Amyloid -Protein Dimers Rapidly Form Stable Synaptotoxic Protofibrils

Laboratory for Neurodegenerative Research, Conway Institute, University College Dublin, Belfield, Dublin 4, Republic of Ireland.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 10/2010; 30(43):14411-9. DOI: 10.1523/JNEUROSCI.3537-10.2010
Source: PubMed


Nonfibrillar, water-soluble low-molecular weight assemblies of the amyloid β-protein (Aβ) are believed to play an important role in Alzheimer's disease (AD). Aqueous extracts of human brain contain Aβ assemblies that migrate on SDS-polyacrylamide gels and elute from size exclusion as dimers (∼8 kDa) and can block long-term potentiation and impair memory consolidation in the rat. Such species are detected specifically and sensitively in extracts of Alzheimer brain suggesting that SDS-stable dimers may be the basic building blocks of AD-associated synaptotoxic assemblies. Consequently, understanding the structure and properties of Aβ dimers is of great interest. In the absence of sufficient brain-derived dimer to facilitate biophysical analysis, we generated synthetic dimers designed to mimic the natural species. For this, Aβ(1-40) containing cysteine in place of serine 26 was used to produce disulphide cross-linked dimer, (AβS26C)2. Such dimers had no detectable secondary structure, produced an analytical ultracentrifugation profile consistent for an ∼8.6 kDa protein, and had no effect on hippocampal long-term potentiation (LTP). However, (AβS26C)2 aggregated more rapidly than either AβS26C or wild-type monomers and formed parastable β-sheet rich, thioflavin T-positive, protofibril-like assemblies. Whereas wild-type Aβ aggregated to form typical amyloid fibrils, the protofibril-like structures formed by (AβS26C)2 persisted for prolonged periods and potently inhibited LTP in mouse hippocampus. These data support the idea that Aβ dimers may stabilize the formation of fibril intermediates by a process distinct from that available to Aβ monomer and that higher molecular weight prefibrillar assemblies are the proximate mediators of Aβ toxicity.

