L1CAM‐associated extracellular vesicles: A systematic review of nomenclature, sources, separation, and characterization

When released into biological fluids like blood or saliva, brain extracellular vesicles (EVs) might provide a window into otherwise inaccessible tissue, contributing useful biomarkers of neurodegenerative and other central nervous system (CNS) diseases. To enrich for brain EVs in the periphery, however, cell-specific EV surface markers are needed. The protein that has been used most frequently to obtain EVs of putative neuronal origin is the transmembrane L1 cell adhesion molecule (L1CAM/CD171). In this systematic review, we examine the existing literature on L1CAM and EVs, including investigations of both neurodegenerative disease and cancer through the lens of the minimal information for studies of EVs (MISEV), specifically in the domains of nomenclature usage, EV sources, and EV separation and characterization. Although numerous studies have reported L1CAM-associated biomarker signatures that correlate with disease, interpretation of these results is complicated since L1CAM expression is not restricted to neurons and is also upregulated during cancer progression. A recent study has suggested that L1CAM epitopes are present in biofluids mostly or entirely as cleaved, soluble protein. Our findings on practices and trends in L1CAM-mediated EV separation, enrichment, and characterization yield insights that may assist with interpreting results, evaluating rigor, and suggesting avenues for further exploration.