The glial perspective of autism spectrum disorders

Uncovering convergence and divergence between autism and schizophrenia using genomic tools and patients' neurons

Autism spectrum disorders (ASDs) are highly heritable and result in abnormal repetitive behaviors and impairment in communication and cognitive skills. Previous studies have focused on the genetic correlation between ASDs and other neuropsychiatric disorders, but an in-depth understanding of the correlation to other disorders is required. We conducted an extensive meta-analysis of common variants identified in ASDs by genome-wide association studies (GWAS) and compared it to the consensus genes and single nucleotide polymorphisms (SNPs) of Schizophrenia (SCZ). We found approximately 75% of the GWAS genes that are associated with ASD are also associated with SCZ. We further investigated the cellular phenotypes of neurons derived from induced pluripotent stem cell (iPSC) models in ASD and SCZ. Our findings revealed that ASD and SCZ neurons initially follow divergent developmental trajectories compared to control neurons. However, despite these early diametrical differences, both ASD and SCZ neurons ultimately display similar deficits in synaptic activity as they mature. This significant genetic overlap between ASD and SCZ, coupled with the convergence towards similar synaptic deficits, highlights the intricate interplay of genetic and developmental factors in shaping the shared underlying mechanisms of these complex neurodevelopmental and neuropsychiatric disorders.

Single cell spatial biology over developmental time can decipher pediatric brain pathologies

Pediatric low grade brain tumors and neurodevelopmental disorders share proteins, signaling pathways, and networks. They also share germline mutations and an impaired prenatal differentiation origin. They may differ in the timing of the events and proliferation. We suggest that their pivotal distinct, albeit partially overlapping, outcomes relate to the cell states, which depend on their spatial location, and timing of gene expression during brain development. These attributes are crucial as the brain develops sequentially, and single-cell spatial organization influences cell state, thus function. Our underlying premise is that the root cause in neurodevelopmental disorders and pediatric tumors is impaired prenatal differentiation. Data related to pediatric brain tumors, neurodevelopmental disorders, brain cell (sub)types, locations, and timing of expression in the developing brain are scant. However, emerging single cell technologies, including transcriptomic, spatial biology, spatial high-resolution imaging performed over the brain developmental time, could be transformational in deciphering brain pathologies thereby pharmacology.

Delving into the Complexity of Valproate-Induced Autism Spectrum Disorder: The Use of Zebrafish Models

Autism spectrum disorder (ASD) is a multifactorial neurodevelopmental condition with several identified risk factors, both genetic and non-genetic. Among these, prenatal exposure to valproic acid (VPA) has been extensively associated with the development of the disorder. The zebrafish, a cost- and time-effective model, is useful for studying ASD features. Using validated VPA-induced ASD zebrafish models, we aimed to provide new insights into VPA exposure effects during embryonic development and to identify new potential biomarkers associated with ASD-like features. Dose-response analyses were performed in vivo to study larval phenotypes and mechanisms underlying neuroinflammation, mitochondrial dysfunction, oxidative stress, microglial cell status, and motor behaviour. Wild-type and transgenic Tg(mpeg1:EGFP) zebrafish were water-exposed to VPA doses (5 to 500 µM) from 6 to 120 h post-fertilisation (hpf). Embryos and larvae were monitored daily to assess survival and hatching rates, and numerous analyses and tests were conducted from 24 to 120 hpf. VPA doses higher than 50 µM worsened survival and hatching rates, while doses of 25 µM or more altered morphology, microglial status, and larval behaviours. VPA 50 µM also affected mRNA expression of inflammatory cytokines and neurogenesis-related genes, mitochondrial respiration, and reactive oxygen species accumulation. The study confirmed that VPA alters brain homeostasis, synaptic interconnections, and neurogenesis-related signalling pathways, contributing to ASD aetiopathogenesis. Further studies are essential to identify novel ASD biomarkers for developing new drug targets and tailored therapeutic interventions for ASD.

Choline chloride shows gender-dependent positive effects on social deficits, learning/memory impairments, neuronal loss and neuroinflammation in the lipopolysaccharide-induced rat model of autism

The neuroprotective effects of choline chloride, an essential nutrient, a precursor for the acetylcholine and synthesis of membrane phospholipids, have been associated with neurological and neurodegenerative diseases. Its contribution to autism spectrum disorder, a neurodevelopmental disorder, remains unknown. Thus, we aimed to evaluate the effects of choline chloride on social behaviours, and histopathological and biochemical changes in a rat autism model. The autism model was induced by administration of 100 μg/kg lipopolysaccharide (LPS) on the 10th day of gestation. Choline chloride treatment (100 mg/kg/day) was commenced on PN5 and maintained until PN50. Social deficits were assessed by three-chamber sociability, open field, and passive avoidance learning tests. Tumour necrosis factor alpha (TNF-α), interleukin-2 (IL) and IL-17, nerve growth factor (NGF), and glutamate decarboxylase 67 (GAD67) levels were measured to assess neuroinflammatory responses. In addition, the number of hippocampal and cerebellar neurons and glial fibrillary acidic protein (GFAP) expression were evaluated. Social novelty and passive avoidance learning tests revealed significant differences in choline chloride-treated male rats compared with saline-treated groups. TNF-α, IL-2, and IL-17 were significantly decreased after choline chloride treatment in both males and females. NGF and GAD67 levels were unchanged in females, while there were significant differences in males. Histologically, significant changes in terms of gliosis were detected in hippocampal CA1 and CA3 regions and cerebellum in choline chloride-treated groups. The presence of ameliorative effects of choline chloride treatment on social behaviour and neuroinflammation through neuroinflammatory, neurotrophic, and neurotransmission pathways in a sex-dependent rat model of LPS-induced autism was demonstrated.

Contributions of dysfunctional plasticity mechanisms to the development of atypical perceptual processing

Experimental studies of sensory plasticity during development in birds and mammals have highlighted the importance of sensory experiences for the construction and refinement of functional neural circuits. We discuss how dysregulation of experience-dependent brain plasticity can lead to abnormal perceptual representations that may contribute to heterogeneous deficits symptomatic of several neurodevelopmental disorders. We focus on alterations of somatosensory processing and the dynamic reorganization of cortical synaptic networks that occurs during early perceptual development. We also discuss the idea that the heterogeneity of strengths and weaknesses observed in children with neurodevelopmental disorders may be a direct consequence of altered plasticity mechanisms during early development. Treating the heterogeneity of perceptual developmental trajectories as a phenomenon worthy of study rather than as an experimental confound that should be overcome may be key to developing interventions that better account for the complex developmental trajectories experienced by modern humans.

Transcutaneous auricular vagus nerve stimulation improves social deficits through the inhibition of IL-17a signaling in a mouse model of autism

Background

Maternal exposure to inflammation is one of the causes of autism spectrum disorder (ASD). Electrical stimulation of the vagus nerve exerts a neuroprotective effect via its anti-inflammatory action. We thus investigated whether transcutaneous auricular vagus nerve stimulation (taVNS) can enhance social abilities in a mouse model of ASD induced by maternal immune activation (MIA).

Methods

ASD mouse model were constructed by intraperitoneal injection of polyinosinic:polycytidylic acid (poly (I:C)). TaVNS with different parameters were tested in ASD mouse model and in C57BL/6 mice, then various behavioral tests and biochemical analyses related to autism were conducted. ASD model mice were injected with an interleukin (IL)-17a antibody into the brain, followed by behavioral testing and biochemical analyses.

Results

TaVNS reduced anxiety, improved social function, decreased the number of microglia, and inhibited M1 polarization of microglia. Additionally, taVNS attenuated the expression of the IL-17a protein in the prefrontal cortex and blood of ASD model mice. To examine the possible involvement of IL-17a in taVNS-induced neuroprotection, we injected an IL-17a antibody into the prefrontal cortex of ASD model mice and found that neutralizing IL-17a decreased the number of microglia and inhibited M1 polarization. Furthermore, neutralizing IL-17a improved social function in autism model mice.

