Long-term estrogen therapy worsens the behavioral and neuropathological consequences of chronic brain inflammation

Alzheimer's disease (AD) is accompanied by chronic neuroinflammation and occurs with greater incidence in postmenopausal women. The increased incidence may be delayed by estrogen replacement therapy (ERT). The authors investigated the interaction of chronic ERT and lipopolysaccharide (LPS)-induced neuroinflammation in the female rat. Ovariectomy did not impair water maze performance; however, addition of chronic ERT or neuroinflammation resulted in an impairment that became exacerbated by the simultaneous occurrence of both conditions. Chronic LPS activated microglia, which was not reduced by ERT. Intact females receiving LPS infusion were not impaired in the water maze and had significantly fewer activated microglia. Results suggest that chronic ERT in postmenopausal women may exacerbate the memory impairment induced by the chronic neuroinflammation associated with AD.     

The presence of the APP(swe) mutation in mice does not increase the vulnerability of cholinergic basal forebrain neurons to neuroinflammation

Neuroinflammation, and elevated levels of inflammatory proteins, such as tumor necrosis factor-alpha, and the deposition of beta-amyloid may interact to contribute to the pathogenesis of Alzheimer's disease. We reproduced a component of the neuroinflammatory state within the basal forebrain cholinergic system, a region that is vulnerable to degeneration in Alzheimer's disease, of transgenic Tg2576 mice that express the Swedish double mutation of the human amyloid precursor protein (APPswe). We have previously shown that basal forebrain cholinergic neurons are selectively vulnerable to the consequences of neuroinflammation. In the current study, tumor necrosis factor-alpha was infused into the basal forebrain region of APPswe and nontransgenic control mice for 20 days with the expectation that the presence of the transgene would enhance the loss of cholinergic neurons. Chronic infusion of tumor necrosis factor-alpha significantly decreased cortical choline acetyltransferase activity, reduced the number of choline acetyltransferase-immunoreactive cells and increased the number of activated astrocytes and microglia within the basal forebrain. The presence of the APPswe gene did not enhance the vulnerability of forebrain cholinergic neurons to the chronic neuroinflammation. Furthermore, combined treatment of these mice with memantine demonstrated that the neurotoxic effects of tumor necrosis factor-alpha upon cholinergic cells did not require the activation of the N-methyl-d-aspartate receptors. In contrast, we have previously shown that memantine was able to provide neuroprotection to cholinergic forebrain neurons from the consequences of exposure to the inflammogen lipopolysaccharide. These results provide insight into the mechanism by which neuroinflammation may selectively target specific neural systems during the progression of Alzheimer's disease.     

The effects of a novel NSAID on chronic neuroinflammation are age dependent

Chronic inflammation may play an important role in the pathogenesis of Alzheimer's disease (AD). The present study compared the effects of chronic neuroinflammation, produced by infusion of lipopolysaccharide (LPS) into the fourth ventricle, upon memory in young, adult, and old rats. Nonsteroidal anti-inflammatory drug (NSAID) therapy may delay the onset of AD. We show that NO-Flurbiprofen (NFP), a novel NSAID that lacks gastrointestinal side effects, attenuated the neuroinflammatory reaction and reduced the inflammation-induced memory deficit. Chronic LPS infusions impaired performance of young rats but not adult or old rats. Treatment with NFP improved the performance of LPS-infused young rats, but not LPS-infused adult or old rats. LPS infusions increased the number of activated microglia in young and adult rats but not old rats. NFP treatment attenuated the effects of LPS upon microglia activation in young and adult rats, but not old rats. The results suggest that NSAID therapies designed to influence the onset of AD should be initiated in adults before age-associated inflammatory processes within the brain have a chance to develop.     

