Tau immunotherapy for Alzheimer's disease

Current understanding of Alzheimer's disease diagnosis and treatment

Alzheimer’s disease is the most common cause of dementia worldwide, with the prevalence continuing to grow in part because of the aging world population. This neurodegenerative disease process is characterized classically by two hallmark pathologies: β-amyloid plaque deposition and neurofibrillary tangles of hyperphosphorylated tau. Diagnosis is based upon clinical presentation fulfilling several criteria as well as fluid and imaging biomarkers. Treatment is currently targeted toward symptomatic therapy, although trials are underway that aim to reduce the production and overall burden of pathology within the brain. Here, we discuss recent advances in our understanding of the clinical evaluation and treatment of Alzheimer’s disease, with updates regarding clinical trials still in progress.

Peptides, Peptidomimetics, and Carbohydrate-Peptide Conjugates as Amyloidogenic Aggregation Inhibitors for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder accounting for 60-80% of dementia cases. For many years, AD causality was attributed to amyloid-β (Aβ) aggregated species. Recently, multiple therapies that target Aβ aggregation have failed in clinical trials, since Aβ aggregation is found in AD and healthy patients. Attention has therefore shifted toward the aggregation of the tau protein as a major driver of AD. Numerous inhibitors of tau-based pathology have recently been developed. Diagnosis of AD has shifted from measuring late stage senile plaques to early stage biomarkers, amyloid-β and tau monomers and oligomeric assemblies. Synthetic peptides and some derivative structures are being explored for use as theranostic tools as they possess the capacity both to bind the biomarkers and to inhibit their pathological self-assembly. Several studies have demonstrated that O-linked glycoside addition can significantly alter amyloid aggregation kinetics. Furthermore, natural O-glycosylation of amyloid-forming proteins, including amyloid precursor protein (APP), tau, and α-synuclein, promotes alternative nonamyloidogenic processing pathways. As such, glycopeptides and related peptidomimetics are being investigated within the AD field. Here we review advancements made in the last 5 years, as well as the arrival of sugar-based derivatives.

Contribution of Tau Pathology to Mitochondrial Impairment in Neurodegeneration

Tau is an essential protein that physiologically promotes the assembly and stabilization of microtubules, and participates in neuronal development, axonal transport, and neuronal polarity. However, in a number of neurodegenerative diseases, including Alzheimer’s disease (AD), tau undergoes pathological modifications in which soluble tau assembles into insoluble filaments, leading to synaptic failure and neurodegeneration. Mitochondria are responsible for energy supply, detoxification, and communication in brain cells, and important evidence suggests that mitochondrial failure could have a pivotal role in the pathogenesis of AD. In this context, our group and others investigated the negative effects of tau pathology on specific neuronal functions. In particular, we observed that the presence of these tau forms could affect mitochondrial function at three different levels: (i) mitochondrial transport, (ii) morphology, and (iii) bioenergetics. Therefore, mitochondrial dysfunction mediated by anomalous tau modifications represents a novel mechanism by which these forms contribute to the pathogenesis of AD. In this review, we will discuss the main results reported on pathological tau modifications and their effects on mitochondrial function and their importance for the synaptic communication and neurodegeneration.

Selective targeting of 3 repeat Tau with brain penetrating single chain antibodies for the treatment of neurodegenerative disorders

Alzheimer's disease (AD) is the most common form of dementia in the elderly affecting more than 5 million people in the U.S. AD is characterized by the accumulation of β-amyloid (Aβ) and Tau in the brain, and is manifested by severe impairments in memory and cognition. Therefore, removing tau pathology has become one of the main therapeutic goals for the treatment of AD. Tau (tubulin-associated unit) is a major neuronal cytoskeletal protein found in the CNS encoded by the gene MAPT. Alternative splicing generates two major isoforms of tau containing either 3 or 4 repeat (R) segments. These 3R or 4RTau species are differentially expressed in neurodegenerative diseases. Previous studies have been focused on reducing Tau accumulation with antibodies against total Tau, 4RTau or phosphorylated isoforms. Here, we developed a brain penetrating, single chain antibody that specifically recognizes a pathogenic 3RTau. This single chain antibody was modified by the addition of a fragment of the apoB protein to facilitate trafficking into the brain, once in the CNS these antibody fragments reduced the accumulation of 3RTau and related deficits in a transgenic mouse model of tauopathy. NMR studies showed that the single chain antibody recognized an epitope at aa 40-62 of 3RTau. This single chain antibody reduced 3RTau transmission and facilitated the clearance of Tau via the endosomal-lysosomal pathway. Together, these results suggest that targeting 3RTau with highly specific, brain penetrating, single chain antibodies might be of potential value for the treatment of tauopathies such as Pick's Disease.

Tau-targeting therapies for Alzheimer disease

Alzheimer disease (AD) is the most common form of dementia. Pathologically, AD is characterized by amyloid plaques and neurofibrillary tangles in the brain, with associated loss of synapses and neurons, resulting in cognitive deficits and eventually dementia. Amyloid-β (Aβ) peptide and tau protein are the primary components of the plaques and tangles, respectively. In the decades since Aβ and tau were identified, development of therapies for AD has primarily focused on Aβ, but tau has received more attention in recent years, in part because of the failure of various Aβ-targeting treatments in clinical trials. In this article, we review the current status of tau-targeting therapies for AD. Initially, potential anti-tau therapies were based mainly on inhibition of kinases or tau aggregation, or on stabilization of microtubules, but most of these approaches have been discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting therapies in clinical trials are immunotherapies, which have shown promise in numerous preclinical studies. Given that tau pathology correlates better with cognitive impairments than do Aβ lesions, targeting of tau is expected to be more effective than Aβ clearance once the clinical symptoms are evident. With future improvements in diagnostics, these two hallmarks of the disease might be targeted prophylactically.

Targeting Prion-like Cis Phosphorylated Tau Pathology in Neurodegenerative Diseases

Tau is a microtubule-associated protein heavily implicated in neurodegenerative diseases collectively known as tauopathies, including Alzheimer's disease and chronic traumatic encephalopathy. Phosphorylation of tau at Thr231 allows for the isomerization of phosphorylated tau (p-tau) into distinct cis and trans conformations. Cis, but not trans, p-tau is detectable not only in Alzheimer's disease and chronic traumatic encephalopathy, but also right after traumatic brain injury depending on injury severity and frequency both in humans and animal models. Cis p-tau is not only neurotoxic but also spreads from a neuron to another in a prion-like fashion, functioning as a primary driver of neurodegeneration, which can be effectively neutralized by cis p-tau antibody. This represents an exciting new opportunity for understanding disease development and developing early biomarkers and effective therapies of tauopathies.

RNA binding proteins and the pathological cascade in ALS/FTD neurodegeneration

Advanced genetic approaches have accelerated the identification of causative genes linked to the neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Most of the disease-related proteins encoded by these genes form aggregates in the cellular machineries that regulate RNA and protein quality control in cells. Cross-talk among the signaling pathways governing these machineries leads to pathological cascades mediated by the accumulation of mutant RNA binding proteins. We outline the molecular basis of ALS and FTD pathogenesis and discuss the prospects for therapeutic strategies to treat these diseases.

