参考文献

BACKGROUND: Human embryonic stem cells (hESCs) are a potentially inexhaustible source of cells for replacement therapy. However,successful preclinical and clinical progress requires efficient and controlled differentiation towards the specific differentiated cell fate. METHODS: We previously developed a strategy to generate blast cells (BCs) from hESCs that were capable of differentiating into vascular structures as well as into all hematopoietic cell lineages. Although the BCs were shown to repair damaged vasculature in multiple animal models,the large-scale generation of cells under these conditions was challenging. Here we report a simpler and more efficient method for robust generation of hemangioblastic progenitors. RESULTS: In addition to eliminating several expensive factors that are unnecessary,we demonstrate that bone morphogenetic protein (BMP)-4 and VEGF are necessary and sufficient to induce hemangioblastic commitment and development from hESCs during early stages of differentiation. BMP-4 and VEGF significantly upregulate T-brachyury,KDR,CD31 and Lmo2 gene expression,while dramatically downregulating Oct-4 expression. The addition of basic FGF during growth and expansion was found to further enhance BC development,consistently generating approximately 1 x 10(8) BCs from one six well plate of hESCs. CONCLUSION: This new method represents a significantly improved system for generating hemangioblasts from hESCs,and although simplified,results in an eightfold increase in cell yield. View Publication

Given their self-renewing and pluripotent capabilities,human embryonic stem cells (hESCs) are well poised as a cellular source for tissue regeneration therapy. However,the host immune response against transplanted hESCs is not well characterized. In fact,controversy remains as to whether hESCs have immune-privileged properties. To address this issue,we used in vivo bioluminescent imaging to track the fate of transplanted hESCs stably transduced with a double-fusion reporter gene consisting of firefly luciferase and enhanced GFP. We show that survival after transplant is significantly limited in immunocompetent as opposed to immunodeficient mice. Repeated transplantation of hESCs into immunocompetent hosts results in accelerated hESC death,suggesting an adaptive donor-specific immune response. Our data demonstrate that transplanted hESCs trigger robust cellular and humoral immune responses,resulting in intragraft infiltration of inflammatory cells and subsequent hESC rejection. Moreover,we have found CD4(+) T cells to be an important modulator of hESC immune-mediated rejection. Finally,we show that immunosuppressive drug regimens can mitigate the anti-hESC immune response and that a regimen of combined tacrolimus and sirolimus therapies significantly prolongs survival of hESCs for up to 28 days. Taken together,these data suggest that hESCs are immunogenic,trigger both cellular and humoral-mediated pathways,and,as a result,are rapidly rejected in xenogeneic hosts. This process can be mitigated by a combined immunosuppressive regimen as assessed by molecular imaging approaches. View Publication

BACKGROUND: Embryonic stem (ES) cells self-renew as coherent colonies in which cells maintain tight cell-cell contact. Although intercellular communications are essential to establish the basis of cell-specific identity,molecular mechanisms underlying intrinsic cell-cell interactions in ES cells at the signaling level remain underexplored.backslashnbackslashnMETHODOLOGY/PRINCIPAL FINDINGS: Here we show that endogenous Rho signaling is required for the maintenance of cell-cell contacts in ES cells. siRNA-mediated loss of function experiments demonstrated that Rock,a major effector kinase downstream of Rho,played a key role in the formation of cell-cell junctional assemblies through regulation of myosin II by controlling a myosin light chain phosphatase. Chemical engineering of this signaling axis by a Rock-specific inhibitor revealed that cell-cell adhesion was reversibly controllable and dispensable for self-renewal of mouse ES cells as confirmed by chimera assay. Furthermore,a novel culture system combining a single synthetic matrix,defined medium,and the Rock inhibitor fully warranted human ES cell self-renewal independent of animal-derived matrices,tight cell contacts,or fibroblastic niche-forming cells as determined by teratoma formation assay.backslashnbackslashnCONCLUSIONS/SIGNIFICANCE: These findings demonstrate an essential role of the Rho-Rock-Myosin signaling axis for the regulation of basic cell-cell communications in both mouse and human ES cells,and would contribute to advance in medically compatible xeno-free environments for human pluripotent stem cells. View Publication

Some cases of pre-B cell acute lymphoblastic leukemia (pre-B-ALL) are caused by the Philadelphia (Ph) chromosome-encoded BCR-ABL oncogene,and these tend to have a poor prognosis. Inhibitors of the PI3K/AKT pathway reduce BCR-ABL-mediated transformation in vitro; however,the specific PI3K isoforms involved are poorly defined. Using a murine model of Ph+ pre-B-ALL,we found that deletion of both Pik3r1 and Pik3r2,genes encoding class IA PI3K regulatory isoforms,severely impaired transformation. BCR-ABL-dependent pre/pro-B cell lines could be established at low frequency from progenitors that lacked these genes,but the cells were smaller,proliferated more slowly,and failed to cause leukemia in vivo. These cell lines displayed nearly undetectable PI3K signaling function and were resistant to the PI3K inhibitor wortmannin. However,they maintained activation of mammalian target of rapamycin (mTOR) and were more sensitive to rapamycin. Treatment with rapamycin caused feedback activation of AKT in WT cell lines but not PI3K-deficient lines. A dual inhibitor of PI3K and mTOR,PI-103,was more effective than rapamycin at suppressing proliferation of mouse pre-B-ALL and human CD19+CD34+)Ph+ ALL leukemia cells treated with the ABL kinase inhibitor imatinib. Our findings provide mechanistic insights into PI3K dependency in oncogenic networks and provide a rationale for targeting class IA PI3K,alone or together with mTOR,in the treatment of Ph+ ALL. View Publication

