Abeta immunotherapy leads to clearance of early, but not late, hyperphosphorylated tau aggregates via the proteasome

Tomoregulin-2 is found extensively in plaques in Alzheimer's disease brain

Tomoregulin (TR)2 is a transmembrane protein predominantly expressed in brain. It has a unique extracellular domain, containing epidermal growth factor-like and follistatin-like modules. The ectodomain is released from the cell surface, and thought to function as a neurotrophic factor and dendritogenic agent. During CNS development and in the neuronal storage disease GM2 gangliosidosis, which is characterized by ectopic dendrites, the TR2 ectodomain is present in neuronal nuclei where it may function in dendrite initiation. Data presented here demonstrate that TR2 is found extensively in Alzheimer's disease (AD) plaques. Confocal microscopy shows that TR2 is present throughout plaques. Interestingly, TR2 is absent from plaques in the presenilin-1/amyloid precursor protein mouse model of AD. From these data, and what is known about TR2, it is hypothesized that TR2 may participate in amyloid plaque formation and contribute to the pathogenesis of AD. The human TR2 gene is located on chromosome 2q32.3, near a locus linked to Parkinson's disease. TR2 is reported to be a trophic factor for dopaminergic mesencephalic neurons.

Nonviral Abeta DNA vaccine therapy against Alzheimer's disease: long-term effects and safety

It was recently demonstrated that amyloid beta (Abeta) peptide vaccination was effective in reducing the Abeta burden in Alzheimer model mice. However, the clinical trial was halted because of the development of meningoencephalitis in some patients. To overcome this problem, anti-Abeta antibody therapy and other types of vaccination are now in trial. In this study, we have developed safe and effective nonviral Abeta DNA vaccines against Alzheimer's disease. We administered these vaccines to model (APP23) mice and evaluated Abeta burden reduction. Prophylactic treatments started before Abeta deposition reduced Abeta burden to 15.5% and 38.5% of that found in untreated mice at 7 and 18 months of age, respectively. Therapeutic treatment started after Abeta deposition reduced Abeta burden to approximately 50% at the age of 18 months. Importantly, this therapy induced neither neuroinflammation nor T cell responses to Abeta peptide in both APP23 and wild-type B6 mice, even after long-term vaccination. Although it is reported that other anti-Abeta therapies have pharmacological and/or technical difficulties, nonviral DNA vaccines are highly secure and easily controllable and are promising for the treatment of Alzheimer's disease.

Immunology and immunotherapy of Alzheimer's disease

Although Alzheimer's disease is considered to be a degenerative brain disease, it is clear that the immune system has an important role in the disease process. As discussed in this Review, immune-based therapies that are designed to remove amyloid-beta peptide from the brain have produced positive results in animal models of the disease and are being tested in humans with Alzheimer's disease. Although immunotherapy holds great promise for the treatment of Alzheimer's disease, clinical trials of active amyloid-beta vaccination of patients with Alzheimer's disease were discontinued after some patients developed meningoencephalitis. New immunotherapies using humoral and cell-based approaches are currently being investigated for the treatment and prevention of Alzheimer's disease.

Relative paucity of tau accumulation in the small areas with abundant Abeta42-positive capillary amyloid angiopathy within a given cortical region in the brain of patients with Alzheimer pathology

Cerebral amyloid angiopathy (CAA) is a manifestation of amyloid beta-protein (Abeta) accumulation in the elderly as well as in patients with Alzheimer's disease (AD). Two types of CAA have been noted, based on the type of vasculature in which Abeta is deposited: cerebral capillary amyloid angiopathy (capCAA) and non-capCAA. Non-capCAA is a common form of CAA that consists of Abeta deposited in arteries and arterioles. Recent information on Abeta metabolism in the brain suggests that non-capCAA is associated with Abeta secretion into the cerebrospinal fluid via the perivascular space, whereas capCAA is associated with Abeta removal to blood plasma via the capillary endothelium. Abeta40, a major and relatively soluble Abeta isoform, is deposited predominantly in non-capCAA, and Abeta42, which is insoluble and associated more closely than Abeta40 with AD, is deposited predominantly in capCAA. Studying small areas of microscopic size within a given cortical region, we found an inverse association of capCAA and senile plaques. We also found a relative paucity of tau pathology in the small areas with abundant capCAA compared with the small areas with abundant senile plaques within a cortical region with the same cytoarchitecture. We suppose that both capCAA and senile plaques indicate high Abeta42 in the neuropil but that only Abeta42 in the form of insoluble deposits in senile plaques promotes tau abnormality.

Assessments of the accumulation severities of amyloid β-protein and hyperphosphorylated tau in the medial temporal cortex of control and Alzheimer's brains

Alzheimer's disease (AD) is characterized neuropathologically by neuritic plaques (NPs), and neurofibrillary tangles (NFTs). So far, the following key issues are not yet answered to the disease: (1) the accumulation degrees of three Abeta variants, and tau phosphorylation epitopes in AD as compared to control; (2) the correlation degrees of levels of three Abeta variants with different tau phosphorylation epitopes; (3) the correlation degrees of levels of three Abeta variants and different tau phosphorylation epitopes with Braak and CERAD staging systems. To address these issues, levels of Abeta40, Abeta42, and Abeta43, and phosphorylated tau were assessed by dot blots in homogenates of the medial temporal cortex from AD and control brains in the present study. These data implied different roles of tau phosphorylation epitopes in formation of NFTs, and in this process, Abeta might play a key role. Assessments of levels of these abnormal proteins by dot blots may serve as a useful complement to the morphological evaluations in diagnosis of AD.

Amyloid-beta immunotherapy for the prevention and treatment of Alzheimer disease: lessons from mice, monkeys, and humans

Alzheimer disease (AD), the most common form of dementia, is without an effective cure or preventive treatment. Recently, amyloid-beta protein (Abeta) has become a major therapeutic target. Many efforts are underway to either reduce the production of Abeta or enhance its clearance. In 1999, Schenk and colleagues first showed that active immunization with full-length Abeta lowered cerebral Abeta levels in transgenic mice. These findings have been confirmed and extended in various transgenic mouse models of AD using both active and passive Abeta immunization. Cognitive improvement also has been reported in association with active and passive Abeta vaccination in AD-like mouse models, even in the absence of significant reductions in cerebral Abeta loads. In 2004, the authors reported that active immunization with full-length Abeta in aged nonhuman primates, Caribbean vervets, reduced cerebral Abeta levels and gliosis. Proposed mechanisms of Abeta clearance by immunotherapy include disruption of Abeta aggregates, Abeta phagocytosis by microglia, neutralization of Abeta oligomers at the synapse, and increased efflux of Abeta from brain to blood. A phase IIa clinical trial was halted in 2002 because of the appearance of meningoencephalitis in approximately 6% of the AD patients. Although the exact cause of these adverse events is unknown, the immunogen, full-length Abeta1-42, may have been recognized as a self-antigen leading to an autoimmune response in some patients. Limited cognitive stabilization and apparent plaque clearance have been reported in subsets of patients who generated antibody titers. Currently, a passive immunization trial with a recombinant humanized monoclonal Abeta antibody is underway in humans. In the meantime, the authors are developing novel Abeta peptide immunogens for active immunization to target Abeta B cell epitope(s) and avoid Abeta-specific T-cell reactions in order to generate a safe and effective AD vaccine. The authors remain optimistic about the potential of such a vaccine for the prevention and treatment of AD.

