Microglia in the developing brain: a potential target with lifetime effects

Stem Cell Secretions as a Potential Therapeutic Agent for Autism Spectrum Disorder: A Narrative Review

Autism spectrum disorder (ASD) is a neurodevelopmental illness characterized by impaired social interaction and restricted repetitive behaviors or interests. The rising prevalence of ASD diagnosis has triggered a surge in research into investigating the underlying neuropathological processes and finding new therapeutic approaches. ASD is characterized by neuroinflammation and dysregulation of neuro-immune cross-talk, which suggests that stem cell treatment might be a potential therapeutic approach. The beneficial and restorative effects of stem cells are mainly due to their paracrine activity, in which stem cells generate and release extracellular vesicles such as exosomes and distinct secreted non-vesicle soluble proteins, including, growth factors, chemokines, cytokines, and immunomodulatory molecules referred to as the Secretome. In this paper, we reviewed the existing research exploring the therapeutic potential of stem cell secretome focusing on their role in addressing ASD pathology. Furthermore, we proposed a comprehensive mechanism of action for stem cell secretions, encompassing the broader secretome as well as the specific contribution of exosomes, in alleviating ASD neuropathology. Across the reviewed studies, exosomes and secreted soluble factors of the transplanted stem cell demonstrate a potential efficacy in ameliorating autistic-like behaviors. The proposed mechanism of action involves the modulation of signaling pathways implicated in neuroinflammation, angiogenesis, cellular apoptosis, and immunomodulation.

Inflammatory mediators in major depression and bipolar disorder

Major depressive disorder (MDD) and bipolar disorder (BD) are highly disabling illnesses defined by different psychopathological, neuroimaging, and cognitive profiles. In the last decades, immune dysregulation has received increasing attention as a central factor in the pathophysiology of these disorders. Several aspects of immune dysregulations have been investigated, including, low-grade inflammation cytokines, chemokines, cell populations, gene expression, and markers of both peripheral and central immune activation. Understanding the distinct immune profiles characterizing the two disorders is indeed of crucial importance for differential diagnosis and the implementation of personalized treatment strategies. In this paper, we reviewed the current literature on the dysregulation of the immune response system focusing our attention on studies using inflammatory markers to discriminate between MDD and BD. High heterogeneity characterized the available literature, reflecting the heterogeneity of the disorders. Common alterations in the immune response system include high pro-inflammatory cytokines such as IL-6 and TNF-α. On the contrary, a greater involvement of chemokines and markers associated with innate immunity has been reported in BD together with dynamic changes in T cells with differentiation defects during childhood which normalize in adulthood, whereas classic mediators of immune responses such as IL-4 and IL-10 are present in MDD together with signs of immune-senescence.

Allopregnanolone and its antagonist modulate neuroinflammation and neurological impairment

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease.

Neuron Derived Cytokine Interleukin-34 Controls Developmental Microglia Function

Neuron-microglia interactions dictate the development of neuronal circuits in the brain. However, the factors that support and broadly regulate these processes across developmental stages are largely unknown. Here, we find that IL34, a neuron-derived cytokine, is upregulated in development and plays a critical role in supporting and maintaining neuroprotective, mature microglia in the anterior cingulate cortex (ACC) of mice. We show that IL34 mRNA and protein is upregulated in neurons in the second week of postnatal life and that this increase coincides with increases in microglia number and expression of mature, homeostatic markers, e.g., TMEM119. We also found that IL34 mRNA is higher in more active neurons, and higher in excitatory (compared to inhibitory) neurons. Genetic KO of IL34 prevents the functional maturation of microglia and results in an anxiolytic phenotype in these mice by adulthood. Acute, low dose blocking of IL34 at postnatal day (P)15 in mice decreased microglial TMEM119 expression and increased aberrant microglial phagocytosis of thalamocortical synapses within the ACC. In contrast, viral overexpression of IL34 early in life (P1-P8) caused early maturation of microglia and prevented microglial phagocytosis of thalamocortical synapses during the appropriate neurodevelopmental refinement window. Taken together, these findings establish IL34 as a key regulator of neuron-microglia crosstalk in postnatal brain development, controlling both microglial maturation and synapse engulfment.

Enhanced levels of fractalkine and HSP60 in cerebrospinal fluid of sporadic amyotrophic lateral sclerosis patients

Amyotrophic Lateral Sclerosis (ALS) is a multifactorial neurodegenerative disorder with a significant contribution of non-cell autonomous mechanisms to motor neuronal degeneration. Amongst a plethora of molecules, fractalkine (C-X3-C motif chemokine ligand 1), and Heat Shock Protein 60 (HSP60), are key modulators of microglial activation. The contribution of these molecules in Sporadic ALS (SALS) remains unexplored. To investigate this, fractalkine levels were estimated in Cerebrospinal fluid (CSF) of SALS patients (ALS-CSF; n = 44) by Enzyme-linked Immunosorbent Assay (ELISA) and correlated with clinical parameters including disease severity and duration. CSF HSP60 levels were estimated by Western blotting (ALS-CSF; n = 19). Also, CSF levels of Chitotriosidase-1 (CHIT-1), a microglia-specific neuroinflammatory molecule, were measured and its association, if any, with fractalkine and HSP60 was investigated. Both fractalkine and HSP60 levels were significantly elevated in ALS-CSF. Similar to our earlier observation, CHIT-1 levels were also upregulated. Fractalkine showed a moderate negative correlation with the ALS-Functional Rating Scale (ALSFRS) score indicating its significant rise in mild cases which plateaued in cases with high disease severity. However, no obvious correlation was found between fractalkine, HSP60, and CHIT-1. Our study hints that high fractalkine levels in mild cases might be conferring neuroprotection by combating microglial activation and highlights its importance as a novel therapeutic target for SALS. On the other hand, significantly enhanced levels of HSP60, a pro-inflammatory molecule, hint towards its role in accentuating microgliosis, although, it doesn't act synergistically with CHIT-1. Our study suggests that fractalkine and HSP60 act independently of CHIT-1 to suppress and accentuate neuroinflammation, respectively.

Developmental Toxicity of Fine Particulate Matter: Multifaceted Exploration from Epidemiological and Laboratory Perspectives

Particulate matter of size ≤ 2.5 μm (PM2.5) is a critical environmental threat that considerably contributes to the global disease burden. However, accompanied by the rapid research progress in this field, the existing research on developmental toxicity is still constrained by limited data sources, varying quality, and insufficient in-depth mechanistic analysis. This review includes the currently available epidemiological and laboratory evidence and comprehensively characterizes the adverse effects of PM2.5 on developing individuals in different regions and various pollution sources. In addition, this review explores the effect of PM2.5 exposure to individuals of different ethnicities, genders, and socioeconomic levels on adverse birth outcomes and cardiopulmonary and neurological development. Furthermore, the molecular mechanisms involved in the adverse health effects of PM2.5 primarily encompass transcriptional and translational regulation, oxidative stress, inflammatory response, and epigenetic modulation. The primary findings and novel perspectives regarding the association between public health and PM2.5 were examined, highlighting the need for future studies to explore its sources, composition, and sex-specific effects. Additionally, further research is required to delve deeper into the more intricate underlying mechanisms to effectively prevent or mitigate the harmful effects of air pollution on human health.

Medicinal herbal remedies in neurodegenerative diseases: an update on antioxidant potential

It has been widely documented that medicinal herbal remedies are effective, have fewer side effects than conventional medicine, and have a synergistic effect on health collaborations in the fight against complicated diseases. Traditional treatments for neurological problems in ancient times sometimes involved the use of herbal remedies and conventional methods from East Asian countries including India, Japan, China, and Korea. We collected and reviewed studies on plant-derived neuroprotective drugs and tested them in neurotoxic models. Basic research, preclinical and clinical transgene research can benefit from in silico, in vitro, and in vivo investigations. Research, summaries of the extracts, fractions, and herbal ingredients were compiled from popular scientific databases, which were then examined according to origin and bioactivity. Given the complex and varied causes of neurodegeneration, it may be beneficial to focus on multiple mechanisms of action and a neuroprotection approach. This approach aims to prevent cell death and restore function to damaged neurons, offering promising strategies for preventing and treating neurodegenerative diseases. Neurodegenerative illnesses can potentially be treated with natural compounds that have been identified as neuroprotective agents. To gain deeper insights into the neuropharmacological mechanisms underlying the neuroprotective and therapeutic properties of naturally occurring antioxidant phytochemical compounds in diverse neurodegenerative diseases, this study aims to comprehensively review such compounds, focusing on their modulation of apoptotic markers such as caspase, Bax, Bcl-2, and proinflammatory markers. In addition, we delve into a range of efficacies of antioxidant phytochemical compounds as neuroprotective agents in animal models. They reduce the oxidative stress of the brain and have been shown to have anti-apoptotic effects. Many researches have demonstrated that plant extracts or bioactive compounds can fight neurodegenerative disorders. Herbal medications may offer neurodegenerative disease patients' new treatments. This may be a cheaper and more culturally appropriate alternative to standard drugs for millions of people with age-related NDDs.

