Nrf2, a Critical Regulator of Oxidative Stress, Is Required for HSC Function and Cytokine Response.

Abstract Abstract 1492 Poster Board I-515 Previous studies have established an important role for reactive oxygen species (ROS) in regulating the function and life-span of hematopoietic stem cells (HSC). Nuclear factor erythroid-2–related factor 2 (Nrf2) is a redox-sensitive transcription factor that regulates cellular responses to ROS and detoxification pathways implicated in chemoresistance, however, its role in normal stem cells is unknown. We analyzed Nrf2null mice and found increased total bone marrow cellularity, cKit+Sca1+Lin− (KSL) stem-progenitor cells, and long-term quiescent HSC (CD34−KSL) compared to wild type mice (p<0.05). Transplantation of equal numbers of KSL cells from Nrf2wt and Nrf2null resulted in a five-fold decrease in peripheral blood chimerism from Nrf2null derived cells at 16 weeks (15% wild type vs. 3% null, p<0.05). Unlike other models of deficiencies in genes associated with ROS handling, such as ATM or the FoxO family of transcription factors, basal ROS levels were not elevated in Nrf2null HSC. However, Nrf2null bone marrow cells demonstrated increased sensitivity to induced oxidative stress and in vitro treatment with H2O2 resulted in a 2 fold decrease in colony formation in methylcellulose. We also examined the in vivo sensitivity of Nrf2null cells to oxidative stress by irradiating (400 rads) stably chimeric mice 20 weeks following transplantation with either Nrf2wt or Nrf2null HSC. Mice receiving Nrf2null HSC demonstrated a 50% decrease in peripheral blood chimerism at 4 months following radiation compared to no change in Nrf2wt recipients (p<0.05) confirming that loss of Nrf2 leads to increased sensitivity to oxidative stress. Microarray gene expression analysis from Nrf2wt and Nrf2null mice revealed down regulation of the G-CSF cytokine receptor in Nrf2null HSC and suggested that defective cytokine signaling may contribute to the HSC dysfunction seen in Nrf2null bone marrow cells. To test this hypothesis, we attempted to rescue the function of Nrf2null HSC by treating mice with exogenous G-CSF. Nrf2wt and Nrf2null mice were treated with one week of daily G-CSF and then HSC were harvested and transplanted. In contrast to the defects in engraftment of untreated Nrf2null HSC, there was no significant difference in peripheral blood chimerism following transplantation of G-CSF treated Nrf2wt or Nrf2null HSC, thus demonstrating that G-CSF treatment could rescue the HSC defect in mutant mice. In conclusion, the Nrf2 transcription factor appears to be a novel and essential regulator of normal HSC function through the modulation of oxidative stress response and cytokine signaling. Disclosures: No relevant conflicts of interest to declare.

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Adult Mice With Targeted Mutation of the Interleukin-11 Receptor (IL11Ra) Display Normal Hematopoiesis

Blood ◽

10.1182/blood.v90.6.2148 ◽

1997 ◽

Vol 90 (6) ◽

pp. 2148-2159 ◽

Cited By ~ 118

Author(s):

Harshal H. Nandurkar ◽

Lorraine Robb ◽

David Tarlinton ◽

Louise Barnett ◽

Frank Köntgen ◽

...

Keyword(s):

Bone Marrow ◽

Peripheral Blood ◽

Blood Cells ◽

Bone Marrow Cells ◽

White Blood Cells ◽

Null Mutation ◽

Wild Type ◽

Normal Numbers ◽

Interleukin 11 ◽

Marrow Cells

Abstract Interleukin-11 (IL-11) is a pleiotropic growth factor with a prominent effect on megakaryopoiesis and thrombopoiesis. The receptor for IL-11 is a heterodimer of the signal transduction unit gp130 and a specific receptor component, the α-chain (IL-11Rα). Two genes potentially encode the IL-11Rα: the IL11Ra and IL11Ra2 genes. The IL11Ra gene is widely expressed in hematopoietic and other organs, whereas the IL11Ra2 gene is restricted to only some strains of mice and its expression is confined to testis, lymph node, and thymus. To investigate the essential actions mediated by the IL-11Rα, we have generated mice with a null mutation of IL11Ra (IL11Ra−/−) by gene targeting. Analysis of IL11Ra expression by Northern blot and reverse transcriptase-polymerase chain reaction, as well as the absence of response of IL11Ra−/− bone marrow cells to IL-11 in hematopoietic assays, further confirmed the null mutation. Compensatory expression of the IL11Ra2 in bone marrow cells was not detected. IL11Ra−/− mice were healthy with normal numbers of peripheral blood white blood cells, hematocrit, and platelets. Bone marrow and spleen contained normal numbers of cells of all hematopoietic lineages, including megakaryocytes. Clonal cultures did not identify any perturbation of granulocyte-macrophage (GM), erythroid, or megakaryocyte progenitors. The number of day-12 colony-forming unit-spleen progenitors were similar in wild-type and IL11Ra−/− mice. The kinetics of recovery of peripheral blood white blood cells, platelets, and bone marrow GM progenitors after treatment with 5-flurouracil were the same in IL11Ra−/− and wild-type mice. Acute hemolytic stress was induced by phenylhydrazine and resulted in a 50% decrease in hematocrit. The recovery of hematocrit was comparable in IL11Ra−/− and wild-type mice. These observations indicate that IL-11 receptor signalling is dispensable for adult hematopoiesis.

