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DEVELOPMENTAL PHYSIOLOGY AND PREGNANCY

Influence of gestational age and fetal iron status on IRP activity and iron transporter protein expression in third-trimester human placenta

¹Department of Pediatrics, University of Minnesota School of Medicine, Minneapolis, Minnesota 55455; ²Department of Medicine, Eccles Program for Human Molecular Biology and Genetics, University of Utah, Salt Lake City, Utah 84112; ³Department of Pediatrics, Johns Hopkins School of Medicine, Baltimore, Maryland 21205; and ⁴Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706

Submitted 11 September 2003 ; accepted in final form 18 May 2004

Placental iron transport during the last trimester of pregnancy determines the iron endowment of the neonate. Iron transport is a function of the major iron transport proteins: transferrin receptor-1 (TfR-1) and ferroportin-1 (FPN-1). The mRNAs for TfR-1 and, potentially, FPN-1 are posttranscriptionally regulated by iron regulatory protein (IRP)-1 and IRP-2. We assessed the effect of gestational age and fetal iron status on IRP-1- and IRP-2-binding activity and on the localization and protein expression of TfR-1 and FPN-1 protein at 24–40 wk of gestation in 21 placentas obtained from iron-sufficient nonanemic mothers. Gestational age had no effect on cord serum ferritin concentration, IRP-2 RNA-binding activity, transporter protein location, and TfR-1 or FPN-1 protein expression. IRP-1 activity remained constant until full term, when it decreased (P = 0.01). Placental ferritin (r = 0.76, P < 0.001) and FPN-1 (r = 0.44, P < 0.05) expression increased with gestational age. Fetal iron status, as indexed by cord serum ferritin concentration, was inversely related to placental IRP-1 (r = –0.66, P < 0.001) and IRP-2 (r = –0.42, P = 0.05) activities. Placental ferritin protein expression correlated better with IRP-1 (r = –0.45, P = 0.04) than with IRP-2 (r = –0.35, P = 0.10) activity. Placental TfR-1 and FPN-1 protein expression was independent of fetal or placental iron status and IRP activities. Iron status had no effect on transport protein localization. We conclude that, toward the end of the third trimester of iron-sufficient human pregnancy, the placenta accumulates ferritin and potentially increases placental-fetal iron delivery through increased FPN-1 expression. IRP-1 may have a more dominant role than IRP-2 activity in regulating ferritin expression.

ferroportin; ferritin; transferrin receptor; syncytiotrophoblast; pregnancy

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