Mesenchymal stem cells

About 40 years ago Friedenstein described stromal cells in the bone marrow that were spindle shaped and proliferate to form colonies. These cells attach to plastic and are able to differentiate under defined in vitro conditions into multiple cell types present in many different tissues, e.g. osteoblasts, chondroblasts, adipocytes, etc. Later on these cells, obtained from postnatal bone marrow, were called mesenchymal stem cells (MSC) or stromal stem cells. Recently the presence of somewhat similar cells has been demonstrated in many other tissues too. In spite of extensive attempts to characterize these cells we are still lacking definitive in vivo markers of MSC although retrospective functional data strongly support the existence of common adult stem cells that have the capacity to differentiate along various specific differentiation lineages. Since MSC can be rather easily isolated from the bone marrow and can also be expanded in vitro they have become a prime target for researchers of tissue regeneration. These cells have now been extensively used for transplantation experiments in animals and also for some therapeutic trials in humans. However, much new research is needed to learn enough on the molecular mechanisms of MSC differentiation to evaluate their full capacity for tissue regeneration.     

Adipose stem cell side population in the mouse

Adipose tissue has become a reliable source of adult stem cells, which appear to possess a yet‐undetermined degree of plasticity. With the difficulties associated with harvesting adult bone marrow stem cells, adipose tissue may represent a valuable and easily acquired source of stem cells. Stem cells have been identified using the DNA binding dye Hoechst 33342 and flow cytometry in various tissues known as the side population (SP). The present study shows, for the first time, the presence of side population stem cells in adult adipose tissues. Flow cytometric identification and isolation of this subpopulation of stem cells revealed that in the mouse there are 2.5% of adipose SP cells within the stromal vascular fraction of adipose tissue. In culture, mouse adipose SP cells showed the capacity to undergo in vitro differentiation into osteogenic, chondrogenic and adipogenic lineages. In NOD/SCID mice, freshly sorted mouse adipose SP cells were able to engraft and assist in wound healing. This animal model study showed that adipose SP cells were able to regenerate epithelial layers and connective tissue with minor scar formation. The ability of this novel cell population within adipose tissue to undergo directional differentiation in vitro and to regenerate skin in vivo has potential impact for uses in surgical dermal applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of in vitro‐cultivation of human mesenchymal stroma/stem cells derived from bone marrow and umbilical cord

Cell‐mediated therapy is currently considered as a novel approach for many human diseases. Potential uses range from topic applications with the regeneration of confined tissue areas to systemic applications. Stem cells including mesenchymal stroma/stem cells (MSCs) represent a highly attractive option. Their potential to cure or alleviate human diseases is investigated in a number of clinical trials. A wide variety of methods has been established in the past years for isolation, cultivation and characterization of human MSCs as expansion is presently deemed a prerequisite for clinical application with high numbers of cells carrying reproducible properties. MSCs have been retrieved from various tissues and used in a multitude of settings whereby numerous experimental protocols are available for expansion of MSCs in vitro. Accordingly, different isolation, culture and upscaling techniques contribute to the heterogeneity of MSC characteristics and the, sometimes, controversial results. Therefore, this review discusses and summarizes certain experimental conditions for MSC in vitro culture focusing on adult bone marrow‐derived and neonatal umbilical cord‐derived MSCs in order to enhance our understanding for MSC tissue sources and to stratify different procedures. Copyright © 2016 John Wiley & Sons, Ltd.     

