Implication of oxidative lesions and base excision repair in the tissue selectivity of the somatic instability of CAG repeats in Huntington’s diseease

La maladie de Huntington (MH) est une maladie neurodégénérative fatale, causée par l’expansion des répétitions CAG du gène de Huntingtine. La longueur de l’expansion est instable et proportionnelle à la gravité de la maladie. L’instabilité varie selon les tissus, p.ex. le striatum est très instable et dégénère, alors que le cervelet a une instabilité limitée et est épargné par la maladie. Nous avons étudié le rôle des lésions oxydantes et du mécanisme de réparation par excision de base (BER) dans la sélectivité tissulaire de l'instabilité dans ces deux tissus de souris R6/1. Le niveau des lésions était similaire dans ces tissus, alors que les niveaux et les activités des principales protéines BER étaient globalement diminués dans le striatum. L’efficacité de réparation dépendait de la stoechiométrie de BER, la position de la lésion et la séquence d’ADN. Nos résultats suggèrent une faible coopération entre les activités BER associée à la spécificité tissulaire de l’instabilité de la MH.Huntington’s disease (HD) is a neurodegenerative fatal disease caused by the expansion of CAG repeats in the Huntingtin gene. The expansion length is unstable and proportional to the disease severity. The instability affects differently several tissues, among which the striatum that shows a high instability and degenerates, whereas the cerebellum that shows limited instability is spared from the disease. We addressed the role of oxidative lesions and Base Excision Repair (BER) in the tissue-selectivity of the instability in striatum and cerebellum of R6/1 mouse model. Interestingly, we observed a similar level of oxidative lesions at both tissues. Levels and activities of main BER proteins were globally decreased in striatum relative to cerebellum. Moreover we found that repair outcome is dependent upon BER stoichiometries, lesion location and sequence. Our results suggest a poor cooperation between BER activities that could underlie tissue-specificity of somatic instability in HD

Implication des lésions oxydantes et du mécanisme de réparation par excision de base dans la sélectivité tissulaire de l'instabilité somatique des répétitions CAG dans la maladie de Huntington

Huntington’s disease (HD) is a neurodegenerative fatal disease caused by the expansion of CAG repeats in the Huntingtin gene. The expansion length is unstable and proportional to the disease severity. The instability affects differently several tissues, among which the striatum that shows a high instability and degenerates, whereas the cerebellum that shows limited instability is spared from the disease. We addressed the role of oxidative lesions and Base Excision Repair (BER) in the tissue-selectivity of the instability in striatum and cerebellum of R6/1 mouse model. Interestingly, we observed a similar level of oxidative lesions at both tissues. Levels and activities of main BER proteins were globally decreased in striatum relative to cerebellum. Moreover we found that repair outcome is dependent upon BER stoichiometries, lesion location and sequence. Our results suggest a poor cooperation between BER activities that could underlie tissue-specificity of somatic instability in HD.La maladie de Huntington (MH) est une maladie neurodégénérative fatale, causée par l’expansion des répétitions CAG du gène de Huntingtine. La longueur de l’expansion est instable et proportionnelle à la gravité de la maladie. L’instabilité varie selon les tissus, p.ex. le striatum est très instable et dégénère, alors que le cervelet a une instabilité limitée et est épargné par la maladie. Nous avons étudié le rôle des lésions oxydantes et du mécanisme de réparation par excision de base (BER) dans la sélectivité tissulaire de l'instabilité dans ces deux tissus de souris R6/1. Le niveau des lésions était similaire dans ces tissus, alors que les niveaux et les activités des principales protéines BER étaient globalement diminués dans le striatum. L’efficacité de réparation dépendait de la stoechiométrie de BER, la position de la lésion et la séquence d’ADN. Nos résultats suggèrent une faible coopération entre les activités BER associée à la spécificité tissulaire de l’instabilité de la MH

Implication of oxidative lesions and base excision repair in the tissue selectivity of the somatic instability of CAG repeats in Huntington’s diseease

