NCAM in Neuropsychiatric and Neurodegenerative Disorders

Genome-wide association study of traumatic brain injury in U.S. military veterans enrolled in the VA million veteran program

Large-scale genetic studies of traumatic brain injury (TBI) are lacking; thus, our understanding of the influence of genetic factors on TBI risk and recovery is incomplete. This study aimed to conduct a genome-wide association study (GWAS) of TBI in VA Million Veteran Program (MVP) enrollees. Participants included a multi-ancestry cohort (European, African, and Hispanic ancestries; N = 304,485; 111,494 TBI cases, 192,991 controls). TBI was assessed using MVP survey data and International Classification of Diseases (ICD) codes from the Veterans Health Administration's electronic health record. GWAS was performed using logistic regression in PLINK, and meta-analyzed in METAL. FUMA was used for post-GWAS analysis. Genomic structural equation modeling (gSEM) was conducted to investigate underlying genetic associations with TBI, and bivariate MiXeR was used to estimate phenotype specific and shared polygenicity. SNP-based heritability was 0.060 (SE = 0.004, p = 7.83×10-66). GWAS analysis identified 15 genome-wide significant (GWS) loci at p < 5×10-8. Gene-based analyses revealed 14 gene-wide significant genes; top genes included NCAM1, APOE, FTO, and FOXP2. Gene tissue expression analysis identified the brain as significantly enriched, particularly in the frontal cortex, anterior cingulate cortex, and nucleus accumbens. Genetic correlations with TBI were significant for risk-taking behaviors and psychiatric disorders, but generally not significant for the neurocognitive variables investigated. gSEM analysis revealed stronger associations with risk-taking traits than with psychiatric traits. Finally, the genetic architecture of TBI was similar to polygenic psychiatric disorders. Neurodegenerative disorders including Alzheimer's and Parkinson's disease showed much less polygenicity, however, the proportion of shared variance with TBI was high. This first well-powered GWAS of TBI identified 15 loci including genes relevant to TBI biology, and showed that TBI is a heritable trait with comparable genetic architecture and high genetic correlation with psychiatric traits. Our findings set the stage for future TBI GWASs that focus on injury severity and diversity and chronicity of symptom sequelae.

Gene expression in the primate orbitofrontal cortex related to anxious temperament

Anxiety disorders are among the most prevalent psychiatric disorders, causing significant suffering and disability. Relative to other psychiatric disorders, anxiety disorders tend to emerge early in life, supporting the importance of developmental mechanisms in their emergence and maintenance. Behavioral inhibition (BI) is a temperament that emerges early in life and, when stable and extreme, is linked to an increased risk for the later development of anxiety disorders and other stress-related psychopathology. Understanding the neural systems and molecular mechanisms underlying this dispositional risk could provide insight into treatment targets for anxiety disorders. Nonhuman primates (NHPs) have an anxiety-related temperament, called anxious temperament (AT), that is remarkably similar to BI in humans, facilitating the design of highly translational models for studying the early risk for stress-related psychopathology. Because of the recent evolutionary divergence between humans and NHPs, many of the anxiety-related brain regions that contribute to psychopathology are highly similar in terms of their structure and function, particularly with respect to the prefrontal cortex. The orbitofrontal cortex plays a critical role in the flexible encoding and regulation of threat responses, in part through connections with subcortical structures like the amygdala. Here, we explore individual differences in the transcriptional profile of cells within the region, using laser capture microdissection and single nuclear sequencing, providing insight into the molecules underlying individual differences in AT-related function of the pOFC, with a particular focus on previously implicated cellular systems, including neurotrophins and glucocorticoid signaling.

Increased peripheral of brain-derived neurotrophic factor levels in phenylketonuric patients treated with l-carnitine

Phenylketonuria (PKU) is the most common inherited metabolic disorders caused by severe deficiency or absence of phenylalanine hydroxylase activity that converts phenylalanine (Phe) to tyrosine. PKU patients were treated with a Phe restricted diet supplemented with a special formula containing l-carnitine (L-car), well-known antioxidant compound. The lack of treatment can cause neurological and cognitive impairment, as severe mental retardation, neuronal cell loss and synaptic density reduction. Although Phe has been widely demonstrated to be involved in PKU neurotoxicity, the mechanisms responsible for the CNS injury are still not fully known. In this work, we evaluated markers of neurodegeneration, namely BDNF (brain-derived neurotrophic factor), PAI-1 total (Plasminogen activator inhibitor-1 total), Cathepsin D, PDGF AB/BB (platelet-derived growth factor), and NCAM (neuronal adhesion molecule) in plasma of PKU patients at early and late diagnosis and under treatment. We found decreased Phe levels and increased L-car concentrations in PKU patients treated with L-car compared to the other groups, indicating that the proposed treatment was effective. Furthermore, we found increased BDNF levels in the patients under treatment compared to patients at early diagnosis, and a positive correlation between BDNF and L-car and a negative correlation between BDNF and Phe. Our results may indicate that in PKU patients treated with L-car there is an attempt to adjust neuronal plasticity and recover the damage suffered, reflecting a compensatory response to brain injury.

Rescue of synaptic and cognitive functions in polysialic acid-deficient mice and dementia models by short polysialic acid fragments

Dysregulated cortical expression of the neural cell adhesion molecule (NCAM) and deficits of its associated polysialic acid (polySia) have been found in Alzheimer's disease and schizophrenia. However, the functional role of polySia in cortical synaptic plasticity remains poorly understood. Here, we show that acute enzymatic removal of polySia in medial prefrontal cortex (mPFC) slices leads to increased transmission mediated by the GluN1/GluN2B subtype of N-methyl-d-aspartate receptors (NMDARs), increased NMDAR-mediated extrasynaptic tonic currents, and impaired long-term potentiation (LTP). The latter could be fully rescued by pharmacological suppression of GluN1/GluN2B receptors, or by application of short soluble polySia fragments that inhibited opening of GluN1/GluN2B channels. These treatments and augmentation of synaptic NMDARs with the glycine transporter type 1 (GlyT1) inhibitor sarcosine also restored LTP in mice deficient in polysialyltransferase ST8SIA4. Furthermore, the impaired performance of polySia-deficient mice and two models of Alzheimer's disease in the mPFC-dependent cognitive tasks could be rescued by intranasal administration of polySia fragments. Our data demonstrate the essential role of polySia-NCAM in the balancing of signaling through synaptic/extrasynaptic NMDARs in mPFC and highlight the therapeutic potential of short polySia fragments to restrain GluN1/GluN2B-mediated signaling.

