scholarly journals Ineffective Erythropoiesis inβ-Thalassemia

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Jean-Antoine Ribeil ◽  
Jean-Benoit Arlet ◽  
Michael Dussiot ◽  
Ivan Cruz Moura ◽  
Geneviève Courtois ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Premature Death ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Ineffective Erythropoiesis ◽  
Molecular Defects ◽  
Erythroid Precursors ◽  
Underlying Mechanisms

In humans,β-thalassemia dyserythropoiesis is characterized by expansion of early erythroid precursors and erythroid progenitors and then ineffective erythropoiesis. This ineffective erythropoiesis is defined as a suboptimal production of mature erythrocytes originating from a proliferating pool of immature erythroblasts. It is characterized by (1) accelerated erythroid differentiation, (2) maturation blockade at the polychromatophilic stage, and (3) death of erythroid precursors. Despite extensive knowledge of molecular defects causingβ-thalassemia, less is known about the mechanisms responsible for ineffective erythropoiesis. In this paper, we will focus on the underlying mechanisms leading to premature death of thalassemic erythroid precursors in the bone marrow.

scholarly journals Erythropoiesis in ha/ha and sph/sph mice, mutants which produce spectrin-deficient erythrocytes

Blood ◽  
1982 ◽  
Vol 59 (3) ◽  
pp. 646-651 ◽  
Author(s):  
D Brookoff ◽  
L Maggio-Price ◽  
S Bernstein ◽  
L Weiss
Keyword(s):  
Bone Marrow ◽  
Membrane Protein ◽  
Stromal Cells ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Plasma Clot ◽  
Dark Cells ◽  
Erythroid Precursors ◽  
The Status ◽  
Deficient Mice

Abstract In order to characterize chronically accelerated erythropoiesis, we studied the ultrastructure of bone marrow and spleen of ha/ha and sph/sph mice, two mutants with profound hemolytic anemia secondary to deficiency of the erythrocyte membrane protein spectrin. The marrows and spleens of both varieties were extremely erythropoietic and were without histological abnormalities directly related to spectrin deficiency. Erythropoiesis was consistently associated with distinctive, dark branched cells which constituted large proportions of the stroma of the mutant spleens and marrow. These dark cells were not present in untreated and acutely bled controls. Plasma clot assays for erythroid progenitors revealed that CFU-E concentrations in the mutant marrows were significantly increased over those in untreated controls while BFU-E concentrations were approximately half. In addition, mutant CFU-E often gave rise to abnormal appearing colonies. Spectrin, though crucial to erythrocyte function is probably not important to the process of erythroid differentiation and maturation. The status of erythroid precursors in the marrows of the spectrin deficient mice is similar to that of mice subjected to an acute bleed. The divergent changes in CFU-E and BFU-E may indicate that these two cells play different roles in accelerated erythropoiesis. The dark cells that we describe are similar to stromal cells observed in models of the early stages of erythropoiesis.

RAP-536 Promotes Terminal Erythroid Differentiation and Reduces Anemia in a Murine Model of Myelodysplastic Syndromes

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 3796-3796 ◽  
Author(s):  
Rajasekhar NVS Suragani ◽  
Robert Li ◽  
Dianne Sako ◽  
Asya Grinberg ◽  
R. Scott Pearsall ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Bone Marrow ◽  
Erythroid Differentiation ◽  
Severe Anemia ◽  
Ineffective Erythropoiesis ◽  
Employment Equity ◽  
Erythroid Hyperplasia ◽  
Erythroid Precursors ◽  
Equity Ownership ◽  
Terminal Erythroid Differentiation

