A novel purification method for multipotential skeletal stem cells

At least some cells within bone marrow stromal populations are multipotential (i.e., differentiate in vitro into osteoblasts, chondrocytes, and adipocytes) and thus designated skeletal stem cells (SSCs) or mesenchymal stem cells (MSCs) amongst other names. Recently, a subpopulation of stromal cells, notably osteoblasts or their progenitors, has been identified as a definitive regulatory component of the hematopoietic stem cell (HSC) niche. Thus, the development of methods for purifying not only SSCs but cells comprising the HSC niche is of interest. Here, we report a method for purifying a novel bone marrow‐derived population with a high frequency of osteoprogenitors and high expression levels of osteoblast differentiation markers (highly purified osteoprogenitors (HipOPs)) as well as markers of the bone niche for HSCs. In vivo transplantation experiments demonstrated that donor HipOPs differentiated into not only osteoblasts, osteocytes and cells around sinusoids but also hematopoietic cells. Thus, HipOPs represent a novel population for simultaneous reconstruction of bone and bone marrow microenvironments. J. Cell. Biochem. 108: 368–377, 2009. © 2009 Wiley‐Liss, Inc.     

Periosteum-derived podoplanin-expressing stromal cells regulate nascent vascularization during epiphyseal marrow development

Bone marrow development and endochondral bone formation occur simultaneously. During endochondral ossification, periosteal vasculatures and stromal progenitors invade the primary avascular cartilaginous anlage, which induces primitive marrow development. We previously determined that bone marrow podoplanin (PDPN)-expressing stromal cells exist in the perivascular microenvironment and promote megakaryopoiesis and erythropoiesis. In this study, we aimed to examine the involvement of PDPN-expressing stromal cells in postnatal bone marrow generation. Using histological analysis, we observed that periosteum-derived PDPN-expressing stromal cells infiltrated the cartilaginous anlage of the postnatal epiphysis and populated on the primitive vasculature of secondary ossification center. Furthermore, immunophenotyping and cellular characteristic analyses indicated that the PDPN-expressing stromal cells constituted a subpopulation of the skeletal stem cell lineage. In vitro xenovascular model cocultured with human umbilical vein endothelial cells and PDPN-expressing skeletal stem cell progenies showed that PDPN-expressing stromal cells maintained vascular integrity via the release of angiogenic factors and vascular basement membrane-related extracellular matrices. We show that in this process, Notch signal activation committed the PDPN-expressing stromal cells into a dominant state with basement membrane-related extracellular matrices, especially type IV collagens. Our findings suggest that the PDPN-expressing stromal cells regulate the integrity of the primitive vasculatures in the epiphyseal nascent marrow. To the best of our knowledge, this is the first study to comprehensively examine how PDPN-expressing stromal cells contribute to marrow development and homeostasis.     

Osteogenic Potency of Nacre on Human Mesenchymal Stem Cells

Nacre seashell is a natural osteoinductive biomaterial with strong effects on osteoprogenitors, osteoblasts, and osteoclasts during bone tissue formation and morphogenesis. Although nacre has shown, in one study, to induce bridging of new bone across large non-union bone defects in 8 individual human patients, there have been no succeeding human surgical studies to confirm this outstanding potency. But the molecular mechanisms associated with nacre osteoinduction and the influence on bone marrow-derived mesenchymal stem cells (BMSC’s), skeletal stem cells or bone marrow stromal cells remain elusive. In this study we highlight the phenotypic and biochemical effects of Pinctada maxima nacre chips and the global nacre soluble protein matrix (SPM) on primary human bone marrow-derived stromal cells (hBMSCs) in vitro. In static co-culture with nacre chips, the hBMSCs secreted Alkaline phosphatase (ALP) at levels that exceeded bone morphogenetic protein (rhBMP-2) treatment. Concentrated preparation of SPM applied to Stro-1 selected hBMSC’s led to rapid ALP secretions, at concentrations exceeding the untreated controls even in osteogenic conditions. Within 21 days the same population of Stro-1 selected hBMSCs proliferated and secreted collagens I–IV, indicating the premature onset of an osteoblast phenotype. The same SPM was found to promote unselected hBMSC differentiation with osteocalcin detected at 7 days, and proliferation increased at 7 days in a dose-dependent manner. In conclusion, nacre particles and nacre SPM induced the early stages of human bone cell differentiation, indicating that they may be promising soluble factors with osteoinductive capacity in primary human bone cell progenitors such as, hBMSC’s.     

