Stromal stem cells (CFU-f) in yolk sac, liver, spleen and bone marrow of pre- and postnatal mice

Human Foetal Mesenchymal Stem Cells

Finding suitable cell sources is one of the main challenges in regenerative medicine. In addition to improving the dysfunctional tissue requiring reconstruction, low immunogenicity is beneficial. Mesenchymal stem cells (MSCs) are immune-privileged multipotent stromal cells that can easily multiply and differentiate along many lineages with a minimal oncogenic risk. MSCs derived from foetal tissues present characteristics that suggest an even stronger cell therapeutic potential in comparison to adult MSCs. Due to these characteristics, they have been and are currently being tested in clinical trials for a diverse variety of disorders.

Yolk sac mesenchymal progenitor cells from New World mice (Necromys lasiurus) with multipotent differential potential

Fetal membranes are abundant, ethically acceptable and readily accessible sources of stem cells. In particular, the yolk sac is a source of cell lineages that do not express MHCs and are mainly free from immunological incompatibles when transferred to a recipient. Although data are available especially for hematopoietic stem cells in mice and human, whereas other cell types and species are dramatically underrepresented. Here we studied the nature and differentiation potential of yolk sac derived mesenchymal stem cells from a New World mouse, Necromys lasiurus. Explants from mid-gestation were cultured in DMEM-High glucose medium with 10% defined fetal bovine serum. The cells were characterized by standard methods including immunophenotyping by fluorescence and flow cytometry, growth and differentiation potential and tumorigenicity assays. The first adherent cells were observed after 7 days of cell culture and included small, elongated fibroblast-like cells (92.13%) and large, round epithelial-like cells with centrally located nuclei (6.5%). Only the fibroblast-like cells survived the first passages. They were positive to markers for mesenchymal stem cells (Stro-1, CD90, CD105, CD73) and pluripotency (Oct3/4, Nanog) as well as precursors of hematopoietic stem cells (CD117). In differentiation assays, they were classified as a multipotent lineage, because they differentiated into osteogenic, adipogenic, and chondrogenic lineages and, finally, they did not develop tumors. In conclusion, mesenchymal progenitor cells with multipotent differentiation potential and sufficient growth and proliferation abilities were able to be obtained from Necromys yolk sacs, therefore, we inferred that these cells may be promising for a wide range of applications in regenerative medicine.

The gap between the physiological and therapeutic roles of mesenchymal stem cells

Several investigators have cultivated marrow stromal cells and have identified a population of mesenchymal stem cells (MSCs). These cells expand extensively in vitro and exhibit multilineage differentiation potential. The lack of MSC-specific markers impedes identification of MSC functions. Further in vivo studies of these cells may elucidate the nature of MSCs. Although the nature of MSCs remains unclear, nonclonal stromal cultures are used as a source of putative MSCs for therapeutic purposes. Preclinical studies and clinical trials assumed that transplanted MSCs exert their effects through their differentiation properties or through the release of molecules that restore tissue functions and modulate immune cells. These studies reported contradictory results and failed to meet expectations. Thus, it is important to note that current protocols for MSC therapy are primarily based on the use of in vitro expanded nonclonal MSCs. Clearly defining the physiological features of in situ MSCs and the in vitro and in vivo properties of nonclonal cultures of stromal cells, which are often misidentified as pure stem cell cultures, may explain the reported failures of MSC therapy. This review will address these issues.

Hematopoietic Microenvironment in the Fetal Liver: Roles of Different Cell Populations

Hematopoiesis is the main function of the liver during a considerable period of mammalian prenatal development. Hematopoietic cells of the fetal liver exist in a specific microenvironment that controls their proliferation and differentiation. This microenvironment is created by different cell populations, including epitheliocytes, macrophages, various stromal elements (hepatic stellate cells, fibroblasts, myofibroblasts, vascular smooth muscle and endothelial cells, mesenchymal stromal cells), and also cells undergoing epithelial-to-mesenchymal transition. This paper considers the involvement of these cell types in the regulation of fetal liver hematopoiesis.

