Novel exosome biomarker candidates for Alzheimer´s disease unraveled through Mass Spectrometry analysis

Background Exosomes are small extracellular vesicles (EVs) present in human biofluids that can carry disease-specific molecules. Blood-derived exosomes emerged as interesting peripheral sources of biomarkers for a wide range of diseases, and their potential is also being addressed in Alzheimer’s disease (AD) context. There is no effective cure or blood-based molecular diagnostic tools for a first clinical AD screening, which motivates research in this area to identify putative valuable blood-derived disease biomarkers. The ultimate goal is to produce a cost-effective and widely available alternative to the current molecular AD diagnosis that monitors a biomarker triplet in the CSF. Methods In the study here presented, EVs with exosome-like characteristics were isolated from the serum of Controls and AD cases through two distinct methods, precipitation- and column-based methods, followed by mass spectrometry analysis. The resulting proteomes from Controls and AD cases were characterized by Gene Ontology (GO) functional enrichment and multivariate analysis. Putative candidate targets identified were validated in distinct cohorts using antibody-based approaches. Results Both methodologies isolated particles with the expected morphology and size range. Although GO terms were similar for Controls and AD cases exosomes in both methodologies, the multivariate analysis revealed a clear segregation between Controls and AD cases obtained by the precipitation method. Nine significantly different abundant proteins were identified between Controls and AD cases and exosome levels of AACT and C4BPα, two Aβ-binding proteins, were validated in individuals from independent cohorts. Conclusions Serum-derived exosome proteomes were unraveled for the first time in the context of AD through two distinct isolation methodologies, holding disease discriminatory potential. The work carried out gives an important contribution to the identification of novel exosomal biomarker candidates potentially useful as blood-based tools for AD diagnosis.