Hereditary hemochromatosis is a prevalent genetic disorder of iron hyperabsorption leading to hyperferremia, tissue iron deposition and complications including cirrhosis, hepatocarcinoma, cardiomyopathy and diabetes. Most individuals affected with hereditary hemochromatosis are homozygous with respect to a missense mutation that disrupts the conformation of HFE, an atypical HLA class I molecule (ref. 1; OMIM 235200). Mice lacking Hfe or producing a C282Y mutant Hfe protein develop hyperferremia and have high hepatic iron levels. In both humans and mice, hereditary hemochromatosis is associated with a paucity of iron in reticuloendothelial cells. It has been suggested that HFE modulates uptake of transferrin-bound iron by undifferentiated intestinal crypt cells, thereby programming the absorptive capacity of enterocytes derived from these cells; however, this model is unproven and controversial. Hepcidin, a peptide hormone (HAMP; OMIM 606464), seems to act in the same regulatory pathway as HFE. Although expression of mouse Hamp is normally greater during iron overload, Hfe-/- mice have inappropriately low expression of Hamp. We crossed Hfe-/- mice with transgenic mice overexpressing Hamp and found that Hamp inhibited the iron accumulation normally observed in the Hfe-/- mice. This argues against the crypt programming model and suggests that failure of Hamp induction contributes to the pathogenesis of hemochromatosis, providing a rationale for the use of HAMP in the treatment of this disease.

We previously reported that mice made deficient for the transcriptional factor USF2 fail to express hepcidin 1 and hepcidin 2 genes as a consequence of targeted disruption of the Usf2 gene lying just upstream in the locus. These mice developed an iron overload phenotype with excess iron deposition in parenchymal cells and decreased reticuloendothelial iron. At that time, although the role of USF2 was still confounding, we proposed for the first time the role of hepcidin as a negative regulator of iron absorption and iron release from macrophages. Accordingly, we subsequently demonstrated that hyperexpression of hepcidin 1, but not hepcidin 2, resulted in a profound hyposideremic anemia. To analyze the consequences of hepcidin 1 deletion on iron metabolism without any disturbance due to USF2 deficiency, we disrupted the hepcidin 1 gene by targeting almost all the coding region. Confirming our prior results, Hepc1 ؊/؊ mice developed early and severe multivisceral iron overload, with sparing of the spleen macrophages, and demonstrated increased serum iron and ferritin levels as compared with their con-

Evidence is accumulating that hepcidin, a liver regulatory peptide, could be the common pathogenetic denominator of all forms of iron overload syndromes including HFE-related hemochromatosis, the most prevalent genetic disorder characterized by inappropriate iron absorption. To understand the mechanisms whereby hepcidin controls iron homeostasis in vivo, we have analyzed the level of iron-related proteins by Western blot and immunohistochemistry in hepcidin-deficient mice, a mouse model of severe hemochromatosis. These mice showed important increased levels of duodenal cytochrome b (Dcytb), divalent metal transporter 1 (DMT1), and ferroportin compared with control mice. Interestingly, the level of ferroportin was coordinately up-regulated in the duodenum, the spleen, and the liver (predominantly in the Kupffer cells). Finally, we also evidenced a decrease of ceruloplasmin in the liver of hepcidin-deficient mice. We hypothesized that the deregulation of these proteins might be central in the pathogenesis of iron overload, providing key therapeutic targets for iron disorders. (Blood. 2005;105:4861-4864)