Targeting Neuronal Activity with Ampakine: A Therapeutic Approach for Rett Syndrome

Rett syndrome (RTT) is a rare and severe neurodevelopmental disorder, primarily affecting females. Patients are characterized by an apparently normal early development followed by a regression phase between 6 and 18 months of age, which marks the onset of progressive motor and intellectual impairments. The majority of Rett cases are caused by mutations in the X-linked MECP2 gene, which encodes for a master regulator of gene expression, ubiquitously expressed, but mainly present in the brain. In line with its role, MeCP2-null neurons show widespread transcriptional and functional deficits, including impaired maturation and reduced responsiveness to external stimuli. Although clinical symptoms emerge after the first year of life, increasing evidence indicates that MeCP2 deficiency disrupts brain development from early stages. In particular, Mecp2-null cortical neurons display early defects in transcription, neuronal activity, and morphology, which appear interconnected in a feed-forward mechanism where neuronal activity drives transcriptional and structural changes that further increase network maturity. We thus investigated the therapeutic potential of a high-impact Ampakine, a positive modulator of AMPA receptors, to restore neuronal activity in Mecp2-deficient models. Initially, we tested its efficacy in vitro using primary Mecp2-null mouse neurons. We were able to show a restoration of synaptic density in Mecp2 KO treated neurons, as well as a rescue in neuronal functionality. Then, we focused on two in vivo strategies. Since it was previously demonstrated that an early ampakine treatment (P3-P9) is able to improve RTT phenotype in male KO mouse model, we first evaluated the same therapy on female heterozygous mice, being the most clinically relevant model of Rett syndrome. Afterwards, we implemented a prolonged intermittent treatment (P3–P75) in both male null and female heterozygous mice, to assess whether a sustained modulation of neuronal activity could enhance and maintain long-term benefits. As we proved that early intervention is crucial to obtain beneficial effects, we evaluated molecular and functional consequences of the early treatment by profiling gene expression in the prefrontal cortex at two developmental stages (P10 and P30), capturing both acute and late transcriptional effects. Additionally, ex vivo electrophysiological recordings were performed.