体外扩增过程中人骨髓间充质干细胞的增殖与分化规律

目的：系统考察体外扩增过程中人骨髓间充质干细胞（MSC）的增殖与分化规律，为MSC任组织修复以及细胞治疗中的应用提供参考、方法：以全骨髓贴壁法分离成人肋骨骨髓MSC，在相同条件下分别考察各代细胞形态、生长、表面标记、细胞周期、成骨、成软骨及成脂肪能力的变化情况。结果：随代次增加，MSC增殖能力、成骨、成脂肪能力均有所下降，而成软骨能力无明显降低；成骨、成软骨及成脂肪能乃均保持到细胞衰老。存扩增过程中，MSC始终保持较高的纯度，CD29、CD44、CD105的阳性率均在90％以上，CD14、CD34和CD45的阳性率均在4％以下、结论：在体外培养过程中MSC干细胞特性逐渐丢失，其中向骨、脂肪方向的分化潜能较软骨方向更易失去；而多向分化能力的保持较之自我更新能力更为持久。MSC在7代以前可作为基础研究及临床应用的良好对象。     

A comprehensive analysis of the dual roles of BMPs in regulating adipogenic and osteogenic differentiation of mesenchymal progenitor cells

Pluripotent mesenchymal stem cells (MSCs) are bone marrow stromal progenitor cells that can differentiate into osteogenic, chondrogenic, adipogenic, and myogenic lineages. Several signaling pathways have been shown to regulate the lineage commitment and terminal differentiation of MSCs. Here, we conducted a comprehensive analysis of the 14 types of bone morphogenetic protein (BMPs) for their abilities to regulate multilineage specific differentiation of MSCs. We found that most BMPs exhibited distinct abilities to regulate the expression of Runx2, Sox9, MyoD, and PPARgamma2. Further analysis indicated that BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 effectively induced both adipogenic and osteogenic differentiation in vitro and in vivo. BMP-induced commitment to osteogenic or adipogenic lineage was shown to be mutually exclusive. Overexpression of Runx2 enhanced BMP-induced osteogenic differentiation, whereas knockdown of Runx2 expression diminished BMP-induced bone formation with a decrease in adipocyte accumulation in vivo. Interestingly, overexpression of PPARgamma2 not only promoted adipogenic differentiation, but also enhanced osteogenic differentiation upon BMP-2, BMP-6, and BMP-9 stimulation. Conversely, MSCs with PPARgamma2 knockdown or mouse embryonic fibroblasts derived from PPARgamma2(-/-) mice exhibited a marked decrease in adipogenic differentiation, coupled with reduced osteogenic differentiation and diminished mineralization upon BMP-9 stimulation, suggesting that PPARgamma2 may play a role in BMP-induced osteogenic and adipogenic differentiation. Thus, it is important to understand the molecular mechanism behind BMP-regulated lineage divergence during MSC differentiation, as this knowledge could help us to understand the pathogenesis of skeletal diseases and may lead to the development of strategies for regenerative medicine.     

Comparison of potentials of stem cells isolated from tendon and bone marrow for musculoskeletal tissue engineering

The use of tendon-derived stem cells (TDSCs) as a cell source for musculoskeletal tissue engineering has not been compared with that of bone marrow stromal cells (BMSC). This study compared the mesenchymal stem cell (MSC) and embryonic stem cells (ESC) markers, clonogenicity, proliferative capacity, and multilineage differentiation potential of rat TDSC and BMSC in vitro. The MSC and ESC marker profiles of paired TDSC and BMSC were compared using flow cytometry and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Their clonogenicity and proliferative capacity were compared using colony-forming and 5-bromo-2'-deoxyuridine assays, respectively. The expression of tenogenic, osteogenic, and chondrogenic markers at basal state were examined using qRT-PCR. Their osteogenic, chondrogenic, and adipogenic differentiation potentials were compared using standard assays. TDSC and BMSC showed similar expression of CD90 and CD73. TDSC expressed higher levels of Oct4 than BMSC. TDSC exhibited higher clonogenicity, proliferated faster, and expressed higher tenomodulin, scleraxis, collagen 1 α 1 (Col1A1), decorin, alkaline phosphatase, Col2A1, and biglycan messenger RNA levels than BMSC. There was higher calcium nodule formation and osteogenic marker expression in TDSC than BMSC upon osteogenic induction. More chondrocyte-like cells and higher glycosaminoglycan deposition and chondrogenic marker expression were observed in TDSC than BMSC upon chondrogenic induction. There were more oil droplets and expression of an adipogenic marker in TDSC than BMSC upon adipogenic induction. TDSC expressed higher Oct4 levels, which was reported to positively regulate mesendodermal lineage differentiation, showed higher clonogenicity and proliferative capacity, and had greater tenogenic, osteogenic, chondrogenic, and adipogenic markers and differentiation potential than BMSC. TDSC might be a better cell source than BMSC for musculoskeletal tissue regeneration.     

