Heparan sulfates and heparan sulfate proteoglycans in hematopoiesis

ABSTRACT

From signaling mediators in stem cells to markers of differentiation and lineage commitment to facilitators for the entry of viruses, such as HIV-1, cell surface heparan sulfate (HS) glycans with distinct modification patterns play important roles in hematopoietic biology. In this review, we provide an overview of the importance of HS and the proteoglycans (HSPGs) to which they are attached within the major cellular subtypes of the hematopoietic system. We summarize the roles of HSPGs, HS, and HS modifications within each main hematopoietic cell lineage of both myeloid and lymphoid arms. Lastly, we discuss the biological advances in the detection of HS modifications and their potential to further discriminate cell types within hematopoietic tissue.

Computational studies on glycosaminoglycan recognition of sialyl transferases

Despite decades of research, glycosaminoglycans (GAGs) have not been known to interact with sialyl transferases (STs). Using our in-house combinatorial virtual library screening (CVLS) technology, we studied seven human isoforms, including ST6GAL1, ST6GAL2, ST3GAL1, ST3GAL3, ST3GAL4, ST3GAL5, and ST3GAL6, and predicted that GAGs, especially heparan sulfate (HS), are likely to differentially bind to STs. Exhaustive CVLS and molecular dynamics studies suggested that the common hexasaccharide sequence of HS preferentially recognized ST6GAL1 in a site overlapping the binding site of the donor substrate CMP-Sia. Interestingly, CVLS did not ascribe any special role for the rare 3-O-sulfate modification of HS in ST6GAL1 recognition. The computational predictions were tested using spectrofluorimetric studies, which confirmed preferential recognition of HS over other GAGs. A classic chain length-dependent binding of GAGs to ST6GAL1 was observed with polymeric HS displaying a tight affinity of ~65 nM. Biophysical studies also confirmed a direct competition between CMP-Sia and an HS oligosaccharide and CS polysaccharide for binding to ST6GAL1. Overall, our novel observation that GAGs bind to ST6GAL1 with high affinity and compete with the donor substrate is likely to be important because modulation of sialylation of glycan substrates on cells has considerable physiological/pathological consequences. Our work also brings forth the possibility of developing GAG-based chemical probes of ST6GAL1.

N-desulfated and reacetylated modification of heparin modulates macrophage polarization

Heparin as a widely used anticoagulant drug has potent anti-inflammatory effects, which have been rarely reported to be involved in macrophage polarization. Furthermore, the effects of structural modifications of heparin on the plasticity of macrophage functions have not been clearly understood. In this study, the N-desulfated reacetylated derivative of heparin (NDeSAcH) was prepared and its immunoregulatory effects of macrophage polarization were evaluated. The findings indicated that NDeSAcH could effectively promote the release of more nitric oxide (NO), interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) in RAW264.7 cells than heparin. Moreover, the production of NO, IL-6 and TNF-α was significantly inhibited by NDeSAcH in LPS-induced RAW264.7 cells, while the secretion of transforming growth factor-β (TGF-β) was suppressed in M2 macrophages. The N-desulfated and reacetylated group of heparin was proved to have two-side adjusting effects on the polarization of macrophages. This study suggested that NDeSAcH might be a promising candidate for modulating macrophage polarization and treating inflammation-related diseases.

Cancer stem cell-immune cell collusion in immunotherapy

Immunotherapy has pioneered a new era of tumor treatment, in which the immune checkpoint blockade (ICB) exerts significant superiority in overcoming tumor immune escape. However, the formation of an immune-suppressive tumor microenvironment (TME) and the lack of effective activation of the immune response have become major obstacles limiting its development. Emerging reports indicate that cancer stem cells (CSCs) potentially play important roles in treatment resistance and progressive relapse, while current research is usually focused on CSCs themselves. In this review, we mainly emphasize the collusions between CSCs and tumor-infiltrating immune cells. We focus on the summary of CSC-immune cell crosstalk signaling pathways in ICB resistance and highlight the application of targeted drugs to improve the ICB response.

Distinct Effects of Heparin and Interleukin-4 Functionalization on Macrophage Polarization and In Situ Arterial Tissue Regeneration Using Resorbable Supramolecular Vascular Grafts in Rats

Two of the greatest challenges for successful application of small-diameter in situ tissue-engineered vascular grafts are 1) preventing thrombus formation and 2) harnessing the inflammatory response to the graft to guide functional tissue regeneration. This study evaluates the in vivo performance of electrospun resorbable elastomeric vascular grafts, dual-functionalized with anti-thrombogenic heparin (hep) and anti-inflammatory interleukin 4 (IL-4) using a supramolecular approach. The regenerative capacity of IL-4/hep, hep-only, and bare grafts is investigated as interposition graft in the rat abdominal aorta, with follow-up at key timepoints in the healing cascade (1, 3, 7 days, and 3 months). Routine analyses are augmented with Raman microspectroscopy, in order to acquire the local molecular fingerprints of the resorbing scaffold and developing tissue. Thrombosis is found not to be a confounding factor in any of the groups. Hep-only-functionalized grafts resulted in adverse tissue remodeling, with cases of local intimal hyperplasia. This is negated with the addition of IL-4, which promoted M2 macrophage polarization and more mature neotissue formation. This study shows that with bioactive functionalization, the early inflammatory response can be modulated and affect the composition of neotissue. Nevertheless, variability between graft outcomes is observed within each group, warranting further evaluation in light of clinical translation.

Heparin-based, injectable microcarriers for controlled delivery of interleukin-13 to the brain

The anti-inflammatory cytokine IL-13 can be loaded and released from heparin-based cryogel biomaterials for sustained delivery to the brain.

