scholarly journals Cell Intrinsic and Extrinsic Mechanisms Mediate the Role of c-Myc Haploinsufficiency in Controlling HSC Fate

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 2561-2561
Author(s):  
Yue Sheng ◽  
Chunjie Yu ◽  
Rui Ma ◽  
Zhijian Qian
Keyword(s):  
Bone Marrow ◽  
Conflicts Of Interest ◽  
White Blood Count ◽  
Bone Marrow Niche ◽  
Severe Anemia ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Deficient Mice

Abstract It has been shown that loss of c-Myc leads to accumulation of hematopoietic stem cells (HSCs) and severe cytopenia as a consequence of a blockage of HSC differentiation. Here we report a role of c-Myc haploinsufficiency in regulating HSC quiescence and self-renewal. We showed that c-Myc haploinsufficient mice displayed decreased white blood count and number of lymphocytes with normal myeloid cell differentiation. The number of HSCs and hematopoietic progenitor cells (HPCs) were all decreased significantly in c-Myc haploinsufficient mice as compared with control mice. We found that c-Myc haploinsufficiency inhibited HSC self-renewal capacity, increased proliferation and decreased quiescence of HSCs in vivo. By transplantation assays, we showed that c-Myc haploinsufficiency has extrinsic and intrinsic effects on the maintenance of HSCs in vivo. Our study suggests that loss of c-Myc activity and reduced dosage of c-Myc have distinct effects on HSC functions. c-Myc is a critical downstream mediator of the Wnt/b-catenin pathway. We showed that c-Myc haploinsufficiency is sufficient to prevent severe anemia in Apc heterozygous mice, and to significantly prolong the survival of Apc heterozygous mice. In addition, treatment of Apc haploinsufficient mice by a c-Myc inhibitor significantly reversed anemia in Apc-deficient mice. By transplantation assay, we further demonstrated that reduced expression of c-Myc in the bone marrow niche is responsible for prevention of severe anemia in Apc-deficient mice. However, we found that reduction of c-Myc by loss of a single allele of c-Myc did not rescue defective self-renewal capacity of Apc haploinsufficient HSCs. Taken together, our studies indicate that c-Myc mediates the function of the Wnt/b-catenin signaling pathway in bone marrow niche but not in HSCs. Disclosures No relevant conflicts of interest to declare.

Further Evidence That HO-1 Regulates SDF-1 Expression in the Bone Marrow Microenvironment and That HO-1-Deficient Mice Show a Defect in the SDF-1–CXCR4 Retention Axis of Hematopoietic Stem/Progenitor Cells in Bone Marrow and Thus Are Easy Mobilizers - Studies in HO-1 Mutant Mice, Irradiation Chimeras, and the Effect of in Vivo Pharmacological Inhibition of HO-1

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 344-344
Author(s):  
Marcin Wysoczynski ◽  
Janina Ratajczak ◽  
Gregg Rokosh ◽  
Roberto Bolli ◽  
Mariusz Z Ratajczak
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Crucial Role ◽  
Conflicts Of Interest ◽  
Wild Type ◽  
Hematopoietic Stem ◽  
Cell Counts ◽  
Deficient Mice

