Genetic and Environmental Contributions to Autism Spectrum Disorder Through Mechanistic Target of Rapamycin

Methods for Assessing Neurodevelopmental Disorders in Mice: A Critical Review of Behavioral Tests and Methodological Considerations Searching to Improve Reliability

Many neurobehavioral tests are used for the assessment of human-like behaviors in animals. Most of them were developed in rodents and are used for the assessment of animal models that mimic human neurodevelopmental and neuropsychiatric disorders (NDDs). We have described tests for assessing social behavior, social interaction, and social communication; tests for restricted and repetitive behaviors; tests for cognitive impairment, for sensory stimuli, for anxiety like behavior, and for motor coordination deviations. These tests are used to demonstrate autistic-like behavior as well as other NDDs. We described possible general pitfalls in the performance of such studies, as well as probable individual errors for each group of tests assessing specific behavior. The mentioned pitfalls may induce crucial errors in the interpretation of the results, minimizing the reliability of specific models of defined human NDD. It is imperative to minimize these pitfalls and use sufficient and reliable tests that can demonstrate as many of the traits of the human disorder, grade the severity of the specific deviations and the severity of the tested NDD by using a scoring system. Due to possible gender differences in the clinical presentations of NDD, it is important to carry out studies on males and females.

Soluble epoxide hydrolase deletion rescues behavioral and synaptic deficits by AMPK-mTOR pathway in autism animals

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social defects often accompanied with emotional comorbidities. Aberrations in synaptic function and plasticity are the core feature in the pathophysiology of ASD. Targeting soluble epoxide hydrolase (sEH) has been found to exert protection in a wide-range of pathological conditions. However, the regulation of sEH deficiency on the synaptic deficits of ASD and the underlying mechanisms remain unclear. The valproate (VPA)-treated ASD animal model with genetic sEH knockout was applied in the present study. The results showed that the sEH expression was significantly increased in the prefrontal cortex of VPA-treated animals. Although no effect was found on tail malformation and body weight loss, genetic sEH deletion alleviated social deficits, and fear learning and memory extinction in the VPA-treated mice. After a series of electrophysiological assessments, we found that the beneficial effects of sEH deletion focused on the long-term synaptic plasticity, rather than presynaptic efficiency, in the VPA-treated mice. Furthermore, we observed that the dysregulated AMPK-mTOR pathway was restored under genetic sEH deletion in VPA-treated mice. Taken together, these findings uncovered an important role of sEH deficiency in the synaptic dysfunctions of ASD mediated by AMPK-mTOR pathway, providing a novel therapeutic target for ASD.

The Development of Methods of BLOTCHIP®-MS for Peptidome: Small Samples in Tuberous Sclerosis

Mutations in TSC1 or TSC2 in axons induce tuberous sclerosis complex. Neurological manifestations mainly include epilepsy and autism spectrum disorder (ASD). ASD is the presenting symptom (25-50% of patients). ASD was observed at significantly higher frequencies in participants with TSC2 than those with TSC1 mutations. The occurrence of TSC2 mutations is about 50% larger than TSC1. Therefore, ASD may develop due to TSC2 deficiency. TSC2 regulates microRNA biogenesis and Microprocessor activity via GSK3β. Of reference, everolimus has the best treatment target because of the higher potency of interactions with mTORC2 rather than rapamycin. Mutations in the TSC1 and TSC2 genes result in the constitutive hyperactivation of the mammalian target of the rapamycin (mTOR) pathway, contributing to the growth of benign tumors or hamartomas in various organs. TSC2 mutations were associated with a more severe phenotypic spectrum than TSC1 mutations because of the inhibition of the mTOR cascade. There are few studies on the peptide analysis of this disorder in relation to everolimus. Only one study reported that, in ten plasma samples, pre-melanosome protein (PMEL) and S-adenosylmethionine (SAM) were significantly changed as diagnostic prognostic effects. Our study on peptide analysis in Protosera Inc (Osaka, Japan) revealed that three peptides that were related to inflammation in two patients with tuberous sclerosis, who showed a 30% decrease in ASD symptoms following everolimus treatment. TSC2 mutations were associated with a more severe phenotypic spectrum due to the inhibition of the mTOR cascade. PMEL and SAM were significantly changed as diagnostic effects.

