Low level of c-kit expression marks deeply quiescent murine hematopoietic stem cells

Although c-kit is expressed highly on murine hematopoietic stem cells (HSCs) and essential for bone marrow (BM) hematopoiesis, the significance of the high level of expression of c-kit on HSCs was not well determined. We show here that CD150(+) CD48(-) Lineage(-) Sca-1(+) c-kit(+) HSCs in adult BM are distributed within the range of roughly a 20-fold difference in the expression level of c-kit, and that c-kit density correlates with the cycling status of the HSC population. This predisposition is more evident in the BM of mice older than 30 weeks. The HSCs in G(0) phase express a lower level of c-kit both on the cell surface and inside the cells, which cannot be explained by ligand receptor binding and internalization. It is more likely that the low level of c-kit expression is a unique property of HSCs in G(0). Despite functional differences in the c-kit gradient, the HSCs are uniformly hypoxic and accessible to blood perfusion. Therefore, our data indicate the possibility that the hypoxic state of the HSCs is actively regulated, rather than them being passively hypoxic through a simple anatomical isolation from the circulation.     

Characterization, isolation, and differentiation of murine skin cells expressing hematopoietic stem cell markers

As the phenotype of adult dermal stem cells is still elusive, and the hematopoietic stem cell is one of the best-characterized stem cells in the body, we tested dermal cell suspensions, sections, and wholemounts in newborn and adult mice for hematopoietic stem cell marker expression. Phenotypic analysis revealed that a small population of CD45(+) cells and a large population of CD45(-) cells expressed CD34, CD117, and stem cell antigen-1 molecules. When cultivated in selected media supplemented with hematopoietic cytokines, total dermal cells, lineage(-), and/or highly enriched phenotypically defined cell subsets produced hematopoietic and nonhematopoietic colonies. When injected into lethally irradiated recipient mice, a small percentage of newborn dermal cells was able to migrate into hematopoietic tissues and the skin and survived through the 11-month monitoring period. Our ability to isolate a candidate autologous stem cell pool will make these cells ideal vehicles for genetic manipulation and gene therapy.     

Abcg2 expression marks tissue-specific stem cells in multiple organs in a mouse progeny tracking model

The side population phenotype is associated with the Hoechst dye efflux activity of the Abcg2 transporter and identifies hematopoietic stem cells (HSCs) in the bone marrow. This association suggests the direct use of Abcg2 expression to identify adult stem cells in various other organs. We have generated a lineage tracing mouse model based on an allele that coexpresses both Abcg2 and a CreERT2 expression cassette. By crossing these mice with lox-STOP-lox reporter lines (LacZ or YFP), cells that express Abcg2 and their progeny were identified following treatment with tamoxifen (Tam). In the liver and kidney, in which mature cells express Abcg2, reporter gene expression verified the expected physiologic expression pattern of the recombinant allele. Long-term marking of HSCs was seen in multiple peripheral blood lineages from adult mice, demonstrating that Abcg2(+) bone marrow HSCs contribute to steady-state hematopoiesis. Stem cell tracing patterns were seen in the small intestine and in seminiferous tubules in the testis 20 months after Tam treatment, proving that stem cells from these organs express Abcg2. Interstitial cells from skeletal and cardiac muscle were labeled, and some cells were costained with endothelial markers, raising the possibility that these cells may function in the repair response to muscle injury. Altogether, these studies prove that Abcg2 is a stem cell marker for blood, small intestine, testicular germ cells, and possibly for injured skeletal and/or cardiac muscle and provide a new model for studying stem cell activity that does not require transplant-based assays.     

人主动脉-性腺-中肾区基质细胞诱导胚胎干细胞分化为造血干细胞及体内造血重建

背景：研究证实多种造血生长因子、基质细胞饲养层及其条件培养液可促进胚胎干细胞向造血干细胞分化。 目的：以人主动脉-性腺-中肾(aorta-gonad-mesonephros,AGM)区基质细胞为饲养层体外诱导小鼠胚胎干细胞分化为造血干细胞,并比较不同移植途径对造血干细胞体内造血重建能力的影响。 方法：将小鼠E14 胚胎干细胞诱导为拟胚体,采用Transwell非接触共培养体系在人AGM区基质细胞饲养层上诱导6 d,接种NOD-SCID小鼠检测体内致瘤性。再将诱导后的拟胚体细胞移植经致死量60Co γ射线辐照的BALB/C雌鼠,受鼠随机分为静脉移植组、骨髓腔移植组、照射对照组及正常对照组。 结果与结论：拟胚体细胞经人AGM区基质细胞诱导后Sca-1⁺c-Kit⁺细胞占(13.12±1.30)%。NOD-SCID小鼠皮下接种经人AGM区基质细胞诱导的拟胚体细胞可出现畸胎瘤,经骨髓腔接种未见肿瘤形成。静脉移植组动物全部死亡,骨髓腔移植组生存率为55.6%,移植后21 d外周血象基本恢复,存活受鼠检测到供体来源Sry基因。提示小鼠胚胎干细胞经人AGM区基质细胞诱导分化的造血干细胞通过骨髓腔移植安全并具有一定的造血重建能力。     

