Characterization of New Polyclonal Antibodies Specific for 40 and 42 Amino Acid-Long Amyloid β Peptides: Their Use to Examine the Cell Biology of Presenilins and the Immunohistochemistry of Sporadic Alzheimer’s Disease and Cerebral Amyloid Angiopathy Cases

Dipeptidyl peptidase 4 contributes to Alzheimer's disease-like defects in a mouse model and is increased in sporadic Alzheimer's disease brains

The amyloid cascade hypothesis, which proposes a prominent role for full-length amyloid β peptides in Alzheimer's disease, is currently being questioned. In addition to full-length amyloid β peptide, several N-terminally truncated fragments of amyloid β peptide could well contribute to Alzheimer's disease setting and/or progression. Among them, pyroGlu3-amyloid β peptide appears to be one of the main components of early anatomical lesions in Alzheimer's disease-affected brains. Little is known about the proteolytic activities that could account for the N-terminal truncations of full-length amyloid β, but they appear as the rate-limiting enzymes yielding the Glu3-amyloid β peptide sequence that undergoes subsequent cyclization by glutaminyl cyclase, thereby yielding pyroGlu3-amyloid β. Here, we investigated the contribution of dipeptidyl peptidase 4 in Glu3-amyloid β peptide formation and the functional influence of its genetic depletion or pharmacological blockade on spine maturation as well as on pyroGlu3-amyloid β peptide and amyloid β 42-positive plaques and amyloid β 42 load in the triple transgenic Alzheimer's disease mouse model. Furthermore, we examined whether reduction of dipeptidyl peptidase 4 could rescue learning and memory deficits displayed by these mice. Our data establish that dipeptidyl peptidase 4 reduction alleviates anatomical, biochemical, and behavioral Alzheimer's disease-related defects. Furthermore, we demonstrate that dipeptidyl peptidase 4 activity is increased early in sporadic Alzheimer's disease brains. Thus, our data demonstrate that dipeptidyl peptidase 4 participates in pyroGlu3-amyloid β peptide formation and that targeting this peptidase could be considered as an alternative strategy to interfere with Alzheimer's disease progression.

A 4R tauopathy develops without amyloid deposits in aged cat brains

Human tauopathies are neurodegenerative diseases with accumulation of abnormally phosphorylated and aggregated tau proteins forming neurofibrillary tangles. We investigated the development of tau pathology in aged cat brains as a model of neurofibrillary tangle formation occurring spontaneously during aging. In 4 of 6 cats aged between 18 and 21 years, we found a somatodendritic accumulation of phosphorylated and aggregated tau in neurons and oligodendrocytes. Two of these 4 cats had no amyloid immunoreactivity. These tau inclusions were mainly composed of 4R tau isoforms and straight filaments and colocalized with the active form of the glycogen synthase kinase-3 (GSK3). Cat brains with a tau pathology showed a significant cortical atrophy and neuronal loss. We demonstrate in this study the presence of a tau pathology in aged cat brains that develop independently of amyloid deposits. The colocalization of the active form of the GSK3 with tau inclusions as observed in human tauopathies suggests that this kinase could be responsible for the abnormal tau phosphorylation observed in aged cat brains, representing a mechanism of tau pathology development shared between a naturally occurring tauopathy in aged cats and human tauopathies.

Aβ and the dementia syndrome: Simple versus complex perspectives

BACKGROUND

The amyloid cascade hypothesis (ACH) has dominated strategy in dementia research for decades despite evidence of its limitations including known heterogeneity of the dementia syndrome in the population and the narrow focus on a single molecule - the amyloid beta protein (Aβ) as causal for all Alzheimer-type dementia. Other hypotheses relevant to Aβ are the presenilin (PS) hypothesis (PSH) relating to the involvement of PS in the generation of Aβ, and the amyloid precursor protein (APP) matrix approach (AMA), relating to the complex and dynamic breakdown of APP, from which Aβ derives.

MATERIALS AND METHODS

In this article we explore perspectives relating to complex disorders occurring mainly in older populations through a detailed case study of the role of Aβ in AD.

RESULTS

Scrutiny of the evidence generated so far reveals and a lack of understanding of the wider APP proteolytic system and how narrow research into the dementia syndrome has been to date. Confounding factors add significant limitations to the understanding of the current evidence base.

CONCLUSIONS

A better characterisation of the entire APP proteolytic system in the human brain is urgently required to place Aβ in its complex physiological context. From a molecular perspective, a combination of the alternative hypotheses, the PSH and the AMA may better describe the complexity of the APP proteolytic system leading to new therapeutic approaches. The reductionist approach is widespread throughout biomedical research and this example highlights how neglect of complexity can undermine investigations of complex disorders, particularly those arising in the oldest in our populations.

Label-free imaging of amyloid plaques in Alzheimer's disease with stimulated Raman scattering microscopy

One of the key pathological features of Alzheimer's disease (AD) is the existence of extracellular deposition of amyloid plaques formed with misfolded amyloid-β (Aβ). The conformational change of proteins leads to enriched contents of β sheets, resulting in remarkable changes of vibrational spectra, especially the spectral shifts of the amide I mode. Here, we applied stimulated Raman scattering (SRS) microscopy to image amyloid plaques in the brain tissue of an AD mouse model. We have demonstrated the capability of SRS microscopy as a rapid, label-free imaging modality to differentiate misfolded from normal proteins based on the blue shift (~10 cm^-1) of amide I SRS spectra. Furthermore, SRS imaging of Aβ plaques was verified by antibody staining of frozen thin sections and fluorescence imaging of fresh tissues. Our method may provide a new approach for studies of AD pathology, as well as other neurodegenerative diseases associated with protein misfolding.

Alzheimer's Transgenic Model Is Characterized by Very Early Brain Network Alterations and β-CTF Fragment Accumulation: Reversal by β-Secretase Inhibition

Alzheimer's disease (AD) is defined by the presence of amyloid-β (Aβ) and tau protein aggregates. However, increasing data is suggesting that brain network alterations rather than protein deposition could account for the early pathogenesis of the disease. In the present study, we performed in vitro extracellular field recordings in the CA1/subiculum area of the hippocampus from 30 days old J20-TG-AD mice. Here, we found that theta oscillations were significantly less rhythmic than those recorded from control group. In addition, J20 mice displayed significantly less theta-gamma cross-frequency coupling (CFC) as peak modulation indexes for slow (25-45 Hz) and fast (150-250 Hz) gamma frequency oscillations were reduced. Because inhibitory parvalbumin (PV) cells play a vital role in coordinating hippocampal theta and gamma oscillations, whole-cell patch-clamp recordings and extracellular stimulation were performed to access their intrinsic and synaptic properties. Whereas neither the inhibitory output of local interneurons to pyramidal cells (PCs) (inhibitory→PC) nor the excitatory output of PCs to PV cells (PC→PV) differed between control and J20 animals, the intrinsic excitability of PV cells was reduced in J20 mice compared to controls. Interestingly, optogenetic activation of PV interneurons which can directly drive theta oscillations in the hippocampus, did not rescue CFC impairments, suggesting the latter did not simply result from alteration of the underlying theta rhythm. Altered young J20 mice was characterized by the presence of β-CTF, but not with Aβ accumulation, in the hippocampus. Importantly, the β secretase inhibitor AZD3839-AstraZeneca significantly rescued the abnormal early electrophysiological phenotype of J20 mice. In conclusion, our data show that brain network alterations precede the canonical Aβ protein deposition and that, such alterations can be related to β-CTF fragment.