Alleviation of Autophagic Deficits and Neuroinflammation by Histamine H3 Receptor Antagonist E159 Ameliorates Autism-Related Behaviors in BTBR Mice

BACKGROUND/OBJECTIVES

Autism spectrum disorder (ASD) is a neurodevelopmental condition marked by social interaction difficulties, repetitive behaviors, and immune dysregulation with elevated pro-inflammatory markers. Autophagic deficiency also contributes to social behavior deficits in ASD. Histamine H3 receptor (H3R) antagonism is a potential treatment strategy for brain disorders with features overlapping ASD, such as schizophrenia and Alzheimer's disease.

METHODS

This study investigated the effects of sub-chronic systemic treatment with the H3R antagonist E159 on social deficits, repetitive behaviors, neuroinflammation, and autophagic disruption in male BTBR mice.

RESULTS

E159 (2.5, 5, and 10 mg/kg, i.p.) improved stereotypic repetitive behavior by reducing self-grooming time and enhancing spontaneous alternation in addition to attenuating social deficits. It also decreased pro-inflammatory cytokines in the cerebellum and hippocampus of treated BTBR mice. In BTBR mice, reduced expression of autophagy-related proteins LC3A/B and Beclin 1 was observed, which was elevated following treatment with E159, attenuating the disruption in autophagy. The co-administration with the H3R agonist MHA (10 mg/kg, i.p.) reversed these effects, highlighting the role of histaminergic neurotransmission in observed behavioral improvements.

CONCLUSIONS

These preliminary findings suggest the therapeutic potential of H3R antagonists in targeting neuroinflammation and autophagic disruption to improve ASD-like behaviors.

Role of FMRP in AKT/mTOR pathway-mediated hippocampal autophagy in fragile X syndrome

Fragile X syndrome (FXS) is caused by epigenetic silencing of the Fmr1 gene, leading to the deletion of the coding protein FMRP. FXS induces abnormal hippocampal autophagy and mTOR overactivation. However, it remains unclear whether FMRP regulates hippocampal autophagy through the AKT/mTOR pathway, which influences the neural behavior of FXS. Our study revealed that FMRP deficiency increased the protein levels of p-ULK-1 and p62 and decreased LC3II/LC3I level in Fmr1 knockout (KO) mice. The mouse hippocampal neuronal cell line HT22 with knockdown of Fmr1 by lentivirus showed that the protein levels of p-ULK-1 and p62 were increased, whereas LC3II/LC3I was unchanged. Further observations revealed that FMRP deficiency obstructed autophagic flow in HT22 cells. Therefore, FMRP deficiency inhibited autophagy in the mouse hippocampus and HT22 cells. Moreover, FMRP deficiency increased reactive oxygen species (ROS) level, decreased the co-localization between the mitochondrial outer membrane proteins TOM20 and LC3 in HT22 cells, and caused a decrease in the mitochondrial autophagy protein PINK1 in HT22 cells and Fmr1 KO mice, indicating that FMRP deficiency caused mitochondrial autophagy disorder in HT22 cells and Fmr1 KO mice. To explore the mechanism by which FMRP deficiency inhibits autophagy, we examined the AKT/mTOR signaling pathway in the hippocampus of Fmr1 KO mice, found that FMRP deficiency caused overactivation of the AKT/mTOR pathway. Rapamycin-mediated mTOR inhibition activated and enhanced mitochondrial autophagy. Finally, we examined whether rapamycin affected the neurobehavior of Fmr1 KO mice. The Fmr1 KO mice exhibited stereotypical behavior, impaired social ability, and learning and memory impairment, while rapamycin treatment improved behavioral disorders in Fmr1 KO mice. Thus, our study revealed the molecular mechanism by which FMRP regulates autophagy function, clarifying the role of hippocampal neuron mitochondrial autophagy in the pathogenesis of FXS, and providing novel insights into potential therapeutic targets of FXS.

