A quadripotential mesenchymal progenitor cell isolated from the marrow of an adult mouse

Bone marrow microenvironment and tumor progression

The bone marrow constitutes an unique microenvironment for cancer cells in three specific aspects. First, the bone marrow actively recruits circulating tumor cells where they find a sanctuary rich in growth factors and cytokines that promote their proliferation and survival. When in the bone marrow, tumor cells profoundly affect the homeostasis of the bone and the balance between osteogenesis and osteolysis. As a consequence, growth and survival factors normally sequestered into the bone matrix are released, further fueling cancer progression. Second, tumor cells actively recruit bone marrow-derived precursor cells into their own microenvironment. When in the tumors, these bone marrow-derived cells contribute to an inflammatory reaction and to the formation of the tumor vasculature. Third, bone marrow-derived cells can home in distant organs, where they form niches that attract circulating tumor cells. Our understanding of the contribution of the bone marrow microenvironment to cancer progression has therefore dramatically improved over the last few years. The importance of this new knowledge cannot be underestimated considering that the vast majority of cancer treatments such as cytotoxic and myeloablative chemotherapy, bone marrow transplantation and radiation therapy inflict a trauma to the bone marrow microenvironment. How such trauma affects the influence that the bone marrow microenvironment exerts on cancer is still poorly understood. In this article, the reciprocal relationship between the bone marrow microenvironment and tumor cells is reviewed, and its potential impact on cancer therapy is discussed.

Partial recovery of dopaminergic pathway after graft of adult mesenchymal stem cells in a rat model of Parkinson's disease

Cellular therapy with adult stem cells appears as an opportunity for treatment of Parkinson's disease. To validate this approach, we studied the effects of transplantation of rat adult bone-marrow mesenchymal stem cells in a rat model of Parkinson's disease. Animals were unilaterally lesioned in the striatum with 6-hydroxydopamine. Two weeks later, group I did not undergo grafting, group II underwent sham grafting, group III was intra-striatal grafted with cells cultured in an enriched medium and group IV was intra-striatal grafted with cells cultured in a standard medium. Rotational amphetamine-induced behavior was measured weekly until animals were killed 6 weeks later. One week after graft, the number of rotations/min was stably decreased by 50% in groups III and IV as compared with groups I and II. At 8 weeks post-lesion, the density of dopaminergic markers in the nerve terminals and cell bodies, i.e. immunoreactive tyrosine hydroxylase, membrane dopamine transporter and vesicular monoamine transporter-2 was significantly higher in group III as compared with group I. Moreover, using microdialysis studies, we observed that while the rate of pharmacologically induced release of dopamine was significantly reduced in lesioned versus intact striatum in no grafted rats, it was similar in both sides in animals transplanted with mesemchymal stem cells. These data demonstrate that graft of adult mesemchymal stem cells reduces behavioral effects induced by 6-hydroxydopamine lesion and partially restores the dopaminergic markers and vesicular striatal pool of dopamine. This cellular approach might be a restorative therapy in Parkinson's disease.

Murine bone marrow derived stromal progenitor cells fail to prevent or treat acute graft-versus-host disease

Human and murine stromal progenitor cells (SPCs) can suppress alloresponse in vitro, suggesting that SPCs may have clinical application toward prevention or treatment of graft-versus-host disease (GVHD). However, th eresults of in vivo studies have been conflicting. This study utilized an established murine model of acute GVHD to assess the ability of bone marrow derived murine SPCs (mSPCs) to prevent or treat GVHD. GVHD was established by transplantation of B6 bone marrow and spleen cells into lethally irradiated (900 cGy) B6 x BALB/c F(1) recipients. mSPCs were administered using various dose and timing protocols designed to either prevent or treat GVHD. After transplantation, mice were monitored daily for weight and survival. Differences in symptom severity were compared using a clinical GVHD scoring system. All GVHD control mice died of lethal GVHD. All groups treated with mSPCs for the prevention of GVHD went on to develop clinical GVHD with no alteration of the disease course or severity compared to controls. Administration of mSPC after the development of GVHD failed to improve the disease course. We conclude that in this model, the ability of SPCs to suppress alloresponse in vitro does not correlate with in vivo prevention or treatment of acute GVHD.

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro, MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro. On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.

Flexible and dynamic organization of bone marrow stromal compartment

The bone marrow mesenchymal compartment contains putative stem/progenitors of skeletal tissue components such as bone, cartilage, haematopoiesis-supporting stroma and adipocytes. Previously appreciated as vital to the support of haematopoiesis, these cells have also been recently recognized as having significant immunomodulatory properties with implications for allogeneic haematopoietic cell transplantation. Despite having been studied for more than three decades and currently being used in different clinical settings, their biology remains elusive. The aim of this review is to critically analyse the field of mesenchymal stem/progenitor cell biology, in respect of their relationship with other mesenchymal cell-types. Several issues concerning lineage commitment and inter-conversion potential between different mesenchymal cell-types are reviewed.

Bone tissue engineering using human adipose-derived stem cells and honeycomb collagen scaffold

Human adipose-derived stem cells (ASCs) have the capacity to regenerate and the potential to differentiate into multiple lineages of mesenchymal cells. The aim of this study was to investigate the possibility of using honeycomb collagen scaffold to culture ASCs in bone tissue engineering. The osteogenic capacity of ASCs in vitro, was confirmed by histology and measuring the expression of cbfa-1. After that, ASCs were cultured for up to 14 days in the honeycomb scaffold to allow a high density, three-dimensional culture. Scanning electron microscopy data showed that the scaffold was filled with the grown ASCs, and calcification, stained black with von Kossa, was confirmed. Furthermore, The ASC-loaded honeycomb collagen scaffolds cultured for 14 days were subcutaneously transplanted into nude mice, and excised after 8 weeks. Bone formation in vivo was examined using HE stain, von Kossa stain, and osteocalcin immunostain. Those histological views showed significant positive stains in the samples of osteogenic medium in the three types of stain. These results suggest that this carrier is a suitable scaffold for ASCs and will be useful as a three-dimensional bone tissue engineering scaffold in vitro and in vivo.

Concise review: MicroRNA expression in multipotent mesenchymal stromal cells

Mesenchymal stem cells, or multipotent mesenchymal stromal cells (MSC), isolated from various adult tissue sources have the capacities to self-renew and to differentiate into multiple lineages. Both of these processes are tightly regulated by genetic and epigenetic mechanisms. Emerging evidence indicates that the class of single-stranded noncoding RNAs known as microRNAs also plays a critical role in this process. First described in nematodes and plants, microRNAs have been shown to modulate major regulatory mechanisms in eukaryotic cells involved in a broad array of cellular functions. Studies with various types of embryonic as well as adult stem cells indicate an intricate network of microRNAs regulating key transcription factors and other genes, which in turn determine cell fate. In addition, expression of unique microRNAs in specific cell types serves as a useful diagnostic marker to define a particular cell type. MicroRNAs are also found to be regulated by extracellular signaling pathways that are important for differentiation into specific tissues, suggesting that they play a role in specifying tissue identity. In this review, we describe the importance of microRNAs in stem cells, focusing on our current understanding of microRNAs in MSC and their derivatives.

