GCP-2/CXCL6 synergizes with other endothelial cell-derived chemokines in neutrophil mobilization and is associated with angiogenesis in gastrointestinal tumors

The precise role of chemokines in neovascularization during inflammation or tumor growth is not yet fully understood. We show here that the chemokines granulocyte chemotactic protein-2 (GCP-2/CXCL6), interleukin-8 (IL-8/CXCL8), and monocyte chemotactic protein-1 (MCP-1/CCL2) are co-induced in microvascular endothelial cells after stimulation with pro-inflammatory stimuli. In contrast with its weak proliferative effect on endothelial cells, GCP-2 synergized with MCP-1 in neutrophil chemotaxis. This synergy may represent a mechanism for tumor development and metastasis by providing efficient leukocyte infiltration in the absence of exogenous immune modulators. To mimic endothelial cell-derived GCP-2 in vivo, GCP-2 was intravenously injected and shown to provoke a dose-dependent systemic response, composed of an immediate granulopenia, followed by a profound granulocytosis. By immunohistochemistry, GCP-2 was further shown to be expressed by endothelial cells from human patients with gastrointestinal (GI) malignancies. GCP-2 staining correlated with leukocyte infiltration into the tumor and with the expression of the matrix metalloproteinase-9 (MMP-9/gelatinase B). Together with previous findings, these data suggest that the production of GCP-2 by endothelial cells within the tumor can contribute to tumor development through neovascularization due to endothelial cell chemotaxis and to tumor cell invasion and metastasis by attracting and activating neutrophils loaded with proteases that promote matrix degradation.     

Monokine-induced gene expression of a human endothelial cell-derived neutrophil chemotactic factor

Monokines have been increasingly recognized as communication signals that interact with both immune and non-immune cells during inflammation. Specifically, interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) possess potent effector activities on various cell types. We present novel data demonstrating that human endothelial cells are a major source of a neutrophil chemotactic factor (NCF) synthesized upon stimulation with either IL-1 alpha, IL-1 beta, or TNF-alpha; but not with interleukin-6 (IL-6). Northern blot analysis demonstrated that 20 ng/ml of either IL-1 or TNF-alpha could induce endothelial cells to express significant levels of NCF mRNA, while IL-6 was not active in this system. These data demonstrate that monokines play an important role in mediating acute inflammation via induction of an endothelial cell-derived NCF.     

An endothelial cell-derived growth factor

Cell-free plasma-derived serum (PDS) is deficient in the platelet- derived growth factor and will not support the growth of 3T3 cells, fibroblasts, or smooth muscle cells. However, when PDS-containing medium is preincubated with endothelial cells, the medium becomes modified so that it will support growth. The activity produced by the endothelial cells results from a polypeptide of 10,000 to 30,000 daltons which has several features that differ from those of the platelet-derived growth factor, including heat instability and lack of adsorption to CM Sephadex.     

The effects and comparative differences of neutrophil specific chemokines on neutrophil chemotaxis of the neonate

Neutrophil specific chemokines are potent chemoattractants for neutrophils. IL-8/CXCL8 is the most extensively studied member of this group, and its concentrations increase during inflammatory conditions of the newborn infant including sepsis and chronic lung disease. A significant amount of information exists on the effects of IL-8/CXCL8 on neutrophil chemotaxis of neonates, but little is known about the other neutrophil specific chemokines. The aim of this study was to determine the relative potency of the neutrophil specific chemokines on chemotaxis of neonatal neutrophils and to compare this effect with the effect on adult neutrophils. Neutrophils were isolated from cord blood or healthy adult donors and incubated in a Neuroprobe chemotaxis chamber. Chemokine concentrations ranging from 1-1000 ng/mL were used. Differences in chemotactic potency existed among the seven neutrophil specific chemokines. Specifically, at 100 ng/mL, the order was IL-8/CXCL8>GRO-alpha/CXCL1>GCP-2/CXCL6>NAP-2/CXCL7>ENA-78/CXCL5>GRO-gamma/CXCL2>GRO-beta/CXCL3. This pattern was observed for adult and neonatal neutrophils. We conclude that (1) neutrophils from cord blood exhibit the same pattern of potency for each ELR chemokine as neutrophils from adults, and (2) migration of neonatal neutrophils is significantly less than that of adults at every concentration examined except the lowest (1 ng/mL).     

