Fcgamma receptors contribute to pyramidal cell death in the mouse hippocampus following local kainic acid injection

Unveiling the hidden connection: the blood-brain barrier's role in epilepsy

Epilepsy is characterized by abnormal synchronous electrical activity of neurons in the brain. The blood-brain barrier, which is mainly composed of endothelial cells, pericytes, astrocytes and other cell types and is formed by connections between a variety of cells, is the key physiological structure connecting the blood and brain tissue and is critical for maintaining the microenvironment in the brain. Physiologically, the blood-brain barrier controls the microenvironment in the brain mainly by regulating the passage of various substances. Disruption of the blood-brain barrier and increased leakage of specific substances, which ultimately leading to weakened cell junctions and abnormal regulation of ion concentrations, have been observed during the development and progression of epilepsy in both clinical studies and animal models. In addition, disruption of the blood-brain barrier increases drug resistance through interference with drug trafficking mechanisms. The changes in the blood-brain barrier in epilepsy mainly affect molecular pathways associated with angiogenesis, inflammation, and oxidative stress. Further research on biomarkers is a promising direction for the development of new therapeutic strategies.

Maternal immunoglobulin G affects brain development of mouse offspring

Maternal immunoglobulin (Ig)G is present in breast milk and has been shown to contribute to the development of the immune system in infants. In contrast, maternal IgG has no known effect on early childhood brain development. We found maternal IgG immunoreactivity in microglia, which are resident macrophages of the central nervous system of the pup brain, peaking at postnatal one week. Strong IgG immunoreactivity was observed in microglia in the corpus callosum and cerebellar white matter. IgG stimulation of primary cultured microglia activated the type I interferon feedback loop by Syk. Analysis of neonatal Fc receptor knockout (FcRn KO) mice that could not take up IgG from their mothers revealed abnormalities in the proliferation and/or survival of microglia, oligodendrocytes, and some types of interneurons. Moreover, FcRn KO mice also exhibited abnormalities in social behavior and lower locomotor activity in their home cages. Thus, changes in the mother-derived IgG levels affect brain development in offsprings.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

Repeated mild traumatic brain injury in mice elicits long term innate immune cell alterations in blood, spleen, and brain

Mild traumatic brain injury is an insidious event whereby the initial injury leads to ongoing secondary neuro- and systemic inflammation through various cellular pathways lasting days to months after injury. Here, we investigated the impact of repeated mild traumatic brain injury (rmTBI) and the resultant systemic immune response in male C57B6 mice using flow cytometric methodology on white blood cells (WBCs) derived from the blood and spleen. Isolated mRNA derived from spleens and brains of rmTBI mice was assayed for changes in gene expression at one day, one week, and one month following the injury paradigm. We observed increases in Ly6C+, Ly6C-, and total monocyte percentages in both blood and spleen at one month after rmTBI. Differential gene expression analysis for the brain and spleen tissues uncovered significant changes in many genes, including csf1r, itgam, cd99, jak1,cd3ε, tnfaip6, and nfil3. Additional analysis revealed alterations in several immune signaling pathways over the course of one month in the brain and spleen of rmTBI mice. Together, these results indicate that rmTBI produces pronounced gene expression changes in the brain and spleen. Furthermore, our data suggest that monocyte populations may reprogram towards the proinflammatory phenotype over extended periods of time after rmTBI.

Targeting tau only extracellularly is likely to be less efficacious than targeting it both intra- and extracellularly

Aggregation of the tau protein is thought to be responsible for the neurodegeneration and subsequent functional impairments in diseases that are collectively named tauopathies. Alzheimer's disease is the most common tauopathy, but the group consists of over 20 different diseases, many of which have tau pathology as their primary feature. The development of tau therapies has mainly focused on preventing the formation of and/or clearing these aggregates. Of these, immunotherapies that aim to either elicit endogenous tau antibodies or deliver exogenous ones are the most common approach in clinical trials. While their mechanism of action can involve several pathways, both extra- and intracellular, pharmaceutical companies have primarily focused on antibody-mediated clearance of extracellular tau. As we have pointed out over the years, this is rather surprising because it is well known that most of pathological tau protein is found intracellularly. It has been repeatedly shown by several groups over the past decades that antibodies can enter neurons and that their cellular uptake can be enhanced by various means, particularly by altering their charge. Here, we will briefly describe the potential extra- and intracellular mechanisms involved in antibody-mediated clearance of tau pathology, discuss these in the context of recent failures of some of the tau antibody trials, and finally provide a brief overview of how the intracellular efficacy of tau antibodies can potentially be further improved by certain modifications that aim to enhance tau clearance via specific intracellular degradation pathways.

