Cerebellar Shank2 Regulates Excitatory Synapse Density, Motor Coordination, and Specific Repetitive and Anxiety-Like Behaviors

Probing cognitive flexibility in Shank2-deficient mice: Effects of D-cycloserine and NMDAR signaling hub dynamics

Neurodevelopmental disorders such as autism spectrum disorder (ASD) have a heterogeneous etiology but are largely associated with genetic factors. Robust evidence from recent human genetic studies has linked mutations in the Shank2 gene to idiopathic ASD. Modeling these Shank2 mutations in animal models recapitulates behavioral changes, e.g. impaired social interaction and repetitive behavior of ASD patients. Shank2-deficient mice exhibit NMDA receptor (NMDAR) hypofunction and associated behavioral deficits. Of note, NMDARs are strongly implicated in cognitive flexibility. Their hypofunction, e.g. observed in schizophrenia, or their pharmacological inhibition leads to impaired cognitive flexibility. However, the association between Shank2 mutations and cognitive flexibility is poorly understood. Using Shank2-deficient mice, we explored the role of Shank2 in cognitive flexibility measured by the attentional set shifting task (ASST) and whether ASST performance in Shank2-deficient mice can be modulated by treatment with the partial NMDAR agonist D-cycloserine (DCS). Furthermore, we investigated the effects of Shank2 deficiency, ASST training, and DCS treatment on the expression level of NMDAR signaling hub components in the orbitofrontal cortex (OFC), including NMDAR subunits (GluN2A, GluN2B, GluN2C), phosphoglycerate dehydrogenase and serine racemase. Surprisingly, Shank2 deficiency did not affect ASST performance or alter the expression of the investigated NMDAR signaling hub components. Importantly, however, DCS significantly improved ASST performance, demonstrating that positive NMDAR modulation facilitates cognitive flexibility. Furthermore, DCS increased the expression of GluN2A in the OFC, but not that of other NMDAR signaling hub components. Our findings highlight the potential of DCS as a pharmacological intervention to improve cognitive flexibility impairments downstream of NMDAR modulation and substantiate the key role of NMDAR in cognitive flexibility.

Unravelling the Cerebellar Involvement in Autism Spectrum Disorders: Insights into Genetic Mechanisms and Developmental Pathways

Autism spectrum disorders (ASDs) are complex neurodevelopmental conditions characterized by deficits in social interaction and communication, as well as repetitive behaviors. Although the etiology of ASD is multifactorial, with both genetic and environmental factors contributing to its development, a strong genetic basis is widely recognized. Recent research has identified numerous genetic mutations and genomic rearrangements associated with ASD-characterizing genes involved in brain development. Alterations in developmental programs are particularly harmful during critical periods of brain development. Notably, studies have indicated that genetic disruptions occurring during the second trimester of pregnancy affect cortical development, while disturbances in the perinatal and early postnatal period affect cerebellar development. The developmental defects must be viewed in the context of the role of the cerebellum in cognitive processes, which is now well established. The present review emphasizes the genetic complexity and neuropathological mechanisms underlying ASD and aims to provide insights into the cerebellar involvement in the disorder, focusing on recent advances in the molecular landscape governing its development in humans. Furthermore, we highlight when and in which cerebellar neurons the ASD-associated genes may play a role in the development of cortico-cerebellar circuits. Finally, we discuss improvements in protocols for generating cerebellar organoids to recapitulate the long period of development and maturation of this organ. These models, if generated from patient-induced pluripotent stem cells (iPSC), could provide a valuable approach to elucidate the contribution of defective genes to ASD pathology and inform diagnostic and therapeutic strategies.

Sex-specific modulation of safety learning in Shank2-deficient mice

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by impaired perceptual processing and social communication, intellectual disabilities, and repetitive behaviors. Interestingly, while not a core symptom, anxiety disorders frequently co-occur in individuals with ASD and deficits in safety learning have been described in patients with anxiety-related disorders. Because genetic factors, such as SHANK deficiency (loss-of-function mutations), have been linked to ASD, the aim of the present study was to investigate whether Shank2 deficiency interferes with associative fear and safety signal learning. To first investigate trait anxiety, male and female Shank2-deficient mice were exposed to a light-dark box test. Mice were then submitted to a combination of contextual fear conditioning and single-cue safety conditioning. The results show that Shank2 deficiency increases trait anxiety but reduces contextual fear learning. In male but not female Shank2-deficient mice, reduced single-cued safety learning was observed. This safety learning deficit was not caused by altered anxiety levels, increased locomotor activity, or reduced contextual fear since these changes were also observed in female Shank2-deficient mice. Concluding, our data indicate that the observed safety learning deficits in Shank2-deficient male mice could contribute to the emotional symptoms observed in ASD and the high comorbidity with anxiety-related disorders.

Converging and Diverging Cerebellar Pathways for Motor and Social Behaviors in Mice

Evidence from clinical and preclinical studies has shown that the cerebellum contributes to cognitive functions, including social behaviors. Now that the cerebellum's role in a wider range of behaviors has been confirmed, the question arises whether the cerebellum contributes to social behaviors via the same mechanisms with which it modulates movements. This review seeks to answer whether the cerebellum guides motor and social behaviors through identical pathways. It focuses on studies in which cerebellar cells, synapses, or genes are manipulated in a cell-type specific manner followed by testing of the effects on social and motor behaviors. These studies show that both anatomically restricted and cerebellar cortex-wide manipulations can lead to social impairments without abnormal motor control, and vice versa. These studies suggest that the cerebellum employs different cellular, synaptic, and molecular pathways for social and motor behaviors. Future studies warrant a focus on the diverging mechanisms by which the cerebellum contributes to a wide range of neural functions.

Mapping proteomic composition of excitatory postsynaptic sites in the cerebellar cortex

Functions of the cerebellar cortex, from motor learning to emotion and cognition, depend on the appropriate molecular composition at diverse synapse types. Glutamate receptor distributions have been partially mapped using immunogold electron microscopy. However, information is lacking on the distribution of many other components, such as Shank2, a postsynaptic scaffolding protein whose cerebellar dysfunction is associated with autism spectrum disorders. Here, we used an adapted Magnified Analysis of the Proteome, an expansion microscopy approach, to map multiple glutamate receptors, scaffolding and signaling proteins at single synapse resolution in the cerebellar cortex. Multiple distinct synapse-selective distribution patterns were observed. For example, AMPA receptors were most concentrated at synapses on molecular layer interneurons and at climbing fiber synapses, Shank1 was most concentrated at parallel fiber synapses on Purkinje cells, and Shank2 at both climbing fiber and parallel fiber synapses on Purkinje cells but little on molecular layer interneurons. Our results are consistent with gene expression data but also reveal input-selective targeting within Purkinje cells. In specialized glomerular structures of the granule cell layer, AMPA receptors as well as most other synaptic components preferentially targeted to synapses. However, NMDA receptors and the synaptic GTPase activating protein SynGAP preferentially targeted to extrasynaptic sites. Thus, glomeruli may be considered integrative signaling units through which mossy fibers differentially activate synaptic AMPA and extrasynaptic NMDA receptor complexes. Furthermore, we observed NMDA receptors and SynGAP at adherens junctions, suggesting a role in structural plasticity of glomeruli. Altogether, these data contribute to mapping the cerebellar 'synaptome'.

