Isolation and characterization of heparan sulfate from various murine tissues

Extended N-sulfated domains reside at the nonreducing end of heparan sulfate chains

Heparan sulfate (HS) serves as a cell-surface co-receptor for growth factors, morphogens, and chemokines. These HS and protein binding events depend on the fine structure and distribution of domains along an HS chain. A given domain can vary in terms of uronic acid epimer, N- and O-sulfate, and N-acetate content. The most highly sulfated regions of HS chains, N-sulfated (NS) domains, play prominent roles in HS and protein binding. We have analyzed HS oligosaccharides from various mammalian sources and provide evidence that NS domains residing at the nonreducing end (NRE) are, on average, longer than those residing in the internal regions of the chain. Additionally, they are more highly sulfated than their internal counterparts. These features are independent of the sulfation pattern of the bulk HS chains. From disaccharide analysis, it is clear that NS domains do not always occupy HS NREs. However, when they do, they tend to terminate in a subset of N-sulfated disaccharides. Our observations are consistent with a significant role of NRE NS domains in HS-growth factor interactions.

Quantitative and qualitative alterations of heparan sulfate in fibrogenic liver diseases and hepatocellular cancer

Heparan sulfate (HS), due to its ability to interact with a multitude of HS-binding factors, is involved in a variety of physiological and pathological processes. Remarkably diverse fine structure of HS, shaped by non-exhaustive enzymatic modifications, influences the interaction of HS with its partners. Here we characterized the HS profile of normal human and rat liver, as well as alterations of HS related to liver fibrogenesis and carcinogenesis, by using sulfation-specific antibodies. The HS immunopattern was compared with the immunolocalization of selected HS proteoglycans. HS samples from normal liver and hepatocellular carcinoma (HCC) were subjected to disaccharide analysis. Expression changes of nine HS-modifying enzymes in human fibrogenic diseases and HCC were measured by quantitative RT-PCR. Increased abundance and altered immunolocalization of HS was paralleled by elevated mRNA levels of HS-modifying enzymes in the diseased liver. The strong immunoreactivity of the normal liver for 3-O-sulfated epitope further increased with disease, along with upregulation of 3-OST-1. Modest 6-O-undersulfation of HCC HS is probably explained by Sulf overexpression. Our results may prompt further investigation of the role of highly 3-O-sulfated and partially 6-O-desulfated HS in pathological processes such as hepatitis virus entry and aberrant growth factor signaling in fibrogenic liver diseases and HCC.

Gel-forming exopolysaccharides explain basic differences between structures of aerobic sludge granules and floccular sludges

The sol-gel transition of extracellular polymeric substances (EPS) derived from sludge flocs and granules is investigated in order to explain basic differences between the two aggregates. A reversible, pH dependent sol-gel transition was observed at pH 9.0-12.0 in EPS extracted from granules. At pH <9 granule EPS existed as a strong gel, indicating that their EPS exist in a gel state at normal operating pH of a wastewater treatment system (i.e. 6.0-8.5). This characteristic transition from solution to strong gel was not observed in any of the EPS samples derived from floccular sludges. A transition to a weak gel was however, observed at pH 4.0-5.0. Enriched exopolysaccharides from the granular EPS exhibited rheological behaviour analogous to the granules and the granule EPS. The critical overlap concentration (c*) of the exopolysaccharide concentrate was 0.33% w/w, similar to the c* of other known bacterial exopolysaccharides. Additionally, the protein content was found to be not contributing to the storage modulus of granule EPS gels. These factors suggest that exopolysaccharides or glycosides were the gelling agent in aerobic sludge granules. Given that EPS derived from aerobic sludge granules and flocs are distinguished by such a sol-strong gel transition, these exopolysaccharides therefore likely play an important role in granulation.

TAT-mediated intracellular protein delivery to primary brain cells is dependent on glycosaminoglycan expression

Although some studies have shown that the cell penetrating peptide (CPP) TAT can enter a variety of cell lines with high efficiency, others have observed little or no transduction in vivo or in vitro under conditions mimicking the in vivo environment. The mechanisms underlying TAT-mediated transduction have been investigated in cell lines, but not in primary brain cells. In this study we demonstrate that transduction of a green fluorescent protein (GFP)-TAT fusion protein is dependent on glycosaminoglycan (GAG) expression in both the PC12 cell line and primary astrocytes. GFP-TAT transduced PC12 cells and did so with even higher efficiency following NGF differentiation. In cultures of primary brain cells, TAT significantly enhanced GFP delivery into astrocytes grown under different conditions: (1) monocultures grown in serum-containing medium; (2) monocultures grown in serum-free medium; (3) cocultures with neurons in serum-free medium. The efficiency of GFP-TAT transduction was significantly higher in the monocultures than in the cocultures. The GFP-TAT construct did not significantly enter neurons. Experimental modulation of GAG content correlated with alterations in TAT transduction in PC12 cells and astrocyte monocultures grown in the presence of serum. In addition, this correlation was predictive of TAT-mediated transduction in astrocyte monocultures grown in serum free medium and in coculture. We conclude that culture conditions affect cellular GAG expression, which in turn dictates TAT-mediated transduction efficiency, extending previous results from cell lines to primary cells. These results highlight the cell-type and phenotype-dependence of TAT-mediated transduction, and underscore the necessity of controlling the phenotype of the target cell in future protein engineering efforts aimed at creating more efficacious CPPs.