Simple and efficient isolation of hematopoietic stem cells from H2K-zFP transgenic mice

We have generated a transgenic mouse line that allows for simple and highly efficient enrichment for mouse hematopoietic stem cells (HSCs). The transgene expresses a green fluorescent protein variant (zFP) under the control of H2Kb promoter/enhancer element. Despite the broad zFP expression, transgenic HSCs express exceptionally high levels of zFP, allowing prospective isolation of a population highly enriched in HSCs by sorting the 0.2% of the brightest green cells from the enriched bone marrow of H2K-zFP mice. Up to 90% of zFP(bright) cells are also c-kit(high), Sca-1(high), Lin(neg), Flk-2(neg), which is a bona fide phenotype for long-term HSCs. Double-sorted zFP(bright) HSCs were capable of long-term multilineage reconstitution at a limiting dilution dose of approximately 12 cells, which is comparable to that of highly purified HSCs obtained by conventional multicolor flow cytometry. Thus, the H2K-zFP transgenic mice provide a straightforward and easy setup for the simple and highly efficient enrichment for genetically labeled HSCs without using fluorescence-conjugated monoclonal antibodies. This approach will greatly facilitate gene transfer, including short interfering RNA for gene knockdown, into HSCs and, consequently, into all other hematopoietic lineages.     

Normal hematopoiesis after conditional targeting of RXRalpha in murine hematopoietic stem/progenitor cells

Because of the retinoic acid receptor-alpha (RARalpha) gene's involvement in acute promyelocytic leukemia, the important role of RARs in hematopoiesis is now well established. However, relatively few studies of hematopoiesis have focused on the role of the retinoid X receptors (RXRs), the obligate heterodimeric partners of the RARs. We sought to establish whether conditional targeting of RXRalpha in early hematopoietic progenitors, ideally to the level of the hematopoietic stem cell (HSC), would compromise hematopoiesis. For hematopoietic targeting of RXRalpha, we characterized IFN-inducible MxCre mice for use in studying the role of RXRalpha in hematopoiesis. We established that MxCre executes recombination of loxP-flanked RXRalpha in hematopoietic progenitors immunophenotypically enriched for HSC, leading to widespread and sustained targeting of RXRalpha in hematopoietic cells. However, we found no evidence of hematologic compromise in mice lacking RXRalpha, suggesting that RXRalpha is dispensable for normal murine hematopoiesis. Nonetheless, RXRalpha null bone marrow cells cultured in methylcellulose form colonies more efficiently than bone marrow cells obtained from control mice. This result suggests that although RXRalpha is not required for murine hematopoiesis, there may be hematopoietic signaling pathways that respond selectively to RXRalpha or settings in which combined expression of RXR (alpha, beta, and gamma) is limiting.     

Unexpectedly efficient homing capacity of purified murine hematopoietic stem cells

Single-cell transplantation analysis revealed that the cells that had the strongest dye efflux activity ("Tip"-SP cells) and had the phenotype CD34- c-Kit+ Sca-1+ Lin- (CD34- KSL cells) exhibited very strong proliferation and multilineage differentiation capacity. Ninety-six percent of the lethally irradiated mice that received a single "Tip"-SP CD34- KSL cell showed significant donor cell engraftment for long term. These findings support the hypothesis that "Tip"-SP CD34- KSL cells represent the most primitive hematopoietic stem cells that are capable of migrating into the primary site and surviving and/or proliferating with nearly absolute efficiency. This led us to propose high marrow-seeding efficiency as a specific characteristic of primitive HSCs, in addition to their self-renewal and multipotent capacity.     