Abstract Abstract 344 Background: Stromal derived factor-1 (SDF-1), which binds to the CXCR4 receptor expressed on the surface of hematopoietic stem/progenitor cells (HSPCs), plays an important role in the retention of HSPCs in BM niches. Heme oxygenase (HO-1) is a stress-responsive enzyme that catalyzes the degradation of heme and plays an important function in various physiological and pathophysiological states associated with cellular stress, such as ischemic/reperfusion injury, atherosclerosis, and cancer. Interestingly, it has also been reported that HO-1 regulates the expression of SDF-1 in myocardium (J Mol Cell Cardiol. 2008;45:44–55). Aim of study: Since SDF-1 plays a crucial role in retention and survival of HSPCs in BM, we become interested in whether HO-1 is expressed by BM stromal cells and whether deficiency of HO-1 affects normal hematopoiesis and retention of HSPCs in BM. Experimental approach: To address this issue, we employed several complementary strategies to investigate HO-1–/–, HO-1+/–, and wild type (wt) mouse littermates for i) the expression level of SDF-1 in BM, ii) the number of clonogenic progenitors from major hematopoietic lineages in BM, iii) peripheral blood (PB) cell counts, iv) the chemotactic responsiveness of HSPCs to an SDF-1 gradient as well as to other chemoattractants, including sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), and extracellular nucleotiodes (ATP, UTP), iv) the adhesiveness of clonogenic progenitors to immobilized SDF-1 and stroma, v) the number of circulating HSPCs in PB, and vi) the degree of mobilization in response to granulocyte-colony stimulating factor (G-CSF) or AMD3100, assessed by enumerating the number of CD34–SKL cells and clonogeneic progenitors (CFU-GM) circulating in PB. We also exposed mice to the small HO-1 molecular inhibitor tin protoporphyrin IX (SnPP) and studied the effect of this treatment on G-CSF- or AMD3100-induced mobilization of HSPCs. Finally, to prove an environmental HSPC retention defect in HO-1-deficient mice, we created radiation chimeras, wild type mice transplanted with HO-1-deficient BM cells, and, vice versa, HO-1-deficient mice reconstituted with wild type BM cells. Results: Our data indicate that under normal, steady-state conditions, HO-1–/– and HO+/– mice have normal PB cell counts and numbers of circulating CFU-GM, while a lack of HO-1 leads to an increase in the number of erythroid (BFU-E) and megakaryocytic (CFU-GM) progenitors in BM. However, while BMMNCs from HO-1–/– have normal expression of the SDF-1-binding receptor, CXCR4, we observed that the mRNA level for SDF-1 in BM-derived fibroblasts was ∼4 times lower. This corresponded with the observation in vitro that HSPCs from HO-1–/– animals respond more robustly to an SDF-1 gradient, and HO-1–/– animals mobilized a higher number of CD34–SKL cells and CFU-GM progenitors into PB in response to G-CSF and AMD3100. Both G-CSF and AMD3100 mobilization were also significantly enhanced in normal wild type mice after in vivo administration of HO-1 inhibitor. Finally, mobilization studies in irradiation chimeras confirmed the crucial role of the microenvironmental SDF-1-based retention mechanism of HSPCs in BM niches. Conclusions: Our data demonstrate for the first time that HO-1 plays an important and underappreciated role in modulating the SDF-1 level in the BM microenvironment and thus plays a role in retention of HSPCs in BM niches. Furthermore, our recent data showing a mobilization effect by a small non-toxic molecular inhibitor of HO-1 (SnPP), suggest that blockage of HO-1 could be a promising strategy to facilitate mobilization of HSPCs. Further studies are also needed to evaluate the role of HO-1 in homing of HSPCs after transplantation to BM stem cell niches. Disclosures: No relevant conflicts of interest to declare.

Absence of the Rho GTPase Activating Protein p190-B Enhances Long Term Hematopoietic Stem Cell Engraftment

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 614-614 ◽  
Author(s):  
Haiming Xu ◽  
Hartmut Geiger ◽  
Kathleen Szczur ◽  
Deidra Deira ◽  
Yi Zheng ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Ex Vivo ◽  
Gtpase Activating Protein ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Proliferation And Differentiation ◽  
Serial Transplantation

