慢性氟中毒大鼠脑组织Erk激酶、AMPA受体亚基GluR1和GluR2的表达及硫酸软骨素的保护作用

摘要

Objective To study the mechanism of central nervous system (CNS) injury in chronic fluorosis and the neuroprotective effect of chondroitin sulfate (CS).Methods Forty-eight female Sprague-Dawley rats weighting 90-120 g were divided into 8 groups according to body weight by random number table,6 rats in each group:control group,drinking tap water freely;low dose and high dose fluoride groups,freely drinking tap water with fluoride content of 10 and 50 mg/L,respectively;control + normal saline (NS),low dose fluoride + NS,and high dose fluoride + NS groups,each group was fed for 180 d,and treated with intraperitoneal injection of 0.66 mg/kg NS for 5 d (once a day);low dose fluoride + CS and high dose fluoride + CS groups,each group was fed for 180 d,0.66 mg/kg CS was injected intraperitoneally for 5 d (once a day).All groups were fed standard nutritive animal feed for 185 d and dissected for brain tissue.The pathologic change was observed after hematoxylin-eosin (HE)staining;the expression levels of phosphorylated extracellular signal-regulated protein kinase 1/2 (phospho-Erk1/2)and glutamate receptors 1,2 (GluR1,GluR2) in the brain cortex were detected by immunohistochemistry;the protein levels of Erk1/2,phospho-Erk1/2,GluR1,and GluR2 in the brain cortex were detected by Western blotting.Results Brain cortex of all rats in the fluoride groups showed eosinophilic degeneration,loss and disordered arrangement of neurons,and the brain morphological changes in each fluoride + CS groups were significantly improved compared with those in the fluoride groups.Immunohistochemistry results showed that compared with the control group [(0.44 ± 0.09)％,(1.49 ± 0.05)％,(2.51 ± 0.54)％],the expression levels of phospho-Erk1/2 [(1.47 ±0.09)％,(1.03 ± 0.05)％],and GluR2 [(2.37 ± 0.06)％,(3.38 ± 0.12)％] in the low dose and high dose fluoride groups were increased,and the expression levels of GluR1 [(1.49 ± 0.02)％,(0.99 ± 0.19)％] were decreased (P ＜ 0.05).Western blotting results showed that compared with the control group (1.00 ± 0.12,1.76 ± 0.33),the protein levels of Erk1/2 (3.10 ± 0.76,1.99 ± 0.01) and phospho-Erk1/2 (3.27 ± 0.25,2.67 ± 0.05) in low dose and high dose fluoride groups were significantly increased (P ＜ 0.05);compared with low dose fluoride group,the protein levels of Erk1/2,and phospho-Erk1/2 (1.30 ± 0.31,2.20 ± 0.34) in low dose fluoride + CS group decreased significantly (P ＜0.05).Compared with control group (1.86 ± 0.47,1.17 ± 0.27),the protein levels of GluR1 (1.09 ± 0.26,0.61 ± 0.14) in low dose and high dose fluoride groups decreased significantly,while the protein level of GluR2 (1.99 ± 0.42,3.38 ±0.27) increased significantly (P ＜ 0.05);compared with low dose and high dose fluoride groups,the protein levels of GluR2 in low dose fluoride + CS and high dose fluoride + CS groups (1.53 ± 0.41,2.65 ± 0.32) decreased significantly (P ＜ 0.05).The protein level of phospho-Erk1/2 was negatively correlated with GluR1 protein level (r =-0.975,-0.991,P ＜ 0.05) in low dose and high dose fluoride groups,and it was positively correlated with the protein level of GluR2 (r =0.986,0.993,P ＜ 0.05).Conclusion The CNS injury caused by chronic fluorosis may be related to GluR1 and GluR2 activated Erk1/2 signaling pathway,and CS has certain protection to the injury.%目的 研究慢性氟中毒中枢神经系统损伤的机制,探讨硫酸软骨素的神经保护作用.方法 48只雌性SD大鼠,体重为90～120 g.按体重采用随机数字表法分为8组,每组6只,分别为对照组,自由饮用自来水;低、高剂量染氟组,自由饮用含氟量为10、50 mg/L的自来水;对照、低剂量染氟、高剂量染氟分别加生理盐水组,按要求饲养180 d后,用0.66 mg/kg生理盐水连续腹腔注射5d(每天1次);低、高剂量染氟分别加硫酸软骨素组,按要求饲养180 d后,用0.66 mg/kg硫酸软骨素连续腹腔注射5d(每天1次).上述各组均饲以标准营养动物饲料,饲养周期为185 d,饲养结束后处死大鼠取脑组织.采用HE染色观察各组大鼠脑组织病理改变;免疫组织化学法(免疫组化)检测脑皮质中磷酸化细胞外信号调节蛋白激酶1/2(phospho-Erk1/2),谷氨酸受体1、2(GluR1、GluR2)表达水平;免疫印迹法(Western Blot)检测脑皮质中Erk 1/2、phospho-Erk1/2、GluR1、GluR2蛋白水平.结果 各染氟组大鼠大脑皮质均可见神经元嗜酸性变化、丢失和层次排列不整齐,各染氟+硫酸软骨素组形态学改变均较各染氟组有明显改善.免疫组化结果显示,与对照组[(0.44±0.09)％、(1.49±0.05)％、(2.51±0.54)％]比较,低、高剂量染氟组phospho-Erk 1/2[(1.47±0.09)％、(1.03±0.05)％]、GluR2[(2.37±0.06)％、(3.38±0.12)％]表达水平升高,GluR1[(1.49±0.02)％、(0.99±0.19)％]表达水平降低(P均＜ 0.05).Western Blot结果显示,与对照组(1.00±0.12、1.76±0.33)比较,低、高剂量染氟组Erk 1/2(3.10±0.76、1.99±0.01)、phospho-Erk1/2(3.27±0.25、2.67±0.05)蛋白水平升高(P均＜0.05);与低剂量染氟组比较,低剂量染氟+硫酸软骨素组Erk1/2、phospho-Erk1/2蛋白水平(1.30±0.31、2.20±0.34)明显降低(P均＜ 0.05).与对照组(1.86±0.47、1.17±0.27)比较,低、高剂量染氟组GluR1蛋白水平(1.09±0.26、0.61±0.14)明显下降,GluR2蛋白水平(1.99±0.42、3.38±0.27)显著升高(P均＜0.05);与低、高剂量染氟组比较,低剂量染氟+硫酸软骨素、高剂量染氟+硫酸软骨素组GluR2蛋白水平(1.53±0.41、2.65±0.32)显著降低(P均＜ 0.05).低、高剂量染氟组phospho-Erk1/2蛋白水平与GluR1蛋白水平呈负相关(r=-0.975、-0.991,P均＜ 0.05),与GluR2蛋白水平呈正相关(r=0.986、0.993,P均＜0.05).结论 慢性氟中毒引起的中枢神经系统损伤可能与GluR1、GluR2激活Erk1/2信号通路有关,硫酸软骨素对这种损伤有一定的保护作用.