Current Status of Clinical Trials on Tau Immunotherapies

Tau immunotherapies have advanced from proof-of-concept studies to over a dozen clinical trials for Alzheimer's disease (AD) and other tauopathies. Mechanistic studies in animal and culture models have provided valuable insight into how these therapies may work but multiple pathways are likely involved. Different groups have emphasized the importance of intracellular vs extracellular antibody-mediated clearance of the tau protein and there is no consensus on which pool of tau should ideally be targeted. Likewise, various normal and disease-selective epitopes are being targeted, and the antibody isotypes either favor phagocytosis of the tau-antibody complex or are neutral in that aspect. Most of the clinical trials are in early stages, thus their efficacy is not yet known, but all have been without any major adverse effects and some have reported target engagement. A few have been discontinued. One in phase I, presumably because of a poor pharmacokinetic profile, and three in phase II for a lack of efficacy although this trial stage is not well powered for efficacy measures. In these phase II studies, trials with two antibodies in patients with progressive supranuclear palsy or other primary tauopathies were halted but are continuing in patients with AD, and one antibody trial was stopped in early-stage AD but is continuing in moderate AD. These three antibodies have been reported to only work extracellularly and tau is not increased in the cerebrospinal fluid of primary tauopathies, which may explain the failures of two of them. In the discontinued AD trial, there are some concerns about how much of extracellular tau contains the N-terminal epitope that is being targeted. In addition, extracellular tau is only a small part of total tau, compared to intracellular tau. Targeting only the former may not be sufficient for functional benefits. Given these outcomes, decision makers within the pharmaceutical companies who green light these trials should attempt to target tau not only extracellularly but also intracellularly to increase their chances of success. Hopefully, some of the ongoing trials will provide some functional benefits to the large number of patients with tauopathies.

The role of inflammatory mediators in epilepsy: Focus on developmental and epileptic encephalopathies and therapeutic implications

In recent years, there has been an increasing interest in the potential involvement of neuroinflammation in the pathogenesis of epilepsy. Specifically, the role of innate immunity (that includes cytokines and chemokines) has been extensively investigated either in animal models of epilepsy and in clinical settings. Developmental and epileptic encephalopathies (DEE) are a heterogeneous group of epileptic disorders, in which uncontrolled epileptic activity results in cognitive, motor and behavioral impairment. By definition, epilepsy in DEE is poorly controlled by common antiepileptic drugs but may respond to alternative treatments, including steroids and immunomodulatory drugs. In this review, we will focus on how cytokines and chemokines play a role in the pathogenesis of DEE and why expanding our knowledge about the role of neuroinflammation in DEE may be crucial to develop new and effective targeted therapeutic strategies to prevent seizure recurrence and developmental regression.

Tau immunotherapies: Lessons learned, current status and future considerations

The majority of clinical trials targeting the tau protein in Alzheimer's disease and other tauopathies are tau immunotherapies. Because tau pathology correlates better with the degree of dementia than amyloid-β lesions, targeting tau is likely to be more effective in improving cognition than clearing amyloid-β in Alzheimer's disease. However, the development of tau therapies is in many ways more complex than for amyloid-β therapies as briefly outlined in this review. Most of the trials are on humanized antibodies, which may have very different properties than the original mouse antibodies. The impact of these differences are to a large extent unknown, can be difficult to decipher, and may not always be properly considered. Furthermore, the ideal antibody properties for efficacy are not well established and can depend on several factors. However, considering the varied approaches in clinical trials, there is a general optimism that at least some of these trials may provide functional benefits to patients suffering of various tauopathies. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Molecular Mechanism Involved in the Pathogenesis of Early-Onset Epileptic Encephalopathy

