Inhibition of soluble TNF signaling in a mouse model of Alzheimer's disease prevents pre-plaque amyloid-associated neuropathology

Allergy influences the inflammatory status of the brain and enhances tau-phosphorylation

Despite the existing knowledge regarding the neuropathology of Alzheimer's disease (AD), the cause of sporadic forms of the disease is unknown. It has been suggested that systemic inflammation may have a role, but the exact mechanisms through which inflammatory processes influence the pathogenesis and progress of AD are not obvious. Allergy is a chronic inflammatory disease affecting more than 20% of the Western population, but the effects of allergic conditions on brain functions are largely unknown. The aim of this study was to investigate whether or not chronic peripheral inflammation associated with allergy affects the expression of AD-related proteins and inflammatory markers in the brain. On the basis of previously described models for allergy in mice we developed a model of chronic airway allergy in mouse, with ovalbumin as allergen. The validity of the chronic allergy model was confirmed by a consistent and reproducible eosinophilia in the bronchoalveolar lavage (BAL) fluid of allergic animals. Allergic mice were shown to have increased brain levels of both immunoglobulin (Ig) G and IgE with a widespread distribution. Allergy was also found to increase phosphorylation of tau protein in the brain. The present data support the notion that allergy-dependent chronic peripheral inflammation modifies the brain inflammatory status, and influences phosphorylation of an AD-related protein, indicating that allergy may be yet another factor to be considered for the development and/or progression of neurodegenerative diseases such as AD.

Long-term treatment of thalidomide ameliorates amyloid-like pathology through inhibition of β-secretase in a mouse model of Alzheimer's disease

Thalidomide is a tumor necrosis factor alpha (TNFα) inhibitor which has been found to have abilities against tumor growth, angiogenesis and inflammation. Recently, it has been applied in clinic for the treatment of multiple myeloma as well as some inflammatory diseases. However, whether thalidomide has any therapeutic effects on neurodegenerative disorders, i.e. Alzheimer’s disease (AD) is not clear. AD is characterized by excessive amount of amyloid β peptides (Aβ), which results in a significant release of inflammatory factors, including TNFα in the brain. Studies have shown that inhibition of TNFα reduces amyloid-associated pathology, prevents neuron loss and improves cognition. Our recent report showed that genetic inhibition of TNFα/TNF receptor signal transduction down-regulates β amyloid cleavage enzyme 1 (BACE1) activity, reduces Aβ generation and improves learning and memory deficits. However, the mechanism of thalidomide involving in the mitigation of AD neuropathological features remains unclear. Here, we chronically administrated thalidomide on human APPswedish mutation transgenic (APP23) mice from 9 months old (an onset of Aβ deposits and early stage of AD-like changes) to 12 months old. We found that, in addition of dramatic decrease in the activation of both astrocytes and microglia, thalidomide significantly reduces Aβ load and plaque formation. Furthermore, we found a significant decrease in BACE1 level and activity with long-term thalidomide application. Interestingly, these findings cannot be observed in the brains of 12-month-old APP23 mice with short-term treatment of thalidomide (3 days). These results suggest that chronic thalidomide administration is an alternative approach for AD prevention and therapeutics.

Astrocytes: conductors of the Alzheimer disease neuroinflammatory symphony

Alzheimer disease (AD) is the most prevalent cause of dementia in humans, and the symptoms are commonly manifested after the seventh decade of life. Numerous pathological changes have been described in the postmortem brains of AD patients, including senile plaques, neurofibrillary tangles, neuroinflammation, synapse loss, and neuronal death. Reactive astrocytes surrounding senile plaques seem to be responsible for the ongoing inflammatory process in the disease through the release of cytokines and other toxic products. However, little is known about the regulation of these cells in the AD brain. Here we discuss the potential translational impact of the recent findings of Carrero and colleagues, published in Experimental Neurology, that shows the underlying molecular mechanism of astrocyte activation in response to β-amyloid (Aβ). Likewise, the relevance of pro-inflammatory mediators tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2) and nuclear factor-κB (NF-κB), as integral players in disease progression will be discussed.

Tumor necrosis factor-induced cerebral insulin resistance in Alzheimer's disease links numerous treatment rationales

The evident limitations of the amyloid theory of the pathogenesis of Alzheimer's disease are increasingly putting alternatives in the spotlight. We argue here that a number of independently developing approaches to therapy-including specific and nonspecific anti-tumor necrosis factor (TNF) agents, apolipoprotein E mimetics, leptin, intranasal insulin, the glucagon-like peptide-1 mimetics and glycogen synthase kinase-3 (GSK-3) antagonists-are all part of an interlocking chain of events. All these approaches inform us that inflammation and thence cerebral insulin resistance constitute the pathway on which to focus for a successful clinical outcome in treating this disease. The key link in this chain presently absent is a recognition by Alzheimer's research community of the long-neglected history of TNF induction of insulin resistance. When this is incorporated into the bigger picture, it becomes evident that the interventions we discuss are not competing alternatives but equally valid approaches to correcting different parts of the same pathway to Alzheimer's disease. These treatments can be expected to be at least additive, and conceivably synergistic, in effect. Thus the inflammation, insulin resistance, GSK-3, and mitochondrial dysfunction hypotheses are not opposing ideas but stages of the same fundamental, overarching, pathway of Alzheimer's disease pathogenesis. The insight this provides into progenitor cells, including those involved in adult neurogenesis, is a key part of this approach. This pathway also has therapeutic implications for other circumstances in which brain TNF is pathologically increased, such as stroke, traumatic brain injury, and the infectious disease encephalopathies.