Protective effects of Alpinae Oxyphyllae Fructus extracts on lipopolysaccharide-induced animal model of Alzheimer's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinae Oxyphyllae Fructus (AOF) with warming and tonifying the kidney and spleen, anti-salivation, anti-polyuria and anti-diarrhea functions is the dried ripe fruits of Alpinia oxyphylla Miq. (Zingiberaceae). As a traditional Chinese medicine, its application history is very long.

AIMS OF THE STUDY

The purpose of our study is to investigate the effects of different solvent extracts from AOF on lipopolysaccharide (LPS)-induced animal model of Alzheimer's disease (AD) to elucidate the traditional medical theories with modern pharmacological methods and provide a reference for further clarifying its active components and mechanisms.

MATERIALS AND METHODS

The method of stepwise screening was adopted in this paper. The animals were divided into 9 groups, including control (CT) group, model (MD) group, donepezil (DPZ) group, total extract (TT) group, petroleum ether extract (PE) group, chloroform extract (CF) group, ethyl acetate extract (EA) group, n-butanol extract (NB) group and water extract (WT) group. The anti-amnesic effects of different solvent extracts from AOF were measured in LPS-induced memory deficits mice by Y maze test and Morris water maze (MWM) test. Hematoxylin eosin (HE) staining was applied to observe pathological changes in hippocampus and cerebral cortex tissue of different groups. Biochemical indicators including ionized calcium-binding adaptor molecule 1 (IBA-1), interleukin beta 1 (IL-1β), Aβ_1-42 and hyperphosphorylated tau proteins (p-tau) in hippocampus and cortex after treatment with LPS were measured according to the manufacturer's instructions of ELISA kits. HPLC was used to evaluate the major components of different extracts.

RESULTS

It was found that successive intragastric administration of AOF (360 mg/kg) extracts for 14 days showed different degrees of improvement on LPS-induced AD model as measured by Y-maze test, Morris water maze test, and Histopathological examination. Moreover, the results of ELISA suggested petroleum ether (PE) extracts were worth recommending for inhibiting the high level of IBA-1, IL-1β, Aβ_1-42 and p-tau in hippocampus and cortex after treatment with LPS.

CONCLUSIONS

The present study demonstrated for the first time that AOF attenuated LPS-induced learning and memory impairment, which may be associated with its inhibitory effect on neuroinflammation, amyloids-β (Aβ) deposition and p-tau. This research provided a theoretical basis for elucidating the traditional theory of AOF, and was also the stepping stone to the next step.

Alzheimer's disease drug development pipeline: 2018

Introduction

Treatments for Alzheimer's disease (AD) are needed due to the growing number of individuals with preclinical, prodromal, and dementia forms of AD. Drug development for AD therapies can be examined by inspecting the drug development pipeline as represented on clinicaltrials.gov.

Methods

Clinicaltrials.gov was assessed as of January 30, 2018 to determine AD therapies represented in phase I, phase II, and phase III.

Results

There are 112 agents in the current AD treatment pipeline. There are 26 agents in 35 trials in phase III, 63 agents in 75 trials in phase II, and 23 agents in 25 trials in phase I. A review of the mechanisms of actions of the agents in the pipeline shows that 63% are disease-modifying therapies, 22% are symptomatic cognitive enhancers, and 12% are symptomatic agents addressing neuropsychiatric and behavioral changes. Trials in phase III are larger and longer than phase II or phase I trials, particularly those involving disease-modifying agents. Comparison with the 2017 pipeline shows that there are four new agents in phase III, 14 in phase II, and eight in phase I. Inspection of the use of biomarkers as revealed on clinicaltrials.gov shows that amyloid biomarkers are used as entry criterion in 14 phase III disease-modifying agent trials and 17 disease-modifying agent trials in phase II. Twenty-one trials of disease-modifying agents in phase II did not require biomarker confirmation for AD at trial entry.

Discussion

The AD drug development pipeline is slightly larger in 2018 than in 2017. Trials increasingly include preclinical and prodromal populations. There is an increase in nonamyloid mechanisms of action for drugs in earlier phases of drug development. Biomarkers are increasingly used in AD drug development but are not used uniformly for AD diagnosis confirmation.

Tau: A Common Denominator and Therapeutic Target for Neurodegenerative Disorders

There is compelling evidence that a number of neurodegenerative diseases share common pathogenic mechanisms. Better understanding these mechanisms will allow us to develop new therapeutic strategies. This commentary follows up on our recent findings that tau pathology can be found in healthy fetal tissue transplanted into the brain of patients with either Huntington or Parkinson disease. We will examine how tau appears to be shared in a number of different conditions and how its expression relates to cognitive decline and disease progression. We will further review pathogenic mechanisms and especially the relevance of the possible prion-like behavior of tau. We will conclude by discussing how all this work opens up novel therapeutic approaches to treating the cognitive impairments related to neurodegenerative diseases using a common strategy.

Antibody Engineering for Optimized Immunotherapy in Alzheimer's Disease

There are nearly 50 million people with Alzheimer's disease (AD) worldwide and currently no disease modifying treatment is available. AD is characterized by deposits of Amyloid-β (Aβ), neurofibrillary tangles, and neuroinflammation, and several drug discovery programmes studies have focussed on Aβ as therapeutic target. Active immunization and passive immunization against Aβ leads to the clearance of deposits in humans and transgenic mice expressing human Aβ but have failed to improve memory loss. This review will discuss the possible explanations for the lack of efficacy of Aβ immunotherapy, including the role of a pro-inflammatory response and subsequent vascular side effects, the binding site of therapeutic antibodies and the timing of the treatment. We further discuss how antibodies can be engineered for improved efficacy.

Tau Antibody Structure Reveals a Molecular Switch Defining a Pathological Conformation of the Tau Protein

Tau antibodies have shown therapeutic potential for Alzheimer's disease and several are in clinical trials. As a microtubule-associated protein, tau relies on dynamic phosphorylation for its normal functions. In tauopathies, it becomes hyperphosphorylated and aggregates into toxic assemblies, which collectively lead to neurodegeneration. Of the phospho-epitopes, the region around Ser396 has received particular attention because of its prominence and stability in tauopathies. Here we report the first structure of a monoclonal tau antibody in complex with the pathologically important phospho-Ser396 residue. Its binding region reveals tau residues Tyr394 to phospho-Ser396 stabilized in a β-strand conformation that is coordinated by a phospho-specific antigen binding site. These details highlight a molecular switch that defines this prominent conformation of tau and ways to target it. Overall, the structure of the antibody-antigen complex clarifies why certain phosphorylation sites in tau are more closely linked to neurodegeneration than others.