Abstract Hematopoietic stem cell (HSC) engraftment is a multistep process involving HSC homing to bone marrow (BM), self-renewal, proliferation and differentiation to mature blood cells. However, the molecular regulation of HSC engraftment is still poorly defined. Small Rho GTPases are critical regulator of cell migration, proliferation and differentiation in multiple cell types. While their role in HSC functions has begun to be understood, the role of their regulator in vivo has been understudied. P190-B GTPase Activating Protein (GAP), a negative regulator of Rho activity, has been implicated in regulating cell size and adipogenesis-myogenesis cell fate determination during fetal development (Sordella, Dev Cell, 2002; Cell 2003). Here, we investigated the role of p190-B in HSC/P engraftment. Since mice lacking p190-B die before birth, serial competitive repopulation assay was performed using fetal liver (FL) tissues from day E14.5 WT and p190-B−/− embryos. WT and p190-B−/− FL cells exhibited similar levels of engraftment in primary recipients. However, the level of contribution of p190-B−/− cells to peripheral blood and bone marrow was maintained between the primary and secondary recipients and still easily detectable in tertiary recipients, while the level of contribution of FL WT cells dramatically decreased with successive serial transplantion and was barely detectable in tertiary recipients. The contribution to T cell, B cell and myeloid cell reconstitution was similar between the genotypes. A pool of HSC was maintained in serially transplanted p190-B−/− animals, since LinnegScaposKitpos (LSK) cells were still present in the BM of p190-B−/− secondary engrafted mice while this population disappeared in WT controls. Importantly, this enhanced long term engraftment was due to a difference in the functional capacity of p190-B−/− HSC compared to WT HSC since highly enriched p190-B−/− HSC (LSK) demonstrated similar enhanced serial transplantation potential. Because previous studies have suggested that the loss of long term function of HSC during serial transplantation can depend, at least in part, on the upregulation of the cyclin dependent kinase inhibitor p16Ink4a (Ito et al, Nat Med 2006), the expression of p16Ink4a was examined during serial transplantation. While expression of p16Ink4a increased in WT HSC in primary and secondary recipients, p16Ink4a remained low in p190-B−/− HSC, which indicated that p190-B-deficiency represses the upregulation of p16Ink4a in HSC in primary and secondary transplant recipients. This provides a possible mechanism of p190-B-mediated HSC functions. We next examined whether p190-B-deficiency may preserve the repopulating capacity of HSC/P during ex vivo cytokine-induced culture. While freshly isolated LSK cells from WT and p190-B−/− mice exhibited comparable intrinsic clonogenic capacity, the frequency of colony-forming unit after 7 days in culture was 2 fold-higher in p190-B−/− compared with WT cultures, resulting in a net CFU expansion. Furthermore, competitive repopulation assays showed significantly higher repopulating activity in mice that received p190-B−/− cultured cells compared with WT cells equivalent to a 4.4-fold increase in the estimated frequency of repopulating units. Interestingly, p190-deficiency did not alter cell cycling rate or survival both in vivo and in vitro. Therefore, p190-B-deficiency maintains key HSC functions either in vivo or in ex vivo culture without altering cycling rate and survival of these cells. These findings define p190-B as a critical regulator of HSC functions regulating self renewal activity while maintaining a balance between proliferation and differentiation.

Non-Canonical NF-Kb Signaling Regulates Hematopoietic Stem Cell Self-Renewal and Microenvironment Interactions

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 859-859 ◽  
Author(s):  
Chen Zhao ◽  
Yan Xiu ◽  
John M Ashton ◽  
Lianping Xing ◽  
Yoshikazu Morita ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Conflicts Of Interest ◽  
Wild Type ◽  
Double Knockout ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Physiological Processes ◽  
Marrow Cells

Abstract Abstract 859 RelB and NF-kB2 are the main effectors of NF-kB non-canonical signaling and play critical roles in many physiological processes. However, their role in hematopoietic stem/progenitor cell (HSPC) maintenance has not been characterized. To investigate this, we generated RelB/NF-kB2 double-knockout (dKO) mice and found that dKO HSPCs have profoundly impaired engraftment and self-renewal activity after transplantation into wild-type recipients. Transplantation of wild-type bone marrow cells into dKO mice to assess the role of the dKO microenvironment showed that wild-type HSPCs cycled more rapidly, were more abundant, and had developmental aberrancies: increased myeloid and decreased lymphoid lineages, similar to dKO HSPCs. Notably, when these wild-type cells were returned to normal hosts, these phenotypic changes were reversed, indicating a potent but transient phenotype conferred by the dKO microenvironment. However, dKO bone marrow stromal cell numbers were reduced, and bone-lining niche cells supported less HSPC expansion than controls. Further, increased dKO HSPC proliferation was associated with impaired expression of niche adhesion molecules by bone-lining cells and increased inflammatory cytokine expression by bone marrow cells. Thus, RelB/NF-kB2 signaling positively and intrinsically regulates HSPC self-renewal and maintains stromal/osteoblastic niches and negatively and extrinsically regulates HSPC expansion and lineage commitment through the marrow microenvironment. Disclosures: No relevant conflicts of interest to declare.