Functional structure of adipocytes differentiated from human umbilical cord stroma-derived stem cells

It has been previously demonstrated that human umbilical cord stroma-derived stem cells (HUCSCs) are competent to differentiate into adipocytes. However, controversies have arisen as to whether HUCSCs can become mature adipocytes or not, and to what extent these cells can be induced in adipogenic pathway. Here, we extensively analyzed their adipogenic potency with a structural and functional approach by determining lipid formation dynamics in concordance to adipocyte-specific markers. During a 35-day period, HUCSCs respond to adipogenic induction, at which point 88% of cells exhibited multilocular lipid granules (LGs) having a mean diameter of 3 mum in round-shaped, F-actin-poor cells. Although the 1st week of induction did not generally display typical lipidogenic phenotypes, the degree of adipogenesis was dissected and confirmed by mRNA expressions of peroxisome proliferator-activated receptor gamma, C/EBP-beta, sterol regulatory element-binding transcription factor 1, adipophilin, stearoyl-CoA desaturase, glycerol 3-phosphate dehydrogenase 1, LIPE, adiponectin, and leptin. All markers tested were found elevated in various amounts (3-70-fold) around day 7 and reached a plateau after day 14 or 21 (5-335-fold). Perilipin as a surface protein around the LGs was confined exclusively to the enlarging LGs. Conclusively, we propose that after the termination of proliferation, HUCSCs possess the biochemical and cellular machinery to successfully differentiate into maturing adipocytes under adipogenic conditions, and this feature will ultimately allow these fetus-derived stem cells to be used for various therapeutic or esthetic purposes.

Isolation of mesenchymal stem cells from murine bone marrow by immunodepletion

Mesenchymal stem cells are typically enriched from bone marrow via their preferential attachment to tissue culture plastic. However, this isolation method has proven ineffective for murine MSCs because various hematopoietic cell lineages survive and/or proliferate on stromal layers in the absence of exogenous cytokines and therefore constitute a large percentage of the plastic adherent population. Although various methods have been described to remove contaminating hematopoietic populations from these cultures none have gained widespread acceptance. Consequently, we developed a method based on immunodepletion to fractionate hematopoietic and endothelial lineages from plastic adherent fibroblastoid (stromal) cells elaborated from murine bone marrow. Colony-forming assays, immunostaining and flow cytometry has been used to validate the effectiveness of this method. Moreover, immunodepleted populations have been shown to exhibit the capacity for multilineage differentiation in vitro and in vivo and therefore retain the characteristics of MSCs. Most recently, we also catalogued the transcriptome of immunodepleted populations via serial analysis of gene expression. Therefore, our immunodepletion scheme provides a means to enrich from murine bone marrow MSCs that's molecular and biological characteristics are well described. Importantly, this immunodepletion method does not employ long-term expansion of plastic adherent cells ex vivo, thereby avoiding the generation of immortalized cell lines.

Mesenchymal stem cells from adult bone marrow

Mesenchymal stem cells (MSCs), sometimes referred to as marrow stromal cells or multipotential stromal cells, represent a class of adult progenitor cells capable of differentiation to several mesenchymal lineages. They can be isolated from many tissues although bone marrow has been used most often. The MSCs may prove useful for repair and regeneration of a variety of mesenchymal tissues such as bone, cartilage, muscle, marrow stroma, and the cells produce useful growth factors and cytokines that may help repair additional tissues. There is also evidence for their differentiation to nonmesenchymal lineages, but that work will not be considered here. This chapter will provide the researcher with some background, and then provide details on MSC isolation, expansion and multilineage differentiation. These are the beginning steps toward formulating tissue repair strategies. The methods provided here have been used in many laboratories around the world and the reader can begin by following the methods presented here, and then test other methods if these prove unsatisfactory for your intended purpose.

Wharton's jelly-derived cells are a primitive stromal cell population

Here, the literature was reviewed to evaluate whether a population of mesenchymal stromal cells derived from Wharton's jelly cells (WJCs) is a primitive stromal population. A clear case can be made for WJCs as a stromal population since they display the characteristics of MSCs as defined by the International Society for Cellular Therapy; for example, they grow as adherent cells with mesenchymal morphology, they are self-renewing, they express cell surface markers displayed by MSCs, and they may be differentiated into bone, cartilage, adipose, muscle, and neural cells. Like other stromal cells, WJCs support the expansion of other stem cells, such as hematopoietic stem cells, are well-tolerated by the immune system, and they have the ability to home to tumors. In contrast to bone marrow MSCs, WJCs have greater expansion capability, faster growth in vitro, and may synthesize different cytokines. WJCs are therapeutic in several different pre-clinical animal models of human disease such as neurodegenerative disease, cancer, heart disease, etc. The preclinical work suggests that the WJCs are therapeutic via trophic rescue and immune modulation. In summary, WJCs meet the definition of MSCs. Since WJCs expand faster and to a greater extent than adult-derived MSCs, these findings suggest that WJCs are a primitive stromal cell population with therapeutic potential. Further work is needed to determine whether WJCs engraft long-term and display self-renewal and multipotency in vivo and, as such, demonstrate whether Wharton's jelly cells are a true stem cell population.

Identification of mesenchymal stem cells in aorta-gonad-mesonephros and yolk sac of human embryos

Mesenchymal stem cells (MSCs) are multipotent stem cells that can generate various microenvironment components in bone marrow, ensuring a precise control over self-renewal and multilineage differentiation of hematopoietic stem cells. Nevertheless, their spatiotemporal correlation with embryonic hematopoiesis remains rudimentary, particularly in relation to the human being. Here, we reported that human aorta-gonad-mesonephros (AGM) resided with bona fide MSCs. They were highly proliferative as fibroblastoid population bearing uniform surface markers (CD45(-), CD34(-), CD105(+), CD73(+), CD29(+), and CD44(+)), expressed pluripotential molecules Oct-4 and Nanog, and clonally demonstrated trilineage differentiation capacity (osteocytes, chondrocytes, and adipocytes). The frequency and absolute number of MSCs in aorta plus surrounding mesenchyme (E26-E27) were 0.3% and 164, respectively. Moreover, they were functionally equivalent to MSCs from adult bone marrow, that is, supporting long-term hematopoiesis and suppressing T-lymphocyte proliferation in vitro. In comparison, the matching yolk sac contained bipotent mesenchymal precursors that propagated more slowly and failed to generate chondrocytes in vitro. Together with previous knowledge, we propose that a proportion of MSCs initially develop in human AGM prior to their emergence in embryonic circulation and fetal liver.

Gene targeting of mutant COL1A2 alleles in mesenchymal stem cells from individuals with osteogenesis imperfecta

Mesenchymal stem cells (MSCs) are adult cells with the capacity to differentiate into multiple cell types, including bone, fat, cartilage, and muscle cells. In order to effectively utilize autologous MSCs in cell-based therapies, precise genetic manipulations are required to eliminate the effects of disease-causing mutations. We previously used adeno-associated virus (AAV) vectors to target and inactivate mutant COL1A1 genes in MSCs from individuals with the brittle bone disorder, osteogenesis imperfecta (OI). Here we have used AAV vectors to inactivate mutant COL1A2 genes in OI MSCs, thereby demonstrating that both type I collagen genes responsible for OI can be successfully targeted. We incorporated improved vector designs so as to minimize the consequences of random integration, facilitate the removal of potential antigens, and avoid unwanted exon skipping. MSCs targeted at mutant COL1A2 alleles produced normal type I procollagen and formed bone, thereby demonstrating their therapeutic potential.

