Cellular and Molecular Mechanisms of Environmental Pollutants on Hematopoiesis

Hematopoiesis is a complex and intricate process that aims to replenish blood components in a constant fashion. It is orchestrated mostly by hematopoietic progenitor cells (hematopoietic stem cells (HSCs)) that are capable of self-renewal and differentiation. These cells can originate other cell subtypes that are responsible for maintaining vital functions, mediate innate and adaptive immune responses, provide tissues with oxygen, and control coagulation. Hematopoiesis in adults takes place in the bone marrow, which is endowed with an extensive vasculature conferring an intense flow of cells. A myriad of cell subtypes can be found in the bone marrow at different levels of activation, being also under constant action of an extensive amount of diverse chemical mediators and enzymatic systems. Bone marrow platelets, mature erythrocytes and leukocytes are delivered into the bloodstream readily available to meet body demands. Leukocytes circulate and reach different tissues, returning or not returning to the bloodstream. Senescent leukocytes, specially granulocytes, return to the bone marrow to be phagocytized by macrophages, restarting granulopoiesis. The constant high production and delivery of cells into the bloodstream, alongside the fact that blood cells can also circulate between tissues, makes the hematopoietic system a prime target for toxic agents to act upon, making the understanding of the bone marrow microenvironment vital for both toxicological sciences and risk assessment. Environmental and occupational pollutants, therapeutic molecules, drugs of abuse, and even nutritional status can directly affect progenitor cells at their differentiation and maturation stages, altering behavior and function of blood compounds and resulting in impaired immune responses, anemias, leukemias, and blood coagulation disturbances. This review aims to describe the most recently investigated molecular and cellular toxicity mechanisms of current major environmental pollutants on hematopoiesis in the bone marrow.

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Hematopoietic stem and progenitor cells are present in healthy gingiva tissue

Journal of Experimental Medicine ◽

10.1084/jem.20200737 ◽

2021 ◽

Vol 218 (4) ◽

Author(s):

Siddharth Krishnan ◽

Kelly Wemyss ◽

Ian E. Prise ◽

Flora A. McClure ◽

Conor O’Boyle ◽

...

Keyword(s):

Bone Marrow ◽

Immune Responses ◽

Progenitor Cells ◽

Myeloid Cell ◽

Extramedullary Hematopoiesis ◽

Innate Immune ◽

Innate Immune Cells ◽

Hematopoietic Stem ◽

Effector Cells ◽

Stem And Progenitor Cells

Hematopoietic stem cells reside in the bone marrow, where they generate the effector cells that drive immune responses. However, in response to inflammation, some hematopoietic stem and progenitor cells (HSPCs) are recruited to tissue sites and undergo extramedullary hematopoiesis. Contrasting with this paradigm, here we show residence and differentiation of HSPCs in healthy gingiva, a key oral barrier in the absence of overt inflammation. We initially defined a population of gingiva monocytes that could be locally maintained; we subsequently identified not only monocyte progenitors but also diverse HSPCs within the gingiva that could give rise to multiple myeloid lineages. Gingiva HSPCs possessed similar differentiation potentials, reconstitution capabilities, and heterogeneity to bone marrow HSPCs. However, gingival HSPCs responded differently to inflammatory insults, responding to oral but not systemic inflammation. Combined, we highlight a novel pathway of myeloid cell development at a healthy barrier, defining a gingiva-specific HSPC network that supports generation of a proportion of the innate immune cells that police this barrier.

