Alzheimer's disease-type neuronal tau hyperphosphorylation induced by A beta oligomers

Amyloid-β oligomers induce differential gene expression in adult human brain slices

Cognitive decline in Alzheimer disease (AD) is increasingly attributed to the neuronal impact of soluble oligomers of the amyloid-β peptide (AβOs). Current knowledge on the molecular and cellular mechanisms underlying the toxicity of AβOs stems largely from rodent-derived cell/tissue culture experiments or from transgenic models of AD, which do not necessarily recapitulate the complexity of the human disease. Here, we used DNA microarray and RT-PCR to investigate changes in transcription in adult human cortical slices exposed to sublethal doses of AβOs. The results revealed a set of 27 genes that showed consistent differential expression upon exposure of slices from three different donors to AβOs. Functional classification of differentially expressed genes revealed that AβOs impact pathways important for neuronal physiology and known to be dysregulated in AD, including vesicle trafficking, cell adhesion, actin cytoskeleton dynamics, and insulin signaling. Most genes (70%) were down-regulated by AβO treatment, suggesting a predominantly inhibitory effect on the corresponding pathways. Significantly, AβOs induced down-regulation of synaptophysin, a presynaptic vesicle membrane protein, suggesting a mechanism by which oligomers cause synapse failure. The results provide insight into early mechanisms of pathogenesis of AD and suggest that the neuronal pathways affected by AβOs may be targets for the development of novel diagnostic or therapeutic approaches.

Alzheimer's disease and amyloid: culprit or coincidence?

Alzheimer's disease (AD) is the largest unmet medical need in neurology today. This most common form of irreversible dementia is placing a considerable and increasing burden on patients, caregivers, and society, as more people live long enough to become affected. Current drugs improve symptoms but do not have profound neuroprotective and/or disease-modifying effects. AD is characterized by loss of neurons, dystrophic neurites, senile/amyloid/neuritic plaques, neurofibrillary tangles, and synaptic loss. Beta-amyloid (Aβ) peptide deposition is the major pathological feature of AD. Increasing evidence suggests that overexpression of the amyloid precursor protein and subsequent generation of the 39-43 amino acid residue, Aβ, are central to neuronal degeneration observed in AD patients possessing familial AD mutations, while transgenic mice overexpressing amyloid precursor protein develop AD-like pathology. Despite the genetic and cell biological evidence that supports the amyloid hypothesis, it is becoming increasing clear that AD etiology is complex and that Aβ alone is unable to account for all aspects of AD. The fact that vast overproduction of Aβ peptides in the brain of transgenic mouse models fails to cause overt neurodegeneration raises the question as to whether accumulation of Aβ peptides is indeed the culprit for neurodegeneration in AD. There is increasing evidence to suggest that Aβ/amyloid-independent factors, including the actions of AD-related genes (microtubule-associated protein tau, polymorphisms of apolipoprotein E4), inflammation, and oxidative stress, also contribute to AD pathogenesis. This chapter reviews the current state of knowledge on these factors and their possible interactions, as well as their potential for neuroprotection targets.

Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer's mice hippocampus

Dystrophic neurites associated with amyloid plaques precede neuronal death and manifest early in Alzheimer's disease (AD). In this work we have characterized the plaque-associated neuritic pathology in the hippocampus of young (4- to 6-month-old) PS1(M146L)/APP(751SL) mice model, as the initial degenerative process underlying functional disturbance prior to neuronal loss. Neuritic plaques accounted for almost all fibrillar deposits and an axonal origin of the dystrophies was demonstrated. The early induction of autophagy pathology was evidenced by increased protein levels of the autophagosome marker LC3 that was localized in the axonal dystrophies, and by electron microscopic identification of numerous autophagic vesicles filling and causing the axonal swellings. Early neuritic cytoskeletal defects determined by the presence of phosphorylated tau (AT8-positive) and actin-cofilin rods along with decreased levels of kinesin-1 and dynein motor proteins could be responsible for this extensive vesicle accumulation within dystrophic neurites. Although microsomal Aβ oligomers were identified, the presence of A11-immunopositive Aβ plaques also suggested a direct role of plaque-associated Aβ oligomers in defective axonal transport and disease progression. Most importantly, presynaptic terminals morphologically disrupted by abnormal autophagic vesicle buildup were identified ultrastructurally and further supported by synaptosome isolation. Finally, these early abnormalities in axonal and presynaptic structures might represent the morphological substrate of hippocampal dysfunction preceding synaptic and neuronal loss and could significantly contribute to AD pathology in the preclinical stages.

GSK3β is involved in the relief of mitochondria pausing in a Tau-dependent manner

Mitochondrial trafficking deficits have been implicated in the pathogenesis of several neurological diseases, including Alzheimer's disease (AD). The Ser/Thre kinase GSK3β is believed to play a fundamental role in AD pathogenesis. Given that GSK3β substrates include Tau protein, here we studied the impact of GSK3β on mitochondrial trafficking and its dependence on Tau protein. Overexpression of GSK3β in neurons resulted in an increase in motile mitochondria, whereas a decrease in the activity of this kinase produced an increase in mitochondria pausing. These effects were dependent on Tau proteins, as Tau (−/−) neurons did not respond to distinct GSK3β levels. Furthermore, differences in GSK3β expression did not affect other parameters like mitochondria velocity or mitochondria run length. We conclude that GSK3B activity regulates mitochondrial axonal trafficking largely in a Tau-dependent manner.

The Aβ oligomer hypothesis for synapse failure and memory loss in Alzheimer's disease

Alzheimer's disease (AD) is the 3rd most costly disease and the leading cause of dementia. It can linger for many years, but ultimately is fatal, the 6th leading cause of death. Alzheimer's disease (AD) is fatal and affected individuals can sometimes linger many years. Current treatments are palliative and transient, not disease modifying. This article reviews progress in the search to identify the primary AD-causing toxins. We summarize the shift from an initial focus on amyloid plaques to the contemporary concept that AD memory failure is caused by small soluble oligomers of the Aβ peptide, toxins that target and disrupt particular synapses. Evidence is presented that links Aβ oligomers to pathogenesis in animal models and humans, with reference to seminal discoveries from cell biology and new ideas concerning pathogenic mechanisms, including relationships to diabetes and Fragile X. These findings have established the oligomer hypothesis as a new molecular basis for the cause, diagnosis, and treatment of AD.