Autism patient-derived SHANK2BY29X mutation affects the development of ALDH1A1 negative dopamine neuron

Autism spectrum disorder (ASD) encompasses a range of neurodevelopmental conditions. Different mutations on a single ASD gene contribute to heterogeneity of disease phenotypes, possibly due to functional diversity of generated isoforms. SHANK2, a causative gene in ASD, demonstrates this phenomenon, but there is a scarcity of tools for studying endogenous SHANK2 proteins in an isoform-specific manner. Here, we report a point mutation on SHANK2, which is found in a patient with autism, located on exon of the SHANK2B transcript variant (NM_133266.5), hereby SHANK2BY29X. This mutation results in an early stop codon and an aberrant splicing event that impacts SHANK2 transcript variants distinctly. Induced pluripotent stem cells (iPSCs) carrying this mutation, from the patient or isogenic editing, fail to differentiate into functional dopamine (DA) neurons, which can be rescued by genetic correction. Available SMART-Seq single-cell data from human midbrain reveals the abundance of SHANK2B transcript in the ALDH1A1 negative DA neurons. We then show that SHANK2BY29X mutation primarily affects SHANK2B expression and ALDH1A1 negative DA neurons in vitro during early neuronal developmental stage. Mice knocked in with the identical mutation exhibit autistic-like behavior, decreased occupancy of ALDH1A1 negative DA neurons and decreased dopamine release in ventral tegmental area (VTA). Our study provides novel insights on a SHANK2 mutation derived from autism patient and highlights SHANK2B significance in ALDH1A1 negative DA neuron.

Purkinje-cell-specific MeCP2 deficiency leads to motor deficits and autistic-like behavior due to aberrations in PTP1B-TrkB-SK signaling

Patients with Rett syndrome suffer from a loss-of-function mutation of the Mecp2 gene, which results in various symptoms including autistic traits and motor deficits. Deletion of Mecp2 in the brain mimics part of these symptoms, but the specific function of methyl-CpG-binding protein 2 (MeCP2) in the cerebellum remains to be elucidated. Here, we demonstrate that Mecp2 deletion in Purkinje cells (PCs) reduces their intrinsic excitability through a signaling pathway comprising the small-conductance calcium-activated potassium channel PTP1B and TrkB, the receptor of brain-derived neurotrophic factor. Aberration of this cascade, in turn, leads to autistic-like behaviors as well as reduced vestibulocerebellar motor learning. Interestingly, increasing activity of TrkB in PCs is sufficient to rescue PC dysfunction and abnormal motor and non-motor behaviors caused by Mecp2 deficiency. Our findings highlight how PC dysfunction may contribute to Rett syndrome, providing insight into the underlying mechanism and paving the way for rational therapeutic designs.

Expression profiles of the autism-related SHANK proteins in the human brain

BACKGROUND

SHANKs are major scaffolding proteins at postsynaptic densities (PSDs) in the central nervous system. Mutations in all three family members have been associated with neurodevelopmental disorders such as autism spectrum disorders (ASDs). Despite the pathophysiological importance of SHANK2 and SHANK3 mutations in humans, research on the expression of these proteins is mostly based on rodent model organisms.

RESULTS

In the present study, cellular and neuropil SHANK2 expression was analyzed by immunofluorescence (IF) staining of post mortem human brain tissue from four male individuals (19 brain regions). Mouse brains were analyzed in comparison to evaluate the degree of phylogenetic conservation. Furthermore, SHANK2 and SHANK3 isoform patterns were compared in human and mouse brain lysates. While isoform expression and subcellular distribution were largely conserved, differences in neuropil levels of SHANK2 were found by IF staining: Maximum expression was concordantly measured in the cerebellum; however, higher SHANK2 expression was detected in the human brainstem and thalamus when compared to mice. One of the lowest SHANK2 levels was found in the human amygdala, a moderately expressing region in mouse. Quantification of SHANK3 IF in mouse brains unveiled a distribution comparable to humans.

CONCLUSIONS

In summary, these data show that the overall expression pattern of SHANK is largely conserved in defined brain regions; however, differences do exist, which need to be considered in the translation of rodent studies. The summarized expression patterns of SHANK2 and SHANK3 should serve as a reference for future studies.

Critical periods and Autism Spectrum Disorders, a role for sleep

Brain development relies on both experience and genetically defined programs. Time windows where certain brain circuits are particularly receptive to external stimuli, resulting in heightened plasticity, are referred to as "critical periods". Sleep is thought to be essential for normal brain development. Importantly, studies have shown that sleep enhances critical period plasticity and promotes experience-dependent synaptic pruning in the developing mammalian brain. Therefore, normal plasticity during critical periods depends on sleep. Problems falling and staying asleep occur at a higher rate in Autism Spectrum Disorder (ASD) relative to typical development. In this review, we explore the potential link between sleep, critical period plasticity, and ASD. First, we review the importance of critical period plasticity in typical development and the role of sleep in this process. Next, we summarize the evidence linking ASD with deficits in synaptic plasticity in rodent models of high-confidence ASD gene candidates. We then show that the high-confidence rodent models of ASD that show sleep deficits also display plasticity deficits. Given how important sleep is for critical period plasticity, it is essential to understand the connections between synaptic plasticity, sleep, and brain development in ASD. However, studies investigating sleep or plasticity during critical periods in ASD mouse models are lacking. Therefore, we highlight an urgent need to consider developmental trajectory in studies of sleep and plasticity in neurodevelopmental disorders.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

The cerebellum and anxiety

Although the cerebellum is traditionally known for its role in motor functions, recent evidence points toward the additional involvement of the cerebellum in an array of non-motor functions. One such non-motor function is anxiety behavior: a series of recent studies now implicate the cerebellum in anxiety. Here, we review evidence regarding the possible role of the cerebellum in anxiety-ranging from clinical studies to experimental manipulation of neural activity-that collectively points toward a role for the cerebellum, and possibly a specific topographical locus within the cerebellum, as one of the orchestrators of anxiety responses.

Genetic Mapping of Behavioral Traits Using the Collaborative Cross Resource

The complicated interactions between genetic background, environment and lifestyle factors make it difficult to study the genetic basis of complex phenotypes, such as cognition and anxiety levels, in humans. However, environmental and other factors can be tightly controlled in mouse studies. The Collaborative Cross (CC) is a mouse genetic reference population whose common genetic and phenotypic diversity is on par with that of humans. Therefore, we leveraged the power of the CC to assess 52 behavioral measures associated with locomotor activity, anxiety level, learning and memory. This is the first application of the CC in novel object recognition tests, Morris water maze tasks, and fear conditioning tests. We found substantial continuous behavioral variations across the CC strains tested, and mapped six quantitative trait loci (QTLs) which influenced these traits, defining candidate genetic variants underlying these QTLs. Overall, our findings highlight the potential of the CC population in behavioral genetic research, while the identified genomic loci and genes driving the variation of relevant behavioral traits provide a foundation for further studies.

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.

Synaptic genes and neurodevelopmental disorders: From molecular mechanisms to developmental strategies of behavioral testing

Synaptopathies are a class of neurodevelopmental disorders caused by modification in genes coding for synaptic proteins. These proteins oversee the process of neurotransmission, mainly controlling the fusion and recycling of synaptic vesicles at the presynaptic terminal, the expression and localization of receptors at the postsynapse and the coupling between the pre- and the postsynaptic compartments. Murine models, with homozygous or heterozygous deletion for several synaptic genes or knock-in for specific pathogenic mutations, have been developed. They have proved to be extremely informative for understanding synaptic physiology, as well as for clarifying the patho-mechanisms leading to developmental delay, epilepsy and motor, cognitive and social impairments that are the most common clinical manifestations of neurodevelopmental disorders. However, the onset of these disorders emerges during infancy and adolescence while the behavioral phenotyping is often conducted in adult mice, missing important information about the impact of synaptic development and maturation on the manifestation of the behavioral phenotype. Here, we review the main achievements obtained by behavioral testing in murine models of synaptopathies and propose a battery of behavioral tests to improve classification, diagnosis and efficacy of potential therapeutic treatments. Our aim is to underlie the importance of studying behavioral development and better focusing on disease onset and phenotypes.

