Expansion and Biased Commitment of Hematopoietic Stem Cells Towards Erythroid Cells upon Acute Anemia Induction

Abstract The majority of adult hematopoietic stem cells (HSCs) are maintained in a dormant state under homeostatic conditions. In contrast, under stressed conditions such as myeloablation and infection, HSCs are known to proliferate and rapidly give rise to downstream progeny. However, it is unclear whether and how HSCs respond to severe anemic conditions. Here we report that HSCs rapidly expand with a biased differentiation towards erythroid cells upon the induction of acute anemia. Injection of 60 mg/kg of phenylhydrazine (PHZ) was used to induce hemolytic anemia, after which the peripheral blood (PB), bone marrow (BM) and spleen of the mice were analyzed for the blood profiles and stem/progenitor cell content. The red blood cell (RBC) count of the PHZ treated mice was at its lowest at day 6 post injection. BM analysis showed that the number of HSCs (CD150+CD34-c-kit+Sca-I+Lineage-) immediately started increasing, as well as megakaryocyte-erythroid progenitors (MEP, CD34-FcγIII/IIR-c-kit+Sca-I-Lineage-) with a peak at day 3-4 (3.0 and 3.4 fold increase, respectively). Interestingly, the number of common myeloid progenitors (CMP, CD34+FcγIII/IIR-c-kit+Sca-I-Lineage-) did not show a clear increase over time and the number of erythroid progenitors (Ter119+) started increasing at a later time point than the HSC/MEP expansion, suggesting that the expansion of primitive cells is a primary response to the anemic condition that possibly skips some of the regular stages that are observed in the normal differentiation towards erythrocytes. In contrast to the BM, in the spleen HSC expansion was modest while MEP and CMP were robustly expanded (5.7 and 6.6 fold increase, respectively). These findings indicate that the BM and spleen have distinct roles in the response to the anemic conditions. In order to accurately evaluate the lineage potential of HSCs in vitro, we developed a combined assay utilizing colony formation and flow cytometry analysis (CFU-FACS), with which all generated colonies were analyzed for the morphology and the frequency of each lineage. The result showed that HSCs isolated from control mice had a balanced differentiation towards megakaryocyte and erythroid cells with 20-25% of the colonies containing only granulocytes/macrophages and megakaryocytes, but not erythroid cells (GMMk colonies). In contrast, HSCs isolated from PHZ treated mice showed significantly increased the number of colonies containing a higher content of erythroid cells, whereas the ratio of GMMk colonies was decreased. Furthermore, 3-dimensional analysis of the three lineage potentials (myeloid, megakaryocyte and erythroid) in the colonies revealed an imbalanced lineage potential of HSCs from anemic mice, showing higher erythroid potential instead of the megakaryocyte potential. As an alternative method, phlebotomy was performed to induce acute anemia. Although phlebotomized mice did not display a clear expansion of the HSC population, CFU-FACS analysis showed an erythroid-biased lineage potential of the HSCs, indicating that the HSC expansion and the lineage bias may be caused by independent mechanisms. To demonstrate if the alterations in the HSCs affect the in vivo function of these cells, 50 HSCs isolated from control or PHZ injected Kusabira Orange (KuO) mice were transplanted into lethally irradiated mice. Two weeks after the transplantation, the ratio of KuO+ RBCs against KuO+ platelets was higher in the PHZ-HSC transplanted mice than control-HSC transplanted mice. This difference was not seen four weeks after transplantation and the long-term reconstitution (>12 weeks) levels did not differ between both groups, suggesting that the enhanced erythropoiesis is a transient event that does not reduce the stem cell capacity. In summary, we demonstrated that not only progenitor cells but also HSCs respond to severe anemic conditions and contribute to erythropoiesis through rapid expansion and a transient fate change, depicting a novel model of stress response. Disclosures No relevant conflicts of interest to declare.

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Evidence That High-Mobility Group A2 (Hmga2) Expression Contributes to the Ontogeny-Dependent Properties of Fetal Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v116.21.2634.2634 ◽

2010 ◽

Vol 116 (21) ◽

pp. 2634-2634

Author(s):

Michael R. Copley ◽

David G. Kent ◽

Claudia Benz ◽

Keegan M. Rowe ◽

Stefan H. Woehrer ◽

...