Rapid purification and high sensitivity analysis of heparan sulfate from cells and tissues: toward glycomics profiling

Studies on glycosaminoglycans and proteoglycans (PGs) have been hampered by difficulties in isolation and analysis by traditional methods that are laborious and lack sensitivity and throughput. Here we demonstrate a simple method for rapid isolation of proteoglycans (RIP) employing phenol/guanidine/chloroform reagent to purify heparan sulfate (HS) PGs quantitatively from various tissues and cells. We further show that this generic purification methodology, when applied in concert with a BODIPY fluorescent label, permits structural analyses on RIP-purified HS at approximately 1,000-fold higher sensitivity than standard UV detection methods and approximately 10-100-fold higher sensitivity than previous fluorescence detection methods. The utility of RIP-BODIPY methodology was demonstrated by rapid profiling of HS structural composition from small tissue samples, multiple mouse organs, and as little as a few thousand cultured cells. It was also used to generate novel insights into in vivo structural changes in HS from Sulf1 knock-out mice for the first time that differed significantly from previous observations limited to tissue culture experiments. RIP was also applied to purify HS for bioassay testing, exemplified by cell assays of fibroblast growth factor signaling activation; this generated data from 2-O-sulfotransferase knock-out mice and revealed an unexpected deficiency in fibroblast growth factor activation by HS from heterozygous mice. These data demonstrate that RIP will underpin emerging efforts to develop glycomics profiling strategies for HS and other glycosaminoglycans to explore their structure-function relationships in complex biological systems.

Quantification of heparan sulfate disaccharides using ion-pairing reversed-phase microflow high-performance liquid chromatography with electrospray ionization trap mass spectrometry

The glycosaminoglycan (GAG) family of biomacromolecules is composed acidic and linear chains of repeating disaccharide units. Quantitative disaccharide composition analysis is essential for the study and characterization of GAGs. Heparan sulfate and heparin consist of multiple disaccharide units and can be well-separated by ion-pairing reversed-phase microflow high-performance liquid chromatography (IPRP-Mf-HPLC). Each disaccharide can be detected and its mass confirmed by electrospray ionization mass spectrometry (ESI-MS). Isotopically enriched disaccharides were prepared chemoenzymatically from a uniformly (13)C,(15)N-labeled N-acetylheparosan (-GlcA(1-->4)GlcNAc-) obtained from the fermentation of E. coli K5. These isotopically enriched disaccharides have identical HPLC retention times and mass spectra as their unlabeled counterparts and were used in liquid chromatography-mass spectrometry (LC-MS) as internal standards. The ratio of intensities between each pair of enriched and nonenriched disaccharides showed a linear relationship as a function of concentration. With the use of these calibration curves, the amount of each disaccharide (> or = 2 ng/disaccharide) could be quantified in four heparan sulfate samples analyzed by this method.

Organ-specific heparan sulfate structural phenotypes

The functions of heparan sulfate (HS) depend on the expression of structural domains that interact with protein partners. Glycosaminoglycans (GAGs) exhibit a high degree of polydispersity in their composition, chain length, sulfation, acetylation, and epimerization patterns. It is essential for the understanding of GAG biochemistry to produce detailed structural information as a function of spatial and temporal factors in biological systems. Toward this end, we developed a set of procedures to extract GAGs from various rat organ tissues and examined and compared HS expression levels using liquid chromatography/mass spectrometry. Here we demonstrate detailed variations in HS GAG chains as a function of organ location. These studies shed new light on the structural variation of GAG chains with respect to average length, disaccharide composition, and expression of low abundance structural epitopes, including unsubstituted amino groups and lyase-resistant oligosaccharides. The data show the presence of a disaccharide with an unsubstituted amino group that is endogenous and widely expressed in mammalian organ tissues.

