Environmental cues to guide stem cell fate decision for tissue engineering applications

The human body contains a variety of stem cells capable of both repeated self-renewal and production of specialised, differentiated progeny. Critical to the implementation of these cells in tissue engineering strategies is a thorough understanding of which external signals in the stem cell microenvironment provide cues to control their fate decision in terms of proliferation or differentiation into a desired, specific phenotype. These signals must then be incorporated into tissue regeneration approaches for regulated exposure to stem cells. The precise spatial and temporal presentation of factors directing stem cell behaviour is extremely important during embryogenesis, development and natural healing events, and it is possible that this level of control will be vital to the success of many regenerative therapies. This review covers existing tissue engineering approaches to guide the differentiation of three disparate stem cell populations: mesenchymal, neural and endothelial. These progenitor cells will be of central importance in many future connective, neural and vascular tissue regeneration technologies.     

Environmental cues to guide stem cell fate decision for tissue engineering applications

The human body contains a variety of stem cells capable of both repeated self-renewal and production of specialised, differentiated progeny. Critical to the implementation of these cells in tissue engineering strategies is a thorough understanding of which external signals in the stem cell microenvironment provide cues to control their fate decision in terms of proliferation or differentiation into a desired, specific phenotype. These signals must then be incorporated into tissue regeneration approaches for regulated exposure to stem cells. The precise spatial and temporal presentation of factors directing stem cell behaviour is extremely important during embryogenesis, development and natural healing events, and it is possible that this level of control will be vital to the success of many regenerative therapies. This review covers existing tissue engineering approaches to guide the differentiation of three disparate stem cell populations: mesenchymal, neural and endothelial. These progenitor cells will be of central importance in many future connective, neural and vascular tissue regeneration technologies.     

骨髓微环境变化引发的疾病

背景：骨髓微环境发生改变与血液疾病的发生和发展密切相关。目的：通过综述骨髓微环境中的细胞组分,非细胞组分和信号通路的调控作用,探讨骨髓微环境改变与疾病发生的关系。方法：应用计算机检索2001年1月至2012年4月的Pubmed数据库和万方数据库,英文检索词为＂bone marrow niche,hematopoietic stem cell（HSC）＂,中文检索词为＂骨髓微环境,造血干细胞＂,检索文献总量为424篇,最终纳入61篇进入结果分析。结果与结论：骨髓中的成体造血干细胞是血液系统和淋巴系统的发源细胞。骨髓微环境是支持造血干细胞自我更新和分化的场所,它由多种造血细胞成分、非造血细胞、胞外基质和其他信号蛋白组成。正常的骨髓微环境对造血干细胞发挥正常功能十分重要。一旦发生紊乱,会引发血液疾病和癌症等病症。因此,深入研究骨髓微环境,揭示调控机制以及相关的干细胞命运决定机制,将极大的推动骨髓移植、组织修复和再生医学等领域的发展。     

恶性血液病间充质干细胞改变的研究进展

间充质干细胞(mesenchymal stem cells,MSC)因其来源广泛、多分化潜能、支持造血、免疫调节等多个特性而受到人们高度关注,在组织工程和细胞治疗等方面显示出巨大的应用潜能.骨髓微环境在许多恶性血液病的发病机制中发挥了作用,MSC作为造血微环境的重要组成部分,它与肿瘤微环境间存在着复杂的联系.最近研究发现,AML、MDS、ALL、MM等血液病部分患者的MSC存在细胞遗传学异常,病理状态下MSC的表型、分化能力、免疫调节功能也存在不同程度的改变,提示MSC在恶性血液系统疾病病理生理机制中发挥了一定作用.此外,还有实验证实,MSC参与了白血病细胞化疗耐药的过程.由于MSC支持造血和免疫调节等独特优点,近年来MSC被应用于造血干细胞移植术后支持造血及防治GVHD.本文就MSC在恶性血液系统疾病中的改变及其作为临床细胞治疗手段的研究进展作一综述.     

Tissue engineering and microRNAs: future perspectives in regenerative medicine

Introduction: Tissue engineering is a growing area of biomedical research, holding great promise for a broad range of potential applications in the field of regenerative medicine. In recent decades, multiple tissue engineering strategies have been adopted to mimic and improve specific biological functions of tissues and organs, including biomimetic materials, drug-releasing scaffolds, stem cells, and dynamic culture systems. MicroRNAs (miRNAs), noncoding small RNAs that negatively regulate the expression of downstream target mRNAs, are considered a novel class of molecular targets and therapeutics that may play an important role in tissue engineering.

Areas covered: Herein, we highlight the latest achievements in regenerative medicine, focusing on the role of miRNAs as key modulators of gene expression, stem cell self-renewal, proliferation and differentiation, and eventually in driving cell fate decisions. Finally, we will discuss the contribution of miRNAs in regulating the rearrangement of the tissue microenvironment and angiogenesis, and the range of strategies for miRNA delivery into target cells and tissues.