Perinatal exposure to the immune-suppressant di-n-octyltin dichloride affects brain development in rats

Disruption of the immune system during embryonic brain development by environmental chemicals was proposed as a possible cause of neurodevelopmental disorders. We previously found adverse effects of di-n-octyltin dichloride (DOTC) on maternal and developing immune systems of rats in an extended one-generation reproductive toxicity study according to the OECD 443 test guideline. We hypothesize that the DOTC-induced changes in the immune system can affect neurodevelopment. Therefore, we used in-vivo MRI and PET imaging and genomics, in addition to behavioral testing and neuropathology as proposed in OECD test guideline 443, to investigate the effect of DOTC on structural and functional brain development. Male rats were exposed to DOTC (0, 3, 10, or 30 mg/kg of diet) from 2 weeks prior to mating of the F0-generation until sacrifice of F1-animals. The brains of rats, exposed to DOTC showed a transiently enlarged volume of specific brain regions (MRI), altered specific gravity, and transient hyper-metabolism ([18F]FDG PET). The alterations in brain development concurred with hyper-responsiveness in auditory startle response and slight hyperactivity in young adult animals. Genomics identified altered transcription of key regulators involved in neurodevelopment and neural function (e.g. Nrgrn, Shank3, Igf1r, Cck, Apba2, Foxp2); and regulators involved in cell size, cell proliferation, and organ development, especially immune system development and functioning (e.g. LOC679869, Itga11, Arhgap5, Cd47, Dlg1, Gas6, Cml5, Mef2c). The results suggest the involvement of immunotoxicity in the impairment of the nervous system by DOTC and support the hypothesis of a close connection between the immune and nervous systems in brain development.

Abnormal Microglial Density and Morphology in the Brain of Cyclooxygenase 2 Knockin Mice

Prostaglandin E2 (PGE2) is a signaling molecule produced by cyclooxygenase-2 (COX-2) that is important in healthy brain development. Anomalies in the COX-2/PGE2 pathway due to genetic or environmental factors have been linked to Autism Spectrum Disorders (ASD). Our previous studies showed that COX-2 deficient (COX-2-KI) mice exhibit sex-dependent molecular changes in the brain and associated autism-related behaviors. Here, we aim to determine the effect of COX-2-KI on microglial density and morphology in the developing brain. Microglia normally transition between an amoeboid or ramified morphology depending on their surroundings and are important for the development of the healthy brain, assisting with synaptogenesis, synaptic pruning, and phagocytosis. We use COX-2-KI male and female mice to evaluate microglia density, morphology, and branch length and number in five brain regions (cerebellum, hippocampus, olfactory bulb, prefrontal cortex, and thalamus) at the gestational day 19 (G19) and postnatal day 25 (PN25). We discovered that COX2-KI females were affected at G19 with increased microglial density, altered percentage of amoeboid and ramified microglia, affected branch length, and decreased branching networks in a region-specific manner; these effects persisted to PN25 in select regions. Interestingly, while limited changes were found in G19 COX-2-KI males, at PN25 we found increased microglial density, higher percentages of ramified microglia, and increased branch counts, and length observed in nearly all brain regions tested. Overall, we show for the first time that the COX-2 deficiency in our ASD mouse model influences microglia morphology in a sex- and region- and stage-dependent manner.

Brain microglia serve as a persistent HIV reservoir despite durable antiretroviral therapy

Brain microglia (MG) may serve as a human immunodeficiency virus 1 (HIV) reservoir and ignite rebound viremia following cessation of antiretroviral therapy (ART), but they have yet to be proven to harbor replication-competent HIV. Here, we isolated brain myeloid cells (BrMCs) from nonhuman primates and rapid autopsy of people with HIV (PWH) on ART and sought evidence of persistent viral infection. BrMCs predominantly displayed microglial markers, in which up to 99.9% of the BrMCs were TMEM119+ MG. Total and integrated SIV or HIV DNA was detectable in the MG, with low levels of cell-associated viral RNA. Provirus in MG was highly sensitive to epigenetic inhibition. Outgrowth virus from parietal cortex MG in an individual with HIV productively infected both MG and PBMCs. This inducible, replication-competent virus and virus from basal ganglia proviral DNA were closely related but highly divergent from variants in peripheral compartments. Phenotyping studies characterized brain-derived virus as macrophage tropic based on the ability of the virus to infect cells expressing low levels of CD4. The lack of genetic diversity in virus from the brain suggests that this macrophage-tropic lineage quickly colonized brain regions. These data demonstrate that MG harbor replication-competent HIV and serve as a persistent reservoir in the brain.

Variation along P2RX7 interacts with early traumas on severity of anxiety suggesting a role for neuroinflammation

Emotional stress is a leading risk factor in the development of neuropsychiatric disorders possibly via immune activation. P2X7 receptors promote neuroinflammation, and research suggests a relationship between chromosome region 12q2431, in which the P2X7R gene is located, and development of mood disorders, however, few studies concentrate on its association with anxiety. Our aim was to investigate the effects of P2RX7 variation in interaction with early childhood traumas and recent stressors on anxiety. 1752 participants completed questionnaires assessing childhood adversities and recent negative life events, provided data on anxiety using the Brief Symptom Inventory, and were genotyped for 681 SNPs in the P2RX7 gene, 335 of which passed quality control and were entered into linear regression models followed by a linkage disequilibrium-based clumping procedure to identify clumps of SNPs with a significant main or interaction effect. We identified a significant clump with top SNP rs67881993 and containing a set of 29SNPs that are in high LD, which significantly interacted with early childhood traumas but not with recent stress conveying a protective effect against increased anxiety in those exposed to early adversities. Our study demonstrated that P2RX7 variants interact with distal and more etiological stressors in influencing the severity of anxiety symptoms, supporting previous scarce results and demonstrating its role in moderating the effects of stress.

Toward discovering a novel family of peptides targeting neuroinflammatory states of brain microglia and astrocytes

Microglia are immune-derived cells critical to the development and healthy function of the brain and spinal cord, yet are implicated in the active pathology of many neuropsychiatric disorders. A range of functional phenotypes associated with the healthy brain or disease states has been suggested from in vivo work and were modeled in vitro as surveying, reactive, and primed sub-types of primary rat microglia and mixed microglia/astrocytes. It was hypothesized that the biomolecular profile of these cells undergoes a phenotypical change as well, and these functional phenotypes were explored for potential novel peptide binders using a custom 7 amino acid-presenting M13 phage library (SX7) to identify unique peptides that bind differentially to these respective cell types. Surveying glia were untreated, reactive were induced with a lipopolysaccharide treatment, recovery was modeled with a potent anti-inflammatory treatment dexamethasone, and priming was determined by subsequently challenging the cells with interferon gamma. Microglial function was profiled by determining the secretion of cytokines and nitric oxide, and expression of inducible nitric oxide synthase. After incubation with the SX7 phage library, populations of SX7-positive microglia and/or astrocytes were collected using fluorescence-activated cell sorting, SX7 phage was amplified in Escherichia coli culture, and phage DNA was sequenced via next-generation sequencing. Binding validation was done with synthesized peptides via in-cell westerns. Fifty-eight unique peptides were discovered, and their potential functions were assessed using a basic local alignment search tool. Peptides potentially originated from proteins ranging in function from a variety of supportive glial roles, including synapse support and pruning, to inflammatory incitement including cytokine and interleukin activation, and potential regulation in neurodegenerative and neuropsychiatric disorders.

The Ketogenic Diet and Neuroinflammation: The Action of Beta-Hydroxybutyrate in a Microglial Cell Line

The ketogenic diet (KD), a diet high in fat and protein but low in carbohydrates, is gaining much interest due to its positive effects, especially in neurodegenerative diseases. Beta-hydroxybutyrate (BHB), the major ketone body produced during the carbohydrate deprivation that occurs in KD, is assumed to have neuroprotective effects, although the molecular mechanisms responsible for these effects are still unclear. Microglial cell activation plays a key role in the development of neurodegenerative diseases, resulting in the production of several proinflammatory secondary metabolites. The following study aimed to investigate the mechanisms by which BHB determines the activation processes of BV2 microglial cells, such as polarization, cell migration and expression of pro- and anti-inflammatory cytokines, in the absence or in the presence of lipopolysaccharide (LPS) as a proinflammatory stimulus. The results showed that BHB has a neuroprotective effect in BV2 cells, inducing both microglial polarization towards an M2 anti-inflammatory phenotype and reducing migratory capacity following LPS stimulation. Furthermore, BHB significantly reduced expression levels of the proinflammatory cytokine IL-17 and increased levels of the anti-inflammatory cytokine IL-10. From this study, it can be concluded that BHB, and consequently the KD, has a fundamental role in neuroprotection and prevention in neurodegenerative diseases, presenting new therapeutic targets.

