Human bone marrow stromal cell: coexpression of markers specific for multiple mesenchymal cell lineages

Design Strategies of Tissue Engineering Scaffolds with Controlled Fiber Orientation

Tissue engineering is an emerging area of applied research with a goal of repairing or regenerating the functions of damaged tissue that fails to heal spontaneously by using cells and synthetic functional components called scaffolds. Scaffolds made of nanofibers (herein called "nano-fibrous scaffolds") play a key role in the success of tissue engineering by providing a structural support for the cells to accommodate and guiding their growth in the three-dimensional space into a specific tissue. The orientation of these fibers is considered as one of the important features of a perfect tissue scaffold, because the fiber orientation greatly influences cell growth and related functions. Therefore, engineering scaffolds with a control over fiber orientation is essential and a prerequisite for controlling cell orientation and tissue growth. Recent advances in electrospinning have made it possible to create nano-featured scaffolds with controlled fiber orientation. Electrospinning is a straightforward, cost-effective, and versatile method, which is recently applied in engineering well-defined nano-fibrous scaffolds that hold promise in serving as a synthetic extra-cellular matrix (ECM). This article reviews the current trends in electrospinning nano-fibrous scaffolds with fiber orientation. A detailed mechanism involved in the spinning process is discussed, followed by experimental examples that show how the fiber orientation influences cellular growth behavior. This review is expected to be useful for readers to gain knowledge on the state-of-the-art of scaffold engineering by electrospinning.

Influence of engineered titania nanotubular surfaces on bone cells

A goal of current orthopedic biomaterials research is to design implants that induce controlled, guided, and rapid healing. In addition to acceleration of normal wound healing phenomena, these implants should result in the formation of a characteristic interfacial layer with adequate biomechanical properties. To achieve these goals, however, a better understanding of events at the bone-material interface is needed, as well as the development of new materials and approaches that promote osseointegration. Using anodization, titania interfaces can be fabricated with controlled nanoarchitecture. This study demonstrates the ability of these surfaces to promote osteoblast differentiation and matrix production, and enhance short- and long-term osseointegration in vitro. Titania nanotubular surfaces were fabricated using an anodization technique. Marrow stromal cells (MSCs) were isolated from male Lewis rats and seeded on these surfaces along with control surfaces. The interaction of cells with these surfaces was investigated in terms of their ability to adhere, proliferate and differentiate on them. The experiments were repeated three times with cells from different cultures. All the results were analyzed using analysis of variance (ANOVA). Statistical significance was considered at p<0.05. Furthermore, in vivo biocompatibility was assessed by implanting surfaces subcutaneously in male Lewis rat and performing histological analysis after 4 weeks. Our results indicate that the nanotubular titania surfaces provide a favorable template for the growth and maintenance of bone cells. The cells cultured on nanotubular surfaces showed higher adhesion, proliferation, ALP activity and bone matrix deposition compared to those grown on flat titanium surfaces. In vivo biocompatibility results suggest that nanotubular titania does not cause chronic inflammation or fibrosis. The fabrication routes of titania nano-architectures are flexible and cost-effective, enabling realization of desired platform topologies on existing non-planar orthopedic implants.

Osteogenic differentiation of marrow stromal cells cultured on nanoporous alumina surfaces

A major goal in orthopedic biomaterials research is to design implant surfaces, which will enhance osseointegration in vivo. Several microscale as well as nanoscale architectures have been shown to significantly affect the functionality of bone cells i.e., osteoblasts. In this work, nanoporous alumina surfaces fabricated by a two-step anodization process were used. The nanostructure of these surfaces can be controlled by varying the voltage used for anodization process. Marrow stromal cells were isolated from mice and seeded on nanoporous and amorphous (control) alumina surfaces. Cell adhesion, proliferation, and viability were investigated for up to 7 days of culture. Furthermore, the cell functionality was investigated by calcein staining. The cells were provided with differentiation media after 7 days of culture. The alkaline phosphatase (ALP) activity and matrix production were quantified using a colorimetric assay and X-ray photoelectron spectroscopy (XPS) for up to 3 weeks of culture (2 weeks after providing differentiation media). Further, scanning electron microscopy (SEM) was used to investigate osteoblast morphology on these nanoporous surfaces. Over the 3-week study, the nanoporous alumina surfaces demonstrated approximately 45% increase in cell adhesion, proliferation, and viability, 35% increase in ALP activity, and 50% increase in matrix production when compared with the control surfaces.

A proteomic analysis during serial subculture and osteogenic differentiation of human mesenchymal stem cell

Although previous studies have reported the effects of extensive subculturing on proliferation rates and osteogenic potential of human mesenchymal stem cells (hMSCs), the results remain controversial. The aim of our study was to characterize the proliferation and osteogenic potential of hMSCs during serial subculture, and also to identify proteins that are differentially regulated in hMSCs during serial subculture and osteogenic differentiation using proteome analysis. Here we show that the proliferation and osteogenic capacity of hMSCs decrease during serial subculturing. Several proteins were shown to be differentially regulated during serial subculture; among these the expression of T-complex protein 1 alpha subunit (TCP-1alpha), a protein known to be associated with cell proliferation, cell cycle, morphological changes, and apoptosis, gradually decreased during serial subculture. Among proteins that were differentially regulated during osteogenic differentiation, chloride intracellular channel 1 (CLIC1) was downregulated only during the early passages eukaryotic translation elongation factor, and acidic ribosomal phosphoprotein P0 was downregulated during the middle passages, while annexin V, LIM, and SH3 domain protein 1 (LASP-1), and 14-3-3 protein gamma (YWHAG) were upregulated during the later passage. These studies suggest that differentially regulated passage-specific proteins may play a role in the decrease of osteogenic differentiation potential under serial subculturing.

