Absence of preference for social novelty and increased grooming in integrin β3 knockout mice: initial studies and future directions

SINE-VNTR-Alu retrotransposon insertion as a novel mutational event underlying Glanzmann thrombasthenia

BACKGROUND

Glanzmann thrombasthenia (GT) is an autosomal recessive platelet aggregation disorder caused by mutations in ITGA2B or ITGB3.

OBJECTIVES

We aimed to assess the phenotype and investigate the genetic etiology of a GT pedigree.

METHODS

A patient with bleeding manifestations and mild mental retardation was enrolled. Complete blood count, coagulation, and platelet aggregation tests were performed. Causal mutations were identified via whole exome and genome sequencing and subsequently confirmed through polymerase chain reaction and Sanger sequencing. The transcription of ITGB3 was characterized using RNA sequencing and reverse transcription polymerase chain reaction. The αⅡb and β3 biosynthesis was investigated via whole blood flow cytometry and in vitro studies.

RESULTS

GT was diagnosed in a patient with defective platelet aggregation. Novel compound heterozygous ITGB3 variants were identified, with a maternal nonsense mutation (c.2222G>A, p.Trp741∗) and a paternal SINE-VNTR-Alu (SVA) retrotransposon insertion. The 5' truncated SVA element was inserted in a sense orientation in intron 11 of ITGB3, resulting in aberrant splicing of ITGB3 and significantly reducing β3 protein content. Meanwhile, both the expression and transportation of β3 were damaged by the ITGB3 c.2222G>A. Almost no αⅡb and β3 expressions were detected on the patient's platelets surface.

CONCLUSION

Novel compound heterozygous ITGB3 mutations were identified in the GT pedigree, resulting in defects of αⅡbβ3 biosynthesis. This is the first report of SVA retrotransposon insertion in the genetic pathogenesis of GT. Our study highlights the importance of combining multiple high-throughput sequencing technologies for the molecular diagnosis of genetic disorders.

The role of integrin beta in schizophrenia: a preliminary exploration

Integrins are transmembrane heterodimeric (αβ) receptors that transduce mechanical signals between the extracellular milieu and the cell in a bidirectional manner. Extensive research has shown that the integrin beta (β) family is widely expressed in the brain and that they control various aspects of brain development and function. Schizophrenia is a relatively common neurological disorder of unknown etiology and has been found to be closely related to neurodevelopment and neurochemicals in neuropathological studies of schizophrenia. Here, we review literature from recent years that shows that schizophrenia involves multiple signaling pathways related to neuronal migration, axon guidance, cell adhesion, and actin cytoskeleton dynamics, and that dysregulation of these processes affects the normal function of neurons and synapses. In fact, alterations in integrin β structure, expression and signaling for neural circuits, cortex, and synapses are likely to be associated with schizophrenia. We explored several aspects of the possible association between integrin β and schizophrenia in an attempt to demonstrate the role of integrin β in schizophrenia, which may help to provide new insights into the study of the pathogenesis and treatment of schizophrenia.

Integrin β3 regulates apical dendritic morphology of pyramidal neurons throughout hippocampal CA3

In excitatory hippocampal pyramidal neurons, integrin β3 is critical for synaptic maturation and plasticity in vitro. Itgb3 is a potential autism susceptibility gene that regulates dendritic morphology in the cerebral cortex in a cell-specific manner. However, it is unknown what role Itgb3 could have in regulating hippocampal pyramidal dendritic morphology in vivo, a key feature that is aberrant in many forms of autism and intellectual disability. We found that Itgb3 mRNA is expressed in the stratum pyramidale of CA3. We examined the apical dendritic morphology of CA3 hippocampal pyramidal neurons in conditional Itgb3 knockouts and controls, utilizing the Thy1-GFP-M line. We fully reconstructed the apical dendrite of each neuron and determined each neuron's precise location along the dorsoventral, proximodistal, and radial axes of the stratum pyramidale. We found a very strong effect for Itgb3 expression on CA3 apical dendritic morphology: neurons from conditional Itgb3 knockouts had longer and thinner apical dendrites than controls, particularly in higher branch orders. We also assessed potential relationships between pairs of topographic or morphological variables, finding that most variable pairs were free from any linear relationships to each other. We also found that some neurons from controls, but not conditional Itgb3 knockouts, had a graded pattern of overall diameter along the dorsoventral and proximodistal axes of the stratum pyramidale of CA3. Taken together, Itgb3 is essential for constructing normal dendritic morphology in pyramidal neurons throughout CA3.

Regulation of dendritic spine length in corticopontine layer V pyramidal neurons by autism risk gene β3 integrin

The relationship between autism spectrum disorder (ASD) and dendritic spine abnormalities is well known, but it is unclear whether the deficits relate to specific neuron types and brain regions most relevant to ASD. Recent genetic studies have identified a convergence of ASD risk genes in deep layer pyramidal neurons of the prefrontal cortex. Here, we use retrograde recombinant adeno-associated viruses to label specifically two major layer V pyramidal neuron types of the medial prefrontal cortex: the commissural neurons, which put the two cerebral hemispheres in direct communication, and the corticopontine neurons, which transmit information outside the cortex. We compare the basal dendritic spines on commissural and corticopontine neurons in WT and KO mice for the ASD risk gene Itgb3, which encodes for the cell adhesion molecule β3 integrin selectively enriched in layer V pyramidal neurons. Regardless of the genotype, corticopontine neurons had a higher ratio of stubby to mushroom spines than commissural neurons. β3 integrin affected selectively spine length in corticopontine neurons. Ablation of β3 integrin resulted in corticopontine neurons lacking long (> 2 μm) thin dendritic spines. These findings suggest that a deficiency in β3 integrin expression compromises specifically immature spines on corticopontine neurons, thereby reducing the cortical territory they can sample. Because corticopontine neurons receive extensive local and long-range excitatory inputs before relaying information outside the cortex, specific alterations in dendritic spines of corticopontine neurons may compromise the computational output of the full cortex, thereby contributing to ASD pathophysiology.

Loss of GABA co-transmission from cholinergic neurons impairs behaviors related to hippocampal, striatal, and medial prefrontal cortex functions

Introduction: Altered signaling or function of acetylcholine (ACh) has been reported in various neurological diseases, including Alzheimer's disease, Tourette syndrome, epilepsy among others. Many neurons that release ACh also co-transmit the neurotransmitter gamma-aminobutyrate (GABA) at synapses in the hippocampus, striatum, substantia nigra, and medial prefrontal cortex (mPFC). Although ACh transmission is crucial for higher brain functions such as learning and memory, the role of co-transmitted GABA from ACh neurons in brain function remains unknown. Thus, the overarching goal of this study was to investigate how a systemic loss of GABA co-transmission from ACh neurons affected the behavioral performance of mice. Methods: To do this, we used a conditional knock-out mouse of the vesicular GABA transporter (vGAT) crossed with the ChAT-Cre driver line to selectively ablate GABA co-transmission at ACh synapses. In a comprehensive series of standardized behavioral assays, we compared Cre-negative control mice with Cre-positive vGAT knock-out mice of both sexes. Results: Loss of GABA co-transmission from ACh neurons did not disrupt the animal's sociability, motor skills or sensation. However, in the absence of GABA co-transmission, we found significant alterations in social, spatial and fear memory as well as a reduced reliance on striatum-dependent response strategies in a T-maze. In addition, male conditional knockout (CKO) mice showed increased locomotion. Discussion: Taken together, the loss of GABA co-transmission leads to deficits in higher brain functions and behaviors. Therefore, we propose that ACh/GABA co-transmission modulates neural circuitry involved in the affected behaviors.