3,6'-Dithiothalidomide, a new TNF-α synthesis inhibitor, attenuates the effect of Aβ1-42 intracerebroventricular injection on hippocampal neurogenesis and memory deficit

Evidence indicates altered neurogenesis in neurodegenerative diseases associated with inflammation, including Alzheimer's disease (AD). Neuroinflammation and its propagation have a critical role in the degeneration of hippocampal neurons, cognitive impairment, and altered neurogenesis. Particularly, tumor necrosis factor (TNF)-α plays a central role in initiating and regulating the cytokine cascade during an inflammatory response and is up-regulated in brain of AD patients. In this study, we investigated the effects of a novel thalidomide-based TNF-α lowering drug, 3,6'-dithiothalidomide, on hippocampal progenitor cell proliferation, neurogenesis and, memory tasks after intracerebroventricular injection of β-amyloid (Aß)(1-42) peptide. Seven days after Aβ(1-42) injection, a significant proliferation of hippocampal progenitor cells and memory impairment were evident. Four weeks after Aβ(1-42) peptide injection, elevated numbers of surviving 5-bromo-2'-deoxyuridine cells and newly formed neurons were detected. Treatment with 3,6'-dithiothalidomide attenuated these Aβ(1-42) provoked effects. Our data indicate that although treatment with 3,6'-dithiothalidomide in part attenuated the increase in hippocampal neurogenesis caused by Aβ(1-42) -induced neuroinflammation, the drug prevented memory deficits associated with increased numbers of activated microglial cells and inflammatory response. Therefore, 3,6'-dithiothalidomide treatment likely reduced neuronal tissue damage induced by neuroinflammation following Aβ(1-42) injection. Understanding the modulation of neurogenesis, and its relationship with memory function could open new therapeutic interventions for AD and other neurodegenerative disorders with an inflammatory component.

Design and synthesis of neuroprotective methylthiazoles and modification as NO-chimeras for neurodegenerative therapy

Learning and memory deficits in Alzheimer's disease (AD) result from synaptic failure and neuronal loss, the latter caused in part by excitotoxicity and oxidative stress. A therapeutic approach is described that uses NO-chimeras directed at restoration of both synaptic function and neuroprotection. 4-Methylthiazole (MZ) derivatives were synthesized, based upon a lead neuroprotective pharmacophore acting in part by GABA(A) receptor potentiation. MZ derivatives were assayed for protection of primary neurons against oxygen-glucose deprivation and excitotoxicity. Selected neuroprotective derivatives were incorporated into NO-chimera prodrugs, coined nomethiazoles. To provide proof of concept for the nomethiazole drug class, selected examples were assayed for restoration of synaptic function in hippocampal slices from AD-transgenic mice, reversal of cognitive deficits, and brain bioavailability of the prodrug and its neuroprotective MZ metabolite. Taken together, the assay data suggest that these chimeric nomethiazoles may be of use in treatment of multiple components of neurodegenerative disorders, such as AD.

Extensive innate immune gene activation accompanies brain aging, increasing vulnerability to cognitive decline and neurodegeneration: a microarray study

Background

This study undertakes a systematic and comprehensive analysis of brain gene expression profiles of immune/inflammation-related genes in aging and Alzheimer’s disease (AD).

Methods

In a well-powered microarray study of young (20 to 59 years), aged (60 to 99 years), and AD (74 to 95 years) cases, gene responses were assessed in the hippocampus, entorhinal cortex, superior frontal gyrus, and post-central gyrus.

Results

Several novel concepts emerge. First, immune/inflammation-related genes showed major changes in gene expression over the course of cognitively normal aging, with the extent of gene response far greater in aging than in AD. Of the 759 immune-related probesets interrogated on the microarray, approximately 40% were significantly altered in the SFG, PCG and HC with increasing age, with the majority upregulated (64 to 86%). In contrast, far fewer immune/inflammation genes were significantly changed in the transition to AD (approximately 6% of immune-related probesets), with gene responses primarily restricted to the SFG and HC. Second, relatively few significant changes in immune/inflammation genes were detected in the EC either in aging or AD, although many genes in the EC showed similar trends in responses as in the other brain regions. Third, immune/inflammation genes undergo gender-specific patterns of response in aging and AD, with the most pronounced differences emerging in aging. Finally, there was widespread upregulation of genes reflecting activation of microglia and perivascular macrophages in the aging brain, coupled with a downregulation of select factors (TOLLIP, fractalkine) that when present curtail microglial/macrophage activation. Notably, essentially all pathways of the innate immune system were upregulated in aging, including numerous complement components, genes involved in toll-like receptor signaling and inflammasome signaling, as well as genes coding for immunoglobulin (Fc) receptors and human leukocyte antigens I and II.

Conclusions

Unexpectedly, the extent of innate immune gene upregulation in AD was modest relative to the robust response apparent in the aged brain, consistent with the emerging idea of a critical involvement of inflammation in the earliest stages, perhaps even in the preclinical stage, of AD. Ultimately, our data suggest that an important strategy to maintain cognitive health and resilience involves reducing chronic innate immune activation that should be initiated in late midlife.

Psychotropic drug effects on gene transcriptomics relevant to Alzheimer disease

Psychotropics are widely prescribed in Alzheimer disease (AD) without regard to their pathobiological effects. Results summarize a comprehensive survey of psychotropic effects on messenger ribonucleic acid (mRNA) expression for 52 genes linked to AD. Pending future investigations, current data indicate that atypical antipsychotics, lithium, and fluoxetine reduce AD risk, whereas other drug classes promote risk. Risk may be attenuated by antipsychotics and lithium (down-regulate TNF), atypical antipsychotics (down-regulate TF), risperidone (down-regulates IL1B), olanzapine (up-regulates TFAM, down-regulates PRNP), fluoxetine (up-regulates CLU, SORCS1, NEDD9, GRN, and ECE1), and lithium coadministered with antipsychotics (down-regulates IL1B). Risk may be enhanced by neuroleptics (up-regulate TF), haloperidol (up-regulates IL1B and PION), olanzapine (down-regulates THRA and PRNP, up-regulates IL1A), and chlorpromazine, imipramine, maprotiline, fluvoxamine, and diazepam (up-regulate IL1B). There were no results for dextromethorphan-plus-quinidine. Fluoxetine effects on CLU, NEDD9, and GRN were statistically robust. Drug effects on specific variants, polymorphisms, genotypes, and other genes (CCR2, TF, and PRNP) are detailed. Translational AD risk applications and their limitations related to specific genes, mutations, variants, polymorphisms, genotypes, brain site, sex, clinical population, AD stage, and other factors are discussed. This report provides an initial summary and framework to understand the potential impact of psychotropic drugs on AD-relevant genes.

