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

Colony-stimulating factor 1 receptor inhibition prevents microglial plaque association and improves cognition in 3xTg-AD mice

Background

Microglia are dependent upon colony-stimulating factor 1 receptor (CSF1R) signaling for their survival in the adult brain, with administration of the dual CSF1R/c-kit inhibitor PLX3397 leading to the near-complete elimination of all microglia brainwide. Here, we determined the dose-dependent effects of a specific CSF1R inhibitor (PLX5622) on microglia in both wild-type and the 3xTg-AD mouse model of Alzheimer’s disease.

Methods

Wild-type mice were treated with PLX5622 for up to 21 days, and the effects on microglial numbers were assessed. 3xTg-AD mice were treated with PLX5622 for 6 or 12 weeks and effects on microglial numbers and pathology subsequently assessed.

Results

High doses of CSF1R inhibitor eliminate most microglia from the brain, but a 75 % lower-dose results in sustained elimination of ~30 % of microglia in both wild-type and 3xTg-AD mice. No behavioral or cognitive deficits were found in mice either depleted of microglia or treated with lower CSF1R inhibitor concentrations. Aged 3xTg-AD mice treated for 6 or 12 weeks with lower levels of PLX5622 resulted in improved learning and memory. Aβ levels and plaque loads were not altered, but microglia in treated mice no longer associated with plaques, revealing a role for the CSF1R in the microglial reaction to plaques, as well as in mediating cognitive deficits.

Conclusions

We find that inhibition of CSF1R alone is sufficient to eliminate microglia and that sustained microglial elimination is concentration-dependent. Inhibition of the CSF1R at lower levels in 3xTg-AD mice prevents microglial association with plaques and improves cognition.

Impact of amyloid β aggregate maturation on antibody treatment in APP23 mice

Introduction

The deposition of the amyloid β protein (Aβ) in the brain is a hallmark of Alzheimer's disease (AD). Removal of Aβ by Aβ-antibody treatment has been developed as a potential treatment strategy against AD. First clinical trials showed neither a stop nor a reduction of disease progression. Recently, we have shown that the formation of soluble and insoluble Aβ aggregates in the human brain follows a hierarchical sequence of three biochemical maturation stages (B-Aβ stages). To test the impact of the B-Aβ stage on Aβ immunotherapy, we treated transgenic mice expressing human amyloid precursor protein (APP) carrying the Swedish mutation (KM670/671NL; APP23) with the Aβ-antibody β1 or phosphate-buffered saline (PBS) beginning 1) at 3 months, before the onset of dendrite degeneration and plaque deposition, and 2) at 7 months, after the start of Aβ plaque deposition and dendrite degeneration.

Results

At 5 months of age, first Aβ aggregates in APP23 brain consisted of non-modified Aβ (representing B-Aβ stage 1) whereas mature Aβ-aggregates containing N-terminal truncated, pyroglutamate-modified Aβ_N3pE and phosphorylated Aβ (representing B-Aβ stage 3) were found at 11 months of age in both β1- and PBS-treated animals. Protective effects on commissural neurons with highly ramified dendritic trees were observed only in 3-month-old β1-treated animals sacrificed at 5 months. When treatment started at 7 months of age, no differences in the numbers of healthy commissural neurons were observed between β1- and PBS-treated APP23 mice sacrificed with 11 months.

Conclusions

Aβ antibody treatment was capable of protecting neurons from dendritic degeneration as long as Aβ aggregation was absent or represented B-Aβ stage 1 but had no protective or curative effect in later stages with mature Aβ aggregates (B-Aβ stage 3). These data indicate that the maturation stage of Aβ aggregates has impact on potential treatment effects in APP23 mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0217-z) contains supplementary material, which is available to authorized users.

Encapsulated cellular implants for recombinant protein delivery and therapeutic modulation of the immune system

Ex vivo gene therapy using retrievable encapsulated cellular implants is an effective strategy for the local and/or chronic delivery of therapeutic proteins. In particular, it is considered an innovative approach to modulate the activity of the immune system. Two recently proposed therapeutic schemes using genetically engineered encapsulated cells are discussed here: the chronic administration of monoclonal antibodies for passive immunization against neurodegenerative diseases and the local delivery of a cytokine as an adjuvant for anti-cancer vaccines.

Growth factor treatment to overcome Alzheimer's dysfunctional signaling

The number of people suffering from Alzheimer's disease (AD) will increase as the world population ages, creating a huge socio-economic burden. The three pathophysiological hallmarks of AD are the cholinergic system dysfunction, the β-amyloid peptide deposition and the Tau protein hyperphosphorylation. Current treatments have only transient effects and each tends to concentrate on a single pathophysiological aspect of AD. This review first provides an overall view of AD in terms of its pathophysiological symptoms and signaling dysfunction. We then examine the therapeutic potential of growth factors (GFs) by showing how they can overcome the dysfunctional cell signaling that occurs in AD. Finally, we discuss new alternatives to GFs that help overcome the problem of brain uptake, such as small peptides, with evidence from some of our unpublished data on human neuronal cell line.

Tau aggregation and its interplay with amyloid-β

Neurofibrillary tangles and amyloid plaques constitute the hallmark brain lesions of Alzheimer's disease (AD) patients. Tangles are composed of fibrillar aggregates of the microtubule-associated protein tau, and plaques comprise fibrillar forms of a proteolytic cleavage product, amyloid-β (Aβ). Although plaques and tangles are the end-stage lesions in AD, small oligomers of Aβ and tau are now receiving increased attention as they are shown to correlate best with neurotoxicity. One key question of debate, however, is which of these pathologies appears first and hence is upstream in the pathocascade. Studies suggest that there is an intense crosstalk between the two molecules and, based on work in animal models, there is increasing evidence that Aβ, at least in part, exerts its toxicity via tau, with the Src kinase Fyn playing a crucial role in this process. In other experimental paradigms, Aβ and tau have been found to exert both separate and synergistic modes of toxicity. The challenge, however, is to integrate these different scenarios into a coherent picture. Furthermore, the ability of therapeutic interventions targeting just one of these molecules, to successfully neutralize the toxicity of the other, needs to be ascertained to improve current therapeutic strategies, such as immunotherapy, for the treatment of AD. Although this article is not intended to provide a comprehensive review of the currently pursued therapeutic strategies, we will discuss what has been achieved by immunotherapy and, in particular, how the inherent limitations of this approach can possibly be overcome by novel strategies that involve single-chain antibodies.