Proteome of endothelial cell-derived procoagulant microparticles

Microparticles (MP) are small membrane vesicles that are released from cells upon activation or during apoptosis. Cellular MP in body fluids constitute a heterogeneous population, differing in cellular origin, numbers, size, antigenic composition and functional properties. MP support coagulation by exposure of tissue factor (TF), the initiator of coagulation in vivo. Moreover, MP may transfer bioactive molecules to other cells, thereby stimulating them to produce cytokines, cell-adhesion molecules, growth factors and TF, and modulate endothelial functions. However, a comprehensive characterization of the antigenic composition of MP has been poorly defined. This study describes the protein composition of endothelial cell (EC)-derived MP (EMP) using a proteomic approach. MS analysis indicated the presence of newly described protein such as metabolic enzymes, proteins involved in adhesion and fusion processes, members of protein folding event, cytoskeleton associated proteins and nucleosome. In conclusion, circulating EMP behave as an actual storage pool, able to disseminate blood-borne TF activity and other bioactive effectors, as confirmed by our experiments showing an increased procoagulant activity of EC exposed to EMP.     

Regulated expression of endothelial cell-derived lipase

A lipoprotein lipase-like gene was recently cloned from endothelial cells. In vitro functional experiments have suggested that this endothelial-derived lipase (EDL) has phospholipase activity, and preliminary in vivo studies have suggested a role in the regulation of high-density lipoprotein metabolism. To investigate local control of lipase activity and lipid metabolism in the blood vessel wall, we have examined the regulation of EDL expression in cultured human umbilical vein and coronary artery endothelial cells. EDL mRNA levels were upregulated in both cell types by inflammatory cytokines implicated in vascular disease etiology, including TNF-alpha and IL-1beta. In addition, both fluid shear stress and cyclic stretch were found to increase the EDL mRNA levels in these cultured cells. This highly regulated expression of EDL in vascular endothelial cells suggests that this recently identified lipase is intricately involved in modulating vessel wall lipid metabolism and may play a role in vascular diseases such as atherosclerosis.     

Application of proteomics to neutrophil biology

Polymorphonuclear leukocytes or neutrophils are a primary effector cell of the innate immune system and contribute to the development of adaptive immunity. Neutrophils participate in both the initiation and resolution of inflammatory responses through a series of highly coordinated molecular and phenotypic changes. To accomplish these changes, neutrophils express numerous receptors and use multiple overlapping and redundant signal transduction pathways. Dysregulation of the activation or resolution pathways plays a role in a number of human diseases. A comprehensive understanding of the regulation of neutrophil responses can be provided by high throughput proteomic technologies and sophisticated computational analysis. The first steps in the application of proteomics to understanding neutrophil biology have been taken. Here we review the application of expression, structural, and functional proteomic studies to neutrophils. Although defining the complex molecular events associated with neutrophil activation is in the early stages, the data generated to date suggest that proteomic technologies will dramatically enhance our understanding of neutrophil biology.     

Effects of CXC chemokines on neutrophil activation and sequestration in hepatic vasculature

