Ankyrin-G regulates forebrain connectivity and network synchronization via interaction with GABARAP

Live imaging of excitable axonal microdomains in ankyrin-G-GFP mice

The axon initial segment (AIS) constitutes not only the site of action potential initiation, but also a hub for activity-dependent modulation of output generation. Recent studies shedding light on AIS function used predominantly post-hoc approaches since no robust murine in vivo live reporters exist. Here, we introduce a reporter line in which the AIS is intrinsically labeled by an ankyrin-G-GFP fusion protein activated by Cre recombinase, tagging the native Ank3 gene. Using confocal, superresolution, and two-photon microscopy as well as whole-cell patch-clamp recordings in vitro, ex vivo, and in vivo, we confirm that the subcellular scaffold of the AIS and electrophysiological parameters of labeled cells remain unchanged. We further uncover rapid AIS remodeling following increased network activity in this model system, as well as highly reproducible in vivo labeling of AIS over weeks. This novel reporter line allows longitudinal studies of AIS modulation and plasticity in vivo in real-time and thus provides a unique approach to study subcellular plasticity in a broad range of applications.

Pharmacogenetic testing may benefit people receiving low-dose lithium in clinical practice

BACKGROUND

Mental illnesses are leading causes of disability in the United States. Some evidence supports that pharmacogenetic testing may be beneficial in select populations and that lithium is beneficial for treating mood disorders and anxiety in some populations.

PURPOSE

This research aimed to determine whether low-dose lithium effectively decreases depression and anxiety in adults with a risk allele for CACNA1C genotypes.

METHODOLOGY

The study design was correlational. Fifty patients were treated at a nurse practitioner-owned clinic in Prairie Village, Kansas. Chart review was used. Adults older than 18 years diagnosed with major depressive disorder, bipolar disorder, or generalized anxiety disorder presenting with an abnormality in the CACNA1C gene single-nucleotide polymorphism rs1006737 were included in this research. Assessment tools used were the Patient Health Questionnaire-9 for depression and GAD-7 for anxiety.

RESULTS

Low-dose lithium significantly decreased depression by 66% ( p < .001) and anxiety by 65% ( p = <.001). There was a significant difference in pretest depression levels based on CACNA1C genotype ( p = .033). The A allele frequency was 60% higher (48%) in this population than found in general population (30%).

CONCLUSIONS

Low-dose lithium significantly decreased anxiety and depression compared with baseline. People with different versions of the CACNA1C genotype had responses that differed significantly. The A risk allele was 60% more common than in the general population.

IMPLICATIONS

This study could aid in establishing genetic testing as an effective clinical tool for treating depression and anxiety using lithium, an inexpensive and widely available medication.

Physical and functional convergence of the autism risk genes Scn2a and Ank2 in neocortical pyramidal cell dendrites

Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder (ASD). In particular, the genes SCN2A, which encodes the sodium channel NaV1.2, and ANK2, which encodes ankyrin-B, have strong ASD association. Recent studies indicate that ASD-associated haploinsufficiency in Scn2a impairs dendritic excitability and synaptic function in neocortical pyramidal cells, but how NaV1.2 is anchored within dendritic regions is unknown. Here, we show that ankyrin-B is essential for scaffolding NaV1.2 to the dendritic membrane of mouse neocortical neurons and that haploinsufficiency of Ank2 phenocopies intrinsic dendritic excitability and synaptic deficits observed in Scn2a+/- conditions. These results establish a direct, convergent link between two major ASD risk genes and reinforce an emerging framework suggesting that neocortical pyramidal cell dendritic dysfunction can contribute to neurodevelopmental disorder pathophysiology.

Abnormal patterns of sleep and waking behaviors are accompanied by neocortical oscillation disturbances in an Ank3 mouse model of epilepsy-bipolar disorder comorbidity

ANK3 is a leading bipolar disorder (BD) candidate gene in humans and provides a unique opportunity for studying epilepsy-BD comorbidity. Previous studies showed that deletion of Ank3-1b, a BD-associated variant of Ank3 in mice leads to increased firing threshold and diminished action potential dynamic range of parvalbumin (PV) interneurons and absence epilepsy, thus providing a biological mechanism linking epilepsy and BD. To explore the behavioral overlap of these disorders, we characterized behavioral patterns of Ank3-1b KO mice during overnight home-cage activity and examined network activity during these behaviors using paired video and EEG recordings. Since PV interneurons contribute to the generation of high-frequency gamma oscillations, we anticipated changes in the power of neocortical EEG signals in the gamma frequency range (> 25 Hz) during behavioral states related to human BD symptoms, including abnormal sleep, hyperactivity, and repetitive behaviors. Ank3-1b KO mice exhibited an overall increase in slow gamma (~25-45 Hz) power compared to controls, and slow gamma power correlated with seizure phenotype severity across behaviors. During sleep, increased slow gamma power correlated with decreased time spent in the rapid eye movement (REM) stage of sleep. Seizures were more common during REM sleep compared to non-REM (NREM) sleep. We also found that Ank3-1b KO mice were hyperactive and exhibited a repetitive behavior phenotype that co-occurred with increased slow gamma power. Our results identify a novel EEG biomarker associating Ank3 genetic variation with BD and epilepsy and suggest modulation of gamma oscillations as a potential therapeutic target.

