技术资料

The recent development of porcine induced pluripotent stem cells (piPSCs) capable of generating chimeric animals,a feat not previously accomplished with embryonic stem cells or iPSCs in a species outside of rodents,has opened the doors for in-depth study of iPSC tumorigenicity,autologous transplantation,and other key aspects to safely move iPSC therapies to the clinic. The study of iPSC tumorigenicity is critical as previous research in the mouse showed that iPSC-derived chimeras possessed large numbers of tumors,rising significant concerns about the safety of iPSC therapies. Additionally,piPSCs capable of generating germline chimeras could revolutionize the transgenic animal field by enabling complex genetic manipulations (e.g.,knockout or knockin of genes) to produce biomedically important large animal models or improve livestock production. In this study,we demonstrate for the first time in a nonrodent species germline transmission of iPSCs with the live birth of a transgenic piglet that possessed genome integration of the human POU5F1 and NANOG genes. In addition,gross and histological examination of necropsied porcine chimeras at 2,7,and 9 months showed that these animals lacked tumor formation and demonstrated normal development. Tissue samples positive for human POU5F1 DNA showed no C-MYC gene expression,further implicating C-MYC as a cause of tumorigenicity. The development of germline-competent porcine iPSCs that do not produce tumors in young chimeric animals presents an attractive and powerful translational model to study the efficacy and safety of stem cell therapies and perhaps to efficiently produce complex transgenic animals. View Publication

Metabolism is vital to every aspect of cell function,yet the metabolome of induced pluripotent stem cells (iPSCs) remains largely unexplored. Here we report,using an untargeted metabolomics approach,that human iPSCs share a pluripotent metabolomic signature with embryonic stem cells (ESCs) that is distinct from their parental cells,and that is characterized by changes in metabolites involved in cellular respiration. Examination of cellular bioenergetics corroborated with our metabolomic analysis,and demonstrated that somatic cells convert from an oxidative state to a glycolytic state in pluripotency. Interestingly,the bioenergetics of various somatic cells correlated with their reprogramming efficiencies. We further identified metabolites that differ between iPSCs and ESCs,which revealed novel metabolic pathways that play a critical role in regulating somatic cell reprogramming. Our findings are the first to globally analyze the metabolome of iPSCs,and provide mechanistic insight into a new layer of regulation involved in inducing pluripotency,and in evaluating iPSC and ESC equivalence. View Publication

Human embryonic stem cells (hESC) and hESC-derived cardiomyocytes (hESC-CM) hold great promise for the treatment of cardiovascular diseases. However the mechanobiological properties of hESC and hESC-CM remains elusive. In this paper,we examined the dynamic and static micromechanical properties of hESC and hESC-CM,by manipulating via optical tweezers at the single-cell level. Theoretical approaches were developed to model the dynamic and static mechanical responses of cells during optical stretching. Our experiments showed that the mechanical stiffness of differentiated hESC-CM increased after cardiac differentiation. Such stiffening could associate with increasingly organized myofibrillar assembly that underlines the functional characteristics of hESC-CM. In summary,our findings lay the ground work for using hESC-CMs as models to study mechanical and contractile defects in heart diseases. View Publication

The International Stem Cell Initiative analyzed 125 human embryonic stem (ES) cell lines and 11 induced pluripotent stem (iPS) cell lines,from 38 laboratories worldwide,for genetic changes occurring during culture. Most lines were analyzed at an early and late passage. Single-nucleotide polymorphism (SNP) analysis revealed that they included representatives of most major ethnic groups. Most lines remained karyotypically normal,but there was a progressive tendency to acquire changes on prolonged culture,commonly affecting chromosomes 1,12,17 and 20. DNA methylation patterns changed haphazardly with no link to time in culture. Structural variants,determined from the SNP arrays,also appeared sporadically. No common variants related to culture were observed on chromosomes 1,12 and 17,but a minimal amplicon in chromosome 20q11.21,including three genes expressed in human ES cells,ID1,BCL2L1 and HM13,occurred in textgreater20% of the lines. Of these genes,BCL2L1 is a strong candidate for driving culture adaptation of ES cells. View Publication