An In Vivo Functional Screen Identifies miRNA-150 As a Regulator of Hematopoietic Regeneration Post Chemotherapeutic Injury

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2333-2333
Author(s):  
Brian D. Adams ◽  
Shangqin Guo ◽  
Haitao Bai ◽  
Changchun Xiao ◽  
E. Premkumar Reddy ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Conflicts Of Interest ◽  
Negative Regulator ◽  
Post Transplantation ◽  
Hematopoietic Stem ◽  
Hematopoietic Recovery ◽  
Expression Construct

Abstract Abstract 2333 . MicroRNAs are important regulators of many hematopoietic processes, yet little is known with regard to the role of microRNAs in controlling normal hematopoietic regeneration. The most common methodology for in vivo microRNA studies follows a hypothesis-driven candidate approach. Here, we report the establishment of an unbiased, in vivo, microRNA gain-of-function screen, and the identification of miR-150 as a negative regulator of hematopoietic recovery post chemotherapeutic challenge. Specifically, a retroviral-library consisting of 135 hematopoietic-expressed microRNAs was generated, with each expression construct containing a barcode sequence that can be specifically recognized using a novel bead-based platform. Hematopoietic-stem-and-progenitor-cell (HSPC)-enriched wild-type bone marrow was transduced with this library and transplanted into lethally-irradiated recipients. Analysis of peripheral blood samples from each recipient up to 11 weeks post transplantation revealed that 87% of the library barcodes are reliably detected. To identify microRNAs that regulate hematopoietic regeneration after chemotherapy-induced injury, we measured the change in barcode abundance for specific microRNA constructs after 5-fluorouracil (5-FU) challenge. Notably, a small number of barcodes were consistently depleted in multiple recipient mice after treatment. Among the top hits was the miR-150-associated barcode, which was selected for further experimentation. Indeed, overexpression of miR-150 in a competitive environment resulted in significantly lower recovery rates for peripheral myeloid and platelet populations after 5-FU treatment, whereas the effects on B- and T-cells were milder. Furthermore, full recovery of these cell populations did not occur until ∼12 weeks after treatment, suggesting the involvement of HSPCs and/or common lineage progenitors. Conversely, knocking out miR-150 led to an opposite phenotype, with platelets and myeloid cells displaying faster recovery in both competitive and non-competitive settings. Interestingly, we could not observe the described effects of miR-150 in bone marrow primary cell cultures, suggesting that such effects cannot be recapitulated in vitro. Overall, these data indicate that miR-150 is a novel regulator of hematopoietic recovery after chemotherapeutic-induced injury, and highlight the important role of microRNAs in the intrinsic wiring of the hematopoietic regeneration program. Our experiments also demonstrate the feasibility and power of functional in vivo screens for studying normal hematopoietic functions, which can become an important tool in the hematology field. Disclosures: No relevant conflicts of interest to declare.

