Organ-specific heparan sulfate structural phenotypes

Targeting Human Cancer by a Glycosaminoglycan Binding Malaria Protein

Plasmodium falciparum engineer infected erythrocytes to present the malarial protein, VAR2CSA, which binds a distinct type chondroitin sulfate (CS) exclusively expressed in the placenta. Here, we show that the same CS modification is present on a high proportion of malignant cells and that it can be specifically targeted by recombinant VAR2CSA (rVAR2). In tumors, placental-like CS chains are linked to a limited repertoire of cancer-associated proteoglycans including CD44 and CSPG4. The rVAR2 protein localizes to tumors in vivo and rVAR2 fused to diphtheria toxin or conjugated to hemiasterlin compounds strongly inhibits in vivo tumor cell growth and metastasis. Our data demonstrate how an evolutionarily refined parasite-derived protein can be exploited to target a common, but complex, malignancy-associated glycosaminoglycan modification.

Heparin and related polysaccharides: synthesis using recombinant enzymes and metabolic engineering

Glycosaminoglycans are linear anionic polysaccharides that exhibit a number of important biological and pharmacological activities. The two most prominent members of this class of polysaccharides are heparin/heparan sulfate and the chondroitin sulfates (including dermatan sulfate). These polysaccharides, having complex structures and polydispersity, are biosynthesized in the Golgi of most animal cells. The chemical synthesis of these glycosaminoglycans is precluded by their structural complexity. Today, we depend on food animal tissues for their isolation and commercial production. Ton quantities of these glycosaminoglycans are used annually as pharmaceuticals and nutraceuticals. The variability of animal-sourced glycosaminoglycans, their inherent impurities, the limited availability of source tissues, the poor control of these source materials, and their manufacturing processes suggest a need for new approaches for their production. Over the past decade, there have been major efforts in the biotechnological production of these glycosaminoglycans. This mini-review focuses on the use of recombinant enzymes and metabolic engineering for the production of heparin and chondroitin sulfates.

Fell-Muir Lecture: Heparan sulphate and the art of cell regulation: a polymer chain conducts the protein orchestra

Heparan sulphate (HS) sits at the interface of the cell and the extracellular matrix. It is a member of the glycosaminoglycan family of anionic polysaccharides with unique structural features designed for protein interaction and regulation. Its client proteins include soluble effectors (e.g. growth factors, morphogens, chemokines), membrane receptors and cell adhesion proteins such as fibronectin, fibrillin and various types of collagen. The protein-binding properties of HS, together with its strategic positioning in the pericellular domain, are indicative of key roles in mediating the flow of regulatory signals between cells and their microenvironment. The control of transmembrane signalling is a fundamental element in the complex biology of HS. It seems likely that, in some way, HS orchestrates diverse signalling pathways to facilitate information processing inside the cell. A dictionary definition of an orchestra is 'a large group of musicians who play together on various instruments …' to paraphrase, the HS orchestra is 'a large group of proteins that play together on various receptors'. HS conducts this orchestra to ensure that proteins hit the right notes on their receptors but, in the manner of a true conductor, does it also set 'the musical pulse' and create rhythm and harmony attractive to the cell? This is too big a question to answer but fun to think about as you read this review.

A microscopic view on the renal endothelial glycocalyx

Endothelial cells perform key homeostatic functions such as regulating blood flow, permeability, and aiding immune surveillance for pathogens. While endothelial activation serves normal physiological adaptation, maladaptation of these endothelial functions has been identified as an important effector mechanism in the progression of renal disease as well as the associated development of cardiovascular disease. The primary interface between blood and the endothelium is the glycocalyx. This carbohydrate-rich gel-like structure with its associated proteins mediates most of the regulatory functions of the endothelium. Because the endothelial glycocalyx is a highly dynamic and fragile structure ex vivo, and traditional tissue processing for staining and perfusion-fixation usually results in a partial or complete loss of the glycocalyx, studying its dimensions and function has proven to be challenging. In this review, we will outline the core functions of the glycocalyx and focus on different techniques to study structure-function relationships in kidney and vasculature.

Effects of restoring normoglycemia in type 1 diabetes on inflammatory profile and renal extracellular matrix structure after simultaneous pancreas and kidney transplantation

AIMS

Patients with type 1 diabetes and end-stage renal disease with simultaneous pancreas and kidney (SPK) or kidney transplants alone (KA) were recruited 9-12 years post transplantation. We investigated differences between these groups with regard to inflammatory parameters and long-term structural changes in kidneys.

METHODS

Blood samples were analyzed by ELISA and multiplex for chemokines, cytokines, growth factors, cell adhesion molecules and matrix metalloproteinases. Kidney graft biopsies were analyzed by electron microscopy for glomerular basement membrane thickness. Heparan- and chondroitin sulfate disaccharide structures were determined by size exclusion chromatography mass-spectrometry.

RESULTS

The SPK and the KA group had average glycated hemoglobin A1c (HbA1c) of 5.8% (40 mmol/mol) and 8.6% (70 mmol/mol) respectively. SPK recipients also had 16.2% lower body mass index (BMI) and 46.4% lower triglyceride levels compared with KA recipients, compatible with an improved metabolic profile in the SPK group. Plasminogen activator inhibitor (PAI-1), C-reactive protein (CRP) and vascular endothelial growth factor (VEGF) were lower in the SPK group. In kidney graft biopsies of the KA-patients an 81.2% increase in average glomerular basement membrane thickness was observed, accompanied by alterations in heparan sulfate proteoglycan structure. In addition to a decrease in 6-O-sulfated disaccharides, an increase in non-N-sulfated disaccharides with a corresponding slight decrease in N-sulfation was found in kidney biopsies from hyperglycemic patients.

CONCLUSIONS

Patients with end stage renal disease subjected to KA transplantation showed impaired inflammatory profile, increased thickness of basement membranes and distinct changes in heparan sulfate structures compared with SPK recipients.

Informatics tools to advance the biology of glycosaminoglycans and proteoglycans

Glycomics researchers have identified the need for integrated database systems for collecting glycomics information in a consistent format. The goal is to create a resource for knowledge discovery and dissemination to wider research communities. This has the potential to extend the research community to include biologists, clinicians, chemists, and computer scientists. This chapter discusses the technology and approach needed to create integrated data resources to empower the broader community to leverage extant glycomics data. The focus is on glycosaminoglycan (GAGs) and proteoglycan research, but the approach can be generalized. The methods described span the development of glycomics standards from CarbBank to Glyco Connection Tables. The existence of integrated data sets provides a foundation for novel methods of analysis such as machine learning for knowledge discovery. The implications of predictive analysis are examined in relation to disease biomarker to expand the target audience of GAG and proteoglycan research.