Antibodies against beta-amyloid reduce Abeta oligomers, glycogen synthase kinase-3beta activation and tau phosphorylation in vivo and in vitro

Although active and passive immunization against the beta-amyloid peptide (Abeta) of amyloid plaque-bearing transgenic mice markedly reduces amyloid plaque deposition and improves cognition, the mechanisms of neuroprotection and impact on toxic oligomer species are not understood. We demonstrate that compared to control IgG2b, passive immunization with intracerebroventricular (icv) anti-Abeta (1-15) antibody into the AD HuAPPsw (Tg2576) transgenic mouse model reduced specific oligomeric forms of Abeta, including the dodecamers that correlate with cognitive decline. Interestingly, the reduction of soluble Abeta oligomers, but not insoluble Abeta, significantly correlated with reduced tau phosphorylation by glycogen synthase kinase-3beta (GSK-3beta), a major tau kinase implicated previously in mediating Abeta toxicity. A conformationally-directed antibody against amyloid oligomers (larger than tetramer) also reduced Abeta oligomer-induced activation of GSK3beta and protected human neuronal SH-SY5Y cells from Abeta oligomer-induced neurotoxicity, supporting a role for Abeta oligomers in human tau kinase activation. These data suggest that antibodies that are highly specific for toxic oligomer subspecies may reduce toxicity via reduction of GSK-3beta, which could be an important strategy for Alzheimer's disease (AD) therapeutics.

Suppression of cyclin-dependent kinase 5 activation by amyloid precursor protein: a novel excitoprotective mechanism involving modulation of tau phosphorylation

Alzheimer's disease is cytopathologically characterized by loss of synapses and neurons, neuritic amyloid plaques consisting of beta-amyloid (Abeta) peptides, and neurofibrillary tangles consisting of hyperphosphorylated tau protein in susceptible brain regions. Abeta, which triggers a cascade of pathogenic events including tau phosphorylation and neuronal excitotoxicity, is proteolytically derived from beta-amyloid precursor protein (APP); the pathological and physiological functions of APP, however, remain undefined. Here we demonstrate that the level of tau phosphorylation in cells and brains deficient in APP is significantly higher than that in wild-type controls, resulting from activation of cyclin-dependent kinase 5 (CDK5) but not glycogen synthase kinase 3, the two major tau kinases. In addition, we show that overexpression of APP or its non-amyloidogenic homolog amyloid precursor-like protein 1 suppresses both basal and stress-induced CDK5 activation. The ectodomain of APP, sAPPalpha, is responsible for inhibiting CDK5 activation. Furthermore, neurons derived from APP-deficient mice exhibit reduced metabolism and survival rates and are more susceptible to excitotoxic glutamate-induced apoptosis. These neurons also manifest significant defects in neurite outgrowth compared with neurons from the wild-type littermates. The observed neuronal excitotoxicity/apoptosis is mediated through a mechanism involving CDK5 activation. Our study defines a novel neuroprotective function for APP in preventing tau hyperphosphorylation via suppressing overactivation of CDK5. We suggest that CDK5 activation, through a calcium/calpain/p25 pathway, plays a key role in neuronal excitotoxicity and represents an underlying mechanism for the physiological functions of APP.

IgG-assisted age-dependent clearance of Alzheimer's amyloid beta peptide by the blood-brain barrier neonatal Fc receptor

The role of blood-brain barrier (BBB) transport in clearance of amyloid beta-peptide (Abeta) by Abeta immunotherapy is not fully understood. To address this issue, we studied the effects of peripherally and centrally administered Abeta-specific IgG on BBB influx of circulating Abeta and efflux of brain-derived Abeta in APPsw(+/-) mice, a model that develops Alzheimer's disease-like amyloid pathology, and wild-type mice. Our data show that anti-Abeta IgG blocks the BBB influx of circulating Abeta in APPsw(+/-) mice and penetrates into the brain to sequester brain Abeta. In young mice, Abeta-anti-Abeta complexes were cleared from brain to blood by transcytosis across the BBB via the neonatal Fc receptor (FcRn) and the low-density lipoprotein receptor-related protein (LRP), whereas in older mice, there was an age-dependent increase in FcRn-mediated IgG-assisted Abeta BBB efflux and a decrease in LRP-mediated clearance of Abeta-anti-Abeta complexes. Inhibition of the FcRn pathway in older APPsw(+/-) mice blocked clearance of endogenous Abeta40/42 by centrally administered Abeta immunotherapy. Moreover, deletion of the FcRn gene in wild-type mice inhibited clearance of endogenous mouse Abeta40/42 by systemically administered anti-Abeta. Our data suggest that the FcRn pathway at the BBB plays a crucial role in IgG-assisted Abeta removal from the aging brain.

Cerebrovascular P-glycoprotein expression is decreased in Creutzfeldt-Jakob disease

The abnormal conformation and assembly of proteins in the central nervous system is increasingly thought to be a critical pathogenic mechanism in neurodegenerative disorders such as Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease (AD). CJD is marked primarily by the buildup of misfolded prion protein (PrP(Sc)) in brain, whereas the accrual of beta-amyloid protein (Abeta) and tau protein are characteristic for AD. Prior studies have shown that the ATP-binding cassette transporter P-glycoprotein (P-gp) is a cellular efflux pump for Abeta, and that age-associated deficits in P-gp may be involved in the pathogenesis of Alzheimer's disease. In the present study, we investigated the relationship between P-gp and idiopathic CJD, and found that CJD, like AD, is associated with a decrease in the expression of cerebrovascular P-gp. In some instances, Abeta and PrP deposits coexist in cases of CJD, suggesting the possibility of pathogenic interactions. Since there is, to date, no evidence that PrP itself is a substrate for P-gp, we hypothesize that the age-related deficits in P-gp could promote the accumulation of PrP(Sc) either by promoting the buildup of Abeta (which could act as a seed for the aggregation of PrP(Sc)), or by overloading the ubiquitin-proteasomal catabolic system, and thereby facilitating the accumulation of PrP. Alternatively, the loss of P-gp could be a non-specific response to neurodegenerative changes in the central nervous system. In either case, dysfunction of this critical toxin-elimination pathway in CJD and AD suggests that selectively increasing cerebrovascular P-gp function could open new therapeutic pathways for the prevention and/or treatment of a number of proteopathic disorders of the central nervous system.

Abeta peptide immunization restores blood-brain barrier integrity in Alzheimer disease

Immunization with amyloid beta (Abeta) peptides or passive immunization with antibodies against Abeta has been reported to reduce plaque burden, neuritic dystrophy, early Tau pathology, microgliosis as well as reversing learning and memory deficits. This has created a central paradox: how does vaccination in peripheral tissues reduce plaque burden in the brain? No single explanation for these phenomena has yet been presented. To reconcile these observations, we demonstrate that the integrity of the blood-brain barrier (BBB), a structural barrier between the brain and the blood, is compromised in Tg2576 Alzheimer disease (AD) model mice. We immunized Tg2576 mice with Abeta before and after the onset of AD-type neuropathology and observed that BBB permeability, amyloid burden, and microgliosis are decreased in immunized mice. It is concluded that the integrity of the BBB is disrupted in AD mice, and after Abeta immunization the immune system clears Abeta from sources in the brain as it would in peripheral organs lacking barriers. Once Abeta is removed, the integrity of the BBB is restored. The data therefore provide an intellectual framework for understanding how the immune system can clear amyloid deposits from AD brains and suggest new strategies for limiting disease progression in amyloidopathies.