Cultured cell‐derived extracellular matrices to enhance the osteogenic differentiation and angiogenic properties of human mesenchymal stem/stromal cells

Cell‐derived extracellular matrix (ECM) consists of a complex assembly of fibrillary proteins, matrix macromolecules, and associated growth factors that mimic the composition and organization of native ECM micro‐environment. Therefore, cultured cell‐derived ECM has been used as a scaffold for tissue engineering settings to create a biomimetic micro‐environment, providing physical, chemical, and mechanical cues to cells, and support cell adhesion, proliferation, migration, and differentiation. Here, we present a new strategy to produce different combinations of decellularized cultured cell‐derived ECM (dECM) obtained from different cultured cell types, namely, mesenchymal stem/stromal cells (MSCs) and human umbilical vein endothelial cells (HUVECs), as well as the coculture of MSC:HUVEC and investigate the effects of its various compositions on cell metabolic activity, osteogenic differentiation, and angiogenic properties of human bone marrow (BM)‐derived MSCs, vital features for adult bone tissue regeneration and repair. Our findings demonstrate that dECM presented higher cell metabolic activity compared with tissue culture polystyrene. More importantly, we show that MSC:HUVEC ECM enhanced the osteogenic and angiogenic potential of BM MSCs, as assessed by in vitro assays. Interestingly, MSC:HUVEC (1:3) ECM demonstrated the best angiogenic response of MSCs in the conditions tested. To the best of our knowledge, this is the first study that demonstrates that dECM derived from a coculture of MSC:HUVEC impacts the osteogenic and angiogenic capabilities of BM MSCs, suggesting the potential use of MSC:HUVEC ECM as a therapeutic product to improve clinical outcomes in bone regeneration.     

Epigenetic approaches to regeneration of bone and cartilage from stem cells

Introduction: Embryonic stem cells (ESCs) or adult stem cells, especially mesenchymal stem cells (MSCs), have been intensively studied for skeletal tissue regeneration including bone and cartilage. Epigenetic mechanisms play essential roles in stem cell maintenance and differentiation. However, little is known about the epigenetic regulation of osteogenesis and chondrogenesis of stem cells.

Areas covered: In this review, features of ESCs and adult stem cells, epigenetics and chromatin structure, as well as epigenetic mechanisms, such as chromatin remodeling, DNA methylation and histone modifications, polycomb group (PcG) proteins and microRNAs are described. Epigenetic researches of stem cell are introduced.

Expert opinion: Epigenetic alterations of stem cell during the in vitro differentiation can be controlled for clinical applications. MSCs are effective resources for skeletal tissue regeneration in both undifferentiated and differentiated states. Understanding epigenetic signatures of MSC is crucial to maintain the stemness. In addition, investigation of epigenetic changes in the differentiation of MSCs is very important to develop methods or chemicals to promote efficient differentiation of MSCs. Inhibition of PcG protein enhancer of zeste (Ezh2) a chromatin modifier, could be a promising candidate to improve MSC differentiation by decreasing Ezh2-mediated H3K27me3.     

犬骨髓基质干细胞片层制备及向成骨细胞的分化

背景: 目前传统的胰酶消化法和单细胞悬液转移细胞的方法存在诸多缺点,限制了骨组织工程学的发展.目的: 培养骨髓基质干细胞并向成骨细胞诱导分化,制备细胞片层.方法: 密度梯度离心法分离犬骨髓基质干细胞,接种于DMEM成骨诱导培养基,向成骨细胞诱导分化,采用细胞片层技术,利用温度反应性培养基的温度变化,收获完整的细胞片层.结果与结论: 刚接种至培养皿的原代细胞在培养瓶底散在分布,呈圆形,胞体透亮,折光性好,12 d时细胞呈长梭形,完全融合,呈旋涡状生长;成骨诱导后的骨髓基质干细胞大部分变为方形、多角形和鳞片形,21-28 d形成明显的圆形或卵圆形钙化结节;温度反应性培养皿中的间充质干细胞降温至临界温度32℃以下时,细胞便逐步从培养皿底分离,形成完整的骨髓基质干细胞片层.实验结果证实密度梯度离心法可成功分离培养犬骨髓基质干细胞并向成骨细胞诱导分化,应用细胞片层技术可获取完整的骨髓基质干细胞片层.     