Abstract Abstract 3796 Myelodysplastic syndromes (MDS) are a group of hematopoietic stem cell disorders characterized by peripheral blood cytopenias such as anemia, neutropenia or thrombocytopenia. Ineffective erythropoiesis due to increased proliferation and abortive maturation of precursors leads to severe anemia, the most common cytopenia observed in MDS syndromes. Despite elevated erythropoietin (EPO) and erythroid hyperplasia, MDS patients are often given recombinant EPO therapy to stimulate erythropoiesis. However, only a small proportion of patients respond to EPO therapy. Frequent blood transfusions as supportive care result in iron overloading and recently iron overloading is also linked to enhanced progression to AML. Therefore, alternative therapies are necessary to treat anemia in MDS patients. Signaling by members of the TGFβ superfamily are known regulators of erythropoiesis. We developed ACE-536, a ligand trap consisting of a modified activin receptor Type IIB extracellular domain linked to a human Fc domain. In vitro assays revealed that ACE-536 inhibits smad 2/3 ligands of the signaling pathway but not smad 1/5/8 ligands. Dose dependent studies using ACE-536 in mice, rats and monkeys revealed that ACE-536 treatment resulted in increased red blood parameters but did not affect other cell types. These data suggests that ACE-536 inhibits smad 2/3 phosphorylation modulating the expression of downstream genes involved in erythroid development pathway. BFU-E and CFU-E colony formation assays from bone marrow and spleen in mice following ACE-536 treatment revealed that ACE-536 did not affect the proliferation stages of erythropoiesis. In mice, terminal erythroid differentiation analysis by flow cytometry at 72hrs following RAP-536 (10mg/kg) treatment demonstrated decreased basophilic and increased ortho- and poly-chromatophilic erythroblasts and reticulocytes compared to VEH treatment. Cell cycle analysis of bone marrow and splenic erythroblasts counterstained with BrdU and 7-AAD after RAP-536 (10mg/kg, for 24 hours) or VEH treatment to EPO pre-treated (1500 units/kg, for 40 hours) mice (N=5/group) revealed that EPO+RAP-536 treatment resulted in significant decrease in S-phase and increase in G1/G2-phases of cell cycle compared to EPO+VEH treatment. In addition, EPO+RAP-536 treatment resulted in a greater increase in RBC parameters than either of the treatments alone. Together, these results demonstrate that ACE-536 increases red blood cell formation by promoting maturation of late stage erythroblasts. We then investigated the effect of ACE-536 on anemia in NUP98-HOXD13 (NHD13) transgenic murine model of MDS. NHD13 mice develop anemia, neutropenia and lymphopenia, with normal or hyper cellular bone marrow. A Majority of the mice die by 14 months due to severe pancytopenia or progression to acute myeloid leukemia. In this study, mice were divided into three groups based on age. Early (∼4 months old), mid (∼8 months old) and late stage (∼10 months) groups were randomized and dosed with either RAP-536 at 10 mg/kg or VEH twice per week for 6–8 weeks. NHD13 mice in each group had severe anemia characterized by reduced RBC, Hemoglobin and HCT and compared to wild-type littermates prior to treatment. Treatment of RAP-536 for 6–8 weeks significantly increased RBC parameters and reversed anemia at all stages. Peripheral blood smear analysis revealed no indication of increased leukemic progression due to RAP-536 treatment. Cell differential and flow cytometric evaluation of erythroid precursors from bone marrow demonstrated decreased erythroid precursors and hyperplasia after RAP-536 treatment compared to vehicle treated control. Our data demonstrate that RAP-536 can increase hematology parameters by enhancing maturation of terminally differentiated red blood cells. We have shown RAP-536 corrects ineffective erythropoiesis, decreases erythroid hyperplasia and normalizes myeloid: erythroid ratios without enhanced progression to AML in a murine MDS model. Therefore ACE-536 may represent a novel treatment for anemia associated with MDS, particularly in patients that are refractory to EPO therapy. ACE-536 has completed Phase I clinical trials in healthy human volunteers and Phase II study in MDS patients is planned. Disclosures: Suragani: Acceleron Pharma Inc: Employment, Equity Ownership. Li:Acceleron Pharma Inc: Employment, Equity Ownership. Sako:Acceleron Pharma Inc: Employment, Equity Ownership. Grinberg:Acceleron Pharma Inc: Employment, Equity Ownership. Pearsall:Acceleron Pharma Inc: Employment, Equity Ownership. Kumar:Acceleron Pharma Inc: Employment, Equity Ownership.

