Pluripotent stem cell-derived neural stem cells: From basic research to applications

Basic research on pluripotent stem cells is designed to enhance understanding of embryogenesis, whereas applied research is designed to develop novel therapies and prevent diseases. Attainment of these goals has been enhanced by the establishment of embryonic stem cell lines, the technological development of genomic reprogramming to generate induced-pluripotent stem cells, and improvements in vitro techniques to manipulate stem cells. This review summarizes the techniques required to generate neural cells from pluripotent stem cells. In particular, this review describes current research applications of a simple neural differentiation method, the neural stem sphere method, which we developed.     

Circular RNAs in and out of Cells: Therapeutic Usages of Circular RNAs

RNAs are versatile molecules that are primarily involved in gene regulation and can thus be widely used to advance the fields of therapeutics and diagnostics. In particular, circular RNAs which are highly stable, have emerged as strong candidates for use on next-generation therapeutic platforms. Endogenous circular RNAs control gene regulatory networks by interacting with other biomolecules or through translation into polypeptides. Circular RNAs exhibit cell-type specific expression patterns, which can be altered in tissues and body fluids depending on pathophysiological conditions. Circular RNAs that are aberrantly expressed in diseases can function as biomarkers or therapeutic targets. Moreover, exogenous circular RNAs synthesized in vitro can be introduced into cells as therapeutic molecules to modulate gene expression networks in vivo. Depending on the purpose, synthetic circular RNA sequences can either be identical to endogenous circular RNA sequences or artificially designed. In this review, we introduce the life cycle and known functions of intracellular circular RNAs. The current stage of endogenous circular RNAs as biomarkers and therapeutic targets is also described. Finally, approaches and considerations that are important for applying the available knowledge on endogenous circular RNAs to design exogenous circular RNAs for therapeutic purposes are presented.     

Cancer stem cells: A review from origin to therapeutic implications

Cancer stem cells (CSCs), also known as tumor-initiating cells (TICs), are elucidated as cells that can perpetuate themselves via autorestoration. These cells are highly resistant to current therapeutic approaches and are the main reason for cancer recurrence. Radiotherapy has made a lot of contributions to cancer treatment. However, despite continuous achievements, therapy resistance and tumor recurrence are still prevalent in most patients. This resistance might be partly related to the existence of CSCs. In the present study, recent advances in the investigation of different biological properties of CSCs, such as their origin, markers, characteristics, and targeting have been reviewed. We have also focused our discussion on radioresistance and adaptive responses of CSCs and their related extrinsic and intrinsic influential factors. In summary, we suggest CSCs as the prime therapeutic target for cancer treatment.     

肝癌干细胞分子标志物和干性维持机制研究进展

原发性肝癌是一种发生在肝脏的侵袭性肿瘤,具有极易发生转移和复发的特点.原发性肝癌主要包括肝细胞癌、肝内胆管癌、混合肝细胞胆管癌和纤维板层型肝细胞癌等.目前,手术切除、放射性和化学治疗仍是肝癌治疗的主要手段,但其特异性差、临床效果有限,肝癌患者5年总生存率仅为18％.肝癌干细胞是存在于肝癌组织中特定的细胞亚群,具有自我更...     

Therapeutic potential of dental pulp stem cells and their derivatives: Insights from basic research toward clinical applications

For more than 20 years, researchers have isolated and identified postnatal dental pulp stem cells (DPSCs) from different teeth, including natal teeth, exfoliated deciduous teeth, healthy teeth, and diseased teeth. Their mesenchymal stem cell (MSC)-like immunophenotypic characteristics, high proliferation rate, potential for multidirectional differentiation and biological features were demonstrated to be superior to those of bone marrow MSCs. In addition, several main application forms of DPSCs and their derivatives have been investigated, including stem cell injections, modified stem cells, stem cell sheets and stem cell spheroids. In vitro and in vivo administration of DPSCs and their derivatives exhibited beneficial effects in various disease models of different tissues and organs. Therefore, DPSCs and their derivatives are regarded as excellent candidates for stem cell-based tissue regeneration. In this review, we aim to provide an overview of the potential application of DPSCs and their derivatives in the field of regenerative medicine. We describe the similarities and differences of DPSCs isolated from donors of different ages and health conditions. The methodologies for therapeutic administration of DPSCs and their derivatives are introduced, including single injections and the transplantation of the cells with a support, as cell sheets, or as cell spheroids. We also summarize the underlying mechanisms of the regenerative potential of DPSCs.     

