Involvement of synaptic genes in the pathogenesis of autism spectrum disorders: the case of synapsins

Multi-omics study reveals differential expression and phosphorylation of autophagy-related proteins in autism spectrum disorder

Our multi-omics study investigated the molecular mechanisms underlying autism spectrum disorder (ASD) using Shank3Δ4-22 and Cntnap2-/- mouse models. Through global- and phospho- proteomics of the mouse cortex, we focused on shared molecular changes and found that autophagy was particularly affected in both models. Global proteomics identified a small number of differentially expressed proteins that significantly impact postsynaptic components and synaptic function, including key pathways such as mTOR signaling. Phosphoproteomics revealed unique phosphorylation sites in autophagy-related proteins such as ULK2, RB1CC1, ATG16L1, and ATG9, suggesting that altered phosphorylation patterns contribute to impaired autophagic flux in ASD. SH-SY5Y cells with SHANK3 gene deletion showed elevated LC3-II and p62 levels, indicating autophagosome accumulation and autophagy initiation, while the reduced level of the lysosomal activity marker LAMP1 suggested impaired autophagosome-lysosome fusion. The study highlights the involvement of reactive nitrogen species and nitric oxide (NO) on autophagy disruption. Importantly, inhibition of neuronal NO synthase (nNOS) by 7-NI normalized autophagy markers levels in the SH-SY5Y cells and primary cultured neurons. We have previously shown that nNOS inhibition improved synaptic and behavioral phenotypes in Shank3Δ4-22 and Cntnap2-/- mouse models. Our multi-omics study reveals differential expression and phosphorylation of autophagy-related proteins in ASD but further investigation is needed to prove the full involvement of autophagy in ASD. Our study underscores the need for further examination into the functional consequences of the identified phosphorylation sites, which may offer potential novel therapeutic autophagy-related targets for ASD treatment.

Genetic Variant Analyses Identify Novel Candidate Autism Risk Genes from a Highly Consanguineous Cohort of 104 Families from Oman

Deficits in social communication, restricted interests, and repetitive behaviours are hallmarks of autism spectrum disorder (ASD). Despite high genetic heritability, the majority of clinically diagnosed ASD cases have unknown genetic origins. We performed genome sequencing on mothers, fathers, and affected individuals from 104 families with ASD in Oman, a Middle Eastern country underrepresented in international genetic studies. This approach identified 48 novel candidate genes significantly associated with ASD in Oman. In particular, 35 of these genes have been previously implicated in neurodevelopmental disorders (NDDs) in other populations, underscoring the conserved genetic basis of ASD across ethnicities. Genetic variants within these candidate genes that would impact the encoded protein included 1 insertion, 4 frameshift, 6 splicing, 12 nonsense, and 67 missense changes. Notably, 61% of the SNVs were homozygous, suggesting a prominent recessive genetic architecture for ASD in this unique population. The scarcity of genetic studies on ASD in the Arabian Peninsula has impeded the understanding of the unique genetic landscape of ASD in this region. These findings help bridge this knowledge gap and provide valuable insights into the complex genetic basis of ASD in Oman.

Autism Spectrum Disorder Pathogenesis-A Cross-Sectional Literature Review Emphasizing Molecular Aspects

The etiology of autism spectrum disorder (ASD) has not yet been completely elucidated. Through time, multiple attempts have been made to uncover the causes of ASD. Different theories have been proposed, such as being caused by alterations in the gut-brain axis with an emphasis on gut dysbiosis, post-vaccine complications, and genetic or even autoimmune causes. In this review, we present data covering the main streams that focus on ASD etiology. Data collection occurred in many countries covering ethnically diverse subjects. Moreover, we aimed to show how the progress in genetic techniques influences the explanation of medical White Papers in the ASD area. There is no single evidence-based pathway that results in symptoms of ASD. Patient management has constantly only been symptomatic, and there is no ASD screening apart from symptom-based diagnosis and parent-mediated interventions. Multigene sequencing or epigenetic alterations hold promise in solving the disjointed molecular puzzle. Further research is needed, especially in the field of biogenetics and metabolomic aspects, because young children constitute the patient group most affected by ASD. In summary, to date, molecular research has confirmed multigene dysfunction as the causative factor of ASD, the multigene model with metabolomic influence would explain the heterogeneity in ASD, and it is proposed that ion channel dysfunction could play a core role in ASD pathogenesis.

Molecular and in silico analyses of SYN III gene variants in autism spectrum disorder

BACKGROUND

Defects in neurotransmission and synaptogenesis are noteworthy in the pathogenesis of ASD. Synapsin III (SYN III) is defined as a synaptic vesicle protein that plays an important role in synaptogenesis and regulation of neurotransmitter release and neurite outgrowth. Therefore, SYN III may associate with many neurodevelopmental diseases, including ASD.

AIM

The aim of this study was to investigate whether the SYN III gene -631 C > G (rs133946) and -196 G > A (rs133945) polymorphisms are associated with susceptibility to ASD.

METHODS

SYN III variants and the risk of ASD were investigated in 26 healthy children and 24 ASD children. SYN III gene variants were genotyped by PCR-RFLP methods. The differences in genotype and allele frequencies between the ASD and control groups were calculated using the chi-square (χ2). We analysed the SYN III gene using web-based tools.

RESULTS

Our results suggest that the presence of the AA genotype of the SYN III -196 G > A (rs133945) polymorphism affects the characteristics and development of ASD in children (p = 0.012). SYN III -631 C > G (rs133946) polymorphism was not associated with ASD (p = 0.524). We have shown the prediction of gene-gene interaction that SYN III is co-expressed with 17 genes, physical interaction with 3 genes, and co-localization with 12 genes. The importance of different genes (SYN I, II, III, GABRD, NOS1AP, GNAO1) for ASD pathogenesis was revealed by GO analysis.

