Showing papers on "Haematopoiesis published in 2010"
TL;DR: It is demonstrated that mesenchymal stem cells (MSCs), identified using nestin expression, constitute an essential HSC niche component and are indicative of a unique niche in the bone marrow made of heterotypic stem-cell pairs.
Abstract: The cellular constituents forming the haematopoietic stem cell (HSC) niche in the bone marrow are unclear, with studies implicating osteoblasts, endothelial and perivascular cells. Here we demonstrate that mesenchymal stem cells (MSCs), identified using nestin expression, constitute an essential HSC niche component. Nestin(+) MSCs contain all the bone-marrow colony-forming-unit fibroblastic activity and can be propagated as non-adherent 'mesenspheres' that can self-renew and expand in serial transplantations. Nestin(+) MSCs are spatially associated with HSCs and adrenergic nerve fibres, and highly express HSC maintenance genes. These genes, and others triggering osteoblastic differentiation, are selectively downregulated during enforced HSC mobilization or beta3 adrenoreceptor activation. Whereas parathormone administration doubles the number of bone marrow nestin(+) cells and favours their osteoblastic differentiation, in vivo nestin(+) cell depletion rapidly reduces HSC content in the bone marrow. Purified HSCs home near nestin(+) MSCs in the bone marrow of lethally irradiated mice, whereas in vivo nestin(+) cell depletion significantly reduces bone marrow homing of haematopoietic progenitors. These results uncover an unprecedented partnership between two distinct somatic stem-cell types and are indicative of a unique niche in the bone marrow made of heterotypic stem-cell pairs.
3,012 citations
TL;DR: Mutational and epigenetic profiling of a large acute myeloid leukemia (AML) patient cohort revealed that IDH1/2-mutant AMLs display global DNA hypermethylation and a specificHypermethylation signature, suggesting a shared proleukemogenic effect.
2,372 citations
TL;DR: This work has identified a broader spectrum of stem cells influenced by hypoxia that includes cancer stem cells and induced pluripotent stem cells, and elucidate an added dimension of stem cell control within the niche.
1,332 citations
TL;DR: It is shown that, 33 months after lentiviral β-globin gene transfer, an adult patient with severe βE/β0-thalassaemia dependent on monthly transfusions since early childhood has become transfusion independent for the past 21 months.
Abstract: Blood disorders caused by abnormal β-globin — β-thalassaemia and sickle cell disease — are the most prevalent inherited disorders worldwide, with patients often remaining dependent on blood transfusions throughout their lives So a report of the successful use of gene therapy in a case of severe β-thalassaemia — using a lentiviral vector expressing the β-globin gene — is an eagerly awaited event More than two years after gene transfer, the adult male patient has been transfusion-independent for 21 months The therapeutic benefit seems to result from a dominant, myeloid-biased cell clone that may remain benign, although it could yet develop into leukaemia — a reminder that gene therapy is still at an early stage Disorders caused by abnormal β-globin, such as β-thalassaemia, are the most prevalent inherited disorders worldwide For treatment, many patients are dependent on blood transfusions; thus far the only cure has involved matched transplantation of haematopoietic stem cells Here it is shown that lentiviral β-globin gene transfer can be an effective substitute for regular transfusions in a patient with severe β-thalassaemia The β-haemoglobinopathies are the most prevalent inherited disorders worldwide Gene therapy of β-thalassaemia is particularly challenging given the requirement for massive haemoglobin production in a lineage-specific manner and the lack of selective advantage for corrected haematopoietic stem cells Compound βE/β0-thalassaemia is the most common form of severe thalassaemia in southeast Asian countries and their diasporas1,2 The βE-globin allele bears a point mutation that causes alternative splicing The abnormally spliced form is non-coding, whereas the correctly spliced messenger RNA expresses a mutated βE-globin with partial instability1,2 When this is compounded with a non-functional β0 allele, a profound decrease in β-globin synthesis results, and approximately half of βE/β0-thalassaemia patients are transfusion-dependent1,2 The only available curative therapy is allogeneic haematopoietic stem cell transplantation, although most patients do not have a human-leukocyte-antigen-matched, geno-identical donor, and those who do still risk rejection or graft-versus-host disease Here we show that, 33 months after lentiviral β-globin gene transfer, an adult patient with severe βE/β0-thalassaemia dependent on monthly transfusions since early childhood has become transfusion independent for the past 21 months Blood haemoglobin is maintained between 9 and 10 g dl−1, of which one-third contains vector-encoded β-globin Most of the therapeutic benefit results from a dominant, myeloid-biased cell clone, in which the integrated vector causes transcriptional activation of HMGA2 in erythroid cells with further increased expression of a truncated HMGA2 mRNA insensitive to degradation by let-7 microRNAs The clonal dominance that accompanies therapeutic efficacy may be coincidental and stochastic or result from a hitherto benign cell expansion caused by dysregulation of the HMGA2 gene in stem/progenitor cells
1,220 citations
TL;DR: The results demonstrate that Tet2 is important for normal myelopoiesis, and suggest that disruption of TET2 enzymatic activity favours myeloid tumorigenesis, which may prove valuable as a diagnostic and prognostic tool to tailor therapies and assess responses to anticancer drugs.