Anemia and Ineffective Erythropoiesis Caused by Somatic RAS Mutation.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3419-3419
Author(s):  
Benjamin S. Braun ◽  
Jessica van Ziffle ◽  
Joehleen Gavin ◽  
David A. Tuveson ◽  
Tyler Jacks ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Fetal Liver ◽  
Intrinsic Property ◽  
Direct Consequence ◽  
Erythroid Differentiation ◽  
Myeloproliferative Disorders ◽  
Ras Signaling ◽  
Erythroid Progenitors ◽  
Ineffective Erythropoiesis ◽  
Oncogenic Ras

Abstract Ras proteins modulate cell fates by integrating extracellular stimuli and transducing signals that regulate proliferation, survival, and differentiation via downstream effector cascades. Somatic activating mutations in RAS oncogenes are found in approximately one third of cases of myelodysplastic syndrome (MDS), and are common in myeloproliferative disorders (MPDs) such as CMML and JMML that frequently have a dysplastic component. We have modeled these human diseases in the mouse using a conditional allele of oncogenic Kras, which is activated in mice bearing the inducible Mx1-Cre transgene by injection with polyinosinic-polycytidilic acid (pI-pC). Mice treated with pI-pC to induce K-rasG12D expression at 21 days of life develop not only myeloid proliferation, but also progressive anemia which is the likely cause of death with median survival 84 days after injection. Erythroid precursors are abundant in spleens of anemic mice, suggesting ineffective erythropoiesis. These features are highly reminiscent of human MDS, and suggest that anemia in MDS is a direct consequence of hyperactive RAS signaling. Further analysis reveals that although erythroblasts are absent from the bone marrow, earlier erythroid progenitors such as BFU-E and CFU-E are abundant in both bone marrow and spleens of anemic mice. However, despite hyperproliferation of primitive erythroid cells, there is a block in terminal erythroid differentiation. This is also seen in primary E14.5 fetal liver cells acutely induced to express K-rasG12Din vitro, and in wild type recipients of Mx1-Cre, KrasG12D bone marrow, demonstrating this to be a cell-intrinsic property of erythroid progenitors expressing oncogenic Ras. Together, these findings support a model in which RAS mutations in MDS both confer a proliferative advantage to a neoplastic clone as well as directly impede differentiation, resulting in ineffective erythropoiesis and anemia. The improved efficiency of differentiation observed in spleen relative to bone marrow also suggests that microenvironmental influences modify the cell-intrinsic effects of oncogenic Ras.

scholarly journals SFL 23.6: a monoclonal antibody reactive with CFU-E, erythroblasts, and erythrocytes

Blood ◽  
1985 ◽  
Vol 66 (3) ◽  
pp. 522-526 ◽  
Author(s):  
AD Gupta ◽  
MK Samoszuk ◽  
T Papayannopoulou ◽  
G Stamatoyannopoulos
Keyword(s):  
Monoclonal Antibody ◽  
Bone Marrow ◽  
Cell Sorting ◽  
Antigenic Determinant ◽  
Mononuclear Cells ◽  
Bone Marrow Cells ◽  
Fetal Liver ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Erythroid Precursors

Abstract A cytotoxic (IgG2b) monoclonal antibody (McAb) for a novel erythroid differentiation antigen was generated by hyperimmunizing young mice with mononuclear cells obtained from livers of 20- to 22-week-old fetuses. This McAb, designated SFL 23.6, shows an extremely well- defined reactivity with the cells of the erythroid lineage at all stages of maturation as evident from the labeling of morphologically identifiable erythroid precursors and of erythrocytes present in peripheral blood, bone marrow, and fetal liver, and from its reactivity with culture-derived erythroblasts. The nonerythroid cells present in these and other tissue preparations were not labeled by SFL 23.6. The erythroid lineage specificity of McAb SFL 23.6 was confirmed by a cell- sorting experiment in which 97% of the cells in the fluorescent fraction sorted from SFL 23.6-treated bone marrow cells were erythroid precursors at various stages of maturation. Complement-mediated cytotoxicity and progenitor cell-sorting experiments showed that most (greater than 90%) of the late erythroid progenitors (CFU-E) and only a small proportion of the early erythroid progenitors (BFU-E) express the antigenic determinant identified by SFL 23.6. The myeloid progenitors (CFU-GM) and multilineage progenitors (CFU-GEMM) were negative for the SFL 23.6 antigenic determinant. The antigen recognized by SFL 23.6 has not been determined as yet. Because of the pattern of its reactivity and its dependence on sialic acid residues, the possibility of its relationship to glycophoria A was entertained. However, previous work using antiglycophorin McAbs (R-10) has shown that this determinant is not expressed in CFU-E. Therefore, among the erythroid lineage-specific McAbs described thus far, SFL 23.6 is unique in its reactivity with CFU- E and the mature erythron. Reagents with such specificity may be useful in studies of erythroid differentiation and commitment.