CONCLUSION

Considering the role of SYN III and related genes, especially in the synaptic vesicle pathway and neurotransmission, its effect on ASD can be further investigated.

Transcriptomic analysis reveals distinct adaptive molecular mechanism in the hippocampal CA3 from rats susceptible or not-susceptible to hyperthermia-induced seizures

Febrile seizures during early childhood are a relevant risk factor for the development of mesial temporal lobe epilepsy. Nevertheless, the molecular mechanism induced by febrile seizures that render the brain susceptible or not-susceptible to epileptogenesis remain poorly understood. Because the temporal investigation of such mechanisms in human patients is impossible, rat models of hyperthermia-induced febrile seizures have been used for that purpose. Here we conducted a temporal analysis of the transcriptomic and microRNA changes in the ventral CA3 of rats that develop (HS group) or not-develop (HNS group) seizures after hyperthermic insult on the eleventh postnatal day. The selected time intervals corresponded to acute, latent, and chronic phases of the disease. We found that the transcriptional differences between the HS and the HNS groups are related to inflammatory pathways, immune response, neurogenesis, and dendritogenesis in the latent and chronic phases. Additionally, the HNS group expressed a greater number of miRNAs (some abundantly expressed) as compared to the HS group. These results indicate that HNS rats were able to modulate their inflammatory response after insult, thus presenting better tissue repair and re-adaptation. Potential therapeutic targets, including genes, miRNAs and signaling pathways involved in epileptogenesis were identified.

Modernising autism spectrum disorder model engineering and treatment via CRISPR-Cas9: A gene reprogramming approach

A neurological abnormality called autism spectrum disorder (ASD) affects how a person perceives and interacts with others, leading to social interaction and communication issues. Limited and recurring behavioural patterns are another feature of the illness. Multiple mutations throughout development are the source of the neurodevelopmental disorder autism. However, a well-established model and perfect treatment for this spectrum disease has not been discovered. The rising era of the clustered regularly interspaced palindromic repeats (CRISPR)-associated protein 9 (Cas9) system can streamline the complexity underlying the pathogenesis of ASD. The CRISPR-Cas9 system is a powerful genetic engineering tool used to edit the genome at the targeted site in a precise manner. The major hurdle in studying ASD is the lack of appropriate animal models presenting the complex symptoms of ASD. Therefore, CRISPR-Cas9 is being used worldwide to mimic the ASD-like pathology in various systems like in vitro cell lines, in vitro 3D organoid models and in vivo animal models. Apart from being used in establishing ASD models, CRISPR-Cas9 can also be used to treat the complexities of ASD. The aim of this review was to summarize and critically analyse the CRISPR-Cas9-mediated discoveries in the field of ASD.

Alterations of presynaptic proteins in autism spectrum disorder

The expanded use of hypothesis-free gene analysis methods in autism research has significantly increased the number of genetic risk factors associated with the pathogenesis of autism. A further examination of the implicated genes directly revealed the involvement in processes pertinent to neuronal differentiation, development, and function, with a predominant contribution from the regulators of synaptic function. Despite the importance of presynaptic function in synaptic transmission, the regulation of neuronal network activity, and the final behavioral output, there is a relative lack of understanding of the presynaptic contribution to the pathology of autism. Here, we will review the close association among autism-related mutations, autism spectrum disorders (ASD) phenotypes, and the altered presynaptic protein functions through a systematic examination of the presynaptic risk genes relating to the critical stages of synaptogenesis and neurotransmission.

Vesicle trafficking with snares: a perspective for autism

Vesicle-mediated membrane traffic is the mechanism fundamental to many biological events, especially the release of neurotransmitters. The main proteins of the mechanism that mediates membrane fusion in vesicle-mediated membrane traffic are N-ethylmaleimide sensitive factor (NSF) supplemental protein (SNAP) receptor (SNAREs) proteins. SNAREs are classified into vesicle-associated SNAREs (vesicle-SNAREs/v-SNAREs) and target membrane-associated SNAREs (target-SNARE/t-SNAREs). Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by many symptoms, especially complications in social communication and stereotypical behaviours. Defects in synaptogenesis and neurotransmission, oxidative stress, and developmental defects in the early stages of development are defined in the pathogenesis of the disease. SNARE proteins are on the basis of synaptogenesis and neurotransmission. Although the formation mechanisms and underlying causes of the SNARE complex are not fully understood, expression differences, polymorphisms, abnormal expressions or dysfunctions of the proteins that make up the SNARE complex have been associated with many neurodevelopmental diseases, including autism. Further understanding of SNARE mechanisms is crucial both for understanding ASD and for developing new treatments. In this review, the formation mechanisms of the SNARE complex and the roles of various factors involved in this process are explained. In addition, a brief evaluation of clinical and basic studies on the SNARE complex in autism spectrum disorders was made.

Calcium signaling in neurodevelopment and pathophysiology of autism spectrum disorders

BACKGROUND

Autism spectrum disorder (ASD) covers a group of neurodevelopmental disorders with complex genetic background. Several genetic mutations, epigenetic alterations, copy number variations and single nucleotide polymorphisms have been reported that cause ASD or modify its phenotype. Among signaling pathways that influence pathogenesis of ASD, calcium signaling has a prominent effect.

METHODS

We searched PubMed and Google Scholar databases with key words "Calcium signaling" and "Autism spectrum disorder".