Microglia and neurodegeneration: the role of systemic inflammation

It is well accepted that CNS inflammation has a role in the progression of chronic neurodegenerative disease, although the mechanisms through which this occurs are still unclear. The inflammatory response during most chronic neurodegenerative disease is dominated by the microglia and mechanisms by which these cells contribute to neuronal damage and degeneration are the subject of intense study. More recently it has emerged that systemic inflammation has a significant role to play in the progression of these diseases. Well-described adaptive pathways exist to transduce systemic inflammatory signals to the brain, but activation of these pathways appears to be deleterious to the brain if the acute insult is sufficiently robust, as in severe sepsis, or sufficiently prolonged, as in repeated stimulation with robust doses of inflammogens such as lipopolysaccharide (LPS). Significantly, moderate doses of inflammogens produce new pathology in the brain and exacerbate or accelerate features of disease when superimposed upon existing pathology or in the context of genetic predisposition. It is now apparent in multiple chronic disease states, and in ageing, that microglia are primed by prior pathology, or by genetic predisposition, to respond more vigorously to subsequent inflammatory stimulation, thus transforming an adaptive CNS inflammatory response to systemic inflammation, into one that has deleterious consequences for the individual. In this review, the preclinical and clinical evidence supporting a significant role for systemic inflammation in chronic neurodegenerative diseases will be discussed. Mechanisms by which microglia might effect neuronal damage and dysfunction, as a consequence of systemic stimulation, will be highlighted.

Tumor necrosis factor-α synthesis inhibitor 3,6'-dithiothalidomide attenuates markers of inflammation, Alzheimer pathology and behavioral deficits in animal models of neuroinflammation and Alzheimer's disease

BACKGROUND

Neuroinflammation is associated with virtually all major neurodegenerative disorders, including Alzheimer's disease (AD). Although it remains unclear whether neuroinflammation is the driving force behind these disorders, compelling evidence implicates its role in exacerbating disease progression, with a key player being the potent proinflammatory cytokine TNF-α. Elevated TNF-α levels are commonly detected in the clinic and animal models of AD.

METHODS

The potential benefits of a novel TNF-α-lowering agent, 3,6'-dithiothalidomide, were investigated in cellular and rodent models of neuroinflammation with a specific focus on AD. These included central and systemic inflammation induced by lipopolysaccharide (LPS) and Aβ(1-42) challenge, and biochemical and behavioral assessment of 3xTg-AD mice following chronic 3,6'-dithiothaliodmide.

RESULTS

3,6'-Dithiothaliodmide lowered TNF-α, nitrite (an indicator of oxidative damage) and secreted amyloid precursor protein (sAPP) levels in LPS-activated macrophage-like cells (RAW 264.7 cells). This translated into reduced central and systemic TNF-α production in acute LPS-challenged rats, and to a reduction of neuroinflammatory markers and restoration of neuronal plasticity following chronic central challenge of LPS. In mice centrally challenged with A(β1-42) peptide, prior systemic 3,6'-dithiothalidomide suppressed Aβ-induced memory dysfunction, microglial activation and neuronal degeneration. Chronic 3,6'-dithiothalidomide administration to an elderly symptomatic cohort of 3xTg-AD mice reduced multiple hallmark features of AD, including phosphorylated tau protein, APP, Aβ peptide and Aβ-plaque number along with deficits in memory function to levels present in younger adult cognitively unimpaired 3xTg-AD mice. Levels of the synaptic proteins, SNAP25 and synaptophysin, were found to be elevated in older symptomatic drug-treated 3xTg-AD mice compared to vehicle-treated ones, indicative of a preservation of synaptic function during drug treatment.

CONCLUSIONS

Our data suggest a strong beneficial effect of 3,6'-dithiothalidomide in the setting of neuroinflammation and AD, supporting a role for neuroinflammation and TNF-α in disease progression and their targeting as a means of clinical management.

Inhibition of soluble tumor necrosis factor ameliorates synaptic alterations and Ca2+ dysregulation in aged rats

The role of tumor necrosis factor α (TNF) in neural function has been investigated extensively in several neurodegenerative conditions, but rarely in brain aging, where cognitive and physiologic changes are milder and more variable. Here, we show that protein levels for TNF receptor 1 (TNFR1) are significantly elevated in the hippocampus relative to TNF receptor 2 (TNFR2) in aged (22 months) but not young adult (6 months) Fischer 344 rats. To determine if altered TNF/TNFR1 interactions contribute to key brain aging biomarkers, aged rats received chronic (4–6 week) intracranial infusions of XPro1595: a soluble dominant negative TNF that preferentially inhibits TNFR1 signaling. Aged rats treated with XPro1595 showed improved Morris Water Maze performance, reduced microglial activation, reduced susceptibility to hippocampal long-term depression, increased protein levels for the GluR1 type glutamate receptor, and lower L-type voltage sensitive Ca²⁺ channel (VSCC) activity in hippocampal CA1 neurons. The results suggest that diverse functional changes associated with brain aging may arise, in part, from selective alterations in TNF signaling.

Is TNF a link between aging-related reproductive endocrine dyscrasia and Alzheimer's disease?

This commentary addresses a novel mechanism by which aging-related changes in reproductive hormones could mediate their action in the brain. It presents the evidence that dyotic endocrine signals modulate the expression of tumor necrosis factor (TNF) and related cytokines, and that these cytokines are a functionally important downstream link mediating neurodegeneration and dysfunction. This convergence of dyotic signaling on TNF-mediated degeneration and dysfunction has important implications for understanding the pathophysiology of AD, stroke, and traumatic brain disease, and also for the treatment of these diseases.

Minocycline corrects early, pre-plaque neuroinflammation and inhibits BACE-1 in a transgenic model of Alzheimer's disease-like amyloid pathology

Background

A growing body of evidence indicates that inflammation is one of the earliest neuropathological events in Alzheimer's disease. Accordingly, we have recently shown the occurrence of an early, pro-inflammatory reaction in the hippocampus of young, three-month-old transgenic McGill-Thy1-APP mice in the absence of amyloid plaques but associated with intracellular accumulation of amyloid beta petide oligomers. The role of such a pro-inflammatory process in the progression of the pathology remained to be elucidated.

Methods and results

To clarify this we administered minocycline, a tetracyclic derivative with anti-inflammatory and neuroprotective properties, to young, pre-plaque McGill-Thy1-APP mice for one month. The treatment ended at the age of three months, when the mice were still devoid of plaques. Minocycline treatment corrected the up-regulation of inducible nitric oxide synthase and cyclooxygenase-2 observed in young transgenic placebo mice. Furthermore, the down-regulation of inflammatory markers correlated with a reduction in amyloid precursor protein levels and amyloid precursor protein-related products. Beta-site amyloid precursor protein cleaving enzyme 1 activity and levels were found to be up-regulated in transgenic placebo mice, while minocycline treatment restored these levels to normality. The anti-inflammatory and beta-secretase 1 effects could be partly explained by the inhibition of the nuclear factor kappa B pathway.

