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Background Human embryonic stem cells (hESCs) serve as a potential unlimited ex vivo source of cardiomyocytes for disease modeling,cardiotoxicity screening,drug discovery,and cell-based therapies. Despite the fundamental importance of Ca2+-induced Ca2+ release in excitation-contraction coupling,the mechanistic basis of Ca2+ handling of hESC-derived ventricular cardiomyocytes (VCMs) remains elusive. Objectives To study Ca2+ sparks as unitary events of Ca2+ handling for mechanistic insights. Methods To avoid ambiguities owing to the heterogeneous nature,we experimented with hESC-VCMs,purified on the basis of zeocin resistance and signature ventricular action potential after LV-MLC2v-tdTomato-T2A-Zeo transduction. Results Ca2+ sparks that were sensitive to inhibitors of sarco/endoplasmic reticulum Ca2+-ATPase (thapsigargin and cyclopiazonic acid) and ryanodine receptor (RyR; ryanodine,tetracaine) but not inositol trisphosphate receptors (xestospongin C and 2-aminoethyl diphenylborinate) could be recorded. In a permeabilization model,we further showed that RyRs could be sensitized by Ca2+. Increasing external Ca2+ dramatically escalated the basal Ca2+ and spark frequency. Furthermore,RyR-mediated Ca2+ release sensitized nearby RyRs,leading to compound Ca2+ sparks. Depolarization or L-type Ca2+ channel agonist (FPL 64176 and Bay K8644) pretreatment induced an extracellular Ca2+-dependent cytosolic Ca2+ increase and reduced the sarcoplasmic reticulum content. By contrast,removal of external Na+ or the addition of the Na+-Ca2+ exchanger inhibitor (KB-R7943 and SN-6) had no effect,suggesting that the Na+-Ca2+ exchanger is not involved in triggering sparks. Inhibition of mitochondrial Ca2+ uptake by carbonyl cyanide m-chlorophenyl hydrazone promoted Ca2+ waves. Conclusion Taken collectively,our findings provide the first lines of direct evidence that hESC-VCMs have functional Ca2+-induced Ca2+ release. However,the sarcoplasmic reticulum is leaky and without a mature terminating mechanism in early development. View Publication

Applications of human induced pluripotent stem cell derived-cardiac myocytes (hiPSC-CMs) would be strengthened by the ability to generate specific cardiac myocyte (CM) lineages. However,purification of lineage-specific hiPSC-CMs is limited by the lack of cell marking techniques. Here,we have developed an iPSC-CM marking system using recombinant adenoviral reporter constructs with atrial- or ventricular-specific myosin light chain-2 (MLC-2) promoters. MLC-2a and MLC-2v selected hiPSC-CMs were purified by fluorescence-activated cell sorting and their biochemical and electrophysiological phenotypes analyzed. We demonstrate that the phenotype of both populations remained stable in culture and they expressed the expected sarcomeric proteins,gap junction proteins and chamber-specific transcription factors. Compared to MLC-2a cells,MLC-2v selected CMs had larger action potential amplitudes and durations. In addition,by immunofluorescence,we showed that MLC-2 isoform expression can be used to enrich hiPSC-CM consistent with early atrial and ventricular myocyte lineages. However,only the ventricular myosin light chain-2 promoter was able to purify a highly homogeneous population of iPSC-CMs. Using this approach,it is now possible to develop ventricular-specific disease models using iPSC-CMs while atrial-specific iPSC-CM cultures may require additional chamber-specific markers. ?? 2013 Elsevier B.V. View Publication

Summary Rett syndrome (RTT) is caused by mutations of MECP2,a methyl CpG binding protein thought to act as a global transcriptional repressor. Here we show,using an isogenic human embryonic stem cell model of RTT,that MECP2 mutant neurons display key molecular and cellular features of this disorder. Unbiased global gene expression analyses demonstrate that MECP2 functions as a global activator in neurons but not in neural precursors. Decreased transcription in neurons was coupled with a significant reduction in nascent protein synthesis and lack of MECP2 was manifested as a severe defect in the activity of the AKT/mTOR pathway. Lack of MECP2 also leads to impaired mitochondrial function in mutant neurons. Activation of AKT/mTOR signaling by exogenous growth factors or by depletion of PTEN boosted protein synthesis and ameliorated disease phenotypes in mutant neurons. Our findings indicate a vital function for MECP2 in maintaining active gene transcription in human neuronal cells. View Publication

