Regulation of neural cell adhesion molecule polysialylation: evidence for nontranscriptional control and sensitivity to an intracellular pool of calcium

PSA-NCAM Regulatory Gene Expression Changes in the Alzheimer's Disease Entorhinal Cortex Revealed with Multiplexed in situ Hybridization

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia and is characterized by a substantial reduction of neuroplasticity. Our previous work demonstrated that neurons involved in memory function may lose plasticity because of decreased protein levels of polysialylated neural cell adhesion molecule (PSA-NCAM) in the entorhinal cortex (EC) of the human AD brain, but the cause of this decrease is unclear.

OBJECTIVE

To investigate genes involved in PSA-NCAM regulation which may underlie its decrease in the AD EC.

METHODS

We subjected neurologically normal and AD human EC sections to multiplexed fluorescent in situ hybridization and immunohistochemistry to investigate genes involved in PSA-NCAM regulation. Gene expression changes were sought to be validated in both human tissue and a mouse model of AD.

RESULTS

In the AD EC, a cell population expressing a high level of CALB2 mRNA and a cell population expressing a high level of PST mRNA were both decreased. CALB2 mRNA and protein were not decreased globally, indicating that the decrease in CALB2 was specific to a sub-population of cells. A significant decrease in PST mRNA expression was observed with single-plex in situ hybridization in middle temporal gyrus tissue microarray cores from AD patients, which negatively correlated with tau pathology, hinting at global loss in PST expression across the AD brain. No significant differences in PSA-NCAM or PST protein expression were observed in the MAPT P301S mouse brain at 9 months of age.

CONCLUSION

We conclude that PSA-NCAM dysregulation may cause subsequent loss of structural plasticity in AD, and this may result from a loss of PST mRNA expression. Due PSTs involvement in structural plasticity, intervention for AD may be possible by targeting this disrupted plasticity pathway.

Polysialic Acid in the Immune System

Polysialic acid (polySia) is a highly regulated polymer of sialic acid (Sia) with such potent biophysical characteristics that when expressed drastically influences the interaction properties of cells. Although much of what is known of polySia in mammals has been elucidated from the study of its role in the central nervous system (CNS), polySia is also expressed in other tissues, including the immune system where it presents dynamic changes during differentiation, maturation, and activation of different types of immune cells of the innate and adaptive response, being involved in key regulatory mechanisms. At least six polySia protein carriers (CCR7, ESL-1, NCAM, NRP2, ST8Sia 2, and ST8Sia 4) are expressed in different types of immune cells, but there is still much to be explored in regard not only to the regulatory mechanisms that determine their expression and the structure of polySia chains but also to the identification of the cis- and trans- ligands of polySia that establish signaling networks. This review summarizes the current knowledge on polySia in the immune system, addressing its biosynthesis, its tools for identification and structural characterization, and its functional roles and therapeutic implications.

Ketamine and Calcium Signaling-A Crosstalk for Neuronal Physiology and Pathology

Ketamine is a non-competitive antagonist of NMDA (N-methyl-D-aspartate) receptor, which has been in clinical practice for over a half century. Despite recent data suggesting its harmful side effects, such as neuronal loss, synapse dysfunction or disturbed neural network formation, the drug is still applied in veterinary medicine and specialist anesthesia. Several lines of evidence indicate that structural and functional abnormalities in the nervous system caused by ketamine are crosslinked with the imbalanced activity of multiple Ca²⁺-regulated signaling pathways. Due to its ubiquitous nature, Ca²⁺ is also frequently located in the center of ketamine action, although the precise mechanisms underlying drug’s negative or therapeutic properties remain mysterious for the large part. This review seeks to delineate the relationship between ketamine-triggered imbalance in Ca²⁺ homeostasis and functional consequences for downstream processes regulating key aspects of neuronal function.

Potential mechanisms for phencyclidine/ketamine-induced brain structural alterations and behavioral consequences

Evidence of structural abnormalities in the nervous system of recreational drug [e.g., phencyclidine (PCP) or ketamine] users and/or preclinical animal research models suggests interference with the activity of multiple neurotransmitters, particularly glutamate neurotransmission. The damage to the central nervous system (CNS) may include neuronal loss, synaptic changes, disturbed neural network formation and reduced projections to subcortical fields. Notably, the reduced projections may considerably compromise the establishment of the subcortical areas, such as the nucleus accumbens located in the basal forebrain. With its abundant dopaminergic innervation, the nucleus accumbens is believed to be directly associated with addictive behaviors and mental disorders. This review seeks to delineate the relationship between PCP/ketamine-induced loss of cortical neurons and the reduced level of polysialic acid neural cell adhesion molecule (PSA-NCAM) in the striatum, and the likely changes in striatal synaptogenesis during development. The basic mechanism of how PSA-NCAM cell surface expression may be regulated will also be discussed, as well as the hypothesis that PSA-NCAM activity is critical to the regulation of synaptic protein expression. Overall, the present review will address the general hypothesis that damage/interruption of cortico-striatal communication and subcortical synaptogenesis could underlie the erratic/sensitization or addictive states produced by chronic or prolonged PCP/ketamine usage.

Insulin promotes cell migration by regulating PSA-NCAM

Cellular interactions with the extracellular environment are modulated by cell surface polysialic acid (PSA) carried by the neural cell adhesion molecule (NCAM). PSA-NCAM is involved in cellular processes such as differentiation, plasticity, and migration, and is elevated in Alzheimer's disease as well as in metastatic tumour cells. Our previous work demonstrated that insulin enhances the abundance of cell surface PSA by inhibiting PSA-NCAM endocytosis. In the present study we have identified a mechanism for insulin-dependent inhibition of PSA-NCAM turnover affecting cell migration. Insulin enhanced the phosphorylation of the focal adhesion kinase leading to dissociation of αv-integrin/PSA-NCAM clusters, and promoted cell migration. Our results show that αv-integrin plays a key role in the PSA-NCAM turnover process. αv-integrin knockdown stopped PSA-NCAM from being endocytosed, and αv-integrin/PSA-NCAM clusters co-labelled intracellularly with Rab5, altogether indicating a role for αv-integrin as a carrier for PSA-NCAM during internalisation. Furthermore, inhibition of p-FAK caused dissociation of αv-integrin/PSA-NCAM clusters and counteracted the insulin-induced accumulation of PSA at the cell surface and cell migration was impaired. Our data reveal a functional association between the insulin/p-FAK-dependent regulation of PSA-NCAM turnover and cell migration through the extracellular matrix. Most importantly, they identify a novel mechanism for insulin-stimulated cell migration.

Expression of neural cell adhesion molecule and polysialic acid in human bone marrow-derived mesenchymal stromal cells

BACKGROUND

In order to develop novel clinical applications and to gain insights into possible therapeutic mechanisms, detailed molecular characterization of human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) is needed. Neural cell adhesion molecule (NCAM, CD56) is a transmembrane glycoprotein modulating cell-cell and cell-matrix interactions. An additional post-translational modification of NCAM is the α2,8-linked polysialic acid (polySia). Because of its background, NCAM is often considered a marker of neural lineage commitment. Generally, hBM-MSCs are considered to be devoid of NCAM expression, but more rigorous characterization is needed.