Cannabinoid receptor stimulation is anti-inflammatory and improves memory in old rats

The number of activated microglia increase during normal aging. Stimulation of endocannabinoid receptors can reduce the number of activated microglia, particularly in the hippocampus, of young rats infused chronically with lipopolysaccharide (LPS). In the current study we demonstrate that endocannabinoid receptor stimulation by administration of WIN-55212-2 (2 mg/kg day) can reduce the number of activated microglia in hippocampus of aged rats and attenuate the spatial memory impairment in the water pool task. Our results suggest that the action of WIN-55212-2 does not depend upon a direct effect upon microglia or astrocytes but is dependent upon stimulation of neuronal cannabinoid receptors. Aging significantly reduced cannabinoid type 1 receptor binding but had no effect on cannabinoid receptor protein levels. Stimulation of cannabinoid receptors may provide clinical benefits in age-related diseases that are associated with brain inflammation, such as Alzheimer's disease.     

The toxicity of tumor necrosis factor-alpha upon cholinergic neurons within the nucleus basalis and the role of norepinephrine in the regulation of inflammation: implications for Alzheimer's disease

Inflammation and reduced forebrain norepinephrine are features of Alzheimer's disease that may interact to contribute to the degeneration of specific neural systems. We reproduced these conditions within the basal forebrain cholinergic system, a region that is vulnerable to degeneration in Alzheimer's disease. Tumor necrosis factor-alpha was infused into the basal forebrain of young mice pretreated with a norepinephrine neuronal toxin, N-(2-chloroethyl)-N-ethyl-2 bromobenzylamine (DSP4), with the expectation that the loss of noradrenergic input would enhance the loss of cholinergic neurons. The results indicate that chronic infusion of tumor necrosis factor-alpha alone significantly decreased cortical choline acetyltransferase activity and increased the number of activated microglia and astrocytes within the basal forebrain. The loss of forebrain norepinephrine following systemic treatment with DSP4 did not alter the level of cortical choline acetyltransferase activity or activate microglia but significantly activated astrocytes within the basal forebrain. Infusion of tumor necrosis factor-alpha into DSP4-pretreated mice also reduced cortical choline acetyltransferase activity on the side of the infusion; however, the decline was not significantly greater than that produced by the infusion of tumor necrosis factor-alpha alone. The neurodegeneration seen may be indirect since a double-immunofluorescence investigation did not find evidence for the co-existence of tumor necrosis factor-alpha type I receptors on choline acetyltransferase-positive cells in the basal forebrain. The results suggest that noradrenergic cell loss in Alzheimer's disease does not augment the consequences of the chronic neuroinflammation and does not enhance neurodegeneration of forebrain cholinergic neurons.     

The chemokine receptor CCR5-Delta32 gene mutation is not protective against Alzheimer's disease

Chronic local inflammatory reaction involving reactive microglia is one of the major pathological events in Alzheimer's disease (AD). There is growing evidence that the chemokine receptor CCR5 is up-regulated in AD brain and plays a role in the recruitment and accumulation of microglia in senile plaques. A 32-base pair deletion in the CCR5 gene (CCR5-Delta32 mutant allele) confers resistance to HIV-1 infection by preventing expression of the receptor on the cell surface. Several other reports have shown a similar protective effect of CCR5-Delta32 mutation towards certain chronic inflammatory diseases. Given the potential importance of CCR5 in brain inflammation, we hypothesized that individuals carrying the CCR5-Delta32 allele would show a reduced risk of AD. So, we performed a case-control study in 376 Spanish AD patients and 369 healthy controls. The frequency of the CCR5-Delta32 allele in our AD sample was 7.8%, not significantly different from our control sample group (5.8%). The present study indicates that the CCR5-Delta32 allele is not a preventive factor for AD.     

CC chemokine receptor 8 in the central nervous system is associated with phagocytic macrophages

CC chemokine receptor 8 (CCR8) has been detected in vitro on type 2 helper and regulatory lymphocytes, which might exert beneficial functions in multiple sclerosis (MS) and on macrophages and microglia, possibly promoting tissue injury in MS lesions. To discriminate the relevant expression pattern in vivo, we defined the cell types that expressed CCR8 in MS lesions and determined the relationship of CCR8 expression and demyelinating activity. CCR8 was not expressed on T cells but was associated with phagocytic macrophages and activated microglia in MS lesions and directly correlated with demyelinating activity. To identify factors associated with CCR8 expression, the study was extended to other central nervous system (CNS) pathologies. CCR8 was consistently expressed on phagocytic macrophages and activated microglia in stroke and progressive multifocal leukoencephalopathy, but not expressed on microglia in pathologies that lacked phagocytic macrophages such as senile change of the Alzheimer's type. CCR8 was up-regulated by macrophage differentiation and activating stimuli in vitro. In summary CNS CCR8 expression was associated with phagocytic macrophages and activated microglial cells in human CNS diseases, suggesting that CCR8 may be a feasible target for therapeutic intervention in MS. CCR8 expression may also indicate a selective program of mononuclear phagocyte gene expression.     

