参考文献

In vitro differentiation of embryonic stem cells is tightly regulated by the same key signaling pathways that control pattern formation during embryogenesis. Small molecules that selectively target these developmental pathways,including Wnt,and BMP signaling may be valuable for directing differentiation of pluripotent stem cells toward many desired tissue types,but to date only few such compounds have been shown to promote cardiac differentiation. Here,we show that XAV939,a recently discovered small molecule inhibitor of Wnt/β-catenin signaling,can robustly induce cardiomyogenesis in mouse ES cells. Our results suggest that a timely administration of XAV939 immediately following the formation of mesoderm progenitor cells promotes cardiomyogenic development at the expense of other mesoderm derived lineages,including the endothelial,smooth muscle,and hematopoietic lineages. Given the critical role that Wnt/β-catenin signaling plays in many aspects of embryogenesis and tissue regeneration,XAV939 is a valuable chemical probe to dissect in vitro differentiation of stem cells and to explore their regenerative potential in a variety of contexts. View Publication

To exploit the full potential of human pluripotent stem cells for regenerative medicine,developmental biology and drug discovery,defined culture conditions are needed. Media of known composition that maintain human embryonic stem (hES) cells have been developed,but finding chemically defined,robust substrata has proven difficult. We used an array of self-assembled monolayers to identify peptide surfaces that sustain pluripotent stem cell self-renewal. The effective substrates displayed heparin-binding peptides,which can interact with cell-surface glycosaminoglycans and could be used with a defined medium to culture hES cells for more than 3 months. The resulting cells maintained a normal karyotype and had high levels of pluripotency markers. The peptides supported growth of eight pluripotent cell lines on a variety of scaffolds. Our results indicate that synthetic substrates that recognize cell-surface glycans can facilitate the long-term culture of pluripotent stem cells. View Publication

The ability of hematopoietic stem cells (HSCs) to undergo self-renewal is partly regulated by external signals originating from the stem cell niche. Our previous studies with HSCs obtained from fetal liver of mice deficient for the calcium-sensing receptor (CaR) have shown the crucial role of this receptor in HSC lodgment and engraftment in the bone marrow (BM) endosteal niche. Using a CaR agonist,Cinacalcet,we assessed the effects of stimulating the CaR on the function of murine HSCs. Our results show that CaR stimulation increases primitive hematopoietic cell activity in vitro,including growth in stromal cell cocultures,adhesion to extracellular matrix molecules such as collagen I and fibronectin,and migration toward the chemotactic stimulus,stromal cell-derived factor 1α. Receptor stimulation also led to augmented in vivo homing,CXCR4-mediated lodgment at the endosteal niche,and engraftment capabilities. These mechanisms by which stimulating the CaR dictates preferential localization of HSCs in the BM endosteal niche provide additional insights into the fundamental interrelationship between the stem cell and its niche. These studies also have implications in the area of clinical stem cell transplantation,where ex vivo modulation of the CaR may be envisioned as a strategy to enhance HSC engraftment in the BM. View Publication

Haploinsufficiency for ribosomal protein genes has been implicated in the pathophysiology of Diamond-Blackfan anemia (DBA) and the 5q-syndrome,a subtype of myelodysplastic syndrome. The p53 pathway is activated by ribosome dysfunction,but the molecular basis for selective impairment of the erythroid lineage in disorders of ribosome function has not been determined. We found that p53 accumulates selectively in the erythroid lineage in primary human hematopoietic progenitor cells after expression of shRNAs targeting RPS14,the ribosomal protein gene deleted in the 5q-syndrome,or RPS19,the most commonly mutated gene in DBA. Induction of p53 led to lineage-specific accumulation of p21 and consequent cell cycle arrest in erythroid progenitor cells. Pharmacologic inhibition of p53 rescued the erythroid defect,whereas nutlin-3,a compound that activates p53 through inhibition of HDM2,selectively impaired erythropoiesis. In bone marrow biopsies from patients with DBA or del(5q) myelodysplastic syndrome,we found an accumulation of nuclear p53 staining in erythroid progenitor cells that was not present in control samples. Our findings indicate that the erythroid lineage has a low threshold for the induction of p53,providing a basis for the failure of erythropoiesis in the 5q-syndrome,DBA,and perhaps other bone marrow failure syndromes. View Publication

