Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells

Stem celltherapy for ischemic heart failure

As the prevalence and incidence of ischemic heart disease continue to increase, so does interest in ischemic heart failure management. Limitations of current therapies have led to research aimed at regenerating and repairing ischemically damaged myocardium through stem-cell therapy. Cell types being evaluated include embryonic stem cells, fetal and neonatal cardiomyocytes, skeletal myoblasts, bone marrow stem cells, peripheral blood CD34+ cells, endothelial progenitor cells, cardiac progenitor cells, and fibroblasts. Preclinical animal studies and promising early results of clinical trials now under way suggest that stem-cell therapy may soon become an important new tool in heart failure management.

Stem cells and pulmonary metamorphosis: New concepts in repair and regeneration

Adult stem cells are likely to have much more versatile differentiation capabilities than once believed. Numerous studies have appeared over the past decade demonstrating the ability of adult stem cells to differentiate into a variety of cells from non-hematopoietic organs, including the lung. The goal of this review is to provide an overview of the growth factors which are thought to be involved in lung development and disease, describe the cells within the lung that are believed to replace cells that have been injured, review the studies that have demonstrated the transformation of bone marrow-derived stem cells into lung cells, and describe potential clinical applications with respect to human pulmonary disease.

Cell therapy for cardiovascular disease: what cells, what diseases and for whom?

Experimental and human data suggesting progenitor cells possess the capacity to regenerate tissue and augment repair in injured organs has generated widespread interest in the basic research and clinical communities. Nowhere have these findings been more tantalizing than in human cardiovascular disease, in which vasculogenesis and myocardial regeneration logically and understandably remain as attractive therapeutic targets. Burgeoning experimental evidence attests to the proangiogenic, vasculogenic and tissue reparative capabilities of a broad range of progenitor cells derived from the bone marrow, circulation and a number of other tissues in vivo. Studies demonstrating the most apparent therapeutic success are those implicated in revascularization and repair of acute or chronically ischemic tissues in the heart and the peripheral vascular system. Numerous small clinical trials have yielded promising preliminary results without clear evidence of a superiority for a specific cell type or clinical disease entity as the most suitable target for cell therapy. This review will evaluate the scientific rationale for use of a specific cell or cells, the cardiovascular disease states most appropriate for targeted cell therapy, and the patient-specific barriers to therapeutic success, including emerging hurdles such as cardiovascular risk factors and comorbidities in eligible subjects.

Cardiomyocytes derived from stem cells

One way to restore failing heart function following myocardial infarction would be to replace lost or damaged cardiac cells by local or systemic injection. The sources of replacement cells presently discussed include embryonic stem cells, hematopoietic and non-hematopoietic stem cells from bone marrow or cord blood and small stem cell populations thought to reside in the heart itself or in skeletal muscle. Here we review this area of stem cell research with focus particularly on recent laboratory advances towards producing cardiomyocytes from embryonic stem cells. We conclude that embryonic stem cells and cardiac progenitors in the heart itself are the only proven sources of cardiomyocytes and that reported clinical effects of bone marrow stem currently undergoing validation are likely mediated by other mechanisms.

The mammary gland "side population": a putative stem/progenitor cell marker?

Hematopoietic Stem Cells have been isolated by their ability to pump out Hoechst 33342 dye and form a distinct population definable by flow cytometry--the Side Population (SP). The membrane pump Bcrp has been identified as the molecular determinant of the SP phenotype. An SP population with Bcrp activity has been defined in a number of tissues, including mouse mammary and human breast epithelium, and it has been proposed that the SP phenotype is a universal stem cell marker. Studies of mouse and human breast SP suggest that the population is undifferentiated but capable of differentiating into epithelial structures of both luminal and myoepithelial lineages both in vitro and in vivo. However, evidence that the SP is enriched for stem cells is, at the moment, only correlative, and there are potentially confounding technical issues. We still await formal proof that the SP contains a stem cell population.

