AUTHOR=Schindler Franziska , Praedel Nicole , Neuendorf Nancy , Kunz Severine , Schnoegl Sigrid , Mason Michael A. , Taxy Bridget A. , Bates Gillian P. , Khoshnan Ali , Priller Josef , Grimm Jan , Maier Marcel , Boeddrich Annett , Wanker Erich E. TITLE=Small, Seeding-Competent Huntingtin Fibrils Are Prominent Aggregate Species in Brains of zQ175 Huntington’s Disease Knock-in Mice JOURNAL=Frontiers in Neuroscience VOLUME=15 YEAR=2021 URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2021.682172 DOI=10.3389/fnins.2021.682172 ISSN=1662-453X ABSTRACT=

The deposition of mutant huntingtin (mHTT) protein aggregates in neurons of patients is a pathological hallmark of Huntington’s disease (HD). Previous investigations in cell-free and cell-based disease models showed mHTT exon-1 (mHTTex1) fragments with pathogenic polyglutamine (polyQ) tracts (>40 glutamines) to self-assemble into highly stable, β-sheet-rich protein aggregates with a fibrillar morphology. HD knock-in mouse models have not been extensively studied with regard to mHTT aggregation. They endogenously produce full-length mHTT with a pathogenic polyQ tract as well as mHTTex1 fragments. Here, we demonstrate that seeding-competent, fibrillar mHTT aggregates can be readily detected in brains of zQ175 knock-in HD mice. To do this, we applied a highly sensitive FRET-based protein amplification assay that is capable of detecting seeding-competent mHTT aggregate species down to the femtomolar range. Furthermore, we show that fibrillar structures with an average length of ∼200 nm can be enriched with aggregate-specific mouse and human antibodies from zQ175 mouse brain extracts through immunoprecipitations, confirming that such structures are formed in vivo. Together these studies indicate that small, fibrillar, seeding-competent mHTT structures are prominent aggregate species in brains of zQ175 mice.