Allopregnanolone enhances the neurogenesis of midbrain dopaminergic neurons in APPswe/PSEN1 mice

An earlier study has demonstrated that exogenous allopregnanolone (APα) can reverse the reduction of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) of 3-month-old male triple transgenic Alzheimer's disease mouse (3xTgAD). This paper is focused on further clarifying the origin of these new-born TH-positive neurons induced by exogenous APα treatment. We performed a deeper research in another AD mouse model, 4-month-old male APPswe/PSEN1 double transgenic AD mouse (2xTgAD) by measuring APα concentration and counting immunopositive neurons using enzyme-linked immunosorbent assay (ELISA) and unbiased stereology. It was found that endogenous APα level and the number of TH-positive neurons were reduced in the 2xTgAD mice, and these reductions were present prior to the appearance of β-amyloid (Aβ)-positive plaques. Furthermore, a single 20mg/kg of exogenous APα treatment prevented the decline of total neurons, TH-positive neurons and TH/bromodeoxyuridine (BrdU) double-positive neurons in the SNpc of 2xTgAD mice although the decreased intensity of TH-positive fibers was not rescued in the striatum. It was also noted that exogenous APα administration had an apparent increase in the doublecortin (DCX)-positive neurons and DCX/BrdU double-positive neurons of subventricular zone (SVZ), as well as in the percentage of neuronal nuclear antigen (NeuN)/BrdU double-positive neurons of the SNpc in the 2xTgAD mice. These findings indicate that a lower level of endogenous APα is implicated in the loss of midbrain dopaminergic neurons in the 2xTgAD mice, and exogenous APα-induced a significant increase in the new-born dopaminergic neurons might be derived from the proliferating and differentiation of neural stem niche of SVZ.

¹⁸F-FDG PET for the early diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI)

BACKGROUND

¹⁸F-FDFG uptake by brain tissue as measured by positron emission tomography (PET) is a well-established method for assessment of brain function in people with dementia. Certain findings on brain PET scans can potentially predict the decline of mild cognitive Impairment (MCI) to Alzheimer's disease dementia or other dementias.

OBJECTIVES

To determine the diagnostic accuracy of the ¹⁸F-FDG PET index test for detecting people with MCI at baseline who would clinically convert to Alzheimer's disease dementia or other forms of dementia at follow-up.

SEARCH METHODS

We searched the Cochrane Register of Diagnostic Test Accuracy Studies, MEDLINE, EMBASE, Science Citation Index, PsycINFO, BIOSIS previews, LILACS, MEDION, (Meta-analyses van Diagnostisch Onderzoek), DARE (Database of Abstracts of Reviews of Effects), HTA (Health Technology Assessment Database), ARIF (Aggressive Research Intelligence Facility) and C-EBLM (International Federation of Clinical Chemistry and Laboratory Medicine Committee for Evidence-based Laboratory Medicine) databases to January 2013. We checked the reference lists of any relevant studies and systematic reviews for additional studies.

SELECTION CRITERIA

We included studies that evaluated the diagnostic accuracy of ¹⁸F-FDG PET to determine the conversion from MCI to Alzheimer's disease dementia or to other forms of dementia, i.e. any or all of vascular dementia, dementia with Lewy bodies, and fronto-temporal dementia. These studies necessarily employ delayed verification of conversion to dementia and are sometimes labelled as 'delayed verification cross-sectional studies'.

DATA COLLECTION AND ANALYSIS

Two blinded review authors independently extracted data, resolving disagreement by discussion, with the option to involve a third review author as arbiter if necessary. We extracted and summarised graphically the data for two-by-two tables. We conducted exploratory analyses by plotting estimates of sensitivity and specificity from each study on forest plots and in receiver operating characteristic (ROC) space. When studies had mixed thresholds, we derived estimates of sensitivity and likelihood ratios at fixed values (lower quartile, median and upper quartile) of specificity from the hierarchical summary ROC (HSROC) models.

MAIN RESULTS

We included 14 studies (421 participants) in the analysis. The sensitivities for conversion from MCI to Alzheimer's disease dementia were between 25% and 100% while the specificities were between 15% and 100%. From the summary ROC curve we fitted we estimated that the sensitivity was 76% (95% confidence interval (CI): 53.8 to 89.7) at the included study median specificity of 82%. This equates to a positive likelihood ratio of 4.03 (95% CI: 2.97 to 5.47), and a negative likelihood ratio of 0.34 (95% CI: 0.15 to 0.75). Three studies recruited participants from the same Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort but only the largest ADNI study (Herholz 2011) is included in the meta-analysis. In order to demonstrate whether the choice of ADNI study or discriminating brain region (Chételat 2003) or reader assessment (Pardo 2010) make a difference to the pooled estimate, we performed five additional analyses. At the median specificity of 82%, the estimated sensitivity was between 74% and 76%. There was no impact on our findings. In addition to evaluating Alzheimer's disease dementia, five studies evaluated the accuracy of ¹⁸F-FDG PET for all types of dementia. The sensitivities were between 46% and 95% while the specificities were between 29% and 100%; however, we did not conduct a meta-analysis because of too few studies, and those studies which we had found recruited small numbers of participants. Our findings are based on studies with poor reporting, and the majority of included studies had an unclear risk of bias, mainly for the reference standard and participant selection domains. According to the assessment of Index test domain, more than 50% of studies were of poor methodological quality.

AUTHORS' CONCLUSIONS

It is difficult to determine to what extent the findings from the meta-analysis can be applied to clinical practice. Given the considerable variability of specificity values and lack of defined thresholds for determination of test positivity in the included studies, the current evidence does not support the routine use of ¹⁸F-FDG PET scans in clinical practice in people with MCI. The ¹⁸F-FDG PET scan is a high-cost investigation, and it is therefore important to clearly demonstrate its accuracy and to standardise the process of ¹⁸F-FDG PET diagnostic modality prior to its being widely used. Future studies with more uniform approaches to thresholds, analysis and study conduct may provide a more homogeneous estimate than the one available from the included studies we have identified.

Biometals and their therapeutic implications in Alzheimer's disease

No disease modifying therapy exists for Alzheimer's disease (AD). The growing burden of this disease to our society necessitates continued investment in drug development. Over the last decade, multiple phase 3 clinical trials testing drugs that were designed to target established disease mechanisms of AD have all failed to benefit patients. There is, therefore, a need for new treatment strategies. Changes to the transition metals, zinc, copper, and iron, in AD impact on the molecular mechanisms of disease, and targeting these metals might be an alternative approach to treat the disease. Here we review how metals feature in molecular mechanisms of AD, and we describe preclinical and clinical data that demonstrate the potential for metal-based drug therapy.

Tau immunization: a cautionary tale?

