In vitro interactions between bone marrow stromal cells and hippocampal slice cultures

Bone marrow stromal cells (BMSCs) are capable of differentiating into various cell types including brain cells. Several groups have also demonstrated trophic effects of MSC grafts in experimental ischemia models. However, the underlying molecular mechanisms of these effects are not fully understood. We developed an “in vitro graft model” which consisted in a coculture of GFP-expressing BMSCs and hippocampal organotypic slice cultures. Total marrow cells (MCs) or BMSCs after one (BMSC^1P) or five passages (BMSC^5P) were transplanted on hippocampal slices. During the 10 days of our experiments, MCs and BMSC^1P migrated toward the tissue, but their total number remained constant. Conversely, the number of BMSC^5P decreased over the 10 days of the experiment, and no migration could be detected. Using immunohistochemistry, we observed that the hippocampal slices induced the expression of neural antigens in very few grafted cells, but MCs and BMSC^1P improved the conservation of the hippocampal slice culture. Similar experiments using BMSC^5P did not produce any significant change. We conclude that the number of passages greatly influence BMSCs survival rate, migration and neuroprotective capacities.     

Expression of bone morphogenetic proteins in stromal cells from human bone marrow long-term culture.

Highly purified primitive hemopoietic stem cells express BMP receptors but do not synthesize bone morphogenetic proteins (BMPs). However, exogenously added BMPs regulate their proliferation, differentiation, and survival. To further explore the mechanism by which BMPs might be involved in hemopoietic differentiation, we tested whether stromal cells from long-term culture (LTC) of normal human bone marrow produce BMPs, BMP receptors, and SMAD signaling molecules. Stromal cells were immunohistochemically characterized by the presence of lyzozyme, CD 31, factor VIII, CD 68, S100, alkaline phosphatase, and vimentin. Gene expression was analyzed by RT-PCR and the presence of BMP protein was confirmed by immunohistochemistry (IHC). The supportive role of the stromal cell layer in hemopoiesis in vitro was confirmed by a colony assay of clonogenic progenitors. Bone marrow stromal cells express mRNA and protein for BMP-3, -4, and -7 but not for BMP-2, -5, and -6 from the first to the eighth week of culture. Furthermore, stromal cells express the BMP type I receptors, activin-like kinase-3 (ALK-3), ALK-6, and the downstream transducers SMAD-1, -4, and -5. Thus, human bone marrow stromal cells synthesize BMPs, which might exert their effects on hemopoietic stem cells in a paracrine manner through specific BMP receptors.     

Prostaglandin E2 regulates macrophage colony stimulating factor secretion by human bone marrow stromal cells.

Bone marrow stromal cells regulate marrow haematopoiesis by secreting growth factors such as macrophage colony stimulating factor (M-CSF) that regulates the proliferation, differentiation and several functions of cells of the mononuclear-phagocytic lineage. By using a specific ELISA we found that their constitutive secretion of M-CSF is enhanced by tumour necrosis factor-alpha (TNF-alpha). The lipid mediator prostaglandin E2 (PGE2) markedly reduces in a time- and dose-dependent manner the constitutive and TNF-alpha-induced M-CSF synthesis by bone marrow stromal cells. In contrast, other lipid mediators such as 12-HETE, 15-HETE, leukotriene B4, leukotriene C4 and lipoxin A4 have no effect. EP2/EP4 selective agonists (11-deoxy PGE1 and 1-OH PGE1) and EP2 agonist (19-OH PGE2) inhibit M-CSF synthesis by bone marrow stromal cells while an EP1/EP3 agonist (sulprostone) has no effect. Stimulation with PGE2 induces an increase of intracellular cAMP levels in bone marrow stromal cells. cAMP elevating agents (forskolin and cholera toxin) mimic the PGE2-induced inhibition of M-CSF production. In conclusion, PGE2 is a potent regulator of M-CSF production by human bone marrow stromal cells, its effects being mediated via cAMP and PGE receptor EP2/EP4 subtypes.     

