Why are MSCs therapeutic? New data: new insight

Mesenchymal stem cells inhibit complement activation by secreting factor H

Mesenchymal stem cells (MSCs) possess potent and broad immunosuppressive capabilities, and have shown promise in clinical trials treating many inflammatory diseases. Previous studies have found that MSCs inhibit dendritic cell, T-cell, and B-cell activities in the adaptive immunity; however, whether MSCs inhibit complement in the innate immunity, and if so, by which mechanism, have not been established. In this report, we found that MSCs constitutively secrete factor H, which potently inhibits complement activation. Depletion of factor H in the MSC-conditioned serum-free media abolishes their complement inhibitory activities. In addition, production of factor H by MSCs is augmented by inflammatory cytokines TNF-α and interferon-γ (IFN-γ) in dose- and time-dependent manners, while IL-6 does not have a significant effect. Furthermore, the factor H production from MSCs is significantly suppressed by the prostaglandin E2 (PGE2) synthesis inhibitor indomethacin and the indoleamine 2,3-dioxygenase (IDO) inhibitor 1-methyl-d-tryptophan (1-MT), both of which inhibitors are known to efficiently dampen MSCs immunosuppressive activity. These results indicate that MSCs inhibit complement activation by producing factor H, which could be another mechanism underlying MSCs broad immunosuppressive capabilities.

Potential therapeutic applications of muscle-derived mesenchymal stem and progenitor cells

IMPORTANCE OF THE FIELD

Mesenchymal adult stem cells have properties that make them attractive for use in tissue engineering and regenerative medicine. They are inherently plastic, enabling them to differentiate along different lineages, and promote wound healing and regeneration of surrounding tissues by modulating immune and inflammatory responses, promoting angiogenesis and secreting other trophic factors. Unlike embryonic stem cells, clinical uses of mesenchymal stem cells are not encumbered by ethical considerations or legal restrictions.

AREAS COVERED IN THIS REVIEW

We discuss skeletal muscle as a source of mesenchymal stem and progenitor cells by reviewing their biology and current applications in tissue engineering and regenerative medicine. This paper covers literature from the last 5 - 10 years.

WHAT THE READER WILL GAIN

Skeletal muscle is a plentiful source of mesenchymal stem and progenitor cells. This tissue may be obtained via routine biopsy or collection after surgical debridement. We describe the biology of these cells and provide an overview of therapeutic applications currently being developed to take advantage of their regenerative properties.

TAKE HOME MESSAGE

There is potential for stem and progenitor cells derived from skeletal muscle to be incorporated in clinical interventions, either as a cellular therapy to modify the natural history of disease or as a component of engineered tissue constructs that can replace diseased or damaged tissues.

Oxygen tension differentially influences osteogenic differentiation of human adipose stem cells in 2D and 3D cultures

Skeletal defects commonly suffer from poor oxygen microenvironments resulting from compromised vascularization associated with injury or disease. Adipose stem cells (ASCs) represent a promising cell population for stimulating skeletal repair by differentiating toward the osteogenic lineage or by secreting trophic factors. However, the osteogenic or trophic response of ASCs to reduced oxygen microenvironments is poorly understood. Moreover, a direct comparison between 2D and 3D response of ASCs to hypoxia is lacking. Thus, we characterized the osteogenic and angiogenic potential of human ASCs under hypoxic (1%), normoxic (5%), and atmospheric (21%) oxygen tensions in both 2D and 3D over 4 weeks in culture. We detected greatest alkaline phosphatase activity and extracellular calcium deposition in cells cultured in both 2D and 3D under 21% oxygen, and reductions in enzyme activity corresponded to reductions in oxygen tension. ASCs cultured in 1% oxygen secreted more vascular endothelial growth factor (VEGF) over the 4-week period than cells cultured in other conditions, with cells cultured in 2D secreting VEGF in a more sustained manner than those in 3D. Expression of osteogenic markers revealed temporal changes under different oxygen conditions with peak expression occurring earlier in 3D. In addition, the increase of most osteogenic markers was significantly higher in 2D compared to 3D cultures at 1% and 5% oxygen. These results suggest that oxygen, in conjunction with dimensionality, affects the timing of the differentiation program in ASCs. These findings offer new insights for the use of ASCs in bone repair while emphasizing the importance of the culture microenvironment.

Adult stem cells in the endometrium

Rare cells with adult stem cell activity were recently discovered in human endometrium. Endometrial stem/progenitor cell candidates include epithelial, mesenchymal and endothelial cells, and all may contribute to the rapid endometrial regeneration following menstruation, rather than a single candidate. Endometrial mesenchymal stem-like cells (eMSC) are prospectively isolated as CD146(+)PDGF-Rβ(+) cells and are found in both basalis and functionalis as perivascular cells. Epithelial progenitor cells are detected in colony forming unit assays but their identity awaits elucidation. They are postulated to reside in the basalis in gland bases. Endometrial stem/progenitor cells may be derived from endogenous stem cells, but emerging evidence suggests a bone marrow contribution. Endometrial endothelial progenitor cells are detected as side population cells, which express several endothelial cell markers and differentiate into endometrial glandular epithelial, stromal and endothelial cells. Investigating endometrial stem cell biology is crucial to understanding normal endometrial physiology and to determine their roles in endometrial proliferative diseases. The nature of endometriosis suggests that initiation of ectopic endometrial lesions involves endometrial stem/progenitor cells, a notion compatible with Sampson's retrograde menstruation theory and supported by the demonstration of eMSC in menstrual blood. Evidence of cancer stem cells (CSC) in endometrial cancer indicates that new avenues for developing therapeutic options targeting CSC may become available. We provide an overview of the accumulating evidence for endometrial stem/progenitor cells and their possible roles in endometrial proliferative disorders, and discuss the unresolved issues.

