The Osteogenic Compartment of Bone Marrow: Cell Biology and Clinical Application

How is mechanobiology involved in mesenchymal stem cell differentiation toward the osteoblastic or adipogenic fate?

Mechanobiology plays a major role in transducing physical cues from the dynamic cellular environment into biochemical modifications that promote cell-specific differentiation paths. Mesenchymal stem cells in the bone marrow or in other mesenchymal tissues will differentiate according to the expression of transcription factors (TFs) that govern their lineage commitment. The favoring of either osteogenic or adipogenic differentiation relies on TF expression as well as mechanical properties of the cells' niche that are translated into the activation of certain signaling pathways. Physical factors can induce significant shifts in bipotential lineage commitment between osteogenesis and adipogenesis. The stiffness of the extracellular matrix (ECM) surrounding a cell, varying greatly from rigid environments close to the bone surface to softer regions in the bone marrow, can influence the path of differentiation. Additionally, mechanical loading through exercise appears to favor osteogenesis whereas disuse conditions seem to promote adipogenesis.

Implications of adipose-derived stromal cells in a 3D culture system for osteogenic differentiation: an in vitro and in vivo investigation

BACKGROUND CONTEXT

Healthy mammalian cells in normal tissues are organized in complex three-dimensional (3D) networks that display nutrient and signaling gradients. Conventional techniques that grow cells in a 2D monolayer fail to reproduce the environment that is observed in vivo. In recent years, 3D culture systems have been used to mimic tumor microenvironments in cancer research and to emulate embryogenesis in stem cell cultures. However, there have been no studies exploring the ability for adipose-derived stromal (ADS) cells in a 3D culture system to undergo osteogenic differentiation.

PURPOSE

To characterize and investigate the in vitro and in vivo potential for human ADS cells in a novel 3D culture system to undergo osteogenic differentiation.

STUDY DESIGN

Basic science and laboratory study.

METHODS

Human ADS cells were isolated and prepared as either a 2D monolayer or 3D multicellular aggregates (MAs). Multicellular aggregates were formed using the hanging droplet technique. Cells were treated in osteogenic medium in vitro, and cellular differentiation was investigated using gene expression, histology, and microCT at 1-, 2-, and 4-week time points. In vivo investigation involved creating a muscle pouch by developing the avascular muscular interval in the vastus lateralis of male athymic rats. Specimens were then pretreated with osteogenic medium and surgically implanted as (1) carrier (Matrigel) alone (control), (2) carrier with human ADS cells in monolayer, or (3) human ADS cells as MAs. In vivo evidence of osteogenic differentiation was evaluated with micro computed tomography and histologic sectioning at a 2-week time point.

RESULTS

Human ADS cells cultured by the hanging droplet technique successfully formed MAs at the air-fluid interface. Adipose-derived stromal cells cultured in monolayer or as 3D MAs retain their ability to self-replicate and undergo multilineage differentiation as confirmed by increased runx2/Cbfa2, ALP, and OCN and increased matrix mineralization on histologic sectioning. Multicellular aggregate cells expressed increased differentiation potential and extracellular matrix production over the same human ADS cells cultured in monolayer. Furthermore, MAs reseeded onto monolayer retained their stem cell capabilities. When implanted in vivo, significantly greater bone volume and extracellular matrix were present in the implanted specimens of MAs confirmed on both microCT and histological sectioning.

CONCLUSIONS

This is the first study to investigate the capability of human ADS cells in a 3D culture system to undergo osteogenic differentiation. The results confirm that MAs maintain their stem cell characteristics. Compared with analogous cells in monolayer culture, the human ADS cells as MAs exhibit elevated levels of osteogenic differentiation and increased matrix mineralization. Furthermore, the creation of uniform spheroids allows for improved handling and manipulation during transplantation. These findings strongly support the concept that 3D culture systems remain not only a viable option for stem cell culture but also possibly a more attractive alternative to traditional culture techniques to improve the osteogenic potential of human adipose stem cells.

