CD40L disruption enhances Abeta vaccine-mediated reduction of cerebral amyloidosis while minimizing cerebral amyloid angiopathy and inflammation

Neuroimmune mechanisms underlying Alzheimer's disease: Insights into central and peripheral immune cell crosstalk

Alzheimer's disease (AD) is a highly life-threatening neurodegenerative disease. Dysregulation of the immune system plays a critical role in promoting AD, which has attracted extensive attention recently. Central and peripheral immune responses are involved in the pathogenesis of AD. Immune changes precede Aβ-associated senile plaque formation and tau-related neurofibrillary tangles, which are the recognised pathological features of AD. Therefore, elucidating immune-related mechanisms underlying the development of AD can help to prevent and treat AD at the source by blocking its progression before the development of pathological changes. To understand the specific pathogenesis of AD, it is important to examine the role of central and peripheral immunity in AD. This review summarises immune-related mechanisms underlying the pathogenesis of AD, focusing on the effect of various central and peripheral immune cells, and describes the possible crosstalk between central and peripheral immunity during the development of AD. This review provides novel insights into the treatment of AD and offers a new direction for immune-related research on AD in the future.

Acquired immunity and Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive defects. The role of the central immune system dominated by microglia in the progression of AD has been extensively investigated. However, little is known about the peripheral immune system in AD pathogenesis. Recently, with the discovery of the meningeal lymphatic vessels and glymphatic system, the roles of the acquired immunity in the maintenance of central homeostasis and neurodegenerative diseases have attracted an increasing attention. The T cells not only regulate the function of neurons, astrocytes, microglia, oligodendrocytes and brain microvascular endothelial cells, but also participate in the clearance of β-amyloid (Aβ) plaques. Apart from producing antibodies to bind Aβ peptides, the B cells affect Aβ-related cascades via a variety of antibody-independent mechanisms. This review systemically summarizes the recent progress in understanding pathophysiological roles of the T cells and B cells in AD.

Microglial priming of antigen presentation and adaptive stimulation in Alzheimer's disease

The prominent pathological consequences of Alzheimer's disease (AD) are the misfolding and mis-sorting of two cellular proteins, amyloid-β and microtubule-associated protein Tau. The accumulation of toxic phosphorylated Tau inside the neurons induces the increased processing of amyloid-β-associated signaling cascade and vice versa. Neuroinflammation-driven synaptic depletion and cognitive decline are substantiated by the cross talk of activated microglia and astroglia, leading to neuron degeneration. Microglia are the brain-resident immune effectors that prove their diverse functions in maintaining CNS homeostasis via collaboration with astrocytes and T lymphocytes. Age-related senescence and chronic inflammation activate microglia with increased pro-inflammatory markers, oxidative damage and phagocytosis. But the improper processing of misfolded protein via lysosomal pathway destines the spreading of 'seed' constituents to the nearby healthy neurons. Primed microglia process and present self-antigen such as amyloid-β and modified Tau to the infiltrated T lymphocytes through MHC I/II molecules. After an effective conversation with CD4+ T cells, microglial phenotype can be altered from pro-active M1 to neuro-protective M2 type, which corresponds to the tissue remodeling and homeostasis. In this review, we are focusing on the change in functionality of microglia from innate to adaptive immune response in the context of neuroprotection, which may help in the search of novel immune therapy in AD.

Immunological alteration & toxic molecular inductions leading to cognitive impairment & neurotoxicity in transgenic mouse model of Alzheimer's disease

AIMS

Inflammation is considered to be one of the crucial pathological factors associated with the development of Alzheimer's disease, although supportive experimental evidence remains undiscovered. Therefore, the current study was carried out to better understand and establish the pathophysiological involvement of chronic inflammation in a double transgenic mouse model of Alzheimer's disease.

MAIN METHODS

We analyzed amyloid-beta deposition, oxidative stress, biochemical, neurochemical and immunological markers in a 10month old (APΔE9) mouse model. Memory functions were assessed by behavioral testing followed by measurement of synaptic plasticity via extracellular field recordings.

KEY FINDINGS

Substantial increases in amyloid-beta levels, beta-secretase activity, and oxidative stress, along with significant neurochemical alterations in glutamate and GABA levels were detected in the brain of APΔE9 mice. Interestingly, marked elevations of pro-inflammatory cytokines in whole brain lysate of APΔE9 mice were observed. Flow cytometric analysis revealed a higher frequency of CD4+ IL-17a and IFN-γ secreting T-cells in APΔE9 brain, indicating a robust T-cell infiltration and activation. Behavioral deficits in learning and memory tasks, along with impairment in long-term potentiation and associated biochemical changes in the expression of glutamatergic receptor subunits were evident.