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Characterization of Hematopoietic Stem Cell Frequency and Function In Unexplained Anemia of the Elderly

Blood ◽

10.1182/blood.v116.21.2047.2047 ◽

2010 ◽

Vol 116 (21) ◽

pp. 2047-2047

Author(s):

Wendy Pang ◽

Elizabeth Price ◽

Irving L. Weissman ◽

Stanley L. Schrier

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

In Vitro Culture ◽

Progenitor Cells ◽

The Elderly ◽

Elderly Subjects ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

And Function

Abstract Abstract 2047 Anemia is both a highly prevalent and clinically important condition that causes significant morbidity and mortality in the elderly population. While anemia in the elderly can be attributed to a number of causes, approximately 30% of elderly subjects with anemia have no overt etiology and fall under the category of unexplained anemia of the elderly (UA). There is increasing evidence to suggest that changes in the frequency and/or function of hematopoietic stem and progenitor cells may contribute to the onset and pathophysiology of age-associated hematological conditions, such as UA. Hematopoietic stem cells (HSC) reside at the top of the hematopoietic hierarchy and can differentiate, via increasingly committed downstream progenitors, into all the mature cells of the hematopoietic system. Human myelo-erythroid development proceeds through a set of oligopotent progenitors: HSC give rise to multipotent progenitors (MPP), which give rise to common myeloid progenitors (CMP), which in turn give rise to granulocyte-macrophage progenitors (GMP) and megakaryocyte-erythrocyte progenitors (MEP). We use flow cytometry and in vitro culture of sorted human HSC (Lin-CD34+CD38-CD90+CD45RA-), MPP (Lin-CD34+CD38-CD90-CD45RA-), CMP (Lin-CD34+CD38+CD123+CD45RA-), GMP (Lin-CD34+CD38+CD123+CD45RA+), and MEP (Lin-CD34+CD38+CD123-CD45RA-) from hematologically normal young (23 samples; age 20–35) and elderly (11 samples; age 65+) and UA (5 samples; age 65+) bone marrow samples in order to characterize the changes in the distribution and function of hematopoietic stem and progenitor populations during the aging process and, in particular, in the development of UA. We found that UA patients contain higher frequencies of HSC compared to both elderly normal (1.5-fold; p<0.03) and young normal samples (2.8-fold; p<10-5). We also found increased frequencies of MPP from UA patients compared to MPP from elderly normal (2.6-fold; p<0.002) and young normal samples (5.8-fold; p<0.04). While we observed similar frequencies of CMP among the three groups, we found a notable trend suggesting decreased frequencies of GMP and corresponding increased frequencies of MEP in UA patients. Functionally, HSC from the three groups exhibit statistically insignificant differences in the efficiency of colony formation under the myeloid differentiation-promoting methylcellulose-based in vitro culture conditions; however, on average, HSC from elderly bone marrow samples, regardless of the presence or absence of anemia, tend to form fewer colonies in methylcellulose. Interestingly, HSC from UA patients produce more granulocyte-monocyte (CFU-GM) colonies and fewer erythroid (CFU-E and BFU-E) colonies, compared to HSC from normal samples (p<0.001). Similarly, CMP from UA patients, compared to normal CMP, yield skewed distributions of myeloid-erythroid colonies when plated in methylcellulose, significantly favoring production of CFU-GM colonies over CFU-E and BFU-E colonies (p<0.003). Additionally, MEP from UA patients form both CFU-E and BFU-E colonies in methylcellulose albeit at a significantly lower efficiency than MEP from normal bone marrow samples (p<0.01). This is the first study to examine the changes in hematopoietic stem and progenitor populations in UA patients. The changes in the distribution of hematopoietic stem and progenitor cells in UA patients indicate that the HSC and MPP populations, and possibly also the MEP population, expand in the context of anemia, potentially in response to homeostatic feedback mechanisms. Nevertheless, these expanded populations are functionally impaired in their ability to differentiate towards the erythroid lineage. Our data suggest that there are intrinsic defects in the HSC population of UA patients that lead to poor erythroid differentiation, which can be readily observed even in the earliest committed myelo-erythroid progenitors. We have generated gene expression profiling data from these purified hematopoietic stem and progenitor populations from UA patients to try to identify biological pathways and markers relevant to disease pathogenesis and potential therapeutic targets. Disclosures: Weissman: Amgen, Systemix, Stem cells Inc, Cellerant: Consultancy, Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Schrier:Celgene: Research Funding.

