参考文献

The G protein-coupled receptor (GPCR),chemokine CXC-type receptor 4 (CXCR4),and its ligand,CXCL12,mediate the retention of polymorphonuclear neutrophils (PMNs) and hematopoietic stem and progenitor cells (HSPCs) in the bone marrow. Agents that disrupt CXCL12-mediated chemoattraction of CXCR4-expressing cells mobilize PMNs and HSPCs into the peripheral circulation and are therapeutically useful for HSPC collection before autologous bone marrow transplantation (ABMT). Our aim was to develop unique CXCR4-targeted therapeutics using lipopeptide GPCR modulators called pepducins. A pepducin is a synthetic molecule composed of a peptide derived from the amino acid sequence of one of the intracellular (IC) loops of a target GPCR coupled to a lipid tether. We prepared and screened a small CXCR4-targeted pepducin library and identified several pepducins with in vitro agonist activity,including ATI-2341,whose peptide sequence derives from the first IC loop. ATI-2341 induced CXCR4- and G protein-dependent signaling,receptor internalization,and chemotaxis in CXCR4-expressing cells. It also induced dose-dependent peritoneal recruitment of PMNs when administered i.p. to mice. However,when administered systemically by i.v. bolus,ATI-2341 acted as a functional antagonist and dose-dependently mediated release of PMNs from the bone marrow of both mice and cynomolgus monkeys. ATI-2341-mediated release of granulocyte/macrophage progenitor cells from the bone marrow was confirmed by colony-forming assays. We conclude that ATI-2341 is a potent and efficacious mobilizer of bone marrow PMNs and HSPCs and could represent a previously undescribed therapeutic approach for the recruitment of HSPCs before ABMT. View Publication

The molecular basis of CNS myelin regeneration (remyelination) is poorly understood. We generated a comprehensive transcriptional profile of the separate stages of spontaneous remyelination that follow focal demyelination in the rat CNS and found that transcripts that encode the retinoid acid receptor RXR-γ were differentially expressed during remyelination. Cells of the oligodendrocyte lineage expressed RXR-γ in rat tissues that were undergoing remyelination and in active and remyelinated multiple sclerosis lesions. Knockdown of RXR-γ by RNA interference or RXR-specific antagonists severely inhibited oligodendrocyte differentiation in culture. In mice that lacked RXR-γ,adult oligodendrocyte precursor cells efficiently repopulated lesions after demyelination,but showed delayed differentiation into mature oligodendrocytes. Administration of the RXR agonist 9-cis-retinoic acid to demyelinated cerebellar slice cultures and to aged rats after demyelination caused an increase in remyelinated axons. Our results indicate that RXR-γ is a positive regulator of endogenous oligodendrocyte precursor cell differentiation and remyelination and might be a pharmacological target for regenerative therapy in the CNS. View Publication

The mechanisms by which megakaryocytes (MKs) differentiate and release platelets into the circulation are not well understood. However,growing evidence indicates that a complex regulatory mechanism involving MK-matrix interactions may contribute to the quiescent or permissive microenvironment related to platelet release within bone marrow. To address this hypothesis,in this study we demonstrate that human MKs express and synthesize cellular fibronectin (cFN) and transglutaminase factor XIII-A (FXIII-A). We proposed that these 2 molecules are involved in a new regulatory mechanism of MK-type I collagen interaction in the osteoblastic niche. In particular,we demonstrate that MK adhesion to type I collagen promotes MK spreading and inhibits pro-platelet formation through the release and relocation to the plasma membrane of cFN. This regulatory mechanism is dependent on the engagement of FN receptors at the MK plasma membrane and on transglutaminase FXIII-A activity. Consistently,the same mechanism regulated the assembly of plasma FN (pFN) by adherent MKs to type I collagen. In conclusion,our data extend the knowledge of the mechanisms that regulate MK-matrix interactions within the bone marrow environment and could serve as an important step for inquiring into the origins of diseases such as myelofibrosis and congenital thrombocytopenias that are still poorly understood. View Publication