Reduction of Shp-2 expression by small interfering RNA reduces murine embryonic stem cell-derived in vitro hematopoietic differentiation

Shp-2 is a member of a small family of cytoplasmic Src homology 2 (SH2) domain-containing protein tyrosine phosphatases. Although Shp-2 has been shown to be necessary for hematopoiesis using a mouse model expressing a mutant residual protein (Shp-2(delta/delta)), we used small interfering RNA (siRNA) to reduce Shp-2 expression and examined the consequences on embryonic stem cell (ESC)-derived hemangioblast, primitive, and definitive hematopoietic development. We found that at a concentration of 50 nM, Shp-2 siRNA effectively diminished Shp-2 expression in differentiating embryoid bodies. Hemangioblast, primitive, and definitive hematopoietic progenitor formation was decreased significantly after transfection with Shp-2 siRNA but not with scrambled siRNA. Because Shp-2 is involved in signals emanating from the basic fibroblast growth factor (bFGF) receptor, we asked whether Shp-2 functions in bFGF-mediated hemangioblast development. Reduction of Shp-2 expression using siRNA, but not scrambled siRNA, blocked the bFGF-induced increase in hemangioblast development. Using siRNA as an independent method of reducing Shp-2 function, in contrast to the mutant mouse model (Shp-2(delta/delta)) previously used, we demonstrate that Shp-2 is required in hemangioblast, primitive, and definitive progenitor hematopoietic development and that Shp-2 is integrally necessary for bFGF-mediated hemangioblast production.     

Expression of CD27 on murine hematopoietic stem and progenitor cells

Hematopoietic stem cells (HSC) are defined by self-renewal and multilineage differentiation potentials. In order to uncover the genetic program of HSC, we utilized high-density arrays to compare gene expression in highly purified mouse HSC and their mature progeny. One molecule specifically expressed in immature cells is CD27, a member of the TNF receptor family previously shown to play roles in lymphoid proliferation, differentiation, and apoptosis. We show here that the CD27 protein is expressed by about 90% of cells in a purified HSC population. Interestingly, the CD27pos cells are enriched for cells with short-term hematopoietic activities (colony forming potential in vivo and in vitro), while the minority CD27neg population is more effective in clonal long-term transplantation.     

Prospective isolation of skeletal muscle stem cells with a Pax7 reporter

Muscle regeneration occurs through activation of quiescent satellite cells whose progeny proliferate, differentiate, and fuse to make new myofibers. We used a transgenic Pax7-ZsGreen reporter mouse to prospectively isolate stem cells of skeletal muscle by flow cytometry. We show that Pax7-expressing cells (satellite cells) in the limb, head, and diaphragm muscles are homogeneous in size and granularity and uniformly labeled by certain cell surface markers, including CD34 and CD29. The frequency of the satellite cells varies between muscle types and with age. Clonal analysis demonstrated that all colonies arising from single cells within the Pax7-sorted fraction have myogenic potential. In response to injury, Pax7(+) cells reduce CD34, CD29, and CXCR4 expression, increase in size, and acquire Sca-1. When directly isolated and cultured in vitro, Pax7(+) cells display the hallmarks of activation and proliferate, initially as suspension aggregates and later distributed between suspension and adherence. During in vitro expansion, Pax7 (ZsGreen) and CD34 expression decline, whereas expression of PSA-NCAM is acquired. The nonmyogenic, Pax7(neg) cells expand as Sca1(+) PDGRalpha(+) PSA-NCAM(neg) cells. Satellite cells expanded exclusively in suspension can engraft and produce dystrophin(+) fibers in mdx(-/-) mice. These results establish a novel animal model for the study of muscle stem cell physiology and a culture system for expansion of engraftable muscle progenitors.     

Expression of cell surface determinant(s) on murine myeloma stem cells and hematopoietic stem cells

Murine B cell lymphomas and myelomas were examined for the expression of a determinant previously found exclusively on normal pluripotent stem cells colony-forming unit-spleen (CFU-s). This determinant(s), which is defined by a rabbit antimouse brain antiserum (R alpha MB), is present on the tumor stem cell population of some but not all B cell neoplasms examined. The determinant is not detected on tumor cells of the macrophage or T cell lineage. Absorption of the activity in R alpha MB with myeloma cells, concomitantly removed reactivity with the normal stem cell, CFU-s, and the myeloma stem cell, plasmacytoma CFU-s. Sorting analysis further showed that the antigen was diminished within a positive tumor population as cells acquired the capacity to secrete immunoglobulin. These studies suggest that this normal stem cell-associated antigen may also be an early differentiation antigen for the B cell lineage, and is expressed on some stem cells of B cell tumors.     

