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Fragments of HdhQ150 Mutant Huntingtin Form a Soluble Oligomer Pool That Declines with Aggregate Deposition upon Aging

Marcellin, David and Abramowski, Dorothee and Douglas, Young and Richter, Jens and Weiss, Andreas and Marcel, Audrey and Maassen, Julia and Kauffmann, Muriel and Bibel, Miriam and Shimshek, Derya and Richard, Faull and Bates, Gillian and Kuhn, Rainer R and Van Der Putten, P. Herman and Schmid, Peter and Lotz, Gregor (2012) Fragments of HdhQ150 Mutant Huntingtin Form a Soluble Oligomer Pool That Declines with Aggregate Deposition upon Aging. PloS One.

Abstract

Cleavage of the full-length mutant huntingtin (mhtt) protein into smaller, soluble aggregation-prone mhtt fragments
appears to be a key process in the neuropathophysiology of Huntington’s Disease (HD). Recent quantification studies using
TR-FRET-based immunoassays showed decreasing levels of soluble mhtt correlating with an increased load of aggregated
mhtt in the aging HdhQ150 mouse brain. To better characterize the nature of these changes at the level of native mhtt
species, we developed a detection method that combines size exclusion chromatography (SEC) and time-resolved
fluorescence resonance energy transfer (TR-FRET) that allowed us to resolve and define the formation, aggregation and
temporal dynamics of native soluble mhtt species and insoluble aggregates in the brain of the HdhQ150 knock-in mouse.
We found that mhtt fragments and not full-length mhtt form oligomers in the brains of one month-old mice long before
disease phenotypes and mhtt aggregate histopathology occur. As the HdhQ150 mice age, brain levels of soluble full-length
mhtt protein remain similar. In contrast, the soluble oligomeric pool of mhtt fragments slightly increases during the first two
months before it declines between 3 and 8 months of age. This decline inversely correlates with the formation of insoluble
mhtt aggregates. We also found that the pool-size of soluble mhtt oligomers is similar in age-matched heterozygous and
homozygous HdhQ150 mouse brains whereas insoluble aggregate formation is greatly accelerated in the homozygous
mutant brain. The capacity of the soluble mhtt oligomer pool therefore seems exhausted already in the heterozygous state
and likely kept constant by changes in flux and, as a consequence, increased rate of insoluble aggregate formation. We
demonstrate that our novel findings in mice translate to human HD brain but not HD patient fibroblasts.

Item Type: Article
Date Deposited: 13 Oct 2015 13:14
Last Modified: 13 Oct 2015 13:14
URI: https://oak.novartis.com/id/eprint/6897

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