Osteoblasts play a crucial role in the hematopoietic stem cell (HSC) niche; however,an overall increase in their number does not necessarily promote hematopoiesis. Because the activity of osteoblasts and osteoclasts is coordinately regulated,we hypothesized that active bone-resorbing osteoclasts would participate in HSC niche maintenance. Mice treated with bisphosphonates exhibited a decrease in proportion and absolute number of Lin(-)cKit(+)Sca1(+) Flk2(-) (LKS Flk2(-)) and long-term culture-initiating cells in bone marrow (BM). In competitive transplantation assays,the engraftment of treated BM cells was inferior to that of controls,confirming a decrease in HSC numbers. Accordingly,bisphosphonates abolished the HSC increment produced by parathyroid hormone. In contrast,the number of colony-forming-unit cells in BM was increased. Because a larger fraction of LKS in the BM of treated mice was found in the S/M phase of the cell cycle,osteoclast impairment makes a proportion of HSCs enter the cell cycle and differentiate. To prove that HSC impairment was a consequence of niche manipulation,a group of mice was treated with bisphosphonates and then subjected to BM transplantation from untreated donors. Treated recipient mice experienced a delayed hematopoietic recovery compared with untreated controls. Our findings demonstrate that osteoclast function is fundamental in the HSC niche. View Publication

Tissue-specific stem cell (TSC) behavior is determined by the stem cell niche. However,delineation of the TSC-niche interaction requires purification of both entities. We reasoned that the niche could be defined by the location of the TSC. We demonstrate that a single CD49f(bright)/Sca1(+)/ALDH(+) basal cell generates rare label-retaining cells and abundant label-diluting cells. Label-retaining and label-diluting cells were located in the rimmed domain of a unique clone type,the rimmed clone. The TSC property of self-renewal was tested by serial passage at clonal density and analysis of clone-forming cell frequency. A single clone could be passaged up to five times and formed only rimmed clones. Thus,rimmed clone formation was a cell-intrinsic property. Differentiation potential was evaluated in air-liquid interface cultures. Homogenous cultures of rimmed clones were highly mitotic but were refractory to standard differentiation signals. However,rimmed clones that were cocultured with unfractionated tracheal cells generated each of the cell types found in the tracheal epithelium. Thus,the default niche is promitotic: Multipotential differentiation requires adaptation of the niche. Because lung TSCs are typically evaluated after injury,the behavior of CD49f(bright)/Sca1(+)/ALDH(+) cells was tested in normal and naphthalene-treated mice. These cells were mitotically active in the normal and repaired epithelium,their proliferation rate increased in response to injury,and they retained label for 34 days. We conclude that the CD49f(bright)/Sca1(+)/ALDH(+) tracheal basal cell is a TSC,that it generates its own niche in vitro,and that it participates in tracheal epithelial homeostasis and repair. View Publication

Integrins are cell adhesion receptors that mediate cell-to-cell,or cell-to-extracellular matrix adhesion. They represent an attractive target for treatment of multiple diseases. Two classes of small molecule integrin inhibitors have been developed. Competitive antagonists bind directly to the integrin ligand binding pocket and thus disrupt the ligand-receptor interaction. Allosteric antagonists have been developed primarily for α(L)β(2)- integrin (LFA-1,lymphocyte function-associated antigen-1). Here we present the results of screening the Prestwick Chemical Library using a recently developed assay for the detection of α(4)β(1)-integrin allosteric antagonists. Secondary assays confirmed that the compounds identified: 1) do not behave like competitive (direct) antagonists; 2) decrease ligand binding affinity for VLA-4 ∼2 orders of magnitude; 3) exhibit antagonistic properties at low temperature. In a cell based adhesion assay in vitro,the compounds rapidly disrupted cellular aggregates. In accord with reports that VLA-4 antagonists in vivo induce mobilization of hematopoietic progenitors into the peripheral blood,we found that administration of one of the compounds significantly increased the number of colony-forming units in mice. This effect was comparable to AMD3100,a well known progenitor mobilizing agent. Because all the identified compounds are structurally related,previously used,or currently marketed drugs,this result opens a range of therapeutic possibilities for VLA-4-related pathologies. View Publication

Cancer-associated IDH mutations are characterized by neomorphic enzyme activity and resultant 2-hydroxyglutarate (2HG) production. Mutational and epigenetic profiling of a large acute myeloid leukemia (AML) patient cohort revealed that IDH1/2-mutant AMLs display global DNA hypermethylation and a specific hypermethylation signature. Furthermore,expression of 2HG-producing IDH alleles in cells induced global DNA hypermethylation. In the AML cohort,IDH1/2 mutations were mutually exclusive with mutations in the α-ketoglutarate-dependent enzyme TET2,and TET2 loss-of-function mutations were associated with similar epigenetic defects as IDH1/2 mutants. Consistent with these genetic and epigenetic data,expression of IDH mutants impaired TET2 catalytic function in cells. Finally,either expression of mutant IDH1/2 or Tet2 depletion impaired hematopoietic differentiation and increased stem/progenitor cell marker expression,suggesting a shared proleukemogenic effect. View Publication

