ASD-linked Genes Research Articles

Investigating gene-environment interaction on attention in a double-hit model for Autism Spectrum Disorder.

Autism Spectrum Disorder (ASD) is a neurodevelopmental behavioral disorder characterized by social, communicative, and motor deficits. There is no single etiological cause for ASD, rather, there are various genetic and environmental factors that increase the risk for ASD. It is thought that some of these factors influence the same underlying neural mechanisms, and that an interplay of both genetic and environmental factors would better explain the pathogenesis of ASD. To better appreciate the influence of genetic-environment interaction on ASD-related behaviours, rats lacking a functional copy of the ASD-linked gene Cntnap2 were exposed to maternal immune activation (MIA) during pregnancy and assessed in adolescence and adulthood. We hypothesized that Cntnap2 deficiency interacts with poly I:C MIA to aggravate ASD-like symptoms in the offspring. In this double-hit model, we assessed attention, a core deficit in ASD due to prefrontal cortical dysfunction. We employed a well-established attentional paradigm known as the 5-choice serial reaction time task (5CSRTT). Cntnap2-/- rats exhibited greater perseverative responses which is indicative of repetitive behaviors. Additionally, rats exposed to poly I:C MIA exhibited premature responses, a marker of impulsivity. The rats exposed to both the genetic and environmental challenge displayed an increase in impulsive activity; however, this response was only elicited in the presence of an auditory distractor. This implies that exacerbated symptomatology in the double-hit model may situation-dependent and not generally expressed.

Fetal exposure to valproic acid dysregulates the expression of autism-linked genes in the developing cerebellum

Autism spectrum disorder (ASD) includes a set of highly heritable neurodevelopmental syndromes characterized by social and communication impairment, repetitive behaviour, and intellectual disability. Although mutations in multiple genes have been associated to ASD, most patients lack detectable genetic alterations. For this reason, environmental factors are commonly thought to also contribute to ASD aetiology. Transcriptome analyses have revealed that autistic brains possess distinct gene expression signatures, whose elucidation can provide insights about the mechanisms underlying the effects of ASD-causing genetic and environmental factors. Herein, we have identified a coordinated and temporally regulated programme of gene expression in the post-natal development of cerebellum, a brain area whose defects are strongly associated with ASD. Notably, this cerebellar developmental programme is significantly enriched in ASD-linked genes. Clustering analyses highlighted six different patterns of gene expression modulated during cerebellar development, with most of them being enriched in functional processes that are frequently dysregulated in ASD. By using the valproic acid mouse model of ASD, we found that ASD-linked genes are dysregulated in the developing cerebellum of ASD-like mice, a defect that correlates with impaired social behaviour and altered cerebellar cortical morphology. Moreover, changes in transcript levels were reflected in aberrant protein expression, indicating the functional relevance of these alterations. Thus, our work uncovers a complex ASD-related transcriptional programme regulated during cerebellar development and highlight genes whose expression is dysregulated in this brain area of an ASD mouse model.

A Critical Period for Development of Cerebellar-Mediated Autism-Relevant Social Behavior.

The cerebellum has been increasingly implicated in autism spectrum disorder (ASD) with many ASD-linked genes impacting both cerebellar function and development. However, the precise timing and critical periods of when abnormal cerebellar neurodevelopment contributes to ASD-relevant behaviors remains poorly understood. In this study, we identify a critical period for the development of ASD-relevant behaviors in a cerebellar male mouse model of tuberous sclerosis complex (TSC), by using the mechanistic target of rapamycin (mTOR) inhibitor, rapamycin, to pharmacologically inhibit dysregulated downstream signaling. We find independent critical periods during which abnormal ASD-relevant behaviors develop for the two core ASD diagnostic criteria, social impairments and behavioral flexibility, and delineate an anatomic, physiological, and behavioral framework. These findings not only further our understanding of the genetic mechanisms underlying the timing of ASD-relevant behaviors but also have the capacity to inform potential therapies to optimize treatment interventions.SIGNIFICANCE STATEMENT No targeted treatments currently exist for autism spectrum disorder (ASD). This complex developmental disorder has established links to genetic and circuit aberrations, yet the precise timing and coordination of these underlying mechanisms that contribute to the spectrum of physiological and behavioral abnormalities remains unclear. Cerebellar pathology is consistently seen in ASD individuals; therefore, we sought to identify the specific windows for cerebellar involvement in the development of ASD-relevant behaviors. Using pharmacologic treatment paradigms, we outline distinct critical periods of developmental vulnerability for ASD-relevant social and inflexible behaviors. From this study, we posit a refined window of time during which ASD symptoms develop that will inform therapeutic timing.