Dendrimer-based postnatal therapy for neuroinflammation and cerebral palsy in a rabbit model

Cerebral palsy (CP) is a chronic childhood disorder with no effective cure. Neuroinflammation, caused by activated microglia and astrocytes, plays a key role in the pathogenesis of CP and disorders such as Alzheimer's disease and multiple sclerosis. Targeting neuroinflammation can be a potent therapeutic strategy. However, delivering drugs across the blood-brain barrier to the target cells for treating diffuse brain injury is a major challenge. We show that systemically administered polyamidoamine dendrimers localize in activated microglia and astrocytes in the brain of newborn rabbits with CP, but not healthy controls. We further demonstrate that dendrimer-based N-acetyl-l-cysteine (NAC) therapy for brain injury suppresses neuroinflammation and leads to a marked improvement in motor function in the CP kits. The well-known and safe clinical profile for NAC, when combined with dendrimer-based targeting, provides opportunities for clinical translation in the treatment of neuroinflammatory disorders in humans. The effectiveness of the dendrimer-NAC treatment, administered in the postnatal period for a prenatal insult, suggests a window of opportunity for treatment of CP in humans after birth.     

Pathological and biochemical consequences of acute and chronic neuroinflammation within the basal forebrain cholinergic system of rats

Inflammatory processes may play a critical role in the degeneration of basal forebrain cholinergic cells that underlies some of the cognitive impairments associated with Alzheimer's disease. In the present study, the proinflammagen lipopolysaccharide, from the cell wall of Gram-negative bacteria, was used to produce inflammation within the basal forebrain of rats. The effects of acute, high-dose injections of lipopolysaccharide (2, 20 or 40 microg) upon basal forebrain chemistry and neuronal integrity were compared with the effects of chronic, low-dose lipopolysaccharide infusions (0.18, 0.25, 1.8 or 5.0 microg/h) for either 14, 37, 74 or 112 days. Acute exposure to lipopolysaccharide decreased cortical choline acetyltransferase activity and the number of immunoreactive choline acetyltransferase-positive cells within a small region of the basal forebrain. Regional levels of five different neuropeptides were unchanged by acute, high-dose lipopolysaccharide injections. Chronic lipopolysaccharide infusions produced (i) a time-dependent, but not dose-dependent, decrease in cortical choline acetyltransferase activity that paralleled a decline in the number of choline acetyltransferase- and p75-immunoreactive cells within the basal forebrain, and (ii) a dense distribution of reactive astrocytes and microglia within the basal forebrain. Chronic neuroinflammation might underlie the genesis of some neuropathological changes associated with normal ageing or Alzheimer's disease.     

The peripheral benzodiazepine receptor (Translocator protein 18kDa) in microglia: from pathology to imaging

Microglia constitute the primary resident immune surveillance cell in the brain and are thought to play a significant role in the pathogenesis of several neurodegenerative disorders, such as Alzheimer's disease, multiple sclerosis, Parkinson's disease and HIV-associated dementia. Measuring microglial activation in vivo in patients suffering from these diseases may help chart progression of neuroinflammation as well as assess efficacy of therapies designed to modulate neuroinflammation. Recent studies suggest that activated microglia in the CNS may be detected in vivo using positron emission tomography (PET) utilizing pharmacological ligands of the mitochondrial peripheral benzodiazepine receptor (PBR (recently renamed as Translocator protein (18 kDa)). Beginning with the molecular characterization of PBR and regulation in activated microglia, we examine the rationale behind using PBR ligands to image microglia with PET. Current evidence suggests these findings might be applied to the development of clinical assessments of microglial activation in neurological disorders.     