Therapeutic Potential of Targeting Regulated Intramembrane Proteolysis Mechanisms of Voltage-Gated Ion Channel Subunits and Cell Adhesion Molecules

Several integral membrane proteins undergo regulated intramembrane proteolysis (RIP), a tightly controlled process through which cells transmit information across and between intracellular compartments. RIP generates biologically active peptides by a series of proteolytic cleavage events carried out by two primary groups of enzymes: sheddases and intramembrane-cleaving proteases (iCLiPs). Following RIP, fragments of both pore-forming and non-pore-forming ion channel subunits, as well as immunoglobulin super family (IgSF) members, have been shown to translocate to the nucleus to function in transcriptional regulation. As an example, the voltage-gated sodium channel β1 subunit, which is also an IgSF-cell adhesion molecule (CAM), is a substrate for RIP. β1 RIP results in generation of a soluble intracellular domain, which can regulate gene expression in the nucleus. In this review, we discuss the proposed RIP mechanisms of voltage-gated sodium, potassium, and calcium channel subunits as well as the roles of their generated proteolytic products in the nucleus. We also discuss other RIP substrates that are cleaved by similar sheddases and iCLiPs, such as IgSF macromolecules, including CAMs, whose proteolytically generated fragments function in the nucleus. Importantly, dysfunctional RIP mechanisms are linked to human disease. Thus, we will also review how understanding RIP events and subsequent signaling processes involving ion channel subunits and IgSF proteins may lead to the discovery of novel therapeutic targets. SIGNIFICANCE STATEMENT: Several ion channel subunits and immunoglobulin superfamily molecules have been identified as substrates of regulated intramembrane proteolysis (RIP). This signal transduction mechanism, which generates polypeptide fragments that translocate to the nucleus, is an important regulator of gene transcription. RIP may impact diseases of excitability, including epilepsy, cardiac arrhythmia, and sudden death syndromes. A thorough understanding of the role of RIP in gene regulation is critical as it may reveal novel therapeutic strategies for the treatment of previously intractable diseases.

Relationship Between Neural Cell Adhesion Molecule-1 and Cognitive Functioning in Schizophrenia Spectrum Disorder

Abnormal synaptic plasticity leads to cognitive impairment in schizophrenia. Markers of synaptic plasticity are known to be altered in schizophrenia, but there are limited data available about neural cell adhesion molecule-1 (NCAM-1) levels and its association with cognitive functions in schizophrenia. The objective of the study was to analyze NCAM-1 levels and its association with various cognitive domains in schizophrenia. One hundred and seventy-six schizophrenia cases and 176 controls were recruited for the study. Serum NCAM-1 levels were analysed in both the groups. Cognitive examination was performed using Addenbrooke cognitive examination-III (ACE-III) and disease severity was assessed using Positive and negative symptoms scale (PANSS). Serum NCAM-1 levels were elevated in schizophrenia cases (p = 0.006) compared to controls. NCAM-1 was positively associated with attention (r = 0.196, p = 0.009), language (r = 0.192, p = 0.011), visuospatial abilities (r = 0.207, p = 0.006) and total ACE-III score (r = 0.189, p = 0.012). We conclude that elevated levels of NCAM-1 are associated with better cognitive functioning in schizophrenia.

Interactions between the Polysialylated Neural Cell Adhesion Molecule and the Transient Receptor Potential Canonical Channels 1, 4, and 5 Induce Entry of Ca2+ into Neurons

The neural cell adhesion molecule (NCAM) plays important functional roles in the developing and mature nervous systems. Here, we show that the transient receptor potential canonical (TRPC) ion channels TRPC1, -4, and -5 not only interact with the intracellular domains of the transmembrane isoforms NCAM140 and NCAM180, but also with the glycan polysialic acid (PSA) covalently attached to the NCAM protein backbone. NCAM antibody treatment leads to the opening of TRPC1, -4, and -5 hetero- or homomers at the plasma membrane and to the influx of Ca²⁺ into cultured cortical neurons and CHO cells expressing NCAM, PSA, and TRPC1 and -4 or TRPC1 and -5. NCAM-stimulated Ca²⁺ entry was blocked by the TRPC inhibitor Pico145 or the bacterial PSA homolog colominic acid. NCAM-stimulated Ca²⁺ influx was detectable neither in NCAM-deficient cortical neurons nor in TRPC1/4- or TRPC1/5-expressing CHO cells that express NCAM, but not PSA. NCAM-induced neurite outgrowth was reduced by TRPC inhibitors and a function-blocking TRPC1 antibody. A characteristic signaling feature was that extracellular signal-regulated kinase 1/2 phosphorylation was also reduced by TRPC inhibitors. Our findings indicate that the interaction of NCAM with TRPC1, -4, and -5 contributes to the NCAM-stimulated and PSA-dependent Ca²⁺ entry into neurons thereby influencing essential neural functions.

Autoantibodies against NCAM1 from patients with schizophrenia cause schizophrenia-related behavior and changes in synapses in mice

From genetic and etiological studies, autoimmune mechanisms underlying schizophrenia are suspected; however, the details remain unclear. In this study, we describe autoantibodies against neural cell adhesion molecule (NCAM1) in patients with schizophrenia (5.4%, cell-based assay; 6.7%, ELISA) in a Japanese cohort (n = 223). Anti-NCAM1 autoantibody disrupts both NCAM1-NCAM1 and NCAM1-glial cell line-derived neurotrophic factor (GDNF) interactions. Furthermore, the anti-NCAM1 antibody purified from patients with schizophrenia interrupts NCAM1-Fyn interaction and inhibits phosphorylation of FAK, MEK1, and ERK1 when introduced into the cerebrospinal fluid of mice and also reduces the number of spines and synapses in frontal cortex. In addition, it induces schizophrenia-related behavior in mice, including deficient pre-pulse inhibition and cognitive impairment. In conclusion, anti-NCAM1 autoantibodies in patients with schizophrenia cause schizophrenia-related behavior and changes in synapses in mice. These antibodies may be a potential therapeutic target and serve as a biomarker to distinguish a small but treatable subgroup in heterogeneous patients with schizophrenia.

•

Some patients with schizophrenia are positive for anti-NCAM1 autoantibodies

•

Anti-NCAM1 antibody from schizophrenia patients inhibits NCAM1-NCAM1 interactions

•

Anti-NCAM1 antibody from schizophrenia patients reduces spines and synapses in mice

•

Anti-NCAM1 antibody from patients induces schizophrenia-related behavior in mice

A functional SNP rs895819 on pre-miR-27a is associated with bipolar disorder by targeting NCAM1

The aberrant expression or genomic mutations of microRNA are associated with several human diseases. This study analyzes the relationship between genetic variations of miRNA and schizophrenia or bipolar disorder. We performed case-control studies for ten SNPs in a total sample of 1584 subjects. All these ten SNPs were on or near mature microRNAs. We identified the association between bipolar disorder and the T/C polymorphism at rs895819. To illustrate the function of miR-27a, we constructed several miR-27a knockout (KO) cell lines, determined candidates of miR-27a, and then verified NCAM1 as a target gene of miR-27a. Further studies revealed that the T/C polymorphism on miR-27a led to the differential expression of mature and precursor miR-27a without affecting the expression of primary miR-27a. Furthermore, the C mutation on pre-miR-27a suppresses cell migration and dopamine expression levels. Our study highlights the importance of miR-27a and its polymorphism at rs895819 in bipolar disorder.