An Overview on the Clinical Development of Tau-Based Therapeutics

Tauopathies such as Alzheimer's disease (AD), frontotemporal lobar degeneration, or progressive supranuclear palsy constitute a group of brain disorders defined by neurodegeneration and the presence of tau aggregates in the affected brains regions. Tau is a microtubule-associated protein that accumulates in the cytosol under pathological conditions, steering the formation of aggregates or inclusions thought to be involved in the degeneration and neuronal death associated with these diseases. Despite a substantial and unmet medical need for novel, more effective disease-modifying therapies for the treatment of AD and tauopathies, the last couple of decades have seen numerous drug development undertakings primarily focused on β-amyloid, with disappointing results to date. On the other hand, tau-focused approaches have not received much attention until recently, notwithstanding that the presence of extensive tau pathology is fundamental for the disease and tau pathology shows a better correlation with impaired cognitive function than with amyloid pathology in AD patients. The last few years have brought us advances in our comprehension of tau biological functions beyond its well-established role as a microtubule-associated protein, unveiling novel physiological tau functions that may also be involved in pathogenesis and thus provide novel targets for therapeutic intervention. This review describes several emerging, encouraging therapeutic approaches aimed at tackling the underlying causes of tau pathology in AD and other tauopathies that have recently reached the clinical development stage.

Emerging Diagnostic and Therapeutic Strategies for Tauopathies

PURPOSE OF REVIEW

Tauopathies represent a spectrum of incurable and progressive age-associated neurodegenerative diseases that currently are diagnosed definitively only at autopsy. Few clinical diagnoses, such as classic Richardson's syndrome of progressive supranuclear palsy, are specific for underlying tauopathy and no clinical syndrome is fully sensitive to reliably identify all forms of clinically manifest tauopathy. Thus, a major unmet need for the development and implementation of tau-targeted therapies is precise antemortem diagnosis. This article reviews new and emerging diagnostic therapies for tauopathies including novel imaging techniques and biomarkers and also reviews recent tau therapeutics.

RECENT FINDINGS

Building evidence from animal and cell models suggests that prion-like misfolding and propagation of pathogenic tau proteins between brain cells are central to the neurodegenerative process. These rapidly growing developments build rationale and motivation for the development of therapeutics targeting this mechanism through altering phosphorylation and other post-translational modifications of the tau protein, blocking aggregation and spread using small molecular compounds or immunotherapy and reducing or silencing expression of the MAPT tau gene. New clinical criteria, CSF, MRI, and PET biomarkers will aid in identifying tauopathies earlier and more accurately which will aid in selection for new clinical trials which focus on a variety of agents including immunotherapy and gene silencing.

AD-Related N-Terminal Truncated Tau Is Sufficient to Recapitulate In Vivo the Early Perturbations of Human Neuropathology: Implications for Immunotherapy

The NH₂tau 26-44 aa (i.e., NH₂htau) is the minimal biologically active moiety of longer 20-22-kDa NH₂-truncated form of human tau-a neurotoxic fragment mapping between 26 and 230 amino acids of full-length protein (htau40)-which is detectable in presynaptic terminals and peripheral CSF from patients suffering from AD and other non-AD neurodegenerative diseases. Nevertheless, whether its exogenous administration in healthy nontransgenic mice is able to elicit a neuropathological phenotype resembling human tauopathies has not been yet investigated. We explored the in vivo effects evoked by subchronic intracerebroventricular (i.c.v.) infusion of NH₂htau or its reverse counterpart into two lines of young (2-month-old) wild-type mice (C57BL/6 and B6SJL). Six days after its accumulation into hippocampal parenchyma, significant impairment in memory/learning performance was detected in NH₂htau-treated group in association with reduced synaptic connectivity and neuroinflammatory response. Compromised short-term plasticity in paired-pulse facilitation paradigm (PPF) was detected in the CA3/CA1 synapses from NH₂htau-impaired animals along with downregulation in calcineurin (CaN)-stimulated pCREB/c-Fos pathway(s). Importantly, these behavioral, synaptotoxic, and neuropathological effects were independent from the genetic background, occurred prior to frank neuronal loss, and were specific because no alterations were detected in the control group infused with its reverse counterpart. Finally, a 2.0-kDa peptide which biochemically and immunologically resembles the injected NH₂htau was endogenously detected in vivo, being present in hippocampal synaptosomal preparations from AD subjects. Given that the identification of the neurotoxic tau species is mandatory to develop a more effective tau-based immunological approach, our evidence can have important translational implications for cure of human tauopathies.

Non-Phosphorylated Tau as a Potential Biomarker of Alzheimer's Disease: Analytical and Diagnostic Characterization

BACKGROUND

Virtually nothing is known about a potential diagnostic role of non-phospho-epitopes of Tau (Non-P-Tau) in cerebrospinal fluid (CSF).

OBJECTIVE

To establish and analytically and clinically characterize the first assay capable to measure concentrations of Non-P-Tau in human CSF.

METHODS

An antibody (1G2) was developed that selectively binds to the Tau molecule non-phosphorylated at the positions T175 and T181, and was used in establishing a sandwich ELISA capable to measure Non-P-Tau in human CSF, following analytical and clinical validation of the method.

RESULTS

The 1G2 antibody shows decreasing reactivity to tau peptides containing phosphorylation mainly at positions T175 and T181. Detection limit of the assay is 25 pg/ml; the coefficients of variation (CVs) of the optical densities of the repeated standard curves were between 3.6-15.9%. Median intra-assay imprecision of double measurements was 4.8%; inter-assay imprecision was in the range of 11.2% - 15.3%. Non-P-Tau concentrations are stable in the CSF samples sent to distinct laboratories under ambient temperature; inter-laboratory variation was approximately 30%. The Non-P-Tau CSF concentrations were highly significantly increased in patients with Alzheimer's disease in stage of mild cognitive impairment or dementia (AD/MCI, n = 58, 109.2±32.0 pg/mL) compared to the non-demented Controls (n = 42, 62.1±9.3 pg/mL, p < 0.001). At the cut-off of 78.3 pg/mL, the sensitivity and the specificity were 94.8% and 97.6%, respectively.

CONCLUSION

For the first time, an assay is reported to reliably measure concentrations of non-phosphorylated Tau in human CSF.

The development of biological therapies for neurological diseases: moving on from previous failures

INTRODUCTION

Although years of research have expanded the use of biologics for several clinical conditions, such development has not yet occurred in the treatment of neurological diseases. With the advancement of biologic technologies, there is promise for these therapeutics as novel therapeutic approaches for neurological diseases. Areas covered: In this article, the authors review the therapeutic potential of different types of biologics for the treatment of neurological diseases. Preclinical and clinical studies that investigate the efficacy and safety of biologics in the treatment of neurological diseases, namely Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson disease, multiple sclerosis, and stroke, were reviewed. Moreover, the authors describe the key challenges in the development of therapeutically safe and effective biologics for the treatment of neurological diseases. Expert opinion: Several biologics have shown promise in the treatment of neurological diseases. However, the complexity of the CNS, as well as a limited understanding of disease progression, and restricted access of biologics to the CNS has limited successful development. Therefore, more research needs to be conducted to overcome these hurdles before developing effective and safe biologics for neurological diseases. The emergence of new technologies for the design, production and delivery of biologics will accelerate translating biologics to the clinic.