Ovarian stem cells: From basic to clinical applications

The field of reproductive biology has undergone significant developments in the last decade. The notion that there is a fixed reserve pool of oocytes before birth was established by Zuckerman in 1951. However, in 2004, an article published in nature challenged this central dogma of mammalian reproductive biology. Tilly’s group reported the existence of ovarian germline stem cells (GSCs) in postnatal ovaries of mice and suggested that the bone marrow could be an extragonadal source of ovarian GSCs. These findings were strongly criticized; however, several independent groups have since successfully isolated and characterized ovarian GSCs in postnatal mice. The ovarian GSCs are located in the ovarian surface epithelium and express markers of undifferentiated GSCs. When transplanted into mouse ovaries, mouse ovarian GSCs could differentiate and produce embryos and offspring. Similarly, in a recent study, ovarian GSCs were found to be present in the ovaries of women of reproductive age. Conversely, there is increasing evidence that stem cells responsible for maintaining a healthy state in normal tissue may be a source of some cancers, including ovarian cancer. Cancer stem cells (CSCs) have been found in many tissues, including ovaries. Some researchers have suggested that ovarian cancer may be a result of the transformation and dysfunction of ovarian GSCs with self-renewal properties. Drug resistant and metastasis-generating CSCs are responsible for many important problems affecting ovarian cancer patients. Therefore, the identification of CSCs will provide opportunities for the development of new therapeutic strategies for treatments for infertility and ovarian cancer. In this article, we summarize the current understanding of ovarian GSCs in adult mammals, and we also discuss whether there is a relationship between GSCs and CSCs.     

Methods to produce induced pluripotent stem cell-derived mesenchymal stem cells: Mesenchymal stem cells from induced pluripotent stem cells

Mesenchymal stem cells (MSCs) have received significant attention in recent years due to their large potential for cell therapy. Indeed, they secrete a wide variety of immunomodulatory factors of interest for the treatment of immune-related disorders and inflammatory diseases. MSCs can be extracted from multiple tissues of the human body. However, several factors may restrict their use for clinical applications: the requirement of invasive procedures for their isolation, their limited numbers, and their heterogeneity according to the tissue of origin or donor. In addition, MSCs often present early signs of replicative senescence limiting their expansion in vitro, and their therapeutic capacity in vivo. Due to the clinical potential of MSCs, a considerable number of methods to differentiate induced pluripotent stem cells (iPSCs) into MSCs have emerged. iPSCs represent a new reliable, unlimited source to generate MSCs (MSCs derived from iPSC, iMSCs) from homogeneous and well-characterized cell lines, which would relieve many of the above mentioned technical and biological limitations. Additionally, the use of iPSCs prevents some of the ethical concerns surrounding the use of human embryonic stem cells. In this review, we analyze the main current protocols used to differentiate human iPSCs into MSCs, which we classify into five different categories: MSC Switch, Embryoid Body Formation, Specific Differentiation, Pathway Inhibitor, and Platelet Lysate. We also evaluate common and method-specific culture components and provide a list of positive and negative markers for MSC characterization. Further guidance on material requirements to produce iMSCs with these methods and on the phenotypic features of the iMSCs obtained is added. The information may help researchers identify protocol options to design and/or refine standardized procedures for large-scale production of iMSCs fitting clinical demands.     

Mesenchymal stem cell basic research and applications in dog medicine

The stem cells, owing to their special characteristics like self-renewal, multiplication, homing, immunomodulation, anti-inflammatory, and dedifferentiation are considered to carry an “all-in-one-solution” for diverse clinical problems. However, the limited understanding of cellular physiology currently limits their definitive therapeutic use. Among various stem cell types, currently mesenchymal stem cells are extensively studied for dog clinical applications owing to their readily available sources, easy harvesting, and ability to differentiate both into mesodermal, as well as extramesodermal tissues. The isolated, culture expanded, and characterized cells have been applied both at preclinical as well as clinical settings in dogs with variable but mostly positive results. The results, though positive, are currently inconclusive and demands further intensive research on the properties and their dependence on the applications. Further, numerous clinical conditions of dog resemble to that of human counterparts and thus, if proved rewarding in the former may act as basis of therapy for the latter. The current review throws some light on dog mesenchymal stem cell properties and their potential therapeutic applications.     

Teratomas from pluripotent stem cells: A clinical hurdle

Although basic research on human embryonic stem cells (hESCs) at the laboratory bench has progressed with enviable speed there has been little head way in terms of its clinical application. A look at the Internet however shows several stem cell clinics worldwide offering direct transplantation of undifferentiated hESCs to patients for the cure of a variety of diseases before bona fide evidence‐based results can be demonstrated from large controlled studies. This raises concern because reliable protocols have to be first developed to resolve the three major hurdles delaying clinical trials such as inadequate cell numbers, immunorejection and tumorigenesis. Cell expansion methods using bioreactors, rotary culture and mitotic agents have now been developed to generate stem cell derivatives in large numbers. The problem of immunorejection can now be overcome with the development of indirect and direct reprogramming protocols to personalize tissues to patients (human induced pluripotent stem cells, hiPSCs; nuclear transfer stem cells, NTSCs; induced neuronal cells, iN). However, hESC, hiPSC, and NTSCs being pluripotent have the disadvantage of teratoma formation in vivo which has to be carefully addressed so as to provide safe stem cell based therapies to the patient. This review addresses the issue of tumorigenesis and discusses approaches by which this concern may be overcome and at the same time emphasizes the need to concurrently explore alternative stem cell sources that do not confer the disadvantages of pluripotency but are widely multipotent so as to yield safe desirable tissues for clinical application as soon as possible. J. Cell. Biochem. 111: 769–781, 2010. © 2010 Wiley‐Liss, Inc.     

