Vaccination reduces central nervous system IL-1ß and memory deficits after COVID-19 in mice.

Up to 25% of individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exhibit postacute cognitive sequelae. Although millions of cases of coronavirus disease 2019 (COVID-19)-mediated memory dysfunction are accumulating worldwide, the underlying mechanisms and how vaccination lowers risk are unknown. Interleukin-1 (IL-1), a key component of innate immune defense against SARS-CoV-2 infection, is elevated in the hippocampi of individuals with COVID-19. Here we show that intranasal infection of C57BL/6J mice with SARS-CoV-2 Beta variant leads to central nervous system infiltration of Ly6Chi monocytes and microglial activation. Accordingly, SARS-CoV-2, but not H1N1 influenza virus, increases levels of brain IL-1ß and induces persistent IL-1R1-mediated loss of hippocampal neurogenesis, which promotes postacute cognitive deficits. Vaccination with a low dose of adenoviral-vectored spike protein prevents hippocampal production of IL-1ß during breakthrough SARS-CoV-2 infection, loss of neurogenesis and subsequent memory deficits. Our study identifies IL-1ß as one potential mechanism driving SARS-CoV-2-induced cognitive impairment in a new mouse model that is prevented by vaccination.

Microglia and Macrophages in Neuroprotection, Neurogenesis, and Emerging Therapies for Stroke.

Stroke remains the number one cause of morbidity in the United States. Within weeks to months after an ischemic event, there is a resolution of inflammation and evidence of neurogenesis; however, years following a stroke, there is evidence of chronic inflammation in the central nervous system, possibly by the persistence of an autoimmune response to brain antigens as a result of ischemia. The mechanisms underlying the involvement of macrophage and microglial activation after stroke are widely acknowledged as having a role in ischemic stroke pathology; thus, modulating inflammation and neurological recovery is a hopeful strategy for treating the long-term outcomes after ischemic injury. Current treatments fail to provide neuroprotective or neurorestorative benefits after stroke; therefore, to ameliorate brain injury-induced deficits, therapies must alter both the initial response to injury and the subsequent inflammatory process. This review will address differences in macrophage and microglia nomenclature and summarize recent work in elucidating the mechanisms of macrophage and microglial participation in antigen presentation, neuroprotection, angiogenesis, neurogenesis, synaptic remodeling, and immune modulating strategies for treating the long-term outcomes after ischemic injury.

In situ and transcriptomic identification of microglia in synapse-rich regions of the developing zebrafish brain.

Microglia are brain resident macrophages that play vital roles in central nervous system (CNS) development, homeostasis, and pathology. Microglia both remodel synapses and engulf apoptotic cell corpses during development, but whether unique molecular programs regulate these distinct phagocytic functions is unknown. Here we identify a molecularly distinct microglial subset in the synapse rich regions of the zebrafish (Danio rerio) brain. We found that ramified microglia increased in synaptic regions of the midbrain and hindbrain between 7 and 28 days post fertilization. In contrast, microglia in the optic tectum were ameboid and clustered around neurogenic zones. Using single-cell mRNA sequencing combined with metadata from regional bulk sequencing, we identified synaptic-region associated microglia (SAMs) that were highly enriched in the hindbrain and expressed multiple candidate synapse modulating genes, including genes in the complement pathway. In contrast, neurogenic associated microglia (NAMs) were enriched in the optic tectum, had active cathepsin activity, and preferentially engulfed neuronal corpses. These data reveal that molecularly distinct phagocytic programs mediate synaptic remodeling and cell engulfment, and establish the zebrafish hindbrain as a model for investigating microglial-synapse interactions.

Overexpression of EphB4 promotes neurogenesis, but inhibits neuroinflammation in mice with acute ischemic stroke.