Interaction between α-synuclein and other proteins in neurodegenerative disorders

Protein aggregation is a common characteristic of many neurodegenerative disorders, and the interaction between pathological/toxic proteins to cause neurodegeneration is a hot topic of current neuroscience research. Despite clinical, genetic, and experimental differences, evidence increasingly indicates considerable overlap between synucleinopathies and tauopathies or other protein-misfolding diseases. Inclusions, characteristics of these disorders, also occurring in other neurodegenerative diseases, suggest interactions of pathological proteins engaging common downstream pathways. Novel findings that have shifted our understanding in the role of pathologic proteins in the pathogenesis of Parkinson and Alzheimer diseases have confirmed correlations/overlaps between these and other neurodegenerative disorders. The synergistic effects of α-synuclein, hyperphosphorylated tau, amyloid-β, and other pathologic proteins, and the underlying molecular pathogenic mechanisms, including induction and spread of protein aggregates, are critically reviewed, suggesting a dualism or triad of neurodegeneration in protein-misfolding disorders, although the etiology of most of these processes is still mysterious.

The modulating effect of mechanical changes in lipid bilayers caused by apoE-containing lipoproteins on Aβ induced membrane disruption

A major feature of Alzheimer's disease (AD), a late-onset neurodegenerative disorder, is the ordered aggregation of the β-amyloid peptide (Aβ) into fibrils that comprise extracellular neuritic plaques found in the disease brain. One of many potential pathways for Aβ toxicity may be modulation of lipid membrane function. Here, we show by in situ atomic force microscopy (AFM) that astrocyte secreted lipoprotein particles (ASLPs) containing different isoforms of apolipoprotein E (apoE), of which the apoE4 allele is a major risk factor for the development of AD, can protect total brain lipid extract bilayers from Aβ(1-40) induced disruption. The apoE4 allele was less effective in protecting lipid bilayers from disruption compared with apoE3. Size analysis of apoE-containing ASLPs and mechanical studies of bilayer properties revealed that apoE-containing ASLPs modulate the mechanical properties of bilayers by acquiring some bilayer components (most likely cholesterol and/or oxidatively damaged lipids). Measurement of bilayer mechanical properties was accomplished with scanning probe acceleration microscopy (SPAM). These measurements demonstrated that apoE4 was also less effective in modulating mechanical properties of bilayers in comparison with apoE3. This ability of apoE to alter the mechanical properties of lipid membranes may represent a potential mechanism for the suppression of Aβ(1-40) induced bilayer disruption.

Sinomenine inhibits microglial activation by Aβ and confers neuroprotection

Background

Neuroinflammation is an important contributor to the development of neurodegenerative diseases, including Alzheimer's disease. Thus, there is a keen interest in identifying compounds, especially from herbal sources, that can inhibit neuroinflammation. Amyloid-β (Aβ) is a major component of the amyloid plaques present in the brains of Alzheimer's disease patients. Here, we examined whether sinomenine, present in a Chinese medicinal plant, prevents oligomeric Aβ-induced microglial activation and confers protection against neurotoxicity.

Methods

Oligomeric amyloid-β was prepared from Aβ(1-42). Intracellular reactive oxygen species production was determined using the dye 2',7'-dichlorodihydrofluorescin diacetate. Nitric oxide level was assessed using the Griess reagent. Flow cytometry was used to examine the levels of inflammatory molecules. BV2-conditioned medium was used to treat hippocampal cell line (HT22) and primary hippocampal cells in indirect toxicity experiments. Toxicity was assessed using MTT reduction and TUNEL assays.

Results

We found that sinomenine prevents the oligomeric Aβ-induced increase in levels of reactive oxygen species and nitric oxide in BV2 microglial cells. In addition, sinomenine reduces levels of Aβ-induced inflammatory molecules. Furthermore, sinomenine protects hippocampal HT22 cells as well as primary hippocampal cells from indirect toxicity mediated by Aβ-treated microglial cells, but has no effect on Aβ-induced direct toxicity to HT22 cells. Finally, we found that conditioned medium from Aβ-treated BV2 cells contains increased levels of nitric oxide and inflammatory molecules, but the levels of these molecules are reduced by sinomenine.

Conclusions

Sinomenine prevents oligomeric Aβ-induced microglial activation, and confers protection against indirect neurotoxicity to hippocampal cells. These results raise the possibility that sinomenine may have therapeutic potential for the treatment of Alzheimer's diseases as well as other diseases that involve neuroinflammation.

Possible implications of insulin resistance and glucose metabolism in Alzheimer's disease pathogenesis

Type 2 diabetes mellitus (DM) appears to be a significant risk factor for Alzheimer disease (AD). Insulin and insulin-like growth factor-1 (IGF-1) also have intense effects in the central nervous system (CNS), regulating key processes such as neuronal survival and longevity, as well as learning and memory. Hyperglycaemia induces increased peripheral utilization of insulin, resulting in reduced insulin transport into the brain. Whereas the density of brain insulin receptor decreases during age, IGF-1 receptor increases, suggesting that specific insulin-mediated signals is involved in aging and possibly in cognitive decline. Molecular mechanisms that protect CNS neurons against β-amyloid-derived-diffusible ligands (ADDL), responsible for synaptic deterioration underlying AD memory failure, have been identified. The protection mechanism does not involve simple competition between ADDLs and insulin, but rather it is signalling dependent down-regulation of ADDL-binding sites. Defective insulin signalling make neurons energy deficient and vulnerable to oxidizing or other metabolic insults and impairs synaptic plasticity. In fact, destruction of mitochondria, by oxidation of a dynamic-like transporter protein, may cause synapse loss in AD. Moreover, interaction between Aβ and τ proteins could be cause of neuronal loss. Hyperinsulinaemia as well as complete lack of insulin result in increased τ phosphorylation, leading to an imbalance of insulin-regulated τ kinases and phosphatates. However, amyloid peptides accumulation is currently seen as a key step in the pathogenesis of AD. Inflammation interacts with processing and deposit of β-amyloid. Chronic hyperinsulinemia may exacerbate inflammatory responses and increase markers of oxidative stress. In addition, insulin appears to act as 'neuromodulator', influencing release and reuptake of neurotransmitters, and improving learning and memory. Thus, experimental and clinical evidence show that insulin action influences cerebral functions. In this paper, we reviewed several mechanisms by which insulin may affect pathophysiology in AD.