Mutations in human induced pluripotent stem cells (iPSCs) pose a risk for their clinical use due to preferential reprogramming of mutated founder cell and selection of mutations during maintenance of iPSCs in cell culture. It is unknown,however,if mutations in iPSCs are due to stress associated with oncogene expression during reprogramming. We performed whole exome sequencing of human foreskin fibroblasts and their derived iPSCs at two different passages. We found that in vitro passaging contributed 7% to the iPSC coding point mutation load,and ultradeep amplicon sequencing revealed that 19% of the mutations preexist as rare mutations in the parental fibroblasts suggesting that the remaining 74% of the mutations were acquired during cellular reprogramming. Simulation suggests that the mutation intensity during reprogramming is ninefold higher than the background mutation rate in culture. Thus the factor induced reprogramming stress contributes to a significant proportion of the mutation load of iPSCs. View Publication

Realizing the potential of human pluripotent stem cell (hPSC)-based therapy requires the development of defined scalable culture systems with efficient expansion,differentiation and isolation protocols. We report an engineered 3D microfiber system that efficiently supports long-term hPSCs self-renewal under chemically defined conditions. The unique feature of this system lies in the application of a 3D ECM-like environment in which cells are embedded,that affords: (i) uniform high cell loading density in individual cell-laden constructs (∼10 7 cells/ml); (ii) quick recovery of encapsulated cells (textless10min at 37°C) with excellent preservation of cell viability and 3D multicellular structure; (iii) direct cryopreservation of the encapsulated cells in situ in the microfibers with textgreater17-fold higher cell viability compared to those cultured on Matrigel surface; (iv) long-term hPSC propagation under chemically defined conditions. Four hPSC lines propagated in the microfibrous scaffold for 10 consecutive passages were capable of maintaining an undifferentiated phenotype as demonstrated by the expression of stem cell markers and stable karyotype invitro and the ability to form derivatives of the three germ layers both invitro and invivo. Our 3D microfibrous system has the potential for large-scale cultivation of transplantable hESCs and derivatives for clinical applications. textcopyright 2011 Elsevier Ltd. View Publication

HUCB (human umbilical cord blood) has been frequently used in clinical allogeneic HSC (haemopoietic stem cell) transplant. However,HUCB is poorly recognized as a rich source of MSC (mesenchymal stem cell). The aim of this study has been to establish a new method for isolating large number of MSC from HUCB to recognize it as a good source of MSC. HUCB samples were collected from women following their elective caesarean section. The new method (Clot Spot method) was carried out by explanting HUCB samples in mesencult complete medium and maintained in 37°C,in a 5% CO2 and air incubator. MSC presence was established by quantitative and qualitative immunophenotyping of cells and using FITC attached to MSC phenotypic markers (CD29,CD73,CD44 and CD105). Haematopoietic antibodies (CD34 and CD45) were used as negative control. MSC differentiation was examined in neurogenic and adipogenic media. Immunocytochemistry was carried out for the embryonic markers: SOX2 (sex determining region Y-box 2),OLIG-4 (oligodendrocyte-4) and FABP-4 (fatty acid binding protein-4). The new method was compared with the conventional Rosset Sep method. MSC cultures using the Clot Spot method showed 3-fold increase in proliferation rate compared with conventional method. Also,the cells showed high expression of MSC markers CD29,CD73,CD44 and CD105,but lacked the expression of specific HSC markers (CD34 and CD45). The isolated MSC showed some differentiation by expressing the neurogenic (SOX2 and Olig4) and adipogenic (FABP-4) markers respectively. In conclusion,HUCB is a good source of MSC using this new technique. View Publication