Stem cells for tissue engineering of articular cartilage

Articular cartilage injuries are one of the most common disorders in the musculo-skeletal system. Injured cartilage tissue cannot spontaneously heal and, if not treated, can lead to osteoarthritis of the affected joints. Although a variety of procedures are being employed to repair cartilage damage, methods that result in consistent durable repair tissue are not yet available. Tissue engineering is a recently developed science that merges the fields of cell biology, engineering, material science, and surgery to regenerate new functional tissue. Three critical components in tissue engineering of cartilage are as follows: first, sufficient cell numbers within the defect, such as chondrocytes or multipotent stem cells capable of differentiating into chondrocytes; second, access to growth and differentiation factors that modulate these cells to differentiate through the chondrogenic lineage; third, a cell carrier or matrix that fills the defect, delivers the appropriate cells, and supports cell proliferation and differentiation. Stem cells that exist in the embyro or in adult somatic tissues are able to renew themselves through cell division without changing their phenotype and are able to differentiate into multiple lineages including the chondrogenic lineage under certain physiological or experimental conditions. Here the application of stem cells as a cell source for cartilage tissue engineering is reviewed.

Age- and dose-related effects on MSC engraftment levels and anatomical distribution in the central nervous systems of nonhuman primates: identification of novel MSC subpopulations that respond to guidance cues in brain

Mesenchymal stem cells (MSCs) have demonstrated efficacy as therapeutic vectors in rodent models of neurological diseases, but few studies have evaluated their safety and efficacy in a relevant large animal model. Previously, we reported that MSCs transplanted to the central nervous systems (CNS) of adult rhesus macaques engrafted at low levels without adversely affecting animal health, behavior, or motor function. Herein, we injected MSCs intracranially into 10 healthy infant macaques and quantified their engraftment levels and mapped their anatomical distribution in brain by real-time polymerase chain reaction using an sry gene-specific probe. These analyses revealed that MSC engraftment levels in brain were on average 18-fold higher with a maximal observed difference of 180-fold in neonates as compared with that reported previously for young adult macaques. Moreover, engraftment levels were 30-fold higher after injection of a low versus high cell dose and engrafted MSCs were nonrandomly distributed throughout the infant brain and localized to specific anatomical regions. Identification of unique subpopulations of macaque and human MSCs that express receptor proteins known to regulate tangential migration of interneurons may explain their migration patterns in brain. Extensive monitoring of infant transplant recipients using a battery of age appropriate tests found no evidence of any long-term adverse effects on the health or social, behavioral, cognitive, or motor abilities of animals up to 6 months post-transplant. Therefore, direct intracranial injection represents a safe means to deliver therapeutic levels of MSCs to the CNS. Moreover, expressed guidance receptors on MSC subpopulations may regulate migration of cells in the host brain. Disclosure of potential conflicts of interest is found at the end of this article.

Characterization of ScAP-23, a new cell line from murine subcutaneous adipose tissue, identifies genes for the molecular definition of preadipocytes

The 3T3-L1 model of in vitro adipogenesis has provided key insights into the molecular nature of this process. However, given that 3T3-L1 are of an embryonic origin, it is not clear to what extent they represent adipogenesis as it occurs in white adipose tissue (WAT). With the goal of better defining preadipocytes and adipogenesis in WAT, we have generated a new cell culture model from adipocyte precursors present in C57BL/6 mouse subcutaneous WAT. ScAP-23 preadipocytes show fibroblastic morphology, and on treatment with dexamethasone, 3-methylisobutylxanthine, insulin, and indomethacin, convert to nearly 100% adipocyte morphology. ScAP-23 adipocytes contain abundant lipid droplets and express transcripts for PPARγ, C/EBP family, and SREBP-1c transcription factors, SCD1, aFABP, ATGL, GLUT4, FAS, LDL, and GPDH, and are insulin responsive. Differential screening of 1,176 genes using nylon DNA arrays identified 10 transcripts enriched in ScAP-23 adipocytes vs. preadipocytes and 26 transcripts enriched in ScAP-23 preadipocytes vs. adipocytes. Semiquantitative or real-time PCR analyses identified a common cohort of 14 transcripts markedly downregulated in both ScAP-23 and 3T3-L1 adipogenesis. These included catenin-β1, chemokine ligand-2, serine or cysteine peptidase inhibitor f1, aurora kinase B, thrombospondin2, and solute carrier-7a5. Five of these transcripts (Ccl2, Serpinf1, Aurkb, Thbs2, and Slc7a5) demonstrated at least a twofold increase in WAT from obese ( ob/ob) mice compared with that of wild-type mice. This suggests that comparative gene expression studies of ScAP-23 and 3T3-L1 adipogenesis may be particularly fruitful in identifying preadipocyte-expressed genes that play a role in adipose tissue physiology and/or pathophysiology.

Clinical-Scale Expansion of a Mixed Population of Bone Marrow-Derived Stem and Progenitor Cells for Potential Use in Bone Tissue Regeneration

Preclinical and clinical studies have demonstrated the ability of bone marrow derived stem and progenitor cells to regenerate many tissues, including bone. Methods to expand or enrich progenitors from bone marrow are common; however, these methods include many steps not amenable to clinical use. A closed automated cell production culture system was developed for clinical-scale ex vivo production of bone marrow-derived stem and progenitor cells for hematopoietic reconstitution. The current study tested the ability of this bioreactor system to produce progenitor cells, termed tissue repair cells (TRC), possessing osteogenic potential. Three TRC formulations were evaluated: (a) cells cultured without exogenous cytokines (TRC); (b) cells cultured with exogenous cytokines (TRC-C); and (c) an adherent subset of TRC-C (TRC-C(Ad)). Starting human bone marrow mononuclear cells (BM MNC) and TRC products were characterized for the expression of cell surface markers, in vitro colony forming ability, and in vivo osteogenic potential. Results showed significant expansion of mesenchymal progenitors (CD90+, CD105+, and CD166+) in each TRC formulation. In vivo bone formation, measured by histology, was highest in the TRC group, followed by TRC-C(Ad) and TRC-C. The TRC product outperformed starting BM MNC and had equivalent bone forming potential to purified MSCs at the same cell dose. Post hoc analysis revealed that the presence of CD90+, CD105+, and CD166+ correlated strongly with in vivo bone formation scores (r(2) > .95). These results demonstrate that this bioreactor system can be used to generate, in a single step, a population of progenitor cells with potent osteogenic potential. Disclosure of potential conflicts of interest is found at the end of this article.

Concise review: mesenchymal stem/multipotent stromal cells: the state of transdifferentiation and modes of tissue repair--current views

Mesenchymal stem cells or multipotent stromal cells (MSCs) isolated from the bone marrow of adult organisms were initially characterized as plastic adherent, fibroblastoid cells with the capacity to generate heterotopic osseous tissue when transplanted in vivo. In recent years, MSCs or MSC-like cells have been shown to reside within the connective tissue of most organs, and their surface phenotype has been well described. A large number of reports have also indicated that the cells possess the capacity to transdifferentiate into epithelial cells and lineages derived from the neuroectoderm. The broad developmental plasticity of MSCs was originally thought to contribute to their demonstrated efficacy in a wide variety of experimental animal models of disease as well as in human clinical trials. However, new findings suggest that the ability of MSCs to alter the tissue microenvironment via secretion of soluble factors may contribute more significantly than their capacity for transdifferentiation in tissue repair. Herein, we critically evaluate the literature describing the plasticity of MSCs and offer insight into how the molecular and functional heterogeneity of this cell population, which reflects the complexity of marrow stroma as an organ system, may confound interpretation of their transdifferentiation potential. Additionally, we argue that this heterogeneity also provides a basis for the broad therapeutic efficacy of MSCs.

