Article

Gene expression profiling of R6/2 transgenic mice with different CAG repeat lengths reveals genes associated with disease onset and progression in Huntington's disease

Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA.
Neurobiology of Disease (Impact Factor: 5.2). 02/2011; 42(3):459-67. DOI: 10.1016/j.nbd.2011.02.008
Source: PubMed

ABSTRACT R6/2 transgenic mice with expanded CAG repeats (>300) have a surprisingly prolonged disease progression and longer lifespan than prototypical parent R6/2 mice (carrying 150 CAGs); however, the mechanism of this phenotype amelioration is unknown. We compared gene expression profiles in the striatum of R6/2 transgenic mice carrying ~300 CAG repeats (R6/2(Q300) transgenic mice) to those carrying ~150 CAG repeats (R6/2(Q150) transgenic mice) and littermate wildtype controls in order to identify genes that may play determinant roles in the time course of phenotypic expression in these mice. Of the top genes showing concordant expression changes in the striatum of both R6/2 lines, 85% were decreased in expression, while discordant expression changes were observed mostly for genes upregulated in R6/2(Q300) transgenic mice. Upregulated genes in the R6/2(Q300) mice were associated with the ubiquitin ligase complex, cell adhesion, protein folding, and establishment of protein localization. We qPCR-validated increases in expression of genes related to the latter category, including Lrsam1, Erp29, Nasp, Tap1, Rab9b, and Pfdn5 in R6/2(Q300) mice, changes that were not observed in R6/2 mice with shorter CAG repeats, even in late stages (i.e., 12 weeks of age). We further tested Lrsam1 and Erp29, the two genes showing the greatest upregulation in R6/2(Q300) transgenic mice, for potential neuroprotective effects in primary striatal cultures overexpressing a mutated human huntingtin (htt) fragment. Overexpression of Lrsam1 prevented the loss of NeuN-positive cell bodies in htt171-82Q cultures, concomitant with a reduction of nuclear htt aggregates. Erp29 showed no significant effects in this model. This is consistent with the distinct pattern of htt inclusion localization observed in R6/2(Q300) transgenic mice, in which smaller cytoplasmic inclusions represent the major form of insoluble htt in the cell, as opposed to large nuclear inclusions observed in R6/2(Q150) transgenic mice. We suggest that the prolonged onset and disease course observed in R6/2 mice with greatly expanded CAG repeats might result from differential upregulation of genes related to protein localization and clearance. Such genes may represent novel therapeutic avenues to decrease htt aggregate toxicity and cell death in HD patients, with Lrsam1 being a promising, novel candidate disease modifier.

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    • "The range of HD models included in the library show a range of CAG repeat lengths. There is a growing body of data from behavioural and gene expression studies suggesting that mice carrying extremely long CAG repeat lengths show a delayed onset of phenotype [7], [35], [36]. The explanation for this delay in onset remains unclear, since the mice still die prematurely of a neurological disease [7]. "
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    ABSTRACT: Magnetic resonance imaging (MRI) has proved to be an ideal modality for non-destructive and highly detailed assessment of structural morphology in biological tissues. Here we used MRI to make a dataset of ex vivo brains from two different rodent models of Huntington's disease (HD), the R6/2 line and the YAC 128 mouse. We are making the whole dataset (399 transgenic HD and wildtype (WT) brains, from mice aged 9-80 weeks) publicly available. These data will be useful, not only to investigators interested in the study of HD, but also to researchers of computational neuroanatomy who may not have access to such large datasets from mouse models. Here we demonstrate a number of uses of such data, for example to produce maps of grey and white matter and cortical thickness. As an example of how the library might provide insights in mouse models of HD, we calculated whole brain grey matter volumes across different age groups with different numbers of cytosine-adenine-guanine (CAG) repeats in a fragment of the gene responsible for HD in humans. (The R6/2 dataset was obtained from an allelic series of R6/2 mice carrying a range of CAG repeat lengths between 109 and 464.) This analysis revealed different trajectories for each fragment length. In particular there was a gradient of decreasing pathology with longer CAG repeat lengths, reflecting our previous findings with behavioural and histological studies. There will be no constraints placed on the use of the datasets included here. The original data will be easily and permanently accessible via the University of Cambridge data repository (http://www.dspace.cam.ac.uk/handle/1810/243361).
    PLoS ONE 12/2012; 7(12):e53361. DOI:10.1371/journal.pone.0053361 · 3.23 Impact Factor
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    • "In the present study, we confirmed and extended earlier findings that increasing CAG expansion size leads to delays in phenotypic onset in R6/2 mice [23] [24] [25] [26] and further illustrate that this phenomenon is robust and observed on at least two distinct genetic backgrounds. However, the recent study by Menalled et al. [25] raises the question whether this phenomenon transcends genetic background entirely. "
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    ABSTRACT: Huntington's disease (HD) is caused by the expansion of the polyglutamine tract expressed in the huntingtin protein. Data from patients show a strong negative correlation between CAG repeat size and age of disease onset. Recent studies in mixed background C57×CBA R6/2 mice suggest the inverse correlation observed in the human disease may not be replicated in some animal models of HD. To further clarify the relationship between repeat length and age of onset, congenic C57BL6/J R6/2 transgenic mice expressing 110, 260 or 310 CAG were tested in a comprehensive behavioral battery at multiple ages. Data confirmed the findings of earlier studies and indicate that on a pure C57BL6/J genetic background, R6/2 mice with larger repeats exhibit a delay in phenotypic onset with increasing polyglutamine size (6 weeks in 110 CAG and 17 weeks in 310 CAG mice). Further analysis confirmed a decrease in transgene transcript expression in 310 CAG mice as well as differential aggregated protein localization in association with repeat length. Mice expressing 110 CAG developed aggregates that localized almost exclusively to the nucleus of neuronal cells in the striatum and cortex. In contrast, tissue from 310 CAG mice exhibited predominantly extranuclear inclusions. Novel mutant protein analysis obtained using time-resolved fluorescence resonance energy transfer (FRET) revealed that soluble protein levels decreased with disease onset in R6/2 mice while aggregated protein levels increased. We believe that these data suggest a role for aggregation and inclusion localization in HD pathogenesis and propose a mechanism for the age of onset delay observed in R6/2 mice.
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    • "Morton and coworkers (2009) suggest that the htt produced by the highly expanded CAG repeats is expressed, as double-mutant mice die earlier than CAG repeat-length-matched mice carrying single copies of the transgene. A recent report suggests further that the prolonged onset and course of progression in R6/2 mice with expanded CAG repeats may result from differential upregulation of genes related to protein regulation and clearance (Tang et al. 2011). "
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