Atmospheric particulate matter impairs cognition by modulating synaptic function via the nose-to-brain route

Atmospheric particulate matter (PM), a ubiquitous air pollutant, is the leading environmental risk factor for mortality worldwide. Experimental and epidemiological studies consistently suggest a strong link between long-term exposure to PM_2.5 (<2.5 μm, fine PM) and cognitive impairment. The neuroinflammatory response is presumed to be one of the main mechanisms of PM_2.5-induced cognitive impairment, possibly leading to synaptic dysfunction. However, the main route and mechanism underlying the cause of cognitive dysfunction and pathogenic alterations in PM_2.5-exposure mice remain poorly understood. Therefore, this study aimed to investigate the main route and mechanism of PM_2.5-induced cognitive impairment. Our results showed that PM_2.5 directly entered the brain following nasal administration, and both the short-term PM_2.5 administration via atomization and nasal drops induced learning and memory impairments and neuronal damage in adult mice. Moreover, astrocytes and microglia were both activated in the two short-term PM_2.5 exposure models, while few changes in the inflammatory response were observed in the peripheral circulatory system. Furthermore, a further transcriptional analysis revealed that short-term PM_2.5 administration led to cognitive impairment mainly by modulating synaptic functions and that although glia were activated, the glia-related pathological pathways were not significantly activated. Notably, following PM_2.5 exposure, PLX3397-induced microglial deletion did not restore the cognitive function of the mice. In conclusion, our results provide evidence that PM_2.5 enters the brain via the nose-to-brain route to impair cognitive function, and short-term exposure to PM_2.5 directly alters synaptic function rather than the neuroinflammatory response to affect cognition.

Microglia isolation from aging mice for cell culture: A beginner's guide

Microglia, the innate immune cell of the central nervous system, play significant roles in brain development, maintenance, homeostasis, and neuroinflammation. Although numerous methods have been developed to isolate microglia from embryonic or postnatal mouse brains, still major difficulties exist in isolating microglia from adult mice, often resulting in low yield and risk of cellular activation. Therefore, there is a need for a more efficient method to isolate pure and high-yield microglia from adult mice to study various neurodegenerative diseases. The aim of this study was to develop a fully functional protocol for the isolation of microglia by comparing different protocols. We investigated the efficacy of three protocols in terms of cell yield, purity, cellular activation, cellular aging, and migration properties and proposed the modified protocol (PROTOCOL 1), which provides an optimal yield of functional microglial cells with a minimum of material and equipment and allows young researchers with little experience to isolate microglia and helps them to delve deeper into the world of neuroscience.

SARS-CoV-2 (COVID-19) as a possible risk factor for neurodevelopmental disorders

Pregnant women constitute one of the most vulnerable populations to be affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the cause of coronavirus disease 2019. SARS-CoV-2 infection during pregnancy could negatively impact fetal brain development via multiple mechanisms. Accumulating evidence indicates that mother to fetus transmission of SARS-CoV-2 does occur, albeit rarely. When it does occur, there is a potential for neuroinvasion via immune cells, retrograde axonal transport, and olfactory bulb and lymphatic pathways. In the absence of maternal to fetal transmission, there is still the potential for negative neurodevelopmental outcomes as a consequence of disrupted placental development and function leading to preeclampsia, preterm birth, and intrauterine growth restriction. In addition, maternal immune activation may lead to hypomyelination, microglial activation, white matter damage, and reduced neurogenesis in the developing fetus. Moreover, maternal immune activation can disrupt the maternal or fetal hypothalamic-pituitary-adrenal (HPA) axis leading to altered neurodevelopment. Finally, pro-inflammatory cytokines can potentially alter epigenetic processes within the developing brain. In this review, we address each of these potential mechanisms. We propose that SARS-CoV-2 could lead to neurodevelopmental disorders in a subset of pregnant women and that long-term studies are warranted.

Microglia sequelae: brain signature of innate immunity in schizophrenia

Schizophrenia is a psychiatric disorder with significant impact on individuals and society. The current pharmacologic treatment, which principally alleviates psychosis, is focused on neurotransmitters modulation, relying on drugs with severe side effects and ineffectiveness in a significant percentage of cases. Therefore, and due to difficulties inherent to diagnosis and treatment, it is vital to reassess alternative cellular and molecular drug targets. Distinct risk factors - genetic, developmental, epigenetic, and environmental - have been associated with disease onset and progression, giving rise to the proposal of different pathophysiological mechanisms and putative pharmacological targets. Immunity is involved and, particularly microglia - innate immune cells of the central nervous system, critically involved in brain development - have captured attention as cellular players. Microglia undergo marked morphologic and functional alterations in the human disease, as well as in animal models of schizophrenia, as reported in several original papers. We cluster the main findings of clinical studies by groups of patients: (1) at ultra-high risk of psychosis, (2) with a first episode of psychosis or recent-onset schizophrenia, and (3) with chronic schizophrenia; in translational studies, we highlight the time window of appearance of particular microglia alterations in the most well studied animal model in the field (maternal immune activation). The organization of clinical and translational findings based on schizophrenia-associated microglia changes in different phases of the disease course may help defining a temporal pattern of microglia changes and may drive the design of novel therapeutic strategies.

Immunosenescence and Aging: Neuroinflammation Is a Prominent Feature of Alzheimer's Disease and Is a Likely Contributor to Neurodegenerative Disease Pathogenesis

Alzheimer's disease (AD) is a chronic multifactorial and complex neuro-degenerative disorder characterized by memory impairment and the loss of cognitive ability, which is a problem affecting the elderly. The pathological intracellular accumulation of abnormally phosphorylated Tau proteins, forming neurofibrillary tangles, and extracellular amyloid-beta (Aβ) deposition, forming senile plaques, as well as neural disconnection, neural death and synaptic dysfunction in the brain, are hallmark pathologies that characterize AD. The prevalence of the disease continues to increase globally due to the increase in longevity, quality of life, and medical treatment for chronic diseases that decreases the mortality and enhance the survival of elderly. Medical awareness and the accurate diagnosis of the disease also contribute to the high prevalence observed globally. Unfortunately, no definitive treatment exists that can be used to modify the course of AD, and no available treatment is capable of mitigating the cognitive decline or reversing the pathology of the disease as of yet. A plethora of hypotheses, ranging from the cholinergic theory and dominant Aβ cascade hypothesis to the abnormally excessive phosphorylated Tau protein hypothesis, have been reported. Various explanations for the pathogenesis of AD, such as the abnormal excitation of the glutamate system and mitochondrial dysfunction, have also been suggested. Despite the continuous efforts to deliver significant benefits and an effective treatment for this distressing, globally attested aging illness, multipronged approaches and strategies for ameliorating the disease course based on knowledge of the underpinnings of the pathogenesis of AD are urgently needed. Immunosenescence is an immune deficit process that appears with age (inflammaging process) and encompasses the remodeling of the lymphoid organs, leading to alterations in the immune function and neuroinflammation during advanced aging, which is closely linked to the outgrowth of infections, autoimmune diseases, and malignant cancers. It is well known that long-standing inflammation negatively influences the brain over the course of a lifetime due to the senescence of the immune system. Herein, we aim to trace the role of the immune system in the pathogenesis of AD. Thus, we explore alternative avenues, such as neuroimmune involvement in the pathogenesis of AD. We determine the initial triggers of neuroinflammation, which is an early episode in the pre-symptomatic stages of AD and contributes to the advancement of the disease, and the underlying key mechanisms of brain damage that might aid in the development of therapeutic strategies that can be used to combat this devastating disease. In addition, we aim to outline the ways in which different aspects of the immune system, both in the brain and peripherally, behave and thus to contribute to AD.

