Foxo3 Modulation of ATM and Oxidative Stress Mediates Distinct Functions in the Regulation of Hematopoietic Stem and Progenitor Cell Fate.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1272-1272 ◽  
Author(s):  
Safak Yalcin ◽  
Julia P. Luciano ◽  
Xin Zhang ◽  
Cecile Vercherat ◽  
Reshma Taneja ◽  
...  
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Cell Fate ◽  
Hematopoietic Stem Cell ◽  
Progenitor Cell ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Atm Gene

Abstract FOXO transcription factors are required for hematopoietic stem cell self renewal. In this study, we demonstrate that Foxo3 plays a specific and essential function in the regulation of both hematopoietic stem and progenitor cell fate. Foxo3 null mice display a myeloproliferative syndrome characterized by splenomegaly, a major expansion of the myeloid compartment in the blood, bone marrow and spleen, cytokine hypersensitivity of progenitors in hematopoietic organs and associated with the repression of the B lymphoid compartment. In addition, loss of Foxo3 leads to significant defects in hematopoietic stem cell numbers and activity. In particular, the numbers of long-term culture initiating cells (LTC-IC) was significantly reduced and the ability to repopulate lethally irradiated mice was severely compromised in Foxo3-defcient mice. This effect was mediated at least partially by enhanced accumulation of reactive oxygen species (ROS) in Foxo3-deficient hematopoietic stem cells as demonstrated by reduced QRT-PCR expression of several anti-oxidant enzymes leading to accumulation of ROS, (as measured by chloromethyl,dichlorodihydrofluorescein diacetate assay) in Foxo3 null hematopoietic stem cells, and in vitro and in vivo rescue of the phenotype using ROS scavengers. Furthermore, we demonstrate that while ROS accumulation results in suppression of Foxo3 null hematopoietic stem cell compartment, it enhances the activity of multipotential cells. By measuring RNA versus DNA content, and BrdU uptake, we determined that Foxo3-deficient hematopoietic stem cells exit quiescence (G0) and are impaired in their cycling at the G2/M phase. In particular, we identified ROS activation of p19ARF/p53 pathway and ROS-independent modulation of ataxia telangiectasia mutated (ATM) gene and p16INK4a, as major contributors to the interference with Foxo3-deficient hematopoietic stem cell self renewal and cycling. Loss of ATM has been shown to lead to hematopoietic stem cell deficiency. Importantly, we show that ATM gene expression is significantly suppressed in Foxo3-deficient hematopoietic stem cells suggesting that ATM lies downstream of Foxo3. Retroviral expression of a constitutively active form of Foxo3 in Foxo3-deficient bone marrow mononuclear cells enhances significantly the ATM expression suggesting that Foxo3 regulate expression of ATM gene. These combined findings suggest that Foxo3 functions in a tumor suppressor network to protect hematopoietic stem cells against deleterious effects of oxidative damage, to maintain hematopoietic lineage fate determination and to restrict the activity of long term repopulating hematopoietic stem cells. These findings provide insights into the mechanisms underlying hematopoietic stem cell fate.

scholarly journals Osteoblast ablation reduces normal long-term hematopoietic stem cell self-renewal but accelerates leukemia development

Blood ◽  
2015 ◽  
Vol 125 (17) ◽  
pp. 2678-2688 ◽  
Author(s):  
Marisa Bowers ◽  
Bin Zhang ◽  
Yinwei Ho ◽  
Puneet Agarwal ◽  
Ching-Cheng Chen ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Key Points ◽  
Leukemia Development

Key Points Bone marrow OB ablation leads to reduced quiescence, long-term engraftment, and self-renewal capacity of hematopoietic stem cells. Significantly accelerated leukemia development and reduced survival are seen in transgenic BCR-ABL mice following OB ablation.

scholarly journals Clonal-level lineage commitment pathways of hematopoietic stem cells in vivo