Bone marrow-derived mesenchymal stem cells

Human mesenchymal stem cells (MSCs) contribute to the regeneration of mesenchymal tissues, and are essential in providing support for the growth and differentiation of primitive hemopoietic cells within the bone marrow microenvironment. Techniques are now available to isolate human MSCs and manipulate their expansion in vitro under defined culture conditions without change of phenotype or loss of function. Mesenchymal stem cells have generated a great deal of interest in many clinical settings, including that of regenerative medicine, immune modulation and tissue engineering. Studies have already demonstrated the feasibility of transplanted MSCs providing crucial new cellular therapy. In this review, many aspects of the MSC will be discussed, with the main focus being on clinical studies that describe the potential of MSCs to treat patients with hematological malignancies who are undergoing chemotherapy and/or radiotherapy.

Mesenchymal stem cells from different organs are characterized by distinct topographic Hox codes

Mesenchymal stem cells (MSC) are multipotent cells found as part of the stromal compartment of the bone marrow and in many other organs. They can be identified in vitro as CFU-F (colony forming unit-fibroblast) based on their ability to form adherent colonies of fibroblast-like cells in culture. MSC expanded in vitro retain characteristics appropriate to their tissue of origin. This is reflected in their propensity for differentiating towards specific lineages, and their capacity to generate, upon retransplantation in vivo, a stroma supporting typical lineages of hematopoietic cells. Hox genes encode master regulators of regional specification and organ development in the embryo and are widely expressed in the adult. We investigated whether they could be involved in determining tissue-specific properties of MSC. Hox gene expression profiles of individual CFU-F colonies derived from various organs and anatomical locations were generated, and the relatedness between these profiles was determined using hierarchical cluster analysis. This revealed that CFU-F have characteristic Hox expression signatures that are heterogeneous but highly specific for their anatomical origin. The topographic specificity of these Hox codes is maintained during differentiation, suggesting that they are an intrinsic property of MSC. Analysis of Hox codes of CFU-F from vertebral bone marrow suggests that MSC originate over a large part of the anterioposterior axis, but may not originate from prevertebral mesenchyme. These data are consistent with a role for Hox proteins in specifying cellular identity of MSC.

Bone Marrow - Home of Versatile Stem Cells

SUMMARY: Bone marrow (BM) has been for many years primarily envisioned as the 'home organ' of hematopoietic stem cells (HSC). In this review we will discuss current views of the BM stem cell compartment and present data showing that BM in addition to HSC also contains a heterogeneous population of non-hematopoietic stem cells. These cells have been variously described in the literature as i) endothelial progenitor cells (EPC), ii) mes-enchymal stem cells (MSC), iii) multipotent adult progenitor cells (MAPC), iv) marrow-isolated adult multilineage inducible (MIAMI) cells, v) multipotent adult stem cells (MACS) and vi) very small embryonic-like (VSEL) stem cells. It is likely that in many cases similar or overlapping populations of primitive stem cells in the BM were detected using different experimental strategies and hence were assigned different names.

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.

The role of mesenchymal stem cells in haemopoiesis

The ontogeny of haemopoiesis during fetal life and the differentiation of blood cells in adult life depend upon a fully competent microenvironment to provide appropriate signals via production of soluble factors and cell contact interactions. The cellular constituents of the microenvironment, also defined as the haemopoietic niche, largely derive from a common progenitor of mesenchymal origin. Mesenchymal stem cells (MSC), initially identified in adult bone marrow, have also been described in fetal haemopoietic tissues where they accompany the migration of haemopoietic development. Their precise identity remains ill-defined because of the lack of specific markers. Their ability to self-renew and differentiate into tissues of mesodermal origin (osteocytes, adipocytes, chondrocytes) and their lack of expression of haemopoietic molecules are currently the main criteria for isolation. In the bone marrow the most important elements of the niche appear to be osteoblasts, whilst a less defined population of fibroblasts regulates the maturation of immature T cells in the thymus. Recently, MSC have been shown to exert a profound immunosuppressive effect on polyclonal as well as antigen-specific T cell responses by inducing a state of division arrest anergy. Thus, the multipotent capacity of MSC, their role in supporting haemopoiesis, and their immunoregulatory activity make MSC particularly attractive for therapeutic exploitation.