Expert opinion: Manipulation of miRNAs is an alternative approach and an attractive strategy for controlling several aspects of tissue engineering, although some issues concerning their in vivo effects and optimal delivery methods still remain uncovered.     

成体干细胞及其分化机理

成体干细胞是存在于胎儿和成人组织器官中具有自我更新，高度增殖和多向分化潜能的细胞，在适当的诱导条件下。可变成不同类型的细胞。成体干细胞的分化是指成体干细胞具有可在体内、体外分化成不同类型细胞的能力，将其分化物植入体内后在各种情况下都能稳定地存活。目前认为分化的可能机制是：多种成体干细胞可能在不同的器官中存在，包括出生后体内仍存在的多能性干细胞。美国Minnesota大学干细胞研究所一系列的研究证明成体骨髓中确实存在具有多分化潜能的成体干细胞，命名为MAPC，能在体外由单细胞分化为具有中胚层系、外胚层系或内胚层系特征的细胞；将其注入胚泡，能分化成各种组织细胞。多能的成体干细胞在今后能用于多个不同器官的变性或遗传性疾病的治疗。     

HOXB4转录因子在造血干细胞中表达调控机制的研究进展

作为同源盒基因（homeobox gene，hox）家族成员，HOXB4编码一类同源盒DNA依赖的结构域核蛋白，是一类特异性的转录因子，对造血干细胞（hematopoietic stem cells，HSC）自我更新及分化之间的平衡起着重要的调节作用。为此，hoxB4在HSC中的表达调控机制备受关注。相关研究证明，hoxB4的一些上游调控因子，如上游激活因子-1（USF—1）、上游激活因子-2（USF-2）和核因子Y（NF—Y），以及一些造血细胞因子如血小板生成因子（TPO）及Wnt3a信号蛋白等，对hoxB4在HSC中的表达均起着重要调控作用。本文就hoxB4基因的结构、生物学特点及其在HSC中表达的调控机制作一综述。     

Specific complexes derived from extracellular matrix facilitate generation of structural and drug‐responsive human salivary gland microtissues through maintenance stem cell homeostasis

Three‐dimensional cultured salivary glands (SGs) microtissues hold great potentials for clinical research. However, most SGs microtissues still lack convincing structure and function due to poor supplementation of factors to maintain stem cell homeostasis. Extracellular matrix (ECM) plays a crucial role in regulating stem cell behavior. Thus, it is necessary to model stem cell microenvironment in vitro by supplementing culture medium with proteins derived from ECM. We prepared specific complexes from human SG ECM (s‐Ecx) and analyzed the components of the s‐Ecx. Human SG epithelial and mesenchymal cells were used to generate microtissues, and the optimum seeding cell number and ratio of two cell types were determined. Then, the s‐Ecx was introduced to the culture medium to assess its effect on stem cell behavior. Multiple specific factors were presented in s‐Ecx. s‐Ecx promoted maintenance of the stem cell and formation of specific structures resembling that of salivary glands and containing mucins, which suggested stem cell differentiation potential. Moreover, treatment of the microtissues with s‐Ecx increased their sensitivity to neurotransmitters. On the basis of the analysis of components, we believed that the presented growth factors are able to interact with stem cell they encountered in vivo, which promote the capacity to maintain stem cell homeostasis. This work provided foundations to study molecular mechanism of stem cell homeostasis in SGs and develop novel therapies for dry mouth through new drug discovery and disease modeling.     

间充质干细胞在造血干细胞移植术中应用的研究进展

造血干细胞移植(HSCT)是近年来治疗血液系统恶性疾病的有效手段,目前已在临床得到广泛应用.由于移植物排斥、造血恢复延迟、免疫重建缓慢而增加感染及早期移植相关死亡,以及供、受体组织不相容引发的移植物抗宿主病(GVHD),成为了临床医生亟待解决的棘手问题.作为造血微环境重要组成的间充质干细胞(MSC)由于其来源广泛、取材方便、可进行体外扩增、具有多分化潜能、促进造血和具有免疫调节能力等优点,成为了近年来研究的热点,并逐渐被应用于临床治疗,以下就其在造血干细胞移植术中的应用作一综述.     

