Auswahl der wissenschaftlichen Literatur zum Thema „Cockayne, Syndrome de – Étiologie“

La compréhension des altérations moléculaires du syndrome de Cockayne (CS), une maladie génétique rare dans laquelle le vieillissement est accéléré, est essentielle pour développer des traitements, et élucider les dysfonctionnements impliqués dans le vieillissement physiologique. Le CS présente un large spectre de sévérité clinique qui ne repose pas sur une simple corrélation génotype/phénotype. Ce projet est basé sur une altération spécifique aux cellules CS, démontrée dans le laboratoire, qui implique la déplétion de l'ADN polymérase mitochondriale POLG1 conduisant à un dysfonctionnement de l’organelle. Cette altération est due à la surexpression de la protéase HTRA3, qui est déclenchée par un stress oxydatif/nitrosatif accru. La réduction de ces espèces réactives a permis de corriger ces altérations et a ouvert la voie à un traitement pour le CS. Ce travail de thèse i) a contribué à la découverte que la voie défectueuse du CS est récapitulée au cours de la sénescence réplicative des cellules normales, un processus lié au vieillissement physiologique, ii) a identifié le mécanisme HTRA3-dépendant de dégradation de POLG1 dans les cellules CS et dans les cellules sénescentes, iii) a développé de multiples modèles cellulaires isogéniques (fibroblastes, cellules souches pluripotentes induites et organoïdes cérébraux) avec CRISPR-Cas9, permettant des études mécanistiques et de corrélation génotype/phénotype. Ces études fournissent de nouvelles informations sur les mécanismes conduisant aux altérations progeroïdes dans le CS, sur leurs liens avec le vieillissement physiologique, et établissent des modèles expérimentaux uniques pour l'étude de la pathogenèse de cette maladie<br>Dissecting the molecular defects in rare genetic disorders like Cockayne syndrome (CS), in which ageing is dramatically accelerated, is critical to develop treatments, which are missing to date, and elucidate dysfunctions that are possibly implicated in physiological ageing. CS also displays a large spectrum of clinical severity which does not rely on simple genotype/phenotype correlation. This project is based on a working model established in the lab that identified CS-specific depletion of the mitochondrial DNA polymerase POLG1 leading to mitochondrial dysfunction, as a possible cause of CS progeroid defects. POLG1 depletion required overexpression of the HTRA3 protease, which was trigged by increased oxidative/nitrosative stress. Scavenging both reactive species, rescued these defects and opened the path to a treatment for CS. This PhD work: i) Contributed to the discovery that the CS-defective pathway is recapitulated in replicative senescence of normal cells, a process linked to regular aging. ii) Identified the mechanism of HTRA3-dependent POLG1 degradation in CS and senescent cells with implications for POLG1 homeostasis in normal cells. iii) Developed multiple isogenic cellular models (skin fibroblasts, induced pluripotent stem cells and cerebral organoids) with CRISPR-Cas9 that are essential for mechanistic studies and to address genotype/phenotype correlations, in the absence of a reliable mouse model for CS. Taken together, these studies provide novel insights into the mechanisms leading to defects in progeroid CS and their links with physiological ageing. They also establish unique CS models for studying CS pathogenesis

Le syndrome de Cockayne (CS) est une maladie autosomale récessive rare montrant des symptômes cliniques divers tels qu’une déficience du développement physique, un nanisme cachetique une dégénérescence neurologique progressive, une hypomyélination de la matière blanche, une calcification du système nerveux central, une surdité, une absence de graisse sous-cutanée, des cataractes, une rétinopathie et une hypersensibilité à la lumière du soleil. Le syndrome de Cockayne est typiquement causé par des mutations dans les gènes CSA et CSB, codant pour des protéines impliquées dans la réparation par excision de nucléotides couplée à la transcription (TC-NER). Un défaut de la TC-NER causé par des mutations dans CSA ou CSB conduit un blocage de l’ARN pol II par les lésions induites par le rayonnement UV. Au cours des dernières années, une question reste d’actualité: comment expliquer les changements transcriptionels gène-spéficiques observés dans des cellules CS soumises à des attaques génotoxiques. Intrigué par cette question, nous avons étudié plus particulièrement la transcription de deux gènes: un gène dérégulé dans CS (DHFR) et un gène normalement régulé dans CS (GADD45). Sur le promoteur du gène dérégulé, nous avons découvert un site de régulation potentiel CRE/ATF, qui est connu pour provoquer la répression de la transcription en ciblant ATF3. En utilisant la technique de western blot et des immunoprécipitations de la chromatine, nous avons trouvé, qu’en réponse à une irradiation UV, ATF3 est surexprimé dans les cellules CS, et est alors recruté sur le site CRE/ATF localisé sur le promoteur du gène DHFR, empêchant alors la mise en place de la machinerie de transcription basale et inhibant donc la transcription de ce gène. Finalement, nous avons montré que la surexpression de ATF3 pourrait être induite dans des cellules sauvages par une légère inhibition de l’élongation de la transcription par l’ARN pol II reliant ainsi les changements transcriptionels observés dans CS à une déficience de la TC-NER dans ces cellules<br>Cockayne Syndrome is a rare inherited autosomal recessive disease with diverse clinical