Hydrogen gas treatment prolongs replicative lifespan of bone marrow multipotential stromal cells in vitro while preserving differentiation and paracrine potentials

Cell therapy with bone marrow multipotential stromal cells/mesenchymal stem cells (MSCs) represents a promising approach in the field of regenerative medicine. Low frequency of MSCs in adult bone marrow necessitates ex vivo expansion of MSCs after harvest; however, such a manipulation causes cellular senescence with loss of differentiation, proliferative, and therapeutic potentials of MSCs. Hydrogen molecules have been shown to exert organ protective effects through selective reduction of hydroxyl radicals. As oxidative stress is one of the key insults promoting cell senescence in vivo as well as in vitro, we hypothesized that hydrogen molecules prevent senescent process during MSC expansion. Addition of 3% hydrogen gas enhanced preservation of colony forming early progenitor cells within MSC preparation and prolonged the in vitro replicative lifespan of MSCs without losing differentiation potentials and paracrine capabilities. Interestingly, 3% hydrogen gas treatment did not decrease hydroxyl radical, protein carbonyl, and 8-hydroxydeoxyguanosine, suggesting that scavenging hydroxyl radical might not be responsible for these effects of hydrogen gas in this study.

In vitro human bone marrow analog: clinical potential

Bone marrow is the primary site of hematopoiesis in adult humans. Bone marrow can be cultured in vitro but few simple culture systems fully support hematopoiesis beyond a few months. Human bone marrow analogs are long-term in vitro cultures of marrow stromal and hematopoietic stem cells that can be used to produce cells and products normally harvested from human donors. Bone marrow analog systems should exhibit confluence of the stromal cell populations, persistence of hematopoietic progenitor cells, presence of active regions of hematopoiesis and capacity to produce mature cell types for extended periods of time. Although we are still years away from realizing clinical application of products formed by artificial bone marrow analogs, the process of transitioning this research tool from bench to bedside should be fairly straightforward. The most obvious application of artificial marrow would be for production of autologous hematopoietic CD34(+) stem cells as a stem cell therapy for individuals experiencing bone marrow failure due to disease or injury. Another logical application is for 'blood farming', a process for large-scale in vitro production of red blood cells, white blood cells or platelets, for transfusion or treatment. Other possibilities include production of nonhematopoietic stem cells such as osteogenic stromal cells, osteoblasts and rare pluripotent stem cells. Bone marrow analogs also have great potential as ex vivo human test systems and could play a critical role in drug discovery, drug development and toxicity testing in the future.

Characterization of stem and progenitor cells in the dental pulp of erupted and unerupted murine molars

In the past few years there have been significant advances in the identification of putative stem cells also referred to as "mesenchymal stem cells" (MSC) in dental tissues including the dental pulp. It is thought that MSC in dental pulp share certain similarities with MSC isolated from other tissues. However, cells in dental pulp are still poorly characterized. This study focused on the characterization of progenitor and stem cells in dental pulps of erupted and unerupted mice molars. Our study showed that dental pulps from unerupted molars contain a significant number of cells expressing CD90+/CD45-, CD117+/CD45-, Sca-1+/CD45- and little if any CD45+ cells. Our in vitro functional studies showed that dental pulp cells from unerupted molars displayed extensive osteo-dentinogenic potential but were unable to differentiate into chondrocytes and adipocytes. Dental pulps from erupted molars displayed a reduced number of cells, contained a higher percentage of CD45+ and a lower percentage of cells expressing CD90+/CD45-, CD117+/CD45- as compared to unerupted molars. In vitro functional assays demonstrated the ability of a small fraction of cells to differentiate into odontoblasts, osteoblasts, adipocytes and chondrocytes. There was a significant reduction in the osteo-dentinogenic potential of the pulp cells derived from erupted molars compared to unerupted molars. Furthermore, the adipogenic and chondrogenic differentiation of pulp cells from erupted molars was dependent on a long induction period and were infrequent. Based on these findings we propose that the dental pulp of the erupted molars contain a small population of multipotent cells, whereas the dental pulp of the unerupted molars does not contain multipotent cells but is enriched in osteo-dentinogenic progenitors engaged in the formation of coronal and radicular odontoblasts.

Concentrated autologous bone marrow aspirate transplantation treatment for corticosteroid-induced osteonecrosis of the femoral head in systemic lupus erythematosus

The purpose of this study was to evaluate concentrated autologous bone marrow aspirate transplantation (CABMAT) treatment for corticosteroid-induced osteonecrosis of the femoral head (ONFH) in systemic lupus erythematosus (SLE). Bone marrow was aspirated from iliac crests, concentrated on a conventional manual blood bag centrifugation technique that is used to extract buffy coats and then injected into nine hips with drilling. The mean number of nucleated cells for transplantation was 5.32 × 10(7) cells/ml. This cell concentration was significantly higher after concentration, and the mean concentration ratio was 5.5. At follow-up (minimum: three years), significant improvement in pain and Harris Hip Score was observed. For eight of nine hips, we successfully preserved the femoral head. However, one hip required total hip arthroplasty 45 months after the operation. CABMAT using our centrifugation technique is an effective, safe and low-cost procedure of therapeutic osteogenesis for corticosteroid-induced ONFH in SLE.

Autologous bone grafting on steroids: preliminary clinical results. A novel treatment for nonunions and segmental bone defects

Clinical management of delayed healing or nonunion of long bone fractures and segmental bone defects poses a substantial orthopaedic challenge. Surgical advances and bone tissue engineering are providing new avenues to stimulate bone growth in cases of bone loss and nonunion. The reamer-irrigator-aspirator (RIA) device allows surgeons to aspirate the medullary contents of long bones and use the progenitor-rich "flow-through" fraction in autologous bone grafting. Dexamethasone (DEX) is a synthetic steroid that has been shown to induce osteoblastic differentiation. A series of 13 patients treated with RIA bone grafting enhanced with DEX for nonunion or segmental defect was examined retrospectively to assess the quality of bony union and clinical outcomes. Despite the initial poor prognoses, promising results were achieved using this technique; and given the complexity of these cases the observed success is of great value and warrants controlled study into both standardisation of the procedure and concentration of the grafting material.