Differential effects on light chain amyloid formation depend on mutations and type of glycosaminoglycans

Amyloid light chain (AL) amyloidosis is a protein misfolding disease where immunoglobulin light chains sample partially folded states that lead to misfolding and amyloid formation, resulting in organ dysfunction and death. In vivo, amyloid deposits are found in the extracellular space and involve a variety of accessory molecules, such as glycosaminoglycans, one of the main components of the extracellular matrix. Glycosaminoglycans are a group of negatively charged heteropolysaccharides composed of repeating disaccharide units. In this study, we investigated the effect of glycosaminoglycans on the kinetics of amyloid fibril formation of three AL cardiac amyloidosis light chains. These proteins have similar thermodynamic stability but exhibit different kinetics of fibril formation. We also studied single restorative and reciprocal mutants and wild type germ line control protein. We found that the type of glycosaminoglycan has a different effect on the kinetics of fibril formation, and this effect seems to be associated with the natural propensity of each AL protein to form fibrils. Heparan sulfate accelerated AL-12, AL-09, κI Y87H, and AL-103 H92D fibril formation; delayed fibril formation for AL-103; and did not promote any fibril formation for AL-12 R65S, AL-103 delP95aIns, or κI O18/O8. Chondroitin sulfate A, on the other hand, showed a strong fibril formation inhibition for all proteins. We propose that heparan sulfate facilitates the formation of transient amyloidogenic conformations of AL light chains, thereby promoting amyloid formation, whereas chondroitin sulfate A kinetically traps partially unfolded intermediates, and further fibril elongation into fibrils is inhibited, resulting in formation/accumulation of oligomeric/protofibrillar aggregates.

Discovery of a heparan sulfate 3-O-sulfation specific peeling reaction

Heparan sulfate (HS) 3-O-sulfation determines the binding specificity of HS/heparin for antithrombin III and plays a key role in herpes simplex virus (HSV) infection. However, the low natural abundance of HS 3-O-sulfation poses a serious challenge for functional studies other than the two cases mentioned above. By contrast, multiple distinct isoforms of 3-O-sulfotranserases exist in mammals (up to seven isoenzymes). Here we describe a novel peeling reaction that specifically degrades HS chains with 3-O-sulfated glucosamine at the reducing-end. When HS/heparin is enzymatically depolymerized for compositional analysis, 3-O-sulfated glucosamine at the reducing ends appears to be susceptible to degradation under mildly basic conditions. We propose a 3-O-desulfation initiated peeling reaction mechanism based on the intermediate and side-reaction products observed. Our discovery calls for the re-evaluation of the natural abundance and functions of HS 3-O-sulfation by taking into consideration the negative impact of this novel peeling reaction.

A liquid chromatography-mass spectrometry-based approach to characterize the substrate specificity of mammalian heparanase

Extracellular heparanase activity releases growth factors and angiogenic factors from heparan sulfate (HS) storage sites and alters the integrity of the extracellular matrix. These activities lead to a loss of normal cell matrix adherent junctions and correlate with invasive cellular phenotypes. Elevated expression of heparanase is associated with several human cancers and with vascular remodeling. Heparanase cleaves only a limited fraction of glucuronidic linkages in HS. There have been few investigations of the functional consequences of heparanase activity, largely due to the heterogeneity and complexity of HS. Here, we report a liquid chromatography-mass spectrometry (LC-MS)-based approach to profile the terminal structures created by heparanase digestion and reconstruct the heparanase cleavage sites from the products. Using this method, we demonstrate that heparanase cleaves at the non-reducing side of highly sulfated HS domains, exposing cryptic growth factor binding sites. This cleavage pattern is observed in HS from several tissue sources, regardless of overall sulfation degree, indicating a common recognition pattern. We further demonstrate that heparanase cleavage of HS chains leads to increased ability to support FGF2-dependent cell proliferation. These results suggest a new mechanism to explain how heparanase might potentiate the uncontrolled cell proliferation associated with cancer through its ability to activate nascent growth factor-promoting domains within HS.

A broad spectrum of genomic changes in latinamerican patients with EXT1/EXT2-CDG

Multiple osteochondromatosis (MO), or EXT1/EXT2-CDG, is an autosomal dominant O-linked glycosylation disorder characterized by the formation of multiple cartilage-capped tumors (osteochondromas). In contrast, solitary osteochondroma (SO) is a non-hereditary condition. EXT1 and EXT2, are tumor suppressor genes that encode glycosyltransferases involved in heparan sulfate elongation. We present the clinical and molecular analysis of 33 unrelated Latin American patients (27 MO and 6 SO). Sixty-three percent of all MO cases presented severe phenotype and two malignant transformations to chondrosarcoma (7%). We found the mutant allele in 78% of MO patients. Ten mutations were novel. The disease-causing mutations remained unknown in 22% of the MO patients and in all SO patients. No second mutational hit was detected in the DNA of the secondary chondrosarcoma from a patient who carried a nonsense EXT1 mutation. Neither EXT1 nor EXT2 protein could be detected in this sample. This is the first Latin American research program on EXT1/EXT2-CDG.

Oligosaccharide substrate preferences of human extracellular sulfatase Sulf2 using liquid chromatography-mass spectrometry based glycomics approaches

Sulfs are extracellular endosulfatases that selectively remove the 6-O-sulfate groups from cell surface heparan sulfate (HS) chain. By altering the sulfation at these particular sites, Sulfs function to remodel HS chains. As a result of the remodeling activity, HSulf2 regulates a multitude of cell-signaling events that depend on interactions between proteins and HS. Previous efforts to characterize the substrate specificity of human Sulfs (HSulfs) focused on the analysis of HS disaccharides and synthetic repeating units. In this study, we characterized the substrate preferences of human HSulf2 using HS oligosaccharides with various lengths and sulfation degrees from several naturally occurring HS sources by applying liquid chromatography mass spectrometry based glycomics methods. The results showed that HSulf2 preferentially digests highly sulfated HS oligosaccharides with zero acetyl groups and this preference is length dependent. In terms of length of oligosaccharides, HSulf2 digestion induced more sulfation decrease on DP6 (DP: degree of polymerization) compared to DP2, DP4 and DP8. In addition, the HSulf2 preferentially digests the oligosaccharide domain located at the non-reducing end (NRE) of the HS and heparin chain. In addition, the HSulf2 digestion products were altered only for specific isomers. HSulf2 treated NRE oligosaccharides also showed greater decrease in cell proliferation than those from internal domains of the HS chain. After further chromatographic separation, we identified the three most preferred unsaturated hexasaccharide for HSulf2.