Acute rapamycin treatment reveals novel mechanisms of behavioral, physiological, and functional dysfunction in a maternal inflammation mouse model of autism and sensory over-responsivity

Maternal inflammatory response (MIR) during early gestation in mice induces a cascade of physiological and behavioral changes that have been associated with autism spectrum disorder (ASD). In a prior study and the current one, we find that mild MIR results in chronic systemic and neuro-inflammation, mTOR pathway activation, mild brain overgrowth followed by regionally specific volumetric changes, sensory processing dysregulation, and social and repetitive behavior abnormalities. Prior studies of rapamycin treatment in autism models have focused on chronic treatments that might be expected to alter or prevent physical brain changes. Here, we have focused on the acute effects of rapamycin to uncover novel mechanisms of dysfunction and related to mTOR pathway signaling. We find that within 2 hours, rapamycin treatment could rapidly rescue neuronal hyper-excitability, seizure susceptibility, functional network connectivity and brain community structure, and repetitive behaviors and sensory over-responsivity in adult offspring with persistent brain overgrowth. These CNS-mediated effects are also associated with alteration of the expression of several ASD-,ion channel-, and epilepsy-associated genes, in the same time frame. Our findings suggest that mTOR dysregulation in MIR offspring is a key contributor to various levels of brain dysfunction, including neuronal excitability, altered gene expression in multiple cell types, sensory functional network connectivity, and modulation of information flow. However, we demonstrate that the adult MIR brain is also amenable to rapid normalization of these functional changes which results in the rescue of both core and comorbid ASD behaviors in adult animals without requiring long-term physical alterations to the brain. Thus, restoring excitatory/inhibitory imbalance and sensory functional network modularity may be important targets for therapeutically addressing both primary sensory and social behavior phenotypes, and compensatory repetitive behavior phenotypes.

Copy number variations in autistic children

Autism spectrum disorder (ASD) manifests as a neurodevelopmental condition marked by challenges in social communication, interaction and the performing of repetitive behaviors. The prevalence of autism increases markedly on an annual basis; however, the etiology remains incompletely understood. Cytogenetically visible chromosomal abnormalities, including copy number variations (CNVs), have been shown to contribute to the pathogenesis of ASD. More than 1% of ASD conditions can be explained based on a known genetic locus, whereas CNVs account for 5-10% of cases. However, there are no studies on the Saudi Arabian population for the detection of CNVs linked to ASD, to the best of our knowledge. Therefore, the aim of the present study was to explore the prevalence of CNVs in autistic Saudi Arabian children. Genomic DNA was extracted from the peripheral blood of 14 autistic children along with four healthy control children and then array-based comparative genomic hybridization (aCGH) was used to detect CNVs. Bioinformatics analysis of the aCGH results showed the presence of recurrent and non-recurrent deletion/duplication CNVs in several regions of the genome of autistic children. The most frequent CNVs were 1q21.2, 3p26.3, 4q13.2, 6p25.3, 6q24.2, 7p21.1, 7q34, 7q11.1, 8p23.2, 13q32.3, 14q11.1-q11.2 and 15q11.1-q11.2. In the present study, CNVs in autistic Saudi Arabian children were identified to improve the understanding of the etiology of autism and facilitate its diagnosis. Additionally, the present study identified certain possible pathogenic genes in the CNV region associated with several developmental and neurogenetic diseases.

Targeting Microglia in Neuroinflammation: H3 Receptor Antagonists as a Novel Therapeutic Approach for Alzheimer's Disease, Parkinson's Disease, and Autism Spectrum Disorder

Histamine performs dual roles as an immune regulator and a neurotransmitter in the mammalian brain. The histaminergic system plays a vital role in the regulation of wakefulness, cognition, neuroinflammation, and neurogenesis that are substantially disrupted in various neurodegenerative and neurodevelopmental disorders. Histamine H3 receptor (H3R) antagonists and inverse agonists potentiate the endogenous release of brain histamine and have been shown to enhance cognitive abilities in animal models of several brain disorders. Microglial activation and subsequent neuroinflammation are implicated in impacting embryonic and adult neurogenesis, contributing to the development of Alzheimer's disease (AD), Parkinson's disease (PD), and autism spectrum disorder (ASD). Acknowledging the importance of microglia in both neuroinflammation and neurodevelopment, as well as their regulation by histamine, offers an intriguing therapeutic target for these disorders. The inhibition of brain H3Rs has been found to facilitate a shift from a proinflammatory M1 state to an anti-inflammatory M2 state, leading to a reduction in the activity of microglial cells. Also, pharmacological studies have demonstrated that H3R antagonists showed positive effects by reducing the proinflammatory biomarkers, suggesting their potential role in simultaneously modulating crucial brain neurotransmissions and signaling cascades such as the PI3K/AKT/GSK-3β pathway. In this review, we highlight the potential therapeutic role of the H3R antagonists in addressing the pathology and cognitive decline in brain disorders, e.g., AD, PD, and ASD, with an inflammatory component.