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Enforced Expression of the GATA-2 Transcription Factor Blocks Normal Hematopoiesis

Blood ◽

10.1182/blood.v93.2.488 ◽

1999 ◽

Vol 93 (2) ◽

pp. 488-499 ◽

Cited By ~ 157

Author(s):

Derek A. Persons ◽

James A. Allay ◽

Esther R. Allay ◽

Richard A. Ashmun ◽

Donald Orlic ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Transcription Factor ◽

Blood Cell ◽

Fluorescent Protein ◽

Bone Marrow Cells ◽

Hematopoietic Cells ◽

Immunoblot Analysis ◽

Marrow Cells

Abstract The zinc finger transcription factor GATA-2 is highly expressed in immature hematopoietic cells and declines with blood cell maturation. To investigate its role in normal adult hematopoiesis, a bicistronic retroviral vector encoding GATA-2 and the green fluorescent protein (GFP) was used to maintain the high levels of GATA-2 that are normally present in primitive hematopoietic cells. Coexpression of the GFP marker facilitated identification and quantitation of vector-expressing cells. Bone marrow cells transduced with the GATA-2 vector expressed GFP as judged by flow cytometry and GATA-2 as assessed by immunoblot analysis. A 50% to 80% reduction in hematopoietic progenitor-derived colony formation was observed with GATA-2/GFP-transduced marrow, compared with marrow transduced with a GFP-containing vector lacking the GATA-2 cDNA. Culture of purified populations of GATA-2/GFP-expressing and nonexpressing cells confirmed a specific ablation of the colony-forming ability of GATA-2/GFP-expressing progenitor cells. Similarly, loss of spleen colony-forming ability was observed for GATA-2/GFP-expressing bone marrow cells. Despite enforced GATA-2 expression, marrow cells remained viable and were negative in assays to evaluate apoptosis. Although efficient transduction of primitive Sca-1+Lin- cells was observed with the GATA-2/GFP vector, GATA-2/GFP-expressing stem cells failed to substantially contribute to the multilineage hematopoietic reconstitution of transplanted mice. Additionally, mice transplanted with purified, GATA-2/GFP-expressing cells showed post-transplant cytopenias and decreased numbers of total and gene-modified bone marrow Sca-1+ Lin−cells. Although Sca-1+ Lin− bone marrow cells expressing the GATA-2/GFP vector were detected after transplantation, no appreciable expansion in their numbers occurred. In contrast, control GFP-expressing Sca-1+Lin− cells expanded at least 40-fold after transplantation. Thus, enforced expression of GATA-2 in pluripotent hematopoietic cells blocked both their amplification and differentiation. There appears to be a critical dose-dependent effect of GATA-2 on blood cell differentiation in that downregulation of GATA-2 expression is necessary for stem cells to contribute to hematopoiesis in vivo.

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Loss of P-Selectin Promotes the Function of Aged Hematopoietic and Leukemic Stem Cells.

Blood ◽

10.1182/blood.v116.21.1577.1577 ◽

2010 ◽

Vol 116 (21) ◽

pp. 1577-1577

Author(s):