13-Desmethyl spirolide-C is neuroprotective and reduces intracellular Aβ and hyperphosphorylated tau in vitro

Spirolides are marine compounds of the cyclic imine group. Although the mechanism of action is not fully elucidated yet, cholinergic (muscarinic and nicotinic) receptors have been proposed as the main targets of these toxins. In this study we examined the effect of 13-desmethyl spirolide-C (SPX) on amyloid-beta (Aβ) accumulation and tau hyperphosphorylation in a neuronal model from triple transgenic mice (3xTg) for Alzheimer disease (AD). In vitro treatment of 3xTg cortical neurons with SPX reduced intracellular Aβ accumulation and the levels of phosphorylated tau. SPX treatment did not affect the steady-state levels of neither the M1 and M2 muscarinic nor the α7 nicotinic acetylcholine receptors (AChRs), while it decreased the amplitude of acetylcholine-evoked responses and increased ACh (acetylcholine) levels in 3xTg neurons. Additionally, SPX treatment decreased the levels of two protein kinases involved in tau phosphorylation, glycogen synthase kinase 3β (GSK-3β) and extracellular-regulated kinase (ERK). Also SPX abolished the glutamate-induced neurotoxicity in both control and 3xTg neurons. The results presented here constitute the first report indicating that exposure of 3xTg neurons to nontoxic concentrations of SPX produces a simultaneous reduction in the main pathological characteristics of AD. In spite of the few reports analyzing the mode of action of the toxin we suggest that SPX could ameliorate AD pathology increasing the intracellular ACh levels and simultaneously diminishing the levels of kinases involved in tau phosphorylation.

A glycine zipper motif mediates the formation of toxic β-amyloid oligomers in vitro and in vivo

Background

The β-amyloid peptide (Aβ) contains a Gly-XXX-Gly-XXX-Gly motif in its C-terminal region that has been proposed to form a "glycine zipper" that drives the formation of toxic Aβ oligomers. We have tested this hypothesis by examining the toxicity of Aβ variants containing substitutions in this motif using a neuronal cell line, primary neurons, and a transgenic C. elegans model.

Results

We found that a Gly37Leu substitution dramatically reduced Aβ toxicity in all models tested, as measured by cell dysfunction, cell death, synaptic alteration, or tau phosphorylation. We also demonstrated in multiple models that Aβ Gly37Leu is actually anti-toxic, thereby supporting the hypothesis that interference with glycine zipper formation blocks assembly of toxic Aβ oligomers. To test this model rigorously, we engineered second site substitutions in Aβ predicted by the glycine zipper model to compensate for the Gly37Leu substitution and expressed these in C. elegans. We show that these second site substitutions restore in vivo Aβtoxicity, further supporting the glycine zipper model.

Conclusions

Our structure/function studies support the view that the glycine zipper motif present in the C-terminal portion of Aβ plays an important role in the formation of toxic Aβ oligomers. Compounds designed to interfere specifically with formation of the glycine zipper could have therapeutic potential.

The many faces of tau

While the microtubule-binding capacity of the protein tau has been known for many years, new functions of tau in signaling and cytoskeletal organization have recently emerged. In this review, we highlight these functions and the potential roles of tau in neurodegenerative disease. We also discuss the therapeutic potential of drugs targeting various aspects of tau biology.

Rat hippocampal proteomic alterations following intrahippocampal injection of amyloid beta peptide (1-40)

Amyloid beta peptide 1-40 (Aβ(1-40)) is closely associated with the progressive neuronal loss and cognitive decline observed in Alzheimer's disease (AD). This study aimed to establish a proteomic strategy for the profiling of AD tissues for disease-specific changes in protein abundance. Intrahippocampal injection of Aβ(1-40) induced spatial memory and learning decline in rats. Proteomic analysis revealed the changes in protein expression in the rat hippocampus treated with Aβ(1-40). Four proteins of interest which was in abundance was significantly altered in Aβ(1-40)-treated rats were identified by peptide mass fingerprint (PMF). These proteins corresponded to synapsin Ib, protein disulfide-isomerase A3 precursor, tubulin β chain and ATP synthase β subunit. Our results provide new insights into the relationship between Aβ and the pathogenesis of AD, and suggest potential targets for the therapy of AD.

Age-dependent accumulation of soluble amyloid beta (Abeta) oligomers reverses the neuroprotective effect of soluble amyloid precursor protein-alpha (sAPP(alpha)) by modulating phosphatidylinositol 3-kinase (PI3K)/Akt-GSK-3beta pathway in Alzheimer mouse model

Neurotrophins, activating the PI3K/Akt signaling pathway, control neuronal survival and plasticity. Alterations in NGF, BDNF, IGF-1, or insulin signaling are implicated in the pathogenesis of Alzheimer disease. We have previously characterized a bigenic PS1×APP transgenic mouse displaying early hippocampal Aβ deposition (3 to 4 months) but late (17 to 18 months) neurodegeneration of pyramidal cells, paralleled to the accumulation of soluble Aβ oligomers. We hypothesized that PI3K/Akt/GSK-3β signaling pathway could be involved in this apparent age-dependent neuroprotective/neurodegenerative status. In fact, our data demonstrated that, as compared with age-matched nontransgenic controls, the Ser-9 phosphorylation of GSK-3β was increased in the 6-month PS1×APP hippocampus, whereas in aged PS1×APP animals (18 months), GSK-3β phosphorylation levels displayed a marked decrease. Using N2a and primary neuronal cell cultures, we demonstrated that soluble amyloid precursor protein-α (sAPPα), the predominant APP-derived fragment in young PS1×APP mice, acting through IGF-1 and/or insulin receptors, activated the PI3K/Akt pathway, phosphorylated the GSK-3β activity, and in consequence, exerted a neuroprotective action. On the contrary, several oligomeric Aβ forms, present in the soluble fractions of aged PS1×APP mice, inhibited the induced phosphorylation of Akt/GSK-3β and decreased the neuronal survival. Furthermore, synthetic Aβ oligomers blocked the effect mediated by different neurotrophins (NGF, BDNF, insulin, and IGF-1) and sAPPα, displaying high selectivity for NGF. In conclusion, the age-dependent appearance of APP-derived soluble factors modulated the PI3K/Akt/GSK-3β signaling pathway through the major neurotrophin receptors. sAPPα stimulated and Aβ oligomers blocked the prosurvival signaling. Our data might provide insights into the selective vulnerability of specific neuronal groups in Alzheimer disease.

