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Definitive mesoderm arises from a bipotent mesendodermal population,and to study processes controlling its development at this stage,embryonic stem (ES) cells can be employed. SHB (Src homology 2 protein in beta-cells) is an adapter protein previously found to be involved in ES cell differentiation to mesoderm. To further study the role of SHB in this context,we have established ES cell lines deficient for one (SHB+/-) or both SHB alleles (SHB-/-). Differentiating embryoid bodies (EBs) derived from these ES cell lines were used for gene expression analysis. Alternatively,EBs were stained for the blood vessel marker CD31. For hematopoietic differentiation,EBs were differentiated in methylcellulose. SHB-/- EBs exhibited delayed down-regulation of the early mesodermal marker Brachyury. Later mesodermal markers relatively specific for the hematopoietic,vascular,and cardiac lineages were expressed at lower levels on day 6 or 8 of differentiation in EBs lacking SHB. The expression of vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 was also reduced in SHB-/- EBs. SHB-/- EBs demonstrated impaired blood vessel formation after vascular endothelial growth factor stimulation. In addition,the SHB-/- ES cells formed fewer blood cell colonies than SHB+/+ ES cells. It is concluded that SHB is required for appropriate hematopoietic and vascular differentiation and that delayed down-regulation of Brachyury expression may play a role in this context. View Publication

Human embryonic stem cells hold great promise in furthering our treatment of disease and increasing our understanding of early development. This chapter describes protocols for the derivation and maintenance of human embryonic stem cells. In addition,it summarizes briefly several alternative methods for the culture of human embryonic stem cells. Thus,this chapter provides a good starting point for researchers interested in harnessing the potential of human embryonic stem cells. View Publication

The amyloid-beta precursor protein (AbetaPP) is a ubiquitously expressed adhesion and neuritogenic protein whose processing has previously been shown to be regulated by reproductive hormones including the gonadotropin luteinizing hormone (LH) in human neuroblastoma cells. We report for the first time the expression of AbetaPP in human embryonic stem (hES) cells at the mRNA and protein levels. Using N- and C-terminal antibodies against AbetaPP,we detected both the mature and immature forms of AbetaPP as well as truncated variants ( approximately 53kDa,47kDa,and 29kDa) by immunoblot analyses. Expression of AbetaPP is regulated by both the stemness of the cells and pregnancy-associated hormones. Addition of human chorionic gonadotropin,the fetal equivalent of LH that is dramatically elevated during pregnancy,markedly increased the expression of all AbetaPP forms. These results indicate a critical molecular signaling link between the hormonal environment of pregnancy and the expression of AbetaPP in hES cells that is suggestive of an important function for this protein during early human embryogenesis prior to the formation of neural precursor cells. View Publication

We have previously shown that coculture of human embryonic stem cells (hESCs) for 14 days with immortalized fetal hepatocytes yields CD34(+) cells that can be expanded in serum-free liquid culture into large numbers of megaloblastic nucleated erythroblasts resembling yolk sac-derived cells. We show here that these primitive erythroblasts undergo a switch in hemoglobin (Hb) composition during late terminal erythroid maturation with the basophilic erythroblasts expressing predominantly Hb Gower I (zeta(2)epsilon(2)) and the orthochromatic erythroblasts hemoglobin Gower II (alpha(2)epsilon(2)). This suggests that the switch from Hb Gower I to Hb Gower II,the first hemoglobin switch in humans is a maturation switch not a lineage switch. We also show that extending the coculture of the hESCs with immortalized fetal hepatocytes to 35 days yields CD34(+) cells that differentiate into more developmentally mature,fetal liver-like erythroblasts,that are smaller,express mostly fetal hemoglobin,and can enucleate. We conclude that hESC-derived erythropoiesis closely mimics early human development because the first 2 human hemoglobin switches are recapitulated,and because yolk sac-like and fetal liver-like cells are sequentially produced. Development of a method that yields erythroid cells with an adult phenotype remains necessary,because the most mature cells that can be produced with current systems express less than 2% adult beta-globin mRNA. View Publication

