Alzheimer's disease amyloid propagation by a template-dependent dock-lock mechanism

Amyloid plaques composed of the peptide Abeta are an integral part of Alzheimer's disease (AD) pathogenesis. We have modeled the process of amyloid plaque growth by monitoring the deposition of soluble Abeta onto amyloid in AD brain tissue or synthetic amyloid fibrils and show that it is mediated by two distinct kinetic processes. In the first phase, "dock", Abeta addition to the amyloid template is fully reversible (dissociation t(1/2) approximately 10 min), while in the second phase, "lock", the deposited peptide becomes irreversibly associated (dissociation t(1/2) > 1000 min) with the template in a time-dependent manner. The most recently deposited peptide dissociates first while Abeta previously deposited becomes irreversibly "locked" onto the template. Thus, the transition from monomer to neurotoxic amyloid is mediated by interaction with the template, a mechanism that has also been proposed for the prion diseases. Interestingly, two Abeta peptides bearing primary sequence alterations implicated in heritable Abeta amyloidoses displayed faster lock-phase kinetics than wild-type Abeta. Inhibiting the initial weak docking interaction between depositing Abeta and the template is a viable therapeutic target to prevent the critical conformational transition in the conversion of Abeta((solution)) to Abeta((amyloid)) and thus prevent stable amyloid accumulation. While thermodynamics suggest that inhibiting amyloid assembly would be difficult, the present study illustrates that the protein misfolding diseases are kinetically vulnerable to intervention.     

Deposition of monomeric, not oligomeric, Abeta mediates growth of Alzheimer's disease amyloid plaques in human brain preparations.

Senile plaques composed of the peptide Abeta contribute to the pathogenesis of Alzheimer's disease (AD), and mechanisms underlying their formation and growth may be exploitable as therapeutic targets. To examine the process of amyloid plaque growth in human brain, we have utilized size exclusion chromatography (SEC), translational diffusion measured by NMR, and in vitro models of Abeta amyloid growth to identify the oligomerization state of Abeta that is competent to add onto an existing amyloid deposit. SEC of radiolabeled and unlabeled Abeta over a concentration range of 10(-)(10)-10(-)(4) M demonstrated that the freshly dissolved peptide eluted as a single low molecular weight species, consistent with monomer or dimer. This low molecular weight Abeta species isolated by SEC was competent to deposit onto preexisting amyloid in preparations of AD cortex, with first-order kinetic dependence on soluble Abeta concentration, establishing that solution-phase oligomerization is not rate limiting. Translational diffusion measurements of the low molecular weight Abeta fraction demonstrate that the form of the peptide active in plaque deposition is a monomer. In deliberately aged (>6 weeks) Abeta solutions, a high molecular weight (>100 000 M(r)) species was detectable in the SEC column void. In contrast to the active monomer, assembled Abeta isolated from the column showed little or no focal association with AD tissue. These studies establish that, at least in vitro, Abeta exists as a monomer at physiological concentrations and that deposition of monomers, rather than of oligomeric Abeta assemblies, mediates the growth of existing amyloid in human brain preparations.     

Characterization of amyloid beta peptides from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein

Alzheimer's disease (AD) is marked by the presence of neurofibrillary tangles and amyloid plaques in the brain of patients. To study plaque formation, we report on further quantitative and qualitative analysis of human and mouse amyloid beta peptides (Abeta) from brain extracts of transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP). Using enzyme-linked immunosorbant assays (ELISAs) specific for either human or rodent Abeta, we found that the peptides from both species aggregated to form plaques. The ratios of deposited Abeta1-42/1-40 were in the order of 2-3 for human and 8-9 for mouse peptides, indicating preferential deposition of Abeta42. We also determined the identity and relative levels of other Abeta variants present in protein extracts from soluble and insoluble brain fractions. This was done by combined immunoprecipitation and mass spectrometry (IP/MS). The most prominent peptides truncated either at the carboxyl- or the amino-terminus were Abeta1-38 and Abeta11-42, respectively, and the latter was strongly enriched in the extracts of deposited peptides. Taken together, our data indicate that plaques of APP-London transgenic mice consist of aggregates of multiple human and mouse Abeta variants, and the human variants that we identified were previously detected in brain extracts of AD patients.     