Abstract: TET2 is a close relative of TET1, an enzyme that converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. The gene encoding TET2 resides at chromosome 4q24, in a region showing recurrent microdeletions and copy-neutral loss of heterozygosity (CN-LOH) in patients with diverse myeloid malignancies. Somatic TET2 mutations are frequently observed in myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), MDS/MPN overlap syndromes including chronic myelomonocytic leukaemia (CMML), acute myeloid leukaemias (AML) and secondary AML (sAML). We show here that TET2 mutations associated with myeloid malignancies compromise catalytic activity. Bone marrow samples from patients with TET2 mutations displayed uniformly low levels of 5hmC in genomic DNA compared to bone marrow samples from healthy controls. Moreover, small hairpin RNA (shRNA)-mediated depletion of Tet2 in mouse haematopoietic precursors skewed their differentiation towards monocyte/macrophage lineages in culture. There was no significant difference in DNA methylation between bone marrow samples from patients with high 5hmC versus healthy controls, but samples from patients with low 5hmC showed hypomethylation relative to controls at the majority of differentially methylated CpG sites. Our results demonstrate that Tet2 is important for normal myelopoiesis, and suggest that disruption of TET2 enzymatic activity favours myeloid tumorigenesis. Measurement of 5hmC levels in myeloid malignancies may prove valuable as a diagnostic and prognostic tool, to tailor therapies and assess responses to anticancer drugs.
1,193 citations
TL;DR: It is shown that deletion of Dicer1 specifically in mouse osteoprogenitors, but not in mature osteoblasts, disrupts the integrity of haematopoiesis, and primary stromal dysfunction can result in secondary neoplastic disease, supporting the concept of niche-induced oncogenesis.
Abstract: Mesenchymal cells contribute to the ‘stroma’ of most normal and malignant tissues, with specific mesenchymal cells participating in the regulatory niches of stem cells. By examining how mesenchymal osteolineage cells modulate haematopoiesis, here we show that deletion of Dicer1 specifically in mouse osteoprogenitors, but not in mature osteoblasts, disrupts the integrity of haematopoiesis. Myelodysplasia resulted and acute myelogenous leukaemia emerged that had acquired several genetic abnormalities while having intact Dicer1. Examining gene expression altered in osteoprogenitors as a result of Dicer1 deletion showed reduced expression of Sbds, the gene mutated in Schwachman–Bodian–Diamond syndrome—a human bone marrow failure and leukaemia pre-disposition condition. Deletion of Sbds in mouse osteoprogenitors induced bone marrow dysfunction with myelodysplasia. Therefore, perturbation of specific mesenchymal subsets of stromal cells can disorder differentiation, proliferation and apoptosis of heterologous cells, and disrupt tissue homeostasis. Furthermore, primary stromal dysfunction can result in secondary neoplastic disease, supporting the concept of niche-induced oncogenesis. Although a series of genetic and epigenetic events in a single cell may be necessary for oncogenesis, it has been suggested that for malignancy to develop fully a permissive microenvironment or niche is required. Support for this view comes from a new mouse model in which haematopoietic malignancies are caused by genetic changes in the microenvironment of blood cells. Deletion in bone progenitor cells of Dicer1, a gene involved in microRNA processing, leads to a myelodysplastic syndrome-like phenotype that can progress to leukaemia. The progenitor cells have reduced levels of Sbds, the gene mutated in Schwachman–Bodian–Diamond syndrome, a bone marrow failure that predisposes to leukaemia. A new mouse model is developed in which haematopoietic malignancies are caused by genetic changes in the microenvironment of blood cells. Deletion in bone progenitor cells of Dicer1, a gene involved in microRNA processing, leads to a myelodysplastic syndrome-like phenotype which can progress to leukaemia. Deregulation of Sbds, which is mutated in human Schwachman–Bodian–Diamond syndrome, may be involved in this process.
