BMP Signaling Modulates Hepcidin Expression in Zebrafish Embryos Independent of Hemojuvelin

Yann Gibert,Victoria J Lattanzi,Matthias Hammerschmidt,Lea Vedder,Paula G Fraenkel,Herbert Y Lin,Aileen W Zhen,Frédéric Brunet,Jodie L Babitt,Sarah A Faasse,Vincent Laudet

doi:10.1371/journal.pone.0014553

Yann Gibert, Victoria J Lattanzi + Show 9 more

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https://doi.org/10.1371/journal.pone.0014553

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Journal: PloS one	Publication Date: Jan 21, 2011
Citations: 72	License type: CC BY 4.0

Affiliation: University of Cologne, Massachusetts General Hospital

Abstract

Hemojuvelin (Hjv), a member of the repulsive-guidance molecule (RGM) family, upregulates transcription of the iron regulatory hormone hepcidin by activating the bone morphogenetic protein (BMP) signaling pathway in mammalian cells. Mammalian models have identified furin, neogenin, and matriptase-2 as modifiers of Hjv's function. Using the zebrafish model, we evaluated the effects of hjv and its interacting proteins on hepcidin expression during embryonic development. We found that hjv is strongly expressed in the notochord and somites of the zebrafish embryo and that morpholino knockdown of hjv impaired the development of these structures. Knockdown of hjv or other hjv-related genes, including zebrafish orthologs of furin or neogenin, however, failed to decrease hepcidin expression relative to liver size. In contrast, overexpression of bmp2b or knockdown of matriptase-2 enhanced the intensity and extent of hepcidin expression in zebrafish embryos, but this occurred in an hjv-independent manner. Furthermore, we demonstrated that zebrafish hjv can activate the human hepcidin promoter and enhance BMP responsive gene expression in vitro, but is expressed at low levels in the zebrafish embryonic liver. Taken together, these data support an alternative mechanism for hepcidin regulation during zebrafish embryonic development, which is independent of hjv.

Highlights

Bone morphogenetic proteins (BMPs), originally identified for their ability to induce bone differentiation, are members of the TGF-b superfamily
We demonstrate that activation of the BMP pathway increased the intensity and extent of hepatic hepcidin expression during embryonic development, and suppression of BMP signaling by the chemical inhibitor dorsomorphin eliminated hepcidin expression
Quantitative real-time RT-PCR revealed a 2000-fold increase in bmp2b expression in the transgenic embryos two hours after heat shock compared to nontransgenic embryos subjected to heat shock (486663556 vs 1.1260.184, p,0.001) or 100-fold increase compared to transgenic embryos not subjected to heat shock (486663556 vs 44.85614.85, p,0.01)

Summary

Introduction

Bone morphogenetic proteins (BMPs), originally identified for their ability to induce bone differentiation, are members of the TGF-b superfamily. Binding of a BMP molecule to a BMP receptor complex results in phosphorylation of Smad , and 8. These proteins form hetero-oligomers with Smad, translocate to the nucleus, and activate transcription of a target gene (reviewed in [1] and [2]). Hemojuvelin (Hjv, known as RGMc), a protein belonging to the repulsive-guidance molecule (RGM) family, was originally identified as the affected gene in several families with severe early onset iron overload and reduced levels of hepcidin.[3] Hepcidin, a transcriptionally regulated peptide hormone, is produced in the liver[4] and modulates intestinal iron absorption and macrophage iron release[5,6,7]. Subsequent studies revealed that membrane-bound Hjv binds Neogenin[8], increases intracellular iron accumulation[8], and enhances BMP-mediated induction of hepcidin expression in vitro[9], while Neogenin deficiency decreases hepatic hjv protein levels, impairs BMP signaling, and reduces hepcidin expression in postnatal mice.[10]

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