Between Dysbiosis, Maternal Immune Activation and Autism: Is There a Common Pathway?

Autism spectrum disorder (ASD) is a neuropsychiatric condition characterized by impaired social interactions and repetitive stereotyped behaviors. Growing evidence highlights an important role of the gut-brain-microbiome axis in the pathogenesis of ASD. Research indicates an abnormal composition of the gut microbiome and the potential involvement of bacterial molecules in neuroinflammation and brain development disruptions. Concurrently, attention is directed towards the role of short-chain fatty acids (SCFAs) and impaired intestinal tightness. This comprehensive review emphasizes the potential impact of maternal gut microbiota changes on the development of autism in children, especially considering maternal immune activation (MIA). The following paper evaluates the impact of the birth route on the colonization of the child with bacteria in the first weeks of life. Furthermore, it explores the role of pro-inflammatory cytokines, such as IL-6 and IL-17a and mother's obesity as potentially environmental factors of ASD. The purpose of this review is to advance our understanding of ASD pathogenesis, while also searching for the positive implications of the latest therapies, such as probiotics, prebiotics or fecal microbiota transplantation, targeting the gut microbiota and reducing inflammation. This review aims to provide valuable insights that could instruct future studies and treatments for individuals affected by ASD.

Long-term effects of prophylactic MgSO4 in maternal immune activation rodent model at adolescence and adulthood

The effects of MgSO₄ as an anti-inflammatory agent in pregnant women have been investigated in the last few years. Infections can cause an inflammatory reaction involving the placenta membranes and amniotic cavity. They may have short-term effects on the mother and her fetuses, like preterm birth, cerebral palsy, and developmental delay. Despite the alleged advantages of MgSO₄ as a neuroprotective agent in the preterm brain, the long-term molecular and behavioral function of MgSO₄ has not been fully elucidated. Here, we investigated the long-term effect of antenatal MgSO₄ , during late gestation, on offspring's behavior focusing on cognitive function, motor activity, and social cognition in adolescence and adulthood, and explored its influence on brain gene expression (e.g., ErbB signaling, pro-inflammatory, and dopaminergic markers) in adulthood. A significant abnormal exploratory behavior of offspring of MgSO₄ -treated dams was found compared to the control group in both adolescence and adulthood. Furthermore, we found that adult females exposed to MgSO₄ under inflammation displayed working and recognition memory impairment. A reduction in IL-6 expression was detected in the prefrontal cortex, and hippocampus specimens derived from LPS-Mg-treated group. In contrast, an imbalanced expression of dopamine 1 and 2 receptors was detected only in prefrontal cortex specimens. Besides, we found that MgSO₄ ameliorated the overexpression of the Nrg1 and Erbb4 receptors induced by LPS in the hippocampus. Thus, MgSO₄ treatment for preventing brain injuries can adversely affect offspring cognition behavior later in life, depending on the sex and age of the offspring.

Progressive disruption of neurodevelopment by mid-gestation exposure to lipopolysaccharides and the ameliorating effect of continuous alpha-glycosyl isoquercitrin treatment

We investigated the effect of lipopolysaccharide (LPS)-induced maternal immune activation used as a model for producing neurodevelopmental disorders on hippocampal neurogenesis and behaviors in rat offspring by exploring the antioxidant effects of alpha-glycosyl isoquercitrin (AGIQ). Pregnant Sprague-Dawley rats were intraperitoneally injected with LPS (50 μg/kg body weight) at gestational days 15 and 16. AGIQ was administered in the diet to dams at 0.5% (w/w) from gestational day 10 until weaning at postnatal day 21 and then to offspring until adulthood at postnatal day 77. During postnatal life, offspring of LPS-injected animals did not show neuroinflammation or oxidative stress in the brain. At weaning, LPS decreased the numbers of type-2b neural progenitor cells (NPCs) and PCNA⁺ proliferating cells in the subgranular zone, FOS-expressing granule cells, and GAD67⁺ hilar interneurons in the dentate gyrus. In adulthood, LPS decreased type-1 neural stem cells, type-2a NPCs, and GAD67⁺ hilar interneurons, and downregulated Dpysl3, Sst, Fos, Mapk1, Mapk3, Grin2a, Grin2b, Bdnf, and Ntrk2. In adults, LPS suppressed locomotor activity in the open field test and suppressed fear memory acquisition and fear extinction learning in the contextual fear conditioning test. These results indicate that mid-gestation LPS injections disrupt programming of normal neurodevelopment resulting in progressive suppression of hippocampal neurogenesis and synaptic plasticity of newborn granule cells by suppressing GABAergic and glutamatergic neurotransmitter signals and BDNF/TrkB signaling to result in adult-stage behavioral deficits. AGIQ ameliorated most aberrations in hippocampal neurogenesis and synaptic plasticity, as well as behavioral deficits. Effective amelioration by continuous AGIQ treatment starting before LPS injections may reflect both anti-inflammatory and anti-oxidative stress effects during gestation and neuroprotective effects of continuous exposure through adulthood.