TGFbeta1 limits the expansion of the osteoprogenitor fraction in cultures of human bone marrow stromal cells

Currently, there is considerable interest in the possibility of using cultured human bone marrow stromal cells (BMSCs) for skeletal tissue engineering. However, the factors that regulate their ex vivo expansion and promote their osteogenic maturation remain poorly defined. Using BMSCs obtained from a large cohort of adult donors, the effects of transforming growth factor (TGF)beta1 on these processes have been determined. BMSCs were found to express TGFbeta receptors (TbetaRs) I, II, III (betaglycan) and CD105/endoglin. The expression of TbetaRs I and II, but not TbetaR III or endoglin, was linked to the cells' state of maturation. Treatment with TGFbeta increased the colony-forming efficiency (CFE) of marrow cell suspensions but reduced the median diameter of the colonies that formed and the number of cells harvested at the end of primary culture. Treatment with TGFbeta also resulted in a significant downregulation in the expression of the developmental markers alkaline phosphatase (AP) and STRO-1. The reduction in AP was due to a decrease in the absolute number of cells expressing this enzyme and in the level (sites/cell) at which it was expressed. Overall, the changes in the expression of STRO-1 and AP are consistent with TGFbeta acting to decrease the size of the osteoprogenitor fraction, and hence the potential clinical utility of the cultured cell population.     

Secretome analysis of human bone marrow derived mesenchymal stromal cells

As an essential cellular component of the bone marrow (BM) microenvironment mesenchymal stromal cells (MSC) play a pivotal role for the physiological regulation of hematopoiesis, in particular through the secretion of cytokines and chemokines. Mass spectrometry (MS) facilitates the identification and quantification of a large amount of secreted proteins (secretome), but can be hampered by the false-positive identification of contaminating proteins released from dead cells or derived from cell medium. To reduce the likelihood of contaminations we applied an approach combining secretome and proteome analysis to characterize the physiological secretome of BM derived human MSC. Our analysis revealed a secretome consisting of 315 proteins. Pathway analyses of these proteins revealed a high abundance of proteins related to cell growth and/or maintenance, signal transduction and cell communication thereby representing key biological functions of BM derived MSC on protein level. Within the MSC secretome we identified several cytokines and growth factors such as VEGFC, TGF-β1, TGF-β2 and GDF6 which are known to be involved in the physiological regulation of hematopoiesis. By comparing the peptide patterns of secretomes and cell lysates 17 proteins were identified as candidates for proteolytic processing. Taken together, our combined MS work-flow reduced the likelihood of contaminations and enabled us to carve out a specific overview about the composition of the secretome from human BM derived MSC. This methodological approach and the specific secretome signature of BM derived MSC may serve as basis for future comparative analyses of the interplay of MSC and HSPC in patients with hematological malignancies.     

Adenovirus-mediated BMP2 expression in human bone marrow stromal cells

Recombinant adenoviral vectors have been shown to be potential new tools for a variety of musculoskeletal defects. Much emphasis in the field of orthopedic research has been placed on developing systems for the production of bone. This study aims to determine the necessary conditions for sustained production of high levels of active bone morphogenetic protein 2 (BMP2) using a recombinant adenovirus type 5 (Ad5BMP2) capable of eliciting BMP2 synthesis upon infection and to evaluate the consequences for osteoprogenitor cells. The results indicate that high levels (144 ng/ml) of BMP2 can be produced in non-osteoprogenitor cells (A549 cell line) by this method and the resultant protein appears to be three times more biologically active than the recombinant protein. Surprisingly, similar levels of BMP2 expression could not be achieved after transduction with Ad5BMP2 of either human bone marrow stromal cells or the mouse bone marrow stromal cell line W20-17. However, human bone marrow stromal cells cultured with 1 microM dexamethasone for four days, or further stimulated to become osteoblast-like cells with 50 microg/ml ascorbic acid, produced high levels of BMP2 upon Ad5BMP2 infection as compared to the undifferentiated cells. The increased production of BMP2 in adenovirus transduced cells following exposure to 1 microM dexamethasone was reduced if the cells were not given 50 microg/ml ascorbic acid. When bone marrow stromal cells were allowed to become confluent in culture prior to differentiation, BMP2 production in response to Ad5BMP2 infection was lost entirely. Furthermore, the increase in BMP2 synthesis seen during differentiation was greatly decreased when Ad5BMP2 was administered prior to dexamethasone treatment. In short, the efficiency of adenovirus mediated expression of BMP2 in bone marrow stromal cells appears to be dependent on the differentiation state of these cells.     