CONCLUSION

This type of signaling has essential roles in the cell physiology. Endoplasmic reticulum and mitochondria are the key organelles involved in this signaling. It is vastly accepted that organellar disorders intensely influence the central nervous system (CNS). Several lines of evidence indicate alterations in the function of calcium channels in polygenic disorders affecting CNS. In the current review, we describe the role of calcium signaling in normal function of CNS and pathophysiology of ASD.

Multiple Recurrent Copy Number Variations (CNVs) in Chromosome 22 Including 22q11.2 Associated with Autism Spectrum Disorder

Introduction

Autism spectrum disorder (ASD) is a developmental disorder that can cause substantial social, communication, and behavioral challenges. Genetic factors play a significant role in ASD, where the risk of ASD has been increased for unclear reasons. Twin studies have shown important evidence of both genetic and environmental contributions in ASD, where the level of contribution of these factors has not been proven yet. It has been suggested that copy number variation (CNV) duplication and the deletion of many genes in chromosome 22 (Ch22) may have a strong association with ASD. This study screened the CNVs in Ch22 in autistic Saudi children and assessed the candidate gene in the CNVs region of Ch22 that is most associated with ASD.

Methods

This study included 15 autistic Saudi children as well as 4 healthy children as controls; DNA was extracted from samples and analyzed using array comparative genomic hybridization (aCGH) and DNA sequencing.

Results

The aCGH detected (in only 6 autistic samples) deletion and duplication in many regions of Ch22, including some critical genes. Moreover, DNA sequencing determined a genetic mutation in the TBX1 gene sequence in autistic samples. This study, carried out using aCGH, found that six autistic patients had CNVs in Ch22, and DNA sequencing revealed mutations in the TBX1 gene in autistic samples but none in the control.

Conclusion

CNV deletion and the duplication of the TBX1 gene could be related to ASD; therefore, this gene needs more analysis in terms of expression levels.

Clinical Discordance in Monozygotic Twins With Autism Spectrum Disorder

There is a significant concordance of autism spectrum disorder in monozygotic (MZ) twins, where behavioral manifestations are heavily influenced by genetic factors. We describe a case of male monozygotic twins with autism spectrum disorder (ASD), raised in the same household, that present with different clinical manifestations. One of the twins presents with intermittent frank syncopal episodes, sinus bradycardia, and elevated alkaline phosphatase (ALP), while the other has symptoms of attention-deficit/hyperactivity disorder (ADHD), normal cardiological findings, and normal ALP level. The clinical discordance in this pair of monozygotic twins may be due to any of the following: 1) neuroanatomic cerebellar differences, 2) variable expression of genotype, and 3) inconsistent neurotransmitter regulation.

A systematic review of common genetic variation and biological pathways in autism spectrum disorder

Background

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by persistent deficits in social communication and interaction. Common genetic variation appears to play a key role in the development of this condition. In this systematic review, we describe the relationship between genetic variations and autism. We created a gene dataset of the genes involved in the pathogenesis of autism and performed an over-representation analysis to evaluate the biological functions and molecular pathways that may explain the associations between these variants and the development of ASD.

Results

177 studies and a gene set composed of 139 were included in this qualitative systematic review. Enriched pathways in the over-representation analysis using the KEGG pathway database were mostly associated with neurotransmitter receptors and their subunits. Major over-represented biological processes were social behavior, vocalization behavior, learning and memory. The enriched cellular component of the proteins encoded by the genes identified in this systematic review were the postsynaptic membrane and the cell junction.

Conclusions

Among the biological processes that were examined, genes involved in synaptic integrity, neurotransmitter metabolism, and cell adhesion molecules were significantly involved in the development of autism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00662-z.

The epigenetic regulation of synaptic genes contributes to the etiology of autism

Epigenetic mechanisms greatly affect the developing brain, as well as the maturation of synapses with pervasive, long-lasting consequences on behavior in adults. Substantial evidence exists that implicates dysregulation of epigenetic mechanisms in the etiology of neurodevelopmental disorders. Therefore, this review explains the role of enzymes involved in DNA methylation and demethylation in neurodevelopment by emphasizing changes of synaptic genes and proteins. Epigenetic causes of sex-dependent differences in the brain are analyzed in conjunction with the pathophysiology of autism spectrum disorders. Special attention is devoted to the epigenetic regulation of the melanoma-associated antigen-like gene 2 (MAGEL2) found in Prader-Willi syndrome, which is known to be accompanied by autistic symptoms.

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

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

Neuroligin dependence of social behaviour in Caenorhabditis elegans provides a model to investigate an autism-associated gene

Autism spectrum disorder (ASD) is characterized by a triad of behavioural impairments including social behaviour. Neuroligin, a trans-synaptic adhesion molecule, has emerged as a penetrant genetic determinant of behavioural traits that signature the neuroatypical behaviours of autism. However, the function of neuroligin in social circuitry and the impact of genetic variation to this gene is not fully understood. Indeed, in animal studies designed to model autism, there remains controversy regarding the role of neuroligin dysfunction in the expression of disrupted social behaviours. The model organism, Caenorhabditis elegans, offers an informative experimental platform to investigate the impact of genetic variants on social behaviour. In a number of paradigms, it has been shown that inter-organismal communication by chemical cues regulates C. elegans social behaviour. We utilize this social behaviour to investigate the effect of autism-associated genetic variants within the social domain of the research domain criteria. We have identified neuroligin as an important regulator of social behaviour and segregate the importance of this gene to the recognition and/or processing of social cues. We also use CRISPR/Cas9 to edit an R-C mutation that mimics a highly penetrant human mutation associated with autism. C. elegans carrying this mutation phenocopy the behavioural dysfunction of a C. elegans neuroligin null mutant, thus confirming its significance in the regulation of animal social biology. This highlights that quantitative behaviour and precision genetic intervention can be used to manipulate discrete social circuits of the worm to provide further insight into complex social behaviour.

