Mesenchymal stem cells reside in virtually all post-natal organs and tissues

Coordinated changes of mitochondrial biogenesis and antioxidant enzymes during osteogenic differentiation of human mesenchymal stem cells

The multidifferentiation ability of mesenchymal stem cells holds great promise for cell therapy. Numerous studies have focused on the establishment of differentiation protocols, whereas little attention has been paid to the metabolic changes during the differentiation process. Mitochondria, the powerhouse of mammalian cells, vary in their number and function in different cell types with different energy demands, but how these variations are associated with cell differentiation remains elusive. In this study, we investigated the changes of mitochondrial biogenesis and bioenergetic function using human mesenchymal stem cells (hMSCs) because of their well-defined differentiation potentials. Upon osteogenic induction, the copy number of mitochondrial DNA, protein subunits of the respiratory enzymes, oxygen consumption rate, and intracellular ATP content were increased, indicating the upregulation of aerobic mitochondrial metabolism. On the other hand, undifferentiated hMSCs showed higher levels of glycolytic enzymes and lactate production rate, suggesting that hMSCs rely more on glycolysis for energy supply in comparison with hMSC-differentiated osteoblasts. In addition, we observed a dramatic decrease of intracellular reactive oxygen species (ROS) as a consequence of upregulation of two antioxidant enzymes, manganese-dependent superoxide dismutase and catalase. Finally, we found that exogenous H(2)O(2) and mitochondrial inhibitors could retard the osteogenic differentiation. These findings suggested an energy production transition from glycolysis to oxidative phosphorylation in hMSCs upon osteogenic induction. Meanwhile, antioxidant enzymes were concurrently upregulated to prevent the accumulation of intracellular ROS. Together, our findings suggest that coordinated regulation of mitochondrial biogenesis and antioxidant enzymes occurs synergistically during osteogenic differentiation of hMSCs.

Adult mesenchymal stem cells for tissue engineering versus regenerative medicine

Adult mesenchymal stem cells (MSCs) can be isolated from bone marrow or marrow aspirates and because they are culture-dish adherent, they can be expanded in culture while maintaining their multipotency. The MSCs have been used in preclinical models for tissue engineering of bone, cartilage, muscle, marrow stroma, tendon, fat, and other connective tissues. These tissue-engineered materials show considerable promise for use in rebuilding damaged or diseased mesenchymal tissues. Unanticipated is the realization that the MSCs secrete a large spectrum of bioactive molecules. These molecules are immunosuppressive, especially for T-cells and, thus, allogeneic MSCs can be considered for therapeutic use. In this context, the secreted bioactive molecules provide a regenerative microenvironment for a variety of injured adult tissues to limit the area of damage and to mount a self-regulated regenerative response. This regenerative microenvironment is referred to as trophic activity and, therefore, MSCs appear to be valuable mediators for tissue repair and regeneration. The natural titers of MSCs that are drawn to sites of tissue injury can be augmented by allogeneic MSCs delivered via the bloodstream. Indeed, human clinical trials are now under way to use allogeneic MSCs for treatment of myocardial infarcts, graft-versus-host disease, Crohn's Disease, cartilage and meniscus repair, stroke, and spinal cord injury. This review summarizes the biological basis for the in vivo functioning of MSCs through development and aging.

Mesenchymal stem cells: a promising candidate in regenerative medicine

Mesenchymal stem cells were initially characterized as plastic adherent, fibroblastoid cells. In recent years, there has been an increasing focus on mesenchymal stem cells since they have great plasticity and are potential for therapeutic applications. Mesenchymal stem cells or mesenchymal stem cell-like cells have been shown to reside within the connective tissues of most organs. These cells can differentiate into osteogenic, adipogenic and chondrogenic lineages under appropriate conditions. A number of reports have also indicated that these cells possess the capacity to trans-differentiate into epithelial cells and lineages derived from the neuro-ectoderm, and in addition, mesenchymal stem cells can migrate to the sites of injury, inflammation, and to tumors. These properties of mesenchymal stem cells make them promising candidates for use in regenerative medicine and may also serve as efficient delivery vehicles in site-specific therapy.

Derivation and immunological characterization of mesenchymal stromal cells from human embryonic stem cells

OBJECTIVE

We have previously shown the simultaneous generation of CD73(+) mesenchymal stromal cells (MSCs) along with CD34(+) hematopoietic cells from human embryonic stem cells (ESCs) when they are cocultured with OP9 murine stromal cells. We investigated whether MSCs can be derived from human ESCs without coculturing with OP9 cells, and if such cells exhibit immunological properties similar to MSCs derived from adult human bone marrow (BM).

MATERIALS AND METHODS

Our starting populations were undifferentiated human ESCs cultured on Matrigel-coated plates without feeder cells. The differentiated fibroblast-looking cells were tested for expression of MSC markers and their potential for multilineage differentiation. We investigated surface expression of human leukocyte antigen (HLA) molecules on these MSCs before and after treatment with interferon-gamma (IFN-gamma). We also tested the proliferative response of T-lymphocytes toward MSCs and the effects of MSCs in mixed lymphocyte reaction (MLR) assays.

RESULTS

We derived populations of MSCs from human ESCs with morphology, cell surface marker characteristics, and differentiation potential similar to adult BM-derived MSCs. Similar to BM-derived MSCs, human ESC-derived MSCs express cell surface HLA class I (HLA-ABC) but not HLA class II (HLA-DR) molecules. However, stimulation with IFN-gamma induced the expression of HLD-DR molecules. Human ESC-derived MSCs did not induce proliferation of T-lymphocytes when cocultured with peripheral blood mononuclear cells. Furthermore, ESC-derived MSCs suppressed proliferation of responder T-lymphocytes in MLR assays.

CONCLUSIONS

MSCs can be derived from human ESCs without feeder cells. These human ESC-derived MSCs have cell surface markers, differentiation potentials, and immunological properties in vitro that are similar to adult BM-derived MSCs.

Recent advances in cancer stem/progenitor cell research: therapeutic implications for overcoming resistance to the most aggressive cancers

Overcoming intrinsic and acquired resistance of cancer stem/progenitor cells to current clinical treatments represents a major challenge in treating and curing the most aggressive and metastatic cancers. This review summarizes recent advances in our understanding of the cellular origin and molecular mechanisms at the basis of cancer initiation and progression as well as the heterogeneity of cancers arising from the malignant transformation of adult stem/progenitor cells. We describe the critical functions provided by several growth factor cascades, including epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), stem cell factor (SCF) receptor (KIT), hedgehog and Wnt/beta-catenin signalling pathways that are frequently activated in cancer progenitor cells and are involved in their sustained growth, survival, invasion and drug resistance. Of therapeutic interest, we also discuss recent progress in the development of new drug combinations to treat the highly aggressive and metastatic cancers including refractory/relapsed leukaemias, melanoma and head and neck, brain, lung, breast, ovary, prostate, pancreas and gastrointestinal cancers which remain incurable in the clinics. The emphasis is on new therapeutic strategies consisting of molecular targeting of distinct oncogenic signalling elements activated in the cancer progenitor cells and their local microenvironment during cancer progression. These new targeted therapies should improve the efficacy of current therapeutic treatments against aggressive cancers, and thereby preventing disease relapse and enhancing patient survival.