The humoral nature of the colony-stimulating action of bone marrow cells on stromal colony formation in bone marrow cultures

In 24 hours adherent marrow cell cultures (AMCC) were represented by single stretched fibroblasts. In non-feeder-supplemented AMCC most of the CFU-f remained single fibroblasts or passed through 1-3 cell doublings [correction of dudlings]. The colony stimulating activity of irradiated marrow cells was found to be diffuse across the Millipore filter, which seems to indicate that haemopoietic marrow cells produce a colony stimulating factor which is required for triggering the CFU-f from the Go-period of the cell cycle into cell proliferation.     

Receptor tyrosine kinase expression in human bone marrow stromal cells

Bone marrow stromal cells (BMSCs) are a heterogeneous population of cells derived from colony-forming units-fibroblastic (CFU-Fs). These cells reside in the bone marrow cavity and are capable of differentiating into several cell phenotypes including osteoblasts, chondroblasts, hematopoiesis-supporting stromal cells, and adipocytes. However, the factors that regulate the proliferation and differentiation of the BMSC population are for the most part unknown. Since many members of the receptor tyrosine kinase (RTK) family have been shown to participate in growth control of various mesenchymal cell populations, in this study we examined the expression and function of RTKs in the BMSC population. Degenerate oligonucleotides corresponding to two conserved catalytic domains of the RTK family and RT-PCR were used initially to determine which RTKs are expressed in the human BMSC (hBMSC) system. After subcloning the amplification product generated from mRNA of a multicolony-derived hBMSC strain, PDGF receptor (β), EGF receptor, FGF receptor 1, and Axl were identified by DNA sequencing of 26 bacterial colonies. Furthermore, PDGF and EGF were found to enhance BMSC growth in a dose-dependent manner and to induce tyrosine phosphorylation of intracellular molecules, including the PDGF and EGF receptors themselves, demonstrating the functionality of these receptors. On the other hand, bFGF was found to have little effect on proliferation or tyrosine phosphorylation. Since single colony-derived hBMSC strains are known to vary from one colony to another in colony habit (growth rate and colony structure) and the ability to form bone in vivo, the expression levels of these RTKs were determined in 18 hBMSC clonal strains by semiquantitative RT-PCR and were found to vary from one clonal strain to another. While not absolutely predictive of the osteogenic capacity of individual clonal strains, on average, relatively high levels of PDGF-receptor were found in bone-forming strains, while on average, nonbone-forming strains had relatively high levels of EGF-receptor. Taken together, these results indicate that RTKs play a role in the control of hBMSC proliferation, and that the differential pattern of RTK expression may be useful in correlating the biochemical properties of individual clonal strains with their ability to produce bone in vivo. J. Cell. Physiol. 177:426–438, 1998. © 1998 Wiley-Liss, Inc.     

Regulation of hormone secretion in primary cell cultures of human somatotropinomas]

The effects of somatostatin and thyroliberin (thyrotropin-releasing hormone; TRH) on growth hormone (GH) and prolactin (PRL) secretion were studied in short-term (0.5-3h) or long-term (21-24h) incubations using monolayer cell cultures of somatotropin obtained from surgical material of patients with acromegaly. High sensitivity of both GH and PRL release to inhibitory action of somatostatin (10(-11) M) was established. We could not reveal the unambiguous influence of TRH on somatotropic function in the in vivo and in vitro conditions, as compared to the action of this tripeptide on PRL secretion. The results obtained permit us to propose that cell cultures of pituitary adenomata represent adequate and convenient models for studying the pathogenesis of tumor processes in the pituitary gland and for the development of new procedures of pharmacotherapy.     