Genistein suppresses microglial activation and inhibits apoptosis in different brain regions of hypoxia-exposed mice model of amnesia

Genistein (GE) or 4',5,7-trihydroxyflavone, a plant derived isoflavone, is a biologically active compound having several beneficial properties. Studies showed that GE possesses anti-neoplastic, anti-tumor, anti-helminthic, anti-oxidant, and anti-inflammatory activities. Herein, we investigated the neuroprotective effects of GE in a mouse model of hypoxia-induced amnesia. Mice were exposed to hypoxic conditions (10% O2) in a designated hypoxia chamber and co-treated with GE (10, 20, or 30 mg/kg) for 4 weeks. Following this, behavioral tests were performed to evaluate memory performance. We assessed microglial activation in the hippocampus, amygdala, and pre-frontal cortex (PFC) regions by evaluating the Iba-1 and GFAP transcript levels, and MIP-1β, Cox-2, and IL6 protein levels. Apoptosis was assessed by evaluating Bax, BAD, and Bcl-2 mRNA levels, and caspase-3 activity. To uncover the underlying molecular mechanism, we evaluated the levels of Nrf2, HO-1, and NQO1 in different brain regions of mice from all groups. Results showed that hypoxia-exposed mice have reduced performance in the behavioral tests and GE treatment enhanced the memory performance in hypoxia-exposed mice. Moreover, hypoxia-exposed mice showed increased expression of microglial activation markers and enhanced apoptosis in the hippocampus, amygdala, and PFC. GE treatment suppressed microglial activation and prevented apoptosis in the brain of hypoxia-exposed mice. Furthermore, hypoxia-exposure reduced the expression of Nrf2, NQO1, and HO-1 while GE treatment ameliorated this decrease in different regions of hypoxia-exposed mice brain. In conclusion, GE prevents cognitive dysfunction by suppressing microglial activation and inhibiting apoptosis in the hypoxia-exposed mice brain.

Photobiomodulation for the treatment of neuroinflammation: A systematic review of controlled laboratory animal studies

Background

Neuroinflammation is a response that involves different cell lineages of the central nervous system, such as neurons and glial cells. Among the non-pharmacological interventions for neuroinflammation, photobiomodulation (PBM) is gaining prominence because of its beneficial effects found in experimental brain research. We systematically reviewed the effects of PBM on laboratory animal models, specially to investigate potential benefits of PBM as an efficient anti-inflammatory therapy.

Methods

We conducted a systematic search on the bibliographic databases (PubMed and ScienceDirect) with the keywords based on MeSH terms: photobiomodulation, low-level laser therapy, brain, neuroinflammation, inflammation, cytokine, and microglia. Data search was limited from 2009 to June 2022. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. The initial systematic search identified 140 articles. Among them, 54 articles were removed for duplication and 59 articles by screening. Therefore, 27 studies met the inclusion criteria.

Results

The studies showed that PBM has anti-inflammatory properties in several conditions, such as traumatic brain injury, edema formation and hyperalgesia, ischemia, neurodegenerative conditions, aging, epilepsy, depression, and spinal cord injury.

Conclusion

Taken together, these results indicate that transcranial PBM therapy is a promising strategy to treat brain pathological conditions induced by neuroinflammation.

Microglia-derived CCL2 has a prime role in neocortex neuroinflammation

Background

In myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), several areas of demyelination are detectable in mouse cerebral cortex, where neuroinflammation events are associated with scarce inflammatory infiltrates and blood–brain barrier (BBB) impairment. In this condition, the administration of mesenchymal stem cells (MSCs) controls neuroinflammation, attenuating astrogliosis and promoting the acquisition of stem cell traits by astrocytes. To contribute to the understanding of the mechanisms involved in the pathogenesis of EAE in gray matter and in the reverting effects of MSC treatment, the neocortex of EAE-affected mice was investigated by analyzing the cellular source(s) of chemokine CCL2, a molecule involved in immune cell recruitment and BBB-microvessel leakage.

Methods

The study was carried out by immunohistochemistry (IHC) and dual RNAscope IHC/in situ hybridization methods, using astrocyte, NG2-glia, macrophage/microglia, and microglia elective markers combined with CCL2.

Results

The results showed that in EAE-affected mice, hypertrophic microglia are the primary source of CCL2, surround the cortex neurons and the damaged BBB microvessels. In EAE-affected mice treated with MSCs, microgliosis appeared diminished very soon (6 h) after treatment, an observation that was long-lasting (tested after 10 days). This was associated with a reduced CCL2 expression and with apparently preserved/restored BBB features. In conclusion, the hallmark of EAE in the mouse neocortex is a condition of microgliosis characterized by high levels of CCL2 expression.

Conclusions

This finding supports relevant pathogenetic and clinical aspects of the human disease, while the demonstrated early control of neuroinflammation and BBB permeability exerted by treatment with MSCs may have important therapeutic implications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00365-5.

Perinatal arsenic exposure-induced sustained microglial activation leads to impaired cognitive response in BALB/c mice

Arsenic is infamous for its adverse health effects worldwide. It is known to induce cognitive impairment in experimental model animals and children in the arsenic-affected area. Although the effect of arsenic on neuronal health is well studied, but the involvement of the brain immune component, microglia, has not been well explored. The present study is focused on examining the role of microglia in arsenic-induced cognitive impairment. We have used balb/c mice for the study. Pregnant dams were gavaged with sodium arsenite (0.38 mg/kg body weight) from gestational day 5 (GD5) till postnatal day 22 (PND22). Mice were sacrificed on PND 7, 14, 22 and isolated brains were used for various assays. The study reveals that perinatal arsenic exposure keeps the microglia activated and skews them towards the M1 phenotype. Increased microglial proliferation, ROS, NO, higher levels of proinflammatory cytokines and chemokines were observed in the arsenic exposed group. Enhanced phagocytosis and phagocytic receptor TREM2, along with decreased expression of SNAP25 and PSD95, were correlated for enhanced neuronal pruning leading to impaired learning and memory response. Taken together, the study reveals an association between arsenic exposure and altered cognitive response where enhanced neuronal pruning by arsenic-activated microglia plays an important role in developing mice.

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

In human demyelinating diseases such as multiple sclerosis (MS), an imbalance between demyelination and remyelination can trigger progressive degenerative processes. The clearance of myelin debris (phagocytosis) from the site of demyelination by microglia is critically important to achieve adequate remyelination and to slow the progression of the disease. However, how microglia phagocytose the myelin debris, and why clearance is impaired in MS, is not fully known; likewise, the role of the microglia in remyelination remains unclear. Recent studies using cuprizone (CPZ) as an animal model of central nervous system demyelination revealed that the up‐regulation of signaling proteins in microglia facilitates effective phagocytosis of myelin debris. Moreover, during demyelination, protective mediators are released from activated microglia, resulting in the acceleration of remyelination in the CPZ model. In contrast, inadequate microglial activation or recruitment to the site of demyelination, and the production of toxic mediators, impairs remyelination resulting in progressive demyelination. In addition to the microglia‐mediated phagocytosis, astrocytes play an important role in the phagocytic process by recruiting microglia to the site of demyelination and producing regenerative mediators. The current review is an update of these emerging findings from the CPZ animal model, discussing the roles of microglia and astrocytes in phagocytosis and myelination.

Current understandings and perspectives of petroleum hydrocarbons in Alzheimer's disease and Parkinson's disease: a global concern

Over the last few decades, the global prevalence of neurodevelopmental and neurodegenerative illnesses has risen rapidly. Although the aetiology remains unclear, evidence is mounting that exposure to persistent hydrocarbon pollutants is a substantial risk factor, predisposing a person to neurological diseases later in life. Epidemiological studies correlate environmental hydrocarbon exposure to brain disorders including neuropathies, cognitive, motor and sensory impairments; neurodevelopmental disorders like autism spectrum disorder (ASD); and neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). Particulate matter, benzene, toluene, ethylbenzene, xylenes, polycyclic aromatic hydrocarbons and endocrine-disrupting chemicals have all been linked to neurodevelopmental problems in all class of people. There is mounting evidence that supports the prevalence of petroleum hydrocarbon becoming neurotoxic and being involved in the pathogenesis of AD and PD. More study is needed to fully comprehend the scope of these problems in the context of unconventional oil and natural gas. This review summarises in vitro, animal and epidemiological research on the genesis of neurodegenerative disorders, highlighting evidence that supports inexorable role of hazardous hydrocarbon exposure in the pathophysiology of AD and PD. In this review, we offer a summary of the existing evidence gathered through a Medline literature search of systematic reviews and meta-analyses of the most important epidemiological studies published so far.

Molecular Mechanisms and Therapeutic Potential of α- and β-Asarone in the Treatment of Neurological Disorders

Neurological disorders are important causes of morbidity and mortality around the world. The increasing prevalence of neurological disorders, associated with an aging population, has intensified the societal burden associated with these diseases, for which no effective treatment strategies currently exist. Therefore, the identification and development of novel therapeutic approaches, able to halt or reverse neuronal loss by targeting the underlying causal factors that lead to neurodegeneration and neuronal cell death, are urgently necessary. Plants and other natural products have been explored as sources of safe, naturally occurring secondary metabolites with potential neuroprotective properties. The secondary metabolites α- and β-asarone can be found in high levels in the rhizomes of the medicinal plant Acorus calamus (L.). α- and β-asarone exhibit multiple pharmacological properties including antioxidant, anti-inflammatory, antiapoptotic, anticancer, and neuroprotective effects. This paper aims to provide an overview of the current research on the therapeutic potential of α- and β-asarone in the treatment of neurological disorders, particularly neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), as well as cerebral ischemic disease, and epilepsy. Current research indicates that α- and β-asarone exert neuroprotective effects by mitigating oxidative stress, abnormal protein accumulation, neuroinflammation, neurotrophic factor deficit, and promoting neuronal cell survival, as well as activating various neuroprotective signalling pathways. Although the beneficial effects exerted by α- and β-asarone have been demonstrated through in vitro and in vivo animal studies, additional research is required to translate laboratory results into safe and effective therapies for patients with AD, PD, and other neurological and neurodegenerative diseases.

