Juxtaparanodal clustering of Shaker-like K+ channels in myelinated axons depends on Caspr2 and TAG-1

Cryo-EM structures of the full-length human contactin-2

Contactin-2 (CNTN2), an immunoglobulin cell adhesion molecule (IgCAM) expressed on the neural cell surface, regulates the formation of myelin sheaths, facilitates communication between neurons and axoglial cells, and coordinates the migration of neural cells. However, the assembly of full-length CNTN2 is still not fully elucidated. Here, we found that the full-length human CNTN2 forms a concentration-dependent homodimer. We further determined the cryo-EM structures of the full-length CNTN2, revealing a novel bowknot-shaped scaffold constituted of the Ig1-6 repeats from two protomers, with the flexible ribbon-like FNIII repeats extending outward in opposite directions. The Ig1-6 domains, rather than the previously proposed Ig1-4 domains, have an indispensable role in mediating CNTN2-dependent cell adhesion and clustering. Moreover, structure-guided mutagenesis analyses supported the idea that CNTN2 homodimerization observed in our structure is essential for cell adhesion. Our findings offer novel insights into the mechanism through which CNTN2 forms a homodimer to maintain cell-cell contacts in the nervous system.

GABA/Glutamate Neuron Differentiation Imbalance and Increased AKT/mTOR Signaling in CNTNAP2-/- Cerebral Organoids

Background

The polygenic nature of autism spectrum disorder (ASD) requires the identification of converging genetic pathways during early development to elucidate its complexity and varied manifestations.

Methods

We developed a human cerebral organoid model from induced pluripotent stem cells with targeted genome editing to abolish protein expression of the CNTNAP2 ASD risk gene.

Results

CNTNAP2-/- cerebral organoids displayed accelerated cell cycle, ventricular zone disorganization, and increased cortical folding. Proteomic analysis revealed disruptions in glutamatergic/GABAergic (gamma-aminobutyric acidergic) synaptic pathways and neurodevelopment, and transcriptomic analysis revealed differentially expressed genes belonging to inhibitory neuron-related gene networks. Interestingly, there was a weak correlation between the 2 datasets, suggesting nuanced translational control mechanisms. Along these lines, we found upregulated AKT/mTOR (mechanistic target of rapamycin) signaling in CNTNAP2-/- organoids. Spatial transcriptomic analysis of CNTNAP2-/- ventricular-like zones demonstrated pervasive changes in gene expression, implicating upregulation of cell cycle regulation, synaptic, and glutamatergic/GABAergic pathways. We noted significant overlap of all day-30 organoid omics datasets differentially expressed genes from idiopathic ASD (macrocephaly) induced pluripotent stem cell-derived telencephalic organoids, where FOXG1 was upregulated. Moreover, we detected increased GAD1-expressing and decreased TBR1-expressing cells, suggesting altered GABAergic/glutamatergic neuron development.

Conclusions

These findings potentially highlight a shared mechanism in the early cortical development of various forms of ASD, further elucidate the role of CNTNAP2 in ASD pathophysiology and cortical development, and pave the way for targeted therapies that use cerebral organoids as preclinical models.

Low Plasma Levels of Contactin-Associated Protein-Like 2 in Children with Autism Spectrum Disorder: Links to Neural Development

Background

Autism spectrum disorder (ASD) is a condition of atypical neurodevelopment and is characterized by social communication problems and repetitive patterns of behavior. Early diagnosis and intervention are decisive for managing symptoms and improving outcomes. Contactin-associated protein-like 2 (CNTNAP2) protein is implicated in neural development and plays a role in brain connectivity and synapse formation. Genetic research has shown a possible link between CNTNAP2 and ASD.

Aim

We aimed to discover the blood plasma levels of CNTNAP2 in children with ASD and explore the potential association between CNTNAP2 concentrations and ASD severity.

Methodology

This case-control study included children with ASD (n=40) and aged-matched healthy controls (n=40). Blood plasma levels of CNTNAP2 were measured using enzyme-linked immunosorbent assay (ELISA). The Children Autism Rating Scale (CARS) and Social Responsiveness Scale (SRS) were used to assess the severity of the ASD. Spearman correlation coefficient (r) was used to correlate the variables.

Results

Children with severe ASD had significantly lower CNTNAP2 levels (0.31 (0.14) ng/mL, p=0.003) compared to normal controls (0.47 (0.24) ng/mL). However, CNTNAP2 levels of children with mild autism (0.44(0.22), ng/mL, p=0.77) were not significantly different as compared to normal controls (0.47 (0.24) ng/mL). Furthermore, a significant difference was found between CNTNAP2 levels, by comparing the mild and severe groups based on the CARS (p= 0.05). Furthermore, no significant correlation between CNTNAP2 levels, and severity scores (CARS and SRS), was obtained. However, a significant correlation between CNTNAP2 and age was observed.

Conclusion

The low CNTNAP2 plasma level in children with ASD indicated that it might be involved in the pathophysiology of ASD. Nevertheless, these results should be interpreted with care till more studies are achieved using a larger population to decide whether the reduction in CNTNAP2 plasma level is a mere outcome of ASD or it plays a pathogenic role in the disease.

The neurobiology and immunology of CASPR2-associated neurological disorders

CASPR2-associated neurological disorders encompass a wide clinical spectrum broadly divided into overlapping three autoimmune syndromes: CASPR2 limbic encephalitis, Morvan syndrome, and Isaacs syndrome. CASPR2 is a neuronal protein expressed at different sites in the central and peripheral nervous system and has a variety of roles and functions regarding neuronal excitability, synaptic plasticity, and homeostasis of inhibitory networks, most of which are only partially understood. CASPR2 antibodies have various pathogenic effects including internalization of CASPR2, disruption of protein-protein interactions, and, possibly, complement activation. Their pathogenic effect is well demonstrated in the limbic encephalitis phenotype, but the role of pathogenic antibodies in the development of other clinical manifestations is less clear. CASPR2 limbic encephalitis also differ from the other CASPR2-associated disorders in regard to HLA allele and paraneoplastic associations, suggesting it has immunological mechanisms distinct from the other clinical forms. Future studies are needed to better understand how the immunological alterations lead to the different phenotypes associated with CASPR2 antibodies.

Roles of KCNA2 in Neurological Diseases: from Physiology to Pathology

Potassium voltage-gated channel subfamily a member 2 (Kv1.2, encoded by KCNA2) is highly expressed in the central and peripheral nervous systems. Based on the patch clamp studies, gain-of function (GOF), loss-of-function (LOF), and a mixed type (GOF/LOF) variants can cause different conditions/disorders. KCNA2-related neurological diseases include epilepsy, intellectual disability (ID), attention deficit/hyperactive disorder (ADHD), autism spectrum disorder (ASD), pain as well as autoimmune and movement disorders. Currently, the molecular mechanisms for the reported variants in causing diverse disorders are unknown. Consequently, this review brings up to date the related information regarding the structure and function of Kv1.2 channel, expression patterns, neuronal localizations, and tetramerization as well as important cell and animal models. In addition, it provides updates on human genetic variants, genotype-phenotype correlations especially highlighting the deep insight into clinical prognosis of KCNA2-related developmental and epileptic encephalopathy, mechanisms, and the potential treatment targets for all KCNA2-related neurological disorders.

Molecular mechanism of contactin 2 homophilic interaction

Contactin 2 (CNTN2) is a cell adhesion molecule involved in axon guidance, neuronal migration, and fasciculation. The ectodomains of CNTN1-CNTN6 are composed of six Ig domains (Ig1-Ig6) and four FN domains. Here, we show that CNTN2 forms transient homophilic interactions (KD ∼200 nM). Cryo-EM structures of full-length CNTN2 and CNTN2_Ig1-Ig6 reveal a T-shaped homodimer formed by intertwined, parallel monomers. Unexpectedly, the horseshoe-shaped Ig1-Ig4 headpieces extend their Ig2-Ig3 tips outwards on either side of the homodimer, while Ig4, Ig5, Ig6, and the FN domains form a central stalk. Cross-linking mass spectrometry and cell-based binding assays confirm the 3D assembly of the CNTN2 homodimer. The interface mediating homodimer formation differs between CNTNs, as do the homophilic versus heterophilic interaction mechanisms. The CNTN family thus encodes a versatile molecular platform that supports a very diverse portfolio of protein interactions and that can be leveraged to strategically guide neural circuit development.