METHODS

We have studied NCAM and polySia expression in five hBM-MSC lines at mRNA and protein levels. Cell surface localization was confirmed by immunofluorescence staining and expression frequency in the donor-specific lines by flow cytometry. For the detection of poorly immunogenic polySia, a fluorochrome-tagged catalytically defective enzyme was employed.

RESULTS

All five known NCAM isoforms are expressed in these cells at mRNA level and the three main isoforms are present at protein level. Both polysialyltransferases, generally responsible for NCAM polysialylation, are expressed at mRNA level, but only very few cells express polySia at the cell surface.

CONCLUSIONS

Our results underline the need for a careful control of methods and conditions in the characterization of MSCs. This study shows that, against the generally held view, clinical-grade hBM-MSCs do express NCAM. In contrast, although both polysialyltransferase genes are transcribed in these cells, very few express polySia at the cell surface. NCAM and polySia represent new candidate molecules for influencing MSC interactions.

A human anti-polysialic acid antibody as a potential treatment to improve function in multiple sclerosis patients

We previously identified a human monoclonal antibody, termed HIgM12 that stimulates spontaneous locomotor activity in a chronically demyelinating mouse model of multiple sclerosis. When tested as a molecular substrate, HIgM12 stimulated neurite outgrowth in vitro. We recently reported that polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM) is one of the cellular antigens for HIgM12. Fluorescent double-labeling of astrocytes using HIgM12 and commercially available anti-PSA antibody showed dramatic co-localization. Neural tissue homogenates and primary CNS cultures from mice lacking the three major NCAM splice variants NCAM180, NCAM140 and NCAM120 (NCAM KO) were no longer able to bind HIgM12. Furthermore, enzymatic digestion of PSA on wild type (WT) glia abolished HIgM12-binding. Moreover, neurons and glia from NCAM KO animals did not attach to HIgM12-coated nitrocellulose in neurite outgrowth assays. We conclude that HIgM12 targets PSA attached to NCAM, and that the PSA moiety mediates neuronal and glial adhesion and subsequent neurite outgrowth in our in vitro assay. Therefore, this anti-PSA antibody may serve as a future therapeutic to stimulate functional improvement in multiple sclerosis patients and other neurodegenerative diseases.

Abnormal cartilage development and altered N-glycosylation in Tmem165-deficient zebrafish mirrors the phenotypes associated with TMEM165-CDG

The congenital disorders of glycosylation (CDG), a group of inherited diseases characterized by aberrant glycosylation, encompass a wide range of defects, including glycosyltransferases, glycosidases, nucleotide-sugar transporters as well as proteins involved in maintaining Golgi architecture, pH and vesicular trafficking. Mutations in a previously undescribed protein, TMEM165, were recently shown to cause a new form of CDG, termed TMEM165-CDG. TMEM165-CDG patients exhibit cartilage and bone dysplasia and altered glycosylation of serum glycoproteins. We utilized a morpholino knockdown strategy in zebrafish to investigate the physiologic and pathogenic functions of TMEM165. Inhibition of tmem165 expression in developing zebrafish embryos caused craniofacial abnormalities, largely attributable to fewer chondrocytes. Decreased expression of several markers of cartilage and bone development suggests that Tmem165 deficiency alters both chondrocyte and osteoblast differentiation. Glycomic analysis of tmem165 morphants also revealed altered initiation, processing and extension of N-glycans, paralleling some of the glycosylation changes noted in human patients. Collectively, these findings highlight the utility of zebrafish to elucidate pathogenic mechanisms associated with glycosylation disorders and suggest that the cartilage and bone dysplasia manifested in TMEM165-CDG patients may stem from abnormal development of chondrocytes and osteoblasts.

Insulin and IGF1 modulate turnover of polysialylated neural cell adhesion molecule (PSA-NCAM) in a process involving specific extracellular matrix components

Cellular interactions mediated by the neural cell adhesion molecule (NCAM) are critical in cell migration, differentiation and plasticity. Switching of the NCAM-interaction mode, from adhesion to signalling, is determined by NCAM carrying a particular post-translational modification, polysialic acid (PSA). Regulation of cell-surface PSA-NCAM is traditionally viewed as a direct consequence of polysialyltransferase activity. Taking advantage of the polysialyltransferase Ca²⁺-dependent activity, we demonstrate in TE671 cells that downregulation of PSA-NCAM synthesis constitutes a necessary but not sufficient condition to reduce cell-surface PSA-NCAM; instead, PSA-NCAM turnover required internalization of the molecule into the cytosol. PSA-NCAM internalization was specifically triggered by collagen in the extracellular matrix (ECM) and prevented by insulin-like growth factor (IGF1) and insulin. Our results pose a novel role for IGF1 and insulin in controlling cell migration through modulation of PSA-NCAM turnover at the cell surface. Neural cell adhesion molecules (NCAMs) are critically involved in cell differentiation and migration. Polysialylation (PSA)/desialylation of NCAMs switches their functional interaction mode and, in turn, migration and differentiation. We have found that the desialylation process of PSA-NCAM occurs via endocytosis, induced by collagen-IV and blocked by insulin-like growth factor (IGF1) and insulin, suggesting a novel association between PSA-NCAM, IGF1/insulin and brain/tumour plasticity.

Withania somnifera water extract as a potential candidate for differentiation based therapy of human neuroblastomas

Neuroblastoma is an aggressive childhood disease of the sympathetic nervous system. Treatments are often ineffective and have serious side effects. Conventional therapy of neuroblastoma includes the differentiation agents. Unlike chemo-radiotherapy, differentiation therapy shows minimal side effects on normal cells, because normal non-malignant cells are already differentiated. Keeping in view the limited toxicity of Withania somnifera (Ashwagandha), the current study was aimed to investigate the efficacy of Ashwagandha water extract (ASH-WEX) for anti-proliferative potential in neuroblastoma and its underlying signalling mechanisms. ASH-WEX significantly reduced cell proliferation and induced cell differentiation as indicated by morphological changes and NF200 expression in human IMR-32 neuroblastoma cells. The induction of differentiation was accompanied by HSP70 and mortalin induction as well as pancytoplasmic translocation of the mortalin in ASH-WEX treated cells. Furthermore, the ASH-WEX treatment lead to induction of neural cell adhesion molecule (NCAM) expression and reduction in its polysialylation, thus elucidating its anti-migratory potential, which was also supported by downregulation of MMP 2 and 9 activity. ASH-WEX treatment led to cell cycle arrest at G0/G1 phase and increase in early apoptotic population. Modulation of cell cycle marker Cyclin D1, anti-apoptotic marker bcl-xl and Akt-P provide evidence that ASH-WEX may prove to be a promising phytotherapeutic intervention in neuroblatoma related malignancies.

Water extract from the leaves of Withania somnifera protect RA differentiated C6 and IMR-32 cells against glutamate-induced excitotoxicity

Glutamate neurotoxicity has been implicated in stroke, head trauma, multiple sclerosis and neurodegenerative disorders. Search for herbal remedies that may possibly act as therapeutic agents is an active area of research to combat these diseases. The present study was designed to investigate the neuroprotective role of Withania somnifera (Ashwagandha), also known as Indian ginseng, against glutamate induced toxicity in the retinoic acid differentiated rat glioma (C6) and human neuroblastoma (IMR-32) cells. The neuroprotective activity of the Ashwagandha leaves derived water extract (ASH-WEX) was evaluated. Cell viability and the expression of glial and neuronal cell differentiation markers was examined in glutamate challenged differentiated cells with and without the presence of ASH-WEX. We demonstrate that RA-differentiated C6 and IMR-32 cells, when exposed to glutamate, undergo loss of neural network and cell death that was accompanied by increase in the stress protein HSP70. ASH-WEX pre-treatment inhibited glutamate-induced cell death and was able to revert glutamate-induced changes in HSP70 to a large extent. Furthermore, the analysis on the neuronal plasticity marker NCAM (Neural cell adhesion molecule) and its polysialylated form, PSA-NCAM revealed that ASH-WEX has therapeutic potential for prevention of neurodegeneration associated with glutamate-induced excitotoxicty.

