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Rescue of Fragile X syndrome neurons by DNA methylation editing of the FMR1 gene [methylation]

ABSTRACT: Fragile X syndrome (FXS), the most common genetic form of intellectual disability in male, is caused by silencing of the FMR1 gene by hypermethylation of the CGG expansion mutation in the 5’UTR region of FMR1 in FXS patients. Here, we applied recently developed DNA methylation editing tools to reverse this hypermethylation event. Targeted demethylation of the CGG expansion by dCas9-Tet1/sgRNA switched the heterochromatin status of the upstream FMR1 promoter to an active chromatin state restoring a persistent expression of FMR1 in FXS iPSCs. Neurons derived from methylation edited FXS iPSCs rescued the electrophysiological abnormalities and restored a wild-type phenotype upon the mutant neurons. FMR1 expression in edited neurons was maintained in vivo after engrafting into the mouse brain. Finally, demethylation of the CGG repeats in post-mitotic FXS neurons also reactivated FMR1. Our data establish demethylation of the CGG expansion is sufficient for FMR1 reactivation, suggesting potential therapeutic strategies for FXS.

ORGANISM(S): Homo sapiens

PROVIDER: GSE108171 | GEO | 2018/02/16

REPOSITORIES: GEO

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Rescue of Fragile X syndrome neurons by DNA methylation editing of the FMR1 gene [RNA-seq]

Project description:Fragile X syndrome (FXS), the most common genetic form of intellectual disability in male, is caused by silencing of the FMR1 gene by hypermethylation of the CGG expansion mutation in the 5’UTR region of FMR1 in FXS patients. Here, we applied recently developed DNA methylation editing tools to reverse this hypermethylation event. Targeted demethylation of the CGG expansion by dCas9-Tet1/sgRNA switched the heterochromatin status of the upstream FMR1 promoter to an active chromatin state restoring a persistent expression of FMR1 in FXS iPSCs. Neurons derived from methylation edited FXS iPSCs rescued the electrophysiological abnormalities and restored a wild-type phenotype upon the mutant neurons. FMR1 expression in edited neurons was maintained in vivo after engrafting into the mouse brain. Finally, demethylation of the CGG repeats in post-mitotic FXS neurons also reactivated FMR1. Our data establish demethylation of the CGG expansion is sufficient for FMR1 reactivation, suggesting potential therapeutic strategies for FXS.

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Project description:The primary mechanism causing Fragile X syndrome (FXS) is the expansion and silencing of a repetitive CGG sequence in the 5’-UTR of the FMR1 gene. Previous work has demonstrated that chemical disruption of DNA methylation induces FMR1 expression in FXS-iPSCs. To further explore the maintenance of DNA methylation in the FMR1 locus, and to test the possibility of FMR1 reactivation using gene targeting of a single epigenetic factor, we performed a global transcriptional analysis of FXS-iPSCs infected with a lentiviral construct containing Cas9 and sgRNA targeting DNMT1.

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Project description:Fragile X syndrome (FXS) is caused primarily by a CGG repeat expansion mutation in the FMR1 gene that triggers its epigenetic silencing. In order to investigate the role of different epigenetic regulatory layers in the silencing of FMR1 expression, we tested a collection of epigenetic modulators for the ability to reactivate the FMR1 locus. While inhibitors of DNA methylatransferase induced the highest levels of FMR1 mRNA expression, a combination of a DNMT inhibitor and a novel epigenetic agent was able to potentiate the effect of reactivating treatment. To better assess the rescue effect observed following direct demethylation, we characterized the long-term and genome-wide effects of FMR1 reactivation, and established an in vivo system for FMR1 reactivating therapy analysis. Systemic treatment with a DNMT inhibitor in mice carrying transplants of differentiated FXS-iPSCs was able to robustly induce FMR1 expression in the affected tissue, which was maintained for a prolonged period of time. Finally, we show a proof-of-principle for FMR1 reactivating therapy in the context of the central nervous system.

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