褪黑素减轻内质网应激改善发育早期铅暴露小鼠海马组织的tau蛋白过度磷酸化

Melatonin Ameliorates Tau Hyperphosphorylation of Mice with Exposure to Lead(Pb) at Early Development Stage by Mediating ER Stress in Hippocampus

目的探讨褪黑素(Melatonin,MT)对发育早期铅暴露小鼠海马组织tau蛋白磷酸化的影响及可能的作用机制。方法健康C57BL/6小鼠随机分为4组:正常对照组(Con组,全程正常饮用水喂养)、发育早期铅暴露组(Pb组,出生至出生后第21天母鼠给予0.2%醋酸铅水)、单独MT干预组(MT组,正常非暴露对照鼠在12月龄后给予含50mg/mL MT饮用水干预3个月)及MT干预联合铅暴露组(MT+Pb组,出生至出生后第21天母鼠给予0.2%醋酸铅水,并于12月龄后给予含50mg/mL MT饮用水干预3个月)。采用石墨炉原子吸收光谱仪测定各组小鼠的血铅和海马铅含量,Morris水迷宫检测空间学习记忆功能,Western blot检测海马tau蛋白的磷酸化程度、内质网应激标志分子GRP78和CHOP的蛋白表达水平。结果与Con组相比,Pb组小鼠血铅和海马铅含量均明显升高(均P<0.05),给予MT干预并未影响血铅和海马铅含量;且Pb组小鼠海马tau蛋白磷酸化水平增强(P<0.01),而给予MT干预后,相比Pb组,MT+Pb组小鼠海马tau蛋白磷酸化水平明显降低(P<0.05);与Con组相比,Pb组小鼠海马内质网应激标志分子GRP78和CHOP蛋白表达水平均明显升高(均P<0.05),而MT干预后,相比Pb组,MT+Pb组GRP78和CHOP蛋白表达水平显著下降(均P<0.05)。结论 MT可改善发育早期铅暴露小鼠海马tau蛋白的过度磷酸化,并改善其学习记忆功能,其具体机制可能与调控内质网应激有关。

Objective To investigate the effect of melatonin（MT）on tau hyperphosphorylation in hippocampus of mice with exposure to lead（Pb）at early development stage and its possible mechanism.Methods Healthy C57BL/6mice were randomly divided into four groups：control group（received normal water）,lead exposure group（exposed to 0.2% Pb acetate from postnatal day 1（PND 1）to PND 21 through drinking water）,MT group（received 50 mg/mL MT through drinking water since 12-month-old for 3months）and MT combined with lead exposure group（exposed to 0.2% Pb acetate from PND 1to PND 21 and then given 50mg/mL MT since 12-month-old for 3months through drinking water）.The Pb levels in the blood and hippocampus were determined by graphite furnace atomic absorption spectrometry.Morris water maze was used to detect the spatial learning and memory.The phosphorylation level of tau and the protein level of GRP78 and CHOP in hippocampus were detected by Western blotting.Results Compared with the control group,the Pb levels in the blood and hippocampus were significantly increased in lead exposure group（P0.05）,while MT treatment did not affect the Pb levels both in the blood and hippocampus.In the lead exposure group,the phosphorylation level of tau in the hippocampus was significantly increased compared with control group（P0.01）,and after treatment with MT,the phosphorylation level of tau in MT combined with lead exposure group was significantly decreased compared with the lead exposure group（P0.05）.Furthermore,the expression of GRP78 and CHOP in the hippocampus was significantly higher in lead exposure group than in control group（P0.05）,and after treatment with MT,the expression levels of GRP78 and CHOP were lower than those of the control group.Conclusion MT can ameliorate the phosphorylation level of tau in the hippocampus and defects of learning and memory in C57BL/6mice with exposure to lead at early development stage,and this may be related with the modulation of endoplasmic reticulum stress.