Cancer drug repurposing in autism spectrum disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with uncertain origins. Understanding of the mechanisms underlying ASD remains limited, and treatments are lacking. Genetic diversity complicates drug development. Given the complexity and severity of ASD symptoms and the rising number of diagnoses, exploring novel therapeutic strategies is essential. Here, we focus on shared molecular pathways between ASD and cancer and highlight recent progress on the repurposing of cancer drugs for ASD treatment, such as mTOR inhibitors, histone deacetylase inhibitors, and anti-inflammatory agents. We discuss how to improve trial design considering drug dose and patient age. Lastly, the discussion explores the critical aspects of side effects, commercial factors, and the efficiency of drug-screening pipelines; all of which are essential considerations in the pursuit of repurposing cancer drugs for addressing core features of ASD.

mTOR Signaling Disruption and Its Association with the Development of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by impairments in social interaction and communication along with repetitive stereotypic behaviors. Currently, there are no specific biomarkers for diagnostic screening or treatments available for autistic patients. Numerous genetic disorders are associated with high prevalence of ASD, including tuberous sclerosis complex, phosphatase and tensin homolog, and fragile X syndrome. Preclinical investigations in animal models of these diseases have revealed irregularities in the PI3K/Akt/mTOR signaling pathway as well as ASD-related behavioral defects. Reversal of the downstream molecular irregularities, associated with mTOR hyperactivation, improved the behavioral deficits observed in the preclinical investigations. Plant bioactive molecules have shown beneficial pre-clinical evidence in ASD treatment by modulating the PI3K/Akt/mTOR pathway. In this review, we summarize the involvement of the PI3K/Akt/mTOR pathway as well as the genetic alterations of the pathway components and its critical impact on the development of the autism spectrum disorder. Mutations in negative regulators of mTORC1, such as TSC1, TSC2, and PTEN, result in ASD-like phenotypes through the disruption of the mTORC1-mediated signaling. We further discuss the various naturally occurring phytoconstituents that have been identified to be bioactive and modulate the pathway to prevent its disruption and contribute to beneficial therapeutic effects in ASD.

Exposure to GABAA Receptor Antagonist Picrotoxin in Pregnant Mice Causes Autism-Like Behaviors and Aberrant Gene Expression in Offspring

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that is characterized by impairments in social interaction and restricted/repetitive behaviors. The neurotransmitter γ-aminobutyric acid (GABA) through GABAA receptor signaling in the immature brain plays a key role in the development of neuronal circuits. Excitatory/inhibitory imbalance in the mature brain has been investigated as a pathophysiological mechanism of ASD. However, whether and how disturbances of GABA signaling in embryos that are caused by GABAA receptor inhibitors cause ASD-like pathophysiology are poorly understood. The present study examined whether exposure to the GABAA receptor antagonist picrotoxin causes ASD-like pathophysiology in offspring by conducting behavioral tests from the juvenile period to adulthood and performing gene expression analyses in mature mouse brains. Here, we found that male mice that were prenatally exposed to picrotoxin exhibited a reduction of active interaction time in the social interaction test in both adolescence and adulthood. The gene expression analyses showed that picrotoxin-exposed male mice exhibited a significant increase in the gene expression of odorant receptors. Weighted gene co-expression network analysis showed a strong correlation between social interaction and enrichment of the "odorant binding" pathway gene module. Our findings suggest that exposure to a GABAA receptor inhibitor during the embryonic period induces ASD-like behavior, and impairments in odorant function may contribute to social deficits in offspring.