54 results found
Beerman I, Luis TC, Singbrant S, et al., 2017, The evolving view of the hematopoietic stem cell niche., Exp Hematol, Vol: 50, Pages: 22-26, ISSN: 0301-472X
Hematopoietic stem cells (HSCs) reside in specialized microenvironments known as niches. The niche is essential to support HSC function and to maintain a correct balance between self-renewal and differentiation. Recent advances in defining different mesenchymal and endothelial bone marrow cell populations, as well as hematopoietic stem and progenitor cells, greatly enhanced our understanding of these niches and of the molecular mechanisms by which they regulate HSC function. In addition to the role in maintaining HSC homeostasis, the niche has also been implicated in the pathogenesis of blood disorders including hematological malignancies. Characterizing the extrinsic regulators and the cellular context in which the niches interact with HSCs will be crucial to define new strategies to enhance blood regeneration. Furthermore, a better understanding of the role of the niche in leukemia development will open new possibilities for the treatment of these disorders by using therapies aiming to target the leukemic niche specifically. To update on recent findings on this topic, the International Society for Experimental Hematology (ISEH) organized a webinar, presented by Prof. Sean J. Morrison and Dr. Simón Méndez-Ferrer and moderated by Dr. Cristina Lo Celso, entitled "The evolving view of the hematopoietic stem cell niche," which we summarize here.
Lo Celso C, Lo Celso C, Lo Celso C, et al., 2017, Revealing the inner workings of human HSC adhesion, BLOOD, Vol: 129, Pages: 921-922, ISSN: 0006-4971
© 2017 by The American Society of Hematology. In this issue of Blood, Rak et al identify cytohesin 1 (CYTH1) as an important intracellular mediator of human hematopoietic stem cell (HSC) adhesion that plays a role in HSC homing and lodging in the bone marrow and subsequent engraftment. 1 This finding contributes to our understanding of the mechanisms involved in regulating HSC-niche interaction, which we know is critical in regulating HSC function. 2
MacLean AL, Lo Celso C, Stumpf MPH, et al., 2017, Concise Review: Stem Cell Population Biology: Insights from Hematopoiesis, STEM CELLS, Vol: 35, Pages: 80-88, ISSN: 1066-5099
Stem cells are fundamental to human life and offer great therapeutic potential, yet their biology remains incompletely-or in cases even poorly-understood. The field of stem cell biology has grown substantially in recent years due to a combination of experimental and theoretical contributions: the experimental branch of this work provides data in an ever-increasing number of dimensions, while the theoretical branch seeks to determine suitable models of the fundamental stem cell processes that these data describe. The application of population dynamics to biology is amongst the oldest applications of mathematics to biology, and the population dynamics perspective continues to offer much today. Here we describe the impact that such a perspective has made in the field of stem cell biology. Using hematopoietic stem cells as our model system, we discuss the approaches that have been used to study their key properties, such as capacity for self-renewal, differentiation, and cell fate lineage choice. We will also discuss the relevance of population dynamics in models of stem cells and cancer, where competition naturally emerges as an influential factor on the temporal evolution of cell populations. Stem Cells 2017;35:80-88.
Secklehner J, Lo Celso C, Carlin LM, et al., 2017, Intravital microscopy in historic and contemporary immunology, IMMUNOLOGY AND CELL BIOLOGY, Vol: 95, Pages: 506-513, ISSN: 0818-9641
In this review, we discuss intravital microscopy of immune cells, starting from its historic origins to current applications in diverse organs. It is clear from a quantitative review of the literature that intravital microscopy is a key tool in both historic and contemporary immunological research, providing unique advances in our understanding of immune responses. We have chosen to focus this review on how intravital microscopy methodologies are used to image specific organs or systems and we present recent descriptions of fundamental immunological processes that could not have been achieved by other methods. The following target organs/systems are discussed in more detail: cremaster muscle, skin (ear and dorsal skin fold chamber), lymph node, liver, lung, mesenteric vessels, carotid artery, bone marrow, brain, spleen, foetus and lastly vessels of the knee joint.