The use of fibrin based matrices and fibrin microbeads (FMB) for cell based tissue regeneration

Background: Due to its good cell attachment capabilities and promotion of cell migration, fibrin serves as an interim cell-binding matrix in wounded tissues. Due to their fast degradation, unprocessed fibrin matrices have limited use in tissue engineering. Objective: To describe stable fibrin-based matrices for isolation, growth and delivery of stem cells for implantation to enhance tissue regeneration. Methods: Fibrin microbeads (FMB) were produced by moderate-heat condensation of fibrin particles in oil without compromising the cell binding capability of the fibrin. Results: Mesenchymal stem cells (MSC) were separated from different sources at much higher yields with FMB. They were further expanded on them in suspension without trypsinization and passages. Cells on FMB could be induced to differentiate into different phenotypes, such as bone and cartilage. This enabled implantation of the cells on FMB for cell-based tissue regeneration. Conclusions: FMB technology provides a simple and effective method for cell separation, expansion in suspension and delivery for tissue regeneration.     

Polysaccharides immobilized in polypyrrole matrices are able to induce osteogenic differentiation in mouse mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) have attracted considerable interest due to their ability to differentiate and contribute to the regeneration of mesenchymal tissues. The present study illustrates that the proper immobilization of heparin (Hep) and hyaluronic acid (HA) into a polypyrrole (PPy) matrix by electropolymerization results in an optimal interface for MSC differentiation towards osteoblast lineage. The obtained thin films showed good thermal stability, hydrophilicity and slow controlled polysaccharide release. The in vitro tests showed the main role of the interface chemical composition. Indeed, PPyHep and PPyHA thin films were able to induce osteogenic differentiation as determined by levels of specific early osteogenic markers (Runx2 and osterix) even in the absence of differentiating medium. Increased levels of ALP and Alizarin red staining, both indicating mineralization processes, confirmed the presence of mature osteoblasts. Copyright © 2012 John Wiley & Sons, Ltd.     

The Stromal Activity of Mesenchymal Stromal Cells

SUMMARY: The mechanism that regulates self-renewal and differentiation of hematopoietic stem cells (HSC) is a central question in stem cell biology that might ultimately lead to reliable protocols for in vitro expansion of HSC. Cellular fate is governed by cell-cell interaction with the microenvironment in the bone marrow, the stem cell niche. Mesenchymal stromal cells (MSC) are precursors of the cellular components, and they secrete extracellular matrix proteins of the bone marrow stroma. Therefore, MSC feeder layer might provide a suitable in vitro model system for the stem cell niche. In vitro assays demonstrate that MSC maintain the stem cell function of HSC and that MSC from bone marrow have a higher hematopoiesis supportive activity than MSC from adipose tissue. Co-cultivation with MSC might pave the way for expansion of long-term repopulating HSC, and various clinical trials indicate that co-transplantation of HSC and MSC might enhance engraftment. Thus, MSC are promising tools to elucidate the underlying mechanism of the cellular microenvironment. The large variety of preparative protocols for isolation and cultivation of MSC affects their stromal activity. Standardized isolation methods and molecular characterization of MSC are of utmost importance for reproducible isolation of hematopoiesis supportive stromal cells and for their potential clinical application.     

Molecular‐ and microarray‐based analysis of diversity among resting and osteogenically induced porcine mesenchymal stromal cells of several tissue origin