Understanding the roles of mutations in the amyloid precursor protein in Alzheimer disease

Many models of disease progression in Alzheimer's disease (AD) have been proposed to help guide experimental design and aid the interpretation of results. Models focussing on the genetic evidence include the amyloid cascade (ACH) and presenilin (PSH) hypotheses and the amyloid precursor protein (APP) matrix approach (AMA), of which the ACH has held a dominant position for over two decades. However, the ACH has never been fully accepted and has not yet delivered on its therapeutic promise. We review the ACH, PSH and AMA in relation to levels of APP proteolytic fragments reported from AD-associated mutations in APP. Different APP mutations have diverse effects on the levels of APP proteolytic fragments. This evidence is consistent with at least three disease pathways that can differ between familial and sporadic AD and two pathways associated with cerebral amyloid angiopathy. We cannot fully evaluate the ACH, PSH and AMA in relation to the effects of mutations in APP as the APP proteolytic system has not been investigated systematically. The confounding effects of sequence homology, complexity of competing cleavages and antibody cross reactivities all illustrate limitations in our understanding of the roles these fragments and the APP proteolytic system as a whole in normal aging and disease play. Current experimental design should be refined to generate clearer evidence, addressing both aging and complex disorders with standardised reporting formats. A more flexible theoretical framework capable of accommodating the complexity of the APP proteolytic system is required to integrate available evidence.

Post-translational remodeling of ryanodine receptor induces calcium leak leading to Alzheimer's disease-like pathologies and cognitive deficits

The mechanisms underlying ryanodine receptor (RyR) dysfunction associated with Alzheimer disease (AD) are still not well understood. Here, we show that neuronal RyR2 channels undergo post-translational remodeling (PKA phosphorylation, oxidation, and nitrosylation) in brains of AD patients, and in two murine models of AD (3 × Tg-AD, APP ^+/- /PS1 ^+/-). RyR2 is depleted of calstabin2 (KFBP12.6) in the channel complex, resulting in endoplasmic reticular (ER) calcium (Ca²⁺) leak. RyR-mediated ER Ca²⁺ leak activates Ca²⁺-dependent signaling pathways, contributing to AD pathogenesis. Pharmacological (using a novel RyR stabilizing drug Rycal) or genetic rescue of the RyR2-mediated intracellular Ca²⁺ leak improved synaptic plasticity, normalized behavioral and cognitive functions and reduced Aβ load. Genetically altered mice with congenitally leaky RyR2 exhibited premature and severe defects in synaptic plasticity, behavior and cognitive function. These data provide a mechanism underlying leaky RyR2 channels, which could be considered as potential AD therapeutic targets.

Phenotypic Alterations in Hippocampal NPY- and PV-Expressing Interneurons in a Presymptomatic Transgenic Mouse Model of Alzheimer's Disease

Interneurons, key regulators of hippocampal neuronal network excitability and synchronization, are lost in advanced stages of Alzheimer’s disease (AD). Given that network changes occur at early (presymptomatic) stages, we explored whether alterations of interneurons also occur before amyloid-beta (Aβ) accumulation. Numbers of neuropeptide Y (NPY) and parvalbumin (PV) immunoreactive (IR) cells were decreased in the hippocampus of 1 month-old TgCRND8 mouse AD model in a sub-regionally specific manner. The most prominent change observed was a decrease in the number of PV-IR cells that selectively affected CA1/2 and subiculum, with the pyramidal layer (PY) of CA1/2 accounting almost entirely for the reduction in number of hippocampal PV-IR cells. As PV neurons were decreased selectively in CA1/2 and subiculum, and given that they are critically involved in the control of hippocampal theta oscillations, we then assessed intrinsic theta oscillations in these regions after a 4-aminopyridine (4AP) challenge. This revealed increased theta power and population bursts in TgCRND8 mice compared to non-transgenic (nTg) controls, suggesting a hyperexcitability network state. Taken together, our results identify for the first time AD-related alterations in hippocampal interneuron function as early as at 1 month of age. These early functional alterations occurring before amyloid deposition may contribute to cognitive dysfunction in AD.

Intraneuronal aggregation of the β-CTF fragment of APP (C99) induces Aβ-independent lysosomal-autophagic pathology

Endosomal-autophagic-lysosomal (EAL) dysfunction is an early and prominent neuropathological feature of Alzheimers’s disease, yet the exact molecular mechanisms contributing to this pathology remain undefined. By combined biochemical, immunohistochemical and ultrastructural approaches, we demonstrate a link between EAL pathology and the intraneuronal accumulation of the β-secretase-derived βAPP fragment (C99) in two in vivo models, 3xTgAD mice and adeno-associated viral-mediated C99-infected mice. We present a pathological loop in which the accumulation of C99 is both the effect and causality of impaired lysosomal-autophagic function. The deleterious effect of C99 was found to be linked to its aggregation within EAL-vesicle membranes leading to disrupted lysosomal proteolysis and autophagic impairment. This effect was Aβ independent and was even exacerbated when γ-secretase was pharmacologically inhibited. No effect was observed in inhibitor-treated wild-type animals suggesting that lysosomal dysfunction was indeed directly linked to C99 accumulation. In some brain areas, strong C99 expression also led to inflammatory responses and synaptic dysfunction. Taken together, this work demonstrates a toxic effect of C99 which could underlie some of the early-stage anatomical hallmarks of Alzheimer’s disease pathology. Our work also proposes molecular mechanisms likely explaining some of the unfavorable side-effects associated with γ-secretase inhibitor-directed therapies.

Novel bio-spectroscopic imaging reveals disturbed protein homeostasis and thiol redox with protein aggregation prior to hippocampal CA1 pyramidal neuron death induced by global brain ischemia in the rat

Global brain ischemia resulting from cardiac arrest and cardiac surgery can lead to permanent brain damage and mental impairment. A clinical hallmark of global brain ischemia is delayed neurodegeneration, particularly within the CA1 subsector of the hippocampus. Unfortunately, the biochemical mechanisms have not been fully elucidated, hindering optimization of current therapies (i.e., therapeutic hypothermia) or development of new therapies. A major limitation to elucidating the mechanisms that contribute to neurodegeneration and understanding how these are influenced by potential therapies is the inability to relate biochemical markers to alterations in the morphology of individual neurons. Although immunocytochemistry allows imaging of numerous biochemical markers at the sub-cellular level, it is not a direct chemical imaging technique and requires successful "tagging" of the desired analyte. Consequently, important biochemical parameters, particularly those that manifest from oxidative damage to biological molecules, such as aggregated protein levels, have been notoriously difficult to image at the cellular or sub-cellular level. It has been hypothesized that reactive oxygen species (ROS) generated during ischemia and reperfusion facilitate protein aggregation, impairing neuronal protein homeostasis (i.e., decreasing protein synthesis) that in turn promotes neurodegeneration. Despite indirect evidence for this theory, direct measurements of morphology and ROS induced biochemical damage, such as increased protein aggregates and decreased protein synthesis, within the same neuron is lacking, due to the unavailability of a suitable imaging method. Our experimental approach has incorporated routine histology with novel wide-field synchrotron radiation Fourier transform infrared imaging (FTIRI) of the same neurons, ex vivo within brain tissue sections. The results demonstrate for the first time that increased protein aggregation and decreased levels of total protein occur in the same CA1 pyramidal neurons 1 day after global ischemia. Further, analysis of serial tissue sections using X-ray absorption spectroscopy at the sulfur K-edge has revealed that CA1 pyramidal neurons have increased disulfide levels, a direct indicator of oxidative stress, at this time point. These changes at 1 day after ischemia precede a massive increase in aggregated protein and disulfide levels concomitant with loss of neuron integrity 2 days after ischemia. Therefore, this study has provided direct support for a correlative mechanistic link in both spatial and temporal domains between oxidative stress, protein aggregation and altered protein homeostasis prior to irreparable neuron damage following global ischemia.

