S100B-induced microglial and neuronal IL-1 expression is mediated by cell type-specific transcription factors

Thiadiazolidinone (TDZD) Analogs Inhibit Aggregation-Mediated Pathology in Diverse Neurodegeneration Models, and Extend C. elegans Life- and Healthspan

Chronic, low-grade inflammation has been implicated in aging and age-dependent conditions, including Alzheimer's disease, cardiomyopathy, and cancer. One of the age-associated processes underlying chronic inflammation is protein aggregation, which is implicated in neuroinflammation and a broad spectrum of neurodegenerative diseases such as Alzheimer's, Huntington's, and Parkinson's diseases. We screened a panel of bioactive thiadiazolidinones (TDZDs) from our in-house library for rescue of protein aggregation in human-cell and C. elegans models of neurodegeneration. Among the tested TDZD analogs, PNR886 and PNR962 were most effective, significantly reducing both the number and intensity of Alzheimer-like tau and amyloid aggregates in human cell-culture models of pathogenic aggregation. A C. elegans strain expressing human Aβ1-42 in muscle, leading to AD-like amyloidopathy, developed fewer and smaller aggregates after PNR886 or PNR962 treatment. Moreover, age-progressive paralysis was reduced 90% by PNR886 and 75% by PNR962, and "healthspan" (the median duration of spontaneous motility) was extended 29% and 62%, respectively. These TDZD analogs also extended wild-type C. elegans lifespan by 15-30% (p < 0.001), placing them among the most effective life-extension drugs. Because the lead drug in this family, TDZD-8, inhibits GSK3β, we used molecular-dynamic tools to assess whether these analogs may also target GSK3β. In silico modeling predicted that PNR886 or PNR962 would bind to the same allosteric pocket of inactive GSK3β as TDZD-8, employing the same pharmacophore but attaching with greater avidity. PNR886 and PNR962 are thus compelling candidate drugs for treatment of tau- and amyloid-associated neurodegenerative diseases such as AD, potentially also reducing all-cause mortality.

Intracellular DAMPs in Neurodegeneration and Their Role in Clinical Therapeutics

Neuroinflammation is the major implication of neurodegeneration. This is a complex process which initiates from the cellular injury triggering the innate immune system which gives rise to damage-associated molecular patterns (DAMPs) which are also recognized as endogenous danger indicators. These originate from various compartments of the cell under pathological stimulus. These are very popular candidates having their origin in the intracellular compartments and organelles of the cell and may have their site of action itself in the intracellular or at the extracellular spaces. Under the influence of the pathological stimuli, they interact with the pattern-recognition receptor to initiate their pro-inflammatory cascade followed by the cytokine release. This provides a good opportunity for diagnostic and therapeutic interventions creating better conditions for repair and reversal. Since the major contributors arise from the intracellular compartment, in this review, we have attempted to focus on the DAMP molecules arising from the intracellular compartments and their specific roles in the neurodegenerative events explaining their downstream mediators and signaling. Moreover, we have tried to cover the latest interventions in terms of DAMPs as clinical biomarkers which can assist in detecting the disease and also target it to reduce the innate-immune activation response which can help in reducing the sterile neuroinflammation having an integral role in the neurodegenerative processes.

Glial Fibrillary Acidic Protein: A Biomarker and Drug Target for Alzheimer’s Disease

Glial fibrillary acidic protein (GFAP) is an intermediate filament structural protein involved in cytoskeleton assembly and integrity, expressed in high abundance in activated glial cells. GFAP is neuroprotective, as knockout mice are hypersensitive to traumatic brain injury. GFAP in cerebrospinal fluid is a biomarker of Alzheimer’s disease (AD), dementia with Lewy bodies, and frontotemporal dementia (FTD). Here, we present novel evidence that GFAP is markedly overexpressed and differentially phosphorylated in AD hippocampus, especially in AD with the apolipoprotein E [ε4, ε4] genotype, relative to age-matched controls (AMCs). Kinases that phosphorylate GFAP are upregulated in AD relative to AMC. A knockdown of these kinases in SH-SY5Y-APP_Sw human neuroblastoma cells reduced amyloid accrual and lowered protein aggregation and associated behavioral traits in C. elegans models of polyglutamine aggregation (as observed in Huntington’s disease) and of Alzheimer’s-like amyloid formation. In silico screening of the ChemBridge structural library identified a small molecule, MSR1, with stable and specific binding to GFAP. Both MSR1 exposure and GF AP-specific RNAi knockdown reduce aggregation with remarkably high concordance of aggregate proteins depleted. These data imply that GFAP and its phosphorylation play key roles in neuropathic aggregate accrual and provide valuable new biomarkers, as well as novel therapeutic targets to alleviate, delay, or prevent AD.

The Potential Roles of Glial Cells in the Neuropathogenesis of Cerebral Malaria

Cerebral malaria (CM) is a severe neurological complication of malaria caused by the Plasmodium falciparum parasite. It is one of the leading causes of death in children under 5 years of age in Sub-Saharan Africa. CM is associated with blood-brain barrier disruption and long-term neurological sequelae in survivors of CM. Despite the vast amount of research on cerebral malaria, the cause of neurological sequelae observed in CM patients is poorly understood. In this article, the potential roles of glial cells, astrocytes, and microglia, in cerebral malaria pathogenesis are reviewed. The possible mechanisms by which glial cells contribute to neurological damage in CM patients are also examined.

Elevated serum S100B levels in medication naïve children and adolescents with obsessive-compulsive disorder

PURPOSE

Obsessive-compulsive disorder (OCD) is a condition characterized by obsessions and/or compulsions. S100B protein is shown to be involved in microglial activation besides intracellular signaling, intercellular communication and cell growth. The relation between S100B protein and various psychiatric disorders except OCD has been studied so far. This study aimed to analyze serum S100B levels for the first time in medication naive OCD diagnosed children and adolescents and to compare them with the control group.

MATERIALS AND METHODS

Peripheral blood S100B levels of 27 children and adolescents with OCD were compared to 27 control group subjects to assess any possible association between OCD and S100B levels. All the children and adolescents completed the child version of the Obsessive-Compulsive Inventory (OCI - CV).

RESULTS

Compared to control group, higher serum S100B levels were found in OCD group (z = -2.258, p = 0.024). We also found that obsessing and washing subscales' scores and total score of OCI - CV were statistically significantly correlated with S100B levels (respectively, r = .292, p = 0.032; r = .306, p = 0.025; r = .296, p = 0.030).

CONCLUSIONS

The present study's findings are in accord with previous studies demonstrating the significance of S100B protein in other psychiatric disorders and suggesting a relation in children and adolescents with OCD for the first time. The role of S100B protein in OCD etiology and pathogenesis should be evaluated further.

Innate Immune System Activation and Neuroinflammation in Down Syndrome and Neurodegeneration: Therapeutic Targets or Partners?

Innate immune system activation and inflammation are associated with and may contribute to clinical outcomes in people with Down syndrome (DS), neurodegenerative diseases such as Alzheimer's disease (AD), and normal aging. In addition to serving as potential diagnostic biomarkers, innate immune system activation and inflammation may play a contributing or causal role in these conditions, leading to the hypothesis that effective therapies should seek to dampen their effects. However, recent intervention studies with the innate immune system activator granulocyte-macrophage colony-stimulating factor (GM-CSF) in animal models of DS, AD, and normal aging, and in an AD clinical trial suggest that activating the innate immune system and inflammation may instead be therapeutic. We consider evidence that DS, AD, and normal aging are accompanied by innate immune system activation and inflammation and discuss whether and when during the disease process it may be therapeutically beneficial to suppress or promote such activation.