A T/C variant in miR-27a is associated with bipolar disorder, potentially by reducing the ability of this microRNA to target important neurodevelopmental genes like NCAM1.

Distinct and dementia-related synaptopathy in the hippocampus after military blast exposures

Explosive shockwaves, and other types of blast exposures, are linked to injuries commonly associated with military service and to an increased risk for the onset of dementia. Neurological complications following a blast injury, including depression, anxiety, and memory problems, often persist even when brain damage is undetectable. Here, hippocampal explants were exposed to the explosive 1,3,5-trinitro-1,3,5-triazinane (RDX) to identify indicators of blast-induced changes within important neuronal circuitries. Highly controlled detonations of small, 1.7-gram RDX spherical charges reduced synaptic markers known to be downregulated in cognitive disorders, but without causing overt neuronal loss or astroglial responses. In the absence of neuromorphological alterations, levels of synaptophysin, GluA1, and synapsin IIb were significantly diminished within 24 hr, and these synaptic components exhibited progressive reductions following blast exposure as compared to their stable maintenance in control explants. In contrast, labeling of the synapsin IIa isoform remained unaltered, while neuropilar staining of other markers decreased, including synapsin IIb and neural cell adhesion molecule (NCAM) isoforms, along with evidence of NCAM proteolytic breakdown. NCAM180 displayed a distinct decline after the RDX blasts, whereas NCAM140 and NCAM120 exhibited smaller or no deterioration, respectively. Interestingly, the extent of synaptic marker reduction correlated with AT8-positive tau levels, with tau pathology stochastically found in CA1 neurons and their dendrites. The decline in synaptic components was also reflected in the size of evoked postsynaptic currents recorded from CA1 pyramidals, which exhibited a severe and selective reduction. The identified indicators of blast-mediated synaptopathy point to the need for early biomarkers of explosives altering synaptic integrity with links to dementia risk, to advance strategies for both cognitive health and therapeutic monitoring.

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.

A Preliminary Investigation on Plasma Cell Adhesion Molecules Levels by Protein Microarray Technology in Major Depressive Disorder

Objectives: Major depressive disorder (MDD) is a serious mental disorder, and there is a great difficulty to diagnose and treat. Hitherto, relatively few studies have explored the correlation between the levels of plasma cell adhesion molecules and MDD. Methods: Thirty outpatients with acute episodes of MDD in Shanghai Mental Health Center and 34 healthy volunteers from the community were recruited as subjects. Protein microarray technology was applied to compared the differences in plasma levels of 17 kinds of adhesion molecular proteins between the two groups. Meanwhile, the diagnostic value of different proteins in depression was discussed by using the receiver operating characteristic curve. Results: The levels of Carcinoembryonic Antigen Related Cell Adhesion Molecule-1(CEACAM-1) and Neural Cell Adhesion Molecule (NrCAM) in MDD patients were significantly higher than those in healthy controls (P < 0.05). The area under ROC curve of CEACAM-1 combined with NrCAM was 0.723, with the sensitivity 0.800 and the specificity 0.676. Conclusion: The plasma levels of CEACAM-1 and NrCAM were significantly up-regulated in MDD, and their combined application was of potential diagnostic value, deserving to expand the sample size for further verification.

Developmental effects of maternal smoking during pregnancy on the human frontal cortex transcriptome

Cigarette smoking during pregnancy is a major public health concern. While there are well-described consequences in early child development, there is very little known about the effects of maternal smoking on human cortical biology during prenatal life. We therefore performed a genome-wide differential gene expression analysis using RNA sequencing (RNA-seq) on prenatal (N = 33; 16 smoking-exposed) as well as adult (N = 207; 57 active smokers) human postmortem prefrontal cortices. Smoking exposure during the prenatal period was directly associated with differential expression of 14 genes; in contrast, during adulthood, despite a much larger sample size, only two genes showed significant differential expression (FDR < 10%). Moreover, 1,315 genes showed significantly different exposure effects between maternal smoking during pregnancy and direct exposure in adulthood (FDR < 10%)-these differences were largely driven by prenatal differences that were enriched for pathways previously implicated in addiction and synaptic function. Furthermore, prenatal and age-dependent differentially expressed genes were enriched for genes implicated in non-syndromic autism spectrum disorder (ASD) and were differentially expressed as a set between patients with ASD and controls in postmortem cortical regions. These results underscore the enhanced sensitivity to the biological effect of smoking exposure in the developing brain and offer insight into how maternal smoking during pregnancy affects gene expression in the prenatal human cortex. They also begin to address the relationship between in utero exposure to smoking and the heightened risks for the subsequent development of neuropsychiatric disorders.

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.

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.

Systems biology reveals reprogramming of the S-nitroso-proteome in the cortical and striatal regions of mice during aging process

Cell aging depends on the rate of cumulative oxidative and nitrosative damage to DNA and proteins. Accumulated data indicate the involvement of protein S-nitrosylation (SNO), the nitric oxide (NO)-mediated posttranslational modification (PTM) of cysteine thiols, in different brain disorders. However, the changes and involvement of SNO in aging including the development of the organism from juvenile to adult state is still unknown. In this study, using the state-of-the-art mass spectrometry technology to identify S-nitrosylated proteins combined with large-scale computational biology, we tested the S-nitroso-proteome in juvenile and adult mice in both cortical and striatal regions. We found reprogramming of the S-nitroso-proteome in adult mice of both cortex and striatum regions. Significant biological processes and protein–protein clusters associated with synaptic and neuronal terms were enriched in adult mice. Extensive quantitative analysis revealed a large set of potentially pathological proteins that were significantly upregulated in adult mice. Our approach, combined with large scale computational biology allowed us to perform a system-level characterization and identification of the key proteins and biological processes that can serve as drug targets for aging and brain disorders in future studies.