Antibody-Mediated Nodo- and Paranodopathies

The recent discovery of pathogenic antibodies targeting cell adhesion molecules of the node of Ranvier has prompted efforts to develop a new classification for a subset of antibody-mediated peripheral neuropathies. These autoimmune nodo- and paranodopathies encompass epitopes such as neurofascin 155, neurofascin 186, contactin-1, and contactin-associated protein 1, with a high likelihood of involving additional yet unidentified proteins. So far, the investigation of this subset of patients was primarily focused on adults, with only rare reports of pediatric cases. Low awareness among pediatricians and insufficient availability of appropriate diagnostic methods in many laboratories may mask a higher pediatric incidence than currently observed. Diagnosis is made by transfected cell-based assays and ELISA to characterize the specific target antigen and antibody subclass that provides insight into the pathophysiology. Clinical features often resemble those of CIDP or GBS in adults, whilst in pediatric patients, although rare, an atypical CIDP phenotype has predominantly been reported. Yet, in contrast to classical immune-mediated neuropathies, the clinical course is usually rapidly progressive, and response to classical first-line therapy often poor. Although electrophysiological signs of demyelination are observed, segmental demyelination and inflammation are not present on pathological examination. Rather, few neuropathological reports demonstrate features of axonal neuropathy without signs of true de- or remyelination. This review aims to summarize recent findings on such nodo- and paranodoneuropathies, shining light on features of these disorders in pediatric patients, a still little-explored field with only a few reports currently present.

Degraded tactile coding in the Cntnap2 mouse model of autism

Atypical sensory processing is common in autism, but how neural coding is disrupted in sensory cortex is unclear. We evaluate whisker touch coding in L2/3 of somatosensory cortex (S1) in Cntnap2-/- mice, which have reduced inhibition. This classically predicts excess pyramidal cell spiking, but this remains controversial, and other deficits may dominate. We find that c-fos expression is elevated in S1 of Cntnap2-/- mice under spontaneous activity conditions but is comparable to that of control mice after whisker stimulation, suggesting normal sensory-evoked spike rates. GCaMP8m imaging from L2/3 pyramidal cells shows no excess whisker responsiveness, but it does show multiple signs of degraded somatotopic coding. This includes broadened whisker-tuning curves, a blurred whisker map, and blunted whisker point representations. These disruptions are greater in noisy than in sparse sensory conditions. Tuning instability across days is also substantially elevated in Cntnap2-/-. Thus, Cntnap2-/- mice show no excess sensory-evoked activity, but a degraded and unstable tactile code in S1.

Cntnap2 loss drives striatal neuron hyperexcitability and behavioral inflexibility

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by two major diagnostic criteria - persistent deficits in social communication and interaction, and the presence of restricted, repetitive patterns of behavior (RRBs). Evidence from both human and animal model studies of ASD suggest that alteration of striatal circuits, which mediate motor learning, action selection, and habit formation, may contribute to the manifestation of RRBs. CNTNAP2 is a syndromic ASD risk gene, and loss of function of Cntnap2 in mice is associated with RRBs. How loss of Cntnap2 impacts striatal neuron function is largely unknown. In this study, we utilized Cntnap2-/- mice to test whether altered striatal neuron activity contributes to aberrant motor behaviors relevant to ASD. We find that Cntnap2-/- mice exhibit increased cortical drive of striatal projection neurons (SPNs), with the most pronounced effects in direct pathway SPNs. This enhanced drive is likely due to increased intrinsic excitability of SPNs, which make them more responsive to cortical inputs. We also find that Cntnap2-/- mice exhibit spontaneous repetitive behaviors, increased motor routine learning, and cognitive inflexibility. Increased corticostriatal drive, in particular of the direct pathway, may contribute to the acquisition of repetitive, inflexible behaviors in Cntnap2 mice.

Contactin-associated protein-like 2 (CNTNAP2) mutations impair the essential α-secretase cleavages, leading to autism-like phenotypes

Mutations in the Contactin-associated protein-like 2 (CNTNAP2) gene are associated with autism spectrum disorder (ASD), and ectodomain shedding of the CNTNAP2 protein plays a role in its function. However, key enzymes involved in the C-terminal cleavage of CNTNAP2 remain largely unknown, and the effect of ASD-associated mutations on this process and its role in ASD pathogenesis remain elusive. In this report we showed that CNTNAP2 undergoes sequential cleavages by furin, ADAM10/17-dependent α-secretase and presenilin-dependent γ-secretase. We identified that the cleavage sites of ADAM10 and ADAM17 in CNTNAP2 locate at its C-terminal residue I79 and L96, and the main α-cleavage product C79 by ADAM10 is required for the subsequent γ-secretase cleavage to generate CNTNAP2 intracellular domain (CICD). ASD-associated CNTNAP2 mutations impair the α-cleavage to generate C79, and the inhibition leads to ASD-like repetitive and social behavior abnormalities in the Cntnap2-I1254T knock-in mice. Finally, exogenous expression of C79 improves autism-like phenotypes in the Cntnap2-I1254T knock-in and Cntnap2-/- knockout mice. This data demonstrates that the α-secretase is essential for CNTNAP2 processing and its function. Our study indicates that inhibition of the cleavage by pathogenic mutations underlies ASD pathogenesis, and upregulation of its C-terminal fragments could have therapeutical potentials for ASD treatment.

From synaptic dysfunction to atypical emotional processing in autism

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition mainly characterized by social impairments and repetitive behaviors. Among these core symptoms, a notable aspect of ASD is the presence of emotional complexities, including high rates of anxiety disorders. The inherent heterogeneity of ASD poses a unique challenge in understanding its etiological origins, yet the utilization of diverse animal models replicating ASD traits has enabled researchers to dissect the intricate relationship between autism and atypical emotional processing. In this review, we delve into the general findings about the neural circuits underpinning one of the most extensively researched and evolutionarily conserved emotional states: fear and anxiety. Additionally, we explore how distinct ASD animal models exhibit various anxiety phenotypes, making them a crucial tool for dissecting ASD's multifaceted nature. Overall, to a proper display of fear response, it is crucial to properly process and integrate sensorial and visceral cues to the fear-induced stimuli. ASD individuals exhibit altered sensory processing, possibly contributing to the emergence of atypical phobias, a prevailing anxiety disorder manifested in this population. Moreover, these individuals display distinctive alterations in a pivotal fear and anxiety processing hub, the amygdala. By examining the neurobiological mechanisms underlying fear and anxiety regulation, we can gain insights into the factors contributing to the distinctive emotional profile observed in individuals with ASD. Such insights hold the potential to pave the way for more targeted interventions and therapies that address the emotional challenges faced by individuals within the autism spectrum.

Contactin 2 homophilic adhesion structure and conformational plasticity

The cell-surface attached glycoprotein contactin 2 is ubiquitously expressed in the nervous system and mediates homotypic cell-cell interactions to organize cell guidance, differentiation, and adhesion. Contactin 2 consists of six Ig and four fibronectin type III domains (FnIII) of which the first four Ig domains form a horseshoe structure important for homodimerization and oligomerization. Here we report the crystal structure of the six-domain contactin 2Ig1-6 and show that the Ig5-Ig6 combination is oriented away from the horseshoe with flexion in interdomain connections. Two distinct dimer states, through Ig1-Ig2 and Ig3-Ig6 interactions, together allow formation of larger oligomers. Combined size exclusion chromatography with multiangle light scattering (SEC-MALS), small-angle X-ray scattering (SAXS) and native MS analysis indicates contactin 2Ig1-6 oligomerizes in a glycan dependent manner. SAXS and negative-stain electron microscopy reveals inherent plasticity of the contactin 2 full-ectodomain. The combination of intermolecular binding sites and ectodomain plasticity explains how contactin 2 can function as a homotypic adhesion molecule in diverse intercellular environments.