Template-directed self-assembly and growth of insulin amyloid fibrils

The formation of amyloid aggregates in tissue is a pathological feature of many neurodegenerative diseases and type II diabetes. Amyloid deposition, the process of amyloid growth by the association of individual soluble amyloid molecules with a pre-existing amyloid template (i.e., plaque), is known to be critical for amyloid formation in vivo. The requirement for a natural amyloid template, however, has made amyloid deposition study difficult and cumbersome. In the present work, we developed a novel, synthetic amyloid template by attaching amyloid seeds covalently onto an N-hydroxysuccinimide-activated surface, where insulin was chosen as a model amyloidogenic protein. According to ex situ atomic force microscopy observations, insulin monomers in solution were deposited onto the synthetic amyloid template to form fibrils, like hair growth. The fibril formation on the template occurred without lag time, and its rate was highly accelerated than in the solution. The fibrils were long, over 2 mum, and much thinner than those in the solution, which was caused by limited nucleation sites on the template surface and lack of lateral twisting between fibrils. According to our investigations using thioflavin T-induced fluorescence, birefringent Congo red binding, and circular dichroism, fibrils grown on the template were identified to be amyloids that formed through a conformational rearrangement of insulin monomers upon interaction with the template. The amyloid deposition rate followed saturation kinetics with respect to insulin concentration in the solution. The characteristics of amyloid deposition on the synthetic template were in agreement with previous studies performed with human amyloid plaques. It is demonstrated that the synthetic amyloid template can be used for the screening of inhibitors on amyloid deposition in vitro.     

Metal ions differentially influence the aggregation and deposition of Alzheimer's beta-amyloid on a solid template

The abnormal deposition and aggregation of beta-amyloid (Abeta) on brain tissues are considered to be one of the characteristic neuropathological features of Alzheimer's disease (AD). Environmental conditions such as metal ions, pH, and cell membranes are associated with Abeta deposition and plaque formation. According to the amyloid cascade hypothesis of AD, the deposition of Abeta42 oligomers as diffuse plaques in vivo is an important earliest event, leading to the formation of fibrillar amyloid plaques by the further accumulation of soluble Abeta under certain environmental conditions. In order to characterize the effect of metal ions on amyloid deposition and plaque growth on a solid surface, we prepared a synthetic template by immobilizing Abeta oligomers onto a N-hydroxysuccinimide ester-activated solid surface. According to our study using ex situ atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and thioflavin T (ThT) fluorescence spectroscopy, Cu2+ and Zn2+ ions accelerated both Abeta40 and Abeta42 deposition but resulted only in the formation of "amorphous" aggregates. In contrast, Fe3+ induced the deposition of "fibrillar" amyloid plaques at neutral pH. Under mildly acidic environments, the formation of fibrillar amyloid plaques was not induced by any metal ion tested in this work. Using secondary ion mass spectroscopy (SIMS) analysis, we found that binding Cu ions to Abeta deposits on a solid template occurred by the possible reduction of Cu ions during the interaction of Abeta with Cu2+. Our results may provide insights into the role of metal ions on the formation of fibrillar or amorphous amyloid plaques in AD.     

