Exercise-induced re-programming of age-related metabolic changes in microglia is accompanied by a reduction in senescent cells.

Microglial activation and neuroinflammatory changes are characteristic of the aged brain and contribute to age-related cognitive impairment. Exercise improves cognitive function in aged animals, perhaps because of a modulatory effect on microglial activation. Recent evidence indicates that inflammatory microglia are glycolytic, driven by an increase in 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), an enzyme that is described as the master regulator of glycolysis. Here we investigated whether microglia from aged animals exhibited a glycolytic signature and whether exercise exerted a modulatory effect on this metabolic profile. Young (4 month-old) and aged (18 month-old) mice were trained for 10 days on a treadmill. One day before sacrifice, animals were assessed in the novel object recognition and the object displacement tests. Animals were sacrificed after the last bout of exercise, microglial cells were isolated, cultured for 5 days and assessed for metabolic profile. Performance in both behavioural tests was impaired in sedentary aged animals and exercise attenuated this age-related effect. A significant increase in glycolysis, glycolytic capacity and PFKFB3 was observed in microglia from aged animals and exercise ameliorated these effects, while it also increased the phagocytic capacity of cells. The senescent markers, ß-galactosidase and p16INK4A, were increased in microglia from sedentary aged mice, and expression of these markers was significantly decreased by exercise. The data demonstrate that the exercise-related improved cognition is orchestrated by a normalization of the metabolic profile and functionality of microglia.

Lung CD4 Tissue-Resident Memory T Cells Mediate Adaptive Immunity Induced by Previous Infection of Mice with Bordetella pertussis.

Th1 and Th17 cells have an established role in protective immunity to Bordetella pertussis, but this evidence is based largely on peripheral T cells. There is emerging evidence that local tissue-resident memory T (TRM) cells that accumulate in tissue following mucosal infection may be crucial for long-term immunity. In this study, we examined the role of respiratory CD4 TRM cells in immunity to B. pertussis Natural immunity to B. pertussis induced by infection is considered long lasting and effective at preventing reinfection. Consistent with this, we found that convalescent mice rapidly cleared the bacteria after reinfection. Furthermore, CD4 T cells with a TRM cell phenotype (CD44+CD62L-CD69+ or CD44+CD62L-CD69+CD103+) accumulated in the lungs of mice during infection with B. pertussis and significantly expanded through local proliferation following reinfection. These CD4 TRM cells were B. pertussis specific and secreted IL-17 or IL-17 and IFN-γ. Treatment of mice with FTY720, which prevented migration of T and B cells from lymph nodes to the circulation, significantly exacerbated B. pertussis infection. This was associated with significantly reduced infiltration of central memory T cells and B cells into the lungs. However, the local expansion of TRM cells and the associated rapid clearance of the secondary infection were not affected by treatment with FTY720 before rechallenge. Moreover, adoptive transfer of lung CD4 TRM cells conferred protection in naive mice. Our findings reveal that Ag-specific CD4 TRM cells play a critical role in adaptive immunity against reinfection and memory induced by natural infection with B. pertussis.

Anti-TLR2 antibody triggers oxidative phosphorylation in microglia and increases phagocytosis of ß-amyloid.

BACKGROUND: Microglia are multifunctional cells that are primarily neuroprotective and a deficit in their functional integrity is likely to be a contributory factor in the deteriorating neuronal function that occurs with age and neurodegeneration. One aspect of microglial dysfunction is reduced phagocytosis, and this is believed to contribute to the accumulation of amyloid-ß (Aß) in Alzheimer's disease (AD). Therefore, improving phagocytosis should be beneficial in limiting the amyloidosis that characterises AD. METHODS: Here, we investigated whether an antibody that targets toll-like receptor (TLR)2 might attenuate the inflammatory and metabolic changes induced by lipopolysaccharide (LPS) and amyloid-ß. The impact on phagocytosis was assessed by immunohistochemistry. We evaluated the metabolic changes with the SeaHorse Extracellular Flux Analyser and studied the expression of key enzymes driving glycolysis by western blotting. For all experiments, statistical significance was determined by unpaired Student's t test and two-way analysis of variance (ANOVA). RESULTS: We have reported that, when exposed to an inflammatory stimulus, microglia switch their metabolism towards the metabolically- inefficient glycolysis; this potentially impacts on metabolically demanding functions like phagocytosis. Anti-TLR2 antibody increased phagocytosis of Aß in LPS + Aß-stimulated microglia and this was linked with the ability of the antibody to attenuate the LPS + Aß-triggered inflammasome activation. LPS + Aß increased glycolysis in microglia and increased the expression of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)3, an enzyme that plays a key role in driving glycolysis; these effects were inhibited when cells were incubated with the anti-TLR2 antibody. The data also show that antibody treatment increased oxidative metabolism. CONCLUSIONS: Thus, microglia with an inflammatory phenotype, specifically cells in which the inflammasome is activated, are glycolytic; this may compromise the metabolic efficiency of microglia and thereby provide an explanation for the reduced phagocytic function of the cells. We propose that, by restoring oxidative metabolism and reducing inflammasome activation in microglia, phagocytic function is also restored.

