Effect and mechanism of cyclooxygenase-2 on sodium arsenic-induced microglia activation in mice

Abstract

Objective To investigate the effect and mechanism of cyclooxygenase-2 (COX-2) on sodium arsenic-induced microglia activation in mice. Methods Twenty of C57BL/6J male mice were randomly divided into a control group supplied with tap water and an arsenic exposure group administered with drinking water containing 50 mg/L sodium arsenite (NaAsO 2 ) continuously for 12 weeks to establish a chronic arsenic exposure model. Morris water maze was used to test learning and memory ability of the mice. Hematoxylin-eosin (HE) staining and transmission electron microscopy were used to observe pathological changes of neuron and ultrastructure in hippocampus. Immunofluorescence microscopy was used to determine expression of ionized calcium-binding adapter molecule 1 (IBA-1) in hippocampus. The protein expressions of IBA-1, COX-2, transcription factor nuclear factor kappa-Bp65 (NF- κ Bp65) were detected with Western blot. The concentration of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF- α ) was measured with enzyme-linked immunosorbent assay (ELISA). Results Compared to the control group, the mice with arsenic exposure had significantly increased escape latency time (50.79 ± 12.30 vs. 29.01 ± 18.10 seconds) but decreased effectively traveled distance (9.34 ± 2.34 vs. 11.78 ± 1.25 centimeters) (both P < 0.05l). Pathological changes such as disarrangement of cells, edema and nuclei atrophy were observed in the hippocampus of arsenic exposed mice. The protein expression of IBA-1 was increased in arsenic exposed mice based on observation of green fluorescence aggregation with fluorescence microscope. In comparison with those in hippocampus of the control mice, significantly higher levels of IBA-1 (1.01 ± 0.12 vs. 0.75 ± 0.13), NF- κ Bp65 (1.23 ± 0.11 vs. 0.86 ± 0.14), COX-2 (1.14 ± 0.13 vs. 0.74 ± 0.12), IL-6 (93.61 ± 3.18 vs. 43.37 ± 1.11 pg/mL) and TNF- α (604.00 ± 25.02 vs. 198.46 ± 9.93 pg/mL) were detected in arsenic exposed mice ( P < 0.05 for all). Conclusion Chronic arsenic exposure-induced learning and memory impairment are associated with the activation of microglia by the activation of NF- κ B and the increase in the secretion of pro-inflammatory cytokines by upregulation of COX-2 in mice 【摘 要】 目的 探讨环氧合酶-2（COX-2）在亚砷酸钠诱导小鼠小胶质细胞活化中的作用及机制。 方法 建立慢性小鼠饮水砷暴露模型，将 20 只 C57BL/6J 雄性小鼠随机分为对照组（自来水）和砷暴露组（50 mg/L NaAsO 2 ），连续自由饮水暴露 12 周。Morris 水迷宫实验检测小鼠学习记忆能力；苏木精-伊红染色和透射电镜观察海马区神经元病理变化及超微结构改变；免疫荧光检测海马区离子钙结合配适分子-1（IBA-1）表达；蛋白印迹法（WB）检测海马区 IBA-1、COX-2、核因子 κ B p65（NF- κ B p65）蛋白表达；酶联免疫吸附法（ELISA）检测海马区白细胞介素-6（IL-6）和肿瘤坏死因子 α （TNF- α ）表达。 结果 与对照组小鼠[逃避潜伏期（29.01 ± 18.10）s、有效停留距离（11.78 ± 1.25）cm]比较，砷暴露组小鼠逃避潜伏期[（50.79 ± 12.30）s]延长，有效停留距离明显缩短[（9.34 ± 2.34）cm]（ P < 0.05）；砷暴露组小鼠海马区出现细胞排列紊乱、水肿、皱缩等病理改变，荧光显微镜下 IBA-1 绿色荧光表达增多。与对照组[IBA-1 （0.75 ± 0.13）、NF- κ B p65（0.86 ± 0.14）、COX-2（0.74 ± 0.12）表达水平及 IL-6（43.37 ± 1.11）pg/mL、TNF- α （198.46 ± 9.93）pg/mL 含量]比较，砷暴露组小鼠海马 IBA-1（1.01 ± 0.12）、NF- κ Bp65（1.23 ± 0.11）、COX-2（1.14 ± 0.13）表达水平及 IL-6 和 TNF-α 含量[分别为（93.61 ± 3.18）、（604.00 ± 25.02）pg/mL]明显升高，差异均具有统计学意义（ P < 0.05）。 结论 慢性砷暴露导致小鼠学习记忆损伤机制可能与小胶质细胞活化，激活 NF- κ B 上调 COX-2 分泌促炎性细胞因子，促进神经炎症有关。