Brain region and gene dosage-differential transcriptomic changes in Shank2-mutant mice

Shank2 is an abundant excitatory postsynaptic scaffolding protein that has been implicated in various neurodevelopmental and psychiatric disorders, including autism spectrum disorder (ASD), intellectual disability, attention-deficit/hyperactivity disorder, and schizophrenia. Shank2-mutant mice show ASD-like behavioral deficits and altered synaptic and neuronal functions, but little is known about how different brain regions and gene dosages affect the transcriptomic phenotypes of these mice. Here, we performed RNA-Seq-based transcriptomic analyses of the prefrontal cortex, hippocampus, and striatum in adult Shank2 heterozygous (HT)- and homozygous (HM)-mutant mice lacking exons 6–7. The prefrontal cortical, hippocampal, and striatal regions showed distinct transcriptomic patterns associated with synapse, ribosome, mitochondria, spliceosome, and extracellular matrix (ECM). The three brain regions were also distinct in the expression of ASD-related and ASD-risk genes. These differential patterns were stronger in the prefrontal cortex where the HT transcriptome displayed increased synaptic gene expression and reverse-ASD patterns whereas the HM transcriptome showed decreased synaptic gene expression and ASD-like patterns. These results suggest brain region- and gene dosage-differential transcriptomic changes in Shank2-mutant mice.

Enhanced fear limits behavioral flexibility in Shank2-deficient mice

Background

A core symptom of autism spectrum disorder (ASD) is repetitive and restrictive patterns of behavior. Cognitive inflexibility has been proposed as a potential basis for these symptoms of ASD. More generally, behavioral inflexibility has been proposed to underlie repetitive and restrictive behavior in ASD. Here, we investigated whether and how behavioral flexibility is compromised in a widely used animal model of ASD.

Methods

We compared the behavioral performance of Shank2-knockout mice and wild-type littermates in reversal learning employing a probabilistic classical trace conditioning paradigm. A conditioned stimulus (odor) was paired with an unconditioned appetitive (water, 6 µl) or aversive (air puff) stimulus in a probabilistic manner. We also compared air puff-induced eye closure responses of Shank2-knockout and wild-type mice.

Results

Male, but not female, Shank2-knockout mice showed impaired reversal learning when the expected outcomes consisted of a water reward and a strong air puff. Moreover, male, but not female, Shank2-knockout mice showed stronger anticipatory eye closure responses to the air puff compared to wild-type littermates, raising the possibility that the impairment might reflect enhanced fear. In support of this contention, male Shank2-knockout mice showed intact reversal learning when the strong air puff was replaced with a mild air puff and when the expected outcomes consisted of only rewards.

Limitations

We examined behavioral flexibility in one behavioral task (reversal learning in a probabilistic classical trace conditioning paradigm) using one ASD mouse model (Shank2-knockout mice). Thus, future work is needed to clarify the extent to which our findings (that enhanced fear limits behavioral flexibility in ASD) can explain the behavioral inflexibility associated with ASD. Also, we examined only the relationship between fear and behavioral flexibility, leaving open the question of whether abnormalities in processes other than fear contribute to behavioral inflexibility in ASD. Finally, the neurobiological mechanisms linking Shank2-knockout and enhanced fear remain to be elucidated.

Conclusions

Our results indicate that enhanced fear suppresses reversal learning in the presence of an intact capability to learn cue-outcome contingency changes in Shank2-knockout mice. Our findings suggest that behavioral flexibility might be seriously limited by abnormal emotional responses in ASD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13229-022-00518-1.

Modelling Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) Using Mice and Zebrafish

Autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD) are two debilitating neurodevelopmental disorders. The former is associated with social impairments whereas the latter is associated with inattentiveness, hyperactivity, and impulsivity. There is recent evidence that both disorders are somehow related and that genes may play a large role in these disorders. Despite mounting human and animal research, the neurological pathways underlying ASD and ADHD are still not well understood. Scientists investigate neurodevelopmental disorders by using animal models that have high similarities in genetics and behaviours with humans. Mice have been utilized in neuroscience research as an excellent animal model for a long time; however, the zebrafish has attracted much attention recently, with an increasingly large number of studies using this model. In this review, we first discuss ASD and ADHD aetiology from a general point of view to their characteristics and treatments. We also compare mice and zebrafish for their similarities and discuss their advantages and limitations in neuroscience. Finally, we summarize the most recent and existing research on zebrafish and mouse models of ASD and ADHD. We believe that this review will serve as a unique document providing interesting information to date about these models, thus facilitating research on ASD and ADHD.

The Hole-Board Test in Mutant Mice

First described by Boissier and Simon in (Ther Recreat J 17:1225-1232, 1962), the hole-board has become a recognized test of anxiety and spatial memory. Benzodiazepines acting at the GABA_A-BZD site increase hole-pokes in rats and mice, indicating a loss in behavioral inhibition concordant with the behavior of mutant mice deficient in the GABA transporter. Hole-poking also depends on arousal mechanisms dependent on dopaminergic transmission, as indicated by drug and null mutant studies. In addition, the behavior is modified in natural and null mutants affecting the cerebellum as well as null mutants affecting neuropeptides, growth factors, cell adhesion, and inflammation. Further research is required to determine convergences between genetic and pharmacological effects.

The Cerebellar Involvement in Autism Spectrum Disorders: From the Social Brain to Mouse Models

Autism spectrum disorders (ASD) are pervasive neurodevelopmental disorders that include a variety of forms and clinical phenotypes. This heterogeneity complicates the clinical and experimental approaches to ASD etiology and pathophysiology. To date, a unifying theory of these diseases is still missing. Nevertheless, the intense work of researchers and clinicians in the last decades has identified some ASD hallmarks and the primary brain areas involved. Not surprisingly, the areas that are part of the so-called “social brain”, and those strictly connected to them, were found to be crucial, such as the prefrontal cortex, amygdala, hippocampus, limbic system, and dopaminergic pathways. With the recent acknowledgment of the cerebellar contribution to cognitive functions and the social brain, its involvement in ASD has become unmistakable, though its extent is still to be elucidated. In most cases, significant advances were made possible by recent technological developments in structural/functional assessment of the human brain and by using mouse models of ASD. Mouse models are an invaluable tool to get insights into the molecular and cellular counterparts of the disease, acting on the specific genetic background generating ASD-like phenotype. Given the multifaceted nature of ASD and related studies, it is often difficult to navigate the literature and limit the huge content to specific questions. This review fulfills the need for an organized, clear, and state-of-the-art perspective on cerebellar involvement in ASD, from its connections to the social brain areas (which are the primary sites of ASD impairments) to the use of monogenic mouse models.