Hippocampal and peripheral blood DNA methylation signatures correlate at the gene and pathway level in a mouse model of autism

Autism spectrum disorders (ASD) are polygenic multifactorial disorders influenced by environmental factors. ASD-related differential DNA methylation has been found in human peripheral tissues, such as placenta, paternal sperm, buccal epithelium, and blood. However, these data lack direct comparison of DNA methylation levels with brain tissue from the same individual to determine the extent that peripheral tissues are surrogates for behavior-related disorders. Here, whole genome methylation profiling at all the possible sites throughout the mouse genome (>25 million) from both brain and blood tissues revealed novel insights into the systemic contributions of DNA methylation to ASD. Sixty-six differentially methylated regions (DMRs) share the same genomic coordinates in these two tissues, many of which are linked to risk genes for neurodevelopmental disorders and intellectual disabilities (e.g. Prkch, Ptn, Hcfc1, Mid1, and Nfia). Gene ontological pathways revealed a significant number of common terms between brain and blood (N = 65 terms), and nearly half (30/65) were associated with brain/neuronal development. Furthermore, seven DMR-associated genes among these terms contain methyl-sensitive transcription factor sequence motifs within the DMRs of both tissues; four of them (Cux2, Kcnip2, Fgf13, and Mrtfa) contain the same methyl-sensitive transcription factor binding sequence motifs (HES1/2/5, TBX2 and TFAP2C), suggesting DNA methylation influences the binding of common transcription factors required for gene expression. Together, these findings suggest that peripheral blood is a good surrogate tissue for brain and support that DNA methylation contributes to altered gene regulation in the pathogenesis of ASD.

CDKL5-mediated developmental tuning of neuronal excitability and concomitant regulation of transcriptome

Cyclin-dependent kinase-like 5 (CDKL5) is a serine-threonine kinase enriched in the forebrain to regulate neuronal development and function. Patients with CDKL5 deficiency disorder (CDD), a severe neurodevelopmental condition caused by mutations of CDKL5 gene, present early-onset epilepsy as the most prominent feature. However, spontaneous seizures have not been reported in mouse models of CDD, raising vital questions on the human-mouse differences and the roles of CDKL5 in early postnatal brains. Here, we firstly measured electroencephalographic (EEG) activities via a wireless telemetry system coupled with video-recording in neonatal mice. We found that mice lacking CDKL5 exhibited spontaneous epileptic EEG discharges, accompanied with increased burst activities and ictal behaviors, specifically at postnatal day 12 (P12). Intriguingly, those epileptic spikes disappeared after P14. We next performed an unbiased transcriptome profiling in the dorsal hippocampus and motor cortex of Cdkl5 null mice at different developmental timepoints, uncovering a set of age-dependent and brain region-specific alterations of gene expression in parallel with the transient display of epileptic activities. Finally, we validated multiple differentially expressed genes, such as glycine receptor alpha 2 and cholecystokinin, at the transcript or protein levels, supporting the relevance of these genes to CDKL5-regulated excitability. Our findings reveal early-onset neuronal hyperexcitability in mouse model of CDD, providing new insights into CDD etiology and potential molecular targets to ameliorate intractable neonatal epilepsy.

Loss of CNTNAP2 Alters Human Cortical Excitatory Neuron Differentiation and Neural Network Development

BACKGROUND

Loss-of-function mutations in the contactin-associated protein-like 2 (CNTNAP2) gene are causal for neurodevelopmental disorders, including autism, schizophrenia, epilepsy, and intellectual disability. CNTNAP2 encodes CASPR2, a single-pass transmembrane protein that belongs to the neurexin family of cell adhesion molecules. These proteins have a variety of functions in developing neurons, including connecting presynaptic and postsynaptic neurons, and mediating signaling across the synapse.

METHODS

To study the effect of loss of CNTNAP2 function on human cerebral cortex development, and how this contributes to the pathogenesis of neurodevelopmental disorders, we generated human induced pluripotent stem cells from one neurotypical control donor null for full-length CNTNAP2, modeling cortical development from neurogenesis through to neural network formation in vitro.

RESULTS

CNTNAP2 is particularly highly expressed in the first two populations of early-born excitatory cortical neurons, and loss of CNTNAP2 shifted the relative proportions of these two neuronal types. Live imaging of excitatory neuronal growth showed that loss of CNTNAP2 reduced neurite branching and overall neuronal complexity. At the network level, developing cortical excitatory networks null for CNTNAP2 had complex changes in activity compared with isogenic controls: an initial period of relatively reduced activity compared with isogenic controls, followed by a lengthy period of hyperexcitability, and then a further switch to reduced activity.

CONCLUSIONS

Complete loss of CNTNAP2 contributes to the pathogenesis of neurodevelopmental disorders through complex changes in several aspects of human cerebral cortex excitatory neuron development that culminate in aberrant neural network formation and function.

Loss of ASD-related molecule Cntnap2 affects colonic motility in mice

Gastrointestinal (GI) symptoms are highly prevalent among individuals with autism spectrum disorder (ASD), but the molecular link between ASD and GI dysfunction remains poorly understood. The enteric nervous system (ENS) is critical for normal GI motility and has been shown to be altered in mouse models of ASD and other neurological disorders. Contactin-associated protein-like 2 (Cntnap2) is an ASD-related synaptic cell-adhesion molecule important for sensory processing. In this study, we examine the role of Cntnap2 in GI motility by characterizing Cntnap2's expression in the ENS and assessing GI function in Cntnap2 mutant mice. We find Cntnap2 expression predominately in enteric sensory neurons. We further assess in vivo and ex vivo GI motility in Cntnap2 mutants and show altered transit time and colonic motility patterns. The overall organization of the ENS appears undisturbed. Our results suggest that Cntnap2 plays a role in GI function and may provide a molecular link between ASD and GI dysfunction.

Gene Expression Profiling in Trigeminal Ganglia from Cntnap2-/- and Shank3b-/- Mouse Models of Autism Spectrum Disorder

Sensory difficulties represent a crucial issue in the life of autistic individuals. The diagnostic and statistical manual of mental disorders describes both hyper- and hypo-responsiveness to sensory stimulation as a criterion for the diagnosis autism spectrum disorders (ASD). Among the sensory domain affected in ASD, altered responses to tactile stimulation represent the most commonly reported sensory deficits. Although tactile abnormalities have been reported in monogenic cohorts of patients and genetic mouse models of ASD, the underlying mechanisms are still unknown. Traditionally, autism research has focused on the central nervous system as the target to infer the neurobiological bases of such tactile abnormalities. Nonetheless, the peripheral nervous system represents the initial site of processing of sensory information and a potential site of dysfunction in the sensory cascade. Here we investigated the gene expression deregulation in the trigeminal ganglion (which directly receives tactile information from whiskers) in two genetic models of syndromic autism (Shank3b and Cntnap2 mutant mice) at both adult and juvenile ages. We found several neuronal and non-neuronal markers involved in inhibitory, excitatory, neuroinflammatory and sensory neurotransmission to be differentially regulated within the trigeminal ganglia of both adult and juvenile Shank3b and Cntnap2 mutant mice. These results may help in disentangling the multifaced complexity of sensory abnormalities in autism and open avenues for the development of peripherally targeted treatments for tactile sensory deficits exhibited in ASD.

