The fourth immunoglobulin-like domain of NCAM contains a carbohydrate recognition domain for oligomannosidic glycans implicated in association with L1 and neurite outgrowth

A neural cell adhesion molecule from oyster Crassostrea gigas: Molecular identification and immune functional characterization

Neural cell adhesion molecules (NCAMs) are large cell-surface glycoproteins playing important roles in cell-cell and cell-extracellular matrix interactions in nervous system. Recent study identified a homologue of NCAM (CgNCAM) from the Pacific oyster Crassostrea gigas. Its ORF was of 2634 bp which encodes a protein (877 amino acids) consisting of five immunoglobulin domains and two fibronectin type III domains. CgNCAM transcripts were broadly distributed in oyster tissues especially in mantle, labial palp and haemolymph. CgNCAM showed up-regulated expression in haemocytes of oysters after Vibrio splendidus and Staphylococcus aureus stimulation. The recombinant CgNCAM protein (rCgNCAM) was able to bind manose, lipopolysaccharide and glucan, as well as different microbes including Gram-negative bacteria and fungi. rCgNCAM displayed bacterial agglutination and hemagglutination activity. CgNCAM improved the phagocytosis of haemocytes towards V. splendidus by regulating the expression of CgIntegrin, CgRho J and CgMAPKK. Moreover, CgNCAM was involved in the extracellular trap establishment of haemocytes after V. splendidus stimulation. The results collectively indicated that CgNCAM acted as a recognition receptor executing multiple immune functions to recognize and eliminate invading microorganisms in innate immunity of oysters.

Carbohydrate based biomaterials for neural interface applications

Neuroprosthetic devices that record and modulate neural activities have demonstrated immense potential for bypassing or restoring lost neurological functions due to neural injuries and disorders. However, implantable electrical devices interfacing with brain tissue are susceptible to a series of inflammatory tissue responses along with mechanical or electrical failures which can affect the device performance over time. Several biomaterial strategies have been implemented to improve device-tissue integration for high quality and stable performance. Ranging from developing smaller, softer, and more flexible electrode designs to introducing bioactive coatings and drug-eluting layers on the electrode surface, such strategies have shown different degrees of success but with limitations. With their hydrophilic properties and specific bioactivities, carbohydrates offer a potential solution for addressing some of the limitations of the existing biomolecular approaches. In this review, we summarize the role of polysaccharides in the central nervous system, with a primary focus on glycoproteins and proteoglycans, to shed light on their untapped potential as biomaterials for neural implants. Utilization of glycosaminoglycans for neural interface and tissue regeneration applications is comprehensively reviewed to provide the current state of carbohydrate-based biomaterials for neural implants. Finally, we will discuss the challenges and opportunities of applying carbohydrate-based biomaterials for neural tissue interfaces.

Mammalian brain glycoproteins exhibit diminished glycan complexity compared to other tissues

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses. Here, using several methodologies, we analyze Asn-linked and Ser/Thr/Tyr-linked protein glycosylation between brain regions and sexes in mice. Brain N-glycans are less complex in sequence and variety compared to other tissues, consisting predominantly of high-mannose and fucosylated/bisected structures. Most brain O-glycans are unbranched, sialylated O-GalNAc and O-mannose structures. A consistent pattern is observed between regions, and sex differences are minimal compared to those in plasma. Brain glycans correlate with RNA expression of their synthetic enzymes, and analysis of glycosylation genes in humans show a global downregulation in the brain compared to other tissues. We hypothesize that this restricted repertoire of protein glycans arises from their tight regulation in the brain. These results provide a roadmap for future studies of glycosylation in neurodevelopment and disease.

Towards Mapping of the Human Brain N-Glycome with Standardized Graphitic Carbon Chromatography

The brain N-glycome is known to be crucial for many biological functions, including its involvement in neuronal diseases. Although large structural studies of brain N-glycans were recently carried out, a comprehensive isomer-specific structural analysis has still not been achieved, as indicated by the recent discovery of novel structures with galactosylated bisecting GlcNAc. Here, we present a detailed, isomer-specific analysis of the human brain N-glycome based on standardized porous graphitic carbon (PGC)-LC-MS/MS. To achieve this goal, we biosynthesized glycans with substitutions typically occurring in the brain N-glycome and acquired their normalized retention times. Comparison of these values with the standardized retention times of neutral and desialylated N-glycan fractions of the human brain led to unambiguous isomer specific assignment of most major peaks. Profound differences in the glycan structures between naturally neutral and desialylated glycans were found. The neutral and sialylated N-glycans derive from diverging biosynthetic pathways and are biosynthetically finished end products, rather than just partially processed intermediates. The focus on structural glycomics defined the structure of human brain N-glycans, amongst these are HNK-1 containing glycans, a bisecting sialyl-lactose and structures with fucose and N-acetylgalactosamine on the same arm, the so-called LDNF epitope often associated with parasitic worms.

Membrane Domain Localization and Interaction of the Prion-Family Proteins, Prion and Shadoo with Calnexin

The cellular prion protein (PrP^C) is renowned for its infectious conformational isoform PrP^Sc, capable of templating subsequent conversions of healthy PrP^Cs and thus triggering the group of incurable diseases known as transmissible spongiform encephalopathies. Besides this mechanism not being fully uncovered, the protein’s physiological role is also elusive. PrP^C and its newest, less understood paralog Shadoo are glycosylphosphatidylinositol-anchored proteins highly expressed in the central nervous system. While they share some attributes and neuroprotective actions, opposing roles have also been reported for the two; however, the amount of data about their exact functions is lacking. Protein–protein interactions and membrane microdomain localizations are key determinants of protein function. Accurate identification of these functions for a membrane protein, however, can become biased due to interactions occurring during sample processing. To avoid such artifacts, we apply a non-detergent-based membrane-fractionation approach to study the prion protein and Shadoo. We show that the two proteins occupy similarly raft and non-raft membrane fractions when expressed in N2a cells and that both proteins pull down the chaperone calnexin in both rafts and non-rafts. These indicate their possible binding to calnexin in both types of membrane domains, which might be a necessary requisite to aid the inherently unstable native conformation during their lifetime.