An integrated approach to mapping the proteome of the human bone marrow stromal cell

Bone marrow stromal cells, also known as mesenchymal stem or progenitor cells, are thought to play a critical role in hematopoiesis. Because hematopoiesis is dysregulated in leukemic individuals, expression profiling in leukemic stromal cells might yield valuable insights into mechanisms of normal and dysregulated hematopoiesis. Here, proteomics was used to identify expressed proteins in normal and leukemic bone marrow stromal cells. Isobaric tags for relative and absolute quantification (iTRAQ) technology and MS/MS were used to identify and quantify proteins in bone marrow stromal cells from two normal and two leukemic individuals. Approximately 900 distinct proteins were identified with >95% confidence, 73 of which were differentially expressed in leukemic stromal cells. cDNA microarray analysis on Affymetrix oligonucleotide gene chips showed that transcripts correlated with approximately 90% of the expressed proteins. A novel integrated approach for mining and visualization of iTRAQ data is presented. The results provide an initial assessment of the proteome in human bone marrow stromal cells, laying the groundwork for comprehensive analysis of the proteome in these cells, and ultimately, for improved understanding of normal and dysregulated hematopoiesis.

Substrate induction of osteogenesis from marrow-derived mesenchymal precursors

Therapeutic modalities aimed at bone regeneration are increasingly employing extracellular matrix (ECM) constituents to control bone marrow progenitor cell (BMPC) commitment, growth, and differentiation. However, the precise role these ECM elements play during stem cell differentiation remains unclear. (See also Salaszynk et al., Stem Cells Dev 14(6):608-620, 2005; and Schwartz et al., Stem Cells Dev. 14(6), 643-655, 2005, both in this issue.) Because bone formation ultimately begins with the recruitment and commitment of BMPCs into the osteogenic lineage, factors that enhance this process are clearly therapeutic targets. We hypothesized that BMPC attachment, proliferation, and osteogenic differentiation would be potentiated when cultured on ECM proteins normally found in the bone niche. To examine this, we cultured murine BMPCs on laminin-1, fibronectin, and collagen type-1 substrates for up to 14 days and assessed their homogeneity, attachment, proliferation, and expression of the specific bone lineage markers RUNX2, collagen-1, alkaline phosphatase, and osteocalcin. We found that freshly harvested mBMPCs contain a mixed population of progenitor cells and that the mesenchymal pool can be enriched by adherent culture in the presence of leucine methyl ester. Furthermore, mBMPCs attached to laminin, fibronectin, and collagen-1 with varying affinity up to 3 h (fibronectin>or=collagen>laminin), after which time no difference could be detected. Despite this, growth was unaffected; cells thereafter proliferated equally well on all substrates up to confluence (7 days). Notably, commitment to the osteoblast lineage (RUNX2) increased up to 14 days for cells cultured on the various substrates, yet no difference was observed at day 14 in the expression of collagen-1, alkaline phosphatase, or osteocalcin. We conclude that mBMPC differentiation down the osteoblastic lineage is time-dependent in osteogenic culture and that attachment to ECM matrices potentiates lineage commitment rather than growth.

Role of adult mesenchymal stem cells in bone tissue engineering applications: current status and future prospects

Mesenchymal stem cells (MSCs) have been demonstrated as an attractive cell source for tissue-engineering applications because of their ability to be easily isolated and expanded from adult bone marrow aspirates and their versatility for pluripotent differentiation into mesenchymal tissues. This review highlights advances and progress in bone reconstruction techniques for both the repair of site-specific bone defects and the attenuation of musculoskeletal disease symptoms associated with osteoporosis and osteogenesis imperfecta. Despite the enormous potential benefits of MSCs within these approaches, conventional tissue culture methods limit the clinical utility of these cells because of the gradual loss of both their proliferative and differentiation potential during ex vivo expansion. Novel strategies to overcome these limitations are discussed including cultivation in the presence of basic fibroblastic growth factor 2, induction of ectopotic telomerase expression, and ex vivo expansion on various collagenous biomaterials. In addition, this review also outlines mechanistic theories on the potential role of MSC-extracellular matrix interactions in mediating the retention of MSC proliferative and differentiation capacity after ex vivo expansion on collagenous biomaterials.

Galectin-1 induces skeletal muscle differentiation in human fetal mesenchymal stem cells and increases muscle regeneration

Cell therapy for degenerative muscle diseases such as the muscular dystrophies requires a source of cells with the capacity to participate in the formation of new muscle fibers. We investigated the myogenic potential of human fetal mesenchymal stem cells (hfMSCs) using a variety of stimuli. The use of 5-azacytidine or steroids did not produce skeletal muscle differentiation, whereas myoblast-conditioned medium resulted in only 1%-2% of hfMSCs undergoing muscle differentiation. However, in the presence of galectin-1, 66.1% +/- 5.7% of hfMSCs, but not adult bone marrow-derived mesenchymal stem cells, assumed a muscle phenotype, forming long, multinucleated fibers expressing both desmin and sarcomeric myosin via activation of muscle regulatory factors. Continuous exposure to galectin-1 resulted in more efficient muscle differentiation than pulsed exposure (62.3% vs. 39.1%; p < .001). When transplanted into regenerating murine muscle, galectin-1-exposed hfMSCs formed fourfold more human muscle fibers than nonstimulated hfMSCs (p = .008), with similar results obtained in a scid/mdx dystrophic mouse model. These data suggest that hfMSCs readily undergo muscle differentiation in response to galectin-1 through a stepwise progression similar to that which occurs during embryonic myogenesis. The high degree of myogenic conversion achieved by this method has relevance for the development of therapies for muscular dystrophies.

