Iron metabolism by BeWo cells : the role of copper and iron in the regulation of placental iron transfer
In this thesis, the regulation of placental Fe metabolism is investigated, using a placental choriocarcinoma cell line (BeWo). Both copper (Cu) and iron (Fe) status are examined for a possible role in the process of placental Fe transfer. Firstly, the involvement of Cu in Fe release is tested. Ceruloplasmin (Cp), a plasma Cu carrier and ferroxidase, is implicated in Fe release from a variety of cell types, but does not stimulate Fe release from BeWo cells. Instead, evidence is presented for a membrane-associated ferroxidase with homology to Cp, expressed by BeWo cells. This placental protein has a peri-nuclear location, but does not co-localise with classical markers for organelles. Expression of the placental Cu oxidase is inversely regulated by Fe status, indicating a possible role in Fe metabolism. Further, it is regulated by cellular Cu status, with protein levels and enzyme activity decreasing in Cu deficiency. In an environment of limited oxygen supply, Cu deficient BeWo cells display a decrease in Fe release, providing additional support for a role of the placental Cu oxidase in Fe release. Secondly, the role of Cu in Fe uptake in investigated. Cu status does not affect Fe uptake through transferrin-receptor mediated endocytosis. However, a non-transferrin dependent pathway of Fe uptake is up-regulated in Cu deficiency. Cu and Fe compete for uptake by this pathway, indicating that it may be mediated by a non-specific transporter, such as DMT1. Finally, the effect of Fe deficiency on Fe transfer by BeWo cells was investigated. It is demonstrated that Fe uptake and Fe release both increase in Fe deficient cells.