技术资料

Long-term marrow cultures (LTMC) allow the proliferation and differentiation of primitive human hematopoietic progenitor cells to be maintained for many weeks in the absence of exogenously provided hematopoietic growth factors. Previous investigations focused on defining various types of cells that are present in this culture system and on measuring the cycling behavior of the different subpopulations of colony-forming cells maintained within it. These studies suggested that mesenchymal stromal elements derived from the input marrow play a key role in regulating the turnover of the most primitive,high-proliferative potential erythroid and granulopoietic colony-forming cells that are found almost exclusively in the adherent layer of LTMC. In this study we show that the re-entry into S-phase of these primitive hematopoietic progenitors that occurs after each weekly medium change is due to an as yet undefined constituent of horse serum,which is absent from fetal calf serum. However,this effect is not unique to the factor present in horse serum. It is also elicited by the addition to LTMC of several well-defined growth regulatory molecules,ie,platelet-derived growth factor (PDGF),interleukin-1 (IL-1),transforming growth factor alpha (TGF-alpha),and IL-2. None of these was able to stimulate hematopoietic colony-forming cells in methylcellulose assays,although all have known actions on mesenchymal cells including,in some cases,the ability to increase production of growth factors that can stimulate primitive high-proliferative potential hematopoietic progenitors in clonogenic assays. Interestingly,a stimulating effect was not obtained after addition of endotoxin to LTMC. TGF-beta,a direct-acting negative regulator that acts selectively on primitive hematopoietic progenitor cells if added to LTMC simultaneously with new medium or IL-1,blocked their stimulating activity. These results suggest a model in which indirect,local modulation of both positive and negative regulatory factors via effects on mesenchymal elements determines the rate of turnover of adjacent populations of very primitive hematopoietic cells that are normally maintained in a quiescent state in vivo. View Publication

Reprogramming somatic cells into induced pluripotent stem cells (iPSCs) has provided huge insight into the pathways,mechanisms and transcription factors that control differentiation. Here we use high-throughput RT-PCR technology to take a snapshot of splicing changes in the full spectrum of high- and low-expressed genes during induction of fibroblasts,from several donors,into iPSCs and their subsequent redifferentiation. We uncover a programme of concerted alternative splicing changes involved in late mesoderm differentiation and controlled by key splicing regulators MBNL1 and RBFOX2. These critical splicing adjustments arise early in vertebrate evolution and remain fixed in at least 10 genes (including PLOD2,CLSTN1,ATP2A1,PALM,ITGA6,KIF13A,FMNL3,PPIP5K1,MARK2 and FNIP1),implying that vertebrates require alternative splicing to fully implement the instructions of transcriptional control networks. 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

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

A prerequisite for the realization of human pluripotent stem cell (hPSC) therapies is the development of bioprocesses for generating clinically relevant quantities of undifferentiated hPSCs and their derivatives under xeno-free conditions. Microcarrier stirred-suspension bioreactors are an appealing modality for the scalable expansion and directed differentiation of hPSCs. Comparative analyses of commercially available microcarriers clearly show the need for developing synthetic substrates supporting the adhesion and growth of hPSCs in three-dimensional cultures under agitation-induced shear. Moreover,the low seeding efficiencies during microcarrier loading with hPSC clusters poses a significant process bottleneck. To that end,a novel protocol was developed increasing hPSC seeding efficiency from 30% to over 80% and substantially shortening the duration of microcarrier loading. Importantly,this method was combined with the engineering of polystyrene microcarriers by surface conjugation of a vitronectin-derived peptide,which was previously shown to support the growth of human embryonic stem cells. Cells proliferated on peptide-conjugated beads in static culture but widespread detachment was observed after exposure to stirring. This prompted additional treatment of the microcarriers with a synthetic polymer commonly used to enhance cell adhesion. hPSCs were successfully cultivated on these microcarriers in stirred suspension vessels for multiple consecutive passages with attachment efficiencies close to 40%. Cultured cells exhibited on average a 24-fold increase in concentration per 6-day passage,over 85% viability,and maintained a normal karyotype and the expression of pluripotency markers such as Nanog,Oct4,and SSEA4. When subjected to spontaneous differentiation in embryoid body cultures or directed differentiation to the three embryonic germ layers,the cells adopted respective fates displaying relevant markers. Lastly,engineered microcarriers were successfully utilized for the expansion and differentiation of hPSCs to mesoderm progeny in stirred suspension vessels. Hence,we demonstrate a strategy for the facile engineering of xeno-free microcarriers for stirred-suspension cultivation of hPSCs. Our findings support the use of microcarrier bioreactors for the scalable,xeno-free propagation and differentiation of human stem cells intended for therapies. View Publication