Characterization of mesenchymal stem cells isolated from mouse fetal bone marrow

Mesenchymal stem cells (MSCs) are defined as cells that can differentiate into multiple mesenchymal lineage cells. MSCs have some features (surface molecules and cytokine production, etc.) common to so-called traditional bone marrow (BM) stromal cells, which have the capacity to support hemopoiesis. In the present study, we isolated murine MSCs (mMSCs) from the fetal BM using an anti-PA6 monoclonal antibody (mAb) that is specific for bone marrow stromal cells. The mMSCs, called FMS/PA6-P cells, are adherent, fibroblastic, and extensively expanded and have the ability to differentiate not only into osteoblasts and adipocytes but also into vascular endothelial cells. The FMS/PA6-P cells produce a broad spectrum of cytokines and growth factors closely related to hemopoiesis and show good hemopoiesis-supporting capacity both in vivo and in vitro, suggesting that they are a component of the hemopoietic stem cell niche in vivo. Interestingly, although the FMS/PA6-P cells express a high level of the PA6 molecule, which is reactive with anti-PA6 mAb, they gradually lose their ability to express this molecule during the course of differentiation into osteoblasts and adipocytes, indicating that the PA6 molecule might serve as a novel marker of mMSCs.

Human umbilical cord blood-derived stromal cell, a new resource of feeder layer to expand human umbilical cord blood CD34+ cells in vitro

Allogeneic transplantation with human umbilical cord blood (hUCB) in adult recipients is mainly limited by a low CD34+ cell dose. To break the limit, hUCB as a novel source of hUCB-derived stromal cells was incorporated in an attempt to expand CD34+ cells from hUCB in vitro. Cord blood CD34 cells were separated by MACS system. HUCB-derived stromal cells were cultured by the Dexter system and characterized by morphologic, immunophenotypical, and functional analysis. We studied the effects of hUCB-derived stromal cells, cytokines, and hUCB-derived stromal cells combined with cytokines on expansion of hUCB CD34 cells. The CD34+ cells were assessed for the degree of expansion and the number of colony-forming units in semisolid culture. Our research found that hUCB-derived stromal cells were mainly composed of three kinds of cell components, with CD106, CD29, CD44, CD45, CD50, CD68, CD31, Fn, Lm, and collagen IV positive, but CD34 negative immunophenotype. Functionally, it was discovered by cell cycle and growth curve analyses that the capability of colony and parietal layer formation of hUCB-derived stromal cells was poorer than that of BM stromal cells, and the doubling time of hUCB-derived stromal cells was longer than that of BM stromal cells. It was indicated by ELISA and RT-PCR that hUCB-derived stromal cells express higher level of TPO and less GM-CSF and SCF than BM stromal cell. Adherent layer of hUCB-derived stromal cells alone or combining with cytokines, increased CD34+ cell expansion. In vitro formation of CFUs by expanded CCD34 cells was significantly higher than that of unexpanded CD34+ cells (P < 0.05). When cocultured with hUCB-derived stromal cells in the presence of cytokines, cell growth was significantly enhanced: CD34 cells by 8.02 +/- 0.96-fold, CFU-GM by 217.60 +/- 6.72-fold, CFU-E by 1940.80 +/- 52.78-fold, and CFU-Mg by 142.60 +/- 4.39-fold. HUCB-derived stromal cells have significant superiority on the expansion of CFU-Mg (P < 0.05). The results indicate that human umbilical cord blood-derived stromal cells may be a suitable feeder layer for expansion of hematopoietic progenitors from hUCB in vitro.

Cytoplasmic overexpression of ALCAM is prognostic of disease progression in breast cancer

BACKGROUND

Activated leucocyte cell adhesion molecule (ALCAM, CD166) is a cell surface member of the immunoglobulin superfamily. ALCAM expression has prognostic relevance in prostate and colon cancer.

OBJECTIVE

To evaluate ALCAM protein expression in breast cancer by immunohistochemistry and to correlate expression levels with clinicopathological data.

METHODS

162 primary breast carcinomas with a mean clinical follow up time of 53 months were immunostained using a monoclonal ALCAM antibody. The staining was evaluated as an immunoreactive score (IRS) and grouped into low v high for both membranous and cytoplasmic staining.

RESULTS

Intraductal and invasive carcinomas showed a higher ALCAM expression (median IRS 4 and 6 respectively) than normal breast tissue (IRS 2). In univariate survival analyses a significant association of high cytoplasmic ALCAM expression with shortened patient disease-free survival (mean (SD) five year non-progression rate, 69.4 (4.6)% v 49.4 (11.1)%, p = 0.0142) was found. In multivariate analyses of disease-free survival times, high cytoplasmic ALCAM expression (relative risk (RR) = 2.086, p = 0.026) and nodal status (RR = 2.246, p = 0.035) were significantly associated with earlier disease progression, whereas tumour grading (RR = 1.6, p = 0.052) was of borderline significance.

CONCLUSIONS

The data suggest that strong cytoplasmic ALCAM expression in primary breast cancer, as detected by immunohistochemistry, might be a new marker for a more aggressive breast cancer biology.

