Reduced Sensitivity of the Ferroportin Q248H Mutant to Low Concentrations of Hepcidin.

Abstract 2002

Poster Board I-1024

The iron exporter protein, ferroportin (Fpn), is expressed by enterocytes and macrophages. It transports iron taken up from the gut by enterocytes to portal plasma transferrin and iron recycled by macrophages to systemic plasma transferrin. Hepcidin, which is secreted by hepatocytes, interacts with Fpn, leading to its internalization and degradation. Mutations that lead to decreased production of hepcidin or that reduce the sensitivity of Fpn to hepcidin lead to higher dietary iron uptake and increased parenchymal cell iron stores. The Fpn Q248H mutation, which is common in Africans and African-Americans, has been associated with increase serum ferritin concentrations in adults and with protection from iron deficiency in Zimbabwean children (Kasvosve et al., Am J Clin Nutr. 2005 82:1102-6). Other investigators have reported that the Fpn Q248H has normal sensitivity to hepcidin concentration of 0.5 mM (Drakesmith et al., Blood 2005 106:1092-7). We hypothesized that there may be differential sensitivity on the part of Fpn Q248H to lower levels of hepcidin (0.03-0.1 uM versus 0.5 uM). We subcloned WT and Q248H ferroportins to EGFP-expression vector, transfected 293T cells and measured EGFP fluorescence in response to hepcidin. We observed about 50% less reduction of Fpn Q248H-EGFP comparing to WT Fpn in response to 0.03 mM hepcidin treatment for 3 h but the effect was lost at 0.1 mM or higher concentrations of hepcidin or when the cells were treated with hepcidin for 18 h. This observation possibly explains why this mutation was previously not identified as having lower sensitivity to hepcidin. Similar results were obtained when Fpn was detected by immunoblotting or when ferritin concentrations were measured. Ferritin concentrations were higher in monocytes and macrophages derived from patients with Fpn Q248H mutation, suggesting that there may be differential sensitivity to hepcidin of Fpn expressed on macrophages versus enterocytes. Our results suggest that Africans and African-Americans with Fpn Q248H mutation may develop higher iron stores due to lower sensitivity of this Fpn mutant to low concentrations of hepcidin.