Enhanced susceptibility of S-100B transgenic mice to neuroinflammation and neuronal dysfunction induced by intracerebroventricular infusion of human β-amyloid

Neuroprotection elicited by taurine in sporadic Alzheimer-like disease: benefits on memory and control of neuroinflammation in the hippocampus of rats

This study aimed to analyze whether taurine has a nootropic effect on short-term and long-term memory in a model of sporadic dementia of the Alzheimer's type (SDAT). Moreover, we evaluated the immunoreactivity and insulin receptor (IR) distribution and markers for neurons and glial cells in the hippocampus of rats with SDAT and treated with taurine. For this, Male Wistar rats received STZ (ICV, 3 mg/kg, bilateral, 5ul per site, aCFS vehicle) and were treated with taurine (100 mg/kg orally, 1 time per day, saline vehicle) for 25 days. The animals were divided into 4 groups: vehicle (VE), taurine (TAU), ICV-STZ (STZ) and ICV-STZ plus taurine (STZ + TAU). At the end of taurine treatment, short- and long-term memory were assessed by performance on object recognition and Y-maze tasks. Insulin receptor (IR) was evaluated by immunoperoxidase while mature neurons (NeuN), astrocytes (GFAP, S100B, SOX9), and microglia (Iba-1) were evaluated by immunofluorescence. STZ induced worse spatial and recognition memory (INDEX) in YM and ORT tasks. Taurine protected against STZ-induced memory impairment. SDAT reduced the population of mature neurons as well as increased astrocytic and microglial reactivity, and taurine protected against these STZ-induced effects, mainly in the CA1 region of the hippocampus. Taurine increases IR expression in the hippocampus, and protects against the reduction in the density of this receptor in CA1 induced by STZ. In conclusion, these findings demonstrate that taurine is able to enhance memory, up-regulates IR in the hippocampus, protects the neuron population, and reduces the astrogliosis found in SDAT.

Myo-Inositol Levels in the Dorsal Hippocampus Serve as Glial Prognostic Marker of Mild Cognitive Impairment in Mice

Dementia is a devastating age-related disorder. Its therapy would largely benefit from the identification of susceptible subjects at early, prodromal stages of the disease. To search for such prognostic markers of cognitive impairment, we studied spatial navigation in male BALBc vs. B6N mice in combination with in vivo magnetic resonance spectroscopy (1H-MRS). BALBc mice consistently showed higher escape latencies than B6N mice, both in the Water Cross Maze (WCM) and the Morris water maze (MWM). These performance deficits coincided with higher levels of myo-inositol (mIns) in the dorsal hippocampus before and after training. Subsequent biochemical analyses of hippocampal specimens by capillary immunodetection and liquid chromatography mass spectrometry-based (LC/MS) metabolomics revealed a higher abundance of glial markers (IBA-1, S100B, and GFAP) as well as distinct alterations in metabolites including a decrease in vitamins (pantothenic acid and nicotinamide), neurotransmitters (acetylcholine), their metabolites (glutamine), and acetyl-L-carnitine. Supplementation of low abundant acetyl-L-carnitine via the drinking water, however, failed to revert the behavioral deficits shown by BALBc mice. Based on our data we suggest (i) BALBc mice as an animal model and (ii) hippocampal mIns levels as a prognostic marker of mild cognitive impairment (MCI), due to (iii) local changes in microglia and astrocyte activity, which may (iv) result in decreased concentrations of promnesic molecules.

Lactobacillus plantarum PS128 prevents cognitive dysfunction in Alzheimer's disease mice by modulating propionic acid levels, glycogen synthase kinase 3 beta activity, and gliosis

Background

According to recent evidence, psychobiotics exert beneficial effects on central nervous system-related diseases, such as mental disorders. Lactobacillus plantarum PS128 (PS128), a novel psychobiotic strain, improves motor function, depression, and anxiety behaviors. However, the psychobiotic effects and mechanisms of PS128 in Alzheimer’s disease (AD) remain to be explored.

Objectives

The goal of the current study was to evaluate the beneficial effects of PS128 and to further elucidate its mechanism in AD mice.

Methods

PS128 (10¹⁰ colony-forming unit (CFU)/ml) was administered via oral gavage (o.g.) to 6-month-old male wild-type B6 and 3 × Tg-AD mice (harboring the PS1M146V, APPswe and TauP30IL transgenes) that received an intracerebroventricular injection of streptozotocin (icv-STZ, 3 mg/kg) or vehicle (saline) for 33 days. After serial behavioral tests, fecal short-chain fatty acid levels and AD-related pathology were assessed in these mice.

Results

Our findings show that intracerebroventricular injection of streptozotocin accelerated cognitive dysfunction associated with increasing levels of glycogen synthase kinase 3 beta (GSK3β) activity, tau protein phosphorylation at the T231 site (pT231), amyloid-β (Aβ) deposition, amyloid-β protein precursor (AβPP), β-site AβPP-cleaving enzyme (BACE1), gliosis, fecal propionic acid (PPA) levels and cognition-related neuronal loss and decreasing postsynaptic density protein 95 (PSD95) levels in 3 × Tg-AD mice. PS128 supplementation effectively prevented the damage induced by intracerebroventricular injection of streptozotocin in 3 × Tg-AD mice.

Conclusions

Based on the experimental results, intracerebroventricular injection of streptozotocin accelerates the progression of AD in the 3 × Tg-AD mice, primarily by increasing the levels of gliosis, which were mediated by the propionic acid and glycogen synthase kinase 3 beta pathways. PS128 supplementation prevents damage induced by intracerebroventricular injection of streptozotocin by regulating the propionic acid levels, glycogen synthase kinase 3 beta activity, and gliosis in 3 × Tg-AD mice. Therefore, we suggest that PS128 supplementation is a potential strategy to prevent and/or delay the progression of AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03426-8.

