Human Molecular Genetics Advance Access originally published online on November 25, 2005
Human Molecular Genetics 2006 15(1):33-44; doi:10.1093/hmg/ddi423
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Proteasome impairment does not contribute to pathogenesis in R6/2 Huntington's disease mice: exclusion of proteasome activator REG
as a therapeutic target
1Department of Medical and Molecular Genetics, GKT School of Medicine, King's College London, 8th Floor Guy's Tower, Guy's Hospital, London SE1 9RT, UK and 2Department of Biochemistry, University of Utah School of Medicine, 50 N Medical Drive, Salt Lake City, UT 84132, USA
* To whom correspondence should be addressed. Tel: +44 2071883722; Fax: +44 2071882585; Email: gillian.bates{at}genetics.kcl.ac.uk
Received September 22, 2005; Accepted November 10, 2005
Huntington's disease (HD) is one of a group of neurodegenerative disorders caused by the pathological expansion of a glutamine tract. A hallmark of these so-called polyglutamine diseases is the presence of ubiquitylated inclusion bodies, which sequester various components of the 19S and 20S proteasomes. In addition, the ubiquitinproteasome system (UPS) has been shown to be severely impaired in vitro in cells overexpressing mutant huntingtin. Thus, because of its fundamental housekeeping function, impairment of the UPS in neurons could contribute to neurotoxicity. We have recently proposed that the proteasome activator REG
could contribute to UPS impairment in polyglutamine diseases by suppressing the proteasomal catalytic sites responsible for cleaving GlnGln bonds. Capping of proteasomes with REG
could therefore contribute to a potential clogging of the proteasome by pathogenic polyglutamines. We show here that genetic reduction of REG
has no effect on the well-defined neurological phenotype of R6/2 HD mice and does not affect inclusion body formation in the R6/2 brain. Surprisingly, we observe increased proteasomal chymotrypsin-like activity in 13-week-old R6/2 brains relative to non-R6/2, irrespective of REG
levels. However, assays of 26S proteasome activity in mouse brain extracts reveal no difference in proteolytic activity regardless of R6/2 or REG
genotype. These findings suggest that REG
is not a viable therapeutic target in polyglutamine disease and that overall proteasome function is not impaired by trapped mutant polyglutamine in R6/2 mice.
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