The amyloid β (Aβ)-protein and microtubule-associated protein, tau, are the major components of the amyloid plaques and neurofibrillary tangles that typify Alzheimer's disease (AD) pathology. As such both Aβ and tau have long been proposed as therapeutic targets. Immunotherapy, particularly targeting Aβ, is currently the most advanced clinical strategy for treating AD. However, several Aβ-directed clinical trials have failed, and there is concern that targeting this protein may not be useful. In contrast, there is a growing optimism that tau immunotherapy may prove more efficacious. Here, for the first time, we studied the effects of chronic administration of an anti-tau monoclonal antibody (5E2) in amyloid precursor protein transgenic mice. For our animal model, we chose the J20 mouse line because prior studies had shown that the cognitive deficits in these mice require expression of tau. Despite the fact that 5E2 was present and active in the brains of immunized mice and that this antibody appeared to engage with extracellular tau, 5E2-treatment did not recover age-dependent spatial reference memory deficits. These results indicate that the memory impairment evident in J20 mice is unlikely to be mediated by a form of extracellular tau recognized by 5E2. In addition to the lack of positive effect of anti-tau immunotherapy, we also documented a significant increase in mortality among J20 mice that received 5E2. Because both the J20 mice used here and tau transgenic mice used in prior tau immunotherapy trials are imperfect models of AD our results recommend extensive preclinical testing of anti-tau antibody-based therapies using multiple mouse models and a variety of different anti-tau antibodies.

Advances in the therapy of Alzheimer's disease: targeting amyloid beta and tau and perspectives for the future

Worldwide multidisciplinary translational research has led to a growing knowledge of the genetics and molecular pathogenesis of Alzheimer's disease (AD) indicating that pathophysiological brain alterations occur decades before clinical signs and symptoms of cognitive decline can be diagnosed. Consequently, therapeutic concepts and targets have been increasingly focused on early-stage illness before the onset of dementia; and distinct classes of compounds are now being tested in clinical trials. At present, there is a growing consensus that therapeutic progress in AD delaying disease progression would significantly decrease the expanding global burden. The evolving hypothesis- and evidence-based generation of new diagnostic research criteria for early-stage AD has positively impacted the development of clinical trial designs and the characterization of earlier and more specific target populations for trials in prodromal as well as in pre- and asymptomatic at-risk stages of AD.

Cerebrospinal fluid biomarkers in trials for Alzheimer and Parkinson diseases

Alzheimer disease (AD) and Parkinson disease (PD) are the most common neurodegenerative disorders. For both diseases, early intervention is thought to be essential to the success of disease-modifying treatments. Cerebrospinal fluid (CSF) can reflect some of the pathophysiological changes that occur in the brain, and the number of CSF biomarkers under investigation in neurodegenerative conditions has grown rapidly in the past 20 years. In AD, CSF biomarkers are increasingly being used in clinical practice, and have been incorporated into the majority of clinical trials to demonstrate target engagement, to enrich or stratify patient groups, and to find evidence of disease modification. In PD, CSF biomarkers have not yet reached the clinic, but are being studied in patients with parkinsonism, and are being used in clinical trials either to monitor progression or to demonstrate target engagement and downstream effects of drugs. CSF biomarkers might also serve as surrogate markers of clinical benefit after a specific therapeutic intervention, although additional data are required. It is anticipated that CSF biomarkers will have an important role in trials aimed at disease modification in the near future. In this Review, we provide an overview of CSF biomarkers in AD and PD, and discuss their role in clinical trials.

Amyloid-beta: a crucial factor in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia which affects people older than 60 years of age. In AD, the dysregulation of the amyloid-beta (Aβ) level leads to the appearance of senile plaques which contain Aβ depositions. Aβ is a complex biological molecule which interacts with many types of receptors and/or forms insoluble assemblies and, eventually, its nonphysiological depositions alternate with the normal neuronal conditions. In this situation, AD signs appear and the patients experience marked cognitional disabilities. In general, intellect, social skills, personality, and memory are influenced by this disease and, in the long run, it leads to a reduction in quality of life and life expectancy. Due to the pivotal role of Aβ in the pathobiology of AD, a great deal of effort has been made to reveal its exact role in neuronal dysfunctions and to finding efficacious therapeutic strategies against its adverse neuronal outcomes. Hence, the determination of its different molecular assemblies and the mechanisms underlying its pathological effects are of interest. In the present paper, some of the well-established structural forms of Aβ, its interactions with various receptors and possible molecular and cellular mechanisms underlying its neurotoxicity are discussed. In addition, several Aβ-based rodent models of AD are reviewed.

Failure of ubiquitin proteasome system: risk for neurodegenerative diseases

The ubiquitin proteasome system (UPS) is the primary proteolytic quality control system in cells and has an essential function in the nervous system. UPS dysfunction has been linked to neurodegenerative conditions, including Alzheimer's, Parkinson's and Huntington's diseases. The pathology of neurodegenerative diseases is characterized by the abnormal accumulation of insoluble protein aggregates or inclusion bodies within neurons. The failure or dysregulation of the UPS prevents the degradation of misfolded/aberrant proteins, leading to deficient synaptic function that eventually affects the nervous system. In this review, we discuss the UPS and its physiological roles in the nervous system, its influence on neuronal function, and how UPS dysfunction contributes to the development of neurodegenerative diseases.

Models of β-amyloid induced Tau-pathology: the long and "folded" road to understand the mechanism

The amyloid cascade hypothesis has been the prevailing hypothesis in Alzheimer’s Disease research, although the final and most wanted proof i.e. fully successful anti-amyloid clinical trials in patients, is still lacking. This may require a better in depth understanding of the cascade. Particularly, the exact toxic forms of Aβ and Tau, the molecular link between them and their respective contributions to the disease process need to be identified in detail. Although the lack of final proof has raised substantial criticism on the hypothesis per se, accumulating experimental evidence in in vitro models, in vivo models and from biomarkers analysis in patients supports the amyloid cascade and particularly Aβ-induced Tau-pathology, which is the focus of this review. We here discuss available models that recapitulate Aβ-induced Tau-pathology and review some potential underlying mechanisms. The availability and diversity of these models that mimic the amyloid cascade partially or more complete, provide tools to study remaining questions, which are crucial for development of therapeutic strategies for Alzheimer’s Disease.

Cognitive and emotional alterations in young Alzheimer's disease (3xTgAD) mice: effects of neonatal handling stimulation and sexual dimorphism

Alzheimer disease is the most common neurodegenerative disorder and cause of senile dementia. It is characterized by an accelerated memory loss, and alterations of mood, reason, judgment and language. The main neuropathological hallmarks of the disorder are β-amyloid (βA) plaques and neurofibrillary Tau tangles. The triple transgenic 3xTgAD mouse model develops βA and Tau pathologies in a progressive manner which mimicks the pattern that takes place in the human brain with AD, and showing cognitive alterations characteristic of the disease. The present study intended to examine whether 3xTgAD mice of both sexes present cognitive, emotional and other behavioral alterations at the early age of 4 months, an age in which only some intraneuronal amyloid accumulation is found. Neonatal handling (H) is an early-life treatment known to produce profound and long-lasting behavioral and neurobiological effects in rodents, as well as improvements in cognitive functions. Therefore, we also aimed at evaluating the effects of H on the behavioral/cognitive profile of 4-month-old male and female 3xTgAD mice. The results indicate that, (1) 3xTgAD mice present spatial learning/memory deficits and emotional alterations already at the early age of 4 months, (2) there exists sexual dimorphism effects on several behavioral variables at this age, (3) neonatal handling exerts a preventive effect on some cognitive (spatial learning) and emotional alterations appearing in 3xTgAD mice already at early ages, and 4) H treatment appears to produce stronger positive effects in females than in males in several spatial learning measures and in the open field test.