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Fetal Liver ◽

Rapid Expansion ◽

High Expression ◽

Primary Host ◽

Self Renewal ◽

Hematopoietic Stem ◽

Renewal Program

Abstract Abstract 2634 Fetal and early neonatal hematopoietic stem cells (HSCs) are distinct from their adult counterparts by their rapid turnover and expansion rates in vivo. However, the mechanisms underlying the regulation of these properties are poorly understood. In previous studies using serial limiting-dilution competitive repopulating transplant assays, our lab has shown that the rapid expansion phenotype of fetal HSCs is at least partially intrinsically determined since significantly more daughter HSCs are produced from fetal as compared to adult HSCs when similar numbers are transplanted into the same type of irradiated adult host. Additionally, we have observed a conversion of fetal HSCs to the adult regeneration phenotype that occurs within six weeks of transplantation in the primary host. To facilitate a comparison of highly-purified subsets of fetal and adult HSCs identified by an identical phenotype, we adopted the use of the CD45+EPCR+CD150+CD48− (E-SLAM) phenotype which we found gave HSC purities of 20–50% for hematopoietic tissues from early fetal to aged adulthood. We then used comparative gene expression analysis to identify candidate regulators of the fetal HSC high self-renewal program. This gave 20 candidate genes whose transcript levels were measured by quantitative real time PCR in E-SLAM cells isolated from E14.5 fetal liver (FL) and adult bone marrow (ABM). Of these genes only Hmga2 and Smarcc1 showed significant differences (p<.05) in expression between fetal and adult HSCs and only Hmga2 maintained this differential expression when the same cells were stimulated to divide for 48 hrs in vitro. To test the hypothesis that high expression of Hmga2 is a necessary and sufficient factor in determining the fetal HSC self-renewal program, purified adult E-SLAM HSCs were transduced with Hmga2-overexpressing or control lentiviruses and the kinetics of transduced vs untransduced hematopoietic cells in a congenic serial-transplantation model were then analyzed. Interestingly, when BM cells from the primary repopulated mice (transplanted 6-weeks earlier) were injected into secondary animals and the peripheral blood was analyzed for donor-type %Y/GFP chimerism, the Hmga2-overexpressing cells were observed to have a competititve advantage and exhibited an ∼6-fold expansion relative to the untransduced cells. In contrast, the control virus-infected BM cells were found to be equally competitive. These findings support the hypothesis that high expression of Hmga2 may be a critical mediator of the high self-renewal phenotype of fetal HSCs. Disclosures: No relevant conflicts of interest to declare.

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Growth Factor Independence 1 b (Gfi1b) as a New Regulator of Hematopoietic Stem Cell Fate

Blood ◽

10.1182/blood.v116.21.837.837 ◽

2010 ◽

Vol 116 (21) ◽

pp. 837-837

Author(s):

Cyrus Khandanpour ◽

Lothar Vassen ◽

Marie-Claude Gaudreau ◽

Christian Kosan ◽

Tarik Moroy

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Cell Fate ◽

Conflicts Of Interest ◽

Fold Increase ◽

Surface Proteins ◽

Expression Array ◽

Hematopoietic Stem

Abstract Abstract 837 Donor matched transplantation of bone marrow or hematopoietic stem cells (HSCs) are widely used to treat hematological malignancies, but are associated with high mortality. Methods for expansion of HSC numbers and their mobilization into the bloodstream of a donor could significantly improve therapy. We show here that the zinc finger transcriptional repressor Gfi1b is highly expressed in hematopoietic stem cells (defined as CD 150+, CD 48-, Lin-, Sca1+ and c-kit+) cells and is down-regulated more than 10 fold upon differentiation into multipotential progenitors (defined as CD 150+ or CD150-, CD 48+, Lin-, Sca1+ and c-kit+). Constitutive germline deletion of Gfi1b is lethal at midgestation due to impaired development of erythrocytes and megakaryocytes. We have therefore developed a conditional knock-out of Gfi1b to study its role specifically in the adult hematopoietic system. Deletion of Gfi1b leads to a 30-fold increase of HSC numbers in bone marrow and around a100 fold increase in spleen and peripheral blood. This was due to a higher rate of HSCs undergoing cell cycling. Concomitantly, the number of quiescent HSCs was reduced 5–6 times. We then performed an gene expression array of wt and Gfi1b deficient HSCs and observed that loss of Gfi1b leads to an altered RNA expression of integrins and adhesion molecules, for instance CXCR4, VCAM-1 and Tenascin C, which usually retain HSCs in a dormant state in the endosteal niche. These changes were also confirmed on protein level. Finally, we could observe a higher levels of Reactive Oxygen Species (ROS) in the Gfi1b deficient HSCs compared to wt HSCs. We verified whether elevated level of ROS are causative for the expansion of HSCs and noticed that application of N-Acetyl-Cystein, which counteracts the effects of ROS, limits significantly the expansion of HSCs, underscoring the important role of ROS in the expansion of Gfi1b deficient HSCs. Despite markedly increased proliferation, Gfi1b-/- HSCs can reconstitute lymphoid and myeloid lineages to the same extent as wt HSCs when transplanted in competition with wt HSCs. Furthermore, Gfi1b deficient HSCs also feature an expansion after transplantation and expand 5–10 fold more than wt HSC when transplanted initially in equal numbers with wt HSCs. It is possible that lower expression of CXCR4, VCAM-1 and other surface proteins leads to release and egression of Gfi1b deficient HSCs from the hypoxic endosteal stem cell niche and exposes the HSCs to more oxygen which in turn increases ROS levels. Elevated ROS could promote entry of Gfi1b-/- HSCs into cell cycle. In conclusion Gfi1b regulates HSC dormancy, pool size and potentially also the egress and mobilization of HSCs and might offer a new therapeutic approach to improve human HSC transplantation. Disclosures: No relevant conflicts of interest to declare.

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Toll like Receptor 2 Signaling Regulates Hematopoietic Stem Cells Via Cell Autonomous and Cell Non-Autonomous Mechanisms

Blood ◽

10.1182/blood.v126.23.1174.1174 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1174-1174

Author(s):

Darlene Monlish ◽

Angela Herman ◽

Molly Romine ◽

Sima Bhatt ◽

Laura G. Schuettpelz

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Immune Cells ◽

Conflicts Of Interest ◽

Wild Type ◽

Erythroid Progenitors ◽

Hematopoietic Stem ◽

Tlr2 Agonist ◽

Tlr2 Signaling

Abstract Toll like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that shape the innate immune system by identifying foreign pathogen-associated molecular patterns (PAMPS) and host-derived damage associated patterns (DAMPS). TLRs are widely expressed on both immune cells and non-immune cells, including hematopoietic stem and progenitor cells (HSPCs). Of clinical significance, both lymphoproliferative and myelodysplastic syndromes have been linked to aberrant TLR signaling (Schuettpelz, et al., Front Immunol 2013; Varney, et al., Exp Hematol 2015). Despite extensive studies focused on the influence of TLRs through committed effector cell populations, more recent evidence suggests that these PRRs may elicit immune regulation from the more primitive level of hematopoietic stem cells (HSCs). As TLR2 is expressed on HSCs, in the present study, we sought to elucidate the effect of TLR2 signaling on HSCs, and determine the cell-autonomous versus non-autonomous effects of this signaling. To this end, we utilized the synthetic TLR2 agonist, PAM3CSK4, to assess the effects of augmented TLR2 signaling on HSC mobilization, function, cycling, and differentiation. In previous studies, we found that TLR2 is not required for HSC function (Schuettpelz et al., Leukemia 2014); however, in the present study, treatment of wild-type mice with PAM3CSK4 led to HSC expansion in both the bone marrow and spleen, and a reduction in bone marrow megakaryocyte-erythroid progenitors (MEPs). Further, we observed increased HSC cycling and loss of function in competitive bone marrow transplantation assays in response to TLR2 agonist exposure. Treatment of chimeric animals (Tlr2-/- + Tlr2+/+ bone marrow transplanted into Tlr2+/+ or Tlr2-/- recipients) showed that these effects are largely cell non-autonomous, with a minor contribution from cell-autonomous TLR2 signaling. Analysis of serum, bone marrow, and spleen samples by cytokine expression arrays revealed an increase in G-CSF (serum) and TNFα (bone marrow) following TLR2 agonist treatment in wild-type mice. To further characterize the influence of these cytokines, respective receptor knockout models were employed. Inhibition of G-CSF enhanced HSC bone marrow expansion in response to PAM3CSK4, but partially rescued the expansion of spleen HSPCs. Likewise, loss of TNFa partially mitigated the expansion of spleen HSPCs in response to PAM3CSK4, and abrogated the PAM3CSK4-induced spleen HSC cycling. Further, we observed that loss of TNFa rescued the PAM3CSK4-mediated loss of bone marrow MEPs. Taken together, these data suggest that TLR2 signaling affects HSCs via both cell cell-autonomous and non-autonomous cues, with G-CSF and TNFa contributing to TLR2 agonist-mediated effects on HSC cycling, mobilization, and function. Ongoing studies aim to determine the particular cell types that are crucial for mediating the effects of TLR2 signaling on HSCs and elucidate the role of this pathway on HSCs in myelodysplastic syndrome (MDS) pathogenesis and other hematologic malignancies. Disclosures No relevant conflicts of interest to declare.

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Geminin Regulates Hematopoietic Stem Cell Proliferation and Differentiation.

Blood ◽

10.1182/blood.v114.22.1478.1478 ◽

2009 ◽

Vol 114 (22) ◽

pp. 1478-1478

Author(s):

Kathryn M. Shinnick ◽

Kelly A. Barry ◽

Elizabeth A. Eklund ◽

Thomas J. McGarry

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Transcription Factors ◽

Cell Division ◽

Dna Replication ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Regulatory Protein ◽

Hematopoietic Stem ◽

Proliferation And Differentiation

Abstract Abstract 1478 Poster Board I-501 Hematopoietic stem cells supply the circulation with mature blood cells throughout life. Progenitor cell division and differentiation must be carefully balanced in order to supply the proper numbers and proportions of mature cells. The mechanisms that control the choice between continued cell division and terminal differentiation are incompletely understood. The unstable regulatory protein Geminin is thought to maintain cells in an undifferentiated state while they proliferate. Geminin is a bi-functional protein. It limits the extent of DNA replication to one round per cell cycle by binding and inhibiting the essential replication factor Cdt1. Loss of Geminin leads to replication abnormalities that activate the DNA replication checkpoint and the Fanconi Anemia (FA) pathway. Geminin also influences patterns of cell differentiation by interacting with Homeobox (Hox) transcription factors and chromatin remodeling proteins. To examine how Geminin affects the proliferation and differentiation of hematopoietic stem cells, we created a mouse strain in which Geminin is deleted from the proliferating cells of the bone marrow. Geminin deletion has profound effects on all three hematopoietic lineages. The production of mature erythrocytes and leukocytes is drastically reduced and the animals become anemic and neutropenic. In contrast, the population of megakaryocytes is dramatically expanded and the animals develop thrombocytosis. Interestingly, the number of c-Kit+ Sca1+ Lin- (KSL) stem cells is maintained, at least in the short term. Myeloid colony forming cells are also preserved, but the colonies that grow are smaller. We conclude that Geminin deletion causes a maturation arrest in some lineages and directs cells down some differentiation pathways at the expense of others. We are now testing how Geminin loss affects cell cycle checkpoint pathways, whether Geminin regulates hematopoietic transcription factors, and whether Geminin deficient cells give rise to leukemias or lymphomas. Disclosures: No relevant conflicts of interest to declare.