Toward brain tumor gene therapy using multipotent mesenchymal stromal cell vectors

Gene therapy of solid cancers has been severely restricted by the limited distribution of vectors within tumors. However, cellular vectors have emerged as an effective migratory system for gene delivery to invasive cancers. Implanted and injected multipotent mesenchymal stromal cells (MSCs) have shown tropism for several types of primary tumors and metastases. This capacity of MSCs forms the basis for their use as a gene vector system in neoplasms. Here, we review the tumor-directed migratory potential of MSCs, mechanisms of the migration, and the choice of therapeutic transgenes, with a focus on malignant gliomas as a model system for invasive and highly vascularized tumors. We examine recent findings demonstrating that MSCs share many characteristics with pericytes and that implanted MSCs localize primarily to perivascular niches within tumors, which might have therapeutic implications. The use of MSC vectors in cancer gene therapy raises concerns, however, including a possible MSC contribution to tumor stroma and vasculature, MSC-mediated antitumor immune suppression, and the potential malignant transformation of cultured MSCs. Nonetheless, we highlight the novel prospects of MSC-based tumor therapy, which appears to be a promising approach.

Stem cell paracrine actions and tissue regeneration

Stem cells have emerged as a key element of regenerative medicine therapies due to their inherent ability to differentiate into a variety of cell phenotypes, thereby providing numerous potential cell therapies to treat an array of degenerative diseases and traumatic injuries. A recent paradigm shift has emerged suggesting that the beneficial effects of stem cells may not be restricted to cell restoration alone, but also due to their transient paracrine actions. Stem cells can secrete potent combinations of trophic factors that modulate the molecular composition of the environment to evoke responses from resident cells. Based on this new insight, current research directions include efforts to elucidate, augment and harness stem cell paracrine mechanisms for tissue regeneration. This article discusses the existing studies on stem/progenitor cell trophic factor production, implications for tissue regeneration and cancer therapies, and development of novel strategies to use stem cell paracrine delivery for regenerative medicine.

Engineered mesenchymal stem cells with self-assembled vesicles for systemic cell targeting

Cell therapy has the potential to impact the quality of life of suffering patients. Systemic infusion is a convenient method of cell delivery; however, the efficiency of engraftment presents a major challenge. It has been shown that modification of the cell surface with adhesion ligands is a viable approach to improve cell homing, yet current methods including genetic modification suffer potential safety concerns, are practically complex and are unable to accommodate a wide variety of homing ligands or are not amendable to multiple cell types. We report herein a facile and generic approach to transiently engineer the cell surface using lipid vesicles to present biomolecular ligands that promote cell rolling, one of the first steps in the homing process. Specifically, we demonstrated that lipid vesicles rapidly fuse with the cell membrane to introduce biotin moieties on the cell surface that can subsequently conjugate streptavidin and potentially any biotinylated homing ligand. Given that cell rolling is a pre-requisite to firm adhesion for systemic cell homing, we examined the potential of immobilizing sialyl Lewis X (SLeX) on mesenchymal stem cells (MSCs) to induce cell rolling on a P-selectin surface, under dynamic flow conditions. MSCs modified with SLeX exhibit significantly improved rolling interactions with a velocity of 8 microm/s as compared to 61 microm/s for unmodified MSCs at a shear stress of 0.5 dyn/cm(2). The cell surface modification does not impact the phenotype of the MSCs including their viability and multi-lineage differentiation potential. These results show that the transitory modification of cell surfaces with lipid vesicles can be used to efficiently immobilize adhesion ligands and potentially target systemically administered cells to the site of inflammation.

More insight into mesenchymal stem cells and their effects inside the body

IMPORTANCE OF THE FIELD

The pan-tissue existence and multipotency of differentiation make mesenchymal stem cells (MSCs) an attractive source of cells as tissue repair cells, seeds of engineered tissue, vehicles for gene therapy or in combination to promote tissue regeneration in wound healing and disease recovery.

AREAS COVERED IN THIS REVIEW

This review focuses on recent understanding on MSC's basic biological characteristics and the mechanisms underlying the therapeutic effects of MSCs in vivo.

WHAT THE READER WILL GAIN

The gene expression profiles for mRNA, protein, microRNA and cell surface marker of MSCs are summarized. Special attention is given to miRNA expression and its relationship with the characteristics of MSCs. The mechanisms of therapeutic effects of MSCs are attributed to their ability to migrate along chemokine gradients, differentiate into tissue-specific cells, enhance angiogenesis of wound tissue and regulate immune response. As examples, a detailed description is given on the regeneration of functional sweat glands on burned skin as well as neural cells in middle cerebral artery occlusion (MCAO) animals upon MSC transplantation.

TAKE HOME MESSAGE

Based on current data, although limited, the mesenchymal-epithelial transition is proposed to be one of the important ways for MSCs to participate tissue repair.

A novel serum-free medium for the expansion of human mesenchymal stem cells

Introduction

Human multipotent mesenchymal stem cell (MSC) therapies are being tested clinically for a variety of disorders, including Crohn's disease, multiple sclerosis, graft-versus-host disease, type 1 diabetes, bone fractures, and cartilage defects. However, despite the remarkable clinical advancements in this field, most applications still use traditional culture media containing fetal bovine serum. The ill-defined and highly variable nature of traditional culture media remains a challenge, hampering both the basic and clinical human MSC research fields. To date, no reliable serum-free medium for human MSCs has been available.

Methods

In this study, we developed and tested a serum-free growth medium on human bone marrow-derived MSCs through the investigation of multiple parameters including primary cell isolation, multipassage expansion, mesoderm differentiation, cellular phenotype, and gene-expression analysis.

Results

Similar to that achieved with traditional culture medium, human MSCs expanded in serum-free medium supplemented with recombinant human platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF), and transforming growth factor (TGF)-β1 showed extensive propagation with retained phenotypic, differentiation, and colony-forming unit potential. To monitor global gene expression, the transcriptomes of bone marrow-derived MSCs expanded under serum-free and serum-containing conditions were compared, revealing similar expression profiles. In addition, the described serum-free culture medium supported the isolation of human MSCs from primary human marrow aspirate with continual propagation.