Caffeine attenuates lipopolysaccharide-induced neuroinflammation

Caffeine is an antagonist at A1 and A2A adenosine receptors and epidemiological evidence suggests that caffeine consumption reduces the risk of Alzheimer's and Parkinson's diseases. Neuroinflammation plays a role in the etiology of these diseases and caffeine may provide protection through the modulation of inflammation. Adenosine has a known role in the propagation of inflammation and caffeine may reduce microglia activation directly by blocking adenosine receptors on microglia. Chronic neuroinflammation is associated with an increase in extracellular levels of glutamate and drugs that limit the effects of glutamate at neuronal receptors have been shown to indirectly reduce the neuroinflammatory response of microglia cells. A1 and A2A receptors have been shown to regulate the pre-synaptic release of glutamate, therefore, caffeine may also reduce neuroinflammation via its ability to regulate glutamate release. Caffeine was administered at various doses to young rats with experimentally induced neuroinflammation by chronic infusion of lipopolysaccharide (LPS) over two or four weeks into the 4th ventricle and to aged rats with naturally elevated levels of microglia activation. Caffeine attenuated the number of activated microglia within the hippocampus of animals with LPS-induced and age-related inflammation.     

CCR2+ and CCR5+ CD8+ T cells increase during viral infection and migrate to sites of infection

Chemokines and their receptors play a critical role in the selective recruitment of various leukocyte subsets. In this study, we correlated the expression of multiple chemokine and CC chemokine receptor (CCR) genes during the course of intracerebral (i.c.) infection with lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis virus (VSV), which are prototypic of a noncytopathic and a cytopathic virus, respectively. Infection of mice with either virus resulted in rapid activation and overlapping cerebral expression of a number of chemokine genes. Infection with VSV i.c. causes a rapidly lethal, T cell-independent encephalitis, and infection resulted in a dramatic early up-regulation of chemokine gene expression. Similar marked up-regulation of chemokine expression was not seen until late after LCMV infection and required the presence of activated T cells. Cerebral CCR gene expression was dominated by CCR1, CCR2 and CCR5. However, despite a stronger initial chemokine signal in VSV-infected mice, only LCMV-induced T cell-dependent inflammation was found to be associated with substantially increased expression of CCR genes. Virus-activated CD8+ T cells were found to express CCR2 and CCR5, whereas activated monocytes/macrophages expressed CCR1 in addition to CCR2 and CCR5. Together, these CCR profiles readily account for the CCR profile prominent during CD8+-dependent CNS inflammation.     

Chronic brain inflammation impairs two forms of long-term potentiation in the rat hippocampal CA1 area

Neuroinflammation plays an important role in the progression of Alzheimer's disease (AD) and is characterized by the presence of activated microglia. We investigated whether chronic neuroinflammation affects the induction of N-methyl-d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) and NMDAR-independent LTP which is expressed by voltage-dependent calcium channel (VDCC). Chronic neuroinflammation was induced by administration of lipopolysaccharide (LPS) (28 days, 0.35 μg/h) to the fourth ventricle. The Morris water maze test was conducted to measure the memory impairment and then excitatory postsynaptic potentials were recorded extracelluarly from stratum radiatum in the rat hippocampal CA1 area to examine the changes in synaptic plasticity induced by LPS infusion. Chronic administration of LPS induced remarkable memory impairment. The field recording experiments revealed that the induction of both NMDAR-dependent LTP and NMDAR-independent LTP were impaired in the hippocampal Schaffer collateral-CA1 synapse in animals chronically infused with LPS. The present results show that chronic neuroinflammation can lead to the impaired spatial memory and attenuation of VDCC-dependent LTP as well as NMDAR-dependent LTP. The attenuation of synaptic plasticity may be caused by the impairment of both NMDAR and L-type Ca²⁺ via elevated levels of inflammatory proteins, which may underlie aspects of dementia.     