Yaoyu Chen ◽

Sullivan Con ◽

Yiguo Hu ◽

Linghong Kong ◽

Cong Peng ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Flow Cytometry ◽

Stem Cell ◽

Bone Marrow Cells ◽

Leukemic Stem Cells ◽

Wild Type ◽

Post Transplant ◽

Marrow Cells

Abstract Abstract 1577 Hematopoiesis is a tightly regulated biological process that relies upon complicated interactions between the blood cells and their microenvironment. Adhesion molecules like P-selectin are essential to hematopoiesis, and their dysregulation has been implicated in leukemogenesis. We have previously shown a role for P-selectin in chronic myeloid leukemia and demonstrated that in its absence the disease process accelerates. Recently, there has also been speculation that P-selectin may play a role in the aging hematopoietic stem cells (HSCs), as its expression in upregulated as a mouse ages. In this study, we show that the loss of P-selectin function dysregulates the balance of stem cells and progenitors and that these differences become more pronounced with age. We compared the percentages of HSCs, long-term (LT)-HSCs, short-term (ST)-HSCs, multipotent progenitors (MPPs), CMPs, GMPs and MEPs in bone marrow by flow cytometry between wild type (WT) and Selp-/- mice. An age-dependent LT-HSC expansion was observed in WT mice. However, this expansion was prevented by the loss of Selp as observed in Selp-/-mice. Further, we demonstrate that with age LT-HSCs in particular express more elevated levels of P-selectin. LT-HSCs and ST-HSC/MPPs were isolated from the bone marrow of young (2 months old) and old (15 months old) WT mice and examined P-selectin expression by FACS. A significant increase in P-selectin expression was observed in LT-HSCs of old mice, and this increase was not observed in the ST-HSC+MPP subpopulations. We also show that the loss of P-selectin gene has profound effects of stem cell function, altering the capacity of these cells to home. Despite impaired homing capacity, stem cells lacking P-selectin possess a competitive advantage over their wild type counterparts. Using a stem cell competition assay, HSCs derived from Selp-/- mice (CD45.2+) and WT control mice (CD45.2+GFP+) were mixed in 1:1 ratio and transplanted into irradiated WT recipients (CD45.1). The initial findings were potentially indicative of the ability of cells derived from GFP mice to more efficiently home and engraft. Despite this initial advantage, cells derived from Selp-/- eventually exhibited a competitive and statistically significant advantage over the cells derived from GFP mice. At 30 days post-transplant, 49.9±1.4% of the CD45.2 subpopulation was GFP+. At 86 days post-transplant, 25.7±3.3 % of the CD45.2 cells derived from the peripheral blood were GFP+. Similarly, 23.0±3.7% of the CD45.2 cells derived from the bone marrow of these mice were GFP+. Indeed, we demonstrate that recipients of P-selectin deficient bone marrow cells more efficiently repopulate the bone marrow than controls and that this advantage extends and expands in the long-term. Finally, we demonstrate that recipients of leukemic cells lacking P-selectin develop a more accelerated form of leukemia accompanied by significant increases in stem and progenitor cells. Bone marrow cells from donor WT and Selp-/- mice were infected with retrovirus expressing BCR-ABL-GFP, and irradiated WT recipients were transplanted with 2×105 of these transduced donor cells. At 14 days post-transplant, recipient mice from each of the groups were sacrificed, and bone marrow cells were harvested and analyzed by flow cytometry. Recipients of leukemic Selp-/- cells possessed 3.5-fold more LSCs than recipients of wild-type cells. There were 3.1-fold more LT-LSCs and 3.8-fold more ST-LSCs and MPPs in recipients of Selp-/- cells than WT cells. In addition, recipients of leukemic Selp-/- cells possessed significantly more CMP (16.9-fold) and MEP (4.5-fold) cells. Because P-selectin expression increases with age on LT-HSCs, we sought to determine the role that age plays in CML development and progression. Bone marrow cells derived from 15-month-old donor Selp-/- and WT mice were transduced with BCR-ABL, respectively, followed by transplantation of the transduced cells into recipient mice. All recipients of BCR-ABL transduced Selp-/- cells died by 23 days after induction of CML and had a median survival of 19 days, whereas recipients of the transduced WT cells survived significantly longer. This pro-leukemic role for cells lacking P-selectin expression is leukemic stem cell-specific rather than stromal cell-specific and supports an essential role for P-selectin on leukemic stem cells. Disclosures: No relevant conflicts of interest to declare.

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PRKD2 Serine-Threonine Kinase, a Downstream Effector Of GABP, Plays Essential Roles For The Maintenance Of HSCs

Blood ◽

10.1182/blood.v122.21.2430.2430 ◽

2013 ◽

Vol 122 (21) ◽

pp. 2430-2430

Author(s):

Zhong-Fa Yang ◽

Wang Junling ◽

Alan G. Rosmarin

Keyword(s):