Astrocytes in Down Syndrome Across the Lifespan

Down Syndrome (DS) is the most common genetic cause of intellectual disability in which delays and impairments in brain development and function lead to neurological and cognitive phenotypes. Traditionally, a neurocentric approach, focusing on neurons and their connectivity, has been applied to understanding the mechanisms involved in DS brain pathophysiology with an emphasis on how triplication of chromosome 21 leads to alterations in neuronal survival and homeostasis, synaptogenesis, brain circuit development, and neurodegeneration. However, recent studies have drawn attention to the role of non-neuronal cells, especially astrocytes, in DS. Astrocytes comprise a large proportion of cells in the central nervous system (CNS) and are critical for brain development, homeostasis, and function. As triplication of chromosome 21 occurs in all cells in DS (with the exception of mosaic DS), a deeper understanding of the impact of trisomy 21 on astrocytes in DS pathophysiology is warranted and will likely be necessary for determining how specific brain alterations and neurological phenotypes emerge and progress in DS. Here, we review the current understanding of the role of astrocytes in DS, and discuss how specific perturbations in this cell type can impact the brain across the lifespan from early brain development to adult stages. Finally, we highlight how targeting, modifying, and/or correcting specific molecular pathways and properties of astrocytes in DS may provide an effective therapeutic direction given the important role of astrocytes in regulating brain development and function.

A Novel Microtubule-Binding Drug Attenuates and Reverses Protein Aggregation in Animal Models of Alzheimer's Disease

Age-progressive neurodegenerative pathologies, including Alzheimer’s disease (AD), are distinguished and diagnosed by disease-specific components of intra- or extra-cellular aggregates. Increasing evidence suggests that neuroinflammation promotes protein aggregation, and is involved in the etiology of neurological diseases. We synthesized and tested analogs of the naturally occurring tubulin-binding compound, combretastatin A-4. One such analog, PNR502, markedly reduced the quantity of Alzheimer-associated amyloid aggregates in the BRI-Aβ_1–42 mouse model of AD, while blunting the ability of the pro-inflammatory cytokine IL-1β to raise levels of amyloid plaque and its protein precursors in a neuronal cell-culture model. In transgenic Caenorhabditis elegans (C. elegans) strains that express human Aβ_1–42 in muscle or neurons, PNR502 rescued Aβ-induced disruption of motility (3.8-fold, P < 0.0001) or chemotaxis (1.8-fold, P < 0.05), respectively. Moreover, in C. elegans with neuronal expression of Aβ_1–42, a single day of PNR502 exposure reverses the chemotaxis deficit by 54% (P < 0.01), actually exceeding the protection from longer exposure. Moreover, continuous PNR502 treatment extends nematode lifespan 23% (P ≤ 0.001). Given that PNR502 can slow, prevent, or reverse Alzheimer-like protein aggregation in human-cell-culture and animal models, and that its principal predicted and observed binding targets are proteins previously implicated in Alzheimer’s, we propose that PNR502 has therapeutic potential to inhibit cerebral Aβ_1–42 aggregation and prevent or reverse neurodegeneration.

Interleukin-1β drives NEDD8 nuclear-to-cytoplasmic translocation, fostering parkin activation via NEDD8 binding to the P-ubiquitin activating site

Background

Neuroinflammation, typified by elevated levels of interleukin-1 (IL-1) α and β, and deficits in proteostasis, characterized by accumulation of polyubiquitinated proteins and other aggregates, are associated with neurodegenerative disease independently and through interactions of the two phenomena. We investigated the influence of IL-1β on ubiquitination via its impact on activation of the E3 ligase parkin by either phosphorylated ubiquitin (P-Ub) or NEDD8.

Methods

Immunohistochemistry and Proximity Ligation Assay were used to assess colocalization of parkin with P-tau or NEDD8 in hippocampus from Alzheimer patients (AD) and controls. IL-1β effects on PINK1, P-Ub, parkin, P-parkin, and GSK3β—as well as phosphorylation of parkin by GSK3β—were assessed in cell cultures by western immunoblot, using two inhibitors and siRNA knockdown to suppress GSK3β. Computer modeling characterized the binding and the effects of P-Ub and NEDD8 on parkin. IL-1α, IL-1β, and parkin gene expression was assessed by RT-PCR in brains of 2- and 17-month-old PD-APP mice and wild-type littermates.

Results

IL-1α, IL-1β, and parkin mRNA levels were higher in PD-APP mice compared with wild-type littermates, and IL-1α-laden glia surrounded parkin- and P-tau-laden neurons in human AD. Such neurons showed a nuclear-to-cytoplasmic translocation of NEDD8 that was mimicked in IL-1β-treated primary neuronal cultures. These cultures also showed higher parkin levels and GSK3β-induced parkin phosphorylation; PINK1 levels were suppressed. In silico simulation predicted that binding of either P-Ub or NEDD8 at a singular position on parkin opens the UBL domain, exposing Ser₆₅ for parkin activation.

Conclusions

The promotion of parkin- and NEDD8-mediated ubiquitination by IL-1β is consistent with an acute neuroprotective role. However, accumulations of P-tau and P-Ub and other elements of proteostasis, such as translocated NEDD8, in AD and in response to IL-1β suggest either over-stimulation or a proteostatic failure that may result from chronic IL-1β elevation, easily envisioned considering its early induction in Down’s syndrome and mild cognitive impairment. The findings further link autophagy and neuroinflammation, two important aspects of AD pathogenesis, which have previously been only loosely related.

Identification of biomarkers for the detection of subtle brain injury after cannabis and/or tramadol administration

Background

There is a need to identify biomarkers which could indicate the occurrence of brain injury in drug abuse.

Objectives

We aimed to investigate ubiquitin-C-terminal hydrolase-1 (UCH-L1), a neuronal cell body injury marker, the glial protein S-100 beta (S100β), and the glial fibrillary acidic protein (GFAP) as putative markers for neuronal injury due to cannabis, tramadol, or their combined use.

Materials and methods

Rats were treated with cannabis and/or tramadol subcutaneously daily for 6 weeks and UCH-L1, S100β, and GFAP were immunoassayed in the brain and serum.

Results

The results are as follows: (i) either cannabis or tramadol increased UCH-L1 and GFAP in the brain, (ii) serum UCH-L1 and GFAP increased by the highest dose of cannabis or tramadol, (iii) there was no additive effect for cannabis and tramadol on UCH-L1 or GFAP level in the brain or serum, (iv) S100β decreased in the brain by 5–20 mg/kg of cannabis and in the serum following 20 mg/kg of cannabis, and (v) S100β levels increased in the brain after 20 mg/kg of tramadol but decreased the brain and serum after both cannabis and tramadol. Cytoplasmic vacuolations, apoptotic cells, and gliosis were observed in the brain tissue of cannabis and/or tramadol-treated rats.

Conclusions

These results suggest that changes in UCH-L1, GFAP, or S100β are likely to reflect neurotoxicity and serum levels could be used to detect neuronal damage in chronic users.

S100 Proteins in Alzheimer's Disease

S100 proteins are calcium-binding proteins that regulate several processes associated with Alzheimer's disease (AD) but whose contribution and direct involvement in disease pathophysiology remains to be fully established. Due to neuroinflammation in AD patients, the levels of several S100 proteins are increased in the brain and some S100s play roles related to the processing of the amyloid precursor protein, regulation of amyloid beta peptide (Aβ) levels and Tau phosphorylation. S100 proteins are found associated with protein inclusions, either within plaques or as isolated S100-positive puncta, which suggests an active role in the formation of amyloid aggregates. Indeed, interactions between S100 proteins and aggregating Aβ indicate regulatory roles over the aggregation process, which may either delay or aggravate aggregation, depending on disease stage and relative S100 and Aβ levels. Additionally, S100s are also known to influence AD-related signaling pathways and levels of other cytokines. Recent evidence also suggests that metal-ligation by S100 proteins influences trace metal homeostasis in the brain, particularly of zinc, which is also a major deregulated process in AD. Altogether, this evidence strongly suggests a role of S100 proteins as key players in several AD-linked physiopathological processes, which we discuss in this review.

