LPS诱导小鼠脑星形胶质细胞激活及Bcl-2表达的变化

Astrocyte activation and Bcl-2 protein expression induced by lipopolysaccharide in mouse brain

目的:探讨神经元和星形胶质细胞对外源性内毒素脂多糖(lipopolysaccharide,LPS)刺激的反应,以及在对抗炎症反应时二者的相互关系。方法:成年C57BL/6J小鼠分成实验对照组和实验组,采用免疫组织化学和GFAP和Bcl-2免疫荧光双重标记技术,观察小鼠单次注射LPS入侧脑室后,GFAP和Bcl-2在脑内的分布、表达及时程变化,以及GFAP阳性星形胶质细胞与Bcl-2阳性神经元之间的关系。结果:PBS注射的对照组动物脑内GFAP阳性的星形胶质细胞主要分布于海马、梨状皮质、内嗅皮质、隔区、纹状体、杏仁核及主要的纤维束。LPS注射2d后,GFAP阳性的星形胶质细胞明显被激活,尤其在脑室周围的脑实质,表现为细胞胞体相对增大,突起变粗。Bcl-2阳性神经元在注射后1d出现表达,2d明显增加,4d为表达高峰。Bcl-2阳性神经元分布在第一、二运动皮质和躯体感觉皮质、隔、斜角带核、海马和中脑红核等。LPS注射4d后,GFAP和Bcl-2免疫荧光双重标记染色切片显示:在脑内没有发现GFAP和Bcl-2双标细胞,但可见GFAP阳性星形胶质细胞和Bcl-2阳性神经元重叠。星形胶质细胞的突起可见于Bcl-2免疫荧光阳性神经元的鞘中。结论:LPS能诱导脑室周围的脑实质星形胶质细胞和神经元的激活,激活的星形胶质细胞和神经元可能参与脑内的免疫调节和保护性反应。星形胶质细胞的突起可见于Bcl-2免疫荧光阳性神经元的鞘中,表明两者之间关系密切。

Objective To investigate the changes of anti-apoptotic protein Bcl-2 expression in neurons and activation of brain astroglial cells, and the relationship between astrocytes and neurons in mice after a single intracerebroventricular （ICV） stereotaxic injection of lipopolysaccharide （LPS）. Methods C57BL/6J mice of different ages were divided into a control group and an experiment group. Immunohistochemistry to Bcl-2 and that to GFAP were conducted to observe the expression of Bcl-2 protein in neurons and GFAP in astrocytes in the brain at different time-points after the LPS injection. The glial cell type expressing Bcl-2 was characterized with immunofluorescence double labeling. Results GFAP-immunoreactive cells in the control mice were observed mainly within hippocampal formation, piriform, entorhinal cortex, septum, striatum, amygdaloid nucleus, subcortical white matter, as well as in the main fiber tracts. At 24 h after the LPS treatment there was no obvious difference in GFAP immunoreactivity compared with the controls. Astrocytes were markedly activated in periventricular brain regions such as hippocampus, the hypothalamic parenchyma surrounding the third ventricle, with larger cell body and hypertrophic processes 2 days after the endotoxin treatment. After the LPS injection, Bcl-2 positive cells were distributed widely in the brain, sush as in the cortex （ primary and secondary motor cortex, somatosensory cortex ） , hypothalamic parenchyma surrounding the third ventricle, diagonal band, hippocampus, septum and the red nucleus of the midbrain. At these sites, Bcl-2 induction increased significantly 2 days after the ICV LPS injection, with some subregional differences, peaking on 4th day. No immunofluorescent double labeling cells for GFAP and Bcl-2 were observed in the brain of the mice after the LPS administration, but merging GFAP positive astrocytes and Bcl-2 positive neurons were seen. Double staining for Bcl-2 and GFAP also showed that the projections of activated astrocytes were found in the sheath of Bcl-2 positive neurons 4 days after the ICV LPS administration. Conclusion LPS can activate astroglial cells and upregulate of Bcl-2 expression in the neurons in the mouse brain, which may participate in the administration of central nervous system to central-immunity stimulated regulation and the protective response to the inflammatory stimulus. The projections of activated astrocytes are found in the sheath of Bcl-2 positive neurons, indicating that there is close relationship between astrocytes and neurons.