A multistep computational approach reveals a neuro-mesenchymal cell population in the embryonic hematopoietic stem cell niche

The first hematopoietic stem and progenitor cells (HSPCs) emerge in the Aorta-Gonad-Mesonephros (AGM) region of the mid-gestation mouse embryo. However, the precise nature of their supportive mesenchymal microenvironment remains largely unexplored. Here, we profiled transcriptomes of laser micro-dissected aortic tissues at three developmental stages and individual AGM cells. Computational analyses allowed the identification of several cell subpopulations within the E11.5 AGM mesenchyme, with the presence of a yet unidentified subpopulation characterized by the dual expression of genes implicated in adhesive or neuronal functions. We confirmed the identity of this cell subset as a neuro-mesenchymal population, through morphological and lineage tracing assays. Loss of function in the zebrafish confirmed that Decorin, a characteristic extracellular matrix component of the neuro-mesenchyme, is essential for HSPC development. We further demonstrated that this cell population is not merely derived from the neural crest, and hence, is a bona fide novel subpopulation of the AGM mesenchyme.

Portal fibroblasts with mesenchymal stem cell features form a reservoir of proliferative myofibroblasts in liver fibrosis

BACKGROUND AND AIMS

In liver fibrosis, myofibroblasts derive from HSCs and as yet undefined mesenchymal cells. We aimed to identify portal mesenchymal progenitors of myofibroblasts.

APPROACH AND RESULTS

Portal mesenchymal cells were isolated from mouse bilio-vascular tree and analyzed by single-cell RNA-sequencing. Thereby, we uncovered the landscape of portal mesenchymal cells in homeostatic mouse liver. Trajectory analysis enabled inferring a small cell population further defined by surface markers used to isolate it. This population consisted of portal fibroblasts with mesenchymal stem cell features (PMSCs), i.e., high clonogenicity and trilineage differentiation potential, that generated proliferative myofibroblasts, contrasting with nonproliferative HSC-derived myofibroblasts (-MF). Using bulk RNA-sequencing, we built oligogene signatures of the two cell populations that remained discriminant across myofibroblastic differentiation. SLIT2, a prototypical gene of PMSC/PMSC-MF signature, mediated profibrotic and angiogenic effects of these cells, which conditioned medium promoted HSC survival and endothelial cell tubulogenesis. Using PMSC/PMSC-MF 7-gene signature and slit guidance ligand 2 fluorescent in situ hybridization, we showed that PMSCs display a perivascular portal distribution in homeostatic liver and largely expand with fibrosis progression, contributing to the myofibroblast populations that form fibrotic septa, preferentially along neovessels, in murine and human liver disorders, irrespective of etiology. We also unraveled a 6-gene expression signature of HSCs/HSC-MFs that did not vary in these disorders, consistent with their low proliferation rate.

CONCLUSIONS

PMSCs form a small reservoir of expansive myofibroblasts, which, in interaction with neovessels and HSC-MFs that mainly arise through differentiation from a preexisting pool, underlie the formation of fibrotic septa in all types of liver diseases.

In vivo screen identifies a SIK inhibitor that induces β cell proliferation through a transient UPR

It is known that β cell proliferation expands the β cell mass during development and under certain hyperglycemic conditions in the adult, a process that may be used for β cell regeneration in diabetes. Here, through a new high-throughput screen using a luminescence ubiquitination-based cell cycle indicator (LUCCI) in zebrafish, we identify HG-9-91-01 as a driver of proliferation and confirm this effect in mouse and human β cells. HG-9-91-01 is an inhibitor of salt-inducible kinases (SIKs), and overexpression of Sik1 specifically in β cells blocks the effect of HG-9-91-01 on β cell proliferation. Single-cell transcriptomic analyses of mouse β cells demonstrate that HG-9-91-01 induces a wave of activating transcription factor (ATF)6-dependent unfolded protein response (UPR) before cell cycle entry. Importantly, the UPR wave is not associated with an increase in insulin expression. Additional mechanistic studies indicate that HG-9-91-01 induces multiple signalling effectors downstream of SIK inhibition, including CRTC1, CRTC2, ATF6, IRE1 and mTOR, which integrate to collectively drive β cell proliferation.

Inferring Gene Networks in Bone Marrow Hematopoietic Stem Cell-Supporting Stromal Niche Populations

The cardinal property of bone marrow (BM) stromal cells is their capacity to contribute to hematopoietic stem cell (HSC) niches by providing mediators assisting HSC functions. In this study we first contrasted transcriptomes of stromal cells at different developmental stages and then included large number of HSC-supportive and non-supportive samples. Application of a combination of algorithms, comprising one identifying reliable paths and potential causative relationships in complex systems, revealed gene networks characteristic of the BM stromal HSC-supportive capacity and of defined niche populations of perivascular cells, osteoblasts, and mesenchymal stromal cells. Inclusion of single-cell transcriptomes enabled establishing for the perivascular cell subset a partially oriented graph of direct gene-to-gene interactions. As proof of concept we showed that R-spondin-2, expressed by the perivascular subset, synergized with Kit ligand to amplify ex vivo hematopoietic precursors. This study by identifying classifiers and hubs constitutes a resource to unravel candidate BM stromal mediators.

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A correlation network with predictor genes for the BM HSPC-supportive stromal niche

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An information theoretic network for the supportive perivascular stromal niche

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Wnt facilitator Rspo2 together with SCF to amplify ex vivo hematopoietic precursors

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Resource combining bioinformatics algorithms to search for novel stromal mediators

Notch ligand Dll4 impairs cell recruitment to aortic clusters and limits blood stem cell generation

Hematopoietic stem cells (HSCs) develop from the hemogenic endothelium in cluster structures that protrude into the embryonic aortic lumen. Although much is known about the molecular characteristics of the developing hematopoietic cells, we lack a complete understanding of their origin and the three-dimensional organization of the niche. Here, we use advanced live imaging techniques of organotypic slice cultures, clonal analysis, and mathematical modeling to show the two-step process of intra-aortic hematopoietic cluster (IACH) formation. First, a hemogenic progenitor buds up from the endothelium and undergoes division forming the monoclonal core of the IAHC. Next, surrounding hemogenic cells are recruited into the IAHC, increasing their size and heterogeneity. We identified the Notch ligand Dll4 as a negative regulator of the recruitment phase of IAHC. Blocking of Dll4 promotes the entrance of new hemogenic Gfi1⁺ cells into the IAHC and increases the number of cells that acquire HSC activity. Mathematical modeling based on our data provides estimation of the cluster lifetime and the average recruitment time of hemogenic cells to the cluster under physiologic and Dll4-inhibited conditions.

