Relationship between ST8SIA2, polysialic acid and its binding molecules, and psychiatric disorders

Sialic acid and anti-ganglioside M1 antibodies are invaluable biomarkers correlated with the severity of autism spectrum disorder

BACKGROUND

Autism spectrum disorders (ASD) are devastating neurodevelopmental disorders that showed global increased prevalence. They are characterized by impairment of social communication and stereotyped patterns.

OBJECTIVE

This study aimed at measuring the levels of total sialic acid (SA) and anti-ganglioside M1 (anti- GM1) IgG antibodies as essential biomarkers in a cohort of children with ASD to identify their diagnostic yield as well as their correlation with the severity of autistic behaviors.

METHODS

The demographic characteristics, anthropometric measurements, and clinical data were recorded. The levels of total plasma SA and serum anti-GM1 IgG antibodies levels were measured in 100 children with ASD and 100 healthy controls. The severity of ASD-related symptoms was assessed by using the Childhood Autism Rating Scale (CARS).

RESULTS

Children with ASD had significantly higher levels of both SA and anti-GM1 antibodies than healthy controls (p < 0.001). SA showed a statistically significant moderate diagnostic performance while anti-GM1 antibody showed a statistically significant high diagnostic in differentiating severe from mild to moderate autism. Moreover, both SA and anti-GM1 antibodies levels were significantly correlated to the severity of ASD symptoms (p < 0.001).

CONCLUSION

The significantly increased levels of SA and anti-GM1 antibodies in children with ASD and their correlation with autism-related symptoms suggest their possible etiopathogenic role in autism as one of the pediatric autoimmune neuropsychiatric disorders. However, further large-scale studies are still needed to explore their possible bidirectional relationship as biomarkers for autism.

Association of polysialic acid serum levels with schizophrenia spectrum and bipolar disorder-related structural brain changes and hospitalization

Expression of polysialic acid (polySia) in the adult brain is enriched in areas of continuous neurogenesis and plasticity such as the hippocampus. Genome-wide association studies identified variants of glycosylation enzyme-encoding genes, required for the generation of polySia, to be associated with the development of schizophrenia and bipolar disorder. Here, we report that serum levels of polySia are increased in patients with schizophrenia spectrum disorder compared to patients with major depressive disorders or demographically matched healthy controls. Furthermore, elevated polySia serum levels are associated with structural hippocampal gray matter decline in schizophrenia spectrum and bipolar disorder. In patients with schizophrenia spectrum disorder, polySia serum levels correlate with the number, duration of disease-related hospitalizations, early retirement and medical leave as estimators of detrimental long-term disease trajectories. Our data show that polySia serum levels are linked to structural hippocampal brain changes in schizophrenia spectrum and bipolar disorders, and suggest a contribution of polySia to the pathophysiology of these diseases.

Altered expression of glycobiology-related genes in Parkinson's disease brain

The precise mechanisms initiating and perpetuating the cellular degeneration in Parkinson's disease (PD) remain unclear. There is decreased expression of the main brain gangliosides, and GM1 ganglioside in particular, in the PD brain along with decreased expression of the genes coding for the glycosyltranferase and the sialyltransferase responsible for the synthesis of these brain gangliosides. However, potentially important pathogenic mechanisms contributing to the neurodegeneration in PD may also include altered levels of expression of genes involved in glycosylation, sialylation and sphingolipid synthesis and metabolism. Although various studies have described pathological lipid and glycolipid changes in PD brain, there have been limited studies of expression of glycobiology-related genes in PD brain. The current study was performed as an initial attempt to gain new information regarding potential changes in glycoprotein and glycolipid-related genes in PD by investigating the gene expression status for select glycosyltransferases, sialyltransferases, sialidases, sphingosine kinases, and lysosomal enzymes in the substantia nigra and putamen from patients with PD and neurologically normal controls. Results showed altered expression of glycosyltransferase genes (B3GALT2 and B4GALT1) potentially involved in microglial activation and neuroinflammation, sphingosine-1-phosphate (S1P) modulators (SPHK1, SPHK2, and SGPL1) involved in sphingolipid synthesis and metabolism, polysialyltransferase genes (ST8SIA2 and ST8SIA4) that encode enzymes responsible for polysialic acid (polySia) biosynthesis, and the sialidase NEU4, expression of which has been linked to the clearance of storage materials from lysosomes. The data presented here underscore the complexity of the glycolipid/sphingolipid dysregulation in the PD brain and continued and expanded study of these processes may not only provide a greater understanding of the complex roles of aberrant glycosylation sialylation, and sphingolipid synthesis/metabolism in the pathophysiology of PD but may identify potential druggable targets for PD therapeutics.

