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Amyloid-β oligomer specificity mediated by the IgM isotype: implications for a specific protective mechanism exerted by endogenous auto-antibodies
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
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2010 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 5, no 11, e13928- p.Article in journal (Refereed) Published
Abstract [en]

Background Alzheimers disease (AD) has been strongly linked to an anomalous self-assembly of the amyloid-β peptide (Aβ). The correlation between clinical symptoms of AD and Aβ depositions is, however, weak. Instead small and soluble Aβ oligomers are suggested to exert the major pathological effects. In strong support of this notion, immunological targeting of Aβ oligomers in AD mice-models shows that memory impairments can be restored without affecting the total burden of Aβ deposits. Consequently a specific immunological targeting of Aβ oligomers is of high therapeutic interest.

Methodology/Principal Findings Previously the generation of conformational-dependent oligomer specific anti-Aβ antibodies has been described. However, to avoid the difficult task of identifying a molecular architecture only present on oligomers, we have focused on a more general approach based on the hypothesis that all oligomers expose multiple identical epitopes and therefore would have an increased binding to a multivalent receptor. Using the polyvalent IgM immunoglobulin we have developed a monoclonal anti-Aβ antibody (OMAB). OMAB only demonstrates a weak interaction with Aβ monomers and dimers having fast on and off-rate kinetics. However, as an effect of avidity, its interaction with Aβ-oligomers results in a strong complex with an exceptionally slow off-rate. Through this mechanism a selectivity towards Aβ oligomers is acquired and OMAB fully inhibits the cytotoxic effect exerted by Aβ(1-42) at highly substoichiometric ratios. Anti-Aβ auto-antibodies of IgM isotype are frequently present in the sera of humans. Through a screen of endogenous anti-Aβ IgM auto-antibodies from a group of healthy individuals we show that all displays a preference for oligomeric Aβ.

Conclusions/Significance Taken together we provide a simple and general mechanism for targeting of oligomers without the requirement of conformational-dependent epitopes. In addition, our results suggest that IgM anti-Aβ auto-antibodies may exert a more specific protective mechanism in vivo than previously anticipated.

Place, publisher, year, edition, pages
Public Library of Science , 2010. Vol. 5, no 11, e13928- p.
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Research subject
Medical Biochemistry
Identifiers
URN: urn:nbn:se:umu:diva-40238DOI: 10.1371/journal.pone.0013928ISI: 000284036800019OAI: oai:DiVA.org:umu-40238DiVA: diva2:398635
Funder
Swedish Research Council
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2012-04-13Bibliographically approved
In thesis
1. Targeting cytotoxic species in amyloid diseases
Open this publication in new window or tab >>Targeting cytotoxic species in amyloid diseases
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyloid diseases are a world-wide problem causing great human suffer and large economical costs. Although amyloid deposits, a common denominator in all amyloid disorders, are detrimental to the surrounding tissue, there is a poor correlation between total amyloid burden and clinical symptoms. Soluble oligomers are much more potent to exert a tissue damaging effect. 

Alzheimer’s disease (AD) is strongly linked to self-assembly of the amyloid-β (Aβ) peptide. Antibodies selectively targeting cytotoxic Aβ-species are useful both for understanding oligomer formation and for their therapeutic abilities. We hypothesized that the effect of avidity would compensate for a low single site affinity and be enough to selectively target oligomers. To evaluate this hypothesis, we focused on the IgM isotype having ten antigen-binding sites. In accordance with the hypothesis, the IgM isotype effectively bound oligomeric Aβ also in presence of a vast excess of its monomeric counterpart, clearly illustrating the potentiating effect of avidity. As a continuation of this work, we have shown that the avidity effect from a bivalent binding is enough to induce oligomer specificity. This finding facilitates a direct application on the clinically more useful IgG isotype, where the binding properties now can be controlled in detail. The method is general and we have, using this technique, also designed oligomer specific antibodies targeting α-synuclein.

Transthyretin (TTR) is an amyloidogenic protein involved in both hereditary and sporadic amyloidosis. The cytotoxicity of TTR is intriguing since studies have shown cytotoxic potential from oligomers, tetramers and even monomers. Elucidation of the molecular properties associated with TTR cytotoxicity is hence of interest. By preventing tetramer dissociation, TTR aggregation and TTR-induced cytotoxicity is abolished. Based on this rationale, a current therapeutic strategy is to stabilize the TTR tetramer with small molecules. The kinetic stability within the spectra of known TTR mutations spans more than three orders of magnitude. However, although the most stable mutants are inert, a poor correlation within the group of cytotoxic variants exists where the cytotoxic effect is not potentiated in proportion to their kinetic stability. Through analysis of a large spectra of TTR variants, our results indicate that TTR induced cytotoxicity requires an intermediate stability of the TTR molecule. The kinetic stability should be low enough to permit tetramer dissociation and the thermodynamic stability high enough to prevent instant aggregation and to allow formation of the cytotoxic fold. 

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2012. 63 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1494
Keyword
Alzheimer's disease, Amyloid-beta, transthyretin, FAP, amyloid, cytotoxic species, oligomers
National Category
Cell and Molecular Biology Other Basic Medicine
Research subject
Medical Biochemistry
Identifiers
urn:nbn:se:umu:diva-54006 (URN)978-91-7459-414-0 (ISBN)
Public defence
2012-05-04, KB3A9, KBC, Umeå universitet, Umeå, 10:00 (English)
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Available from: 2012-04-12 Created: 2012-04-11 Last updated: 2012-04-12Bibliographically approved

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Lindhagen-Persson, MalinBrännström, KristofferOlofsson, Anders

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