Mesenchymal stromal cells (MSCs) play a pivotal role in modern therapeutic approaches in bone‐healing disorders. Although bone marrow‐derived MSCs are most frequently used, the knowledge that many other adult tissues represent promising sources for potent MSCs has gained acceptance. In the present study, the osteogenic differentiation potential of porcine skin fibroblasts (FBs), as well as bone marrow‐ (BMSCs), adipose tissue‐ (ASCs) and dental pulp‐derived stromal cells (DSCs) were evaluated. However, additional application of BMP‐2 significantly elevated the delayed osteogenic differentiation capacity of ASC and FB cultures, and in DSC cultures the supplementation of platelet‐rich plasma increased osteogenic differentiation potential to a comparable level of the good differentiable BMSCs. Furthermore, microarray gene expression performed in an exemplary manner for ASCs and BMSCs revealed that ASCs and BMSCs use different gene expression patterns for osteogenic differentiation under standard media conditions, as diverse MSCs are imprinted dependent from their tissue niche. However, after increasing the differentiation potential of ASCs to a comparable level as shown in BMSCs, a small subset of identical key molecules was used to differentiate in the osteogenic lineage. Until now, the importance of identified genes seems to be underestimated for osteogenic differentiation. Apparently, the regulation of transmembrane protein 229A, interleukin‐33 and the fibroblast growth factor receptor‐2 in the early phase of osteogenic differentiation is needed for optimum results. Based on these results, bone regeneration strategies of MSCs have to be adjusted, and in vivo studies on the osteogenic capacities of the different types of MCSs are warranted. Copyright © 2016 The Authors Tissue Engineering and Regenerative Medicine published by John Wiley & Sons, Ltd.     

Synergistic Actions of Hematopoietic and Mesenchymal Stem/Progenitor Cells in Vascularizing Bioengineered Tissues

Poor angiogenesis is a major road block for tissue repair. The regeneration of virtually all tissues is limited by angiogenesis, given the diffusion of nutrients, oxygen, and waste products is limited to a few hundred micrometers. We postulated that co-transplantation of hematopoietic and mesenchymal stem/progenitor cells improves angiogenesis of tissue repair and hence the outcome of regeneration. In this study, we tested this hypothesis by using bone as a model whose regeneration is impaired unless it is vascularized. Hematopoietic stem/progenitor cells (HSCs) and mesenchymal stem/progenitor cells (MSCs) were isolated from each of three healthy human bone marrow samples and reconstituted in a porous scaffold. MSCs were seeded in micropores of 3D calcium phosphate (CP) scaffolds, followed by infusion of gel-suspended CD34⁺ hematopoietic cells. Co-transplantation of CD34⁺ HSCs and CD34⁻ MSCs in microporous CP scaffolds subcutaneously in the dorsum of immunocompromized mice yielded vascularized tissue. The average vascular number of co-transplanted CD34⁺ and MSC scaffolds was substantially greater than MSC transplantation alone. Human osteocalcin was expressed in the micropores of CP scaffolds and was significantly increased upon co-transplantation of MSCs and CD34⁺ cells. Human nuclear staining revealed the engraftment of transplanted human cells in vascular endothelium upon co-transplantation of MSCs and CD34⁺ cells. Based on additional in vitro results of endothelial differentiation of CD34⁺ cells by vascular endothelial growth factor (VEGF), we adsorbed VEGF with co-transplanted CD34⁺ and MSCs in the microporous CP scaffolds in vivo, and discovered that vascular number and diameter further increased, likely owing to the promotion of endothelial differentiation of CD34⁺ cells by VEGF. Together, co-transplantation of hematopoietic and mesenchymal stem/progenitor cells may improve the regeneration of vascular dependent tissues such as bone, adipose, muscle and dermal grafts, and may have implications in the regeneration of internal organs.     

Mesenchymal Stem Cells - Sources and Clinical Applications

SUMMARY: Although mesenchymal stem cells (MSC) from different tissue sources share many characteristics and generally fulfill accepted criteria for MSC (plastic adherence, certain surface marker expression, and ability to differentiate into mesenchymal tissues), we are increasingly learning that they can be distinguished at the level of cytokine production and gene expression profiles. Their ability to differentiate into different tissues including endodermal and ectodermal lineages, also varies according to tissue origin. Importantly, MSC from fetal sources can undergo more cell divisions before they reach senescence than MSC from adult tissue such as bone marrow or adipose tissue. As we learn more about the differentiation and plasticity of MSC from different sources, health care providers in the future will use them tailored to different medical indications.     

