Counter-balancing X-linkedMecp2hypofunction by hyperfunction ameliorates disease features in a model of Rett syndrome: implications for genetic therapies

Abstract

ABSTRACTTreating monogenic neurodevelopmental disorders remains challenging and mostly symptomatic. X-linked disorders affecting women such as the postnatal neurodevelopmental disorder Rett syndrome (caused by mutations in the geneMECP2) have additional challenges due to dosage sensitivity and to cellular mosaicism caused by random X-chromosome inactivation. An approach to augmentMECP2expression from wild-type cells in RTT may be feasible and simpler than gene replacement but has never been tested due to known toxicity ofMECP2over-expression, as evidenced by the distinct neurological condition known asMECP2Duplication Syndrome. Here, using genetic techniques, we find that “counter-balancing”Mecp2-null cells in femaleMecp2-null/+ mice by a complementary population of cells harboring an X-linked transgene associated with 3X normal levels ofMECP2leads to normalization of multiple whole animal phenotypic outcomes without noticeable toxicity. In addition,in vivoLFP recordings demonstrate that counter-balancingMecp2loss-of-function improves select within-region and between-region abnormalities. By comparing the counter-balance approach with an approach based on cell autonomous restoration of MeCP2 using an autosomal transgene expressing 2X normal levels ofMECP2in all cells (mimicking gene replacement), we identify neurobehavioral and electrographic features best suited for preclinical biomarkers of a therapeutic response to cell autonomous versus non-cell autonomous correction. Notably, these proof-of-concept findings demonstrate how non-cell autonomous suppression of MeCP2 deficiency by boosting overall wild-type MeCP2 levels may be a viable disease-modifying therapy for RTT, with potential implications for genetic-based therapies of monogenic X-linked disorders.One Sentence SummaryIn a mouse model of Rett syndrome, counterbalancing mosaic LOF with complementary mosaic GOF improves phenotypic outcome.