Synapse Maturation and Developmental Impairment in the Medial Nucleus of the Trapezoid Body.

Sound localization requires rapid interpretation of signal speed, intensity, and frequency. Precise neurotransmission of auditory signals relies on specialized auditory brainstem synapses including the calyx of Held, the large encapsulating input to principal neurons in the medial nucleus of the trapezoid body (MNTB). During development, synapses in the MNTB are established, eliminated, and strengthened, thereby forming an excitatory/inhibitory (E/I) synapse profile. However, in neurodevelopmental disorders such as autism spectrum disorder (ASD), E/I neurotransmission is altered, and auditory phenotypes emerge anatomically, molecularly, and functionally. Here we review factors required for normal synapse development in this auditory brainstem pathway and discuss how it is affected by mutations in ASD-linked genes.

GABAB Receptor Agonist R-Baclofen Reverses Altered Auditory Reactivity and Filtering in the Cntnap2 Knock-Out Rat.

Altered sensory information processing, and auditory processing, in particular, is a common impairment in individuals with autism spectrum disorder (ASD). One prominent hypothesis for the etiology of ASD is an imbalance between neuronal excitation and inhibition. The selective GABAB receptor agonist R-Baclofen has been shown previously to improve social deficits and repetitive behaviors in several mouse models for neurodevelopmental disorders including ASD, and its formulation Arbaclofen has been shown to ameliorate social avoidance symptoms in some individuals with ASD. The present study investigated whether R-Baclofen can remediate ASD-related altered sensory processing reliant on excitation/inhibition imbalance in the auditory brainstem. To assess a possible excitation/inhibition imbalance in the startle-mediating brainstem underlying ASD-like auditory-evoked behaviors, we detected and quantified brain amino acid levels in the nucleus reticularis pontis caudalis (PnC) of rats with a homozygous loss-of-function mutation in the ASD-linked gene Contactin-associated protein-like 2 (Cntnap2) and their wildtype (WT) littermates using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS). Abnormal behavioral read-outs of brainstem auditory signaling in Cntnap2 KO rats were accompanied by increased levels of GABA, glutamate, and glutamine in the PnC. We then compared the effect of R-Baclofen on behavioral read-outs of brainstem auditory signaling in Cntnap2 KO and WT rats. Auditory reactivity, sensory filtering, and sensorimotor gating were tested in form of acoustic startle response input-output functions, short-term habituation, and prepulse inhibition before and after acute administration of R-Baclofen (0.75, 1.5, and 3 mg/kg). Systemic R-Baclofen treatment improved disruptions in sensory filtering in Cntnap2 KO rats and suppressed exaggerated auditory startle responses, in particular to moderately loud sounds. Lower ASR thresholds in Cntnap2 KO rats were increased in a dose-dependent fashion, with the two higher doses bringing thresholds close to controls, whereas shorter ASR peak latencies at the threshold were further exacerbated. Impaired prepulse inhibition increased across various acoustic prepulse conditions after administration of R-Baclofen in Cntnap2 KO rats, whereas R-Baclofen did not affect prepulse inhibition in WT rats. Our findings suggest that GABAB receptor agonists may be useful for pharmacologically targeting multiple aspects of sensory processing disruptions involving neuronal excitation/inhibition imbalances in ASD.

Autism-linked mutations of CTTNBP2 reduce social interaction and impair dendritic spine formation via diverse mechanisms