Recent studies have shown that neurologic inflammation may both precipitate and sustain seizures, suggesting that inflammation may be involved not only in epileptogenesis but also in determining the drug-resistant profile. Extensive literature data during these last years have identified a number of inflammatory markers involved in these processes of “neuroimmunoinflammation” in epilepsy, with key roles for pro-inflammatory cytokines such as: IL-6, IL-17 and IL-17 Receptor (IL-17R) axis, Tumor-Necrosis-Factor Alpha (TNF-α) and Transforming-Growth-Factor Beta (TGF-β), all responsible for the induction of processes of blood-brain barrier (BBB) disruption and inflammation of the Central Nervous System (CNS) itself. Nevertheless, many of these inflammatory biomarkers have also been implicated in the pathophysiologic process of other neurological diseases. Future studies will be needed to identify the disease-specific biomarkers in order to distinguish epilepsies from other neurological diseases, as well as recognize different epileptic semiology. In this context, biological markers of BBB disruption, as well as those reflecting its integrity, can be useful tools to determine the pathological process of a variety of neurological diseases. However; how these molecules may help in the diagnosis and prognostication of epileptic disorders remains yet to be determined. Herein, authors present an extensive literature review on the involvement of both, systemic and neuronal immune systems, in the early onset of epileptic encephalopathy.

Immunization Elicits Antigen-Specific Antibody Sequestration in Dorsal Root Ganglia Sensory Neurons

The immune and nervous systems are two major organ systems responsible for host defense and memory. Both systems achieve memory and learning that can be retained, retrieved, and utilized for decades. Here, we report the surprising discovery that peripheral sensory neurons of the dorsal root ganglia (DRGs) of immunized mice contain antigen-specific antibodies. Using a combination of rigorous molecular genetic analyses, transgenic mice, and adoptive transfer experiments, we demonstrate that DRGs do not synthesize these antigen-specific antibodies, but rather sequester primarily IgG1 subtype antibodies. As revealed by RNA-seq and targeted quantitative PCR (qPCR), dorsal root ganglion (DRG) sensory neurons harvested from either naïve or immunized mice lack enzymes (i.e., RAG1, RAG2, AID, or UNG) required for generating antibody diversity and, therefore, cannot make antibodies. Additionally, transgenic mice that express a reporter fluorescent protein under the control of Igγ1 constant region fail to express Ighg1 transcripts in DRG sensory neurons. Furthermore, neural sequestration of antibodies occurs in mice rendered deficient in neuronal Rag2, but antibody sequestration is not observed in DRG sensory neurons isolated from mice that lack mature B cells [e.g., Rag1 knock out (KO) or μMT mice]. Finally, adoptive transfer of Rag1-deficient bone marrow (BM) into wild-type (WT) mice or WT BM into Rag1 KO mice revealed that antibody sequestration was observed in DRG sensory neurons of chimeric mice with WT BM but not with Rag1-deficient BM. Together, these results indicate that DRG sensory neurons sequester and retain antigen-specific antibodies released by antibody-secreting plasma cells. Coupling this work with previous studies implicating DRG sensory neurons in regulating antigen trafficking during immunization raises the interesting possibility that the nervous system collaborates with the immune system to regulate antigen-mediated responses.

Fc gamma receptors are expressed in the developing rat brain and activate downstream signaling molecules upon cross-linking with immune complex

Background

Exposure of the developing brain to immune mediators, including antibodies, is postulated to increase risk for neurodevelopmental disorders and neurodegenerative disease. It has been suggested that immunoglobulin G-immune complexes (IgG-IC) activate Fc gamma receptors (FcγR) expressed on neurons to modify signaling events in these cells. However, testing this hypothesis is hindered by a paucity of data regarding neuronal FcγR expression and function.

Methods

FcγR transcript expression in the hippocampus, cortex, and cerebellum of neonatal male and female rats was investigated ex vivo and in mixed cultures of primary hippocampal and cortical neurons and astrocytes using quantitative PCR analyses. Expression at the protein level in mixed cultures of primary hippocampal and cortical neurons and astrocytes was determined by immunocytochemistry, western blotting, proteotype analysis, and flow cytometry. The functionality of these receptors was assessed by measuring changes in intracellular calcium levels, Erk phosphorylation, and IgG internalization following stimulation with IgG-immune complexes.