In the hematopoietic hierarchy,only stem cells are thought to be capable of long-term self-renewal. Erythroid progenitors derived from fetal or adult mammalian hematopoietic tissues are capable of short-term,or restricted (10(2)- to 10(5)-fold),ex vivo expansion in the presence of erythropoietin,stem cell factor,and dexamethasone. Here,we report that primary erythroid precursors derived from early mouse embryos are capable of extensive (10(6)- to 10(60)-fold) ex vivo proliferation. These cells morphologically,immunophenotypically,and functionally resemble proerythroblasts,maintaining both cytokine dependence and the potential,despite prolonged culture,to generate enucleated erythrocytes after 3-4 maturational cell divisions. This capacity for extensive erythroblast self-renewal is temporally associated with the emergence of definitive erythropoiesis in the yolk sac and its transition to the fetal liver. In contrast,hematopoietic stem cell-derived definitive erythropoiesis in the adult is associated almost exclusively with restricted ex vivo self-renewal. Primary primitive erythroid precursors,which lack significant expression of Kit and glucocorticoid receptors,lack ex vivo self-renewal capacity. Extensively self-renewing erythroblasts,despite their near complete maturity within the hematopoietic hierarchy,may ultimately serve as a renewable source of red cells for transfusion therapy. View Publication

Somatic cells can be reprogrammed into induced pluripotent stem (iPS) cells by ectopic expression of four transcription factors. However,the efficiency of human iPS cell generation is extremely low and therefore elucidating the mechanisms underlying cellular reprogramming is of prime importance. We demonstrate that 8-Bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) improves the reprogramming efficiency of human neonatal foreskin fibroblast (HFF1) cells transduced with the four transcription factors by 2-fold. The combination of 8-Br-cAMP and VPA synergistically increases the efficiency to 6.5-fold. The effect of 8-Br-cAMP or VPA may in part be due to the up-regulation of cytokine-related and inflammatory pathways. Remarkably,the synergistic effect of 8-Br-cAMP and VPA on cellular reprogramming may be due to the transient decrease of p53 protein during the early stages of reprogramming. However,it could also be due to additional differentially regulated genes and pathways such as the up-regulation of cytokine-related,inflammatory pathways and self-renewal supporting gene,namely cyclin-encoding CCND2,and the associated genes CCNA1 and CCNE1. Conversely,we also see the down-regulation of the p53 (CCNB2,GTSE1,SERPINE1) and cell cycle (PLK1,CCNB2) pathways. Our data demonstrates that a cyclic AMP analog,8-Br-cAMP,enhances the efficiency of cellular reprogramming. In addition,8-Br-cAMP and VPA have a synergistic effect on cellular reprogramming,which may be in part due to the transient down-regulation of the p53 signaling pathway during the early stages of reprogramming. View Publication

MicroRNA miR-125b has been implicated in several kinds of leukemia. The chromosomal translocation t(2;11)(p21;q23) found in patients with myelodysplasia and acute myeloid leukemia leads to an overexpression of miR-125b of up to 90-fold normal. Moreover,miR-125b is also up-regulated in patients with B-cell acute lymphoblastic leukemia carrying the t(11;14)(q24;q32) translocation. To decipher the presumed oncogenic mechanism of miR-125b,we used transplantation experiments in mice. All mice transplanted with fetal liver cells ectopically expressing miR-125b showed an increase in white blood cell count,in particular in neutrophils and monocytes,associated with a macrocytic anemia. Among these mice,half died of B-cell acute lymphoblastic leukemia,T-cell acute lymphoblastic leukemia,or a myeloproliferative neoplasm,suggesting an important role for miR-125b in early hematopoiesis. Furthermore,coexpression of miR-125b and the BCR-ABL fusion gene in transplanted cells accelerated the development of leukemia in mice,compared with control mice expressing only BCR-ABL,suggesting that miR-125b confers a proliferative advantage to the leukemic cells. Thus,we show that overexpression of miR-125b is sufficient both to shorten the latency of BCR-ABL-induced leukemia and to independently induce leukemia in a mouse model. View Publication