Liver iron modulates hepcidin expression during chronically elevated erythropoiesis in mice

Area of Science:

• Hematology
• Iron Metabolism
• Molecular Biology

Background:

• Hepcidin, a liver peptide, regulates iron balance by inhibiting ferroportin, controlling iron absorption and release from stores.
• Hepcidin regulation involves multiple signals, but the precise mechanisms, especially during altered erythropoiesis, remain incompletely understood.

Purpose of the Study:

• To investigate the primary signals controlling hepcidin expression in mice with constitutively overexpressed erythropoietin (Epo) and excessive erythropoiesis.
• To elucidate the role of liver iron content and the BMP6/SMAD pathway in hepcidin regulation under conditions of high erythropoietic demand.

Main Methods:

• Studied iron metabolism and hepcidin expression in Tg6 mice overexpressing Epo.
• Manipulated iron availability (iron supplementation) and erythropoiesis-dependent iron consumption (splenectomy).
• Analyzed hepcidin expression, ferroportin, divalent metal transporter-1, and BMP6/SMAD pathway components (ID1, SMAD7, TMPRSS6).

Main Results:

• Tg6 mice showed down-regulated hepcidin, increased ferroportin and DMT1, and enhanced iron absorption, yet developed iron deficiency.
• Increasing iron availability or reducing iron consumption up-regulated hepcidin and the BMP6/SMAD pathway, irrespective of high Epo levels.
• ID1 and SMAD7 were up-regulated by increased iron, suggesting their involvement in hepcidin regulation.

Conclusions:

• Liver iron content, modulated by erythropoiesis-driven iron consumption, is a key regulator of hepcidin expression.
• The BMP6/SMAD pathway mediates hepcidin regulation in response to changes in liver iron during excessive erythropoiesis.
• Erythropoietic signals do not directly control hepcidin in this context; rather, iron availability is the dominant factor.