VXX-401, a novel anti-PCSK9 vaccine, reduces LDL-C in cynomolgus monkeys

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of disease burden in the world and is highly correlated with chronic elevations of LDL-C. LDL-C-lowering drugs, such as statins or monoclonal antibodies against proprotein convertase subtilisin/kexin type 9 (PCSK9), are known to reduce the risk of cardiovascular diseases; however, statins are associated with limited efficacy and poor adherence to treatment, whereas PCSK9 inhibitors are only prescribed to a "high-risk" patient population or those who have failed other therapies. Based on the proven efficacy and safety profile of existing monoclonal antibodies, we have developed a peptide-based vaccine against PCSK9, VXX-401, as an alternative option to treat hypercholesterolemia and prevent ASCVD. VXX-401 is designed to trigger a safe humoral immune response against PCSK9, resulting in the production of endogenous antibodies and a subsequent 30-40% reduction in blood LDL-C. In this article, VXX-401 demonstrates robust immunogenicity and sustained serum LDL-C-lowering effects in nonhuman primates. In addition, antibodies induced by VXX-401 bind to human PCSK9 with high affinity and block the inhibitory effect of PCSK9 on LDL-C uptake in a hepatic cell model. A repeat-dose toxicity study conducted in nonhuman primates under good laboratory practices toxicity indicated a suitable safety and tolerability profile, with injection site reactions being the main findings. As a promising safe and effective LDL-C-lowering therapy, VXX-401 may represent a broadly accessible and convenient option to treat hypercholesterolemia and prevent ASCVD.

RBD-Protein/Peptide Vaccine UB-612 Elicits Mucosal and Fc-Mediated Antibody Responses against SARS-CoV-2 in Cynomolgus Macaques

Antibodies provide critical protective immunity against COVID-19, and the Fc-mediated effector functions and mucosal antibodies also contribute to the protection. To expand the characterization of humoral immunity stimulated by subunit protein-peptide COVID-19 vaccine UB-612, preclinical studies in non-human primates were undertaken to investigate mucosal secretion and the effector functionality of vaccine-induced antibodies in antibody-dependent monocyte phagocytosis (ADMP) and antibody-dependent NK cell activation (ADNKA) assays. In cynomolgus macaques, UB-612 induced potent serum-neutralizing, RBD-specific IgG binding, ACE2 binding-inhibition antibodies, and antibodies with Fc-mediated effector functions in ADMP and ADNKA assays. Additionally, immunized animals developed mucosal antibodies in bronchoalveolar lavage fluids (BAL). The level of mucosal or serum ADMP and ADNKA antibodies was found to be UB-612 dose-dependent. Our results highlight that the novel subunit UB-612 vaccine is a potent B-cell immunogen inducing polyfunctional antibody responses contributing to anti-viral immunity and vaccine efficacy.

Safety, tolerability, immunogenicity, and efficacy of UB-311 in participants with mild Alzheimer's disease: a randomised, double-blind, placebo-controlled, phase 2a study

BACKGROUND

Anti-amyloid vaccines may offer a convenient, affordable, and accessible means of preventing and treating Alzheimer's disease. UB-311 is an anti-amyloid-β active immunotherapeutic vaccine shown to be well-tolerated and to have a durable antibody response in a phase 1 trial. This phase 2a study assessed the safety, immunogenicity, and preliminary efficacy of UB-311 in participants with mild Alzheimer's disease.

METHODS

A 78-week, randomised, double-blind, placebo-controlled, parallel-group, multicentre, phase 2a study was conducted in Taiwan. Participants were randomised in a 1:1:1 ratio to receive seven intramuscular injections of UB-311 (Q3M arm), or five doses of U311 with two doses of placebo (Q6M arm), or seven doses of placebo (placebo arm). The primary endpoints were safety, tolerability, and immunogenicity of UB-311. Safety was assessed in all participants who received at least one dose of investigational product. This study was registered at ClinicalTrials.gov (NCT02551809).

FINDINGS

Between 7 December 2015 and 28 August 2018, 43 participants were randomised. UB-311 was safe, well-tolerated, and generated a robust immune response. The three treatment-emergent adverse events (TEAEs) with the highest incidence were injection-site pain (14 TEAEs in seven [16%] participants), amyloid-related imaging abnormality with microhaemorrhages and haemosiderin deposits (12 TEAEs in six [14%] participants), and diarrhoea (five TEAEs in five [12%] participants). A 97% antibody response rate was observed and maintained at 93% by the end of the study across both UB-311 arms.

INTERPRETATION

These results support the continued development of UB-311.

FUNDING

Vaxxinity, Inc. (Formerly United Neuroscience Ltd.).

Amyloid-β and α-Synuclein Immunotherapy: From Experimental Studies to Clinical Trials

Alzheimer’s disease and Lewy body diseases are the most common causes of neurodegeneration and dementia. Amyloid-beta (Aβ) and alpha-synuclein (αSyn) are two key proteins involved in the pathogenesis of these neurodegenerative diseases. Immunotherapy aims to reduce the harmful effects of protein accumulation by neutralising toxic species and facilitating their removal. The results of the first immunisation trial against Aβ led to a small percentage of meningoencephalitis cases which revolutionised vaccine design, causing a shift in the field of immunotherapy from active to passive immunisation. While the vast majority of immunotherapies have been developed for Aβ and tested in Alzheimer’s disease, the field has progressed to targeting other proteins including αSyn. Despite showing some remarkable results in animal models, immunotherapies have largely failed final stages of clinical trials to date, with the exception of Aducanumab recently licenced in the US by the FDA. Neuropathological findings translate quite effectively from animal models to human trials, however, cognitive and functional outcome measures do not. The apparent lack of translation of experimental studies to clinical trials suggests that we are not obtaining a full representation of the effects of immunotherapies from animal studies. Here we provide a background understanding to the key concepts and challenges involved in therapeutic design. This review further provides a comprehensive comparison between experimental and clinical studies in Aβ and αSyn immunotherapy and aims to determine the possible reasons for the disconnection in their outcomes.

Variant-selective stereopure oligonucleotides protect against pathologies associated with C9orf72-repeat expansion in preclinical models

A large G₄C₂-repeat expansion in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Neuronal degeneration associated with this expansion arises from a loss of C9orf72 protein, the accumulation of RNA foci, the expression of dipeptide repeat (DPR) proteins, or all these factors. We report the discovery of a new targeting sequence that is common to all C9orf72 transcripts but enables preferential knockdown of repeat-containing transcripts in multiple cellular models and C9BAC transgenic mice. We optimize stereopure oligonucleotides that act through this site, and we demonstrate that their preferential activity depends on both backbone stereochemistry and asymmetric wing design. In mice, stereopure oligonucleotides produce durable depletion of pathogenic signatures without disrupting protein expression. These oligonucleotides selectively protect motor neurons harboring C9orf72-expansion mutation from glutamate-induced toxicity. We hypothesize that targeting C9orf72 with stereopure oligonucleotides may be a viable therapeutic approach for the treatment of C9orf72-associated neurodegenerative disorders.

Novel antibodies detect additional α-synuclein pathology in synucleinopathies: potential development for immunotherapy

BACKGROUND

Alpha-synuclein (α-Syn) aggregation is the primary characteristic of synucleinopathies including Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Immunotherapy targeting α-Syn has shown promising results in animal models of the disease. This study investigates the target specificity of three different active vaccines for pathological α-Syn aggregates found in human brain tissue from synucleinopathies.

METHODS

Guinea pigs were immunised with 3 vaccines developed by United Neuroscience, and IgG fractions purified from the resulting immune sera (IGG-1, IGG-2 or IGG-3) were used to perform immunohistochemical staining of human cases of PD, DLB and MSA. The resulting immunoreactivity was compared to a commercially available α-Syn antibody from Novacastra (NOV) commonly used for diagnostic purposes. Images were captured from the substantia nigra (SN), temporal lobe, internal capsule, insular cortex and putamen and quantified for the percentage area with α-Syn immunoreactivity. Lewy bodies (LB) and Lewy neurites (LN) were further analysed in PD and DLB cases.

RESULTS

Vaccine-generated antibodies detected more α-Syn pathology compared to NOV. The levels of α-Syn immunoreactivity varied between brain region and disease type with IGG-3 recognising the highest levels of α-Syn in most cases and in all brain regions that are affected early in disease progression. IGG-3 had a high recognition for glial inclusions found in MSA which are known to have a more compact conformation. Slot blot analysis confirmed the specificity of IGG-3 for native oligomers and fibrillar α-Syn. Higher levels of α-Syn were recognised by IGG-2 in cortical regions, and by IGG-3 in SN of PD and DLB cases. This was due to increased immunolabelling of LNs in these brain regions suggesting that IGG-2 and IGG-3 recognised additional α-Syn pathology compared to IGG-1 and NOV. Whether the unique binding properties of the antibodies produced in guinea pigs will translate in the clinic remains to be addressed, which is the main limitation of this study.