The Role of Forced and Voluntary Training on Accumulation of Neural Cell Adhesion Molecule and Polysialic Acid in Muscle of Mice with Experimental Autoimmune Encephalomyelitis

It has been suggested that depletion of adhesion molecules is one of the factors associated with or possibly responsible for multiple sclerosis (MS) progression. The aim of this study was to investigate the effect of forced and voluntary training before and after induction of experimental autoimmune encephalomyelitis (EAE) on accumulation of neural cell adhesion molecule (NCAM) and polysialic acid (PSA) in neuromuscular junction denervation in plantaris and soleus muscles in C57BL/6 female mice. A total of 40 female C57BL/6 mice, 10-week-old, were randomly divided into four groups, including induced control groups without EAE induction, induced EAE without training, and forced and voluntary training groups. Myelin oligodendrocyte glycoprotein peptide 35–55 (300 μg in saline; MOG 35–55; KJ Ross-Petersen ApS, Denmark) was injected subcutaneously at the base of the tail of each mouse. Clinical assessment of EAE was performed daily using a 15-point scoring system following immunization. Training groups performed the swimming program for 30 min/day, 5 times/week, for 4 weeks. Mice had access to a treadmill for one hour per day, 5times/week, for 4 weeks in individual cage. The mice were scarified, and the plantaris and soleus muscles were then isolated for investigation of proteins expression using IHC. An analysis of the preventive exercise (before) and recovery exercise (after) of the EAE was performed. Images of the stained sections were taken using a fluorescent microscope. Quantitative image analysis was performed using ImageJ software package. The obtained data from the mean percentage expression of PSA and NCAM in pre- and post-soleus and plantaris muscles showed that the highest and lowest expression levels of PSA and NCAM belonged to control and swim EAE (SE) groups, respectively. The low expression levels of PSA and NCAM were detected in rat with MS without intervention. In conclusion, the relationship between increasing levels of NCAM and PSA protein expression and voluntary and compulsory activity were detectable both in pre and post-soleus and plantaris. However, voluntary activity resulted in more expression levels of NCAM and PSA than that of compulsory. In conclusion, since it has been suggested that depletion of NCAM is one of the factors associated with or possibly responsible for MS progression, these findings show exercise MS progression may be reduced by increasing expression of exercise-related adhesion molecule such as NCAM and PSA (a glycan modification of the NCAM).

NCAM regulates temporal specification of neural progenitor cells via profilin2 during corticogenesis

The development of cerebral cortex requires spatially and temporally orchestrated proliferation, migration, and differentiation of neural progenitor cells (NPCs). The molecular mechanisms underlying cortical development are, however, not fully understood. The neural cell adhesion molecule (NCAM) has been suggested to play a role in corticogenesis. Here we show that NCAM is dynamically expressed in the developing cortex. NCAM expression in NPCs is highest in the neurogenic period and declines during the gliogenic period. In mice bearing an NPC-specific NCAM deletion, proliferation of NPCs is reduced, and production of cortical neurons is delayed, while formation of cortical glia is advanced. Mechanistically, NCAM enhances actin polymerization in NPCs by interacting with actin-associated protein profilin2. NCAM-dependent regulation of NPCs is blocked by mutations in the profilin2 binding site. Thus, NCAM plays an essential role in NPC proliferation and fate decision during cortical development by regulating profilin2-dependent actin polymerization.

Relationship of elevated neural cell adhesion molecule 1 with interleukin-10 and disease severity in bipolar disorder

Neural plasticity and inflammation are known to play a role in the pathogenesis of Bipolar disorder. The data related to markers of neural plasticity in bipolar disorder are limited. The objective of the study was to assess the levels of neural cell adhesion molecule 1 (NCAM 1) and interleukin-10 and their association with disease severity in bipolar disorder. 40 bipolar disorder I patients with acute manic symptoms and 40 age matched controls were enrolled in the study. Neural cell adhesion molecule 1 and interleukin-10 (IL-10) levels were assessed in both the groups. NCAM 1 and interleukin-10 levels were significantly increased in bipolar disorder when compared with controls. There was significant positive correlation of Young Mania Rating score with NCAM 1 (r = 0.538, p = < 0.001) in patients with BD. Multi variate analysis revealed that IL-10 (p = 0.021) was lower in controls by 0.012 ng/L and NCAM 1(p = 0.048) was lower in controls by 0.002 ng/L compared to BD cases and this difference was statistically significant. Based on the findings we conclude that neural cell adhesion molecule 1 is increased and associated with disease severity in bipolar disorder.

Effects of the Genetic Depletion of Polysialyltransferases on the Structure and Connectivity of Interneurons in the Adult Prefrontal Cortex

Polysialic acid (polySia) is a complex sugar that in the nervous system appears mainly as a posttranslational modification of the neural cell adhesion molecule (NCAM). PolySia plays important roles during brain development, but also in its plasticity during adulthood. Two polysialyltransferases (polyST), ST8SIA2 and ST8SIA4, are involved in the synthesis and attachment of polySia. Both polyST are relevant for developmental migration of cortical interneurons and their establishment in the prefrontal cortex (PFC). In contrast, only ST8SIA4 appears to be important for the structural plasticity of a subpopulation of cortical interneurons in the adult. Interestingly, ST8SIA2 and NCAM are candidate genes for schizophrenia, a disorder in which interneuronal circuits are altered. However, there is still no data on the effects of polyST depletion on the dendritic structure or the connectivity of cortical interneurons. Here, we studied the contribution of each polyST on these parameters in the medial PFC (mPFC) of polyST knock-out mice with GAD67-GFP-labeled interneurons. Genetic depletion of ST8SIA4, but not ST8SIA2, resulted in a decrease in the complexity of the dendritic arbor of interneurons. In contrast, ablation of either of the two polyST induced a decrease in the density of parvalbumin (PV) expressing perisomatic puncta on pyramidal neurons. Thus, the depletion of each polyST results in similar impairments of not only developmental migration but also efferent synaptic connectivity of interneurons. In contrast, the loss of ST8SIA4 has a unique effect on dendritic structure, hence on afferent connectivity, suggesting differential and independent contributions of each polyST to neuritogenesis and synaptogenesis.

Neural cell adhesion molecule peptide mimetics modulate emotionality: pharmacokinetic and behavioral studies in rats and non-human primates

Recent evidence highlights the fibroblast growth factor (FGF) family in emotion modulation. Although ligands that activate FGF receptors have antidepressant and anxiolytic effects in animal models, FGF ligands have a broad range of actions both in the brain and the periphery. Therefore, identifying molecular partners that may function as allosteric modulators could offer new avenues for drug development. Since neural cell adhesion molecule (NCAM) activates FGF receptors, we asked whether peripherally administered NCAM peptide mimetics penetrate the brain and alter the behavior of standardized tests that have predictive validity for drug treatments of anxiety or depression. The NCAM peptide mimetic, plannexin, acutely increased and chronically decreased anxiety, but did not have antidepressant effects in rats. Another NCAM peptide mimetic, FGL_L, had acute anxiogenic effects and chronic antidepressant effects in rats. A related NCAM peptide mimetic, FGL_S, had antidepressant effects without modulating anxiety-like behavior, and these antidepressant effects were blocked by an AMPA receptor antagonist. Cisternal cerebrospinal fluid (CSF) levels of FGLs correlated with blood plasma levels in rats and non-human primates, and CSF-to-blood ratios of FGL_S were comparable in both species. Results indicate that NCAM peptide mimetics penetrate the brain and support the suggestion that FGL_S may be a candidate for further development as a novel treatment for major depressive disorder in humans.