Growing role of S100B protein as a putative therapeutic target for neurological- and nonneurological-disorders

S100B is a calcium-binding protein mainly expressed by astrocytes, but also localized in other definite neural and extra-neural cell types. While its presence in biological fluids is widely recognized as a reliable biomarker of active injury, growing evidence now indicates that high levels of S100B are suggestive of pathogenic processes in different neural, but also extra-neural, disorders. Indeed, modulation of S100B levels correlates with the occurrence of clinical and/or toxic parameters in experimental models of diseases such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, muscular dystrophy, multiple sclerosis, acute neural injury, inflammatory bowel disease, uveal and retinal disorders, obesity, diabetes and cancer, thus directly linking the levels of S100B to pathogenic mechanisms. In general, deletion/inactivation of the protein causes the improvement of the disease, whereas its over-expression/administration induces a worse clinical presentation. This scenario reasonably proposes S100B as a common therapeutic target for several different disorders, also offering new clues to individuate possible unexpected connections among these diseases.

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.

The neuronal S100B protein is a calcium-tuned suppressor of amyloid-β aggregation

Amyloid-β (Aβ) aggregation and neuroinflammation are consistent features in Alzheimer's disease (AD) and strong candidates for the initiation of neurodegeneration. S100B is one of the most abundant proinflammatory proteins that is chronically up-regulated in AD and is found associated with senile plaques. This recognized biomarker for brain distress may, thus, play roles in amyloid aggregation which remain to be determined. We report a novel role for the neuronal S100B protein as suppressor of Aβ42 aggregation and toxicity. We determined the structural details of the interaction between monomeric Aβ42 and S100B, which is favored by calcium binding to S100B, possibly involving conformational switching of disordered Aβ42 into an α-helical conformer, which locks aggregation. From nuclear magnetic resonance experiments, we show that this dynamic interaction occurs at a promiscuous peptide-binding region within the interfacial cleft of the S100B homodimer. This physical interaction is coupled to a functional role in the inhibition of Aβ42 aggregation and toxicity and is tuned by calcium binding to S100B. S100B delays the onset of Aβ42 aggregation by interacting with Aβ42 monomers inhibiting primary nucleation, and the calcium-bound state substantially affects secondary nucleation by inhibiting fibril surface-catalyzed reactions through S100B binding to growing Aβ42 oligomers and fibrils. S100B protects cells from Aβ42-mediated toxicity, rescuing cell viability and decreasing apoptosis induced by Aβ42 in cell cultures. Together, our findings suggest that molecular targeting of S100B could be translated into development of novel approaches to ameliorate AD neurodegeneration.

Metals and Neuronal Metal Binding Proteins Implicated in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent age-related dementia affecting millions of people worldwide. Its main pathological hallmark feature is the formation of insoluble protein deposits of amyloid-β and hyperphosphorylated tau protein into extracellular plaques and intracellular neurofibrillary tangles, respectively. Many of the mechanistic details of this process remain unknown, but a well-established consequence of protein aggregation is synapse dysfunction and neuronal loss in the AD brain. Different pathways including mitochondrial dysfunction, oxidative stress, inflammation, and metal metabolism have been suggested to be implicated in this process. In particular, a body of evidence suggests that neuronal metal ions such as copper, zinc, and iron play important roles in brain function in health and disease states and altered homeostasis and distribution as a common feature across different neurodegenerative diseases and aging. In this focused review, we overview neuronal proteins that are involved in AD and whose metal binding properties may underlie important biochemical and regulatory processes occurring in the brain during the AD pathophysiological process.

Normal cerebellar development in S100B-deficient mice

The calcium-binding protein S100B has been shown to support neuron proliferation, migration and neurite growth in vitro, while the significance of S100B for neuronal development in vivo is controversial. We have investigated the effect of S100B deficiency on cerebellar development in S100B knockout mice at an age of 5 and 10 days after birth (P5 and P10). This time range covers important developmental steps in the cerebellum such as granule cell proliferation and migration, as well as dendritic growth of Purkinje cells. Bergmann glial cells contain a particularly high concentration of S100B and serve as scaffold for both migrating granule cells and growing Purkinje cell dendrites. This renders the postnatal cerebellum ideal as a model system to study the importance of S100B for glial and neuronal development. We measured the length of Bergmann glial processes, the width of the external granule cell layer as a measure of granule cell proliferation, the decrease in width of the external granule cell layer between P5 and P10 as a measure of granule cell migration, and the length of Purkinje cell dendrites in wild-type and S100B knockout mice. None of these parameters showed significant differences between wild-type and knockout mice. In addition, wild-type and knockout mice performed equally in locomotor behaviour tests. The results indicate that S100B-deficient mice have normal development of the cerebellum and no severe impairment of motor function.

Does neuroinflammation turn on the flame in Alzheimer's disease? Focus on astrocytes

Data from animal models and Alzheimer's disease (AD) subjects provide clear evidence for an activation of inflammatory pathways during the pathogenetic course of such illness. Biochemical and neuropathological studies highlighted an important cause/effect relationship between inflammation and AD progression, revealing a wide range of genetic, cellular, and molecular changes associated with the pathology. In this context, glial cells have been proved to exert a crucial role. These cells, in fact, undergo important morphological and functional changes and are now considered to be involved in the onset and progression of AD. In particular, astrocytes respond quickly to pathology with changes that have been increasingly recognized as a continuum, with potentially beneficial and/or negative consequences. Although it is now clear that activated astrocytes trigger the neuroinflammatory process, however, the precise mechanisms have not been completely elucidated. Neuroinflammation is certainly a multi-faceted and complex phenomenon and, especially in the early stages, exerts a reparative intent. However, for reasons not yet all well known, this process goes beyond the physiologic control and contributes to the exacerbation of the damage. Here we scrutinize some evidence supporting the role of astrocytes in the neuroinflammatory process and the possibility that these cells could be considered a promising target for future AD therapies.

Inflammation in Alzheimer disease-a brief review of the basic science and clinical literature

Biochemical and neuropathological studies of brains from individuals with Alzheimer disease (AD) provide clear evidence for an activation of inflammatory pathways, and long-term use of anti-inflammatory drugs is linked with reduced risk to develop the disease. As cause and effect relationships between inflammation and AD are being worked out, there is a realization that some components of this complex molecular and cellular machinery are most likely promoting pathological processes leading to AD, whereas other components serve to do the opposite. The challenge will be to find ways of fine tuning inflammation to delay, prevent, or treat AD.