Microglia activation in postmortem brains with schizophrenia demonstrates distinct morphological changes between brain regions

Schizophrenia (SCZ) is a psychiatric disorder that can include symptoms of disorganized speech and thoughts with uncertain underlying mechanisms possibly linked to over-activated microglia. In this study, we used brain samples from sixteen donors with SCZ and thirteen control donors to assess the differential activation of microglia by quantifying density and 3D reconstruction of microglia stained with ionized calcium-binding adaptor molecule-1 (Iba1). Our samples consisted of sections from the frontal, temporal, and cingulate cortical gray matter, subcortical white matter regions (SCWM), and included the anterior corpus callosum. In the first series of studies, we performed a density analysis followed by a spatial analysis to ascertain the microglial density, distribution, and soma size in SCZ brains. Second, we performed a series of morphological quantification techniques to investigate the arborization patterns of the microglia in SCZ. The results demonstrated an increase in microglia density in the cortical gray matter regions in SCZ cases, while in the SCWM, there was a significant increase in microglia density in the frontal and temporal, but not in the other brain regions of interest (ROIs). Spatial analysis using the "nearest neighbor" demonstrated that there was no effect in "clustering", but there were shorter distances between microglia seen in the SCZ cases. The morphological measures showed that there was a region-dependent increase in the microglia soma size in the SCZ cases while the Sholl analysis revealed a significant decrease in the microglia arborization in the SCZ cases across all the ROI's studied. An in-depth 3D reconstruction of microglia in Brodmann area 9 cortical region found that there was a significant association between age and reduced microglial arborization in the SCZ cases. This region-dependent age association can help determine whether longitudinal changes in microglial activation across age are brain region-dependent, which may point to potential therapeutic targets.

Neuronal Cell Adhesion Molecules May Mediate Neuroinflammation in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by restrictive and repetitive behaviors, alongside deficits in social interaction and communication. The etiology of ASD is largely unknown but is strongly linked to genetic variants in neuronal cell adhesion molecules (CAMs), cell-surface proteins that have important roles in neurodevelopment. A combination of environmental and genetic factors are believed to contribute to ASD pathogenesis. Inflammation in ASD has been identified as one of these factors, demonstrated through the presence of proinflammatory cytokines, maternal immune activation, and activation of glial cells in ASD brains. Glial cells are the main source of cytokines within the brain and, therefore, their activity is vital in mediating inflammation in the central nervous system. However, it is unclear whether the aforementioned neuronal CAMs are involved in modulating neuroimmune signaling or glial behavior. This review aims to address the largely unexplored role that neuronal CAMs may play in mediating inflammatory cascades that underpin neuroinflammation in ASD, primarily focusing on the Notch, nuclear factor-κB (NF-κB), and mitogen-activated protein kinase (MAPK) cascades. We will also evaluate the available evidence on how neuronal CAMs may influence glial activity associated with inflammation. This is important when considering the impact of environmental factors and inflammatory responses on ASD development. In particular, neural CAM1 (NCAM1) can regulate NF-κB transcription in neurons, directly altering proinflammatory signaling. Additionally, NCAM1 and contactin-1 appear to mediate astrocyte and oligodendrocyte precursor proliferation which can alter the neuroimmune response. Importantly, although this review highlights the limited information available, there is evidence of a neuronal CAM regulatory role in inflammatory signaling. This warrants further investigation into the role other neuronal CAM family members may have in mediating inflammatory cascades and would advance our understanding of how neuroinflammation can contribute to ASD pathology.

Prenatal Pollutant Exposures and Hypothalamic Development: Early Life Disruption of Metabolic Programming

Environmental contaminants in ambient air pollution pose a serious risk to long-term metabolic health. Strong evidence shows that prenatal exposure to pollutants can significantly increase the risk of Type II Diabetes (T2DM) in children and all ethnicities, even without the prevalence of obesity. The central nervous system (CNS) is critical in regulating whole-body metabolism. Within the CNS, the hypothalamus lies at the intersection of the neuroendocrine and autonomic systems and is primarily responsible for the regulation of energy homeostasis and satiety signals. The hypothalamus is particularly sensitive to insults during early neurodevelopmental periods and may be susceptible to alterations in the formation of neural metabolic circuitry. Although the precise molecular mechanism is not yet defined, alterations in hypothalamic developmental circuits may represent a leading cause of impaired metabolic programming. In this review, we present the current knowledge on the links between prenatal pollutant exposure and the hypothalamic programming of metabolism.

Neutrophil/lymphocyte, platelet/lymphocyte and monocyte/lymphocyte ratios in mood disorders

Major depressive disorder (MDD) and bipolar disorders (BDs), the most severe types of mood disorders (MDs), are considered as among the most disabling illnesses worldwide. Several studies suggested that inflammatory neuroinflammation might be involved in the pathophysiology of MDs, while reporting increasing data on the relationships between these processes and classical neurotransmitters, hypothalamus-pituitary-adrenal axis (HPA), and neurotrophic factors. The assessment of neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR) and monocyte/lymphocyte ratio (MLR) in peripheral blood represents a simple method to evaluate the inflammatory status. The aim of the present paper was to review the literature on the possible relationships between NLR, PLR and MLR in MDs, and to comment on their possible wider use in clinical research. Thirty-five studies were included in the present review. The majority of them higher values of these parameters, particularly NLR values, in patients with MDs, when compared to healthy subjects. The increase would appear more robust in patients with BD during a manic episode, thus indicating that it could be considered as both state and trait markers. In addition, increased NLR and PLR levels seem to represent prognostic elements for the early discovery of post-stroke depression. The findings of the present review would indicate the need to carry our further studies in this field. In particular, NLR, PLR and MLR seem to be promising tools to detect economically and easily the activation of the inflammatory system, and to perhaps evaluate the etiology and course of MDs. Again, they could suggest some information to better understand the relationship between inflammatory and cardiovascular disease and MDs, and thus, to provide clinical implications in terms of management and treatment.

Role of macrophages in fetal development and perinatal disorders

In the fetus and the neonate, altered macrophage function has been implicated not only in inflammatory disorders but also in developmental abnormalities marked by altered onset, interruption, or imbalance of key structural changes. The developmental role of macrophages were first noted nearly a century ago, at about the same time when these cells were being identified as central effectors in phagocytosis and elimination of microbes. Since that time, we have made considerable progress in understanding the diverse roles that these cells play in both physiology and disease. Here, we review the role of fetal and neonatal macrophages in immune surveillance, innate immunity, homeostasis, tissue remodeling, angiogenesis, and repair of damaged tissues. We also discuss the possibility of therapeutic manipulation of the relative abundance and activation status of macrophage subsets in various diseases. This article combines peer-reviewed evidence from our own studies with results of an extensive literature search in the databases PubMed, EMBASE, and Scopus. IMPACT: We have reviewed the structure, differentiation, and classification of macrophages in the neonatal period. Neonatal macrophages are derived from embryonic, hepatic, and bone marrow precursors. Macrophages play major roles in tissue homeostasis, innate immunity, inflammation, tissue repair, angiogenesis, and apoptosis of various cellular lineages in various infectious and inflammatory disorders. Macrophages and related inflammatory mediators could be important therapeutic targets in several neonatal diseases.

Lower pro- to anti-inflammatory ratios associated with reduced neurocognitive flexibility in symptomatic adolescents with bipolar disorder

INTRODUCTION

Peripheral inflammatory markers, such as C-reactive protein (CRP), are elevated among adolescents and adults with bipolar disorder (BD), particularly during symptomatic episodes. Neurocognition, predominantly in the domain of executive function, is also impaired among adults and youth with BD. In adults with BD, CRP is negatively associated with neurocognitive functioning. We aim to investigate this relationship in BD adolescents.

METHODS

Serum levels of CRP and five other inflammatory markers (interleukin (IL)-1β, IL-6, IL-10, IL-4 and tumor necrosis factor α (TNF)) were examined in 60 adolescents with BD (34 symptomatic, 26 asymptomatic) age- and sex-matched to 51 healthy controls (HC). Diagnoses were confirmed using semi-structured interviews. Pro- to anti-inflammatory marker ratios were also examined. Neurocognitive flexibility was assessed via the intra/extradimensional shift (IED) task from the CANTAB battery. Multivariate linear regression controlled for age, sex and race.