Recent highlights on bone stem cells: a report from Bone Stem Cells 2009, and not only…

The use of stem cells has opened new prospects for the treatment of orthopaedic conditions characterized by large bone defects. However, many issues still exist to which answers are needed before routine, large-scale application becomes possible. Bone marrow stromal cells (MSC), which are clonogenic, multipotential precursors present in the bone marrow stroma, are generally employed for bone regeneration. Stem cells with multilineage differentiation similar to MSC have also been demonstrated in adipose tissue, peripheral blood, umbilical cord and amniotic fluid. Each source presents its own advantages and drawbacks. Unfortunately, no unique surface antigen is expressed by MSC, and this hampers simple MSC enrichment from heterogeneous populations. MSC are identified through a combination of physical, morphological and functional assays. Different in vitro and in vivo models have been described for the research on bone stem cells. These models should predict the in vivo bone healing capacity of MSC and if the induced osteogenesis is similar to the physiological one. Although stem cells offer an exciting possibility of a renewable source of cells and tissues for replacement, orthopaedic applications often represent case reports whereas controlled randomized trials are still lacking. Further biological aspects of bone stem cells should be elucidated and a general consensus on the best models, protocols and proper use of scaffolds and growth factors should be achieved.     

Wnt modulators, SFRP-1, and SFRP-2 are expressed in osteoblasts and differentially regulate hematopoietic stem cells

Wnt signaling has been implicated in the self-renewal of hematopoietic stem cells (HSCs). Secreted frizzled-related proteins (SFRPs) are a family of soluble proteins containing a region homologous to a receptor for Wnt, Frizzled, and are thought to act as endogenous modulators for Wnt signaling. This study examined the role of SFRPs in HSC regulation. Among the four family members, SFRP-1 and SFRP-2 are specifically induced in the bone marrow in response to myelosuppression, and immunostaining revealed that both proteins were expressed in osteoblasts. Interestingly, SFRP-1 reduced the number of multipotent progenitors in in vitro culture of CD34⁻KSL cells, while SFRP-2 did not. Furthermore, SFRP-1 compromised the long-term repopulating activity of HSCs, whereas SFRP-2 did not affect or even enhanced it in the same setting. These results indicate that although both SFRP-1 and SFRP-2 act as inhibitors for Wnt signaling in vitro, they differentially affect the homeostasis of HSCs.     

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

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.     

Isolation and therapeutic potential of human haemopoietic stem cells

The haemopoietic stem cell (HSC) has long been regarded as an archetypal, tissue specific, stem cell, capable of completely regenerating haemopoiesis after myeloablation. It has proved relatively easy to harvest HSC, from bone marrow or peripheral blood. In turn, isolation of these cells has allowed therapeutic stem cell transplantation protocols to be developed, that capitalise on their prodigious self renewal and proliferative capabilities. Ex vivo approaches have been described to isolate, genetically manipulateand expand pluripotent stem cell subsets. These techniques have been crucial to the development of gene therapy, and may allow adults to enjoy the potential advantages of cord blood transplantation. Recently, huge conceptual changes have occurred in stem cell biology. In particular, the dogma that, in adults, stem cells are exclusively tissue restricted has been questioned and there is great excitement surrounding the potential plasticity of these cells, with the profound implications that this has, for developing novel cellular therapies. Mesenchymal stem cells, multipotent adult progenitor cells and embryonic stem cells are potential sources of cells for transplantation purposes. These cells may be directed toproduce HSC, in vitro and in the future may be used for therapeutic, or drug development, purposes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Odontogenic capability: bone marrow stromal stem cells versus dental pulp stem cells

Background information. Although adult bone‐marrow‐derived cell populations have been used to make teeth when recombined with embryonic oral epithelium, the differences between dental and non‐dental stem‐cell‐mediated odontogenesis remain an open question. Results. STRO‐1⁺ (stromal precursor cell marker) DPSCs (dental pulp stem cells) and BMSSCs (bone marrow stromal stem cells) were isolated from rat dental pulp and bone marrow respectively by magnetic‐activated cell‐sorting techniques. Their odontogenic capacity was compared under the same inductive microenvironment produced by ABCs (apical bud cells) from 2‐day‐old rat incisors. Co‐cultured DPSCs/ABCs in vitro showed more active odontogenic differentiation ability than mixed BMSSCs/ABCs, as indicated by the accelerated matrix mineralization, up‐regulated alkaline phosphatase activity, cell‐cycle modification, and the expression of tooth‐specific proteins and genes. After cultured for 14 days in the renal capsules of rat hosts, recombined DPSC/ABC pellets formed typical tooth‐shaped tissues with balanced amelogenesis and dentinogenesis, whereas BMSSC/ABC recombinants developed into atypical dentin—pulp complexes without enamel formation. DPSC and BMSSC pellets in vivo produced osteodentin‐like structures and fibrous connective tissues respectively. Conclusions. DPSCs presented more striking odontogenic capability than BMSSCs under the induction of postnatal ABCs. This report provides critical insights into the selection of candidate cells for tooth regeneration between dental and non‐dental stem cell populations.     

