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Thrombocytopenia is a critical problem that occurs in many hematologic diseases,as well as after cancer therapy and radiation exposure. Platelet transfusion is the most commonly used therapy but has limitations of alloimmunization,availability,and expense. Thus,the development of safe,small,molecules to enhance platelet production would be advantageous for the treatment of thrombocytopenia. Herein,we report that an important lipid mediator and a peroxisome proliferator-activated receptor gamma (PPARgamma) ligand called 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)),increases Meg-01 maturation and platelet production. 15d-PGJ(2) also promotes platelet formation from culture-derived mouse and human megakaryocytes and accelerates platelet recovery after in vivo radiation-induced bone marrow injury. Interestingly,the platelet-enhancing effects of 15d-PGJ(2) in Meg-01 cells are independent of PPARgamma,but dependent on reactive oxygen species (ROS) accumulation; treatment with antioxidants such as glutathione ethyl ester (GSH-EE); or N-acetylcysteine (NAC) attenuate 15d-PGJ(2)-induced platelet production. Collectively,these data support the concept that megakaryocyte redox status plays an important role in platelet generation and that small electrophilic molecules may have clinical efficacy for improving platelet numbers in thrombocytopenic patients. View Publication

Overexpression of high mobility group AT-hook 2 (HMGA2) is found in a number of benign and malignant tumors,including the clonal PIGA(-) cells in 2 cases of paroxysmal nocturnal hemoglobinuria (PNH) and some myeloproliferative neoplasms (MPNs),and recently in hematopoietic cell clones resulting from gene therapy procedures. In nearly all these cases overexpression is because of deletions or translocations that remove the 3' untranslated region (UTR) which contains binding sites for the regulatory micro RNA let-7. We were therefore interested in the effect of HMGA2 overexpression in hematopoietic tissues in transgenic mice (ΔHmga2 mice) carrying a 3'UTR-truncated Hmga2 cDNA. ΔHmga2 mice expressed increased levels of HMGA2 protein in various tissues including hematopoietic cells and showed proliferative hematopoiesis with increased numbers in all lineages of peripheral blood cells,hypercellular bone marrow (BM),splenomegaly with extramedullary erythropoiesis and erythropoietin-independent erythroid colony formation. ΔHmga2-derived BM cells had a growth advantage over wild-type cells in competitive repopulation and serial transplantation experiments. Thus overexpression of HMGA2 leads to proliferative hematopoiesis with clonal expansion at the stem cell and progenitor levels and may account for the clonal expansion in PNH and MPNs and in gene therapy patients after vector insertion disrupts the HMGA2 locus. View Publication

BACKGROUND Human embryonic stem cells (hESCs) have been derived and maintained on mouse embryonic fibroblast feeders to keep their undifferentiated status. To realize their clinical potential,a feeder-free and scalable system for large scale production of hESCs and their differentiated derivatives is required. MATERIALS & METHODS hESCs were cultured and passaged on serum/feeder-free 3D microcarriers for five passages. For embryoid body (EB) formation and hemangioblast differentiation,the medium for 3D microcarriers was directly switched to EB medium. RESULTS hESCs on 3D microcarriers maintained pluripotency and formed EBs,which were ten-times more efficient than hESCs cultured under 2D feeder-free conditions (0.11 ± 0.03 EB cells/hESC input 2D vs 1.19 ± 0.32 EB cells/hESC input 3D). After replating,EB cells from 3D culture readily developed into hemangioblasts with the potential to differentiate into hematopoietic and endothelial cells. Furthermore,this 3D system can also be adapted to human induced pluripotent stem cells,which generate functional hemangioblasts with high efficiency. CONCLUSION This 3D serum- and stromal-free microcarrier system is important for future clinical applications,with the potential of developing to a GMP-compatible scalable system. View Publication

SHP2,a cytoplasmic protein-tyrosine phosphatase encoded by the PTPN11 gene,plays a critical role in developmental hematopoiesis in the mouse,and gain-of-function mutations of SHP2 are associated with hematopoietic malignancies. However,the role of SHP2 in adult hematopoiesis has not been addressed in previous studies. In addition,the role of SHP2 in human hematopoiesis has not been described. These questions are of considerable importance given the interest in development of SHP2 inhibitors for cancer treatment. We used shRNA-mediated inhibition of SHP2 expression to investigate the function of SHP2 in growth factor (GF) signaling in normal human CD34(+) cells. SHP2 knockdown resulted in markedly reduced proliferation and survival of cells cultured with GF,and reduced colony-forming cell growth. Cells expressing gain-of-function SHP2 mutations demonstrated increased dependency on SHP2 expression for survival compared with cells expressing wild-type SHP2. SHP2 knockdown was associated with significantly reduced myeloid and erythroid differentiation with retention of CD34(+) progenitors with enhanced proliferative capacity. Inhibition of SHP2 expression initially enhanced and later inhibited STAT5 phosphorylation and reduced expression of the antiapoptotic genes MCL1 and BCLXL. These results indicate an important role for SHP2 in STAT5 activation and GF-mediated proliferation,survival,and differentiation of human progenitor cells. View Publication