CRISPR-mediated activation of autism gene Itgb3 restores cortical network excitability via mGluR5 signaling

Many mutations in autism spectrum disorder (ASD) affect a single allele, indicating a key role for gene dosage in ASD susceptibility. Recently, haplo-insufficiency of ITGB3, the gene encoding the extracellular matrix receptor β3 integrin, was associated with ASD. Accordingly, Itgb3 knockout (KO) mice exhibit autism-like phenotypes. The pathophysiological mechanisms of Itgb3 remain, however, unknown, and the potential of targeting this gene for developing ASD therapies uninvestigated. By combining molecular, biochemical, imaging, and pharmacological analyses, we establish that Itgb3 haplo-insufficiency impairs cortical network excitability by promoting extra-synaptic over synaptic signaling of the metabotropic glutamate receptor mGluR5, which is similarly dysregulated in fragile X syndrome, the most frequent monogenic form of ASD. To assess the therapeutic potential of regulating Itgb3 gene dosage, we implemented CRISPR activation and compared its efficacy with that of a pharmacological rescue strategy for fragile X syndrome. Correction of neuronal Itgb3 haplo-insufficiency by CRISPR activation rebalanced network excitability as effectively as blockade of mGluR5 with the selective antagonist MPEP. Our findings reveal an unexpected functional interaction between two ASD genes, thereby validating the pathogenicity of ITGB3 haplo-insufficiency. Further, they pave the way for exploiting CRISPR activation as gene therapy for normalizing gene dosage and network excitability in ASD.

D-aspartate oxidase gene duplication induces social recognition memory deficit in mice and intellectual disabilities in humans

The D-aspartate oxidase (DDO) gene encodes the enzyme responsible for the catabolism of D-aspartate, an atypical amino acid enriched in the mammalian brain and acting as an endogenous NMDA receptor agonist. Considering the key role of NMDA receptors in neurodevelopmental disorders, recent findings suggest a link between D-aspartate dysmetabolism and schizophrenia. To clarify the role of D-aspartate on brain development and functioning, we used a mouse model with constitutive Ddo overexpression and D-aspartate depletion. In these mice, we found reduced number of BrdU-positive dorsal pallium neurons during corticogenesis, and decreased cortical and striatal gray matter volume at adulthood. Brain abnormalities were associated with social recognition memory deficit at juvenile phase, suggesting that early D-aspartate occurrence influences neurodevelopmental related phenotypes. We corroborated this hypothesis by reporting the first clinical case of a young patient with severe intellectual disability, thought disorders and autism spectrum disorder symptomatology, harboring a duplication of a chromosome 6 region, including the entire DDO gene.

Integrins Bidirectionally Regulate the Efficacy of Inhibitory Synaptic Transmission and Control GABAergic Plasticity

For many decades, synaptic plasticity was believed to be restricted to excitatory transmission. However, in recent years, this view started to change, and now it is recognized that GABAergic synapses show distinct forms of activity-dependent long-term plasticity, but the underlying mechanisms remain obscure. Herein, we asked whether signaling mediated by β1 or β3 subunit-containing integrins might be involved in regulating the efficacy of GABAergic synapses, including the NMDA receptor-dependent inhibitory long-term potentiation (iLTP) in the hippocampus. We found that activation of β3 integrin with fibrinogen induced a stable depression, whereas inhibition of β1 integrin potentiated GABAergic synapses at CA1 pyramidal neurons in male mice. Additionally, compounds that interfere with the interaction of β1 or β3 integrins with extracellular matrix blocked the induction of NMDA-iLTP. In conclusion, we provide the first evidence that integrins are key players in regulating the endogenous modulatory mechanisms of GABAergic inhibition and plasticity in the hippocampus.SIGNIFICANCE STATEMENT Epilepsy, schizophrenia, and anxiety are just a few medical conditions associated with dysfunctional inhibitory synaptic transmission. GABAergic synapses are known for their extraordinary susceptibility to modulation by endogenous factors and exogenous pharmacological agents. We describe here that integrins, adhesion proteins, play a key role in the modulation of inhibitory synaptic transmission. Specifically, we show that interference with integrin-dependent adhesion results in a variety of effects on the amplitude and frequency of GABAergic mIPSCs. Activation of β3 subunit-containing integrins induces inhibitory long-term depression, whereas the inhibition of β1 subunit-containing integrins induces iLTP. Our results unveil an important mechanism controlling synaptic inhibition, which opens new avenues into the usage of integrin-aimed pharmaceuticals as modulators of GABAergic synapses.

Oxytocin and serotonin in the modulation of neural function: Neurobiological underpinnings of autism-related behavior

Autism spectrum disorders (ASD) is a group of generalized neurodevelopmental disorders. Its main clinical features are social communication disorder and repetitive stereotyped behavioral interest. The abnormal structure and function of brain network is the basis of social dysfunction and stereotyped performance in patients with autism spectrum disorder. The number of patients diagnosed with ASD has increased year by year, but there is a lack of effective intervention and treatment. Oxytocin has been revealed to effectively improve social cognitive function and significantly improve the social information processing ability, empathy ability and social communication ability of ASD patients. The change of serotonin level also been reported affecting the development of brain and causes ASD-like behavioral abnormalities, such as anxiety, depression like behavior, stereotyped behavior. Present review will focus on the research progress of serotonin and oxytocin in the pathogenesis, brain circuit changes and treatment of autism. Revealing the regulatory effect and neural mechanism of serotonin and oxytocin on patients with ASD is not only conducive to a deeper comprehension of the pathogenesis of ASD, but also has vital clinical significance.

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.

Integrin β3 in forebrain Emx1-expressing cells regulates repetitive self-grooming and sociability in mice

Background

Autism spectrum disorder (ASD) is characterized by repetitive behaviors, deficits in communication, and overall impaired social interaction. Of all the integrin subunit mutations, mutations in integrin β3 (Itgb3) may be the most closely associated with ASD. Integrin β3 is required for normal structural plasticity of dendrites and synapses specifically in excitatory cortical and hippocampal circuitry. However, the behavioral consequences of Itgb3 function in the forebrain have not been assessed. We tested the hypothesis that behaviors that are typically abnormal in ASD—such as self-grooming and sociability behaviors—are disrupted with conditional Itgb3 loss of function in forebrain circuitry in male and female mice.

Methods

We generated male and female conditional knockouts (cKO) and conditional heterozygotes (cHET) of Itgb3 in excitatory neurons and glia that were derived from Emx1-expressing forebrain cells during development. We used several different assays to determine whether male and female cKO and cHET mice have repetitive self-grooming behaviors, anxiety-like behaviors, abnormal locomotion, compulsive-like behaviors, or abnormal social behaviors, when compared to male and female wildtype (WT) mice.

Results

Our findings indicate that only self-grooming and sociability are altered in cKO, but not cHET or WT mice, suggesting that Itgb3 is specifically required in forebrain Emx1-expressing cells for normal repetitive self-grooming and social behaviors. Furthermore, in cKO (but not cHET or WT), we observed an interaction effect for sex and self-grooming environment and an interaction effect for sex and sociability test chamber.

Limitations

While this study demonstrated a role for forebrain Itgb3 in specific repetitive and social behaviors, it was unable to determine whether forebrain Itgb3 is required for a preference for social novelty, whether cHET are haploinsufficient with respect to repetitive self-grooming and social behaviors, or the nature of the interaction effect for sex and environment/chamber in affected behaviors of cKO.

Conclusions

Together, these findings strengthen the idea that Itgb3 has a specific role in shaping forebrain circuitry that is relevant to endophenotypes of autism spectrum disorder.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00691-2.

Sex-Dependent Social and Repetitive Behavior and Neurochemical Profile in Mouse Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social interaction, impaired communication, and repetitive behaviors. ASD presents a 3:1 ratio of diagnosed boys and girls, raising the question regarding sexual dimorphic mechanisms underlying ASD symptoms, and their molecular basis. Here, we performed in vivo proton magnetic resonance spectroscopy in juvenile male and female Tsc2^+/- mice (an established genetic animal model of ASD). Moreover, behavior and ultrasonic vocalizations during social and repetitive tasks were analyzed. We found significant sexual dimorphisms in the levels of metabolites in the hippocampus and prefrontal cortex. Further, we observed that female mutant animals had a differential social behavior and presented an increase in repetitive behavior. Importantly, while mutant females displayed a more simplified communication during social tasks, mutant males exhibited a similar less complex vocal repertoire but during repetitive tasks. These results hint toward sex-dependent alterations in molecular and metabolic pathways, which can lead to the sexual dimorphic behaviors and communication observed in social and repetitive environments.