RESULTS

Within symptomatic BD adolescents, but not asymptomatic BD or HC adolescents, lower IL-6/IL-10 and lower CRP/IL-10 ratios were significantly associated with worse performance on the neurocognitive flexibility task (p = 0.03 and p = 0.04, respectively). Both models accounted for 13.3% of variance in neurocognitive flexibility. No significant CRP by diagnosis interaction effects were observed on neurocognitive flexibility.

LIMITATIONS

Limited sample-size restricted ability to separate the symptomatic BD adolescents into varying mood states.

CONCLUSION

More balanced pro- to anti-inflammatory ratios were associated with better neurocognitive flexibility in symptomatic BD adolescents. Prospective studies are warranted to assess the direction of these findings.

MAO-A Inhibition by Metaxalone Reverts IL-1β-Induced Inflammatory Phenotype in Microglial Cells

Experimental and clinical studies have suggested that several neurological disorders are associated with the occurrence of central nervous system neuroinflammation. Metaxalone is an FDA-approved muscle relaxant that has been reported to inhibit monoamine oxidase A (MAO-A). The aim of this study was to investigate whether metaxalone might exert antioxidant and anti-inflammatory effects in HMC3 microglial cells. An inflammatory phenotype was induced in HMC3 microglial cells through stimulation with interleukin-1β (IL-1β). Control cells and IL-1β-stimulated cells were subsequently treated with metaxalone (10, 20, and 40 µM) for six hours. IL-1β stimulated the release of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), but reduced the anti-inflammatory cytokine interleukin-13 (IL-13). The upstream signal consisted of an increased priming of nuclear factor-kB (NF-kB), blunted peroxisome proliferator-activated receptor gamma (PPARγ), and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression. IL-1β also augmented MAO-A expression/activity and malondialdehyde levels and decreased Nrf2 mRNA expression and protein levels. Metaxalone decreased MAO-A activity and expression, reduced NF-kB, TNF-α, and IL-6, enhanced IL-13, and also increased PPARγ, PGC-1α, and Nrf2 expression. The present experimental study suggests that metaxalone has potential for the treatment of several neurological disorders associated with neuroinflammation.

Chronic intermittent ethanol and lipopolysaccharide exposure differentially alter Iba1-derived microglia morphology in the prelimbic cortex and nucleus accumbens core of male Long-Evans rats

Accumulating evidence has linked pathological changes associated with chronic alcohol exposure to neuroimmune signaling mediated by microglia. Prior characterization of the microglial structure-function relationship demonstrates that alterations in activity states occur concomitantly with reorganization of cellular architecture. Accordingly, gaining a better understanding of microglial morphological changes associated with ethanol exposure will provide valuable insight into how neuroimmune signaling may contribute to ethanol-induced reshaping of neuronal function. Here we have used Iba1-staining combined with high-resolution confocal imaging and 3D reconstruction to examine microglial structure in the prelimbic (PL) cortex and nucleus accumbens (NAc) in male Long-Evans rats. Rats were either sacrificed at peak withdrawal following 15 days of exposure to chronic intermittent ethanol (CIE) or 24 hr after two consecutive injections of the immune activator lipopolysaccharide (LPS), each separated by 24 hr. LPS exposure resulted in dramatic structural reorganization of microglia in the PL cortex, including increased soma volume, overall cellular volume, and branching complexity. In comparison, CIE exposure was associated with a subtle increase in somatic volume and differential effects on microglia processes, which were largely absent in the NAc. These data reveal that microglial activation following a neuroimmune challenge with LPS or exposure to chronic alcohol exhibits distinct morphometric profiles and brain region-dependent specificity.

Microglia Diversity in Healthy and Diseased Brain: Insights from Single-Cell Omics

Microglia are the resident immune cells of the central nervous system (CNS) that have distinct ontogeny from other tissue macrophages and play a pivotal role in health and disease. Microglia rapidly react to the changes in their microenvironment. This plasticity is attributed to the ability of microglia to adapt a context-specific phenotype. Numerous gene expression profiling studies of immunosorted CNS immune cells did not permit a clear dissection of their phenotypes, particularly in diseases when peripheral cells of the immune system come to play. Only recent advances in single-cell technologies allowed studying microglia at high resolution and revealed a spectrum of discrete states both under homeostatic and pathological conditions. Single-cell technologies such as single-cell RNA sequencing (scRNA-seq) and mass cytometry (Cytometry by Time-Of-Flight, CyTOF) enabled determining entire transcriptomes or the simultaneous quantification of >30 cellular parameters of thousands of individual cells. Single-cell omics studies demonstrated the unforeseen heterogeneity of microglia and immune infiltrates in brain pathologies: neurodegenerative disorders, stroke, depression, and brain tumors. We summarize the findings from those studies and the current state of knowledge of functional diversity of microglia under physiological and pathological conditions. A precise definition of microglia functions and phenotypes may be essential to design future immune-modulating therapies.

Effect of exercise on microglial activation and transcriptome of hippocampus in fluorosis mice

Fluorosis is a widespread endemic disease. Reports have shown that high fluoride causes the dysfunction of central nervous system (CNS) in animals. The neurotoxicity of fluoride may be related to the activation of microglia. Moreover, numerous studies have found that exercise facilitates the plasticity of structure and function in CNS, partly owing to the regulation of microglia activation. The present study was conducted to explore the effect of exercise on the microglial activation of hippocampus in fluorosis mice. One hundred adult female Institute of Cancer Research (ICR) mice were randomly divided into 4 groups: control group (group C, distilled water by gavage); exercise group (group E, distilled water by gavage and treadmill exercise); fluoride group [group F, 24 mg/kg sodium fluoride (NaF) by gavage]; fluoride plus exercise group (group F + E, 24 mg/kg NaF by gavage and treadmill exercise). After 8 weeks, hippocampal morphological structure, microglial activation and RNA transcriptome of mice in each group were evaluated by hematoxylin and eosin (HE) staining, Nissl staining, immunohistochemistry (IHC), quantitative real time PCR (QRT-PCR) and transcriptome sequencing. We discovered that the number of M1-type microglia in fluorosis-mice hippocampus was significantly increased when compared to group C; group F + E showed a decrease in the number of M1-type microglia with the comparison to group F. In addition, the hippocampal transcriptome analysis showed that 576 differential expression genes (DEG) were confirmed in group F, compared to group C, and 670 DEG were differently expressed in group F + E when compared to group F. Gene Ontology (GO) analysis showed that changed genes were implicated in regulation of transcription, DNA-templated, integral component of membrane and adenosine triphosphate (ATP) binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of 670 DEG was helpful to find neuroactive ligand-receptor interaction pathway. In conclusion, these results indicate that treadmill running inhibits the excessive activation of microglia in hippocampus of the fluoride-toxic mice, accompanied with the alteration of neuroactive ligand-receptor interaction pathway.

Early life exposure to air pollution impacts neuronal and glial cell function leading to impaired neurodevelopment

The World Health Organisation recently listed air pollution as the most significant threat to human health. Air pollution comprises particulate matter (PM), metals, black carbon and gases such as ozone (O₃ ), nitrogen dioxide (NO₂ ) and carbon monoxide (CO). In addition to respiratory and cardiovascular disease, PM exposure is linked with increased risk of neurodegeneration as well as neurodevelopmental impairments. Critically, studies suggest that PM crosses the placenta, making direct in utero exposure a reality. Rodent models reveal that neuroinflammation, neurotransmitter imbalance and oxidative stress are triggered following gestational/early life exposure to PM, and may be exacerbated by concomitant mitochondrial dysfunction. Gestational PM exposure (potentiated by mitochondrial impairment in the metabolically active neonatal brain) not only impacts neurodevelopment but may sensitise the brain to subsequent cognitive impairment. Having reviewed this field, we conclude that strategies are urgently required to reduce exposure to PM during this sensitive developmental period.

Outdoor Air Pollution and Depression in Canada: A Population-Based Cross-Sectional Study from 2011 to 2016

To assess whether exposure to increased levels of outdoor air pollution is associated with psychological depression, six annual iterations of the Canadian Community Health Survey (n ≈ 127,050) were used to estimate the prevalence of a major depressive episode (2011-2014) or severity of depressive symptoms (2015-2016). Survey data were linked with outdoor air pollution data obtained from the Canadian Urban Environmental Health Research Consortium, with outdoor air pollution represented by fine particulate matter ≤2.5 micrometers (μm) in diameter (PM_2.5), ozone (O₃), sulfur dioxide (SO₂), and nitrogen dioxide (NO₂). Log-binomial models were used to estimate the association between outdoor air pollution and depression, and included adjustment for age, sex, marital status, income, education, employment status, urban versus rural households, cigarette smoking, and chronic illness. No evidence of associations for either depression outcomes were found. Given the generally low levels of outdoor air pollution in Canada, these findings should be generalized with caution. It is possible that a meaningful association with major depression may be observed in regions of the world where the levels of outdoor air pollution are greater, or during high pollution events over brief time intervals. Future research is needed to replicate these findings and to further investigate these associations in other regions and populations.