Targeting innate immunity for neurodegenerative disorders of the central nervous system.

Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview of physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia and astrocyte cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article. Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer's disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview on physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article.

Inhibiting TLR2 activation attenuates amyloid accumulation and glial activation in a mouse model of Alzheimer's disease.

The effects of Toll-like receptor (TLR) activation in peripheral cells are well characterized but, although several TLRs are expressed on cells of the brain, the consequences of their activation on neuronal function remain to be fully investigated, particularly in the context of assessing their potential as therapeutic targets in neurodegenerative diseases. Several endogenous TLR ligands have been identified, many of which are soluble factors released from cells exposed to stressors. In addition, amyloid-ß (Aß) the main constituent of the amyloid plaques in Alzheimer's disease (AD), activates TLR2, although it has also been shown to bind to several other receptors. The objective of this study was to determine whether activation of TLR2 played a role in the developing inflammatory changes and Aß accumulation in a mouse model of AD. Wild type and transgenic mice that overexpress amyloid precursor protein and presenilin 1 (APP/PS1 mice) were treated with anti-TLR2 antibody for 7months from the age of 7-14months. We demonstrate that microglial and astroglial activation, as assessed by MHCII, CD68 and GFAP immunoreactivity was decreased in anti-TLR2 antibody-treated compared with control (IgG)-treated mice. This was associated with reduced Aß plaque burden and improved performance in spatial learning. The data suggest that continued TLR2 activation contributes to the developing neuroinflammation and pathology and may be provide a strategy for limiting the progression of AD.

Involvement of IGF-1 and Akt in M1/M2 activation state in bone marrow-derived macrophages.

Macrophages can be polarised to adopt the M1 or M2 phenotype and functional outcomes of activation include altered secretion of immune molecules such as insulin-like growth factor (IGF)-1 as well as upregulation of cell surface molecules specifically associated with each state. Interleukin (IL)-4 mediates its effects through two receptors, the type I and II receptors and activation of these receptors results in phosphorylation of signal transducers and activators of transcription (STAT)6. JAK3 is activated as a consequence of ligation of the type I IL-4R, which participates in Akt activation. We set out to investigate the impact of perturbation of IGF-1 tone on IL-4- and interferon (IFN)γ-induced activation, the mechanisms by which this may occur and the contribution of type I IL-4R activation to adoption of the M2 state. The data presented here indicate that IL-4-induced activation of Akt is JAK3-dependent, enhanced by release of IGF-1 and necessary for full adoption of the M2 phenotype, since blocking IGF-1 activity blunts the ability of IL-4 to induce activation of Akt and to upregulate expression of some M2-associated molecules. In addition, differential control of the expression of mannose receptor (MRC1), arginase-1 (Arg-1), chitinase-3 like 3 (Chi3l3) and found in inflammatory zone 1 (FIZZ1) was observed. The IFNγ-induced decrease in IGF-1 was exacerbated by inhibition of phosphatidylinositol-3 (PI3) kinase, indicating that Akt may regulate its own activation via IGF-1. Overall, a deficit in IGF-1/Akt signalling is associated with decreased capacity to induce the M2 state and an increased responsiveness to IFNγ.

Innate IFN-γ promotes development of experimental autoimmune encephalomyelitis: a role for NK cells and M1 macrophages.

