Characterisation of genetic variation in ST8SIA2 and its interaction region in NCAM1 in patients with bipolar disorder

Genome-wide association study in a rat model of temperament identifies multiple loci for exploratory locomotion and anxiety-like traits

Common genetic factors likely contribute to multiple psychiatric diseases including mood and substance use disorders. Certain stable, heritable traits reflecting temperament, termed externalizing or internalizing, play a large role in modulating vulnerability to these disorders. To model these heritable tendencies, we selectively bred rats for high and low exploration in a novel environment [bred High Responders (bHR) vs. Low Responders (bLR)]. To identify genes underlying the response to selection, we phenotyped and genotyped 538 rats from an F₂ cross between bHR and bLR. Several behavioral traits show high heritability, including the selection trait: exploratory locomotion (EL) in a novel environment. There were significant phenotypic and genetic correlations between tests that capture facets of EL and anxiety. There were also correlations with Pavlovian conditioned approach (PavCA) behavior despite the lower heritability of that trait. Ten significant and conditionally independent loci for six behavioral traits were identified. Five of the six traits reflect different facets of EL that were captured by three behavioral tests. Distance traveled measures from the open field and the elevated plus maze map onto different loci, thus may represent different aspects of novelty-induced locomotor activity. The sixth behavioral trait, number of fecal boli, is the only anxiety-related trait mapping to a significant locus on chromosome 18 within which the Pik3c3 gene is located. There were no significant loci for PavCA. We identified a missense variant in the Plekhf1 gene on the chromosome 1:95 Mb QTL and Fancf and Gas2 as potential candidate genes that may drive the chromosome 1:107 Mb QTL for EL traits. The identification of a locomotor activity-related QTL on chromosome 7 encompassing the Pkhd1l1 and Trhr genes is consistent with our previous finding of these genes being differentially expressed in the hippocampus of bHR vs. bLR rats. The strong heritability coupled with identification of several loci associated with exploratory locomotion and emotionality provide compelling support for this selectively bred rat model in discovering relatively large effect causal variants tied to elements of internalizing and externalizing behaviors inherent to psychiatric and substance use disorders.

The association between ST8SIA2 gene and behavioral phenotypes in children with autism spectrum disorder

Objective

ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 2 (ST8SIA2) encodes a type II membrane protein that is thought to catalyze the transfer of sialic acid (SA) from CMP-SA to N-linked oligosaccharides and glycoproteins. Some population and animal studies have indicated an association between the ST8SIA2 gene and autism spectrum disorder (ASD). However, there is limited information on the correlation between ST8SIA2 and autistic behavioral symptoms.

Methods

In this study, 69 ASD and 76 normal control children who were age- and sex-matched were recruited. ST8SIA2 expression and methylation levels were measured by reverse transcription quantitative real-time PCR and pyrosequencing, respectively, and the behavioral phenotypes of ASD children were assessed.

Results

The ASD group had lower ST8SIA2 gene expression levels than the control group [t(0.05/2,143) = 2.582, p = 0.011]. Moreover, ST8SIA2 expression levels were positively correlated with daily life skills (rs = 0.381, p = 0.008) and negatively associated with stereotyped behaviors in the ASD group (rs = -0.510, p = 0.004). The methylation levels of the Chr. 15: 92984625 and Chr. 15: 92998561 sites of the ST8SIA2 gene in ASD children were higher than those of controls. The Chr. 15: 92984625 site was positively correlated with the stereotyped behaviors of ASD children (rs = 0.41, p = 0.039).

Conclusion

This study provides a scientific basis to elucidate the relationship between the ST8SIA2 gene and behavioral phenotypes of ASD.