Human heart, spleen, and perirenal fat-derived mesenchymal stem cells have immunomodulatory capacities

Mesenchymal stem cells (MSCs) have important tissue repair functions and show potent immunosuppressive capacities in vitro. Although usually isolated from the bone marrow, MSCs have been identified in other tissues, including the skin and liver. In the present study, we isolated and characterized MSCs from human heart, spleen, and perirenal adipose tissue. MSCs from these different tissue sites were similar to those derived from bone marrow in that they expressed comparable levels of the cell-surface markers CD90, CD105, CD166, and HLA class I, were negative for CD34, CD45, HLA class II, CD80, and CD86 expression, and were capable of osteogenic and adipogenic differentiation. Like bone marrow-derived MSCs, MSCs from these different tissue sources inhibited the proliferation of alloactivated peripheral blood mononuclear cells (PBMCs), giving 85%, 79%, 79%, and 81% inhibition, respectively. Also in line with bone marrow-derived MSCs they inhibited proliferative responses of PBMCs to phytohemagglutinin, a nonspecific stimulator of lymphocyte proliferation, and reduced-memory T lymphocyte responses to tetanus toxoid. The results of this study demonstrate that MSCs from various tissues have similar immunophenotypes, in vitro immunosuppressive properties, and differentiation potential.

Human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have elicited a great clinical interest, particularly in the areas of regenerative medicine and induction of tolerance in allogeneic transplantation. Previous reports demonstrated the feasibility of transplanting MSCs, which generates new prospects in cellular therapy. Recently, injection of MSCs induced remission of steroid-resistant acute graft-versus-host disease (GVHD). This review summarizes the knowledge and possible future clinical uses of MSCs.

Development of Custom-Built Bone Scaffolds Using Mesenchymal Stem Cells and Apatite-Wollastonite Glass-Ceramics

There is a clinical need for new bone replacement materials that combine long implant life with complete integration and appropriate mechanical properties. We have used human mesenchymal stem cells (MSCs) to populate porous apatite-wollastonite (A-W) glass-ceramic scaffolds produced by the layer manufacturing technique, selective laser sintering, to create custom-built bone replacements. Confocal and scanning electron microscopy were used to determine optimal seeding densities and to demonstrate that MSCs adhered and retained viability on the surface of A-W scaffolds over a culture period of 21 days. We found a significant increase in the number of MSCs growing on the scaffolds over 7 days. Using bromodeoxyuridine incorporation we demonstrated that MSCs proliferated on the scaffolds. Using real-time PCR we analyzed the expression of the osteogenic markers alkaline phosphatase, collagen type-I, Cbfa-1, osteocalcin, osteonectin, and osteopontin by MSCs cultured in the absence of osteogenic supplements. The expression of the osteogenic markers by MSCs was equivalent to or significantly greater on A-W scaffolds than on tissue culture plastic. We also identified significantly higher alkaline phosphatase activity on A-W compared to a commercial calcium phosphate scaffold. These results indicate for the first time the biocompatibility and osteo-supportive capacity of A-W scaffolds and their potential as patient-specific bone replacement materials.

Mesenchymal stem cells for the treatment of heart failure

Heart failure is one of the most important cardiovascular health problems throughout the world and has high mortality, and there is a need to develop more effective therapeutic strategies to replace such specialized treatment as mechanical circulatory support and cardiac transplantation. Mesenchymal stem cells (MSC) are multipotent plastic-adherent cells obtained from bone marrow, adipose tissue, and other tissues and can be easily expanded in culture. The ability of MSC to differentiate into a variety of cells, including cardiomyocytes and vascular endothelial cells, make them an attractive therapeutic tool for heart failure. Recent in vitro and in vivo studies have revealed the underlying mechanisms of MSC in cardiac repair. MSC exert their role in cardiac regeneration not only by differentiating into specific cell types such as cardiomyocytes and vascular endothelial cells but also through paracrine effects via secretion of a variety of angiogenic, antiapoptotic, and mitogenic factors. Endogenous MSC as well as exogenously administered MSC have also been suggested to migrate and participate in cardiac repair. On the basis of information obtained from basic and translational research, several clinical trials have recently been started to evaluate the safety and efficacy of autologous MSC for heart failure.

The antiproliferative effect of mesenchymal stem cells is a fundamental property shared by all stromal cells

Although it has been widely demonstrated that human mesenchymal stem cells exert potent immunosuppressive effects, there is little information as to whether more mature mesenchymal stromal cells (SC) share the same property. Accordingly, we set out to test the ability of SC from different human tissues to inhibit the proliferation of PBMC following polyclonal stimuli. Chondrocytes, as well as fibroblasts from synovial joints, lung, and skin, were used as a source of SC. Irrespective of their differentiation potential and/or content of progenitor cells, SC from all tissues exhibited antiproliferative functions. This was in marked contrast to parenchymal cells. Although SC did not interfere with early T lymphocyte activation, they arrested stimulated T cells in the G(0)/G(1) phase of the cell cycle and rescued them from apoptosis. In addition, IFN-gamma and TNF-alpha production were reduced. We observed that the inhibitory effect is ultimately mediated by soluble factors, the production of which requires SC to be licensed in an inflammatory environment by cell contact. We conclude that the immunosuppressive effect of mesenchymal cells is not confined to multipotent stem cells, but is a fundamental characteristic of all stroma. Our data suggest that SC, appropriately licensed, regulate T cell homeostasis.

Systemic delivery of adult stem cells improves cardiac function in spontaneously hypertensive rats

1. Heart regeneration after myocardial infarction (MI) can occur after cell therapy, but the mechanisms, cell types and delivery methods responsible for this improvement are still under investigation. In the present study, we evaluated the impact of systemic delivery of bone marrow cells (BMC) and cultivated mesenchymal stem cells (MSC) on cardiac morphology, function and mortality in spontaneously hypertensive rats (SHR) submitted to coronary occlusion. 2. Female syngeneic adult SHR, submitted or not (control group; C) to MI, were treated with intravenous injection of MSC (MI + MSC) or BMC (MI + BM) from male rats and evaluated after 1, 15 and 30 days by echocardiography. Systolic blood pressure (SBP), functional capacity, histology, mortality rate and polymerase chain reaction for the Y chromosome were also analysed. 3. Myocardial infarction induced a decrease in SBP and BMC, but not MSC, prevented this decrease. An improvement in functional capacity and ejection fraction (38 +/- 4, 39 +/- 3 and 58 +/- 2% for MI, MI + MSC and MI + BM, respectively; P < 0.05), as well as a reduction of the left ventricle infarcted area, were observed in rats from the MI + BM group compared with the other three groups. Treated animals had a significantly reduced lesion tissue score. The mortality rate in the C, MI + BM, MI + MSC and MI groups was 0, 0, 16.7 and 44.4%, respectively (P < 0.05 for the MI + MSC and MI groups compared with the C and MI + BM groups). 4. The results of the present study suggest that systemic administration of BMC can improve left ventricular function, functional capacity and, consequently, reduce mortality in an animal model of MI associated with hypertension. We speculate that the cells transiently home to the myocardium, releasing paracrine factors that recruit host cells to repair the lesion.

