PF506 EVIDENCE FOR AN ALTERNATIVE MECHANISM SUPPRESSING HEPCIDIN DURING THE RECOVERY FROM HEMORRHAGE‐INDUCED ANEMIA

Background: Iron is an essential functional component of hemoglobin, with red cells containing two‐thirds of the total body iron. The liver‐produced hormone hepcidin controls the major flows of iron into plasma: absorption of dietary iron in intestine, recycling of iron by macrophages, which phagocytose old erythrocytes and other cells, and mobilization of stored iron from hepatocytes. When iron supply to the marrow comes under particular strain during stress erythropoiesis (e.g. after hemorrhage or hemolysis), the erythroid hormone erythroferrone (ERFE) suppresses hepcidin to intensify iron absorption and its release from stores to meet the requirements for red blood cells synthesis. Although Erfe ‐deficient mice fail to suppress hepcidin during the first 24 h following hemorrhage, they manage to recover from anemia with a few days delay suggesting that the absence of ERFE can be compensated. Aims: We therefore decided to study the kinetic of hepcidin during the recovery from anemia induced by bleeding in Erfe ‐deficient mice. Methods: Six to eight week‐old C57BL/6 WT and Erfe ‐deficient mice were phlebotomized (500 μL) and analyzed 1, 2, 3, 4, 5 and 6 days after phlebotomy until recovery. To determine whether another erythroid regulator of hepcidin may exist, C57BL/6 WT and Erfe −/− mice were irradiated with a sub‐lethal dose of X‐rays (400 rad) to deplete the erythroid compartment and hepcidin levels were assessed 48 h after phlebotomy. Results: Liver hepcidin mRNA expression was suppressed 5‐fold one to five days after phlebotomy in WT mice. In contrast with the sustained inhibition of hepcidin, serum ERFE concentration progressively decreased after 24 hours to reach its baseline at day 4. Interestingly, although hepcidin levels were unchanged after 24 hours, Erfe ‐deficient exhibited significantly reduced hepcidin levels after 48 hours. Hepcidin mRNA and protein levels were comparable to those of WT mice 2 to 5 days after phlebotomy. The repression of hepcidin occurred without any change in phosphorylation of the effectors Smad1/5/8 and in hepatic expression of the BMP/SMAD target genes ( Id1 , Smad7 ) nor in the mRNA expression of the proposed negative regulators of hepcidin ( Gdf15 , Twsg1 and Gdf11 ) in the spleen and the bone marrow of phlebotomized mice compared to control mice. Moreover, disruption of the erythroid compartment prevented the suppression of hepcidin in WT and Erfe ‐deficient mice. Analysis of Glycophorin A expression indicated that extramedullary erythropoiesis was maximally induced in the spleen and the liver 48–72 h after phlebotomy and spleen Glycophorin A expression inversely correlated with hepatic hepcidin levels. We therefore hypothesized that the unknown regulator could originate from the spleen or the liver during extramedullary erythropoiesis. However, hepcidin was appropriately suppressed 48 h after phlebotomy in splenectomized animals. We are currently analyzing the expression profiles of marrows and livers of phlebotomized Erfe‐deficient mice by microarray. Summary/Conclusion: A second yet unknown erythroid regulator regulates hepcidin during stress erythropoiesis. This abstract was submitted at the 2018 annual ASH meeting. Additional data include further evidence that an additional erythroid regulator exist, the analysis of splenectomized animals and the transcriptomic profiles of livers and marrows of phlebotomized Erfe−/− mice.