News and Views on Polysialic Acid: From Tumor Progression and Brain Development to Psychiatric Disorders, Neurodegeneration, Myelin Repair and Immunomodulation

Polysialic acid (polySia) is a sugar homopolymer consisting of at least eight glycosidically linked sialic acid units. It is a posttranslational modification of a limited number of proteins with the neural cell adhesion molecule NCAM being the most prominent. As extensively reviewed before, polySia-NCAM is crucial for brain development and synaptic plasticity but also modulates tumor growth and malignancy. Functions of polySia have been attributed to its polyanionic character, its spatial expansion into the extracellular space, and its modulation of NCAM interactions. In this mini-review, we first summarize briefly, how the modulation of NCAM functions by polySia impacts tumor cell growth and leads to malformations during brain development of polySia-deficient mice, with a focus on how the latter may be linked to altered behaviors in the mouse model and to neurodevelopmental predispositions to psychiatric disorders. We then elaborate on the implications of polySia functions in hippocampal plasticity, learning and memory of mice in light of recently described polySia changes related to altered neurogenesis in the aging human brain and in neurodegenerative disease. Furthermore, we highlight recent progress that extends the range of polySia functions across diverse fields of neurobiology such as cortical interneuron development and connectivity, myelination and myelin repair, or the regulation of microglia activity. We discuss possible common and distinct mechanisms that may underlie these seemingly divergent roles of polySia, and provide prospects for new therapeutic approaches building on our improved understanding of polySia functions.

Compromised mammillary body connectivity and psychotic symptoms in mice with di- and mesencephalic ablation of ST8SIA2

Altered long-range connectivity is a common finding across neurodevelopmental psychiatric disorders, but causes and consequences are not well understood. Genetic variation in ST8SIA2 has been associated with schizophrenia, autism, and bipolar disorder, and St8sia2^-/- mice show a number of related neurodevelopmental and behavioral phenotypes. In the present study, we use conditional knockout (cKO) to dissect neurodevelopmental defects and behavioral consequences of St8sia2 deficiency in cortical interneurons, their cortical environment, or in the di- and mesencephalon. Neither separate nor combined cortical and diencephalic ablation of St8sia2 caused the disturbed thalamus-cortex connectivity observed in St8sia2^-/- mice. However, cortical ablation reproduced hypoplasia of corpus callosum and fornix and mice with di- and mesencephalic ablation displayed smaller mammillary bodies with a prominent loss of parvalbumin-positive projection neurons and size reductions of the mammillothalamic tract. In addition, the mammillotegmental tract and the mammillary peduncle, forming the reciprocal connections between mammillary bodies and Gudden's tegmental nuclei, as well as the size of Gudden's ventral tegmental nucleus were affected. Only mice with these mammillary deficits displayed enhanced MK-801-induced locomotor activity, exacerbated impairment of prepulse inhibition in response to apomorphine, and hypoanxiety in the elevated plus maze. We therefore propose that compromised mammillary body connectivity, independent from hippocampal input, leads to these psychotic-like responses of St8sia2-deficient mice.

A schizophrenia subgroup with elevated inflammation displays reduced microglia, increased peripheral immune cell and altered neurogenesis marker gene expression in the subependymal zone

Inflammation regulates neurogenesis, and the brains of patients with schizophrenia and bipolar disorder have reduced expression of neurogenesis markers in the subependymal zone (SEZ), the birthplace of inhibitory interneurons. Inflammation is associated with cortical interneuron deficits, but the relationship between inflammation and reduced neurogenesis in schizophrenia and bipolar disorder remains unexplored. Therefore, we investigated inflammation in the SEZ by defining those with low and high levels of inflammation using cluster analysis of IL6, IL6R, IL1R1 and SERPINA3 gene expression in 32 controls, 32 schizophrenia and 29 bipolar disorder cases. We then determined whether mRNAs for markers of glia, immune cells and neurogenesis varied with inflammation. A significantly greater proportion of schizophrenia (37%) and bipolar disorder cases (32%) were in high inflammation subgroups compared to controls (10%, p < 0.05). Across the high inflammation subgroups of psychiatric disorders, mRNAs of markers for phagocytic microglia were reduced (P2RY12, P2RY13), while mRNAs of markers for perivascular macrophages (CD163), pro-inflammatory macrophages (CD64), monocytes (CD14), natural killer cells (FCGR3A) and adhesion molecules (ICAM1) were increased. Specific to high inflammation schizophrenia, quiescent stem cell marker mRNA (GFAPD) was reduced, whereas neuronal progenitor (ASCL1) and immature neuron marker mRNAs (DCX) were decreased compared to low inflammation control and schizophrenia subgroups. Thus, a heightened state of inflammation may dampen microglial response and recruit peripheral immune cells in psychiatric disorders. The findings elucidate differential neurogenic responses to inflammation within psychiatric disorders and highlight that inflammation may impair neuronal differentiation in the SEZ in schizophrenia.