A population of multipotent CD34-positive adipose stromal cells share pericyte and mesenchymal surface markers, reside in a periendothelial location, and stabilize endothelial networks

It has been shown that stromal-vascular fraction isolated from adipose tissues contains an abundance of CD34+ cells. Histological analysis of adipose tissue revealed that CD34+ cells are widely distributed among adipocytes and are predominantly associated with vascular structures. The majority of CD34+ cells from freshly isolated stromal-vascular fraction were CD31-/CD144- and could be separated from a distinct population of CD34+/CD31+/CD144+ (endothelial) cells by differential attachment on uncoated plastic. The localization of CD34+ cells within adipose tissue suggested that the nonendothelial population of these cells occupied a pericytic position. Analysis of surface and intracellular markers of the freshly isolated CD34+/CD31-/CD144- adipose-derived stromal cells (ASCs) showed that >90% coexpress mesenchymal (CD10, CD13, and CD90), pericytic (chondroitin sulfate proteoglycan, CD140a, and CD140b), and smooth muscle (alpha-actin, caldesmon, and calponin) markers. ASCs demonstrated polygonal self-assembly on Matrigel, as did human microvascular endothelial cells. Coculture of ASCs with human microvascular endothelial cells on Matrigel led to cooperative network assembly, with enhanced stability of endothelial networks and preferential localization of ASCs on the abluminal side of cords. Bidirectional paracrine interaction between these cells was supported by identification of angiogenic factors (vascular endothelial growth factor, hepatocyte growth factor, basic fibroblast growth factor), inflammatory factors (interleukin-6 and -8 and monocyte chemoattractant protein-1 and -2), and mobilization factors (macrophage colony-stimulating factor and granulocyte/macrophage colony-stimulating factor) in media conditioned by CD34+ ASCs, as well a robust mitogenic response of ASCs to basic fibroblast growth factor, epidermal growth factor, and platelet-derived growth factor-BB, factors produced by endothelial cells. These results demonstrate for the first time that the majority of adipose-derived adherent CD34+ cells are resident pericytes that play a role in vascular stabilization by mutual structural and functional interaction with endothelial cells.

Multipotent stem cells from umbilical cord: cord is richer than blood!

The identification of mesenchymal stem cell (MSC) sources that are easily obtainable is of utmost importance. Several studies have shown that MSCs could be isolated from umbilical cord (UC) units. However, the presence of MSCs in umbilical cord blood (UCB) is controversial. A possible explanation for the low efficiency of MSCs from UCB is the use of different culture conditions by independent studies. Here, we compared the efficiency in obtaining MSCs from unrelated paired UCB and UC samples harvested from the same donors. Samples were processed simultaneously, under the same culture conditions. Although MSCs from blood were obtained from only 1 of the 10 samples, we were able to isolate large amounts of multipotent MSCs from all UC samples, which were able to originate different cell lineages. Since the routine procedure in UC banks has been to store the blood and discard other tissues, such as the cord and/or placenta, we believe our results are of immediate clinical value. Furthermore, the possibility of originating different cell lines from the UC of neonates born with genetic defects may provide new cellular research models for understanding human malformations and genetic disorders, as well as the possibility of testing the effects of different therapeutic drugs.

Concise Review: Role and Function of the Ubiquitin-Proteasome System in Mammalian Stem and Progenitor Cells

Highly ordered degradation of cell proteins by the ubiquitin-proteasome system, a sophisticated cellular proteolytic machinery, has been identified as a key regulatory mechanism in many eukaryotic cells. Accumulating evidence reveals that the ubiquitin-proteasome system is involved in the regulation of fundamental processes in mammalian stem and progenitor cells of embryonic, neural, hematopoietic, and mesenchymal origin. Such processes, including development, survival, differentiation, lineage commitment, migration, and homing, are directly controlled by the ubiquitin-proteasome system, either via proteolytic degradation of key regulatory proteins of signaling and gene expression pathways or via nonproteolytic mechanisms involving the proteasome itself or posttranslational modifications of target proteins by ubiquitin or other ubiquitin-like modifiers. Future characterization of the precise roles and functions of the ubiquitin-proteasome system in mammalian stem and early progenitor cells will improve our understanding of stem cell biology and may provide an experimental basis for the development of novel therapeutic strategies in regenerative medicine. Disclosure of potential conflicts of interest is found at the end of this article.

Discordant proliferation and differentiation in pituitary tumor-transforming gene-null bone marrow stem cells

The mammalian securin, pituitary tumor-transforming gene ( Pttg), regulates sister chromatid separation during mitosis. Mice deficient in Pttg expression exhibit organ-specific hypoplasia of the testis, spleen, pituitary, and postmaturity pancreatic β-cells, pointing to a possible adult stem cell defect. Bone marrow stem cells (BMSCs) contribute to bone, cartilage, and fat tissue repair and regeneration, and multipotent adult progenitor cells (MAPCs) have broader differentiation ability. Bone marrow cells derived under MAPC conditions are involved in a spectrum of tissue repair. We therefore tested whether Pttg deletion affects stem cell proliferation and differentiation. BMSCs were isolated under MAPC conditions, although unlike MAPCs, wild-type (WT) and Pttg−/− BMSCs do not express octamer-binding transcription factor 4 and are stem cell antigen-I positive. WT and Pttg−/− cells did not differ in their ability to differentiate into adipogenic, osteogenic, or hepatocyte-like cells or in phenotypic markers. Cells underwent >100 population doublings, with no observed transforming events. Pttg-null BMSCs replicated 27% slower than WT BMSCs, and under hypoxic conditions, this difference widened. Although apoptosis was not enhanced in Pttg−/− cells, Pttg−/− BMSC senescence-associated β-galactosidase activity was elevated, consistent with enhanced p21 protein levels. Using gene array assays, DNA repair genes were shown to be upregulated in Pttg−/− BMSCs, whereas genes involved in cell cycle progression, including cyclin D1, were decreased. Separase, the protease regulated by Pttg, has been implicated in DNA damage repair and was downregulated in Pttg−/− BMSCs. Separase was constitutively phosphorylated in Pttg−/− cells, a modification likely serving as a compensatory mechanism for Pttg deletion. The results indicate that Pttg deletion reduces BMSC proliferation, renders cells more sensitive to hypoxia, and enhances senescent features, thus pointing to a role for Pttg in the maintenance and proliferation of BMSCs.

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.