2019 ◽  
Vol 116 (4) ◽  
pp. 1447-1456 ◽  
Author(s):  
Rong Lu ◽  
Agnieszka Czechowicz ◽  
Jun Seita ◽  
Du Jiang ◽  
Irving L. Weissman
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Lineage Commitment ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Hematopoietic System ◽  
Different Levels

While the aggregate differentiation of the hematopoietic stem cell (HSC) population has been extensively studied, little is known about the lineage commitment process of individual HSC clones. Here, we provide lineage commitment maps of HSC clones under homeostasis and after perturbations of the endogenous hematopoietic system. Under homeostasis, all donor-derived HSC clones regenerate blood homogeneously throughout all measured stages and lineages of hematopoiesis. In contrast, after the hematopoietic system has been perturbed by irradiation or by an antagonistic anti-ckit antibody, only a small fraction of donor-derived HSC clones differentiate. Some of these clones dominantly expand and exhibit lineage bias. We identified the cellular origins of clonal dominance and lineage bias and uncovered the lineage commitment pathways that lead HSC clones to different levels of self-renewal and blood production under various transplantation conditions. This study reveals surprising alterations in HSC fate decisions directed by conditioning and identifies the key hematopoiesis stages that may be manipulated to control blood production and balance.

scholarly journals PEDF Can Rescue the Inhibition of Injured Endothelial Cells on Hematopoietic Stem Cell Expansion Ex Vivo

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 5008-5008
Author(s):  
Lingyu Zeng ◽  
Wenyi Lu ◽  
Lan Ding ◽  
Wen Ju ◽  
Jianlin Qiao ◽  
...  
Keyword(s):  
Stem Cells ◽  
Endothelial Cells ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Mesenchymal Transition ◽  
Endothelial To Mesenchymal Transition

Introduction: Endothelial cells (ECs) provide a fertile niche for hematopoietic stem cell (HSC) maintenance, differentiation, and migration.Several studies have indicated that bone marrow (BM) vascular niche was impaired after HSC transplantation and severely inhibited hematopoietic reconstruction. Pigment epithelium-derived factor (PEDF) is an important potential cytoprotection and therapeutic agent for injured cells. The direct role of the injured endothelial cells on hematopoietic stem cells and whether PEDF has protective effect in this system remain unknown. This study aims to observe the influence of enjured ECs on HSCs and to explore the role of PEDF in endothelial-HSC coculture system. Methods: Injury of Endothelial cells by two important preparative regimenconditioning radiation and Busulfan respectively was evaluated with CCK8 assay. The expression of endothelial tight junctions(TJs),adherent junctions related molecules and endothelial to Mesenchymal Transition molecules such as ZO-1, Occludin,VE-cadherin, ICAM, α-SMA, CD31 and VCAM were detected by RT-qPCR, flow cytometry, immunofluorescence and western blot. The effects of injured endothelial cells on HSC self-renewal, differentiation, cell cycle and apoptosis were evaluated by flow cytometry, photography, viable cell count and clone formation assay. Hematopoiesis regulation factors SCF, IL-6, TGF-β and TNF-α were detected by ELISA. The protective effect of PEDF was also explored. Results: Both radiation and Busulfan could decrease cell viability of endothelial cells. The expression level of ZO-1, Occludin, VE-cadherin, ICAM, CD31 and VCAM were decreased and α-SMA was increased when EC exposed to radiation or Busulfan suggesting endothelial activation, impaired EC permeability and endothelial to Mesenchymal Transition after EC injured. Compared with normal endothelial cells and hematopoietic stem cell co-culture group, the HSC% of injured endothelial cells and hematopoietic stem cells co-cultured group were significantly decreased, the cell colony formation ability was decreased, the proportion of mature cells increased, and the damage of endothelial cells could not maintain the characteristics of HSC, weakened the self-renewal and multidirectional differentiation potential of HSC and promoted the maturation of HSC. After the administration of PEDF, endothelial to Mesenchymal Transition of EC was suppressed and the EC permeability was improved. Most importantly, the proportion of HSC was significantly increased, and the proportion of mature cells decreased in the coculture system. Conclusion: Injured endothelial cells can inhibit proliferation of hematopoietic stem cells, self-renewal and promote HSC differentiation. PEDF could ameliorate endothelial injury and promote HSC expansion by suppressing endothelial-mesenchymal transition and protecting TJs and AJs. Disclosures No relevant conflicts of interest to declare.