Dielectric screening of early differentiation patterns in mesenchymal stem cells induced by steroid hormones

In the framework of this study, target identification and localization of differentiation patterns by means of dielectric spectroscopy is presented. Here, a primary pre-osteoblastic bone marrow-derived MBA-15 cellular system was used to study the variations in the dielectric properties of mesenchymal stem cells while exposed to differentiation regulators. Using the fundamentals of mixed dielectric theories combined with finite numerical tools, the permittivity spectra of MBA-15 cell suspensions have been uniquely analyzed after being activated by steroid hormones to express osteogenic phenotypes. Following the spectral analysis, significant variations were revealed in the dielectric properties of the activated cells in comparison to the untreated populations. Based on the differentiation patterns of MBA-15, the electrical modifications were found to be highly correlated with the activation of specific cellular mechanisms which directly react to the hormonal inductions. In addition, by describing the dielectric dispersion in terms of transfer functions, it is shown that the spectral perturbations are well adapted to variations in the electrical characteristics of the cells. The reported findings vastly emphasize the tight correlation between the cellular and electrical state of the differentiated cells. It therefore emphasizes the vast abilities of impedance-based techniques as potential screening tools for stem cell analysis.

Morphological cell typing of osteoid clones derived from human bone marrow

OBJECTIVE

Bone Marrow Stem Cells (BMSC) are a 'reservoir' for bone regeneration. BMSC can be studied in vitro by cloning cells which are improperly named colonyforming units of fibroblasts (CFU-f). Thus we decided to study CFU-f organization and morphology to have (A) a parameter by which to compare normal and pathologic conditions and (B) to potentially select the most osteogenic clones.

METHODS

Two hundred and forty bone samples were collected from 109 patients and primary cultures performed.

RESULTS

After two weeks 9 cell types and 6 well organized types of colonies were detectable. Some have alkaline phosphatase (AP) activity.

CONCLUSION

These data could be relevant to estimate the potential regeneration of bone.

Application of the laser capture microdissection technique for molecular definition of skeletal cell differentiation in vivo

Laser capture microdissection (LCM) method allows selection of individual or clustered cells from intact tissues. This technology enables one to pick cells from tissues that are difficult to study individually, sort the anatomical complexity of these tissues, and make the cells available for molecular analyses. Following the cells' extraction, the nucleic acids and proteins can be isolated and used for multiple applications that provide an opportunity to uncover the molecular control of cellular fate in the natural microenvironment. Utilization of LCM for the molecular analysis of cells from skeletal tissues will enable one to study differential patterns of gene expression in the native intact skeletal tissue with reliable interpretation of function for known genes as well as to discover novel genes. Variability between samples may be caused either by differences in the tissue samples (different areas isolated from the same section) or some variances in sample handling. LCM is a multi-task technology that combines histology, microscopy work, and dedicated molecular biology. The LCM application will provide results that will pave the way toward high throughput profiling of tissue-specific gene expression using Gene Chip arrays. Detailed description of in vivo molecular pathways will make it possible to elaborate on control systems to apply for the repair of genetic or metabolic diseases of skeletal tissues.

Dynamic interactions of chromatin-related mesenchymal modulator, a chromodomain helicase-DNA-binding protein, with promoters in osteoprogenitors

The newly identified protein chromatin-related mesenchymal modulator (CReMM) is expressed by marrow stromal progenitors in vivo and ex vivo. CReMM belongs to a recently identified subgroup of chromodomain helicase-DNA-binding proteins composed of multiple domains including chromodomains, SNF2/ATPase, helicase-C domain, SANT, and A/T-hook-DNA binding domain. Chromatin immunoprecipitation assay was applied to follow the dynamics of CReMM binding to A/T-rich regions on promoters of genes that play a role in osteoblast maturation. CReMM interaction with BMP4 and biglycan promoters in the marrow stromal cells was challenged with transforming growth factor-beta. Treatment with 17beta-estradiol enhanced the binding to estrogen receptor and abolished binding to the prolactin receptor promoters; CReMM interaction with osteocalcin promoter was identified constantly. CReMM binding to the analyzed endogenous promoters suggests its direct role in the transcriptional program activated during osteogenic cell differentiation, which may be a useful tool for following the molecular mechanism of the "stemness" of mesenchymal cells.