Interactions between heparan sulfate and proteins-design and functional implications

Heparan sulfate (HS) proteoglycans at cell surfaces and in the extracellular matrix of most animal tissues are essential in development and homeostasis, and variously implicated in disease processes. Functions of HS polysaccharide chains depend on ionic interactions with a variety of proteins including growth factors and their receptors. Negatively charged sulfate and carboxylate groups are arranged in various types of domains, generated through strictly regulated biosynthetic reactions and with enormous potential for structural variability. The level of specificity of HS-protein interactions is assessed through binding experiments in vitro using saccharides of defined composition, signaling assays in cell culture, and targeted disruption of genes for biosynthetic enzymes followed by phenotype analysis. While some protein ligands appear to require strictly defined HS structure, others bind to variable saccharide domains without any apparent dependence on distinct saccharide sequence. These findings raise intriguing questions concerning the functional significance of regulation in HS biosynthesis.

Molecular structure of heparan sulfate from Spalax. Implications of heparanase and hypoxia

Spalax, a subterranean blind mole rat, is well adapted to live in an extreme hypoxic environment through up-regulated expression of growth factors and enzymes for ensuring sufficient oxygen supply. One of the overexpressed enzymes is heparanase, an endoglucuronidase that selectively cleaves heparan sulfate (HS) and is implicated in angiogenesis. To assess the implications of the heparanase in Spalax, we have characterized the structure of HS isolated from various organs of the animal. The oligosaccharides obtained after deaminative cleavage of HS samples from the tissues show an overall higher sulfation degree, distinct from that of murine tissues. Of particular significance was the appearance of a trisaccharide moiety in the tissues examined, apart of the even numbered oligosaccharide fractions typically found in HS from human and mouse tissues. The formation of this odd-numbered saccharide is a consequence of heparanase action, in agreement with the notion of high expression of the enzyme in this species. Analysis of HS extracted from human embryonic kidney cells (HEK293) after exposure to hypoxic condition revealed a structural change in the distribution of oligosaccharides similar to HS derived from Spalax organs. The alterations are likely due to up-regulated activity of heparanase, as real-time RT-PCR showed a 2-fold increase in heparanase mRNA expression in the hypoxia treated cells. HEK293 cells stably overexpressing Spalax heparanase produced HS sharing similarity with that from the Spalax organs, and exhibited enhanced MAPK activity in comparison with HEK293 cells, indicating a regulation role of the heparanase in the activity of growth factors.

Tetrasulfated disaccharide unit in heparan sulfate: enzymatic formation and tissue distribution

We previously reported that the heparan sulfate 3-O-sulfotransferase (3OST)-5 produces a novel component of heparan sulfate, i.e. the tetrasulfated disaccharide (Di-tetraS) unit ( Mochizuki, H., Yoshida, K., Gotoh, M., Sugioka, S., Kikuchi, N., Kwon, Y.-D., Tawada, A., Maeyama, K., Inaba, N., Hiruma, T., Kimata, K., and Narimatsu, H. (2003) J. Biol. Chem. 278, 26780-26787 ). In the present study, we investigated the potential of other 3OST isoforms to produce Di-tetraS with heparan sulfate and heparin as acceptor substrates. 3OST-2, 3OST-3, and 3OST-4 produce Di-tetraS units as a major product from both substrates. 3OST-5 showed the same specificity for heparin, but the production from heparan sulfate was very low. Di-tetraS production by 3OST-1 was negligible. We then investigated the presence of Di-tetraS units in heparan sulfates from various rat tissues. Di-tetraS was detected in all of the tissues analyzed. Liver and spleen contain relatively high levels of Di-tetraS, 1.6 and 0.95%, respectively. However, the content of this unit in heart, large intestine, ileum, and lung is low, less than 0.2%. We further determined the expression levels of 3OST transcripts by quantitative real time PCR. The 3OST-3 transcripts are highly expressed in spleen and liver. The 3OST-2 and -4 are specifically expressed in brain. These results indicate that the Di-tetraS unit is widely distributed throughout the body as a rare and unique component of heparan sulfate and is synthesized by tissue-specific 3OST isoforms specific for Di-tetraS production.

Human follicular fluid heparan sulfate contains abundant 3-O-sulfated chains with anticoagulant activity

Anticoagulant heparan sulfate proteoglycans bind and activate antithrombin by virtue of a specific 3-O-sulfated pentasaccharide. They not only occur in the vascular wall but also in extravascular tissues, such as the ovary, where their functions remain unknown. The rupture of the ovarian follicle at ovulation is one of the most striking examples of tissue remodeling in adult mammals. It involves tightly controlled inflammation, proteolysis, and fibrin deposition. We hypothesized that ovarian heparan sulfates may modulate these processes through interactions with effector proteins. Our previous work has shown that anticoagulant heparan sulfates are synthesized by rodent ovarian granulosa cells, and we now have set out to characterize heparan sulfates from human follicular fluid. Here we report the first anticoagulant heparan sulfate purified from a natural human extravascular source. Heparan sulfate chains were fractionated according to their affinity for antithrombin, and their structure was analyzed by 1H NMR and MS/MS. We find that human follicular fluid is a rich source of anticoagulant heparan sulfate, comprising 50.4% of total heparan sulfate. These antithrombin-binding chains contain more than 6% 3-O-sulfated glucosamine residues, convey an anticoagulant activity of 2.5 IU/ml to human follicular fluid, and have an anti-Factor Xa specific activity of 167 IU/mg. The heparan sulfate chains that do not bind antithrombin surprisingly exhibit an extremely high content in 3-O-sulfated glucosamine residues, which suggest that they may exhibit biological activities through interactions with other proteins.