Glycosaminoglycan-based biomaterials for growth factor and cytokine delivery: Making the right choices

Controlled, localized drug delivery is a long-standing goal of medical research, realization of which could reduce the harmful side-effects of drugs and allow more effective treatment of wounds, cancers, organ damage and other diseases. This is particularly the case for protein "drugs" and other therapeutic biological cargoes, which can be challenging to deliver effectively by conventional systemic administration. However, developing biocompatible materials that can sequester large quantities of protein and release them in a sustained and controlled manner has proven challenging. Glycosaminoglycans (GAGs) represent a promising class of bio-derived materials that possess these key properties and can additionally potentially enhance the biological effects of the delivered protein. They are a diverse group of linear polysaccharides with varied functionalities and suitabilities for different cargoes. However, most investigations so far have focused on a relatively small subset of GAGs - particularly heparin, a readily available, promiscuously-binding GAG. There is emerging evidence that for many applications other GAGs are in fact more suitable for regulated and sustained delivery. In this review, we aim to illuminate the beneficial properties of various GAGs with reference to specific protein cargoes, and to provide guidelines for informed choice of GAGs for therapeutic applications.

Preparation of gentiobiose-derived oligosaccharides by glucansucrase E81 and determination of prebiotic and immune-modulatory functions

Gentiobiose-derived oligosaccharides were synthesized by the acceptor reaction of glucansucrase E81 obtained from Lactobacillus reuteri E81 with sucrose and gentiobiose as donor-acceptor sugars, respectively. The reaction products were monitored by TLC analysis and gentiobiose-derived oligosaccharides up to DP 8 were formed during the acceptor reaction as determined by ESI-MS/MS analysis. The glycosylation of the gentiobiose with α-(1 → 6) linkages and α-(1 → 3) linkages was shown by ¹H and ¹³C NMR analysis confirming the structure of these gentiobiose-derived oligosaccharides. The in vitro prebiotic function of the oligosaccharides was determined in which probiotic strains were stimulated whereas no growth was observed in pathogen strains. Gentiobiose-derived oligosaccharides showed immune-modulatory functions in vitro and triggered the production of IL-4, IL12 and TNF-α cytokines in HT29 cells in a dose dependent manner. This study showed the production and functional characterisation of gentiobiose-derived oligosaccharides establishing a promising avenue for future applications.

Distinct release strategies are required to modulate macrophage phenotype in young versus aged animals

The role of innate immunity and macrophages in the host response to biomaterials has received renewed attention. A context-dependent spectrum of macrophage phenotypes are shown to affect tissue integration and performance of implanted biomaterials and medical devices. Recent studies by our group demonstrated that the host response in aged animals was characterized by delayed macrophage recruitment, differences in marker expression and a shifted pro-inflammatory (M1) response, associated with an unresolved host response in the long-term. The present work sought to study the effects of single and sequential cytokine delivery regimens in aged mice to restore delayed recruitment of macrophages and shift the inflammatory host response towards an M2-like phenotype, using MCP-1 (macrophage chemotactic protein-1) and IL-4 (interleukin-4), respectively. Implantation of cytokine-eluting implants showed a preserved response to MCP-1 in both young and aged animals, restoring delayed macrophage recruitment in aged mice. However, the response elicited by IL-4, sequential delivery of MCP-1/IL-4 and coating components was distinct in young versus aged mice. While single delivery of IL-4 did not counteract the high inflammatory response observed in aged mice, the sequential delivery of MCP-1/IL-4 was capable of restoring both recruitment and shifting the macrophage response towards an M2-like phenotype, associated with decreased implant scarring in the long-term. In young mice, sequential delivery was not as effective as IL-4 alone at promoting an M2-like response, but did result in a reduction of M1 macrophages and capsule deposition downstream. These results demonstrate that a proper understanding of patient/context-dependent biological responses are needed to design biomaterial-based therapies with improved outcomes in the setting of aging.

STAT Family Protein Expression and Phosphorylation State during moDC Development Is Altered by Platinum-Based Chemotherapeutics

The STAT signaling pathway is important in dendritic cell (DC) development and function. Tumor cells can induce STAT signaling, thereby inhibiting DC maturation and immunostimulatory functions, leading to hampered efficacy of DC-based immunotherapies. Platinum-based chemotherapeutics can inhibit STAT signaling, thereby making them an interesting tool to improve DC development and function. In this study, we provide a comprehensive overview of STAT expression and phosphorylation during DC differentiation and maturation and investigate the effects of platinum drugs on STAT signaling during these processes. Monocytes were differentiated into monocyte-derived DCs (moDCs) with IL-4 and GM-CSF and matured with cytokines or TLR ligands. STAT expression and phosphorylation were analyzed by western blotting, and moDC viability and phenotype were analyzed by flow cytometry. Platinum drugs were added at day 3 of differentiation or at the start of maturation to investigate regulation of the STAT signaling pathway. All STAT proteins were expressed during moDC differentiation and STAT1, STAT5, and STAT6 were phosphorylated. No significant changes occurred in the expression and phosphorylation state of the STAT proteins during differentiation. After maturation with TLR ligands, the expression of STAT1 increased, but other STAT proteins were not affected. Phosphorylation of STAT1 and STAT3 increased during maturation, where TLR ligands induced significantly higher levels of phosphorylation than cytokines. Platinum drugs cisplatin and oxaliplatin significantly inhibited phosphorylation of STAT6 during differentiation and maturation. Treatment did not affect the phenotype or viability of the cells. As STAT6 is an important regulator of DC function, these findings suggest a role for platinum-based chemotherapeutics to enhance DC function via inhibition of STAT signaling, thereby potentially enhancing efficacy of DC-based immunotherapies.