Sensory experience differentially modulates the mRNA expression of the polysialyltransferases ST8SiaII and ST8SiaIV in postnatal mouse visual cortex

Polysialic acid (PSA) is a unique carbohydrate composed of a linear homopolymer of α-2,8 linked sialic acid, and is mainly attached to the fifth immunoglobulin-like domain of the neural cell adhesion molecule (NCAM) in vertebrate neural system. In the brain, PSA is exclusively synthesized by the two polysialyltransferases ST8SiaII (also known as STX) and ST8SiaIV (also known as PST). By modulating adhesive property of NCAM, PSA plays a critical role in several neural development processes such as cell migration, neurite outgrowth, axon pathfinding, synaptogenesis and activity-dependent plasticity. The expression of PSA is temporally and spatially regulated during neural development and a tight regulation of PSA expression is essential to its biological function. In mouse visual cortex, PSA is downregulated following eye opening and its decrease allows the maturation of GABAergic synapses and the opening of the critical period for ocular dominance plasticity. Relatively little is known about how PSA levels are regulated by sensory experience and neuronal activity. Here, we demonstrate that while both ST8SiaII and ST8SiaIV mRNA levels decrease around the time of eye opening in mouse visual cortex, only ST8SiaII mRNA level reduction is regulated by sensory experience. Using an organotypic culture system from mouse visual cortex, we further show that ST8SiaII gene expression is regulated by spiking activity and NMDA-mediated excitation. Further, we show that both ST8SiaII and ST8SiaIV mRNA levels are positively regulated by PKC-mediated signaling. Therefore, sensory experience-dependent ST8SiaII gene expression regulates PSA levels in postnatal visual cortex, thus acting as molecular link between visual activity and PSA expression.

Synthesis and structural characterization of sialic acid-glutamic acid hybrid foldamers as conformational surrogates of alpha-2,8-linked polysialic acid

Surface expression of alpha-(2,8)-linked polymers of sialic acid in adult tissues has been correlated with metastasis of several human cancers. One approach to chemotherapeutic intervention against the spread of these cancers involves the development of immunogenic molecules that elicit an antibody response against alpha-(2,8)-linked polysialic acids. Naturally occurring polysialic acids are not viable candidates because they are present during embryonic development and are recognized as self by the immune system. These natural polymers also have poor pharmacokinetic properties because they are readily degraded by neuraminidase enzymes. We have been interested in developing structural surrogates of polysialic acids in an effort to overcome these limitations. Reported herein are microwave-assisted solid-phase peptide syntheses and structural characterization studies of a series of alpha/delta hybrid peptides derived from Fmoc-Neu2en and Fmoc-Glu(OtBu)-OH. Conformational experiments including circular dichroism, NH/ND exchange, and ROESY in aqueous solution were performed to study the secondary structures of these hybrid foldamers. ROESY data were analyzed with the assistance of XPLOR-NIH that was modified to include parameter and topology files to accommodate unnatural amino acids and the delta amide linkages. The results indicate that stable secondary structure is dependent upon both the amino acid sequence and the configuration of Glu. The most stable foldamer was composed of a total of 6 residues beginning with L-Glu at the carboxy terminus and alternating Neu2en and L-Glu residues. In water, this foldamer adopts a right-handed helical conformation with 3.7 residues per turn, 7.4 A pitch, 5.8 A diameter, and a length of 18.5 A, which is stabilized by both classical C=O...H-N backbone interactions and by pyranose ring O and L-Glu HN H-bonding. These structural features orient the L-Glu carboxylates along the helical backbone with a periodicity that matches the carboxylate positions along the reported G2(+) left-handed helix of alpha-(2,8)-polysialic acid. However, the charge density of the foldamer is one-half that of the natural polymer. These findings provide a fundamental understanding of the factors that influence stable secondary structure in hybrid Neu2en/Glu systems, and the tools we have developed establish a viable platform for the rational design of alpha-(2,8)-polysialic acid surrogates.

Polysialic acid neural cell adhesion molecule (PSA-NCAM) is an adverse prognosis factor in glioblastoma, and regulates olig2 expression in glioma cell lines

BACKGROUND

Glioblastoma multiforme (GBM) is the most aggressive and frequent brain tumor, albeit without cure. Although patient survival is limited to one year on average, significant variability in outcome is observed. The assessment of biomarkers is needed to gain better knowledge of this type of tumor, help prognosis, design and evaluate therapies. The neurodevelopmental polysialic acid neural cell adhesion molecule (PSA-NCAM) protein is overexpressed in various cancers. Here, we studied its expression in GBM and evaluated its prognosis value for overall survival (OS) and disease free survival (DFS).

METHODS

We set up a specific and sensitive enzyme linked immunosorbent assay (ELISA) test for PSA-NCAM quantification, which correlated well with PSA-NCAM semi quantitative analysis by immunohistochemistry, and thus provides an accurate quantitative measurement of PSA-NCAM content for the 56 GBM biopsies analyzed. For statistics, the Spearman correlation coefficient was used to evaluate the consistency between the immunohistochemistry and ELISA data. Patients' survival was estimated by using the Kaplan-Meier method, and curves were compared using the log-rank test. On multivariate analysis, the effect of potential risk factors on the DFS and OS were evaluated using the cox regression proportional hazard models. The threshold for statistical significance was p = 0.05.

RESULTS

We showed that PSA-NCAM was expressed by approximately two thirds of the GBM at variable levels. On univariate analysis, PSA-NCAM content was an adverse prognosis factor for both OS (p = 0.04) and DFS (p = 0.0017). On multivariate analysis, PSA-NCAM expression was an independent negative predictor of OS (p = 0.046) and DFS (p = 0.007). Furthermore, in glioma cell lines, PSA-NCAM level expression was correlated to the one of olig2, a transcription factor required for gliomagenesis.

CONCLUSION

PSA-NCAM represents a valuable biomarker for the prognosis of GBM patients.

N-CAM dysfunction and unexpected accumulation of PSA-NCAM in brain of adult-onset autosomal-dominant leukodystrophy

Previously, myelin from cerebral white matter (CWM) of two subjects of a family with orthochromatic adult-onset autosomal-dominant leukodystrophy (ADLD) was disclosed to exhibit defective large isoform of myelin-associated glycoprotein (L-MAG) and patchy distribution only in the elder subject. L-MAG and neural cell adhesion molecule (N-CAM) (N-CAM 180, 140, and 120) are structurally related and concur to myelin/axon interaction. In early developmental stages, in neurons and glia N-CAM is converted into polysialylated (PSA)-NCAM by two sialyltransferases sialyltransferase-X (STX) and polysialyltransferase-1 (PST). Notably, PSA-NCAM disrupts N-CAM adhesive properties and is nearly absent in the adult brain. Here, CWM extracts and myelin of the two subjects were searched for the expression pattern of the N-CAM isoforms and PSA-NCAM, and their CWM was evaluated for N-CAM, STX and PST gene copy number and gene expression as mRNA. Biochemically, we disclosed that in CWM extracts and myelin from both subjects, PSA-NCAM accumulates, N-CAM 180 considerably increases, N-CAM 140 is modestly modified and N-CAM 120 remarkably decreases; duplication of genes encoding N-CAM, STX and PST was not revealed, whereas PST mRNA was clearly increased. Immunohistochemically, in CWM of both subjects, we found an unusually diffuse accumulation of PSA-NCAM without inflammation markers. PSA-NCAM persistence, up-regulated PST mRNA and previously uncovered defective L-MAG may be early pathogenetic events in this ADLD form.