Progenitor cell therapy of ischemic heart disease: the new frontier

The discovery of circulating cells capable of differentiating into vascular structures (endothelial progenitor cells) has both altered our understanding of the pathophysiology of atherosclerosis and offered the possibility of using nature's reparative mechanisms to accelerate vascular restoration and regeneration. Epidemiologic studies indicate a correlation between cardiac risk factors, the presence of coronary disease and the numbers and function of endothelial progenitor cells. Preclinical animal models have demonstrated the therapeutic potential of cellular therapies for repair of ischemic myocardial damage. Several human trials investigating either the use of progenitor cells derived from bone marrow or peripheral blood, or pharmacologic therapies aimed at increasing mobilization of such cells for the treatment of ischemic heart disease, are currently underway. Some basic tenets of progenitor cell biology, key preclinical results suggesting the utility of this therapy, and the strengths and limitations of current human trials are briefly summarized, and the role of cellular therapies, today and in the future, are explored.

Stem cell plasticity

The central dogma in stem cell biology has been that cells isolated from a particular tissue can renew and differentiate into lineages of the tissue it resides in. Several studies have challenged this idea by demonstrating that tissue specific cell have considerable plasticity and can cross-lineage restriction boundary and give rise to cell types of other lineages. However, the lack of a clear definition for plasticity has led to confusion with several reports failing to demonstrate that a single cell can indeed differentiate into multiple lineages at significant levels. Further, differences between results obtained in different labs has cast doubt on some results and several studies still await independent confirmation. In this review, we critically evaluate studies that report stem cell plasticity using three rigid criteria to define stem cell plasticity; differentiation of a single cell into multiple cell lineages, functionality of differentiated cells in vitro and in vivo, robust and persistent engraft of transplanted cells.

Modulation of gene expression in neonatal rat cardiomyocytes by surface modification of polylactide-co-glycolide substrates

Myocardial tissue engineering presents a potential treatment option for heart disease. Cardiomyocytes isolated at various stages of development retain the ability to form contractile networks in vitro, which suggests that it should be possible to reconstitute viable myocardium given the appropriate architecture, stimuli, and cardiomyogenic cell source. This study investigates the effects of modifying substrate surface energy (by plasma etching) and protein coating (by fibronectin adsorption) on neonatal rat ventricular myocyte (NRVM) function. Primary NRVMs were cultured for 96 h on modified and control films of a common degradable polymer, polylactide-co-glycolide. Cultures were analyzed for cell spreading, protein content, and mRNA expression of atrial natriuretic factor and beta-myosin heavy chain. The results demonstrate that NRVMs cultured on etched films significantly increased in spreading, myofibril development, protein content, and gene expression of atrial natriuretic factor and beta-myosin heavy chain compared with unetched films, and that this surface energy effect is overwhelmed by the addition of fibronectin. Conclusions from this study are that surface energy and protein adsorption influence the gene expression of adherent NRVMs, and may be important for modulating the function of engineered myocardium.

Hematopoietic and nonhematopoietic potentials of Hoechst(low)/side population cells isolated from adult rat kidney

BACKGROUND

Although the regenerative stem cell is expected to exist in many adult tissues, the cell contributing to the regeneration of the kidney remains unknown in its type and origin.

METHODS

In this study, we isolated cells that show low stain with a DNA-binding dye Hoechst 33342 (Hoechst(low) cells) from adult rat kidney, and investigated their differentiation potentials.

RESULTS

Hoechst(low) cells, generally termed side population cells, existed at a frequency of 0.03% to 0.1% in the cell suspension of the digested kidney. Analysis of the kidney-derived Hoechst(low) cells after bone marrow transplantation indicated that some of the cells were derived from bone marrow. When enhanced green fluorescent protein (EGFP)-labeled kidney-derived Hoechst(low) cells were intravenously transplanted into wild-type adult rats, EGFP(+) cells were not detected in the kidney, but EGFP(+) skeletal muscle, EGFP(+) hepatocytes and EGFP(+) bone marrow cells were observed. Even after the induction of the experimental glomerulonephritis and gentamicin-induced nephropathy that promote the differentiation of bone marrow-derived cells into repopulating mesangial cells and tubular component cells, respectively, EGFP(+) mesangial or tubular cells were not observed. Neither with an in vitro system, which we established to produce mesangial-like cells from crude bone marrow culture, did Hoechst(low) cells yield mesangial-like cells.

CONCLUSION

These findings implicate that Hoechst(low) cells in the kidney may have potentials for hematopoietic and nonhematopoietic lineages, but are not stem cells for renal cells, especially mesangial and tubular cells.