Heparan sulfate containing unsubstituted glucosamine residues: biosynthesis and heparanase-inhibitory activity

Degradation of heparan sulfate (HS) in the extracellular matrix by heparanase is linked to the processes of tumor invasion and metastasis. Thus, a heparanase inhibitor can be a potential anticancer drug. Because HS with unsubstituted glucosamine residues accumulates in heparanase-expressing breast cancer cells, we assumed that these HS structures are resistant to heparanase and can therefore be utilized as a heparanase inhibitor. As expected, chemically synthetic HS-tetrasaccharides containing unsubstituted glucosamine residues, GlcAβ1-4GlcNH3 (+)(6-O-sulfate)α1-4GlcAβ1-4GlcNH3 (+)(6-O-sulfate), inhibited heparanase activity and suppressed invasion of breast cancer cells in vitro. Bifunctional NDST-1 (N-deacetylase/N-sulfotransferase-1) catalyzes the modification of N-acetylglucosamine residues within HS chains, and the balance of N-deacetylase and N-sulfotransferase activities of NDST-1 is thought to be a determinant of the generation of unsubstituted glucosamine. We also report here that EXTL3 (exostosin-like 3) controls N-sulfotransferase activity of NDST-1 by forming a complex with NDST-1 and contributes to generation of unsubstituted glucosamine residues.

Remodeling of marrow hematopoietic stem and progenitor cells by non-self ST6Gal-1 sialyltransferase

Glycans occupy the critical cell surface interface between hematopoietic cells and their marrow niches. Typically, glycosyltransferases reside within the intracellular secretory apparatus, and each cell autonomously generates its own cell surface glycans. In this study, we report an alternate pathway to generate cell surface glycans where remotely produced glycosyltransferases remodel surfaces of target cells and for which endogenous expression of the cognate enzymes is not required. Our data show that extracellular ST6Gal-1 sialyltransferase, originating mostly from the liver and released into circulation, targets marrow hematopoietic stem and progenitor cells (HSPCs) and mediates the formation of cell surface α2,6-linked sialic acids on HSPCs as assessed by binding to the specific lectins Sambucus nigra agglutinin and Polysporus squamosus lectin and confirmed by mass spectrometry. Marrow HSPCs, operationally defined as the Lin-c-Kit+ and Lin-Sca-1+c-Kit+ populations, express negligible endogenous ST6Gal-1. Animals with reduced circulatory ST6Gal-1 have marrow Lin-Sca-1+c-Kit+ cells with reduced S. nigra agglutinin reactivity. Bone marrow chimeras demonstrated that α2,6-sialylation of HSPCs is profoundly dependent on circulatory ST6Gal-1 status of the recipients and independent of the ability of HSPCs to express endogenous ST6Gal-1. Biologically, HSPC abundance in the marrow is inversely related to circulatory ST6Gal-1 status, and this relationship is recapitulated in the bone marrow chimeras. We propose that remotely produced, rather than the endogenously expressed, ST6Gal-1 is the principal modifier of HSPC glycans for α2,6-sialic acids. In so doing, liver-produced ST6Gal-1 may be a potent systemic regulator of hematopoiesis.

Mass spectral profiling of glycosaminoglycans from histological tissue surfaces

Glycosaminoglycans (GAGs) are found in intracellular granules, cell surfaces, and extracellular matrices in a spatially and temporally regulated fashion, constituting the environment for cells to interact, migrate, and proliferate. Through binding with a great number of proteins, GAGs regulate many facets of biological processes from embryonic development to normal physiological functions. GAGs have been shown to be involved in pathologic changes and immunological responses including cancer metastasis and inflammation. Past analyses of GAGs have focused on cell lines, body fluids, and relatively large tissue samples. Structures determined from such samples reflect the heterogeneity of the cell types present. To gain an understanding of the roles played by GAG expression during pathogenesis, it is very important to be able to detect and profile GAGs at the histological scale so as to minimize cell heterogeneity to potentially inform diagnosis and prognosis. Heparan sulfate (HS) belongs to one major class of GAGs, characterized by dramatic structural heterogeneity and complexity. To demonstrate feasibility of analysis of HS, 15 μm frozen bovine brain stem, cortex, and cerebellum tissue sections were washed with a series of solvent solutions to remove lipids before applying heparin lyases I, II, and III on the tissue surfaces within 5 mm × 5 mm digestion spots. The digested HS disaccharides were extracted from tissue surfaces and then analyzed by using size exclusion chromatography/mass spectrometry (SEC-MS). The results from bovine brain stem, cortex, and cerebellum demonstrated the reproducibility and reliability of our profiling method. We applied our method to detect HS from human astrocytoma (WHO grade II) and glioblastoma (GBM, WHO grade IV) frozen slides. Higher HS abundances and lower average sulfation level of HS were detected in glioblastoma (GBM, WHO grade IV) slides compared to astrocytoma (WHO grade II) slides.

Brittlestars contain highly sulfated chondroitin sulfates/dermatan sulfates that promote fibroblast growth factor 2-induced cell signaling

Glycosaminoglycans (GAGs) isolated from brittlestars, Echinodermata class Ophiuroidea, were characterized, as part of attempts to understand the evolutionary development of these polysaccharides. A population of chondroitin sulfate/dermatan sulfate (CS/DS) chains with a high overall degree of sulfation and hexuronate epimerization was the major GAG found, whereas heparan sulfate (HS) was below detection level. Enzymatic digestion with different chondroitin lyases revealed exceptionally high proportions of di- and trisulfated CS/DS disaccharides. The latter unit appears much more abundant in one of four individual species of brittlestars, Amphiura filiformis, than reported earlier in other marine invertebrates. The brittlestar CS/DS was further shown to bind to growth factors such as fibroblast growth factor 2 and to promote FGF-stimulated cell signaling in GAG-deficient cell lines in a manner similar to that of heparin. These findings point to a potential biological role for the highly sulfated invertebrate GAGs, similar to those ascribed to HS in vertebrates.

