Dissertation

Conformation-specific Antibodies Distinguish Amyloid Polymorphisms Associated with Alzheimer's Disease

Hatami, Asa

2013

Overview

The aggregation of misfolded amyloid proteins has been linked to the pathogenesis of a large number of degenerative diseases, including but not limited to Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, prion diseases, and diabetes. While the misfolded proteins implicated in these diseases are unique in terms of their primary sequence, they all tend to aggregate into amyloid structures, which are in turn hypothesized to mediate the toxicity and pathological effects of these proteins. Amyloid structures may be divided into prefibrillar oligomeric species containing anti-parallel β-sheets and fibrillar species characterized by parallel in-register cross-β sheets. The OC and A11 polyclonal antisera are able to immunologically distinguish the two broad groups of amyloids. Here, we introduce a series of 23 unique OC-type monoclonal antibodies developed in our lab, which display conformation-specific reactivity patterns against distinct fibrillar amyloid aggregates made from Aβ, along with aggregates formed by other amyloidogenic proteins. The wide range of reactivity profiles of these monoclonal antibodies highlights the remarkably diverse nature of the immune response against fibrillar amyloids, which in turn is a reflection of the heterogeneity of fibrillar structures formed by amyloid proteins. Interestingly, many of these monoclonal antibodies react with linear segments of the Aβ peptide while reacting in a conformational manner with amyloid aggregates of proteins with no sequence homology with Aβ. This observation indicates that antibody reactivity with linear segments of an amyloid peptide is not a reliable predictor of an antibody's specificity toward the protein in question. In fact, here we report conformational reactivity patterns observed with 2 commercially available monoclonal antibodies proposed to be sequence-specific to Aβ and -synuclein. Since the mOC antibodies are able to discern a wide range of unique conformations within fibrillar aggregates of WT Aβ, we decided to use these antibodies to study potential differences in the immunological reactivity patterns and aggregation kinetics of Aβ peptides containing familial Alzheimer's disease (FAD) mutations. Here we present data demonstrating clear differences in the amyloid conformations adopted by 11 Aβ isotypes containing FAD mutations. Furthermore, we report significant differences in the aggregation kinetics and β-sheet stacking conformation of these peptides. These data suggest that the heterogeneity of FAD cases due to mutations localized to the Aβ sequence may be due to differences in the amyloid conformations adopted by these peptides. Taken together, our data demonstrate that the immune response to fibrillar amyloid structures is diverse and leads to the production of monoclonal antibodies with a wide range of specificities. This observation in turn highlights the importance of the selection of the appropriate antibody in passive immunization therapeutic strategies, as well as raising the possibility of the use of these antibodies in imaging studies and as important in vitro tools in distinguishing different strains of fibrillar amyloid.

• Publisher: ProQuest Dissertations & Theses
• Subject: Biochemistry / Neurosciences
• ISBN: 1303587254, 9781303587252