Fetal stem cells

Fetal stem cells can be isolated from fetal blood and bone marrow as well as from other fetal tissues, including liver and kidney. Fetal blood is a rich source of haemopoietic stem cells (HSC), which proliferate more rapidly than those in cord blood or adult bone marrow. First trimester fetal blood also contains a population of non-haemopoietic mesenchymal stem cells (MSC), which support haemopoiesis and can differentiate along multiple lineages. In terms of eventual downstream application, both fetal HSC and MSC have advantages over their adult counterparts, including better intrinsic homing and engraftment, greater multipotentiality and lower immunogenicity. Fetal stem cells are less ethically contentious than embryonic stem cells and their differentiation potential appears greater than adult stem cells. Fetal stem cells represent powerful tools for exploring many aspects of cell biology and hold considerable promise as therapeutic tools for cell transplantation and ex vivo gene therapy.

Limited Contribution of Circulating Cells to the Development and Maintenance of Nonhematopoietic Bovine Tissues

Bone marrow-derived stem cells appear surprisingly multipotent in experimental settings, but the physiological significance of such plasticity is unclear. We have used sex-mismatched cattle twins with stably chimeric hematopoietic systems to investigate the general extent of integration of circulating cells to the nonhematopoietic cell lineages in an unmanipulated large mammal. The donor-derived (Y+) nonhematopoietic cells in female recipient tissues were visualized by Y-chromosome specific in situ hybridization combined with pan-leukocyte labeling. Y+ leukocytes were frequent in all tissues, but in 11 of 12 animals, average contribution to nonhematopoietic lineages was in any tissue below 1% (in brain <0.001%). Significantly higher integration rate was detected in regenerating granulation tissue. Also, one animal showed a high frequency of nonhematopoietic Y+ cells in several tissues, including intestinal epithelium and mammary gland stroma. In conclusion, circulating cells do not appear significant in the development and maintenance of nonhematopoietic bovine tissues, but may be important in regeneration and other special conditions.

Morphological Analysis and Lentiviral Transduction of Fetal Monkey Bone Marrow-Derived Mesenchymal Stem Cells

We explored the transduction kinetics of HIV-1-derived lentiviral vectors containing the CMV, EF1alpha, or PGK promoter expressing EGFP in fetal rhesus monkey bone marrow-derived mesenchymal stem cells (rhMSC). Studies included the effects of transduction (MOI 0-100) on growth, cell cycle, and differentiation toward an osteogenic lineage. Flow cytometric analysis indicated an approximate 8- to 10-fold greater quantity of EGFP-expressing rhMSC when cells were transduced with the CMV or EF1alpha promoter compared to PGK, although quantitative PCR revealed no differences at the DNA level. The CMV promoter initially expressed 10- to 100-fold higher levels of EGFP compared to EF1alpha or PGK, respectively, at increasing MOI, although a significant decline in transgene expression was observed posttransduction and with advancing passage (P < 0.01), whereas a significant increase in the level of expression was observed over time with the EF1alpha promoter. At an MOI of 100, a transient arrest at the S phase of the cell cycle was observed for both vector constructs. Transduced rhMSC differentiated toward an osteogenic lineage comparable to untransduced rhMSC and showed equivalent levels of alkaline phosphatase activity. These findings suggest that the SIN HIV-1-derived lentiviral vectors used in these studies can efficiently transduce rhMSC in vitro (CMV > EF1alpha > PGK) without inhibiting differentiation potential, although the cell cycle was transiently altered at high MOI

MicroSAGE analysis of 2,353 expressed genes in a single cell-derived colony of undifferentiated human mesenchymal stem cells reveals mRNAs of multiple cell lineages