Heparin-dependent regulation of fibronectin matrix conformation

Extracellular matrix (ECM) conformation is regulated by a variety of stimuli in vivo, including mechanical forces and allosteric binding partners, and these conformational changes contribute to the regulation of cell behavior. Heparin and heparan sulfate, for example, have been shown to regulate the sequestration and presentation of numerous growth factors, including vascular endothelial growth factor, on the heparin 2 binding domain in fibronectin (Fn). However, mechanical force also alters Fn conformation, indicating that the growth factor binding region may be co-regulated by both heparin and mechanical force. Herein, we describe a simple antibody-based method for evaluating the conformation of the heparin 2 binding domain in Fn, and use it to determine the relative contributions of heparin and mechanical strain to the regulation of Fn conformation. We achieved specificity in quantifying conformational changes in this region of Fn by measuring the ratio of two fluorescent monoclonal antibodies, one that is insensitive to Fn conformational changes and a second whose binding is reduced or enhanced by non-equilibrium conformational changes. Importantly, this technique is shown to work on Fn adsorbed on surfaces, single Fn fibers, and Fn matrix fibers in cell culture. Using our dual antibody approach, we show that heparin and mechanical strain co-regulate Fn conformation in matrix fibrils, which is the first demonstration of heparin-dependent regulation of Fn in its physiologically-relevant fibrillar state. Furthermore, the dual antibody approach utilizes commercially available antibodies and simple immunohistochemistry, thus making it accessible to a wide range of scientists interested in Fn mechanobiology.

LC-MS and LC-MS/MS studies of incorporation of 34SO3 into glycosaminoglycan chains by sulfotransferases

The specificities of glycosaminoglycan (GAG) modification enzymes, particularly sulfotransferases, and the locations and concentrations of these enzymes in the Golgi apparatus give rise to the mature GAG polysaccharides that bind protein ligands. We studied the substrate specificities of sulfotransferases with a stable isotopically labeled donor substrate, 3'-phosphoadenosine-5'-phosphosulfate. The sulfate incorporated by in vitro sulfation using recombinant sulfotransferases was easily distinguished from those previously present on the GAG chains using mass spectrometry. The enrichment of the [M + 2] isotopic peak caused by (34)S incorporation, and the [M + 2]/[M + 1] ratio, provided reliable and sensitive measures of the degree of in vitro sulfation. It was found that both CHST3 and CHST15 have higher activities at the non-reducing end (NRE) units of chondroitin sulfate, particularly those terminating with a GalNAc monosaccharide. In contrast, both NDST1 and HS6ST1 showed lower activities at the NRE of heparan sulfate (HS) chains than at the interior of the chain. Contrary to the traditional view of HS biosynthesis processes, NDST1 also showed activity on O-sulfated GlcNAc residues.

Comparative glycomics of leukocyte glycosaminoglycans

Glycosaminoglycans (GAGs) vary widely in disaccharide and oligosaccharide content in a tissue-specific manner. Nonetheless, there are common structural features, such as the presence of highly sulfated non-reducing end domains on heparan sulfate (HS) chains. Less clear are the patterns of expression of GAGs on specific cell types. Leukocytes are known to express GAGs primarily of the chondroitin sulfate (CS) type. However, little is known regarding the properties and structures of the GAG chains, their variability among normal subjects, and changes in structure associated with disease conditions. We isolated peripheral blood leukocyte populations from four human donors and extracted GAGs. We determined the relative and absolute disaccharide abundances for HS and CS GAGs classes using size exclusion chromatography-mass spectrometry (SEC-MS). We found that all leukocytes express HS chains with a level of sulfation that is more similar to heparin than to organ-derived HS. The levels of HS expression follows the trend T cells/B cells > monocytes/natural killer cells > polymorphonuclear leukocytes (PMNs). In addition, CS abundances were considerably higher than total HS but varied considerably in a leukocyte cell type-specific manner. Levels of CS were higher for myeloid lineage cells (PMNs and monocytes) than for lymphoid cells (B, T and natural killer (NK) cells). This information establishes the range of GAG structures expressed on normal leukocytes and is necessary for subsequent inquiry into disease conditions.

Glycosaminoglycan glycomics using mass spectrometry

The fact that sulfated glycosaminoglycans (GAGs) are necessary for the functioning of all animal physiological systems drives the need to understand their biology. This understanding is limited, however, by the heterogeneous nature of GAG chains and their dynamic spatial and temporal expression patterns. GAGs have a regulated structure overlaid by heterogeneity but lack the detail necessary to build structure/function relationships. In order to provide this information, we need glycomics platforms that are sensitive, robust, high throughput, and information rich. This review summarizes progress on mass-spectrometry-based GAG glycomics methods. The areas covered include disaccharide analysis, oligosaccharide profiling, and tandem mass spectrometric sequencing.

Disaccharide analysis of glycosaminoglycans using hydrophilic interaction chromatography and mass spectrometry

Heparan sulfate (HS) and chondroitin sulfate/dermatan sulfate (CS/DS) glycosaminoglycans (GAGs) participate in many important biological processes. Quantitative disaccharide analysis of HS and CS/DS is essential for the characterization of GAGs and enables modeling of the GAG domain structure. Methods involving enzymatic digestion and chemical depolymerization have been developed to determine the type and location of sulfation/acetylation modifications as well as uronic acid epimerization. Enzymatic digestion generates disaccharides with Δ-4,5-unsaturation at the nonreducing end. Chemical depolymerization with nitrous acid retains the uronic acid epimerization. This work shows the use of hydrophilic interaction liquid chromatography mass spectrometry (HILIC-MS) for quantification of both enzyme-derived and nitrous acid depolymerization products for structural analysis of HS and CS/DS. This method enables biomedical researchers to determine complete disaccharide profiles on GAG samples using a single LC-MS platform.