Antisera to an amino-terminal peptide detect the amyloid protein precursor of Alzheimer's disease and recognize senile plaques

The cerebral amyloid deposited in Alzheimer's disease (AD) contains a 4.2 kDa beta amyloid polypeptide (beta AP) that is derived from a larger beta amyloid protein precursor (beta APP). Three beta APP mRNAs encoding proteins of 695, 751, and 770 amino acids have previously been identified. In each of these, there is a single membrane-spanning domain close to the carboxyl-terminus of the beta APP, and the 42 amino acid beta AP sequence extends from within the membrane-spanning domain into the large extracellular region of the beta APP. We raised rabbit antisera to a peptide corresponding to amino acids 45-62 near the amino-terminus of the beta APP. We show that these antisera detect the beta APP by demonstrating that they (i) label a set of approximately 120 kDa membrane-associated proteins in human brain previously detected by antisera to the carboxyl-terminus of beta APP and (ii) label a set of approximately 120 kDa membrane-associated proteins that are selectively overexpressed in cells transfected with a full length beta APP expression construct. The beta APP45-62 antisera specifically stain senile plaques in AD brains. This finding, along with the previous demonstration that antisera to the carboxyl-terminus of the beta APP label senile plaques, indicates that both near amino-terminal and carboxyl-terminal domains of the beta APP are present in senile plaques and suggests that proteolytic processing of the full length beta APP molecule into insoluble amyloid fibrils occurs in a highly localized fashion at the sites of amyloid deposition in AD brains.     

Differential accumulation of soluble amyloid β peptides 1–40 and 1–42 in human monocytic and neuroblastoma cell lines

Alzheimer's disease (AD) is characterized by the massive deposition in the brain of the 40-42-residue amyloid beta protein (A(beta)). While A(beta)1-40 predominates in the vascular system, A(beta)1-42 is the major component of the senile plaques in the neuropil. The concentration of both A(beta) species required to form amyloid fibrils in vitro is micromolar, yet soluble A(betas) found in normal and AD brains are in the low nanomolar range. It has been recently proposed that the levels of A(beta) sufficient to trigger amyloidogenesis may be reached intracellularly. To study the internalization and intracellular accumulation of the major isoforms of A(beta), we used THP-1 and IMR-32 neuroblastoma cells as models of human monocytic and/or macrophagic and neuronal lineages, respectively. We tested whether these cells were able to internalize and accumulate 125I-A(beta)1-40 and 125I-A(beta)1-42 differentially when offered at nanomolar concentrations and free of large aggregates, conditions that mimic a prefibrillar stage of A(beta) in AD brain. Our results showed that THP-1 monocytic cells internalized at least 10 times more 125I-A(betas) than IMR-32 neuroblastoma cells, either isolated or in a coculture system. Moreover, 125I-A(beta)1-42 presented a higher adsorption, internalization, and accumulation of undigested peptide inside cells, as opposed to 125I-A(beta)1-40. These results support that A(beta)1-42, the major pathogenic form in AD, may reach supersaturation and generate competent nuclei for amyloid fibril formation intracellularly. In light of the recently reported strong neurotoxicity of soluble, nonfibrillar A(beta)1-42, we propose that intracellular amyloidogenesis in microglia is a protective mechanism that may delay neurodegeneration at early stages of the disease.     

Assembly and aggregation properties of synthetic Alzheimer's A4/beta amyloid peptide analogs.

The amyloid A4 or beta peptide is a major component of extracellular amyloid deposits that are a characteristic feature of Alzheimer's disease. We synthesized a series of peptide analogs of the A4/beta peptide which are progressively longer at their carboxyl termini, including 42- and 39-residue peptides which represent the major forms of the A4/beta peptide in senile plaque and the hereditary cerebral hemorrhage with amyloidosis form, respectively. All peptides tested, beta 1-28 through beta 1-42, formed amyloid-like fibrils and previously unreported thin sheet-like structures which stained with thioflavin T and Congo Red. The solubility of beta 1-42 and shorter peptides was pH and concentration dependent, with a broad insolubility profile in the pH range of 3.5-6.5 and at concentrations above 0.75 mg/ml. Only peptides of 42 residues or longer were significantly insoluble at pH 7.4. beta 1-47 and beta 1-52 peptides are highly insoluble in aqueous media but are soluble at 40 mg/ml in the alpha helix-promoting solvent, 1,1,1,3,3,3-hexafluoro-2-propanol. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the beta 1-42 peptide migrates as a series of higher molecular mass aggregates whereas shorter peptides migrate as monomers. Aggregation is also dependent on pH, peptide concentration, and time of incubation in aqueous medium. These results indicate that the length of the hydrophobic carboxyl terminus of the A4/beta peptide is important in determining the solubility and aggregation properties of the A4/beta peptide and that acid pH environment, high peptide concentration, and long incubation time would be predicted to be important factors in promoting amyloid deposition.     

