Developmental and regional expression of heparan sulfate sulfotransferase genes in the mouse brain

Protein interactors of 3-O sulfated heparan sulfates in human MCI and age-matched control cerebrospinal fluid

Heparan sulfates (HS) proteoglycans are commonly found on the cell surface and mediate many processes. Binding of HS ligands is determined by the sulfation code on the HS chain that can be N-/2-O/6-O- or 3-O-sulfated, generating heterogenous sulfation patterns. 3-O sulfated HS (3S-HS) play a role in several (patho)physiological processes such as blood coagulation, viral pathogenesis and binding and internalization of tau in Alzheimer's disease. However, few 3S-HS-specific interactors are known. Thus, our insight into the role of 3S-HS in health and disease is limited, especially in the central nervous system. Using human CSF, we determined the interactome of synthetic HS with defined sulfation patterns. Our affinity-enrichment mass spectrometry studies expand the repertoire of proteins that may interact with (3S-)HS. Validating our approach, ATIII, a known 3S-HS interactor, was found to require GlcA-GlcNS6S3S for binding, similar to what has been reported. Our dataset holds novel, potential HS and 3S-HS protein ligands, that can be explored in future studies focusing on molecular mechanisms that depend on 3S-HS in (patho)physiological conditions.

Role of neurexin heparan sulfate in the molecular assembly of synapses - expanding the neurexin code?

Synapses are the minimal information processing units of the brain and come in many flavors across distinct circuits. The shape and properties of a synapse depend on its molecular organisation, which is thought to largely depend on interactions between cell adhesion molecules across the synaptic cleft. An established example is that of presynaptic neurexins and their interactions with structurally diverse postsynaptic ligands: the diversity of neurexin isoforms that arise from alternative promoters and alternative splicing specify synaptic properties by dictating ligand preference. The recent finding that a majority of neurexin isoforms exist as proteoglycans with a single heparan sulfate (HS) polysaccharide adds to this complexity. Sequence motifs within the HS polysaccharide may differ between neuronal cell types to contribute specificity to its interactions, thereby expanding the coding capacity of neurexin diversity. However, an expanding number of HS-binding proteins have been found capable to recruit neurexins via the HS chain, challenging the concept of a code provided by neurexin splice isoforms. Here we discuss the possible roles of the neurexin HS in light of what is known from other HS-protein interactions, and propose a model for how the neurexin HS polysaccharide may contribute to synaptic assembly. We also discuss how the neurexin HS may be regulated by co-secreted carbonic anhydrase-related and FAM19A proteins, and highlight some key issues that should be resolved to advance the field.

The 3-O sulfation of heparan sulfate proteoglycans contributes to the cellular internalization of tau aggregates

BACKGROUND

Considering the high correlation between the functional decline in Alzheimer's disease (AD) and the propagation of aggregated tau protein, many research efforts are focused on determining the underlying molecular mechanisms of tau spreading. Heparan sulfate proteoglycans (HSPGs) were reported to mediate cellular uptake of tau aggregates. Specifically, the heparan sulfates (HS) sulfation plays a critical role in the interaction of HSPGs with aggregated tau. HS can be N-/2-O/6-O- or 3-O-sulfated, some of which have been reported to take part in the interaction with tau aggregates. However, the role of the 3-O sulfation remains enigmatic.

RESULTS

Here, we studied the contribution of HS 3-O sulfation in the binding and cellular uptake of tau aggregates. We observed reduced tau aggregates uptake in absence of 3-O sulfation or when outcompeting available cellular 3-O sulfated HS (3S-HS) with antithrombin III. The lack of HS3ST1-generated HS products in the HS3ST1-/- cells was further corroborated with an LC-MS/MS using 13C-labeled HS calibrants. Here, we showed that these functional changes can be explained by a higher affinity of aggregated tau to 3S-HS. When targeting tau aggregates with 3-O sulfation-containing HS, we observed an increase in inhibition of tau aggregates uptake.

CONCLUSIONS

These data indicate that HS 3-O sulfation plays a role in the binding of tau aggregates and, thus, contributes to their cellular uptake, highlighting a potential target value to modulate tau pathogenesis.

Galnt17 loss-of-function leads to developmental delay and abnormal coordination, activity, and social interactions with cerebellar vermis pathology

GALNT17 encodes a N-acetylgalactosaminyltransferase (GalNAc-T) protein specifically involved in mucin-type O-linked glycosylation of target proteins, a process important for cell adhesion, cell signaling, neurotransmitter activity, neurite outgrowth, and neurite sensing. GALNT17, also known as WBSCR17, is located at the edge of the Williams-Beuren Syndrome (WBS) critical region and adjacent to the AUTS2 locus, genomic regions associated with neurodevelopmental phenotypes that are thought to be co-regulated. Although previous data have implicated Galnt17 in neurodevelopment, the in vivo functions of this gene have not been investigated. In this study, we have analyzed behavioral, brain pathology, and molecular phenotypes exhibited by Galnt17 knockout (Galnt17-/-) mice. We show that Galnt17-/- mutants exhibit developmental neuropathology within the cerebellar vermis, along with abnormal activity, coordination, and social interaction deficits. Transcriptomic and protein analysis revealed reductions in both mucin type O-glycosylation and heparan sulfate synthesis in the developing mutant cerebellum along with disruption of pathways central to neuron differentiation, axon pathfinding, and synaptic signaling, consistent with the mutant neuropathology. These brain and behavioral phenotypes and molecular data confirm a specific role for Galnt17 in brain development and suggest new clues to factors that could contribute to phenotypes in certain WBS and AUTS2 syndrome patients.

3-O-Sulfation induces sequence-specific compact topologies in heparan sulfate that encode a dynamic sulfation code

Heparan sulfate (HS) is arguably the most diverse linear biopolymer that is known to modulate hundreds of proteins. Whereas the configurational and conformational diversity of HS is well established in terms of varying sulfation patterns and iduronic acid (IdoA) puckers, a linear helical topology resembling a cylindrical rod is the only topology thought to be occupied by the biopolymer. We reasoned that 3-O-sulfation, a rare modification in natural HS, may induce novel topologies that contribute to selective recognition of proteins. In this work, we studied a library of 24 distinct HS hexasaccharides using molecular dynamics (MD). We discovered novel compact (C) topologies that are populated significantly by a unique group of 3-O-sulfated sequences containing IdoA residues. 3-O-sulfated sequences containing glucuronic acid (GlcA) residue and sequences devoid of 3-O-sulfate groups did not exhibit high levels of the C topology and primarily exhibited only the canonical linear (L) form. The C topology arises under dynamical conditions due to rotation around an IdoA → GlcN glycosidic linkage, especially in psi (Ψ) torsion. At an atomistic level, the L → C transformation is a multi-factorial phenomenon engineered to reduce like-charge repulsion, release one or more HS-bound water molecules, and organize a bi-dentate "IdoA-cation-IdoA" interaction. These forces also drive an L → C transformation in a 3-O-sulfated octasaccharide, which has shown evidence of the unique C topology in the co-crystallized state. The 3-O-sulfate-based generation of unique, sequence-specific, compact topologies indicate that natural HS encodes a dynamic sulfation code that could be exploited for selective recognition of target proteins.

HS3ST2 expression induces the cell autonomous aggregation of tau

Heparan sulfates have long been known to intracellularly accumulate in Alzheimer’s disease neurons, where they colocalize with neurofibrillary tangles made of abnormally phosphorylated and aggregated tau protein. However, the reasons and consequences of the heparan sulfates accumulation in the Alzheimer’s cells are not yet well understood. Previously, we showed that the neural heparan sulfate 3-O-sulfotransferase HS3ST2 is critical for the abnormal phosphorylation of tau in Alzheimer's disease-related tauopathy. Using cell models of tauopathy we showed that intracellular 3-O-sulfatated heparan sulfates interact with tau inducing its abnormal phosphorylation. However, it is unknown whether HS3ST2 expression induces the intracellular aggregation of tau in cells. Here, by using replicative pEBV plasmids, we engineered HEK293 cells to stably express HS3ST2 together with human tau carrying or not the P301S mutation. We show that HS3ST2 gain of function induces the cell autonomous aggregation of tau not only in cells expressing tau_P301S, but also in cells expressing the wild type tau. Our engineered cells mimicked both the HS intracellular accumulation observed in neurons of Alzheimer’s disease and the tau aggregation characteristic of tauopathy development and evolution. These results give evidence that the neural HS3ST2 plays a critical role in the cell autonomous self-aggregation of tau.