Allogeneic bone marrow stromal cells promote glial-axonal remodeling without immunologic sensitization after stroke in rats

We evaluated the effects of allogeneic bone marrow stromal cell treatment of stroke on functional outcome, glial-axonal architecture, and immune reaction. Female Wistar rats were subjected to 2 h of middle cerebral artery occlusion. Rats were injected intravenously with PBS, male allogeneic ACI--or syngeneic Wistar--bone marrow stromal cells at 24 h after ischemia and sacrificed at 28 days. Significant functional recovery was found in both cell-treated groups compared to stroke rats that did not receive BMSCs, but no difference was detected between allogeneic and syngeneic cell-treated rats. No evidence of T cell priming or humoral antibody production to marrow stromal cells was found in recipient rats after treatment with allogeneic cells. Similar numbers of Y-chromosome+ cells were detected in the female rat brains in both groups. Significantly increased thickness of individual axons and myelin, and areas of the corpus callosum and the numbers of white matter bundles in the striatum were detected in the ischemic boundary zone of cell-treated rats compared to stroked rats. The areas of the contralateral corpus callosum significantly increased after cell treatment compared to normal rats. Processes of astrocytes remodeled from hypertrophic star-like to tadpole-like shape and oriented parallel to the ischemic regions after cell treatment. Axonal projections emanating from individual parenchymal neurons exhibited an overall orientation parallel to elongated radial processes of reactive astrocytes of the cell-treated rats. Allogeneic and syngeneic bone marrow stromal cell treatment after stroke in rats improved neurological recovery and enhanced reactive oligodendrocyte and astrocyte related axonal remodeling with no indication of immunologic sensitization in adult rat brain.

Mesenchymal stem cells: isolation, in vitro expansion and characterization

Mesenchymal stem cells (MSC), one type of adult stem cell, are easy to isolate, culture, and manipulate in ex vivo culture. These cells have great plasticity and the potential for therapeutic applications, but their properties are poorly understood. MSCs can be found in bone marrow and in many other tissues, and these cells are generally identified through a combination of poorly defined physical, phenotypic, and functional properties; consequently, multiple names have been given to these cell populations. Murine MSCs have been directly applied to a wide range of murine models of diseases, where they can act as therapeutic agents per se, or as vehicles for the delivery of therapeutic genes. In addition to their systemic engraftment capabilities, MSCs show great potential for the replacement of damaged tissues such as bone, cartilage, tendon, and ligament. Their pharmacological importance is related to four points: MSCs secrete biologically important molecules, express specific receptors, can be genetically manipulated, and are susceptible to molecules that modify their natural behavior. Due to their low frequency and the lack of knowledge on cell surface markers and their location of origin, most information concerning MSCs is derived from in vitro studies. The search for the identity of the mesenchymal stem cell has depended mainly on three culture systems: the CFU-F assay, the analysis of bone marrow stroma, and the cultivation of mesenchymal stem cell lines. Other cell populations, more or less related to the MSC, have also been described. Isolation and culture conditions used to expand these cells rely on the ability of MSCs, although variable, to adhere to plastic surfaces. Whether these conditions selectively favor the expansion of different bone marrow precursors or cause similar cell populations to acquire different phenotypes is not clear. The cell populations could also represent different points of a hierarchy or a continuum of differentiation. These issues reinforce the urgent need for a more comprehensive view of the mesenchymal stem cell identity and characteristics.

Rapid isolation, expansion, and differentiation of osteoprogenitors from full-term umbilical cord blood

There is an urgent clinical requirement for appropriate bone substitutes that can be used for the repair and regeneration of diseased or damaged skeletal tissues. Cell-sourcing limitations in particular have affected progress, largely because of the shortage of accessible tissues capable of yielding sufficient numbers of viable osteoprogenitor cells. Previous work has suggested that umbilical cord blood (UCB) contains circulating progenitor cells (mesenchymal stem cells) capable of osteogenic differentiation, although a comparable number of reports refute this claim. From a screen of more than 20 different culture conditions, we have identified an optimal, simple, and reliable technique to generate, from full-term human UCB, stromal cells with the ability to undergo rapid osteogenic differentiation. By comparing different sorting and culture strategies, we demonstrated that early exposure of mononuclear UCB cells to medium conditioned by osteoblastic cells in the presence of osteogenic supplements and human plasma, markedly increased the frequency of stromal cell growth, the rate of osteogenic differentiation, and their attachment to and spreading on calcium phosphate scaffolds. These findings suggest that full-term UCB may act as an appropriate source of osteoprogenitor cells, which will impact significantly on the development of autologous tissue- engineered bone constructs.

First experience of the use bone marrow mesenchymal stem cells for the treatment of a patient with deep skin burns

Female patient with extensive skin burn (I-II-IIIAB skin burn, total area 40%, area of IIIB degree 30%) was treated using transplantation of allogenic fibroblast-like bone marrow mesenchymal stem cells onto the surface of deep thermal burn. The study of wound healing dynamics after transplantation of allogenic fibroblast-like mesenchymal stem cells confirmed high tempo of wound regeneration in the presence of active neoangiogenesis. Due to this, autodermoplasty of burn wounds could be carried out with good results as early as on day 4 after transplantation of fibroblast-like mesenchymal stem cells; this led to more rapid healing of donor zones and accelerated rehabilitation of the patient.

Activated leukocyte cell adhesion molecule (ALCAM/CD166): signaling at the divide of melanoma cell clustering and cell migration?

Orchestrated modulation of cell adhesion is essential for development and homeostasis in multicellular organisms. It optimizes embedding of the cell in its dynamic environment and facilitates appropriate cell responses and intercellular communication. Chronic disturbance of this delicate equilibrium causes defects in tissue architecture and sometimes cancer. In tumor cell biology, dynamic control of adhesion molecules is important to proceed through the metastatic cascade and to allow cell release from the primary tumor, invasion of the surrounding matrix, intravasation and adhesion to vascular endothelial cells to facilitate extravasation. Intertwined and multiple adhesive interactions rather than individual interactions presumably play critical roles in neoplastic development. Yet, knowledge of the contribution of each individual adhesion molecule is essential to unravel this network of interactions. This review will focus on activated leukocyte cell adhesion molecule (ALCAM/CD166) and its role in human melanoma progression. It is hypothesized that ALCAM may function as a cell surface sensor to register local growth saturation and to regulate cellular signaling and dynamic responses.

