Differences in sulfation patterns of heparan sulfate derived from human bone marrow and umbilical vein endothelial cells

Structural glycobiology - from enzymes to organelles

Biological carbohydrate polymers represent some of the most complex molecules in life, enabling their participation in a huge range of physiological functions. The complexity of biological carbohydrates arises from an extensive enzymatic repertoire involved in their construction, deconstruction and modification. Over the past decades, structural studies of carbohydrate processing enzymes have driven major insights into their mechanisms, supporting associated applications across medicine and biotechnology. Despite these successes, our understanding of how multienzyme networks function to create complex polysaccharides is still limited. Emerging techniques such as super-resolution microscopy and cryo-electron tomography are now enabling the investigation of native biological systems at near molecular resolutions. Here, we review insights from classical in vitro studies of carbohydrate processing, alongside recent in situ studies of glycosylation-related processes. While considerable technical challenges remain, the integration of molecular mechanisms with true biological context promises to transform our understanding of carbohydrate regulation, shining light upon the processes driving functional complexity in these essential biomolecules.

Endothelial cell surface limits coagulation without modulating the antithrombin potency

Antithrombin (AT) binds in vitro and in vivo to endothelial cells through various receptors, including heparan sulphate glycosaminoglycan (HSPG) that could modulate the AT activity. A thrombin generation assay (TGA) was set up at the surface of HUVEC and HMVEC evaluating their participation in the coagulation-anticoagulation processes. TGA induced by 0.5 pM Tissue Factor was performed in normal or AT-deficient plasma spiked with various amounts of recombinant or plasma-derived AT (0, 0.1, 0.5 and 1.0 U/ml). To evaluate the role of HSPG or cellular anticoagulant receptors, cells were treated or not with heparin, a mix of heparanase I, II and III, a neutralizing anti-Endothelial Protein C Receptor (EPCR) or with an anti-Tissue Factor Pathway Inhibitor (TFPI) antibody. The presence of the cells diminished the TG in normal plasma and maintained anticoagulation in AT-deficient plasma. Spiking the AT-deficient plasma with different doses of AT demonstrated that the cells did not amplify the anticoagulant activity of AT. The recombinant AT binds the cells with a higher avidity than the plasma-derived one but this did not affect its anticoagulant potency. Moreover both bindings are independent of the HSPG. The antithrombotic activity kept in absence of AT was not inhibited by blocking antibodies directed against EPCR or TFPI. Our data did not reveal a major co-factor activity for AT from endothelial cells that could have been mediated by HSPG. In contrast, it reveals the presence of alternative anti-coagulant system(s) in two venous cell types that maintain an antithrombotic activity.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Incipient renal transplant dysfunction associates with tubular syndecan-1 expression and shedding

Syndecan-1 is a transmembrane heparan sulfate proteoglycan involved in regenerative growth and cellular adhesion. We hypothesized that the induction of tubular syndecan-1 is a repair response to incipient renal damage in apparently stable, uncomplicated renal transplant recipients. We quantified tubular syndecan-1 in unselected renal protocol biopsies taken 1 yr after transplantation. Spearman rank correlation analysis revealed an inverse correlation between tubular syndecan-1 expression and creatinine clearance at the time of biopsy ( r = −0.483, P < 0.03). In a larger panel of protocol and indication biopsies from renal transplant recipients, tubular syndecan-1 correlated with tubular proliferation marker Ki67 ( r = 0.518, P < 0.0001). In a rat renal transplantation model, 2 mo after transplantation, mRNA expression of syndecan-1 and its major sheddase, A disintegrin and metalloproteinase-17, were upregulated (both P < 0.03). Since shed syndecan-1 might end up in the circulation, in a stable cross-sectional human renal transplant population ( n = 510), we measured plasma syndecan-1. By multivariate regression analysis, we showed robust independent associations of plasma syndecan-1 with renal (plasma creatinine and plasma urea) and endothelial function parameters (plasma VEGF-A, all P < 0.01). By various approaches, we were not able to localize syndecan-1 in vessel wall or endothelial cells, which makes shedding of syndecan-1 from the endothelial glycocalyx unlikely. Our data suggest that early damage in transplanted kidneys induces repair mechanisms within the graft, namely, tubular syndecan-1 expression for tubular regeneration and VEGF production for endothelial repair. Elevated plasma syndecan-1 levels in renal transplantation patients might be interpreted as repair/survival factor related to loss of tubular and endothelial function in transplanted kidneys.