Human bronchial fibroblasts exhibit a mesenchymal stem cell phenotype and multilineage differentiating potentialities

Mesenchymal stem cells (MSCs) are multipotent cells able to differentiate along different pathways including chondrogenic, osteogenic and adipogenic lineages. MSCs with a fibroblast-like morphology have been identified in human fetal lung. However, their frequency and characterization in human adult lung have not been yet evaluated. Therefore, we analyzed the mesenchymal phenotype and differentiation ability of cultured human adult bronchial fibroblast-like cells (Br) in comparison with those of mesenchymal cell progenitors isolated from fetal lung (ICIG7) and adult bone marrow (BM212) tissues. Surface immunophenotyping by flow cytometry revealed a similar expression pattern of antigens characteristic of marrow-derived MSCs, including CD34 (-), CD45 (-), CD90/Thy-1 (+), CD73/SH3, SH4 (+), CD105/SH2 (+) and CD166/ALCAM (+) in Br, ICIG7 and BM212 cells. There was one exception, STRO-1 antigen, which was only weakly expressed in Br cells. Analysis of cytoskeleton and matrix composition by immunostaining showed that lung and marrow-derived cells homogeneously expressed vimentin and nestin proteins in intermediate filaments while they were all devoid of epithelial cytokeratins. Additionally, alpha-smooth muscle actin was also present in microfilaments of a low number of cells. All cell types predominantly produced collagen and fibronectin extracellular matrix as evidenced by staining with the monoclonal antibodies to collagen prolyl 4-hydroxylase and fibronectin isoforms containing the extradomain (ED)-A together with ED-B in ICIG7 cells. Br cells similarly to fetal lung and marrow fibroblasts were able to differentiate along the three adipogenic, osteogenic and chondrogenic mesenchymal pathways when cultured under appropriate inducible conditions. Altogether, these data indicate that MSCs are present in human adult lung. They may be actively involved in lung tissue repair under physiological and pathological circumstances.     

Isolation and characterization of chorionic mesenchymal stromal cells from human full term placenta

This study focused on the characterization of mesenchymal stromal cells (MSCs) from the chorion of human full term placenta from 15 donors. Chorionic MSCs revealed homologous fibroblast-like morphology and expressed CD73, CD29, CD105, and CD90. The hematopoietic stem cell markers including HLA DR, CD11b, CD34, CD79a, and CD45 were not expressed. The growth kinetics of their serial passage was steady at the later passages (passage 10). The multilineage capability of chorionic MSCs was demonstrated by successful adipogenic, osteogenic and chondrogenic differentiation and associated gene expression. Chorionic MSCs expressed genes associated with undifferentiated cells (NANOG, OCT4, REX1) and cardiogenic or neurogenic markers such as SOX2, FGF4, NES, MAP2, and NF. TERT was negative in all the samples. These findings suggest that chorionic MSCs undifferentiated stem cells and less likely to be transformed into cancer cells. A low HLA DR expression suggests that chorionic MSCs may serve as a great source of stem cells for transplantation because of their immune-privileged status and their immunosuppressive effect. Based on these unique properties, it is concluded that chorionic MSCs are pluripotent stem cells that are probably less differentiated than BM-MSCs, and they have considerable potential for use in cell-based therapies.     