CONCLUSIONS

These vaccines induce antibodies that bind α-Syn oligomers and aggregates in the human brain and specifically support the choice of the vaccine generating IGG-3 (i.e. UB-312) as a candidate for clinical trials for synucleinopathies.

Peri-arterial pathways for clearance of α-Synuclein and tau from the brain: Implications for the pathogenesis of dementias and for immunotherapy

Introduction

Accumulation of amyloid beta (Aβ), α-synuclein (αSyn), and tau in dementias indicates their age-related failure of elimination from the brain. Aβ is eliminated along basement membranes in walls of cerebral arterioles and leptomeningeal arteries (intramural peri-arterial drainage [IPAD]); IPAD is impaired with age. We test the hypothesis that αSyn and tau are also eliminated from the normal brain along IPAD pathways.

Methods

Soluble αSyn or tau was injected into mouse hippocampus. Animals were perfused 5 minutes to 7 days post-injection. Blood vessels were identified by ROX-SE for light-sheet and immunolabeling for confocal microscopy. IPAD was quantified by measuring the proportion of arterioles with αSyn/tau.

Results

αSyn and tau are eliminated from the brain by IPAD but with different dynamics.

Discussion

Age-related failure of IPAD may play a role in the pathogenesis of synucleinopathies and tauopathies. αSyn persists within IPAD at 24 hours, which may affect immunotherapy for αSyn.

Antisense oligonucleotide therapeutics in neurodegenerative diseases: the case of polyglutamine disorders

Polyglutamine (polyQ) disorders are a group of nine neurodegenerative diseases that share a common genetic cause, which is an expansion of CAG repeats in the coding region of the causative genes that are otherwise unrelated. The trinucleotide expansion encodes for an expanded polyQ tract in the respective proteins, resulting in toxic gain-of-function and eventually in neurodegeneration. Currently, no disease-modifying therapies are available for this group of disorders. Nevertheless, given their monogenic nature, polyQ disorders are ideal candidates for therapies that target specifically the gene transcripts. Antisense oligonucleotides (ASOs) have been under intense investigation over recent years as gene silencing tools. ASOs are small synthetic single-stranded chains of nucleic acids that target specific RNA transcripts through several mechanisms. ASOs can reduce the levels of mutant proteins by breaking down the targeted transcript, inhibit mRNA translation or alter the maturation of the pre-mRNA via splicing correction. Over the years, chemical optimization of ASO molecules has allowed significant improvement of their pharmacological properties, which has in turn made this class of therapeutics a very promising strategy to treat a variety of neurodegenerative diseases. Indeed, preclinical and clinical strategies have been developed in recent years for some polyQ disorders using ASO therapeutics. The success of ASOs in several animal models, as well as encouraging results in the clinic for Huntington's disease, points towards a promising future regarding the application of ASO-based therapies for polyQ disorders in humans, offering new opportunities to address unmet medical needs for this class of disorders. This review aims to present a brief overview of key chemical modifications, mechanisms of action and routes of administration that have been described for ASO-based therapies. Moreover, it presents a review of the most recent and relevant preclinical and clinical trials that have tested ASO therapeutics in polyQ disorders.

Discovery of a Brain-Penetrant ATP-Competitive Inhibitor of the Mechanistic Target of Rapamycin (mTOR) for CNS Disorders

Recent clinical evaluation of everolimus for seizure reduction in patients with tuberous sclerosis complex (TSC), a disease with overactivated mechanistic target of rapamycin (mTOR) signaling, has demonstrated the therapeutic value of mTOR inhibitors for central nervous system (CNS) indications. Given that everolimus is an incomplete inhibitor of the mTOR function, we sought to develop a new mTOR inhibitor that has improved properties and is suitable for CNS disorders. Starting from an in-house purine-based compound, optimization of the physicochemical properties of a thiazolopyrimidine series led to the discovery of the small molecule 7, a potent and selective brain-penetrant ATP-competitive mTOR inhibitor. In neuronal cell-based models of mTOR hyperactivity, 7 corrected the mTOR pathway activity and the resulting neuronal overgrowth phenotype. The new mTOR inhibitor 7 showed good brain exposure and significantly improved the survival rate of mice with neuronal-specific ablation of the Tsc1 gene. These results demonstrate the potential utility of this tool compound to test therapeutic hypotheses that depend on mTOR hyperactivity in the CNS.