Conclusions

Although the described serum-free MSC culture medium is not free of xenogeneic components, this medium provides a substitute for serum-containing medium for research applications, setting the stage for future clinical applications.

Direct and indirect effects of microstructured titanium substrates on the induction of mesenchymal stem cell differentiation towards the osteoblast lineage

Microstructured and high surface energy titanium substrates increase osseointegration in vivo. In vitro, osteoblast differentiation is increased, but effects of the surface directly on multipotent mesenchymal stem cells (MSCs) and consequences for MSCs in the peri-implant environment are not known. We evaluated responses of human MSCs to substrate surface properties and examined the underlying mechanisms involved. MSCs exhibited osteoblast characteristics (alkaline phosphatase, RUNX2, and osteocalcin) when grown on microstructured Ti; this effect was more robust with increased hydrophilicity. Factors produced by osteoblasts grown on microstructured Ti were sufficient to induce co-cultured MSC differentiation to osteoblasts. Silencing studies showed that this was due to signaling via alpha2beta1 integrins in osteoblasts on the substrate surface and paracrine action of secreted Dkk2. Thus, human MSCs are sensitive to substrate properties that induce osteoblastic differentiation; osteoblasts interact with these surface properties via alpha2beta1 and secrete Dkk2, which acts on distal MSCs.

Mesenchymal stem cell therapy: Two steps forward, one step back

Mesenchymal stem cell (MSC) therapy is poised to establish a new clinical paradigm; however, recent trials have produced mixed results. Although MSC were originally considered to treat connective tissue defects, preclinical studies revealed potent immunomodulatory properties that prompted the use of MSC to treat numerous inflammatory conditions. Unfortunately, although clinical trials have met safety endpoints, efficacy has not been demonstrated. We believe the challenge to demonstrate efficacy can be attributed in part to an incomplete understanding of the fate of MSC following infusion. Here, we highlight the clinical status of MSC therapy and discuss the importance of cell-tracking techniques, which have advanced our understanding of the fate and function of systemically infused MSC and might improve clinical application.

Bone marrow derived pluripotent cells are pericytes which contribute to vascularization

Pericytes are essential to vascularization, but the purification and characterization of pericytes remain unclear. Smooth muscle actin alpha (alpha-SMA) is one marker [corrected] of pericytes. The aim of this study is to purify the alpha-SMA positive cells from bone marrow and study the characteristics of these cells and the interaction between alpha-SMA positive cells and endothelial cells. The bone marrow stromal cells were harvested from alpha-SMA-GFP transgenic mice, and the alpha-SMA-GFP positive cells were sorted by FACS. The proliferative characteristics and multilineage differentiation ability of the alpha-SMA-GFP positive cells were tested. A 3-D culture model was then applied to test their vascularization by loading alpha-SMA-GFP positive cells and endothelial cells on collagen-fibronectin gel. Results demonstrated that bone marrow stromal cells are mostly alpha-SMA-GFP positive cells which are pluripotent, and these cells expressed alpha-SMA during differentiation. The alpha-SMA-GFP positive cells could stimulate the endothelial cells to form tube-like structures and subsequently robust vascular networks in 3-D culture. In conclusion, the bone marrow derived pluripotent cells include [corrected] pericytes and can contribute to vascularization.

Immune regulatory cells in umbilical cord blood: T regulatory cells and mesenchymal stromal cells

A major goal in haematopoietic cell transplantation (HCT) is to retain the lymphohaematopoietic potential of the cell transfer without its side effects. In addition to the physical injury caused by the conditioning regimen, donor T cells can react to alloantigens of the recipient and cause graft-versus-host disease (GVHD), which accounts for the largest share of morbidity and mortality after HCT. Immune modulator cells, such as regulatory T cells (Tregs) and mesenchymal stromal cells (MSCs) have shown promise in their ability to control GVHD and yet, in preclinical models, preserve the graft-versus-malignancy effect. Initially, MSCs and Tregs have been isolated from adult sources, such as bone marrow or peripheral blood, respectively. More recent studies have indicated that umbilical cord blood (UCB) is a rich source of both cell types. We will review the current data on UCB-derived Tregs and MSCs and their therapeutic implications.

Epidermal growth factor (EGF) treatment on multipotential stromal cells (MSCs). Possible enhancement of therapeutic potential of MSC

Adult bone marrow multipotential stromal cells (MSCs) hold great promise in regenerative medicine and tissue engineering. However, due to their low numbers upon harvesting, MSCs need to be expanded in vitro without biasing future differentiation for optimal utility. In this concept paper, we focus on the potential use of epidermal growth factor (EGF), prototypal growth factor for enhancing the harvesting and/or differentiation of MSCs. Soluble EGF was shown to augment MSC proliferation while preserving early progenitors within MSC population, and thus did not induce differentiation. However, tethered form of EGF was shown to promote osteogenic differentiation. Soluble EGF was also shown to increase paracrine secretions including VEGF and HGF from MSC. Thus, soluble EGF can be used not only to expand MSC in vitro, but also to enhance paracrine secretion through drug-releasing MSC-encapsulated scaffolds in vivo. Tethered EGF can also be utilized to direct MSC towards osteogenic lineage both in vitro and in vivo.

Osteoarthritis treated with mesenchymal stem cells on hyaluronan-based scaffold in rabbit

OBJECTIVE

Osteoarthritis (OA) is a disease that limits the mobility of patients and is of considerable economical importance. Up to now, despite the increasing number of patients with OA, treatments to manage the disease remain symptomatic, designed to control pain, and improve function and quality of life limiting adverse events. With the aim to explore a new approach to treat OA patients suffering from early degenerative lesions of hyaline cartilage, we transplanted in an experimental animal model of OA a hyaluronan-based scaffold (Hyaff11) seeded with mesenchymal stem cells (MSCs) obtained from bone marrow and expanded in culture.