Disruption of the NMDA receptor GluN2A subunit abolishes inflammation-induced depression

Recent reports have demonstrated that lipopolysaccharide (LPS)-induced depressive-like behaviour is mediated via NMDA receptor. In this study, we further investigated the role of GluN2 A subunit of NMDA receptor in synaptic processes in the prefrontal cortex (PFC) and hippocampus of GluN2 A knockout (KO) mice in LPS-induced depressive-like behavior. Our data suggest that LPS-treated mice, lacking GluN2 A subunit, did not exhibit depressive-like behaviour. This was accompanied by unaltered levels of IL-6 and significant changes in neuroplasticity markers and glutamate receptor subunits composition in PFC and hippocampus. In particular, an immune challenge in GluN2 A KO mice resulted in unchanged PSA-NCAM levels and proBDNF increase in both brain structures as well as in increase in BDNF levels in hippocampus. Furthermore, the absence of GluN2 A resulted in increased levels of all NCAM isoforms in PFC upon LPS which was followed with a decrease in GluN1 and GluN2B subunits. The levels of AMPA receptor subunits (GluA1, GluA3, and GluA4) in the hippocampus of GluN2 A mice were unaltered upon the treatment and abundantly present in the PFC of KO mice. These results indicate that the GluN2 A subunit is critical in neuroinflammation-related depression, that its absence abolishes LPS-induced depressive phenotype, sustains PSA-NCAM levels, increases proBDNF signalling in the PFC and hippocampus and potentiates synaptic stabilization through NCAM in the PFC upon an immune challenge.

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.

Role of the adhesion molecule F3/Contactin in synaptic plasticity and memory

Cell adhesion molecules (CAMs) have a pivotal role in building and maintaining synaptic structures during brain development participating in axonal elongation and pathfinding, glial guidance of neuronal migration, as well as myelination. CAMs expression persists in the adult brain particularly in structures undergoing postnatal neurogenesis and involved in synaptic plasticity and memory as the hippocampus. Among the neural CAMs, we have recently focused on F3/Contactin, a glycosylphosphatidyl inositol-anchored glycoprotein belonging to the immunoglobulin superfamily, involved in neuronal development, synaptic maintenance and organization of neuronal networks. Here, we discuss our recent data suggesting that F3/Contactin exerts a role in hippocampal synaptic plasticity and memory in adult and aged mice. In particular, we have studied long-term potentiation (LTP), spatial and object recognition memory, and phosphorylation of the transcription factor cAMP-Responsive-Element Binding protein (CREB) in a transgenic mouse model of F3/Contactin overexpression. We also investigated whether F3/Contactin might influence neuronal apoptosis and the production of amyloid-beta peptide (Aβ), known to be one of the main pathogenetic hallmarks of Alzheimer's disease (AD). In conclusion, a further understanding of F3/Contactin role in synaptic plasticity and memory might have interesting clinical outcomes in cognitive disorders, such as aging and AD, offering innovative therapeutic opportunities.

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.

Modeling neurodevelopmental cognitive deficits in tasks with cross-species translational validity

Numerous psychiatric disorders whose cognitive dysfunction links to functional outcome have neurodevelopmental origins including schizophrenia, autism and bipolar disorder. Treatments are needed for these cognitive deficits, which require development using animal models. Models of neurodevelopmental disorders are as varied and diverse as the disorders themselves, recreating some but not all aspects of the disorder. This variety may in part underlie why purported procognitive treatments translated from these models have failed to restore functioning in the targeted patient populations. Further complications arise from environmental factors used in these models that can contribute to numerous disorders, perhaps only impacting specific domains, while diagnostic boundaries define individual disorders, limiting translational efficacy. The Research Domain Criteria project seeks to 'develop new ways to classify mental disorders based on behavioral dimensions and neurobiological measures' in hopes of facilitating translational research by remaining agnostic toward diagnostic borders derived from clinical presentation in humans. Models could therefore recreate biosignatures of cognitive dysfunction irrespective of disease state. This review highlights work within the field of neurodevelopmental models of psychiatric disorders tested in cross-species translational cognitive paradigms that directly inform this newly developing research strategy. By expounding on this approach, the hopes are that a fuller understanding of each model may be attainable in terms of the cognitive profile elicited by each manipulation. Hence, conclusions may begin to be drawn on the nature of cognitive neuropathology on neurodevelopmental and other disorders, increasing the chances of procognitive treatment development for individuals affected in specific cognitive domains.

The GDNF-GFRα1 complex promotes the development of hippocampal dendritic arbors and spines via NCAM

The formation of synaptic connections during nervous system development requires the precise control of dendrite growth and synapse formation. Although glial cell line-derived neurotrophic factor (GDNF) and its receptor GFRα1 are expressed in the forebrain, the role of this system in the hippocampus remains unclear. Here, we investigated the consequences of GFRα1 deficiency for the development of hippocampal connections. Analysis of conditional Gfra1 knockout mice shows a reduction in dendritic length and complexity, as well as a decrease in postsynaptic density specializations and in the synaptic localization of postsynaptic proteins in hippocampal neurons. Gain- and loss-of-function assays demonstrate that the GDNF-GFRα1 complex promotes dendritic growth and postsynaptic differentiation in cultured hippocampal neurons. Finally, in vitro assays revealed that GDNF-GFRα1-induced dendrite growth and spine formation are mediated by NCAM signaling. Taken together, our results indicate that the GDNF-GFRα1 complex is essential for proper hippocampal circuit development.