Mechanisms of murine cerebral malaria: Multimodal imaging of altered cerebral metabolism and protein oxidation at hemorrhage sites

Using a multimodal biospectroscopic approach, we settle several long-standing controversies over the molecular mechanisms that lead to brain damage in cerebral malaria, which is a major health concern in developing countries because of high levels of mortality and permanent brain damage. Our results provide the first conclusive evidence that important components of the pathology of cerebral malaria include peroxidative stress and protein oxidation within cerebellar gray matter, which are colocalized with elevated nonheme iron at the site of microhemorrhage. Such information could not be obtained previously from routine imaging methods, such as electron microscopy, fluorescence, and optical microscopy in combination with immunocytochemistry, or from bulk assays, where the level of spatial information is restricted to the minimum size of tissue that can be dissected. We describe the novel combination of chemical probe-free, multimodal imaging to quantify molecular markers of disturbed energy metabolism and peroxidative stress, which were used to provide new insights into understanding the pathogenesis of cerebral malaria. In addition to these mechanistic insights, the approach described acts as a template for the future use of multimodal biospectroscopy for understanding the molecular processes involved in a range of clinically important acute and chronic (neurodegenerative) brain diseases to improve treatment strategies.

Clinical-pathologic correlations in vascular cognitive impairment and dementia

The most common causes of cognitive impairment and dementia are Alzheimer's disease (AD) and vascular brain injury (VBI), either independently, in combination, or in conjunction with other neurodegenerative disorders. The contribution of VBI to cognitive impairment and dementia, particularly in the context of AD pathology, has been examined extensively yet remains difficult to characterize due to conflicting results. Describing the relative contribution and mechanisms of VBI in dementia is important because of the profound impact of dementia on individuals, caregivers, families, and society, particularly the stability of health care systems with the rapidly increasing age of our population. Here we discuss relationships between pathologic processes of VBI and clinical expression of dementia, specific subtypes of VBI including microvascular brain injury, and what is currently known regarding contributions of VBI to the development and pathogenesis of the dementia syndrome. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Study on Aβ34 biology and detection in transgenic mice brains

The β-amyloid precursor protein undergoes cleavages by β- and γ-secretasses yielding amyloid-β peptides (Aβ) that accumulate in Alzheimer's disease. Subsequently, Aβ peptides are targets of additional truncations or endoproteolytic cleavages explaining the diversity of Aβ-related fragments recovered in cell media or pathologic human fluids. Here, we focused on Aβ1-34 (Aβ34) that has been detected both in vitro and in vivo and that derives from the hydrolysis of Aβ by β-secretase. We have obtained and fully characterized by immunologic and biochemical approaches, a polyclonal antibody that specifically recognizes the C-terminus of Aβx-34. We present immunohistochemical evidence for the presence of Aβx-34 in the brain of 3xTg mice and Alzheimer's disease-affected human brains. Finally, we demonstrate a neprilysin-mediated degradation process of Aβ34 and the ability of synthetic Aβ34 to protect HEK cells overexpressing either wild type or Swedish-mutated β-amyloid precursor protein from apoptosis.

Amyloid beta immunization worsens iron deposits in the choroid plexus and cerebral microbleeds

Anti-amyloid beta (Aβ) immunotherapy provides potential benefits in Alzheimer's disease patients. Nevertheless, strategies based on Aβ1-42 peptide induced encephalomyelitis and possible microhemorrhages. These outcomes were not expected from studies performed in rodents. It is critical to determine if other animal models better predict side effects of immunotherapies. Mouse lemur primates can develop amyloidosis with aging. Here we used old lemurs to study immunotherapy based on Aβ1-42 or Aβ-derivative (K6Aβ1-30). We followed anti-Aβ40 immunoglobulin G and M responses and Aβ levels in plasma. In vivo magnetic resonance imaging and histology were used to evaluate amyloidosis, neuroinflammation, vasogenic edema, microhemorrhages, and brain iron deposits. The animals responded mainly to the Aβ1-42 immunogen. This treatment induced immune response and increased Aβ levels in plasma and also microhemorrhages and iron deposits in the choroid plexus. A complementary study of untreated lemurs showed iron accumulation in the choroid plexus with normal aging. Worsening of iron accumulation is thus a potential side effect of Aβ-immunization at prodromal stages of Alzheimer's disease, and should be monitored in clinical trials.

Nuclear factor-κB regulates βAPP and β- and γ-secretases differently at physiological and supraphysiological Aβ concentrations

Anatomical lesions in Alzheimer disease-affected brains mainly consist of senile plaques, inflammation stigmata, and oxidative stress. The nuclear factor-κB (NF-κB) is a stress-activated transcription factor that is activated around senile plaques. We have assessed whether NF-κB could be differentially regulated at physiological or supraphysiological levels of amyloid β (Aβ) peptides. Under these experimental conditions, we delineated the putative NF-κB-dependent modulation of all cellular participants in Aβ production, namely its precursor βAPP (β-amyloid precursor protein) and the β- and γ-secretases, the two enzymatic machines involved in Aβ genesis. Under physiological conditions, NF-κB lowers the transcriptional activity of the promoters of βAPP, β-secretase (β-site APP-cleaving enzyme 1, BACE1), and of the four protein components (Aph-1, Pen-2, nicastrin, presenilin-1, or presenilin-2) of the γ-secretase in HEK293 cells. This was accompanied by a reduction of both protein levels and enzymatic activities, thereby ultimately yielding lower amounts of Aβ and AICD (APP intracellular domain). In stably transfected Swedish βAPP-expressing HEK293 cells triggering supraphysiological concentrations of Aβ peptides, NF-κB activates the transcription of βAPP, BACE1, and some of the γ-secretase members and increases protein expression and enzymatic activities, resulting in enhanced Aβ production. Our pharmacological approach using distinct NF-κB kinase modulators indicates that both NF-κB canonical and alternative pathways are involved in the control of Aβ production. Overall, our data demonstrate that under physiological conditions, NF-κB triggers a repressive effect on Aβ production that contributes to maintaining its homeostasis, while NF-κB participates in a degenerative cycle where Aβ would feed its own production under pathological conditions.

α-Secretase-derived fragment of cellular prion, N1, protects against monomeric and oligomeric amyloid β (Aβ)-associated cell death

In physiological conditions, both β-amyloid precursor protein (βAPP) and cellular prion (PrP(c)) undergo similar disintegrin-mediated α-secretase cleavage yielding N-terminal secreted products referred to as soluble amyloid precursor protein-α (sAPPα) and N1, respectively. We recently demonstrated that N1 displays neuroprotective properties by reducing p53-dependent cell death both in vitro and in vivo. In this study, we examined the potential of N1 as a neuroprotector against amyloid β (Aβ)-mediated toxicity. We first show that both recombinant sAPPα and N1, but not its inactive parent fragment N2, reduce staurosporine-stimulated caspase-3 activation and TUNEL-positive cell death by lowering p53 promoter transactivation and activity in human cells. We demonstrate that N1 also lowers toxicity, cell death, and p53 pathway exacerbation triggered by Swedish mutated βAPP overexpression in human cells. We designed a CHO cell line overexpressing the London mutated βAPP (APP(LDN)) that yields Aβ oligomers. N1 protected primary cultured neurons against toxicity and cell death triggered by oligomer-enriched APP(LDN)-derived conditioned medium. Finally, we establish that N1 also protects neurons against oligomers extracted from Alzheimer disease-affected brain tissues. Overall, our data indicate that a cellular prion catabolite could interfere with Aβ-associated toxicity and that its production could be seen as a cellular protective mechanism aimed at compensating for an sAPPα deficit taking place at the early asymptomatic phase of Alzheimer disease.

Interaction between NH(2)-tau fragment and Aβ in Alzheimer's disease mitochondria contributes to the synaptic deterioration

Although amyloid beta (Aβ) peptide can promote tau pathology and its toxicity is concurrently tau-dependent, the underlying mechanisms of the in vivo interplay of these proteins remain unsolved. Structural and functional mitochondrial alterations play an early, precipitating role in synaptic failure of Alzheimer's disease (AD) pathogenesis and an aggravated mitochondrial impairment has been described in triple APP/PS/tau transgenic mice carrying both plaques and tangles, if compared with mice overexpressing tau or amyloid precursor protein (APP) alone. Here, we show that a neurotoxic aminoterminal (NH(2))-derived tau fragment mapping between 26 and 230 amino acids of the human tau40 isoform (441 amino acids)-but not the physiological full-length protein-preferentially interacts with Aβ peptide(s) in human AD synapses in association with mitochondrial adenine nucleotide translocator-1 (ANT-1) and cyclophilin D. The two peptides-Aβ 1-42 and the smaller and more potent NH(2)-26-44 peptide of the longest 20-22 kDa NH(2)-tau fragment-inhibit the ANT-1-dependent adenosine diphosphate-adenosine triphosphate (ADP/ATP) exchange in a noncompetitive and competitive manner, respectively, and together further aggravate the mitochondrial dysfunction by exacerbating the ANT-1 impairment. Taken together, these data establish a common, direct and synergistic toxicity of pathological APP and tau products on synaptic mitochondria and suggest potential, new pathway(s) and target(s) for a combined, more efficient therapeutic intervention of early synaptic dysfunction in AD.

A novel mouse model of Alzheimer's disease with chronic estrogen deficiency leads to glial cell activation and hypertrophy

The role of estrogens in Alzheimer's disease (AD) involving β-amyloid (Aβ) generation and plaque formation was mostly tested in ovariectomized mice with or without APP mutations. The aim of the present study was to explore the abnormalities of neural cells in a novel mouse model of AD with chronic estrogen deficiency. These chimeric mice exhibit a total FSH-R knockout (FORKO) and carry two transgenes, one expressing the β-amyloid precursor protein (APPsw, Swedish mutation) and the other expressing presenilin-1 lacking exon 9 (PS1Δ9). The most prominent changes in the cerebral cortex and hippocampus of these hypoestrogenic mice were marked hypertrophy of both cortical neurons and astrocytes and an increased number of activated microglia. There were no significant differences in the number of Aβ plaques although they appeared less compacted and larger than those in APPsw/PS1Δ9 control mice. Similar glia abnormalities were obtained in wild-type primary cortical neural cultures treated with letrozole, an aromatase inhibitor. The concordance of results from APPsw/PS1Δ9 mice with or without FSH-R deletion and those with letrozole treatment in vitro (with and without Aβ treatment) of primary cortical/hippocampal cultures suggests the usefulness of these models to explore molecular mechanisms involved in microglia and astrocyte activation in hypoestrogenic states in the central nervous system.

A cortical form of CADASIL with cerebral Aβ amyloidosis

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) was diagnosed by genetic testing in a 53-year-old patient, 10 years before death. Following two strokes with partial recovery, he developed rapidly progressive cognitive decline 3 years before death. Neuropathology confirmed CADASIL. Characteristic arteriolar changes were associated with subcortical infarcts, and status cribrosus in basal ganglia and the cortico-subcortical junctions. Leukoencephalopathy was very mild. Severe arteriolar changes in the cerebral cortex and leptomeninges were associated with numerous intracortical microinfarcts. There was abundant Abeta deposition throughout the cerebral cortex, mainly as Aβ42 diffuse plaques, frequently periarteriolar. There was no cerebral amyloid angiopathy apart from rare Aβ40 deposits around Notch3-positive deposits. Amyloid plaques were rare. Tau pathology was minimal. Alzheimer disease associated with CADASIL has been described, but the few reported cases had abundant amyloid plaques, amyloid angiopathy, fibrillar plaques and neurofibrillary tangles. Aβ accumulation could result from abnormal Aβ synthesis or impaired elimination due to the arteriolar changes of CADASIL. We did not find Aβ deposits in our other CADASIL cases with milder cortical arteriolar changes. Additional genetic predisposing factors were not identified. This case suggests that besides the classical, purely subcortical form of CADASIL, a "cortical" form with numerous lacunar infarcts and Aβ deposition in the cerebral cortex may occur and may be difficult to differentiate clinically from Alzheimer disease.

Novel demonstration of amyloid-β oligomers in sporadic inclusion-body myositis muscle fibers

Accumulation of amyloid-β (Aβ) within muscle fibers has been considered an upstream step in the development of the s-IBM pathologic phenotype. Aβ42, which is considered more cytotoxic than Aβ40 and has a higher propensity to oligomerize, is preferentially increased in s-IBM muscle fibers. In Alzheimer disease (AD), low-molecular weight Aβ oligomers and toxic oligomers, also referred to as "Aβ-Derived Diffusible Ligands" (ADDLs), are considered strongly cytotoxic and proposed to play an important pathogenic role. ADDLs have been shown to be increased in AD brain. We now report for the first time that in s-IBM muscle biopsies Aβ-dimer, -trimer, and -tetramer are identifiable by immunoblots. While all the s-IBM samples we studied had Aβ-oligomers, their molecular weights and intensity varied between the patient samples. None of the control muscle biopsies had Aβ oligomers. Dot-immunoblots using highly specific anti-ADDL monoclonal antibodies also showed highly increased ADDLs in all s-IBM biopsies studied, while controls were negative. By immunofluorescence, in some of the abnormal s-IBM muscle fibers ADDLs were accumulated in the form of plaque-like inclusions, and were often increased diffusely in very small fibers. Normal and disease-controls were negative. By gold-immuno-electron microscopy, ADDL-immunoreactivities were in close proximity to 6-10 nm amyloid-like fibrils, and also were immunodecorating amorphous and floccular material. In cultured human muscle fibers, we found that inhibition of autophagy led to the accumulation of Aβ oligomers. This novel demonstration of Aβ42 oligomers in s-IBM muscle biopsy provides additional evidence that intra-muscle fiber accumulation of Aβ42 oligomers in s-IBM may contribute importantly to s-IBM pathogenic cascade.

Days to criterion as an indicator of toxicity associated with human Alzheimer amyloid-beta oligomers

OBJECTIVE

Recent evidence suggests that high molecular weight soluble oligomeric Abeta (oAbeta) assemblies (also known as Abeta-derived diffusible ligands, or ADDLs) may represent a primary neurotoxic basis for cognitive failure in Alzheimer disease (AD). To date, most in vivo studies of oAbeta/ADDLs have involved injection of assemblies purified from the cerebrospinal fluid of human subjects with AD or from the conditioned media of Abeta-secreting cells into experimental animals. We sought to study the bioactivities of endogenously formed oAbeta/ADDLs generated in situ from the physiological processing of human amyloid precursor protein (APP) and presenitin1 (PS1) transgenes.

METHODS

We produced and histologically characterized single transgenic mice overexpressing APP(E693Q) or APP(E693Q) X PS1DeltaE9 bigenic mice. APP(E693Q) mice were studied in the Morris water maze (MWM) task at 6 and 12 months of age. Following the second MWM evaluation, mice were sacrificed, and brains were assayed for Abetatotal, Abeta40, Abeta42, and oAbeta/ADDLs by enzyme-linked immunosorbent assay (ELISA) and were also histologically examined. Based on results from the oAbeta/ADDL ELISA, we assigned individual APP(E693Q) mice to either an undetectable oAbeta/ADDLs group or a readily detectable oAbeta/ADDLs group. A days to criterion (DTC) analysis was used to determine delays in acquisition of the MWM task.

RESULTS

Both single transgenic and bigenic mice developed intraneuronal accumulation of APP/Abeta, although only APP(E693Q) X PS1Delta9 bigenic mice developed amyloid plaques. The APP(E693Q) mice did not develop amyloid plaques at any age studied, up to 30 months. APP(E693Q) mice were tested for spatial learning and memory, and only 12-month-old APP(E693Q) mice with readily detectable oAbeta/ADDLs displayed a significant delay in acquisition of the MWM task when compared to nontransgenic littermates.

INTERPRETATION

These data suggest that cerebral oAbeta/ADDL assemblies generated in brain in situ from human APP transgenes may be associated with cognitive impairment. We propose that a DTC analysis may be a sensitive method for assessing the cognitive impact in mice of endogenously generated oligomeric human Abeta assemblies. ANN NEUROL 2010.

