Erythropoietin enhances iron bioavailability in HepG2 cells by downregulating hepcidin through mTOR, C/EBPα and HIF-1α

Abstract

The regulation of iron (Fe) levels is essential to maintain an adequate supply for erythropoiesis, among otherprocesses, and to avoid possible toxicity. The liver-produced peptide hepcidin is regarded as the main regulatorof Fe absorption in enterocytes and release from hepatocytes and macrophages, as it impairs Fe export throughferroportin. The glycoprotein erythropoietin (Epo) drives erythroid progenitor survival and differentiation in thebone marrow, and has been linked to the mobilization of Fe reserves necessary for hemoglobin production.Herein we show that Epo inhibits hepcidin expression directly in the HepG2 hepatic cell line, thus leading to adecrease in intracellular Fe levels. Such inhibition was dependent on the Epo receptor-associated kinase JAK2, aswell as on the PI3K/AKT/mTOR pathway, which regulates nutrient homeostasis. Epo was also found to decreasebinding of the C/EBP-α transcription factor to the hepcidin promoter, which could be attributed to an increasedexpression of its inhibitor CHOP. Epo did not only hinder the stimulating effect of C/EBP-α on hepcidin transcription,but also favored hepcidin inhibition by HIF-1α, by increasing is nuclear translocation as well as itsprotein levels. Moreover, in assays with the inhibitor genistein, this transcription factor was found necessary forEpo-induced hepcidin suppression. Our findings support the involvement of the PI3K/AKT/mTOR pathway in theregulation of Fe levels by Epo, and highlight the contrasting roles of the C/EBP-α and HIF-1α transcription factorsas downstream effectors of the cytokine in this process.