N-terminal region of myelin basic protein reduces fibrillar amyloid-β deposition in Tg-5xFAD mice

Alzheimer's disease is a progressive neurodegenerative disorder that is characterized by extensive deposition of fibrillar amyloid-β (Aβ) in the brain. Previously, myelin basic protein (MBP) was identified to be a potent inhibitor to Aβ fibril formation, and this inhibitory activity was localized to the N-terminal residues 1-64, a fragment designated MBP1. Here, we show that the modest neuronal expression of a fusion protein of the biologically active MBP1 fragment and the enhanced green fluorescent protein (MBP1-EGFP) significantly improved the performance of spatial learning memory in Tg-5xFAD mice, a model of pathologic Aβ accumulation in brain. The levels of insoluble Aβ and fibrillar amyloid were significantly reduced in bigenic Tg-5xFAD/Tg-MBP1-EGFP mice. Quantitative stereological analysis revealed that the reduction in amyloid was because of a reduction in the size of fibrillar plaques rather than a decrease in plaque numbers. The current findings support previous studies showing that MBP1 inhibits Aβ fibril formation in vitro and demonstrate the ability of MBP1 to reduce Aβ pathology and improve behavioral performance.

Inconsistencies and controversies surrounding the amyloid hypothesis of Alzheimer's disease

The amyloid hypothesis has driven drug development strategies for Alzheimer's disease for over 20 years. We review why accumulation of amyloid-beta (Aβ) oligomers is generally considered causal for synaptic loss and neurodegeneration in AD. We elaborate on and update arguments for and against the amyloid hypothesis with new data and interpretations, and consider why the amyloid hypothesis may be failing therapeutically. We note several unresolved issues in the field including the presence of Aβ deposition in cognitively normal individuals, the weak correlation between plaque load and cognition, questions regarding the biochemical nature, presence and role of Aβ oligomeric assemblies in vivo, the bias of pre-clinical AD models toward the amyloid hypothesis and the poorly explained pathological heterogeneity and comorbidities associated with AD. We also illustrate how extensive data cited in support of the amyloid hypothesis, including genetic links to disease, can be interpreted independently of a role for Aβ in AD. We conclude it is essential to expand our view of pathogenesis beyond Aβ and tau pathology and suggest several future directions for AD research, which we argue will be critical to understanding AD pathogenesis.

Mitogen-activated protein kinase signaling pathways are involved in regulating α7 nicotinic acetylcholine receptor-mediated amyloid-β uptake in SH-SY5Y cells

Intraneuronal accumulation of beta-amyloid protein (Aβ) is an early pathological change in Alzheimer's disease (AD). Recent studies demonstrate that α7 nicotinic acetylcholine receptor (α7nAChR) binds to soluble Aβ with a high affinity. In vitro and in vivo experiments also show that Aβ activates p38 MAPK and ERK1/2 signaling pathways via the α7nAChR. Interestingly, it has been reported that p38 MAPK and ERK1/2 signaling pathways affect the regulation of receptor-mediated endocytosis. These data suggest that MAPK signaling pathways maybe involved in the regulation of α7nAChR-mediated Aβ uptake. However, the evidence for this hypothesis is lacking. In the present study, we examined whether Aβ1-42 oligomers activate MAPK signaling pathways via α7nAChR, and assessed the role of MAPK signaling pathways in the regulation of Aβ1-42 uptake by α7nAChR. We confirm that undifferentiated SH-SY5Y cells are capable of taking up extracellular Aβ1-42. The internalization of Aβ1-42 accumulates in the endosomes/lysosomes and mitochondria. MAPK signaling pathways are activated by Aβ1-42 via α7nAChR. Aβ1-42 and α7nAChR are co-localized in SH-SY5Y cells and the expression of α7nAChR involves in Aβ1-42 uptake and accumulation in SH-SY5Y cells. Our data demonstrate that Aβ1-42 induces an α7nAChR-dependent pathway that relates to the activation of p38 MAPK and ERK1/2, resulting in internalization of Aβ1-42. Our findings suggest that α7nAChR and MAPK signaling pathways play an important role in the uptake and accumulation of Aβ1-42 in SH-SY5Y cells. Blockade of α7nAChR may have a beneficial effect by limiting intracellular accumulation of amyloid in AD brain and serves a potential therapeutic target for AD.

(11)C-PIB-PET for the early diagnosis of Alzheimer's disease dementia and other dementias in people with mild cognitive impairment (MCI)

BACKGROUND

According to the latest revised National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (now known as the Alzheimer's Association) (NINCDS-ADRDA) diagnostic criteria for Alzheimer's disease dementia, the confidence in diagnosing mild cognitive impairment (MCI) due to Alzheimer's disease dementia is raised with the application of imaging biomarkers. These tests, added to core clinical criteria, might increase the sensitivity or specificity of a testing strategy. However, the accuracy of biomarkers in the diagnosis of Alzheimer's disease dementia and other dementias has not yet been systematically evaluated. A formal systematic evaluation of the sensitivity, specificity, and other properties of positron emission tomography (PET) imaging with the (11)C-labelled Pittsburgh Compound-B ((11)C-PIB) ligand was performed.

OBJECTIVES

To determine the diagnostic accuracy of the (11)C- PIB-PET scan for detecting participants with MCI at baseline who will clinically convert to Alzheimer's disease dementia or other forms of dementia over a period of time.

SEARCH METHODS

The most recent search for this review was performed on 12 January 2013. We searched MEDLINE (OvidSP), EMBASE (OvidSP), BIOSIS Previews (ISI Web of Knowledge), Web of Science and Conference Proceedings (ISI Web of Knowledge), PsycINFO (OvidSP), and LILACS (BIREME). We also requested a search of the Cochrane Register of Diagnostic Test Accuracy Studies (managed by the Cochrane Renal Group).No language or date restrictions were applied to the electronic searches and methodological filters were not used so as to maximise sensitivity.

SELECTION CRITERIA

We selected studies that had prospectively defined cohorts with any accepted definition of MCI with baseline (11)C-PIB-PET scan. In addition, we only selected studies that applied a reference standard for Alzheimer's dementia diagnosis for example NINCDS-ADRDA or Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria.

DATA COLLECTION AND ANALYSIS

We screened all titles generated by electronic database searches. Two review authors independently assessed the abstracts of all potentially relevant studies. The identified full papers were assessed for eligibility and data were extracted to create two by two tables. Two independent assessors performed quality assessment using the QUADAS 2 tool. We used the hierarchical summary receiver operating characteristic (ROC) model to produce a summary ROC curve.