ELECTRON DETACHMENT DISSOCIATION OF SYNTHETIC HEPARAN SULFATE GLYCOSAMINOGLYCAN TETRASACCHARIDES VARYING IN DEGREE OF SULFATION AND HEXURONIC ACID STEREOCHEMISTRY

Glycosaminoglycan (GAG) carbohydrates provide a challenging analytical target for structural determination due to their polydisperse nature, non-template biosynthesis, and labile sulfate modifications. The resultant structures, although heterogeneous, contain domains which indicate a sulfation pattern or code that correlates to specific function. Mass spectrometry, in particular electron detachment dissociation Fourier transform ion cyclotron resonance (EDD FT-ICR MS), provides a highly sensitive platform for GAG structural analysis by providing cross-ring cleavages for sulfation location and product ions specific to hexuronic acid stereochemistry. To investigate the effect of sulfation pattern and variations in stereochemistry on EDD spectra, a series of synthetic heparan sulfate (HS) tetrasaccharides are examined. Whereas previous studies have focused on lowly sulfated compounds (0.5-1 sulfate groups per disaccharide), the current work extends the application of EDD to more highly sulfated tetrasaccharides (1-2 sulfate groups per disaccharide) and presents the first EDD of a tetrasaccharide containing a sulfated hexuronic acid. For these more highly sulfated HS oligomers, alternative strategies are shown to be effective for extracting full structural details. These strategies inlcude sodium cation replacement of protons, for determining the sites of sulfation, and desulfation of the oligosaccharides for the generation of product ions for assigning uronic acid stereochemistry.

Enterovirus 71 uses cell surface heparan sulfate glycosaminoglycan as an attachment receptor

Enterovirus 71 (EV-71) infections are usually associated with mild hand, foot, and mouth disease in young children but have been reported to cause severe neurological complications with high mortality rates. To date, four EV-71 receptors have been identified, but inhibition of these receptors by antagonists did not completely abolish EV-71 infection, implying that there is an as yet undiscovered receptor(s). Since EV-71 has a wide range of tissue tropisms, we hypothesize that EV-71 infections may be facilitated by using receptors that are widely expressed in all cell types, such as heparan sulfate. In this study, heparin, polysulfated dextran sulfate, and suramin were found to significantly prevent EV-71 infection. Heparin inhibited infection by all the EV-71 strains tested, including those with a single-passage history. Neutralization of the cell surface anionic charge by polycationic poly-d-lysine and blockage of heparan sulfate by an anti-heparan sulfate peptide also inhibited EV-71 infection. Interference with heparan sulfate biosynthesis either by sodium chlorate treatment or through transient knockdown of N-deacetylase/N-sulfotransferase-1 and exostosin-1 expression reduced EV-71 infection in RD cells. Enzymatic removal of cell surface heparan sulfate by heparinase I/II/III inhibited EV-71 infection. Furthermore, the level of EV-71 attachment to CHO cell lines that are variably deficient in cell surface glycosaminoglycans was significantly lower than that to wild-type CHO cells. Direct binding of EV-71 particles to heparin-Sepharose columns under physiological salt conditions was demonstrated. We conclude that EV-71 infection requires initial binding to heparan sulfate as an attachment receptor.

Sulfated glycosaminoglycan-assisted receptor specificity of human fibroblast growth factor (FGF) 19 signaling in a mouse system is different from that in a human system

The endocrine action of human (h) intestine-derived fibroblast growth factor 19 (hFGF19) toward liver cells necessitates a highly specific recognition system. We previously reported that at physiological concentrations (~30 pM), hFGF19 requires sulfated glycosaminoglycans (sGAGs) for its signaling via human FGF receptor 4 (hFGFR4) in the presence of a co-receptor, human βKlotho (hKLB), thus establishing specific targeting. Here we report that the specificity of hFGF19 signaling is greatly altered in a mouse model system. In in vitro cellular systems, at concentrations achievable in transgenic animals and in pharmacologic animal experiments (1-100 nM), hFGF19 activates mouse (m)FGFR1c, mFGFR2c, and mFGFR3c but not mFGFR4 in the presence of mKLB and nonheparin authentic sGAGs. Furthermore, in the presence of hepatic sGAGs or heparin, nanomolar hFGF19 activates mFGFR4, even in the absence of co-expressed mKLB. Taken together, these results indicate that the sGAG-assisted receptor specificity of hFGF19 signaling achieved in experimental mouse systems differs greatly from that in physiological human systems. This suggests the function and mechanism of hFGF19 signaling identified using mouse systems should be reevaluated.

GlycReSoft: a software package for automated recognition of glycans from LC/MS data

Glycosylation modifies the physicochemical properties and protein binding functions of glycoconjugates. These modifications are biosynthesized in the endoplasmic reticulum and Golgi apparatus by a series of enzymatic transformations that are under complex control. As a result, mature glycans on a given site are heterogeneous mixtures of glycoforms. This gives rise to a spectrum of adhesive properties that strongly influences interactions with binding partners and resultant biological effects. In order to understand the roles glycosylation plays in normal and disease processes, efficient structural analysis tools are necessary. In the field of glycomics, liquid chromatography/mass spectrometry (LC/MS) is used to profile the glycans present in a given sample. This technology enables comparison of glycan compositions and abundances among different biological samples, i.e. normal versus disease, normal versus mutant, etc. Manual analysis of the glycan profiling LC/MS data is extremely time-consuming and efficient software tools are needed to eliminate this bottleneck. In this work, we have developed a tool to computationally model LC/MS data to enable efficient profiling of glycans. Using LC/MS data deconvoluted by Decon2LS/DeconTools, we built a list of unique neutral masses corresponding to candidate glycan compositions summarized over their various charge states, adducts and range of elution times. Our work aims to provide confident identification of true compounds in complex data sets that are not amenable to manual interpretation. This capability is an essential part of glycomics work flows. We demonstrate this tool, GlycReSoft, using an LC/MS dataset on tissue derived heparan sulfate oligosaccharides. The software, code and a test data set are publically archived under an open source license.