Anti-Aβ antibodies incapable of reducing cerebral Aβ oligomers fail to attenuate spatial reference memory deficits in J20 mice

Compelling genetic evidence links the amyloid precursor protein (APP) to Alzheimer's disease (AD). A leading hypothesis proposes that a small amphipathic fragment of APP, the amyloid β-protein (Aβ), self-associates to form soluble assemblies loosely referred to as "oligomers" and that these are primary mediators of synaptic dysfunction. As such, Aβ, and specifically Aβ oligomers, are targets for disease modifying therapies. Currently, the most advanced experimental treatment for AD relies on the use of anti-Aβ antibodies. In this study, we tested the ability of the monomer-preferring antibody, m266 and a novel aggregate-preferring antibody, 1C22, to attenuate spatial reference memory impairments in J20 mice. Chronic treatment with m266 resulted in a ~70-fold increase in Aβ detected in the bloodstream, and a ~50% increase in water-soluble brain Aβ--and in both cases Aβ was bound to m266. In contrast, 1C22 increased the levels of free Aβ in the bloodstream, and bound to amyloid deposits in J20 brain. However, neither 1C22 nor m266 attenuated the cognitive deficits evident in 12month old J20 mice. Moreover, both antibodies failed to alter the levels of soluble Aβ oligomers in J20 brain. These results suggest that Aβ oligomers may mediate the behavioral deficits seen in J20 mice and highlight the need for the development of aggregate-preferring antibodies that can reach the brain in sufficient levels to neutralize bioactive Aβ oligomers. Aside from the lack of positive effect of m266 and 1C22 on cognition, a substantial number of deaths occurred in m266- and 1C22-immunized J20 mice. These fatalities were specific to anti-Aβ antibodies and to the J20 mouse line since treatment of wild type or PDAPP mice with these antibodies did not cause any deaths. These and other recent results indicate that J20 mice are particularly susceptible to targeting of the APP/Aβ/tau axis. Notwithstanding the specificity of fatalities for J20 mice, it is worrying that the murine precursor (m266) of a lead experimental therapeutic, Solanezumab, did not engage with putatively pathogenic Aβ oligomers.

Altered social behavior and neuronal development in mice lacking the Uba6-Use1 ubiquitin transfer system

The Uba6 (E1)-Use1 (E2) ubiquitin transfer cascade is a poorly understood alternative arm of the ubiquitin proteasome system (UPS) and is required for mouse embryonic development, independent of the canonical Uba1-E2-E3 pathway. Loss of neuronal Uba6 during embryonic development results in altered patterning of neurons in the hippocampus and the amygdala, decreased dendritic spine density, and numerous behavioral disorders. The levels of the E3 ubiquitin ligase Ube3a (E6-AP) and Shank3, both linked with dendritic spine function, are elevated in the amygdala of Uba6-deficient mice, while levels of the Ube3a substrate Arc are reduced. Uba6 and Use1 promote proteasomal turnover of Ube3a in mouse embryo fibroblasts (MEFs) and catalyze Ube3a ubiquitylation in vitro. These activities occur in parallel with an independent pathway involving Uba1-UbcH7, but in a spatially distinct manner in MEFs. These data reveal an unanticipated role for Uba6 in neuronal development, spine architecture, mouse behavior, and turnover of Ube3a.

Prefrontal cortex lesions and scopolamine impair attention performance of C57BL/6 mice in a novel 2-choice visual discrimination task

Sustained attention is defined as the ability or capacity to remain focused on the occurrence of rare events over long periods of time. We describe here the development of a novel, operant-based attention task that can be learned by mice in 8-10 days. Mice were trained on a 2-choice visual discrimination task in an operant chamber, wherein the correct response on any given trial was a lever-press cued by a stimulus light. Upon reaching a criterion of greater than 80% correct responses, all subjects were tested in a mixed-trial attention paradigm combining four different stimulus durations within a single session (0.5, 1, 2, or 10 s). During attention testing, the percentage of correct responses decreased as a function of stimulus duration, indicating a performance decrement which parallels increasing attentional demand within the task. Pretreatment with the muscarinic-receptor antagonist scopolamine yielded a reliable, dose-dependent performance deficit whereas nicotine treatment improved the percentage of correct responses during trials with the greatest attentional demand. Moreover, medial prefrontal cortex lesions impaired attention performance without affecting acquisition or retention of the discrimination rule. These results underscore the utility of this task as a novel means of assessing attentional processes in mice in a relatively high-throughput manner.