Implication of the social function of excessive self-grooming behavior in BTBR T+ltpr3tf/J mice as an idiopathic model of autism

Autism spectrum disorder (ASD) is defined by two core behavioral characteristics, namely, restricted repetitive behaviors and impaired social-communicative functioning. BTBR T⁺ltpr3^tf/J (BTBR) mice provide a valuable animal model for ASD to elucidate the underlying mechanisms of these two behavioral characteristics of ASD. This study examined the social function of excessive grooming behavior in BTBR mice as a phenotype of restricted repetitive behaviors. Compared to the control C57BL/6 J (B6) strain, BTBR mice showed increased self-grooming when placed alone in a test apparatus, and this behavior was even more evident when confronted with a stimulus mouse (either B6 or BTBR) in a three-chamber test apparatus. While B6 mice tended to groom their face/snout region on the empty side of the chamber, BTBR mice showed excessive grooming with frequent transitions among grooming body regions on the side of the chamber containing a social stimulus. Acute systemic injection of buspirone,a serotonin 1A receptor agonist, as an anxiolytic, facilitated approach behavior toward social stimuli in the three-chamber setting in both B6 and BTBR mice. However, this treatment did not affect grooming behavior in B6 mice and significantly enhanced self-grooming in BTBR mice. These behaviors in BTBR mice suggest a potential signaling function of grooming in response to social stimuli, in which bodywide grooming of BTBR mice expressed in the proximity of social opponents may stimulate the release of olfactory (possibly dismissive) signals. Consequently, the putative neural mechanisms underlying excessive grooming may differ from those regulating social approaches that are associated with anxiolytic mechanisms.

Altered neuronal physiology, development, and function associated with a common chromosome 15 duplication involving CHRNA7

BACKGROUND

Copy number variants (CNVs) linked to genes involved in nervous system development or function are often associated with neuropsychiatric disease. While CNVs involving deletions generally cause severe and highly penetrant patient phenotypes, CNVs leading to duplications tend instead to exhibit widely variable and less penetrant phenotypic expressivity among affected individuals. CNVs located on chromosome 15q13.3 affecting the alpha-7 nicotinic acetylcholine receptor subunit (CHRNA7) gene contribute to multiple neuropsychiatric disorders with highly variable penetrance. However, the basis of such differential penetrance remains uncharacterized. Here, we generated induced pluripotent stem cell (iPSC) models from first-degree relatives with a 15q13.3 duplication and analyzed their cellular phenotypes to uncover a basis for the dissimilar phenotypic expressivity.

RESULTS

The first-degree relatives studied included a boy with autism and emotional dysregulation (the affected proband-AP) and his clinically unaffected mother (UM), with comparison to unrelated control models lacking this duplication. Potential contributors to neuropsychiatric impairment were modeled in iPSC-derived cortical excitatory and inhibitory neurons. The AP-derived model uniquely exhibited disruptions of cellular physiology and neurodevelopment not observed in either the UM or unrelated controls. These included enhanced neural progenitor proliferation but impaired neuronal differentiation, maturation, and migration, and increased endoplasmic reticulum (ER) stress. Both the neuronal migration deficit and elevated ER stress could be selectively rescued by different pharmacologic agents. Neuronal gene expression was also dysregulated in the AP, including reduced expression of genes related to behavior, psychological disorders, neuritogenesis, neuronal migration, and Wnt, axonal guidance, and GABA receptor signaling. The UM model instead exhibited upregulated expression of genes in many of these same pathways, suggesting that molecular compensation could have contributed to the lack of neurodevelopmental phenotypes in this model. However, both AP- and UM-derived neurons exhibited shared alterations of neuronal function, including increased action potential firing and elevated cholinergic activity, consistent with increased homomeric CHRNA7 channel activity.

CONCLUSIONS

These data define both diagnosis-associated cellular phenotypes and shared functional anomalies related to CHRNA7 duplication that may contribute to variable phenotypic penetrance in individuals with 15q13.3 duplication. The capacity for pharmacological agents to rescue some neurodevelopmental anomalies associated with diagnosis suggests avenues for intervention for carriers of this duplication and other CNVs that cause related disorders.

Social isolation impairs the prefrontal-nucleus accumbens circuit subserving social recognition in mice

Although medial prefrontal cortex (mPFC) is known to play important roles in social behaviors, how early social experiences affect the mPFC and its subcortical circuit remains unclear. We report that mice singly housed (SH) for 8 weeks after weaning show a social recognition deficit, even after 4 weeks of resocialization. In SH mice, prefrontal infralimbic (IL) neurons projecting to the shell region of nucleus accumbens (NAcSh) show decreased excitability compared with group-housed (GH) mice. NAcSh-projecting IL neurons are activated when GH mice encounter a familiar conspecific, which is not observed in SH mice. Chemogenetic inhibition of NAcSh-projecting IL neurons in normal mice impairs social recognition without affecting social preference, whereas activation of these neurons reverses social recognition deficit in SH mice. Our findings demonstrate that early social experience critically affects mPFC IL-NAcSh projection, the activation of which is required for social recognition by encoding information for social familiarity.

3D biomaterial models of human brain disease

Inherent limitations of the traditional approaches to study brain function and disease, such as rodent models and 2D cell culture platforms, have led to the development of 3D in vitro cell culture systems. These systems, products of multidisciplinary efforts encompassing stem cell biology, materials engineering, and biofabrication, have quickly shown great potential to mimic biochemical composition, structural properties, and cellular morphology and diversity found in the native brain tissue. Crucial to these developments have been the advancements in stem cell technology and cell reprogramming protocols that allow reproducible generation of human subtype-specific neurons and glia in laboratory conditions. At the same time, biomaterials have been designed to provide cells in 3D with a microenvironment that mimics functional and structural aspects of the native extracellular matrix with increasing fidelity. In this article, we review the use of biomaterials in 3D in vitro models of neurological disorders with focus on hydrogel technology and with biochemical composition and physical properties of the in vivo environment as reference.

Dissecting the contribution of host genetics and the microbiome in complex behaviors

The core symptoms of many neurological disorders have traditionally been thought to be caused by genetic variants affecting brain development and function. However, the gut microbiome, another important source of variation, can also influence specific behaviors. Thus, it is critical to unravel the contributions of host genetic variation, the microbiome, and their interactions to complex behaviors. Unexpectedly, we discovered that different maladaptive behaviors are interdependently regulated by the microbiome and host genes in the Cntnap2-/- model for neurodevelopmental disorders. The hyperactivity phenotype of Cntnap2-/- mice is caused by host genetics, whereas the social-behavior phenotype is mediated by the gut microbiome. Interestingly, specific microbial intervention selectively rescued the social deficits in Cntnap2-/- mice through upregulation of metabolites in the tetrahydrobiopterin synthesis pathway. Our findings that behavioral abnormalities could have distinct origins (host genetic versus microbial) may change the way we think about neurological disorders and how to treat them.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

Integrin β3 organizes dendritic complexity of cerebral cortical pyramidal neurons along a tangential gradient