Tg2576 cortical neurons that express human Ab are susceptible to extracellular Aβ-induced, K+ efflux dependent neurodegeneration

Background

One of the key pathological features of AD is the formation of insoluble amyloid plaques. The major constituent of these extracellular plaques is the beta-amyloid peptide (Aβ), although Aβ is also found to accumulate intraneuronally in AD. Due to the slowly progressive nature of the disease, it is likely that neurons are exposed to sublethal concentrations of both intracellular and extracellular Aβ for extended periods of time.

Results

In this study, we report that daily exposure to a sublethal concentration of Aβ_1-40 (1 µM) for six days induces substantial apoptosis of cortical neurons cultured from Tg2576 mice (which express substantial but sublethal levels of intracellular Aβ). Notably, untreated Tg2576 neurons of similar age did not display any signs of apoptosis, indicating that the level of intracellular Aβ present in these neurons was not the cause of toxicity. Furthermore, wildtype neurons did not become apoptotic under the same chronic Aβ_1-40 treatment. We found that this apoptosis was linked to Tg2576 neurons being unable to maintain K⁺ homeostasis following Aβ treatment. Furthermore, blocking K⁺ efflux protected Tg2576 neurons from Aβ-induced neurotoxicity. Interestingly, chronic exposure to 1 µM Aβ_1-40 caused the generation of axonal swellings in Tg2576 neurons that contained dense concentrations of hyperphosphorylated tau. These were not observed in wildtype neurons under the same treatment conditions.

Conclusions

Our data suggest that when neurons are chronically exposed to sublethal levels of both intra- and extra-cellular Aβ, this causes a K⁺-dependent neurodegeneration that has pathological characteristics similar to AD.

Soluble amyloid beta-protein dimers isolated from Alzheimer cortex directly induce Tau hyperphosphorylation and neuritic degeneration

Alzheimer disease is a major cause of cognitive failure, and a pathogenically related but more subtle process accounts for many cases of mild memory symptoms in older humans. Insoluble fibrillar plaques of amyloid β-proteins (Aβ) and neurofibrillary deposits of hyperphosphorylated tau proteins are the diagnostic lesions of AD, but their temporal mechanistic relationship has long been debated. The recent recognition that small, diffusible oligomers may be the principal bioactive form of Aβ raises the key question of whether these are sufficient to initiate cytoskeletal change and neurite degeneration. A few studies have examined the effects of oligomers of synthetic Aβ peptides of one defined length at supraphysiological concentrations, but the existence of such assemblies in the AD brain is not established. Here, we isolated Aβ dimers, the most abundant form of soluble oligomer detectable in the human brain, from the cortices of typical AD subjects and found that at subnanomolar concentrations, they first induced hyperphosphorylation of tau at AD-relevant epitopes in hippocampal neurons and then disrupted the microtubule cytoskeleton and caused neuritic degeneration, all in the absence of amyloid fibrils. Application of pure, synthetic dimers confirmed the effects of the natural AD dimers, although the former were far less potent. Knocking down endogenous tau fully prevented the neuritic changes, whereas overexpressing human tau accelerated them. Coadministering Aβ N-terminal antibodies neutralized the cytoskeletal disruption. We conclude that natural dimers isolated from the AD brain are sufficient to potently induce AD-type tau phosphorylation and then neuritic dystrophy, but passive immunotherapy mitigates this.

Amyloid β-peptide oligomers stimulate RyR-mediated Ca2+ release inducing mitochondrial fragmentation in hippocampal neurons and prevent RyR-mediated dendritic spine remodeling produced by BDNF

Soluble amyloid β-peptide oligomers (AβOs), increasingly recognized as causative agents of Alzheimer's disease (AD), disrupt neuronal Ca(2+) homeostasis and synaptic function. Here, we report that AβOs at sublethal concentrations generate prolonged Ca(2+) signals in primary hippocampal neurons; incubation in Ca(2+)-free solutions, inhibition of ryanodine receptors (RyRs) or N-methyl-d-aspartate receptors (NMDARs), or preincubation with N-acetyl-l-cysteine abolished these signals. AβOs decreased (6 h) RyR2 and RyR3 mRNA and RyR2 protein, and promoted mitochondrial fragmentation after 24 h. NMDAR inhibition abolished the RyR2 decrease, whereas RyR inhibition prevented significantly the RyR2 protein decrease and mitochondrial fragmentation induced by AβOs. Incubation with AβOs (6 h) eliminated the RyR2 increase induced by brain-derived nerve factor (BDNF) and the dendritic spine remodeling induced within minutes by BDNF or the RyR agonist caffeine. Addition of BDNF to neurons incubated with AβOs for 24 h, which had RyR2 similar to and slightly higher RyR3 protein content than those of controls, induced dendritic spine growth but at slower rates than in controls. These combined effects of sublethal AβOs concentrations (which include redox-sensitive stimulation of RyR-mediated Ca(2+) release, decreased RyR2 protein expression, mitochondrial fragmentation, and prevention of RyR-mediated spine remodeling) may contribute to impairing the synaptic plasticity in AD.

Transformation of amyloid β(1-40) oligomers into fibrils is characterized by a major change in secondary structure

Alzheimer's disease (AD) is a neurodegenerative disorder occurring in the elderly. It is widely accepted that the amyloid beta peptide (Aβ) aggregation and especially the oligomeric states rather than fibrils are involved in AD onset. We used infrared spectroscopy to provide structural information on the entire aggregation pathway of Aβ(1-40), starting from monomeric Aβ to the end of the process, fibrils. Our structural study suggests that conversion of oligomers into fibrils results from a transition from antiparallel to parallel β-sheet. These structural changes are described in terms of H-bonding rupture/formation, β-strands reorientation and β-sheet elongation. As antiparallel β-sheet structure is also observed for other amyloidogenic proteins forming oligomers, reorganization of the β-sheet implicating a reorientation of β-strands could be a generic mechanism determining the kinetics of protein misfolding. Elucidation of the process driving aggregation, including structural transitions, could be essential in a search for therapies inhibiting aggregation or disrupting aggregates.

