Effects Of Lanthanum Chloride Exposure During Pregnancy And Lactation On The Expression Of Ribosomal Protein S6 And Its Upstream Signaling Pathways In The Hippocampus And Cerebral Cortex Of Offspring Rats

Objective:Rare earth elements?REEs?have been widely used in China in recent years.REEs accumulate in human body through food chain and cause damage to human body.The impact of REEs on human health has become a public health concern.Many studies have shown that REEs can cause damage to the nervous system.Lanthanum?La?is often used as a representative substance to study the neurotoxicity of REEs.In this study,the effects of different doses of lanthanum chloride?LaCl₃?on learning ability and memory level of rats and the damage of LaCl₃ on neurosynapses in hippocampus and cerebral cortex of rats were investigated by means of holistic animal experiments,including neurobehavioral,molecular biology and pathology techniques.To explore whether LaCl₃exposure during pregnancy and lactation affects the ribosomal protein S6 in the hippocampus and cerebral cortex of offspring rats by changing theexpression of Ras-Raf-1-MEK-ERK-RSK pathway and PI3K-Akt-mTOR-S6K1 pathway,then it can affect the damage of synapses and produce neurotoxic effects.This study provides basic information and scientific reference for further elucidating the effect of La on learning and memory,and for further studying the neurotoxic mechanism of La and REEs.Methods:Thirty-two healthy adult male and female Wistar rats weighing 250?+10 g?were provided by the Laboratory Animal Center of China Medical University.The temperature of the laboratory animal room was kept at 17-23 C and the corresponding humidity was kept at 45-55%.Animal feed was purchased from Shenyang Maohua Biotechnology Company.One week after adaptive feeding,they were randomly divided into control group and low,medium and high dose of LaCl₃ groups.The males and females mated in cages at a ratio of 1:1.The next morning,those who found a vaginal embolus or vaginal secretions with sperm examined by microscopy were identified as pregnant,and the day was recorded as the 0th day of pregnancy.From conception,the control group drank distilled water,and the low,medium and high dose of LaCl₃ groups drank distilled water containing 0.125%,0.25%and 0.5%LaCl₃,respectively,and fed their offspring rats until the offspring rats were weaned.Morris water maze was used to test the spatial discrimination learning and memory ability of offspring rats.HE staining and transmission electron microscopy were used to study the morphological structure and synaptic ultrastructure of neurons in hippocampus and cerebral cortex of offspring rats.The expressions of Ras,Raf-1,MEK,ERK,RSK,PI3K,Akt,mTOR,S6K1 and ribosomal protein S6 in the hippocampus and cerebral cortex of offspring rats were determined by western blot and immunofluorescence.Results:The effect of LaCl₃ on learning and memory ability of offspring rats.Compared with the control group,the learning and memory abilities of the offspring rats in each of LaCl₃ dose group decreased significantly,and the decrease became more and more obvious with the increase of dose of LaCl₃.In morris water maze test,the escape latency of LaCl₃dose groups of offspring rats was significantly longer than that of control group,and the escape latency was gradually prolonged with the increase of the dose of LaCl₃.In the space exploration experiment,the number of passages through the target quadrant in LaCl₃ dose groups was significantly less than that in the control group,and the number of passages decreased with the increase of the dose of LaCl₃.The cumulative residence time in the target quadrant of the LaCl₃ dose groups was significantly less than that of the control group,and gradually decreased with the increase of the dose of LaCl₃.2.The effects of LaCl₃ on the morphological structure and synaptic ultrastructure of neurons in hippocampus and cerebral cortex of offspring rats.Compared with the control group,the neuron arranged loosely in hippocampus and cerebral cortex of the offspring,and the cell gap became larger with the increase of the dose of LaCl₃.Compared with the control group,the synaptic ultrastructure of cerebral cortex and hippocampus showed abnormal changes,such as shorter synaptic activity band and thinner postsynaptic densities,especially in the high dose group.3.The effect of LaCl₃ on the expression of ribosomal protein S6 in hippocampus and cerebral cortex of the offspring rats.Compared with the control group,the expression level of p-S6 protein in cerebral cortex and hippocampus of the offspring rats in LaCl₃ dose groups decreased significantly,and decreased gradually with the increase of the dose of LaCl₃.There were significant differences in the expression of p-S6 protein among the groups.The expression level of S6 protein in hippocampus and cerebral cortex of the offspring rats in LaCl₃ dose groups was not significantly different from that in control group.4.The effect of LaCl₃ on Ras-Raf-1-MEK-ERK-RSK pathway and PI3K-Akt-mTOR-S6K1 pathway in hippocampus and cerebral cortex of the offspring rats.The levels of Ras,Raf-1,p-MEK,p-ERK,p-RSK,PI3K,p-Akt,mTOR and S6K1 protein in hippocampus and cerebral cortex of the offspring rats in LaCl₃ dose groups were lower than those in the control group,and decreased with the increase of the dose of LaCl₃.The levels of MEK,ERK,RSK and Akt protein in hippocampus and cerebral cortex of the offspring rats in LaCl₃ dose groups had no significant changes compared with the control group.Conclusion:1.LaCl₃ exposure during pregnancy and lactation can decrease the learning and memory ability of offspring rats.2.LaCl₃ exposure during pregnancy and lactation impairs the morphology of neurons in the hippocampus and cerebral cortex of offspring and the ultrastructure of synapses.3.LaCl₃ exposure during pregnancy and lactation reduced the phosphorylation/activation of ribosomal protein S6 in hippocampus and cerebral cortex of offspring rats,affected the structure and function of neurosynapses,and consequently led to impairment of learning and memory function.4.LaCl₃ exposure during pregnancy and lactation can inhibit Ras-Raf-1-MEK-ERK-RSK pathway in hippocampus and cerebral cortex of the offspring rats.5.LaCl₃ exposure during pregnancy and lactation can inhibit PI3K-Akt-mTOR-S6K1 pathway in hippocampus and cerebral cortex of the offspring rats.6.The mechanism of impairment of learning and memory ability and synapses in hippocampus and cerebral cortex of the offspring rats induced by LaCl₃exposure during pregnancy and lactation may be related to the decrease of phosphorylation/activation of ribosomal protein S6 induced by inhibited of Ras-Raf-1-MEK-ERK-RSK and PI3K-Akt-mTOR-S6K1 pathways.