Overview on rodent models of Alzheimer's disease

In Alzheimer's disease (AD), characteristic lesions develop in brain regions that subserve cognitive functions, ultimately leading to dementia. There are now several lesioned or transgenic small-animal models of the disease that model select aspects of cognitive deficits and/or recapitulate many, but not all, of the characteristic pathologic lesions observed in AD. This overview describes the most common approaches used to model AD in rodents, highlights their utility, and discusses some of their deficiencies.

Middle-aged human apoE4 targeted-replacement mice show retention deficits on a wide range of spatial memory tasks

Apolipoprotein (apo) E4, one of three human apoE (h-apoE) isoforms, has been identified as a major genetic risk factor for Alzheimer's disease and for cognitive deficits associated with aging. However, the biological mechanisms involving apoE in learning and memory processes are unclear. A potential isoform-dependent role of apoE in cognitive processes was studied in human apoE targeted-replacement (TR) mice. These mice express either the human apoE3 or apoE4 gene under the control of endogenous murine apoE regulatory sequences, resulting in physiological expression of h-apoE in both a temporal and spatial pattern similar to humans. Male and female apoE3-TR, apoE4-TR, apoE-knockout and C57BL/6J mice (15-18 months) were tested with spatial memory and avoidance conditioning tasks. Compared to apoE3-TR mice, spatial memory in female apoE4-TR mice was impaired based on their poor performances in; (i) the probe test of the water-maze reference memory task, (ii) the water-maze working memory task and (iii) an active avoidance Y-maze task. Retention performance on a passive avoidance task was also impaired in apoE4-TR mice, but not in other genotypes. These deficits in both spatial and avoidance memory tasks may be related to the anatomical and functional abnormalities previously reported in the hippocampus and the amygdala of apoE4-TR mice. We conclude that the apoE4-TR mice provide an excellent model for understanding the mechanisms underlying apoE4-dependent susceptibility to cognitive decline.

Gene delivery of human apolipoprotein E alters brain Abeta burden in a mouse model of Alzheimer's disease

Apolipoprotein E (apoE) alleles are important genetic risk factors for Alzheimer's disease (AD), with the epsilon4 allele increasing and the epsilon2 allele decreasing risk for developing AD. ApoE has been shown to influence brain amyloid-beta peptide (Abeta) and amyloid burden, both in humans and in transgenic mice. Here we show that direct intracerebral administration of lentiviral vectors expressing the three common human apoE isoforms differentially alters hippocampal Abeta and amyloid burden in the PDAPP mouse model of AD. Expression of apoE4 in the absence of mouse apoE increases hippocampal Abeta(1-42) levels and amyloid burden. By contrast, expression of apoE2, even in the presence of mouse apoE, markedly reduces hippocampal Abeta burden. Our data demonstrate rapid apoE isoform-dependent effects on brain Abeta burden in a mouse model of AD. Gene delivery of apoE2 may prevent or reduce brain Abeta burden and the subsequent development of neuritic plaques.

Human apoE targeted replacement mouse lines: h-apoE4 and h-apoE3 mice differ on spatial memory performance and avoidance behavior

Apolipoprotein E4 (apoE4), one of the three most common human apoE (h-apoE) isoforms, is a major genetic risk factor for Alzheimer's disease and for cognitive deficits associated with aging. The biological mechanisms involving apoE in learning and memory processes are unclear. A potential isoform-dependent effect of h-apoE on cognitive performance was studied in gene-targeted mice, which show physiological expression levels and distribution of h-apoE3 or h-apoE4. Male and female h-apoE3 and h-apoE4, apoE-deficient and C57BL/6J mice (4-5 months) were subjected to tasks evaluating spatial memory and avoidance conditioning. Female h-apoE4 mice did not detect changes in the spatial configuration of objects as opposed to female h-apoE3 mice. Female h-apoE3 mice failed to improve their performance during training in a reference memory version of the spatial water-maze task, but performed well during the probe trial 24 h after the last training trial. Memory retention performances of h-apoE4 mice were impaired during this probe trial. Both h-apoE3 and h-apoE4 mice did not improve their performance in a water-maze delayed matching to place task. Finally, h-apoE3 mice showed mild perturbations in a Y-maze active avoidance task, whereas both h-apoE mouse lines performed well in a passive avoidance task. Thus, spatial memory performances appeared particularly sensitive to h-apoE-isoform-dependent effects. Deficits occurred predominantly in female h-apoE4 mice, which support the hypothesis that humans carrying h-apoE4, especially women, have impaired spatial memory compared to those carrying h-apoE3.