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Poly I:C Stimulates Sca-1 Expression in Murine Bone Marrow and Increases the Number of Phenotypic Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v114.22.2504.2504 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2504-2504

Author(s):

Russell Garrett ◽

Gerd Bungartz ◽

Alevtina Domashenko ◽

Stephen G. Emerson

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Poly I:C ◽

Hematopoietic Stem ◽

Marrow Cells ◽

Myeloid Progenitors

Abstract Abstract 2504 Poster Board II-481 Polyinosinic:polycytidlyic acid (poly I:C) is a synthetic double-stranded RNA used to mimic viral infections in order to study immune responses and to activate gene deletion in lox-p systems employing a Cre gene responsive to an Mx-1 promoter. Recent observations made by us and others have suggested hematopoietic stem cells, responding to either poly I:C administration or interferon directly, enter cell cycle. Twenty-two hours following a single 100mg intraperitoneal injection of poly I:C into 10-12 week old male C57Bl/6 mice, the mice were injected with a single pulse of BrdU. Two hours later, bone marrow was harvested from legs and stained for Lineage, Sca-1, ckit, CD48, IL7R, and BrdU. In two independent experiments, each with n = 4, 41 and 33% of Lin- Sca-1+ cKit+ (LSK) IL-7R- CD48- cells from poly I:C-treated mice had incorporated BrdU, compared to 7 and 10% in cells from PBS-treated mice. These data support recently published reports. Total bone marrow cellularity was reduced to 45 and 57% in the two experiments, indicating either a rapid death and/or mobilization of marrow cells. Despite this dramatic loss of hematopoietic cells from the bone marrow of poly I:C treated mice, the number of IL-7R- CD48- LSK cells increased 145 and 308% in the two independent experiments. Importantly, the level of Sca-1 expression increased dramatically in the bone marrow of poly I:C-treated mice. Both the percent of Sca-1+ cells and the expression level of Sca-1 on a per cell basis increased after twenty-four hours of poly I:C, with some cells acquiring levels of Sca-1 that are missing from control bone marrow. These data were duplicated in vitro. When total marrow cells were cultured overnight in media containing either PBS or 25mg/mL poly I:C, percent of Sca-1+ cells increased from 23.6 to 43.7%. Within the Sca-1+ fraction of poly I:C-treated cultures, 16.7% had acquired very high levels of Sca-1, compared to only 1.75% in control cultures. Quantitative RT-PCR was employed to measure a greater than 2-fold increase in the amount of Sca-1 mRNA in poly I:C-treated cultures. Whereas the numbers of LSK cells increased in vivo, CD150+/− CD48- IL-7R- Lin- Sca-1- cKit+ myeloid progenitors almost completely disappeared following poly I:C treatment, dropping to 18.59% of control marrow, a reduction that is disproportionately large compared to the overall loss of hematopoietic cells in the marrow. These cells are normally proliferative, with 77.1 and 70.53% accumulating BrdU during the 2-hour pulse in PBS and poly I:C-treated mice, respectively. Interestingly, when Sca-1 is excluded from the analysis, the percent of Lin- IL7R- CD48- cKit+ cells incorporating BrdU decreases following poly I:C treatment, in keeping with interferon's published role as a cell cycle repressor. One possible interpretation of these data is that the increased proliferation of LSK cells noted by us and others is actually the result of Sca-1 acquisition by normally proliferating Sca-1- myeloid progenitors. This new hypothesis is currently being investigated. Disclosures: No relevant conflicts of interest to declare.

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Characterization of Histone Modifications on Lineage-Affiliated Genes During Hematopoietic Stem Cell Differentiation

Blood ◽

10.1182/blood.v116.21.4784.4784 ◽

2010 ◽

Vol 116 (21) ◽

pp. 4784-4784

Author(s):

