参考文献

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

Sirtuins (SIRTs),NAD+-dependent class III histone deacetylases (HDACs),play an important role in the regulation of cell division,survival and senescence. Although a number of effective SIRT inhibitors have been developed,little is known about the specific mechanisms of their anticancer activity. In this study,we investigated the anticancer effects of sirtinol,a SIRT inhibitor,on MCF-7 human breast cancer cells. Apoptotic and autophagic cell death were measured. Sirtinol significantly inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. The IC50 values of sirtinol were 48.6 µM (24 h) and 43.5 µM (48 h) in MCF-7 cells. As expected,sirtinol significantly increased the acetylation of p53,which has been reported to be a target of SIRT1/2. Flow cyto-metry analysis revealed that sirtinol significantly increased the G1 phase of the cell cycle. The upregulation of Bax,downregulation of Bcl-2 and cytochrome c release into the cytoplasm,which are considered as mechanisms of apoptotic cell death,were observed in the MCF-7 cells treated with sirtinol. The annexin V-FITC assay was used to confirm sirtinol-induced apoptotic cell death. Furthermore,the expression of LC3-II,an autophagy-related molecule,was significantly increased in MCF-7 cells after sirtinol treatment. Autophagic cell death was confirmed by acridine orange and monodansylcadaverine (MDC) staining. Of note,pre-treatment with 3-methyladenine (3-MA) increased the sirtinol-induced MCF-7 cell cytotoxicity,which is associated with blocking autophagic cell death and increasing apoptotic cell death. Based on our results,the downregulation of SIRT1/2 expression may play an important role in the regulation of breast cancer cell death; thus,SIRT1/2 may be a novel molecular target for cancer therapy and these findings may provide a molecular basis for targeting SIRT1/2 in future cancer therapy. View Publication

Considerable progress has been made in identifying signaling pathways that direct the differentiation of human pluripotent stem cells (hPSCs) into specialized cell types,including neurons. However,differentiation of hPSCs with extrinsic factors is a slow,step-wise process,mimicking the protracted timing of human development. Using a small-molecule screen,we identified a combination of five small-molecule pathway inhibitors that yield hPSC-derived neurons at textgreater75% efficiency within 10 d of differentiation. The resulting neurons express canonical markers and functional properties of human nociceptors,including tetrodotoxin (TTX)-resistant,SCN10A-dependent sodium currents and response to nociceptive stimuli such as ATP and capsaicin. Neuronal fate acquisition occurs about threefold faster than during in vivo development,suggesting that use of small-molecule pathway inhibitors could become a general strategy for accelerating developmental timing in vitro. The quick and high-efficiency derivation of nociceptors offers unprecedented access to this medically relevant cell type for studies of human pain. View Publication

Canonical Wnt/β-catenin signaling has been suggested to promote self-renewal of pluripotent mouse and human embryonic stem cells. Here,we show that SB-216763,a glycogen synthase kinase-3 (GSK3) inhibitor,can maintain mouse embryonic stem cells (mESCs) in a pluripotent state in the absence of exogenous leukemia inhibitory factor (LIF) when cultured on mouse embryonic fibroblasts (MEFs). MESCs maintained with SB-216763 for one month were morphologically indistinguishable from LIF-treated mESCs and expressed pluripotent-specific genes Oct4,Sox2,and Nanog. Furthermore,Nanog immunostaining was more homogenous in SB-216763-treated colonies compared to LIF. Embryoid bodies (EBs) prepared from these mESCs expressed early-stage markers for all three germ layers,and could efficiently differentiate into cardiac-like cells and MAP2-immunoreactive neurons. To our knowledge,SB-216763 is the first GSK3 inhibitor that can promote self-renewal of mESC co-cultured with MEFs for more than two months. View Publication