The endothelial deprotection hypothesis for lupus pathogenesis: the dual role of C1q as a mediator of clearance and regulator of endothelial permeability

Systemic lupus erythematosus (SLE) is a heterogeneous multifactorial systemic autoimmune disease affecting several organs. SLE can start relatively early in life and results in impaired quality of life and shortened life expectancy because of a gradual disease progression leading to cardiovascular, renal and neoplastic disease. The basic mechanisms of the pathogenesis of the disease still remain to be clarified. It is clear that complement proteins play a key and complex role in the development of SLE. Complement component C1q has been known to be a fundamental component of lupus development, but most explanations focus on its role in apoptotic debris removal. Importantly, C1q was recently found to play a key role in the maintenance of vascular endothelial integrity.We suggest that apoptotic products, endothelial cells and extracellular matrix components, which display negatively charged moieties, compete for binding to molecules of the innate humoral immune response, like C1q. Genetic or acquired factors leading to an increased load of apoptotic cell debris and decrease or absence of C1q therefore interfere with the regulation of endothelial permeability and integrity. Furthermore, we suggest that lupus is the net result of an imbalance between the two functions of immune clearance and vascular endothelial integrity maintenance, an imbalance triggered and sustained by autoimmunity, which skews C1q consumption by IgG-mediated complement classical pathway activation on autoantigens. In this triangle of innate clearance, autoimmunity and endothelial integrity, C1q plays a central role.Hence, we interpret the pathogenesis of lupus by identifying three key components, namely innate immune clearance, autoimmunity and endothelial integrity and we establish a link between these components based on the protective role that innate clearance molecules play in endothelial renewal. By including the vasoprotective role of C1q in the interpretation of SLE development we attempt to provide novel explanations for the symptoms, organ damage, diagnostic and therapeutic difficulties of the disease.

The endothelial deprotection hypothesis for lupus pathogenesis: the dual role of C1q as a mediator of clearance and regulator of endothelial permeability

Systemic lupus erythematosus (SLE) is a heterogeneous multifactorial systemic autoimmune disease affecting several organs. SLE can start relatively early in life and results in impaired quality of life and shortened life expectancy because of a gradual disease progression leading to cardiovascular, renal and neoplastic disease. The basic mechanisms of the pathogenesis of the disease still remain to be clarified. It is clear that complement proteins play a key and complex role in the development of SLE. Complement component C1q has been known to be a fundamental component of lupus development, but most explanations focus on its role in apoptotic debris removal. Importantly, C1q was recently found to play a key role in the maintenance of vascular endothelial integrity.

We suggest that apoptotic products, endothelial cells and extracellular matrix components, which display negatively charged moieties, compete for binding to molecules of the innate humoral immune response, like C1q. Genetic or acquired factors leading to an increased load of apoptotic cell debris and decrease or absence of C1q therefore interfere with the regulation of endothelial permeability and integrity. Furthermore, we suggest that lupus is the net result of an imbalance between the two functions of immune clearance and vascular endothelial integrity maintenance, an imbalance triggered and sustained by autoimmunity, which skews C1q consumption by IgG-mediated complement classical pathway activation on autoantigens. In this triangle of innate clearance, autoimmunity and endothelial integrity, C1q plays a central role.

Hence, we interpret the pathogenesis of lupus by identifying three key components, namely innate immune clearance, autoimmunity and endothelial integrity and we establish a link between these components based on the protective role that innate clearance molecules play in endothelial renewal. By including the vasoprotective role of C1q in the interpretation of SLE development we attempt to provide novel explanations for the symptoms, organ damage, diagnostic and therapeutic difficulties of the disease.

Exogenous endothelial cells as accelerators of hematopoietic reconstitution

Despite the successes of recombinant hematopoietic-stimulatory factors at accelerating bone marrow reconstitution and shortening the neutropenic period post-transplantation, significant challenges remain such as cost, inability to reconstitute thrombocytic lineages, and lack of efficacy in conditions such as aplastic anemia. A possible means of accelerating hematopoietic reconstitution would be administration of cells capable of secreting hematopoietic growth factors. Advantages of this approach would include: a) ability to regulate secretion of cytokines based on biological need; b) long term, localized production of growth factors, alleviating need for systemic administration of factors that possess unintended adverse effects; and c) potential to actively repair the hematopoietic stem cell niche. Here we overview the field of hematopoietic growth factors, discuss previous experiences with mesenchymal stem cells (MSC) in accelerating hematopoiesis, and conclude by putting forth the rationale of utilizing exogenous endothelial cells as a novel cellular therapy for acceleration of hematopoietic recovery.

Stromal-derived factor-1/CXCR4 signaling: indispensable role in homing and engraftment of hematopoietic stem cells in bone marrow

Homing and engraftment of hematopoietic stem/progenitor cells (HSPCs) in bone marrow is the major determining factor in success of hematopoietic stem cell transplantation. This is a complex, multistep process orchestrated by the coordinated interplay between adhesion molecules, cytokines, growth factors, and regulatory cofactors, many of which remain to be defined. Recent studies have highlighted the pivotal role of unique stromal-derived factor-1 (SDF-1)/CXCR4 signaling in the regulation of HSPC homing and subsequent engraftment. In addition, studies suggest that SDF-1/CXCR4 signaling acts as an essential survival-promoting factor of transplanted HSPCs as well as maintenance of quiescent HSCs in bone marrow niche. These pleiotropic effects exerted by SDF-1/CXCR4 axis make this unique signaling initiator very promising, not only for optimal hematopoietic reconstitution but also for the development of innovative approaches to achieve restoration, regeneration, or repair of other damaged tissues potentially amendable to reversal by stem cell transplantation. This goal can only be achieved when the role of SDF-1/CXCR4 axis in hematopoietic transplantation is clearly defined. Hence, this review presents current knowledge of the mechanisms through which SDF-1/CXCR4 signaling promotes restoration of hematopoiesis by regulating the homing and engraftment of HSPCs.