Dysfunctional dendritic arborization is a key feature of many developmental neurological disorders. Across various human brain regions, basal dendritic complexity is known to increase along a caudal-to-rostral gradient. We recently discovered that basal dendritic complexity of layer II/III cortical pyramidal neurons in the mouse increases along a caudomedial-to-rostrolateral gradient spanning multiple regions, but at the time, no molecules were known to regulate that exquisite pattern. Integrin subunits have been implicated in dendritic development, and the subunit with the strongest associations with autism spectrum disorder and intellectual disability is integrin β3 (Itgb3). In mice, global knockout of Itgb3 leads to autistic-like neuroanatomy and behavior. Here, we tested the hypothesis that Itgb3 is required for increasing dendritic complexity along the recently discovered tangential gradient among layer II/III cortical pyramidal neurons. We targeted a subset of layer II/III cortical pyramidal neurons for Itgb3 loss-of-function via Cre-loxP-mediated excision of Itgb3. We tracked the rostrocaudal and mediolateral position of the targeted neurons and reconstructed their dendritic arbors. In contrast to controls, the basal dendritic complexity of Itgb3 mutant neurons was not related to their cortical position. Basal dendritic complexity of mutant and control neurons differed because of overall changes in branch number across multiple branch orders (primary, secondary, etc.), rather than any changes in the average length at those branch orders. Furthermore, dendritic spine density was related to cortical position in control but not mutant neurons. Thus, the autism susceptibility gene Itgb3 is required for establishing a tangential pattern of basal dendritic complexity among layer II/III cortical pyramidal neurons, suggesting an early role for this molecule in the developing brain.

Mechanical Forces Orchestrate Brain Development

During brain development, progenitors generate successive waves of neurons that populate distinct cerebral regions, where they settle and differentiate within layers or nuclei. While migrating and differentiating, neurons are subjected to mechanical forces arising from the extracellular matrix, and their interaction with neighboring cells. Changes in brain biomechanical properties, during its formation or aging, are converted in neural cells by mechanotransduction into intracellular signals that control key neurobiological processes. Here, we summarize recent findings that support the contribution of mechanobiology to neurodevelopment, with focus on the cerebral cortex. Also discussed are the existing toolbox and emerging technologies made available to assess and manipulate the physical properties of neurons and their environment.

Integrin adhesion in brain assembly: From molecular structure to neuropsychiatric disorders

Integrins are extracellular matrix receptors that mediate biochemical and mechanical bi-directional signals between the extracellular and intracellular environment of a cell thanks to allosteric conformational changes. In the brain, they are found in both neurons and glial cells, where they play essential roles in several aspects of brain development and function, such as cell migration, axon guidance, synaptogenesis, synaptic plasticity and neuro-inflammation. Although there are many successful examples of how regulating integrin adhesion and signaling can be used for therapeutic purposes, for example for halting tumor progression, this is not the case for the brain, where the growing evidence of the importance of integrins for brain pathophysiology has not translated yet into medical applications. Here, we review recent literature showing how alterations in integrin structure, expression and signaling may be involved in the etiology of autism spectrum disorder, epilepsy, schizophrenia, addiction, depression and Alzheimer's disease. We focus on common mechanisms and recurrent signaling pathways, trying to bridge studies on the genetics and molecular structure of integrins with those on synaptic physiology and brain pathology. Further, we discuss integrin-targeting strategies and their potential benefits for therapeutic purposes in neuropsychiatric disorders.

Sex-linked roles of the CRF1 and the CRF2 receptor in social behavior

Dysfunctional social behavior is a major clinical feature of mood, anxiety, autism spectrum, and substance-related disorders, and may dramatically contribute to the poor outcome of these diseases. Nevertheless, the mechanisms underlying social behavior deficits are still largely unknown. The corticotropin-releasing factor (CRF) system, a major coordinator of the stress response, has been hypothesized to modulate social behavior. CRF signaling is mediated by two receptor types, termed CRF₁ and CRF₂ . Using the three-chamber task for sociability (i.e., preference for an unfamiliar conspecific vs. an object), this study demonstrates that CRF₂ receptor null mutation (CRF₂ -/-) reduces sociability in female mice but increases it in male mice. Both female and male CRF₂ -/- mice display a preference for social odor cues over neutral cues, indicating that sex- and CRF₂ receptor-dependent sociability is not due to altered olfaction or impaired social cues discrimination. Moreover, treatment with the CRF₁ receptor-preferring antagonist, antalarmin, consistently induces sociability in non-social mice but disrupts it in social mice, independently of CRF₂ receptor deficiency. Sex, CRF₂ receptor deficiency, or antalarmin affect locomotor activity during the three-chamber test. However, throughout the study CRF₁ and CRF₂ receptor-linked sociability is independent of locomotor activity. The present findings highlight major functions for the CRF system in the regulation of social behavior. Moreover, they provide initial evidence of sex-linked roles for the CRF₁ and the CRF₂ receptor, emphasizing the importance of sex as a major biological variable to be taken into consideration in preclinical and clinical studies.

GABAA receptor β3 subunit mutation D120N causes Lennox-Gastaut syndrome in knock-in mice

The Lennox-Gastaut syndrome is a devastating early-onset epileptic encephalopathy, associated with severe behavioural abnormalities. Its pathophysiology, however, is largely unknown. A de novo mutation (c.G358A, p.D120N) in the human GABA type-A receptor β3 subunit gene (GABRB3) has been identified in a patient with Lennox-Gastaut syndrome. To determine whether the mutation causes Lennox-Gastaut syndrome in vivo in mice and to elucidate its mechanistic effects, we generated the heterozygous Gabrb3^+/D120N knock-in mouse and found that it had frequent spontaneous atypical absence seizures, as well as less frequent tonic, myoclonic, atonic and generalized tonic-clonic seizures. Each of these seizure types had a unique and characteristic ictal EEG. In addition, knock-in mice displayed abnormal behaviours seen in patients with Lennox-Gastaut syndrome including impaired learning and memory, hyperactivity, impaired social interactions and increased anxiety. This Gabrb3 mutation did not alter GABA type-A receptor trafficking or expression in knock-in mice. However, cortical neurons in thalamocortical slices from knock-in mice had reduced miniature inhibitory post-synaptic current amplitude and prolonged spontaneous thalamocortical oscillations. Thus, the Gabrb3^+/D120N knock-in mouse recapitulated human Lennox-Gastaut syndrome seizure types and behavioural abnormalities and was caused by impaired inhibitory GABAergic signalling in the thalamocortical loop. In addition, treatment with antiepileptic drugs and cannabinoids ameliorated atypical absence seizures in knock-in mice. This congenic knock-in mouse demonstrates that a single-point mutation in a single gene can cause development of multiple types of seizures and multiple behavioural abnormalities. The knock-in mouse will be useful for further investigation of the mechanisms of Lennox-Gastaut syndrome development and for the development of new antiepileptic drugs and treatments.

Machine learning analysis of exome trios to contrast the genomic architecture of autism and schizophrenia

BACKGROUND

Machine learning (ML) algorithms and methods offer great tools to analyze large complex genomic datasets. Our goal was to compare the genomic architecture of schizophrenia (SCZ) and autism spectrum disorder (ASD) using ML.

METHODS

In this paper, we used regularized gradient boosted machines to analyze whole-exome sequencing (WES) data from individuals SCZ and ASD in order to identify important distinguishing genetic features. We further demonstrated a method of gene clustering to highlight which subsets of genes identified by the ML algorithm are mutated concurrently in affected individuals and are central to each disease (i.e., ASD vs. SCZ "hub" genes).

RESULTS

In summary, after correcting for population structure, we found that SCZ and ASD cases could be successfully separated based on genetic information, with 86-88% accuracy on the testing dataset. Through bioinformatic analysis, we explored if combinations of genes concurrently mutated in patients with the same condition ("hub" genes) belong to specific pathways. Several themes were found to be associated with ASD, including calcium ion transmembrane transport, immune system/inflammation, synapse organization, and retinoid metabolic process. Moreover, ion transmembrane transport, neurotransmitter transport, and microtubule/cytoskeleton processes were highlighted for SCZ.

CONCLUSIONS

Our manuscript introduces a novel comparative approach for studying the genetic architecture of genetically related diseases with complex inheritance and highlights genetic similarities and differences between ASD and SCZ.

