Author ORCID Identifier

https://orcid.org/0000-0002-0180-5375

Semester

Summer

Date of Graduation

2026

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Fabian Goulay

Committee Co-Chair

Justin Legleiter

Committee Member

Mark Tinsley

Committee Member

Terry Gullion

Committee Member

Werner Geldenhuys

Abstract

Abstract

Investigating the Impact of Human Huntingtin Protein Expression on a C. elegans Disease Model

Ephraim C. Ezeigbo

Huntington’s disease (HD) is a fatal neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) tract in the huntingtin protein (HTT), leading to protein misfolding, aggregation, and progressive neuronal degeneration. Although HTT aggregation in the brain has been extensively studied, the protein is ubiquitously expressed, and the peripheral consequences of mutant HTT (mHTT) expression remain poorly understood. Furthermore, the structural heterogeneity of HTT aggregates, including oligomers, fibrils, and intermediate species, has complicated efforts to identify the specific toxic forms responsible for pathology. This dissertation addresses these gaps through three complementary objectives: identifying the most toxic HTT aggregate species and strategies to modulate their toxicity, characterizing proteome remodeling in peripheral tissues expressing mHTT, and investigating metabolic dysregulation associated with peripheral mHTT expression. Using Caenorhabditis elegans as a model system, the first study employed a centrifugation based fractionation strategy to generate well characterized HTT aggregate populations in vitro. Exposure of wild-type (N2) worms to these species revealed that HTT oligomers were the most acutely toxic, whereas monomeric HTT and fibrillar aggregates had minimal effects on viability. Oligomer toxicity could be modulated through structural stabilization approaches including chemical cross linking, acetylation mimicking Nt17 derived peptides, and treatment with small molecules such as epigallocatechin gallate (EGCG) and riluzole, which altered aggregation behavior and reduced toxicity. The second study examined the effects of peripheral mHTT expression on proteome remodeling using C. elegans models expressing non pathogenic (15Q) and pathogenic (128Q) N terminal HTT fragments in body wall muscle cells. Longitudinal proteomic analyses revealed stage dependent and non linear proteome disruption, with early stage pathogenic worms exhibiting reduced abundance of ribosomal and cytoskeletal proteins alongside increased expression of stress associated galectin, while later stages showed enrichment of proteins involved in stress responses, proteostasis, protein folding, and cytoskeletal remodeling. Finally, untargeted metabolomics analysis revealed widespread metabolic alterations associated with peripheral mHTT expression. Control animals undergoing normal aging showed enrichment of pathways linked to growth and metabolism, including biosynthesis of unsaturated fatty acids, vitamin B6 metabolism, and arginine biosynthesis, whereas disease animals exhibited dysregulation of immune and metabolic pathways such as retinol, purine, and carbohydrate metabolism. Early stage disease comparisons revealed mild metabolic perturbations, while later stage comparisons demonstrated pronounced disruptions in vitamin B6 metabolism, the pentose phosphate pathway, and porphyrin metabolism, indicative of progressive metabolic dysfunction. Collectively, these findings identify oligomeric HTT as a key toxic species and demonstrate that peripheral mHTT expression drives progressive proteomic and metabolic remodeling, highlighting the systemic nature of HD pathology and revealing molecular pathways that may represent potential therapeutic targets.

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