Mechanism Study Of MAPK And CaMKⅡ Signal Pathway In The Entorhinal Cortex Of Iodine Deficient And Hypothyroid Pup Rats

ObjectiveThrough gestation and lactation,iodine deficient or hypothyroid dam rats were administered either an iodine-deficient diet or PTU-added drinking water.We have tested whether congenital iodine deficiency and hypothyroidism could regulate ERK1/2, p-ERK1/2,CREB,p-CREB in MAPK signal pathway and CaMKâ…¡,p-CaMKâ…¡,CaM, Ng in CaMKâ…¡signal pathway in pup entorhinal cortex.To figure out the mechanism that iodine deficiency and hypothyroidism impair long-term synaptic plasticity and learning and memory.MethodsFemale Wistar rats(n=28)aging 2 after pregenancy were randomly divided into four groups:control group,iodine deficient group,hypothyroid-1 group(5ppm)and hypothyroid-2 group(15ppm).The control group was fed a normal diet and tap water during the experiment.The iodine deficient group was fed an iodine-deficient diet and tap-water.The hypothyroid-1 group was fed a normal diet and had 5ppm PTU-added water and the hypothyroid-2 group had 15ppm PTU-added water.All the groups were from GD6 through to postnatal day(PN)28.On PN7,PN14,PN21,PN28,pups in each group were weighed and blood samples were taken for the FT₃,FT₄ and TSH super-sensitive chemiluminescence immunoassay.Pup Cerebrums were weighed and the part of the entorhinal cortex was separated from the brain for protein detection by immunohistochemistry and Western blotting.On PN30,we tested the ethology by water maze and suttle box.Following ethology,pups were weighed and blood sampled for FT₃,FT₄ and TSH.The brains were removed for immunochemistry and Western blotting.ResultsWeights of dam,pup and cerebrums,eye opening:In all three groups of dam rats, dams from iodine-deficient groups were significantly lighter than controls in pregancy and gestation(P＜0.05).Weights of pup and cerebrums from iodine-deficient and 15ppm groups were significantly smaller than controls(P＜0.05)from PN3 to PN42. Eye opening was delayed in iodine-deficient and 15ppm treatment groups,and the ratio of pups within a litter with both eyes opening was lower than controls in the same time.Effects of iodine deficiency and hypothyroidism on MAPK signal pathway:In the result of immunohistochemistry:on the PN7 there were no significantly difference in all the groups.On PN14-PN28,ERK1/2 and CREB in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05),EPK1/2 in 5ppm group were significantly lower than those of controls(P＜0.05).Western blotting:On PN14-PN28,ERK1/2 in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05).On PN14,CREB in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05).On PN21-PN28,CREB, p-ERK1/2 in 5ppm,15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05);p-CREB in 15ppm and iodine deficient groups were significantly lower than those of controls and 5ppm groups(P＜0.05).Effects of iodine deficiency and hypothyroidism on CaMKâ…¡signal pathway:In the result of immunohistochemistry:on PN7-PN28,CaMKâ…¡in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05).On PN28, CaMKâ…¡in 5ppm group were also significantly lower than those of controls(P＜0.05). On PN7,Ng in all the groups were no significantly difference.On PN14-PN28,Ng in 15ppm and iodine deficient groups were significantly lower than those of controls (P＜0.05).Western blotting:on PN14-PN28,CaMKâ…¡in 15ppm and iodine deficient groups were significantly lower than those of controls and 5ppms(P＜0.05),on PN21, CaMKâ…¡in 5ppm,15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05),on PN14-PN28,Ng and CaM in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05),on PN21,p-CaMKâ…¡in 15ppm and iodine deficient groups were significantly lower than those of controls (P＜0.05),on PN28,p-CaMKâ…¡in 5ppm,15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05).Effects of ethology on the protein in the entorhinal cortex:comparing with control group on PN42,in the result of immunohistochemistry:ERK1/2,CaMKâ…¡,Ng in 5ppm, 15ppm and iodine deficient groups were significantly lower than those of controls (P＜0.05),CREB in 15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05).Western blotting:onPN42,p-ERK1/2,ERK1,Ng and CaM in15ppm and iodine deficient groups were significantly lower than those of controls (P＜0.05),ERK2,CREB,p-CREB,CaMKâ…¡and p-CaMKâ…¡in 5ppm,15ppm and iodine deficient groups were significantly lower than those of controls(P＜0.05). Comparing with PN28,on PN42,ERK1/2,p-ERK2,CREB,CaMKâ…¡in all the groups were no significantly difference,p-ERK1 in the control and 5ppm groups were significantly higher(P＜0.05),but no change in 15ppm and iodine deficient groups.Ng and CaM in 15ppm and iodine deficient groups were significantly higher(P＜0.05),but no change in control and 5ppm groups.P-CREB and p-CaMKâ…¡in all the groups were significantly higher(P＜0.05).Conclusion1.Iodine deficiency and hypothyroidism may effect pups development and lead to the body and cerebrum weights decrease and eye opening delay.2.Iodine deficiency and hypothyroidism may reduce the expression of ERK1/2, p-ERK1/2,CREB,p-CREB in MAPK signal pathway in entorhinal cortex 3.Iodine deficiency and hypothyroidism may reduce the expression of CaMKâ…¡,p-CaMKâ…¡,Ng,CaM in CaMKâ…¡signal pathway in entorhinal cortexIn summary,our results demonstrate that transient exposure to a period of iodine deficiency and hypothyroidism during a period of brain development reduced the protein in MAPK signal pathway and in CaMKâ…¡signal pathway in entorhinal cortex. The changes are likely to contribute to learning and memory deficits associated with developmental iodine deficiency and hypothyroidism.