技术资料

One of the factors that can impact human embryonic stem cell expansion in stirred microcarrier culture reactors is mechanical stress caused by agitation. Therefore,we have investigated the effects of agitation on human embryonic stem cell growth and expression of pluripotent markers. Agitation of HES-2 cell line in microcarrier cultures in stirred spinner and agitated six-well plates did not affect expression of pluripotent markers,cell viability,and cell doubling times even after seven passages. However,HES-3 cell line was found to be shear sensitive,showing downregulation of three pluripotent markers Oct-4,mAb 84,and Tra-1-60,and lower cell densities in agitated as compared with static cultures,even after one passage. Cell viability was unaffected. The HES-3-agitated cultures showed increased expression of genes and proteins of the three germ layers. We were unable to prevent loss of pluripotent markers or restore doubling times in agitated HES-3 microcarrier cultures by addition of five different known cell protective polymers. In addition,the human induced pluripotent cell line IMR90 was also shown to differentiate in agitated conditions. These results indicate that the effect of agitation on cell growth and differentiation is cell line specific. We assume that the changes in the growth and differentiation of the agitation-sensitive (HES-3) cell line do not result from the effect of shear stress directly on cell viability,but rather by signaling effects that influence the cells to differentiate resulting in slower growth. View Publication

Pluripotent human embryonic stem (hES) cells are an important experimental tool for basic and applied research,and a potential source of different tissues for transplantation. However,one important challenge for the clinical use of these cells is the issue of immunocompatibility,which may be dealt with by the establishment of hES cell banks to attend different populations. Here we describe the derivation and characterization of a line of hES cells from the Brazilian population,named BR-1,in commercial defined medium. In contrast to the other hES cell lines established in defined medium,BR-1 maintained a stable normal karyotype as determined by genomic array analysis after 6 months in continuous culture (passage 29). To our knowledge,this is the first reported line of hES cells derived in South America. We have determined its genomic ancestry and compared the HLA-profile of BR-1 and another 22 hES cell lines established elsewhere with those of the Brazilian population,finding they would match only 0.011% of those individuals. Our results highlight the challenges involved in hES cell banking for populations with a high degree of ethnic admixture. View Publication

Biomaterials are increasingly being used to engineer the biochemical and biophysical properties of the extracellular stem cell microenvironment in order to tailor niche characteristics and direct cell phenotype. To date,stem cell-biomaterial interactions have largely been studied by introducing stem cells into artificial environments,such as 2D cell culture on biomaterial surfaces,encapsulation of cell suspensions within hydrogel materials,or cell seeding on 3D polymeric scaffolds. In this study,microparticles fabricated from different materials,such as agarose,PLGA and gelatin,were stably integrated,in a dose-dependent manner,within aggregates of pluripotent stem cells (PSCs) prior to differentiation as a means to directly examine stem cell-biomaterial interactions in 3D. Interestingly,the presence of the materials within the stem cell aggregates differentially modulated the gene and protein expression patterns of several differentiation markers without adversely affecting cell viability. Microparticle incorporation within 3D stem cell aggregates can control the spatial presentation of extracellular environmental cues (i.e. soluble factors,extracellular matrix and intercellular adhesion molecules) as a means to direct the differentiation of stem cells for tissue engineering and regenerative medicine applications. In addition,these results suggest that the physical presence of microparticles within stem cell aggregates does not compromise PSC differentiation,but in fact the choice of biomaterials can impact the propensity of stem cells to adopt particular differentiated cell phenotypes. View Publication

Induced pluripotent stem (iPS) cells derived from terminally differentiated human fibroblasts are reprogrammed to possess stem cell like properties. However,the extent to which iPS cells exhibit unique properties of the human embryonic stem (hES) cell cycle remains to be established. hES cells are characterized by an abbreviated G1 phase (∼ 2.5 h) and accelerated organization of subnuclear domains that mediate the assembly of regulatory machinery for histone gene expression [i.e.,histone locus bodies (HLBs)]. We therefore examined cell cycle parameters of iPS cells in comparison to hES cells. Analysis of DNA synthesis [5-bromo-2'-deoxy-uridine (BrdU) incorporation],cell cycle distribution (FACS analysis and Ki67 staining) and subnuclear organization of HLBs [immunofluorescence microscopy and fluorescence in situ hybridization (FISH)] revealed that human iPS cells have a short G1 phase (∼ 2.5 h) and an abbreviated cell cycle (16-18 h). Furthermore,HLBs are formed and reorganized rapidly after mitosis (within 1.5-2 h). Thus,reprogrammed iPS cells have cell cycle kinetics and dynamic subnuclear organization of regulatory machinery that are principal properties of pluripotent hES cells. Our findings support the concept that the abbreviated cell cycle of hES and iPS cells is functionally linked to pluripotency. View Publication

