Extracellular ezrin: a novel biomarker for traumatic brain injury

Traumatic brain injury (TBI) is a heterogeneous disease, and the discovery of diagnostic and prognostic TBI biomarkers is highly desirable in order to individualize patient care. We have previously published a study in which we identified possible TBI biomarkers by mass spectrometry 24 h after injury in a cell culture model. Ezrin-radixin-moesin (ERM) proteins were found abundantly in the medium after trauma, and in the present study we have identified extracellular ezrin as a possible biomarker for brain trauma by analyzing cell culture medium from injured primary neurons and glia and by measuring ezrin in cerebrospinal fluid (CSF) from both rats and humans. Our results show that extracellular ezrin concentration was substantially increased in cell culture medium after injury, but that the intracellular expression of the protein remained stable over time. Controlled cortical impact injured rats showed an increased amount of ezrin in CSF at both day 3 and day 7 after trauma. Moreover, ezrin was present in all ventricular CSF samples from seven humans with severe TBI. In contrast to intracellular ezrin, which is distinctly activated following TBI, extracellular ezrin is nonphosphorylated. This is the first report of extracellular ERM proteins in human and experimental models of TBI, providing a scientific foundation for further assessment of ezrin as a potential biomarker.