1,005 citations
TL;DR: Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR) and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.
Abstract: Although practiced clinically for more than 40 years, the use of hematopoietic stem cell (HSC) transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.
981 citations
TL;DR: It is shown that LT-HSCs utilize glycolysis instead of mitochondrial oxidative phosphorylation to meet their energy demands and that Meis1 regulates HSC metabolism through transcriptional activation of Hif-1alpha.
920 citations
TL;DR: The unique strengths of the zebrafish embryo are used to image directly the generation of HSCs from the ventral wall of the dorsal aorta and it is demonstrated that the H SCs generated from haemogenic endothelium are the lineal founders of the adult haematopoietic system.
Abstract: A major goal of regenerative medicine is to instruct formation of multipotent, tissue-specific stem cells from induced pluripotent stem cells (iPSCs) for cell replacement therapies. Generation of haematopoietic stem cells (HSCs) from iPSCs or embryonic stem cells (ESCs) is not currently possible, however, necessitating a better understanding of how HSCs normally arise during embryonic development. We previously showed that haematopoiesis occurs through four distinct waves during zebrafish development, with HSCs arising in the final wave in close association with the dorsal aorta. Recent reports have suggested that murine HSCs derive from haemogenic endothelial cells (ECs) lining the aortic floor. Additional in vitro studies have similarly indicated that the haematopoietic progeny of ESCs arise through intermediates with endothelial potential. Here we have used the unique strengths of the zebrafish embryo to image directly the generation of HSCs from the ventral wall of the dorsal aorta. Using combinations of fluorescent reporter transgenes, confocal time-lapse microscopy and flow cytometry, we have identified and isolated the stepwise intermediates as aortic haemogenic endothelium transitions to nascent HSCs. Finally, using a permanent lineage tracing strategy, we demonstrate that the HSCs generated from haemogenic endothelium are the lineal founders of the adult haematopoietic system.
912 citations
TL;DR: It is demonstrated that the aortic floor is haemogenic and that HSCs emerge from it into the sub-aortic space, not by asymmetric cell division but through a new type of cell behaviour, which is called an endothelial haematopoietic transition.
Abstract: In zebrafish, haematopoietic stem cells (HSCs) arise from the dorsal aorta of the embryo. In vitro studies have suggested that there are in the dorsal aorta a population of intermediate progenitors that can give rise to both endothelial (or blood vessel lineage) and blood cells. In this issue, two groups present images showing the birth of HSCs from the ventral wall of the dorsal aorta in live zebrafish embryos. Bertrand et al. combined fluorescent reporter transgenes, confocal time-lapse microscopy and flow cytometry to identify and isolate the stepwise intermediates as aortic haemogenic endothelium transitions to nascent HSCs. They also show that the HSCs generated from this haemogenic endothelium are the lineal founders of virtually all of the adult haematopoietic system. Karima Kissa and Philippe Herbomel similarly use imaging of live zebrafish to show HSCs emerge directly from the aorta floor, They show this process that does not involve cell division but movement of single endothelial cells out of the aorta ventral wall into the sub-aortic space, where they transform into haematopoietic cells. They call this new type of cell behaviour endothelial haematopoietic transition (EHT). In a third report, Boisset et al. confirm that this process also occurs in mice, using a dissection procedure to visualize the deeply located aorta. They showed de novo emergence of phenotypically defined HSCs directly from ventral aortic haemogenic endothelial cells. One of two papers showing the generation of haematopoietic stem cells (HSCs) from the ventral wall of the dorsal aorta in live zebrafish embryos. Here, using imaging of live zebrafish, HSCs are shown to emerge directly from the aorta floor. This process does not involve cell division but movement of single endothelial cells out of the aorta ventral wall into the sub aortic space, where they transform into haematopoietic cells. The ontogeny of haematopoietic stem cells (HSCs) during embryonic development is still highly debated, especially their possible lineage relationship to vascular endothelial cells1,2. The first anatomical site from which cells with long-term HSC potential have been isolated is the aorta-gonad-mesonephros (AGM), more specifically the vicinity of the dorsal aortic floor3. But although some authors have presented evidence that HSCs may arise directly from the aortic floor into the dorsal aortic lumen4, others support the notion that HSCs first emerge within the underlying mesenchyme5. Here we show by non-invasive, high-resolution imaging of live zebrafish embryos, that HSCs emerge directly from the aortic floor, through a stereotyped process that does not involve cell division but a strong bending then egress of single endothelial cells from the aortic ventral wall into the sub-aortic space, and their concomitant transformation into haematopoietic cells. The process is polarized not only in the dorso-ventral but also in the rostro-caudal versus medio-lateral direction, and depends on Runx1 expression: in Runx1-deficient embryos, the exit events are initially similar, but much rarer, and abort into violent death of the exiting cell. These results demonstrate that the aortic floor is haemogenic and that HSCs emerge from it into the sub-aortic space, not by asymmetric cell division but through a new type of cell behaviour, which we call an endothelial haematopoietic transition.
