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. 2013 Apr;12(2):280-91.
doi: 10.1111/acel.12052. Epub 2013 Feb 28.

Testosterone Administration Inhibits Hepcidin Transcription and Is Associated With Increased Iron Incorporation Into Red Blood Cells

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Testosterone Administration Inhibits Hepcidin Transcription and Is Associated With Increased Iron Incorporation Into Red Blood Cells

Wen Guo et al. Aging Cell. .
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Abstract

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin mRNA expression, upregulated renal erythropoietin mRNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound (58) Fe, the amount of (58) Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor (AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein (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. Testosterone did not affect hepcidin mRNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells.

Figures

Figure 1
Figure 1. Effects of Testosterone on Red Cell Indices, Reticulocyte Count, Reticulocyte Hemoglobin Ratio, and Circulating Iron Indices
A: Time course of hematocrit change after subcutaneous insertion of empty or testosterone implants in female mice (*p=0.0002, **p<0.0001, ***p=0.0002 for between-group comparison at each time). The slope of hematocrit change over time was 0.65 for testosterone group (p<0.0001) and 0.02 for control group (p=0.6121). B: The mice treated with testosterone implants for 2-weeks had significantly higher hemoglobin (Hgb), hematocrit (Hct), and a trend towards higher mean corpuscular hemoglobin (CHm) than mice that received empty implants. C: Testosterone-treated mice had significantly higher serum iron, lower total iron binding capacity (TIBC), and higher transferrin (Tf) saturation than controls 2 weeks after insertion of either empty (C) or testosterone implants (T). D. Testosterone-treated mice (T) had significantly higher reticulocyte count (Retic-C) and higher reticulocyte hemoglobin ratio (CHr) than controls (C) after 2 weeks of treatment. The data are mean±SEM, n=10-20 mice for each measurement.
Figure 2
Figure 2. The effects of testosterone on hepcidin mRNA expression and on hematocrit, hemoglobin, and serum iron in wild type and hepcidin transgenic mice
A. Testosterone suppresses hepatic hepcidin expression. Testosterone administration was associated with a greater decrease in hepatic hepcidin mRNA expression than vehicle after 96h (left panel, *p<0.0001, **p< 0.0001, ***p<0.0001 for between-group comparison at each time) and 2 weeks of treatment (right panel). B. Hematocrit (Hct) (upper panel) and hemoglobin (Hgb) (lower panel) in wild type (wt) and transgenic female mice that carried either a silent (Tg) or a constitutively active (Tg+) hepcidin transgene at baseline (day 0) or on day 14 after administration of either empty or testosterone implants. Wt and Tg mice both displayed higher Hgb and Hct on day 14 compared to baseline in response to testosterone administration, whereas Tg+ mice displayed a slight decrease in Hgb and Hct. Wild-type mice treated with empty implants displayed a small decrease in Hgb and Hct likely due to repeated blood drawing. C. Serum iron levels in female wild type (wt) and mice carrying silent (Tg) or constitutively active (Tg+) hepcidin transgene. Testosterone treatment for 2 weeks was associated with significantly higher serum iron levels in wt and Tg mice than in vehicle-treated controls and in testosterone-treated Tg+ mice. Tg+ mice had significantly lower serum iron than all other groups.
Figure 3
Figure 3. Effect of testosterone on splenic ferroportin expression and ferric iron staining, hemoglobin accumulation in K562 erythroleukemia cells, and on 58Fe incorporation into red blood cells
A. Western analysis of splenic ferroportin (fpn) expression (N=5 for each group). Ferroportin protein level, normalized by actin expression, was significantly higher in spleens of testosterone-treated (T) mice than in controls (C). B. Prussian blue staining for iron in the spleen of mice treated with either empty (C) or testosterone-containing (T) implants (N=3 for each group). Ferric iron stains greenish-blue and background tissue is stained with hematoxylin. Testosterone treatment significantly reduced splenic ferric iron, measured either as area of iron staining (upper left panel) or as the size of iron stains (lower left panel). This result is consistent with the increased expression of iron-exporter ferroportin in this tissue. C. Iron incorporation into red blood cells. Female mice were injected testosterone twice weekly for 2 weeks. 58Fe/transferrin complex was injected into tail vein at 10 ng/g body weight. After 8 h, blood was taken to measure 58Fe/56Fe ratio using MC-ICPMASS. The amount of iron incorporated into red cells was calculated from specific activity of 58Fe in steady-state serum iron pool size. D. Effects of testosterone on hemoglobin accumulation in K562 cells. Erythroid differentiation was induced by sodium butyrate (0.5 mM) for 48 h. Cells were incubated with 10% serum from female mice pre-treated with vehicle (C) or testosterone (T). Serum iron concentrations were 17.5±0.9uM and 25.1±0.6uM and transferrin saturation 31.0±0.7% and 36.7±0.3% for the control and T-treated mice, respectively. A negative control was incubated with serum-free medium (N). Cells were harvested after 24 h and stained with benzidine (upper panel). Cells were lysed with 0.2% Triton and hemoglobin was measured after benzidine staining at OD600.