Hematopoietic Stem Cell Expansion by HOXB4 Is Greatly Enhanced in p21 Deficient Stem Cells.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1688-1688 ◽  
Author(s):  
Noriko Miyake ◽  
Ann C.M. Brun ◽  
Mattias Magnusson ◽  
David T. Scadden ◽  
Stefan Karlsson
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Bone Marrow Cells ◽  
Ex Vivo ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Hox transcription factors have emerged as important regulators of hematopoiesis. In particular, enforced expression of HOXB4 is a potent stimulus for murine hematopoietic stem cell (HSC) self-renewal. Murine HSCs engineered to overexpress HoxB4 expand significantly more than control cells in vivo and ex vivo while maintaining a normal differentiation program. HSCs are regulated by the cell proliferation machinery that is intrinsically controlled by cyclin-dependent kinase inhibitors such as p21Cip1/Waf1(p21) and p27Kip1 (p27). The p21 protein restricts cell cycling of the hematopoietic stem cell pool and maintains hematopoietic stem cell quiescence. In order to ask whether enhanced proliferation due to HOXB4 overexpression is mediated through suppression of p21 we overexpressed HOXB4 in hematopoietic cells from p21−/− mice. First, we investigated whether human HOXB4 enhances in vitro expansion of BM cells from p21−/− mice compared to p21+/+ mice. 5FU treated BM cells from p21−/− or p21+/+ mice were pre-stimulated with SCF, IL-6, IL-3 for 2 days followed by transduction using retroviral vector expressing HOXB4 together with GFP (MIGB4) or the control GFP vector (MIG). The cells were maintained in suspension cultures for 13 days and analyzed for GFP positive cells by flow-cytometry. Compared to MIG transduced BM cells from p21+/+ mice (MIG/p21+), the numbers of GFP positive cells were increased 1.1-fold in MIG/p21−, 3.2-fold in MIGB4/p21+ and 10.0-fold in MIGB4/p21− respectively (n=5). CFU assays were performed after 13 days of culture. The numbers of CFU were increased 4.8-fold in MIG/p21−, 19.5-fold in MIG/p21+ and 33.9 -fold in MIGB4/p21− respectively. Next, we evaluated level of HSCs expansion by bone marrow repopulation assays. After 12-days of culture, 1.5 x 105 MIGB4 or MIG-transduced cells (Ly5.2) were transplanted into lethally irradiated mice in combination with 8 x 105 fresh Ly5.1 bone marrow cells. Sixteen weeks after transplantation, no Ly5.2 cells could be detected in MIG/p21+ or MIG/p21− transplanted mice (n=6). In contrast, Ly5.2 positive cells were detected in both MIGB4/p21+/+ and MIGB4/p21−/− cells. The % of Ly5.2 positive cells in MIGB4/p21− transplanted mice was 9.9-fold higher than MIGB4/p21+ transplanted mice. (38.4 % vs 3.9 %, P<0.02, n=5). These Ly5.2 positive cells differentiated into all lineages, as determined by proportions of Mac-1, B-220, CD3 and Ter119 positive populations. Currently, we are enumerating the expansion of HOXB4 transduced HSCs in p21 deficient BM cells using the CRU assay. Our findings suggest that HOXB4 increases the self-renewal of hematopoietic stem cells by a mechanism that is independent of p21. In addition, the findings demonstrate that deficiency of p21 in combination with enforced expression of HOXB4 can be used to rapidly and effectively expand hematopoietic stem cells.