symptoms including severe impairment of physical development, cachectic dwarfism, progressive neurological degeneration, white matter hypomyelination, central nervous system calcification, sensorineural hearingloss, lack of subcutaneous fat, cataracts, retinopathy and hypersensitivity to sunlight. Cockayne Syndrome is typically caused by mutations in the CSA and CSB genes, encoding proteins involved in transcription coupled nucleotide excision repair (TC-NER). TC-NER defect caused by CSA and CSB mutation, results in unintended stalling of Pol II at bulky UV induced DNA lesions. During the last years an open question has been, how to explain transcriptional gene-specific changes in CS cells upon genotoxic attack. Intrigued by this question, we studied extensively the transcription of two different genes: one gene misregulated in CS (DHFR), and one gene normally regulated in CS (GADD45). On the promoter of the misregulated gene, we discovered a putative CRE/ATF regulatory site, which is known to cause repression by targeting of ATF3. Using western blotting and chromatin immunoprecipitation we found that, in response to UV irradiation ATF3 was highly overexpressed in CS cells, and was subsequently recruited to the CRE/ATF site on DHFR promoter, thereby preventing the recruitment of basal transcription factors and inhibiting transcription of the gene. Finally, we showed that the overexpression of ATF3 could be induced in wild type cells by a slight inhibition of Pol II elongation, connecting the transcriptional changes observed in CS, to the TC-NER deficiency of these cells

Le syndrome de Cockayne est une maladie autosomique récessive, liée à des mutations dans les gènes CSA ou CSB, et caractérisée par un retard de croissance, une atteinte neurologique, une atteinte sensorielle et une photosensibilité cutanée. Les cellules des patients atteints par cette maladie présentent un défaut d’une voie de réparation de l’ADN, dite « par excision de nucléotides ». Nous avons réalisé une étude exhaustive d’une cohorte de 39 patients. Nous avons testé la validité des critères diagnostiques classiques et proposé des modifications pour en améliorer la valeur prédictive. Nous avons identifié 31 nouvelles mutations du gène CSB (en plus des 26 mutations connues à ce jour) et 6 nouvelles mutations du gène CSA (en plus des 16 mutations connues), et nous discutons différentes hypothèses concernant les corrélations entre génotype et phénotype<br>Cockayne syndrome is an autosomal recessive disorder caused by mutations in the CSA and CSB genes, and is characterized by growth failure, neurological involvement, sensorial impairment and cutaneous photosensitivity. Cells derived from Cockayne patients show a specific defect in a DNA repair pathway (“nucleotide excision repair”). We have conducted an exhaustive study of 39 patients. We have tested the validity of the classical diagnostic criteria and proposed modifications to improve their specificity. We have identified 31 novel mutations in CSB (in addition to the 26 mutations known to date) and 6 novel mutations in CSA (in addition to the 16 mutations known to date), and we discuss different hypotheses regarding genotype-phenotype correlations

Cockayne Syndrome (CS) is a rare autosomal recessive disorder characterised by neurodegeneration, dwarfism and at least three of the following; hearing loss, dental caries, pigmentary retinopathy, characteristic facial appearance and photosensitivity. Cells from CS patients fail to recover RNA synthesis after irradiation and exhibit a loss of transcription-coupled repair, with overall genome repair being unaffected. There are two genetic complementation groups of CS alone, A and B, with the majority of patients belonging to group B. The genes defective in each of the complementation groups have been cloned, the CSA gene in 1995 and CSB in 1990. For the purposes of this study the CSB gene was sequenced in patients from complementation group B, in an attempt to identify the causative mutations. The analysis of thirteen patients from different backgrounds has revealed a wide variety of mutations in the CSB gene. A considerable number of the mutations found in CS-B patients resulted in severely truncated products. Several patients possessed two alleles affected in this way and it is unlikely that any functional protein is produced, confirming that CSB is a nonessential gene. The mutations identified did not reveal any regions within the gene that could be termed as hotspots. There was, however a tendency for the mutations to be located towards the 3' two thirds of the gene, indicated by the clustering of the mutations in this region. The severity of the mutation does not however correlate with the site or type of mutation. Clustering of the mutations towards the 3' end and the high levels of conservation in the central part of the gene prompted a study into the functional significance of the N- and Cterminal ends of the protein. Also, the presence of a highly acidic region of amino acids and a stretch of glycine residues led to a study of the effects of removing and replacing these regions. Removal of the glycine domain results in non-functional protein with respect to cell survival after UV irradiation, whereas the removal of seven glutamic acid residues from the acidic rich region, does not appear to have a particularly dramatic effect. Deletion of the C-terminal 25 amino acids of CSB totally destroys the repair ability of the gene. In contrast, cDNAs deleted at the N-terminus are able to at least, partially retain repair activity.