[G-protein coupled receptor Smo positively regulates proliferation and migration of adult neural stem cells in vitro]

OBJECTIVE

To investigate the role of G-protein coupled receptor Smoothened (Smo) in regulating proliferation and migration of adult neural stem cells (ANSCs) and explore the underlying mechanism.

METHODS

Cultured ANSCs were treated with purmorphamine (PM, an agonist of Smo) or cyclopamine (CPM, an inhibitor of Smo), and the changes in cell proliferation migration abilities were assessed using cell counting kit-8 (CCK8) assay and wound healing assay, respectively. The mRNA expressions of membrane receptor Patched 1 (Ptch1), Smo, glioma-associated oncogene homolog 1 (Gli1), axon guidance cue slit1 (Slit1) and brain-derived neurotrophic factor (BDNF) in the treated cells were detected using real-time quantitative PCR (RT-PCR).

RESULTS

PM significantly promoted the proliferation (P < 0.01) and migration of ANSCs (P < 0.01), and up-regulated the mRNA expressions of Ptch1, Smo, Gli1, Slit1 and BDNF. Treatment with CPM significantly inhibited the proliferation and migration of ANSCs.

CONCLUSION

Modulating Smo activity can positively regulate the proliferation and migration of ANSCs possibly by regulating the expressions of BDNF and Slit1.

Synthesis of 3-O-Sulfated Heparan Sulfate Oligosaccharides Using 3-O-Sulfotransferase Isoform 4

Heparan sulfate (HS) 3-O-sulfotransferase isoform 4 (3-OST-4) is a specialized carbohydrate sulfotransferase participating in the biosynthesis of heparan sulfate. Here, we report the expression and purification of the recombinant 3-OST-4 enzyme and use it for the synthesis of a library of 3-O-sulfated hexasaccharides and 3-O-sulfated octasaccharides. The unique structural feature of the library is that each oligosaccharide contains a disaccharide domain with a 2-O-sulfated glucuronic acid (GlcA2S) and 3-O-sulfated glucosamine (GlcNS3S). By rearranging the order of the enzymatic modification steps, we demonstrate the synthesis of oligosaccharides with different saccharide sequences. The structural characterization was completed by electrospray ionization mass spectrometry and NMR. These 3-O-sulfated oligosaccharides show weak to very weak anti-Factor Xa activity, a measurement of anticoagulant activity. We discovered that HSoligo 7 (HS oligosaccharide 7), a 3-O-sulfated octasaccharide, binds to high mobility group box 1 protein (HMGB1) and tau protein, both believed to be involved in the process of inflammation. Access to the recombinant 3-OST-4 expands the capability of the chemoenzymatic method to synthesize novel 3-O-sulfated oligosaccharides. The oligosaccharides will become valuable reagents to probe the biological functions of 3-O-sulfated HS and to develop HS-based therapeutic agents.

Specific heparan sulfate modifications stabilize the synaptic organizer MADD-4/Punctin at C. elegans neuromuscular junctions

Heparan sulfate proteoglycans contribute to the structural organization of various neurochemical synapses. Depending on the system, their role involves either the core protein or the glycosaminoglycan chains. These linear sugar chains are extensively modified by heparan sulfate modification enzymes, resulting in highly diverse molecules. Specific modifications of glycosaminoglycan chains may thus contribute to a sugar code involved in synapse specificity. Caenorhabditis elegans is particularly useful to address this question because of the low level of genomic redundancy of these enzymes, as opposed to mammals. Here, we systematically mutated the genes encoding heparan sulfate modification enzymes in C. elegans and analyzed their impact on excitatory and inhibitory neuromuscular junctions. Using single chain antibodies that recognize different heparan sulfate modification patterns, we show in vivo that these two heparan sulfate epitopes are carried by the SDN-1 core protein, the unique C. elegans syndecan orthologue, at neuromuscular junctions. Intriguingly, these antibodies differentially bind to excitatory and inhibitory synapses, implying unique heparan sulfate modification patterns at different neuromuscular junctions. Moreover, while most enzymes are individually dispensable for proper organization of neuromuscular junctions, we show that 3-O-sulfation of SDN-1 is required to maintain wild-type levels of the extracellular matrix protein MADD-4/Punctin, a central synaptic organizer that defines the identity of excitatory and inhibitory synaptic domains at the plasma membrane of muscle cells.

Glypicans and Heparan Sulfate in Synaptic Development, Neural Plasticity, and Neurological Disorders

Heparan sulfate proteoglycans (HSPGs) are components of the cell surface and extracellular matrix, which bear long polysaccharides called heparan sulfate (HS) attached to the core proteins. HSPGs interact with a variety of ligand proteins through the HS chains, and mutations in HSPG-related genes influence many biological processes and cause various diseases. In particular, recent findings from vertebrate and invertebrate studies have raised the importance of glycosylphosphatidylinositol-anchored HSPGs, glypicans, as central players in the development and functions of synapses. Glypicans are important components of the synapse-organizing protein complexes and serve as ligands for leucine-rich repeat transmembrane neuronal proteins (LRRTMs), leukocyte common antigen-related (LAR) family receptor protein tyrosine phosphatases (RPTPs), and G-protein-coupled receptor 158 (GPR158), regulating synapse formation. Many of these interactions are mediated by the HS chains of glypicans. Neurexins (Nrxs) are also synthesized as HSPGs and bind to some ligands in common with glypicans through HS chains. Therefore, glypicans and Nrxs may act competitively at the synapses. Furthermore, glypicans regulate the postsynaptic expression levels of ionotropic glutamate receptors, controlling the electrophysiological properties and non-canonical BMP signaling of synapses. Dysfunctions of glypicans lead to failures in neuronal network formation, malfunction of synapses, and abnormal behaviors that are characteristic of neurodevelopmental disorders. Recent human genetics revealed that glypicans and HS are associated with autism spectrum disorder, neuroticism, and schizophrenia. In this review, we introduce the studies showing the roles of glypicans and HS in synapse formation, neural plasticity, and neurological disorders, especially focusing on the mouse and Drosophila as potential models for human diseases.

A quantitative method to detect non-antithrombin-binding 3-O-sulfated units in heparan sulfate

Heparan sulfate is synthesized by most animal cells and interacts with numerous proteins via specific sulfation motifs to regulate various physiological processes. Various 3-O-sulfated motifs are considered to be key in controlling the binding specificities to the functional proteins. One such motif synthesized by 3-O-sulfotransferase-1 (3OST-1) serves as a binding site for antithrombin (AT) and has been thoroughly studied because of its pharmacological importance. However, the physiological roles of 3-O-sulfates produced by other 3OST isoforms, which do not bind AT, remain obscure, in part due to the lack of a standard method to analyze this rare modification. This study aims to establish a method for quantifying 3-O-sulfated components of heparan sulfate, focusing on non-AT-binding units. We previously examined the reaction products of human 3OST isoforms and identified five 3-O-sulfated components, including three non-AT-binding disaccharides and two AT-binding tetrasaccharides, as digestion products of heparin lyases. In this study, we prepared these five components as a standard saccharide for HPLC analysis. Together with eight non-3-O-sulfated disaccharides, a standard mixture of 13 units was prepared. Using reverse-phase ion-pair HPLC with a postcolumn fluorescent labeling system, the separation conditions were optimized to quantify the 13 units. Finally, we analyzed the compositional changes of 3-O-sulfated units in heparan sulfate from P19 cells before and after neuronal differentiation. We successfully detected the 3-O-sulfated units specifically expressed in the differentiated neurons. This is the first report that shows the quantification of three non-AT-binding 3-O-sulfated units and establishes a new approach to explore the physiological functions of 3-O-sulfate.

