Transcriptional malfunctioning of heat shock protein gene expression in spinocerebellar ataxias

Among the various dominantly-inherited spinocerebellar ataxias (SCAs), at least seven of them belong to the polyglutamine disease group and are caused by glutamine-coding CAG triplet repeat expansion. The expanded coding CAG repeat translates into a polyglutamine stretch in the disease protein, which leads to late-onset and progressive neurodegeneration. Expanded polyglutamine adopts a misfolded protein conformation, and is itself a cellular stressor which induces robust heat shock response (HSR). Under polyglutamine stress, heat shock proteins ( Hsps) are produced in neurons to assist refolding and/or promote the degradation of misfolded proteins. Along with the progressive nature of polyglutamine degeneration, a gradual decline of HSR in degenerating neurons was observed. Such kind of reduction can be observed in a large family of hsp gene expression, including hsp22, 26, 27, and 70. This underscores an intimate relationship between the inducibility of hsp gene expression and the disease progression. In this review, we describe the current understandings of hsp gene dysregulation in polyglutamine disease.