Role of substrate biomechanics in controlling (stem) cell fate: Implications in regenerative medicine

Tissue‐specific stem cells reside in a specialized environment known as niche. The niche plays a central role in the regulation of cell behaviour and, through the concerted action of soluble molecules, supportive somatic cells, and extracellular matrix components, directs stem cells to proliferate, differentiate, or remain quiescent. Great efforts have been done to decompose and separately analyse the contribution of these cues in the in vivo environment. Specifically, the mechanical properties of the extracellular matrix influence many aspects of cell behaviour, including self‐renewal and differentiation. Deciphering the role of biomechanics could thereby provide important insights to control the stem cells responses in a more effective way with the aim to promote their therapeutic potential. In this review, we provide a wide overview of the effect that the microenvironment stiffness exerts on the control of cell behaviour with a particular focus on the induction of stem cells differentiation. We also describe the process of mechanotransduction and the molecular effectors involved. Finally, we critically discuss the potential involvement of tissue biomechanics in the design of novel tissue engineering strategies.     

Global analysis of proliferation and cell cycle gene expression in the regulation of hematopoietic stem and progenitor cell fates

Knowledge of the molecular networks controlling the proliferation and fate of hematopoietic stem cells (HSC) is essential to understand their function in maintaining blood cell production during normal hematopoiesis and upon clinical transplantation. Using highly purified stem and progenitor cell populations, we define the proliferation index and status of the cell cycle machinery at discrete stages of hematopoietic differentiation and during cytokine-mediated HSC mobilization. We identify distinct sets of cell cycle proteins that specifically associate with differentiation, self-renewal, and maintenance of quiescence in HSC and progenitor cells. Moreover, we describe a striking inequality of function among in vivo cycling and quiescent HSC by demonstrating that their long-term engraftment potential resides predominantly in the G(0) fraction. These data provide a direct link between HSC proliferation and function and identify discrete molecular targets in regulating HSC cell fate decisions that could have implications for both the therapeutic use of HSC and the understanding of leukemic transformation.     

Notch信号通路与间充质干细胞分化

间充质干细胞(MSC)是具有多向分化能力的成体干细胞,在体外培养中可以被诱导分化为骨、软骨、脂肪、肌肉细胞;另外,MSC也可跨系分化为神经细胞、心肌细胞、肝脏细胞等多种其他组织细胞。Notch信号通路广泛存在于各种动物细胞中,在调节细胞分化、增殖和凋亡中发挥重要作用,它的配体和受体都是细胞膜表面蛋白,因此是介导细胞间通讯的一种重要方式。现有研究表明:在MSC多条分化途径中都有Notch通路存在。本文针对Notch信号通路在MSC分化中的影响做一综述。     

Mechanical stimulations on human bone marrow mesenchymal stem cells enhance cells differentiation in a three‐dimensional layered scaffold

Scaffolds laden with stem cells are a promising approach for articular cartilage repair. Investigations have shown that implantation of artificial matrices, growth factors or chondrocytes can stimulate cartilage formation, but no existing strategies apply mechanical stimulation on stratified scaffolds to mimic the cartilage environment. The purpose of this study was to adapt a spraying method for stratified cartilage engineering and to stimulate the biosubstitute. Human mesenchymal stem cells from bone marrow were seeded in an alginate (Alg)/hyaluronic acid (HA) or Alg/hydroxyapatite (Hap) gel to direct cartilage and hypertrophic cartilage/subchondral bone differentiation, respectively, in different layers within a single scaffold. Homogeneous or composite stratified scaffolds were cultured for 28 days and cell viability and differentiation were assessed. The heterogeneous scaffold was stimulated daily. The mechanical behaviour of the stratified scaffolds were investigated by plane–strain compression tests. Results showed that the spraying process did not affect cell viability. Moreover, cell differentiation driven by the microenvironment was increased with loading: in the layer with Alg/HA, a specific extracellular matrix of cartilage, composed of glycosaminoglycans and type II collagen was observed, and in the Alg/Hap layer more collagen X was detected. Hap seemed to drive cells to a hypertrophic chondrocytic phenotype and increased mechanical resistance of the scaffold. In conclusion, mechanical stimulations will allow for the production of a stratified biosubstitute, laden with human mesenchymal stem cells from bone marrow, which is capable in vivo to mimic all depths of chondral defects, thanks to an efficient combination of stem cells, biomaterial compositions and mechanical loading.     

Chemical and physical properties of regenerative medicine materials controlling stem cell fate

Abstract

Regenerative medicine is a multidisciplinary field utilizing the potential of stem cells and the regenerative capability of the body to restore, maintain, or enhance tissue and organ functions. Stem cells are unspecialized cells that can self-renew but also differentiate into several somatic cells when subjected the appropriate environmental cues. The ability to reliably direct stem cell fate would provide tremendous potential for basic research and clinical therapies. Proper tissue function and regeneration rely on the spatial and temporal control of biophysical and biochemical cues, including soluble molecules, cell–cell contacts, cell–extracellular matrix contacts, and physical forces. The mechanisms involved remain poorly understood. This review focuses on the stem cell–extracellular matrix interactions by summarizing the observations of the effects of material variables (such as overall architecture, surface topography, charge, ζ-potential, surface energy, and elastic modulus) on the stem cell fate. It also deals with the mechanisms underlying the effects of these extrinsic, material variables. Insight in the environmental interactions of the stem cells is crucial for the development of new material-based approaches for cell culture experiments and future experimental and clinical regenerative medicine applications.     