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia in the United States and globally. Despite the availability of pneumococcal capsular polysaccharide (PPS) and protein conjugate-based vaccines,the prevalence of antibiotic-resistant pneumococcal strains,serotype (ST) replacement in nonconjugate vaccine strains,and uncertainty as to whether the PPS vaccine that is used in adults protects against pneumonia emphasize the need for continued efforts to understand the nature of protective PPS antibody responses. In this study,we generated mouse monoclonal antibodies (MAbs) to a conjugate consisting of the PPS of serotype 8 (PPS8) S. pneumoniae and tetanus toxoid. Thirteen MAbs,including four IgMs that bound to PPS8 and phosphorylcholine (PC) and five IgMs and four IgG1s that bound to PPS8 but not PC,were produced,and their nucleotide sequences,epitope and fine specificity,and efficacy against lethal challenge with ST8 S. pneumoniae were determined. MAbs that bound to PPS8 exhibited gene use that was distinct from that exhibited by MAbs that bound to PC. Only PPS8-binding MAbs that did not bind PC were protective in mice. All 13 MAbs used germ line variable-region heavy (V(H)) and light (V(L)) chain genes,with no evidence of somatic hypermutation. Our data reveal a relationship between PPS specificity and V(H) gene use and MAb efficacy in mice. These findings provide insight into the relationship between antibody molecular structure and function and hold promise for the development of novel surrogates for pneumococcal vaccine efficacy. View Publication

Endocannabinoids are arachidonic acid derivatives and part of a novel bioactive lipid signaling system,along with their G-coupled cannabinoid receptors (CB�? and CB₂) and the enzymes involved in their biosynthesis and degradation. However,their roles in hematopoiesis and hematopoietic stem and progenitor cell (HSPC) functions are not well characterized. Here,we show that bone marrow stromal cells express endocannabinoids (anandamide and 2-arachidonylglycerol),whereas CB₂ receptors are expressed in human and murine HSPCs. On ligand stimulation with CB₂ agonists,CB₂ receptors induced chemotaxis,migration,and enhanced colony formation of bone marrow cells,which were mediated via ERK,PI3-kinase,and Gαi-Rac1 pathways. In vivo,the CB₂ agonist AM1241 induced mobilization of murine HSPCs with short- and long-term repopulating abilities. In addition,granulocyte colony-stimulating factor -induced mobilization of HSPCs was significantly decreased by specific CB₂ antagonists and was impaired in Cnr2(-/-) cannabinoid type 2 receptor knockout mice. Taken together,these results demonstrate that the endocannabinoid system is involved in hematopoiesis and that CB₂/CB₂ agonist axis mediates repopulation of hematopoiesis and mobilization of HSPCs. Thus,CB₂ agonists may be therapeutically applied in clinical conditions,such as bone marrow transplantation. View Publication

Bruton tyrosine kinase (Btk) is essential for B cell development and function and also appears to be important for myeloid cells. The bone marrow of Btk-deficient mice shows enhanced granulopoiesis compared with that of wild-type mice. In purified granulocyte-monocyte-progenitors (GMP) from Btk-deficient mice,the development of granulocytes is favored at the expense of monocytes. However,Btk-deficient neutrophils are impaired in maturation and function. Using bone marrow chimeras,we show that this defect is cell-intrinsic to neutrophils. In GMP and neutrophils,Btk plays a role in GM-CSF- and Toll-like receptor-induced differentiation. Molecular analyses revealed that expression of the lineage-determining transcription factors C/EBPα,C/EBPβ,and PU.1,depends on Btk. In addition,expression of several granule proteins,including myeloperoxidase,neutrophilic granule protein,gelatinase and neutrophil elastase,is Btk-dependent. In the Arthus reaction,an acute inflammatory response,neutrophil migration into tissues,edema formation,and hemorrhage are significantly reduced in Btk-deficient animals. Together,our findings implicate Btk as an important regulator of neutrophilic granulocyte maturation and function in vivo. View Publication

