Inhibition of Mutant Ataxin-3 Proteolysis by Calpains in a Lentiviral Mouse Model of Machado-Joseph Disease
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1
University of Coimbra, Faculty of Pharmacy, Portugal
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2
University of Coimbra, Center for Neuroscience and Cell Biology, Portugal
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3
Institute of Biomedical Imaging and MIRCen, CEA, France
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4
University of Gottingen, Department of Neurology, Vector Laboratory, Germany
Machado-Joseph Disease (MJD), also known as Spinocerebellar ataxia type 3 (SCA3), is caused by polyglutamine repeat expansions of more than 55 CAGs within the coding region of the causative gene-MJD1. Originally described in people of Portuguese descent, MJD is the most frequent form among the autosomal dominantly inherited cerebellar ataxias. Neuronal loss in MJD has been proposed to be associated with a toxic cleavage fragment of mutant ataxin-3, which may aggregate, recruit other proteins including normal ataxin-3, and seed the formation of intranuclear inclusions.
In this study, we aimed at overexpressing mutant ataxin-3 in the mouse brain using lentiviral vectors (LV), to generate an in vivo MJD genetic model and to investigate a role of the calcium-dependent proteases, calpains, in the generation of toxic ataxin-3 fragments.
Co-injection of adeno-associated viral vectors (AAV) encoding the endogenous calpain inhibitor protein, calpastatin, with LV-mutant ataxin-3 (72Q) reduced the number of mutant ataxin-3 intranuclear inclusions and significantly decreased neuronal dysfunction and neurodegeneration evaluated by DARPP-32 immunoreactivity and number of pycnotic nuclei, respectively. Furthermore, overexpression of calpastatin altered the subcellular localization of mutant ataxin-3 in a dose dependent manner, restraining the protein in the cytoplasm, and overcoming calpastatin depletion observed upon mutant ataxin-3 expression. These data suggest that mutant ataxin-3 proteolysis by calpains is essential for its aggregation, translocation to the nucleus and consequent toxicity. Therefore, these results are an in vivo proof of principle that inhibition of this mechanism may provide a new therapeutic approach for MJD.
Supported by the Portuguese Foundation for Science and Technology, grant PTDC/SAU-FCF/70384/2006 and fellowship SFRH/BD/38636/2007
Conference:
11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009.
Presentation Type:
Poster Presentation
Topic:
Neurodegenerative Disorders
Citation:
Simões
AT,
Goncalves
N,
Nóbrega
C,
Déglon
N,
Bandeira Duarte
C,
Kügler
S and
Pereira De Almeida
L
(2009). Inhibition of Mutant Ataxin-3 Proteolysis by Calpains in a Lentiviral Mouse Model of Machado-Joseph Disease.
Front. Neurosci.
Conference Abstract:
11th Meeting of the Portuguese Society for Neuroscience.
doi: 10.3389/conf.neuro.01.2009.11.100
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Received:
10 Aug 2009;
Published Online:
10 Aug 2009.
*
Correspondence:
L. Pereira De Almeida, University of Coimbra, Faculty of Pharmacy, Coimbra, Portugal, luispa@ci.uc.pt