Amyloid-beta-peptide reduces copper(II) to copper(I) independent of its aggregation state

Alzheimer's disease (AD) is characterized by the deposition of amyloid beta-peptide (A beta) and neuronal degeneration in brain regions involved in learning and memory. One of the leading etiologic hypotheses regarding AD is the involvement of free radical-mediated oxidative stress in neuronal degeneration. Recent evidence suggests that metals concentrated in amyloid deposits may contribute to the oxidative insults observed in AD-affected brains. We hypothesized that A beta peptide in the presence of copper enhances its neurotoxicity generating free radicals via copper reduction. In the present study, we have examined the effect of the aggregation state of amyloid-beta-peptide on copper reduction. In independent experiments we measured the copper-reducing ability of soluble and fibrillar A beta(1-40) forms by bathocuproine assays. As it was previously observed for the amyloid precursor protein (APP), the A beta peptide showed copper-reducing ability. The capacity of A beta to reduce copper was independent of the aggregation state. Finally, the A beta peptide derived from the human sequence has a greater effect than the A beta peptide derived from the rat sequence, suggesting that histidine 13 may play a role in copper reduction. In agreement with this possibility, the A beta peptide reduces less copper in the presence of exogenous histidine.     

Amyloid beta.

Amyloid beta (A beta) is a 39-43 residue amyloidogenic peptide that is deposited into the extracellular amyloid plaques which characterize an Alzheimer's disease (AD) brain. A beta is derived from the amyloid precursor protein (APP) and undergoes a toxic conformational change (gain of toxic function). The length of the A beta peptide dramatically influences its properties with the longer 42 and 43 residue species being more amyloidogenic. The genetics of familial AD (FAD) supports a central role for A beta in AD since mutations in the FAD causing genes APP and the presenilins (PS1 and PS2) increase the formation of A beta 42,43. Considerable activity is directed towards A beta as a therapeutic target. These strategies aim to inhibit A beta synthesis, A beta fibril formation, its toxic actions on cells or promote its clearance from the brain.     

Activation barriers to structural transition determine deposition rates of Alzheimer's disease a beta amyloid

Brain amyloid composed of the approximately 40-amino-acid human beta-amyloid peptide A beta is integral to Alzheimer's disease pathology. To probe the importance of a conformational transition in Abeta during amyloid growth, we synthesized and examined the solution conformation and amyloid deposition activity of A beta congeners designed to have similar solution structures but to vary substantially in their barriers to conformational transition. Although all these peptides adopt similar solution conformations, a covalently restricted Abeta congener designed to have a very high barrier to conformational rearrangement was inactive, while a peptide designed to have a reduced barrier to conformational transition displayed an enhanced deposition rate relative to wild-type A beta. The hyperactive peptide, which is linked to a heritable A beta amyloidosis characterized by massive amyloid deposition at an early age, displayed a reduced activation barrier to deposition consistent with a larger difference in activation entropy than in activation enthalpy relative to wild-type A beta. These results suggest that in Alzheimer's disease, as in the prion diseases, a conformational transition in the depositing peptide is essential for the conversion of soluble monomer to insoluble amyloid, and alterations in the activation barrier to this transition affect amyloidogenicity and directly contribute to human disease.     