Conclusion

Our study revealed that reduced neuroinflammation is an important mechanism of taVNS-mediated social improvement and neuroprotection against autism. This effect of taVNS could be attributed to the inhibition of the IL-17a pathway.

The role of glia in the dysregulation of neuronal spinogenesis in Ube3a-dependent ASD

Overexpression of the Ube3a gene and the resulting increase in Ube3a protein are linked to autism spectrum disorder (ASD). However, the cellular and molecular processes underlying Ube3a-dependent ASD remain unclear. Using both male and female mice, we find that neurons in the somatosensory cortex of the Ube3a 2× Tg ASD mouse model display reduced dendritic spine density and increased immature filopodia density. Importantly, the increased gene dosage of Ube3a in astrocytes alone is sufficient to confer alterations in neurons as immature dendritic protrusions, as observed in primary hippocampal neuron cultures. We show that Ube3a overexpression in astrocytes leads to a loss of astrocyte-derived spinogenic protein, thrombospondin-2 (TSP2), due to a suppression of TSP2 gene transcription. By neonatal intraventricular injection of astrocyte-specific virus, we demonstrate that Ube3a overexpression in astrocytes in vivo results in a reduction in dendritic spine maturation in prelimbic cortical neurons, accompanied with autistic-like behaviors in mice. These findings reveal an astrocytic dominance in initiating ASD pathobiology at the neuronal and behavior levels. SIGNIFICANCE STATEMENT: Increased gene dosage of Ube3a is tied to autism spectrum disorders (ASDs), yet cellular and molecular alterations underlying autistic phenotypes remain unclear. We show that Ube3a overexpression leads to impaired dendritic spine maturation, resulting in reduced spine density and increased filopodia density. We find that dysregulation of spine development is not neuron autonomous, rather, it is mediated by an astrocytic mechanism. Increased gene dosage of Ube3a in astrocytes leads to reduced production of the spinogenic glycoprotein thrombospondin-2 (TSP2), leading to abnormalities in spines. Astrocyte-specific Ube3a overexpression in the brain in vivo confers dysregulated spine maturation concomitant with autistic-like behaviors in mice. These findings indicate the importance of astrocytes in aberrant neurodevelopment and brain function in Ube3a-depdendent ASD.

Germline PTEN genotype-dependent phenotypic divergence during the early neural developmental process of forebrain organoids

PTEN germline mutations account for ~0.2-1% of all autism spectrum disorder (ASD) cases, as well as ~17% of ASD patients with macrocephaly, making it one of the top ASD-associated risk genes. Individuals with germline PTEN mutations receive the molecular diagnosis of PTEN Hamartoma Tumor Syndrome (PHTS), an inherited cancer predisposition syndrome, about 20-23% of whom are diagnosed with ASD. We generated forebrain organoid cultures from gene-edited isogenic human induced pluripotent stem cells (hiPSCs) harboring a PTENG132D (ASD) or PTENM134R (cancer) mutant allele to model how these mutations interrupt neurodevelopmental processes. Here, we show that the PTENG132D allele disrupts early neuroectoderm formation during the first several days of organoid generation, and results in deficient electrophysiology. While organoids generated from PTENM134R hiPSCs remained morphologically similar to wild-type organoids during this early stage in development, we observed disrupted neuronal differentiation, radial glia positioning, and cortical layering in both PTEN-mutant organoids at the later stage of 72+ days of development. Perifosine, an AKT inhibitor, reduced over-activated AKT and partially corrected the abnormalities in cellular organization observed in PTENG132D organoids. Single cell RNAseq analyses on early-stage organoids revealed that genes related to neural cell fate were decreased in PTENG132D mutant organoids, and AKT inhibition was capable of upregulating gene signatures related to neuronal cell fate and CNS maturation pathways. These findings demonstrate that different PTEN missense mutations can have a profound impact on neurodevelopment at diverse stages which in turn may predispose PHTS individuals to ASD. Further study will shed light on ways to mitigate pathological impact of PTEN mutants on neurodevelopment by stage-specific manipulation of downstream PTEN signaling components.

Exposure to metam sodium-based pesticide impaired cognitive performances in adult mice: Involvement of oxidative damage and glial activation

Cognitive integrity is a critical aspect of neurological function, and a decline in cognitive function is a hallmark of neurotoxicity. Oxidative stress is a significant pathological feature contributing to cognitive deficits that can arise from exposure to environmental pollutants such as pesticides. Among these, Metam sodium-based pesticides (MS-BP) are an emergent type of pesticide widely used in the agriculture and public health sectors for controlling pests and diseases. Our prior research has shown that animals exposed to MS-BP during the early stages of brain development caused cognitive impairments. In the present study, we tested whether exposure to this compound in a fully matured brain would affect cognitive performance and induce oxidative damage to the central nervous system. In this context, adult mice received chronic treatment with increasing doses of MS-BP and subjected to a set of behavioral paradigms. Following behavioral assessment, oxidative stress and glial activation were evaluated. Our main findings showed that MS-BP chronic exposure impaired recognition and short- and long-term memory. These alterations were accompanied by increased superoxide dismutase activity and malondialdehyde level and a marked decrease in catalase activity in specific brain areas. Moreover, exposure to MS-BP is associated with a significant rise in the density of astrocytic and microglial markers, indicating a possible glial cell response within the prefrontal cortex and hippocampus. The present work demonstrated that MS-BP altered cognitive performance likely through oxidative damage to the brain.

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

Astrocytes and the Psychiatric Sequelae of COVID-19: What We Learned from the Pandemic

COVID-19, initially regarded as specific lung disease, exhibits an extremely broad spectrum of symptoms. Extrapulmonary manifestations of the disease also include important neuropsychiatric symptoms with atypical characteristics. Are these disturbances linked to stress accompanying every systemic infection, or are due to specific neurobiological changes associated with COVID-19? Evidence accumulated so far indicates that the pathophysiology of COVID-19 is characterized by systemic inflammation, hypoxia resulting from respiratory failure, and neuroinflammation (either due to viral neurotropism or in response to cytokine storm), all affecting the brain. It is reasonable to hypothesize that all these events may initiate or worsen psychiatric and cognitive disorders. Damage to the brain triggers a specific type of reactive response mounted by neuroglia cells, in particular by astrocytes which are the homeostatic cell par excellence. Astrocytes undergo complex morphological, biochemical, and functional remodeling aimed at mobilizing the regenerative potential of the central nervous system. If the brain is not directly damaged, resolution of systemic pathology usually results in restoration of the physiological homeostatic status of neuroglial cells. The completeness and dynamics of this process in pathological conditions remain largely unknown. In a subset of patients, glial cells could fail to recover after infection thus promoting the onset and progression of COVID-19-related neuropsychiatric diseases. There is evidence from post-mortem examinations of the brains of COVID-19 patients of alterations in both astrocytes and microglia. In conclusion, COVID-19 activates a huge reactive response of glial cells, that physiologically act as the main controller of the inflammatory, protective and regenerative events. However, in some patients the restoration of glial physiological state does not occur, thus compromising glial function and ultimately resulting in homeostatic failure underlying a set of specific neuropsychiatric symptoms related to COVID-19.

Developmental pyrethroid exposure causes a neurodevelopmental disorder phenotype in mice

Neurodevelopmental disorders (NDDs) are a widespread and growing public health challenge, affecting as many as 17% of children in the United States. Recent epidemiological studies have implicated ambient exposure to pyrethroid pesticides during pregnancy in the risk for NDDs in the unborn child. Using a litter-based, independent discovery-replication cohort design, we exposed mouse dams orally during pregnancy and lactation to the Environmental Protection Agency's reference pyrethroid, deltamethrin, at 3 mg/kg, a concentration well below the benchmark dose used for regulatory guidance. The resulting offspring were tested using behavioral and molecular methods targeting behavioral phenotypes relevant to autism and NDD, as well as changes to the striatal dopamine system. Low-dose developmental exposure to the pyrethroid deltamethrin (DPE) decreased pup vocalizations, increased repetitive behaviors, and impaired both fear conditioning and operant conditioning. Compared with control mice, DPE mice had greater total striatal dopamine, dopamine metabolites, and stimulated dopamine release, but no difference in vesicular dopamine capacity or protein markers of dopamine vesicles. Dopamine transporter protein levels were increased in DPE mice, but not temporal dopamine reuptake. Striatal medium spiny neurons showed changes in electrophysiological properties consistent with a compensatory decrease in neuronal excitability. Combined with previous findings, these results implicate DPE as a direct cause of an NDD-relevant behavioral phenotype and striatal dopamine dysfunction in mice and implicate the cytosolic compartment as the location of excess striatal dopamine.