Effects of secreted oligomers of amyloid beta-protein on hippocampal synaptic plasticity: a potent role for trimers

The accumulation of amyloid beta-protein (Abeta) in brain regions serving memory and cognition is a central pathogenic feature of Alzheimer's disease (AD). We have shown that small soluble oligomers of human Abeta that are naturally secreted by cultured cells inhibit hippocampal long-term potentiation (LTP) in vitro and in vivo and transiently impair the recall of a complex learned behaviour in rats. These results support the hypothesis that diffusible oligomers of Abeta initiate a synaptic dysfunction that may be an early event in AD. We now report detailed electrophysiological analyses that define conditions under which acute application of soluble Abeta inhibits hippocampal synaptic plasticity in wild-type mice. To ascertain which Abeta assemblies contribute to the impairment of LTP, we fractionated oligomers by size-exclusion chromatography and found that Abeta trimers fully inhibit LTP, whereas dimers and tetramers have an intermediate potency. Natural Abeta oligomers are sensitive to heat denaturation, primarily inhibit the induction phase of LTP, and cause a sustained impairment of LTP even after extensive washout. We observed no effects of Abeta oligomers on presynaptic vesicle release. LTP in juvenile mice is resistant to the effects of Abeta oligomers, as is brain-derived-neurotrophic-factor-induced LTP in adult hippocampus. We conclude that specific assemblies, particularly timers, of naturally secreted Abeta oligomers are potent and selective inhibitors of certain forms of hippocampal LTP.

Association between CSF biomarkers and incipient Alzheimer's disease in patients with mild cognitive impairment: a follow-up study

BACKGROUND

Disease-modifying treatment strategies for Alzheimer's disease have led to an urgent need for biomarkers to identify the disease at a very early stage. Here, we assess the association between CSF biomarkers and incipient Alzheimer's in patients with mild cognitive impairment (MCI).

METHODS

From a series of 180 consecutive patients with MCI, we assessed 137 who underwent successful lumbar puncture at baseline. Patients at risk of developing dementia were followed clinically for 4-6 years. Additionally, 39 healthy individuals, cognitively stable over 3 years, served as controls. We analysed CSF concentrations of beta amyloid(1-42) (Abeta42), total tau (T-tau), and phosphorylated tau (P-tau181) using Luminex xMAP technology.

FINDINGS

During follow-up, 57 (42%) patients with MCI developed Alzheimer's disease, 21 (15%) developed other forms of dementia, and 56 (41%) remained cognitively stable for 5.2 years (range 4.0-6.8). A combination of CSF T-tau and Abeta42 at baseline yielded a sensitivity of 95% and a specificity of 83% for detection of incipient AD in patients with MCI. The relative risk of progression to Alzheimer's disease was substantially increased in patients with MCI who had pathological concentrations of T-tau and Abeta42 at baseline (hazard ratio 17.7, p<0.0001). The association between pathological CSF and progression to Alzheimer's disease was much stronger than, and independent of, established risk factors including age, sex, education, APOE genotype, and plasma homocysteine. The combination of T-tau and Abeta42/P-tau181 ratio yielded closely similar results (sensitivity 95%, specificity 87%, hazard ratio 19.8).

INTERPRETATION

Concentrations of T-tau, P-tau181, and Abeta42 in CSF are strongly associated with future development of Alzheimer's disease in patients with MCI.

Amyloid-β Immunotherapies in Mice and Men

Given the compelling genetic and biochemical evidence that has implicated amyloid-beta (Abeta) in the pathogenesis of Alzheimer's disease, many studies have focused on ways to inhibit Abeta production, to reverse or impede the formation of toxic forms of Abeta, or to facilitate the clearance of Abeta from the brain, in the hope of developing viable treatments for the disease. Using transgenic mouse models of Alzheimer's disease, many advances have been made in methodologies using different immunization techniques designed to clear soluble and aggregated forms of Abeta from the brain. We have highlighted how data derived from studies using transgenic mouse models have shaped our understanding of immunization-dependent Abeta clearance mechanisms and how these studies have influenced the development of anti-Abeta immunotherapies in humans.

Current concepts in therapeutic strategies targeting cognitive decline and disease modification in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder and the leading cause of dementia in the Western world. Postmortem, it is characterized neuropathologically by the presence of amyloid plaques, neurofibrillary tangles, and a profound gray matter loss. Neurofibrillary tangles are composed of an abnormally hyperphosphorylated intracellular protein called tau, tightly wound into paired helical filaments and thought to impact microtubule assembly and protein trafficking, resulting in the eventual demise of neuronal viability. The extracellular amyloid plaque deposits are composed of a proteinacious core of insoluble aggregated amyloid-beta (Abeta) peptide and have led to the foundation of the amyloid hypothesis. This hypothesis postulates that Abeta is one of the principal causative factors of neuronal death in the brains of Alzheimer's patients. With multiple drugs now moving through clinical development for the treatment of Alzheimer's disease, we will review current and future treatment strategies aimed at improving both the cognitive deficits associated with the disease, as well as more novel approaches that may potentially slow or halt the deadly neurodegenerative progression of the disease.

A dynamic relationship between intracellular and extracellular pools of Abeta

The accumulation of the amyloid-beta peptide (Abeta) in the brain is considered to have a primary role in Alzheimer's disease (AD). In addition to the extracellular accumulation of Abeta in the parenchyma and cerebrovasculature, emerging evidence indicates that intraneuronal Abeta also plays a pathophysiological role in AD. It is unclear, however, if the intracellular and extracellular pools of Abeta are unrelated or connected. In these studies, we sought to establish a relationship between these two pools of Abeta. We identified an inverse relationship between intracellular and extracellular Abeta in the 3xTg-AD transgenic model of AD. Using an immunotherapy approach, we further found that extracellular Abeta was cleared before intracellular Abeta. After the antibody dissipated, however, the reappearance of extracellular plaques was preceded by the accumulation of intraneuronal Abeta. Taken together, these results provide strong experimental evidence that intraneuronal Abeta may serve as a source for some of the extracellular amyloid deposits.

M1 Receptors Play a Central Role in Modulating AD-like Pathology in Transgenic Mice

We investigated the therapeutic efficacy of the selective M1 muscarinic agonist AF267B in the 3xTg-AD model of Alzheimer disease. AF267B administration rescued the cognitive deficits in a spatial task but not contextual fear conditioning. The effect of AF267B on cognition predicted the neuropathological outcome, as both the Abeta and tau pathologies were reduced in the hippocampus and cortex, but not in the amygdala. The mechanism underlying the effect on the Abeta pathology was caused by the selective activation of ADAM17, thereby shifting APP processing toward the nonamyloidogenic pathway, whereas the reduction in tau pathology is mediated by decreased GSK3beta activity. We further demonstrate that administration of dicyclomine, an M1 antagonist, exacerbates the Abeta and tau pathologies. In conclusion, AF267B represents a peripherally administered low molecular weight compound to attenuate the major hallmarks of AD and to reverse deficits in cognition. Therefore, selective M1 agonists may be efficacious for the treatment of AD.

