Suppression of hepcidin during anemia requires erythropoietic activity

Abstract

Hepcidin, the principal iron regulatory hormone, regulates the absorption of iron from the diet and the mobilization of iron from stores. Previous studies indicated that hepcidin is suppressed during anemia, a response that would appropriately increase the absorption of iron and its release from stores. Indeed, in the mouse model, hepcidin-1 was suppressed after phlebotomy or erythropoietin administration but the suppression was reversed by inhibitors of erythropoiesis. The suppression of hepcidin necessary to match iron supply to erythropoietic demand thus requires increased erythropoiesis and is not directly mediated by anemia, tissue hypoxia, or erythropoietin.

Figure 1.

Possible regulators of hepcidin during increased erythropoiesis.

Figure 2.

Hepcidin is regulated by erythropoietic activity, not anemia. Prior to phlebotomy (Phleb) mice were pretreated with NS (Phleb Alone), carboplatin (Cp + Phleb), doxorubicin (Dox + Phleb), or anti-EPO. Control mice (No Phleb) were pretreated with NS but did not undergo phlebotomy. (A) Hemoglobin concentration. (B) Reticulocyte fraction measured by flow cytometry. (C) Serum iron. (D) Hepcidin mRNA is the hepatic relative concentration normalized to the amount of β-actin relative to no phlebotomy samples. Means and SDs are shown, with superscripts indicating P < .001 compared to no phlebotomy by t test* or rank sum test^&; ^#P < .001 compared to phlebotomy alone by rank sum test, ^%P < .01 by rank sum test compared to no phlebotomy.

Figure 3.

Inhibitors of erythropoiesis do not act by inducing a hepatic acute-phase response or interfering with hypoxic sensing or EPO production. Prior to phlebotomy (Phleb), mice were pretreated with NS (Phleb Alone), carboplatin (Cp + Phleb), doxorubicin (Dox + Phleb), or anti-EPO. Control mice (No Phleb) were pretreated with NS but did not undergo phlebotomy. Messenger RNAs for SAA-1 (A, ▪), FGN-γ (A, ), and VEGF (B) were measured by real-time qRT-PCR relative to actin mRNA concentrations, and expressed as a ratio to no phlebotomy samples. Serum EPO concentration (C) was measured by enzyme-linked immunosorbent assay. Means and SDs are shown with superscripts indicating *P = .001, ^#P < .05, ^&P < .001 by rank sum test compared to no phlebotomy, and ^%P = .003 by rank sum test compared to phlebotomy alone.

Figure 4.

EPO suppresses hepcidin indirectly by inducing erythropoiesis. Reticulocyte fractions (A), serum iron (B), and hepcidin mRNA (C) were determined after each indicated treatment and compared by rank sum test to “no EPO” (*P < .005, ^#P = .01, ^%P < .05) or compared by rank sum test to “EPO” (^&P ≤ .002). Hepcidin mRNA was normalized to actin mRNA and ratios to “no EPO” are shown. Error bars indicate one standard deviation.