Apolipoprotein E, amyloid, and Alzheimer disease

Despite important inroads into the molecular pathology of Alzheimer disease, effective long-term treatment for the condition remains elusive. Among the many gene products that are recognized as factors in the disease is apolipoprotein ( (apoE). The risk that specific isoforms of apoE pose with regard to Alzheimer Disease clearly varies, and so the roles that apoE plays in the brain will be crucial to a full understanding of the disease and to efforts to develop effective therapies.

Immunotherapy for Alzheimer's disease: will vaccination work?

Active or passive immunization against the beta-amyloid peptide (Abeta) has been proposed as a method for preventing and/or treating Alzheimer's disease (AD). In addition to lowering brain Abeta and amyloid burden in transgenic mouse models of AD, a beneficial effect of immunization on previously characterized memory impairment(s) has also been reported in these mice. Whether these preclinical data will predict efficacy in AD patients remains to be seen. A clinical trial of active immunization (vaccination) was halted, owing to a serious adverse event (meningoencephalitis), raising questions about the safety of this approach. Two recent reports suggest that immunotherapy-based approaches to treating and preventing AD will require careful antigen and antibody selection, to maximize efficacy and minimize serious adverse events. However, given the potential efficacy of this approach, we believe that immunotherapy for AD should not be prematurely abandoned.

Apolipoprotein E alters the processing of the beta-amyloid precursor protein in APP(V717F) transgenic mice

We have recently reported a critical role for apolipoprotein E (apoE) in the process of amyloid deposition and neuritic plaque formation in APP(V717F) transgenic (Tg) mice, an animal model of Alzheimer's disease (AD). In the present study, we have investigated whether the presence or absence of apoE alters the processing of the amyloid precursor protein (APP) to various fragments, including the beta-amyloid peptides (Abeta). Here we show that, in contrast to APP(V717F) Tg mice expressing apoE, APP(V717F) Tg mice deficient in apoE develop anti-Abeta immunoreactive multifocal aggregates, which contain the beta-cleaved C-terminal fragments (beta-CTFs) of APP. Tg mice deficient in apoE also display altered levels of mature full-length APP, increased amounts of beta-CTFs, as well as elevated levels of Abeta(1-40) and Abeta(1-42) in an age- and region-dependent manner when compared to Tg mice expressing apoE. Taken together, these data support a role for apoE in APP processing in vivo.

Does my mouse have Alzheimer's disease?

Small animal models that manifest many of the characteristic neuropathological and behavioral features of Alzheimer's disease (AD) have been developed and have proven of great value for studying the pathogenesis of this disorder at the molecular, cellular and behavioral levels. The great progress made in our understanding of the genetic factors that either cause or contribute to the risk of developing AD has prompted many laboratories to create transgenic (tg) mice that overexpress specific genes which cause familial forms of the disease. Several of these tg mice display neuropathological and behavioral features of AD including amyloid beta-peptide (A beta) and amyloid deposits, neuritic plaques, gliosis, synaptic alterations and signs of neurodegeneration as well as memory impairment. Despite these similarities, important differences in neuropathology and behavior between these tg mouse models and AD have also been observed, and to date no perfect animal model has emerged. Moreover, ascertaining which elements of the neuropathological and behavioral phenotype of these various strains of tg mice are relevant to that observed in AD continues to be a challenge. Here we provide a critical review of the AD-like neuropathology and behavioral phenotypes of several well-known and utilized tg mice that express human APP transgenes.

Immunization reverses memory deficits without reducing brain Abeta burden in Alzheimer's disease model

We have previously shown that chronic treatment with the monoclonal antibody m266, which is specific for amyloid beta-peptide (Abeta), increases plasma concentrations of Abeta and reduces Abeta burden in the PDAPP transgenic mouse model of Alzheimer's disease (AD). We now report that administration of m266 to PDAPP mice can rapidly reverse memory deficits in both an object recognition task and a holeboard learning and memory task, but without altering brain Abeta burden. We also found that an Abeta/antibody complex was present in both the plasma and the cerebrospinal fluid of m266-treated mice. Our data indicate that passive immunization with this anti-Abeta monoclonal antibody can very rapidly reverse memory impairment in certain learning and memory tasks in the PDAPP mouse model of AD, owing perhaps to enhanced peripheral clearance and (or) sequestration of a soluble brain Abeta species.

