Soluble Abeta Oligomers Research Articles

Neuronal expression of a single‐chain variable fragment antibody against Aβ oligomers protects synapses and rescues memory in Alzheimer models

AbstractBackgroundAlzheimer's disease (AD) is the main cause of dementia in the elderly and is characterized by abnormal accumulation of the beta‐amyloid peptide (Aß) in the brain. Considerable evidence has shown that soluble Abeta oligomers (AßOs) are the main neurotoxins involved in synaptic dysfunction and the memory loss.MethodWe evaluated the therapeutic potential of NUsc1, a single chain variable Fragment (scFv) antibody isolated from a screen to identify scFv’s targeting AβOs. Using an adeno‐associated virus derived vector (AAV) we analyzed its protective effects both in vitro and in vivo models of AD. AAV‐NUsc1 capability to induce NUsc1 expression and secretion in humans was tested using human brain slices in culture.ResultWe here show that recombinant NUsc1, a single‐chain variable fragment (scFv) antibody that selectively targets a subset of neurotoxic AβOs, prevented AβO‐induced inhibition of long‐term potentiation in hippocampal slices, and blocked memory impairment induced by intracerebroventricular infusion of AβOs in mice. We next developed an adeno‐associated virus vector to drive neuronal expression of NUsc1 (AAV‐NUsc1) as a novel therapeutic approach for AD. Importantly, transduction by AAV‐NUsc1 induced NUsc1 expression and secretion in adult human brain slices. In primary hippocampal cultures, transduction by AAV‐NUsc1 reduced AβO binding to neurons and prevented AβO‐induced loss of dendritic spines. Remarkably, AAV‐NUsc1 prevented memory impairment caused by AβO infusion in mice and reversed memory deficits in APPswe/PS1ΔE9 AD mice.ConclusionAAV‐NUsc1 represents a potential tool for gene therapy in AD by using an AAV vector to induce in vivo sustained expression of a single chain variable fragment antibody to neutralize AβOs.

Differential Inhibition of E-S Potentiation and Long-term Potentiation by Cell-Derived and Arctic Amyloid Beta

Soluble oligomers of amyloid-beta peptide (Abeta) have been implicated in the onset of memory deficits in Alzheimer's disease, perhaps due to their reported ability to impair long-term potentiation (LTP) of synaptic strength. We previously showed the effect of Abeta on LTP depends on the strength of LTP induction. Furthermore, Abeta affects EPSP-Spike (E-S) potentiation more robustly than LTP, suggesting that E-S potentiation may be equally important to learning and memory in the context of Alzheimer's disease. Here we extend our findings to two additional forms of Abeta that form higher concentrations of soluble Abeta oligomers and show that they also affect E-S potentiation at induction strengths where there is no effect on LTP in hippocampal slices.

Pathogenesis of Abeta Oligomers in Synaptic Failure

The soluble Abeta oligomers in brain are highly correlated with memory related synaptic dysfunctions in Alzheimer's disease (AD). However, more recent studies implicate the involvement of Abeta dimers and trimers in memory related AD pathology. Apparently, Abeta oligomers can bind with cellular prion protein at the membrane receptors, forming annular amyloid pores and membrane ion channels to induce aberrant spine cytoskeletal changes. Hence synapse targeting of Abeta oligomers involves activation of many receptors such as N-Methyl-D-aspartate (NMDA), alpha-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), nicotinic acetylcholine (nAChRs), p75 neurotrophin (p75NTR) following aberrant clustering of metabotropic glutamate receptors (mGluR5) leading to neuronal loss and LTP failure. In particular, NMDA and AMPA receptor activation by soluble amyloid oligomers involves calcium mediated mitochondrial dysfunction, decreased Ca((2+))/calmodulin-dependent protein kinase II (CaMKII) levels at the synapses accompanying dramatic loss of synaptic proteins such as postsynaptic density-95 (PSD-95), dynamin-1 and synaptophysin. This kind of receptor-Abeta oligomer interaction might eventually affect the neuronal membrane integrity by altering dielectric barrier, various synaptic proteins, spine morphology and density and P/Q calcium currents that might provoke a cascade of events leading to neuronal loss and memory failure. In this review, we try to explain in detail the various possible mechanisms that connect Abeta oligomers with synapse damage and memory failure.

