Effects Of Vanadium On Learning And Memory Function And Endoplasmic Reticulum PERK-eif2α Signaling Pathway In Rats

With the rapid development of vanadium industry,the environmental pollution caused by vanadium is getting worse and worse.Long-term exposure to vanadium smoke and dust can damage the nervous system of occupational population.At present,there are few experimental studies on the changes of learning and memory ability after long-term exposure to vanadium compounds in simulated occupational environment.Therefore,in this study,the limit standard（0.5 mg/m³）of workers exposed to vanadium pentoxide dust in occupational places was taken as the minimum basic exposure,and a rat model of respiratory tract exposed to vanadium based on occupational exposure concentration was established.The most in-depth research topic in neuroscience is mainly learning and memory function,and the change of synaptic plasticity is considered as the reason for the change of learning and memory.Abnormal aggregation of misfolded proteins produces neurotoxic damage,which plays a key role in the occurrence and development of learning and memory.However,there is no direct evidence that excessive vanadium will lead to the damage of learning and memory function in rats through synaptic structural changes and expression of proteins related to PERK-eIF2α signal pathway in endoplasmic reticulum.Objective: The rat model of subchronic vanadium poisoning was established by exposure of V₂O₅ through respiratory tract,and the effects of vanadium on learning and memory function and related proteins in PERK-eIF2α signal pathway were investigated.Methods: Seventy-two SPF male SD rats were randomly divided into control group（0 mg/m³）,low dose group（0.5 mg/m³）,middle dose group（1.0 mg/m³）and high dose group（2.0 mg/m³）,with 18 rats in each group.The V₂O₅ was inhaled orally by a liquidgas dynamic exposure control device for 3 consecutive months,2 hours a day,5 days a week,and weighed every other week.Morris water maze was used to detect the learning and memory ability of rats before exposure（n=18）and after 1,2 and 3 months（n=6）,and Western blot was used to detect the expression level of microtubule-associated protein tau（Tau）in hippocampus and striatum.Determination of vanadium in hippocampus,striatum and serum by graphite furnace atomic spectrophotometry;Histomorphological changes of hippocampus and striatum were observed by HE staining.Ultrastructure of hippocampus and striatum was observed by transmission electron microscope,and the expression of synaptically related p-CREB,BDNF,SYT-1 and SYP in hippocampus and striatum was detected by Western blot.The apoptotic rate was detected by TUNEL method in the hippocampus and striatum,and the expression of related proteins in the PERK-eIF2α signaling pathway in the hippocampus and striatum was detected by Western blot.Results: 1.General manifestations: All rats had good general conditions during vanadium exposure,and no rat died.At the third month after vanadium exposure,the body weight of rats in the high-dose group was lower than that in the control group（P < 0.05）.2.Vanadium content in serum,striatum,hippocampus: With the prolongation of vanadium exposure and the increase of dose,the vanadium content in hippocampus,striatum and serum increased gradually.The vanadium content in hippocampus and striatum of high dose group increased significantly in the third month.The vanadium content in high dose group was higher than that in the control,low and medium dose groups（P < 0.05）.3.Changes of learning and memory function:（1）Positioning navigation experiment: With the prolongation of vanadium exposure time and the increase of dose,the escape latency of rats increased.After exposure for 3 months,the escape latency of rats in high dose group was prolonged for 4 consecutive days,2,3,4 days in middle dose group and 4 days in low dose group（P < 0.05）.（2）Space exploration experiment: Compared with the control group,the platform crossing times of rats in the medium and high dose groups after 3 months of vanadium exposure and the high dose group after 2 months of vanadium exposure were less（P < 0.05）.With the prolongation of vanadium exposure and the increase of dose,the number of rats crossing the platform was gradually reduced.4.The effect of V₂O₅ on the expression of Tau protein in the hippocampus and striatum of rats:The Tau content in hippocampus and striatum decreased gradually with the prolongation of vanadium exposure and the increase of dose.At 3 months,Tau protein expression was significantly reduced in the high-dose group compared with the control group（P < 0.05）.5.Histological observation of hippocampus and striatum: The number of neurons in the hippocampal CA1 region and striatum of rats in each vanadium exposure group gradually decreased with the time of vanadium exposure,and the cells became smaller in size,with obvious gaps,incomplete cell outline and abnormal neuron morphology.6.Ultrastructural observation of hippocampus and striatum neurons: Changes of synaptic structure in hippocampus and striatum of rats in each vanadium exposure group With the prolongation of vanadium exposure,the synaptic structure gradually became incomplete,the synaptic cleft became blurred,and the density of postsynaptic membrane decreased.7.The effect of V₂O₅ on the expression levels of synaptic proteins in hippocampus and striatum of rats: The contents of SYT-1,SYP,BDNF,and p-CREB decreased gradually with the increase of vanadium dose after 2 and 3 months of vanadium exposure.At the third month,compared with the control group,the protein expression levels of SYT-1,SYP,BDNF,and p-CREB in the hippocampus and striatum of rats in the high-dose group were decreased significantly（P < 0.05）.8.Apoptosis rate in hippocampus and striatum: The apoptotic rates in hippocampus and striatum of rats in the high-dose group were higher than those in the control group（P < 0.05）.With the prolongation of vanadium exposure and the increase of dose,the apoptotic rate in hippocampus and striatum increased.9.V₂O₅,striatum,hippocampus of rat in the endoplasmic reticulum PERK-eIF2 alpha signaling pathways related protein expression level of influence: With the prolongation of vanadium exposure and the increase of dose,the contents of GRP78,p-PERK,peIF2α,CHOP and Caspase12 in the hippocampus and striatum were gradually increased.At the third month,compared with the control group,the protein expression levels of GRP78,p-PERK,p-eIF2α,CHOP and Caspase12 in the hippocampus and striatum of rats in the high-dose group were significantly increased（P < 0.05）.Conclusion: 1.Inhalation of high concentration V₂O₅ for three consecutive months resulted in impaired learning and memory function in rats;2.Apoptosis of neurons in hippocampus and striatum;3.Abnormal neuronal morphology and synaptic destruction in hippocampus and striatum.