An embeddable molecular code for Lewis X modification through interaction with fucosyltransferase 9

N-glycans are diversified by a panel of glycosyltransferases in the Golgi, which are supposed to modify various glycoproteins in promiscuous manners, resulting in unpredictable glycosylation profiles in general. In contrast, our previous study showed that fucosyltransferase 9 (FUT9) generates Lewis X glycotopes primarily on lysosome-associated membrane protein 1 (LAMP-1) in neural stem cells. Here, we demonstrate that a contiguous 29-amino acid sequence in the N-terminal domain of LAMP-1 is responsible for promotion of the FUT9-catalyzed Lewis X modification. Interestingly, Lewis X modification was induced on erythropoietin as a model glycoprotein both in vitro and in cells, just by attaching this sequence to its C-terminus. Based on these results, we conclude that the amino acid sequence from LAMP-1 functions as a “Lewis X code”, which is deciphered by FUT9, and can be embedded into other glycoproteins to evoke a Lewis X modification, opening up new possibilities for protein engineering and cell engineering.

A 29-amino acid sequence in the N-terminal domain of LAMP-1 promotes its Lewis X glycosylation and is embeddable to other proteins for Lewis X glycoengineering.

Lower promoter activity of the ST8SIA2 gene has been favored in evolving human collective brains

ST8SIA2 is an important molecule regulating expression of the phenotype involved in schizophrenia. Lowered promoter activity of the ST8SIA2 gene is considered to be protective against schizophrenia by conferring tolerance to psychosocial stress. Here, we examined the promoter-type composition of anatomically modern humans (AMHs) and archaic humans (AHs; Neanderthals and Denisovans), and compared the promoter activity at the population level (population promoter activity; PPA) between them. In AMHs, the TCT-type, showing the second lowest promoter activity, was most prevalent in the ancestral population of non-Africans. However, the detection of only the CGT-type from AH samples and recombination tracts in AH sequences showed that the CGT- and TGT-types, exhibiting the two highest promoter activities, were common in AH populations. Furthermore, interspecies gene flow occurred into AMHs from AHs and into Denisovans from Neanderthals, influencing promoter-type compositions independently in both AMHs and AHs. The difference of promoter-type composition makes PPA unique in each population. East and Southeast Asian populations show the lowest PPA. This results from the selective increase of the CGC-type, showing the lowest promoter activity, in these populations. Every non-African population shows significantly lower PPA than African populations, resulting from the TCT-type having the highest prevalence in the ancestral population of non-Africans. In addition, PPA reduction is also found among subpopulations within Africa via a slight increase of the TCT-type. These findings indicate a trend toward lower PPA in the spread of AMHs, interpreted as a continuous adaptation to psychosocial stress arising in migration. This trend is considered as genetic tuning for the evolution of collective brains. The inferred promoter-type composition of AHs differed markedly from that of AMHs, resulting in higher PPA in AHs than in AMHs. This suggests that the trend toward lower PPA is a unique feature in AMH spread.

Growth factors improve the proliferation of Jeju black pig muscle cells by regulating myogenic differentiation 1 and growth-related genes

OBJECTIVE

The growth rate of pigs is related to differentiation and proliferation of muscle cells, which are regulated by growth factors and expression of growth-related genes. Thus, the objective of this study was to establish optimal culture conditions for Jeju black pig (JBP) muscle cells and determine the relationship of various factors involved in muscle growth with the proliferation of JBP muscle cells.

METHODS

Muscles were taken from the femur skeletal muscle of JBP embryos. After isolation of the muscle cells, cells were cultured in a 6-well plate under four different culture conditions to optimize culture conditions for JBP muscle cells. To analyze proliferation rate of JBP muscle cells, these muscle cells were seeded into 6-well plates at a density of 1.5×105 cells per well and cultured for 3 days. Western blot and quantitative real-time polymerase chain reaction were applied to verify the myogenic differentiation 1 (MyoD) expression and growth-related gene expression in JBP muscle cells, respectively.

RESULTS

We established a muscle cell line from JBP embryos and optimized its culture conditions. These muscle cells were positive for MyoD, but not for paired box 7. The proliferation rate of these muscle cells was significantly higher in a culture medium containing bFGF and epidermal growth factor + basic fibroblast growth factor (EGF+bFGF) than that without a growth factor or containing EGF alone. Treatment with EGF and bFGF significantly induced the expression of MyoD protein, an important transcription factor in muscle cells. Moreover, we checked the changes of expression of growth-related genes in JBP muscle cells by presence or absence of growth factors. Expression level of collagen type XXI alpha 1 gene was changed only when EGF and bFGF were added together to culture media for JBP muscle cells.

CONCLUSION

Concurrent use of EGF and bFGF increased the expression of MyoD protein, thus regulating the proliferation of JBP muscle cells and the expression of growth-related genes.