Aspergillus fumigatus Challenged by Human Dendritic Cells: Metabolic and Regulatory Pathway Responses Testify a Tight Battle

Dendritic cells (DCs) are antigen presenting cells which serve as a passage between the innate and the acquired immunity. Aspergillosis is a major lethal condition in immunocompromised patients caused by the adaptable saprophytic fungus Aspergillus fumigatus. The healthy human immune system is capable to ward off A. fumigatus infections however immune-deficient patients are highly vulnerable to invasive aspergillosis. A. fumigatus can persist during infection due to its ability to survive the immune response of human DCs. Therefore, the study of the metabolism specific to the context of infection may allow us to gain insight into the adaptation strategies of both the pathogen and the immune cells. We established a metabolic model of A. fumigatus central metabolism during infection of DCs and calculated the metabolic pathway (elementary modes; EMs). Transcriptome data were used to identify pathways activated when A. fumigatus is challenged with DCs. In particular, amino acid metabolic pathways, alternative carbon metabolic pathways and stress regulating enzymes were found to be active. Metabolic flux modeling identified further active enzymes such as alcohol dehydrogenase, inositol oxygenase and GTP cyclohydrolase participating in different stress responses in A. fumigatus. These were further validated by qRT-PCR from RNA extracted under these different conditions. For DCs, we outlined the activation of metabolic pathways in response to the confrontation with A. fumigatus. We found the fatty acid metabolism plays a crucial role, along with other metabolic changes. The gene expression data and their analysis illuminate additional regulatory pathways activated in the DCs apart from interleukin regulation. In particular, Toll-like receptor signaling, NOD-like receptor signaling and RIG-I-like receptor signaling were active pathways. Moreover, we identified subnetworks and several novel key regulators such as UBC, EGFR, and CUL3 of DCs to be activated in response to A. fumigatus. In conclusion, we analyze the metabolic and regulatory responses of A. fumigatus and DCs when confronted with each other.

Characterization of a 4,6‑α‑glucanotransferase from Lactobacillus reuteri E81 and production of malto-oligosaccharides with immune-modulatory roles

A wide number of Lactic Acid Bacteria (LAB) species produce α-glucans with their ability to synthesize glucansucrases (GS) which use sucrose as substrate for the glucan production. Recently another group of enzymes in LAB gained special interest for their ability to produce α-glucans targeting the substrates containing α1-4-linkages and synthesizing new (α1-6) or (α1-3)-linkages as α‑glucanotransferases. In this study, a putative 4,6‑α‑glucanotransferase (GTFB) from sourdough isolate Lactobacillus reuteri E81 was identified and expressed in Escherichia coli. The biochemical characterization of the GTFB-E81 confirmed its function as it cleaved the α1-4-linkages in different substrates and produced new gluco-oligomers/polymers containing α1-6 linkages together with the α1-4-linkages detected by NMR analysis. GTFB-E81 produced malto-oligosaccharides targeting maltose and maltoheptaose as substrates with up to DP 8 detected by TLC and ESI-MS/MS analysis. The functional roles of these malto-oligosaccharides were determined by testing their immune-modulatory functions in HT29 cells and they triggered the production of anti-inflammatory 1L-4 and pro-inflammatory IL-12 cytokines.

Modulation of macrophage phenotype and protein secretion via heparin-IL-4 functionalized supramolecular elastomers

Hallmark of the in situ tissue engineering approach is the use of bioresorbable, synthetic, acellular scaffolds, which are designed to modulate the inflammatory response and actively trigger tissue regeneration by the body itself at the site of implantation. Much research is devoted to the design of synthetic materials modulating the polarization of macrophages, which are essential mediators of the early stages of the inflammatory response. Here, we present a novel method for the functionalization of elastomers based on synthetic peptide chemistry, supramolecular self-assembly, and immobilization of heparin and interleukin 4 (IL-4), which is known to skew the polarization of macrophages into the wound healing "M2" phenotype. Ureido-pyrimidinone (UPy)-modified chain extended polycaprolactone (CE-UPy-PCL) was mixed with a UPy-modified heparin binding peptide (UPy-HBP) to allow for immobilization of heparin, and further functionalization with IL-4 via its heparin binding domain. As a first proof of principle, CE-UPy-PCL and UPy-HBP were premixed in solution, dropcast and exposed to primary human monocyte-derived macrophages, in the presence or absence of IL-4-heparin functionalization. It was demonstrated that the supramolecular IL-4-heparin functionalization effectively promoted macrophage polarization into an anti-inflammatory phenotype, in terms of morphology, immunohistochemistry and cytokine secretion. Moreover, the supramolecular functionalization approach used was successfully translated to 3D electrospun scaffolds for in situ tissue engineering purposes, where UPy-HBP retention, and heparin and IL-4 attachment to the supramolecular scaffolds were proven over 7 days. Lastly, human monocyte-derived macrophages were cultured on 3D scaffolds, which, in case of IL-4-heparin functionalization, were proven to promote of an anti-inflammatory environment on protein level. This study presents a novel method in designing a versatile class of functionalized elastomers that effectively harness the anti-inflammatory behavior of macrophages in vitro, and as such, may be instrumental for the development of a new class of synthetic materials for in situ tissue engineering purposes.

