Hepcidin suppression and defective iron recycling account for dysregulation of iron homeostasis in heme oxygenase-1 deficiency

Department of Clinical Chemistry, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Journal of Cellular and Molecular Medicine (Impact Factor: 4.01). 10/2008; 13(9B):3091-102. DOI: 10.1111/j.1582-4934.2008.00494.x
Source: PubMed


Heme oxygenase-1 (HO-1) contribution to iron homeostasis has been postulated, because it facilitates iron recycling by liberating iron mostly from heme catabolism. This enzyme also appears to be responsible for the resolution of inflammatory conditions. In a patient with HO-1 deficiency, inflammation and dysregulation of body iron homeostasis, including anemia and liver and kidney hemosiderosis, are evidenced. Here we postulated that HO-1 is critical in the regulation of ferroportin, the major cellular iron exporter, and hepcidin, the key regulator of iron homeostasis central in the pathogenesis of anemia of inflammation. Our current experiments in human THP-1 monocytic cells indicate a HO-1-induced iron-mediated surface-ferroportin expression, consistent with the role of HO-1 in iron recycling. Surprisingly, we observed low hepcidin levels in the HO-1-deficient patient, despite the presence of inflammation and hemosiderosis, both inducers of hepcidin. Instead, we observed highly increased soluble transferrin receptor levels. This suggests that the decreased hepcidin levels in HO-1 deficiency reflect the increased need for iron in the bone marrow due to the anaemia. Using human hepatoma cells, we demonstrate that HO-activity did not have a direct modulating effect on expression of HAMP, the gene that encodes for hepcidin. Therefore, we argue that the decreased iron recycling may, in part, have contributed to the low hepcidin levels. These findings indicate that dysregulation of iron homeostasis in HO-1 deficiency is the result of both defective iron recycling and erythroid activity-associated inhibition of hepcidin expression. This study therefore shows a crucial role for HO-1 in maintaining body iron balance.

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    • "In this case, iron deficiency-induced AtHO1 may facilitate the catabolism of heme with the concomitant recycling of iron in tissues, making more free iron available to iron-limited cells. This could be supported not only by our observation that more water-soluble iron was available to plants (Fig. 4C), but also by recent animal studies showing that HO1-mediated degradation of heme is necessary for iron reutilization in counteracting stress conditions in certain cell types (Poss and Tonegawa 1997, Kartikasari et al. 2009). Another possible pathway of heme Fig. 6 Heme accumulation in seedlings (A) and generation of endogenous CO in shoots (B) and roots (C) of all 35S:HO1 and 35S:AntiHO1 transgenic lines under iron deficiency. "
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    • "Heme oxygenase-1 deficiency in humans appears to be an extremely rare condition with only two live births reported [33, 34]. Both patients presented with severe anemia [33, 34]. "
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