Arsenic exposure via drinking water during pregnancy and lactation induces autism-like behaviors in male offspring mice

Exposure to arsenic (As), an environmental toxicant, causes damages to the central nervous system (CNS) structure and function. Emerging epidemiological studies support that exposure to As, especially during the critical periods of the CNS development, may act as an environmental risk factor of autism spectrum disorders (ASD), which is characterized by behavioral changes, including abnormal social behaviors, restricted interests and repetitive behaviors. However, direct evidence supporting the cause-effect relationship between As exposure and the risk of ASD is still missing. Thus, we aimed to investigate whether As exposure during pregnancy and lactation led to autism-like behaviors in offspring mice in the present study. We established a mice model of exposure to As via drinking water during pregnancy and lactation and conducted a battery of behavioral tests to evaluate social behaviors, repetitive behaviors, anxiety behaviors and learning and memory ability in offspring mice. We found that perinatal exposure to As caused autism-like behaviors in male offspring, which demonstrated by abnormal social behaviors and repetitive behaviors. Anxiety-like behaviors, and learning and memory impairments, known as concomitant behavioral phenotypes in mice with autism-like behaviors, were also observed. Decreases of synaptic density, especially in cortex, hippocampus and cerebellum, are extensively observed in both ASD patients and animal models of ASD. Thus, immunofluorescence staining and western blotting were used to observe the expression of PSD-95 and SYP, well-known markers for presynaptic and postsynaptic membranes, to assess the synaptic density in offspring cortex, hippocampus and cerebellum. We found perinatal exposure to As decreased the expression of PSD-95 and SYP in these brain regions. This indicated that perinatal exposure to As caused decreases of synaptic density, a typical autism-like cellular alteration in brains, which may contribute to autism-like behaviors in offspring.

Cerebellar and Striatal Implications in Autism Spectrum Disorders: From Clinical Observations to Animal Models

Autism spectrum disorders (ASD) are complex conditions that stem from a combination of genetic, epigenetic and environmental influences during early pre- and postnatal childhood. The review focuses on the cerebellum and the striatum, two structures involved in motor, sensory, cognitive and social functions altered in ASD. We summarize clinical and fundamental studies highlighting the importance of these two structures in ASD. We further discuss the relation between cellular and molecular alterations with the observed behavior at the social, cognitive, motor and gait levels. Functional correlates regarding neuronal activity are also detailed wherever possible, and sexual dimorphism is explored pointing to the need to apprehend ASD in both sexes, as findings can be dramatically different at both quantitative and qualitative levels. The review focuses also on a set of three recent papers from our laboratory where we explored motor and gait function in various genetic and environmental ASD animal models. We report that motor and gait behaviors can constitute an early and quantitative window to the disease, as they often correlate with the severity of social impairments and loss of cerebellar Purkinje cells. The review ends with suggestions as to the main obstacles that need to be surpassed before an appropriate management of the disease can be proposed.

Shankopathies in the Developing Brain in Autism Spectrum Disorders

The SHANK family of proteins play critical structural and functional roles in the postsynaptic density (PSD) at excitatory glutamatergic synapses. Through their multidomain structure they form a structural platform across the PSD for protein–protein interactions, as well as recruiting protein complexes to strengthen excitatory synaptic transmission. Mutations in SHANKs reflect their importance to synapse development and plasticity. This is evident in autism spectrum disorder (ASD), a neurodevelopmental disorder resulting in behavioural changes including repetitive behaviours, lack of sociability, sensory issues, learning, and language impairments. Human genetic studies have revealed ASD mutations commonly occur in SHANKs. Rodent models expressing these mutations display ASD behavioural impairments, and a subset of these deficits are rescued by reintroduction of Shank in adult animals, suggesting that lack of SHANK during key developmental periods can lead to permanent changes in the brain’s wiring. Here we explore the differences in synaptic function and plasticity from development onward in rodent Shank ASD models. To date the most explored brain regions, relate to the behavioural changes observed, e.g., the striatum, hippocampus, sensory, and prefrontal cortex. In addition, less-studied regions including the hypothalamus, cerebellum, and peripheral nervous system are also affected. Synaptic phenotypes include weakened but also strengthened synaptic function, with NMDA receptors commonly affected, as well as changes in the balance of excitation and inhibition especially in cortical brain circuits. The effects of shankopathies in activity-dependent brain wiring is an important target for therapeutic intervention. We therefore highlight areas of research consensus and identify remaining questions and challenges.

Shank2/3 double knockout-based screening of cortical subregions links the retrosplenial area to the loss of social memory in autism spectrum disorders

Members of the Shank protein family are master scaffolds of the postsynaptic architecture and mutations within the SHANK genes are causally associated with autism spectrum disorders (ASDs). We generated a Shank2-Shank3 double knockout mouse that is showing severe autism related core symptoms, as well as a broad spectrum of comorbidities. We exploited this animal model to identify cortical brain areas linked to specific autistic traits by locally deleting Shank2 and Shank3 simultaneously. Our screening of 10 cortical subregions revealed that a Shank2/3 deletion within the retrosplenial area severely impairs social memory, a core symptom of ASD. Notably, DREADD-mediated neuronal activation could rescue the social impairment triggered by Shank2/3 depletion. Data indicate that the retrosplenial area has to be added to the list of defined brain regions that contribute to the spectrum of behavioural alterations seen in ASDs.

Social Deficits and Cerebellar Degeneration in Purkinje Cell Scn8a Knockout Mice

Mutations in the SCN8A gene encoding the voltage-gated sodium channel α-subunit Nav1. 6 have been reported in individuals with epilepsy, intellectual disability and features of autism spectrum disorder. SCN8A is widely expressed in the central nervous system, including the cerebellum. Cerebellar dysfunction has been implicated in autism spectrum disorder. We investigated conditional Scn8a knockout mice under C57BL/6J strain background that specifically lack Scn8a expression in cerebellar Purkinje cells (Scn8a ^flox/flox , L7Cre ⁺ mice). Cerebellar morphology was analyzed by immunohistochemistry and MR imaging. Mice were subjected to a battery of behavioral tests including the accelerating rotarod, open field, elevated plus maze, light-dark transition box, three chambers, male-female interaction, social olfaction, and water T-maze tests. Patch clamp recordings were used to evaluate evoked action potentials in Purkinje cells. Behavioral phenotyping demonstrated that Scn8a ^flox/flox , L7Cre ⁺ mice have impaired social interaction, motor learning and reversal learning as well as increased repetitive behavior and anxiety-like behaviors. By 5 months of age, Scn8a ^flox/flox , L7Cre ⁺ mice began to exhibit cerebellar Purkinje cell loss and reduced molecular thickness. At 9 months of age, Scn8a ^flox/flox , L7Cre ⁺ mice exhibited decreased cerebellar size and a reduced number of cerebellar Purkinje cells more profoundly, with evidence of additional neurodegeneration in the molecular layer and deep cerebellar nuclei. Purkinje cells in Scn8a ^flox/flox , L7Cre ⁺ mice exhibited reduced repetitive firing. Taken together, our experiments indicated that loss of Scn8a expression in cerebellar Purkinje cells leads to cerebellar degeneration and several ASD-related behaviors. Our study demonstrated the specific contribution of loss of Scn8a in cerebellar Purkinje cells to behavioral deficits characteristic of ASD. However, it should be noted that our observed effects reported here are specific to the C57BL/6 genome type.

Postsynaptic autism spectrum disorder genes and synaptic dysfunction

This review provides an overview of the synaptic dysfunction of neuronal circuits and the ensuing behavioral alterations caused by mutations in autism spectrum disorder (ASD)-linked genes directly or indirectly affecting the postsynaptic neuronal compartment. There are plenty of ASD risk genes, that may be broadly grouped into those involved in gene expression regulation (epigenetic regulation and transcription) and genes regulating synaptic activity (neural communication and neurotransmission). Notably, the effects mediated by ASD-associated genes can vary extensively depending on the developmental time and/or subcellular site of expression. Therefore, in order to gain a better understanding of the mechanisms of disruptions in postsynaptic function, an effort to better model ASD in experimental animals is required to improve standardization and increase reproducibility within and among studies. Such an effort holds promise to provide deeper insight into the development of these disorders and to improve the translational value of preclinical studies.