STATEMENT OF SIGNIFICANCE

Macrophages and their phenotypic and functional plasticity play a pivotal role in metabolic homeostasis and tissue repair. Based on this notion, bioactivated materials modulating macrophage polarization were extensively investigated in the past. Here, we designed immunomodulating, synthetic materials based on supramolecular immobilization of a heparin binding peptide, and further bioactivation with heparin and IL-4, an anti-inflammatory cytokine responsible for M2 activation and polarization. Human monocyte-derived macrophages cultured on heparin-IL-4 bioactivated materials displayed an elongated morphology and an anti-inflammatory phenotype, with downregulation of pro-inflammatory cytokines and promotion of anti-inflammatory cytokines over time. This study represents the first step in designing a novel class of synthetic, bioactivated materials that harness the regenerative behavior of host macrophages towards in situ tissue regeneration.

Cell Penetrating Peptide Derived from Human Eosinophil Cationic Protein Decreases Airway Allergic Inflammation

Cell penetrating peptide derived from human eosinophil cationic protein (CPPecp) is a 10-amino-acid peptide containing a core heparan sulfate (HS)-binding motif of human eosinophil cationic protein (ECP). It binds and penetrates bronchial epithelial cells without cytotoxic effects. Here we investigated airway-protective effects of CPPecp in BEAS-2B cell line and mite-induced airway allergic inflammation in BALB/c mice. In BEAS-2B cell, CPPecp decreases ECP-induced eotaxin mRNA expression. CPPecp also decreases eotaxin secretion and p-STAT6 activation induced by ECP, as well as by IL-4. In vivo studies showed CPPecp decreased mite-induced airway inflammation in terms of eosinophil and neutrophil count in broncho-alveolar lavage fluid, peri-bronchiolar and alveolar pathology scores, cytokine production in lung protein extract including interleukin (IL)-5, IL-13, IL-17A/F, eotaxin; and pause enhancement from methacholine stimulation. CPPecp treated groups also showed lower serum mite-specific IgE level. In this study, we have demonstrated the in vitro and in vivo anti-asthma effects of CPPecp.

Effects of aging upon the host response to implants

Macrophage polarization during the host response is now a well-accepted predictor of outcomes following material implantation. Immunosenescence, dysregulation of macrophage function, and delayed resolution of immune responses in aged individuals have all been demonstrated, suggesting that host responses to materials in aged individuals should differ from those in younger individuals. However, few studies examining the effects of aging upon the host response have been performed. The present work sought to elucidate the impacts of aging upon the host response to polypropylene mesh implanted into 8-week-old and 18-month-old mice. The results showed that there are significant differences in macrophage surface marker expression, migration, and polarization during the early host macrophage response and delayed resolution of the host response in 18-month-old versus 8-week-old mice. These differences could not be attributed to cell-intrinsic defects alone, suggesting that the host macrophage response to implants is likely also dictated to a significant degree by the local tissue microenvironment. These results raise important questions about the design and testing of materials and devices often intended to treat aged individuals and suggest that an improved understanding of patient- and context-dependent macrophage responses has the potential to improve outcomes in aged individuals. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1281-1292, 2017.

StarPEG-Heparin Hydrogels to Protect and Sustainably Deliver IL-4

A major limitation for the therapeutic applications of cytokines is their short half-life time. Glycosaminoglycans (GAGs), known to complex and stabilize cytokines in vivo, are therefore used to form 3D-biohybrid polymer networks capable of aiding the effective administration of Interleukin-4, a key regulator of the inflammatory response. Mimicking the in vivo situation of a protease-rich inflammatory milieu, star-shaped poly(ethylene glycol) (starPEG)-heparin hydrogels and starPEG reference hydrogels without heparin are loaded with Interleukin-4 and subsequently exposed to trypsin as a model protease. Heparin-containing hydrogels retain significantly higher amounts of the Interleukin-4 protein thus exhibiting a significantly higher specific activity than the heparin-free controls. StarPEG-heparin hydrogels are furthermore shown to enable a sustained delivery of the cytokine for time periods of more than two weeks. Primary murine macrophages adopt a wound healing supporting (M2) phenotype when conditioned with Interleukin-4 releasing starPEG-heparin hydrogels. The reported results suggest that GAG-based hydrogels offer valuable options for the effective administration of cytokines in protease-rich proinflammatory milieus such as chronic wounds of diabetic patients.

Shifts in macrophage phenotype at the biomaterial interface via IL-4 eluting coatings are associated with improved implant integration

The present study tests the hypothesis that transient, early-stage shifts in macrophage polarization at the tissue-implant interface from a pro-inflammatory (M1) to an anti-inflammatory/regulatory (M2) phenotype mitigates the host inflammatory reaction against a non-degradable polypropylene mesh material and improves implant integration downstream. To address this hypothesis, a nanometer-thickness coating capable of releasing IL-4 (an M2 polarizing cytokine) from an implant surface at early stages of the host response has been developed. Results of XPS, ATR-FTIR and Alcian blue staining confirmed the presence of a uniform, conformal coating consisting of chitosan and dermatan sulfate. Immunolabeling showed uniform loading of IL-4 throughout the surface of the implant. ELISA assays revealed that the amount and release time of IL-4 from coated implants were tunable based upon the number of coating bilayers and that release followed a power law dependence profile. In-vitro macrophage culture assays showed that implants coated with IL-4 promoted polarization to an M2 phenotype, demonstrating maintenance of IL-4 bioactivity following processing and sterilization. Finally, in-vivo studies showed that mice with IL-4 coated implants had increased percentages of M2 macrophages and decreased percentages of M1 macrophages at the tissue-implant interface during early stages of the host response. These changes were correlated with diminished formation of fibrotic capsule surrounding the implant and improved tissue integration downstream. The results of this study demonstrate a versatile cytokine delivery system for shifting early-stage macrophage polarization at the tissue-implant interface of a non-degradable material and suggest that modulation of the innate immune reaction at early stages of the host response may represent a preferred strategy for promoting biomaterial integration and success.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

