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1 Hopital Notre-Dame, CR-CHUM, Montreal, Canada
2 Hopital Saint-Luc, CR-CHUM, Montreal, Canada
* To whom correspondence should be addressed. E-mail: manuela.santos{at}umontreal.ca.
Hepcidin is a negative regulator of iron absorption produced mainly by the liver in response to changes in iron stores and inflammation, and its levels have been shown to regulate the intestinal basolateral iron transporter ferroportin1 (Fp1). Hereditary hemochromatosis patients and Hfe-deficient mice show inappropriate expression of hepcidin, but in apparent contradiction, still retain the ability to regulate iron absorption in response to alterations of iron metabolism. To further understand the molecular relationships between Hfe, hepcidin and Fp1, we investigated hepcidin and Fp1 regulation in Hfe-deficient mice (Hfe-/- and
2m-/-) in response to iron-deprivation, iron-loading and acute inflammation. We found that while basal hepcidin levels were manifestly dependent on the presence of Hfe and on the mouse background, all Hfe-deficient mice were still able to regulate hepcidin in situations of altered iron homeostasis. In the liver Fp1 was modulated in opposite directions by iron and lipopolysaccharide (LPS), and its regulation in Hfe-deficient mice was similar to that observed in wild-type mice. In addition, we found that iron-deprived mice were able to mount a robust response after LPS challenge, and that toll-like receptor 4 (Tlr4)-deficient mice fail to regulate hepcidin expression in response to LPS.
In conclusion, these results suggest that while Hfe is necessary for the establishment of hepcidin basal levels, it is dispensable for hepcidin regulation through both the iron-sensing and inflammatory pathways, and hepatic Fp1 regulation is largely independent of hepcidin and Hfe. The inflammatory pathway overrides the iron-sensing pathway and is Tlr4-dependent.
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