Mutant Ataxin-3 with an Abnormally Expanded Polyglutamine Chain Disrupts Dendritic Development and Metabotropic Glutamate Receptor Signaling in Mouse Cerebellar Purkinje Cells

• DOI: 10.1007/s12311-013-0516-5
• Publication Date: 2013-08-19T00:06:07Z
• Authors: Ayumu Konno; Anton N. Shuvaev; Noriko Miyake; Koichi Miyake; Akira Iizuka; Serina Matsuura; Fathul Huda; Kazuhiro Nakamura; Shigeru Yanagi; Takashi Shimada; Hirokazu Hirai
• Keywords: Cell Nucleus; 0301 basic medicine; 0303 health sciences; Action Potentials; Nuclear Proteins; Mice, Transgenic; Nuclear Receptor Subfamily 1, Group F, Member 1; Dendrites; Machado-Joseph Disease; In Vitro Techniques; Electric Capacitance; Receptors, Metabotropic Glutamate; Membrane Potentials; 3. Good health; Mice, Inbred C57BL; Mice; Purkinje Cells; 03 medical and health sciences; Cerebellum; Mutation; Animals; Receptors, AMPA; Ataxin-3; Peptides

Spinocerebellar ataxia type 3 (SCA3) is caused by the abnormal expansion of CAG repeats within the ataxin-3 gene. Previously, we generated transgenic mice (SCA3 mice) that express a truncated form of ataxin-3 containing abnormally expanded CAG repeats specifically in cerebellar Purkinje cells (PCs). Here, we further characterize these SCA3 mice. Whole-cell patch-clamp analysis of PCs from advanced-stage SCA3 mice revealed a significant decrease in membrane capacitance due to poor dendritic arborization and the complete absence of metabotropic glutamate receptor subtype1 (mGluR1)-mediated retrograde suppression of synaptic transmission at parallel fiber terminals, with an overall preservation of AMPA receptor-mediated fast synaptic transmission. Because these cerebellar phenotypes are reminiscent of retinoic acid receptor-related orphan receptor α (RORα)-defective staggerer mice, we examined the levels of RORα in the SCA3 mouse cerebellum by immunohistochemistry and found a marked reduction of RORα in the nuclei of SCA3 mouse PCs. To confirm that the defects in SCA3 mice were caused by postnatal deposition of mutant ataxin-3 in PCs, not by genome disruption via transgene insertion, we tried to reduce the accumulation of mutant ataxin-3 in developing PCs by viral vector-mediated expression of CRAG, a molecule that facilitates the degradation of stress proteins. Concomitant with the removal of mutant ataxin-3, CRAG-expressing PCs had greater numbers of differentiated dendrites compared to non-transduced PCs and exhibited retrograde suppression of synaptic transmission following mGluR1 activation. These results suggest that postnatal nuclear accumulation of mutant ataxin-3 disrupts dendritic differentiation and mGluR-signaling in SCA3 mouse PCs, and this disruption may be caused by a defect in a RORα-driven transcription pathway.