Brain structure, cognition and negative symptoms in schizophrenia are associated with serum levels of polysialic acid-modified NCAM

Secondary deficiency of neuraminidase 1 contributes to CNS pathology in neurological mucopolysaccharidoses via hypersialylation of brain glycoproteins

Mucopolysaccharidoses (MPS) are lysosomal storage diseases caused by defects in catabolism of glycosaminoglycans. MPS I, II, III and VII are associated with lysosomal accumulation of heparan sulphate and manifest with neurological deterioration. Most of these neurological MPS currently lack effective treatments. Here, we report that, compared to controls, neuraminidase 1 (NEU1) activity is drastically reduced in brain tissues of neurological MPS patients and in mouse models of MPS I, II, IIIA, IIIB and IIIC, but not of other neurological lysosomal disorders not presenting with heparan sulphate storage. We further show that accumulated heparan sulphate disrupts the lysosomal multienzyme complex of NEU1 with cathepsin A (CTSA), β-galactosidase (GLB1) and glucosamine-6-sulfate sulfatase (GALNS) necessary to maintain enzyme activity, and that NEU1 deficiency is linked to partial deficiencies of GLB1 and GALNS in cortical tissues and iPSC-derived cortical neurons of neurological MPS patients. Increased sialylation of N-linked glycans in brain samples of human MPS III patients and MPS IIIC mice implicated insufficient processing of brain N-linked sialylated glycans, except for polysialic acid, which was reduced in the brains of MPS IIIC mice. Correction of NEU1 activity in MPS IIIC mice by lentiviral gene transfer ameliorated previously identified hallmarks of the disease, including memory impairment, behavioural traits, and reduced levels of the excitatory synapse markers VGLUT1 and PSD95. Overexpression of NEU1 also restored levels of VGLUT1-/PSD95-positive puncta in cortical neurons derived from iPSC of an MPS IIIA patient. Together, our data demonstrate that heparan sulphate-induced secondary NEU1 deficiency and aberrant sialylation of glycoproteins implicated in synaptogenesis, memory, and behaviour constitute a novel pathological pathway in neurological MPS spectrum crucially contributing to CNS pathology.

Graphical abstract

Site-specific immobilization of the endosialidase reveals QSOX2 is a novel polysialylated protein

Polysialic acid (polySia) is a linear polymer of α2,8-linked sialic acid residues that is of fundamental biological interest due to its pivotal roles in the regulation of the nervous, immune, and reproductive systems in healthy human adults. PolySia is also dysregulated in several chronic diseases, including cancers and mental health disorders. However, the mechanisms underpinning polySia biology in health and disease remain largely unknown. The polySia-specific hydrolase, endoneuraminidase NF (EndoN), and the catalytically inactive polySia lectin EndoNDM, have been extensively used for studying polySia. However, EndoN is heat stable and remains associated with cells after washing. When studying polySia in systems with multiple polysialylated species, the residual EndoN that cannot be removed confounds data interpretation. We developed a strategy for site-specific immobilization of EndoN on streptavidin-coated magnetic beads. We showed that immobilizing EndoN allows for effective removal of the enzyme from samples, while retaining hydrolase activity. We used the same strategy to immobilize the polySia lectin EndoNDM, which enabled the enrichment of polysialylated proteins from complex mixtures such as serum for their identification via mass spectrometry. We used this methodology to identify a novel polysialylated protein, QSOX2, which is secreted from the breast cancer cell line MCF-7. This method of site-specific immobilization can be utilized for other enzymes and lectins to yield insight into glycobiology.

The pathophysiological role of circulating adhesion molecules in schizophrenia: A systematic review and meta-analysis

BACKGROUND

Increasing evidence suggests an association between schizophrenia and atherosclerosis. We conducted a systematic review and meta-analysis of cell adhesion molecules, critically involved in early atherosclerosis, in schizophrenia.

