ICAM-5: A Novel Marker for Neuronally Derived Extracellular Vesicles

Current methods for isolating neuronal-derived extracellular vesicles (NDEVs) from human biofluids lack specificity. In addition, some of the reported markers for NDEV isolation are present as soluble proteins instead of extracellular vesicle (EV) associated proteins. To address the research gap, this study aimed to identify a novel marker for NDEV isolation that is NDEV associate and highly specific to the central nervous system. To achieve this, human cortical neurons were used for isolation of EVs invitro. Mass spectroscopy was performed to screen for potential EV surface markers. This analysis yielded 63 brain specific proteins among which ICAM-5 was selected for further validations in human serum and cerebrospinal fluid (CSF) samples. Our analysis shows that ICAM-5 is present on the surface of NDEVs, colocalizing with standard extracellular vesicle markers like CD-63 and CD-9. We further confirm that NDEVs isolated using ICAM-5 contain neuronal proteins (tau, neuronal specific enolase) but not glial markers. Using ICAM-5 as a NDEV marker, EVs were eluted from human serum samples of with traumatic brain injury. Our results show enhanced levels of ubiquitin C-terminal hydrolase L1 (UCH-L1), a marker of neurological injury, in serum samples from patients with TBI when compared to currently known markers of NDEV. Our findings demonstrate that ICAM-5 is specific EV associated marker for isolating NDEVs from human biofluids that can potentially improve the enrichment of NDEVs from biofluids thereby improving diagnosis and monitoring of neurological conditions.