MAIN RESULTS

Conversion from MCI to Alzheimer's disease dementia was evaluated in nine studies. The quality of the evidence was limited. Of the 274 participants included in the meta-analysis, 112 developed Alzheimer's dementia. Based on the nine included studies, the median proportion converting was 34%. The studies varied markedly in how the PIB scans were done and interpreted.The sensitivities were between 83% and 100% while the specificities were between 46% and 88%. Because of the variation in thresholds and measures of (11)C-PIB amyloid retention, we did not calculate summary sensitivity and specificity. Although subject to considerable uncertainty, to illustrate the potential strengths and weaknesses of (11)C-PIB-PET scans we estimated from the fitted summary ROC curve that the sensitivity was 96% (95% confidence interval (CI) 87 to 99) at the included study median specificity of 58%. This equated to a positive likelihood ratio of 2.3 and a negative likelihood ratio of 0.07. Assuming a typical conversion rate of MCI to Alzheimer's dementia of 34%, for every 100 PIB scans one person with a negative scan would progress and 28 with a positive scan would not actually progress to Alzheimer's dementia.There were limited data for formal investigation of heterogeneity. We performed two sensitivity analyses to assess the influence of type of reference standard and the use of a pre-specified threshold. There was no effect on our findings.

AUTHORS' CONCLUSIONS

Although the good sensitivity achieved in some included studies is promising for the value of (11)C-PIB-PET, given the heterogeneity in the conduct and interpretation of the test and the lack of defined thresholds for determination of test positivity, we cannot recommend its routine use in clinical practice.(11)C-PIB-PET biomarker is a high cost investigation, therefore it is important to clearly demonstrate its accuracy and standardise the process of the (11)C-PIB diagnostic modality prior to it being widely used.

Potential therapeutic strategies for Alzheimer's disease targeting or beyond β-amyloid: insights from clinical trials

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with two hallmarks: β-amyloid plagues and neurofibrillary tangles. It is one of the most alarming illnesses to elderly people. No effective drugs and therapies have been developed, while mechanism-based explorations of therapeutic approaches have been intensively investigated. Outcomes of clinical trials suggested several pitfalls in the choice of biomarkers, development of drug candidates, and interaction of drug-targeted molecules; however, they also aroused concerns on the potential deficiency in our understanding of pathogenesis of AD, and ultimately stimulated the advent of novel drug targets tests. The anticipated increase of AD patients in next few decades makes development of better therapy an urgent issue. Here we attempt to summarize and compare putative therapeutic strategies that have completed clinical trials or are currently being tested from various perspectives to provide insights for treatments of Alzheimer's disease.

Diverse molecular targets for therapeutic strategies in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia caused by neurodegenerative process and is tightly related to amyloid β (Aβ) and neurofibrillary tangles. The lack of early diagnostic biomarker and therapeutic remedy hinders the prevention of increasing population of AD patients every year. In spite of accumulated scientific information, numerous clinical trials for candidate drug targets have failed to be preceded into therapeutic development, therefore, AD-related sufferers including patients and caregivers, are desperate to seek the solution. Also, effective AD intervention is desperately needed to reduce AD-related societal threats to public health. In this review, we summarize various drug targets and strategies in recent preclinical studies and clinical trials for AD therapy: Allopathic treatment, immunotherapy, Aβ production/aggregation modulator, tau-targeting therapy and metabolic targeting. Some has already failed in their clinical trials and the others are still in various stages of investigations, both of which give us valuable information for future research in AD therapeutic development.

Dipeptidyl peptidase 10 (DPP10(789)): a voltage gated potassium channel associated protein is abnormally expressed in Alzheimer's and other neurodegenerative diseases

The neuropathological features associated with Alzheimer's disease (AD) include the presence of extracellular amyloid-β peptide-containing plaques and intracellular tau positive neurofibrillary tangles and the loss of synapses and neurons in defined regions of the brain. Dipeptidyl peptidase 10 (DPP10) is a protein that facilitates Kv4 channel surface expression and neuronal excitability. This study aims to explore DPP10789 protein distribution in human brains and its contribution to the neurofibrillary pathology of AD and other tauopathies. Immunohistochemical analysis revealed predominant neuronal staining of DPP10789 in control brains, and the CA1 region of the hippocampus contained strong reactivity in the distal dendrites of the pyramidal cells. In AD brains, robust DPP10789 reactivity was detected in neurofibrillary tangles and plaque-associated dystrophic neurites, most of which colocalized with the doubly phosphorylated Ser-202/Thr-205 tau epitope. DPP10789 positive neurofibrillary tangles and plaque-associated dystrophic neurites also appeared in other neurodegenerative diseases such as frontotemporal lobar degeneration, diffuse Lewy body disease, and progressive supranuclear palsy. Occasional DPP10789 positive neurofibrillary tangles and neurites were seen in some aged control brains. Western blot analysis showed both full length and truncated DPP10789 fragments with the later increasing significantly in AD brains compared to control brains. Our results suggest that DPP10789 is involved in the pathology of AD and other neurodegenerative diseases.

Animal models of neurodegenerative diseases

The prevalence of neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), increases with age, and the number of affected patients is expected to increase worldwide in the next decades. Accurately understanding the etiopathogenic mechanisms of these diseases is a crucial step for developing disease-modifying drugs able to preclude their emergence or at least slow their progression. Animal models contribute to increase the knowledge on the pathophysiology of neurodegenerative diseases. These models reproduce different aspects of a given disease, as well as the histopathological lesions and its main symptoms. The purpose of this review is to present the main animal models for AD, PD, and Huntington's disease.

p-Tau immunotherapy reduces soluble and insoluble tau in aged 3xTg-AD mice

Alzheimer's disease (AD) is a proteinopathy characterized by the accumulation of β-amyloid (Aβ) and tau. To date, clinical trials indicate that Aβ immunotherapy does not improve cognition. Consequently, it is critical to modulate other aspects of AD pathology. As such, tau represents an excellent target, as its accumulation better correlates with cognitive impairment. To determine the effectiveness of targeting pathological tau, with Aβ pathology present, we administered a single injection of AT8, or control antibody, into the hippocampus of aged 3xTg-AD mice. Extensive data indicates that phosphorylated Ser(202) and Thr(205) sites of tau (corresponding to the AT8 epitope) represent a pathologically relevant target for AD. We report that immunization with AT8 reduced somatodendritic tau load, p-tau immunoreactivity, and silver stained positive neurons, without affecting Aβ pathology. We also discovered that tau pathology soon reemerges post-injection, possibly due to persistent Aβ pathology. These studies provide evidence that targeting p-tau may represent an effective treatment strategy: potentially in conjunction with Aβ immunotherapy.