The development of anti-amyloid therapy for Alzheimer's disease : from secretase modulators to polymerisation inhibitors

The leading hypothesis of the pathophysiology of Alzheimer's disease holds that the pivotal event is cleavage of the amyloid precursor protein to release intact the 42-amino-acid amyloid-beta peptide (Abeta); this hypothesis best explains the known genetic causes of Alzheimer's disease. If this theory is correct, optimal strategies for altering the disease process should be directed toward modifying the generation, clearance and/or toxicity of Abeta. Abeta is highly aggregable, spontaneously assuming a beta-sheet conformation and polymerising into oligomers, protofibrils, fibrils and plaques. The relative contribution of the various forms of Abeta to neuronal dysfunction in Alzheimer's disease remains uncertain; however, recent evidence implicates diffusible oligomeric species. This article reviews the range of strategies that have been investigated to target Abeta to slow the progression of Alzheimer's disease, from secretase modulators to anti-polymerisation agents. One amyloid-binding drug, tramiprosate (3-amino-1-propanesulfonic acid; Alzhemed), which is effective in reducing polymerisation in vitro and plaque deposition in animals, has now reached phase III clinical trials. Thus, it is plausible that an effective anti-amyloid strategy will become available for the treatment of Alzheimer's disease within the next few years.

Transgenic models of Alzheimer's disease: learning from animals

As the scope of the problem of Alzheimer's disease (AD) grows due to an aging population, research into the devastating condition has taken on added urgency. Rare inherited forms of AD provide insight into the molecular pathways leading to degeneration and have made possible the development of transgenic animal models. Several of these models are based on the overexpression of amyloid precursor protein (APP), presenilins, or tau to cause production and accumulation of amyloid-beta into plaques or hyperphosphorylated tau into neurofibrillary tangles. Producing these characteristic neuropathological lesions in animals causes progressive neurodegeneration and in some cases similar behavioral disruptions to those seen in AD patients. Knockout models of proteins involved in AD have also been generated to explore the native functions of these genes and examine whether pathogenesis is due to loss of function or toxic gain of function in these systems. Although none of the transgenic lines models the human condition exactly, the ability to study similar pathological processes in living animals have provided numerous insights into disease mechanisms and opportunities to test therapeutic agents. This chapter reviews animal models of AD and their contributions to developing therapeutic approaches for AD.

Intraneuronal Abeta accumulation and origin of plaques in Alzheimer's disease

Plaques are a defining neuropathological hallmark of Alzheimer's disease (AD) and the major constituent of plaques, the beta-amyloid peptide (Abeta), is considered to play an important role in the pathophysiology of AD. But the biological origin of Abeta plaques and the mechanism whereby Abeta is involved in pathogenesis have been unknown. Abeta plaques were thought to form from the gradual accumulation and aggregation of secreted Abeta in the extracellular space. More recently, the accumulation of Abeta has been demonstrated to occur within neurons with AD pathogenesis. Moreover, intraneuronal Abeta accumulation has been reported to be critical in the synaptic dysfunction, cognitive dysfunction and the formation of plaques in AD. Here we provide a historical overview on the origin of plaques and a discussion on potential biological and therapeutic implications of intraneuronal Abeta accumulation for AD.

Modulation of the humoral and cellular immune response in Abeta immunotherapy by the adjuvants monophosphoryl lipid A (MPL), cholera toxin B subunit (CTB) and E. coli enterotoxin LT(R192G)

Abeta vaccination or passive transfer of human-specific anti-Abeta antibodies are approaches under investigation to prevent and/or treat Alzheimer's disease (AD). Successful active Abeta vaccination requires a strong and safe adjuvant to induce anti-Abeta antibody formation. We compared the adjuvants monophosphoryl lipid A (MPL)/trehalose dicorynomycolate (TDM), cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin LT(R192G) for their ability to induce a humoral and cellular immune reaction, using fibrillar Abeta1-40/42 as a common immunogen in wildtype B6D2F1 mice. Subcutaneous (s.c.) administration with MPL/TDM resulted in anti-Abeta antibodies levels up to four times higher compared to s.c. LT(R192G). Using MPL/TDM, the anti-Abeta antibodies induced were mainly IgG2b, IgG1 and lower levels of IgG2a and IgM, with a moderate splenocyte proliferation and IFN-gamma production in vitro upon stimulation with Abeta1-40/42. LT(R192G), previously shown by us to induce robust titers of anti-Abeta antibodies, generated predominantly IgG2b and IgG1 anti-Abeta antibodies with very low splenocyte proliferation and IFN-gamma production. Weekly intranasal (i.n.) administration over 11 weeks of Abeta40/42 with CTB induced only moderate levels of antibodies. All immunogens generated antibodies that recognized mainly the Abeta1-7 epitope and specifically detected amyloid plaques on AD brain sections. In conclusion, MPL/TDM, in addition to LT(R192G), is an effective adjuvant when combined with Abeta40/42 and may aid in the design of Abeta immunotherapy.

Immunotherapy for Alzheimer's Disease and Other Dementias

OBJECTIVE

The aim of this article is to review the role of immunotherapy in the removal of proteins which accumulate abnormally in neurodegenerative disorders associated with dementia, in particular amyloid-beta accumulation in Alzheimer's disease.

RESULTS

In both transgenic mouse models and in two trials of amyloid-beta immunotherapy for human Alzheimer's disease, active immunization with amyloid-beta 1-42 results in the removal of amyloid-beta plaques from the cerebral cortex associated with, in the mouse models, improvement in cognitive function. Cerebral amyloid angiopathy and neurofibrillary tangles persist, however, and there is also concern about T lymphocyte immune reactions in the meninges in the human cases. Active immunization schedules are being developed to minimize T lymphocyte reactions and to maximize antibody production and passive immunization protocols are being devised. Immunotherapy for removal of the proteins which accumulate in other neurodegenerative disorders associated with dementia such as prion proteins and alpha-synuclein are in the early stages of development.

CONCLUSION

Dementias in the elderly are an increasing medical, social and economic problem and current treatments are only effective. In the majority of dementias, proteins accumulate within cells and in the extracellular compartments of the brain. In the most common dementia, Alzheimer's disease, amyloid-beta accumulates as plaques in the extracellular space of the grey matter and in artery walls as cerebral amyloid angiopathy and tau protein accumulates as neurofibrillary tangles within neurons.

The Arctic Alzheimer mutation facilitates early intraneuronal Aβ aggregation and senile plaque formation in transgenic mice

The Arctic mutation (APP E693G) is unique, since it is located within the amyloid-beta (Abeta) sequence and leads to Alzheimer's disease (AD). Arctic Abeta peptides more easily form Abeta protofibrils in vitro, but little is known about the pathogenic mechanism of the Arctic mutation in vivo. Here, we analyzed APP transgenic mice with both the Swedish and Arctic mutations (tg-APPArcSwe) and transgenic mice with the Swedish mutation alone (tg-APPSwe). Intense intraneuronal Abeta-immunoreactive staining was present in young tg-APPArcSwe mice, but not in tg-APPSwe mice. Intracellular Abeta aggregates in tg-APPArcSwe were strongly stained by antibodies recognizing the N-terminus of Abeta, while those recognizing the C-terminus of Abeta stained weakly. The Abeta aggregates inside neurons increased with age and predated extracellular Abeta deposition in both tg-APPArcSwe and tg-APPSwe mice. Senile plaque deposition was markedly accelerated in tg-APPArcSwe mice, as compared to tg-APPSwe mice. We conclude that the Arctic mutation causes AD by facilitating amyloidosis through early accumulation of intracellular Abeta aggregates in association with a rapid onset of senile plaque deposition.