Donor‐matched comparison of dental pulp stem cells and bone marrow‐derived mesenchymal stem cells in a rat model

Dental pulp stem cells (DPSCs) have drawn much interest for the regeneration of mineralized tissues, and several studies have compared DPSCs to bone marrow‐derived mesenchymal stem cells (BMMSCs). However, conflicting results, possibly due to donor‐associated variability, have been published and the regenerative potential of DPSCs is currently unclear. In the present study we have sought to address this problem using a donor‐matched experimental design to robustly compare the biological properties of DPSCs and BMMSCs. All experiments were performed using cells isolated from a single adult Sprague–Dawley rat. Our results show that DPSCs and BMMSCs had similar morphologies and flow cytometry profiles, were capable of forming colonies in vitro and were capable of osteogenic, chondrogenic and adipogenic differentiation. However, quantitative comparisons revealed that DPSCs had a faster population doubling time and a higher percentage of stem/progenitor cells in the population, as determined by clonogenic assays. Furthermore, while both cell populations formed mineral in vitro, DPSCs had significantly higher alkaline phosphatase activity than BMMSCs after 3 weeks in osteogenic medium. These data show several key differences between DPSCs and BMMSCs and support the possibility of using DPSCs for mineralized tissue regeneration. Copyright © 2009 John Wiley & Sons, Ltd.     

Mesenchymal stem cells from rat olfactory bulbs can differentiate into cells with cardiomyocyte characteristics

Mesenchymal stromal/stem cells (MSCs) are widely distributed in different tissues such as bone marrow, adipose tissues, peripheral blood, umbilical cord and amnionic fluid. Recently, MSC‐like cells were also found to exist in rat olfactory bulb and are capable of inducing differentiation into mesenchymal lineages – osteocytes, chondrocytes and adipocytes. However, whether these cells can differentiate into myocardial cells is not known. In this study, we examined whether olfactory bulb‐derived MSCs could differentiate into myocardial cells in vitro. Fibroblast‐like cells isolated from the olfactory bulb of neonatal rats were grown under four conditions: no treatment; in the presence of growth factors (neuregulin‐1, bFGF and forskolin); co‐cultured with cardiomyocytes; and co‐cultured with cardiomyocytes plus neuregulin‐1, bFGF and forskolin. Cell differentiation into myocardial cells was monitored by RT–PCR, light microscopy immunofluorescence, western blot analysis and contractile response to pharmacological treatments. The isolated olfactory bulb‐derived fibroblast‐like cells expressed CD29, CD44, CD90, CD105, CD166 but not CD34 and CD45, consistent with the characteristics of MSCs. Long cylindical cells that spontaneously contracted were only observed following 7 days of co‐culture of MSCs with rat cardiomyocytes plus neuregulin‐1, bFGF and forskolin. RT–PCR and western blot analysis indicated that the cylindrical cells expressed myocardial markers, such as Nkx2.5, GATA4, sarcomeric α‐actinin, cardiac troponin I, cardiac myosin heavy chain, atrial natriuretic peptide and connexin 43. They also contained sarcomeres and gap junction and were sensitive to pharmacological treatments (adrenal and cholinergic agonists and antagonists). These findings indicate that rat olfactory bulb‐derived fibroblast‐like cells with MSC characteristics can differentiate into myocardial‐like cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Fibrogenic Potential of Human Multipotent Mesenchymal Stromal Cells in Injured Liver

