A mouse model of anemia of inflammation: complex pathogenesis with partial dependence on hepcidin

Abstract

• An injection of heat-killedBrucella abortus in mice causes prolonged anemia with features similar to human anemia of inflammation.• Ablation of hepcidin ameliorates anemia of inflammation in this model and allows faster recovery.Anemia is a common complication of infections and inflammatory diseases, but the few mouse models of this condition are not well characterized. We analyzed in detail the pathogenesis of anemia induced by an injection of heat-killed Brucella abortus and examined the contribution of hepcidin by comparing wild-type (WT) to iron-depleted hepcidin-1 knockout (Hamp-KO) mice. B abortus-treated WT mice developed severe anemia with a hemoglobin nadir at 14 days and partial recovery by 28 days. After an early increase in inflammatory markers and hepcidin, WT mice manifested hypoferremia, despite iron accumulation in the liver. Erythropoiesis was suppressed between days 1 and 7, and erythrocyte destruction was increased as evidenced by schistocytes on blood smears and shortened red blood cell lifespan. Erythropoietic recovery began after 14 days but was iron restricted. In B abortus-treated Hamp-KO compared with WT mice, anemia was milder, not iron restricted, and had a faster recovery. Similarly to severe human anemia of inflammation, the B abortus model shows multifactorial pathogenesis of inflammatory anemia including iron restriction from increased hepcidin, transient suppression of erythropoiesis, and shortened erythrocyte lifespan. Ablation of hepcidin relieves iron restriction and improves the anemia. (Blood. 2014;123(8):1129-1136 Introduction Anemia of inflammation (AI) is a feature of a wide spectrum of inflammatory disorders, including connective tissue disease, infections, certain malignancies, and chronic kidney disease.1 AI is typically a normocytic normochromic anemia with a shortened erythrocyte lifespan and suppressed erythropoiesis, despite adequate levels of circulating erythropoietin.2 Perhaps the most consistent feature of AI is a derangement of systemic iron homeostasis characterized by hypoferremia with intact iron stores 1 and decreased availability of iron for erythrocyte production.Hepcidin, a 25-amino acid peptide hormone produced primarily by hepatocytes, 3 is the principal regulator of iron homeostasis in health and during inflammation. 4 Excessive production of this hormone causes iron sequestration in macrophages and hypoferremia, as was shown in transgenic mice with hepcidin overexpression 5 and in the human genetic syndrome of hepcidin excess, iron-refractory iron-deficiency anemia due to mutations in matriptase-2/TMPRSS6. 6 Hepcidin acts by binding to ferroportin, the sole known cellular iron exporter, displayed on the surface of macrophages, hepatocytes, and the basolateral membranes of enterocytes. Hepcidin binding to ferroportin causes ferroportin endocytosis and degradation.7 During inflammation or infection, hepcidin is strongly induced, largely by interleukin 6 (IL-6) 8 via the Janus kinase-signal transducer and activator of transcription pathway.9-11 The ex...

Regulation of Iron Metabolism by Hepcidin under Conditions of Inflammation

“…Accordingly, new rodent models of cancer (94) and infection (82,83) have been recently generated. These model systems will be essential for dissecting the more intricate interactions between hepcidin regulation and changes in iron homeostasis induced by inflammation or infection.…”

“…Significantly, ERFE also appears to play a role in the recovery of organisms from the anemia of inflammation (81). Heat-killed Brucella abortus (HKBA) is known to induce an anemia of inflammation response in rodents (82,83). Mice lacking ERFE have both a more severe and a more prolonged anemia, and more greatly elevated hepcidin expression, as compared with wild type animals upon exposure to HKBA.…”

Erythroferrone contributes to recovery from anemia of inflammation

“…The mouse model of systemic inflammation induced by heat-killed Brucella abortus (BA) allows the study of recovery from inflammation-induced anemia in mice. [8][9][10][11] Mice exhibit a transient but severe anemia and elevated EPO levels 14 days after injection of BA followed by the suppression of hepcidin and partial recovery from anemia by 28 days. Wild-type (WT) mice injected with BA develop a very rapid inflammatory response associated with increased hepcidin production 6 hours after BA administration and present decreased serum iron concentration and transferrin saturation, typical of iron-restricted anemia.…”

“…The role of hepcidin in AI is confirmed by the milder anemia and the faster recovery of mice lacking interleukin-6 or hepcidin compared with their WT counterparts. 10,11 We recently described the new erythroid factor erythroferrone (ERFE), which is responsible for early hepcidin suppression during erythropoietic activity stimulated by endogenous or exogenous EPO. 12 We showed that Erfe-deficient mice fail to suppress hepcidin after erythropoietic stimulation resulting in a significant delay in the recovery from hemorrhage-induced anemia.…”

“…Mice were maintained on a standard chow (270 ppm iron; Harlan Teklad, Indianapolis, IN) until the age of 6 weeks and were then switched to an adequate iron diet (50 ppm iron; Harlan Teklad) for 10 days prior to injection of BA or saline as previously described. 10 To induce AI, animals were injected intraperitoneally with 2.5 3 10 8 particles per mouse of a commercial heat-killed BA preparation (strain 1119-3; US Department of Agriculture, Animal and Plant Health Inspection Service, National Veterinary Services Laboratories). Control mice were injected intraperitoneally with normal saline.…”