Nanostructured gold electrodes promote neural maturation and network connectivity

Progress in the clinical application of recording and stimulation devices for neural diseases is still limited, mainly because of suboptimal material engineering and unfavorable interactions with biological entities. Nanotechnology is providing upgraded designs of materials to better mimic the native extracellular environment and attain more intimate contacts with individual neurons, besides allowing for the miniaturization of the electrodes. However, little progress has been done to date on the understanding of the biological impact that such neural interfaces have on neural network maturation and functionality. In this work, we elucidate the effect of a gold (Au) highly ordered nanostructure on the morphological and functional interactions with neural cells and tissues. Alumina-templated Au nanostructured electrodes composed of parallel nanowires of 160 nm in diameter and 1.2 μm in length (Au-NWs), with 320 nm of pitch, are designed and characterized. Equivalent non-structured Au electrodes (Au-Flat) are used for comparison. By using diverse techniques in in vitro cell cultures including live calcium imaging, we found that Au-NWs interfaced with primary neural cortical cells for up to 14 days allow neural networks growth and increase spontaneous activity and ability of neuronal synchronization, thus indicating that nanostructured features favor neuronal network. The enhancement in the number of glial cells found is hypothesized to be behind these beneficial functional effects. The in vivo effect of the implantation of these nanostructured electrodes and its potential relevance for future clinical applicability has been explored in an experimental model of rat spinal cord injury. Subacute responses to implanted Au-NWs show no overt reactive or toxic biological reactions besides those triggered by the injury itself. These results highlight the translational potential of Au-NWs electrodes for in vivo applications as neural interfaces in contact with central nervous tissues including the injured spinal cord.

Human Lectins, Their Carbohydrate Affinities and Where to Find Them

Lectins are a class of proteins responsible for several biological roles such as cell-cell interactions, signaling pathways, and several innate immune responses against pathogens. Since lectins are able to bind to carbohydrates, they can be a viable target for targeted drug delivery systems. In fact, several lectins were approved by Food and Drug Administration for that purpose. Information about specific carbohydrate recognition by lectin receptors was gathered herein, plus the specific organs where those lectins can be found within the human body.

Neural glycomics: the sweet side of nervous system functions

The success of investigations on the structure and function of the genome (genomics) has been paralleled by an equally awesome progress in the analysis of protein structure and function (proteomics). We propose that the investigation of carbohydrate structures that go beyond a cell's metabolism is a rapidly developing frontier in our expanding knowledge on the structure and function of carbohydrates (glycomics). No other functional system appears to be suited as well as the nervous system to study the functions of glycans, which had been originally characterized outside the nervous system. In this review, we describe the multiple studies on the functions of LewisX, the human natural killer cell antigen-1 (HNK-1), as well as oligomannosidic and sialic (neuraminic) acids. We attempt to show the sophistication of these structures in ontogenetic development, synaptic function and plasticity, and recovery from trauma, with a view on neurodegeneration and possibilities to ameliorate deterioration. In view of clinical applications, we emphasize the need for glycomimetic small organic compounds which surpass the usefulness of natural glycans in that they are metabolically more stable, more parsimonious to synthesize or isolate, and more advantageous for therapy, since many of them pass the blood brain barrier and are drug-approved for treatments other than those in the nervous system, thus allowing a more ready access for application in neurological diseases. We describe the isolation of such mimetic compounds using not only Western NIH, but also traditional Chinese medical libraries. With this review, we hope to deepen the interests in this exciting field.

Region-Specific Characterization of N-Glycans in the Striatum and Substantia Nigra of an Adult Rodent Brain

N-glycan alterations in the nervous system can result in different neuropathological symptoms such as mental retardation, seizures, and epilepsy. Studies have reported the characterization of N-glycans in rodent brains, but there is a lack of spatial resolution as either the tissue samples were homogenized or specific proteins were selected for analysis of glycosylation. We hypothesize that region-specific resolution of N-glycans isolated from the striatum and substantia nigra (SN) can give an insight into the establishment and pathophysiological degeneration of neural circuitry in Parkinson's disease. Specific objectives of the study include isolation of N-glycans from the rat striatum and SN; reproducibility, resolution, and relative quantitation of N-glycome using ultra-performance liquid chromatography (UPLC), weak anion exchange-UPLC, and lectin histochemistry. The total N-glycomes from the striatum and SN were characterized using database mining (GlycoStore), exoglycosidase digestions, and liquid chromatography-mass spectrometry. It revealed significant differences in complex and oligomannose type N-glycans, sialylation (mono-, di-, and tetra-), fucosylation (tri-, core, and outer arm), and galactosylation (di-, tri-, and tetra-) between striatum and SN N-glycans with the detection of phosphorylated N-glycans in SN which were not detected in the striatum. This study presents the most comprehensive comparative analysis of relative abundances of N-glycans in the striatum and SN of rodent brains, serving as a foundation for identifying "brain-type" glycans as biomarkers or therapeutic targets and their modulation in neurodegenerative disorders.

Different Shades of L1CAM in the Pathophysiology of Cancer Stem Cells

L1 cell adhesion molecule (L1CAM) is aberrantly expressed in several tumor types where it is causally linked to malignancy and therapy resistance, acting also as a poor prognosis factor. Accordingly, several approaches have been developed to interfere with L1CAM function or to deliver cytotoxic agents to L1CAM-expressing tumors. Metastatic dissemination, tumor relapse and drug resistance can be fueled by a subpopulation of neoplastic cells endowed with peculiar biological properties that include self-renewal, efficient DNA repair, drug efflux machineries, quiescence, and immune evasion. These cells, known as cancer stem cells (CSC) or tumor-initiating cells, represent, therefore, an ideal target for tumor eradication. However, the molecular and functional traits of CSC have been unveiled only to a limited extent. In this context, it appears that L1CAM is expressed in the CSC compartment of certain tumors, where it plays a causal role in stemness itself and/or in biological processes intimately associated with CSC (e.g., epithelial-mesenchymal transition (EMT) and chemoresistance). This review summarizes the role of L1CAM in cancer focusing on its functional contribution to CSC pathophysiology. We also discuss the clinical usefulness of therapeutic strategies aimed at targeting L1CAM in the context of anti-CSC treatments.