Multilineage differentiation potential of equine blood-derived fibroblast-like cells

Tissue engineering (TE) has emerged as a promising new therapy for the treatment of damaged tissues and organs. Adult stem cells are considered as an attractive candidate cell type for cell-based TE. Mesenchymal stem cells (MSC) have been isolated from a variety of tissues and tested for differentiation into different cell lineages. While clinical trials still await the use of human MSC, horse tendon injuries are already being treated with autologous bone marrow-derived MSC. Given that the bone marrow is not an optimal source for MSC due to the painful and risk-containing sampling procedure, isolation of stem cells from peripheral blood would bring an attractive alternative. Adherent fibroblast-like cells have been previously isolated from equine peripheral blood. However, their responses to the differentiation conditions, established for human bone marrow MSC, were insufficient to fully confirm their multilineage potential. In this study, differentiation conditions were optimized to better evaluate the multilineage capacities of equine peripheral blood-derived fibroblast-like cells (ePB-FLC) into adipogenic, osteogenic, and chondrogenic pathways. Adipogenic differentiation using rabbit serum resulted in a high number of large-size lipid droplets three days upon induction. Cells' expression of alkaline phosphatase and calcium deposition upon osteogenic induction confirmed their osteogenic differentiation capacities. Moreover, an increase of dexamethasone concentration resulted in faster osteogenic differentiation and matrix mineralization. Finally, induction of chondrogenesis in pellet cultures resulted in an increase in cartilage-specific gene expression, namely collagen II and aggrecan, followed by protein deposition after a longer induction period. This study therefore demonstrates that ePB-FLC have the potential to differentiate into adipogenic, osteogenic, and chondrogenic mesenchymal lineages. The presence of cells with confirmed multilineage capacities in peripheral blood has important clinical implications for cell-based TE therapies in horses.

Stem cells in veterinary medicine--attempts at regenerating equine tendon after injury

Stem cells have evoked considerable excitement in the animal-owning public because of the promise that stem cell technology could deliver tissue regeneration for injuries for which natural repair mechanisms do not deliver functional recovery and for which current therapeutic strategies have minimal effectiveness. This review focuses on the current use of stem cells within veterinary medicine, whose practitioners have used mesenchymal stem cells (MSCs), recovered from either bone marrow or adipose tissue, in clinical cases primarily to treat strain-induced tendon injury in the horse. The background on why this treatment has been advocated, the data supporting its use and the current encouraging outcome from clinical use in horses treated with bone-marrow-derived cells are presented together with the future challenges of stem-cell therapy for the veterinary community.

Clonally amplified cardiac stem cells are regulated by Sca-1 signaling for efficient cardiovascular regeneration

Recent studies have shown that cardiac stem cells (CSCs) from the adult mammalian heart can give rise to functional cardiomyocytes; however, the definite surface markers to identify a definitive single entity of CSCs and the molecular mechanisms regulating their growth are so far unknown. Here, we demonstrate a single-cell deposition analysis to isolate individually selected CSCs from adult murine hearts and investigate the signals required for their proliferation and survival. Clonally proliferated CSCs express stem cell antigen-1 (Sca-1) with embryonic stem (ES) cell-like and mesenchymal cell-like characteristics and are associated with telomerase reverse transcriptase (TERT). Using a transgene that expresses a GFP reporter under the control of the TERT promoter, we demonstrated that TERT(GFP)-positive fractions from the heart were enriched for cells expressing Sca-1. Knockdown of Sca-1 transcripts in CSCs led to retarded ex vivo expansion and apoptosis through Akt inactivation. We also show that ongoing CSC proliferation and survival after direct cell-grafting into ischemic myocardium require Sca-1 to upregulate the secreted paracrine effectors that augment neoangiogenesis and limit cardiac apoptosis. Thus, Sca-1 might be an essential component to promote CSC proliferation and survival to directly facilitate early engraftment, and might indirectly exert the effects on late cardiovascular differentiation after CSC transplantation.

Stem cells: a revolution in therapeutics-recent advances in stem cell biology and their therapeutic applications in regenerative medicine and cancer therapies

Basic and clinical research accomplished during the last few years on embryonic, fetal, amniotic, umbilical cord blood, and adult stem cells has constituted a revolution in regenerative medicine and cancer therapies by providing the possibility of generating multiple therapeutically useful cell types. These new cells could be used for treating numerous genetic and degenerative disorders. Among them, age-related functional defects, hematopoietic and immune system disorders, heart failures, chronic liver injuries, diabetes, Parkinson's and Alzheimer's diseases, arthritis, and muscular, skin, lung, eye, and digestive disorders as well as aggressive and recurrent cancers could be successfully treated by stem cell-based therapies. This review focuses on the recent advancements in adult stem cell biology in normal and pathological conditions. We describe how these results have improved our understanding on critical and unique functions of these rare sub-populations of multipotent and undifferentiated cells with an unlimited self-renewal capacity and high plasticity. Finally, we discuss some major advances to translate the experimental models on ex vivo and in vivo expanded and/or differentiated stem cells into clinical applications for the development of novel cellular therapies aimed at repairing genetically altered or damaged tissues/organs in humans. A particular emphasis is made on the therapeutic potential of different tissue-resident adult stem cell types and their in vivo modulation for treating and curing specific pathological disorders.

Simplified protocol to isolate, purify, and culture expand mesenchymal stem cells

Mesenchymal stem cells (MSCs) are widely used for experimental regenerative strategies. Due to their differentiation capacity into mesenchymal lineages, they are a potential cellular source for tissue regeneration. Because there is no specific antigen that can be used to define MSCs directly, there is no consensus about how to isolate them. Here we describe a simple protocol to isolate, purify, and culture expand murine bone marrow MSCs using magnetic cell sorting and plastic adherence. We further show that cytokine supplementation enhances MSC proliferation without jeopardizing their pluripotency.

Human Mesenchymal Stem Cells Promote Survival of T Cells in a Quiescent State

Mesenchymal stem cells (MSC) are part of the bone marrow that provides signals supporting survival and growth of bystander hematopoietic stem cells (HSC). MSC modulate also the immune response, as they inhibit proliferation of lymphocytes. In order to investigate whether MSC can support survival of T cells, we investigated MSC capacity of rescuing T lymphocytes from cell death induced by different mechanisms. We observed that MSC prolong survival of unstimulated T cells and apoptosis-prone thymocytes cultured under starving conditions. MSC rescued T cells from activation induced cell death (AICD) by downregulation of Fas receptor and Fas ligand on T cell surface and inhibition of endogenous proteases involved in cell death. MSC dampened also Fas receptor mediated apoptosis of CD95 expressing Jurkat leukemic T cells. In contrast, rescue from AICD was not associated with a significant change of Bcl-2, an inhibitor of apoptosis induced by cell stress. Accordingly, MSC exhibited a minimal capacity of rescuing Jurkat cells from chemically induced apoptosis, a process disrupting the mitochondrial membrane potential regulated by Bcl-2. These results suggest that MSC interfere with the Fas receptor regulated process of programmed cell death. Overall, MSC can inhibit proliferation of activated T cells while supporting their survival in a quiescent state, providing a model of their activity inside the HSC niche. Disclosure of potential conflicts of interest is found at the end of this article.