Heterogeneity in the Making of Blood

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. SCI-27-SCI-27
Author(s):  
David T. Scadden
Keyword(s):  
Bone Marrow ◽  
Conflicts Of Interest ◽  
Bone Marrow Niche ◽  
Cell Selection ◽  
Hematopoietic Progenitor ◽  
Marrow Space ◽  
And Function ◽  
Osteolineage Cells

It is increasingly clear that the bone marrow is comprised of a heterogeneous complex of niches for hematopoietic cells, some for stem cells in the perivascular space and some for progenitors. We have used two approaches to define the role of specific cells in the marrow. First, single cell selection and characterization based on in vivo proximity to HSPC. This method has defined a subset of endosteal lining cells that can be immunophenotypically defined and isolated and reveals IL-18 as a regulator of hematopoietic progenitor quiescence. Second, candidate cell depletion that revealed mature osteolineage cells expressing osteocalcin as regulating the production of thymic emigrants through the expression of Dll4. Deletion of these cells reduces the number and function of T-biased lymphoid progenitors in the marrow space as well as thymic populations and mature T cells in the blood. These data suggest that specific niche subsets can be defined and through them, novel molecular regulators of HSPC function. The bone marrow niche is a heterogeneous composite of distinctive niches. Disclosures No relevant conflicts of interest to declare.

scholarly journals Differential impact of Ink4a and Arf on hematopoietic stem cells and their bone marrow microenvironment in Bmi1-deficient mice

2006 ◽  
Vol 203 (10) ◽  
pp. 2247-2253 ◽  
Author(s):  
Hideyuki Oguro ◽  
Atsushi Iwama ◽  
Yohei Morita ◽  
Takehiko Kamijo ◽  
Maarten van Lohuizen ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Polycomb Group ◽  
The Self ◽  
Differential Impact ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Loss Of Self ◽  
Deficient Mice

The polycomb group (PcG) protein Bmi1 plays an essential role in the self-renewal of hematopoietic and neural stem cells. Derepression of the Ink4a/Arf gene locus has been largely attributed to Bmi1-deficient phenotypes in the nervous system. However, its role in hematopoietic stem cell (HSC) self-renewal remained undetermined. In this study, we show that derepressed p16Ink4a and p19Arf in Bmi1-deficient mice were tightly associated with a loss of self-renewing HSCs. The deletion of both Ink4a and Arf genes substantially restored the self-renewal capacity of Bmi1−/− HSCs. Thus, Bmi1 regulates HSCs by acting as a critical failsafe against the p16Ink4a- and p19Arf-dependent premature loss of HSCs. We further identified a novel role for Bmi1 in the organization of a functional bone marrow (BM) microenvironment. The BM microenvironment in Bmi1−/− mice appeared severely defective in supporting hematopoiesis. The deletion of both Ink4a and Arf genes did not considerably restore the impaired BM microenvironment, leading to a sustained postnatal HSC depletion in Bmi1−/−Ink4a-Arf−/− mice. Our findings unveil a differential role of derepressed Ink4a and Arf on HSCs and their BM microenvironment in Bmi1-deficient mice. Collectively, Bmi1 regulates self-renewing HSCs in both cell-autonomous and nonautonomous manners.