Brain region-dependent alterations in polysialic acid immunoreactivity across the estrous cycle in mice

N-glycosylation is a posttranslational modification that plays significant roles in regulating protein function. One form of N-glycosylation, polysialylation, has been implicated in many processes including learning and memory, addiction, and neurodegenerative disease. Polysialylation appears to be modulated by the estrous cycle in the hypothalamus in rat, but this has not been assessed in other brain regions. To determine if polysialylation was similarly estrous phase-dependent in other neuroanatomical structures, the percent area of polysialic acid (PSA) immunoreactivity in subregions of the medial prefrontal cortex, hippocampus, and nucleus accumbens was assessed in each of the four phases in adult female mice. In this study, we found that PSA immunoreactivity fluctuated across the estrous cycle in a subregion-specific manner. In the prefrontal cortex, PSA immunoreactivity was significantly lower in proestrus phase compared to estrus in the prelimbic cortex, but did not differ across the estrous cycle in the infralimbic cortex. In the hippocampus, PSA immunoreactivity was significantly increased in proestrus compared to metestrus in the CA1 and CA2 and compared to diestrus in CA3, but remain unchanged in the dentate gyrus. PSA immunoreactivity did not vary across the estrous cycle in the nucleus accumbens core or shell. These findings may have implications for estrous cycle-dependent alterations in behavior.

Polysialylation and disease

Polysialic acid (polySia, PSA) is a unique constituent of the glycocalyx on the surface of bacterial and vertebrate cells. In vertebrates, its biosynthesis is highly regulated, not only in quantity and quality, but also in time and location, which allows polySia to be involved in various important biological phenomena. Therefore, impairments in the expression and structure of polySia sometimes relate to diseases, such as schizophrenia, bipolar disorder, and cancer. Some bacteria express polySia as a tool for protecting themselves from the host immune system during invasion. PolySia is proven to be a biosafe material; polySia, as well as polySia-recognizing molecules, are key therapeutic agents. This review first comprehensive outlines the occurrence, features, biosynthesis, and functions of polySia and subsequently focuses on the related diseases.

Human-specific microglial Siglec-11 transcript variant has the potential to affect polysialic acid-mediated brain functions at a distance

CD33-related Siglecs are often found on innate immune cells and modulate their reactivity by recognition of sialic acid-based "self-associated molecular patterns" and signaling via intracellular tyrosine-based cytosolic motifs. Previous studies have shown that Siglec-11 specifically binds to the brain-enriched polysialic acid (polySia/PSA) and that its microglial expression in the brain is unique to humans. Furthermore, human microglial Siglec-11 exists as an alternate splice form missing the exon encoding the last (fifth) Ig-like C2-set domain of the extracellular portion of the protein, but little is known about the functional consequences of this variation. Here, we report that the recombinant soluble human microglial form of Siglec-11 (hSiglec-11(4D)-Fc) binds endogenous and immobilized polySia better than the tissue macrophage form (hSiglec-11(5D)-Fc) or the chimpanzee form (cSiglec-11(5D)-Fc). The Siglec-11 protein is also prone to aggregation, potentially influencing its ligand-binding ability. Additionally, Siglec-11 protein can be secreted in both intact and proteolytically cleaved forms. The microglial splice variant has reduced proteolytic release and enhanced incorporation into exosomes, a process that appears to be regulated by palmitoylation of cysteines in the cytosolic tail. Taken together, these data demonstrate that human brain specific microglial hSiglec-11(4D) has different molecular properties and can be released on exosomes and/or as proteolytic products, with the potential to affect polySia-mediated brain functions at a distance.

Advances in molecular mechanisms of drugs affecting abnormal glycosylation and metastasis of breast cancer

Breast cancer remains the leading cause of cancer-related death among women worldwide, and its incidence is also increasing. High recurrence rate and metastasis rate are the key causes of poor prognosis and death. It is suggested that abnormal glycosylation plays an important role in the growth, invasion, metastasis and resistance to therapy of breast cancer cells. Meanwhile, it can be used as the biomarkers for the early detection and prognosis of breast cancer and the potential attractive targets for drug treatment. However, only a few attentions have been paid to the molecular mechanism of abnormal glycosylation in the epithelial-mesenchymal transition (EMT) of breast cancer cells and the related intervention of drugs. This manuscript thus investigated the relationship between abnormal glycosylation, the EMT, and breast cancer metastasis. Then, the process of abnormal glycosylation, the classification and their molecular regulatory mechanisms of breast cancer were analyzed in detail. Last, potential drugs are introduced in different categories, which are expected to reverse or intervene the abnormal glycosylation of breast cancer. This review is conducive to an in-depth understanding of the metastasis and drug resistance of breast cancer cells, which will provide new ideas for the clinical regulation of glycosylation and related drug treatments in breast cancer.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

Amygdala GluN2B-NMDAR dysfunction is critical in abnormal aggression of neurodevelopmental origin induced by St8sia2 deficiency

