H2O2 rapidly activates the systemic iron hormone hepcidin independent of the IL-6/BMP6 network

Aims: The liver-secreted peptide hepcidin is the key iron hormone at the systemic level. It decreases duodenal iron absorption and iron release by macrophages during conditions of excess iron by blocking the iron exporter ferroportin. In addition, IL-6 mediated upregulation of hepcidin during inflammation is the major mechanism of the so-called ‘anemia of chronic disease’. We here identify H2O2 which is co-released by inflammatory cells as potent transcriptional activator of hepcidin independent of upstream regulators IL-6 and BMP6.

Material and Methods: H2O2 release (1–8µM) by immune cells was mimicked using purified enzymes glucose oxidase and catalase as recently described (GOX/CAT system). Huh7 hepatoma cells were treated with either IL-6 or BMP6 alone, or in combination with steady state H2O2 over 24h. Hepcidin regulation was assessed by quantitative real time PCR. Members of the intracellular signaling cascade such as STAT3 were assessed by Western blotting. Promotor studies were performed using hepcidin-promoter constructs with various deletions fused to luciferase as reporter gene with Renilla as control reporter gene.

Results: Steady state non-toxic H2O2 concentrations comparable to those by inflammatory cells rapidly and drastically upregulate hepcidin in a dose-dependent way in Huh7 cells by a factor of 10. In addition, H2O2 further potentiates IL6 and BMP6 mediated upregulation of hepcidin 5-fold. Promoter studies identified the STAT3 element as major promoter region of H2O2 mediated hepcidin induction. Indeed, phosphorylation of STAT3 was confirmed under these conditions using Western blotting.

Conclusions: Our studies suggest H2O2 as potent transcriptional inducer of hepcidin independent of the IL-6/BMP6 network. Thus, H2O2 should be seen as mediator that co-orchestrates the iron shift from serum to tissue during inflammation.

hepcidin - iron - reactive oxygen species