Environmental Endocrine Disruptor Cypermethrin Affects Fetal Intrauterine Development Through IGF1R-PI3K-AKT Signaling Pathway

Objective:Pyrethroid pesticides are considered to be one of the important endocrine disruptors in the environment.They have a long half-life in the environment and will exist for a long time,causing serious harm.Cypermethrin(CYP)is a kind of type II pyrethroid insecticide and widely used in pest control.CYP can lead to abnormal functions of the endocrine system and reproductive system.Previous epidemiological studies about the relationship between CYP exposure during pregnancy and pregnant outcomes have drawn contradictory conclusions.Some studies have shown that CYP exposure during pregnancy is associated with the reduction of fetal birth weight,but others have found no correlation between the two.Pyrethroids can pass through the placenta and directly affect the development of the fetus.The nutrient acquisition and metabolic exchange of the fetus during pregnancy all depend on the existence of the placenta.As an organ specific to pregnancy,placenta is essential for the maintenance of pregnancy and the development of the fetus.Placental dysplasia or dysfunction can lead to various pregnant complications.At present,the placental mechanism of intrauterine growth restriction(IUGR)caused by CYP exposure during pregnancy is not clear.Thyroid hormones regulate the metabolic process during pregnancy and affect embryo growth and development.Existing evidences have shown that thyroid hormones can affect the formation and function of placenta,which is the pathogenesis and pathophysiological basis of pregnant complications,like IUGR.Whether thyroid hormones or thyroid hormone receptors are involved in the placental mechanism of IUGR caused by CYP exposure during pregnancy is still unclear.The purpose of this study was to determine the effects of CYP exposure during pregnancy on maternal and fetal thyroid function and fetal intrauterine development,as well as,to explore the potential placental mechanism which affected the relationship between CYP and IUGR.Research methods:1.To establish a model of pregnant rats exposed to CYP during pregnancy,9-weekold Wistar female rats at the first day of pregnancy(GD 0)were randomly divided into 4groups.Their body weights were recorded every day during the whole pregnancy(GD 0-GD17),and the female rats were given CYP by gavage.The four groups were :(1)corn oil control group(CYP-0);(2)5mg/kg CYP exposure group(CYP-5);(3)20mg/kg CYP exposure group(CYP-20)and(4)50mg/kg CYP exposure group(CYP-50).All rats were killed on GD18.The number of implantation,live fetuses and dead fetuses,the weights of uterus and placentas and the birth weights of offspring were recorded and the incidence of intrauterine growth restriction(IUGR)was calculated.The diagnostic criteria for IUGR were fetal weight below the tenth percentile of the mean weight of fetals with the same gestational age.The maternal serum,placentas and offspring’s tissues were collected.2.The morphological changes of placenta were observed by HE staining.ELISA was used to detect thyroid hormone levels in the serum of maternal rats and tissues of offspring.The gene expressions of thyroid hormone receptor,transporter,deiodinase and related growth factors in placenta were detected by RT-PCR.The protein expression of IGF1R-PI3K-AKT signaling pathway in placenta was detected by Western blot.Results:1.The birth weights of offspring rats in CYP exposure groups decreased gradually with the increase of CYP concentration in a dose-dependent manner.Compared with the control group,the incidences of IUGR were significantly higher in 20 mg/kg and 50 mg/kg CYP exposure groups,and the placental weights were significantly lower in 5 mg/kg and50 mg/kg CYP exposure groups.2.On GD18,compared with the control group,TSH and TT4 levels of maternal rats in CYP exposure groups were increased,with no significant difference of TT3 levels.For offspring rats,CYP exposure makes TSH higher,TT3 lower and no effect on TT4 levels.3.The results of HE staining showed that the proportions of placental labyrinth area in 20 mg/kg and 50 mg/kg CYP exposure groups were significantly lower than that in the control group.4.Compared with the control group,the gene expressions of OATP1c1 in placenta were significantly down-regulated in CYP exposure groups.The expressions of deiodinase2(Dio2)and deiodinase 3(Dio3)were up-regulated only in 50 mg/kg CYP exposure group.The gene expressions of placenta growth factor(PGF)and insulin-like growth factor-1(IGF1)were significantly down-regulated in every CYP exposure group while insulin-like growth factor-1 receptor(IGF1R)was significantly down-regulated only in 20 mg/kg and50 mg/kg CYP exposure groups.5.Compared with the control group,the protein expression levels of placental thyroid hormone receptor α(TRα)were significantly decreased in 20mg/kg and 50mg/kg CYP exposure groups.Exposure to CYP during pregnancy significantly inhibited the phosphorylation level of PI3 K protein.However,the phosphorylation levels of IGF1 R and AKT proteins decreased only in the 50 mg/kg group.Conclusion: Cypermethrin exposure during pregnancy can inhibit phosphorylation levels of IGF1R-PI3K-AKT by interfering with the expression of thyroid hormone receptor in placenta,leading to intrauterine growth restriction of offspring.