853 citations
TL;DR: Time-lapse confocal imaging and a new dissection procedure are used and shown the dynamic de novo emergence of phenotypically defined HSCs (Sca1+, c-kit+, CD41+) directly from ventral aortic haemogenic endothelial cells.
Abstract: Haematopoietic stem cells (HSCs), responsible for blood production in the adult mouse, are first detected in the dorsal aorta starting at embryonic day 10.5 (E10.5). Immunohistological analysis of fixed embryo sections has revealed the presence of haematopoietic cell clusters attached to the aortic endothelium where HSCs might localize. The origin of HSCs has long been controversial and several candidates of the direct HSC precursors have been proposed (for review see ref. 7), including a specialized endothelial cell population with a haemogenic potential. Such cells have been described both in vitro in the embryonic stem cell (ESC) culture system and retrospectively in vivo by endothelial lineage tracing and conditional deletion experiments. Whether the transition from haemogenic endothelium to HSC actually occurs in the mouse embryonic aorta is still unclear and requires direct and real-time in vivo observation. To address this issue we used time-lapse confocal imaging and a new dissection procedure to visualize the deeply located aorta. Here we show the dynamic de novo emergence of phenotypically defined HSCs (Sca1(+), c-kit(+), CD41(+)) directly from ventral aortic haemogenic endothelial cells.
TL;DR: The hypothesis that blocking TGFβ-induced signalling in the tumour microenvironment enhances antitumour immunity and may be beneficial for cancer therapy is favoured.
Abstract: Transforming growth factor-beta (TGFbeta) is an immunosuppressive cytokine produced by tumour cells and immune cells that can polarize many components of the immune system. This Review covers the effects of TGFbeta on natural killer (NK) cells, dendritic cells, macrophages, neutrophils, CD8(+) and CD4(+) effector and regulatory T cells, and NKT cells in animal tumour models and in patients with cancer. Collectively, many recent studies favour the hypothesis that blocking TGFbeta-induced signalling in the tumour microenvironment enhances antitumour immunity and may be beneficial for cancer therapy. An overview of the current drugs and reagents available for inhibiting TGFbeta-induced signalling and their phase in clinical development is also provided.
TL;DR: It is shown that normal HSCs maintain intracellular hypoxia and stabilize Hypoxia-inducible factor-1 alpha (HIF-1alpha) protein, which indicates that H SCs maintain cell cycle quiescence through the precise regulation of HIF- 1alpha levels.
TL;DR: The ability to generate progenitors and mature cells of the haematopoietic fate directly from human dermal fibroblasts without establishing pluripotency is demonstrated and an alternative approach to cellular reprogramming for autologous cell-replacement therapies that avoids complications associated with the use of human pluripotent stem cells is suggested.
Abstract: As is the case for embryo-derived stem cells, application of reprogrammed human induced pluripotent stem cells is limited by our understanding of lineage specification. Here we demonstrate the ability to generate progenitors and mature cells of the haematopoietic fate directly from human dermal fibroblasts without establishing pluripotency. Ectopic expression of OCT4 (also called POU5F1)-activated haematopoietic transcription factors, together with specific cytokine treatment, allowed generation of cells expressing the pan-leukocyte marker CD45. These unique fibroblast-derived cells gave rise to granulocytic, monocytic, megakaryocytic and erythroid lineages, and demonstrated in vivo engraftment capacity. We note that adult haematopoietic programs are activated, consistent with bypassing the pluripotent state to generate blood fate: this is distinct from haematopoiesis involving pluripotent stem cells, where embryonic programs are activated. These findings demonstrate restoration of multipotency from human fibroblasts, and suggest an alternative approach to cellular reprogramming for autologous cell-replacement therapies that avoids complications associated with the use of human pluripotent stem cells.