DESIGN

Rabbit knee joints were bilaterally subjected to anterior cruciate ligament transection to surgically induce OA. After 8 weeks, the time necessary to the development of cartilage surface damage, animals were treated with MSCs seeded onto Hyaff-11 scaffold in the left condyle and unseeded Hyaff-11 in the controlateral knee. Untreated rabbits were used as controls. All the animals were sacrificed at 3 and 6 months after surgery. Histological, histomorphometric, and immunohistological evaluations were performed.

RESULTS

OA changes developed in all animals subjected to anterior cruciate ligament transection. The predominant macroscopically observed OA changes were mild (lateral femoral condyle) or moderate (medial femoral condyle) ulcerations. Statistically significant differences in the quality of the regenerated tissue were found between the implants with scaffolds carrying MSCs compared to the scaffold alone or controls in particular at 6 months.

CONCLUSIONS

From the observations, it is possible to demonstrate that Hyaff-11, a hyaluronan-based scaffold, has potential for MSC implantation and that may have application for the treatment of early OA in humans.

Non-invasive stem cell therapy in a rat model for retinal degeneration and vascular pathology

BACKGROUND

Retinitis pigmentosa (RP) is characterized by progressive night blindness, visual field loss, altered vascular permeability and loss of central vision. Currently there is no effective treatment available except gene replacement therapy has shown promise in a few patients with specific gene defects. There is an urgent need to develop therapies that offer generic neuro-and vascular-protective effects with non-invasive intervention. Here we explored the potential of systemic administration of pluripotent bone marrow-derived mesenchymal stem cells (MSCs) to rescue vision and associated vascular pathology in the Royal College Surgeons (RCS) rat, a well-established animal model for RP.

METHODOLOGY/PRINCIPAL FINDINGS

Animals received syngeneic MSCs (1x10(6) cells) by tail vein at an age before major photoreceptor loss.

PRINCIPAL RESULTS

both rod and cone photoreceptors were preserved (5-6 cells thick) at the time when control animal has a single layer of photoreceptors remained; Visual function was significantly preserved compared with controls as determined by visual acuity and luminance threshold recording from the superior colliculus; The number of pathological vascular complexes (abnormal vessels associated with migrating pigment epithelium cells) and area of vascular leakage that would ordinarily develop were dramatically reduced; Semi-quantitative RT-PCR analysis indicated there was upregulation of growth factors and immunohistochemistry revealed that there was an increase in neurotrophic factors within eyes of animals that received MSCs.

CONCLUSIONS/SIGNIFICANCE

These results underscore the potential application of MSCs in treating retinal degeneration. The advantages of this non-invasive cell-based therapy are: cells are easily isolated and can be expanded in large quantity for autologous graft; hypoimmunogenic nature as allogeneic donors; less controversial in nature than other stem cells; can be readministered with minor discomfort. Therefore, MSCs may prove to be the ideal cell source for auto-cell therapy for retinal degeneration and other ocular vascular diseases.

Mesenchymal stem cells inhibition of chronic ethanol-induced oxidative damage via upregulation of phosphatidylinositol-3-kinase/Akt and modulation of extracellular signal-regulated kinase 1/2 activation in PC12 cells and neurons

It is well known that chronic ethanol consumption damages CNS through oxidative stress which results in many dysfunctions. Recently, it has been demonstrated that as a promising strategy to treat several neurological diseases, transplanted bone marrow-derived mesenchymal stem cells (MSCs) can secrete lots of protective factors that in turn promote function recovery. In the present study, we assessed the potential effects of MSCs conditioned medium (MSC-CM) against chronic ethanol-associated damage on PC12 cells and primary cortical neurons. We found that pretreatment with MSC-CM notably improved cell survival, prevented chronic ethanol-associated apoptosis and abolished the robust deterioration in oxidative status. In addition, we also discovered that chronic ethanol exposure induced an inactivation of phosphatidylinositol-3-kinase (PI3K)/Akt and a lasting activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in both PC12 cells and primary cortical neurons which were able to be reversed by MSC-CM. The PI3K inhibitor (LY294002) was able to reduce the antioxidative and cytoprotective effects conferred by MSC-CM, in part, and the ERK1/2 inhibitor (PD98059) was able to elicit significant protection from chronic ethanol cytotoxicity but not rescue the deterioration in oxidative status induced by chronic ethanol. Taken together, these findings provide the first evidence that MSCs might have potent antioxidant action to shield the apoptotic impairment from chronic ethanol exposure in PC12 cells and neurons, which is involved in upregulation of PI3K/Akt and modulation of ERK1/2 activation, at least partially.

Comparison between Culture Conditions Improving Growth and Differentiation of Blood and Bone Marrow Cells Committed to the Endothelial Cell Lineage

The aim of this study was to compare different cell sources and culture conditions to obtain endothelial progenitor cells (EPCs) with predictable antigen pattern, proliferation potential and in vitro vasculogenesis. Pig mononuclear cells were isolated from blood (PBMCs) and bone marrow (BMMCs). Mesenchymal stem cells (MSCs) were also derived from pig bone marrow. Cells were cultured on fibronectin in the presence of a high concentration of VEGF and low IGF-1 and FGF-2 levels, or on gelatin with a lower amount of VEGF and higher IGF-1 and FGF-2 concentrations. Endothelial commitment was relieved in almost all PBMCs and BMMCs irrespective of the protocol used, whilst MSCs did not express a reliable pattern of EPC markers under these conditions. BMMCs were more prone to expand on gelatin and showed a better viability than PBMCs. Moreover, about 90% of the BMMCs pre-cultured on gelatin could adhere to a hyaluronan-based scaffold and proliferate on it up to 3 days. Pre-treatment of BMMCs on fibronectin generated well-shaped tubular structures on Matrigel, whilst BMMCs exposed to the gelatin culture condition were less prone to form vessel-like structures. MSCs formed rough tubule-like structures, irrespective of the differentiating condition used. In a relative short time, pig BMMCs could be expanded on gelatin better than PBMCs, in the presence of a low amount of VEGF. BMMCs could better specialize for capillary formation in the presence of fibronectin and an elevated concentration of VEGF, whilst pig MSCs anyway showed a limited capability to differentiate into the endothelial cell lineage.