A functional mouse retroposed gene Rps23r1 reduces Alzheimer's beta-amyloid levels and tau phosphorylation

Senile plaques consisting of beta-amyloid (Abeta) and neurofibrillary tangles composed of hyperphosphorylated tau are major pathological hallmarks of Alzheimer's disease (AD). Elucidation of factors that modulate Abeta generation and tau hyperphosphorylation is crucial for AD intervention. Here, we identify a mouse gene Rps23r1 that originated through retroposition of ribosomal protein S23. We demonstrate that RPS23R1 protein reduces the levels of Abeta and tau phosphorylation by interacting with adenylate cyclases to activate cAMP/PKA and thus inhibit GSK-3 activity. The function of Rps23r1 is demonstrated in cells of various species including human, and in transgenic mice overexpressing RPS23R1. Furthermore, the AD-like pathologies of triple transgenic AD mice were improved and levels of synaptic maker proteins increased after crossing them with Rps23r1 transgenic mice. Our studies reveal a new target/pathway for regulating AD pathologies and uncover a retrogene and its role in regulating protein kinase pathways.

Retinoid X receptor-alpha mediates (R )-flurbiprofen's effect on the levels of Alzheimer's beta-amyloid

Alzheimer's disease (AD) is characterized by the formation of extracellular senile plaques in the brain, whose major component is a small peptide called beta-amyloid (Abeta). Long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) has been found beneficial for AD and several reports suggest that NSAIDs reduce the generation of Abeta, especially the more amyloidogenic form Abeta42. However, the exact mechanism underlying NSAIDs' effect on AD risk remains largely inconclusive and all clinical trials using NSAIDs for AD treatment show negative results so far. Recent studies have shown that some NSAIDs can bind to certain nuclear receptors, suggesting that nuclear receptors may be involved in NSAID's effect on AD risk. Here we find that (R)-flurbiprofen, the R-enantiomer of the racemate NSAID flurbiprofen, can significantly reduce Abeta secretion, but at the same time, increases the level of intracellular Abeta. In addition, we find that a nuclear receptor, retinoid X receptor alpha (RXRalpha), can regulate Abeta generation and that down-regulation of RXRalpha significantly increases Abeta secretion. We also show that (R)-flurbiprofen can interfere with the interaction between RXRalpha and 9-cis-retinoid acid, and that 9-cis-retinoid acid decreases (R)-flurbiprofen's reduction of Abeta secretion. Moreover, the modulation effect of (R)-flurbiprofen on Abeta is abolished upon RXRalpha down-regulation. Together, these results suggest that RXRalpha can regulate Abeta generation and is also required for (R)-flurbiprofen-mediated Abeta generation.

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Abeta accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoepsilon 4 alleles. Parenchymal as well as vascular Abeta deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Abeta peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

Amyloid-beta42 is preferentially accumulated in muscle fibers of patients with sporadic inclusion-body myositis

Sporadic inclusion-body myositis (s-IBM) is the only muscle disease in which accumulation of amyloid-beta (Abeta) in abnormal muscle fibers appears to play a key pathogenic role. Increased amyloid-beta precursor protein (AbetaPP) and Abeta accumulation have been reported to be upstream steps in the development of the s-IBM pathologic phenotype, based on cellular and animal models. Abeta is released from AbetaPP as a 40 or 42 aminoacid peptide. Abeta42 is considered more cytotoxic than Abeta40, and it has a higher propensity to aggregate and form amyloid fibrils. Using highly specific antibodies, we evaluated in s-IBM muscle biopsies intra-muscle fiber accumulation of Abeta40 and Abeta42-immunoreactive aggregates by light- and electron-microscopic immunocytochemistry, and quantified their amounts by ELISA. In s-IBM, 80-90% of the vacuolated muscle fibers and 5-20% of the non-vacuolated muscle fibers contained plaque-like Abeta42-immunoreactive inclusions, while only 69% of those fibers also contained Abeta40 deposits. By immuno-electronmicroscopy, Abeta42 was associated with 6-10 nm amyloid-like fibrils, small electron-dense floccular clumps and larger masses of amorphous material. Abeta40 was present only on small patches of floccular clumps and amorphous material; it was not associated with 6-10 nm amyloid fibrils. By ELISA, in s-IBM muscle biopsies Abeta42 was present in values 8.53-44.7 pg/ml, while Abeta40 was not detectable; normal age-matched control biopsies did not have any detectable Abeta42 or Abeta40. Thus, in s-IBM muscle fibers, Abeta42 is accumulated more than Abeta40. We suggest that Abeta42 oligomers and their cytotoxicity may play an important role in the s-IBM pathogenesis.

Aminopeptidase A contributes to the N-terminal truncation of amyloid beta-peptide

Several lines of data previously indicated that N-terminally truncated forms of amyloid-beta (Abeta) peptides are likely the earliest and more abundant species immunohistochemically detectable in Alzheimer's disease-affected brains. It is noteworthy that the free N-terminal residue of full-length Abeta (fl-Abeta) is an aspartyl residue, suggesting that Abeta could be susceptible to exopeptidasic attack by aminopeptidase A (APA)-like proteases. In this context, we have examined whether APA could target Abeta peptides in both cell-free and cellular models. We first show that the general aminopeptidase inhibitor amastatin as well as two distinct aminopeptidase A inhibitors EC33 and pl302 both significantly increase the recovery of genuine fl-Abeta peptides generated by cells over-expressing Swedish-mutated beta amyloid precursor protein (APP) while the aminopeptidase N blocker pl250 did not modify fl-Abeta recovery. In agreement with this observation, we establish that over-expressed APA drastically reduces, in a calcium dependent manner, fl-Abeta but not APP IntraCellular Domain in a cell-free model of Abeta production. In agreement with the above data, we show that recombinant APA degrades fl-Abeta in a pl302-sensitive manner. Interestingly, we also show that EC33 and pl302 lower staurosporine-stimulated activation of caspase-3 in wild-type fibroblasts but not in betaAPP/beta-amyloid precursor protein-like protein 2 (APLP2) double knockout fibroblasts, suggesting that protecting endogenous fl-Abeta physiological production triggers neuroprotective phenotype. By contrast, EC33 does not modify staurosporine-induced caspase-3 activation in wild-type and Swedish-mutated betaAPP-HEK293 expressing cells that display exacerbated production of Abeta. Overall, our data establish that APA contributes to the N-terminal truncation of Abeta and suggest that this cleavage is likely abrogating a protective function associated with physiological but not supraphysiological levels of genuine fl-Abeta peptides.

Protection against amyloid beta cytotoxicity by sulforaphane: role of the proteasome

The 26S proteasome plays a major role in degradation of abnormal proteins within the cell. The indirect antioxidant including sulforaphane (SFN) protects cells from oxidative damage by increasing the expression of Nrf2-target genes. It has been observed that the expression of multiple subunits of the proteasome was up-regulated by indirect antioxidants through the Nrf2 pathway. In the current study, the role of SFN in amyloid beta(1-42) (Abeta(1-42))-induced cytotoxicity has been investigated in murine neuroblastoma cells. Treatment with SFN protected cells from Abeta(1-42)-mediated cell death in Neuro2A and N1E 115 cells. Inhibition of proteasome activities by MG132 could abolish the protective effect of SFN against Abeta(1-42). Neuro2A cells, which were stably overexpressing the catalytic subunit of the proteasome PSMB5, showed an elevated resistance toward Abeta(1-42) toxicity compared to control cells. Furthermore, the in vitro assay demonstrated that the Abeta(1-42) peptide is degraded by the proteasome fraction. These results suggest that proteasome-inducing indirect antioxidants may facilitate the removal of the Abeta(1-42) peptide and lead to the amelioration of abnormal protein-associated etiologies.

Single-domain antibodies recognize selectively small oligomeric forms of amyloid beta, prevent Abeta-induced neurotoxicity and inhibit fibril formation

Neurotoxic oligomers of amyloid beta (Abeta) peptide have been incriminated in the pathogenesis of Alzheimer's disease. Further exploration of this issue has been hampered to this date by the fact that all previously described anti-Abeta antibodies are unable to discriminate between the different conformations of the peptide (oligomers, protofibrils and fibrils). Here, we describe the generation of novel camelid single-chain binding domains (VHHs) that recognizes specifically low molecular-weight (MW) oligomers. Three VHH specific for Abeta were obtained from an immunized alpaca phage display library. Two were able to recognize selectively intraneuronal Abeta oligomers; furthermore, one of them, V31-1, prevented Abeta-induced neurotoxicity and inhibited fibril formation. This study confirms that VHHs may recognize non-conventional epitopes and illustrates their potential for the immunodiagnostic of diseases due to protein accumulation.