Results

FcgrIa, FcgrIIa, FcgrIIb, FcgrIIIa, and Fcgrt transcripts were detectable in the cortex, hippocampus, and cerebellum at postnatal days 1 and 7. These transcripts were also present in primary hippocampal and cortical cell cultures, where their expression was modulated by IFNγ. Expression of FcγRIa, FcγRIIb, and FcγRIIIa, but not FcγRIIa or FcRn proteins, was confirmed in cultured hippocampal and cortical neurons and astrocytes at the single cell level. A subpopulation of these cells co-expressed the activating FcγRIa and the inhibitory FcγRIIb. Functional analyses demonstrated that exposure of hippocampal and cortical cell cultures to IgG-IC increases intracellular calcium and Erk phosphorylation and triggers FcγR-mediated internalization of IgG.

Conclusions

Our data demonstrate that developing neurons and astrocytes in the hippocampus and the cortex express signaling competent FcγR. These findings suggest that IgG antibodies may influence normal neurodevelopment or function via direct interactions with FcγR on non-immune cells in the brain.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1050-z) contains supplementary material, which is available to authorized users.

FcγRIIb-SHIP2 axis links Aβ to tau pathology by disrupting phosphoinositide metabolism in Alzheimer's disease model

Amyloid-β (Aβ)-containing extracellular plaques and hyperphosphorylated tau-loaded intracellular neurofibrillary tangles are neuropathological hallmarks of Alzheimer's disease (AD). Although Aβ exerts neuropathogenic activity through tau, the mechanistic link between Aβ and tau pathology remains unknown. Here, we showed that the FcγRIIb-SHIP2 axis is critical in Aβ_1-42-induced tau pathology. Fcgr2b knockout or antagonistic FcγRIIb antibody inhibited Aβ_1-42-induced tau hyperphosphorylation and rescued memory impairments in AD mouse models. FcγRIIb phosphorylation at Tyr273 was found in AD brains, in neuronal cells exposed to Aβ_1-42, and recruited SHIP2 to form a protein complex. Consequently, treatment with Aβ_1-42 increased PtdIns(3,4)P₂ levels from PtdIns(3,4,5)P₃ to mediate tau hyperphosphorylation. Further, we found that targeting SHIP2 expression by lentiviral siRNA in 3xTg-AD mice or pharmacological inhibition of SHIP2 potently rescued tau hyperphosphorylation and memory impairments. Thus, we concluded that the FcγRIIb-SHIP2 axis links Aβ neurotoxicity to tau pathology by dysregulating PtdIns(3,4)P₂ metabolism, providing insight into therapeutic potential against AD.

Validation of Flow Cytometry and Magnetic Bead-Based Methods to Enrich CNS Single Cell Suspensions for Quiescent Microglia

Microglia are resident mononuclear phagocytes within the CNS parenchyma that intimately interact with neurons and astrocytes to remodel synapses and extracellular matrix. We briefly review studies elucidating the molecular pathways that underlie microglial surveillance, activation, chemotaxis, and phagocytosis; we additionally place these studies in a clinical context. We describe and validate an inexpensive and simple approach to obtain enriched single cell suspensions of quiescent parenchymal and perivascular microglia from the mouse cerebellum and hypothalamus. Following preparation of regional CNS single cell suspensions, we remove myelin debris, and then perform two serial enrichment steps for cells expressing surface CD11b. Myelin depletion and CD11b enrichment are both accomplished using antigen-specific magnetic beads in an automated cell separation system. Flow cytometry of the resultant suspensions shows a significant enrichment for CD11b(+)/CD45(+) cells (perivascular microglia) and CD11b(+)/CD45(-) cells (parenchymal microglia) compared to starting suspensions. Of note, cells from these enriched suspensions minimally express Aif1 (aka Iba1), suggesting that the enrichment process does not evoke significant microglial activation. However, these cells readily respond to a functional challenge (LPS) with significant changes in the expression of molecules specifically associated with microglia. We conclude that methods employing a combination of magnetic-bead based sorting and flow cytometry produce suspensions highly enriched for microglia that are appropriate for a variety of molecular and cellular assays.