scholarly journals SFL 23.6: a monoclonal antibody reactive with CFU-E, erythroblasts, and erythrocytes

Blood ◽  
1985 ◽  
Vol 66 (3) ◽  
pp. 522-526
Author(s):  
AD Gupta ◽  
MK Samoszuk ◽  
T Papayannopoulou ◽  
G Stamatoyannopoulos
Keyword(s):  
Monoclonal Antibody ◽  
Bone Marrow ◽  
Cell Sorting ◽  
Antigenic Determinant ◽  
Mononuclear Cells ◽  
Bone Marrow Cells ◽  
Fetal Liver ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Erythroid Precursors

A cytotoxic (IgG2b) monoclonal antibody (McAb) for a novel erythroid differentiation antigen was generated by hyperimmunizing young mice with mononuclear cells obtained from livers of 20- to 22-week-old fetuses. This McAb, designated SFL 23.6, shows an extremely well- defined reactivity with the cells of the erythroid lineage at all stages of maturation as evident from the labeling of morphologically identifiable erythroid precursors and of erythrocytes present in peripheral blood, bone marrow, and fetal liver, and from its reactivity with culture-derived erythroblasts. The nonerythroid cells present in these and other tissue preparations were not labeled by SFL 23.6. The erythroid lineage specificity of McAb SFL 23.6 was confirmed by a cell- sorting experiment in which 97% of the cells in the fluorescent fraction sorted from SFL 23.6-treated bone marrow cells were erythroid precursors at various stages of maturation. Complement-mediated cytotoxicity and progenitor cell-sorting experiments showed that most (greater than 90%) of the late erythroid progenitors (CFU-E) and only a small proportion of the early erythroid progenitors (BFU-E) express the antigenic determinant identified by SFL 23.6. The myeloid progenitors (CFU-GM) and multilineage progenitors (CFU-GEMM) were negative for the SFL 23.6 antigenic determinant. The antigen recognized by SFL 23.6 has not been determined as yet. Because of the pattern of its reactivity and its dependence on sialic acid residues, the possibility of its relationship to glycophoria A was entertained. However, previous work using antiglycophorin McAbs (R-10) has shown that this determinant is not expressed in CFU-E. Therefore, among the erythroid lineage-specific McAbs described thus far, SFL 23.6 is unique in its reactivity with CFU- E and the mature erythron. Reagents with such specificity may be useful in studies of erythroid differentiation and commitment.

scholarly journals Erythropoiesis in ha/ha and sph/sph mice, mutants which produce spectrin-deficient erythrocytes

Blood ◽  
1982 ◽  
Vol 59 (3) ◽  
pp. 646-651 ◽  
Author(s):  
D Brookoff ◽  
L Maggio-Price ◽  
S Bernstein ◽  
L Weiss
Keyword(s):  
Bone Marrow ◽  
Membrane Protein ◽  
Stromal Cells ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Plasma Clot ◽  
Dark Cells ◽  
Erythroid Precursors ◽  
The Status ◽  
Deficient Mice