Extracellular vesicles of stromal origin target and support hematopoietic stem and progenitor cells

Extracellular vesicles (EVs) are emerging as crucial mediators in cell-to-cell communication. Stik et al. provide evidence that EVs released by supportive stromal cells target hematopoietic stem and progenitor cells in vivo and in vitro and influence their gene expression and potential.

Extracellular vesicles (EVs) have been recently reported as crucial mediators in cell-to-cell communication in development and disease. In this study, we investigate whether mesenchymal stromal cells that constitute a supportive microenvironment for hematopoietic stem and progenitor cells (HSPCs) released EVs that could affect the gene expression and function of HSPCs. By taking advantage of two fetal liver–derived stromal lines with widely differing abilities to maintain HSPCs ex vivo, we demonstrate that stromal EVs play a critical role in the regulation of HSPCs. Both supportive and nonsupportive stromal lines secreted EVs, but only those delivered by the supportive line were taken up by HSPCs ex vivo and in vivo. These EVs harbored a specific molecular signature, modulated the gene expression in HSPCs after uptake, and maintained the survival and clonogenic potential of HSPCs, presumably by preventing apoptosis. In conclusion, our study reveals that EVs are an important component of the HSPC niche, which may have major applications in regenerative medicine.

Bistable Epigenetic States Explain Age-Dependent Decline in Mesenchymal Stem Cell Heterogeneity

The molecular mechanisms by which heterogeneity, a major characteristic of stem cells, is achieved are yet unclear. We here study the expression of the membrane stem cell antigen-1 (Sca-1) in mouse bone marrow mesenchymal stem cell (MSC) clones. We show that subpopulations with varying Sca-1 expression profiles regenerate the Sca-1 profile of the mother population within a few days. However, after extensive replication in vitro, the expression profiles shift to lower values and the regeneration time increases. Study of the promoter of Ly6a unravels that the expression level of Sca-1 is related to the promoter occupancy by the activating histone mark H3K4me3. We demonstrate that these findings can be consistently explained by a computational model that considers positive feedback between promoter H3K4me3 modification and gene transcription. This feedback implicates bistable epigenetic states which the cells occupy with an age-dependent frequency due to persistent histone (de-)modification. Our results provide evidence that MSC heterogeneity, and presumably that of other stem cells, is associated with bistable epigenetic states and suggest that MSCs are subject to permanent state fluctuations. Stem Cells 2017;35:694-704.

CD200 expression in human cultured bone marrow mesenchymal stem cells is induced by pro-osteogenic and pro-inflammatory cues

Similar to other adult tissue stem/progenitor cells, bone marrow mesenchymal stem/stromal cells (BM MSCs) exhibit heterogeneity at the phenotypic level and in terms of proliferation and differentiation potential. In this study such a heterogeneity was reflected by the CD200 protein. We thus characterized CD200(pos) cells sorted from whole BM MSC cultures and we investigated the molecular mechanisms regulating CD200 expression. After sorting, measurement of lineage markers showed that the osteoblastic genes RUNX2 and DLX5 were up-regulated in CD200(pos) cells compared to CD200(neg) fraction. At the functional level, CD200(pos) cells were prone to mineralize the extra-cellular matrix in vitro after sole addition of phosphates. In addition, osteogenic cues generated by bone morphogenetic protein 4 (BMP4) or BMP7 strongly induced CD200 expression. These data suggest that CD200 expression is related to commitment/differentiation towards the osteoblastic lineage. Immunohistochemistry of trephine bone marrow biopsies further corroborates the osteoblastic fate of CD200(pos) cells. However, when dexamethasone was used to direct osteogenic differentiation in vitro, CD200 was consistently down-regulated. As dexamethasone has anti-inflammatory properties, we assessed the effects of different immunological stimuli on CD200 expression. The pro-inflammatory cytokines interleukin-1β and tumour necrosis factor-α increased CD200 membrane expression but down-regulated osteoblastic gene expression suggesting an additional regulatory pathway of CD200 expression. Surprisingly, whatever the context, i.e. pro-inflammatory or pro-osteogenic, CD200 expression was down-regulated when nuclear-factor (NF)-κB was inhibited by chemical or adenoviral agents. In conclusion, CD200 expression by cultured BM MSCs can be induced by both osteogenic and pro-inflammatory cytokines through the same pathway: NF-κB.

A systems biology approach for defining the molecular framework of the hematopoietic stem cell niche

Despite progress in identifying the cellular composition of hematopoietic stem/progenitor cell (HSPC) niches, little is known about the molecular requirements of HSPC support. To address this issue, we used a panel of six recognized HSPC-supportive stromal lines and less-supportive counterparts originating from embryonic and adult hematopoietic sites. Through comprehensive transcriptomic meta-analyses, we identified 481 mRNAs and 17 microRNAs organized in a modular network implicated in paracrine signaling. Further inclusion of 18 additional cell strains demonstrated that this mRNA subset was predictive of HSPC support. Our gene set contains most known HSPC regulators as well as a number of unexpected ones, such as Pax9 and Ccdc80, as validated by functional studies in zebrafish embryos. In sum, our approach has identified the core molecular network required for HSPC support. These cues, along with a searchable web resource, will inform ongoing efforts to instruct HSPC ex vivo amplification and formation from pluripotent precursors.

Granulocyte-colony-stimulating factor stimulation of bone marrow mesenchymal stromal cells promotes CD34+ cell migration via a matrix metalloproteinase-2-dependent mechanism

Human hematopoietic stem/progenitor cells (HSPCs) can be mobilized into the circulation using granulocyte-colony stimulating factor (G-CSF), for graft collection in view of hematopoietic transplantation. This process has been related to bone marrow (BM) release of serine proteases and of the matrix metalloproteinase-9 (MMP-9). Yet, the role of these mediators in HSC egress from their niches remains questionable, because they are produced by nonstromal cells (mainly neutrophils and monocytes/macrophages) that are not a part of the niche. We show here that the G-CSF receptor (G-CSFR) is expressed by human BM mesenchymal stromal/stem cells (MSCs), and that G-CSF prestimulation of MSCs enhances the in vitro trans-stromal migration of CD34+ cells. Zymography analysis indicates that pro-MMP-2 (but not pro-MMP-9) is expressed in MSCs, and that G-CSF treatment increases its expression and induces its activation at the cell membrane. We further demonstrate that G-CSF-stimulated migration depends on G-CSFR expression and is mediated by a mechanism that involves MMPs. These results suggest a molecular model whereby G-CSF infusion may drive, by the direct action on MSCs, HSPC egress from BM niches via synthesis and activation of MMPs. In this model, MMP-2 instead of MMP-9 is implicated, which constitutes a major difference with mouse mobilization models.