Cancer stem cells (CSC) are rare drug-resistant cancer cell subsets proposed to be responsible for the maintenance and recurrence of cancer and metastasis. Telomerase is constitutively active in both bulk tumor cell and CSC populations but has only limited expression in normal tissues. Thus,inhibition of telomerase has been shown to be a viable approach in controlling cancer growth in nonclinical studies and is currently in phase II clinical trials. In this study,we investigated the effects of imetelstat (GRN163L),a potent telomerase inhibitor,on both the bulk cancer cells and putative CSCs. When breast and pancreatic cancer cell lines were treated with imetelstat in vitro,telomerase activity in the bulk tumor cells and CSC subpopulations were inhibited. Additionally,imetelstat treatment reduced the CSC fractions present in the breast and pancreatic cell lines. In vitro treatment with imetelstat,but not control oligonucleotides,also reduced the proliferation and self-renewal potential of MCF7 mammospheres and resulted in cell death after textless4 weeks of treatment. In vitro treatment of PANC1 cells showed reduced tumor engraftment in nude mice,concomitant with a reduction in the CSC levels. Differences between telomerase activity expression levels or telomere length of CSCs and bulk tumor cells in these cell lines did not correlate with the increased sensitivity of CSCs to imetelstat,suggesting a mechanism of action independent of telomere shortening for the effects of imetelstat on the CSC subpopulations. Our results suggest that imetelstat-mediated depletion of CSCs may offer an alternative mechanism by which telomerase inhibition may be exploited for cancer therapy. View Publication

Head and neck squamous cell carcinoma (HNSCC) is a prevalent cancer worldwide. Signal transducers and activators of transcription 3 (STAT3) signaling is reported to promote tumor malignancy and recurrence in HNSCC. Cucurbitacins,triterpenoid derivatives,are strong STAT3 inhibitors with anticancer properties. Recent studies have shown aldehyde dehydrogenase 1 (ALDH1) to be a marker of cancer stem cells (CSC) in HNSCC. The aim of this study was to investigate the therapeutic effect of cucurbitacin I in HNSCC-derived CSCs. Using immunohistochemical analysis,we firstly showed that CD44,ALDH1,and phosphorylated STAT3 (p-STAT3) were higher in high-grade HNSCCs,and that triple positivity for CD44/ALDH1/p-STAT3 indicated a worse prognosis for HNSCC patients. Secondly,CD44(+)ALDH1(+) cells isolated from seven HNSCC patients showed greater tumorigenicity,radioresistance,and high expression of stemness (Bmi-1/Oct-4/Nanog) and epithelial-mesenchymal-transitional (Snail/Twist) genes as p-STAT3 level increased. Furthermore,we found that cucurbitacin I (JSI-124) can effectively inhibit the expression of p-STAT3 and capacities for tumorigenicity,sphere formation,and radioresistance in HNSCC-CD44(+)ALDH1(+). Notably,150 nmol/L cucurbitacin I effectively blocked STAT3 signaling and downstream survivin and Bcl-2 expression,and it induced apoptosis in HNSCC-CD44(+)ALDH1(+). Moreover,microarray data indicated that 100 nmol/L cucurbitacin I facilitated CD44(+)ALDH1(+) cells to differentiate into CD44�?�ALDH1�?� and enhanced the radiosensitivity of HNSCC-CD44(+)ALDH1(+). Xenotransplant experiments revealed that cucurbitacin I combined with radiotherapy significantly suppressed tumorigenesis and lung metastasis and further improved the survival rate in HNSCC-CD44(+)ALDH1(+)-transplanted immunocompromised mice. Taken together,our data show that cucurbitacin I,STAT3 inhibitor,reduces radioresistant,distant-metastatic,and CSC-like properties of HNSCC-CD44(+)ALDH1(+) cells. The potential of cucurbitacin I as a radiosensitizer should be verified in future anti-CSC therapy. View Publication