METHODS

We searched electronic databases from inception to 11 November 2023 for case-control studies assessing vascular cell, VCAM-1, intercellular, ICAM-1, platelet endothelial cell, PECAM-1, neural cell, NCAM, and Down syndrome cell, DSCAM, adhesion molecules, selectins (E-, L-, and P-selectin), integrins, and cadherins in patients with schizophrenia and healthy controls. Risk of bias and certainty of evidence were assessed using the JBI checklist and GRADE, respectively.

RESULTS

In 19 eligible studies, there were non-significant between-group differences in the concentrations of cell adhesion molecules, barring higher P-selectin in patients with schizophrenia (standard mean difference, SMD = 2.05, 95 % CI 0.72 to 3.38, p = 0.003; I2 = 97.2 %, p<0.001; very low certainty of evidence). Limited or no information was available regarding PECAM-1, DSCAM, ESAM, integrins, and cadherins. In meta-regression and subgroup analysis, there were significant associations between the SMD of ICAM-1 and matrix used (plasma or serum) and pharmacological treatment of schizophrenia, and between the SMD of VCAM-1 and pharmacological treatment, but not with other study and patient characteristics.

CONCLUSIONS

The results of our systematic review and meta-analysis do not support a significant role of immunoglobulin-like adhesion molecules, selectins, integrins, or cadherins in mediating the associations between schizophrenia, atherosclerosis, and cardiovascular disease. Further studies are warranted to investigate these associations in patients with different cardiovascular risk and the effects of antipsychotic treatments on cell adhesion molecules and surrogate markers of atherosclerosis (PROSPERO registration number: CRD42023463916).

Physicochemical Principles of Adhesion Mechanisms in the Brain

The brain functions through neuronal circuits and networks that are synaptically connected. This type of connection can exist due to physical forces that interact to stabilize local contacts in the brain. Adhesion is a fundamental physical phenomenon that allows different layers, phases, and tissues to connect. Similarly, synaptic connections are stabilized by specialized adhesion proteins. This review discusses the basic physical and chemical properties of adhesion. Cell adhesion molecules (CAMs) such as cadherins, integrins, selectins, and immunoglobulin family of cell adhesion molecules (IgSF) will be discussed, and their role in physiological and pathological brain function. Finally, the role of CAMs at the synapse will be described. In addition, methods for studying adhesion in the brain will be presented.

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.

Ubiquitous Neural Cell Adhesion Molecule (NCAM): Potential Mechanism and Valorisation in Cancer Pathophysiology, Drug Targeting and Molecular Transductions

Neural cell adhesion molecule, an integrated molecule of immunoglobulin protein superfamily involved in cell-cell adhesion, undergoes various structural modifications through numerous temporal-spatial regulations that generously alter their expressions on cell surfaces. These varied expression patterns are mostly envisioned in the morphogenesis and innervations of different human organs and systems. The considerable role of NCAM in neurite growth, brain development and etc. and its altered expression of NCAM in proliferating tumour cells and metastasis of various human melanomas clearly substantiate its appropriateness as a cell surface marker for diagnosis and potential target for several therapeutic moieties. This characteristic behaviour of NCAM is confined to its novel biochemistry, structural properties, signalling interactions and polysialylation. In particular, the characteristic expressions of NCAM are mainly attributed by its polysialylation, a post-translational modification that attaches polysialyl groups to the NCAM. The altered expression of NCAM on cell surface develops curiosity amidst pharmaceutical scientists, which drives them to understand its role of such expressions in various human melanomas and to elucidate the promising therapeutic strategies that are currently available to target NCAM appositely. Therefore, this review article is articulated with an insight on the altered expressions of NCAM, the clinical significances and the consequences of such atypical expression patterns in various human organs and systems.

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.

Genome-wide identification of the shared genetic basis of cannabis and cigarette smoking and schizophrenia implicates NCAM1 and neuronal abnormality

OBJECTIVES

Confirming the existence and composition of the shared genetic basis of Schizophrenia and cannabis and cigarette smoking has critical values for the clinical prevention and intervention of psychosis.