Differential gene expression profiling of human bone marrow-derived mesenchymal stem cells during adipogenic development

BACKGROUND

Adipogenesis is the developmental process by which mesenchymal stem cells (MSC) differentiate into pre-adipocytes and adipocytes. The aim of the study was to analyze the developmental strategies of human bone marrow MSC developing into adipocytes over a defined time scale. Here we were particularly interested in differentially expressed transcription factors and biochemical pathways. We studied genome-wide gene expression profiling of human MSC based on an adipogenic differentiation experiment with five different time points (day 0, 1, 3, 7 and 17), which was designed and performed in reference to human fat tissue. For data processing and selection of adipogenic candidate genes, we used the online database SiPaGene for Affymetrix microarray expression data.

RESULTS

The mesenchymal stem cell character of human MSC cultures was proven by cell morphology, by flow cytometry analysis and by the ability of the cells to develop into the osteo-, chondro- and adipogenic lineage. Moreover we were able to detect 184 adipogenic candidate genes (85 with increased, 99 with decreased expression) that were differentially expressed during adipogenic development of MSC and/or between MSC and fat tissue in a highly significant way (p < 0.00001). Subsequently, groups of up- or down-regulated genes were formed and analyzed with biochemical and cluster tools. Among the 184 genes, we identified already known transcription factors such as PPARG, C/EBPA and RTXA. Several of the genes could be linked to corresponding biochemical pathways like the adipocyte differentiation, adipocytokine signalling, and lipogenesis pathways. We also identified new candidate genes possibly related to adipogenesis, such as SCARA5, coding for a receptor with a putative transmembrane domain and a collagen-like domain, and MRAP, encoding an endoplasmatic reticulum protein.

CONCLUSIONS

Comparing differential gene expression profiles of human MSC and native fat cells or tissue allowed us to establish a comprehensive differential kinetic gene expression network of adipogenesis. Based on this, we identified known and unknown genes and biochemical pathways that may be relevant for adipogenic differentiation. Our results encourage further and more focused studies on the functional relevance of particular adipogenic candidate genes.

Comparison of Gene Expression in Human Embryonic Stem Cells, hESC-Derived Mesenchymal Stem Cells and Human Mesenchymal Stem Cells

We present a strategy to identify developmental/differentiation and plasma membrane marker genes of the most primitive human Mesenchymal Stem Cells (hMSCs). Using sensitive and quantitative TaqMan Low Density Arrays (TLDA) methodology, we compared the expression of 381 genes in human Embryonic Stem Cells (hESCs), hESC-derived MSCs (hES-MSCs), and hMSCs. Analysis of differentiation genes indicated that hES-MSCs express the sarcomeric muscle lineage in addition to the classical mesenchymal lineages, suggesting they are more primitive than hMSCs. Transcript analysis of membrane antigens suggests that IL1R1^low, BMPR1B^low, FLT4^low, LRRC32^low, and CD34 may be good candidates for the detection and isolation of the most primitive hMSCs. The expression in hMSCs of cytokine genes, such as IL6, IL8, or FLT3LG, without expression of the corresponding receptor, suggests a role for these cytokines in the paracrine control of stem cell niches. Our database may be shared with other laboratories in order to explore the considerable clinical potential of hES-MSCs, which appear to represent an intermediate developmental stage between hESCs and hMSCs.

[Human mesenchymal stem cell biology]

This brief overview summarises the main characteristics of bone marrow mesenchymal stem cells and of adipose-derived stem cells: methods of obtention, phenotype, differentiation potential, hematopoiesis-supportive (stromal) capacity, and immunosuppressive properties. Two points are discussed in detail: 1) criteria for stemness: multipotency, self-renewal, plasticity, and 2) the repair mechanisms implicated in the different indications of cell therapy using these cells: reconstitution of the tissue functional compartment by repopulation consequent to proliferation and differentiation or reprogrammation, stromal effects by secretion of angiogenic, anti-apoptotic, anti-fibrogenic factors, molecules involved in the regulation of inflammation, etc.

Bone marrow mesenchymal stem cells: historical overview and concepts

This review describes the historical emergence of the concept of bone marrow mesenchymal stem cells (MSCs), summarizing data on Wolf and Trentin's hematopoietic inductive microenvironment; Dexter's hematopoiesis-supportive stromal cells; Friedenstein's osteogenic cells; and Pittenger's trilineal osteoblastic, chondrocytic, and adipocytic precursors; to finally introduce the specific bone marrow mesenchymal stem cells with differentiation potential to four lineages (mesenchymal and vascular smooth muscle lineages), and stromal and immunomodulatory capacities. Two points are the object of detailed discussion. The first point envisions the stem cell attributes (multipotentiality, self-renewal, tissue regeneration, population heterogeneity, plasticity, and lineage priming) compared with that of the paradigmatic hematopoietic stem cell. In the second point, we discuss the possible existence of bone marrow cells with greater differentiation potential, eventually pluripotential cells. The latter point raises the issues of cell fusion, reprogramming, or selection under nonstandardized conditions of rare populations of neuroectodermal origin, or of cells that had undergone mesenchymal-to-epithelial transition. In the last section, we review data on MSC senescence and possible malignant transformation secondary to extensive culture, gene transfer of telomerase, or mutations such as leading to Ewing's sarcoma. The set of data leads to the conclusion that bone marrow MSCs constitute a specific adult tissue stem cell population. The multiple characteristics of this stem cell type account for the versatility of the mechanisms of injured tissue repair. Although MSC administration may be extremely useful in a number of clinical applications, their transplantation is not without risks that must not be overlooked when developing cell therapy protocols.

The human nose harbors a niche of olfactory ectomesenchymal stem cells displaying neurogenic and osteogenic properties

We previously identified multipotent stem cells within the lamina propria of the human olfactory mucosa, located in the nasal cavity. We also demonstrated that this cell type differentiates into neural cells and improves locomotor behavior after transplantation in a rat model of Parkinson's disease. Yet, next to nothing is known about their specific stemness characteristics. We therefore devised a study aiming to compare olfactory lamina propria stem cells from 4 individuals to bone marrow mesenchymal stem cells from 4 age- and gender-matched individuals. Using pangenomic microarrays and immunostaining with 34 cell surface marker antibodies, we show here that olfactory stem cells are closely related to bone marrow stem cells. However, olfactory stem cells also exhibit singular traits. By means of techniques such as proliferation assay, cDNA microarrays, RT-PCR, in vitro and in vivo differentiation, we report that when compared to bone marrow stem cells, olfactory stem cells display (1) a high proliferation rate; (2) a propensity to differentiate into osseous cells; and (3) a disinclination to give rise to chondrocytes and adipocytes. Since peripheral olfactory stem cells originate from a neural crest-derived tissue and, as shown here, exhibit an increased expression of neural cell-related genes, we propose to name them olfactory ectomesenchymal stem cells (OE-MSC). Further studies are now required to corroborate the therapeutic potential of OE-MSCs in animal models of bone and brain diseases.