Pituitary adenylate cyclase-activating polypeptide deficient mice show length abnormalities of the axon initial segment

We previously found that pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient (PACAP-/-) mice exhibit dendritic spine morphology impairment and neurodevelopmental disorder (NDD)-like behaviors such as hyperactivity, increased novelty-seeking behavior, and deficient pre-pulse inhibition. Recent studies have indicated that rodent models of NDDs (e.g., attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder) show abnormalities in the axon initial segment (AIS). Here, we revealed that PACAP-/- mice exhibited a longer AIS length in layer 2/3 pyramidal neurons of the primary somatosensory barrel field compared with wild-type control mice. Further, we previously showed that a single injection of atomoxetine, an ADHD drug, improved hyperactivity in PACAP-/- mice. In this study, we found that repeated treatments of atomoxetine significantly improved AIS abnormality along with hyperactivity in PACAP-/- mice. These results suggest that AIS abnormalities are associated with NDDs-like behaviors in PACAP-/- mice. Thus, improvement in AIS abnormalities will be a novel drug therapy for NDDs.

Effects of chronic lithium treatment on neuronal excitability and GABAergic transmission in an Ank3 mutant mouse model

Bipolar disorder (BD) is a common psychiatric disease that can lead to psychosocial disability, decreased quality of life, and high risk for suicide. Genome-wide association studies have shown that the ANK3 gene is a significant risk factor for BD, but the mechanisms involved in BD pathophysiology are not yet fully understood. Previous work has shown that ankyrin-G, the protein encoded by ANK3, stabilizes inhibitory synapses in vivo through its interaction with the GABAA receptor-associated protein (GABARAP). We generated a mouse model with a missense p.W1989R mutation in Ank3, that abolishes the interaction between ankyrin-G and GABARAP, which leads to reduced inhibitory signaling in the somatosensory cortex and increased pyramidal cell excitability. Humans with the same mutation exhibit BD symptoms, which can be attenuated with lithium therapy. In this study, we describe that chronic treatment of Ank3 p.W1989R mice with lithium normalizes neuronal excitability in cortical pyramidal neurons and increases inhibitory GABAergic postsynaptic currents. The same outcome in inhibitory transmission was observed when mice were treated with the GSK-3β inhibitor Tideglusib. These results suggest that lithium treatment modulates the excitability of pyramidal neurons in the cerebral cortex by increasing GABAergic neurotransmission, likely via GSK-3 inhibition. In addition to the importance of these findings regarding ANK3 variants as a risk factor for BD development, this study may have significant implications for treating other psychiatric disorders associated with alterations in inhibitory signaling, such as schizophrenia, autism spectrum disorder, and major depressive disorder.

Lithium rescues dendritic abnormalities in Ank3 deficiency models through the synergic effects of GSK3β and cyclic AMP signaling pathways

Bipolar disorder (BD) is a highly heritable mood disorder with intermittent episodes of mania and depression. Lithium is the first-in-line medication to treat BD, but it is only effective in a subset of individuals. Large-scale human genomic studies have repeatedly linked the ANK3 gene (encoding ankyrin-G, AnkG) to BD. Ank3 knockout mouse models mimic BD behavioral features and respond positively to lithium treatment. We investigated cellular phenotypes associated with BD, including dendritic arborization of pyramidal neurons and spine morphology in two models: (1) a conditional knockout mouse model which disrupts Ank3 expression in adult forebrain pyramidal neurons, and (2) an AnkG knockdown model in cortical neuron cultures. We observed a decrease in dendrite complexity and a reduction of dendritic spine number in both models, reminiscent of reports in BD. We showed that lithium treatment corrected dendrite and spine deficits in vitro and in vivo. We targeted two signaling pathways known to be affected by lithium using a highly selective GSK3β inhibitor (CHIR99021) and an adenylate cyclase activator (forskolin). In our cortical neuron culture model, CHIR99021 rescues the spine morphology defects caused by AnkG knockdown, whereas forskolin rescued the dendrite complexity deficit. Interestingly, a synergistic action of both drugs was required to rescue dendrite and spine density defects in AnkG knockdown neurons. Altogether, our results suggest that dendritic abnormalities observed in loss of function ANK3 variants and BD patients may be rescued by lithium treatment. Additionally, drugs selectively targeting GSK3β and cAMP pathways could be beneficial in BD.

Extracellular Tau Oligomers Damage the Axon Initial Segment

BACKGROUND

In Alzheimer's disease (AD) brain, neuronal polarity and synaptic connectivity are compromised. A key structure for regulating polarity and functions of neurons is the axon initial segment (AIS), which segregates somatodendritic from axonal proteins and initiates action potentials. Toxic tau species, including extracellular oligomers (xcTauOs), spread tau pathology from neuron to neuron by a prion-like process, but few other cell biological effects of xcTauOs have been described.

OBJECTIVE

Test the hypothesis that AIS structure is sensitive to xcTauOs.

METHODS

Cultured wild type (WT) and tau knockout (KO) mouse cortical neurons were exposed to xcTauOs, and quantitative western blotting and immunofluorescence microscopy with anti-TRIM46 monitored effects on the AIS. The same methods were used to compare TRIM46 and two other resident AIS proteins in human hippocampal tissue obtained from AD and age-matched non-AD donors.

RESULTS

Without affecting total TRIM46 levels, xcTauOs reduce the concentration of TRIM46 within the AIS and cause AIS shortening in cultured WT, but not TKO neurons. Lentiviral-driven tau expression in tau KO neurons rescues AIS length sensitivity to xcTauOs. In human AD hippocampus, the overall protein levels of multiple resident AIS proteins are unchanged compared to non-AD brain, but TRIM46 concentration within the AIS and AIS length are reduced in neurons containing neurofibrillary tangles.