A class-specific effect of dysmyelination on the excitability of hippocampal interneurons

The role of myelination for axonal conduction is well-established in projection neurons but little is known about its significance in GABAergic interneurons. Myelination is discontinuous along interneuron axons and the mechanisms controlling myelin patterning and segregation of ion channels at the nodes of Ranvier have not been elucidated. Protein 4.1B is implicated in the organization of the nodes of Ranvier as a linker between paranodal and juxtaparanodal membrane proteins to the spectrin cytoskeleton. In the present study, 4.1B KO mice are used as a genetic model to analyze the functional role of myelin in Lhx6-positive parvalbumin (PV) and somatostatin (SST) neurons, two major classes of GABAergic neurons in the hippocampus. We show that 4.1B-deficiency induces disruption of juxtaparanodal K+ channel clustering and mislocalization of nodal or heminodal Na+ channels. Strikingly, 4.1B-deficiency causes loss of myelin in GABAergic axons in the hippocampus. In particular, stratum oriens SST cells display severe axonal dysmyelination and a reduced excitability. This reduced excitability is associated with a decrease in occurrence probability of small amplitude synaptic inhibitory events on pyramidal cells. In contrast, stratum pyramidale fast-spiking PV cells do not appear affected. In conclusion, our results indicate a class-specific effect of dysmyelination on the excitability of hippocampal interneurons associated with a functional alteration of inhibitory drive.

Degraded tactile coding in the Cntnap2 mouse model of autism

Atypical sensory processing in autism involves altered neural circuit function and neural coding in sensory cortex, but the nature of coding disruption is poorly understood. We characterized neural coding in L2/3 of whisker somatosensory cortex (S1) of Cntnap2-/- mice, an autism model with pronounced hypofunction of parvalbumin (PV) inhibitory circuits. We tested for both excess spiking, which is often hypothesized in autism models with reduced inhibition, and alterations in somatotopic coding, using c-fos immunostaining and 2-photon calcium imaging in awake mice. In Cntnap2-/- mice, c-fos-(+) neuron density was elevated in L2/3 of S1 under spontaneous activity conditions, but comparable to control mice after whisker stimulation, suggesting that sensory-evoked spiking was relatively normal. 2-photon GCaMP8m imaging in L2/3 pyramidal cells revealed no increase in whisker-evoked response magnitude, but instead showed multiple signs of degraded somatotopic coding. These included broadening of whisker tuning curves, blurring of the whisker map, and blunting of the point representation of each whisker. These altered properties were more pronounced in noisy than sparse sensory conditions. Tuning instability, assessed over 2-3 weeks of longitudinal imaging, was also significantly increased in Cntnap2-/- mice. Thus, Cntnap2-/- mice show no excess spiking, but a degraded and unstable tactile code in S1.

Loss of ASD-Related Molecule Cntnap2 Affects Colonic Motility in Mice

Gastrointestinal (GI) symptoms are highly prevalent among individuals with autism spectrum disorder (ASD), but the molecular link between ASD and GI dysfunction remains poorly understood. The enteric nervous system (ENS) is critical for normal GI motility and has been shown to be altered in mouse models of ASD and other neurological disorders. Contactin-associated protein-like 2 (Cntnap2) is an ASD-related synaptic cell-adhesion molecule important for sensory processing. In this study, we examine the role of Cntnap2 in GI motility by characterizing Cntnap2's expression in the ENS and assessing GI function in Cntnap2 mutant mice. We find Cntnap2 expression predominately in enteric sensory neurons. We further assess in-vivo and ex-vivo GI motility in Cntnap2 mutants and show altered transit time and colonic motility patterns. The overall organization of the ENS appears undisturbed. Our results suggest that Cntnap2 plays a role in GI function and may provide a molecular link between ASD and GI dysfunction.

Combined GWAS and single cell transcriptomics uncover the underlying genes and cell types in disorders of gut-brain interaction

Disorders of gut-brain interaction (DGBIs), formerly known as functional gastrointestinal disorders, are extremely common and historically difficult to manage. This is largely because their cellular and molecular mechanisms have remained poorly understood and understudied. One approach to unravel the molecular underpinnings of complex disorders such as DGBIs is performing genome wide association studies (GWASs). However, due to the heterogenous and non-specific nature of GI symptoms, it has been difficult to accurately classify cases and controls. Thus, to perform reliable studies, we need to access large patient populations which has been difficult to date. Here, we leveraged the UK Biobank (UKBB) database, containing genetic and medical record data of over half a million individuals, to perform GWAS for five DGBI categories: functional chest pain, functional diarrhea, functional dyspepsia, functional dysphagia, and functional fecal incontinence. By applying strict inclusion and exclusion criteria, we resolved patient populations and identified genes significantly associated with each condition. Leveraging multiple human single-cell RNA-sequencing datasets, we found that the disease associated genes were highly expressed in enteric neurons, which innervate and control GI functions. Further expression and association testing-based analyses revealed specific enteric neuron subtypes consistently linked with each DGBI. Furthermore, protein-protein interaction analysis of each of the disease associated genes revealed protein networks specific to each DGBI, including hedgehog signaling for functional chest pain and neuronal function and neurotransmission for functional diarrhea and functional dyspepsia. Finally, through retrospective medical record analysis we found that drugs that inhibit these networks are associated with an increased disease risk, including serine/threonine kinase 32B drugs for functional chest pain, solute carrier organic anion transporter family member 4C1, mitogen-activated protein kinase 6, and dual serine/threonine and tyrosine protein kinase drugs for functional dyspepsia, and serotonin transporter drugs for functional diarrhea. This study presents a robust strategy for uncovering the tissues, cell types, and genes involved in DGBIs, presenting novel predictions of the mechanisms underlying these historically intractable and poorly understood diseases.

The Node of Ranvier as an Interface for Axo-Glial Interactions: Perturbation of Axo-Glial Interactions in Various Neurological Disorders

The action potential conduction along the axon is highly dependent on the healthy interactions between the axon and myelin-producing glial cells. Myelin, which facilitates action potential, is the protective insulation around the axon formed by Schwann cells and oligodendrocytes in the peripheral (PNS) and central nervous system (CNS), respectively. Myelin is a continuous structure with intermittent gaps called nodes of Ranvier, which are the sites enriched with ion channels, transmembrane, scaffolding, and cytoskeletal proteins. Decades-long extensive research has identified a comprehensive proteome with strictly regularized localization at the node of Ranvier. Concurrently, axon-glia interactions at the node of Ranvier have gathered significant attention as the pathophysiological targets for various neurodegenerative disorders. Numerous studies have shown the alterations in the axon-glia interactions culminating in neurological diseases. In this review, we have provided an update on the molecular composition of the node of Ranvier. Further, we have discussed in detail the consequences of disruption of axon-glia interactions during the pathogenesis of various CNS and PNS disorders.

Neuroanatomical Alterations in the CNTNAP2 Mouse Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is associated with neurodevelopmental alterations, including atypical forebrain cellular organization. Mutations in several ASD-related genes often result in cerebral cortical anomalies, such as the abnormal developmental migration of excitatory pyramidal cells and the malformation of inhibitory neuronal circuitry. Notably here, mutations in the CNTNAP2 gene result in ectopic superficial cortical neurons stalled in lower cortical layers and alterations to the balance of cortical excitation and inhibition. However, the broader circuit-level implications of these findings have not been previously investigated. Therefore, we assessed whether ectopic cortical neurons in CNTNAP2 mutant mice form aberrant connections with higher-order thalamic nuclei, potentially accounting for some autistic behaviors, such as repetitive and hyperactive behaviors. Furthermore, we assessed whether the development of parvalbumin-positive (PV) cortical interneurons and their specialized matrix support structures, called perineuronal nets (PNNs), were altered in these mutant mice. We found alterations in both ectopic neuronal connectivity and in the development of PNNs, PV neurons and PNNs enwrapping PV neurons in various sensory cortical regions and at different postnatal ages in the CNTNAP2 mutant mice, which likely lead to some of the cortical excitation/inhibition (E/I) imbalance associated with ASD. These findings suggest neuroanatomical alterations in cortical regions that underlie the emergence of ASD-related behaviors in this mouse model of the disorder.