Hawkins ED, Duarte D, Akinduro O, et al., 2016, T-cell acute leukaemia exhibits dynamic interactions with bone marrow microenvironments, NATURE, Vol: 538, Pages: 518-+, ISSN: 0028-0836
It is widely accepted that complex interactions between cancer cells and their surrounding microenvironment contribute to disease development, chemo-resistance and disease relapse. In light of this observed interdependency, novel therapeutic interventions that target specific cancer stroma cell lineages and their interactions are being sought. Here we studied a mouse model of human T-cell acute lymphoblastic leukaemia (T-ALL) and used intravital microscopy to monitor the progression of disease within the bone marrow at both the tissue-wide and single-cell level over time, from bone marrow seeding to development/selection of chemo-resistance. We observed highly dynamic cellular interactions and promiscuous distribution of leukaemia cells that migrated across the bone marrow, without showing any preferential association with bone marrow sub-compartments. Unexpectedly, this behaviour was maintained throughout disease development, from the earliest bone marrow seeding to response and resistance to chemotherapy. Our results reveal that T-ALL cells do not depend on specific bone marrow microenvironments for propagation of disease, nor for the selection of chemo-resistant clones, suggesting that a stochastic mechanism underlies these processes. Yet, although T-ALL infiltration and progression are independent of the stroma, accumulated disease burden leads to rapid, selective remodelling of the endosteal space, resulting in a complete loss of mature osteoblastic cells while perivascular cells are maintained. This outcome leads to a shift in the balance of endogenous bone marrow stroma, towards a composition associated with less efficient haematopoietic stem cell function. This novel, dynamic analysis of T-ALL interactions with the bone marrow microenvironment in vivo, supported by evidence from human T-ALL samples, highlights that future therapeutic interventions should target the migration and promiscuous interactions of cancer cells with the surrounding microenvironment
Khorshed RA, Lo Celso C, 2016, Automated identification and measurement of Hematopoietic Stem Cells in 3D Intravital Microscopy Data, Microscopy and Analysis, Editors: Stanciu, Publisher: InTech, ISBN: 978-953-51-2578-5
Image analysis and quantification of Haematopoietic stem cells (HSCs) position within their surrounding microenvironment in the bone marrow is a fast growing area of research, as it holds the key to understanding the dynamics of HSC-niche interactions and their multiple implications in normal tissue development and in response to various stress events. However, this area of research is very challenging due to the complex cellular structure of such images. Therefore, automated image analysis tools are required to simplify the biological interpretation of 3D HSC microenvironment images. In this chapter, we describe how 3D intravital microscopy data can be visualised and analysed using a computational method that allows the automated quantification of HSC position relative to surrounding niche components.
Khorshed RA, Lo Celso C, Khorshed R, et al., 2016, MACHINE LEARNING CLASSIFICATION OF COMPLEX VASCULATURE STRUCTURES FROM IN-VIVO BONE MARROW 3D DATA, IEEE 13th International Symposium on Biomedical Imaging (ISBI), Publisher: IEEE, Pages: 1217-1220, ISSN: 1945-7928
Blood vessels inside the bone marrow (BM) play a vital role in the maintenance of hematopoietic stem cell (HSCs). Investigating the interaction of HSCs relative to vasculature has become the main headline for many recent studies. Advances in microscopy and image analysis using mouse models have allowed detection, identification and automated quantification of HSCs alongside their vascular niche. This resulted in new hypotheses concerning the activation state of HSCs adjacent to different blood vessel types (for example sinusoids vs. arterioles). Identifying the different types of BM vasculature has become critically important, however it still requires the use of complex immunostainings ex vivo or transgenic reporter mouse lines in vivo. To eliminate these requirements and increase the throughput of studies focusing on the HSC niche, we present a machine learning classification approach based on the Decision Tree Classifier to classify different regions of bone marrow vasculature into four distinct classes based on their discriminative features.