Impaired differentiation potential of human trabecular bone mesenchymal stromal cells from elderly patients

BACKGROUND AIMS

Advances in bone tissue engineering with mesenchymal stromal cells (MSC) as an alternative to conventional orthopedic procedures has opened new horizons for the treatment of large bone defects. Bone marrow (BM) and trabecular bone are both sources of MSC. Regarding clinical use, we tested the potency of MSC from different sources.

METHODS

We obtained MSC from 17 donors (mean age 64.6 years) by extensive washing of trabecular bone from the femoral head and trochanter, as well as BM aspirates of the iliac crest and trochanter. The starting material was evaluated by histologic analysis and assessment of colony-forming unit-fibroblasts (CFU-F). The MSC populations were compared for proliferation and differentiation potential, at RNA and morphologic levels.

RESULTS

MSC proliferation potential and immunophenotype (expression of CD49a, CD73, CD90, CD105, CD146 and Stro-1) were similar whatever the starting material. However, the differentiation potential of MSC obtained by bone washing was impaired compared with aspiration; culture-amplified cells showed few Oil Red O-positive adipocytes and few mineralized areas and formed inconsistent Alcian blue-positive high-density micropellets after growth under adipogenic, osteogenic and chondrogenic conditions, respectively. MSC cultured with 1 ng/mL fibroblast growth factor 2 (FGF-2) showed better differentiation potential.

CONCLUSIONS

Trabecular bone MSC from elderly patients is not good starting material for use in cell therapy for bone repair and regeneration, unless cultured in the presence of FGF-2.

Gene expression profile of multipotent mesenchymal stromal cells: Identification of pathways common to TGFbeta3/BMP2-induced chondrogenesis

Multipotent mesenchymal stromal cells (MSC) display a high potential for the development of novel treatment strategies for cartilage repair. However, the pathways involved in their differentiation to functional non hypertrophic chondrocytes remain largely unknown, despite the work on embryologic development and the identification of key growth factors including TGFbeta, Hh, Wnt and FGF. In this study, we asked if we could identify specific biological networks common to the growth factors used (TGFbeta3 or BMP-2). To address this question, we used DNA microarrays and performed large-scale expression profiling of MSC at different time points during their chondrogenic differentiation. By comparing these data with those obtained during the differentiation of MSC into osteoblasts and adipocytes, we identified 318 genes specific for chondrogenesis and developed a new algorithm to classify the genes according to their kinetic profile. We distributed the selected genes in five classes according to their kinetic of expression. We could reconstruct three phases characterized by functional pathways. The first phase corresponds to cell attachment and apoptosis induction; the second phase is characterized by a proliferation/differentiation step, and the third phase is characterized by a differentiation/hypertrophy pathway. Indeed, these data propose new pathways to understand the complexity of MSC differentiation to chondrocytes.

Isolation of human bone marrow mesenchymal stem cells using different membrane markers: comparison of colony/cloning efficiency, differentiation potential, and molecular profile

Bone marrow (BM) mesenchymal stem cells (MSCs) represent an interesting field of research for their in vitro properties and the in vivo therapeutic applications. In the present study, we compared the clonogenic and differentiation capacity of MSCs present in three BM-derived populations-namely, the CD105(+)/CD45(-) cells, the glycophorin A (GlycoA)(-)/CD45(-) cells, and the BM mononuclear cells (BMMCs)-by growing/expanding clones from single colony-forming unit fibroblasts (CFU-F). We also quantified the Oct-4 and Nanog mRNA in the CD105(+)/CD45(-) and GlycoA(-)/CD45(-) cells to define the fraction containing more immature MSCs. We found that basic-fibroblast growth factor (bFGF) favors the long-term survival and growth of the more immature MSCs but has no significant effect on MSC clonogenic potential. CFU-F number and clone recovery were higher in CD105(+)/CD45(-) compared to GlycoA(-)/CD45(-) (p < 0.0001 and p = 0.0364, respectively) cells or BMMCs (p < 0.0001 and p = 0.0007, respectively). The relative mRNA expression of Oct-4 and Nanog was significantly increased in CD105(+)/CD45(-) compared to GlycoA(-)/CD45(-) cells (p < 0.0001 and p < 0.0001, respectively). No significant difference was found in the immunophenotypic characteristics and differentiation potential of clones derived from all three cellular sources. These data suggest that the CD105(+)/CD45(-) BM cell fraction is enriched in immature MSCs and, accordingly, represents an appropriate source for MSC culture initiation.

Adhesion, proliferation, and osteogenic differentiation of a mouse mesenchymal stem cell line (BMC9) seeded on novel melt-based chitosan/polyester 3D porous scaffolds

The aim of the present work was to study the biological behavior of a mouse mesenchymal stem cell line when seeded and cultured under osteogenic conditions onto novel processed melt-based chitosan scaffolds. Scaffolds were produced by compression molding, followed by salt leaching. Scanning electron microscopy (SEM) observations and microCT analysis showed the pore sizes ranging between 250 and 500 microm and the interconnectivity of the porous structure. The chitosan-poly(butylenes succinate) scaffolds presented high mechanical properties, similar to the ones of trabecular bone (E1% approximately 75 MPa). Cytotoxicity assays were carried out using standard tests (accordingly to ISO/EN 10993 part 5 guidelines), namely, MTS test with a 24 h extraction period, revealing that L929 cells had similar metabolic activities to that obtained for the negative control. Cell culture studies were conducted using a mouse mesenchymal stem cell line (BMC9). Cells were seeded onto the scaffold and allowed to proliferate for 3 weeks under osteogenic conditions. SEM observations demonstrated that cells were able to proliferate and massively colonize the scaffolds structure. The cell viability assay MTS demonstrated that BMC9 cells were viable after 3 weeks of culture. The cells clearly evidenced a positive differentiation toward the osteogenic lineage, as confirmed by the high ALP activity levels. Moreover, energy dispersive spectroscopy (EDS) analysis revealed the presence of Ca and P in the elaborated extracellular matrix (ECM). These combined results indicate that the novel melt-based chitosan/polyester scaffolds support the adhesion, proliferation, and osteogenic differentiation of the mouse MSCs and shows adequate physicochemical and biological properties for being used as scaffolds in bone tissue engineering-related strategies.