Bone Marrow ◽

Transcription Factor ◽

Protein Kinase ◽

Bone Marrow Cells ◽

Specific Cell ◽

Wild Type ◽

Serine Threonine Kinase ◽

Hematopoietic Stem ◽

Threonine Kinase ◽

Marrow Cells

Abstract Hematopoietic stem cells (HSCs) are the source of all blood lineages, and HSCs must balance quiescence, self-renewal, and differentiation to meet lifelong needs for blood cell development. GABP is an ets-related transcription factor that controls critical genes in myeloid and lymphoid development, and has been implicated in control of HSC growth. GABP is an obligate multimeric transcription factor that includes the DNA-binding ets component, GABPa, along with various GABPb partner proteins. We conditionally deleted Gabpa in mouse bone marrow and found that Gabpa cells have a profound growth disadvantage due to cell cycle arrest in HSCs. We identified Protein Kinase D2 (PRKD2) as a candidate effector of GABP. PRKD2 is a diacyl glycerol- and Protein Kinase C-activated serine-threonine kinase, because deletion of Gabpa markedly reduced PRKD2 expression in normal HSCs and progenitor cells. In a Prkd2ki/ki mouse model, in which two functionally essential phosphorylation serines were inactivated genetically, their bone marrow long term HSCs reduced dramatically and the short term HSCs increased accordingly. Mice transplanted with a 1:1 mixture of Prkd2ki/ki and wild type bone marrow cells demonstrated the decreased proportion of the Prkd2ki/ki bone marrow cells with the corresponding increase of the wild type cells. Although ectopic expression of the human Chronic Myeloid Leukemia (CML) fusion oncogene BCR-ABL in wild type bone marrow cells induced rapid CML development, expression of BCR-ABL in Prkd2ki/ki bone marrow cells failed to develop CML in transplanted recipient mice. Analysis of the peripheral blood, bone marrow and spleen of these mice revealed that the BCR-ABL+, Prkd2ki/ki cells did not express myeloid or lymphoid specific cell surface antigens CD11b, Gr1, B220, or CD3e. They demonstrated an immature blast-like microscopic morphology, and recipient mice transplanted with these cells died before the onset of CML development. We conclude that the phosphorylation activated Prkd2 is required for the maintenance of HSC pool and the development of mature hematopoietic lineages from HSCs. These findings suggest that PRKD2 kinase mediate key downstream events of both PKC and transcription factor GABP, and that PRKD2 may serve as a novel therapeutic target in leukemia. Disclosures: No relevant conflicts of interest to declare.

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Enrichment and characterization of murine hematopoietic stem cells that express c-kit molecule

Blood ◽

10.1182/blood.v78.7.1706.bloodjournal7871706 ◽

1991 ◽

Vol 78 (7) ◽

pp. 1706-1712 ◽

Cited By ~ 5

Author(s):

S Okada ◽

H Nakauchi ◽

K Nagayoshi ◽

S Nishikawa ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Peripheral Blood ◽

Bone Marrow Cells ◽

Flow Cytometric Analysis ◽

Tyrosine Kinase Receptor ◽

Dependent Manner ◽

Hematopoietic Stem ◽

Marrow Cells

The proto-oncogene c-kit encodes a transmembrane tyrosine kinase receptor for stem cell factor (SCF). The c-kit/SCF signal is expected to have an important role in hematopoiesis. A monoclonal antibody (ACK- 2) against the murine c-kit molecule was prepared. Flow cytometric analysis showed that the bone marrow cells that expressed the c-kit molecule (approximately 5%) were B220(B)-, TER119(erythroid)-, Thy1negative-low, and WGA+. A small number of Mac-1(macrophage)+ or Gr- 1(granulocyte)+ cells were c-kit-low positive. Colony-forming unit in culture (CFU-C) and day-8 and day-12 CFU-spleen (CFU-S) existed exclusively in the c-kit-positive fraction. About 20% of the Lin(lineage)-c-kit+ cells were rhodamine-123low and this fraction contained more day-12 CFU-S than day-8 CFU-S. On the basis of these findings, murine hematopoietic stem cells were enriched with normal bone marrow cells. One of two and one of four Thy-1lowLin-WGA+c-kit+ cells were CFU-C and CFU-S, respectively. Long-term repopulating ability was investigated using B6/Ly5 congenic mice. Eight and 25 weeks after transplantation of Lin-c-kit+ cells, donor-derived cells were found in the bone marrow, spleen, thymus, and peripheral blood. In peripheral blood, T cells, B cells, and granulocyte-macrophages were derived from donor cells. Injection of ACK-2 into the irradiated mice after bone marrow transplantation decreased the numbers of day-8 and day-12 CFU-S in a dose-dependent manner. Day-8 spleen colony formation was completely suppressed by the injection of 100 micrograms ACK-2, but a small number of day-12 colonies were spared. Our data show that the c- kit molecule is expressed in primitive stem cells and plays an essential role in the early stages of hematopoiesis.

