Semester

Summer

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Justin Legleiter

Committee Member

Fabien Goulay

Committee Member

Terry Gullion

Committee Member

Blake Mertz

Committee Member

David Smith

Abstract

Huntington’s Disease (HD) is a genetic neurodegenerative disease caused by the expansion of polyglutamine (polyQ) domain within the first exon (exon1) of the huntingtin (htt) protein. Due to this mutation within the polyQ domain, htt aggregates into various toxic species such as oligomers, fibrils, and other amorphous aggregates. While the aggregation of htt strongly correlates with polyQ length, other factors, e.g. interaction with membranes or organelles and posttranslational modifications (PTMs), modulate aggregation. The first 17 N-terminal amino acids (Nt17) that precede the polyQ in htt-exon1 enhances aggregation and facilitated binding of htt to membranous organelles, promoting morphological changes and disfunction. In addition, several PTMs occur within Nt17, including oxidation. Here, mechanistic insights into the impact of mitochondrial association and oxidation of htt-exon1 on its aggregation are presented. To investigate how htt aggregation is altered in the presence of mitochondria, htt-exon1 with an expanded polyQ domain was exposed to mitochondria membrane mimics and mitochondria enriched fractions (MEFs). Mitochondrial membrane mimics significantly reduced htt aggregation into fibrils. However, inner mitochondrial membrane mimic (IMM) had a greater inhibitory effect on htt-exon1 fibrillization compared with outer mitochondrial membrane mimic (OMM). Cardiolipin, a mitochondria-exclusive-lipid that is more abundant in IMM, played a primary role in altering htt aggregation. Similarly, MEFs suppressed fibril formation. With regard to htt oxidation, aggregation was inhibited by treatment with hydrogen peroxide (H2O2) in a dose dependent manner. Specifically, fibril elongation and accumulation were prevented at high peroxide doses. The presence of total brain lipid extract (TBLE) vesicles did not alter the observed inverse relationship between htt aggregation and oxidant concentration. However, the combined effects of lipid presence and H2O2 treatment caused larger reduction in fibrillization compared with H2O2 treatment alone. Oxidation of htt-exon1 and/or lipid membranes altered aggregation patterns directly on a bilayer surface. Oxidation of both the protein and lipid promoted the appearance of plateau-like regions containing htt-exon1 aggregates. Collectively, these results demonstrate that htt-lipid interactions play significant roles in modulating htt aggregation pathways.

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