Blood platelet research in autism spectrum disorders: In search of biomarkers

Autism spectrum disorder (ASD) is a clinically heterogeneous neurodevelopmental disorder that is caused by gene-environment interactions. To improve its diagnosis and treatment, numerous efforts have been undertaken to identify reliable biomarkers for autism. None of them have delivered the holy grail that represents a reproducible, quantifiable, and sensitive biomarker. Though blood platelets are mainly known to prevent bleeding, they also play pivotal roles in cancer, inflammation, and neurological disorders. Platelets could serve as a peripheral biomarker or cellular model for autism as they share common biological and molecular characteristics with neurons. In particular, platelet-dense granules contain neurotransmitters such as serotonin and gamma-aminobutyric acid. Molecular players controlling granule formation and secretion are similarly regulated in platelets and neurons. The major platelet integrin receptor αIIbβ3 has recently been linked to ASD as a regulator of serotonin transport. Though many studies revealed associations between platelet markers and ASD, there is an important knowledge gap in linking these markers with autism and explaining the altered platelet phenotypes detected in autism patients. The present review enumerates studies of different biomarkers detected in ASD using platelets and highlights the future needs to bring this research to the next level and advance our understanding of this complex disorder.

Altered kynurenine pathway metabolites in a mouse model of human attention-deficit hyperactivity/autism spectrum disorders: A potential new biological diagnostic marker

Deleterious mutations in patchd1 domain containing 1 (PTCHD1) gene have been identified in patients with intellectual disability and/or autism spectrum disorder (ASD). To clarify the causal relationship between Ptchd1 deficiency and behavioral defects relevant to neurodevelopmental disorders, we generated global Ptchd1 knockout (KO) mice. Ptchd1 KO mice displayed hyperlocomotion, increased impulsivity, and lower recognition memory, which resemble attention-deficit hyperactivity disorder (ADHD)-like behaviors. Acute or chronic treatment with atomoxetine ameliorated almost all behavioral deficits in Pthcd1 KO mice. We next determined possible involvement of the kynurenine pathway (KP) metabolites in neurodevelopmental disorders in Ptchd1 KO mice and assessed the potential of KP metabolites as biomarkers for ADHD and/or ASD. Ptchd1 KO mice showed drastic changes in KP metabolite concentrations in the serum and the brain, indicating that the activated KP is associated with ADHD-like behaviors. Our findings indicate that Ptchd1 KO mice can be used as an animal model of human ADHD and/or ASD, and KP metabolites are potential diagnostic biomarkers for neurodevelopmental disorders.

Neurogenesis in Neurodegenerative Diseases: Role of MFG-E8

Neurodegenerative diseases are devastating medical conditions with no effective treatments. Restoration of impaired neurogenesis represents a promising therapeutic strategy for neurodegenerative diseases. Milk fat globule-epidermal growth factor-factor VIII (MFG-E8) is a secretory glycoprotein that plays a wide range of cellular functions including phagocytosis of apoptotic cells, anti-inflammation, tissue regeneration, and homeostasis. The beneficial role of MFG-E8 has been shown in cerebral ischemia (stroke), neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, and traumatic brain injury. In stroke, MFG-E8 promotes neural stem cell proliferation and their migration toward the ischemic brain tissues. These novel functions of MFG-E8 are primarily mediated through its receptor α_vβ₃-integrin. Here, we focus on the pivotal role of MFG-E8 in protecting against neuronal diseases by promoting neurogenesis. We also discuss the mechanisms of MFG-E8-mediated neural stem/progenitor cell (NSPC) proliferation and migration, and the potential of MFG-E8 for neural stem cell niche maintenance via angiogenesis. We propose further investigation of the molecular pathways for MFG-E8 signaling in NSPC and effective strategies for MFG-E8 delivery across the blood–brain barrier, which will help develop MFG-E8 as a future drug candidate for the bedside management of neurodegenerative diseases.

Enhanced Social Dominance and Altered Neuronal Excitability in the Prefrontal Cortex of Male KCC2b Mutant Mice

The K-Cl cotransporter KCC2 is essential in the development of the "GABA switch" that produces a change in neuronal responses to GABA signaling from excitatory to inhibitory early in brain development, and alterations in this progression have previously been hypothesized to play a causal role in autism spectrum disorder (ASD). We investigated the KCC2b (Slc12a5) heterozygous knockout mouse using a battery of rodent behavioral tests relevant to core and comorbid ASD symptoms. Compared to wild-type littermates, KCC2^+/- mice were normal in standard measures of locomotor activity, grooming and digging behaviors, and social, vocalization, and anxiety-like behaviors. However, KCC2^+/- mice exhibited increased social dominance behaviors and increased amplitude of spontaneous postsynaptic currents in the medial prefrontal cortex (PFC) that were previously implicated in governing social hierarchy and dominance behaviors. Treatment of wild-type mouse brain slices with the KCC2 inhibitor VU0240511 increased the amplitude and frequency of excitatory postsynaptic currents, partially recapitulating the phenotype of KCC2^+/- mice. These findings indicate that the activity of KCC2 plays a role in social dominance, in parallel with effects on PFC signaling, further suggesting that KCC2 function has some relevance to social behavior but without the breadth of impact on autism-like behavior suggested by previous studies. Further testing could assess whether KCC2 alters other circuits and whether additional factors such as environmental insults may precipitate autism-related behavioral phenotypes. Autism Research 2019, 12: 732-743. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: A mouse model of altered chloride transporter expression was used to look for a role in behaviors and brain function relevant to autism. There was an imbalance in signaling in the prefrontal cortex, and increased social dominance behavior, although other autism-related behaviors were not changed. These findings indicate that altered chloride transporter function affects prefrontal cortex function and social dominance without a broader impact on autism-like behaviors.

Prenatal selective serotonin reuptake inhibitor (SSRI) exposure induces working memory and social recognition deficits by disrupting inhibitory synaptic networks in male mice

Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed antidepressant drugs in pregnant women. Infants born following prenatal exposure to SSRIs have a higher risk for behavioral abnormalities, however, the underlying mechanisms remains unknown. Therefore, we examined the effects of prenatal fluoxetine, the most commonly prescribed SSRI, in mice. Intriguingly, chronic in utero fluoxetine treatment impaired working memory and social novelty recognition in adult males. In the medial prefrontal cortex (mPFC), a key region regulating these behaviors, we found augmented spontaneous inhibitory synaptic transmission onto the layer 5 pyramidal neurons. Fast-spiking interneurons in mPFC exhibited enhanced intrinsic excitability and serotonin-induced excitability due to upregulated serotonin (5-HT) 2A receptor (5-HT_2AR) signaling. More importantly, the behavioral deficits in prenatal fluoxetine treated mice were reversed by the application of a 5-HT_2AR antagonist. Taken together, our findings suggest that alterations in inhibitory neuronal modulation are responsible for the behavioral alterations following prenatal exposure to SSRIs.

Extreme enhancement or depletion of serotonin transporter function and serotonin availability in autism spectrum disorder

A variety of human and animal studies support the hypothesis that serotonin (5-hydroxytryptamine or 5-HT) system dysfunction is a contributing factor to the development of autism in some patients. However, many questions remain about how developmental manipulation of various components that influence 5-HT signaling (5-HT synthesis, transport, metabolism) persistently impair social behaviors. This review will summarize key aspects of central 5-HT function important for normal brain development, and review evidence implicating perinatal disruptions in 5-HT signaling in the pathophysiology of autism spectrum disorder. We discuss the importance, and relative dearth, of studies that explore the possible correlation to autism in the interactions between important intrinsic and extrinsic factors that may disrupt 5-HT homeostasis during development. In particular, we focus on exposure to 5-HT transport altering mechanisms such as selective serotonin-reuptake inhibitors or genetic polymorphisms in primary or auxiliary transporters of 5-HT, and how they relate to neurological stores of serotonin and its precursors. A deeper understanding of the many mechanisms by which 5-HT signaling can be disrupted, alone and in concert, may contribute to an improved understanding of the etiologies and heterogeneous nature of this disorder. We postulate that extreme bidirectional perturbations of these factors during development likely compound or synergize to facilitate enduring neurochemical changes resulting in insufficient or excessive 5-HT signaling, that could underlie the persistent behavioral characteristics of autism spectrum disorder.