Laser Capture Microdissection and Laser Pressure Catapulting as Tools to Study Gene Expression in Individual Cells of a Complex Tissue

Laser capture microdissection (LCM) method allows the selection of individual or clustered cells from intact tissues. LCM enables to pick cells from tissues that are difficult to study individually, to sort the anatomical complexity of tissues, and to make the cells available for molecular analyses. This technology provides an opportunity to uncover the molecular control of cellular fate in the natural microenvironment. It is a difficult task to obtain cells from skeletal tissues, such as cartilage, periost, bone, and muscle, that are structured together and do not exist as individual organs. LCM allows isolation of desired cells from the native tissue environment for the analysis of gene expression. We earlier described the selection of cells from skeletal tissues that were analyzed for expression of transcription factors, receptors for cytokines, nuclear receptors, and functional genes such as alkaline phosphatase and structural proteins. Current results acquired using the LCM technology demonstrate expression of known genes that are in agreement with their reported in vivo and in vitro function in skeletal cells. The obtained knowledge will provide molecular information in the context of the cell and tissue biology. Such analysis will enable a reliable interpretation of function of known and novel genes expression in the skeletal tissues under various physiological conditions.

Osteoimmunology

Osteoimmunology is an interdisciplinary research field combining the exciting fields of osteology and immunology. An observation that contributed enormously to the emergence of osteoimmunology was the accelerated bone loss caused by inflammatory diseases such as rheumatoid arthritis. Receptor activator of nuclear factor kappaB ligand (RANKL), which is the main regulator of osteoclastogenesis, was found to be the primary culprit responsible for the enhanced activation of osteoclasts: activated T cells directly and indirectly increased the expression of RANKL, and thereby promoted osteoclastic activity. Excessive bone loss is not only present in inflammatory diseases but also in autoimmune diseases and cancer. Furthermore, there is accumulating evidence that the very prevalent skeletal disorder osteoporosis is associated with alterations in the immune system. Meanwhile, numerous connections have been discovered in osteoimmunology beyond merely the actions of RANKL. These include the importance of osteoblasts in the maintenance of the hematopoietic stem cell niche and in lymphocyte development as well as the functions of immune cells participating in osteoblast and osteoclast development. Furthermore, research is being done investigating cytokines, chemokines, transcription factors and co-stimulatory molecules which are shared by both systems. Research in osteoimmunology promises the discovery of new strategies and the development of innovative therapeutics to cure or alleviate bone loss in inflammatory and autoimmune diseases as well as in osteoporosis. This review gives an introduction to bone remodeling and the cells governing that process and summarizes the most recent discoveries in the interdisciplinary field of osteoimmunology. Furthermore, an alternative large animal model will be discussed and the pathophysiological alterations of the immune system in osteoporosis will be highlighted.

In vivo association of CReMM/CHD9 with promoters in osteogenic cells

Molecular mechanisms that control cell differentiation involve with chromatin remodeling activities. We recently identified Chromatin Related Mesenchymal Modulator (CReMM), a CHD protein expressed by mesenchymal cells. In this study, we analyzed CReMM expression on RNA and protein levels during embryonic development in mouse skeletal tissues. CReMM appears transiently during mesenchymal cell differentiation, being detected first in osteoprogenitors and declining in mature cells. A novel aspect of the study elaborates on in vivo association of CReMM with promoters in cells obtained by laser capture micro-dissection (LCM) technique from periosteum and endochondreal ossification regions. Using chromatin immunoprecipitation (ChIP), we proved that CReMM binds to skeletal tissue-specific promoters: CBFA1, biglycan, osteocalcin (OC), collagen-II, and myosin in a differential manner. The results imply that CReMM selectively interacts with analyzed promoters activated in the tissue at the appropriate time of development. The identification of CReMM and its tissue distribution and function provides an attractive clue for the study of transcriptional regulation of osteogenic cells' maturation.

