Probing and Trapping a Sensitive Conformation: Amyloid-β Fibrils, Oligomers, and Dimers

Article type: Research Article

Authors: Fawver, Janelle N.^{a; 1} | Duong, Karen T.^{a; 1} | Wise-Scira, Olivia^{b; 1} | Petrofes Chapa, Rachel^a | Schall, Hayley E.^a | Coskuner, Orkid^b | Zhu, Xiongwei^c | Colom, Luis V.^d | Murray, Ian V.J.^{a; *}

Affiliations: [a] Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M Health Science Center, Bryan, TX, USA | [b] Department of Chemistry, University of Texas San Antonio, San Antonio, TX, USA | [c] Department of Pathology, Case Western Reserve University, Cleveland, OH, USA | [d] Department of Biomedicine and Center of Biomedical Studies, The University of Texas at Brownsville, Brownsville, TX, USA

Correspondence: [*] Correspondence to: Dr. Ian V.J. Murray, Rm 4104, Medical Research and Education Building, Texas A&M Health Science Center, Bryan, TX 77807, USA. Tel.: +1 979 436 0331; Fax: +1 979 436 0086; E-mail: [email protected].

Note: [1] These authors contributed equally to the manuscript.

Abstract: Alzheimer's disease (AD) is a devastating neurodegenerative disease with pathological misfolding of amyloid-β protein (Aβ). The recent interest in Aβ misfolding intermediates necessitates development of novel detection methods and ability to trap these intermediates. We speculated that two regions of Aβ may allow for detection of specific Aβ species: the N-terminal and 22-35, both likely important in oligomer interaction and formation. We determined via epitomics, proteomic assays, and electron microscopy that the Aβ42 species (wild type, ΔE22, and MetOx) predominantly formed fibrils, oligomers, or dimers, respectively. The 2H4 antibody to the N-terminal of Aβ, in the presence of 2% SDS, primarily detected fibrils, and an antibody to the 22-35 region detected low molecular weight Aβ species. Simulated molecular modeling provided insight into these SDS-induced structural changes. We next determined if these methods could be used to screen anti-Aβ drugs as well as identify compounds that trap Aβ in various conformations. Immunoblot assays determined that taurine, homotaurine (Tramiprosate), myoinositol, methylene blue, and curcumin did not prevent Aβ aggregation. However, calmidazolium chloride trapped Aβ at oligomers, and berberine reduced oligomer formation. Finally, pretreatment of AD brain tissues with SDS enhanced 2H4 antibody immunostaining of fibrillar Aβ. Thus we identified and characterized Aβs that adopt specific predominant conformations (modified Aβ or via interactions with compounds), developed a novel assay for aggregated Aβ, and applied it to drug screening and immunohistochemistry. In summary, our novel approach facilitates drug screening, increases the probability of success of antibody therapeutics, and improves antibody-based detection and identification of different conformations of Aβ.

Keywords: Alzheimer's disease, amyloid, antibodies, berberine, curcumin, homotaurine, methylene blue, molecular modeling, protein folding, taurine

DOI: 10.3233/JAD-2012-120880

Journal: Journal of Alzheimer's Disease, vol. 32, no. 1, pp. 197-215, 2012