Epileptic seizures as a manifestation of cow's milk allergy: a studied relationship and description of our pediatric experience

Adverse reactions after ingestion of cow's milk proteins can occur at any age, from birth and even amongst exclusively breast-fed infants, although not all of these are hypersensitivity reactions. The most common presentations related to cow's milk protein allergy are skin reactions, failure to thrive, anaphylaxis as well as gastrointestinal and respiratory disorders. In addition, several cases of cow's milk protein allergy in the literature have documented neurological involvement, manifesting with convulsive seizures in children. This may be due to CNS spread of a peripheral inflammatory response. Furthermore, there is evidence that pro-inflammatory cytokines are responsible for disrupting the blood-brain barrier, causing focal CNS inflammation thereby triggering seizures, although further studies are needed to clarify the pathogenic relationship between atopy and its neurological manifestations. This review aims to analyze current published data on the link between cow's milk protein allergy and epileptic events, highlighting scientific evidence for any potential pathogenic mechanism and describing our clinical experience in pediatrics.

Targeting inflammation as a therapeutic strategy for drug-resistant epilepsies: an update of new immune-modulating approaches

An increasing body of literature data suggests that inflammation, and in particular neuroinflammation, is involved in the pathophysiology of particular forms of epilepsy and convulsive disorders. Animal models have been used to identify inflammatory triggers in epileptogenesis and inflammation has recently been shown to enhance seizures. For example, pharmacological blockade of the IL-1beta/IL-1 receptor type 1 axis during epileptogenesis has been demonstrated to provide neuroprotection in temporal lobe epilepsy. Furthermore, experimental models have suggested that neural damage and the onset of spontaneous recurrent seizures are modulated via complex interactions between innate and adaptive immunity. However, it has also been suggested that inflammation can occur as a result of epilepsy, since animal models have also shown that seizure activity can induce neuroinflammation, and that recurrent seizures maintain chronic inflammation, thereby perpetuating seizures. On the basis of these observations, it has been suggested that immune-mediated therapeutic strategies may be beneficial for treating some drug resistant epilepsies with an underlying demonstrable inflammatory process. Although the potential mechanisms of immunotherapeutic strategies in drug-resistant seizures have been extensively discussed, evidence on the efficacy of such therapy is limited. However, recent research efforts have been directed toward utilizing the potential therapeutic benefits of anti-inflammatory agents in neurological disease and these are now considered prime candidates in the ongoing search for novel anti-epileptic drugs. The objective of our review is to highlight the immunological features of the pathogenesis of seizures and to analyze possible immunotherapeutic approaches for drug resistant epilepsies that can alter the immune-mediated pathogenesis.

The proinflammatory effect of C-reactive protein on human endothelial cells depends on the FcγRIIa genotype

INTRODUCTION

The stimulatory effects of CRP (C-reactive protein) on endothelial cells are mainly mediated via FcγRIIa. This receptor exists in two different allotypes bearing either arginine (R131) or histidine (H131) at the extracellular amino acid position 131 of the mature protein, but only FcγRIIa-R131 displays high avidity for CRP. This study investigated the role of the FcγRIIa genotype in CRP-stimulated endothelial cells.

MATERIALS AND METHODS

We tested the effects of CRP on expression of the adhesion molecules ICAM-1, VCAM-1, and E-selectin, as well as the endothelial release of pro-inflammatory molecules as a function of the FcγRIIa-genotype (FcγRIIa-H/H131, FcγRIIa-H/R131, FcγRIIa-R/R131) in HUVEC (Human Umbilical Vein Endothelial Cells). HUVEC were grouped according to their FcγRIIa status by genotyping with an allele specific nested-PCR. The expression of ICAM-1, VCAM-1, and E-selectin on HUVEC was detected by flow cytometry. The release of soluble markers (sCD40L, IL-6, IL-8, MCP-1, tPA, sP-selectin, and sVCAM-1) was measured using a multiplex assay for flow cytometry.