Hybridomas producing mouse monoclonal antibodies to antigens of the human mammary carcinoma cell line,MCF-7,have been generated by electric field-mediated fusion at a frequency ten times higher than by polyethylene glycol. One of the monoclonal antibodies obtained recognizes a cytoskeletal structure restricted to epithelial cells and carcinomas with a distribution pattern resembling cytokeratin 19. View Publication

AIMS: Mesenchymal stem cells (MSCs) are widely used for cell therapy,particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity,critical elements for their survival and differentiation,have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and,more generally,to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation. METHODS AND RESULTS: MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes,a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand,A-769662,a well-characterized AMPK activator,was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice,providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation,we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved,whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation. CONCLUSION: MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation,p27 being involved in this regulation. View Publication

Induced pluripotent stem cells (iPSC) offer a unique opportunity for developmental studies,disease modeling and regenerative medicine approaches in humans. The aim of our study was to create an in vitro 'patient-specific cell-based system' that could facilitate the screening of new therapeutic molecules for the treatment of catecholaminergic polymorphic ventricular tachycardia (CPVT),an inherited form of fatal arrhythmia. Here,we report the development of a cardiac model of CPVT through the generation of iPSC from a CPVT patient carrying a heterozygous mutation in the cardiac ryanodine receptor gene (RyR2) and their subsequent differentiation into cardiomyocytes (CMs). Whole-cell patch-clamp and intracellular electrical recordings of spontaneously beating cells revealed the presence of delayed afterdepolarizations (DADs) in CPVT-CMs,both in resting conditions and after $\$-adrenergic stimulation,resembling the cardiac phenotype of the patients. Furthermore,treatment with KN-93 (2-[N-(2-hydroxyethyl)]-N-(4methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine),an antiarrhythmic drug that inhibits Ca(2+)/calmodulin-dependent serine-threonine protein kinase II (CaMKII),drastically reduced the presence of DADs in CVPT-CMs,rescuing the arrhythmic phenotype induced by catecholaminergic stress. In addition,intracellular calcium transient measurements on 3D beating clusters by fast resolution optical mapping showed that CPVT clusters developed multiple calcium transients,whereas in the wild-type clusters,only single initiations were detected. Such instability is aggravated in the presence of isoproterenol and is attenuated by KN-93. As seen in our RyR2 knock-in CPVT mice,the antiarrhythmic effect of KN-93 is confirmed in these human iPSC-derived cardiac cells,supporting the role of this in vitro system for drug screening and optimization of clinical treatment strategies. View Publication

Neutrophils are recruited from the blood to sites of inflammation,where they contribute to immune defense but may also cause tissue damage. During inflammation,neutrophils roll along the microvascular endothelium before arresting and transmigrating. Arrest requires conformational activation of the integrin lymphocyte function-associated antigen 1 (LFA-1),which can be induced by selectin engagement. Here,we demonstrate that a subset of P-selectin glycoprotein ligand-1 (PSGL-1) molecules is constitutively associated with L-selectin. Although this association does not require the known lectin-like interaction between L-selectin and PSGL-1,the signaling output is dependent on this interaction and the cytoplasmic tail of L-selectin. The PSGL-1-L-selectin complex signals through Src family kinases,ITAM domain-containing adaptor proteins,and other kinases to ultimately result in LFA-1 activation. The PSGL-1-L-selectin complex-induced signaling effects on neutrophil slow rolling and recruitment in vivo demonstrate the functional importance of this pathway. We conclude that this is a signaling complex specialized for sensing adhesion under flow. View Publication