Conclusions

Our study suggests that the pharmacological modulation of neuroinflammation might represent a promising approach for preventing or delaying the development of Alzheimer's disease neuropathology at its initial, pre-clinical stages. The results open new vistas to the interplay between inflammation and amyloid pathology.

The immunology of neurodegeneration

While immune responses in neurodegeneration were regarded as little more than a curiosity a decade ago, they are now increasingly moving toward center stage. Factors driving this movement include the recognition that most of the relevant immune molecules are produced within the brain, that microglia are proficient immune cells shaping neuronal circuitry and fate, and that systemic immune responses affect brain function. We will review this complex field from the perspective of neurons, extra-neuronal brain cells, and the systemic environment and highlight the possibility that cell intrinsic innate immune molecules in neurons may function in neurodegenerative processes.

Regulation of microglia effector functions by tumor necrosis factor signaling

The exact biological role of the cytokine tumor necrosis factor (TNF) in the central nervous system (CNS) is not well understood; but overproduction of TNF by activated microglia has been implicated in neuronal death, suggesting that TNF inhibition in the CNS may be a viable neuroprotective strategy. We investigated the role of TNF signaling in regulation of microglia effector functions using molecular, cellular, and functional analyses of postnatal and adult microglia populations in the CNS. No differences were found by flow cytometric analyses in the basal activation state between TNF-null and wild-type mice. Although TNF-null microglia displayed an atypical morphology with cytoplasmic vacuoles in response to stimulation with lipopolysaccharide (LPS), the phagocytic response of TNF-null microglia to Escherichia coli particles in vitro was normal and there were no signs of enhanced caspase 3 activation or apoptosis. Functionally, conditioned media from LPS-stimulated TNF-null microglia was found to have significantly reduced levels of IL-10, IL-6, IL-1β, IL-12, and CXCL1 relative to wild-type microglia and exerted no cytotoxic effects on neurally differentiated dopaminergic (DA) MN9D cells. In contrast, incubation of wild-type microglia with TNF inhibitors selectively depleted the levels of soluble TNF and its cytotoxicity on MN9D cells. To distinguish whether reduced cytotoxicity by LPS-activated TNF-null microglia could be attributed to deficient autocrine TNF signaling, we employed primary microglia deficient in one or both TNF receptors (TNFR1 and TNFR2) in co-culture with MN9D cells and found that neither receptor is required to elicit LPS-evoked TNF production and cytotoxicity on DA cells.

Neurological impacts from inhalation of pollutants and the nose-brain connection

The effects of inhaled particles have focused heavily on the respiratory and cardiovascular systems. Most studies have focused on inhaled metals, whereas less information is available for other particle types regarding the effects on the brain and other extra-pulmonary organs. We review here the key available literature on nanoparticle uptake and transport through the olfactory pathway, the experimental data from animal and in vitro studies, and human epidemiological observations. Nanoparticles (<0.1 μm in one dimension) may easily reach the brain from the respiratory tract via sensory neurons and transport from the distal alveoli into the blood or lymph as free particles or inside phagocytic cells. These mechanisms and subsequent biologic responses may be influenced by the chemical composition of inhaled particles. Animal studies with ambient particulate matter and certain other particles show alterations in neuro-inflammatory markers of oxidative stress and central neurodegeneration. Human observations indicate motor, cognitive, and behavioral changes especially after particulate metal exposure in children. Exposure to co-pollutants and/or underlying disease states could also impact both the biokinetics and effects of airborne particles in the brain. Data are needed from the areas of inhalation, neurology, and metal toxicology in experimental and human studies after inhalation exposure. An increased understanding of the neurotoxicity associated with air pollution exposure is critical to protect susceptible individuals in the workplace and the general population.

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

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

Inhibition of soluble tumour necrosis factor is therapeutic in experimental autoimmune encephalomyelitis and promotes axon preservation and remyelination

Tumour necrosis factor is linked to the pathophysiology of various neurodegenerative disorders including multiple sclerosis. Tumour necrosis factor exists in two biologically active forms, soluble and transmembrane. Here we show that selective inhibition of soluble tumour necrosis factor is therapeutic in experimental autoimmune encephalomyelitis. Treatment with XPro1595, a selective soluble tumour necrosis factor blocker, improves the clinical outcome, whereas non-selective inhibition of both forms of tumour necrosis factor with etanercept does not result in protection. The therapeutic effect of XPro1595 is associated with axon preservation and improved myelin compaction, paralleled by increased expression of axon-specific molecules (e.g. neurofilament-H) and reduced expression of non-phosphorylated neurofilament-H which is associated with axon damage. XPro1595-treated mice show significant remyelination accompanied by elevated expression of myelin-specific genes and increased numbers of oligodendrocyte precursors. Immunohistochemical characterization of tumour necrosis factor receptors in the spinal cord following experimental autoimmune encephalomyelitis shows tumour necrosis factor receptor 1 expression in neurons, oligodendrocytes and astrocytes, while tumour necrosis factor receptor 2 is localized in oligodendrocytes, oligodendrocyte precursors, astrocytes and macrophages/microglia. Importantly, a similar pattern of expression is found in post-mortem spinal cord of patients affected by progressive multiple sclerosis, suggesting that pharmacological modulation of tumour necrosis factor receptor signalling may represent an important target in affecting not only the course of mouse experimental autoimmune encephalomyelitis but human multiple sclerosis as well. Collectively, our data demonstrate that selective inhibition of soluble tumour necrosis factor improves recovery following experimental autoimmune encephalomyelitis, and that signalling mediated by transmembrane tumour necrosis factor is essential for axon and myelin preservation as well as remyelination, opening the possibility of a new avenue of treatment for multiple sclerosis.

Early molecular and synaptic dysfunctions in the prodromal stages of Alzheimer’s disease: focus on TNF-α and IL-1β

Alterations in cytokine expression as well as deficits in synaptic activity are two features observed in early, prodromal stages of Alzheimer’s disease (AD). The cytokines TNF-α and IL-1β are not only mediators of immune responses, but are also involved in regulating synaptic activity through their effects on neuronal excitability and Hebbian plasticity. We propose that early changes occurring in the AD brain, such as increases in soluble amyloid-β oligomers, may increase the expression of certain cytokines and subsequently cause alterations in cytokine-mediated synaptic activity. A shift of focus towards the prodromal stages of AD, which incorporate the earliest detectable molecular, electrophysiological and behavioral alterations, may provide novel therapeutic targets and potential biomarkers for this currently incurable neurodegenerative disease.