Assessment of the suitability of chitosan/polybutylene succinate scaffolds seeded with mouse mesenchymal progenitor cells for a cartilage tissue engineering approach

In this work, scaffolds derived from a new biomaterial originated from the combination of a natural material and a synthetic material were tested for assessing their suitability for cartilage tissue engineering applications. In order to obtain a better outcome result in terms of scaffolds' overall properties, different blends of natural and synthetic materials were created. Chitosan and polybutylene succinate (C-PBS) 50/50 (wt%) were melt blended using a twin-screw extruder and processed into 5 x 5 x 5 mm scaffolds by compression moulding with salt leaching. Micro-computed tomography analysis calculated an average of 66.29% porosity and 92.78% interconnectivity degree for the presented scaffolds. The salt particles used ranged in size between 63 and 125 mum, retrieving an average pore size of 251.28 mum. Regarding the mechanical properties, the compressive modulus was of 1.73 +/- 0.4 MPa (E(sec) 1%). Cytotoxicity evaluation revealed that the leachables released by the developed porous structures were not harmful to the cells and hence were noncytotoxic. Direct contact assays were carried out using a mouse bone marrow-derived mesenchymal progenitor cell line (BMC9). Cells were seeded at a density of 5 x 10(5) cells/scaffold and allowed to grow for periods up to 3 weeks under chondrogenic differentiating conditions. Scanning electron microscopy analysis revealed that the cells were able to proliferate and colonize the scaffold structure, and MTS test demonstrated cell viability during the time of the experiment. Finally, Western blot performed for collagen type II, a natural cartilage extracellular matrix component, showed that this protein was being expressed by the end of 3 weeks, which seems to indicate that the BMC9 cells were being differentiated toward the chondrogenic pathway. These results indicate the adequacy of these newly developed C-PBS scaffolds for supporting cell growth and differentiation toward the chondrogenic pathway, suggesting that they should be considered for further studies in the cartilage tissue engineering field.

Distinct osteoblastic differentiation potential of murine fetal liver and bone marrow stroma-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSC) are able to differentiate into osteoblasts under appropriate induction. Although MSC-derived osteoblasts are part of the hematopoietic niche, the nature of the stromal component in fetal liver remains elusive. Here, we determined the in vitro osteoblastic differentiation potential of murine clonal fetal liver-derived cells (AFT024, BFC012, 2012) in comparison with bone marrow-derived cell lines (BMC9, BMC10). Bone morphogenetic protein-2 (BMP2) increased alkaline phosphatase (ALP) activity, an early osteoblastic marker, in AFT024 and 2012 cells, whereas dexamethasone had little or no effect. BMP2, but not dexamethasone, increased ALP activity in BMC9 cells, and both inducers increased ALP activity in BMC10 cells. BMP2 increased ALP mRNA in AFT024, 2012 and BMC9 cells. By contrast, ALP was not detected in BMC10 and BFC012 cells. BMP2 and dexamethasone increased osteopontin and osteocalcin mRNA expression in 2012 cells. Furthermore, bone marrow-derived cells showed extensive matrix mineralization, whereas fetal liver-derived cell lines showed no or very limited matrix mineralization capacity. These results indicate that the osteoblast differentiation potential differs in bone marrow and fetal liver-derived cell lines, which may be due to a distinct developmental program or different microenvironment in the two hematopoietic sites.

Properties and potential of bone marrow mesenchymal stromal cells from children with hematologic diseases

BACKGROUND

Mesenchymal stromal cells (MSC) have become the focus of cellular therapeutics but little is known regarding bone marrow (BM) MSC derived from children. As MSC constitute part of BM stroma, we examined their properties in children with hematologic diseases.

METHODS

BM MSC from children with non-malignant hematologic disorders and acute lymphoblastic leukemia (ALL) were isolated and expanded. MSC were immunophenotypically characterized and their functional characteristics were assessed by CFU-F assay and cell doubling time calculation. Their ability for trilineage differentiation was verified by molecular and histochemical methods. Apoptosis was evaluated and clonal analysis was performed.

RESULTS

MSC were isolated from BM of all groups. They acquired the mesenchymal-related markers from the first passage, with a simultaneous decrease of hematopoietic markers. A very low percentage of apoptotic cells was detected in all passages. The proliferative and clonogenic capacity did not differ among groups, with the exception of ALL at diagnosis, in which they were defective. Histochemical and molecular analysis of differentiated MSC yielded characteristics for adipocytes, osteoblasts and chondrocytes. Clonal analysis in a number of BM samples revealed a highly heterogeneous population of cells within each clone.

DISCUSSION

MSC from BM of children with hematologic disorders, with the exception of ALL at diagnosis, can be isolated in sufficient number and quality to serve as a potential source for clinical applications.

Partial recovery of dopaminergic pathway after graft of adult mesenchymal stem cells in a rat model of Parkinson's disease

Cellular therapy with adult stem cells appears as an opportunity for treatment of Parkinson's disease. To validate this approach, we studied the effects of transplantation of rat adult bone-marrow mesenchymal stem cells in a rat model of Parkinson's disease. Animals were unilaterally lesioned in the striatum with 6-hydroxydopamine. Two weeks later, group I did not undergo grafting, group II underwent sham grafting, group III was intra-striatal grafted with cells cultured in an enriched medium and group IV was intra-striatal grafted with cells cultured in a standard medium. Rotational amphetamine-induced behavior was measured weekly until animals were killed 6 weeks later. One week after graft, the number of rotations/min was stably decreased by 50% in groups III and IV as compared with groups I and II. At 8 weeks post-lesion, the density of dopaminergic markers in the nerve terminals and cell bodies, i.e. immunoreactive tyrosine hydroxylase, membrane dopamine transporter and vesicular monoamine transporter-2 was significantly higher in group III as compared with group I. Moreover, using microdialysis studies, we observed that while the rate of pharmacologically induced release of dopamine was significantly reduced in lesioned versus intact striatum in no grafted rats, it was similar in both sides in animals transplanted with mesemchymal stem cells. These data demonstrate that graft of adult mesemchymal stem cells reduces behavioral effects induced by 6-hydroxydopamine lesion and partially restores the dopaminergic markers and vesicular striatal pool of dopamine. This cellular approach might be a restorative therapy in Parkinson's disease.

