Exosomal proteome changes induced by human tau expression are modulated by the presence of the microtubule-binding domain and alternatively spliced exons 2-3 in SH-SY5Y neuroblastoma cell

Alzheimer's disease (AD) is a widespread dementing illness with a complex and poorly understood etiology and pathogenesis. One way to improve our understanding of the disease process is to model disease-associated changes in tau, a protein known to mediate events essential to the onset and progression of AD. In order to evaluate the respective roles of the microtubule binding region (MTBR) and alternatively spliced exons in the N-terminal projection domains in AD, we have constructed SHSY-5Y cell lines that stably overexpress four different species of tau protein (4R2N, 4RON, N(E-2), N(E+2)). Since the toxicity and spreading of tau lesions in AD depends on the interactions of tau with other proteins, we have performed a bioinformatic analysis of exosome-fraction interactomes for cell lysates and media samples isolated from each of these lines. Functional analysis of tau interactomes based on gene ontology (GO) terms was performed using the String 10.5 database program. The highest number of exosomes proteomes and tau associated proteins were found with 4R2N isoform (2771 and 159) in cell lysate and high strength of connectivity (78%) between proteins, while N(E-2) isoform in the media proteomes has the highest number of proteins and tau associated protein (1829 and 205). Moreover, known AD markers were significantly enriched in secreted interactomes relative to lysate interactomes in the SHSY-5Y cells of tau isoforms lacking the N terminal exons 2-3. Enriched functions in the secreted E2- interactome includes signaling and developmental pathways that have been linked to a) tau misprocessing and lesion development and b) tau secretion and which therefore could play novel roles in AD pathogenesis.