Immunoregulatory properties of mouse limbal stem cells

Stem cells have been demonstrated in nearly all adult mammalian tissues and play a vital role in their physiological renewal and healing after injury. Due to their irreplaceable role in tissue repair, these cells had to develop mechanisms protecting them from deleterious inflammatory immune reactions and ensuring their increased resistance to various apoptosis-inducing agents. In this study, we demonstrate that a population of mouse limbal cells highly enriched for cells expressing markers and characteristics of limbal stem cells (LSCs) suppresses in a dose-dependent manner the proliferation of lymphocytes elicited by mitogens or TCR-triggering and significantly inhibits the production of proinflammatory cytokines by activated T cells. The suppression was mediated by soluble factor(s) and did not affect early cell activation. LSCs were even more suppressive than mesenchymal stem cells or natural regulatory T cells. In addition, the cells expressing markers and characteristics of LSC had significantly higher levels of mRNA for Fas ligand and for the antiapoptotic molecules Mcl-1, XIAP, and survivin than other limbal cell populations. LSCs were also more resistant to staurosporin-induced apoptotic cell death and to cell-mediated cytotoxic reaction than other limbal cells. Collectively, these results suggest that SC isolated from fresh adult limbal tissue possess immunomodulatory properties and inhibit proinflammatory immune reactions. Simultaneously, these cells express high levels of mRNA for antiapoptotic molecules, which can protect them against cell-mediated cytotoxic reactions and various apoptosis-inducing agents.

Treatment of stress urinary incontinence with adipose tissue-derived stem cells

BACKGROUND AIMS

Effective treatment for stress urinary incontinence (SUI) is lacking. This study investigated whether transplantation of adipose tissue-derived stem cells (ADSC) can treat SUI in a rat model.

METHODS

Rats were induced to develop SUI by postpartum vaginal balloon dilation and bilateral ovariectomy. ADSC were isolated from the peri-ovary fat, examined for stem cell properties, and labeled with thymidine analog BrdU or EdU. Ten rats received urethral injection of saline as a control. Twelve rats received urethral injection of EdU-labeled ADSC and six rats received intravenous injection of BrdU-labeled ADSC through the tail vein. Four weeks later, urinary voiding function was assessed by conscious cystometry. The rats were then killed and their urethras harvested for tracking of ADSC and quantification of elastin, collagen and smooth muscle contents.

RESULTS

Cystometric analysis showed that eight out 10 rats in the control group had abnormal voiding, whereas four of 12 (33.3%) and two of six (33.3%) rats in the urethra-ADSC and tail vein-ADSC groups, respectively, had abnormal voiding. Histologic analysis showed that the ADSC-treated groups had significantly higher elastin content than the control group and, within the ADSC-treated groups, rats with normal voiding pattern also had significantly higher elastin content than rats with voiding dysfunction. ADSC-treated normal-voiding rats had significantly higher smooth muscle content than control or ADSC-treated rats with voiding dysfunction.

CONCLUSIONS

Transplantation of ADSC via urethral or intravenous injection is effective in the treatment and/or prevention of SUI in a pre-clinical setting.

Regulation of stemness and stem cell niche of mesenchymal stem cells: implications in tumorigenesis and metastasis

Human mesenchymal stem cells (MSCs) derived from adult tissues have been considered a candidate cell type for cell-based tissue engineering and regenerative medicine. These multipotent cells have the ability to differentiate along several mesenchymal lineages and possibly along non-mesenchymal lineages. MSCs possess considerable immunosuppressive properties that can influence the surrounding tissue positively during regeneration, but perhaps negatively towards the pathogenesis of cancer and metastasis. The balance between the naïve stem state and differentiation is highly dependent on the stem cell niche. Identification of stem cell niche components has helped to elucidate the mechanisms of stem cell maintenance and differentiation. Ultimately, the fate of stem cells is dictated by their microenvironment. In this review, we describe the identification and characterization of bone marrow-derived MSCs, the properties of the bone marrow stem cell niche, and the possibility and likelihood of MSC involvement in cancer progression and metastasis.

Mesenchymal stem cell-educated macrophages: a novel type of alternatively activated macrophages

OBJECTIVE

Mesenchymal stem cells (MSCs) are capable of modulating the immune system through interaction with a wide range of immune cells. This study investigates the hypothesis that interaction of MSCs with macrophages could play a significant role in their antiinflammatory/immune modulatory effects.

MATERIALS AND METHODS

MSCs were derived from bone marrow and monocytes were isolated from peripheral blood of healthy donors. We cultured human monocytes for 7 days without any added cytokines to generate macrophages, and then cocultured them for 3 more days with culture-expanded MSCs. We used cell surface antigen expression and intracellular cytokine expression patterns to study the immunophenotype of macrophages at the end of this coculture period, and phagocytic assays to investigate their functional activity in vitro.

RESULTS

Macrophages cocultured with MSCs consistently showed high-level expression of CD206, a marker of alternatively activated macrophages. Furthermore, these macrophages expressed high levels of interleukin (IL)-10 and low levels of IL-12, as determined by intracellular staining, typical of alternatively activated macrophages. However, macrophages cocultured with MSCs also expressed high levels of IL-6 and low levels of tumor necrosis factor-alpha (TNF-alpha) compared to controls. Functionally, macrophages cocultured with MSCs showed a higher level of phagocytic activity.

CONCLUSIONS

We describe a novel type of human macrophage generated in vitro after coculture with MSCs that assumes an immunophenotype defined as IL-10-high, IL-12-low, IL-6-high, and TNF-alpha-low secreting cells. These MSC-educated macrophages may be a unique and novel type of alternatively activated macrophage with a potentially significant role in tissue repair.

Mesenchymal stem cell-educated macrophages: a novel type of alternatively activated macrophages

OBJECTIVE

Mesenchymal stem cells (MSCs) are capable of modulating the immune system through interaction with a wide range of immune cells. This study investigates the hypothesis that interaction of MSCs with macrophages could play a significant role in their antiinflammatory/immune modulatory effects.