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R-Ras Regulates Hematopoietic Stem/Progenitor Cell Adhesion, Migration, and Mobilization through Rac GTPase-Mediated Signals.

Blood ◽

10.1182/blood.v110.11.221.221 ◽

2007 ◽

Vol 110 (11) ◽

pp. 221-221

Author(s):

Xun Shang ◽

Lina Li ◽

Jose Concelas ◽

Fukun Guo ◽

Deidre Daria ◽

...

Keyword(s):

Bone Marrow ◽

Cell Adhesion ◽

Peripheral Blood ◽

Bone Marrow Cells ◽

Wild Type ◽

Rac Gtpase ◽

Hematopoietic Stem ◽

And Migration ◽

Marrow Cells

Abstract Hematopoietic stem/progenitor cells (HSPCs) are maintained by strictly regulated signals in the bone marrow microenvironment. One challenge in understanding the complex mode of HSPC regulation is to link intracellular signal components with extracellular stimuli. R-Ras is a member of the Ras family small GTPases. Previous mouse genetic studies suggest that R-Ras mRNA is primarily expressed in endothelial cells and R-Ras is involved in vascular angiogenesis. In clonal cell lines, although dominant mutant overexpression studies suggest a possible role of R-Ras in regulating cell adhesion and spreading, proliferation and/or differentiation in a cell-type dependent manner, it remains controversial whether R-Ras activity may promote or inhibit cell adhesion and migration. Here, in a mouse knockout model, we have examined the role of R-Ras in HSPC regulation by a combined in vivo and in vitro approach. Firstly, we found that R-Ras is expressed in the Lin− low density bone marrow cells of wild-type mice, and R-Ras activity in the cells is downregulated by cytokines and chemokines such as SCF and SDF-1a (∼ 20% and 40% of unstimulated control, respectively). Secondly, R-Ras deficiency did not significantly affect peripheral blood CBC, nor alter the frequency or distribution of long-term and short-term hematopoietic stem cells (defined by IL7Ra−Lin−Sca-1+c-Kit+CD34− and IL7Ra−Lin−Sca-1+c-Kit+CD34+ genotypes, respectively) in the bone marrow, peripheral blood and spleen. Competitive repopulation experiments using the wild-type and R-Ras−/− bone marrow cells at 1:1 ratio in lethally irradiated recipient mice showed no significant difference of blood cells of the two genotypes in the recipients up to 6 months post-transplantation. R-Ras−/− bone marrow cells did not show a detectable difference in colony forming unit activities assayed in the presence of various combinations of SCF, TPO, EPO, IL3, G-CSF and serum, compared with the matching wild-type cells. Thirdly, upon challenge with G-CSF, a HSPC mobilizing agent, R-Ras−/− mice demonstrated a markedly enhanced ability to mobilize HSPCs from bone marrow to peripheral blood as revealed by genotypic and colony-forming unit analyses (WT: 150 vs. KO: 320 per 200uL blood, p=0.018), and R-Ras−/− HSPCs exhibit significantly decreased homing activity (WT: 4.3% vs. KO: 2.8%, p<0.001). Fourthly, isolated R-Ras−/− HSPCs displayed a constitutively assembled cortical actin cytoskeleton structure in the absence of cytokine or chemokine stimulation, similar to that of activated wild-type HSPCs. The R-Ras−/− HSPCs were defective in adhesion of cobblestone area-forming cells to a bone marrow-derived stroma cell line (FBMD-1) and in adhesion to fibronectin CH296 fragment, and showed a drastically increased ability to migrate toward a SDF-1a gradient (WT: 16% vs. KO: 38%, p<0.001). These data point to a HSPC-intrinsic role of R-Ras in adhesion and migration. Finally, the functional changes of R-Ras−/− cells were associated with a ∼3 fold increase in Rac-GTP species and constitutively elevated Rac downstream signals of phsopho-PAK1 and phospho-myosin light chain. Partial inhibition of Rac activity by NSC23766, a Rac GTPase-specific inhibitor, readily reversed the migration phenotype under SDF-1a stimulation. Taken together, these studies demonstrate that R-Ras is a critical signal regulator for HSPC adhesion, homing, migration, and mobilization through a mechanism involving Rac GTPase-regulated cytoskeleton and adhesion machinery.

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The Tumor Suppressor Role of the Msr1 Gene in Cancer Stem Cells of Chronic Myeloid Leukemia.