Les mutations dans les gènes codant pour les facteurs NER donnent lieu à des maladies autosomiques récessives telles que Xeroderma pigmentosum (XP), le syndrome de Cockayne (CS) et la trichothiodystrophie (TTD). Les phénotypes associés à ces syndromes génétiques se caractérisent par une sensibilité extrême à la lumière UV, avec prédisposition accrue à certains cancers (pour XP et XP / CS combiné, principalement), ainsi qu’un retard mental et des signes de progeria (pour CS et XP / CS combiné). Si on peut admettre une corrélation entre réparation de l'ADN endommagé et sensibilité aux UV / cancer, celle avec les symptômes neurologiques/progéroïdes est encore sujet à débat. Une explication pourrait provenir du rôle des facteurs NER dans la régulation de la transcription. Nous proposons une vue d’ensemble des roles de XPG et XPC dans la régulation de la transcription en absence des stress exogènes et comment CSA et CSB orchestrent l’arret de la transcription après une attaque génotoxique. XPC était capable d’interagir stablement avec la methyltransferase NSD3. Des mutations dans XPC altèrent le transcriptôme et la distribution des H3K36me3. Les mutations dans XPG dérégulent l’expression génique et XPG est capable d’etre recruté sur l’ensemble du genôme avec TFIIH. CSA et CSB faisant partie de la machinerie ubiquitin/proteasôme, régulent le recrutement de facteurs fixant l’ADN et contrôlant le programme transcriptionnel après irradiation aux UV. Nos donnés mettent en évidence le rôle des facteurs NER dans la transcription et leur défaut d’action provoque les maladies XP et XP/CS. En plus, nos données fournissent des explications sur le méchanisme d’arrêt de la transcription après un stress genotoxique et pose la question de l’origine du phenotype CS<br>Mutations in genes coding for NER factors give rise to autosomal recessive diseases such as Xeroderma pigmentosum (XP), Cockayne syndrome (CS), and trichothiodystrophy (TTD). The phenotypes associated with these genetic syndromes spans from extreme sensitivity to UV light, with increased predisposition to cancer (for XP and combined XP/CS, mostly), mental retardation and progeria (for CS and combined XP/CS). Whether the correlation between defective DNA repair reactions and UV-sensitivity/cancer may be more intuitive, a link with neurological/progeroid symptoms is still a matter of debate. As a possible explanation, it has been proposed a connection between NER and transcription regulation. We propose additional insights on XPG and XPC roles in transcription regulation in absence of exogenous stress and how CSA and CSB orchestrate transcription arrest due to genotoxic attack. XPC was able to stably interact with NSD3 methyltransferase. Mutations in XPC also disturbed the transcriptome and the H3K36me3 distribution. Mutations in XPG deregulate gene expression and XPG is able to be recruited genome wide together with TFIIH. CSA and CSB can, as part of the ubiquitin/proteasome machinery, regulate the recruitment timing of DNA binding factors and control transcriptional program after UV irradiation. Hence, our data shed more light in NER factors role in transcription and their defective action as a cause of XP and XP/CS disorders. Additionally, our data provide explanations on the mechanism of transcription arrest following genotoxic stress and pose questions about the origins of CS phenotype

O funcionamento pleno e harmônico de uma célula está intimamente associado à sua capacidade de manter a integridade genômica. Diversos agentes químicos e físicos exógenos, bem como produtos do próprio metabolismo celular, podem interagir com o DNA, causando danos a esta molécula. Em respota a esses eventos, um intrincado mecanismo de resposta a danos ao DNA é ativado, podendo culminar tanto na correção das lesões, como na ativação de programas de morte celular, como a apoptose, sempre com o intuito de preservar a homeostase tecidual. Falhas neste mecanismo estão associadas a um aumento nas taxas de mutação, que apesar de constituírem a base da diversidade genética e evolução das espécies, está intimimamente associado à tumorigênese e ao envelhecimento. Neste trabalho, dividido em duas partes, utilizamos células de glioma humano como modelo de estudo para