Alzheimer's disease and control brain contain soluble derivatives of the amyloid protein precursor that end within the beta amyloid protein region.

The 39-43 amino acid beta amyloid protein (A beta) that deposits as amyloid in the brains of patients with Alzheimer's disease (AD) is encoded as an internal sequence within a larger membrane-associated protein known as the amyloid protein precursor (APP). In cultured cells, the APP is normally cleaved within the A beta to generate a large secreted derivative and a small membrane-associated fragment. Neither of these derivatives can produce amyloid because neither contains the entire A beta. Our study was designed to determine whether the soluble APP derivatives in human brain end within the A beta as described in cell culture or whether AD brain produces potentially amyloidogenic soluble derivatives that contain the entire A beta. We find that both AD and control brain contain nonamyloidogenic soluble derivatives that end at position 15 of the A beta. We have been unable to detect any soluble derivatives that contain the entire A beta in either the AD or control brain.     

Kinetics of amyloid aggregation of mammal apomyoglobins and correlation with their amino acid sequences

In protein deposition disorders, a normally soluble protein is deposited as insoluble aggregates, referred to as amyloid. The intrinsic effects of specific mutations on the rates of protein aggregation and amyloid formation of unfolded polypeptide chains can be correlated with changes in hydrophobicity, propensity to convert alpha-helical to beta sheet conformation and charge. In this paper, we report the aggregation rates of buffalo, horse and bovine apomyoglobins. The experimental values were compared with the theoretical ones evaluated considering the amino acid differences among the sequences. Our results show that the mutations which play critical roles in the rate-determining step of apomyoglobin aggregation are those located within the N-terminal region of the molecule.     

Aggregation and secondary structure of synthetic amyloid beta A4 peptides of Alzheimer's disease

The deposition of amyloid beta A4 in the brain is a major pathological hallmark of Alzheimer's disease. Amyloid beta A4 is a peptide composed of 42 or 43 amino acid residues. In brain, it appears in the form of highly insoluble, filamentous aggregates. Using synthetic peptides corresponding to the natural beta A4 sequence as well as analog peptides, we demonstrate requirements for filament formation in vitro. We also determine aggregational properties and the secondary structure of beta A4. A comparison of amino-terminally truncated beta A4 peptides identifies a peptide spanning residues 10 to 43 as a prototype for amyloid beta A4. Infrared spectroscopy of beta A4 peptides in the solid state shows that their secondary structure consists of a beta-turn flanked by two strands of antiparallel beta-pleated sheet. Analog peptides containing a disulfide bridge were designed to stabilize different putative beta-turn positions. Limited proteolysis of these analogs allowed a localization of the central beta-turn at residues 26 to 29 of the entire sequence. Purified beta A4 peptides are soluble in water. Size-exclusion chromatography shows that they form dimers that, according to circular dichroism spectroscopy, adopt a beta-sheet conformation. Upon addition of salts, the bulk fraction of peptides precipitates and adopts a beta-sheet structure. Only a small fraction of peptides remains solubilized. They are monomeric and adopt a random coil conformation. This suggests that the formation of aggregates depends upon a hydrophobic effect that leads to intra- and intermolecular interactions between hydrophobic parts of the beta A4 sequence. This model is sustained by the properties of beta A4 analogs in which hydrophobic residues were substituted. These peptides show a markedly increased solubility in salt solutions and have lost the ability to form filaments. In contrast, the substitution of hydrophilic residues leads only to small deviations in the shape of filaments, indicating that hydrophilic residues contribute to the specificity of interactions between beta A4 peptides.     

