Placental Thyroid Hormone Receptor Signaling Mediates Fenvalerate-induced Fetal Growth Restriction

Backgrounds and ObjectivesFenvalerate is an endocrine disrupter.More and more studies have have shown that it has potential developmental toxicity..The aim of this study is to investigate whether maternal fenvalerate exposure causes fetal intrauterine growth restriction(IUGR)and to explore the role of placental thyroid hormone receptor(TR)signaling in fenvalerate-induced fetal IUGR.MethodsEstablishment of a model that fenvalerate-induced fetal IUGR: The ICR mice(8~10week-old;male mice: 32~34 g;female mice: 28~30g)were purchased from Beijing Vital River.The animals were allowed free access to food(Beijing Keao Xieli Feed Co,LTD,Beijing 100107)and water at all times and were housed in a room with controlled lighting(12h light/12 h dark cycle)and temperature(20~25℃)for one week before use.For mating purposes,four females were housed overnight with two males starting at 9:00P.M.Females were checked by 7:00 A.M the next morning,and the presence of a vaginal plug was designated as gestational day(GD)0.In fenvalerate pregnant mice,pregnant mice were daily administered with fenvalerate(0.2,2.0,20 mg/kg,dissolved in corn oil)by gavage from GD0 to GD17.The control pregnant mice were daily administered with corn oil by gavage from GD0 to GD17.Our preliminary data showed that no signs of maternal toxicity were observed in dams that were administered with fenvalerate(20 mg/kg)during pregnancy.56 pregnant mice(n=11-16)were divided into four groups,all dams were sacrificed on GD18.Gravid uterine weights,fetal weight,the number of implantation,live fetuses,dead fetuses and resorption sites were counted.Fetal serum and placentas were collected.Serum total triiodothyronine(TT3)and total thyronine(TT4)were measured by Electrochemiluminescence Immunoassay(ECLIA).The mRNA levels of Fatty acid transport protein-1(Fatp1),Fatty acid translocase(Fat /CD36),Sodium-dependent neutral amino acid transporter-1(Snat1)and Sodium-dependent neutral amino acid transporter-2(Snat2),Insulin-like growth factor-1(Igf1)and Insulin-like growth factor-2(Igf2)were measured by RT-PCR.To investigate the role of placental thyroid hormone receptor signaling in fenvalerate-induced fetal IUGR : In fenvalerate pregnant mice(n=6),pregnant mice were daily administered with fenvalerate(0.2,2.0,20 mg/kg by gavage from GD0 to GD14.The control pregnant mice(n=6)were daily administered with corn oil by gavage from GD0 to GD14.All dams were sacrificed on GD15.Hematoxylin and eosin(H&E)stained placental sections were analyzed for blood sinusoidal area.Maternal serum and placentas were collected.Serum TT3 and TT4 were measured by ECLIA.The mRNA levels of Thyroid hormone receptor α(TRα),thyroid hormone receptor β(TRβ),Vascular endothelial growth factor a(Vegfa)and Vascular endothelial growth factor receptor-1(Vegfr1)were measured by RT-PCR.The nuclear transcription levels of TRαand TRβ were measured with Western blotting.ResultsIn this study,the body weight of fetal mice treated with fenvalerate(0.2 mg/kg,2mg/kg and 20.0 mg/ kg)was(1.354 ± 0.010)g,(1.328 ± 0.013)g and(1.280 ± 0.021)g respectively.Body weight of control fetal mice was(1.347 ± 0.025)g.Fetal weight was lowered in dams that were administered with fenvalerate(F=3.764,P<0.05).Moreover,the rate of IUGR in fetal mice treated with fenvalerate(0.2 mg/kg,2 mg/kg and 20.0mg/kg)was 3.34%、5.94% and 22.23% respectively.The rate of IUGR in control fetal mice was 5.76%.The rate of IUGR was elevated in fenvalerate-treated fetal mice(H=11.851,P<0.05).Then,the rate of IUGR in male and femal fetal mice was analizedrespectively.the rate of IUGR in male fetal mice treated with fenvalerate(0.2 mg/kg,2mg/kg and 20.0 mg/kg)was 1.56%、6.51% and 17.61% respectively.The rate of IUGR in control male fetal mice was 5.18%.The rate of IUGR was elevated in male fenvalerate-treated fetal mice(H=7.849,P < 0.05).The rate of IUGR in female fetal mice treated with fenvalerate(0.2 mg/kg,2 mg/kg and 20.0 mg/kg)was 8.22%,7.94%and 25.17% respectively.The rate of IUGR in control female fetal mice was 2.95%.The rate of IUGR was elevated in female fenvalerate-treated fetal mice(H=8.482,P<0.05).Histopathology showed that the internal space of blood vessels in the labyrinth layer was smaller in placentas of mice exposed to fenvalerate(H=7.849,P<0.05).Mechanistic study found no significant difference on TT4 level in maternal serum,although TT3 level in maternal serum was slightly reduced in dams exposed to 2.0 mg/kg of fenvalerate.Interestingly,placental TRα1 and TRβ1 mRNAs were reduced in mice exposed to fenvalerate.Moreover,nuclear translocation of placental TRβ1 was suppressed in fenvalerate-exposed mice.Further analysis showed that placental Vegfαand Igf2,several target genes of TR signaling,were down-regulated in fenvalerate-exposed mice.In addition,mRNA level of placental CD36,Snat1 and Snat2,three nutrient transporters,were reduced in fenvalerate-exposed mice.ConclusionPlacental thyroid hormone receptor signaling may mediate fenvalerate-induced fetal IUGR.