CREB Signaling Mediates Dose-Dependent Radiation Response in the Murine Hippocampus Two Years after Total Body Exposure

The impact of low-dose ionizing radiation (IR) on the human brain has recently attracted attention due to the increased use of IR for diagnostic purposes. The aim of this study was to investigate low-dose radiation response in the hippocampus. Female B6C3F1 mice were exposed to total body irradiation with 0 (control), 0.063, 0.125, or 0.5 Gy. Quantitative label-free proteomic analysis of the hippocampus was performed after 24 months. CREB signaling and CREB-associated pathways were affected at all doses. The lower doses (0.063 and 0.125 Gy) induced the CREB pathway, whereas the exposure to 0.5 Gy deactivated CREB. Similarly, the lowest dose (0.063 Gy) was anti-inflammatory, reducing the number of activated microglia. In contrast, induction of activated microglia and reactive astroglia was found at 0.5 Gy, suggesting increased inflammation and astrogliosis, respectively. The apoptotic markers BAX and cleaved CASP-3 and oxidative stress markers were increased only at the highest dose. Since the activated CREB pathway plays a central role in learning and memory, these data suggest neuroprotection at the lowest dose (0.063 Gy) but neurodegeneration at 0.5 Gy. The response to 0.5 Gy resembles alterations found in healthy aging and thus may represent radiation-induced accelerated aging of the brain.