RAGE is a key cellular target for Abeta-induced perturbation in Alzheimer's disease

RAGE, a receptor for advanced glycation endproducts, is an immunoglobulin-like cell surface receptor that is often described as a pattern recognition receptor due to the structural heterogeneity of its ligand. RAGE is an important cellular cofactor for amyloid beta-peptide (Abeta)-mediated cellular perturbation relevant to the pathogenesis of Alzheimer's disease (AD). The interaction of RAGE with Abeta in neurons, microglia, and vascular cells accelerates and amplifies deleterious effects on neuronal and synaptic function. RAGE-dependent signaling contributes to Abeta-mediated amyloid pathology and cognitive dysfunction observed in the AD mouse model. Blockade of RAGE significantly attenuates neuronal and synaptic injury. In this review, we summarize the role of RAGE in the pathogenesis of AD, specifically in Abeta-induced cellular perturbation.

PSAPP mice exhibit regionally selective reductions in gliosis and plaque deposition in response to S100B ablation

BACKGROUND

Numerous studies have reported that increased expression of S100B, an intracellular Ca2+ receptor protein and secreted neuropeptide, exacerbates Alzheimer's disease (AD) pathology. However, the ability of S100B inhibitors to prevent/reverse AD histopathology remains controversial. This study examines the effect of S100B ablation on in vivo plaque load, gliosis and dystrophic neurons.

METHODS

Because S100B-specific inhibitors are not available, genetic ablation was used to inhibit S100B function in the PSAPP AD mouse model. The PSAPP/S100B-/- line was generated by crossing PSAPP double transgenic males with S100B-/- females and maintained as PSAPP/S100B+/- crosses. Congo red staining was used to quantify plaque load, plaque number and plaque size in 6 month old PSAPP and PSAPP/S100B-/- littermates. The microglial marker Iba1 and astrocytic marker glial fibrillary acidic protein (GFAP) were used to quantify gliosis. Dystrophic neurons were detected with the phospho-tau antibody AT8. S100B immunohistochemistry was used to assess the spatial distribution of S100B in the PSAPP line.

RESULTS

PSAPP/S100B-/- mice exhibited a regionally selective decrease in cortical but not hippocampal plaque load when compared to PSAPP littermates. This regionally selective reduction in plaque load was accompanied by decreases in plaque number, GFAP-positive astrocytes, Iba1-positive microglia and phospho-tau positive dystrophic neurons. These effects were not attributable to regional variability in the distribution of S100B. Hippocampal and cortical S100B immunoreactivity in PSAPP mice was associated with plaques and co-localized with astrocytes and microglia.

CONCLUSIONS

Collectively, these data support S100B inhibition as a novel strategy for reducing cortical plaque load, gliosis and neuronal dysfunction in AD and suggest that both extracellular as well as intracellular S100B contribute to AD histopathology.

Gender differences in the long-term effects of chronic prenatal stress on the HPA axis and hypothalamic structure in rats

Stress during pregnancy can impair biological and behavioral responses in the adult offspring and some of these effects are associated with structural changes in specific brain regions. Furthermore, these outcomes can vary according to strain, gender, and type and duration of the maternal stress. Indeed, early stress can induce sexually dimorphic long-term effects on diverse endocrine axes, including subsequent responses to stress. However, whether hypothalamic structural modifications are associated with these endocrine disruptions has not been reported. Thus, we examined the gender differences in the long-term effects of prenatal and adult immobilization stress on the hypothalamic-pituitary-adrenocortical (HPA) axis and the associated changes in hypothalamic structural proteins. Pregnant Wistar rats were subjected to immobilization stress three times daily (45 min each) during the last week of gestation. One half of the offspring were subjected to the same regimen of stress on 10 consecutive days starting at postnatal day (PND) 90. At sacrifice (PND 180), serum corticosterone levels were significantly higher in females compared to males and increased significantly in females subjected to both stresses with no change in males. Prenatal stress increased pituitary ACTH content in males, with no effect in females. Hypothalamic CRH mRNA levels were significantly increased by prenatal stress in females, but decreased in male rats. In females neither stress affected hypothalamic cell death, as determined by cytoplasmic histone-associated DNA fragment levels or proliferation, determined by proliferating cell nuclear antigen levels (PCNA); however, in males there was a significant decrease in cell death in response to prenatal stress and a decrease in PCNA levels with both prenatal and adult stress. In all groups BrdU immunoreactivity colocalized in glial fibrillary acidic protein (GFAP) positive cells, with few BrdU/NeuN labelled cells found. Furthermore, in males the astrocyte marker S100β increased with prenatal stress and decreased with adult stress, suggesting affectation of astrocytes. Synapsin-1 levels were increased by adult stress in females and by prenatal stress in males, while, PSD95 levels were increased in females and decreased in males by both prenatal and adult stress. In conclusion, hypothalamic structural rearrangement appears to be involved in the long-term endocrine outcomes observed after both chronic prenatal and adult stresses. Furthermore, many of these changes are not only different between males and females, but opposite, which could underlie the gender differences in the long-term sequelae of chronic stress, including subsequent responses to stress.

Targeting S100B in Cerebral Ischemia and in Alzheimer's Disease

S100B is an EF-hand calcium-binding protein that exerts both intracellular and extracellular effects on a variety of cellular processes. The protein is predominantly expressed in the central nervous system by astrocytes, both physiologically and during the course of neurological disease. In the healthy adult brain and during development, constitutive S100B expression acts as a trophic factor to drive neurite extension and to referee neuroplasticity. Yet, when induced during central nervous system disease, the protein can take on maladaptive roles and thereby exacerbate brain pathology. Based on genetic and pharmacological lines of evidence, we consider such deleterious roles of S100B in two common brain pathologies: ischemic stroke and Alzheimer's disease (AD). In rodent models of ischemic brain damage, S100B is induced early on during the subacute phase, where it exacerbates gliosis and delayed infarct expansion and thereby worsens functional recovery. In mouse models of AD, S100B drives brain inflammation and gliosis that accelerate cerebral amyloidosis. Pharmacological inhibition of S100B synthesis mitigates hallmark pathologies of both brain diseases, opening the door for translational approaches to treat these devastating neurological disorders.