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Hematopoietic Stem and Progenitor Cells as Effectors in Innate Immunity

Bone Marrow Research ◽

10.1155/2012/165107 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 27

Author(s):

Jennifer L. Granick ◽

Scott I. Simon ◽

Dori L. Borjesson

Keyword(s):

Bone Marrow ◽

Immune Response ◽

Progenitor Cells ◽

Innate Immune Response ◽

Innate Immune ◽

Phenotypic Characterization ◽

Hematopoietic Stem ◽

Effector Cells ◽

Stem And Progenitor Cells ◽

And Function

Recent research has shed light on novel functions of hematopoietic stem and progenitor cells (HSPC). While they are critical for maintenance and replenishment of blood cells in the bone marrow, these cells are not limited to the bone marrow compartment and function beyond their role in hematopoiesis. HSPC can leave bone marrow and circulate in peripheral blood and lymph, a process often manipulated therapeutically for the purpose of transplantation. Additionally, these cells preferentially home to extramedullary sites of inflammation where they can differentiate to more mature effector cells. HSPC are susceptible to various pathogens, though they may participate in the innate immune response without being directly infected. They express pattern recognition receptors for detection of endogenous and exogenous danger-associated molecular patterns and respond not only by the formation of daughter cells but can themselves secrete powerful cytokines. This paper summarizes the functional and phenotypic characterization of HSPC, their niche within and outside of the bone marrow, and what is known regarding their role in the innate immune response.

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Hematopoietic stem and progenitor cells regulate the regeneration of their niche by secreting Angiopoietin-1

eLife ◽

10.7554/elife.05521 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 84

Author(s):

Bo O Zhou ◽

Lei Ding ◽

Sean J Morrison

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Stromal Cells ◽

Leptin Receptor ◽

Hematopoietic Cells ◽

Perivascular Niche ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

And Function ◽

Angiopoietin 1

Hematopoietic stem cells (HSCs) are maintained by a perivascular niche in bone marrow but it is unclear whether the niche is reciprocally regulated by HSCs. Here, we systematically assessed the expression and function of Angiopoietin-1 (Angpt1) in bone marrow. Angpt1 was not expressed by osteoblasts. Angpt1 was most highly expressed by HSCs, and at lower levels by c-kit+ hematopoietic progenitors, megakaryocytes, and Leptin Receptor+ (LepR+) stromal cells. Global conditional deletion of Angpt1, or deletion from osteoblasts, LepR+ cells, Nes-cre-expressing cells, megakaryocytes, endothelial cells or hematopoietic cells in normal mice did not affect hematopoiesis, HSC maintenance, or HSC quiescence. Deletion of Angpt1 from hematopoietic cells and LepR+ cells had little effect on vasculature or HSC frequency under steady-state conditions but accelerated vascular and hematopoietic recovery after irradiation while increasing vascular leakiness. Hematopoietic stem/progenitor cells and LepR+ stromal cells regulate niche regeneration by secreting Angpt1, reducing vascular leakiness but slowing niche recovery.

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Reversible Expansion of Hematopoietic Stem Cells (HSC) and CML-Like Disease in Transgenic Mice Expressing BCR-ABL under the Control of the SCL 3′ Enhancer.

Blood ◽

10.1182/blood.v104.11.715.715 ◽

2004 ◽

Vol 104 (11) ◽

pp. 715-715

Author(s):

Steffen Koschmieder ◽

Berthold Goettgens ◽

Pu Zhang ◽

Tajhal Dayaram ◽

Kristin Geary ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Transgenic Mice ◽

