Littérature scientifique sur le sujet « Epigenome editors »

Imprinting diseases (IDs) are rare congenital disorders caused by aberrant dosages of imprinted genes. Rare IDs are comprised by a group of several distinct disorders that share a great deal of homology in terms of genetic etiologies and symptoms. Disruption of genetic or epigenetic mechanisms can cause issues with regulating the expression of imprinted genes, thus leading to disease. Genetic mutations affect the imprinted genes, duplications, deletions, and uniparental disomy (UPD) are reoccurring phenomena causing imprinting diseases. Epigenetic alterations on methylation marks in imprinting control centers (ICRs) also alters the expression patterns and the majority of patients with rare IDs carries intact but either silenced or overexpressed imprinted genes. Canonical CRISPR/Cas9 editing relying on double-stranded DNA break repair has little to offer in terms of therapeutics for rare IDs. Instead CRISPR/Cas9 can be used in a more sophisticated way by targeting the epigenome. Catalytically dead Cas9 (dCas9) tethered with effector enzymes such as DNA de- and methyltransferases and histone code editors in addition to systems such as CRISPRa and CRISPRi have been shown to have high epigenome editing efficiency in eukaryotic cells. This new era of CRISPR epigenome editors could arguably be a game-changer for curing and treating rare IDs by refined activation and silencing of disturbed imprinted gene expression. This review describes major CRISPR-based epigenome editors and points out their potential use in research and therapy of rare imprinting diseases.

Development of CRISPR-based epigenome editing tools is important for the study and engineering of biological behavior. Here, we describe the design of a reporter system for quantifying the ability of CRISPR epigenome editors to produce a stable gene repression. We characterize the dynamics of durable gene silencing and reactivation, as well as the induced epigenetic changes of this system. We report the creation of single-protein CRISPR constructs bearing combinations of three epigenetic editing domains, termed KAL, that can stably repress the gene expression. This system should allow for the development of novel epigenome editing tools which will be useful in a wide array of biological research and engineering applications.

Designer effectors based on the DNA binding domain (DBD) of Xanthomonas transcription activator-like effectors (TALEs) are powerful sequence-specific tools with an excellent reputation for their specificity in editing the genome, transcriptome, and more recently the epigenome in multiple cellular systems. However, the repetitive structure of the TALE arrays composing the DBD impedes their generation as gene synthesis product and prevents the delivery of TALE-based genes using lentiviral vectors (LVs), a widely used system for human gene therapy. To overcome these limitations, we aimed at chimerizing the DNA sequence encoding for the TALE-DBDs by introducing sufficient diversity to facilitate both their gene synthesis and enable their lentiviral delivery. To this end, we replaced three out of 17 Xanthomonas TALE repeats with TALE-like units from the bacterium Burkholderia rhizoxinica. This was combined with extensive codon variation and specific amino acid substitutions throughout the DBD in order to maximize intra- and inter-repeat sequence variability. We demonstrate that chimerized TALEs can be easily generated using conventional Golden Gate cloning strategy or gene synthesis. Moreover, chimerization enabled the delivery of TALE-based designer nucleases, transcriptome and epigenome editors using lentiviral vectors. When delivered as plasmid DNA, chimerized TALEs targeting the CCR5 and CXCR4 loci showed comparable activities in human cells. However, lentiviral delivery of TALE-based transcriptional activators was only successful in the chimerized form. Similarly, delivery of a chimerized CXCR4-specific epigenome editor resulted in rapid silencing of endogenous CXCR4 expression. In conclusion, extensive codon variation and chimerization of TALE-based DBDs enables both the simplified generation and the lentiviral delivery of designer TALEs, and therefore facilitates the clinical application of these tools to precisely edit the genome, transcriptome and epigenome.

