Published online March 24, 2008
doi:10.1083/jcb.200709080
The Journal of Cell Biology, Vol. 180, No. 6, 1177-1189
The Rockefeller University Press, 0021-9525 $30.00
© 2008 Wang et al.
Impaired ubiquitin–proteasome system activity in the synapses of Huntington's disease mice
Jianjun Wang,
Chuan-En Wang,
Adam Orr,
Suzanne Tydlacka,
Shi-Hua Li, and
Xiao-Jiang Li
Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322
Correspondence to Xiao-Jiang Li: xiaoli{at}genetics.emory.edu
Huntington's disease (HD) is caused by the expansion of a polyglutamine tract in the N-terminal region of huntingtin (htt) and is characterized by selective neurodegeneration. In addition to forming nuclear aggregates, mutant htt accumulates in neuronal processes as well as synapses and affects synaptic function. However, the mechanism for the synaptic toxicity of mutant htt remains to be investigated. We targeted fluorescent reporters for the ubiquitin–proteasome system (UPS) to presynaptic or postsynaptic terminals of neurons. Using these reporters and biochemical assays of isolated synaptosomes, we found that mutant htt decreases synaptic UPS activity in cultured neurons and in HD mouse brains that express N-terminal or full-length mutant htt. Given that the UPS is a key regulator of synaptic plasticity and function, our findings offer insight into the selective neuronal dysfunction seen in HD and also establish a method to measure synaptic UPS activity in other neurological disease models.
Abbreviations used in this paper: HD, Huntington's disease; htt, huntingtin; polyQ, polyglutamine; PSD, postsynaptic density; RFP, DsRed fusion protein; SDH, succinate dehydrogenase; UPS, ubiquitin–proteasome system.

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