A New Strategy to Uncover Fragile X Proteomic Biomarkers Using the Nascent Proteome of Peripheral Blood Mononuclear Cells (PBMCs)

Abstract

Background: Fragile X syndrome (FXS) is the most prevalent inherited cause of intellectual disabilities and autism spectrum disorders. FXS result from the loss of expression of the FMRP protein, an RNA binding protein that regulate the expression of key synaptic effectors. FXS is also characterized by a wide array of behavioral, cognitive and metabolic impairments. The severity and penetrance of those comorbidities are extremely variable, meaning that a considerable phenotypic heterogeneity is found among fragile X individuals. Unfortunately, clinicians currently have no tools at their disposal to assay patient’s prognosis upon diagnosis. Since the absence of FMRP was repeatedly associated with an aberrant translational metabolism, we decided to study the nascent proteome in order to screen for potential proteomic biomarkers of FXS.Method: We used a BONCAT (Bioothogonal Non-canonical Amino Acids Tagging) method coupled to label-free mass spectrometry to purify and quantify nascent proteins of peripheral blood mononuclear cells from 7 fragile X male patients that do not express FMRP and 7 age-matched controls. Candidate biomarkers were confirmed by Western blot. Results: The proteomic analysis identified several proteins which were either up or downregulated in absence of FMRP in FXS individuals as compared to controls. Eleven of those proteins were considered as potential biomarkers, from which 5 were further validated by Western blot. The gene ontology enrichment analysis highlighted molecular pathway that may contribute to FXS physiopathology. Conclusions: Our results showed that the nascent proteome is well suited for the discovery of FXS biomarkers. In fact, taking advantage of a key alteration in FXS physiopathology led us to successfully identified 11 potential biomarkers.