BACKGROUND: Although methods for generating cardiomyocytes from pluripotent stem cells have been reported,current methods produce heterogeneous mixtures of cardiomyocytes and noncardiomyocyte cells. Here,we report an entirely novel system in which pluripotent stem cell-derived cardiomyocytes are purified by cardiomyocyte-specific molecular beacons (MBs). MBs are nanoscale probes that emit a fluorescence signal when hybridized to target mRNAs.backslashnbackslashnMETHOD AND RESULTS: Five MBs targeting mRNAs of either cardiac troponin T or myosin heavy chain 6/7 were generated. Among 5 MBs,an MB that targeted myosin heavy chain 6/7 mRNA (MHC1-MB) identified up to 99% of HL-1 cardiomyocytes,a mouse cardiomyocyte cell line,but textless3% of 4 noncardiomyocyte cell types in flow cytometry analysis,which indicates that MHC1-MB is specific for identifying cardiomyocytes. We delivered MHC1-MB into cardiomyogenically differentiated pluripotent stem cells through nucleofection. The detection rate of cardiomyocytes was similar to the percentages of cardiac troponin T- or cardiac troponin I-positive cardiomyocytes,which supports the specificity of MBs. Finally,MHC1-MB-positive cells were sorted by fluorescence-activated cell sorter from mouse and human pluripotent stem cell differentiating cultures,and ≈97% cells expressed cardiac troponin T or cardiac troponin I as determined by flow cytometry. These MB-based sorted cells maintained their cardiomyocyte characteristics,which was verified by spontaneous beating,electrophysiological studies,and expression of cardiac proteins. When transplanted in a myocardial infarction model,MB-based purified cardiomyocytes improved cardiac function and demonstrated significant engraftment for 4 weeks without forming tumors.backslashnbackslashnCONCLUSIONS: We developed a novel cardiomyocyte selection system that allows production of highly purified cardiomyocytes. These purified cardiomyocytes and this system can be valuable for cell therapy and drug discovery. View Publication

RATIONALE: Human embryonic stem cell (hESC) derivatives are attractive candidates for therapeutic use. The engraftment and survival of hESC derivatives as xenografts or allografts require effective immunosuppression to prevent immune cell infiltration and graft destruction.backslashnbackslashnOBJECTIVE: To test the hypothesis that a short-course,dual-agent regimen of two costimulation-adhesion blockade agents can induce better engraftment of hESC derivatives compared to current immunosuppressive agents.backslashnbackslashnMETHODS AND RESULTS: We transduced hESCs with a double fusion reporter gene construct expressing firefly luciferase (Fluc) and enhanced green fluorescent protein,and differentiated these cells to endothelial cells (hESC-ECs). Reporter gene expression enabled longitudinal assessment of cell engraftment by bioluminescence imaging. Costimulation-adhesion therapy resulted in superior hESC-EC and mouse EC engraftment compared to cyclosporine therapy in a hind limb model. Costimulation-adhesion therapy also promoted robust hESC-EC and hESC-derived cardiomyocyte survival in an ischemic myocardial injury model. Improved hESC-EC engraftment had a cardioprotective effect after myocardial injury,as assessed by magnetic resonance imaging. Mechanistically,costimulation-adhesion therapy is associated with systemic and intragraft upregulation of T-cell immunoglobulin and mucin domain 3 (TIM3) and a reduced proinflammatory cytokine profile.backslashnbackslashnCONCLUSIONS: Costimulation-adhesion therapy is a superior alternative to current clinical immunosuppressive strategies for preventing the post-transplant rejection of hESC derivatives. By extending the window for cellular engraftment,costimulation-adhesion therapy enhances functional preservation following ischemic injury. This regimen may function through a TIM3-dependent mechanism. View Publication