Contributions of Chondroitin Sulfate, Keratan Sulfate and N-linked Oligosaccharides to Inhibition of Neurite Outgrowth by Aggrecan

The role of proteoglycans in the central nervous system (CNS) is a rapidly evolving field and has major implications in the field of CNS injury. Chondroitin sulfate proteoglycans (CSPGs) increase in abundance following damage to the spinal cord and inhibit neurite outgrowth. Major advances in understanding the interaction between outgrowing neurites and CSPGs has created a need for more robust and quantitative analyses to further our understanding of this interaction. We report the use of a high-throughput assay to determine the effect of various post-translational modifications of aggrecan upon neurite outgrowth from NS-1 cells (a PC12 cell line derivative). Aggrecan contains chondroitin sulfate, keratan sulfate, and N-linked oligosaccharides (N-glycans), each susceptible to removal through different enzymatic digestions. Using a sequential digestion approach, we found that chondroitin sulfate and N-glycans, but not keratan sulfate, contribute to inhibition of neurite outgrowth by substrate-bound aggrecan. For the first time, we have shown that N-linked oligosaccharides on aggrecan contribute to its inhibition of neuritogenesis.

High N-glycan multiplicity is critical for neuronal adhesion and sensitizes the developing cerebellum to N-glycosylation defect

Proper brain development relies highly on protein N-glycosylation to sustain neuronal migration, axon guidance and synaptic physiology. Impairing the N-glycosylation pathway at early steps produces broad neurological symptoms identified in congenital disorders of glycosylation. However, little is known about the molecular mechanisms underlying these defects. We generated a cerebellum specific knockout mouse for Srd5a3, a gene involved in the initiation of N-glycosylation. In addition to motor coordination defects and abnormal granule cell development, Srd5a3 deletion causes mild N-glycosylation impairment without significantly altering ER homeostasis. Using proteomic approaches, we identified that Srd5a3 loss affects a subset of glycoproteins with high N-glycans multiplicity per protein and decreased protein abundance or N-glycosylation level. As IgSF-CAM adhesion proteins are critical for neuron adhesion and highly N-glycosylated, we observed impaired IgSF-CAM-mediated neurite outgrowth and axon guidance in Srd5a3 mutant cerebellum. Our results link high N-glycan multiplicity to fine-tuned neural cell adhesion during mammalian brain development.

Different properties of polysialic acids synthesized by the polysialyltransferases ST8SIA2 and ST8SIA4

Polysialic acid (polySia) is mainly found as a modification of neural cell adhesion molecule (NCAM) in whole embryonic brains, as well as restricted areas of adult vertebrate brains, including the hippocampus. PolySia shows not only repulsive effects on NCAM-involved cell-cell interactions due to its bulky and hydrated properties, but also attractive effects on the interaction with neurologically active molecules, which exerts a reservoir function. Two different polysialyltransferases, ST8SIA2 and ST8SIA4, are involved in the synthesis of polySia chains; however, to date, the differences of the properties between polySia chains synthesized by these two enzymes remain unknown. In this study, to clarify this point, we first prepared polySia-NCAMs from HEK293 cells stably expressing ST8SIA4 and ST8SIA2, or ST8SIA2 (SNP-7), a mutant ST8SIA2 derived from a schizophrenia patient. The conventional sensitive chemical and immunological characterizations showed that the quantity and quality (structural features) of polySia are not so much different between ST8SIA4- and ST8SIA2-synthesized ones, apart from those of ST8SIA2 (SNP-7). Then, we assessed the homophilic and heterophilic interactions mediated by polySia-NCAM by adopting a surface plasmon resonance measurement as an in vitro analytical method. Our novel findings are as follows: (i) the ST8SIA2- and ST8SIA4-synthesized polySia-NCAMs exhibited different attractive and repulsive effects than each other; (ii) both polySia- and oligoSia-NCAMs synthesized by ST8SIA2 were able to bind polySia-NCAMs; (iii) the polySia-NCAM synthesized by a ST8SIA2 (SNP-7) showed markedly altered attractive and repulsive properties. Collectively, polySia-NCAM is suggested to simultaneously possess both attractive and repulsive properties that are highly regulated by the two polysialyltransferases.

Glycosylphosphatidylinositol-Anchored Immunoglobulin Superfamily Cell Adhesion Molecules and Their Role in Neuronal Development and Synapse Regulation

Immunoglobulin superfamily (IgSF) cell adhesion molecules (CAMs) are cell surface glycoproteins that not only mediate interactions between neurons but also between neurons and other cells in the nervous system. While typical IgSF CAMs are transmembrane molecules, this superfamily also includes CAMs, which do not possess transmembrane and intracellular domains and are instead attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. In this review, we focus on the role GPI-anchored IgSF CAMs have as signal transducers and ligands in neurons, and discuss their functions in regulation of neuronal development, synapse formation, synaptic plasticity, learning, and behavior. We also review the links between GPI-anchored IgSF CAMs and brain disorders.

Metabolic Glycoengineering with N-Acyl Side Chain Modified Mannosamines

In metabolic glycoengineering (MGE), cells or animals are treated with unnatural derivatives of monosaccharides. After entering the cytosol, these sugar analogues are metabolized and subsequently expressed on newly synthesized glycoconjugates. The feasibility of MGE was first discovered for sialylated glycans, by using N-acyl-modified mannosamines as precursor molecules for unnatural sialic acids. Prerequisite is the promiscuity of the enzymes of the Roseman-Warren biosynthetic pathway. These enzymes were shown to tolerate specific modifications of the N-acyl side chain of mannosamine analogues, for example, elongation by one or more methylene groups (aliphatic modifications) or by insertion of reactive groups (bioorthogonal modifications). Unnatural sialic acids are incorporated into glycoconjugates of cells and organs. MGE has intriguing biological consequences for treated cells (aliphatic MGE) and offers the opportunity to visualize the topography and dynamics of sialylated glycans in vitro, ex vivo, and in vivo (bioorthogonal MGE).