Genetic determinants of autism spectrum disorders - a review

Introduction: It is estimated that various types of abnormalities from the autistic spectrum disorder occur in up to 2% of the population. These include difficulties in maintaining relationships, communication, and repetitive behaviours. Literature describes them quite well, in contrast to the causes of these disorders, which include both environmental factors and a very long list of genetic aberrations.

Materials and methods: The papers available on the PubMed platform and other sources were reviewed to describe the most important genetic factors responsible for the development of autism spectrum disorders.

Results: There are many genes and their mutations associated with the prevalence of autism spectrum disorders in patients. One of the main factors is the SHANK gene family, with the type and degree of abnormality in patients depending on the damage to particular genes: SHANK1-SHANK3. Research also shows the potential of targeted symptom-relieving therapies in patients with SHANK3 mutations. A correlation with the occurrence of autism has also been demonstrated for genes responsible for calcium signaling - especially the group of IP3R calcium channels. Their calcium transmission is abnormal in the majority of patients with autism spectrum disorders. A number of mutations in the 7q region were discovered - including the AUTS2, GNAI1, RELN, KMT2E, BRAF genes - the occurrence of which is associated with the presence of symptoms of autism. Autism spectrum disorders occur in about 10% of patients suffering from monogenic syndromes such as fragile X chromosome syndrome, Timothy syndrome, tuberous sclerosis, Rett syndrome or hamartomatic tumor syndrome.

Conclusions: Research shows that many mutations can contribute to the development of autism spectrum disorders. Further studies are necessary to discover their therapeutic and diagnostic potential for autism.

Loss of Tsc1 in cerebellar Purkinje cells induces transcriptional and translation changes in FMRP target transcripts

Tuberous sclerosis complex (TSC) is a genetic disorder that is associated with multiple neurological manifestations. Previously, we demonstrated that Tsc1 loss in cerebellar Purkinje cells (PCs) can cause altered social behavior in mice. Here, we performed detailed transcriptional and translational analyses of Tsc1-deficient PCs to understand the molecular alterations in these cells. We found that target transcripts of the Fragile X Mental Retardation Protein (FMRP) are reduced in mutant PCs with evidence of increased degradation. Surprisingly, we observed unchanged ribosomal binding for many of these genes using translating ribosome affinity purification. Finally, we found that multiple FMRP targets, including SHANK2, were reduced, suggesting that compensatory increases in ribosomal binding efficiency may be unable to overcome reduced transcript levels. These data further implicate dysfunction of FMRP and its targets in TSC and suggest that treatments aimed at restoring the function of these pathways may be beneficial.

The BMP antagonist gremlin 1 contributes to the development of cortical excitatory neurons, motor balance and fear responses

Bone morphogenetic protein (BMP) signaling is required for early forebrain development and cortical formation. How the endogenous modulators of BMP signaling regulate the structural and functional maturation of the developing brain remains unclear. Here, we show that expression of the BMP antagonist Grem1 marks committed layer V and VI glutamatergic neurons in the embryonic mouse brain. Lineage tracing of Grem1-expressing cells in the embryonic brain was examined by administration of tamoxifen to pregnant Grem1creERT; Rosa26LSLTdtomato mice at 13.5 days post coitum (dpc), followed by collection of embryos later in gestation. In addition, at 14.5 dpc, bulk mRNA-seq analysis of differentially expressed transcripts between FACS-sorted Grem1-positive and -negative cells was performed. We also generated Emx1-cre-mediated Grem1 conditional knockout mice (Emx1-Cre;Grem1^flox/flox) in which the Grem1 gene was deleted specifically in the dorsal telencephalon. Grem1^Emx1cKO animals had reduced cortical thickness, especially layers V and VI, and impaired motor balance and fear sensitivity compared with littermate controls. This study has revealed new roles for Grem1 in the structural and functional maturation of the developing cortex.

Summary: The BMP antagonist Grem1 is expressed by committed deep-layer glutamatergic neurons in the embryonic mouse cortex. Grem1 conditional knockout mice display cortical and behavioral abnormalities.

Gene Dosage- and Age-Dependent Differential Transcriptomic Changes in the Prefrontal Cortex of Shank2-Mutant Mice

Shank2 is an abundant postsynaptic scaffolding protein that is known to regulate excitatory synapse assembly and synaptic transmission and has been implicated in various neurodevelopmental disorders, including autism spectrum disorders (ASD). Previous studies on Shank2-mutant mice provided mechanistic insights into their autistic-like phenotypes, but it remains unclear how transcriptomic patterns are changed in brain regions of the mutant mice in age- and gene dosage-dependent manners. To this end, we performed RNA-Seq analyses of the transcripts from the prefrontal cortex (PFC) of heterozygous and homozygous Shank2-mutant mice lacking exons 6 and 7 at juvenile (week 3) and adult (week 12) stages. Juvenile heterozygous Shank2-mutant mice showed upregulation of glutamate synapse-related genes, downregulation of ribosomal and mitochondrial genes, and transcriptomic changes that are opposite to those observed in ASD (anti-ASD) such as upregulation of ASD_down (downregulated in ASD), GABA neuron-related, and oligodendrocyte-related genes. Juvenile homozygous Shank2 mice showed upregulation of chromatin-related genes and transcriptomic changes that are in line with those occurring in ASD (pro-ASD) such as downregulation of ASD_down, GABA neuron-related, and oligodendrocyte-related genes. Adult heterozygous and homozygous Shank2-mutant mice both exhibited downregulation of ribosomal and mitochondrial genes and pro-ASD transcriptomic changes. Therefore, the gene dosage- and age-dependent effects of Shank2 deletions in mice include differential transcriptomic changes across distinct functional contexts, including synapses, chromatin, ribosomes, mitochondria, GABA neurons, and oligodendrocytes.

Cerebellar Dysfunction in Autism Spectrum Disorders: Deriving Mechanistic Insights from an Internal Model Framework

Autism spectrum disorders (ASD) are highly prevalent neurodevelopmental disorders; however, the neurobiological mechanisms underlying disordered behavior in ASD remain poorly understood. Notably, individuals with ASD have demonstrated difficulties generating implicitly derived behavioral predictions and adaptations. Although many brain regions are involved in these processes, the cerebellum contributes an outsized role to these behavioral functions. Consistent with this prominent role, cerebellar dysfunction has been increasingly implicated in ASD. In this review, we will utilize the foundational, theoretical contributions of the late neuroscientist Masao Ito to establish an internal model framework for the cerebellar contribution to ASD-relevant behavioral predictions and adaptations. Additionally, we will also explore and then apply his key experimental contributions towards an improved, mechanistic understanding of the contribution of cerebellar dysfunction to ASD.