Differential Expression of Endogenous Retroviruses and Inflammatory Mediators in Female and Male Offspring in a Mouse Model of Maternal Immune Activation

Maternal infections during pregnancy and the consequent maternal immune activation (MIA) are the major risk factors for autism spectrum disorder (ASD). Epidemiological evidence is corroborated by the preclinical models in which MIA leads to ASD-like behavioral abnormalities and altered neuroinflammatory profiles, with an increase in pro-inflammatory cytokines and microglial markers. In addition to neuroinflammatory response, an abnormal expression of endogenous retroviruses (ERVs) has been identified in neurodevelopmental disorders and have been found to correlate with disease severity. Our aim was to evaluate the transcriptional profile of several ERV families, ERV-related genes, and inflammatory mediators (by RT real-time PCR) in mouse offspring of both sexes, prenatally exposed to polyinosinic:polycytidylic acid (Poly I:C), a synthetic double-stranded RNA molecule targeting TLR-3 that mimics viral maternal infection during pregnancy. We found that prenatal exposure to Poly I:C deregulated the expression of some ERVs and ERV-related genes both in the prefrontal cortex (PFC) and hippocampus, while no changes were detected in the blood. Interestingly, sex-related differences in the expression levels of some ERVs, ERV-related genes, and inflammatory mediators that were higher in females than in males emerged only in PFC. Our findings support the tissue specificity of ERV and ERV-related transcriptional profiles in MIA mice.

Corrigendum: Virus-Induced Maternal Immune Activation as an Environmental Factor in the Etiology of Autism and Schizophrenia

[This corrects the article DOI: 10.3389/fnins.2022.834058.].

Advantages and Limitations of Animal Schizophrenia Models

Mental illness modeling is still a major challenge for scientists. Animal models of schizophrenia are essential to gain a better understanding of the disease etiopathology and mechanism of action of currently used antipsychotic drugs and help in the search for new and more effective therapies. We can distinguish among pharmacological, genetic, and neurodevelopmental models offering various neuroanatomical disorders and a different spectrum of symptoms of schizophrenia. Modeling schizophrenia is based on inducing damage or changes in the activity of relevant regions in the rodent brain (mainly the prefrontal cortex and hippocampus). Such artificially induced dysfunctions approximately correspond to the lesions found in patients with schizophrenia. However, notably, animal models of mental illness have numerous limitations and never fully reflect the disease state observed in humans.

Virus-Induced Maternal Immune Activation as an Environmental Factor in the Etiology of Autism and Schizophrenia

Maternal immune activation (MIA) is mediated by activation of inflammatory pathways resulting in increased levels of cytokines and chemokines that cross the placental and blood-brain barriers altering fetal neural development. Maternal viral infection is one of the most well-known causes for immune activation in pregnant women. MIA and immune abnormalities are key players in the etiology of developmental conditions such as autism, schizophrenia, ADHD, and depression. Experimental evidence implicating MIA in with different effects in the offspring is complex. For decades, scientists have relied on either MIA models or human epidemiological data or a combination of both. MIA models are generated using infection/pathogenic agents to induce an immunological reaction in rodents and monitor the effects. Human epidemiological studies investigate a link between maternal infection and/or high levels of cytokines in pregnant mothers and the likelihood of developing conditions. In this review, we discuss the importance of understanding the relationship between virus-mediated MIA and neurodevelopmental conditions, focusing on autism and schizophrenia. We further discuss the different methods of studying MIA and their limitations and focus on the different factors contributing to MIA heterogeneity.