Cytoskeletal Transport in the Aging Brain: Focus on the Cholinergic System

There is now compelling evidence for the aging-related breakdown of cytoskeletal support in neurons. Similarly affected are the principal components of the intracellular microtubule system, the transport units involved in active shuttle of organelles and molecules in an antero- and retrograde manner, and the proteins stabilizing the cytoskeleton and providing trophic support. Here, we review the basic organization of the cytoskeleton, and describe its elements and their interactions. We then critically assess the role of these cytoskeletal proteins in physiological aging and aging-related malfunction. Our focus is on the microtubule-associated protein tau, for which comprehensive investigations suggest a critical role in neurodegenerative diseases, for instance tauopathies. These diseases frequently lead to cognitive decline and are often paralleled by reductions in cholinergic neurotransmission. We propose this reduction to be due to destabilization of the cytoskeleton and protein transport mechanisms in these neurons. Therefore, maintenance of the neuronal cytoskeleton during aging may prevent or delay neurodegeneration as well as cognitive decline during physiological aging.

Anti-Abeta42- and anti-Abeta40-specific mAbs attenuate amyloid deposition in an Alzheimer disease mouse model

Accumulation and aggregation of amyloid beta peptide 1-42 (Abeta42) in the brain has been hypothesized as triggering a pathological cascade that causes Alzheimer disease (AD). To determine whether selective targeting of Abeta42 versus Abeta40 or total Abeta is an effective way to prevent or treat AD, we compared the effects of passive immunization with an anti-Abeta42 mAb, an anti-Abeta40 mAb, and multiple Abeta(1-16) mAbs. We established in vivo binding selectivity of the anti-Abeta42 and anti-Abeta40 mAbs using novel TgBRI-Abeta mice. We then conducted a prevention study in which the anti-Abeta mAbs were administered to young Tg2576 mice, which have no significant Abeta deposition, and therapeutic studies in which mAbs were administered to Tg2576 or CRND8 mice with modest levels of preexisting Abeta deposits. Anti-Abeta42, anti-Abeta40, and anti-Abeta(1-16) mAbs attenuated plaque deposition in the prevention study. In contrast, anti-Abeta42 and anti-Abeta40 mAbs were less effective in attenuating Abeta deposition in the therapeutic studies and were not effective in clearing diffuse plaques following direct injection into the cortex. These data suggest that selective targeting of Abeta42 or Abeta40 may be an effective strategy to prevent amyloid deposition, but may have limited benefit in a therapeutic setting.

Novel Abeta peptide immunogens modulate plaque pathology and inflammation in a murine model of Alzheimer's disease

BACKGROUND

Alzheimer's disease, a common dementia of the elder, is characterized by accumulation of protein amyloid deposits in the brain. Immunization to prevent this accumulation has been proposed as a therapeutic possibility, although adverse inflammatory reactions in human trials indicate the need for novel vaccination strategies.

METHOD

Here vaccination with novel amyloid peptide immunogens was assessed in a transgenic mouse model displaying age-related accumulation of fibrillar plaques.

RESULTS

Immunization with any conformation of the amyloid peptide initiated at 12 months of age (at which time fibrillar amyloid has just begun to accumulate) showed significant decrease in total and fibrillar amyloid deposits and in glial reactivity relative to control transgenic animals. In contrast, there was no significant decrease in amyloid deposition or glial activation in mice in which vaccination was initiated at 16 months of age, despite the presence of similar levels anti-Abeta antibodies in young and old animals vaccinated with a given immunogen. Interestingly, immunization with an oligomeric conformation of Abeta was equally as effective as other amyloid peptides at reducing plaque accumulation. However, the antibodies generated by immunization with the oligomeric conformation of Abeta have more limited epitope reactivity than those generated by fAbeta, and the microglial response was significantly less robust.

CONCLUSION

These results suggest that a more specific immunogen such as oligomeric Abeta can be designed that achieves the goal of depleting amyloid while reducing potential detrimental inflammatory reactions. In addition, the data show that active immunization of older Tg2576 mice with any amyloid conformation is not as efficient at reducing amyloid accumulation and related pathology as immunization of younger mice, and that serum anti-amyloid antibody levels are not quantitatively related to reduced amyloid-associated pathology.

Prototype Alzheimer's disease epitope vaccine induced strong Th2-type anti-Abeta antibody response with Alum to Quil A adjuvant switch

Beta-amyloid (Abeta) peptide has been proposed to be a causal factor in Alzheimer's disease (AD). Currently being investigated, active and passive Abeta-immunotherapy significantly reduce Abeta plaque deposition, neuritic dystrophy, and astrogliosis in the brains of APP transgenic (APP/Tg) mice. Immunization with Abeta42 formulated in the Th1-type adjuvant QS21 was beneficial for AD patients with significant titers of anti-Abeta antibodies, however, 6% of participants developed meningoencephalitis, likely due to anti-Abeta-specific autoimmune Th1 cells. Thus, successful Abeta vaccination requires the development of strong antibody responses without Th1-type cellular immunity. In this study, we compared the induction of humoral immune responses with Th1-type (Quil A) and Th2-type (Alum) adjuvants singly and in combination, using our novel epitope vaccine composed of self B cell epitope Abeta(1-15) and foreign T cell epitope PADRE (PADRE-Abeta(1-15)-MAP). Formulated in Quil A, this vaccine resulted in significantly higher anti-Abeta antibody responses in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, compared with Alum. Anti-Abeta antibodies induced by Alum were predominantly IgG1 type accompanied by lower levels of IgG2a and IgG2b. Quil A induced robust and almost equal titers of anti-Abeta antibodies of IgG1 and IgG2a isotypes and slightly lower levels of IgG2b. Switching adjuvants from Alum to Quil A induced higher concentrations of antibodies than injections with Alum only, however slightly lower than Quil A only. Switching both adjuvants did not change the profile of antibody responses generated by the initial adjuvant injected. These results suggest that switching from Alum to Quil A would be beneficial for AD patients because anti-Abeta antibody production was enhanced without changing the initially generated and likely beneficial Th2-type humoral response.

Persistent amyloidosis following suppression of Abeta production in a transgenic model of Alzheimer disease

BACKGROUND

The proteases (secretases) that cleave amyloid-beta (Abeta) peptide from the amyloid precursor protein (APP) have been the focus of considerable investigation in the development of treatments for Alzheimer disease. The prediction has been that reducing Abeta production in the brain, even after the onset of clinical symptoms and the development of associated pathology, will facilitate the repair of damaged tissue and removal of amyloid lesions. However, no long-term studies using animal models of amyloid pathology have yet been performed to test this hypothesis.

METHODS AND FINDINGS

We have generated a transgenic mouse model that genetically mimics the arrest of Abeta production expected from treatment with secretase inhibitors. These mice overexpress mutant APP from a vector that can be regulated by doxycycline. Under normal conditions, high-level expression of APP quickly induces fulminant amyloid pathology. We show that doxycycline administration inhibits transgenic APP expression by greater than 95% and reduces Abeta production to levels found in nontransgenic mice. Suppression of transgenic Abeta synthesis in this model abruptly halts the progression of amyloid pathology. However, formation and disaggregation of amyloid deposits appear to be in disequilibrium as the plaques require far longer to disperse than to assemble. Mice in which APP synthesis was suppressed for as long as 6 mo after the formation of Abeta deposits retain a considerable amyloid load, with little sign of active clearance.