Neonatal loss of FGFR2 in astroglial cells affects locomotion, sociability, working memory, and glia-neuron interactions in mice

Fibroblast growth factor receptor 2 (FGFR2) is almost exclusively expressed in glial cells in postnatal mouse brain, but its impact in glia for brain behavioral functioning is poorly understood. We compared behavioral effects from FGFR2 loss in both neurons and astroglial cells and from FGFR2 loss in astroglial cells by using either the pluripotent progenitor-driven hGFAP-cre or the tamoxifen-inducible astrocyte-driven GFAP-creERT2 in Fgfr2 floxed mice. When FGFR2 was eliminated in embryonic pluripotent precursors or in early postnatal astroglia, mice were hyperactive, and had small changes in working memory, sociability, and anxiety-like behavior. In contrast, FGFR2 loss in astrocytes starting at 8 weeks of age resulted only in reduced anxiety-like behavior. Therefore, early postnatal loss of FGFR2 in astroglia is critical for broad behavioral dysregulation. Neurobiological assessments demonstrated that astrocyte-neuron membrane contact was reduced and glial glutamine synthetase expression increased only by early postnatal FGFR2 loss. We conclude that altered astroglial cell function dependent on FGFR2 in the early postnatal period may result in impaired synaptic development and behavioral regulation, modeling childhood behavioral deficits like attention deficit hyperactivity disorder (ADHD).

Modelling the Interplay Between Neuron-Glia Cell Dysfunction and Glial Therapy in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complicated, interpersonally defined, static condition of the underdeveloped brain. Although the aetiology of autism remains unclear, disturbance of neuronglia interactions has lately been proposed as a significant event in the pathophysiology of ASD. In recent years, the contribution of glial cells to autism has been overlooked. In addition to neurons, glial cells play an essential role in mental activities, and a new strategy that emphasises neuron-glia interactions should be applied. Disturbance of neuron-glia connections has lately been proposed as a significant event in the pathophysiology of ASD because aberrant neuronal network formation and dysfunctional neurotransmission are fundamental to the pathology of the condition. In ASD, neuron and glial cell number changes cause brain circuits to malfunction and impact behaviour. A study revealed that reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Recent discoveries also suggest that dysfunction or changes in the ability of microglia to carry out physiological and defensive functions (such as failure in synaptic elimination or aberrant microglial activation) may be crucial for developing brain diseases, especially autism. The cerebellum, white matter, and cortical regions of autistic patients showed significant microglial activation. Reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Replacement of defective glial cells (Cell-replacement treatment), glial progenitor cell-based therapy, and medication therapy (inhibition of microglia activation) are all utilised to treat glial dysfunction. This review discusses the role of glial cells in ASD and the various potential approaches to treating glial cell dysfunction.

A molecular framework for autistic experiences: Mitochondrial allostatic load as a mediator between autism and psychopathology

Molecular autism research is evolving toward a biopsychosocial framework that is more informed by autistic experiences. In this context, research aims are moving away from correcting external autistic behaviors and toward alleviating internal distress. Autism Spectrum Conditions (ASCs) are associated with high rates of depression, suicidality and other comorbid psychopathologies, but this relationship is poorly understood. Here, we integrate emerging characterizations of internal autistic experiences within a molecular framework to yield insight into the prevalence of psychopathology in ASC. We demonstrate that descriptions of social camouflaging and autistic burnout resonate closely with the accepted definitions for early life stress (ELS) and chronic adolescent stress (CAS). We propose that social camouflaging could be considered a distinct form of CAS that contributes to allostatic overload, culminating in a pathophysiological state that is experienced as autistic burnout. Autistic burnout is thought to contribute to psychopathology via psychological and physiological mechanisms, but these remain largely unexplored by molecular researchers. Building on converging fields in molecular neuroscience, we discuss the substantial evidence implicating mitochondrial dysfunction in ASC to propose a novel role for mitochondrial allostatic load in the relationship between autism and psychopathology. An interplay between mitochondrial, neuroimmune and neuroendocrine signaling is increasingly implicated in stress-related psychopathologies, and these molecular players are also associated with neurodevelopmental, neurophysiological and neurochemical aspects of ASC. Together, this suggests an increased exposure and underlying molecular susceptibility to ELS that increases the risk of psychopathology in ASC. This article describes an integrative framework shaped by autistic experiences that highlights novel avenues for molecular research into mechanisms that directly affect the quality of life and wellbeing of autistic individuals. Moreover, this framework emphasizes the need for increased access to diagnoses, accommodations, and resources to improve mental health outcomes in autism.

Impaired macroglial development and axonal conductivity contributes to the neuropathology of DYRK1A-related intellectual disability syndrome

The correct development and activity of neurons and glial cells is necessary to establish proper brain connectivity. DYRK1A encodes a protein kinase involved in the neuropathology associated with Down syndrome that influences neurogenesis and the morphological differentiation of neurons. DYRK1A loss-of-function mutations in heterozygosity cause a well-recognizable syndrome of intellectual disability and autism spectrum disorder. In this study, we analysed the developmental trajectories of macroglial cells and the properties of the corpus callosum, the major white matter tract of the brain, in Dyrk1a^+/- mice, a mouse model that recapitulates the main neurological features of DYRK1A syndrome. We found that Dyrk1a^+/- haploinsufficient mutants present an increase in astrogliogenesis in the neocortex and a delay in the production of cortical oligodendrocyte progenitor cells and their progression along the oligodendroglial lineage. There were fewer myelinated axons in the corpus callosum of Dyrk1a^+/- mice, axons that are thinner and with abnormal nodes of Ranvier. Moreover, action potential propagation along myelinated and unmyelinated callosal axons was slower in Dyrk1a^+/- mutants. All these alterations are likely to affect neuronal circuit development and alter network synchronicity, influencing higher brain functions. These alterations highlight the relevance of glial cell abnormalities in neurodevelopmental disorders.

Dopamine, Psychosis, and Symptom Fluctuation: A Narrative Review

It has been hypothesized since the 1960s that the etiology of schizophrenia is linked to dopamine. In the intervening 60 years, sophisticated brain imaging techniques, genetic/epigenetic advances, and new experimental animal models of schizophrenia have transformed schizophrenia research. The disease is now conceptualized as a heterogeneous neurodevelopmental disorder expressed phenotypically in four symptom domains: positive, negative, cognitive, and affective. The aim of this paper is threefold: (a) to review recent research into schizophrenia etiology, (b) to review papers that elicited subjective evidence from patients as to triggers and repressors of symptoms such as auditory hallucinations or paranoid thoughts, and (c) to address the potential role of dopamine in schizophrenia in general and, in particular, in the fluctuations in schizophrenia symptoms. The review also includes new discoveries in schizophrenia research, pointing to the involvement of both striatal neurons and glia, signaling pathway convergence, and the role of stress. It also addresses potential therapeutic implications. We conclude with the hope that this paper opens up novel avenues of research and new possibilities for treatment.