Passive immunization with Tau oligomer monoclonal antibody reverses tauopathy phenotypes without affecting hyperphosphorylated neurofibrillary tangles

Recent findings suggest that tau oligomers, which form before neurofibrillary tangles (NFTs), are the true neurotoxic tau entities in neurodegenerative tauopathies, including Alzheimer's disease (AD). Studies in animal models of tauopathy suggest that tau oligomers play a key role in eliciting behavioral and cognitive impairments. Here, we used a novel tau oligomer-specific monoclonal antibody (TOMA) for passive immunization in mice expressing mutant human tau. A single dose of TOMA administered either intravenously or intracerebroventricularly was sufficient to reverse both locomotor and memory deficits in a mouse model of tauopathy for 60 d, coincident with rapid reduction of tau oligomers but not phosphorylated NFTs or monomeric tau. Our data demonstrate that antibody protection is mediated by extracellular and rapid peripheral clearance. These findings provide the first direct evidence in support of a critical role for tau oligomers in disease progression and validate tau oligomers as a target for the treatment of AD and other neurodegenerative tauopathies.

Neural stem cells genetically-modified to express neprilysin reduce pathology in Alzheimer transgenic models

INTRODUCTION

Short-term neural stem cell (NSC) transplantation improves cognition in Alzheimer's disease (AD) transgenic mice by enhancing endogenous synaptic connectivity. However, this approach has no effect on the underlying beta-amyloid (Aβ) and neurofibrillary tangle pathology. Long term efficacy of cell based approaches may therefore require combinatorial approaches.

METHODS

To begin to examine this question we genetically-modified NSCs to stably express and secrete the Aβ-degrading enzyme, neprilysin (sNEP). Next, we studied the effects of sNEP expression in vitro by quantifying Aβ-degrading activity, NSC multipotency markers, and Aβ-induced toxicity. To determine whether sNEP-expressing NSCs can also modulate AD-pathogenesis in vivo, control-modified and sNEP-NSCs were transplanted unilaterally into the hippocampus of two independent and well characterized transgenic models of AD: 3xTg-AD and Thy1-APP mice. After three months, stem cell engraftment, neprilysin expression, and AD pathology were examined.

RESULTS

Our findings reveal that stem cell-mediated delivery of NEP provides marked and significant reductions in Aβ pathology and increases synaptic density in both 3xTg-AD and Thy1-APP transgenic mice. Remarkably, Aβ plaque loads are reduced not only in the hippocampus and subiculum adjacent to engrafted NSCs, but also within the amygdala and medial septum, areas that receive afferent projections from the engrafted region.

CONCLUSIONS

Taken together, our data suggest that genetically-modified NSCs could provide a powerful combinatorial approach to not only enhance synaptic plasticity but to also target and modify underlying Alzheimer's disease pathology.

Tau acts as a mediator for Alzheimer's disease-related synaptic deficits

The two histopathological hallmarks of Alzheimer's disease (AD) are amyloid plaques containing multiple forms of amyloid beta (Aβ) and neurofibrillary tangles containing phosphorylated tau proteins. As mild cognitive impairment frequently occurs long before the clinical diagnosis of AD, the scientific community has been increasingly interested in the roles of Aβ and tau in earlier cellular changes that lead to functional deficits. Therefore, great progress has recently been made in understanding how Aβ or tau causes synaptic dysfunction. However, the interaction between the Aβ and tau-initiated intracellular cascades that lead to synaptic dysfunction remains elusive. The cornerstone of the two-decade-old hypothetical amyloid cascade model is that amyloid pathologies precede tau pathologies. Although the premise of Aβ-tau pathway remains valid, the model keeps evolving as new signaling events are discovered that lead to functional deficits and neurodegeneration. Recent progress has been made in understanding Aβ-PrP(C) -Fyn-mediated neurotoxicity and synaptic deficits. Although still elusive, many novel upstream and downstream signaling molecules have been found to modulate tau mislocalization and tau hyperphosphorylation. Here we will discuss the mechanistic interactions between Aβ-PrP(C) -mediated neurotoxicity and tau-mediated synaptic deficits in an updated amyloid cascade model with calcium and tau as the central mediators.

Soluble Aβ oligomers are rapidly sequestered from brain ISF in vivo and bind GM1 ganglioside on cellular membranes

Soluble Aβ oligomers contribute importantly to synaptotoxicity in Alzheimer's disease, but their dynamics in vivo remain unclear. Here, we found that soluble Aβ oligomers were sequestered from brain interstitial fluid onto brain membranes much more rapidly than nontoxic monomers and were recovered in part as bound to GM1 ganglioside on membranes. Aβ oligomers bound strongly to GM1 ganglioside, and blocking the sialic acid residue on GM1 decreased oligomer-mediated LTP impairment in mouse hippocampal slices. In a hAPP transgenic mouse model, substantial levels of GM1-bound Aβ₄₂ were recovered from brain membrane fractions. We also detected GM1-bound Aβ in human CSF, and its levels correlated with Aβ₄₂, suggesting its potential as a biomarker of Aβ-related membrane dysfunction. Together, these findings highlight a mechanism whereby hydrophobic Aβ oligomers become sequestered onto GM1 ganglioside and presumably other lipids on neuronal membranes, where they may induce progressive functional and structural changes.

Dipeptidyl peptidase-4 inhibition by Pterocarpus marsupium and Eugenia jambolana ameliorates streptozotocin induced Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by the loss of normal functions of brain cells and neuronal death, ultimately leading to memory loss. Recent accumulating evidences have demonstrated the therapeutic potential of anti-diabetic agents, such as dipeptidyl peptidase-4 (DPP-4) inhibitors, for the treatment of Alzheimer's disease (AD), providing opportunities to explore and test the DPP-4 inhibitors for treating this fatal disease. Prior studies determining the efficacy of Pterocarpus marsupium (PM, Fabaceae) and Eugenia jambolana (EJ, Myrtaceae) extracts for ameliorating type 2 diabetes have demonstrated the DPP-4 inhibitory properties indicating the possibility of using of these extracts even for the treating AD. Therefore, in the present study, the neuroprotective roles of PM and EJ for ameliorating the streptozotocin (STZ) induced AD have been tested in rat model. Experimentally, PM and EJ extracts, at a dose range of 200 and 400mg/kg, were administered orally to STZ induced AD Wistar rats and cognitive evaluation tests were performed using radial arm maze and hole-board apparatus. Following 30 days of treatment with the extracts, a dose- and time-dependent attenuation of AD pathology, as evidenced by decreasing amyloid beta 42, total tau, phosphorylated tau and neuro-inflammation with an increase in glucagon-like peptide-1 (GLP-1) levels was observed. Therefore, PM and EJ extracts contain cognitive enhancers as well as neuroprotective agents against STZ induced AD.