Stress-Mediated Activation of Dormant Hematopoietic Stem Cells In Vivo

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. SCI-41-SCI-41
Author(s):  
Andreas Trumpp ◽  
Marieke Essers
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Conflicts Of Interest ◽  
Negative Regulator ◽  
Strong Increase ◽  
Interferon Α ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Abstract SCI-41 Maintenance of the blood system is dependent on dormant hematopoietic stem cells (HSCs), which are characterized by pluripotency and lifelong self-renewal capacity. In order to both maintain a supply of mature blood cells and not exhaust HSCs throughout the lifespan of the organism, most adult HSCs remain deeply quiescent during homeostasis, and only a limited number are cycling at any given time. The balance between self-renewal and differentiation of HSCs is controlled by external factors such as chemokines and cytokines, as well as by interactions of HSCs with their niche environment. The transcriptome of dormant CD34-CD150+CD48-LSK- HSCs significantly differs from that of active HSCs with the same phenotype, while the latter are highly similar to MPP1 progenitors which express CD34. One of the genes differentially expressed is the cylindromatosis (CYLD) gene, which encodes a negative regulator of the NF-κB signaling pathway. HSCs failing to express functional CYLD show various defects associated with a disturbed balance between dormant and active HSCs, suggesting a role for NF-κB signaling in establishing dormancy in HSCs. In addition, our studies have recently shown that the cytokine interferon-α (IFNα) very efficiently activates dormant HSCs in vivo. Within hours after treatment of mice with IFNα, HSCs exit G0 and enter an active cell cycle. In general, IFNα is produced in response to viral infections by cells of the immune system, and plays an important role in the antiviral host defense. We now questioned whether endogenous IFNα is also produced in response to other types of bone marrow stress and whether this affects the proliferation rate of HSCs. To monitor IFNα production in the bone marrow in vivo, we have generated MxCre ROSA-R26-EYFP mice and found that treatment with both the chemotherapeutic agent 5-FU as well as the endotoxin LPS leads to the production of IFNα in the vicinity of HSCs and progenitors. In addition, LPS treatment in vivo induced a strong increase in HSC cycling. Surprisingly, since mice lacking the IFNα receptor (Ifnar−/−) still respond to LPS, this effect is independent of IFNAR signaling. Strikingly, LPS-induced HSC activation correlated with increased expression of Sca-1, similar to what occurs upon IFNα treatment. Moreover, as for IFNα, the upregulation of SCA-1 is required for LPS-induced proliferation, since Sca-1−/− mice fail to respond to LPS stimulation. In summary, these data suggest that not only virus-inducible IFNα, but also infections by gram-negative-bacteria-produced LPS induce cycling of progenitors and otherwise dormant HSCs. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Foxo1 Expressed in Osteoblasts Promotes the Leukemogenic Properties of β-Catenin By Activating Notch Signaling

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2356-2356
Author(s):  
Aruna Kode ◽  
Ioanna Mosialou ◽  
Sanil J Manavalan ◽  
Julie Teruya Feldstein ◽  
Govind Bhagat ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Notch Signaling ◽  
Conflicts Of Interest ◽  
Bone Marrow Niche ◽  
Differentiation Potential ◽  
Genetic Event ◽  
Hematopoietic Stem ◽  
New Strategy ◽  
Subsequent Activation

Abstract Osteoblasts affect self-renewal and expansion of hematopoietic stem cells (HSCs) and homing of healthy hematopoietic and tumor cells into the bone marrow. Moreover, in the mouse, constitutive activation of b-catenin (Ctnnb1CAosb mice) in osteoblasts is sufficient to alter the differentiation potential of myeloid and lymphoid progenitors and to trigger the development of acute myeloid leukemia (AML). Because the same genetic event is associated with AML development in humans we sought to better understand its molecular bases. For that purpose we examined in vivo whether FoxO1, a transcription factor known to interact with β-catenin, affects its AML inducing properties. Deleting one allele of FoxO1 mice from the osteoblasts of leukemic Ctnnb1CAosb mice prevented the appearance of anemia, peripheral monocytosis, neutrophilia and lymphocytopenia that are otherwise observed in Ctnnb1CAosb mice. Similarly, FoxO1 haploinsufficiency in osteoblasts of Ctnnb1CAosb mice prevented the shift in the differentiation of HSCs to the myeloid lineage and the increase in the LSK+/CD150+/CD48- subset of long term repopulating HSC progenitors (LT-HSCs). Histological analysis showed that myeloid and megakaryocyte dysplasias observed in Ctnnb1CAosb mice and associated with their AML phenotype were also rescued in Ctnnb1CAosb;FoxO1osb+/-animals. As a result FoxO1 haploinsufficiency in osteoblasts prevented the early lethality of Ctnnb1CAosb mice since Ctnnb1CAosb;FoxO1osb+/-mice lived and were healthy for at least one year, the entire time that they were observed. At the molecular level FoxO1 interacts with b-catenin in osteoblasts to induce expression of the Notch ligand Jagged-1 which initiates the dysmyelopoiesis leading to AML. ChiP/Re-ChiP assays and transient transfection experiments showed that this interaction requires the formation of a b-catenin/Foxo1 complex at two distinct locations in the regions of the Jagged-1 promoter. It also leads to subsequent activation of Notch signaling in LT- HSC progenitors. These events induce the leukemogenic transformation of HSCs. These findings identify FoxO1 through its expression in osteoblasts as a factor affecting hematopoiesis and provide a molecular mechanism whereby the FoxO1/ activated b-catenin interaction results in AML. They further support the notion that targeting the bone marrow niche may be a new strategy to treat leukemia and raise the prospect that FoxO1 oncogenic properties may occur in other tissues. Disclosures No relevant conflicts of interest to declare.