Novel insights for the treatment of Alzheimer's disease

The development of treatments for Alzheimer's disease (AD) is currently shifting away from the correction of neurotransmitter abnormalities and from attempts to remove the pathognomonic protein deposits. Drug discovery is heading towards novel types of pharmacological interventions which are aimed at more central and upstream pathophysiological events. The large number of upcoming treatment targets can be grouped into two major categories. The first category consists of antecedents of beta amyloid peptide (Aβ) and TAU deposition including Aβ production, degradation and clearance, TAU hyperphosphorylation and aggregation. The second consists of protectors against neuronal dysfunction and premature death such as mitochondrial functioning, nerve growth and regeneration, and neuronal membrane integrity. It is hoped that some of these strategies will not only have larger symptomatic effects than the currently available drugs but also an impact on the underlying neurodegeneration. Since the novel treatments will be typically administered over years they must meet high standards of safety, drug-drug compatibility, and tolerability. Probably the most important target groups for novel treatments are carriers of mutations causing AD, and individuals with minor cognitive impairment representing a pre-dementia stage of the disease. To minimise incorrect case identifications, drug development must be paralleled by improved diagnostic techniques. Novel pharmacological strategies may be cost-effective if disability and need of full-time care can be postponed or prevented without prolonging time lived with dementia or extending survival. We are uncertain whether the advent of novel disease-retarding strategies will revolutionise the management of AD. Symptomatic treatments will continue to be needed, and psychosocial approaches will retain an essential role in supporting affected individuals and their families.

Widespread distribution of reticulon-3 in various neurodegenerative diseases

Reticulons are a group of membrane-bound proteins involved in diverse cellular functions, and are suggested to act as inhibitors of β-secretase enzyme 1 (BACE1) activity that cleaves amyloid precursor protein. Reticulons are known to accumulate in the dystrophic neurites of Alzheimer's disease (AD), and studies have suggested that alterations in reticulons, such as increased aggregation, impair BACE1 binding, increasing amyloid-β production, and facilitating reticulon deposition in dystrophic neurites. To further characterize the cellular distribution of reticulon, we examined reticulon-3 expression in cases of AD, Parkinson's disease, and diffuse Lewy body disease. A more widespread cellular distribution of reticulon-3 was noted than in previous reports, including deposits in dystrophic neurites, neuropil threads, granulovacuolar degeneration, glial cells, morphologically normal neurons in both hippocampal pyramidal cell layer and cerebral neocortex, and specifically neurofibrillary tangles and Lewy bodies. These results are compatible with reticulon alterations as nonspecific downstream stress responses, consistent with its expression during periods of endoplasmic reticulum stress. This emphasizes the increasing recognition that much of the AD pathological spectrum represents a response to the disease rather than cause, and emphasizes the importance of examining upstream processes, such as oxidative stress, that have functional effects prior to the onset of structural alterations.

Point mutations in Aβ result in the formation of distinct polymorphic aggregates in the presence of lipid bilayers

A hallmark of Alzheimer's disease (AD) is the rearrangement of the β-amyloid (Aβ) peptide to a non-native conformation that promotes the formation of toxic, nanoscale aggregates. Recent studies have pointed to the role of sample preparation in creating polymorphic fibrillar species. One of many potential pathways for Aβ toxicity may be modulation of lipid membrane function on cellular surfaces. There are several mutations clustered around the central hydrophobic core of Aβ near the α-secretase cleavage site (E22G Arctic mutation, E22K Italian mutation, D23N Iowa mutation, and A21G Flemish mutation). These point mutations are associated with hereditary diseases ranging from almost pure cerebral amyloid angiopathy (CAA) to typical Alzheimer's disease pathology with plaques and tangles. We investigated how these point mutations alter Aβ aggregation in the presence of supported lipid membranes comprised of total brain lipid extract. Brain lipid extract bilayers were used as a physiologically relevant model of a neuronal cell surface. Intact lipid bilayers were exposed to predominantly monomeric preparations of Wild Type or different mutant forms of Aβ, and atomic force microscopy was used to monitor aggregate formation and morphology as well as bilayer integrity over a 12 hour period. The goal of this study was to determine how point mutations in Aβ, which alter peptide charge and hydrophobic character, influence interactions between Aβ and the lipid surface. While fibril morphology did not appear to be significantly altered when mutants were prepped similarly and incubated under free solution conditions, aggregation in the lipid membranes resulted in a variety of polymorphic aggregates in a mutation dependent manner. The mutant peptides also had a variable ability to disrupt bilayer integrity.

Amyloid-β triggers the release of neuronal hexokinase 1 from mitochondria

Brain accumulation of the amyloid-β peptide (Aβ) and oxidative stress underlie neuronal dysfunction and memory loss in Alzheimer's disease (AD). Hexokinase (HK), a key glycolytic enzyme, plays important pro-survival roles, reducing mitochondrial reactive oxygen species (ROS) generation and preventing apoptosis in neurons and other cell types. Brain isozyme HKI is mainly associated with mitochondria and HK release from mitochondria causes a significant decrease in enzyme activity and triggers oxidative damage. We here investigated the relationship between Aβ-induced oxidative stress and HK activity. We found that Aβ triggered HKI detachment from mitochondria decreasing HKI activity in cortical neurons. Aβ oligomers further impair energy metabolism by decreasing neuronal ATP levels. Aβ-induced HKI cellular redistribution was accompanied by excessive ROS generation and neuronal death. 2-deoxyglucose blocked Aβ-induced oxidative stress and neuronal death. Results suggest that Aβ-induced cellular redistribution and inactivation of neuronal HKI play important roles in oxidative stress and neurodegeneration in AD.

Atorvastatin and pitavastatin improve cognitive function and reduce senile plaque and phosphorylated tau in aged APP mice

In addition to simply reducing the serum level of cholesterol, 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have various pleiotrophic effects such as reducing oxidative stress, neuroinflammation, and neurotoxicity. However, such a pleiotrophic effect has not been fully studied in a new statin (pitavastatin). We examined and compared the effects of two strong statins (atorvastatin, 30 mg/kg/day, p.o.; pitavastatin, 3mg/kg/day, p.o.) on the serum level of lipids, cognitive dysfunction, senile plaque (SP) and phosphorylated tau-positive dystrophic neuritis (pτDN) in amyloid precursor protein (APP) transgenic (Tg) mice from 5 months (M) of age to 20 M. These two statins improved behavioral memory and reduced the numbers of SP and pτDN at 15 and 20 M without affecting serum lipid levels, but preserved mice brain weight in pitavastatin group at 20 M. These protective effects of statins took 10 M from the beginning of treatment to show an improvement in the present model mice, and sensitivity to the statin treatment was linked to behavioral memory, SP and pτDN in this order. These findings suggest that early treatment with both atorvastatin and pitavastatin prevented subsequent worsening of cognitive function and the amyloidogenic process, probably due to pleiotrophic effects, suggesting a therapeutic potential for Alzheimer's disease (AD).