Ischemic stroke is one of the most common diseases that has a high rate of mortality, and has become a burden to the healthcare system. Previous research has shown that EPH receptor B4 (EphB4) promotes neural stem cell proliferation and differentiation in vitro. However, little is known regarding its role in the neurogenesis of ischemic stroke in vivo. Thus, the present study aimed to verify whether EphB4 was a key regulator of neurogenesis in ischemic stroke in vivo. Cerebral ischemia was induced in C57BL/6J mice via middle cerebral artery occlusion (MCAO), followed by reperfusion. Immunofluorescence staining was performed to evaluate the effect of EphB4 on the neurogenesis in cerebral cortex. The levels of inflammatory cytokines were determined using an ELISA kit. The expression levels of ABL proto­oncogene 1, non­receptor tyrosine kinase (ABL1)/Cyclin D1 signaling pathway­related proteins were detected via western blotting. The current findings indicated that EphB4 expression was significantly increased in the cerebral cortex of MCAO model mice in comparison with sham­operated mice. Moreover, EphB4 appeared to be expressed in neural stem cells (Nestin+), and persisted as these cells became neuronal progenitors (Sox2+), neuroblasts [doublecortin (DCX)+], and eventually mature neurons [neuronal nuclei (NeuN)+]. Overexpression of EphB4 elevated the number of proliferating (bromodeoxyuridine+, Ki67+) and differentiated cells (Nestin+, Sox2+, DCX+ and NeuN+), indicating the promoting effect of EphB4 on the neurogenesis of ischemic stroke. Furthermore, EphB4 overexpression alleviated the inflammation injury in MCAO model mice. The expression levels of proteins­related to the ABL1/Cyclin D1 signaling pathway were significantly increased by the overexpression of EphB4, which suggested that restoration of EphB4 promoted the activation of the ABL1/Cyclin D1 signaling pathway. In conclusion, this study contributes to the current understanding of the mechanisms of EphB4 in exerting neurorestorative effects and may recommend a potential new strategy for ischemic stroke treatment.

Galantamine prevents and reverses neuroimmune induction and loss of adult hippocampal neurogenesis following adolescent alcohol exposure.

BACKGROUND: Binge ethanol exposure during adolescence reduces hippocampal neurogenesis, a reduction which persists throughout adulthood despite abstinence. This loss of neurogenesis, indicated by reduced doublecortin+ immunoreactivity (DCX+IR), is paralleled by an increase in hippocampal proinflammatory signaling cascades. As galantamine, a cholinesterase inhibitor, has anti-inflammatory actions, we tested the hypothesis that galantamine would prevent (study 1) or restore (study 2) AIE induction of proinflammatory signals within the hippocampus as well as AIE-induced loss of hippocampal neurogenesis. METHODS: Galantamine (4 mg/kg) or vehicle (saline) was administered to Wistar rats during adolescent intermittent ethanol (AIE; 5.0 g/kg ethanol, 2 days on/2 days off, postnatal day [P] 25-54) (study 1, prevention) or after AIE during abstinent maturation to adulthood (study 2, restoration). RESULTS: Results indicate AIE reduced DCX+IR and induced cleaved caspase3 (Casp3) in DCX-expressing immature neurons. Excitingly, AIE induction of activated Casp3 in DCX-expressing neurons is both prevented and reversed by galantamine treatment, which also resulted in prevention and restoration of neurogenesis (DCX+IR). Similarly, galantamine prevented and/or reversed AIE induction of proinflammatory markers, including the chemokine (C-C motif) ligand 2 (CCL2), cyclooxygenase-2 (COX-2), and high mobility group box 1 (HMGB1) protein, suggesting that AIE induction of proinflammatory signaling mediates both cell death cascades and hippocampal neurogenesis. Interestingly, galantamine treatment increased Ki67+IR generally as well as increased pan-Trk expression specifically in AIE-treated rats but failed to reverse AIE induction of NADPH-oxidase (gp91phox). CONCLUSIONS: Collectively, our studies suggest that (1) loss of neurogenesis after AIE is mediated by persistent induction of proinflammatory cascades which drive activation of cell death machinery in immature neurons, and (2) galantamine can prevent and restore AIE disruptions in the hippocampal environmental milieu to then prevent and restore AIE-mediated loss of neurogenesis.

Microglia, Cytokines, and Neural Activity: Unexpected Interactions in Brain Development and Function.

Intercellular signaling molecules such as cytokines and their receptors enable immune cells to communicate with one another and their surrounding microenvironments. Emerging evidence suggests that the same signaling pathways that regulate inflammatory responses to injury and disease outside of the brain also play powerful roles in brain development, plasticity, and function. These observations raise the question of how the same signaling molecules can play such distinct roles in peripheral tissues compared to the central nervous system, a system previously thought to be largely protected from inflammatory signaling. Here, we review evidence that the specialized roles of immune signaling molecules such as cytokines in the brain are to a large extent shaped by neural activity, a key feature of the brain that reflects active communication between neurons at synapses. We discuss the known mechanisms through which microglia, the resident immune cells of the brain, respond to increases and decreases in activity by engaging classical inflammatory signaling cascades to assemble, remodel, and eliminate synapses across the lifespan. We integrate evidence from (1) in vivo imaging studies of microglia-neuron interactions, (2) developmental studies across multiple neural circuits, and (3) molecular studies of activity-dependent gene expression in microglia and neurons to highlight the specific roles of activity in defining immune pathway function in the brain. Given that the repurposing of signaling pathways across different tissues may be an important evolutionary strategy to overcome the limited size of the genome, understanding how cytokine function is established and maintained in the brain could lead to key insights into neurological health and disease.