Compromised Myelin and Axonal Molecular Organization Following Adult-Onset Sulfatide Depletion

3-O-sulfogalactosylceramide, or sulfatide, is a prominent myelin glycosphingolipid reduced in the normal appearing white matter (NAWM) in Multiple Sclerosis (MS), indicating that sulfatide reduction precedes demyelination. Using a mouse model that is constitutively depleted of sulfatide, we previously demonstrated that sulfatide is essential during development for the establishment and maintenance of myelin and axonal integrity and for the stable tethering of certain myelin proteins in the sheath. Here, using an adult-onset depletion model of sulfatide, we employ a combination of ultrastructural, immunohistochemical and biochemical approaches to analyze the consequence of sulfatide depletion from the adult CNS. Our findings show a progressive loss of axonal protein domain organization, which is accompanied by axonal degeneration, with myelin sparing. Similar to our previous work, we also observe differential myelin protein anchoring stabilities that are both sulfatide dependent and independent. Most notably, stable anchoring of neurofascin155, a myelin paranodal protein that binds the axonal paranodal complex of contactin/Caspr1, requires sulfatide. Together, our findings show that adult-onset sulfatide depletion, independent of demyelination, is sufficient to trigger progressive axonal degeneration. Although the pathologic mechanism is unknown, we propose that sulfatide is required for maintaining myelin organization and subsequent myelin-axon interactions and disruptions in these interactions results in compromised axon structure and function.

CNTNAP2 Protein Is Degraded by the Ubiquitin-Proteasome System and the Macroautophagy-Lysosome Pathway

Contactin-associated protein-like 2 (CNTNAP2) gene, located on chromosome 7q35, is one of the largest genes in the human genome. CNTNAP2 protein is a type-I transmembrane protein specifically expressed in the nervous system, with versatile roles in the axonal organization, synaptic functions, neuronal migration, and functional connectivity. CNTNAP2 has been widely investigated as a risk gene for autism spectrum disorder (ASD), and recent studies also implicated CNTNAP2 in Alzheimer's disease (AD). Knowledge of the regulations on CNTNAP2's life cycle is necessary for understanding the related physiological functions and pathological conditions. However, the mechanisms underlying CNTNAP2 protein degradation remain elusive. Therefore, we systematically investigated the half-life and degradation pathway of the human CNTNAP2 protein. We discovered that CNTNAP2 has C-terminal fragments (CTF), which may have essential physiological functions. Our results demonstrated that CNTNAP2 full-length protein and CTF have a short half-life of about 3-4 h. CNTNAP2 proteins are degraded by the ubiquitin-proteasome system and the macroautophagy-lysosome pathway, while the lysosome pathway is more common for CNTNAP2 degradation. This study will provide novel insights and valuable tools for CNTNAP2 functional research in physiological and pathological scenarios.

LGI3/2-ADAM23 interactions cluster Kv1 channels in myelinated axons to regulate refractory period

Along myelinated axons, Shaker-type potassium channels (Kv1) accumulate at high density in the juxtaparanodal region, directly adjacent to the paranodal axon-glia junctions that flank the nodes of Ranvier. However, the mechanisms that control the clustering of Kv1 channels, as well as their function at this site, are still poorly understood. Here we demonstrate that axonal ADAM23 is essential for both the accumulation and stability of juxtaparanodal Kv1 complexes. The function of ADAM23 is critically dependent on its interaction with its extracellular ligands LGI2 and LGI3. Furthermore, we demonstrate that juxtaparanodal Kv1 complexes affect the refractory period, thus enabling high-frequency burst firing of action potentials. Our findings not only reveal a previously unknown molecular pathway that regulates Kv1 channel clustering, but they also demonstrate that the juxtaparanodal Kv1 channels that are concealed below the myelin sheath, play a significant role in modifying axonal physiology.

Robust odor identification in novel olfactory environments in mice

Relevant odors signaling food, mates, or predators can be masked by unpredictable mixtures of less relevant background odors. Here, we developed a mouse behavioral paradigm to test the role played by the novelty of the background odors. During the task, mice identified target odors in previously learned background odors and were challenged by catch trials with novel background odors, a task similar to visual CAPTCHA. Female wild-type (WT) mice could accurately identify known targets in novel background odors. WT mice performance was higher than linear classifiers and the nearest neighbor classifier trained using olfactory bulb glomerular activation patterns. Performance was more consistent with an odor deconvolution method. We also used our task to investigate the performance of female Cntnap2^-/- mice, which show some autism-like behaviors. Cntnap2^-/- mice had glomerular activation patterns similar to WT mice and matched WT mice target detection for known background odors. However, Cntnap2^-/- mice performance fell almost to chance levels in the presence of novel backgrounds. Our findings suggest that mice use a robust algorithm for detecting odors in novel environments and this computation is impaired in Cntnap2^-/- mice.

Differential impacts of Cntnap2 heterozygosity and Cntnap2 null homozygosity on axon and myelinated fiber development in mouse

Over the last decade, a large variety of alterations of the Contactin Associated Protein 2 (CNTNAP2) gene, encoding Caspr2, have been identified in several neuronal disorders, including neurodevelopmental disorders and peripheral neuropathies. Some of these alterations are homozygous but most are heterozygous, and one of the current challenges is to estimate to what extent they could affect the functions of Caspr2 and contribute to the development of these pathologies. Notably, it is not known whether the disruption of a single CNTNAP2 allele could be sufficient to perturb the functions of Caspr2. To get insights into this issue, we questioned whether Cntnap2 heterozygosity and Cntnap2 null homozygosity in mice could both impact, either similarly or differentially, some specific functions of Caspr2 during development and in adulthood. We focused on yet poorly explored functions of Caspr2 in axon development and myelination, and performed a morphological study from embryonic day E17.5 to adulthood of two major brain interhemispheric myelinated tracts, the anterior commissure (AC) and the corpus callosum (CC), comparing wild-type (WT), Cntnap2 ^-/- and Cntnap2 ^+/- mice. We also looked for myelinated fiber abnormalities in the sciatic nerves of mutant mice. Our work revealed that Caspr2 controls the morphology of the CC and AC throughout development, axon diameter at early developmental stages, cortical neuron intrinsic excitability at the onset of myelination, and axon diameter and myelin thickness at later developmental stages. Changes in axon diameter, myelin thickness and node of Ranvier morphology were also detected in the sciatic nerves of the mutant mice. Importantly, most of the parameters analyzed were affected in Cntnap2 ^+/- mice, either specifically, more severely, or oppositely as compared to Cntnap2 ^-/- mice. In addition, Cntnap2 ^+/- mice, but not Cntnap2 ^-/- mice, showed motor/coordination deficits in the grid-walking test. Thus, our observations show that both Cntnap2 heterozygosity and Cntnap2 null homozygosity impact axon and central and peripheral myelinated fiber development, but in a differential manner. This is a first step indicating that CNTNAP2 alterations could lead to a multiplicity of phenotypes in humans, and raising the need to evaluate the impact of Cntnap2 heterozygosity on the other neurodevelopmental functions of Caspr2.

Case report: Autoimmune encephalitis associated with anti-CASPR2 antibody mimicking cerebral infarction

Autoimmune encephalitis associated with antibody against contactin-associated protein-like 2 (CASPR2) varies in its clinical presentation. The disease is difficult to distinguish from some other conditions without testing for anti-CASPR2 antibody in blood serum or cerebrospinal fluid. Cerebral lesions are typically detected by magnetic resonance imaging (MRI) in the medial temporal lobe or hippocampus. Here, we describe a patient with anti-CASPR2 antibody autoimmune encephalitis whose imaging manifestations mimicked infarction in the left frontal lobe. The 48-year-old man reported memory loss, convulsions, and disturbed consciousness one day after drinking wine. The right upper arm showed reduced autonomous movement after painful stimuli, and MRI showed abnormal hyperintensities in the left frontal lobe on T2 and fluid-attenuated inversion recovery sequences, restricted diffusion, and decreased cerebral blood flow, mimicking acute cerebral infarction. Contrast-enhanced T1-weighted MRI showed gyral enhancement involving the cortex and subcortical white matter. Computed tomography angiography did not identify culprit blood vessels. Symptoms did not improve with anti-platelet or lipid-lowering therapy. Screening for serum antibodies associated with autoimmune encephalitis detected antibody against CASPR2, and intravenous immunoglobulin therapy substantially improved symptoms. This case provides the first indication that anti-CASPR2 antibody-associated autoimmune encephalitis can manifest as involvement of the cortex and subcortical white matter in the frontal lobe based on MRI. It emphasizes the need for thorough investigation, including analysis of potential autoimmunity, of patients whose imaging findings mimic ischemic infarction.

