Evidence-based approach to treat hyperexcitability in Rett syndrome through splicing modulation

Rett syndrome is a severe X-linked neurodevelopmental disorder primarily caused by Mecp2 mutations, sharing traits with the autistic spectrum. Affected girls exhibit stereotypies, loss of behavioral milestones such as language and movement, and drug-resistant epileptic crises. Recent studies unveiled increased spontaneous glutamate release and glutamate-related excitotoxicity which contribute to hyperexcitability and maladaptive neural wiring, potentially contributing to Rett syndrome pathological features. Our lab identified an epigenetic mechanism regulating glutamatergic homeostasis, likely evolved to prevent excessive excitation in the mammalian brain. This system relies on alternative splicing of the transcriptional corepressor LSD1, which suppresses excitatory neuroplastic genes, including Immediate Early Genes and key post-synaptic actors like SAP proteins, AMPA receptors, and PSD95, limiting neuronal excitability. In the brain, LSD1 activity is hampered by the inclusion of microexon E8a, which disrupts its co-repressive function. Upon neuronal activation, mature transcripts exclude E8a, favoring LSD1-mediated repression to maintain homeostasis. Our project demonstrated that genetically enhancing LSD1 activity in MeCP2Y/- mice reduces seizure susceptibility and doubles survival rate after chemoconvulsant treatment. We are now exploring a pharmacological approach using an exon-E8a-skipping antisense oligonucleotide (ASO-E8a) to enhance corepressive LSD1 activity in the mouse hippocampus, a key epileptic region. Based on preliminary genetic evidence, we believe this strategy could effectively increase the excitatory threshold, reducing brain hyperexcitability as a primary outcome in Rett syndrome. Our initial findings, following a single-dose administration of ASO-E8a into the central hippocampus of MeCP2Y/- mice, suggest an improvement in locomotor activity, gait, and overall health of the model.