Many physiological perturbations can cause anemia. In cancer patients, activation of the immune system leads to the production of proinflammatory cytokines including tumor necrosis factor alpha (TNF), that have been shown to inhibit red-cell production via poorly understood mechanisms. Treatment of anemia by human recombinant erythropoietin (EPO) is strongly suspected to induce tumor growth.This study focuses on the mechanisms involved in TNF-mediated inhibition of erythropoiesis. CD34 + hematopoietic stem/progenitor cells (HSPC) were isolated from human cord blood. Erythropoiesis was achieved in vitro by stimulating cells with EPO. We show that TNF clearly affected erythroid development, as assessed by May-Grünwald/Giemsa staining, flow cytometry analysis and fluorescent microscopy. The amount of hemoglobinproducing cells as well as the expression of GATA-1 target erythro-specific genes (EPO receptor, glycophorin A and globins) was found decreased after TNF treatment of HSPC. In correlation, TNF induced the expression of the transcription factors GATA-2 and PU.1, described as inhibitors of erythropoiesis. In this regard, TNF promoted the formation of the GATA-1/PU.1 complex that has been reported to block the transcriptional activity of GATA-1. Our results clearly demonstrate that TNF prevents EPO-mediated erythropoiesis of HSPC as an early event, by directly affecting erythroid cell development.Keywords: anemia; inflammation; TNF; GATA-1; GATA-2; PU.1Page 3 of 38 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 -3 -
IntroductionThe majority of tumors are largely infiltrated by inflammatory cells, such as myelomonocytes and macrophages [1]. In response to the inflammatory environment, these cells produce inflammatory mediators including chemokines and cytokines. These mediators are tightly associated with cancer progression in combination with genetic alterations [2]. One of them, the Tumor Necrosis Factor alpha (TNF), is widely found in the inflammationassociated cancer microenvironment [3][4][5][6]. Interestingly, because TNF is commonly present in cancer and inflammatory diseases, it has been implicated in cancer-and inflammationrelated anemia. Indeed, patients suffering from cancer and chronic inflammation are often anemic [7]. Moreover, in vitro and in vivo studies have led to the conclusion that TNF inhibits hematopoietic progenitors from undergoing erythroid differentiation [8][9][10][11][12][13][14][15]. Anti-TNF treatment is effectively used for the treatment of chronic inflammatory diseases, but leads to increased risk of infection [16,17]. Despite the beneficial effects of anti-TNF, this treatment may promote different types of cancers [18,19].Several events may trigger anemia, including iron deficiency, hemolysis and hemorrhage. In non-hematopo...