N-methyl-D-aspartate receptor independent changes in expression of polysialic acid-neural cell adhesion molecule despite blockade of homosynaptic long-term potentiation and heterosynaptic long-term depression in the awake freely behaving rat dentate gyrus

Investigations examining the role of polysialic acid (PSA) on the neural cell adhesion molecule (NCAM) in synaptic plasticity have yielded inconsistent data. Here, we addressed this issue by determining whether homosynaptic long-term potentiation (LTP) and heterosynaptic long-term depression (LTD) induce changes in the distribution of PSA-NCAM in the dentate gyrus (DG) of rats in vivo. In addition, we also examined whether the observed modifications were initiated via the activation of N-methyl-D-aspartate (NMDA) receptors. Immunocytochemical analysis showed an increase in PSA-NCAM positive cells both at 2 and 24 h following high-frequency stimulation of either medial or lateral perforant paths, leading to homosynaptic LTP and heterosynaptic LTD, respectively, in the medial molecular layer of the DG. Analysis of sub-cellular distribution of PSA-NCAM by electron microscopy showed decreased PSA dendritic labelling in LTD rats and a sub-cellular relocation towards the spines in LTP rats. Importantly, these modifications were found to be independent of the activation of NMDA receptors. Our findings suggest that strong activation of the granule cells up-regulates PSA-NCAM synthesis which then incorporates into activated synapses, representing NMDA-independent plastic processes that act synergistically on LTP/LTD mechanisms without participating in their expression.

Transcriptional regulation of PSA-NCAM expression by NMDA receptor activation in RA-differentiated C6 glioma cultures

N-Methyl-d-aspartate (NMDA) receptors exhibit a dichotomy of signaling with both toxic and plastic responses. Recent reports have shown that exposure to subtoxic concentration of NMDA results in a neuroprotective state that was measured when these neurons were subsequently challenged with toxic doses of glutamate or kainate. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The perception of glial role in CNS function has changed dramatically over the past few years from simple trophic functions to that of cells with important roles in development and maintenance of CNS in cooperation with neurons. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid differentiated C6 glioma cell cultures. C6 glioma cell cultures differentiated with retinoic acid (10microM) were exposed to NMDA (100microM) or to antagonist MK-801 (200nM) prior to treatment with NMDA and cells were harvested after 24h of treatment to study the expression of total NCAM, PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of PST mRNA by fluorescent in situ hybridization (FISH). Significant increase in the levels of PSA-NCAM, NF-kappaB, AP-1 and PST mRNA was observed in NMDA treated cultures. Treatment of cultures with MK-801, a non-competitive NMDA receptor antagonist, prior to NMDA exposure prevented the NMDA-mediated changes indicating the involvement of NMDA receptor activation. The results elucidate the possible cellular and molecular mechanisms of regulation of PSA-NCAM expression in astroglial cultures by extracellular signals.

Transcriptional regulation of polysialylated neural cell adhesion molecule expression by NMDA receptor activation in retinoic acid-differentiated SH-SY5Y neuroblastoma cultures

NMDA receptors exhibit a dichotomy of signaling with excessive stimulation leading to neuronal damage that occurs during neurodegenerative disorders, whereas the normal burst of activity results in plastic responses with the expression of molecular substrates of long-term plasticity, growth and survival. Control of polysialylated neural cell adhesion molecule (PSA-NCAM) expression by NMDA receptor activation has been described in several systems, suggesting a functional link between these two proteins. The coordinated induction of several different transcription factors initiated by NMDA receptor stimulation may be a key mechanism in the orchestration of specific target gene expression that underlies various aspects of CNS function, including plastic responses. We report here the transcriptional regulation of PSA-NCAM expression by subtoxic dose of NMDA in retinoic acid-differentiated SH-SY5Y cell cultures. SH-SY5Y cell cultures differentiated with retinoic acid (10 microM) were exposed to NMDA (100 microM) or to antagonist MK-801 (200 nM) prior to treatment with NMDA and cells were harvested after 24 h of treatment to study the expression of PSA-NCAM, nuclear factor kappaB (NF-kappaB) and activator protein-1 (AP-1) by Western blotting and dual immunocytofluorescence and expression of polysialyltransferase (PST) mRNA by fluorescent in situ hybridization (FISH). We observed the induction of transcription factors NF-kappaB and AP-1 along with PSA-NCAM expression in response to NMDA receptor activation. Also, PSA-NCAM regulation in response to NMDA receptor activity was shown to be transcriptionally controlled, as seen by temporal and spatial changes observed in the expression of PST mRNA in NMDA-treated SH-SY5Y cell cultures. This raises the interesting possibility that NF-kappaB and AP-1 expression is involved in propagating the signals of NMDA receptor activity that leads to downstream strengthening of long-term plasticity changes in differentiated SH-SY5Y neuroblastoma cell cultures. Thus understanding the regulation of PSA-NCAM expression by NMDA receptor-mediated activity may represent a fundamental prerequisite for the development of therapies in order to maintain neuronal plasticity throughout life and functional recovery after brain damage.

SgIGSF is a novel biliary-epithelial cell adhesion molecule mediating duct/ductule development

Spermatogenic immunoglobulin superfamily (SgIGSF) is an intercellular adhesion molecule of the nectin-like family. While screening its tissue distribution, we found that it was expressed in fetal liver but not adult liver. In the present study, we examined which cells in developing and regenerating liver express SgIGSF via immunohistochemistry and Western blot analysis. In developing mouse liver, SgIGSF expression was transiently upregulated at perinatal ages and was restricted to the lateral membrane of biliary epithelial cells (BECs). In regenerating rat livers from the 2-acetylaminofluorene/partial hepatectomy model, SgIGSF was detected exclusively in oval cells that aligned in ductal and trabecular patterns by the second week posthepatectomy. In human livers, fetal and newborn bile ducts and cirrhotic bile ductules were clearly positive for SgIGSF, whereas disease-free adult bile ducts were negative. To investigate the role of SgIGSF in bile duct/ductule formation, we used an in vitro model in which rat hepatocyte aggregates embedded in collagen gels containing insulin and epidermal growth factor extend epithelial sheets and processes in the first week and form ductules within a month. The process and ductular cells were continuously positive for SgIGSF and cytokeratin 19, a BEC marker. When the aggregate culture was started in the presence of a function-blocking anti-SgIGSF antibody, the number of epithelial processes per aggregate was reduced by 80%.

CONCLUSION

We propose that SgIGSF is a novel and functional BEC adhesion molecule that is expressed for a limited time during active bile duct/ductule formation.

