Differentiation of muscle, fat, cartilage, and bone from progenitor cells present in a bone-derived clonal cell population: effect of dexamethasone

A tryptamine derivative, SST-VEDI-1, inhibits apoptosis and stimulates mineralization in osteoblasts

SST-VEDI-1(VEDI-1) is a new synthetic compound that is synthesized from tryptamine, and has structural similarity to the SSH-BM family of compounds. However, the biological effects of VEDI-1 have yet to be well characterized. A recent report has demonstrated that SSH-BM-type compounds can stimulate osteoblast activity in cultured scales of goldfish. In this study, we examined the effects of VEDI-1 on osteoblastic differentiation as well as its effects on apoptosis, which is known to be closely related to osteoblastic differentiation. We found that VEDI-1 enhanced the formation of mineralized nodules in rat osteoblast cell lines, including ROS17/2.8 cells, and in mouse pre-osteoblast cell lines, including MC3T3-E1 cells, in a dose dependent manner, which was accompanied by increased expression of late osteoblast markers, bone sialoprotein (BSP) and osteocalcin (OC). Furthermore, VEDI-I inhibited apoptotic cell death and regulated the expression of proteins in the Bcl-2 family. These results suggest that VEDI-1 may facilitate late differentiation of osteoblasts and may have an inhibitory effect on apoptosis.

Osteogenic and adipogenic cell fractions isolated from postnatal mouse calvaria

The use of stem/progenitor cells represents a promising approach to treat craniofacial bone defects, but successful treatments will rely on the availability of cells that can be expanded in vitro and which will differentiate appropriately in vivo. The calvaria may represent a source of autologous cells for such purposes. We demonstrate expression of stem cell antigen-1 (Sca-1) in mouse calvaria. We isolated Sca-1(+) and Sca-1(-) cells at high purity and tested the ability of these cells to differentiate into adipose and bone. We show that the Sca-1(+) cell fraction has adipogenic differentiation potential and that the cell Sca-1(-) fraction has osteogenic differentiation potential. The Sca-1(+) cell fraction partially retains its adipogenic differentiation potential and the Sca-1(-) cell fraction partially retains its osteogenic differentiation potential after in vitro expansion. These data suggest that the calvaria may be used as a source of stem/progenitor cells that can be expanded in vitro and transplanted in vivo for craniofacial tissue regeneration.

The effect of oxygen tension on the in vitro assay of human osteoblastic connective tissue progenitor cells

Connective tissue progenitors (CTPs) are defined as the heterogeneous set of stem and progenitor cells that reside in native tissues and are capable of proliferation and differentiation into one or more connective tissue phenotypes. CTPs play important roles in tissue formation, repair, and remodeling. Therefore, in vitro assays of CTP prevalence and biological potential have important scientific and clinical relevance. This study evaluated oxygen tension as an important variable in optimizing in vitro conditions for quantitative assays of human CTPs. Bone marrow aspirates were collected from 20 human subjects and cultured using established medium conditions at ambient oxygen tensions of 1, 5, 10, and 20%. Colony-forming efficiency (CFE), proliferation, and colony density were assessed. CFE and proliferation were greatest at 5% O(2). Traditional conditions using atmospheric oxygen tension (20% O(2)) reduced CFE by as much as 32%. CFE and proliferation at 1% O(2) were less than 5% O(2) but comparable to that seen at 20% O(2), suggesting that CTPs are relatively resilient under hypoxic conditions, a fact that may be relevant to their function in wound repair and their potential use in tissue engineering applications involving transplantation into settings of moderate to severe hypoxia. These data demonstrate that optimization of quantitative assays for CTPs will require control of oxygen tension.

Use of an alpha-smooth muscle actin GFP reporter to identify an osteoprogenitor population

Identification of a reliable marker of skeletal precursor cells within calcified and soft tissues remains a major challenge for the field. To address this, we used a transgenic model in which osteoblasts can be eliminated by pharmacological treatment. Following osteoblast ablation a dramatic increase in a population of alpha-smooth muscle actin (alpha-SMA) positive cells was observed. During early recovery phase from ablation we have detected cells with the simultaneous expression of alpha-SMA and a preosteoblastic 3.6GFP marker, indicating the potential for transition of alpha-SMA+ cells towards osteoprogenitor lineage. Utilizing alpha-SMAGFP transgene, alpha-SMAGFP+ positive cells were detected in the microvasculature and in the osteoprogenitor population within bone marrow stromal cells. Osteogenic and adipogenic induction stimulated expression of bone and fat markers in the alpha-SMAGFP+ population derived from bone marrow or adipose tissue. In adipose tissue, alpha-SMA+ cells were localized within the smooth muscle cell layer and in pericytes. After in vitro expansion, alpha-SMA+/CD45-/Sca1+ progenitors were highly enriched. Following cell sorting and transplantation of expanded pericyte/myofibroblast populations, donor-derived differentiated osteoblasts and new bone formation was detected. Our results show that cells with a pericyte/myofibroblast phenotype have the potential to differentiate into functional osteoblasts.

Peripheral blood stem cell mobilization: new regimens, new cells, where do we stand

PURPOSE OF REVIEW

Granulocyte colony-stimulating factor-mobilized peripheral blood stem cells are widely used to reconstitute hematopoiesis; however, preclinical and clinical studies show that improvements to this mobilization can be achieved. We discuss the development of new mobilizing regimens and evaluation of new findings on mobilized stem cell populations that may improve the utility and convenience of peripheral blood stem cell transplant.

RECENT FINDINGS

Chemokines and their receptors regulate leukocyte trafficking, and altering chemokine signaling pathways mobilizes stem cells. In recent trials, combination use of the chemokine (C-X-C motif) receptor 4 antagonist AMD3100 and granulocyte colony-stimulating factor mobilized more CD34 cells in fewer days than granulocyte colony-stimulating factor alone and allowed more patients to proceed to autotransplant. In preclinical studies the chemokine GRObeta synergizes with granulocyte colony-stimulating factor and when used alone or with granulocyte colony-stimulating factor mobilizes more primitive hematopoietic stem cells with less apoptosis, higher integrin activation, lower CD26 expression and enhanced marrow homing compared with granulocyte colony-stimulating factor. Hematopoietic stem cells mobilized by GRObeta or AMD3100 demonstrate superior engraftment and contribution to chimerism in primary and secondary transplant studies in mice, and peripheral blood stem cells mobilized by AMD3100 and granulocyte colony-stimulating factor in patients demonstrate enhanced engraftment capabilities in immunodeficient mice.

SUMMARY

Alternate regimens differentially mobilize stem cell populations with unique intrinsic properties with the potential to expand the utility of hematopoietic transplantation. Continued mechanistic evaluation will be critical to our understanding of mechanisms of mobilization and their use in regenerative medicine.

