High level expression of expanded full-length ataxin-3 in vitro causes cell death and formation of intranuclear inclusions in neuronal cells

Spinocerebellar ataxia type 3 (SCAB) is caused by a CAG/polyglutamine repea t expansion in the SCA3 gene. To analyse the pathogenic mechanisms in SCAB, we have generated ataxin-3-expressing rat mesencephalic CSM14.1 cells. In these cells, a post-mitotic neuronal phenotype is induced by temperature sh ift. The isolated stable cell lines provided high level expression of non-e xpanded (Q23) or expanded (Q70) human full-length ataxin-3. CSM14.1 cells e xpressing the expanded full-length ataxin-3 developed nuclear inclusion bod ies, strong indentations of the nuclear envelope and cytoplasmic vacuolatio n. These ultrastructural alterations were present prior to a significantly decreased viability of neuronally differentiated cells expressing expanded ataxin-3. The observed spontaneous cell death did not correlate with format ion of intranuclear inclusions and was not apoptotic by ultrastructural ana lysis. No increased susceptibility to staurosporine-induced apoptosis was f ound for the expanded or non-expanded ataxin-3-expressing cell lines. These data show that high level expression of expanded full-length ataxin-3 in a neuron-like cell line generates ultrastructural alterations of SCAB pathog enesis and results in increased spontaneous non-apoptotic cell death.