LPYFDa Neutralizes Amyloid-β-Induced Memory Impairment and Toxicity

Misfolding, oligomerization, and aggregation of the amyloid-beta (Abeta) peptide is widely recognized as a central event in the pathogenesis of Alzheimer's disease (AD). Recent studies have identified soluble Abeta oligomers as the main pathogenic agents and provided evidence that such oligomeric Abeta aggregates are neurotoxic, disrupt synaptic plasticity, and inhibit long-term potentiation. A promising therapeutic strategy in the battle against AD is the application of short synthetic peptides which are designed to bind to specific Abeta-regions thereby neutralizing or interfering with the devastating properties of oligomeric Abeta species. In the present study, we investigated the neuroprotective properties of the amyloid sequence derived pentapeptide LPYFDa in vitro as well as its memory preserving capacity against Abeta(42)-induced learning deficits in vivo. In vitro we showed that neurons in culture treated with LPYFDa are protected against Abeta (42) -induced cell death. Moreover, in vivo LPYFDa prevented memory impairment tested in a contextual fear conditioning paradigm in mice after bilateral intrahippocampal Abeta (42) injections. We thus showed for the first time that an anti-amyloid peptide like LPYFDa can preserve memory by reverting Abeta (42) oligomer-induced learning deficits.

Reduced IGF-1 Signaling Delays Age-Associated Proteotoxicity in Mice

The insulin/insulin growth factor (IGF) signaling (IIS) pathway is a key regulator of aging of worms, flies, mice, and likely humans. Delayed aging by IIS reduction protects the nematode C. elegans from toxicity associated with the aggregation of the Alzheimer's disease-linked human peptide, Abeta. We reduced IGF signaling in Alzheimer's model mice and discovered that these animals are protected from Alzheimer's-like disease symptoms, including reduced behavioral impairment, neuroinflammation, and neuronal loss. This protection is correlated with the hyperaggregation of Abeta leading to tightly packed, ordered plaques, suggesting that one aspect of the protection conferred by reduced IGF signaling is the sequestration of soluble Abeta oligomers into dense aggregates of lower toxicity. These findings indicate that the IGF signaling-regulated mechanism that protects from Abeta toxicity is conserved from worms to mammals and point to the modulation of this signaling pathway as a promising strategy for the development of Alzheimer's disease therapy.

Copper in the brain and Alzheimer’s disease

Alzheimer's disease (AD) is the most common form of neurodegenerative disease. The brain is particularly vulnerable to oxidative damage induced by unregulated redox-active metals such as copper and iron, and the brains of AD patients display evidence of metal dyshomeostasis and increased oxidative stress. The colocalisation of copper and amyloid beta (Abeta) in the glutamatergic synapse during NMDA-receptor-mediated neurotransmission provides a microenvironment favouring the abnormal interaction of redox-potent Abeta with copper under conditions of copper dysregulation thought to prevail in the AD brain, resulting in the formation of neurotoxic soluble Abeta oligomers. Interactions between Abeta oligomers and copper can further promote the aggregation of Abeta, which is the core component of extracellular amyloid plaques, a central pathological hallmark of AD. Copper dysregulation is also implicated in the hyperphosphorylation and aggregation of tau, the main component of neurofibrillary tangles, which is also a defining pathological hallmark of AD. Therefore, tight regulation of neuronal copper homeostasis is essential to the integrity of normal brain functions. Therapeutic strategies targeting interactions between Abeta, tau and metals to restore copper and metal homeostasis are discussed.

Mechanism of docosahexaenoic acid‐induced inhibition of in vitro Aβ1–42 fibrillation and Aβ1–42‐induced toxicity in SH‐S5Y5 cells

The mechanism of the effect of docosahexaenoic acid (DHA; C22:6, n-3), one of the essential brain nutrients, on in vitro fibrillation of amyloid beta (Abeta(1-42)), Abeta(1-42)-oligomers and its toxicity imparted to SH-S5Y5 cells was studied with the use of thioflavin T fluorospectroscopy, laser confocal microfluorescence, and transmission electron microscopy. The results clearly indicated that DHA inhibited Abeta(1-42)-fibrill formation with a concomitant reduction in the levels of soluble Abeta(1-42) oligomers. The polymerization (into fibrils) of preformed oligomers treated with DHA was inhibited, indicating that DHA not only obstructs their formation but also inhibits their transformation into fibrils. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (12.5%), Tris-Tricine gradient(4-20%) gel electrophoresis and western blot analyses revealed that DHA inhibited at least 2 species of Abeta(1-42) oligomers of 15-20 kDa, indicating that it hinders these on-pathway tri/tetrameric intermediates during fibrillation. DHA also reduced the levels of dityrosine and tyrosine intrinsic fluorescence intensity, indicating DHA interrupts the microenvironment of tyrosine in the Abeta(1-42) backbone. Furthermore, DHA protected the tyrosine from acrylamide collisional quenching, as indicated by decreases in Stern-Volmer constants. 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide-reduction efficiency and immunohistochemical examination suggested that DHA inhibits Abeta(1-42)-induced toxicity in SH-S5Y5 cells. Taken together, these data suggest that by restraining Abeta(1-42) toxic tri/tetrameric oligomers, DHA may limit amyloidogenic neurodegenerative diseases, Alzheimer's disease.