Tau passive immunization blocks seeding and spread of Alzheimer hyperphosphorylated Tau-induced pathology in 3 × Tg-AD mice

Background

Accumulating evidence indicates that Tau pathology can spread from neuron to neuron by intake and coaggregation of the hyperphosphorylated Tau (p-Tau) seeds with the host neuron protein. Thus, clearance of Tau seeds by immunization with Tau antibodies could provide a potential therapeutic opportunity to block the spread of the pathology in Alzheimer’s disease (AD) and other tauopathies. We report prevention of the seeding and spread of tau pathology with mouse monoclonal antibody 43D against the N-terminal projection domain of Tau (Tau 6–18) in triple-transgenic AD (3 × Tg-AD) mice.

Methods

Female 11- to 12-month-old 3 × Tg-AD mice were intravenously immunized weekly for 6 weeks with 15 μg/injection of mouse monoclonal antibody 43D or with mouse immunoglobulin G as a control. AD p-Tau isolated from a frozen autopsied AD brain was unilaterally injected into the right hippocampus on the day of the second dose of immunization. Tau pathology and its effect on Aβ pathology were assessed by immunohistochemical staining.

Results

We found that the injection of AD p-Tau into the hippocampus of 11- to 12-month-old 3 × Tg-AD mice time-dependently induced Tau aggregation in the hippocampus and promoted the spread of Tau pathology to the contralateral hippocampus. Tau pathology was observed as early as 6 weeks after AD p-Tau injection. Tau pathology templated by AD p-Tau was thioflavin-S-positive and was about two-fold greater than that seen in naive 18-month-old 3 × Tg-AD mice; Tau pathology in the latter was thioflavin-S-negative. Immunization with Tau antibody 43D dramatically blocked AD p-Tau seeding in the ipsilateral hippocampus and inhibited its propagation to the contralateral side in 3 × Tg-AD mice. Furthermore, AD p-Tau injection enhanced the amyloid plaque load in the ipsilateral side, and immunization with 43D showed a tendency to attenuate it.

Conclusions

These findings indicate that AD p-Tau-injected 3 × Tg-AD mice represent a practical model to study the seeding and spread of Tau pathology, their effect on Aβ pathology, and the effect of Tau immunotherapy on both Tau and Aβ pathologies. Immunization with Tau antibody 43D to Tau 6–18 can prevent the seeding and spread of Tau pathology, making it a potential therapeutic treatment for AD and related tauopathies.

Update on Alzheimer's Disease Therapy and Prevention Strategies

Alzheimer's disease (AD) is the primary cause of age-related dementia. Effective strategies to prevent and treat AD remain elusive despite major efforts to understand its basic biology and clinical pathophysiology. Significant investments in therapeutic drug discovery programs over the past two decades have yielded some important insights but no blockbuster drugs to alter the course of disease. Because significant memory loss and cognitive decline are associated with neuron death and loss of gray matter, especially in the frontal cortex and hippocampus, some focus in drug development has shifted to early prevention of cellular pathology. Although clinical trial design is challenging, due in part to a lack of robust biomarkers with predictive value, some optimism has come from the identification and study of inherited forms of early-onset AD and genetic risk factors that provide insights about molecular pathophysiology and potential drug targets. In addition, better understanding of the Aβ amyloid pathway and the tau pathway-leading to amyloid plaques and neurofibrillary tangles, respectively, which are histopathological hallmarks of AD-continues to drive significant drug research and development programs. The main focus of this review is to summarize the most recent basic biology, biochemistry, and pharmacology that serve as a foundation for more than 50 active advanced-phase clinical trials for AD prevention and therapy.

Live Imaging of Pathological Tau Protein and Tau Antibodies in a Neuron-Like Cellular Model

Several tau antibody therapies are now in clinical trials and numerous other tau antibodies are in various stages of preclinical development to treat Alzheimer's disease and related tauopathies. This involves long-term studies in mouse models that are necessary but time consuming and typically provide only a limited mechanistic understanding of how the antibodies work and why some are not effective. Live cellular imaging with fluorescently tagged pathological tau proteins and tau antibodies provides a valuable insight into their dynamic interaction outside or within the cell. Furthermore, this acute technique may have predictive validity to assess the potential efficacy of different tau antibodies in neutralizing and/or clearing tau aggregates, and can likely be applied to other amyloid diseases. Overall, it should facilitate identifying candidate antibodies for more detailed long-term validation. Due to the human origin of the model, it may be particularly useful to characterize humanized antibodies that utilize receptor-mediated uptake to reach their intracellular target.

Tau Proteolysis in the Pathogenesis of Tauopathies: Neurotoxic Fragments and Novel Biomarkers

With predictions showing that 131.5 million people worldwide will be living with dementia by 2050, an understanding of the molecular mechanisms underpinning disease is crucial in the hunt for novel therapeutics and for biomarkers to detect disease early and/or monitor disease progression. The metabolism of the microtubule-associated protein tau is altered in different dementias, the so-called tauopathies. Tau detaches from microtubules, aggregates into oligomers and neurofibrillary tangles, which can be secreted from neurons, and spreads through the brain during disease progression. Post-translational modifications exacerbate the production of both oligomeric and soluble forms of tau, with proteolysis by a range of different proteases being a crucial driver. However, the impact of tau proteolysis on disease progression has been overlooked until recently. Studies have highlighted that proteolytic fragments of tau can drive neurodegeneration in a fragment-dependent manner as a result of aggregation and/or transcellular propagation. Proteolytic fragments of tau have been found in the cerebrospinal fluid and plasma of patients with different tauopathies, providing an opportunity to develop these fragments as novel disease progression biomarkers. A range of therapeutic strategies have been proposed to halt the toxicity associated with proteolysis, including reducing protease expression and/or activity, selectively inhibiting protease-substrate interactions, and blocking the action of the resulting fragments. This review highlights the importance of tau proteolysis in the pathogenesis of tauopathies, identifies putative sites during tau fragment-mediated neurodegeneration that could be targeted therapeutically, and discusses the potential use of proteolytic fragments of tau as biomarkers for different tauopathies.

In Vivo Imaging of Tauopathy in Mice

Alzheimer's disease is characterized by amyloid-β plaques and neurofibrillary tangles composed of tau aggregates. Several β-sheet dyes are already in clinical use to detect amyloid-β plaques by in vivo positron emission tomography (PET), and related dye compounds are being developed for targeting pathological tau aggregates. In contrast to β-sheet binders, antibody-derived ligands should provide greater specificity for detecting tau lesions, and can be tailored to detect various pathological tau epitopes.For preclinical in vivo evaluation of these ligands prior to PET development, we have established an in vivo imaging system (IVIS) protocol to detect tauopathy in live mice. Antibodies and their derivatives are conjugated with a near infrared fluorescent dye and injected intravenously into anesthetized mice, which subsequently are imaged at various intervals to assess their pathological tau burden, and clearance of the ligand from the brain. The in vivo signal obtained through the skull correlates well with the degree of tau pathology in the mice, and the injected ligand can be found intraneuronally within the brain bound to tau aggregates. Control IgG and injections of the tau antibodies/fragments into wild-type mice or mice with amyloid-β plaques lead to minimal or no signal, confirming the specificity of the approach.