Regulation of bone matrix protein expression and induction of differentiation of human osteoblasts and human bone marrow stromal cells by bone morphogenetic protein-2

We have examined the effects of BMP-2 on the expression of bone matrix proteins in both human bone marrow stromal cells (HBMSC) and human osteoblasts (HOB) and their proliferation and mineralization. Both HBMSC and HOB express BMP-2/-4 type I and type II receptors. Treatment of these two cell types with BMP-2 for 4 weeks in the presence of β-glycerophosphate and ascorbic acid results in mineralization of their matrix. BMP-2 increases the mRNA level and activities of alkaline phosphatase and elevates the mRNA levels and protein synthesis of osteopontin, bone sialoprotein, osteocalcin, and α1(I) collagen in both cell types. Whereas the mRNA level of decorin is increased, the mRNA concentration of biglycan is not altered by BMP-2. No effect on osteonectin is observed. The effect of BMP-2 on bone matrix protein expression is dose dependent from 25 to 100 ng/ml and is evident after 1–7 days treatment. In the presence of BMP-2, proliferation of HBMSC and HOB is decreased under either serum-free condition or in the presence of serum. Thus, BMP-2 has profound effects on the proliferation, expression of most of the bone matrix proteins and the mineralization of both relatively immature human bone marrow stromal preosteoblasts and mature human osteoblasts. J. Cell. Biochem. 67:386–398, 1997. © 1997 Wiley-Liss, Inc.     

Giant eosinophil colonies from cultures of bone marrow cells

Summary To date, the small size and slow growth of eosinophil colonies in vitro has hampered study of cloned eosinophils. We found enhanced eosinophil colony size and numbers in methylcellulose cultures of bone marrow cells utilizing defined supplemented bovine calf serum (DSBCS) in combination with EL4 conditioned medium (EL4-CM). At days 9, 16 and 23 significantly more eosinophil colonies and more cells/colony were present in cultures incubated with DSBCS/EL4-CM than in cultures incubated with fetal calf serum/EL4-CM. The ability to generate large numbers of eosinophils in vitro should facilitate study of cloned eosinophils. Supported in part by a grant from the National Institutes of Health, AI 20416, and by the Mayo Foundation. Editor's statement Previous approaches to in vitro culture of eosinophils generally have achieved, at best, mixed cultures of colonies of these cells and granulocyte-macrophage colonies. The improved culture methods described in this report produce more homogeneous eosinophil cultures and larger colonies of these cells. The procedure employs EL4 murine thymoma-conditioned medium, which apparently contains eosinophil colony-stimulating activity in the absence of granulocyte-macrophage colony-stimulating activity. David W. Barnes     

The immunosuppressive capacity of human mesenchymal stromal cells derived from amnion and bone marrow

Mesenchymal stromal cells derived from amnion (AM-MSCs) can be easily obtained in large quantity by less invasive method in comparison to bone marrow-derived MSCs (BM-MSCs). However, the biological and immunosuppressive properties of AM-MSCs are still poorly characterized. Previous studies demonstrated that BM-MSCs expressed indoleamine 2,3-dioxygenase (IDO) to suppress T-cell responses. This study was designed to address whether IDO contributes to the immunosuppressive function of AM-MSCs. MSCs isolated from amnion were cultured in complete medium similar to BM-MSCs. After culture, AM-MSCs exhibited spindle shape morphology and expressed MSC markers similar to that of BM-MSCs. In addition, AM-MSCs were able to differentiate into adipocytes and osteoblasts. Fascinatingly, AM-MSCs and BM-MSCs exhibited comparable degree of immunosuppressive effect when they were co-cultured with activated T-cells. In addition, IDO secreted by AM-MSCs was responsible for induction of immunosuppressive activities in the same manner as BM-MSCs. Taken together; the results of the present study demonstrate that while AM-MSCs and BM-MSCs show similar immunosuppressive effect, AM-MSCs may have additional advantage over the BM-MSCs in terms of availability. Therefore, AM-MSCs might be considered a potential source for therapeutic applications especially for treatment of immune related diseases.     