The novel beta-secretase inhibitor KMI-429 reduces amyloid beta peptide production in amyloid precursor protein transgenic and wild-type mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. The major component of the plaques, amyloid beta peptide (Abeta), is generated from amyloid precursor protein (APP) by beta- and gamma-secretase-mediated cleavage. Because beta-secretase/beta-site APP cleaving enzyme 1 (BACE1) knockout mice produce much less Abeta and grow normally, a beta-secretase inhibitor is thought to be one of the most attractive targets for the development of therapeutic interventions for AD without apparent side-effects. Here, we report the in vivo inhibitory effects of a novel beta-secretase inhibitor, KMI-429, a transition-state mimic, which effectively inhibits beta-secretase activity in cultured cells in a dose-dependent manner. We injected KMI-429 into the hippocampus of APP transgenic mice. KMI-429 significantly reduced Abeta production in vivo in the soluble fraction compared with vehicle, but the level of Abeta in the insoluble fraction was unaffected. In contrast, an intrahippocampal injection of KMI-429 in wild-type mice remarkably reduced Abeta production in both the soluble and insoluble fractions. Our results indicate that the beta-secretase inhibitor KMI-429 is a promising candidate for the treatment of AD.     

Secretory processing of the Alzheimer amyloid beta/A4 protein precursor is increased by protein phosphorylation.

The 39-43 residue polypeptide (amyloid beta protein, beta A4) deposited as amyloid in Alzheimer's disease (AD) is derived from a set of 695-770 residue precursors referred to as the amyloid beta A4 protein precursor (beta APP). In each of the 695, 751, and 770 residue precursors, the 43 residue beta A4 is an internal peptide that begins 99 residues from the COOH-terminus of the beta APP. Each holoform is normally cleaved within the beta A4 to produce a large secreted derivative as well as a small membrane associated fragment. Neither of these derivatives can produce amyloid because neither contains the entire beta A4 peptide. In this study, we employ cells stably transfected with full length beta APP695, beta APP751, or beta APP770 expression constructs to show that phorbol ester activation of protein kinase C substantially increases the production of secreted forms from each isoform. By increasing processing of beta APP in the secretory pathway, PKC phosphorylation may help to prevent amyloid deposition.     

Potentiation of beta-amyloid polymerisation by low-density lipoprotein enhances the peptide's vasoactivity

Alzheimer's disease (AD) is characterised by the accumulation of insoluble beta-amyloid (A beta) fibrils in the brain. Factors that promote A beta fibrillogenesis may influence the pathogenesis of AD and represent targets for therapeutic intervention. Some A beta deposited in AD may originate in the circulation and plasma factors could promote A beta deposition, particularly in the cerebrovasculature. We investigated the effects of plasma low-density lipoprotein (LDL), in both its native and oxidised forms, on A beta(1-40) fibrillogenesis and vasoactivity. LDL enhanced A beta fibrillogenesis in a process dependent on LDL concentration and the oxidative state of the lipoprotein, as indicated by measurements of thiobarbituric acid reactive substances (TBARS) and conjugated dienes. LDL's actions were inhibited by the iA beta 5 peptide, suggesting that LDL-induced A beta polymerisation involved beta-pleated sheet formation. Potentiated A beta polymerisation was reflected by enhanced A beta-mediated vascular responses. Human endothelial cells exposed to fibrillar A beta generated with LDL, especially oxidised LDL, exhibited decreased 20S proteasome activity. Rat aortic ring constriction induced by noradrenaline was enhanced by A beta fibrils generated with LDL, with oxidised LDL producing the more marked effects. Should plasma lipoproteins prove to play a role in cerebral A beta deposition their modification with statins or antioxidants may offer therapeutic benefit.     