CONCLUSION

This study demonstrates that amyloid lesions in transgenic mice are highly stable structures in vivo that are slow to disaggregate. Our findings suggest that arresting Abeta production in patients with Alzheimer disease should halt the progression of pathology, but that early treatment may be imperative, as it appears that amyloid deposits, once formed, will require additional intervention to clear.

Immunotherapy for Alzheimer's disease and other dementias

PURPOSE OF REVIEW

The aim of this article is to review the role of immunotherapy in the removal of proteins which accumulate abnormally in neurodegenerative disorders associated with dementia, in particular amyloid-beta accumulation in Alzheimer's disease.

RECENT FINDINGS

In both transgenic mouse models and in two trials of amyloid-beta immunotherapy for human Alzheimer's disease, active immunization with amyloid-beta 1-42 results in the removal of amyloid-beta plaques from the cerebral cortex associated with, in the mouse models, improvement in cognitive function. Cerebral amyloid angiopathy and neurofibrillary tangles persist, however, and there is also concern about T lymphocyte immune reactions in the meninges in the human cases. Active immunization schedules are being developed to minimize T lymphocyte reactions and to maximize antibody production and passive immunization protocols are being devised. Immunotherapy for removal of the proteins which accumulate in other neurodegenerative disorders associated with dementia such as prion proteins and alpha-synuclein are in the early stages of development.

SUMMARY

Dementias in the elderly are an increasing medical, social and economic problem and current treatments are only effective. In the majority of dementias, proteins accumulate within cells and in the extracellular compartments of the brain. In the most common dementia, Alzheimer's disease, amyloid-beta accumulates as plaques in the extracellular space of the grey matter and in artery walls as cerebral amyloid angiopathy and tau protein accumulates as neurofibrillary tangles within neurons.

Refining an Alzheimer’s vaccine to avoid an inflammatory response

The utility of vaccine strategies to treat neurodegenerative diseases such as Alzheimer's disease may still hold promise. Phase IIa clinical trials were halted due to a small but significant occurrence of meningoencephalitis. Knowledge gained from studies on amyloid-beta peptide (Abeta) immunotherapy will allow optimisation of new-generation vaccines, targeting highly specific epitopes while reducing undesired side effects. In harnessing and steering the immune system, an effective response can be generated against Abeta, one that might have attenuated immune responses with robust disease-altering activity.

Active immunization trial in Abeta42-injected P301L tau transgenic mice

Amyloid beta-peptide (Abeta) containing plaques and neurofibrillary tangles (NFT) are the two major histopathological hallmarks of Alzheimer's disease (AD). According to the amyloid cascade hypothesis, deposition of Abeta is an initial and essential step in the pathogenesis of AD, and formation of NFT has been proposed to be caused by increased Abeta levels. Several previous studies revealed that Abeta plaque formation can be reduced or even prevented by active immunization with Abeta preparations or by administration of Abeta-specific antibodies. To assess the role of fibrillar preparations of Abeta42 in NFT formation, we previously performed intracerebral (i.c.) injections of Abeta42 into brains of NFT-forming P301L tau transgenic mice which caused significant increases in NFT numbers. To determine whether these increases in NFT can be blocked or reduced by active immunization, P301L tau mice were immunized with intraperitoneal injections of preaggregated Abeta42. Abeta42-specific titers were monitored and the mice injected i.c. with Abeta42. We found that i.c. injection of Abeta42 caused significant increases in NFT formation. However, this induction was not affected by active immunization despite high serum anti-Abeta42 titer levels and binding of anti-Abeta42 antibodies to the injected Abeta42 aggregates. We conclude that active immunization is not sufficient to prevent the effect of Abeta42 on tau aggregation in our model system. Further studies are required to determine whether modifications of our protocol could affect the Abeta42-mediated induction of NFT formation.

Temporal profile of amyloid-beta (Abeta) oligomerization in an in vivo model of Alzheimer disease. A link between Abeta and tau pathology

Accumulation of amyloid-beta (Abeta) is one of the earliest molecular events in Alzheimer disease (AD), whereas tau pathology is thought to be a later downstream event. It is now well established that Abeta exists as monomers, oligomers, and fibrils. To study the temporal profile of Abeta oligomer formation in vivo and to determine their interaction with tau pathology, we used the 3xTg-AD mice, which develop a progressive accumulation of plaques and tangles and cognitive impairments. We show that SDS-resistant Abeta oligomers accumulate in an age-dependent fashion, and we present evidence to show that oligomerization of Abeta appears to first occur intraneuronally. Finally, we show that a single intrahippocampal injection of a specific oligomeric antibody is sufficient to clear Abeta pathology, and more importantly, tau pathology. Therefore, Abeta oligomers may play a role in the induction of tau pathology, making the interference of Abeta oligomerization a valid therapeutic target.

Can herbs provide a new generation of drugs for treating Alzheimer's disease?

The overall aim of this review is to discuss cellular mechanisms at work in the progression of AD and current therapeutic strategies for treating AD, with a focus on the potential efficacy of herbal treatments. Recent advances in molecular, cellular, and animal model studies have revealed that formation of the 4-kDa amyloid beta peptide is a key factor in the development and progression of AD. Several cellular changes have been identified that are related to amyloid beta plaques and neurofibrillary tangles found in the autopsied brains of AD patients and in AD animal models. Several therapeutic strategies have been developed to treat AD, including anti-inflammatory, anti-oxidant, and anti-amyloid approaches. Recently, herbal treatments have been tested in animal and cellular models of AD and in clinical trials with AD subjects. In AD animal models and cell models, herbal extracts appear to have fewer adverse effects than beneficial effects on A beta and cognitive functions. These extracts have multi-functional properties (pro-cholinergic, anti-oxidant, anti-amyloid, and anti-inflammatory), and their use in the treatment of AD patients looks promising. The chemical compositions of herbs and their potential for alleviating or reducing symptoms of AD or for affecting the disease mechanism need to be further studied.

The F(ab′)2 fragment of an Aβ-specific monoclonal antibody reduces Aβ deposits in the brain

This work examines whether administering the F(ab' )2 fragment of an IgG1 monoclonal antibody (mAb) targeting the N-terminal 1-13 amino acids of the beta-amyloid peptide (Abeta mAb) reduces amyloid deposition in Alzheimer's disease (AD). The F(ab')2 fragment was injected intraperitoneally or intracranially into Tg2576 mice, a murine model of human AD. Both routes of administration significantly reduced Abeta plaque formation in the brain, as determined immunohistochemically and by monitoring levels of Abeta1-40 and Abeta1-42 peptide. Use of the F(ab')2 fragment significantly reduced phagocytic infiltration in the CNS when compared to intact mAb. Since IgG1 Abs do not fix complement, these findings suggest that effective in vivo clearance of amyloid deposits can be achieved without stimulation of FcR-reactive phagocytes or activation of the complement cascade.

