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A precise identification of adult human hemangioblast is still lacking. To identify circulating precursors having the developmental potential of the hemangioblast,we established a new ex vivo long-term culture model supporting the differentiation of both hematopoietic and endothelial cell lineages. We identified from peripheral blood a population lacking the expression of CD34,lineage markers,CD45 and CD133 (CD34⁻Lin⁻CD45⁻CD133⁻ cells),endowed with the ability to differentiate after a 6-week culture into both hematopoietic and endothelial lineages. The bilineage potential of CD34⁻Lin⁻CD45⁻CD133⁻ cells was determined at the single-cell level in vitro and was confirmed by transplantation into NOD/SCID mice. In vivo,CD34⁻Lin⁻CD45⁻CD133⁻ cells showed the ability to reconstitute hematopoietic tissue and to generate functional endothelial cells that contribute to new vessel formation during tumor angiogenesis. Molecular characterization of CD34⁻Lin⁻D45⁻CD133⁻ cells unveiled a stem cell profile compatible with both hematopoietic and endothelial potentials,characterized by the expression of c-Kit and CXCR4 as well as EphB4,EphB2,and ephrinB2. Further molecular and functional characterization of CD34⁻Lin⁻CD45⁻CD133⁻ cells will help dissect their physiologic role in blood and blood vessel maintenance and repair in adult life. View Publication

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We present a method to perform absolute quantification of glycogen in human embryonic stem cells (hESCs) in situ based on the use of Raman microspectroscopy. The proposed quantification method was validated by comparison to a commonly used commercial glycogen assay kit. With Raman microspectroscopy,we could obtain the glycogen content of hESCs faster and apparently more accurately than with the kit. In addition,glycogen distributions across a colony could be obtained. Raman spectroscopy can provide reliable estimates of the in situ glycogen content in hESCs,and this approach should also be extensible to their other biochemical constituents as well as to other cell types. View Publication

Patient-specific human induced pluripotent stem (hiPS) cells not only provide a promising tool for cellular disease models in general,but also open up the opportunity to establish cell-type-specific systems for personalized medicine. One of the crucial prerequisites for these strategies,however,is a fast and efficient reprogramming strategy from easy accessible somatic cell populations. Keratinocytes from plucked human hair had been introduced as a superior cell source for reprogramming purposes compared with the widely used skin fibroblasts. The starting cell population is,however,limited and thereby further optimization in terms of time,efficiency,and quality is inevitable. Here we show that rat embryonic fibroblasts (REFs) should replace mouse embryonic fibroblasts as feeder cells in the reprogramming process. REFs enable a significantly more efficient reprogramming procedure as shown by colony number and total amount of SSEA4-positive cells. We successfully produced keratinocyte-derived hiPS (k-hiPS) cells from various donors. The arising k-hiPS cells display the hallmarks of pluripotency such as expression of stem cell markers and differentiation into all 3 germ layers. The increased reprogramming efficiency using REFs as a feeder layer occurred independent of the proliferation rate in the parental keratinocytes and acts,at least in part,in a non-cell autonomous way by secreting factors known to facilitate pluripotency such as Tgfb1,Inhba and Grem1. Hence,we provide an easy to use and highly efficient reprogramming system that could be very useful for a broad application to generate human iPS cells. View Publication

BACKGROUND: Human pluripotent stem cells have the ability to generate all cell types present in the adult organism,therefore harboring great potential for the in vitro study of differentiation and for the development of cell-based therapies. Nonetheless their use may prove challenging as incomplete differentiation of these cells might lead to tumoregenicity. Interestingly,many cancer types have been reported to display metabolic modifications with features that might be similar to stem cells. Understanding the metabolic properties of human pluripotent stem cells when compared to their differentiated counterparts can thus be of crucial importance. Furthermore recent data has stressed distinct features of different human pluripotent cells lines,namely when comparing embryo-derived human embryonic stem cells (hESCs) and induced pluripotent stem cells (IPSCs) reprogrammed from somatic cells.backslashnbackslashnMETHODOLOGY/PRINCIPAL FINDINGS: We compared the energy metabolism of hESCs,IPSCs,and their somatic counterparts. Focusing on mitochondria,we tracked organelle localization and morphology. Furthermore we performed gene expression analysis of several pathways related to the glucose metabolism,including glycolysis,the pentose phosphate pathway and the tricarboxylic acid (TCA) cycle. In addition we determined oxygen consumption rates (OCR) using a metabolic extracellular flux analyzer,as well as total intracellular ATP levels by high performance liquid chromatography (HPLC). Finally we explored the expression of key proteins involved in the regulation of glucose metabolism.backslashnbackslashnCONCLUSIONS/FINDINGS: Our results demonstrate that,although the metabolic signature of IPSCs is not identical to that of hESCs,nonetheless they cluster with hESCs rather than with their somatic counterparts. ATP levels,lactate production and OCR revealed that human pluripotent cells rely mostly on glycolysis to meet their energy demands. Furthermore,our work points to some of the strategies which human pluripotent stem cells may use to maintain high glycolytic rates,such as high levels of hexokinase II and inactive pyruvate dehydrogenase (PDH). View Publication