Design of an orally efficacious hydroxyethylamine (HEA) BACE-1 inhibitor in a preclinical animal model

In this Letter, we describe our efforts to design HEA BACE-1 inhibitors that are highly permeable coupled with negligible levels of permeability-glycoprotein activity. These efforts culminate in producing 16 which lowers Αβ by 28% and 32% in the cortex and CSF, respectively, in the preclinical wild type Hartley guinea pig animal model when dosed orally at 30mpk BID for 2.5days.

Amyloid-beta peptide oligomers disrupt axonal transport through an NMDA receptor-dependent mechanism that is mediated by glycogen synthase kinase 3beta in primary cultured hippocampal neurons

Disruption of axonal transport is a hallmark of several neurodegenerative diseases, including Alzheimer's disease (AD). Even though defective transport is considered an early pathologic event, the mechanisms by which neurodegenerative insults impact transport are poorly understood. We show that soluble oligomers of the amyloid-beta peptide (AbetaOs), increasingly recognized as the proximal neurotoxins in AD pathology, induce disruption of organelle transport in primary hippocampal neurons in culture. Live imaging of fluorescent protein-tagged organelles revealed a marked decrease in axonal trafficking of dense-core vesicles and mitochondria in the presence of 0.5 microm AbetaOs. NMDA receptor (NMDAR) antagonists, including d-AP5, MK-801, and memantine, prevented the disruption of trafficking, thereby identifying signals for AbetaO action at the cell membrane. Significantly, both pharmacological inhibition of glycogen synthase kinase-3beta (GSK-3beta) and transfection of neurons with a kinase-dead form of GSK-3beta prevented the transport defect. Finally, we demonstrate by biochemical and immunocytochemical means that AbetaOs do not affect microtubule stability, indicating that disruption of transport involves a more subtle mechanism than microtubule destabilization, likely the dysregulation of intracellular signaling cascades. Results demonstrate that AbetaOs negatively impact axonal transport by a mechanism that is initiated by NMDARs and mediated by GSK-3beta and establish a new connection between toxic Abeta oligomers and AD pathology.

Staging of Alzheimer's pathology in triple transgenic mice: a light and electron microscopic analysis

The age-related pathological cascade underlying intraneuronal tau formation in 3xTg-AD mice, which harbor the human APP_Swe, PS1_M126V , and Tau_P301L gene mutations, remains unclear. At 3 weeks of age, AT180, Alz50, MC1, AT8, and PHF-1 intraneuronal immunoreactivity appeared in the amygdala and hippocampus and at later ages in the cortex of 3xTg-AD mice. AT8 and PHF-1 staining was fixation dependent in young mutant mice. 6E10 staining was seen at all ages. Fluorescent immunomicroscopy revealed CA1 neurons dual stained for 6E10 and Alz50 and single Alz50 immunoreactive neurons in the subiculum at 3 weeks and continuing to 20 months. Although electron microscopy confirmed intraneuronal cytoplasmic Alz50, AT8, and 6E10 reaction product in younger 3xTg-AD mice, straight filaments appeared at 23 months of age in female mice. The present data suggest that other age-related biochemical mechanisms in addition to early intraneuronal accumulation of 6E10 and tau underlie the formation of tau filaments in 3xTg-AD mice.

A mouse model of amyloid beta oligomers: their contribution to synaptic alteration, abnormal tau phosphorylation, glial activation, and neuronal loss in vivo

Although amyloid beta (Abeta) oligomers are presumed to cause synaptic and cognitive dysfunction in Alzheimer's disease (AD), their contribution to other pathological features of AD remains unclear. To address the latter, we generated APP transgenic mice expressing the E693Delta mutation, which causes AD by enhanced Abeta oligomerization without fibrillization. The mice displayed age-dependent accumulation of intraneuronal Abeta oligomers from 8 months but no extracellular amyloid deposits even at 24 months. Hippocampal synaptic plasticity and memory were impaired at 8 months, at which time the presynaptic marker synaptophysin began to decrease. Furthermore, we detected abnormal tau phosphorylation from 8 months, microglial activation from 12 months, astrocyte activation from 18 months, and neuronal loss at 24 months. These findings suggest that Abeta oligomers cause not only synaptic alteration but also other features of AD pathology and that these mice are a useful model of Abeta oligomer-induced pathology in the absence of amyloid plaques.

Tau phosphorylated at tyrosine 394 is found in Alzheimer's disease tangles and can be a product of the Abl-related kinase, Arg

Tau is a microtubule-associated protein and a main component of neurofibrillary tangles, one of the pathologic hallmarks of Alzheimer's disease. The paired helical filaments (PHF) that comprise neurofibrillary tangles contain an abnormally hyperphosphorylated form of tau. Historically, most of the tau phosphorylation sites that have been characterized are serine and threonine residues. Recent reports state that tau can be phosphorylated at tyrosine residues by kinases including Fyn, Syk, and c-abl (Abl). Proteomic analyses show that tau phosphorylated at tyrosine 394 (Y394) exists within PHF samples taken from Alzheimer's disease brains. This study also confirms phosphorylation of Y394 as an Alzheimer's disease-specific event by immunohistochemistry. To date, only Abl is known to phosphorylate this particular site on tau. We report, for the first time, that Arg, the other member of the Abl family of tyrosine kinases, also phosphorylates tau at Y394 in a manner independent of Abl activity. Given the reported role of Arg in oxidative stress response and neural development, the ability to phosphorylate tau at Y394 implicates Arg as a potential player in the pathogenesis of Alzheimer's disease and other tauopathies.