Nonstimulated Human Uncommitted Mesenchymal Stem Cells Express Cell Markers of Mesenchymal and Neural Lineages

Ex vivo cultures of human bone marrow-derived mesenchymal stem cells (MSCs) contain subsets of progenitors exhibiting dissimilar properties. One of these subsets comprises uncommitted progenitors displaying distinctive features, such as morphology, a quiescent condition, growth factor production, and restricted tissue biodistribution after transplantation. In this study, we assessed the competence of these cells to express, in the absence of differentiation stimuli, markers of mesoderm and ectodermic (neural) cell lineages. Fluorescence microscopy analysis showed a unique pattern of expression of osteogenic, chondrogenic, muscle, and neural markers. The depicted "molecular signature" of these early uncommitted progenitors, in the absence of differentiation stimuli, is consistent with their multipotentiality and plasticity as suggested by several in vitro and in vivo studies.

In vitro and in vivo evaluation of differentially demineralized cancellous bone scaffolds combined with human bone marrow stromal cells for tissue engineering

Mineralized and partially or fully demineralized biomaterials derived from bovine bone matrix were evaluated for their ability to support human bone marrow stromal cell (BMSC) osteogenic differentiation in vitro and bone-forming capacity in vivo in order to assess their potential use in clinical tissue-engineering strategies. BMSCs were either seeded on bone-derived scaffolds and cocultured in direct cell-to-scaffold contact, allowing for the exposure of soluble and insoluble matrix-incorporated factors, or cocultured with the scaffold preparations in a transwell system, exposing them to soluble matrix-incorporated factors alone. Osteoblast-related markers, alkaline phosphatase (ALP) activity and bone sialoprotein (BSP) and osteopontin (OP) mRNA expression were evaluated in BMSCs following 14 days of cocultivation in both systems. The data demonstrate that BMSCs from some donors express significantly higher levels of all osteoblast-related markers following cocultivation in direct cell-to-scaffold contact with mineralized scaffolds in comparison to fully demineralized preparations, while BMSCs from other donors display no significant differences in response to various scaffold preparations. In contrast, BMSCs cocultured independently with soluble matrix-incorporated factors derived from each scaffold preparation displayed significantly lower levels of ALP activity and BSP mRNA expression in comparison to untreated controls, while no significant differences were observed in marker levels between cells cocultured similarly with different biomaterial preparations. In addition, BMSCs were seeded directly on mineralized and partially or fully demineralized biomaterials and implanted in subcutaneous sites of athymic mice for 8 weeks to evaluate their in vivo bone-forming capacity. The ex vivo incorporation of BMSCs into all bone-derived scaffold preparations substantially increased the mean extent and frequency of samples containing de novo bone formation over similar nonseeded controls, as determined by histological and histomorphometrical analysis. No statistically significant differences were observed in the extent or frequency of bone formation between various scaffold preparations seeded with BMSCs from different donors. These results demonstrate that the in vivo osteoinductivity of bone-derived scaffolds can be modulated by ex vivo incorporated BMSCs and the extent of scaffold demineralization plays a significant role in influencing in vitro osteogenic differentiation of BMSCs depending on the coculture system and BMSC donor.

Neuronal differentiation of bone marrow-derived stromal stem cells involves suppression of discordant phenotypes through gene silencing

Tissue engineering involves the construction of transplantable tissues in which bone marrow aspirates may serve as an accessible source of autogenous multipotential mesenchymal stem cells. Increasing reports indicate that the lineage restriction of adult mesenchymal stem cells may be less established than previously believed, and stem cell-based therapeutics await the establishment of an efficient protocol capable of achieving a prescribed phenotype differentiation. We have investigated how adult mouse bone marrow-derived stromal cells (BMSCs) are guided to neurogenic and osteogenic phenotypes. Naïve BMSCs were found surprisingly active in expression of a wide range of mRNAs and proteins, including those normally reported in terminally differentiated neuronal cells and osteoblasts. The naïve BMSCs were found to exhibit voltage-dependent membrane currents similar to the neuronally guided BMSCs, although with smaller amplitudes. Once BMSCs were exposed to the osteogenic culture condition, the neuronal characteristics quickly disappeared. Our data suggest that the loss of discordant phenotypes during BMSC differentiation cannot be explained by the selection and elimination of unfit cells from the whole BMSC population. The percent ratio of live to dead BMSCs examined did not change during the first 8-10 days in either neurogenic or osteogenic differentiation media, and cell detachment was estimated at <1%. However, during this period, bone-associated extracellular matrix genes were selectively down-regulated in neuronally guided BMSCs. These data indicate that the suppression of discordant phenotypes of differentiating adult stem cells is achieved, at least in part, by silencing of superfluous gene clusters.

Engagement of integrin alpha4beta1 enhances thrombopoietin-induced megakaryopoiesis

OBJECTIVE

Studies in numerous adherent cell systems have indicated that engagement of integrins is required for cell survival and proliferation. Although not classically thought of as an adherent cell type, megakaryocytes in the marrow develop in juxtaposition to endothelial cells which display a number of integrin counter-receptors. Moreover, a number of other hematopoietic cell types, including stem cells and erythroid progenitors, have been shown to engage and be affected by integrin ligands.

METHODS

The role of beta1 integrins in thrombopoietin-mediated megakaryopoiesis was studied using both gain-of-function and loss-of-function strategies.

