Exogenous Huntingtin-Exon1 Aggregates Exhibit Distinct Levels of Toxicity to Caenorhabditis elegans

Many neurodegenerative diseases, including Alzheimer's (AD), Parkinson's (PD), and Huntington's disease (HD), are associated with proteinaceous deposits in the brain comprising amyloid. The aggregation process leading to these deposits proceeds through a variety of intermediates, i.e., oligomers and fibrils. The heterogeneity of aggregates produced complicates the assignment of specific toxic functions to distinct aggregate species. Here, a simple centrifugation strategy was employed to produce well-characterized and relatively homogeneous populations of huntingtin (htt) aggregates in vitro. After characterization of the resulting aggregate populations, C. elegans were exogenously exposed to these different aggregates species to assess their impact on worm viability. Htt oligomers were identified as the most acutely toxic aggregate form. Nonaggregated htt and fibrils did not significantly reduce C. elegans viability. A variety of methods to manipulate htt oligomers were then tested to demonstrate the ability to modify oligomer toxicity in this model system. Chemically cross-linking htt oligomers reduced their toxicity, suggesting that structural flexibility is important in oligomer toxicity. Stabilizing oligomers with truncated peptides based on the first 17 N-terminal amino acids (Nt17) impacted toxicity when specific acetylation-mimicking point mutations were introduced. Nt17-derived peptides without any mutations did not alter toxicity; however, the addition of acetylation-mimicking mutations toward the C-terminus of the peptide reduces toxicity. Finally, two small molecules that modify htt aggregation, EGCG and riluzole, were tested for their impact on oligomer toxicity. In general, this approach provides a simple method to investigate and manipulate the toxicity of aggregate subpopulation in a quasi-controlled manner.