Effects of S100B on Serotonergic Plasticity and Neuroinflammation in the Hippocampus in Down Syndrome and Alzheimer's Disease: Studies in an S100B Overexpressing Mouse Model

S100B promotes development and maturation in the mammalian brain. However, prolonged or extensive exposure can lead to neurodegeneration. Two important functions of S100B in this regard, are its role in the development and plasticity of the serotonergic neurotransmitter system, and its role in the cascade of glial changes associated with neuroinflammation. Both of these processes are therefore accelerated towards degeneration in disease processes wherein S100B is increased, notably, Alzheimer's disease (AD) and Down syndrome (DS). In order to study the role of S100B in this context, we have examined S100B overexpressing transgenic mice. Similar to AD and DS, the transgenic animals show a profound change in serotonin innervation. By 28 weeks of age, there is a significant loss of terminals in the hippocampus. Similarly, the transgenic animals show neuroinflammatory changes analogous with AD and DS. These include decreased numbers of mature, stable astroglial cells, increased numbers of activated microglial cells and increased microglial expression of the cell surface receptor RAGE. Eventually, the S100B transgenic animals show neurodegeneration and the appearance of hyperphosphorylated tau structures, as seen in late stage DS and AD. The role of S100B in these conditions is discussed.

The S100B/RAGE Axis in Alzheimer's Disease

Increasing evidence suggests that the small EF-hand calcium-binding protein S100B plays an important role in Alzheimer's disease. Among other evidences are the increased levels of both S100B and its receptor, the Receptor for Advanced Glycation Endproducts (RAGEs) in the AD diseased brain. The regulation of RAGE signaling by S100B is complex and probably involves other ligands including the amyloid beta peptide (Aβ), the Advanced Glycation Endproducts (AGEs), or transtheyretin. In this paper we discuss the current literature regarding the role of S100B/RAGE activation in Alzheimer's disease.

Transcritpional effects of S100B on neuroblastoma cells: perturbation of cholesterol homeostasis and interference on the cell cycle

S100B is a Ca2+ binding protein mainly secreted by astrocytes in the vertebrate brain that is considered a multifunctional cytokine and/or a damage-associated molecular pattern (DAMP) protein and a marker of brain injury and neurodegeneration when measured in different body fluids. It has been widely shown that this protein can exert diverse effects in neural cultures depending on its concentration, having detrimental effects at micromolar concentrations. The molecular mechanisms underlying this effect are still largely unknown. This study attempts to delineate the genome-wide gene expression analysis of the events associated with exposure to micromolar concentration of S100B in a human neuroblastoma cell line. In this experimental condition cells undergo a severe perturbation of lipid homeostasis along with cell cycle arrest. These mechanisms might reasonably mediate some aspects of the S100B-related detrimental effects of S100B, although obvious differences between mature neurons and neuroblastoma cells have to be considered.

Protective effects of naloxone in two-hit seizure model

PURPOSE

Early life status epilepticus (SE) could enhance the vulnerability of the immature brain to a second SE in adulthood (two-hit seizure model). Naloxone has been proved to possess inflammation inhibitory effects in nervous system. This study was designed to evaluate the dose-dependent protective effects of naloxone in kainic acid (KA)-induced two-hit seizure model.

METHODS

After KA-induced SE at postnatal day 15 (P15), Sprague-Dawley rats were infused with either saline or different doses (1.92, 3.84, 5.76, and 7.68 mg/kg) of naloxone continuously for 12 h. De novo synthesis of cytokines (interleukin-1 beta [IL-1 beta], S100B) was assessed by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) at 12 h after P15 SE. Glial activation states were analyzed by western blotting of glial markers (glial fibrillary acidic protein [GFAP], S100B, Iba1) both at 12 h after P15 SE and at P45. After a second SE at P45, cognitive deteriorations were evaluated by Morris water tests and neuron injuries were evaluated by TdT-mediated dUTP nick end labeling (TUNEL) assays.

RESULTS

Naloxone reduced IL-1 beta synthesis and microglial activation most potently at a dose of 3.84 mg/kg. Attenuation of S100B synthesis and astrocyte activation were achieved most dramatically by naloxone at a dose of 5.76 mg/kg, which is equal to the most powerful dose in ameliorating cognitive injuries and neuron apoptosis after second SE.

CONCLUSIONS

Naloxone treatment immediately after early life SE could dose-dependently reduce cytokine production, glial activation, and further lower the vulnerability of immature brains to a second hit in adulthood.

S100B's double life: intracellular regulator and extracellular signal

The Ca2+-binding protein of the EF-hand type, S100B, exerts both intracellular and extracellular functions. Recent studies have provided more detailed information concerning the mechanism(s) of action of S100B as an intracellular regulator and an extracellular signal. Indeed, intracellular S100B acts as a stimulator of cell proliferation and migration and an inhibitor of apoptosis and differentiation, which might have important implications during brain, cartilage and skeletal muscle development and repair, activation of astrocytes in the course of brain damage and neurodegenerative processes, and of cardiomyocyte remodeling after infarction, as well as in melanomagenesis and gliomagenesis. As an extracellular factor, S100B engages RAGE (receptor for advanced glycation end products) in a variety of cell types with different outcomes (i.e. beneficial or detrimental, pro-proliferative or pro-differentiative) depending on the concentration attained by the protein, the cell type and the microenvironment. Yet, RAGE might not be the sole S100B receptor, and S100B's ability to engage RAGE might be regulated by its interaction with other extracellular factors. Future studies using S100B transgenic and S100B null mice might shed more light on the functional role(s) of the protein.

The p38alpha mitogen-activated protein kinase as a central nervous system drug discovery target

Protein kinases are critical modulators of a variety of cellular signal transduction pathways, and abnormal phosphorylation events can be a cause or contributor to disease progression in a variety of disorders. This has led to the emergence of protein kinases as an important new class of drug targets for small molecule therapeutics. A serine/threonine protein kinase, p38α mitogen-activated protein kinase (MAPK), is an established therapeutic target for peripheral inflammatory disorders because of its critical role in regulation of proinflammatory cytokine production. There is increasing evidence that p38α MAPK is also an important regulator of proinflammatory cytokine levels in the central nervous system, raising the possibility that the kinase may be a drug discovery target for central nervous system disorders where cytokine overproduction contributes to disease progression. Development of bioavailable, central nervous system-penetrant p38α MAPK inhibitors provides the required foundation for drug discovery campaigns targeting p38α MAPK in neurodegenerative disorders.

