Ceruloplasmin and ceruloplasmin homologue hephaestin in the brain : regulation of expression and role in iron transport

Abstract

Ceruloplasmin (CP) is a copper-containing ferroxidase that is essential for normal iron homeostasis. Whereas CP in plasma is produced and secreted by hepatocytes, recent study has shown that a glycosylphosphatidylinositol (GPI)-anchored form of CP is expressed on the surface of astrocytes in the brain. The precise biological role of CP remains unclear despite decades of investigation. Hephaestin (Heph) is a newly identified membrane-bound multi-copper ferroxidase necessary for iron egress from intestinal enterocytes into the circulation. The molecule is highly homologous to CP (50% identity, 68% similarity) and, significantly, all the residues involved in copper binding and disulfide bond formation in CP are conserved in Heph. Studies in this thesis demonstrated the presence of CP and identified for the first time, Heph protein synthesis in the rat brain. We determined the effects of iron status and age on expression of CP and Heph genes in different rat brain regions. We also studied the role of CP in iron release in C6 glioma cells and obtained stronger evidence for its proposed role in brain iron metabolism. In order to detect the specificity of regulation in different organs in vivo and in vitro, the effect of iron status on iron-related metabolism proteins (ferroportin 1, FP 1; transferrin receptor, TfR) was examined in rat hearts and C6 glioma cells was examined. In addition, the regulation of CP, Heph, divalent metal transporter 1 (DMT1), FP1 and TfR expression by gamma-aminobutyric acid (GABA), glutamate and L-DOPA in C6 glioma cells was investigated. Studies in the thesis, also ascertain for the first time, the possibility that neurotransmitters regulate the iron metabolism though control of iron transport proteins. This thesis consists of 9 chapters, beginning with a general introduction, followed by the methodology section, and 6 chapters on results, and ends with a general discussion.