Hematopoietic Stem Cells ◽

Progenitor Cells ◽

Peripheral Blood ◽

Molecular Mechanisms ◽

Leukemic Cells ◽

Hematopoietic Stem ◽

Double Transgenic Mice

Abstract Chronic myeloid leukemia (CML) is a malignant disorder originating from the transformation of hematopoietic stem cells (HSC) by the BCR-ABL oncogene. Using the tet-off system, we have generated double-transgenic mice in which BCR-ABL is expressed under the control of the murine SCL 3′ enhancer, which targets expression to the vast majority of HSC and progenitors. After induction of BCR-ABL, all mice developed progressive chronic neutrophilia and leukocytosis (20–40 K/ul), and the animals died or were sacrificed in moribund condition within 58+/−28 days. Upon necropsy, bone marrow granulocytic hyperplasia, splenomegaly as well as organ infiltration by leukemic cells (liver, kidney, lung, small intestine, skin) were found. In addition, 31% of the mice subsequently developed ALL or lymphomas. BCR-ABL mRNA and protein expression were demonstrated in the affected organs. Expression of the transactivating transgene tTA was high in HSC, CMP, and CLP, but low in GMP and MEP, as assessed by real-time PCR, suggesting that the SCL 3′ enhancer indeed directed BCR-ABL expression to the most primitive hematopoietic cells within the bone marrow. The percentage of HSC in the bone marrow was expanded 7- and 26-fold in double-transgenic as compared to single-transgenic or wild-type control mice within 12 and 21 days, respectively, after BCR-ABL induction. GMP were increased 2- and 3-fold while the number of CMP was decreased 2-fold after 12 days but was increased 1.5-fold after 21 days. MEP were decreased 3-fold at both time points. In keeping with these results, the percentage of Ter-119 positive erythroid cells was decreased while the percentage of Gr-1 positive granulocytic cells was increased in the bone marrow. To assess reversibility of the phenotype, we readministered tetracycline to abrogate BCR-ABL expression. Double-transgenic mice showed rapid clinical improvement, reversion of neutrophilia and leukocytosis, normalization of Gr-1/Mac-1 positive cells in the peripheral blood and spleen, and reversion of splenomegaly. In addition, in mice that had developed lymphoblastic disease, readministration of tetracycline led to disappearance of lymphomas and of B220/BP-1 positive lymphoblastic cells in the peripheral blood. Furthermore, expansion of the HSC compartment in the bone marrow was also reversible, and the percentage of HSC decreased to levels observed in control mice. Repeated induction of BCR-ABL expression by removal of tetracycline led to reappearance of the myeloid and lymphoid phenotype. Again, the disease was reversible, and none of the animals relapsed while on tetracycline, suggesting that the phenotype remained completely dependent on the expression of the oncogene. In conclusion, we present a model of BCR-ABL mediated CML-like disease with expansion of phenotypic hematopoietic stem cells and myeloid progenitor cells in the bone marrow. The target cell population in this model closely resembles the origin of transformation in patients with CML, allowing for in vivo monitoring of early molecular mechanisms of BCR-ABL transformation. We are currently studying the function of the expanded HSC and progenitor cells in transplantation experiments.

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Dendritic Cell Homeostasis Is Maintained by Non-Hematopoietic and T Cell-Produced Flt3-Ligand In Steady-State and During Immune Responses.

Blood ◽

10.1182/blood.v116.21.1547.1547 ◽

2010 ◽

Vol 116 (21) ◽

pp. 1547-1547

Author(s):

Chandra Sekhar Boddupalli ◽

Dior Baumjohann ◽

Tim Sparwasser ◽

Markus G Manz

Keyword(s):