Myeloid neoplasm-related gene abnormalities differentially affect dendritic cell differentiation from murine hematopoietic stem/progenitor cells

Dendritic cells (DCs) play important roles in tumor immunology. Leukemic cells in patients with myeloid neoplasms can differentiate into DCs in vivo (referred to as in vivo leukemic DCs), which are postulated to affect anti-leukemia immune responses. We established a reproducible culture system of in vitro FLT3 ligand-mediated DC (FL-DC) differentiation from murine lineage(-) Sca-1(+) c-Kit(high) cells (LSKs), which made it possible to analyse the effects of target genes on steady-state DC differentiation from hematopoietic stem/progenitor cells. Using this system, we analysed the effects of various myeloid neoplasm-related gene abnormalities, termed class I and class II mutations, on FL-DC differentiation from LSKs. All class II mutations uniformly impaired FL-DC differentiation maintaining a plasmacytoid DC (pDC)/conventional DC (cDC) ratio comparable to the control cells. In contrast, class I mutations differentially affected FL-DC differentiation from LSKs. FLT3-ITD and a constitutively active form of Ras (CA-N-Ras) yielded more FL-DCs than the control, whereas the other class I mutations tested yielded less FL-DCs. Both FLT3-ITD and FLT3-tyrosine kinase domain (TKD) mutation showed a comparable pDC/cDC ratio as the control. CA-N-Ras, c-Kit-TKD, TEL/PDGFRβ, and FIP1L1/PDGFRα showed a severe decrease in the pDC/cDC ratio. CA-STAT5 and CA-MEK1 severely inhibited pDC differentiation. FLT3-ITD, CA-N-Ras, and TEL/PDGFRβ aberrantly induced programmed death ligand-1 (PD-L1)-expressing DCs. In conclusion, we have established a simple, efficient, and reproducible in vitro FL-DC differentiation system from LSKs. This system could uncover novel findings on how myeloid neoplasm-related gene abnormalities differentially affect FL-DC differentiation from murine hematopoietic stem/progenitor cells in a gene-specific manner.     

含不同启动子的GFP载体在不同种属的胚胎干细胞系中表达效率的研究

目的 对比含不同启动子的GFP表达载体在hESC及小鼠胚胎干细胞(mouse embryonic stem cell, mESC)的表达效率,为探索ESC及其衍生细胞移植在体内的存活、迁移、分化及整合提供细胞模型.方法 阳离子脂质体转染hESC及mESC ES-D3,荧光显微镜下观察阳性克隆,流式细胞术(flow cytometry, FCM)计算不同载体pCX-hrGFP、pIRES-hrGFP在不同种属细胞中的表达效率.结果 两种载体在mESC的表达效率分别为pCX-hrGFP 90±2.5%, pIRES-hrGFP 0.67±0.02%, 两组间比较差异有统计学意义(P＜0.05).在hESC的表达效率分别为pCX-hrGFP 0.8±0.1%, pIRES-hrGFP 0.62±0.08%,两组间比较有统计学差异(P＜0.05).pCX-hrGFP在mESC及hESC间的表达效率差异有统计学意义 (P＜0.01),pIRES-hrGFP在mESC及hESC间的表达效率差异无统计学意义 (P＞0.05).结论 (1)CBA启动子引导的GFP表达效率高于CMV启动子.(2)同一载体在不同种属细胞内表达效率不同.     

Efficient hematopoietic redifferentiation of induced pluripotent stem cells derived from primitive murine bone marrow cells

Heterogeneity among induced pluripotent stem cell (iPSC) lines with regard to their gene expression profile and differentiation potential has been described and at least partly linked to the tissue of origin. Here, we generated iPSCs from primitive [lineage negative (Lin(neg))] and nonadherent differentiated [lineage positive (Lin(pos))] bone marrow cells (BM-iPSC), and compared their differentiation potential to that of fibroblast-derived iPSCs (Fib-iPSC) and embryonic stem cells (ESC). In the undifferentiated state, individual iPSC clones but also ESCs proved remarkably similar when analyzed for alkaline phosphatase and SSEA-1 staining, endogenous expression of the pluripotency genes Nanog, Oct4, and Sox2, or global gene expression profiles. However, substantial differences between iPSC clones were observed after induction of differentiation, which became most obvious upon cytokine-mediated instruction toward the hematopoietic lineage. All 3 BM-iPSC lines derived from undifferentiated Lin(neg) cells yielded high proportions of cells expressing the hematopoietic differentiation marker CD41 and in 2 of these lines high proportions of CD41+/ CD45+ cells were detected. In contrast, little hematopoiesis-specific surface marker expression was detected in 4 Lin(pos) BM-iPSC and 3 Fib-iPSC lines. These results were corroborated by functional studies demonstrating robust colony outgrowth from hematopoietic progenitors in 2 of the Lin(neg) BM-iPSCs only. Thus, in conclusion, our data demonstrate efficient generation of iPSCs from primitive hematopoietic tissue as well as efficient hematopoietic redifferentiation for Lin(neg) BM-iPSC lines, thereby supporting the notion of an epigenetic memory in iPSCs.     