TL;DR: The haematopoietic response to chronic bacterial infection involves the activation not only of intermediate blood progenitors but of long-term repopulating HSCs as well, and implicate IFN-γ both as a regulator of H SCs during homeostasis and under conditions of infectious stress.
Abstract: Using a mouse model of Mycobacterium avium infection, it is shown here that interferon-γ regulates the proliferation of primitive haematopoietic cells during chronic infection.
TL;DR: HSCs from CAR cell-depleted mice were reduced in number and cell size, were more quiescent, and had increased expression of early myeloid selector genes, similar to the phenotype of wild-type HSCs cultured without a niche.
TL;DR: It is shown that the Wnt/β-catenin signaling pathway is required for self-renewal of LSCs that are derived from either hematopoietic stem cells (HSC) or more differentiated granulocyte-macrophage progenitors (GMP).
Abstract: Leukemia stem cells (LSCs) are capable of limitless self-renewal and are responsible for the maintenance of leukemia. Because selective eradication of LSCs could offer substantial therapeutic benefit, there is interest in identifying the signaling pathways that control their development. We studied LSCs in mouse models of acute myelogenous leukemia (AML) induced either by coexpression of the Hoxa9 and Meis1a oncogenes or by the fusion oncoprotein MLL-AF9. We show that the Wnt/beta-catenin signaling pathway is required for self-renewal of LSCs that are derived from either hematopoietic stem cells (HSC) or more differentiated granulocyte-macrophage progenitors (GMP). Because the Wnt/beta-catenin pathway is normally active in HSCs but not in GMP, these results suggest that reactivation of beta-catenin signaling is required for the transformation of progenitor cells by certain oncogenes. beta-catenin is not absolutely required for self-renewal of adult HSCs; thus, targeting the Wnt/beta-catenin pathway may represent a new therapeutic opportunity in AML.
TL;DR: It is established that bone marrow macrophages are pivotal to maintain the endosteal HSC niche and that the loss of such macrophage leads to the egress of HSCs into the blood.
TL;DR: The demonstration that a minority of CCR5−/− HSPCs can populate an infected animal with HIV-1-resistant, CCR4+/− progeny supports the use of ZFN-modified autologous hematopoietic stem cells as a clinical approach to treating HIV- 1.
Abstract: CCR5 is the major HIV-1 co-receptor, and individuals homozygous for a 32-bp deletion in CCR5 are resistant to infection by CCR5-tropic HIV-1. Using engineered zinc-finger nucleases (ZFNs), we disrupted CCR5 in human CD34(+) hematopoietic stem/progenitor cells (HSPCs) at a mean frequency of 17% of the total alleles in a population. This procedure produces both mono- and bi-allelically disrupted cells. ZFN-treated HSPCs retained the ability to engraft NOD/SCID/IL2rgamma(null) mice and gave rise to polyclonal multi-lineage progeny in which CCR5 was permanently disrupted. Control mice receiving untreated HSPCs and challenged with CCR5-tropic HIV-1 showed profound CD4(+) T-cell loss. In contrast, mice transplanted with ZFN-modified HSPCs underwent rapid selection for CCR5(-/-) cells, had significantly lower HIV-1 levels and preserved human cells throughout their tissues. The demonstration that a minority of CCR5(-/-) HSPCs can populate an infected animal with HIV-1-resistant, CCR5(-/-) progeny supports the use of ZFN-modified autologous hematopoietic stem cells as a clinical approach to treating HIV-1.
TL;DR: The power of genome-wide analysis of complex binding patterns and combinatorial interactions for ten key regulators of blood stem/progenitor cells is reported, providing the most comprehensive TF data set for any adult stem/ Progenitor cell type to date.
TL;DR: Angiogenic models are developed to demonstrate that EC-derived angiocrine growth factors support in vitro self-renewal and in vivo repopulation of authentic LT-HSCs, and establish an instructive vascular niche for clinical-scale expansion of LT- HSCs and a cellular platform to identify stem cell-active trophogens.
TL;DR: Deletes chromosome 5q and identifies Toll–interleukin-1 receptor domain–containing adaptor protein (TIRAP) and tumor necrosis factor receptor–associated factor-6 (TRAF6) as respective targets of these miRNAs.
