Human Molecular Genetics Advance Access originally published online on October 18, 2007
Human Molecular Genetics 2008 17(3):345-356; doi:10.1093/hmg/ddm311
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Soluble polyglutamine oligomers formed prior to inclusion body formation are cytotoxic
1 School of Health Sciences, Faculty of Medicine 2 Department of Neurology, Clinical Neuroscience Branch, Brain Research Institute and 3 Department of Molecular Neuroscience, Resource Branch for Brain Disease Research, Center for Bioresource-Based Research, Brain Research Institute, Niigata University, 1-757 Asahimachi, Niigata 951-8122, Japan 4 Division of Clinical Genetics, Department of Medical Genetics, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan
* To whom correspondence should be addressed. Tel: +81 252270684; Fax: +81 252270682; Email: onodera{at}bri.niigata-u.ac.jp
Received July 10, 2007; Revised September 21, 2007; Accepted October 16, 2007
Expanded polyglutamine (polyQ) repeats cause neurodegenerative disorders, but their cytotoxic structures remain to be elucidated. Although soluble polyQ oligomers have been proposed as a cytotoxic structure, the cytotoxicity of soluble polyQ oligomers, not inclusion bodies (IBs), has not been proven in living cells. To clarify the cytotoxicity of soluble polyQ oligomers, we carried our fluorescence resonance energy transfer (FRET) confocal microscopy and distinguished oligomers from monomers and IBs in a single living cell. FRET signals were detected when donor and acceptor fluorescent proteins were attached to the same side, not the opposite side, of polyQ repeats, which agrees with a parallel β-sheet or a head-to-tail cylindrical β-sheet model. These FRET signals disappeared in semi-intact cells, indicating that these polyQ oligomers are soluble. PolyQ monomers assembled into soluble oligomers in a length-dependent manner, which was followed by the formation of IBs. Notably, survival assay of neuronally differentiated cells revealed that cells with soluble oligomers died faster than those with IBs or monomers. These results indicate that a length-dependent formation of oligomers is an essential mechanism underlying neurodegeneration in polyQ-mediated disorders.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.