Multipotent mesenchymal stromal cells (MSC) are currently investigated clinically as cellular therapy for a variety of diseases. Differentiation of MSC toward endodermal lineages, including hepatocytes and their therapeutic effect on fibrosis has been described but remains controversial. Recent evidence attributed a fibrotic potential to MSC. As differentiation potential might be dependent of donor age, we studied MSC derived from adult and pediatric human bone marrow and their potential to differentiate into hepatocytes or myofibroblasts in vitro and in vivo. Following characterization, expanded adult and pediatric MSC were co-cultured with a human hepatoma cell line, Huh-7, in a hepatogenic differentiation medium containing Hepatocyte growth factor, Fibroblast growth factor 4 and oncostatin M. In vivo, MSC were transplanted into spleen or liver of NOD/SCID mice undergoing partial hepatectomy and retrorsine treatment. Expression of mesenchymal and hepatic markers was analyzed by RT-PCR, Western blot and immunohistochemistry. In vitro, adult and pediatric MSC expressed characteristic surface antigens of MSC. Expansion capacity of pediatric MSC was significantly higher when compared to adult MSC. In co-culture with Huh-7 cells in hepatogenic differentiation medium, albumin expression was more frequently detected in pediatric MSC (5/8 experiments) when compared to adult MSC (2/10 experiments). However, in such condition pediatric MSC expressed alpha smooth muscle more strongly than adult MSC. Stable engraftment in the liver was not achieved after intrasplenic injection of pediatric or adult MSC. After intrahepatic injection, MSC permanently remained in liver tissue, kept a mesenchymal morphology and expressed vimentin and alpha smooth muscle actin, but no hepatic markers. Further, MSC localization merges with collagen deposition in transplanted liver and no difference was observed using adult or pediatric MSC. In conclusion, when transplanted into an injured or regenerating liver, MSC differentiated into myofibroblasts with development of fibrous tissue, regardless of donor age. These results indicate that MSC in certain circumstances might be harmful due to their fibrogenic potential and this should be considered before potential use of MSC for cell therapy.     

骨髓基质干细胞治疗骨不连的新进展

背景：骨髓基质干细胞体外培养增殖力强、易于向成骨细胞及软骨细胞方向分化且成骨性能稳定等特点,成为骨组织工程中合适的种子细胞.目的：总结分析采用骨髓基质干细胞作为种子细胞,分析其直接移植于骨不连部位或复合支架或转基因治疗骨不连所具有的优劣势.方法：检索1992/2011西文生物医学期刊文献数据及CNKI 数据库有关骨不连研究,骨髓基质干细胞分离、培养,在骨不连方面的应用,骨组织工程细胞支架方面的文献,英文检索词为＂bone marrow stromal stem cells,nonunions,repairing,tissue engineering＂,中文检索词为＂骨髓基质干细胞,骨修复,骨不连,组织工程＂.排除重复性研究,保留23篇进一步归纳总结.结果与结论：利用骨髓基质干细胞作为种子细胞,直接植入骨不连部位,或与适当的支架材料结合,或用骨髓基质干细胞作为靶细胞,导入外源目的基因诱导成骨的基因治疗来修复骨缺损的方法,给骨缺损的治疗带来光明的前景.但同时也存在骨髓基质干细胞增殖、分化合适条件难以准确确定,经皮移植自体骨髓基质干细胞植入体内后容易流失,不能在植入部位形成有效的细胞浓度,支架材料尚不能完全符合临床要求,以及如何将骨组织工程与基因治疗的方法结合起来等问题,需要进一步的研究.     

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

Introduction: Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

Areas covered: In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

Expert opinion: Enhanced results have been found when combining bone marrow–derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue–derived stem cells and umbilical cord tissue–derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.     

Role of mesenchymal stem cells in regenerative medicine: application to bone and cartilage repair

Background: Mesenchymal stem cells (MSC) are multipotent cells with the ability to differentiate into mesenchyme-derived cells including osteoblasts and chondrocytes. Objective: To provide an overview and expert opinion on the in vivo ability of MSC to home into tissues, their regenerative properties and potential applications for cell-based therapies to treat bone and cartilage disorders. Methods: Data sources including the PubMed database, abstract booklets and conference proceedings were searched for publications pertinent to MSC and their properties with emphasis on the in vivo studies and clinical use in cartilage and bone regeneration and repair. The search included the most current information possible. Conclusion: MSC can migrate to injured tissues and some of their reparative properties are mediated by paracrine mechanisms including their immunomodulatory actions. MSC possess a critical potential in regenerative medicine for the treatment of skeletal diseases, such as osteoarthritis or fracture healing failure, where treatments are partially effective or palliative.     