Tau Immunotherapies for Alzheimer's Disease and Related Tauopathies: Progress and Potential Pitfalls

Tau immunotherapies have now advanced from proof-of-concept studies to Phase II clinical trials. This review briefly outlines developments in the field and discusses how these therapies may work, which involves multiple variables that are connected in complex ways. These various factors are likely to define therapeutic success in humans and have not been thoroughly investigated, at least based on published reports.

Prophylactic Active Tau Immunization Leads to Sustained Reduction in Both Tau and Amyloid-β Pathologies in 3xTg Mice

Amyloid-β (Aβ) and tau pathologies are intertwined in Alzheimer's disease, and various immunotherapies targeting these hallmarks are in clinical trials. To determine if tau pathology influences Aβ burden and to assess prophylactic benefits, 3xTg and wild-type mice received tau immunization from 2-6 months of age. The mice developed a high IgG titer that was maintained at 22 months of age. Pronounced tau and Aβ pathologies were primarily detected in the subiculum/CA1 region, which was therefore the focus of analysis. The therapy reduced histopathological tau aggregates by 70-74% overall (68% in males and 78-86% in females), compared to 3xTg controls. Likewise, western blot analysis revealed a 41% clearance of soluble tau (38-76% in males and 48% in females) and 42-47% clearance of insoluble tau (47-58% in males and 49% in females) in the immunized mice. Furthermore, Aβ burden was reduced by 84% overall (61% in males and 97% in females). These benefits were associated with reductions in microgliosis and microhemorrhages. In summary, prophylactic tau immunization not only prevents tau pathology but also Aβ deposition and related pathologies in a sustained manner, indicating that tau pathology can promote Aβ deposition, and that a short immunization regimen can have a long-lasting beneficial effect.

"Tau immunotherapy: Hopes and hindrances"

Alzheimer's disease (AD) is a progressive neurological disorder having two major pathological hallmarks: the extracellular senile plaques and intracellular neurofibrillary tangles composed of amyloid beta protein and hyperphosphorylated tau respectively. Removal of protein deposits from AD brains are the newer attempts for treating AD. The major developments in this direction have been the amyloid and tau based therapeutics. While senile plaque removal employing monoclonal antibodies (mAbs) restore brain function in mouse models of AD, tau has been recently introduced as the major neurodegenerative factor mediating neural cell death. So, several research groups have focused on tau therapy. So far, the outcome of tau immunotherapy has been promising and clearance of hyperphosphorylated tau has been shown to restore the brain function in animal models. But the point is which phosphorylated tau is the most critical form to be removed from the brain, especially because removal of physiologic tau can cause neurodegenerative consequence. Recently, we have shown that phosphorylated tau at Thr231 in the cis conformation is a very early driver of neurodegeneration and cis mAb treatment efficiently restores brain structure and function in TBI models. Because of efficient therapeutic effects in mice model of TBI and considering cis pT231-tau accumulation in AD brains, it could be a very good candidate for tau immunotherapy upon several tauopathy disorders including AD.

Cis P-tau is induced in clinical and preclinical brain injury and contributes to post-injury sequelae

Traumatic brain injury (TBI) is characterized by acute neurological dysfunction and associated with the development of chronic traumatic encephalopathy (CTE) and Alzheimer's disease. We previously showed that cis phosphorylated tau (cis P-tau), but not the trans form, contributes to tau pathology and functional impairment in an animal model of severe TBI. Here we found that in human samples obtained post TBI due to a variety of causes, cis P-tau is induced in cortical axons and cerebrospinal fluid and positively correlates with axonal injury and clinical outcome. Using mouse models of severe or repetitive TBI, we showed that cis P-tau elimination with a specific neutralizing antibody administered immediately or at delayed time points after injury, attenuates the development of neuropathology and brain dysfunction during acute and chronic phases including CTE-like pathology and dysfunction after repetitive TBI. Thus, cis P-tau contributes to short-term and long-term sequelae after TBI, but is effectively neutralized by cis antibody treatment.Induction of the cis form of phosphorylated tau (cis P-tau) has previously been shown to occur in animal models of traumatic brain injury (TBI), and blocking this form of tau using antibody was beneficial in a rodent model of severe TBI. Here the authors show that cis P-tau induction is a feature of several different forms of TBI in humans, and that administration of cis P-tau targeting antibody to rodents reduces or delays pathological features of TBI.

The Prion-Like Behavior of Assembled Tau in Transgenic Mice

Tauopathies constitute neurodegenerative diseases that are characterized by the intracellular deposition of filaments made of hyperphosphorylated tau protein. The pattern of tau deposition in Alzheimer's disease follows a stereotypical progression, with the first lesions appearing in the locus coeruleus and entorhinal cortex, from where they appear to spread to the hippocampus and neocortex. Propagation of pathological tau is also characteristic of argyrophilic grain disease, where the lesions seem to spread through distinct regions of the limbic system. In chronic traumatic encephalopathy, tauopathy appears to spread from the neocortex to the brainstem. These findings implicate neuron-to-neuron propagation of tau aggregates. Isoform compositions and morphologies of tau filaments can differ between tauopathies, which is consistent with the existence of distinct tau strains. Here, we review recent findings that support prion-like mechanisms in the pathogenesis of tauopathies through the experimental use of transgenic mice.

Local and distant relationships between amyloid, tau and neurodegeneration in Alzheimer's Disease

The relationships between β-amyloid (Aβ), tau and neurodegeneration within Alzheimer's Disease pathogenesis are not fully understood. To explore these associations in vivo, we evaluated 30 Aβ PET-positive patients (mean ± sd age 62.4 ± 8.3) with mild probable AD and 12 Aβ PET-negative healthy controls (HC) (mean ± sd age 77.3 ± 6.9) as comparison. All participants underwent 3 T MRI, ¹¹C-PiB (Aβ) PET and ¹⁸F-AV1451 (tau) PET. Multimodal correlation analyses were run at both voxel- and region-of-interest levels. ¹¹C-PiB retention in AD showed the most diffuse uptake pattern throughout association neocortex, whereas ¹⁸F-AV1451 and gray matter volume reduction (GMR) showed a progressive predilection for posterior cortices (p<0.05 Family-Wise Error-[FWE]-corrected). Voxel-level analysis identified negative correlations between ¹⁸F-AV1451 and gray matter peaking in medial and infero-occipital regions (p<0.01 False Discovery Rate-[FDR]-corrected). ¹⁸F-AV1451 and ¹¹C-PiB were positively correlated in right parietal and medial/inferior occipital regions (p<0.001 uncorrected). ¹¹C-PiB did not correlate with GMR at the voxel-level. Regionally, ¹⁸F-AV1451 was largely associated with local/adjacent GMR whereas frontal ¹¹C-PiB correlated with GMR in posterior regions. These findings suggest that, in mild AD, tau aggregation drives local neurodegeneration, whereas the relationships between Aβ and neurodegeneration are not region specific and may be mediated by the interaction between Aβ and tau.