A toll-like receptor 9 antagonist restores below-level glial glutamate transporter expression in the dorsal horn following spinal cord injury

Spinal cord (SC) trauma elicits pathological changes at the primary lesion and in regions distant from the injury epicenter. Therapeutic agents that target mechanisms at the injury site are likely to exert additional effects in these remote regions. We previously reported that a toll-like receptor 9 (TLR9) antagonist, oligodeoxynucleotide 2088 (ODN 2088), improves functional deficits and modulates the milieu at the epicenter in mice sustaining a mid-thoracic contusion. The present investigations use the same paradigm to assess ODN 2088-elicited alterations in the lumbar dorsal horn (LDH), a region remote from the injury site where SCI-induced molecular alterations have been well defined. We report that ODN 2088 counteracts the SCI-elicited decrease in glial glutamate aspartate transporter (GLAST) and glutamate transporter 1 (GLT1) levels, whereas the levels of the neuronal glutamate transporter excitatory amino acid carrier 1 (EAAC1) and astroglial GABA transporter 3 (GAT3) were unaffected. The restoration of GLAST and GLT1 was neither paralleled by a global effect on astrocyte and microglia activation nor by changes in the expression of cytokines and growth factors reported to regulate these transporters. We conclude that the effects of intrathecal ODN 2088 treatment extend to loci beyond the epicenter by selectively targeting glial glutamate transporters.

Association of Polymorphisms of the Receptor for Advanced Glycation Endproducts Gene with Schizophrenia in a Han Chinese Population

Receptor for Advanced Glycation Endproducts (RAGE) is a member of the immunoglobulin superfamily that binds diverse ligands involved in the development of inflammatory damage and diverse chronic diseases including schizophrenia. Here, three single-nucleotide polymorphisms (SNPs) (G82S, -374T/A, and -429T/C) in the RAGE gene were genotyped in 923 patients with schizophrenia and 874 healthy-matched controls in a Han Chinese population using the SNaPshot technique. Additionally, we investigated the association among aforementioned SNPs with the clinical psychotic symptoms of the patients and neurocognitive function. Our study demonstrated that the frequencies of the TC + CC genotypes and the C allele in the -429T/C polymorphism were significantly lower in the patients compared with the controls (p = 0.031 and p = 0.034, resp.). However, the significant effect disappeared when using Bonferroni correction (p = 0.093 and p = 0.102, resp.). And there were no significant differences in the genotype and allele frequencies between the patients and the controls for G82S and -374T/A polymorphisms. Additionally, the -429T/C C allele carriers had marginally higher Symbol coding scores than the subjects with the TT genotypes [p = 0.031 and p (corr) = 0.093]. Our data indicate that the RAGE -429T/C polymorphism may be associated with the susceptibility of schizophrenia.

Gene regulation and genetics in neurochemistry, past to future

Ask any neuroscientist to name the most profound discoveries in the field in the past 60 years, and at or near the top of the list will be a phenomenon or technique related to genes and their expression. Indeed, our understanding of genetics and gene regulation has ushered in whole new systems of knowledge and new empirical approaches, many of which could not have even been imagined prior to the molecular biology boon of recent decades. Neurochemistry, in the classic sense, intersects with these concepts in the manifestation of neuropeptides, obviously dependent upon the central dogma (the established rules by which DNA sequence is eventually converted into protein primary structure) not only for their conformation but also for their levels and locales of expression. But, expanding these considerations to non-peptide neurotransmitters illustrates how gene regulatory events impact neurochemistry in a much broader sense, extending beyond the neurochemicals that translate electrical signals into chemical ones in the synapse, to also include every aspect of neural development, structure, function, and pathology. From the beginning, the mutability - yet relative stability - of genes and their expression patterns were recognized as potential substrates for some of the most intriguing phenomena in neurobiology - those instances of plasticity required for learning and memory. Near-heretical speculation was offered in the idea that perhaps the very sequence of the genome was altered to encode memories. A fascinating component of the intervening progress includes evidence that the central dogma is not nearly as rigid and consistent as we once thought. And this mutability extends to the potential to manipulate that code for both experimental and clinical purposes. Astonishing progress has been made in the molecular biology of neurochemistry during the 60 years since this journal debuted. Many of the gains in conceptual understanding have been driven by methodological progress, from automated high-throughput sequencing instruments to recombinant-DNA vectors that can convey color-coded genetic modifications in the chromosomes of live adult animals. This review covers the highlights of these advances, both theoretical and technological, along with a brief window into the promising science ahead. This article is part of the 60th Anniversary special issue.

Prenatal immune activation causes hippocampal synaptic deficits in the absence of overt microglia anomalies

Prenatal exposure to infectious or inflammatory insults can increase the risk of developing neuropsychiatric disorder in later life, including schizophrenia, bipolar disorder, and autism. These brain disorders are also characterized by pre- and postsynaptic deficits. Using a well-established mouse model of maternal exposure to the viral mimetic polyriboinosinic-polyribocytidilic acid [poly(I:C)], we examined whether prenatal immune activation might cause synaptic deficits in the hippocampal formation of pubescent and adult offspring. Based on the widely appreciated role of microglia in synaptic pruning, we further explored possible associations between synaptic deficits and microglia anomalies in offspring of poly(I:C)-exposed and control mothers. We found that prenatal immune activation induced an adult onset of presynaptic hippocampal deficits (as evaluated by synaptophysin and bassoon density). The early-life insult further caused postsynaptic hippocampal deficits in pubescence (as evaluated by PSD95 and SynGAP density), some of which persisted into adulthood. In contrast, prenatal immune activation did not change microglia (or astrocyte) density, nor did it alter their activation phenotypes. The prenatal manipulation did also not cause signs of persistent systemic inflammation. Despite the absence of overt glial anomalies or systemic inflammation, adult offspring exposed to prenatal immune activation displayed increased hippocampal IL-1β levels. Taken together, our findings demonstrate that age-dependent synaptic deficits and abnormal pro-inflammatory cytokine expression can occur during postnatal brain maturation in the absence of microglial anomalies or systemic inflammation.

Genome-Wide Expression Profiling Reveals S100B as Biomarker for Invasive Aspergillosis

Invasive aspergillosis (IA) is a devastating opportunistic infection and its treatment constitutes a considerable burden for the health care system. Immunocompromised patients are at an increased risk for IA, which is mainly caused by the species Aspergillus fumigatus. An early and reliable diagnosis is required to initiate the appropriate antifungal therapy. However, diagnostic sensitivity and accuracy still needs to be improved, which can be achieved at least partly by the definition of new biomarkers. Besides the direct detection of the pathogen by the current diagnostic methods, the analysis of the host response is a promising strategy toward this aim. Following this approach, we sought to identify new biomarkers for IA. For this purpose, we analyzed gene expression profiles of hematological patients and compared profiles of patients suffering from IA with non-IA patients. Based on microarray data, we applied a comprehensive feature selection using a random forest classifier. We identified the transcript coding for the S100 calcium-binding protein B (S100B) as a potential new biomarker for the diagnosis of IA. Considering the expression of this gene, we were able to classify samples from patients with IA with 82.3% sensitivity and 74.6% specificity. Moreover, we validated the expression of S100B in a real-time reverse transcription polymerase chain reaction (RT-PCR) assay and we also found a down-regulation of S100B in A. fumigatus stimulated DCs. An influence on the IL1B and CXCL1 downstream levels was demonstrated by this S100B knockdown. In conclusion, this study covers an effective feature selection revealing a key regulator of the human immune response during IA. S100B may represent an additional diagnostic marker that in combination with the established techniques may improve the accuracy of IA diagnosis.