Tracking adult stem cells

The maintenance of stem-cell-driven tissue homeostasis requires a balance between the generation and loss of cell mass. Adult stem cells have a close relationship with the surrounding tissue--known as their niche--and thus, stem-cell studies should preferably be performed in a physiological context, rather than outside their natural environment. The mouse is an attractive model in which to study adult mammalian stem cells, as numerous experimental systems and genetic tools are available. In this review, we describe strategies commonly used to identify and functionally characterize adult stem cells in mice and discuss their potential, limitations and interpretations, as well as how they have informed our understanding of adult stem-cell biology. An accurate interpretation of physiologically relevant stem-cell assays is crucial to identify adult stem cells and elucidate how they self-renew and give rise to differentiated progeny.     

肝干细胞的几个生物学问题

对肝干细胞的认识,自卵圆细胞发现以来已经经历了五十多年。期间许多的研究提示和证明肝干细胞具有很好的生物医学应用前景。近年来,肝干细胞的概念已被广泛接受和认可,肝干细胞的生物学特性及其医学应用的探索也成为了研究的热点。目前在该领域中,主要以肝干细胞存在的位置、与其所处微环境的相互作用、肝干细胞的分子标记以及其分化特性等方面备受关注。肝干细胞的研究为肝脏疾病及其他相关疾病的治疗带来了新希望。然而,肝干细胞研究的过程中仍存在很多未解的问题,因此将肝干细胞研究引入临床应用则还需要更加深入的探索。     

小分子RNA决定果蝇生殖干细胞命运的分子机制研究

生殖干细胞是具有自我更新能力的一群生殖细胞,充当配子生成的源泉。果蝇生殖干细胞的特征在于通过不对称分裂产生两个子代细胞,一个通过自我更新维持干细胞特性,另一个则进行分化。生殖干细胞的命运受其周围的微环境——"干细胞niche"控制,而"niche"的功能又通过干细胞的外源和内源信号间的相互作用来完成。小分子RNA通过复杂的RNAi途径调控基因的表达。大量证据表明生殖干细胞的维持和分化需要小分子RNA参与,小分子RNA生成的紊乱会导致干细胞的"丢失"或"未分化"。该文综述了小分子RNA对果蝇生殖干细胞命运调控的研究进展,并讨论新发现的小分子RNA在生殖干细胞命运决定中的相关功能。     

新物种诱导多能干细胞的研究进展

胚胎干细胞（embryonic stem cells,ESC）在人类遗传病学研究、疾病模型建立、器官再生以及动物物种改良和定向变异等方面的地位是其他类型的细胞不可取代的。但是,由于实验技术和体外培养条件的限制,除了小鼠、恒河猴和人之外,大鼠、猪、牛、羊等其他哺乳动物的ES细胞系被证明很难获得。先后有多个研究小组报道了他们利用新兴的诱导多能干细胞（induced pluripotent stem cells,iPS细胞）技术成功建立大鼠和猪的iPS细胞系的研究成果。迄今为止,这两个物种是在未成功建立ES细胞系之前利用iPS技术建立多能干细胞系的成功范例。这些研究对于那些还未建立ES细胞的物种建立多能干细胞系提供了一种新的方案,也将给这些物种的胚胎干细胞的建立、基因修饰动物的产生以及人类医疗事业的促进和发展带来新的希望。     

胚胎干细胞向血液干细胞定向分化的研究进展

骨髓移植是目前治疗恶性白血病以及遗传性血液病最有效的方法之一。但是HLA相匹配的骨髓捐献者严重短缺,骨髓造血干细胞（hematopoietic stem cells,HSCs）体外培养困难,在体外修复患者骨髓造血干细胞技术不成熟,这些都大大限制了骨髓移植在临床上的应用。多能性胚胎干细胞（embryonic stem cells,ESCs）具有自我更新能力,在合适的培养条件下分化形成各种血系细胞,是造血干细胞的另一来源。在过去的二十多年里,血发生的研究是干细胞生物学中最为活跃的领域之一。小鼠及人的胚胎干细胞方面的研究最近取得了重大进展。这篇综述总结了近年来从胚胎干细胞获得造血干细胞的成就,以及在安全和技术上的障碍。胚胎干细胞诱导生成可移植性血干细胞的研究能够使我们更好地了解正常和异常造血发生的机制,同时也为造血干细胞的临床应用提供理论和实验依据。     

诱导多能干细胞研究进展

人类诱导多能干细胞（induced pluripotent stem cells,iPS细胞）的建立被公认为目前最重要的科技进展之一。iPS细胞在动物疾病模型上的成功治疗,病患特异性iPS细胞的研究及iPS细胞的定向分化研究将有可能使人们避开治疗性克隆的伦理和技术障碍,给人类疾病的干细胞治疗带来光明的前景。本文从iPS细胞的诱导策略和方法,来源细胞及筛选、重编程机制的研究现状、应用前景以及研究中存在的问题等方面对其作一综述和讨论。