The role of IFN-γ in the pathogenesis of autoimmune diseases is controversial. Although Th1 cells can induce experimental autoimmune encephalomyelitis (EAE), IFN-γ can suppress Th17 cells that are pathogenic in EAE. Here we show that NK cells provide an early source of IFN-γ during development of EAE. Depletion of NK cells or neutralization of IFN-γ delayed the onset of EAE and was associated with reduced infiltration of IL-17(+) and GM-CSF(+) T cells into the CNS. In the passive transfer model, immune cells from myelin oligodendrocyte glycoprotein (MOG)-immunized IFN-γ(-/-) mice failed to induce EAE, despite producing IL-17 and GM-CSF. The macrophages expressed markers of M2 activation and the T cells had low very late antigen-4 (VLA-4) expression and failed to infiltrate the CNS. Addition of recombinant IFN-γ to immune cells from the IFN-γ(-/-) mice activated M1 macrophages and restored VLA-4 expression, migratory, and encephalitogenic activity of T cells. Furthermore, treatment of recipient mice with anti-VLA-4 neutralizing antibody abrogated EAE induced by transfer of T cells from WT mice. Our findings demonstrate IFN-γ-producing T cells are not required for development of EAE, but NK cell-derived IFN-γ has a key role in promoting M1 macrophage expansion and VLA-4-mediated migration of encephalitogenic T cells into the CNS.

Bone marrow-derived macrophages from aged rats are more responsive to inflammatory stimuli.

BACKGROUND: Lipopolysaccharide (LPS) and interferon-γ (IFNγ) increase expression of tumour necrosis factor-α (TNFα) that characterizes the M1 activation state of macrophages. Whereas it is accepted that the immune system undergoes changes with age, there is inconsistency in the literature with respect to the impact of age on the response of macrophages to inflammatory stimuli. Here, we investigate the effect of age on the responsiveness of bone marrow-derived macrophages (BMDMs) to LPS and IFNγ. The context for addressing this question is that macrophages, which infiltrate the brain of aged animals, will encounter the neuroinflammatory environment that has been described with age. METHODS: Brain tissue, prepared from young and aged rats, was assessed for expression of inflammatory markers by PCR and for evidence of infiltration of macrophages by flow cytometry. BMDMs were prepared from the long bones of young and aged rats, maintained in culture for 8 days and incubated in the presence or absence of LPS (100 ng/ml) or IFNγ (50 ng/ml). Cells were harvested and assessed for mRNA expression of markers of M1 activation including TNFα and NOS2, or for expression of IFNγR1 and TLR4 by western immunoblotting. To assess whether BMDMs induced glial activation, mixed glial cultures were incubated in the presence of conditioned media obtained from unstimulated BMDMs of young and aged rats and evaluated for expression of inflammatory markers. RESULTS: Markers associated with M1 activation were expressed to a greater extent in BMDMs from aged rats in response to LPS and IFNγ, compared with cells from young rats. The increased responsiveness was associated with increases in IFNγ receptor (IFNγR) and Toll-like receptor 4 (TLR4). The data show that conditioned media from BMDMs of aged rats increased the expression of pro-inflammatory mediators in glial cells. Significantly, there was an age-related increase in macrophage infiltration into the brain, and this was combined with increased expression of IFNγ and the Toll-like receptor 4 agonist, high-mobility group protein B1 (HMGB1). CONCLUSION: Exposure of infiltrating macrophages to the inflammatory microenvironment that develops in the brain with age is likely to contribute to a damaging cascade that negatively impacts neuronal function.

α-TLR2 antibody attenuates the Aß-mediated inflammatory response in microglia through enhanced expression of SIGIRR.