The potential for human disease treatment using human pluripotent stem cells,including embryonic stem cells and induced pluripotent stem cells (iPSCs),also carries the risk of added genomic instability. Genomic instability is most often linked to DNA repair deficiencies,which indicates that screening/characterization of possible repair deficiencies in pluripotent human stem cells should be a necessary step prior to their clinical and research use. In this study,a comparison of DNA repair pathways in pluripotent cells,as compared to those in non-pluripotent cells,demonstrated that DNA repair capacities of pluripotent cell lines were more heterogeneous than those of differentiated lines examined and were generally greater. Although pluripotent cells had high DNA repair capacities for nucleotide excision repair,we show that ultraviolet radiation at low fluxes induced an apoptotic response in these cells,while differentiated cells lacked response to this stimulus,and note that pluripotent cells had a similar apoptotic response to alkylating agent damage. This sensitivity of pluripotent cells to damage is notable since viable pluripotent cells exhibit less ultraviolet light-induced DNA damage than do differentiated cells that receive the same flux. In addition,the importance of screening pluripotent cells for DNA repair defects was highlighted by an iPSC line that demonstrated a normal spectral karyotype,but showed both microsatellite instability and reduced DNA repair capacities in three out of four DNA repair pathways examined. Together,these results demonstrate a need to evaluate DNA repair capacities in pluripotent cell lines,in order to characterize their genomic stability,prior to their pre-clinical and clinical use. View Publication

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a structurally endogenous peptide with many biological roles. Maxadilan,a 61-amino acid vasodilatory peptide,specifically activates the PACAP type I receptor (PAC1). Although PAC1 has been identified in embryonic stem cells,little is known about its presence or effects in human induced pluripotent stem (iPS) cells. In the present study,we investigated the expression of PAC1 in human iPS cells by reverse transcriptase polymerase chain reaction (RT-PCR) and western blot analysis. To study the physiological effects mediated by PAC1,we evaluated the role of maxadilan in preventing apoptotic cell death induced by ultraviolet C (UVC). After exposure to UVC,the iPS cells showed a marked reduction in cell viability and a parallel increase of apoptotic cells,as demonstrated by WST-8 analysis,annexin V/propidium iodide (PI) analysis and the terminal transferase dUTP nick end labeling (TUNEL) assay. The addition of 30 nM of maxadilan dramatically increased iPS cell viability and reduced the percentage of apoptotic cells. The anti-apoptotic effects of maxadilan were correlated to the downregulation of caspase-3 and caspase-9. Concomitantly,immunofluorescence,western blot analysis,real-time quantitative polymerase chain reaction (RT-qPCR) analysis and in vitro differentiation results showed that maxadilan did not affect the pluripotent state of iPS cells. Moreover,karyotype analysis showed that maxadilan did not affect the karyotype of iPS cells. In summary,these results demonstrate that PAC1 is present in iPS cells and that maxadilan effectively protects iPS cells against UVC-induced apoptotic cell death while not affecting the pluripotent state or karyotype. View Publication

Deriving lung progenitors from patient-specific pluripotent cells is a key step in producing differentiated lung epithelium for disease modeling and transplantation. By mimicking the signaling events that occur during mouse lung development,we generated murine lung progenitors in a series of discrete steps. Definitive endoderm derived from mouse embryonic stem cells (ESCs) was converted into foregut endoderm,then into replicating Nkx2.1+ lung endoderm,and finally into multipotent embryonic lung progenitor and airway progenitor cells. We demonstrated that precisely-timed BMP,FGF,and WNT signaling are required for NKX2.1 induction. Mouse ESC-derived Nkx2.1+ progenitor cells formed respiratory epithelium (tracheospheres) when transplanted subcutaneously into mice. We then adapted this strategy to produce disease-specific lung progenitor cells from human Cystic Fibrosis induced pluripotent stem cells (iPSCs),creating a platform for dissecting human lung disease. These disease-specific human lung progenitors formed respiratory epithelium when subcutaneously engrafted into immunodeficient mice. View Publication