Microglia from offspring of dams with allergic asthma exhibit epigenomic alterations in genes dysregulated in autism

Developmental functions of microglia: Impact of psychosocial and physiological early life stress

Microglia play numerous important roles in brain development. From early embryonic stages through adolescence, these immune cells influence neuronal genesis and maturation, guide connectivity, and shape brain circuits. They also interact with other glial cells and structures, influencing the brain's supportive microenvironment. While this central role makes microglia essential, it means that early life perturbations to microglia can have widespread effects on brain development, potentially resulting in long-lasting behavioral impairments. Here, we will focus on the effects of early life psychosocial versus physiological stressors in rodent models. Psychosocial stress refers to perceived threats that lead to stress axes activation, including prenatal stress, or chronic postnatal stress, including maternal separation and resource scarcity. Physiological stress refers to physical threats, including maternal immune activation, postnatal infection, and traumatic brain injury. Differing sources of early life stress have varied impacts on microglia, and these effects are moderated by factors such as developmental age, brain region, and sex. Overall, these stressors appear to either 1) upregulate basal microglia numbers and activity throughout the lifespan, while possibly blunting their responsivity to subsequent stressors, or 2) shift the developmental curve of microglia, resulting in differential timing and function, impacting the critical periods they govern. Either could contribute to behavioral dysfunctions that occur after the resolution of early life stress. Exploring how different stressors impact microglia, as well as how multiple stressors interact to alter microglia's developmental functions, could deepen our understanding of how early life stress changes the brain's developmental trajectory. This article is part of the Special Issue on "Microglia".

Bi-allelic NRXN1α deletion in microglia derived from iPSC of an autistic patient increases interleukin-6 production and impairs supporting function on neuronal networking

Autism spectrum disorder (ASD) is a set of heterogeneous neurodevelopmental conditions, with a highly diverse genetic hereditary component, including altered neuronal circuits, that has an impact on communication skills and behaviours of the affected individuals. Beside the recognised role of neuronal alterations, perturbations of microglia and the associated neuroinflammatory processes have emerged as credible contributors to aetiology and physiopathology of ASD. Mutations in NRXN1, a member of the neurexin family of cell-surface receptors that bind neuroligin, have been associated to ASD. NRXN1 is known to be expressed by neurons where it facilitates synaptic contacts, but it has also been identified in glial cells including microglia. Asserting the impact of ASD-related genes on neuronal versus microglia functions has been challenging. Here, we present an ASD subject-derived induced pluripotent stem cells (iPSC)-based in vitro system to characterise the effects of the ASD-associated NRXN1 gene deletion on neurons and microglia, as well as on the ability of microglia to support neuronal circuit formation and function. Using this approach, we demonstrated that NRXN1 deletion, impacting on the expression of the alpha isoform (NRXN1α), in microglia leads to microglial alterations and release of IL6, a pro-inflammatory interleukin associated with ASD. Moreover, microglia bearing the NRXN1α-deletion, lost the ability to support the formation of functional neuronal networks. The use of recombinant IL6 protein on control microglia-neuron co-cultures or neutralizing antibody to IL6 on their NRXN1α-deficient counterparts, supported a direct contribution of IL6 to the observed neuronal phenotype. Altogether, our data suggest that, in addition to neurons, microglia are also negatively affected by NRXN1α-deletion, and this significantly contributes to the observed neuronal circuit aberrations.

The role of microglia in early neurodevelopment and the effects of maternal immune activation

Activation of the maternal immune system during gestation has been associated with an increased risk for neurodevelopmental disorders in the offspring, particularly schizophrenia and autism spectrum disorder. Microglia, the tissue-resident macrophages of the central nervous system, are implicated as potential mediators of this increased risk. Early in development, microglia start populating the embryonic central nervous system and in addition to their traditional role as immune responders under homeostatic conditions, microglia are also intricately involved in various early neurodevelopmental processes. The timing of immune activation may interfere with microglia functioning during early neurodevelopment, potentially leading to long-term consequences in postnatal life. In this review we will discuss the involvement of microglia in brain development during the prenatal and early postnatal stages of life, while also examining the effects of maternal immune activation on microglia and neurodevelopmental processes. Additionally, we discuss recent single cell RNA-sequencing studies focusing on microglia during prenatal development, and hypothesize how early life microglial priming, potentially through epigenetic reprogramming, may be related to neurodevelopmental disorders.

Development of a High-Throughput Pipeline to Characterize Microglia Morphological States at a Single-Cell Resolution

As rapid responders to their environments, microglia engage in functions that are mirrored by their cellular morphology. Microglia are classically thought to exhibit a ramified morphology under homeostatic conditions which switches to an ameboid form during inflammatory conditions. However, microglia display a wide spectrum of morphologies outside of this dichotomy, including rod-like, ramified, ameboid, and hypertrophic states, which have been observed across brain regions, neurodevelopmental timepoints, and various pathological contexts. We applied dimensionality reduction and clustering to consider contributions of multiple morphology measures together to define a spectrum of microglial morphological states in a mouse dataset that we used to demonstrate the utility of our toolset. Using ImageJ, we first developed a semiautomated approach to characterize 27 morphology features from hundreds to thousands of individual microglial cells in a brain region-specific manner. Within this pool of features, we defined distinct sets of highly correlated features that describe different aspects of morphology, including branch length, branching complexity, territory span, and circularity. When considered together, these sets of features drove different morphological clusters. Our tools captured morphological states similarly and robustly when applied to independent datasets and using different immunofluorescent markers for microglia. We have compiled our morphology analysis pipeline into an accessible, easy-to-use, and fully open-source ImageJ macro and R package that the neuroscience community can expand upon and directly apply to their own analyses. Outcomes from this work will supply the field with new tools to systematically evaluate the heterogeneity of microglia morphological states across various experimental models and research questions.

AllergoOncology: Biomarkers and refined classification for research in the allergy and glioma nexus-A joint EAACI-EANO position paper

Epidemiological studies have explored the relationship between allergic diseases and cancer risk or prognosis in AllergoOncology. Some studies suggest an inverse association, but uncertainties remain, including in IgE-mediated diseases and glioma. Allergic disease stems from a Th2-biased immune response to allergens in predisposed atopic individuals. Allergic disorders vary in phenotype, genotype and endotype, affecting their pathophysiology. Beyond clinical manifestation and commonly used clinical markers, there is ongoing research to identify novel biomarkers for allergy diagnosis, monitoring, severity assessment and treatment. Gliomas, the most common and diverse brain tumours, have in parallel undergone changes in classification over time, with specific molecular biomarkers defining glioma subtypes. Gliomas exhibit a complex tumour-immune interphase and distinct immune microenvironment features. Immunotherapy and targeted therapy hold promise for primary brain tumour treatment, but require more specific and effective approaches. Animal studies indicate allergic airway inflammation may delay glioma progression. This collaborative European Academy of Allergy and Clinical Immunology (EAACI) and European Association of Neuro-Oncology (EANO) Position Paper summarizes recent advances and emerging biomarkers for refined allergy and adult-type diffuse glioma classification to inform future epidemiological and clinical studies. Future research is needed to enhance our understanding of immune-glioma interactions to ultimately improve patient prognosis and survival.

Innate Immune Dysfunction and Neuroinflammation in Autism Spectrum Disorder (ASD)

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by communication and social behavior deficits. The presence of restricted and repetitive behaviors often accompanies these deficits, and these characteristics can range from mild to severe. The past several decades have seen a significant rise in the prevalence of ASD. The etiology of ASD remains unknown; however, genetic and environmental risk factors play a role. Multiple hypotheses converge to suggest that neuroinflammation, or at least the interaction between immune and neural systems, may be involved in the etiology of some ASD cases or groups. Repeated evidence of innate immune dysfunction has been seen in ASD, often associated with worsening behaviors. This evidence includes data from circulating myeloid cells and brain resident macrophages/microglia in both human and animal models. This comprehensive review presents recent findings of innate immune dysfunction in ASD, including aberrant innate cellular function, evidence of neuroinflammation, and microglia activation. Appeared originally in Brain Behav Immun 2023; 108:245-254.