3-O-sulfated heparan sulfate interactors target synaptic adhesion molecules from neonatal mouse brain and inhibit neural activity and synaptogenesis in vitro

Heparan sulfate (HS) chains, covalently linked to heparan sulfate proteoglycans (HSPG), promote synaptic development and functions by connecting various synaptic adhesion proteins (AP). HS binding to AP could vary according to modifications of HS chains by different sulfotransferases. 3-O-sulfotransferases (Hs3sts) produce rare 3-O-sulfated HSs (3S-HSs), of poorly known functions in the nervous system. Here, we showed that a peptide known to block herpes simplex virus by interfering with 3S-HSs in vitro and in vivo (i.e. G2 peptide), specifically inhibited neural activity, reduced evoked glutamate release, and impaired synaptic assembly in hippocampal cell cultures. A role for 3S-HSs in promoting synaptic assembly and neural activity is consistent with the synaptic interactome of G2 peptide, and with the detection of Hs3sts and their products in synapses of cultured neurons and in synaptosomes prepared from developing brains. Our study suggests that 3S-HSs acting as receptors for herpesviruses might be important regulators of neuronal and synaptic development in vertebrates.

Lysosomal sulfatases: a growing family

Sulfatases constitute a family of enzymes that specifically act in the hydrolytic degradation of sulfated metabolites by removing sulfate monoesters from various substrates, particularly glycolipids and glycosaminoglycans. A common essential feature of all known eukaryotic sulfatases is the posttranslational modification of a critical cysteine residue in their active site by oxidation to formylglycine (FGly), which is mediated by the FGly-generating enzyme in the endoplasmic reticulum and is indispensable for catalytic activity. The majority of the so far described sulfatases localize intracellularly to lysosomes, where they act in different catabolic pathways. Mutations in genes coding for lysosomal sulfatases lead to an accumulation of the sulfated substrates in lysosomes, resulting in impaired cellular function and multisystemic disorders presenting as lysosomal storage diseases, which also cover the mucopolysaccharidoses and metachromatic leukodystrophy. Bioinformatics analysis of the eukaryotic genomes revealed, besides the well described and long known disease-associated sulfatases, additional genes coding for putative enzymes with sulfatases activity, including arylsulfatase G as well as the arylsulfatases H, I, J and K, respectively. In this article, we review current knowledge about lysosomal sulfatases with a special focus on the just recently characterized family members arylsulfatase G and arylsulfatase K.

Breed Differences in Dog Cognition Associated with Brain-Expressed Genes and Neurological Functions

Given their remarkable phenotypic diversity, dogs present a unique opportunity for investigating the genetic bases of cognitive and behavioral traits. Our previous work demonstrated that genetic relatedness among breeds accounts for a substantial portion of variation in dog cognition. Here, we investigated the genetic architecture of breed differences in cognition, seeking to identify genes that contribute to variation in cognitive phenotypes. To do so, we combined cognitive data from the citizen science project Dognition.com with published breed-average genetic polymorphism data, resulting in a dataset of 1654 individuals with cognitive phenotypes representing 49 breeds. We conducted a breed-average genome-wide association study to identify specific polymorphisms associated with breed differences in inhibitory control, communication, memory, and physical reasoning. We found five single nucleotide polymorphisms (SNPs) that reached genome-wide significance after Bonferroni correction, located in EML1, OR52E2, HS3ST5, a U6 spliceosomal RNA, and a long noncoding RNA. When we combined results across multiple SNPs within the same gene, we identified 188 genes implicated in breed differences in cognition. This gene set included more genes than expected by chance that were (1) differentially expressed in brain tissue and (2) involved in nervous system functions including peripheral nervous system development, Wnt signaling, presynapse assembly, and synaptic vesicle exocytosis. These results advance our understanding of the genetic underpinnings of complex cognitive phenotypes and identify specific genetic variants for further research.

The enigmatic fetal subplate compartment forms an early tangential cortical nexus and provides the framework for construction of cortical connectivity

The most prominent transient compartment of the primate fetal cortex is the deep, cell-sparse, synapse-containing subplate compartment (SPC). The developmental role of the SPC and its extraordinary size in humans remain enigmatic. This paper evaluates evidence on the development and connectivity of the SPC and discusses its role in the pathogenesis of neurodevelopmental disorders. A synthesis of data shows that the subplate becomes a prominent compartment by its expansion from the deep cortical plate (CP), appearing well-delineated on MR scans and forming a tangential nexus across the hemisphere, consisting of an extracellular matrix, randomly distributed postmigratory neurons, multiple branches of thalamic and long corticocortical axons. The SPC generates early spontaneous non-synaptic and synaptic activity and mediates cortical response upon thalamic stimulation. The subplate nexus provides large-scale interareal connectivity possibly underlying fMR resting-state activity, before corticocortical pathways are established. In late fetal phase, when synapses appear within the CP, transient the SPC coexists with permanent circuitry. The histogenetic role of the SPC is to provide interactive milieu and capacity for guidance, sorting, "waiting" and target selection of thalamocortical and corticocortical pathways. The new evolutionary role of the SPC and its remnant white matter neurons is linked to the increasing number of associative pathways in the human neocortex. These roles attributed to the SPC are regulated using a spatiotemporal gene expression during critical periods, when pathogenic factors may disturb vulnerable circuitry of the SPC, causing neurodevelopmental cognitive circuitry disorders.

Quantitative analysis of chondroitin sulfate disaccharides from human and rodent fixed brain tissue by electrospray ionization-tandem mass spectrometry

Chondroitin sulfates (CS) are long, negatively charged, unbranched glycosaminoglycan (GAG) chains attached to CS-proteoglycan (CSPG) core proteins that comprise the glycan component in both loose interstitial extracellular matrices (ECMs) and in rigid, structured perineuronal net (PNN) scaffolds within the brain. As aberrant CS-PNN formations have been linked to a range of pathological states, including Alzheimer's disease (AD) and schizophrenia, the analysis of CS-GAGs in brain tissue at the disaccharide level has great potential to enhance disease diagnosis and prognosis. Two mass-spectrometry (MS)-based approaches were adapted to detect CS disaccharides from minute fixed tissue samples with low picomolar sensitivity and high reproducibility. The first approach employed a straightforward, quantitative direct infusion (DI)-tandem mass spectrometry (MS/MS) technique to determine the percentages of Δ4S- and Δ6S-CS disaccharides within the 4S/6S-CS ratio, while the second used a comprehensive liquid chromatography (LC)-MS/MS technique to determine the relative percentages of Δ0S-, Δ4S-, Δ6S-, Δ4S6S-CS and Δ2S6S-CS disaccharides, with internal validation by full chondroitin lyase activity. The quantitative accuracy of the five primary biologically relevant CS disaccharides was validated using a developmental time course series in fixed rodent brain tissue. We then analyzed the CS disaccharide composition in formalin-fixed human brain tissue, thus providing the first quantitative report of CS sulfation patterns in the human brain. The ability to comprehensively analyze the CS disaccharide composition from fixed brain tissue provides a means with which to identify alterations in the CS-GAG composition in relation to the onset and/or progression of neurological diseases.

Glycosaminoglycans from Alzheimer's disease hippocampus have altered capacities to bind and regulate growth factors activities and to bind tau

Glycosaminoglycans (GAGs), including heparan sulfates and chondroitin sulfates, are major components of the extracellular matrix. Upon interacting with heparin binding growth factors (HBGF), GAGs participate to the maintaintenance of tissue homeostasis and contribute to self-healing. Although several processes regulated by HBGF are altered in Alzheimer’s disease, it is unknown whether the brain GAG capacities to bind and regulate the function of HBGF or of other heparin binding proteins, as tau, are modified in this disease. Here, we show that total sulfated GAGs from hippocampus of Alzheimer’s disease have altered capacities to bind and potentiate the activities of growth factors including FGF-2, VEGF, and BDNF while their capacity to bind to tau is remarkable increased. Alterations of GAG structures and capacities to interact with and regulate the activity of heparin binding proteins might contribute to impaired tissue homeostasis in the Alzheimer’s disease brain.

Heparan Sulfate as a Therapeutic Target in Tauopathies: Insights From Zebrafish

Microtubule-associated protein tau (MAPT) hyperphosphorylation and aggregation, are two hallmarks of a family of neurodegenerative disorders collectively referred to as tauopathies. In many tauopathies, including Alzheimer's disease (AD), progressive supranuclear palsy (PSP) and Pick's disease, tau aggregates are found associated with highly sulfated polysaccharides known as heparan sulfates (HSs). In AD, amyloid beta (Aβ) peptide aggregates associated with HS are also characteristic of disease. Heparin, an HS analog, promotes misfolding, hyperphosphorylation and aggregation of tau protein in vitro. HS also provides cell surface receptors for attachment and uptake of tau seeds, enabling their propagation. These findings point to HS-tau interactions as potential therapeutic targets in tauopathies. The zebrafish genome contains genes paralogous to MAPT, genes orthologous to HS biosynthetic and chain modifier enzymes, and other genes implicated in AD. The nervous system in the zebrafish bears anatomical and chemical similarities to that in humans. These homologies, together with numerous technical advantages, make zebrafish a valuable model for investigating basic mechanisms in tauopathies and identifying therapeutic targets. Here, we comprehensively review current knowledge on the role of HSs in tau pathology and HS-targeting therapeutic approaches. We also discuss novel insights from zebrafish suggesting a role for HS 3-O-sulfated motifs in tau pathology and establishing HS antagonists as potential preventive agents or therapies for tauopathies.