Expression and regulation of CReMM, a chromodomain helicase-DNA-binding (CHD), in marrow stroma derived osteoprogenitors

This study follows the expression of CReMM, a new CHD family member, in osteoprogenitors. CReMM expression was analyzed in primary cultured mesnchymal cells from rat and human. Analysis in ex vivo cultured marrow stromal cells (MSC) from rats revealed higher level of CReMM in cells from young (3 months), when compared to cells from old (15 months) rats. CReMM level was higher in human MSC then in mature trabecular bone cells (TBC). Within the MSC population, osteogenic clones showed higher levels of CReMM then non-osteogenic ones. We used bone marrow derived osteogenic cell line (MBA-15) to elaborate on the regulation of CReMM expression in correlation with cell proliferation and co-expression with alkaline phosphatase (ALK). CReMM is highly expressed in proliferating cells and is inversely related to expression of ALK. MBA-15 cells were challenged with dexamethasone (Dex) or 17beta-estradiol and quantification of CReMM at the protein (ELISA) and mRNA (RT-PCR) levels had shown that Dex upregulated CReMM levels. Since CReMM is regulated by Dex, we analyzed the interaction of CReMM with the glucocorticoid receptor (GR), which mediates Dex action. Co-immunopercipitation (Co-IP) demonstrated an association between CReMM and GR. In summary, CReMM is a CHD protein expressed by osteoprogenitors, and we suggest it plays a role in mediating transcriptional response to hormones that coordinate osteoblast function.

Expression and regulation of CReMM, a chromodomain helicase-DNA-binding (CHD), in marrow stroma derived osteoprogenitors

This study follows the expression of CReMM, a new CHD family member, in osteoprogenitors. CReMM expression was analyzed in primary cultured mesnchymal cells from rat and human. Analysis in ex vivo cultured marrow stromal cells (MSC) from rats revealed higher level of CReMM in cells from young (3 months), when compared to cells from old (15 months) rats. CReMM level was higher in human MSC then in mature trabecular bone cells (TBC). Within the MSC population, osteogenic clones showed higher levels of CReMM then non-osteogenic ones. We used bone marrow derived osteogenic cell line (MBA-15) to elaborate on the regulation of CReMM expression in correlation with cell proliferation and co-expression with alkaline phosphatase (ALK). CReMM is highly expressed in proliferating cells and is inversely related to expression of ALK. MBA-15 cells were challenged with dexamethasone (Dex) or 17beta-estradiol and quantification of CReMM at the protein (ELISA) and mRNA (RT-PCR) levels had shown that Dex upregulated CReMM levels. Since CReMM is regulated by Dex, we analyzed the interaction of CReMM with the glucocorticoid receptor (GR), which mediates Dex action. Co-immunopercipitation (Co-IP) demonstrated an association between CReMM and GR. In summary, CReMM is a CHD protein expressed by osteoprogenitors, and we suggest it plays a role in mediating transcriptional response to hormones that coordinate osteoblast function.

Transcriptional profiling of mesenchymal stromal cells from young and old rats in response to Dexamethasone

Background

Marrow-derived stromal cells (MSCs) maintain the capability of self-renewal and differentiation into multiple lineages in adult life. Age-related changes are recognized by a decline in the stemness potential that result in reduced regeneration potential of the skeleton. To explore the molecular events that underline skeletal physiology during aging we catalogued the profile of gene expression in ex vivo cultured MSCs derived from 3 and 15 month old rats. The ex vivo cultured cells were analyzed following challenge with or without Dexamethasone (Dex). RNA retrieved from these cells was analyzed using Affymetrix Gene Chips to compare the effect of Dex on gene expression in both age groups.