Molecular characterization of pig ST8Sia IV--a critical gene for the formation of neural cell adhesion molecule and its response to sialic acid supplement in piglets

ST8Sia IV (polysialyltransferase IV gene) encodes a key enzyme that is required for polysialic acid synthesis. Polysialic acid is a component of the neural cell adhesion molecule and is necessary for synaptic plasticity of neural cells. We characterized 5.3 kb of pig ST8Sia IV cDNA and determined its expression profile in different organs. In hippocampus, ST8Sia IV mRNA levels were increased approximately 4.5-fold in piglets with sialic acid as a milk supplement, which suggested that exogenous sialic acid is a conditionally essential nutrient for early brain development. Extensive analyses were also performed among its orthologs from human, mouse, rat, chicken, frog and zebrafish. Our results supported that the piglet is a better animal model than other nonprimate species in the studies of ST8Sia IV related metabolism and nutrition in human infants. This pig cDNA provides a basis for uncovering the roles of ST8Sia IV during piglet development and maturation.

Blockade of N-methyl-D-aspartate receptors by ketamine produces loss of postnatal day 3 monkey frontal cortical neurons in culture

Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, is used as a general pediatric anesthetic. Recent data suggest that anesthetic drugs may cause neurodegeneration during development. The purpose of this study was to determine the robustness of ketamine-induced developmental neurotoxicity using rhesus monkey frontal cortical cultures and also to determine if dysregulation of NMDA receptor subunits promotes ketamine-induced cell death. Frontal cortical cells collected from the neonatal monkey were incubated for 24 h with 1, 10, or 20 microM ketamine alone or with ketamine plus either NR1 antisense oligonucleotides or the nuclear factor kB translocation inhibitor, SN-50. Ketamine caused a marked reduction in the neuronal marker polysialic acid neural cell adhesion molecule and mitochondrial metabolism, as well as an increase in DNA fragmentation and release of lactate dehydrogenase. Ketamine-induced effects were blocked by NR1 antisenses and SN-50. These data suggest that NR1 antisenses and SN-50 offer neuroprotection from the enhanced degeneration induced by ketamine in vitro.

Application of a systems biology approach to developmental neurotoxicology

Systems biology can be applied to enhance the understanding of complex biological processes such as apoptosis in the developing brain. Systems biology, as applied to toxicology, provides a structure to arrange information in the form of a biological model. The approach allows for the subsequent and iterative perturbation of the initial model with the use of toxicants, and the comparison of the resulting data against the proposed biological model. It is postulated that the exposure of the developing rat to NMDA antagonists, e.g., ketamine or phencyclidine (PCP), causes a compensatory up-regulation of NMDA receptors, thereby making cells bearing these receptors more vulnerable to excitotoxic effects of endogenous glutamate. Although comprehensive gene expression/proteomic studies and mathematical modeling remain to be accomplished, a biological model has been established and perturbed in an iterative manner to allow confirmation of the biological pathway for NMDA antagonist-induced brain cell death in the developing rat.

Migrating and myelinating potential of neural precursors engineered to overexpress PSA-NCAM

Polysialic acid (PSA) on NCAM is an important modulator of cell-cell interactions during development and regeneration. Here we investigated whether PSA overexpression influences neural cell migration and myelination. We stably expressed a GFP-tagged polysialytransferase, PSTGFP, in mouse neurospheres and induced prolonged PSA synthesis. Using a chick xenograft assay for migration, we show that PSA can instruct precursor migration along the ventral pathway. PSA persistence did not change neural precursor multipotentiality in vitro but induced a delay in oligodendrocyte differentiation. PSTGFP+ precursors showed widespread engraftment in shiverer brain, closely similar to that observed with control precursors expressing a fluorescent protein. Initially, myelination by oligodendrocytes was delayed but, eventually, down-regulation of PSTGFP occurred, allowing myelination to proceed. Thus down-regulation of polysialyltransferases takes place even in cells where its RNA is under the control of a heterologous promoter and engineering PSA overexpression in neural precursors does not cause irreversible unphysiological effects.

Blockade of N-methyl-D-aspartate receptors by phencyclidine causes the loss of corticostriatal neurons

Perinatal administration of the N-methyl-Dd-aspartate (NMDA) receptor antagonist phencyclidine (PCP) has been reported to produce regionally selective apoptotic cell death in the frontal cortex. The development of certain behavioral abnormalities following PCP treatment suggested that extracortical regions such as the striatum also could be affected. In this study, perinatal PCP treatment caused a marked reduction in striatal, but not hippocampal, staining for polysialic acid-neural cell adhesion molecule (PSA-NCAM), an NMDA-regulated molecule important in synaptogenesis. In order to isolate striatal influences to the cortex, this investigation was continued in vitro using corticostriatal slices. For these experiments we cultured coronal corticostriatal slices from postnatal day 7 rats. After 4 days in vitro, PCP was added for 48 h and then washed out for 24 h before harvesting the tissue. Similar to what was observed in vivo, we found that PCP treatment results in a marked reduction in striatal staining for PSA-NCAM. No change was observed in the mature form of NCAM. In striatal synaptoneurosomes, immunoblot analysis confirmed that the levels of PSA-NCAM and synaptophysin, a molecule often used as a marker of synaptogenesis, were substantially down-regulated by PCP. These effects were prevented by M40403, a superoxide dismutase mimetic that also prevented the PCP-induced terminal dUTP nick-end labeling of DNA fragments that was observed selectively in the cortex. These data suggest that PCP causes cell death by apoptosis selectively in the cortex, but not in the striatum, following either in vivo treatment of perinatal rat pups or in vitro treatment of corticostriatal slices. Further, cortical apoptosis induced by PCP negatively impacts striatal synaptogenesis, a process important in normal neural development. This deficit is probably caused by a reduction in corticostriatal neurotransmission. It is possible that the dysregulation of striatal synaptogenesis contributes to the behavioral abnormalities observed following perinatal PCP administration in vivo.

Glycans and neural cell interactions

Carbohydrate-carrying molecules in the nervous system have important roles during development, regeneration and synaptic plasticity. Carbohydrates mediate interactions between recognition molecules, thereby contributing to the formation of a complex molecular meshwork at the cell surface and in the extracellular matrix. The tremendous structural diversity of glycan chains allows for immense combinatorial possibilities that might underlie the fine-tuning of cell-cell and cell-matrix interactions.

Differential regulation of polysialyltransferase expression during hippocampus development: Implications for neuronal survival

Polysialyltransferases ST8SiaII/STX and ST8SiaIV/PST add polysialic acid (PSA) to the neural cell adhesion molecule (NCAM). Surface-located PSA is involved in cell-cell interactions participating in structural and functional plasticity of neuronal circuits. This study was undertaken to investigate the polysialyltransferase regulation pattern during hippocampal development. Polysialyltransferase expression levels analyzed by real-time RT-PCR indicated that ST8SiaII/STX mRNA is markedly down-regulated in vivo, decreasing abruptly at about the first week of postnatal development. ST8SiaII/STX mRNA is also down-regulated in hippocampal cells in culture, accompanying the morphological differentiation of neuronal interconnectivity. In contrast, ST8SiaIV/PST levels remain comparatively low during hippocampus ontogeny. Immunolabeling of primary hippocampal culture assays demonstrated that PSA expression parallels ST8SiaII/STX mRNA levels. In comparison, polysialyltransferase mRNA levels are not regulated in neuroblastoma cells during their proliferation. Sequence analysis of the 3'-untranslated region of ST8SiaII/STX cDNA indicated putative regulatory motifs. This information and the observed changes in mRNA half-life during development suggest that ST8SiaII/STX might be also regulated at the posttranscriptional level. To understand the reasons for the tight control of ST8SiaII/STX expression during development, we overexpressed the enzyme in hippocampal primary cultures by transfection. Overexpression of ST8SiaII/STX wild type as well as of a mutant lacking enzymatic activity affected neuronal viability, leading to cell death. However, this phenomenon was abolished by a double mutation in the ST8SiaII/STX that prevents formation of its three-dimentional structure. Interestingly, the overexpressed polysialyltransferase accumulates not only in the perinuclear region but also in the plasma membrane. Thus, overexpression of an ST8SiaII/STX that conserves its structure leads to abnormal accumulation of the protein, probably on the neuronal surface, affecting cell viability. This result explains the importance of an accurate regulation of polysialyltransferase expression during development.

