参考文献

Human embryonic stem cells (hESCs) offer tremendous potential for not only treating neurological disorders but also for their ability to serve as vital reagents to model and investigate human disease. To further our understanding of a key protein involved in Alzheimer disease pathogenesis,we stably overexpressed amyloid precursor protein (APP) in hESCs. Remarkably,we found that APP overexpression in hESCs caused a rapid and robust differentiation of pluripotent stem cells toward a neural fate. Despite maintenance in standard hESC media,up to 80% of cells expressed the neural stem cell marker nestin,and 65% exhibited the more mature neural marker β-3 tubulin within just 5 days of passaging. To elucidate the mechanism underlying the effects of APP on neural differentiation,we examined the proteolysis of APP and performed both gain of function and loss of function experiments. Taken together,our results demonstrate that the N-terminal secreted soluble forms of APP (in particular sAPPβ) robustly drive neural differentiation of hESCs. Our findings not only reveal a novel and intriguing role for APP in neural lineage commitment but also identify a straightforward and rapid approach to generate large numbers of neurons from human embryonic stem cells. These novel APP-hESC lines represent a valuable tool to investigate the potential role of APP in development and neurodegeneration and allow for insights into physiological functions of this protein. View Publication

The differentiation of patient-derived induced pluripotent stem cells (iPSCs) to committed fates such as neurons,muscle and liver is a powerful approach for understanding key parameters of human development and disease. Whether undifferentiated iPSCs themselves can be used to probe disease mechanisms is uncertain. Dyskeratosis congenita is characterized by defective maintenance of blood,pulmonary tissue and epidermal tissues and is caused by mutations in genes controlling telomere homeostasis. Short telomeres,a hallmark of dyskeratosis congenita,impair tissue stem cell function in mouse models,indicating that a tissue stem cell defect may underlie the pathophysiology of dyskeratosis congenita. Here we show that even in the undifferentiated state,iPSCs from dyskeratosis congenita patients harbour the precise biochemical defects characteristic of each form of the disease and that the magnitude of the telomere maintenance defect in iPSCs correlates with clinical severity. In iPSCs from patients with heterozygous mutations in TERT,the telomerase reverse transcriptase,a 50% reduction in telomerase levels blunts the natural telomere elongation that accompanies reprogramming. In contrast,mutation of dyskerin (DKC1) in X-linked dyskeratosis congenita severely impairs telomerase activity by blocking telomerase assembly and disrupts telomere elongation during reprogramming. In iPSCs from a form of dyskeratosis congenita caused by mutations in TCAB1 (also known as WRAP53),telomerase catalytic activity is unperturbed,yet the ability of telomerase to lengthen telomeres is abrogated,because telomerase mislocalizes from Cajal bodies to nucleoli within the iPSCs. Extended culture of DKC1-mutant iPSCs leads to progressive telomere shortening and eventual loss of self-renewal,indicating that a similar process occurs in tissue stem cells in dyskeratosis congenita patients. These findings in iPSCs from dyskeratosis congenita patients reveal that undifferentiated iPSCs accurately recapitulate features of a human stem cell disease and may serve as a cell-culture-based system for the development of targeted therapeutics. View Publication

HSCs are rare cells that have the unique ability to self-renew and differentiate into cells of all hematopoietic lineages. The lack of donors and current inability to rapidly and efficiently expand HSCs are roadblocks in the development of successful cell therapies. Thus,the challenge of ex vivo human HSC expansion remains a fertile and critically important area of investigation. Here,we show that either SALL4A- or SALL4B-transduced human HSCs obtained from the mobilized peripheral blood are capable of rapid and efficient expansion ex vivo by textgreater10 000-fold for both CD34(+)/CD38(-) and CD34(+)/CD38(+) cells in the presence of appropriate cytokines. We found that these cells retained hematopoietic precursor cell immunophenotypes and morphology as well as normal in vitro or vivo potential for differentiation. The SALL4-mediated expansion was associated with enhanced stem cell engraftment and long-term repopulation capacity in vivo. Also,we demonstrated that constitutive expression of SALL4 inhibited granulocytic differentiation and permitted expansion of undifferentiated cells in 32D myeloid progenitors. Furthermore,a TAT-SALL4B fusion rapidly expanded CD34(+) cells,and it is thus feasible to translate this study into the clinical setting. Our findings provide a new avenue for investigating mechanisms of stem cell self-renewal and achieving clinically significant expansion of human HSCs. View Publication