Functional network analysis of the transcriptomes of mesenchymal stem cells derived from amniotic fluid, amniotic membrane, cord blood, and bone marrow

Using high-density oligonucleotide microarrays and functional network analyses, we examined whether MSCs derived from four different origins exhibited unique gene expression profiles individually and then compared the gene expression profiles of all MSCs with those of fetal organs. Our results indicated that within each group of MSCs from the same origin, the variability of the gene expression levels was smaller than that between groups of different origins. Functional genomic studies revealed the specific roles of MSCs from different origins. Our results suggest that amniotic fluid MSCs may initiate interactions with the uterus by upregulating oxytocin and thrombin receptors. Amniotic membrane MSCs may play a role in maintaining homeostasis of fluid and electrolytes by regulating the networks of endothelin, neprilysin, bradykinin receptors, and atrial natriuretic peptide. Cord blood MSCs may be involved in innate immune systems as the neonatal defense system against the earliest encountered pathogens. Adult bone marrow MSCs may be an important source not only of all blood lineages but also of bone formation. However, in spite of the different gene expression profiles seen in MSCs derived from different origins, a set of core gene expression profiles was preserved in these four kinds of MSCs. The core signature transcriptomes of all MSCs, when contrasted against those of fetal organs, included genes involved in the regulation of extracellular matrix and adhesion, transforming growth factor-beta receptor signaling, and the Wnt signaling pathways. Disclosure of potential conflicts of interest is found at the end of this article.

Rho inhibition induces migration of mesenchymal stromal cells

Although mesenchymal stromal cells (MSCs) are being increasingly used as cell therapeutics in clinical trials, the mechanisms that regulate their chemotactic migration behavior are incompletely understood. We aimed to better define the ability of the GTPase regulator of cytoskeletal activation, Rho, to modulate migration induction in MSCs in a transwell chemotaxis assay. We found that culture-expanded MSCs migrate poorly toward exogenous phospholipids lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) in transwell assays. Moreover, plasma-induced chemotactic migration of MSCs was even inhibited after pretreatment with LPA. LPA treatment activated intracellular Rho and increased actin stress fibers in resident MSCs. Very similar cytoskeletal changes were observed after microinjection of a cDNA encoding constitutively active RhoA (RhoAV14) in MSCs. In contrast, microinjection of cDNA encoding Rho inhibitor C3 transferase led to resolution of actin stress fibers, appearance of a looser actin meshwork, and increased numbers of cytoplasmic extensions in the MSCs. Surprisingly, in LPA-pretreated MSCs migrating toward plasma, simultaneous addition of Rho inhibitor C2I-C3 reversed LPA-induced migration suppression and led to improved migration. Moreover, addition of Rho inhibitor C2I-C3 resulted in an approximately 3- to 10-fold enhancement of chemotactic migration toward LPA, S1P, as well as platelet-derived growth factor or hepatocyte growth factor. Thus, inhibition of Rho induces rearrangement of actin cytoskeleton in MSCs and renders them susceptible to induction of migration by physiological stimuli. Disclosure of potential conflicts of interest is found at the end of this article.

Mesenchymal stromal cells. Biology of adult mesenchymal stem cells: regulation of niche, self-renewal and differentiation

Recent advances in understanding the cellular and molecular signaling pathways and global transcriptional regulators of adult mesenchymal stem cells have provided new insights into their biology and potential clinical applications, particularly for tissue repair and regeneration. This review focuses on these advances, specifically in the context of self-renewal and regulation of lineage-specific differentiation of mesenchymal stem cells. In addition we review recent research on the concept of stem cell niche, and its relevance to adult mesenchymal stem cells.

IFN-gamma and TNF-alpha differentially regulate immunomodulation by murine mesenchymal stem cells

Murine mesenchymal stem cells (MSC) have the ability to inhibit allogeneic immune responses. Two different mechanisms, either cell contact-dependent or independent, have been proposed to account for this immunosuppression. The focus of this study was to elucidate the involvement of soluble suppressive factors secreted by murine MSC in an inflammatory setting, and their role in MSC immunomodulation. In a non-inflammatory environment, bone marrow derived murine MSC constitutively expressed low levels of COX-2, PGE-2, TGF-beta1 and HGF, but not IL-10, PD-1, PD-L1 or PD-L2. These MSC were able to significantly reduce alloantigen driven proliferation in mixed lymphocyte reactions as well as mitogen driven proliferation. The pro-inflammatory cytokines IFN-gamma and TNF-alpha did not ablate MSC mediated immunosuppression. MSC expression of PGE-2, IDO and PD-L1 was differentially regulated by these cytokines. COX-2 and PGE-2 expression by MSC were upregulated by both IFN-gamma and TNF-alpha, and using a biochemical inhibitor this was shown to have an essential, non-redundant role in modulating alloantigen-driven proliferation. However, the surface expression of PD-L1 was induced by IFN-gamma but not TNF-alpha and similarly functional IDO expression was only induced by IFN-gamma stimulation. Blocking studies using neutralising antibodies and biochemical antagonists revealed that while PD-L1 induction was not essential, IDO expression was a prerequisite for IFN-gamma mediated MSC immunomodulation. These data demonstrate that murine MSC expression of immunomodulatory factors dramatically changes in a pro-inflammatory environment and that IFN-gamma in particular has an important role in regulating MSC immunomodulatory factor expression.

Prepare cells to repair the heart: mesenchymal stem cells for the treatment of heart failure

Heart failure is one of the most important cardiovascular diseases, with high mortality, and invasive treatment such as mechanical circulatory support and cardiac transplantation is sometimes required for severe heart failure. Therefore, the development of less invasive and more effective therapeutic strategies is desired. Cell therapy is attracting growing interest as a new approach for the treatment of heart failure. As a cell source, various kinds of stem/progenitor cells such as bone marrow cells, endothelial progenitor cells, mesenchymal stem cells (MSC) and cardiac stem cells have been investigated for their efficacy and safety. Especially, bone marrow-derived MSC possess multipotency and can be easily expanded in culture, and are thus an attractive therapeutic tool for heart failure. Recent studies have revealed the underlying mechanisms of MSC in cardiac repair: MSC not only differentiate into specific cell types such as cardiomyocytes and vascular endothelial cells, but also secrete a variety of paracrine angiogenic and cytoprotective factors. It has also been suggested that endogenous MSC as well as exogenously transplanted MSC migrate and participate in cardiac repair. Based on these findings, several clinical trials have just been started to evaluate the safety and efficacy of MSC for the treatment of heart failure.

Treatment of diabetic wounds with fetal murine mesenchymal stromal cells enhances wound closure

Diabetes impairs multiple aspects of the wound-healing response. Delayed wound healing continues to be a significant healthcare problem for which effective therapies are lacking. We have hypothesized that local delivery of mesenchymal stromal cells (MSC) at a wound might correct many of the wound-healing impairments seen in diabetic lesions. We treated excisional wounds of genetically diabetic (Db-/Db-) mice and heterozygous controls with either MSC, CD45(+) cells, or vehicle. At 7 days, treatment with MSC resulted in a decrease in the epithelial gap from 3.2 +/- 0.5 mm in vehicle-treated wounds to 1.3 +/- 0.4 mm in MSC-treated wounds and an increase in granulation tissue from 0.8 +/- 0.3 mm(2) to 2.4 +/- 0.6 mm(2), respectively (mean +/- SD, P < 0.04). MSC-treated wounds also displayed a higher density of CD31(+) vessels and exhibited increases in the production of mRNA for epidermal growth factor, transforming growth factor beta 1, vascular endothelial growth factor, and stromal-derived growth factor 1-alpha. MSC also demonstrated greater contractile ability than fibroblast controls in a collagen gel contraction assay. The effects of locally applied MSC are thus sufficient to improve healing in diabetic mice. Possible mechanisms of this effect include augmented local growth-factor production, improved neovascularization, enhanced cellular recruitment to wounds, and improved wound contraction.