Notch信号介导共培养脐带间充质干细胞和造血干细胞的相互作用

目的:探讨脐带间充质干细胞(UC-MSC)体外与造血干细胞共培养后Notch信号分子的改变。方法:通过胶原酶消化方法分离UC-MSC,通过流式细胞仪检测以及成脂、成骨和成软骨诱导鉴定UC-MSC具备间充质干细胞的特性。进而,将UC-MSC与脐血CD34+造血干细胞(HSC)体外培养,实时PCR方法检测MSC及CD34+细胞表面Notch配体及受体表达以及表达是否存在变化;在共培养体系中加入Notch信号阻滞剂DAPT(γ-secretase抑制剂),比较Hes-1基因活化状态的改变。结果:体外实验显示:UC-MSC在形态学、细胞表面表型和诱导分化能力上均具备间充质干细胞的特性。UC-MSC及CD34+细胞表面存在Notch信号配体及受体的表达,共培养后Jagged 1、Notch1基因表达明显增加;共培养后CD34+细胞中的Hes-1基因表达明显增加而加入DAPT后Hes-1基因表达未检出明显改变。结论:UC-MSC支持造血中,Notch信号可能发挥重要作用。     

Age-dependent accumulation of mtDNA mutations in murine hematopoietic stem cells is modulated by the nuclear genetic background

Alterations in mitochondrial DNA (mtDNA) and consequent loss of mitochondrial function underlie the mitochondrial theory of aging. In this study, we systematically analyzed the mtDNA control region somatic mutation pattern in 2864 single hematopoietic stem cells (HSCs) and progenitors, isolated by flow cytometry sorting on Lin(-)Kit(+)CD34(-) parameters from young and old C57BL/6 (B6) and BALB/cBy (BALB) mice, to test the hypothesis that the accumulated mtDNA mutations in HSCs were strain-correlated and associated with HSC functional senescence during aging. An increased level of mtDNA mutations in single HSCs was observed in old B6 when compared with young B6 mice (P=0.003); in contrast, no significant age-dependent accumulation of mutations was observed in BALB mice (old versus young, P=0.202) and the level of mutations in both young and old BALB mice was close to that of old B6 mice (P>0.280). Cellular reactive oxygen species (ROS) in mouse HSCs could not be correlated with the level of mtDNA mutations in these cells, although B6 mice had a higher proportion of ROS(-) cells when compared with the BALB mice. Propagation assays of single HSCs showed B6 cells form larger colonies compared with cells from BALB mice, irrespective of age and mtDNA mutation load. We infer from our data that age-related mtDNA somatic mutation accumulation in mouse HSCs is influenced by the nuclear genetic background and that these mutations may not obviously correlate to either cellular ROS content or HSC senescence.     

Murine embryonic stem cells secrete cytokines/growth modulators that enhance cell survival/anti-apoptosis and stimulate colony formation of murine hematopoietic progenitor cells

Stromal cell-derived factor (SDF)-1/CXCL12, released by murine embryonic stem (ES) cells, enhances survival, chemotaxis, and hematopoietic differentiation of murine ES cells. Conditioned medium (CM) from murine ES cells growing in the presence of leukemia inhibitory factor (LIF) was generated while the ES cells were in an undifferentiated Oct-4 expressing state. ES cell-CM enhanced survival of normal murine bone marrow myeloid progenitors (CFU-GM) subjected to delayed growth factor addition in vitro and decreased apoptosis of murine bone marrow c-kit(+)lin- cells. ES CM contained interleukin (IL)-1alpha, IL-10, IL-11, macrophage-colony stimulating factor (CSF), oncostatin M, stem cell factor, vascular endothelial growth factor, as well as a number of chemokines and other proteins, some of which are known to enhance survival/anti-apoptosis of progenitors. Irradiation of ES cells enhanced release of some proteins and decreased release of others. IL-6, FGF-9, and TNF-alpha, not detected prior to irradiation was found after ES cells were irradiated. ES cell CM also stimulated CFU-GM colony formation. Thus, undifferentiated murine ES cells growing in the presence of LIF produce/release a number of biologically active interleukins, CSFs, chemokines, and other growth modulatory proteins, results which may be of physiological and/or practical significance.