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Tau tangles show tight and local associations with gray matter volume.

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Amyloid plaques show long-distance and indirect effects on gray matter volume.

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Local relationships between tau and amyloid may evolve and vary by disease stage.

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Amyloid accumulates homogeneously and uniformly across association cortices.

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Tau accumulation begins locally and spreads to functionally connected regions.

Extracellular truncated tau causes early presynaptic dysfunction associated with Alzheimer's disease and other tauopathies

The largest part of tau secreted from AD nerve terminals and released in cerebral spinal fluid (CSF) is C-terminally truncated, soluble and unaggregated supporting potential extracellular role(s) of NH2 -derived fragments of protein on synaptic dysfunction underlying neurodegenerative tauopathies, including Alzheimer's disease (AD). Here we show that sub-toxic doses of extracellular-applied human NH2 tau 26-44 (aka NH 2 htau) -which is the minimal active moiety of neurotoxic 20-22kDa peptide accumulating in vivo at AD synapses and secreted into parenchyma- acutely provokes presynaptic deficit in K+ -evoked glutamate release on hippocampal synaptosomes along with alteration in local Ca2+ dynamics. Neuritic dystrophy, microtubules breakdown, deregulation in presynaptic proteins and loss of mitochondria located at nerve endings are detected in hippocampal cultures only after prolonged exposure to NH 2 htau. The specificity of these biological effects is supported by the lack of any significant change, either on neuronal activity or on cellular integrity, shown by administration of its reverse sequence counterpart which behaves as an inactive control, likely due to a poor conformational flexibility which makes it unable to dynamically perturb biomembrane-like environments. Our results demonstrate that one of the AD-relevant, soluble and secreted N-terminally truncated tau forms can early contribute to pathology outside of neurons causing alterations in synaptic activity at presynaptic level, independently of overt neurodegeneration.

Alzheimer's Disease: Characterization of the Brain Sites of the Initial Tau Cytoskeletal Pathology Will Improve the Success of Novel Immunological Anti-Tau Treatment Approaches

Alzheimer's disease (AD) represents the most frequent neurodegenerative disease of the human brain worldwide. Currently practiced treatment strategies for AD only include some less effective symptomatic therapeutic interventions, which unable to counteract the disease course of AD. New therapeutic attempts aimed to prevent, reduce, or remove the extracellular depositions of the amyloid-β protein did not elicit beneficial effects on cognitive deficits or functional decline of AD. In view of the failure of these amyloid-β-based therapeutic trials and the close correlation between the brain pathology of the cytoskeletal tau protein and clinical AD symptoms, therapeutic attention has since shifted to the tau cytoskeletal protein as a novel drug target. The abnormal hyperphosphorylation and intraneuronal aggregation of this protein are early events in the evolution of the AD-related neurofibrillary pathology, and the brain spread of the AD-related tau aggregation pathology may possibly follow a corruptive protein templating and seeding-like mechanism according to the prion hypothesis. Accordingly, immunotherapeutic targeting of the tau aggregation pathology during the very early pre-tangle phase is currently considered to represent an effective and promising therapeutic approach for AD. Recent studies have shown that the initial immunoreactive tau aggregation pathology already prevails in several subcortical regions in the absence of any cytoskeletal changes in the cerebral cortex. Thus, it may be hypothesized that the subcortical brain regions represent the "port of entry" for the pathogenetic agent from which the disease ascends anterogradely as an "interconnectivity pathology".

Current Understanding of Neurodegenerative Diseases Associated With the Protein Tau

Primary tauopathies are a group of neurodegenerative diseases in which tau is believed to be the major contributing factor of the neurodegenerative process. In primary tauopathies, there is a disassociation between tau (a microtubule-associated protein) and microtubules as a result of tau hyperphosphorylation. This disassociation between tau and microtubules results in tau fibrillization and inclusion formation as well as in microtubule dysfunction. There are different clinical syndromes associated with different primary tauopathies, and some clinical syndromes can be associated with multiple primary tauopathies. Hence, although some clinical syndromes are highly specific and almost diagnostic of a primary tauopathy, many are not, making it difficult to diagnose a primary tauopathy. Recently, radioligands that bind to tau and can be combined with positron emission tomography to detect fibrillary tau antemortem have been developed, although preliminary data suggest that these ligands may not be sensitive in detecting tau associated with many primary tauopathies. Another recent advancement in the field is evidence suggesting that tau may exhibit properties similar to those of prions, although infective transmission has not been shown. There have been a few clinical trials targeting tau and microtubule dysfunction, although none have had any disease-modifying effects. Understanding tau biology is critical to the development of pharmacological agents that could have disease-modifying effects on primary tauopathies.

Vectored Intracerebral Immunization with the Anti-Tau Monoclonal Antibody PHF1 Markedly Reduces Tau Pathology in Mutant Tau Transgenic Mice

Passive immunization with anti-tau monoclonal antibodies has been shown by several laboratories to reduce age-dependent tau pathology and neurodegeneration in mutant tau transgenic mice. These studies have used repeated high weekly doses of various tau antibodies administered systemically for several months and have reported reduced tau pathology of ∼40-50% in various brain regions. Here we show that direct intrahippocampal administration of the adeno-associated virus (AAV)-vectored anti-phospho-tau antibody PHF1 to P301S tau transgenic mice results in high and durable antibody expression, primarily in neurons. Hippocampal antibody levels achieved after AAV delivery were ∼50-fold more than those reported following repeated systemic administration. In contrast to systemic passive immunization, we observed markedly reduced (≥80-90%) hippocampal insoluble pathological tau species and neurofibrillary tangles following a single dose of AAV-vectored PHF1 compared with mice treated with an AAV-IgG control vector. Moreover, the hippocampal atrophy observed in untreated P301S mice was fully rescued by treatment with the AAV-vectored PHF1 antibody. Vectored passive immunotherapy with an anti-tau monoclonal antibody may represent a viable therapeutic strategy for treating or preventing such tauopathies as frontotemporal dementia, progressive supranuclear palsy, or Alzheimer's disease.

SIGNIFICANCE STATEMENT

We have used an adeno-associated viral (AAV) vector to deliver the genes encoding an anti-phospho-tau monoclonal antibody, PHF1, directly to the brain of mice that develop neurodegeneration due to a tau mutation that causes frontotemporal dementia (FTD). When administered systemically, PHF1 has been shown to modestly reduce tau pathology and neurodegeneration. Since such antibodies do not readily cross the blood-brain barrier, we used an AAV vector to deliver antibody directly to the hippocampus and observed much higher antibody levels and a much greater reduction in tau pathology. Using AAV vectors to deliver antibodies like PHF1 directly to brain may constitute a novel approach to treating various neurodegenerative disorders, such as FTD and Alzheimer's disease.