Activation of Dormant Hematopoietic Stem Cells In Vivo by the Endotoxin LPS.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1613-1613 ◽  
Author(s):  
Marieke Essers ◽  
Raphael Lutz ◽  
Andrea Kern ◽  
Stephan Wurzer ◽  
Andreas Trumpp
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Viral Infections ◽  
Conflicts Of Interest ◽  
Strong Increase ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
General Role ◽  
Lps Treatment

Abstract Abstract 1613 Maintenance of the blood system is dependent on dormant haematopoietic stem cells (HSCs), which are characterized by pluripotency and life long self-renewal capacity. In order to both maintain a supply of mature blood cells and not exhaust HSCs throughout the lifespan of the organism, most adult HSCs remain deeply quiescent during homeostasis and only a limited number are cycling at any given time. The balance between self-renewal and differentiation of HSCs is controlled by external factors such as chemokines and cytokines, as well as interactions of HSCs with its niche environment. We have recently shown that the cytokine IFNa very efficiently activates dormant HSCs in vivo. Within hours after treatment of mice with IFNa, HSCs exit G0 and enter an active cell cycle. In general, IFNa is produced in response to viral infections by cells of the immune system, and plays an important role in the antiviral host defense. We now questioned whether endogenous IFNa is also produced in response to other types of bone marrow stress and whether this affects the proliferation rate of HSCs. To monitor IFNa production in the bone marrow in vivo, we have generated MxCre; ROSA-R26-EYFP mice and found that treatment with both the chemotherapeutic agent 5-FU as well as the endotoxin LPS leads to the production of IFNa in the vicinity of HSCs and progenitors. In addition, LPS treatment in vivo induced a strong increase in HSC cycling. Surprisingly, since mice lacking the IFNa receptor (Ifnar-/-) still respond to LPS this effect is independent of IFNAR signaling. LPS binds and signals via the TLR4-CD14 receptor complex and HSCs of mice lacking TLR4 (TLR4-/-) are no longer activated by LPS. Strikingly, LPS induced HSC activation correlated with increased expression of Sca-1, similar to what occurs upon IFNa treatment. Moreover, as for IFNa, the upregulation of Sca-1 is required for LPS induced proliferation, since Sca-1-/- mice fail to respond to LPS stimulation. In summary, these data suggest that not only virus inducible IFNa, but also infections by gram negative bacteria produced LPS induces cycling of progenitors and otherwise dormant HSCs. Finally, both IFNa and LPS induced activation of HSCs are dependent on the up-regulation of Sca-1, suggesting a more general role for Sca-1 in the activation of dormant stem cells in response to injury signals. Disclosures: No relevant conflicts of interest to declare.

S6K1 Regulates Self-Renewal of Leukemia Initiating Cells and Normal Hematopoietic Stem Cells

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 442-442
Author(s):  
Joydeep Ghosh ◽  
Anindya Chatterjee ◽  
Baskar Ramdas ◽  
Michihiro Kobayashi ◽  
Peilin Ma ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Absolute Number ◽  
The Self ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Mtorc1 Pathway ◽  
Deficient Mice