Chen Fangping ◽

Huarong Tang

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Histone Modifications ◽

Conflicts Of Interest ◽

Embryonic Stem ◽

Stem Cell Differentiation ◽

Differentiation Potential ◽

Hematopoietic Stem ◽

Low Level ◽

Lineage Specific Genes

Abstract Abstract 4784 Hematopoietic stem cells (HSCs) are multipotent stem cells capable of self-renewal and multi-lineage differentiation. Though it has been shown that multiple factors take part in the maintenance of HSCs’ multipotency and differentiation potential, the mechanisms are unclear. Recent studies showed that histone modifications play an important role in maintenance of embryonic stem cells pluripotency and differentiation. To characterize the histone modification patterns of different lineages, HSCs were collected from umbilical cord blood and induced to differentiate to granulocytic, erythroid, and megakarytic in vitro. genes during HSC differentiation. Chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) technology was adopted to investigate the dynamic changes of histone modifications on lineage specific transcription factors and lineage–affiliated genes. Our results showed a certain level of H4 acetylation and H3 acetylation together with high level of H3K4me2 and low level of H3K4me3, H3K9me3 and H3K27me3 were present in lineage specific genes in CD34+CD38- HSCs. As CD34+CD38- cells differentiated, the modification level of acH3, acH4, H3K4me2, H3K9me3 and H3K27me3 on lineage specific genes remained the same, while H3K4me3 level increased greatly. In non-lineage specific genes, the acH3 and acH4 levels decreased, and H3K4me3 level remain at low level, while H3K9me3 and H3K27me3 levels increased. Thus, our data suggested that histone modifications played an important role in maintenaning the multipotency and differentiation capability of hematopoietic stem cells. Disclosures: No relevant conflicts of interest to declare.

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Stability of Self-Renewal in Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v116.21.sci-42.sci-42 ◽

2010 ◽

Vol 116 (21) ◽

pp. SCI-42-SCI-42

Author(s):

Norman N. Iscove

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Expression Profiles ◽

Single Cells ◽

Gene Expression Profiles ◽

Short Term ◽

Blood Leukocytes ◽

Hematopoietic Stem

Abstract Abstract SCI-42 For many years a distinction was drawn between prospectively separable murine HSC populations with long-term, essentially permanent reconstituting potential (LT-HSC), versus HSC populations yielding short-term engraftment lasting only 4 – 6 weeks after transplantation (ST-HSC). Recent work based on transplantation of single cells shows that highly purified populations of LT-HSC prepared by standard sorting parameters consist in fact predominantly of a distinct, newly recognized class of intermediate- term reconstituting cells (IT-HSC) whose grafts endure longer than short-term HSC but also eventually fail (1). IT-HSC are separable from long-term reconstituting cells on the basis of expression of more alpha2 integrin and less SLAM150. Crucial to recognition of the distinction between LT- and IT-HSC are the endpoints used to evaluate reconstitution. If blood erythroid or myeloid reconstitution is measured, IT reconstitution is readily distinguished by the disappearance of these elements by 16 wk post-transplant. If instead reconstitution is measured simply by presence of blood leukocytes of donor origin, which in the mouse are almost entirely lymphocytes, the distinction is not made because lymphoid elements persist even in fading IT clones to 24 wk or beyond. The observations imply a need for reinterpretation of most of the published descriptions of the biology and gene expression profiles previously attributed to LT-HSC but in fact derived from analysis of populations that consisted mainly of IT-HSC. The capacity now to separate LT- from IT-HSC creates new opportunities for probing the mechanisms that specify and sustain long term function in the former but not the latter. 1. Benveniste P, Frelin C, Janmohamed S, Barbara M, Herrington R, Hyam D, Iscove NN. Intermediate-term hematopoietic stem cells with extended but time-limited reconstitution potential. Cell Stem Cell. 2010;6:48–58 Disclosures: No relevant conflicts of interest to declare.

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Bcr-Abl Impairs T Cell Development From Murine Induced Pluripotent Stem Cells and Hematopoietic Stem Cells; A Partial Explanation for the Concept That Ph+ Clone Never Involves T Cell Lineage in CML,

Blood ◽

10.1182/blood.v118.21.3748.3748 ◽

2011 ◽

Vol 118 (21) ◽

pp. 3748-3748

Author(s):

Bidisha Chanda ◽

Kiyoko Izawa ◽

Ratanakanit Harnprasopwat ◽

Keisuke Takahashi ◽

Seiichiro Kobayashi ◽

...

