Effects of 60Co γ-rays on brain injury and polarization of microglia/macrophages in mice / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To analyze the damage in hippocampal tissues of mice after whole-body irradiation with high- or low-dose ionizing radiation and to investigate the roles of microglia/macrophages polarization in the injury.Methods:C57BL/6 mice were randomly divided into three groups sham irradiation group, low-dose group (0.05 Gy) and high-dose group (7 Gy). Low- and high-dose groups were respectively treated by whole-body irradiation with single dose of 60Co γ-rays. Hippocampal tissues of the mice were collected at 6 h, 1 d, 3 d and 7 d after irradiation. The morphology, structure and apoptosis of neurons were detected by HE staining, Nissl staining and Tunnel staining, respectively. RT-PCR and immunofluorescence assay were performed to detect the expression of M1 and M2 microglial markers at mRNA and protein levels in hippocampus tissues. The cognitive and emotional behaviors of mice were evaluated one month after the irradiation by Morris water maze, open field test, elevated plus maze and tail suspension test. Results:There were morphological and structural changes in the nerve cells in the hippocampus region of mice after irradiation, accompanied by apoptosis. Acute injuries occurred at 6 h after radiation, alleviated at 1 d and 3 d, and persisted at 7 d in a dose-dependent manner. The results of immunofluorescence staining and confocal imaging analysis showed that compared with the sham irradiation group, the high-dose group showed increased number of microglia, down-regulated expression of M1 microglial markers and up-regulated expression of M2 microglial markers in the hippocampus at 6 h and 1 d after radiation, while M2 microglial markers decreased at 3 d and 7 d after irradiation. PCR results showed that the expression of M1 and M2 microglial markers at mRNA level in the irradiation groups increased at 6 h after irradiation, but there was no statistical significance. The expression of related proinflammatory/anti-inflammatory factors was significantly up-regulated. The results of behavioral experiments showed that compared with the sham irradiation group, there was no statistical difference in cognitive or emotional behaviors at one month after irradiation.Conclusions:60Co γ-rays could damage mouse hippocampal tissues and result in the overexpression and different polarization patterns of microglia/macrophages in mice.