Geometric factors including the size,shape,density,and spacing of pluripotent stem cell colonies play a significant role in the maintenance of pluripotency and in cell fate determination. These factors are impossible to control using standard tissue culture methods. As such,there can be substantial batch-to-batch variability in cell line maintenance and differentiation yield. Here,we demonstrate a simple,robust technique for pluripotent stem cell expansion and cardiomyocyte differentiation by patterning cell colonies with a silicone stencil. We have observed that patterning human induced pluripotent stem cell (hiPSC) colonies improves the uniformity and repeatability of their size,density,and shape. Uniformity of colony geometry leads to improved homogeneity in the expression of pluripotency markers SSEA4 and Nanog as compared with conventional clump passaging. Patterned cell colonies are capable of undergoing directed differentiation into spontaneously beating cardiomyocyte clusters with improved yield and repeatability over unpatterned cultures seeded either as cell clumps or uniform single cell suspensions. Circular patterns result in a highly repeatable 3D ring-shaped band of cardiomyocytes which electrically couple and lead to propagating contraction waves around the ring. Because of these advantages,geometrically patterning stem cells using stencils may offer greater repeatability from batch-to-batch and person-to-person,an increase in differentiation yield,a faster experimental workflow,and a simpler protocol to communicate and follow. Furthermore,the ability to control where cardiomyocytes arise across a culture well during differentiation could greatly aid the design of electrophysiological assays for drug-screening. View Publication

There is need in the pharmaceutical and chemical industries for high-throughput human cell-based assays for identifying hazardous chemicals,thereby reducing the overall reliance on animal studies for predicting the risk of toxic responses in humans. Despite instances of human-specific teratogens such as thalidomide,the use of human cell-teratogenicity assays has just started to be explored. Herein,a human pluripotent stem cell test (hPST) for identifying teratogens is described,benchmarking the in vitro findings to traditional preclinical toxicology teratogenicity studies and when available to teratogenic outcomes in humans. The hPST method employs a 3-day monolayer directed differentiation of human embryonic stem cells. The teratogenic risk of a compound is gauged by measuring the reduction in nuclear translocation of the transcription factor SOX17 in mesendodermal cells. Decreased nuclear SOX17 in the hPST model was strongly correlated with in vivo teratogenicity. Specifically,71 drug-like compounds with known in vivo effects,including thalidomide,were examined in the hPST. A threshold of 5μM demonstrated 94% accuracy (97% sensitivity and 92% specificity). Furthermore,15 environmental toxicants with physicochemical properties distinct from small molecule pharmaceutical agents were examined and a similarly strong concordance with teratogenicity outcomes from in vivo studies was observed. Finally,to assess the suitability of the hPST for high-throughput screens,a small library of 300 kinase inhibitors was tested,demonstrating the hPST platform's utility for interrogating teratogenic mechanisms and drug safety prediction. Thus,the hPST assay is a robust predictor of teratogenicity and appears to be an improvement over existing in vitro models. View Publication

Elotuzumab is a monoclonal antibody in development for multiple myeloma (MM) that targets CS1,a cell surface glycoprotein expressed on MM cells. In preclinical models,elotuzumab exerts anti-MM efficacy via natural killer (NK)-cell-mediated antibody-dependent cellular cytotoxicity (ADCC). CS1 is also expressed at lower levels on NK cells where it acts as an activating receptor. We hypothesized that elotuzumab may have additional mechanisms of action via ligation of CS1 on NK cells that complement ADCC activity. Herein,we show that elotuzumab appears to induce activation of NK cells by binding to NK cell CS1 which promotes cytotoxicity against CS1(+) MM cells but not against autologous CS1(+) NK cells. Elotuzumab may also promote CS1-CS1 interactions between NK cells and CS1(+) target cells to enhance cytotoxicity in a manner independent of ADCC. NK cell activation appears dependent on differential expression of the signaling intermediary EAT-2 which is present in NK cells but absent in primary,human MM cells. Taken together,these data suggest elotuzumab may enhance NK cell function directly and confer anti-MM efficacy by means beyond ADCC alone. View Publication