Genetic Uncoupling of the Regulation of Hematopoietic Stem Cell Quiescence and Self-Renewal.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1347-1347
Author(s):  
Yan Liu ◽  
Yasuhiko Miyata ◽  
Goro Sashida ◽  
Anthony Debalsio ◽  
Yuhui Liu ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Quiescent State ◽  
Double Knockout ◽  
Ki 67 ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract It is usually stated that HSCs must choose to either self-renew or to differentiate and lose some of their multi potentiality. Recently, we demonstrated that MEF, an ETS family of transcription factor, played an important role in regulating HSC quiescence, illustrating a third choice for the HSC, namely to make an “active” choice and remain quiescent, without undergoing either self-renewal, or differentiation. MEF null HSCs are more quiescent than normal HSCs. In addition, MEF null mice exhibit greater numbers of hematopoietic stem cells and show resistance to chemotherapy and radiation. Little is known about the regulation of self-renewal vs. quiescence of HSCs, however the cdk inhibitor p21 has been implicated in regulating both HSC quiescence and proliferation. In the absence of p21, hematopoietic stem cell numbers are reported to be increased, but so is proliferation, leading to stem cell exhaustion. This implies that while p21 may maintain HSCs in their quiescent state, MEF functions to facilitate the entry of quiescent HSCs into the cycle, To investigate the potential opposing roles of MEF and p21 in HSC quiescence and self-renewal and to test whether the quiescent state of MEF null HSCs is dependent on the presence of p21, we have generated MEF / p21 double-knockout (DKO) mice. These mice are viable and born at normal mendelian frequency. MEF / p21 DKO mice have a higher than normal proportion of HSCs in the G0 phase, based on Pyronin Y/Hoechst staining and staining for the proliferation antigen Ki-67. Thus, the increased quiescence is not dependent on the presence of p21. However, by measuring LSK cells, we have observed a normal number of HSCs in the bone marrow of MEF / p21 DKO mice, in contrast to the increased number of HSCs in the bone marrow of MEF null mice. This suggests that the increased number of hematopoietic stem cells in MEF null mice is dependent on p21. Ongoing studies will further address the unique mechanisms that control HSC vs. stem cell expansion.

ETO2 Controls Hematopoietic Stem Cell Expansion.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 396-396
Author(s):  
Stephane Barakat ◽  
Julie Lambert ◽  
Guy Sauvageau ◽  
Trang Hoang
Keyword(s):  
Stem Cells ◽  
Transcription Factor ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Short Term ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Abstract 396 Hematopoietic stem cells that provide short term reconstitution (ST-HSCs) as well as hematopoietic progenitors expand from a small population of long term hematopoietic stem cells (LT-HSCs) that are mostly dormant cells. The mechanisms underlying this expansion remain to be clarified. SCL (stem cell leukemia), is a bHLH transcription factor that controls HSC quiescence and long term competence. Using a proteomics approach to identify components of the SCL complex in erythroid cells, we and others recently showed that the ETO2 co-repressor limits the activity of the SCL complex via direct interaction with the E2A transcription factor. ETO2/CBF2T3 is highly homologous to ETO/CBFA2T1 and both are translocation partners for AML1. We took several approaches to identify ETO2 function in HSCs. We initially found by Q-PCR that ETO2 is highly expressed in populations of cells enriched in short-term HSC (CD34+Flt3-Kit+Sca+Lin-) and lympho-myeloid progenitors (CD34+Flt3+Kit+Sca+Lin-) and at lower levels in LT-HSCs (CD34-Kit+Sca+Lin- or CD150+CD48-Kit+Sca+Lin-). Next, the role of ETO2 was studied by overexpression or downregulation combined with transplantation in mice. Ectopic ETO2 expression induces a 100 fold expansion of LT-HSCs in vivo in transplanted mice associated with differentiation blockade in all lineages, suggesting that ETO2 overexpression overcomes the mechanisms that limit HSC expansion in vivo. We are currently testing the role of the NHR1 domain of ETO2 in this expansion. Conversely, shRNAs directed against ETO2 knock down ET02 levels in Kit+Sca+Lin- cells, causing a ten-fold decrease in this population after transplantation, associated with reduced short-term reconstitution in mice. Finally, proliferation assays using Hoechst and CFSE indicate that ETO2 downregulation affects cell division (CFSE) and leads to an accumulation of Kit+Sca+Lin-cells in G0/G1 state (Hoescht). In conclusion, we show that ETO2 is highly expressed in ST-HSCs and lymphoid progenitors, and controls their expansion by regulating cell cycle entry at the G1-S checkpoint. In addition, ETO2 overexpression converts the self-renewal of maintenance into self-renewal of expansion in LT-HSCs. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Long-Term Human Hematopoietic Stem Cell Culture in Microdroplets

