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Granulocyte colony-stimulating factor (G-CSF),the prototypical mobilizing cytokine,induces hematopoietic stem and progenitor cell (HSPC) mobilization from the bone marrow in a cell-nonautonomous fashion. This process is mediated,in part,through suppression of osteoblasts and disruption of CXCR4/CXCL12 signaling. The cellular targets of G-CSF that initiate the mobilization cascade have not been identified. We use mixed G-CSF receptor (G-CSFR)-deficient bone marrow chimeras to show that G-CSF-induced mobilization of HSPCs correlates poorly with the number of wild-type neutrophils. We generated transgenic mice in which expression of the G-CSFR is restricted to cells of the monocytic lineage. G-CSF-induced HSPC mobilization,osteoblast suppression,and inhibition of CXCL12 expression in the bone marrow of these transgenic mice are intact,demonstrating that G-CSFR signals in monocytic cells are sufficient to induce HSPC mobilization. Moreover,G-CSF treatment of wild-type mice is associated with marked loss of monocytic cells in the bone marrow. Finally,we show that bone marrow macrophages produce factors that support the growth and/or survival of osteoblasts in vitro. Together,these data suggest a model in which G-CSFR signals in bone marrow monocytic cells inhibit the production of trophic factors required for osteoblast lineage cell maintenance,ultimately leading to HSPC mobilization. View Publication

Polymorphonuclear neutrophils (PMNs) are critical for the formation,maintenance,and resolution of bacterial abscesses. However,the mechanisms that regulate PMN survival and proliferation during the evolution of an abscess are not well defined. Using a mouse model of Staphylococcus aureus abscess formation within a cutaneous wound,combined with real-time imaging of genetically tagged PMNs,we observed that a high bacterial burden elicited a sustained mobilization of PMNs from the bone marrow to the infected wound,where their lifespan was markedly extended. A continuous rise in wound PMN number,which was not accounted for by trafficking from the bone marrow or by prolonged survival,was correlated with the homing of c-kit(+)-progenitor cells from the blood to the wound,where they proliferated and formed mature PMNs. Furthermore,by blocking their recruitment with an antibody to c-kit,which severely limited the proliferation of mature PMNs in the wound and shortened mouse survival,we confirmed that progenitor cells are not only important contributors to PMN expansion in the wound,but are also functionally important for immune protection. We conclude that the abscess environment provides a niche capable of regulating PMN survival and local proliferation of bone marrow-derived c-kit(+)-progenitor cells. View Publication

The immune system is replenished by self-renewing hematopoietic stem cells (HSCs) that produce multipotent progenitors (MPPs) with little renewal capacity. E-proteins,the widely expressed basic helix-loop-helix transcription factors,contribute to HSC and MPP activity,but their specific functions remain undefined. Using quantitative in vivo and in vitro approaches,we show that E47 is dispensable for the short-term myeloid differentiation of HSCs but regulates their long-term capabilities. E47-deficient progenitors show competent myeloid production in short-term assays in vitro and in vivo. However,long-term myeloid and lymphoid differentiation is compromised because of a progressive loss of HSC self-renewal that is associated with diminished p21 expression and hyperproliferation. The activity of E47 is shown to be cell-intrinsic. Moreover,E47-deficient HSCs and MPPs have altered expression of genes associated with cellular energy metabolism,and the size of the MPP pool but not downstream lymphoid precursors in bone marrow or thymus is rescued in vivo by antioxidant. Together,these observations suggest a role for E47 in the tight control of HSC proliferation and energy metabolism,and demonstrate that E47 is not required for short-term myeloid differentiation. View Publication

Tristetraprolin (TTP,Zfp36,Nup475,Tis11) dramatically reduces the stability of target mRNAs by binding to AU-rich elements in their 3' untranslated regions. Through this mechanism,TTP functions as a rheostatic,temporal regulator of gene expression. TTP knockout (KO) mice exhibit completely penetrant granulocytic hyperplasia. We have shown that the hematopoietic stem-progenitor cell compartment in TTP KO mice is also altered. Although no change was detected in long-term hematopoietic stem cell (HSC) frequency or function,as assayed by immunophenotypic markers or limiting dilution transplants,we observed increases in the frequencies and numbers of short-term HSCs,multipotent progenitors,and granulocyte-monocyte progenitors. This pattern is consistent with reactive granulopoiesis View Publication