Systems biology reveals reprogramming of the S-nitroso-proteome in the cortical and striatal regions of mice during aging process

Cell aging depends on the rate of cumulative oxidative and nitrosative damage to DNA and proteins. Accumulated data indicate the involvement of protein S-nitrosylation (SNO), the nitric oxide (NO)-mediated posttranslational modification (PTM) of cysteine thiols, in different brain disorders. However, the changes and involvement of SNO in aging including the development of the organism from juvenile to adult state is still unknown. In this study, using the state-of-the-art mass spectrometry technology to identify S-nitrosylated proteins combined with large-scale computational biology, we tested the S-nitroso-proteome in juvenile and adult mice in both cortical and striatal regions. We found reprogramming of the S-nitroso-proteome in adult mice of both cortex and striatum regions. Significant biological processes and protein–protein clusters associated with synaptic and neuronal terms were enriched in adult mice. Extensive quantitative analysis revealed a large set of potentially pathological proteins that were significantly upregulated in adult mice. Our approach, combined with large scale computational biology allowed us to perform a system-level characterization and identification of the key proteins and biological processes that can serve as drug targets for aging and brain disorders in future studies.

Cortical Gray Matter Injury in Encephalopathy of Prematurity: Link to Neurodevelopmental Disorders

Preterm-born infants frequently suffer from an array of neurological damage, collectively termed encephalopathy of prematurity (EoP). They also have an increased risk of presenting with a neurodevelopmental disorder (e.g., autism spectrum disorder; attention deficit hyperactivity disorder) later in life. It is hypothesized that it is the gray matter injury to the cortex, in addition to white matter injury, in EoP that is responsible for the altered behavior and cognition in these individuals. However, although it is established that gray matter injury occurs in infants following preterm birth, the exact nature of these changes is not fully elucidated. Here we will review the current state of knowledge in this field, amalgamating data from both clinical and preclinical studies. This will be placed in the context of normal processes of developmental biology and the known pathophysiology of neurodevelopmental disorders. Novel diagnostic and therapeutic tactics required integration of this information so that in the future we can combine mechanism-based approaches with patient stratification to ensure the most efficacious and cost-effective clinical practice.

Brain Opioid Activity and Oxidative Injury: Different Molecular Scenarios Connecting Celiac Disease and Autistic Spectrum Disorder

Celiac Disease (CD) is an immune-mediated disease triggered by the ingestion of wheat gliadin and related prolamins from other cereals, such as barley and rye. Immunity against these cereal-derived proteins is mediated by pro-inflammatory cytokines produced by both innate and adaptive system response in individuals unable to adequately digest them. Peptides generated in this condition are absorbed across the gut barrier, which in these patients is characterized by the deregulation of its permeability. Here, we discuss a possible correlation between CD and Autistic Spectrum Disorder (ASD) pathogenesis. ASD can be induced by an excessive and inappropriate brain opioid activity during the neonatal period. Cereal-derived peptides produced in celiac patients cross the blood-brain barrier and bind to endogenous opioid receptors interfering with neurotransmission and generating deleterious effects on brain maturation, learning and social relations. Moreover, an increase in oxidative stress and a decrease in the antioxidant capacity, as well as an extended mitochondrial impairment in the brain, could represent a possible connection between ASD and CD. Therefore, we critically discuss the proposed relationship between ASD and CD and the possible usefulness of a gluten-free diet in ASD patients.

Maternal Immune Activation Induces Neuroinflammation and Cortical Synaptic Deficits in the Adolescent Rat Offspring

Maternal immune activation (MIA), induced by infection during pregnancy, is an important risk factor for neuro-developmental disorders, such as autism. Abnormal maternal cytokine signaling may affect fetal brain development and contribute to neurobiological and behavioral changes in the offspring. Here, we examined the effect of lipopolysaccharide-induced MIA on neuro-inflammatory changes, as well as synaptic morphology and key synaptic protein level in cerebral cortex of adolescent male rat offspring. Adolescent MIA offspring showed elevated blood cytokine levels, microglial activation, increased pro-inflammatory cytokines expression and increased oxidative stress in the cerebral cortex. Moreover, pathological changes in synaptic ultrastructure of MIA offspring was detected, along with presynaptic protein deficits and down-regulation of postsynaptic scaffolding proteins. Consequently, ability to unveil MIA-induced long-term alterations in synapses structure and protein level may have consequences on postnatal behavioral changes, associated with, and predisposed to, the development of neuropsychiatric disorders.

DNA Methylation Associated with Mitochondrial Dysfunction in a South African Autism Spectrum Disorder Cohort

Autism spectrum disorder (ASD) is characterized by phenotypic heterogeneity and a complex genetic architecture which includes distinctive epigenetic patterns. We report differential DNA methylation patterns associated with ASD in South African children. An exploratory whole‐epigenome methylation screen using the Illumina 450 K MethylationArray identified differentially methylated CpG sites between ASD and controls that mapped to 898 genes (P ≤ 0.05) which were enriched for nine canonical pathways converging on mitochondrial metabolism and protein ubiquitination. Targeted Next Generation Bisulfite Sequencing of 27 genes confirmed differential methylation between ASD and control in our cohort. DNA pyrosequencing of two of these genes, the mitochondrial enzyme Propionyl‐CoA Carboxylase subunit Beta (PCCB) and Protocadherin Alpha 12 (PCDHA12), revealed a wide range of methylation levels (9–49% and 0–54%, respectively) in both ASD and controls. Three CpG loci were differentially methylated in PCCB (P ≤ 0.05), while PCDHA12, previously linked to ASD, had two significantly different CpG sites (P ≤ 0.001) between ASD and control. Differentially methylated CpGs were hypomethylated in ASD. Metabolomic analysis of urinary organic acids revealed that three metabolites, 3‐hydroxy‐3‐methylglutaric acid (P = 0.008), 3‐methyglutaconic acid (P = 0.018), and ethylmalonic acid (P = 0.043) were significantly elevated in individuals with ASD. These metabolites are directly linked to mitochondrial respiratory chain disorders, with a putative link to PCCB, consistent with impaired mitochondrial function. Our data support an association between DNA methylation and mitochondrial dysfunction in the etiology of ASD. Autism Res 2020, 13: 1079‐1093. © 2020 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc.