METHODS

To achieve this goal, we leveraged Genome-Wide summary statistics of Schizophrenia (n = 99,934), cigarette smoking (n = 518,633) and cannabis usage (n = 162,082). We applied Causal Analysis Using Summary Effect Estimates (CAUSE) and genomic structural equation modeling (GenomicSEM) to quantify the contribution of a common genetic factor of cannabis and cigarette smoking and schizophrenia (referred to as SCZ_SMO), then identified genome-wide loci that made up SCZ_SMO.

RESULTS

We estimated that SCZ_SMO explained 8.6% of Schizophrenia heritability (Z score <-2.5 in CAUSE, p<10^-20 in Genomic SEM). There were 20 independent loci showing association with SCZ_SMO at the genome-wide threshold of p<5 × 10^-8. At the top locus on chromosome 11, fine-mapping identified rs7945073 (posterior inclusion probability =0.12, p = 2.24 × 10^-32) as the top risk variants. Gene-level association and fine-mapping highlighted NCAM1, PHC2, and SEMA6D as risk genes of SCZ_SMO. Other risk genes were enriched in cortex, neuron, and dendritic spines (adjusted p<0.05). SCZ_SMO showed significant positive correlation (p<10^-6) with the genetic risk of attention deficit hyperactivity disorder (r = 0.50), lifestyle problems (r = 0.83), social deprivation (r = 0.58) and all-cause pregnant loss (r = 0.60).

CONCLUSION

Our result provided new evidence on the shared genetic basis model for the association between Schizophrenia and smoking and provided genetic and biological insights into their shared mechanism.

New Insights Regarding Diagnosis and Medication for Schizophrenia Based on Neuronal Synapse-Microglia Interaction

Schizophrenia is a common psychiatric disorder that usually develops during adolescence and young adulthood. Since genetic and environmental factors are involved in the disease, the molecular status of the pathology of schizophrenia differs across patients. Recent genetic studies have focused on the association between schizophrenia and the immune system, especially microglia–synapse interactions. Microglia physiologically eliminate unnecessary synapses during the developmental period. The overactivation of synaptic pruning by microglia is involved in the pathology of brain disease. This paper focuses on the synaptic pruning function and its molecular machinery and introduces the hypothesis that excessive synaptic pruning plays a role in the development of schizophrenia. Finally, we suggest a strategy for diagnosis and medication based on modulation of the interaction between microglia and synapses. This review provides updated information on the involvement of the immune system in schizophrenia and proposes novel insights regarding diagnostic and therapeutic strategies for this disease.

Hyperfunction of the stress response system and novelty-induced hyperactivity correlate with enhanced cocaine-induced conditioned place preference in NCAM-deficient mice

Several studies in humans and rodents suggest an association between impulsivity and activity of the stress response on the one hand and addiction vulnerability on the other. The neural cell adhesion molecule (NCAM) has been related to several neuropsychiatric disorders in humans. Constitutively NCAM-deficient (-/-) mice display enhanced novelty-induced behavior and hyperfunction of the hypothalamic-pituitary-adrenal axis. Here we hypothesize that NCAM deficiency causes an altered response to cocaine. Cocaine-induced behaviors of NCAM-/- mice and wild-type (+/+) littermates were analyzed in the conditioned place preference (CPP) test. c-fos mRNA levels were investigated by quantitative polymerase chain reaction (qPCR) to measure neural activation after exposure to the cocaine-associated context. NCAM-/- mice showed an elevated cocaine-induced sensitization, enhanced CPP, impaired extinction, and potentiated cocaine-induced hyperlocomotion and CPP after extinction. NCAM-/- showed no potentiated CPP as compared with NCAM+/+ littermates when a natural rewarding stimulus (ie, an unfamiliar female) was used, suggesting that the behavioral alterations of NCAM-/- mice observed in the CPP test are specific to the effects of cocaine. Activation of the prefrontal cortex and nucleus accumbens induced by the cocaine-associated context was enhanced in NCAM-/- compared with NCAM+/+ mice. Finally, cocaine-induced behavior correlated positively with novelty-induced behavior and plasma corticosterone levels in NCAM-/- mice and negatively with NCAM mRNA levels in the hippocampus and nucleus accumbens in wild-type mice. Our findings indicate that NCAM deficiency affects cocaine-induced CPP in mice and support the view that hyperfunction of the stress response system and reactivity to novelty predict the behavioral responses to cocaine.