Characterization of a mGluR5 Knockout Rat Model with Hallmarks of Fragile X Syndrome

The number of reported cases of neurodevelopmental disorders has increased significantly in the last few decades, but the etiology of these diseases remains poorly understood. There is evidence of a fundamental link between genetic abnormalities and symptoms of autism spectrum disorders (ASDs), and the most common monogenetic inheritable form of ASDs is Fragile X Syndrome (FXS). Previous studies indicate that FXS is linked to glutamate signaling regulation by the G-protein-coupled metabotropic glutamate receptor 5 (mGluR5), which has been shown to have a regulatory role in neuroinflammation. We characterized the effect of knocking out mGluR5 in an organism known to have complex cognitive functions—the rat. The heterozygous phenotype is the most clinically relevant; therefore, we performed analysis in heterozygous pups. We showed developmental abnormalities in heterozygous mGluR5 knockout rats, as well as a significant increase in chemokine (C-X-C motif) ligand 1 (CXCL) expression, a hallmark indicator of early onset inflammation. We quantified an increase in microglial density in the knockout pups and quantified morphological phenotypes representative of greater reactivity in the male vs. female and postnatal day 28 heterozygous pups compared to postnatal day 14 heterozygous pups. In response to injury, reactive microglia release matrix metalloproteases, contribute to extracellular matrix (ECM) breakdown, and are responsible for eradicating cellular and molecular debris. In our study, the changes in microglial density and reactivity correlated with abnormalities in the mRNA expression levels of ECM proteins and with the density of perineuronal nets. We saw atypical neuropsychiatric behavior in open field and elevated plus tests in heterozygous pups compared to wild-type litter and age-matched controls. These results demonstrate the pathological potential of the mGluR5 knockout in rats and further support the presence of neuroinflammatory roots in ASDs.

Novel role of peroxisome proliferator activated receptor-α in valproic acid rat model of autism: Mechanistic study of risperidone and metformin monotherapy versus combination

Autism spectrum disorder (ASD) is a neurodevelopmental disorder of heterogenous etiology exhibiting a challenge in understanding its exact neuro-pathophysiology. Recently, peroxisome proliferator activated receptor (PPAR)-α activation was found to play a fundamental role in neuroprotection and improving autistic-like-behaviors in experimental animal models of ASD through alleviating neuroinflammation, oxidative-stress, astrocyte reactivity, tauopathy in addition to its favorable role in metabolic regulation, thus attracting attention as a possible target in treatment of ASD. This study aimed to investigate the role of PPAR-α, astrocytic dysfunction and tauopathy in ASD and detect the possible neuroprotective effects of metformin (MET), through PPAR-α activation, and risperidone (RIS) either monotherapy or in combination in alleviating autistic-like-changes at behavioral and neurobiological levels in male Wistar rats. Pregnant female Wistar rats received valproic-acid (VPA) to induce autistic-like-behavioral and neurobiological alterations in their offspring. Chronic intra-peritoneal MET (100 mg/kg/day) and RIS (1 mg/kg/day) either monotherapy or in combination started from postnatal day (PND) 24 till PND61 (38 days). Prenatal VPA exposure simulated the autistic core behaviors associated with neurochemical and histopathological neurodevelopmental degenerative changes. Both MET and RIS either monotherapy or in combination were able to reverse these changes. The effect of MET was comparable to RIS. Moreover, MET was able to alleviate the RIS induced weight gain and improve cognitive functions highlighting its promising adjunctive role in alleviating ASD pathophysiology. Our study highlighted the favorable effects of MET and RIS both in monotherapy and in combination in alleviating the autistic-like-changes and proposed PPAR-α activation along with restoring astrocytes homeostasis as promising targets in novel therapeutic strategies in ASD.

Astroglial Serotonin Receptors as the Central Target of Classic Antidepressants

Major depressive disorder (MDD) presents multiple clinical phenotypes and has complex underlying pathological mechanisms. Existing theories cannot completely explain the pathophysiological mechanism(s) of MDD, while the pharmacology of current antidepressants is far from being fully understood. Astrocytes, the homeostatic and defensive cells of the central nervous system, contribute to shaping behaviors, and regulating mood and emotions. A detailed introduction on the role of astrocytes in depressive disorders is thus required, to which this chapter is dedicated. We also focus on the interactions between classic antidepressants and serotonin receptors, overview the role of astrocytes in the pharmacological mechanisms of various antidepressants, and present astrocytes as targets for the treatment of bipolar disorder. We provide a foundation of knowledge on the role of astrocytes in depressive disorders and astroglial 5-HT_2B receptors as targets for selective serotonin reuptake inhibitors in vivo and in vitro.

Principles of Astrogliopathology

The role of astrocytes in the nervous system pathology was early on embraced by neuroscientists at end of the nineteenth and the beginning of the twentieth century, only to be pushed aside by neurone-centric dogmas during most of the twentieth century. However, the last decade of the twentieth century and the twenty-first century have brought the astroglial "renaissance", which has put astroglial cells as key players in pathophysiology of most if not all disorders of the nervous system and has regarded astroglia as a fertile ground for therapeutic intervention.Astrocytic contribution to neuropathology can be primary, whereby cell-autonomous changes, such as mutations in gene encoding for glial fibrillary acidic protein, can drive the pathologic progression, in this example, Alexander disease. They can also be secondary, when astrocytes respond to a variety of insults to the nervous tissue. Regardless of their origin, being cell-autonomous or not, changes in astroglia that occur in pathology, that is, astrogliopathology, can be contemporary and arbitrary classified into four forms: (i) reactive astrogliosis, (ii) astrocytic atrophy with loss of function, (iii) pathological remodelling of astrocytes and (iv) astrodegeneration morphologically manifested as clasmatodendrosis. Inevitably, as with any other classification, this classification of astrogliopathology awaits its revision that shall be rooted in new discoveries and concepts.

Targeting the Oxytocinergic System: A Possible Pharmacological Strategy for the Treatment of Inflammation Occurring in Different Chronic Diseases

Unresolved inflammation represents a central feature of different human pathologies including neuropsychiatric, cardiovascular, and metabolic diseases. The epidemiologic relevance of such disorders justifies the increasing interest in further understanding the mechanisms underpinning the inflammatory process occurring in such chronic diseases to provide potential novel pharmacological approaches. The most common and effective therapies for controlling inflammation are glucocorticoids; however, a variety of other molecules have been demonstrated to have an anti-inflammatory potential, including neuropeptides. In recent years, the oxytocinergic system has seen an explosion of scientific studies, demonstrating its potential to contribute to a variety of physiological processes including inflammation. Therefore, the aim of the present review was to understand the role of oxytocin in the modulation of inflammation occurring in different chronic diseases. The criterion we used to select the diseases was based on the emerging literature showing a putative involvement of the oxytocinergic system in inflammatory processes in a variety of pathologies including neurological, gastrointestinal and cardiovascular disorders, diabetes and obesity. The evidence reviewed here supports a beneficial role of oxytocin in the control of both peripheral and central inflammatory response happening in the aforementioned pathologies. Although future studies are necessary to elucidate the mechanistic details underlying such regulation, this review supports the idea that the modulation of the endogenous oxytocinergic system might represent a new potential pharmacological approach for the treatment of inflammation.

Transcriptome-wide analysis reveals core sets of transcriptional regulators of sensome and inflammation genes in retinal microglia

BACKGROUND

Retinal microglial cells (RMCs) play crucial roles in maintaining normal visual functions in a healthy eye. However, the underlying mechanisms of RMCs over-activation manifesting the alterations of sensome profile and inflammation state, which contribute to various retinal neurodegenerative diseases, remain elusive. Here, we aimed to identify the core set of sensome and pro-inflammatory genes and their regulators using transcriptome and data mining approaches.

METHODS

We performed paired-end RNA-sequencing in primary microglial cell cultures treated with TNFα/IFNϒ (10 ng/ml for 12 h) and PBS as a control. Gene enrichment analysis and hierarchical clustering for the differentially expressed transcripts highlight functional pathways and network perturbations. We examined overlaps of the mouse microglial gene expression profiles with the data-mined human sensome and pro-inflammatory marker genes. The core sets of sensome and pro-inflammatory genes were selected and predicted for transcription factors (TFs). The identified TFs in RNA-Seq are validated by the quantitative PCR method.