Silberstein L, Goncalves KA, Kharchenko PV, et al., 2016, Proximity-Based Differential Single-Cell Analysis of the Niche to Identify Stem/Progenitor Cell Regulators., Cell Stem Cell, Vol: 19, Pages: 530-543, ISSN: 1934-5909
Physiological stem cell function is regulated by secreted factors produced by niche cells. In this study, we describe an unbiased approach based on the differential single-cell gene expression analysis of mesenchymal osteolineage cells close to, and further removed from, hematopoietic stem/progenitor cells (HSPCs) to identify candidate niche factors. Mesenchymal cells displayed distinct molecular profiles based on their relative location. We functionally examined, among the genes that were preferentially expressed in proximal cells, three secreted or cell-surface molecules not previously connected to HSPC biology-the secreted RNase angiogenin, the cytokine IL18, and the adhesion molecule Embigin-and discovered that all of these factors are HSPC quiescence regulators. Therefore, our proximity-based differential single-cell approach reveals molecular heterogeneity within niche cells and can be used to identify novel extrinsic stem/progenitor cell regulators. Similar approaches could also be applied to other stem cell/niche pairs to advance the understanding of microenvironmental regulation of stem cell function.
Vainieri ML, Blagborough AM, MacLean AL, et al., 2016, Systematic tracking of altered haematopoiesis during sporozoite-mediated malaria development reveals multiple response points, OPEN BIOLOGY, Vol: 6, Pages: 160038-160038, ISSN: 2046-2441
Haematopoiesis is the complex developmental process that maintains the turnover of all blood cell lineages. It critically depends on the correct functioning of rare, quiescent haematopoietic stem cells (HSCs) and more numerous, HSC-derived, highly proliferative and differentiating haematopoietic progenitor cells (HPCs). Infection is known to affect HSCs, with severe and chronic inflammatory stimuli leading to stem cell pool depletion, while acute, non-lethal infections exert transient and even potentiating effects. Both whether this paradigm applies to all infections and whether the HSC response is the dominant driver of the changes observed during stressed haematopoiesis remain open questions. We use a mouse model of malaria, based on natural, sporozoite-driven Plasmodium berghei infection, as an experimental platform to gain a global view of haematopoietic perturbations during infection progression. We observe coordinated responses by the most primitive HSCs and multiple HPCs, some starting before blood parasitaemia is detected. We show that, despite highly variable inter-host responses, primitive HSCs become highly proliferative, but mathematical modelling suggests that this alone is not sufficient to significantly impact the whole haematopoietic cascade. We observe that the dramatic expansion of Sca-1(+) progenitors results from combined proliferation of direct HSC progeny and phenotypic changes in downstream populations. We observe that the simultaneous perturbation of HSC/HPC population dynamics is coupled with early signs of anaemia onset. Our data uncover a complex relationship between Plasmodium and its host's haematopoiesis and raise the question whether the variable responses observed may affect the outcome of the infection itself and its long-term consequences on the host.
Khorshed RA, Hawkins ED, Duarte D, et al., 2015, Automated Identification and Localization of Hematopoietic Stem Cells in 3D Intravital Microscopy Data, STEM CELL REPORTS, Vol: 5, Pages: 139-153, ISSN: 2213-6711
Measuring three-dimensional (3D) localization of hematopoietic stem cells (HSCs) within the bone marrow microenvironment using intravital microscopy is a rapidly expanding research theme. This approach holds the key to understanding the detail of HSC-niche interactions, which are critical for appropriate stem cell function. Due to the complex tissue architecture of the bone marrow and to the progressive introduction of scattering and signal loss at increasing imaging depths, there is no ready-made software to handle efficient segmentation and unbiased analysis of the data. To address this, we developed an automated image analysis tool that simplifies and standardizes the biological interpretation of 3D HSC microenvironment images. The algorithm identifies HSCs and measures their localization relative to surrounding osteoblast cells and bone collagen. We demonstrate here the effectiveness, consistency, and accuracy of the proposed approach compared to current manual analysis and its wider applicability to analyze other 3D bone marrow components.
