In search of molecular signatures preceding full symptoms appearance: towards earlier interventions for Rett Syndrome

Rett syndrome (RTT) is a rare and incurable neurologic disorder affecting mainly females carrying de novo mutations in the epigenetic factor methyl-CpG-binding protein 2 (MECP2). The clinical phenotype is usually mutation-dependent, and is mainly characterized by intellectual disability, inability to speak and walk, autistic-like behavior and motor stereotypies, which appear around 18 months of age, after a period of apparent normal development. Mounting evidence suggests that mild phenotypical alterations are already present before the overt symptoms appearance, arguing for the presence of precocious disruptions at the brain level. However, the patterns of molecular alterations in RTT brain at prodromal stages have been barely addressed. By exploiting extensively validated mouse models carrying different RTT-causing mutations, we aimed at dissecting the neuromolecular underpinnings of early abnormalities and uncover alterations in signaling pathways that may constitute novel targets for precocious interventions. To this end, cortical tissue from mouse pups from four MeCP2-mutant colonies and wild type siblings were collected during the first two postnatal weeks, and a label free approach following mass spectrometry data independent acquisition was performed to analyze the proteome. Classical statistical approaches suggest the occurrence of substantial heterogeneity across different MeCP2 mutations. While machine learning strategies confirmed mutation-dependent variability, they also uncovered age-dependent patterns of molecular alteration that were relatively consistent across RTT models. The present results reveal early, transient disruptions in the RTT brain proteome, and highlight novel pathways that could be targeted to redirect neurodevelopmental trajectories and mitigate the accumulation of alterations that ultimately trigger full symptoms manifestation. Funding: Funded by the European Union - Next Generation EU - NRRP M6C2 - Investment 2.1 Enhancement and strengthening of biomedical research in the NHS (code PNRR-MR1-2022-12376808).