Neurogenic hypothesis of positive psychology in stress-induced depression: Adult hippocampal neurogenesis, neuroinflammation, and stress resilience.

Stress is an important risk factor for depression. Emerging evidence supports the hypothesis that stress-mediated neuroinflammation destroys brain function and leads to anxiety-like and depression-like behaviors. Previous studies of stress-induced depression have mainly focused on pathological damage; however, the rise of positive psychology has attracted the interest of many researchers in environmental enrichment to promote stress resilience. The hippocampus is one of the most severely damaged brain regions in stress-induced depression. In addition, the hippocampus is one of the most unique regions in the brain, as new neurons are produced in the adult hippocampus, a process known as adult hippocampal neurogenesis (AHN). AHN is an important core component of the neurogenic hypothesis and has also become a major innovative breakthrough in positive psychology, in which environmental enrichment mediates stress resilience. Neuroinflammation, by activating microglia and releasing some proinflammatory cytokines, is increasingly shown to be one of the key determinant pathophysiological factors that negatively affects AHNand cognitive reserve. AHN is mainly related to remodeling stress response mechanisms, such as memory clearing, emotional control, and pattern separation, suggesting that a correlation may exist between neuroinflammation and AHN in stress resilience. Therefore, we summarized the previous research results to systematically expound on the relationship between AHN, stress resilience, and neuroinflammation. We hope this neurogenic hypothesis of positive psychology in stress-induced depression will provide a new perspective for the study of depression and antidepressant therapy.

Inhibition of innate immune response ameliorates Zika virus-induced neurogenesis deficit in human neural stem cells.

Global Zika virus (ZIKV) outbreaks and their strong link to microcephaly have raised major public health concerns. ZIKV has been reported to affect the innate immune responses in neural stem/progenitor cells (NS/PCs). However, it is unclear how these immune factors affect neurogenesis. In this study, we used Asian-American lineage ZIKV strain PRVABC59 to infect primary human NS/PCs originally derived from fetal brains. We found that ZIKV overactivated key molecules in the innate immune pathways to impair neurogenesis in a cell stage-dependent manner. Inhibiting the overactivated innate immune responses ameliorated ZIKV-induced neurogenesis reduction. This study thus suggests that orchestrating the host innate immune responses in NS/PCs after ZIKV infection could be promising therapeutic approach to attenuate ZIKV-associated neuropathology.

Effects of Platelet-Rich Plasma on Cellular Populations of the Central Nervous System: The Influence of Donor Age.

Platelet-rich plasma (PRP) is a biologic therapy that promotes healing responses across multiple medical fields, including the central nervous system (CNS). The efficacy of this therapy depends on several factors such as the donor's health status and age. This work aims to prove the effect of PRP on cellular models of the CNS, considering the differences between PRP from young and elderly donors. Two different PRP pools were prepared from donors 65‒85 and 20‒25 years old. The cellular and molecular composition of both PRPs were analyzed. Subsequently, the cellular response was evaluated in CNS in vitro models, studying proliferation, neurogenesis, synaptogenesis, and inflammation. While no differences in the cellular composition of PRPs were found, the molecular composition of the Young PRP showed lower levels of inflammatory molecules such as CCL-11, as well as the presence of other factors not found in Aged PRP (GDF-11). Although both PRPs had effects in terms of reducing neural progenitor cell apoptosis, stabilizing neuronal synapses, and decreasing inflammation in the microglia, the effect of the Young PRP was more pronounced. In conclusion, the molecular composition of the PRP, conditioned by the age of the donors, affects the magnitude of the biological response.

A conformation-specific antibody against oligomeric ß-amyloid restores neuronal integrity in a mouse model of Alzheimer's disease.