BACKGROUND: Induced pluripotent stem (iPS) cells have the capability to undergo self-renewal and differentiation into all somatic cell types. Since they can be produced through somatic cell reprogramming,which uses a defined set of transcription factors,iPS cells represent important sources of patient-specific cells for clinical applications. However,before these cells can be used in therapeutic designs,it is essential to understand their genetic stability. METHODOLOGY/PRINCIPAL FINDINGS: Here,we describe DNA damage responses in human iPS cells. We observe hypersensitivity to DNA damaging agents resulting in rapid induction of apoptosis after γ-irradiation. Expression of pluripotency factors does not appear to be diminished after irradiation in iPS cells. Following irradiation,iPS cells activate checkpoint signaling,evidenced by phosphorylation of ATM,NBS1,CHEK2,and TP53,localization of ATM to the double strand breaks (DSB),and localization of TP53 to the nucleus of NANOG-positive cells. We demonstrate that iPS cells temporary arrest cell cycle progression in the G(2) phase of the cell cycle,displaying a lack of the G(1)/S cell cycle arrest similar to human embryonic stem (ES) cells. Furthermore,both cell types remove DSB within six hours of γ-irradiation,form RAD51 foci and exhibit sister chromatid exchanges suggesting homologous recombination repair. Finally,we report elevated expression of genes involved in DNA damage signaling,checkpoint function,and repair of various types of DNA lesions in ES and iPS cells relative to their differentiated counterparts. CONCLUSIONS/SIGNIFICANCE: High degrees of similarity in DNA damage responses between ES and iPS cells were found. Even though reprogramming did not alter checkpoint signaling following DNA damage,dramatic changes in cell cycle structure,including a high percentage of cells in the S phase,increased radiosensitivity and loss of DNA damage-induced G(1)/S cell cycle arrest,were observed in stem cells generated by induced pluripotency. View Publication

Large scale purification of endothelial cells is of great interest as it could improve tissue transplantation,reperfusion of ischemic tissues and treatment of pathologies in which an endothelial cell dysfunction exists. In this study,we describe a novel genetic approach that selects for endothelial cells from differentiating embryonic stem (ES) cells. Our strategy is based on the establishment of ES-cell clones that carry an integrated puromycin resistance gene under the control of a vascular endothelium-specific promoter,tie-1. Using EGFP as a reporter gene,we first confirmed the endothelial specificity of the tie-1 promoter in the embryoid body model and in cells differentiated in 2D cultures. Subsequently,tie-1-EGFP ES cells were used as recipients for the tie-1-driven puror transgene. The resulting stable clones were expanded and differentiated for seven days in the presence of VEGF before puromycin selection. As expected,puromycin-resistant cells were positive for EGFP and also expressed several endothelial markers,including CD31,CD34,VEGFR-1,VEGFR-2,Tie-1,VE-cadherin and ICAM-2. Release from the puromycin selection resulted in the appearance of alpha-smooth muscle actin-positive cells. Such cells became more numerous when the population was cultured on laminin-1 or in the presence of TGF-beta1,two known inducers of smooth muscle cell differentiation. The hypothesis that endothelial cells or their progenitors may differentiate towards a smooth muscle cell phenotype was further supported by the presence of cells expressing both CD31 and alpha-smooth muscle actin markers. Finally,we show that purified endothelial cells can incorporate into the neovasculature of transplanted tumors in nude mice. Taken together,these results suggest that application of endothelial lineage selection to differentiating ES cells may become a useful approach for future pro-angiogenic and endothelial cell replacement therapies. View Publication