Peripheral anti-A beta antibody alters CNS and plasma A beta clearance and decreases brain A beta burden in a mouse model of Alzheimer's disease

Active immunization with the amyloid beta (A beta) peptide has been shown to decrease brain A beta deposition in transgenic mouse models of Alzheimer's disease and certain peripherally administered anti-A beta antibodies were shown to mimic this effect. In exploring factors that alter A beta metabolism and clearance, we found that a monoclonal antibody (m266) directed against the central domain of A beta was able to bind and completely sequester plasma A beta. Peripheral administration of m266 to PDAPP transgenic mice, in which A beta is generated specifically within the central nervous system (CNS), results in a rapid 1,000-fold increase in plasma A beta, due, in part, to a change in A beta equilibrium between the CNS and plasma. Although peripheral administration of m266 to PDAPP mice markedly reduces A beta deposition, m266 did not bind to A beta deposits in the brain. Thus, m266 appears to reduce brain A beta burden by altering CNS and plasma A beta clearance.

The beta-amyloid precursor protein and its derivatives: from biology to learning and memory processes

Intensive investigation towards the understanding of the biology and physiological functions of the beta-amyloid precursor protein (APP) have been supported since it is known that a 39-43 amino acid fragment of APP, called the beta-amyloid protein (Abeta), accumulates in the brain parenchyma to form the typical lesions associated with Alzheimer's disease (AD). It emerges from extensive data that APP and its derivatives show a wide range of contrasting physiological properties and therefore might be involved in distinct physiological functions. Abeta has been shown to disrupt neuronal activity and to demonstrate neurotoxic properties in a wide range of experimental procedures. In contrast, both in vitro and in vivo studies suggest that APP and/or its secreted forms are important factors involved in the viability, growth and morphological and functional plasticity of nerve cells. Furthermore, several recent studies suggest that APP and its derivatives have an important role in learning and memory processes. Memory impairments can be induced in animals by intracerebral treatment with Abeta. Altered expression of the APP gene in aged animals or in genetically-modified animals also leads to memory deficits. By contrast, secreted forms of APP have recently been shown to facilitate learning and memory processes in mice. These interesting findings open novel perspectives to understand the involvement of APP in the development of cognitive deficits associated with AD. In this review, we summarize the current data concerning the biology and the behavioral effects of APP and its derivatives which may be relevant to the roles of these proteins in memory and in AD pathology.

Neuroanatomical abnormalities in behaviorally characterized APP(V717F) transgenic mice

Histological analyses were performed on the brains of APP(V717F) transgenic (Tg)mice previously studied in a battery of behavioral tests. We describe here the regional and age-dependent deposition of amyloid in both heterozygous and homozygous Tg mice. We also report that Tg mice show significant and age-dependent changes in synaptic density measured by synaptophysin immunoreactivity. Surprisingly, a rather marked hippocampal atrophy is observed as early as 3 months of age in Tg mice (20-40%). Statistical analyses revealed that the deficits in object recognition memory are related to the number of amyloid deposits in specific brain regions, whereas deficits in spatial reference and working memory are related to the changes in synaptic density and hippocampal atrophy. Our study suggests that the behavioral deficits observed in Tg mice are only in part related to amyloid deposition, but are also related to neuroanatomical alterations secondary to overexpression of the APP(V717F) transgene and independent of amyloid deposition.

Behavioral deficits in APP(V717F) transgenic mice deficient for the apolipoprotein E gene

Both the beta-amyloid precursor protein (APP) and the apoliprotein E (apoE) genes are involved in the pathogenesis of Alzheimer's disease (AD). We previously showed that mice over-expressing a human mutated form of APP (APP(V717F)) display age-dependent recognition memory deficits associated with the progression of amyloid deposition. Here, we asked whether 10- to 12-month-old APP(V717F) mice lacking the apoE gene, which do not present obvious amyloid deposition, differ from APP(V717F) mice in the object recognition task. The recognition performance is decreased in both transgenic mouse groups compared to control groups. Moreover, some behavioral disturbances displayed by APP mice lacking apoE are even more pronounced than those of APP mice expressing apoE. Our results suggest that the recognition memory deficits are related to high levels of soluble Abeta rather than to amyloid deposits.