Cntnap2-dependent molecular networks in autism spectrum disorder revealed through an integrative multi-omics analysis

Autism spectrum disorder (ASD) is a major neurodevelopmental disorder in which patients present with core symptoms of social communication impairment, restricted interest, and repetitive behaviors. Although various studies have been performed to identify ASD-related mechanisms, ASD pathology is still poorly understood. CNTNAP2 genetic variants have been found that represent ASD genetic risk factors, and disruption of Cntnap2 expression has been associated with ASD phenotypes in mice. In this study, we performed an integrative multi-omics analysis by combining quantitative proteometabolomic data obtained with Cntnap2 knockout (KO) mice with multi-omics data obtained from ASD patients and forebrain organoids to elucidate Cntnap2-dependent molecular networks in ASD. To this end, a mass spectrometry-based proteometabolomic analysis of the medial prefrontal cortex in Cntnap2 KO mice led to the identification of Cntnap2-associated molecular features, and these features were assessed in combination with multi-omics data obtained on the prefrontal cortex in ASD patients to identify bona fide ASD cellular processes. Furthermore, a reanalysis of single-cell RNA sequencing data obtained from forebrain organoids derived from patients with CNTNAP2-associated ASD revealed that the aforementioned identified ASD processes were mainly linked to excitatory neurons. On the basis of these data, we constructed Cntnap2-associated ASD network models showing mitochondrial dysfunction, axonal impairment, and synaptic activity. Our results may shed light on the Cntnap2-dependent molecular networks in ASD.

The Role of Zinc and NMDA Receptors in Autism Spectrum Disorders

NMDA-type glutamate receptors are critical for synaptic plasticity in the central nervous system. Their unique properties and age-dependent arrangement of subunit types underpin their role as a coincidence detector of pre- and postsynaptic activity during brain development and maturation. NMDAR function is highly modulated by zinc, which is co-released with glutamate and concentrates in postsynaptic spines. Both NMDARs and zinc have been strongly linked to autism spectrum disorders (ASDs), suggesting that NMDARs are an important player in the beneficial effects observed with zinc in both animal models and children with ASDs. Significant evidence is emerging that these beneficial effects occur via zinc-dependent regulation of SHANK proteins, which form the backbone of the postsynaptic density. For example, dietary zinc supplementation enhances SHANK2 or SHANK3 synaptic recruitment and rescues NMDAR deficits and hypofunction in Shank3^ex13-16-/- and Tbr1^+/- ASD mice. Across multiple studies, synaptic changes occur in parallel with a reversal of ASD-associated behaviours, highlighting the zinc-dependent regulation of NMDARs and glutamatergic synapses as therapeutic targets for severe forms of ASDs, either pre- or postnatally. The data from rodent models set a strong foundation for future translational studies in human cells and people affected by ASDs.

Parallel roles of neuroinflammation in feline and human epilepsies

Autoimmune encephalitis refers to a group of disorders characterised by a non-infectious encephalitis, often with prominent seizures and surface neuronal autoantibodies. AE is an important cause of new-onset refractory status epilepticus in humans and is frequently responsive to immunotherapies including corticosteroids, plasma exchange, intravenous immunoglobulin G and rituximab. Recent research suggests that parallel autoantibodies can be detected in non-human mammalian species. The best documented example is leucine-rich glioma-inactivated 1 (LGI1)-antibodies in domestic cats with limbic encephalitis (LE). In this review, we discuss the role of neuroinflammation and autoantibodies in human and feline epilepsy and LE.

Pathology of Initial Axon Segments in Chronic Inflammatory Demyelinating Polyradiculoneuropathy and Related Disorders

The diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is based on a combination of clinical, electrodiagnostic and laboratory features. The different entities of the disease include chronic immune sensory polyradiculopathy (CISP) and autoimmune nodopathies. It is debatable whether CIDP occurring in the course of other conditions, i.e., monoclonal IgG or IgA gammopathy, should be treated as a separate disease entity from idiopathic CIDP. This study aims to evaluate the molecular differences of the nodes of Ranvier and the initial axon segment (AIS) and juxtaparanode region (JXP) as the potential cause of phenotypic variation of CIDP while also seeking new pathomechanisms since JXP is sequestered behind the paranode and autoantibodies may not access the site easily. The authors initially present the structure of the different parts of the neuron and its functional significance, then discuss the problem of whether damage to the juxtaparanodal region, Schwann cells and axons could cause CIDP or if these damages should be separated as separate disease entities. In particular, AIS's importance for modulating neural excitability and carrying out transport along the axon is highlighted. The disclosure of specific pathomechanisms, including novel target antigens, in the heterogeneous CIDP syndrome is important for diagnosing and treating these patients.

Nodo-paranodopathies: Concepts, Clinical Implications, and Management

Peripheral neuropathies are traditionally categorized into demyelinating or axonal. It has been proposed that dysfunction at nodal/paranodal region may be a key for better understanding of pathophysiology in patients with immune mediated neuropathies. In last few years, antibodies targeting node and paranode of myelinated nerves have been increasingly detected in patients with immune mediated neuropathies. These patients have clinical phenotype similar common inflammatory neuropathies like Guillain Barre syndrome and chronic inflammatory demyelinating polyradiculoneuropathy with some additional atypical neurological and systemic features, and they respond poorly to conventional first line immunotherapies like IVIG. This review summarizes the structure of the node, concept and pathophysiology of nodopathies. We provide an overview of clinical phenotypes in patients with specific nodal/paranodal antibodies, along with electrophysiological and other diagnostic features and suggest therapeutic line of management based on current evidence.

Level of Potassium Is Associated with Saturated Fatty Acids in Cell Membranes and Influences the Activation of the 9 and 13 HODE and 5 HETE Synthesis Pathways in PCOS

Potassium helps to maintain the water–electrolyte and acid–base balance. There is little research on the relationship between plasma fatty acids (FAs), inflammatory mediators and red blood cell potassium levels in women with polycystic ovary syndrome (PCOS). This study included 38 Caucasian women with PCOS. Potassium in the erythrocytes was determined by inductively coupled atomic plasma emission spectrometry. The FAs were analysed with gas chromatography, and liquid chromatography was used to separate the eicosanoids. The relationships between the potassium content and the amounts of fatty acids, as well as potassium and arachidonic acid (AAs) derivatives, were analysed. Significant negative correlations were found with, among others, pentadecanoic acid, palmitic acid, stearic acid and arachidic acid, whereas a positive correlation was found with neuronic acid. Positive correlations were observed with 9, 13 HODE (derivatives synthetized from linolenic acid) and 5 oxo ETE and 5 HETE (from 5 LOX pathway). Saturated fatty acids reduce the influx of potassium into the cell by destabilizing the pH of the cytosol, and thus exacerbating the inflammatory response through the activation of the AA cascade. Therefore, improving the flow of potassium inside the cell is important in the treatment of patients.