RESULTS

We found that pan-blockade of integrins with a relatively nonspecific disintegrin blocked TPO-induced MK growth, but that an alpha5beta1 disintegrin, and a function-blocking monoclonal antibody, failed to affect megakaryopoiesis in vitro. In contrast, a neutralizing alpha4beta1 monoclonal antibody blocked TPO-induced MK growth, and an integrin alpha4beta1 ligand, the H296 fragment of fibronectin, enhanced MK growth at all concentrations of TPO.

CONCLUSIONS

These findings have important implications for thrombopoiesis in general, and potentially for the enhanced platelet production found in states of systemic inflammation and following the use of therapeutic strategies designed to block alpha4beta1 integrin engagement in states of chronic inflammation and autoimmunity.

Mesenchymal stem cells: isolation and therapeutics

Mesenchymal stem cells (MSCs) are progenitors of all connective tissue cells. In adults of multiple vertebrate species, MSCs have been isolated from bone marrow (BM) and other tissues, expanded in culture, and differentiated into several tissue-forming cells such as bone, cartilage, fat, muscle, tendon, liver, kidney, heart, and even brain cells. Recent advances in the practical end of application of MSCs toward regeneration of a human-shaped articular condyle of the synovial joint is one example of their functionality and versatility. The present review not only outlines several approaches relevant to the isolation and therapeutic use of MSCs, but also presents several examples of phenotypic and functional characterization of isolated MSCs and their progeny.

Mesenchymal stem cells: paradoxes of passaging

The field of stem cell biology continues to evolve with the ongoing characterization of multiple types of stem cells with their inherent potential for experimental and clinical application. Mesenchymal stem cells (MSC) are one of the most promising stem cell types due to their availability and the relatively simple requirements for in vitro expansion and genetic manipulation. Multiple populations described as "MSCs" have now been isolated from various tissues in humans and other species using a variety of culture techniques. Despite extensive in vitro characterization, relatively little has been demonstrated regarding their in vivo biology and therapeutic potential. Nevertheless, clinical trials utilizing MSCs are currently underway. The aim of this review is to critically analyze the field of MSC biology, particularly with respect to the current paradox between in vitro promise and in vivo efficacy. It is the authors' opinion that until this paradox is better understood, therapeutic applications will remain limited.

Mechanical stimulation promotes osteogenic differentiation of human bone marrow stromal cells on 3-D partially demineralized bone scaffolds in vitro

Bone is a dynamic tissue that is able to sense and adapt to mechanical stimuli by modulating its mass, geometry, and structure. Bone marrow stromal cells (BMSCs) are known to play an integral part in bone formation by providing an osteoprogenitor cell source capable of differentiating into mature osteoblasts in response to mechanical stresses. Characteristics of the in vivo bone environment including the three dimensional (3-D) lacunocanalicular structure and extracellular matrix composition have previously been shown to play major roles in influencing mechanotransduction processes within bone cells. To more accurately model this phenomenon in vitro, we cultured human BMSCs on 3-D, partially demineralized bone scaffolds in the presence of four-point bending loads within a novel bioreactor. The effect of mechanical loading and dexamethasone concentration on BMSC osteogenic differentiation and mineralized matrix production was studied for 8 and 16 days of culture. Mechanical stimulation after 16 days with 10 nM dexamethasone promoted osteogenic differentiation of BMSCs by significantly elevating alkaline phosphatase activity as well as alkaline phosphatase and osteopontin transcript levels over static controls. Mineralized matrix production also increased under these culture conditions. Dexamethasone concentration had a dramatic effect on the ability of mechanical stimulation to modulate these phenotypic and genotypic responses. These results provide increased insight into the role of mechanical stimulation on osteogenic differentiation of human BMSCs in vitro and may lead to improved strategies in bone tissue engineering.

Osteogenic Differentiation of Human Bone Marrow Stromal Cells on Partially Demineralized Bone Scaffoldsin Vitro

Tissue engineering has been used to enhance the utility of biomaterials for clinical bone repair by the incorporation of an osteogenic cell source into a scaffold followed by the in vitro promotion of osteogenic differentiation before host implantation. In this study, three-dimensional, partially demineralized bone scaffolds were investigated for their ability to support osteogenic differentiation of human bone marrow stromal cells (BMSCs) in vitro. Dynamic cell seeding resulted in homogeneous cell attachment and infiltration within the matrix and produced significantly higher seeding efficiencies when compared with a conventional static seeding method. Dynamically seeded scaffolds were cultured for 7 and 14 days in the presence of dexamethasone and evaluated on biochemical, molecular, and morphological levels for osteogenic differentiation. Significant elevation in alkaline phosphatase activity was observed versus controls over the 14-day culture, with a transient peak indicative of early mineralization on day 7. On the basis of RT-PCR, dexamethasone-treated samples showed elevations in alkaline phosphatase and osteocalcin expression levels at 7 and 14 days over nontreated controls, while bone sialoprotein was produced only in the presence of dexamethasone at 14 days. Scanning electron microscopy evaluation of dexamethasone-treated samples at 14 days revealed primarily cuboidal cells indicative of mature osteoblasts, in contrast to nontreated controls displaying a majority of cells with a fibroblastic cell morphology. These results demonstrate that partially demineralized bone can be successfully used with human BMSCs to support osteogenic differentiation in vitro. This osseous biomaterial may offer new potential benefits as a tool for clinical bone replacement.