Micromachines ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 90
Author(s):  
Pilar Carreras ◽  
Itziar González ◽  
Miguel Gallardo ◽  
Alejandra Ortiz-Ruiz ◽  
Maria Luz Morales ◽  
...  
Keyword(s):  
Stem Cells ◽  
Cell Culture ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Stem Cell Niche ◽  
Hematopoietic Stem ◽  
Stem Cell Culture ◽  
Cell Niche

We previously reported a new approach for micromanipulation and encapsulation of human stem cells using a droplet-based microfluidic device. This approach demonstrated the possibility of encapsulating and culturing difficult-to-preserve primary human hematopoietic stem cells using an engineered double-layered bead composed by an inner layer of alginate and an outer layer of Puramatrix. We also demonstrated the maintenance and expansion of Multiple Myeloma cells in this construction. Here, the presented microfluidic technique is applied to construct a 3D biomimetic model to recapitulate the human hematopoietic stem cell niche using double-layered hydrogel beads cultured in 10% FBS culture medium. In this model, the long-term maintenance of the number of cells and expansion of hHSCS encapsulated in the proposed structures was observed. Additionally, a phenotypic characterization of the human hematopoietic stem cells generated in the presented biomimetic model was performed in order to assess their long-term stemness maintenance. Results indicate that the ex vivo cultured human CD34+ cells from bone marrow were viable, maintained, and expanded over a time span of eight weeks. This novel long-term stem cell culture methodology could represent a novel breakthrough to improve Hematopoietic Progenitor cell Transplant (HPT) as well as a novel tool for further study of the biochemical and biophysical factors influencing stem cell behavior. This technology opens a myriad of new applications as a universal stem cell niche model potentially able to expand other types of cells.

Superior Impact of p18INK4c over p27kip1 on Long-Term Repopulating Ability of Hematopoietic Stem Cells.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 796-796
Author(s):  
Hui Yu ◽  
Hongmei Shen ◽  
Xianmin Song ◽  
Paulina Huang ◽  
Tao Cheng
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Cell Biology ◽  
Wild Type ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
The Impact