SIGNIFICANCE

Thus, this study establishes the role by which oxidative stress, alterations in glutamate and GABA levels and inflammation increases hippocampal and cortical neurotoxicity resulting in the cognitive deficits associated with Alzheimer's disease.

How to get from here to there: macrophage recruitment in Alzheimer's disease

Alzheimer's disease (AD) is pathologically defined by presence of intracellular neurofibrillary tangles and extracellular amyloid plaques comprised of amyoid-β (Aβ) peptides. Despite local recruitment of brain microglia to sites of amyloid deposition, these mononuclear phagocytes ultimately fail at restricting β-amyloid plaque formation. On the other hand, it is becoming increasingly clear that professional phagocytes from the periphery possess Aβ clearance aptitude. Yet, in order to harness this beneficial innate immune response, effective strategies must be developed to coax monocytes/macrophages from the periphery into the brain. It has previously been suggested that Aβ 'immunotherapy' clears cerebral Aβ deposits via mononuclear phagocytes, and recent evidence suggests that targeting transforming growth factor-β-Smad 2/3 signaling and chemokine pathways such as Ccr2 impacts blood-to-brain trafficking of these cells in transgenic mouse models of AD. It has also been shown that the fractalkine receptor (Cx3cr1) pathway plays a critical role in chemotaxis of mononuclear phagocytes toward neurons destined for death in AD model mice. In order to translate these basic science findings into AD treatments, a key challenge will be to develop a new generation of pharmacotherapeutics that safely and effectively promote recruitment of peripheral amyloid phagocytes into the AD brain.

Murine models of Alzheimer's disease and their use in developing immunotherapies

Alzheimer's disease (AD) is one of the categories of neurodegenerative diseases characterized by a conformational change of a normal protein into a pathological conformer with a high beta-sheet content that renders it resistant to degradation and neurotoxic. In AD, the normal soluble amyloid beta (sAbeta) peptide is converted into oligomeric/fibrillar Abeta. The oligomeric forms of Abeta are thought to be the most toxic, while fibrillar Abeta becomes deposited as amyloid plaques and congophilic angiopathy, which both serve as neuropathological markers of the disease. An additional important feature of AD is the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles. Many therapeutic interventions are under investigation to prevent and treat AD. The testing of these diverse approaches to ameliorate AD pathology has been made possible by the existence of numerous transgenic mouse models which each mirror specific aspects of AD pathology. None of the current murine models is a perfect match of the human disease. Perhaps the most exciting of the therapeutic approaches being developed is immunomodulation targeting the aggregating proteins, Abeta and tau. This type of AD therapy is currently being assessed in many transgenic mouse models, and promising findings have led to clinical trials. However, there is a discrepancy between results in murine models and ongoing clinical trials, which highlight the limitations of these models and also of our understanding of the underlying etiology and pathogenesis of AD. Because of these uncertainties, Tg models for AD are continuously being refined with the aim to better understand the disease and to enhance the predictive validity of potential treatments such as immunotherapies.

Impact of the CD40-CD40L dyad in Alzheimer's disease

As the number of elderly individuals rises, Alzheimer's disease (AD), marked by amyloid-beta deposition, neurofibrillary tangle formation, and low-level neuroinflammation, is expected to lead to an ever-worsening socioeconomic burden. AD pathoetiologic mechanisms are believed to involve chronic microglial activation. This phenomenon is associated with increased expression of membrane-bound CD40 with its cognate ligand, CD40 ligand (CD40L), as well as increased circulating levels of soluble forms of CD40 (sCD40) and CD40L (sCD40L). Here, we review the role of this inflammatory dyad in the pathogenesis of AD. In addition, we examine potential therapeutic strategies such as statins, flavonoids, and human umbilical cord blood transplantation, all of which have been shown to modulate CD40-CD40L interaction in mouse models of AD. Importantly, therapeutic approaches focusing on CD40-CD40L dyad regulation, either alone or in combination with amyloid-beta immunotherapy, may provide for a safe and effective AD prophylaxis or treatment in the near future.