quimioterapia adjuvante, bem como também utilizamos neurônios humanos obtidos à partir de células-tronco pluripotente-induzidas como modelo de estudo para a neurodegeneração característica da síndrome de Cockayne, uma doença genética na qual os pacientes apresentam deficiências em mecanismos de reparo de DNA, bem como envelhecimento precoce. Na primeira etapa, avaliamos a resposta de células de glioma a cloroquina, um promissor adjuvante no tratamento desta enfermidade, e notamos que a resistência das células a esta droga estava intimamente relacionada ao seu potencial de membrana mitocondrial, o qual podia ser desfeito por meio da inibição da quinase ATR. Apesar da função canônica desta proteína se dar através da regência da resposta a danos ao DNA, notamos que a sua participação como agente promotor de resistência à cloroquina se dava independentemente deste mecanismo. Também notamos que a combinação da cloroquina com a inibição de ATR via silenciamento gênico exercia um potente efeito tóxico sobre as células tumorais tratadas com o quimioterápico Temozolomida. Já na etapa final desta tese, através do emprego da reprogramação celular, obtivemos, pela primeira vez, neurônios humanos de pacientes portadores da síndrome de Cockayne a partir de fibroblastos de pele. Com este modelo de estudo, foi possível observar que esses neurônios apresentavam uma reduzida densidade de puncta sináptica, bem como uma aparente deficiência na sincronia de suas atividades. Por fim, por meio do sequenciamento do RNA destes neurônios, identificamos uma desregulação na expressão de diversas vias relacionadas ao funcionamento e comunicação neural. As implicações para o uso da cloroquina como adjuvante no tratamento de gliomas, bem como as vantagens do uso de neurônios humanos de Cockayne em detrimento aos modelos atualmente disponíveis, também são discutidos.<br>Genome integrity is constantly threatened by chemical and physical exogenous agents, as well as products of cells own metabolism, and capability of cells to overcome these challenges is essential to achieve homeostasis. In response to DNA lesions, cells activate a dynamic and intricate DNA damage response that ultimately results either in lesion resolution, or in cell death through apoptosis. Regardless the fate chosen, tissue homeostasis is the ultimate goal. Flaws in this mechanism are associated to an increase in mutation rates. Although it constitutes the basis of genetic diversity and evolution, it is also strictly associated to tumorigenesis and aging. In this thesis, separated in two chapters, we used human glioma cells as a model to study adjuvant chemotherapy, and induced pluripotent stem cells-derived human neurons as a model to study neurodegeneration in Cockayne syndrome, a genetic disease in which patients display defects in DNA repair mechanisms, and also premature aging. In the first chapter, we investigated the response of cancer cells to chloroquine, a promising adjuvant drug in glioma therapy, and we noticed that cellsresistance to this drug was strictly associated to its mitochondrial membrane potential values, which could be dismantled through ATR inhibition. Interestingly, we noticed that the ability of ATR to promote resistance of glioma cells to chloroquine was independent of its canonical role in the DNA damage response. We also noticed that combined treatment of chloroquine to ATR inhibition through gene silencing exerted a powerful toxic effect on glioma cells treated with the chemotherapeutic Temozolomide. In the second chapter of this thesis, we employed cell reprogramming technique to obtain, for the first time, human neurons from Cockayen Syndrome patients from skin fibroblasts. With this model, we were able to identify a reduced density of synaptic puncta, as well as reduced synchrony in the activity of the patients neurons. Through RNA sequencing, we noticed several pathways related to synapses and neuronal function deregulated in Cockayne Sydrome patients neurons. Implications for the use of chloroquine as an adjuvant drug in glioma therapy, as well as the advantage of using iduced pluripotent stem cells-derived Cockayne syndrome human neurons (instead of currently available models) to study this disease, are also discussed.