BACKGROUND: A few reports suggested that low levels of Wnt signaling might drive cell reprogramming,but these studies could not establish a clear relationship between Wnt signaling and self-renewal networks. There are ongoing debates as to whether and how the Wnt/β-catenin signaling is involved in the control of pluripotency gene networks. Additionally,whether physiological β-catenin signaling generates stem-like cells through interactions with other pathways is as yet unclear. The nasopharyngeal carcinoma HONE1 cells have low expression of β-catenin and wild-type expression of p53,which provided a possibility to study regulatory mechanism of stemness networks induced by physiological levels of Wnt signaling in these cells.backslashnbackslashnRESULTS: Introduction of increased β-catenin signaling,haploid expression of β-catenin under control by its natural regulators in transferred chromosome 3,resulted in activation of Wnt/β-catenin networks and dedifferentiation in HONE1 hybrid cell lines,but not in esophageal carcinoma SLMT1 hybrid cells that had high levels of endogenous β-catenin expression. HONE1 hybrid cells displayed stem cell-like properties,including enhancement of CD24(+) and CD44(+) populations and generation of spheres that were not observed in parental HONE1 cells. Signaling cascades were detected in HONE1 hybrid cells,including activation of p53- and RB1-mediated tumor suppressor pathways,up-regulation of Nanog-,Oct4-,Sox2-,and Klf4-mediated pluripotency networks,and altered E-cadherin expression in both in vitro and in vivo assays. qPCR array analyses further revealed interactions of physiological Wnt/β-catenin signaling with other pathways such as epithelial-mesenchymal transition,TGF-β,Activin,BMPR,FGFR2,and LIFR- and IL6ST-mediated cell self-renewal networks. Using β-catenin shRNA inhibitory assays,a dominant role for β-catenin in these cellular network activities was observed. The expression of cell surface markers such as CD9,CD24,CD44,CD90,and CD133 in generated spheres was progressively up-regulated compared to HONE1 hybrid cells. Thirty-four up-regulated components of the Wnt pathway were identified in these spheres.backslashnbackslashnCONCLUSIONS: Wnt/β-catenin signaling regulates self-renewal networks and plays a central role in the control of pluripotency genes,tumor suppressive pathways and expression of cancer stem cell markers. This current study provides a novel platform to investigate the interaction of physiological Wnt/β-catenin signaling with stemness transition networks. View Publication

Biochemical factors can help reprogram somatic cells into pluripotent stem cells,yet the role of biophysical factors during reprogramming is unknown. Here,we show that biophysical cues,in the form of parallel microgrooves on the surface of cell-adhesive substrates,can replace the effects of small-molecule epigenetic modifiers and significantly improve reprogramming efficiency. The mechanism relies on the mechanomodulation of the cells' epigenetic state. Specifically,decreased histone deacetylase activity and upregulation of the expression of WD repeat domain 5 (WDR5)—a subunit of H3 methyltranferase—by microgrooved surfaces lead to increased histone H3 acetylation and methylation. We also show that microtopography promotes a mesenchymal-to-epithelial transition in adult fibroblasts. Nanofibrous scaffolds with aligned fibre orientation produce effects similar to those produced by microgrooves,suggesting that changes in cell morphology may be responsible for modulation of the epigenetic state. These findings have important implications in cell biology and in the optimization of biomaterials for cell-engineering applications. View Publication

We present an integrated platform comprised of a biomimetic substrate and physiologically aligned human pluripotent stem cell-derived cardiomyocytes (CMs) with optical detection and algorithms to monitor subtle changes in cardiac properties under various conditions. In the native heart,anisotropic tissue structures facilitate important concerted mechanical contraction and electrical propagation. To recapitulate the architecture necessary for a physiologically accurate heart response,we have developed a simple way to create large areas of aligned CMs with improved functional properties using shrink-wrap film. Combined with simple bright field imaging,obviating the need for fluorescent labels or beads,we quantify and analyze key cardiac contractile parameters. To evaluate the performance capabilities of this platform,the effects of two drugs,E-4031 and isoprenaline,were examined. Cardiac cells supplemented with E-4031 exhibited an increase in contractile duration exclusively due to prolonged relaxation peak. Notably,cells aligned on the biomimetic platform responded detectably down to a dosage of 3nm E-4031,which is lower than the IC50 in the hERG channel assay. Cells supplemented with isoprenaline exhibited increased contractile frequency and acceleration. Interestingly,cells grown on the biomimetic substrate were more responsive to isoprenaline than those grown on the two control surfaces,suggesting topography may help induce more mature ion channel development. This simple and low-cost platform could thus be a powerful tool for longitudinal assays as well as an effective tool for drug screening and basic cardiac research. ?? 2013 Elsevier Ltd. View Publication