Abnormal synaptic formation and signaling is one of the key molecular features of autism spectrum disorders (ASD). Cortactin binding protein 2 (CTTNBP2), an ASD-linked gene, is known to regulate the subcellular distribution of synaptic proteins, such as cortactin, thereby controlling dendritic spine formation and maintenance. However, it remains unclear how ASD-linked mutations of CTTNBP2 influence its function. Here, using cultured hippocampal neurons and knockin mouse models, we screen seven ASD-linked mutations in the short form of the Cttnbp2 gene and identify that M120I, R533* and D570Y mutations impair CTTNBP2 protein–protein interactions via divergent mechanisms to reduce dendritic spine density in neurons. R533* mutation impairs CTTNBP2 interaction with cortactin due to lack of the C-terminal proline-rich domain. Through an N–C terminal interaction, M120I mutation at the N-terminal region of CTTNBP2 also negatively influences cortactin interaction. D570Y mutation increases the association of CTTNBP2 with microtubule, resulting in a dendritic localization of CTTNBP2, consequently reducing the distribution of CTTNBP2 in dendritic spines and impairing the synaptic function of CTTNBP2. Finally, we generated heterozygous M120I knockin mice to mimic the genetic variation of patients and found they exhibit reduced social interaction. Our study elucidates that different ASD-linked mutations of CTTNBP2 result in diverse molecular deficits, but all have the similar consequence of synaptic impairment.

Loss of Cntnap2 in the Rat Causes Autism-Related Alterations in Social Interactions, Stereotypic Behavior, and Sensory Processing.

Autism spectrum disorder (ASD) is characterized by social interaction and communication impairments, as well as restrictive/repetitive patterns of behavior, interests or activities, which can coexist with intellectual disability and altered sensory processing. To study the mechanisms underlying these core features of ASD, preclinical research has developed animal models with manipulations in ASD-linked genes, such as CNTNAP2. In order to fully interpret the findings from mechanistic studies, the extent to which these models display behaviors consistent with ASD must be determined. Toward that goal, we conducted an investigation of the consequences of a functional loss of Cntnap2 on ASD-related behaviors by comparing the performance of rats with a homozygous or heterozygous knockout of Cntnap2 to their wildtype littermates across a comprehensive test battery. Cntnap2-/- rats showed deficits in sociability and social novelty, and they displayed repetitive circling and hyperlocomotion. Moreover, Cntnap2-/- rats demonstrated exaggerated acoustic startle responses, increased avoidance to sounds of moderate intensity, and a lack of rapid audiovisual temporal recalibration; indicating changes in sensory processing at both the pre-attentive and perceptual levels. Notably, sensory behaviors requiring learned associations did not reveal genotypic differences, whereas tasks relying on automatic/implicit behaviors did. Ultimately, because these collective alterations in social, stereotypic, and sensory behaviors are phenotypically similar to those reported in individuals with ASD, our results establish the Cntnap2 knockout rat model as an effective platform to study not only the molecular and cellular mechanisms associated with ASD, but also the complex relationship between altered sensory processing and other core ASD-related behaviors. LAY SUMMARY: Autism spectrum disorder (ASD) is characterized by social interaction differences, and restrictive/repetitive patterns of behavior. We studied the behavioral alterations caused by the loss of an autism-linked gene, Cntnap2, in the rat to determine how mutations in this gene contribute to autism-related behaviors. We show the loss of Cntnap2 leads to changes in social, stereotypic, and sensory behaviors, indicating this rat model can be used to better understand the brain changes underlying ASD. Autism Res 2020, 13: 1698-1717. © 2020 International Society for Autism Research and Wiley Periodicals LLC.

Regulation of autism-relevant behaviors by cerebellar-prefrontal cortical circuits.

Cerebellar dysfunction has been demonstrated in autism spectrum disorders (ASDs); however, the circuits underlying cerebellar contributions to ASD-relevant behaviors remain unknown. In this study, we demonstrated functional connectivity between the cerebellum and the medial prefrontal cortex (mPFC) in mice; showed that the mPFC mediates cerebellum-regulated social and repetitive/inflexible behaviors; and showed disruptions in connectivity between these regions in multiple mouse models of ASD-linked genes and in individuals with ASD. We delineated a circuit from cerebellar cortical areas Right crus 1 (Rcrus1) and posterior vermis through the cerebellar nuclei and ventromedial thalamus and culminating in the mPFC. Modulation of this circuit induced social deficits and repetitive behaviors, whereas activation of Purkinje cells (PCs) in Rcrus1 and posterior vermis improved social preference impairments and repetitive/inflexible behaviors, respectively, in male PC-Tsc1 mutant mice. These data raise the possibility that these circuits might provide neuromodulatory targets for the treatment of ASD.