The pathogenesis of malarial anemia is multifactorial,and the mechanisms responsible for its high mortality are poorly understood. Studies indicate that host mediators produced during malaria infection may suppress erythroid progenitor development (Miller,K.L.,J.C. Schooley,K.L. Smith,B. Kullgren,L.J. Mahlmann,and P.H. Silverman. 1989. Exp. Hematol. 17:379-385; Yap,G.S.,and M.M. Stevenson. 1991. Ann. NY Acad. Sci. 628:279-281). We describe an intrinsic role for macrophage migration inhibitory factor (MIF) in the development of the anemic complications and bone marrow suppression that are associated with malaria infection. At concentrations found in the circulation of malaria-infected patients,MIF suppressed erythropoietin-dependent erythroid colony formation. MIF synergized with tumor necrosis factor and gamma interferon,which are known antagonists of hematopoiesis,even when these cytokines were present in subinhibitory concentrations. MIF inhibited erythroid differentiation and hemoglobin production,and it antagonized the pattern of mitogen-activated protein kinase phosphorylation that normally occurs during erythroid progenitor differentiation. Infection of MIF knockout mice with Plasmodium chabaudi resulted in less severe anemia,improved erythroid progenitor development,and increased survival compared with wild-type controls. We also found that human mononuclear cells carrying highly expressed MIF alleles produced more MIF when stimulated with the malarial product hemozoin compared with cells carrying low expression MIF alleles. These data suggest that polymorphisms at the MIF locus may influence the levels of MIF produced in the innate response to malaria infection and the likelihood of anemic complications. View Publication

Although aldehyde dehydrogenase (ALDH) activity has become a surrogate of hematopoietic stem and progenitor cells (HSPCs),its function during hematopoiesis was unclear. Here,we examined its role in zebrafish hematopoiesis based on pharmacological inhibition and morpholino (MO) knockdown. Zebrafish embryos were treated with diethylaminobenzaldehyde (DEAB,1 μmol/l) between 0- and 48 hour-post-fertilization (hpf). MOs targeting aldhs were injected between 1 and 4-cell stage. The effects on hematopoiesis were evaluated at different stages. DEAB treatment between 0 and 18 hpf increased gene expression associated with HSPC (scl,lmo2),erythropoiesis (gata1,α- and β-eHb) and myelopoiesis (spi1) as well as gfp(+) cells in dissociated Tg(gata1:gfp) embryos. The effects were ameliorated by all-trans retinoic acid (1 nmol/l). Definitive hematopoiesis and the erythromyeloid precursors were unaffected. In all,14 out of 15 zebrafish aldhs were detectable by reverse transcription PCR in 18 hpf embryos,of which only aldh1a2 and aldh16a1 were expressed in sites pertinent to hematopoiesis. Molecular targeting by MOs was demonstrated for 15 aldhs,but none of them,even in combined aldh1a2 and aldh1a3 knockdown,recapitulated the hematopoietic expansion in DEAB-treated embryos. In conclusion,DEAB expands HSPC population during primitive hematopoiesis through inhibition of aldh and retinoic acid synthesis. The specific aldh isoform(s) remains to be determined. View Publication

A defect in cell trafficking and chemotaxis plays an important role in the immune deficiency observed in Wiskott-Aldrich syndrome (WAS). In this report,we show that marrow cells from WAS protein (WASP)-deficient mice also have a defect in chemotaxis. Serial transplantation and competitive reconstitution experiments demonstrated that marrow cells,including hematopoietic progenitors and stem cells (HSCs),have decreased homing capacities that were associated with a defect in adhesion to collagen. During development,HSCs migrate from the liver to the marrow and the spleen,prompting us to ask if a defect in HSC homing during development may explain the skewed X-chromosome inactivation in WAS carriers. Preliminary evidence has shown that,in contrast to marrow progenitor cells,fetal liver progenitor cells from heterozygous females had a random X-chromosome inactivation. When fetal liver cells from WASP-carrier females were injected into irradiated recipients,a nonrandom inactivation of the X-chromosome was found at the level of hematopoietic progenitors and HSCs responsible for the short- and long-term hematopoietic reconstitution. Therefore,the mechanism of the skewed X-chromosomal inactivation observed in WAS carriers may be related to a migration defect of WASP-deficient HSCs. View Publication