白血病干细胞及其微环境

白血病干细胞研究是肿瘤干细胞研究的先驱，不仅有重要的理论意义，也有潜在的应用前景。干细胞的生存和发展受其微环境的直接影响，白血病干细胞及其微环境成为研究热点。作者认为白血病干细胞是群体，具有异质性和阶梯性，不能分离单个细胞形成克隆；白血病干细胞与微环境的作用可以用白血病干细胞生态位（1eu-kemia stem cell niche）的概念表述。本文就白血病细胞群体的阶梯性和异质性及白血病干细胞的生态位问题进行了评述。     

纳米纤维三维支架材料提供适宜微环境调控干细胞的命运

背景：三维纤维支架材料立足于模拟干细胞体内微环境的物理和化学特性,可以在极大程度上维持干细胞的活性,保证组织修复或干细胞治疗的疗效。目的：综述纳米纤维三维支架材料的制备方法及其与干细胞的相互作用,以及立足于这种材料的组织工程研究进展。方法：由作者在web of science以“tissue engineering, nanofiber scaffold, stem cel fate”为关键词,检索与干细胞组织工程和纳米纤维三维支架密切相关的研究。结果与结论：纳米纤维三维支架能够模拟干细胞微环境的物理结构,在其基础上进行表面改性可以进一步模拟微环境的化学信号,可为干细胞移植提供一个可靠的载体。纳米纤维三维支架材料的制备方法主要有分子自组装技术、溶液相分离和静电纺丝技术等。三维支架材料可以调控包括造血干细胞、胚胎干细胞、间充质干细胞和神经干细胞等干细胞的体外增殖。具有特定物理结构和生物化学表面的三维支架还可以在体外诱导干细胞向骨骼/软骨、神经或者肌肉等方向分化,还可以为干细胞移植提供适宜的微环境,保证干细胞治疗的效果。     

Temporal establishment of neural cell identity in vivo and in vitro

Understanding cell fate specification is particularly useful because it enables biologists to generate specific neural cell types for treating currently untreatable neurological diseases. Traditionally, lineage‐specific progenitors are generated in vitro from pluripotent cells, after which they may be channeled into more mature cell types in a stage‐specific manner, which is similar to the way cells behave during development. However, the emergence of induced pluripotent stem cells means that specific cell types can be generated directly from fibroblasts or other somatic cell types, thus bypassing all of the necessary steps that happen in vivo. Based on this information, the present review first explores the regulatory circuitry that drives cell fate specification over time in vivo. In particular, it describes how the appearance of specific neuronal and glial cell types is governed by an intrinsic biological clock, followed by a discussion of how this can be achieved through the temporal expression of intracellular regulators in relation to cell‐specific Dnase I hypersensitivity sites, promoters and enhancers. Cell fate acquisition in vitro was then examined in an attempt to evaluate whether the temporal regulation neural cell fate in vivo is still relevant to the generation of reprogrammed neural stem cells and neurons. Copyright © 2016 John Wiley & Sons, Ltd.     

间充质干细胞在急性辐射损伤治疗中的应用前景

间充质干细胞是一种具有自我更新和多向分化潜能的成体干细胞。鉴于其独特的生物学特性,诸如分泌多种造血生长因子、重建造血微环境、低免疫原性、易于外源基因转染和表达等,可以部分弥补传统治疗手段的不足。本文对MSC的生物学特性以及其在放射病模型中的应用研究作一综述。     

体细胞重编程为干细胞的方法研究与进展

背景：克隆人类胚胎会引起伦理问题,这使科学家寻找替代的方法来逆向分化细胞为多能/全能干细胞,这个过程称为重编程。重编程的新方法是研究者关注的焦点。目的：探讨重编程技术的研究现状,并对体细胞重编程为干细胞的各种方法做一综述。方法：应用计算机检索CNKI和Pubmed数据库中1983年1月至2006年12月关于重编程的文章,在标题和摘要中以＂重编程,方法,体细胞,干细胞,分化＂或＂reprogramming,method,somatic cell,stem cell,differentiation＂为检索词进行检索。选择文章内容与重编程有关者,同一领域文献则选择近期发表或发表在权威杂志文章。最终选择17篇文献进行综述。结果与结论：一个多能干细胞重编程状态是细胞结构逐步重构,染色质表观遗传改变,转录表达和转录后调控的结果。靶细胞的重塑要求重编程有一个稳定的状态,最终可以被重新定向到特定的分化程序。有充分的证据表明,细胞鉴定可以被体外操作影响,重编程细胞的命运需要进一步体内检测。