Investigations of Iron, Hypoxia and Adipocyte Hypoxia on Hepcidin Promoter Activity

Abstract

Hepcidin plays a key role in regulating organismal iron metabolism by blocking iron efflux from enterocytes and macrophages. Hepcidin is synthesized in the liver and its expression is increased by iron overload and inflammation and decreased by hypoxia. To determine if iron, hypoxia or conditioned media from hypoxic adipocytes modulates hepcidin promoter activity; the human hepcidin promoter (1207 b.p. fragment upstream of the transcription start site) was cloned into a luciferase reporter construct. Constructs were transfected into Huh7 hepatocytes. Treatment of transfected cells with ferric ammonium citrate for 24h (50, 100 and 200 µM) modestly increased hepcidin promoter activity over controls (1.39‐fold ± 0.27, P=0.06; 1.46‐fold ± 0.16, P < 0.01 and 1.47‐fold ± 0.14, P < 0.01 respectively). Hemin (10 µm) increased hepcidin promoter activity 1.6‐fold ± 0.11 over controls, (P < 0.01). Cells cultured for 24h at 19% O2 had 2.6‐fold ± 0.15 higher (P < 0.01) promoter activity compared to cells cultured at 1% O2. Treatment of Huh7 cells with media from 3T3‐L1 adipocytes cultured at 1% O2 increased promoter activity 2.9‐fold ± 0.7 (P < 0.01) over cells treated with 3T3‐L1 media cultured at 19% O2. These data suggest that changes in hepcidin expression by iron or hypoxia may be partially mediated through the hepcidin promoter. Furthermore, adipocyte hypoxia (a feature of central obesity) may increase hepcidin expression.