Lay Summary

Epigenetic changes are chemical modifications of DNA which can change gene function. DNA methylation, a type of epigenetic modification, is linked to autism. We examined DNA methylation in South African children with autism and identified mitochondrial genes associated with autism. Mitochondria are power‐suppliers in cells and mitochondrial genes are essential to metabolism and energy production, which are important for brain cells during development. Our findings suggest that some individuals with ASD also have mitochondrial dysfunction.

Changes in the Expression of SNAP-25 Protein in the Brain of Juvenile Rats in Two Models of Autism

The results of genetic studies suggest a possible role for SNAP-25 polymorphism in the development of autism spectrum disorders (ASDs); however, there are no data available on whether changes in SNAP-25 expression also affect animals in rodent models of ASD. The aim of the present study was to explore this issue. The studies included 1-month-old rats representing valproic acid (VPA)- and thalidomide (THAL)-induced models of autism. Their mothers received single doses of VPA (800 mg/kg) or THAL (500 mg/kg) per os on the 11th day of gestation. SNAP-25 protein content in the cerebellum, hippocampus, and frontal lobe was determined using Western blotting, while changes of mRNA levels of Snap25 gene were determined using real-time polymerase chain reaction. Compared to controls, SNAP-25 content was decreased by approximately 35% in all brain structures tested, in both males and females, exclusively in the VPA group. In contrast to this, Snap25 expression, studied in males, was increased in the hippocampus and cerebellum in both, VPA- and THAL-treated rats. We discuss the compliance of these results with the hypothesized role of SNAP-25 in the pathophysiology of ASD and the adequacy of the experimental models used.

Genetic Causes and Modifiers of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is one of the most prevalent neurodevelopmental disorders, affecting an estimated 1 in 59 children. ASD is highly genetically heterogeneous and may be caused by both inheritable and de novo gene variations. In the past decade, hundreds of genes have been identified that contribute to the serious deficits in communication, social cognition, and behavior that patients often experience. However, these only account for 10-20% of ASD cases, and patients with similar pathogenic variants may be diagnosed on very different levels of the spectrum. In this review, we will describe the genetic landscape of ASD and discuss how genetic modifiers such as copy number variation, single nucleotide polymorphisms, and epigenetic alterations likely play a key role in modulating the phenotypic spectrum of ASD patients. We also consider how genetic modifiers can alter convergent signaling pathways and lead to impaired neural circuitry formation. Lastly, we review sex-linked modifiers and clinical implications. Further understanding of these mechanisms is crucial for both comprehending ASD and for developing novel therapies.

Identification of rare copy number variations reveals PJA2, APCS, SYNPO, and TAC1 as novel candidate genes in Autism Spectrum Disorders

Background

There is a strong evidence for genetic factors as the main causes of Autism Spectrum Disorders (ASD). To date, hundreds of genes have been identified either by copy number variations (CNVs) and/or single nucleotide variations. However, despite all the findings, the genetics of these disorders have not been totally explored.

Methods

Thus, the aim of our work was to identify rare CNVs and genes present in these regions in ASD children, using a high‐resolution comparative genomic hybridization technique and quantitative PCR (qPCR) approach.

Results

Our results have shown 60–70 chromosomal aberrations per patient. We have initially selected 66 CNVs that have been further assessed using qPCR. Finally, we have validated 22 CNVs including 11 deletions and 11 duplications. Ten CNVs are de novo, 11 are inherited and one of unknown origin of transmission. Among the CNVs detected, novel ASD candidate genes PJA2, SYNPO, APCS, and TAC1 have been identified in our group of Lebanese patients. In addition, previously described CNVs have been identified containing genes such as SHANK3, MBP, CHL1, and others.

Conclusion

Our study broadens the population spectrum of studied ASD patients and adds new candidates at the list of genes contributing to these disorders.

Retinal alterations in a pre-clinical model of an autism spectrum disorder

Background

Autism spectrum disorders (ASD) affect around 1.5% of people worldwide. Symptoms start around age 2, when children fail to maintain eye contact and to develop speech and other forms of communication. Disturbances in glutamatergic and GABAergic signaling that lead to synaptic changes and alter the balance between excitation and inhibition in the developing brain are consistently found in ASD. One of the hallmarks of these disorders is hypersensitivity to sensory stimuli; however, little is known about its underlying causes. Since the retina is the part of the CNS that converts light into a neuronal signal, we set out to study how it is affected in adolescent mice prenatally exposed to valproic acid (VPA), a useful tool to study ASD endophenotypes.

Methods

Pregnant female mice received VPA (600 mg/kg, ip) or saline at gestational day 11. Their male adolescent pups (P29–35) were behaviorally tested for anxiety and social interaction. Proteins known to be related with ASD were quantified and visualized in their retinas by immunoassays, and retinal function was assessed by full-field scotopic electroretinograms (ERGs).

Results

Early adolescent mice prenatally exposed to VPA displayed impaired social interest and increased anxiety-like behaviors consistent with an ASD phenotype. The expression of GABA, GAD, synapsin-1, and FMRP proteins were reduced in their retinas, while mGluR5 was increased. The a-wave amplitudes of VPA-exposed were smaller than those of CTR animals, whereas the b-wave and oscillatory potentials were normal.