The initiating step of neutrophil-induced cytotoxicity in the liver is the recruitment of these phagocytes into sinusoids. The aim of our study was to compare the efficacy of systemic exposure with individual inflammatory mediators on neutrophil activation and sequestration in the hepatic vasculature of C3Heb/FeJ mice as assessed by flow cytometry and histochemistry, respectively. The CXC chemokine macrophage inflammatory protein-2 (MIP-2; 20 microg/kg) induced a time-dependent upregulation of Mac-1 (318% at 4 h) and shedding of L-selectin (41% at 4 h). MIP-2 treatment caused a temporary increase of sinusoidal neutrophil accumulation at 0.5 h [97 +/- 6 polymorphonuclear leukocytes (PMN)/50 high-power fields (HPF)], which declined to baseline (8 +/- 2) at 4 h. The CXC chemokine KC was largely ineffective in activating neutrophils or recruiting them into the liver. Cytokines (tumor necrosis factor-alpha and interleukin-1alpha) and cobra venom factor substantially increased Mac-1 expression and L-selectin shedding on neutrophils and caused stable sinusoidal neutrophil accumulation (170-220 PMN/50 HPF). Only cytokines induced venular neutrophil margination. Thus CXC chemokines in circulation are less effective than cytokines or complement in activation of neutrophils and their recruitment into the hepatic vasculature in vivo.     

Molecular cloning of nonsecreted endothelial cell-derived lipase isoforms

To expand our knowledge of factors involved in lipid metabolism in the blood vessel wall, we have cloned unique molecular isoforms of endothelial cell-derived lipase (EDL) (HGMW-approved symbol/LIPG). One isoform encoded a truncated protein (EDL2a) lacking the first 80 amino acid residues of the previously characterized EDL1a isoform, including the signal peptide. A similar second clone (EDL2b) was identified that lacked not only the first 80 amino acids, but also a 74-amino-acid region that encodes a portion of the lid domain. RT-PCR analysis confirmed expression of EDL2a/2b isoforms in several human tissues and cultured cells, including endothelial cells. Western blot and immunofluorescence studies using stable transfectants revealed that EDL2a and EDL2b were localized in the cytosol, while, EDL1a was secreted into the culture medium. Cell extracts of EDL2a/2b transfectants did not have triglyceride or phospholipase activity. Thus endothelial cells express three EDL isoforms, two of which remain intracellular and do not function as lipases.     

Carboxyterminal cleavage of the chemokines MIG and IP-10 by gelatinase B and neutrophil collagenase

Proteolytic processing is an important regulatory mechanism for chemokines. Matrix metalloproteinases (MMPs), such as gelatinase A/MMP-2 and gelatinase B/MMP-9, are known to process the aminoterminal end of various chemokines, including interleukin-8 (IL-8/CXCL-8) and monocyte chemotactic protein-3 (MCP-3/CXCL-7). In the present study, two proteases, gelatinase B and neutrophil collagenase/MMP-8, are shown for the first time to process the carboxyterminal end of two chemokines, monokine induced by interferon (IFN)-gamma (MIG/CXCL-9) and IFN-inducible protein-10 (IP-10/CXCL-10). Neutrophil collagenase degrades MIG into small fragments and cleaves IP-10 behind positions 71 and 73. Gelatinase B degrades IP-10 and cleaves MIG at three different sites in its extended carboxyterminal region. This results in the formation of MIG(1-94), MIG(1-93), and MIG(1-90). In general, gelatinase B was more efficient than neutrophil collagenase in processing these chemokines. Alignment of the CXC chemokines with the respective cleavage sites by both MMPs identified the ELR motif as a possible determinant for amino terminal cleavage by these MMPs.     

Effects of endothelial basement membrane on neutrophil adhesion and migration

The influence of the sub-endothelial basement membrane (BM) on the adhesion and migration of leukocytes is not well-defined. We therefore investigated the behaviour of human neutrophils on purified BM proteins and on BM deposited by short- or long-term cultures of endothelial cells (EC). The adhesion, but not migration velocities, of neutrophils activated with interleukin-8 was dependent on the coating concentrations of purified collagen, laminin or fibronectin. In contrast, adhesion was similar on matrices deposited by 3-day or 20-day cultures of EC, but neutrophils migrated more slowly on the distinct BM that formed over 20 days. In addition, while adhesion on all surfaces was greatly reduced when neutrophils were treated with antibody against β₂-integrins, antibody against β₁-integrins only inhibited adhesion to the 20-day BM. Thus, the native BM has distinct effects on integrin usage and migration by neutrophils, which are not reproduced by purified proteins or matrix deposited early during endothelial culture.     