Reduced retinal function in amyloid precursor protein-over-expressing transgenic mice via attenuating glutamate-N-methyl-d-aspartate receptor signaling

Here, we examined whether amyloid-beta (Abeta) protein participates in cell death and retinal function using three types of transgenic (Tg) mice in vivo [human mutant amyloid precursor protein (APP) Tg (Tg 2576) mice, mutant presenilin-1 (PS-1) knock-in mice, and APP/PS-1 double Tg mice]. ELISA revealed that the insoluble form of Abeta(1-40) was markedly accumulated in the retinas of APP and APP/PS-1, but not PS-1 Tg, mice (vs. wild-type mice). In APP Tg and APP/PS-1 Tg mice, immunostaining revealed accumulations of intracellular Abeta(1-42) in retinal ganglion cells and in the inner and outer nuclear layers. APP Tg and APP/PS-1 Tg, but not PS-1 Tg, mice had less NMDA-induced retinal damage than wild-type mice, and the reduced damage in APP/PS-1 Tg mice was diminished by the pre-treatment of N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester, a gamma-secretase inhibitor. Furthermore, the number of TUNEL-positive cells was significantly less in ganglion cell layer of APP/PS-1 Tg mice than PS-1 Tg mice 24 h after NMDA injection. The phosphorylated form of calcium/calmodulin-dependent protein kinase IIalpha (CaMKIIalpha), but not total CaMKIIalpha or total NMDA receptor 1 (NR1) subunit, in total retinal extracts was decreased in non-treated retinas of APP/PS-1 Tg mice (vs. wild-type mice). CaMKIIalpha and NR2B proteins, but not NR1, in retinal membrane fraction were significantly decreased in APP/PS-1 Tg mice as compared with wild-type mice. The NMDA-induced increase in p-CaMKIIalpha in the retina was also lower in APP/PS-1 Tg mice than in wild-type mice. In electroretinogram and visual-evoked potential recordings, the implicit time to each peak from a light stimulus was prolonged in APP/PS-1 mice versus wild-type mice. Hence, Abeta may impair retinal function by reducing activation of NMDA-receptor signaling pathways.

TMP21 regulates Abeta production but does not affect caspase-3, p53, and neprilysin

The presenilin (PS)-dependent gamma-secretase activity refers to a high molecular mass-complex including, besides PS1 or PS2, three other proteins recently identified, namely nicastrin, Aph-1, and Pen-2. This proteolytic complex has been shown to contribute to both gamma- and epsilon-cleavages of the beta-amyloid precursor protein (betaAPP), thereby generating beta-amyloid peptides (Abeta) and the APP intracellular domain (AICD), respectively. TMP21, a member of the p24 cargo protein family, was recently shown to interact with PS complexes. Interestingly, TMP21 modulates gamma-secretase-mediated Abeta production but does not regulate epsilon-secretase-derived AICD formation [F. Chen, H. Hasegawa, G. Schmitt-ulms, T. Kawarai, C. Bohm, T. Katayama, Y. Gu, N. Sanjo, M. Glista, E. Rogaeva, Y. Wakutami, R. Pardossi-Piquard, X. Ruan, A. Tandon, F. Checler, P. Marambaud, K. Hansen, D. Westaway, P. St. George-Hyslop, P. Fraser, TMP21 is a presenilin complex component that modulates gamma- but not epsilon-secretase activities, Nature 440 (2006) 1208-1212]. Here we investigate the functional incidence of the over-expression or depletion of TMP21 on both intracellular and secreted Abeta recoveries and AICD-associated phenotypes. First we confirm that TMP21 depletion yields increased levels of secreted Abeta40. However, we demonstrate that both staurosporine-stimulated caspase-3 activation, p53 and neprilysin expression and activity were not affected by TMP21 over-expression or depletion. Overall, our functional data further reinforce the view that TMP21 behaves as a regulator of gamma- but not epsilon-cleavages generated by PS-dependent gamma-secretase complex.

Analysis of Abeta interactions using ProteinChip technology

Abeta peptides are now acknowledged to play a central role in the pathogenesis of Alzheimer's disease. Their generation results from the sequential cleavage of amyloid precursor protein by beta and gamma secretases. The resulting peptide fragments impart toxicity via their ability to form soluble oligomers and bind to cell membranes. In this chapter we describe the use of ProteinChip technology to study the physicochemical behaviour of Abeta and its mechanisms of toxicity. These include analyzing (1) Abeta processing and quantitation of peptide fragments, (2) Abeta aggregation and the quantitation of oligomers, and (3) Abeta-lipid interactions.

Humoral immune responses to peptides derived from the beta-amyloid peptide C-terminal sequence

There is a continuing interest in the immunochemical quantification of isoforms of amyloid beta-peptide (Abeta) in body fluids of patients with Alzheimer's disease (AD); however, at present there is no general procedure to produce and test the required antibodies. We examined various methods to generate rabbit anti-Abeta; antibodies that are specific for Abeta(38), Abeta(40) and Abeta(42), and we tested their specificity and sensitivity by ELISA and Western blotting. To produce high-affinity antibodies required repeated inoculations of small doses of peptide conjugates over a period of at least 6 months. Antibodies generated to peptides derived from the Abeta(42) sequence showed some cross-reactivity with Abeta(40), but antibodies generated to Abeta4 peptides did not cross-react with Abeta(42). The shortest peptide capable of generating antibodies of moderate affinity possessed the sequence Met(35)-Ala(42); however, antibodies raised to the peptide Gly(33)-Ala(42) possessed the greatest affinity (K(D) = 1 nM) and specificity for Abeta(42). The latter antibodies were over 50,000-fold more reactive with Abeta(42) than with Abeta(40). They can detect Abeta isoforms in extracts of normal brain, where the peptides are present at levels below one part per billion. Our results provide methods to generate and characterize the specificity and affinity of anti-Abeta antibodies. This information is necessary to develop sensitive and specific immunoassays to quantify Abeta isoforms in brain extracts and in body fluids.

Deposition of mouse amyloid β in human APP/PS1 double and single AD model transgenic mice

The deposition of amyloid beta (Abeta) peptides and neurofibrillary tangles are the two characteristic pathological features of Alzheimer's disease (AD). To investigate the relation between amyloid precursor protein (APP) production, amyloid beta deposition and the type of Abeta in deposits, i.e., human and/or mouse, we performed a histopathological analysis, using mouse and human specific antibodies, of the neocortex and hippocampus in 6, 12 and 19 months old APP/PS1 double and APP and PS1 single transgenic mice. There was a significant correlation between the human amyloid beta deposits and the intrinsic rodent amyloid beta deposits, that is, all plaques contained both human and mouse Abeta, and the diffuse amyloid beta deposits also colocalized human and mouse Abeta. Furthermore, some blood vessels (mainly leptomeningeal vessels) show labeling with human Abeta, and most of these vessels also label with mouse Abeta. Our findings demonstrate that the human amyloid deposits in APP/PS1 transgenic mice are closely associated with mouse Abeta, however, they do not precisely overlap. For instance, the core of plaques consists of primarily human Abeta, whereas the rim of the plaque contains both human and mouse amyloid beta, similarly, human and mouse Abeta are differentially localized in the blood vessel wall. Finally, as early as amyloid beta deposits can be detected, they show the presence of both human and mouse Abeta. Together, these data indicate that mouse Abeta is formed and deposited in significant amounts in the AD mouse brain and that it is deposited together with the human Abeta.