The Complement Inhibitor Factor H Generates an Anti-Inflammatory and Tolerogenic State in Monocyte-Derived Dendritic Cells

The activation of the complement system is a key initiating step in the protective innate immune-inflammatory response against injury, although it may also cause harm if left unchecked. The structurally related soluble complement inhibitors C4b-binding protein (C4BP) and factor H (FH) exert a tight regulation of the classical/lectin and alternative pathways of complement activation, respectively, attenuating the activity of the C3/C5 convertases and, consequently, avoiding serious damage to host tissues. We recently reported that the acute-phase C4BP isoform C4BP lacking the β-chain plays a pivotal role in the modulation of the adaptive immune responses. In this study, we demonstrate that FH acts in the early stages of monocyte to dendritic cell (DC) differentiation and is able to promote a distinctive tolerogenic and anti-inflammatory profile on monocyte-derived DCs (MoDCs) challenged by a proinflammatory stimulus. Accordingly, FH-treated and LPS-matured MoDCs are characterized by altered cytoarchitecture, resembling immature MoDCs, lower expression of the maturation marker CD83 and the costimulatory molecules CD40, CD80, and CD86, decreased production of key proinflammatory Th1-cytokines (IL-12, TNF-α, IFN-γ, IL-6, and IL-8), and preferential production of immunomodulatory mediators (IL-10 and TGF-β). Moreover, FH-treated MoDCs show low Ag uptake and, when challenged with LPS, display reduced CCR7 expression and chemotactic migration, impaired CD4(+) T cell alloproliferation, inhibition of IFN-γ secretion by the allostimulated T cells, and, conversely, induction of CD4(+)CD127(low/negative)CD25(high)Foxp3(+) regulatory T cells. Thus, this novel noncanonical role of FH as an immunological brake able to directly affect the function of MoDCs in an inflammatory environment may exhibit therapeutic potential in hypersensitivity, transplantation, and autoimmunity.

Platelet transactivation by monocytes promotes thrombosis in heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is characterized by a high incidence of thrombosis, unlike other antibody-mediated causes of thrombocytopenia. We have shown that monocytes complexed with surface-bound platelet factor 4 (PF4) activated by HIT antibodies contribute to the prothrombotic state in vivo, but the mechanism by which this occurs and the relationship to the requirement for platelet activation via fragment crystallizable (Fc)γRIIA is uncertain. Using a microfluidic model and human or murine blood, we confirmed that activation of monocytes contributes to the prothrombotic state in HIT and showed that HIT antibodies bind to monocyte FcγRIIA, which activates spleen tyrosine kinase and leads to the generation of tissue factor (TF) and thrombin. The combination of direct platelet activation by HIT immune complexes through FcγRIIA and transactivation by monocyte-derived thrombin markedly increases Annexin V and factor Xa binding to platelets, consistent with the formation of procoagulant coated platelets. These data provide a model of HIT wherein a combination of direct FcγRIIA-mediated platelet activation and monocyte-derived thrombin contributes to thrombosis in HIT and identifies potential new targets for lessening this risk.

Non-Anticoagulant Fractions of Enoxaparin Suppress Inflammatory Cytokine Release from Peripheral Blood Mononuclear Cells of Allergic Asthmatic Individuals

BACKGROUND

Enoxaparin, a low-molecular-weight heparin, is known to possess anti-inflammatory properties. However, its clinical exploitation as an anti-inflammatory agent is hampered by its anticoagulant effect and the associated risk of bleeding.

OBJECTIVE

The aim of the current study was to examine the ability of non-anticoagulant fractions of enoxaparin to inhibit the release of key inflammatory cytokines in primed peripheral blood mononuclear cells derived from allergic mild asthmatics.

METHODS

Peripheral blood mononuclear cells from allergic asthmatics were activated with phytohaemag glutinin (PHA), concanavalin-A (ConA) or phorbol 12-myristate 13-acetate (PMA) in the presence or absence of enoxaparin fractions before cytokine levels were quantified using specific cytokine bead arrays. Together with nuclear magnetic resonance analysis,time-dependent and target-specific effects of enoxaparin fractions were used to elucidate structural determinants for their anti-inflammatory effect and gain mechanistic insights into their anti-inflammatory activity.

RESULTS

Two non-anticoagulant fractions of enoxaparin were identified that significantly inhibited T-cell activation. A disaccharide fraction of enoxaparin inhibited the release of IL-4, IL-5, IL-13 and TNF-α by more than 57% while a tetrasaccharide fraction was found to inhibit the release of tested cytokines by more than 68%. Our data suggest that the observed response is likely to be due to an interaction of 6-O-sulfated tetrasaccharide with cellular receptor(s).

CONCLUSION AND CLINICAL RELEVANCE

The two identified anti-inflammatory fractions lacked anticoagulant activity and are therefore not associated with risk of bleeding. The findings highlight the potential therapeutic use of enoxaparin-derived fractions, in particular tetrasaccharide, in patients with chronic inflammatory disorders.

