Study On The Effect Of Magnesium-l-threonate To Rescue The Lead-induced Learning And Memory Deficits In Rats

Heavy metal pollution of food is a worldwide security problem,and lead(Pb)pollution is the most serious one.Food-derived Pb is an important source Pb poisoning in human body.Pb exposure cause serious damage to the reproductive system,central nervous system and growth and development,the influence of lead on children’s health is hot spot in research of toxicology.Pb exposure has been implicated in the impairment of learning and memory.Elevation of brain magnesium by magnesium-L-threonate(MgT)enhances spatial memory and synaptic plasticity.The effect of elevation of brain magnesium on the impairment of memory by Pb have not been studied.Enhancer of zeste homolog 2(Ezh2)is the catalytic subunit of polycomb repressive complex 2(PRC2),which modify chromatin and participate in the development of mammalian brain.Ezh2 are differentially expressed during hippocampal development.Subunits of N-methyl-D-aspartate receptor(NMDAR)complexes NR1,NR2A and NR2B have different expression level at the differently developmental time and in different hippocampal region.Both of the Ezh2 and NMDAR subunits expression are regulated by lead.But the mechanism how Pb modulates their expression is still elusive and how MgT affects on them has not been studied.Objective:1.To explore the effect and the possible mechanism of chronic dietary intake of MgT on impaired spatial memory induced by developmental Pb exposure in rats.2.To explore the mechanism of Pb exposure on expression of NMDAR1 and the effect of MgT on them.Methods:1.We performed the Morris water maze(MWM experiments to explore the effect of chronic dietary intake of MgT on impaired spatial memory induced by developmental Pb exposure in rats.2.The Golgi-Cox staining method was used to morphometric analysis of dendritic spine density.3.Western Blot was used to examine protein expression of synaptic relative proteins in adult rats,and to examine such proteins as Ezh2,H3K27me3 and H3 expression in PC 12,developmental rats and adult rats.QPCR and RT-PCR were used to examine NR1 mRNA level in PC 12,developmental rats and adult rats.Results:1.In MWM test,Pb exposure significantly impaired spatial memory,While with the supplement of MgT,the rat impaired spatial memory were rescued.2.Dendrite spine density was raised by MgT in Pb-exposed rats.3.MgT elevated such synaptic relative protein expression as NR2B and PSD-95(postsynaptic density protein 95)in control rats and elevated GluRl and NR2A protein expression level in control rats and Pb-exposed rats significantly.MgT increased the NR2A mRNA significantly in control rats and Pb-exposed rats but have no significantly effect on the GluRl mRNA level.4.The density of dendritic spine of primary hippocampal neurons induced by lead was repaired by Mg2+,and the mRNA expression of NR2A,NR2B,GluRl,GluR2 and PSD-95 were also increased。5.Pb exposure significantly decreased the protein level of Ezh2 and the ratio of H3K27me3 proteins vs H3 proteins in PC12 and developmental rats,significantly increased NR1 mRNA level relative to control.6.Pb exposure significantly increased the protein level of Ezh2 and the ratio of H3K27me3 proteins vs H3 proteins in adult rats,significantly decreased NR1 mRNA level relative to control.7.MgT increased the ratio of H3K27me3 proteins vs H3 proteins and NR1 mRNA level in control and Pb-exposed rats.Conclusion:1.Pb exposure impaired the spatial memory ability,which is related to the declined spine density and NR2A and GluRl expression level.MgT rescued impaired spatial memory ability in Pb-exposed rats,this effect is relative to increasing dendrite spine density and the expression of NR2A and GluR1.2.The increased density of dendritic spines in hippocampal neurons and the outgrowth of PC 12 cells which were damaged by lead induced by MgT,are related to the increased expression of the synaptic proteins NR2A,NR2B,GluRl,GluR2 and psd-95 by MgT or Mg2+.3.Pb modulated the NR1 subunit mRNA expression possibly by regulating Ezh2-mediated H3K27 trimethylation,but did not regulate NR2A and NR2B subunits expression by Ezh2-mediated H3K27 trimethylation.MgT rescued impaired NR1 subunit mRNA expression in Pb-exposed rats,but this was not regulated by H3K27 trimethylation.