The role of heparan sulfates in protein aggregation and their potential impact on neurodegeneration

Neurodegenerative disorders, such as Alzheimer's, Parkinson's, and prion diseases, are directly linked to the formation and accumulation of protein aggregates in the brain. These aggregates, principally made of proteins or peptides that clamp together after acquisition of β-folded structures, also contain heparan sulfates. Several lines of evidence suggest that heparan sulfates centrally participate in the protein aggregation process. In vitro, they trigger misfolding, oligomerization, and fibrillation of amyloidogenic proteins, such as Aβ, tau, α-synuclein, prion protein, etc. They participate in the stabilization of protein aggregates, protect them from proteolysis, and act as cell-surface receptors for the cellular uptake of proteopathic seeds during their spreading. This review focuses attention on the importance of heparan sulfates in protein aggregation in brain disorders including Alzheimer's, Parkinson's, and prion diseases. The presence of these sulfated polysaccharides in protein inclusions in vivo and their capacity to trigger protein aggregation in vitro strongly suggest that they might play critical roles in the neurodegenerative process. Further advances in glyco-neurobiology will improve our understanding of the molecular and cellular mechanisms leading to protein aggregation and neurodegeneration.

Increased soluble heterologous expression of a rat brain 3-O-sulfotransferase 1 - A key enzyme for heparin biosynthesis

Heparan sulfate (HS), is a glycosaminoglycan (GAG) involved in various biological processes, including blood coagulation, wound healing and embryonic development. HS 3-O-sulfotransferases (3-OST), which transfer the sulfo group to the 3-hydroxyl group of certain glucosamine residues, is a key enzyme in the biosynthesis of a number of biologically important HS chains. The 3-OST-1 isoform is one of the 7 known 3-OST isoforms and is important for the biosynthesis of anticoagulant HS chains. In this study, we cloned 3-OST-1 from the rat brain by reverse transcription-polymerase chain reaction (RT-PCR). After codon optimization and removal of the signal peptide, the recombinant plasmid was transformed into Escherichia coli BL21 (DE3) to obtain a His tagged-3-OST-1 fusion protein. SDS-PAGE analysis showed that the expressed 3-OST-1 was mainly found in inclusion bodies. The 3-OST-1 was purified by Ni affinity column and refolded by dialysis. The activity of obtained 3-OST-1 was 0.04 U/mL with a specific activity of 0.55 U/mg after renaturation. Furthermore, a co-expressed recombinant plasmid pET-28a-3-OST-1 with the chaperone expression system (pGro7) was constructed and transferred to E. coli BL21 (DE3) to co-express recombinant strain E. coli BL21 (DE3)/pET-28a-3-OST-1 + pGro7. The soluble expression of 3-OST-1 was significantly improved in the co-expressed recombinant strain, with enzyme activity reaching 0.06 U/mL and having a specific activity of 0.83 U/mg. N-sulfo, N-acetylheparosan (NSNAH) was modified by the recombinant expressed 3-OST-1 and the product was confirmed by ¹H NMR showing the sulfo group was successfully transferred to NSNAH.

HSV-1 interaction to 3-O-sulfated heparan sulfate in mouse-derived DRG explant and profiles of inflammatory markers during virus infection

The molecular mechanism of herpes simplex virus (HSV) entry and the associated inflammatory response in the nervous system remain poorly understood. Using mouse-derived ex vivo dorsal root ganglia (DRG) explant model and single cell neurons (SCNs), in this study, we provided a visual evidence for the expression of heparan sulfate (HS) and 3-O-sulfated heparan sulfate (3-OS HS) followed by their interactions with HSV-1 glycoprotein B (gB) and glycoprotein D (gD) during cell entry. Upon heparanase treatment of DRG-derived SCN, a significant inhibition of HSV-1 entry was observed suggesting the involvement of HS role during viral entry. Finally, a cytokine array profile generated during HSV-1 infection in DRG explant indicated an enhanced expression of chemokines (LIX, TIMP-2, and M-CSF)—known regulators of HS. Taken together, these results highlight the significance of HS during HSV-1 entry in DRG explant. Further investigation is needed to understand which isoforms of 3-O-sulfotransferase (3-OST)-generated HS contributed during HSV-1 infection and associated cell damage.

Sugar glues for broken neurons

Proteoglycans (PGs) regulate diverse functions in the central nervous system (CNS) by interacting with a number of growth factors, matrix proteins, and cell surface molecules. Heparan sulfate (HS) and chondroitin sulfate (CS) are two major glycosaminoglycans present in the PGs of the CNS. The functionality of these PGs is to a large extent dictated by the fine sulfation patterns present on their glycosaminoglycan (GAG) chains. In the past 15 years, there has been a significant expansion in our knowledge on the role of HS and CS chains in various neurological processes, such as neuronal growth, regeneration, plasticity, and pathfinding. However, defining the relation between distinct sulfation patterns of the GAGs and their functionality has thus far been difficult. With the emergence of novel tools for the synthesis of defined GAG structures, and techniques for their characterization, we are now in a better position to explore the structure-function relation of GAGs in the context of their sulfation patterns. In this review, we discuss the importance of GAGs on CNS development, injury, and disorders with an emphasis on their sulfation patterns. Finally, we outline several GAG-based therapeutic strategies to exploit GAG chains for ameliorating various CNS disorders.

Histochemical analysis of heparan sulfate 3-O-sulfotransferase expression in mouse brain

In situ hybridization provides information for understanding the localization of gene expression in various tissues. The relative expression levels of mRNAs in a single cell can be sensitively visualized by this technique. Furthermore, since in situ hybridization is a histological technique, tissue structure is maintained after fixation, and it is possible to accurately identify cell types. We have examined the expression of heparan sulfate sulfotransferases by in situ hybridization to better understand the functions of heparan sulfate in the development of mouse nervous system. This chapter describes methods of in situ hybridization analyses using cRNA probes labeled with nonradioactive nucleotides.

HS3ST2 expression is critical for the abnormal phosphorylation of tau in Alzheimer's disease-related tau pathology

Heparan sulphate (glucosamine) 3-O-sulphotransferase 2 (HS3ST2, also known as 3OST2) is an enzyme predominantly expressed in neurons wherein it generates rare 3-O-sulphated domains of unknown functions in heparan sulphates. In Alzheimer's disease, heparan sulphates accumulate at the intracellular level in disease neurons where they co-localize with the neurofibrillary pathology, while they persist at the neuronal cell membrane in normal brain. However, it is unknown whether HS3ST2 and its 3-O-sulphated heparan sulphate products are involved in the mechanisms leading to the abnormal phosphorylation of tau in Alzheimer's disease and related tauopathies. Here, we first measured the transcript levels of all human heparan sulphate sulphotransferases in hippocampus of Alzheimer's disease (n = 8; 76.8 ± 3.5 years old) and found increased expression of HS3ST2 (P < 0.001) compared with control brain (n = 8; 67.8 ± 2.9 years old). Then, to investigate whether the membrane-associated 3-O-sulphated heparan sulphates translocate to the intracellular level under pathological conditions, we used two cell models of tauopathy in neuro-differentiated SH-SY5Y cells: a tau mutation-dependent model in cells expressing human tau carrying the P301L mutation hTau(P301L), and a tau mutation-independent model in where tau hyperphosphorylation is induced by oxidative stress. Confocal microscopy, fluorescence resonance energy transfer, and western blot analyses showed that 3-O-sulphated heparan sulphates can be internalized into cells where they interact with tau, promoting its abnormal phosphorylation, but not that of p38 or NF-κB p65. We showed, in vitro, that the 3-O-sulphated heparan sulphates bind to tau, but not to GSK3B, protein kinase A or protein phosphatase 2, inducing its abnormal phosphorylation. Finally, we demonstrated in a zebrafish model of tauopathy expressing the hTau(P301L), that inhibiting hs3st2 (also known as 3ost2) expression results in a strong inhibition of the abnormally phosphorylated tau epitopes in brain and in spinal cord, leading to a complete recovery of motor neuronal axons length (n = 25; P < 0.005) and of the animal motor response to touching stimuli (n = 150; P < 0.005). Our findings indicate that HS3ST2 centrally participates to the molecular mechanisms leading the abnormal phosphorylation of tau. By interacting with tau at the intracellular level, the 3-O-sulphated heparan sulphates produced by HS3ST2 might act as molecular chaperones allowing the abnormal phosphorylation of tau. We propose HS3ST2 as a novel therapeutic target for Alzheimer's disease.

