Early and reversible neuropathology induced by tetracycline-regulated lentiviral overexpression of mutant huntingtin in rat striatum

The ability to overexpress full-length huntingtin or large fragments represents an important challenge to mimic Huntington's pathology and reproduce all stages of the disease in a time frame compatible with rodent life span. In the present study, tetracycline-regulated lentiviral vectors leading to high expression levels were used to accelerate the pathological process. Rats were simultaneously injected with vectors coding for the transactivator and wild type (WT) or mutated huntingtin (TRE-853-19Q/82Q) in the left and right striatum, respectively, and analyzed in the ‘on' and ‘off' conditions. Overexpression of TRE-853-19Q protein or residual expression of TRE-853-82Q in ‘off' condition did not cause any significant neuronal pathology. Overexpressed TRE-853-82Q protein led to proteolytic release of N-terminal htt fragments, nuclear aggregation, and a striatal dysfunction as revealed by decrease of DARPP-32 staining but absence of NeuN down-regulation. The differential effect on the DARPP-32/NeuN neuronal staining was observed as early as 1 month after injection and maintained at 3 months. In contrast, expression of a shorter htt form (htt171-82Q) did not require processing prior formation of nuclear aggregates and caused decrease of both DARPP-32 and NeuN neuronal markers at one month post-injection suggesting that polyQ pathology may be dependent on protein context. Finally, the reversibility of the pathology was assessed. Huntingtin expression was turn ‘on' for 1 month and then shut ‘off' for 2 months. Recovery of DARPP-32 immunoreactivity and clearance of huntingtin aggregates were observed in animals treated with doxycycline. These results suggest that a tetracycline-regulated system may be particularly attractive to model Huntington's disease and induce early and reversible striatal neuropathology in viv

PML clastosomes prevent nuclear accumulation of mutant ataxin-7 and other polyglutamine proteins

The pathogenesis of spinocerebellar ataxia type 7 and other neurodegenerative polyglutamine (polyQ) disorders correlates with the aberrant accumulation of toxic polyQ-expanded proteins in the nucleus. Promyelocytic leukemia protein (PML) nuclear bodies are often present in polyQ aggregates, but their relation to pathogenesis is unclear. We show that expression of PML isoform IV leads to the formation of distinct nuclear bodies enriched in components of the ubiquitin-proteasome system. These bodies recruit soluble mutant ataxin-7 and promote its degradation by proteasome-dependent proteolysis, thus preventing the aggregate formation. Inversely, disruption of the endogenous nuclear bodies with cadmium increases the nuclear accumulation and aggregation of mutant ataxin-7, demonstrating their role in ataxin-7 turnover. Interestingly, β-interferon treatment, which induces the expression of endogenous PML IV, prevents the accumulation of transiently expressed mutant ataxin-7 without affecting the level of the endogenous wild-type protein. Therefore, clastosomes represent a potential therapeutic target for preventing polyQ disorders

SCA8 CAG/CTG Expansions, a Tale of Two TOXICities: A Unique or Common Case?

International audienc

PLoS Genet.

The 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 following values have no corresponding Zotero field:alt-title: PLoS Genet.number: 11remote-database-provider: PubMe

Glutamine-Expanded Ataxin-7 Alters TFTC/STAGA Recruitment and Chromatin Structure Leading to Photoreceptor Dysfunction

Spinocerebellar ataxia type 7 (SCA7) is one of several inherited neurodegenerative disorders caused by a polyglutamine (polyQ) expansion, but it is the only one in which the retina is affected. Increasing evidence suggests that transcriptional alterations contribute to polyQ pathogenesis, although the mechanism is unclear. We previously demonstrated that theSCA7 gene product, ataxin-7 (ATXN7), is a subunit of the GCN5 histone acetyltransferase–containing coactivator complexes TFTC/STAGA. We show here that TFTC/STAGA complexes purified from SCA7 mice have normal TRRAP, GCN5, TAF12, and SPT3 levels and that their histone or nucleosomal acetylation activities are unaffected. However, rod photoreceptors from SCA7 mouse models showed severe chromatin decondensation. In agreement, polyQ-expanded ataxin-7 induced histone H3 hyperacetylation, resulting from an increased recruitment of TFTC/STAGA to specific promoters. Surprisingly, hyperacetylated genes were transcriptionally down-regulated, and expression analysis revealed that nearly all rod-specific genes were affected, leading to visual impairment in SCA7 mice. In conclusion, we describe here a set of events accounting for SCA7 pathogenesis in the retina, in which polyQ-expanded ATXN7 deregulated TFTC/STAGA recruitment to a subset of genes specifically expressed in rod photoreceptors, leading to chromatin alterations and consequent progressive loss of rod photoreceptor function

Transcriptional Activation of REST by Sp1 in Huntington's Disease Models

In Huntington's disease (HD), mutant huntingtin (mHtt) disrupts the normal transcriptional program of disease neurons by altering the function of several gene expression regulators such as Sp1. REST (Repressor Element-1 Silencing Transcription Factor), a key regulator of neuronal differentiation, is also aberrantly activated in HD by a mechanism that remains unclear. Here, we show that the level of REST mRNA is increased in HD mice and in NG108 cells differentiated into neuronal-like cells and expressing a toxic mHtt fragment. Using luciferase reporter gene assay, we delimited the REST promoter regions essential for mHtt-mediated REST upregulation and found that they contain Sp factor binding sites. We provide evidence that Sp1 and Sp3 bind REST promoter and interplay to fine-tune REST transcription. In undifferentiated NG108 cells, Sp1 and Sp3 have antagonistic effect, Sp1 acting as an activator and Sp3 as a repressor. Upon neuronal differentiation, we show that the amount and ratio of Sp1/Sp3 proteins decline, as does REST expression, and that the transcriptional role of Sp3 shifts toward a weak activator. Therefore, our results provide new molecular information to the transcriptional regulation of REST during neuronal differentiation. Importantly, specific knockdown of Sp1 abolishes REST upregulation in NG108 neuronal-like cells expressing mHtt. Our data together with earlier reports suggest that mHtt triggers a pathogenic cascade involving Sp1 activation, which leads to REST upregulation and repression of neuronal genes

