Quantitative proteomic analysis shows alterations in patient Rett syndrome iPSC cultures at early neuronal progenitor stages

Abstract

BackgroundRett syndrome (RTT) is a progressive neurodevelopmental disease that is characterized by abnormalities in cognitive, social and motor skills. RTT is often caused by mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2). The mechanism by which impaired MeCP2 induces the pathological abnormalities in the brain is not understood. Both patients and mouse models have shown abnormalities at molecular and cellular level before typical RTT-associated symptoms appear. This implies that underlying mechanisms are already affected during neurodevelopmental stages.MethodsTo understand the molecular mechanisms involved in disease onset, we used an RTT patient induced pluripotent stem cell (iPSC)-based model with isogenic controls and performed time-series of proteomic analysis using in-depth high-resolution quantitative mass spectrometry during early stages of neuronal development. ResultsWe provide mass spectrometry-based quantitative proteomic data, depth of about 7000 proteins, at neuronal progenitor developmental stages of RTT patient cells and isogenic controls. Our data gives evidence of proteomic alteration at early neurodevelopmental stages, suggesting alterations long before the phase that symptoms of RTT syndrome become apparent. We found changes in proteins involved in pathway associated with RTT phenotypes, including dendrite morphology and synaptogenesis. Differential expression increased from early to late neural stem cell phases, although proteins involved in immunity, metabolic processes and calcium signaling were affected throughout all stages analyzed. LimitationsThe limitation of our study is the number of biological replicates. As the aim of our study was to investigate a large number of proteins, only a limited amount of biological replicates were suitable for inclusions without reducing the number of target proteins. Therefore, larger sample sizes derived from RTT patients will be needed to validate results. ConclusionsOur results provide a valuable resource of proteins to study potential targets for early treatment of RTT symptoms. We found consistent and time-point specific alterations during early neuronal differentiation in RTT cultures. Insight into altered protein levels can help development of new biomarkers and therapeutic approaches in RTT syndrome. Therefore, we hope that our results give awareness of the early pre-natal onset of RTT, providing new insights to explore early diagnosis and treatment.