Disentangling the complex interactions that govern stem cell fate choices of self-renewal,differentiation,or death presents a formidable challenge. Image-based phenotype-driven screening meets this challenge by providing means for rapid testing of many small molecules simultaneously. Pluripotent embryonal carcinoma (EC) cells offer a convenient substitute for embryonic stem (ES) cells in such screens because they are simpler to maintain and control. The authors developed an image-based screening assay to identify compounds that affect survival or differentiation of the human EC stem cell line NTERA2 by measuring the effect on cell number and the proportion of cells expressing a pluripotency-associated marker SSEA3. A pilot screen of 80 kinase inhibitors identified several compounds that improved cell survival or induced differentiation. The survival compounds Y-27632,HA-1077,and H-8 all strongly inhibit the kinases ROCK and PRK2,highlighting the important role of these kinases in EC cell survival. Two molecules,GF109203x and rottlerin,induced EC differentiation. The effects of rottlerin were also investigated in human ES cells. Rottlerin inhibited the self-renewal ability of ES cells,caused the cell cycle arrest,and repressed the expression of pluripotency-associated genes. View Publication

Directed hepatocyte differentiation from human induced pluripotent stem cells (iPSCs) potentially provides a unique platform for modeling liver genetic diseases and performing drug-toxicity screening in vitro. Wilson's disease is a genetic disease caused by mutations in the ATP7B gene,whose product is a liver transporter protein responsible for coordinated copper export into bile and blood. Interestingly,the spectrum of ATP7B mutations is vast and can influence clinical presentation (a variable spectrum of hepatic and neural manifestations),though the reason is not well understood. We describe the generation of iPSCs from a Chinese patient with Wilson's disease that bears the R778L Chinese hotspot mutation in the ATP7B gene. These iPSCs were pluripotent and could be readily differentiated into hepatocyte-like cells that displayed abnormal cytoplasmic localization of mutated ATP7B and defective copper transport. Moreover,gene correction using a self-inactivating lentiviral vector that expresses codon optimized-ATP7B or treatment with the chaperone drug curcumin could reverse the functional defect in vitro. Hence,our work describes an attractive model for studying the pathogenesis of Wilson's disease that is valuable for screening compounds or gene therapy approaches aimed to correct the abnormality. In the future,once relevant safety concerns (including the stability of the mature liver-like phenotype) and technical issues for the transplantation procedure are solved,hepatocyte-like cells from similarly genetically corrected iPSCs could be an option for autologous transplantation in Wilson's disease. View Publication

We present a novel and efficient non-integrating gene expression system in human embryonic stem cells (hESc) utilizing human artificial chromosomes (HAC),which behave as autonomous endogenous host chromosomes and segregate correctly during cell division. HAC are important vectors for investigating the organization and structure of the kinetochore,and gene complementation. HAC have so far been obtained in immortalized or tumour-derived cell lines,but never in stem cells,thus limiting their potential therapeutic application. In this work,we modified the herpes simplex virus type 1 amplicon system for efficient transfer of HAC DNA into two hESc. The deriving stable clones generated green fluorescent protein gene-expressing HAC at high frequency,which were stably maintained without selection for 3 months. Importantly,no integration of the HAC DNA was observed in the hESc lines,compared with the fibrosarcoma-derived control cells,where the exogenous DNA frequently integrated in the host genome. The hESc retained pluripotency,differentiation and teratoma formation capabilities. This is the first report of successfully generating gene expressing de novo HAC in hESc,and is a significant step towards the genetic manipulation of stem cells and potential therapeutic applications. View Publication

