Article

Amyloid beta-protein dimers rapidly form stable synaptotoxic protofibrils.

Laboratory for Neurodegenerative Research, Conway Institute, University College Dublin, Belfield, Dublin 4, Republic of Ireland.
Journal of Neuroscience (Impact Factor: 6.75). 10/2010; 30(43):14411-9. DOI: 10.1523/JNEUROSCI.3537-10.2010
Source: PubMed

ABSTRACT 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.

1 Bookmark
 · 
123 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Neuroinflammation is a characteristic feature of the Alzheimer's disease (AD) brain. Significant inflammatory markers such as activated microglia and cytokines can be found surrounding the extracellular senile plaques predominantly composed of amyloid-β protein (Aβ). Several innate immune pathways, including Toll-like receptors (TLRs) and the NLRP3 inflammasome, have been implicated in AD inflammation. Aβ plays a primary role in activating these pathways which likely contributes to the progressive neurodegeneration in AD. In order to better understand the complexities of this interaction we investigated the inflammatory response of primary microglia to Aβ(1-42) protofibrils. Aβ(1-42) protofibrils triggered a time- and MyD88-dependent process that produced tumor necrosis factor alpha (TNFα) and interleukin-1β (IL-1β) mRNA, and intracellular pro and mature forms of IL-1β protein. The accumulation of both IL-1β forms indicated that Aβ(1-42) protofibrils were able to prime and activate the NLRP3 inflammasome. Surprisingly, Aβ-induced accumulation of intracellular mature IL-1β did not translate into greater IL-1β secretion. Instead, we found that Aβ elicited a quantized burst of secreted IL-1β and this process occurred even prior to Aβ priming of the microglia suggesting a basal level of either pro or mature IL-1β in the cultured primary microglia. The IL-1β secretion burst was rapid but not sustained, yet could be re-evoked with additional Aβ stimulation. The findings from this study demonstrated multiple sites of IL-1β regulation by Aβ(1-42) protofibrils including TLR/MyD88-mediated priming, NLRP3 inflammasome activation, and modulation of the IL-1β secretory process. These results underscore the wide-ranging effects of Aβ on the innate immune response.
    Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease 08/2014; · 5.09 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recently, amyloid-beta (Aβ) phosphorylation at position 8 has been shown to be associated with pathogenesis of Alzheimer’s disease. Since the modification occurs in the key fragment of the metal-binding domain of Aβ and should seriously affect the interaction of pS8-Aβ with zinc ions, this isoform may be a potential precursor of pathogenic oligomer forms of Aβ. Hence the level of pS8-Aβ in human biological fluids (blood, urine, cerebrospinal fluid) may reflect various stages of pathogenesis of the Alzheimer’s disease. The aim of the work was to develop a prototype of an analytical method for quantitative determination of the level of pS8-Aβ isoform in binary mixtures with native Aβ in order to further use it to estimate the levels of phosphorylated amyloid-beta in blood plasma samples of patients diagnosed with Alzheimer’s disease.
    Molecular Biology 07/2014; 48(4):607-614. · 0.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A decade following the paradigm-shifting concept that endogenous forms of soluble, non-fibrillar amyloid-β (Aβ) might constitute the major bioactive entity causing synaptic loss and cognitive decline in Alzheimer's disease (AD), our understanding of these oligomeric species still remains conspicuously superficial. The current lack of direct evaluation tools for each endogenous Aβ oligomer hampers our ability to readily address crucial question such as: (i) where they form and accumulate?; (ii) when they first appear in human brains and body fluids?; (iii) what is the longitudinal expression of these putative toxins during the course of the disease?; (iv) and how do these soluble Aβ assemblies alter synaptic and neuronal function in the brain? Despite these limitations, indirect ex vivo measurement and isolation from biological specimens has been possible and have allowed parsing out intrinsic differences between putative endogenous Aβ oligomers. In this review, I integrated recent findings and extrapolated emerging hypotheses derived from these studies with the hope to provide a clarified view on the putative role of endogenous Aβ oligomers in AD, with a particular emphasis on the timing at which these soluble species might act in the aging and diseased brain.
    Swiss medical weekly: official journal of the Swiss Society of Infectious Diseases, the Swiss Society of Internal Medicine, the Swiss Society of Pneumology 01/2014; 144:w14021. · 1.88 Impact Factor

Full-text (2 Sources)

Download
48 Downloads
Available from
May 30, 2014