Dynamic regulation of polysialylated neural cell adhesion molecule in the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) prominently expresses polysialic acid (PSA), a carbohydrate polymer that is attached to neural cell adhesion molecule (NCAM) and promotes changes in cell interactions. Previous studies have shown that expression of PSA is important for circadian rhythm stability under constant darkness, and for photic entrainment of the SCN circadian clock. In the present study, immunoblot analyses of the Syrian hamster SCN revealed marked diurnal fluctuations in PSA under a 24-h light/dark cycle. PSA levels were reduced by >90% during the mid-to-late dark phase, and were elevated to maximal daytime levels approximately 1 h after lights-on. A similar pattern of PSA fluctuation persisted under constant darkness. Exposure of animals under a 24-h light/dark cycle to a 30-min light pulse during the late dark phase dramatically increased SCN contents of PSA within 60 min, and these values returned to basal levels 1-2 h later. There was no effect of light-on expression of PSA in the hippocampus. Parallel studies revealed changes in the NCAM-180 isoform that carries PSA in the brain, suggesting that regulation of PSA may include protein as well as carbohydrate-associated mechanisms. Immunohistological analysis revealed light-induced enhancement of PSA in the SCN subregion containing calbindin D(28K) cells. PSA staining was also closely associated with the majority of SCN cells expressing light-inducible Fos protein. This rhythmic, light-inducible expression of PSA within the SCN suggests that dynamic cell interactions are important for the photic regulation of circadian clock phase.

Intrinsic role of polysialylated neural cell adhesion molecule in photic phase resetting of the Mammalian circadian clock

The suprachiasmatic nuclei (SCN), the location of the mammalian circadian clock, are one of the few adult brain regions that express the highly polysialylated form of neural cell adhesion molecule (PSA-NCAM). A role for the polysialic acid (PSA) component of PSA-NCAM, which is known to promote tissue plasticity, has been reported for photic entrainment of circadian rhythmicity in vivo. The in vivo results, however, do not discriminate between PSA acting upstream or downstream of the glutamatergic synapses that convey photic information to the SCN. To address this key issue, we exploited an in vitro rat brain slice preparation that retains robust circadian function. As in the intact SCN, PSA levels in the isolated SCN are rhythmic, with higher levels during the early subjective day and lower levels during subjective night. Importantly, bath application of glutamate to SCN slices rapidly and transiently increases PSA levels during both the subjective day and night. Pretreating the slices with endoneuraminidase, which selectively removes PSA from NCAM and thereby prevents this increase, abolishes glutamate- and optic chiasm stimulation-induced phase delays of the SCN circadian neuronal activity rhythm. These results support the hypothesis that PSA expression in the SCN is controlled by both the circadian clock and photic input to the clock and that expression of PSA in the SCN is critical for photic-like phase shifts of the clock. Together, these results establish that such actions of PSA are manifested downstream from presynaptic retinohypothalamic terminals and therefore are intrinsic to the SCN itself.

Intrinsic role of polysialylated neural cell adhesion molecule in photic phase resetting of the Mammalian circadian clock

The suprachiasmatic nuclei (SCN), the location of the mammalian circadian clock, are one of the few adult brain regions that express the highly polysialylated form of neural cell adhesion molecule (PSA-NCAM). A role for the polysialic acid (PSA) component of PSA-NCAM, which is known to promote tissue plasticity, has been reported for photic entrainment of circadian rhythmicity in vivo. The in vivo results, however, do not discriminate between PSA acting upstream or downstream of the glutamatergic synapses that convey photic information to the SCN. To address this key issue, we exploited an in vitro rat brain slice preparation that retains robust circadian function. As in the intact SCN, PSA levels in the isolated SCN are rhythmic, with higher levels during the early subjective day and lower levels during subjective night. Importantly, bath application of glutamate to SCN slices rapidly and transiently increases PSA levels during both the subjective day and night. Pretreating the slices with endoneuraminidase, which selectively removes PSA from NCAM and thereby prevents this increase, abolishes glutamate- and optic chiasm stimulation-induced phase delays of the SCN circadian neuronal activity rhythm. These results support the hypothesis that PSA expression in the SCN is controlled by both the circadian clock and photic input to the clock and that expression of PSA in the SCN is critical for photic-like phase shifts of the clock. Together, these results establish that such actions of PSA are manifested downstream from presynaptic retinohypothalamic terminals and therefore are intrinsic to the SCN itself.

Transneuronal induction of the highly sialylated isoform of the neural cell adhesion molecule following nerve injury

The polysialylated, embryonic form of the neuronal cell adhesion molecule (PSA-NCAM) is known to participate in a whole series of synaptic rearrangements even in adult animals. The possible role of this molecule in neuroplastic changes of the adult rat somatosensory cortex induced by unilateral transection of the infraorbital branch of the trigeminal nerve was studied with PSA-NCAM immunostaining at light microscopic level. Two- and three-month-old CFY albino rats were sacrificied on days 1, 4, 6, 14 and 21 following operation and PSA-NCAM immunoreaction was examined at three levels of the vibrissa-cortex neuraxis, namely, in the principal nucleus of the trigeminal nerve, in the ventral posteromedial nucleus of the thalamus and in the somatosensory cortex. The lower levels of the neuraxis remained free of PSA-NCAM labeling, similarly to control, intact animals. However, a large number of scattered small neurons became PSA-NCAM immunoreactive in layers IV-VI on both ipsi- and contralateral sides of the somatosensory cortex from day 6 onwards, suggesting a possible transynaptic regulation of NCAM sialylation state.

Distribution of PSA-NCAM expression in the amygdala of the adult rat

Synaptic plasticity in the amygdala appears to be necessary for the generation of emotional memories. However, the molecular bases of this plasticity are not fully understood. Because the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) has been implicated in memory consolidation in the hippocampus and temporal cortex, we have studied in detail the expression of this molecule in the adult rat amygdala with an antibody against PSA-NCAM. Our results demonstrate for the first time the presence of PSA-NCAM in the adult rat amygdala. Immunoreactive somata and processes are abundant in the amygdalo-hippocampal transition area, central nucleus, intra-amygdaloid bed nucleus of the stria terminalis, anterior and posterior cortical nuclei, periamygdaloid cortex and medial nucleus of the amygdala. In addition PSA-NCAM immunoreactive neuronal somata and processes exist in the lateral, basal and accessory basal nuclei, anterior amygdaloid area and amygdalo-striatal area. The presence of this molecule in areas that receive olfactory or vomeronasal input could reflect the intrinsic plasticity of these chemosensory systems. PSA-NCAM expression in the lateral amygdala could indicate its participation in the plastic events that lead to the generation of emotional memories such as those related to fear conditioning.