Mass spectrometric method for determining the uronic acid epimerization in heparan sulfate disaccharides generated using nitrous acid

Heparan sulfate (HS) glycosaminoglycans (GAGs) regulate a host of biological functions. To better understand their biological roles, it is necessary to gain understanding about the structure of HS, which requires identification of the sulfation pattern as well as the uronic acid epimerization. In order to model HS structure, it is necessary to quantitatively profile depolymerization products. To date, liquid chromatography-mass spectrometry (LC-MS) methods for profiling heparin lyase decomposition products have been shown. These enzymes, however, destroy information about uronic acid epimerization. Deaminative cleavage using nitrous acid (HONO) is a classic method for GAG depolymerization that retains uronic acid epimerization. Several chromatographic methods have been used for analysis of deaminative cleavage products. The chromatographic methods have the disadvantage that there is no direct readout on the structures producing the observed peaks. This report demonstrates a porous graphitized carbon (PGC)-MS method for the quantification of HONO generated disaccharides to obtain information about the sulfation pattern and uronic acid epimerization. Here, we demonstrate the separation and identification of uronic acid epimers as well as geometric sulfation isomers. The results are comparable to those expected for benchmark HS and heparin samples. The data demonstrate the utility of PGC-MS for quantification of HS nitrous acid depolymerization products for structural analysis of HS and heparin.

Heparan sulfate 6-O-endosulfatases (Sulfs) coordinate the Wnt signaling pathways to regulate myoblast fusion during skeletal muscle regeneration

Skeletal muscle regeneration is mediated by satellite cells (SCs). Upon injury, SCs undergo self-renewal, proliferation, and differentiation into myoblasts followed by myoblast fusion to form new myofibers. We previously showed that the heparan sulfate (HS) 6-O-endosulfatases (Sulf1 and -2) repress FGF signaling to induce SC differentiation during muscle regeneration. Here, we identify a novel role of Sulfs in myoblast fusion using a skeletal muscle-specific Sulf double null (Sulf(SK)-DN) mouse. Regenerating Sulf(SK)-DN muscles exhibit reduced canonical Wnt signaling and elevated non-canonical Wnt signaling. In addition, we show that Sulfs are required to repress non-canonical Wnt signaling to promote myoblast fusion. Notably, skeletal muscle-relevant non-canonical Wnt ligands lack HS binding capacity, suggesting that Sulfs indirectly repress this pathway. Mechanistically, we show that Sulfs reduce the canonical Wnt-HS binding and regulate colocalization of the co-receptor LRP5 with caveolin3. Therefore, Sulfs may increase the bioavailability of canonical Wnts for Frizzled receptor and LRP5/6 interaction in lipid raft, which may in turn antagonize non-canonical Wnt signaling. Furthermore, changes in subcellular distribution of active focal adhesion kinase (FAK) are associated with the fusion defect of Sulf-deficient myoblasts and upon non-canonical Wnt treatment. Together, our findings uncover a critical role of Sulfs in myoblast fusion by promoting antagonizing canonical Wnt signaling activities against the noncanonical Wnt pathway during skeletal muscle regeneration.

A model of GAG/MIP-2/CXCR2 interfaces and its functional effects

MIP-2/CXCL2 is a murine chemokine related to human chemokines that possesses the Glu-Leu-Arg (ELR) activation motif and activates CXCR2 for neutrophil chemotaxis. We determined the structure of MIP-2 to 1.9 Å resolution and created a model with its murine receptor CXCR2 based on the coordinates of human CXCR4. Chemokine-induced migration of cells through specific G-protein coupled receptors is regulated by glycosaminoglycans (GAGs) that oligomerize chemokines. MIP-2 GAG-binding residues were identified that interact with heparin disaccharide I-S by NMR spectroscopy. A model GAG/MIP-2/CXCR2 complex that supports a 2:2 complex between chemokine and receptor was created. Mutants of these disaccharide-binding residues were made and tested for heparin binding, in vitro neutrophil chemotaxis, and in vivo neutrophil recruitment to the mouse peritoneum and lung. The mutants have a 10-fold decrease in neutrophil chemotaxis in vitro. There is no difference in neutrophil recruitment between wild-type MIP-2 and mutants in the peritoneum, but all activity of the mutants is lost in the lung, supporting the concept that GAG regulation of chemokines is tissue-dependent.

Dermatan sulfate is involved in the tumorigenic properties of esophagus squamous cell carcinoma

Extracellular matrix, either produced by cancer cells or by cancer-associated fibroblasts, influences angiogenesis, invasion, and metastasis. Chondroitin/dermatan sulfate (CS/DS) proteoglycans, which occur both in the matrix and at the cell surface, play important roles in these processes. The unique feature that distinguishes DS from CS is the presence of iduronic acid (IdoA) in DS. Here, we report that CS/DS is increased five-fold in human biopsies of esophagus squamous cell carcinoma (ESCC), an aggressive tumor with poor prognosis, as compared with normal tissue. The main IdoA-producing enzyme, DS epimerase 1 (DS-epi1), together with the 6-O- and 4-O-sulfotransferases, were highly upregulated in ESCC biopsies. Importantly, CS/DS structure in patient tumors was significantly altered compared with normal tissue, as determined by sensitive mass spectrometry. To further understand the roles of IdoA in tumor development, DS-epi1 expression, and consequently IdoA content, was downregulated in ESCC cells. IdoA-deficient cells exhibited decreased migration and invasion capabilities in vitro, which was associated with reduced cellular binding of hepatocyte growth factor, inhibition of pERK-1/2 signaling, and deregulated actin cytoskeleton dynamics and focal adhesion formation. Our findings show that IdoA in DS influences tumorigenesis by affecting cancer cell behavior. Therefore, downregulation of IdoA by DS-epi1 inhibitors may represent a new anticancer therapy.

Differential Characterization and Classification of Tissue Specific Glycosaminoglycans by Tandem Mass Spectrometry and Statistical Methods

The biological functions of glycoconjugate glycans arise in the context of structural heterogeneity resulting from non-template driven biosynthetic reactions. Such heterogeneity is particularly apparent for the glycosaminoglycan (GAG) classes, of which heparan sulfate (HS) is of particular interest for its properties in binding to many classes of growth factors and growth factor receptors. The structures of HS chains vary according to spatial and temporal factors in biological systems as a mechanism where by the functions of the relatively limited number of associated proteoglycan core proteins is elaborated. Thus, there is a strong driver for the development of methods to discover functionally relevant structures in HS preparations for different sources. In the present work, a set of targeted tandem mass spectra were acquired in automated mode on HS oligosaccharides deriving from two different tissue sources. Statistical methods were used to determine the precursor and product ions, the abundances of which differentiate between the tissue sources. The results demonstrate considerable potential for using this approach to constrain the number of positional glycoform isomers present in different biological preparations toward the end of discovery of functionally relevant structures.