Transient lymphopenia is a hallmark of measles virus (MV)-induced immunosuppression. To address to what extent replenishment of the peripheral lymphocyte compartment from bone marrow (BM) progenitor/stem cells might be affected,we analyzed the interaction of wild-type MV with hematopoietic stem and progenitor cells (HS/PCs) and stroma cells in vitro. Infection of human CD34(+) HS/PCs or stroma cells with wild-type MV is highly inefficient yet noncytolytic. It occurs independently of CD150 in stroma cells but also in HS/PCs,where infection is established in CD34(+) CD150(-) and CD34(+) CD150(+) (in humans representing HS/PC oligopotent precursors) subsets. Stroma cells and HS/PCs can mutually transmit MV and may thereby create a possible niche for continuous viral exchange in the BM. Infected lymphocytes homing to this compartment may serve as sources for HS/PC or stroma cell infection,as reflected by highly efficient transmission of MV from both populations in cocultures with MV-infected B or T cells. Though MV exposure does not detectably affect the viability,expansion,and colony-forming activity of either CD150(+) or CD150(-) HS/PCs in vitro,it efficiently interferes with short- but not long-term hematopoietic reconstitution in NOD/SCID mice. Altogether,these findings support the hypothesis that MV accession of the BM compartment by infected lymphocytes may contribute to peripheral blood mononuclear cell lymphopenia at the level of BM suppression. View Publication

The platelet glycoprotein Ib-IX-V complex (GPIb-IX-IV) is the receptor for VWF and is responsible for VWF-mediated platelet activation and aggregation. Loss of the GPIb-IX-V complex is pathogenic for Bernard-soulier Syndrome (BSS),which is characterized by macrothrombocytopenia and impaired platelet function. It remains unclear how the GPIb-IX-V complex is assembled and whether there is a role for a specific molecular chaperone in the process. In the present study,we report that the assembly of the GPIb-IX-V complex depends critically on a molecular chaperone in the endoplasmic reticulum (ER): gp96 (also known as grp94 and HSP90b1). gp96/grp94 deletion in the murine hematopoietic system results in thrombocytopenia,prolonged bleeding time,and giant platelets that are clinically indistinguishable from human BSS. Loss of gp96/grp94 in vivo and in vitro leads to the concomitant reduction in GPIb-IX complex expression due to ER-associated degradation. We further demonstrate that gp96/grp94 binds selectively to the GPIX subunit,but not to gpIbα or gpIbβ. Therefore,we identify the platelet GPIX subunit of the GPIb-IX-V complex as an obligate and novel client of gp96/grp94. View Publication

Human induced pluripotent stem (iPS) cells potentially provide a unique resource for generating patient-specific cardiomyocytes to study cardiac disease mechanisms and treatments. However,existing approaches to cardiomyocyte production from human iPS cells are inefficient,limiting the application of iPS cells in basic and translational cardiac research. Furthermore,strategies to accurately record changes in iPS cell-derived cardiomyocyte action potential duration (APD) are needed to monitor APD-related cardiac disease and for rapid drug screening. We examined whether modulation of the bone morphogenetic protein 4 (BMP-4) and Wnt/β-catenin signaling pathways could induce efficient cardiac differentiation of human iPS cells. We found that early treatment of human iPS cells with BMP-4 followed by late treatment with small molecule Wnt inhibitors led to a marked increase in production of cardiomyocytes compared to existing differentiation strategies. Using immunocytochemical staining and real-time intracellular calcium imaging,we showed that these induced cardiomyocytes expressed typical sarcomeric markers,exhibited normal rhythmic Ca(2+) transients,and responded to both β-adrenergic and electric stimulation. Furthermore,human iPS cell-derived cardiomyocytes demonstrated characteristic changes in action potential duration in response to cardioactive drugs procainamide and verapamil using voltage-sensitive dye-based optical recording. Thus,modulation of the BMP-4 and Wnt signaling pathways in human iPS cells leads to highly efficient production of cardiomyocytes with typical electrophysiological function and pharmacologic responsiveness. The use of human iPS cell-derived cardiomyocytes and the application of calcium- and voltage-sensitive dyes for the direct,rapid measurement of iPS cell-derived cardiomyocyte activity promise to offer attractive platforms for studying cardiac disease mechanisms and therapeutics. View Publication