The influence of asthma on neuroinflammation and neurodevelopment: From epidemiology to basic models

Asthma is a highly heterogeneous inflammatory disease that can have a significant effect on both the respiratory system and central nervous system. Population based studies and animal models have found asthma to be comorbid with a number of neurological conditions, including depression, anxiety, and neurodevelopmental disorders. In addition, maternal asthma during pregnancy has been associated with neurodevelopmental disorders in the offspring, such as autism spectrum disorders and attention deficit hyperactivity disorder. In this article, we review the most current epidemiological studies of asthma that identify links to neurological conditions, both as it relates to individuals that suffer from asthma and the impacts asthma during pregnancy may have on offspring neurodevelopment. We also discuss the relevant animal models investigating these links, address the gaps in knowledge, and explore the potential future directions in this field.

Preclinical models of maternal asthma and progeny outcomes: a scoping review

There is an increased risk of adverse perinatal outcomes in the ∼17% of women with asthma during pregnancy. The mechanisms linking maternal asthma and adverse outcomes are largely unknown, but reflect joint effects of genetics and prenatal exposure to maternal asthma. Animal models are essential to understand the underlying mechanisms independent of genetics and comorbidities, and enable safe testing of interventions. This scoping review aimed to explore the methodology, phenotype, characteristics, outcomes and quality of published studies using preclinical maternal asthma models. MEDLINE (PubMed), Embase (Elsevier) and Web of Science were systematically searched using previously validated search strings for maternal asthma and for animal models. Two reviewers independently screened titles and abstracts, full texts, and then extracted and assessed the quality of each study using the Animal Research: Reporting of In Vivo Experiments (ARRIVE) 2.0 guidelines. Out of 3618 studies identified, 39 were eligible for extraction. Most studies were in rodents (86%) and all were models of allergic asthma. Maternal and progeny outcomes included airway hyperresponsiveness, airway resistance, inflammation, lung immune cells, lung structure and serum immunoglobulins and cytokines. Experimental design (100%), procedural details (97%) and rationale (100%) were most often reported. Conversely, data exclusion (21%), blinding (18%) and adverse events (8%) were reported in a minority of studies. Species differences in physiology and timing of development, the use of allergens not relevant to humans and a lack of comparable outcome measures may impede clinical translation. Future studies exploring models of maternal asthma should adhere to the minimum core outcomes set presented in this review.

Inflammatory Conditions During Pregnancy and Risk of Autism and Other Neurodevelopmental Disorders

Background

Maternal inflammation can result from immune dysregulation and metabolic perturbations during pregnancy. Whether conditions associated with inflammation during pregnancy increase the likelihood of autism spectrum disorder (ASD) or other neurodevelopmental disorders (DDs) is not well understood.

Methods

We conducted a case-control study among children born in California from 2011 to 2016 to investigate maternal immune-mediated and cardiometabolic conditions during pregnancy and risk of ASD (n = 311) and DDs (n = 1291) compared with children from the general population (n = 967). Data on maternal conditions and covariates were retrieved from electronic health records. Maternal genetic data were used to assess a causal relationship.

Results

Using multivariable logistic regression, we found that mothers with asthma were more likely to deliver infants later diagnosed with ASD (odds ratio [OR] = 1.62, 95% CI: 1.15-2.29) or DDs (OR = 1.30, 95% CI: 1.02-1.64). Maternal obesity was also associated with child ASD (OR = 1.51, 95% CI: 1.07-2.13). Mothers with both asthma and extreme obesity had the greatest odds of delivering an infant later diagnosed with ASD (OR = 16.9, 95% CI: 5.13-55.71). These increased ASD odds were observed among female children only. Polygenic risk scores for obesity, asthma, and their combination showed no association with ASD risk. Mendelian randomization did not support a causal relationship between maternal conditions and ASD.

Conclusions

Inflammatory conditions during pregnancy are associated with risk for neurodevelopmental disorders in children. These risks do not seem to be due to shared genetic risk; rather, inflammatory conditions may share nongenetic risk factors with neurodevelopmental disorders. Children whose mothers have both asthma and obesity during pregnancy may benefit from earlier screening and intervention.

Maternal autoimmune disease and risk of offspring autism spectrum disorder - a nationwide population-based cohort study

Introduction

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders which cause long term social and behavior impairment, and its prevalence is on the rise. Studies about the association between maternal autoimmune diseases and offspring ASD have controversial results. The aim of this study was to investigate whether maternal autoimmune diseases increase the risk of ASD in offspring from a population-based perspective.

Methods

The data sources were Taiwan's National Health Insurance Research Database (NHIRD) and Taiwan's Maternal and Child Health Database (MCHD), which were integrated and used to identify newborns whose mothers were diagnosed with autoimmune disease. Newborns were matched by maternal age, neonatal gender, and date of birth with controls whose mothers were without autoimmune disease using a ratio of 1:4 between 2004 and 2019. Data on diagnoses of autoimmune disease and autism spectrum disorders were retrieved from NHIRD. Patients who had at least 3 outpatient visits or at least 1 admission with a diagnosis of autoimmune disease and autism spectrum disorders were defined as incidence cases. The risks of ASD in offspring were compared between mothers with or without autoimmune disorders.

Results

We identified 20,865 newborns whose mothers had been diagnosed with autoimmune disease before pregnancy and matched them at a ratio of 1:4 with a total of 83,460 newborn whose mothers were without autoimmune disease, by maternal age, neonatal gender, and date of birth. They were randomly selected as the control group. The cumulative incidence rates of autism spectrum disorders (ASD) were significantly higher among the offspring of mothers with autoimmune diseases. After adjusting for cofactors, the risk of ASD remained significantly higher in children whose mother had autoimmune diseases. Regarding to specific maternal autoimmune disease, Sjögren's syndrome and rheumatoid arthritis were both associated with elevated risks of ASD in offspring.

Conclusion

Mother with autoimmune disease might be associated with increasing the risk of autism spectrum disorder in offspring.

Characterizing the neuroimmune environment of offspring in a novel model of maternal allergic asthma and particulate matter exposure

Inflammation during pregnancy is associated with an increased risk for neurodevelopmental disorders (NDD). Increased gestational inflammation can be a result of an immune condition/disease, exposure to infection, and/or environmental factors. Epidemiology studies suggest that cases of NDD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with NDD such as autism spectrum disorders (ASD). Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were sensitized for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA to induce allergic asthma or phosphate buffered saline (PBS) for 1 h. Following the 1-h exposure, pregnant females were then exposed to UIS with a size distribution of 55 to 169 nm at an average concentration of 176 ± 45 μg/m3) (SD), or clean air for 4 h, over 8 exposure sessions. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. There was a suppressive effect of the combined MAA plus UIS on the anti-inflammatory cytokine IL-10. Potentially shifting the cytokine balance towards more neuroinflammation. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Maternal atopic conditions and autism spectrum disorder: a systematic review

Autism spectrum disorder (ASD) is a disabling neurodevelopmental condition with complex etiology. Emerging evidence has pointed to maternal atopy as a possible risk factor. It is hypothesized that maternal atopic disease during pregnancy can lead to increased levels of inflammatory cytokines in fetal circulation via placental transfer or increased production. These cytokines can then pass through the immature blood-brain barrier, causing aberrant neurodevelopment via mechanisms including premature microglial activation. The objective of this study is to systematically review observational studies that investigate whether a maternal history of atopic disease (asthma, allergy, or eczema/atopic dermatitis) is associated with a diagnosis of ASD in offspring. A search was conducted in Ovid MEDLINE, PsycINFO, and Embase databases for relevant articles up to November 2021; this was later updated in January 2022. Observational studies published in peer-reviewed journals were included. Data were synthesized and qualitatively analyzed according to the specific atopic condition. Quality assessment was done using the Newcastle-Ottawa Scale. Nine articles were identified, with all including asthma as an exposure, alongside four each for allergy and eczema. Findings were inconsistent regarding the association between a maternal diagnosis of either asthma, allergy, or eczema, and ASD in offspring, with variations in methodology contributing to the inconclusiveness. More consistent associations were demonstrated regarding maternal asthma that was treated or diagnosed during pregnancy. Evidence suggests that symptomatic maternal asthma during pregnancy could be associated with ASD in offspring, underscoring the importance of effective management of atopic conditions during pregnancy. Further research is needed, particularly longitudinal studies that use gold-standard assessment tools and correlate clinical outcomes with laboratory and treatment data.PROSPERO Registration Number and Date: CRD42018116656, 26.11.2018.