Keyword(s):

Stem Cells ◽

Stem Cell ◽

T Cell ◽

Hematopoietic Stem Cells ◽

Pluripotent Stem Cells ◽

Conflicts Of Interest ◽

T Cell Development ◽

Cell Lineage ◽

Cell Development ◽

Hematopoietic Stem

Abstract Abstract 3748 Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder generally believed to originate from a hematopoietic stem cell carrying the BCR-ABL fusion gene, which generally encodes 210kD and 190kD constitutively active tyrosine kinases termed as p210 and p190, respectively. In spite of the putative stem cell origin and the competence for differentiation toward mature B cells, there is a longstanding consensus that CML never involves the T cell lineage at least in chronic phase. To gain insight into this apparent conflict, we used in vitro T cell differentiation model from murine pluripotent stem cells (PSCs) as well as hematopoietic stem cells (HSCs). C57BL/6 MEFs were reprogrammed using a polycistronic lentiviral Tet-On vector encoding human Oct4, Sox2 and Klf4, which were tandemly linked via porcine teschovirus-1 2A peptides, together with another lentiviral vector expressing rtTA driven by the EF-1a promoter. Almost all the vector sequences including the transgenes were deleted by adenovirus-mediated transduction of Crerecombinase after derivation of iPSCs, and only remnant 291-bp LTRs containing a single loxP site remained in the genome. A clone of MEF-iPSCs were retrovirally transduced with p190DccER, a ligand-controllable p190-estrogen receptor fusion protein, whose tyrosine kinase activity absolutely depends on 4-hydroxytamoxyfen (4-HT).For T cell lineage differentiation, p190DccER-MEF-iPSCs were recovered from a feeder-free culture supplemented with LIF and plated onto a subconfluent OP9-DL1 monolayer in the presence of Flt3 ligand and IL7 with or without 0.5 mM 4-HT.After 3 weeks of culture, iPSC-derived blood cells were collected and subjected to FACS analysis for their lineage confirmation. About 70% of lymphocyte-like cells from the 4-HT(-) culture expressed CD3, but only 20% of counterparts from the 4-HT(+)culture expressed CD3, suggesting impaired T cell development by Bcr-Abl. Next, c-Kit+Sca1+Lin− (KSL) bone marrow cells were prepared by FACS from 8-weeks old C57BL/6 mice treated with 5-FU. KSL cells were similarly transduced with p190DccER and were subjected to the OP9-DL1co-culture system with or without 0.5 mM 4-HT.After 2 weeks of culture, 90% of lymphocytes from the 4-HT(-)culture revealed CD3+TCRβ+ phenotype, but only 30% of those were double positive in the presence of 4-HT(+). In addition, 96% of lymphocytes from the 4-HT(-) culture progressed to the DN2 stage with c-Kit−CD44+CD25+phenotype, whereas 40% of those from the 4-HT(+) culture arrested at the DN1 stage showing c-Kit+CD44+CD25−.Since IL7 plays a central role at the stage from DN1 to DN2 of progenitor T cells, Bcr-Abl is suggested to impair T cell development possibly through interfering with the IL7 signal. The precise mechanism underlying impaired T lymphopoiesis by Bcr-Abl is under investigation. Disclosures: No relevant conflicts of interest to declare.

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Metabolic Regulation of Hematopoietic Stem Cells During Stress

Blood ◽

10.1182/blood.v120.21.sci-42.sci-42 ◽

2012 ◽

Vol 120 (21) ◽

pp. SCI-42-SCI-42

Author(s):