CB2 receptor deficiency increases amyloid pathology and alters tau processing in a transgenic mouse model of Alzheimer's disease

The endocannabinoid CB2 receptor system has been implicated in the neuropathology of Alzheimer's disease (AD). In order to investigate the impact of the CB2 receptor system on AD pathology, a colony of mice with a deleted CB2 receptor gene, CNR2, was established on a transgenic human mutant APP background for pathological comparison with CB2 receptor-sufficient transgenic mice. J20 APP (PDGFB-APPSwInd) mice were bred over two generations with CNR2(-/-) (Cnr2(tm1Dgen)/J) mice to produce a colony of J20 CNR2(+/+) and J20 CNR2(-/-) mice. Seventeen J20 CNR2(+/+) mice (12 females, 5 males) and 16 J20 CNR2(-/-) mice (11 females, 5 males) were killed at 12 months, and their brains were interrogated for AD-related pathology with both biochemistry and immunocytochemistry (ICC). In addition to amyloid-dependent endpoints such as soluble Aβ production and plaque deposition quantified with 6E10 staining, the effect of CB2 receptor deletion on total soluble mouse tau production was assayed by using a recently developed high-sensitivity assay. Results revealed that soluble Aβ42 and plaque deposition were significantly increased in J20 CNR2(-/-) mice relative to CNR2(+/+) mice. Microgliosis, quantified with ionized calcium-binding adapter molecule 1 (Iba-1) staining, did not differ between groups, whereas plaque associated microglia was more abundant in J20 CNR2(-/-) mice. Total tau was significantly suppressed in J20 CNR2(-/-) mice relative to J20 CNR2(+/+) mice. The results confirm the constitutive role of the CB2 receptor system both in reducing amyloid plaque pathology in AD and also support tehpotential of cannabinoid therapies targeting CB2 to reduce Aβ; however, the results suggest that interventions may have a divergent effect on tau pathology.

Tauopathy contributes to synaptic and cognitive deficits in a murine model for Alzheimer's disease

Tau alterations are now considered an executor of neuronal demise and cognitive dysfunction in Alzheimer's disease (AD). Mouse models combining amyloidosis and tauopathy and their parental counterparts are important tools to further investigate the interplay of abnormal amyloid-β (Aβ) and Tau species in pathogenesis, synaptic and neuronal dysfunction, and cognitive decline. Here, we crossed APP/PS1 mice with 5 early-onset familial AD mutations (5xFAD) and TauP301S (PS19) transgenic mice, denoted F(+)/T(+) mice, and phenotypically compared them to their respective parental strains, denoted F(+)/T(-) and F(-)/T(+) respectively, as controls. We found dramatically aggravated tauopathy (~10-fold) in F(+)/T(+) mice compared to the parental F(-)/T(+) mice. In contrast, amyloidosis was unaltered compared to the parental F(+)/T(-) mice. Tauopathy was invariably and very robustly aggravated in hippocampal and cortical brain regions. Most important, F(+)/T(+) displayed aggravated cognitive deficits in a hippocampus-dependent spatial navigation task, compared to the parental F(+)/T(-) strain, while parental F(-)/T(+) mice did not display cognitive impairment. Basal synaptic transmission was impaired in F(+)/T(+) mice compared to nontransgenic mice and the parental strains (≥40%). Finally, F(+)/T(+) mice displayed a significant hippocampal atrophy (~20%) compared to nontransgenic mice, in contrast to the parental strains. Our data indicate for the first time that pathological Aβ species (or APP/PS1) induced changes in Tau contribute to cognitive deficits correlating with synaptic deficits and hippocampal atrophy in an AD model. Our data lend support to the amyloid cascade hypothesis with a role of pathological Aβ species as initiator and pathological Tau species as executor.

Is there still any hope for amyloid-based immunotherapy for Alzheimer's disease?

PURPOSE OF REVIEW

We reviewed clinical trials on active and passive anti-β-amyloid (Aβ) immunotherapy for the treatment of Alzheimer's disease with a particular focus on monoclonal antibodies against Aβ.

RECENT FINDINGS

Studies on anti-Alzheimer's disease immunotherapy published in the period from January 2012 to October 2013 were reviewed.

SUMMARY

Both active and passive anti-Aβ immunotherapies were shown to clear brain Aβ deposits. However, an active anti-Aβ vaccine (AN1792) has been discontinued because it caused meningoencephalitis in 6% of Alzheimer's disease patients treated. Among passive immunotherapeutics, two Phase III clinical trials in mild-to-moderate Alzheimer's disease patients with bapineuzumab, a humanized monoclonal antibody directed at the N-terminal sequence of Aβ, were disappointing. Another antibody, solanezumab, directed at the mid-region of Aβ, failed in two Phase III clinical trials in mild-to-moderate Alzheimer's disease patients. A third Phase III study with solanezumab is ongoing in mildly affected Alzheimer's disease patients based on encouraging results in this subgroup of patients. Second-generation active Aβ vaccines (ACC-001, CAD106, and Affitope AD02) and new passive anti-Aβ immunotherapies (gantenerumab and crenezumab) are being tested in prodromal Alzheimer's disease patients, in presymptomatic individuals with Alzheimer's disease-related mutations, or in asymptomatic individuals at risk of developing Alzheimer's disease to definitely test the Aβ cascade hypothesis of Alzheimer's disease.

Hsp90-Tau complex reveals molecular basis for specificity in chaperone action

Protein folding in the cell relies on the orchestrated action of conserved families of molecular chaperones, the Hsp70 and Hsp90 systems. Hsp70 acts early and Hsp90 late in the folding path, yet the molecular basis of this timing is enigmatic, mainly because the substrate specificity of Hsp90 is poorly understood. Here, we obtained a structural model of Hsp90 in complex with its natural disease-associated substrate, the intrinsically disordered Tau protein. Hsp90 binds to a broad region in Tau that includes the aggregation-prone repeats. Complementarily, a 106-Å-long substrate-binding interface in Hsp90 enables many low-affinity contacts. This allows recognition of scattered hydrophobic residues in late folding intermediates that remain after early burial of the Hsp70 sites. Our model resolves the paradox of how Hsp90 specifically selects for late folding intermediates but also for some intrinsically disordered proteins-through the eyes of Hsp90 they look the same.

Biomarker modeling of Alzheimer's disease

Alzheimer's disease (AD) is a slowly progressing disorder in which pathophysiological abnormalities, detectable in vivo by biomarkers, precede overt clinical symptoms by many years to decades. Five AD biomarkers are sufficiently validated to have been incorporated into clinical diagnostic criteria and commonly used in therapeutic trials. Current AD biomarkers fall into two categories: biomarkers of amyloid-β plaques and of tau-related neurodegeneration. Three of the five are imaging measures and two are cerebrospinal fluid analytes. AD biomarkers do not evolve in an identical manner but rather in a sequential but temporally overlapping manner. Models of the temporal evolution of AD biomarkers can take the form of plots of biomarker severity (degree of abnormality) versus time. In this Review, we discuss several time-dependent models of AD that take into consideration varying age of onset (early versus late) and the influence of aging and co-occurring brain pathologies that commonly arise in the elderly.