Abstract: 5q- syndrome is a subtype of myelodysplastic syndrome characterized by severe anemia and variable neutropenia but normal or high platelet counts with dysplastic megakaryocytes. We examined expression of microRNAs (miRNAs) encoded on chromosome 5q as a possible cause of haploinsufficiency. We show that deletion of chromosome 5q correlates with loss of two miRNAs that are abundant in hematopoietic stem/progenitor cells (HSPCs), miR-145 and miR-146a, and we identify Toll-interleukin-1 receptor domain-containing adaptor protein (TIRAP) and tumor necrosis factor receptor-associated factor-6 (TRAF6) as respective targets of these miRNAs. TIRAP is known to lie upstream of TRAF6 in innate immune signaling. Knockdown of miR-145 and miR-146a together or enforced expression of TRAF6 in mouse HSPCs resulted in thrombocytosis, mild neutropenia and megakaryocytic dysplasia. A subset of mice transplanted with TRAF6-expressing marrow progressed either to marrow failure or acute myeloid leukemia. Thus, inappropriate activation of innate immune signals in HSPCs phenocopies several clinical features of 5q- syndrome.
TL;DR: The results directly demonstrate that modulation of DNA methylation occurs during lineage-specific differentiation and defines a comprehensive map of the methylation and transcriptional changes that accompany myeloid versus lymphoid fate decisions.
Abstract: Epigenetic modifications must underlie lineage-specific differentiation as terminally differentiated cells express tissue-specific genes, but their DNA sequence is unchanged Haematopoiesis provides a well-defined model to study epigenetic modifications during cell-fate decisions, as multipotent progenitors (MPPs) differentiate into progressively restricted myeloid or lymphoid progenitors Although DNA methylation is critical for myeloid versus lymphoid differentiation, as demonstrated by the myeloerythroid bias in Dnmt1 hypomorphs, a comprehensive DNA methylation map of haematopoietic progenitors, or of any multipotent/oligopotent lineage, does not exist Here we examined 46 million CpG sites throughout the genome for MPPs, common lymphoid progenitors (CLPs), common myeloid progenitors (CMPs), granulocyte/macrophage progenitors (GMPs), and thymocyte progenitors (DN1, DN2, DN3) Marked epigenetic plasticity accompanied both lymphoid and myeloid restriction Myeloid commitment involved less global DNA methylation than lymphoid commitment, supported functionally by myeloid skewing of progenitors following treatment with a DNA methyltransferase inhibitor Differential DNA methylation correlated with gene expression more strongly at CpG island shores than CpG islands Many examples of genes and pathways not previously known to be involved in choice between lymphoid/myeloid differentiation have been identified, such as Arl4c and Jdp2 Several transcription factors, including Meis1, were methylated and silenced during differentiation, indicating a role in maintaining an undifferentiated state Additionally, epigenetic modification of modifiers of the epigenome seems to be important in haematopoietic differentiation Our results directly demonstrate that modulation of DNA methylation occurs during lineage-specific differentiation and defines a comprehensive map of the methylation and transcriptional changes that accompany myeloid versus lymphoid fate decisions
TL;DR: The findings indicate that ABCA1, ABCG1, and HDL inhibit the proliferation of hematopoietic stem and multipotential progenitor cells and connect expansion of these populations with leukocytosis and accelerated atherosclerosis.
Abstract: Elevated leukocyte cell numbers (leukocytosis), and monocytes in particular, promote atherosclerosis; however, how they become increased is poorly understood. Mice deficient in the adenosine triphosphate-binding cassette (ABC) transporters ABCA1 and ABCG1, which promote cholesterol efflux from macrophages and suppress atherosclerosis in hypercholesterolemic mice, displayed leukocytosis, a transplantable myeloproliferative disorder, and a dramatic expansion of the stem and progenitor cell population containing Lin(-)Sca-1(+)Kit+ (LSK) in the bone marrow. Transplantation of Abca1(-/-) Abcg1(-/-) bone marrow into apolipoprotein A-1 transgenic mice with elevated levels of high-density lipoprotein (HDL) suppressed the LSK population, reduced leukocytosis, reversed the myeloproliferative disorder, and accelerated atherosclerosis. The findings indicate that ABCA1, ABCG1, and HDL inhibit the proliferation of hematopoietic stem and multipotential progenitor cells and connect expansion of these populations with leukocytosis and accelerated atherosclerosis.
