Mustapić, Maja

Abstract Isolation of neuron‐derived extracellular vesicles (NDEVs) with L1 Cell Adhesion Molecule (L1CAM)‐specific antibodies has been widely used to identify blood biomarkers of CNS disorders. However, full methodological validation requires demonstration of L1CAM in individual NDEVs and lower levels or absence of L1CAM in individual EVs from other cells. Here, we used multiple single‐EV techniques to establish the neuronal origin and determine the abundance of L1CAM‐positive EVs in human blood. L1CAM epitopes of the ectodomain are shown to be co‐expressed on single‐EVs with the neuronal proteins β‐III‐tubulin, GAP43, and VAMP2, the levels of which increase in parallel with the enrichment of L1CAM‐positive EVs. Levels of L1CAM‐positive EVs carrying the neuronal proteins VAMP2 and β‐III‐tubulin range from 30% to 63%, in contrast to 0.8%–3.9% of L1CAM‐negative EVs. Plasma fluid‐phase L1CAM does not bind to single‐EVs. Our findings support the use of L1CAM as a target for isolating plasma NDEVs and leveraging their cargo to identify biomarkers reflecting neuronal function.

AbstractTranscription factors that mediate neuronal defenses against diverse stresses were quantified in plasma neural‐derived exosomes of Alzheimer's disease or frontotemporal dementia patients and matched controls. Exosomal levels of low‐density lipoprotein receptor‐related protein 6, heat‐shock factor‐1, and repressor element 1‐silencing transcription factor all were significantly lower in Alzheimer's disease patients than controls (P < 0.0001). In frontotemporal dementia, the only significant difference was higher levels of repressor element 1‐silencing transcription factor than in controls. Exosomal transcription factors were diminished 2–10 years before clinical diagnosis of Alzheimer's disease. Low exosomal levels of survival proteins may explain decreased neuronal resistance to Alzheimer's disease neurotoxic proteins.