The PPARgamma-selective ligand BRL-49653 differentially regulates the fate choices of rat calvaria versus rat bone marrow stromal cell populations

Background

Osteoblasts and adipocytes are derived from a common mesenchymal progenitor and an inverse relationship between expression of the two lineages is seen with certain experimental manipulations and in certain diseases, i.e., osteoporosis, but the cellular pathway(s) and developmental stages underlying the inverse relationship is still under active investigation. To determine which precursor mesenchymal cell types can differentiate into adipocytes, we compared the effects of BRL-49653 (BRL), a selective ligand for peroxisome proliferators-activated receptor (PPAR)γ, a master transcription factor of adipogenesis, on osteo/adipogeneis in two different osteoblast culture models: the rat bone marrow (RBM) versus the fetal rat calvaria (RC) cell system.

Results

BRL increased the number of adipocytes and corresponding marker expression, such as lipoprotein lipase, fatty acid-binding protein (aP2), and adipsin, in both culture models, but affected osteoblastogenesis only in RBM cultures, where a reciprocal decrease in bone nodule formation and osteoblast markers, e.g., osteopontin, alkaline phosphatase (ALP), bone sialoprotein, and osteocalcin was seen, and not in RC cell cultures. Even though adipocytes were histologically undetectable in RC cultures not treated with BRL, RC cells expressed PPAR and CCAAT/enhancer binding protein (C/EBP) mRNAs throughout osteoblast development and their expression was increased by BRL. Some single cell-derived BRL-treated osteogenic RC colonies were stained not only with ALP/von Kossa but also with oil red O and co-expressed the mature adipocyte marker adipsin and the mature osteoblast marker OCN, as well as PPAR and C/EBP mRNAs.

Conclusion

The data show that there are clear differences in the capacity of BRL to alter the fate choices of precursor cells in stromal (RBM) versus calvarial (RC) cell populations and that recruitment of adipocytes can occur from multiple precursor cell pools (committed preadipocyte pool, multi-/bipotential osteo-adipoprogenitor pool and conversion of osteoprogenitor cells or osteoblasts into adipocytes (transdifferentiation or plasticity)). They also show that mechanisms beyond activation of PPARγ by its ligand are required for changing the fate of committed osteoprogenitor cells and/or osteoblasts into adipocytes.

Multilineage differentiation potential of human dermal skin-derived fibroblasts

Dermal skin-derived fibroblasts from rodent and human have been found to exhibit mesenchymal surface antigen immunophenotype and differentiation potential along the three main mesenchymal-derived tissues: bone, cartilage and fat. Human dermal skin-derived mesenchymal stem cells constitute a promising cell source in clinical applications. Therefore, we isolated fibroblastic mesenchymal stem-cell-like cells from human dermis derived from juvenile foreskins, which share a mesenchymal stem cell phenotype and multi-lineage differentiation potential. We could show similar expression patterns for CD14(-), CD29(+), CD31(-), CD34(-), CD44(+), CD45(-), CD71(+), CD73/SH3-SH4(+), CD90/Thy-1(+), CD105/SH2(+), CD133(-) and CD166/ALCAM(+) in well-established adipose tissue derived-stem cells and fibroblastic mesenchymal stem-cell-like cells by flow cytometry. Immunostainings showed that fibroblastic mesenchymal stem-cell-like cells expressed vimentin, fibronectin and collagen; they were less positive for alpha-smooth muscle actin and nestin, while they were negative for epithelial cytokeratins. When cultured under appropriate inducible conditions, both cell types could differentiate along the adipogenic and osteogenic lineages. Additionally, fibroblastic mesenchymal stem-cell-like cells demonstrated a high proliferation potential. These findings are of particular importance, because skin or adipose tissues are easily accessible for autologous cell transplantations in regenerative medicine. In summary, these data indicate that dermal fibroblasts with multilineage differentiation potential are present in human dermis and they might play a key role in cutaneous wound healing.

Role of gender and anatomical region on induction of osteogenic differentiation of human adipose-derived stem cells

Adipose-derived stem cells (ASCs) display multilineage plasticity and, under appropriate conditions, can mineralize their extracellular matrix and undergo osteogenesis. The aims of this study are to examine in vitro osteogenic differentiation properties of ASCs to assess the role of gender, fat depot, and optimal duration as variables for differentiation. Human ASCs were isolated from superficial and deep adipose layers of the abdominoplasty specimens obtained from patients undergoing elective surgeries. ASCs were cultured in osteogenic media (OM). After 1, 2, and 4 weeks of differentiation, cultures were assessed for markers of osteogenesis. Alkaline phosphatase (AP), alizarin red (AR) and Masson trichrome (MT) stainings for osteoblastic transformation, matrix mineralization, and collagen production; enzyme-linked immunosorbent assay (ELISA) for Gla-osteocalcin; and Western blot analysis for osteonectin protein expression were performed. Osteogenic differentiation began as early as 1 week. Cells exhibited a vertical growth pattern, lacunae formed in the cultures, matrix volume increased, and mineralization was observed. Differences in AP staining were most evident during the first week. AR activity progressively increased over 4 weeks, and collagen was secreted only by differentiated ASCs. There was no significant difference in the degree of osteogenic differentiation between the ASCs from both depots in the female. In the male, the superficial depot ASCs differentiated faster and more efficiently than those of the deep depot. Male ASCs from both depots differentiated more effectively than female ASCs from both depots. We describe a hierarchy of osteogenic differentiation potential based on gender and anatomic harvest site by layering adipose tissues of the abdominal wall. ASCs derived from male superficial layer were most efficient in achieving osteogenesis. In future clinical applications using stem cells for osseous healing, these gender and depot differences will guide our clinical methods.

Mechanical modulation of osteochondroprogenitor cell fate

Mesenchymal cells are natural tissue builders. They exhibit an extraordinary capacity to metamorphize into differentiated cells, using extrinsic spatial and temporal inputs and intrinsic algorithms, as well as to build and adapt their own habitat. In addition to providing a habitat for osteoprogenitor cells, tissues of the skeletal system provide mechanical support and protection for the multiple organs of vertebrate organisms. This review examines the role of mechanics on determination of cell fate during pre-, peri- and postnatal development of the skeleton as well as during tissue genesis and repair in postnatal life. The role of cell mechanics is examined and brought into context of intrinsic cues during mesenchymal condensation. Remarkable new insights regarding structure function relationships in mesenchymal stem cells, and their influence on determination of cell fate are integrated in the context of de novo tissue generation and postnatal repair. Key differences in the formation of osteogenic and chondrogenic condensations are discussed in relation to direct intramembranous and indirect endochondral ossification. New approaches are discussed to elucidate and exploit extrinsic cues to generate tissues in the laboratory and in the clinic.

Proliferation, osteogenic differentiation, and distribution of rat bone marrow stromal cells in nonwoven fabrics by different culture methods

The proliferation, osteogenic differentiation, and distribution patterns of stromal cells from rat bone marrow were investigated in a three-dimensional nonwoven fabric of polyethylene terephthalate fiber by the static, agitated, and stirred culture methods; stirring speeds were 10, 50, and 100 rpm in the stirred culture method. The culture method affected the time profile of proliferation and osteogenic differentiation of cells or their distribution in the fabric. The extent of cell proliferation and osteogenic differentiation became higher in order of the stirred at 100 rpm = the stirred at 50 rpm > the stirred at 10 rpm > the agitated > the static methods. In addition, the cells were more uniformly proliferated in the fabric by the stirred culture method with time than they were proliferated in the fabric by other methods. The alkaline phosphatase (ALP) activity and calcium content were higher for cells cultured by the stirred culture method than those cultured by other methods. The total ALP activity, calcium content, and bone mineral density were higher for every stirred method than those for other methods. However, the distribution uniformity of cells differentiated was low irrespective of the culture method. It is concluded that the extent of proliferation and differentiation of cells or their distribution uniformity in the nonwoven fabrics was influenced by the culture method.