Dynamic changes of phosphorylated tau in mouse hippocampus after cold water stress

The abnormal hyperphosphorylation of tau protein in brain is attributed to a number of neurodegenerative diseases such as Alzheimer disease. It has been reported that cold water stress (CWS) could cause rapid reversible tau phosphorylation in brain. To explore the possible long-tem effects of CWS on tau phosphorylation, we employed the immunoblot and immunohistochemical methods to analyze the phosphorylation of tau in the hippocampus of mice subjected to CWS. Results showed that CWS stimulation caused not only an early phase reversible tau phosphorylation, but also a later phase tau phosphorylation after 6h. The distribution pattern of phosphorylated tau (P-tau) in the later phase was different to that of early phase. At 1h after CWS, defined as early phase, P-tau was strikingly located in the mossy fibers and nerve terminals at the molecular layer of dentate gray (DG), whereas at 12h, defined as later phase, P-tau was dominantly located in the somatodendritic compartments of neurons in DG and CA3/CA1 regions, but obviously decreased in the mossy fibers and nerve terminals of molecular layer. These findings demonstrate that CWS leads to prominent changes of tau phosphorylation and P-tau localization in the hippocampus in a time dependent manner.

The proteasome in Alzheimer's disease and Parkinson's disease: lessons from ubiquitin B+1

Ubiquitin-containing cellular inclusions are characteristic of major neurodegenerative diseases and suggest an involvement of the ubiquitin-proteasome system. The frameshifted form of ubiquitin has proved to be a valuable tool for studying the role of the ubiquitin-proteasome system. It is an endogenous reporter for proteasome activity in human pathology but it is also capable of inhibiting proteasomal degradation. Current studies have revealed that the frameshifted form of ubiquitin accumulates in the brains of patients with Alzheimer's disease but not in those with Parkinson's disease.

Protease inhibitors as potential disease-modifying therapeutics for Alzheimer’s disease

The current lack of an effective treatment for Alzheimer's disease (AD) has fuelled an intense search for novel therapies for this neurodegenerative condition. Aberrant production or decreased clearance of amyloid-beta peptides is widely accepted to be causative for AD. Amyloid-beta peptides are produced by sequential processing of the beta-amyloid precursor protein by the two aspartyl-type proteases beta-secretase and gamma-secretase. Because proteases are generally classified as druggable, these secretases are a centre of attraction for various drug discovery efforts. Although a large number of specific drug-like gamma-secretase inhibitors have been discovered, progress towards the clinic has been slowed by the broad substrate specificity of this unusual intramembrane-cleaving enzyme. In particular, the Notch receptor depends on gamma-secretase for its signalling function and, thus, gamma-secretase inhibition produces distinct phenotypes related to a disturbance of this pathway in preclinical animal models. The main task now is to define the therapeutic window in man between desired central efficacy and Notch-related side effects. In contrast, most studies with knockout animals have indicated that beta-secretase inhibition may have minimal adverse effects; however, the properties of the active site of this enzyme make it difficult to find small-molecule inhibitors that bind with high affinity. In most instances, inhibitors are large and peptidic in nature and, therefore, unsuitable as drug candidates. Thus, there are many issues associated with the development of protease inhibitors for AD that must be addressed before they can be used to test the 'amyloid cascade hypothesis' in the clinic. The outcomes of such trials will provide new directions to the scientific community and hopefully new treatment options for AD patients.

Gene expression correlates of neurofibrillary tangles in Alzheimer's disease

Neurofibrillary tangles (NFT) constitute one of the cardinal histopathological features of Alzheimer's disease (AD). To explore in vivo molecular processes involved in the development of NFTs, we compared gene expression profiles of NFT-bearing entorhinal cortex neurons from 19 AD patients, adjacent non-NFT-bearing entorhinal cortex neurons from the same patients, and non-NFT-bearing entorhinal cortex neurons from 14 non-demented, histopathologically normal controls (ND). Of the differentially expressed genes, 225 showed progressively increased expression (AD NFT neurons > AD non-NFT neurons > ND non-NFT neurons) or progressively decreased expression (AD NFT neurons < AD non-NFT neurons < ND non-NFT neurons), raising the possibility that they may be related to the early stages of NFT formation. Immunohistochemical studies confirmed that many of the implicated proteins are dysregulated and preferentially localized to NFTs, including apolipoprotein J, interleukin-1 receptor-associated kinase 1, tissue inhibitor of metalloproteinase 3, and casein kinase 2, beta. Functional validation studies are underway to determine which candidate genes may be causally related to NFT neuropathology, thus providing therapeutic targets for the treatment of AD.

Conformational diseases: an umbrella for various neurological disorders with an impaired ubiquitin-proteasome system

It is increasingly appreciated that failures in the ubiquitin-proteasome system play a pivotal role in the neuropathogenesis of many neurological disorders. This system, involved in protein quality control, should degrade misfolded proteins, but apparently during neuropathogenesis, it is unable to cope with a number of proteins that, by themselves, can consequently accumulate. Ubiquitin is essential for ATP-dependent protein degradation by the proteasome. Ubiquitin+1 (UBB+1) is generated by a dinucleotide deletion (DeltaGU) in UBB mRNA. The aberrant protein has a 19 amino acid extension and has lost the ability to ubiquitinate. Instead of targeting proteins for degradation, it has acquired a dual substrate-inhibitor function; ubiquitinated UBB+1 is a substrate for proteasomal degradation, but can at higher concentrations inhibit, proteasomal degradation. Furthermore, UBB+1 protein accumulates in neurons and glial cells in a disease-specific way, and this event is an indication for proteasomal dysfunction. Many neurological and non-neurological conformational diseases have the accumulation of misfolded proteins and of UBB+1 in common, and this combined accumulation results in the promotion of insoluble protein deposits and neuronal cell death as shown in a cellular model of Huntington's disease.

Dynamic complexity of the microglial activation response in transgenic models of amyloid deposition: implications for Alzheimer therapeutics

The presence of activated microglia in postmortem Alzheimer disease specimens is used to support the argument that inflammation contributes to Alzheimer pathogenesis. Transgenic mice overexpressing the amyloid precursor protein (APP) gene form amyloid plaques that are accompanied by local activation of microglia/macrophages in a manner similar to the human disease. Many markers of microglial activation and inflammation increase in an age-dependent manner in these mice. However, manipulation of these inflammatory reactions can lead to unexpected outcomes with several instances of reduced pathology when microglia/macrophages are activated further. In particular, anti-Abeta immunotherapy in amyloid-depositing transgenic mice causes a complex series of changes in microglial markers, negating the implicit belief that such activation is monotonic and represented equally well by any of several "activation" markers. A survey of the peripheral macrophage literature identifies at least 2 distinct activation states of macrophages with different consequences for the surrounding tissue. These different activation states can often be distinguished by the markers that are expressed. Several markers are identified from studies outside the brain that neuroscientists might consider evaluating when attempting to more definitively describe the activation state of the monocyte-derived cells in the brain.