Transplantation of hematopoietic stem cells from the peripheral blood

Hematopoietic stem cells can be collected from the peripheral blood. These hematopoietic stem cells (HSC), or better progenitor cells, are mostly expressed as the percentage of cells than react with CD34 antibodies or that form colonies in semi-solid medium (CFU-GM). Under steady-state conditions the number of HSC is much lower in peripheral blood than in bone marrow. Mobilization with chemotherapy and/or growth factors may lead to a concentration of HSC in the peripheral blood that equals or exceeds the concentration in bone marrow. Transplantation of HSC from the peripheral blood results in faster hematologic recovery than HSC from bone marrow. This decreases the risk of infection and the need for blood-product support. For autologous stem-cell transplantation (SCT), the use of peripheral blood cells has completely replaced the use of bone marrow. For allogeneic SCT, on the other hand, the situation is more complex. Since peripheral blood contains more T-lymphocytes than bone marow, the use of HSC from the peripheral blood increases the risk of graft-versus-host disease after allogeneic SCT. For patients with goodrisk leukemia, bone marrow is still preferred, but for patients with high-risk disease, peripheral blood SCT has become the therapy of choice.     

Dock2 participates in bone marrow lympho-hematopoiesis

Dock2 has been shown to be indispensable for chemotaxis of mature lymphocytes as a critical Rac activator. However, the functional expression of Dock2 in immature hematopoietic cells is unclear. In this study, we demonstrate that Dock2 is broadly expressed in bone marrow (BM) hematopoietic compartment, including hematopoietic stem/progenitor cell (HSC/HPC) fraction. Response of Dock2−/− HPCs to CXCL12 in chemotaxis and actin polymerization in vitro was impaired, although α4 integrin activation by CXCL12 was not altered. Myelosuppressive stress on HSCs in vivo, such as consecutive 5-FU administration and serial bone marrow transplantation, did not show hematopoietic defect in Dock2−/− mice. Long-term engraftment of transplanted Dock2−/− BM cells was severely impaired in competitive reconstitution. However, this was not intrinsic to HSCs but originated from the defective competition of Dock2−/− lymphoid precursors. These results suggest that Dock2 plays a significant role in BM lymphopoiesis, but is dispensable for HSC engraftment and self-renewal.     

Hematopoietic stem cell aging is associated with functional decline and delayed cell cycle progression

The molecular mechanisms underlying hematopoietic stem cell (HSC) aging remain to be elucidated. In this study, we investigated age-related changes in the functional and phenotypic properties of murine HSCs. Consistent with previous studies, we found that the number and frequency of CD34^−/lowc-Kit⁺Sca-1⁺lineage marker⁻ (CD34⁻KSL) cells, a highly enriched HSC population, significantly increased in old mice, though their repopulating ability was reduced. Continuous bromodeoxyuridine labeling revealed a significant delay in the cell cycle progression of CD34⁻KSL cells in old mice. This delay was also observed in young recipients transplanted with whole bone marrow cells from old mice. When cultured in vitro, CD34⁻KSL cells from old mice showed a greater capacity to give rise to primitive CD48⁻KSL cells with reduced HSC activity. Gene expression profiling identified age-related changes in the expression of several cell cycle regulatory genes, including p21/Cdkn1a and p18/Cdkn2c. These results support the notion that HSC aging is largely regulated by an intrinsic genetic program.     

Phenotypic Analysis and Isolation of Murine Hematopoietic Stem Cells and Lineage-committed Progenitors