The autism-associated protein CHD8 is required for cerebellar development and motor function

Mutations in the gene encoding the chromatin remodeler chromodomain helicase DNA-binding protein 8 (CHD8) are a highly penetrant risk factor for autism spectrum disorder (ASD). Although cerebellar abnormalities have long been thought to be related to ASD pathogenesis, it has remained largely unknown whether dysfunction of CHD8 in the cerebellum contributes to ASD phenotypes. We here show that cerebellar granule neuron progenitor (GNP)-specific deletion of Chd8 in mice impairs the proliferation and differentiation of these cells as well as gives rise to cerebellar hypoplasia and a motor coordination defect, but not to ASD-like behavioral abnormalities. CHD8 is found to regulate the expression of neuronal genes in GNPs. It also binds preferentially to promoter regions and modulates local chromatin accessibility of transcriptionally active genes in these cells. Our results have thus uncovered a key role for CHD8 in cerebellar development, with important implications for understanding the contribution of this brain region to ASD pathogenesis.

Conditional knockout of MET receptor tyrosine kinase in cortical excitatory neurons leads to enhanced learning and memory in young adult mice but early cognitive decline in older adult mice

Human genetic studies established MET gene as a risk factor for autism spectrum disorders. We have previously shown that signaling mediated by MET receptor tyrosine kinase, expressed in early postnatal developing forebrain circuits, controls glutamatergic neuron morphological development, synapse maturation, and cortical critical period plasticity. Here we investigated how MET signaling affects synaptic plasticity, learning and memory behavior, and whether these effects are age-dependent. We found that in young adult (postnatal 2-3 months) Met conditional knockout (Met^fx/fx:emx1^cre, cKO) mice, the hippocampus exhibits elevated plasticity, measured by increased magnitude of long-term potentiation (LTP) and depression (LTD) in hippocampal slices. Surprisingly, in older adult cKO mice (10-12 months), LTP and LTD magnitudes were diminished. We further conducted a battery of behavioral tests to assess learning and memory function in cKO mice and littermate controls. Consistent with age-dependent LTP/LTD findings, we observed enhanced spatial memory learning in 2-3 months old young adult mice, assessed by hippocampus-dependent Morris water maze test, but impaired spatial learning in 10-12 months mice. Contextual and cued learning were further assessed using a Pavlovian fear conditioning test, which also revealed enhanced associative fear acquisition and extinction in young adult mice, but impaired fear learning in older adult mice. Lastly, young cKO mice also exhibited enhanced motor learning. Our results suggest that a shift in the window of synaptic plasticity and an age-dependent early cognitive decline may be novel circuit pathophysiology for a well-established autism genetic risk factor.

Insulin-like growth factor 1 partially rescues early developmental defects caused by SHANK2 knockdown in human neurons

SHANK2 is a scaffold protein that serves as a protein anchor at the postsynaptic density in neurons. Genetic variants of SHANK2 are strongly associated with synaptic dysfunction and the pathophysiology of autism spectrum disorder. Recent studies indicate that early neuronal developmental defects play a role in the pathogenesis of autism spectrum disorder, and that insulin-like growth factor 1 has a positive effect on neurite development. To investigate the effects of SHANK2 knockdown on early neuronal development, we generated a sparse culture system using human induced pluripotent stem cells, which then differentiated into neural progenitor cells after 3-14 days in culture, and which were dissociated into single neurons. Neurons in the experimental group were infected with shSHANK2 lentivirus carrying a red fluorescent protein reporter (shSHANK2 group). Control neurons were infected with scrambled shControl lentivirus carrying a red fluorescent protein reporter (shControl group). Neuronal somata and neurites were reconstructed based on the lentiviral red fluorescent protein signal. Developmental dendritic and motility changes in VGLUT1+ glutamatergic neurons and TH+ dopaminergic neurons were then evaluated in both groups. Compared with shControl VGLUT1+ neurons, the dendritic length and arborizations of shSHANK2 VGLUT1+ neurons were shorter and fewer, while cell soma speed was higher. Furthermore, dendritic length and arborization were significantly increased after insulin-like growth factor 1 treatment of shSHANK2 neurons, while cell soma speed remained unaffected. These results suggest that insulin-like growth factor 1 can rescue morphological defects, but not the change in neuronal motility. Collectively, our findings demonstrate that SHANK2 deficiency perturbs early neuronal development, and that IGF1 can partially rescue the neuronal defects caused by SHANK2 knockdown. All experimental procedures and protocols were approved by the Laboratory Animal Ethics Committee of Jinan University, China (approval No. 20170228010) on February 28, 2017.

Experimental Models to Study Autism Spectrum Disorders: hiPSCs, Rodents and Zebrafish

Autism Spectrum Disorders (ASD) affect around 1.5% of the global population, which manifest alterations in communication and socialization, as well as repetitive behaviors or restricted interests. ASD is a complex disorder with known environmental and genetic contributors; however, ASD etiology is far from being clear. In the past decades, many efforts have been put into developing new models to study ASD, both in vitro and in vivo. These models have a lot of potential to help to validate some of the previously associated risk factors to the development of the disorder, and to test new potential therapies that help to alleviate ASD symptoms. The present review is focused on the recent advances towards the generation of models for the study of ASD, which would be a useful tool to decipher the bases of the disorder, as well as to conduct drug screenings that hopefully lead to the identification of useful compounds to help patients deal with the symptoms of ASD.

Cyclin Y, a novel actin-binding protein, regulates spine plasticity through the cofilin-actin pathway

While positive regulators of hippocampal long-term potentiation (LTP) have extensively been investigated, relatively little is known about the inhibitory regulators of LTP. We previously reported that Cyclin Y (CCNY), a member of cyclin family generally known to function in proliferating cells, is a novel postsynaptic protein that serves as a negative regulator of functional LTP. However, whether CCNY plays a role in structural LTP, which is mechanistically linked to functional LTP, and which mechanisms are involved in the CCNY-mediated suppression of LTP at the molecular level remain elusive. Here, we report that CCNY negatively regulates the plasticity-induced changes in spine morphology through the control of actin dynamics. We observed that CCNY directly binds to filamentous actin and interferes with LTP-induced actin polymerization as well as depolymerization by blocking the activation of cofilin, an actin-depolymerizing factor, thus resulting in less plastic spines and the impairment of structural LTP. These data suggest that CCNY acts as an inhibitory regulator for both structural and functional LTP by modulating actin dynamics through the cofilin-actin pathway. Collectively, our findings provide a mechanistic insight into the inhibitory modulation of hippocampal LTP by CCNY, highlighting a novel function of a cyclin family protein in non-proliferating neuronal cells.

Behavioural and histological changes in cuprizone-fed mice

Feeding cuprizone (CPZ) to mice causes demyelination and reactive gliosis in the central nervous system (CNS), hallmarks of some neurodegenerative diseases like multiple sclerosis. However, relatively little is known regarding the behavioural deficits associated with CPZ-feeding and much of what is known is contradictory. This study investigated whether 37 days oral feeding of 0.2% CPZ to young adult mice evoked sensorimotor behavioural changes. Behavioural tests included measurements of nociceptive withdrawal reflex responses and locomotor tests. Additionally, these were compared to histological analysis of the relevant CNS regions by analysis of neuronal and glial cell components. CPZ-fed mice exhibited more foot slips in walking ladder and beam tests compared to controls. In contrast, no changes in nociceptive thresholds to thermal or mechanical stimuli occurred between groups. Histological analysis showed demyelination throughout the CNS, which was most prominent in white matter tracts in the cerebrum but was also elevated in areas such as the hippocampus, basal ganglia and diencephalon. Profound demyelination and gliosis was seen in the deep cerebellar nuclei and brain stem regions associated with the vestibular system. However, in the spinal cord changes were minimal. No loss of oligodendrocytes, neurons or motoneurons occurred but a significant increase in astrocyte staining ensued throughout the white matter of the spinal cord. The results suggest that CPZ differentially affects oligodendrocytes throughout the CNS and induces subtle motor changes such as ataxia. This is associated with deficits in CNS regions associated with motor and balance functions such as the cerebellum and brain stem.