PTPRD and CNTNAP2 as markers of tumor aggressiveness in oligodendrogliomas

Oligodendrogliomas are typically associated with the most favorable prognosis among diffuse gliomas. However, many of the tumors progress, eventually leading to patient death. To characterize the changes associated with oligodendroglioma recurrence and progression, we analyzed two recurrent oligodendroglioma tumors upon diagnosis and after tumor relapse based on whole-genome and RNA sequencing. Relapsed tumors were diagnosed as glioblastomas with an oligodendroglioma component before the World Health Organization classification update in 2016. Both patients died within 12 months after relapse. One patient carried an inactivating POLE mutation leading to a clearly hypermutated progressed tumor. Strikingly, both relapsed tumors carried focal chromosomal rearrangements in PTPRD and CNTNAP2 genes with associated decreased gene expression. TP53 mutation was also detected in both patients after tumor relapse. In The Cancer Genome Atlas (TCGA) diffuse glioma cohort, PTPRD and CNTNAP2 expression decreased by tumor grade in oligodendrogliomas and PTPRD expression also in IDH-mutant astrocytomas. Low expression of the genes was associated with poor overall survival. Our analysis provides information about aggressive oligodendrogliomas with worse prognosis and suggests that PTPRD and CNTNAP2 expression could represent an informative marker for their stratification.

Guillain-Barré-like syndrome: an uncommon feature of CASPR2 and LGI1 autoimmunity

Contactin-associated protein-like 2 (CASPR2) and leucine-rich glioma-inactivated 1 (LGI1) are essential components of the voltage-gated Kv1 potassium channel complex and are extensively expressed in both central and peripheral nervous system. Autoimmune CASPR2 and LGI1 disorders commonly present with Morvan syndrome (Mos) and/or limbic encephalitis, but whether Guillain-Barré syndrome (GBS) is a specific clinical phenotype is unknown. Here, we first reported an adult patient with dual CASPR2 and LGI1 antibodies in both serum and cerebrospinal fluid, who initially presented with a GBS-like syndrome and developed a typical MoS and respiratory paralysis, with a rapid resolution of his neurological symptoms and disappearance of autoantibodies after treatment with plasma exchange. Additionally, we also provided an overview of the previously reported GBS cases associated with CASPR2 or LGI1 antibodies. These cases expand the phenotypic spectrum of CASPR2 and LGI1 autoimmune syndromes, implying that these two antigens, especially CASPR2, are likely to participate in the etiology of GBS as a potential new target antigen, which deserves further exploration.

Genetic and Epigenetic Regulation of Brain Organoids

Revealing the mechanisms of neural development and the pathogenesis of neural diseases are one of the most challenging missions in life science. Pluripotent stem cells derived brain organoids mimic the development, maturation, signal generation, and function of human brains, providing unique advantage for neurology. Single-cell RNA sequencing (scRNA-Seq) and multielectrode array independently revealed the similarity between brain organoids and immature human brain at early developmental stages, in the context of gene transcription and dynamic network of neuronal signals. Brain organoids provided the unique opportunity to investigate the underlying mechanism of neural differentiation, senescence, and pathogenesis. In this review, we summarized the latest knowledge and technology in the brain organoid field, the current and potential applications in disease models and pre-clinic studies, with emphasizing the importance of transcriptional and epigenetic analysis.

The Roles of Par3, Par6, and aPKC Polarity Proteins in Normal Neurodevelopment and in Neurodegenerative and Neuropsychiatric Disorders

Normal neural circuits and functions depend on proper neuronal differentiation, migration, synaptic plasticity, and maintenance. Abnormalities in these processes underlie various neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Neural development and maintenance are regulated by many proteins. Among them are Par3, Par6 (partitioning defective 3 and 6), and aPKC (atypical protein kinase C) families of evolutionarily conserved polarity proteins. These proteins perform versatile functions by forming tripartite or other combinations of protein complexes, which hereafter are collectively referred to as "Par complexes." In this review, we summarize the major findings on their biophysical and biochemical properties in cell polarization and signaling pathways. We next summarize their expression and localization in the nervous system as well as their versatile functions in various aspects of neurodevelopment, including neuroepithelial polarity, neurogenesis, neuronal migration, neurite differentiation, synaptic plasticity, and memory. These versatile functions rely on the fundamental roles of Par complexes in cell polarity in distinct cellular contexts. We also discuss how cell polarization may correlate with subcellular polarization in neurons. Finally, we review the involvement of Par complexes in neuropsychiatric and neurodegenerative disorders, such as schizophrenia and Alzheimer's disease. While emerging evidence indicates that Par complexes are essential for proper neural development and maintenance, many questions on their in vivo functions have yet to be answered. Thus, Par3, Par6, and aPKC continue to be important research topics to advance neuroscience.

TADeus2: a web server facilitating the clinical diagnosis by pathogenicity assessment of structural variations disarranging 3D chromatin structure

In recent years great progress has been made in identification of structural variants (SV) in the human genome. However, the interpretation of SVs, especially located in non-coding DNA, remains challenging. One of the reasons stems in the lack of tools exclusively designed for clinical SVs evaluation acknowledging the 3D chromatin architecture. Therefore, we present TADeus2 a web server dedicated for a quick investigation of chromatin conformation changes, providing a visual framework for the interpretation of SVs affecting topologically associating domains (TADs). This tool provides a convenient visual inspection of SVs, both in a continuous genome view as well as from a rearrangement’s breakpoint perspective. Additionally, TADeus2 allows the user to assess the influence of analyzed SVs within flaking coding/non-coding regions based on the Hi-C matrix. Importantly, the SVs pathogenicity is quantified and ranked using TADA, ClassifyCNV tools and sampling-based P-value. TADeus2 is publicly available at https://tadeus2.mimuw.edu.pl.

Somatosensory cortex hyperconnectivity and impaired whisker-dependent responses in Cntnap2-/- mice

Sensory abnormalities are a common feature in autism spectrum disorders (ASDs). Tactile responsiveness is altered in autistic individuals, with hypo-responsiveness being associated with the severity of ASD core symptoms. Similarly, sensory abnormalities have been described in mice lacking ASD-associated genes. Loss-of-function mutations in CNTNAP2 result in cortical dysplasia-focal epilepsy syndrome (CDFE) and autism. Likewise, Cntnap2^-/- mice show epilepsy and deficits relevant with core symptoms of human ASDs, and are considered a reliable model to study ASDs. Altered synaptic transmission and synchronicity found in the cerebral cortex of Cntnap2^-/- mice would suggest a network dysfunction. Here, we investigated the neural substrates of whisker-dependent responses in Cntnap2^+/+ and Cntnap2^-/- adult mice. When compared to controls, Cntnap2^-/- mice showed focal hyper-connectivity within the primary somatosensory cortex (S1), in the absence of altered connectivity between S1 and other somatosensory areas. This data suggests the presence of impaired somatosensory processing in these mutants. Accordingly, Cntnap2^-/- mice displayed impaired whisker-dependent discrimination in the textured novel object recognition test (tNORT) and increased c-fos mRNA induction within S1 following whisker stimulation. S1 functional hyperconnectivity might underlie the aberrant whisker-dependent responses observed in Cntnap2^-/- mice, indicating that Cntnap2 mice are a reliable model to investigate sensory abnormalities that characterize ASDs.

Autoimmune Encephalitis in COVID-19 Infection: Our Experience and Systematic Review of the Literature

The neurologic complications of COVID-19 infection are frequent in hospitalized patients; a high percentage of them present neurologic manifestations at some point during the course of their disease. Headache, muscle pain, encephalopathy and dizziness are among the most common complications. Encephalitis is an inflammatory condition with many etiologies. There are several forms of encephalitis associated with antibodies against intracellular neuronal proteins, cell surfaces or synaptic proteins, referred to as autoimmune encephalitis. Several case reports published in the literature document autoimmune encephalitis cases triggered by COVID-19 infection. Our paper first presents our experience in this issue and then systematically reviews the literature on autoimmune encephalitis that developed in the background of SARS-CoV-2 infections and also discusses the possible pathophysiological mechanisms of auto-immune-mediated damage to the nervous system. This review contributes to improve the management and prognosis of COVID-19-related autoimmune encephalitis.