Divergent roles of murine neutrophil chemokines in hemorrhage induced priming for acute lung injury

Neutrophil associated lung injury is identified with a variety of local and systemic priming insults. In vitro studies have shown that TNF-alpha mediated suppression of neutrophil apoptosis is due to the secretion of interleukin-8 (IL-8), a human chemokine shown to alter neutrophil chemotaxis. Our initial in vitro antibody neutralization studies with neutrophil chemotactic proteins, keratinocyte-derived chemokine (KC) and macrophage inflammatory protein-2alpha (MIP-2alpha), mouse IL-8 homologues, indicate that MIP-2alpha but not KC appears to mediate TNF-alpha suppression of mouse neutrophil apoptosis. Therefore, we hypothesized that in vivo neutralization of KC or MIP-2alpha during an initial priming insult would produce differential effects on the extent of lung injury by restoring normal neutrophil apoptotic function. To assess this, mice were hemorrhaged followed with septic challenge at 24 h. Antibody against KC or MIP-2alpha or a nonspecific IgG was given during resuscitation immediately following hemorrhage. Anti-MIP-2alpha treatment resulted in a significant reduction in lung tissue IL-6 and myeloperoxidase levels. Percentage of neutrophil apoptosis increased significantly in the anti-KC group. Tissue and plasma KC and MIP-2alpha were reduced in their respective treatment groups. These data suggest that KC and MIP-2alpha differ in their mediation of neutrophil function (apoptosis and chemotaxis) and contribution to the pathogenesis of lung injury following hemorrhage subsequent to sepsis.     

Activation of endothelial extracellular signal-regulated kinase is essential for neutrophil transmigration: potential involvement of a soluble neutrophil factor in endothelial activation

During an inflammatory response induced by infection or injury, leukocytes traverse the endothelial barrier into the tissue space. Extravasation of leukocytes is a multistep process involving rolling, tethering, firm adhesion to the endothelium, and finally, transendothelial migration, the least characterized step in the process. The resting endothelium is normally impermeable to leukocytes; thus, during inflammation, intracellular signals that modulate endothelial permeability are activated to facilitate the paracellular passage of leukocytes. Using a static in vitro assay of neutrophil transmigration across human umbilical vein endothelium, a panel of inhibitors of intracellular signaling was screened for their ability to inhibit transmigration. PD98059, a specific inhibitor of extracellular signal-regulated kinase (ERK) 1/2 activation, inhibited both transmigration across TNF-alpha-activated endothelium and transmigration induced by the chemoattractant fMLP in a dose-dependent manner. PD98059 did not inhibit neutrophil chemotaxis in the absence of an endothelial barrier nor neutrophil adhesion to the endothelium, suggesting that its effect was on the endothelium, and furthermore, that endothelial ERK activation may be important for transmigration. We demonstrate in this study that endothelial ERK is indeed activated during neutrophil transmigration and that its activation is dependent on the addition of neutrophils to the endothelium. Further characterization showed that the trigger for endothelial ERK activation is a soluble protein of molecular mass approximately 30 kDa released from neutrophils after activation.     

Electronegative low-density lipoprotein induces cardiomyocyte apoptosis indirectly through endothelial cell-released chemokines