Hyperglycemia enhances adipogenic induction of lipid accumulation: involvement of extracellular signal-regulated protein kinase 1/2, phosphoinositide 3-kinase/Akt, and peroxisome proliferator-activated receptor gamma signaling

The molecular events of hyperglycemia-triggered increase in adipogenic induction of lipid accumulation remain unclear. We examined the effects of hyperglycemia on adipogenic induction of lipid accumulation and its involved signaling molecules, such as phosphoinositide 3-kinase (PI3K), ERKs, and peroxisome proliferator-activated receptor gamma (PPAR gamma). Bone marrow-derived mesenchymal stem cells (MSCs) isolated from FVB/N mice were capable of differentiating into adipocytes in adipogenic medium. The effects of high glucose (HG) (25.5 mm) were assessed in vitro by RT-PCR, ELISA, flow cytometry, immunostaining, and immunoblotting. The in vivo effect of hyperglycemia was further studied in streptozotocin (STZ)-induced diabetic FVB/N mice. Exposure of MSCs to HG enhanced adipogenic induction of lipid accumulation as compared with 5.5 mm glucose. HG increased PPAR gamma expression and PI3K activity and its downstream effector Akt phosphorylation during adipogenesis. Inhibition of PI3K/Akt activity with PI3K inhibitor LY294002 or by expressing the dominant negative p85 or Akt prevented the HG-enhanced PPAR gamma-dependent adipogenic induction of lipid accumulation. Moreover, HG increased the phosphorylation of ERK1/2 during adipogenesis. MAPK/ERK inhibitor PD98059 inhibited the PI3K activity, Akt phosphorylation, and lipid accumulation triggered by HG. PI3K inhibitor LY294002 did not affect the HG-increased ERK1/2 phosphorylation during adipogenesis. We next observed that adipogenic induction of lipid accumulation of MSCs isolated from STZ-induced diabetic mice is enhanced. Moreover, triglyceride, PPAR gamma expression, phosphorylated Akt and ERK1/2, and marrow fat in bones of STZ-diabetic mice were also increased. These results suggest that hyperglycemia enhances the adipogenic induction of lipid accumulation through an ERK1/2-activated PI3K/Akt-regulated PPAR gamma pathway.

The therapeutic potential of mesenchymal stem cells. Cell- & tissue-based therapy

Mesenchymal stem cells (MSCs) are multipotent cells with a number of potential therapeutic applications. At present, they are being used in a clinical trial for the treatment of myocardial infarction and are being studied as a therapy for other vascular disorders. Treatments of neurologic disorders and anticancer therapy with MSCs have progressed in light of the migratory properties of MSCs to brain injury and tumors. The osteogenic potential of MSCs is being exploited in work investigating their use in bone regeneration therapy, and the immunomodulatory function of MSCs is being evaluated as a possible therapy for graft-versus-host disease. Here, the authors review recent work contributing to the knowledge of MSC biology and the advances in gene therapy and tissue regeneration using MSCs.

Myogenesis in hemopoietic tissue mesenchymal stem cell culture

The myogenic differentiation capacity of prenatal mesenchymal stem cells from the main sites of hemopoiesis (bone marrow, thymus, liver, and spleen) was studied. Myogenesis was observed in all studied cell cultures except splenic mesenchymal stem cells. Differentiating cells from the thymus, bone marrow, and liver were positively stained for skeletal muscle markers (myogenin and MyoD). Autonomously contracting structures positively stained for cardiotroponin I and slow muscle myosin, were detected in the same cultures. Our experiments revealed differences in differentiation of mesenchymal stem cells from hemopoietic organs depending on the source of cells.

Reduced chondrogenic potential of adipose tissue derived stromal cells correlates with an altered TGFbeta receptor and BMP profile and is overcome by BMP-6

Recent interest has focused on mesenchymal stem cells (MSC) for tissue engineering and regenerative therapy of cartilage defects. MSC originating from adipose tissue (ATSC) are attractive as they are easily available and abundant. They have similar properties like bone marrow derived MSC (BMSC), except for a reduced chondrogenic potential under standard culture conditions driven by TGFbeta. Aim of this study was to search for possible differences explaining the reduced differentiation capacity of ATSC and to eliminate it by adaptation of induction protocols. Expanded MSC were analyzed for their growth factor and related receptor repertoire and ATSC spheroid cultures were supplemented with BMP-2,-4,-6,-7, TGFbeta, FGFa, FGFb, IGF-1, and PTHrP alone or in combination with TGFbeta. In contrast to BMSC, ATSC showed reduced expression of BMP-2, -4, and -6 mRNA and did not express TGFbeta-receptor-I protein. Consistent with this, increased concentrations of TGFbeta did not improve chondrogenesis of ATSC. BMP6 treatment induced TGFbeta-receptor-I expression and combined application of TGFbeta and BMP-6 eliminated the reduced chondrogenic potential of ATSC inducing a gene expression profile similar to differentiated BMSC. Like in BMSC, chondrogenesis of ATSC was associated with hypertrophy according to premature collagen Type X expression, upregulation of alkaline-phosphatase activity and in vivo calcification of spheroids after ectopic transplantation in SCID mice. In conclusion, a distinct BMP and TGFbeta-receptor repertoire may explain the reduced chondrogenic capacity of ATSC in vitro, which could be compensated by exogenous application of lacking factors. Further studies should now be directed to induce chondrogenesis in the absence of hypertrophy.

The concept of mesenchymal stem cells

In this chapter we examine whether criteria usually defining adult tissue stem cells apply to mesenchymal stem cells (MSCs) that give rise to cells of the skeletal connective tissues. MSCs appear to constitute a heterogeneous population of undifferentiated and committed, lineage-primed cells, capable of: homing upon engraftment to a number of growth microenvironments, extensive proliferation, producing large numbers of differentiated progeny, and functional tissue repair after injury. In addition, MSCs are extensively distributed throughout tissues, and bone marrow MSCs provide the stromal component of the niche of hematopoietic stem cells. The capacity of apparently differentiated mesenchymal cells to shift their differentiation pathway with changing microenvironmental conditions (known as differentiation plasticity) may be due to de-differentiation and reprogramming in MSCs. Because they present several features setting them apart from other stem cells, MSCs may constitute another paradigm for stem cell systems, where self-renewal and hierarchy are no longer essential, but where plasticity is the major characteristic.

Osteogenic differentiation of human marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) are adherent cells that differentiate into chondroblasts, osteoblasts and adipocytes. In this short review, we summarize the molecular mechanisms that are known to control osteoblast differentiation and osteogenic potential of MSCs in vitro. We discuss the advances made in gene-based therapy to promote osteogenic differentiation of MSCs and the perspectives for an optimal use of MSCs for bone tissue regeneration or repair. One important challenge at the present time is to identify factors and pathways that promote osteogenic commitment of MSCs in order to use MSCs with functional potential for optimal bone repair in humans. In this context, genomic and proteomic analyses may help to identify molecules that could be used to promote osteogenic differentiation of human MSCs. In the future this may lead to selective therapeutic strategies for tissue engineering application in bone regeneration and repair in humans.