CONCLUSION

xcTauOs cause partial AIS damage in cultured neurons by a mechanism dependent on intracellular tau, thereby raising the possibility that the observed AIS reduction in AD neurons in vivo is caused by xcTauOs working in concert with endogenous neuronal tau.

DSCAM gene triplication causes excessive GABAergic synapses in the neocortex in Down syndrome mouse models

Down syndrome (DS) is caused by the trisomy of human chromosome 21 (HSA21). A major challenge in DS research is to identify the HSA21 genes that cause specific symptoms. Down syndrome cell adhesion molecule (DSCAM) is encoded by a HSA21 gene. Previous studies have shown that the protein level of the Drosophila homolog of DSCAM determines the size of presynaptic terminals. However, whether the triplication of DSCAM contributes to presynaptic development in DS remains unknown. Here, we show that DSCAM levels regulate GABAergic synapses formed on neocortical pyramidal neurons (PyNs). In the Ts65Dn mouse model for DS, where DSCAM is overexpressed due to DSCAM triplication, GABAergic innervation of PyNs by basket and chandelier interneurons is increased. Genetic normalization of DSCAM expression rescues the excessive GABAergic innervations and the increased inhibition of PyNs. Conversely, loss of DSCAM impairs GABAergic synapse development and function. These findings demonstrate excessive GABAergic innervation and synaptic transmission in the neocortex of DS mouse models and identify DSCAM overexpression as the cause. They also implicate dysregulated DSCAM levels as a potential pathogenic driver in related neurological disorders.

Ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic membrane scaffolding of voltage-gated sodium channel NaV1.2 in neurons

Neuronal ankyrin-B is an intracellular scaffolding protein that plays multiple roles in the axon. By contrast, relatively little is known about the function of ankyrin-B in dendrites, where ankyrin-B is also localized in mature neurons. Recently, we showed that ankyrin-B acts as a scaffold for the voltage-gated sodium channel, NaV1.2, in dendrites of neocortical pyramidal neurons. How ankyrin-B is itself targeted to the dendritic membrane is not well understood. Here, we report that ankyrin-B is lipid-modified by S-palmitoylation to promote dendritic localization of NaV1.2. We identify the palmitoyl acyl transferase zDHHC17 as a key mediator of ankyrin-B palmitoylation in heterologous cells and in neurons. Additionally, we find that zDHHC17 regulates ankyrin-B protein levels independently of its S-acylation function through a conserved binding mechanism between the ANK repeat domain of zDHHC17 and the zDHHC ankyrin-repeat binding motif of ankyrin-B. We subsequently identify five cysteines in the N-terminal ankyrin repeat domain of ankyrin-B that are necessary for ankyrin-B palmitoylation. Mutation of these five cysteines to alanines not only abolishes ankyrin-B palmitoylation, but also prevents ankyrin-B from scaffolding NaV1.2 at dendritic membranes of neurons due to ankyrin-B's inability to localize properly at dendrites. Thus, we show palmitoylation is critical for localization and function of ankyrin-B at dendrites. Strikingly, loss of ankyrin-B palmitoylation does not affect ankyrin-B-mediated axonal cargo transport of synaptic vesicle synaptotagmin-1 in neurons. This is the first demonstration of S-palmitoylation of ankyrin-B as an underlying mechanism required for ankyrin-B localization and function in scaffolding NaV1.2 at dendrites.

The Amyloid Precursor Protein Modulates the Position and Length of the Axon Initial Segment

The amyloid precursor protein (APP) is linked to the genetics and pathogenesis of Alzheimer's disease (AD). It is the parent protein of the β-amyloid (Aβ) peptide, the main constituent of the amyloid plaques found in an AD brain. The pathways from APP to Aβ are intensively studied, yet the normal functions of APP itself have generated less interest. We report here that glutamate stimulation of neuronal activity leads to a rapid increase in App gene expression. In mouse and human neurons, elevated APP protein changes the structure of the axon initial segment (AIS) where action potentials are initiated. The AIS is shortened in length and shifts away from the cell body. The GCaMP8f Ca2+ reporter confirms the predicted decrease in neuronal activity. NMDA antagonists or knockdown of App block the glutamate effects. The actions of APP on the AIS are cell-autonomous; exogenous Aβ, either fibrillar or oligomeric, has no effect. In culture, APPSwe (a familial AD mutation) induces larger AIS changes than wild type APP. Ankyrin G and βIV-spectrin, scaffolding proteins of the AIS, both physically associate with APP, more so in AD brains. Finally, in humans with sporadic AD or in the R1.40 AD mouse model, both females and males, neurons have elevated levels of APP protein that invade the AIS. In vivo as in vitro, this increased APP is associated with a significant shortening of the AIS. The findings outline a new role for the APP and encourage a reconsideration of its relationship to AD.SIGNIFICANCE STATEMENT While the amyloid precursor protein (APP) has long been associated with Alzheimer's disease (AD), the normal functions of the full-length Type I membrane protein have been largely unexplored. We report here that the levels of APP protein increase with neuronal activity. In vivo and in vitro, modest amounts of excess APP alter the properties of the axon initial segment. The β-amyloid peptide derived from APP is without effect. Consistent with the observed changes in the axon initial segment which would be expected to decrease action potential firing, we show that APP expression depresses neuronal activity. In mouse AD models and human sporadic AD, APP physically associates with the scaffolding proteins of the axon initial segment, suggesting a relationship with AD dementia.