Tissue engineering craniofacial defects with adult stem cells? Are we ready yet?

Over three-quarters of all craniofacial defects observed in the US per year are cleft palates. Usually involving significant bony defects in both the hard palate and alveolar process of the maxilla, repair of these defects is typically performed surgically using autologous bone grafts taken from appropriate sites (i.e., iliac crest). However, surgical intervention is not without its complications. As such, the reconstructive surgeon has turned to the scientist and engineer for help. In this review, the application of the field of tissue engineering to craniofacial defects (e.g., cleft palates) is discussed. Specifically the use of adult stem cells, such as mesenchymal stem cells from bone marrow and Adipose-derived Stem Cells (ASCs) in combination with currently available biomaterials is presented in the context of healing craniofacial defects like the cleft palate. Finally, future directions with regards to the use of ASCs in craniofacial repair are discussed, including possible scaffold-driven and gene-driven approaches.

Phenotypic transcription factors epigenetically mediate cell growth control

Ribosomal RNA (rRNA) genes are down-regulated during osteogenesis, myogenesis, and adipogenesis, necessitating a mechanistic understanding of interrelationships between growth control and phenotype commitment. Here, we show that cell fate-determining factors [MyoD, myogenin (Mgn), Runx2, C/EBPbeta] occupy rDNA loci and suppress rRNA expression during lineage progression, concomitant with decreased rRNA expression and reciprocal loss of occupancy by c-Myc, a proliferation-specific activator of rRNA transcription. We find interaction of phenotypic factors with the polymerase I activator upstream binding factor UBF-1 at interphase nucleoli, and this interaction is epigenetically retained on mitotic chromosomes at nucleolar organizing regions. Ectopic expression and RNA interference establish that MyoD, Mgn, Runx2, and C/EBPbeta each functionally suppress rRNA genes and global protein synthesis. We conclude that epigenetic control of ribosomal biogenesis by lineage-specific differentiation factors is a general developmental mechanism for coordinate control of cell growth and phenotype.

Growth and differentiation factors for cartilage healing and repair

Chondrocyte differentiation and the maintenance of function requires both transient and long-lasting control through humoral factors, particularly under stress, repair and regeneration in vivo or in vitro as in cell and tissue culture. To date, humoral factors from all major classes of molecules are known to contribute: ions (calcium), steroids (estrogens), terpenoids (retinoic acid), peptides (PTHRP, PTH, insulin, FGFs) and complex proteins (IGF-1, BMPs). They may act indirectly through membrane receptors and signal pathways or directly on transcriptional control elements. Those molecules may reach chondrocytes via free diffusion or may be bound to collagens or proteoglycans on extracellular matrix superstructures becoming available on metabolic processing of collagens and/or proteoglycans. Depending on their position in the metabolic cascade controlling chondrocyte development and homeostasis, they may be used in tissue engineering and regenerative approaches towards cartilage repair by direct application, carrier-mediated release or genetic delivery.

Porcine peroxisome proliferator-activated receptor gamma induces transdifferentiation of myocytes into adipocytes

Peroxisome proliferator-activated receptor gamma2 (PPARgamma) is a nuclear transcription factor that regulates adipocyte differentiation and lipogenic genes during adipogenesis. The activity of rodent PPARgamma is regulated by phosphorylation of serine 112. The current experiment was designed to study the ability of porcine PPARgamma to stimulate transdifferentiation of myoblasts to adipocytes by overexpressing wild-type PPARgamma or mutated PPARgamma (serine 112 was mutated to alanine) in mouse myoblast cells. The expression of adipogenic marker genes (adipocyte fatty acid binding protein, lipoprotein lipase, and glycerol-3 phosphate dehydrogenase) in cells stably expressing mutated porcine PPARgamma was greater than in cells with wild-type PPARgamma, indicating that the mutated PPARgamma has greater adipogenic capability than the wild-type PPARgamma. Under treatment with a ligand, both wild-type and mutant porcine PPARgamma-expressing C2C12 myoblasts differentiated into adipocytes in 10 d. The expression of myogenic marker genes (myogenin, myogenic regulatory factor-4) was suppressed in cells transfected with the mutated PPARgamma or wild-type PPARgamma. Moreover, wild-type and mutant PPARgamma were able to inhibit myogenesis without addition of a ligand. Our results suggest that porcine wild-type PPARgamma and mutated PPARgamma can both convert myoblast cells into adipocytes, and also that the ability to transdifferentiate was greater in cells containing the mutated PPARgamma than in cells containing the wild-type PPARgamma. Therefore, the existence of serine 112 in PPARgamma may have a role in regulating adipocyte differentiation.

Immortalized mouse articular cartilage cell lines retain chondrocyte phenotype and respond to both anabolic factor BMP-2 and pro-inflammatory factor IL-1

Articular cartilage chondrocytes help in the maintenance of tissue homeostasis and function of the articular joint. Study of primary chondrocytes in culture provides information closely related to in vivo functions of these cells. Limitations in the primary culture of chondrocytes have lead to the development of cells lines that serve as good surrogate models for the study of chondrocyte biology. In this study, we report the establishment and characterization of chondrocyte cell lines, MM-Sv/HP and MM-Sv/HP-2 from mouse articular cartilage. Cells were isolated from mouse femoral head articular cartilage, immortalized and maintained in culture through numerous passages. The morphology of the cells was from fibroblastic to polygonal in nature. Gene expression studies using quantitative PCR (Q-PCR) were performed on cells in monolayer culture and cells embedded in a three-dimensional alginate matrix. Stimulation of cells in monolayer culture with anabolic factor, BMP-2, resulted in increased gene expression of the extracellular matrix molecules, aggrecan and type II collagen and their regulator transcription factor, Sox9. Treatment by pro-inflammatory IL-1 resulted in increased gene expression of catabolic effectors including Aggrecanases (ADAMTS4, ADAMTS5), MMP-13 and nitric oxide synthase (Nos2). Cells in alginate treated with BMP-2 resulted in increased synthesis of proteoglycan which was released into the conditioned media on IL-1 stimulation. Western analysis of conditioned media showed the presence of Aggrecanase-cleaved aggrecan fragments. In summary, MM-Sv/HP and MM-Sv/HP-2 show preservation of important characteristics of articular chondrocytes as examined under multiple culture conditions and would provide a useful reagent in the study of chondrocyte biology.