Generation of reactive oxygen species by beta amyloid fibrils and oligomers involves different intra/extracellular pathways

A neuropathological characteristic of Alzheimer's disease is the extracellular accumulation of amyloid beta peptide (Abeta) in neuritic plaques. Recent evidences suggested that soluble Abeta oligomers are the predominant neurotoxic species for neurons. Thus, considerable attention has been paid to discriminate the cytotoxic pathways of Abeta pre-fibrillar aggregates and mature fibrils. We showed that the mechanisms by which Abeta oligomers and fibrils generated reactive oxygen species differ in terms of site of production and kinetics, suggesting the involvement of different intra/extracellular pathways.

Quantitation and Mapping of Cerebral Detergent‐Insoluble Proteins in the Elderly

Accumulation of abnormal protein aggregates, detergent-insoluble (DI) proteins and amyloid in the brain are shared features of many neurodegenerative diseases. Previous studies correlating DI proteins and cognitive performance are limited. We addressed these limitations using two sets of autopsy brains, one selected from our Alzheimer's Disease Research Center and the other an unselected series from Adult Changes in Thought (ACT), a population-based study of brain aging. We observed concentrations of 11 proteins and 6 protein variants that can be grouped into three highly correlated clusters: amyloid (A)beta, tau and alpha-synuclein (alpha-syn). While abnormal proteins from each cluster independently correlated with cognitive performance in ACT participants, only increased soluble Abeta oligomers in temporal cortex and increased DI Abeta 42 and DI alpha-syn in prefrontal cortex were negatively correlated with cognitive performance. These data underscore the therapeutic imperative to suppress processes leading to accumulation of soluble Abeta oligomers, DI Abeta 42 and DI alpha-syn, highlight an at least partially independent contribution to cognitive impairment and raise the possibility that the priority for therapeutic targets may vary by brain region in a typical elderly US population.

Soluble Oligomers of Amyloid β Protein Facilitate Hippocampal Long-Term Depression by Disrupting Neuronal Glutamate Uptake

In Alzheimer's disease (AD), the impairment of declarative memory coincides with the accumulation of extracellular amyloid-beta protein (Abeta) and intraneuronal tau aggregates. Dementia severity correlates with decreased synapse density in hippocampus and cortex. Although numerous studies show that soluble Abeta oligomers inhibit hippocampal long-term potentiation, their role in long-term synaptic depression (LTD) remains unclear. Here, we report that soluble Abeta oligomers from several sources (synthetic, cell culture, human brain extracts) facilitated electrically evoked LTD in the CA1 region. Abeta-enhanced LTD was mediated by mGluR or NMDAR activity. Both forms of LTD were prevented by an extracellular glutamate scavenger system. Abeta-facilitated LTD was mimicked by the glutamate reuptake inhibitor TBOA, including a shared dependence on extracellular calcium levels and activation of PP2B and GSK-3 signaling. In accord, synaptic glutamate uptake was significantly decreased by soluble Abeta. We conclude that soluble Abeta oligomers perturb synaptic plasticity by altering glutamate recycling at the synapse and promoting synapse depression.

β-Amyloid Impairs AMPA Receptor Trafficking and Function by Reducing Ca2+/Calmodulin-dependent Protein Kinase II Synaptic Distribution

A fundamental feature of Alzheimer disease (AD) is the accumulation of beta-amyloid (Abeta), a peptide generated from the amyloid precursor protein (APP). Emerging evidence suggests that soluble Abeta oligomers adversely affect synaptic function, which leads to cognitive failure associated with AD. The Abeta-induced synaptic dysfunction has been attributed to the synaptic removal of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs); however, it is unclear how Abeta induces the loss of AMPARs at the synapses. In this study we have examined the potential involvement of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), a signaling molecule critical for AMPAR trafficking and function. We found that the synaptic pool of CaMKII was significantly decreased in cortical neurons from APP transgenic mice, and the density of CaMKII clusters at synapses was significantly reduced by Abeta oligomer treatment. In parallel, the surface expression of GluR1 subunit as well as AMPAR-mediated synaptic response and ionic current was selectively decreased in APP transgenic mice and Abeta-treated cultures. Moreover, the reducing effect of Abeta on AMPAR current density was mimicked and occluded by knockdown of CaMKII and blocked by overexpression of CaMKII. These results suggest that the Abeta-induced change in CaMKII subcellular distribution may underlie the removal of AMPARs from synaptic membrane by Abeta.

