Three-dimensional nanofibrillar surfaces promote self-renewal in mouse embryonic stem cells

The regulation of mouse embryonic stem cell (mESC) fate is controlled by the interplay of signaling networks that either promote self-renewal or induce differentiation. Leukemia inhibitory factor (LIF) is a cytokine that is required for stem cell renewal in mouse but not in human embryonic stem cells. However, feeder layers of embryonic fibroblasts are capable of inducing stem cell renewal in both cell types, suggesting that the self-renewal signaling pathways may also be promoted by other triggers, such as alternative cytokines and/or chemical or physical properties of the extracellular matrix (ECM) secreted by feeder fibroblasts. We have recently used a synthetic polyamide matrix (Ultra-Web) whose three-dimensional (3D) nanofibrillar organization resembles the ECM/basement membrane. Growth of mESCs on this nanofibrillar surface greatly enhanced proliferation and self-renewal in comparison with growth on tissue culture surfaces without nanofibers, despite the presence of LIF in both systems. Enhanced proliferation and self-renewal of the stem cells on nanofibrillar surfaces were correlated with the activation of the small GTPase Rac, the activation of phosphoinositide 3-kinase (PI3K) pathway, and the enhanced expression of Nanog, a homeoprotein required for maintenance of pluripotency. Inhibitors of PI3K reduced the expression level of Nanog in mESCs cultured on 3D nanofibrillar surfaces. These results provide support for the view that the three-dimensionality of the culture surface may function as a cue for the activation of Rac and PI3K signaling pathways, resulting in stem cell proliferation and self-renewal.     

The use of leukemia inhibitory factor immobilized on virus-derived polyhedra to support the proliferation of mouse embryonic and induced pluripotent stem cells

Human leukemia inhibitory factor (LIF) was immobilized into insect virus-derived microcrystals (polyhedra) to generate LIF polyhedra (LIF-PH) that can slowly release LIF into embryonic stem (ES) cell culture media and thus maintain ES cells in an undifferentiated state. Assays of the biological activities of LIF-PH indicated that a single addition of LIF-PH to the ES cell culture medium can support the proliferation of mouse ES and induced pluripotent stem (iPS) cells continuously for 14 days, and suggest that LIF-PH can be successfully used in the place of a periodic addition of recombinant LIF to the media every 2-3 days. The release of LIF protein from LIF-PH was determined by enzyme-linked immunosorbent assay (ELISA). Maintenance of undifferentiated state of mouse ES and iPS cells cultured with LIF-PH was determined by the detection of pluripotency-related biomarkers Oct3/4 and stage-specific embryonic antigen-1 (SSEA-1) through immunostaining and measurement of alkaline phosphatase activity. In this paper, we propose a closed culture system for mass production of ES and iPS cells that utilize a slow-releasing agent of LIF.     

小鼠胚胎干细胞来源的神经干细胞的稳定传代体系探索

目的探讨体外诱导、获取均一的神经干细胞群(NSCs)的有效方法,并建立神经干细胞体外稳定传代扩增体系。方法首先采用无血清的诱导培养基贴壁诱导mESCs形成神经上皮祖细胞(NPCs)。然后将经添加表皮生长因子(EGF)和成纤维细胞生长因子-2(FGF2)的无血清培养基短暂悬浮培养后的NPCs再贴壁培养,诱导形成NSCs。通过细胞系46C监测NPCs的形成,同时对分化细胞进行定量PCR和免疫荧光染色,在不同水平检测细胞分化效果。结果 mESCs神经诱导5 d出现大量Sox1+的NPCs;NPCs悬浮培养后,进一步诱导可得到形态均一的NSCs。第2代和第6代NSCs的神经干细胞标志定量PCR检测结果为:Pax6、Nestin、Mash1、BLBP高表达。第8代NSCs免疫荧光染色显示90%以上的细胞均为Nestin、RC2和Pax6阳性。结论成功诱导mESC生成神经干细胞群,并且可以在体外连续稳定的传代。     