Aggression is frequently observed in neurodevelopmental psychiatric disorders such as schizophrenia, autism, and bipolar disorder. Due to a lack of understanding of its underlying mechanisms, effective treatments for abnormal aggression are still missing. Recently, genetic variations in Sialyltransferase 2 (St8sia2) have been linked to these disorders and aggression. Here we identify abnormal aggressive behaviors and concomitant blunted fear learning in St8sia2 knockout (-/-) mice. It is worth noting that the amygdala of St8sia2-/- mice shows diminished threat-induced activation, as well as alterations in synaptic structure and function, including impaired GluN2B-containing NMDA receptor-mediated synaptic transmission and plasticity. Pharmacological rescue of NMDA receptor activity in the amygdala of St8sia2-/- mice with the partial agonist D-cycloserine restores synaptic plasticity and normalizes behavioral aberrations. Pathological aggression and associated traits were recapitulated by specific amygdala neonatal St8sia2 silencing. Our results establish a developmental link between St8sia2 deficiency and a pathological aggression syndrome, specify synaptic targets for therapeutic developments, and highlight D-cycloserine as a plausible treatment.

PSA-NCAM Colocalized with Cholecystokinin-Expressing Cells in the Hippocampus Is Involved in Mediating Antidepressant Efficacy

The extracellular glycan polysialic acid linked to neural cell adhesion molecule (PSA-NCAM) is principally expressed in the developing brain and the adult neurogenic regions. Although colocalization of PSA-NCAM with cholecystokinin (CCK) was found in the adult brain, the role of PSA-NCAM remains unclear. In this study, we aimed to elucidate the functional significance of PSA-NCAM in the CA1 region of the male mouse hippocampus. Combined fluorescence in situ hybridization and immunohistochemistry showed that few vesicular glutamate transporter 3-negative/CCK-positive (VGluT3^-/CCK⁺) cells were colocalized with PSA-NCAM, but most of the VGluT3⁺/CCK⁺ cells were colocalized with PSA-NCAM. The somata of PSA-NCAM⁺/CCK⁺ cells were highly innervated by serotonergic boutons than those of PSA-NCAM^-/CCK⁺ cells. The expression ratios of 5-HT_3A receptors and p11, a serotonin receptor-interacting protein, were higher in PSA-NCAM⁺/CCK⁺ cells than in PSA-NCAM^-/CCK⁺ cells. Pharmacological digestion of PSA-NCAM impaired the efficacy of antidepressant fluoxetine (FLX), a selective serotonin reuptake inhibitor, but not the efficacy of benzodiazepine anxiolytic diazepam. A Western blot showed that restraint stress decreased the expressions of p11 and mature brain-derived neurotrophic factor (BDNF), and FLX increased them. Interestingly, the FLX-induced elevation of expression of p11, but not mature BDNF, was impaired by the digestion of PSA-NCAM. Quantitative reverse transcription-polymerase chain reaction showed that restraint stress reduced the expression of polysialyltransferase ST8Sia IV and FLX elevated it. Collectively, PSA-NCAM colocalized with VGluT3⁺/CCK⁺ cells in the CA1 region of the hippocampus may play a unique role in the regulation of antidepressant efficacy via the serotonergic pathway.SIGNIFICANCE STATEMENT Polysialic acid (PSA) is composed of eight or more α2,8-linked sialic acids. Here, we examined the functional significance of polysialic acid linked to the neural cell adhesion molecule (PSA-NCAM) in the adult mouse hippocampus. Few vesicular glutamate transporter 3-negative/cholecystokinin-positive (VGluT3^-/CCK⁺) cells were colocalized with PSA-NCAM, but most of the VGluT3⁺/CCK⁺ cells were colocalized with PSA-NCAM. The expression ratios of 5-HT_3A receptors and p11, a serotonin receptor-interacting protein, were higher in PSA-NCAM⁺/CCK⁺ cells than in PSA-NCAM^-/CCK⁺ cells. The efficacy of antidepressants, but not anxiolytics, was impaired by the digestion of PSA-NCAM. The antidepressant-induced increase in p11 expression was inhibited following PSA-NCAM digestion. We hence hypothesize that PSA-NCAM colocalized with VGluT3⁺/CCK⁺ cells may play a unique role in regulating antidepressant efficacy.

Levels of Salivary Sialic Acid in Children with Autism Spectrum Disorder; Could It Be Related to Stereotypes and Hyperactivity?

Objective

Sialic acid (Sia) is an essential nutrient for brain development, learning, memory and cognition and plays a role in neurodevelopment of infants. The aim of this study was to determine whether Sia levels are significantly associated with the autism spectrum disorder (ASD).

Methods

Forty-six ASD children and 30 typically developing children aged 3 to 10 years were included in the study. Behavioral symptoms in ASD children was assessed by the Autism Behavior Checklist (AuBC), the Childhood Autism Rating Scale, and the Aberrant Behavior Checklist (ABC). After the collection of saliva samples, the supernatant was separated. All the samples kept at −80°C until Sia analysis was done.