Dextran sulfate and stromal cell derived factor-1 promote CXCR4 expression and improve bone marrow homing efficiency of infused hematopoietic stem cells

Although the homing of hematopoietic stem cells (HSC) to the bone marrow (BM) is a crucial step in hematopoietic development and BM repopulation, the mechanisms underlying these processes have not been fully clarified. Recent studies suggest that interaction between the chemokine receptor CXCR4 and its ligand, stromal cell-derived factor 1 (SDF-1), plays a critical role in these processes. In addition, dextran sulfate increases plasma SDF-1 levels in mice and nonhuman primates. Thus, we examined the effects of preconditioning with SDF-1 and dextran sulfate on the homing efficiency of HSCs following BM transplantation in mice. We found that the preconditioning of donor mice with either SDF-1 or dextran sulfate enhanced the homing efficiency of infused HSCs in vivo. The greatest effects were obtained with dextran sulfate. Moreover, reverse transcriptase polymerase chain reaction analysis demonstrated that SDF-1 and dextran sulfate increased transcription of a variety of homing-related genes, including those for CXCR4, lymphocyte function associated antigen-1, matrix metalloproteinase-9, very late antigen-4/5, and macrophage inflammatory protein-1. We suggest that whereas SDF-1 directly acts to upregulate CXCR4 expression in HSCs, dextran sulfate acts via multiple pathways involved in the induction of various homing-related molecules, in addition to SDF-1. Thus, preconditioning donors with dextran sulfate offers a novel clinical approach for improving the homing and engraftment of HSCs in the BM.

Improved workup for glycosaminoglycan disaccharide analysis using CE with LIF detection

This work describes improved workup and instrumental conditions to enable robust, sensitive glycosaminoglycan (GAG) disaccharide analysis from complex biological samples. In the process of applying CE with LIF to GAG disaccharide analysis in biological samples, we have made improvements to existing methods. These include (i) optimization of reductive amination conditions, (ii) improvement in sensitivity through the use of a cellulose cleanup procedure for the derivatization, and (iii) optimization of separation conditions for robustness and reproducibility. The improved method enables analysis of disaccharide quantities as low as 1 pmol prior to derivatization. Biological GAG samples were exhaustively digested using lyase enzymes, the disaccharide products and standards were derivatized with the fluorophore 2-aminoacridone and subjected to reversed polarity CE-LIF detection. These conditions resolved all known chondroitin sulfate (CS) disaccharides or 11 of 12 standard heparin/heparan sulfate disaccharides, using 50 mM phosphate buffer, pH 3.5, and reversed polarity at 30 kV with 0.3 psi pressure. Relative standard deviation in migration times of CS ranged from 0.1 to 2.0% over 60 days, and the relative standard deviations of peak areas were less than 3.2%, suggesting that the method is reproducible and precise. The CS disaccharide compositions are similar to those obtained by our group using tandem MS. The reversed polarity CE-LIF disaccharide analysis protocol yields baseline resolution and quantification of heparin/heparan sulfate and CS/dermatan sulfate disaccharides from both standard preparations and biologically relevant proteoglycan samples. The improved CE-LIF method enables disaccharide quantification of biologically relevant proteoglycans from small samples of intact tissue.

Selective human endothelial cell activation by chemokines as a guide to cell homing

An original model of organo-specific, immortalized and stabilized endothelial cell lines was used to delineate the part played by some chemokines (CCL21, CX3CL1, CCL5 and CXCL12) and their receptors in endothelium organo-specificity. Chemokine receptor expression and chemokine presentation were investigated on organo-specific human endothelial cell lines. Although the chemokines showed distinct binding patterns for the various endothelial cell lines, these were not correlated with the expression of the corresponding receptors (CX3CR1, CXCR4, CCR5 and CCR7). Experiments with CCL21 on peripheral lymph node endothelial cells demonstrated that the chemokine did not co-localize with its receptor but was associated with extracellular matrix components. The specific activity of chemokines was clearly shown to be related to the endothelial cell origin. Indeed, CX3CL1 and CCL21 promoted lymphocyte recruitment by endothelial cells from the appendix and peripheral lymph nodes, respectively, while CX3CL1 pro-angiogenic activity was restricted to endothelial cells from the appendix and skin. The high specificity of the chemokine/endothelium interaction allowed the design of a direct in vitro endothelial cell targeting assay. This unique cellular model demonstrated a fundamental role for chemokines in conferring on the endothelium its organo-specificity and its potential for tissue targeting through the selective binding, presentation and activation properties of chemokines.