Synergistic effects of amyloid-beta and wild-type human tau on dendritic spine loss in a floxed double transgenic model of Alzheimer's disease

Synapse number is the best indicator of cognitive impairment In Alzheimer's disease (AD), yet the respective contributions of Aβ and tau, particularly human wild-type tau, to synapse loss remain undefined. Here, we sought to elucidate the Aβ-dependent changes in wild-type human tau that trigger synapse loss and cognitive decline in AD by generating two novel transgenic mouse models. The first overexpresses floxed human APP with Swedish and London mutations under the thy1 promoter, and recapitulates important features of early AD, including accumulation of soluble Aβ and oligomers, but no plaque formation. Transgene excision via Cre-recombinase reverses cognitive decline, even at 18-months of age. Secondly, we generated a human wild-type tau-overexpressing mouse. Crossing of the two animals accelerates cognitive impairment, causes enhanced accumulation and aggregation of tau, and results in reduction of dendritic spines compared to single transgenic hTau or hAPP mice. These results suggest that Aβ-dependent acceleration of wild-type human tau pathology is a critical component of the lasting changes to dendritic spines and cognitive impairment found in AD.

Therapeutic options in Alzheimer’s disease

Alzheimer's disease (AD) places an enormous burden on individuals, families and society. Consequently, a tremendous effort is being devoted to the development of drugs that prevent or delay neurodegeneration. Current pharmacological treatments are based on the use of acetylcholinesterase inhibitors or memantine, a N-methyl-D-aspartate channel blocker. However, new therapeutic approaches, including those more closely targeted to the pathogenesis of the disease, are being developed. These potentially disease-modifying therapeutics include secretase inhibitors, cholesterol-lowering drugs, amyloid-beta immunotherapy, nonsteroidal anti-inflammatory drugs, hormonal modulation and the use of antioxidants. The possibility that oxidative stress is a primary event in AD indicates that antioxidant-based therapies are perhaps the most promising weapons against this devastating neurodegenerative disorder.

Alzheimer disease therapy--moving from amyloid-β to tau

Disease-modifying treatments for Alzheimer disease (AD) have focused mainly on reducing levels of amyloid-β (Aβ) in the brain. Some compounds have achieved this goal, but none has produced clinically meaningful results. Several methodological issues relating to clinical trials of these agents might explain this failure; an additional consideration is that the amyloid cascade hypothesis--which places amyloid plaques at the heart of AD pathogenesis--does not fully integrate a large body of data relevant to the emergence of clinical AD. Importantly, amyloid deposition is not strongly correlated with cognition in multivariate analyses, unlike hyperphosphorylated tau, neurofibrillary tangles, and synaptic and neuronal loss, which are closely associated with memory deficits. Targeting tau pathology, therefore, might be more clinically effective than Aβ-directed therapies. Furthermore, numerous immunization studies in animal models indicate that reduction of intracellular levels of tau and phosphorylated tau is possible, and is associated with improved cognitive performance. Several tau-related vaccines are in advanced preclinical stages and will soon enter clinical trials. In this article, we present a critical analysis of the failure of Aβ-directed therapies, discuss limitations of the amyloid cascade hypothesis, and suggest the potential value of tau-targeted therapy for AD.

CB₂ receptor deficiency increases amyloid pathology and alters tau processing in a transgenic mouse model of Alzheimer's disease

The endocannabinoid CB₂ receptor system has been implicated in the neuropathology of Alzheimer's disease (AD). In order to investigate the impact of the CB₂ receptor system on AD pathology, a colony of mice with a deleted CB₂ receptor gene, CNR2, was established on a transgenic human mutant APP background for pathological comparison with CB₂ receptor-sufficient transgenic mice. J20 APP (PDGFB-APPSwInd) mice were bred over two generations with CNR2⁻/⁻ (Cnr2(tm1Dgen)/J) mice to produce a colony of J20 CNR2⁺/⁺ and J20 CNR2⁻/⁻ mice. Seventeen J20 CNR2⁺/⁺ mice (12 females, 5 males) and 16 J20 CNR2⁻/⁻ mice (11 females, 5 males) were killed at 12 months, and their brains were interrogated for AD-related pathology with both biochemistry and immunocytochemistry (ICC). In addition to amyloid-dependent endpoints such as soluble Aβ production and plaque deposition quantified with 6E10 staining, the effect of CB2 receptor deletion on total soluble mouse tau production was assayed by using a recently developed high-sensitivity assay. Results revealed that soluble Aβ42 and plaque deposition were significantly increased in J20 CNR2⁻/⁻ mice relative to CNR2⁺/⁺ mice. Microgliosis, quantified with ionized calcium-binding adapter molecule 1 (Iba-1) staining, did not differ between groups, whereas plaque associated microglia was more abundant in J20 CNR2⁻/⁻ mice. Total tau was significantly suppressed in J20 CNR2⁻/⁻ mice relative to J20 CNR2⁺/⁺ mice. The results confirm the constitutive role of the CB₂ receptor system both in reducing amyloid plaque pathology in AD and also support tehpotential of cannabinoid therapies targeting CB₂ to reduce Aβ; however, the results suggest that interventions may have a divergent effect on tau pathology.

The absence of myelin basic protein promotes neuroinflammation and reduces amyloid β-protein accumulation in Tg-5xFAD mice

BACKGROUND

Abnormal accumulation of amyloid β-protein (Aβ) in the brain plays an important role in the pathogenesis \of Alzheimer's disease (AD). Aβ monomers assemble into oligomers and fibrils that promote neuronal dysfunction. This assembly pathway is influenced by naturally occurring brain molecules, the Aβ chaperone proteins, which bind to Aβ and modulate its aggregation. Myelin basic protein (MBP) was previously identified as a novel Aβ chaperone protein and a potent inhibitor for Aβ fibril assembly in vitro.

METHODS

In this study, we determined whether the absence of MBP would influence Aβ pathology in vivo by breeding MBP knockout mice (MBP-/-) with Tg-5xFAD mice, a model of AD-like parenchymal Aβ pathology.

RESULTS

Through biochemical and immunohistochemical experiments, we found that bigenic Tg-5xFAD/MBP-/- mice had a significant decrease of insoluble Aβ and parenchymal plaque deposition at an early age. The expression of transgene encoded human AβPP, the levels of C-terminal fragments generated during Aβ production and the intracellular Aβ were unaffected in the absence of MBP. Likewise, we did not find a significant difference in plasma Aβ or cerebrospinal fluid Aβ, suggesting these clearance routes were unaltered in bigenic Tg-5xFAD/MBP-/- mice. However, MBP-/- mice and bigenic Tg-5xFAD/MBP-/- mice exhibited elevated reactive astrocytes and activated microglia compared with Tg-5xFAD mice. The Aβ degrading enzyme matrix metalloproteinase 9 (MMP-9), which is expressed by activated glial cells, was significantly increased in the Tg-5xFAD/MBP-/- mice.

CONCLUSIONS

These findings indicate that the absence of MBP decreases Aβ deposition in transgenic mice and that this consequence may result from increased glial activation and expression of MMP-9, an Aβ degrading enzyme.