Maternal Chronic Ultrasound Stress Provokes Immune Activation and Behavioral Deficits in the Offspring: A Mouse Model of Neurodevelopmental Pathology

Neurodevelopmental disorders stemming from maternal immune activation can significantly affect a child's life. A major limitation in pre-clinical studies is the scarcity of valid animal models that accurately mimic these challenges. Among the available models, administration of lipopolysaccharide (LPS) to pregnant females is a widely used paradigm. Previous studies have reported that a model of 'emotional stress', involving chronic exposure of rodents to ultrasonic frequencies, induces neuroinflammation, aberrant neuroplasticity, and behavioral deficits. In this study, we explored whether this model is a suitable paradigm for maternal stress and promotes neurodevelopmental abnormalities in the offspring of stressed females. Pregnant dams were exposed to ultrasound stress for 21 days. A separate group was injected with LPS on embryonic days E11.5 and E12.5 to mimic prenatal infection. The behavior of the dams and their female offspring was assessed using the sucrose test, open field test, and elevated plus maze. Additionally, the three-chamber sociability test and Barnes maze were used in the offspring groups. ELISA and qPCR were used to examine pro-inflammatory changes in the blood and hippocampus of adult females. Ultrasound-exposed adult females developed a depressive-like syndrome, hippocampal overexpression of GSK-3β, IL-1β, and IL-6 and increased serum concentrations of IL-1β, IL-6, IL-17, RANTES, and TNFα. The female offspring also displayed depressive-like behavior, as well as cognitive deficits. These abnormalities were comparable to the behavioral changes induced by LPS. The ultrasound stress model can be a promising animal paradigm of neurodevelopmental pathology associated with prenatal 'emotional stress'.

Characterizing the Neuroimmune Environment of Offspring in a Novel Model of Maternal Allergic Asthma and Particulate Matter Exposure

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by the presence of decreased social interactions and an increase in stereotyped and repetitive behaviors. Epidemiology studies suggest that cases of ASD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with ASD. Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders including ASD. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were primed for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA or phosphate buffered saline (PBS) for 1 hour. Following the 1-hour exposure, pregnant females were then exposed to UIS or clean air for 4 hours. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), IL-2, IL-13, and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely interferon gamma (IFNγ) and IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Correlation of mutated gene and signalling pathways in ASD

Autism is a complicated spectrum of neurodevelopmental illnesses characterized by repetitive and constrained behaviors and interests, as well as social interaction and communication difficulties that are first shown in infancy. More than 18 million Indians, according to the National Health Portal of India, and 1 in 160 children worldwide, according to the WHO, are diagnosed with autism spectrum disorders. This review aims to discuss the complex genetic architecture that underlies autism and summarizes the role of proteins likely to play in the development of autism. We also consider how genetic mutations can affect convergent signaling pathways and hinder the development of brain circuitry and the role of cognition development and theory of mind with Cognition-behavior therapy benefits in autism.

Modelling Microglial Innate Immune Memory In Vitro: Understanding the Role of Aerobic Glycolysis in Innate Immune Memory

Microglia, the resident macrophages of the central nervous system, play important roles in maintaining brain homeostasis and facilitating the brain's innate immune responses. Following immune challenges microglia also retain immune memories, which can alter responses to secondary inflammatory challenges. Microglia have two main memory states, training and tolerance, which are associated with increased and attenuated expression of inflammatory cytokines, respectively. However, the mechanisms differentiating these two distinct states are not well understood. We investigated mechanisms underlying training versus tolerance memory paradigms in vitro in BV2 cells using B-cell-activating factor (BAFF) or bacterial lipopolysaccharide (LPS) as a priming stimulus followed by LPS as a second stimulus. BAFF followed by LPS showed enhanced responses indicative of priming, whereas LPS followed by LPS as the second stimulus caused reduced responses suggestive of tolerance. The main difference between the BAFF versus the LPS stimulus was the induction of aerobic glycolysis by LPS. Inhibiting aerobic glycolysis during the priming stimulus using sodium oxamate prevented the establishment of the tolerized memory state. In addition, tolerized microglia were unable to induce aerobic glycolysis upon LPS restimulus. Therefore, we conclude that aerobic glycolysis triggered by the first LPS stimulus was a critical step in the induction of innate immune tolerance.

Allergic airway inflammation delays glioblastoma progression and reinvigorates systemic and local immunity in mice

BACKGROUND

Numerous patient-based studies have highlighted the protective role of immunoglobulin E-mediated allergic diseases on glioblastoma (GBM) susceptibility and prognosis. However, the mechanisms behind this observation remain elusive. Our objective was to establish a preclinical model able to recapitulate this phenomenon and investigate the role of immunity underlying such protection.

METHODS

An immunocompetent mouse model of allergic airway inflammation (AAI) was initiated before intracranial implantation of mouse GBM cells (GL261). RAG1-KO mice served to assess tumor growth in a model deficient for adaptive immunity. Tumor development was monitored by MRI. Microglia were isolated for functional analyses and RNA-sequencing. Peripheral as well as tumor-associated immune cells were characterized by flow cytometry. The impact of allergy-related microglial genes on patient survival was analyzed by Cox regression using publicly available datasets.

RESULTS

We found that allergy establishment in mice delayed tumor engraftment in the brain and reduced tumor growth resulting in increased mouse survival. AAI induced a transcriptional reprogramming of microglia towards a pro-inflammatory-like state, uncovering a microglia gene signature, which correlated with limited local immunosuppression in glioma patients. AAI increased effector memory T-cells in the circulation as well as tumor-infiltrating CD4⁺ T-cells. The survival benefit conferred by AAI was lost in mice devoid of adaptive immunity.

CONCLUSION

Our results demonstrate that AAI limits both tumor take and progression in mice, providing a preclinical model to study the impact of allergy on GBM susceptibility and prognosis, respectively. We identify a potentiation of local and adaptive systemic immunity, suggesting a reciprocal crosstalk that orchestrates allergy-induced immune protection against GBM.

Innate immune dysfunction and neuroinflammation in autism spectrum disorder (ASD)

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by communication and social behavior deficits. The presence of restricted and repetitive behaviors often accompanies these deficits, and these characteristics can range from mild to severe. The past several decades have seen a significant rise in the prevalence of ASD. The etiology of ASD remains unknown; however, genetic and environmental risk factors play a role. Multiple hypotheses converge to suggest that neuroinflammation, or at least the interaction between immune and neural systems, may be involved in the etiology of some ASD cases or groups. Repeated evidence of innate immune dysfunction has been seen in ASD, often associated with worsening behaviors. This evidence includes data from circulating myeloid cells and brain resident macrophages/microglia in both human and animal models. This comprehensive review presents recent findings of innate immune dysfunction in ASD, including aberrant innate cellular function, evidence of neuroinflammation, and microglia activation.

Microglia and astrocytes underlie neuroinflammation and synaptic susceptibility in autism spectrum disorder

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder with onset in childhood. The mechanisms underlying ASD are unclear. In recent years, the role of microglia and astrocytes in ASD has received increasing attention. Microglia prune the synapses or respond to injury by sequestrating the injury site and expressing inflammatory cytokines. Astrocytes maintain homeostasis in the brain microenvironment through the uptake of ions and neurotransmitters. However, the molecular link between ASD and microglia and, or astrocytes remains unknown. Previous research has shown the significant role of microglia and astrocytes in ASD, with reports of increased numbers of reactive microglia and astrocytes in postmortem tissues and animal models of ASD. Therefore, an enhanced understanding of the roles of microglia and astrocytes in ASD is essential for developing effective therapies. This review aimed to summarize the functions of microglia and astrocytes and their contributions to ASD.