Bone Marrow ◽

T Cells ◽

Steady State ◽

Immune Responses ◽

Lymph Nodes ◽

Progenitor Cells ◽

T And B Cells ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

Abstract Abstract 1547 Lymphoid tissue dendritic cells (DCs) have a short life-span of a few days and need to be continuously replenished from hematopoietic stem and progenitor cells. Flt3-Ligand (Flt3L) plays non-redundant role in development of DCs (McKenna. H.J. et al., Blood; 2000). Previously we found that Flk2 (fetal liver kinase-2), the cognate receptor for Flt3L is expressed on early dendritic cell progenitors and Flt3L-Flk2 signalling efficiently supports DC development from early progenitors to steady-state DCs in mice and men (Karsunky, H. et al., J Exp Med; 2003; Chicha L. et al. J Exp Med; 2004). Flk2 is also expressed on mature steady-state lymphoid organ DCs; however its function on mature cells remains to be determined. Flt3L is expressed in almost all the tissues in both mice and men (Hannum, C. et al., Nature; 1994) and this cytokine is critical in the maintenance of DC/T regulatory (Treg) cell homeostasis (Darrase-Jéze. G et al., J Exp Med; 2009; Swee LK et al., Blood; 2009; Manz MG, Blood 2009). However, the precise cellular source of Flt3L and the regulation of production in steady-state and immune responses in vivo is not well understood. Genetic ablation of the Flk2 receptor lead to 10-fold elevated Flt3L levels in the serum of mice. To evaluate if hematopoietic or non-hematopoietic cells are the main consumers of Flt3L in vivo, we generated bone marrow chimeras by transplanting wild type (WT) or Flt3L-/- c-Kit+ hematopoietic stem and progenitor cells into lethally irradiated Flk2-/- mice. This demonstrated that hematopietic progenitors and DCs expressing Flk2 receptor are the main consumers of Flt3L in vivo. Previously we showed that in vivo Flk2 tyrosine kinase inhibition and consecutive DC reduction lead to 10fold elevated levels of serum Flt3L (Tussiwand. R. et al., J Immunol; 2005). By using CD11c DTR mice (Zaft, T. et al., J Immunol; 2005) in which diphtheria toxin (DT) receptor is cloned under the CD11c promoter and treatment of mice with DT lead to selective depletion of DCs we here show that ablation Flk2 expressing DCs lead to immediate, about 4-fold elevated serum Flt3L levels in mice. However, we observed no change in mRNA expression of Flt3L, which strongly indicates that Flk2 expressed on DCs is acting as “scavenger” for Flt3L. We then studied sources of Flt3L in vivo. To this end we generated bone marrow chimeras by transplanting WT c-Kit+ hematopoietic stem and progenitor cells in to lethally irradiated Flt3L-/- hosts and vice versa (WT to Fllt3L-/-, Flt3L-/- to WT), and found that in vivo DC homeostasis can be achieved by non-hematopoietic and to lesser extend by hematopoietic cell produced Flt3L. Furhtermore, we found that compared to other hematopoietic cells Flt3L mRNA is highly expressed in lymphocytes (T and B cells) and in lymphoid tissues like thymus, spleen and lymph nodes. We thus used bone marrow c-Kit+ hematopoietic stem and progenitor cells from mice that lack T and B cells (Rag1-/-) or that lack T cells (CD3ε-/-) as donors to transplant lethally conditioned Flt3L-/- mice, and found that Flt3L produced by T and B cells is necessary to support DC development in non hematopoietic Flt3L deficient mice. Using BrdU incorporation we evaluated the functional relevance of Flt3L produced by T cells in an ongoing immune response. Experiments revealed that in lymph nodes with proliferating T cells producing Flt3L a higher percent of BrdU+ DCs, i.e. DCs derived from proliferating progenitors were detected. This indicates that Flt3L produced by T cells in an ongoing immune response helps in faster regeneration of DCs from DC committed progenitors. Earlier it has been shown that Treg ablation in Foxp3-DTR mice lead to expansion of DCs in lymph nodes and spleen through Flk2 mediated pathway (Liu, K. et al., Science; 2009); however, the source of Flt3L remained unknown. Here we provide evidence that Treg ablation leads to activation and proliferation of CD4+ T cells that in turn release Flt3L to enhance DC development. These key observations provide insight into the regulation of DC homeostasis and function via tailored adaptation of the Flt3L cytokine milieu by non-hematopoietic and T cells during steady state and during adaptive immune responses. Supported by the Swiss National Science Foundation (310000-116637) and the European Commission FP6 Network of Excellence initiative (LSHB-CT-2004-512074 DC-THERA) Disclosures: No relevant conflicts of interest to declare.