Integrin activity in neuronal connectivity

The formation of correct synaptic structures and neuronal connections is paramount for normal brain development and a functioning adult brain. The integrin family of cell adhesion receptors and their ligands play essential roles in the control of several processes regulating neuronal connectivity - including neurite outgrowth, the formation and maintenance of synapses, and synaptic plasticity - that are affected in neurodevelopmental disorders, such as autism spectrum disorders (ASDs) and schizophrenia. Many ASD- and schizophrenia-associated genes are linked to alterations in the genetic code of integrins and associated signalling pathways. In non-neuronal cells, crosstalk between integrin-mediated adhesions and the actin cytoskeleton, and the regulation of integrin activity (affinity for extracellular ligands) are widely studied in healthy and pathological settings. In contrast, the roles of integrin-linked pathways in the central nervous system remains less well defined. In this Review, we will provide an overview of the known pathways that are regulated by integrin-ECM interaction in developing neurons and in adult brain. We will also describe recent advances in the identification of mechanisms that regulate integrin activity in neurons, and highlight the interesting emerging links between integrins and neurodevelopment.

The neural circuitry of restricted repetitive behavior: Magnetic resonance imaging in neurodevelopmental disorders and animal models

Restricted, repetitive behaviors (RRBs) are patterns of behavior that exhibit little variation in form and have no obvious function. RRBs although transdiagonstic are a particularly prominent feature of certain neurodevelopmental disorders, yet relatively little is known about the neural circuitry of RRBs. Past work in this area has focused on isolated brain regions and neurotransmitter systems, but implementing a neural circuit approach has the potential to greatly improve understanding of RRBs. Magnetic resonance imaging (MRI) is well-suited to studying the structural and functional connectivity of the nervous system, and is a highly translational research tool. In this review, we synthesize MRI research from both neurodevelopmental disorders and relevant animal models that informs the neural circuitry of RRB. Together, these studies implicate distributed neural circuits between the cortex, basal ganglia, and cerebellum. Despite progress in neuroimaging of RRB, there are many opportunities for conceptual and methodological improvement. We conclude by suggesting future directions for MRI research in RRB, and how such studies can benefit from complementary approaches in neuroscience.

Abnormal behaviours relevant to neurodevelopmental disorders in Kirrel3-knockout mice

In the nervous system, Kirrel3 is involved in neuronal migration, axonal fasciculation, and synapse formation. Recently, genetic links have been reported between mutations in the KIRREL3 gene and increased risk of neurodevelopmental disorders, including autism spectrum disorder (ASD) and intellectual disability. To elucidate the causal relationship between KIRREL3 deficiency and behavioural abnormalities relevant to neurodevelopmental disorders, we generated global Kirrel3-knockout (Kirrel3^−/−) mice and investigated the detailed behavioural phenotypes. In the three-chambered social approach test, Kirrel3^−/− mice displayed a significant preference for a mouse over a non-social object but no significant preference for a stranger mouse over a familiar mouse. Ultrasonic communications, including pup-to-mother calls, male-female courtship vocalisation and resident responses to intruder, were significantly impaired in Kirrel3^−/− mice. Significant increases in locomotor activity and repetitive rearing were also observed in Kirrel3^−/− mice. Furthermore, the performance of Kirrel3^−/− mice in the rotarod test was significantly better than that of wild-type mice. In the acoustic startle test, Kirrel3^−/− mice were significantly hypersensitive to acoustic stimuli. Anxiety-related behaviours and spatial or fear memory acquisition were normal in Kirrel3^−/− mice. These findings suggest that Kirrel3^−/− mice exhibit autistic-like behaviours, including social and communicative deficits, repetitive behaviours, and sensory abnormalities, as well as hyperactivity.

Deficiency of a brain-specific chemokine-like molecule, SAM3, induces cardinal phenotypes of autism spectrum disorders in mice

Chemokines are small secreted signaling proteins produced by a broad range of cells, including immune cells. Several studies have recently suggested potential roles of chemokines and their receptors in the pathophysiology of autism spectrum disorders (ASDs). SAM3 is a novel brain-specific chemokine-like molecule with an unknown physiological function. We explored the relevance of chemokines in the development of ASD in mice, with a focus on SAM3. We generated Sam3 gene knockout (KO) mice and characterized their behavioral phenotypes, with a focus on those relevant to ASD. Sam3-deficient mice displayed all three core phenotypes of ASD: impaired responses to social novelty, defects in social communication, and increased repetitive behavior. In addition, they showed increased anxiety. Interestingly, gender differences were identified for several behaviors: only male Sam3 KO mice exhibited increased anxiety and increased repetitive behaviors. Sam3 KO mice did not exhibit changes in other behaviors, including locomotor activities, fear learning and memory, and object recognition memory. These findings indicate that a deficiency of SAM3, a novel brain-specific chemokine-like molecule, may lead to the pathogenesis of ASDs and suggest the possibility that SAM3, a soluble factor, could be a novel therapeutic target for ASD treatment.

MicroRNA-Mediated Regulation of ITGB3 and CHL1 Is Implicated in SSRI Action

Background: Selective serotonin reuptake inhibitor (SSRI) antidepressant drugs are the first-line of treatment for major depressive disorder (MDD) but are effective in <70% of patients. Our earlier genome-wide studies indicated that two genes encoding for cell adhesion proteins, close homolog of L1 (CHL1) and integrin beta-3 (ITGB3), and microRNAs, miR-151a-3p and miR-221/222, are implicated in the variable sensitivity and response of human lymphoblastoid cell lines (LCL) from unrelated individuals to SSRI drugs.

Methods: The microRNAs miR-221, miR-222, and miR-151-a-3p, along with their target gene binding sites, were explored in silico using miRBase, TargetScan, microRNAviewer, and the UCSC Genome Browser. Luciferase reporter assays were conducted for demonstrating the direct functional regulation of ITGB3 and CHL1 expression by miR-221/222 and miR-151a-3p, respectively. A human LCL exhibiting low sensitivity to paroxetine was utilized for studying the phenotypic effect of CHL1 regulation by miR-151a-3p on SSRI response.

Results: By showing direct regulation of CHL1 and ITGB3 by miR-151a-3p and miR-221/222, respectively, we link these microRNAs and genes with cellular SSRI sensitivity phenotypes. We report that miR-151a-3p increases cell sensitivity to paroxetine via down-regulating CHL1 expression.

Conclusions: miR-151a-3p, miR-221/222 and their (here confirmed) respective target-genes, CHL1 and ITGB3, are implicated in SSRI responsiveness, and possibly in the clinical response to antidepressant drugs.