Sex Differences in Neurodevelopmental Disorders: A Key Role for the Immune System

Sex differences are prominent defining features of neurodevelopmental disorders. Understanding the sex biases in these disorders can shed light on mechanisms leading to relative risk and resilience for the disorders, as well as more broadly advance our understanding of how sex differences may relate to brain development. The prevalence of neurodevelopmental disorders is increasing, and the two most common neurodevelopmental disorders, Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) exhibit male-biases in prevalence rates and sex differences in symptomology. While the causes of neurodevelopmental disorders and their sex differences remain to be fully understood, increasing evidence suggests that the immune system plays a critical role in shaping development. In this chapter we discuss sex differences in prevalence and symptomology of ASD and ADHD, review sexual differentiation and immune regulation of neurodevelopment, and discuss findings from human and rodent studies of immune dysregulation and perinatal immune perturbation as they relate to potential mechanisms underlying neurodevelopmental disorders. This chapter will give an overview of how understanding sex differences in neuroimmune function in the context of neurodevelopmental disorders could lend insight into their etiologies and better treatment strategies.

Work hard, play hard: how sexually differentiated microglia work to shape social play and reproductive behavior

Microglia are brain-resident immune cells that play a critical role in synaptic pruning and circuit fine-tuning during development. In the adult brain, microglia actively survey their local environment and mobilize inflammatory responses to signs of damage or infection. Sex differences in microglial gene expression and function across the lifespan have been identified, which play a key role in shaping brain function and behavior. The levels of sex hormones such as androgens, estrogens, and progesterone vary in an age-dependent and sex-dependent manner. Microglia respond both directly and indirectly to changes in hormone levels, altering transcriptional gene expression, morphology, and function. Of particular interest is the microglial function in brain regions that are highly sexually differentiated in development such as the amygdala as well as the pre-optic and ventromedial hypothalamic regions. With a focus on hormone-sensitive developmental windows, this review compares male and female microglia in the embryonic, developing, and adult brain with a particular interest in the influence of sex hormones on microglial wiring of social, reproductive, and disordered behavior circuits in the brain.

Cell-type-specific epigenetic effects of early life stress on the brain

Early life stress (ELS) induces long-term phenotypic adaptations that contribute to increased vulnerability to a host of neuropsychiatric disorders. Epigenetic mechanisms, including DNA methylation, histone modifications and non-coding RNA, are a proposed link between environmental stressors, alterations in gene expression, and phenotypes. Epigenetic modifications play a primary role in shaping functional differences between cell types and can be modified by environmental perturbations, especially in early development. Together with contributions from genetic variation, epigenetic mechanisms orchestrate patterns of gene expression within specific cell types that contribute to phenotypic variation between individuals. To date, many studies have provided insights into epigenetic changes resulting from ELS. However, most of these studies have examined heterogenous brain tissue, despite evidence of cell-type-specific epigenetic modifications in phenotypes associated with ELS. In this review, we focus on rodent and human studies that have examined epigenetic modifications induced by ELS in select cell types isolated from the brain or associated with genes that have cell-type-restricted expression in neurons, microglia, astrocytes, and oligodendrocytes. Although significant challenges remain, future studies using these approaches can enable important mechanistic insight into the role of epigenetic variation in the effects of ELS on brain function.

Maternal Allergic Asthma Induces Prenatal Neuroinflammation

Autism spectrum disorder (ASD) is a class of neurodevelopmental disorders characterized by impaired social interactions and communication skills and repetitive or stereotyped behaviors. Rates of ASD diagnosis continue to rise, with current estimates at 1 in 44 children in the US (Maenner 2021). Epidemiological studies have suggested a link between maternal allergic asthma and an increased likelihood of having a child diagnosed with ASD. However, a lack of robust laboratory models prevents mechanistic research from being carried out. We developed a novel mouse model of maternal asthma-allergy (MAA) and previously reported that offspring from these mothers exhibit behavioral deficits compared to controls. In addition, it was shown that epigenetic regulation of gene expression in microglia was altered in these offspring, including several autism candidate genes. To further elucidate if there is neuroinflammation in the fetus following MAA, we investigated how allergic asthma impacts the maternal environment and inflammatory markers in the placenta and fetal brain during gestation. Female C57Bl/6 mice were primed with ovalbumin (OVA) prior to allergic asthma induction during pregnancy by administering aerosolized ovalbumin or PBS control to pregnant dams at gestational days (GD)9.5, 12.5, and 17.5. Four hours after the final induction, placenta and fetal brains were collected and measured for changes in cytokines using a Luminex bead-based multiplex assay. Placental MAA tissue showed a decrease in interleukin (IL)-17 in male and female offspring. There was a sex-dependent decrease in female monocyte chemoattractant protein 1 (MCP-1). In male placentas, IL-4, C-X-C motif chemokine 10 (CXCL10)-also known as interferon γ-induced protein 10 kDa (IP-10)-and chemokine (C-C motif) ligand 5 (RANTES) were decreased. In fetal brains, elevated inflammatory cytokines were found in MAA offspring when compared to controls. Specifically, interferon-gamma (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 1α (IL-1α), IL-6, and tumor necrosis factor α (TNFα) were elevated in both males and females. In contrast, a decrease in the cytokine IL-9 was also observed. There were slight sex differences after OVA exposures. Male fetal brains showed elevated levels of macrophage inflammatory protein-2 (MIP-2), whereas female brains showed increased keratinocytes-derived chemokine (KC). In addition, IL-1𝛽 and IP-10 in male fetal brains were decreased. Together, these data indicate that repeated exposure to allergic asthma during pregnancy alters cytokine expression in the fetal environment in a sex-dependent way, resulting in homeostatic and neuroinflammatory alterations in the fetal brain.

Effect of Short-Term Deep-Pressure Portable Seat on Behavioral and Biological Stress in Children with Autism Spectrum Disorders: A Pilot Study

Children with autism spectrum disorder (ASD) have challenging behaviors, which are associated with difficulties in parenting. Deep pressure is a therapeutic modality in occupational therapy, and it was reported to produce a calming effect. This study aimed to determine whether the short-term use of an autism hug machine portable seat (AHMPS) improves behavioral and neurobiological stress in children with ASD, and to determine whether AHMPS with an inflatable wrap or manual pull is more effective. This study enrolled children with ASD who were administered with the inflatable wrap (group I) and manual pull (group II) for 20 min twice a week for 3 weeks. Conners’ Parent Rating Scale-48 (CPRS-48) was used to rate behavioral improvements, and galvanic skin response (GSR) was used to measure sympathetic stress response. A total of 20 children with ASD (14 boys and 6 girls; aged 7–13 years) were included. CPRS-48 presented conduct problems: behavior was significantly decreased in the inflatable group (p = 0.007) compared to the manual pull group. The GSR captured a significant reduction in sympathetic response (p = 0.01) only in group I. Neurobiological stress was reduced in children who were wearing the AHMPS inflatable wrap; therefore, AHMPS inflatable wrap is an effective method to reduce emotional arousal.

MGEnrichment: A web application for microglia gene list enrichment analysis

Gene expression analysis is becoming increasingly utilized in neuro-immunology research, and there is a growing need for non-programming scientists to be able to analyze their own genomic data. MGEnrichment is a web application developed both to disseminate to the community our curated database of microglia-relevant gene lists, and to allow non-programming scientists to easily conduct statistical enrichment analysis on their gene expression data. Users can upload their own gene IDs to assess the relevance of their expression data against gene lists from other studies. We include example datasets of differentially expressed genes (DEGs) from human postmortem brain samples from Autism Spectrum Disorder (ASD) and matched controls. We demonstrate how MGEnrichment can be used to expand the interpretations of these DEG lists in terms of regulation of microglial gene expression and provide novel insights into how ASD DEGs may be implicated specifically in microglial development, microbiome responses and relationships to other neuropsychiatric disorders. This tool will be particularly useful for those working in microglia, autism spectrum disorders, and neuro-immune activation research. MGEnrichment is available at https://ciernialab.shinyapps.io/MGEnrichmentApp/ and further online documentation and datasets can be found at https://github.com/ciernialab/MGEnrichmentApp. The app is released under the GNU GPLv3 open source license.