Blood ◽

10.1182/blood.v114.22.188.188 ◽

2009 ◽

Vol 114 (22) ◽

pp. 188-188

Author(s):

Yaoyu Chen ◽

Con Sullivan ◽

Shaoguang Li

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Chronic Myeloid Leukemia ◽

Tumor Suppressor ◽

Myeloid Leukemia ◽

Bone Marrow Cells ◽

Leukemia Cells ◽

Wild Type ◽

Marrow Cells

Abstract Abstract 188 We have previously shown that the arachidonate 5-lipoxygenase gene (Alox5) functions as a critical regulator of leukemia stem cells (LSCs) in BCR-ABL-induced chronic myeloid leukemia (CML) in mice (Chen Y, Hu Y, Zhang H, Peng C, Li S. Loss of the Alox5 gene impairs leukemia stem cells and prevents chronic myeloid leukemia. Nature Genetics 41:783-792, 2009). We believe that the Alox5 pathway represents a major molecular network in LSCs. Therefore, we decided to further dissect this pathway by comparing gene expression profiles between wild type and Alox5−/− LSCs from CML mice using the DNA microarray analysis. We identified a small group of candidate genes that were changed in expression in the absence of Alox5. Among these genes, we have identified the Msr1 gene and chosen to test the function of this gene in regulating LSC function, because this gene was up-regulated, indicating that it might play a tumor suppressor role in LSCs. In our CML mouse model, we observed that recipients of BCR-ABL transduced Msr1−/− bone marrow cells developed CML much rapidly than recipients of BCR-ABL transduced wide type bone marrow cells. To test whether this accelerated CML is related to abnormal function of LSCs, we carried out a serial transplantation assay by transferring bone marrow cells from primary recipients of BCR-ABL-transduced wild type or Msr1−/− donor bone marrow cells into secondary and next-generation of recipient mice to biologically assess the effect of Msr1 on LSCs. BCR-ABL-expressing wild type leukemia cells from bone marrow of CML mice were only able to transfer CML once, whereas BCR-ABL-expressing Msr1−/− leukemia cells were able to transfer lethal CML for five genrations. This observation indicates that BCR-ABL-expressing Msr1−/− LSCs have markedly increased stem cell function. To further compare the stem cell function, we performed the leukemia stem cell competition assay by 1:1 mixing wild type (CD45.1) and Msr1−/− (CD45.2) bone marrow cells from CML mice. At day 25 or 30 after transplantation, more than 60% and 95% of GFP+Gr-1+ cells in peripheral blood of the mice were CD45.2+Msr1−/− myeloid leukemia cells, and all these mice developed CML and died of CML derived from Msr1−/− LSCs. To confirm the tumor suppressor role of Msr1 in CML development, we co-expressed BCR-ABL and Msr1 in MSR1−/− bone marrow cells by retroviral transduction, followed by transplantation of these cells into recipient mice. The ectopically-expressed Msr1 in MSR1−/− bone marrow cells rescued the accelerated CML phenotype, and some recipient mice did not even develop the CML. Together, these results demonstrate that Msr1 plays a tumor suppressor role in LSCs. The Msr1 pathway is a novel molecular network in LSCs, and it will be important to fully study this pathway for developing curative therapeutic strategies for CML. Disclosures: No relevant conflicts of interest to declare.

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Runx1 Haploinsufficiency Permits Lineage-Commitment but Impairs Activation of a Key Late Differentiation Gene

Blood ◽

10.1182/blood.v118.21.2442.2442 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2442-2442

Author(s):