Abstract Precision epigenome editing has gained significant attention as a method to modulate gene expression without altering genetic information. However, a major limiting factor has been that the gene expression changes are often transient, unlike the life-long epigenetic changes that occur frequently in nature. Here, we systematically interrogate the ability of CRISPR/dCas9-based epigenome editors (Epi-dCas9) to engineer persistent epigenetic silencing. We elucidated cis regulatory features that contribute to the differential stability of epigenetic reprogramming, such as the active transcription histone marks H3K36me3 and H3K27ac strongly correlating with resistance to short-term repression and resistance to long-term silencing, respectively. H3K27ac inversely correlates with increased DNA methylation. Interestingly, the dependance on H3K27ac was only observed when a combination of KRAB-dCas9 and targetable DNA methyltransferases (DNMT3A-dCas9 + DNMT3L) was used, but not when KRAB was replaced with the targetable H3K27 histone methyltransferase Ezh2. In addition, programmable Ezh2/DNMT3A + L treatment demonstrated enhanced engineering of localized DNA methylation and was not sensitive to a divergent chromatin state. Our results highlight the importance of local chromatin features for heritability of programmable silencing and the differential response to KRAB- and Ezh2-based epigenetic editing platforms. The information gained in this study provides fundamental insights into understanding contextual cues to more predictably engineer persistent silencing.

The tremendous evolution of genome-editing tools in the last two decades has provided innovative and effective approaches for gene therapy of congenital and acquired diseases. Zinc-finger nucleases (ZFNs), transcription activator- like effector nucleases (TALENs) and CRISPR-Cas9 have been already applied by ex vivo hematopoietic stem cell (HSC) gene therapy in genetic diseases (i.e., Hemoglobinopathies, Fanconi anemia and hereditary Immunodeficiencies) as well as infectious diseases (i.e., HIV), and the recent development of CRISPR-Cas9-based systems using base and prime editors as well as epigenome editors has provided safer tools for gene therapy. The ex vivo approach for gene addition or editing of HSCs, however, is complex, invasive, technically challenging, costly and not free of toxicity. In vivo gene addition or editing promise to transform gene therapy from a highly sophisticated strategy to a “user-friendly’ approach to eventually become a broadly available, highly accessible and potentially affordable treatment modality. In the present review article, based on the lessons gained by more than 3 decades of ex vivo HSC gene therapy, we discuss the concept, the tools, the progress made and the challenges to clinical translation of in vivo HSC gene editing.

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and its associated proteins (Cas) is an adaptive immune system in archaea and most bacteria. By repurposing these systems for use in eukaryote cells, a substantial revolution has arisen in the genome engineering field. In recent years, CRISPR-Cas technology was rapidly developed and different types of DNA or RNA sequence editors, gene activator or repressor, and epigenome modulators established. The versatility and feasibility of CRISPR-Cas technology has introduced this system as the most suitable tool for discovering and studying the mechanism of specific genes and also for generating appropriate cell and animal models. SOX genes play crucial roles in development processes and stemness. To elucidate the exact roles of SOX factors and their partners in tissue hemostasis and cell regeneration, generating appropriate in vitro and in vivo models is crucial. In line with these premises, CRISPR-Cas technology is a promising tool for studying different family members of SOX transcription factors. In this review, we aim to highlight the importance of CRISPR-Cas and summarize the applications of this novel, promising technology in studying and decoding the function of different members of the SOX gene family.

Breast cancer (BC) is a widespread malignancy that affects the lives of millions of women each year, and its resulting financial and healthcare hardships cannot be overstated. These issues, in combination with side effects and obstacles associated with the current standard of care, generate considerable interest in new potential targets for treatment as well as means for BC prevention. One potential preventive compound is Withaferin A (WFA), a traditional medicinal compound found in winter cherries. WFA has shown promise as an anticancer agent and is thought to act primarily through its effects on the epigenome, including, in particular, the methylome. However, the relative importance of specific genes’ methylation states to WFA function remains unclear. To address this, we utilized human BC cell lines in combination with CRISPR-dCas9 fused to DNA methylation modifiers (i.e., epigenetic editors) to elucidate the importance of specific genes’ promoter methylation states to WFA function and cancer cell viability. We found that targeted demethylation of promoters of the tumor suppressors p21 and p53 within MDA-MB-231/MCF7 cells resulted in around 1.7×/1.5× and 1.2×/1.3× increases in expression, respectively. Targeted methylation of the promoter of the oncogene CCND1 within MDA-MB-231/MCF7 cells resulted in 0.5×/0.8× decreases in gene expression. These changes to p21, p53, and CCND1 were also associated with decreases in cell viability of around 25%/50%, 5%/35%, and 12%/16%, respectively, for MDA-MB-231/MCF7 cells. When given in combination with WFA in both p53 mutant and wild type cells, we discovered that targeted methylation of the p21 promoter was able to modulate the anticancer effects of WFA, while targeted methylation or demethylation of the promoters of p53 and CCND1 had no significant effect on viability decreases from WFA treatment. Taken together, these results indicate that p21, p53, and CCND1 may be important targets for future in vivo studies that may lead to epigenetic editing therapies and that WFA may have utility in the prevention of BC through its effect on p21 promoter methylation independent of p53 function.