RESULTS AND CONCLUSIONS

CRP-stimulated expression of ICAM-1 and E-selectin was dependent on the specific FcγRIIa-genotype, with most pronounced induction in HUVEC with the FcγRIIa-R/R genotype, followed by H/R and H/H. In accordance with this finding, the supernatants of stimulated HUVEC with the R/R genotype showed significantly higher levels of tPA, MCP-1, and IL-6. Our data show that CRP stimulates the expression of adhesion molecules and the release of soluble markers by HUVEC as a function of the FcγRIIa-genotype. These findings could be relevant in the context of risk stratification in patients with cardiovascular disease.

Is a subtype of autism an allergy of the brain?

BACKGROUND

Autism spectrum disorders (ASDs) are characterized by deficits in social communication and language and the presence of repetitive behaviors that affect as many as 1 in 50 US children. Perinatal stress and environmental factors appear to play a significant role in increasing the risk for ASDs. There is no definitive pathogenesis, which therefore significantly hinders the development of a cure.

OBJECTIVE

We aimed to identify publications using basic or clinical data that suggest a possible association between atopic symptoms and ASDs, as well as evidence of how such an association could lead to brain disease, that may explain the pathogenesis of ASD.

METHODS

PubMed was searched for articles published since 1995 that reported any association between autism and/or ASDs and any one of the following terms: allergy, atopy, brain, corticotropin-releasing hormone, cytokines, eczema, food allergy, food intolerance, gene mutation, inflammation, mast cells, mitochondria, neurotensin, phenotype, stress, subtype, or treatment.

RESULTS

Children with ASD respond disproportionally to stress and also present with food and skin allergies that involve mast cells. Brain mast cells are found primarily in the hypothalamus, which participates in the regulation of behavior and language. Corticotropin-releasing hormone is secreted from the hypothalamus under stress and, together with neurotensin, stimulates brain mast cells that could result in focal brain allergy and neurotoxicity. Neurotensin is significantly increased in serum of children with ASD and stimulates mast cell secretion of mitochondrial adenosine triphosphate and DNA, which is increased in these children; these mitochondrial components are misconstrued as innate pathogens, triggering an autoallergic response in the brain. Gene mutations associated with higher risk of ASD have been linked to reduction of the phosphatase and tensin homolog, which inhibits the mammalian target of rapamycin (mTOR). These same mutations also lead to mast cell activation and proliferation. Corticotropin-releasing hormone, neurotensin, and environmental toxins could further trigger the already activated mTOR, leading to superstimulation of brain mast cells in those areas responsible for ASD symptoms. Preliminary evidence indicates that the flavonoid luteolin is a stronger inhibitor of mTOR than rapamycin and is a potent mast cell blocker.

CONCLUSION

Activation of brain mast cells by allergic, environmental, immune, neurohormonal, stress, and toxic triggers, especially in those areas associated with behavior and language, lead to focal brain allergies and subsequent focal encephalitis. This possibility is more likely in the subgroup of patients with ASD susceptibility genes that also involve mast cell activation.

Antibody uptake into neurons occurs primarily via clathrin-dependent Fcγ receptor endocytosis and is a prerequisite for acute tau protein clearance

Tau immunotherapy is effective in transgenic mice, but the mechanisms of Tau clearance are not well known. To this end, Tau antibody uptake was analyzed in brain slice cultures and primary neurons. Internalization was rapid (<1 h), saturable, and substantial compared with control mouse IgG. Furthermore, temperature reduction to 4 °C, an excess of unlabeled mouse IgG, or an excess of Tau antibodies reduced uptake in slices by 63, 41, and 62%, respectively (p = 0.002, 0.04, and 0.005). Uptake strongly correlated with total and insoluble Tau levels (r(2) = 0.77 and 0.87 and p = 0.002 and 0.0002), suggesting that Tau aggregates influence antibody internalization and/or retention within neurons. Inhibiting phagocytosis did not reduce uptake in slices or neuronal cultures, indicating limited microglial involvement. In contrast, clathrin-specific inhibitors reduced uptake in neurons (≤ 78%, p < 0.0001) and slices (≤ 35%, p = 0.03), demonstrating receptor-mediated endocytosis as the primary uptake pathway. Fluid phase endocytosis accounted for the remainder of antibody uptake in primary neurons, based on co-staining with internalized dextran. The receptor-mediated uptake is to a large extent via low affinity FcγII/III receptors and can be blocked in slices (43%, p = 0.04) and neurons (53%, p = 0.008) with an antibody against these receptors. Importantly, antibody internalization appears to be necessary for Tau reduction in primary neurons. Overall, these findings clarify that Tau antibody uptake is primarily receptor-mediated, that these antibodies are mainly found in neurons with Tau aggregates, and that their intracellular interaction leads to clearance of Tau pathology, all of which have major implications for therapeutic development of this approach.