Conclusions

This study establishes that adolescent male mice of the VPA-induced ASD model have alterations in retinal function and protein expression compatible with those found in several brain areas of other autism models. These results support the view that synaptic disturbances with excitatory/inhibitory imbalance early in life are associated with ASD and point to the retina as a window to understand their subjacent mechanisms.

Electronic supplementary material

The online version of this article (10.1186/s13229-019-0270-8) contains supplementary material, which is available to authorized users.

Growth and excitability at synapsin II deficient hippocampal neurons

Synapsins are neuronal phosphoproteins that fine-tune synaptic transmission and suppress seizure activity. Synapsin II (SynII) deletion produces epileptic seizures and overexcitability in neuronal networks. Early studies in primary neuronal cultures have shown that SynII deletion results in a delay in synapse formation. More recent studies at hippocampal slices have revealed increased spontaneous activity in SynII knockout (SynII(-)) mice. To reconcile these observations, we systematically re-examined synaptic transmission, synapse formation, and neurite growth in primary hippocampal neuronal cultures. We find that spontaneous glutamatergic synaptic activity was suppressed in SynII(-) neurons during the initial developmental epoch (7 days in vitro, DIV) but was enhanced at later times (12 and18 DIV). The density of synapses, transmission between connected pairs of neurons, and the number of docked synaptic vesicles were not affected by SynII deletion. However, we found that neurite outgrowth in SynII(-) neurons was suppressed during the initial developmental epoch (7 DIV) but enhanced at subsequent developmental stages (12 and18 DIV). This finding can account for the observed effect of SynII deletion on synaptic activity. To test whether the observed phenotype resulted directly from the deletion of SynII we expressed SynII in SynII(-) cultures using an adeno-associated virus (AAV). Expression of SynII at 2 DIV rescued the SynII deletion-dependent alterations in both synaptic activity and neuronal growth. To test whether the increased neurite outgrowth in SynII(-) observed at DIV 12 and18 represents an overcompensation for the initial developmental delay or results directly from SynII deletion we performed "late expression" experiments, transfecting SynII(-) cultures with AAV at 7 DIV. The late SynII expression suppressed neurite outgrowth at 12 and 18 DIV to the levels observed in control neurons, suggesting that these phenotypes directly depend on SynII. These results reveal a novel developmentally regulated role for SynII function in the control of neurite growth.

Environmental and Genetic Factors in Autism Spectrum Disorders: Special Emphasis on Data from Arabian Studies

One of the most common neurodevelopmental disorders worldwide is autism spectrum disorder (ASD), which is characterized by language delay, impaired communication interactions, and repetitive patterns of behavior caused by environmental and genetic factors. This review aims to provide a comprehensive survey of recently published literature on ASD and especially novel insights into excitatory synaptic transmission. Even though numerous genes have been discovered that play roles in ASD, a good understanding of the pathophysiologic process of ASD is still lacking. The protein⁻protein interactions between the products of NLGN, SHANK, and NRXN synaptic genes indicate that the dysfunction in synaptic plasticity could be one reason for the development of ASD. Designing more accurate diagnostic tests for the early diagnosis of ASD would improve treatment strategies and could enhance the appropriate monitoring of prognosis. This comprehensive review describes the psychotropic and antiepileptic drugs that are currently available as effective pharmacological treatments and provides in-depth knowledge on the concepts related to clinical, diagnostic, therapeutic, and genetic perspectives of ASD. An increase in the prevalence of ASD in Gulf Cooperation Council countries is also addressed in the review. Further, the review emphasizes the need for international networking and multidimensional studies to design novel and effective treatment strategies.

Role of Ectonucleotidases in Synapse Formation During Brain Development: Physiological and Pathological Implications

BACKGROUND

Extracellular adenine nucleotides and nucleosides, such as ATP and adenosine, are among the most recently identified and least investigated diffusible signaling factors that contribute to the structural and functional remodeling of the brain, both during embryonic and postnatal development. Their levels in the extracellular milieu are tightly controlled by various ectonucleotidases: ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPP), alkaline phosphatases (AP), ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) and ecto-5'- nucleotidase (eN).

METHODS

Studies related to the expression patterns of ectonucleotidases and their known features during brain development are reviewed, highlighting involvement of these enzymes in synapse formation and maturation in physiological as well as in pathological states.

RESULTS

During brain development and in adulthood all ectonucleotidases have diverse expression pattern, cell specific localization and function. NPPs are expressed at early embryonic days, but the expression of NPP3 is reduced and restricted to ependymal area in adult brain. NTPDase2 is dominant ectonucleotidase existing in the progenitor cells as well as main astrocytic NTPDase in the adult brain, while NTPDase3 is fully expressed after third postnatal week, almost exclusively on varicose fibers. Specific brain AP is functionally associated with synapse formation and this enzyme is sufficient for adenosine production during neurite growth and peak of synaptogenesis. eN is transiently associated with synapses during synaptogenesis, however in adult brain it is more glial than neuronal enzyme.

CONCLUSION

Control of extracellular adenine nucleotide levels by ectonucleotidases are important for understanding the role of purinergic signaling in developing tissues and potential targets in developmental disorders such as autism.