Use of copper and insulin-resistance to accelerate cognitive deficits and synaptic protein loss in a rat Abeta-infusion Alzheimer's disease model

The rat amyloid-beta (Abeta) intracerebroventricular infusion can model aspects of Alzheimer's disease (AD) and has predicted efficacy of therapies such as ibuprofen and curcumin in transgenic mouse models. High density lipoprotein (HDL), a normal plasma carrier of Abeta, is used to attenuate Abeta aggregation within the pump, causing Abeta-dependent toxicity and cognitive deficits within 3 months. Our goal was to identify factors that might accelerate onset of Abeta-dependent deficits to improve efficiency and cost-effectiveness of model. We focused on: 1) optimizing HDL-Abeta preparation for maximal toxicity; 2) evaluating the role of copper, a factor typically in water that can impact oligomer stability; and 3) determining impact of insulin resistance (type II diabetes), a risk factor for AD. In vitro studies were performed to determine doses of copper and methods of Abeta-HDL preparation that maximized toxicity. These preparations when infused resulted in earlier onset of cognitive deficits within 6 weeks post-infusion. Induction of insulin resistance did not exacerbate Abeta-dependent cognitive deficits, but did exacerbate synaptic protein loss. In summary, the newly described in vivo infusion model may be useful cost-effective method for screening for new therapeutic drugs for AD.

RAGE signaling contributes to neuroinflammation in infantile neuronal ceroid lipofuscinosis

Palmitoyl-protein thioesterase-1 (PPT1) deficiency causes infantile neuronal ceroid lipofuscinosis (INCL), a devastating childhood neurodegenerative storage disorder. We previously reported that neuronal apoptosis in INCL is mediated by endoplasmic reticulum-stress. ER-stress disrupts Ca(2+)-homeostasis and stimulates the expression of Ca(2+)-binding proteins. We report here that in the PPT1-deficient human and mouse brain the levels of S100B, a Ca(2+)-binding protein, and its receptor, RAGE (receptor for advanced glycation end-products) are elevated. We further demonstrate that activation of RAGE signaling in astroglial cells mediates pro-inflammatory cytokine production, which is inhibited by SiRNA-mediated suppression of RAGE expression. We propose that RAGE signaling contributes to neuroinflammation in INCL.

Blockade of chloride intracellular ion channel 1 stimulates Abeta phagocytosis

In amyloid-beta (Abeta)-stimulated microglial cells, blockade of chloride intracellular ion channel 1 (CLIC1) reverts the increase in tumor necrosis factor-alpha and nitric oxide (NO) production and results in neuroprotection of cocultured neurons. This effect could be of therapeutic efficacy in Alzheimer's disease (AD), where microglial activation may contribute to neurodegeneration, but it could reduce Abeta phagocytosis, which could facilitate amyloid plaque removal. Here, we analyzed the CLIC1 blockade effect on Abeta-stimulated mononuclear phagocytosis. In the microglial cell line BV-2, Abeta25-35 treatment enhanced fluorescent bead phagocytosis, which persisted also in the presence of IAA-94, a CLIC1 channel blocker. The same result was obtained in rat primary microglia and in BV2 cells, where CLIC1 expression had been knocked down with a plasmid producing small interfering RNAs. To address specifically the issue of Abeta phagocytosis, we treated BV-2 cells with biotinylated Abeta1-42 and measured intracellular amyloid by morphometric analysis. IAA-94-treated cells showed an increased Abeta phagocytosis after 24 hr and efficient degradation of ingested material after 72 hr. In addition, we tested Abeta1-42 phagocytosis in adult rat peritoneal macrophages. Also, these cells actively phagocytosed Abeta1-42 in the presence of IAA-94. However, the increased expression of inducible NO synthase (iNOS), stimulated by Abeta, was reverted by IAA-94. In parallel, a decrease in NO release was detected. These results suggest that blockade of CLIC1 stimulates Abeta phagocytosis in mononuclear phagocytes while inhibiting the induction of iNOS and further point to CLIC1 as a possible therapeutic target in AD.

Glia maturation factor modulates beta-amyloid-induced glial activation, inflammatory cytokine/chemokine production and neuronal damage

Glia maturation factor (GMF), discovered and characterized in our laboratory, is a highly conserved protein primarily localized in mammalian central nervous system. Previously we demonstrated that GMF is required in the induced production of proinflammatory cytokines and chemokines in brain cells. We now report that ventricular infusion of human amyloid beta peptide1-42 (Abeta1-42) in mouse brain caused glial activation and large increases in the levels of GMF as well as induction of inflammatory cytokine/chemokine known for launching the neuro inflammatory cascade in Alzheimer's disease (AD). To test the hypothesis that GMF is involved in the pathogenesis of AD, we infused Abeta1-42 in the brain of GMF-deficient (GMF-KO) mice, recently prepared in our laboratory. GMF-deficient mice showed reduced glial activation and significantly suppressed proinflammatory cytokine/chemokine production following Abeta infusion compared to wild type (Wt) mice. The decrease in glial activation in the GMF-KO mice is also associated with significant reduction in Abeta induced loss of pre-synaptic marker, synaptophysin, and post-synaptic density protein-95 (PSD 95). We also examined the potential relationship between GMF or lack of it with learning and memory using the T-maze, Y-maze, and water maze, hippocampal-dependent spatial memory tasks. Our results show that memory retention was improved in GMF-KO mice compared to Wt controls following Abeta infusion. Diminution of these Abeta1-42 effects in primary cultures of GMF-KO astrocyte and microglia were reversed by reconstituted expression of GMF. Taken together, our results indicate a novel mediatory role of GMF in the neuro-inflammatory pathway of Abeta and its pro-inflammatory functions.