Skeletal stem cells: phenotype, biology and environmental niches informing tissue regeneration

Advances in our knowledge of the biology of skeletal stem cells, together with an increased understanding of the regeneration of normal tissue offer exciting new therapeutic approaches in musculoskeletal repair. Skeletal stem cells from various adult tissues such as bone marrow can be identified and isolated based on their expression of a panel of markers associated with smooth muscle cells, pericytes and endothelial cells. Thus, skeletal stem cell-like populations within bone marrow may share a common perivascular stem cell niche within the microvascular network. To date, the environmental niche that nurtures and maintains the stromal stem cell at different anatomical sites remains poorly understood. However, an understanding of the osteogenic and perivascular niches will inform identification of the key growth factors, matrix constituents and physiological conditions that will enhance the ex vivo amplification and differentiation of osteogenic stem cells to mimic native tissue critical for tissue repair. This review will examine skeletal stem cell biology, the advances in our understanding of the skeletal and perivascular niche and interactions therein and the opportunities to harness that knowledge for musculoskeletal regeneration.

Chemokines: novel targets for breast cancer metastasis

Recent studies have highlighted the possible involvement of chemokines and their receptors in breast cancer progression and metastasis. Chemokines and their receptors constitute a superfamily of signalling factors whose prognosis value in breast cancer progression remains unclear. We will examine here the expression pattern of chemokines and their receptors in mammary gland physiology and carcinogenesis. The nature of the cells producing chemokines or harboring chemokine receptors appears to be crucial in certain conditions for example, the infiltration of the primary tumor by leukocytes and angiogenesis. In addition, chemokines, their receptors and the interaction with glycosaminoglycan (GAGs) are key players in the homing of cancer cells to distant metastasis sites. Several lines of evidence, including in vitro and in vivo models, suggest that the mechanism of action of chemokines in cancer development involves the modulation of proliferation, apoptosis, invasion, leukocyte recruitment or angiogenesis. Furthermore, we will discuss the regulation of chemokine network in tumor neovascularity by decoy receptors. The reasons accounting for the deregulation of chemokines and chemokine receptors expression in breast cancer are certainly crucial for the comprehension of chemokine role in breast cancer and are in several cases linked to estrogen receptor status. The targeting of chemokines and chemokine receptors by antibodies, small molecule antagonists, viral chemokine binding proteins and heparins appears as promising tracks to develop therapeutic strategies. Thus there is significant interest in developing strategies to antagonize the chemokine function, and an opportunity to interfere with metastasis, the leading cause of death in most patients.

Mutual, reciprocal SDF-1/CXCR4 interactions between hematopoietic and bone marrow stromal cells regulate human stem cell migration and development in NOD/SCID chimeric mice

The chemokine SDF-1 (CXCL12) and its receptor CXCR4 are involved in regulation of migration, survival, and development of multiple cell types, including human hematopoietic CD34+/CD38-/low and stromal STRO-1+ stem cells. During steady-state homeostasis, CXCR4 is expressed by hematopoietic cells and also by stromal cells, which are the main source for SDF-1 in the bone marrow (BM). Stress-induced modulations in SDF-1 and CXCR4 levels participate in recruitment of immature and maturing leukocytes from the BM reservoir to damaged organs as part of host defense and repair mechanism. In addition, trafficking of SDF-1 is mediated by CXCR4, expressed by endothelial and various stromal cell types in the BM, spleen, and other organs, but not by hematopoietic cells. Transcytosis of functional SDF-1 to the BM takes place also in the stem cell-rich endothelium and endosteum regions, regulating hematopoietic and stromal interactions in the stem cell niche. Dynamic levels of SDF-1 and CXCR4 expression induce proliferation of hematopoietic and mesenchymal progenitors, recruitment of bone-resorbing osteoclasts, osteoblasts, neutrophils, and other myeloid cells, leading to leukocyte mobilization. These studies will be reviewed together with the mechanisms that regulate SDF-1 and CXCR4 physiologic function, inactivation, presentation, and availability. Moreover, the role and the dynamic modulations of this ligand and its receptor in alarm and pathologic conditions will be discussed as well.

Heparin accelerates gelsolin amyloidogenesis

The chemical environment of the extracellular matrix may influence the tissue-selective deposition observed there in gelsolin amyloid disease. Previously, we have identified the proteases that generate the amyloidogenic fragments from the full-length gelsolin variants and demonstrated that heparin is capable of accelerating gelsolin amyloidogenesis. Herein, we identify the structural features of heparin that promote the 8 kDa disease-associated gelsolin fragments (residues 173-243) generated at the cell surface to form amyloid. In conjunction with electron microscopy analyses, our kinetic studies demonstrate that heparin efficiently accelerates the formation of gelsolin amyloid by enabling intermolecular beta-sheet formation. The use of heparin analogues reveals that sulfation is important in accelerating amyloidogenesis and that the extent of acceleration is proportional to the molecular weight of heparin. In addition, heparin accelerated aggregation at both early and late stages of amyloidogenesis. Dynamic light scattering coupled to size exclusion chromatography showed that heparin promotes the formation of soluble aggregates. Collectively, these data reveal that heparin templates fibril formation and affords solubility to the aggregating peptides through its sulfated structure. By extension, the biochemical results herein suggest that tissue-selective deposition characteristic of the gelsolin amyloidoses is likely influenced by the extracellular localization of distinct glycosaminoglycans.

