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Stem-cell fate can be influenced by metabolite levels in culture, but it is not known whether physiological variations in metabolite levels in normal tissues regulate stem-cell function in vivo. Here we describe a metabolomics method for the analysis of rare cell populations isolated directly from tissues and use it to compare mouse haematopoietic stem cells (HSCs) to restricted haematopoietic progenitors. Each haematopoietic cell type had a distinct metabolic signature. Human and mouse HSCs had unusually high levels of ascorbate, which decreased with differentiation. Systemic ascorbate depletion in mice increased HSC frequency and function, in part by reducing the function of Tet2, a dioxygenase tumour suppressor. Ascorbate depletion cooperated with Flt3 internal tandem duplication (Flt3[sup.ITD]) leukaemic mutations to accelerate leukaemogenesis, through cell-autonomous and possibly non-cell-autonomous mechanisms, in a manner that was reversed by dietary ascorbate. Ascorbate acted cell-autonomously to negatively regulate HSC function and myelopoiesis through Tet2-dependent and Tet2-independent mechanisms. Ascorbate therefore accumulates within HSCs to promote Tet activity in vivo, limiting HSC frequency and suppressing leukaemogenesis., Author(s): Michalis Agathocleous [1]; Corbin E. Meacham [1]; Rebecca J. Burgess [1]; Elena Piskounova [1]; Zhiyu Zhao [1]; Genevieve M. Crane [1]; Brianna L. Cowin [1]; Emily Bruner [1]; Malea [...]

Extramedullary hematopoiesis (EMH) Is Induced during pregnancy to support rapid expansion of maternal blood volume. EMH activation requires hematopoietic stem cell (HSC) proliferation and mobilization, processes that depend upon estrogen receptor [alpha] (ER[alpha]) in HSCs. Here we show that treating mice with estradiol to model estradiol increases during pregnancy induced HSC proliferation in the bone marrow but not HSC mobilization. Treatment with the alternative ER[alpha] ligand 27-hydroxycholesterol (27HC) induced ER[alpha]-dependent HSC mobilization and EMH but not HSC division in the bone marrow. During pregnancy, 27HC levels increased in hematopoietic stem/progenitor cells as a result of CYP27A1, a cholesterol hydroxylase. Cyp27o1-deficient mice had significantly reduced 27HC levels, HSC mobilization, and EMH during pregnancy but normal bone marrow hematopoiesis and EMH in response to bleeding or G-CSF treatment. Distinct hematopoietic stresses thus induce EMH through different mechanisms. Two different ER[alpha] ligands, estradiol and 27HC, work together to promote EMH during pregnancy, revealing a collaboration of hormonal and metabolic mechanisms as well as a physiological function for 27HC in normal mice., Introduction Adult hematopoietic stem cells (HSCs) reside primarily in the bone marrow, and their number is tightly regulated under steady-state conditions. However, hematopoietic stresses promote HSC proliferation and mobilization to [...]

Haematopoietic stresses mobilize haematopoietic stem cells (HSCs) from the bone marrow to the spleen and induce extramedullary haematopoiesis (EMH). However, the cellular nature of the EMH niche is unknown. Here [...]

Solid cancer cells commonly enter the blood and disseminate systemically, but are highly inefficient at forming distant metastases for poorly understood reasons. Here we studied human melanomas that differed in their metastasis histories in patients and in their capacity to metastasize in [NOD-SCID-Il2rg.sup.-/-] (NSG) mice. We show that melanomas had high frequencies of cells that formed subcutaneous tumours, but much lower percentages of cells that formed tumours after intravenous or intrasplenic transplantation, particularly among inefficiently metastasizing melanomas. Melanoma cells in the blood and visceral organs experienced oxidative stress not observed in established subcutaneous tumours. Successfully metastasizing melanomas underwent reversible metabolic changes during metastasis that increased their capacity to withstand oxidative stress, including increased dependence on NADPH-generating enzymes in the folate pathway. Antioxidants promoted distant metastasis in NSG mice. Folate pathway inhibition using low-dose methotrexate, ALDH1L2 knockdown, or MTHFD1 knockdown inhibited distant metastasis without significantly affecting the growth of subcutaneous tumours in the same mice. Oxidative stress thus limits distant metastasis by melanoma cells in vivo., Circulating cancer cells are commonly observed in the blood of patients and mice with various cancers (1-4). However, metastasis is a very inefficient process (5) in which few disseminated cancer [...]