Homozygous Missense Variant in the N-Terminal Region of ANK3 Gene Is Associated with Developmental Delay, Seizures, Speech Abnormality, and Aggressive Behavior

Introduction

Intellectual disability (ID) is a lifelong disability that affects an individual‧s learning capacity and adaptive behavior. Such individuals depend on their families for day-to-day survival and pose a significant challenge to the healthcare system, especially in developing countries. ID is a heterogeneous condition, and genetic studies are essential to unravel the underlying cellular pathway for brain development and functioning.

Methods

Here we studied a female index patient, born to a consanguineous Pakistani couple, showing clinical symptoms of ID, ataxia, hypotonia, developmental delay, seizures, speech abnormality, and aggressive behavior. Whole exome sequencing (WES) coupled with Sanger sequencing was performed for molecular diagnosis. Further, 3D protein modeling was performed to see the effect of variant on protein structure.

Results

WES identified a novel homozygous missense variant (c.178T>C; p.Tyr60His) in the ANK3 gene. In silico analysis and 3-dimensional (3D) protein modeling supports the deleterious impact of this variant on the encoding protein, which compromises the protein‧s overall structure and function.

Conclusion

Our finding supports the clinical and genetic diversity of the ANK3 gene as a plausible candidate gene for ID syndrome. Intelligence is a complex polygenic human trait, and understanding molecular and biological pathways involved in learning and memory can solve the complex puzzle of how cognition develops. Intellectual disability (ID) is defined as a deficit in an individual‧s learning and adaptive behavior at an early age of onset [American Psychiatric Association, 2013]. It is one of the major medical, and cognitive disorders with a prevalence of 1-3% in the population worldwide [Leonard and Wen, 2002]. ID often exists with other disabling mental conditions such as autism, attention deficit hyperactivity disorder, epilepsy, schizophrenia, bipolar disorder, or depression. Almost half of the cases appear to have a genetic explanation that ranges from cytogenetically visible abnormalities to monogenic defects [Flint, 2001; Ropers, 2010; Tucker-Drob et al., 2013]. Intellectual disability is a genetically heterogeneous condition, and more than 700 genes have been identified to cause ID alone or as a part of the syndrome. Research in X-linked ID has identified more than 100 disease-causing genes on the X chromosome that play a role in cognition; however, research into autosomal causes of ID is still ongoing [Vissers et al., 2016].

Autophagy Balances Neuroinflammation in Alzheimer's Disease

Autophagy is a highly evolutionary conserved process that degrades cytosolic macromolecules or damaged organelles (e.g., mitochondria), as well as intracellular pathogens for energy and survival. Dysfunction of autophagy has been associated with the pathologies of Alzheimer's disease (AD), including Aβ plaques and neurofibrillary tangles. Recently, the presence of sustained immune response in the brain has been considered a new core pathology in AD. Accumulating evidence suggests that autophagy activation may suppress inflammation response through degrading inflammasomes or pro-inflammatory cytokines and improving immune system function in both clinical trials and preclinical studies. This review provides an overview of updated information on autophagy and inflammation and their potential mediators in AD. In summary, we believe that understanding the relationship between autophagy and inflammation will provide insightful knowledge for future therapeutic implications in AD.

Roles and mechanisms of ankyrin-G in neuropsychiatric disorders

Ankyrin proteins act as molecular scaffolds and play an essential role in regulating cellular functions. Recent evidence has implicated the ANK3 gene, encoding ankyrin-G, in bipolar disorder (BD), schizophrenia (SZ), and autism spectrum disorder (ASD). Within neurons, ankyrin-G plays an important role in localizing proteins to the axon initial segment and nodes of Ranvier or to the dendritic shaft and spines. In this review, we describe the expression patterns of ankyrin-G isoforms, which vary according to the stage of brain development, and consider their functional differences. Furthermore, we discuss how posttranslational modifications of ankyrin-G affect its protein expression, interactions, and subcellular localization. Understanding these mechanisms leads us to elucidate potential pathways of pathogenesis in neurodevelopmental and psychiatric disorders, including BD, SZ, and ASD, which are caused by rare pathogenic mutations or changes in the expression levels of ankyrin-G in the brain.

Mutations affecting the production, distribution, or function of the ankyrin-G protein may contribute to a variety of different neuropsychiatric disorders. Ankyrin-G is typically observed at the synapses between neurons, and contributes to intercellular adhesion and signaling along with other important functions. Peter Penzes and colleagues at Northwestern University, Chicago, USA, review the biology of this protein and identify potential mechanisms by which ankyrin-G mutations might impair healthy brain development. Mutations in the gene encoding this protein are strongly linked with bipolar disorder, but have also been tentatively connected to autism spectrum disorders and schizophrenia. The authors highlight physiologically important interactions with a diverse array of other brain proteins, which can in turn be modulated by various chemical modifications to ankyrin-G, and conclude that drugs that influence these modifications could have potential therapeutic value.