Drépanocytose et bêta-thalassémie sont dues à des mutations affectant la production de la chaîne de globine β. La sévérité clinique est atténuée par des mutations augmentant la quantité d'hémoglobine fœtale (HbF), une condition appelée persistance héréditaire d'HbF à l'âge adulte. La transplantation autologue de cellules souches/progénitrices hématopoïétiques (CSPH) génétiquement corrigées est prometteuse. Une approche CRISPR/Cas9 pour réprimer BCL11A, un répresseur de la globine γ, a été approuvée mais comporte des risques de génotoxicité dues aux cassures double brin (CDB). Nous avons ciblé les sites de liaison (SL) des activateurs transcriptionnels GATA1 et ATF4, présents dans les régions +58-kb et +55-kb, respectivement, des enhancers érythroïdes de BCL11A, avec des éditeurs de base (BEs) pour introduire des mutations ponctuelles précises sans créer de CDBs. Des ARN guides (ARNg) ont été testés dans des cellules souches hématopoïétiques (CSH) de patients drépanocytaires en combinaison avec des BEs, générant différents nucléotides dans les motifs de liaison avec une efficacité d'édition atteignant 90 %, avec peu ou pas d'indels induits par les CDB. La réactivation d'HbF a été observée dans tous les échantillons édités, mesurée par HPLC, mais pas suffisante pour un sauvetage complet du phénotype dans les cellules érythroïdes issues des CSPHs drépanocytaires éditées. Nous avons donc ciblé simultanément les SL de GATA1 et ATF4 pour augmenter les niveaux d'HbF. Les cellules éditées au niveau des enhancers +58 et +55 ont montré une augmentation de l'expression d'HbF par rapport aux cellules recevant des ARNg individuels, dépassant les niveaux atteints avec la stratégie CRISPR/Cas9. Enfin, la réactivation de l'HbF était suffisante pour permettre un sauvetage substantiel du phénotype malade, diminuant le nombre de cellules drépanocytaires à 16,4%. Pour évaluer les effets hors cibles, nous avons utilisé le GUIDE-seq couplé au séquençage ciblé, le séquençage de l'exome entier et le RNA-seq, tandis que les effets indésirables présent dans les sites cibles ont été évalués par séquençage Long read. L'efficacité du BE pour repeupler les CSH a été démontrée en transplantant des CSH éditées dans des souris immunodéficientes, prouvant l'efficacité de l'édition simultanée des éléments transrégulateurs de la globine γ pour la réactivation de l'HbF. Cette preuve de concept permettra le développement préclinique et clinique de CSH modifiées pour le traitement des β-hémoglobinopathies. Cependant, des travaux récents montrent que les BEs peuvent également générer de larges délétions ou indels (Antoniou et al. 2022). Ainsi, une nouvelle stratégie basée sur l'édition de l'épigénome a été développée pour moduler l'expression des gènes sans modifier la séquence d'ADN sous-jacente. Nous avons analysé les marques épigénétiques dans deux régions cis-régulatrices clés, les promoteurs de HBG et les enhancers de BCL11A, dans des cellules érythroïdes dérivées de CSPH. Des marques épigénétiques répressives, telles que la méthylation de l'ADN, ont été détectées au niveau des promoteurs de HBG dans des cellules érythroïdes adultes n'exprimant pas la globine γ. En revanche, la déméthylation de l'ADN et les marques épigénétiques activatrices telles que l'acétylation de la lysine 27 de l'histone 3 (H3K27ac) et la triméthylation de la lysine 4 (H3K4me3) ont été détectées au niveau des promoteurs de HBG dans les cellules érythroïdes exprimant la globine γ. La forte expression de BCL11A dans les cellules érythroïdes adultes est associée à de faibles niveaux de méthylation de l'ADN au niveau des enhancers de BCL11A. L'inactivation des enhancers de BCL11A est associée à une augmentation de la méthylation de l'ADN. Ces données nous ont permis de concevoir des modificateurs de l'épigénome pour manipuler l'architecture épigénétique des promoteurs de HBG et des enhancers de BCL11A afin d'atteindre des niveaux thérapeutiques d'HbF
