Sex-specific microglia state in the Neuroligin-4 knock-out mouse model of autism spectrum disorder

Minocycline treatment attenuates neurobehavioural abnormalities and neurostructural aberrations in the medial prefrontal cortex in mice fed a high-fat diet during adolescence

A preference for and overconsumption of a high-fat diet (HFD) are common among adolescents and are recognized as risk factors for multiple mental disorders. The protracted maturation of the medial prefrontal cortex (mPFC), a key brain structure that plays a critical role in mental functions that are essential for both developing and mature individuals (including emotional processing, decision making, risk assessment, and creative thinking), during adolescence renders it more vulnerable to the environmental insults experienced during this critical developmental window. However, the effects of HFD consumption during adolescence on mPFC-related behaviours and the underlying mechanisms need to be further investigated. In this study, we observed that mice fed a HFD throughout adolescence developed depressive- and anxiety-like behaviours and distinctively increased risk-avoidance behaviour, accompanied by morphological aberrations of both pyramidal neuron and microglia in the mPFC. The systemic administration of minocycline, a well-known broad-spectrum antibiotic, effectively attenuated the adverse effects of HFD consumption during adolescence on neurobehaviours and the morphology of pyramidal neurons in the mPFC. This study provides new insights into the psychological effects of long-term HFD consumption during adolescence and indicates the existence of a window during which microglial stabilization may be a promising strategy to protect against the HFD consumption-induced increase in the risk of psychiatric disorders.

Neonatal infection with Bordetella pertussis promotes autism-like phenotypes in mice

Autism spectrum disorder (ASD) has been linked with infections early in life. Here we demonstrate that the infection of neonatal mice with the respiratory pathogen Bordetella pertussis leads to neuroinflammation, neurodevelopmental defects, and ASD-like behaviors. Following the respiratory challenge of neonatal mice with B. pertussis, multiple atypical CNS findings were observed, including blood-brain barrier disruption, dissemination of live B. pertussis bacteria to the brain with the concomitant infiltration of inflammatory monocytes, neutrophils, and activated IL-17A- and IFN-γ-producing CD4 T cells. Microglia from infected mice were activated, with impaired phagocytic function, resulting in defective synaptic pruning and disrupted neuronal circuit formation. Impaired neurodevelopment in B. pertussis-infected post-natal mice was associated with ASD-like behavioral abnormalities in young adulthood. Our data indicate that infection with virulent B. pertussis during infancy increases the risk of autism-like behavior in young adult mice. A study into the potential role of B. pertussis in human ASD is warranted.

From womb to world: The interplay between maternal immune activation, neuroglia, and neurodevelopment

This chapter introduces and discusses maternal immune activation (MIA) as a contributing factor in increasing the risk of neurodevelopmental disorders, particularly in relation to its interactions with neuroglia. Here we first provide an overview of the neuroglia-astroglia, oligodendroglia, microglia, and radial glial cells-and their important role during early brain development and in adulthood. We then present and discuss MIA, followed by a critical overview of inflammatory molecules and temporal stages associated to maternal inflammation during pregnancy. We provide an overview of animal and human models used to mimic and study MIA. Furthermore, we review the possible interaction between MIA and neuroglia, focusing on the current advances in both modeling and therapeutics. Additionally, we discuss and provide preliminary and interesting insights into the most recent pandemic, COVID-19, and how the infection may be associated to MIA and increased risk for neurodevelopmental disorders. Finally, we provide a critical overview of challenges and future opportunities to study how MIA may contribute to higher risk of developing neurodevelopmental disorders.

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.