Self-renewal of human embryonic stem cells (ESCs) is promoted by FGF and TGFbeta/Activin signaling,and differentiation is promoted by BMP signaling,but how these signals regulate genes critical to the maintenance of pluripotency has been unclear. Using a defined medium,we show here that both TGFbeta and FGF signals synergize to inhibit BMP signaling; sustain expression of pluripotency-associated genes such as NANOG,OCT4,and SOX2; and promote long-term undifferentiated proliferation of human ESCs. We also show that both TGFbeta- and BMP-responsive SMADs can bind with the NANOG proximal promoter. NANOG promoter activity is enhanced by TGFbeta/Activin and FGF signaling and is decreased by BMP signaling. Mutation of putative SMAD binding elements reduces NANOG promoter activity to basal levels and makes NANOG unresponsive to BMP and TGFbeta signaling. These results suggest that direct binding of TGFbeta/Activin-responsive SMADs to the NANOG promoter plays an essential role in sustaining human ESC self-renewal. View Publication

BACKGROUND: Methylation of CpG dinucleotides is a fundamental mechanism of epigenetic regulation in eukaryotic genomes. Development of methods for rapid genome wide methylation profiling will greatly facilitate both hypothesis and discovery driven research in the field of epigenetics. In this regard,a single molecule approach to methylation profiling offers several unique advantages that include elimination of chemical DNA modification steps and PCR amplification. RESULTS: A single molecule approach is presented for the discernment of methylation profiles,based on optical mapping. We report results from a series of pilot studies demonstrating the capabilities of optical mapping as a platform for methylation profiling of whole genomes. Optical mapping was used to discern the methylation profile from both an engineered and wild type Escherichia coli. Furthermore,the methylation status of selected loci within the genome of human embryonic stem cells was profiled using optical mapping. CONCLUSION: The optical mapping platform effectively detects DNA methylation patterns. Due to single molecule detection,optical mapping offers significant advantages over other technologies. This advantage stems from obviation of DNA modification steps,such as bisulfite treatment,and the ability of the platform to assay repeat dense regions within mammalian genomes inaccessible to techniques using array-hybridization technologies. View Publication

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation,we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells,cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid,B-lymphoid,and erythroid lineages,but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization,which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice. View Publication

Mouse embryonic stem (mES) cells will give rise to all of the cells of the adult mouse,but they failed to rejoin half of the DNA double-strand breaks (dsb) produced by high doses of ionizing radiation. A deficiency in DNA-PK(cs) appears to be responsible since mES cells expressed textless10% of the level of mouse embryo fibroblasts (MEFs) although Ku70/80 protein levels were higher than MEFs. However,the low level of DNA-PK(cs) found in wild-type cells appeared sufficient to allow rejoining of dsb after doses textless20Gy even in G1 phase cells. Inhibition of DNA-PK(cs) with wortmannin and NU7026 still sensitized mES cells to radiation confirming the importance of the residual DNA-PK(cs) at low doses. In contrast to wild-type cells,mES cells lacking H2AX,a histone protein involved in the DNA damage response,were radiosensitive but they rejoined double-strand breaks more rapidly. Consistent with more rapid dsb rejoining,H2AX(-/-) mES cells also expressed 6 times more DNA-PK(cs) than wild-type mES cells. Similar results were obtained for ATM(-/-) mES cells. Differentiation of mES cells led to an increase in DNA-PK(cs),an increase in dsb rejoining rate,and a decrease in Ku70/80. Unlike mouse ES,human ES cells were proficient in rejoining of dsb and expressed high levels of DNA-PK(cs). These results confirm the importance of homologous recombination in the accurate repair of double-strand breaks in mES cells,they help explain the chromosome abnormalities associated with deficiencies in H2AX and ATM,and they add to the growing list of differences in the way rodent and human cells deal with DNA damage. View Publication

Defined growth conditions are essential for many applications of human embryonic stem cells (hESC). Most defined media are presently used in combination with Matrigel,a partially defined extracellular matrix (ECM) extract from mouse sarcoma. Here,we defined ECM requirements of hESC by analyzing integrin expression and ECM production and determined integrin function using blocking antibodies. hESC expressed all major ECM proteins and corresponding integrins. We then systematically replaced Matrigel with defined medium supplements and ECM proteins. Cells attached efficiently to natural human vitronectin,fibronectin,and Matrigel but poorly to laminin + entactin and collagen IV. Integrin-blocking antibodies demonstrated that alphaVbeta5 integrins mediated adhesion to vitronectin,alpha5beta1 mediated adhesion to fibronectin,and alpha6beta1 mediated adhesion to laminin + entactin. Fibronectin in feeder cell-conditioned medium partially supported growth on all natural matrices,but in defined,nonconditioned medium only Matrigel or (natural and recombinant) vitronectin was effective. Recombinant vitronectin was the only defined functional alternative to Matrigel,supporting sustained self-renewal and pluripotency in three independent hESC lines. View Publication

Mature mammary epithelial cells are generated from undifferentiated precursors through a hierarchical process,but the molecular mechanisms involved,particularly in the human mammary gland,are poorly understood. To address this issue,we isolated highly purified subpopulations of primitive bipotent and committed luminal progenitor cells as well as mature luminal and myoepithelial cells from normal human mammary tissue and compared their transcriptomes obtained using three different methods. Elements unique to each subset of mammary cells were identified,and changes that accompany their differentiation in vivo were shown to be recapitulated in vitro. These include a stage-specific change in NOTCH pathway gene expression during the commitment of bipotent progenitors to the luminal lineage. Functional studies further showed NOTCH3 signaling to be critical for this differentiation event to occur in vitro. Taken together,these findings provide an initial foundation for future delineation of mechanisms that perturb primitive human mammary cell growth and differentiation. View Publication