Proteoglycans and neuronal migration in the cerebral cortex during development and disease

Chondroitin sulfate proteoglycans and heparan sulfate proteoglycans are major constituents of the extracellular matrix and the cell surface in the brain. Proteoglycans bind with many proteins including growth factors, chemokines, axon guidance molecules, and cell adhesion molecules through both the glycosaminoglycan and the core protein portions. The functions of proteoglycans are flexibly regulated due to the structural variability of glycosaminoglycans, which are generated by multiple glycosaminoglycan synthesis and modifying enzymes. Neuronal cell surface proteoglycans such as PTPζ, neuroglycan C and syndecan-3 function as direct receptors for heparin-binding growth factors that induce neuronal migration. The lectican family, secreted chondroitin sulfate proteoglycans, forms large aggregates with hyaluronic acid and tenascins, in which many signaling molecules and enzymes including matrix proteases are preserved. In the developing cerebrum, secreted chondroitin sulfate proteoglycans such as neurocan, versican and phosphacan are richly expressed in the areas that are strategically important for neuronal migration such as the striatum, marginal zone, subplate and subventricular zone in the neocortex. These proteoglycans may anchor various attractive and/or repulsive cues, regulating the migration routes of inhibitory neurons. Recent studies demonstrated that the genes encoding proteoglycan core proteins and glycosaminoglycan synthesis and modifying enzymes are associated with various psychiatric and intellectual disorders, which may be related to the defects of neuronal migration.

Development of a photoreactive probe-based system for detecting heparin

We previously identified a peptide heparin-associated peptide Y (HappY) that binds specifically to heparin. In this article, we report a novel heparin detection system using chemically modified HappY as a probe. The photoreactive HappY probe was serially diluted and dispensed into a 96-well plate coated with biotinylated heparin. After ultraviolet irradiation, the HappY probe crosslinked to the heparin on the plate was detected with fluorescein isothiocyanate-conjugated streptavidin. Furthermore, the photoreactive HappY probe was used to stain cutaneous tissue sections obtained from dermatitis-affected or mastocytoma-affected cats and dogs. The photoreactive HappY probe stained limited resident mast cells in the connective tissue of skin compared with the anti-heparan sulfate monoclonal antibody 10E4, suggesting that the probe can be used to distinguish the structure of heparin in tissues. The interactions between glycosaminoglycans and proteins in vivo tend to be weak. Therefore, our method for enhancing such weak interactions may be a promising tool for intermolecular interaction studies in glycobiology research.

Diversity of heparan sulfate and HSV entry: basic understanding and treatment strategies

A modified form of heparan sulfate (HS) known as 3-O-sulfated heparan sulfate (3-OS HS) generates fusion receptor for herpes simplex virus (HSV) entry and spread. Primary cultures of corneal fibroblasts derived from human eye donors have shown the clinical significance of this receptor during HSV corneal infection. 3-OS HS- is a product of a rare enzymatic modification at C3 position of glucosamine residue which is catalyzed by 3-O-sulfotransferases (3-OSTs) enzymes. From humans to zebrafish, the 3-OST enzymes are highly conserved and widely expressed in cells and tissues. There are multiple forms of 3-OSTs each producing unique subset of sulfated HS making it chemically diverse and heterogeneous. HSV infection of cells or zebrafish can be used as a unique tool to understand the structural-functional activities of HS and 3-OS HS and likewise, the infection can be used as a functional assay to screen phage display libraries for identifying HS and 3-OS HS binding peptides or small molecule inhibitors. Using this approach over 200 unique 12-mer HS and 3-OS HS recognizing peptides were isolated and characterized against HSV corneal infection where 3-OS HS is known to be a key receptor. In this review we discuss emerging role of 3-OS HS based therapeutic strategies in preventing viral infection and tissue damage.

Ataxia is the major neuropathological finding in arylsulfatase G-deficient mice: similarities and dissimilarities to Sanfilippo disease (mucopolysaccharidosis type III)

Deficiency of arylsulfatase G (ARSG) leads to a lysosomal storage disease in mice resembling biochemical and pathological features of the mucopolysaccharidoses and particularly features of mucopolysaccharidosis type III (Sanfilippo syndrome). Here we show that Arsg KO mice share common neuropathological findings with other Sanfilippo syndrome models and patients, but they can be clearly distinguished by the limitation of most phenotypic alterations to the cerebellum, presenting with ataxia as the major neurological finding. We determined in detail the expression of ARSG in the central nervous system and observed highest expression in perivascular macrophages (which are characterized by abundant vacuolization in Arsg KO mice) and oligodendrocytes. To gain insight into possible mechanisms leading to ataxia, the pathology in older adult mice (>12 months) was investigated in detail. This study revealed massive loss of Purkinje cells and gliosis in the cerebellum, and secondary accumulation of glycolipids like GM2 and GM3 gangliosides and unesterified cholesterol in surviving Purkinje cells, as well as neurons of some other brain regions. The abundant presence of ubiquitin and p62-positive aggregates in degenerating Purkinje cells coupled with the absence of significant defects in macroautophagy is consistent with lysosomal membrane permeabilization playing a role in the pathogenesis of Arsg-deficient mice and presumably Sanfilippo disease in general. Our data delineating the phenotype of mucopolysaccharidosis IIIE in a mouse KO model should help in the identification of possible human cases of this disease.

Structural alteration of cell surface heparan sulfate through the stimulation of the signaling pathway for heparan sulfate 6-O-sulfotransferase-1 in mouse fibroblast cells

Heparan sulfate (HS) is a randomly sulfated polysaccharide that is present on the cell surface and in the extracellular matrix. The sulfated structures of HS were synthesized by multiple HS sulfotransferases, thereby regulating various activities such as growth factor signaling, cell differentiation, and tumor metastasis. Therefore, if the sulfated structures of HS could be artificially controlled, those manipulations would help to understand the various functions depending on HS. However, little knowledge is currently available to realize the mechanisms controlling the expression of such enzymes. In this study, we found that the ratio of 6-O-sulfated disaccharides increased at 3 h after adrenaline stimulation in mouse fibroblast cells. Furthermore, adrenaline-induced up-regulation of HS 6-O-sulfotransferase-1 (6-OST-1) was controlled by Src-ERK1/2 signaling pathway. Finally, inhibiting the signaling pathways for 6-OST-1 intentionally suppressed the adrenaline-induced structural alteration of HS. These observations provide fundamental insights into the understanding of structural alterations in HS by extracellular cues.

Transcriptional Activity of Heparan Sulfate Biosynthetic Machinery is Specifically Impaired in Benign Prostate Hyperplasia and Prostate Cancer

Heparan sulfates (HSs) are key components of mammalian cells surface and extracellular matrix. Structure and composition of HS, generated by HS-biosynthetic system through non-template-driven process, are significantly altered in cancer tissues. The aim of this study was to investigate the involvement of HS-metabolic machinery in prostate carcinogenesis. Transcriptional patterns of HS-metabolic enzymes (EXT1, EXT2, NDST1, NDST2, GLCE, 3OST1/HS3ST1, SULF1, SULF2, HPSE) were determined in normal, benign, and cancer human prostate tissues and cell lines (PNT2, LNCaP, PC3, DU145). Stability of the HS-metabolic system patterns under the pressure of external or internal stimuli was studied. Overall impairment of transcriptional activity of HS-metabolic machinery was detected in benign prostate hyperplasia, while both significant decrease in the transcriptional activity and changes in the expression patterns of HS metabolism-involved genes were observed in prostate tumors. Prostate cancer cell lines possessed specific transcriptional patterns of HS metabolism-involved genes; however, expression activity of the system was similar to that of normal prostate PNT2 cells. HS-metabolic system was able to dynamically react to different external or internal stimuli in a cell type-dependent manner. LNCaP cells were sensitive to the external stimuli (5-aza-deoxycytidin or Trichostatin A treatments; co-cultivation with human fibroblasts), whereas PC3 cells almost did not respond to the treatments. Ectopic GLCE over-expression resulted in transcriptional activation of HS-biosynthetic machinery in both cell lines, suggesting an existence of a self-regulating mechanism for the coordinated transcription of HS metabolism-involved genes. Taken together, these findings demonstrate impairment of HS-metabolic system in prostate tumors in vivo but not in prostate cancer cells in vitro, and suggest that as a potential microenvironmental biomarker for prostate cancer diagnostics and treatment.