The immunoregulatory function of single-Ig-interleukin-1 related receptor (SIGIRR) is derived from its ability to constrain the inflammatory consequences of interleukin (IL)-1R and toll-like receptor (TLR)4 activation. This role extends to the brain, where SIGIRR deficiency increases the synaptic and cognitive dysfunction associated with IL-1R- and TLR4-mediated signalling. The current study set out to investigate the interaction between SIGIRR and TLR2 in brain tissue and the data demonstrate that the response to the TLR2 agonist, Pam3CysSK4 (Pam3Cys4), is enhanced in glial cells from SIGIRR(-/-) animals. Consistent with the view that ß-amyloid peptide (Aß) signals through activation of TLR2, the data also show that Aß-induced changes are exaggerated in glia from SIGIRR(-/-) animals. We report that microglia, rather than astrocytes, are the primary glial cell expressing both TLR2 and SIGIRR. While Aß increased TLR2 expression, it decreased SIGIRR expression in microglia. This was mimicked by direct activation of TLR2 with Pam3Cys4. We investigated the effect of an anti-TLR2 antibody (αTLR2) on the Aß-induced inflammatory responses and demonstrate that it prevented the expression and release of the pro-inflammatory cytokines TNFα and IL-6 from microglia. In addition, application of αTLR2 alleviated the Aß-mediated impairment in long-term potentiation (LTP) of hippocampal synaptic activity. The protective effects of αTLR2 were accompanied by an up-regulation in SIGIRR expression. We propose that a mechanism involving activation of PI3 kinase/Akt and the transcription factor peroxisome proliferator-activated receptor (PPAR)γ may facilitate this increase in SIGIRR. These findings highlight a novel role of SIGIRR as a negative regulator of TLR2-mediated inflammation in the brain.

IFN-γ Production by amyloid ß-specific Th1 cells promotes microglial activation and increases plaque burden in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the presence of amyloid-ß (Aß)-containing plaques, neurofibrillary tangles, and neuronal loss in the brain. Inflammatory changes, typified by activated microglia, particularly adjacent to Aß plaques, are also a characteristic of the disease, but it is unclear whether these contribute to the pathogenesis of AD or are a consequence of the progressive neurodegenerative processes. Furthermore, the factors that drive the inflammation and neurodegeneration remain poorly understood. CNS-infiltrating T cells play a pivotal role in the pathogenesis of multiple sclerosis, but their role in the progression of AD is still unclear. In this study, we examined the role of Aß-specific T cells on Aß accumulation in transgenic mice that overexpress amyloid precursor protein and presenilin 1 (APP/PS1). We found significant infiltration of T cells in the brains of APP/PS1 mice, and a proportion of these cells secreted IFN-γ or IL-17. Aß-specific CD4 T cells generated by immunization with Aß and a TLR agonist and polarized in vitro to Th1-, Th2-, or IL-17-producing CD4(+) T cells, were adoptively transferred to APP/PS1 mice at 6 to 7 mo of age. Assessment of animals 5 wk later revealed that Th1 cells, but not Th2 or IL-17-producing CD4(+) T cells, increased microglial activation and Aß deposition, and that these changes were associated with impaired cognitive function. The effects of Th1 cells were attenuated by treatment of the APP/PS1 mice with an anti-IFN-γ Ab. Our study suggests that release of IFN-γ from infiltrating Th1 cells significantly accelerates markers of diseases in an animal model of AD.

The impact of neuroimmune changes on development of amyloid pathology; relevance to Alzheimer's disease.

Neuroinflammatory changes are a characteristic of several, if not all, neurodegenerative diseases including Alzheimer's disease and are typified by increased microglial activation. Microglia express several receptors making them highly reactive and plastic cells, and, at least in vitro, they adopt different phenotypes in a manner analogous to their peripheral counterparts, macrophages. Microglia also express numerous cell surface proteins enabling them to interact with cells and the evidence indicates that maintenance of microglia in a quiescent state relies, at least to some extent, on an interaction with neurons by means of specific ligand-receptor pairs, for example CD200-CD200R. It is clear that microglia also interact with T cells and recent evidence indicates that co-incubation of microglia with T helper type 1 cells markedly increases their activation. Under normal conditions, small numbers of activated T cells gain entry to the brain and are involved in immune surveillance but infiltration of significant numbers of T cells occurs in disease and following injury. The consequences of T cell infiltration appear to depend on the conditions, with descriptions of both neurodestructive and neuroprotective effects in animal models of different diseases. This review will discuss the modulatory effect of T cells on microglia and the impact of infiltration of T cells into the brain with a focus on Alzheimer's disease, and will propose that infiltration of interferon-γ-producing cells may be an important factor in triggering inflammation that is pathogenic and destructive.

