The Role Of JAK₂/STAT₃ Signaling Pathway And Klotho In Learning And Memory Dysfunction Induced By Chronic Cadmium Exposure In Rats

Objective By establishing the model of chronic cadmium exposure in rat,to abserve the effect of chronic cadmium exposure on the spatial learning and memory,the morphological structure of hippocampal tissue CA1,the klotho gene expression and the level of JAK₂/STAT₃ signal pathway related protein expression and the phosphorylation expression.And to explore the hippocampal morphology、klotho gene and JAK₂/STAT₃ signaling pathway play a role in cadmium-induced learning and memory dysfunction.Methods Choosing 48 healthy SPF SD rats,were randomly divided into control group,high dose group,middle dose group and low dose group,each group of12.The rats were using intraperitoneal injection（0,0.306,0.612,1.224 mg/kg cadmium chloride solution）for 5 times a week for14 weeks.At the end of the exposure,learning and memory of the rats were examined by the morris water maze test.Fasting for 12 hours,intraperitoneal injection of pentobarbital sodium anesthetized rats and collected biological samples,to measure the organ weight and calculate the organ coefficient.The expression levels of the mRNA of JAK₂ gene,STAT₃ gene and klotho gene in hippocampus were detected using real-time quantitative PCR.The expression levels of JAK₂ and p-JAK₂,STAT₃ and p-STAT₃ in hippocampus were detected using immunohistochemical method.The expression levels of klotho protein in hippocampus was detected by Elisa kit.The hippocampal morphological structure was detected by hematoxylin-eosin stainingResults1.With the increase of cadmium concentration,the rats weightincreased slowly,and the rats weight of all cadmium exposure dose groups were significantly lower than control group（P<0.05）.The liver viscera coefficients of each dose group of cadmium exposure in the male rats were significantly higher than control group（P<0.05）.The spleen viscera coefficients of the high dose group and middle dose group of the cadmium exposure in the male rats wre significantly higher than control group（P<0.05）.The kidney viscera coefficient of the high dose group of the cadmium exposure in the male rats was significantly higher thanthe other dose groups（P<0.05）.The middle dose group of the cadmium exposure,the heart viscera coefficient in the male rats was significantly higher than control group.The high dose group and the middle dose group of the cadmium exposure,the visceral coefficients of liver and kidney were significantly higher than control group in the female rats（P<0.05）.The coefficients of spleen visceral in the female rats,each dose group of the cadmium exposure was significantly higher than the control group（P<0.05）.The middle dose group of the cadmium exposure,the heart visceral coefficient in the male rats was significantly higher than the control group（P<0.05）.2.At the result of the plase navigation test of the Morris water maze,the mean escape latency in the middle dose group of the cadmium exposure in the male rats was significantly longer than that in control group and the low dose group of the cadmium exposure（P<0.05）.In the female rats the escape latency of the middle dose group was significantly higher than that in the control group（P<0.05）.In the female and male rats the escape latency of the high dose group of the cadmium exposure was no significant difference than the control group（P>0.05）.At the results of the spatial probe test of the Morris water maze,the numbers of platform crossings in the male rats,the middle dose group of the cadmium exposure was significantly lower than the control group and the low dose group of the cadmium exposure（P<0.05）.The numbers of platform crossings in the female rats had no statistical difference in middle dose group of the cadmium exposure compared with the control group（P>0.05）.In the female and male rats the spatial probe test of the high dose group of the cadmium exposure was no significant difference than the control group（P>0.05）.3.At the results of histopathological examination of the HE staining,the high and the middle dose groups of the cadmium exposure in male and female rats,the numbers of neurons in CA1 of hippocampus were significantly fewer than the control group（P<0.05）.The number of neurons in CA1 of hippocampus in the male and female rats had no statistical difference in low dose group of the cadmium exposure compared with the control group（P>0.05）.4.The RT-qPCR experiments results show with the increase of cadmium dose,the expression levels of JAK₂ and STAT₃ mRNA in hippocampus of the male and female rats were significantly higher（P<0.05）.The JAK₂ and STAT₃mRNA expression levels,each dose group of the cadmium exposure was significantly higher than control group（P<0.05）.The high dose group of the cadmium exposure,JAK₂ and STAT₃ mRNA expression also was significantly more than the middle dose group and low dose group（P<0.05）.The middle dose group of the cadmium exposure,JAK₂ and STAT₃ mRNA expression was significantly higher than the low dose group and control group（P<0.05）.5.The immunohistochemical test of the hippocampus CA1 results showed the p-JAK₂ protein expression in the male and female rats was significantly more（P<0.05）,with the increase of cadmium dose.The high and middle dose groups of the p-JAK₂ protein expression in the male and female rats were significantly higher than in the control group（P<0.05）.The high dose group and the middle dose group of cadmium exposure in the male rats also were significantly higher than the low dose group（P<0.05）.The high dose group of the cadmium exposure in the female rats also was significantly higher than the low dose group（P<0.05）.With the increase of cadmium dose,the p-STAT₃protein expression was significantly more（P<0.05）.The expression of the p-STAT₃ protein in the high and middle dose groups of the cadmium in the male and female rats were significantly higher than in control group（P<0.05）.The expression of the p-STAT₃ protein in the high and middle dose groups of the cadmium exposure in the male rats was significantly higher than in low dose group（P<0.05）.The expression of JAK₂ and STAT₃ protein in hippocampus CA1 was not significantly different in each group（P>0.05）.6.The RT-qPCR experiments results show the mRNA expression of klotho gene in hippocampus of male and female rats was decreased significantly（P<0.05）,with the increase of cadmium dose.The levels of klotho mRNA expression was significantly lower in each group of the cadmium exposure than in control group（P<0.05）.The middle dose group of the levels of klotho mRNA expression was significantly lower than the low dose group（P<0.05）.With the increase of cadmium concentration,the expression of klotho protein was significantly lower（P<0.05）.The klotho protein expression in each group of the cadmium exposure was significantly lower than the control group（P<0.05）.Conclusion1.Chronic cadmium exposure caused the spatial learning and memory capacity of rats decrease,may be related to hippocampal morphology changes.2.Chronic cadmium exposure induced the spatial learning and memory capacity of rats decrease,may be related to the decline in klotho expression3.Chronic cadmium exposure caused the spatial learning and memory capacity of rats decrease,may be related to activation of JAK₂/STAT₃signaling pathway.