Treatment of TNF mediated diseases by selective inhibition of soluble TNF or TNFR1

The TNF signaling pathway is a valuable target in the therapy of autoimmune diseases, and anti-TNF drugs are successfully used to treat diseases such as rheumatoid arthritis, Crohn's disease and psoriasis. By their ability to interfere with inflammatory processes at multiple levels, these TNF blockers have become invaluable tools to inhibit the inflammation induced damage and allow recovery of the affected tissues. Unfortunately this therapy has some drawbacks, including increased risk of infection and malignancy, and remarkably, the onset of new auto-immune diseases. Some of these effects are caused by the unwanted abrogation of beneficial TNF signaling. More specific targeting of the pathological TNF-induced signaling might lead to broader applicability and improved safety. Specificity might be increased by inhibiting the soluble TNF/TNFR1 axis while leaving the often beneficial transmembrane TNF/TNFR2 signaling untouched. This approach looks promising because it inhibits the pathological effects of TNF and reduces the side effects, and it opens the way for the treatment of other diseases in which TNFR2 inhibition is detrimental. In this review we give an overview of in vivo mouse studies of TNF mediated pathologies demonstrating that the blockade or genetic deletion of sTNF or TNFR1 is preferable over total TNF blockade.

Regulator of G-protein signaling-10 negatively regulates NF-κB in microglia and neuroprotects dopaminergic neurons in hemiparkinsonian rats

Microglia are the brain-resident macrophages responsible for immune surveillance that become activated in response to injury, infection, environmental toxins, and other stimuli that threaten neuronal survival. Previous work from our group demonstrated that mice deficient in Regulator of G-protein Signaling 10 (RGS10), a microglia-enriched GTPase activating protein (GAP) for G-protein α subunits, displayed increased microglial burden in the CNS at birth and developed a parkinsonian phenotype after exposure to chronic systemic inflammation, implicating a neuroprotective role for RGS10 in the nigrostriatal pathway. While it is known that RGS10 is expressed in both microglia and certain subsets of neurons, it is not known whether RGS10 functions similarly in both cells types. In this study we sought to delineate the specific role of RGS10 in microglia and identify the molecular pathway(s) required for RGS10 to exert its actions in microglia. Here, we identify RGS10 as a negative regulator of the nuclear factor κB(NF-κB) pathway in microglia and demonstrate that the proinflammatory and cytotoxic phenotype of Rgs10-null microglia can be reversed by lentiviral-mediated restoration of RGS10 expression. In vivo gene transfer of RGS10 into the substantia nigra pars compacta (SNpc) of rats reduced microgliosis and protected against 6-OHDA neurotoxin-induced death of dopaminergic (DA) neurons. Together, our findings suggest that modulation of RGS10 activity in microglia may afford therapeutic benefit in the treatment of chronic neuroinflammatory conditions as well as neuroprotection against inflammation-related degeneration in Parkinson's disease (PD), the second most common neurodegenerative disorder affecting individuals over age 65.

Ablation of TNF-RI/RII expression in Alzheimer's disease mice leads to an unexpected enhancement of pathology: implications for chronic pan-TNF-α suppressive therapeutic strategies in the brain

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by severe memory loss and cognitive impairment. Neuroinflammation, including the extensive production of pro-inflammatory molecules and the activation of microglia, has been implicated in the disease process. Tumor necrosis factor (TNF)-α, a prototypic pro-inflammatory cytokine, is elevated in AD, is neurotoxic, and colocalizes with amyloid plaques in AD animal models and human brains. We previously demonstrated that the expression of TNF-α is increased in AD mice at ages preceding the development of hallmark amyloid and tau pathological features and that long-term expression of this cytokine in these mice leads to marked neuronal death. Such observations suggest that TNF-α signaling promotes AD pathogenesis and that therapeutics suppressing this cytokine's activity may be beneficial. To dissect TNF-α receptor signaling requirements in AD, we generated triple-transgenic AD mice (3xTg-AD) lacking both TNF-α receptor 1 (TNF-RI) and 2 (TNF-RII), 3xTg-ADxTNF-RI/RII knock out, the cognate receptors of TNF-α. These mice exhibit enhanced amyloid and tau-related pathological features by the age of 15 months, in stark contrast to age-matched 3xTg-AD counterparts. Moreover, 3xTg-ADxTNF-RI/RII knock out-derived primary microglia reveal reduced amyloid-β phagocytic marker expression and phagocytosis activity, indicating that intact TNF-α receptor signaling is critical for microglial-mediated uptake of extracellular amyloid-β peptide pools. Overall, our results demonstrate that globally ablated TNF receptor signaling exacerbates pathogenesis and argues against long-term use of pan-anti-TNF-α inhibitors for the treatment of AD.

Intraneuronal APP, not free Aβ peptides in 3xTg-AD mice: implications for tau versus Aβ-mediated Alzheimer neurodegeneration

Alzheimer's disease (AD) is characterized by the accumulation of intraneuronal tau and extracellular amyloid-β (Aβ) peptide. A triple transgenic (Tg) mouse (3xTg-AD) was reported to develop Aβ plaques and tau inclusions as well as remarkable accumulations of intracellular Aβ that were suggested to be the initiators of AD pathogenesis. However, it was unclear whether the anti-Aβ antibodies were able to distinguish Aβ peptide from the same Aβ epitopes within the amyloid precursor protein (APP). To further elucidate the identity of the immunoreactive intraneuronal material in 3xTg-AD mice, we conducted immunohistochemical, biochemical, and ultrastructural studies using a well characterized panel of antibodies that distinguish Aβ within APP from cleaved Aβ peptides. We found that the intraneuronal material shared epitopes with full-length APP but not free Aβ. To demonstrate unequivocally that this intraneuronal material was not free Aβ peptide, we generated 3xTg-AD mice deficient for β-secretase (BACE), the protease required for Aβ generation from APP. In the absence of Aβ production, robust intraneuronal APP immunostaining was detected in the 3xTg-AD/BACE(-/-) mice. Finally, we found that the formation of tau lesions was not different between 3xTg-AD versus 3xTg-AD/BACE(-/-) mice, thereby demonstrating that tau pathology forms independently from Aβ peptide generation in this mouse model. Although we cannot corroborate the presence of intraneuronal Aβ peptide in 3xTg-AD mice, our findings warrant further study as to the role of aberrant APP accumulation in this unique model of AD.