Combination material delivery of dexamethasone and growth factor in hydrogel blended with hyaluronic acid constructs for neocartilage formation

The aim of this study was to assess the efficacy of poly(NiPAAm-co-AAc) blended with hyaluronic acid (HA) as an injectable cell vehicle and a cell therapeutic agent in the form of a supporting matrix for the chondrogenic differentiation of rabbit chondrocytes. Specially, rabbit chondrocytes were embedded in blended hydrogels co-encapsulation with dexamethasone (Dex) and growth factors for enhancing the chondrogenic differentiation. Blended hydrogel constructs consisting of embedded cells co-encapsulating Dex and TGF beta-3 or unloaded Dex and sTGF beta-3 served as controls to assess the effects of Dex on chondrogenic differentiation. Hydrogel constructs consisting of embedded cells co-encapsulating Dex and TGF beta-3 on chondrogenic differentiation. The hydrogel constructs were injected subcutaneously into the nude mice and monitored for 1, 4, and 8 weeks after the injection. The level of the cartilage-associated ECM proteins was determined by immunohistochemical (collagen type II; specific marker for chondrogenic differentiation), Safranin-O, and Alcian blue (GAG) staining. Over the same time period, the glycosamingoglycan content per cell remained constant for all formulations, indicating that the dramatic increase in cell number for samples with Dex and TGF beta-3 loaded in hydrogel constructs was accompanied by maintenance of the cell phenotypes.

Molecular biology of bone remodelling

Bone remodelling is an active and dynamic process that relies on the correct balance between bone resorption by osteoclasts and bone deposition by osteoblasts. Moreover, these two functions must be tightly coupled not only quantitatively, but also in time and space. When the coupling is lost, the correct bone mass could be compromised, leading to several skeletal pathologies. Indeed, bone loss and osteoporosis are the result of an increased osteoclast function and/or a reduced osteoblast activity. In contrast, other pathologies are related to osteoclast failure to resorbe bone, such as osteopetrosis, a rare genetic disorder characterized by an increased bone mass and also linked to an impairment of bone marrow functions. Starting from these assumptions, it is necessary to more deeply understand the molecular mechanisms regulating bone cell functions. Indeed, recent studies evidenced a complex interplay between the immune and skeletal systems, which share several regulatory molecules including cytokines, receptors and transcription factors. These data allowed to more deeply understand the mechanisms underlying bone mass regulation and could open new avenue to identify target molecules for alterantive therapies more efficacious against bone diseases.

Long-term imatinib therapy promotes bone formation in CML patients

Imatinib inhibits tyrosine kinases important in osteoclast (c-Fms) and osteoblast (platelet-derived growth factor receptor [PDGF-R], c-Abl) function, suggesting that long-term therapy may alter bone homeostasis. To investigate this question, we measured the trabecular bone volume (TBV) in iliac crest bone biopsies taken from chronic myeloid leukemia (CML) patients at diagnosis and again after 2 to 4 years of imatinib therapy. Half the patients (8 of 17) showed a substantive increase in TBV (> 2-fold), after imatinib therapy, with the TBV in the posttreatment biopsy typically surpassing the normal upper limit for the patient's age group. Imatinib-treated patients exhibited reduced serum calcium and phosphate levels with hypophosphatemia evident in 53% (9 of 17) of patients. In vitro, imatinib suppressed osteoblast proliferation and stimulated osteogenic gene expression and mineralized-matrix production by inhibiting PDGF receptor function. In PDGF-stimulated cultures, imatinib dose-dependently inhibited activation of Akt and Crk-L. Using pharmacologic inhibitors, inhibition of PI3-kinase/Akt activation promoted mineral formation, suggesting a possible molecular mechanism for the imatinib-mediated increase in TBV in vivo. Further investigation is required to determine whether the increase in TBV associated with imatinib therapy may represent a novel therapeutic avenue for the treatment of diseases that are characterized by generalized bone loss.

Enhanced proliferation and osteogenic differentiation of rat mesenchymal stem cells in collagen sponge reinforced with different poly(ethylene terephthalate) fibers

The objective of this study was to investigate the feasibility of collagen sponges mechanically reinforced by the incorporation of poly(ethylene terephthalate) (PET) fibers in stem cell culture. A collagen solution with homogeneously dispersed PET fibers was freeze-dried, followed by dehydrothermal cross-linking to obtain the collagen sponge incorporating PET fibers. By scanning electron microscopy observation, the collagen sponges exhibited isotropic and interconnected pore structures with an average size of 200 microm, irrespective of PET fiber incorporation. As expected, PET fibers incorporation significantly enhanced the compression strength of collagen sponge. When used for rat mesenchymal stem cells (MSC), the collagen sponge incorporating PET fibers was superior to the original collagen sponge without PET fibers incorporation in terms of the initial attachment, proliferation and osteogenic differentiation of cells, irrespective of the amount and diameter of fibers incorporated. The shrinkage of sponges during cell culture was significantly suppressed by the fiber incorporation. It is possible that the shrinkage suppression maintains the three-dimensional inner pore structure of collagen sponges without impairing the cell compatibility, resulting in the superior MSC attachment and the subsequent osteogenic differentiation in the sponge incorporating PET fiber.

GSMA: Gene Set Matrix Analysis, An Automated Method for Rapid Hypothesis Testing of Gene Expression Data

Background

Microarray technology has become highly valuable for identifying complex global changes in gene expression patterns. The assignment of functional information to these complex patterns remains a challenging task in effectively interpreting data and correlating results from across experiments, projects and laboratories. Methods which allow the rapid and robust evaluation of multiple functional hypotheses increase the power of individual researchers to data mine gene expression data more efficiently.

Results

We have developed (gene set matrix analysis) GSMA as a useful method for the rapid testing of group-wise up- or down-regulation of gene expression simultaneously for multiple lists of genes (gene sets) against entire distributions of gene expression changes (datasets) for single or multiple experiments. The utility of GSMA lies in its flexibility to rapidly poll gene sets related by known biological function or as designated solely by the end-user against large numbers of datasets simultaneously.

Conclusions

GSMA provides a simple and straightforward method for hypothesis testing in which genes are tested by groups across multiple datasets for patterns of expression enrichment.

Chondrogenesis, osteogenesis and adipogenesis of canine mesenchymal stem cells: a biochemical, morphological and ultrastructural study

Musculoskeletal diseases with osteochondrotic articular cartilage defects, such as osteoarthritis, are an increasing problem for humans and companion animals which necessitates the development of novel and improved therapeutic strategies. Canine mesenchymal stem cells (cMSCs) offer significant promise as a multipotent source for cell-based therapies and could form the basis for the differentiation and cultivation of tissue grafts to replace damaged tissue. However, no comprehensive analysis has been undertaken to characterize the ultrastructure of in vitro differentiated cMSCs. The main goal of this paper was to focus on cMSCs and to analyse their differentiation capacity. To achieve this aim, bone marrow cMSCs from three canine patients were isolated, expanded in monolayer culture and characterized with respect to their ability for osteogenic, adipogenic and chondrogenic differentiation capacities. cMSCs showed proliferative potential and were capable of osteogenic, adipogenic and chondrogenic differentiation. cMSCs treated with the osteogenic induction medium differentiated into osteoblasts, produced typical bone matrix components, beta1-integrins and upregulated the osteogenic specific transcription factor Cbfa-1. cMSCs treated with the adipogenic induction medium showed typical adipocyte morphology, produced adiponectin, collagen type I and beta1-integrins, and upregulated the adipogenic specific transcription factor PPAR-gamma. cMSCs treated with the chondrogenic induction medium exhibited a round to oval shape, produced a cartilage-specific extracellular matrix, beta1-integrins and upregulated the chondrogenic specific transcription factor Sox9. These results demonstrate, at the biochemical, morphological and ultrastructural levels, the multipotency of cMSCs and thus highlight their potential therapeutic value for cell-based tissue engineering.

