参考文献

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) hold promise for therapeutic applications. To serve these functions,the hiPSC-CM must recapitulate the electrophysiologic properties of native adult cardiomyocytes. This study examines the electrophysiologic characteristics of hiPSC-CM between 11 and 121 days of maturity. Embryoid bodies (EBs) were generated from hiPS cell line reprogrammed with Oct4,Nanog,Lin28 and Sox2. Sharp microelectrodes were used to record action potentials (AP) from spontaneously beating clusters (BC) micro-dissected from the EBs (n = 103; 37°C) and to examine the response to 5 µM E-4031 (n = 21) or BaCl(2) (n = 22). Patch-clamp techniques were used to record I(Kr) and I(K1) from cells enzymatically dissociated from BC (n = 49; 36°C). Spontaneous cycle length (CL) and AP characteristics varied widely among the 103 preparations. E-4031 (5 µM; n = 21) increased Bazett-corrected AP duration from 291.8±81.2 to 426.4±120.2 msec (ptextless0.001) and generated early afterdepolarizations in 8/21 preparations. In 13/21 BC,E-4031 rapidly depolarized the clusters leading to inexcitability. BaCl(2),at concentrations that selectively block I(K1) (50-100 µM),failed to depolarize the majority of clusters (13/22). Patch-clamp experiments revealed very low or negligible I(K1) in 53% (20/38) of the cells studied,but presence of I(Kr) in all (11/11). Consistent with the electrophysiological data,RT-PCR and immunohistochemistry studies showed relatively poor mRNA and protein expression of I(K1) in the majority of cells,but robust expression of I(Kr.) In contrast to recently reported studies,our data point to major deficiencies of hiPSC-CM,with remarkable diversity of electrophysiologic phenotypes as well as pharmacologic responsiveness among beating clusters and cells up to 121 days post-differentiation (dpd). The vast majority have a maximum diastolic potential that depends critically on I(Kr) due to the absence of I(K1). Thus,efforts should be directed at producing more specialized and mature hiPSC-CM for future therapeutic applications. View Publication

PURPOSE We aimed to assess the biologic activity of PF-03084014 in breast xenograft models. The biomarkers for mechanism and patient stratification were also explored. EXPERIMENTAL DESIGN The in vitro and in vivo properties of PF-03084014 were investigated. The mRNA expressions of 40 key Notch pathway genes at baseline or after treatment were analyzed to link with the antitumor efficacy of PF-03084014 in a panel of breast cancer xenograft models. RESULTS In vitro,PF-03084014 exhibited activity against tumor cell migration,endothelial cell tube formation,and mammosphere formation. In vivo,we observed apoptosis,antiproliferation,reduced tumor cell self-renewal ability,impaired tumor vasculature,and decreased metastasis activity after the treatment of PF-03084014. PF-03084014 treatment displayed significant antitumor activity in 10 of the 18 breast xenograft models. However,the antitumor efficacy in most models did not correlate with the in vitro antiproliferation results in the corresponding cell lines,suggesting the critical involvement of tumor microenvironment during Notch activation. In the tested breast xenograft models,the baseline expressions of the Notch receptors,ligands,and the cleaved Notch1 failed to predict the antitumor response to PF-03084014,whereas several Notch pathway target genes,including HEY2,HES4,and HES3,strongly corresponded with the response with a P value less than 0.01. Many of the best molecular predictors of response were also significantly modulated following PF-03084014 treatment. CONCLUSIONS PF-03084014 showed antitumor and antimetastatic properties via pleiotropic mechanisms. The Notch pathway downstream genes may be used to predict the antitumor activity of PF-03084014 and enrich for responders among breast cancer patients. View Publication

We developed a protocol of in vitro differentiation of human embryonic stem cells into three-dimensional structures histologically and molecularly similar to the developing retina. View Publication