Recent technological and computational advances have produced a massive amount of sequencing data that is often inaccessible to the non-bioinformatician. This is particularly true in multi-disciplinary areas of study such as neuro-immunology, where scientists come from a diversity of background fields. We developed a tool to allow wet-lab scientists without computational skills to utilize previous findings on microglia, the innate immune cells of the brain. Our web hosted tool allows users to compare their genes of interest against a large database of previously published gene lists relevant to microglia and brain disorders. With just a few clicks on the interface, users can upload their genes of interest from mouse or human studies, and query their list by selecting options for running statistical analysis. The application compares the user input to each database list, performs a statistical comparison and returns the results to the user, which can be viewed within the application or downloaded for publication. We have included two example datasets of genes from Autism Spectrum Disorder human brain samples. With these example datasets we demonstrate that this type of analysis can be utilized to identify new biological insights and high priority targets for further study in the lab.

Maternal immune activation and neuroinflammation in human neurodevelopmental disorders

Maternal health during pregnancy plays a major role in shaping health and disease risks in the offspring. The maternal immune activation hypothesis proposes that inflammatory perturbations in utero can affect fetal neurodevelopment, and evidence from human epidemiological studies supports an association between maternal inflammation during pregnancy and offspring neurodevelopmental disorders (NDDs). Diverse maternal inflammatory factors, including obesity, asthma, autoimmune disease, infection and psychosocial stress, are associated with an increased risk of NDDs in the offspring. In addition to inflammation, epigenetic factors are increasingly recognized to operate at the gene-environment interface during NDD pathogenesis. For example, integrated brain transcriptome and epigenetic analyses of individuals with NDDs demonstrate convergent dysregulated immune pathways. In this Review, we focus on the emerging human evidence for an association between maternal immune activation and childhood NDDs, including autism spectrum disorder, attention-deficit/hyperactivity disorder and Tourette syndrome. We refer to established pathophysiological concepts in animal models, including immune signalling across the placenta, epigenetic 'priming' of offspring microglia and postnatal immune-brain crosstalk. The increasing incidence of NDDs has created an urgent need to mitigate the risk and severity of these conditions through both preventive strategies in pregnancy and novel postnatal therapies targeting disease mechanisms.

Neuroinflammation in autism spectrum disorders: Exercise as a "pharmacological" tool

The worldwide prevalence of ASD is around 1%. Although the pathogenesis of ASD is not entirely understood, it is recognized that a combination of genetic, epigenetics, environmental factors and immune system dysfunction can play an essential role in its development. It has been suggested that autism results from the central nervous system derangements due to low-grade chronic inflammatory reactions associated with the immune system activation. ASD individuals have increased microglial activation, density, and increased proinflammatory cytokines in the several brain regions. Autism has no available pharmacological treatments, however there are pedagogical and psychotherapeutic therapies, and pharmacological treatment, that help to control behavioral symptoms. Recent data indicate that exercise intervention programs may improve cognitive and behavioral symptoms in children with ASD. Exercise can also modify inflammatory profiles that will ameliorate associated metabolic disorders. This review highlights the involvement of neuroinflammation in ASD and the beneficial effects of physical exercise on managing ASD symptoms and associated comorbidities.

Early postnatal allergic airway inflammation induces dystrophic microglia leading to excitatory postsynaptic surplus and autism-like behavior

Microglia play key roles in synaptic pruning, which primarily occurs from the postnatal period to adolescence. Synaptic pruning is essential for normal brain development and its impairment is implicated in neuropsychiatric developmental diseases such as autism spectrum disorders (ASD). Recent epidemiological surveys reported a strong link between ASD and atopic/allergic diseases. However, few studies have experimentally investigated the relationship between allergy and ASD-like manifestations, particularly in the early postnatal period, when allergic disorders occur frequently. Therefore, we aimed to characterize how allergic inflammation in the early postnatal period influences microglia and behavior using mouse models of short- and long-term airway allergy. Male mice were immunized by an intraperitoneal injection of aluminum hydroxide and ovalbumin (OVA) or phosphate-buffered saline (control) on postnatal days (P) 3, 7, and 11, followed by intranasal challenge with OVA or phosphate-buffered saline solution twice a week until P30 or P70. In the hippocampus, Iba-1-positive areas, the size of Iba-1-positive microglial cell bodies, and the ramification index of microglia by Sholl analysis were significantly smaller in the OVA group than in the control group on P30 and P70, although Iba-1-positive microglia numbers did not differ significantly between the two groups. In Iba-1-positive cells, postsynaptic density protein 95 (PSD95)-occupied areas and CD68-occupied areas were significantly decreased on P30 and P70, respectively, in the OVA group compared with the control group. Immunoblotting using hippocampal tissues demonstrated that amounts of PSD95, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor 2, and N-methyl-D-aspartate (NMDA) receptor 2B were significantly increased in the OVA group compared with the control group on P70, and a similar increasing trend for PSD95 was observed on P30. Neurogenesis was not significantly different between the two groups on P30 or P70 by doublecortin immunohistochemistry. The social preference index was significantly lower in the three chamber test and the number of buried marbles was significantly higher in the OVA group than in the control group on P70 but not on P30, whereas locomotion and anxiety were not different between the two groups. Compared with the control group, serum basal corticosterone levels were significantly elevated and hippocampal glucocorticoid receptor (GR) amounts and nuclear GR translocation in microglia, but not in neurons or astrocytes, were significantly decreased in the OVA group on P70 but not on P30. Gene set enrichment analysis of isolated microglia revealed that genes related to immune responses including Toll-like receptor signaling and chemokine signaling pathways, senescence, and glucocorticoid signaling were significantly upregulated in the OVA group compared with the control group on P30 and P70. These findings suggest that early postnatal allergic airway inflammation induces dystrophic microglia that exhibit defective synaptic pruning upon short- and long-term allergen exposure. Furthermore, long-term allergen exposure induced excitatory postsynaptic surplus and ASD-like behavior. Hypothalamo-pituitary-adrenal axis activation and the compensatory downregulation of microglial GR during long-term allergic airway inflammation may also facilitate these changes.

Maternal allergic inflammation in rats impacts the offspring perinatal neuroimmune milieu and the development of social play, locomotor behavior, and cognitive flexibility

Maternal systemic inflammation increases risk for neurodevelopmental disorders like autism, ADHD, and schizophrenia in offspring. Notably, these disorders are male-biased. Studies have implicated immune system dysfunction in the etiology of these disorders, and rodent models of maternal immune activation provide useful tools to examine mechanisms of sex-dependent effects on brain development, immunity, and behavior. Here, we employed an allergen-induced model of maternal inflammation in rats to characterize levels of mast cells and microglia in the perinatal period in male and female offspring, as well as social, emotional, and cognitive behaviors throughout the lifespan. Adult female rats were sensitized to ovalbumin (OVA), bred, and challenged intranasally on gestational day 15 of pregnancy with OVA or saline. Allergic inflammation upregulated microglia in the fetal brain, increased mast cell number in the hippocampus on the day of birth, and conferred region-, time- and sex- specific changes in microglia measures. Additionally, offspring of OVA-exposed mothers subsequently exhibited abnormal social behavior, hyperlocomotion, and reduced cognitive flexibility. These data demonstrate the long-term effects of maternal allergic challenge on offspring development and provide a basis for understanding neurodevelopmental disorders linked to maternal systemic inflammation in humans.

Repeated allergic asthma in early versus late pregnancy differentially impacts offspring brain and behavior development

BACKGROUND

Stress during pregnancy and maternal inflammation are two common prenatal factors that impact offspring development. Asthma is the leading chronic condition complicating pregnancy and a common source of prenatal stress and inflammation.

OBJECTIVE

The goal of this study was to characterize the developmental impact of repeated allergic asthma inflammation during pregnancy on offspring behavioral outcomes and brain inflammation.

METHODS

Pregnant female C57BL/6 mice were sensitized with ovalbumin (OVA) or PBS vehicle control and then randomly assigned to receive daily aerosol exposures to the same OVA or PBS treatment during early, gestational days (GD) 2-GD9, or late pregnancy, GD10-GD17. Maternal sera were collected after the first and last aerosol induction regimen and measured for concentrations of corticosterone, anti-OVA IgE, and cytokine profiles. Juvenile male and female offspring were assessed for locomotor and social behaviors and later as adults assessed for anxiety-like, and marble burying behaviors using a series of behavioral tasks. Offspring brains were evaluated for region-specific differences in cytokine concentrations.