Differential role of Dok1 and Dok2 in TLR2-induced inflammatory signaling in glia.

Accumulating evidence continues to underpin the role of the innate immune system in pathologies associated with neuroinflammation. Innate immunity is regulated by pattern recognition receptors that detect pathogens, and in the case of Gram-positive bacteria, binding of bacterial lipopeptides to toll-like receptor (TLR)2 is emerging as an important mechanism controlling glial cell activation. In the present study, we employed the use of the synthetic bacterial lipoprotein and a selective TLR2 agonist, Pam3CSK4, to induce inflammatory signaling in microglia and astrocytes. The adaptor proteins, downstream of kinase (Dok)1 and Dok2, are known to have a role in negatively regulating the Ras-ERK signaling cascade, with downstream consequences on pro-inflammatory cytokine expression. Data presented herein demonstrate that TLR2 enhanced the tyrosine phosphorylation of Dok1 and Dok2 in astrocytes and microglia, and that knockdown of these adaptors using small interfering RNA robustly elevated TLR2-induced ERK activation. Importantly, TLR2-induced NF-κB activation, and IL-6 production was exacerbated in astrocytes transfected with Dok1 and Dok2 siRNA, indicating that both Dok proteins negatively regulate TLR2-induced inflammatory signaling in astrocytes. In contrast, Dok1 knockdown attenuated TLR2-induced NF-κB activation and IL-6 production in microglia, while Dok2 siRNA failed to affect TLR2-induced NF-κB activity and subsequent cytokine expression in this cell type. Overall, this indicates that Dok1 and Dok2 are novel adaptors for TLR2 in glial cells and importantly indicates that Dok1 and Dok2 differentially regulate TLR2-induced pro-inflammatory signaling in astrocytes and microglia.

A case for seeking sex-specific treatments in Alzheimer's disease.

There is no satisfactory explanation for the sex-related differences in the incidence of many diseases and this is also true of Alzheimer's disease (AD), where females have a higher lifetime risk of developing the disease and make up about two thirds of the AD patient population. The importance of understanding the cause(s) that account for this disproportionate distribution cannot be overestimated, and is likely to be a significant factor in the search for therapeutic strategies that will combat the disease and, furthermore, potentially point to a sex-targeted approach to treatment. This review considers the literature in the context of what is known about the impact of sex on processes targeted by drugs that are in clinical trial for AD, and existing knowledge on differing responses of males and females to these drugs. Current knowledge strongly supports the view that trials should make assessing sex-related difference in responses a priority with a focus on exploring the sex-stratified treatments.

Toll-like receptor 3 activation modulates hippocampal network excitability, via glial production of interferon-ß.

The family of toll-like receptors (TLR) plays a major role in innate immunity due to their pathogen-recognition abilities. TLR3 is a sensor for double-stranded RNA, and regulates host-defense responses to several viruses, via the production of type I interferons. Interferon-ß (IFNß) is a primary product of TLR3 activation, and its transcription is elevated in the CNS response to the synthetic TLR3 ligand, polyinosinic-polycytidylic acid (poly(I:C)). Peripheral infections, along with TLR-induced inflammatory mediators, are known to have detrimental effects on brain function, exerting a negative impact on cognition and enhancing seizure susceptibility. In this study, we assessed hippocampal function in vitro, in response to systemic delivery of a TLR3 agonist. Unlike agonists of other TLRs, intraperitoneal injection of poly(I:C) did not adversely affect evoked short- and long-term synaptic plasticity in mouse hippocampal slices. However, sustained and interictal-like spontaneous activity was observed in CA1 pyramidal cells in response to poly(I:C) and this was associated with alterations in the expression of phosphorylated NR2B subunit-containing NMDA receptors and an astrocyte-specific glutamate/aspartate transporter (GLAST) which impact on extracellular glutamate concentration and contribute to the genesis of epileptiform activity. We provide evidence for the production of IFNß from microglia and astrocytes, and using mice deficient in the type I IFN receptor α 1 (IFNAR1), demonstrate that its subsequent activation is likely to underlie the TLR3-mediated modulation of hippocampal excitability.