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

Chondroitin sulfate proteoglycans: structure-function relationship with implication in neural development and brain disorders

Chondroitin sulfate proteoglycans (CSPGs) are extracellular matrix components that contain two structural parts with distinct functions: a protein core and glycosaminoglycan (GAG) side chains. CSPGs are known to be involved in important cell processes like cell adhesion and growth, receptor binding, or cell migration. It is recognized that the presence of CSPGs is critical in neuronal growth mechanisms including axon guidance following injury of nervous system components such as spinal cord and brain. CSPGs are upregulated in the central nervous system after injury and participate in the inhibition of axon regeneration mainly through their GAG side chains. Recently, it was shown that some CSPGs members like aggrecan, versican, and neurocan were strongly involved in brain disorders like bipolar disorder (BD), schizophrenia, and ADHD. In this paper, we present the chemical structure-biological functions relationship of CSPGs, both in health state and in genetic disorders, addressing methods represented by genome-wide and crystallographic data as well as molecular modeling and quantitative structure-activity relationship.

ATP interferes with neural cell adhesion molecule-induced neurite outgrowth

The neural cell adhesion molecule (NCAM) is a member of the immunoglobulin superfamily and involved in the development and regeneration of the nervous system. NCAM is expressed in three major isoforms. Two of them have large intracellular domains of different lengths and are named according to their apparent molecular weight as NCAM140 or NCAM180. NCAM140 is known to promote neurite outgrowth, whereas NCAM180 stabilizes cell-cell contacts. Beside its role in neurite outgrowth, NCAM also shows ATPase activity on its extracellular domain. Here, we quantified neurite outgrowth of neuroblastoma cells, which were transfected with either NCAM140 or NCAM180 in the absence or presence of ATP. We could confirm that NCAM140 strongly promotes neurite outgrowth, whereas NCAM180 stimulates neurite outgrowth only to a minor extent. Furthermore, application of ATP reduced the NCAM-induced neurite outgrowth to background levels in a concentration-dependent and isoform-dependent manner.

NCAM function in the adult brain: lessons from mimetic peptides and therapeutic potential

Neural cell adhesion molecules (NCAMs) are complexes of transmembranal proteins critical for cell-cell interactions. Initially recognized as key players in the orchestration of developmental processes involving cell migration, cell survival, axon guidance, and synaptic targeting, they have been shown to retain these functions in the mature adult brain, in relation to plastic processes and cognitive abilities. NCAMs are able to interact among themselves (homophilic binding) as well as with other molecules (heterophilic binding). Furthermore, they are the sole molecule of the central nervous system undergoing polysialylation. Most interestingly polysialylated and non-polysialylated NCAMs display opposite properties. The precise contributions each of these characteristics brings in the regulations of synaptic and cellular plasticity in relation to cognitive processes in the adult brain are not yet fully understood. With the aim of deciphering the specific involvement of each interaction, recent developments led to the generation of NCAM mimetic peptides that recapitulate identified binding properties of NCAM. The present review focuses on the information such advances have provided in the understanding of NCAM contribution to cognitive function.

Neural cell adhesion molecules in brain plasticity and disease

Neural cell adhesion molecule (NCAM) has been studied extensively. But it is only in recent times that interest in this molecule has shifted to conditions such as Alzheimer's disease, Multiple Sclerosis and Schizophrenia, focusing on its role in neurodegeneration and abnormal neurodevelopment. NCAM is important in neurite outgrowth, long-term potentiation in the hippocampus and synaptic plasticity. Reduced as well as increased levels in NCAM have been linked to pathology in the brain suggesting that a shift in the equilibrium may be the key. Hence, increasing our understanding of the role of NCAM in health and disease should clear some of the ambiguity surrounding the molecule and even lead to newer potential therapeutic targets. This review consolidates our current understanding of NCAM, focusing on the consequences of dysregulation, its role in neurodegenerative and neurodevelopmental disorders, and the future of NCAM plus potential options for therapy.

Polysialylation of the neural cell adhesion molecule: interfering with polysialylation and migration in neuroblastoma cells

Polysialic acid represents a unique posttranslational modification of the neural cell adhesion molecule (NCAM). It is built as a homopolymer of up to 150 molecules of alpha 2-8-linked sialic acids on N-glycans of the fifth immunoglobulin-like domain of NCAM. Besides its role in cell migration and axonal growth during development, polysialic acids are closely related to tumor malignancy as they are linked to the malignant potential of several tumors, such as undifferentiated neuroblastoma. Polysialic acid expression is significantly more frequent in high-grade tumors than in low-grade tumors. It is synthesized in the Golgi apparatus by the activity of two closely related enzymes, the polysialyltransferases ST8SiaII and ST8SiaIV. Interestingly, polysialylation of tumors is not equally synthesized by both polysialyltransferases. It has been shown that especially the ST8SiaII gene is not expressed in some normal tissue, but is strongly expressed in tumor tissue. Here we summarize some knowledge on the role of polysialic acid in cell migration and tumor progression and present novel evidence that interfering with polysialylation using unnatural sialic acid precursors decreases the migration of neuroblastoma cells.