In-vitro suppression of IL-6 and IL-8 release from human pulmonary epithelial cells by non-anticoagulant fraction of enoxaparin

BACKGROUND

Enoxaparin, a mixture of anticoagulant and non-anticoagulant fractions, is widely used as an anticoagulant agent. However, it is also reported to possess anti-inflammatory properties. Our study indicated that enoxaparin inhibits the release of IL-6 and IL-8 from A549 pulmonary epithelial cells. Their release causes extensive lung tissue damage. The use of enoxaparin as an anti-inflammatory agent is hampered due to the risk of bleeding associated with its anticoagulant fractions. Therefore, we aimed to identify the fraction responsible for the observed anti-inflammatory effect of enoxaparin and to determine the relationship between its structure and biological activities.

METHODS

A549 pulmonary epithelial cells were pre-treated in the presence of enoxaparin and its fractions. The levels of IL-6 and IL-8 released from the trypsin-stimulated cells were measured by ELISA. The anticoagulant activity of the fraction responsible for the effect of enoxaparin was determined using an anti-factor-Xa assay. The fraction was structurally characterised using nuclear magnetic resonance. The fraction was 2-O, 6-O or N-desulfated to determine the position of sulfate groups required for the inhibition of interleukins. High-performance size-exclusion chromatography was performed to rule out that the observed effect was due to the interaction between the fraction and trypsin or interleukins.

RESULTS

Enoxaparin (60 μg/mL) inhibited the release of IL-6 and IL-8 by >30%. The fraction responsible for this effect of enoxaparin was found to be a disaccharide composed of α-L-iduronic-acid and α-D-glucosamine-6-sulfate. It (15 μg/mL) inhibited the release of interleukins by >70%. The 6-O sulphate groups were responsible for its anti-inflammatory effect. The fraction did not bind to trypsin or interleukins, suggesting the effect was not due to an artefact of the experimental model.

CONCLUSION

The identified disaccharide has no anticoagulant activity and therefore eliminates the risk of bleeding associated with enoxaparin. Future in-vivo studies should be designed to validate findings of the current study.

Secreted Toxoplasma gondii molecules interfere with expression of MHC-II in interferon gamma-activated macrophages

The obligate intracellular protozoan parasite Toxoplasma gondii interferes with major histocompatibility complex class II antigen presentation to dampen host CD4(+) T cell responses. While it is known that T. gondii inhibits major histocompatibility complex class II gene transcription and expression in infected host cells, the mechanism of this host manipulation is unknown. Here, we show that soluble parasite proteins inhibit IFNγ-induced expression of major histocompatibility complex class II on the surface of the infected cell in a dose-dependent response that was abolished by protease treatment. Subcellular fractionation of T. gondii tachyzoites revealed that the major histocompatibility complex class II inhibitory activity co-partitioned with rhoptries and/or dense granules. However, parasite mutants deleted for single rhoptries or dense granules genes (ROP1, 4/7, 14, 16 and 18 or GRA 2-9 and 12 knock-out strains) retained the ability to inhibit expression of major histocompatibility complex class II. In addition, excreted/secreted antigens released by extracellular tachyzoites displayed immunomodulatory activity characterized by an inhibition of major histocompatibility complex class II expression, and reduced expression and release of TNFα by macrophages. Tandem MS analysis of parasite excreted/secreted antigens generated a list of T. gondii secreted proteins that may participate in major histocompatibility complex class II inhibition and the modulation of host immune functions.

Elevated postinjury thrombospondin 1-CD47 triggering aids differentiation of patients' defective inflammatory CD1a+dendritic cells

A subset of Pts develops dysfunctional MO to inflammatory DC differentiation and immunosuppression. MDDC, a newly described DC subset, is pivotal in initiating antibacterial responses. Endogenous proteins are known to alter MO to MDDC differentiation. In particular, trauma-elevated TSP-1, a protein that is known to affect MO functions, could trigger MDDC differentiation defects. We hypothesized that TSP-1-deranged differentiation of inflammatory CD1a(+)MDDC would negatively alter activation of immune functions, thereby increasing the risk of postinjury infections. Post-trauma increased TSP-1 levels in patients' plasma and MO correlated with two distinct MDDC differentiation dysfunctions: the previously described decreased CD1a(+)DC yields but also, development of an immunoincompetent CD1a(+)MDDC. The Pts' development of Dysf DC correlated to increased infectious complications. TSP-1 triggered its inhibitory receptor, CD47, activating an inhibitory phosphatase, SHP-1. Increased pSHP-1, decreased antigen processing, and depressed T cell stimulation characterized Pt Dysf DC. TSP-1 mimics added during Cnt MDDC differentiation depressed CD1a(+)DC yields but more importantly, also induced defective CD1a(+)MDDC, reproducing Pts' MDDC differentiation dysfunctions. CD47 triggering during Cnt MDDC differentiation increased SHP-1 activation, inhibiting IL-4-induced STAT-6 activation (critical for CD1a(+)MDDC differentiation). SHP-1 inhibition during MDDC differentiation in the presence of TSP-1 mimics restored pSTAT-6 levels and CD1a(+)MDDC immunogenicity. Thus, postinjury-elevated TSP-1 can decrease CD1a(+)DC yields but more critically, also induces SHP-1 hyperactivity, deviating MDDC differentiation to defective CD1a(+) inflammatory MDDCs by inhibiting STAT-6.