Anti-ADDL antibodies differentially block oligomer binding to hippocampal neurons

Abeta-derived diffusible ligands (ADDLs) are abundant in AD brain, bind to hippocampal neurons and induce deficits in rodent cognition. To further investigate ADDL binding to neurons and identify antibodies that block this association, a panel of anti-Abeta and anti-ADDL antibodies was characterized for their ability to immuno-detect neuronally bound ADDLs and attenuate the binding of ADDLs to neurons. The results showed that anti-Abeta and anti-ADDL antibodies were able to abate ADDLs binding to hippocampal neurons, but to different degrees. Quantitative assessment of binding showed that one antibody, ACU-954 was markedly more effective at blocking ADDL binding than other antibodies assessed. ACU-954 was also found to block ADDL binding to hippocampal slice cultures, attenuate the ADDL-induced loss of dendritic spines and detect "natural ADDLs" in human AD tissue. These results demonstrated that antibodies that bind to and block ADDL binding to neurons can be identified, although their efficacy is conformationally specific since it is not readily apparent or predictable based on the core linear epitope or affinity for monomeric Abeta.

Basic mechanisms of neurodegeneration: a critical update

Neurodegenerative diseases are characterized by progressive dysfunction of specific populations of neurons, determining clinical presentation. Neuronal loss is associated with extra and intracellular accumulation of misfolded proteins, the hallmarks of many neurodegenerative proteinopathies. Major basic processes include abnormal protein dynamics due to deficiency of the ubiquitin-proteosome-autophagy system, oxidative stress and free radical formation, mitochondrial dysfunction, impaired bioenergetics, dysfunction of neurotrophins, 'neuroinflammatory' processes and (secondary) disruptions of neuronal Golgi apparatus and axonal transport. These interrelated mechanisms lead to programmed cell death is a long run over many years. Neurodegenerative disorders are classified according to known genetic mechanisms or to major components of protein deposits, but recent studies showed both overlap and intraindividual diversities between different phenotypes. Synergistic mechanisms between pathological proteins suggest common pathogenic mechanisms. Animal models and other studies have provided insight into the basic neurodegeneration and cell death programs, offering new ways for future prevention/treatment strategies.

Effects of insulinic therapy on cognitive impairment in patients with Alzheimer disease and diabetes mellitus type-2

BACKGROUND

Type-2 Diabetes Mellitus (DM-2) is an important risk factor for Alzheimer disease (AD) and vascular dementia (VD). The role of insulinic therapy on cognitive decline is controversial.

OBJECTIVE

To evaluate cognitive impairment in patients with AD and DM-2 treated with either oral antidiabetic drugs or combination of insulin with other diabetes medications.

METHODS

104 patients with mild-to-moderate AD and DM-2 were divided into two groups, according to antidiabetic pharmacotherapy: group A, patients treated with oral antidiabetic drugs and group B, patients treated with insulin combined with other oral antidiabetic medications. Cognitive functions were assessed by the Mini Mental State Examination (MMSE) and the Clinician's Global Impression (CGI), with a follow-up of 12 months.

RESULTS

At the end of the study, the MMSE scores showed a significant worsening in 56.5% patients of group A and in 23.2% patients of group B, compared to baseline MMSE scores (P=.001). Also CGI-C scores showed a significant worsening for all domains after 12 months in group A vs group B (P=.001). The two groups were matched for body mass index, serum lipids, triglycerides, Apo epsilon4 allele and smoke habit. Conversely, ischemic heart disease and hypertension were significantly higher in group B (P=.002). After adjustment for this risk variables, our results remained significant (P=.001).

CONCLUSIONS

Our study suggests that insulinic therapy could be effective in slowing cognitive decline in patients with AD.

Synthetic amyloid-beta oligomers impair long-term memory independently of cellular prion protein

Inability to form new memories is an early clinical sign of Alzheimer's disease (AD). There is ample evidence that the amyloid-beta (Abeta) peptide plays a key role in the pathogenesis of this disorder. Soluble, bio-derived oligomers of Abeta are proposed as the key mediators of synaptic and cognitive dysfunction, but more tractable models of Abeta-mediated cognitive impairment are needed. Here we report that, in mice, acute intracerebroventricular injections of synthetic Abeta(1-42) oligomers impaired consolidation of the long-term recognition memory, whereas mature Abeta(1-42) fibrils and freshly dissolved peptide did not. The deficit induced by oligomers was reversible and was prevented by an anti-Abeta antibody. It has been suggested that the cellular prion protein (PrP(C)) mediates the impairment of synaptic plasticity induced by Abeta. We confirmed that Abeta(1-42) oligomers interact with PrP(C), with nanomolar affinity. However, PrP-expressing and PrP knock-out mice were equally susceptible to this impairment. These data suggest that Abeta(1-42) oligomers are responsible for cognitive impairment in AD and that PrP(C) is not required.

Menopause and mitochondria: windows into estrogen effects on Alzheimer's disease risk and therapy

Metabolic derangements and oxidative stress are early events in Alzheimer's disease pathogenesis. Multi-faceted effects of estrogens include improved cerebral metabolic profile and reduced oxidative stress through actions on mitochondria, suggesting that a woman's endogenous and exogenous estrogen exposures during midlife and in the late post-menopause might favourably influence Alzheimer risk and symptoms. This prediction finds partial support in the clinical literature. As expected, early menopause induced by oophorectomy may increase cognitive vulnerability; however, there is no clear link between age at menopause and Alzheimer risk in other settings, or between natural menopause and memory loss. Further, among older post-menopausal women, initiating estrogen-containing hormone therapy increases dementia risk and probably does not improve Alzheimer's disease symptoms. As suggested by the 'critical window' or 'healthy cell' hypothesis, better outcomes might be expected from earlier estrogen exposures. Some observational results imply that effects of hormone therapy on Alzheimer risk are indeed modified by age at initiation, temporal proximity to menopause, or a woman's health. However, potential methodological biases warrant caution in interpreting observational findings. Anticipated results from large, ongoing clinical trials [Early Versus Late Intervention Trial with Estradiol (ELITE), Kronos Early Estrogen Prevention Study (KEEPS)] will help settle whether midlife estrogen therapy improves midlife cognitive skills but not whether midlife estrogen exposures modify late-life Alzheimer risk. Estrogen effects on mitochondria adumbrate the potential relevance of estrogens to Alzheimer's disease. However, laboratory models are inexact embodiments of Alzheimer pathogenesis and progression, making it difficult to surmise net effects of estrogen exposures. Research needs include better predictors of adverse cognitive outcomes, biomarkers for risks associated with hormone therapy, and tools for monitoring brain function and disease progression.