Phenotypes, mechanisms and therapeutics: insights from bipolar disorder GWAS findings

Genome-wide association studies (GWAS) have reported substantial genomic loci significantly associated with clinical risk of bipolar disorder (BD), and studies combining techniques of genetics, neuroscience, neuroimaging, and pharmacology are believed to help tackle clinical problems (e.g., identifying novel therapeutic targets). However, translating findings of psychiatric genetics into biological mechanisms underlying BD pathogenesis remains less successful. Biological impacts of majority of BD GWAS risk loci are obscure, and the involvement of many GWAS risk genes in this illness is yet to be investigated. It is thus necessary to review the progress of applying BD GWAS risk genes in the research and intervention of the disorder. A comprehensive literature search found that a number of such risk genes had been investigated in cellular or animal models, even before they were highlighted in BD GWAS. Intriguingly, manipulation of many BD risk genes (e.g., ANK3, CACNA1C, CACNA1B, HOMER1, KCNB1, MCHR1, NCAN, SHANK2 etc.) resulted in altered murine behaviors largely restoring BD clinical manifestations, including mania-like symptoms such as hyperactivity, anxiolytic-like behavior, as well as antidepressant-like behavior, and these abnormalities could be attenuated by mood stabilizers. In addition to recapitulating phenotypic characteristics of BD, some GWAS risk genes further provided clues for the neurobiology of this illness, such as aberrant activation and functional connectivity of brain areas in the limbic system, and modulated dendritic spine morphogenesis as well as synaptic plasticity and transmission. Therefore, BD GWAS risk genes are undoubtedly pivotal resources for modeling this illness, and might be translational therapeutic targets in the future clinical management of BD. We discuss both promising prospects and cautions in utilizing the bulk of useful resources generated by GWAS studies. Systematic integrations of findings from genetic and neuroscience studies are called for to promote our understanding and intervention of BD.

Involvement of Paired Immunoglobulin-like Receptor B in Diabetes-Associated Cognitive Dysfunction Through Modulation of Axon Outgrowth and Dendritic Remodeling

Type 2 diabetic patients have high risk of developing cognitive dysfunction, in which neural structural plasticity has played a pivotal role. Paired immunoglobulin-like receptor B (PirB), a receptor mainly expressed in neurons, acts as a critical inhibitor of neurite outgrowth and neural plasticity. However, the role of PirB in type 2 diabetes-associated cognitive dysfunction remains unknown. In this study, learning and memory impairment was observed in 24-week-old db/db mice by performing Morris water maze task, and the number of synapses along with the length of postsynaptic density by transmission electron microscopy were reduced in the hippocampus of db/db mice. Furthermore, PirB expression in the hippocampus of db/db mice was significantly upregulated using western blotting and immunofluorescence analysis. In cultured hippocampal neurons, high glucose treatment reduced the length of the longest neurite as well as axon initial segment (AIS), whereas silencing PirB expression rescued high glucose-induced neurite outgrowth inhibition, but not AIS. Additionally, cognitive deficits, dendrite morphology defects, and synapse-related proteins loss in db/db mice were alleviated when PirB knockdown was performed by adeno-associated virus injection. In conclusion, PirB is involved in diabetes-associated cognitive dysfunction through modulation of axon outgrowth and dendritic remodeling, providing a potential therapeutic target for diabetes-associated cognitive dysfunction.

Length impairments of the axon initial segment in rodent models of attention-deficit hyperactivity disorder and autism spectrum disorder

The axon initial segment (AIS) is a structural neuronal compartment of the proximal axon that plays key roles in sodium channel clustering, action potential initiation, and signal propagation of neuronal outputs. Mutations in constitutive genes of the AIS, such as ANK3, have been identified in patients with neurodevelopmental disorders. Nevertheless, morphological changes in the AIS in neurodevelopmental disorders have not been characterized. In this study, we investigated the length of the AIS in rodent models of attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). We observed abnormalities in AIS length in both animal models. In ADHD model rodents, we observed shorter AIS length in layer 2/3 (L2/3) neurons of the medial prefrontal cortex (mPFC) and primary somatosensory barrel field (S1BF). Further, we observed shorter AIS length in S1BF L5 neurons. In ASD model mice, we observed shorter AIS length in L2/3 and L5 neurons of the S1BF. These results suggest that impairments in AIS length are common phenomena in neurodevelopmental disorders such as ADHD and ASD and may be conserved across species. Our findings provide novel insight into the potential contribution of the AIS to the pathophysiology and pathogenesis of neurodevelopmental disorders.

Calcium imaging reveals depressive- and manic-phase-specific brain neural activity patterns in a murine model of bipolar disorder: a pilot study

Brain pathological features during manic/hypomanic and depressive episodes in the same patients with bipolar disorder (BPD) have not been described precisely. The study aimed to investigate depressive and manic-phase-specific brain neural activity patterns of BPD in the same murine model to provide information guiding investigation of the mechanism of phase switching and tailored prevention and treatment for patients with BPD. In vivo two-photon imaging was used to observe brain activity alterations in the depressive and manic phases in the same murine model of BPD. Two-photon imaging showed significantly reduced Ca²⁺ activity in temporal cortex pyramidal neurons in the depression phase in mice exposed to chronic unpredictable mild stress (CUMS), but not in the manic phase in mice exposed to CUMS and ketamine. Total integrated calcium values correlated significantly with immobility times. Brain Ca²⁺ hypoactivity was observed in the depression and manic phases in the same mice exposed to CUMS and ketamine relative to naïve controls. The novel object recognition preference ratio correlated negatively with the immobility time in the depression phase and the total distance traveled in the manic phase. With recognition of its limitations, this study revealed brain neural activity impairment indicating that intrinsic emotional network disturbance is a mechanism of BPD and that brain neural activity is associated with cognitive impairment in the depressive and manic phases of this disorder. These findings are consistent with those from macro-imaging studies of patients with BPD. The observed correlation of brain neural activity with the severity of depressive, but not manic, symptoms need to be investigated further.