MATERIALS AND METHODS

MSCs were derived from bone marrow and monocytes were isolated from peripheral blood of healthy donors. We cultured human monocytes for 7 days without any added cytokines to generate macrophages, and then cocultured them for 3 more days with culture-expanded MSCs. We used cell surface antigen expression and intracellular cytokine expression patterns to study the immunophenotype of macrophages at the end of this coculture period, and phagocytic assays to investigate their functional activity in vitro.

RESULTS

Macrophages cocultured with MSCs consistently showed high-level expression of CD206, a marker of alternatively activated macrophages. Furthermore, these macrophages expressed high levels of interleukin (IL)-10 and low levels of IL-12, as determined by intracellular staining, typical of alternatively activated macrophages. However, macrophages cocultured with MSCs also expressed high levels of IL-6 and low levels of tumor necrosis factor-alpha (TNF-alpha) compared to controls. Functionally, macrophages cocultured with MSCs showed a higher level of phagocytic activity.

CONCLUSIONS

We describe a novel type of human macrophage generated in vitro after coculture with MSCs that assumes an immunophenotype defined as IL-10-high, IL-12-low, IL-6-high, and TNF-alpha-low secreting cells. These MSC-educated macrophages may be a unique and novel type of alternatively activated macrophage with a potentially significant role in tissue repair.

The stimulation of angiogenesis and collagen deposition by copper

Copper is known to trigger endothelial cells towards angiogenesis. Different approaches have been investigated to develop vascularisation in biomaterials. The angiogenic and healing potential of copper ions in combination with two major angiogenic factors was examined. A 3D culture system in which, under stimulation by FGF-2 and to a lesser degree with VEGF, endothelial cells assembled into structures resembling to an angiogenic process was used. The combination of CuSO(4) with increasing doses of VEGF or FGF-2 enhanced the complexity of angiogenic networks in a significant manner. In vivo studies were also conducted by incorporating FGF-2 with CuSO(4) in a cylindrical collagen-based scaffold. CuSO(4) enhanced significantly the invasion of microvessel compared to control implants and to 20ng FGF-2+/-CuSO(4). Vascular infiltration was also significantly improved by combination of CuSO(4) with FGF-2, compared to FGF-2 alone (0.2 and 1microg). Nevertheless, in comparison with CuSO(4) alone, there was a significant increase only with 1microg of FGF-2 combined with CuSO(4). Significantly, collagen fiber deposition was enhanced following the combinatory loading in comparison to that with FGF-2 alone but not with CuSO(4) only. Thus, copper associated with growth factors may have synergistic effects which are highly attractive in the fields of tissue engineering (e.g., bone) and biomaterials.

Vascular endothelial growth factor (VEGF) as a key therapeutic trophic factor in bone marrow mesenchymal stem cell-mediated cardiac repair

We recently demonstrated a novel effective therapeutic regimen for treating hamster heart failure based on injection of bone marrow mesenchymal stem cells (MSCs) or MSC-conditioned medium into the skeletal muscle. The work highlights an important cardiac repair mechanism mediated by the myriad of trophic factors derived from the injected MSCs and local musculature that can be explored for non-invasive stem cell therapy. While this therapeutic regimen provides the ultimate proof that MSC-based cardiac repair is mediated by the trophic actions independent of MSC differentiation or stemness, the trophic factors responsible for cardiac regeneration after MSC therapy remain largely undefined. Toward this aim, we took advantage of the finding that human and porcine MSCs exhibit species-related differences in expression of trophic factors. We demonstrate that human MSCs when compared to porcine MSCs express and secrete 5-fold less vascular endothelial growth factor (VEGF) in conditioned medium (40+/-5 and 225+/-17 pg/ml VEGF, respectively). This deficit in VEGF output was associated with compromised cardiac therapeutic efficacy of human MSC-conditioned medium. Over-expression of VEGF in human MSCs however completely restored the therapeutic potency of the conditioned medium. This finding indicates VEGF as a key therapeutic trophic factor in MSC-mediated myocardial regeneration, and demonstrates the feasibility of human MSC therapy using trophic factor-based cell-free strategies, which can eliminate the concern of potential stem cell transformation.

p75 neurotrophin receptor is involved in proliferation of undifferentiated mouse embryonic stem cells

Neurotrophins and their receptors are known to play a role in the proliferation and survival of many different cell types of neuronal and non-neuronal lineages. In addition, there is much evidence in the literature showing that the p75 neurotrophin receptor (p75(NTR)), alone or in association with members of the family of Trk receptors, is expressed in a wide variety of stem cells, although its role in such cells has not been completely elucidated. In the present work we have investigated the expression of p75(NTR) and Trks in totipotent and pluripotent cells, the mouse pre-implantation embryo and embryonic stem and germ cells (ES and EG cells). p75(NTR) and TrkA can be first detected in the blastocyst from which ES cell lines are derived. Mouse ES cells retain p75(NTR)/TrkA expression. Nerve growth factor is the only neurotrophin able to stimulate ES cell growth in culture, without affecting the expression of stem cell markers, alkaline phosphatase, Oct4 and Nanog. Such proliferation effect was blocked by antagonizing either p75(NTR) or TrkA. Interestingly, immunoreactivity to anti-p75(NTR) antibodies is lost upon ES cell differentiation. The expression pattern of neurotrophin receptors in murine ES cells differs from human ES cells, that only express TrkB and C, and do not respond to NGF. In this paper we also show that, while primordial germ cells (PGC) do not express p75(NTR), when they are made to revert to an ES-like phenotype, becoming EG cells, expression of p75(NTR) is turned on.