B-thalassemia and sickle cell disease (SCD) result from mutations that affect the synthesis or structure of adult hemoglobin. Historically, allogeneic hematopoietic stem cell (HSC) transplantation from a compatible donor was the only curative treatment. Transplantation of autologous, genetically modified HSCs offers a promising therapeutic alternative for patients lacking a suitable donor. The clinical severity in b-hemoglobinopathies is mitigated by co-inheritance of hereditary persistence of fetal hemoglobin (HPFH), a benign condition characterized by mutations occurring in the genes encoding the fetal y-globin chains, which lead to increased fetal hemoglobin (HbF, a2y2) expression, which can rescue the b-thalassemic and SCD phenotypes. HbF reactivation can be achieved by down-regulating BCL11A, encoding a key repressor of HbF. A CRISPR/Cas9 strategy targeting the GATA1 binding site (BS) within the +58-kb erythroid-specific enhancer of BCL11A has recently been approved as the first gene-editing therapy for b-thalassemia and SCD. Indeed, the targeting of the BCL11A erythroid-specific enhancer led to an efficient reduction of BCL11A in the erythroid cells, without impacting the differentiation of HSPCs in the other cell lineages. However, site-specific nucleases induce double strand breaks (DSBs), posing significant risks, such apoptosis and generation of large genomic rearrangements. In addition, to obtain an adequate number of corrected cells to transplant, several collections of HSCs are necessary to compensate for the cell loss due to DSB-induced apoptosis. Finally, the clinical study showed variability in the extent of HbF reactivation, still high HbS levels and modest correction of ineffective erythropoiesis. Novel CRISPR/Cas9 derived tools are currently available and can be used to develop therapeutic strategies associated with a low risk of DSB generation and increased HbF expression. In this project, we intend to develop universal, safe and efficacious therapeutic strategies for b-hemoglobinopathies aimed at modifying HSCs using base editors (BEs) and epigenome editors to reactivate HbF expression in their erythroid progeny. BEs are a CRISPR-Cas9-based genome editing technology that allows the introduction of point mutations with little DSB generation. In this work we used this technology to inactivate the GATA1 or the ATF4 transcriptional activator BS in the +58-kb and +55-kb BCL11A erythroid-specific enhancers through the insertion of point mutations. In particular, to reach levels of HbF sufficient to rescue the sickling phenotype, we performed simultaneous targeting of the two BS, achieving similar HbF levels compared to CRISPR/Cas9 nuclease-based approach. Additionally, we showed that BEs generated fewer DSBs and genomic rearrangements compared to the CRISPR/Cas9 nuclease approach. In parallel, we developed a novel epigenome-editing strategy aimed at modulating gene expression without altering the DNA sequence (e.g. without generating DSBs). We designed two approaches to upregulate HbF expression: a first strategy targeting and activating the y-globin promoters and a second approach downregulating BCL11A by targeting its erythroid-specific enhancers. We first identified the epigenetic marks in these trans- and cis-regulatory regions that are associated with active or inactive transcription in adult versus fetal erythroid cells. Then we used epigenome editors to deposit active histone modifications at the y-globin promoters and remove inactive marks such as DNA methylation. In parallel, we decorated the BCL11A enhancers with inactive epigenetic marks. Preliminary results demonstrated y-globin reactivation using both strategies, though the effects diminished over time, indicating the need for further optimization. In conclusion, we proposed two different editing approaches that allow to reduce DSB-associate issues as strategies to treat b-hemoglobinopathies