Human cerebrospinal fluid contains exosomes that represent a novel reservoir for
therapeutic biomarker discovery
J.M. Street1, R.T.A. Chalmers2, T.S. Walsh2, D.J. Webb1, J.W. Dear1. 1University of
Edinburgh, Edinburgh, United Kingdom, 2Royal Infirmary of Edinburgh, Edinburgh, United
Kingdom.
One of the pathological hallmarks of neurodegenerative diseases, such as spongiform
encephalopathies (TSEs) and Alzheimer's dementia (AD), is the accumulation of abnormal
proteins within brain tissue (prions in TSEs and b-amyloid in AD). Studies in cell culture have
demonstrated these proteins are released from cells within lipid vesicles termed exosomes. In
vitro, the exosomal protein content changes with drug therapy, which suggests that exosomes
could represent a reservoir for therapeutic biomarker discovery. Our aim was to determine if
exosomes are present in human cerebrospinal fluid (CSF). CSF was collected from patients
undergoing thoraco-abdominal aortic aneurysm repair (with full ethical approval). This group
was chosen as they have a CSF drain inserted peri-operatively as part of routine clinical
management. The CSF was ultracentrifuged (as per established protocols for urinary
exosome isolation) and the presence of exosomes was tested by western blotting for specific
markers, sucrose gradient centrifugation, immunoelectron microscopy and the proteome was
explored by tandem mass spectrometry. The exosomal markers TSG101 and Flotillin-1 were
found to be enriched in the ultracentrifugation pellet over the unfractionated CSF. Using
sucrose gradient centrifugation, the density of the 'microvesicles' was established as 1.14 -
1.20 g.cm-3, consistent with the density previously reported for exosomes. Staining for
Flotillin-1 during electron microscopy revealed the presence of Flotillin-1 on structures
consistent in size and shape with previous reports for exosomes. Alpha-2-macroglobulin,
which is involved in the clearance of A-beta, and filamin-A, which is linked to periventricular
heterotopia, were identified in the exosomes by tandem mass spectrometry. Based on this
evidence, we conclude that human CSF contains exosomes. The existence of exosomes
provides a source for new diagnostic and therapeutic biomarkers and proteomic discovery
studies are ongoing.