Sex Differences in the Effects of Prenatal Bisphenol A Exposure on Genes Associated with Autism Spectrum Disorder in the Hippocampus

Autism spectrum disorder (ASD) is a neurodevelopmental disorder inexplicably biased towards males. Although prenatal exposure to bisphenol A (BPA) has recently been associated with the ASD risk, whether BPA dysregulates ASD-related genes in the developing brain remains unclear. In this study, transcriptome profiling by RNA-seq analysis of hippocampi isolated from neonatal pups prenatally exposed to BPA was conducted and revealed a list of differentially expressed genes (DEGs) associated with ASD. Among the DEGs, several ASD candidate genes, including Auts2 and Foxp2, were dysregulated and showed sex differences in response to BPA exposure. The interactome and pathway analyses of DEGs using Ingenuity Pathway Analysis software revealed significant associations between the DEGs in males and neurological functions/disorders associated with ASD. Moreover, the reanalysis of transcriptome profiling data from previously published BPA studies consistently showed that BPA-responsive genes were significantly associated with ASD-related genes. The findings from this study indicate that prenatal BPA exposure alters the expression of ASD-linked genes in the hippocampus and suggest that maternal BPA exposure may increase ASD susceptibility by dysregulating genes associated with neurological functions known to be negatively impacted in ASD, which deserves further investigations.

AutDB: a platform to decode the genetic architecture of autism.

AutDB is a deeply annotated resource for exploring the impact of genetic variations associated with autism spectrum disorders (ASD). First released in 2007, AutDB has evolved into a multi-modular resource of diverse types of genetic and functional evidence related to ASD. Current modules include: Human Gene, which annotates all ASD-linked genes and their variants; Animal Model, which catalogs behavioral, anatomical and physiological data from rodent models of ASD; Protein Interaction (PIN), which builds interactomes from direct relationships of protein products of ASD genes; and Copy Number Variant (CNV), which catalogs deletions and duplications of chromosomal loci identified in ASD. A multilevel data-integration strategy is utilized to connect the ASD genes to the components of the other modules. All information in this resource is manually curated by expert scientists from primary scientific publications and is referenced to source articles. AutDB is actively maintained with a rigorous quarterly data release schedule. As of June 2017, AutDB contains detailed annotations for 910 genes, 2197 CNV loci, 1060 rodent models and 38 296 PINs. With its widespread use by the research community, AutDB serves as a reference resource for analysis of large datasets, accelerating ASD research and potentially leading to targeted drug treatments. AutDB is available at http://autism.mindspec.org/autdb/Welcome.do.

Genetic Overlap Found in Socially Unresponsive Bees and Human ASD-linked Genes

Genetic Overlap Found in Socially Unresponsive Bees and Human ASD-linked Genes

Sexual divergence in microtubule function: the novel intranasal microtubule targeting SKIP normalizes axonal transport and enhances memory.

Activity-dependent neuroprotective protein (ADNP), essential for brain formation, is a frequent autism spectrum disorder (ASD)-mutated gene. ADNP associates with microtubule end-binding proteins (EBs) through its SxIP motif, to regulate dendritic spine formation and brain plasticity. Here, we reveal SKIP, a novel four-amino-acid peptide representing an EB-binding site, as a replacement therapy in an outbred Adnp-deficient mouse model. We discovered, for the first time, axonal transport deficits in Adnp(+/-) mice (measured by manganese-enhanced magnetic resonance imaging), with significant male-female differences. RNA sequencing evaluations showed major age, sex and genotype differences. Function enrichment and focus on major gene expression changes further implicated channel/transporter function and the cytoskeleton. In particular, a significant maturation change (1 month-five months) was observed in beta1 tubulin (Tubb1) mRNA, only in Adnp(+/+) males, and sex-dependent increase in calcium channel mRNA (Cacna1e) in Adnp(+/+) males compared with females. At the protein level, the Adnp(+/-) mice exhibited impaired hippocampal expression of the calcium channel (voltage-dependent calcium channel, Cacnb1) as well as other key ASD-linked genes including the serotonin transporter (Slc6a4), and the autophagy regulator, BECN1 (Beclin1), in a sex-dependent manner. Intranasal SKIP treatment normalized social memory in 8- to 9-month-old Adnp(+/-)-treated mice to placebo-control levels, while protecting axonal transport and ameliorating changes in ASD-like gene expression. The control, all d-amino analog D-SKIP, did not mimic SKIP activity. SKIP presents a novel prototype for potential ASD drug development, a prevalent unmet medical need.