A specific amyloid-beta protein assembly in the brain impairs memory

Memory function often declines with age, and is believed to deteriorate initially because of changes in synaptic function rather than loss of neurons. Some individuals then go on to develop Alzheimer's disease with neurodegeneration. Here we use Tg2576 mice, which express a human amyloid-beta precursor protein (APP) variant linked to Alzheimer's disease, to investigate the cause of memory decline in the absence of neurodegeneration or amyloid-beta protein amyloidosis. Young Tg2576 mice (< 6 months old) have normal memory and lack neuropathology, middle-aged mice (6-14 months old) develop memory deficits without neuronal loss, and old mice (> 14 months old) form abundant neuritic plaques containing amyloid-beta (refs 3-6). We found that memory deficits in middle-aged Tg2576 mice are caused by the extracellular accumulation of a 56-kDa soluble amyloid-beta assembly, which we term Abeta*56 (Abeta star 56). Abeta*56 purified from the brains of impaired Tg2576 mice disrupts memory when administered to young rats. We propose that Abeta*56 impairs memory independently of plaques or neuronal loss, and may contribute to cognitive deficits associated with Alzheimer's disease.

APPepsilon, the epsilon-secretase-derived N-terminal product of the beta-amyloid precursor protein, behaves as a type I protein and undergoes alpha-, beta-, and gamma-secretase cleavages

beta-Amyloid peptide accumulates in the brain of patients affected by sporadic or familial forms of Alzheimer's disease. It derives from the proteolytic attacks of the beta-amyloid precursor protein (betaAPP) by beta- and gamma-secretase activities. An additional epsilon cleavage taking place a few residues C-terminal to the gamma-site has been reported, leading to the formation of an intracellular fragment referred to as APP intracellular domain C50. This epsilon cleavage received particular attention because it resembles the S3 Notch cleavage generating Notch intracellular domain. Indeed, APP intracellular domain, like its Notch counterpart, appears to mediate important physiological functions. gamma and epsilon cleavages on betaAPP appear spatio-temporally linked but pharmacologically distinct and discriminable by mutagenesis approaches. As these cleavages could be seen as either deleterious (gamma-site) or beneficial (epsilon-site), it appears of most interest to set up models aimed at studying these activities separately, particularly to design specific and bioavailable inhibitors. On the other hand, it is important to respect the topology of the substrates in order to examine physiologically relevant cleavages. Here we describe the obtention of cells overexpressing APPepsilon, the epsilon-secretase-derived N-terminal fragment of betaAPP. Interestingly, this N-terminal fragment of betaAPP was shown by biochemical and immunohistochemical approaches to behave as a genuine membrane-bound protein. APPepsilon undergoes constitutive and protein kinase C-regulated alpha-secretase cleavages. Furthermore, APPepsilon is targeted by the beta-secretase beta-site APP-cleaving enzyme and is subsequently cleaved by gamma-secretase. The resulting beta-amyloid peptide production is fully prevented by various gamma-secretase inhibitors. Altogether, our study shows that APPepsilon is a relevant betaAPP derivative to study gamma-secretase activities and to design specific inhibitors without facing any rate-limiting effect of epsilon-secretase-derived cleavage.

A presenilin-independent aspartyl protease prefers the gamma-42 site cleavage

beta-Amyloid peptides (Abeta40 and Abeta42) are the major constituents of amyloid plaques, which are one of the hallmarks of Alzheimer's disease (AD). The Abeta is derived from sequential cleavages of amyloid precursor protein (APP) by beta- and gamma-secretases. gamma-Secretase consists of at least four proteins where presenilins (PS1 and PS2 or PS) are the catalytic subunit involved in the gamma-site cleavage of APP. Secretion of both Abeta40 and Abeta42 is significantly reduced in PS1 knock-out cells and completely abolished in cells deficient for both PS1 and PS2. Consequently, both the PS proteins play essential roles in the production of the secretory of Abeta from cells. Recent studies in primary neurons, however, suggest that PSs are not required for intracellular Abeta42 accumulation; thus the intracellular Abeta42 appears to be generated in a PS-independent manner. Here we present the first biochemical evidence indicating that Abeta, especially Abeta42, can be generated in the absence of PS based on an in vitrogamma-secretase assay employing membranes prepared from PS-deficient Blastocyst-derived (BD) cells. This PS-independent gamma-secretase (PSIG) activity is sensitive to the changes in pH and displays an optimal activity at pH 6.0. Pepstatin A is a potent inhibitor for this proteolytic activity with IC50 of 1.2 nm and 0.4 nm for Abeta40 and Abeta42 generation, respectively. These results indicate that these PS-independent gamma-site cleavages are mediated by an aspartyl protease. More importantly, the PSIG activity displays a distinct preference in mediating the 42-site cleavage over the 40-site cleavage, thereby generating Abeta42 as the predominant product.

Resveratrol Promotes Clearance of Alzheimer's Disease Amyloid-β Peptides

Several epidemiological studies indicate that moderate consumption of wine is associated with a lower incidence of Alzheimer's disease. Wine is enriched in antioxidant compounds with potential neuroprotective activities. However, the exact molecular mechanisms involved in the beneficial effects of wine intake on the neurodegenerative process in Alzheimer's disease brain remain to be clearly defined. Here we show that resveratrol (trans-3,4',5-trihydroxystilbene), a naturally occurring polyphenol mainly found in grapes and red wine, markedly lowers the levels of secreted and intracellular amyloid-beta (Abeta) peptides produced from different cell lines. Resveratrol does not inhibit Abeta production, because it has no effect on the Abeta-producing enzymes beta- and gamma-secretases, but promotes instead intracellular degradation of Abeta via a mechanism that involves the proteasome. Indeed, the resveratrol-induced decrease of Abeta could be prevented by several selective proteasome inhibitors and by siRNA-directed silencing of the proteasome subunit beta5. These findings demonstrate a proteasome-dependent anti-amyloidogenic activity of resveratrol and suggest that this natural compound has a therapeutic potential in Alzheimer's disease.

Design and characterization of a new cell-permeant inhibitor of the beta-secretase BACE1

1 The beta-secretase BACE1 is one of the enzymes that contribute to the production of the Abeta peptide, in vitro and in vivo. JMV1195 was previously shown to inhibit BACE activity in vitro but was unable to block cellular BACE activity. We have designed a new permeable inhibitor, JMV2764 that corresponds to a derivative of JMV1195 to which a penetratin sequence had been added at its N-terminus. We have assessed the ability of JMV2764 to affect BACE1 activity in vitro, and to modify Abeta production in various cell systems. 2 Endogenous beta-secretase or BACE1 activities were monitored in vitro by means of two distinct fluorimetric substrates in HEK293 extracts of cells expressing either wild-type betaAPP, Swedish mutated betaAPP or SPA4CT constructs. Abeta40 recovery was monitored by immunoprecipitation and Western blot analysis. 3 JMV2764 and JMV1195 inhibited endogenous beta-secretase activity of HEK293 cellular homogenates with IC(50)s of 0.8 and 6.6 microM, respectively. Interestingly, JMV2764 also inhibited beta-secretase activity after preincubation with intact cells while JMV1195 was inactive, indicating that unlike JMV1195, JMV2764 could penetrate into the cells. 4 JMV2764 but not JMV1195 also prevented Abeta production by HEK293 cells overexpressing wild-type and Swedish-mutated betaAPP. However, JMV2764 was unable to affect Abeta production from cells expressing SPA4CT, a betaAPP-derived sequence that does not need beta-secretase to produce Abeta. 5 Altogether, we have designed a new cell-permeable BACE1 inhibitor that allows to envision to prevent Abeta production in vivo. Work is in progress to assess the potential of these compounds to prevent Abeta production in transgenic mice overproducing Abeta.