Serum Markers of Neurodegeneration in Maple Syrup Urine Disease

Maple syrup urine disease (MSUD) is an inherited disorder caused by deficient activity of the branched-chain α-keto acid dehydrogenase complex involved in the degradation pathway of branched-chain amino acids (BCAAs) and their respective α-keto-acids. Patients affected by MSUD present severe neurological symptoms and brain abnormalities, whose pathophysiology is poorly known. However, preclinical studies have suggested alterations in markers involved with neurodegeneration. Because there are no studies in the literature that report the neurodegenerative markers in MSUD patients, the present study evaluated neurodegenerative markers (brain-derived neurotrophic factor (BDNF), cathepsin D, neural cell adhesion molecule (NCAM), plasminogen activator inhibitor-1 total (PAI-1 (total)), platelet-derived growth factor AA (PDGF-AA), PDGF-AB/BB) in plasma from 10 MSUD patients during dietary treatment. Our results showed a significant decrease in BDNF and PDGF-AA levels in MSUD patients. On the other hand, NCAM and cathepsin D levels were significantly greater in MSUD patients compared to the control group, while no significant changes were observed in the levels of PAI-1 (total) and PDGF-AB/BB between the control and MSUD groups. Our data show that MSUD patients present alterations in proteins involved in the neurodegenerative process. Thus, the present findings corroborate previous studies that demonstrated that neurotrophic factors and lysosomal proteases may contribute, along with other mechanisms, to the intellectual deficit and neurodegeneration observed in MSUD.

Synaptic Mechanisms of Blast-Induced Brain Injury

Blast wave-induced traumatic brain injury (TBI) is one of the most common injuries to military personnel. Brain tissue compression/tension due to blast-induced cranial deformations and shear waves due to head rotation may generate diffuse micro-damage to neuro-axonal structures and trigger a cascade of neurobiological events culminating in cognitive and neurodegenerative disorders. Although diffuse axonal injury is regarded as a signature wound of mild TBI (mTBI), blast loads may also cause synaptic injury wherein neuronal synapses are stretched and sheared. This synaptic injury may result in temporary disconnect of the neural circuitry and transient loss in neuronal communication. We hypothesize that mTBI symptoms such as loss of consciousness or dizziness, which start immediately after the insult, could be attributed to synaptic injury. Although empirical evidence is beginning to emerge; the detailed mechanisms underlying synaptic injury are still elusive. Coordinated in vitro-in vivo experiments and mathematical modeling studies can shed light into the synaptic injury mechanisms and their role in the potentiation of mTBI symptoms.

Vinorelbine and epirubicin share common features with polysialic acid and modulate neuronal and glial functions

Polysialic acid (PSA), a large, linear glycan composed of 8 to over 100 α2,8-linked sialic acid residues, modulates development of the nervous system by enhancing cell migration, axon pathfinding, and synaptic targeting and by regulating differentiation of progenitor cells. PSA also functions in developing and adult immune systems and is a signature of many cancers. In this study we identified vinorelbine, a semi-synthetic third generation vinca alkaloid, and epirubicin, an anthracycline and 4'-epimer of doxorubicin, as PSA mimetics. Similar to PSA, vinorelbine and epirubicin bind to the PSA-specific monoclonal antibody 735 and compete with the bacterial analog of PSA, colominic acid in binding to monoclonal antibody 735. Vinorelbine and epirubicin stimulate neurite outgrowth of cerebellar neurons via the neural cell adhesion molecule, via myristoylated alanine-rich C kinase substrate, and via fibroblast growth factor receptor, signaling through Erk pathways. Furthermore, the two compounds enhance process formation of Schwann cells and migration of cerebellar neurons in culture, and reduce migration of astrocytes after injury. These novel results show that the structure and function of PSA can be mimicked by the small organic compounds vinorelbine and epirubicin, thus raising the possibility to re-target drugs used in treatment of cancers to nervous system repair. Vinorelbine and epirubicin, identified as PSA mimetics, enhance, like PSA, neuronal migration, neuritogenesis, and formation of Schwann cell processes, and reduce astrocytic migration. Ablating NCAM, inhibiting fibroblast growth factor (FGFR) receptor, or adding the effector domain of myristoylated alanine-rich C kinase substrate (MARCKS) minimize the vinorelbine and epirubicin effects, indicating that they are true PSA mimetics triggering PSA-mediated functions.

NCAM-deficient mice show prominent abnormalities in serotonergic and BDNF systems in brain - Restoration by chronic amitriptyline

Mood disorders are associated with alterations in serotonergic system, deficient BDNF (brain-derived neurotrophic factor) signaling and abnormal synaptic plasticity. Increased degradation and reduced functions of NCAM (neural cell adhesion molecule) have recently been associated with depression and NCAM deficient mice show depression-related behavior and impaired learning. The aim of the present study was to investigate potential changes in serotonergic and BDNF systems in NCAM knock-out mice. Serotonergic nerve fiber density and SERT (serotonin transporter) protein levels were robustly reduced in the hippocampus, prefrontal cortex and basolateral amygdala of adult NCAM(-)(/-) mice. This SERT reduction was already evident during early postnatal development. [(3)H]MADAM binding experiments further demonstrated reduced availability of SERT in cell membranes of NCAM(-)(/-) mice. Moreover, the levels of serotonin and its major metabolite 5-HIAA were down regulated in the brains of NCAM(-)(/-) mice. NCAM(-)(/-) mice also showed a dramatic reduction in the BDNF protein levels in the hippocampus and prefrontal cortex. This BDNF deficiency was associated with reduced phosphorylation of its receptor TrkB. Importantly, chronic administration of antidepressant amitriptyline partially or completely restored these changes in serotonergic and BDNF systems, respectively. In conclusion, NCAM deficiency lead to prominent and persistent abnormalities in brain serotonergic and BDNF systems, which likely contributes to the behavioral and neurobiological phenotype of NCAM(-/-) mice.

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

The neural cell adhesion molecule (NCAM) is a glycoprotein implicated in cell-cell adhesion, neurite outgrowth and synaptic plasticity. Polysialic acid (polySia) is mainly attached to NCAM (polySia-NCAM) and has an essential role in regulating NCAM-dependent developmental processes that require plasticity, that is, cell migration, axon guidance and synapse formation. Post-mortem and genetic evidence suggests that dysregulation of polySia-NCAM is involved in schizophrenia (SZ). We enrolled 45 patients diagnosed with SZ and 45 healthy individuals who were submitted to polySia-NCAM peripheral quantification, cognitive and psychopathological assessment and structural neuroimaging (brain volumes and diffusion tensor imaging). PolySia-NCAM serum levels were increased in SZ patients, independently of antipsychotic treatment, and were associated with negative symptoms, blunted affect and declarative memory impairment. The increased polySia-NCAM levels were associated with decreased volume in the left prefrontal cortex, namely Brodmann area 46, in patients and increased volume in the same brain area of healthy individuals. As this brain region is involved in the pathophysiology of SZ and its associated phenomenology, the data indicate that polySia-NCAM deserves further scrutiny because of its possible role in early neurodevelopmental mechanisms of the disorder.

