Immuno-digital invasive cleavage assay for analyzing Alzheimer's amyloid ß-bound extracellular vesicles

Background The protracted preclinical stage of Alzheimer's disease (AD) provides the opportunity for early intervention to prevent the disease; however, the lack of minimally invasive and easily detectable biomarkers and their measurement technologies remain unresolved. Extracellular vesicles (EVs) are nanosized membrane vesicles released from a variety of cells and play important roles in cell-cell communication. Neuron-derived and ganglioside-enriched EVs capture amyloid-ß protein, a major AD agent, and transport it into glial cells for degradation; this suggests that EVs influence Aß accumulation in the brain. EV heterogeneity, however, requires the use of a highly sensitive technique for measuring specific EVs in biofluid. In this study, immuno-digital invasive cleavage assay (idICA) was developed for quantitating target-intact EVs. Methods EVs were captured onto ganglioside GM1-specific cholera toxin B subunit (CTB)-conjugated magnetic beads and detected with a DNA oligonucleotide-labeled Aß antibody. Fluorescence signals for individual EVs were then counted using an invasive cleavage assay (ICA). This idICA examines the Aß-bound and GM1-containing EVs isolated from the culture supernatant of human APP-overexpressing N2a (APP-N2a) cells and APP transgenic mice sera. Results The idICA quantitatively detected Aß-bound and GM1-containing EVs isolated from culture supernatants of APP-N2a cells and sera of AD model mice. The idICA levels of Aß-associated EVs in blood gradually increased from 3- to 12-month-old mice, corresponding to the progression of Aß accumulations in the brain of AD model mice. Conclusions The present findings suggest that peripheral EVs harboring Aß and GM1 reflect Aß burden in mice. The idICA is a valuable tool for easy quantitative detection of EVs as an accessible biomarker for preclinical AD diagnosis

Additional file 4 of Immuno-digital invasive cleavage assay for analyzing Alzheimer’s amyloid ß-bound extracellular vesicles

Additional file 4: Supplemental Fig. 4. (A) Size distribution of APP Tg serum-derived EVs analyzed by a nanoparticle analyzer, qNano. (B) Representative image of APP Tg serum-derived EVs by electron microscopy. (C) Western blot analysis of Aß, ganglioside GM1, CD9, and ßIII tubulin in APP Tg serum-derived EVs. (D) Representative images of hippocampal sections immunostained with Aβ. Scale bars, 200 μm. (E) The levels of Aβ1-40 and Aβ1-42 in whole sera and serum-derived EVs of 12-month-old APP Tg mice were measured by conventional ELISA (n = 4 each). n.d., not detected