Tigogenin inhibits adipocytic differentiation and induces osteoblastic differentiation in mouse bone marrow stromal cells

We investigated the effect of tigogenin on adipocytic and osteoblastic differentiation in mouse bone marrow stromal cells (BMSCs). Tigogenin enhanced the proliferation of BMSCs significantly. Tigogenin treatment reduced the adipogenic induction of lipid accumulation, visfatin secretion, and the expressions of peroxisome proliferation-activated receptor (PPAR)gamma2 and adipocyte fatty acid-binding protein (ap)2. Moreover, tigogenin had no effect on the mitotic clonal expansion. On the other hand, tigogenin significantly elevated alkaline phosphatase (ALP) activity and the expressions of Cbfa1, collagen type I (COL I) and osteocalcin (OCN), as well as the content of matrix calcium in BMSCs. Further, SB-203580 antagonized the tigogenin-promoted osteogenesis. These observations suggested that tigogenin may modulate differentiation of BMSCs to cause a lineage shift away from the adipocytes and toward the osteoblasts, which is at least mediated by inhibition of PPARgamma and via p38 MAPK pathway, and is a potential drug preventing the development of osteoporosis and the related disorders.

Growth and differentiation factor-5 (GDF-5) stimulates osteogenic differentiation and increases vascular endothelial growth factor (VEGF) levels in fat-derived stromal cells in vitro

Fat-derived adult mesenchymal stem cells can differentiate into different phenotypes reflecting their potential to regenerate various skeletal tissues. These properties together with the association of adipose with skeletal tissues formed the basis of our study to establish an experimental model for using fat-derived stromal cells to undergo osteogenic differentiation in vitro under the influence of either growth and differentiation factor-5 (GDF-5) or bone morphogenetic protein-2 (BMP-2). Members of the BMP/GDF family of proteins are known for their ability to elicit skeletal morphogenesis, but little is known about the mechanism whereby these morphogens exert their effect on the osteogenic differentiation of fat-derived stromal cells. We compared the effects of GDF-5 and BMP-2 in their recombinant forms to qualitatively and quantitatively determine their influence on the osteogenic differentiation of fat derived stromal cells by examining the effects on mineralization, extracellular matrix, cell proliferation, biochemistry, and gene expression. We identified that GDF-5 not only promotes osteogenic differentiation of rat fat-derived stromal cells, but also may promote angiogenic activity of stromal cells by increasing vascular endothelial growth factor (VEGF) gene expression in vitro. These data suggest that several distinct regulatory mechanisms may exist in association with osteogenic differentiation.

Repair of full-thickness cartilage defects with cells of different origin in a rabbit model

PURPOSE

The purpose of this study was to evaluate the repaired tissues formed in full-thickness cartilage defects in a rabbit model implanted with 4 types of chondrogenic cells, including chondrocytes, mesenchymal stem cells (MSCs) and fibroblasts from rabbit, and human umbilical cord blood (hUCB) stem cells.

METHODS

Chondrocytes, MSCs, and fibroblasts were isolated from 6-week-old New Zealand rabbits; hUCB stem cells were isolated from the umbilical cord blood of newborn children. These 4 types of cells were cultured in vitro and embedded in polylactic acid (PLA) matrices. Full-thickness defects were produced in the femoral trochlear grooves of both knees in 36 adult New Zealand White rabbits. Cell/PLA composites were transplanted into cartilage defects. A total of 5 groups were formed according to implanted cell type: Group A, chondrocytes; Group B, MSCs; Group C, fibroblasts; Group D, hUCB stem cells; and Group E, no cells (control group). Repaired tissues were evaluated grossly, histologically, and immunohistochemically at 6 weeks and 12 weeks after implantation.

RESULTS

In Groups A and B, defects were repaired with hyaline-like cartilage. In Group C, defects were repaired with fibrous tissue. In Group D, defects were repaired primarily with fibrous tissue and scattered chondrocytes; in some specimens, defects were repaired with a thin layer of hyaline-like cartilage at 12 weeks. In Group E, defects were repaired with fibrous tissue. Histologic scores in Groups A and B were significantly higher than those in Groups C, D, and E at 6 and 12 weeks after transplantation.

CONCLUSIONS

Full-thickness cartilage defects treated with chondrocyte or MSC transplantation were repaired with hyaline-like cartilage tissue, and repair was significantly better than in tissues treated with fibroblasts and hUCB stem cells, as well as in the control group. Repaired tissues treated with MSCs appeared to have better cell arrangement, subchondral bone remodeling, and integration with surrounding cartilage than did repaired tissues generated by chondrocyte implantation. MSCs might be the most suitable cell source for cartilage repair. Further investigation into hUCB stem cell transplantation is needed.

CLINICAL RELEVANCE

In our study of rabbits, MSCs supplied the most promising cell source for cartilage repair.

Hematopoietic stem-cell contribution to ectopic skeletogenesis

BACKGROUND

Fibrodysplasia ossificans progressiva is a rare genetic disorder of ectopic skeletogenesis associated with dysregulation of bone morphogenetic protein (BMP) signaling. Hematopoietic cells have been implicated in the ectopic skeletogenesis of fibrodysplasia ossificans progressiva, and their replacement has been postulated as a possible cure. However, the definitive contribution of hematopoietic cells to the pathogenesis of ectopic skeletogenesis remains obscure.

METHODS

We employed both careful clinical observation and in vivo murine transplantation studies to more precisely determine the contribution of hematopoietic cells to ectopic skeletogenesis. We identified a patient with fibrodysplasia ossificans progressiva who had undergone bone marrow transplantation for the treatment of intercurrent aplastic anemia twenty-five years earlier and investigated whether the clinical course of the fibrodysplasia ossificans progressiva had been influenced by bone marrow replacement or immunosuppression, or both. In complementary studies, we transplanted hematopoietic stem cells from constitutively expressing LacZ transgenic mice to identify the contribution of hematopoietic cells to BMP4-induced heterotopic ossification, a histopathologic model of fibrodysplasia ossificans progressiva.

RESULTS

We found that replacement of hematopoietic cells was not sufficient to prevent ectopic skeletogenesis in the patient with fibrodysplasia ossificans progressiva but pharmacologic suppression of the apparently normal donor immune system following transplantation in the new host modulated the activity of the fibrodysplasia ossificans progressiva and diminished the expression of skeletal ectopia. In complementary murine transplantation studies, we found that cells of hematopoietic origin contributed to the early inflammatory and late marrow-repopulating stages of BMP4-induced heterotopic ossification but were not represented in the fibroproliferative, chondrogenic, or osteogenic stages of heterotopic ossification. Interestingly, both recombinant human BMP4 induction in an animal model and the dysregulated BMP signaling pathway in a patient with fibrodysplasia ossificans progressiva were sufficient to recruit at least two populations of cells, one of hematopoietic origin and at least one of non-hematopoietic origin, that contribute to the formation of an ectopic skeleton.

CONCLUSIONS

Taken together, these findings demonstrate that bone marrow transplantation did not cure fibrodysplasia ossificans progressiva in the patient in this study, most likely because the hematopoietic cell population is not the site, or at least not the dominant site, of the intrinsic dysregulation of the BMP signaling pathway in fibrodysplasia ossificans progressiva. However, following transplantation of bone marrow from a presumably normal donor, immunosuppression of the immune system appeared to ameliorate activation of ectopic skeletogenesis in a genetically susceptible host. Thus, cells of hematopoietic origin may contribute to the formation of an ectopic skeleton, although they are not sufficient to initiate the process alone.