Cell fate specification during calvarial bone and suture development

In this study we have addressed the fundamental question of what cellular mechanisms control the growth of the calvarial bones and conversely, what is the fate of the sutural mesenchymal cells when calvarial bones approximate to form a suture. There is evidence that the size of the osteoprogenitor cell population determines the rate of calvarial bone growth. In calvarial cultures we reduced osteoprogenitor cell proliferation; however, we did not observe a reduction in the growth of parietal bone to the same degree. This discrepancy prompted us to study whether suture mesenchymal cells participate in the growth of the parietal bones. We found that mesenchymal cells adjacent to the osteogenic fronts of the parietal bones could differentiate towards the osteoblastic lineage and could become incorporated into the growing bone. Conversely, mid-suture mesenchymal cells did not become incorporated into the bone and remained undifferentiated. Thus mesenchymal cells have different fate depending on their position within the suture. In this study we show that continued proliferation of osteoprogenitors in the osteogenic fronts is the main mechanism for calvarial bone growth, but importantly, we show that suture mesenchyme cells can contribute to calvarial bone growth. These findings help us understand the mechanisms of intramembranous ossification in general, which occurs not only during cranial and facial bone development but also in the surface periosteum of most bones during modeling and remodeling.

Expression profiling of Dexamethasone-treated primary chondrocytes identifies targets of glucocorticoid signalling in endochondral bone development

Background

Glucocorticoids (GCs) are widely used anti-inflammatory drugs. While useful in clinical practice, patients taking GCs often suffer from skeletal side effects including growth retardation in children and adolescents, and decreased bone quality in adults. On a physiological level, GCs have been implicated in the regulation of chondrogenesis and osteoblast differentiation, as well as maintaining homeostasis in cartilage and bone. We identified the glucocorticoid receptor (GR) as a potential regulator of chondrocyte hypertrophy in a microarray screen of primary limb bud mesenchyme micromass cultures. Some targets of GC regulation in chondrogenesis are known, but the global effects of pharmacological GC doses on chondrocyte gene expression have not been comprehensively evaluated.

Results

This study systematically identifies a spectrum of GC target genes in embryonic growth plate chondrocytes treated with a synthetic GR agonist, dexamethasone (DEX), at 6 and 24 hrs. Conventional analysis of this data set and gene set enrichment analysis (GSEA) was performed. Transcripts associated with metabolism were enriched in the DEX condition along with extracellular matrix genes. In contrast, a subset of growth factors and cytokines were negatively correlated with DEX treatment. Comparing DEX-induced gene expression data to developmental changes in gene expression in micromass cultures revealed an additional layer of complexity in which DEX maintains the expression of certain chondrocyte marker genes while inhibiting factors that promote vascularization and ultimately ossification of the cartilaginous template.

Conclusion

Together, these results provide insight into the mechanisms and major molecular classes functioning downstream of DEX in primary chondrocytes. In addition, comparison of our data with microarray studies of DEX treatment in other cell types demonstrated that the majority of DEX effects are tissue-specific. This study provides novel insights into the effects of pharmacological GC on chondrocyte gene transcription and establishes the foundation for subsequent functional studies.

In vivo osteogenic potential of human adipose-derived stem cells/poly lactide-co-glycolic acid constructs for bone regeneration in a rat critical-sized calvarial defect model

Recent studies suggest that human adipose tissue contains pluripotent stem cells, which are similar to bone marrow-derived stem cells. The objective of the present study was to assess the effect in bone regenerating capability of human adipose-derived stem cells (ADSCs) cultured in osteogenic media layered over poly lactide-co-glycolic acid (PLGA) and implanted in a critical nude rat calvarial defect. Twenty-seven nude rats were randomized into 3 groups (n = 9): 1) PLGA alone (control), 2) PLGA with undifferentiated ADSCs, and 3) PLGA with differentiated ADSCs. These 3 groups were divided into 9 subgroups (n = 3) according to in vitro pre-cultured periods (day 1 pre-culture (Group1), day 7 pre-culture (Group2), and day 14 pre-culture (Group3)) before implantation. An 8 mm critical-size circular calvarial defect was made in each nude rat. Specimens were harvested at 12 weeks post-implantation and evaluated radiographically and histologically. Radiodensitometric analysis revealed significantly higher bone growth in implants pre-cultured in osteogenic media for 14 days for Group 3. Histomorphometric analysis demonstrated that Groups 2 and 3 had bone formation filling 35% to 72% of the area of the defect after transplantation with cells that had been pre-cultured for 14 days. Constructs with differentiated ADSCs (Group 3) had noticeably more maximal and robust bone tissue regeneration than constructs with undifferentiated ADSCs (Group 2). These data provide evidence that constructs or implants made of PLGA and osteogenically differentiated ADSCs pre-cultured for 14 days before transplantation have better, more-robust bone regeneration capability in critical-sized skeletal defects than constructs with undifferentiated ADSCs. Human adipose derived stem cells can therefore be used as seed cells to construct tissue-engineered bone.

Proteomic identification of differently expressed proteins responsible for osteoblast differentiation from human mesenchymal stem cells

Human mesenchymal stem cells (hMSC) are a population of multipotent cells that can differentiate into osteoblasts, chondrocytes, adipocytes, and other cells. The exact mechanism governing the differentiation of hMSC into osteoblasts remains largely unknown. Here, we analyzed protein expression profiles of undifferentiated as well as osteogenic induced hMSC using 2-D gel electrophoresis (2-DE), mass spectrometry (MS), and peptide mass fingerprinting (PMF) to investigate the early gene expression in osteoblast differentiation. We have generated proteome maps of undifferentiated hMSC and osteogenic induced hMSC on day 3 and day 7. 2-DE revealed 102 spots with at least 2.0-fold changes in expression and 52 differently expressed proteins were successfully identified by MALDI-TOF-MS. These proteins were classified into 7 functional categories: metabolism, signal transduction, transcription, calcium-binding protein, protein degradation, protein folding and others. The expression of some identified proteins was confirmed by further RT-PCR analyses. This study clarifies the global proteome during osteoblast differentiation. Our results will play an important role in better elucidating the underlying molecular mechanism in hMSC differentiation into osteoblasts.