Abstract The G1-phase is a critical window during the cell cycle in which stem cell self-renewal may be balanced with differentiation and apoptosis. Increasing evidence suggests that the cyclin-dependent kinase inhibitors (CKIs) such as p21Cip1/Waf1, p27kip1, p16INK4A, and p18INK4C (p21, p27, p16 and p18 hereafter) are involved in stem cell self-renewal, as largely demonstrated in murine hematopoietic stem cells (HSCs). For example, we have recently demonstrated a significant increase of HSC self-renewal in the absence of p18 (Yuan et al, Nature Cell Biology 2004). But the actual roles of these CKIs in HSCs appear to be distinct as p21 and p18 have opposite effects (Yu H et al, ASH 2004) whereas p16 has a limited effect (Stepanova et al, Blood 2005) on HSC exhaustion after serial bone marrow transfer. Like p18, however, p27 was recently reported to also inhibit HSC self-renewal due to the fact that the competitive repopulating units (CRUs) were increased in p27−/− mouse bone marrow (Walkley et al, Nature Cell Biology 2005) in contrast to the results in a previous report (Cheng T et al, Nature Medicine 2000). To further gauge the impact of p18 versus p27 on the long-term repopulating ability (LTRA) of HSCs, we have generated different congenic strains (CD45.1 and CD45.2) of p18−/− or p27−/− mice in the C57BL/6 background, allowing us to compare them with the competitive repopulation model in the same genetic background. The direct comparison of LTRA between p18−/− and p27−/− HSCs was assessed with the competitive bone marrow transplantation assay in which equal numbers of p18−/− (CD45.2) and p27−/− cells (CD45.1) were co-transplanted. Interestingly, the p18−/− genotype gradually dominated the p27−/− genotype in multiple hematopoietic lineages and p18−/− HSCs showed 4-5 times more LTRA than p27−/− HSCs 12 months after cBMT. Further self-renewal potential of HSCs was examined with secondary transplantation in which primarily transplanted p18−/− or p27−/− cells were equally mixed with wild-type unmanipulated cells. Notably, while the p18−/− cells continued to outcompete the wild-type cells as we previously observed, the p27−/− cells did not behave so in the secondary recipients. Based on the flow cytometric measurement and bone marrow cellularity, we estimated that transplanted p18−/− HSCs (defined with the CD34−LKS immunophenotype) had undergone a 230-fold expansion, while transplanted p27−/− and wild-type HSCs had only achieved a 6.6- and 2.4-fold expansion in the secondary recipients respectively. We further calculated the yield of bone marrow nucleated cells (BMNCs) per HSC. There were approximately 44 x 103, 20.6 x 103, and 15 x 103 BMNCs generated per CD34−LKS cell in p18−/−, p27−/− and wild-type transplanted recipients respectively. Therefore, the dramatic expansion of p18−/− HSCs in the hosts was not accompanied by decreased function per stem cell. Our current study demonstrates that hematopoietic engraftment in the absence of p18 is more advantageous than that in the absence of p27, perhaps due to a more specific role of p18 on self-renewal of the long-term repopulating HSCs.

A Recessive Embryonic Screen for Genes Regulating Hematopoietic Stem Cell and Blood Cell Generation and Function.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 2527-2527
Author(s):  
Peter Papathanasiou ◽  
Robert Tunningley ◽  
Diwakar Ram Pattabiraman ◽  
Ping Ye ◽  
Thomas J Gonda ◽  
...  
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Transcriptional Activation ◽  
Cellular Reprogramming ◽  
Chemical Mutagenesis ◽  
Hematopoietic Stem ◽  
Factor C

Abstract Abstract 2527 Poster Board II-504 Identifying the genes that regulate the development, self-renewal and differentiation of stem cells is of vital importance for understanding normal organogenesis, tailoring tissue engineering for regenerative medicine, cellular reprogramming and cancer. A forward genetic screen for aberrant long-term hematopoietic stem cells and progenitors provides an unbiased and tractable approach to finding genes responsible for stem cell homeostasis and differentiation. Here we demonstrate that chemical mutagenesis of mice combined with advances in hematopoietic stem cell reagents and genome/mapping resources can identify genes essential for mammalian stem cells and blood development. A pilot flow cytometry-based recessive screen comprehensively analyzed nine subsets of hematopoietic stem, progenitor, and red cells in over one thousand mouse embryos at embryonic day (E) 14.5 from 34 pedigrees and recovered five strains with defects in early hematopoiesis. One mutant strain (Booreana - an Australian Aboriginal name meaning white) which has excess long-term hematopoietic stem cells and platelets but reduced myelo-erythroid progenitors was outcrossed and the genetic mutation mapped and identified as a novel mis-sense mutation in the transcription factor c-Myb. The mutation in the trans-activation domain (TA) completely ablates transcriptional activation in a reporter assay which contrasts with other TA domain mutants which are partly dysfunctional[TJG1] . Moreover, the Booreana (Boo) mutation completely abrogates interaction with the transcriptional co-activator, CBP. Boo/Boo homozygous mutant mice survive into adulthood, albeit with severe anemia and massively increased platelet counts, whereas c-Myb−/− mice die by E15.5 of development, suggesting c-Myb has essential functions in vivo which are independent of transcriptional activation. This ENU-generated mutation provides another allele of c-Myb with a phenotype in between the complete loss-of-function allele and previously identified mutant alleles from other ENU screens. ENU-generated point mutants such as the Booreana mutation can provide novel informative insights into key functional domains of proteins, and protein interactions and networks, which are missed in gene knockout mice. Other phenodeviants generated in our screen are currently being mapped and will be presented. [TJG1]Not so in our hands, at least -– the Sandberg M303V is just as dead. Disclosures: No relevant conflicts of interest to declare.