The limited ability of the heart to regenerate has prompted development of new systems to produce cardiomyocytes for therapeutics. While differentiation of human embryonic stem cells (hESCs) into cardiomyocytes has been well documented,the process remains inefficient and/or expensive,and progress would be facilitated by better understanding the early genetic events that cause cardiac specification. By maintaining a transgenic cardiac-specific MYH6-monomeric red fluorescent protein (mRFP) reporter hESC line in conditions that promote pluripotency,we tested the ability of combinations of 15 genes to induce cardiac specification. Screening identified GATA4 plus TBX5 as the minimum requirement to activate the cardiac gene regulatory network and produce mRFP(+) cells,while a combination of GATA4,TBX5,NKX2.5,and BAF60c (GTNB) was necessary to generate beating cardiomyocytes positive for cTnI and α-actinin. Including the chemotherapeutic agent,Ara-C,from day 10 of induced differentiation enriched for cTnI/α-actinin double positive cells to 45%. Transient expression of GTNB for 5-7 days was necessary to activate the cardiogenesis through progenitor intermediates in a manner consistent with normal heart development. This system provides a route to test the effect of different factors on human cardiac differentiation and will be useful in understanding the network failures that underlie disease phenotypes. View Publication

OBJECTIVE: The molecular mechanisms that maintain human pluripotent stem (PS) cells are not completely understood. Here we sought to identify new candidate PS cell regulators to facilitate future improvements in their generation,expansion,and differentiation. MATERIALS AND METHODS: We used bioinformatic analyses of multiple serial-analysis-of-gene-expression libraries (generated from human PS cells and their differentiated derivatives),together with small interfering RNA (siRNA) screening to identify candidate pluripotency regulators. Validation of candidate regulators involved promoter analyses,Affymetrix profiling,real-time PCR,and immunoprecipitation. RESULTS: Promoter analysis of genes differentially expressed across multiple serial-analysis-of-gene-expression libraries identified E2F motifs in the promoters of many PS cell-specific genes (e.g.,POU5F1,NANOG,SOX2,FOXD3). siRNA analyses identified two retinoblastoma binding proteins (RBBP4,RBBP9) as required for maintenance of multiple human PS cell types. Both RBBPs were bound to RB in human PS cells,and E2F motifs were present in the promoters of genes whose expression was altered by decreasing RBBP4 and RBBP9 expression. Affymetrix and real-time PCR studies of siRNA-treated human PS cells showed that reduced RBBP4 or RBBP9 expression concomitantly decreased expression of POU5F1,NANOG,SOX2,and/or FOXD3 plus certain cell cycle genes (e.g.,CCNA2,CCNB1),while increasing expression of genes involved in organogenesis (particularly neurogenesis). CONCLUSIONS: These results reveal new candidate positive regulators of human PS cells,providing evidence of their ability to regulate expression of pluripotency,cell cycle,and differentiation genes in human PS cells. These data provide valuable new leads for further elucidating mechanisms of human pluripotency. View Publication

Genome stability of human embryonic stem cells (hESC) is an important issue because even minor genetic alterations can negatively impact cell functionality and safety. The incorrect repair of DNA double-stranded breaks (DSBs) is the ultimate cause of the formation of chromosomal aberrations. Using G2 radiosensitivity assay,we analyzed chromosomal aberrations in pluripotent stem cells and somatic cells. The chromatid exchange aberration rates in hESCs increased manifold 2 hours after irradiation as compared with their differentiated derivatives,but the frequency of radiation-induced chromatid breaks was similar. The rate of radiation-induced chromatid exchanges in hESCs and differentiated cells exhibited a quadratic dose response,revealing two-hit mechanism of exchange formation suggesting that a non-homologous end joining (NHEJ) repair may contribute to their formation. Inhibition of DNA-PK,a key NHEJ component,by NU7026 resulted in a significant decrease in radiation-induced chromatid exchanges in hESCs but not in somatic cells. In contrast,NU7026 treatment increased the frequency of radiation-induced breaks to a similar extent in pluripotent and somatic cells. Thus,DNA-PK dependent NHEJ efficiently participates in the elimination of radiation-induced chromatid breaks during the late G2 in both cell types and DNA-PK activity leads to a high level of misrejoining specifically in pluripotent cells. View Publication