In order to characterize chronically accelerated erythropoiesis, we studied the ultrastructure of bone marrow and spleen of ha/ha and sph/sph mice, two mutants with profound hemolytic anemia secondary to deficiency of the erythrocyte membrane protein spectrin. The marrows and spleens of both varieties were extremely erythropoietic and were without histological abnormalities directly related to spectrin deficiency. Erythropoiesis was consistently associated with distinctive, dark branched cells which constituted large proportions of the stroma of the mutant spleens and marrow. These dark cells were not present in untreated and acutely bled controls. Plasma clot assays for erythroid progenitors revealed that CFU-E concentrations in the mutant marrows were significantly increased over those in untreated controls while BFU-E concentrations were approximately half. In addition, mutant CFU-E often gave rise to abnormal appearing colonies. Spectrin, though crucial to erythrocyte function is probably not important to the process of erythroid differentiation and maturation. The status of erythroid precursors in the marrows of the spectrin deficient mice is similar to that of mice subjected to an acute bleed. The divergent changes in CFU-E and BFU-E may indicate that these two cells play different roles in accelerated erythropoiesis. The dark cells that we describe are similar to stromal cells observed in models of the early stages of erythropoiesis.

scholarly journals Comparative Proteome-Wide Analysis of Bone Marrow Microenvironment of β-Thalassemia/Hemoglobin E

Proteomes ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 8 ◽  
Author(s):  
Saranyoo Ponnikorn ◽  
Rungrawee Mongkolrob ◽  
Suwit Klongthalay ◽  
Sittiruk Roytrakul ◽  
Kitima Srisanga ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Bone Marrow ◽  
Clinical Symptoms ◽  
Premature Death ◽  
Ineffective Erythropoiesis ◽  
Western Blot Assay ◽  
Hemoglobin E ◽  
Hb E ◽  
Global Health Issue ◽  
Alpha Globin

β-thalassemia/Hb E is a global health issue, which is characterized by a range of clinical symptoms from a mild and asymptomatic anemia to severe disorders that require transfusions from infancy. Pathological mechanisms of the disease involve the excess of unmatched alpha globin and iron overload, leading to ineffective erythropoiesis and ultimately to the premature death of erythroid precursors in bone marrow (BM) and peripheral organs. However, it is unclear as to how BM microenvironment factors contribute to the defective erythropoiesis in β-thalassemia/Hb E patients. Here, we employed mass spectrometry-based comparative proteomics to analyze BM plasma that was collected from six β-thalassemia/Hb E patients and four healthy donors. We identified that the differentially expressed proteins are enriched in secretory or exosome-associated proteins, many of which have putative functions in the oxidative stress response. Using Western blot assay, we confirmed that atypical lipoprotein, Apolipoprotein D (APOD), belonging to the Lipocalin transporter superfamily, was significantly decreased in BM plasma of the tested pediatric β-thalassemia/Hb E patients. Our results highlight that the disease condition of ineffective erythropoiesis and oxidative stress found in BM microenvironment of β-thalassemia/Hb E patients is associated with the impaired expression of APOD protein.

scholarly journals Decreased PGC1β expression results in disrupted human erythroid differentiation, impaired hemoglobinization and cell cycle exit

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Taha Sen ◽  
Jun Chen ◽  
Sofie Singbrant
Keyword(s):  
Cell Cycle ◽  
Bone Marrow ◽  
Mitochondrial Function ◽  
Iron Homeostasis ◽  
Erythroid Differentiation ◽  
Refractory Anemia ◽  
Cell Cycle Exit ◽  
Erythroid Progenitors ◽  
Hematopoietic Stem ◽  
Terminal Erythroid Differentiation