La maladie de Huntington (MH) est une maladie neurodégénérative fatale, causée par l’expansion des répétitions CAG du gène de Huntingtine. La longueur de l’expansion est instable et proportionnelle à la gravité de la maladie. L’instabilité varie selon les tissus, p.ex. le striatum est très instable et dégénère, alors que le cervelet a une instabilité limitée et est épargné par la maladie. Nous avons étudié le rôle des lésions oxydantes et du mécanisme de réparation par excision de base (BER) dans la sélectivité tissulaire de l'instabilité dans ces deux tissus de souris R6/1. Le niveau des lésions était similaire dans ces tissus, alors que les niveaux et les activités des principales protéines BER étaient globalement diminués dans le striatum. L’efficacité de réparation dépendait de la stoechiométrie de BER, la position de la lésion et la séquence d’ADN. Nos résultats suggèrent une faible coopération entre les activités BER associée à la spécificité tissulaire de l’instabilité de la MH.Huntington’s disease (HD) is a neurodegenerative fatal disease caused by the expansion of CAG repeats in the Huntingtin gene. The expansion length is unstable and proportional to the disease severity. The instability affects differently several tissues, among which the striatum that shows a high instability and degenerates, whereas the cerebellum that shows limited instability is spared from the disease. We addressed the role of oxidative lesions and Base Excision Repair (BER) in the tissue-selectivity of the instability in striatum and cerebellum of R6/1 mouse model. Interestingly, we observed a similar level of oxidative lesions at both tissues. Levels and activities of main BER proteins were globally decreased in striatum relative to cerebellum. Moreover we found that repair outcome is dependent upon BER stoichiometries, lesion location and sequence. Our results suggest a poor cooperation between BER activities that could underlie tissue-specificity of somatic instability in HD

Abnormal Base Excision Repair at Trinucleotide Repeats Associated with Diseases: A Tissue-Selective Mechanism

More than fifteen genetic diseases, including Huntington’s disease, myotonic dystrophy 1, fragile X syndrome and Friedreich ataxia, are caused by the aberrant expansion of a trinucleotide repeat. The mutation is unstable and further expands in specific cells or tissues with time, which can accelerate disease progression. DNA damage and base excision repair (BER) are involved in repeat instability and might contribute to the tissue selectivity of the process. In this review, we will discuss the mechanisms of trinucleotide repeat instability, focusing more specifically on the role of BER

Implication of oxidative lesions and base excision repair in the tissue selectivity of the somatic instability of CAG repeats in Huntington s diseease

La maladie de Huntington (MH) est une maladie neurodégénérative fatale, causée par l expansion des répétitions CAG du gène de Huntingtine. La longueur de l expansion est instable et proportionnelle à la gravité de la maladie. L instabilité varie selon les tissus, p.ex. le striatum est très instable et dégénère, alors que le cervelet a une instabilité limitée et est épargné par la maladie. Nous avons étudié le rôle des lésions oxydantes et du mécanisme de réparation par excision de base (BER) dans la sélectivité tissulaire de l'instabilité dans ces deux tissus de souris R6/1. Le niveau des lésions était similaire dans ces tissus, alors que les niveaux et les activités des principales protéines BER étaient globalement diminués dans le striatum. L efficacité de réparation dépendait de la stoechiométrie de BER, la position de la lésion et la séquence d ADN. Nos résultats suggèrent une faible coopération entre les activités BER associée à la spécificité tissulaire de l instabilité de la MH.Huntington s disease (HD) is a neurodegenerative fatal disease caused by the expansion of CAG repeats in the Huntingtin gene. The expansion length is unstable and proportional to the disease severity. The instability affects differently several tissues, among which the striatum that shows a high instability and degenerates, whereas the cerebellum that shows limited instability is spared from the disease. We addressed the role of oxidative lesions and Base Excision Repair (BER) in the tissue-selectivity of the instability in striatum and cerebellum of R6/1 mouse model. Interestingly, we observed a similar level of oxidative lesions at both tissues. Levels and activities of main BER proteins were globally decreased in striatum relative to cerebellum. Moreover we found that repair outcome is dependent upon BER stoichiometries, lesion location and sequence. Our results suggest a poor cooperation between BER activities that could underlie tissue-specificity of somatic instability in HD.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