Mesenchymal stem cells: a new strategy for immunosuppression?

In vitro-generated mesenchymal stem cells (MSCs) initially attracted interest for their ability to undergo differentiation toward cells of different lineages. More recently, a major breakthrough was the discovery that MSCs exert a profound inhibitory effect on T cell proliferation in vitro and in vivo. Subsequently, MSCs were shown also to exert similar effects on B cells, dendritic cells and natural killer cells. These results suggested that MSCs could be used to dampen immune-mediated diseases and transplant rejection. It is possible that some of the beneficial effects of MSCs might reflect, in part, the trophic and protective activities they exert on injured cells and tissues, rather than resulting from a true transdifferentiation. In immune-mediated diseases, the protective effects might function in concert with the immunosuppressive and anti-inflammatory activities.

Isolation of an adult mouse lung mesenchymal progenitor cell population

Contained within the adult lung are differentiated mesenchymal cell types (cartilage, smooth muscle, and myofibrobasts) that provide structural support for airways and vessels. Alterations in the number and phenotype of these cells figure prominently in the pathogenesis of a variety of lung diseases. While these cells are thought to arise locally, progenitors have yet to be purified. In previous work, we developed a method for isolating progenitors from lung tissue: this technique takes advantage of the unique ability of cell populations enriched for somatic stem and progenitor activity to efflux the vital dye Hoechst 33342, a feature that permits isolation by flow cytometry-based procedures. Using this method, we determined that a rare population of mesenchymal progenitors resides within the CD45- CD31- Hoechst low fraction of the adult murine lung. Similar to other mesenchymal progenitors, these cells express Sca-1, CD106, and CD44; can be serially passaged; and can differentiate to smooth muscle, cartilage, bone, and fat. Overall, these findings demonstrate that a phenotypically distinct mesenchymal progenitor resides within the adult murine lung, and provide a scheme for their isolation and study.

Contribution of VCAF-positive cells to neovascularization and calcification in atherosclerotic plaque development

Calcification of the vessel wall is a regulated process with many similarities to osteogenesis. Progenitor cells may play a role in this process. Previously, we identified a novel gene, Vascular Calcification Associated Factor (VCAF), which was shown to be important in pericyte osteogenic differentiation. The aim of this study was to determine the localization and expression pattern of VCAF in human cells and tissues. Immunohistochemical analysis of seven atherosclerotic arteries confirmed VCAF protein expression within calcified lesions. In addition, individual VCAF-positive cells were detected within the intima and adventitia in areas where sporadic 3G5-positive pericytes were localized. Furthermore, VCAF-positive cells were identified in newly formed microvessels in association with CD34-positive/CD146-positive/c-kit-positive cells as well as in intact CD31-positive endothelium in internal mammary arteries. Western blot analysis confirmed the presence of VCAF (18 kD) in protein lysates extracted from human smooth muscle cells, endothelial cells, macrophages, and osteoblasts. In fracture callus samples from three patients, VCAF was detected in osteoblasts and microvessels. This study demonstrates the presence of VCAF in neovessels and raises the possibility that VCAF could be a new marker for vascular progenitor cells involved in a number of differentiation pathways. These data may have implications for the prevention or treatment of vascular disease.

The role of mesenchymal stem cells in maintenance and repair of bone

The maintenance of stable bone mass during adult life, following rapid skeletal growth during childhood, is the result of a carefully controlled balance between the activities of bone forming (osteoblast) and bone resorbing (osteoclast) cells. Although skeletal turnover continues throughout adult life, the net effect of formation and resorption on bone mass is zero in healthy individuals. Later in life, bone mass begins to fall as resorption outpaces formation, particularly in post-menopausal women, which leads to increased fracture risk. The opposing actions of these two cell types are coupled by molecular interactions between them that are thought to be influenced by the actions of the precursor cells of the osteoblast lineage, mesenchymal stem cells (MSCs). In addition to regulating normal skeletal homeostasis, MSCs also play an important role in fracture repair. Bone fracture or injury initiates a series of cellular and molecular pathways that commence with hematoma formation and an inflammatory cascade that regulates MSCs activity leading to fracture healing and the reestablishment of skeletal integrity. Although tremendous strides have been made in increasing our understanding of bone biology, there is surprisingly little data about the role of MSCs in vivo in the maintenance of skeletal integrity or fracture repair. In recent years, the pivotal importance of anabolic therapies in the setting of osteoporosis in which bone mass is substantially increased above and beyond what is attainable with the bisphosphonate class of drugs has put MSC biology firmly on the scientific agenda. Although the biology of cultured MSCs is reasonably well understood, the biology of MSCs in vivo in both bone turnover and fracture repair remains poorly understood. The recent phenotypic characterization of in vivo MSCs and the ability to prospectively purify such cells will open up new avenues of research into a better understanding of the role of MSCs in bone turnover. The purpose of this article is to review bone and fracture biology from the perspective of recent advances in our understanding of MSCs and to highlight the major deficiencies in our current knowledge.

Mesenchymal stem cells: Immunobiology and therapeutic potential in kidney disease (Review Article)

Mesenchymal stem cells (MSC) are non-haematopoietic cells that are prevalent in the adult bone marrow but can also be isolated from a variety of other postnatal tissues. MSC are non-immunogenic and are immunosuppressive, with the ability to inhibit maturation of dendritic cells and suppress the function of naïve and memory T cells, B cells and NK cells. In addition to their immunomodulatory properties, MSC are capable of differentiating into various tissues of mesenchymal and non-mesenchymal origin and migrating to sites of tissue injury and inflammation to participate in tissue repair. A number of studies in animal models of cardiac injury, stroke and ischaemic renal injury have demonstrated the clinical potential of MSC in tissue regeneration and repair. MSC are currently being evaluated in various preclinical and clinical studies in humans and offer significant potential as a novel cellular therapy for tissue regeneration and immunological conditions. The present review focuses on the unique immunomodulatory and regenerative properties of MSC and their potential role in the treatment of kidney disease.

Reflections on lineage potential of skeletal muscle satellite cells: do they sometimes go MAD?

Postnatal muscle growth and repair is supported by satellite cells--myogenic progenitors positioned between the myofiber basal lamina and plasma membrane. In adult muscles, satellite cells are quiescent but become activated and contribute differentiated progeny when myofiber repair is needed. The development of cells expressing osteogenic and adipogenic genes alongside myoblasts in myofiber cultures raised the hypothesis that satellite cells possess mesenchymal plasticity. Clonal studies of myofiber-associated cells further suggest that satellite cell myogeneity and diversion into Mesenchymal Alternative Differentiation (MAD) occur in vitro by a stochastic mechanism. However, in vivo this potential may be executed only when myogenic signals are impaired and the muscle tissue is compromised. Such a mechanism may contribute to the increased adiposity of aging muscles. Alternatively, it is possible that mesenchymal interstitial cells (sometimes co-isolated with myofibers), rather than satellite cells, account for the nonmyogenic cells observed in myogenic cultures. Herein, we first elaborate on the myogenic potential of satellite cells. We then introduce definitions of adult stem-cell unipotency, multipotency, and plasticity, as well as elaborate on recent studies that established the status of satellite cells as myogenic stem cells. Last, we highlight evidence in favor of satellite cell plasticity and emerging hurdles restraining this hypothesis.