AbstractProduction of red blood cells relies on proper mitochondrial function, both for their increased energy demands during differentiation and for proper heme and iron homeostasis. Mutations in genes regulating mitochondrial function have been reported in patients with anemia, yet their pathophysiological role often remains unclear. PGC1β is a critical coactivator of mitochondrial biogenesis, with increased expression during terminal erythroid differentiation. The role of PGC1β has however mainly been studied in skeletal muscle, adipose and hepatic tissues, and its function in erythropoiesis remains largely unknown. Here we show that perturbed PGC1β expression in human hematopoietic stem/progenitor cells from both bone marrow and cord blood results in impaired formation of early erythroid progenitors and delayed terminal erythroid differentiation in vitro, with accumulations of polychromatic erythroblasts, similar to MDS-related refractory anemia. Reduced levels of PGC1β resulted in deregulated expression of iron, heme and globin related genes in polychromatic erythroblasts, and reduced hemoglobin content in the more mature bone marrow derived reticulocytes. Furthermore, PGC1β knock-down resulted in disturbed cell cycle exit with accumulation of erythroblasts in S-phase and enhanced expression of G1-S regulating genes, with smaller reticulocytes as a result. Taken together, we demonstrate that PGC1β is directly involved in production of hemoglobin and regulation of G1-S transition and is ultimately required for proper terminal erythroid differentiation.

L-Carnitine and Apoptosis in Thalassemia Major Patients.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3767-3767
Author(s):  
Ali Taher ◽  
H. Seoud ◽  
A. Ibrahim ◽  
H. Gabre ◽  
I. Youssry Ibrahim ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Enzyme Immunoassay ◽  
Gel Electrophoresis ◽  
Large Scale ◽  
Early Stage ◽  
Thalassemia Major ◽  
Agarose Gel ◽  
Agarose Gel Electrophoresis ◽  
Erythroid Progenitors ◽  
Erythroid Precursors

Abstract Background and Objectives: Thalassemia major patients suffer from severe anemia due to intramedullary hemolysis of erythroid progenitors. Depending on the severity of their disease, thalassemic patients exhibit different patterns of apoptosis. In cases of β-thalassemia major, apoptosis appears to be greatly enhanced in the early-stage erythroid precursors in the bone marrow and it is considered to be the machinery via which ineffective erythropoiesis develops. L-Carnitine is a butyrate derivative found to strongly reduce apoptosis in different diseases. We investigated the effect of oral L-carnitine therapy on apoptosis in thalassemia major patients. Methods: eighteen Thalassemia major patients were included. Detection of apoptosis was done by Photometric enzyme immunoassay (Elisa) and agarose gel electrophoresis before and after 6 months oral therapy with L-Carnitine (50mg/kg/day). Results: The mean age was 12.2±6.6 years. All patients tolerated L-carnitine with no side effects. A significant decrease of apoptosis rates in the erythroid precursors in the bone marrow of studied cases was noted after therapy by. The enrichment factor measured by the photometric enzyme immunoassay dropped from 3.65±1.338 before therapy to 1.60±0.65 after therapy (p=0.005). A positive ladder pattern reflecting apoptosis on agarose gel electrophoresis was detected in 88.9% of cases prior to treatment (figure 1) versus 11.1% after therapy (figure 2) (p=0.006). Patients also had significant decrease in the frequency of transfusions and increase in the pre-transfusion hemoglobin levels after therapy. These results were found to significantly correlate with the reduction in apoptosis rates (p=0.006, r = 0.543 and p=0.027 &r = −0.7762 respectively). Conclusion: Apoptosis plays a major role in the underlying pathophysiology of anemia in thalassemic patients. L-Carnitine seems to be a good modulator of apoptotic processes in such patients leading to decreased rates of programmed erythroblast death and general improvement of the disease condition. Further large-scale studies are needed to evaluate the overall role of L-Carnitine in the management of these patients. Figure Figure

Erythroid Transcription Factor GATA-1 Binds and Represses PU.1 Gene – Candidate Mechanism Of Epigenetic Repression Of PU.1 and Inefficient Erythropoiesis In MDS

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1558-1558
Author(s):  
Pavel Burda ◽  
Nikola Curik ◽  
Nina Dusilkova ◽  
Giorgio L Papadopoulos ◽  
John Strouboulis ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Transcription Factors ◽  
High Risk ◽  
Cell Growth ◽  
Progenitor Cells ◽  
Cell Lines ◽  
Chromatin Structure ◽  
Binding Sites ◽  
Erythroid Differentiation ◽  
Ineffective Erythropoiesis