Lack of ABCA1 considerably decreases brain ApoE level and increases amyloid deposition in APP23 mice

ABCA1 (ATP-binding cassette transporter A1) is a major regulator of cholesterol efflux and high density lipoprotein (HDL) metabolism. Mutations in human ABCA1 cause severe HDL deficiencies characterized by the virtual absence of apoA-I and HDL and prevalent atherosclerosis. Recently, it has been reported that the lack of ABCA1 causes a significant reduction of apoE protein level in the brain of ABCA1 knock-out (ABCA1-/-) mice. ApoE isoforms strongly affect Alzheimer disease (AD) pathology and risk. To determine further the effect of ABCA1 on amyloid deposition, we used APP23 transgenic mice in which the human familial Swedish AD mutant is expressed only in neurons. We demonstrated that the targeted disruption of ABCA1 increases amyloid deposition in APP23 mice, and the effect is manifested by an increased level of Abeta immunoreactivity, as well as thioflavine S-positive plaques in brain parenchyma. We found that the lack of ABCA1 also considerably increased the level of cerebral amyloid angiopathy and exacerbated cerebral amyloid angiopathy-related microhemorrhage in APP23/ABCA1-/- mice. Remarkably, the elevation in parenchymal and vascular amyloid in APP23/ABCA1-/- mice was accompanied by a dramatic decrease in the level of soluble brain apoE, although insoluble apoE was not changed. The elevation of insoluble Abeta fraction in old APP23/ABCA1-/- mice, accompanied by a lack of changes in APP processing and soluble beta-amyloid in young APP23/ABCA1-/- animals, supports the conclusion that the ABCA1 deficiency increases amyloid deposition. These results suggest that ABCA1 plays a role in the pathogenesis of parenchymal and cerebrovascular amyloid pathology and thus may be considered a therapeutic target in AD.     

Systemic vaccination with anti‐oligomeric monoclonal antibodies improves cognitive function by reducing Aβ deposition and tau pathology in 3xTg‐AD mice

Alzheimer's disease (AD) is a devastating disorder that is clinically characterized by a comprehensive cognitive decline. Accumulation of the amyloid‐beta (Aβ) peptide plays a pivotal role in the pathogenesis of AD. In AD, the conversion of Aβ from a physiological soluble monomeric form into insoluble fibrillar conformation is an important event. The most toxic form of Aβ is oligomers, which is the intermediate step during the conversion of monomeric form to fibrillar form. There are at least two types of oligomers: oligomers that are immunologically related to fibrils and those that are not. In transgenic AD animal models, both active and passive anti‐Aβ immunotherapies improve cognitive function and clear the parenchymal accumulation of amyloid plaques in the brain. In this report we studied effect of immunotherapy of two sequence‐independent non‐fibrillar oligomer specific monoclonal antibodies on the cognitive function, amyloid load and tau pathology in 3xTg‐AD mice. Anti‐oligomeric monoclonal antibodies significantly reduce the amyloid load and improve the cognition. The clearance of amyloid load was significantly correlated with reduced tau hyperphosphorylation and improvement in cognition. These results demonstrate that systemic immunotherapy using oligomer‐specific monoclonal antibodies effectively attenuates behavioral and pathological impairments in 3xTg‐AD mice. These findings demonstrate the potential of using oligomer specific monoclonal antibodies as a therapeutic approach to prevent and treat Alzheimer's disease.     

Oligomers on the brain: the emerging role of soluble protein aggregates in neurodegeneration

Extracellular fibrous amyloid deposits or intracellular inclusion bodies containing abnormal protein fibrils characterize many different neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), dementia with Lewy bodies, multiple system atrophy, Huntington's disease, and the transmissible 'prion' dementias. There is strong evidence from genetic, transgenic mouse and biochemical studies to support the idea that the accumulation of protein aggregates in the brain plays a seminal role in the pathogenesis of these diseases. How monomeric proteins ultimately convert to highly polymeric deposits is unknown. However, studies employing, synthetic, cell-derived and purified recombinant proteins suggest that amyloid proteins first come together to form soluble low n-oligomers. Further association of these oligomers results in higher molecular weight assemblies including so-called 'protofibrils' and 'ADDLs' and these eventually exceed solubility limits until, finally, they are deposited as amyloid fibrils. With particular reference to AD and PD, we review recent evidence that soluble oligomers are the principal pathogenic species that drive neuronal dysfunction.