Batista S, Maniati E, Reynolds LE, et al., 2014, Haematopoietic focal adhesion kinase deficiency alters haematopoietic homeostasis to drive tumour metastasis, NATURE COMMUNICATIONS, Vol: 5, Pages: 5054-5054, ISSN: 2041-1723
Metastasis is the main cause of cancer-related death and thus understanding the molecular and cellular mechanisms underlying this process is critical. Here, our data demonstrate, contrary to established dogma, that loss of haematopoietic-derived focal adhesion kinase (FAK) is sufficient to enhance tumour metastasis. Using both experimental and spontaneous metastasis models, we show that genetic ablation of haematopoietic FAK does not affect primary tumour growth but enhances the incidence of metastasis significantly. At a molecular level, haematopoietic FAK deletion results in an increase in PU-1 levels and decrease in GATA-1 levels causing a shift of hematopoietic homeostasis towards a myeloid commitment. The subsequent increase in circulating granulocyte number, with an increase in serum CXCL12 and granulocyte CXCR4 levels, was required for augmented metastasis in mice lacking haematopoietic FAK. Overall our findings provide a mechanism by which haematopoietic FAK controls cancer metastasis.
Rashidi NM, Lo Celso C, Rashidi NM, et al., 2014, Flying back to the nest: Intravital microscopy reveals how the niche can induce stemness., Intravital, Vol: 3, Pages: e29653-e29653, ISSN: 2165-9087
Rashidi NM, Scott MK, Scherf N, et al., 2014, In vivo time-lapse imaging shows diverse niche engagement by quiescent and naturally activated hematopoietic stem cells, BLOOD, Vol: 124, Pages: 79-83, ISSN: 0006-4971
Hematopoietic stem cells (HSCs) maintain the turnover of mature blood cells during steady state and in response to systemic perturbations such as infections. Their function critically depends on complex signal exchanges with the bone marrow (BM) microenvironment in which they reside, but the cellular mechanisms involved in HSC-niche interactions and regulating HSC function in vivo remain elusive. We used a natural mouse parasite, Trichinella spiralis, and multipoint intravital time-lapse confocal microscopy of mouse calvarium BM to test whether HSC-niche interactions may change when hematopoiesis is perturbed. We find that steady-state HSCs stably engage confined niches in the BM whereas HSCs harvested during acute infection are motile and therefore interact with larger niches. These changes are accompanied by increased long-term repopulation ability and expression of CD44 and CXCR4. Administration of a CXCR4 antagonist affects the duration of HSC-niche interactions. These findings suggest that HSC-niche interactions may be modulated during infection.
Scott MK, Akinduro O, Lo Celso C, et al., 2014, In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow, JOVE-JOURNAL OF VISUALIZED EXPERIMENTS, ISSN: 1940-087X
Through a delicate balance between quiescence and proliferation, self renewal and production of differentiated progeny, hematopoietic stem cells (HSCs) maintain the turnover of all mature blood cell lineages. The coordination of the complex signals leading to specific HSC fates relies upon the interaction between HSCs and the intricate bone marrow microenvironment, which is still poorly understood([1-2]). We describe how by combining a newly developed specimen holder for stable animal positioning with multi-step confocal and two-photon in vivo imaging techniques, it is possible to obtain high-resolution 3D stacks containing HSPCs and their surrounding niches and to monitor them over time through multi-point time-lapse imaging. High definition imaging allows detecting ex vivo labeled hematopoietic stem and progenitor cells (HSPCs) residing within the bone marrow. Moreover, multi-point time-lapse 3D imaging, obtained with faster acquisition settings, provides accurate information about HSPC movement and the reciprocal interactions between HSPCs and stroma cells. Tracking of HSPCs in relation to GFP positive osteoblastic cells is shown as an exemplary application of this method. This technique can be utilized to track any appropriately labeled hematopoietic or stromal cell of interest within the mouse calvarium bone marrow space.