Evaluation of machining methods for trabecular metal implants in a rabbit intramedullary osseointegration model

Implant success is dependent in part on the interaction of the implant with the surrounding tissues. Porous tantalum implants (Trabecular Metal, TM) have been shown to have excellent osseointegration. Machining this material to complex shapes with close tolerances is difficult because of its open structure and the ductile nature of metallic tantalum. Conventional machining results in occlusion of most of the surface porosity by the smearing of soft metal. This study compared TM samples finished by three processing techniques: conventional machining, electrical discharge machining, and nonmachined, "as-prepared." The TM samples were studied in a rabbit distal femoral intramedullary osseointegration model and in cell culture. We assessed the effects of these machining methods at 4, 8, and 12 weeks after implant placement. The finishing technique had a profound effect on the physical presentation of the implant interface: conventional machining reduced surface porosity to 30% compared to bulk porosities in the 70% range. Bone ongrowth was similar in all groups, while bone ingrowth was significantly greater in the nonmachined samples. The resulting mechanical properties of the bone implant-interface were similar in all three groups, with only interface stiffness and interface shear modulus being significantly higher in the machined samples.

Molecular profile of mouse stromal mesenchymal stem cells

We determined a transcriptional profile specific for clonal stromal mesenchymal stem cells from adult and fetal hematopoietic sites. To identify mesenchymal stem cell-like stromal cell lines, we evaluated the adipocytic, osteoblastic, chondrocytic, and vascular smooth muscle differentiation potential and also the hematopoietic supportive (stromal) capacity of six mouse stromal cell lines from adult bone marrow and day 14.5 fetal liver. We found that two lines were quadripotent and also supported hematopoiesis, BMC9 from bone marrow and AFT024 from fetal liver. We then ascertained the set of genes differentially expressed in the intersection set of AFT024 and BMC9 compared with those expressed in the union set of two negative control lines, 2018 and BFC012 (both from fetal liver); 346 genes were upregulated and 299 downregulated. Using Ingenuity software, we found two major gene networks with highly significant scores. One network contained downregulated genes that are known to be implicated in osteoblastic differentiation, proliferation, or transformation. The other network contained upregulated genes that belonged to two categories, cytoskeletal genes and genes implicated in the transcriptional machinery. The data extend the concept of stromal mesenchymal stem cells to clonal cell populations derived not only from bone marrow but also from fetal liver. The gene networks described should discriminate this cell type from other types of stem cells and help define the stem cell state.

Biology of stem cells in human umbilical cord stroma: in situ and in vitro surveys

Cells in the umbilical cord stroma have gained attention in recent years; however, differentiation to certain lineages in humans has been demonstrated in few studies. Unlike bone marrow MSCs, human umbilical cord stroma cells (HUCSCs) are far from being well characterized. This study attempts to describe proliferation, structural, and differentiation properties of these cells to account for their exceptional nature in many aspects. Cellular dynamics, cellular structure, and the degree of transformations during expansion and differentiation into mesenchymal and neuronal lineages were examined in vitro over a 10-month period. Comparisons with human bone marrow MSCs regarding differentiation were performed. HUCSCs in culture revealed two distinct cell populations, type 1 and type 2 cells, that possessed differential vimentin and cytokeratin filaments. Corresponding cells were encountered in cord sections displaying region-specific localization. alpha-Smooth muscle actin and desmin filaments, which were evident in cord sections, diminished through passages. No difference was noted regarding type 1 and type 2 cells in differentiation to chondrogenic, adipogenic, and osteogenic lineages, whereas a preferential differentiation was noted in neuronal lineage. Relative success was achieved by production of chondrocytic spheres and osteogenic monolayers, whereas adipocytes were immature compared with bone marrow MSCs. The presence of neuronal markers suggests that they transform into a certain state of maturity under neurogenic induction. Conclusively, HUCSCs retain their original phenotype in culture without spontaneous differentiation, have a limited lifespan, and bear multipotent stem cell characteristics. Given these characteristics, they may be generally considered progenitor cells if manipulated under appropriate conditions and deserve further study to be potentially used in cell-based therapies.

Mesenchymal stem cells as trophic mediators

Adult marrow-derived Mesenchymal Stem Cells (MSCs) are capable of dividing and their progeny are further capable of differentiating into one of several mesenchymal phenotypes such as osteoblasts, chondrocytes, myocytes, marrow stromal cells, tendon-ligament fibroblasts, and adipocytes. In addition, these MSCs secrete a variety of cytokines and growth factors that have both paracrine and autocrine activities. These secreted bioactive factors suppress the local immune system, inhibit fibrosis (scar formation) and apoptosis, enhance angiogenesis, and stimulate mitosis and differentiation of tissue-intrinsic reparative or stem cells. These effects, which are referred to as trophic effects, are distinct from the direct differentiation of MSCs into repair tissue. Several studies which tested the use of MSCs in models of infarct (injured heart), stroke (brain), or meniscus regeneration models are reviewed within the context of MSC-mediated trophic effects in tissue repair.

Murine mesenchymal stem cells transplanted to the central nervous system of neonatal versus adult mice exhibit distinct engraftment kinetics and express receptors that guide neuronal cell migration

Mesenchymal stem cells (MSCs) have demonstrated efficacy as cellular vectors for treating a variety of nervous system disorders. Nevertheless, few studies have quantified MSC engraftment levels or explored the mechanisms that promote their survival and migration in nervous tissue. In this study, we compared the engraftment kinetics and anatomical distribution of murine, male MSCs injected intracranially into neonatal versus adult female mice using a real-time PCR assay that targets the mouse SRY gene. These analyses revealed that MSCs exhibited low but equivalent engraftment levels in the central nervous system (CNS) of neonatal and adult transplant recipients at 12 days post-injection. However, MSC engraftment levels were significantly greater at 60 and 150 days post-transplantation in neonates as compared to adults. Despite these differences, engrafted MSCs were widely distributed along the neuraxis of the CNS in both transplant groups. Collectively, these data indicate that proliferation, but not engraftment and migration, of MSCs in brain are regulated by the host microenvironment. Using a genomics approach, we also identified MSC subpopulations that express neural adhesion proteins and receptors that regulate neuronal cell migration in brain, including cadherin 2, neurexin 1, ninjurin 1, neogenin 1, neuropilin 2, and roundabout homolog 1 and 4. Functional studies indicate these proteins confer cell adhesion and migration of MSCs in response to the appropriate chemoattractant. On the basis of these findings, we conclude that the unique molecular composition of MSC subpopulations imparts to them an inherent capacity to engraft and migrate in brain. These subpopulations may represent more potent cellular vectors for treating CNS disorders.

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.

Multipotential mesenchymal stem cells are mobilized into peripheral blood by hypoxia

MSCs constitute a population of multipotential cells giving rise to adipocytes, osteoblasts, chondrocytes, and vascular-smooth muscle-like hematopoietic supportive stromal cells. It remains unclear whether MSCs can be isolated from adult peripheral blood under stationary conditions and whether they can be mobilized in a way similar to hematopoietic stem cells. In this report, we show that MSCs are regularly observed in the circulating blood of rats and that the circulating MSC pool is consistently and dramatically increased (by almost 15-fold) when animals are exposed to chronic hypoxia. The immunophenotype and the adipocytic, osteoblastic, and chondrocytic differentiation potential of circulating MSCs were similar to those of bone marrow MSCs. Hypoxia-induced mobilization appears to be specific for MSCs since total circulating hematopoietic progenitor cells were not significantly increased. Our data provide an in vivo model amenable to analysis of MSC-mobilizing factors.