Long QT syndrome (LQTS) is a genetic disease characterized by a prolonged QT interval in an electrocardiogram (ECG),leading to higher risk of sudden cardiac death. Among the 12 identified genes causal to heritable LQTS,∼90% of affected individuals harbor mutations in either KCNQ1 or human ether-a-go-go related genes (hERG),which encode two repolarizing potassium currents known as I(Ks) and I(Kr). The ability to quantitatively assess contributions of different current components is therefore important for investigating disease phenotypes and testing effectiveness of pharmacological modulation. Here we report a quantitative analysis by simulating cardiac action potentials of cultured human cardiomyocytes to match the experimental waveforms of both healthy control and LQT syndrome type 1 (LQT1) action potentials. The quantitative evaluation suggests that elevation of I(Kr) by reducing voltage sensitivity of inactivation,not via slowing of deactivation,could more effectively restore normal QT duration if I(Ks) is reduced. Using a unique specific chemical activator for I(Kr) that has a primary effect of causing a right shift of V(1/2) for inactivation,we then examined the duration changes of autonomous action potentials from differentiated human cardiomyocytes. Indeed,this activator causes dose-dependent shortening of the action potential durations and is able to normalize action potentials of cells of patients with LQT1. In contrast,an I(Kr) chemical activator of primary effects in slowing channel deactivation was not effective in modulating action potential durations. Our studies provide both the theoretical basis and experimental support for compensatory normalization of action potential duration by a pharmacological agent. View Publication

Fibroblast growth factor receptor 1 (Fgfr1) gene knockout impairs cardiomyocyte differentiation in murine embryonic stem cells (mESC). Here,various chemical compounds able to enhance cardiomyocyte differentiation in mESC [including dimethylsulfoxide,ascorbic acid (vitC),free radicals and reactive oxygen species] were tested for their ability to rescue the cardiomyogenic potential of Fgfr1(-/-) mESC. Among them,only the reduced form of vitC,l-ascorbic acid,was able to recover beating cell differentiation in Fgfr1(-/-) mESC. The appearance of contracting cells was paralleled by the expression of early and late cardiac gene markers,thus suggesting their identity as cardiomyocytes. In the attempt to elucidate the mechanism of action of vitC on Fgfr1(-/-) mESC,we analyzed several parameters related to the intracellular redox state,such as reactive oxygen species content,Nox4 expression,and superoxide dismutase activity. The results did not show any relationship between the antioxidant capacity of vitC and cardiomyocyte differentiation in Fgfr1(-/-) mESC. No correlation was found also for the ability of vitC to modulate the expression of pluripotency genes. Then,we tested the hypothesis that vitC was acting as a prolyl hydroxylase cofactor by maintaining iron in a reduced state. We first analyze hypoxia inducible factor (HIF)-1α mRNA and protein levels that were found to be slightly upregulated in Fgfr1(-/-) cells. We treated mESC with Fe(2+) or the HIF inhibitor CAY10585 during the first phases of the differentiation process and,similar to vitC,the two compounds were able to rescue cardiomyocyte formation in Fgfr1(-/-) mESC,thus implicating HIF-1α modulation in Fgfr1-dependent cardiomyogenesis. View Publication

Human embryonic stem cells (hESCs) hold great promise for regenerative medicine because they can undergo unlimited self-renewal and retain the capability to differentiate into all cell types in the body. Although numerous genes/proteins such as Oct4 and Gata6 have been identified to play critical regulatory roles in self-renewal and differentiation of hESC,the majority of the regulators in these cellular processes and more importantly how these regulators co-operate with each other and/or with epigenetic modifications are still largely unknown. We propose here a systematic approach to integrate genomic and epigenomic data for identification of direct regulatory interactions. This approach allows reconstruction of cell-type-specific transcription networks in embryonic stem cells (ESCs) and fibroblasts at an unprecedented scale. Many links in the reconstructed networks coincide with known regulatory interactions or literature evidence. Systems-level analyses of these networks not only uncover novel regulators for pluripotency and differentiation,but also reveal extensive interplays between transcription factor binding and epigenetic modifications. Especially,we observed poised enhancers characterized by both active (H3K4me1) and repressive (H3K27me3) histone marks that contain enriched Oct4- and Suz12-binding sites. The success of such a systems biology approach is further supported by experimental validation of the predicted interactions. View Publication