Figure 4
Figure 4. Erythropoietin is not essential for testosterone-mediated suppression of hepcidin
A: Time-course of testosterone-induced changes in renal EPO mRNA expression (upper panel) and serum EPO concentrations (lower panel) in female mice. Results are mean±SEM, N=8 for each group. Testosterone administration induced a rapid increase in renal EPO mRNA expression which was followed by an increase in serum EPO levels. B: To determine whether EPO is the mediator of testosterone-induced hepcidin suppression, we treated female mice with testosterone (T) with and without an anti-EPO neutralizing antibody (anti-EPO). EPO and hepcidin mRNA expression levels were assessed 72h (left panel) and 2 weeks (right panel) after treatment initiation. Testosterone administration was associated with a 2 fold increase in renal EPO mRNA expression at 72 h and ~75% decrease in hepatic hepcidin mRNA expression. The administration of anti-EPO antibody alone resulted in a 2 fold increase in renal EPO mRNA. Combined administration of testosterone and anti-EPO antibody resulted in greater increase in renal EPO mRNA expression than either intervention alone. The administration of anti-EPO antibody resulted in a nearly 2 fold increase in hepatic hepcidin mRNA expression. However, co-treatment with anti-EPO did not prevent testosterone-induced suppression of hepcidin either at 72h or 2 weeks. Thus, EPO is not essential for mediating the inhibitory effects of testosterone on hepcidin expression. Results are mean±SEM, N=5 for each group.
Figure 5
Figure 5. Androgen receptor associates with Smad1 and Smad4, blocks BMP/Smad signaling, and reduces Smad1 binding to the BMP-response elements (BMP-RE1 and BMP-RE2) in the hepcidin promoter
A: Testosterone administration for 48h upregulated the expression of androgen receptor (AR) and phospho-Smad1, but had no effect on the expression of total Smad1 and Smad4. The results are representative of 3 experiments. Each lane represents the result from one animal. B: Liver nuclear extracts were immunoprecipitated with goat-anti-Smad4 (left panel) or rabbit-anti-AR (right panel) antibodies. Immune complexes were separated by gel electrophoresis and detected using anti-Smad1, anti-Smad4, anti-CBP/p300, and anti-AR antibodies. Immune complexes immunoprecipitated with anti-Smad4 antibody contained AR, Smad1 and p300 proteins (left panel). Similarly, Immune complexes immunoprecipitated with anti-AR antibody contained Smad4, Smad1, and p300 (right panel). All samples were pre-cleared with agarose gel conjugated with normal goat IgG (for ip with Smad4) or rabbit IgG (for ip with AR) before first antibody was added to the reaction. Equal inputs were confirmed by Western blot for LaminA/C (not shown). Results are representative of 4 experiments. These data provide evidence of association of AR with Smad1, Smad4, and CBP/p300. C: Liver hepcidin mRNA expression in mice treated with vehicle (C), dorsomorphin (DM) (an inhibitor of BMP/Smad1 signaling), DM plus testosterone (DM+T), or T alone. Administration of DM and T each down-regulated liver hepcidin mRNA expression. However, combination of both did not decrease it any more than T alone, suggesting that T and DM likely share overlapping pathways for hepcidin regulation. Results are mean± SEM, N=4 for each group. D: Liver tissue isolated from mice treated with vehicle (C) or testosterone (T) was subjected to ChIP analysis. Immuno-precipitation of Smad1 protein-DNA complexes was performed using anti-Smad1 (Cell Signaling#6944). Negative controls (Neg) were immuno-precipitated with rabbit IgG and positive controls (Pos) were immuno-precipitated with rabbit anti-histone 3 (H3). Real-time PCR was performed using primer sets flanking BMP-RE1 and BMP-RE2 of mouse hepcidin promoter. Results were normalized to the corresponding inputs (sonicated chromatin before immuno-precipitation). Treatment with testosterone for 48h reduced the association between Smad1 and the BMP-RE1 (left panel) and BMP-RE2 (middle panel) on the hepcidin promoter. The assay specificity was validated by primers designed for RPL3 intron 2 (Cell Signaling, #7015) which strongly binds to H3 but not Smad1 or rabbit IgG (right panel). Results are mean±SEM, N=3 for each group.
Figure 6
Figure 6. Androgen receptor attenuates BMP2-induced activation of hepcidin promoter activity and BMP2-induced hepcidin mRNA expression in HepG2 cells
A: HepG2 cells were transfected with control vector, low dose (200 ng/well), and high dose (800 ng/well) of AR encoding plasmid, all in combination with a pGL4 luciferase reporter driven by a 3kb wild-type hepcidin promoter (300 ng/well). A CMV-driven Renilla luciferase vector (30 ng/well) was used as transfection control. 12h after transfection, cells were switched to 1% FBS in low glucose DMEM containing graded dose of DHT and flutamide. After 12h, BMP2 (10 ng/ml) was added to selected wells and incubation was extended for 12h. Results were normalized to Renilla luciferase activity. Experiments were repeated 3 times. Data are mean±SEM. B: HepG2 cells were transfected with control vector or AR-encoding plasmid (800 ng/well). The AR-transfected cells were treated with DHT (100nM). BMP2 was added at 0, 25, 50, and 100ng/ml and incubation was extended for 4h. Hepcidin mRNA was analyzed by real-time PCR and normalized to HPRT. Results are mean±SEM, N=4 for each treatment.

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