Potential key pathophysiological participant and treatment target in autism spectrum disorder: Microglia

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by social and communication deficits, as well as restricted or repetitive behaviors or interests. Although the etiology of ASD remains unclear, there is abundant evidence suggesting that microglial dysfunction is likely to be a significant factor in the pathophysiology of ASD. Microglia, the primary innate immune cells in the central nervous system (CNS), play a crucial role in brain development and homeostasis. Recently, numerous studies have shown that microglia in ASD models display various abnormalities including morphology, function, cellular interactions, genetic and epigenetic factors, as well as the expression of receptors, transcription factors, and cytokines. They impact normal neural development through various mechanisms contributing to ASD, such as neuroinflammation, and alterations in synaptic formation and pruning. The focus of this review is on recent studies regarding microglial abnormalities in ASD and their effects on the onset and progression of ASD at both cellular and molecular levels. It can provide insight into the specific contribution of microglia to ASD pathogenesis and help in designing potential therapeutic and preventative strategies targeting microglia.

Sex-specific effects of subchronic NMDA receptor antagonist MK-801 treatment on hippocampal gamma oscillations

N-methyl-D-aspartate (NMDA) receptor antagonists are widely used to pharmacologically model schizophrenia and have been recently established in the treatment of treatment-resistant major depression demonstrating that the pharmacology of this substance class is complex. Cortical gamma oscillations, a rhythmic neuronal activity associated with cognitive processes, are increased in schizophrenia and deteriorated in depressive disorders and are increasingly used as biomarker in these neuropsychiatric diseases. The opposite use of NMDA receptor antagonists in schizophrenia and depression raises the question how their effects are in accordance with the observed disease pathophysiology and if these effects show a consequent sex-specificity. In this study in rats, we investigated the effects of subchronic (14 days) intraperitoneal injections of the NMDA receptor antagonist MK-801 at a subanesthetic daily dose of 0.2 mg/kg on the behavioral phenotype of adult female and male rats and on pharmacologically induced gamma oscillations measured ex vivo from the hippocampus. We found that MK-801 treatment leads to impaired recognition memory in the novel object recognition test, increased stereotypic behavior and reduced grooming, predominantly in female rats. MK-801 also increased the peak power of hippocampal gamma oscillations induced by kainate or acetylcholine only in female rats, without affecting the peak frequency of the oscillations. The findings indicate that blockade of NMDA receptors enhances gamma oscillations predominantly in female rats and this effect is associated with behavioral changes in females. The results are in accordance with clinical electrophysiological findings and highlight the importance of hippocampal gamma oscillations as a biomarker in schizophrenia and depression.

Towards understanding sex differences in autism spectrum disorders

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterized by social deficits, repetitive behaviours and lack of empathy. Its significant genetic heritability and potential comorbidities often lead to diagnostic and therapeutic challenges. This review addresses the biological basis of ASD, focusing on the sex differences in gene expression and hormonal influences. ASD is more commonly diagnosed in males at a ratio of 4:1, indicating a potential oversight in female-specific ASD research and a risk of underdiagnosis in females. We consider how ASD manifests differently across sexes by exploring differential gene expression in female and male brains and consider how variations in steroid hormones influence ASD characteristics. Synaptic function, including excitation/inhibition ratio imbalance, is influenced by gene mutations and this is explored as a key factor in the cognitive and behavioural manifestations of ASD. We also discuss the role of micro RNAs (miRNAs) and highlight a novel mutation in miRNA-873, which affects a suite of key synaptic genes, neurexin, neuroligin, SHANK and post-synaptic density proteins, implicated in the pathology of ASD. Our review suggests that genetic predisposition, sex differences in brain gene expression, and hormonal factors significantly contribute to the presentation, identification and severity of ASD, necessitating sex-specific considerations in diagnosis and treatments. These findings advocate for personalized interventions to improve the outcomes for individuals with ASD.

Physical exercise regulates microglia in health and disease

There is a well-established link between physical activity and brain health. As such, the effectiveness of physical exercise as a therapeutic strategy has been explored in a variety of neurological contexts. To determine the extent to which physical exercise could be most beneficial under different circumstances, studies are needed to uncover the underlying mechanisms behind the benefits of physical activity. Interest has grown in understanding how physical activity can regulate microglia, the resident immune cells of the central nervous system. Microglia are key mediators of neuroinflammatory processes and play a role in maintaining brain homeostasis in healthy and pathological settings. Here, we explore the evidence suggesting that physical activity has the potential to regulate microglia activity in various animal models. We emphasize key areas where future research could contribute to uncovering the therapeutic benefits of engaging in physical exercise.