Influence of hormones on osteogenic differentiation processes of mesenchymal stem cells

Bone development, regeneration and maintenance are governed by osteogenic differentiation processes from mesenchymal stem cells through to mature bone cells, which are directed by local growth and differentiation factors and modulated strongly by hormones. Mesenchymal stem cells develop from both mesoderm and neural crest and can give rise to development, regeneration and maintenance of mesenchymal tissues, such as bone, cartilage, muscle, tendons and discs. There are only limited data regarding the effects of hormones on early events, such as regulation of stemness and maintenance of the mesenchymal stem cell pool. Hormones, such as estrogens, vitamin D-hormone and parathyroid hormone, besides others, are important modulators of osteogenic differentiation processes and bone formation, starting off with fate decision and the development of osteogenic offspring from mesenchymal stem cells, which end up in osteoblasts and osteocytes. Hormones are involved in fetal bone development and regeneration and, in childhood, adolescence and adulthood, they control adaptive needs for growth and reproduction, nutrition, physical power and crisis adaptation. As in other tissues, aging in mesenchymal stem cells and their osteogenic offspring is accompanied by the accumulation of genomic and proteomic damage caused by oxidative burden and insufficient repair. Failsafe programs, such as apoptosis and cellular senescence avoid tumorigenesis. Hormones can influence the pace of such events, thus supporting the quality of tissue regeneration in aging organisms in vivo; for example, by delaying osteoporosis development. The potential for hormones in systemic therapeutic strategies is well appreciated and some concepts are approved for clinical use already. Their potential for cell-based therapeutic strategies for tissue regeneration is probably underestimated and could enhance the quality of tissue-engineering constructs for transplantation and the concept of in situ-guided tissue regeneration.

Adult bone marrow–derived stem cells for organ regeneration and repair

Stem cells have been recognized as a potential tool for the development of innovative therapeutic strategies. There are in general two types of stem cells, embryonic and adult stem cells. While embryonic stem cell therapy has been riddled with problems of allogeneic rejection and ethical concerns, adult stem cells have long been used in the treatment of hematological malignancies. With the recognition of additional, potentially therapeutic characteristics, bone marrow-derived stem cells have become a tool in regenerative medicine. The bone marrow is an ideal source of stem cells because it is easily accessible and harbors two types of stem cells. Hematopoietic stem cells give rise to all blood cell types and have been shown to exhibit plasticity, while multipotent marrow stromal cells are the source of osteocytes, chondrocytes, and fat cells and have been shown to support and generate a large number of different cell types. This review describes the general characteristics of these stem cell populations and their current and potential future applications in regenerative medicine.

Polyethylene Glycol-Mediated Fusion between Primary Mouse Mesenchymal Stem Cells and Mouse Fibroblasts Generates Hybrid Cells with Increased Proliferation and Altered Differentiation

Bone marrow-derived mesenchymal stem cells (MSCs) can differentiate into different cell lineages with the appropriate stimulation in vitro. Transplantation of MSCs in human and other animal models was found to repair tissues through the fusion of transplanted MSCs with indigenous cells. We have generated mouseâmouse hybrid cell lines in vitro by polyethylene glycol-mediated fusion of primary mouse MSCs with mouse fibroblasts to investigate the characteristics of hybrid cells, including their potentials for proliferation and differentiation. Similar to the parental MSCs, hybrid cells are positive for the cell-surface markers CD29, CD44, CD49e, and Sca-1, and negative for Gr-1, CD11b, CD13, CD18, CD31, CD43, CD45, CD49d, CD90.2, CD445R/B220, and CD117 markers. The hybrid cells also produce a high level of tissue nonspecific alkaline phosphatase compared to the parental cells. Conditioned medium of hybrid cells contain biologically active factors that are capable of stimulating proliferation of other cells. Although the parental MSCs can differentiate into adipogenic and osteogenic lineages, hybrid cells held disparate differentiation capacity. Hybrid cell lines in general have increased proliferative capacity than the primary MSCs. Our study demonstrates that proliferative hybrid cell lines can be generated in vitro by induced fusion of both immortal and primary somatic cells with primary MSCs.

Immunoregulatory function of mesenchymal stem cells

Mesenchymal stem cells (MSC) are a rare subset of stem cells residing in the bone marrow where they closely interact with hematopoietic stem cells and support their growth and differentiation. MSC can differentiate into multiple mesenchymal and non-mesenchymal lineages, providing a promising tool for tissue repair. In addition, MSC suppress many T cell, B cell and NK cell functions and may affect also dendritic cell activities. Due to their limited immunogenicity, MSC are poorly recognized by HLA-incompatible hosts. Based on these unique properties, MSC are currently under investigation for their possible use to treat immuno-mediated diseases. However, both their condition of immunoprivilege and their immunosuppressive function have recently been challenged when analyzed under particular experimental conditions. Thus, it is likely that MSC effects on the immune system may be deeply influenced not only by cell-to-cell interactions, but also by environmental factors shaping their phenotype and functions.

Human cardiac stem cells exhibit mesenchymal features and are maintained through Akt/GSK-3beta signaling

Recent evidence suggested that human cardiac stem cells (hCSCs) may have the clinical application for cardiac repair; however, their characteristics and the regulatory mechanisms of their growth have not been fully investigated. Here, we show the novel property of hCSCs with respect to their origin and tissue distribution in human heart, and demonstrate the signaling pathway that regulates their growth and survival. Telomerase-active hCSCs were predominantly present in the right atrium and outflow tract of the heart (infant > adult) and had a mesenchymal cell-like phenotype. These hCSCs expressed the embryonic stem cell markers and differentiated into cardiomyocytes to support cardiac function when transplanted them into ischemic myocardium. Inhibition of Akt pathway impaired the hCSC proliferation and induced apoptosis, whereas inhibition of glycogen synthase kinase-3 (GSK-3) enhanced their growth and survival. We conclude that hCSCs exhibit mesenchymal features and that Akt/GSK-3beta may be crucial modulators for hCSC maintenance in human heart.

Skeletal myosphere-derived progenitor cell transplantation promotes neovascularization in delta-sarcoglycan knockdown cardiomyopathy

Bone marrow cells have been shown to contribute to neovascularization in ischemic hearts, whereas their impaired maturation to restore the delta-sarcoglycan (delta-SG) expression responsible for focal myocardial degeneration limits their utility to treat the pathogenesis of cardiomyopathy. Here, we report the isolation of multipotent progenitor cells from adult skeletal muscle, based on their ability to generate floating-myospheres. Myosphere-derived progenitor cells (MDPCs) are distinguishable from myogenic C2C12 cells and differentiate into vascular smooth muscle cells and mesenchymal progeny. The mutation in the delta-SG has been shown to develop vascular spasm to affect sarcolemma structure causing cardiomyopathy. We originally generated delta-SD knockdown (KD) mice and transplanted MDPCs into the hearts. MDPCs enhanced neoangiogenesis and restored delta-SG expression in impaired vasculatures through trans-differentiation, leading to improvement of cardiac function associated with paracrine effectors secretion. We propose that MDPCs may be the promising progenitor cells in skeletal muscle to treat delta-sarcoglycan complex mutant cardiomyopathy.