Results

The molecular mechanisms that underline skeletal senescence were studied by gene expression analysis of RNA harvested from MSCs. The analysis resulted in complex profiles of gene expression of various differentiation pathways. We revealed changes of lineage-specific gene expression; in general the pattern of expression included repression of proliferation and induction of differentiation. The functional analysis of genes clustered were related to major pathways; an increase in bone remodeling, osteogenesis and muscle formation, coupled with a decrease in adipogenesis. We demonstrated a Dex-related decrease in immune response and in genes that regulate bone resorption and an increase in osteoblastic differentiation. Myogenic-related genes and genes that regulate cell cycle were induced by Dex. While Dex repressed genes related to adipogenesis and catabolism, this decrease was complementary to an increase in expression of genes related to osteogenesis.

Conclusion

This study summarizes the genes expressed in the ex vivo cultured mesenchymal cells and their response to Dex. Functional clustering highlights the complexity of gene expression in MSCs and will advance the understanding of major pathways that trigger the natural changes underlining physiological aging. The high throughput analysis shed light on the anabolic effect of Dex and the relationship between osteogenesis, myogenesis and adipogenesis in the bone marrow cells.

Molecular and cellular characterization of SEL-OB/SVEP1 in osteogenic cells in vivo and in vitro

We describe a novel human gene, named SEL-OB/SVEP1, expressed by skeletal tissues in vivo and by cultured osteogenic cells. The mRNA expression was analyzed on frozen tissues retrieved by laser-capture microscope dissection (LCM) and was detected in osteogenic tissues (periosteum and bone) but not in cartilage or skeletal muscle. The SEL-OB/SVEP1 cDNA of 11,139 bp was in silico translated into a 3574AA protein with expected molecular weight of 370 kDa. The protein is composed of multiple domains including complement control protein (CCP) modules with selectin superfamily signature; sushi and other domains, such as vWA, EGF, PTX, and HYR. Stromal osteogenic cells were analyzed for the protein expression using anti-SEL-OB/SVEP1 for immuno-precipitation and Western blot application confirm the presence of high molecular weight protein. Immuno-histochemistry and fluorescence-activated cell sorting (FACS) were applied to detect SEL-OB/SVEP1 on the surface of stromal cells. ELISA quantified the dependence of protein expression on cell density. Bioinformatic analysis of SEL-OB/SVEP1 revealed domains compositions recognized in cell surface molecules and suggested its role in cell adhesion. Analysis of mesechymal osteogenic cells' adhesion in presence of anti-SEL-OB/SVEP1 antibody demonstrated its interference with initial adhesion stages. In summary, present study describes novel SEL-OB/SVEP1 protein with a unique composition of functional domains, restricted pattern of expression in skeletal cells and demonstrated involvement in attachment of mesenchymal cells. The unusual composition of functional domains puts SEL-OB/SVEP1 in the discrete new group of membrane proteins involved in cell adhesion processes. All together makes SEL-OB/SVEP1 an attractive marker for studying the role of stromal osteogenic cells and their interactions within the bone marrow microenvironment creating a network that regulates the skeletal homeostasis.

Molecular and cellular characterization of mesenchymal progenitors for skeletal biomedical devices

Mesenchymal cells are successfully used to create cell-loaded devices in tissue engineering. Molecular properties of the cells and interaction with polymer scaffolds regulate the development of desired tissues. The present study compared the molecular markers in mesenchymal pleuripotent C3H10T1/2 and osteogenic MBA-15 cells. The cells express transcription factors (TF) of chondro-ostegenic pathway (cbfa-1 and c-fos) and MyoD - TF of muscle differentiation pathway, but not myogenin. Analyzed cells expressed receptors for glucocorticoids, growth hormone, prolactin, and PTH, which indicates their potential responsiveness to systemic signals. Analysis of mRNA encoding for receptors of TGFbeta, TNF, and various interleukins revealed differential expression of IL-2r and TGFbeta-1r receptors, which were expressed by MBA-15 but not by C3H10T1/2 cells. Expression of functional genes indicates differences in the stages of cell differentiation: ALK was present in MBA-15 only, while both cell types expressed collagen-I. Furthermore, we evaluated the expression of adhesion proteins that mediate cell-polymer interactions by flow cytometry analysis. Cell adhesion molecules (CAMs) analyzed were integrinalpha-M (CD11b), selectin-E (CD62E), and PECAM-1 (CD31), which have shown differential expression on cells cultured on plastic, poly(L-lactic acid) (PLLA) or poly(DL-lactide-glycolide acid) (PDLGA) polymer films. Detailed molecular characterization of mesenchymal cells will enable optimization of culture conditions for successful creation of implantable cell-loaded constructs.