Characterizing medullary and human mesenchymal stem cell-derived adipocytes

Throughout postnatal years, medullary adipocytes (MAs) increase in both number and size; however, knowledge of these cells pales in comparison to that of other adipocyte depots. It is widely hypothesized that MAs derive from multipotent progenitor cells of the bone marrow, such as human mesenchymal stem cells (hMSCs). Nevertheless, there is a paucity of comparative, molecular-level studies in support of this hypothesis. In the present article, RTPCR was used to examine similarities and differences in gene expression among MAs, hMSC-derived adipocytes, and subcutaneous adipocytes. While little or no message for lineage-specific markers was detected in undifferentiated hMSCs, the data demonstrate that hMSC-derived adipocytes, MAs, and subcutaneous adipocytes commonly express mRNA encoding for adipogenic transcription factors (PPARgamma2, C/EBPalpha, and SREBP1), adipokines (adipsin, leptin, APM1, and angiotensinogen), and lipid-metabolizing agents (aP2 and LPL), among other genes. None of the cell populations examined expressed a detectable level of the brown fat marker UCP1. This suggests highly similar gene expression between human subcutaneous and MAs, not previously substantiated to this degree. Coupled with the hMSC-derived adipocyte analysis, these data provide a framework ultimately for characterizing MAs and identifying their origin and function.

Matricellular proteins: Extracellular modulators of bone development, remodeling, and regeneration

Matricellular proteins are components of the extracellular matrix which are highly expressed in the developing and mature skeleton. Members of this protein class serve as biological mediators of cell function by interacting directly with cells or by modulating the activity of growth factors, proteases, and other extracellular matrix proteins. Although skeletons of matricellular protein-null mice are grossly normal, they each display unique deficiencies that are often magnified under pathological conditions. In addition, bone cells from wild-type and matricellular protein-null mice behave differently in various in vitro models of bone matrix synthesis and turnover. In this review, osteopontin, bone sialoprotein, tenascin C, SPARC, and thrombospondins 1 and 2 will each be discussed in the context of bone cell biology. Because the biological effects of matricellular proteins are largely context dependent, in vivo and in vitro results must be considered together in order to fully appreciate the specific contributions that matricellular proteins make to bone physiology and pathophysiology. In particular, it is clear that although matricellular proteins are not required for bone development and function, the proteins act to modulate post-natal bone structure in response to aging, ovariectomy, mechanical loading, and bone regeneration.

Gene-mediated osteogenic differentiation of stem cells by bone morphogenetic proteins-2 or -6

Bone marrow-derived mesenchymal stem cells (BMDMSC) hold promise for targeted osteogenic differentiation and can be augmented by delivery of genes encoding bone morphogenetic proteins (BMP). The feasibility of promoting osteogenic differentiation of BMDMSC was investigated using two BMP genes in monolayer and three-dimensional alginate culture systems. Cultured BMDMSC were transduced with E1-deleted adenoviral vectors containing either human BMP2 or BMP6 coding sequence under cytomegalovirus (CMV) promoter control [17:1 multiplicities of infection (moi)] and either sustained in monolayer or suspended in 1 mL 1.2% alginate beads for 22 days. Adenovirus (Ad)-BMP-2 and Ad-BMP-6 transduction resulted in abundant BMP-2 and BMP-6 mRNA and protein expression in monolayer culture and BMP-2 protein expression in alginate cultures. Ad-BMP-2 and Ad-BMP-6 transduced BMDMSC in monolayer had earlier and robust alkaline phosphatase-positive staining and mineralization and were sustained for a longer duration with better morphology scores than untransduced or Ad-beta-galactosidase-transduced cells. Ad-BMP-2- and, to a lesser degree, Ad-BMP-6-transduced BMDMSC suspended in alginate demonstrated greater mineralization than untransduced cells. Gene expression studies at day 2 confirmed an inflammatory response to the gene delivery process with upregulation of interleukin 8 and CXCL2. Upregulation of genes consistent with response to BMP exposure and osteogenic differentiation, specifically endochondral ossification and extracellular matrix proteins, occurred in BMP-transduced cells. These data support that transduction of BMDMSC with Ad-BMP-2 or Ad-BMP-6 can accelerate osteogenic differentiation and mineralization of stem cells in culture, including in three-dimensional culture. BMP-2-transduced stem cells suspended in alginate culture may be a practical carrier system to support bone formation in vivo. BMP-6 induced a less robust cellular response than BMP-2, particularly in alginate culture.

Comparison of osteogenic potentials of visceral and subcutaneous adipose-derived cells of rabbits

BACKGROUND

The demand for a large amount of osteogenic cells required in bone tissue engineering warranted exploration of a new source of osteoprogenitor cells. Recent studies have demonstrated that adipose-derived stromal cells possess multiple differentiation capacities, including osteogenic potential, as bone marrow mesenchymal stem cells. In the present study, the authors compared the osteogenic potentials of adipose-derived stromal cells from different anatomical sites of rabbits.

METHODS

Different adipose-derived stromal cells were isolated from rabbit visceral and subcutaneous adipose tissues by enzymatic digestion and in vitro differentiation into osteogenic lineage. Osteogenic markers representing differentiation potentials of adipose-derived stromal cells from different anatomical sites were compared by biochemical and immunohistochemical assessment (n = 3).

RESULTS

Fibroblast-like cells were digested from both visceral and subcutaneous adipose tissues. After exposure to osteogenic differentiation medium, visceral adipose-derived cells were found to possess greater osteogenic potentials than cells isolated from subcutaneous adipose tissues, evidenced by significantly different amounts of osteogenic markers including alkaline phosphatase, osteocalcin, and mineral deposition.

CONCLUSION

This study indicates that osteogenic potentials of adipose-derived cells vary by their anatomical sites, with visceral adipose-derived cells exhibiting higher osteogenic potential than those isolated from subcutis. However, the mechanism is still unidentified.

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.

Neotendon formation induced by manipulation of the Smad8 signalling pathway in mesenchymal stem cells

Tissue regeneration requires the recruitment of adult stem cells and their differentiation into mature committed cells. In this study we describe what we believe to be a novel approach for tendon regeneration based on a specific signalling molecule, Smad8, which mediates the differentiation of mesenchymal stem cells (MSCs) into tendon-like cells. A biologically active Smad8 variant was transfected into an MSC line that coexpressed the osteogenic gene bone morphogenetic protein 2 (BMP2). The engineered cells demonstrated the morphological characteristics and gene expression profile of tendon cells both in vitro and in vivo. In addition, following implantation in an Achilles tendon partial defect, the engineered cells were capable of inducing tendon regeneration demonstrated by double quantum filtered MRI. The results indicate what we believe to be a novel mechanism in which Smad8 inhibits the osteogenic pathway in MSCs known to be induced by BMP2 while promoting tendon differentiation. These findings may have considerable importance for the therapeutic replacement of tendons or ligaments and for engineering other tissues in which BMP plays a pivotal developmental role.