Differentiation and activation of equine monocyte-derived dendritic cells are not correlated with CD206 or CD83 expression

Dendritic cells (DC) are the main immune mediators inducing primary immune responses. DC generated from monocytes (MoDC) are a model system to study the biology of DC in vitro, as they represent inflammatory DC in vivo. Previous studies on the generation of MoDC in horses indicated that there was no distinct difference between immature and mature DC and that the expression profile was distinctly different from humans, where CD206 is expressed on immature MoDC whereas CD83 is expressed on mature MoDC. Here we describe the kinetics of equine MoDC differentiation and activation, analysing both phenotypic and functional characteristics. Blood monocytes were first differentiated with equine granulocyte-macrophage colony-stimulating factor and interleukin-4 generating immature DC (iMoDC). These cells were further activated with a cocktail of cytokines including interferon-γ) but not CD40 ligand to obtain mature DC (mMoDC). To determine the expression of a broad range of markers for which no monoclonal antibodies were available to analyse the protein expression, microarray and quantitative PCR analysis were performed to carry out gene expression analysis. This study demonstrates that equine iMoDC and mMoDC can be distinguished both phenotypically and functionally but the expression pattern of some markers including CD206 and CD83 is dissimilar to the human system.

Insights into the mechanism by which interferon-γ basic amino acid clusters mediate protein binding to heparan sulfate

The extensive functional repertoire of heparin and heparan sulfate, which relies on their ability to interact with a large number of proteins, has recently emerged. To understand the forces that drive such interactions the binding of heparin to interferon-γ (IFNγ), used as a model system, was investigated. NMR-based titration experiments demonstrated the involvement of two adjacent cationic domains (D1: KTGKRKR and D2: RGRR), both of which are present within the carboxy-terminal sequence of the cytokine. Kinetic analysis showed that these two domains contribute differently to the interaction: D1 is required to form a complex and constitutes the actual binding site, whereas D2, although unable to associate with heparin by itself, increased the association rate of the binding. These data are consistent with the view that D2, through nonspecific electrostatic forces, places the two molecules in favorable orientations for productive binding within the encounter complex. This mechanism was supported by electrostatic potential analysis and thermodynamic investigations. They showed that D1 association to heparin is driven by both favorable enthalpic and entropic contributions, as expected for a binding sequence, but that D2 gives rise to entropic penalty, which opposes binding in a thermodynamic sense. The binding mechanism described herein, by which the D2 domain kinetically drives the interaction, has important functional consequences and gives a structural framework to better understand how specific are the interactions between proteins and heparin.

Platinum-based drugs disrupt STAT6-mediated suppression of immune responses against cancer in humans and mice

Tumor microenvironments feature immune inhibitory mechanisms that prevent T cells from generating effective antitumor immune responses. Therapeutic interventions aimed at disrupting these inhibitory mechanisms have been shown to enhance antitumor immunity, but they lack direct cytotoxic effects. Here, we investigated the effect of cytotoxic cancer chemotherapeutics on immune inhibitory pathways. We observed that exposure to platinum-based chemotherapeutics markedly reduced expression of the T cell inhibitory molecule programmed death receptor-ligand 2 (PD-L2) on both human DCs and human tumor cells. Downregulation of PD-L2 resulted in enhanced antigen-specific proliferation and Th1 cytokine secretion as well as enhanced recognition of tumor cells by T cells. Further analysis revealed that STAT6 controlled downregulation of PD-L2. Consistent with these data, patients with STAT6-expressing head and neck cancer displayed enhanced recurrence-free survival upon treatment with cisplatin-based chemoradiation compared with patients with STAT6-negative tumors, demonstrating the clinical relevance of platinum-induced STAT6 modulation. We therefore conclude that platinum-based anticancer drugs can enhance the immunostimulatory potential of DCs and decrease the immunosuppressive capability of tumor cells. This dual action of platinum compounds may extend their therapeutic application in cancer patients and provides a rationale for their use in combination with immunostimulatory compounds.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.

Pregnancy-specific glycoprotein 1 induces endothelial tubulogenesis through interaction with cell surface proteoglycans

Pregnancy-specific β1 glycoproteins (PSGs) are the most abundant fetal proteins in the maternal bloodstream in late pregnancy. They are secreted by the syncytiotrophoblast and are detected around day 14 postfertilization. There are 11 human PSG genes, which encode a family of proteins exhibiting significant conservation at the amino acid level. We and others have proposed that PSGs have an immune modulatory function. In addition, we recently postulated that they are proangiogenic due to their ability to induce the secretion of VEGF-A and the formation of tubes by endothelial cells. The cellular receptor(s) for human PSGs remain unknown. Therefore, we conducted these studies to identify the receptor for PSG1, the highest expressed member of the family. We show that removal of cell surface glycosaminoglycans (GAGs) by enzymatic or chemical treatment of cells or competition with heparin completely inhibited binding of PSG1. In addition, PSG1 did not bind to cells lacking heparan or chondroitin sulfate on their surface, and binding was restored upon transfection with all four syndecans and glypican-1. Importantly, the presence of GAGs on the surface of endothelial cells was required for the ability of PSG1 to induce tube formation. This finding indicates that the PSG1-GAG interaction mediates at least some of the PSG1 proposed functions.

Cell culture plastics with immobilized interleukin-4 for monocyte differentiation

Standard cell culture plastic was surface modified by passive adsorption or covalent attachment of interleukin (IL)-4 and investigated for its ability to induce differentiation of human monocytes into mature dendritic cells, a process dose-dependently regulated by IL-4. Covalent attachment of IL-4 proceeded via anthraquinone photochemistry to introduce amine functionalities at the surface followed by coupling of IL-4 through a bifunctional amine-reactive linker. X-ray photoelectron spectroscopy showed that undesirable multilayer formation of the photoactive compound could be avoided by reaction in water instead of phosphate-buffered saline. Passively adsorbed IL-4 was observed to induce differentiation to dendritic cells, but analysis of cell culture supernatants revealed that leakage of IL-4 into solution could account for the differentiation observed. Covalent attachment resulted in bound IL-4 at similar concentrations to the passive adsorption process, as measured by enzyme-linked immunosorbent assays, and the bound IL-4 did not leak into solution to any measurable extent during cell culture. However, covalently bound IL-4 was incapable of inducing monocyte differentiation. This may be caused by IL-4 denaturation or improper epitope presentation induced by the immobilization process, or by biological irresponsiveness of monocytes to IL-4 in immobilized formats.