Abstract Introduction Myelodysplastic syndrome (MDS) is often manifested by anemia due to ineffective erythropoiesis. Upon transformation to MDS/AML the uniform population of leukemic blasts overgrow dysplastic bone marrow. Hematopoiesis is regulated by transcription factors GATA-1 and PU.1 that interact and mutually inhibit each other in progenitor cells to guide multilineage commitment and subsequent lineage differentiation. Expression of PU.1 is controlled by several transcription factors including PU.1 itself at distal URE enhancer. It has been well established that underexpression of PU.1 in progenitor cells leads to AML (Rosenbauer F et al. 2004). In addition, co-expression of PU.1 and GATA-1 in AML-erythroleukemia (EL) blasts prevents induction of differentiation programs regulated by these transcription factors. In our laboratory, we recently observed that MDS/AML erythroblasts display repressive histone modifications and methylation status of PU.1 gene that respond to 5-azacitidine leading to inhibited blast cell proliferation and stimulated myeloid differentiation (Curik N et al. 2012). Inhibition of transcriptional activity of PU.1 protein by GATA-1 has been reported (Nerlov C et al. 2000) however it is not known whether GATA-1 can inhibit PU.1 gene in human early erythroblasts directly. Hypothesis GATA-1 inhibits PU.1 levels directly and modulates its transcriptional outcome in early erythroblasts. We also hypothesize that GATA-1-mediated repression of PU.1 transcription is delayed and this may play a role in ineffective erythropoiesis. Material and Methods Cell lines: MDS-derived OCI-M2 EL and other two human ELs (HEL, K562) and one murine EL (MEL); all co-expressing GATA-1 and PU.1. Patients: MDS patients (N=5) with rather advanced disease; MDS/AML (4) and RAEBI (1). Four received AZA; response: PR (2), SD (2) with HI. Median OS>24 Mo. For chromatin immunoprecipitation (ChIP) analysis either cell lines or CD19/CD3-depleted bone marrow cells were used. Results Direct association of GATA-1 with PU.1 gene was demonstrated in all three human ELs using ChIP. Occupancy of GATA-1 was detected upstream the PU.1 promoter and distally at GATA-1 binding sites or at PU.1 binding sites together with PU.1. Comparable data documenting occupancy of GATA-1 at PU.1 gene were observed also in MEL cells and in normal murine fetal erythroblasts using ChIP-sequencing. To test how GATA-1 regulates PU.1 expression we overexpressed GATA-1 in erythroblasts and tested expression of PU.1, histone H3 modification (near GATA-1 occupancy) and cell growth. We found that GATA-1 inhibited PU.1 expression, facilitated enrichment of repressive modifications at PU.1 gene (H3K9Me, H3K27Me) while depleted activation modifications (H3K9Ac, H3K4Me), and also inhibited cell growth. Next, we tested effects of GATA-1 knockdown using siRNA. Indeed, inhibition of GATA-1 expression in erythroblasts leads to increase in PU.1 level as well as of its targets (CEBPA, MAC1). Using Luciferase assay we confirmed that both endogenously produced PU.1 and GATA-1 are capable to stimulate exogenously inserted reporters. Next, we compared chromatin structure of PU.1 gene between data from ELs, normal controls and high risk MDS. Our data revealed that PU.1 gene in MDS is enriched with repressive modifications (H3K9Me, H3K27Me) while depleted with activation modifications (H3K9Ac, H3K4Me) suggesting defects in dynamic regulation of PU.1 expression in MDS. Conclusion Our data from ELs provide a) evidence of GATA-1-mediated repression of PU.1 gene in erythroblasts and that b) manipulation of GATA-1 affected PU.1 level in opposite direction. In high risk MDS, the chromatin structure of PU.1 gene displays accumulation of repressive epigenetic marks that are responsive to AZA. We think that during early erythroid differentiation GATA-1 binds and represses PU.1 gene, however this is not fully completed in MDS and therefore erythroid differentiation is not efficient. Grants: P301/12/P380, P305/12/1033, NT14174-3/2013, UNCE204021, FR-TI2/509, SVV-2013-266509, PRVOUK-P24/LF1/3 Disclosures: No relevant conflicts of interest to declare.

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