Protective action of neuronal nitric oxide synthase inhibitor in the MPTP mouse model of Parkinson's disease

We examined the effects of 7-nitroindazole on the dopaminergic system in mice after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. The mice received four intraperitoneal injections of MPTP (20 mg/kg) at 2 h-intervals. Administration of 7-nitroindazole showed dose-dependent neuroprotective effects against striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) depletion 7 days after MPTP treatment. Behavioral testing showed that MPTP-treated mice exhibited motor deficits in the catalepsy test after 7 days, but 7-nitroindazole prevented the appearance of motor abnormalities in this test. The MPTP-treated mice exhibited the loss of tyrosine hydroxylase-containing dopaminergic neurons in mice after 1, 3 and 7 days, but 7-nitroindazole-treated mice showed a protective effect. GFAP (glial fibrillary acidic protein)-positive astrocytes were accumulated in the striatum 3 and 7 days and in the substantia nigra 1, 3 and 7 days after MPTP treatment. In contrast, 7-nitroindazole prevented a significant increase in the number of GFAP-positive astrocytes in the striatum and substantia nigra after MPTP treatment. The reactive astrocytes in the striatum and substantia nigra after MPTP treatment increased the production of S100beta protein, which is thought to promote neuronal damage, but 7-nitoindazole suppressed the expression of S100 beta protein. Activation of microglia, with an increase in staining intensity and morphological changes, was observed in the striatum and substantia nigra 1 and 3 days after MPTP treatment, but 7-nitroindazole prevented a significant increase in the number of isolectin B(4) positive microglia in the striatum and substantia nigra. On the other hand, nestin-immunoreactive cells were increased significantly in the striatum 3 and 7 days after MPTP treatment. 7-Nitroindazole treatment facilitated nestin expression in the striatum 7 days after MPTP treatment. Thus, nNOS inhibitor 7-nitroindazole protected dopaminergic neurons against MPTP neurotoxicity in mice and ameliorated neurological deficits. The results suggest that the neuroprotection is mediated though the modulation of glial activation, including the inhibition of S100beta synthesis and the prevention of microglial activation. These results suggest the therapeutic strategy targeted to glial modulation with 7-nitoindazole offers a great potential for the development of new neuroprotective therapies for Parkinson's disease.

A novel p38 alpha MAPK inhibitor suppresses brain proinflammatory cytokine up-regulation and attenuates synaptic dysfunction and behavioral deficits in an Alzheimer's disease mouse model

Background

An accumulating body of evidence is consistent with the hypothesis that excessive or prolonged increases in proinflammatory cytokine production by activated glia is a contributor to the progression of pathophysiology that is causally linked to synaptic dysfunction and hippocampal behavior deficits in neurodegenerative diseases such as Alzheimer's disease (AD). This raises the opportunity for the development of new classes of potentially disease-modifying therapeutics. A logical candidate CNS target is p38α MAPK, a well-established drug discovery molecular target for altering proinflammatory cytokine cascades in peripheral tissue disorders. Activated p38 MAPK is seen in human AD brain tissue and in AD-relevant animal models, and cell culture studies strongly implicate p38 MAPK in the increased production of proinflammatory cytokines by glia activated with human amyloid-beta (Aβ) and other disease-relevant stressors. However, the vast majority of small molecule drugs do not have sufficient penetrance of the blood-brain barrier to allow their use as in vivo research tools or as therapeutics for neurodegenerative disorders. The goal of this study was to test the hypothesis that brain p38α MAPK is a potential in vivo target for orally bioavailable, small molecules capable of suppressing excessive cytokine production by activated glia back towards homeostasis, allowing an improvement in neurologic outcomes.

Methods

A novel synthetic small molecule based on a molecular scaffold used previously was designed, synthesized, and subjected to analyses to demonstrate its potential in vivo bioavailability, metabolic stability, safety and brain uptake. Testing for in vivo efficacy used an AD-relevant mouse model.

Results

A novel, CNS-penetrant, non-toxic, orally bioavailable, small molecule inhibitor of p38α MAPK (MW01-2-069A-SRM) was developed. Oral administration of the compound at a low dose (2.5 mg/kg) resulted in attenuation of excessive proinflammatory cytokine production in the hippocampus back towards normal in the animal model. Animals with attenuated cytokine production had reductions in synaptic dysfunction and hippocampus-dependent behavioral deficits.

Conclusion

The p38α MAPK pathway is quantitatively important in the Aβ-induced production of proinflammatory cytokines in hippocampus, and brain p38α MAPK is a viable molecular target for future development of potential disease-modifying therapeutics in AD and related neurodegenerative disorders.

Glial Activation Links Early-Life Seizures and Long-Term Neurologic Dysfunction: Evidence Using a Small Molecule Inhibitor of Proinflammatory Cytokine Upregulation

PURPOSE

Early-life seizures increase vulnerability to subsequent neurologic insult. We tested the hypothesis that early-life seizures increase susceptibility to later neurologic injury by causing chronic glial activation. To determine the mechanisms by which glial activation may modulate neurologic injury, we examined both acute changes in proinflammatory cytokines and long-term changes in astrocyte and microglial activation and astrocyte glutamate transporters in a "two-hit" model of kainic acid (KA)-induced seizures.

METHODS

Postnatal day (P) 15 male rats were administered KA or phosphate buffered saline (PBS). On P45 animals either received a second treatment of KA or PBS. On P55, control (PBS-PBS), early-life seizure (KA-PBS), adult seizure (PBS-KA), and "two-hit" (KA-KA) groups were examined for astrocyte and microglial activation, alteration in glutamate transporters, and expression of the glial protein, clusterin.

RESULTS

P15 seizures resulted in an acute increase in hippocampal levels of IL-1beta and S100B, followed by behavioral impairment and long-term increases in GFAP and S100B. Animals in the "two-hit" group showed greater microglial activation, neurologic injury, and susceptibility to seizures compared to the adult seizure group. Glutamate transporters increased following seizures but did not differ between these two groups. Treatment with Minozac, a small molecule inhibitor of proinflammatory cytokine upregulation, following early-life seizures prevented both the long-term increase in activated glia and the associated behavioral impairment.

CONCLUSIONS

These data suggest that glial activation following early-life seizures results in increased susceptibility to seizures in adulthood, in part through priming microglia and enhanced microglial activation. Glial activation may be a novel therapeutic target in pediatric epilepsy.

