Abstract 1665 Neonatal Nutrition and Metabolism I Poster Symposium, Saturday, 5/1

Gestations complicated by intrauterine growth retardation have altered fetal iron metabolism with 50% of IUGR infants being born with iron stores <5th percentile (cord serum ferritin <60 ng/ml). Maternal-fetal iron transport is mediated by TfR, located on the syncytiotrophoblastic membrane. TfR surface expression is regulated post-transcriptionally by cellular iron status, with increased expression occurring during iron deficiency. To characterize TfR expression in iron deficient IUGR placentas, we localized, quantified and isolated TfR and localized its putative membrane regulatory protein HFE in 6 placentas from iron deficient (mean±SD ferritin: 34±29 ng/ml) and 6 iron sufficient control infants. Based on similar studies in iron deficient infants of diabetic mothers, we hypothesized 1) increased syncytiotrophoblast TfR expression in IUGRs, 2) increased molecular weight (MW) of TfR due to incomplete trimming of oligosacharide residues; 3) co-localization of HFE with TfR on the syncytiotrophoblast. TfR was localized by a mouse monoclonal anti-human TfR antibody and visualized with a Cy-3-tagged secondary. Surface TfR expression was quantified by relative optical densitometry using Image-1. TfR was isolated from placental membranes with a Sepharose 4B anti-transferrin column and its MW determined by PAGE. HFE was localized by a polyclonal rabbit antibody to HFE and visualized with a Cy-3 tagged secondary. For co-localization experiments, the TfR secondary was tagged with FITC; TfR and HFE were compared on adjacent sections. TfR was localized exclusively to the syncytiotrophblast membrane and had 31% greater expression in the IUGR samples. The MW of the TfR monomer was similar in both groups (IUGR: 92.4±1.6 kD vs. Control: 92.5±0.1 kD). HFE, like TfR was localized to the syncytiotrophoblastic membrane, but was not expressed on every part of the membrane on which TfR was. We conclude that regulation of TfR expression in the IUGR placenta is normal, with appropriate upregulation of surface receptor during fetal iron deficiency. TfR from IUGR placentas has normal MW, implying that the increased TfR MW in diabetic placenta is due to hyperglycosylation from diabetes, rather than early release of incompletely trimmed receptor from the Golgi. Thus, TfR from IUGR placenta likely has normal binding characteristics for diferric transferrin (unlike the hyperglycosylated receptor which has reduced binding capacity). The presence of HFE with TfR is consistent with other reports of a potential role for HFE in TfR regulation.

Supported by NICHD.