Abstract The mixed-lineage leukemia (MLL) gene is required for the maintenance of adult hematopoietic stem cells (HSCs) and regulation of progenitor population. Translocations in MLL have been detected in approximately 5-10% of adult acute leukemia patients and in approximately 70% of acute leukemias in infants. Various genes, including AF4, AF5, AF9, ELL and ENL have been identified as partners for translocation in MLL-rearranged leukemia. In hematopoietic cells, expression of MLL fusion proteins result in a block of differentiation. AML patients who successfully undergo treatment but relapse suggest the importance of targeting leukemia initiating cells (LICs) within the MLL leukemia. LICs remain in a quiescent state and are capable of survival despite treatment with chemotherapeutic agents or targeted molecular inhibitors. In mouse models, LICs are defined by the capability of successfully propagating disease upon serial transplantation. In order to prevent disease relapse, identification of molecules, which regulate the self-renewal of LICs, is essential. The phosphatidylinositol 3-kinase (PI3K)-Akt-mechanistic target of rapamycin complex1 (mTORC1) pathway is a key regulator of self-renewal of both HSCs and LICs. Deletion of Raptor, a subunit of mTORC1, does not affect initiation and progression of acute myeloid leukemia (AML), but Raptor deficiency results in delayed propagation of AML. Upon its activation, mTORC1 phosphorylates and activates p70 ribosomal protein S6 kinase (S6K1) and inhibits the activity of eukaryote translation initiation factor 4E binding protein 1 (4E-BP1). S6K1 has been shown to be hyperactivated in hematopoietic cells expressing oncogenic MLL-AF9 fusion protein. In our study, we have assessed the role of S6K1 in the initiation, progression and propagation of AML using a genetic model of S6K1 knockout mice (S6K1-/-). We expressed MLL-AF9 fusion oncoprotein in WT and S6K1-/- hematopoietic stem and progenitor cells (HSC/Ps) and transplanted them into lethally irradiated recipients. Recipients of both WT and S6K1-/- HSC/Ps bearing MLL-AF9 displayed high white blood cell (WBC) count, splenomegaly and developed AML. There was no difference in survival between the WT and S6K1-/- recipients. In order to determine whether S6K1 regulates the self-renewal of LICs, we transplanted lethally irradiated mice with cells from WT and S6K1-/- primary recipients who developed AML. Recipients of S6K1 deficient AML cells survived significantly longer compared to controls (n=17/group, p<0.001). S6K1 deficient HSC/Ps expressing MLL-AF9 showed reduced activation of Akt as well as decreased mTORC1 activity, suggesting that deletion of S6K1 results in reduced activation of PI-3K-Akt-mTORC1 pathway both upstream and downstream of mTORC1 which indicates that S6K1 might be involve in a feedback loop within this pathway. To determine the role of S6K1 in normal HSC development and maintenance, we analyzed bone marrow derived HSCs in WT and S6K1-/- mice. S6K1 deficiency did not alter the frequency of long term HSCs (LT-HSCs) as defined by CD150+ CD48- Lin- Sca1+ c-Kit+ surface markers, but the absolute number of LT-HSCs were significantly reduced in S6K1 deficient mice (p<0.02). The absolute number of multipotent progenitors (MPPs) (p<0.001), common myeloid progenitors (CMPs) (p<0.01) and megakaryocyte-erythroid progenitors (MEPs) (p<0.01) were also significantly reduced in S6K1 deficient mice. Deficiency of S6K1 resulted in reduced quiescence of LT-HSCs (p<0.05). Expression level of p21, an inhibitor of cell cycle progression, was significantly decreased in LT-HSCs derived from S6K1-/- mice compared to LT-HSCs from control group. To study the role of S6K1 in HSCs' function, we performed competitive repopulation assay. Sorted LT-HSCs from bone marrow cells derived from either WT or S6K1-/- mice were transplanted with competitor cells into lethally irradiated recipients. S6K1 deficient LT-HSCs displayed reduced repopulating ability in secondary recipients (n=9-10/group, p<0.001). Expression level of p21 was downregulated in donor-derived HSCs isolated from secondary recipients of S6K1 deficient HSCs compared to control. Overall, our study establishes S6K1 as a critical regulator of self-renewal of both LICs and HSCs. Deficiency of S6K1 in AML cells results in delayed propagation of disease and deficiency of S6K1 in HSCs results in decreased self-renewal potential. Disclosures No relevant conflicts of interest to declare.

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