General Pathophysiology of Astroglia

Astroglial cells are involved in most if not in all pathologies of the brain. These cells can change the morpho-functional properties in response to pathology or innate changes of these cells can lead to pathologies. Overall pathological changes in astroglia are complex and diverse and often vary with different disease stages. We classify astrogliopathologies into reactive astrogliosis, astrodegeneration with astroglial atrophy and loss of function, and pathological remodelling of astrocytes. Such changes can occur in neurological, neurodevelopmental, metabolic and psychiatric disorders as well as in infection and toxic insults. Mutation in astrocyte-specific genes leads to specific pathologies, such as Alexander disease, which is a leukodystrophy. We discuss changes in astroglia in the pathological context and identify some molecular entities underlying pathology. These entities within astroglia may repent targets for novel therapeutic intervention in the management of brain pathologies.

Postsynaptic movement disorders: clinical phenotypes, genotypes, and disease mechanisms

Movement disorders comprise a group of heterogeneous diseases with often complex clinical phenotypes. Overlapping symptoms and a lack of diagnostic biomarkers may hamper making a definitive diagnosis. Next-generation sequencing techniques have substantially contributed to unraveling genetic etiologies underlying movement disorders and thereby improved diagnoses. Defects in dopaminergic signaling in postsynaptic striatal medium spiny neurons are emerging as a pathogenic mechanism in a number of newly identified hyperkinetic movement disorders. Several of the causative genes encode components of the cAMP pathway, a critical postsynaptic signaling pathway in medium spiny neurons. Here, we review the clinical presentation, genetic findings, and disease mechanisms that characterize these genetic postsynaptic movement disorders.

Altered synaptobrevin-II trafficking in neurons expressing a synaptophysin mutation associated with a severe neurodevelopmental disorder

Following exocytosis, synaptic vesicles (SVs) have to be reformed with the correct complement of proteins in the correct stoichiometry to ensure continued neurotransmission. Synaptophysin is a highly abundant, integral SV protein necessary for the efficient retrieval of the SV SNARE protein, synaptobrevin II (sybII). However the molecular mechanism underpinning synaptophysin-dependent sybII retrieval is still unclear. We recently identified a male patient with severe intellectual disability, hypotonia, epilepsy and callosal agenesis who has a point mutation in the juxtamembrane region of the fourth transmembrane domain of synaptophysin (T198I). This mutation had no effect on the activity-dependent retrieval of synaptophysin that was tagged with the genetically-encoded pH-sensitive reporter (pHluorin) in synaptophysin knockout hippocampal cultures. This suggested the mutant has no global effect on SV endocytosis, which was confirmed when retrieval of a different SV cargo (the glutamate transporter vGLUT1) was examined. However neurons expressing this T198I mutant did display impaired activity-dependent sybII retrieval, similar to that observed in synaptophysin knockout neurons. Interestingly this impairment did not result in an increased stranding of sybII at the plasma membrane. Screening of known human synaptophysin mutations revealed a similar presynaptic phenotype between T198I and a mutation found in X-linked intellectual disability. Thus this novel human synaptophysin mutation has revealed that aberrant retrieval and increased plasma membrane localisation of SV cargo can be decoupled in human disease.

Hsc70 chaperone activity is required for the cytosolic slow axonal transport of synapsin

Soluble cytosolic proteins vital to axonal and presynaptic function are synthesized in the neuronal soma and conveyed via slow axonal transport. Our previous studies suggest that the overall slow transport of synapsin is mediated by dynamic assembly/disassembly of cargo complexes followed by short-range vectorial transit (the "dynamic recruitment" model). However, neither the composition of these complexes nor the mechanistic basis for the dynamic behavior is understood. In this study, we first examined putative cargo complexes associated with synapsin using coimmunoprecipitation and multidimensional protein identification technology mass spectrometry (MS). MS data indicate that synapsin is part of a multiprotein complex enriched in chaperones/cochaperones including Hsc70. Axonal synapsin-Hsc70 coclusters are also visualized by two-color superresolution microscopy. Inhibition of Hsc70 ATPase activity blocked the slow transport of synapsin, disrupted axonal synapsin organization, and attenuated Hsc70-synapsin associations, advocating a model where Hsc70 activity dynamically clusters cytosolic proteins into cargo complexes, allowing transport. Collectively, our study offers insight into the molecular organization of cytosolic transport complexes and identifies a novel regulator of slow transport.

Selective lowering of synapsins induced by oligomeric α-synuclein exacerbates memory deficits

Mounting evidence indicates that soluble oligomeric forms of amyloid proteins linked to neurodegenerative disorders, such as amyloid-β (Aβ), tau, or α-synuclein (αSyn) might be the major deleterious species for neuronal function in these diseases. Here, we found an abnormal accumulation of oligomeric αSyn species in AD brains by custom ELISA, size-exclusion chromatography, and nondenaturing/denaturing immunoblotting techniques. Importantly, the abundance of αSyn oligomers in human brain tissue correlated with cognitive impairment and reductions in synapsin expression. By overexpressing WT human αSyn in an AD mouse model, we artificially enhanced αSyn oligomerization. These bigenic mice displayed exacerbated Aβ-induced cognitive deficits and a selective decrease in synapsins. Following isolation of various soluble αSyn assemblies from transgenic mice, we found that in vitro delivery of exogenous oligomeric αSyn but not monomeric αSyn was causing a lowering in synapsin-I/II protein abundance. For a particular αSyn oligomer, these changes were either dependent or independent on endogenous αSyn expression. Finally, at a molecular level, the expression of synapsin genes SYN1 and SYN2 was down-regulated in vivo and in vitro by αSyn oligomers, which decreased two transcription factors, cAMP response element binding and Nurr1, controlling synapsin gene promoter activity. Overall, our results demonstrate that endogenous αSyn oligomers can impair memory by selectively lowering synapsin expression.