Diminished perisomatic GABAergic terminals on cortical neurons adjacent to amyloid plaques

One of the main pathological hallmarks of Alzheimer's disease (AD) is the accumulation of plaques in the cerebral cortex, which may appear either in the neuropil or in direct association with neuronal somata. Since different axonal systems innervate the dendritic (mostly glutamatergic) and perisomatic (mostly GABAergic) regions of neurons, the accumulation of plaques in the neuropil or associated with the soma might produce different alterations to synaptic circuits. We have used a variety of conventional light, confocal and electron microscopy techniques to study their relationship with neuronal somata in the cerebral cortex from AD patients and APP/PS1 transgenic mice. The main finding was that the membrane surfaces of neurons (mainly pyramidal cells) in contact with plaques lack GABAergic perisomatic synapses. Since these perisomatic synapses are thought to exert a strong influence on the output of pyramidal cells, their loss may lead to the hyperactivity of the neurons in contact with plaques. These results suggest that plaques modify circuits in a more selective manner than previously thought.

Nicotinic receptors, amyloid-beta, and synaptic failure in Alzheimer's disease

Dysfunctional cholinergic transmission is thought to underlie, at least in part, memory impairment and cognitive deficits in Alzheimer's disease (AD). However, it is still unclear whether this is a consequence of the loss of cholinergic neurons and elimination of nicotinic acetycholine receptors (nAChRs) in AD brain or of a direct impact of molecular interactions of the amyloid-beta (Abeta) peptide with nAChRs, leading to dysregulation of receptor function. This review examines recent progress in our understanding of the roles of nicotinic receptors in mechanisms of synaptic plasticity, molecular interactions of Abeta with nAChRs, and how Abeta-induced dysregulation of nicotinic receptor function may underlie synaptic failure in AD.

Does Alzheimer's disease begin in the brainstem?

Although substantial evidence indicates that the progression of pathological changes of the neuronal cytoskeleton is crucial in determining the severity of dementia in Alzheimer's disease (AD), the exact causes and evolution of these changes, the initial site at which they begin, and the neuronal susceptibility levels for their development are poorly understood. The current clinical criteria for diagnosis of AD are focused mostly on cognitive deficits produced by dysfunction of hippocampal and high-order neocortical areas, whereas noncognitive, behavioural and psychological symptoms of dementia such as disturbances in mood, emotion, appetite, and wake-sleep cycle, confusion, agitation and depression have been less considered. The early occurrence of these symptoms suggests brainstem involvement, and more specifically of the serotonergic nuclei. In spite of the fact that the Braak and Braak staging system and National Institutes of Aging - Reagan Institute (NIA-RI) criteria do not include their evaluation, several recent reports drew attention to the possibility of selective and early involvement of raphe nuclei, particularly the dorsal raphe nucleus (DRN), in the pathogenesis of AD. Based on these findings of differential susceptibility and anatomical connectivity, a novel pathogenetic scheme of AD progression was proposed. Although the precise mechanisms of neurofibrillary degeneration still await elucidation, we speculated that cumulative oxidative damage may be the main cause of DRN alterations, as the age is the main risk factor for sporadic AD. Within such a framework, beta-amyloid production is considered only as one of the factors (although a significant one in familial cases) that promotes molecular series of events underlying AD-related neuropathological changes.

Cytoskeletal pathologies of Alzheimer disease

The histopathological hallmarks of Alzheimer disease are the extracellular amyloid plaques, composed principally of the amyloid beta peptide, and the intracellular neurofibrillary tangles, composed of paired helical filaments of the microtubule-associated protein, tau. Other histopathological structures involving actin and the actin-binding protein, cofilin, have more recently been recognized. Here we review new findings about these cytoskeletal pathologies, and, emphasize how plaques, tangles, the actin-containing inclusions and their respective building blocks may contribute to Alzheimer pathogenesis and the primary behavioral symptoms of the disease. Cell Motil. Cytoskeleton, 2009. (c) 2009 Wiley-Liss, Inc.

Alzheimer's-associated Abeta oligomers show altered structure, immunoreactivity and synaptotoxicity with low doses of oleocanthal

It now appears likely that soluble oligomers of amyloid-beta1-42 peptide, rather than insoluble fibrils, act as the primary neurotoxin in Alzheimer's disease (AD). Consequently, compounds capable of altering the assembly state of these oligomers (referred to as ADDLs) may have potential for AD therapeutics. Phenolic compounds are of particular interest for their ability to disrupt Abeta oligomerization and reduce pathogenicity. This study has focused on oleocanthal (OC), a naturally-occurring phenolic compound found in extra-virgin olive oil. OC increased the immunoreactivity of soluble Abeta species, when assayed with both sequence- and conformation-specific Abeta antibodies, indicating changes in oligomer structure. Analysis of oligomers in the presence of OC showed an upward shift in MW and a ladder-like distribution of SDS-stable ADDL subspecies. In comparison with control ADDLs, oligomers formed in the presence of OC (Abeta-OC) showed equivalent colocalization at synapses but exhibited greater immunofluorescence as a result of increased antibody recognition. The enhanced signal at synapses was not due to increased synaptic binding, as direct detection of fluorescently-labeled ADDLs showed an overall reduction in ADDL signal in the presence of OC. Decreased binding to synapses was accompanied by significantly less synaptic deterioration assayed by drebrin loss. Additionally, treatment with OC improved antibody clearance of ADDLs. These results indicate oleocanthal is capable of altering the oligomerization state of ADDLs while protecting neurons from the synaptopathological effects of ADDLs and suggest OC as a lead compound for development in AD therapeutics.

Variations in the neuropathology of familial Alzheimer's disease

Mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes cause autosomal dominant familial Alzheimer's disease (AD). PSEN1 and PSEN2 are essential components of the gamma-secretase complex, which cleaves APP to affect Abeta processing. Disruptions in Abeta processing have been hypothesised to be the major cause of AD (the amyloid cascade hypothesis). These genetic cases exhibit all the classic hallmark pathologies of AD including neuritic plaques, neurofibrillary tangles (NFT), tissue atrophy, neuronal loss and inflammation, often in significantly enhanced quantities. In particular, these cases have average greater hippocampal atrophy and NFT, more significant cortical Abeta42 plaque deposition and more substantial inflammation. Enhanced cerebral Abeta40 angiopathy is a feature of many cases, but particularly those with APP mutations where it can be the dominant pathology. Additional frontotemporal neuronal loss in association with increased tau pathology appears unique to PSEN mutations, with mutations in exons 8 and 9 having enlarged cotton wool plaques throughout their cortex. The mechanisms driving these pathological differences in AD are discussed.