Reduced brain tissue perfusion in TGF-β1 transgenic mice showing Alzheimer's disease-like cerebrovascular abnormalities

We have studied the functional repercussions of cerebrovascular abnormalities in transgenic mice overexpressing TGF-beta1. These mice develop Alzheimer's disease-like vascular and meningeal alterations without parenchymal degeneration. Autoradiographic cerebral blood flow measurements in 9-month-old TGF-beta1 mice compared to non-transgenic littermates provided evidence of reduced tissue perfusion, most prominent in limbic regions. A highly significant inverse correlation was found between the density of thioflavin-S-positive blood vessels and blood flow in the hippocampus and the cortex. An inverse correlation was likewise found between meningeal staining and blood flow in thalamic nuclei and regions of high blood flow. Thus, the vascular abnormalities were associated locally with reduced perfusion rate and more widely with limitation in the blood flow. These chronic changes may be related to fibrillar and soluble A beta peptides, the amount of which was almost doubled in the brains of TGF-beta1 mice. Comparison with previous results of cerebral glucose utilization in TGF-beta1 mice shows that reduced utilization preferentially occurred in regions with a high metabolic rate and a relatively low blood flow, suggesting that the metabolic needs are not met by blood supply in these regions.

Acute treatment with the PPARγ agonist pioglitazone and ibuprofen reduces glial inflammation and Aβ1–42 levels in APPV717I transgenic mice

Neuritic plaques in the brain of Alzheimer's disease patients are characterized by beta-amyloid deposits associated with a glia-mediated inflammatory response. Non-steroidal anti-inflammatory drug (NSAID) therapy reduces Alzheimer's disease risk and ameliorates microglial reactivity in Alzheimer's disease brains; however, the molecular mechanisms subserving this effect are not yet clear. Since several NSAIDs bind to and activate the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) which acts to inhibit the expression of proinflammatory genes, this receptor appears a good candidate to mediate the observed anti-inflammatory effects. Recent data in vitro suggested that NSAIDs negatively regulate microglial activation and immunostimulated amyloid precursor protein processing via PPARgamma activation. We report that an acute 7 day oral treatment of 10-month-old APPV717I mice with the PPARgamma agonist pioglitazone or the NSAID ibuprofen resulted in a reduction in the number of activated microglia and reactive astrocytes in the hippocampus and cortex. Drug treatment reduced the expression of the proinflammatory enzymes cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS). In parallel to the suppression of inflammatory markers, pioglitazone and ibuprofen treatment decreased beta-secretase-1 (BACE1) mRNA and protein levels. Importantly, we observed a significant reduction of the total area and staining intensity of Abeta1-42-positive amyloid deposits in the hippocampus and cortex. Additionally, animals treated with pioglitazone revealed a 27% reduction in the levels of soluble Abeta1-42 peptide. These findings demonstrate that anti-inflammatory drugs can act rapidly to inhibit inflammatory responses in the brain and negatively modulate amyloidogenesis.

Subcellular topography of neuronal Abeta peptide in APPxPS1 transgenic mice

In transgenic mice expressing human mutant beta-amyloid precursor protein (APP) and mutant presenilin-1 (PS1), Abeta antibodies labeled granules, about 1 microm in diameter, in the perikaryon of neurons clustered in the isocortex, hippocampus, amygdala, thalamus, and brainstem. The granules were present before the onset of Abeta deposits; their number increased up to 9 months and decreased in 15-month-old animals. They were immunostained by antibodies against Abeta 40, Abeta 42, and APP C-terminal region. In double immunofluorescence experiments, the intracellular Abeta co-localized with lysosome markers and less frequently with MG160, a Golgi marker. Abeta accumulation correlated with an increased volume of lysosomes and Golgi apparatus, while the volume of endoplasmic reticulum and early endosomes did not change. Some granules were immunolabeled with an antibody against flotillin-1, a raft marker. At electron microscopy, Abeta, APP-C terminal, cathepsin D, and flotillin-1 epitopes were found in the lumen of multivesicular bodies. This study shows that Abeta peptide and APP C-terminal region accumulate in multivesicular bodies containing lysosomal enzymes, while APP N-terminus is excluded from them. Multivesicular bodies could secondarily liberate their content in the extracellular space as suggested by the association of cathepsin D with Abeta peptide in the extracellular space.

A disintegrin-metalloproteinase prevents amyloid plaque formation and hippocampal defects in an Alzheimer disease mouse model

Alzheimer disease (AD) is characterized by excessive deposition of amyloid beta-peptides (A beta peptides) in the brain. In the nonamyloidogenic pathway, the amyloid precursor protein (APP) is cleaved by the alpha-secretase within the A beta peptide sequence. Proteinases of the ADAM family (adisintegrin and metalloproteinase) are the main candidates as physiologically relevant alpha-secretases, but early lethality of knockout animals prevented a detailed analysis in neuronal cells. To overcome this restriction, we have generated transgenic mice that overexpress either ADAM10 or a catalytically inactive ADAM10 mutant. In this report we show that a moderate neuronal overexpression of ADAM10 in mice transgenic for human APP([V717I]) increased the secretion of the neurotrophic soluble alpha-secretase-released N-terminal APP domain (APPs alpha), reduced the formation of A beta peptides, and prevented their deposition in plaques. Functionally, impaired long-term potentiation and cognitive deficits were alleviated. Expression of mutant catalytically inactive ADAM10 led to an enhancement of the number and size of amyloid plaques in the brains of double-transgenic mice. The results provide the first in vivo evidence for a proteinase of the ADAM family as an alpha-secretase of APP, reveal activation of ADAM10 as a promising therapeutic target, and support the hypothesis that a decrease in alpha-secretase activity contributes to the development of AD.

Modulation of β-amyloid metabolism by non-steroidal anti-inflammatory drugs in neuronal cell cultures

Alzheimer disease (AD) is characterized by cerebral deposits of beta-amyloid (Abeta) peptides, which are surrounded by neuroinflammatory cells. Epidemiological studies have shown that prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs) reduces the risk of developing AD. In addition, biological data indicate that certain NSAIDs specifically lower Abeta42 levels in cultures of peripheral cells independently of cyclooxygenase (COX) activity and reduce cerebral Abeta levels in AD transgenic mice. Whether other NSAIDs, including COX-selective compounds, modulate Abeta levels in neuronal cells remains unexploited. Here, we investigated the effects of compounds from every chemical class of NSAIDs on Abeta40 and Abeta42 secretion using both Neuro-2a cells and rat primary cortical neurons. Among non-selective NSAIDs, flurbiprofen and sulindac sulfide concentration-dependently reduced the secretion not only of Abeta42 but also of Abeta40. Surprisingly, both COX-2 (celecoxib; sc-125) or COX-1 (sc-560) selective compounds significantly increased Abeta42 secretion, and either did not alter (sc-560; sc-125) or reduced (celecoxib) Abeta40 levels. The levels of betaAPP C-terminal fragments and Notch cleavage were not altered by any of the NSAIDs, indicating that gamma-secretase activity was not overall changed by these drugs. The present findings show that only a few non-selective NSAIDs possess Abeta-lowering properties and therefore have a profile potentially relevant to their clinical use in AD.

JLK isocoumarin inhibitors: Selective ?-secretase inhibitors that do not interfere with notch pathway in vitro or in vivo

gamma-Secretase activity is involved in the generation of Abeta and therefore likely contributes to the pathology of Alzheimer's disease. Blocking this activity was seen as a major therapeutic target to slow down or arrest Abeta-related AD progression. This strategy seemed more doubtful when it was established that gamma-secretase also targets other substrates including Notch, a particularly important transmembrane protein involved in vital functions, at both embryonic and adulthood stages. We have described previously new non-peptidic inhibitors able to selectively inhibit Abeta cellular production in vitro without altering Notch pathway. We show here that in vivo, these inhibitors do not alter the Notch pathway responsible for somitogenesis in the zebrafish embryo. In addition, we document further the selectivity of JLK inhibitors by showing that, unlike other described gamma-secretase inhibitors, these agents do not affect E-cadherin processing. Finally, we establish that JLKs do not inhibit beta-site APP cleaving enzymes (BACE) 1 and BACE2, alpha-secretase, the proteasome, and GSK3beta kinase. Altogether, JLK inhibitors are the sole agents to date that are able to prevent Abeta production without triggering unwanted cleavages of other proteins.