Functional and immunophenotypic characteristics of isolated CD105(+) and fibroblast(+) stromal cells from AML: implications for their plasticity along endothelial lineage

BACKGROUND

In vitro cultures of BM cells from newly diagnosed patients with AML displayed a defective BM stromal compartment, with a reduced number of fibroblast-colony-forming unit (CFU-F: 1 +/- 1.25 SD) and a decreased proliferative ability. The purposes of our study were: 1). to select BM mesenchymal stem cells (MSC) and BM-derived stromal cells (BMDSCs) from AML patients at diagnosis and from healthy subjects, using an immunomagnetic system and either anti-CD105 or anti-fibroblast MAbs; 2). to study the immunophenotypic and functional properties of freshly isolated and cultured mesenchymal cells; 3). to test the in vitro plasticity of the selected cells to differentiate towards an endothelial phenotype.

METHODS

Fresh mononuclear cells obtained from BM of 20 patients newly diagnosed with AML and from eight healthy subjects were selected by using anti-fibroblast and anti-CD105 MAbs. Freshly isolated cells were analyzed, characterized by flow cytometry using a wide panel of MAbs and seeded in long-term culture medium to assess CFU-F formation. The level of confluence after 30 days and functional capacity in a long-term colony-forming cell culture (LTC-CFC) were tested. Furthermore, the cultured selected cell populations were assayed for their ability to differentiate into an endothelial-like cell phenotype with the addition of vascular endothelial growth factor (VEFG) and endothelial cell growth supplement (ECGS).

RESULTS

In normal subjects the selection produced an increase of the CFU-F number of 2.6-fold with anti-fibroblast MAb and 2.7-fold with the anti-CD105 MAb. Anti-fibroblast and anti-CD105 MAb selection from AML BM cells resulted in a statistically significant greater count of CFU-F that was respectively 10.6-fold (P = 0.04) and 14.4-fold (P = 0.00001) higher in comparison with the unselected AML samples. Interestingly, in 80% of AML samples immunoselection was also able to restore the capacity of the CFU-F to proliferate and form confluent stromal layers. The isolation of those layers sustained the proliferation and differentiation of hematopoietic stem cells in the LTC-CFC. The phenotypic profile of cultured BMDSCs was different from that of the freshly isolated cells, and changed in relation to the culture conditions: CD105+ selected cells cultured with VEGF and ECGS expressed endothelial markers, a finding that suggests that this cell subpopulation may have the potential to differentiate toward an endothelial-like phenotype.

DISCUSSION

We report that immunomagnetic selection represents a valid tool for the selection of BM mesenchymal cells in samples obtained from both healthy subjects and patients with AML. This technique was able to rescue two functional and immunophenotypic compartments related to two different selected populations. In particular, the CD105+ cells isolated in AML displayed, after stimulation with VEGF and ECGS, the ability to change towards an endothelial-like cell phenotype, thus revealing an unexpected plasticity. Both CD105+ and fibroblast+ cells once successfully isolated might represent sources of mesenchymal cells populations useful for in vitro investigations and, above all, as therapeutic devices.

Multilineage gene expression in human bone marrow stromal cells as evidenced by single-cell microarray analysis

The nonhematopoietic stromal cells of the bone marrow are critical for the development of hematopoietic stem cells into functionally competent blood cells. This study addresses the question of whether bone marrow stromal cell cultures in the Dexter system propagate multiple different mesenchymal stromal cell types or one stromal cell type that expresses multiple phenotypes. Results show that isolated single stromal cells simultaneously express transcripts associated with osteoblast, fibroblast, muscle, and adipocyte differentiation. Furthermore, isolated single stromal cells simultaneously express transcripts characteristic of epithelial cells, endothelial cells, and neural/glial cells. Isolated single stromal cells also express transcripts for CD45, CD19, CD10, CD79a, and representative proto-oncogenes and transcription factors, which are typically associated with normal and neoplastic hematopoietic cells. These findings suggest that the nonhematopoietic mesenchymal cells and the hematopoietic B-lymphocytes have a common progenitor. This is consistent with the idea that progenitor cells express genes that are characteristic of the multiple lineage paths that such cells may be capable of adopting. This study demonstrates the technical feasibility of transcriptome analysis of individual primary cell-culture grown stromal cells and supports the concept that bone marrow stromal cells are relatively homogeneous and show a phenotypic signature of potential multilineage differentiation capacity.

The effect of bone marrow stromal cells on neuronal differentiation of mesencephalic neural stem cells in Sprague-Dawley rats

There are numerous parallels between the heamatolymphopoietic and nervous systems in terms of the mechanisms regulating their development. We proposed that neural stem cells (NSCs) may respond to the microenvironmental signals provided by bone marrow stromal cells (BMSCs) which regulate the differentiation and maturation of hematolymphopoietic stem cells. First, we isolated and proliferated BMSCs from the femur and tibia, and NSCs from the midbrain of Sprague-Dawley (SD) rats, and then investigated the effects of BMSCs on the differentiation of NSCs into neurons, astrocytes and oligodendrocytes by directly plating neurospheres on BMSC monolayers in serum-free conditions. The results confirmed that BMSCs induced NSCs to differentiate selectively into neurons. The percentage of neurons significantly increased in 7 days in vitro co-cultures of NSCs and BMSCs as compared to NSCs cultures alone. When the duration of the cultures was extended to 12 days in vitro, BMSCs enhanced the survival of neurons derived from these NSCs; our investigation then focused on the underlying mechanism for this effect of BMSCs. NSCs were cultured with BMSC conditioned-medium and co-cultured with membrane fragments of live BMSCs or paraformaldehyde fixed BMSCs, the inducing activity of BMSCs was solely detectable in BMSC conditioned-medium, indicating that soluble factors secreted by BMSCs were responsible for its effect on the neuronal differentiation of NSCs. Therefore, BMSCs may provide a powerful tool for therapeutic neurological applications.