The Hidden Side of NCAM Family: NCAM2, a Key Cytoskeleton Organization Molecule Regulating Multiple Neural Functions

Although it has been over 20 years since Neural Cell Adhesion Molecule 2 (NCAM2) was identified as the second member of the NCAM family with a high expression in the nervous system, the knowledge of NCAM2 is still eclipsed by NCAM1. The first studies with NCAM2 focused on the olfactory bulb, where this protein has a key role in axonal projection and axonal/dendritic compartmentalization. In contrast to NCAM1, NCAM2's functions and partners in the brain during development and adulthood have remained largely unknown until not long ago. Recent studies have revealed the importance of NCAM2 in nervous system development. NCAM2 governs neuronal morphogenesis and axodendritic architecture, and controls important neuron-specific processes such as neuronal differentiation, synaptogenesis and memory formation. In the adult brain, NCAM2 is highly expressed in dendritic spines, and it regulates synaptic plasticity and learning processes. NCAM2's functions are related to its ability to adapt to the external inputs of the cell and to modify the cytoskeleton accordingly. Different studies show that NCAM2 interacts with proteins involved in cytoskeleton stability and proteins that regulate calcium influx, which could also modify the cytoskeleton. In this review, we examine the evidence that points to NCAM2 as a crucial cytoskeleton regulation protein during brain development and adulthood. This key function of NCAM2 may offer promising new therapeutic approaches for the treatment of neurodevelopmental diseases and neurodegenerative disorders.

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.

Post-translational protein modifications in schizophrenia

Research investigating the pathophysiology of schizophrenia has not yet precisely defined the molecular phenotype of this disorder. Many studies have investigated cellular dysfunction by examining expression levels of molecular targets in postmortem patient brain; however, inconsistencies between transcript and protein measures in schizophrenia are common in the field and represent a challenge to the identification of a unified model of schizophrenia pathogenesis. In humans, >4800 unique proteins are expressed, and the majority of these are modified by glycans and/or lipids. Estimates indicate ~70% of all eukaryotic proteins are modified by at least one type of glycosylation, while nearly 20% of all proteins are known to be lipid-modified. Protein post-translational modification (PTM) by glycosylation and lipidation rely on the spatiotemporal colocalization of enzyme, substrate, and glycan or lipid donor molecule and do not require an upstream “blueprint” or specialized processing machinery for synthesis. Glycan and lipid PTMs can thus facilitate cellular adaptation to environmental signals more rapidly than changes of gene or protein expression, and can significantly impact the localization, function, and interactions of modified substrates, though relatively few studies in schizophrenia have evaluated the PTM status of target proteins. A growing body of literature reports glycosylation and lipidation abnormalities in schizophrenia brain as well as in patient peripheral fluids. In this review, we explain the functional significance of key glycan and lipid PTMs and summarize current findings associated with abnormal glycosylation and lipidation in this illness.

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.

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.

Differential effect of disease-associated ST8SIA2 haplotype on cerebral white matter diffusion properties in schizophrenia and healthy controls