Ischemic brain injury: a consortium analysis of key factors involved in mesenchymal stem cell-mediated inflammatory reduction.

Increasing global birth rate, coupled with the aging population surviving into their eighth decade has lead to increased incidence diseases, hitherto designated as rare. Brain related ischemia, at birth, or later in life, during, for example stroke, is increasing in global prevalence. Reactive microglia can contribute to neuronal damage as well as compromising transplantion. One potential treatment strategy is cellular therapy, using mesenchymal stem cells (hMSCs), which possess immunomodulatory and cell repair properties. For effective clinical therapy, mechanisms of action must be understood better. Here multicentre international laboratories assessed this question together investigating application of hMSCs neural involvement, with interest in the role of reactive microglia. Modulation by hMSCs in our in vivo and in vitro study shows they decrease markers of microglial activation (lower ED1 and Iba) and astrogliosis (lower GFAP) following transplantation in an ouabain-induced brain ischemia rat model and in organotypic hippocampal cultures. The anti-inflammatory effect in vitro was demonstrated to be CD200 ligand dependent with ligand expression shown to be increased by IL-4 stimulation. hMSC transplant reduced rat microglial STAT3 gene expression and reduced activation of Y705 phosphorylated STAT3, but STAT3 in the hMSCs themselves was elevated upon grafting. Surprisingly, activity was dependent on heterodimerisation with STAT1 activated by IL-4 and Oncostatin M. Our study paves the way to preclinical stages of a clinical trial with hMSC, and suggests a non-canonical JAK-STAT signaling of unphosphorylated STAT3 in immunomodulatory effects of hMSCs.

Classical activation of microglia in CD200-deficient mice is a consequence of blood brain barrier permeability and infiltration of peripheral cells.

The interaction between CD200, expressed on several cell types, and its receptor CD200R, expressed on cells of the myeloid lineage, has been shown to be an important factor in modulating inflammation in macrophage function in several conditions including colitis and arthritis. More recently its modulatory effect on microglial activation has been identified and CD200-deficiency has been associated with increased microglial activation accompanied by increased production of inflammatory cytokines. The response of glia prepared from CD200-deficient mice to stimuli like lipopolysaccharide (LPS) is markedly greater than the response of cells prepared from wildtype mice and, consistent with this, is the recent observation that expression of Toll-like receptor (TLR)4 and signalling through NFκB are increased in microglia prepared from CD200-deficient mice. Here we show that glia from CD200-deficient mice are also more responsive to interferon-γ (IFNγ) which triggers classical activation of microglia. We investigated the effects of CD200-deficiency in vivo and report that there is an increase in expression of several markers of microglial activation including tumor necrosis factor (TNF)-α, which is a hallmark of classically-activated microglia. These changes are accompanied by increased IFNγ, and the evidence suggests that this is produced by infiltrating cells including T cells and macrophages. We propose that these cells enter the brain as a consequence of increased blood brain barrier (BBB) permeability in CD200-deficient mice and that infiltration is assisted by increased expression of the chemokines, monocyte chemotactic protein-1 (MCP-1), IFNγ-induced protein-10 (IP-10) and RANTES. This may have implications in neurodegenerative diseases where BBB permeability is compromised.

The age-related gliosis and accompanying deficit in spatial learning are unaffected by dimebon.

A non-selective antihistamine, dimebon, has recently emerged as a potential treatment for Alzheimer's disease and Huntington's disease. Dimebon exerts several effects in addition to its anti-histaminergic effect, and of particular interest is its ability to enhance cognitive function in several models. The mechanism underlying this is unknown though it has been suggested that it may be associated with its anti-cholinergic action. Dimebon has also been reported to be neuroprotective, perhaps as a result of its ability to stabilize mitochondria. We considered that these effects might impact on the well-described age-related impairment in spatial learning and therefore examined the effect of repeated administration of dimebon on performance of young and aged animals in the Morris water maze. Whereas a clear age-related deficit was observed, dimebon failed to exert any effect on performance. Similarly, dimebon exerted no effect on the age-related increase in hippocampal expression of several markers of microglial and astroglial activation. We conclude that, despite its cognitive enhancing effects in some models, dimebon failed to modulate the deficit in spatial learning in aged rats and the evidence suggests that the drug does not possess anti-inflammatory properties.