Amyloid-beta immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive, degenerative disorder of the brain and the most common form of dementia among the elderly. As the population grows and lifespan is extended, the number of AD patients will continue to rise. Current clinical therapies for AD provide partial symptomatic benefits for some patients; however, none of them modify disease progression. Amyloid-beta (Abeta) peptide, the major component of senile plaques in AD patients, is considered to play a crucial role in the pathogenesis of AD thereby leading to Abeta as a target for treatment. Abeta immunotherapy has been shown to induce a marked reduction in amyloid burden and an improvement in cognitive function in animal models. Although preclinical studies were successful, the initial human clinical trial of an active Abeta vaccine was halted due to the development of meningoencephalitis in approximately 6% of the vaccinated AD patients. Some encouraging outcomes, including signs of cognitive stabilization and apparent plaque clearance, were obtained in subset of patients who generated antibody titers. These promising preliminary data support further efforts to refine Abeta immunotherapy to produce highly effective and safer active and passive vaccines for AD. Furthermore, some new human clinical trials for both active and passive Abeta immunotherapy are underway. In this review, we will provide an update of Abeta immunotherapy in animal models and in human beings, as well as discuss the possible mechanisms underlying Abeta immunotherapy for AD.

Vaccination as a therapeutic approach to Alzheimer's disease

Alzheimer's disease is the most common cause of dementia worldwide. Alzheimer's disease is a member of a broad range of neurodegenerative diseases characterized pathologically by the conformational change of a normal protein into a pathological conformer with a high beta-sheet content that renders it neurotoxic. In the case of Alzheimer's disease, the normal soluble amyloid beta peptide is converted into oligomeric/fibrillar amyloid beta. The oligomeric forms of amyloid beta have been hypothesized to be the most toxic, whereas fibrillar amyloid beta becomes deposited as amyloid plaques and congophilic angiopathy, which both serve as neuropathological markers of the disease. In addition, the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles is a critical part of the pathology. Numerous therapeutic interventions are under investigation to prevent and treat Alzheimer's disease. Among the most exciting and advanced of these approaches is vaccination. Immunomodulation is being tried for a range of neurodegenerative disorders, with great success being reported in most model animal trials; however, the much more limited human data have shown more modest clinical success so far, with encephalitis occurring in a minority of patients treated with active immunization. The immunomodulatory approaches for neurodegenerative diseases involve targeting a self-protein, albeit in an abnormal conformation; hence, effective enhanced clearance of the disease-associated conformer has to be balanced with the potential risk of stimulating excessive toxic inflammation within the central nervous system. The design of future immunomodulatory approaches that are more focused is dependent on addressing a number of questions, including when is the best time to start immunization, what are the most appropriate targets for vaccination, and is amyloid central to the pathogenesis of Alzheimer's disease or is it critical to target tau-related pathology also. In this review, we discuss the past experience with vaccination for Alzheimer's disease and the development of possible future strategies that target both amyloid beta-related and tau-related pathologies.

Immunotherapeutic approaches for Alzheimer's disease in transgenic mouse models

Alzheimer's disease (AD) is a member of a category of neurodegenerative diseases characterized by the conformational change of a normal protein into a pathological conformer with a high beta-sheet content that renders it resistant to degradation and neurotoxic. In the case of AD the normal soluble amyloid beta (sAbeta) peptide is converted into oligomeric/fibrillar Abeta. The oligomeric forms of Abeta are thought to be the most toxic, while fibrillar Abeta becomes deposited as amyloid plaques and congophilic angiopathy, which both serve as neuropathological markers of the disease. In addition, the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles is an essential part of the pathology. Many therapeutic interventions are under investigation to prevent and treat AD. The testing of these diverse approaches to ameliorate AD pathology has been made possible by the existence of numerous transgenic mouse models which each mirror different aspects of AD pathology. Perhaps the most exciting of these approaches is immunomodulation. Vaccination is currently being tried for a range of age associated CNS disorders with great success being reported in many transgenic mouse models. However, there is a discrepancy between these results and current human clinical trials which highlights the limitations of current models and also uncertainties in our understanding of the underlying pathogenesis of AD. No current AD Tg mouse model exactly reflects all aspects of the human disease. Since the underlying etiology of sporadic AD is unknown, the process of creating better Tg models is in constant evolution. This is an essential goal since it will be necessary to develop therapeutic approaches which will be highly effective in humans.