Interferon-gamma-dependent cytotoxic activation of human astrocytes and astrocytoma cells

Astrocytes and microglia become activated in a broad spectrum of inflammatory neurodegenerative diseases. Activated microglia are widely believed to be the principal source of inflammation-induced neuronal degeneration in these disorders. To investigate the neurotoxic potential of human astrocytes, we exposed them and human astrocytic U-373 MG cells to a variety of inflammatory stimulants. We then assessed the effects of their supernatants on human SH-SY5 cells. When astrocytes and U-373 MG cells were stimulated with interferon (IFN)-γ (150 U/ml), their supernatants significantly reduced SH-SY5Y cell viability. Other powerful inflammatory stimulants such as lipopolysaccharide (0.5 μg/ml), tumor necrosis factor-α (10 ng/ml) and interleukin-1β (10 ng/ml), alone or in combination, were without effect. These combinations were also unable to enhance the IFN-γ effect. The induced cytotoxicities were reversed by JAK inhibitor I, a potent and specific inhibitor of JAKs. This result indicates that the neurotoxic effect was proceeding through the IFN-γ receptor (IFNGR)-JAK-STAT intracellular pathway. To establish that the IFNGR is expressed on both cultured astrocytes and U-373 MG cells, we performed RT-PCR on total RNA extracts to identify a specific IFNGR product. We showed the protein product on these cultured cells by immunocytochemistry using an antibody to IFNGR. Finally, using human postmortem material, we showed sharp upregulation of the IFNGR on activated astrocytes in affected areas in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. These findings suggest that activated astrocytes may become neurotoxic when stimulated by IFN-γ and may therefore exacerbate the pathology in a spectrum of neurodegenerative diseases.     

Memantine protects against LPS-induced neuroinflammation, restores behaviorally-induced gene expression and spatial learning in the rat

Neuroinflammation is reliably associated with the pathogenesis of a number of neurodegenerative diseases, and can be detected by the presence of activated microglia. Neuroinflammation can be induced by chronic lipopolysaccharide (LPS) infusion into the 4th ventricle of the rat resulting in region-selective microglia activation and impaired hippocampal-dependent memory. Furthermore, this treatment results in altered behaviorally-induced expression of the immediate early gene Arc, indicating altered network activity. LPS is known to activate microglia directly, leading to increased glutamate release, and in enhanced N-methyl-d-aspartate (NMDA) -dependent signaling. Taken together, the foregoing suggests that decreasing NMDA receptor activation during early stages of chronic neuroinflammation should reduce a) microglia activation, b) overexpression of Arc, and c) spatial memory deficits. Memantine, a low to moderate affinity open channel uncompetitive NMDA receptor antagonist, at low doses was used here to test these hypotheses. Rats were chronically infused into the 4th ventricle for 28 days with LPS alone, vehicle alone (via osmotic minipump) or LPS and memantine (10 mg/kg/day memantine s.c.). The results reported here demonstrate that memantine reduces OX6-immunolabeling for activated microglia, spares resident microglia, returns Arc (activity-regulated cytoskeletal associated protein, protein) -expressing neuronal populations to control levels (as revealed by Arc immunolabeling and fluorescence in situ hybridization), and ameliorates the spatial memory impairments produced by LPS alone. These data indicate that memantine therapy at low doses, recreating plasma levels similar to those of therapeutic doses in human, acts in part through its ability to reduce the effects of neuroinflammation, resulting in normal gene expression patterns and spatial learning. Combined, these findings suggest that low, therapeutically relevant doses of memantine delivered early in the development of neuroinflammation-influenced diseases may confer neural and cognitive protection.     

TGF-β1 blockade of microglial chemotaxis toward Aβ aggregates involves SMAD signaling and down-regulation of CCL5

Background  

Overactivated microglia that cluster at neuritic plaques constantly release neurotoxins, which actively contribute to progressive neurodegeneration in Alzheimer's disease (AD). Therefore, attenuating microglial clustering can reduce focal neuroinflammation at neuritic plaques. Previously, we identified CCL5 and CCL2 as prominent chemokines that mediate the chemotaxis of microglia toward beta-amyloid (Aβ)aggregates. Although transforming growth factor-β1 (TGF-β1) has been shown to down-regulate the expression of chemokines in activated microglia, whether TGF-β1 can reduce the chemotaxis of microglia toward neuritic plaques in AD remains unclear.     