Decreased serum NCAM is positively correlated with hippocampal volumes and negatively correlated with positive symptoms in first-episode schizophrenia patients

BACKGROUND

Neural cell adhesion molecule (NCAM) plays an important role in neurodevelopmental processes and regulates hippocampal plasticity. This study investigated the relationship between the serum NCAM concentrations and hippocampal volume and psychotic symptoms in first-episode drug naïve schizophrenia (FES) patients.

METHODS

Forty-four FES patients and forty-four healthy controls (HC) were recruited in this study. Serum concentrations of NCAM were measured by ELISA. Psychiatric symptoms were assessed by the positive and negative syndrome scale (PANSS). Brain structural images were obtained using a 3T MRI Scanner and obtained T1 images were processed in order to determine hippocampal grey matter volumes.

RESULTS

Schizophrenia patients revealed significantly decreased serum NCAM concentrations (p = 0.017), which were positively correlated with the left (r = 0.523, p < 0.001) and right (r = 0.449, p = 0.041) hippocampal volumes, but negatively correlated with the PANSS positive symptom scores (r = -0.522 p = 0.001). However, no such correlations existed in the HC group.

CONCLUSIONS

This is the first time to report that decreased serum NCAM concentrations were associated with hippocampal volumes and symptom severity in FES patients. Our data indicate that the low NCAM is possible neuropathology that is associated with the decreased hippocampus in FES patients.

Neurocan genome-wide psychiatric risk variant affects explicit memory performance and hippocampal function in healthy humans

Alterations of the brain extracellular matrix (ECM) can perturb the structure and function of brain networks like the hippocampus, a key region in human memory that is commonly affected in psychiatric disorders. Here, we investigated the potential effects of a genome-wide psychiatric risk variant in the NCAN gene encoding the ECM proteoglycan neurocan (rs1064395) on memory performance, hippocampal function and cortical morphology in young, healthy volunteers. We assessed verbal memory performance in two cohorts (N = 572, 302) and found reduced recall performance in risk allele (A) carriers across both cohorts. In 117 participants, we performed functional magnetic resonance imaging using a novelty-encoding task with visual scenes. Risk allele carriers showed higher false alarm rates during recognition, accompanied by inefficiently increased left hippocampal activation. To assess effects of rs1064395 on brain morphology, we performed voxel-based morphometry in 420 participants from four independent cohorts and found lower grey matter density in the ventrolateral and rostral prefrontal cortex of risk allele carriers. In silico eQTL analysis revealed that rs1064395 SNP is linked not only to increased prefrontal expression of the NCAN gene itself, but also of the neighbouring HAPLN4 gene, suggesting a more complex effect of the SNP on ECM composition. Our results suggest that the NCAN rs1064395 A allele is associated with lower hippocampus-dependent memory function, variation of prefrontal cortex structure and ECM composition. Considering the well-documented hippocampal and prefrontal dysfunction in bipolar disorder and schizophrenia, our results may reflect an intermediate phenotype by which NCAN rs1064395 contributes to disease risk.

