Divergence of Iodine and Thyroid Hormones in the Fetal and Maternal Parts of Human-Term Placenta
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The human placenta is an important organ that forms a barrier where maternal and fetal exchange takes place. The placenta transport iodine to the fetal circulation by transfer of maternal iodine and deiodination of thyroid hormones (THs). The aim of the study was to examine the distribution of iodine and thyroid hormone transporters in the maternal and fetal sides of human-term placenta. A cross-sectional study was performed at the First Affiliated Hospital of China Medical University. Placental samples (maternal and fetal surfaces) were collected from 113 healthy-term pregnant women. The iodine content; the concentration of thyroxine (T4), triiodothyronine (T3), and reverse T3 (rT3); and the enzyme activity of placental type 2 iodothyronine deiodinase (D2) and D3 were examined. The mRNA and protein localization/expression of iodine and thyroid hormone transporters in the placenta were also studied. We also analyzed the association between expression level of Na+/I− symporter (NIS), thyroid hormone transporter protein, D3 activity in maternal and fetal surfaces of placenta with iodine content, and thyroid hormone levels. Iodine levels in placental samples from the maternal side were significantly higher than those in samples from the fetal side. T3 and T4 expression in fetal placenta was significantly lower than in maternal placenta. D3 activity in the fetal side of the placentas was significantly higher than that in the maternal side. The mRNA and protein expression of monocarboxylate transporters 8 (MCT8), L-amino acid transporters 1 (LAT1), organic anion transporting polypeptides 4A1 (OATP4A1), and TH binding protein transthyretin (TTR) were significantly increased in maternal side, while the NIS expression was higher in fetal side of human-term placenta. In conclusion, the enzymatic deiodination of thyroid hormones forms a barrier which reduces transplacental passage of the hormones and that the maternal part of the placenta is the primary factor in the mechanism regulating the hormonal transfer.
KeywordsIodine Thyroid hormone transporter Maternal placenta Fetal placenta Deiodination
SP and CL performed the experimental work, analyzed the results, and composed the manuscript. XX, XZ, and DW performed the study and collected the samples. XL reviewed and edited the manuscript. MS and TM participated in the experiments. SW and YJ collected the general information of study populations and contributed to the interpretation and analysis of data; ZS helped with coordination of this study; WT supervised the statistical analyses; contributed to the design of the study, analyses, and interpretation of the results; and produced the final version of the manuscript.
This study was funded by the Chinese National Science Foundation (grant numbers 81170730, 81570709, 81670719) and 973 Plan preliminary research project (2011CB512112).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
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