小鼠骨髓间充质干细胞生物学特性和体外诱导分化

目的研究小鼠骨髓间充质干细胞的生物学性状和多系分化潜能。方法取Balb／c小鼠骨髓单个核细胞在低糖的培养液中培养出贴壁生长的细胞,进行形态学观察、细胞周期和免疫表型分析;在不同的因子作用下诱导向成骨细胞、软骨细胞,脂肪细胞分化,并检测诱导后细胞相应的基因表达。结果小鼠骨髓间充质干细胞贴壁生长后形态较均一,增殖能力随着传代逐渐增强,但从第8代后增殖能力明显减退。细胞表达CD29,CD38,CD44,CD106等标记,但CD34和H-2k表达阴性。在不同的诱导培养体系里间充质干细胞能分化为成骨细胞、软骨细胞和脂肪细胞,相应的骨钙蛋白基因,Ⅱ型胶原基因,脂蛋白脂酶基因表达都明显增强。结论从小鼠骨髓可以分离培养出间充质干细胞,在体外有效扩增和诱导分化。表明可以以小鼠为模型研究间充质干细胞在组织工程、细胞移植、基因治疗等领域的运用。     

Ultrastructural and immunocytochemical analysis of multilineage differentiated human dental pulp- and umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are one of the most promising stem cell types due to their availability and relatively simple requirements for in vitro expansion and genetic manipulation. Besides the well-characterized MSCs derived from bone marrow, there is growing evidence suggesting that dental pulp and the umbilical cord matrix both contain a substantial amount of cells having properties similar to those of MSCs. In order to assess the potential of dental pulp-derived MSCs (DPSC) and umbilical cord-derived MSCs (UCSC) in future clinical applications, it is essential to gain more insight into their differentiation capacity and to evaluate the tissues formed by these cells. In the present study, the morphological and ultrastructural characteristics of DPSC and UCSC induced towards osteogenic, adipogenic, and chondrogenic lineages were investigated. Cultured DPSC and UCSC showed a similar expression pattern of antigens characteristic of MSCs including CD105, CD29, CD44, CD146, and STRO-1. Under appropriate culture conditions, both DPSC and UCSC showed chondrogenic and osteogenic potential. Adipogenesis could be only partially induced in DPSC resulting in the de novo expression of fatty acid binding protein (FABP), whereas UCSC expressed FABP combined with a very high accumulation of lipid droplets in the cytoplasm. Our results demonstrate, at the biochemical and ultrastructural level, that DPSC display at least bilineage potential, whereas UCSC, which are developmentally more primitive cells, show trilineage potential. We emphasize that transmission electron microscopical analysis is useful to elucidate detailed structural information and provides indisputable evidence of differentiation. These findings highlight their potential therapeutic value for cell-based tissue engineering.     

Characterization and multipotentiality of human fetal femur-derived cells: implications for skeletal tissue regeneration

To date, the plasticity, multipotentiality, and characteristics of progenitor cells from fetal skeletal tissue remain poorly defined. This study has examined cell populations from human fetal femurs in comparison with adult-derived mesenchymal cell populations. Real-time quantitative polymerase chain reaction demonstrated expression of mesenchymal progenitor cell markers by fetal-derived cells in comparison with unselected adult-derived and immunoselected STRO-1-enriched adult populations. Multipotentiality was examined using cells derived from femurs and single-cell clones, culture-expanded from explants, and maintained in basal medium prior to exposure to adipogenic, osteogenic, and chondrogenic conditions. Adipocyte formation was confirmed by Oil Red O lipid staining and aP2 immunocytochemistry, with expression of peroxisome proliferation-activated receptor-gamma detected only in adipogenic conditions. In chondrogenic pellets, chondrocytes lodged within lacunae and embedded within dense proteoglycan matrix were observed using Alcian blue/Sirius red staining and type II collagen immunocytochemistry. Osteogenic differentiation was confirmed by alkaline phosphatase staining and type I collagen immunocytochemistry as well as by gene expression of osteopontin and osteocalcin. Single-cell clonal analysis was used to demonstrate multipotentiality of the fetal-derived populations with the formation of adipogenic, chondrogenic, and osteogenic populations. Mineralization and osteoid formation were observed after culture on biomimetic scaffolds with extensive matrix accumulation both in vitro and in vivo after subcutaneous implantation in severely compromised immunodeficient mice. These studies demonstrate the proliferative and multipotential properties of fetal femur-derived cells in comparison with adult-derived cells. Selective differentiation and immunophenotyping will determine the potential of these fetal cells as a unique alternative model and cell source in the restoration of damaged tissue.     