Chronic lithium treatment alters the excitatory/ inhibitory balance of synaptic networks and reduces mGluR5-PKC signalling in mouse cortical neurons

Background

Bipolar disorder is characterized by cyclical alternation between mania and depression, often comorbid with psychosis and suicide. Compared with other medications, the mood stabilizer lithium is the most effective treatment for the prevention of manic and depressive episodes. However, the pathophysiology of bipolar disorder and lithium’s mode of action are yet to be fully understood. Evidence suggests a change in the balance of excitatory and inhibitory activity, favouring excitation in bipolar disorder. In the present study, we sought to establish a holistic understanding of the neuronal consequences of lithium exposure in mouse cortical neurons, and to identify underlying mechanisms of action.

Methods

We used a range of technical approaches to determine the effects of acute and chronic lithium treatment on mature mouse cortical neurons. We combined RNA screening and biochemical and electrophysiological approaches with confocal immunofluorescence and live-cell calcium imaging.

Results

We found that only chronic lithium treatment significantly reduced intracellular calcium flux, specifically by activating metabotropic glutamatergic receptor 5. This was associated with altered phosphorylation of protein kinase C and glycogen synthase kinase 3, reduced neuronal excitability and several alterations to synapse function. Consequently, lithium treatment shifts the excitatory–inhibitory balance toward inhibition.

Limitations

The mechanisms we identified should be validated in future by similar experiments in whole animals and human neurons.

Conclusion

Together, the results revealed how lithium dampens neuronal excitability and the activity of the glutamatergic network, both of which are predicted to be overactive in the manic phase of bipolar disorder. Our working model of lithium action enables the development of targeted strategies to restore the balance of overactive networks, mimicking the therapeutic benefits of lithium but with reduced toxicity.

Cross-Disorder Analysis of De Novo Mutations in Neuropsychiatric Disorders

The clinical similarity among different neuropsychiatric disorders (NPDs) suggested a shared genetic basis. We catalogued 23,109 coding de novo mutations (DNMs) from 6511 patients with autism spectrum disorder (ASD), 4,293 undiagnosed developmental disorder (UDD), 933 epileptic encephalopathy (EE), 1022 intellectual disability (ID), 1094 schizophrenia (SCZ), and 3391 controls. We evaluated that putative functional DNMs contribute to 38.11%, 34.40%, 33.31%, 10.98% and 6.91% of patients with ID, EE, UDD, ASD and SCZ, respectively. Consistent with phenotype similarity and heterogeneity in different NPDs, they show different degree of genetic association. Cross-disorder analysis of DNMs prioritized 321 candidate genes (FDR < 0.05) and showed that genes shared in more disorders were more likely to exhibited specific expression pattern, functional pathway, genetic convergence, and genetic intolerance.

Ankyrins and neurological disease

Ankyrins are scaffolding proteins widely expressed throughout the nervous system. Ankyrins recruit diverse membrane proteins, including ion channels and cell adhesion molecules, into specialized subcellular membrane domains. These domains are stabilized by ankyrins interacting with the spectrin cytoskeleton. Ankyrin genes are highly associated with a number of neurological disorders, including Alzheimer's disease, schizophrenia, autism spectrum disorders, and bipolar disorder. Here, we discuss ankyrin function and their role in neurological disease. We propose mutations in ankyrins contribute to disease through two primary mechanisms: 1) altered neuronal excitability by disrupting ion channel clustering at key excitable domains, and 2) altered neuronal connectivity via impaired stabilization of membrane proteins.

Structural basis of GABARAP-mediated GABAA receptor trafficking and functions on GABAergic synaptic transmission

GABAA receptors (GABAARs) are the primary fast inhibitory ion channels in the central nervous system. Dysfunction of trafficking and localization of GABAARs to cell membranes is clinically associated with severe psychiatric disorders in humans. The GABARAP protein is known to support the stability of GABAARs in synapses, but the underlying molecular mechanisms remain to be elucidated. Here, we show that GABARAP/GABARAPL1 directly binds to a previously unappreciated region in the γ2 subunit of GABAAR. We demonstrate that GABARAP functions to stabilize GABAARs via promoting its trafficking pathway instead of blocking receptor endocytosis. The GABARAPL1-γ2-GABAAR crystal structure reveals the mechanisms underlying the complex formation. We provide evidence showing that phosphorylation of γ2-GABAAR differentially modulate the receptor's binding to GABARAP and the clathrin adaptor protein AP2. Finally, we demonstrate that GABAergic synaptic currents are reduced upon specific blockage of the GABARAP-GABAAR complex formation. Collectively, our results reveal that GABARAP/GABARAPL1, but not other members of the Atg8 family proteins, specifically regulates synaptic localization of GABAARs via modulating the trafficking of the receptor.

Roles of palmitoylation in structural long-term synaptic plasticity

Long-term potentiation (LTP) and long-term depression (LTD) are important cellular mechanisms underlying learning and memory processes. N-Methyl-d-aspartate receptor (NMDAR)-dependent LTP and LTD play especially crucial roles in these functions, and their expression depends on changes in the number and single channel conductance of the major ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) located on the postsynaptic membrane. Structural changes in dendritic spines comprise the morphological platform and support for molecular changes in the execution of synaptic plasticity and memory storage. At the molecular level, spine morphology is directly determined by actin cytoskeleton organization within the spine and indirectly stabilized and consolidated by scaffold proteins at the spine head. Palmitoylation, as a uniquely reversible lipid modification with the ability to regulate protein membrane localization and trafficking, plays significant roles in the structural and functional regulation of LTP and LTD. Altered structural plasticity of dendritic spines is also considered a hallmark of neurodevelopmental disorders, while genetic evidence strongly links abnormal brain function to impaired palmitoylation. Numerous studies have indicated that palmitoylation contributes to morphological spine modifications. In this review, we have gathered data showing that the regulatory proteins that modulate the actin network and scaffold proteins related to AMPAR-mediated neurotransmission also undergo palmitoylation and play roles in modifying spine architecture during structural plasticity.