The development of strategies to eradicate primary human acute myelogenous leukemia (AML) cells is a major challenge to the leukemia research field. In particular,primitive leukemia cells,often termed leukemia stem cells,are typically refractory to many forms of therapy. To investigate improved strategies for targeting of human AML cells we compared the molecular mechanisms regulating oxidative state in primitive (CD34(+)) leukemic versus normal specimens. Our data indicate that CD34(+) AML cells have elevated expression of multiple glutathione pathway regulatory proteins,presumably as a mechanism to compensate for increased oxidative stress in leukemic cells. Consistent with this observation,CD34(+) AML cells have lower levels of reduced glutathione and increased levels of oxidized glutathione compared with normal CD34(+) cells. These findings led us to hypothesize that AML cells will be hypersensitive to inhibition of glutathione metabolism. To test this premise,we identified compounds such as parthenolide (PTL) or piperlongumine that induce almost complete glutathione depletion and severe cell death in CD34(+) AML cells. Importantly,these compounds only induce limited and transient glutathione depletion as well as significantly less toxicity in normal CD34(+) cells. We further determined that PTL perturbs glutathione homeostasis by a multifactorial mechanism,which includes inhibiting key glutathione metabolic enzymes (GCLC and GPX1),as well as direct depletion of glutathione. These findings demonstrate that primitive leukemia cells are uniquely sensitive to agents that target aberrant glutathione metabolism,an intrinsic property of primary human AML cells. View Publication

Human embryonic stem cells (hESCs),due to their self-renewal capacity and pluripotency,have become a potential source of transplantable $\$-cells for the treatment of diabetes. However,it is imperative that the derived cells fulfill the criteria for clinical treatment. In this study,we replaced common Matrigel with a synthetic peptide-acrylate surface (Synthemax) to expand undifferentiated hESCs and direct their differentiation in a defined and serum-free medium. We confirmed that the cells still expressed pluripotent markers,had the ability to differentiate into three germ layers,and maintained a normal karyotype after 10 passages of subculture. Next,we reported an efficient protocol for deriving nearly 86% definitive endoderm cells from hESCs under serum-free conditions. Moreover,we were able to obtain insulin-producing cells within 21 days following a simple three-step protocol. The results of immunocytochemical and quantitative gene expression analysis showed that the efficiency of induction was not significantly different between the Synthemax surface and the Matrigel-coated surface. Thus,we provided a totally defined condition from hESC culture to insulin-producing cell differentiation,and the derived cells could be a therapeutic resource for diabetic patients in the future. View Publication

How tumor suppressor p53 selectively responds to specific signals,especially in normal cells,is poorly understood. We performed genome-wide profiling of p53 chromatin interactions and target gene expression in human embryonic stem cells (hESCs) in response to early differentiation,induced by retinoic acid,versus DNA damage,caused by adriamycin. Most p53-binding sites are unique to each state and define stimulus-specific p53 responses in hESCs. Differentiation-activated p53 targets include many developmental transcription factors and,in pluripotent hESCs,are bound by OCT4 and NANOG at chromatin enriched in both H3K27me3 and H3K4me3. Activation of these genes occurs with recruitment of p53 and H3K27me3-specific demethylases,UTX and JMJD3,to chromatin. In contrast,genes associated with cell migration and motility are bound by p53 specifically after DNA damage. Surveillance functions of p53 in cell death and cell cycle regulation are conserved in both DNA damage and differentiation. Comparative genomic analysis of p53-targets in mouse and human ESCs supports an inter-species divergence in p53 regulatory functions during evolution. Our findings expand the registry of p53-regulated genes to define p53-regulated opposition to pluripotency during early differentiation,a process highly distinct from stress-induced p53 response in hESCs. View Publication

Hematopoietic stem cells (HSCs) develop from a specialized subpopulation of endothelial cells known as hemogenic endothelium (HE). Although the HE origin of HSCs is now well established in different species,the signaling pathways that control this transition remain poorly understood. Here,we show that activation of retinoic acid (RA) signaling in aorta-gonad-mesonephros-derived HE ex vivo dramatically enhanced its HSC potential,whereas conditional inactivation of the RA metabolizing enzyme retinal dehydrogenase 2 in VE-cadherin expressing endothelial cells in vivo abrogated HSC development. Wnt signaling completely blocked the HSC inductive effects of RA modulators,whereas inhibition of the pathway promoted the development of HSCs in the absence of RA signaling. Collectively,these findings position RA and Wnt signaling as key regulators of HSC development and in doing so provide molecular insights that will aid in developing strategies for their generation from pluripotent stem cells. 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