RESULTS

TNFα/IFNϒ induced 668 differentially expressed transcripts in retinal microglial cells relative to the control. Furthermore, gene enrichment analysis and the gene expression network revealed activated microglial genes, biological, molecular and inflammatory pathways. The overlapping analysis of the TNFα/IFNϒ-activated microglia genes and the data-mined human gene sets revealed 22 sensome and 61 pro-inflammatory genes. Based on network analysis, we determined 10 genes as the core sets of sensome and pro-inflammatory genes and predicted the top ten TFs that regulate them. The SP110, IRF1, FLI1, SP140 (sensome) and RELB, BATF2, NFKB2, TRAFD1, SP100, NFKB1 (inflammation) are differentially expressed between the TNFα/IFNϒ activated and the non-activated microglia which were validated by quantitative PCR. The outcomes indicate that these transcriptional regulators are highly expressed and may regulate the sensome and inflammatory genes of RMCs and switch them to over-activation.

CONCLUSION

Our results comprise a powerful, cross-species functional genomics resource for sensome and inflammation of RMCs, which may provide novel therapeutic approaches to prevent retinal neurodegenerative diseases.

Resveratrol prevents brain edema, blood-brain barrier permeability, and altered aquaporin profile in autism animal model

Autism spectrum disorder can present a plethora of clinical conditions associated with the disorder, such as greater brain volume in the first years of life in a significant percentage of patients. We aimed to evaluate the brain water content, the blood-brain barrier permeability, and the expression of aquaporin 1 and 4, and GFAP in a valproic acid-animal model, assessing the effect of resveratrol. On postnatal day 30, Wistar rats of the valproic acid group showed greater permeability of the blood-brain barrier to the Evans blue dye and a higher proportion of brain water volume, prevented both by resveratrol. Prenatal exposition to valproic acid diminished aquaporin 1 in the choroid plexus, in the primary somatosensory area, in the amygdala region, and in the medial prefrontal cortex, reduced aquaporin 4 in medial prefrontal cortex and increased aquaporin 4 levels in primary somatosensory area (with resveratrol prevention). Valproic acid exposition also increased the number of astrocytes and GFAP fluorescence in both primary somatosensory area and medial prefrontal cortex. In medial prefrontal cortex, resveratrol prevented the increased fluorescence. Finally, there was an effect of resveratrol per se on the number of astrocytes and GFAP fluorescence in the amygdala region and in the hippocampus. Thus, this work demonstrates significant changes in blood-brain barrier permeability, edema formation, distribution of aquaporin 1 and 4, in addition to astrocytes profile in the animal model of autism, as well as the use of resveratrol as a tool to investigate the mechanisms involved in the pathophysiology of autism spectrum disorder.

Immunology and microbiology: how do they affect social cognition and emotion recognition?

Social interactions profoundly influence animals' life. The quality of social interactions and many everyday life decisions are determined by a proper perception, processing and reaction to others' emotions. Notably, alterations in these social processes characterize a number of neurodevelopmental disorders, including autism spectrum disorders and schizophrenia. Increasing evidences support an implication of immune system vulnerability and inflammatory processes in disparate behavioral functions and the aforementioned neurodevelopmental disorders. In this review, we show a possible unifying view on how immune responses, within and outside the brain, and the communication between the immune system and brain responses might influence emotion recognition and related social responses. In particular, we highlight the importance of combining genetics, immunology and microbiology factors in understanding social behaviors. We underline the importance of better disentangling the whole machinery between brain-immune system interactions to better address the complexity of social processes.

8p23.2-pter Microdeletions: Seven New Cases Narrowing the Candidate Region and Review of the Literature

To date only five patients with 8p23.2-pter microdeletions manifesting a mild-to-moderate cognitive impairment and/or developmental delay, dysmorphisms and neurobehavioral issues were reported. The smallest microdeletion described by Wu in 2010 suggested a critical region (CR) of 2.1 Mb including several genes, out of which FBXO25, DLGAP2, CLN8, ARHGEF10 and MYOM2 are the main candidates. Here we present seven additional patients with 8p23.2-pter microdeletions, ranging from 71.79 kb to 4.55 Mb. The review of five previously reported and nine Decipher patients confirmed the association of the CR with a variable clinical phenotype characterized by intellectual disability/developmental delay, including language and speech delay and/or motor impairment, behavioral anomalies, autism spectrum disorder, dysmorphisms, microcephaly, fingers/toes anomalies and epilepsy. Genotype analysis allowed to narrow down the 8p23.3 candidate region which includes only DLGAP2, CLN8 and ARHGEF10 genes, accounting for the main signs of the broad clinical phenotype associated to 8p23.2-pter microdeletions. This region is more restricted compared to the previously proposed CR. Overall, our data favor the hypothesis that DLGAP2 is the actual strongest candidate for neurodevelopmental/behavioral phenotypes. Additional patients will be necessary to validate the pathogenic role of DLGAP2 and better define how the two contiguous genes, ARHGEF10 and CLN8, might contribute to the clinical phenotype.

Associations of Serum Cytokine Levels and Interleukin-6-572C/G Polymorphism with Myelin Damage in Chinese Children with Autism Spectrum Disorder

Increasing evidence suggests that immunological disturbances and abnormalities in axonal myelination are involved in the pathophysiology of autism spectrum disorder (ASD). The present study aimed to determine the role of cytokines in myelin damage in Chinese children with ASD and the role of cytokine dysregulation, myelin damage, and cytokine polymorphisms in ASD in Chinese children. The present case-control study included 98 ASD subjects and 252 typically developing (TD) controls; the levels of serum cytokines and myelin basic protein (MBP) were determined using enzyme-linked immunosorbent assay. Cytokine polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism analysis. Autistic clinical manifestations were assessed by the Childhood Autism Rating Scale (CARS). The results showed that serum levels of interleukin (IL)-1β, IL-2R, IL-6, IL-8, and MBP were higher in children with ASD compared with those in TD children. In individuals with ASD, serum MBP level was significantly positively associated with the CARS total score, and serum levels of IL-1β, IL-2R, IL-6, and MBP demonstrated positive correlations. The data identified IL-6*MBP as a factor that influenced the risk of ASD, and IL-2R*MBP was identified as a factor that influenced symptom severity, which influenced auxiliary diagnosis of ASD. The presence of the interleukin-6-572CC genotype was associated with significantly higher serum levels of IL-6 and MBP but did not influence the risk and symptom severity of ASD. Therefore, the results suggested inflammatory responses and myelin damage in Chinese children with ASD. Cytokine dysregulation influenced myelin damage in ASD; moreover, the interactions of the cytokines and myelin damage influenced the risk and symptom severity of ASD. The IL-6-572C/G genotypes may be associated with myelin damage in ASD by influencing the circulating level of IL-6.

Orchestrating aquaporin-4 and connexin-43 expression in brain: Differential roles of α1- and β1-syntrophin

Aquaporin-4 (AQP4) water channels and gap junction proteins (connexins) are two classes of astrocytic membrane proteins critically involved in brain water and ion homeostasis. AQP4 channels are anchored by α1-syntrophin to the perivascular astrocytic endfoot membrane domains where they control water flux at the blood-brain interface while connexins cluster at the lateral aspects of the astrocytic endfeet forming gap junctions that allow water and ions to dissipate through the astrocyte syncytium. Recent studies have pointed to an interdependence between astrocytic AQP4 and astrocytic gap junctions but the underlying mechanism remains to be explored. Here we use a novel transgenic mouse line to unravel whether β1-syntrophin (coexpressed with α1-syntrophin in astrocytic plasma membranes) is implicated in the expression of AQP4 isoforms and formation of gap junctions in brain. Our results show that while the effect of β1-syntrophin deletion is rather limited, double knockout of α1- and β1-syntrophin causes a downregulation of the novel AQP4 isoform AQP4ex and an increase in the number of astrocytic gap junctions. The present study highlight the importance of syntrophins in orchestrating specialized functional domains of brain astrocytes.