Importance of adiponectin activity in the pathogenesis of Alzheimer's disease

A recent study suggested that insulin resistance may play a central role in the pathogenesis of Alzheimer's disease (AD). In this regard, it is of note that upregulation of plasma adiponectin (APN), a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation, has recently been associated with the severities of amyloid deposits and cognitive deficits in the elderly, suggesting that APN may enhance the risk of AD. These results are unanticipated because AD has been linked to type II diabetes and other metabolic disorders in which hypoadiponectinemia has been firmly established, and because APN ameliorated neuropathological features in a mouse model of neurodegeneration. Therefore, the objective of this study is to discuss the possible mechanisms underlying the biological actions of APN in the context of AD. Given that insulin receptor signaling is required for normal function of the nervous system, we predict that APN may be upregulated to compensate for compromised activity of the insulin receptor signaling pathway. However, increased APN might be sequestered by tau in the brain, leading to neurotoxic protein aggregation in AD. Alternatively, misfolding of APN may result in downregulation of the insulin/APN signal transduction network, leading to decreased neuroprotective and neurotrophic activities. Thus, it is possible that both ‘gain of function’ and ‘loss of function’ of APN may underlie synaptic dysfunction and neuronal cell death in AD. Such a unique biological mechanism underlying APN function in AD may require a novel therapeutic strategy that is distinct from previous treatment for metabolic disorders.

Tau-based therapeutics for Alzheimer's disease: active and passive immunotherapy

Pharmacological manipulation of tau protein in Alzheimer's disease included microtubule-stabilizing agents, tau protein kinase inhibitors, tau aggregation inhibitors, active and passive immunotherapies and, more recently, inhibitors of tau acetylation. Animal studies have shown that both active and passive approaches can remove tau pathology and, in some cases, improve cognitive function. Two active vaccines targeting either nonphosphorylated (AAD-vac1) and phosphorylated tau (ACI-35) have entered Phase I testing. Notwithstanding, the recent discontinuation of the monoclonal antibody RG7345 for Alzheimer's disease, two other antitau antibodies, BMS-986168 and C2N-8E12, are also currently in Phase I testing for progressive supranuclear palsy. After the recent impressive results in animal studies obtained by salsalate, the dimer of salicylic acid, inhibitors of tau acetylation are being actively pursued.

A Brief Overview of Tauopathy: Causes, Consequences, and Therapeutic Strategies

There are currently no disease-modifying therapies for the treatment of tauopathies, a group of progressive neurodegenerative disorders that are pathologically defined by the presence of tau protein aggregates in the brain. Current challenges for the treatment of tauopathies include the inability to diagnose early and to confidently discriminate between distinct tauopathies in patients, alongside an incomplete understanding of the cellular mechanisms involved in pathogenic tau-induced neuronal death and dysfunction. In this review, we describe current diagnostic and therapeutic strategies, known drivers of pathogenic tau formation, recent contributions to our current mechanistic understanding of how pathogenic tau induces neuronal death, and potential diagnostic and therapeutic approaches.

Overview and Current Status of Alzheimer's Disease in Bangladesh

Alzheimer’s disease (AD) is a complex neurological disorder with economic, social, and medical burdens which is acknowledged as leading cause of dementia marked by the accumulation and aggregation of amyloid-β peptide and phosphorylated tau (p-tau) protein and concomitant dementia, neuron loss and brain atrophy. AD is the most prevalent neurodegenerative brain disorder with sporadic etiology, except for a small fraction of cases with familial inheritance where familial forms of AD are correlated to mutations in three functionally related genes: the amyloid-β protein precursor and presenilins 1 and 2, two key γ-secretase components. The common clinical features of AD are memory impairment that interrupts daily life, difficulty in accomplishing usual tasks, confusion with time or place, trouble understanding visual images and spatial relationships. Age is the most significant risk factor for AD, whereas other risk factors correlated with AD are hypercholesterolemia, hypertension, atherosclerosis, coronary heart disease, smoking, obesity, and diabetes. Despite decades of research, there is no satisfying therapy which will terminate the advancement of AD by acting on the origin of the disease process, whereas currently available therapeutics only provide symptomatic relief but fail to attain a definite cure and prevention. This review also represents the current status of AD in Bangladesh.

Advances in progressive supranuclear palsy: new diagnostic criteria, biomarkers, and therapeutic approaches

Progressive supranuclear palsy (PSP), previously believed to be a common cause of atypical parkinsonism, is now recognised as a range of motor and behavioural syndromes that are associated with a characteristic 4-repeat tau neuropathology. New research criteria that recognise early presentations of PSP and operationalise diagnosis of the full spectrum of clinical phenotypes have been reported. The Movement Disorders Society PSP diagnostic criteria include syndromes with few or mild symptoms that are suggestive of underlying PSP pathology and could provide an opportunity for earlier therapeutic interventions in the future. These criteria also include definitions for variant PSP syndromes with different patterns of movement, language, or behavioural features than have been conclusively associated with PSP pathology. Data from new diagnostic biomarkers can be combined with the clinical features of disease to increase the specificity of the new criteria for underlying PSP pathology. Because PSP is associated with tau protein abnormalities, there is growing interest in clinical trials of new tau-directed therapies. These therapies are hypothesised to have disease-modifying effects by reducing the concentration of toxic forms of tau in the brain or by compensating for loss of tau function. Since tau pathology is also central to Alzheimer's disease and chronic traumatic encephalopathy, a successful tau therapeutic for PSP might inform treatment of other neurodegenerative diseases.

Cognition and anatomy of adult Niemann-Pick disease type C: Insights for the Alzheimer field

Niemann-Pick disease type C (NPC) is a rare lysosomal storage disorder causing an intracellular lipid trafficking defect and varying damage to the spleen, liver, and central nervous system. The adult form, representing approximately 20% of the cases, is associated with progressive cognitive decline. Intriguingly, brains of adult NPC patients exhibit neurofibrillary tangles, a characteristic hallmark of Alzheimer's disease (AD). However, the cognitive, psychiatric, and neuropathological features of adult NPC and their relation to AD have yet to be explored. We systematically reviewed the literature on adult NPC with a particular focus on cognitive and neuroanatomical abnormalities. The careful study of cognition in adult NPC allows drawing critical insights in our understanding of the pathophysiology of AD as well as normal cognition.

Anti-tau antibody administration increases plasma tau in transgenic mice and patients with tauopathy

Tauopathies are a group of disorders in which the cytosolic protein tau aggregates and accumulates in cells within the brain, resulting in neurodegeneration. A promising treatment being explored for tauopathies is passive immunization with anti-tau antibodies. We previously found that administration of an anti-tau antibody to human tau transgenic mice increased the concentration of plasma tau. We further explored the effects of administering an anti-tau antibody on plasma tau. After peripheral administration of an anti-tau antibody to human patients with tauopathy and to mice expressing human tau in the central nervous system, there was a dose-dependent increase in plasma tau. In mouse plasma, we found that tau had a short half-life of 8 min that increased to more than 3 hours after administration of anti-tau antibody. As tau transgenic mice accumulated insoluble tau in the brain, brain soluble and interstitial fluid tau decreased. Administration of anti-tau antibody to tau transgenic mice that had decreased brain soluble tau and interstitial fluid tau resulted in an increase in plasma tau, but this increase was less than that observed in tau transgenic mice without these brain changes. Tau transgenic mice subjected to acute neuronal injury using 3-nitropropionic acid showed increased interstitial fluid tau and plasma tau. These data suggest that peripheral administration of an anti-tau antibody results in increased plasma tau, which correlates with the concentration of extracellular and soluble tau in the brain.

