Transcriptional regulation of hepcidin expression in mice by testosterone

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 338-357-Steroid Hormone Actions
Basic/Translational
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-345
Wen Guo*1, Eric Scott Bachman2, Michelle Li3, Cindy Roy4, Jerzy Blusztajn5, Siu Wong6, Stephen Y Chan7, Carlo Serra7, Ravi Jasuja8, Thomas G Travison9, Martina U Muckenthaler10, Elizabeta Nemeth11 and Shalender Bhasin8
1Boston University, Boston, MA, 2Novartis Inst. for Biomedical Rs, Swampscott, MA, 3Brigham and Women's Hospital, 4Johns Hopkins University, 5Woods Hole Oceanographic Institution, 6Boston University, 7Brigham and Women’s Hospital, 8Brigham & Women's Hospital, Boston, MA, 9Boston University Medical Center, Boston, MA, 10University of Heidelberg, 11David Geffen School of Medicine at UCLA
Background. Hepcidin is a hepatocyte-secreted hormone transcriptionally regulated by the BMP/Smad1 signaling pathway. Hepcidin functions by inhibiting iron release from tissue store into bloodstream, hence indirectly limiting iron availability for erythropoiesis. Testosterone is known to increase hemoglobin and hematocrit in human and animal models. This pro-erythropoietic effect is associated with a reduction of serum hepcidin in men after testosterone supplementation. Hypothesis. Testosterone, via its nuclear receptor, may directly down-regulate hepcidin expression; this effect may contribute to increase iron bioavailability to enhance erythropoiesis and increase red cell mass. Methods. Testosterone was administered to female and castrated male mice. The effect of testosterone on liver expression of hepcidin and its upstream regulatory pathway was examined by real-time PCR, Western analysis, and ChIP. The effect of testosterone on hepcidin promoter activity was measured by luciferase reporter assays in HepG2 cells. The model of signal interference between androgen receptor (AR) and BMP/Smad1 was further tested in vivo by co-treatment of testosterone with dorsomorphin, a Smad1 inhibitor and in vitro by co-treatment of testosterone with BMP2, a Smad1 activator, for their collective effect on hepcidin expression. Functional readouts were measured as the effect of testosterone on splenic ferroportin expression, splenic iron store, serum iron, and iron incorporation into red cells in vivo as well as serum-induced hemoglobin accumulation in K562 erythroleukemia cells. Results. Testosterone down-regulated hepatic hepcidin mRNA expression in mice, in association with increased splenic ferroportin protein level, reduced splenic iron store, and increased serum iron. Testosterone-treated mice showed increased red cell mass and greater red cell iron incorporation after i.v. administration of transferrin-bound 58Fe. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 cells more than serum from vehicle-treated mice. The pro-erythropoietic effect of testosterone was abolished in mice with liver-specific transgenic expression of hepcidin. Administration of Smad1 inhibitor alone inhibited hepcidin expression similar to testosterone but the effect was not enhanced further by co-treatment with both. Testosterone promoted the association of AR with Smad1 and Smad4 and reduced their binding to the BMP-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide and by Smad1 activator BMP2. Conclusion. Testosterone inhibits hepcidin transcription through its interaction with BMP-Smad signaling, which may contribute to the increased serum iron and enhanced erythropoietic activity.

Nothing to Disclose: WG, ESB, ML, CR, JB, SW, SYC, CS, RJ, TGT, MUM, EN, SB

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: NIH5RO1AG037193 and 1UO1AG14369 to SB; R21AG037859 and Department of Medicine Bridge grant to WG; R01DK082722 to CNR.