人胚胎纹状体来源神经干细胞的体外培养

背景：目前神经干细胞多由动物获得,不适合人类临床移植治疗。 目的：探索体外环境下人胚胎纹状体来源神经干细胞的培养方法,同时观察其生物学特性。 方法：取经水囊引产的孕8-16周人胚胎纹状体,体外用无血清DMEM培养基进行培养,待细胞形成神经球后进行传代,并应用含体积分数10%胎牛血清的DMEM/ F12培养液进行诱导分化。 结果与结论：体外培养的人胚胎纹状体来源神经干细胞生长迅速,表达神经干细胞标志物nestin。克隆形成实验显示细胞克隆形成率为6.0%-7.0%;BrdU掺入实验显示细胞增殖率为37.9%。免疫荧光染色显示经诱导分化的细胞表达神经元标志物Ⅲ型β微管蛋白、星形胶质细胞标志物胶质纤维酸性蛋白及神经干细胞标志物nestin,但不表达少突胶质细胞标志物髓鞘碱性蛋白。可见人胚胎纹状体来源神经干细胞在体外无血清条件下可保持其生物学特点,具有自我更新能力,经胎牛血清诱导后可向神经元及星形胶质细胞分化。     

Self-renewal and scalability of human embryonic stem cells for human therapy

Human embryonic stem cells (hESCs) can undergo unlimited self-renewal and retain the pluripotency to differentiate into all cell types in the body. Therefore, as a renewable source of various cell types, hESCs hold great promise for human cell replacement therapy. While significant progress has been made in establishing the culture conditions for the long-term self-renewal of hESCs, several challenges remain to be overcome for the clinical application of hESCs. One such challenge is to develop strategies to scale-up the production of clinic-grade hESCs in xeno-free and chemically defined medium without inducing genomic instability. To achieve this goal, it is critical to elucidate the molecular pathways required to maintain the self-renewal, survival and genomic stability of hESCs. This article describes recent progress in addressing this challenge and discusses the strategies to improve the scalability of the production of hESCs by inhibiting their apoptosis.     

Self-renewal of embryonic stem cells through culture on nanopattern polydimethylsiloxane substrate

Embryonic stem (ES) cells can undergo continual proliferation and differentiation into cells of all somatic cell lineages in vitro; they are an unlimited cell source for regenerative medicine. However, techniques for maintaining undifferentiated ES cells are often inefficient and result in heterogeneous cell populations. Here, we determined effects of nanopattern polydimethylsiloxane (PDMS) as a culture substrate in promoting the self-renewal of mouse ES (mES) cells, compared to commercial plastic culture dishes. After many passages, mES cells efficiently maintained their undifferentiated state on nanopattern PDMS, but randomly differentiated on commercial plastic culture dishes, as indicated by partially altered morphologies and decreases in alkaline phosphatase activity and stage-specific expression of embryonic antigen-1. Under nanopattern PDMS conditions, we found increased activities of STAT3 and Akt, important proteins involved in maintaining the self-renewal of mES cells. The substrate-cell interactions also enhanced leukemia inhibitory factor (LIF)-downstream signaling and inhibited spontaneous differentiation, concomitant with reduced focal adhesion kinase (FAK) signaling. This reduction in FAK signaling was shown to be important for promoting mES cell self-renewal. Thus, our data demonstrates that nanopattern PDMS contributes to maintaining the self-renewal of mES cells and may be applicable in the large-scale production of homogeneously undifferentiated mES cells.     

Autocrine fibroblast growth factor 2 signaling is critical for self-renewal of human multipotent adipose-derived stem cells