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The Lymphoblastic Leukemia Gene 1 (Lyl1) Regulates Lymphoid Specification and Maintenance of Early T Lineage Progenitors

Blood ◽

10.1182/blood.v118.21.548.548 ◽

2011 ◽

Vol 118 (21) ◽

pp. 548-548

Author(s):

Fabian Zohren ◽

George Souroullas ◽

Min Luo ◽

Ulrike Gerdemann ◽

Nicola K Wilson ◽

...

Keyword(s):

Bone Marrow ◽

T Cell ◽

Progenitor Cells ◽

Molecular Mechanisms ◽

Cell Lineage ◽

Lineage Commitment ◽

Hematopoietic Stem ◽

Enhancer Element ◽

Fold Reduction ◽

Donor Cells

Abstract Abstract 548 Long-term thymopoiesis crucially depends on the recruitment and expansion of bone marrow derived progenitor cells. Therefore, a tight regulation of the thymus-settling progenitor cells is required to maintain T cell lineage homeostasis. Lyl1, a transcription factor involved in homeostatic control of immature hematopoietic cells, remains expressed in early T-lineage progenitors (ETPs) until T cell lineage commitment. Here we demonstrate a critical requirement for Lyl1 in lymphoid priming of bone marrow (BM) progenitors and in the maintenance of ETPs. Lyl1 deficient hematopoiesis was unable to generate sufficient numbers of lymphoid-primed progenitor populations such as LMPPs, CLPs and in particular ETPs. We found a significant (p>0.001) 4-fold reduction of LMPPs in the BM and a 20-fold reduction (p<0.001) of ETPs in the thymus of Lyl1 KO mice compared to wildtype controls. Transplantation assays revealed a selective defect of Lyl1−/− LMPPs for thymic engraftment and T lineage development. Intra-thymic injections of Lyl1−/− LMPPs demonstrated, in absence of homing requirements, a cell autonomous defect of Lyl1−/− progenitors in their ability to undergo the ETP to DN2 transition and to expand in response to Notch. Injection of Lyl1+/+ LMPPs resulted in a 5-fold higher recovery of total donor cells compared to injections of Lyl1−/− LMPPs (p<0.001). 40% of the donor cells derived after intra-thymic injection of Lyl1+/+ LMPPs were committed to the T cell lineage (DN3, DP, SP), whereas T lineage commitment after injection of Lyl1−/− cells was only seen in 20% of the recovered cells (p<0.01). By absolute numbers, wildtype LMPPs had generated more DN3 (8-fold), more DP (21-fold) and more SP (9-fold) T cell lineage committed thymocytes, and fewer Lyl1+/+ cells remained in the c-kit positive “ETP/LMPP-like” stage (-0.5-fold). In contrast, reintroduction of Lyl1 cDNA into Lyl1−/− BM progenitors using retroviral vectors restored the thymic progenitor pool and enhanced T cell lineage output. At 12 weeks after transplantation of MIG-Lyl1 transduced cells we observed a significant expansion of transfected (GFPpos) cells in the peripheral blood solely attributable to expansion of normal, mature and poly-clonal T cells (p<0.001). The thymuses of MIG-Lyl1 transplanted recipients showed significantly greater overall cellularity (p<0.01) attributable to a significantly higher proportion of GFPpos thymocytes (p<0.01) compared to the MIG-GFP transplanted control group. To gain a more detailed understanding of the underlying molecular mechanisms of Lyl1-mediated T-lymphoid specification, we performed global gene expression profiling of wildtype and Lyl1−/− LMPPs as well as whole genome ChIP-seqencing in HPC-7 cells after pull-down with anti-Lyl1 antibodies. Here, we identified the lymphoid-promoting factor Gfi1 as a critical transcriptional target of Lyl1-mediated T lymphopoiesis. We found that Gfi1 expression was decreased in Lyl1−/− LMPPs and ETPs by 2- and 7.5- fold respectively. ChIP assays using ckitpos BM cells from Lyl1+/+ and Lyl1−/− mice revealed a strong enrichment of Lyl1 at a known enhancer region of the Gfi1 locus located 35kb upstream of Gfi1 (p<0.001). Binding of Lyl1 activated the Gfi1 35kb enhancer element in transactivation assays (p<0.001). Finally, intra-thymic injection of Lyl1−/− progenitors after retroviral transduction with Gfi1 cDNA allowed lymphoid development and enhanced the T cell lineage output compared to GFP-transduced controls (p=0.08). Collectively, our data provide evidence that pro-T cell expansion in the thymus is regulated through intrinsic control of thymus progenitor cells that employ a transcriptional program already established in hematopoietic stem and progenitor cells. We identify Lyl1 as a critical component of this regulatory network, which is vital for the maintenance of T cell lineage homeostasis. Finally, identification of important downstream mediators of Lyl1 function not only illuminates the molecular mechanisms underlying early T-cell development, but also suggests previously unrecognized pathways likely to play a role in Lyl1-mediated development of leukemia and lymphoma. Disclosures: No relevant conflicts of interest to declare.

