Melatonin Ameliorates Tau Hyperphosphorylation of Mice with Exposure to Lead(Pb)at Early Development Stage by Mediating ER Stress in Hippocampus / 华中科技大学学报(医学版)

ABSTRACT

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/6 mice were randomly divided into four groupscontrol 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 3 months)and MT combined with lead exposure group(exposed to 0.2% Pb acetate from PND 1 to PND 21 and then given 50 mg/mL MT since 12-month-old for 3 months 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(P<0.05),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(P<0.01),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(P<0.05).Furthermore,the expression of GRP78 and CHOP in the hippocampus was significantly higher in lead exposure group than in control group(P<0.05),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/6 mice with exposure to lead at early development stage,and this may be related with the modulation of endoplasmic reticulum stress.