Multiplex Epigenome Editing of MECP2 to Rescue Rett Syndrome Neurons

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by loss-of-function heterozygous mutations of Methyl CpG-binding Protein 2 (MECP2) on the X chromosome in girls. Reactivation of the silent wild-type MECP2 allele from the inactive X chromosome (Xi) represents a promising therapeutic opportunity for female patients with RTT. Here, we applied a multiplex epigenome editing approach to reactivate MECP2 from Xi in RTT human embryonic stem cells (hESCs) and derived neurons. Demethylation of the MECP2 promoter by dCas9-Tet1 with target sgRNA reactivated MECP2 from Xi in RTT hESCs without detectable off-target effects at the transcriptional level. Neurons derived from methylation-edited RTT hESCs maintained MECP2 reactivation and reversed the smaller soma size and electrophysiological abnormalities, two hallmarks of RTT. In RTT neurons, insulation of the methylation edited MECP2 locus by dCpf1-CTCF with target CRISPR RNA enhanced MECP2 reactivation and rescued RTT-related neuronal defects, providing a proof-of-concept study for epigenome editing to treat RTT and potentially other dominant X-linked diseases. One-Sentence SummaryReactivation of MECP2 from the inactive X chromosome by multiplex epigenome editing rescues Rett syndrome neurons in vitro.