Cryo-electron tomography provides topological insights into mutant huntingtin exon 1 and polyQ aggregates

Huntington disease (HD) is a neurodegenerative trinucleotide repeat disorder caused by an expanded poly-glutamine (polyQ) tract in the mutant huntingtin (mHTT) protein. The formation and topology of filamentous mHTT inclusions in the brain (hallmarks of HD implicated in neurotoxicity) remain elusive. Using cryo-electron tomography and subtomogram averaging, here we show that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogenous and filamentous, similar to prior observations with other methods. Yet, we find filaments in both types of aggregates under similar to 2 nm in width, thinner than previously reported, and regions forming large sheets. In addition, our data show a prevalent subpopulation of filaments exhibiting a lumpy slab morphology in both aggregates, supportive of the polyQ core model. This provides a basis for future cryoET studies of various aggregated mHTT and polyQ constructs to improve their structure-based modeling as well as their identification in cells without fusion tags.

Automated summary

Recent research using cryo-electron tomography and subtomogram averaging revealed that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogeneous and filamentous, with thin filaments and large sheet regions. Moreover, a prevalent subpopulation of filaments exhibiting a lumpy slab morphology in both types of aggregates was observed, supporting the polyQ core model. These findings provide a basis for future cryoET studies of various aggregated mHTT and polyQ constructs.