Synaptic UNC13A protein variant causes increased neurotransmission and dyskinetic movement disorder

Munc13 proteins are essential regulators of neurotransmitter release at nerve cell synapses. They mediate the priming step that renders synaptic vesicles fusion-competent, and their genetic elimination causes a complete block of synaptic transmission. Here we have described a patient displaying a disorder characterized by a dyskinetic movement disorder, developmental delay, and autism. Using whole-exome sequencing, we have shown that this condition is associated with a rare, de novo Pro814Leu variant in the major human Munc13 paralog UNC13A (also known as Munc13-1). Electrophysiological studies in murine neuronal cultures and functional analyses in Caenorhabditis elegans revealed that the UNC13A variant causes a distinct dominant gain of function that is characterized by increased fusion propensity of synaptic vesicles, which leads to increased initial synaptic vesicle release probability and abnormal short-term synaptic plasticity. Our study underscores the critical importance of fine-tuned presynaptic control in normal brain function. Further, it adds the neuronal Munc13 proteins and the synaptic vesicle priming process that they control to the known etiological mechanisms of psychiatric and neurological synaptopathies.

Translational potential of astrocytes in brain disorders

Fundamentally, all brain disorders can be broadly defined as the homeostatic failure of this organ. As the brain is composed of many different cells types, including but not limited to neurons and glia, it is only logical that all the cell types/constituents could play a role in health and disease. Yet, for a long time the sole conceptualization of brain pathology was focused on the well-being of neurons. Here, we challenge this neuron-centric view and present neuroglia as a key element in neuropathology, a process that has a toll on astrocytes, which undergo complex morpho-functional changes that can in turn affect the course of the disorder. Such changes can be grossly identified as reactivity, atrophy with loss of function and pathological remodeling. We outline the pathogenic potential of astrocytes in variety of disorders, ranging from neurotrauma, infection, toxic damage, stroke, epilepsy, neurodevelopmental, neurodegenerative and psychiatric disorders, Alexander disease to neoplastic changes seen in gliomas. We hope that in near future we would witness glial-based translational medicine with generation of deliverables for the containment and cure of disorders. We point out that such as a task will require a holistic and multi-disciplinary approach that will take in consideration the concerted operation of all the cell types in the brain.

Analysis of Extracellular Nucleotide Metabolism in Adult Zebrafish After Embryological Exposure to Valproic Acid

Autism is a neurodevelopmental disorder characterized by symptoms related to stereotyped movements, deficits in social interaction, impaired communication, anxiety, hyperactivity, and the presence of restricted interests. Evidence indicates an important role of extracellular ATP and adenosine as signaling molecules in autism. ATP hydrolysis by ectonucleotidases is an important source of adenosine, and adenosine deaminase (ADA) contributes to the control of the nucleoside concentrations. Considering zebrafish is an animal model that may contribute towards to understanding the mechanisms that underlie social behavior, we investigated the purinergic signaling in a model of embryological exposure to valproic acid (VPA) that induces social interaction deficit in adult zebrafish. We demonstrated embryological exposure to VPA did not change ATP and ADP hydrolysis in zebrafish at 120 dpf, and the cytosolic (soluble) ADA activity was not altered. However, we observed an increase of AMP hydrolysis (12.5 %) whereas the ecto-ADA activity was decreased (19.2 %) in adult zebrafish submitted to embryological exposure to VPA. Quantitative reverse transcription PCR (RT-PCR) analysis showed changes on ntpd8, ADA 2.1, and A2a1 mRNA transcript levels. Brain ATP metabolism showed a rapid catabolism of ATP and ADP, whereas the extracellular metabolism of AMP and adenosine (ADO) occurred slowly. We demonstrated that embryological exposure to VPA altered biochemical and molecular parameters related to purinergic system in adult zebrafish. These findings indicate that the enzyme activities involved in the control of ATP and adenosine levels may be involved in the pathophysiological mechanisms of diseases related to the impairment of social interaction, such as autism.

Autism and Epilepsy: Exploring the Relationship Using Experimental Models

The common co-occurrence of autism and epilepsy suggests that certain neurobiological mechanisms are shared between these disorders. In particular, the profusion of novel genetic mutations being discovered in autism and epilepsy points to abnormalities in synapse formation and function that alter the balance between neuronal excitation and inhibition. Animal models can be informative in sorting out the medical and behavioral complexities in autism and epilepsy and the relationship between them. As mechanistic information accrues, it is anticipated that mutation- and pathway-specific targeted treatments can be developed.

Identification of a human synaptotagmin-1 mutation that perturbs synaptic vesicle cycling

Synaptotagmin-1 (SYT1) is a calcium-binding synaptic vesicle protein that is required for both exocytosis and endocytosis. Here, we describe a human condition associated with a rare variant in SYT1. The individual harboring this variant presented with an early onset dyskinetic movement disorder, severe motor delay, and profound cognitive impairment. Structural MRI was normal, but EEG showed extensive neurophysiological disturbances that included the unusual features of low-frequency oscillatory bursts and enhanced paired-pulse depression of visual evoked potentials. Trio analysis of whole-exome sequence identified a de novo SYT1 missense variant (I368T). Expression of rat SYT1 containing the equivalent human variant in WT mouse primary hippocampal cultures revealed that the mutant form of SYT1 correctly localizes to nerve terminals and is expressed at levels that are approximately equal to levels of endogenous WT protein. The presence of the mutant SYT1 slowed synaptic vesicle fusion kinetics, a finding that agrees with the previously demonstrated role for I368 in calcium-dependent membrane penetration. Expression of the I368T variant also altered the kinetics of synaptic vesicle endocytosis. Together, the clinical features, electrophysiological phenotype, and in vitro neuronal phenotype associated with this dominant negative SYT1 mutation highlight presynaptic mechanisms that mediate human motor control and cognitive development.