Tumor necrosis factor-alpha and the roles it plays in homeostatic and degenerative processes within the central nervous system

Tumor Necrosis Factor-alpha (TNF-α) is a prototypic pro-inflammatory cytokine involved in the innate immune response. TNF-α ligation and downstream signaling with one of its cognate receptors, TNF-RI or TNF-RII, modulates fundamental processes in the brain including synapse formation and regulation, neurogenesis, regeneration, and general maintenance of the central nervous system (CNS). During states of chronic neuroinflammation, extensive experimental evidence implicates TNF-α as a key mediator in disease progression, gliosis, demyelination, inflammation, blood-brain-barrier deterioration, and cell death. This review explores the complex roles of TNF-α in the CNS under normal physiologic conditions and during neurodegeneration. We focus our discussion on Multiple Sclerosis, Parkinson's disease, and Alzheimer's disease, relaying the outcomes of preclinical and clinical testing of TNF-α directed therapeutic strategies, and arguing that despite the wealth of functions attributed to this central cytokine, surprisingly little is known about the cell type- and stage-specific roles of TNF-α in these debilitating disorders.

Prevention of the β-amyloid peptide-induced inflammatory process by inhibition of double-stranded RNA-dependent protein kinase in primary murine mixed co-cultures

Background

Inflammation may be involved in the pathogenesis of Alzheimer's disease (AD). There has been little success with anti-inflammatory drugs in AD, while the promise of anti-inflammatory treatment is more evident in experimental models. A new anti-inflammatory strategy requires a better understanding of molecular mechanisms. Among the plethora of signaling pathways activated by β-amyloid (Aβ) peptides, the nuclear factor-kappa B (NF-κB) pathway could be an interesting target. In virus-infected cells, double-stranded RNA-dependent protein kinase (PKR) controls the NF-κB signaling pathway. It is well-known that PKR is activated in AD. This led us to study the effect of a specific inhibitor of PKR on the Aβ42-induced inflammatory response in primary mixed murine co-cultures, allowing interactions between neurons, astrocytes and microglia.

Methods

Primary mixed murine co-cultures were prepared in three steps: a primary culture of astrocytes and microglia for 14 days, then a primary culture of neurons and astrocytes which were cultured with microglia purified from the first culture. Before exposure to Aβ neurotoxicity (72 h), co-cultures were treated with compound C16, a specific inhibitor of PKR. Levels of tumor necrosis factor-α (TNFα), interleukin (IL)-1β, and IL-6 were assessed by ELISA. Levels of P_T451-PKR and activation of IκB, NF-κB and caspase-3 were assessed by western blotting. Apoptosis was also followed using annexin V-FITC immunostaining kit. Subcellular distribution of P_T451-PKR was assessed by confocal immunofluorescence and morphological structure of cells by scanning electron microscopy. Data were analysed using one-way ANOVA followed by a Newman-Keuls' post hoc test

Results

In these co-cultures, PKR inhibition prevented Aβ42-induced activation of IκB and NF-κB, strongly decreased production and release of tumor necrosis factor (TNFα) and interleukin (IL)-1β, and limited apoptosis.

Conclusion

In spite of the complexity of the innate immune response, PKR inhibition could be an interesting anti-inflammatory strategy in AD.

Targeting TNF-α to elucidate and ameliorate neuroinflammation in neurodegenerative diseases

Inflammatory signals generated within the brain and peripheral nervous system direct diverse biological processes. Key amongst the inflammatory molecules is tumor necrosis factor-α (TNF-α), a potent pro-inflammatory cytokine that, via binding to its associated receptors, is considered to be a master regulator of cellular cascades that control a number of diverse processes coupled to cell viability, gene expression, synaptic integrity and ion homeostasis. Whereas a self-limiting neuroinflammatory response generally results in the resolution of an intrinsically or extrinsically triggered insult by the elimination of toxic material or injured tissue to restore brain homeostasis and function, in the event of an unregulated reaction, where the immune response persists, inappropriate chronic neuroinflammation can ensue. Uncontrolled neuroinflammatory activity can induce cellular dysfunction and demise, and lead to a self-propagating cascade of harmful pathogenic events. Such chronic neuroinflammation is a typical feature across a range of debilitating common neurodegenerative diseases, epitomized by Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, in which TNF-α expression appears to be upregulated and may represent a valuable target for intervention. Elaboration of the protective homeostasis signaling cascades from the harmful pathogenic ones that likely drive disease onset and progression could aid in the clinical translation of approaches to lower brain and peripheral nervous system TNF-α levels, and amelioration of inappropriate neuroinflammation.

Inflammation induced by infection potentiates tau pathological features in transgenic mice

Comorbidities that promote the progression of Alzheimer's disease (AD) remain to be uncovered and evaluated in animal models. Because elderly individuals are vulnerable to viral and bacterial infections, these microbial agents may be considered important comorbidities that could potentiate an already existing and tenuous inflammatory condition in the brain, accelerating cognitive decline, particularly if the cellular and molecular mechanisms can be defined. Researchers have recently demonstrated that triggering inflammation in the brain exacerbates tau pathological characteristics in animal models. Herein, we explore whether inflammation induced via viral infection, compared with inflammation induced via bacterial lipopolysaccharide, modulates AD-like pathological features in the 3xTg-AD mouse model and provide evidence to support the hypothesis that infectious agents may act as a comorbidity for AD. Our study shows that infection-induced acute or chronic inflammation significantly exacerbates tau pathological characteristics, with chronic inflammation leading to impairments in spatial memory. Tau phosphorylation was increased via a glycogen synthase kinase-3β-dependent mechanism, and there was a prominent shift of tau from the detergent-soluble to the detergent-insoluble fraction. During chronic inflammation, we found that inhibiting glycogen synthase kinase-3β activity with lithium reduced tau phosphorylation and the accumulation of insoluble tau and reversed memory impairments. Taken together, infectious agents that trigger central nervous system inflammation may serve as a comorbidity for AD, leading to cognitive impairments by a mechanism that involves exacerbation of tau pathological characteristics.

Epigenetic mechanisms in Alzheimer's disease

Epigenetic modifications help orchestrate sweeping developmental, aging, and disease-causing changes in phenotype by altering transcriptional activity in multiple genes spanning multiple biologic pathways. Although previous epigenetic research has focused primarily on dividing cells, particularly in cancer, recent studies have shown rapid, dynamic, and persistent epigenetic modifications in neurons that have significant neuroendocrine, neurophysiologic, and neurodegenerative consequences. Here, we provide a review of the major mechanisms for epigenetic modification and how they are reportedly altered in aging and Alzheimer's disease (AD). Because of their reach across the genome, epigenetic mechanisms may provide a unique integrative framework for the pathologic diversity and complexity of AD.