TL;DR: Data is presented supporting a model in which clonal expansion of a class of intrinsically myeloid-biased HSCs with robust self-renewal potential is a central component of hematopoietic aging.
Abstract: Aging of the hematopoietic stem cell compartment is believed to contribute to the onset of a variety of age-dependent blood cell pathophysiologies. Mechanistic drivers of hematopoietic stem cell (HSC) aging include DNA damage accumulation and induction of tumor suppressor pathways that combine to reduce the regenerative capacity of aged HSCs. Such mechanisms do not however account for the change in lymphoid and myeloid lineage potential characteristic of HSC aging, which is believed to be central to the decline of immune competence and predisposition to myelogenous diseases in the elderly. Here we have prospectively isolated functionally distinct HSC clonal subtypes, based on cell surface phenotype, bearing intrinsically different capacities to differentiate toward lymphoid and myeloid effector cells mediated by quantitative differences in lineage priming. Finally, we present data supporting a model in which clonal expansion of a class of intrinsically myeloid-biased HSCs with robust self-renewal potential is a central component of hematopoietic aging.
TL;DR: It is shown that in ∼80% of primary human CD34+ acute myeloid leukemia (AML), two expanded populations with hemopoietic progenitor immunophenotype coexist in most patients, suggesting that in most cases primaryCD34+ AML is a progenitors disease where LSCs acquire abnormal self-renewal potential.
TL;DR: This study demonstrates definitive isolation of lineage-biased HSC subtypes and contributes to the fundamental change in view that the hematopoietic system is maintained by a continuum of H SC subtypes, rather than a functionally uniform pool.
TL;DR: It is found that HSCs have unique cell-intrinsic mechanisms ensuring their survival in response to ionizing irradiation (IR), which include enhanced prosurvival gene expression and strong activation of p53-mediated DNA damage response.
TL;DR: Comprehensive insertion-site analysis showed vector integration that targeted multiple genes controlling growth and immunologic responses in a persistently polyclonal hematopoiesis in the Wiskott-Aldrich syndrome.
Abstract: The Wiskott–Aldrich syndrome (WAS) is an X-linked recessive primary immunodeficiency disorder associated with thrombocytopenia, eczema, and autoimmunity. We treated two patients who had this disorder with a transfusion of autologous, genetically modified hematopoietic stem cells (HSC). We found sustained expression of WAS protein expression in HSC, lymphoid and myeloid cells, and platelets after gene therapy. T and B cells, natural killer (NK) cells, and monocytes were functionally corrected. After treatment, the patients' clinical condition markedly improved, with resolution of hemorrhagic diathesis, eczema, autoimmunity, and predisposition to severe infection. Comprehensive insertion-site analysis showed vector integration that targeted multiple genes controlling growth and immunologic responses in a persistently polyclonal hematopoiesis. (Funded by Deutsche Forschungsgemeinschaft and others; German Clinical Trials Register number, DRKS00000330.)
TL;DR: Differences in metabolic and cell-cycle regulation between HSCs and some other haematopoietic progenitors are revealed, revealed through AMPK-dependent and AM PK-independent mechanisms.
Abstract: Little is known about metabolic regulation in stem cells and how this modulates tissue regeneration or tumour suppression. We studied the Lkb1 tumour suppressor and its substrate AMP-activated protein kinase (AMPK), kinases that coordinate metabolism with cell growth. Deletion of the Lkb1 (also called Stk11) gene in mice caused increased haematopoietic stem cell (HSC) division, rapid HSC depletion and pancytopenia. HSCs depended more acutely on Lkb1 for cell-cycle regulation and survival than many other haematopoietic cells. HSC depletion did not depend on mTOR activation or oxidative stress. Lkb1-deficient HSCs, but not myeloid progenitors, had reduced mitochondrial membrane potential and ATP levels. HSCs deficient for two catalytic α-subunits of AMPK (AMPK-deficient HSCs) showed similar changes in mitochondrial function but remained able to reconstitute irradiated mice. Lkb1-deficient HSCs, but not AMPK-deficient HSCs, exhibited defects in centrosomes and mitotic spindles in culture, and became aneuploid. Lkb1 is therefore required for HSC maintenance through AMPK-dependent and AMPK-independent mechanisms, revealing differences in metabolic and cell-cycle regulation between HSCs and some other haematopoietic progenitors.