CNVs inform the biological network of Autism spectrum disorder

Autism spectrum disorder (ASD) is a heterogeneous condition linked to an anomalous neurodevelopment. Although the underlying causes of ASD are not well described, literature data strongly suggests a genetic component, with a complex inheritance pattern. It has recently been observed that CNVs (copy number variation) may play an important role in ASD manifestation and partially explain the complex heritability of this tract. Another factor That adds another level of complexity to ASD is its potential genetic heterogeneity. In this paper, we hypothesize that the different patterns of alteration within individuals with ASD may converge towards the same function. We genotyped a sample of 107 individuals through aCGH analysis for CNVs that were related (by localization) to approximately 1400 genes. The genes were tested for functional interactions and clustered in functional groups. We highlighted a functional genetic cluster of 256 genes potentially related to ASD. These altered genes may contribute to the same function, alterations of which increase the risk of ASD. After testing our functional cluster for biological functions, processes related to oxidative stress, immune system and energy metabolism are the pathways potentially involved with the biological alterations underlying ASD.

Neuroglia in Psychiatric Disorders

In the twentieth century, neuropsychiatric disorders have been perceived solely from a neurone-centric point of view, which considers neurones as the key cellular elements of pathological processes. This dogma has been challenged thanks to the better comprehension of the brain functioning, which, even if far from being complete, has revealed the complexity of interactions that exist between neurones and neuroglia. Glial cells represent a highly heterogeneous population of cells of neural (astroglia and oligodendroglia) and non-neural (microglia) origin populating the central nervous system. The variety of glia reflects the innumerable functions that glial cells perform to support functions of the nervous system. Aberrant execution of glial functions contributes to the development of neuropsychiatric pathologies. Arguably, all types of glial cells are implicated in the neuropathology; however, astrocytes have received particular attention in recent years because of their pleiotropic functions that make them decisive in maintaining cerebral homeostasis. This chapter describes the multiple roles of astrocytes in the healthy central nervous system and discusses the diversity of astroglial responses in neuropsychiatric disorders suggesting that targeting astrocytes may represent an effective therapeutic strategy.

Role of Oligodendrocytes and Myelin in the Pathophysiology of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is an early neurodevelopmental disorder that involves deficits in interpersonal communication, social interaction, and repetitive behaviors. Although ASD pathophysiology is still uncertain, alterations in the abnormal development of the frontal lobe, limbic areas, and putamen generate an imbalance between inhibition and excitation of neuronal activity. Interestingly, recent findings suggest that a disruption in neuronal connectivity is associated with neural alterations in white matter production and myelination in diverse brain regions of patients with ASD. This review is aimed to summarize the most recent evidence that supports the notion that abnormalities in the oligodendrocyte generation and axonal myelination in specific brain regions are involved in the pathophysiology of ASD. Fundamental molecular mediators of these pathological processes are also examined. Determining the role of alterations in oligodendrogenesis and myelination is a fundamental step to understand the pathophysiology of ASD and identify possible therapeutic targets.

Synthetic analogues of memantine as neuroprotective and influenza viral inhibitors: in vitro and physicochemical studies

Drug compounds including memantine moieties are an important group of biologically active agents for different pathologies, including the Alzheimer's disease. In the present study, a series of memantine derivatives incorporating amino acid residues have been synthesized and their neuroprotective in vitro evaluation in respect of the Alzheimer's disease, involving the effects on the resistance to Aβ toxicity, excitotoxicity, oxidative stress, hypoxia, and neuroinflammation has been studied. The cytotoxicities of the compounds were detected by CPE assay. TC₅₀ and IC₅₀ were determined using Reed and Muench method. Solubility and distribution were measured using a shake-flask method. Permeability of the compounds was studied using Franz diffusion cell and Permeapad™ barrier. These compounds displayed apparent multi-neuroprotective effects against copper-triggered Aβ toxicity, glutamate-induced excitotoxicity, and oxidative and hypoxic injuries. They also showed the ability to inhibit the inflammatory cytokine release from the activated microglia and potential anti-neuroinflammatory effects. Especially, two most promising compounds H-4-F-Phe-memantine and H-Tyr-memantine demonstrated the equivalent functional bioactivities in comparison with the positive control memantine hydrochloride. Higher solubility in muriatic buffer than in phosphate buffer was detected. The distribution coefficients showed the optimal lipophilicity for compounds. The presented results propose new class of memantine derivatives as potential drug compounds. Based on the experimental results, the correlations have been obtained between the biological, physicochemical parameters and structural descriptors. The correlation equations have been proposed to predict the properties of new memantine derivatives knowing only the structural formula.

Neuropathobiology of COVID-19: The Role for Glia

SARS-CoV-2, which causes the Coronavirus Disease 2019 (COVID-19) pandemic, has a brain neurotropism through binding to the receptor angiotensin-converting enzyme 2 expressed by neurones and glial cells, including astrocytes and microglia. Systemic infection which accompanies severe cases of COVID-19 also triggers substantial increase in circulating levels of chemokines and interleukins that compromise the blood-brain barrier, enter the brain parenchyma and affect its defensive systems, astrocytes and microglia. Brain areas devoid of a blood-brain barrier such as the circumventricular organs are particularly vulnerable to circulating inflammatory mediators. The performance of astrocytes and microglia, as well as of immune cells required for brain health, is considered critical in defining the neurological damage and neurological outcome of COVID-19. In this review, we discuss the neurotropism of SARS-CoV-2, the implication of neuroinflammation, adaptive and innate immunity, autoimmunity, as well as astrocytic and microglial immune and homeostatic functions in the neurological and psychiatric aspects of COVID-19. The consequences of SARS-CoV-2 infection during ageing, in the presence of systemic comorbidities, and for the exposed pregnant mother and foetus are also covered.

Microglia mediated neuroinflammation in autism spectrum disorder

BACKGROUND

Although the precise pathophysiologies underlying autism spectrum disorder (ASD) has not yet been fully clarified, growing evidence supports the involvement of neuroinflammation in the pathogenesis of this disorder, with microglia being particular relevance in the pathophysiologic processes.

OBJECTIVE

The present review aimed to systematically characterize existing literature regarding the role of microglia mediated neuroinflammation in the etiology of ASD.

METHODS

A systematic search was conducted for records indexed within Pubmed, EMBASE, or Web of Science to identify potentially eligible publications. Study selection and data extraction were performed by two authors, and the discrepancies in each step were settled through discussions.

RESULTS

A total of 14 studies comprising 1007 subjects met the eligibility criteria for this review, including 8 immunohistochemistry (IHC) studies, 5 genetic analysis studies, and 1 positron emission tomography (PET) studies. Although small in quantity, the included studies collectively pointed to a role of microglia mediated neuroinflammation in the pathogenesis of ASD.

CONCLUSION

Findings generated from this review consistently supported the involvement of neuroinflammation in the development of ASD, confirmed by the activation of microglia in different brain regions, involving increased cell number or cell density, morphological alterations, and phenotypic shifts.

Lateral septum microglial changes and behavioral abnormalities of mice exposed to valproic acid during the prenatal period

Most animal model studies of autism spectrum disorder (ASD) have been performed in males, which may be a reflex of the 3-times higher prevalence in boys than in girls. For this reason, little is known about the mechanisms underlying disease progression in females, and nothing is known about potential associations between microglial changes in the lateral septum (LS) and adult female cognition. Prenatal exposure to valproic acid (VPA) in mice has been widely used as an experimental model of autism-like behaviors associated with cellular changes. However, no study has reported the influence of VPA exposure in utero and its consequences on limbic system-dependent tasks or the microglial response in the LS in adult female mice. We compared the exploratory activity and risk assessment in novel environments of BALB/c control mice to mice exposed in utero to VPA and estimated the total number of microglia in the LS using an optical fractionator. On day 12.5 of pregnancy, females received diluted VPA or saline by gavage. After weaning, VPA exposed or control pups were separately housed in standard laboratory cages. At 5 months of age, all mice underwent behavioral testing and their brain sections were immunolabelled using IBA-1 antibody. In the open field test, VPA group showed a greater distance traveled, which was accompanied by less immobility, less time spent on the periphery and a greater number, crossed lines. Similar findings were found in the elevated plus maze test, where VPA mice traveled greater distances, immobility was significantly higher than that of control and VPA group spent less time on the closed arms of apparatus. Stereological analysis demonstrated higher microglial total number and density in the LS of VPA mice, as the cell count was greater, but the volume was similar. Therefore, we suggest that an increase in microglia in the LS may be part of the cellular changes associated with behavioral dysfunction in the VPA model of ASD.

