The carboxy-terminal fragment of α1A calcium channel preferentially aggregates in the cytoplasm of human spinocerebellar ataxia type 6 Purkinje cells

Department of Neurology and Neurological Science, Graduate School, Tokyo Medical and Dental University, Yushima 1-5-45, Bunkyo-ku, Tokyo 113-8519, Japan.
Acta Neuropathologica (Impact Factor: 9.78). 04/2010; 119(4):447-64. DOI: 10.1007/s00401-009-0630-0
Source: PubMed

ABSTRACT Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominant neurodegenerative disease caused by a small polyglutamine (polyQ) expansion (control: 4-20Q; SCA6: 20-33Q) in the carboxyl(C)-terminal cytoplasmic domain of the alpha(1A) voltage-dependent calcium channel (Ca(v)2.1). Although a 75-85-kDa Ca(v)2.1 C-terminal fragment (CTF) is toxic in cultured cells, its existence in human brains and its role in SCA6 pathogenesis remains unknown. Here, we investigated whether the small polyQ expansion alters the expression pattern and intracellular distribution of Ca(v)2.1 in human SCA6 brains. New antibodies against the Ca(v)2.1 C-terminus were used in immunoblotting and immunohistochemistry. In the cerebella of six control individuals, the CTF was detected in sucrose- and SDS-soluble cytosolic fractions; in the cerebella of two SCA6 patients, it was additionally detected in SDS-insoluble cytosolic and sucrose-soluble nuclear fractions. In contrast, however, the CTF was not detected either in the nuclear fraction or in the SDS-insoluble cytosolic fraction of SCA6 extracerebellar tissues, indicating that the CTF being insoluble in the cytoplasm or mislocalized to the nucleus only in the SCA6 cerebellum. Immunohistochemistry revealed abundant aggregates in cell bodies and dendrites of SCA6 Purkinje cells (seven patients) but not in controls (n = 6). Recombinant CTF with a small polyQ expansion (rCTF-Q28) aggregated in cultured PC12 cells, but neither rCTF-Q13 (normal-length polyQ) nor full-length Ca(v)2.1 with Q28 did. We conclude that SCA6 pathogenesis may be associated with the CTF, normally found in the cytoplasm, being aggregated in the cytoplasm and additionally distributed in the nucleus.

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Available from: Hidehiro Mizusawa, Jul 30, 2015
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    • "However, given the level of Ca V 2.1 knockdown observed in human SK-N-SH cells following SIS-RNAi, it will be important to assess, in vivo, the extent to which SIS-RNAi targeting of polyQ-encoding Ca V 2.1 mRNAs affects overall Ca V 2.1 levels. Finally, several studies support a model of SCA6 pathogenesis that includes the accumulation and aberrant nuclear translocation of an expanded polyQ-containing Ca V 2.1 fragment (Ishiguro et al., 2009; Kordasiewicz et al., 2006; Kubodera et al., 2003; Marqueze-Pouey et al., 2008). Thus, SIS-RNAi-mediated suppression of the polyQ-encoding Ca V 2.1 splice variant should also reduce levels of putative pathogenic Ca V 2.1 fragments and be of therapeutic benefit in SCA6. "
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