Formation of highly toxic soluble amyloid beta oligomers by the molecular chaperone prefoldin

Alzheimer's disease (AD) is a neurological disorder characterized by the presence of amyloid beta (Abeta) peptide fibrils and oligomers in the brain. It has been suggested that soluble Abeta oligomers, rather than Abeta fibrils, contribute to neurodegeneration and dementia due to their higher level of toxicity. Recent studies have shown that Abeta is also generated intracellularly, where it can subsequently accumulate. The observed inhibition of cytosolic proteasome by Abeta suggests that Abeta is located within the cytosolic compartment. To date, although several proteins have been identified that are involved in the formation of soluble Abeta oligomers, none of these have been shown to induce in vitro formation of the high-molecular-mass (> 50 kDa) oligomers found in AD brains. Here, we examine the effects of the jellyfish-shaped molecular chaperone prefoldin (PFD) on Abeta(1-42) peptide aggregation in vitro. PFD is thought to play a general role in de novo protein folding in archaea, and in the biogenesis of actin, tubulin and possibly other proteins in the cytosol of eukaryotes. We found that recombinant Pyrococcus PFD produced high-molecular-mass (50-250 kDa) soluble Abeta oligomers, as opposed to Abeta fibrils. We also demonstrated that the soluble Abeta oligomers were more toxic than Abeta fibrils, and were capable of inducing apoptosis. As Pyrococcus PFD shares high sequence identity to human PFD and the PFD-homolog protein found in human brains, these results suggest that PFD may be involved in the formation of toxic soluble Abeta oligomers in the cytosolic compartment in vivo.

A new amyloid β variant favoring oligomerization in Alzheimer's‐type dementia

Soluble oligomers of amyloid beta (Abeta), rather than amyloid fibrils, have been proposed to initiate synaptic and cognitive dysfunction in Alzheimer's disease (AD). However, there is no direct evidence in humans that this mechanism can cause AD. Here, we report a novel amyloid precursor protein (APP) mutation that may provide evidence to address this question. A Japanese pedigree showing Alzheimer's-type dementia was examined for mutations in APP, PSEN1, and PSEN2. In addition, 5,310 Japanese people, including 2,121 patients with AD, were screened for the novel APP mutation. The pathogenic effects of this mutation on Abeta production, degradation, aggregation, and synaptotoxicity were also investigated. We identified a novel APP mutation (E693Delta) producing variant Abeta lacking gulutamate-22 (E22Delta) in Japanese pedigrees showing Alzheimer's-type dementia and AD. Although the secretion of total Abeta was markedly reduced by this mutation, the variant Abeta was more resistant to proteolytic degradation. The mutant peptides showed the unique aggregation property of enhanced oligomerization but no fibrillization, and inhibited hippocampal long-term potentiation more potently than wild-type peptide in rats in vivo. Consistent with the nonfibrillogenic property of the variant Abeta, a very low amyloid signal was observed in the patient's brain on positron emission tomography using Pittsburgh compound-B. The E693Delta mutation has been suggested as a cause of dementia because of enhanced formation of synaptotoxic Abeta oligomers. Our findings may provide genetic validation in humans for the emerging hypothesis that the synaptic and cognitive impairment in AD is primarily caused by soluble Abeta oligomers.

Advances on the understanding of the origins of synaptic pathology in AD.