Mesenchymal stem cells (MSCs) isolated from the bone marrow of adult organisms are capable of differentiating into adipocytes, chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. We recently demonstrated that MSCs also adopt glial cell fates when transplanted into the developing central nervous system and hence can produce tissue elements derived from a separate embryonic layer. Despite these remarkable properties, it has been difficult to establish specific criteria to characterize MSCs. Using a modified protocol for micro-serial analysis of gene expression, we cataloged 2,353 unique genes expressed by a single cell-derived colony of undifferentiated human MSCs. This analysis revealed that the MSC colony simultaneously expressed transcripts characteristic of various mesenchymal cell lineages including chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. Therefore, the profile of expressed transcripts reflects the developmental potential of the cells. Additionally, the MSC colony expressed mRNAs characteristic of endothelial, epithelial and neuronal cell lineages, a combination that provides a unique molecular signature for the cells. Other expressed transcripts included various products involved in wound repair as well as several neurotrophic factors. A total of 268 novel transcripts were also identified, one of which is the most abundantly expressed mRNA in MSCs. This study represents the first extensive gene expression analysis of MSCs and as such reveals new insight into the biology, ontogeny, and in vivo function of the cells.

Identification of mesenchymal stem/progenitor cells in human first-trimester fetal blood, liver, and bone marrow

Human mesenchymal stem/progenitor cells (MSCs) have been identified in adult bone marrow, but little is known about their presence during fetal life. MSCs were isolated and characterized in first-trimester fetal blood, liver, and bone marrow. When 10(6) fetal blood nucleated cells (median gestational age, 10(+2) weeks [10 weeks, 2 days]) were cultured in 10% fetal bovine serum, the mean number (+/- SEM) of adherent fibroblastlike colonies was 8.2 +/- 0.6/10(6) nucleated cells (69.6 +/- 10/microL fetal blood). Frequency declined with advancing gestation. Fetal blood MSCs could be expanded for at least 20 passages with a mean cumulative population doubling of 50.3 +/- 4.5. In their undifferentiated state, fetal blood MSCs were CD29(+), CD44(+), SH2(+), SH3(+), and SH4(+); produced prolyl-4-hydroxylase, alpha-smooth muscle actin, fibronectin, laminin, and vimentin; and were CD45(-), CD34(-), CD14(-), CD68(-), vWF(-), and HLA-DR(-). Fetal blood MSCs cultured in adipogenic, osteogenic, or chondrogenic media differentiated, respectively, into adipocytes, osteocytes, and chondrocytes. Fetal blood MSCs supported the proliferation and differentiation of cord blood CD34(+) cells in long-term culture. MSCs were also detected in first-trimester fetal liver (11.3 +/- 2.0/10(6) nucleated cells) and bone marrow (12.6 +/- 3.6/10(6) nucleated cells). Their morphology, growth kinetics, and immunophenotype were comparable to those of fetal blood-derived MSCs and similarly differentiated along adipogenic, osteogenic, and chondrogenic lineages, even after sorting and expansion of a single mesenchymal cell. MSCs similar to those derived from adult bone marrow, fetal liver, and fetal bone marrow circulate in first-trimester human blood and may provide novel targets for in utero cellular and gene therapy.

Haemopoietic cell proliferation in murine bone marrow cells exposed to extreme low frequency (ELF) electromagnetic fields