Toshio Suda

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Hematopoietic Stem Cells ◽

Metabolic Regulation ◽

Conflicts Of Interest ◽

Hypoxia Inducible Factor ◽

Ros Generation ◽

Hematopoietic Stem

Abstract Abstract SCI-42 Tissue homeostasis over the life of an organism relies on both self-renewal and multipotent differentiation of stem cells. Hematopoietic stem cells (HSCs) are sustained in a specific microenvironment known as the stem cell niche. Adult HSCs are kept quiescent during the cell cycle in the endosteal niche of the bone marrow. Normal HSCs maintain intracellular hypoxia, stabilize the hypoxia-inducible factor-1a (HIF-1a) protein, and generate ATP by anaerobic metabolism. In HIF-1a deficiency, HSCs became metabolically aerobic, lost cell cycle quiescence, and finally became exhausted. An increased dose of HIF-1a protein in VHL-mutated HSCs and their progenitors induced cell cycle quiescence and accumulation of HSCs in the bone marrow (BM), which were not transplantable. This metabolic balance promotes HSC maintenance by limiting the production of reactive oxygen species (ROS), but leaves HSCs susceptible to changes in redox status (1). We have performed the metabolomic analysis in HSCs. Upregulation of pyruvate dehydrogenase kinases enhanced the glycolytic pathway, cell cycle quiescence, and stem cell capacity. Thus, HSCs directly utilize the hypoxic microenvironment to maintain their slow cell cycle by HIF-1a-dependent metabolism. Downregulation of mitochondrial metabolism might be reasonable, since it reduces ROS generation. On the other hand, at the time of BM transplantation, HSCs activate oxidative phosphorylation to acquire more ATP for proliferation. Autophagy also energizes HSCs by providing amino acids during transplantation. ATG (autophagy-related) 7 is essential for transplantation and metabolic homeostasis. The relationship between mitochondrial heat shock protein, mortalin, and metabolism in HSCs will also be discussed. Disclosures: No relevant conflicts of interest to declare.

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Periostin Acts As An Important Cell Cycle Regulator Of Adult Hematopoietic Stem Cells Via Binding To Integrin-αvβ3

Blood ◽

10.1182/blood.v122.21.341.341 ◽

2013 ◽

Vol 122 (21) ◽

pp. 341-341 ◽

Cited By ~ 2

Author(s):

Satish Khurana ◽

Catherine M. Verfaillie

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Integrin Αvβ3 ◽

Brdu Incorporation ◽

Hematopoietic Stem ◽

Hematopoietic System ◽

Cell Cycle Regulator ◽

Blocking Antibodies

Osteoblasts are one of the important cellular components of the niche for hematopoietic stem cells (HSCs) in mammalian bone marrow (BM). Integrin receptors not only play a key role in HSC adhesion within the BM niche but also transfer regulatory signals from the microenvironment to HSCs. Periostin (Postn or osteoblast specific factor-1; OSF-1) is expressed in osteoblasts in addition to many other tissues, and acts as a ligand for Integrin-αvβ3 (ITGAV-B3). We identified POSTN as an important regulator of the cell cycle in adult murine HSCs. POSTN inhibited culture induced proliferation of HSCs thereby decreasing the total number of cells following 2-5 day culture of primitive HSCs, identified as CD150+CD48-Lin-Sca-1+c-kit+ (CD150 KLS) cells with SCF and TPO, while increasing the proportion of long-term (LT-) HSCs. Culture for 5 days with POSTN decreased the short-term (ST-) engraftment of progeny of 200 CD150 KLS cells, while significantly increasing LT- engraftment of the donor derived cells. A significant fraction of CD150 KLS cells expressed ITGAV as well as ITGB3. POSTN did not affect proliferation of HSCs in vitro following blocking of ITGAV with neutralizing antibodies. Among the important cell cycle regulators, we found an increase in p27kip1 expression in HSCs. Preliminary studies on possible signaling mechanisms involved, showed that POSTN inhibits Akt phosphorylation, known to mediate inhibition of both expression and activation of p27Kip1. Intravenous infusion of recombinant POSTN protein significantly decreased proliferation of hematopoietic progenitors as shown by Brdu incorporation and Hoechst/Pyronin staining. Interestingly, POSTN infusion also led to an increase in the number of KLS as well as CD150 KLS cells in the BM. Studies on characterization of the hematopoietic system of Postn-/- mice are underway. To further determine the role of ITGAV in HSCs, we used blocking antibodies against ITGAV and performed homing and engraftment studies. No effect on either homing potential or engraftment of ST- and LT- engraftment was seen. However, the competitive repopulation of ITGAV- CD150 KLS cells was significantly lower that that of ITGAV+ CD150 KLS cells (isolated using non-blocking antibodies). Therefore, our studies confirm the importance of ITGAV expression on primitive HSCs as well as presents POSTN as an important cell cycle regulator in the hematopoietic system. Disclosures: No relevant conflicts of interest to declare.

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