Dissimilar accumulation of human β-amyloid and tau from enriched extracts in neuronal and endothelial cells

AbstractBACKGROUND: While Aβ and Tau cellular distribution has been largely studied, the comparative internalization and subcellular accumulation of Tau and Aβ isolated from human brain extracts in endothelial and neuronal cells has not yet been unveiled. We have previously demonstrated that controlled enrichment of Aβ from human brain extracts constitutes a valuable tool to monitor cellular internalizationin vitroandin vivo. METHODS: Herein, we establish an alternative method to strongly enrich Aβ and Tau aggregates from human AD brains, which has allowed us to study and compare the cellular internalization, distribution and toxicity of both proteins within brain barrier endothelial (bEnd.3) and neuronal (Neuro2A) cells. RESULTS: Our findings demonstrate the suitability of human enriched brain extracts to monitor the intracellular distribution of human Aβ and Tau, which, once internalized, show dissimilar sorting to different organelles within the cell and differential toxicity, exhibiting higher toxic effects on neuronal cells than on endothelial cells. While tau is strongly concentrated preferentially in mitochondria, Aβ is distributed predominantly within the endolysosomal system in endothelial cells, whereas the endoplasmic reticulum was its preferential location in neurons. Altogether, our findings display a picture of the cellular events that might occur in AD. CONCLUSIONS: Monitoring the transit of internalized human Aβ and tau comparatively uncovers, for the first time, differences regarding their accumulation within the endolysosomal system, endoplasmic reticulum, mitochondria and autophagosomes, which might explain their differential cell-dependent toxicity. Overall, this study constitutes the first approach aimed at identifying the mechanism used by Aβ, tau and potential cofactors to exert cellular toxicity. Future studies must address the consequences of the accumulation of these proteins in different organelles and their relation to cell-to-cell transmission proposed for both proteins as part of the prion-like hypothesis of AD.