The Hepcidin-Anemia Axis: Pathogenesis of Anemia in Chronic Kidney Disease.

The pathogenesis of anemia in chronic kidney disease (CKD) could be multifactorial. In recent animal studies, hepcidin knockout (KO) mice with adenine-induced CKD did not exhibit anemia and iron deficiency. Hepcidin has emerged as a major player in the development of anemia in CKD. We suspected that erythropoietin (EPO) deficiency may not be the mainstay of anemia in CKD, although relative EPO deficiency could contribute to the failure to increase hemoglobin (Hb) levels. Some factors may interfere with the differentiation of erythroids.Based on previous flow cytometric analysis, the differentiation and maturation of bone marrow erythroid precursors were compared between 2 mouse models of anemia, namely, EPO-KO mice and adenine-induced CKD mice. EPO-KO mice exhibited greater than 50% reduction in the CD71-low/Ter119-high population, which represents a mature erythroid stage in the bone marrow. In contrast, these mice exhibited no reduction in the CD71-high/Ter119-low and CD71-high/Ter119-high cell populations, which represent an early erythroid stage. However, in CKD mice, the percentages of CD71-high/Ter119-low and CD71-high/Ter119-high erythroid cells, which correspond to proerythroblasts and basophilic erythroblasts, respectively, were decreased in bone marrow. Thus, the CKD mice exhibited a decrease in the number of cells expressing transferrin receptor 1 (TfR1) or early stage erythroblasts, which was completely different from the results obtained for EPO-KO mice. Thus, in CKD, decreased expression of TfR1 in erythroblasts as well as increased hepcidin levels in circulation may hamper erythroblast differentiation by decreasing the iron supply, as iron is an indispensable component of erythroblast differentiation. We conclude that deregulated iron metabolism could be the principal cause of anemia in CKD, impeding the differentiation of erythroblasts. We propose that the "hepcidin-anemia axis" is involved in the pathogenesis of CKD-associated anemia. For the treatment of anemia in CKD, declining hepcidin levels are essential for efficient erythropoiesis. Key Messages: These findings have led us to target the hepcidin-anemia axis as a new treatment strategy for anemia in CKD, including via newly developed erythropoiesis-stimulating agent and hypoxia inducible factor stabilizers.