Recent advances in the analysis of polysialic acid from complex biological systems

Polysialic acid (polySia) is a unique, well-characterised carbohydrate polymer highly-expressed on the cell surface of neurons in the early stages of mammalian brain development. Post-embryogenesis, it is also re-expressed in a number of tumours of neuroendocrine origin. It plays important roles in modulating cell-cell, and cell-matrix adhesion and migration, tumour invasion and metastasis. Techniques for structural and quantitative characterisation of polySia from tumours and cancer cells are thus essential in exploring the relationship between polySia expression levels and structural and functional changes associated with cancer progression and metastasis. A variety of techniques have been developed to structurally and quantitatively analyse polySia in clinical tissues and other biological samples. In this review, analytical approaches used for the determination of polySia in biological matrices in the past 20 years are discussed, with a particular focus on chemical approaches, and quantitative analysis.

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.

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.

Polysialic Acid in Human Plasma Can Compensate the Cytotoxicity of Histones

The innate immune system has numerous mechanisms to fight against pathogens, including the formation of neutrophil extracellular traps (NETs). By spreading out chromatin, antimicrobial peptides and enzymes, neutrophils efficiently trap pathogens like bacteria and facilitate their elimination. During this process, high concentrations of extracellular histones can be reached. Several researchers have demonstrated that the cytotoxic characteristics of these histones can trigger diseases like sepsis. Interestingly, the carbohydrate polysialic acid (polySia) can bind histones and reduce histone-mediated cytotoxicity in a chain length-dependent manner. In the present study, we examined the chain length of polySia in plasma and tested its ability to decrease the cytotoxic characteristics of extracellular histones. Remarkably, we detected polySia not only in the soluble fraction of plasma, but also on enriched extracellular vesicles (EVs). Chain length analysis revealed that polySia chains originating from human plasma can consists of more than 40 sialic acid residues and show a cytoprotective effect against extracellular histones. Intriguingly, polySia is not only present in human plasma but also in fish and other branches of vertebrates. Thus, polySia is a physiological element in plasma and may represent a natural buffer for extracellular histones.

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.

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.

Exome sequences of multiplex, multigenerational families reveal schizophrenia risk loci with potential implications for neurocognitive performance

Schizophrenia is a serious mental illness, involving disruptions in thought and behavior, with a worldwide prevalence of about one percent. Although highly heritable, much of the genetic liability of schizophrenia is yet to be explained. We searched for susceptibility loci in multiplex, multigenerational families affected by schizophrenia, targeting protein-altering variation with in silico predicted functional effects. Exome sequencing was performed on 136 samples from eight European-American families, including 23 individuals diagnosed with schizophrenia or schizoaffective disorder. In total, 11,878 non-synonymous variants from 6,396 genes were tested for their association with schizophrenia spectrum disorders. Pathway enrichment analyses were conducted on gene-based test results, protein-protein interaction (PPI) networks, and epistatic effects. Using a significance threshold of FDR < 0.1, association was detected for rs10941112 (p = 2.1 × 10-5 ; q-value = 0.073) in AMACR, a gene involved in fatty acid metabolism and previously implicated in schizophrenia, with significant cis effects on gene expression (p = 5.5 × 10-4 ), including brain tissue data from the Genotype-Tissue Expression project (minimum p = 6.0 × 10-5 ). A second SNP, rs10378 located in TMEM176A, also shows risk effects in the exome data (p = 2.8 × 10-5 ; q-value = 0.073). PPIs among our top gene-based association results (p < 0.05; n = 359 genes) reveal significant enrichment of genes involved in NCAM-mediated neurite outgrowth (p = 3.0 × 10-5 ), while exome-wide SNP-SNP interaction effects for rs10941112 and rs10378 indicate a potential role for kinase-mediated signaling involved in memory and learning. In conclusion, these association results implicate AMACR and TMEM176A in schizophrenia risk, whose effects may be modulated by genes involved in synaptic plasticity and neurocognitive performance.

