| Our previous study demonstrated that reactive astrogliosis is involved in the D-galactose-induced brain ageing. However, whether activation of astrocytes precedes or follows neuron cell death remains to be determined. Therefore, we investigated neuronal damage and astrocyte activation in the hippocampus at the early stage of this model. We also evaluated whether reactive astrocytes enhance the capabilities of glutamate uptake and water transport to prevent glutamate excitotoxicity induced by D-galactose injection. To prepare ageing model by D-galactose, the mice were randomly divided into 2 groups: D-galactose group and control group, receiving daily intraperitoneal injection of 200mg/kg 2% D-galactose or saline respectively for 2 weeks. After 2 weeks of administration, we detected biochemical levels of oxidative stress in the hippocampus by biochemical spectrophotometer. We observed neuronal apoptosis by Hoechst staining and caspase-3 immunohistochemistry. We also observed changes neuronal processes and axonal terminals in the hippocampus of two groups by using immunohistochemistryβ-tubulin III and synaptophysin. Moreover, we analysized glutamate and c-fos expression by immunofluorescence, and observed glial fibrillary acidic protein (GFAP) and its membrane glutamate transporter-1 (GLT1), glutamate-aspartate transporter (GLAST), and aquaporin-4 (AQP4) expression by immunohistochemistry. Biochemical analyses showed that mice injected with D-galactose for 2 week had no obvious changes in brain oxidative and antioxidative parameters compared with vehicle controls. Pathological results also indicated no obvious impairments in neuronal soma, process and synapse in the hippocampus of model mice. In contrast, GFAP immunohistochemistry revealed a prominent increase in the percentage of reactive hippocampal astrocytes in D-galactose-treated mice. Moreover, the increased immunostaining levels of GLT1 and AQP4, but not GLAST were observed in the model hippocampus, which were consistent with activation of hippocampal glutamatergic neurons as revealed by glutamate and c-Fos protein double immunostaining. These results suggest that astrocyte reactivity is a primary event during the ageing process. Moreover, these findings indicate that, via up-regulations of glutamate and water transport proteins, reactivated astrocytes maintain glutamate homeostasis at the early stage of brain ageing. Thus, regulating the plasticity of astrocytes may be a new target to delay brain ageing. |
