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

• Published in: Cerebellum (London, England) Vol. 13; no. 1; pp. 29 - 41
• Main Authors: Konno, Ayumu, Shuvaev, Anton N., Miyake, Noriko, Miyake, Koichi, Iizuka, Akira, Matsuura, Serina, Huda, Fathul, Nakamura, Kazuhiro, Yanagi, Shigeru, Shimada, Takashi, Hirai, Hirokazu
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-02-2014; Springer Nature B.V
• Subjects: Action Potentials; Animals; Ataxin-3; Biomedical and Life Sciences; Biomedicine; Cell Nucleus - physiology; Cerebellum - growth & development; Cerebellum - physiology; Dendrites - pathology; Dendrites - physiology; Electric Capacitance; In Vitro Techniques; Machado-Joseph Disease - genetics; Machado-Joseph Disease - pathology; Machado-Joseph Disease - physiopathology; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Neurobiology; Neurology; Neurosciences; Nuclear Proteins - chemistry; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Nuclear Receptor Subfamily 1, Group F, Member 1 - metabolism; Original Paper; Peptides; Purkinje Cells - pathology; Purkinje Cells - physiology; Receptors, AMPA - metabolism; Receptors, Metabotropic Glutamate - metabolism; Synaptic Transmission; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Patch clamp; Spinocerebellar ataxia type 3; Purkinje cell; Endocannabinoid; Metabotropic glutamate receptor
• ISSN: 1473-4222; 1473-4230
• DOI: 10.1007/s12311-013-0516-5

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.