Adipose tissue-derived stem cells for cell therapy of airway allergic diseases in mouse

The purpose of this study was to compare murine mesenchymal stem cells (MSCs) isolated from bone marrow (BM) and adipose tissue (AT) for the selection of suitable MSCs in cell therapy of an airway allergic animal model. We compared MSCs of BALB/c mice derived from BM and AT with respect to proliferation potential, immunophenotype, and multilineage differentiation capacity. In proliferation potential, MSCs from AT (ASCs) showed higher fibroblastoid colony-forming units frequencies and colony-forming efficiency than MSCs from BM (BMSCs). The flow cytometry analysis showed that both ASCs and BMSCs expressed MSCs-related antigens (CD90 and CD105), whereas they did not express hematopoiesis-related antigens (CD45 and CD11b). There was no significant difference in adipogenic, osteogenic, and chondrogenic differentiation between the murine ASCs and BMSCs. In conclusion, the present study has shown that ASCs had higher CFU-F frequencies and colony-forming efficiency than BMSCs. ASCs and BMSCs presented a similar surface immunophenotype and multilineage differentiation capacity. Therefore, ASCs in BALB/c mice might be a more useful material for cell therapy of the airway allergic experiment due to the abundance, relatively easy harvesting and high proliferation potential.     

兔骨髓间充质干细胞定向诱导分化为脂肪细胞及成骨细胞的研究

用密度梯度离心和贴壁法分离和纯化兔骨髓间充干细胞，建立诱导兔MSCs向脂肪细胞及成骨细胞表型转化的方法及条件。在成脂诱导剂或成骨诱导剂作用下，对原代和第2代兔MSCs进行成脂和成骨诱导培养，并鉴定成脂及成骨表型。结果表明：原代及第2代兔MSCs均有一定的成脂、成骨能力，且第2代细胞的分化能力较原代低。在诱导培养条件下，原代及第2代兔MSCs均能分化，成脂诱导21d，75％的兔MSCs转化为脂肪细胞；成骨诱导21d，75％的兔MSCs转化为成骨细胞。兔MSCs在适当的诱导条件下可快速分化为脂肪细胞或成骨细胞。     

小鼠骨髓来源Flk-1+间充质干细胞分离制备与生物学特点

背景：骨髓间充质干细胞具有广泛的应用前途,其三系分化的能力和免疫诱导特性使其具有再生医学的应用前景。 目的：从小鼠骨髓中研究分离制备Flk-1⁺间充质干细胞的新方法,检测了这类细胞的生物特性。 方法：以小鼠骨髓为研究对象,分离单个核细胞,体外培养并 扩增原始间充质干细胞,检测它们的细胞周期、表型和多系分化的能力。 结果与结论：小鼠来源的骨髓来源的原始间充质干细胞呈成纤维样生长,大部分细胞处于G₀/G₁期,并且高表达Flk1,CD13,CD29,CD44,小鼠骨髓来源Flk-1⁺间充质干细胞在光镜下均呈成纤维样或多角型贴壁生长,在体外相应的诱导液环境中均可以向三系分化。提示小鼠骨髓来源Flk-1⁺间充质干细胞具有多向分化潜能。     

Comparison of proliferative and multilineage differentiation potential of human mesenchymal stem cells derived from umbilical cord and bone marrow

Human umbilical cord perivascular cells (HUCPVCs) have been shown to have a high proliferative potential and the capacity to differentiate into an osteogenic phenotype. HUCPVCs have thus been considered a possible extra-embryonic mesenchymal stem cell (MSC) source for cell-based therapies. To assess this potential, we compared HUCPVCs to the "gold standard" bone marrow mesenchymal stromal cells (BMSCs) with respect to their proliferation, differentiation, and transfection capacities. HUCPVCs showed a higher proliferative potential than BMSCs and were capable of osteogenic, chondrogenic, and adipogenic differentiation. Interestingly, osteogenic differentiation of HUCPVCs proceeded more rapidly than BMSCs. Additionally, HUCPVCs expressed higher levels of CD146, a putative MSC marker, relative to BMSCs. HUCPVCs showed comparable transfection efficiency as BMSCs using a nucleofection method but were more amenable to transfection with liposomal methods (FuGENE). Gene array analysis showed that HUCPVCs also expressed Wnt signaling pathway genes that have been implicated in the regulation of MSCs. The similar characteristics between HUCPVCs and MSCs support the applicability of HUCPVCs for cell-based therapies. Disclosure of potential conflicts of interest is found at the end of this article.     