Heparan sulfate: a key regulator of embryonic stem cell fate

Heparan sulfate (HS) belongs to a class of glycosaminoglycans and is a highly sulfated, linear polysaccharide. HS biosynthesis and modification involves numerous enzymes. HS exists as part of glycoproteins named HS proteoglycans, which are expressed abundantly on the cell surface and in the extracellular matrix. HS interacts with numerous proteins, including growth factors, morphogens, and adhesion molecules, and thereby regulates important developmental processes in invertebrates and vertebrates. Embryonic stem cells (ESCs) are distinguished by their characteristics of self-renewal and pluripotency. Self-renewal allows ESCs to proliferate indefinitely in their undifferentiated state, whereas pluripotency implies their capacity to differentiate into the three germ layers and ultimately all cell types of the adult body. Both traits are tightly regulated by numerous cell signaling pathways. Recent studies have highlighted the importance of HS in the modulation of ESC functions, specifically their lineage fate. Here, we review the current advances that have been made in understanding the structural changes of HS during ESC differentiation and in deciphering the molecular mechanisms by which HS modulates cell fate. Finally, we discuss the applications of heparinoids and chemical inhibitors of HS biosynthesis for the manipulation of ESC culture and directed differentiation.

Implications of heparan sulfate and heparanase in neuroinflammation

Heparan sulfate proteoglycans (HSPGs), expressed on the cell surface and in the extracellular matrix of most animal tissues, have essential functions in development and homeostasis, and have been implicated in several pathological conditions. The functions of HSPGs are mainly mediated through interactions of the heparan sulfate (HS) polysaccharide side chains with different protein ligands. The molecular structure of HS is highly diverse, expressed in a cell-type specific manner. The flexible yet controlled structure of HS is primarily generated through a strictly regulated biosynthesis process and is further modified post-synthetically, such as desulfation by endosulfatases and fragmentation by heparanase. Heparanase is an endo-glucuronidase expressed in all tissues. The enzyme has been found up-regulated in a number of pathological conditions, implying a role in diseases mainly through degradation of HS. Emerging evidence demonstrates important roles of HS and heparanase in inflammatory reactions, particularly in the regulation of leukocyte activation and extravasation. Neuroinflammation is a common feature of various central nervous system disorders, thus it is a great interest to understand the implications of HS and heparanase in neuroinflammation.

Heparan sulfate 3-O-sulfation: a rare modification in search of a function

Many protein ligands bind to heparan sulfate, which results in their presentation, protection, oligomerization or conformational activation. Binding depends on the pattern of sulfation and arrangement of uronic acid epimers along the chains. Sulfation at the C3 position of glucosamine is a relatively rare, yet biologically significant modification, initially described as a key determinant for binding and activation of antithrombin and later for infection by type I herpes simplex virus. In mammals, a family of seven heparan sulfate 3-O-sulfotransferases installs sulfate groups at this position and constitutes the largest group of sulfotransferases involved in heparan sulfate formation. However, to date very few proteins or biological systems have been described that are influenced by 3-O-sulfation. This review describes our current understanding of the prevalence and structure of 3-O-sulfation sites, expression and substrate specificity of the 3-O-sulfotransferase family and the emerging roles of 3-O-sulfation in biology.

Distinct 3-O-sulfated heparan sulfate modification patterns are required for kal-1-dependent neurite branching in a context-dependent manner in Caenorhabditis elegans

Heparan sulfate (HS) is an unbranched glycosaminoglycan exhibiting substantial molecular diversity due to multiple, nonuniformly introduced modifications, including sulfations, epimerization, and acetylation. HS modifications serve specific and instructive roles in neuronal development, leading to the hypothesis of a HS code that regulates nervous system patterning. Although the in vivo roles of many of the HS modifications have been investigated, very little is known about the function of HS 3-O-sulfation in vivo. By examining patterning of the Caenorhabditis elegans nervous system in loss of function mutants of the two 3-O-sulfotransferases, hst-3.1 and hst-3.2, we found HS 3-O-sulfation to be largely dispensable for overall neural development. However, generation of stereotypical neurite branches in hermaphroditic-specific neurons required hst-3.1, hst-3.2, as well as an extracellular cell adhesion molecule encoded by kal-1, the homolog of Kallmann Syndrome associated gene 1/anosmin-1. In contrast, kal-1−dependent neurite branching in AIY neurons required catalytic activity of hst-3.2 but not hst-3.1. The context-dependent requirement for hst-3.2 and hst-3.1 indicates that both enzymes generate distinct types of HS modification patterns in different cell types, which regulate kal-1 to promote neurite branching. We conclude that HS 3-O-sulfation does not play a general role in establishing the HS code in C. elegans but rather plays a specialized role in a context-dependent manner to establish defined aspects of neuronal circuits.

Dense-map genome scan for dyslexia supports loci at 4q13, 16p12, 17q22; suggests novel locus at 7q36

Analysis of genetic linkage to dyslexia was performed using 133,165 array-based SNPs genotyped in 718 persons from 101 dyslexia-affected families. Results showed five linkage peaks with lod scores >2.3 (4q13.1, 7q36.1-q36.2, 7q36.3, 16p12.1, and 17q22). Of these five regions, three have been previously implicated in dyslexia (4q13.1, 16p12.1, and 17q22), three have been implicated in attention-deficit hyperactivity disorder (ADHD, which highly co-occurs with dyslexia; 4q13.1, 7q36.3, 16p12.1) and four have been implicated in autism (a condition characterized by language deficits; 7q36.1-q36.2, 7q36.3, 16p12.1, and 17q22). These results highlight the reproducibility of dyslexia linkage signals, even without formally significant lod scores, and suggest dyslexia predisposing genes with relatively major effects and locus heterogeneity. The largest lod score (2.80) occurred at 17q22 within the MSI2 gene, involved in neuronal stem cell lineage proliferation. Interestingly, the 4q13.1 linkage peak (lod 2.34) occurred immediately upstream of the LPHN3 gene, recently reported both linked and associated with ADHD. Separate analyses of larger pedigrees revealed lods >2.3 at 1-3 regions per family; one family showed strong linkage (lod 2.9) to a known dyslexia locus (18p11) not detected in our overall data, demonstrating the value of analyzing single large pedigrees. Association analysis identified no SNPs with genome-wide significance, although a borderline significant SNP (P = 6 × 10(-7)) occurred at 5q35.1 near FGF18, involved in laminar positioning of cortical neurons during development. We conclude that dyslexia genes with relatively major effects exist, are detectable by linkage analysis despite genetic heterogeneity, and show substantial overlapping predisposition with ADHD and autism.

A peptide found by phage display discriminates a specific structure of a trisaccharide in heparin

A number of recent studies have shown that heparan sulfate can control several important biological events on the cell surface through changes in sulfation pattern. The in vivo modification of sugar chains with sulfates, however, is complicated, and the discrimination of different sulfation patterns is difficult. Heparin, which is primarily produced by mast cells, is closely approximated by the structural analog heparan sulfate. Screening of heparin-associating peptides using phage display and antithrombin-bound affinity chromatography identified a peptide, heparin-associating peptide Y (HappY), that acts as a target of immobilized heparin. The peptide consists of 12 amino acid residues with characteristic three arginines and exclusively binds to heparin and heparan sulfate but does not associate with other glycosaminoglycans. HappY recognizes three consecutive monosaccharide residues in heparin through its three arginine residues. HappY should be a useful probe to detect heparin and heparan sulfate in studies of glycobiology.