Human stem cells derived from human fertilized oocytes,fetal primordial germ cells,umbilical cord blood,and adult tissues provide potential cell-based therapies for repair of degenerating or damaged tissues. However,the diversity of major histocompatibility complex (MHC) antigens in the general population and the resultant risk of immune-mediated rejection complicates the allogenic use of established stem cells. We assessed an alternative approach,employing chemical activation of nonfertilized metaphase II oocytes for producing stem cells homozygous for MHC. By using F1 hybrid mice (H-2-B/D),we established stem cell lines homozygous for H-2-B and H-2-D,respectively. The undifferentiated cells retained a normal karyotype,expressed stage-specific embryonic antigen-1 and Oct4,and were positive for alkaline phosphatase and telomerase. Teratomatous growth of these cells displayed the development of a variety of tissue types encompassing all three germ layers. In addition,these cells demonstrated the potential for in vitro differentiation into endoderm,neuronal,and hematopoietic lineages. We also evaluated this homozygous stem cell approach in human tissue. Five unfertilized blastocysts were derived from a total of 25 human oocytes,and cells from one of the five hatched blastocysts proliferated and survived beyond two passages. Our studies demonstrate a plausible homozygous stem cell" approach for deriving pluripotent stem cells that can overcome the immune-mediated rejection response common in allotransplantation� View Publication

Experimental evidence indicates that shear stress (SS) exerts a morphogenetic function during cardiac development of mouse and zebrafish embryos. However,the molecular basis for this effect is still elusive. Our previous work described that in adult endothelial cells,SS regulates gene expression by inducing epigenetic modification of histones and activation of transcription complexes bearing acetyltransferase activity. In this study,we evaluated whether SS treatment could epigenetically modify histones and influence cell differentiation in mouse embryonic stem (ES) cells. Cells were exposed to a laminar SS of 10 dyne per cm2/s(-1),or kept in static conditions in the presence or absence of the histone deacetylase inhibitor trichostatin A (TSA). These experiments revealed that SS enhanced lysine acetylation of histone H3 at position 14 (K14),as well as serine phosphorylation at position 10 (S10) and lysine methylation at position 79 (K79),and cooperated with TSA,inducing acetylation of histone H4 and phosphoacetylation of S10 and K14 of histone H3. In addition,ES cells exposed to SS strongly activated transcription from the vascular endothelial growth factor (VEGF) receptor 2 promoter. This effect was paralleled by an early induction of cardiovascular markers,including smooth muscle actin,smooth muscle protein 22-alpha,platelet-endothelial cell adhesion molecule-1,VEGF receptor 2,myocyte enhancer factor-2C (MEF2C),and alpha-sarcomeric actin. In this condition,transcription factors MEF2C and Sma/MAD homolog protein 4 could be isolated from SS-treated ES cells complexed with the cAMP response element-binding protein acetyltransferase. These results provide molecular basis for the SS-dependent cardiovascular commitment of mouse ES cells and suggest that laminar flow may be successfully applied for the in vitro production of cardiovascular precursors. View Publication

Global gene expression profiling was performed on murine embryonic stem cells (ESCs) induced to differentiate by removal of leukemia inhibitory factor (LIF) to identify genes whose change in expression correlates with loss of pluripotency. To identify appropriate time points for the gene expression analysis,the dynamics of loss of pluripotency were investigated using three functional assays: chimeric mouse formation,embryoid body generation,and colony-forming ability. A rapid loss of pluripotency was detected within 24 hours,with very low residual activity in all assays by 72 hours. Gene expression profiles of undifferentiated ESCs and ESCs cultured for 18 and 72 hours in the absence of LIF were determined using the Affymetrix GeneChip U74v2. In total,473 genes were identified as significantly differentially expressed,with approximately one third having unknown biological function. Among the 275 genes whose expression decreased with ESC differentiation were several factors previously identified as important for,or markers of,ESC pluripotency,including Stat3,Rex1,Sox2,Gbx2,and Bmp4. A significant number of the decreased genes also overlap with previously published mouse and human ESC data. Furthermore,several membrane proteins were among the 48 decreased genes correlating most closely with the functional assays,including the stem cell factor receptor c-Kit. Through identification of genes whose expression closely follows functional properties of ESCs during early differentiation,this study lays the foundation for further elucidating the molecular mechanisms regulating the maintenance of ESC pluripotency and facilitates the identification of more reliable molecular markers of the undifferentiated state. View Publication