Insertion of a transgene into a defined genomic locus in human embryonic stem cells (hESCs) is crucial in preventing random integration-induced insertional mutagenesis,and can possibly enable persistent transgene expression during hESC expansion and in their differentiated progenies. Here,we employed homologous recombination in hESCs to introduce heterospecific loxP sites into the AAVS1 locus,a site with an open chromatin structure that allows averting transgene silencing phenomena. We then performed Cre recombinase mediated cassette exchange using baculoviral vectors to insert a transgene into the modified AAVS1 locus. Targeting efficiency in the master hESC line with the loxP-docking sites was up to 100%. Expression of the inserted transgene lasted for at least 20 passages during hESC expansion and was retained in differentiated cells derived from the genetically modified hESCs. Thus,this study demonstrates the feasibility of genetic manipulation at the AAVS1 locus with homologous recombination and using viral transduction in hESCs to facilitate recombinase-mediated cassette exchange. The method developed will be useful for repeated gene targeting at a defined locus of the hESC genome. View Publication

Amyotrophic lateral sclerosis (ALS) is an incurable neuromuscular disease that leads to a profound loss of life quality and premature death. Around 10% of the cases are inherited and ALS8 is an autosomal dominant form of familial ALS caused by mutations in the vamp-associated protein B/C (VAPB) gene. The VAPB protein is involved in many cellular processes and it likely contributes to the pathogenesis of other forms of ALS besides ALS8. A number of successful drug tests in ALS animal models could not be translated to humans underscoring the need for novel approaches. The induced pluripotent stem cells (iPSC) technology brings new hope,since it can be used to model and investigate diseases in vitro. Here we present an additional tool to study ALS based on ALS8-iPSC. Fibroblasts from ALS8 patients and their non-carrier siblings were successfully reprogrammed to a pluripotent state and differentiated into motor neurons. We show for the first time that VAPB protein levels are reduced in ALS8-derived motor neurons but,in contrast to over-expression systems,cytoplasmic aggregates could not be identified. Our results suggest that optimal levels of VAPB may play a central role in the pathogenesis of ALS8,in agreement with the observed reduction of VAPB in sporadic ALS. View Publication

By providing access to affected neurons,human induced pluripotent stem cells (iPSc) offer a unique opportunity to model human neurodegenerative diseases. We generated human iPSc from the skin fibroblasts of children with mucopolysaccharidosis type IIIB. In this fatal lysosomal storage disease,defective α-N-acetylglucosaminidase interrupts the degradation of heparan sulfate (HS) proteoglycans and induces cell disorders predominating in the central nervous system,causing relentless progression toward severe mental retardation. Partially digested proteoglycans,which affect fibroblast growth factor signaling,accumulated in patient cells. They impaired isolation of emerging iPSc unless exogenous supply of the missing enzyme cleared storage and restored cell proliferation. After several passages,patient iPSc starved of an exogenous enzyme continued to proliferate in the presence of fibroblast growth factor despite HS accumulation. Survival and neural differentiation of patient iPSc were comparable with unaffected controls. Whereas cell pathology was modest in floating neurosphere cultures,undifferentiated patient iPSc and their neuronal progeny expressed cell disorders consisting of storage vesicles and severe disorganization of Golgi ribbons associated with modified expression of the Golgi matrix protein GM130. Gene expression profiling in neural stem cells pointed to alterations of extracellular matrix constituents and cell-matrix interactions,whereas genes associated with lysosome or Golgi apparatus functions were downregulated. Taken together,these results suggest defective responses of patient undifferentiated stem cells and neurons to environmental cues,which possibly affect Golgi organization,cell migration and neuritogenesis. This could have potential consequences on post-natal neurological development,once HS proteoglycan accumulation becomes prominent in the affected child brain. View Publication

A practical synthesis of the Rho-Kinase inhibitor Y-27632 and two new fluoro derivatives was achieved in seven steps and with a good overall yield of 45% starting from commercially available (R)-1-phenylethylamine. Compared to Y-27632 the new fluoro derivatives showed reduced or no effect on hPSC vitality and expansion after dissociation in human pluripotent stem cells. View Publication