Advances toward precision medicine for bipolar disorder: mechanisms & molecules

Given its chronicity, contribution to disability and morbidity, and prevalence of more than 2%, the effective treatment, and prevention of bipolar disorder represents an area of significant unmet medical need. While more than half a century has passed since the introduction of lithium into widespread use at the birth of modern psychopharmacology, that medication remains a mainstay for the acute treatment and prevention of recurrent mania/hypomania and depression that characterize bipolar disorder. However, the continued limited understanding of how lithium modulates affective behavior and lack of validated cellular and animal models have resulted in obstacles to discovering more effective mood stabilizers with fewer adverse side effects. In particular, while there has been progress in developing new pharmacotherapy for mania, developing effective treatments for acute bipolar depression remain inadequate. Recent large-scale human genetic studies have confirmed the complex, polygenic nature of the risk architecture of bipolar disorder, and its overlap with other major neuropsychiatric disorders. Such discoveries have begun to shed light on the pathophysiology of bipolar disorder. Coupled with broader advances in human neurobiology, neuropharmacology, noninvasive neuromodulation, and clinical trial design, we can envision novel therapeutic strategies informed by defined molecular mechanisms and neural circuits and targeted to the root cause of the pathophysiology. Here, we review recent advances toward the goal of better treatments for bipolar disorder, and we outline major challenges for the field of translational neuroscience that necessitate continued focus on fundamental research and discovery.

In utero exposure to endogenous maternal polyclonal anti-Caspr2 antibody leads to behavioral abnormalities resembling autism spectrum disorder in male mice

The concept that exposure in utero to maternal anti-brain antibodies contributes to the development of autism spectrum disorders (ASD) has been entertained for over a decade. We determined that antibodies targeting Caspr2 are present at high frequency in mothers with brain-reactive serology and a child with ASD, and further demonstrated that exposure in utero to a monoclonal anti-Caspr2 antibody, derived from a mother of an ASD child, led to an-ASD like phenotype in male offspring. Now we propose a new model to study the effects of in utero exposure to anti-Caspr2 antibody. Dams immunized with the extracellular portion of Caspr2 express anti-Caspr2 antibodies throughout gestation to better mimic the human condition. Male but not female mice born to dams harboring polyclonal anti-Caspr2 antibodies showed abnormal cortical development, decreased dendritic complexity of excitatory neurons and reduced numbers of inhibitory neurons in the hippocampus, as well as repetitive behaviors and impairments in novelty interest in the social preference test as adults. These data supporting the pathogenicity of anti-Caspr2 antibodies are consistent with the concept that anti-brain antibodies present in women during gestation can alter fetal brain development, and confirm that males are peculiarly susceptible.

Atg8-Family Proteins-Structural Features and Molecular Interactions in Autophagy and Beyond

Autophagy is a common name for a number of catabolic processes, which keep the cellular homeostasis by removing damaged and dysfunctional intracellular components. Impairment or misbalance of autophagy can lead to various diseases, such as neurodegeneration, infection diseases, and cancer. A central axis of autophagy is formed along the interactions of autophagy modifiers (Atg8-family proteins) with a variety of their cellular counter partners. Besides autophagy, Atg8-proteins participate in many other pathways, among which membrane trafficking and neuronal signaling are the most known. Despite the fact that autophagy modifiers are well-studied, as the small globular proteins show similarity to ubiquitin on a structural level, the mechanism of their interactions are still not completely understood. A thorough analysis and classification of all known mechanisms of Atg8-protein interactions could shed light on their functioning and connect the pathways involving Atg8-proteins. In this review, we present our views of the key features of the Atg8-proteins and describe the basic principles of their recognition and binding by interaction partners. We discuss affinity and selectivity of their interactions as well as provide perspectives for discovery of new Atg8-interacting proteins and therapeutic approaches to tackle major human diseases.

β spectrin-dependent and domain specific mechanisms for Na+ channel clustering

Previously, we showed that a hierarchy of spectrin cytoskeletal proteins maintains nodal Na+ channels (Liu et al., 2020). Here, using mice lacking β1, β4, or β1/β4 spectrins, we show this hierarchy does not function at axon initial segments (AIS). Although β1 spectrin, together with AnkyrinR (AnkR), compensates for loss of nodal β4 spectrin, it cannot compensate at AIS. We show AnkR lacks the domain necessary for AIS localization. Whereas loss of β4 spectrin causes motor impairment and disrupts AIS, loss of β1 spectrin has no discernable effect on central nervous system structure or function. However, mice lacking both neuronal β1 and β4 spectrin show exacerbated nervous system dysfunction compared to mice lacking β1 or β4 spectrin alone, including profound disruption of AIS Na+ channel clustering, progressive loss of nodal Na+ channels, and seizures. These results further define the important role of AIS and nodal spectrins for nervous system function.