Zhenbo Hu ◽

Kwok Peng Ng ◽

Quteba Ebrahem ◽

Yogen Saunthararajah

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Bone Marrow Cells ◽

Cpg Methylation ◽

Lineage Commitment ◽

Wild Type ◽

Differentiation Gene ◽

Wild Type Control ◽

Marrow Cells

Abstract Abstract 2442 Inactivating or dominant-negative RUNX1 mutations are a frequent first-hit in the multi-hit process of leukemogenesis. First-hits that target RUNX1 occur in stem cells, or in familial acute myeloid leukemia (AML), in the germ-line. However, self-renewing AML cells (leukemia-initiating cells, LIC) frequently display surface markers of lineage-committment, and AML cells appear lineage-committed in critical aspects, expressing high levels of key lineage-specifying transcription factors (TF) such as CEBPA with promoter CpG methylation patterns resembling mature hematopoietic cells (HSC) (Negrotto et al, Leukemia 2011). To investigate a possible basis for differentiation advancement of LIC from stem cell origins, hematopoietic stem cells from wild-type and Runx1 haploinsufficient (+/−) mice were cultured with granulocyte-colony stimulating factor (G-CSF). Repression of Hoxb4 (a stem cell associated factor) and activation of Cebpa by G-CSF was similar in wild-type and Runx1+/− lineage-negative hematopoietic precursor cells. However, the expression of Cebpe, a key late-differentiation driving TF upregulated with the transition from proliferating pro-myelocytes to non-proliferating myelocytes, and which terminates proliferation in myeloid and AML cells, was significantly decreased in the Runx1+/− cells (>2-fold, t-test p<0.01), even after 15 days of culture with G-CSF. This pattern of Cebpa and Cebpe expression was also documented at the protein level. High CEBPA, but relatively low HOXB4 and CEBPE expression, is also characteristic of human primary AML cells, including CD34+ subsets (Negrotto et al, Leukemia 2011) and leukemia initiating cells (analysis of Geo Database GSE24006 and GSE17054). Indicating epigenetic repression of Cebpe, methylation of CpG in the Cebpe promoter was significantly increased in Runx1+/− compared to wild-type cells (p<0.05). Consistent with partial maturation of Runx1+/− cells, expression of the granulocyte-lineage markers Ly6G and CD11b increased during culture with G-CSF, but to a much lesser extent than in wild-type control (30 v 40% and 11 v 30% respectively). After 15 days of culture with G-CSF, in morphological analyses, Runx1+/− cells included granulocytes (with less neutrophilic granulation than observed in wild-type), some cells with high nuclear-cytoplasmic ratio, and mitotic figures, in comparison to mostly mature granulocytes in wild-type control. Repression of Cebpe might confer a growth advantage after lineage-commitment. In liquid culture with and without G-CSF, Runx1+/− cells demonstrated more rapid and persistent proliferation than wild-type control (cumulative increase in cell numbers >2-fold, p<0.001), with this advantage more prominent in the presence of G-CSF. In semi-solid media supplemented with G-CSF, Runx1+/− lineage-negative cells produced a greater number and larger-sized colonies than wild-type control. CEBPE promoter CpG that become less methylated during G-CSF-induced differentiation of normal human CD34+ precursors into granulocytes were identified by mass-spectrometry. These CpG were in proximity to RUNX1 and CEBPA consensus binding sequences. Two of the three CpG sites were significantly hypermethylated in AML (n=27) compared to normal (n=11) and/or remission bone marrow cells (n=6) (1.5 to >2-fold, p<0.01, Wilcoxon test). In contrast to the CEBPE promoter CpG, methylation levels at LINE-1 repetitive DNA element CpGs were similar in normal, remission, and AML bone marrow cells. In conclusion, Runx1+/− abnormality present in stem cells is permissive of lineage-commitment but represses a key late-differentiation gene, hence conferring a proliferative advantage to lineage-committed daughter cells. This mechanism could explain differentiation advancement of LIC from stem cell origins, and likely contributes to the terminal maturation observed upon treatment of AML cells (including LIC) with corepressor antagonists (histone deacetylase and DNMT1 inhibitors). In contrast, treatment of normal HSC with these drugs has the opposite effect, maintaining self-renewal, possibly by preventing repression of stem cell genes by differentiation stimuli (Hu et al, Mol Ca Ther 2010). Hence, the difference in maturation level of LIC and normal HSC can potentially be exploited for AML selective therapy. Disclosures: No relevant conflicts of interest to declare.

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Functional Hematopoietic Cells Derived From Mouse Embryonic Stem Cells.

Blood ◽

10.1182/blood.v120.21.2304.2304 ◽

2012 ◽

Vol 120 (21) ◽

pp. 2304-2304

Author(s):