Etoposide differentially affects bone marrow and dermal derived endothelial cells

Chemotherapy alteration of the bone marrow microenvironment has the potential to influence hematopoietic recovery following transplantation. To discern the effect of specific drugs on components of the complex marrow microenvironment, in vitro models have significant utility. In the current study we sought to determine whether dermal (HMEC-1) and marrow derived endothelial cells (BMEC-1) respond differently to identical chemotherapy exposure. BMEC-1 cells were consistently more sensitive to etoposide exposure than HMEC-1 cells, measured as reduced viability. BMEC-1 also had reduced focal adhesion kinase (FAK) and VCAM-1 protein expression following chemotherapy, in contrast to dermal derived endothelial cells in which neither protein was influenced dramatically by etoposide. The two endothelial cell lines had markedly different levels of baseline VE-Cadherin protein, which was modestly altered by treatment. These data indicate that marrow derived endothelial cells have disruption of specific proteins following chemotherapy that may influence their ability to facilitate hematopoietic cell entry or egress from the marrow. In addition, these observations suggest that while BMEC-1 and HMEC-1 share a variety of characteristics, they differ significantly in their response to stress and should be incorporated into specific models with this consideration.

The bone marrow vascular niche: home of HSC differentiation and mobilization

The bone marrow vascular niche consists of a network of thin-walled and fenestrated sinusoidal vessels whose integrity is maintained and supported by surrounding hematopoietic cells. However, this dependence is highly reciprocal in that the bone marrow vasculature provides not only a conduit for mature hematopoietic cells to the peripheral circulation but also a site where hematopoietic progenitors, especially megakaryocytes, differentiate and set the stage for full reconstitution of hematopoiesis.

Proangiogenic stimulation of bone marrow endothelium engages mTOR and is inhibited by simultaneous blockade of mTOR and NF-kappaB

Most bone marrow (BM) malignancies develop in association with an angiogenic phenotype and increased numbers of endothelial cells. The molecular mechanisms involved in the modulation and recruitment of BM endothelium are largely unknown and may provide novel therapeutic targets for neoplastic diseases. We observed that angiogenic stimulation of BM endothelial cells activates mTOR and engages its downstream pathways 4E-BP1 and S6K1, which are inhibited by the mTOR-specific blockers rapamycin and CCI-779. Both mTOR blockers significantly inhibit growth factor- and leukemia-induced proliferation of BM endothelium by inducing G0/G1 cell-cycle arrest. This effect is associated with down-regulation of cyclin D1 and cdk2 phosphorylation, and up-regulation of the cdk inhibitors p27(kip1) and p21(cip1). Under conditions that reproduce the biomechanical fluidic environment of the BM, CCI-779 is equally effective in inhibiting BM endothelial-cell proliferation. Finally, simultaneous blockade of mTOR and NF-kappaB pathways synergize to significantly inhibit or abrogate the proliferative responses of BM endothelial cells to mitogenic stimuli. This study identifies mTOR as an important pathway for the proangiogenic stimulation of BM endothelium. Modulation of this pathway may serve as a valid therapeutic intervention in BM malignancies evolving in association with an angiogenic phenotype.

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.

Soluble mediators of inflammation during tumor development

Tissues maintain homeostasis by monitoring and responding to varied physical interactions between cells and their microenvironment. In situations where acute tissue damage occurs, such as wounding, pathogenic assault, or toxic exposure, regulatory circuits that monitor tissue homeostasis are rapidly engaged to initiate tissue repair by regulating cell polarity, proliferation and death, matrix metabolism, inflammation, and vascular and lymphatic function. The critical feature of regulating these acute responses is the innate ability to discriminate between homeostatic versus damaged tissue states and engage or disengage regulatory machinery as appropriate; thus, a major distinction between acute versus chronic disease is the altered ability to appropriately activate and?or inactivate reparative regulatory programs. Since cancer is a chronic disease characterized by altered cell polarity, enhanced cell survival, inflammation, increased matrix metabolism, and enhanced vascular and lymphatic function, considerable attention is now focused on understanding the cellular and molecular mechanisms regulating these responsive pathways. Since chemoattractant cytokines are important mediators of leukocyte recruitment following acute tissue stress, and demonstrate altered characteristics of expression and activation in chronically inflamed tissue, they have been implicated as key regulators of inflammation and angiogenesis during cancer development. This chapter focuses on the clinical and experimental data implicating proinflammatory cytokines and chemokines as important potentiators of carcinogenesis.