Understanding how hematopoietic stem cells (HSCs) are generated and the signals that control this process is a crucial issue for regenerative medicine applications that require in vitro production of HSC. HSCs emerge during embryonic life from an endothelial-like cell population that resides in the aorta-gonad-mesonephros (AGM) region. We show here that β-catenin is nuclear and active in few endothelial nonhematopoietic cells closely associated with the emerging hematopoietic clusters of the embryonic aorta during mouse development. Importantly,Wnt/β-catenin activity is transiently required in the AGM to generate long-term HSCs and to produce hematopoietic cells in vitro from AGM endothelial precursors. Genetic deletion of β-catenin from the embryonic endothelium stage (using VE-cadherin-Cre recombinase),but not from embryonic hematopoietic cells (using Vav1-Cre),precludes progression of mutant cells toward the hematopoietic lineage; however,these mutant cells still contribute to the adult endothelium. Together,those findings indicate that Wnt/β-catenin activity is needed for the emergence but not the maintenance of HSCs in mouse embryos. View Publication

Sox2 (sex-determining region Y-box protein 2) is a transcription factor regulating pluripotency in embryonic stem cells. Sox2 is aberrantly expressed in breast and other cancers,though its biological significance remains widely unexplored. To understand the significance of this aberrancy,we assessed the transcription activity of Sox2 in two Sox2-expressing breast cancer cell lines,MCF7 and ZR751,using a lentiviral Sox2 GFP reporter vector. Surprisingly,Sox2 transcription activity,as measured by GFP expression encoded in a Sox2 reporter construct,was detectable only in a small subset of cells in both cell lines. Purification of GFP+ cells (cells with Sox2 activity) and GFP- cells (cells without Sox2 activity) was enriched for two phenotypically distinct cell populations in both MCF7 and ZR751 cell lines. Specifically,GFP+ cells formed significantly more colonies in methylcellulose and more mammospheres in vitro compared to GFP- cells. These phenotypic differences are directly linked to Sox2 as siRNA knockdown of Sox2 in GFP+ cells abolished these abilities. To provide a mechanistic explanation to our observations,we performed gel shift and chromatin immunoprecipitation studies; Sox2 was found to bind to its DNA binding consensus sequence and the promoters of Cyclin D1 and Nanog (two known Sox2 downstream targets) only in GFP+ cells. GFP+ cells also up-regulated CD49f,phospho-GSK3$$,and $$-catenin. In summary,we have identified two novel phenotypically distinct cell subsets in two breast cancer cell lines based on their differential Sox2 transcription activity. We demonstrate that Sox2 transcription activity,and not its protein expression alone,underlies the tumorigenicity and cancer stem cell-like phenotypes in breast cancers. View Publication

Bromodomains are readers of the epigenetic code that specifically bind acetyl-lysine containing recognition sites on proteins. Recently the BET family of bromodomains has been demonstrated to be druggable through the discovery of potent inhibitors,sparking an interest in protein-protein interaction inhibitors that directly target gene transcription. Here,we assess the druggability of diverse members of the bromodomain family using SiteMap and show that there are significant differences in predicted druggability. Furthermore,we trace these differences in druggability back to unique amino acid signatures in the bromodomain acetyl-lysine binding sites. These signatures were then used to generate a new classification of the bromodomain family,visualized as a classification tree. This represents the first analysis of this type for the bromodomain family and can prove useful in the discovery of inhibitors,particularly for anticipating screening hit rates,identifying inhibitors that can be explored for lead hopping approaches,and selecting proteins for selectivity screening. View Publication

VIDEO ABSTRACT: Although endogenous recruitment of adult neural stem cells has been proposed as a therapeutic strategy,clinical approaches for achieving this are lacking. Here,we show that metformin,a widely used drug,promotes neurogenesis and enhances spatial memory formation. Specifically,we show that an atypical PKC-CBP pathway is essential for the normal genesis of neurons from neural precursors and that metformin activates this pathway to promote rodent and human neurogenesis in culture. Metformin also enhances neurogenesis in the adult mouse brain in a CBP-dependent fashion,and in so doing enhances spatial reversal learning in the water maze. Thus,metformin,by activating an aPKC-CBP pathway,recruits neural stem cells and enhances neural function,thereby providing a candidate pharmacological approach for nervous system therapy. View Publication