High affinity binding of long-chain polysialic acid to antibody, and modulation by divalent cations and polyamines

Long-chain polysialic acid (PSA) is expressed on the vertebrate neural cell adhesion molecule (NCAM) during neuronal plasticity. Its structural similarity to the capsular PSAs of some pathogenic bacteria has hampered the development of polysaccharide vaccines against meningitis. The antibodies formed during immunization require a long epitope for binding, and cross-react with host tissue PSA. The nature of the epitope and possible external effectors involved are still unclear. We have evaluated the interaction of PSA with its antibody mAb735 by surface plasmon resonance. The influences of PSA chain length, pH, temperature, ionic environment, and polyamines were also determined. The antibody binding affinity was found to dramatically increase with PSA chain length. A sub-nanomolar dissociation constant (K(D)=8.5 x 10(-10)M) was obtained for the binding of very long chain native MenB polysaccharides (approximately 200 Neu5Ac-residues). Colominic acid from Escherichia coli K1 (approximately 100 residues) and shorter polymers exhibited progressively weaker affinities. The antibody also bound tightly (K(D) approximately 5 x 10(-9)M) to polysialylated glycopeptides from human embryonal brain. The effects of pH and ionic strength suggested that the interaction is largely electrostatic. Ca2+ and Mn2+ ions promoted the observed surface plasmon resonance response in a concentration dependent fashion. Spermine increased the response in a similar way. Our results suggest that divalent cations and polyamines may play significant role in the regulation of the PSA epitope presentation in vivo.

ST8Sia II and ST8Sia IV polysialyltransferases exhibit marked differences in utilizing various acceptors containing oligosialic acid and short polysialic acid. The basis for cooperative polysialylation by two enzymes

Polysialylation of the neural cell adhesion molecule (NCAM) is thought to play a critical role in neural development. Two polysialyltransferases, ST8Sia II and ST8Sia IV, play dominant roles in polysialic acid synthesis on NCAM. However, the individual roles and mechanisms by which these two enzymes form large amounts of polysialic acid on NCAM were heretofore unknown. Previous studies indicate that ST8Sia IV forms more highly polysialylated N-glycans on NCAM than ST8Sia II in vitro. In the present study, we first demonstrated that a combination of ST8Sia II and ST8Sia IV cooperatively polysialylated NCAM, resulting in NCAM N-glycans containing more, and thus longer, polysialic acid than when the enzymes were used individually. There was also an increase in polysialylated NCAM when we used ST8Sia II and ST8Sia IV sequentially, whereas there appeared to be a subtle increase when the enzymes were used in the reverse order. Furthermore, ST8Sia IV was able to add polysialic acid to oligosialylated oligosaccharides and unpolysialylated antennas in N-glycans attached to NCAM, even when polysialic acid was attached to at least one of the other antennas. By contrast, ST8Sia II added little polysialic acid to the same acceptors. On the other hand, neither ST8Sia II nor ST8Sia IV could add polysialic acid to a polysialylated antenna of NCAM N-glycans. These combined results indicate that the synergistic effect of ST8Sia II and ST8Sia IV is caused by: 1) the ability of ST8Sia IV to add polysialic acid to oligosialic acid formed by ST8Sia II, 2) the potential of ST8Sia IV to act on more antennas of N-glycans than ST8Sia II, and 3) the ability of ST8Sia II and ST8Sia IV in combination to act on the fifth and sixth N-glycosylation sites of NCAM.

Polysialic acid and the formation of oculomotor synapses on chick ciliary neurons

The polysialic acid (PSA) moiety of the neural cell adhesion molecule (NCAM) participates in a variety of developmental processes, including axonal guidance and cell migration. PSA's function in these contexts stems from its ability to reduce cell interactions. The present study examines the regulation of PSA expression during formation of the calyciform synapse by the oculomotor axons on chick ciliary neurons. Prior to synaptogenesis, PSA is abundantly and uniformly expressed on the surface of the ciliary neuron body. However, at the time synaptic bonds start to form, as reflected in the localized accumulation of synaptic vesicles, PSA is lost from the point of synaptic contact. Thereafter, PSA is progressively lost from the ciliary neuron surface as the calyx grows. The dense mats of pseudodendritic-like somatic spines, which extend from the postsynaptic cell body, form an exception. These spines, which are known to undergo morphological remodeling, retain PSA expression until the end of embryogenesis. The experimental removal of PSA did not affect synaptogenesis itself, in that no significant changes were observed in the surface covered by the calyx, the number of spine aggregates, the size of acetylcholine receptor clusters, the cell surface area covered by these receptors, or the ultrastructure of the calyx, spine mats, and active zones. Together, these observations suggest that the synapse eliminates PSA as a part of its normal development and that the loss of PSA from the site of axon-target interaction may serve to stabilize structures formed during synaptogenesis.

ST8Sia IV mRNA corresponds with the biosynthesis of alpha2,8sialyl polymers but not oligomers in rat oligodendrocytes

As oligodendrocytes mature they progress through a series of distinct differentiation steps characterized by the expression of specific markers. One such marker, polysialic acid found on the neural cell adhesion molecule (NCAM), is detected by antibodies and is present on progenitor oligodendrocytes, but is not detected to the same extent on mature oligodendrocytes. Two closely related polysialyltransferases, ST8Sia II (STX) and ST8Sia IV (PST) have been cloned previously and shown to synthesize polysialic acid on NCAM and other glycoproteins. To determine whether or not polyalpha2,8sialyltransferases are downregulated during the differentiation of oligodendrocytes, the enzyme activity and expression of ST8Sia II and ST8Sia IV mRNA at two stages of maturation in JS12/1 and JS3/16 oligodendrocytes were examined. Differentiation in both oligodendroglial cell lines was accompanied by more than a 50% reduction in the biosynthesis of polymers of alpha2,8sialic acid when fetuin was used as substrate. Most interestingly, extracts of JS12/1 mature cells synthesized 60% more short oligomers of alpha2,8sialic acid than the progenitor cells, whereas JS3/16 mature cells synthesized barely detectable amounts of the short oligomers. Transcripts for ST8Sia IV mRNA were present in both JS12/1 and JS3/16 and were reduced when the biosynthesis was markedly reduced. In contrast ST8Sia II mRNA was barely detectable in JS3/16 cells and although detectable in JS12/1 cells, there was no clear modulation with maturation. These results were supported by the examination of the brains of rats from embryonic to Day 21 ages. The enzyme activity and mRNA experiments show that polyalpha2,8sialyltransferase itself is down regulated to cause the reduction in sialyl polymers on mature oligodendrocytes. Moreover, ST8Sia IV is responsible for the polysialylation of NCAM in oligodendrocytes.