Transcription Elongation and Tissue-Specific Somatic CAG Instability

International audienceThe expansion of CAG/CTG repeats is responsible for many diseases, including Huntington's disease (HD) and myotonic dystrophy 1. CAG/CTG expansions are unstable in selective somatic tissues, which accelerates disease progression. The mechanisms underlying repeat instability are complex, and it remains unclear whether chromatin structure and/or transcription contribute to somatic CAG/CTG instability in vivo. To address these issues, we investigated the relationship between CAG instability, chromatin structure, and transcription at the HD locus using the R6/1 and R6/2 HD transgenic mouse lines. These mice express a similar transgene, albeit integrated at a different site, and recapitulate HD tissue-specific instability. We show that instability rates are increased in R6/2 tissues as compared to R6/1 matched-samples. High transgene expression levels and chromatin accessibility correlated with the increased CAG instability of R6/2 mice. Transgene mRNA and H3K4 trimethylation at the HD locus were increased, whereas H3K9 dimethylation was reduced in R6/2 tissues relative to R6/1 matched-tissues. However, the levels of transgene expression and these specific histone marks were similar in the striatum and cerebellum, two tissues showing very different CAG instability levels, irrespective of mouse line. Interestingly, the levels of elongating RNA Pol II at the HD locus, but not the initiating form of RNA Pol II, were tissue-specific and correlated with CAG instability levels. Similarly, H3K36 trimethylation, a mark associated with transcription elongation, was specifically increased at the HD locus in the striatum and not in the cerebellum. Together, our data support the view that transcription modulates somatic CAG instability in vivo. More specifically, our results suggest for the first time that transcription elongation is regulated in a tissue-dependent manner, contributing to tissue-selective CAG instability

The Nucleotide Sequence, DNA Damage Location, and Protein Stoichiometry Influence the Base Excision Repair Outcome at CAG/CTG Repeats

International audienc

Me3H3K4 at the HD locus in R6/1 and R6/2 striatum and cerebellum.

<p>A. Schematic representation of the HD transgene expressed in R6 mice, showing location of primers used to amplify the region just downstream of the TSS in HD exon-1. B. ChIP analyses from the striatum and the cerebellum of R6/1 mice at 13- and 36-wk and from the striatum and cerebellum of R6/2 mice at 12-wk, using antibody to Me3H3K4. Error bars, sem; *, inter-tissue comparisons; §, inter-mouse line comparisons. *, p<0.05; §, p<0.05. C. Left panel. Global analysis of the level of Me3H3K4 at the HD locus. Me3H3K4 levels at the HD locus correspond to mean ChIP values at the HD promoter, HD exon-1 and HD intron-1. Error bars, sem; §, p<0.05. Right panel. Correlative analysis of CAG instability rates and Me3H3K4 levels at the HD locus. R6/1 mice of 13 and 36 weeks and R6/2 mice of 12 weeks were used for correlation analysis.</p

HD transgene expression in R6/1 and R6/2 striatum and cerebellum.

<p>A. Expression of the HD transgene in the striatum and in the cerebellum of R6/1 and R6/2 mice of various ages, as assessed by qRT-PCR using primers located upstream of CAG repeats in HD exon-1. Expression values were normalized to <i>Gapdh</i> expression. Error bars, sem; *, p<0.05; **, p<0.01. B. Correlative analysis of CAG instability rates and HD transgene mRNA levels at 6 weeks of age. C. Absolute quantification of HD transgene transcript levels, as assessed by qRT-PCR using primers upstream of the repeats (upstream primers) and primers amplifying the repeats (CAG primers), from the striatum and cerebellum of R6/1 and R6/2 mice of 6 weeks of age. Corresponding genomic DNAs were used as standards. Levels of PCR products are expressed as equivalent DNA (1 ng eq. DNA corresponds to the PCR signal obtained using 1 ng of DNA). Error bars, sem; *, p<0.05; **, p<0.01.</p

H3 and AcH3K9 at the HD locus in R6/1 and R6/2 striatum and cerebellum.

<p>A. Left panel. ChIP analyses from the striatum and the cerebellum of R6/1 and R6/2 mice using antibodies to H3. R6/1 mice at early and late-pathological stages (13- and 36-wk), and R6/2 mice at late pathological stage (12-wk) were used. Right panel. Global analysis of the level of H3 at the HD locus, assessed as in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003051#pgen-1003051-g002" target="_blank">Figure 2</a>. Error bars, sem. B. ChIP analyses from the striatum and the cerebellum of R6/1 mice at late-pathological stage (36-wk) and R6/2 mice at late-pathological stage (12-wk), using antibody to AcH3K9. C. Upper panel. Global analysis of the level of AcH3K9 at the HD locus, assessed as in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003051#pgen-1003051-g002" target="_blank">Figure 2</a>. Error bars, sem; §, p<0.05. Lower panel. Correlative analysis of CAG instability rates with mean levels of AcH3K9 at the HD locus. R6/1 mice of 36 weeks and R6/2 mice of 12 weeks were used for correlation analysis.</p