Theurl Igor, Theurl Milan, Seifert Markus, Mair Sabine, Nairz Manfred, Rumpold Holger, Zoller Heinz, Bellmann-Weiler Rosa, Niederegger Harald, Talasz Heribert, Weiss Günter
Department of General Internal Medicine, Medical University, Innsbruck, Innsbruck, Austria.
Blood. 2008 Feb 15;111(4):2392-9. doi: 10.1182/blood-2007-05-090019. Epub 2007 Dec 11.
Hepcidin, a master regulator of iron homeostasis, is produced in small amounts by inflammatory monocytes/macrophages. Chronic immune activation leads to iron retention within monocytes/macrophages and the development of anemia of chronic disease (ACD). We questioned whether monocyte-derived hepcidin exerts autocrine regulation toward cellular iron metabolism. Monocyte hepcidin mRNA expression was significantly induced within 3 hours after stimulation with LPS or IL-6, and hepcidin mRNA expression was significantly higher in monocytes of ACD patients than in controls. In ACD patients, monocyte hepcidin mRNA levels were significantly correlated to serum IL-6 concentrations, and increased monocyte hepcidin mRNA levels were associated with decreased expression of the iron exporter ferroportin and iron retention in these cells. Transient transfection experiments using a ferroportin/EmGFP fusion protein construct demonstrated that LPS inducible hepcidin expression in THP-1 monocytes resulted in internalization and degradation of ferroportin. Transfection of monocytes with siRNA directed against hepcidin almost fully reversed this lipopolysaccharide-mediated effect. Using ferroportin mutation constructs, we found that ferroportin is mainly targeted by hepcidin when expressed on the cell surface. Our results suggest that ferroportin expression in inflammatory monocytes is negatively affected by autocrine formation of hepcidin, thus contributing to iron sequestration within monocytes as found in ACD.
铁调素是铁稳态的主要调节因子,由炎性单核细胞/巨噬细胞少量产生。慢性免疫激活导致铁在单核细胞/巨噬细胞内潴留,并引发慢性病贫血(ACD)。我们质疑单核细胞衍生的铁调素是否对细胞铁代谢发挥自分泌调节作用。用脂多糖(LPS)或白细胞介素-6(IL-6)刺激后3小时内,单核细胞铁调素mRNA表达显著诱导,且ACD患者单核细胞中铁调素mRNA表达显著高于对照组。在ACD患者中,单核细胞铁调素mRNA水平与血清IL-6浓度显著相关,单核细胞铁调素mRNA水平升高与铁输出蛋白铁转运蛋白的表达降低及这些细胞中铁潴留相关。使用铁转运蛋白/增强型绿色荧光蛋白(EmGFP)融合蛋白构建体进行的瞬时转染实验表明,LPS诱导THP-1单核细胞中铁调素表达导致铁转运蛋白内化和降解。用针对铁调素的小干扰RNA(siRNA)转染单核细胞几乎完全逆转了这种脂多糖介导的效应。使用铁转运蛋白突变构建体,我们发现铁转运蛋白在细胞表面表达时主要受铁调素靶向作用。我们的结果表明,炎性单核细胞中铁转运蛋白的表达受到铁调素自分泌形成的负面影响,从而导致ACD中单核细胞内铁的螯合。