Specialized Information Processing Deficits and Distinct Metabolomic Profiles Following TM-Domain Disruption of Nrg1

Although there is considerable genetic and pathologic evidence for an association between neuregulin 1 (NRG1) dysregulation and schizophrenia, the underlying molecular and cellular mechanisms remain unclear. Mutant mice containing disruption of the transmembrane (TM) domain of the NRG1 gene constitute a heuristic model for dysregulation of NRG1-ErbB4 signaling in schizophrenia. The present study focused on hitherto uncharacterized information processing phenotypes in this mutant line. Using a mass spectrometry-based metabolomics approach, we also quantified levels of unique metabolites in brain. Across 2 different sites and protocols, Nrg1 mutants demonstrated deficits in prepulse inhibition, a measure of sensorimotor gating, that is, disrupted in schizophrenia; these deficits were partially reversed by acute treatment with second, but not first-, generation antipsychotic drugs. However, Nrg1 mutants did not show a specific deficit in latent inhibition, a measure of selective attention that is also disrupted in schizophrenia. In contrast, in a "what-where-when" object recognition memory task, Nrg1 mutants displayed sex-specific (males only) disruption of "what-when" performance, indicative of impaired temporal aspects of episodic memory. Differential metabolomic profiling revealed that these behavioral phenotypes were accompanied, most prominently, by alterations in lipid metabolism pathways. This study is the first to associate these novel physiological mechanisms, previously independently identified as being abnormal in schizophrenia, with disruption of NRG1 function. These data suggest novel mechanisms by which compromised neuregulin function from birth might lead to schizophrenia-relevant behavioral changes in adulthood.

Genetic Basis of Positive and Negative Symptom Domains in Schizophrenia

Schizophrenia is a highly heritable disorder, the genetic etiology of which has been well established. Yet despite significant advances in genetics research, the pathophysiological mechanisms of this disorder largely remain unknown. This gap has been attributed to the complexity of the polygenic disorder, which has a heterogeneous clinical profile. Examining the genetic basis of schizophrenia subphenotypes, such as those based on particular symptoms, is thus a useful strategy for decoding the underlying mechanisms. This review of literature examines the recent advances (from 2011) in genetic exploration of positive and negative symptoms in schizophrenia. We searched electronic databases PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature using key words schizophrenia, symptoms, positive symptoms, negative symptoms, cognition, genetics, genes, genetic predisposition, and genotype in various combinations. We identified 115 articles, which are included in the review. Evidence from these studies, most of which are genetic association studies, identifies shared and unique gene associations for the symptom domains. Genes associated with neurotransmitter systems and neuronal development/maintenance primarily constitute the shared associations. Needed are studies that examine the genetic basis of specific symptoms within the broader domains in addition to functional mechanisms. Such investigations are critical to developing precision treatment and care for individuals afflicted with schizophrenia.

Cerebrospinal fluid neural cell adhesion molecule levels and their correlation with clinical variables in patients with schizophrenia, bipolar disorder, and major depressive disorder

PURPOSE

Neural cell adhesion molecule (NCAM) plays an important role in neural plasticity, and its altered function has been implicated in psychiatric disorders. However, previous studies have yielded inconsistent results on cerebrospinal fluid (CSF) NCAM levels in psychiatric disorders. The aim of our study was to examine CSF NCAM levels in patients with schizophrenia, bipolar disorder (BD), and major depressive disorder (MDD), and their possible relationship with clinical variables.

METHODS

The participants comprised 85 patients with schizophrenia, 57 patients with BD, 83 patients with MDD and 111 healthy controls, all matched for age, sex, and Japanese ethnicity. The CSF samples were drawn using a lumbar puncture and NCAM levels were quantified by an enzyme-linked immunosorbent assay.

RESULTS

Analysis of covariance controlling for age and sex revealed that CSF NCAM levels were lower in all patients (p=0.033), and in those with BD (p=0.039), than in the controls. NCAM levels positively correlated with age in patients with BD (p<0.01), MDD (p<0.01), and the controls (p<0.01). NCAM levels negatively correlated with depressive symptom scores in patients with BD (p=0.040). In patients with schizophrenia, NCAM levels correlated negatively with negative symptom scores (p=0.029), and correlated positively with scores for cognitive functions such as category fluency (p=0.011) and letter fluency (p=0.023) scores.