The differential in vitro and in vivo responses of bone marrow stromal cells on novel porous gelatin–alginate scaffolds

Tissue engineering and stem cell therapy hold great potential of being able to fully restore, repair and replace damaged, diseased or lost tissues in the body. Biocompatible porous scaffolds are used for the delivery of cells to the regeneration sites. Marrow stromal cells (MSCs), also referred to as mesenchymal stem cells, are an attractive cell source for tissue engineering, due to the relative ease of isolation and the ability of in vitro expanded MSCs to generate multiple cell types, including osteoblasts, chondrocytes and adipocytes. This study utilized a novel technique called microwave vacuum drying to fabricate porous gelatin–alginate scaffolds for the delivery of MSCs and investigated the differential in vitro and in vivo responses of MSCs seeded on these scaffolds. Scaffold total porosity was found to decrease with increased cross‐link density but the pore size and pore size distribution were not affected. Although highly porous, the scaffold had relatively small pores and limited interconnectivity. The porous gelatin–alginate scaffold demonstrated excellent biocompatibility with neovascularization on the surfaces and was bioresorbed completely in vivo, depending upon the cross‐link density. MSCs were able to attach and proliferate at the same rate on the scaffolds, and the self‐renewal potential of MSC cultures was similar during both in vitro culture and in vivo implantation. However, the subcutaneous microenvironment was found to suppress MSC differentiation along the osteogenic, chondrogenic and adipogenic lineages compared to in vitro conditions, highlighting the differential responses of MSCs cultured in vitro compared to implantation in vivo. Copyright © 2009 John Wiley & Sons, Ltd.     

骨髓基质干细胞向肌细胞分化及移植的治疗作用

背景：骨髓基质干细胞属多能干细胞,在适当的条件下可转分化为各种肌肉细胞,在移植后可改善心脏或骨骼肌的整体功能。如何优化诱导分化方法,改善移植途径以及移植后改善组织功能的机制成为现今研究的热点。目的：就近年来骨髓基质干细胞诱导分化为肌细胞,以及其用作细胞移植治疗心肌梗死、肌肉萎缩等肌细胞坏死性疾病的研究进行综述。方法：应用计算机以bone marrow cell,muscle cell检索词,检索Pubmed数据库（2005/2010）;以＂骨髓基质干细胞、肌细胞＂为检索词,检索中国期刊网全文数据库（2007/2010）;以＂骨髓基质干细胞、肌细胞、分化、心脏＂为检索词,检索万方数据库（2007/2010）。共收集220篇关于外周血干细胞方面的文献,中文61篇,英文159篇,排除发表时间较早、重复及类似研究,纳入21篇符合标准的文献。结果与结论：骨髓基质干细胞可以在体外扩增,但其表面特异性标记尚无定论,因此要分离得到完全纯化的骨髓基质干细胞还有一定的困难,当前只有STRO-1抗原是较为肯定的间质干细胞表面抗原,可用于鉴定分离骨髓中的间质干细胞。大量研究表明,通过体外诱导剂或体内移植可促使骨髓基质干细胞转化成各种组织细胞,包括心肌细胞和骨骼肌细胞,并且在移植后可观察到肌组织功能得到明显改善,但其机制目前尚无充分了解。此外,尽管各种诱导方法诱导骨髓基质干细胞分化的结果是肯定的,以及体内移植也表现出改善坏死肌组织功能的潜能,但目前体外诱导程度仍然较低,且体内功能改善也有局限性,因此,如何改善诱导方法,提高移植效率及功能改善有待进一步研究。