Polyglutamine core is the primary driver of seeded huntingtin aggregation.

Abstract

Huntington's Disease (HD) is a fatal, neurodegenerative disease caused by an expansion of the polyglutamine (polyQ) domain beyond a critical threshold within the first exon of the huntingtin protein (htt). N-terminal fragments of htt containing the abnormal length polyQ domain results in an accumulation of a complex mixture of proteinaceous aggregates, such as oligomers and fibrils, associated with HD. Htt associates with a variety of lipid membranes in the cell which is facilitated by the flanking sequences surrounding the polyQ domain. This htt-lipid interaction alters the aggregation of htt. The accumulated htt aggregates, both free and lipid bound, are able to spread to neighboring neurons in the effected regions of the brain, induce aggregation, and spread the disease in a phenomenon known as seeding. The role of lipids and flanking sequences was investigated as to their part in the seeding phenomenon. A variety of polyQ peptides with different flanking sequences were produced to investigate the effect of flanking sequences on the seeding efficiency of the polyQ domain. The seeding efficiency of the polyQ domain is unaffected by flanking sequences and dependent only on the presence of the polyQ fibril core to initiate aggregation both in pathogenic and nonpathogenic length htt and is the driving force of seeding, as measured by thioflavin T assay (ThT). Upon introduction of lipids, the polyQ seeds are able to initiate and cause seeded aggregation but are unable to fibrilize lipid-bound htt. Fibril morphology remains unchanged through inspection by ex situ atomic force microscopy. Htt seeds are toxic to C. elegans expressing a nontoxic form of htt whereas the control nematodes, lacking htt expression, remained unaffected.