Downregulation of an astrocyte-derived inflammatory protein, S100B, reduces vascular inflammatory responses in brains persistently infected with Borna disease virus

Borna disease virus (BDV) is a neurotropic virus that causes a persistent infection in the central nervous system (CNS) of many vertebrate species. Although a severe reactive gliosis is observed in experimentally BDV-infected rat brains, little is known about the glial reactions contributing to the viral persistence and immune modulation in the CNS. In this regard, we examined the expression of an astrocyte-derived factor, S100B, in the brains of Lewis rats persistently infected with BDV. S100B is a Ca(2+)-binding protein produced mainly by astrocytes. A prominent role of this protein appears to be the promotion of vascular inflammatory responses through interaction with the receptor for advanced glycation end products (RAGE). Here we show that the expression of S100B is significantly reduced in BDV-infected brains despite severe astrocytosis with increased glial fibrillary acidic protein immunoreactivity. Interestingly, no upregulation of the expression of S100B, or RAGE, was observed in the persistently infected brains even when incited with several inflammatory stimuli, including lipopolysaccharide. In addition, expression of the vascular cell adhesion molecule 1 (VCAM-1), as well as the infiltration of encephalitogenic T cells, was significantly reduced in persistently infected brains in which an experimental autoimmune encephalomyelitis was induced by immunization with myelin-basic protein. Furthermore, we demonstrated that the continuous activation of S100B in the brain may be necessary for the progression of vascular immune responses in neonatally infected rat brains. Our results suggested that BDV infection may impair astrocyte functions via a downregulation of S100B expression, leading to the maintenance of a persistent infection.

Glia Proinflammatory Cytokine Upregulation as a Therapeutic Target for Neurodegenerative Diseases: Function‐Based and Target‐Based Discovery Approaches

Inflammation is the body's defense mechanism against threats such as bacterial infection, undesirable substances, injury, or illness. The process is complex and involves a variety of specialized cells that mobilize to neutralize and dispose of the injurious material so that the body can heal. In the brain, a similar inflammation process occurs when glia, especially astrocytes and microglia, undergo activation in response to stimuli such as injury, illness, or infection. Like peripheral immune cells, glia in the central nervous system also increase production of inflammatory cytokines and neutralize the threat to the brain. This brain inflammation, or neuroinflammation, is generally beneficial and allows the brain to respond to changes in its environment and dispose of damaged tissue or undesirable substances. Unfortunately, this beneficial process sometimes gets out of balance and the neuroinflammatory process persists, even when the inflammation-provoking stimulus is eliminated. Uncontrolled chronic neuroinflammation is now known to play a key role in the progression of damage in a number of neurodegenerative diseases. Thus, overproduction of proinflammatory cytokines offers a pathophysiology progression mechanism that can be targeted in new therapeutic development for multiple neurodegenerative diseases. We summarize in this chapter the evidence supporting proinflammatory cytokine upregulation as a therapeutic target for neurodegenerative disorders, with a focus on Alzheimer's disease. In addition, we discuss the drug discovery process and two approaches, function-driven and target-based, that show promise for development of neuroinflammation-targeted, disease-modifying therapeutics for multiple neurodegenerative disorders.

Presenilin-dependent ErbB4 nuclear signaling regulates the timing of astrogenesis in the developing brain

Embryonic multipotent neural precursors are exposed to extracellular signals instructing them to adopt different fates, neuronal or glial. However, the mechanisms by which precursors integrate these signals to make timely fate choices remained undefined. Here we show that direct nuclear signaling by a receptor tyrosine kinase inhibits the responses of precursors to astrocyte differentiation factors while maintaining their neurogenic potential. Upon neuregulin-induced activation and presenilin-dependent cleavage of ErbB4, the receptor's intracellular domain forms a complex with TAB2 and the corepressor N-CoR. This complex undergoes nuclear translocation and binds promoters of astrocytic genes, repressing their expression. Consistent with this observation, astrogenesis occurs precociously in ErbB4 knockout mice. Our studies define how presenilin-dependent nuclear signaling by a receptor tyrosine kinase directly regulates gene transcription and cell fate. This pathway could be of importance for neural stem cell biology and for understanding the pathogenesis of Alzheimer's disease.

Inflammation-Like Glial Response in Lead-Exposed Immature Rat Brain

Numerous studies on lead (Pb) neurotoxicity have indicated this metal to be a dangerous toxin, particularly during developmental stages of higher organisms. Astrocytes are responsible for sequestration of this metal in brain tissue. Activation of astroglia may often lead to loss of the buffering function and contribute to pathological processes. This phenomenon is accompanied by death of neuronal cells and may be connected with inflammatory events arising from the production of a wide range of cytokines and chemokines. The effects of prolonged exposure to Pb upon glial activation are examined in immature rats to investigate this potential proinflammatory effect. When analyzed at the protein level, glial activation is observed after Pb exposure, as reflected by the increased level of glial fibrillary acidic protein and S-100beta proteins in all parts of the brain examined. These changes are associated with elevation of proinflammatory cytokines. Production of interleukin (IL)-1beta and tumor necrosis factor-alpha is observed in hippocampus, and production of IL-6 is seen in forebrain. The expression of fractalkine is observed in both hippocampus and forebrain but inconsiderably in the cerebellum. In parallel with cytokine expression, signs of synaptic damage in hippocampus are seen after Pb exposure, as indicated by decreased levels of the axonal markers synapsin I and synaptophysin. Obtained results indicate chronic glial activation with coexisting inflammatory and neurodegenerative features as a new mechanism of Pb neurotoxicity in immature rat brain.

S100B binding to RAGE in microglia stimulates COX-2 expression

Besides exerting regulatory roles within astrocytes, the Ca2+-modulated protein of the EF-hand type S100B is released into the brain extracellular space, thereby affecting astrocytes, neurons, and microglia. However, extracellular effects of S100B vary, depending on the concentration attained and the protein being trophic to neurons up to nanomolar concentrations and causing neuronal apoptosis at micromolar concentrations. Effects of S100B on neurons are transduced by receptor for advanced glycation end products (RAGE). At high concentrations, S100B also up-regulates inducible NO synthase in and stimulates NO release by microglia by synergizing with bacterial endotoxin and IFN-gamma, thereby participating in microglia activation. We show here that S100B up-regulates cyclo-oxygenase-2 expression in microglia in a RAGE-dependent manner in the absence of cofactors through independent stimulation of a Cdc42-Rac1-JNK pathway and a Ras-Rac1-NF-kappaB pathway. Thus, S100B can be viewed as an astrocytic endokine, which might participate in the inflammatory response in the course of brain insults, once liberated into the brain extracellular space.