Brain white matter abnormalities are evident in individuals with schizophrenia, and also their first-degree relatives, suggesting that some alterations may relate to underlying genetic risk. The ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 2 (ST8SIA2) gene, which encodes the alpha-2,8-sialyltransferase 8B enzyme that aids neuronal migration and synaptic plasticity, was previously implicated as a schizophrenia susceptibility gene. This study examined the extent to which specific haplotypes in ST8SIA2 influence white matter microstructure using diffusion-weighted imaging of individuals with schizophrenia (n = 281) and healthy controls (n = 172), recruited across five Australian sites. Interactions between diagnostic status and the number of haplotype copies (0 or ≥1) were tested across all white matter voxels with cluster-based statistics. Fractional anisotropy (FA) in the right parietal lobe was found to show a significant interaction between diagnosis and ST8SIA2 protective haplotype (p < 0.05, family-wise error rate (FWER) cluster-corrected). The protective haplotype was associated with increased FA in controls, but this effect was reversed in people with schizophrenia. White matter fiber tracking revealed that the region-of-interest was traversed by portions of the superior longitudinal fasciculus, corona radiata, and posterior limb of internal capsule. Post hoc analysis revealed that reduced FA in this regional juncture correlated with reduced IQ in people with schizophrenia. The ST8SIA2 risk haplotype copy number did not show any differential effects on white matter. This study provides a link between a common disease-associated haplotype and specific changes in white matter microstructure, which may relate to resilience or risk for mental illness, providing further compelling evidence for involvement of ST8SIA2 in the pathophysiology of schizophrenia.

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.

In vitro Multi-Species Biofilms of Methicillin-Resistant Staphylococcus aureus and Pseudomonas aeruginosa and Their Host Interaction during In vivo Colonization of an Otitis Media Rat Model

Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) are known to cause biofilm-related infections. MRSA and PA have been frequently isolated from chronically infected wounds, cystic fibrosis, chronic suppurative otitis media (CSOM), and from indwelling medical devices, and these bacteria co-exist; however, their interaction with each-other or with the host is not well known. In this study, we investigated MRSA and PA multi-species biofilm communities in vitro and their interaction with the host during in vivo colonization using an OM rat-model. In-vitro biofilm formation and in-vivo colonization were studied using CV-microtiter plate assay and OM rat-model respectively. The biofilms were viewed under scanning electron microscope and bacteria were enumerated using cfu counts. The differential gene expressions of rat mucosa colonized with single or multi-species of MRSA or PA were studied using RNA-sequencing of total transcriptome. In multi-species in-vitro biofilms PA partially inhibited SA growth. However, no significant inhibition of MRSA was detected during in-vivo colonization of multi-species in rat bullae. A total of 1,797 genes were significantly (p < 0.05) differentially expressed in MRSA or PA or MRSA + PA colonized rat middle ear mucosa with respect to the control. The poly-microbial colonization of MRSA and PA induced the differential expression of a significant number of genes that are involved in immune response, inflammation, signaling, development, and defense; these were not expressed with single species colonization by either MRSA or PA. Genes involved in defense, immune response, inflammatory response, and developmental process were exclusively up-regulated, and genes that are involved in nervous system signaling, development and transmission, regulation of cell growth and development, anatomical and system development, and cell differentiation were down-regulated after multi-species inoculation. These results indicate that poly-microbial colonization induces a host response that is different from that induced by single species infection.

Neural Cell Adhesion Molecules of the Immunoglobulin Superfamily Regulate Synapse Formation, Maintenance, and Function

Immunoglobulin superfamily adhesion molecules are among the most abundant proteins in vertebrate and invertebrate nervous systems. Prominent family members are the neural cell adhesion molecules NCAM and L1, which were the first to be shown to be essential not only in development but also in synaptic function and as key regulators of synapse formation, synaptic activity, plasticity, and synaptic vesicle recycling at distinct developmental and activity stages. In addition to interacting with each other, adhesion molecules interact with ion channels and cytokine and neurotransmitter receptors. Mutations in their genes are linked to neurological disorders associated with abnormal development and synaptic functioning. This review presents an overview of recent studies on these molecules and their crucial impact on neurological disorders.