Cellular Mechanisms Participating in Brain Repair of Adult Zebrafish and Mammals after Injury

Adult neurogenesis is an evolutionary conserved process occurring in all vertebrates. However, striking differences are observed between the taxa, considering the number of neurogenic niches, the neural stem cell (NSC) identity, and brain plasticity under constitutive and injury-induced conditions. Zebrafish has become a popular model for the investigation of the molecular and cellular mechanisms involved in adult neurogenesis. Compared to mammals, the adult zebrafish displays a high number of neurogenic niches distributed throughout the brain. Furthermore, it exhibits a strong regenerative capacity without scar formation or any obvious disabilities. In this review, we will first discuss the similarities and differences regarding (i) the distribution of neurogenic niches in the brain of adult zebrafish and mammals (mainly mouse) and (ii) the nature of the neural stem cells within the main telencephalic niches. In the second part, we will describe the cascade of cellular events occurring after telencephalic injury in zebrafish and mouse. Our study clearly shows that most early events happening right after the brain injury are shared between zebrafish and mouse including cell death, microglia, and oligodendrocyte recruitment, as well as injury-induced neurogenesis. In mammals, one of the consequences following an injury is the formation of a glial scar that is persistent. This is not the case in zebrafish, which may be one of the main reasons that zebrafish display a higher regenerative capacity.

Light at night during development in mice has modest effects on adulthood behavior and neuroimmune activation

Exposure to light at night (LAN) can disrupt the circadian system, thereby altering neuroimmune reactivity and related behavior. Increased exposure to LAN affects people of all ages - and could have particularly detrimental effects during early-life and adolescence. Despite this, most research on the behavioral and physiological effects of LAN has been conducted in adult animals. Here we evaluated the effects of dim LAN during critical developmental windows on adulthood neuroimmune function and affective/sickness behaviors. Male and female C57BL/6 J mice were exposed to dim LAN [12:12 light (150 lx)/dim (15 lx) cycle] during early life (PND10-24) or adolescence (PND30-44) [control: 12:12 light (150 lx)/dark (0 lx) cycle]. Behaviors were assessed during juvenile (PND 42-44) and adult (PND60) periods. Contrary to our hypothesis, juvenile mice that were exposed to dim LAN did not exhibit changes in anxiety- or depressive-like behaviors. By adulthood, adolescent LAN-exposed female mice showed a modest anxiety-like phenotype in one behavioral task but not another. Adolescent LAN exposure also induced depressive-like behavior in a forced swim task in adulthood in both male and female mice. Additionally, developmental LAN exacerbated the hippocampal cytokine response (IL-1β) following peripheral LPS in female, but not male mice. These results suggest female mice may be more susceptible to developmental LAN than male mice: LAN female mice had a modest anxiety-like phenotype in adulthood, and upon LPS challenge, higher hippocampal IL-1β expression. Taken together, developmental LAN exposure in mice promotes a modest increase in susceptibility to anxiety- and depressive-like symptoms.

How stress physically re-shapes the brain: Impact on brain cell shapes, numbers and connections in psychiatric disorders

Severe stress is among the most robust risk factors for the development of psychiatric disorders. Imaging studies indicate that life stress is integral to shaping the human brain, especially regions involved in processing the stress response. Although this is likely underpinned by changes to the cytoarchitecture of cellular networks in the brain, we are yet to clearly understand how these define a role for stress in human psychopathology. In this review, we consolidate evidence of macro-structural morphometric changes and the cellular mechanisms that likely underlie them. Focusing on stress-sensitive regions of the brain, we illustrate how stress throughout life may lead to persistent remodelling of the both neurons and glia in cellular networks and how these may lead to psychopathology. We support that greater translation of cellular alterations to human cohorts will support parsing the psychological sequalae of severe stress and improve our understanding of how stress shapes the human brain. This will remain a critical step for improving treatment interventions and prevention outcomes.

Cytoplasmic-predominant Pten increases microglial activation and synaptic pruning in a murine model with autism-like phenotype

Germline mutations in PTEN account for ~10% of cases of autism spectrum disorder (ASD) with coincident macrocephaly. To explore the importance of nuclear PTEN in the development of ASD and macrocephaly, we previously generated a mouse model with predominantly cytoplasmic localization of Pten (Pten^m3m4/m3m4).Cytoplasmic predominant Pten localization results in a phenotype of extreme macrocephaly and autistic-like traits. Transcriptomic analysis of the Pten^m3m4/m3m4 cortex found upregulated gene pathways related to myeloid cell activation, myeloid cell migration, and phagocytosis. These transcriptomic findings were used to direct in vitro assays on Pten wild-type and Pten^m3m4/m3m4 microglia. We found increased Iba1 and C1q expression with enhanced phagocytic capacity in Pten^m3m4/m3m4 microglia, indicating microglial activation. Moreover, through a series of neuron-microglia co-culture experiments, we found Pten^m3m4/m3m4 microglia are more efficient at synaptic pruning compared with wild-type controls. In addition, we found evidence for neuron-microglia cross-talk, where Pten^m3m4/m3m4 neurons elicit enhanced pruning from innately activated microglia. Subsequent in vivo studies validated our in vitro findings. We observed a concurrent decline in the expression of Pten and synaptic markers in the Pten^m3m4/m3m4 cortex. At ~3 weeks of age, with a 50% drop in Pten expression compared with wild-type levels, we observed enhanced activation of microglia in the Pten^m3m4/m3m4 brain. Collectively, our data provide evidence that dysregulated Pten in microglia has an etiological role in microglial activation, phagocytosis, and synaptic pruning, creating avenues for future studies on the importance of PTEN in maintaining microglia homeostasis.

Minocycline alleviates depression-like symptoms by rescuing decrease in neurogenesis in dorsal hippocampus via blocking microglia activation/phagocytosis

Clinical studies examining the potential of anti-inflammatory agents, specifically of minocycline, as a treatment for depression has shown promising results. However, mechanistic insights into the neuroprotective and anti-inflammatory actions of minocycline need to be provided. We evaluated the effect of minocycline on chronic mild stress (CMS) induced depressive-like behavior, and behavioral assays revealed minocycline ameliorate depressive behaviors. Multiple studies suggest a role of microglia in depression, revealing that microglia activation correlates with a decrease in neurogenesis and increased depressive-like behavior. The effect of minocycline on microglia activation in different areas of the dorsal or ventral hippocampus in stressed mice was examined by immunohistochemistry. We observed the increase in the number of activated microglia expressing CD68 after exposure to three weeks of chronic stress, whereas no changes in total microglia number were observed. These changes were observed throughout the DG, CA1 and CA2 regions in dorsal hippocampus but restricted to the DG of the ventral hippocampus. In vitro experiments including western blotting and phagocytosis assay were used to investigate the effect of minocycline on microglia activation. Activation of primary microglia by LPS in vitro causes and ERK1/2 activation, enhancement of iNOS expression and phagocytic activity, and alterations in cellular morphology that are reversed by minocycline exposure, suggesting that minocycline directly acts on microglia to reduce phagocytic potential. Our results suggest the most probable mechanism by which minocycline reverses the pathogenic phagocytic potential of neurotoxic M1 microglia, and reduces the negative phenotypes associated with reduced neurogenesis caused by exposure to chronic stress.

The role of CCR5 in the protective effect of Esculin on lipopolysaccharide-induced depressive symptom in mice

BACKGROUND

The purpose of this study was to evaluate whether Esculin could improve the depressive symptom induced by LPS in mice and explore the role of CCR5 in its potential mechanism.

METHODS

Mice were stimulated with LPS to establish depression model and treated with Esculin. The emotional alteration was assessed via behavior tests. The ELISA assay and western blot analysis were applied to detect the expressions of inflammatory cytokines and correlative proteins.

RESULTS

As a result, Esculin played a protective role in LPS-induced depressive dysfunction, which was possible through the reduction of M1 microglia, and elevation of M2 microglia by inhibiting TLR4/NF-κB signaling pathway regulated by CCR5. Besides, Esculin led to up-regulation of the CREB/BDNF neuroprotective pathway, and suppression of inflammatory cytokines both in the central and peripheral system. BV2 cells were stimulated with LPS to further elucidate the accordant mechanism in vitro. Molecular docking results suggested that Esc bound to CCR5 at amino acid residues TYR187 and THR105 through hydrogen-bonding.

LIMITATIONS

Transgenic animals might be useful for the further investigation.

