Down-regulation of heat shock protein 27 in neuronal cells and non-neuronal cells expressing mutant ataxin-3.

Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 is an autosomal dominant spinocerebellar degeneration characterized by a wide range of clinical manifestations. Unstable CAG trinucleotide repeat expansion in the MJD gene has been identified as the pathologic mutation of MJD. In this study, human SK-N-SH neuroblastoma cells stably transfected with full-length MJD with 78 CAG repeats were established. Compared with the parental cells, cells expressing mutant ataxin-3 displayed normal morphology for over 80 generations. Less than 1% of the transfected cells contained nuclear aggregates under basal conditions, indicating that this cellular model represented an early disease stage. While t-butyl hydroperoxide (TBH) was used to assess the oxidative tolerance of cells, the results demonstrated that the transfected cells were more susceptible to low concentrations of TBH than the parental cells. Most interestingly, from 2D gel electrophoresis analysis, we identified that the expression of heat shock protein 27 (HSP27), known as a suppressor of poly(Q)-mediated cell death, dramatically decreased in SK-N-SH cells stably transfected with full-length mutant MJD. The same reduction of HSP27 was further confirmed in lymphoblastoid cells from MJD patients. Our results demonstrated that both neuronal and non-neuronal cells with expanded full-length ataxin-3 revealed reduced protein expression of HSP27. We propose that the reduction of HSP27 in the early stage of the disease plays an important role during cell death process in MJD.