Quantitative Relationships between Huntingtin Levels, Polyglutamine Length, Inclusion Body Formation, and Neuronal Death Provide Novel Insight into Huntington's Disease Molecular Pathogenesis

Gladstone Institute of Neurological Disease, University of California, San Francisco, California 94158, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 08/2010; 30(31):10541-50. DOI: 10.1523/JNEUROSCI.0146-10.2010
Source: PubMed

ABSTRACT An expanded polyglutamine (polyQ) stretch in the protein huntingtin (htt) induces self-aggregation into inclusion bodies (IBs) and causes Huntington's disease (HD). Defining precise relationships between early observable variables and neuronal death at the molecular and cellular levels should improve our understanding of HD pathogenesis. Here, we used an automated microscope that tracks thousands of neurons individually over their entire lifetime to quantify interconnected relationships between early variables, such as htt levels, polyQ length, and IB formation, and neuronal death in a primary striatal model of HD. The resulting model revealed that mutant htt increases the risk of death by tonically interfering with homeostatic coping mechanisms rather than producing accumulated damage to the neuron, htt toxicity is saturable, the rate-limiting steps for inclusion body formation and death can be traced to different conformational changes in monomeric htt, and IB formation reduces the impact of the starting levels of htt of a neuron on its risk of death. Finally, the model that emerges from our quantitative measurements places critical limits on the potential mechanisms by which mutant htt might induce neurodegeneration, which should help direct future research.

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    • "E. coli has been employed to follow in vivo the aggregation process of an artificial protein harboring a polyglutamine (polyQ) tract (Ignatova et al., 2007). E. coli growth rate was found to be sensitive to the protein conformational state, and showed that misfolded peptides and soluble aggregates were cytotoxic (Miller et al., 2010). "
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    ABSTRACT: The formation of inclusion bodies (IBs) constitute a frequent event during the production of heterologous proteins in bacterial hosts. Although the mechanisms leading to their formation are not completely understood, empirical data have been exploited trying to predict the aggregation propensity of specific proteins while a great number of strategies have been developed to avoid the generation of IBs. However, in many cases, the formation of such aggregates can be considered an advantage for basic research as for protein production. In this review, we focus on this positive side of IBs formation in bacteria. We present a compilation on recent advances on the understanding of IBs formation and their utilization as a model to understand protein aggregation and to explore strategies to control this process. We include recent information about their composition and structure, their use as an attractive approach to produce low cost proteins and other promising applications in Biomedicine.
    Frontiers in Microbiology 02/2014; 5:56. DOI:10.3389/fmicb.2014.00056 · 3.94 Impact Factor
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    • "G Bates, King's College, London University) as a label for mutant huntingtin expression. Slices were also immunolabelled against tyrosine hydroxylase (TH: Millipore, UK) for a marker of dopamine neurons, and brain derived neurotrophic factor (BDNF: Santa Cruz Biotechnology Inc., CA, USA) using an antibody with demonstrated binding specificity (Calvo et al., 2011; Gomez-Pinilla et al., 2011; Mooney and Miller, 2011; Sui and Li, 2010; Sui et al., 2012). "
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    ABSTRACT: Huntington's disease (HD) is a neurodegenerative disease caused by a mutation within the huntingtin gene that induces degeneration within the striatal nuclei, progressing to widespread brain atrophy and death. The neurodegeneration produces symptoms that reflect a corticostriatal disconnection syndrome involving motor, cognitive and psychiatric disturbance. Environmental enrichment has been demonstrated to be beneficial to patients with neurological disorders, with exercise being central to this effect. Rodent studies have confirmed exercise-induced neurogenesis and increased growth factor levels in the brain and improved behavioural function. The present study sought to determine whether an extended regime of exercise could retard disease progression in the R6/1 mouse model of HD. The study was designed specifically with a translational focus, selecting behavioural assessments with high clinical predictive validity. We found that exercise improved gait function in both control and HD mice and selectively improved performance in the R6/1 mice on a motor coordination aspect of the balance beam task. Exercise also retarded the progression of cognitive dysfunction on water T-maze procedural and reversal learning probes presented serially to probe cognitive flexibility. In addition, exercise reduced striatal neuron loss in the R6/1 mice but increased striatal neuronal intra-nuclear inclusion size and number relative to non-exercised R6/1 mice which demonstrated increased numbers of extra-neuronal inclusions, suggesting that the functional effects were striatally mediated. These results confirm and extend those from previous studies that demonstrate that HD may be amenable to exercise-mediated therapeutics, but suggest that the impact of such interventions may be primarily cognitive.
    Experimental Neurology 07/2013; 248. DOI:10.1016/j.expneurol.2013.07.014 · 4.62 Impact Factor
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    • ") and, in a mechanistic parallel with the pathogenic mechanisms proposed for " classical " amyloids, many studies suggested that the insoluble inclusions played a protective role, sequestering toxic, and misfolded protein conformers (Arrasate et al., 2004; Rub et al., 2006; Miller et al., 2010). Indeed, soluble intermediates in the aggregation pathway such as misfolded β-sheet rich polyQ protein monomers and oligomers have latter been identified and proposed to represent the major toxic species (Kayed et al., 2003; Gales et al., 2005; Nagai et al., 2007; Miller et al., 2011). "
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    ABSTRACT: Trinucleotide repeat (TNR) expansions are present in a wide range of genes involved in several neurological disorders, being directly involved in the molecular mechanisms underlying pathogenesis through modulation of gene expression and/or the function of the RNA or protein it encodes. Structural and functional information on the role of TNR sequences in RNA and protein is crucial to understand the effect of TNR expansions in neurodegeneration. Therefore, this review intends to provide to the reader a structural and functional view of TNR and encoded homopeptide expansions, with a particular emphasis on polyQ expansions and its role at inducing the self-assembly, aggregation and functional alterations of the carrier protein, which culminates in neuronal toxicity and cell death. Detail will be given to the Machado-Joseph Disease-causative and polyQ-containing protein, ataxin-3, providing clues for the impact of polyQ expansion and its flanking regions in the modulation of ataxin-3 molecular interactions, function, and aggregation.
    Frontiers in Neurology 06/2013; 4:76. DOI:10.3389/fneur.2013.00076
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