The Gain-of-Function Integrin β3 Pro33 Variant Alters the Serotonin System in the Mouse Brain

Engagement of integrins by the extracellular matrix initiates signaling cascades that drive a variety of cellular functions, including neuronal migration and axonal pathfinding in the brain. Multiple lines of evidence link the ITGB3 gene encoding the integrin β3 subunit with the serotonin (5-HT) system, likely via its modulation of the 5-HT transporter (SERT). The ITGB3 coding polymorphism Leu33Pro (rs5918, Pl^A2) produces hyperactive αvβ3 receptors that influence whole-blood 5-HT levels and may influence the risk for autism spectrum disorder (ASD). Using a phenome-wide scan of psychiatric diagnoses, we found significant, male-specific associations between the Pro33 allele and attention-deficit hyperactivity disorder and ASDs. Here, we used knock-in (KI) mice expressing an Itgb3 variant that phenocopies the human Pro33 variant to elucidate the consequences of constitutively enhanced αvβ3 signaling to the 5-HT system in the brain. KI mice displayed deficits in multiple behaviors, including anxiety, repetitive, and social behaviors. Anatomical studies revealed a significant decrease in 5-HT synapses in the midbrain, accompanied by decreases in SERT activity and reduced localization of SERTs to integrin adhesion complexes in synapses of KI mice. Inhibition of focal adhesion kinase (FAK) rescued SERT function in synapses of KI mice, demonstrating that constitutive active FAK signaling downstream of the Pro32Pro33 integrin αvβ3 suppresses SERT activity. Our studies identify a complex regulation of 5-HT homeostasis and behaviors by integrin αvβ3, revealing an important role for integrins in modulating risk for neuropsychiatric disorders.SIGNIFICANCE STATEMENT The integrin β3 Leu33Pro coding polymorphism has been associated with autism spectrum disorders (ASDs) within a subgroup of patients with elevated blood 5-HT levels, linking integrin β3, 5-HT, and ASD risk. We capitalized on these interactions to demonstrate that the Pro33 coding variation in the murine integrin β3 recapitulates the sex-dependent neurochemical and behavioral attributes of ASD. Using state-of-the-art techniques, we show that presynaptic 5-HT function is altered in these mice, and that the localization of 5-HT transporters to specific compartments within the synapse, disrupted by the integrin β3 Pro33 mutation, is critical for appropriate reuptake of 5-HT. Our studies provide fundamental insight into the genetic network regulating 5-HT neurotransmission in the CNS that is also associated with ASD risk.

Should studies on Glanzmann thrombasthenia not be telling us more about cardiovascular disease and other major illnesses?

Glanzmann thrombasthenia (GT) is a rare inherited bleeding disorder caused by loss of αIIbβ3 integrin function in platelets. Most genetic variants of β3 also affect the widely expressed αvβ3 integrin. With brief mention of mouse models, I now look at the consequences of disease-causing ITGA2B and ITGB3 mutations on the non-hemostatic functions of platelets and other cells. Reports of arterial thrombosis in GT patients are rare, but other aspects of cardiovascular disease do occur including deep vein thrombosis and congenital heart defects. Thrombophilic and other risk factors for thrombosis and lessons from heterozygotes and variant forms of GT are discussed. Assessed for GT patients are reports of leukemia and cancer, loss of fertility, bone pathology, inflammation and wound repair, infections, kidney disease, autism and respiratory disease. This survey shows an urgent need for a concerted international effort to better determine how loss of αIIbβ3 and αvβ3 influences health and disease.

Integrins in synapse regulation

Integrins are a large family of extracellular matrix (ECM) receptors. In the developing and adult brain, many integrins are present at high levels at synapses. The tetrapartite structure of synapses - which comprises presynaptic and postsynaptic neurons, the ECM and glial processes - places synaptic integrins in an excellent position to sense dynamic changes in the synaptic environment and use this information to coordinate further changes in synapse structure and function that will shape neural circuit properties. Recent developments in our understanding of the cellular and physiological roles of integrins, which range from control of neural process outgrowth and synapse formation to regulation of synaptic plasticity and memory, enable us to attempt a synthesis of synaptic integrin function.

Distortion of the normal function of synaptic cell adhesion molecules by genetic variants as a risk for autism spectrum disorders

Synaptic cell adhesion molecules (SCAMs) are a functional category of cell adhesion molecules that connect pre- and postsynapses by the protein-protein interaction via their extracellular cell adhesion domains. Countless numbers of common genetic variants and rare mutations in SCAMs have been identified in the patients with autism spectrum disorders (ASDs). Among these, NRXN and NLGN family proteins cooperatively function at synaptic terminals both of which genes are strongly implicated as risk genes for ASDs. Knock-in mice carrying a single rare point mutation of NLGN3 (NLGN3 R451C) discovered in the patients with ASDs display a deficit in social interaction and an enhancement of spatial learning and memory ability reminiscent of the clinical phenotype of ASDs. NLGN4 knockout (KO) and NRXN2α KO mice also show a deficit in sociability as well as some specific neuropsychiatric behaviors. In this review, we selected NRXNs/NLGNs, CNTNAP2/CNTNAP4, CNTN4, ITGB3, and KIRREL3 as strong ASD risk genes based on SFARI score and summarize the protein structures, functions at synapses, representative discoveries in human genetic studies, and phenotypes of the mutant model mice in light of the pathophysiology of ASDs.

Autism and cerebellar dysfunction: Evidence from animal models

Autism is a prevalent neurodevelopmental disorder whose origins are not well understood. Cerebellar involvement has been implicated in the pathogenesis of autism spectrum disorders with increasing evidence from both clinical studies and animal models supporting an important role for cerebellar dysfunction in autism spectrum disorders. This article discusses the various cerebellar contributions to autism spectrum disorders. Both clinical and preclinical studies are discussed and future research directions highlighted.

Rodent models of obsessive compulsive disorder: Evaluating validity to interpret emerging neurobiology

Obsessive Compulsive Disorder (OCD) is a common neuropsychiatric disorder with unknown molecular underpinnings. Identification of genetic and non-genetic risk factors has largely been elusive, primarily because of a lack of power. In contrast, neuroimaging has consistently implicated the cortico-striatal-thalamo-cortical circuits in OCD. Pharmacological treatment studies also show specificity, with consistent response of OCD symptoms to chronic treatment with serotonin reuptake inhibitors; although most patients are left with residual impairment. In theory, animal models could provide a bridge from the neuroimaging and pharmacology data to an understanding of pathophysiology at the cellular and molecular level. Several mouse models have been proposed using genetic, immunological, pharmacological, and optogenetic tools. These experimental model systems allow testing of hypotheses about the origins of compulsive behavior. Several models have generated behavior that appears compulsive-like, particularly excessive grooming, and some have demonstrated response to chronic serotonin reuptake inhibitors, establishing both face validity and predictive validity. Construct validity is more difficult to establish in the context of a limited understanding of OCD risk factors. Our current models may help us to dissect the circuits and molecular pathways that can elicit OCD-relevant behavior in rodents. We can hope that this growing understanding, coupled with developing technology, will prepare us when robust OCD risk factors are better understood.

Differential molecular and behavioural alterations in mouse models of GABRG2 haploinsufficiency versus dominant negative mutations associated with human epilepsy

Genetic epilepsy is a common disorder with phenotypic variation, but the basis for the variation is unknown. Comparing the molecular pathophysiology of mutations in the same epilepsy gene may provide mechanistic insights into the phenotypic heterogeneity. GABRG2 is an established epilepsy gene, and mutations in it produce epilepsy syndromes with varying severities. The disease phenotype in some cases may be caused by simple loss of subunit function (functional haploinsufficiency), while others may be caused by loss-of-function plus dominant negative suppression and other cellular toxicity. Detailed molecular defects and the corresponding seizures and related comorbidities resulting from haploinsufficiency and dominant negative mutations, however, have not been compared. Here we compared two mouse models of GABRG2 loss-of-function mutations associated with epilepsy with different severities, Gabrg2+/Q390X knockin (KI) and Gabrg2+/- knockout (KO) mice. Heterozygous Gabrg2+/Q390X KI mice are associated with a severe epileptic encephalopathy due to a dominant negative effect of the mutation, while heterozygous Gabrg2+/- KO mice are associated with mild absence epilepsy due to simple haploinsufficiency. Unchanged at the transcriptional level, KI mice with severe epilepsy had neuronal accumulation of mutant γ2 subunits, reduced remaining functional wild-type subunits in dendrites and synapses, while KO mice with mild epilepsy had no intracellular accumulation of the mutant subunits and unaffected biogenesis of the remaining wild-type subunits. Consequently, KI mice with dominant negative mutations had much less wild-type receptor expression, more severe seizures and behavioural comorbidities than KO mice. This work provides insights into the pathophysiology of epilepsy syndrome heterogeneity and designing mechanism-based therapies.