The growth and differentiation of mesenchymal stem and progenitor cells cultured on aligned collagen matrices

Cell-matrix interactions are paramount for the successful repair and regeneration of damaged and diseased tissue. Since many tissues have an anisotropic architecture, it has been proposed that aligned extracellular matrix (ECM) structures in particular could guide and support the differentiation of resident mesenchymal stem and progenitor cells (MSCs). We therefore created aligned collagen type I structures using a microfluidic set-up with the aim to assess their impact on MSC growth and differentiation. In addition, we refined our aligned collagen matrices by incorporating the glycosaminoglycan (GAG) heparin to demonstrate the versatility of the applied methodology to study multiple ECM components in a single system. Our reconstituted, aligned ECM structures maintained and allowed multilineage (osteogenic/adipogenic/chondrogenic) differentiation of MSCs. Most noticeable was the observation that during osteogenesis, aligned collagen substrates choreographed ordered matrix mineralization. Likewise, myotube assembly of C2C12 cells was profoundly influenced by aligned topographic features resulting in enhanced myotube organization and length. Our results shed light on the regulation of MSCs through directional ECM structures and demonstrate the versatility of these cell culture platforms for guiding the morphogenesis of tissue types with anisotropic structures.     

Mouse adipose-derived stem cells undergo multilineage differentiation in vitro but primarily osteogenic and chondrogenic differentiation in vivo

Human, rat, and mouse studies have demonstrated the existence of a population of adipose-derived adult stem (ADAS) cells that can undergo multilineage differentiation in vitro. However, it remains unclear whether these cells maintain their multilineage potential in vivo. The aim of this study was to examine the in vitro and in vivo characteristics and behavior of a potential population of murine ADAS (muADAS) cells isolated from the visceral fat of the abdominal cavity of C57BL/10J mice. We used flow cytometry to examine the cells' expression of CD29, CD31, CD45, CD34, CD44, CD144, CD146, Flk1, and Sca-1. The isolated cell population was CD45 negative, which precludes contamination by hematopoietic cells, but was partially positive for Sca-1 and CD34: 2 stem-cell markers. After induction in conditioned medium, the muADAS cells gained the ability to undergo adipogenic, osteogenic, chondrogenic, myogenic, and hematopoietic differentiation in vitro. The muADAS cells readily differentiated to form bone and cartilage in vivo for up to 24 weeks, but their ability to regenerate muscle or reconstitute bone marrow was found to be limited.     

豚鼠骨髓间充质干细胞的分离培养及成骨诱导

背景：利用骨髓间充质干细胞的取材灵活性及快捷性,对已掌握的培养技术及成骨诱导进一步探索性研究。 目的：通过建立豚鼠骨髓间充质干细胞的体外分离培养法,探讨豚鼠骨髓间充质干细胞表型特征以及多项分化潜能。 方法：利用贴壁培养法分离纯化豚鼠骨髓间充质干细胞,传代扩增,流式细胞分析检测细胞表面分子CD29、CD44、CD45的表达。分别采用成骨诱导培养液和成脂诱导培养液定向诱导骨髓间充质干细胞向脂肪细胞、成骨细胞分化。 结果与结论：原代分离的骨髓间充质干细胞在接种后96 h贴壁,细胞形态为椭圆形,多角形及短梭形,8 d时细胞呈长梭形并达到90%单层融合。经传代扩增,细胞进一步纯化,细胞形态为均一的长梭形并呈漩涡状排列,而且生长速率加快。流式细胞检测 CD29、CD44阳性率分别为95.7%和65.7%。不同诱导剂定向诱导后,经油红O、茜素红S、碱性磷酸酶染色、免疫组织化学Ι型胶原酶鉴定,P3代骨髓间充质干细胞分别向脂肪细胞及成骨细胞分化。结果表明,通过贴壁筛选方法,体外分离培养的豚鼠骨髓间充质干细胞具有很强的增殖能力,并保持稳定的表型特征及多向分化潜能。     

Autocrine fibroblast growth factor 2 increases the multipotentiality of human adipose-derived mesenchymal stem cells