Abnormal mTOR Activity in Pediatric Autoimmune Neuropsychiatric and MIA-Associated Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by the early onset of communication and behavioral problems. ASD is highly heritable; however, environmental factors also play a considerable role in this disorder. A significant part of both syndromic and idiopathic autism cases could be attributed to disorders caused by mammalian target of rapamycin (mTOR)-dependent translation deregulation. This narrative review analyzes both bioinformatic and experimental evidence that connects mTOR signaling to the maternal autoantibody-related (MAR) autism spectrum and autoimmune neuropsychiatric disorders simultaneously. In addition, we reconstruct a network presenting the interactions between the mTOR signaling and eight MAR ASD genes coding for ASD-specific maternal autoantibody target proteins. The research discussed in this review demonstrates novel perspectives and validates the need for a subtyping of ASD on the grounds of pathogenic mechanisms. The utter necessity of designing ELISA-based test panels to identify all antibodies related to autism-like behavior is also considered.

Social Communication of Maternal Immune Activation-Affected Offspring Is Improved by Si-Based Hydrogen-Producing Agent

Maternal immune activation (MIA) is triggered by infection or autoimmune predisposition during pregnancy, and cytokines produced by MIA are transmitted through the placenta to the fetal brain, implicating at the onset risks and vulnerability for developmental and psychiatric disorders, such as autism spectrum disorder (ASD) and schizophrenia. To address these kinds of problem in child health, we have developed a silicon (Si)-based hydrogen-producing antioxidant (Si-based agent) that continuously and effectively produces hydrogen in the body. Medical hydrogen is known to have antioxidative, anti-inflammatory, and antiapoptotic effects, therefore we applied our Si-based agent as a potential therapeutic agent to MIA. Using a MIA mouse model, we found that the Si-based agent improved the social communication of MIA offspring mice. We also found that the Si-based agent suppressed the expressions of inflammation-associated genes Ifna1 and Il-6 in the mouse brain. These results demonstrate that the Si-based agent is an effective prophylactic agent against MIA during pregnancy, suggesting that our Si-based agent may be a preventative or therapeutic agent for ASD and other disease risks in child health suppressing MIA damage.

Maternal and Adult Interleukin-17A Exposure and Autism Spectrum Disorder

Epidemiological evidence in humans has suggested that maternal infections and maternal autoimmune diseases are involved in the pathogenesis of autism spectrum disorder. Animal studies supporting human results have shown that maternal immune activation causes brain and behavioral alterations in offspring. Several underlying mechanisms, including interleukin-17A imbalance, have been identified. Apart from the pro-inflammatory effects of interleukin-17A, there is also evidence to support the idea that it activates neuronal function and defines cognitive behavior. In this review, we examined the signaling pathways in both immunological and neurological contexts that may contribute to the improvement of autism spectrum disorder symptoms associated with maternal blocking of interleukin-17A and adult exposure to interleukin-17A. We first describe the epidemiology of maternal immune activation then focus on molecular signaling of the interleukin-17 family regarding its physiological and pathological roles in the embryonic and adult brain. In the future, it may be possible to use interleukin-17 antibodies to prevent autism spectrum disorder.