Systemic and central immunity in Alzheimer's disease: therapeutic implications

Clinical pharmaceutical trials aimed at modulating the immune system in Alzheimer's Disease have largely focused on either dampening down central proinflammatory innate immunity or have manipulated adaptive immunity to facilitate the removal of centrally deposited beta amyloid. To date, these trials have had mixed clinical therapeutic effects. However, a number of clinical studies have demonstrated disturbances of both systemic and central innate immunity in Alzheimer's Disease and attention has been drawn to the close communication pathways between central and systemic immunity. This paper highlights the need to take into account the potential systemic effects of drugs aimed at modulating central immunity and the possibility of developing novel therapeutic approaches based on the manipulation of systemic immunity and its communication with the central nervous system.

Hippocampal expression of murine TNFα results in attenuation of amyloid deposition in vivo

Fibrillar amyloid β (fAβ) peptide is the major component of Aβ plaques in the brains of Alzheimer's disease (AD) patients. Inflammatory mediators have previously been proposed to be drivers of Aβ pathology in AD patients by increasing amyloidogenic processing of APP and promoting Aβ accumulation, but recent data have shown that expression of various inflammatory cytokines attenuates Aβ pathology in mouse models. In an effort to further study the role of different inflammatory cytokines on Aβ pathology in vivo, we explored the effect of murine Tumor Necrosis Factor α (mTNFα) in regulating Aβ accumulation. Recombinant adeno-associated virus serotype 1 (AAV2/1) mediated expression of mTNFα in the hippocampus of 4 month old APP transgenic TgCRND8 mice resulted in significant reduction in hippocampal Aβ burden. No changes in APP levels or APP processing were observed in either mTNFα expressing APP transgenic mice or in non-transgenic littermates. Analysis of Aβ plaque burden in mTNFα expressing mice showed that even after substantial reduction compared to EGFP expressing age-matched controls, the Aβ plaque burden levels of the former do not decrease to the levels of 4 month old unmanipulated mice. Taken together, our data suggests that proinflammatory cytokine expression induced robust glial activation can attenuate plaque deposition. Whether such an enhanced microglial response actually clears preexisting deposits without causing bystander neurotoxicity remains an open question.

Novel mutants of human tumor necrosis factor with dominant-negative properties

Tumor necrosis factor (TNF) is a polyfunctional cytokine, one of the key mediators of inflammation and innate immunity. On the other hand, systemic or local TNF overexpression is typical of such pathological states as rheumatoid arthritis, psoriasis, Crohn's disease, septic shock, and multiple sclerosis. Neutralization of TNF activity has a marked curative effect for some diseases; therefore, the search for various TNF blockers is a promising field of protein engineering and biotechnology. According to the previously developed concept concerning the possibility of designing dominant-negative mutants, the following TNF variants have been studied: TNFY87H + A145R, TNFY87H + A96S + A145R, and TNFV91N + A145R. All of these form inactive TNF heterotrimers with the native protein. The ability of mutants to neutralize the effect of TNF was investigated. The addition of mutants to the native protein was shown to provide a concentration-dependent suppression of TNF cytotoxicity against the mouse fibroblast cell line L929. Thus, novel inhibitors of human TNF can be engineered on the basis of these muteins.

Suppressed microglial E prostanoid receptor 1 signaling selectively reduces tumor necrosis factor alpha and interleukin 6 secretion from toll-like receptor 3 activation

Activation of innate immunity via toll-like receptors (TLRs) is associated with neurodegenerative diseases, and some effectors, like tumor necrosis factor alpha (TNFα) and interleukin 6 (IL-6), directly contribute to neurodegeneration. We tested the hypothesis that prostaglandin (PG) E(2) receptor subtype 1 (EP1) was necessary for the induction of microglial cytokines following the activation of innate immunity. Primary murine microglia had cytokine secretion by activators of TLR3 > TLR9 > TLR4 > TLR2. TLR3 activation induced early expression of cyclooxygenase 2 (COX2) and delayed expression of membranous PGE synthase and secretion of PGE(2) . Nonselective and COX2-selective inhibitors blocked TLR3 induction of TNFα and IL-6. Moreover, of the nine of twenty cytokines and chemokines induced by TLR3 activation, only TNFα and IL-6 were significantly dependent on EP1 signaling as determined using microglia from mice homozygous deficient for EP1 gene or wild-type microglia coincubated with an EP1 antagonist. These results were confirmed by blocking intracellular Ca(2+) release with 2-aminoethoxy-diphenyl borate or Xestospongin C, inhibitors of IP3 receptors. Our results show that suppression of microglial EP1 signaling achieves much of the desired effect of COX inhibitors by selectively blocking TLR3-induced microglial secretion of two major effectors of paracrine neuron damage. In combination with the ability of EP1 suppression to ameliorate excitotoxicity, these data point to blockade of EP1 as an attractive candidate therapeutic for neurodegenerative diseases.

Glycogen synthase kinase-3β inactivation inhibits tumor necrosis factor-α production in microglia by modulating nuclear factor κB and MLK3/JNK signaling cascades

BACKGROUND

Deciphering the mechanisms that modulate the inflammatory response induced by microglial activation not only improves our insight into neuroinflammation but also provides avenues for designing novel therapies that could halt inflammation-induced neuronal degeneration. Decreasing glycogen synthase kinase-3β (GSK-3β) activity has therapeutic benefits in inflammatory diseases. However, the exact molecular mechanisms underlying GSK-3β inactivation-mediated suppression of the inflammatory response induced by microglial activation have not been completely clarified. Tumor necrosis factor-α (TNF-α) plays a central role in injury caused by neuroinflammation. We investigated the regulatory effect of GSK-3β on TNF-α production by microglia to discern the molecular mechanisms of this modulation.

METHODS

Lipopolysaccharide (LPS) was used to induce an inflammatory response in cultured primary microglia or murine BV-2 microglial cells. Release of TNF-α was measured by ELISA. Signaling molecules were analyzed by western blotting, and activation of NF-κB and AP-1 was measured by ELISA-based DNA binding analysis and luciferase reporter assay. Protein interaction was examined by coimmunoprecipitation.

