|Institution:||University of Pittsburgh|
|Full text PDF:||http://d-scholarship.pitt.edu/27844/1/DROMBOSKY_THESIS.pdf|
Huntington’s disease (HD) is a uniformly fatal genetic disease causing progressive degeneration of the central nervous system in approximately 250,000 people worldwide. Unlike other neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, HD is explicitly caused by a single genetic defect – a CAG codon expansion in the huntingtin gene, which codes for polyglutamine (polyQ) in the protein huntingtin (htt). People carrying 40 or more CAG/glutamine repeats will develop HD by early adulthood, while those with 36 or less are unaffected. Despite this discovery over two decades ago, there are still no treatments to cure, prevent, or delay the underlying progression of HD. The physical state of the huntingtin “exon1” fragment responsible for triggering HD pathology (amyloid aggregates, non-β oligomers, or monomers) is a controversial roadblock that limits therapeutic discovery. Previous attempts to determine the toxic species have recently been identified as flawed or inconclusive. Herein, we describe mutated htt-exon1 analogs containing only 22-24 glutamine residues that deliver atypical aggregation: a “hyper-amyloid” analog that – despite its short glutamine repeat lengths – aggregates into amyloid fibrils comparable to pathogenic huntingtin, and “hypo-amyloid” analogs whose aggregation stops at the non-β oligomer stage. Hyper-amyloid htt-exon1 produces inclusions, cytotoxicity in rat neurons, and decreased lifespans with movement deficits in flies. Neurons and flies expressing hypo-amyloid htt-exon1 alone have no detectible HD phenotype. Our data strongly supports a toxic amyloid hypothesis, and we find no evidence of a toxic non-β oligomer. Furthermore, the non-toxic hypo-amyloid analogs are also able to inhibit amyloid formation of pathogenic repeat length htt-exon1. Co-expression of hypo-amyloid htt-exon1 with pathogenic htt-exon1 reduces aggregation in vitro, inhibits toxicity in neuron cultures, and rescues behavioral and lifespan HD phenotypes in flies. These exciting results offer novel, rationally designed approaches to HD therapeutics.