Intravenous hMSCs improve myocardial infarction in mice because cells embolized in lung are activated to secrete the anti-inflammatory protein TSG-6

Quantitative assays for human DNA and mRNA were used to examine the paradox that intravenously (i.v.) infused human multipotent stromal cells (hMSCs) can enhance tissue repair without significant engraftment. After 2 x 10(6) hMSCs were i.v. infused into mice, most of the cells were trapped as emboli in lung. The cells in lung disappeared with a half-life of about 24 hr, but <1000 cells appeared in six other tissues. The hMSCs in lung upregulated expression of multiple genes, with a large increase in the anti-inflammatory protein TSG-6. After myocardial infarction, i.v. hMSCs, but not hMSCs transduced with TSG-6 siRNA, decreased inflammatory responses, reduced infarct size, and improved cardiac function. I.v. administration of recombinant TSG-6 also reduced inflammatory responses and reduced infarct size. The results suggest that improvements in animal models and patients after i.v. infusions of MSCs are at least in part explained by activation of MSCs to secrete TSG-6.

Mesenchymal stem cell: present challenges and prospective cellular cardiomyoplasty approaches for myocardial regeneration

Myocardial ischemia and cardiac dysfunction have been known to follow ischemic heart diseases (IHDs). Despite a plethora of conventional treatment options, their efficacies are associated with skepticism. Cell therapies harbor a promising potential for vascular and cardiac repair, which is corroborated by adequate preclinical evidence. The underlying objectives behind cardiac regenerative therapies subsume enhancing angiomyogenesis in the ischemic myocardium, ameliorating cellular apoptosis, regenerating the damaged myocardium, repopulating the lost resident myocardial cells (smooth muscle, cardiomyocyte, and endothelial cells), and finally, decreasing fibrosis with a consequent reduction in ventricular remodeling. Although-cell based cardiomyoplasty approaches have an immense potential, their clinical utilization is limited owing to the increased need for better candidates for cellular cardiomyoplasty, better routes of delivery, appropriate dose for efficient engraftment, and better preconditioning or genetic-modification strategies for the progenitor and stem cells. Mesenchymal stem cells (MSCs) have emerged as powerful candidates in mediating myocardial repair owing to their unique properties of multipotency, transdifferentiation, intercellular connection with the resident cardiomyocytes via connexin 43 (Cx43)-positive gap junctions in the myocardium, and most important, immunomodulation. In this review, we present an in-depth discussion on the complexities associated with stem and progenitor cell therapies, the potential of preclinical approaches involving MSCs for myocardial repair, and an account of the past milestones and ongoing MSC-based trials in humans.

Chemokine, vascular and therapeutic effects of combination Simvastatin and BMSC treatment of stroke

We investigated the additive therapeutic effect of the combination treatment of stroke with sub-therapeutic doses of Simvastatin, a HMG-CoA reductase inhibitor, and bone marrow stromal cells (BMSCs). Rats were administered Simvastatin (0.5 mg/kg), BMSCs (1x10(6)) or combination of Simvastatin and BMSCs starting at 24 h after stroke. Combination treatment significantly improved neurological outcome, enhanced angiogenesis and arteriogenesis, and increased the number of engrafted-BMSCs in the ischemic brain. The number of engrafted-BMSCs and arteriogenesis was significantly correlated with functional outcome. Simvastatin significantly increased stromal cell-derived factor-1 (SDF1) expression in the ischemic brain and chemokine (CXC motif) receptor-4 (CXCR4) in BMSCs, and increased BMSC migration to RBMECs and astrocytes. Combination treatment of stroke upregulates the SDF1/CXCR4 axis and enhances BMSC migration into the ischemic brain, amplifies arteriogenesis and angiogenesis, and improves functional outcome after stroke.

"Opening" the mesenchymal stem cell tool box

Adult mesenchymal stem cells (MSCs) are adherent stromal cells able to self-renew and differentiate into a wide variety of cells and tissues. MSCs can be obtained from distinct tissue sources and have turned out to be successfully manipulated in vitro. As adult stem cells, MSCs are less tumorigenic than their embryonic correlatives and posses another unique characteristic which is their almost null immunogenicity. Moreover, these cells seem to be immunosuppressive in vitro. These facts together with others became MSCs a promising subject of study for future approaches in bioengineering and cell-based therapy. On the other hand, new strategies to achieve long-term integration as well as efficient differentiation of these cells at the area of the lesion are still challenging, and the signalling pathways ruling these processes are not completely well characterized. In this review, we are going summarize the general landscape and current status of the MSC tool as well as their wide potential in tissue engineering, from neuronal to tooth replacement. Highlights and pitfalls for further clinical applications will be discussed.

In vivo self-expanding engineering of bone

In vivo bone formation and vascularization are interdependent process with complex regulatory mechanism. In vitro tissue engineering has meet great difficulty to copy all internal environment conditions, and the technology worked well only for relatively simple, thin tissues such as skin and cartilage that do not depend on a well-formed network of blood vessels to deliver food and oxygen. For more complex tissue of bone segments shot through with vessels, we hypothesize that an altered strategy might be effective: starting from in vitro tissue engineering for a thin sheet of primary product, then transferring to in vivo cultivation with a self-expanding procedure activated by interweaving metal springs of shape memory alloy (SMA). It is easy for thin sheet of engineering tissues to survive after implantation in vivo. Super-elasticity of SMA spring can gradually expand and re-shape the engineering product. More important, the continuous mechano-transduction effect can activate internal environment as a bioreactor for bone regeneration and vascularization. Our hypothesis integrates the existing knowledge and technologies, and could be a hopeful strategy for more convenient and safe use of bone engineering in clinics.

Stem cells in pathobiology and regenerative medicine

This issue of the Journal of Pathology contains 16 articles largely dealing with the role of tissue-specific adult stem cells in the pathogenesis of disease, notably cancer. These authoritative reviews begin by describing the current knowledge regarding the identity and molecular regulation of normal tissue-specific stem cells, before itemizing their role in the aetiology and progression of disease. Fundamental concepts regarding the stem cell niche have been gleaned from studies of germ line stem cells in Drosophila and Caenorhabditis elegans, and these are described in detail in this issue. Somatic cell reprogramming, a process underlying not only therapeutic cloning but also the production of induced pluripotent stem (iPS) cells, is further discussed. Much attention is given to embryonic stem (ES) and iPS cells within the scientific community; this issue of the Journal of Pathology redresses this imbalance by illustrating the pivotal role of adult stem cells in much of human disease.