RESULTS

Inhibition of GSK-3β by selective GSK-3β inhibitors or by RNA interference attenuated LPS-induced TNF-α production in cultured microglia. Exploration of the mechanisms by which GSK-3β positively regulates inflammatory response showed that LPS-induced IκB-α degradation, NF-κBp65 nuclear translocation, and p65 DNA binding activity were not affected by inhibition of GSK-3β activity. However, GSK-3β inactivation inhibited transactivation activity of p65 by deacetylating p65 at lysine 310. Furthermore, we also demonstrated a functional interaction between mixed lineage kinase 3 (MLK3) and GSK-3β during LPS-induced TNF-α production in microglia. The phosphorylated levels of MLK3, MKK4, and JNK were increased upon LPS treatment. Decreasing GSK-3β activity blocked MLK3 signaling cascades through disruption of MLK3 dimerization-induced autophosphorylation, ultimately leading to a decrease in TNF-α secretion.

CONCLUSION

These results suggest that inactivation of GSK-3β might represent a potential strategy to downregulate microglia-mediated inflammatory processes.

Deletion of CD14 attenuates Alzheimer's disease pathology by influencing the brain's inflammatory milieu

Alzheimer's disease (AD) is characterized by the deposition of β-amyloid (Aβ)-containing plaques within the brain that is accompanied by a robust microglial-mediated inflammatory response. This inflammatory response is reliant upon engagement of innate immune signaling pathways involving the toll-like receptors (TLRs). Studies assessing the roles of TLRs in AD pathogenesis have yielded conflicting results. We have assessed the roles of the TLRs through genetic inactivation of the TLR2/4 coreceptor, CD14, in a transgenic murine model of AD. Transgenic mice lacking CD14 exhibited reduced insoluble, but not soluble, levels of Aβ at 7 months of age. This corresponded with decreased plaque burden resulting from a reduction in number and size of both diffuse and thioflavin S-positive plaques and an overall reduction in the number of microglia. These findings are inconsistent with the established actions of these receptors. Moreover, loss of CD14 expression was associated with increased expression of genes encoding the proinflammatory cytokines Tnfα and Ifnγ, decreased levels of the microglial/macrophage alternative activation markers Fizz1 and Ym1, and increased expression of the anti-inflammatory gene Il-10. Thus, the loss of CD14 resulted in a significant change in the inflammatory environment of the brain, likely reflecting a more heterogeneous population of microglia within the brains of the animals. The reduction in plaque burden was not a result of changes in the expression of various Aβ degrading enzymes or proteins associated with Aβ clearance. These data suggest that CD14 is a critical regulator of the microglial inflammatory response that acts to modulate Aβ deposition.

Receptor-mediated abeta amyloid antibody targeting to Alzheimer's disease mouse brain

The goal of this work is the reduction in the Abeta amyloid peptide burden in brain of Alzheimer's disease (AD) transgenic mice without the concomitant elevation in plasma Abeta amyloid peptide. An anti-Abeta amyloid antibody (AAA) was re-engineered as a fusion protein with a blood-brain barrier (BBB) molecular Trojan horse. The AAA was engineered as a single chain Fv (ScFv) antibody, and the ScFv was fused to the heavy chain of a chimeric monoclonal antibody (mAb) against the mouse transferrin receptor (TfR), and this fusion protein was designated cTfRMAb-ScFv. The cTfRMAb-ScFv protein penetrates mouse brain from blood via transport on the BBB TfR, and the brain uptake is 3.5% of injected dose/gram brain following an intravenous administration. Double transgenic APPswe,PSEN1dE9 mice were studied at 12 months of age. The mice were shown to have extensive Abeta amyloid plaques in cerebral cortex based on immunocytochemistry. The mice were treated every 3-4 days by intravenous injections of either saline or the cTfRMAb-ScFv fusion protein at an injection dose of 1 mg/kg for 12 consecutive weeks. The brain Aβ¹⁻⁴² concentration was reduced 40% in the fusion protein treated mice, without any elevation in plasma Aβ¹⁻⁴² concentration. No cerebral microhemorrhage was observed in the treated mice. These results show that brain-penetrating antibody pharmaceutics can be developed for brain disorders such as AD following the re-engineering of the antibody as a fusion protein that is transported across the BBB via receptor-mediated transport.

Reductions in amyloid-beta-derived neuroinflammation, with minocycline, restore cognition but do not significantly affect tau hyperphosphorylation

Cognitive decline in Alzheimer's disease (AD) occurs as a result of the buildup of pathological proteins and downstream events including an elevated and altered inflammatory response. Inflammation has previously been linked to increased abnormal phosphorylation of tau protein. To determine if endogenous amyloid-beta (Abeta)-induced neuroinflammation drives tau phosphorylation in vivo, we treated 8-month-old 3xTg-AD with minocycline, an anti-inflammatory agent, to assess how it influenced cognitive decline and development of pathology. 4 months of treatment restored cognition to non-transgenic performance. Inflammatory profiling revealed a marked decrease in GFAP, TNFalpha, and IL6 and an increase in the CXCL1 chemokines KC and MIP1a. Minocycline also reduced levels of insoluble Abeta and soluble fibrils. Despite reducing levels of the tau kinase cdk5 coactivator p25, minocycline did not have wide effects on tau pathology with only one phospho-epitope showing reduction with treatment (S212/S214). The sum of these findings shows that reduction of the inflammatory events in an AD mouse model prevents cognitive deficits associated with pathology, but that endogenous Abeta-derived neuroinflammation does not contribute significantly to the development of tau pathology.

Anti-TNF-α reduces amyloid plaques and tau phosphorylation and induces CD11c-positive dendritic-like cell in the APP/PS1 transgenic mouse brains

Inflammation plays an important role in the pathogenesis of Alzheimer's disease (AD). Overexpression of tumor necrosis factor-α (TNF-α) occurs in the AD brain. Recent clinical studies have shown that the anti-TNF-α therapy improves cognition function of AD patients rapidly. However, the underlying mechanism remains elusive. The present study investigates the effects of intracerebroventricular injection of the monoclonal TNF-α antibody, Infliximab, on the pathological features of AD in the APP/PS1 double transgenic mice. We found that Infliximab administration reduced the levels of TNF-α, amyloid plaques, and tau phosphorylation as early as three days after daily injection of 150 μg Infliximab for three days. The number of CD11c-positive dendritic-like cells and the expression of CD11c were found to be increased concurrently after Infliximab injection. These data suggested that the CD11c-positive dendritic-like cells might contribute to the Infliximab-induced reduction of AD-like pathology. Furthermore, our results support the use of anti-TNF-α for the treatment of AD.