Synapsin I is an oligomannose-carrying glycoprotein, acts as an oligomannose-binding lectin, and promotes neurite outgrowth and neuronal survival when released via glia-derived exosomes

Oligomannosidic glycans play important roles in nervous system development and function. By performing a phage display screening with oligomannose-specific antibodies, we identified an oligomannose-mimicking peptide that was functionally active in modulating neurite outgrowth and neuron-astrocyte adhesion. Using the oligomannose-mimicking peptide in crosslinking experiments, synapsin I was identified as a novel oligomannose-binding protein in mouse brain. Further analyses not only verified that synapsin I is an oligomannose-binding lectin, but also indicated that it is a glycoprotein carrying oligomannose and Lewis(x). We also found that synapsin I is expressed in glia-enriched cultures and is released from glial cells via exosomes. Incubation of glial-derived exosomes in the presence of high KCl concentrations or subjecting glial cell cultures to either oxygen/glucose deprivation or hydrogen peroxide resulted in release of synapsin I from exosomes. Application of synapsin I promoted neurite outgrowth from hippocampal neurons and increased survival of cortical neurons upon hydrogen peroxide treatment or oxygen/glucose deprivation. Coculture experiments using wild-type hippocampal neurons and wild-type or synapsin-deficient glial cells showed enhanced neurite outgrowth when synapsin was expressed by glial cells. Synapsin-induced neurite outgrowth was dependent on oligomannose on synapsin I and the neural cell adhesion molecule NCAM at the neuronal cell surface. The data indicate that, under conditions of high neuronal activity and/or oxidative stress, synapsin can be released from glial-derived exosomes and promotes neurite outgrowth and neuronal survival by modulating the interactions between glia and neurons.

Alteration of brain glycoproteins during aging

Glycosylation is the most common post-translational modification of proteins. Protein sequence data suggested that more than half of all proteins produced in mammalian cells are glycoproteins. Recent studies showed that glycans of secreted glycoproteins affect many protein properties, such as solubility, stability, protease sensitivity and polarity, whereas glycans on cell-surface glycoproteins are involved in various cellular functions, including cell-cell communication. Accordingly, the investigation of glycoprotein changes caused by aging is expected to help understand the aging process and to elucidate age-associated diseases. The present review will summarize our current knowledge of changes found in brain glycoproteins resulting from the aging process.

Cell surface N-glycans-mediated isolation of mouse neural stem cells

The isolation of neural stem cells (NSCs) has been hampered by the lack of valid cell-surface antigens on NSCs, and novel valuable markers have been proposed. Glycan (oligosaccharide chain) is a potential candidate as a marker to isolate NSCs, because the species and the combination order of saccharides in glycan generate remarkable structural diversity and specificity. At present, the expression of hundreds of glycoconjugates with glycans have been found in the NSCs; however, just a few glycan-epitopes have been identified as valuable cell-surface markers. This review focused on the isolation of NSC using glycoprotein, especially complex type N-glycans. The cell-surface N-glycan-mediated isolation of NSCs is therefore expected to provide a comprehensive understanding of the biologic characteristics of NSCs in the brain, and thereby help to develop novel strategies in the field of regenerative medicine.

Interactome analyses identify ties of PrP and its mammalian paralogs to oligomannosidic N-glycans and endoplasmic reticulum-derived chaperones

The physiological environment which hosts the conformational conversion of the cellular prion protein (PrP(C)) to disease-associated isoforms has remained enigmatic. A quantitative investigation of the PrP(C) interactome was conducted in a cell culture model permissive to prion replication. To facilitate recognition of relevant interactors, the study was extended to Doppel (Prnd) and Shadoo (Sprn), two mammalian PrP(C) paralogs. Interestingly, this work not only established a similar physiological environment for the three prion protein family members in neuroblastoma cells, but also suggested direct interactions amongst them. Furthermore, multiple interactions between PrP(C) and the neural cell adhesion molecule, the laminin receptor precursor, Na/K ATPases and protein disulfide isomerases (PDI) were confirmed, thereby reconciling previously separate findings. Subsequent validation experiments established that interactions of PrP(C) with PDIs may extend beyond the endoplasmic reticulum and may play a hitherto unrecognized role in the accumulation of PrP(Sc). A simple hypothesis is presented which accounts for the majority of interactions observed in uninfected cells and suggests that PrP(C) organizes its molecular environment on account of its ability to bind to adhesion molecules harboring immunoglobulin-like domains, which in turn recognize oligomannose-bearing membrane proteins.

Glycosylation analysis of IgLON family proteins in rat brain by liquid chromatography and multiple-stage mass spectrometry

IgLON family proteins, including limbic-associated membrane protein (LAMP), opioid-binding cell adhesion molecule (OBCAM), neurotrimin, and Kilon, are immunoglobulin (Ig) superfamily cell adhesion molecules. These molecules are composed of three Ig domains and a glycosylphosphatidylinositol (GPI) anchor and contain six or seven potential N-glycosylation sites. Although their glycosylations are supposed to be associated with the development of the central nervous system like other Ig superfamily proteins, they are still unknown because of difficulty in isolating individual proteins with a high degree of homology in performing carbohydrate analysis. In this study, we conducted simultaneous site-specific glycosylation analysis of rat brain IgLON proteins by liquid chromatography and multiple-stage mass spectrometry (LC-MS ( n )). The rat brain GPI-linked proteins were enriched and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The four proteins were extracted from the gel, and subjected to LC-MS ( n ) after proteinase digestions. A set of glycopeptide MS data, including the mass spectrum, the mass spectrum in the selected ion monitoring mode, and the product ion spectra, was selected from all data based on carbohydrate-related ions in the MS/MS spectrum. The peptide portion and the carbohydrate structure were identified on the basis of peptide-related ion and carbohydrate-related ions, and the accurate mass. The site-specific glycosylations of four proteins were elucidated as follows. N-Glycans near the N-terminal were disialic acid-conjugated complex- and hybrid-type oligosaccharides. The first Ig domains were occupied by Man-5-9. Diverse oligosaccharides, including Lewis a/x-modified glycans, a brain-specific glycan known as BA-2, and Man-5, were found to be attached to the third Ig domain. Three common structures of glycans were found in the GPI moiety of LAMP, OBCAM, and neurotrimin.

WITHDRAWN: NCAM and the FGF-Receptor

In this review, the structural biology of interaction between the neural cell adhesion molecule (NCAM) and the fibroblast growth factor (FGF) receptor is described and a possible mechanism of the FGF-receptor activation by NCAM is discussed. Most of the FGF-receptor molecules are thought to be constantly involved in a transient interaction with NCAM. However, the FGF-receptor becomes activated only when NCAM is involved the trans-homophilic binding (mediating cell-cell adhesion). The trans-homophilic binding between the NCAM molecules is believed to result in formation of either one- or two-dimensional 'zipper'-like arrays of the NCAM molecules, which leads to NCAM clustering and as a result to clustering of the FGF-receptor, which in turn may lead to its activation through a direct receptor-receptor dimerization (and thus activation) due to an increase in the local concentration of the receptor.