Identification of Human Hematopoietic Stem Cell-Specific STAT5 Target Genes Involved in Self-Renewal and Transformation.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 568-568
Author(s):  
Szabolcs Fatrai ◽  
Albertus T.J. Wierenga ◽  
Edo Vellenga ◽  
Simon M. G. J. Daenen ◽  
Jan Jacob Schuringa
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Target Gene ◽  
Target Genes ◽  
Differentiation Potential ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Abstract 568 The transcription factor STAT5 fulfils an essential role in self-renewal of both mouse and human HSCs and persistent activation of STAT5 contributes to leukemic transformation. In patients with acute myeloid leukemia, increased STAT5 activity has been observed in over 60% of the cases. Yet, little is known about mechanisms that are involved. To gain further insight into these processes we studied whether STAT5-imposed long-term self-renewal is exclusively restricted to HSCs, or whether long-term self-renewal can also be imposed on progenitor cells. Human cord blood (CB) cells were transduced with control and STAT5-ER retroviral vectors allowing the induction of STAT5 activity by treatment of cells with 4-hydroxytamoxifen (4-OHT). Four populations were isolated: hematopoietic stem cells (HSC, CD34+CD38low), common myeloid progenitors (CMP, CD34+CD38+CD123+CD45RA-), granulocyte-macrophage progenitors (GMP, CD34+CD38+CD123+CD45RA+) and megakaryocyte-erythroid progenitors (MEP, CD34+CD38+CD123-CD45RA-). MS5 bone marrow stromal cocultures were initiated and STAT5 activity was induced by 4-OHT. In HSCs, STAT5 overexpression induced a long-term proliferative advantage as well as a significant increase in cobblestone formation. This coincided with elevated levels of Colony Forming Cells (CFCs) that were maintained over 5 weeks. In contrast, STAT5 was unable to induce cobblestone formation in progenitor cocultures and only a transient STAT5-induced increase in cell numbers was observed. CFC numbers dropped significantly after 2 weeks and progenitor initiated cultures could not be maintained longer than 3 weeks regardless of STAT5 activity. Myelopoiesis was blocked and an increase in erythroid differentiation in STAT5-ER-transduced HSC, CMP, and MEP populations was observed, while the differentiation potential of the GMP remained unaffected. Next, we aimed to identify HSC-specific STAT5 target genes by performing microarray analysis on HSC, CMP, GMP and MEP populations transduced with our STAT5-ER vectors. To limit STAT5 mediated effects on erythropoiesis GATA1 was downmodulated in STAT5-transduced CB cells by a lentiviral RNAi approach, which completely abrogated erythropoiesis but maintained enhanced HSC self-renewal. Microarrays were performed on GATA1 downmodulated STAT5-transduced CB cells and controls, and these data sets were compared to the HSC-specific STAT5 target gene lists. This combined approach resulted in the identification of 36 GATA1-independent STAT5 target genes in the HSC population. One of the identified genes was HIF2a. The involvement of HIF2a in STAT5 phenotypes was studied functionally by using a lentiviral HIF2a RNAi approach in STAT5 transduced CB cells. These studies revealed that expansion of STAT5/HIF2a RNAi-transduced cells on MS5 bone marrow stromal cocultures was reduced, coinciding with reduced CFC and LTC-IC frequencies, while differentiation was not affected. In summary, our data show that hematopoietic stem cells, but not progenitors are the exclusive target for STAT5-induced long-term self-renewal. Furthermore, we show that HIF2a is a novel STAT5 target gene which plays an important role in STAT5-induced stem cell phenotypes. Disclosures: No relevant conflicts of interest to declare.

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