Although Alzheimer’s disease (AD) was first discovered a century ago, we are still facing a lack of definitive diagnosis during the patient’s lifetime and are unable to prescribe a curative treatment. However, the past 10 years have seen a “revamping” of the main hypothesis about AD pathogenesis and the hope to foresee possible treatment. AD is no longer considered an irreversible disease. A major refinement of the classic β-amyloid cascade describing amyloid fibrils as neurotoxins has been made to integrate the key scientific evidences demonstrating that the first pathological event occurring in AD early stages affects synaptic function and maintenance. A concept fully compatible with synapse loss being the best pathological correlate of AD rather than other described neuropathological hallmarks (amyloid plaques, neurofibrillary tangles or neuronal death). The notion that synaptic alterations might be reverted, thus offering a potential curability, was confirmed by immunotherapy experiments targeting β-amyloid protein in transgenic AD mice in which cognitive functions were improved despite no reduction in the amyloid plaques burden. The updated amyloid cascade now integrates the synapse failure triggered by soluble Aβ-oligomers. Still no consensus has been reached on the most toxic Aβ conformations, neither on their site of production nor on their extra- versus intra-cellular actions. Evidence shows that soluble Aβ oligomers or ADDLs bind selectively to neurons at their synaptic loci, and trigger major changes in synapse composition and morphology, which ultimately leads to dendritic spine loss. However, the exact mechanism is not yet fully understood but is suspected to involve some membrane receptor(s).

Discovery of ADDL-Targeting Small Molecule Drugs for Alzheimers Disease

Amyloid beta-derived diffusible ligands (ADDLs) comprise the neurotoxic subset of soluble Abeta(1-42) oligomers, now widely considered to be the molecular cause of memory malfunction and neurodegeneration in Alzheimer's disease (AD). We have developed a screening cascade which identifies small molecule modulators of ADDL-mediated neurotoxicity. The primary screen involves a fluorescence resonance energy transfer (FRET)-based assay which selects inhibitors of Abeta1-42 oligomer assembly. The identified hits were further characterized by assessing their ability to inhibit the assembly and binding of ADDLs to cultures of primary hippocampal neurons. This approach has led to the identification of a number of small molecules which inhibit ADDL assembly and their subsequent binding to neurons. Here we describe our small molecule discovery efforts to identify ADDL assembly blocker and ADDL binding inhibitors, and to transform validated hits into pre-clinical lead compounds.

Design of Peptides That Form Amyloid‐Like Fibrils Capturing Amyloid β1–42 Peptides

Amyloid beta-peptide (Abeta) plays a critical role in Alzheimer's disease (AD). The monomeric state of Abeta can self-assemble into oligomers, protofibrils, and amyloid fibrils. Since the fibrils and soluble oligomers are believed to be responsible for AD, the construction of molecules capable of capturing these species could prove valuable as a means of detecting these potentially toxic species and of providing information pertinent for designing drugs effective against AD. To this aim, we have designed short peptides with various hydrophobicities based on the sequence of Abeta14-23, which is a critical region for amyloid fibril formation. The binding of the designed peptides to Abeta and the amplification of the formation of peptide amyloid-like fibrils coassembled with Abeta are elucidated. A fluorescence assay utilizing thioflavin T, known to bind specifically to amyloid fibrils, revealed that two designed peptides (LF and VF, with the leucine and valine residues, respectively, in the hydrophobic core region) could form amyloid-like fibrils effectively by using mature Abeta1-42 fibrils as nuclei. Peptide LF also coassembled with soluble Abeta oligomers into peptide fibrils. Various analyses, including immunostaining with gold nanoparticles, enzyme-linked immunosorbent assays, and size-exclusion chromatography, confirmed that the LF and VF peptides formed amyloid-like fibrils by capturing and incorporating Abeta1-42 aggregates into their peptide fibrils. In this system, small amounts of mature Abeta1-42 fibrils or soluble oligomers could be transformed into peptide fibrils and detected by amplifying the amyloid-like fibrils with the designed peptides.

Amyloid beta oligomers induce impairment of neuronal insulin receptors

Recent studies have indicated an association between Alzheimer's disease (AD) and central nervous system (CNS) insulin resistance. However, the cellular mechanisms underlying the link between these two pathologies have not been elucidated. Here we show that signal transduction by neuronal insulin receptors (IR) is strikingly sensitive to disruption by soluble Abeta oligomers (also known as ADDLs). ADDLs are known to accumulate in AD brain and have recently been implicated as primary candidates for initiating deterioration of synapse function, composition, and structure. Using mature cultures of hippocampal neurons, a preferred model for studies of synaptic cell biology, we found that ADDLs caused a rapid and substantial loss of neuronal surface IRs specifically on dendrites bound by ADDLs. Removal of dendritic IRs was associated with increased receptor immunoreactivity in the cell body, indicating redistribution of the receptors. The neuronal response to insulin, measured by evoked IR tyrosine autophosphorylation, was greatly inhibited by ADDLs. Inhibition also was seen with added glutamate or potassium-induced depolarization. The effects on IR function were completely blocked by NMDA receptor antagonists, tetrodotoxin, and calcium chelator BAPTA-AM. Downstream from the IR, ADDLs induced a phosphorylation of Akt at serine473, a modification associated with neurodegenerative and insulin resistance diseases. These results identify novel factors that affect neuronal IR signaling and suggest that insulin resistance in AD brain is a response to ADDLs, which disrupt insulin signaling and may cause a brain-specific form of diabetes as part of an overall pathogenic impact on CNS synapses.