Glycomics of proteoglycan biosynthesis in murine embryonic stem cell differentiation

Glycosaminoglycans (GAGs) play a critical role in binding and activation of growth factors involved in cell signaling critical for developmental biology. The biosynthetic pathways for GAGs have been elucidated over the past decade and now analytical methodology makes it possible to determine GAG composition in as few as 10 million cells. A glycomics approach was used to examine GAG content, composition, and the level of transcripts encoding for GAG biosynthetic enzymes as murine embryonic stem cells (mESCs) differentiate to embryoid bodies (EBs) and to extraembryonic endodermal cells (ExE) to better understand the role of GAGs in stem cell differentiation. Hyaluronan synthesis was enhanced by 13- and 24-fold, most likely due to increased expression of hyaluronan synthase-2. Chondroitin sulfate (CS)/dermatan sulfate (DS) synthesis was enhanced by 4- and 6-fold, and heparan sulfate (HS) synthesis was enhanced by 5- and 8-fold following the transition from mESC to EB and ExE. Transcripts associated with the synthesis of the early precursors were largely unaltered, suggesting other factors account for enhanced GAG synthesis. The composition of both CS/DS and HS also changed upon differentiation. Interestingly, CS type E and highly sulfated HS both increase as mESCs differentiate to EBs and ExE. Differentiation was also accompanied by enhanced 2-sulfation in both CS/DS and HS families. Transcript levels for core proteins generally showed increases or remained constant upon mESC differentiation. Finally, transcripts encoding selected enzymes and isoforms, including GlcNAc-4,6-O-sulfotransferase, C5-epimerases, and 3-O-sulfotransferases involved in late GAG biosynthesis, were also enriched. These biosynthetic enzymes are particularly important in introducing GAG fine structure, essential for intercellular communication, cell adhesion, and outside-in signaling. Knowing the changes in GAG fine structure should improve our understanding the biological properties of differentiated stem cells.

Mosquito heparan sulfate and its potential role in malaria infection and transmission

Heparan sulfate has been isolated for the first time from the mosquito Anopheles stephensi, a known vector for Plasmodium parasites, the causative agents of malaria. Chondroitin sulfate, but not dermatan sulfate or hyaluronan, was also present in the mosquito. The glycosaminoglycans were isolated, from salivary glands and midguts of the mosquito in quantities sufficient for disaccharide microanalysis. Both of these organs are invaded at different stages of the Plasmodium life cycle. Mosquito heparan sulfate was found to contain the critical trisulfated disaccharide sequence, -->4)beta-D-GlcNS6S(1-->4)-alpha-L-IdoA2S(1-->, that is commonly found in human liver heparan sulfate, which serves as the receptor for apolipoprotein E and is also believed to be responsible for binding to the circumsporozoite protein found on the surface of the Plasmodium sporozoite. The heparan sulfate isolated from the whole mosquito binds to circumsporozoite protein, suggesting a role within the mosquito for infection and transmission of the Plasmodium parasite.

Polycystic disease caused by deficiency in xylosyltransferase 2, an initiating enzyme of glycosaminoglycan biosynthesis

The basic biochemical mechanisms underlying many heritable human polycystic diseases are unknown despite evidence that most cases are caused by mutations in members of several protein families, the most prominent being the polycystin gene family, whose products are found on the primary cilia, or due to mutations in posttranslational processing and transport. Inherited polycystic kidney disease, the most prevalent polycystic disease, currently affects approximately 500,000 people in the United States. Decreases in proteoglycans (PGs) have been found in tissues and cultured cells from patients who suffer from autosomal dominant polycystic kidney disease, and this PG decrease has been hypothesized to be responsible for cystogenesis. This is possible because alterations in PG concentrations would be predicted to disrupt many homeostatic mechanisms of growth, development, and metabolism. To test this hypothesis, we have generated mice lacking xylosyltransferase 2 (XylT2), an enzyme involved in PG biosynthesis. Here we show that inactivation of XylT2 results in a substantial reduction in PGs and a phenotype characteristic of many aspects of polycystic liver and kidney disease, including biliary epithelial cysts, renal tubule dilation, organ fibrosis, and basement membrane abnormalities. Our findings demonstrate that alterations in PG concentrations can occur due to loss of XylT2, and that reduced PGs can induce cyst development.