More than 10 years after their first isolation,human embryonic stem cells are finally 'coming of age' in research and biotechnology applications as protocols for their differentiation and undifferentiated expansion in culture become robust and scalable,and validated commercial reagents become available. Production of human cardiomyocytes is now feasible on a daily basis for many laboratories with tissue culture expertise. An additional recent surge of interest resulting from the first production of human iPSCs (induced pluripotent stem cells) from somatic cells of patients now makes these technologies of even greater importance since it is likely that (genetic) cardiac disease phenotypes can be captured in the cardiac derivatives of these cells. Although cell therapy based on replacing cardiomyocytes lost or dysfunctional owing to cardiac disease are probably as far away as ever,biotechnology and pharmaceutical applications in safety pharmacology and drug discovery will probably impact this clinical area in the very near future. In the present paper,we review the cutting edge of this exciting area of translational research. View Publication

The aim of the study was to generate dopaminergic (DA) neurons from human embryonic stem cells (ESC) in vitro. It was shown that human ESCs are able to differentiated into DA neurons without co-culture with stromal cells. Terminal differentiation into DA neurons was reached by successive application of noggin and bFGF growth factors on collagen and matrigel substrates during 3-4 weeks. Differentiation efficiency was evaluated by the number of colonies with cells expressing tyrosine hydroxylase (TH),a DA neuron marker,and by the number of TH-positive cells in cell suspension using flow cytometry. No cells with pluripotent markers were detected in DA-differentiated cultures. It makes possible to propose that the protocol of human ESC differentiation might be applied to generate DA neurons for their transplantation into the animals modeling neurodegenerative (Parkinson) disease without the risk of tumor growth. View Publication

Sox6 belongs to the Sry (sex-determining region Y)-related high-mobility-group-box family of transcription factors,which control cell-fate specification of many cell types. Here,we explored the role of Sox6 in human erythropoiesis by its overexpression both in the erythroleukemic K562 cell line and in primary erythroid cultures from human cord blood CD34+ cells. Sox6 induced significant erythroid differentiation in both models. K562 cells underwent hemoglobinization and,despite their leukemic origin,died within 9 days after transduction; primary erythroid cultures accelerated their kinetics of erythroid maturation and increased the number of cells that reached the final enucleation step. Searching for direct Sox6 targets,we found SOCS3 (suppressor of cytokine signaling-3),a known mediator of cytokine response. Sox6 was bound in vitro and in vivo to an evolutionarily conserved regulatory SOCS3 element,which induced transcriptional activation. SOCS3 overexpression in K562 cells and in primary erythroid cells recapitulated the growth inhibition induced by Sox6,which demonstrates that SOCS3 is a relevant Sox6 effector. View Publication

Bone marrow (BM) hematopoietic cells are selectively sensitive to polycyclic aromatic hydrocarbons (PAH) in vivo. 7,12-Dimethylbenz(a)anthracene (DMBA),but not benzo(a)pyrene (BP),depletes BM hematopoietic cells in C57BL/6 mice. This difference is due to a BP-selective aryl hydrocarbon receptor (AhR)-mediated recovery. Colony-forming unit assays show suppression of lymphoid progenitors by each PAH within 6 h but a subsequent recovery,exclusively after BP treatment. Suppression of myeloid progenitors (6 h) occurs only for DMBA. Each progenitor responded equally to DMBA and BP in congenic mice expressing the PAH-resistant AhR (AhR(d)). AhR,therefore,mediates this BP recovery in each progenitor type. These PAH suppressions depend on Cyp1b1-mediated metabolism. Paradoxically,few genes responded to DMBA,whereas 12 times more responded to BP. Progenitor suppression by DMBA,therefore,occurs with minimal effects on the general BM population. Standard AhR-mediated stimulations (Cyp1a1,Cyp1b1,Ahrr) were similar for each PAH and for the specific agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin but were absent in AhR(d) mice. A group of 12 such AhR responses was sustained from 6 to 24 h. A second,larger set of BP responses (chemokines,cytokines,cyclooxygenase 2) differed in two respects; DMBA responses were low and BP responses declined extensively from 6 to 24 h. A third cluster exhibited BP-induced increases in protective genes (Nqo1,GST-mu) that appeared only after 12 h. Conversion of BP to quinones contributes oxidative signaling not seen with DMBA. We propose that genes in this second cluster,which share oxidative signaling and AhR activation,provide the AhR-dependent protection of hematopoietic progenitors seen for BP. View Publication