Organ-specific sulfation patterns of heparan sulfate generated by extracellular sulfatases Sulf1 and Sulf2 in mice

Heparan sulfate endosulfatases Sulf1 and Sulf2 hydrolyze 6-O-sulfate in heparan sulfate, thereby regulating cellular signaling. Previous studies have revealed that Sulfs act predominantly on UA2S-GlcNS6S disaccharides and weakly on UA-GlcNS6S disaccharides. However, the specificity of Sulfs and their role in sulfation patterning of heparan sulfate in vivo remained unknown. Here, we performed disaccharide analysis of heparan sulfate in Sulf1 and Sulf2 knock-out mice. Significant increases in ΔUA2S-GlcNS6S were observed in the brain, small intestine, lung, spleen, testis, and skeletal muscle of adult Sulf1(-/-) mice and in the brain, liver, kidney, spleen, and testis of adult Sulf2(-/-) mice. In addition, increases in ΔUA-GlcNS6S were seen in the Sulf1(-/-) lung and small intestine. In contrast, the disaccharide compositions of chondroitin sulfate were not primarily altered, indicating specificity of Sulfs for heparan sulfate. For Sulf1, but not for Sulf2, mRNA expression levels in eight organs of wild-type mice were highly correlated with increases in ΔUA2S-GlcNS6S in the corresponding organs of knock-out mice. Moreover, overall changes in heparan sulfate compositions were greater in Sulf1(-/-) mice than in Sulf2(-/-) mice despite lower levels of Sulf1 mRNA expression, suggesting predominant roles of Sulf1 in heparan sulfate desulfation and distinct regulation of Sulf activities in vivo. Sulf1 and Sulf2 mRNAs were differentially expressed in restricted types of cells in organs, and consequently, the sulfation patterns of heparan sulfate were locally and distinctly altered in Sulf1 and Sulf2 knock-out mice. These findings indicate that Sulf1 and Sulf2 differentially contribute to the generation of organ-specific sulfation patterns of heparan sulfate.

Disease-specific non-reducing end carbohydrate biomarkers for mucopolysaccharidoses

A considerable need exists for improved biomarkers for differential diagnosis, prognosis and monitoring of therapeutic interventions for mucopolysaccharidoses (MPS), inherited metabolic disorders that involve lysosomal storage of glycosaminoglycans. Here we report a simple, reliable method based on the detection of abundant nonreducing ends of the glycosaminoglycans that accumulate in cells, blood and urine of individuals with MPS. In this method, glycosaminoglycans are enzymatically depolymerized, releasing unique mono-, di- or trisaccharides from the nonreducing ends of the chains. The composition of the released mono- and oligosaccharides depends on the nature of the lysosomal enzyme deficiency, and therefore they serve as diagnostic biomarkers. Analysis by LC/MS allowed qualitative and quantitative assessment of the biomarkers in biological samples. We provide a simple conceptual scheme for diagnosing MPS in uncharacterized samples and a method to monitor efficacy of enzyme replacement therapy or other forms of treatment.

Heparan sulphate: a heparin in miniature

Heparan sulphate (HS), discovered in 1948 in heparin by-products, only emerged slowly from the shadow of heparin. Its inauspicious beginning was followed by the gradual realisation that HS was a separate entity with distinctive features. Both HS and heparin follow a common biosynthetic route but while heparin reaches full maturity, HS holds on to some of its youthful traits. The novel design and complex patterning of sulphation in HS enable it fulfil key roles in many, diverse biological processes.

Heparin and heparan sulfate: analyzing structure and microheterogeneity

The structural microheterogeneity of heparin and heparan sulfate is one of the major reasons for the multifunctionality exhibited by this class of molecules. In a physiological context, these molecules primarily exert their effects extracellularly by mediating key processes of cellular cross-talk and signaling leading to the modulation of a number of different biological activities including development, cell proliferation, and inflammation. This structural diversity is biosynthetically imprinted in a nontemplate-driven manner and may also be dynamically remodeled as cellular function changes. Understanding the structural information encoded in these molecules forms the basis for attempting to understand the complex biology they mediate. This chapter provides an overview of the origin of the structural microheterogeneity observed in heparin and heparan sulfate, and the orthogonal analytical methodologies that are required to help decipher this information.

Improved liquid chromatography-MS/MS of heparan sulfate oligosaccharides via chip-based pulsed makeup flow

Microfluidic chip-based hydrophilic interaction chromatography (HILIC) is a useful separation system for liquid chromatography-mass spectrometry (LC-MS) in compositional profiling of heparan sulfate (HS) oligosaccharides; however, ions observed using HILIC LC-MS are low in charge. Tandem MS of HS oligosaccharide ions with low charge results in undesirable losses of SO(3) from precursor ions during collision induced dissociation. One solution is to add metal cations to stabilize sulfate groups. Another is to add a nonvolatile, polar compound such as sulfolane, a molecule known to supercharge proteins, to produce a similar effect for oligosaccharides. We demonstrate use of a novel pulsed makeup flow (MUF) HPLC-chip. The chip enables controlled application of additives during specified chromatographic time windows and thus minimizes the extent to which nonvolatile additives build up in the ion source. The pulsed MUF system was applied to LC-MS/MS of HS oligosaccharides. Metal cations and sulfolane were tested as additives. The most promising results were obtained for sulfolane, for which supercharging of the oligosaccharide ions increased their signal strengths relative to controls. Tandem MS of these supercharged precursor ions showed decreased abundances of product ions from sulfate losses yet more abundant product ions from backbone cleavages.

Multistage Tandem Mass Spectrometry of Chondroitin Sulfate and Dermatan Sulfate

Chondroitin/dermatan sulfate (CS/DS) is a glycosaminoglycan (GAG) found in abundance in extracellular matrices. In connective tissue, CS/DS proteoglycans play structural roles in maintaining viscoelasticity through the large number of immobilized sulfate groups on CS/DS chains. CS/DS chains also bind protein families including growth factors and growth factor receptors. Through such interactions, CS/DS chains play important roles in neurobiochemical processes, connective tissue homeostasis, coagulation, and cell growth regulation. Expression of DS has been observed to increase in cancerous tissue relative to controls. In earlier studies, MS(2) was used to compare the types of CS/DS isomers present in biological samples. The results demonstrated that product ion abundances reflect the types of CS/DS repeats present and can be used quantitatively. It was not clear, however, to which of the CS/DS repeats the product ions abundances were sensitive. The present work explores the utility of MS(3) for structural characterization of CS/DS oligosaccharides. The data show that MS(3) product ion abundances correlate with the presence of DS-like repeats in specific positions on the oligosaccharide chains.