Culture and characterization of human bone marrow mesenchymal stem cells

Bone marrow (BM) mesenchymal stem cells (MSCs) are non-hematopoietic cells capable of generating colonies of plastic-adherent marrow mesenchymal cells, each derived from a single cell termed a colony-forming unit fibroblasts (CFU-Fs). In addition to their role in establishing the marrow microenvironment, these cells have been shown to differentiate into several types of mesenchymal and non-mesenchymal lineages. Because of their multipotency, MSCs represent an attractive cellular source in the promising field of cellular therapy. In this chapter, we will focus on culture conditions for human BM MSC expansion and CFU-F assays. We also describe the methodologies to analyze the primary cultures obtained, both at the phenotypic and at the functional levels. Phenotypically, MSCs can be defined with a minimal set of markers as CD31-, CD34-, and CD45-negative cells and CD13-, CD29-, CD73-, CD90-, CD105-, and CD166-positive cells. Functionally, we describe the culture conditions (specific media and cellular preparations) for in vitro differentiation of MSCs into the adipogenic, osteogenic, and chondrogenic lineages. The corresponding colorimetric assays (oil red O, Von Kossa and alizarin red S, and safranin O and alcian blue stains, respectively) are also described.

Microenvironmental changes during differentiation of mesenchymal stem cells towards chondrocytes

Chondrogenesis is a process involving stem-cell differentiation through the coordinated effects of growth/differentiation factors and extracellular matrix (ECM) components. Recently, mesenchymal stem cells (MSCs) were found within the cartilage, which constitutes a specific niche composed of ECM proteins with unique features. Therefore, we hypothesized that the induction of MSC differentiation towards chondrocytes might be induced and/or influenced by molecules from the microenvironment. Using microarray analysis, we previously identified genes that are regulated during MSC differentiation towards chondrocytes. In this study, we wanted to precisely assess the differential expression of genes associated with the microenvironment using a large-scale real-time PCR assay, according to the simultaneous detection of up to 384 mRNAs in one sample. Chondrogenesis of bone-marrow-derived human MSCs was induced by culture in micropellet for various periods of time. Total RNA was extracted and submitted to quantitative RT-PCR. We identified molecules already known to be involved in attachment and cell migration, including syndecans, glypicans, gelsolin, decorin, fibronectin, and type II, IX and XI collagens. Importantly, we detected the expression of molecules that were not previously associated with MSCs or chondrocytes, namely metalloproteases (MMP-7 and MMP-28), molecules of the connective tissue growth factor (CTGF); cef10/cyr61 and nov (CCN) family (CCN3 and CCN4), chemokines and their receptors chemokine CXC motif ligand (CXCL1), Fms-related tyrosine kinase 3 ligand (FlT3L), chemokine CC motif receptor (CCR3 and CCR4), molecules with A Disintegrin And Metalloproteinase domain (ADAM8, ADAM9, ADAM19, ADAM23, A Disintegrin And Metalloproteinase with thrombospondin type 1 motif ADAMTS-4 and ADAMTS-5), cadherins (4 and 13) and integrins (alpha4, alpha7 and beta5). Our data suggest that crosstalk between ECM components of the microenvironment and MSCs within the cartilage is responsible for the differentiation of MSCs into chondrocytes.

Functional, molecular and proteomic characterisation of bone marrow mesenchymal stem cells in rheumatoid arthritis

OBJECTIVE

Bone marrow (BM) mesenchymal stem cells (MSCs) are being considered as potential therapeutic agents in various inflammatory autoimmune diseases for their tissue-repair and anti-inflammatory tissue-protective properties. This study investigates the reserves and function, the molecular and proteomic profile and the differentiation potential of BM MSCs in patients with active rheumatoid arthritis (RA).

METHODS

We evaluated the frequency of MSCs in the BM mononuclear cell fraction using a limiting dilution assay, the proliferative/clonogenic potential and the capacity of cells to differentiate towards the osteogenic/chondrogenic/adipogenic lineages using appropriate culture conditions. We also assessed the molecular and proteomic characteristics in terms of inflammatory cytokine gene and protein expression, the relative telomere length and the survival characteristics of BM MSCs.

RESULTS

MSCs from patients with RA (n = 26) and age- and sex-matched healthy individuals (n = 21) were similar in frequency, differentiation potential, survival, immunophenotypic characteristics, and protein profile. Patient MSCs, however, had impaired clonogenic and proliferative potential in association with premature telomere length loss. Transcriptome analysis revealed differential expression of genes related to cell adhesion processes and cell cycle progression beyond the G1 phase. Previous treatment with methotrexate, corticosteroids, anti-cytokine and biological agents or other disease-modifying anti-inflammatory drugs did not correlate with the clonogenic and proliferative impairment of BM MSCs.

CONCLUSION

In spite of some restrictions related to the impaired clonogenic and proliferative potential, our findings support the use of autologous BM MSCs in RA and may have important implications for the ongoing efforts to repair tissue injury commonly seen in the course of the disease.

A sub-population of high proliferative potential-quiescent human mesenchymal stem cells is under the reversible control of interferon alpha/beta

Type I interferon (IFN) is shown to control the reversible quiescence of a primitive human bone marrow mesenchymal stem cell (MSC) subpopulation. A 24 h pre-treatment of Stro1+/GlycoA- or CD45-/GlycoA- subpopulations with a monoclonal antibody (mAb) against the IFNAR1 chain of the human type I IFN receptor (64G12), or with a polyclonal anti-IFNalpha antibody, resulted in a marked increase in the number of very large colonies (CFU-F >3000 cells) obtained in the presence of low, but necessary, concentrations of bFGF. Over a 2-month culture period, this short activation promoted a faster and greater amplification of mesenchymal progenitors for adipocytes and osteoblasts. Activation correlated with inhibition of STAT1 and STAT2 phosphorylation and of STAT1 nuclear translocation. A non-neutralizing anti-IFNAR1 mAb was ineffective. We demonstrate that control and activated MSCs express ST3GAL3, a sialyltransferase necessary to produce the embryonic antigens SSEA-3 and -4. Interestingly, activated MSC progeny expressed SSEA-3 and -4 at a higher level than control cultures, but this was not correlated with a significant expression of other embryonic markers. As MSCs represent an essential tool in tissue regeneration, the use of 64G12, which rapidly recruits a higher number of primitive cells, might increase amplification safety for cell therapy.

The concept of mesenchymal stem cells

In this chapter we examine whether criteria usually defining adult tissue stem cells apply to mesenchymal stem cells (MSCs) that give rise to cells of the skeletal connective tissues. MSCs appear to constitute a heterogeneous population of undifferentiated and committed, lineage-primed cells, capable of: homing upon engraftment to a number of growth microenvironments, extensive proliferation, producing large numbers of differentiated progeny, and functional tissue repair after injury. In addition, MSCs are extensively distributed throughout tissues, and bone marrow MSCs provide the stromal component of the niche of hematopoietic stem cells. The capacity of apparently differentiated mesenchymal cells to shift their differentiation pathway with changing microenvironmental conditions (known as differentiation plasticity) may be due to de-differentiation and reprogramming in MSCs. Because they present several features setting them apart from other stem cells, MSCs may constitute another paradigm for stem cell systems, where self-renewal and hierarchy are no longer essential, but where plasticity is the major characteristic.