Hydrogel effects on bone marrow stromal cell response to chondrogenic growth factors

The aim of this study was to investigate the effects of alginate and agarose on the response of bone marrow stromal cells (BMSCs) to chondrogenic stimuli. Rat BMSCs were expanded in monolayer culture with or without FGF-2 supplementation. Cells were then seeded in 2% alginate and agarose gels and cultured in media with or without TGF-beta1 or dexamethasone (Dex). Sulfated glycosaminoglycans (sGAGs), collagen type II, and aggrecan were expressed in all groups that received TGF-beta1 treatment during hydrogel culture. Expansion of rat BMSCs in the presence of FGF-2 increased production of sGAG in TGF-beta1-treated groups over those cultures that were treated with TGF-beta1 alone in alginate cultures. However, in agarose, cells exposed to FGF-2 during expansion produced less sGAG within TGF-beta1-supplemented groups over those cultures treated with TGF-beta1 alone. Dex was required for optimal matrix synthesis in both hydrogels, but was found to decrease cell viability in agarose constructs. These results indicate that the response of BMSCs to a chondrogenic growth factor regimen is scaffold dependent.

Leukemia inhibitory factor influences the fate choice of mesenchymal progenitor cells

Osteoblasts and adipocytes derive from a common mesenchymal precursor, and in at least some circumstances, differentiation along these two lineages is inversely related. For example, we have recently observed that concomitant with inhibition of osteoblast differentiation and bone nodule formation, leukemia inhibitory factor (LIF) induces genes regulating lipid metabolism in fetal rat calvaria (RC) cell cultures. In this study, we further investigated the adipogenic capacity of LIF-treated RC cells. Quantitative analyses revealed that LIF increased the adipocyte differentiation induced by the peroxisome proliferator-activated receptor gamma agonist BRL49653 (BRL) in RC cell populations. Gene expression profiling of individual RC cell colonies in untreated cells or cells treated with LIF, BRL, or combined LIF-BRL suggested that some adipocytes arose from bipotential or other primitive precursors, including osteoprogenitors, since many colonies co-expressed osteoblast and adipocyte differentiation markers, whereas some arose from other cell pools, most likely committed preadipocytes present in the population. These analyses further suggested that LIF and BRL do not act at the same stages of the mesenchymal hierarchy, but rather that LIF modifies differentiation of precursor cells, whereas BRL acts later to favor adipocyte differentiation. Taken together, our data suggest that LIF increased adipocyte differentiation at least in part by altering the fate of osteoblastic cells and their precursors.

Comparison of intracardiac cell transplantation: autologous skeletal myoblasts versus bone marrow cells

An increasing number of patients living with cardiovascular disease (CVD) and still unacceptably high mortality created an urgent need to effectively treat and prevent disease-related events. Within the past 5 years, skeletal myoblasts (SKMBs) and bone marrow (or blood)-derived mononuclear cells (BMNCs) have demonstrated preclinical efficacy in reducing ischemia and salvaging already injured myocardium, and in preventing left ventricular (LV) remodeling, respectively. These findings have been translated into clinical trials, so far totaling over 200 patients for SKMBs and over 800 patients for BMNCs. These safety/feasibility and early phase II studies showed promising but somewhat conflicting symptomatic and functional improvements, and some safety concerns have arisen. However, the patient population, cell type, dose, time and mode of delivery, and outcome measures differed, making comparisons problematic. In addition, the mechanisms through which cells engraft and deliver their beneficial effects remain to be fully elucidated. It is now time to critically evaluate progress made and challenges encountered in order to select not only the most suitable cells for cardiac repair but also to define appropriate patient populations and outcome measures. Reiterations between bench and bedside will increase the likelihood of cell therapy success, reduce the time to development of combined of drug- and cell-based disease management algorithms, and offer these therapies to patients to achieve a greater reduction of symptoms and allow for a sustained improvement of quality of life.

Glucocorticoids induce the differentiation of a mesenchymal progenitor cell line, ROB-C26 into adipocytes and osteoblasts, but fail to induce terminal osteoblast differentiation

To clarify the effects of glucocorticoids (GCs) on osteoblast and adipocyte differentiation, we investigated the effects of dexamethasone (Dex), a GC analogue on transcription factors for osteoblasts (Runx2, Dlx5 and Osterix) and adipocytes (C/EBPs such as C/EBPalpha, C/EBPbeta and C/EBPdelta, and PPARgamma2), late osteoblastic markers, bone sialoprotein (BSP) and osteocalcin (OC), and adipocyte differentiation-dependent protein, aP2 in a clonal mesenchymal progenitor cell line, ROB-C26 (C26). C26 cells were dose- and time-dependently responsive to Dex in terms of an increase in not only mRNA and protein expressions of the C/EBPs, PPARgamma2 and aP2, but also Runx2, Dlx5, BSP and OC with no induction of Osterix, which is considered to act mainly on terminal osteoblast differentiation. Cycloheximide pretreatment indicated that Dex signaling immediately increases expressions of the C/EBPs and Dlx5, while expressions of the rest of the genes require de novo protein synthesis. Continuous Dex treatment stimulated adipocyte formation, but failed to induce Osterix expression and mineralized matrix formation. However, BMP-2 treatment of Dex-treated cells induced Osterix expression and subsequent mineralized matrix formation. These results indicate that Dex up-regulates the C/EBPs followed by increasing PPARgamma2 and aP2 expressions in C26 cells to induce adipocyte differentiation, while Dex enhances Dlx5 followed by increasing Runx2, BSP and OC expressions at gene and protein levels, but cannot induce Osterix expression, suggesting that Dex does not promote their terminal osteoblast differentiation.

Delivery of dexamethasone, ascorbate, and growth factor (TGF β-3) in thermo-reversible hydrogel constructs embedded with rabbit chondrocytes

The aim of this study was to assess the efficacy of poly(N-isopropylacrylamide-co-acrylic acid) (p(NiPAAm-co-AAc)) as an injectable drug delivery vehicle and a cell therapeutic agent in the form of a supporting matrix for the chondrogenic differentiation of rabbit chondrocytes. The p(NiPAAm-co-AAc) hydrogel itself without specific differentiation-inducing drugs was used as a control in order to determine the effects of these materials on chondrogenic differentiation. The level of cartilage associated extracellular matrix (ECM) proteins was examined by immunohistochemical staining for collagen type II as well as Safranin-O and Alcian blue (GAG) staining. These results highlight the potential of a thermo-reversible hydrogel mixed with chondrocytes and differentiation materials as an injectable delivery vehicle for use in neocartilage formation.

In vitro adipocytic conversion in Meckel's chondrocytes in response to a fatty acid-containing medium

Chick serum (CKS) contains factors that stimulate adipocytes in Meckel's chondrocytes in vitro. In the present study, we analyzed levels of fatty acids in CKS, and further examined whether these had the potential to convert chondrocytes to adipocytes. Phenotypic changes were evaluated by light and electron microscopies, bromodeoxyuridine (BrdU) incorporation, triglyceride assays, and immunocytochemistry. We showed that CKS contained high levels of fatty acids, and a mixed medium containing 5 particular fatty acids inhibited DNA synthesis and the proliferation of chondrocytes as it facilitated their differentiation into adipocytes. The adipocytes produced were sudan-positive multilocular cells that morphologically and histochemically resembled adipocytes induced by the CKS-containing medium. Almost all lipid droplet-containing cells were positive for leptin and alpha-glycerophosphate dehydrogenase (GPDH), as evaluated by immunoperoxidase staining, and their triglyceride concentrations markedly increased during 4 to 6 days of culture. These results suggested that specific fatty acids in CKS are involved in the adipocytic conversion of Meckel's chondrocytes.