Fibronectin type III (FN3) modules of the neuronal cell adhesion molecule L1 interact directly with the fibroblast growth factor (FGF) receptor

The neuronal cell adhesion molecule (CAM) L1 promotes axonal outgrowth, presumably through an interaction with the fibroblast growth factor receptor (FGFR). The present study demonstrates a direct interaction between L1 fibronectin type III (FN3) modules I-V and FGFR1 immunoglobulin (Ig) modules II and III by surface plasmon resonance analysis. Binding of L1 to FGFR1 was enhanced by adenosine 5'-triphosphate (ATP), adenylylmethylenediphosphonate (AMP-PCP), and guanosine-5'-triphosphate (GTP), but not adenosine monophosphate (AMP). The L1-FN3 modules were capable of activating FGFR1, reflected by receptor phosphorylation, and this resulted in the induction of differentiation of primary neurons, reflected by neurite outgrowth. Furthermore, ATP modulated L1-induced neuronal differentiation and FGFR1 phosphorylation through regulation of the L1-FGFR1 interaction.

Pharmacology of cell adhesion molecules of the nervous system

Cell adhesion molecules (CAMs) play a pivotal role in the development and maintenance of the nervous system under normal conditions. They also are involved in numerous pathological processes such as inflammation, degenerative disorders, and cancer, making them attractive targets for drug development. The majority of CAMs are signal transducing receptors. CAM-induced intracellular signalling is triggered via homophilic (CAM-CAM) and heterophilic (CAM - other counter-receptors) interactions, which both can be targeted pharmacologically. We here describe the progress in the CAM pharmacology focusing on cadherins and CAMs of the immunoglobulin (Ig) superfamily, such as NCAM and L1. Structural basis of CAM-mediated cell adhesion and CAM-induced signalling are outlined. Different pharmacological approaches to study functions of CAMs are presented including the use of specific antibodies, recombinant proteins, and synthetic peptides. We also discuss how unravelling of the 3D structure of CAMs provides novel pharmacological tools for dissection of CAM-induced signalling pathways and offers therapeutic opportunities for a range of neurological disorders.

Deficiency of neural cell adhesion molecule or its polysialylation modulates pharmacological effects of the AMPA receptor antagonist NBQX

The neural cell adhesion molecule NCAM and its dynamically regulated posttranslational modification polysialic acid (PSA) are major determinants of cellular interactions during ontogeny. While NCAM in the absence of PSA stabilizes cell-cell interactions, the attachment of the large and polyanionic PSA negatively influences cell adhesion and promotes plasticity. Disease-associated changes in the polysialylation state of NCAM raise the question whether the PSA-NCAM system can affect CNS pharmacology. Here we investigated the pharmacological effects of the competitive AMPA antagonist NBQX in genetic mouse models either lacking NCAM and PSA (female NCAM knockout mice) or being drastically reduced in the level of PSA expression (female ST8SiaIV knockout mice). Studies were carried out with the respective wildtype littermate controls. In mice lacking NCAM and PSA, NBQX-induced ataxia proved to be more intense as compared with wild-type mice. On both mutant backgrounds, NBQX significantly elevated seizure thresholds during i.v. infusion of the chemoconvulsant pentylenetetrazole. In summary, the data demonstrate that the PSA-NCAM system impacts AMPA receptor pharmacology under in vivo conditions. The fact that comparable effects were observed in NCAM- and ST8SiaIV-knockout mice indicates that this impact is not due to a stabilizing effect of NCAM in the absence of PSA. Thus, disease-related changes in the polysialylation of NCAM are likely to be associated with effects on the efficacy and tolerability of AMPA receptor antagonists.

An Essential Oligomannosidic Glycan Chain in the Catalytic Domain of Autotaxin, a Secreted Lysophospholipase-D

Autotaxin/NPP2, a secreted lysophospholipase-D, promotes cell proliferation, survival, and motility by generating the signaling molecule lysophosphatidic acid. Here we show that ectonucleotide pyrophosphatase/phosphodiesterase 2 (NPP2) is N-glycosylated on Asn-53, Asn-410, and Asn-524. Mutagenesis and deglycosylation experiments revealed that only the glycosylation of Asn-524 is essential for the expression of the catalytic and motility-stimulating activities of NPP2. The N-glycan on Asn-524 was identified as Man8/9GlcNAc2, which is rarely present on mature eukaryotic glycoproteins. Additional studies show that this Asn-524-linked glycan is not accessible to alpha-1,2-mannosidase, suggesting that its non-reducing termini are buried inside the folded protein. Consistent with a structural role for the Asn-524-linked glycan, only the mutation of Asn-524 augmented the sensitivity of NPP2 to proteolysis and increased its mobility during Blue Native PAGE. Asn-524 is phylogenetically conserved and maps to the catalytic domain of NPP2, but a structural model of this domain suggests that Asn-524 is remote from the catalytic site. Our study defines an essential role for the Asn-524-linked glycan chain of NPP2.

The role of cytoplasmic serine residues of the cell adhesion molecule L1 in neurite outgrowth, endocytosis, and cell migration

1. The cell adhesion molecule L1 has been implicated in adhesion and migration of cells, in axon growth, guidance, and fasciculation, in myelination and synaptic plasticity. The cytoplasmic domain of neuronal L1 is highly conserved between species and has been shown to be phosphorylated at serine and tyrosine residues. 2. To investigate the significance of L1 serine phosphorylation, mutants of L1 were generated in which ser-1152, ser-1181, ser-1204, and ser-1248 were exchanged for leucine and rat B35 neuroblastoma cells were stably transfected with the L1-cDNA constructs. 3. Neurite outgrowth on poly-L-lysine (PLL) as substrate was determined either with or without differentiation into a neuronal phenotype with dbcAMP. In addition, antibody-induced endocytosis and cell migration were examined. 4. Our observations indicate that phosphorylation of single serine residues of the cytoplasmic domain of L1 contributes to neurite outgrowth through different mechanisms. Neurite growth is increased when ser-1152 or ser-1181 is replaced by a non-phosphorylatable leucine and decreased when ser-1204 or ser-1248 is mutated to leucine. Furthermore, mutation of ser-1181 to leucine results in strongly enhanced antibody-induced endocytosis of L1 and also in enhanced cell migration.