Cargo hold and delivery: Ankyrins, spectrins, and their functional patterning of neurons

The highly polarized, typically very long, and nonmitotic nature of neurons present them with unique challenges in the maintenance of their homeostasis. This architectural complexity serves a rich and tightly controlled set of functions that enables their fast communication with neighboring cells and endows them with exquisite plasticity. The submembrane neuronal cytoskeleton occupies a pivotal position in orchestrating the structural patterning that determines local and long-range subcellular specialization, membrane dynamics, and a wide range of signaling events. At its center is the partnership between ankyrins and spectrins, which self-assemble with both remarkable long-range regularity and micro- and nanoscale specificity to precisely position and stabilize cell adhesion molecules, membrane transporters, ion channels, and other cytoskeletal proteins. To accomplish these generally conserved, but often functionally divergent and spatially diverse, roles these partners use a combinatorial program of a couple of dozens interacting family members, whose code is not fully unraveled. In a departure from their scaffolding roles, ankyrins and spectrins also enable the delivery of material to the plasma membrane by facilitating intracellular transport. Thus, it is unsurprising that deficits in ankyrins and spectrins underlie several neurodevelopmental, neurodegenerative, and psychiatric disorders. Here, I summarize key aspects of the biology of spectrins and ankyrins in the mammalian neuron and provide a snapshot of the latest advances in decoding their roles in the nervous system.

Mechanistic insights into the interactions of dynein regulator Ndel1 with neuronal ankyrins and implications in polarity maintenance

Ankyrin-G (AnkG), a highly enriched scaffold protein in the axon initial segment (AIS) of neurons, functions to maintain axonal polarity and the integrity of the AIS. At the AIS, AnkG regulates selective intracellular cargo trafficking between soma and axons via interaction with the dynein regulator protein Ndel1, but the molecular mechanism underlying this binding remains elusive. Here we report that Ndel1's C-terminal coiled-coil region (CT-CC) binds to giant neuron-specific insertion regions present in both AnkG and AnkB with 2:1 stoichiometry. The high-resolution crystal structure of AnkB in complex with Ndel1 CT-CC revealed the detailed molecular basis governing the AnkB/Ndel1 complex formation. Mechanistically, AnkB binds with Ndel1 by forming a stable 5-helix bundle dominated by hydrophobic interactions spread across 6 distinct interaction layers. Moreover, we found that AnkG is essential for Ndel1 accumulation at the AIS. Finally, we found that cargo sorting at the AIS can be disrupted by blocking the AnkG/Ndel1 complex formation using a peptide designed based on our structural data. Collectively, the atomic structure of the AnkB/Ndel1 complex together with studies of cargo sorting through the AIS establish the mechanistic basis for AnkG/Ndel1 complex formation and for the maintenance of axonal polarity. Our study will also be valuable for future studies of the interaction between AnkB and Ndel1 perhaps at distal axonal cargo transport.

Trans-Synaptic Signaling through the Glutamate Receptor Delta-1 Mediates Inhibitory Synapse Formation in Cortical Pyramidal Neurons

Fine orchestration of excitatory and inhibitory synaptic development is required for normal brain function, and alterations may cause neurodevelopmental disorders. Using sparse molecular manipulations in intact brain circuits, we show that the glutamate receptor delta-1 (GluD1), a member of ionotropic glutamate receptors (iGluRs), is a postsynaptic organizer of inhibitory synapses in cortical pyramidal neurons. GluD1 is selectively required for the formation of inhibitory synapses and regulates GABAergic synaptic transmission accordingly. At inhibitory synapses, GluD1 interacts with cerebellin-4, an extracellular scaffolding protein secreted by somatostatin-expressing interneurons, which bridges postsynaptic GluD1 and presynaptic neurexins. When binding to its agonist glycine or D-serine, GluD1 elicits non-ionotropic postsynaptic signaling involving the guanine nucleotide exchange factor ARHGEF12 and the regulatory subunit of protein phosphatase 1 PPP1R12A. Thus, GluD1 defines a trans-synaptic interaction regulating postsynaptic signaling pathways for the proper establishment of cortical inhibitory connectivity and challenges the dichotomy between iGluRs and inhibitory synaptic molecules.

Neurodevelopmental mutation of giant ankyrin-G disrupts a core mechanism for axon initial segment assembly

Axon initial segments of vertebrate neurons integrate thousands of dendritic inputs and generate a single outgoing action potential. Giant ankyrin-G associates with most of the molecular components of axon initial segments and is required for their assembly. This study identified 3 human mutations of giant ankyrin-G resulting in impaired neurodevelopment in compound heterozygotes. These mutations prevent transition of giant ankyrin-G from a closed to an open conformation, which normally is regulated by phosphorylation of giant ankyrin-G during maturation of axon initial segments. Giant ankyrin-G thus functions in a signaling pathway that may contribute to activity-dependent plasticity of the axon initial segment as well as provide a therapeutic target for treatment of patients bearing giant ankyrin-G mutations.

Giant ankyrin-G (gAnkG) coordinates assembly of axon initial segments (AISs), which are sites of action potential generation located in proximal axons of most vertebrate neurons. Here, we identify a mechanism required for normal neural development in humans that ensures ordered recruitment of gAnkG and β4-spectrin to the AIS. We identified 3 human neurodevelopmental missense mutations located in the neurospecific domain of gAnkG that prevent recruitment of β4-spectrin, resulting in a lower density and more elongated pattern for gAnkG and its partners than in the mature AIS. We found that these mutations inhibit transition of gAnkG from a closed configuration with close apposition of N- and C-terminal domains to an extended state that is required for binding and recruitment of β4-spectrin, and normally occurs early in development of the AIS. We further found that the neurospecific domain is highly phosphorylated in mouse brain, and that phosphorylation at 2 sites (S1982 and S2619) is required for the conformational change and for recruitment of β4-spectrin. Together, these findings resolve a discrete intermediate stage in formation of the AIS that is regulated through phosphorylation of the neurospecific domain of gAnkG.