Anti-inflammatory property of the cannabinoid agonist WIN-55212-2 in a rodent model of chronic brain inflammation

Cannabinoid receptors (CBr) stimulation induces numerous central and peripheral effects. A growing interest in the beneficial properties of manipulating the endocannabinoid system has led to the possible involvement of CBr in the control of brain inflammation. In the present study we examined the effect of the CBr agonist, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)-pyrrolo[1,2,3-de]-1,4benzoxazin-6-yl]-1-naphthalenyl-methanone mesylate (WIN-55212-2), on microglial activation and spatial memory performance, using a well-characterized animal model of chronic brain inflammation produced by the infusion of lipopolysaccharide (LPS, 250 ng/h for 3 weeks) into the fourth ventricle of young rats. WIN-55212-2 (0.5 or 1.0 mg/kg/day, i.p.) was administered for 3 weeks. During the third week of treatment, spatial memory ability was examined using the Morris water-maze task. We found that 0.5 and 1 mg/kg WIN-55212-2 reduced the number of LPS-activated microglia, while 1 mg/kg WIN-55212-2 potentiated the LPS-induced impairment of performance in the water maze task. Cannabinoid receptors 1 were not expressed by microglia and astrocytes, suggesting an indirect effect of WIN-55212-2 on microglia activation and memory impairment. Our results emphasize the potential use of CBr agonists in the regulation of inflammatory processes within the brain; this knowledge may lead to the use of CBr agonists in the treatment of neurodegenerative diseases associated with chronic neuroinflammation, such as Alzheimer disease.     

Expression of scavenger receptor class B, type I, by astrocytes and vascular smooth muscle cells in normal adult mouse and human brain and in Alzheimer's disease brain

In Alzheimer's disease (AD), fibrillar beta-amyloid protein (fAbeta) accumulates in the walls of cerebral vessels associated with vascular smooth muscle cells (SMCs), endothelium, and pericytes, and with microglia and astrocytes in plaques in the brain parenchyma. Scavenger receptor class A (SR-A) and class B, type I (SR-BI) mediate binding and ingestion of fAbeta by cultured human fetal microglia, microglia from newborn mice, and by cultured SMCs. Our findings that SR-BI participates in the adhesion of cultured microglia from newborn SR-A knock-out mice to fAbeta-coated surfaces, and that microglia secrete reactive oxygen species when they adhere to these surfaces prompted us to explore expression of SR-BI in vivo. We report here that astrocytes and SMCs in normal adult mouse and human brains and in AD brains express SR-BI. In contrast, microglia in normal adult mouse and human brains and in AD brains do not express SR-BI. These findings indicate that SR-BI may mediate interactions between astrocytes or SMCs and fAbeta, but not of microglia and fAbeta, in AD, and that expression of SR-BI by rodent microglia is developmentally regulated. They suggest that SR-BI expression also is developmentally regulated in human microglia.     

银杏内脂B抑制脂多糖诱导的神经炎性细胞毒作用

目的:探讨血小板活化因子受体拮抗剂银杏内脂B(BN52021)抑制细菌脂多糖诱导的脑内炎症反应的神经保护作用。方法:SD大鼠随机分为对照组,模型组和治疗组。Morris水迷宫检测学习和记忆功能,免疫组织化学法检测脑内GFAP阳性星形胶质细胞、OX-42阳性小胶质细胞在颢叶皮质、海马及基底核中的表达。结果:脂多糖(LPS)第4脑室注射使模型动物学习和记忆功能减退,模型组GFAP阳性星形胶质细胞和OX-42阳性小胶质细胞在颞叶皮质、海马及基底核中细胞数量明显增加。BN52021治疗后,对照组和治疗组水迷宫逃避潜伏期、平台象限游泳距离百分比与模型组均有显著性差异;GFAP阳性星形胶质细胞和OX-42阳性小胶质细胞在颞叶皮质、海马及基底核中细胞数量明显减少和阳性染色灰度上升。结论:血小板活化因子受体拮抗剂可抑制LPS诱导的脑内神经炎症,对阿尔茨海默病和艾滋病相关痴呆等以中枢炎症为病理特征的神经退行性变均有治疗作用。