Integrin alpha4beta1 involvement in stromal cell-derived factor-1alpha-promoted myeloma cell transendothelial migration and adhesion: role of cAMP and the actin cytoskeleton in adhesion

The chemokine stromal cell-derived factor-1alpha (SDF-1alpha) is expressed by bone marrow (BM) stromal cells and plays key roles in cell homing to and retention into the bone marrow. In multiple myeloma, blood-borne malignant plasma cells home to the BM and accumulate in contact with stromal cells, implicating myeloma cell migration across endothelium. Myeloma cells express the SDF-1alpha receptor CXCR4, as well as the integrin alpha4beta1, which mediates their attachment to BM stroma. We show here that SDF-1alpha promotes transendothelial migration of purified BM myeloma cells and myeloma-derived NCI-H929 cells, involving a transient upregulation of alpha4beta1-dependent cell adhesion to the endothelium. Characterization of intracellular signaling pathways involved in the modulation by SDF-1alpha of alpha4beta1-mediated myeloma cell adhesion revealed that intracellular cAMP amounts associated with the activation of protein kinase A play key roles in this modulation. Furthermore, a functional link between cAMP actions on the dynamics of actin cytoskeleton, RhoA activation, and alpha4beta1-dependent cell adhesion in response to SDF-1alpha has been found. The regulation of alpha4beta1-mediated myeloma cell adhesion by SDF-1alpha could play key roles during myeloma cell homing into and trafficking inside the BM, and characterization of the molecular events involved in SDF-1alpha-activated modulation of this adhesion will contribute to a better understanding of mechanisms participating in cell migration.

Signaling in leukocyte transendothelial migration

Under a variety of (patho) physiological conditions, leukocytes will leave the bloodstream by crossing the endothelial monolayer that lines the vessels and migrate into the underlying tissues. It is now clear that the process of extravasation involves a range of adhesion molecules on both leukocytes and endothelial cells, as well as extensive intracellular signaling that drives adhesion and chemotaxis on the one hand and controls a transient modulation of endothelial integrity on the other. We review here the current knowledge of the intracellular signaling pathways that are activated in the context of transendothelial migration in leukocytes and in endothelial cells. In leukocytes, polarization of receptors and of the signaling machinery is of key importance to drive adhesion and directional migration. Subsequent adhesion-induced signaling in endothelial cells, mediated by Rho-like GTPases and reactive oxygen species, induces a transient and focal loss of endothelial cell-cell adhesion to allow transmigration of the leukocyte. This review underscores the notion that we have likely just scratched the surface in revealing the complexity of the signaling that controls leukocyte transendothelial migration.

In vitro model for hematopoietic progenitor cell homing reveals endothelial heparan sulfate proteoglycans as direct adhesive ligands

Proteoglycans (PGs) play a dominant role within the bone marrow (BM), but their role in homing of transplanted hematopoietic progenitor cells (HPC) is unknown. In this study, the role of heparan sulfate (HS) PGs on BM endothelium as adhesive structures was investigated. HPC (primary CD34+ cells and cell line KG-1a) were able to bind fractionated heparin, which could be competed by highly sulfated heparin/HS-glycosaminoglycans (GAGs). Under flow conditions, HPC adhered to immobilized heparin after rolling over E-selectin. Rolling of KG-1a on BM endothelial cell (EC) line 4LHBMEC was completely E selectin-dependent. Addition of heparin/HS-GAGs, endothelial treatment with chlorate, or anti-HS all partially inhibited firm adhesion. Moreover, enzymatic removal of endothelial HS-GAGs reduced initial adhesion. Finally, HPC-bound PGs isolated from 4LHBMEC, which was largely inhibited by enzymatic HS-degradation. In summary, we identified sulfated structures on BM endothelium, most likely HSPGs, as a novel class of glycoconjugates involved in the multistep homing cascade of HPC.

Endothelial inflammation: the role of differential expression of N-deacetylase/N-sulphotransferase enzymes in alteration of the immunological properties of heparan sulphate

Heparan sulphate N-deacetylase/N-sulphotransferase (NDST) enzymes catalyse the reaction that initiates sulphation and subsequent modification of the oligosaccharide, heparan sulphate (HS). The extent and distribution of sulphate substitution on HS plays a vital role in regulation of the binding of a range of proteins, including IFN-gamma, several interleukins and most chemokines. In this study, the expression of NDST transcripts was found to be non-uniform between a range of cell types, suggesting that different cells produce characteristic HS species. It was found that stimulation of the HMEC-1 microvascular endothelial cell line with the pro-inflammatory cytokines IFN-gamma and TNF-alpha caused a transient decrease in the level of NDST-1 and -2 transcripts after 4 hours (P < 0.05 and P < 0.01 respectively), but the expression of NDST-1 increased above control levels after 16 hours (P < 0.01). The change in NDST expression was concurrent with an increase in the abundance of sulphated HS epitopes on the cell surface; this was not caused by variation in the expression of proteoglycans or by changes in the rate of GAG turnover. Cytokine-stimulated endothelial cells also showed an increase in their potential to bind RANTES (CCL5); this was abrogated by chlorate blockade of sulphotransferase activity or by heparitinase cleavage of cell surface HS. Monolayers of cytokine-stimulated HMEC-1 also supported an enhanced leukocyte chemotactic response towards RANTES. This study demonstrated that pro-inflammatory cytokines can increase NDST expression leading to increased sulphation of HS and a corresponding increase in sequestration of functional RANTES at the apical surface of endothelial cells. This may enhance leukocyte extravasation at sites of inflammation.