Individual Cytokines Modulate the Neurological Symptoms of ATM Deficiency in a Region Specific Manner

Ataxia-telangiectasia (A-T) is a multisystemic neurodegenerative disease of childhood caused by the absence of functional ATM (A-T mutated) protein. The cerebellar cortex has the most obvious neuropathology, yet cells in other brain regions are also abnormal. A-T mouse models have been produced that replicate much, though not all, of the complex A-T phenotype. Nongenetic factors, including modulations of the immune status of the animal, have also recently been found to play a role in the disease phenotype. Here we report that these modulations show both cytokine and brain region specificity. The CNS changes induced by broad-spectrum immune challenges, such as lipopolysaccharide (LPS) injections are a complex mixture of neuroprotective (TNFα) and neurodegenerative (IL1β) cytokine responses that change over time. For example, LPS first induces a protective response in A-T neurons through activation of tissue repair genes through infiltration of monocytes with M2 phenotype, followed over time by a set of more degenerative responses. Additional phenotypic complexity arises because the neuronal response to an immune challenge is regionally variable; cerebellum and cortex differ in important ways in their patterns of cellular and biochemical changes. Tracking these changes reveals an important though not exclusive role for the MAP kinase pathway. Our findings suggest brain responses to cytokine challenges are temporally and regionally specific and that both features are altered by the absence of ATM. This implies that management of the immune status of A-T patients might have significant clinical benefit.

Third Harmonic Generation microscopy as a reliable diagnostic tool for evaluating lipid body modification during cell activation: the example of BV-2 microglia cells

Nonlinear optical processes have found widespread applications in fields ranging from fundamental physics to biomedicine. In this study, we attempted to evaluate cell activation by using the Third Harmonic Generation (THG) imaging microscopy as a new diagnostic tool. The BV-2 microglia cell line with or without activation by lipopolysaccharide was chosen as a representative biological model. The results showed that THG imaging could discriminate between the control versus activated state of BV-2 cells not only as to THG signal intensity but also as to THG signal area, while verifying once more that the majority of the intracellular detected signal corresponds to lipid bodies. Since THG imaging is a real time, non-destructive modality and does not require any prior cell processing and staining, the results presented here provide an important tool for normal versus activated cell discrimination, which could be proved very useful in the study of inflammation.

Exposure to MnCl2 · 4H2O during development induces activation of microglial and perivascular macrophage populations in the hippocampal dentate gyrus of rats

Developmental exposure to Mn caused Mn accumulation in the brain tissue and transient disruption of granule cell neurogenesis, targeting the late stage differentiation of progenitor cells in the subgranular zone of the hippocampal dentate gyrus of rats. Because neurogenesis is influenced by proinflammatory responses, this study was performed to determine whether Mn exposure causes microglial activation in the dentate hilus, a region anatomically close to the subgranular zone of the dentate gyrus. Pregnant rats were treated with dietary MnCl2 · 4H2O at 32, 160 or 800 ppm from gestational day 10 to day 21 after delivery. An immunohistochemical analysis revealed increases in Iba1(+) microglia in the hilus on postnatal day 21 following exposure to MnCl2 · 4H2O in a dose-unrelated manner at 32 and at 800 ppm and an increase in CD163(+) macrophage at 800 ppm in the hilus. Real-time reverse transcription-polymerase chain reaction analysis revealed increases in the mRNA levels of Il1α, Il6, Nos2 and Tnf after 800 ppm MnCl2 · 4H2O. These results suggest that activation of microglia and perivascular macrophages occurs in the hilus after developmental exposure to MnCl2 · 4H2O at 800 ppm, and probably involves the disruption of neurogenesis through the accumulation of Mn in the brain tissue.

The role of inflammasome in Alzheimer's disease

Alzheimer's disease (AD) is a chronic, progressive and irreversible neurodegenerative disease with clinical characteristics of memory loss, dementia and cognitive impairment. Although the pathophysiologic mechanism is not fully understood, inflammation has been shown to play a critical role in the pathogenesis of AD. Inflammation in the central nervous system (CNS) is characterized by the activation of glial cells and release of proinflammatory cytokines and chemokines. Accumulating evidence demonstrates that inflammasomes, which cleave precursors of interleukin-1β (IL-1β) and IL-18 to generate their active forms, play an important role in the inflammatory response in the CNS and in AD pathogenesis. Therefore, modulating inflammasome complex assembly and activation could be a potential strategy for suppressing inflammation in the CNS. This review aims to provide insight into the role of inflammasomes in the CNS, with respect to the pathogenesis of AD, and may provide possible clues for devising novel therapeutic strategies.

S100A9 knockout decreases the memory impairment and neuropathology in crossbreed mice of Tg2576 and S100A9 knockout mice model

Our previous study presented evidence that the inflammation-related S100A9 gene is significantly upregulated in the brains of Alzheimer's disease (AD) animal models and human AD patients. In addition, experiments have shown that knockdown of S100A9 expression improves cognition function in AD model mice (Tg2576), and these animals exhibit reduced amyloid plaque burden. In this study, we established a new transgenic animal model of AD by crossbreeding the Tg2576 mouse with the S100A9 knockout (KO) mouse. We observed that S100A9KO/Tg2576 (KO/Tg) mice displayed an increased spatial reference memory in the Morris water maze task and Y-maze task as well as decreased amyloid beta peptide (Aβ) neuropathology because of reduced levels of Aβ, C-terminal fragments of amyloid precursor protein (APP-CT) and phosphorylated tau and increased expression of anti-inflammatory IL-10 and also decreased expression of inflammatory IL-6 and tumor neurosis factor (TNF)-α when compared with age-matched S100A9WT/Tg2576 (WT/Tg) mice. Overall, these results suggest that S100A9 is responsible for the neurodegeneration and cognitive deficits in Tg2576 mice. The mechanism of S100A9 is able to coincide with the inflammatory process. These findings indicate that knockout of S100A9 is a potential target for the pharmacological therapy of AD.

Epilepsy: neuroinflammation, neurodegeneration, and APOE genotype

Background

Precocious development of Alzheimer-type neuropathological changes in epilepsy patients, especially in APOE ϵ4,4 carriers is well known, but not the ways in which other APOE allelic combinations influence this outcome. Frozen and paraffin-embedded tissue samples resected from superior temporal lobes of 92 patients undergoing temporal lobectomies as a treatment for medication-resistant temporal lobe epilepsy were used in this study. To determine if epilepsy-related changes reflect those in another neurological condition, analogous tissue samples harvested from 10 autopsy-verified Alzheimer brains, and from 10 neurologically and neuropathologically normal control patients were analyzed using immunofluorescence histochemistry, western immunoblot, and real-time PCR to determine genotype effects on neuronal number and size, neuronal and glial expressions of amyloid β (Aβ) precursor protein (βAPP), Aβ, apolipoprotein E (ApoE), S100B, interleukin-1α and β, and α and β secretases; and on markers of neuronal stress, including DNA/RNA damage and caspase 3 expression.

Results

Allelic combinations of APOE influenced each epilepsy-related neuronal and glial response measured as well as neuropathological change. APOE ϵ3,3 conferred greatest neuronal resilience denoted as greatest production of the acute phase proteins and low neuronal stress as assessed by DNA/RNA damage and caspase-3 expression. Among patients having an APOE ϵ2 allele, none had Aβ plaques; their neuronal sizes, like those with APOE ϵ3,3 genotype were larger than those with other genotypes. APOE ϵ4,4 conferred the weakest neuronal resilience in epilepsy as well as in Alzheimer patients, but there were no APOE genotype-dependent differences in these parameters in neurologically normal patients.

Conclusions

Our findings provide evidence that the strength of the neuronal stress response is more related to patient APOE genotype than to either the etiology of the stress or to the age of the patient, suggesting that APOE genotyping may be a useful tool in treatment decisions.

Down's syndrome, neuroinflammation, and Alzheimer neuropathogenesis

Down syndrome (DS) is the result of triplication of chromosome 21 (trisomy 21) and is the prevailing cause of mental retardation. In addition to the mental deficiencies and physical anomalies noted at birth, triplication of chromosome 21 gene products results in the neuropathological and cognitive changes of Alzheimer's disease (AD). Mapping of the gene that encodes the precursor protein (APP) of the β-amyloid (Aβ) present in the Aβ plaques in both AD and DS to chromosome 21 was strong evidence that this chromosome 21 gene product was a principal neuropathogenic culprit in AD as well as DS. The discovery of neuroinflammatory changes, including dramatic proliferation of activated glia overexpressing a chromosome 2 gene product--the pluripotent immune cytokine interleukin-1 (IL-1)--and a chromosome 21 gene product--S100B--in the brains of fetuses, neonates, and children with DS opened the possibility that early events in Alzheimer pathogenesis were driven by cytokines. The specific chromosome 21 gene products and the complexity of the mechanisms they engender that give rise to the neuroinflammatory responses noted in fetal development of the DS brain and their potential as accelerators of Alzheimer neuropathogenesis in DS are topics of this review, particularly as they relate to development and propagation of neuroinflammation, the consequences of which are recognized clinically and neuropathologically as Alzheimer's disease.