In vivo distribution of human adipose-derived mesenchymal stem cells in novel xenotransplantation models

The potential for human adipose-derived mesenchymal stem cells (AMSC) to traffic into various tissue compartments was examined using three murine xenotransplantation models: nonobese diabetic/severe combined immunodeficient (NOD/SCID), nude/NOD/SCID, and NOD/SCID/MPSVII mice. Enhanced green fluorescent protein was introduced into purified AMSC via retroviral vectors to assist in identification of cells after transplantation. Transduced cells were administered to sublethally irradiated immune-deficient mice through i.v., intraperitoneal, or subcutaneous injection. Up to 75 days after transplantation, tissues were harvested and DNA polymerase chain reaction (PCR) was performed for specific vector sequences as well as for human Alu repeat sequences. Duplex quantitative PCR using human beta-globin and murine rapsyn primers assessed the contribution of human cells to each tissue. The use of the novel NOD/SCID/MPSVII mouse as a recipient allowed rapid identification of human cells in the murine tissues, using an enzyme reaction that was independent of surface protein expression or transduction with an exogenous transgene. For up to 75 days after transplantation, donor-derived cells were observed in multiple tissues, consistently across the various administration routes and independent of transduction parameters. Tissue localization studies showed that the primary MSC did not proliferate extensively at the sites of lodgement. We conclude that human AMSC represent a population of stem cells with a ubiquitous pattern of tissue distribution after administration. AMSC are easily obtained and highly amenable to current transduction protocols for retroviral transduction, making them an excellent avenue for cell-based therapies that involve a wide range of end tissue targets.

Transplantation of Myocyte Precursors Derived from Embryonic Stem Cells Transfected with IGFII Gene in a Mouse Model of Muscle Injury

BACKGROUND

Reconstruction of skeletal muscle tissue is hampered by the lack of availability of functional substitution of the tissue.

METHODS

Embryonic stem (ES) cells were transfected with the insulin-like growth factor (IGF) II gene and were selected with G418. The resultant cell clones were analyzed regarding their myogenic differentiation in vitro and in vivo.

RESULTS

The cells expressed early and late myogenic differentiation markers, including myoD, myogenin, and dystrophin in vitro. They had phosphorylated Akt within the cells, suggesting their activation by the secreted IGFII. Transplantation of the cells to injured anterior tibial muscle of mice significantly improved their motor functions compared to injured mice transplanted with undifferentiated ES cells and injured mice given vehicle alone. The transfected cells adapted to the injured muscle, formed myofibers positive for dystrophin and negative for MyoD and myogenin. Trichrome staining and toluidine blue staining support myofiber formation in vivo. The enzymatic activity of acetylcholine esterase suggested the functional activity of the regenerated motor units. The evoked electromyogram of anterior tibial muscle transplanted with the transfected cells showed significantly higher potentials compared to that transplanted with undifferentiated ES cells and that injected with phosphate-buffered saline (control injury). Electron microscopic examination confirmed the myofiber formation in the cells in vivo.

CONCLUSIONS

Transfection of IGFII gene into ES cells may be applicable for transplantation therapy of muscle damage due to injury and myopathies.

Biofabricated marine hydrozoan: a bioactive crystalline material promoting ossification of mesenchymal stem cells

This study introduces a novel three-dimensional biomatrix obtained from the marine hydrocoral Millepora dichotoma as a scaffold for hard tissue engineering. Millepora dichotoma was biofabricated under field and laboratory conditions. Three-dimensional biomatrices were made in order to convert mesenchymal stem cells (MSCs) to exemplify osteoblastic phenotype. We investigated the effect of the biomatrices on MSCs proliferation and differentiation at 2, 3, 4, 7, 10, 14, 21, 28, and 42 days. Different analyses were made: light microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), calcium incorporation to newly formed tissue (alizarin red), bone nodule formation (von Kossa), fat aggregate formation (oil red O), collagen type I immunofluorescence, DNA concentrations, alkaline phosphatase (ALP) activity, and osteocalcin concentrations. MSCs seeded on Millepora dichotoma biomatrices showed higher levels of calcium and phosphate incorporation and higher type I collagen levels than did control Porites lutea biomatrices. ALP activity revealed that MSCs seeded on M. dichotoma biomatrices are highly osteogenic compared to those on control biomatrices. The osteocalcin content of MSCs seeded on M. dichotoma remained constant up to 2 weeks before rising to surpass that of seeded P. lutea biomatrices after 28 days. Our study thus showed that M. dichotoma biomatrices enhance the differentiation of MSCs into osteoblast and hence have excellent potential as bioscaffold for hard tissue engineering.

Activation of Sirt1 decreases adipocyte formation during osteoblast differentiation of mesenchymal stem cells

In vitro, mesenchymal stem cells differentiate to osteoblasts when exposed to bone-inducing medium. However, adipocytes are also formed. We showed that activation of the nuclear protein deacetylase Sirt1 reduces adipocyte formation and promotes osteoblast differentiation.

INTRODUCTION

Mesenchymal stem cells (MSCs) can differentiate into osteoblasts, adipocytes, chondrocytes, and myoblasts. It has been suggested that a reciprocal relationship exists between the differentiation of MSCs into osteoblasts and adipocytes. Peroxisome proliferator-activated receptor gamma2 (PPARgamma2) is a key element for the differentiation into adipocytes. Activation of Sirt1 has recently been shown to decrease adipocyte development from preadipocytes through inhibition of PPARgamma2.

MATERIALS AND METHODS

We used the mouse mesenchymal cell line C3H10T1/2 and primary rat bone marrow cells cultured in osteoblast differentiation medium with or without reagents affecting Sirt1 activity. Adipocyte levels were analyzed by light microscopy and flow cytometry (FACS) after staining with Oil red O and Nile red, respectively. Osteoblast and adipocyte markers were studied with quantitative real-time PCR. Mineralization in cultures of primary rat bone marrow stromal cells was studied by von Kossa and alizarin red staining.

RESULTS

We found that Sirt1 is expressed in the mesenchymal cell line C3H10T1/2. Treatment with the plant polyphenol resveratrol as well as isonicotinamide, both of which activate Sirt1, blocked adipocyte development and increased the expression of osteoblast markers. Nicotinamide, which inhibits Sirt1, increased adipocyte number and increased expression of adipocyte markers. Furthermore, activation of Sirt1 prevented the increase in adipocytes caused by the PPARgamma-agonist troglitazone. Finally, activation of Sirt1 in rat primary bone marrow stromal cells increased expression of osteoblast markers and also mineralization.