Conformationally distinct aggregates of the amyloid ß (Aß) peptide accumulate in brains of patients with Alzheimer's disease (AD), but the roles of the different aggregates in disease progression are not clear. We previously isolated two single-chain variable domain antibody fragments (scFvs), C6T and A4, that selectively bind different toxic conformational variants of oligomeric Aß. Here, we utilize these scFvs to localize the presence of these Aß variants in human AD brain and to demonstrate their potential as therapeutic agents for treating AD. Both A4 and C6T label oligomeric Aß in extracellular amyloid plaques, whereas C6T also labels intracellular oligomeric Aß in human AD brain tissue and in an AD mouse model. For therapeutic studies, the A4 and C6T scFvs were expressed in the AD mice by viral infection of liver cells. The scFvs were administered at 2 months of age, and mice sacrificed at 9 months. The scFvs contained a peptide tag to facilitate transport across the blood brain barrier. While treatment with C6T only slightly decreased Aß deposits and plaque-associated inflammation, it restored neuronal integrity to WT levels, significantly promoted growth of new neurons, and impressively rescued survival rates to WT levels. Treatment with A4 on the other hand significantly decreased Aß deposits but did not significantly decrease neuroinflammation or promote neuronal integrity, neurogenesis, or survival rate. These results suggest that the specific Aß conformation targeted in therapeutic applications greatly affects the outcome, and the location of the targeted Aß variants may also play a critical factor.

Talpid3-Mediated Centrosome Integrity Restrains Neural Progenitor Delamination to Sustain Neurogenesis by Stabilizing Adherens Junctions.

Neurogenesis in the developing neocortex relies on extensive mitosis of radial glial cells (RGCs) in the apical surface. The nuclear migration of epithelial-like RGCs is fundamentally important for proper mitosis, but how the apical processes of RGCs are anchored to ensure the nucleokinetic behavior of RGCs remains unclear. Here we find that Talpid3, related to Joubert syndrome, is localized to the mother centriole of RGCs and is required for their apical mitosis. Genetic silencing of Talpid3 causes abnormal RGC delamination and thereby impairs their interkinetic nuclear migration in both cell-autonomous and non-autonomous manners. Further analyses reveal that Talpid3 associates with Ninein to regulate microtubule organization and maintain the integrity of adherens junctions to anchor RGCs. Moreover, genetic ablation of Talpid3 results in synchronized, ectopic mitosis of neural progenitors and dysregulated neurogenesis. Our study provides an intriguing perspective for the non-ciliogenic role of centriolar proteins in mediating cortical neurogenesis.

Role of Microglia in Modulating Adult Neurogenesis in Health and Neurodegeneration.

Microglia are the resident immune cells of the brain, constituting the powerhouse of brain innate immunity. They originate from hematopoietic precursors that infiltrate the developing brain during different stages of embryogenesis, acquiring a phenotype characterized by the presence of dense ramifications. Microglial cells play key roles in maintaining brain homeostasis and regulating brain immune responses. They continuously scan and sense the brain environment to detect any occurring changes. Upon detection of a signal related to physiological or pathological processes, the cells are activated and transform to an amoeboid-like phenotype, mounting adequate responses that range from phagocytosis to secretion of inflammatory and trophic factors. The overwhelming evidence suggests that microglia are crucially implicated in influencing neuronal proliferation and differentiation, as well as synaptic connections, and thereby cognitive and behavioral functions. Here, we review the role of microglia in adult neurogenesis under physiological conditions, and how this role is affected in neurodegenerative diseases.

In utero exposure to endogenous maternal polyclonal anti-Caspr2 antibody leads to behavioral abnormalities resembling autism spectrum disorder in male mice.

The concept that exposure in utero to maternal anti-brain antibodies contributes to the development of autism spectrum disorders (ASD) has been entertained for over a decade. We determined that antibodies targeting Caspr2 are present at high frequency in mothers with brain-reactive serology and a child with ASD, and further demonstrated that exposure in utero to a monoclonal anti-Caspr2 antibody, derived from a mother of an ASD child, led to an-ASD like phenotype in male offspring. Now we propose a new model to study the effects of in utero exposure to anti-Caspr2 antibody. Dams immunized with the extracellular portion of Caspr2 express anti-Caspr2 antibodies throughout gestation to better mimic the human condition. Male but not female mice born to dams harboring polyclonal anti-Caspr2 antibodies showed abnormal cortical development, decreased dendritic complexity of excitatory neurons and reduced numbers of inhibitory neurons in the hippocampus, as well as repetitive behaviors and impairments in novelty interest in the social preference test as adults. These data supporting the pathogenicity of anti-Caspr2 antibodies are consistent with the concept that anti-brain antibodies present in women during gestation can alter fetal brain development, and confirm that males are peculiarly susceptible.

Partial Purine Nucleoside Phosphorylase Deficiency Helps Determine Minimal Activity Required for Immune and Neurological Development.