Leukocyte-endothelium interaction promotes SDF-1-dependent polarization of CXCR4

Chemokine-driven migration is accompanied by polarization of the cell body and of the intracellular signaling machinery. The extent to which chemokine receptors polarize during chemotaxis is currently unclear. To analyze the distribution of the chemokine receptor CXCR4 during SDF-1 (CXCL12)-induced chemotaxis, we retrovirally expressed a CXCR4-GFP fusion protein in the CXCR4-deficient human hematopoietic progenitor cell line KG1a. This KG1a CXCR4-GFP cell line showed full restoration of SDF-1 responsiveness in assays detecting activation of ERK1/2 phosphorylation, actin polymerization, adhesion to endothelium under conditions of physiological flow, and (transendothelial) chemotaxis. When adhered to cytokine-activated endothelium in the absence of SDF-1, CXCR4 did not localize to the leading edge of the cell but was uniformly distributed over the plasma membrane. In contrast, when SDF-1 was immobilized on cytokine-activated endothelium, the CXCR4-GFP receptors that were present on the cell surface markedly redistributed to the leading edge of migrating cells. In addition, CXCR4-GFP co-localized with lipid rafts in the leading edge of SDF-1-stimulated cells, at the sites of contact with the endothelial surface. Inhibition of lipid raft formation prevents SDF-1-dependent migration, internalization of CXCR4, and polarization to the leading edge of CXCR4, indicating that CXCR4 surface expression and signaling requires lipid rafts. These data show that SDF-1, immobilized on activated human endothelium, induces polarization of CXCR4 to the leading edge of migrating cells, revealing co-operativity between chemokine and substrate in the control of cell migration.

Heparan sulfate proteoglycans modulate monocyte migration across cerebral endothelium

Heparan sulfate proteoglycans (HSPGs) are known to participate in a wide range of biological events, including cellular trafficking. In this study we report that in situ cerebral blood vessels highly express HSPGs. Of the syndecan family, syndecan-2 is highly expressed on virtually all brain vessels and syndecan-1 and -3 are only present on larger blood vessels. These endothelial HSPGs have a functional role in monocyte diapedesis across brain endothelium, as assessed in our in vitro adhesion and migration assays. Our data indicate that heparin prevents monocyte adhesion to brain endothelium by interacting solely with the monocyte. Transendothelial migration of monocytes can be prevented by preincubation of brain endothelium with heparin by enzymatic removal of heparan sulphate side chains or by inhibition of cellular sulfation. Blocking of G-protein-dependent signaling in the monocytes prevented monocyte adhesion and migration to similar extent, suggesting that G-dependent signaling may be involved in HSPG-mediated monocyte adhesion and transendothelial migration. Our data demonstrate that brain endothelial HSPGs have a modulatory role in the transendothelial migration of monocytes in a direct and indirect fashion and may therefore contribute to the formation of neuroinflammatory lesions.

Synoviocyte-derived CXCL12 is displayed on endothelium and induces angiogenesis in rheumatoid arthritis

CXCL12 (stromal cell-derived factor-1) is a potent CXC chemokine that is constitutively expressed by stromal resident cells. Although it is considered a homeostatic rather than an inflammatory chemokine, CXCL12 has been immunodetected in different inflammatory diseases, but also in normal tissues, ant its potential functions and regulation in inflammation are not well known. In this study, we examined the cellular sources of CXCL12 gene expression and the mechanism and effects of its interactions with endothelial cells in rheumatoid arthritis synovium. We show that CXCL12 mRNA was not overexpressed nor induced in cultured rheumatoid synoviocytes, but it specifically accumulated in the rheumatoid hyperplastic lining layer and endothelium. CXCL12 gene expression was restricted to fibroblast-like synoviocytes, whereas endothelial cells did not express CXCL12 mRNA, but displayed the protein on heparitinase-sensitive factors. CXCL12 colocalized with the angiogenesis marker alpha(v)beta(3) integrin in rheumatoid endothelium and induced angiogenesis in s.c. Matrigel plugs in mice. The angiogenic activity of rheumatoid synovial fluid in vivo was abrogated by specific immunodepletion of CXCL12. Our results indicate that synoviocyte-derived CXCL12 accumulates and it is immobilized on heparan sulfate molecules of endothelial cells, where it can promote angiogenesis and inflammatory cell infiltration, supporting a multifaceted function for this chemokine in the pathogenesis of rheumatoid arthritis.