Orally available compound prevents deficits in memory caused by the Alzheimer amyloid‐β oligomers

Despite progress in defining a pathogenic role for amyloid beta protein (Abeta) in Alzheimer's disease, orally bioavailable compounds that prevent its effects on hippocampal synaptic plasticity and cognitive function have not yet emerged. A particularly attractive therapeutic strategy is to selectively neutralize small, soluble Abeta oligomers that have recently been shown to mediate synaptic dysfunction. Using electrophysiological, biochemical, and behavioral assays, we studied how scyllo-inositol (AZD-103; molecular weight, 180) neutralizes the acutely toxic effects of Abeta on synaptic function and memory recall. Scyllo-inositol, but not its stereoisomer, chiro-inositol, dose-dependently rescued long-term potentiation in mouse hippocampus from the inhibitory effects of soluble oligomers of cell-derived human Abeta. Cerebroventricular injection into rats of the soluble Abeta oligomers interfered with learned performance on a complex lever-pressing task, but administration of scyllo-inositol via the drinking water fully prevented oligomer-induced errors. A small, orally available natural product penetrates into the brain in vivo to rescue the memory impairment produced by soluble Abeta oligomers through a mechanism that restores hippocampal synaptic plasticity.

Soluble amyloid-β in the brain: The scarlet pimpernel

Researchers since the 1990s have predominantly focused on the amyloid hypothesis and the formation of amyloid fibrils as the culprit behind AD when we began working on soluble Abeta (sAbeta). Unexpectedly, this work produced several novel findings. First, we observed that N-terminal truncated peptides are the major components of soluble and insoluble Abeta in AD; secondly, that all sAbeta species belong to the 42 form and the sAbeta x-40 species is virtually absent in AD parenchyma; thirdly, that Abeta42 in the soluble form is non-detectable by immunoblots in plaque-free, normal brains. The later observation that sAbeta 42 species is present in amyloid beta protein precursor (AbetaPP) over-expressing brains of patients with Down syndrome in prenatal and early postnatal development argued that sAbeta is present in brain in abnormal conditions and that its appearance seeds Abeta aggregation and accumulation. Although the sAbeta we described in intact brain tissue appeared to match the soluble Abeta oligomers detected in cell media, which were subsequently shown to be the most toxic form of Abeta, our research has been virtually ignored by the Alzheimer field. It continues nevertheless. Recently we demonstrated that the sAbeta species present in physiologically aging brains are different from those present in brains with sporadic AD as the latter form oligomers more quickly, are more toxic to neurons, and produce more severe membrane damage than the Abeta species associated with normal brain aging. Furthermore, in familial AD, the composition of soluble Abeta appears to dictate distinctive features of the disease phenotype introducing the notion of Abeta strains, a concept well established in prion diseases.

Role of apoE in conformation-prone diseases and atherosclerosis

Three isoforms of human plasma apolipoprotein E (apoE) are ligands to lipoprotein receptors and influence in different manner the synthesis and catabolism of pro-atherogenic triglyceride-rich lipoproteins. Among three isoforms, the apoE4 isoform is associated with increased frequency of atherosclerosis and Alzheimer's disease (AD). The conformational transitions of beta-amyloid (Abeta) influenced by apoE and serum amyloid P (SAP) component are key events in AD development, the accumulation of intermediate diffusible and soluble oligomers of Abeta being of particular significance. SAP and apoE, in a different manner for the three isoforms, serve as "pathological" chaperones during the aggregation of Abeta considered as a conformation-prone process. In turn, apoE consisting of two domains self-associates in solution and intermediate structures differently populated for the three isoforms exist. The different structures of the three isoforms determine their different distribution among various plasma lipoproteins. The structural and metabolic consideration of the common apoE pathway(s) in two pathologies assumes four molecular targets for AD correction: (i) inhibition of the accumulation of diffusible soluble Abeta oligomers; (ii) inhibition of apoE synthesis and secretion by astrocytes, in particular, under lipid-lowering therapy; (iii) inhibition of the binding of apoE and/or SAP to Abeta; (iv) stimulation of the expression of cholesterol transporter ABCA1.