As leukemia is one of the health hazards that is sometimes associated with exposure to extreme low frequency fields, we studied the in vitro effects of ELF fields on haemopoietic cell proliferation. First, the cytotoxic effect of 80 microT, 50 Hz magnetic fields on 3T3 cell proliferation was investigated using the neutral red test. Many chemicals are believed to cause damage because they interfere with basal or "housekeeping" cell functions. The basal cell functions are present in every cell. Non-specialized, actively dividing cells are suitable for measuring cytotoxic effects. Cytotoxic doses can be identified by exposing actively dividing cells in vitro and measuring growth inhibition caused by interference with these basal cell functions. 80 microT, 50 Hz magnetic fields caused no cytotoxicity: we were not able to demonstrate any interference with essential cell functions in the non-differentiated 3T3 cell line. Furthermore, the in vitro effects of ELF fields on murine haemopoietic and stromal stem cell proliferation were studied. Haemopoiesis is a continuous process, where mature blood cells are replaced by the proliferation and differentiation of more primitive progenitor and stem cells. Blood formation is tightly regulated by the stromal micro-environment. Exposure of murine bone marrow cells, from male and female mice, to 80 microT (50 Hz) magnetic fields showed a reduction in the proliferation and differentiation of the granulocyte-macrophage progenitor (CFU-GM) compared to non-exposed bone marrow cells. The results on the effect of the ELF-field on stromal stem cell proliferation (CFU-f) are somewhat equivocal at the moment. CFU-f from female mice showed a reduction while CFU-f from male mice were not decreased.

Genetic control of hematopoietic stem cell frequency in mice is mostly cell autonomous

Previously we reported that the size of the stem cell compartment (measured as LTC-IC) is 11-fold greater in DBA/2 than in C57BL/6 mice, and we identified genes that regulate the size of the stem cell pool. To determine whether stem cell intrinsic or extrinsic events account for these differences, we created chimeras by aggregating morulae from the strains C57BL/6 and DBA/2. In these chimeras stem cells of both genotypes are exposed to a common mixed environment. Thus, an equalization of stem cell frequencies is expected if stem cell extrinsic effects dominate. Conversely, the parental ratio of LTC-IC should be preserved if the regulation is stem cell autonomous. For each chimera, individual LTC-IC were genotyped on the clonal levels by analyzing their progeny. We found that most of the difference that regulates the size of the stem cell compartment was intrinsic.

Genetic control of hematopoietic stem cell frequency in mice is mostly cell autonomous

Previously we reported that the size of the stem cell compartment (measured as LTC-IC) is 11-fold greater in DBA/2 than in C57BL/6 mice, and we identified genes that regulate the size of the stem cell pool. To determine whether stem cell intrinsic or extrinsic events account for these differences, we created chimeras by aggregating morulae from the strains C57BL/6 and DBA/2. In these chimeras stem cells of both genotypes are exposed to a common mixed environment. Thus, an equalization of stem cell frequencies is expected if stem cell extrinsic effects dominate. Conversely, the parental ratio of LTC-IC should be preserved if the regulation is stem cell autonomous. For each chimera, individual LTC-IC were genotyped on the clonal levels by analyzing their progeny. We found that most of the difference that regulates the size of the stem cell compartment was intrinsic.

Interleukin 10 inhibits transforming growth factor-beta (TGF-beta) synthesis required for osteogenic commitment of mouse bone marrow cells

Interleukin 10 (IL-10) suppressed TGF-beta synthesis in mouse bone marrow cultures. Coincidingly, IL-10 down-regulated the production of bone proteins including alkaline phosphatase (ALP), collagen and osteocalcin, and the formation of mineralized extracellular matrix. The mAb 1D11.16 which neutralizes TGF-beta 1 and TGF-beta 2, induced suppressive effects comparable to IL-10 when administered before the increase of cell proliferation in the culture. It appears that mainly TGF-beta 1 plays a role in this system since (a) TGF-beta 2 levels were undetectable in supernatants from osteogenic cultures, (b) no effect was observed when the anti-TGF-beta 2 neutralizing mAb 4C7.11 was added and (c) the suppressive effect of IL-10 could be reversed by adding exogenous TGF-beta 1. It is unlikely that TGF-beta 1 modulates osteogenic differentiation by changing the proliferative potential of marrow cells since 1D11.16 did not affect [3H]thymidine ([3H]TdR) incorporation or the number of fibroblast colony forming cells (CFU-F) which harbor the osteoprogenitor cell population. Furthermore, 1D11.16 did not alter [3H]TdR uptake by the cloned osteoprogenitor cell lines MN7 and MC3T3. Light and scanning electron microscopy showed that IL-10 and 1D11.16 induced comparable morphological changes in the marrow cultures. Control cultures contained flat adherent cells embedded in a mineralized matrix. In contrast, IL-10 and 1D11.16 treated cultures were characterized by round non-adherent cells and the absence of a mineralized matrix. In this study, the mechanism by which IL-10 suppresses the osteogenic differentiation of mouse bone marrow was identified as inhibition of TGF-beta 1 production which is essential for osteogenic commitment of bone marrow cells.