Decoding the role of zebrafish neuroglia in CNS disease modeling

Neuroglia, including microglia and astrocytes, is a critical component of the central nervous system (CNS) that interacts with neurons to modulate brain activity, development, metabolism and signaling pathways. Thus, a better understanding of the role of neuroglia in the brain is critical. Complementing clinical and rodent data, the zebrafish (Danio rerio) is rapidly becoming an important model organism to probe the role of neuroglia in brain disorders. With high genetic and physiological similarity to humans and rodents, zebrafish possess some common (shared), as well as some specific molecular biomarkers and features of neuroglia development and functioning. Studying these common and zebrafish-specific aspects of neuroglia may generate important insights into key brain mechanisms, including neurodevelopmental, neurodegenerative, neuroregenerative and neurological processes. Here, we discuss the biology of neuroglia in humans, rodents and fish, its role in various CNS functions, and further directions of translational research into the role of neuroglia in CNS disorders using zebrafish models.

Nuclear Factor Kappa B in Autism Spectrum Disorder: A Systematic Review

BACKGROUND

The nuclear factor kappa B (NF-κB) is composed of a series of transcription factors, which are involved in the expression of a plethora of target genes, many of these genes contributing to the regulation of inflammatory responses. Consistent with its central role in inflammatory responses, existing studies of the neurobiological basis for ASD propose the involvement of NF-κB in the etiology of this disorder.

OBJECTIVES

The present review aimed to systematically characterize extant literatures regarding the role of NF-κB in the etiology of ASD through data derived from both human studies and animal models.

METHODS

A systematic electronic search was conducted for records indexed within Pubmed, EMBASE, or Web of Science to identify potentially eligible studies. Study inclusion and data extraction was agreed by two independent authors after reviewing the abstract and full text.

RESULTS

Among the 371 articles identified in the initial screening, 18 articles met the eligibility criteria for this review, including 14 human case-control studies compared the expression or activation of NF-κB between ASD cases and controls as well as 4 animal studies used mouse model of ASD to examine the level of NF-κB and further evaluate its changes after different drug treatments. These included 18 studies, although relatively small in quantity, appear to support the role of NF-κB in the etiology of ASD.

CONCLUSIONS

Evidence generated from both human studies and animal models supported the involvement of NF-κB in the neurobiological basis of ASD, despite some concern about whether it functions as a primary contributor causes ASD onset or rather an ancillary factor regulates ASD pathogenesis. The increased understanding of NF-κB in the neurobiological basis of ASD could aid the emergence of clinically relevant diagnostic biomarkers and novel therapeutic strategies acting on the underlying disease pathogenesis. These results suggested that potential methodological differences between studies need to be accounted for and keep open the discussion over the existence of aberrantly NF-κB signaling in ASD subjects.

The putative etiology and prevention of autism

Since the initial psychological report by Leo Kanner in 1943, relatively little formal biochemical/neurological research on the cause of autism, other than peripheral searches for genomic mutations, had been carried until the end of the 20th century. As a result of studies on twin sets and the conclusion that autism was largely a hereditary defect, numerous investigations have sought various genetic faults in particular. However, such studies were able to reveal a plausible etiology for this malady in only a small percentage of instances. Key bio-molecular characteristics of this syndrome have been uncovered when the potential roles of the glia were studied in depth. Findings related to biochemical deficiencies appearing early in the newborn, such as depressed IGF-1 (insulin-like growth factor #1) in neurogenesis/myelination, are becoming emphasized in many laboratories. Progress leading to timely diagnoses and subsequent prevention of central nervous system dysconnectivity now seems plausible. The tendency for an infant to develop autism may currently be determinable and preventable before irreversible psychosocial disturbances become established. These discussions about glial function will be inter-spersed with comments about their apparent relevance to autism. The concluding portion of this presentation will be a detailed review and summation of this diagnosis and prevention proposition.

The role of neuroglia in autism spectrum disorders

Neuroglia are a large class of neural cells of ectodermal (astroglia, oligodendroglia, and peripheral glial cells) and mesodermal (microglia) origin. Neuroglial cells provide homeostatic support, protection, and defense to the nervous tissue. Pathological potential of neuroglia has been acknowledged since their discovery. Research of the recent decade has shown the key role of all classes of glial cells in autism spectrum disorders (ASD), although molecular mechanisms defining glial contribution to ASD are yet to be fully characterized. This narrative conceptualizes recent findings of the broader roles of glial cells, including their active participation in the control of cerebral environment and regulation of synaptic development and scaling, highlighting their putative involvement in the etiopathogenesis of ASD.

Oxidative Stress and Immune System Dysfunction in Autism Spectrum Disorders

Autism Spectrum Disorders (ASDs) represent a group of neurodevelopmental disorders associated with social and behavioral impairments. Although dysfunctions in several signaling pathways have been associated with ASDs, very few molecules have been identified as potentially effective drug targets in the clinic. Classically, research in the ASD field has focused on the characterization of pathways involved in neural development and synaptic plasticity, which support the pathogenesis of this group of diseases. More recently, immune system dysfunctions have been observed in ASD. In addition, high levels of reactive oxygen species (ROS), which cause oxidative stress, are present in ASD patients. In this review, we will describe the major alterations in the expression of genes coding for enzymes involved in the ROS scavenging system, in both ASD patients and ASD mouse models. In addition, we will discuss, in the context of the most recent literature, the possibility that oxidative stress, inflammation and immune system dysfunction may be connected to, and altogether support, the pathogenesis and/or severity of ASD. Finally, we will discuss the possibility of novel treatments aimed at counteracting the interplay between ROS and inflammation in people with ASD.

Neuropsychopathology of Autism Spectrum Disorder: Complex Interplay of Genetic, Epigenetic, and Environmental Factors

Autism spectrum disorder (ASD) is a complex heterogeneous consortium of pervasive development disorders (PDD) which ranges from atypical autism, autism, and Asperger syndrome affecting brain in the developmental stage. This debilitating neurodevelopmental disorder results in both core as well as associated symptoms. Core symptoms observed in autistic patients are lack of social interaction, pervasive, stereotyped, and restricted behavior while the associated symptoms include irritability, anxiety, aggression, and several comorbid disorders.ASD is a polygenic disorder and is multifactorial in origin. Copy number variations (CNVs) of several genes that regulate the synaptogenesis and signaling pathways are one of the major factors responsible for the pathogenesis of autism. The complex integration of various CNVs cause mutations in the genes which code for molecules involved in cell adhesion, voltage-gated ion-channels, scaffolding proteins as well as signaling pathways (PTEN and mTOR pathways). These mutated genes are responsible for affecting synaptic transmission by causing plasticity dysfunction responsible, in turn, for the expression of ASD.Epigenetic modifications affecting DNA transcription and various pre-natal and post-natal exposure to a variety of environmental factors are also precipitating factors for the occurrence of ASD. All of these together cause dysregulation of glutamatergic signaling as well as imbalance in excitatory: inhibitory pathways resulting in glial cell activation and release of inflammatory mediators responsible for the aberrant social behavior which is observed in autistic patients.In this chapter we review and provide insight into the intricate integration of various genetic, epigenetic, and environmental factors which play a major role in the pathogenesis of this disorder and the mechanistic approach behind this integration.

Plasma Levels of Glial Cell Marker S100B in Children With Autism

Autism spectrum disorder (ASD) is a neurodevelopmental condition with increasing incidence. Recent evidences suggest glial cells involvement in autism pathophysiology. S100B is a calcium binding protein, mainly found in astrocytes and therefore used as a marker of their activity. In our study, children with autism had higher plasma concentrations of S100B compared to non-autistic controls. No association of S100B plasma levels with behavioral symptoms (ADI-R and ADOS-2 scales) was found. Plasma S100B concentration significantly correlated with urine serotonin, suggesting their interconnection. Correlation of plasma S100B levels with stool calprotectin concentrations was found, suggesting not only brain astrocytes, but also enteric glial cells may take part in autism pathogenesis. Based on our findings, S100B seems to have a potential to be used as a biomarker of human neurodevelopmental disorders, but more investigations are needed to clarify its exact role in pathomechanism of autism.