Postnatal bone marrow stromal cells elicit a potent VEGF-dependent neoangiogenic response in vivo

Bone marrow stromal cells (MSCs) are pluripotent cells capable of differentiation into several tissue types. This present study was performed to determine their functional neoangiogenic potential in vivo. Whole bone marrow was harvested from C57Bl/6 mice, and the adherent cellular fraction was culture expanded for 14 doublings. These MSCs were resuspended in Matrigel and their angiogenic effect assessed in isogenic recipients. At 2 weeks postimplantation, the mean vascular density in Matrigel plugs containing 2 x 10(6) MSCs/ml was 41+/-5.0 blood vessels (BVs)/mm(2) compared to 0.5+/-0.7 for empty Matrigel (P<0.001). In comparison, Matrigel plugs containing either recombinant murine VEGF 165 at 50 ng/ml or bovine bFGF at 1000 ng/ml generated 21+/-5 and 11+/-2.0 BV/mm(2), respectively. Arteriogenesis was observed only in the MSC-containing implants. With the use of LacZ retroviral labeling of ex vivo expanded MSCs, we show that approximately 10% of LacZ(+)MSCs differentiated into CD31(+) and VEGF(+) endothelial cells. More than 99% of the neoangiogenic phenomena arose from recruitment of host-derived LacZ(null) vascular structures. Neutralizing anti-VEGF antibodies inhibited the MSC-initiated angiogenic response in vivo by 85% (P<0.001). In conclusion, MSCs have the ability to effectively recruit and participate in angiogenesis and arteriogenesis de novo and VEGF plays a central role in the observed host-derived angiogenic response. We propose that ex vivo expanded autologous MSCs may serve as cell therapy to promote therapeutic angiogenesis.

Advanced bioreactor with controlled application of multi-dimensional strain for tissue engineering

Advanced bioreactors are essential for meeting the complex requirements of in vitro engineering functional skeletal tissues. To address this need, we have developed a computer controlled bench-top bioreactor system with capability to apply complex concurrent mechanical strains to three-dimensional matrices independently housed in 24 reactor vessels, in conjunction with enhanced environmental and fluidic control. We demonstrate the potential of this new system to address needs in tissue engineering, specifically toward the development of a tissue engineered anterior cruciate ligament from human bone-marrow stromal cells (hBMSC), where complex mechanical and biochemical environment control is essential to tissue function. Well-controlled mechanical strains (resolution of < 0.1 micron for translational and < 0.1 degree for rotational strain) and dissolved oxygen tension (between 0%-95% +/- 1%) could be applied to the developing tissue, while maintaining temperature at 37 +/- 0.2 degrees C about developing tissue over prolonged periods of operation. A total of 48 reactor vessels containing cell culture medium and silk fiber matrices were run for up to 21 days under 90 degrees rotational and 2 mm translational deformations at 0.0167 Hz with only one succumbing to contamination due to a leak at an medium outlet port. Twenty-four silk fiber matrices seeded with human bone marrow stromal cells (hBMSCs) housed within reactor vessels were maintained at constant temperature (37 +/- 0.2 degrees C), pH (7.4 +/- 0.02), and pO2 (20 +/- 0.5%) over 14 days in culture. The system supported cell spreading and growth on the silk fiber matrices based on SEM characterization, as well as the differentiation of the cells into ligament-like cells and tissue (Altman et al., 2001).

Laminin gamma2 chain as a stromal cell marker of the human bone marrow microenvironment

Laminins are large heterotrimeric molecules consisting of alpha, beta and gamma chains. At present, five alpha chains, three beta chains and three gamma chains have been characterized. Laminin-5 (alpha3beta3gamma2) is the only isoform known to date which contains a gamma2 chain. In human bone marrow, non-haematopoietic stromal cells expressed the laminin gamma2 chain, whereas bone marrow mononuclear cells did not. Co-localization of the gamma2 chain was detected with the laminin alpha4 and alpha5 chains, and co-immunoprecipitation studies revealed a new isoform consisting of alpha5, beta2 and gamma2 chains. The laminin gamma2 chain was also co-localized with alpha-sm-actin in bone marrow, but it was not expressed in endothelial cells or megakaryocytes, indicating that the gamma2 chain is exclusively expressed in vivo in bone marrow stromal cells. The laminin gamma2 chain containing isoform LN-5 was shown to be an adhesive substrate for a small subpopulation of bone marrow mononuclear cells and also for peripheral blood platelets. Taken together, these results indicate that (I) laminin isoforms containing the gamma2 chain can act as adhesive substrates for human haematopoietic cells, and (II) the laminin gamma2 chain can be used as a specific marker molecule for human bone-marrow-derived stromal cells.

Adult bone marrow stromal stem cells express germline, ectodermal, endodermal, and mesodermal genes prior to neurogenesis

Bone marrow stromal stem cells (MSCs) normally differentiate into mesenchymal derivatives but recently have also been converted into neurons, classical ectodermal cells. To begin defining underlying mechanisms, we extended our characterization of MSCs and the differentiated neurons. In addition to expected mesodermal mRNAs, populations and clonal lines of MSCs expressed germinal, endodermal, and ectodermal genes. Thus, the MSCs are apparently "multidifferentiated" in addition to being multipotent. Conversely, the differentiating neurons derived from populations and clonal lines of MSCs expressed the specific markers beta-III tubulin, tau, neurofilament-M, TOAD-64, and synaptophysin de novo. The transmitter enzymes tyrosine hydroxylase and choline acetyltransferase were localized to neuronal subpopulations. Our observations suggest that MSCs are already multidifferentiated and that neural differentiation comprises quantitative modulation of gene expression rather than simple on-off switching of neural-specific genes.