Functions of chondroitin sulfate and heparan sulfate in the developing brain

Chondroitin sulfate and heparan sulfate proteoglycans are major components of the cell surface and extracellular matrix in the brain. Both chondroitin sulfate and heparan sulfate are unbranched highly sulfated polysaccharides composed of repeating disaccharide units of glucuronic acid and N-acetylgalactosamine, and glucuronic acid and N-acetylglucosamine, respectively. During their biosynthesis in the Golgi apparatus, these glycosaminoglycans are highly modified by sulfation and C5 epimerization of glucuronic acid, leading to diverse heterogeneity in structure. Their structures are strictly regulated in a cell type-specific manner during development partly by the expression control of various glycosaminoglycan-modifying enzymes. It has been considered that specific combinations of glycosaminoglycan-modifying enzymes generate specific functional microdomains in the glycosaminoglycan chains, which bind selectively with various growth factors, morphogens, axon guidance molecules and extracellular matrix proteins. Recent studies have begun to reveal that the molecular interactions mediated by such glycosaminoglycan microdomains play critical roles in the various signaling pathways essential for the development of the brain.

Glial cells modulate heparan sulfate proteoglycan (HSPG) expression by neuronal precursors during early postnatal cerebellar development

Cerebellum controls motor coordination, balance, eye movement, and has been implicated in memory and addiction. As in other parts of the CNS, correct embryonic and postnatal development of the cerebellum is crucial for adequate performance in the adult. Cellular and molecular defects during cerebellar development can lead to severe phenotypes, such as ataxias and tumors. Knowing how the correct development occurs can shed light into the mechanisms of disease. Heparan sulfate proteoglycans are complex molecules present in every higher eukaryotic cells and changes in their level of expression as well as in their structure lead to drastic functional alterations. This work aimed to investigate changes in heparan sulfate proteoglycans expression during cerebellar development that could unveil control mechanisms. Using real time RT-PCR we evaluated the expression of syndecans, glypicans and modifying enzymes by isolated cerebellar granule cell precursors, and studied the influence of soluble glial factors on the expression of those genes. We evaluated the possible involvement of Runx transcription factors in the response of granule cell precursors to glial factors. Our data show for the first time that cerebellar granule cell precursors express members of the Runx family and that the expression of those genes can also be controlled by glial factors. Our results also show that the expression of all genes studied vary during postnatal development and treatment of precursors with glial factors indicate that the expression of heparan sulfate proteoglycan genes as well as genes encoding heparan sulfate modifying enzymes can be modulated by the microenvironment, reflecting the intricate relations between neuron and glia.

Opposing functions of chondroitin sulfate and heparan sulfate during early neuronal polarization

Axon-dendrite polarity of neurons is essential for information processing in the nervous system. Here we studied the functions of chondroitin sulfate (CS) and heparan sulfate (HS) in neuronal polarization using cultured dissociated hippocampal neurons. Immunohistochemical analyses of early cultured neurons indicated the distribution of these glycosaminoglycans to be quite different. While CS epitopes were accumulated in the focal contacts present in axons and cell bodies, those of HS were detected ubiquitously on the cell surface including on dendrites and axons. Treatment with chondroitinase (CHase) ABC, which degrades CS, and knockdown of a CS sulfotransferase, N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase (4,6-ST), which is involved in the biosynthesis of oversulfated structures, induced the formation of multiple axons in hippocampal neurons. Time-lapse recordings revealed the multiple axons of CHase ABC-treated neurons to be highly unstable, extending and retracting, repeatedly. CHase ABC-treatments suggested that CS is involved in the formation of phosphorylated focal adhesion kinase-positive focal contacts. Thus, CS may enhance integrin signaling in the nascent axons, supporting axon specification. On the other hand, when neurons were treated with heparitinases that specifically degrade HS, neurons with a single axon increased. The axons of HSase-treated neurons extended steadily and showed almost no retraction. These results suggest that CS stabilizes and HS destabilizes the growth of axons in an opposing manner, contributing to early neuronal polarization.

Endothelial heparan sulfate in angiogenesis

Heparan sulfate (HS) is a linear polysaccharide composed of 50-200 glucosamine and uronic acid (glucuronic acid or iduronic acid) disaccharide repeats with epimerization and various sulfation modifications. HS is covalently attached to core proteins to form HS-proteoglycans. Most of the functions of HS-proteoglycans are mediated by their HS moieties. The biosynthesis of HS is initiated by chain polymerization and is followed by stepwise modification reactions, including sulfation and epimerization. These modifications generate ligand-binding sites that modulate cell functions and activities of proteinases and/or proteinase inhibitors. HS is abundantly expressed in developing and mature vasculature, and understanding its roles in vascular biology and related human diseases is an area of intense investigation. In this chapter, we summarize the significant recent advances in our understanding of the roles of HS in developmental and pathological angiogenesis with a major focus on studies using transgenic as well as gene knockout/knockdown models in mice and zebrafish. These studies have revealed that HS critically regulates angiogenesis by playing a proangiogenic role, and this regulatory function critically depends on HS fine structure. The latter is responsible for facilitating cell-surface binding of various proangiogenic growth factors that in turn mediate endothelial growth signaling. In cancer, mouse studies have revealed important roles for endothelial cell-surface HS as well as matrix-associated HS, wherein signaling by multiple growth factors as well as matrix storage of growth factors may be regulated by HS. We also discuss important mediators that may fine-tune such regulation, such as heparanase and sulfatases; and models wherein targeting HS (or core protein) biosynthesis may affect tumor growth and vascularization. Finally, the importance of targeting HS in other human diseases wherein angiogenesis may play pathophysiologic (or even therapeutic) roles is considered.

Expanding the role of 3-O sulfated heparan sulfate in herpes simplex virus type-1 entry

Heparan sulfate (HS) proteoglycans are commonly exploited by multiple viruses for initial attachment to host cells. Herpes simplex virus-1 (HSV-1) is unique because it can use HS for both attachment and penetration, provided specific binding sites for HSV-1 envelope glycoprotein gD are present. The interaction with gD is mediated by specific HS moieties or 3-O sulfated HS (3-OS HS), which are generated by all but one of the seven isoforms of 3-O sulfotransferases (3-OSTs). Here we demonstrate that several common experimental cell lines express unique sets of 3-OST isoforms. While the isoforms 3-OST-3, -5 and -6 were most commonly expressed, isoforms 3-OST-2 and -4 were undetectable in the cell lines examined. Since most cell lines expressed multiple 3-OST isoforms, we addressed the significance of 3-OS HS in HSV-1 entry by down-regulating 2-O-sulfation, a prerequisite for 3-OS HS formation, by knocking down 2-OST expression by RNA interference (RNAi). 2-OST knockdown was verified by reverse-transcriptase PCR and Western blot analysis, while 3-OS HS knockdown was verified by immunofluorescence. Cells showed a significant decrease in viral entry, suggesting an important role for 3-OS HS. Implicating 3-OS HS further, cells knocked down for 2-OST expression also demonstrated decreased cell-cell fusion when cocultivated with effector cells transfected with HSV-1 glycoproteins. Our findings suggest that 3-OS HS may play an important role in HSV-1 entry into many different cell lines.

NDST1-dependent heparan sulfate regulates BMP signaling and internalization in lung development

Heparan sulfate proteoglycans (HSPGs) are required for various signaling pathways, one of which is the bone morphogenetic protein (BMP) signaling pathway. N-deacetylase/N-sulfotransferase-1 (NDST1) participates in synthesizing heparan sulfate (HS) chains of HSPGs, and is involved in bone and lung development. Here, we report that in spite of the redundant expression of Ndst2, Ndst3 and Ndst4 genes, Ndst1–/– mice display defective differentiation of lung cells and increased cell proliferation. Loss of Ndst1 in the lung enhances downstream BMP signaling in vivo. Noggin, which is an antagonist of BMP, can rescue the Ndst1–/– lung morphogenetic defects in explant cultures. Further studies in vitro indicated that loss of Ndst1 significantly impairs BMP internalization by decreasing BMP binding to endogenous HS. Exogenous heparin can rescue both the BMP signaling and BMP internalization abnormalities in Ndst1–/– lung. Thus, we propose that HS regulates BMP signaling by controlling the balance between BMP binding to HS, and that BMP receptors and NDST1-dependent modification are essential for this process. The results suggest that NDST1-dependent HS is essential for proper functioning of BMP in embryonic lung development.