An NCAM mimetic, FGL, alters hippocampal cellular morphometry in young adult (4 month-old) rats.

The neural cell adhesion molecule, NCAM, is ubiquitously expressed within the CNS and has roles in development, cognition, neural plasticity and regulation of the immune system. NCAM is thus potentially an important pharmacological target for treatment of brain diseases. A cell adhesion mimetic FGL, a 15 amino-acid peptide derived from the second fibronectin type-III module of NCAM, has been shown to act as a neuroprotective agent in experimental disease and ageing models, restoring hippocampal/cognitive function and markedly alleviating deleterious changes in the CNS. However, the effects of FGL on the hippocampus of young healthy rats are unknown. The present study has examined the cellular neurobiological consequences of subcutaneous injections of FGL, on hippocampal cell morphometry in young (4 month-old) rats. We determined the effects of FGL on hippocampal volume, pyramidal neuron number/density (using unbiased quantitative stereology), and examined aspects of neurogenesis (using 2D morphometric analyses). FGL treatment reduced total volume of the dorsal hippocampus (associated with a decrease in total pyramidal neuron numbers in CA1 and CA3), and elevated the number of doublecortin immunolabeled neurons in the dentate gyrus, indicating a likely influence on neurogenesis in young healthy rats. These data indicate that FGL has a specific age dependent effect on the hippocampus, differing according to the development and maturity of the CNS.

Acute Stress, Induced by IFNγ + Aß, and Chronic Stress, Induced by Age, Affect Microglia in a Sex-Specific Manner.

Microglial phenotype changes in the aged brain, and also in neurodegenerative diseases, and it is generally accepted that these changes at least contribute to the inflammation that can have detrimental effects on brain health. Accumulating data have determined that there are multiple microglial activation states with consistent findings indicating that with stressors including age, a switch towards an inflammatory phenotype occurs. Among the changes that accompany this is a change in metabolism, whereby glycolysis is increased in microglia. Here, we asked whether sex impacted on the response of microglia to two stressors, interferon-γ + amyloid-ß (IFNγ + Aß) and age. The data show that IFNγ + Aß triggered cells from female mice to adopt a glycolytic phenotype. Metabolism was also altered with age; microglia from aged male mice responded by increasing oxidative phosphorylation, and microglial motility was preserved, contrasting with microglia from female mice where motility was compromised. We conclude that sex is a significant variable in the responses of microglia to stressors.

Interleukin-1alpha and HMGB1 mediate hippocampal dysfunction in SIGIRR-deficient mice.

Single-Ig-interleukin-1 related receptor (SIGIRR) is a member of the interleukin (IL)-1/Toll-like receptor (TLR) family. It negatively regulates inflammation, rendering SIGIRR(-/-) mice more susceptible to inflammatory challenge. This susceptibility extends to the brain, where increased responsiveness to lipopolysaccharide has been observed in SIGIRR-deficient mice. While this is likely due to enhanced TLR4-mediated signaling, the functional consequences of these changes have not yet been described. In the current study, we have investigated the impact of SIGIRR deficiency on hippocampal function, and show that novel object recognition, spatial reference memory, and long-term potentiation (LTP) were impaired in SIGIRR(-/-) mice. These changes were accompanied by increased expression of IL-1RI and TLR4, and upregulation of their downstream signaling events, namely IRAK1 (IL-1R-associated kinase 1), c-Jun N-terminal protein kinase (JNK), and nuclear factor κB (NF-κB). The deficit in LTP was attenuated by the endogenous IL-1 receptor antagonist (IL-1ra) and an anti-TLR4 antibody, and also by inhibition of JNK and NF-κB. We propose that IL-1RI is activated by IL-1α and TLR4 is activated by the endogenous agonist, high mobility group box 1 (HMGB1), as we identified enhanced expression of both cytokines in the hippocampus of SIGIRR(-/-) mice. Additionally, application of HMGB1 increased the activation of JNK and NF-κB and was found to be detrimental to LTP in a TLR4-dependent manner. These findings highlight the functional role of SIGIRR in regulating inflammatory-mediated synaptic and cognitive decline, and describe evidence of the key role of HMGB1 in this process.