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Molecular Regulation of Adult Hematopoiesis By GATA-2

Blood ◽

10.1182/blood.v124.21.4337.4337 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4337-4337

Author(s):

Haiyan Li ◽

Jin Jin ◽

shao-Cong Sun ◽

Stephanie S. Watowich

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Molecular Mechanisms ◽

Conflicts Of Interest ◽

Bone Marrow Failure ◽

Rapid Development ◽

Cell Activity ◽

Tamoxifen Treatment ◽

Hematopoietic Stem ◽

Md Anderson

Abstract GATA-2 is a zinc finger-containing transcriptional regulator that plays important roles in embryonic and adult hematopoiesis. Mutations in human GATA2 are associated with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), as well as immunodeficiency disorders that present with a profound loss of monocytes, dendritic cells and other myeloid lineage populations. Recent work reveals crucial roles for GATA-2 in definitive hematopoietic stem/progenitor cell activity, vascular integrity and lymphatic development. However, the molecular mechanisms by which GATA-2 controls adult hematopoiesis via hematopoietic-cell autonomous functions are largely unknown. To address this question, we generated a tamoxifen-inducible Gata2-deficient mouse strain by breeding Gata2flox/flox mice with Cre-ER transgenic animals. Following tamoxifen treatment, Cre-ER Gata2flox/flox mice show a rapid and profound loss of circulating neutrophils, monocytes and lymphocytes, concomitant with development of anemia. These results are consistent with the requirement for GATA-2 in hematopoietic stem/progenitor cells, and may also reflect GATA-2 function in endothelial cells within the vascular niche. To explore hematopoietic-specific GATA-2 activity, we generated bone marrow chimeric mice with hematopoietic-restricted Gata2-deficiency by transplanting Cre-ER Gata2flox/flox hematopoietic cells into wild type recipients. Cre-ER Gata2flox/flox bone marrow chimeras show rapid development of cytopenias upon tamoxifen exposure, suggesting a cell autonomous role for GATA-2 in maintaining adult hematopoiesis. Strikingly, hematopoietic progenitor cells rapidly lose c-Kit expression upon inducible Gata2 deletion. Chromatin immunoprecipitation and reporter assays suggest GATA-2 cooperates with C/EBPa in regulating kit transcription. Our study suggests conditional deletion of Gata2 restricted to the hematopoietic compartment provides a model for bone marrow failure associated with MDS and mutant GATA2 human immunodeficiencies that may enable further insight into the molecular network by which GATA-2 mediates definitive hematopoiesis. Supported by grants from NIH (AI098099) and the MD Anderson Center for Cancer Epigenetics.(SSW) and the MD Anderson Center for Cancer and Inflammation (HSL). Disclosures No relevant conflicts of interest to declare.

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Disruption of the Osteoblast Niche by G-CSF Induces Hematopoietic Stem Cell Quiescence and Loss of Long-Term Repopulating Activity.