RESULTS

In early gestation, both PBS and OVA-exposed dams had similar serum corticosterone concentration at the start (GD2) and end (GD9) of daily aerosol inductions. Only OVA-exposed dams showed elevations in cytokines that imply a diverse and robust T helper cell-mediated immune response. Male offspring of early OVA-exposed dams showed decreases in open-arm exploration in the elevated plus maze and increased marble burying without concomitant changes in locomotor activity or social interactions. These behavioral deficits in early OVA-exposed male offspring were associated with lower concentrations of G-CSF, IL-4, IL-7, IFNγ, and TNFα in the hypothalamus. In late gestation, both PBS and OVA-exposed dams had increased corticosterone levels at the end of daily aerosol inductions (GD17) compared to at the start of inductions (GD10). Male offspring from both PBS and OVA-exposed dams in late gestation showed similar decreases in open arm exploration on the elevated plus maze compared to OVA male offspring exposed in early gestation. No behavioral differences were present in female offspring across all treatment groups. However, females of dams exposed to OVA during early gestation displayed similar reductions as males in hypothalamic G-CSF, IL-7, IL-4, and IFNγ.

DISCUSSION

The inflammatory responses from maternal allergic asthma in early gestation and resulting increases in anxiety-like behavior in males support a link between the timing of prenatal insults and sex-specific developmental outcomes. Moreover, the heightened stress responses in late gestation and concomitant dampened inflammatory response to allergic asthma suggest that interactions between the maternal immune and stress-response systems shape early life fetal programming.

Understanding the Link Between Allergy and Neurodevelopmental Disorders: A Current Review of Factors and Mechanisms

Both allergic diseases and neurodevelopmental disorders are non-communicable diseases (NCDs) that not only impact on the quality of life and but also result in substantial economic burden. Immune dysregulation and inflammation are typical hallmarks in both allergic and neurodevelopmental disorders, suggesting converging pathophysiology. Epidemiological studies provided convincing evidence for the link between allergy and neurodevelopmental diseases such as attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Possible factors influencing the development of these disorders include maternal depression and anxiety, gestational diabetes mellitus, maternal allergic status, diet, exposure to environmental pollutants, microbiome dysbiosis, and sleep disturbances that occur early in life. Moreover, apart from inflammation, epigenetics, gene expression, and mitochondrial dysfunction have emerged as possible underlying mechanisms in the pathogenesis of these conditions. The exploration and understanding of these shared factors and possible mechanisms may enable us to elucidate the link in the comorbidity.

Preeclampsia and Neurodevelopmental Outcomes: Potential Pathogenic Roles for Inflammation and Oxidative Stress?

Preeclampsia (PE) is a common and serious hypertensive disorder of pregnancy that occurs in approximately 3-5% of first-time pregnancies and is a well-known leading cause of maternal and neonatal mortality and morbidity. In recent years, there has been accumulating evidence that in utero exposure to PE acts as an environmental risk factor for various neurodevelopmental disorders, particularly autism spectrum disorder and ADHD. At present, the mechanism(s) mediating this relationship are uncertain. In this review, we outline the most recent evidence implicating a causal role for PE exposure in the aetiology of various neurodevelopmental disorders and provide a novel interpretation of neuroanatomical alterations in PE-exposed offspring and how these relate to their sub-optimal neurodevelopmental trajectory. We then postulate that inflammation and oxidative stress, two prominent features of the pathophysiology of PE, are likely to play a major role in mediating this association. The increased inflammation in the maternal circulation, placenta and fetal circulation in PE expose the offspring to both prenatal maternal immune activation-a risk factor for neurodevelopmental disorders, which has been well-characterised in animal models-and directly higher concentrations of pro-inflammatory cytokines, which adversely affect neuronal development. Similarly, the exaggerated oxidative stress in the mother, placenta and foetus induces the placenta to secrete factors deleterious to neurons, and exposes the fetal brain to directly elevated oxidative stress and thus adversely affects neurodevelopmental processes. Finally, we describe the interplay between inflammation and oxidative stress in PE, and how both systems interact to potentially alter neurodevelopmental trajectory in exposed offspring.

Maternal acute and chronic inflammation in pregnancy is associated with common neurodevelopmental disorders: a systematic review

Inflammation is increasingly recognized as a cause or consequence of common problems of humanity including obesity, stress, depression, pollution and disease states such as autoimmunity, asthma, and infection. Maternal immune activation (MIA), triggered by both acute and systemic chronic inflammation, is hypothesized to be one of the mechanisms implicated in the pathogenesis of neurodevelopmental disorders (NDD). Although there is substantial preclinical evidence to support the MIA hypothesis, the human evidence is disparate. We performed a systematic review on human studies examining associations between maternal inflammatory states and offspring NDDs (autism spectrum disorder- ASD, attention deficit hyperactivity disorder-ADHD, Tourette syndrome-TS). 32 meta-analyses and 26 additional individual studies were identified. Maternal states associated with ASD include obesity, gestational diabetes mellitus, pre-eclampsia, pollution, stress, depression, autoimmune diseases, and infection. Maternal states associated with ADHD include obesity, pre-eclampsia, smoking, low socioeconomic status (SES), stress, autoimmune disease, and asthma. Maternal states associated with TS include low SES, depression, and autoimmune diseases. Diverse maternal inflammatory states in pregnancy are associated with common offspring NDDs. Given the increased prevalence of NDDs, there is urgent need to explore relative and cumulative maternal risk factors and disease mechanisms. Defining preventable risk factors in high-risk pregnancies could mitigate the expression and severity of NDDs.

Peri-adolescent asthma: Acute impacts on innate immune response, corticosterone, and microglia in mice

Asthma is highly comorbid with anxiety in youth. We investigated the hypothalamic-pituitary-adrenal (HPA) axis and microglia as mechanisms underlying asthma and anxiety comorbidity. We induced asthma symptoms in developing BALB/cJ mice with house dust mite (HDM) for airway inflammation and methacholine (MCH) for bronchoconstriction. On the last day of exposure, we analyzed samples at six timepoints. Lung IL-5 and IL-1β expression peaked 4 h after final HDM exposure. Circulating corticosterone was blunted in a sex- and treatment-specific temporal pattern. Hippocampal IL-1β expression and microglial area were marginally increased 24 h after MCH exposure. These results provide a foundation for further work investigating asthma-anxiety mechanisms.

Maternal immune conditions are increased in males with autism spectrum disorders and are associated with behavioural and emotional but not cognitive co-morbidity

Epidemiological and animal research shows that maternal immune activation increases the risk of autism spectrum disorders (ASD) in offspring. Emerging evidence suggests that maternal immune conditions may play a role in the phenotypic expression of neurodevelopmental difficulties in children with ASD and this may be moderated by offspring sex. This study aimed to investigate whether maternal immune conditions were associated with increased severity of adverse neurodevelopmental outcomes in children with ASD. Maternal immune conditions were examined as predictors of ASD severity, behavioural and emotional well-being, and cognitive functioning in a cohort of 363 children with ASD (n = 363; 252 males, 111 females; median age 3.07 [interquartile range 2.64-3.36 years]). We also explored whether these outcomes varied between male and female children. Results showed that maternal asthma was the most common immune condition reported in mothers of children with ASD. A history of maternal immune conditions (p = 0.009) was more common in male children with ASD, compared to female children. Maternal immune conditions were associated with increased behavioural and emotional problems in male and female children. By contrast, maternal immune conditions were not associated with decreased cognitive function. The findings demonstrate that MIA may influence the expression of symptoms in children with ASD and outcomes may vary between males and females.

Genomics, transcriptomics, proteomics and big data analysis in the discovery of new diagnostic markers and targets for therapy development

Highly complex endophenotypes and underlying molecular mechanisms have prevented effective diagnosis and treatment of autism spectrum disorder. Despite extensive studies to identify relevant biosignatures, no biomarker and therapeutic targets are available in the current clinical practice. While our current knowledge is still largely incomplete, -omics technology and machine learning-based big data analysis have provided novel insights on the etiology of autism spectrum disorders, elucidating systemic impairments that can be translated into biomarker and therapy target candidates. However, more integrated and sophisticated approaches are vital to realize molecular stratification and individualized treatment strategy. Ultimately, systemic approaches based on -omics and big data analysis will significantly contribute to more effective biomarker and therapy development for autism spectrum disorder.