Laser-induced fluorescence as a powerful detection tool for capillary electrophoretic analysis of heparin/heparan sulfate disaccharides

In quest for high sensitivities necessary for determining the disaccharide composition of heparin/heparan sulfate present in trace amounts in biologic samples, an ultrahighly sensitive capillary electrophoresis (CE) method using laser-induced fluorescence (LIF) detection was developed. Heparin/heparan sulfate-derived Delta-disaccharides were derivatized with the fluorophore 2-aminoacridone and resolved by a reversed-polarity CE method. Estimation of the limit of detection in concentration term and limit of quantitation showed that LIF detection of AMAC-derivatives of Delta-disaccharides resulted in 27-744 times higher sensitivity as compared to those detected by UV at 255 nm. These data suggest that CE-LIF is a powerful tool to quantify minute amounts of heparin/heparan sulfate disaccharides.

Proteoglycans on bone marrow endothelial cells bind and present SDF-1 towards hematopoietic progenitor cells

Recognition events between hematopoietic progenitor cells (HPC) and bone marrow endothelial cells (BMEC) initiate homing of HPC to the bone marrow. The chemokine SDF-1 is present on BMEC and plays a crucial role in bone marrow engraftment. We studied the role of proteoglycans (PGs) on BMEC in binding and presentation of SDF-1. SDF-1 mRNA was present in three human BMEC cell lines. Competition experiments showed that 125I-SDF-1 alpha binding to the BMEC cell line 4LHBMEC was inhibited by heparins, heparan sulfate (HS) intestinal mucosa, chondroitin and dermatan sulfate (CS/DS), but not by HS bovine kidney. Pretreatment of 4LHBMEC with glycosaminoglycan (GAG)-degrading enzymes or sodium chlorate demonstrated that SDF-1 bound to both HSPGs and CS/DSPGs in a sulfation-dependent manner, as determined with an SDF-1 antibody recognizing the CXCR4-binding site. 4LHBMEC bound four-fold more SDF-1 than HUVEC. Isolated endothelial PGs did not bind SDF-1 in a filter or microplate-binding assay, suggesting the necessity of membrane association. In flow adhesion experiments, endothelial arrest of CXCR4+ KG-1 and not of CXCR4- KG-1a cells increased significantly when SDF-1 was presented on 4LHBMEC. In conclusion, SDF-1 is produced by BMEC and binds to the BMEC cell surface via HS and CS/DS-GAGs, thereby presenting its CXCR4 binding site to HPC contributing to their arrest.

Leukocyte extravasation: chemokine transport and presentation by the endothelium

At sites of inflammation and in normal immune surveillance, chemokines direct leukocyte migration across the endothelium. Many cell types that are extravascular can produce chemokines, and for these mediators to directly elicit leukocyte migration from the blood, they would need to reach the luminal surface of the endothelium. This article reviews the evidence that endothelial cells are active in transcytosing chemokines to their luminal surfaces, where they are presented to leukocytes. The endothelial binding sites that transport and present chemokines include glycosaminoglycans (GAGs) and possibly the Duffy antigen/receptor for chemokines (DARC). The binding residues on chemokines that interact with GAGs are discussed, as are the carbohydrate structures on GAGs that bind these cytokines. The expression of particular GAG structures by endothelial cells may lend selectivity to the type of chemokine presented in a given tissue, thereby contributing to selective leukocyte recruitment. At the luminal surface of the endothelium, chemokines are preferentially presented to blood leukocytes on the tips of microvillous processes. Similarly, certain adhesion molecules and chemokine receptors are also preferentially distributed on leukocyte and endothelial microvilli, and evidence suggests an important role for these structures in creating the necessary surface topography for leukocyte migration. Finally, the mechanisms of chemokine transcytosis and presentation by endothelial cells are incorporated into the current model of chemokine-driven leukocyte extravasation.

Homing and clonogenic outgrowth of CD34(+) peripheral blood stem cells: a role for L-selectin?

OBJECTIVE

After transplantation of hematopoietic stem cells, adhesion molecules play a major role in the multistep process of engraftment in which L-selectin is suggested to be of relevance. A positive correlation previously was found between the number of reinfused L-selectin(+) stem cells and platelet recovery. In the present study, we determined the role of L-selectin in different engraftment steps, i.e., adhesion to endothelial cells, migration, and clonogenic outgrowth by in vitro assays that closely mimic the in vivo situation.

MATERIALS AND METHODS

Flow adhesion and migration experiments were performed using the human bone marrow endothelial cell line 4LHBMEC and isolated peripheral CD34(+) cells with or without blocking of L-selectin-ligand interaction. Various clonogenic assays, including serum-free colony-forming unit-megakaryocytes (CFU-MK) and burst-forming unit-megakaryocytes (BFU-MK), were performed with sorted L-selectin(+)L-selectin(-) cells or in the presence of antibodies.

RESULTS

Blocking of L-selectin on CD34(+) cells did not significantly affect rolling over and firm adhesion to 4LHBMEC. In addition, no role for L-selectin was found in transendothelial migration experiments. Finally, in clonogenic outgrowth of sorted or anti-L-selectin monoclonal antibody-incubated CD34(+) cells, no key role for L-selectin expression could be defined in BFU-MK and CFU-MK assays.

CONCLUSION

Using in vitro assays for CD34(+) stem cell adhesion, migration, and clonogenic capacity, we were not able to define a major role for L-selectin.