Introduction: Complete or near complete absence of the purine nucleoside phosphorylase (PNP) enzyme causes a profound T cell immunodeficiency and neurological abnormalities that are often lethal in infancy and early childhood. We hypothesized that patients with partial PNP deficiency, characterized by a late and mild phenotype due to residual PNP enzyme, would provide important information about the minimal PNP activity needed for normal development. Methods: Three siblings with a homozygous PNP gene mutation (c.769C>G, p.His257Asp) resulting in partial PNP deficiency were investigated. PNP activity was semi-quantitively assayed by the conversion of [14C]inosine in hemolysates, mononuclear cells, and lymphoblastoid B cells. PNP protein expression was determined by Western Blotting in lymphoblastoid B cells. DNA repair was quantified by measuring viability of lymphoblastoid B cells following ionizing irradiation. Results: A 21-year-old female was referred for recurrent sino-pulmonary infections while her older male siblings, aged 25- and 28- years, did not suffer from significant infections. Two of the siblings had moderately reduced numbers of T, B, and NK cells, while the other had near normal lymphocyte subset numbers. T cell proliferations were normal in the two siblings tested. Hypogammaglobulinemia was noted in two siblings, including one that required immunoglobulin replacement. All siblings had typical (normal) neurological development. PNP activity in various cells from two patients were 8-11% of the normal level. All siblings had normal blood uric acid and increased PNP substrates in the urine. PNP protein expression in cells from the two patients examined was similar to that observed in cells from healthy controls. The survival of lymphoblastoid B cells from 2 partial PNP-deficient patients after irradiation was similar to that of PNP-proficient cells and markedly higher than the survival of cells from a patient with absent PNP activity or a patient with ataxia telangiectasia. Conclusions: Patients with partial PNP deficiency can present in the third decade of life with mild-moderate immune abnormalities and typical development. Near-normal immunity might be achieved with relatively low PNP activity.

T1-11, an adenosine derivative, ameliorates aging-related behavioral physiology and senescence markers in aging mice.

Aging is a natural human process. It is uniquely individual, taking into account experiences, lifestyle habits and environmental factors. However, many disorders and syndromes, such as osteoporosis, neurodegenerative disorders, cognitive decline etc., often come with aging. The present study was designed to investigate the possible anti-aging effect of N6-(4-hydroxybenzyl)adenine riboside (T1-11), an adenosine analog isolated from Gastrodia elata, in a mouse model of aging created by D-galactose (D-gal) and the underlying mechanism, as well as explore the role of adenosine signaling in aging. T1-11 activated A2AR and suppressed D-gal- and BeSO4-induced cellular senescence in vitro. In vivo results in mice revealed that T1-11 abated D-gal-induced reactive oxygen species generation and ameliorated cognitive decline by inducing neurogenesis and lowering D-gal-caused neuron death. T1-11 could be a potent agent for postponing senility and preventing aging-related neuroinflammation and neurodegeneration.

A Balancing Act: The Immune System Supports Neurodegeneration and Neurogenesis.

Decapod crustaceans, like mammals, retain the ability to make new neurons throughout life. In mammals, immune cells are closely associated with stem cells that generate adult-born neurons. In crayfish, evidence suggests that immune cells (hemocytes) originating in the immune system travel to neurogenic regions and transform into neural progenitor cells. This nontraditional immune activity takes place continuously under normal physiological conditions, but little is known under pathological conditions (neurodegeneration). In this study, the immune system and its relationship with neurogenesis were investigated during neurodegeneration (unilateral antennular ablation) in adult crayfish. Our experiments show that after ablation (1) Proliferating cells decrease in neurogenic areas of the adult crayfish brain; (2) The immune response, but not neurogenesis, is ablation-side dependent; (3) Inducible nitric oxide synthase (iNOS) plays a crucial role in the neurogenic niche containing neural progenitors during the immune response; (4) Brain areas targeted by antennular projections respond acutely (15 min) to the lesion, increasing the number of local immune cells; (5) Immune cells are recruited to the area surrounding the ipsilateral neurogenic niche; and (6) The vasculature in the niche responds acutely by dilation and possibly also neovascularization. We conclude that immune cells are important in both neurodegeneration and neurogenesis by contributing in physiological conditions to the maintenance of the number of neural precursor cells in the neurogenic niche (neurogenesis), and in pathological conditions (neurodegeneration) by coordinating NO release and vascular responses associated with the neurogenic niche. Our data suggest that neural damage and recovery participate in a balance between these competing immune cell roles.