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    • "Larger Aβ oligomers have been shown to correlate with higher cytotoxicity [18,19]. The finding here that larger peptide oligomers contain increasing fractions of Aβ42 raises the interesting possibility that the higher toxicity is due to the fact that heterogeneous Aβ oligomers are more toxic than homogeneous ones. "
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    ABSTRACT: Two amyloid-β peptides (Aβ40 and Aβ42) feature prominently in the extracellular brain deposits associated with Alzheimer's disease. While Aβ40 is the prevalent form in the cerebrospinal fluid, the fraction of Aβ42 increases in the amyloid deposits over the course of disease development. The low in vivo concentration (pM-nM) and metastable nature of Aβ oligomers have made identification of their size, composition, cellular binding sites and mechanism of action challenging and elusive. Furthermore, recent studies have suggested that synergistic effects between Aβ40 and Aβ42 alter both the formation and stability of various peptide oligomers as well as their cytotoxicity. These studies often utilized Aβ oligomers that were prepared in solution and at μM peptide concentrations. The current work was performed using physiological Aβ concentrations and single-molecule microscopy to follow peptide binding and association on primary cultured neurons. When the cells were exposed to a 1:1 mixture of nM Aβ40:Aβ42, significantly larger membrane-bound oligomers developed compared to those formed from either peptide alone. Fluorescence resonance energy transfer experiments at the single molecule level reveal that these larger oligomers contained both Aβ40 and Aβ42, but that the growth of these oligomers was predominantly by addition of Aβ42. Both pure peptides form very few oligomers larger than dimers, but either membrane bound Aβ40/42 complex, or Aβ40, bind Aβ42 to form increasingly larger oligomers. These findings may explain how Aβ42-dominant oligomers, suspected of being more cytotoxic, develop on the neuronal membrane under physiological conditions.
    PLoS ONE 12/2013; 8(12):e82139. DOI:10.1371/journal.pone.0082139 · 3.23 Impact Factor
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    • "These results increased the impact of soluble, premature Aβ-aggregates in the disease progression of AD, which has been positioned in the reformulated amyloid cascade hypothesis by Selkoe and Walsh [15]. Huge efforts have been made to identify distinct Aβ-aggregates derived from synthetic peptide and natural sources, resulting in a plethora of described Aβ-species with overlapping size and morphology [16]: the Aβ-dimer [17,18], low-molecular weight oligomers, comprising dimeric to tetrameric Aß [19], pentamers and hexamers [20], the dodecameric Aß56* derived from transgenic mice and human brain [21,22], globulomers [23], Aß-oligomers [24], Alzheimer-derived diffusible ligands – ADDL [10], protofibrils [25], amylospheroids [26] just to mention the major Aβ-preparations in the field. A further complexity comes with the various Aβ-fragments including the N- and C-terminal truncated Aβ-species. "
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    ABSTRACT: Alzheimer's disease (AD) is the most common dementia in the industrialized world, with prevalence rates well over 30% in the over 80-years-old population. The dementia causes enormous costs to the social healthcare systems, as well as personal tragedies for the patients, families and caregivers. AD is strongly associated with Amyloid-beta (Abeta) protein aggregation, which results in extracellular plaques in the brain, and according to the amyloid cascade hypothesis appeared to be a promising target for the development of AD therapeutics. Within the past decade convincing data has arisen positioning the soluble prefibrillar Abeta-aggregates as the prime toxic agents in AD. However, different Abeta aggregate species are described but their remarkable metastability hampers the identification of a target species for immunization. Passive immunotherapy with monoclonal antibodies (mAbs) against Abeta is in late clinical development but recently the two most advanced mAbs, Bapineuzumab and Solanezumab, targeting an N-terminal or central epitope, respectively, failed to meet their target of improving or stabilizing cognition and function. Preliminary data from off-label treatment of a small cohort for 3 years with intravenous polyclonal immunoglobulins (IVIG) that appear to target different conformational epitopes indicate a cognitive stabilization. Thus, it might be the more promising strategy reducing the whole spectrum of Abeta-aggregates than to focus on a single aggregate species for immunization.
    Immunity & Ageing 05/2013; 10(1):18. DOI:10.1186/1742-4933-10-18 · 3.54 Impact Factor
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    • "Belinova et al. recently reviewed these findings and concluded that the identified dimers may aggregate to larger oligomers during toxicity assays and that the observed toxicity may have originated from these larger species [67]. In fact, O’Nuallain confirmed rapid aggregation of these dimers to metastable protofibrils [31]. "
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    ABSTRACT: Aggregates of amyloid-beta (Aβ) peptides are thought to be involved in the development of Alzheimer’s disease because they can change synaptic plasticity and induce neuronal cell death by inflammation, oxidative damage, and transmembrane pore formation. Exactly which oligomeric species underlie these cytotoxic effects remains unclear. The work presented here established well-controlled aggregation conditions of Aβ 1–40 or Aβ1–42 peptides over a 20-day period and characterized these preparations with regard to their β-sheet content, degree of fibril formation, relative abundance of various oligomer sizes, and propensity to induce membrane pore formation and cytotoxicity. Using this multivariate data set, a systematic and inherently unbiased partial least squares (PLS) approach showed that for both peptides the abundance of oligomers in the tetramer to 13-mer range contributed positively to both pore formation and cytotoxicity, while monomers, dimers, trimers, and the largest oligomers (>210 kDa) were negatively correlated to both phenomena. Multivariate PLS analysis is ideally suited to handle complex data sets and interdependent variables such as relative oligomer concentrations, making it possible to elucidate structure function relationships in complex mixtures. This approach, therefore, introduces an enabling tool to the field of amyloid research, in which it is often difficult to interpret the activity of individual species within a complex mixture of bioactive species.
    PLoS ONE 10/2012; 7(10):e47261. DOI:10.1371/journal.pone.0047261 · 3.23 Impact Factor
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