FMR1 Reactivating Treatments in Fragile X iPSC-Derived Neural Progenitors In Vitro and In Vivo

Summary: Fragile X syndrome (FXS) is caused primarily by a CGG repeat expansion in the FMR1 gene that triggers its transcriptional silencing. In order to investigate the regulatory layers involved in FMR1 inactivation, we tested a collection of chromatin modulators for the ability to reactivate the FMR1 locus. Although inhibitors of DNA methyltransferase (DNMT) induced the highest levels of FMR1 expression, a combination of a DNMT inhibitor and another compound potentiated the effect of reactivating treatment. To better assess the rescue effect following direct demethylation, we characterized the long-term and genome-wide effects of FMR1 reactivation and established an in vivo system to analyze FMR1-reactivating therapies. Systemic treatment with a DNMT inhibitor in mice carrying FXS induced pluripotent stem cell (iPSC)-derived transplants robustly induced 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 CNS. : Vershkov et al. use small-molecule screening in fragile X syndrome iPSCs to analyze the ability of chromatin remodeling compounds to target FMR1 inactivation. FMR1-reactivating treatments were assessed for their additive and long-term effects and evaluated using in vivo platforms of differentiated fragile-X-syndrome-affected transplants. Keywords: fragile X syndrome, pluripotent stem cells, disease modeling, drug screening, neurodevelopmental disorder