Calcium-regulated signaling pathways: role in amyloid beta-induced synaptic dysfunction

Amyloid beta (Abeta) peptides have been shown to impair synaptic function, especially long-term synaptic plasticity, in transgenic mouse models of Alzheimer's disease (AD) and in acute hippocampal preparations. In the transgenic mice overexpressing mutant forms of human amyloid precursor protein (APP), the deficits in hippocampal long-term potentiation (LTP) occur prior to synaptic loss and cell death, suggesting early functional changes at these synapses. Recent studies demonstrate that Abeta-induced synaptic dysfunction is linked with altered Ca2+ signaling in hippocampal neurons. While reducing Ca2+ influx through NMDA receptors, Abeta peptides elevate intracellular Ca2+ concentration by enhancing Ca2+ influx from voltage-gated Ca2+ channels or nonselective cation channels, or by stimulating Ca2+ release from intracellular stores. Interestingly, acute application of Abeta or APP overexpression inhibits activity-dependent regulation of several protein kinase pathways that require Ca2+ influx via NMDA receptors for activation, including Ca2+/calmodulin-dependent protein kinase II, protein kinase A, and extracellular regulated kinases (Erk). On the other hand, activation of Ca2+-dependent protein phosphatase 2B (calcineurin) is implicated in Abeta inhibition of LTP. Thus, multiple Ca2+-regulated signaling pathways are involved in the synaptic action of Abeta, and malfunction of these pathways may underlie the synaptic dysfunction in early AD.

Alzheimer's disease: Abeta, tau and synaptic dysfunction

Alzheimer's disease is a progressive neurodegenerative disorder that is characterized by two hallmark lesions: extracellular amyloid plaques and neurofibrillary tangles. The role that these lesions have in the pathogenesis of AD has proven difficult to unravel, in part because of unanticipated challenges of reproducing both pathologic hallmarks in transgenic mice. Recent advances in recapitulating both plaques and tangles in the brains of transgenic mice are leading to novel insights into their role in the degenerative process, including their impact on synaptic activity and plasticity. Transgenic mice that harbor both neuropathological lesions are also facilitating the elucidation of the relationship of these proteinaceous aggregates to one another and providing a crucial in vivo system for developing and evaluating therapies.

Hyperphosphorylated tau and amyloid precursor protein deposition is increased in the brains of young drug abusers

Drug abuse is a major problem worldwide. The incidence of drug-related deaths attributed to opiate abuse is increasing annually. Apart from routine examination, little is known of the neuropathology of drug abuse. We, and others, have shown previously that drug abuse is associated with microglial activation. We hypothesised that neuroinflammation might lead to premature neurodegeneration in drug abusers. We investigated the brains of young opiate abusers (n=34, all<40 years) for the presence of proteins associated with neurodegenerative diseases and compared them with the brains of age-matched, non-drug users (n=16) all of whom died suddenly. Detailed immunohistochemical analysis of the hippocampus, brainstem and basal ganglia for hyperphosphorylated tau, beta-amyloid, beta-amyloid precursor protein (betaAPP) and ubiquitin demonstrated an excess of AT 8-positive neurofibrillary tangles (NFT) in the drug abusers. These were not only more prevalent in the drug abusers than in controls (44%vs. 19%) but also involved more brain areas. In controls NFT were confined to the entorhinal cortex whereas in drug users they were also found in the subiculum, temporal neocortex, nucleus basalis of Meynert and the locus coeruleus. Virtually no amyloid plaques were present but betaAPP positivity was again much more common in drug abusers than controls (73%vs. 20% in the brainstem and 59%vs. 23% in the temporal lobe). There is no suggestion that these drug abusers had displayed major cognitive impairment although detailed neuropsychological assessment is difficult in this subject group. Likely causes of hyperphosphorylated tau deposition in drug abuse include hypoxic-ischaemic injury, microglial-associated cytokine release and possibly drug-associated neurotoxicity or hepatitis. Head injury, which is another major risk factor, does not appear to have contributed to our findings. Genetic factors also merit consideration. It is unclear at present how much of the hyperphosphorylated tau detected in these young drug abusers represents a transitory phenomenon.

Understanding and treating neurodegeneration: insights from the flies

Drosophila has recently emerged as a model system for studying mechanisms of neurodegeneration. Genetic models for most of the major neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), polyglutamine diseases, and tauopathies, have been successfully established. Pharmacological models of some of these diseases have also been created. Genetic modifier screens using these models have uncovered previously implicated mechanisms and molecules as well as novel ones. Fly models have turned out to be excellent system for the in vivo testing of therapeutic potentials of candidate compounds. It is anticipated that further exploration of the fly models will not only provide novel insights into mechanisms of neurodegeneration but also lead to the development of rational treatment of those debilitating degenerative diseases.

Calcium dysregulation in Alzheimer's disease: Recent advances gained from genetically modified animals

Alzheimer's disease is a progressive and irreversible neurodegenerative disorder that leads to cognitive, memory and behavioural impairments. Two decades of research have implicated disturbances of intracellular calcium homeostasis as playing a proximal pathological role in the neurodegeneration associated with Alzheimer's disease. A large preponderance of evidence has been gained from the use of a diverse range of cell lines. Whilst useful in understanding the principal mechanism of neurotoxicity associated with Alzheimer's disease, technical differences, such as cell type or even the form of amyloid-beta used often underlie conflicting results. In this review, we discuss recent contributions that transgenic technology has brought to this field. For example, the triple transgenic mouse model of Alzheimer's disease has implicated intraneuronal accumulation of the amyloid-beta peptide as an initiating factor in synaptic dysfunction and behavioural deficits. Importantly, this synaptic dysfunction occurs prior to cell loss or extracellular amyloid plaque accumulation. The cause of synaptic dysfunction is unknown but it is likely that amyloid-beta and its ability to disrupt intracellular calcium homeostasis plays a key role in this process.

An array of genes implicated in Alzheimer's disease

Studying altered gene expression patterns in Alzheimer's disease may be helpful for identifying novel therapeutic targets and for elucidating key cellular processes that are involved in the neurodegenerative phenotype. To date, the advances that have emerged from these types of studies have been limited, largely confirming prevailing hypotheses and pathways that have already been implicated in the disease process. The potential remains high, particularly when combined with proteomic approaches. In addition, the utilization of transgenic mouse models will no doubt also be of tremendous value for gene expression studies as they permit investigations at well-defined stages of pathology and cognitive function.

Passive Immunization of the Aβ42(43) C-Terminal-Specific Antibody BC05 in a Mouse Model of Alzheimer’s Disease

BACKGROUND

Over the past few years, amyloid beta protein (Abeta) vaccination has become one of the most effective treatments for Alzheimer's disease. However, the appearance of severe side effects during clinical trials has highlighted the need for improved safety and efficacy. Although antibodies directed against the amino (N)-termini of Abeta are highly effective for passive immunization, a substantial risk of inducing cerebral hemorrhage has been documented.

OBJECTIVE

We investigated the effect of the administration of BC05, which was the first antibody developed against the carboxyl (C)-termini of Abeta42(43), on the clearance of brain Abeta42(43).

METHOD

The BC05 antibody was injected into the peritoneal cavity of Tg2576 transgenic mice expressing betaAPP(KM670/671NL) once a week from 3 to 12 months of age.

RESULTS

BC05 caused a selective 44-fold increase in plasma Abeta42(43) and a significant increase in brain soluble Abeta42(43), showing a 156% difference. Brain insoluble Abeta40 and Abeta42(43) levels were decreased by 27.3 and 31.5%, respectively. A reduction in the number of BAN50-labeled plaques was observed.

CONCLUSIONS

BC05 might render Abeta42(43) soluble within the brain and inhibit the insoluble deposition of Abeta40 and Abeta42(43). By analyzing the mechanism of the elevation of soluble Abeta42(43) after passive immunization of BC05, safer and more effective methods of immunotherapy for Alzheimer's disease might be developed.