In anemia of multiple myeloma, hepcidin is induced by increased bone morphogenetic protein 2

Abstract

Hepcidin is the principal iron-regulatory hormone and a pathogenic factor in anemia of inflammation. Patients with multiple myeloma (MM) frequently present with anemia. We showed that MM patients had increased serum hepcidin, which inversely correlated with hemoglobin, suggesting that hepcidin contributes to MMrelated anemia. Searching for hepcidininducing cytokines in MM, we quantified the stimulation of hepcidin promoterluciferase activity in HuH7 cells by MM sera. MM sera activated the hepcidin promoter significantly more than did normal sera. We then examined the role of bone morphogenetic proteins (BMPs) and interleukin-6 (IL-6), the major transcriptional regulators of hepcidin. Mutations in both BMP-responsive elements abrogated the activation dramatically, while mutations in the IL-6-responsive signal transducer and activator of transcription 3-binding site (STAT3-BS) had only a minor effect. Cotreatment with anti-BMP-2/4 or noggin-Fc blocked the promoter induction with all MM sera, anti-IL-6 blocked it with a minority of sera, whereas anti-BMP-4, -6, or -9 antibodies had no effect. BMP-2-immunodepleted MM sera had decreased promoter stimulatory capacity, and BMP-2 concentrations in MM sera were significantly higher than in normal sera. Our results demonstrate that BMP-2 is a major mediator of the hepcidin stimulatory activity of MM sera. (Blood. 2010;116(18):3635-3644) IntroductionMultiple myeloma (MM) is a malignant plasma cell disorder that accounts for approximately 10% of all hematologic cancers. 1 The disease is characterized by monoclonal proliferation of plasma cells together with overproduction of a monoclonal antibody, 2 often accompanied by anemia, hypercalcemia, renal insufficiency, or bone lesions. 3 Approximately 97% of MM patients develop anemia during the course of their illness, and 70% are anemic at diagnosis. The anemia is usually normocytic/normochromic, 4 serum-iron levels are normal to low, serum ferritin is high, and hemosiderin is prominent in bone marrow macrophages. 5 This suggests than iron release from reticuloendothelial macrophages is impaired, consistent with anemia of inflammation. 6 The main mediator of anemia of inflammation is the ironregulatory hormone, hepcidin. Hepcidin is produced by hepatocytes and acts on the iron exporter, ferroportin. Binding of hepcidin to ferroportin induces the internalization and degradation of ferroportin, thereby preventing cellular iron efflux and causing retention of iron, mainly inside enterocytes, macrophages, and hepatocytes. 7 Pathologic induction of hepcidin by inflammation causes hypoferremia, restricting the iron supply for erythropoiesis and, eventually, causing anemia. The interleukin-6 (IL-6)-hepcidin axis was shown to be important for inflammation-related hypoferremia. 8 However, in chronic inflammation, IL-6-independent pathways may also induce hepcidin mRNA. 9 Recently, 2 studies described the involvement of hepcidin in anemia of MM in humans. We reported that patients with stage III MM (n ϭ 44) at diagnosis had higher urinar...

The role of bone morphogenetic proteins in myeloma cell survival

“…[33] Another study found more BMP-2 in sera from multiple myeloma patients than in normal sera, but still at low levels (~ 60 pg/mL). [38] We found increased levels of BMP-9 in myeloma sera compared to normal sera. [35] However, the total BMP-activity in the bone marrow niche of multiple myeloma patients, as measured by in situ SMAD1/5/8-phosphorylation, is not known.…”

“…[84] BMP-2, -4, -6, and -9 all stimulated HAMP promoter activity in vitro whereas TGF-beta did not. [38] Thus, the conclusion drawn from this work was that BMP-2 was the main mediator of hepcidin induction in sera from myeloma patients. Targeting BMP-2 or other BMPs with the intention to treat anemia of multiple myeloma may not be a good approach, considering that there is substantial redundancy in the system regulating hepcidin.…”

Regulation of Iron Metabolism by Hepcidin under Conditions of Inflammation

“…Mice lacking HFE (64) or both HFE and TFR2 (65) are able to mount an appropriate immune response to LPS, but do not elevate hepcidin production nor develop hypoferremia. Furthermore, concomitant stimulation of both the BMP/SMAD and the JAK1/2-STAT3 pathways in rodents causes, at minimum, additive, and also in some experiments synergistic, effects upon up-regulation of hepcidin (59,66,67). In toto, this research suggests that the BMP/SMAD and JAK1/2-STAT3 signaling pathways impinge on one other, leading to increased hepcidin expression under conditions of infection or inflammation.…”

“…Hepcidin is also greatly increased in multiple myeloma, a plasma cell malignancy that is thought to account for a large percentage of hematologic cancers (85). Hepcidin induction in this cancer requires BMP2, another BMP/SMAD pathway ligand, and the inflammatory cytokine IL-6 (67). Furthermore, recent work demonstrated that hepcidin is elevated in breast cancer patients and that diminished tumor expression of ferroportin promotes breast cancer growth (86,87).…”

Liver Congestion in Heart Failure Contributes to Inappropriately Increased Serum Hepcidin despite Anemia

“…2002; Weiss and Goodnough 2005;Maes et al 2010), we analyzed serum hepcidin levels in HF and anemia patients without chronic disease. In this series of HF patients without chronic disease, serum hepcidin levels were higher in LC patients than those in patients without LC; namely, hepcidin levels of LC patients did not decrease despite low Hb levels.…”