Adipose tissue-derived stem cells offer tremendous potential for regenerative medicine. However, characterization of their self-renewal ability has not been performed yet, although it is a crucial feature for in vitro expansion of undifferentiated cells and in vivo maintenance of stem cell pools. We have undertaken the identification of molecular events that are involved in in vitro self-renewal of human multipotent adipose-derived stem (hMADS) cells from young donors, by assessing their proliferation rate, their ability to grow at the single-cell level (clonogenicity), and their differentiation potential. As hMADS cells are propagated in culture, cell morphology changes dramatically, concomitantly to a progressive decrease in proliferation, clonogenicity, and differentiation potential. This decrease is associated with a decrease in fibroblast growth factor 2 (FGF2) expression and can be circumvented by chronic treatment with exogenous FGF2. Moreover, analysis of FGF2 secretion revealed that it is exported to hMADS cell surface without being released into the culture medium, suggesting a strictly autocrine loop. Indeed, treatment of FGF2-expressing hMADS cells with PD173074, a specific FGF receptor inhibitor, decreases dramatically their clonogenicity and differentiation potential. Thus, hMADS cells express a functional autocrine FGF loop that allows maintenance of their self-renewal ability in vitro. Finally, inhibition of mitogen-activated protein kinase kinase 1 reduces the clonogenic potential of hMADS cells but does not affect their differentiation potential, indicating that the extracellular signal-related kinases 1/2 signaling pathway is partly involved in FGF2-mediated self-renewal. Together, our data clearly identify the key function of FGF2 in the maintenance of self-renewal of adipose tissue-derived stem cells.     

胚胎干细胞R1诱导成胰岛素分泌细胞团的研究

目的 建立体外培养和扩增胚胎干细胞R1(ES-R1)的最佳条件;利用多种生长因子,优化培养条件,体外定向诱导ES-R1分化为胰岛素分泌细胞(IPCs).方法 以丝裂霉索-C处理的MEF为饲养层,培养液中加白血病抑制因子(LIF),ES-R1维持未分化状态并扩增,进行碱性磷酸酶染色.胚胎干细胞(ESCs)悬浮培养制成拟胚体(EBs),对培养至第4d的EBs开始定向诱导,依次加入无血清的ITS培养液,胰岛前体细胞增殖培养液和胰岛分化培养液,每种培养液内各培养6d,获得形态功能较成熟的IPCs.采用DTZ染色、免疫荧光染色、胰岛素刺激实验等方法对IPCs进行检测.结果 ESCs在饲养层细胞上呈克隆状生长,经碱性磷酸酶染色为阳性;EBs经3种诱导液诱导成三维立体的IPCs,IPCs被DTZ染成猩红色,胰岛素和胰高血糖素阳性表达,胰岛素刺激实验阳性.结论 ES-R1在体外培养时,用MEF做饲养层,培养液中添加一定浓度的LIF,可以最好地保持未分化状态并大量增殖.用分阶段添加不同生长因子的方法诱导ES-R1定向分化生成的IPCs在形态和功能上具有胰岛的特性.     

白血病抑制因子(LIF)与bFGF协同促进小鼠外胚间充质干细胞(EMSCs)体外自我维持

白血病抑制因子（leukemia inhibitor factor，LIF）可以抑制小鼠胚胎干细胞分化，维持其自我更新，因而用于该干细胞的体外扩增。由于不同的胚胎或成体干细胞分化特性相差很大，因此，LIF可能对不同的干细胞有不同的作用。对新鲜分离的小鼠外胚间充质细胞（ectomesenchymal cells，EMCs）在有或无LIF的培养条件下，观察了细胞生长的特性，表型变化等，并通过检测其中外胚间充质干细胞（ectomesenchymal stem cells，EMSCs）的水平，探讨UF与EMSCs的关系。结果表明：（1）LIF的受体gp130表达于未分化与早期分化的EMSCs表面，提示LIF对于EMSCs具有潜在的调节作用；（2）LIF促进小鼠EMSCs的自我维持，bFGF则对此具有协同作用。因此，UF与bFGF联合对体外培养和扩增小鼠外胚间充质干细胞，以及对其深入研究和应用具有重要意义。     

Growth of primary embryo cells in a microculture system

We present optimal perfusion conditions for the growth of primary mouse embryonic fibroblasts (mEFs) and mouse embryonic stem cells (mESCs) using a microfluidic perfusion culture system. In an effort to balance nutrient renewal while ensuring the presence of cell secreted factors, we found that the optimal perfusion rate for culturing primary embryonic fibroblasts (mEFs) in our experimental setting is 10 nL/min with an average flow velocity 0.55 μm/s in the microchannel. Primary mEFs may have a greater dependence on cell secreted factors when compared to their immortalized counterpart 3T3 fibroblasts cultured under similar conditions. Both the seeding density and the perfusion rate are critical for the proliferation of primary cells. A week long cultivation of mEFs and mESCs using the microculture system exhibited similar morphology and viability to those grown in a petri dish. Both mEFs and mESCs were analyzed using fluorescence immunoassays to determine their proliferative status and protein expression. Our results demonstrate that a perfusion-based microculture environment is capable of supporting the highly proliferative status of pluripotent embryonic stem cells.     