Fibroblasts and myofibroblasts: their source, function and role in disease

Fibroblasts are found in most tissues of the body. They exhibit several phenotypes including non-contractile fibroblasts, contractile myofibroblasts, and intermediate phenotypes including the protomyofibroblast. Fibroblasts are metabolically active cells which play critical roles regulating extracellular matrices, interstitial fluid volume and pressure, and wound healing. Fibroblast numbers can be maintained or expanded by proliferation of resident populations but in addition, recent evidence indicates they can also be derived through epithelial-mesenchymal transition or from circulating and tissue-derived mesenchymal stem cells. Many diseases are associated with dysregulation of the injury repair response and fibroblast function, leading to increased or decreased deposition of extracellular matrix proteins, altered tissue architecture, impaired function and in some cases significant morbidity and mortality. There are currently no specific therapies that target fibroblast-associated pathology but increasing knowledge of pathological mechanisms has led to development of new agents providing hope for improved treatment of these diseases.

Inhibition of in vitro chondrogenesis in RGD-modified three-dimensional alginate gels

The goal of this study was to investigate the effects of adhesion to the arginine-glycine-aspartic acid (RGD) sequence on the chondrogenesis of bone marrow stromal cells (BMSCs). Synthetic RGE- and RGD-containing peptides were conjugated to sodium alginate, and bovine BMSCs were seeded onto 2D alginate surfaces or encapsulated in 3D gels. BMSCs spread specifically on RGD-modified surfaces, and spreading was inhibited by a soluble RGD peptide and by anti-beta1 and anti-alpha(v)beta3 integrin blocking antibodies. After 7 days in 3D gel culture, the chondrogenic supplements (TGF-beta1 and dexamethasone) significantly stimulated chondrocytic gene expression (collagen II, aggrecan, and Sox-9) and matrix accumulation (collagen II and sGAG) in RGE-modified gels, but this response was inhibited in the RGD-modified gels. Inhibition of sGAG synthesis increased with increasing RGD density, and synthesis was partially rescued by adding a soluble RGD peptide. Addition of an anti-alpha(v)beta3 integrin blocking antibody had no effect on chondrogenesis, while an anti-alpha5 antibody reduced sGAG accumulation. Overall, this study demonstrates that interaction with the RGD motif significantly inhibits the initial chondrogenesis of BMSCs within 3D alginate gels. These results provide new insights into the role of cell-matrix interactions in regulating chondrogenesis and highlight the importance of choosing appropriate biomaterials for tissue engineering therapies.

Vascular smooth muscle cell phenotypic plasticity and the regulation of vascular calcification

Vascular smooth muscle cells (VSMCs) exhibit an extraordinary capacity to undergo phenotypic change during development, in vitro and in association with disease. Unlike other muscle cells they do not terminally differentiate. Development and maintenance of the mature contractile phenotype is regulated by a number of interacting transcription factors. In response to injury contractile VSMCs can be induced to change phenotype, proliferate and migrate to effect repair. On completion of the repair process VSMCs return to a nonproliferating contractile phenotype. In this way, in the context of atherosclerosis, a protective fibrous cap is formed and maintained at sites of injury. However in disease, when modulatory signals are perturbed, this phenotypic transition is dysregulated and VSMCs are induced to undergo inappropriate differentiation into cells with features of other mesenchymal lineages such as osteoblasts, chondrocytes and adipocytes. Moreover, evidence is accumulating that these aberrant phenotypic transitions contribute to the pathogenesis of vascular diseases such as atherosclerosis and Monckeberg's Sclerosis. Indeed, the osteo/chondrocytic conversion of VSMCs and the association of this phenotype with vascular calcification is a paradigm for how inappropriate differentiation can influence disease processes. Understanding of the mechanisms and signalling pathways involved in this particular phenotype change is well advanced offering the possibility for the design of successful therapeutic interventions in the future.

Isolation and characterization of a stem cell population from adult human liver

Several studies suggested the presence of stem cells in the adult normal human liver; however, a population with stem cell properties has not yet been isolated. The purpose of the present study was to identify and characterize progenitor cells in normal adult human liver. By stringent conditions of liver cell cultures, we isolated and characterized a population of human liver stem cells (HLSCs). HLSCs expressed the mesenchymal stem cell markers CD29, CD73, CD44, and CD90 but not the hematopoietic stem cell markers CD34, CD45, CD117, and CD133. HLSCs were also positive for vimentin and nestin, a stem cell marker. The absence of staining for cytokeratin-19, CD117, and CD34 indicated that HLSCs were not oval stem cells. In addition, HLSCs expressed albumin, alpha-fetoprotein, and in a small percentage of cells, cytokeratin-8 and cytokeratin-18, indicating a partial commitment to hepatic cells. HLSCs differentiated in mature hepatocytes when cultured in the presence of hepatocyte growth factor and fibroblast growth factor 4, as indicated by the expression of functional cytochrome P450, albumin, and urea production. Under this condition, HLSCs downregulated alpha-fetoprotein and expressed cytokeratin-8 and cytokeratin-18. HLSCs were also able to undergo osteogenic and endothelial differentiation when cultured in the appropriated differentiation media, but they did not undergo lipogenic differentiation. Moreover, HLSCs differentiated in insulin-producing islet-like structures. In vivo, HLSCs contributed to regeneration of the liver parenchyma in severe-combined immunodeficient mice. In conclusion, we here identified a pluripotent progenitor population in adult human liver that could provide a basis for cell therapy strategies.

GFP chimeric models exhibited a biphasic pattern of mesenchymal cell invasion in tendon healing

The healing of an injured musculoskeletal system requires an influx of mesenchymal cells that can differentiate into osteoblasts, fibroblasts, chondroblasts, and skeletal myoblasts. However, whether these mesenchymal cells arise from the circulation (bone marrow) or the injured tissues themselves has been controversial. To reveal the spatiotemporal characteristics of the reparative mesenchymal cells, we investigated the healing process after patellar tendon injury using two types of green fluorescent protein (GFP) chimeric rats; one expressing GFP in the circulating cells, and the other expressing it in the patellar tendon. We analyzed the behavior of GFP-positive cells after experimental tendon injury in both chimeric rats to clarify the origin of reparative cells. At 24 h after the injury, the wound contained circulation-derived cells but not tendon-derived cells. Tendon-derived cells first appeared in the wounded area at 3 days after the injury, and had significantly increased in number with time and had maintained a high level of proliferative activity until 7 days after the injury, whereas the circulation-derived cells had decreased in number and had been replaced by the tendon-derived cells. These findings suggest that circulation-derived and tendon-derived cells contribute to the healing of tendons in different periods as part of a biphasic process.