Differential expression of glycans in the hippocampus of rats trained on an inhibitory learning paradigm

The glycan chains of glycoconjugates play important roles in cell-cell and cell-matrix interactions. In the CNS, previous studies on learning and memory suggest the importance of oligosaccharides attached to glycoconjugates in the modulation of synaptic connections. We studied the hippocampal glycan distribution of rats subject to an inhibitory avoidance task. The expression of glycans was examined by lectin-histochemistry using Vicia villosa lectin (VVL) for terminal alpha/beta N-acetylgalactosamine (alpha/beta GalNAc); Galanthus nivalus lectin (GNL) for terminal mannose alpha-1,3 (Man alpha-1,3); Peanut agglutinin (PNA) for galactose beta-1,3N-acetylgalactosamine (Gal beta-1,3 GalNAc); Erythrina cristagalli lectin (ECL) for galactose beta-1,4 N-acetylglucosamine (Gal beta-1,4 GlcNAc); Sambucus nigra lectin (SNA) for sialic acid alpha-2.6 galactose (SA alpha-2,6 Gal); Maackia amurensis lectin II (MAL II) for sialic acid alpha-2,3 (SA alpha-2,3); Wheat germ agglutinin (WGA) for terminal N-acetylglucosamine with/ without sialic acid (GlcNAc wo SA); succynilated WGA (sWGA) for terminal N-acetylglucosamine without sialic acid (terminal GlcNAc without SA); Griffonia simplicifolia lectin II (GSL II) for terminal alpha/beta N-acetylglucosamine (alpha/beta GlcNAc terminal); and Lotus tetragonolobus lectin (LTL) alpha-fucose. Two groups of 10 animals were examined: non-trained (Control) and Trained rats. ECL, sWGA and GSL II were negative for both groups in all the hippocampal subfields studied. For both groups, VVL was negative in CA4 and granular cells of the Dentate Gyrus (DG) and LTL was negative in the CA4 subfield. Expression of alpha/beta GalNAc, alpha-fucose and GlcNAc in other hippocampal subflields was positive, with no differences between groups. However, expression of Man alpha-1,3 was significantly higher in the CA1, CA2, CA3, and CA4 subfields in the Trained group. On the other hand, expression of Gal beta-1,3 GalNAc was significantly low in CA4 and DG in the Trained group. In conclusion, the results here presented indicate that the exposure of rats to an associative behavioral paradigm related to declarative memory, involves some regulatory mechanism/s for the differential patterns of glycan expression.

Emmprin in epithelioid sarcoma: Expression in tumor cell membrane and stimulation of MMP-2 production in tumor-associated fibroblasts

Emmprin is a transmembrane glycoprotein on tumor cells that stimulates peritumoral fibroblasts to produce matrix metalloproteinases (MMPs). Emmprin and the induced MMPs play a crucial role in tumor progression, invasion and metastasis of human carcinomas (epithelial malignancies). However, only a few reports have addressed its role in soft tissue sarcomas. This study investigated the expression and role of emmprin in epithelioid sarcoma (ES). Immunoblot studies of 2 ES cell lines showed that they express emmprin, and co-culture of these ES cells with dermal fibroblasts resulted in upregulation of gelatinase A (MMP-2) in fibroblasts, as shown by zymography, immunoblotting and enzyme immunoassay. This stimulation was inhibited by an activity-blocking peptide against emmprin and by antiemmprin antibody. In addition, in vivo, immunohistochemical analysis of 5 ES patient cases demonstrated diffuse emmprin expression in ES cells and MMP-2 expression in both ES cells and peritumoral fibroblasts. The histopathological findings that peritumoral fibroblasts that were not in direct contact with emmprin-expressing ES cells exhibit upregulated MMP-2 prompted us to look for a soluble form of emmprin. Soluble full-length emmprin released from ES cells was detected in conditioned medium and shown to stimulate MMP-2 production by fibroblasts. In conclusion, emmprin is expressed in ES in both membrane and soluble forms and stimulates MMP-2 production via interactions with fibroblasts, which could play a role in ES cell stromal invasion and vascular involvement.

In vivo synaptic plasticity in the dentate gyrus of mice deficient in the neural cell adhesion molecule NCAM or its polysialic acid

The neural cell adhesion molecule NCAM and its associated polysialic acid (PSA) play important roles in synaptic plasticity in the CA1 and/or CA3 regions of the hippocampus in vitro. Here, we address the question of whether NCAM and PSA are involved in regulation of synaptic transmission and plasticity also in vivo at synapses formed by entorhinal cortex axons in the dentate gyrus of mice anaesthetized with urethane. We show that basal synaptic transmission, measured as the slope of field excitatory postsynaptic potentials, was reduced strongly in mice lacking ST8SiaII/STX, the enzyme involved in polysialylation of NCAM in stem cell-derived immature granule cells, but not in mice deficient either in the NCAM glycoprotein or the enzyme ST8SiaIV/PST involved in polysialylation of NCAM in mature neurons. Strikingly, only mice deficient in NCAM, but not in PST or STX, were impaired in long-term potentiation (LTP) induced by theta-burst stimulation, suggesting that LTP in the dentate gyrus depends on the NCAM glycoprotein alone rather than on its associated PSA. As also patterns of synaptic activity during and immediately after induction of LTP were impaired in NCAM-deficient mice, it is likely that induction of LTP requires NCAM. These data are the first to describe that NCAM is necessary for induction of synaptic plasticity in identified synapses in vivo and suggest that polysialylation of NCAM expressed by immature granule cells in the dentate gyrus supports development of basal excitatory synaptic transmission in this region.

