ACUTE, TRANSIENT INCREASE IN SECRETION OF NEURODEGENERATION BIOMARKERS AFTER IRRADIATION OF HUMAN CORTICAL NEURONS

Abstract

Radiotherapy is a commonly used therapy for brain tumor control or prevention, but many patients display persistent and deteriorating cognitive function following treatment. Children receiving cranial radiation therapy are especially affected and currently little is known about the underlying mechanisms. The chronic symptoms often become apparent after approximately one year, but could nonetheless be a result of acute cell damage upon irradiation. More understanding of the mechanisms behind radiation-induced acute neuronal damage is needed in order to predict and prevent severe side effects after radiotherapy. We have previously reported a prolonged but transient increase in cerebrospinal fluid levels of the neuronal proteins tau and neurofilament light (NFL) from patients undergoing prophylactic cranial radiotherapy, suggesting a potential for these proteins as biomarkers also for the brain damage observed after irradiation. Here, we use a human cortical cell model to investigate the neuronal release of these proteins in response to ionizing radiation in more detail. Human iPSC-derived cortical neurons were irradiated with a single dose of 0.5-, 1.5- or 4.5-Gy ionizing radiation, respectively, at two time points during differentiation and followed during a four-week period post-irradiation. Cells and media were collected at different time points after irradiation and compared to non-irradiated control. Secreted tau and NFL were measured in the media using electrochemiluminescence assays. Gene expression was monitored with qPCR. Both tau and NFL secretion to the cell media increased dose-dependently during the first four days following irradiation. The secretion peaked after four days and returned to basal or slightly elevated levels within one-two weeks. Despite this, signs of astrocyte activation and altered cell division patterns were still observed one month after irradiation. Effects were more accentuated in cells irradiated at an earlier differentiation stage. Ionizing irradiation of cortical neuronal cultures induced a transient increase in tau and NFL secretion. The observed effects were more accentuated in less differentiated neurons, suggesting that developing neurons are especially sensitive to radiation-induced injury. These results correlate well with the clinical situation, showing the potential for the cell model in further investigation of neuronal responses to radiation-induced cell damage.