The role of Hfe in transferrin-bound iron uptake by hepatocytes.
HFE-related hereditary hemochromatosis results in hepatic iron overload. Hepatocytes acquire transferrin-bound iron via transferrin receptor (Tfr) 1 and Tfr1-independent pathways (possibly Tfr2-mediated). In this study, the role of Hfe in the regulation of hepatic transferrin-bound iron uptake by these pathways was investigated using Hfe knockout mice. Iron and transferrin uptake by hepatocytes from Hfe knockout, non-iron-loaded and iron-loaded wild-type mice were measured after incubation with 50 nM (125)I-Tf-(59)Fe (Tfr1 pathway) and 5 microM (125)I-Tf-(59)Fe (Tfr1-independent or putative Tfr2 pathway). Tfr1 and Tfr2 messenger RNA (mRNA) and protein expression were measured by real-time polymerase chain reaction and western blotting, respectively. Tfr1-mediated iron and transferrin uptake by Hfe knockout hepatocytes were increased by 40% to 70% compared with iron-loaded wild-type hepatocytes with similar iron levels and Tfr1 expression. Iron and transferrin uptake by the Tfr1-independent pathway was approximately 100-fold greater than by the Tfr1 pathway and was not affected by the absence of Hfe. Diferric transferrin increased hepatocyte Tfr2 protein expression, resulting in a small increase in transferrin but not iron uptake by the Tfr1-independent pathway.


CONCLUSIONS
Tfr1-mediated iron uptake is regulated by Hfe in hepatocytes. The Tfr1-independent pathway exhibited a much greater capacity for iron uptake than the Tfr1 pathway but it was not regulated by Hfe. Diferric transferrin up-regulated hepatocyte Tfr2 protein expression but not iron uptake, suggesting that Tfr2 may have a limited role in the Tfr1-independent pathway.
Chua
Anita C G
AC
School of Medicine and Pharmacology, The University of Western Australia, Fremantle Hospital, Western Australia, Australia.
Herbison
Carly E
CE
Drake
Sarah F
SF
Graham
Ross M
RM
Olynyk
John K
JK
Trinder
Debbie
D
D000818:Animals; D001692:Biological Transport; D018929:Cell Culture Techniques; D017931:DNA Primers; D000071020:Hemochromatosis Protein; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000502:physiology*; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics; D014168:Transferrin / Q000378:metabolism*
D017931:DNA Primers; D000071020:Hemochromatosis Protein; C499535:Hfe protein, mouse; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D012333:RNA, Messenger; D014168:Transferrin; D012313:RNA; D007501:Iron