Carlson AL, Fujisaki J, Wu J, et al., 2013, Tracking Single Cells in Live Animals Using a Photoconvertible Near-Infrared Cell Membrane Label, PLOS ONE, Vol: 8, Pages: e69257-e69257, ISSN: 1932-6203
We describe a novel photoconversion technique to track individual cells in vivo using a commercial lipophilic membrane dye, DiR. We show that DiR exhibits a permanent fluorescence emission shift (photoconversion) after light exposure and does not reacquire the original color over time. Ratiometric imaging can be used to distinguish photoconverted from non-converted cells with high sensitivity. Combining the use of this photoconvertible dye with intravital microscopy, we tracked the division of individual hematopoietic stem/progenitor cells within the calvarium bone marrow of live mice. We also studied the peripheral differentiation of individual T cells by tracking the gain or loss of FoxP3-GFP expression, a marker of the immune suppressive function of CD4(+) T cells. With the near-infrared photoconvertible membrane dye, the entire visible spectral range is available for simultaneous use with other fluorescent proteins to monitor gene expression or to trace cell lineage commitment in vivo with high spatial and temporal resolution.
Fink J, Kent D, Li J, et al., 2013, HOMOZYGOUS JAK2V617F DRIVES RAPID HEMATOPOIETIC STEM CELL PROLIFERATION AND DIFFERENTIATION AT THE EXPENSE OF SELF-RENEWAL, 42nd Annual Scientific Meeting of the International-Society-for-Experimental-Hematology-and-Stem-Cells (ISEH), Publisher: ELSEVIER SCIENCE INC, Pages: S15-S15, ISSN: 0301-472X
Hawkins ED, Lo Celso C, Hawkins ED, et al., 2013, Subdivision of bone marrow microenvironments: purpose built homes for haematopoietic stem cells, EMBO JOURNAL, Vol: 32, Pages: 176-177, ISSN: 0261-4189
The identification of distinct bone marrow microenvironments that support haematopoietic stem cell (HSC) survival and function is one of the most significant recent advances in our understanding of HSC biology. While the intricate organization of these structures and their effect on HSC is on its own a fascinating biological question, solving this puzzle remains a key step in the development of more efficient stem cell therapies through improved in vitro HSC culture systems. In this issue, a study conducted byWang and colleagues describes a novel structure within the bone marrow and provides evidence for an additional layer of complexity and compartmentalisation within the bone marrow microenvironment, suggesting the presence of specialised structures that support clonal HSC expansion. © 2013 European Molecular Biology Organization.
Joseph C, Quach JM, Walkley CR, et al., 2013, Deciphering Hematopoietic Stem Cells in Their Niches: A Critical Appraisal of Genetic Models, Lineage Tracing, and Imaging Strategies, CELL STEM CELL, Vol: 13, Pages: 520-533, ISSN: 1934-5909
In recent years, technical developments in mouse genetics and imaging equipment have substantially advanced our understanding of hematopoietic stem cells (HSCs) and their niche. The availability of numerous Cre strains for targeting HSCs and microenvironmental cells provides extensive flexibility in experimental design, but it can also pose significant challenges due to strain-specific differences in cell specificity. Here we outline various genetic approaches for isolating, detecting, and ablating HSCs and niche components and provide a guide for advantages and caveats to consider. We also discuss opportunities and limitations presented by imaging technologies that allow investigation of HSC behavior in situ.