Évaluation des paramètres impliqués dans l'ELISA et leur application au sérodiagnostic de la pleuropneumonie porcine causée par Actinobacillus pleuropneumoniae sérotype 5

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Activation transcriptionnelle d'un répresseur de gènes neuronaux, NRSF, dans la maladie de Huntington (Identification des facteurs impliqués)

La maladie de Huntington (MH) est une maladie neurodégénérative due à une expansion anormale de trinucléotides CAG, codant pour une expansion de polyglutamine dans la protéine huntingtine (htt). Plusieurs mécanismes physiopathologiques ont été proposés, incluant la dérégulation de l expression des gènes. Parmi ces dérégulations, beaucoup de gènes codant pour des protéines essentielles à la morphologie et à la fonction des neurones sont réprimés. NRSF, un facteur de transcription qui réprime spécifiquement l expression de ces gènes, a une activité augmentée dans la MH.L objectif de ce travail est de comprendre les mécanismes conduisant à l activation de NRSF dans la MH. Ainsi, nous montrons dans un modèle cellulaire que l expression de la htt mutée conduit à une augmentation de l expression de NRSF associée à une activation du promoteur du gène. L exploration des mécanismes responsables de cette activation nous a permis d exclure le rôle de deux facteurs de transcription activés dans la MH: AP-1 et NF-KappaB. Finalement, nous mettons en évidence que le promoteur du gène Nrsf est régulé différentiellement par deux facteurs Sp: Sp1 qui est activateur transcriptionnel du gène et Sp3, un répresseur. L identification, pour la première fois, du rôle de ces facteurs dans la régulation transcriptionnelle du gène Nrsf, nous permet d explorer de nouveaux mécanismes par lesquels la htt mutée conduit à l activation du promoteur du gène Nrsf et ouvre de nombreuses perspectives pour comprendre la régulation de ce gène au cours de la différenciation neuronale ainsi que dans d autres pathologies telles que le cancer.Huntington s disease (HD) is a neurodegenerative disorder caused by an abnormal expansion of CAG trinucleotides, which code for polyglutamine expansions in the huntingtin (htt). Several physiopathological mechanisms have been proposed, including deregulated gene expression and can lead to the down-regulation of genes which are essential for neuronal morphology and function. NRSF, a transcription factor that plays a crucial role in controlling neuronal cell fate, by specifically inhibiting the expression of many neuronal genes, displays increased activity in HD which could explain the selective repression of neuronal genes.The goal of this work was to characterize the molecular mechanisms leading to NRSF activation in HD. In a cellular model, we show that the expression of mutant htt leads to increased NRSF expression by activating transcription from the NRSF promoter. We show that this transcriptional up-regulation does not involve two transcription factors known to be activated in HD: AP-1 and NF-KappaB. Finally, we demonstrate that Nrsf gene promoter is differentially regulated by two other transcription factors belonging to Sp family: Sp1 and Sp3, which act as transcriptional activator and repressor of the Nrsf gene promoter, respectively. Thus, we provide the first evidence that Sp factors regulate the transcriptional activity of Nrsf gene promoter. Our findings do not only allow the exploration of new mechanisms by which mutant htt activates the promoter of Nrsf gene, but they also open up fundamental new perspectives to understand the regulation of this gene, which is important during neuronal differentiation, and is deregulated in other disorders such as cancer.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Molecular Mechanisms and Therapeutic Strategies in Spinocerebellar Ataxia Type 7

Spinocerebellar Ataxia type 7 (SCA7, OMIM # 164500) is an autosomal dominant neurodegenerative disorder characterized by adult onset of progressive cerebellar ataxia and blindness. SCA7 is part of the large family of autosomal dominant cerebellar ataxias (ADCAs), and was estimated to account for 1-11.7% of ADCAs in diverse populations. The frequency of SCA7 is higher where local founder effects were observed as in Scandinavia, Korea, South Africa and Mexico. SCA7 is pathomechanistically related to the group of CAG/polyglutamine (polyQ) expansion disorders, which includes other SCAs (1-3, 6 and 17), Huntington's disease, spinal bulbar muscular atrophy and dentatorubro pallidoluysian atrophy. Two distinctive characteristics of SCA7 are the strong anticipation by which earlier onset and more severe symptoms are observed in successive generations of affected families, and the loss of visual acuity due to cone-rod dystrophy of the retina. The pathology is caused by an unstable CAG repeat expansion coding for a polyQ stretch in Ataxin-7 (ATXN7). PolyQ expansion in ATXN7 confers toxic properties and leads to selective neuronal degeneration in the cerebellum, the brain stem and the retina. Herein, we summarize the genetic, clinical and pathological features of SCA7 and review our current knowledge of pathomechanisms and preclinical studies