an essential contribution of co-stimulation-mediated molecular interactions regulating T-cell migration in the development of T-cell immunity and tolerance.

Effect of tumor microenvironment modulation on the efficacy of oncolytic virus therapy

BACKGROUND

The tumor microenvironment is being increasingly recognized as an important determinant of tumor progression as well as of therapeutic response. We investigated oncolytic virus (OV) therapy-induced changes in tumor blood vessels and the impact of modulating tumor vasculature on the efficacy of oncolytic virus therapy.

METHODS

Rat glioma cells (D74/HveC) were implanted intracranially in immune-competent rats. Seven days later, the rats (groups of 3-7 rats) were treated with oncolytic virus (hrR3), and, 3 days later, brains were harvested for evaluation. Some rats were treated with angiostatic cRGD peptide 4 days before oncolytic virus treatment. Some rats were treated with cyclophosphamide (CPA), an immunosuppressant, 2 days before oncolytic virus treatment. Changes in tumor vascular perfusion were evaluated by magnetic resonance imaging of live rats and by fluorescence microscopy of tumor sections from rats perfused with Texas red-conjugated lectin immediately before euthanasia. Leukocyte infiltration in tumors was evaluated by anti-CD45 immunohistochemistry, and the presence of oncolytic virus in tumors was evaluated by viral titration. Changes in cytokine gene expression in tumors were measured by quantitative real-time polymerase chain reaction-based microarrays. Survival was analyzed by the Kaplan-Meier method. All statistical tests were two-sided.

RESULTS

Oncolytic virus treatment of experimental rat gliomas increased tumor vascular permeability, host leukocyte infiltration into tumors, and intratumoral expression of inflammatory cytokine genes, including interferon gamma (IFN-gamma). The increase in vascular permeability was suppressed in rats pretreated with cyclophosphamide. Compared with rats treated with hrR3 alone, rats pretreated with a single dose of cRGD peptide before hrR3 treatment had reduced tumor vascular permeability, leukocyte infiltration, and IFN-gamma protein levels (mean IFN-gamma level for hrR3 versus hrR3 + cRGD = 203 versus 65.6 microg/mg, difference = 137 microg/mg, 95% confidence interval = 72.7 to 202.9 microg/mg, P = .006); increased viral titers in tumor tissue; and longer median survival (21 days versus 17 days, P<.001).

CONCLUSIONS

A single dose of angiostatic cRGD peptide treatment before oncolytic virus treatment enhanced the antitumor efficacy of oncolytic virus.

Getting to the site of inflammation: the leukocyte adhesion cascade updated

Neutrophil recruitment, lymphocyte recirculation and monocyte trafficking all require adhesion and transmigration through blood-vessel walls. The traditional three steps of rolling, activation and firm adhesion have recently been augmented and refined. Slow rolling, adhesion strengthening, intraluminal crawling and paracellular and transcellular migration are now recognized as separate, additional steps. In neutrophils, a second activation pathway has been discovered that does not require signalling through G-protein-coupled receptors and the signalling steps leading to integrin activation are beginning to emerge. This Review focuses on new aspects of one of the central paradigms of inflammation and immunity--the leukocyte adhesion cascade.

Stepping out of the flow: capillary extravasation in cancer metastasis

In order for cancer cells to successfully colonize a metastatic site, they must detach from the primary tumor using extracellular matrix-degrading proteases, intravasate and survive in the circulation, evade the immune response, and extravasate the vasculature to invade the target tissue parenchyma, where metastatic foci are established. Though many of the steps of metastasis are widely studied, the precise cellular interactions and molecular alterations associated with extravasation are unknown, and further study is needed to elucidate the mechanisms inherent to this process. Studies of leukocytes localized to inflamed tissue during the immune response may be used to elucidate the process of cancer extravasation, since leukocyte diapedesis through the vasculature involves critical adhesive interactions with endothelial cells, and both leukocytes and cancer cells express similar surface receptors capable of binding endothelial adhesion molecules. Thus, leukocyte extravasation during the inflammatory response has provided a model for transendothelial migration (TEM) of cancer cells. Leukocyte extravasation is characterized by a process whereby rolling mediated by cytokine-activated endothelial selectins is followed by firmer adhesions with beta1 and beta2 integrin subunits to an activated endothelium and subsequent diapedesis, which most likely involves activation of Rho GTPases, regulators of cytoskeletal rearrangements and motility. It is controversial whether such selectin-mediated rolling is necessary for TEM of cancer cells. However, it has been established that similar stable adhesions between tumor and endothelial cells precede cancer cell transmigration through the endothelium. Additionally, there is support for the preferential attachment of tumor cells to the endothelium and, accordingly, site-specific metastasis of cancer cells. Rho GTPases are critical to TEM of cancer cells as well, and some progress has been made in understanding the specific roles of the Rho GTPase family, though much is still unknown. As the mechanisms of cancer TEM are elucidated, new approaches to study and target metastasis may be utilized and developed.

Y-27632, a Rho-associated protein kinase inhibitor, attenuates neuronal cell death after transient retinal ischemia

PURPOSE

Transient retinal ischemia induces the death of retinal neuronal cells. Postischemic damage is associated with the infiltration of leukocytes into the neural tissue through vascular endothelia. The current study aimed to investigate whether this damage was attenuated by the inhibition of Rho/ROCK (Rho kinases) signaling, recently shown to play a critical role in the transendothelial migration of leukocytes.