Intra-Golgi formation of IgM-glycosaminoglycan complexes promotes Ig deposition

Immune complexes arise from interactions between secreted Ab and Ags in the surrounding milieu. However, it is not known whether intracellular Ag-Ab interactions also contribute to the formation of extracellular immune complexes. In this study, we report that certain murine B cell hybridomas accumulate intracellular IgM and release large, spherical IgM complexes. The complexes (termed "spherons") reach 2 μm in diameter, detach from the cell surface, and settle out of solution. The spherons contain IgM multimers that incorporate the J chain and resist degradation by endoglycosidase H, arguing for IgM passage through the Golgi. Treatment of cells with inhibitors of proteoglycan synthesis, or incubation of spherons with chondroitinase ABC, degrades spherons, indicating that spheron formation and growth depend on interactions between IgM and glycosaminoglycans. This inference is supported by direct binding of IgM to heparin and hyaluronic acid. We conclude that, as a consequence of IgM binding to glycosaminoglycans, multivalent IgM-glycan complexes form in transit of IgM to the cell surface. Intra-Golgi formation of immune complexes could represent a new pathogenic mechanism for immune complex deposition disorders.

WT1-dependent sulfatase expression maintains the normal glomerular filtration barrier

Paracrine signaling between podocytes and glomerular endothelial cells through vascular endothelial growth factor A (VEGFA) maintains a functional glomerular filtration barrier. Heparan sulfate proteoglycans (HSPGs), located on the cell surface or in the extracellular matrix, bind signaling molecules such as VEGFA and affect their local concentrations, but whether modulation of these moieties promotes normal crosstalk between podocytes and endothelial cells is unknown. Here, we found that the transcription factor Wilms' Tumor 1 (WT1) modulates VEGFA and FGF2 signaling by increasing the expression of the 6-O-endosulfatases Sulf1 and Sulf2, which remodel the heparan sulfate 6-O-sulfation pattern in the extracellular matrix. Mice deficient in both Sulf1 and Sulf2 developed age-dependent proteinuria as a result of ultrastructural abnormalities in podocytes and endothelial cells, a phenotype similar to that observed in children with WT1 mutations and in Wt1(+/-) mice. These kidney defects associated with a decreased distribution of VEGFA in the glomerular basement membrane and on endothelial cells. Collectively, these data suggest that WT1-dependent sulfatase expression plays a critical role in maintaining the glomerular filtration barrier by modulating the bioavailability of growth factors, thereby promoting normal crosstalk between podocytes and endothelial cells.

Glycosaminoglycans promote fibril formation by amyloidogenic immunoglobulin light chains through a transient interaction

Amyloid formation occurs when a precursor protein misfolds and aggregates, forming a fibril nucleus that serves as a template for fibril growth. Glycosaminoglycans are highly charged polymers known to associate with tissue amyloid deposits that have been shown to accelerate amyloidogenesis in vitro. We studied two immunoglobulin light chain variable domains from light chain amyloidosis patients with 90% sequence identity, analyzing their fibril formation kinetics and binding properties with different glycosaminoglycan molecules. We find that the less amyloidogenic of the proteins shows a weak dependence on glycosaminoglycan size and charge, while the more amyloidogenic protein responds only minimally to changes in the glycosaminoglycan. These glycosaminoglycan effects on fibril formation do not depend on a stable interaction between the two species but still show characteristic traits of an interaction-dependent mechanism. We propose that transient, predominantly electrostatic interactions between glycosaminoglycans and the precursor proteins mediate the acceleration of fibril formation in vitro.

A comprehensive compositional analysis of heparin/heparan sulfate-derived disaccharides from human serum

The analysis of heparan sulfate glycosaminoglycans (HSGAGs) variations in human serum at the disaccharide level has a great potential for disease diagnosis and prognosis. However, the lack of available analytical methodology for the compositional analysis of HSGAGs in human serum remains to be addressed to delineate the possible role of HSGAGs on the onset and/or progression of a disease. In this study, we have developed a method for the in-depth compositional analysis of the 12 heparin/HS-derived disaccharides from human serum using a combination of technologies--fractionation, exhaustive digestion, solid phase extraction, and LC-MS/MS. The method exhibits high recovery (72-110%) and good reproducibility (standard deviation of less than 5%) with a low limit of detection and quantification. Errors from the method validation were within 1.1%. Nondetectable non- or low-sulfated disaccharides in human serum were also detected using the optimized protocol. Further applying this method, the comprehensive analysis of HSGAGs compositions in human sera from female donors showed considerable variations in disaccharide patterns and compositions.

Comparative assessment of the effects of gender-specific heparan sulfates on mesenchymal stem cells

We compare here the structural and functional properties of heparan sulfate (HS) chains from both male or female adult mouse liver through a combination of molecular sieving, enzymatic cleavage, and strong anion exchange-HPLC. The results demonstrated that male and female HS chains are significantly different by a number of parameters; size determination showed that HS chain lengths were ∼100 and ∼22 kDa, comprising 30-40 and 6-8 disaccharide repeats, respectively. Enzymatic depolymerization and disaccharide composition analyses also demonstrated significant differences in domain organization and fine structure. N-Unsubstituted glucosamine (ΔHexA-GlcNH(3)(+), ΔHexA-GlcNH(3)(+)(6S), ΔHexA(2S)-GlcNH(3)(+), and N-acetylglucosamine (ΔHexA-GlcNAc) are the predominant disaccharides in male mouse liver HS. However, N-sulfated glucosamine (ΔHexA-GlcNSO(3)) is the predominant disaccharide found in female liver. These structurally different male and female liver HS forms exert differential effects on human mesenchymal cell proliferation and subsequent osteogenic differentiation. The present study demonstrates the potential usefulness of gender-specific liver HS for the manipulation of human mesenchymal cell properties, including expansion, multipotentiality, and subsequent matrix mineralization. Our results suggest that HS chains show both tissue- and gender-specific differences in biochemical composition that directly reflect their biological activity.