Gene expression in skeletal tissues: application of laser capture microdissection

Tissue differentiation is based on the expression of transcription factors, receptors for cytokines, and nuclear receptors that regulate a specific phenotype. The purpose of this study was to select cells from various skeletal tissues in order to analyse differential gene expression of cells in the native environment in vivo. It is a difficult task to obtain cells from skeletal tissues, such as cartilage, periost, bone and muscle, that are structured together and do not exist as individual organs. We used laser capture microdissection which permits the selection and isolation of individual cells from tissue sections. The RNA isolated from these tissues was used for reverse transcriptase-polymerase chain reactions for molecular analysis. We analysed the expression of transcription factors (cFOS, cbfa1, MyoD), receptors for cytokines, nuclear receptors, alkaline phosphatase and the structural proteins osteocalcin and collagen II. The results obtained demonstrate differential patterns of gene expression according to the tissue arrangement in their native in vivo environment, with reliable interpretation of the functions of the analysed genes in the context of intact skeletal tissue physiology.

Low-level laser irradiation promotes proliferation and differentiation of human osteoblasts in vitro

OBJECTIVES

The aim of the present study was to investigate the effect of low-level laser irradiation on proliferation and differentiation of a human osteoblast cell line.

BACKGROUND DATA

It was previously found that low-level laser therapy (LLLT) enhances bone repair in experimental models.

MATERIALS AND METHODS

Cultured osteoblast cells were irradiated using He-Ne laser irradiation (632 nm; 10 mW power output). On the second and third day after seeding the osteoblasts were exposed to laser irradiation. The effect of irradiation on osteoblast proliferation was quantified by cell count and colorimetric MTT (dimethylthiazol tetrazolium bromide) assay 24 and 48 h after second irradiation.

RESULTS

A significant 31-58% increase in cell survival (MTT assay) and higher cell count in the once-irradiated as compared to nonirradiated cells was monitored. Differentiation and maturation of the cells was followed by osteogenic markers: alkaline phosphatase (ALP), osteopontin (OP), and bone sialoprotein (BSP). A two-fold enhancement of ALP activity and expression of OP and BSP was much higher in the irradiated cells as compared to non-irradiated osteoblasts.

CONCLUSION

We conclude that LLLT promotes proliferation and maturation of human osteoblasts in vitro. These results may have clinical implications.

Adhesion molecule expression by osteogenic cells cultured on various biodegradable scaffolds

Design of tissue-engineered cell-loaded device involves cells seeding onto scaffolds in vitro, allowing them to settle and grow before in vivo transplantation. Interaction between scaffold and cells is important in the development of desired tissues. The present study aimed to investigate the effect of cell-polymer interactions on cell morphology and expression of surface markers of osteogenic MBA-15 cells cultured on various bioresorbable polymers. In this study, we used various polymers: poly(L-lactic acid) (PLLA), poly(DL-lactic acid) (PDLLA), poly(L-lactic-glycolic acid) (PLGA), and poly(DL-lactide-glycolide acid) PDLGA1 and PDLGA2. Expression of integrinalpha-M (CD11b), selectin-E (CD62E), and PECAM-1 (CD31), important in cell-cell and cell-matrix interactions, were quantified by flow-cytometry analysis. Cells grown on PDLGA1 films demonstrated fivefold increase in CD62E expression and two-folds increase in CD11b expression. None of the polymers affected the levels of CD31. Identified differential effect of polymers on the expression of cell-adhesion molecules by osteoprogenitors in vitro might help to choose optimal parameters for successful engraftment of cell-loaded constructs.