Human amyloid β-induced neuroinflammation is an early event in neurodegeneration

Using a human amyloid beta (Abeta) intracerebroventricular infusion mouse model of Alzheimer's disease-related injury, we previously demonstrated that systemic administration of a glial activation inhibitor could suppress neuroinflammation, prevent synaptic damage, and attenuate hippocampal-dependent behavioral deficits. We report that Abeta-induced neuroinflammation is an early event associated with onset and progression of pathophysiology, can be suppressed by the glial inhibitor over a range of intervention start times, and is amenable to suppression without inhibiting peripheral tissue inflammatory responses. Specifically, hippocampal neuroinflammation and neurodegeneration occur in close time proximity at 4-6 weeks after the start of infusion. Intraperitoneal administration of inhibitor for 2-week intervals starting at various times after initiation of Abeta infusion suppresses progression of pathophysiology. The glial inhibitor is a selective suppressor of neuroinflammation, in that it does not block peripheral tissue production of proinflammatory cytokines or markers of B- and T-cell activation after a systemic lipopolysaccharide challenge. These results support a causal link between neuroinflammation and neurodegeneration, have important implications for future therapeutic development, and provide insight into the relative time window for targeting neuroinflammation with positive neurological outcomes.

Glia as a therapeutic target: selective suppression of human amyloid-beta-induced upregulation of brain proinflammatory cytokine production attenuates neurodegeneration

A corollary of the neuroinflammation hypothesis is that selective suppression of neurotoxic products produced by excessive glial activation will result in neuroprotection. We report here that daily oral administration to mice of the brain-penetrant compound 4,6-diphenyl-3-(4-(pyrimidin-2-yl)piperazin-1-yl)pyridazine (MW01-5-188WH), a selective inhibitor of proinflammatory cytokine production by activated glia, suppressed the human amyloid-beta (Abeta) 1-42-induced upregulation of interleukin-1beta, tumor necrosis factor-alpha, and S100B in the hippocampus. Suppression of neuroinflammation was accompanied by restoration of hippocampal synaptic dysfunction markers synaptophysin and postsynaptic density-95 back toward control levels. Consistent with the neuropathophysiological improvements, MW01-5-188WH therapy attenuated deficits in Y maze behavior, a hippocampal-linked task. Oral MW01-5-188WH therapy begun 3 weeks after initiation of intracerebroventricular infusion of human Abeta decreased the numbers of activated astrocytes and microglia and the cytokine levels in the hippocampus without modifying amyloid plaque burden or altering peripheral tissue cytokine upregulation in response to an in vivo inflammatory challenge. The results provide a novel integrative chemical biology proof in support of the neuroinflammation hypothesis of disease progression, demonstrate that neurodegeneration can be attenuated independently of plaque modulation by targeting innate brain proinflammatory cytokine responses, and indicate the feasibility of developing efficacious, safe, and selective therapies for neurodegenerative disorders by targeting key glial activation pathways.

Active secretion of S100B from astrocytes during metabolic stress

In patients suffering from cerebrovascular diseases and traumatic brain damage, increases in serum levels of protein S100B are positively correlated with the severity of the insult. Since high concentrations of S100B have been shown to exert neurotoxic effects, the objective of this study was to characterize the regulatory mechanisms underlying control of S100B release from astrocytes. To that end, we analyzed the kinetics and amount of S100B release in correlation with regulation of S100B gene expression in an in vitro ischemia model. Astrocyte cultures were treated with combined oxygen, serum and glucose deprivation, serum and glucose deprivation or hypoxia alone for 6, 12 and 24 h, respectively. While oxygen, serum and glucose deprivation triggered the most rapid release of S100B, serum and glucose deprivation provoked comparable levels of released S100B at the later time points. In contrast to oxygen, serum and glucose deprivation and serum and glucose deprivation, hypoxia alone elicited only marginal increases in secreted S100B. Parallel analysis of extracellular lactate dehydrogenase and the number of viable cells revealed only moderate cell death in the cultures, indicating that S100B was actively secreted during in vitro ischemia. Interestingly, S100B mRNA expression was potently downregulated after 12 and 24 h of oxygen, serum and glucose deprivation, and prolonged oxygen, serum and glucose deprivation for 48 h was associated with a significant reduction of S100B release at later time intervals, whereas lactate dehydrogenase levels remained constant. Our data suggest that secretion of S100B during the glial response to metabolic injury is an early and active process.

Interleukin 1 receptor antagonist knockout mice show enhanced microglial activation and neuronal damage induced by intracerebroventricular infusion of human beta-amyloid

Background

Interleukin 1 (IL-1) is a key mediator of immune responses in health and disease. Although classically the function of IL-1 has been studied in the systemic immune system, research in the past decade has revealed analogous roles in the CNS where the cytokine can contribute to the neuroinflammation and neuropathology seen in a number of neurodegenerative diseases. In Alzheimer's disease (AD), for example, pre-clinical and clinical studies have implicated IL-1 in the progression of a pathologic, glia-mediated pro-inflammatory state in the CNS. The glia-driven neuroinflammation can lead to neuronal damage, which, in turn, stimulates further glia activation, potentially propagating a detrimental cycle that contributes to progression of pathology. A prediction of this neuroinflammation hypothesis is that increased IL-1 signaling in vivo would correlate with increased severity of AD-relevant neuroinflammation and neuronal damage.

Methods

To test the hypothesis that increased IL-1 signaling predisposes animals to beta-amyloid (Aβ)-induced damage, we used IL-1 receptor antagonist Knock-Out (IL1raKO) and wild-type (WT) littermate mice in a model that involves intracerebroventricular infusion of human oligomeric Aβ1–42. This model mimics many features of AD, including robust neuroinflammation, Aβ plaques, synaptic damage and neuronal loss in the hippocampus. IL1raKO and WT mice were infused with Aβ for 28 days, sacrificed at 42 days, and hippocampal endpoints analyzed.

Results

IL1raKO mice showed increased vulnerability to Aβ-induced neuropathology relative to their WT counterparts. Specifically, IL1raKO mice exhibited increased mortality, enhanced microglial activation and neuroinflammation, and more pronounced loss of synaptic markers. Interestingly, Aβ-induced astrocyte responses were not significantly different between WT and IL1raKO mice, suggesting that enhanced IL-1 signaling predominately affects microglia.

Conclusion

Our data are consistent with the neuroinflammation hypothesis whereby increased IL-1 signaling in AD enhances glia activation and leads to an augmented neuroinflammatory process that increases the severity of neuropathologic sequelae.