Stable pluripotent feeder-free propagation of human embryonic stem cells (hESCs) prior to their therapeutic applications remains a major challenge. Matrigel™ (BD Singapore) is a murine sarcoma-derived extracellular matrix (ECM) widely used as a cell-free support combined with conditioned or chemically defined media; however,inherent xenogenic and immunological threats invalidate it for clinical applications. Using human fibrogenic cells to generate ECM is promising but currently suffers from inefficient and time-consuming deposition in vitro. We recently showed that macromolecular crowding (MMC) accelerated ECM deposition substantially in vitro. In the current study,we used dextran sulfate 500 kDa as a macromolecular crowder to induce WI-38 fetal human lung fibroblasts at 0.5% serum condition to deposit human ECM in three days. After decellularization,the generated ECMs allowed stable propagation of H9 hESCs over 20 passages in chemically-defined medium (mTEsR1) with an overall improved outcome compared to Matrigel in terms of population doubling while retaining teratoma formation and differentiation capacity. Of significance,only ECMs generated by MMC allowed the successful propagation of hESCs. ECMs were highly complex and in contrast to Matrigel,contained no vitronectin but did contain collagen XII,ig-h3 and novel for hESC-supporting human matrices,substantial amounts of transglutaminase 2. Genome-wide analysis of promoter DNA methylation states revealed high overall similarity between human ECM- and Matrigel-cultured hESCs; however,distinct differences were observed with 49 genes associated with a variety of cellular functions. Thus,human ECMs deposited by MMC by selected fibroblast lines are a suitable human microenvironment for stable hESC propagation and clinically translational settings. View Publication

Based on knowledge of early embryo development,where anterior neural ectoderm (ANE) development is regulated by native inhibitors of bone morphogenic protein (BMP) and Nodal/Activin signaling,most published protocols of human embryonic stem cell differentiation to ANE have demonstrated a crucial role for Smad signaling in neural induction. The drawbacks of such protocols include the use of an embryoid body culture step and use of polypeptide secreted factors that are both expensive and,when considering clinical applications,have significant challenges in terms of good manufacturing practices compliancy. The use of small molecules to direct differentiation of pluripotent stem cells toward a specified lineage represents a powerful approach to generate specific cell types for further understanding of biological function,for understanding disease processes,for use in drug discovery,and finally for use in regenerative medicine. We therefore aimed to find controlled and reproducible animal-component-free differentiation conditions that would use only small molecules. Here,we demonstrate that pluripotent stem cells can be reproducibly and efficiently differentiated to PAX6(+) (a marker of neuroectoderm) and OCT4(-) (a marker of pluripotent stem cells) cells with the use of potent small inhibitors of the BMP and Activin/Nodal pathways,and in animal-component-free conditions,replacing the frequently used Noggin and SB431542. We also show by transcript analysis,both at the population level and for the first time at the single-cell level,that differentiated cells express genes characteristic for the development of ANE,in particular for the development of the future forebrain. View Publication

Induced pluripotent stem cells (iPSCs) with potential for therapeutic applications can be derived from somatic cells via ectopic expression of a set of limited and defined transcription factors. However,due to risks of random integration of the reprogramming transgenes into the host genome,the low efficiency of the process,and the potential risk of virally induced tumorigenicity,alternative methods have been developed to generate pluripotent cells using nonintegrating systems,albeit with limited success. Here,we show that c-KIT+ human first-trimester amniotic fluid stem cells (AFSCs) can be fully reprogrammed to pluripotency without ectopic factors,by culture on Matrigel in human embryonic stem cell (hESC) medium supplemented with the histone deacetylase inhibitor (HDACi) valproic acid (VPA). The cells share 82% transcriptome identity with hESCs and are capable of forming embryoid bodies (EBs) in vitro and teratomas in vivo. After long-term expansion,they maintain genetic stability,protein level expression of key pluripotency factors,high cell-division kinetics,telomerase activity,repression of X-inactivation,and capacity to differentiate into lineages of the three germ layers,such as definitive endoderm,hepatocytes,bone,fat,cartilage,neurons,and oligodendrocytes. We conclude that AFSC can be utilized for cell banking of patient-specific pluripotent cells for potential applications in allogeneic cellular replacement therapies,pharmaceutical screening,and disease modeling. View Publication