Organotypic brain slice cultures of adult transgenic P301S mice--a model for tauopathy studies

BACKGROUND

Organotypic brain slice cultures represent an excellent compromise between single cell cultures and complete animal studies, in this way replacing and reducing the number of animal experiments. Organotypic brain slices are widely applied to model neuronal development and regeneration as well as neuronal pathology concerning stroke, epilepsy and Alzheimer's disease (AD). AD is characterized by two protein alterations, namely tau hyperphosphorylation and excessive amyloid β deposition, both causing microglia and astrocyte activation. Deposits of hyperphosphorylated tau, called neurofibrillary tangles (NFTs), surrounded by activated glia are modeled in transgenic mice, e.g. the tauopathy model P301S.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we explore the benefits and limitations of organotypic brain slice cultures made of mature adult transgenic mice as a potential model system for the multifactorial phenotype of AD. First, neonatal (P1) and adult organotypic brain slice cultures from 7- to 10-month-old transgenic P301S mice have been compared with regard to vitality, which was monitored with the lactate dehydrogenase (LDH)- and the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays over 15 days. Neonatal slices displayed a constant high vitality level, while the vitality of adult slice cultures decreased significantly upon cultivation. Various preparation and cultivation conditions were tested to augment the vitality of adult slices and improvements were achieved with a reduced slice thickness, a mild hypothermic cultivation temperature and a cultivation CO(2) concentration of 5%. Furthermore, we present a substantial immunohistochemical characterization analyzing the morphology of neurons, astrocytes and microglia in comparison to neonatal tissue.

CONCLUSION/SIGNIFICANCE

Until now only adolescent animals with a maximum age of two months have been used to prepare organotypic brain slices. The current study provides evidence that adult organotypic brain slice cultures from 7- to 10-month-old mice independently of the transgenic modification undergo slow programmed cell death, caused by a dysfunction of the neuronal repair systems.

Serum biomarkers of spontaneous intracerebral hemorrhage induced secondary brain injury

Intracerebral hemorrhage (ICH) is a devastating form of stroke associated with a high rate of morbidity and mortality. It is now believed that much of this damage occurs in the subacute period following the initial insult via a cascade of complex pathophysiologic pathways that continues to be investigated. Increased levels of certain serum proteins have been identified as biomarkers that may reflect or directly participate in the inflammation, blood brain barrier disruption, endothelial dysfunction, and neuronal and glial toxicity that occur during this secondary period of cerebral injury. Some of these biomarkers have the potential to serve as therapeutic targets or surrogate endpoints for future research or clinical trials. Others may someday augment current clinical techniques in diagnosis, risk-stratification, prognostication, treatment decision and measurement of therapeutic efficacy. While much work remains to be done, biomarkers show significant potential to expand clinical options and improve clinical management, thereby reducing mortality and improving functional outcomes in ICH patients.

Forkhead box protein p1 is a transcriptional repressor of immune signaling in the CNS: implications for transcriptional dysregulation in Huntington disease

Forkhead box protein p1 (Foxp1), a transcription factor showing highly enriched expression in the striatum, has been implicated in central nervous system (CNS) development, but its role in the mature brain is unknown. In order to ascertain functional roles for Foxp1 in the CNS, we have identified gene targets for Foxp1 both in vitro and in vivo using genome-wide expression microarrays and chromatin-immunoprecipitation followed by high-throughput sequencing (ChIP-seq) assays. We found that mouse Foxp1 overexpression in striatal cells elicited expression changes of genes related to immune signaling, transcriptional regulation and a manually curated Huntington's disease (HD)-signaling pathway. Similar results were found when the gene expression data set was integrated with Foxp1-binding data determined from ChIP-seq analysis. In vivo lentiviral-mediated overexpression of human FOXP1 in the context of mutant huntingtin (Htt) protein resulted in a robust downregulation of glial cell-associated, immune genes, including those encoding a variety of cytokines and chemokines. Furthermore, Foxp1-induced expression changes were significantly negatively correlated with those changes elicited by mutant Htt protein in several different HD mouse models, and most significantly in post-mortem caudate from human HD subjects. We finally show that Foxp1 interacts with mutant Htt protein in mouse brain and is present in nuclear Htt aggregates in the striatum of R6/1 transgenic mice. These findings implicate Foxp1 as a key repressor of immune signaling in the CNS and suggest that the loss of Foxp1-mediated gene regulation in HD contributes to the immune dysfunction in this disease. We further suggest that Foxp1-regulated pathways might be important mediators of neuronal-glial cell communication.

Is the Gly82Ser polymorphism in the RAGE gene relevant to schizophrenia and the personality trait psychoticism?

BACKGROUND

The receptor for advanced glycation end products (RAGE) is the main receptor for S100B, an astrogial proinflammatory mediator that has been suggested to be involved in the pathophysiology of schizophrenia. To further elucidate the possible relevance of inflammation for mental functions, we investigated a functional polymorphism in the gene coding for RAGE in relation to personality traits and susceptibility to schizophrenia.

METHODS

We studied the Gly82Ser polymorphism (rs2070600, 244G>A) in 2 population-based cohorts of middle-aged participants assessed using the Karolinska Scales of Personality. In addition, we compared genotype frequencies between patients with schizophrenia and controls.

RESULTS

The population-based cohorts included 270 women and 247 men, and the case-control study involved 138 patients with schizophrenia and 258 controls. In the population-based cohorts, 82Ser carriers were found to have significantly higher scores for the psychoticism personality trait comprising the detachment and suspicion subscales. The case-control study revealed that the 82Ser allele was significantly more frequent among patients than controls.

LIMITATIONS

This study was limited by the modest sample size and the use of a self-report measure to assess personality traits.

CONCLUSION

Our findings suggest that the proven relation between certain personality traits and schizophrenia can at least to some extent be explained on a genetic level. Also, the activated S100B-RAGE axis may be an underlying cause, not only a consequence, of the disease.

The renaissance of Ca2+-binding proteins in the nervous system: secretagogin takes center stage

Effective control of the Ca(2+) homeostasis in any living cell is paramount to coordinate some of the most essential physiological processes, including cell division, morphological differentiation, and intercellular communication. Therefore, effective homeostatic mechanisms have evolved to maintain the intracellular Ca(2+) concentration at physiologically adequate levels, as well as to regulate the spatial and temporal dynamics of Ca(2+)signaling at subcellular resolution. Members of the superfamily of EF-hand Ca(2+)-binding proteins are effective to either attenuate intracellular Ca(2+) transients as stochiometric buffers or function as Ca(2+) sensors whose conformational change upon Ca(2+) binding triggers protein-protein interactions, leading to cell state-specific intracellular signaling events. In the central nervous system, some EF-hand Ca(2+)-binding proteins are restricted to specific subtypes of neurons or glia, with their expression under developmental and/or metabolic control. Therefore, Ca(2+)-binding proteins are widely used as molecular markers of cell identity whilst also predicting excitability and neurotransmitter release profiles in response to electrical stimuli. Secretagogin is a novel member of the group of EF-hand Ca(2+)-binding proteins whose expression precedes that of many other Ca(2+)-binding proteins in postmitotic, migratory neurons in the embryonic nervous system. Secretagogin expression persists during neurogenesis in the adult brain, yet becomes confined to regionalized subsets of differentiated neurons in the adult central and peripheral nervous and neuroendocrine systems. Secretagogin may be implicated in the control of neuronal turnover and differentiation, particularly since it is re-expressed in neoplastic brain and endocrine tumors and modulates cell proliferation in vitro. Alternatively, and since secretagogin can bind to SNARE proteins, it might function as a Ca(2+) sensor/coincidence detector modulating vesicular exocytosis of neurotransmitters, neuropeptides or hormones. Thus, secretagogin emerges as a functionally multifaceted Ca(2+)-binding protein whose molecular characterization can unravel a new and fundamental dimension of Ca(2+)signaling under physiological and disease conditions in the nervous system and beyond.