Haematopoietic stem cells (HSCs) reside in a perivascular niche but the specific location of this niche remains controversial (1). HSCs are rare and few can be found in thin tissue [...]

Osteolectin is a recently identified osteogenic growth factor that binds to Integrin α11 (encoded by Itga11), promoting Wnt pathway activation and osteogenic differentiation by bone marrow stromal cells. While Osteolectin and Itga11 are not required for the formation of the skeleton during fetal development, they are required for the maintenance of adult bone mass. Genome-wide association studies in humans reported a single-nucleotide variant (rs182722517) 16 kb downstream of Osteolectin associated with reduced height and plasma Osteolectin levels. In this study, we tested whether Osteolectin promotes bone elongation and found that Osteolectin-deficient mice have shorter bones than those of sex-matched littermate controls. Integrin α11 deficiency in limb mesenchymal progenitors or chondrocytes reduced growth plate chondrocyte proliferation and bone elongation. Recombinant Osteolectin injections increased femur length in juvenile mice. Human bone marrow stromal cells edited to contain the rs182722517 variant produced less Osteolectin and underwent less osteogenic differentiation than that of control cells. These studies identify Osteolectin/Integrin α11 as a regulator of bone elongation and body length in mice and humans. [ABSTRACT FROM AUTHOR]

Many aspects of cellular physiology remain unstudied in somatic stem cells, for example, there are almost no data on protein synthesis in any somatic stem cell. Here we set out to compare protein synthesis in haematopoietic stem cells (HSCs) and restricted haematopoietic progenitors. We found that the amount of protein synthesized per hour in HSCs in vivo was lower than in most other haematopoietic cells, even if we controlled for differences in cell cycle status or forced HSCs to undergo self-renewing divisions. Reduced ribosome function in [RpL24.sup.Bst/+] mice further reduced protein synthesis in HSCs and impaired HSC function. Pten deletion increased protein synthesis in HSCs but also reduced HSC function. [Rp124.sup.Bst/+] cell-autonomously rescued the effects of Pten deletion in HSCs; blocking the increase in protein synthesis, restoring HSC function, and delaying leukaemogenesis. Pten deficiency thus depletes HSCs and promotes leukaemia partly by increasing protein synthesis. Either increased or decreased protein synthesis impairs HSC function., Mutations in ribosomes and other gene products that affect protein synthesis are associated with human diseases marked by haematopoietic dysfunction (1,2). Increased protein synthesis can promote the development and progression [...]

Sexually dimorphic mammalian tissues, including sexual organs and the brain, contain stem cells that are directly or indirectly regulated by sex hormones (1-6). An important question is whether stem cells also exhibit sex differences in physiological function and hormonal regulation in tissues that do not show sex-specific morphological differences. The terminal differentiation and function of some haematopoietic cells are regulated by sex hormones (7-10), but haematopoietic stem-cell function is thought to be similar in both sexes. Here we show that mouse haematopoietic stem cells exhibit sex differences in cell-cycle regulation by oestrogen. Haematopoietic stem cells in female mice divide significantly more frequently than in male mice. This difference depends on the ovaries but not the testes. Administration of oestradiol, a hormone produced mainly in the ovaries, increased haematopoietic stem-cell division in males and females. Oestrogen levels increased during pregnancy, increasing haematopoietic stem-cell division, haematopoietic stem cell frequency, cellularity, and erythropoiesis in the spleen. Haematopoietic stem cells expressed high levels of oestrogen receptor-α (ERα). Conditional deletion of ERα from haematopoietic stem cells reduced haematopoietic stem-cell division in female, but not male, mice and attenuated the increases in haematopoietic stem-cell division, haematopoietic stem-cell frequency, and erythropoiesis during pregnancy. Oestrogen/ERα signalling promotes haematopoietic stem-cell self-renewal, expanding splenic haematopoietic stem cells and erythropoiesis during pregnancy., A fundamental question in stem-cell biology concerns the extent to which stem cells are regulated by long-range signals to ensure that stem-cell function within individual tissues is integrated with the [...]