Mesenchymal stem cell features of Ewing tumors

The cellular origin of Ewing tumor (ET), a tumor of bone or soft tissues characterized by specific fusions between EWS and ETS genes, is highly debated. Through gene expression analysis comparing ETs with a variety of normal tissues, we show that the profiles of different EWS-FLI1-silenced Ewing cell lines converge toward that of mesenchymal stem cells (MSC). Moreover, upon EWS-FLI1 silencing, two different Ewing cell lines can differentiate along the adipogenic lineage when incubated in appropriate differentiation cocktails. In addition, Ewing cells can also differentiate along the osteogenic lineage upon long-term inhibition of EWS-FLI1. These in silico and experimental data strongly suggest that the inhibition of EWS-FLI1 may allow Ewing cells to recover the phenotype of their MSC progenitor.

The in vitro migration capacity of human bone marrow mesenchymal stem cells: comparison of chemokine and growth factor chemotactic activities

Adult bone marrow (BM)-derived stem cells, including hematopoietic stem cells (HSCs) and MSCs, represent an important source of cells for the repair of a number of damaged tissues. In contrast to HSCs, the soluble factors able to induce MSC migration have not been extensively studied. In the present work, we compared the in vitro migration capacity of human BM-derived MSCs, preincubated or not with the inflammatory cytokines interleukin 1beta (IL1beta) and tumor necrosis factor alpha (TNFalpha), in response to 16 growth factors (GFs) and chemokines. We show that BM MSCs migrate in response to many chemotactic factors. The GFs platelet-derived growth factor-AB (PDGF-AB) and insulin-like growth factor 1 (IGF-1) are the most potent, whereas the chemokines RANTES, macrophage-derived chemokine (MDC), and stromal-derived factor-1 (SDF-1) have limited effect. Remarkably, preincubation with TNFalpha leads to increased MSC migration toward chemokines, whereas migration toward most GFs is unchanged. Consistent with these results, BM MSCs express the tyrosine kinase receptors PDGF-receptor (R) alpha, PDGF-Rbeta, and IGF-R, as well as the RANTES and MDC receptors CCR2, CCR3, and CCR4 and the SDF-1 receptor CXCR4. TNFalpha increases CCR2, CCR3, and CCR4 expression (as opposed to that of CXCR4), together with RANTES membrane binding. These data indicate that the migration capacity of BM MSCs is under the control of a large range of receptor tyrosine kinase GFs and CC and CXC chemokines. Most chemokines are more effective on TNFalpha-primed cells. Our results suggest that the mobilization of MSCs and their subsequent homing to injured tissues may depend on the systemic and local inflammatory state. Disclosure of potential conflicts of interest is found at the end of this article.

Molecular profile of mouse stromal mesenchymal stem cells

We determined a transcriptional profile specific for clonal stromal mesenchymal stem cells from adult and fetal hematopoietic sites. To identify mesenchymal stem cell-like stromal cell lines, we evaluated the adipocytic, osteoblastic, chondrocytic, and vascular smooth muscle differentiation potential and also the hematopoietic supportive (stromal) capacity of six mouse stromal cell lines from adult bone marrow and day 14.5 fetal liver. We found that two lines were quadripotent and also supported hematopoiesis, BMC9 from bone marrow and AFT024 from fetal liver. We then ascertained the set of genes differentially expressed in the intersection set of AFT024 and BMC9 compared with those expressed in the union set of two negative control lines, 2018 and BFC012 (both from fetal liver); 346 genes were upregulated and 299 downregulated. Using Ingenuity software, we found two major gene networks with highly significant scores. One network contained downregulated genes that are known to be implicated in osteoblastic differentiation, proliferation, or transformation. The other network contained upregulated genes that belonged to two categories, cytoskeletal genes and genes implicated in the transcriptional machinery. The data extend the concept of stromal mesenchymal stem cells to clonal cell populations derived not only from bone marrow but also from fetal liver. The gene networks described should discriminate this cell type from other types of stem cells and help define the stem cell state.

Gene expression in stem cell-supporting stromal cell lines

Cells in the immediate microenvironment together with hematopoietic stem cells (HSCs) constitute the stem cell niche. The microenvironmental or stromal cells provide a complex molecular milieu that helps mediate and balance the self-renewal and commitment potentials of stem cells. The molecules in this milieu are not well defined. In this study, we have intersected previous cDNA subtraction studies with array expression methodologies to define and categorize known gene products expressed by HSC-supportive stromal cell lines. Data were curated from our previously released Stromal Cell Database (StroCDB) containing a set of gene products enriched for expression in the fetal liver stromal cell line AFT024. Global expression analyses were extended to other stem cell-supporting and -nonsupporting fetal liver stromal cell lines using commercially available microarrays. Known and previously described gene products from selected categories were studied: transcription factors, cell membrane proteins, cytoskeleton and related proteins, extracellular matrix proteins, cell adhesion molecules and their corresponding signaling molecules, and cytokines and their related mediators. More than 300 known gene products were selected for expression in HSC-supporting stromal cells compared to nonsupporting lines. Analyses of the data suggest that HSC-supportive cells are immature, sessile, and highly reactive after binding to integrin ligands and cytokines. Therefore, they provide a dynamic space poised to respond to molecular cues elaborated within the stem cell niche. The study provides a survey of known proteins that play key roles in the support of HSCs by fetal liver stromal cells. It also provides insights into the biology of the stem cell niche by highlighting the complex network of intercellular signaling and communication involved in the organization of the niche space.

Multipotential mesenchymal stem cells are mobilized into peripheral blood by hypoxia

MSCs constitute a population of multipotential cells giving rise to adipocytes, osteoblasts, chondrocytes, and vascular-smooth muscle-like hematopoietic supportive stromal cells. It remains unclear whether MSCs can be isolated from adult peripheral blood under stationary conditions and whether they can be mobilized in a way similar to hematopoietic stem cells. In this report, we show that MSCs are regularly observed in the circulating blood of rats and that the circulating MSC pool is consistently and dramatically increased (by almost 15-fold) when animals are exposed to chronic hypoxia. The immunophenotype and the adipocytic, osteoblastic, and chondrocytic differentiation potential of circulating MSCs were similar to those of bone marrow MSCs. Hypoxia-induced mobilization appears to be specific for MSCs since total circulating hematopoietic progenitor cells were not significantly increased. Our data provide an in vivo model amenable to analysis of MSC-mobilizing factors.

Influence of hypoxia on the domiciliation of mesenchymal stem cells after infusion into rats: possibilities of targeting pulmonary artery remodeling via cells therapies?