AIMS: Generation of human induced pluripotent stem cell (hiPSC) lines by reprogramming of fibroblast cells with virus-free methods offers unique opportunities for translational cardiovascular medicine. The aim of the study was to reprogramme fibroblast cells to hiPSCs and to study cardiomyogenic properties and ion channel characteristics of the virus-free hiPSC-derived cardiomyocytes. METHODS AND RESULTS: The hiPSCs generated by episomal vectors generated teratomas in severe combined immunodeficient mice,readily formed embryoid bodies,and differentiated into cardiomyocytes with comparable efficiency to human embryonic stem cells. Temporal gene expression of these hiPSCs indicated that differentiation of cardiomyocytes was initiated by increasing expression of cardio/mesodermal markers followed by cardiac-specific transcription factors,structural,and ion channel genes. Furthermore,the cardiomyocytes showed characteristic cross-striations of sarcomeric proteins and expressed calcium-handling and ion channel proteins,confirming their cardiac ontogeny. Microelectrode array recordings established the electrotonic development of a functional syncytium that responded predictably to pharmacologically active drugs. The cardiomyocytes showed a chronotropic dose-response (0.1-10 µM) to isoprenaline and Bay K 8644. Furthermore,carbamycholine (5 µM) suppressed the response to isoprenaline,while verapamil (2.5 µM) blocked Bay K 8644-induced inotropic activity. Moreover,verapamil (1 µM) reduced the corrected field potential duration by 45%,tetrodotoxin (10 µM) shortened the minimal field potential by 40%,and E-4031 (50 nM) prolonged field repolarization. CONCLUSION: Virus-free hiPSCs differentiate efficiently into cardiomyocytes with cardiac-specific molecular,structural,and functional properties that recapitulate the developmental ontogeny of cardiogenesis. These results,coupled with the potential to generate patient-specific hiPSC lines,hold great promise for the development of an in vitro platform for drug pharmacogenomics,disease modelling,and regenerative medicine. View Publication

Strategies to induce p53 activation in wtp53-retaining tumors carry high potential in cancer therapy. Nutlin,a potent highly selective MDM2 inhibitor,induces non-genotoxic p53 activation. Although Nutlin shows promise in promoting cell death in hematopoietic malignancies,a major roadblock is that most solid cancers do not undergo apoptosis but merely reversible growth arrest. p53 inhibition by unopposed MDMX is one major cause for apoptosis resistance to Nutlin. The Hsp90 chaperone is ubiquitously activated in cancer cells and supports oncogenic survival pathways,many of which antagonize p53. The Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG) is known to induce p53-dependent apoptosis. We show here that in multiple difficult-to-kill solid tumor cells 17AAG modulates several critical components that synergize with Nutlin-activated p53 signaling to convert Nutlin's transient cytostatic response into a cytotoxic killing response in vitro and in xenografts. Combined with Nutlin,17AAG destabilizes MDMX,reduces MDM2,induces PUMA and inhibits oncogenic survival pathways,such as PI3K/AKT,which counteract p53 signaling at multiple levels. Mechanistically,17AAG interferes with the repressive MDMX-p53 axis by inducing robust MDMX degradation,thereby markedly increasing p53 transcription compared with Nutlin alone. To our knowledge Nutlin+17AAG represents the first effective pharmacologic knockdown of MDMX. Our study identifies 17AAG as a promising synthetic lethal partner for a more efficient Nutlin-based therapy. View Publication

Human induced pluripotent stem cells (iPSCs) are a potential source of hepatocytes for liver transplantation to treat end-stage liver disease. In vitro differentiation of human iPSCs into hepatic cells has been achieved using a multi- stage differentiation protocol,but whether these cells are functional and capable of engrafting and regenerating diseased liver tissue is not clear. We show that human iPSC-derived hepatic cells at various differentiation stages can engraft the liver in a mouse transplantation model. Using the same differentiation and transplantation protocols,we also assessed the ability of human iPSCs derived from each of the three developmental germ layer tissues (that is,ectoderm,mesoderm,and endoderm) to regenerate mouse liver. These iPSC lines,with similar but distinct global DNA methylation patterns,differentiated into multistage hepatic cells with an efficiency similar to that of human embryonic stem cells. Human hepatic cells at various differentiation stages derived from iPSC lines of different origins successfully repopulated the liver tissue of mice with liver cirrhosis. They also secreted human-specific liver proteins into mouse blood at concentrations comparable to that of proteins secreted by human primary hepato- cytes. Our results demonstrate the engraftment and liver regenerative capabilities of human iPSC-derived multi- stage hepatic cells in vivo and suggest that human iPSCs of distinct origins and regardless of their parental epigenetic memory can efficiently differentiate along the hepatic lineage. View Publication