Harnessing pain heterogeneity and RNA transcriptome to identify blood-based pain biomarkers: a novel correlational study design and bioinformatics approach in a graded chronic constriction injury model

A quantitative, peripherally accessible biomarker for neuropathic pain has great potential to improve clinical outcomes. Based on the premise that peripheral and central immunity contribute to neuropathic pain mechanisms, we hypothesized that biomarkers could be identified from the whole blood of adult male rats, by integrating graded chronic constriction injury (CCI), ipsilateral lumbar dorsal quadrant (iLDQ) and whole blood transcriptomes, and pathway analysis with pain behavior. Correlational bioinformatics identified a range of putative biomarker genes for allodynia intensity, many encoding for proteins with a recognized role in immune/nociceptive mechanisms. A selection of these genes was validated in a separate replication study. Pathway analysis of the iLDQ transcriptome identified Fcγ and Fcε signaling pathways, among others. This study is the first to employ the whole blood transcriptome to identify pain biomarker panels. The novel correlational bioinformatics, developed here, selected such putative biomarkers based on a correlation with pain behavior and formation of signaling pathways with iLDQ genes. Future studies may demonstrate the predictive ability of these biomarker genes across other models and additional variables.

Immunoglobulin G(1) immune complex upregulates interferon-γ-induced nitric oxide production via ERK1/2 activation in murine microglia

Intrathecal Immunoglobulin G (IgG) is elevated in some central nervous system (CNS) diseases and microglia upregulate Fcγ receptors in various neurological disorders. However, the interaction between IgG or IgG immune complexes and microglial Fcγ receptors is not fully understood. In this study, the effect of IgG(1) immune complexes on microglia was investigated. IgG(1) immune complexes increased nitric oxide production in murine microglia in the presence of interferon (IFN)-γ. These effects were dependent upon IgG(1) immune complex-induced activation of spleen tyrosine kinase with subsequent activation of extracellular signal regulated kinase1/2. Collectively, these results indicate that IgG(1) immune complexes can exert immunomodulatory effects in various central nervous system disorders.

Neuro-inflammation, blood-brain barrier, seizures and autism

Many children with Autism Spectrum Diseases (ASD) present with seizure activity, but the pathogenesis is not understood. Recent evidence indicates that neuro-inflammation could contribute to seizures. We hypothesize that brain mast cell activation due to allergic, environmental and/or stress triggers could lead to focal disruption of the blood-brain barrier and neuro-inflammation, thus contributing to the development of seizures. Treating neuro-inflammation may be useful when anti-seizure medications are ineffective.

Differences in origin of reactive microglia in bone marrow chimeric mouse and rat after transient global ischemia

Current understanding of microglial involvement in disease is influenced by the observation that recruited bone marrow (BM)-derived cells contribute to reactive microgliosis in BM-chimeric mice. In contrast, a similar phenomenon has not been reported for BM-chimeric rats. We investigated the recruitment and microglial transformation of BM-derived cells in radiation BM-chimeric mice and rats after transient global cerebral ischemia, which elicits a characteristic microglial reaction. Both species displayed microglial hyperplasia and rod cell transformation in the hippocampal CA1 region. In mice, a subpopulation of lesion-reactive microglia originated from transformed BM-derived cells. By contrast, no recruitment or microglial transformation of BM-derived cells was observed in BM-chimeric rats. These results suggest that reactive microglia in rats originate from resident microglia, whereas they have a mixed BM-derived and resident origin in mice, depending on the severity of ischemic tissue damage.