Human amniotic fluid cells (AFCs) are routinely obtained for prenatal diagnostics procedures. Recently,it has been illustrated that these cells may also serve as a valuable model system to study developmental processes and for application in regenerative therapies. Cellular reprogramming is a means of assigning greater value to primary AFCs by inducing self-renewal and pluripotency and,thus,bypassing senescence. Here,we report the generation and characterization of human amniotic fluid-derived induced pluripotent stem cells (AFiPSCs) and demonstrate their ability to differentiate into the trophoblast lineage after stimulation with BMP2/BMP4. We further carried out comparative transcriptome analyses of primary human AFCs,AFiPSCs,fibroblast-derived iPSCs (FiPSCs) and embryonic stem cells (ESCs). This revealed that the expression of key senescence-associated genes are down-regulated upon the induction of pluripotency in primary AFCs (AFiPSCs). By defining distinct and overlapping gene expression patterns and deriving the LARGE (Lost,Acquired and Retained Gene Expression) Principle of Cellular Reprogramming,we could further highlight that AFiPSCs,FiPSCs and ESCs share a core self-renewal gene regulatory network driven by OCT4,SOX2 and NANOG. Nevertheless,these cell types are marked by distinct gene expression signatures. For example,expression of the transcription factors,SIX6,EGR2,PKNOX2,HOXD4,HOXD10,DLX5 and RAXL1,known to regulate developmental processes,are retained in AFiPSCs and FiPSCs. Surprisingly,expression of the self-renewal-associated gene PRDM14 or the developmental processes-regulating genes WNT3A and GSC are restricted to ESCs. Implications of this,with respect to the stability of the undifferentiated state and long-term differentiation potential of iPSCs,warrant further studies. View Publication

In hereditary hemochromatosis,mutations in HFE lead to iron overload through abnormally low levels of hepcidin. In addition,HFE potentially modulates cellular iron uptake by interacting with transferrin receptor,a crucial protein during erythropoiesis. However,the role of HFE in this process was never explored. We hypothesize that HFE modulates erythropoiesis by affecting dietary iron absorption and erythroid iron intake. To investigate this,we used Hfe-KO mice in conditions of altered dietary iron and erythropoiesis. We show that Hfe-KO mice can overcome phlebotomy-induced anemia more rapidly than wild-type mice (even when iron loaded). Second,we evaluated mice combining the hemochromatosis and β-thalassemia phenotypes. Our results suggest that lack of Hfe is advantageous in conditions of increased erythropoietic activity because of augmented iron mobilization driven by deficient hepcidin response. Lastly,we demonstrate that Hfe is expressed in erythroid cells and impairs iron uptake,whereas its absence exclusively from the hematopoietic compartment is sufficient to accelerate recovery from phlebotomy. In summary,we demonstrate that Hfe influences erythropoiesis by 2 distinct mechanisms: limiting hepcidin expression under conditions of simultaneous iron overload and stress erythropoiesis,and impairing transferrin-bound iron uptake by erythroid cells. Moreover,our results provide novel suggestions to improve the treatment of hemochromatosis. View Publication

Induced pluripotent stem (iPS) cells have great potential for regenerative medicine and gene therapy. Thus far,iPS cells have typically been generated using integrating viral vectors expressing various reprogramming transcription factors; nonintegrating methods have been less effective and efficient. Because there is a significant risk of malignant transformation and cancer involved with the use of iPS cells,careful evaluation of transplanted iPS cells will be necessary in small and large animal studies before clinical application. Here,we have generated and characterized nonhuman primate iPS cells with the goal of evaluating iPS cell transplantation in a clinically relevant large animal model. We developed stable Phoenix-RD114-based packaging cell lines that produce OCT4,SOX2,c-MYC,and KLF4 (OSCK) expressing gammaretroviral vectors. Using these vectors in combination with small molecules,we were able to efficiently and reproducibly generate nonhuman primate iPS cells from pigtailed macaques (Macaca nemestrina). The established nonhuman primate iPS cells exhibited pluripotency and extensive self-renewal capacity. The facile and reproducible generation of nonhuman primate iPS cells using defined producer cells as a source of individual reprogramming factors should provide an important resource to optimize and evaluate iPS cell technology for studies involving stem cell biology and regenerative medicine. View Publication