The bone marrow is the principal site where HSCs and more mature blood cells lineage progenitors reside and differentiate in an adult organism. HSCs constitute a minute cell population of pluripotent cells capable of generating all blood cell lineages for a life-time¹. The molecular dissection of HSCs homeostasis in the bone marrow has important implications in hematopoiesis, oncology and regenerative medicine. We describe the labeling protocol with fluorescent antibodies and the electronic gating procedure in flow cytometry to score hematopoietic progenitor subsets and HSCs distribution in individual mice (Fig. 1). In addition, we describe a method to extensively enrich hematopoietic progenitors as well as long-term (LT) and short term (ST) reconstituting HSCs from pooled bone marrow cell suspensions by magnetic enrichment of cells expressing c-Kit. The resulting cell preparation can be used to sort selected subsets for in vitro and in vivo functional studies (Fig. 2).Both trabecular osteoblasts^2,3 and sinusoidal endothelium⁴ constitute functional niches supporting HSCs in the bone marrow. Several mechanisms in the osteoblastic niche, including a subset of N-cadherin⁺ osteoblasts³ and interaction of the receptor tyrosine kinase Tie2 expressed in HSCs with its ligand angiopoietin-1⁵ concur in determining HSCs quiescence. "Hibernation" in the bone marrow is crucial to protect HSCs from replication and eventual exhaustion upon excessive cycling activity⁶. Exogenous stimuli acting on cells of the innate immune system such as Toll-like receptor ligands⁷ and interferon-α⁶ can also induce proliferation and differentiation of HSCs into lineage committed progenitors. Recently, a population of dormant mouse HSCs within the lin^- c-Kit⁺ Sca-1⁺ CD150⁺ CD48^- CD34^- population has been described⁸. Sorting of cells based on CD34 expression from the hematopoietic progenitors-enriched cell suspension as described here allows the isolation of both quiescent self-renewing LT-HSCs and ST-HSCs⁹. A similar procedure based on depletion of lineage positive cells and sorting of LT-HSC with CD48 and Flk2 antibodies has been previously described¹⁰. In the present report we provide a protocol for the phenotypic characterization and ex vivo cell cycle analysis of hematopoietic progenitors, which can be useful for monitoring hematopoiesis in different physiological and pathological conditions. Moreover, we describe a FACS sorting procedure for HSCs, which can be used to define factors and mechanisms regulating their self-renewal, expansion and differentiation in cell biology and signal transduction assays as well as for transplantation.     

小鼠骨髓造血干细胞、外周血组成随年龄的变化趋势及其相关性分析

造血干细胞是具有自我更新能力并能分化为血液中各种血细胞组分的多能干细胞。近来研究显示,不同造血干细胞表面标志物标记的造血干细胞具有分化为不同血细胞的趋势,但是这种分化的内在关系仍不清楚。对小鼠CD34~-/Sca-1~+骨髓造血干细胞、外周血组成随小鼠年龄增长的变化情况进行了分析,结果显示:随着年龄的增长,骨髓中的CD34~-/Sca-1~+骨髓造血干细胞比率显著增加;而外周血各组分则随年龄变化呈现不同的趋势。对不同年龄段小鼠的骨髓造血干细胞及其他组分与外周血组分的同步分析发现,外周血中血小板密度变化趋势与CD34~-/Sca-1~+骨髓造血干细胞变化情况相关系数为0.804 8;外周血中淋巴细胞密度变化趋势与CD34~+/Sca-1~-骨髓细胞的变化情况相关系数为0.947 97;外周血中白细胞密度变化趋势与CD34~+/Sca-1~+骨髓细胞变化情况相关系数为0.763 1(大于0.9为极度相关,0.7到0.9为高度相关)。     

应用骨髓干细胞治疗肝硬化研究进展

随着干细胞研究的深入和技术的发展,再生医学的干细胞疗法治疗肝脏疾病已成为研究热点。骨髓来源造血干细胞和间充质干细胞等在肝脏疾病治疗方面有巨大潜力。骨髓干细胞参与肝纤维化与肝硬化修复主要包括迁移、归巢与转化等过程,并需要多种细胞因子和趋化因子的协同作用促进肝细胞再生与减轻肝纤维化。本文拟对骨髓干细胞治疗肝硬化的最新研究进展进行综述。     

The dynamics of murine mammary stem/progenitor cells

The stem/progenitor cells in the murine mammary gland are a highly dynamic population of cells that are responsible for ductal elongation in puberty, homeostasis maintenance in adult, and lobulo-alveolar genesis during pregnancy. In recent years understanding the epithelial cell hierarchy within the mammary gland is becoming particularly important as these different stem/progenitor cells were perceived to be the cells of origin for various subtypes of breast cancer. Although significant advances have been made in enrichment and isolation of stem/progenitor cells by combinations of antibodies against cell surface proteins together with flow cytometry, and in identification of stem/progenitor cells with multi-lineage differentiation and self-renewal using mammary fat pad reconstitution assay and in vivo genetic labeling technique, a clear understanding of how these different stem/progenitors are orchestrated in the mammary gland is still lacking. Here we discuss the different in vivo and in vitro methods currently available for stem/progenitor identification, their associated caveats, and a possible new hierarchy model to reconcile various putative stem/progenitor cell populations identified by different research groups.