Aging-dependent changes of microglial cells and their relevance for neurodegenerative disorders

Among multiple structural and functional brain changes, aging is accompanied by an increase of inflammatory signaling in the nervous system as well as a dysfunction of the immune system elsewhere. Although the long-held view that aging involves neurocognitive impairment is now dismissed, aging is a major risk factor for neurodegenerative diseases such as Alzheimer;s disease, Parkinson;s disease and Huntington's disease, among others. There are many age-related changes affecting the brain, contributing both to certain declining in function and increased frailty, which could singly and collectively affect neuronal viability and vulnerability. Among those changes, both inflammatory responses in aged brains and the altered regulation of toll like receptors, which appears to be relevant for understanding susceptibility to neurodegenerative processes, are linked to pathogenic mechanisms of several diseases. Here, we review how aging and pro-inflammatory environment could modulate microglial phenotype and its reactivity and contribute to the genesis of neurodegenerative processes. Data support our idea that age-related microglial cell changes, by inducing cytotoxicity in contrast to neuroprotection, could contribute to the onset of neurodegenerative changes. This view can have important implications for the development of new therapeutic approaches.

Inflammation in transgenic mouse models of neurodegenerative disorders

Much evidence is available that inflammation contributes to the development of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Our review investigates how well current mouse models reflect this aspect of the pathogenesis. Transgenic models of AD have been available for several years and are the most extensively studied. Modulation of cytokine levels, activation of microglia and, to a lesser extent, activation of the complement system have been reported. Mouse models of PD and HD so far show less evidence for the involvement of inflammation. An increasing number of transgenic mouse strains is being created to model human neurodegenerative diseases. A perfect model should reflect all aspects of a disease. It is important to evaluate continuously the models for their match with the human disease and reevaluate them in light of new findings in human patients. Although none of the transgenic mouse models recapitulates all aspects of the human disorder they represent, all models have provided valuable information on basic molecular pathways. In particular, the mouse models of Alzheimer disease have also led to the development of new therapeutic strategies such as vaccination and modulation of microglial activity.

Neutralization of granulocyte macrophage colony-stimulating factor decreases amyloid beta 1-42 and suppresses microglial activity in a transgenic mouse model of Alzheimer's disease

The purpose of our study was to investigate microglia and astrocytes that are associated with human mutant amyloid precursor protein and amyloid beta (Abeta). We investigated whether the anti-granulocyte-macrophage-colony stimulating factor (GM-CSF) antibody can suppress microglial activity and decrease Abeta production in Alzheimer's disease transgenic mice (Tg2576 line). An antibody to mouse GM-CSF was introduced by intracerebroventricular (ICV) injections into the brains of 10-month-old Tg2576 male mice. We assessed the effect of several GM-CSF-associated cytokines on microglial activities and their association with Abeta using quantitative real-time RT-PCR, immunoblotting, immunohistochemistry analyses in anti-GM-CSF antibody-injected Tg2576 mice. Using sandwich ELISA technique, we measured intraneuronal Abeta in Tg2576 mice injected with GM-CSF antibody and PBS vehicle-injected control Tg2576 mice. Using double-labeling immunofluorescence analysis of intraneuronal Abeta, Abeta deposits and pro-inflammatory cytokines, we assessed the relationship between Abeta deposits and microglial markers in the Tg2576 mice, and also in the anti-GM-CSF antibody-injected Tg2576 mice. Our real-time RT-PCR analysis showed an increase in the mRNA expression of IL6, CD11c, IL1beta, CD40 and CD11b in the cerebral cortices of the Tg2576 mice compared with their littermate non-transgenic controls. Immunohistochemistry findings of microglial markers agreed with our real-time RT-PCR results. Interestingly, we found significantly decreased levels of activated microglia and Abeta deposits in anti-GM-CSF antibody-injected Tg2576 mice compared with PBS vehicle-injected Tg2576 mice. Findings from our real-time RT-PCR and immunoblotting analysis agreed with immunohistochemistry results. Our double-labeling analyses of intraneuronal Abeta and CD40 revealed that intraneuronal Abeta is associated with neuronal expression of CD40 in Tg2576 mice. Our quantitative sandwich ELISA analysis revealed decreased levels of soluble Abeta1-42 and increased levels of Abeta1-40 in Tg2576 mice injected with the anti-GM-CSF antibody, suggesting that anti-GM-CSF antibody alone decreases soluble Abeta1-42 production and suppresses microglial activity in Tg2576 mice. These findings indicating the ability of the anti-GM-CSF antibody to reduce Abeta1-42 and microglial activity in Tg2576 mice may have therapeutic implications for Alzheimer's disease.