Innate immunity in Alzheimer's disease: the relevance of animal models?

The mouse is one of the organisms most widely used as an animal model in biomedical research, due to the particular ease with which it can be handled and reproduced in laboratory. As a member of the mammalian class, mice share with humans many features regarding metabolic pathways, cell morphology and anatomy. However, important biological differences between mice and humans exist and must be taken into consideration when interpreting research results, to properly translate evidence from experimental studies into information that can be useful for human disease prevention and/or treatment. With respect to Alzheimer’s disease (AD), much of the experimental information currently known about this disease has been gathered from studies using mainly mice as models. Therefore, it is notably important to fully characterise the differences between mice and humans regarding important aspects of the disease. It is now widely known that inflammation plays an important role in the development of AD, a role that is not only a response to the surrounding pathological environment, but rather seems to be strongly implicated in the aetiology of the disease as indicated by the genetic studies. This review highlights relevant differences in inflammation and in microglia, the innate immune cell of the brain, between mice and humans regarding genetics and morphology in normal ageing, and the relationship of microglia with AD-like pathology, the inflammatory profile, and cognition. We conclude that some noteworthy differences exist between mice and humans regarding microglial characteristics, in distribution, gene expression, and states of activation. This may have repercussions in the way that transgenic mice respond to, and influence, the AD-like pathology. However, despite these differences, human and mouse microglia also show similarities in morphology and behaviour, such that the mouse is a suitable model for studying the role of microglia, as long as these differences are taken into consideration when delineating new strategies to approach the study of neurodegenerative diseases.

Humanized monoclonal antibody armanezumab specific to N-terminus of pathological tau: characterization and therapeutic potency

Background

The experience from clinical trials indicates that anti-Aβ immunotherapy could be effective in early/pre-clinical stages of AD, whereas at the late stages promoting the clearing of Aβ alone may be insufficient to halt the disease progression. At the same time, pathological tau correlates much better with the degree of dementia than Aβ deposition. Therefore, targeting pathological tau may provide a more promising approach for the treatment of advanced stages of AD. Recent data demonstrates that the N-terminal region of tau spanning aa 2–18 termed “phosphatase activation domain” that is normally hidden in the native protein in ‘paperclip’-like conformation, becomes exposed in pathological tau and plays an essential role in the inhibition of fast axonal transport and in aggregation of tau. Hence, we hypothesized that anti-Tau_2–18 monoclonal antibodies (mAb) may recognize pathological, but not normal tau at very early stages of tauopathy and prevent or decrease the aggregation of this molecule.

Methods

Mouse mAbs were generated using standard hybridoma methodology. CDR grafting was used for humanization of mouse mAb. Humanized mAb (Armanezumab) was characterized and tested in vitro/ex vivo/in vivo using biochemical and immunological methods (HPLC, Biacore, ELISA, IHC, FRET, etc.). Stable DG44 cell line expressing Armanezumab was generated by clone selection with increased concentrations of methotrexate (MTX).

Results

A panel of mouse mAbs was generated, clone 1C9 was selected based on binding to pathological human tau with high affinity and humanized. Fine epitope mapping revealed conservation of the epitope of human tau recognized by the parent murine mAb and Armanezumab. Importantly, Armanezumab (i) bound to tau with high affinity as determined by Biacore; (ii) bound pathological tau in brains from AD, FTD and Pick’s disease cases; (iii) inhibited seeding effect of aggregated tau from brain lysate of P301S Tg mice; (iv) inhibited cytotoxic effect of tau oligomers; (v) reduced total tau (HT7) and AT100, PHF1, AT8, AT180, p212, p214-positive tau species in brains of tau transgenic mice after intracranial injection. A stable CHO cell line producing >1.5 g/l humanized mAb, Armanezumab was generated.

Conclusion

These findings suggest that Armanezumab could be therapeutic in clinical studies for treatment of AD.

Tau Antibody Targeting Pathological Species Blocks Neuronal Uptake and Interneuron Propagation of Tau in Vitro

The clinical progression of Alzheimer disease (AD) is associated with the accumulation of tau neurofibrillary tangles, which may spread throughout the cortex by interneuronal tau transfer. If so, targeting extracellular tau species may slow the spreading of tau pathology and possibly cognitive decline. To identify suitable target epitopes, we tested the effects of a panel of tau antibodies on neuronal uptake and aggregation in vitro. Immunodepletion was performed on brain extract from tau-transgenic mice and postmortem AD brain and added to a sensitive fluorescence resonance energy transfer-based tau uptake assay to assess blocking efficacy. The antibodies reduced tau uptake in an epitope-dependent manner: N-terminal (Tau13) and middomain (6C5 and HT7) antibodies successfully prevented uptake of tau species, whereas the distal C-terminal-specific antibody (Tau46) had little effect. Phosphorylation-dependent (40E8 and p396) and C-terminal half (4E4) tau antibodies also reduced tau uptake despite removing less total tau by immunodepletion, suggesting specific interactions with species involved in uptake. Among the seven antibodies evaluated, 6C5 most efficiently blocked uptake and subsequent aggregation. More important, 6C5 also blocked neuron-to-neuron spreading of tau in a unique three-chamber microfluidic device. Furthermore, 6C5 slowed down the progression of tau aggregation even after uptake had begun. Our results imply that not all antibodies/epitopes are equally robust in terms of blocking tau uptake of human AD-derived tau species.

Tau oligomers in cerebrospinal fluid in Alzheimer's disease

OBJECTIVE

With an increasing incidence of Alzheimer's disease (AD) and neurodegenerative tauopathies, there is an urgent need to develop reliable biomarkers for the diagnosis and monitoring of the disease, such as the recently discovered toxic tau oligomers. Here, we aimed to demonstrate the presence of tau oligomers in the cerebrospinal fluid (CSF) of patients with cognitive deficits, and to determine whether tau oligomers could serve as a potential biomarker for AD.

METHODS

A multicentric collaborative study involving a double-blinded analysis with a total of 98 subjects with moderate to severe AD (N = 41), mild AD (N = 31), and nondemented control subjects (N = 26), and two pilot studies of 33 total patients with AD (N = 19) and control (N = 14) subjects were performed. We carried out biochemical assays to measure oligomeric tau from CSF of these patients with various degrees of cognitive impairment as well as cognitively normal controls.

RESULTS

Using a highly reproducible indirect ELISA method, we found elevated levels of tau oligomers in AD patients compared to age-matched controls. Western blot analysis confirmed the presence of oligomeric forms of tau in CSF. In addition, the ratio of oligomeric to total tau increased in the order: moderate to severe AD, mild AD, and controls.

CONCLUSION

These assays are suitable for the analysis of human CSF samples. These results here suggest that CSF tau oligomer measurements could be optimized and added to the panel of CSF biomarkers for the accurate and early detection of AD.