The neural cell adhesion molecule NCAM regulates neuritogenesis by multiple mechanisms of interaction

The neural cell adhesion molecule NCAM and its glycosylation with polysialic acid (polySia) are crucially involved in proliferation, migration and differentiation of neural progenitors. Modification with polySia, homophilic and heterophilic interactions set the function of NCAM, but little is known on their interplay. We have shown recently that removal of polySia induces neuronal differentiation via heterophilic NCAM interactions at cell contacts between SH-SY5Y neuroblastoma cells. Here we analyze the additional impact of NCAM-positive fibroblasts as a ligand-presenting cellular environment, a model often used to demonstrate the neuritogenic effect of homophilic NCAM interactions. Native SH-SY5Y cells did not respond to interactions with fibroblast NCAM. However, after induction of neuronal differentiation by retinoic acid the previously ineffective NCAM signals activated extracellular signal-regulated kinase (ERK) and promoted neuritogenesis. Removal of polySia increased neuritogenesis in retinoic acid-treated cells additive to the NCAM substrate effect. The change in responsiveness to substrate NCAM was associated with a rearrangement of polysialylated NCAM away from its enrichment at homotypic cell-cell contacts and with the appearance of non-polysialylated NCAM, i.e. changes facilitating NCAM interactions with the substrate. Thus, heterophilic and homophilic NCAM interactions are integrated into the cell's response yet they have the capacity to independently trigger neuritogenesis. The actual occurrence of each of these interactions, however, depends on the cellular context, targeted cell surface presentation of NCAM and the dynamic regulation of its modification by polysialic acid. In summary, this study reveals how the complex interplay of NCAM interactions and polysialylation provides an elaborate system to regulate neuritogenesis.

The molecular pathogenetic role of cell adhesion in endocrine neoplasia

It is becoming increasingly evident that cell adhesion is an important determinant of organised growth and the maintenance of architectural integrity. Indeed, reduced adhesiveness between cells and with the extracellular matrix is a hallmark of neoplastic growth. In neuroendocrine tissues, neural cell adhesion molecule is implicated in modulating cell growth, migration, and differentiation. This review will focus on the molecular pathways involving key growth factor receptors that govern normal adhesive forces. The extent to which disruption of these adhesive forces contributes to the tumorigenic process in neuroendocrine tissues will be highlighted. Validation of the functional relevance of these adhesive pathways will be discussed in light of targeted pharmacotherapeutic studies that are unmasking novel approaches to the treatment of neuroendocrine tumours.

Phosphorylation of the neural cell adhesion molecule on serine or threonine residues is induced by adhesion or nerve growth factor

The neural cell adhesion molecule (NCAM) is a member of the immunoglobulin superfamily and plays a crucial role during development and regeneration. It is expressed in three major isoforms; two of them with intracellular domains of different length and one without any intracellular domain. NCAM is known to be phosphorylated and contains up to 49 serine or threonine residues, which could be phosphorylated. However, the impact of NCAM phosphorylation is still unclear. Here we describe NCAM being phosphorylated during neuronal differentiation of PC12 cells. We provide evidence that protein kinase C is involved in the phosphorylation of NCAM. In agreement with our earlier observation that the protein phosphatase 1 is associated with NCAM, we additionally found that NCAM is a substrate for the protein phosphatase 1 but not for the protein phosphatase 2A.

The glycosylation characteristic of hepatoma-associated antigen HAb18G/CD147 in human hepatoma cells

HAb18G/CD147 is a highly glycosylated transmembrane protein belonging to the immunoglobulin superfamily. Our previous studies have demonstrated that overexpressing HAb18G/CD147 enhances the metastatic potentials of human hepatoma cells. In the present study, to investigate the glycosylation characteristic of HAb18G/CD147 in human hepatoma cells, HAb18G/CD147 was first purified from human FHCC-98 hepatoma cells by immunoaffinity chromatography, and then introduced into human fibroblasts culture system for matrix metalloproteinases induction. As a result, the elevated levels of matrix metalloproteinases secreted by fibroblasts were detected by gelatin zymography. The lysates of human hepatoma FHCC-98 cell revealed two major forms of HAb18G/CD147 (43-66 and 35 kDa) by western blot assay. To elucidate whether the variation of molecule size were caused by different glycosylation, two different approaches were employed to accomplish this goal: deglycosylation with N-glycosylation inhibitor tunicamycin or endoglycosidases. A single deglycosylated core protein with molecular weight approximately 27 kDa was obtained from both methods. Furthermore, the results of endoglycosidases treatment also showed that two forms of HAb18G/CD147 contain different types of oligosaccharide chains, thus sensitive to different endoglycosidase. In conclusion, the present study demonstrated that purified native HAb18G/CD147 has the bioactivity of stimulating human fibroblasts to produce elevated levels of matrix metalloproteinases, and that the two different forms of HAb18G/CD147 are derived from the single core protein but differ in their degree and types of glycosylation.

Genetic Ablation of Polysialic Acid Causes Severe Neurodevelopmental Defects Rescued by Deletion of the Neural Cell Adhesion Molecule

Poly-alpha2,8-sialic acid (polySia) is a unique modification of the neural cell adhesion molecule, NCAM, tightly associated with neural development and plasticity. However, the vital role attributed to this carbohydrate polymer has been challenged by the mild phenotype of mice lacking polySia due to NCAM-deficiency. To dissect polySia and NCAM functions, we generated polySia-negative but NCAM-positive mice by simultaneous deletion of the two polysialyltransferase genes, St8sia-II and St8sia-IV. Beyond features shared with NCAM-null animals, a severe phenotype with specific brain wiring defects, progressive hydrocephalus, postnatal growth retardation, and precocious death was observed. These drastic defects were selectively rescued by additional deletion of NCAM, demonstrating that they originate from a gain of NCAM functions because of polySia deficiency. The data presented in this study reveal that the essential role of polySia resides in the control and coordination of NCAM interactions during mouse brain development. Moreover, this first demonstration in vivo that a highly specific glycan structure is more important than the glycoconjugate as a whole provides a novel view on the relevance of protein glycosylation for the complex process of building the vertebrate brain.