CONCLUSIONS

From the overall results, we concluded that Esculin might exert a beneficial effect on LPS-induced depression in mice and represent an effective treatment for depression.

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.

Neuroinflammation Mechanisms and Phytotherapeutic Intervention: A Systematic Review

Neuroinflammation is indicated in the pathogenesis of several acute and chronic neurological disorders. Acute lesions in the brain parenchyma induce intense and highly complex neuroinflammatory reactions with similar mechanisms among various disease prototypes. Microglial cells in the CNS sense tissue damage and initiate inflammatory responses. The cellular and humoral constituents of the neuroinflammatory reaction to brain injury contribute significantly to secondary brain damage and neurodegeneration. Inflammatory cascades such as proinflammatory cytokines from invading leukocytes and direct cell-mediated cytotoxicity between lymphocytes and neurons are known to cause "collateral damage" in models of acute brain injury. In addition to degeneration and neuronal cell loss, there are secondary inflammatory mechanisms that modulate neuronal activity and affect neuroinflammation which can even be detected at the behavioral level. Hence, several of health conditions result from these pathogenetic conditions which are underlined by progressive neuronal function loss due to chronic inflammation and oxidative stress. In the first part of this Review, we discuss critical neuroinflammatory mediators and their pathways in detail. In the second part, we review the phytochemicals which are considered as potential therapeutic molecules for treating neurodegenerative diseases with an inflammatory component.

Distribution of microglial phenotypes as a function of age and Alzheimer's disease neuropathology in the brains of people with Down syndrome

INTRODUCTION

Microglial cells play an important role in the development of Alzheimer's disease (AD). People with Down syndrome (DS) inevitably develop AD neuropathology (DSAD) by 40 years of age. We characterized the distribution of different microglial phenotypes in the brains of people with DS and DSAD.

METHODS

Autopsy tissue from the posterior cingulate cortex (PCC) from people with DS, DSAD, and neurotypical controls was immunostained with the microglial marker Iba1 to assess five microglia morphological types.

RESULTS

Individuals with DS have more hypertrophic microglial cells in their white matter. In the gray matter, individuals with DSAD had significantly fewer ramified microglia and more dystrophic microglia than controls and the younger individuals with DS. The DSAD group also exhibited more rod-shaped and amoeboid cells than the AD group.

DISCUSSION

Individuals with DS and DSAD show a microglial phenotype that distinguishes them from non-DS controls.

Mitochondrial-related effects of pentabromophenol, tetrabromobisphenol A, and triphenyl phosphate on murine BV-2 microglia cells

The predominant reliance on bromated flame retardants (BFRs) is diminishing with expanded use of alternative organophosphate flame retardants. However, exposure related issues for susceptible populations, the developing, infirmed, or aged, remain given environmental persistence and home-environment detection. In this regard, reports of flame retardant (FR)-related effects on the innate immune system suggest process by which a spectrum of adverse health effects could manifest across the life-span. As representative of the nervous system innate immune system, the current study examined changes in microglia following exposure to representative FRs, pentabromophenol (PBP), tetrabromobisphenol A (2,2',6,6',-tetrabromo-4,4'-isopropylidine diphenol; TBBPA) and triphenyl phosphate (TPP). Following 18hr exposure of murine BV-2 cells, at dose levels resulting in ≥80% viability (10 and 40 μM), limited alterations in pro-inflammatory responses were observed however, changes were observed in mitochondrial respiration. Basal respiration was altered by PBP; ATP-linked respiration by PBP and TBBPA, and maximum respiration by all three FRs. Basal glycolytic rate was altered by PBP and TBBPA and compensatory glycolysis by all three. Phagocytosis was decreased for PBP and TBBPA. NLRP3 inflammasome activation was assessed using BV-2-ASC (apoptosis-associated speck-like protein containing a CARD) reporter cells to visualize aggregate formation. PBP, showed a direct stimulation of aggregate formation and properties as a NLRP3 inflammasome secondary trigger. TBBPA showed indications of possible secondary triggering activity while no changes were seen with TPP. Thus, the data suggests an effect of all three FRs on mitochondria metabolism yet, different functional outcomes including, phagocytic capability and NLRP3 inflammasome activation.

Neuroprotection of hypoxic/ischemic preconditioning in neonatal brain with hypoxic-ischemic injury

The neonatal brain is susceptible to hypoxic-ischemic injury due to its developmental characteristics. Hypoxia-ischemia means a decreased perfusion of oxygen and glucose, which can lead to severe encephalopathy. Although early initiation of therapeutic hypothermia was reported to provide neuroprotection for infants after HI, hypothermia administered alone after the acute insult cannot reverse the severe damage that already has occurred or improve the prognosis of severe hypoxic-ischemic encephalopathy. Therefore, exploring new protective mechanisms for treating hypoxic-ischemic brain damage are imperative. Until now, many studies reported the neuroprotective mechanisms of hypoxic/ischemic preconditioning in protecting the hypoxic-ischemic newborn brains. After hypoxia and ischemia, hypoxia-inducible factor signaling pathway is involved in the transcriptional regulation of many genes and is also play a number of different roles in protecting brains during hypoxic/ischemic preconditioning. Hypoxic/ischemic preconditioning could protect neonatal brain by several mechanisms, including vascular regulation, anti-apoptosis, anti-oxidation, suppression of excitotoxicity, immune regulation, hormone levels regulation, and promote cell proliferation. This review focused on the protective mechanisms underlying hypoxic/ischemic preconditioning for neonatal brain after hypoxia-ischemia and emphasized on the important roles of hypoxia inducible factor 1 signaling pathway.

The prenatal challenge with lipopolysaccharide and polyinosinic:polycytidylic acid disrupts CX3CL1-CX3CR1 and CD200-CD200R signalling in the brains of male rat offspring: a link to schizophrenia-like behaviours

BACKGROUND

The bidirectional communication between neurons and microglia is fundamental for the homeostasis and biological function of the central nervous system. Maternal immune activation (MIA) is considered to be one of the factors affecting these interactions. Accordingly, MIA has been suggested to be involved in several neuropsychiatric diseases, including schizophrenia. The crucial regulatory systems for neuron-microglia crosstalk are the CX3CL1-CX3CR1 and CD200-CD200R axes.

METHODS

We aimed to clarify the impact of MIA on CX3CL1-CX3CR1 and CD200-CD200R signalling pathways in the brains of male Wistar rats in early and adult life by employing two neurodevelopmental models of schizophrenia based on the prenatal challenge with lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (Poly I:C). We also examined the effect of MIA on the expression of microglial markers and the profile of cytokines released in the brains of young offspring, as well as the behaviour of adult animals. Moreover, we visualized the localization of ligand-receptor systems in the hippocampal regions (CA1, CA3 and DG) and the frontal cortex of young rats exposed to MIA. The differences between groups were analysed using Student's t test.

RESULTS

We observed that MIA altered developmental trajectories in neuron-microglia communication in the brains of young offspring, as evidenced by the disruption of CX3CL1-CX3CR1 and/or CD200-CD200R axes. Our data demonstrated the presence of abnormalities after LPS-induced MIA in levels of Cd40, Il-1β, Tnf-α, Arg1, Tgf-β and Il-10, as well as IBA1, IL-1β and IL-4, while after Poly I:C-generated MIA in levels of Cd40, iNos, Il-6, Tgf-β, Il-10, and IBA1, IL-1β, TNF-α, IL-6, TGF-β and IL-4 early in the life of male animals. In adult male rats that experienced prenatal exposure to MIA, we observed behavioural changes resembling a schizophrenia-like phenotype.

CONCLUSIONS

Our study provides evidence that altered CX3CL1-CX3CR1 and/or CD200-CD200R pathways, emerging after prenatal immune challenge with LPS and Poly I:C, might be involved in the aetiology of schizophrenia.

Role of Macrophages and Microglia in Zebrafish Regeneration

Currently, there is no treatment for recovery of human nerve function after damage to the central nervous system (CNS), and there are limited regenerative capabilities in the peripheral nervous system. Since fish are known for their regenerative abilities, understanding how these species modulate inflammatory processes following injury has potential translational importance for recovery from damage and disease. Many diseases and injuries involve the activation of innate immune cells to clear damaged cells. The resident immune cells of the CNS are microglia, the primary cells that respond to infection and injury, and their peripheral counterparts, macrophages. These cells serve as key modulators of development and plasticity and have been shown to be important in the repair and regeneration of structure and function after injury. Zebrafish are an emerging model for studying macrophages in regeneration after injury and microglia in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. These fish possess a high degree of neuroanatomical, neurochemical, and emotional/social behavioral resemblance with humans, serving as an ideal simulator for many pathologies. This review explores literature on macrophage and microglial involvement in facilitating regeneration. Understanding innate immune cell behavior following damage may help to develop novel methods for treating toxic and chronic inflammatory processes that are seen in trauma and disease.