Human mesenchymal progenitor cells derived from alveolar bone and human bone marrow stromal cells: a comparative study

The aim of the present study was to evaluate the potential of intraoral harvested alveolar bone as an alternative source of multipotent mesenchymal stromal cells for future applications in oral and maxillofacial tissue engineering. Explant cultures were established from 20 alveolar bone samples harvested from the oblique line immediately before wisdom tooth removal. Morphology and proliferation characteristics of the in vitro expanded cells, referred to as human alveolar bone-derived cells (hABDCs), were studied using phase-contrast microscopy. Immunocytochemical analysis of their surface marker expression was conducted using monoclonal antibodies defining mesenchymal stromal cells. To evaluate their multilineage differentiation potential, hABDCs were induced to differentiate along the osteogenic, adipogenic, and chondrogenic lineage and compared to bone marrow mesenchymal stromal cells (hBMSCs) on mRNA and protein levels applying RT-PCR and cytochemical staining methods. hABDCs showed typical morphological characteristics comparable to those of hBMSCs such as being mononuclear, fibroblast-like, spindle-shaped, and plastic adherent. Immunophenotypically, cells were positive for CD105, CD90, and CD73 while negative for CD45, CD34, CD14, CD79α, and HLA-DR surface molecules, indicating an antigen expression pattern considered typical for multipotent mesenchymal stromal cells. As evidenced by RT-PCR and cytochemistry, hABDCs showed multilineage differentiation and similar chondrogenic and osteogenic differentiation potentials when compared to hBMSCs. Our findings demonstrate that human alveolar bone contains mesenchymal progenitor cells that can be isolated and expanded in vitro and are capable of trilineage differentiation, providing a reservoir of multipotent mesenchymal cells from an easily accessible tissue source.     

Expression of CD23 by human bone marrow stromal cells.

CD23 is a surface antigen expressed by a variety of human hematopoietic cells and shown to display multiple biological functions. In present work, we assayed CD23 expression by human bone marrow (BM) or by stromal cells derived from this tissue. While freshly isolated BM-cells showed low CD23 expression, a subset of long term BM-culture (LTBMC)-derived stromal cells expressed CD23 mRNA at high levels in their steady state and secreted soluble CD23 in their culture supernatants. To assay the role of CD23 in LTBMC, these cultures were initiated in the presence of neutralizing anti-CD23 mAb. A dramatic decrease in total numbers of hematopoietic cells and CFU-GM recovery was observed in these cultures as compared to controls. These data suggest a role of CD23 expression in stroma cell functions and further confirm the ability of this antigen to regulate human hematopoietic cell development.     

Heterogeneity of stromal precursor cells isolated from rat bone marrow

Bone marrow stroma contains mesenchymal stem cells (MSC) which are precursor for at least mesenchyma-derived cells. Recent investigations revealed a lot of questions concerning MSC biology that should be further refined. The aim of this study was the comparative analysis of rat bone marrow stroma cells cultures. Mesenchymal precursor cells isolated from rat bone marrow were passed up to 50 times. Comparative morphological and immunophenotypical analysis of these cultures was carried out as well as their ability to osteogenic differentiation was studied. The isolated cultures contained morphologically different types of cells and thus showed a high heterogenity level. Morphology of these cell types was described. The heterogeneity level was reported to decrease over time. It was found out that subcultures isolated from different rats shared the same immunophenotype characteristics (CD90+, CD44+, CD54+, CD 106+, CD45-, CD11b-), but differed in their morphology as well as in ability to osteogenic differentiation. Thus MSC identification requires more specific marker and functional tests to be used.     

Effect of cytokines and growth factors on the macrophage colony-stimulating factor secretion by human bone marrow stromal cells

We have investigated the effect of growth factors, inflammatory and anti-inflammatory cytokines on the macrophage colony-stimulating factor (M-CSF) secretion by cultured human bone marrow stromal cells. Their production of M-CSF cultured in serum-free medium is enhanced in a time-dependent manner in response to tumour necrosis factor (TNF-)alpha and interleukin (IL-)4 but not to IL-1, IL-3, IL-6, IL-7, IL-10, SCF, granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, bFGF and transforming growth factor (TGF-)beta. The co-addition of IL-4 and TNF-alpha has a greater than additive effect on the secretion of M-CSF suggesting that they act synergistically. The anti-inflammatory molecules IL-10 and TGF-beta have no effect on the TNF-alpha-induced M-CSF synthesis by marrow stromal cells. In conclusion TNF-alpha and IL-4 are potent stimulators of the M-CSF synthesis by human bone marrow stromal cells, a result of importance regarding the role of M-CSF in the proliferation/differentiation of mononuclear-phagocytic cells and the role of marrow stromal cells as regulators of marrow haematopoiesis.