Hokuto Morita

Publications (3)14.7 Total impact

• Article: Endoplasmic reticulum stress and mitochondrial cell death pathways mediate A53T mutant alpha-synuclein-induced toxicity.

  Wanli W Smith, Haibing Jiang, Zhong Pei, Yuji Tanaka, Hokuto Morita, Akira Sawa, Valina L Dawson, Ted M Dawson, Christopher A Ross
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  ABSTRACT: Parkinson's disease (PD) is a neurodegenerative movement disorder characterized by selective loss of dopaminergic neurons and the presence of Lewy bodies. Alpha-synuclein is a major component of Lewy bodies in sporadic PD, and mutations in alpha-synuclein cause autosomal-dominant hereditary PD. Here, we generated A53T mutant alpha-synuclein-inducible PC12 cell lines using the Tet-off regulatory system. Inducing expression of A53T alpha-synuclein in differentiated PC12 cells decreased proteasome activity, increased the intracellular ROS level and caused up to approximately 40% cell death, which was accompanied by mitochondrial cytochrome C release and elevation of caspase-9 and -3 activities. Cell death was partially blocked by cyclosporine A [an inhibitor of the mitochondrial permeability transition (MPT) process], z-VAD (a pan-caspase inhibitor) and inhibitors of caspase-9 and -3 but not by a caspase-8 inhibitor. Furthermore, induction of A53T alpha-synuclein increased endoplasmic reticulum (ER) stress and elevated caspase-12 activity. RNA interference to knock down caspase-12 levels or salubrinal (an ER stress inhibitor) partially protected against cell death and further reduced A53T toxicity after treatment with z-VAD. Our results indicate that both ER stress and mitochondrial dysfunction contribute to A53T alpha-synuclein-induced cell death. This study sheds light into the pathogenesis of alpha-synuclein cellular toxicity in PD and provides a cell model for screening PD therapeutic agents.
  Human Molecular Genetics 01/2006; 14(24):3801-11. · 7.64 Impact Factor
• Article: Compounds blocking mutant huntingtin toxicity identified using a Huntington's disease neuronal cell model.

  Wenfei Wang, Wenzhen Duan, Shuichi Igarashi, Hokuto Morita, Masayuki Nakamura, Christopher A Ross
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  ABSTRACT: Neuronal cell death in HD is believed to be largely a dominant cell-autonomous effect of the mutant huntingtin protein. We previously developed an inducible PC12 cell model which expresses an N-terminal huntingtin fragment with an expanded poly Q repeat (N63-148Q) under the control of the tet-off system. In order to evaluate the ability of compounds to protect against mutant huntingtin toxicity in our model, we measured LDH released by dead cells into the medium. We have now screened the library of 1040 compounds from the NINDS Custom Collection as part of a National Institute of Neurological Disorders and Stroke (NINDS) collaborative project. Each positive compound was tested at 3-8 concentrations. Five compounds significantly attenuated mutant huntingtin (htt)-induced LDH release without affecting the expression level of huntingtin and independent of effect on aggregates. We also tested a broad spectrum caspase inhibitor Z-VAD-fmk and previously proposed candidate compounds. This cell model can provide a method to screen potential therapeutic compounds for treating Huntington's disease.
  Neurobiology of Disease 12/2005; 20(2):500-8. · 5.40 Impact Factor
• Article: Inducible PC12 cell model of Huntington's disease shows toxicity and decreased histone acetylation.

  Shuichi Igarashi, Hokuto Morita, Kyla M Bennett, Yuji Tanaka, Simone Engelender, Matthew F Peters, Jillian K Cooper, Jonathan D Wood, Akira Sawa, Christopher A Ross
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  ABSTRACT: Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by the abnormal expansion of a polyglutamine tract in the huntingtin protein. We have developed PC12 cell lines in which the expression of an N-terminal truncation of huntingtin (N63) with either wild type (23Q) or expanded polyglutamine (148Q) can be induced by the removal of doxycycline. Differentiated PC12 cells induced to express N63-148Q showed cellular toxicity reaching up to 50% at 6 days post-induction. Histone acetyltransferase (HAT) activity and global histone acetylation was significantly decreased in cells expressing truncated huntingtin with mutant but not normal huntingtin. These data suggest that altered chromatin modification via reduction in coactivator activity may cause neuronal transcriptional dysregulation and contribute to cellular toxicity.
  Neuroreport 04/2003; 14(4):565-8. · 1.66 Impact Factor