Role of MARK2 in the nervous system and cancer

Microtubule-Affinity Regulating Kinase 2 (MARK2), a member of the serine/threonine protein kinase family, phosphorylates microtubule-associated proteins, playing a crucial role in cancer and neurodegenerative diseases. This kinase regulates multiple signaling pathways, including the WNT, PI3K/AKT/mTOR (PAM), and NF-κB pathways, potentially linking it to cancer and the nervous system. As a crucial regulator of the PI3K/AKT/mTOR pathway, the loss of MARK2 inhibits the growth and metastasis of cancer cells. MARK2 is involved in the excessive phosphorylation of tau, thus influencing neurodegeneration. Therefore, MARK2 emerges as a promising drug target for the treatment of cancer and neurodegenerative diseases. Despite its significance, the development of inhibitors for MARK2 remains limited. In this review, we aim to present detailed information on the structural features of MARK2 and its role in various signaling pathways associated with cancer and neurodegenerative diseases. Additionally, we further characterize the therapeutic potential of MARK2 in neurodegenerative diseases and cancer, and hope to facilitate basic research on MARK2 and the development of inhibitors targeting MARK2.

Glial cells are affected more than interneurons by the loss of Engrailed 2 gene in the mouse cerebellum

Glial cells play a pivotal role in the inflammatory processes, which are common features of several neurodevelopmental and neurodegenerative disorders. Their major role in modulating neuroinflammation underscores their significance in these conditions. Engrailed-2 knockout mice (En2-/- ) are considered a valuable model for autism spectrum disorder (ASD) due to their distinctive neuroanatomical and behavioral traits. Given the higher prevalence of ASD in males, our objective was to investigate glial and interneuron alterations in the cerebellum of En2-/- mice compared with wild-type (WT) mice in both sexes. We employed immunohistochemical analysis to assess cell density for all cell types studied and analyzed the area (A) and shape factor (SF) of microglia cell bodies. Our findings revealed the following: (a) In WT mice, the density of microglia and astrocytes was higher in females than in males, while interneuron density was lower in females. Notably, in En2-mutant mice, these differences between males and females were not present. (b) In both male and female En2-/- mice, astrocyte density exceeded that in WT mice, with microglia density being greater only in females. (c) In WT females, microglia cell bodies exhibited a larger area and a lower shape factor compared to WT males. Remarkably, the En2 mutation did not appear to influence these sex-related differences. (d) In both male and female En2-/- mice, we observed a consistent pattern: microglia cell bodies displayed a larger area and a smaller shape factor. Given the ongoing debate surrounding the roles of glia and sex-related factors in ASD, our observations provide valuable insights into understanding how an ASD-associated gene En2 affects specific cell types in the cerebellum.

From synapses to circuits: What mouse models have taught us about how autism spectrum disorder impacts hippocampal function

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that impacts a variety of cognitive and behavioral domains. While a genetic component of ASD has been well-established, none of the numerous syndromic genes identified in humans accounts for more than 1% of the clinical patients. Due to this large number of target genes, numerous mouse models of the disorder have been generated. However, the focus on distinct brain circuits, behavioral phenotypes and diverse experimental approaches has made it difficult to synthesize the overwhelming number of model animal studies into concrete throughlines that connect the data across levels of investigation. Here we chose to focus on one circuit, the hippocampus, and one hypothesis, a shift in excitatory/inhibitory balance, to examine, from the level of the tripartite synapse up to the level of in vivo circuit activity, the key commonalities across disparate models that can illustrate a path towards a better mechanistic understanding of ASD's impact on hippocampal circuit function.

