Wild type Huntingtin reduces the cellular toxicity of mutant Huntingtin in mammalian cell models of Huntington's disease.

Department of Medical Genetics, Wellcome Trust Centre for Molecular Mechanisms of Disease, Cambridge Institute for Medical Research, Wellcome/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK.
Journal of Medical Genetics (Impact Factor: 6.34). 08/2001; 38(7):450-2.
Source: PubMed


Recent data suggest that wild type huntingtin can protect against apoptosis in the testis of mice expressing full length huntingtin transgenes with expanded CAG repeats. It is not clear if this protective effect was confined to particular cell types, or if wild type huntingtin exerted its protective effect in this model by simply reducing the formation of toxic proteolytic fragments from mutant huntingtin.
We cotransfected neuronal (SK-N-SH, human neuroblastoma) and non-neuronal (COS-7, monkey kidney) cell lines with HD exon 1 (containing either 21 or 72 CAG repeats) construct DNA and either full length wild type huntingtin or pFLAG (control vector).
Full length wild type huntingtin significantly reduced cell death resulting from the mutant HD exon 1 fragments containing 72 CAG repeats in both cell lines. Wild type huntingtin did not significantly modulate cell death caused by transfection of HD exon 1 fragments containing 21 CAG repeats in either cell line.
Our results suggest that wild type huntingtin can significantly reduce the cellular toxicity of mutant HD exon 1 fragments in both neuronal and non-neuronal cell lines. This suggests that wild type huntingtin can be protective in different cell types and that it can act against the toxicity caused by a mutant huntingtin fragment as well as against a full length transgene.

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Available from: David C Rubinsztein
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    • "Homozygous deletion of Htt in mice results in embryonic lethality, and hemizygous null mice expressing 50% of Htt levels develop a mild phenotype as adult-onset neurodegeneration in the basal ganglia (Duyao et al. 1995; Nasir et al. 1995; O'Kusky et al. 1999). Htt plays an antiapoptotic role both in in vitro culture systems (Ho et al. 2001) and in vivo HD mice models (Dragatsis et al. 2000; Leavitt et al. 2001, 2006; Van Raamsdonk et al. 2005). Htt expression can block the formation of functional apoptosome complexes and consequent activation of caspases (Rigamonti et al. 2000, 2001; Zhang et al. 2006). "
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    ABSTRACT: Huntington's Disease (HD) is one of many neurodegenerative diseases with reported alterations in brain iron homeostasis that may contribute to neuropathogenesis. Iron accumulation in the specific brain areas of neurodegeneration in HD has been proposed based on observations in post-mortem tissue and magnetic resonance imaging (MRI) studies. Altered MRI signal within specific brain regions undergoing neurodegeneration has been consistently reported and interpreted as altered levels of brain iron. Biochemical studies using various techniques to measure iron species in human samples, mouse tissue, or in vitro has generated equivocal data to support such an association. Whether elevated brain iron occurs in HD, plays a significant contributing role in HD pathogenesis, or is a secondary effect is currently unclear.This article is protected by copyright. All rights reserved.
    Preview · Article · Apr 2014 · Journal of Neurochemistry
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    • "It has been suggested that HD pathology could be caused by a loss of function of the normal HTT protein as much as by a gain of pathological function (see; Zuccato et al. 2010). Several studies in vertebrates thus point to the neuroprotective role of normal HTT (Rigamonti et al. 2000, Rigamonti et al. 2001, Ho et al. 2001), in which removal of HTT or experimental manipulation results in an increased rate of cell death. It is intriguing that HTT partial suppression by morpholino in the present experiments results in a decreased HTT positive cell population consistent with a similar protective role of HTT. "
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    ABSTRACT: Although mutations in the huntingtin gene (HTT) due to poly-Q expansion cause neuropathology in humans (Huntington's disease; HD), the normal function(s) of the gene and its protein (HTT) remain obscure. With new information from recently sequenced invertebrate genomes, the study of new animal models opens the possibility of a better understanding of HTT function and its evolution. To these ends, we studied huntingtin expression pattern and dynamics in the invertebrate chordate Ciona intestinalis. Ciona huntingtin (Ci-HTT) shows a biphasic expression pattern during larval development and prior to metamorphosis. A single form of huntingtin protein is present until the early larval stages, at which time two different mass proteins become evident in the metamorphically competent larva. An antibody against Ci-HTT labeled 50 cells in the trunk mesenchyme regions in pre-hatching and hatched larvae and probably represents the distribution of the light form of the protein. Dual labeling with anti-Ci-HTT and anti-aldoketoreductase confirmed the presence of Ci-HTT in mesenchyme cells. Suppression of Ci-HTT RNA by a morpholino oligonucleotide reduced the number and apparent mobility of Ci-HTT positive cells. In Ciona, HTT expression has a dynamic temporal and spatial expression pattern that in ontogeny precedes metamorphosis. Although our results may reflect a derived function for the protein in pre- and post-metamorphic events in Ciona, we also note that as in vertebrates, there is evidence for multiple differential temporal expression, indicating that this protein probably has multiple roles in ontogeny and cell migration.
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    • "In vitro studies have demonstrated that the over-expression of wild-type htt protects cells against various insults including 3-nitroproprionic acid, a toxin which damages the striatum and has been used to model HD [12]. It has also been shown that over-expression of wild-type htt can specifically protect against polyglutamine toxicity in vitro [13]. This finding has been extended in vivo where increased expression of wild-type htt eliminated apoptotic degeneration in the testis caused by the expression of mutant htt [5,14]. "
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    ABSTRACT: Huntington disease (HD) is an adult onset neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin (htt) protein. Htt function is essential for embryonic survival as well as normal function during the postnatal period. In addition to having roles in transcription and transport, recent evidence demonstrates that wild-type htt is neuroprotective in vivo. To determine whether treatment with wild-type htt would be beneficial in HD, we crossed the YAC128 mouse model of HD with mice that over-express wild-type htt (YAC18 mice) to generate YAC128 mice that over-express wild-type htt (YAC18/128 mice). YAC18/128 mice were found to express mutant htt at the same level as YAC128 mice and wild-type htt at the same level as YAC18 mice. YAC18/128 mice show no significant behavioural improvement compared to YAC128 mice in the rotarod test of motor coordination or in an automated open field test. In the brain, YAC18/128 mice show no significant improvement in striatal volume, striatal neuronal numbers or striatal DARPP-32 expression compared to YAC128 mice. In contrast, striatal neuronal cross-sectional area showed significant improvement in YAC18/128 mice compared to YAC128 mice. While the over-expression of wild-type htt results in a mild improvement in striatal neuropathology in YAC128 mice, our findings suggest that treatment with wild-type htt may not be sufficient to ameliorate the symptoms of HD in this model.
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