The Role of Maternal Immune Activation in the Pathogenesis of Autism: A Review of the Evidence, Proposed Mechanisms and Implications for Treatment

Autism spectrum disorder (ASD) is a neurodevelopmental disease that is characterized by a deficit in social interactions and communication, as well as repetitive and restrictive behaviors. Increasing lines of evidence suggest an important role for immune dysregulation and/or inflammation in the development of ASD. Recently, a relationship between inflammation, oxidative stress, and mitochondrial dysfunction has been reported in the brain tissue of individuals with ASD. Some recent studies have also reported oxidative stress and mitochondrial abnormalities in animal models of maternal immune activation (MIA). This review is focused on the hypothesis that MIA induces microglial activation, oxidative stress, and mitochondrial dysfunction, a deleterious trio in the brain that can lead to neuroinflammation and neurodevelopmental pathologies in offspring. Infection during pregnancy activates the mother’s immune system to release proinflammatory cytokines, such as IL-6, TNF-α, and others. Furthermore, these cytokines can directly cross the placenta and enter the fetal circulation, or activate resident immune cells, resulting in an increased production of proinflammatory cytokines, including IL-6. Proinflammatory cytokines that cross the blood–brain barrier (BBB) may initiate a neuroinflammation cascade, starting with the activation of the microglia. Inflammatory processes induce oxidative stress and mitochondrial dysfunction that, in turn, may exacerbate oxidative stress in a self-perpetuating vicious cycle that can lead to downstream abnormalities in brain development and behavior.

Poly(I:C) Challenge Alters Brain Expression of Oligodendroglia-Related Genes of Adult Progeny in a Mouse Model of Maternal Immune Activation

Background: Altered white matter connectivity, as evidenced by pervasive microstructural changes in myelination and axonal integrity in neuroimaging studies, has been implicated in the development of autism spectrum disorder (ASD) and related neurodevelopmental conditions such as schizophrenia. Despite an increasing appreciation that such white matter disconnectivity is linked to social behavior deficits, virtually no etiologically meaningful myelin-related genes have been identified in oligodendrocytes, the key myelinating cells in the CNS, to furnish an account on the causes. The impact of neurodevelopmental perturbations during pregnancy such as maternal immune activation (MIA) on these genes in memory-related neural networks has not been experimentally scrutinized.

Methods: In this study, a mouse model of MIA by the viral dsRNA analog poly(I:C) was employed to mimic the effects of inflammation during pregnancy. Transcriptional expression levels of selected myelin- or oligodendroglia-related genes implicated in schizophrenia or ASD development were analyzed by in situ hybridization (ISH) and quantitative real-time PCR (qRT-PCR) with brain samples from MIA and control groups. The analysis focused on SOX-10 (SRY-related HMG-box 10), MAG (myelin-associated glycoprotein), and Tf (transferrin) expression in the hippocampus and the surrounding memory-related cortical regions in either hemisphere.

Results: Specifically, ISH reveals that in the brain of prenatal poly(I:C)-exposed mouse offspring in the MIA model (gestation day 9), mRNA expression of the genes SOX10, MAG and Tf were generally reduced in the limbic system including the hippocampus, retrosplenial cortex and parahippocampal gyrus on either side of the hemispheres. qRT-PCR further confirms the reduction of SOX10, MAG, and Tf expression in the medial prefrontal cortex, sensory cortex, amygdala, and hippocampus.

Conclusions: Our present results provide direct evidence that prenatal exposure to poly(I:C) elicits profound and long-term changes in transcript level and spatial distribution of myelin-related genes in multiple neocortical and limbic regions, notably the hippocampus and its surrounding memory-related neural networks. Our work demonstrates the potential utility of oligodendroglia-related genes as biomarkers for modeling neurodevelopmental disorders, in agreement with the hypothesis that MIA during pregnancy could lead to compromised white matter connectivity in ASD.

Maternal Immune Activation in Mice Only Partially Recapitulates the Autism Spectrum Disorders Symptomatology