CONCLUSION

We showed that CSF NCAM levels were lower in psychiatric patients, particularly bipolar patients than in the controls. Furthermore, we found correlations of NCAM levels with clinical symptoms in patients with BD and in those with schizophrenia, suggesting the involvement of central NCAM in the symptom formation of severe psychiatric disorders.

Large-scale interaction effects reveal missing heritability in schizophrenia, bipolar disorder and posttraumatic stress disorder

Genetic susceptibility factors behind psychiatric disorders typically contribute small effects individually. A possible explanation for the missing heritability is that the effects of common variants are not only polygenic but also non-additive, appearing only when interactions within large groups are taken into account. Here, we tested this hypothesis for schizophrenia (SZ) and bipolar disorder (BP) disease risks, and identified genetic factors shared with posttraumatic stress disorder (PTSD). When considered independently, few single-nucleotide polymorphisms (SNPs) reached genome-wide significance. In contrast, when SNPs were selected in groups (containing up to thousands each) and the collective effects of all interactions were estimated, the association strength for SZ/BP rose dramatically with a combined sample size of 7187 cases and 8309 controls. We identified a large number of genes and pathways whose association was significant only when interaction effects were included. The gene with highest association was CSMD1, which encodes a negative regulator of complement activation. Pathways for glycosaminoglycan (GAG) synthesis exhibited strong association in multiple contexts. Taken together, highly associated pathways suggested a pathogenesis mechanism where maternal immune activation causes disruption of neurogenesis (compounded by impaired cell cycle, DNA repair and neuronal migration) and deficits in cortical interneurons, leading to symptoms triggered by synaptic pruning. Increased risks arise from GAG deficiencies causing complement activation and excessive microglial action. Analysis of PTSD data sets suggested an etiology common to SZ/BP: interneuron deficiency can also lead to impaired control of fear responses triggered by trauma. We additionally found PTSD risk factors affecting synaptic plasticity and fatty acid signaling, consistent with the fear extinction model. Our results suggest that much of the missing heritability of psychiatric disorders resides in non-additive interaction effects.

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.

Effect of Clozapine on DNA Methylation in Peripheral Leukocytes from Patients with Treatment-Resistant Schizophrenia

Clozapine is an atypical antipsychotic, that is established as the treatment of choice for treatment-resistant schizophrenia (SCZ). To date, no study investigating comprehensive DNA methylation changes in SCZ patients treated with chronic clozapine has been reported. The purpose of the present study is to reveal the effects of clozapine on DNA methylation in treatment-resistant SCZ. We conducted a genome-wide DNA methylation profiling in peripheral leukocytes (485,764 CpG dinucleotides) from treatment-resistant SCZ patients treated with clozapine (n = 21) in a longitudinal study. Significant changes in DNA methylation were observed at 29,134 sites after one year of treatment with clozapine, and these genes were enriched for “cell substrate adhesion” and “cell matrix adhesion” gene ontology (GO) terms. Furthermore, DNA methylation changes in the CREBBP (CREB binding protein) gene were significantly correlated with the clinical improvements. Our findings provide insights into the action of clozapine in treatment-resistant SCZ.

Regulation of extrasynaptic signaling by polysialylated NCAM: Impact for synaptic plasticity and cognitive functions