Results

Sia level was found to be significantly lower in the ASD group when compared to healthy controls (p = 0.013). There was no correlation between severity of ASD and salivary Sia levels. We found a negative correlation between AuBC scores and Sia levels and a negative correlation in both ABC Stereotypic Behavior and Hyperactivity/Noncompliance subscales with Sia levels in ASD group.

Conclusion

The obtained data indicate that Sia levels could have an effect on autism-like behaviors, particularly on stereotypes and hyperactivity.

Functional roles of ST8SIA3-mediated sialylation of striatal dopamine D2 and adenosine A2A receptors

Sialic acids are typically added to the end of glycoconjugates by sialyltransferases. Among the six ST8 α-N-acetyl-neuraminide α-2,8-sialyltransferases (ST8SIA) existing in adult brains, ST8SIA2 is a schizophrenia-associated gene. However, the in vivo substrates and physiological functions of most sialyltransferases are currently unknown. The ST8SIA3 is enriched in the striatum. Here, we showed that ablation of St8sia3 in mice (St8sia3-KO) led to fewer disialylated and trisialylated terminal glycotopes in the striatum of St8sia3-KO mice. Moreover, the apparent sizes of several striatum-enriched G-protein-coupled receptors (GPCRs) (including the adenosine A_2A receptor (A_2AR) and dopamine D₁/D₂ receptors (D₁R and D₂R)) were smaller in St8sia3-KO mice than in WT mice. A sialidase treatment removed the differences in the sizes of these molecules between St8sia3-KO and WT mice, confirming the involvement of sialylation. Expression of ST8SIA3 in the striatum of St8sia3-KO mice using adeno-associated viruses normalized the sizes of these proteins, demonstrating a direct role of ST8SIA3. The lack of ST8SIA3-mediated sialylation altered the distribution of these proteins in lipid rafts and the interaction between D₂R and A_2AR. Locomotor activity assays revealed altered pharmacological responses of St8sia3-KO mice to drugs targeting these receptors and verified that a greater population of D₂R formed heteromers with A_2AR in the striatum of St8sia3-KO mice. Since the A_2AR-D₂R heteromer is an important drug target for several basal ganglia diseases (such as schizophrenia and Parkinson's disease), the present study not only reveals a crucial role for ST8SIA3 in striatal functions but also provides a new drug target for basal ganglia-related diseases.

Acute stress-induced change in polysialic acid levels mediated by sialidase in mouse brain

Stress is an important environmental factor influencing human behaviour and causing several mental disorders. Alterations in the structure of polysialic acid (polySia/PSA) due to genetic alterations in ST8SIA2, which encodes a polySia-synthesizing enzyme, are related to certain mental disorders. However, whether stress as an environmental factor leads to changes in polySia structure is unknown. Here we studied the effects of acute stress on polySia expression and found reductions in both the quantity and quality of polySia in the olfactory bulb and prefrontal cortex, even with short-term exposure to acute stress. The use of inhibitors for sialidase, microglia and astrocytes revealed that these declines were due to a transient action of sialidase from microglia and astrocytes in the olfactory bulb and prefrontal cortex, respectively. These data suggest that sialidase dynamically regulates polySia expression in a brain region-specific manner.

Metabolomic and glycomic findings in posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a stressor-related disorder that develops in a subset of individuals exposed to a traumatic experience. Factors associated with vulnerability to PTSD are still not fully understood. PTSD is frequently comorbid with various psychiatric and somatic disorders, moderate response to treatment and remission rates. The term "theranostics" combines diagnosis, prognosis, and therapy and offers targeted therapy based on specific analyses. Theranostics, combined with novel techniques and approaches called "omics", which integrate genomics, transcriptomic, proteomics and metabolomics, might improve knowledge about biological underpinning of PTSD, and offer novel therapeutic strategies. The focus of this review is on metabolomic and glycomic data in PTSD. Metabolomics evaluates changes in the metabolome of an organism by exploring the set of small molecules (metabolites), while glycomics studies the glycome, a complete repertoire of glycan structures with their functional roles in biological systems. Both metabolome and glycome reflect the physiological and pathological conditions in individuals. Only a few studies evaluated metabolic and glycomic changes in patients with PTSD. The metabolomics studies in PTSD patients uncovered different metabolites that might be associated with psychopathological alterations in PTSD. The glycomics study in PTSD patients determined nine N-glycan structures and found accelerated and premature aging in traumatized subjects and subjects with PTSD based on a GlycoAge index. Therefore, further larger studies and replications are needed. Better understanding of the biological basis of PTSD, including metabolomic and glycomic data, and their integration with other "omics" approaches, might identify new molecular targets and might provide improved therapeutic approaches.