Multiple inflammatory profiles of microglia and altered neuroimages in APP/PS1 transgenic AD mice.

Aß plaques of Alzheimer's disease (AD) are believed to precede cognitive deficits or clinical manifestation by decades. However, validated biomarkers for early diagnosis of the AD disease are still not available. In this present study, we combined MRI-based neuroimages and histological assessment of the glial response and altered cytokines, neurogenesis during the early course of Aß deposits in TgAPP/PS1 mice to find potential early biomarkers for AD. We found that microglia and astrocytes were initially activated and clustered around Aß plaques at the age of 6 months and significantly increased with age from 6-12 months of age. Confocal microscope analysis revealed that microglia not astrocytes began to phagocytose Aß in 6-month-old TgAPP/PS1 mice, evidenced by the intracellular Aß in Iba1 positive microglia not in GFAP positive astrocytes. In parallel with these observations, we found that mainly clustered microglia significantly upregulated the production of proinflammatory factors including TNF-α, iNOS and IL-1ß, and anti-inflammatory cytokines including IL-4, TGF-ß and extracellular protecting matrix YM-1 and enzyme arginase 1 (Arg1) at 6-12 months of age. Interestingly, reactive astrocyte did not express these cytokines and YM-1 and Arg1. These results may suggest that microglia rather than astrocytes play crucial roles in clearing Aß and neuroinflammation in early stage of AD. In addition, the number of neural stem cells labeled by BrdU and immature neurons labeled by doublecortin was significantly decreased in 3-month-old TgAPP/PS1 mice ahead of Aß deposits. Finally, DTI conforms that reduced fractional anisotropy (FA) in dentate gyrus of hippocampus and rs-MRI shows an increased connectivity in the networks of somatosensory cortex-caudoputamen and insula in TgAPP/PS1 mice at 6 months. These findings provide a clue to early biomarkers for diagnosis of the AD disease.

Perturbation of the immune cells and prenatal neurogenesis by the triplication of the Erg gene in mouse models of Down syndrome.

Some mouse models of Down syndrome (DS), including Ts1Cje mice, exhibit impaired prenatal neurogenesis with yet unknown molecular mechanism. To gain insights into the impaired neurogenesis, a transcriptomic and flow cytometry analysis of E14.5 Ts1Cje embryo brain was performed. Our analysis revealed that the neutrophil and monocyte ratios in the CD45-positive hematopoietic cells were relatively increased, in agreement with the altered expression of inflammation/immune-related genes, in Ts1Cje embryonic brain, whereas the relative number of brain macrophages was decreased in comparison to wild-type mice. Similar upregulation of inflammation-associated mRNAs was observed in other DS mouse models, with variable trisomic region lengths. We used genetic manipulation to assess the contribution of Erg, a trisomic gene in these DS models, known to regulation hemato-immune cells. The perturbed proportions of immune cells in Ts1Cje mouse brain were restored in Ts1Cje-Erg+/+/Mld2 mice, which are disomic for functional Erg but otherwise trisomic on a Ts1Cje background. Moreover, the embryonic neurogenesis defects observed in Ts1Cje cortex were reduced in Ts1Cje-Erg+/+/Mld2 embryos. Our findings suggest that Erg gene triplication contributes to the dysregulation of the homeostatic proportion of the populations of immune cells in the embryonic brain and decreased prenatal cortical neurogenesis in the prenatal brain with DS.

Complement dysregulation in the central nervous system during development and disease.

The complement cascade is an important arm of the immune system that plays a key role in protecting the central nervous system (CNS) from infection. Recently, it has also become clear that complement proteins have fundamental roles in the developing and aging CNS that are distinct from their roles in immunity. During neurodevelopment, complement signalling is involved in diverse processes including neural tube closure, neural progenitor proliferation and differentiation, neuronal migration, and synaptic pruning. In acute neurotrauma and ischamic brain injury, complement drives inflammation and neuronal death, but also neuroprotection and regeneration. In diseases of the aging CNS including dementias and motor neuron disease, chronic complement activation is associated with glial activation, and synapse and neuron loss. Proper regulation of complement is thus essential to allow for an appropriately developed CNS and prevention of excessive damage following neurotrauma or during neurodegeneration. This review provides a comprehensive overview of the evidence for functional roles of complement in brain formation, and its dysregulation during acute and chronic disease. We also provide working models for how complement can lead to neurodevelopmental disorders such as schizophrenia and autism, and either protect, or propagate neurodegenerative diseases including Alzheimer's disease and amyotrophic lateral sclerosis.