Progenitors systemically transplanted into neonatal mice localize to areas of active bone formation in vivo: implications of cell therapy for skeletal diseases

The potential of cell or gene therapy to treat skeletal diseases was evaluated through analysis of transplanted osteoprogenitors into neonatal homozygous and heterozygous osteogenesis imperfecta mice (oim). The osteoprogenitors used for transplantation were prepared by injection of mesenchymal stem cells (MSCs) marked with the green fluorescent protein (GFP) into normal mice with the subsequent retrieval of the cells at 35 days. The retrieved cells referred to here as osteoprogenitors were expanded in culture and transplanted into the 2-day-old oim mice via the superficial temporal vein. The recipient mice were evaluated at 2 and 4 weeks after cell transplantation. Four weeks after transplantation, tissue sections made from femurs and tibias of oim mice showed that the GFP-positive (GFP(+)) cells were distributed on the surfaces of the bone spicules in the spongiosa, the area of active bone formation. In the diaphysis, the GFP(+) cells were distributed in the bone marrow, on the endosteal surfaces, and also in the cortical bone. Immunofluorescence localization for GFP confirmed that the fluorescence seen in tissue sections was due to the engrafted donor cells, not bone autofluorescence. Gene expression analysis by polymerase chain reaction of the GFP(+) cells retrieved from the bones and marrow of the recipient mice demonstrated that the cells from bone were osteoblasts, whereas those from bone marrow were progenitors. These data demonstrate that MSCs delivered systemically to developing osteogenesis imperfecta mice engraft in bones, localize to areas of active bone formation, differentiate into osteoblasts in vivo, and may contribute to bone formation in vivo.

Comparison of gene expression pattern in SP cell populations from four tissues to define common "stemness functions"

The goal of our study was to identify a subset of genes commonly expressed in Side Populations (SP), isolated by Hoechst staining followed by flow cytometry, from adult mouse bone marrow, male adult germinal cells, muscle primary culture, and mesenchymal cells. These SP cells have been proposed to be a "stem-like" population and are used here as a "model" that may reveal mechanisms which would be relevant for a better understanding of stem cell properties. Transcriptional profiles for SP and the more differentiated non-SP cells isolated from the four tissues were compared by hybridization on microarray using a common external reference. Among the 503 genes differentially expressed, which discriminate SP and non-SP cells in all the tissues, the genes upregulated in SP cells are implicated in the quiescent status of the cells, the maintenance of their pluripotency and the capacity to undergo asymmetric division. These genes may be responsible for the decision for self-renewal of these cells, whereas the repression of lineage-affiliated genes in SP cells could be responsible for their undifferentiated state. These genes, acting in concert, may be the key players that mediate the mechanisms that control stem cell functions, and our results suggest that we have identified common "stemness functions" of these "stem-like" cells.

Recombinant growth/differentiation factor-5 stimulates osteogenic differentiation of fat-derived stromal cells in vitro

Fat-derived stromal cells can differentiate into various skeletal tissues. Currently the mechanism that determines whether stromal cells differentiate into osteoblasts is unclear and the role of growth/differentiation factor (GDF)-5 in differentiation of fat-derived stromal cells is not fully understood. It appears that the differentiation of stromal cells is greatly enhanced by GDF-5 that plays a role in a variety of musculoskeletal processes such as joint formation, tendon maintenance, and bone formation. Our study showed that GDF-5 promotes the differentiation of rat fat-derived stromal cells into osteogenic lineages in vitro. Furthermore, these findings were confirmed by histology, biochemical assay for alkaline phosphatase activity, and analysis of gene expression. The ability to preferentially stimulate fat-derived stromal cells down the osteogenic pathway holds significance in a variety of clinical scenarios.

Adult mesenchymal stem cells: characterization, differentiation, and application in cell and gene therapy

A considerable amount of retrospective data is available that describes putative mesenchymal stem cells (MSCs). However, there is still very little knowledge available that documents the properties of a MSC in its native environment. Although the precise identity of MSCs remains a challenge, further understanding of their biological properties will be greatly advanced by analyzing the mechanisms that govern their self-renewal and differentiation potential. This review begins with the current state of knowledge on the biology of MSCs, specifically with respect to their existence in the adult organism and postulation of their biological niche. While MSCs are considered suitable candidates for cell-based strategies owing to their intrinsic capacity to self-renew and differentiate, there is currently little information available regarding the molecular mechanisms that govern their stem cell potential. We propose here a model for the regulation of MSC differentiation, and recent findings regarding the regulation of MSC differentiation are discussed. Current research efforts focused on elucidating the mechanisms regulating MSC differentiation should facilitate the design of optimal in vitro culture conditions to enhance their clinical utility cell and gene therapy.

Low level laser irradiation stimulates osteogenic phenotype of mesenchymal stem cells seeded on a three-dimensional biomatrix

Mesenchymal stem cells (MSCs) seeded on three-dimensional (3D) coralline (Porites lutea) biomatrices were irradiated with low-level laser irradiation (LLLI). The consequent phenotype modulation and development of MSCs towards ossified tissue was studied in this combined 3D biomatrix/LLLI system and in a control group, which was similarly grown, but was not treated by LLLI. The irradiated and non irradiated MSC were tested at 1-7, 10, 14, 21, 28 days of culturing via analysis of cellular distribution on matrices (trypan blue), calcium incorporation to newly formed tissue (alizarin red), bone nodule formation (von Kossa), fat aggregates formation (oil red O), alkaline phosphatase (ALP) activity, scanning electron microscopy (SEM) and electron dispersive spectrometry (EDS). The results obtained from the irradiated samples showed enhanced tissue formation, appearance of phosphorous peaks and calcium and phosphate incorporation to newly formed tissue. Moreover, in irradiated samples ALP activity was significantly enhanced in early stages and notably reduced in late stages of culturing. These findings of cell and tissue parameters up to 28 days of culture revealed higher ossification levels in irradiated samples compared with the control group. We suggest that both the surface properties of the 3D crystalline biomatrices and the LLLI have biostimulatory effects on the conversion of MSCs into bone-forming cells and on the induction of ex-vivo ossification.

Review: mesenchymal stem cells: cell-based reconstructive therapy in orthopedics

Adult stem cells provide replacement and repair descendants for normal turnover or injured tissues. These cells have been isolated and expanded in culture, and their use for therapeutic strategies requires technologies not yet perfected. In the 1970s, the embryonic chick limb bud mesenchymal cell culture system provided data on the differentiation of cartilage, bone, and muscle. In the 1980s, we used this limb bud cell system as an assay for the purification of inductive factors in bone. In the 1990s, we used the expertise gained with embryonic mesenchymal progenitor cells in culture to develop the technology for isolating, expanding, and preserving the stem cell capacity of adult bone marrow-derived mesenchymal stem cells (MSCs). The 1990s brought us into the new field of tissue engineering, where we used MSCs with site-specific delivery vehicles to repair cartilage, bone, tendon, marrow stroma, muscle, and other connective tissues. In the beginning of the 21st century, we have made substantial advances: the most important is the development of a cell-coating technology, called painting, that allows us to introduce informational proteins to the outer surface of cells. These paints can serve as targeting addresses to specifically dock MSCs or other reparative cells to unique tissue addresses. The scientific and clinical challenge remains: to perfect cell-based tissue-engineering protocols to utilize the body's own rejuvenation capabilities by managing surgical implantations of scaffolds, bioactive factors, and reparative cells to regenerate damaged or diseased skeletal tissues.