The serotonin system in autism spectrum disorder: From biomarker to animal models

Elevated whole blood serotonin, or hyperserotonemia, was the first biomarker identified in autism spectrum disorder (ASD) and is present in more than 25% of affected children. The serotonin system is a logical candidate for involvement in ASD due to its pleiotropic role across multiple brain systems both dynamically and across development. Tantalizing clues connect this peripheral biomarker with changes in brain and behavior in ASD, but the contribution of the serotonin system to ASD pathophysiology remains incompletely understood. Studies of whole blood serotonin levels in ASD and in a large founder population indicate greater heritability than for the disorder itself and suggest an association with recurrence risk. Emerging data from both neuroimaging and postmortem samples also indicate changes in the brain serotonin system in ASD. Genetic linkage and association studies of both whole blood serotonin levels and of ASD risk point to the chromosomal region containing the serotonin transporter (SERT) gene in males but not in females. In ASD families with evidence of linkage to this region, multiple rare SERT amino acid variants lead to a convergent increase in serotonin uptake in cell models. A knock-in mouse model of one of these variants, SERT Gly56Ala, recapitulates the hyperserotonemia biomarker and shows increased brain serotonin clearance, increased serotonin receptor sensitivity, and altered social, communication, and repetitive behaviors. Data from other rodent models also suggest an important role for the serotonin system in social behavior, in cognitive flexibility, and in sensory development. Recent work indicates that reciprocal interactions between serotonin and other systems, such as oxytocin, may be particularly important for social behavior. Collectively, these data point to the serotonin system as a prime candidate for treatment development in a subgroup of children defined by a robust, heritable biomarker.

Autism spectrum disorder traits in Slc9a9 knock-out mice

Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders which begin in childhood and persist into adulthood. They cause lifelong impairments and are associated with substantial burdens to patients, families, and society. Genetic studies have implicated the sodium/proton exchanger (NHE) nine gene, Slc9a9, to ASDs and attention-deficit/hyperactivity disorder(ADHD). Slc9a9 encodes, NHE9, a membrane protein of the late recycling endosomes. The recycling endosome plays an important role in synapse development and plasticity by regulating the trafficking of membrane neurotransmitter receptors and transporters. Here we tested the hypothesis that Slc9a9 knock-out (KO) mice would show ADHD-like and ASD-like traits. Ultrasonic vocalization (USV) recording showed that Slc9a9 KO mice emitted fewer calls and had shorter call durations, which suggest communication impairment. Slc9a9 KO mice lacked a preference for social novelty, but did not show deficits in social approach; Slc9a9 KO mice spent more time self-grooming, an indicator for restricted and repetitive behavior. We did not observe hyperactivity or other behavior impairments which are commonly comorbid with ASDs in human, such as anxiety-like behavior. Our study is the first animal behavior study that links Slc9a9 to ASDs. By eliminatingNHE9 activity, it provides strong evidence that lack of Slc9a9leads to ASD-like behaviors in mice and provides the field with a new mouse model of ASDs.

Gender Dependent Evaluation of Autism like Behavior in Mice Exposed to Prenatal Zinc Deficiency

Zinc deficiency has recently been linked to the etiology of autism spectrum disorders (ASD) as environmental risk factor. With an estimated 17% of the world population being at risk of zinc deficiency, especially zinc deficiency during pregnancy might be a common occurrence, also in industrialized nations. On molecular level, zinc deficiency has been shown to affect a signaling pathway at glutamatergic synapses that has previously been identified through genetic mutations in ASD patients, the Neurexin-Neuroligin-Shank pathway, via altering zinc binding Shank family members. In particular, prenatal zinc deficient but not acute zinc deficient animals have been reported to display autism like behavior in some behavioral tests. However, a full behavioral analysis of a possible autism like behavior has been lacking so far. Here, we performed an extensive behavioral phenotyping of mice born from mothers with mild zinc deficiency during all trimesters of pregnancy. Prenatal zinc deficient animals were investigated as adults and gender differences were assessed. Our results show that prenatal zinc deficient mice display increased anxiety, deficits in nest building and various social interaction paradigm, as well as mild alterations in ultrasonic vocalizations. A gender specific analysis revealed only few sex specific differences. Taken together, given that similar behavioral abnormalities as reported here are frequently observed in ASD mouse models, we conclude that prenatal zinc deficient animals even without specific genetic susceptibility for ASD, already show some features of ASD like behavior.

The role of cerebellar circuitry alterations in the pathophysiology of autism spectrum disorders

The cerebellum has been repeatedly implicated in gene expression, rodent model and post-mortem studies of autism spectrum disorder (ASD). How cellular and molecular anomalies of the cerebellum relate to clinical manifestations of ASD remains unclear. Separate circuits of the cerebellum control different sensorimotor behaviors, such as maintaining balance, walking, making eye movements, reaching, and grasping. Each of these behaviors has been found to be impaired in ASD, suggesting that multiple distinct circuits of the cerebellum may be involved in the pathogenesis of patients' sensorimotor impairments. We will review evidence that the development of these circuits is disrupted in individuals with ASD and that their study may help elucidate the pathophysiology of sensorimotor deficits and core symptoms of the disorder. Preclinical studies of monogenetic conditions associated with ASD also have identified selective defects of the cerebellum and documented behavioral rescues when the cerebellum is targeted. Based on these findings, we propose that cerebellar circuits may prove to be promising targets for therapeutic development aimed at rescuing sensorimotor and other clinical symptoms of different forms of ASD.

Autism Spectrum Disorders: Translating human deficits into mouse behavior

Autism Spectrum Disorders are a heterogeneous group of neurodevelopmental disorders, with rising incidence but little effective therapeutic intervention available. Currently two main clinical features are described to diagnose ASDs: impaired social interaction and communication, and repetitive behaviors. Much work has focused on understanding underlying causes of ASD by generating animal models of the disease, in the hope of discovering signaling pathways and cellular targets for drug intervention. Here we review how ASD behavioral phenotypes can be modeled in the mouse, the most common animal model currently in use in this field, and discuss examples of genetic mouse models of ASD with behavioral features that recapitulate various symptoms of ASD.

Integrin β3 Haploinsufficiency Modulates Serotonin Transport and Antidepressant-Sensitive Behavior in Mice

Converging lines of evidence have identified genetic interactions between the serotonin transporter (SERT) gene and ITGB3, which encodes the β3 subunit that forms the αIIbβ3 and αvβ3 integrin receptor complexes. Here we examine the consequences of haploinsufficiency in the mouse integrin β3 subunit gene (Itgb3) on SERT function and selective 5-hydroxytryptamine (5-HT) reuptake inhibitor (SSRI) effectiveness in vivo. Biochemical fractionation studies and immunofluorescent staining of murine brain slices reveal that αvβ3 receptors and SERTs are enriched in presynaptic membranes from several brain regions and that αvβ3 colocalizes with a subpopulation of SERT-containing synapses in raphe nuclei. Notably, we establish that loss of a single allele of Itgb3 in murine neurons is sufficient to decrease 5-HT uptake by SERT in midbrain synaptosomes. Pharmacological assays to elucidate the αvβ3-mediated mechanism of reduced SERT function indicate that decreased integrin β3 subunit expression scales down the population size of active SERT molecules and, as a consequence, lowers the effective dose of SSRIs. These data are consistent with the existence of a subpopulation of SERTs that are tightly modulated by integrin αvβ3 and significantly contribute to global SERT function at 5-HT synapses in the midbrain. Importantly, our screen of a normal human population for single nucleotide polymorphisms in human ITGB3 identified a variant associated with reductions in integrin β3 expression levels that parallel our mouse findings. Thus, polymorphisms in human ITGB3 may contribute to the differential responsiveness of select patients to SSRIs.