Monocyte-bound PF4 in the pathogenesis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a life- and limb-threatening thrombotic disorder that develops after exposure to heparin, often in the setting of inflammation. We have shown previously that HIT is associated with antibodies to complexes that form between platelet factor 4 and glycosaminoglycan (GAG) side chains on the surface of platelets. However, thrombosis can occur in the absence of thrombocytopenia. We now show that platelet factor 4 binds to monocytes and forms antigenic complexes with their surface GAG side chains more efficiently than on platelets likely due to differences in GAG composition. Binding to monocytes is enhanced when the cells are activated by endotoxin. Monocyte accumulation within developing arteriolar thrombi was visualized by situ microscopy. Monocyte depletion or inactivation in vivo attenuates thrombus formation induced by photochemical injury of the carotid artery in a modified murine model of HIT while paradoxically exacerbating thrombocytopenia. These studies demonstrate a previously unappreciated role for monocytes in the pathogenesis of arterial thrombosis in HIT and suggest that therapies targeting these cells might provide an alternative approach to help limit thrombosis in this and possibly other thrombotic disorders that occur in the setting of inflammation.

Monocyte-bound PF4 in the pathogenesis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a life- and limb-threatening thrombotic disorder that develops after exposure to heparin, often in the setting of inflammation. We have shown previously that HIT is associated with antibodies to complexes that form between platelet factor 4 and glycosaminoglycan (GAG) side chains on the surface of platelets. However, thrombosis can occur in the absence of thrombocytopenia. We now show that platelet factor 4 binds to monocytes and forms antigenic complexes with their surface GAG side chains more efficiently than on platelets likely due to differences in GAG composition. Binding to monocytes is enhanced when the cells are activated by endotoxin. Monocyte accumulation within developing arteriolar thrombi was visualized by situ microscopy. Monocyte depletion or inactivation in vivo attenuates thrombus formation induced by photochemical injury of the carotid artery in a modified murine model of HIT while paradoxically exacerbating thrombocytopenia. These studies demonstrate a previously unappreciated role for monocytes in the pathogenesis of arterial thrombosis in HIT and suggest that therapies targeting these cells might provide an alternative approach to help limit thrombosis in this and possibly other thrombotic disorders that occur in the setting of inflammation.

In vivo recruitment of hematopoietic cells using stromal cell-derived factor 1 alpha-loaded heparinized three-dimensional collagen scaffolds

Implantable three-dimensional (3D) constructs to engineer tissue have great therapeutic potential in regenerative medicine and immunotherapy. However, autonomous recruitment of cells into the engineered scaffold in vivo is hampered by lack of attracting scaffolds. As a first step to engineering immune tissue, 3D collagen scaffolds were investigated for their ability to enhance in vivo recruitment and growth of various hematopoietic cells. Scaffolds containing immobilized heparin to trap the stem cell chemo-attractant stromal cell-derived factor 1 alpha (SDF1alpha) were implanted subcutaneously into C57Bl6 mice, and influx of cells was monitored using immunohistochemistry. Five weeks post-implantation, heparinized scaffolds were always populated by cells, but incorporating SDF1alpha considerably stimulated recruitment of cells. SDF1alpha could not exert this effect when the formation of a SDF1alpha gradient was abrogated. Scaffolds were mainly populated by CD11b+ and CD11c+ myeloid cells and fibroblasts. One week after implantation, scaffolds harbored only low numbers of cells. Apparently, not all CXCR4-expressing cells, like large numbers of granulocytes, migrate into the scaffold, but retransplantation of a 1-week-old scaffold from a CD45.2(+) into a CD45.1(+) mouse yielded a scaffold harboring mainly CD45.2(+) cells after 5 weeks. These data confirm that only a few progenitor cells are recruited early after implantation. These cells then proliferate and differentiate along different lineages and determine the outcome after 5 weeks.

Biological implications of glycosaminoglycan interactions with haemopoietic cytokines

Heparan sulphate (HS) glycosaminoglycans (GAGs) are an integral part of the signalling complex of fibroblast derived growth factor (FGF) family members, HS being regarded as a coreceptor. FGFs are also retained in the tissues by binding to HS structures. Early studies on the contribution of the bone marrow stroma to haemopoiesis suggested that cytokines with a role in haemopoiesis were similarly retained in the stroma through interactions with HS. However, the functional outcomes of these cytokines binding HS were poorly understood. Here the GAG-binding properties of cytokines of the four alpha-helical bundle family and the biological consequences of such binding are reviewed. From this analysis it is apparent that although many of these cytokines do bind GAGs, GAG binding is not a consistent feature, nor is the site of GAG binding conserved among these cytokines. The biological outcome of GAG binding depends, in part, on the location of the GAG-binding site on the cytokine. In some cases GAG binding appears to block signalling, whereas in others signalling is likely to be facilitated by binding. It is postulated that the interactions of these cytokines with their receptor complexes evolved independently of GAG binding, with GAG binding being an additional feature for a subset of this cytokine family. Nevertheless, because GAG binding localizes cytokines to sites within tissues, these interactions are likely to be critically important for the biology of these cytokines.