Cerebellar Dysfunction, Cerebro-cerebellar Connectivity and Autism Spectrum Disorders

The cerebellum has long been conceptualized to control motor learning and motor coordination. However, increasing evidence suggests its roles in cognition and emotion behaviors. In particular, the cerebellum has been recognized as one of key brain regions affected in autism spectrum disorder (ASD). To better understand the contribution of the cerebellum in ASD pathogenesis, we here discuss recent behavioral, genetic, and molecular studies from the human and mouse models. In addition, we raise several questions that need to be investigated in future studies from the point view of cerebellar dysfunction, cerebro-cerebellar connectivity and ASD.

Glycine transporter type 1 (GlyT1) inhibition improves conspecific-provoked immobility in BALB/c mice: Analysis of corticosterone response and glucocorticoid gene expression in cortex and hippocampus

Stress reactivity and glucocorticoid signaling alterations are reported in mouse models of autism spectrum disorder (ASD). BALB/c mice display decreased locomotor activity in the presence of stimulus mice and spend less time exploring enclosed stimulus mice; this mouse strain has been validated as an ASD model. VU0410120, a glycine type 1 transporter (GlyT1) inhibitor, improved sociability in BALB/c mice, consistent with data that NMDA Receptor (NMDAR) activation regulates sociability, and the endogenous tone of NMDAR-mediated neurotransmission is altered in this strain. Effects of a prosocial dose of VU0410120 on conspecific-provoked immobility, and relationships between conspecific-provoked immobility and corticosterone response were explored. VU0410120-treated BALB/c mice showed reduced immobility in the presence of conspecifics and increased the conspecific-provoked corticosterone response. However, the intensity of conspecific-provoked immobility in VU0410120-treated BALB/c mice did not differ as a function of corticosterone response. Expression profiles of 88 glucocorticoid signaling associated genes within frontal cortex and hippocampus were examined. BALB/c mice resistant to prosocial effects of VU0410120 had increased mRNA expression of Ddit4, a negative regulator of mTOR signaling. Dysregulated mTOR signaling activity is a convergent finding in several monogenic syndromic forms of ASD. Prosocial effects of VU0410120 in the BALB/c strain may be related to regulatory influences of NMDAR-activation on mTOR signaling activity. Because corticosterone response is a marker of social stress, the current data suggest that the stressfulness of a social encounter alone may not be the sole determinant of increased immobility in BALB/c mice; this strain may also display an element of social disinterest.

A DLG2 deficiency in mice leads to reduced sociability and increased repetitive behavior accompanied by aberrant synaptic transmission in the dorsal striatum

Background

DLG2, also known as postsynaptic density protein-93 (PSD-93) or chapsyn-110, is an excitatory postsynaptic scaffolding protein that interacts with synaptic surface receptors and signaling molecules. A recent study has demonstrated that mutations in the DLG2 promoter region are significantly associated with autism spectrum disorder (ASD). Although DLG2 is well known as a schizophrenia-susceptibility gene, the mechanisms that link DLG2 gene disruption with ASD-like behaviors remain unclear.

Methods

Mice lacking exon 14 of the Dlg2 gene (Dlg2^–/– mice) were used to investigate whether Dlg2 deletion leads to ASD-like behavioral abnormalities. To this end, we performed a battery of behavioral tests assessing locomotion, anxiety, sociability, and repetitive behaviors. In situ hybridization was performed to determine expression levels of Dlg2 mRNA in different mouse brain regions during embryonic and postnatal brain development. We also measured excitatory and inhibitory synaptic currents to determine the impacts of Dlg2 deletion on synaptic transmission in the dorsolateral striatum.

Results

Dlg2^–/– mice showed hypoactivity in a novel environment. They also exhibited decreased social approach, but normal social novelty recognition, compared with wild-type animals. In addition, Dlg2^–/– mice displayed strong self-grooming, both in home cages and novel environments. Dlg2 mRNA levels in the striatum were heightened until postnatal day 7 in mice, implying potential roles of DLG2 in the development of striatal connectivity. In addition, the frequency of excitatory, but not inhibitory, spontaneous postsynaptic currents in the Dlg2^–/– dorsolateral striatum was significantly reduced.

Conclusion

These results suggest that homozygous Dlg2 deletion in mice leads to ASD-like behavioral phenotypes, including social deficits and increased repetitive behaviors, as well as reductions in excitatory synaptic input onto dorsolateral spiny projection neurons, implying that the dorsal striatum is one of the brain regions vulnerable to the developmental dysregulation of DLG2.

Pianp deficiency links GABAB receptor signaling and hippocampal and cerebellar neuronal cell composition to autism-like behavior

Pianp (also known as Leda-1) is a type I transmembrane protein with preferential expression in the mammalian CNS. Its processing is characterized by proteolytic cleavage by a range of proteases including Adam10, Adam17, MMPs, and the γ-secretase complex. Pianp can interact with Pilrα and the GB1a subunit of the GABA_B receptor (GBR) complex. A recent case description of a boy with global developmental delay and homozygous nonsense variant in PIANP supports the hypothesis that PIANP is involved in the control of behavioral traits in mammals. To investigate the physiological functions of Pianp, constitutive, global knockout mice were generated and comprehensively analyzed. Broad assessment did not indicate malformation or malfunction of internal organs. In the brain, however, decreased sizes and altered cellular compositions of the dentate gyrus as well as the cerebellum, including a lower number of cerebellar Purkinje cells, were identified. Functionally, loss of Pianp led to impaired presynaptic GBR-mediated inhibition of glutamate release and altered gene expression in the cortex, hippocampus, amygdala, and hypothalamus including downregulation of Erdr1, a gene linked to autism-like behavior. Behavioral phenotyping revealed that Pianp deficiency leads to context-dependent enhanced anxiety and spatial learning deficits, an altered stress response, severely impaired social interaction, and enhanced repetitive behavior, which all represent characteristic features of an autism spectrum disorder-like phenotype. Altogether, Pianp represents a novel candidate gene involved in autism-like behavior, cerebellar and hippocampal pathology, and GBR signaling.

Shank3 Exons 14-16 Deletion in Glutamatergic Neurons Leads to Social and Repetitive Behavioral Deficits Associated With Increased Cortical Layer 2/3 Neuronal Excitability

Shank3, an abundant excitatory postsynaptic scaffolding protein, has been associated with multiple brain disorders, including autism spectrum disorders (ASD) and Phelan-McDermid syndrome (PMS). However, how cell type-specific Shank3 deletion affects disease-related neuronal and brain functions remains largely unclear. Here, we investigated the impacts of Shank3 deletion in glutamatergic neurons on synaptic and behavioral phenotypes in mice and compared results with those previously obtained from mice with global Shank3 mutation and GABAergic neuron-specific Shank3 mutation. Neuronal excitability was abnormally increased in layer 2/3 pyramidal neurons in the medial prefrontal cortex (mPFC) in mice with a glutamatergic Shank3 deletion, similar to results obtained in mice with a global Shank3 deletion. In addition, excitatory synaptic transmission was abnormally increased in layer 2/3 neurons in mice with a global, but not a glutamatergic, Shank3 deletion, suggesting that Shank3 in glutamatergic neurons are important for the increased neuronal excitability, but not for the increased excitatory synaptic transmission. Neither excitatory nor inhibitory synaptic transmission was altered in the dorsal striatum of Shank3-deficient glutamatergic neurons, a finding that contrasts with the decreased excitatory synaptic transmission in global and Shank3-deficient GABAergic neurons. Behaviorally, glutamatergic Shank3-deficient mice displayed abnormally increased direct social interaction and repetitive self-grooming, similar to global and GABAergic Shank3-deficient mice. These results suggest that glutamatergic and GABAergic Shank3 deletions lead to distinct synaptic and neuronal changes in cortical layer 2/3 and dorsal striatal neurons, but cause similar social and repetitive behavioral abnormalities likely through distinct mechanisms.