The activation of synaptic N-methyl-d-aspartate-receptors (NMDARs) is crucial for induction of synaptic plasticity and supports cell survival, whereas activation of extrasynaptic NMDARs inhibits long-term potentiation and triggers neurodegeneration. A soluble polysialylated form of the neural cell adhesion molecule (polySia-NCAM) suppresses signaling through peri-/extrasynaptic GluN2B-containing NMDARs. Genetic or enzymatic manipulations blocking this mechanism result in impaired synaptic plasticity and learning, which could be repaired by reintroduction of polySia, or inhibition of either GluN1/GluN2B receptors or downstream signaling through RasGRF1 and p38 MAP kinase. Ectodomain shedding of NCAM, and hence generation of soluble NCAM, is controlled by metalloproteases of a disintegrin and metalloprotease (ADAM) family. As polySia-NCAM is predominantly associated with GABAergic interneurons in the prefrontal cortex, it is noteworthy that EphrinA5/EphA3-induced ADAM10 activity promotes polySia-NCAM shedding in these neurons. Thus, in addition to the well-known regulation of synaptic NMDARs by the secreted molecule Reelin, shed polySia-NCAM may restrain activation of extrasynaptic NMDARs. These data support a concept that GABAergic interneuron-derived extracellular proteins control the balance in synaptic/extrasynaptic NMDAR-mediated signaling in principal cells. Strikingly, dysregulation of Reelin or polySia expression is linked to schizophrenia. Thus, targeting of the GABAergic interneuron-principle cell communication and restoring the balance in synaptic/extrasynaptic NMDARs represent promising strategies for treatment of psychiatric diseases.

Making Sense of: Sensitization in Schizophrenia

Sensitization is defined as a process whereby repeated intermittent exposure to a given stimulus results in an enhanced response at subsequent exposures. Next to robust findings of an increased dopamine synthesis capacity in schizophrenia, empirical data and neuroimaging studies support the notion that the mesolimbic dopamine system of patients with schizophrenia is more reactive compared with healthy controls. These studies led to the conceptualization of schizophrenia as a state of endogenous sensitization, as stronger behavioral response and increased dopamine release after amphetamine administration or exposure to stress have been observed in patients with schizophrenia. These findings have also been integrated into the neurodevelopmental model of the disorder, which assumes that vulnerable neuronal circuits undergo progressive changes during puberty and young adulthood that lead to manifest psychosis. Rodent and human studies have made an attempt to identify the exact mechanisms of sensitization of the dopaminergic system and its association with psychosis. Doing so, several epigenetic and molecular alterations associated with dopamine release, neuroplasticity, and cellular energy metabolism have been discovered. Future research aims at targeting these key proteins associated with sensitization in schizophrenia to enhance the knowledge of the pathophysiology of the illness and pave the way for an improved treatment or even prevention of this severe psychiatric disorder.

ST8SIA2 promotes oligodendrocyte differentiation and the integrity of myelin and axons

ST8SIA2 is a polysialyltransferase that attaches polysialic acid to the glycoproteins NCAM1 and CADM1. Polysialylation is involved in brain development and plasticity. ST8SIA2 is a schizophrenia candidate gene, and St8sia2^−/− mice exhibit schizophrenia‐like behavior. We sought to identify new pathological consequences of ST8SIA2 deficiency. Our proteomic analysis suggested myelin impairment in St8sia2^−/− mice. Histological and immune staining together with Western blot revealed that the onset of myelination was not delayed in St8sia2^−/− mice, but the content of myelin was lower. Ultrastructure analysis of the corpus callosum showed thinner myelin sheaths, smaller and irregularly shaped axons, and white matter lesions in adult St8sia2^−/− mice. Then we evaluated oligodendrocyte differentiation in vivo and in vitro. Fewer OLIG2+ cells in the cortex and corpus callosum, together with the higher percentage of undifferentiated oligodenroglia in St8sia2^−/− mice suggested an impairment in oligodendrocyte generation. Experiment on primary cultures of oligodendrocyte precursor cells (OPCs) confirmed a cell‐autonomous effect of ST8SIA2 in oligodendroglia, and demonstrated that OPC to oligodendrocyte transition is inhibited in St8sia2^−/− mice. Concluding, ST8SIA2‐mediated polysialylation influences on oligodendrocyte differentiation, and oligodendrocyte deficits in St8sia2 mice are a possible cause of the demyelination and degeneration of axons, resembling nerve fiber alterations in schizophrenia. GLIA 2016;65:34–49

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.