Niches are local tissue microenvironments that maintain and regulate stem cells. Haematopoiesis provides a model for understanding mammalian stem cells and their niches, but the haematopoietic stem cell (HSC) niche remains incompletely defined and beset by competing models. Recent progress has been made in elucidating the location and cellular components of the HSC niche in the bone marrow. The niche is perivascular, created partly by mesenchymal stromal cells and endothelial cells and often, but not always, located near trabecular bone. Outstanding questions concern the cellular complexity of the niche, the role of the endosteum and functional heterogeneity among perivascular microenvironments., Haematopoietic stem cell (HSC) niches are present in diverse tissues throughout development, beginning in the aorta-gonadmesonephros (AGM) region and the yolk sac, followed by the placenta, fetal liver, spleen and [...]

'Pre-leukaemic' mutations are thought to promote clonal expansion of haematopoietic stem cells (HSCs) by increasing self-renewal and competitiveness (1); however, mutations that increase HSC proliferation tend to reduce competitiveness and self-renewal potential, raising the question of how a mutant HSC can sustainably outcompete wild-type HSCs. Activating mutations in NRAS are prevalent in human myeloproliferative neoplasms and leukaemia (2). Here we show that a single allele of oncogenic [Nras.sup.G12D] increases HSC proliferation but also increases reconstituting and self-renewal potential upon serial transplantation in irradiated mice, all prior to leukaemia initiation. [Nras.sup.G12D] also confers long-term self-renewal potential to multipotent progenitors. To explore the mechanism by which [Nras.sup.G12D]promotes HSC proliferation and self-renewal, we assessed cell-cycle kinetics using H2B-GFP label retention and 5-bromodeoxyuridine (BrdU) incorporation. [Nras.sup.G12D] had a bimodal effect on HSCs, increasing the frequency with which some HSCs divide and reducing the frequency with which others divide. This mirrored bimodal effects on reconstituting potential, as rarely dividing [Nras.sup.G12D] HSCs outcompeted wild-type HSCs, whereas frequently dividing [Nras.sup.G12D] HSCs did not. [Nras.sup.G12D] caused these effects by promoting STAT5 signalling, inducing different transcriptional responses in different subsets of HSCs. One signal can therefore increase HSC proliferation, competitiveness and self-renewal through bimodal effects on HSC gene expression, cycling and reconstituting potential., To gain a durable competitive advantage, mutant HSCs must sustainably self-renew more frequently than wild-type HSCs. Yet increased HSC division is almost always associated with reduced self-renewal potential and HSC [...]

Phenotypic and functional heterogeneity arise among cancer cells within the same tumour as a consequence of genetic change, environmental differences and reversible changes in cell properties. Some cancers also contain a hierarchy in which tumorigenic cancer stem cells differentiate into non-tumorigenic progeny. However, it remains unclear what fraction of cancers follow the stem-cell model and what clinical behaviours the model explains. Studies using lineage tracing and deep sequencing could have implications for the cancer stem-cell model and may help to determine the extent to which it accounts for therapy resistance and disease progression., The cancer stem-cell model provides one explanation for the phenotypic and functional heterogeneity among cancer cells in some tumours (1-5). The model posits that some cancers are organized into a [...]