Lo Celso C, 2013, IN VIVO IMAGING OF QUIESCENT AND PHYSIOLOGICALLY ACTIVATED HAEMATOPOIETIC STEM CELLS, 42nd Annual Scientific Meeting of the International-Society-for-Experimental-Hematology-and-Stem-Cells (ISEH), Publisher: ELSEVIER SCIENCE INC, Pages: S4-S4, ISSN: 0301-472X
MacLean AL, Lo Celso C, Stumpf MPH, et al., 2013, Population dynamics of normal and leukaemia stem cells in the haematopoietic stem cell niche show distinct regimes where leukaemia will be controlled, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 10, Pages: 20120968-20120968, ISSN: 1742-5689
Haematopoietic stem cells (HSCs) are responsible for maintaining immune cells, red blood cells and platelets throughout life. HSCs must be located in their ecological niche (the bone marrow) to function correctly, that is, to regenerate themselves and their progeny; the latter eventually exit the bone marrow and enter circulation. We propose that cells with oncogenic potential-cancer/leukaemia stem cells (LSC)-and their progeny will also occupy this niche. Mathematical models, which describe the dynamics of HSCs, LSCs and their progeny allow investigation into the conditions necessary for defeating a malignant invasion of the niche. Two such models are developed and analysed here. To characterize their behaviour, we use an inferential framework that allows us to study regions in parameter space that give rise to desired behaviour together with an assessment of the robustness of the dynamics. Using this approach, we map out conditions under which HSCs can outcompete LSCs. In therapeutic applications, we clearly want to drive haematopoiesis into such regimes and the current analysis provide some guidance as to how we can identify new therapeutic targets. Our results suggest that maintaining a viable population of HSCs and their progenies in the niche may often already be nearly sufficient to eradicate LSCs from the system.
Progatzky F, Dallman MJ, Lo Celso C, et al., 2013, From seeing to believing: labelling strategies for in vivo cell-tracking experiments, INTERFACE FOCUS, Vol: 3, Pages: 20130001-20130001, ISSN: 2042-8898
Intravital microscopy has become increasingly popular over the past few decades because it provides high-resolution and real-time information about complex biological processes. Technological advances that allow deeper penetration in live tissues, such as the development of confocal and two-photon microscopy, together with the generation of ever-new fluorophores that facilitate bright labelling of cells and tissue components have made imaging of vertebrate model organisms efficient and highly informative. Genetic manipulation leading to expression of fluorescent proteins is undoubtedly the labelling method of choice and has been used to visualize several cell types in vivo. This approach, however, can be technically challenging and time consuming. Over the years, several dyes have been developed to allow rapid, effective and bright ex vivo labelling of cells for subsequent transplantation and imaging. Here, we review and discuss the advantages and limitations of a number of strategies commonly used to label and track cells at high resolution in vivo in mouse and zebrafish, using fluorescence microscopy. While the quest for the perfect label is far from achieved, current reagents are valuable tools enabling the progress of biological discovery, so long as they are selected and used appropriately.
Roeder I, Krinner A, Scherf N, et al., 2013, QUANTIFICATION OF STEM CELL/NICHE INTERACTIONS BY COUPLING IN VIVO IMAGING AND IN SILICO SIMULATION, 42nd Annual Scientific Meeting of the International-Society-for-Experimental-Hematology-and-Stem-Cells (ISEH), Publisher: ELSEVIER SCIENCE INC, Pages: S31-S31, ISSN: 0301-472X
Barrett O, Sottocornola R, Lo Celso C, et al., 2012, In vivo imaging of hematopoietic stem cells in the bone marrow niche., Methods Mol Biol, Vol: 916, Pages: 231-242, ISSN: 1064-3745
Even though hematopoietic stem cells (HSC) are amongst the first somatic stem cells exploited for therapeutic purposes, their application is still limited by the inability to expand them ex vivo without impairing their function. Moreover, it has recently emerged that several types of leukemia develop and relapse through complex interactions with bone marrow (BM) components and may directly affect the HSC and their niche. Increasing attention has therefore been dedicated to the BM microenvironment the HSC reside in, with the view that a better understanding of the molecular regulators of HSC-niche interaction in vivo will allow improving HSC mobilization, collection and transplantation and provide clues for the development of innovative leukemia treatments. This chapter focuses on a recently established technique for the visualization of transplanted hematopoietic stem and progenitor cells (HSPC) within the calvarium bone marrow of live mice (Lo Celso et al. Nature 457:92-96, 2007). Intravital microscopy is a rapidly developing field, driven by constant improvement in both detection technologies (i.e., spatial resolution, depth of penetration, spectral definition) and probe availability (i.e., increasingly sophisticated genetic and chemical reporter systems). We therefore discuss the current limitations and challenges related to intravital microscopy of the HSC niche and introduce a number of potential imaging approaches, which could be promising candidates for future development of this technique.
