Masato Obayashi

Tokyo Medical and Dental University, Tokyo, Tokyo-to, Japan

Are you Masato Obayashi?

Claim your profile

Publications (5)19.65 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: Spinocerebellar ataxia type 31 (SCA31) is an autosomal-dominant cerebellar ataxia showing a Purkinje cell (PC)-predominant neurodegeneration in humans. The mutation is a complex penta-nucleotide repeat containing (TGGAA)n , (TAGAA)n , (TAAAA)n and (TAGAATAAAA)n inserted in an intron shared by two different genes BEAN1 and TK2 located in the long arm of the human chromosome 16. Previous studies have shown that (TGGAA)n is the critical component of SCA31 pathogenesis while the three other repeats, also present in normal Japanese, are not essential. Importantly, it has been shown that BEAN1 and TK2 are transcribed in mutually opposite directions in the human brain. Furthermore, abnormal RNA structures called "RNA foci" are observed by a probe against (UAGAAUAAAA)n in SCA31 patients' PC nuclei, indicating that the BEAN1-direction mutant transcript appears instrumental for the pathogenesis. However, it is not known whether the critical repeat (TGGAA)n contributes to the formation of RNA foci, neither do we understand how the RNA foci formation is relevant to the pathogenesis. To address these issues, we investigated two SCA31 cerebella by fluorescence in situ hybridization using a probe against (UGGAA)n . We also asked whether the mutant BEAN1-transcript containing (UGGAA)n exerts toxicity compared to the other three repeats in cultured cells. Histopathologically, we confirm that the PC is the main target of SCA31 pathogenesis. We find that the RNA foci containing (UGGAA)n are indeed observed in PC nuclei of both SCA31 patients, whereas similar foci were not observed in control individuals. In both transiently and stably expressed cultured cell models, we also find that the mutation transcribed in the BEAN1-direction yields more toxicity than control transcripts and forms RNA foci detected with probes against (UGGAA)n and (UAGAAUAAAA)n . Taking these findings together, we conclude that the RNA foci containing BEAN1-direction transcript (UGGAA)n are associated with PC degeneration in SCA31.
    Neuropathology 04/2013; · 1.91 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The human α1A voltage-dependent calcium channel (Cav2.1) is a pore-forming essential subunit embedded in the plasma membrane. Its cytoplasmic carboxyl(C)-tail contains a small poly-glutamine (Q) tract, whose length is normally 4∼19 Q, but when expanded up to 20∼33Q, the tract causes an autosomal-dominant neurodegenerative disorder, spinocerebellar ataxia type 6 (SCA6). A recent study has shown that a 75-kDa C-terminal fragment (CTF) containing the polyQ tract remains soluble in normal brains, but becomes insoluble mainly in the cytoplasm with additional localization to the nuclei of human SCA6 Purkinje cells. However, the mechanism by which the CTF aggregation leads to neurodegeneration is completely elusive, particularly whether the CTF exerts more toxicity in the nucleus or in the cytoplasm. We tagged recombinant (r)CTF with either nuclear-localization or nuclear-export signal, created doxycyclin-inducible rat pheochromocytoma (PC12) cell lines, and found that the CTF is more toxic in the cytoplasm than in the nucleus, the observations being more obvious with Q28 (disease range) than with Q13 (normal-length). Surprisingly, the CTF aggregates co-localized both with cAMP response element-binding protein (CREB) and phosphorylated-CREB (p-CREB) in the cytoplasm, and Western blot analysis showed that the quantity of CREB and p-CREB were both decreased in the nucleus when the rCTF formed aggregates in the cytoplasm. In human brains, polyQ aggregates also co-localized with CREB in the cytoplasm of SCA6 Purkinje cells, but not in other conditions. Collectively, the cytoplasmic Cav2.1-CTF aggregates are sufficient to cause cell death, and one of the pathogenic mechanisms may be abnormal CREB trafficking in the cytoplasm and reduced CREB and p-CREB levels in the nuclei.
    PLoS ONE 01/2013; 8(3):e50121. · 3.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Spinocerebellar ataxia type 6 (SCA6) is an autosomal-dominant neurodegenerative disorder caused by a small expansion of tri-nucleotide (CAG) repeat encoding polyglutamine (polyQ) in the gene for α(1A) voltage-dependent calcium channel (Ca(v) 2.1). Thus, this disease is one of the nine neurodegenerative disorders called polyQ diseases. The Purkinje cell predominant neuronal loss is the characteristic neuropathology of SCA6, and a 75-kDa carboxy-terminal fragment (CTF) of Ca(v) 2.1 containing polyQ, which remains soluble in normal brains, becomes insoluble in the cytoplasm of SCA6 Purkinje cells. Because the suppression of the brain-derived neurotrophic factor (BDNF) expression is a potentially momentous phenomenon in many other polyQ diseases, we implemented BDNF expression analysis in SCA6 human cerebellum using quantitative RT-PCR for the BDNF mRNA, and by immunohistochemistry for the BDNF protein. We observed significantly reduced BDNF mRNA levels in SCA6 cerebellum (n = 3) compared to controls (n = 6) (Mann-Whitney U-test, P = 0.0201). On immunohistochemistry, BDNF protein was only weakly stained in control cerebellum. On the other hand, we found numerous BDNF-immunoreactive granules in dendrites of SCA6 Purkinje cells. We did not observe similar BDNF-immunoreactive granules in other polyQ diseases, such as Huntington's disease or SCA2. As we often observed that the 1C2-positive Ca(v) 2.1 aggregates existed more proximally than the BDNF-positive granules in the dendrites, we speculated that the BDNF protein trafficking in dendrites may be disturbed by Ca(v) 2.1 aggregates in SCA6 Purkinje cells. We conclude that the SCA6 pathogenic mechanism associates with the BDNF mRNA expression reduction and abnormal localization of BDNF protein.
    Neuropathology 03/2012; · 1.91 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Spinocerebellar ataxia type 15 (SCA15) is an autosomal dominant neurodegenerative disorder clinically characterized by late-onset, slowly progressive pure cerebellar ataxia. This disease is caused by a heterozygous deletion of the inositol 1, 4, 5-triphosphate receptor type 1 (ITPR1) gene, suggesting that haploinsufficiency of the receptor function is the plausible disease mechanism. To clarify the prevalence of SCA15 in Japan, we designed four sets of probes and primers in different regions of ITPR1 and performed TaqMan PCR assay to search for gene deletions in 226 index SCA patients excluded for repeat expansion disorders. Deletion was found in only one patient, in whom gait ataxia started at 51 years of age and progressed to show cerebellar ataxia. This study demonstrates a simple but efficient method for screening ITPR1 deletion. We also conclude that ITPR1 gene deletions are much rare in Japan than in Europe, comprising only 0.3% in all SCAs in Japan.
    Journal of Human Genetics 02/2012; 57(3):202-6. · 2.37 Impact Factor
  • Source
    [show abstract] [hide abstract]
    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.
    Acta Neuropathologica 04/2010; 119(4):447-64. · 9.73 Impact Factor