Prenatal viral/bacterial infections are considered risk factors for autism spectrum disorders (ASD) and rodent models of maternal immune activation (MIA) have been developed and extensively used in preclinical studies. Poly inosinic-cytidylic acid (Poly I:C) was injected in C57BL6/J dams to mimic a viral infection on gestational day 12.5; the experimental design includes 10/12 litters in each treatment group and data were analysed always considering the litter-effect; neonatal (spontaneous motor behaviour and ultrasonic vocalizations) and adult [open field, marble burying, social approach, fear conditioning, prepulse inhibition (PPI)] offspring of both sexes were tested. In vivo magnetic resonance imaging/spectroscopy (MRI-MRS) and high-performance liquid chromatography (HPLC) to quantify both aminoacid and/or neurotransmitter concentration in cortical and striatal regions were also carried out. In both sexes high levels of repetitive motor responses and sensory gating deficits in PPI were the more striking effects of Poly I:C, whereas no alteration of social responses were evidenced. Poly I:C treatment did not affect mean values, but, intriguingly, increased variability in the levels of four aminoacids (aspartate glycine and GABA) selectively in males. As a whole prenatal Poly I:C induced relevant long-term alterations in explorative-stereotyped motor responses and in sensory gating, sparing cognitive and social competences. When systematically assessing differences between male and female siblings within each litter, no significant sex differences were evident except for increased variability of four aminoacid levels in male brains. As a whole, prenatal Poly I:C paradigms appear to be a useful tool to investigate the profound and translationally-relevant effects of developmental immune activation on brain and behavioural development, not necessarily recapitulating the full ASD symptomatology.

Schizophrenia and Influenza at the Centenary of the 1918-1919 Spanish Influenza Pandemic: Mechanisms of Psychosis Risk

Associations between influenza infection and psychosis have been reported since the eighteenth century, with acute "psychoses of influenza" documented during multiple pandemics. In the late 20th century, reports of a season-of-birth effect in schizophrenia were supported by large-scale ecological and sero-epidemiological studies suggesting that maternal influenza infection increases the risk of psychosis in offspring. We examine the evidence for the association between influenza infection and schizophrenia risk, before reviewing possible mechanisms via which this risk may be conferred. Maternal immune activation models implicate placental dysfunction, disruption of cytokine networks, and subsequent microglial activation as potentially important pathogenic processes. More recent neuroimmunological advances focusing on neuronal autoimmunity following infection provide the basis for a model of infection-induced psychosis, potentially implicating autoimmunity to schizophrenia-relevant protein targets including the N-methyl-D-aspartate receptor. Finally, we outline areas for future research and relevant experimental approaches and consider whether the current evidence provides a basis for the rational development of strategies to prevent schizophrenia.

Bacterial-induced maternal interleukin-17A pathway promotes autistic-like behaviors in mouse offspring

Maternal immune activation (MIA) by an infection is considered to be an important environmental factor of fetal brain development. Recent animal model on MIA induced by polyinosinic:polycytidylic acid, a mimic of viral infection, demonstrates that maternal IL-17A signaling is required for the development of autism spectrum disorder (ASD)-like behaviors of offspring. However, there is little information on bacterial infection. In this study, we aim to elucidate the influence of MIA induced by lipopolysaccharide (LPS) to mimic a bacterial infection on fetal brain development. We demonstrated that LPS-induced MIA promoted ASD-like behaviors in mouse offspring. We further found that LPS exposure induced acute phase immune response: elevation of serum IL-17A levels in MIA mothers, upregulation of Il17a mRNA expression and increase of IL-17A-producing γδ T cells in the uterus, and upregulation of Il17ra mRNA expression in the fetal brain. Blocking of IL-17A in LPS-induced MIA ameliorated ASD-like behaviors in offspring. Our data suggest that bacterial-induced maternal IL-17A pathway promotes ASD-like behaviors in offspring.

Molecular mechanisms underlying the models of neurodevelopmental disorders in maternal immune activation relevant to the placenta

The rapid rise in the prevalence of autism spectrum disorders (ASD) and other psychiatric disorders displaying similar traits has increased the need to elucidate their molecular mechanisms. Epidemiological studies have shown that maternal infection during mid-pregnancy is associated with increased risk of neurodevelopmental disorders such as ASD in offspring. Using maternal infection models, researchers have gathered evidence relevant to such disorders. A comprehensive summary of the changes in the brain structure, function, and behavior in offspring induced by maternal immune activation (MIA) has been reported. However, the molecular mechanisms underlying the association between MIA and improper brain development, which ultimately lead to neurodevelopmental disorders, have not been fully reviewed. This paper summarizes the currently known molecular mechanisms associated with the MIA model, with a special focus on the role of the placenta in fetal brain development.