Tissues characterized by constant turnover contain post-mitotic, terminally differentiated cells originating from highly proliferative progenitors, which in turn derive from a relatively small population of stem cells. At the population level, self-renewal and differentiation are the possible outcomes of stem cell proliferation; overall, however, stem cells are quiescent if compared with their direct progeny. The recent discovery of a particularly quiescent, or dormant, subpopulation of hematopoietic stem cells (HSCs) raises a number of fundamental questions. As stem cell fate is influenced by the signals integrated by the stem cell niche, will dormant HSCs reside in specific dormant niches? Is the mechanism of dormancy common to multiple regenerating tissues or specific to the hematopoietic system? If cancer is maintained by a few cancer stem cells, do they also contain a subpopulation of dormant cells, and could this be exploited for therapeutic purposes?
Cornejo MG, Mabialah V, Sykes SM, et al., 2011, Crosstalk between NOTCH and AKT signaling during murine megakaryocyte lineage specification, BLOOD, Vol: 118, Pages: 1264-1273, ISSN: 0006-4971
The NOTCH signaling pathway is implicated in a broad range of developmental processes, including cell fate decisions. However, the molecular basis for its role at the different steps of stem cell lineage commitment is unclear. We recently identified the NOTCH signaling pathway as a positive regulator of megakaryocyte lineage specification during hematopoiesis, but the developmental pathways that allow hematopoietic stem cell differentiation into the erythro-megakaryocytic lineages remain controversial. Here, we investigated the role of downstream mediators of NOTCH during megakaryopoiesis and report crosstalk between the NOTCH and PI3K/AKT pathways. We demonstrate the inhibitory role of phosphatase with tensin homolog and Forkhead Box class O factors on megakaryopoiesis in vivo. Finally, our data annotate developmental mechanisms in the hematopoietic system that enable a decision to be made either at the hematopoietic stem cell or the committed progenitor level to commit to the megakaryocyte lineage, supporting the existence of 2 distinct developmental pathways.
Fujisaki J, Wu J, Carlson AL, et al., 2011, In vivo imaging of T-reg cells providing immune privilege to the haematopoietic stem-cell niche, NATURE, Vol: 474, Pages: 216-U256, ISSN: 0028-0836
Stem cells reside in a specialized regulatory microenvironment or niche, where they receive appropriate support for maintaining self-renewal and multi-lineage differentiation capacity. The niche may also protect stem cells from environmental insults including cytotoxic chemotherapy and perhaps pathogenic immunity. The testis, hair follicle and placenta are all sites of residence for stem cells and are immune-suppressive environments, called immune-privileged sites, where multiple mechanisms cooperate to prevent immune attack, even enabling prolonged survival of foreign allografts without immunosuppression. We sought to determine if somatic stem-cell niches more broadly are immune-privileged sites by examining the haematopoietic stem/progenitor cell (HSPC) niche in the bone marrow, a site where immune reactivity exists. We observed persistence of HSPCs from allogeneic donor mice (allo-HSPCs) in non-irradiated recipient mice for 30 days without immunosuppression with the same survival frequency compared to syngeneic HSPCs. These HSPCs were lost after the depletion of FoxP3 regulatory T (T(reg)) cells. High-resolution in vivo imaging over time demonstrated marked co-localization of HSPCs with T(reg) cells that accumulated on the endosteal surface in the calvarial and trabecular bone marrow. T(reg) cells seem to participate in creating a localized zone where HSPCs reside and where T(reg) cells are necessary for allo-HSPC persistence. In addition to processes supporting stem-cell function, the niche will provide a relative sanctuary from immune attack.
Lane SW, Wang YJ, Lo Celso C, et al., 2011, Differential niche and Wnt requirements during acute myeloid leukemia progression, BLOOD, Vol: 118, Pages: 2849-2856, ISSN: 0006-4971
Hematopoietic stem cells (HSCs) engage in complex bidirectional signals with the hematopoietic microenvironment (HM), and there is emerging evidence that leukemia stem cells (LSCs) may use similar interactions. Using a syngeneic retroviral model of MLL-AF9 induced acute myeloid leukemia (AML), we have identified 2 different stages of leukemia progression, propagated by "pre-LSCs" and established leukemia (LSCs) and compared the homing properties of these distinctive entities to that of normal HSCs. The homing and microlocalization of pre-LSCs was most similar to long-term HSCs and was dependent on cell-intrinsic Wnt signaling. In contrast, the homing of established LSCs was most similar to that of committed myeloid progenitors and distinct from HSCs. Although osteoblast-derived Dickkopf-1, a potent Wnt inhibitor known to impair HSC function, dramatically impaired normal HSC localization within the bone marrow, it did not affect pre-LSCs, LSC homing, or AML development. Mechanistically, cell-intrinsic Wnt activation was observed in human and murine AML samples, explaining the independence of MLL-AF9 LSCs from niche-derived Wnt signals. These data identify differential engagement of HM associated with leukemic progression and identify an LSC niche that is physically distinct and independent of the constraints of Wnt signaling that apply to normal HSCs.
Lo Celso C, Lin CP, Scadden DT, et al., 2011, In vivo imaging of transplanted hematopoietic stem and progenitor cells in mouse calvarium bone marrow, NATURE PROTOCOLS, Vol: 6, Pages: 1-14, ISSN: 1754-2189
In vivo imaging of transplanted hematopoietic stem and progenitor cells (HSPCs) was developed to investigate the relationship between HSPCs and components of their microenvironment in the bone marrow. In particular, it allows a direct observation of the behavior of hematopoietic cells during the first few days after transplantation, when the critical events in homing and early engraftment are occurring. By directly imaging these events in living animals, this method permits a detailed assessment of functions previously evaluated by crude assessments of cell counts (homing) or after prolonged periods (engraftment). This protocol offers a new means of investigating the role of cell-intrinsic and cell-extrinsic molecular regulators of hematopoiesis during the early stages of transplantation, and it is the first to allow the study of cell-cell interactions within the bone marrow in three dimensions and in real time. In this paper, we describe how to isolate, label and inject HSPCs, as well as how to perform calvarium intravital microscopy and analyze the resulting images. A typical experiment can be performed and analyzed in ∼1 week.
Rodriguez S, Wang L, Mumaw C, et al., 2011, The SKP2 E3 ligase regulates basal homeostasis and stress-induced regeneration of HSCs, BLOOD, Vol: 117, Pages: 6509-6519, ISSN: 0006-4971
Exit from quiescence and reentry into cell cycle is essential for HSC self-renewal and regeneration. Skp2 is the F-box unit of the SCF E3-ligase that targets the CDK inhibitors (CKIs) p21(Cip1), p27(Kip1), p57(Kip2), and p130 for degradation. These CKIs inhibit the G(1) to S-phase transition of the cell cycle, and their deletion results in increased cell proliferation and decreased stem cell self-renewal. Skp2 deletion leads to CKIs stabilization inducing cell-cycle delay or arrest, and conversely, increased Skp2 expression is often found in cancers. Here, we show that SKP2 expression is increased in HSC and progenitors in response to hematopoietic stress from myelosuppression or after transplantation. At steady state, SKP2 deletion decreased the mitotic activity of HSC and progenitors resulting in enhanced HSC quiescence, increased HSC pool size, and maintenance. However, the inability to rapidly enter cell cycle greatly impaired the short-term repopulating potential of SKP2 null HSC and their ability to regenerate after myeloablative stress. Mechanistically, deletion of SKP2 in HSC and progenitors stabilized CKIs in vivo, particularly p27(Kip1), p57(Kip2), and p130. Our results demonstrate a previously unrecognized role for SKP2 in regulating HSC and progenitor expansion and hematopoietic regeneration after stress.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.