Physiological Exploration of the Long Term Evolutionary Selection against Expression of N-Glycolylneuraminic Acid in the Brain

All vertebrate cell surfaces display a dense glycan layer often terminated with sialic acids, which have multiple functions due to their location and diverse modifications. The major sialic acids in most mammalian tissues are N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), the latter being derived from Neu5Ac via addition of one oxygen atom at the sugar nucleotide level by CMP-Neu5Ac hydroxylase (Cmah). Contrasting with other organs that express various ratios of Neu5Ac and Neu5Gc depending on the variable expression of Cmah, Neu5Gc expression in the brain is extremely low in all vertebrates studied to date, suggesting that neural expression is detrimental to animals. However, physiological exploration of the reasons for this long term evolutionary selection has been lacking. To explore the consequences of forced expression of Neu5Gc in the brain, we have established brain-specific Cmah transgenic mice. Such Neu5Gc overexpression in the brain resulted in abnormal locomotor activity, impaired object recognition memory, and abnormal axon myelination. Brain-specific Cmah transgenic mice were also lethally sensitive to a Neu5Gc-preferring bacterial toxin, even though Neu5Gc was overexpressed only in the brain and other organs maintained endogenous Neu5Gc expression, as in wild-type mice. Therefore, the unusually strict evolutionary suppression of Neu5Gc expression in the vertebrate brain may be explained by evasion of negative effects on neural functions and by selection against pathogens.

Modeling disease risk through analysis of physical interactions between genetic variants within chromatin regulatory circuitry

SNPs associated with disease susceptibility often reside in enhancer clusters, or super-enhancers. Constituents of these enhancer clusters cooperate to regulate target genes and often extend beyond the linkage disequilibrium (LD) blocks containing risk SNPs identified in genome-wide association studies (GWAS). We identified 'outside variants', defined as SNPs in weak LD with GWAS risk SNPs that physically interact with risk SNPs as part of a target gene's regulatory circuitry. These outside variants further explain variation in target gene expression beyond that explained by GWAS-associated SNPs. Additionally, the clinical risk associated with GWAS SNPs is considerably modified by the genotype of outside variants. Collectively, these findings suggest a potential model in which outside variants and GWAS SNPs that physically interact in 3D chromatin collude to influence target transcript levels as well as clinical risk. This model offers an additional hypothesis for the source of missing heritability for complex traits.

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

Polysialic acid (polySia, PSA) is a unique and functionally important glycan, particularly in vertebrate brains. It is involved in higher brain functions such as learning, memory, and social behaviors. Recently, an association between several genetic variations and single nucleotide polymorphisms (SNPs) of ST8SIA2/STX, one of two polysialyltransferase genes in vertebrates, and psychiatric disorders, such as schizophrenia (SZ), bipolar disorder (BD), and autism spectrum disorder (ASD), was reported based on candidate gene approaches and genome-wide studies among normal and mental disorder patients. It is of critical importance to determine if the reported mutations and SNPs in ST8SIA2 lead to impairments of the structure and function of polySia, which is the final product of ST8SIA2. To date, however, only a few such forward-directed studies have been conducted. In addition, the molecular mechanisms underlying polySia-involved brain functions remain unknown, although polySia was shown to have an anti-adhesive effect. In this report, we review the relationships between psychiatric disorders and polySia and/or ST8SIA2, and describe a new function of polySia as a regulator of neurologically active molecules, such as brain-derived neurotrophic factor (BDNF) and dopamine, which are deeply involved in psychiatric disorders. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

Association between ST8SIA2 and the Risk of Schizophrenia and Bipolar I Disorder across Diagnostic Boundaries

Background

Findings from family studies and recent genome-wide association studies have indicated overlap in the risk genes between schizophrenia and bipolar disorder (BD). After finding a linkage between the ST8SIA2 (ST8 alpha-N-acetyl-neuraminide alpha-2, 8-sicalyltransferase 2 gene) locus (15q26) and mixed families with schizophrenia and BD, several studies have reported a significant association between this gene and schizophrenia or BD. We investigated the genetic association between ST8SIA2 and both schizophrenia and BD in the Korean population.

Methods

A total of 582 patients with schizophrenia, 339 patients with BD, and 502 healthy controls were included. Thirty-one tag single nucleotide polymorphisms (SNPs) across the ST8SIA2 region and three other SNPs showing significant associations in previous studies were genotyped. The associations were evaluated by logistic regression analysis using additive, dominant, and recessive genetic models.