Blocking IL-1 signaling rescues cognition, attenuates tau pathology, and restores neuronal β-catenin pathway function in an Alzheimer's disease model

Inflammation is a key pathological hallmark of Alzheimer's disease (AD), although its impact on disease progression and neurodegeneration remains an area of active investigation. Among numerous inflammatory cytokines associated with AD, IL-1β in particular has been implicated in playing a pathogenic role. In this study, we sought to investigate whether inhibition of IL-1β signaling provides disease-modifying benefits in an AD mouse model and, if so, by what molecular mechanisms. We report that chronic dosing of 3xTg-AD mice with an IL-1R blocking Ab significantly alters brain inflammatory responses, alleviates cognitive deficits, markedly attenuates tau pathology, and partly reduces certain fibrillar and oligomeric forms of amyloid-β. Alterations in inflammatory responses correspond to reduced NF-κB activity. Furthermore, inhibition of IL-1 signaling reduces the activity of several tau kinases in the brain, including cdk5/p25, GSK-3β, and p38-MAPK, and also reduces phosphorylated tau levels. We also detected a reduction in the astrocyte-derived cytokine, S100B, and in the extent of neuronal Wnt/β-catenin signaling in 3xTg-AD brains, and provided in vitro evidence that these changes may, in part, provide a mechanistic link between IL-1 signaling and GSK-3β activation. Taken together, our results suggest that the IL-1 signaling cascade may be involved in one of the key disease mechanisms for AD.

Lipopolysaccharide modulates astrocytic S100B secretion: a study in cerebrospinal fluid and astrocyte cultures from rats

Background

Inflammatory responses in brain are primarily mediated by microglia, but growing evidence suggests a crucial importance of astrocytes. S100B, a calcium-binding protein secreted by astrocytes, has properties of a neurotrophic or an inflammatory cytokine. However, it is not known whether primary signals occurring during induction of an inflammatory response (e.g. lipopolysaccharide, LPS) directly modulate S100B.

Methods

In this work, we evaluated whether S100B levels in cerebrospinal fluid (CSF) and serum of Wistar rats are affected by LPS administered by intraperitoneal (IP) or intracerebroventricular (ICV) injection, as well as whether primary astrocyte cultures respond directly to lipopolysaccharide.

Results

Our data suggest that S100B secretion in brain tissue is stimulated rapidly and persistently (for at least 24 h) by ICV LPS administration. This increase in CSF S100B was transient when LPS was IP administered. In contrast to these S100B results, we observed an increase in in TNFα levels in serum, but not in CSF, after IP administration of LPS. In isolated astrocytes and in acute hippocampal slices, we observed a direct stimulation of S100B secretion by LPS at a concentration of 10 μg/mL. An involvement of TLR4 was confirmed by use of specific inhibitors. However, lower levels of LPS in astrocyte cultures were able to induce a decrease in S100B secretion after 24 h, without significant change in intracellular content of S100B. In addition, after 24 h exposure to LPS, we observed a decrease in astrocytic glutathione and an increase in astrocytic glial fibrillary acidic protein.

Conclusions

Together, these data contribute to the understanding of the effects of LPS on astrocytes, particularly on S100B secretion, and help us to interpret cerebrospinal fluid and serum changes for this protein in neuroinflammatory diseases. Moreover, non-brain S100B-expressing tissues may be differentially regulated, since LPS administration did not lead to increased serum levels of S100B.

Molecular determinants of S100B oligomer formation

Background

S100B is a dimeric protein that can form tetramers, hexamers and higher order oligomers. These forms have been suggested to play a role in RAGE activation.

Methodology/Principal Findings

Oligomerization was found to require a low molecular weight trigger/cofactor and could not be detected for highly pure dimer, irrespective of handling. Imidazol was identified as a substance that can serve this role. Oligomerization is dependent on both the imidazol concentration and pH, with optima around 90 mM imidazol and pH 7, respectively. No oligomerization was observed above pH 8, thus the protonated form of imidazol is the active species in promoting assembly of dimers to higher species. However, disulfide bonds are not involved and the process is independent of redox potential. The process was also found to be independent of whether Ca²⁺ is bound to the protein or not. Tetramers that are purified from dimers and imidazol by gel filtration are kinetically stable, but dissociate into dimers upon heating. Dimers do not revert to tetramer and higher oligomer unless imidazol is again added. Both tetramers and hexamers bind the target peptide from p53 with retained stoichiometry of one peptide per S100B monomer, and with high affinity (lgK = 7.3±0.2 and 7.2±0.2, respectively in 10 mM BisTris, 5 mM CaCl₂, pH 7.0), which is less than one order of magnitude reduced compared to dimer under the same buffer conditions.

Conclusion/Significance

S100B oligomerization requires protonated imidazol as a trigger/cofactor. Oligomers are kinetically stable after imidazol is removed but revert back to dimer if heated. The results underscore the importance of kinetic versus thermodynamic control of S100B protein aggregation.

Pro-inflammatory cytokines derived from West Nile virus (WNV)-infected SK-N-SH cells mediate neuroinflammatory markers and neuronal death

Background

WNV-associated encephalitis (WNVE) is characterized by increased production of pro-inflammatory mediators, glial cells activation and eventual loss of neurons. WNV infection of neurons is rapidly progressive and destructive whereas infection of non-neuronal brain cells is limited. However, the role of neurons and pathological consequences of pro-inflammatory cytokines released as a result of WNV infection is unclear. Therefore, the objective of this study was to examine the role of key cytokines secreted by WNV-infected neurons in mediating neuroinflammatory markers and neuronal death.

Methods

A transformed human neuroblastoma cell line, SK-N-SH, was infected with WNV at multiplicity of infection (MOI)-1 and -5, and WNV replication kinetics and expression profile of key pro-inflammatory cytokines were analyzed by plaque assay, qRT-PCR, and ELISA. Cell death was measured in SK-N-SH cell line in the presence and absence of neutralizing antibodies against key pro-inflammatory cytokines using cell viability assay, TUNEL and flow cytometry. Further, naïve primary astrocytes were treated with UV-inactivated supernatant from mock- and WNV-infected SK-N-SH cell line and the activation of astrocytes was measured using flow cytometry and ELISA.

Results

WNV-infected SK-N-SH cells induced the expression of IL-1β, -6, -8, and TNF-α in a dose- and time-dependent manner, which coincided with increase in virus-induced cell death. Treatment of cells with anti-IL-1β or -TNF-α resulted in significant reduction of the neurotoxic effects of WNV. Furthermore treatment of naïve astrocytes with UV-inactivated supernatant from WNV-infected SK-N-SH cell line increased expression of glial fibrillary acidic protein and key inflammatory cytokines.

Conclusion

Our results for the first time suggest that neurons are one of the potential sources of pro-inflammatory cytokines in WNV-infected brain and these neuron-derived cytokines contribute to WNV-induced neurotoxicity. Moreover, cytokines released from neurons also mediate the activation of astrocytes. Our data define specific role(s) of WNV-induced pro-inflammatory cytokines and provide a framework for the development of anti-inflammatory drugs as much-needed therapeutic interventions to limit symptoms associated with WNVE.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

S100b counteracts neurodegeneration of rat cholinergic neurons in brain slices after oxygen-glucose deprivation

Alzheimer's disease is a severe chronic neurodegenerative disorder characterized by beta-amyloid plaques, tau pathology, cerebrovascular damage, inflammation, reactive gliosis, and cell death of cholinergic neurons. The aim of the present study is to test whether the glia-derived molecule S100b can counteract neurodegeneration of cholinergic neurons after oxygen-glucose deprivation (OGD) in organotypic brain slices of basal nucleus of Meynert. Our data showed that 3 days of OGD induced a marked decrease of cholinergic neurons (60% of control), which could be counteracted by 50 μg/mL recombinant S100b. The effect was dose and time dependent. Application of nerve growth factor or fibroblast growth factor-2 was less protective. C-fos-like immunoreactivity was enhanced 3 hours after OGD indicating metabolic stress. We conclude that S100b is a potent neuroprotective factor for cholinergic neurons during ischemic events.