Alternatively spliced isoforms of a novel stromal RNA regulating factor

Bone marrow stromal cells (MSC) are pluripotent cells that possess a unique capacity to differentiate under appropriate conditions into various lineages. The MSC differentiation is dependent on factors that can switch on and maintain a relevant genetic program to make a particular cell type. The present study describes the cloning and molecular analysis of a novel gene, SRRF (Stromal RNA Regulating Factor), suggested to be involved in RNA processing in MSC. We cloned two alternatively spliced isoforms of this gene, transcripts A and B, from the marrow stromal cells expression library. Differential expression analysis demonstrated a restricted expression of the transcripts to MSC, while other spliced forms of this gene were detected in other tissues. The bioinformatic analysis of the two isoforms revealed RNA binding motifs (RRM), protein-protein and protein-DNA interaction motifs. Participation of SRRF isoforms in post-transcriptional events in MSC is believed to govern the tissue specificity of RNA transcription and to have an important role in regulation of the RNA expression that directs the MSC differentiation pathway.

Characterization of adhesion and differentiation markers of osteogenic marrow stromal cells

Marrow stroma cells (MSC) play a major role in osteogenesis. The potential of the MSC to differentiate to bone-forming cells relies upon molecular regulation. This study analyzed MBA-15 cells for the expression of genes and proteins that are key regulators of osteoblast differentiation. These cells express Cbfa1 and c-fos transcription factors (TF) of osteoprogenitor proliferating cells. RT-PCR and immunohistochemistry were used to demonstrate the message and protein expression of extracellular matrix proteins that are a prerequisite for matrix formation and mineralization, including alkaline phosphatase (ALP), osteocalcin, osteopontin, biglycan, and bone sialoprotein (BSP). The activity of ALP was correlated at various cell densities with co-expression of osteocalcin or osteopontin. Adhering cells must attach to the appropriate matrix to enable survival and differentiation. Using attachment assays, we demonstrated that MBA-15 cells adhered to collagenous matrix and the effect on survival measured by changes in intracellular calcium (Ca) levels. The cells' adhesion to matrix is mediated via cell surface molecules. We quantified the expression of cells surface molecules that are important players in mediating cell-matrix interaction. Flow cytometry analysis (FACS) was used to determine the expression of CD-31 (36%), and lower levels were identified for CD-62E and CD11b. In summary, the present study demonstrates the expression of molecular markers that are distinctive for the osteoblastic phenotype in MBA-15 marrow stroma cells and have crucial role in cell-matrix interaction, in establishing the cellular osteogenic phenotype and their survival.

Analysis of mesenchymal cells derived from an chondrodysplasia punctuate patient and donors

Conradi-Hunermann syndrome (CDPX2) is X-linked dominant disorder appeared with aberrant punctuate calcification. The skeletal cells derived from the marrow stroma are active in maintaining the skeletal formation. We obtained mesenchymal stem cells from a patient with CDPX2 and studied the formation of colony forming unit-fibroblast (CFU-F) in vitro in comparison cells obtained from normal donors. Cultured cells were studied morphologically and subjected to gene expression analysis. Marrow stromal cells (MSC)-chondrodysplasia punctuate (CDP) cells from CDPX2 were identified by their mosaic morphology formed three phenotypically distinct types of CFU-F colonies. One type consisted of normal fibroblasts with developed cell body and cellular processes; the second type contained pathological small cells without processes; and the third type comprised of mixed cells. We compared gene expression by the MSC-CDP to cells from normal donors. Transcription factors analyzed proliferation potential were similar in both normal and mixed colonies of MSC-CDP and similar to normal MSCs. The message expression for cytokines and extra cellular matrix (ECM) proteins revealed similar expression for biglycan, osteocalcin, and osteonectin, while IL-6, IL-11, and M-CSF mRNA levels were significantly higher in normal cells than in MSC-CDP. Mixed cells had elevated levels for IL-6 and M-CSF mRNA, but expressed IL-11 at the normal range. The studied genes were expressed at lower levels by the pathological (MSC-CDP) cells compared to normal ones. Hence, MSC-CDP was demonstrated to display abnormal morphology and transcription of several investigated genes. This study further illuminates the basis of the mosaic pattern of mesenchymal cells derived from a patient affected with CDPX2, and their gene expression involvement.