Location of sialoglycoconjugates containing the Sia(alpha)2-3Gal and Sia(alpha)2-6Gal groups in the rat hippocampus and the effect of aging on their expression

The histochemical distribution of sialoglycoconjugates in the CA1 region in the hippocampus formation of 9-week-old rats and 30-month-old rats was examined using electron microscopy in combination with two lectins, Maackia amurensis lectin, specific for Sia(alpha)2-3Gal, and Sambucus sieboldiana agglutinin, specific for Sia(alpha)2-6Gal. Each lectin stained the plasma membranes of pyramidal cells, indicating that the Sia(alpha)2-3Gal and Sia(alpha)2-6Gal groups were expressed on their plasma membranes. These lectins also bound to synapses in the stratum lacunosum molecular. The staining intensity of the lectins in the synapses in these layers was downregulated in the 30-month-old rats. These results indicated that both the Sia(alpha)2-3Gal and Sia(alpha)2-6Gal groups are expressed on these synapses and that the expression of these sialyl linkages decreases in the aged brain

Dual effects of NMDA receptor activation on polysialylated neural cell adhesion molecule expression during brainstem postnatal development

Here we show a dual role of N-methyl-d-aspartate receptor (NMDAR) activation in controlling polysialylated neural cell adhesion molecule (PSA-NCAM) dynamic expression in the dorsal vagal complex (DVC), a gateway for many primary afferent fibres. In this structure the overall expression of PSA-NCAM decreases during the first 2 weeks after birth to persist only at synapses in the adult. Electrical stimulation of the vagal afferents causes a rapid increase of PSA-NCAM expression both in vivo and in acute slices before postnatal day (P) 14 whereas a similar stimulation induces a decrease after P15. Inhibition of NMDAR activity in vitro completely prevented these changes. These regulations depend on calmodulin activation and cGMP production at all stages. By contrast, blockade of neuronal nitric oxide synthase (nNOS) prevented these changes only after P10 in agreement with its late expression in the DVC. The pivotal role of NMDAR is also supported by the observation that chronic blockade induces a dramatic decrease in PSA-NCAM expression.

Developmental Profile of Neural Cell Adhesion Molecule Glycoforms with a Varying Degree of Polymerization of Polysialic Acid Chains

More precise information on the degree of polymerization (DP) of polysialic acid (polySia) chains expressed on neural cell adhesion molecule (NCAM) and its developmental stage-dependent variation are considered important in understanding the mechanism of regulated polysialylation and fine-tuning of NCAM-mediated cell adhesion by polySia. In this paper, first we performed a kinetic study of acid-catalyzed hydrolysis of polySia and report our findings that (a) in (-->8Neu5Ac alpha 2-->)(n)-->8Neu5Ac alpha 2-->3Gal beta 1-->R, the proximal Neu5Ac residue alpha 2-->3 linked to Gal is cleaved about 2.5-4 times faster than the alpha 2-->8 linkages and (b) in contrary to general belief that alpha 2-->8 linkages in polySia are extremely labile, the kinetic consideration showed that they are not so unstable, and every ketosidic bond is hydrolyzed at the same rate. These findings are the basis of our strategy for DP analysis of polySia on NCAM. Second, using the recently developed method that provides base-line resolution of oligo/polySia from DP 2 to >80 with detection thresholds of 1.4 fmol per resolved peak, we have determined the DP of polySia chains expressed in embryonic chicken brains at different developmental stages. Our results support the presence of numerous NCAM glycoforms differing in DPs of oligo/polySia chains and a delicate change in their distribution during development.

NMDA receptor and nitric oxide synthase activation regulate polysialylated neural cell adhesion molecule expression in adult brainstem synapses

Here we report that synapses in the adult dorsal vagal complex, a gateway for many primary afferent fibers, express a high level of the polysialylated neural cell adhesion molecule (PSA-NCAM). We show that electrical stimulation of the vagal afferents causes a rapid decrease of PSA-NCAM expression both in vivo and in acute slices. Inhibition of NMDA receptor activity completely prevented the decrease. Blockade of calmodulin activation, neuronal nitric oxide (NO) synthase, or soluble guanylyl cyclase and chelation of extracellular NO mimicked this inhibition. Our data provide a mechanistic framework for understanding how activity-linked stimulation of the NMDA-NO-cGMP pathway induces rapid changes in PSA-NCAM expression, which may be associated with long-term depression.

Roles, regulation, and mechanism of polysialic acid function during neural development

The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) appeared during the evolution of vertebrates as a new mechanism for regulation of cell interactions. This large and abundant glycoprotein can exert steric effects at the cell surface that lead to the attenuation of cell-cell bonds mediated not only by NCAM but also a variety of other adhesion receptors. PSA-NCAM expression changes both as a result of developmental programs and physiological inputs. This global modulation of cell-cell attachment has been shown to facilitate cell migration, axon pathfinding and targeting, and plastic changes in the embryonic and adult nervous system.

NMDA receptor and nitric oxide synthase activation regulate polysialylated neural cell adhesion molecule expression in adult brainstem synapses

Here we report that synapses in the adult dorsal vagal complex, a gateway for many primary afferent fibers, express a high level of the polysialylated neural cell adhesion molecule (PSA-NCAM). We show that electrical stimulation of the vagal afferents causes a rapid decrease of PSA-NCAM expression both in vivo and in acute slices. Inhibition of NMDA receptor activity completely prevented the decrease. Blockade of calmodulin activation, neuronal nitric oxide (NO) synthase, or soluble guanylyl cyclase and chelation of extracellular NO mimicked this inhibition. Our data provide a mechanistic framework for understanding how activity-linked stimulation of the NMDA-NO-cGMP pathway induces rapid changes in PSA-NCAM expression, which may be associated with long-term depression.

Polysialylated neural cell adhesion molecule is involved in the neuroplasticity induced by axonal injury in the avian ciliary ganglion

We demonstrated previously in the quail ciliary ganglion, that the immunoreactivity for the neural cell adhesion molecule labeling the postsynaptic specializations of intraganglionic synapses decreases when synaptic remodeling is induced by crushing the postganglionic ciliary nerves. Here we show, in the same experimental conditions, that the immunolabeling for its polysialylated non-stabilizing isoform, which promotes cell plasticity, increases at these subcellular compartments. In control ganglia, poor immunolabeling for the polysialylated neural cell adhesion molecule was occasionally observed surrounding the soma of the ciliary neurons, in correspondence with the calyciform presynaptic ending and the perineuronal satellite cells sheath. At the electron microscope, several neuronal compartments, including some postsynaptic specializations, somatic spines and multivesicular bodies, were immunopositive. Three to six days after ciliary nerve crush, both the number of ciliary neurons labeled for the polysialylated neural cell adhesion molecule and the intensity of their immunolabeling increased markedly. Electron microscopy revealed that, in parallel to the injury-induced detachment of the preganglionic boutons, numerous postsynaptic specializations were found to be immunopositive. Twenty days later, when intraganglionic connections were re-established, polysialylated neural cell adhesion molecule immunoreactivity was comparable to that observed in control ganglia. The increase in immunolabeling also involved the other neuronal compartments mentioned above, the perineuronal satellite cells and the intercellular space between these and the ciliary neurons. From these results we suggest that the switch, at the postsynaptic specializations, between the neural cell adhesion molecule and its polysialylated form may be among the molecular changes occurring in axotomized neurons leading to injury-induced synaptic remodeling. Moreover, from the increase in polysialylated neural cell adhesion molecule immunolabeling, observed at the somatic spines and at the interface between neurons and perineuronal satellite cells, we suggest that this molecule may be involved not only in synaptic remodeling, but also in other more general aspects of injury-induced neuronal plasticity.