Cardiomyocyte apoptosis has a critical role in the pathogenesis of heart failure. L5, the most negatively charged subfraction of human plasma low-density lipoprotein (LDL), induces several atherogenic responses in endothelial cells (ECs), including apoptosis. We hypothesized that L5 also contributes to cardiomyocyte apoptosis and studied whether it does so indirectly by inducing the secretion of factors from ECs. We examined apoptosis of rat cardiomyocytes treated with culture-conditioned medium (CCM) of rat ECs that were exposed to L5 or L1 (the least negatively charged LDL subfraction). Apoptosis at early and late time points was twofold greater in cardiomyocytes treated with L5 CCM than in those treated with L1 CCM. The indirect effect of L5 on cardiomyocyte apoptosis was significantly reduced by pretreating ECs with inhibitors of phosphatidylinositol 3-kinase (PI3K) or CXC receptor 2 (CXCR2). Studies with cytokine protein arrays revealed that L5 CCM, but not L1 CCM, contained high levels of ELR(+) CXC chemokines, including lipopolysaccharide-induced chemokine (LIX) and interleukin (IL)-8. The L5-induced release of these chemokines from ECs was abolished by inhibiting the lectin-like oxidized LDL receptor-1 (LOX-1). Addition of recombinant LIX or IL-8 to CCM-free cardiomyocyte cultures increased apoptosis and enhanced production of tumor necrosis factor (TNF)-α and IL-1β by increasing the translocation of NF-κB into the nucleus; these effects were attenuated by inhibiting PI3K and CXCR2. In conclusion, L5 may indirectly induce cardiomyocyte apoptosis by enhancing secretion of ELR(+) CXC chemokines from ECs, which in turn activate CXCR2/PI3K/NF-κB signaling to increase the release of TNF-α and IL-1β.     

Statins affect the presentation of endothelial chemokines by targeting to multivesicular bodies

BACKGROUND: In addition to lowering cholesterol, statins are thought to beneficially modulate inflammation. Several chemokines including CXCL1/growth-related oncogene (GRO)-α, CXCL8/interleukin (IL)-8 and CCL2/monocyte chemoattractant protein (MCP)-1 are important in the pathogenesis of atherosclerosis and can be influenced by statin-treatment. Recently, we observed that atorvastatin-treatment alters the intracellular content and subcellular distribution of GRO-α in cultured human umbilical vein endothelial cells (HUVECs). The objective of this study was to investigate the mechanisms involved in this phenomenon. METHODOLOGY/ PRINCIPAL FINDINGS: The effect of atorvastatin on secretion levels and subcellular distribution of GRO-α, IL-8 and MCP-1 in HUVECs activated by interleukin (IL)-1β were evaluated by ELISA, confocal microscopy and immunoelectron microscopy. Atorvastatin increased the intracellular contents of GRO-α, IL-8, and MCP-1 and induced colocalization with E-selectin in multivesicular bodies. This effect was prevented by adding the isoprenylation substrate GGPP, but not the cholesterol precursor squalene, indicating that atorvastatin exerts these effects by inhibiting isoprenylation rather than depleting the cells of cholesterol. CONCLUSIONS/ SIGNIFICANCE: Atorvastatin targets inflammatory chemokines to the endocytic pathway and multivesicular bodies and may contribute to explain the anti-inflammatory effect of statins at the level of endothelial cell function.     

Expression of chemokines on the surface of different human endothelia

Expression of chemokines at the endothelial surface depends on their rate of synthesis, the capacity of the endothelium to bind chemokines and the rate of clearance from the surface. The aim of this study was to establish how these factors depend on the chemokine and the tissue of origin of the endothelium. Human lung and dermal microvascular endothelium, saphenous and umbilical vein endothelium, and a bone marrow endothelial line were assayed in vitro. Chemokine expression, localization and transport was measured by immunoassay and confocal microscopy. All endothelia bound CCL3 (MIP-1alpha), CCL5 (RANTES) and CXCL10 (IP-10). CCL3 and CCL5 bound at high levels, and CXCL10 bound less strongly. However, the profile of chemokine expression varied between endothelia, and different chemokines were shown to bind to the endothelial surface by distinct mechanisms. The half-life of CCL3 and CCL5 at the cell surface was approximately 30 min and chemokines were cleared primarily by endocytosis into caveolae. Endothelia from different tissues synthesize distinctive sets of chemokines, but the profile of surface-expressed chemokines also depends on the distinctive characteristics of each endothelia. These two mechanisms may contribute to the differential recruitment of leucocyte subsets to different tissues.