Results

Fourteen of 34 SNPs showed a nominally significant association (p < 0.05) with at least one diagnostic group. These association trends were strongest for the schizophrenia and combined schizophrenia and bipolar I disorder (BD-I) groups. The strongest association was observed in rs11637898 for schizophrenia (p = 0.0033) and BD-I (p = 0.0050) under the dominant model. The association between rs11637898 and the combined schizophrenia and BD-I group (p = 0.0006, under the dominant model) remained significant after correcting for multiple testing.

Discussion

We identified a possible role of ST8SIA2 in the common susceptibility of schizophrenia and BD-I. However, no association trend was observed for bipolar II disorder. Further efforts are needed to identify a specific phenotype associated with this gene crossing the current diagnostic categories.

Polysialic acid: biosynthesis, novel functions and applications

As an anti-adhesive, a reservoir for key biological molecules, and a modulator of signaling, polysialic acid (polySia) is critical for nervous system development and maintenance, promotes cancer metastasis, tissue regeneration and repair, and is implicated in psychiatric diseases. In this review, we focus on the biosynthesis and functions of mammalian polySia, and the use of polySia in therapeutic applications. PolySia modifies a small subset of mammalian glycoproteins, with the neural cell adhesion molecule, NCAM, serving as its major carrier. Studies show that mammalian polysialyltransferases employ a unique recognition mechanism to limit the addition of polySia to a select group of proteins. PolySia has long been considered an anti-adhesive molecule, and its impact on cell adhesion and signaling attributed directly to this property. However, recent studies have shown that polySia specifically binds neurotrophins, growth factors, and neurotransmitters and that this binding depends on chain length. This work highlights the importance of considering polySia quality and quantity, and not simply its presence or absence, as its various roles are explored. The capsular polySia of neuroinvasive bacteria allows these organisms to evade the host immune response. While this "stealth" characteristic has made meningitis vaccine development difficult, it has also made polySia a worthy replacement for polyetheylene glycol in the generation of therapeutic proteins with low immunogenicity and improved circulating half-lives. Bacterial polysialyltransferases are more promiscuous than the protein-specific mammalian enzymes, and new studies suggest that these enzymes have tremendous therapeutic potential, especially for strategies aimed at neural regeneration and tissue repair.

Genetics of psychotropic medication induced side effects in two independent samples of bipolar patients

The treatment of bipolar disorder (BD) usually requires combination therapies, with the critical issue of the emergence of adverse drug reactions (ADRs) and the possibility of low treatment adherence. Genetic polymorphisms are hypothesized to modulate the pharmacodynamics of psychotropic drugs, representing potential biological markers of ADRs. This study investigated genes involved in the regulation of neuroplasticity (BDNF, ST8SIA2), second messenger cascades (GSK3B, MAPK1, and CREB1), circadian rhythms (RORA), transcription (SP4, ZNF804A), and monoaminergic system (HTR2A and COMT) in the risk of neurological, psychic, autonomic, and other ADRs. Two independent samples of BD patients naturalistically treated were included (COPE-BD n = 147; STEP-BD n = 659). In the COPE-BD 34 SNPs were genotyped, while in the STEP-BD polymorphisms in the selected genes were extracted from the genome-wide dataset. Each ADRs group was categorized as absent-mild or moderate-severe and logistic regression with appropriate covariates was applied to identify possible risk genotypes/alleles. 58.5 and 93.5 % of patients were treated with mood stabilizers, 44.2 and 50.7 % were treated with antipsychotics, and 69.4 and 46.1 % were treated with antidepressants in the COPE-BD and STEP-BD, respectively. Our findings suggested that ST8SIA2 may be associated with psychic ADRs, as shown in the COPE-BD (rs4777989 p = 0.0017) and STEP-BD (rs56027313, rs13379489 and rs10852173). A cluster of RORA SNPs around rs2083074 showed an effect on psychic ADRs in the STEP-BD. Trends supporting the association between HTR2A and autonomic ADRs were found in both samples. Confirmations are needed particularly for ST8SIA2 and RORA since the few available data regarding their role in relation to psychotropic ADRs.