Stem cell differentiation is regulated by complex repertoires of signaling ligands which often use multivalent interactions,where multiple ligands tethered to one entity interact with multiple cellular receptors to yield oligomeric complexes. One such ligand is Sonic hedgehog (Shh),whose posttranslational lipid modifications and assembly into multimers enhance its biological potency,potentially through receptor clustering. Investigations of Shh typically utilize recombinant,monomeric protein,and thus the impact of multivalency on ligand potency is unexplored. Among its many activities,Shh is required for ventralization of the midbrain and forebrain and is therefore critical for the development of midbrain dopaminergic (mDA) and forebrain gamma-aminobutyric acid (GABA) inhibitory neurons. We have designed multivalent biomaterials presenting Shh in defined spatial arrangements and investigated the role of Shh valency in ventral specification of human embryonic stem cells (hESCs) into these therapeutically relevant cell types. Multivalent Shh conjugates with optimal valencies,compared to the monomeric Shh,increased the percentages of neurons belonging to mDA or forebrain GABAergic fates from 33% to 60% or 52% to 86%,respectively. Thus,multivalent Shh bioconjugates can enhance neuronal lineage commitment of pluripotent stem cells and thereby facilitate efficient derivation of neurons that could be used to treat Parkinson's and epilepsy patients. View Publication

A significant clinical need exists to differentiate human pluripotent stem cells (hPSCs) into cardiomyocytes,enabling tissue modeling for in vitro discovery of new drugs or cell-based therapies for heart repair in vivo. Chemical and mechanical microenvironmental factors are known to impact the efficiency of stem cell differentiation,but cardiac differentiation protocols in hPSCs are typically performed on rigid tissue culture polystyrene (TCPS) surfaces,which do not present a physiological mechanical setting. To investigate the temporal effects of mechanics on cardiac differentiation,we cultured human embryonic stem cells (hESCs) and their derivatives on polyacrylamide hydrogel substrates with a physiologically relevant range of stiffnesses. In directed differentiation and embryoid body culture systems,differentiation of hESCs to cardiac troponin T-expressing (cTnT+) cardiomyocytes peaked on hydrogels of intermediate stiffness. Brachyury expression also peaked on intermediate stiffness hydrogels at day 1 of directed differentiation,suggesting that stiffness impacted the initial differentiation trajectory of hESCs to mesendoderm. To investigate the impact of substrate mechanics during cardiac specification of mesodermal progenitors,we initiated directed cardiomyocyte differentiation on TCPS and transferred cells to hydrogels at the Nkx2.5/Isl1+ cardiac progenitor cell stage. No differences in cardiomyocyte purity with stiffness were observed on day 15. These experiments indicate that differentiation of hESCs is sensitive to substrate mechanics at early stages of mesodermal induction,and proper application of substrate mechanics can increase the propensity of hESCs to differentiate to cardiomyocytes. textcopyright 2013 Acta Materialia Inc. View Publication

Ex vivo expansion of satellite cells and directed differentiation of pluripotent cells to mature skeletal muscle have proved difficult challenges for regenerative biology. Using a zebrafish embryo culture system with reporters of early and late skeletal muscle differentiation,we examined the influence of 2,400 chemicals on myogenesis and identified six that expanded muscle progenitors,including three GSK3$\$,two calpain inhibitors,and one adenylyl cyclase activator,forskolin. Forskolin also enhanced proliferation of mouse satellite cells in culture and maintained their ability to engraft muscle in vivo. A combination of bFGF,forskolin,and the GSK3$\$ BIO induced skeletal muscle differentiation in human induced pluripotent stem cells (iPSCs) and produced engraftable myogenic progenitors that contributed to muscle repair in vivo. In summary,these studies reveal functionally conserved pathways regulating myogenesis across species and identify chemical compounds that expand mouse satellite cells and differentiate human iPSCs into engraftable muscle. View Publication