Sialic Acids in Neurology

Sialic acid (Sia) is involved in many biological activities and commonly occurs as a monosialyl residue at the nonreducing terminal end of glycoconjugates. The loss of activity of UDP-GlcNAc2-epimerase/ManNAc kinase, which is a key enzyme in Sia biosynthesis, is lethal to the embryo, which clearly indicates the importance of Sia in embryogenesis. Occasionally, oligo/polymeric Sia structures such as disialic acid (diSia), oligosialic acid (oligoSia), and polysialic acid (polySia) occur in glycoconjugates. In particular, polySia, a well-known epitope that commonly occurs in neuroinvasive bacteria and vertebrate brains, is one of the most well-known and biologically/neurologically important glycotopes in vertebrates. The biological effects of polySia, especially on neural cell-adhesion molecules, have been well studied, and in-depth knowledge regarding polySia has been accumulated. In addition, the importance of diSia and oligoSia epitopes has been reported. In this chapter, the recent advances in the study of diSia, oligoSia, and polySia residues in glycoproteins in neurology, and their history, definition, occurrence, analytical methods, biosynthesis, and biological functions evaluated by phenotypes of gene-targeted mice, biochemical features, and related diseases are described.

Persistent reduction in sialylation of cerebral glycoproteins following postnatal inflammatory exposure

BACKGROUND

The extension of sepsis encompassing the preterm newborn's brain is often overlooked due to technical challenges in this highly vulnerable population, yet it leads to substantial long-term neurodevelopmental disabilities. In this study, we demonstrate how neonatal neuroinflammation following postnatal E. coli lipopolysaccharide (LPS) exposure in rat pups results in persistent reduction in sialylation of cerebral glycoproteins.

METHODS

Male Sprague-Dawley rat pups at postnatal day 3 (P3) were injected in the corpus callosum with saline or LPS. Twenty-four hours (P4) or 21 days (P24) following injection, brains were extracted and analyzed for neuraminidase activity and expression as well as for sialylation of cerebral glycoproteins and glycolipids.

RESULTS

At both P4 and P24, we detected a significant increase of the acidic neuraminidase activity in LPS-exposed rats. It correlated with significantly increased neuraminidase 1 (Neu1) mRNA in LPS-treated brains at P4 and with neuraminidases 1 and 4 at P24 suggesting that these enzymes were responsible for the rise of neuraminidase activity. At both P4 and P24, sialylation of N-glycans on brain glycoproteins decreased according to both mass-spectrometry analysis and lectin blotting, but the ganglioside composition remained intact. Finally, at P24, analysis of brain tissues by immunohistochemistry showed that neurons in the upper layers (II-III) of somatosensory cortex had a reduced surface content of polysialic acid.

CONCLUSIONS

Together, our data demonstrate that neonatal LPS exposure results in specific and sustained induction of Neu1 and Neu4, causing long-lasting negative changes in sialylation of glycoproteins on brain cells. Considering the important roles played by sialoglycoproteins in CNS function, we speculate that observed re-programming of the brain sialome constitutes an important part of pathophysiological consequences in perinatal infectious exposure.

Chemical and biological methods for probing the structure and functions of polysialic acids

Owing to its poly-anionic charge and large hydrodynamic volume, polysialic acid (polySia) attached to neural cell adhesion molecule regulates axon–axon and axon–substratum interactions and signalling, particularly, in the development of the central nervous system (CNS). Expression of polySia is spatiotemporally regulated by the action of two polysialyl transferases, namely ST8SiaII and ST8SiaIV. PolySia expression peaks during late embryonic and early post-natal period and maintained at a steady state in adulthood in neurogenic niche of the brain. Aberrant polySia expression is associated with neurological disorders and brain tumours. Investigations on the structure and functions, over the past four decades, have shed light on the physiology of polySia. This review focuses on the biological, biochemical, and chemical tools available for polySia engineering. Genetic knockouts, endo-neuraminidases that cleave polySia, antibodies, exogenous expression, and neuroblastoma cells have provided deep insights into the ability of polySia to guide migration of neuronal precursors in neonatal brain development, neuronal clustering, axonal pathway guidance, and axonal targeting. Advent of metabolic sialic acid engineering using ManNAc analogues has enabled reversible and dose-dependent modulation polySia in vitro and ex vivo. In vivo, ManNAc analogues readily engineer the sialoglycans in peripheral tissues, but show no effect in the brain. A recently developed carbohydrate-neuroactive hybrid strategy enables a non-invasive access to the brain in living animals across the blood–brain barrier. A combination of recent advances in CNS drugs and imaging with ManNAc analogues for polySia modulation would pave novel avenues for understanding intricacies of brain development and tackling the challenges of neurological disorders.