Microglia in animal models of autism spectrum disorders

Various genetic and environmental factors have been suggested to cause autism spectrum disorders (ASDs). A variety of animal models of ASDs have been developed and used to investigate the mechanisms underlying the pathogenesis of ASDs. These animal models have contributed to clarifying that abnormalities in neuronal morphology and neurotransmission are responsible for the onset of ASDs. In recent years, researchers have started to focus not only on neurons but also on glial cells, particularly microglia. This is because microglial malfunction is strongly associated with structural and functional abnormalities of neurons, as well as the inflammation that is commonly observed both in the brains of patients with ASDs and in animal models of ASDs. In this chapter, we first introduce a list of commonly available animal models of ASDs and describe the validity of each model from the viewpoint of behaviors and neuroanatomy. We next detail the malfunction of microglia that has been reported in animal models of ASDs and discuss the roles of microglia in ASD pathogenesis. We will further propose possible therapeutic strategies to tackle ASDs by controlling microglial functions.

Epigenomic Convergence of Neural-Immune Risk Factors in Neurodevelopmental Disorder Cortex

Neurodevelopmental disorders (NDDs) affect 7-14% of all children in developed countries and are one of the leading causes of lifelong disability. Epigenetic modifications are poised at the interface between genes and environment and are predicted to reveal insight into NDD etiology. Whole-genome bisulfite sequencing was used to examine DNA cytosine methylation in 49 human cortex samples from 3 different NDDs (autism spectrum disorder, Rett syndrome, and Dup15q syndrome) and matched controls. Integration of methylation changes across NDDs with relevant genomic and genetic datasets revealed differentially methylated regions (DMRs) unique to each type of NDD but with shared regulatory functions in neurons and microglia. NDD DMRs were enriched within promoter regions and for transcription factor binding sites with identified methylation sensitivity. DMRs from all 3 disorders were enriched for ontologies related to nervous system development and genes with disrupted expression in brain from neurodevelopmental or neuropsychiatric disorders. Genes associated with NDD DMRs showed expression patterns indicating an important role for altered microglial function during brain development. These findings demonstrate an NDD epigenomic signature in human cortex that will aid in defining therapeutic targets and early biomarkers at the interface of genetic and environmental NDD risk factors.

Maternal immune activation modifies the course of Niemann-pick disease, type C1 in a gender specific manner

Niemann-Pick disease, type C1 (NPC1) is a rare neurodegenerative lysosomal storage disease with a wide spectrum of clinical manifestation. Multiple genetic factors influence the NPC1 mouse phenotype, but very little attention has been given to prenatal environmental factors that might have long-term effects on the neuroinflammatory component of NPC1 pathology. Studies in other mouse models of cerebellar ataxia have shown that developmental exposures lead to Purkinje neuron degeneration later in life, suggesting that environmental exposures during development can impact cerebellar biology. Thus, we evaluated the potential effect of maternal immune activation (MIA) on disease progression in an Npc1 mouse model. The MIA paradigm used mimics viral infection using the toll like receptor 3 agonist polyinosinic-polycytidilic acid during gestation. Through phenotypic and pathologic tests, we measured motor and behavioral changes as well as cerebellar neuroinflammation and neurodegeneration. We observed a gender and genotype dependent effect of MIA on the cerebellum. While the effects of MIA have been previously shown to primarily affect male progeny, we observed increased sensitivity of female mutant progeny to prenatal exposure to treatment with polyinosinic-polycytidilic acid. Specifically, prenatal MIA resulted in female NPC1 mutant progeny with greater motor deficits and a corresponding decrease in cerebellar Purkinje neurons. Our data suggest that prenatal environmental exposures may be one factor contributing to the phenotypic variability observed in individuals with NPC1.

Epigenomic and transcriptional determinants of microglial cell identity

Microglia perform multiple tasks that are essential to ensure proper cerebral functions, including synaptic remodeling, clearance of molecular debris, prevention of infections, and so forth. Furthermore, accumulating genetic and pathological evidence implicates microglial cell activity in the etiology of numerous neurodegenerative diseases and psychiatric disorders. Given this, efforts aimed at understanding the molecular mechanisms underlying microglial cell functions hold great potential for the development of novel therapies for various conditions affecting the central nervous system. In that regard, the application of paradigms in epigenomics to study transcription in microglia has provided significant insights into the molecular mechanisms that control the ontogeny and functions of these cells. With a focus on the roles of genomic regulatory elements and the epigenetic marks that control microglial gene expression, we review here recent key advancements in our comprehension of the epigenomic and transcriptional mechanisms that enable microglial cell development and activity.

Novel Neuropathic Pain Mechanisms Associated With Allergic Inflammation

Allergic diseases are associated with central and peripheral nervous system diseases such as autism spectrum disorders and eosinophilic granulomatosis with polyangiitis, which frequently causes mononeuritis multiplex. Thus, it is possible that patients with an atopic constitution might develop multifocal inflammation in central and peripheral nervous system tissues. In a previous study in Japan, we reported a rare form of myelitis with persistent neuropathic pain (NeP) in patients with allergic disorders. However, the underlying mechanism of allergic inflammation-related NeP remains to be elucidated. First, we analyzed the effect of allergic inflammation on the nociceptive system in the spinal cord. Mice with atopy showed microglial and astroglial activation in the spinal cord and tactile allodynia. In a microarray analysis of isolated microglia from the spinal cord, endothelin receptor type B (EDNRB) was the most upregulated cell surface receptor in mice with atopy. Immunohistochemical analysis demonstrated EDNRB expression was upregulated in microglia and astroglia. The EDNRB antagonist BQ788 abolished glial activation and allodynia. These findings indicated that allergic inflammation induced widespread glial activation through the EDNRB pathway and NeP. Second, we investigated whether autoantibody-mediated pathogenesis underlies allergic inflammation-related NeP. We detected specific autoantibodies to small dorsal root ganglion (DRG) neurons and their nerve terminals in the dorsal horns of NeP patients with allergic disorders. An analysis of IgG subclasses revealed a predominance of IgG2. These autoantibodies were mostly colocalized with isolectin B4- and P2X3-positive unmyelinated C-fiber type small DRG neurons. By contrast, immunostaining for S100β, a myelinated DRG neuron marker, showed no colocalization with patient IgG. Immunoprecipitation and liquid chromatography-tandem mass spectrometry identified plexin D1 as a target autoantigen. Patients with anti-plexin D1 antibodies often present with burning pain and thermal hyperalgesia. Immunotherapies, including plasma exchange, are effective for NeP management. Therefore, anti-plexin D1 antibodies may be pathogenic for immune-mediated NeP, especially under allergic inflammation conditions. Thus, allergic inflammation may induce NeP through glial inflammation in the spinal cord and the anti-plexin D1 antibody-mediated impairment of small DRG neurons.

Microglia as Dynamic Cellular Mediators of Brain Function

Originally hypothesized to function solely as immunologic responders within the central nervous system (CNS), emerging evidence has revealed that microglia have more complex roles in normal brain development and in the context of disease. In health, microglia influence neural progenitor fate decisions, astrocyte activation, neuronal homeostasis, and synaptogenesis. In the setting of brain disease, including autism, brain tumors, and neurodegenerative disorders, microglia undergo substantial morphological, molecular, and functional changes, which establish new biological states relevant to disease pathogenesis and progression. In this review, we discuss the function of microglia in health and disease and outline a conceptual framework for elucidating their specific contributions to nervous system pathobiology.