Multipotent mesenchymal stem cells (MSCs), first identified in the bone marrow, have subsequently been found in many other tissues, including fat, cartilage, muscle, and bone. Adipose tissue has been identified as an alternative to bone marrow as a source for the isolation of MSCs, as it is neither limited in volume nor as invasive in the harvesting. This study compares the multipotentiality of bone marrow-derived mesenchymal stem cells (BMSCs) with that of adipose-derived mesenchymal stem cells (AMSCs) from 12 age- and sex-matched donors. Phenotypically, the cells are very similar, with only three surface markers, CD106, CD146, and HLA-ABC, differentially expressed in the BMSCs. Although colony-forming units-fibroblastic numbers in BMSCs were higher than in AMSCs, the expression of multiple stem cell-related genes, like that of fibroblast growth factor 2 (FGF2), the Wnt pathway effectors FRAT1 and frizzled 1, and other self-renewal markers, was greater in AMSCs. Furthermore, AMSCs displayed enhanced osteogenic and adipogenic potential, whereas BMSCs formed chondrocytes more readily than AMSCs. However, by removing the effects of proliferation from the experiment, AMSCs no longer out-performed BMSCs in their ability to undergo osteogenic and adipogenic differentiation. Inhibition of the FGF2/fibroblast growth factor receptor 1 signaling pathway demonstrated that FGF2 is required for the proliferation of both AMSCs and BMSCs, yet blocking FGF2 signaling had no direct effect on osteogenic differentiation. Disclosure of potential conflicts of interest is found at the end of this article.     

Foot fat pad: Characterization by mesenchymal stromal cells in rats

Foot fat pad (FFP) is a highly functionalized fat depot of great significance for weight bearing in the foot. Mesenchymal stromal cells (MSCs) in subcutaneous adipose tissues are widely studied for regenerative potentials. MSCs in FFP, which may contribute to the physiological and pathological conditions of the foot, have not been characterized. In this study, MSCs were isolated from FFP (designated as MSCs-ffp) and subcutaneous adipose tissue (designated as MSCs-sub) from rats. The cell surface markers, proliferation, and efficiency of colony formation were compared between MSCs-ffp and MSCs-sub. In addition, MSCs-ffp were induced for osteogenic, chondrogenic, and adipogenic differentiation. The tri-lineage differentiation potentials were compared between MSCs-ffp and MSCs-sub by the expression of Runx2, Sox9, and proliferator-activated receptor gamma (PPAR-γ), respectively, using quantitative polymerized chain reaction. The expression of elastin and associated genes by MSCs-ffp were also evaluated. MSCs-ffp, like MSCs-sub, expressed CD44, CD73, and CD90. MSCs-ffp and MSCs-sub proliferated at similar rates but MSCs-ffp formed more colonies than MSCs-sub. MSCs-ffp were capable of differentiating into osteogenic, chondrogenic, and adipogenic lineages. Under the conditions of osteogenic and adipogenic differentiation, MSCs-sub expressed more Runx2 and PPAR-γ, respectively, than MSCs-ffp. The undifferentiated MSCs-ffp upregulated the expression of fibulin-5. In conclusion, MSCs-ffp shared common biology with MSCs-sub but were more efficient in colony formation, less adipogenic and osteogenic, and participated in elastogenesis. The unique features of MSCs-ffp may relate to their roles in the physiological functions of FFP.     

Co-expression of two perivascular cell markers isolates mesenchymal stem-like cells from human endometrium

BACKGROUND: Human endometrium has immense regenerative capacity, growing ~5 mm in 7 days every month. We have previously identified a small population of colony-forming endometrial stromal cells which we hypothesize are mesenchymal stem cells (MSC). The aim of this study was to determine if the co-expression of two perivascular cell markers, CD146 and platelet-derived growth factor-receptor beta (PDGF-Rbeta), will prospectively isolate endometrial stromal cells which exhibit MSC properties, and determine their location in human endometrium. METHODS: Single cell suspensions of human endometrial stromal cells were fluorescence activated cell sorting (FACS) sorted into CD146(+)PDGF-Rbeta(+) and CD146(-)PDGF-Rbeta(-) populations and analysed for colony-forming ability, in vitro differentiation and expression of typical MSC markers. Full thickness human endometrial sections were co-stained for CD146 and PDGF-Rbeta. RESULTS: FACS stromal CD146(+)PDGF-Rbeta(+) stromal cells (1.5% of sorted population) were enriched for colony-forming cells compared with CD146(-)PDGF-Rbeta(-) cells (7.7 +/- 1.7 versus 0.7 +/- 0.2% P <0.0001), and also underwent differentiation into adipogenic, osteogenic, myogenic and chondrogenic lineages. They expressed MSC phenotypic surface markers and were located near blood vessels. CONCLUSION: This study shows that human endometrium contains a small population of MSC-like cells that may be responsible for its cyclical growth, and may provide a readily available source of MSC for tissue engineering applications.