Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Chemistry, Biochemistry

Date of Defense

11-10-2017

Graduate Advisor

Michael R. Nichols

Committee

Cynthia M. Dupureur

Wesley R. Harris

Bethany K. Zolman

Abstract

Alzheimer’s disease (AD), the most common cause of dementia, is a neurodegenerative condition characterized by loss of memory and intellectual abilities. Intracellular plaques of aggregated amyloid-beta (Ab) protein are a well-known pathology associated with AD. Although symptoms usually appear late in life, the accumulation of Ab begins decades earlier and causes activation of microglia, the brain’s immune cells. The ensuing inflammation contributes significantly to neurodegeneration. Determination of the particular form of Ab that causes the most damage in the brain is one of the major questions in the AD field. My research focused on the interactions of microglia with monomers, protofibrils, and fibrils of Ab. I found that protofibrils, not monomers or fibrils, bind to microglial surfaces, and I confirmed earlier reports that protofibrils elicit a proinflammatory response from microglia. These results were consistent regardless of changing conditions such as temperature, incubation time and Ab concentrations.

Another aspect of my research was to investigate how microglia internalize different forms of Ab. The distinction between monomers and protofibrils may have physiological significance in AD, yet there are few reports in the literature in which these two forms of Ab are examined separately. Monomers and protofibrils were carefully separated by size exclusion chromatography before cell treatments, which sets apart this work from research done in other labs. Multiple conditions and strategies, including a novel quantitation method for internalized Ab, demonstrated that microglia favor internalization of protofibrils over monomers. Further experiments determined that microglia are capable of internalizing protofibrils in high amounts without degradation. A significant amount of Ab protofibrils remain in the cytoplasm and are not routed to lysosomes, contradicting reports in the literature.

A third research objective involves the study of microvesicles released from microglia. Microvesicles may have a role in AD by transporting Ab within the brain. I conducted experiments in which microglia were stimulated to produce microvesicles, and carried out assays to both confirm the presence of and visualize microvesicles. The studies described here contribute to the understanding of the interactions between microglia and Ab, potentially leading to a possible treatment or cure for AD.

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