Neuroimmune mechanisms in autism etiology - untangling a complex problem using human cellular models

Autism spectrum disorder (ASD) affects 1 in 36 people and is more often diagnosed in males than in females. Core features of ASD are impaired social interactions, repetitive behaviors and deficits in verbal communication. ASD is a highly heterogeneous and heritable disorder, yet its underlying genetic causes account only for up to 80% of the cases. Hence, a subset of ASD cases could be influenced by environmental risk factors. Maternal immune activation (MIA) is a response to inflammation during pregnancy, which can lead to increased inflammatory signals to the fetus. Inflammatory signals can cross the placenta and blood brain barriers affecting fetal brain development. Epidemiological and animal studies suggest that MIA could contribute to ASD etiology. However, human mechanistic studies have been hindered by a lack of experimental systems that could replicate the impact of MIA during fetal development. Therefore, mechanisms altered by inflammation during human pre-natal brain development, and that could underlie ASD pathogenesis have been largely understudied. The advent of human cellular models with induced pluripotent stem cell (iPSC) and organoid technology is closing this gap in knowledge by providing both access to molecular manipulations and culturing capability of tissue that would be otherwise inaccessible. We present an overview of multiple levels of evidence from clinical, epidemiological, and cellular studies that provide a potential link between higher ASD risk and inflammation. More importantly, we discuss how stem cell-derived models may constitute an ideal experimental system to mechanistically interrogate the effect of inflammation during the early stages of brain development.

Autism Spectrum Disorder: Brain Areas Involved, Neurobiological Mechanisms, Diagnoses and Therapies

Autism spectrum disorder (ASD), affecting over 2% of the pre-school children population, includes an important fraction of the conditions accounting for the heterogeneity of autism. The disease was discovered 75 years ago, and the present review, based on critical evaluations of the recognized ASD studies from the beginning of 1990, has been further developed by the comparative analyses of the research and clinical reports, which have grown progressively in recent years up to late 2023. The tools necessary for the identification of the ASD disease and its related clinical pathologies are genetic and epigenetic mutations affected by the specific interaction with transcription factors and chromatin remodeling processes occurring within specific complexes of brain neurons. Most often, the ensuing effects induce the inhibition/excitation of synaptic structures sustained primarily, at dendritic fibers, by alterations of flat and spine response sites. These effects are relevant because synapses, established by specific interactions of neurons with glial cells, operate as early and key targets of ASD. The pathology of children is often suspected by parents and communities and then confirmed by ensuing experiences. The final diagnoses of children and mature patients are then completed by the combination of neuropsychological (cognitive) tests and electro-/magneto-encephalography studies developed in specialized centers. ASD comorbidities, induced by processes such as anxieties, depressions, hyperactivities, and sleep defects, interact with and reinforce other brain diseases, especially schizophrenia. Advanced therapies, prescribed to children and adult patients for the control of ASD symptoms and disease, are based on the combination of well-known brain drugs with classical tools of neurologic and psychiatric practice. Overall, this review reports and discusses the advanced knowledge about the biological and medical properties of ASD.

SRGN amplifies microglia-mediated neuroinflammation and exacerbates ischemic brain injury

BACKGROUND

Microglia is the major contributor of post-stroke neuroinflammation cascade and the crucial cellular target for the treatment of ischemic stroke. Currently, the endogenous mechanism underlying microglial activation following ischemic stroke remains elusive. Serglycin (SRGN) is a proteoglycan expressed in immune cells. Up to now, the role of SRGN on microglial activation and ischemic stroke is largely unexplored.

METHODS

Srgn knockout (KO), Cd44-KO and wild-type (WT) mice were subjected to middle cerebral artery occlusion (MCAO) to mimic ischemic stroke. Exogenous SRGN supplementation was achieved by stereotactic injection of recombinant mouse SRGN (rSRGN). Cerebral infarction was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Neurological functions were evaluated by the modified neurological severity score (mNSS) and grip strength. Microglial activation was detected by Iba1 immunostaining, morphological analysis and cytokines' production. Neuronal death was examined by MAP2 immunostaining and FJB staining.