Neuro-immune crosstalk in CNS diseases

Immune cells infiltrate the central nervous system (CNS) in many neurological diseases, with a primary or secondary inflammatory component. In the CNS, immune cells employ shared mediators to promote crosstalk with neuronal cells. The net effect of this neuro-immune crosstalk critically depends on the context of the interaction. It has long been established that inflammatory reactions in the CNS can cause or augment tissue injury in many experimental paradigms. However, emerging evidence suggests that in other paradigms inflammatory cells can contribute to neuroprotection and repair. This dual role of CNS inflammation is also reflected on the molecular level as it is becoming increasingly clear that immune cells can release both neurodestructive and neuroprotective molecules into CNS lesions. It is thus the balance between destructive and protective factors that ultimately determines the net result of the neuro-immune interaction.

Role of PPARs in Radiation-Induced Brain Injury

Whole-brain irradiation (WBI) represents the primary mode of treatment for brain metastases; about 200 000 patients receive WBI each year in the USA. Up to 50% of adult and 100% of pediatric brain cancer patients who survive >6 months post-WBI will suffer from a progressive, cognitive impairment. At present, there are no proven long-term treatments or preventive strategies for this significant radiation-induced late effect. Recent studies suggest that the pathogenesis of radiation-induced brain injury involves WBI-mediated increases in oxidative stress and/or inflammatory responses in the brain. Therefore, anti-inflammatory strategies can be employed to modulate radiation-induced brain injury. Peroxisomal proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the steroid/thyroid hormone nuclear receptor superfamily. Although traditionally known to play a role in metabolism, increasing evidence suggests a role for PPARs in regulating the response to inflammation and oxidative injury. PPAR agonists have been shown to cross the blood-brain barrier and confer neuroprotection in animal models of CNS disorders such as stroke, multiple sclerosis and Parkinson's disease. However, the role of PPARs in radiation-induced brain injury is unclear. In this manuscript, we review the current knowledge and the emerging insights about the role of PPARs in modulating radiation-induced brain injury.

Inflammation in ischaemic brain injury: current advances and future perspectives

1. Numerous studies have indicated that inflammation plays a key role in ischaemic brain injury. Brain ischaemia-reperfusion-induced inflammatory responses include increased microglial and astrocyte activity, increased production of cytokines, chemokines, adhesion molecules and metalloproteinases and the infiltration of monocytes and leucocytes into injured brain regions. 2. Although a significant proportion of the inflammatory response appears to exacerbate ischaemic brain injury, certain inflammatory responses are beneficial to ischaemic brains. It is necessary to further identify the detrimental and beneficial inflammatory responses so that therapeutic strategies can be designed for stroke patients to selectively inhibit detrimental responses while enhancing beneficial responses. 3. Increasing evidence also indicates significant changes in the peripheral immune system of stroke patients and animals that undergo cerebral ischaemia. It is worth elucidating the effects of these changes in ischaemic brain damage. 4. There are complex interactions in the ischaemic brain between microglia and other cell types, including neurons, astrocytes, endothelial cells and stem cells. It is of particular interest to determine the mechanisms underlying the roles of high-mobility group box-1, advanced glycation end-products receptors (RAGE), S100B and NADPH oxidase in these interactions. 5. Because brain ischaemia-induced inflammation is a relatively long-lasting event with profound effects on brain injury, it is of considerable importance to further investigate the mechanisms underlying inflammation in ischaemic brains.

PPARalpha ligands inhibit radiation-induced microglial inflammatory responses by negatively regulating NF-kappaB and AP-1 pathways

Whole-brain irradiation (WBI) can lead to cognitive impairment several months to years after irradiation. Studies on rodents have shown a rapid and sustained increase in activated microglia (brain macrophages) following brain irradiation, contributing to a chronic inflammatory response and a corresponding decrease in hippocampal neurogenesis. Thus, alleviating microglial activation following radiation represents a key strategy to minimize WBI-induced morbidity. We hypothesized that pretreatment with peroxisomal proliferator-activated receptor (PPAR)alpha agonists would ameliorate the proinflammatory responses seen in the microglia following in vitro radiation. Irradiating BV-2 cells (a murine microglial cell line) with single doses (2-10 Gy) of (137)Cs gamma-rays led to increases in (1) the gene expression of IL-1beta and TNFalpha, (2) Cox-2 protein levels, and (3) intracellular ROS generation. In addition, an increase in the DNA-binding activity of redox-regulated proinflammatory transcription factors AP-1 and NF-kappaB was observed. Pretreating BV-2 cells with the PPARalpha agonists GW7647 and Fenofibrate significantly inhibited the radiation-induced microglial proinflammatory response, in part, via decreasing (i) the nuclear translocation of the NF-kappaB p65 subunit and (ii) phosphorylation of the c-jun subunit of AP-1 in the nucleus. Taken together, these data support the hypothesis that activation of PPARalpha can modulate the radiation-induced microglial proinflammatory response.

S100B secretion is stimulated by IL-1beta in glial cultures and hippocampal slices of rats: Likely involvement of MAPK pathway

S100B is an astrocyte-derived cytokine implicated in the IL-1beta-triggered cytokine cycle in Alzheimer's disease. However, the secretion of S100B following stimulation by IL-1beta has not been directly demonstrated. We investigated S100B secretion in cortical primary astrocyte cultures, C6 glioma cells and acute hippocampal slices exposed to IL-1beta. S100B secretion was induced by IL-1beta in all preparations, involving MAPK pathway and, apparently, NF-small ka, CyrillicB signaling. Astrocytes and C6 cells exhibited different sensitivities to IL-1beta. These results suggest that IL-1beta-induced S100B secretion is a component of the neuroinflammatory response, which would support the involvement of S100B in the genesis of neurodegenerative diseases.

Relationships between expression of apolipoprotein E and beta-amyloid precursor protein are altered in proximity to Alzheimer beta-amyloid plaques: potential explanations from cell culture studies

Theories regarding the initiation and progression of Alzheimer disease (AD) often consider potential roles played by elevations of beta-amyloid precursor protein (betaAPP). Because it is the source of amyloid beta-peptide, betaAPP may simply contribute more pathogenic stimulus when elevated; some analyses have, however, reported a decline in betaAPP in AD. We found a progressive increase in neuronal betaAPP expression with increasing age in the brains of nondemented individuals, whereas in AD patient samples, betaAPP antigenicity decreased in neuronal somata in a manner that correlated with accumulation of mature amyloid beta-peptide plaques. In contrast, apolipoprotein E (ApoE) expression correlated with accumulation of plaques, and even greater amounts of ApoE were detected in plaques. Induction of betaAPP by glutamate in neuronal cell cultures was found to depend upon ApoE levels or activity. Thus, elevations in expression of ApoE and betaAPP by cellular stresses are likely normally linked in vivo, and uncoupling of this link, or other pathologic events in AD initiation, may leave neurons with diminished betaAPP expression, which might in turn reduce their resistance to stressors.