Intraclonal plasticity for bone, smooth muscle, and adipocyte lineages in bone marrow stroma fibroblastoid cells

Bone marrow stroma fibroblastoid cells (BMSFC) develop from a single clone of cells within each of the in vitro fibroblastoid colonies (CFU-F) derived from either murine or human bone marrow. All of the clones represented by these colonies displayed antigenic and product markers for osteoblast, smooth muscle, and adipocyte lineages when tested separately for each marker. Separate sets of fibroblastoid colonies derived from the same individual donor's culture tested positive with antibodies specific for smooth muscle-specific heavy chain myosin (SMMHC), smooth muscle alpha actin-1, bone sialoprotein, osteocalcin, or alkaline phosphatase, and developed von Kossa-positive deposits shown by X-ray microanalysis and electron diffraction to be hydroxyapatite. Individual cells were positive for both SMMHC and osteocalcin. All cells in the multiple clones tested were capable of metabolizing a fatty acid to form intracellular lipid droplets. PCR transcripts obtained from the human cell cultures that provided these BMSFC clones were consistent with the immunocytochemical findings. Transcripts for PPAR (gamma)-2 and Cbfa-1 were dependent upon the culture medium content, suggesting an osteoblast/adipocyte differentiation switch point. Cell lineage specificity for markers and RNA transcripts was determined by comparison to skin fibroblast controls. These findings demonstrate a high degree of interlineage plasticity in vitro for BMSFC.

Identification of cultured progenitor cells from human marrow stroma

The marrow stromal cells (MSC) are essential for regulation of bone remodeling and hematopoiesis. It is of prime importance to isolate MSC and to expand the proliferating cells ex vivo. In this study, we analyzed cultured MSC for various cellular parameters, including cell morphology, cell cycle, and expression of cell surface antigens by flow cytometry. MSC were divided based on cell size to small (S-cells) and large (L-cells) and were visualized by light and electron microscope. The S-cells were proliferating cells correlated with G0/G1 phase of cell cycle, and expressed cFOS. The expression of surface markers CD-34, -44, -51, -61, -62E, -62P, -62L was quantified using flow cytometry. CD-44 was ubiquitously expressed by S and L cells, CD-51 and -61 were expressed by 30%-38% of S-cells. CD-34 and -62 expressed 20% positive of the analyzed cells that were of the proliferating progenitors (S-cells). This study enables the identification of subpopulations from MSC with special attention paid to the proliferating cells from ex vivo cultures of marrow stroma.

Differential gene expression of cultured human osteoblasts

Human cells with osteogenic capacity were studied for differential gene expression. In the first part of the study we compared gene expression of marrow stroma cells (MSC) in comparison to matured osteoblasts cultured from trabecular bone (TBC) that were analyzed by RT-PCR for series of messages. High expression was detected for PTH-r, TGFb1 and biglycan in TBC compared to MSC's. The messages for c-MYC, IL-6, IL-11, M-CSF, osteonectin, and osteocalcin were expressed at the same level in the two populations of cells. In the second part of the study, we analyzed gene expression within the MSC derived from 25 donors (2.5-49 years old) with respect to donors' age and gender. Increased message levels for M-CSF and biglycan were measured in correlation with age of the donors. Gender differences did not affect the expression of cytokines studied (IL-6, IL-11, MCSF, TGFb1). We investigated the effect of Dexamethasone treatment on MSC and monitored an increased expression of IL-11, M-CSF, biglycan, and osteocalcin messages. This study employs primary cell systems (MSC and TBC) to illustrate differential gene expression by osteoblastic cells. The expression was correlated with maturation status of the cells with respect to differences between donors.