BACKGROUND

Bone marrow (BM) cells are promising tools for vascular therapies. Here, we focused on the possibility of targeting the hypoxia-induced pulmonary artery hypertension remodeling with systemic delivery of BM-derived mesenchymal stem cells (MSCs) into non-irradiated rats.

METHODS

Six-week-old Wistar rats were exposed to 3-week chronic hypoxia leading to pulmonary artery wall remodeling. Domiciliation of adhesive BM-derived CD45- CD73+ CD90+ MSCs was first studied after a single intravenous infusion of Indium-111-labeled MSCs followed by whole body scintigraphies and autoradiographies of different harvested organs. In a second set of experiments, enhanced-GFP labeling allowed to observe distribution at later times using sequential infusions during the 3-week hypoxia exposure.

RESULTS

A 30% pulmonary retention was observed by scintigraphies and no differences were observed in the global repartition between hypoxic and control groups. Intrapulmonary radioactivity repartition was homogenous in both groups, as shown by autoradiographies. BM-derived GFP-labeled MSCs were observed with a global repartition in liver, in spleen, in lung parenchyma and rarely in the adventitial layer of remodeled vessels. Furthermore this global repartition was not modified by hypoxia. Interestingly, these cells displayed in vivo bone marrow homing, proving a preservation of their viability and function. Bone marrow homing of GFP-labeled MSCs was increased in the hypoxic group.

CONCLUSION

Adhesive BM-derived CD45- CD73+ CD90+ MSCs are not integrated in the pulmonary arteries remodeled media after repeated intravenous infusions in contrast to previously described in systemic vascular remodeling or with endothelial progenitor cells infusions.

In vivo MR imaging of intravascularly injected magnetically labeled mesenchymal stem cells in rat kidney and liver

PURPOSE

To evaluate in vivo magnetic resonance (MR) imaging with a conventional 1.5-T system for depiction and tracking of intravascularly injected superparamagnetic iron oxide (SPIO)-labeled mesenchymal stem cells (MSCs).

MATERIALS AND METHODS

This study was conducted in accordance with French law governing animal research and met guidelines for animal care and use. Rat MSCs were labeled with SPIO and transfection agent. Relaxation rates at 1.5 T, cell viability, proliferation, differentiation capacity, and labeling stability were assessed in vitro as a function of SPIO concentration. MSCs were injected into renal arteries of healthy rats (labeled cells in four, unlabeled cells in two) and portal veins of rats treated with carbon tetrachloride to induce centrolobular liver necrosis (labeled cells and unlabeled cells in two each). Follow-up serial T2*-weighted gradient-echo MR imaging and R2* mapping were performed. MR imaging findings were compared histologically.

RESULTS

SPIO labeling caused a strong R2* effect that increased linearly with iron dose; R2* increase for cells labeled for 48 hours with 50 microg of iron per milliliter was 50 sec(-1) per million cells per milliliter. R2* was proportional to iron load of cells. SPIO labeling did not affect cell viability (P > .27). Labeled cells were able to differentiate into adipocytes and osteocytes. Proliferation was substantially limited for MSCs labeled with 100 microg Fe/mL or greater. Label half-life was longer than 11 days. In normal kidneys, labeled MSCs caused signal intensity loss in renal cortex. After labeled MSC injection, diseased liver had diffuse granular appearance. Cells were detected for up to 7 days in kidney and 12 days in liver. Signal intensity loss and fading over time were confirmed with serial R2* mapping. At histologic analysis, signal intensity loss correlated with iron-loaded cells, primarily in renal glomeruli and hepatic sinusoids; immunohistochemical analysis results confirmed these cells were MSCs.

CONCLUSION

MR imaging can aid in monitoring of intravascularly administered SPIO-labeled MSCs in vivo in kidney and liver.

Homing of in vitro expanded Stro-1- or Stro-1+ human mesenchymal stem cells into the NOD/SCID mouse and their role in supporting human CD34 cell engraftment

The Stro-1 antigen potentially defines a mesenchymal stem cell (MSC) progenitor subset. We here report on the role of human ex vivo-expanded selected Stro-1(+) or Stro-1(-) MSC subsets on the engraftment of human CD34(+) cord blood cells in the nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mouse model. The data show that cotransplantation of expanded Stro-1(-) cells with CD34(+) cells resulted in a significant increase of human CD45, CD34, CD19, and CD11b cells detected in blood or in bone marrow (BM) and spleen as compared with the infusion of CD34(+) cells alone. Infusion into mice of expanded Stro-1(+) and Stro-1(-) cells (without CD34(+) cells) showed that the numbers of Stro-1(+)-derived (as assessed by DNA analysis of human beta-globin with quantitative polymerase chain reaction [PCR]) were higher than Stro-1(-)-derived cells in spleen, muscles, BM, and kidneys, while more Stro-1(-)-derived than Stro-1(+)-derived cells were found in lungs. The transduction of expanded Stro-1(+) cells with an enhanced green fluorescent protein (eGFP) gene did not modify their cytokine release and their homing in NOD/SCID mouse tissues. The difference between the hematopoietic support and the homing capabilities of expanded Stro-1(+) and Stro-1(-) cells may be of importance for clinical therapeutic applications: Stro-1(+) cells may rather be used for gene delivery in tissues while Stro-1(-) cells may rather be used to support hematopoietic engraftment.

Human endothelial cells derived from circulating progenitors display specific functional properties compared with mature vessel wall endothelial cells

Endothelial progenitor cells (EPCs) were shown to be present in systemic circulation and cord blood. We investigated whether EPCs display specific properties compared with mature endothelial cells. Human cord blood CD34+ cells were isolated and adherent cells were amplified under endothelial conditions. Expression of specific markers identified them as endothelial cells, also called endothelial progenitor-derived cells (EPDCs). When compared to mature endothelial cells, human umbilical vein endothelial cells (HUVECs) and human bone marrow endothelial cells (HBMECs), endothelial markers, were expressed to the same extent except for KDR, which is expressed more in EPDCs. They display a higher proliferation potential. Functional studies demonstrated that EPDCs were more sensitive to angiogenic factors, which afford these cells greater protection against cell death compared with HUVECs. Moreover, EPDCs exhibit more hematopoietic supportive activity than HUVECs. Finally, studies in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice demonstrated that human circulating EPCs are able to colonize a Matrigel plug. EPDCs display the morphology and phenotype of endothelial cells. Their functional features indicate, however, that although these cells have undergone some differentiation steps, they still have the properties of immature cells, suggesting greater tissue repair capabilities. Future use of in vitro amplified peripheral blood EPDCs may constitute a challenging strategy for cell therapy.