SerpinB1 is among the most efficient inhibitors of neutrophil serine proteases--NE,CG,and PR-3--and we investigated here its role in neutrophil development and homeostasis. We found that serpinB1 is expressed in all human bone marrow leukocytes,including stem and progenitor cells. Expression levels were highest in the neutrophil lineage and peaked at the promyelocyte stage,coincident with the production and packaging of the target proteases. Neutrophil numbers were decreased substantially in the bone marrow of serpinB1(-/-) mice. This cellular deficit was associated with an increase in serum G-CSF levels. On induction of acute pulmonary injury,neutrophils were recruited to the lungs,causing the bone marrow reserve pool to be completely exhausted in serpinB1(-/-) mice. Numbers of myeloid progenitors were normal in serpinB1(-/-) bone marrow,coincident with the absence of target protease expression at these developmental stages. Maturation arrest of serpinB1(-/-) neutrophils was excluded by the normal CFU-G growth in vitro and the normal expression in mature neutrophils of early and late differentiation markers. Normal absolute numbers of proliferating neutrophils and pulse-chase kinetic studies in vivo showed that the bone marrow deficit in serpinB1(-/-) mice was largely restricted to mature,postmitotic neutrophils. Finally,upon overnight culture,apoptosis and necrosis were greater in purified bone marrow neutrophils from serpinB1(-/-) compared with WT mice. Collectively,these findings demonstrate that serpinB1 sustains a healthy neutrophil reserve that is required in acute immune responses. View Publication

Gene therapy has proven its potential to cure diseases of the hematopoietic system. However,severe adverse events observed in clinical trials have demanded improved gene-transfer conditions. Whereas progress has been made to reduce the genotoxicity of integrating gene vectors,the role of pretransplantation cultivation is less well investigated. We observed that the STIF (stem cell factor [SCF],thrombopoietin [TPO],insulin-like growth factor-2 [IGF-2],and fibroblast growth factor-1 [FGF-1]) cytokine cocktail developed to effectively expand murine hematopoietic stem cells (HSCs) also supports the expansion of leukemia-initiating insertional mutants caused by gammaretroviral gene transfer. We compared 4 protocols to examine the impact of prestimulation and posttransduction culture in STIF in the context of lentiviral gene transfer. Observing 56 transplanted mice for up to 9.5 months,we found consistent engraftment and gene-marking rates after prolonged ex vivo expansion. Although a lentiviral vector with a validated insertional-mutagenic potential was used,longitudinal analysis identifying textgreater 7000 integration sites revealed polyclonal fluctuations,especially in expanded" groups View Publication

The most frequent translocation t(8;21) in acute myeloid leukemia (AML) generates the chimeric AML1/ETO protein,which blocks differentiation and induces self-renewal in hematopoietic progenitor cells. The underlying mechanisms mediating AML1/ETO-induced self-renewal are largely unknown. Using expression microarray analysis,we identified the Groucho-related amino-terminal enhancer of split (AES) as a consistently up-regulated AML1/ETO target. Elevated levels of AES mRNA and protein were confirmed in AML1/ETO-expressing leukemia cells,as well as in other AML specimens. High expression of AES mRNA or protein was associated with improved survival of AML patients,even in the absence of t(8;21). On a functional level,knockdown of AES by RNAi in AML1/ETO-expressing cell lines inhibited colony formation. Similarly,self-renewal induced by AML1/ETO in primary murine progenitors was inhibited when AES was decreased or absent. High levels of AES expression enhanced formation of immature colonies,serial replating capacity of primary cells,and colony formation in colony-forming unit-spleen assays. These findings establish AES as a novel AML1/ETO-induced target gene that plays an important role in the self-renewal phenotype of t(8;21)-positive AML. View Publication

Adult T-cell leukemia-lymphoma (ATL) is an aggressive disease,incurable by standard chemotherapy. NK314,a new anticancer agent possessing inhibitory activity specific for topoisomerase IIα (Top2α),inhibited the growth of various ATL cell lines (50% inhibitory concentration: 23-70nM) with more potent activity than that of etoposide. In addition to the induction of DNA double-strand breaks by inhibition of Top2α,NK314 induced degradation of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs),resulting in impaired DNA double-strand break repair. The contribution of DNA-PK to inhibition of cell growth was affirmed by the following results: NK314 inhibited cell growth of M059J (a DNA-PKcs-deficient cell line) and M059K (a cell line with DNA-PKcs present) with the same potency,whereas etoposide exhibited weak inhibition of cell growth with M059K cells. A DNA-PK specific inhibitor,NU7026,enhanced inhibitory activity of etoposide on M059K as well as on ATL cells. These results suggest that NK314 is a dual inhibitor of Top2α and DNA-PK. Because ATL cells express a high amount of DNA-PKcs,NK314 as a dual molecular targeting anticancer agent is a potential therapeutic tool for treatment of ATL. View Publication