METHODS

Y-27632, a selective inhibitor of ROCK, was injected intravitreally into rat eyes with transient retinal ischemia. Cell loss of the ganglion cell layer (GCL) and thinning of the inner plexiform layer (IPL) with and without the administration of Y-27632 were evaluated by histological analysis, TUNEL assay and retrograde labeling of retinal ganglion cells (RGCs). To examine the attenuation of leukocyte infiltration in postischemic retinas with the administration of Y-27632, silver nitrate staining and immunohistochemistry using an anti-LCA antibody were performed.

RESULTS

Cell loss of the GCL and thinning of the IPL were significantly attenuated when 100 nmol Y-27632 was administered within three hours of the induction of ischemia. TUNEL assay and retrograde labeling of RGCs showed a decreased number of apoptotic cells and an increased number of RGCs in Y-27632-injected retinas. Moreover, silver nitrate staining and immunohistochemical analysis using an anti-LCA antibody showed that Y-27632 injection dramatically inhibited leukocyte infiltration and endothelial disarrangement.

CONCLUSIONS

Our data suggest that inhibition of Rho/ROCK signaling offers neuroprotective therapy against postischemic neural damage, by regulating leukocyte infiltration in the neural tissue.

Angiopoietin-1 Requires p190 RhoGAP to Protect against Vascular Leakage in Vivo

Angiopoietin-1 (Ang-1), a ligand of the endothelium-specific receptor Tie-2, inhibits permeability in the mature vasculature, but the mechanism remains unknown. Here we show that Ang-1 signals Rho family GTPases to organize the cytoskeleton into a junction-fortifying arrangement that enhances the permeability barrier function of the endothelium. Ang-1 phosphorylates Tie-2 and its downstream effector phosphatidylinositol 3-kinase. This induces activation of one endogenous GTPase, Rac1, and inhibition of another, RhoA. Loss of either part of this dual effect abrogates the cytoskeletal and anti-permeability actions of Ang-1, suggesting that coordinated GTPase regulation is necessary for the vessel-sealing effects of Ang-1. p190 RhoGAP, a GTPase regulatory protein, provides this coordinating function as it is phosphorylated by Ang-1 treatment, requires Rac1 activation, and is necessary for RhoA inhibition. Ang-1 prevents the cytoskeletal and pro-permeability effects of endotoxin but requires p190 RhoGAP to do so. Treatment with p190 RhoGAP small interfering RNA completely abolishes the ability of Ang-1 to rescue endotoxemia-induced pulmonary vascular leak and inflammation in mice. We conclude that Ang-1 prevents vascular permeability by regulating the endothelial cytoskeleton through coordinated and opposite effects on the Rho GTPases Rac1 and RhoA. By linking Rac1 activation and RhoA inhibition, p190 RhoGAP is critical to the protective effects of Ang-1 against endotoxin. These results provide mechanistic evidence that targeting the endothelium through Tie-2 may offer specific therapeutic strategies in life-threatening endotoxemic conditions such as sepsis and acute respiratory distress syndrome.

Endothelial signaling by Ig-like cell adhesion molecules

The migration of leukocytes across the endothelial lining of the vascular wall requires a complicated series of adhesion and signaling events. Endothelial Ig-like cell adhesion molecules (IgCAMs) such as intercellular adhesion molecule-1 play an important role, not only as ligands for leukocyte integrins, but also as signaling initiators. Clustering these IgCAMs triggers a wide range of events in the endothelial cells' interior, of which activation of Rho-like GTPases, induction of cytoskeletal changes, and the transient modulation of cell-cell contact are key events. This review discusses recent insights into this IgCAM-driven endothelial signaling and its consequences for leukocyte transendothelial migration.

C3 exoenzymes, novel insights into structure and action of Rho-ADP-ribosylating toxins

The family of C3-like exoenzymes comprises seven bacterial ADP-ribosyltransferases of different origin. The common hallmark of these exoenzymes is the selective N-ADP-ribosylation of the low molecular mass GTP-binding proteins RhoA, B, and C and inhibition of signal pathways controlled by Rho GTPases. Therefore, C3-like exoenzymes were applied as pharmacological tools for analyses of cellular functions of Rho protein in numerous studies. Recent structural and functional analyses of C3-like exoenzymes provide detailed information on the molecular mechanisms and functional consequences of ADP-ribosylation catalyzed by these toxins. More recently additional non-enzymatic actions of C3-like ADP-ribosyltransferases have been identified showing that C3 transferases from Clostridium botulinum and Clostridium limosum form a GDI-like complex with the Ras-like low molecular mass GTPase Ral without ADP-ribosylation. These results add novel information on the molecular mode of action(s) of C3-like exoenzymes and are discussed in this review.

Induction of transient macroapertures in endothelial cells through RhoA inhibition by Staphylococcus aureus factors

The GTPase RhoA is a major regulator of the assembly of actin stress fibers and the contractility of the actomyosin cytoskeleton. The epidermal cell differentiation inhibitor (EDIN) and EDIN-like ADP-ribosyltransferases of Staphylococcus aureus catalyze the inactivation of RhoA, producing actin cable disruption. We report that purified recombinant EDIN and EDIN-producing S. aureus provoke large transcellular tunnels in endothelial cells that we have named macroapertures (MAs). These structures open transiently, followed by the appearance of actin-containing membrane waves extending over the aperture. Disruption of actin cables, either directly or indirectly, through rhoA RNAi knockdown also triggers the formation of MAs. Intoxication of endothelial monolayers by EDIN produces a loss of barrier function and provides direct access of the endothelium basement membrane to S. aureus.