The CCAAT/enhancer binding protein alpha (C/EBPalpha) is an essential transcription factor for granulocytic differentiation. C/EBPalpha mutations are found in approximately 8% of acute myeloid leukemia (AML) patients. Most of these mutations occur in the N-terminal coding region,resulting in a frame shift and the enhanced translation of a dominant-negative 30-kDa protein,which may be responsible for the differentiation block observed in AML. To test this hypothesis,we introduced a cDNA encoding an N-terminal mutated C/EBPalpha (mut10) into primary hematopoietic progenitors using a retroviral vector. Expression of mut10 in human CD34+ cord blood cells dramatically inhibited differentiation of both myeloid and erythroid lineages. Immunohistochemical analysis demonstrated coexpression of both myeloid and erythroid markers in the immature transformed cells. Surprisingly,mut10 did not block myelocytic differentiation in murine progenitors but did alter their differentiation kinetics and clonogenicity. Experiments were performed to confirm that the differential effect of mut10 on murine and human progenitors was not due to species-specific differences in C/EBPalpha protein sequences,expression levels,or inefficient targeting of relevant cells. Taken together,our results underline the intrinsic differences between hematopoietic controls in mouse and human and support the hypothesis that mutations in CEBPA are critical events in the disruption of myeloid differentiation in AMLs. View Publication

The Sox6 transcription factor plays critical roles in various cell types,including erythroid cells. Sox6-deficient mice are anemic due to impaired red cell maturation and show inappropriate globin gene expression in definitive erythrocytes. To identify new Sox6 target genes in erythroid cells,we used the known repressive double Sox6 consensus within the εy-globin promoter to perform a bioinformatic genome-wide search for similar,evolutionarily conserved motifs located within genes whose expression changes during erythropoiesis. We found a highly conserved Sox6 consensus within the Sox6 human gene promoter itself. This sequence is bound by Sox6 in vitro and in vivo,and mediates transcriptional repression in transient transfections in human erythroleukemic K562 cells and in primary erythroblasts. The binding of a lentiviral transduced Sox6FLAG protein to the endogenous Sox6 promoter is accompanied,in erythroid cells,by strong downregulation of the endogenous Sox6 transcript and by decreased in vivo chromatin accessibility of this region to the PstI restriction enzyme. These observations suggest that the negative Sox6 autoregulation,mediated by the double Sox6 binding site within its own promoter,may be relevant to control the Sox6 transcriptional downregulation that we observe in human erythroid cultures and in mouse bone marrow cells in late erythroid maturation. View Publication

Transforming growth factor-beta1 (TGF-beta1) is a pleiotropic cytokine with major in vitro effects on hematopoietic stem cells (HSCs) and lymphocyte development. Little is known about hematopoiesis from mice with constitutive TGF-beta1 inactivation largely because of important embryonic lethality and development of a lethal inflammatory disorder in TGF-beta1(-/-) pups,making these studies difficult. Here,we show that no sign of the inflammatory disorder was detectable in 8- to 10-day-old TGF-beta1(-/-) neonates as judged by both the number of T-activated and T-regulator cells in secondary lymphoid organs and the level of inflammatory cytokines in sera. After T-cell depletion,the inflammatory disease was not transplantable in recipient mice. Bone marrow cells from 8- to 10-day-old TGF-beta1(-/-) neonates showed strikingly impaired short- and long-term reconstitutive activity associated with a parallel decreased in vivo homing capacity of lineage negative (Lin(-)) cells. In addition an in vitro-reduced survival of immature progenitors (Lin(-) Kit(+) Sca(+)) was observed. Similar defects were found in liver cells from TGF-beta1(-/-) embryos on day 14 after vaginal plug. These data indicate that TGF-beta1 is a critical regulator for in vivo homeostasis of the HSCs,especially for their homing potential. View Publication

The 2 most frequent human MLL hematopoietic malignancies involve either AF4 or AF9 as fusion partners; each has distinct biology but the role of the fusion partner is not clear. We produced Mll-AF4 knock-in (KI) mice by homologous recombination in embryonic stem cells and compared them with Mll-AF9 KI mice. Young Mll-AF4 mice had lymphoid and myeloid deregulation manifest by increased lymphoid and myeloid cells in hematopoietic organs. In vitro,bone marrow cells from young mice formed unique mixed pro-B lymphoid (B220(+)CD19(+)CD43(+)sIgM(-),PAX5(+),TdT(+),IgH rearranged)/myeloid (CD11b/Mac1(+),c-fms(+),lysozyme(+)) colonies when grown in IL-7- and Flt3 ligand-containing media. Mixed lymphoid/myeloid hyperplasia and hematologic malignancies (most frequently B-cell lymphomas) developed in Mll-AF4 mice after prolonged latency; long latency to malignancy indicates that Mll-AF4-induced lymphoid/myeloid deregulation alone is insufficient to produce malignancy. In contrast,young Mll-AF9 mice had predominately myeloid deregulation in vivo and in vitro and developed myeloid malignancies. The early onset of distinct mixed lymphoid/myeloid lineage deregulation in Mll-AF4 mice shows evidence for both instructive" and "noninstructive" roles for AF4 and AF9 as partners in MLL fusion genes. The molecular basis for "instruction" and secondary cooperating mutations can now be studied in our Mll-AF4 model." View Publication