The fetal origins of mental illness

The impact of infections and inflammation during pregnancy on the developing fetal brain remains incompletely defined, with important clinical and research gaps. Although the classic infectious TORCH pathogens (ie, Toxoplasma gondii, rubella virus, cytomegalovirus [CMV], herpes simplex virus) are known to be directly teratogenic, emerging evidence suggests that these infections represent the most extreme end of a much larger spectrum of injury. We present the accumulating evidence that prenatal exposure to a wide variety of viral and bacterial infections-or simply inflammation-may subtly alter fetal brain development, leading to neuropsychiatric consequences for the child later in life. The link between influenza infections in pregnant women and an increased risk for development of schizophrenia in their children was first described more than 30 years ago. Since then, evidence suggests that a range of infections during pregnancy may also increase risk for autism spectrum disorder and depression in the child. Subsequent studies in animal models demonstrated that both pregnancy infections and inflammation can result in direct injury to neurons and neural progenitor cells or indirect injury through activation of microglia and astrocytes, which can trigger cytokine production and oxidative stress. Infectious exposures can also alter placental serotonin production, which can perturb neurotransmitter signaling in the developing brain. Clinically, detection of these subtle injuries to the fetal brain is difficult. As the neuropsychiatric impact of perinatal infections or inflammation may not be known for decades after birth, our construct for defining teratogenic infections in pregnancy (eg, TORCH) based on congenital anomalies is insufficient to capture the full adverse impact on the child. We discuss the clinical implications of this body of evidence and how we might place greater emphasis on prevention of prenatal infections. For example, increasing uptake of the seasonal influenza vaccine is a key strategy to reduce perinatal infections and the risk for fetal brain injury. An important research gap exists in understanding how antibiotic therapy during pregnancy affects the fetal inflammatory load and how to avoid inflammation-mediated injury to the fetal brain. In summary, we discuss the current evidence and mechanisms linking infections and inflammation with the increased lifelong risk of neuropsychiatric disorders in the child, and how we might improve prenatal care to protect the fetal brain.

Long-term Risk of Neuropsychiatric Disease After Exposure to Infection In Utero

IMPORTANCE

The developmental origins of mental illness are incompletely understood. Although the development of autism and schizophrenia are linked to infections during fetal life, it is unknown whether more common psychiatric conditions such as depression might begin in utero.

OBJECTIVE

To estimate the risk of psychopathologic conditions imparted from fetal exposure to any maternal infection while hospitalized during pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

A total of 1 791 520 Swedish children born between January 1, 1973, and December 31, 2014, were observed for up to 41 years using linked population-based registries. Children were excluded if they were born too late to contribute person-time, died before being at risk for the outcome, or were missing particular model data. Infection and psychiatric diagnoses were derived using codes from hospitalizations. Directed acyclic graphs were developed from a systematic literature review to determine Cox proportional hazards regression models for risk of psychopathologic conditions in the children. Results were evaluated using probabilistic and simple bias analyses. Statistical analysis was conducted from February 10 to October 17, 2018.

EXPOSURES

Hospitalization during pregnancy with any maternal infection, severe maternal infection, and urinary tract infection.

MAIN OUTCOMES AND MEASURES

Inpatient diagnosis of autism, depression, bipolar disorder, or psychosis among offspring.

RESULTS

A total of 1 791 520 Swedish-born children (48.6% females and 51.4% males) were observed from birth up to age 41 years, with a total of 32 125 813 person-years. Within the directed acyclic graph framework of assumptions, fetal exposure to any maternal infection increased the risk of an inpatient diagnosis in the child of autism (hazard ratio [HR], 1.79; 95% CI, 1.34-2.40) or depression (HR, 1.24; 95% CI, 1.08-1.42). Effect estimates for autism and depression were similar following a severe maternal infection (autism: HR, 1.81; 95% CI, 1.18-2.78; depression: HR, 1.24; 95% CI, 0.88-1.73) or urinary tract infection (autism: HR, 1.89; 95% CI, 1.23-2.90; depression: HR, 1.30; 95% CI, 1.04-1.61) and were robust to moderate unknown confounding. Within the directed acyclic graph framework of assumptions, the relationship between infection and depression was vulnerable to bias from loss to follow-up, but separate data from the Swedish Death Registry demonstrated increased risk of suicide among individuals exposed to pregnancy infection. No evidence was found for increased risk of bipolar disorder or psychosis among children exposed to infection in utero.

CONCLUSIONS AND RELEVANCE

These findings suggest that fetal exposure to a maternal infection while hospitalized increased the risk for autism and depression, but not bipolar or psychosis, during the child's life. These results emphasize the importance of avoiding infections during pregnancy, which may impart subtle fetal brain injuries contributing to development of autism and depression.

Hippocampal and amygdalar cell-specific translation is similar soon after stress but diverge over time

Stress is known to cause contrasting patterns of morphological and physiological plasticity in the hippocampus and amygdala. An obligatory cellular process underlying such neural changes is de novo translation and alterations in protein expression. Yet the nature of the translational response to stress in neurons remains largely unexplored. Even less is known about how glia are affected. Using a click-chemistry-based method to label the de novo proteome in live brain slices, we monitored translation in neurons and astrocytes of the basolateral amygdala (BLA) and dorsal hippocampal area CA3 (dCA3) in rats at different time-points after a single 2-hr exposure to immobilization stress. We observed enhancements in neuronal translation in both brain regions 1 hour after stress. This initial increase persisted in the BLA up to 10 days afterwards. In contrast, dCA3 neuronal translation gradually decreased to below control levels 10 days later. Translation profiles of dCA3 astrocytes followed timelines similar to neurons, but in BLA astrocytes translation peaked 1 day later and remained elevated 10 days later. Together our results demonstrate that stress causes an immediate upregulation of protein synthesis in both amygdalar and hippocampal neurons and astrocytes. However, these two areas eventually exhibit opposite temporal profiles of protein expression well after the end of stress. These findings identify new metrics of stress-induced plasticity at the level of cell-type specific proteomic landscape that may provide important insights into the molecular basis of the divergent temporal effects of stress across brain regions and biological scales.

Microglia exit the CNS in spinal root avulsion

Microglia are central nervous system (CNS)-resident cells. Their ability to migrate outside of the CNS, however, is not understood. Using time-lapse imaging in an obstetrical brachial plexus injury (OBPI) model, we show that microglia squeeze through the spinal boundary and emigrate to peripheral spinal roots. Although both macrophages and microglia respond, microglia are the debris-clearing cell. Once outside the CNS, microglia re-enter the spinal cord in an altered state. These peripheral nervous system (PNS)-experienced microglia can travel to distal CNS areas from the injury site, including the brain, with debris. This emigration is balanced by two mechanisms—induced emigration via N-methyl-D-aspartate receptor (NMDA) dependence and restriction via contact-dependent cellular repulsion with macrophages. These discoveries open the possibility that microglia can migrate outside of their textbook-defined regions in disease states.

Microglia are normally assumed to be confined to the central nervous system (CNS), but this study shows show that after spinal root injury, microglia can exit the CNS to clear debris. Upon re-entry, the emigrated microglia are altered and can travel to distal areas such as the brain.

Cells are precisely organized in specific anatomical domains to ensure normal functioning of the nervous system. One such cell type, microglia, is usually considered to be confined to the central nervous system (CNS). Using time-lapse imaging to capture microglia as they migrate, we show that their characteristic CNS-residency can be altered after spinal root injury. After such injury, the microglia exit the spinal root to the periphery, where they clear debris at the injury site and then carry that debris back into the CNS. In addition, microglia that leave the CNS after spinal root injury become distinct from those that remain within the CNS. This emigration event of microglia after injury is driven by two mechanisms—dependence on glutamatergic signaling that induces their emigration to the injury and interactions with macrophages that prevent their ectopic exit from the spinal cord. Together, these discoveries raise the possibility that microglia could override their CNS-residency in certain disease contexts.