Purkinje cell-specific Grip1/2 knockout mice show increased repetitive self-grooming and enhanced mGluR5 signaling in cerebellum

Cerebellar Purkinje cell (PC) loss is a consistent pathological finding in autism. However, neural mechanisms of PC-dysfunction in autism remain poorly characterized. Glutamate receptor interacting proteins 1/2 (Grip1/2) regulate AMPA receptor (AMPAR) trafficking and synaptic strength. To evaluate role of PC-AMPAR signaling in autism, we produced PC-specific Grip1/2 knockout mice by crossing Grip2 conventional and Grip1 conditional KO with L7-Cre driver mice. PCs in the mutant mice showed normal morphology and number, and a lack of Grip1/2 expression. Rodent behavioral testing identified normal ambulation, anxiety, social interaction, and an increase in repetitive self-grooming. Electrophysiology studies revealed normal mEPSCs but an impaired mGluR-LTD at the Parallel Fiber-PC synapses. Immunoblots showed increased expression of mGluR5 and Arc, and enhanced phosphorylation of P38 and AKT in cerebellum of PC-specific Grip1/2 knockout mice. Results indicate that loss of Grip1/2 in PCs contributes to increased repetitive self-grooming, a core autism behavior in mice. Results support a role of AMPAR trafficking defects in PCs and disturbances of mGluR5 signaling in cerebellum in the pathogenesis of repetitive behaviors.

Myosin XVI Regulates Actin Cytoskeleton Dynamics in Dendritic Spines of Purkinje Cells and Affects Presynaptic Organization

The actin cytoskeleton is crucial for function and morphology of neuronal synapses. Moreover, altered regulation of the neuronal actin cytoskeleton has been implicated in neuropsychiatric diseases such as autism spectrum disorder (ASD). Myosin XVI is a neuronally expressed unconventional myosin known to bind the WAVE regulatory complex (WRC), a regulator of filamentous actin (F-actin) polymerization. Notably, the gene encoding the myosin’s heavy chain (MYO16) shows genetic association with neuropsychiatric disorders including ASD. Here, we investigated whether myosin XVI plays a role for actin cytoskeleton regulation in the dendritic spines of cerebellar Purkinje cells (PCs), a neuronal cell type crucial for motor learning, social cognition and vocalization. We provide evidence that both myosin XVI and the WRC component WAVE1 localize to PC spines. Fluorescence recovery after photobleaching (FRAP) analysis of GFP-actin in cultured PCs shows that Myo16 knockout as well as PC-specific Myo16 knockdown, lead to faster F-actin turnover in the dendritic spines of PCs. We also detect accelerated F-actin turnover upon interference with the WRC, and upon inhibition of Arp2/3 that drives formation of branched F-actin downstream of the WRC. In contrast, inhibition of formins that are responsible for polymerization of linear actin filaments does not cause faster F-actin turnover. Together, our data establish myosin XVI as a regulator of the postsynaptic actin cytoskeleton and suggest that it is an upstream activator of the WRC-Arp2/3 pathway in PC spines. Furthermore, ultra-structural and electrophysiological analyses of Myo16 knockout cerebellum reveals the presence of reduced numbers of synaptic vesicles at presynaptic terminals in the absence of the myosin. Therefore, we here define myosin XVI as an F-actin regulator important for presynaptic organization in the cerebellum.

Computer Methods for Automatic Locomotion and Gesture Tracking in Mice and Small Animals for Neuroscience Applications: A Survey

Neuroscience has traditionally relied on manually observing laboratory animals in controlled environments. Researchers usually record animals behaving freely or in a restrained manner and then annotate the data manually. The manual annotation is not desirable for three reasons; (i) it is time-consuming, (ii) it is prone to human errors, and (iii) no two human annotators will 100% agree on annotation, therefore, it is not reproducible. Consequently, automated annotation for such data has gained traction because it is efficient and replicable. Usually, the automatic annotation of neuroscience data relies on computer vision and machine learning techniques. In this article, we have covered most of the approaches taken by researchers for locomotion and gesture tracking of specific laboratory animals, i.e. rodents. We have divided these papers into categories based upon the hardware they use and the software approach they take. We have also summarized their strengths and weaknesses.

Behavioral neuroscience of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder. Several genetic causes of ASD have been identified and this has enabled researchers to construct mouse models. Mouse behavioral tests reveal impaired social interaction and communication, as well as increased repetitive behavior and behavioral inflexibility in these mice, which correspond to core behavioral deficits observed in individuals with ASD. However, the connection between these behavioral abnormalities and the underlying dysregulation in neuronal circuits and synaptic function is poorly understood. Moreover, different components of the ASD phenotype may be linked to dysfunction in different brain regions, making it even more challenging to chart the pathophysiological mechanisms involved in ASD. Here we summarize the research on mouse models of ASD and their contribution to understanding pathophysiological mechanisms. Specifically, we emphasize abnormal serotonin production and regulation, as well as the disruption in circadian rhythms and sleep that are observed in a subset of ASD, and propose that spatiotemporal disturbances in brainstem development may be a primary cause of ASD that propagates towards the cerebral cortex.

Early Correction of N-Methyl-D-Aspartate Receptor Function Improves Autistic-like Social Behaviors in Adult Shank2-/- Mice

BACKGROUND

Autism spectrum disorder involves neurodevelopmental dysregulations that lead to visible symptoms at early stages of life. Many autism spectrum disorder-related mechanisms suggested by animal studies are supported by demonstrated improvement in autistic-like phenotypes in adult animals following experimental reversal of dysregulated mechanisms. However, whether such mechanisms also act at earlier stages to cause autistic-like phenotypes is unclear.

METHODS

We used Shank2^-/- mice carrying a mutation identified in human autism spectrum disorder (exons 6 and 7 deletion) and combined electrophysiological and behavioral analyses to see whether early pathophysiology at pup stages is different from late pathophysiology at juvenile and adult stages and whether correcting early pathophysiology can normalize late pathophysiology and abnormal behaviors in juvenile and adult mice.

RESULTS

Early correction of a dysregulated mechanism in young mice prevents manifestation of autistic-like social behaviors in adult mice. Shank2^-/- mice, known to display N-methyl-D-aspartate receptor (NMDAR) hypofunction and autistic-like behaviors at postweaning stages after postnatal day 21 (P21), show the opposite synaptic phenotype-NMDAR hyperfunction-at an earlier preweaning stage (∼P14). Moreover, this NMDAR hyperfunction at P14 rapidly shifts to NMDAR hypofunction after weaning (∼P24). Chronic suppression of the early NMDAR hyperfunction by the NMDAR antagonist memantine (P7-P21) prevents NMDAR hypofunction and autistic-like social behaviors from manifesting at later stages (∼P28 and P56).

CONCLUSIONS

Early NMDAR hyperfunction leads to late NMDAR hypofunction and autistic-like social behaviors in Shank2^-/- mice, and early correction of NMDAR dysfunction has the long-lasting effect of preventing autistic-like social behaviors from developing at later stages.