Cheng Li ◽

Daniel R. George ◽

Nichole M. Havey ◽

Jeffery M. Klco ◽

Timothy J. Ley

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Peripheral Blood ◽

Bone Marrow Cells ◽

Embryonic Stem ◽

Post Injection ◽

Spleen Cells ◽

Short Term ◽

Marrow Cells

Abstract Abstract 2304 Despite two decades of effort, deriving long-term repopulating hematopoietic stem/progenitor cells (HSPCs) from embryonic stem cells (ESCs) has proven to be extremely difficult. Both embryoid body (EB)-based and stroma-based methods have been extensively explored. However, robust production of HSPCs from C57BL/6J-derived mouse ESCs (mESCs) has not yet been reported. Furthermore, in vivo engraftment of mES-derived HSCs (from any strain) has been achieved only with forced expression of HoxB4 or related oncogenes, which creates significant limitations for most studies. Here, we describe a stroma-based co-culture method to differentiate HSCs and progenitor populations from C57BL/6J-derived mESCs. After simple co-culture on OP9 stroma cells for one week, C57BL/6J-derived mESC lines differentiate into cells that mark as HSCs, CMPs, GMPs, and MEPs (by immunophenotyping); these cells are capable of giving rise to erythrocytes, monocytes, and mast cells (by morphology and immunophenotyping) after another week of culture in methylcellulose with hematopoietic cytokines (SCF, IL-3, IL-6, and Epo). Similar in vitro hematopoietic differentiation has been achieved in several different C57BL/6J-derived mESCs (B6/Blu, B6-GFP, LK1, and B6 albino), B6/SVJ129 mESCs (R1), various SVJ129-derived mESCs (SWT16, EDJ22, and SCC10), and five independent C57BL/6J mouse embryonic fibroblast (MEF)-derived induced pluripotent stem cell (iPSC) lines. C57BL/6J ESCs derived from CAGGS-GFP transgenic mice (B6-GFP ESCs, which express high levels of GFP in all hematopoietic lineages) were used to determine whether we could obtain long-term engraftment of the OP9 differentiated ESCs. B6-GFP ESCs cultured for 7 days on OP9 cells were sorted by Kit+ surface staining. Sorted cells (1×105, 2×105, 4×105) were transferred into immunocompromised NSG mice via retro orbital injection (n=1 mouse per dose). Peripheral blood from the recipients injected with 2×105 and 4×105 cells showed 5% GFP positivity in the peripheral blood at weeks 12 and 16 post-transplant, while recipients injected with 1×105 cells had no detectable GFP+ cells in the periphery. Bone marrow cells and spleens were harvested at week 22. The recipient injected with 4×105 cells showed 5% GFP positivity in the bone marrow and 20% in the spleen. Engraftment was multi-lineage. Myeloid compartments (CD34+, CD11b+, Kit+, and Gr-1+) showed similar or less GFP positivity than overall bone marrow and spleen cells. Lymphoid (CD3+ and B220+) and erythroid (Ter119+) compartments also showed similar GFP positivity compared to overall bone marrow cells. However, lymphoid and erythroid compartments contained significantly higher GFP positivity (30–60%) than overall spleen cells. We have now modified the procedure to transfer 1×106 unfractionated B6-GFP ESCs grown for 7 days on OP9 stroma directly into NSG recipients. We have detected short-term engraftment 4 weeks post-injection in the peripheral blood of one recipient and multilineage splenic engraftment 8 weeks post-injection in two recipients, confirming that short-term repopulating cells are indeed generated by this method. Secondary transplants using the GFP+ bone marrow cells from the long-term engrafted mouse have been performed. This approach could be a valuable tool for studying the hematopoietic development of a variety of mESC lines, and potentially, iPSC lines as well. Disclosures: No relevant conflicts of interest to declare.

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A limited role for p16Ink4a and p19Arf in the loss of hematopoietic stem cells during proliferative stress

Blood ◽

10.1182/blood-2004-06-2242 ◽

2005 ◽

Vol 106 (3) ◽

pp. 827-832 ◽

Cited By ~ 51

Author(s):

Lilia Stepanova ◽

Brian P. Sorrentino

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Bone Marrow Cells ◽

Dominant Role ◽

Wild Type ◽

Hematopoietic Stem ◽

Serial Transplantation ◽

Marrow Cells

Abstract It has long been known that prolonged culture or serial transplantation leads to the loss of hematopoietic stem cells (HSCs); however, the mechanisms for this loss are not well understood. We hypothesized that expression of p16Ink4a or p19Arf or both may play a role in the loss of HSCs during conditions of enhanced proliferation, either in vitro or in vivo. Arf was not expressed in freshly isolated HSCs from adult mice but was induced in phenotypically primitive cells after 10 to 12 days in culture. When cultured bone marrow cells from either Arf–/– or Ink4a-Arf–/– mice were compared to wild-type cells in a competitive repopulation assay, no significant differences in HSC activity were seen. We then evaluated the role of p19Arf and p16Ink4a in the loss of HSCs during serial transplantation. Bone marrow cells from Ink4a-Arf–/–, but not Arf–/–, mice had a modestly extended life span and, on average, supported reconstitution of one additional recipient compared to wild-type cells. Mice given transplants of Ink4a-Arf–/–cells eventually did die of hematopoietic failure in the next round of transplantation. We conclude that mechanisms independent of the Ink4a-Arf gene locus play a dominant role in HSC loss during conditions of proliferative stress.

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