Maternal thyroid autoimmunity associated with acute-onset neuropsychiatric disorders and global regression in offspring

Epidemiological studies, animal models, and case-control studies indicate maternal immune activation may be an important factor involved in disease expression of autism spectrum disorder (ASD), Tourette syndrome, and obsessive-compulsive disorder (OCD). We report eight children (mean age 6y 6mo [range 4-15y]; six males and two females) referred over a 2-year period with at least one of these neurodevelopmental disorders plus a maternal history of thyroid autoimmunity. Seven of eight children presented with an abrupt onset of neuropsychiatric symptoms (OCD [n=6], tics [n=5], and/or psychosis [n=1]), associated with an autistic or global regression. Four children had a pre-existing diagnosis of ASD. Six presentations were preceded by infection, and symptoms followed a relapsing-remitting course in seven children. All children responded to immunomodulatory treatment as indicated by a reduction in psychiatric symptoms, and seven children were also managed with conventional treatment with additional improvement. We propose that maternal autoimmunity can activate fetal microglia or alter transcription of neurodevelopmental vulnerability and/or immune genes in utero, and is an environmental factor that increases the expression and severity of neurodevelopmental problems, and susceptibility to deteriorations after infectious or stress stimuli. WHAT THIS PAPER ADDS: Maternal thyroid autoimmunity may represent a risk factor for neuropsychiatric disorders in offspring. Atypical neuropsychiatric features in these children may be due to maternal immune activation in utero.

Neuroimmunology of the female brain across the lifespan: Plasticity to psychopathology

The female brain is highly dynamic and can fundamentally remodel throughout the normal ovarian cycle as well as in critical life stages including perinatal development, pregnancy and old-age. As such, females are particularly vulnerable to infections, psychological disorders, certain cancers, and cognitive impairments. We will present the latest evidence on the female brain; how it develops through the neonatal period; how it changes through the ovarian cycle in normal individuals; how it adapts to pregnancy and postpartum; how it responds to illness and disease, particularly cancer; and, finally, how it is shaped by old age. Throughout, we will highlight female vulnerability to and resilience against disease and dysfunction in the face of environmental challenges.

Essential contributions of enhancer genomic regulatory elements to microglial cell identity and functions

Microglia are the specialized macrophages of the brain and play essential roles in ensuring its proper functioning. Accumulating evidence suggests that these cells coordinate the inflammatory response that accompanies various clinical brain conditions, including neurodegenerative diseases and psychiatric disorders. Therefore, investigating the functions of these cells and how these are regulated have become important areas of research in neuroscience over the past decade. In this regards, recent efforts to characterize the epigenomic mechanisms underlying microglial gene transcription have provided significant insights into the mechanisms that control the ontogeny and the cellular competences of microglia. In particular, these studies have established that a substantial proportion of the microglial repertoire of promoter-distal genomic regulatory elements, or enhancers, is relatively specific to these cells compared to other tissue-resident macrophages. Notably, this specificity is under the regulation of factors present in the brain that modulate activity of target axes of signaling pathways-transcription factors in microglia. Thus, the microglial enhancer repertoire is highly responsive to perturbations in the cerebral tissue microenvironment and this responsiveness has profound implications on the activity of these cells in brain diseases. This article is categorized under: Physiology > Mammalian Physiology in Health and Disease Models of Systems Properties and Processes > Mechanistic Models Biological Mechanisms > Cell Fates Developmental Biology > Lineages.

Prenatal Allergen Exposure Perturbs Sexual Differentiation and Programs Lifelong Changes in Adult Social and Sexual Behavior

Sexual differentiation is the early life process by which the brain is prepared for male or female typical behaviors, and is directed by sex chromosomes, hormones and early life experiences. We have recently found that innate immune cells residing in the brain, including microglia and mast cells, are more numerous in the male than female rat brain. Neuroimmune cells are also key participants in the sexual differentiation process, specifically organizing the synaptic development of the preoptic area and leading to male-typical sexual behavior in adulthood. Mast cells are known for their roles in allergic responses, thus in this study we sought to determine if exposure to an allergic response of the pregnant female in utero would alter the sexual differentiation of the preoptic area of offspring and resulting sociosexual behavior in later life. Pregnant rats were sensitized to ovalbumin (OVA), bred, and challenged intranasally with OVA on gestational day 15, which produced robust allergic inflammation, as measured by elevated immunoglobulin E. Offspring of these challenged mother rats were assessed relative to control rats in the early neonatal period for mast cell and microglia activation within their brains, downstream dendritic spine patterning on POA neurons, or grown to adulthood to assess behavior and dendritic spines. In utero exposure to allergic inflammation increased mast cell and microglia activation in the neonatal brain, and led to masculinization of dendritic spine density in the female POA. In adulthood, OVA-exposed females showed an increase in male-typical mounting behavior relative to control females. In contrast, OVA-exposed males showed evidence of dysmasculinization, including reduced microglia activation, reduced neonatal dendritic spine density, decreased male-typical copulatory behavior, and decreased olfactory preference for female-typical cues. Together these studies show that early life allergic events may contribute to natural variations in both male and female sexual behavior, potentially via underlying effects on brain-resident mast cells.

Inflammatory domains modulate autism spectrum disorder susceptibility during maternal nutritional programming

Autism spectrum disorder (ASD) is a complex neurodevelopmental disease which involves functional and structural defects in selective central nervous system (CNS) regions harming capability to process and respond to external stimuli. In addition to genetic background, etiological causes of ASD have not been fully clarified. Maternal immune activation (MIA) during pregnancy have been proposed as a potential etiological cause leading to aberrant synaptic pruning and microglia-mediated neurogenesis impairment. Several clinical studies suggest that pro-inflammatory profile during maternal obesity associates with a higher risk of having a child with autism. In this context, the effect of maternal programing by high fat diet overconsumption during pregnancy sets a pro-inflammatory profile partly dependent on an epigenetic program of immunity which promotes brain micro and macrostructural abnormalities in the offspring that might last through adulthood accompanied by phenotypic changes in ASD subjects. Of note, maternal programming of inflammation during development seems to integrate the CNS and peripheral immune system cross-talk which arrays central inflammatory domains coordinating ASD behavior. In this review, we discuss basic and clinical studies regarding the effects of obesity-induced MIA on peripheral immune cells and microglia priming and their relationship with brain structural alterations in ASD models. Also, we show supportive evidence stating the role of maternal programming on epigenetic gene activation in immune cells of ASD subjects. We suggest that maternal programming by hypercaloric diets during development sets a central and peripheral immune cross-talk which potentially might modulate brain macro and microstructural defects leading to autism susceptibility.

Genetics and epigenetics of autism spectrum disorder-current evidence in the field

Autism spectrum disorders (ASD) is a heterogenous group of neurodevelopmental disorders characterized by problems in social interaction and communication as well as the presence of repetitive and stereotyped behavior. It is estimated that the prevalence of ASD is 1–2% in the general population with the average male to female ratio 4–5:1. Although the causes of ASD remain largely unknown, the studies have shown that both genetic and environmental factors play an important role in the etiology of these disorders. Array comparative genomic hybridization and whole exome/genome sequencing studies identified common and rare copy number or single nucleotide variants in genes encoding proteins involved in brain development, which play an important role in neuron and synapse formation and function. The genetic etiology is recognized in ~ 25–35% of patients with ASD. In this article, we review the current state of knowledge about the genetic etiology of ASD and also propose a diagnostic algorithm for patients.

Immune Dysfunction and Autoimmunity as Pathological Mechanisms in Autism Spectrum Disorders

Autism spectrum disorders (ASD) are a group of heterogeneous neurological disorders that are highly variable and are clinically characterized by deficits in social interactions, communication, and stereotypical behaviors. Prevalence has risen from 1 in 10,000 in 1972 to 1 in 59 children in the United States in 2014. This rise in prevalence could be due in part to better diagnoses and awareness, however, these together cannot solely account for such a significant rise. While causative connections have not been proven in the majority of cases, many current studies focus on the combined effects of genetics and environment. Strikingly, a distinct picture of immune dysfunction has emerged and been supported by many independent studies over the past decade. Many players in the immune-ASD puzzle may be mechanistically contributing to pathogenesis of these disorders, including skewed cytokine responses, differences in total numbers and frequencies of immune cells and their subsets, neuroinflammation, and adaptive and innate immune dysfunction, as well as altered levels of immunoglobulin and the presence of autoantibodies which have been found in a substantial number of individuals with ASD. This review summarizes the latest research linking ASD, autoimmunity and immune dysfunction, and discusses evidence of a potential autoimmune component of ASD.