Mental disorders and an acidic glycan-from the perspective of polysialic acid (PSA/polySia) and the synthesizing enzyme, ST8SIA2

Mental disorders, such as schizophrenia, bipolar disorder, and autism spectrum disorder, are challenging to manage, worldwide. Understanding the molecular mechanisms underlying these disorders is essential and required. Studies investigating such molecular mechanisms are well performed and important findings are accumulating apace. Based on the fact that these disorders are due in part to the accumulation of genetic and environmental risk factors, consideration of multi-molecular and/or multi-system dependent phenomena might be important. Acidic glycans are an attractive family of molecules for understanding these disorders, because impairment of the fine-tuned glycan system affects a large number of molecules that are deeply involved in normal brain function. One of the candidates of this important family of glycan epitopes in the brain is polysialic acid (PSA/polySia). PSA is a well-known molecule because of its role as an oncodevelopmental antigen and is also widely used as a marker of adult neurogenesis. Recently, several reports have suggested that PSA and PSA-related genes are associated with multiple mental disorders. The relationships among PSA, PSA-related genes, and mental disorders are reviewed here.

Positive selection on schizophrenia-associated ST8SIA2 gene in post-glacial Asia

A number of loci are associated with highly heritable schizophrenia and the prevalence of this mental illness has had considerable negative fitness effects on human populations. Here we focused on one particular schizophrenia-associated gene that encodes a sialyltransferase (ST8SIA2) and is expressed preferentially in the brain with the level being largely determined by three SNPs in the promoter region. It is suggested that the expression level of the ST8SIA2 gene is a genetic determinant of schizophrenia risk, and we found that a geographically differentiated non-risk SNP type (CGC-type) has significantly reduced promoter activity. A newly developed method for detecting ongoing positive selection was applied to the ST8SIA2 genomic region with the identification of an unambiguous sweep signal in a rather restricted region of 18 kb length surrounding the promoter. We also found that while the CGC-type emerged in anatomically modern humans in Africa over 100 thousand years ago, it has increased its frequency in Asia only during the past 20-30 thousand years. These findings support that the positive selection is driven by psychosocial stress due to changing social environments since around the last glacial maximum, and raise a possibility that schizophrenia extensively emerged during the Upper Paleolithic and Neolithic era.

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.

Effects of genetic variants of ST8SIA2 and NCAM1 genes on seasonal mood changes and circadian preference in the general population

ST8SIA2 and NCAM1 are functionally related genes forming polysialic acid (PSA) - neural cell adhesion molecule (NCAM) complex in suprachiasmatic nucleus (SCN), the regulating site of circadian biological rhythm. In this study, the relationship of ST8SIA2 and NCAM1 with circadian and seasonal rhythms of human behavior was explored. Subjects were 261 healthy Korean adults who were free of any history of clinically significant psychiatric symptoms. The phenotypes were circadian preference and seasonal change of mood and behavior (seasonality) measured by the Composite Scale of Morningness and the Seasonal Pattern Assessment Questionnaire, respectively. Thirty-four single nucleotide polymorphisms (SNPs) across the ST8SIA2 region and 15 SNPs of NCAM1 were analyzed. A nominally significant association with seasonality and circadian preference was observed in 21 variants of both genes. After corrections for multiple testing, associations of 8 SNPs of ST8SIA2 and 2 SNPs of NCAM1 with seasonality remained significant. Some of these SNPs were also associated with psychiatric disorders in previous studies. This study demonstrated a meaningful and/or suggestive evidence of association between behavioral phenotypes reflecting human biological rhythm and two interplaying genes involved in the plasticity of SCN's neuronal network.

Microarray gene-expression study in fibroblast and lymphoblastoid cell lines from antipsychotic-naïve first-episode schizophrenia patients

Schizophrenia (SZ) is a chronic psychiatric disorder whose onset of symptoms occurs in late adolescence and early adulthood. The etiology is complex and involves important gene-environment interactions. Microarray gene-expression studies on SZ have identified alterations in several biological processes. The heterogeneity in the results can be attributed to the use of different sample types and other important confounding factors including age, illness chronicity and antipsychotic exposure. The aim of the present microarray study was to analyze, for the first time to our knowledge, differences in gene expression profiles in 18 fibroblast (FCLs) and 14 lymphoblastoid cell lines (LCLs) from antipsychotic-naïve first-episode schizophrenia (FES) patients and healthy controls. We used an analytical approach based on protein-protein interaction network construction and functional annotation analysis to identify the biological processes that are altered in SZ. Significant differences in the expression of 32 genes were found when LCLs were assessed. The network and gene set enrichment approach revealed the involvement of similar biological processes in FCLs and LCLs, including apoptosis and related biological terms such as cell cycle, autophagy, cytoskeleton organization and response to stress and stimulus. Metabolism and other processes, including signal transduction, kinase activity and phosphorylation, were also identified. These results were replicated in two independent cohorts using the same analytical approach. This provides more evidence for altered apoptotic processes in antipsychotic-naïve FES patients and other important biological functions such as cytoskeleton organization and metabolism. The convergent results obtained in both peripheral cell models support their usefulness for transcriptome studies on SZ.