SOLUBLE CD40 LIGAND IN DEMENTIA

Some 15-20% of the population over the age of 65 years suffer from dementia, currently one of the leading causes of death behind cardiovascular diseases, cancer and cerebrovascular diseases. The major forms of dementia share in common overactivation of the CD40-CD40-L complex, leading to high levels of proinflammatory cytokine production by immune cells of the central nervous system (CNS), including microglia and astrocytes. Consequently, both neuronal survival and signaling are negatively affected, leading to the characteristic progressive loss of higher cortical functions. We have reviewed the literature concerning the involvement of this complex in the pathology of three major forms of dementia: Alzheimer's-type, HIV-associated and vascular dementia. This is followed by a discussion of current preclinical and clinical therapies that may influence this interaction, and thus point the way toward a future neuroimmunological approach to inhibiting the effects of CD40-CD40-L in neuropsychiatric disease.

Gene expression differences in infected and noninfected middle ear complementary DNA libraries

OBJECTIVES

To investigate genetic differences in middle ear mucosa (MEM) with nontypeable Haemophilus influenzae (NTHi) infection. Genetic upregulation and downregulation occurs in MEM during otitis media (OM) pathogenesis. A comprehensive assessment of these genetic differences using the techniques of complementary DNA (cDNA) library creation has not been performed.

DESIGN

The cDNA libraries were constructed from NTHi-infected and noninfected chinchilla MEM. Random clones were picked, sequenced bidirectionally, and submitted to the National Center for Biotechnology Information (NCBI) Expressed Sequence Tags database, where they were assigned accession numbers. These numbers were used with the basic local alignment search tool (BLAST) to align clones against the nonredundant nucleotide database at NCBI.

RESULTS

Analysis with the Web-based statistical program FatiGO identified several biological processes with significant differences in numbers of represented genes. Processes involved in immune, stress, and wound responses were more prevalent in the NTHi-infected library. S100 calcium-binding protein A9 (S100A9); secretory leukoprotease inhibitor (SLPI); beta(2)-microglobulin (B2M); ferritin, heavy-chain polypeptide 1 (FTH1); and S100 calcium-binding protein A8 (S100A8) were expressed at significantly higher levels in the NTHi-infected library. Calcium-binding proteins S100A9 and S100A8 serve as markers for inflammation and have antibacterial effects. Secretory leukoprotease inhibitor is an antibacterial protein that inhibits stimuli-induced MUC1, MUC2, and MUC5AC production.

CONCLUSIONS

A number of genes demonstrate changes during the pathogenesis of OM, including SLPI, which has an impact on mucin gene expression; this expression is known to be an important regulator in OM. The techniques described herein provide a framework for future investigations to more thoroughly understand molecular changes in the middle ear, which will likely be important in developing new therapeutic and intervention strategies.

Reduced oligomeric and vascular amyloid-beta following immunization of TgCRND8 mice with an Alzheimer's DNA vaccine

Immunization with amyloid-beta (Abeta) peptide reduces amyloid load in animal studies and in humans; however clinical trials resulted in the development of a pro-inflammatory cellular response to Abeta. Apoptosis has been employed to stimulate humoral and Th2-biased cellular immune responses. Thus, we sought to investigate whether immunization using a DNA vaccine encoding Abeta in conjunction with an attenuated caspase generates therapeutically effective antibodies. Plasmids encoding Abeta and an attenuated caspase were less effective in reducing amyloid pathology than those encoding Abeta alone. Moreover, use of Abeta with an Arctic mutation (E22G) as an immunogen was less effective than wild-type Abeta in terms of improvements in pathology. Low levels of IgG and IgM were generated in response to immunization with a plasmid encoding wild-type Abeta. These antibodies decreased plaque load by as much as 36+/-8% and insoluble Abeta42 levels by 56+/-3%. Clearance of Abeta was most effective when antibodies were directed against N-terminal epitopes of Abeta. Moreover, immunization reduced CAA by as much as 69+/-12% in TgCRND8 mice. Finally, high-molecular-weight oligomers and Abeta trimers were significantly reduced with immunization. Thus, immunization with a plasmid encoding Abeta alone drives an attenuated immune response that is sufficient to clear amyloid pathology in a mouse model of Alzheimer's disease.