The IL-6- and lipopolysaccharide-induced transcription of hepcidin in HFE-, transferrin receptor 2-, and beta 2-microglobulin-deficient hepatocytes - PubMed (original) (raw)

The IL-6- and lipopolysaccharide-induced transcription of hepcidin in HFE-, transferrin receptor 2-, and beta 2-microglobulin-deficient hepatocytes

Pauline Lee et al. Proc Natl Acad Sci U S A. 2004.

Abstract

The antimicrobial peptide hepcidin appears to play a central role in the regulation of iron homeostasis. In intact animals, iron overload or the injection of lipopolysaccharide (LPS) stimulates transcription of HAMP, the gene that encodes hepcidin. In isolated hepatocytes, IL-6, an inflammatory cytokine the production of which is stimulated by LPS, up-regulates transcription of hepcidin. In contrast, iron has no stimulatory effect on hepcidin expression in isolated hepatocytes. There is apparently a signaling pathway, activated by iron, that is present in the intact animal but not in isolated hepatocytes. Studies in humans and mice have shown that this iron-dependent pathway requires the presence of Hfe, hemojuvelin, and probably transferrin receptor 2 (tfr-2). To determine whether activation of hepcidin transcription by IL-6 also requires Hfe and tfr-2, we have studied mice homozygous for targeted disruption of HFE, beta(2)-microglobulin, and for a truncating mutation of TFR-2. We show that these mutant mice react normally to injection of endotoxin and that their isolated hepatocytes react normally to IL-6. This indicates that the signaling pathway activated by IL-6 does not require either Hfe or tfr-2. Mice with disruption of the gene encoding IL-6 seem to have a blunted response to LPS, but the statistical significance of the small response documented is borderline. It is therefore not clear whether LPS stimulates secretion of cytokines other than IL-6 that may stimulate hepcidin transcription.

PubMed Disclaimer

Figures

Fig. 1.

Fig. 1.

The response of isolated hepatocytes to treatment with IL-6. (A) The response of hepatocytes from HFE knockout mice. (B) tfr-2 mutant mice. (C)A β-microglobulin knockout mouse. In each, the response to IL-6 is compared with that of hepatocytes from the congenic strain also treated with IL-6. Open triangles represent the deficient mice; filled circles are the controls.

Fig. 2.

Fig. 2.

The hepcidin mRNA response of mice 6 h after i.p. injection of 1 μg of LPS per gram of body weight. Responses represent the ratio of hepcidin cDNA to TTR cDNA as measured by real-time PCR (see Materials and Methods). The results are presented as the percentage of the average hepcidin/TTR ratio documented in mice of the same age and strain that were injected with saline and killed after 6 h. Each point represents one mouse. The dashed line indicates the level at which there is no stimulation of hepcidin transcription by LPS. The mean and one standard error of the mean are shown.

Fig. 3.

Fig. 3.

Schematic representation of the regulation of transcription of hepcidin by the iron pathway (above) and inflammatory (LPS/IL-6 pathway) (below). The iron pathway requires Hfe, hemojuvelin, and probably tfr-2 outside of the hepatocytes. These components are not required for the inflammatory pathway. Although IL-6 is an effective mediator of the response to LPS, some other mediators formed in response to LPS may also stimulate the transcription of hepcidin, although the evidence for this is unclear.

Similar articles

Cited by

References

    1. Pigeon, C., Ilyin, G., Courselaud, B., Leroyer, P., Turlin, B., Brissot, P. & Loreal, O. (2001) J. Biol. Chem. 276, 7811-7819. - PubMed
    1. Nemeth, E., Valore, E. V., Territo, M., Schiller, G., Lichtenstein, A. & Ganz, T. (2003) Blood 101, 2461-2463. - PubMed
    1. Gehrke, S. G., Kulaksiz, H., Herrmann, T., Riedel, H. D., Bents, K., Veltkamp, C. & Stremmel, W. (2003) Blood 102, 371-376. - PubMed
    1. Ahmad, K. A., Ahmann, J. R., Migas, M. C., Waheed, A., Britton, R. S., Bacon, B. R., Sly, W. S. & Fleming, R. E. (2002) Blood Cells Mol. Dis. 29, 361-366. - PubMed
    1. Frazer, D. M. & Anderson, G. J. (2003) Blood Cells Mol. Dis. 30, 288-297. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources