Unexpectedly efficient homing capacity of purified murine hematopoietic stem cells

Multiple waves of fetal-derived immune cells constitute adult immune system

It has been over three decades since Drs. Herzenberg and Herzenberg proposed the layered immune system hypothesis, suggesting that different types of stem cells with distinct hematopoietic potential produce specific immune cells. This layering of immune system development is now supported by recent studies showing the presence of fetal-derived immune cells that function in adults. It has been shown that various immune cells arise at different embryonic ages via multiple waves of hematopoiesis from special endothelial cells (ECs), referred to as hemogenic ECs. However, it remains unknown whether these fetal-derived immune cells are produced by hematopoietic stem cells (HSCs) during the fetal to neonatal period. To address this question, many advanced tools have been used, including lineage-tracing mouse models, cellular barcoding techniques, clonal assays, and transplantation assays at the single-cell level. In this review, we will review the history of the search for the origins of HSCs, B-1a progenitors, and mast cells in the mouse embryo. HSCs can produce both B-1a and mast cells within a very limited time window, and this ability declines after embryonic day (E) 14.5. Furthermore, the latest data have revealed that HSC-independent adaptive immune cells exist in adult mice, which implies more complicated developmental pathways of immune cells. We propose revised road maps of immune cell development.

Hematopoietic stem cell-derived functional osteoblasts exhibit therapeutic efficacy in a murine model of osteogenesis imperfecta

Currently, there is no cure for osteogenesis imperfecta (OI)-a debilitating pediatric skeletal dysplasia. Herein we show that hematopoietic stem cell (HSC) therapy holds promise in treating OI. Using single-cell HSC transplantation in lethally irradiated oim/oim mice, we demonstrate significant improvements in bone morphometric, mechanics, and turnover parameters. Importantly, we highlight that HSCs cause these improvements due to their unique property of differentiating into osteoblasts/osteocytes, depositing normal collagen-an attribute thus far assigned only to mesenchymal stem/stromal cells. To confirm HSC plasticity, lineage tracing was done by transplanting oim/oim with HSCs from two specific transgenic mice-VavR, in which all hematopoietic cells are GFP+ and pOBCol2.3GFP, where GFP is expressed only in osteoblasts/osteocytes. In both models, transplanted oim/oim mice demonstrated GFP+ HSC-derived osteoblasts/osteocytes in bones. These studies unequivocally establish that HSCs differentiate into osteoblasts/osteocytes, and HSC transplantation can provide a new translational approach for OI.

Inflammation rapidly recruits mammalian GMP and MDP from bone marrow into regional lymphatics

Innate immune cellular effectors are actively consumed during systemic inflammation, but the systemic traffic and the mechanisms that support their replenishment remain unknown. Here, we demonstrate that acute systemic inflammation induces the emergent activation of a previously unrecognized system of rapid migration of granulocyte-macrophage progenitors and committed macrophage-dendritic progenitors, but not other progenitors or stem cells, from bone marrow (BM) to regional lymphatic capillaries. The progenitor traffic to the systemic lymphatic circulation is mediated by Ccl19/Ccr7 and is NF-κB independent, Traf6/IκB-kinase/SNAP23 activation dependent, and is responsible for the secretion of pre-stored Ccl19 by a subpopulation of CD205+/CD172a+ conventional dendritic cells type 2 and upregulation of BM myeloid progenitor Ccr7 signaling. Mature myeloid Traf6 signaling is anti-inflammatory and necessary for lymph node myeloid cell development. This report unveils the existence and the mechanistic basis of a very early direct traffic of myeloid progenitors from BM to lymphatics during inflammation.

Hematopoietic Stem Cell Cultures and Assays

The adult hematopoietic system is repopulated in its entirety from a rare cell type known as hematopoietic stem cells (HSCs) that reside in the marrow space throughout the skeletal system. Here we describe the isolation and identification of HSCs both phenotypically and functionally.

Mitochondrial Transfer in the Leukemia Microenvironment

The bone marrow microenvironment (BMME) is a complex ecosystem that instructs and protects hematopoietic stem cells (HSCs) and their malignant counterparts, the leukemia-initiating cells (LICs). Within the physical and functional crosstalk that takes place between HSCs, LICs, and the BMME, the transfer of organelles and of mitochondria in particular is an important new intercellular communication mode in addition to adhesion molecules, tunneling nanotubes (TNTs), and the paracrine secretion of cytokines, (onco)metabolites, and extracellular vesicles (EVs). In this review we discuss the functional roles of mitochondrial transfer between BMME and leukemic cells, and give insights into this new mechanism of drug resistance whose understanding will open the way to innovative anticancer adjuvant treatments.

Unperturbed vs. post-transplantation hematopoiesis: both in vivo but different

Purpose of review

Hematopoietic stem cell (HSC) transplantation has yielded tremendous information on experimental properties of HSCs. Yet, it remains unclear whether transplantation reflects the physiology of hematopoiesis. A limitation is the difficulty in accessing HSC functions without isolation, in-vitro manipulation and readout for potential. New genetic fate mapping and clonal marking techniques now shed light on hematopoiesis under physiological conditions.

Recent findings

Transposon-based genetic marks were introduced across the entire hematopoietic system to follow the clonal dynamics of these tags over time. A polyclonal source downstream from stem cells was found responsible for the production of at least granulocytes. In independent experiments, HSCs were genetically marked in adult mice, and the kinetics of label emergence throughout the system was followed over time. These experiments uncovered that during physiological steady-state hematopoiesis large numbers of HSCs yield differentiated progeny. Individual HSCs were active only rarely, indicating their very slow periodicity of differentiation rather than quiescence.

Summary

Noninvasive genetic experiments in mice have identified a major role of stem and progenitor cells downstream from HSCs as drivers of adult hematopoiesis, and revealed that post-transplantation hematopoiesis differs quantitatively from normal steady-state hematopoiesis.

Clonal dominance and transplantation dynamics in hematopoietic stem cell compartments

Hematopoietic stem cells in mammals are known to reside mostly in the bone marrow, but also transitively passage in small numbers in the blood. Experimental findings have suggested that they exist in a dynamic equilibrium, continuously migrating between these two compartments. Here we construct an individual-based mathematical model of this process, which is parametrised using existing empirical findings from mice. This approach allows us to quantify the amount of migration between the bone marrow niches and the peripheral blood. We use this model to investigate clonal hematopoiesis, which is a significant risk factor for hematologic cancers. We also analyse the engraftment of donor stem cells into non-conditioned and conditioned hosts, quantifying the impact of different treatment scenarios. The simplicity of the model permits a thorough mathematical analysis, providing deeper insights into the dynamics of both the model and of the real-world system. We predict the time taken for mutant clones to expand within a host, as well as chimerism levels that can be expected following transplantation therapy, and the probability that a preconditioned host is reconstituted by donor cells.

Clonal hematopoiesis—where mature myeloid cells in the blood deriving from a single stem cell are over-represented—is a major risk factor for overt hematologic malignancies. To quantify how likely this phenomena is, we combine existing observations with a novel stochastic model and extensive mathematical analysis. This approach allows us to observe the hidden dynamics of the hematopoietic system. We conclude that for a clone to be detectable within the lifetime of a mouse, it requires a selective advantage. I.e. the clonal expansion cannot be explained by neutral drift alone. Furthermore, we use our model to describe the dynamics of hematopoiesis after stem cell transplantation. In agreement with earlier findings, we observe that niche-space saturation decreases engraftment efficiency. We further discuss the implications of our findings for human hematopoiesis where the quantity and role of stem cells is frequently debated.

Image-guided transplantation of single cells in the bone marrow of live animals

Transplantation of a single hematopoietic stem cell is an important method for its functional characterization, but the standard transplantation protocol relies on cell homing to the bone marrow after intravenous injection. Here, we present a method to transplant single cells directly into the bone marrow of live mice. We developed an optical platform that integrates a multiphoton microscope with a laser ablation unit for microsurgery and an optical tweezer for cell micromanipulation. These tools allow image-guided single cell transplantation with high spatial control. The platform was used to deliver single hematopoietic stem cells. The engraftment of transplants was tracked over time, illustrating that the technique can be useful for studying both normal and malignant stem cells in vivo.

Isolation of dental pulp stem cells with high osteogenic potential

Dental pulp stem cells/progenitor cells (DPSCs) can be easily obtained and can have excellent proliferative and mineralization potentials. Therefore, many studies have investigated the isolation and bone formation of DPSCs. In most previous reports, human DPSCs were traditionally isolated by exploiting their ability to adhere to plastic tissue culture dishes. DPSCs isolated by plastic adherence are frequently contaminated by other cells, which limits the ability to investigate their basic biology and regenerative properties. Additionally, the proliferative and osteogenic potentials vary depending on the isolated cells. It is very difficult to obtain cells of a sufficient quality to elicit the required effect upon transplantation. Considering clinical applications, stem cells used for regenerative medicine need to be purified in order to increase the efficiency of bone regeneration, and a stable supply of these cells must be generated. Here, we review the purification of DPSCs and studies of cranio-maxillofacial bone regeneration using these cells. Additionally, we introduce the prospective isolation of DPSCs using specific cell surface markers: low-affinity nerve growth factor and thymocyte antigen 1.

The hematopoietic stem-cell niche in health and leukemia

Research in the last decade has shown that hematopoietic stem cells (HSCs) interact with and are modulated by a complex multicellular microenvironment in the bone marrow, which includes both the HSC progeny and multiple non-hematopoietic cell types. Intense work is gradually throwing light on the composition of the HSC niche and the molecular cues exchanged between its components, which has implications for HSC production, maintenance and expansion. In addition, it has become apparent that bidirectional interactions between leukemic cells and their niche play a previously unrecognized role in the initiation and development of hematological malignancies. Consequently, targeting of the malignant niche holds considerable promise for more specific antileukemic therapies. Here we summarize the latest insights into HSC niche biology and recent work showing multiple connections between hematological malignancy and alterations in the bone marrow microenvironment.

Therapeutic potential of dental stem cells

Stem cell biology has become an important field in regenerative medicine and tissue engineering therapy since the discovery and characterization of mesenchymal stem cells. Stem cell populations have also been isolated from human dental tissues, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla, dental follicle progenitor cells, and periodontal ligament stem cells. Dental stem cells are relatively easily obtainable and exhibit high plasticity and multipotential capabilities. The dental stem cells represent a gold standard for neural-crest-derived bone reconstruction in humans and can be used for the repair of body defects in low-risk autologous therapeutic strategies. The bioengineering technologies developed for tooth regeneration will make substantial contributions to understand the developmental process and will encourage future organ replacement by regenerative therapies in a wide variety of organs such as the liver, kidney, and heart. The concept of developing tooth banking and preservation of dental stem cells is promising. Further research in the area has the potential to herald a new dawn in effective treatment of notoriously difficult diseases which could prove highly beneficial to mankind in the long run.

Self-renewal of a purified Tie2+ hematopoietic stem cell population relies on mitochondrial clearance

A single hematopoietic stem cell (HSC) is capable of reconstituting hematopoiesis and maintaining homeostasis by balancing self-renewal and cell differentiation. The mechanisms of HSC division balance, however, are not yet defined. Here we demonstrate, by characterizing at the single-cell level a purified and minimally heterogeneous murine Tie2⁺ HSC population, that these top hierarchical HSCs preferentially undergo symmetric divisions. The induction of mitophagy, a quality control process in mitochondria, plays an essential role in self-renewing expansion of Tie2⁺ HSCs. Activation of the PPAR (peroxisome proliferator-activated receptor)-fatty acid oxidation pathway promotes expansion of Tie2⁺ HSCs through enhanced Parkin recruitment in mitochondria. These metabolic pathways are conserved in human TIE2⁺ HSCs. Our data thus identify mitophagy as a key mechanism of HSC expansion and suggest potential methods of cell-fate manipulation through metabolic pathways.

Protective Effect of Ginsenoside Rg1 on Hematopoietic Stem/Progenitor Cells through Attenuating Oxidative Stress and the Wnt/β-Catenin Signaling Pathway in a Mouse Model of d-Galactose-induced Aging

Stem cell senescence is an important and current hypothesis accounting for organismal aging, especially the hematopoietic stem cell (HSC). Ginsenoside Rg1 is the main active pharmaceutical ingredient of ginseng, which is a traditional Chinese medicine. This study explored the protective effect of ginsenoside Rg1 on Sca-1⁺ hematopoietic stem/progenitor cells (HSC/HPCs) in a mouse model of d-galactose-induced aging. The mimetic aging mouse model was induced by continuous injection of d-gal for 42 days, and the C57BL/6 mice were respectively treated with ginsenoside Rg1, Vitamin E or normal saline after 7 days of d-gal injection. Compared with those in the d-gal administration alone group, ginsenoside Rg1 protected Sca-1⁺ HSC/HPCs by decreasing SA-β-Gal and enhancing the colony forming unit-mixture (CFU-Mix), and adjusting oxidative stress indices like reactive oxygen species (ROS), total anti-oxidant (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-px) and malondialdehyde (MDA). In addition, ginsenoside Rg1 decreased β-catenin and c-Myc mRNA expression and enhanced the phosphorylation of GSK-3β. Moreover, ginsenoside Rg1 down-regulated advanced glycation end products (AGEs), 4-hydroxynonenal (4-HNE), phospho-histone H2A.X (r-H2A.X), 8-OHdG, p16(Ink4a), Rb, p21(Cip1/Waf1) and p53 in senescent Sca-1⁺ HSC/HPCs. Our findings indicated that ginsenoside Rg1 can improve the resistance of Sca-1⁺ HSC/HPCs in a mouse model of d-galactose-induced aging through the suppression of oxidative stress and excessive activation of the Wnt/β-catenin signaling pathway, and reduction of DNA damage response, p16(Ink4a)-Rb and p53-p21(Cip1/Waf1) signaling.

Isolation and characterization of hematopoietic stem cells in teleost fish

Despite 400 million years of evolutionary divergence, hematopoiesis is highly conserved between mammals and teleost fish. All types of mature blood cells including the erythroid, myeloid, and lymphoid lineages show a high degree of similarity to their mammalian counterparts at the morphological and molecular level. Hematopoietic stem cells (HSCs) are cells that are capable of self-renewal and differentiating into all hematopoietic lineages over the lifetime of an organism. The study of HSCs has been facilitated through bone marrow transplantation experiments developed in the mouse model. In the last decade, the zebrafish and clonal ginbuna carp (Carassius auratus langsdorfii) have emerged as new models for the study of HSCs. This review highlights the recent progress and future prospects of studying HSCs in teleost fish. Transplantation assays using these teleost models have demonstrated the presence of HSCs in the kidney, which is the major hematopoietic organ in teleost fish. Moreover, it is possible to purify HSCs from the kidney utilizing fluorescent dyes or transgenic animals. These teleost models will provide novel insights into the universal mechanisms of HSC maintenance, homeostasis, and differentiation among vertebrates.

Heartbreak hotel: a convergence in cardiac regeneration

In February 2016, The Company of Biologists hosted an intimate gathering of leading international researchers at the forefront of experimental cardiovascular regeneration, with its emphasis on ‘Transdifferentiation and Tissue Plasticity in Cardiovascular Rejuvenation’. As I review here, participants at the workshop revealed how understanding cardiac growth and lineage decisions at their most fundamental level has transformed the strategies in hand that presently energize the prospects for human heart repair.

Concealed expansion of immature precursors underpins acute burst of adult HSC activity in foetal liver

One day prior to mass emergence of haematopoietic stem cells (HSCs) in the foetal liver at E12.5, the embryo contains only a few definitive HSCs. It is thought that the burst of HSC activity in the foetal liver is underpinned by rapid maturation of immature embryonic precursors of definitive HSCs, termed pre-HSCs. However, because pre-HSCs are not detectable by direct transplantations into adult irradiated recipients, the size and growth of this population, which represents the embryonic rudiment of the adult haematopoietic system, remains uncertain. Using a novel quantitative assay, we demonstrate that from E9.5 the pre-HSC pool undergoes dramatic growth in the aorta-gonad-mesonephros region and by E11.5 reaches the size that matches the number of definitive HSCs in the E12.5 foetal liver. Thus, this study provides for the first time a quantitative basis for our understanding of how the large population of definitive HSCs emerges in the foetal liver.

MHC-compatible bone marrow stromal/stem cells trigger fibrosis by activating host T cells in a scleroderma mouse model

Fibrosis of organs is observed in systemic autoimmune disease. Using a scleroderma mouse, we show that transplantation of MHC compatible, minor antigen mismatched bone marrow stromal/stem cells (BMSCs) play a role in the pathogenesis of fibrosis. Removal of donor BMSCs rescued mice from disease. Freshly isolated PDGFRα⁺ Sca-1⁺ BMSCs expressed MHC class II following transplantation and activated host T cells. A decrease in FOXP3⁺ CD25⁺ Treg population was observed. T cells proliferated and secreted IL-6 when stimulated with mismatched BMSCs in vitro. Donor T cells were not involved in fibrosis because transplanting T cell-deficient RAG2 knock out mice bone marrow still caused disease. Once initially triggered by mismatched BMSCs, the autoimmune phenotype was not donor BMSC dependent as the phenotype was observed after effector T cells were adoptively transferred into naïve syngeneic mice. Our data suggest that minor antigen mismatched BMSCs trigger systemic fibrosis in this autoimmune scleroderma model.

DOI:http://dx.doi.org/10.7554/eLife.09394.001

Systemic scleroderma is an autoimmune disease caused by the immune system attacking the body’s connective tissues, which provide the body with structural support. Immune cells called T cells accumulate in connective tissue, which leads to the hardening of the skin and may also damage the heart, lungs and other internal organs. However, it is not clear what prompts the T cells to accumulate in the connective tissues of these individuals.

Autoimmune diseases develop when the immune system mistakenly identifies host cells as being a threat to the body. Normally, the immune system recognizes healthy body cells by the presence of particular proteins on the surface of the cells. A set of surface proteins called the major histocompatibility complexes (MHCs) play a major role in this process, but there are also many other surface proteins that play more minor roles.

In 2002, researchers developed a method that can trigger the symptoms of systemic scleroderma in mice. This method involves transplanting bone marrow from one mouse into another mouse. Both mice have identical MHC proteins on the surfaces of their cells, but have some differences in other cell surface proteins, and so the bone marrow from the donor mouse triggers an immune response in the recipient.

To better understand how this mouse “model” of systemic scleroderma works, Ogawa, Morikawa et al. refined the method so that they could just transplant specific types of bone marrow cells into the recipient mice. The experiments reveal that bone marrow stromal stem cells, but not so-called “hematopoietic stem cells”, from a donor mouse are responsible for triggering the immune response and disease symptoms in the recipients.

Ogawa, Morikawa et al.’s findings show that mismatched minor cell surface proteins on bone marrow stromal stem cells can trigger symptoms of systemic scleroderma in mice. Further studies are required to find out how these cells encourage T cells to trigger an autoimmune response.

DOI:http://dx.doi.org/10.7554/eLife.09394.002

The Role of Symmetric Stem Cell Divisions in Tissue Homeostasis

Successful maintenance of cellular lineages critically depends on the fate decision dynamics of stem cells (SCs) upon division. There are three possible strategies with respect to SC fate decision symmetry: (a) asymmetric mode, when each and every SC division produces one SC and one non-SC progeny; (b) symmetric mode, when 50% of all divisions produce two SCs and another 50%-two non-SC progeny; (c) mixed mode, when both the asymmetric and two types of symmetric SC divisions co-exist and are partitioned so that long-term net balance of the lineage output stays constant. Theoretically, either of these strategies can achieve lineage homeostasis. However, it remains unclear which strategy(s) are more advantageous and under what specific circumstances, and what minimal control mechanisms are required to operate them. Here we used stochastic modeling to analyze and quantify the ability of different types of divisions to maintain long-term lineage homeostasis, in the context of different control networks. Using the example of a two-component lineage, consisting of SCs and one type of non-SC progeny, we show that its tight homeostatic control is not necessarily associated with purely asymmetric divisions. Through stochastic analysis and simulations we show that asymmetric divisions can either stabilize or destabilize the lineage system, depending on the underlying control network. We further apply our computational model to biological observations in the context of a two-component lineage of mouse epidermis, where autonomous lineage control has been proposed and notable regional differences, in terms of symmetric division ratio, have been noted-higher in thickened epidermis of the paw skin as compared to ear and tail skin. By using our model we propose a possible explanation for the regional differences in epidermal lineage control strategies. We demonstrate how symmetric divisions can work to stabilize paw epidermis lineage, which experiences high level of micro-injuries and a lack of hair follicles as a back-up source of SCs.

Determining c-Myb protein levels can isolate functional hematopoietic stem cell subtypes

The transcription factor c-Myb was originally identified as a transforming oncoprotein encoded by two avian leukemia viruses. Subsequently, through the generation of mouse models that affect its expression, c-Myb has been shown to be a key regulator of hematopoiesis, including having critical roles in hematopoietic stem cells (HSCs). The precise function of c-Myb in HSCs although remains unclear. We have generated a novel c-myb allele in mice that allows direct observation of c-Myb protein levels in single cells. Using this reporter line we demonstrate that subtypes of HSCs can be isolated based upon their respective c-Myb protein expression levels. HSCs expressing low levels of c-Myb protein (c-Myb(low) HSC) appear to represent the most immature, dormant HSCs and they are a predominant component of HSCs that retain bromodeoxyuridine labeling. Hematopoietic stress, induced by 5-fluorouracil ablation, revealed that in this circumstance c-Myb-expressing cells become critical for multilineage repopulation. The discrimination of HSC subpopulations based on c-Myb protein levels is not reflected in the levels of c-myb mRNA, there being no more than a 1.3-fold difference comparing c-Myb(low) and c-Myb(high) HSCs. This illustrates how essential it is to include protein studies when aiming to understand the regulatory networks that control stem cell behavior.

Endometrial side population cells: potential adult stem/progenitor cells in endometrium

Uterine endometrium is one of the most important organs for species preservation. However, the physiology of human endometrium remains poorly understood, because the human endometrium undergoes rapid and large changes during each menstrual cycle and it is very difficult to investigate human endometrium as one organ. This remarkable regenerative capacity of human endometrium strongly suggests the existence of adult stem cells, and physiology of endometrium cannot be explained without adult stem cells. Therefore, investigating endometrial stem/progenitor cells should lead to a breakthrough in understanding the normal endometrial physiology and the pathophysiology of endometrial neoplastic disorders, such as endometriosis and endometrial cancer. Several cell populations have been discovered as putative endometrial stem/progenitor cells. Emerging evidence reveals that the endometrial side population (SP) is one of the potential endometrial stem/progenitor populations. Of all the endometrial stem/progenitor cell candidates, the endometrial SP (ESP) is best investigated in vitro and in vivo, and has the largest number of references. In this review, we provide an overview of the accumulating evidence for the ESP cells, both directly from human endometria and from cultured endometrial cells. Furthermore, SP cells are compared to other potential stem/progenitor cells, and we discuss their stem cell properties. We also discuss the difficulties and unsolved issues in endometrial stem cell biology.

Decitabine enhances stem cell antigen-1 expression in cigarette smoke extract-induced emphysema in animal model

Stem cell antigen-1 (Sca-1) is a mouse glycosyl phosphatidylinositol-anchored protein and a cell surface marker found on hematopoietic stem cells (HSCs). Despite decades of study, its biological functions remain little known. Sca-1 is a typical marker of bone marrow-derived HSCs, it is also expressed by a mixture of tissue-resident stem, progenitor cells in nonhematopoietic organs. Endothelial progenitor cell (EPC) is a subtype of HSC and contributes to endothelial repair by homing in on locations of injury. Abnormal genetic methylation has been detected in smoking-related diseases. The present study aimed to investigate the lung function and histomorphology, the expression of Sca-1 gene in lung tissues, and bone marrow-derived EPCs in cigarette smoke extract (CSE)-induced emphysema mice, and to further determine whether Decitabine (Dec), the most widely used inhibitor of DNA methylation, could protect against the damages caused by CSE. The results of the present study demonstrated that Dec could partly protect against CSE-induced emphysema in mice, enhance Sca-1 expression in lung tissue, and bone marrow-derived EPCs. The results suggested that the depletion of the progenitor cell pool and DNA methylation of Sca-1 gene may be involved in the progression of emphysema in mice.

Forward Programming of Cardiac Stem Cells by Homogeneous Transduction with MYOCD plus TBX5

Adult cardiac stem cells (CSCs) express many endogenous cardiogenic transcription factors including members of the Gata, Hand, Mef2, and T-box family. Unlike its DNA-binding targets, Myocardin (Myocd)-a co-activator not only for serum response factor, but also for Gata4 and Tbx5-is not expressed in CSCs. We hypothesised that its absence was a limiting factor for reprogramming. Here, we sought to investigate the susceptibility of adult mouse Sca1+ side population CSCs to reprogramming by supplementing the triad of GATA4, MEF2C, and TBX5 (GMT), and more specifically by testing the effect of the missing co-activator, Myocd. Exogenous factors were expressed via doxycycline-inducible lentiviral vectors in various combinations. High throughput quantitative RT-PCR was used to test expression of 29 cardiac lineage markers two weeks post-induction. GMT induced more than half the analysed cardiac transcripts. However, no protein was detected for the induced sarcomeric genes Actc1, Myh6, and Myl2. Adding MYOCD to GMT affected only slightly the breadth and level of gene induction, but, importantly, triggered expression of all three proteins examined (α-cardiac actin, atrial natriuretic peptide, sarcomeric myosin heavy chains). MYOCD + TBX was the most effective pairwise combination in this system. In clonal derivatives homogenously expressing MYOCD + TBX at high levels, 93% of cardiac transcripts were up-regulated and all five proteins tested were visualized.

IN SUMMARY

(1) GMT induced cardiac genes in CSCs, but not cardiac proteins under the conditions used. (2) Complementing GMT with MYOCD induced cardiac protein expression, indicating a more complete cardiac differentiation program. (3) Homogeneous transduction with MYOCD + TBX5 facilitated the identification of differentiating cells and the validation of this combinatorial reprogramming strategy. Together, these results highlight the pivotal importance of MYOCD in driving CSCs toward a cardiac muscle fate.

Integrating new discoveries into the "vicious cycle" paradigm of prostate to bone metastases

In prostate to bone metastases, the "vicious cycle" paradigm has been traditionally used to illustrate how metastases manipulate the bone forming osteoblasts and resorbing osteoclasts in order to yield factors that facilitate growth and establishment. However, recent advances have illustrated that the cycle is far more complex than this simple interpretation. In this review, we will discuss the role of exosomes and hematopoietic/mesenchymal stem/stromal cells (MSC) that facilitate the establishment and activation of prostate metastases and how cells including myeloid-derived suppressor cells, macrophages, T cells, and nerve cells contribute to the momentum of the vicious cycle. The increased complexity of the tumor-bone microenvironment requires a system level approach. The evolution of computational models to interrogate the tumor-bone microenvironment is also discussed, and the application of this integrated approach should allow for the development of effective therapies to treat and cure prostate to bone metastases.

Extended multipotency of neural crest cells and neural crest-derived cells

Neural crest cells (NCC) are migratory multipotent cells that give rise to diverse derivatives. They generate various cell types during embryonic development, including neurons and glial cells of the peripheral sensory and autonomic ganglia, Schwann cells, melanocytes, endocrine cells, smooth muscle, and skeletal and connective tissue cells of the craniofacial complex. The multipotency of NCC is thought to be transient at the early stage of NCC generation; once NCC emerge from the neural tube, they change into lineage-restricted precursors. Although many studies have described the clear segregation of NCC lineages right after their delamination from the neural tube, recent reports suggest that multipotent neural crest stem cells (NCSC) are present not only in migrating NCC in the embryo, but also in their target tissues in the fetus and adult. Furthermore, fully differentiated NCC-derived cells such as glial cells and melanocytes have been shown to dedifferentiate or transdifferentiate into other NCC derivatives. The multipotency of migratory and postmigratory NCC-derived cells was found to be similar to that of NCSC. Collectively, these findings support the multipotency or plasticity of NCC and NCC-derived cells.

Migration and differentiation of transplanted enteric neural crest-derived cells in murine model of Hirschsprung's disease

Stem cell therapy offers the potential of rebuilding the enteric nervous system (ENS) in the aganglionic bowel of patients with Hirschsprung's disease. P0-Cre/Floxed-EGFP mice in which neural crest-derived cells express EGFP were used to obtain ENS stem/progenitor cells. ENS stem/progenitor cells were transplanted into the bowel of Ret(-/-) mouse, an animal model of Hirschsprung's disease. Immunohistochemical analysis was performed to determine whether grafted cells gave rise to neurons in the recipient bowel. EGFP expressing neural crest-derived cells accounted for 7.01 ± 2.52 % of total cells of gastrointestinal tract. ENS stem/progenitor cells were isolated using flow cytometry and expanded as neurosphere-like bodies (NLBs) in a serum-free culture condition. Some cells in NLBs expressed neural crest markers, p75 and Sox10 and neural stem/progenitor cells markers, Nestin and Musashi1. Multipotency of isolated ENS stem/progenitor cells was determined as they differentiated into neurons, glial cells, and myofibloblasts in culture. When co-cultured with explants of hindgut of Ret(-/-) mice, ENS stem/progenitor cells migrated into the aganglionic bowel and gave rise to neurons. ENS stem/progenitor cells used in this study appear to be clinically relevant donor cells in cell therapy to treat Hirschsprung's disease capable of colonizing the affected bowel and giving rise to neurons.

Glucocorticoids increase adipocytes in muscle by affecting IL-4 regulated FAP activity

An increase in intramuscular adipocyte tissue (IMAT) is associated with glucose dysregulation, decreased muscle strength, and increased risk of disability. Unfortunately, the mechanisms stimulating intramuscular adipogenesis remain unclear. We found that dexamethasone (Dex) administration to mice with injured muscles stimulates the accumulation of IMAT. To identify precursors of these adipocytes, we isolated satellite cells and fibro/adipogenic progenitors (FAPs) from muscle; satellite cells did not differentiate into adipocytes even following Dex treatment. In contrast, Dex stimulated FAP differentiation into adipocytes. In vivo, we transplanted purified FAPs from transgenic, EGFP mice into the injured muscles of C57/BL6 mice and found that Dex administration stimulated adipogenesis from FAP-EGFP. The increase in adipogenesis depended on Dex-induced inhibition of interleukin-4 (IL-4). In the injured muscle of IL-4-knockout mice, the levels of adipocytes were increased, while in the injured muscles of Dex-treated mice with IL-4 injections, adipogenesis was suppressed. In cultured FAPs, IL-4 inhibited Dex-induced conversion of FAPs into adipocytes; this did not occur in FAPs expressing knockdown of the IL-4 receptor. Thus, we concluded that glucocorticoids stimulate FAPs to differentiate into adipocytes in injured muscles. This process is blocked by IL-4, suggesting that interfering with IL-4 signaling could prevent adipogenesis in muscle.

Hematopoietic stem cell cultures and assays

The adult hematopoietic system is repopulated in its entirety from a rare cell type known as hematopoietic stem cells (HSCs) that reside in the marrow space throughout the skeletal system. Here we describe the isolation and identification of HSCs both phenotypically and functionally.

CD133 is a positive marker for a distinct class of primitive human cord blood-derived CD34-negative hematopoietic stem cells

The identification of human CD34-negative (CD34(-)) hematopoietic stem cells (HSCs) provides a new concept for the hierarchy in the human HSC compartment. Previous studies demonstrated that CD34(-) severe combined immunodeficiency (SCID)-repopulating cells (SRCs) are a distinct class of primitive HSCs in comparison to the well-characterized CD34(+)CD38(-) SRCs. However, the purification level of rare CD34(-) SRCs in 18 lineage marker-negative (Lin(-)) CD34(-) cells (1/1000) is still very low compared with that of CD34(+)CD38(-) SRCs (1/40). As in the mouse, it will be necessary to identify useful positive markers for a high degree of purification of rare human CD34(-) SRCs. Using 18Lin(-)CD34(-) cells, we analyzed the expression of candidate positive markers by flow cytometric analysis. We finally identified CD133 as a reliable positive marker of human CB-derived CD34(-) SRCs and succeeded in highly purifying primitive human CD34(-) HSCs. The limiting dilution analysis demonstrated that the incidence of CD34(-) SRCs in 18Lin(-)CD34(-)CD133(+) cells was 1/142, which is the highest level of purification of these unique CD34(-) HSCs to date. Furthermore, CD133 expression clearly segregated the SRC activities of 18Lin(-)CD34(-) cells, as well as 18Lin(-)CD34(+) cells, in their positive fractions, indicating its functional significance as a common cell surface maker to isolate effectively both CD34(+) and CD34(-) SRCs.

LNGFR(+)THY-1(+)VCAM-1(hi+) cells reveal functionally distinct subpopulations in mesenchymal stem cells

Human mesenchymal stem cells (hMSCs), which conventionally are isolated based on their adherence to plastic, are heterogeneous and have poor growth and differentiation, limiting our ability to investigate their intrinsic characteristics. We report an improved prospective clonal isolation technique and reveal that the combination of three cell-surface markers (LNGFR, THY-1, and VCAM-1) allows for the selection of highly enriched clonogenic cells (one out of three isolated cells). Clonal characterization of LNGFR⁺THY-1⁺ cells demonstrated cellular heterogeneity among the clones. Rapidly expanding clones (RECs) exhibited robust multilineage differentiation and self-renewal potency, whereas the other clones tended to acquire cellular senescence via P16INK4a and exhibited frequent genomic errors. Furthermore, RECs exhibited unique expression of VCAM-1 and higher cellular motility compared with the other clones. The combination marker LNGFR⁺THY-1⁺VCAM-1^hi+ (LTV) can be used selectively to isolate the most potent and genetically stable MSCs.

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The LNGFR⁺THY-1⁺ population is significantly enriched for CFU-Fs in human bone marrow

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Rapidly expanding clones (RECs) exhibited stem-like characteristics

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Expression of VCAM-1 correlated with proliferation and migration ability

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The combination marker LNGFR⁺THY-1⁺VCAM-1^hi+ is useful for isolating multipotent MSCs

The ageing haematopoietic stem cell compartment

Stem cell ageing underlies the ageing of tissues, especially those with a high cellular turnover. There is growing evidence that the ageing of the immune system is initiated at the very top of the haematopoietic hierarchy and that the ageing of haematopoietic stem cells (HSCs) directly contributes to changes in the immune system, referred to as immunosenescence. In this Review, we summarize the phenotypes of ageing HSCs and discuss how the cell-intrinsic and cell-extrinsic mechanisms of HSC ageing might promote immunosenescence. Stem cell ageing has long been considered to be irreversible. However, recent findings indicate that several molecular pathways could be targeted to rejuvenate HSCs and thus to reverse some aspects of immunosenescence.

Basic helix-loop-helix transcriptional factor MyoR regulates BMP-7 in acute kidney injury

MyoR was originally identified as a transcriptional repressor in embryonic skeletal muscle precursors, but its function in adult kidney has not been clarified. In this study, we tried to clarify the functional role of MyoR using MyoR(-/-) mice. Cisplatin induced a significantly higher degree of severe renal dysfunction, tubular injury, and mortality in MyoR(-/-) mice than in wild-type mice. The injection of cisplatin significantly increased the number of apoptotic cells in the kidney tissues of MyoR(-/-) mice, compared with that in wild-type mice. To clarify the mechanism of severe cisplatin-induced damage and apoptosis in MyoR(-/-) mice, we focused on the p53 signaling pathway and bone morphogenic protein-7 (BMP-7). Treatment with cisplatin significantly activated p53 signaling in cultured renal proximal tubular epithelial cells (RTECs) in both wild-type and MyoR(-/-) mice, but no significant difference between the groups was observed. The injection of cisplatin significantly increased the expression of BMP-7 in the kidney tissues of wild-type mice, but no increase was observed in the MyoR(-/-) mice. Treatment with cisplatin significantly increased the expression of BMP-7 in cultured RTECs from wild-type mice but not in those from MyoR(-/-) mice. Moreover, treatment with recombinant BMP-7 rescued the cisplatin-induced apoptosis in RTECs from MyoR(-/-) mice. Taken together, our results demonstrate a new protective role of MyoR in adult kidneys that acts through the regulation of BMP-7.

Hematopoietic stem cells are pluripotent and not just "hematopoietic"

Over a decade ago, several preclinical transplantation studies suggested the striking concept of the tissue-reconstituting ability (often referred to as HSC plasticity) of hematopoietic stem cells (HSCs). While this heralded an exciting time of radically new therapies for disorders of many organs and tissues, the concept was soon mired in controversy and remained dormant for almost a decade. This commentary provides a concise review of evidence for HSC plasticity, including more recent findings based on single HSC transplantation in mouse and clinical transplantation studies. There is strong evidence for the concept that HSCs are pluripotent and are the source for the majority, if not all, of the cell types in our body. Also discussed are some biological and experimental issues that need to be considered in the future investigation of HSC plasticity.

All hematopoietic stem cells engraft in submyeloablatively irradiated mice

Significant controversy exists regarding the impact of hematopoietic stroma damage by irradiation on the efficiency of engraftment of intravenously transplanted stem cells. It was previously demonstrated that in normal syngenic mice, all intravenously transplanted donor stem cells, present in the bone marrow, compete equally with those of the host. In this study, we comprehensively compared the blood cell production derived from transplanted donor stem cells with that from the host stem cells surviving various doses of submyeloablative irradiation. We compared the partial chimerism resulting from transplantation with theoretical estimates that assumed transplantation efficiencies ranging from 100% to 20%. The highest level of consensus between the experimental and the theoretical results was 100% for homing and engraftment (ie, the utilization of all transplanted stem cells). These results point to a very potent mechanism through which intravenously administered hematopoietic stem cells are captured from circulation, engraft in the hematopoietic tissue, and contribute to blood cell production in irradiated recipients. The damage done to hematopoietic stroma and to the trabecular bone by submyeloablative doses of ionizing radiation does not negatively affect the homing and engraftment mechanisms of intravenously transplanted hematopoietic progenitor and stem cells.

Suppression of myeloid cell leukemia-1 (Mcl-1) enhances chemotherapy-associated apoptosis in gastric cancer cells

BACKGROUND

Myeloid cell leukemia-1 (Mcl-1) is an anti-apoptotic protein that regulates apoptosis sensitivity in a variety of cell types. Here we evaluate the roles of Mcl-1 in chemotherapy-associated apoptosis in gastric cancer cells. In addition, our study examined whether Mcl-1 contributed to apoptosis resistance in so-called cancer stem cell (CSC)-like populations in gastric cancer.

METHODS

Seven gastric cancer cell lines were used. The expression of Mcl-1 was assessed by either real-time polymerase chain reaction or Western blot analysis. Apoptosis was quantitated by morphological observation and caspase activity measurement. Adenovirus-mediated RNA interference (RNAi) technology was used to knockdown the expression of Mcl-1. The release of cytochrome c was evaluated by subcellular fractionation and immunoblot analysis. To identify and isolate the CSC-like populations, we used the CSC-associated cell surface marker CD44 and flow cytometry.

RESULTS

Six out of the 7 gastric cancer cell lines overexpressed Mcl-1 protein. These Mcl-1-expressing cell lines were relatively resistant to chemotherapeutic agents such as 5-fluorouracil (5-FU) and cisplatin (CDDP). Depletion of Mcl-1 protein by RNAi technology effectively sensitized the cells to anticancer drug-induced mitochondrial cytochrome c release, caspase activation, and apoptosis. In addition, vast amounts of Mcl-1 mRNA were expressed in CD44-positive CSC-like cells. Mcl-1 suppression enhanced the apoptosis in CD44-positive cells to a level equivalent to that in CD44-negative cells, suggesting that Mcl-1 mediates chemotherapy resistance in CSC-like populations.

CONCLUSION

These results suggest that Mcl-1 mediates the resistance to apoptosis in gastric cancer cells by blocking the mitochondrial pathway of cell death. Mcl-1 depletion appears to be an attractive strategy to overcome chemotherapy resistance in gastric cancer cells.

Comprehensive hematopoietic stem cell isolation methods

The use of flow cytometry has been critical in establishing methods to isolate and characterize hematopoietic stem cells (HSCs) and their progenitors. For more than 30 years, researchers have been uncovering novel markers that when used in combination significantly enhance the purification of HSCs from murine and human bone marrow. The complex interface between HSCs, the lymphohematopoietic system, and their niches, has made identification of HSC markers critical to understanding their biological nature, more so than other adult stem cell populations. Here we review the phenotypic markers and strategies used to purify HSCs, the appropriateness of using these markers for comparisons of HSC function at different stages of ontogeny, and their utility in defining the lineage bias in the HSC compartment.

Stem cell-like differentiation potentials of endometrial side population cells as revealed by a newly developed in vivo endometrial stem cell assay

Background

Endometrial stem/progenitor cells contribute to the cyclical regeneration of human endometrium throughout a woman's reproductive life. Although the candidate cell populations have been extensively studied, no consensus exists regarding which endometrial population represents the stem/progenitor cell fraction in terms of in vivo stem cell activity. We have previously reported that human endometrial side population cells (ESP), but not endometrial main population cells (EMP), exhibit stem cell-like properties, including in vivo reconstitution of endometrium-like tissues when xenotransplanted into immunodeficient mice. The reconstitution efficiency, however, was low presumably because ESP cells alone could not provide a sufficient microenvironment (niche) to support their stem cell activity. The objective of this study was to establish a novel in vivo endometrial stem cell assay employing cell tracking and tissue reconstitution systems and to examine the stem cell properties of ESP through use of this assay.

Methodology/Principal Findings

ESP and EMP cells isolated from whole endometrial cells were infected with lentivirus to express tandem Tomato (TdTom), a red fluorescent protein. They were mixed with unlabeled whole endometrial cells and then transplanted under the kidney capsule of ovariectomized immunodeficient mice. These mice were treated with estradiol and progesterone for eight weeks and nephrectomized. All of the grafts reconstituted endometrium-like tissues under the kidney capsules. Immunofluorescence revealed that TdTom-positive cells were significantly more abundant in the glandular, stromal, and endothelial cells of the reconstituted endometrium in mice transplanted with TdTom-labeled ESP cells than those with TdTom-labeled EMP cells.

Conclusions/Significance

We have established a novel in vivo endometrial stem cell assay in which multi-potential differentiation can be identified through cell tracking during in vivo endometrial tissue reconstitution. Using this assay, we demonstrated that ESP cells differentiated into multiple endometrial lineages in the niche provided by whole endometrial cells, indicating that ESP cells are genuine endometrial stem/progenitor cells.

A PML–PPAR-δ pathway for fatty acid oxidation regulates hematopoietic stem cell maintenance

Stem-cell function is an exquisitely regulated process. Thus far, the contribution of metabolic cues to stem-cell function has not been well understood. Here we identify a previously unknown promyelocytic leukemia (PML)–peroxisome proliferator-activated receptor δ (PPAR-δ)–fatty-acid oxidation (FAO) pathway for the maintenance of hematopoietic stem cells (HSCs). We have found that loss of PPAR-δ or inhibition of mitochondrial FAO induces loss of HSC maintenance, whereas treatment with PPAR-δ agonists improved HSC maintenance. PML exerts its essential role in HSC maintenance through regulation of PPAR signaling and FAO. Mechanistically, the PML–PPAR-δ–FAO pathway controls the asymmetric division of HSCs. Deletion of Ppard or Pml as well as inhibition of FAO results in the symmetric commitment of HSC daughter cells, whereas PPAR-δ activation increased asymmetric cell division. Thus, our findings identify a metabolic switch for the control of HSC cell fate with potential therapeutic implications.

Neural stem cells, adult neurogenesis, and galectin-1: from bench to bedside

Neural stem cells (NSCs) in the adult brain have been a consistent focus of biomedical research largely because of their potential clinical application. To fully exploit this potential, the molecular mechanisms that regulate NSCs must be clarified. Several lines of evidence show that a multifunctional protein, Galectin-1, is expressed and has a functional role in a subset of adult NSCs. Researchers, including our group, have explored the physiological role of Galectin-1 in NSCs and its application in the treatment of animal models of neurological disorders such as brain ischemia and spinal cord injury. Here, we summarize what is currently known regarding the role of Galectin-1 in adult NSCs. Furthermore, we discuss current issues in researching the role of Galectin-1 in adult NSCs under both physiological and pathological conditions.

C/EBPβ is involved in the amplification of early granulocyte precursors during candidemia-induced "emergency" granulopoiesis

Granulopoiesis is tightly regulated to meet host demands during both "steady-state" and "emergency" situations, such as infections. The transcription factor CCAAT/enhancer binding protein β (C/EBPβ) plays critical roles in emergency granulopoiesis, but the precise developmental stages in which C/EBPβ is required are unknown. In this study, a novel flow cytometric method was developed that successfully dissected mouse bone marrow cells undergoing granulopoiesis into five distinct subpopulations (#1-5) according to their levels of c-Kit and Ly-6G expression. After the induction of candidemia, rapid mobilization of mature granulocytes and an increase in early granulocyte precursors accompanied by cell cycle acceleration was followed by a gradual increase in granulocytes originating from the immature populations. Upon infection, C/EBPβ was upregulated at the protein level in all the granulopoietic subpopulations. The rapid increase in immature subpopulations #1 and #2 observed in C/EBPβ knockout mice at 1 d postinfection was attenuated. Candidemia-induced cell cycle acceleration and proliferation of hematopoietic stem/progenitors were also impaired. Taken together, these data suggest that C/EBPβ is involved in the efficient amplification of early granulocyte precursors during candidemia-induced emergency granulopoiesis.

Tug of war in the haematopoietic stem cell niche: do myeloma plasma cells compete for the HSC niche?

In the adult mammal, normal haematopoiesis occurs predominantly in the bone marrow, where primitive haematopoietic stem cells (HSC) and their progeny reside in specialised microenvironments. The bone marrow microenvironment contains specific anatomical areas (termed niches) that are highly specialised for the development of certain blood cell types, for example HSCs. The HSC niche provides important cell–cell interactions and signalling molecules that regulate HSC self-renewal and differentiation processes. These same signals and interactions are also important in the progression of haematological malignancies, such as multiple myeloma (MM). This review provides an overview of the bone marrow microenvironment and its involvement in normal, physiological HSC maintenance and plasma cell growth throughout MM disease progression.

Hematopoietic stem cells give rise to osteo-chondrogenic cells

Repair of bone fracture requires recruitment and proliferation of stem cells with the capacity to differentiate to functional osteoblasts. Given the close association of bone and bone marrow (BM), it has been suggested that BM may serve as a source of these progenitors. To test the ability of hematopoietic stem cells (HSCs) to give rise to osteo-chondrogenic cells, we used a single HSC transplantation paradigm in uninjured bone and in conjunction with a tibial fracture model. Mice were lethally irradiated and transplanted with a clonal population of cells derived from a single enhanced green fluorescent protein positive (eGFP+) HSC. Analysis of paraffin sections from these animals showed the presence of eGFP+ osteocytes and hypertrophic chondrocytes. To determine the contribution of HSC-derived cells to fracture repair, non-stabilized tibial fracture was created. Paraffin sections were examined at 7 days, 2 weeks and 2 months after fracture and eGFP+ hypertrophic chondrocytes, osteoblasts and osteocytes were identified at the callus site. These cells stained positive for Runx-2 or osteocalcin and also stained for eGFP demonstrating their origin from the HSC. Together, these findings strongly support the concept that HSCs generate bone cells and suggest therapeutic potentials of HSCs in fracture repair.

Reconstitution of the central and peripheral nervous system during salamander tail regeneration

We show that after tail amputation in Ambystoma mexicanum (Axolotl) the correct number and spacing of dorsal root ganglia are regenerated. By transplantation of spinal cord tissue and nonclonal neurospheres, we show that the central spinal cord represents a source of peripheral nervous system cells. Interestingly, melanophores migrate from preexisting precursors in the skin. Finally, we demonstrate that implantation of a clonally derived spinal cord neurosphere can result in reconstitution of all examined cell types in the regenerating central spinal cord, suggesting derivation of a cell with spinal cord stem cell properties.