Experimental manipulation of the rodent visceral yolk sac

The visceral yolk sac (VYS) is an especially important placental organ in the rodent because it is the primary source of exchange between the embryo and mother during early organogenesis before the chorioallantoic placenta circulation is established. The VYS is involved with nutritional, endocrine, metabolic, immunologic, secretory, excretory, and hematopoietic functions. The VYS also plays a role in steroid metabolism and interacts with a variety of blood-borne factors: parathyroid hormone, glucocorticoids, insulin, and vitamin D metabolites. The importance of the VYS during development is emphasized by the embryotoxicity resulting from exposure to agents which cause VYS dysfunction when administered to the pregnant animal during organogenesis. Several experimental procedures have provided useful information concerning a variety of VYS functions from early organogenesis to term: Culture of the Embryo, Fetal Incubation, Culture of the Fetus, Giant Yolk Sac, Short- and Long-Term Culture of the Yolk Sac, Modified Ussing's Chamber, Single or Double Diffusion Chamber, and the use of Heterologous Rodent Visceral Yolk Sac Antibodies. Since human yolk sac pathology has been associated with developmental toxicity and spontaneous abortion, it is important to discover whether there are some common functional roles among different mammalian species and to determine if other experimental animal models can be used to study the possible contribution of human yolk sac dysfunction to some human reproductive problems.

Bone marrow from Balb/c mice radiocontaminated with 241Am in utero shows a deficient in vitro haemopoiesis

Radiation damage from 241Am to bone marrow cells was manifest in long-term bone marrow cultures (LTC) from offspring of mice radiocontaminated at the 14th day of gestation (119, 479, 803, 1754 kBq 241Am/kg). Offspring were reared by their own contaminated mother for 3 weeks postnatal. LTC from these offspring were less able to support in vitro CFC proliferation than control LTC from non-contaminated offspring. This radiation damage persisted 71 weeks after radiocontamination in utero. Using this in vitro culture system, damage was observed at lower doses if 241Am contamination occurred at foetal than at adult ages. Radiation damage was observed only using LTC, while the haemopoietic stem cell concentration (CFU-S, in vitro CFC) and the stromal stem cell concentration (CFU-F) from marrow in situ were not impaired after 241Am radiocontamination in utero. After culturing LTC in 25 per cent FCS and recharging the stromal adherent layer with bone marrow cell suspensions originating either from control offspring or from offspring contaminated with 241Am in utero, some evidence was found that the proliferation capacity of the haemopoietic cells was diminished. However, the nature of effects on the stromal elements is currently somewhat equivocal. Following in utero contamination the stromal adherent cells appeared to support better the production of in vitro CFC.

Haemopoiesis in long-term cultures of liver, spleen and bone marrow of pre- and postnatal mice: CFU-GM production

The CFU-GM yield in confluent long-term cultures (LTC) derived from liver, spleen and bone marrow cells at different gestational and postnatal ages has been studied after the stromal adherent layer reached confluency. The stromal cell compartment of fetal and neonatal haemopoietic organs is able to sustain haemopoiesis in vitro. Moreover, the granulocyte-macrophage stem cell (CFU-GM) yield of these LTC reflects the CFU-GM content of the haemopoietic organs from which the cultures are originated. LTC from the liver produce high numbers (between 100 and 150 CFU-GM per well) of CFU-GM if the cultures are derived from fetal livers between 13 d of gestation and birth. Cultures from spleens just before and after birth, give maximal CFU-GM numbers (between 50 and 100 CFU-GM per well). The CFU-GM yield in long-term bone marrow cultures increases 10 times from 17-day-old fetus towards adult life (between 700 and 1000 CFU-GM per well.