Early regional cerebral glucose hypometabolism in transgenic mice overexpressing the V717F beta-amyloid precursor protein

In the present study, we examined whether the relative levels of regional brain [14C]2-deoxyglucose (2-DG) uptake are altered in a transgenic mouse model of Alzheimer's disease which overexpresses a mutated form of the human beta-amyloid precursor protein (mutation V717F). We show that the relative levels of 2-DG uptake are significantly reduced in the septum, thalamus, dentate gyrus and parietal cortex of 3-month-old transgenic mice as compared with wild-type littermates. In 10-month-old transgenic mice, these alterations also extend to the CA3 hippocampal region, the cingulate, retrosplenial, occipital and temporal cortices, suggesting an age-dependent decrease in the regional 2-DG uptake. These results suggest that expression of a mutated APP gene induces an early regional cerebral hypometabolism independently of amyloid deposition per se.

Behavioral disturbances in transgenic mice overexpressing the V717F beta-amyloid precursor protein

PDAPP transgenic mice have been shown to develop age dependently much of the cerebral histopathology associated with Alzheimer's disease. PDAPP mice (3-10 months old) were tested in a battery of memory tasks to determine whether they develop memory-behavioral deficits and whether these deficits occur before or after amyloid deposition. PDAPP mice manifest robust impairments in a radial-maze spatial discrimination task at all ages tested. Mild deficits were observed in a barpress learning task in 3-month-old PDAPP mice. In contrast, PDAPP mice show an age-dependent decrease in spontaneous object-recognition performance that appears to be severe at ages when amyloid deposition is known to occur. Thus, the PDAPP mouse shows severe deficits in the radial maze well before amyloid plaque deposition, whereas object-recognition performance decreases with age and may be associated with amyloid deposition.

Behavioral disturbances in transgenic mice overexpressing the V717F beta-amyloid precursor protein

PDAPP transgenic mice have been shown to develop age dependently much of the cerebral histopathology associated with Alzheimer's disease. PDAPP mice (3-10 months old) were tested in a battery of memory tasks to determine whether they develop memory-behavioral deficits and whether these deficits occur before or after amyloid deposition. PDAPP mice manifest robust impairments in a radial-maze spatial discrimination task at all ages tested. Mild deficits were observed in a barpress learning task in 3-month-old PDAPP mice. In contrast, PDAPP mice show an age-dependent decrease in spontaneous object-recognition performance that appears to be severe at ages when amyloid deposition is known to occur. Thus, the PDAPP mouse shows severe deficits in the radial maze well before amyloid plaque deposition, whereas object-recognition performance decreases with age and may be associated with amyloid deposition.

Memory-enhancing effects of secreted forms of the beta-amyloid precursor protein in normal and amnestic mice

When administered intracerebroventricularly to mice performing various learning tasks involving either short-term or long-term memory, secreted forms of the beta-amyloid precursor protein (APPs751 and APPs695) have potent memory-enhancing effects and block learning deficits induced by scopolamine. The memory-enhancing effects of APPs were observed over a wide range of extremely low doses (0.05-5,000 pg intracerebroventricularly), blocked by anti-APPs antisera, and observed when APPs was administered either after the first training session in a visual discrimination or a lever-press learning task or before the acquisition trial in an object recognition task. APPs had no effect on motor performance or exploratory activity. APPs695 and APPs751 were equally effective in the object recognition task, suggesting that the memory-enhancing effect of APPs does not require the Kunitz protease inhibitor domain. These data suggest an important role for APPss on memory processes.

Scopolamine-induced deficits in a two-trial object recognition task in mice

The purpose of the present study was to design an object recognition task in mice and characterize the effects of scopolamine in this paradigm. This task consisted of exposing mice for 6 or 10 min to an object in an open field (trial 1) and, after a delay (1-24 h), testing mice for 10 min with the object and a novel object (trial 2). Mice explored the novel object more than the familiar object as the inter-trial delay decreased and/or the duration of trial 1 increased. Administration of scopolamine (0.3, 1 and 3 mg kg-1, s.c.) before trial 1 reduced recognition performance on trial 2 after a 3 h inter-trial delay and induced other behavioural effects, including an increase in locomotor activity on trial 1. Methylscopolamine (1 mg kg-1) had no effect on recognition performance. The present results show that this task is a useful model to test recognition memory in mice and that blocking the central cholinergic system impairs this form of memory.