Deficits of olfactory interneurons in polysialyltransferase- and NCAM-deficient mice

The neurogenic niche of the anterior subventricular zone (SVZ) persistently generates neuroblasts, which migrate along the rostral migratory stream (RMS) into the olfactory bulb (OB), where they differentiate into granule and periglomerular cells. Loss of the neural cell adhesion molecule NCAM or its post-translational modification polysialic acid (polySia) impairs migration causing accumulations of cells in the proximal RMS and decreased OB volume. Polysialylation of NCAM is implemented by two polysialyltransferases, ST8SIA2 and ST8SIA4, with overlapping functions. Here, we used mice with Ncam1 and polysialyltransferase deletions to analyze how partial or complete loss of polySia synthesis or a combined loss of polySia and NCAM affects the RMS and the interneuron composition in the OB. Numerous calretinin (CR)-positive cells were detected dispersed around the RMS in Ncam1 knockout, St8sia2, St8sia4 double-knockout, and St8sia2, St8sia4, Ncam1 triple-knockout mice, as well as in St8sia2(-/-) but not in St8sia4(-/-) mice. These changes were not reflected by reductions of CR-positive cells in the granule or glomerular layer of the OB. Instead, calbindin-positive periglomerular interneurons were strongly reduced in all polySia-NCAM negative mice and slightly attenuated in St8sia2(-/-) as well as in the St8sia4(-/-) mice, which were devoid of ectopic CR-positive cells along the RMS. Consistent with the early developmental generation of calbindin- as compared with CR-positive OB interneurons, this phenotype was fully developed at postnatal day 5. Together, these results demonstrate that the early development of calbindin-positive periglomerular interneurons depends on the presentation of polySia on NCAM and requires the activity of both polysialyltransferases.

MicroRNA-572 expression in multiple sclerosis patients with different patterns of clinical progression

Background

Demyelination and failure of remyelination are core mechanisms in the pathogenesis of multiple sclerosis (MS); the factor(s) modulating these processes are still mostly unknown. MicroRNA 572 (miR-572) is deregulated in MS and is suggested to targets neural cell adhesion molecule (NCAM), a glycoprotein involved in CNS reparative mechanisms. The aim of this study is to analyze miR-572 in patients with different clinical phenotypes of MS.

Methods

qPCR quantification of miR-572 isolated from serum was performed in 16 primary progressive (PP), 15 secondary progressive (SP), 31 relapsing remitting (RR) MS patients and 15 sex-and age-matched healthy controls.

Results

miR-572 expression was reduced overall in MS patients (p < 0.05) compared to HC; this miRNA was significantly upregulated in SPMS and in RRMS during disease relapse, whereas it was downregulated in PPMS and in quiescent phases of RRMS. miR-572 expression correlated with EDSS scores (R_Sp = 0.491; p < 0.05) independently of the clinical phenotype. The results suggest that this miRNA might be a tool that helps distinguishing between PPMS and SPMS and between relapsing and remitting phases in RRMS.

Conclusions

Evaluation of miR-572 may serve as a non-invasive biomarker for remyelination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0504-2) contains supplementary material, which is available to authorized users.

Role of F3/contactin expression profile in synaptic plasticity and memory in aged mice

We have recently shown that overexpression of the F3/contactin adhesive glycoprotein (also known as Contactin-1) promotes neurogenesis in adult hippocampus, which correlates with improved synaptic plasticity and memory. Because F3/contactin levels physiologically decrease with age, here, we aim at investigating whether its overexpression might counteract the cognitive decline in aged animals. For this we use 20- to 24-month-old TAG/F3 transgenic mice in which F3/contactin overexpression is driven by regulatory sequences from the gene encoding the transient axonal glycoprotein TAG-1 throughout development. We show that aged TAG/F3 mice display improved hippocampal long-term potentiation and memory compared with wild-type littermates. The same mice undergo a decrease of neuronal apoptosis at the hippocampal level, which correlated to a decrease of active caspase-3; by contrast, procaspase-3 and Bax as well as the anti-apoptotic and plasticity-related pathway BDNF/CREB/Bcl-2 were rather increased. Interestingly, amyloid-precursor protein processing was shifted toward sAPPα generation, with a decrease of sAPPβ and amyloid-beta levels. Our data confirm that F3/contactin plays a role in hippocampal synaptic plasticity and memory also in aged mice, suggesting that it acts on molecular pathways related to apoptosis and amyloid-beta production.

Promoter variant rs2301228 on the neural cell adhesion molecule 1 gene confers risk of schizophrenia in Han Chinese

BACKGROUND

Schizophrenia is recognized as a disorder of the brain and neuronal connectivity. The neural cell adhesion molecule 1 (NCAM1) gene plays a crucial role in regulating neuronal connectivity.

METHODS

We conducted a two-stage association analysis on 17 NCAM1 SNPs in two independent Han Chinese schizophrenia case-control cohorts (discovery sample from Hunan Province: 986 patients and 1040 normal controls; replication sample from Yunnan Province: 564 cases and 547 healthy controls). Allele, genotype and haplotype frequencies were compared between case and control samples. Transcription factor binding site prediction and luciferase reporter assays were employed to assess the potential function of promoter SNPs. We detected developmental changes at the transcriptional level of NCAM1 during neuron differentiation in Macaca mulatta neural progenitor cells (NPC). Serum levels of NCAM1 were measured in 72 cases and 88 controls.

RESULTS

A promoter variant, rs2301228, was found to be associated with schizophrenia at the allelic level and was validated in a replication cohort. Luciferase reporter assays demonstrated that risk allele rs2301228-A significantly down-regulated NCAM1 gene transcription compared to the G-allele. Concordantly, schizophrenia patients had a significantly lower level of serum NCAM1 compared to healthy donors. During the NPC neuronal differentiation, NCAM1 mRNA was significantly increased, suggesting a critical role of this gene in neural development.

CONCLUSIONS

Our results provide direct evidence for NCAM1 as a susceptibility gene for schizophrenia, which offers support to a neurodevelopmental model and neuronal connectivity hypothesis in the onset of schizophrenia.