Sialic acid and anti-ganglioside antibody levels in children with autism spectrum disorders

BACKGROUND

Autism spectrum disorders (ASD) may result from a combination of genetic and environmental factors, and impact neurological functions and behaviors. Sialic acid (SA) is an indispensable nutrient for early brain development, and its polymer polySia (PSA) can modify neural cell adhesion molecules (NCAM), thereby indirectly mediating neuronal outgrowth, synaptic connectivity and memory formation. To investigate the association between SA and ASD, we conducted a case-control study.

METHODS

The study sample included 82 autistic children and 60 healthy children. We measured the levels of plasma SA and serum anti-gangliosides M1 antibodies (anti-GM1 antibodies) in the ASD and control groups. We also examined the severity of autistic children.

RESULTS

The level of plasma SA in the control group was significantly higher than that in the ASD group (p < .01). Autistic children had higher positive rates of anti-GM1 antibodies (37.8%) than controls (21.67%, P = .04). However, there was no correlation between autistic severity and the levels of SA. SA may be as a biomarker for diagnosis of ASD with a positive predictive value of 84.42%, a negative predictive value of 73.85% and an area under the ROC curve value of 0.858.

CONCLUSIONS

These results indicate that SA and anti-GM1 antibodies are associated with ASD. Our data suggested that future studies to explore the function of SA in the etiology of ASD may be needed.

Nuclear fragments of the neural cell adhesion molecule NCAM with or without polysialic acid differentially regulate gene expression

The neural cell adhesion molecule (NCAM) is the major carrier of polysialic acid (PSA) which modulates NCAM functions of neural cells at the cell surface. In previous studies, we have shown that stimulation of cultured neurons with surrogate NCAM ligands leads to the generation and nuclear import of PSA-lacking and -carrying NCAM fragments. Here, we show that the nuclear import of the PSA-carrying NCAM fragment is mediated by positive cofactor 4 and cofilin, which we identified as novel PSA-binding proteins. In the nucleus, the PSA-carrying NCAM fragment interacts via PSA with PC4 and cofilin, which are involved in RNA polymerase II-dependent transcription. Microarray analysis revealed that the nuclear PSA-carrying and -lacking NCAM fragments affect expression of different genes. By qPCR and immunoblot analysis we verified that the nuclear PSA-carrying NCAM fragment increases mRNA and protein expression of nuclear receptor subfamily 2 group F member 6, whereas the PSA-lacking NCAM fragment increases mRNA and protein expression of low density lipoprotein receptor-related protein 2 and α-synuclein. Differential gene expression evoked by nuclear NCAM fragments without and with PSA indicates that PSA-carrying and -lacking NCAM play different functional roles in the nervous system.

Developmental pathway genes and neural plasticity underlying emotional learning and stress-related disorders

The manipulation of neural plasticity as a means of intervening in the onset and progression of stress-related disorders retains its appeal for many researchers, despite our limited success in translating such interventions from the laboratory to the clinic. Given the challenges of identifying individual genetic variants that confer increased risk for illnesses like depression and post-traumatic stress disorder, some have turned their attention instead to focusing on so-called “master regulators” of plasticity that may provide a means of controlling these potentially impaired processes in psychiatric illnesses. The mammalian homolog of Tailless (TLX), Wnt, and the homeoprotein Otx2 have all been proposed to constitute master regulators of different forms of plasticity which have, in turn, each been implicated in learning and stress-related disorders. In the present review, we provide an overview of the changing distribution of these genes and their roles both during development and in the adult brain. We further discuss how their distinct expression profiles provide clues as to their function, and may inform their suitability as candidate drug targets in the treatment of psychiatric disorders.

Increased Polysialylation of the Neural Cell Adhesion Molecule in a Transgenic Mouse Model of Sialuria

Sialuria is a rare autosomal dominant disorder of mammalian metabolism, caused by defective feedback inhibition of the UDP-N-acetylglucosamine-2-epimerase N-acetylmannosamine kinase (GNE), the key enzyme of sialic acid biosynthesis. Sialuria is characterized by overproduction of free sialic acid in the cell cytoplasm. Patients exhibit vastly increased urinary excretion of sialic acid and show differently pronounced developmental delays. The physiopathology of sialuria is not well understood. Here we established a transgenic mouse line that expresses GNE containing the sialuria mutation R263L, in order to investigate the influence of an altered sialic acid concentration on the organism. The transgenic mice that expressed the mutated RNA excreted up to 400 times more N-acetylneuraminic acid than wild-type mice. Additionally, we found higher sialic acid concentration in the brain cytoplasm. Analyzing the (poly)sialylation of neural cell adhesion molecule (NCAM) revealed increased polysialylation in brains of transgenic mice compared to wild-type. However, we found only minor changes in membrane-bound sialylation in various organs but, surprisingly, a significant increase in surface sialylation on leukocytes. Our results suggest that the intracellular sialic acid concentration regulates polysialylation on NCAM in vivo; this could play a role in the manifestation of the developmental delays in sialuria patients.