Alloreactivity negatively influences outcomes of organ transplantation or HCT from allogeneic donors. Standard pharmacologic immune suppression impairs T-cell function and jeopardizes the beneficial reconstitution of Tregs. Murine transplantation models have shown that STAT3 is highly expressed in alloreactive T cells and may be therapeutically targeted. The influence and effects of STAT3 neutralization in human alloreactivity,however,remain to be elucidated. In this study,S3I-201,a selective small-molecule inhibitor of STAT3,suppressed human DC-allosensitized T-cell proliferation and abrogated Th17 responses. STAT3 blockade significantly enhanced the expansion of potent iTregs and permitted CD8(+) cytolytic effector function. Mechanistically,S3I-201 polarized the ratio of STAT phosphorylation in favor of STAT5 over STAT3 and also achieved a significant degree of Foxp3 demethylation among the iTregs. Conversely,selective impairment of STAT5 phosphorylation with CAS 285986-31-4 markedly reduced iTregs. STAT3 represents a relevant target for achieving control over human alloresponses,where its suppression facilitates STAT5-mediated iTreg growth and function. View Publication

The molecular mechanisms underlying the differentiation of neural progenitor cells (NPCs) remain poorly understood. In this study we investigated the role of Ca(2+) and cAMP (cyclic adenosine monophosphate) in the differentiation of NPCs extracted from the subventricular zone of E14.5 rat embryos. Patch clamp recordings revealed that increasing cAMP-signaling with Forskolin or IBMX (3-isobutyl-1-methylxantine) significantly facilitated neuronal functional maturation. A continuous application of IBMX to the differentiation medium substantially increased the functional expression of voltage-gated Na(+) and K(+) channels,as well as neuronal firing frequency. Furthermore,we observed an increase in the frequency of spontaneous synaptic currents and in the amplitude of evoked glutamatergic and GABAergic synaptic currents. The most prominent acute effect of applying IBMX was an increase in L-type Ca(2+)currents. Conversely,blocking L-type channels strongly inhibited dendritic outgrowth and synapse formation even in the presence of IBMX,indicating that voltage-gated Ca(2+) influx plays a major role in neuronal differentiation. Finally,we found that nifedipine completely blocks IBMX-induced CREB phosphorylation (cAMP-response-element-binding protein),indicating that the activity of this important transcription factor equally depends on both enhanced cAMP and voltage-gated Ca(2+)-signaling. Taken together,these data indicate that the up-regulation of voltage-gated L-type Ca(2+)-channels and early electrical excitability are critical steps in the cAMP-dependent differentiation of SVZ-derived NPCs into functional neurons. To our knowledge,this is the first demonstration of the acute effects of cAMP on voltage-gated Ca(+2)channels in NPC-derived developing neurons. View Publication

Alzheimer's disease (AD) is among the most prevalent forms of dementia affecting the aging population,and pharmacological therapies to date have not been successful in preventing disease progression. Future therapeutic efforts may benefit from the development of models that enable basic investigation of early disease pathology. In particular,disease-relevant models based on human pluripotent stem cells (hPSCs) may be promising approaches to assess the impact of neurotoxic agents in AD on specific neuronal populations and thereby facilitate the development of novel interventions to avert early disease mechanisms. We implemented an efficient paradigm to convert hPSCs into enriched populations of cortical glutamatergic neurons emerging from dorsal forebrain neural progenitors,aided by modulating Sonic hedgehog (Shh) signaling. Since AD is generally known to be toxic to glutamatergic circuits,we exposed glutamatergic neurons derived from hESCs to an oligomeric pre-fibrillar forms of Aβ known as globulomers"� View Publication

Generation of functional cells from human pluripotent stem cells (PSCs) through in vitro differentiation is a promising approach for drug screening and cell therapy. However,the observed large and unavoidable variation in the differentiation potential of different human embryonic stem cell (hESC)/induced PSC (iPSC) lines makes the selection of an appropriate cell line for the differentiation of a particular cell lineage difficult. Here,we report identification of WNT3 as a biomarker capable of predicting definitive endoderm (DE) differentiation potential of hESCs. We show that the mRNA level of WNT3 in hESCs correlates with their DE differentiation efficiency. In addition,manipulations of hESCs through WNT3 knockdown or overexpression can respectively inhibit or promote DE differentiation in a WNT3 level-dependent manner. Finally,analysis of several hESC lines based on their WNT3 expression levels allowed accurate prediction of their DE differentiation potential. Collectively,our study supports the notion that WNT3 can serve as a biomarker for predicting DE differentiation potential of hESCs. ?? 2013 The Authors. View Publication