Blood ◽

10.1182/blood.v110.11.2217.2217 ◽

2007 ◽

Vol 110 (11) ◽

pp. 2217-2217

Author(s):

Priya K. Gopalan ◽

Matthew J. Christopher ◽

Daniel C. Link

Keyword(s):

Bone Marrow ◽

Molecular Mechanisms ◽

Bone Marrow Cells ◽

Hematopoietic Stem ◽

Rna Profiling ◽

Stem Cell Quiescence ◽

Cd34 Cells ◽

Cell Quiescence ◽

And Function

Abstract There is evidence that hematopoietic stem cells (HSC) are physically localized to specialized areas in the bone marrow termed the vascular and osteoblast niches. It is not clear if there are differences in the capacity of these niches to support HSC function. We and others previously showed that G-CSF treatment suppresses both osteoblast number and function, effectively eliminating the osteoblast niche. In contrast, G-CSF treatment has no apparent effect on the microvasculature in the bone marrow, suggesting that the vascular niche is intact. In this study, we utilized this system to assess the capacity of each niche to support HSC function. We previously reported that the competitive repopulation capacity of bone marrow isolated from G-CSF treated mice is markedly reduced. This is not due to a simple loss of HSC in the bone marrow, as the number of HSC, phenotypically defined as lineage-CD41-CD48-CD150+ (SLAM) or lineage-Kit+Sca+CD34- cells, was comparable to control mice. Moreover, the long-term repopulating activity of sorted SLAM cells from G-CSF treated mice was reduced. This repopulating defect is not secondary to impaired homing to the bone marrow, as direct intrafemoral injection of G-CSF treated bone marrow cells failed to rescue the engraftment defect. Since G-CSF is able to stimulate HSC proliferation, we predicted that the defect in repopulating activity might be secondary to loss of HSC quiescence. Contrary to our prediction, the percentage of quiescent HSC in the bone marrow was actually increased in G-CSF treated mice. Whereas 28.0 ± 3.4% of control SLAM cells were labeled after treatment with BrdU for 48 hours, only 7.5 ± 0.8% of SLAM cells isolated from G-CSF mice were labeled (p < 0.008). Moreover, the percentage of SLAM cells in G0, as determined by Hoechst and pyronin staining, was increased in G-CSF treated mice (80.3 ± 5.0% versus 65.5 ± 6.8% in untreated mice, p=0.104). To elucidate the molecular mechanisms by which disruption of the osteoblast niche leads to a loss of HSC activity, we performed RNA profiling experiments on SLAM cells sorted from G-CSF or saline-treated mice. Consistent with the quiescent phenotype, a significant increase in the expression of the cell cycle inhibitor, Cdkn1a (p21waf1), was observed in G-CSF treated SLAM cells. Collectively, these data show that the osteoblast and vascular niches are not functionally redundant and suggest that it is the osteoblast niche that is key to maintaining long-term repopulating activity of HSC.

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Current mechanistic scenarios in hematopoietic stem/progenitor cell mobilization

Blood ◽

10.1182/blood-2003-05-1595 ◽

2004 ◽

Vol 103 (5) ◽

pp. 1580-1585 ◽

Cited By ~ 172

Author(s):

Thalia Papayannopoulou

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Progenitor Cell ◽

Molecular Mechanisms ◽

Granulocyte Colony Stimulating Factor ◽

Hematopoietic Stem ◽

Recent Developments ◽

Cell Mobilization ◽

Stimulating Factor ◽

Gene Deficient Mouse

Abstract Uncovering the molecular mechanisms governing the exit of stem/progenitor cells from bone marrow to peripheral blood at steady state or after their enforced migration has been an ongoing challenge. Recently, however, several new avenues or paradigms in mobilization have emerged from ever-expanding work in humans subjected to granulocyte colony-stimulating factor (G-CSF) mobilization, as well as from studies in normal and gene-deficient mouse models. Although these developments represent notable advances that met with considerable excitement, they have been quenched by surprising vacillations in subsequent research. This perspective highlights recent developments in mobilization along with their controversies. A full understanding of the directional cues that control the migratory behavior and the fate of stem/progenitor cells once they migrate out of bone marrow will await further experimentation, aiming to bridge our current gaps in knowledge.

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