S100B induces tau protein hyperphosphorylation via Dickopff-1 up-regulation and disrupts the Wnt pathway in human neural stem cells

Previous studies suggest that levels of the astrocyte-derived S100B protein, such as those occurring in brain extra-cellular spaces consequent to persistent astroglial activation, may have a pathogenetic role in Alzheimer's disease (AD). Although S100B was reported to promote β amyloid precursor protein overexpression, no clear mechanistic relationship between S100B and formation of neurofibrillary tangles (NFTs) is established. This in vitro study has been aimed at investigating whether S100B is able to disrupt Wnt pathway and lead to tau protein hyperphosphorylation. Utilizing Western blot, electrophoretic mobility shift assay, supershift and reverse transcriptase-polymerase chain reaction techniques, it has been demonstrated that micromolar S100B concentrations stimulate c-Jun N-terminal kinase (JNK) phosphorylation through the receptor for advanced glycation ending products, and subsequently activate nuclear AP-1/cJun transcription, in cultured human neural stem cells. In addition, as revealed by Western blot, small interfering RNA and immunofluorescence analysis, S100B-induced JNK activation increased expression of Dickopff-1 that, in turn, promoted glycogen synthase kinase 3β phosphorylation and β-catenin degradation, causing canonical Wnt pathway disruption and tau protein hyperphosphorylation. These findings propose a previously unrecognized link between S100B and tau hyperphosphorylation, suggesting S100B can contribute to NFT formation in AD and in all other conditions in which neuroinflammation may have a crucial role.

Neuro-immune crosstalk in CNS diseases

Immune cells infiltrate the CNS in many neurological diseases with a primary or secondary inflammatory component. In the CNS, immune cells employ shared mediators to promote crosstalk with neuronal cells. The net effect of this neuro-immune crosstalk critically depends on the context of the interaction. It has long been established that inflammatory reactions in the CNS can cause or augment tissue injury in many experimental paradigms. However emerging evidence suggests that in other paradigms inflammatory cells can contribute to neuroprotection and repair. This dual role of CNS inflammation is also reflected on the molecular level as it is becoming increasingly clear that immune cells can release both neurodestructive and neuroprotective molecules in CNS lesions. It is thus the balance between destructive and protective factors that ultimately determines the net result of the neuro-immune interaction.

Gene expression profile of the PDAPP mouse model for Alzheimer's disease with and without Apolipoprotein E

The APOE epsilon 4 allele is a strong risk factor for Alzheimer's disease (AD). However, the molecular basis for this effect remains unclear. We examined expression of approximately 12,000 genes and expressed sequence tags in the hippocampus and cortex of PDAPP (APP(V717)) mice modeling AD that show extensive amyloid beta (A beta) deposition, and in PDAPP mice lacking murine APOE expression, which show marked attenuation of A beta deposition in the brain. Wild type and APOE knockout animals were also examined. Expression levels were determined at the initial stage of A beta deposition, as well as in older animals showing extensive neuropathological changes. Fifty-four transcripts were identified using our statistical analysis as differentially regulated between the PDAPP and PDAPP/APOE ko mice, whereas 31 transcripts were classified as differentially regulated among PDAPP mice and WT animals, and seven transcripts were identified as regulated between the PDAPP/APOE ko animals and the APOE ko animals. Interestingly, many of the differentially regulated genes we detected can be related to biological processes previously shown to be important in AD pathophysiology, including inflammation, calcium homeostasis, cholesterol transport and uptake, kinases and phosphatases involved in tau phosphorylation and dephosphorylation, mitochondrial energy metabolism, protein degradation, neuronal growth, endoplasmic reticulum (ER) stress related proteins, antioxidant activity, cytoskeletal organization, and presenilin binding proteins. Regulated genes also included some not directly associated with AD in the past but likely to be involved in known AD pathophysiologic mechanisms, and others that may represent completely novel factors in the pathogenesis of AD. These results provide a global molecular profile of hippocampal and cortical gene expression during the initial and intermediate stages Abeta deposition, and the effects of APOE deletion on this process.

Altered kynurenine metabolism correlates with infarct volume in stroke

Inflammation and oxidative stress are involved in brain damage following stroke, and tryptophan oxidation along the kynurenine pathway contributes to the modulation of oxidative stress partly via the glutamate receptor agonist quinolinic acid and antagonist kynurenic acid, and via redox-active compounds such as 3-hydroxyanthranilic acid. We have confirmed that following a stroke, patients show early elevations of plasma neopterin, S100B and peroxidation markers, the latter two correlating with infarct volume assessed from computed tomography (CT) scans, and being consistent with a rapid inflammatory response. We now report that the kynurenine pathway of tryptophan metabolism was also activated, with an increased kynurenine : tryptophan ratio, but with a highly significant decrease in the ratio of 3-hydroxyanthranilic acid : anthranilic acid, which was strongly correlated with infarct volume. Levels of kynurenic acid were significantly raised in patients who died within 21 days compared with those who survived. The results suggest that increased tryptophan catabolism is initiated before or immediately after a stroke, and is related to the inflammatory response and oxidative stress, with a major change in 3-hydroxyanthranilic acid levels. Together with previous evidence that inhibiting the kynurenine pathway reduces brain damage in animal models of stroke and cerebral inflammation, and that increased kynurenine metabolism directly promotes oxidative stress, it is proposed that oxidative tryptophan metabolism may contribute to the oxidative stress and brain damage following stroke. Some form of anti-inflammatory intervention between the rise of S100B and the activation of microglia, including inhibition of the kynurenine pathway, may be valuable in modifying patient morbidity and mortality.

Neuron-glia signaling in trigeminal ganglion: implications for migraine pathology

OBJECTIVE

The goal of this study was to investigate neuronal-glial cell signaling in trigeminal ganglia under basal and inflammatory conditions using an in vivo model of trigeminal nerve activation.

BACKGROUND

Activation of trigeminal ganglion nerves and release of calcitonin gene-related peptide (CGRP) are implicated in the pathology of migraine. Cell bodies of trigeminal neurons reside in the ganglion in close association with glial cells. Neuron-glia interactions are involved in all stages of inflammation and pain associated with several central nervous system (CNS) diseases. However, the role of neuron-glia interactions within the trigeminal ganglion under normal and inflammatory conditions is not known.

METHODS

Sprague-Dawley rats were utilized to study neuron-glia signaling in the trigeminal ganglion. Initially, True Blue was used as a retrograde tracer to localize neuronal cell bodies in the ganglion by fluorescent microscopy and multiple image alignment. Dye-coupling studies were conducted under basal conditions and in response to capsaicin injection into the TMJ capsule. S100B and p38 expression in neurons and glia were determined by immunohistochemistry following chemical stimulation. CGRP levels in the ganglion were measured by radioimmunoassay in response to capsaicin. In addition, the effect of CGRP on the release of 19 different cytokines from cultured glial cells was investigated by protein microarray analysis.

RESULTS

In unstimulated control animals, True Blue was detected primarily in neuronal cell bodies localized in clusters within the ganglion corresponding to the V3 region (TMJ capsule), V2 region (whisker pad), or V1 region (eyebrow and eye). However, True Blue was detected in both neuronal cell bodies and adjacent glia in the V3 region of the ganglion obtained from animals injected with capsaicin. Dye movement into the surrounding glia correlated with the time after capsaicin injection. Chemical stimulation of V3 trigeminal nerves was found to increase the expression of the inflammatory proteins S100B and p38 in both neurons and glia within the V3 region. Unexpectedly, increased levels of these proteins were also observed in the V2 and V1 regions of the ganglion. CGRP and the vesicle docking protein SNAP-25 were colocalized in many neuronal cell bodies and processes. Decreased CGRP levels in the ganglion were observed 2 hours following capsaicin stimulation. Using protein microarray analysis, CGRP was shown to differentially regulate cytokine secretion from cultured trigeminal ganglion glia.

CONCLUSIONS

We demonstrated that activation of trigeminal neurons leads to changes in adjacent glia that involve communication through gap junctions and paracrine signaling. This is the first evidence, to our knowledge, of neuron-glia signaling via gap junctions within the trigeminal ganglion. Based on our findings, it is likely that neuronal-glial communication via gap junctions and paracrine signaling are involved in the development of peripheral sensitization within the trigeminal ganglion and, thus, are likely to play an important role in the initiation of migraine. Furthermore, we propose that propagation of inflammatory signals within the ganglion may help to explain commonly reported symptoms of comorbid conditions associated with migraine.