诱导型一氧化氮合酶在脂多糖诱导多巴胺能神经元变性时的变化研究

目的探讨诱导型一氧化氮合酶(iNOS)表达上调是否参与脂多糖(LPS)诱导的多巴胺(DA)能神经元变性。方法脑立体定位注射5μgLPS至大鼠脑黑质,观察不同时间点(6、12h,1、3、7d),iNOSmRNA及蛋白表达的动态变化;化学比色法检测黑质NO释放量以及iNOS活性改变。结果iNOSmRNA和蛋白的动态变化为6h开始出现增高,1d达高峰,3d开始下降,7d后基本消失。1d时iNOS阳性细胞数(45.30±4.63)显著高于PBS对照侧iNOS阳性细胞数(0.11±0.04)(P<0.01)、RT-PCR、Western印迹法显示1d组iNOSmRNA和iNOS蛋白表达明显多于正常对照组和PBS对照侧;同时发现iNOSmRNA和蛋白过度表达,并促进NO释放,iNOS活性升高。结论iNOS上调可能是LPS诱导DA能神经元变性机制中重要的因素之一。

Changes of inducible nitric oxide synthase in lipopolysaccharide-mediated degeneration of dopaminergic neurons

OBJECTIVE: To explore whether the upregulation of inducible nitric oxide synthase (iNOS) is involved in lipopolysaccharide (LPS)-induced neurodegeneration. METHODS: 108 SD rats were randomly divided into 2 groups: experimental group and normal control group, and each group was sub-divided into 5 subgroups of 18 rats to undergo examination at different time points (6 h, 12 h, 1 d, 3 d, and 7 d). LPS was stereotaxically infused into the substantia nigra (SN) of left side of the experimental rats and PBS was used instead for the control rats. At different time points different numbers of rats from each subgroup were killed to take out the SN. Biochemical method was used to test the activity of NO and iNOS in 6 rats from each subgroup, iNOS mRNA expression was tested by RT-PCR in 3 rats from each subgroup, and iNOS protein expression was tested by Western blotting in 4 rats from each subgroup. Immunohistochemistry was used to detect the iNOS positive cells. RESULTS: iNOS positive cells were found since 6h after the intranigral injection of LPS, peaked 1d after, began to decrease 3d after, and basically disappeared 7d after; and were not found in the control group and the SN at the opposite side of the experimental rats. The percentage of iNOS-positive neurons 1d after the injection was 45.30 +/- 4.63, significantly higher than that of the control group (0.11 +/- 0.04, P < 0.01). RT-PCR and Western blotting showed that expression of iNOS mRNA and expression of iNOS protein at all time points were all higher than those of the normal controls and PBS controls (all P < 0.01). iNOS activity and NO amount in the LPS-injected SN began to increase 6 h after the injection, significantly higher then that of the control group (P < 0.05), peaked 1d after, (P < 0.01), began to decrease 3d after, and basically returned to normal level. CONCLUSION: Up-regulation of iNOS may be one of the crucial mechanisms in LPS-induced degeneration of DA neurons.