A crucial role for polysialic acid in developmental interneuron migration and the establishment of interneuron densities in the mouse prefrontal cortex

Polysialic acid (polySia) is a unique glycan modification of the neural cell adhesion molecule NCAM and a major determinant of brain development. Polysialylation of NCAM is implemented by the two polysialyltransferases (polySTs) ST8SIA2 and ST8SIA4. Dysregulation of the polySia-NCAM system and variation in ST8SIA2 has been linked to schizophrenia and other psychiatric disorders. Here, we show reduced interneuron densities in the medial prefrontal cortex (mPFC) of mice with either partial or complete loss of polySia synthesizing capacity by ablation of St8sia2, St8sia4, or both. Cells positive for parvalbumin and perineuronal nets as well as somatostatin-positive cells were reduced in the mPFC of all polyST-deficient lines, whereas calretinin-positive cells and the parvalbumin-negative fraction of calbindin-positive cells were unaffected. Reduced interneuron numbers were corroborated by analyzing polyST-deficient GAD67-GFP knock-in mice. The accumulation of precursors in the ganglionic eminences and reduced numbers of tangentially migrating interneurons in the pallium were observed in polyST-deficient embryos. Removal of polySia by endosialidase treatment of organotypic slice cultures led to decreased entry of GAD67-GFP-positive interneurons from the ganglionic eminences into the pallium. Moreover, the acute loss of polySia caused significant reductions in interneuron velocity and leading process length. Thus, attenuation of polySia interferes with the developmental migration of cortical interneurons and causes pathological changes in specific interneuron subtypes. This provides a possible link between genetic variation in polyST genes, neurodevelopmental alterations and interneuron dysfunction in neuropsychiatric disease.

NCAM deficiency in the mouse forebrain impairs innate and learned avoidance behaviours

The neural cell adhesion molecule (NCAM) has been implicated in the development and plasticity of neural circuits and the control of hippocampus- and amygdala-dependent learning and behaviour. Previous studies in constitutive NCAM null mutants identified emotional behaviour deficits related to disturbances of hippocampal and amygdala functions. Here, we studied these behaviours in mice conditionally deficient in NCAM in the postmigratory forebrain neurons. We report deficits in both innate and learned avoidance behaviours, as observed in elevated plus maze and passive avoidance tasks. In contrast, general locomotor activity, trait anxiety or neophobia were unaffected by the mutation. Altered avoidance behaviour of the conditional NCAM mutants was associated with a deficit in serotonergic signalling, as indicated by their reduced responsiveness to (±)-8-hydroxy-2-(dipropylamino)-tetralin-induced hypothermia. Another serotonin-dependent behaviour, namely intermale aggression that is massively increased in constitutively NCAM-deficient mice, was not affected in the forebrain-specific mutants. Our data suggest that genetically or environmentally induced changes of NCAM expression in the late postnatal and mature forebrain determine avoidance behaviour and serotonin (5-HT)1A receptor signalling.

Sialic acids in the brain: gangliosides and polysialic acid in nervous system development, stability, disease, and regeneration

Every cell in nature carries a rich surface coat of glycans, its glycocalyx, which constitutes the cell's interface with its environment. In eukaryotes, the glycocalyx is composed of glycolipids, glycoproteins, and proteoglycans, the compositions of which vary among different tissues and cell types. Many of the linear and branched glycans on cell surface glycoproteins and glycolipids of vertebrates are terminated with sialic acids, nine-carbon sugars with a carboxylic acid, a glycerol side-chain, and an N-acyl group that, along with their display at the outmost end of cell surface glycans, provide for varied molecular interactions. Among their functions, sialic acids regulate cell-cell interactions, modulate the activities of their glycoprotein and glycolipid scaffolds as well as other cell surface molecules, and are receptors for pathogens and toxins. In the brain, two families of sialoglycans are of particular interest: gangliosides and polysialic acid. Gangliosides, sialylated glycosphingolipids, are the most abundant sialoglycans of nerve cells. Mouse genetic studies and human disorders of ganglioside metabolism implicate gangliosides in axon-myelin interactions, axon stability, axon regeneration, and the modulation of nerve cell excitability. Polysialic acid is a unique homopolymer that reaches >90 sialic acid residues attached to select glycoproteins, especially the neural cell adhesion molecule in the brain. Molecular, cellular, and genetic studies implicate polysialic acid in the control of cell-cell and cell-matrix interactions, intermolecular interactions at cell surfaces, and interactions with other molecules in the cellular environment. Polysialic acid is essential for appropriate brain development, and polymorphisms in the human genes responsible for polysialic acid biosynthesis are associated with psychiatric disorders including schizophrenia, autism, and bipolar disorder. Polysialic acid also appears to play a role in adult brain plasticity, including regeneration. Together, vertebrate brain sialoglycans are key regulatory components that contribute to proper development, maintenance, and health of the nervous system.

The interplay of conditional NCAM-knockout and chronic unpredictable stress leads to increased aggression in mice

The neural cell adhesion molecule (NCAM) is a key regulator of brain plasticity. Substantial evidence indicates that NCAM is down-regulated by exposure to sustained stress and chronic stress seems to lead to increased aggression. In addition, constitutional NCAM deletion in mice has been shown to lead to increased intermale aggression and altered emotionality Forebrain-specific postnatal NCAM knockout was previously shown to impair cognitive function, particularly when animals were exposed to subchronic stress, but the effects on emotional and social behavior remain unclear. In this study, we investigated the potential interplay of a forebrain-specific postnatal NCAM deletion and exposure to different lengths of repeated stress (i.e. subchronic: 14 days; chronic: 29 days) on aggressive and emotional behavior. Our results show that postnatal deletion of NCAM in the forebrain leads to increased aggression and altered emotionality depending on the duration of stress, whereas conditional NCAM knockout has no basal impact on these behaviors. These findings support the involvement of NCAM in the regulation of emotional and aggressive behaviors, suggesting that diminished NCAM expression might be a critical vulnerability factor for the development of these behavioral alterations under repeated exposure to stress.

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

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

The dendritic spines of interneurons are dynamic structures influenced by PSA-NCAM expression

Excitatory neurons undergo dendritic spine remodeling in response to different stimuli. However, there is scarce information about this type of plasticity in interneurons. The polysialylated form of the neural cell adhesion molecule (PSA-NCAM) is a good candidate to mediate this plasticity as it participates in neuronal remodeling and is expressed by some mature cortical interneurons, which have reduced dendritic arborization, spine density, and synaptic input. To study the connectivity of the dendritic spines of interneurons and the influence of PSA-NCAM on their dynamics, we have analyzed these structures in a subpopulation of fluorescent spiny interneurons in the hippocampus of glutamic acid decarboxylase-enhanced green fluorescent protein transgenic mice. Our results show that these spines receive excitatory synapses. The depletion of PSA in vivo using the enzyme Endo-Neuraminidase-N (Endo-N) increases spine density when analyzed 2 days after, but decreases it 7 days after. The dendritic spine turnover was also analyzed in real time using organotypic hippocampal cultures: 24 h after the addition of EndoN, we observed an increase in the apparition rate of spines. These results indicate that dendritic spines are important structures in the control of the synaptic input of hippocampal interneurons and suggest that PSA-NCAM is relevant in the regulation of their morphology and connectivity.