Finding New Ways How to Control BACE1

Recently, all applications of BACE1 inhibitors failed as therapeutical targets for Alzheimer´s disease (AD) due to severe side effects. Therefore, alternative ways for treatment development are a hot research topic. The present analysis investigates BACE1 protein-protein interaction networks and attempts to solve the absence of complete knowledge about pathways involving BACE1. A bioinformatics analysis matched the functions of the non-substrate interaction network with Voltage-gated potassium channels, which also appear as top priority protein nodes. Targeting BACE1 interactions with PS1 and GGA-s, blocking of BACE1 access to APP by BRI3 and RTN-s, activation of Wnt signaling and upregulation of β-catenin, and brain delivery of the extracellular domain of p75^NTR, are the main alternatives to the use of BACE 1 inhibitors highlighted by the analysis. The pathway enrichment analysis also emphasized substrates and substrate candidates with essential biological functions, which cleavage must remain controlled. They include ephrin receptors, ROBO1, ROBO2, CNTN-s, CASPR-s, CD147, CypB, TTR, APLP1/APLP2, NRXN-s, and PTPR-s. The analysis of the interaction subnetwork of BACE1 functionally related to inflammation identified a connection to three cardiomyopathies, which supports the hypothesis of the common molecular mechanisms with AD. A lot of potential shows the regulation of BACE1 activity through post-translational modifications. The interaction network of BACE1 and its phosphorylation enzyme CSNK1D functionally match the Circadian clock, p53, and Hedgehog signaling pathways. The regulation of BACE1 glycosylation could be achieved through N-acetylglucosamine transferases, α-(1→6)-fucosyltransferase, β-galactoside α-(2→6)-sialyltransferases, galactosyltransferases, and mannosidases suggested by the interaction network analysis of BACE1-MGAT3. The present analysis proposes possibilities for the alternative control of AD pathology.

Human CASPR2 antibodies reversibly alter memory and the CASPR2 protein complex

OBJECTIVE

The encephalitis associated with antibodies against contactin-associated protein-like 2 (CASPR2) is presumably antibody-mediated but the antibody effects and whether they cause behavioral alterations are not well-known. Here, we used a mouse model of patients' IgG transfer and super-resolution microscopy to demonstrate the antibody pathogenicity.

METHODS

IgG from patients with anti-CASPR2 encephalitis or healthy controls were infused into the cerebroventricular system of mice. The levels and colocalization of CASPR2 with transient axonal glycoprotein-1 (TAG1) were determined with Stimulated Emission Depletion (STED) microscopy (40-70μm lateral resolution). Hippocampal clusters of Kv1.1 voltage-gated potassium channels (VGKC) and GluA1-containing AMPA receptors were quantified with confocal microscopy. Behavioral alterations were assessed with standard behavioral paradigms. Cultured neurons were used to determine the levels of intracellular CASPR2 and TAG1 after exposure to patients' IgG.

RESULTS

Infusion of patients' IgG, but not control IgG, caused memory impairment along with hippocampal reduction of surface CASPR2 clusters and decreased CASPR2/TAG1 colocalization. In cultured neurons, patients' IgG led to an increase of intracellular CASPR2 without affecting TAG1, suggesting selective CASPR2 internalization. Additionally, mice infused with patients' IgG showed decreased levels of Kv1.1 and GluA1 (two CASPR2 regulated proteins). All these alterations and the memory deficit reverted to normal after removing patients' IgG.

INTERPRETATION

IgG from patients with anti-CASPR2 encephalitis cause reversible memory impairment, inhibit the interaction of CASPR2/TAG1, and decrease the levels of CASPR2 and related proteins (VGKC, AMPAR). These findings fulfill the postulates of antibody-mediated disease and provide a biological basis for antibody-removing treatment approaches. This article is protected by copyright. All rights reserved.

White matter integrity in mice requires continuous myelin synthesis at the inner tongue

Myelin, the electrically insulating sheath on axons, undergoes dynamic changes over time. However, it is composed of proteins with long lifetimes. This raises the question how such a stable structure is renewed. Here, we study the integrity of myelinated tracts after experimentally preventing the formation of new myelin in the CNS of adult mice, using an inducible Mbp null allele. Oligodendrocytes survive recombination, continue to express myelin genes, but they fail to maintain compacted myelin sheaths. Using 3D electron microscopy and mass spectrometry imaging we visualize myelin-like membranes failing to incorporate adaxonally, most prominently at juxta-paranodes. Myelinoid body formation indicates degradation of existing myelin at the abaxonal side and the inner tongue of the sheath. Thinning of compact myelin and shortening of internodes result in the loss of about 50% of myelin and axonal pathology within 20 weeks post recombination. In summary, our data suggest that functional axon-myelin units require the continuous incorporation of new myelin membranes.

Myelin is formed of proteins of long half-lives. The mechanisms of renewal of such a stable structure are unclear. Here, the authors show that myelin integrity requires continuous myelin synthesis at the inner tongue, contributing to the maintenance of a functional axon-myelin unit.

Contemporary advances in antibody-mediated encephalitis: anti-LGI1 and anti-Caspr2 antibody (Ab)-mediated encephalitides

Encephalitides with antibodies directed against leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (Caspr2) represent two increasingly well characterised forms of autoimmune encephalitis. Both share overlapping and distinct clinical features, are mediated by autoantibodies directed against differing proteins complexed with voltage-gated potassium channels, with unique genetic predisposition identified to date. Herein we summarise disease mechanisms, clinical features, treatment considerations, prognostic factors and clinical outcomes regarding these disorders.

Oxytocin normalizes altered circuit connectivity for social rescue of the Cntnap2 knockout mouse

The neural basis of abnormal social behavior in autism spectrum disorders (ASDs) remains incompletely understood. Here we used two complementary but independent brain-wide mapping approaches, mouse resting-state fMRI and c-Fos-iDISCO+ imaging, to construct brain-wide activity and connectivity maps of the Cntnap2 knockout (KO) mouse model of ASD. At the macroscale level, we detected reduced functional coupling across social brain regions despite general patterns of hyperconnectivity across major brain structures. Oxytocin administration, which rescues social deficits in KO mice, strongly stimulated many brain areas and normalized connectivity patterns. Notably, chemogenetically triggered release of endogenous oxytocin strongly stimulated the nucleus accumbens (NAc), a forebrain nucleus implicated in social reward. Furthermore, NAc-targeted approaches to activate local oxytocin receptors sufficiently rescued their social deficits. Our findings establish circuit- and systems-level mechanisms of social deficits in Cntnap2 KO mice and reveal the NAc as a region that can be modulated by oxytocin to promote social interactions.

Shed CNTNAP2 ectodomain is detectable in CSF and regulates Ca2+ homeostasis and network synchrony via PMCA2/ATP2B2

Although many neuronal membrane proteins undergo proteolytic cleavage, little is known about the biological significance of neuronal ectodomain shedding (ES). Here, we show that the neuronal sheddome is detectable in human cerebrospinal fluid (hCSF) and is enriched in neurodevelopmental disorder (NDD) risk factors. Among shed synaptic proteins is the ectodomain of CNTNAP2 (CNTNAP2-ecto), a prominent NDD risk factor. CNTNAP2 undergoes activity-dependent ES via MMP9 (matrix metalloprotease 9), and CNTNAP2-ecto levels are reduced in the hCSF of individuals with autism spectrum disorder. Using mass spectrometry, we identified the plasma membrane Ca2+ ATPase (PMCA) extrusion pumps as novel CNTNAP2-ecto binding partners. CNTNAP2-ecto enhances the activity of PMCA2 and regulates neuronal network dynamics in a PMCA2-dependent manner. Our data underscore the promise of sheddome analysis in discovering neurobiological mechanisms, provide insight into the biology of ES and its relationship with the CSF, and reveal a mechanism of regulation of Ca2+ homeostasis and neuronal network synchrony by a shed ectodomain.