Long-term self-renewal of human pluripotent stem cells on peptide-decorated poly(OEGMA-co-HEMA) brushes under fully defined conditions

Realization of the full potential of human induced pluripotent stem cells (hiPSC) in clinical applications requires the development of well-defined culture conditions for their long-term growth and directed differentiation. This paper describes a novel fully defined synthetic peptide-decorated substrate that supports self-renewal of hiPSC in commercially available xeno-free, chemically defined medium. The Au surface was deposited by a poly(OEGMA-co-HEMA) film, using the surface-initiated polymerization method (SIP) with the further step of carboxylation. The hiPSC generated from umbilical cord mesenchymal cells were successfully cultured for 10 passages on the peptide-tethered poly(OEGMA-co-HEMA) brushes for the first time. Cells maintained their characteristic morphology, proliferation and expressed high levels of markers of pluripotency, similar to the cells cultured on Matrigel?. Moreover, the cell adhesion could be tuned by the pattern and peptide concentration on the substrate. This well-defined, xeno-free and safe substrate, which supports long-term proliferation and self-renewal of hiPSC, will not only help to accelerate the translational perspectives of hiPSC, but also provide a platform to elucidate the underlying molecular mechanisms that regulate stem cell proliferation and differentiation via SIP technology.     

Unique gene expression signature by human embryonic stem cells cultured under serum-free conditions correlates with their enhanced and prolonged growth in an undifferentiated stage

Understanding the interaction between human embryonic stem cells (hESCs) and their microenvironment is crucial for the propagation and the differentiation of hESCs for therapeutic applications. hESCs maintain their characteristics both in serum-containing and serum-replacement (SR) media. In this study, the effects of the serum-containing and SR culture media on the gene expression profiles of hESCs were examined. Although the expression of many known embryonic stem cell markers was similar in cells cultured in either media, surprisingly, 1,417 genes were found to be differentially expressed when hESCs cultured in serum-containing medium were compared with those cultured in SR medium. Several genes upregulated in cells cultured in SR medium suggested increased metabolism and proliferation rates in this medium, providing a possible explanation for the increased growth rate of nondifferentiated cells observed in SR culture conditions compared with that in serum medium. Several genes characteristic for cells with differentiated phenotype were expressed in cells cultured in serum-containing medium. Our data clearly indicate that the manipulation of hESC culture conditions causes phenotypic changes of the cells that were reflected also at the level of gene expression. Such changes may have fundamental importance for hESCs, and gene expression changes should be monitored as a part of cell culture optimization aiming at a clinical use of hESCs for cell transplantation.     

以转染白血病抑制因子基因的人胚肺成纤维细胞为饲养层培养人胚胎生殖细胞

目的 以转染白血病抑制因子(LIF)基因的人胚肺成纤维细胞为饲养层培养人胚胎生殖细胞,为建立无动物成分污染的人胚胎生殖细胞培养体系奠定基础.方法 将LIF真核表达载体pcDNA3.1( )-LIF转染到人胚肺成纤维细胞中,通过筛选和鉴定获得表达LIF的阳性细胞.将原始生殖细胞(PGCs)种植到转染后细胞制备而成的饲养层上,在不添加外源性LIF的条件下培养,并对PGCs来源的细胞集落进行鉴定.结果 经RT-PCR及Western blotting 鉴定证实,转染pcDNA3.1( )-LIF的人胚肺成纤维细胞表达LIF基因.在转染后人胚肺成纤维细胞上生长的PGCs可形成典型的鸟巢状集落,经检测集落碱性磷酸酶活性呈强阳性,表达胚胎阶段特异性抗原SSEA-1、SSEA-4、TRA-1-60、TRA-1-81,及未分化标志Oct-4.结论 用转染LIF基因后的人胚肺成纤维细胞作为饲养层能支持PGCs来源人胚胎生殖细胞的生长,维持自我更新.