Adenovirus-mediated expression of mutant DRPLA proteins with expanded polyglutamine stretches in neuronally differentiated PC12 cells. Preferential intranuclear aggregate formation and apoptosis

To investigate the molecular mechanisms of neuro- degeneration caused by expanded CAG repeats in dentatorubral-pallidoluysian atrophy (DRPLA), an autosomal dominant neurodegenerative disorder caused by unstable expansion of a CAG trinucleotide repeat in the DRPLA gene on 12p13.31, we established an efficient expression system for truncated and full-length DRPLA proteins with normal or expanded polyglutamine stretches in neuronally differentiated PC12 cells and fibroblasts using an adenovirus expression system. Although aggregate body formation was observed both in neuronally differentiated PC12 cells and in fibroblasts expressing truncated DRPLA proteins with Q82, >97% (n = 3) of neuronally differentiated PC12 cells showed intranuclear inclusions, while only 31 +/- 21% (n = 3) of fibroblasts had intranuclear inclusions at 3 days after infection. The percentage of apoptotic cells was significantly higher in neuronally differentiated PC12 cells expressing the truncated DRPLA protein with Q82 than in fibroblasts, suggesting the possibility that intranuclear aggregate bodies are formed preferentially in neuronally differentiated PC12 cells and that these cells are more vulnerable than fibroblasts to the toxic effects of expanded polyglutamine stretches in the DRPLA protein. When the full-length DRPLA protein with Q82 was expressed, aggregate bodies were found exclusively in the nuclei of the neuronally differentiated PC12 cells, while they were found in the cytoplasm of fibroblasts. Despite the presence of aggregate bodies, apoptosis was not induced by expression of the full-length DRPLA protein with Q82 in either neuronally differentiated PC12 cells or fibroblasts, suggesting that the presence of intranuclear aggregate bodies is in itself not necessarily toxic to cells.