RESULTS

The expression of SRGN and its receptor CD44 was significantly elevated in the ischemic mouse brains, especially in microglia. In addition, lipopolysaccharide (LPS) induced SRGN upregulation in microglia in vitro. rSRGN worsened ischemic brain injury in mice and amplified post-stroke neuroinflammation, while gene knockout of Srgn exerted reverse impacts. rSRGN promoted microglial proinflammatory activation both in vivo and in vitro, whereas Srgn-deficiency alleviated microglia-mediated inflammatory response. Moreover, the genetic deletion of Cd44 partially rescued rSRGN-induced excessed neuroinflammation and ischemic brain injury in mice. Mechanistically, SRGN boosted the activation of NF-κB signal, and increased glycolysis in microglia.

CONCLUSION

SRGN acts as a novel therapeutic target in microglia-boosted proinflammatory response following ischemic stroke.

Functional and pathological consequences of being fast on the uptake: Protein kinase G and p38α MAPK regulation of serotonin transporters

Serotonin (5-hydroxytryptamine, 5-HT) signaling plays an important role in dynamic control of peripheral and central nervous system physiology, with altered 5-HT homeostasis implicated in a significant number of disorders, ranging from pulmonary, bowel, and metabolic disease to depression, obsessive-compulsive disorder, and autism spectrum disorder (ASD). The presynaptic, 5-HT transporter (SERT) has a well-established role in regulating 5-HT signaling and is a target of widely prescribed psychotherapeutics, the 5-HT selective reuptake inhibitors (SSRIs). Although SSRI therapy provides symptom relief for many suffering from mood and anxiety disorders, response to these medications is slow (weeks), and too many receive modest or no benefit. At present, all prescribed SSRIs act as competitive SERT antagonists. Although non-serotonergic therapeutics for mood disorders deserve aggressive investigation, the development of agents that target SERT regulatory pathways have yet to be considered for their possible utility and may possibly offer improved efficacy and more rapid onset. Here, we focus attention on a significant body of evidence that SERT transport activity can be rapidly elevated by protein kinase G (PKG) and p38α mitogen activated protein kinase (MAPK) linked pathways, mechanisms that are impacted by disease-associated genetic variation. Here, we provide a brief overview of kinase-linked, posttranslational regulation of SERT, with a particular focus on evidence from pharmacological and genetic studies that the transporter's regulation by PKG/p38α MAPK associated pathways offers an opportunity to more subtly adjust, rather than eliminate, SERT function as a therapeutic strategy.

TREM2 promotes glioma progression and angiogenesis mediated by microglia/brain macrophages

Triggering receptor expressed on myeloid cell 2 (TREM2), a myeloid cell-specific signaling molecule, controls essential functions of microglia and impacts on the pathogenesis of Alzheimer's disease and other neurodegenerative disorders. TREM2 is also highly expressed in tumor-associated macrophages in different types of cancer. Here, we studied whether TREM2 influences glioma progression. We found a gender-dependent effect of glioma growth in wild-type (WT) animals injected with GL261-EGFP glioma cells. Most importantly, TREM2 promotes glioma progression in male but not female animals. The accumulation of glioma-associated microglia/macrophages (GAMs) and CD31+ blood vessel density is reduced in male TREM2-deficient mice. A transcriptomic analysis of glioma tissue revealed that TREM2 deficiency suppresses immune-related genes. In an organotypic slice model devoid of functional vascularization and immune components from periphery, the tumor size was not affected by TREM2-deficiency. In human resection samples from glioblastoma, TREM2 is upregulated in GAMs. Based on the Cancer Genome Atlas Program (TCGA) and the Chinese Glioma Genome Atlas (CGGA) databases, the TREM2 expression levels were negatively correlated with survival. Thus, the TREM2-dependent crosstalk between GAMs and the vasculature formation promotes glioma growth.