CONCLUSIONS

In this study, we targeted Sirt1 to control adipocyte development during differentiation of MSCs into osteoblasts. The finding that resveratrol and isonicotinamide markedly inhibited adipocyte and promoted osteoblast differentiation may be relevant in the search for new treatment regimens of osteoporosis but also important for the evolving field of cell-based tissue engineering.

Comparative study of the ability of mesenchymal stem cells derived from bone marrow, periosteum, and adipose tissue in treatment of partial growth arrest in rabbit

This study evaluates the ability of MSCs isolated from different origins--bone marrow, periosteum, or fat--to treat partial growth arrest in immature (6-week-old) New Zealand White rabbits. Up to 50% of the medial half of the proximal physis of the tibia was excised in these New Zealand White rabbits. Three weeks later, the bony bridge was excised, and fibrin glue with and without MSCs were transferred into the physeal defect of different rabbits. Contralateral tibias, without undergoing operation, served as self-control. Four groups of rabbits were involved in the study. Each group was injected separately with bone marrow-derived MSCs (group I), periosteum-derived MSCs (group II), fat-derived MSCs (group III), and fibrin glue alone (control, group IV). The rabbits were killed 8 and 16 weeks postoperatively. Clinical, radiological, and histological analyses were subsequently performed. Similar proliferative rates for three MSCs were demonstrated on days 4, 7, and 11 of primary culture. However, MSCs derived from bone-marrow and periosteum appeared to be more homogeneous than that from fat. All MSCs demonstrated chondrogenic and osteogenic differentiation potentials in vitro. The tibias in groups I and II showed significant correction of varus angulation at 16 weeks. However, the varus angulation in group III remained significantly obvious when compared with group I (p < 0.05). The length discrepancies between operated and normal tibiae in groups I, II, and III were significantly corrected compared with control (p < 0.01). In conclusion, bone-marrow and periosteum yielded more homogenous MSCs than fat, providing better correction of physeal arrest in rabbits. The source of MSCs itself could influence the success in the treatment of growth arrest.

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.

Myoblast transplantation for inherited myopathies: a clinical approach

Myoblast transplantation (MT) is an experimental strategy for the potential treatment of myopathies. MT has two properties that make it potentially beneficial: genetic complementation and myogenic potential. Preclinical experiments on monkeys have shown that promising results can be obtained with MT in large muscles of primates depending on two conditions: appropriate immunosuppression and cell delivery by a method of high-density injections. Preclinical work on MT is being, or may be, addressed to: develop efficient methods of donor cell delivery applicable to clinics; control or avoid acute rejection by methods with the fewest secondary effects; understand the factors that condition the early survival of donor cells following transplantation; increase the success of each individual injection; re-engineer a functional structure in muscles that degenerates to fibrosis and fat substitution; and search for precursor cells with potential advantages over myoblasts.

Clonal analysis of the differentiation potential of human adipose-derived adult stem cells

Pools of human adipose-derived adult stem (hADAS) cells can exhibit multiple differentiated phenotypes under appropriate in vitro culture conditions. Because adipose tissue is abundant and easily accessible, hADAS cells offer a promising source of cells for tissue engineering and other cell-based therapies. However, it is unclear whether individual hADAS cells can give rise to multiple differentiated phenotypes or whether each phenotype arises from a subset of committed progenitor cells that exists within a heterogeneous population. The goal of this study was to test the hypothesis that single hADAS are multipotent at a clonal level. hADAS cells were isolated from liposuction waste, and ring cloning was performed to select cells derived from a single progenitor cell. Forty-five clones were expanded through four passages and then induced for adipogenesis, osteogenesis, chondrogenesis, and neurogenesis using lineage-specific differentiation media. Quantitative differentiation criteria for each lineage were determined using histological and biochemical analyses. Eighty one percent of the hADAS cell clones differentiated into at least one of the lineages. In addition, 52% of the hADAS cell clones differentiated into two or more of the lineages. More clones expressed phenotypes of osteoblasts (48%), chondrocytes (43%), and neuron-like cells (52%) than of adipocytes (12%), possibly due to the loss of adipogenic ability after repeated subcultures. The findings are consistent with the hypothesis that hADAS cells are a type of multipotent adult stem cell and not solely a mixed population of unipotent progenitor cells. However, it is important to exercise caution in interpreting these results until they are validated using functional in vivo assays.

Stem cells isolated from adult rat muscle differentiate across all three dermal lineages

Adult stem cells capable of differentiating into phenotypes from all three dermal layers were isolated from adult rat muscle. Stem cells were obtained by enzymatic digestion, followed by primary culture in Eagle's minimum essential medium +10% preselected horse serum. When the cells reached confluence, they were released by trypsin, filtered to remove differentiated myotubes, and then slow frozen in 7.5% dimethylsulfoxide to -80 degrees C. Thawed cells were the stem cells and were induced to differentiate with the nonspecific differentiating agent dexamethasone at concentrations of 10(-10)-10(-6) M. After a 6-week treatment with dexamethasone, the cells were assayed by immunohistochemistry for phenotypes of the mesodermal, ectodermal, and endodermal lineages. Examples of mesodermal phenotypes identified were as follows: bone, cartilage, and skeletal, smooth, and cardiac muscle. Ectodermal phenotypes identified were as follows: neurons and oligodendrocytes. Hepatocyte phenotypes identified represented the endodermal lineage. All the phenotypes were observed only with treatment with dexamethasone. However, nestin was observed in the absence of dexamethasone and may be a marker for uncommitted pluripotent stem cells. The results show that adult muscle contains pluripotent stem cells capable of differentiating across all three dermal lineages. Such cells could be used in the context of tissue engineering.

Immortalized cell lines from mouse xiphisternum preserve chondrocyte phenotype

Chondrocytes are unique to cartilage and the study of these cells in vitro is important for advancing our understanding of the role of these cells in normal homeostasis and disease including osteoarthritis (OA). As there are limitations to the culture of primary chondrocytes, cell lines have been developed to overcome some of these obstacles. In this study, we developed a procedure to immortalize and characterize chondrocyte cell lines from mouse xiphisternum. The cells displayed a polygonal to fibroblastic morphology in monolayer culture. Gene expression studies using quantitative PCR showed that the cell lines responded to bone morphogenetic protein 2 (BMP-2) by increased expression of matrix molecules, aggrecan, and type II collagen together with transcriptional factor, Sox9. Stimulation by IL-1 results in the increased expression of catabolic effectors including MMP-13, nitric oxide synthase, ADAMTS4, and ADAMTS5. Cells cultured in alginate responded to BMP-2 by increased synthesis of proteoglycan (PG), a major matrix molecule of cartilage. IL-1 treatment of cells in alginate results in increased release of PG into the conditioned media. Further analysis of the media showed the presence of Aggrecanase-cleaved aggrecan fragments, a signature of matrix degradation. These results show that the xiphisternum chondrocyte cell lines preserve their chondrocyte phenotype cultured in either monolayer or 3-dimensional alginate bead culture systems. In summary, this study describes the establishment of chondrocyte cell lines from the mouse xiphisternum that may be useful as a surrogate model system to understand chondrocyte biology and to shed light on the underlying mechanism of pathogenesis in OA.