Proteoglycan interactions with Sonic Hedgehog specify mitogenic responses

Sonic Hedgehog (Shh) has dual roles in vertebrate development, as it promotes progenitor cell proliferation and induces tissue patterning. Here we show mitogenic and patterning functions of Shh can be uncoupled from one another. Using a genetic approach to selectively inhibit Shh-proteoglycan interactions in a mouse model, we show binding of Shh to proteoglycans is required for proliferation of neural stem/precursor cells but not for tissue patterning. Shh-proteoglycan interactions regulate both spatial and temporal features of Shh signaling. Proteoglycans localize Shh to specialized mitogenic niches and also act at the single cell level to regulate the duration of Shh signaling, thereby promoting a gene expression program important for cell division. As activation of the Shh pathway is a feature of diverse human cancers, selective stimulation of proliferation by Shh-proteoglycan interactions may also figure prominently in neoplastic growth.

Visualizing mechanosensory endings of TrkC-expressing neurons in HS3ST-2-hPLAP mice

Somatosensory neurons are classified into three main types according to their modalities: nociceptive, thermal, and mechanosensory. Within each modality group, neurons can be further divided into morphologically and functionally distinct subclasses. Here we show that heparan sulfate D-glucosaminyl 3-O-sulfotransferase 2 (HS3ST-2) is a marker for specific subsets of TrkC-expressing cutaneous low-threshold mechanosensory and proprioceptive mechanosensory neurons. Two-color in situ analysis revealed that almost all HS3ST-2 signals colocalized with TrkC but not with TrkA or TrkB mRNA. To visualize the morphological subtypes of HS3ST-2/TrkC-expressing neurons, we generated a HS3ST-2-hPLAP knock-in mouse line, in which HS3ST-2-expressing neurons and their projections are labeled by human placental alkaline phosphatase (hPLAP). AP staining in these mice demonstrated that sensory endings of muscle spindles and Golgi tendon organs as well as the cutaneous mechanosensory Merkel and longitudinal lanceolate endings in the whiskers are strongly positive for hPLAP activity. In contrast, no nociceptive endings are labeled. In the glabrous and hairy skin, rare Merkel endings and transverse lanceolate endings are weakly stained. During development, each type of nerve endings forms at different time point. Muscle innervations differentiate first, followed by formation of cutaneous sensory endings. Our results revealed the subtype identities of TrkC-positive mechanosensory neurons and demonstrated the usefulness of HS3ST-2 as a genetic marker for these subclasses of neurons.

Brain heparanase expression is up-regulated during postnatal development and hypoxia-induced neovascularization in adult rats

Heparanase is an endo-beta-d-glucuronidase which specifically cleaves extracellular and cell surface heparan sulphates at intra-chain sites. Its enzymatic activity is strongly implicated in cell dissemination associated with tumor metastasis and inflammation. Indeed, heparanase gene is expressed in various tumors and its over-expression is correlated with increased tumor vascularity and metastatic potential of tumor cells. However, heparanase expression in non-invasive and non-immune tissue, including brain, has received less attention. Using RT-qPCR, western blot and histological analysis, we demonstrate in the adult rat that heparanase transcript is differentially expressed according to brain area, and that heparanase protein is mainly detected in neurons. Furthermore, we provide evidence that heparanase transcript and protein reach their greatest levels at early postnatal stages, in particular within the neocortex characterized by intensive structural plasticity. Using the in vitro model of PC12-induced neuronal differentiation, we suggest that developmental regulation of heparanase may coincide with axonal and dendritic pathfinding. At adulthood, we demonstrate that the increased heparanase transcript level correlates in the hippocampus with enhanced angiogenesis following repeated hypoxia exposures. Taken together, our results emphasize the potential importance of heparanase in brain homeostasis, both during development and adaptative responses to severe environmental challenges.

Essential alterations of heparan sulfate during the differentiation of embryonic stem cells to Sox1-enhanced green fluorescent protein-expressing neural progenitor cells

Embryonic stem (ES) cells can be cultured in conditions that either maintain pluripotency or allow differentiation to the three embryonic germ layers. Heparan sulfate (HS), a highly polymorphic glycosaminoglycan, is a critical cell surface coreceptor in embryogenesis, and in this paper we describe its structural transition from an unusually low-sulfated variant in ES cells to a more highly sulfated form in fluorescence-activated cell sorting-purified neural progenitor cells. The characteristic domain structure of HS was retained during this transformation. However, qualitative variations in surface sulfation patterns between ES and differentiated cells were revealed using HS epitope-specific antibodies and the HS-binding growth factor fibroblast growth factor 2 (FGF-2). Expression profiles of the HS modification enzymes indicated that both "early" (N-sulfotransferases) and "late" (6O- and 3O-sulfotransferases) sulfotransferases contributed to the alterations in sulfation patterning. An HS-null ES line was used to demonstrate the necessity for HS in neural differentiation. HS is a coreceptor for many of the protein effectors implicated in pluripotency and differentiation (e.g., members of the FGF family, bone morphogenic proteins, and fibronectin). We suggest that the stage-specific activities of these proteins are finely regulated by dynamic changes in sulfation motifs in HS chains. Disclosure of potential conflicts of interest is found at the end of this article.

Defective N-sulfation of heparan sulfate proteoglycans limits PDGF-BB binding and pericyte recruitment in vascular development

During vascular development, endothelial platelet-derived growth factor B (PDGF-B) is critical for pericyte recruitment. Deletion of the conserved C-terminal heparin-binding motif impairs PDGF-BB retention and pericyte recruitment in vivo, suggesting a potential role for heparan sulfate (HS) in PDGF-BB function during vascular development. We studied the participation of HS chains in pericyte recruitment using two mouse models with altered HS biosynthesis. Reduction of N-sulfation due to deficiency in N-deacetylase/N-sulfotransferase-1 attenuated PDGF-BB binding in vitro, and led to pericyte detachment and delayed pericyte migration in vivo. Reduced N-sulfation also impaired PDGF-BB signaling and directed cell migration, but not proliferation. In contrast, HS from glucuronyl C5-epimerase mutants, which is extensively N- and 6-O-sulfated, but lacks 2-O-sulfated L-iduronic acid residues, retained PDGF-BB in vitro, and pericyte recruitment in vivo was only transiently delayed. These observations were supported by in vitro characterization of the structural features in HS important for PDGF-BB binding. We conclude that pericyte recruitment requires HS with sufficiently extended and appropriately spaced N-sulfated domains to retain PDGF-BB and activate PDGF receptor beta (PDGFRbeta) signaling, whereas the detailed sequence of monosaccharide and sulfate residues does not appear to be important for this interaction.

Profiling the Sulfation Specificities of Glycosaminoglycan Interactions with Growth Factors and Chemotactic Proteins Using Microarrays

We report a carbohydrate microarray-based approach for the rapid, facile analysis of glycosaminoglycan-protein interactions. The key structural determinants responsible for protein binding, such as sulfate groups that participate in the interactions, were elucidated. Specificities were also readily compared across protein families or functional classes, and comparisons among glycosaminoglycan subclasses provided a more comprehensive understanding of protein specificity. To validate the approach, we showed that fibroblast growth factor family members have distinct sulfation preferences. We also demonstrated that heparan sulfate and chondroitin sulfate interact in a sulfation-dependent manner with various axon guidance proteins, including slit2, netrin1, ephrinA1, ephrinA5, and semaphorin5B. We anticipate that these microarrays will accelerate the discovery of glycosaminoglycan-binding proteins and provide a deeper understanding of their roles in regulating diverse biological processes.

Commissure formation in the mammalian forebrain

Commissural formation in the mammalian brain is highly organised and regulated both by the cell-autonomous expression of transcription factors, and by non-cell-autonomous mechanisms including the formation of midline glial structures and their expression of specific axon guidance molecules. These mechanisms channel axons into the correct path and enable the subsequent connection of specific brain areas to their appropriate targets. Several key findings have been made over the past two years, including the discovery of novel mechanisms of action that 'classical' guidance factors such as the Slits, Netrins, and their receptors have in axon guidance. Moreover, novel guidance factors such as members of the Wnt family, and extracellular matrix components such as heparan sulphate proteoglycans, have been shown to be important for mammalian brain commissure formation. Additionally, there have been significant discoveries regarding the role of FGF signalling in the formation of midline glial structures. In this review, we discuss the most recent advances in the field that have contributed to our current understanding of commissural development in the telencephalon.