Development of Respiratory Stem Cells and Progenitor Cells

Research of stem cells has caught much attention in the past few years with its promise for therapeutic and regenerative applications in a variety of diseases and organ systems. The latest studies have also urged us to understand further the somatic stem cell plasticity or transdifferentiation capability. More vigorous research is urgently required to verify whether or not bone marrow stem cells can differentiate into a variety of cell types in different organs including heart, liver, lung, and so forth. The lung employs a myriad of cell phenotypes in its unique function of inhaling and expiring air. Due to this structural complexity, transdifferentiation of stem cells into the lung is particularly complicated. In addition, assessing the stem cells and lung progenitor cells in the respiratory system is technically difficult. Despite these difficulties, recent studies have advanced our understanding of bone marrow stem cells differentiating into lung progenitors as well as characteristics of the local progenitor cells. This review will briefly discuss the current state of research of stem cell transdifferentiation and development, with a focus on the obstacles that limit use of stem cells in lung regeneration.

Aspects cellulaires de la régénération osseuse

Bone regeneration is only possible if stem cells give rise to progenitors of osteoblasts, chondroblasts or chondroidocytes. Stem cells and osteogenic progenitors were evidenced in bone marrow while only progenitors can be found in periosteum. Bone marrow stem cells did show an amazing plasticity and some cells of the bone surrounding tissues such as perivascular cells, adipocytes, muscle cells or even circulating cells are able to transdifferentiate in osteoblasts when submitted to an osteogenic environment. We have shown that the destruction of both bone marrow and periost impairs the bone healing. It indicates that the periost and bone marrow destruction removes the predetermined osteogenic cells and the informative factors able to induce the transdifferenciation of the cells contained in the peri-osseous tissues.

Mesenchymal stem cells and their potential as cardiac therapeutics

Mesenchymal stem cells (MSCs) represent a stem cell population present in adult tissues that can be isolated, expanded in culture, and characterized in vitro and in vivo. MSCs differentiate readily into chondrocytes, adipocytes, osteocytes, and they can support hematopoietic stem cells or embryonic stem cells in culture. Evidence suggests MSCs can also express phenotypic characteristics of endothelial, neural, smooth muscle, skeletal myoblasts, and cardiac myocyte cells. When introduced into the infarcted heart, MSCs prevent deleterious remodeling and improve recovery, although further understanding of MSC differentiation in the cardiac scar tissue is still needed. MSCs have been injected directly into the infarct, or they have been administered intravenously and seen to home to the site of injury. Examination of the interaction of allogeneic MSCs with cells of the immune system indicates little rejection by T cells. Persistence of allogeneic MSCs in vivo suggests their potential "off the shelf" therapeutic use for multiple recipients. Clinical use of cultured human MSCs (hMSCs) has begun for cancer patients, and recipients have received autologous or allogeneic MSCs. Research continues to support the desirable traits of MSCs for development of cellular therapeutics for many tissues, including the cardiovascular system. In summary, hMSCs isolated from adult bone marrow provide an excellent model for development of stem cell therapeutics, and their potential use in the cardiovascular system is currently under investigation in the laboratory and clinical settings.

Mesenchymal stem cells in osteoarthritis

PURPOSE OF REVIEW

Accumulating evidence indicates that every tissue contains stem cells. Our understanding of the biology of stem cells reveals that these cell populations have a critical role in the homeostasis and repair of tissues. Besides the local stem cell niches, additional compartments in the body such as the bone marrow may serve as reservoirs for stem cell populations. On more extensive tissue damage, and guided by local repair responses, "reparative" cell populations are mobilized from more distant stem cell reservoirs and migrate to the site of injury, thereby contributing in many aspects of local tissue repair.

RECENT FINDINGS

Osteoarthritis has long been regarded as an imbalance between destructive and reparative processes. The lack of repair of the weight-bearing articular cartilage and the associated subchondral bone changes are considered of critical importance in the progression of the disease. Recent findings indicate a depletion and/or functional alteration of mesenchymal stem cell populations in osteoarthritis. These preliminary data suggest that in joint diseases such as osteoarthritis, it is of importance to investigate further the involvement of the stem cell pool in the mechanisms contributing to joint homeostasis and driving disease progression.

SUMMARY

In view of the emerging body of evidence pointing to a potential therapeutic utility of stem cell technology, it is not surprising that local delivery of mesenchymal stem cells has been explored as a therapeutic approach in animal models of osteoarthritis.

Cellular recruitment and the development of the myocardium

The vertebrate embryo experiences very rapid growth following fertilization. This necessitates the establishment of blood circulation, which is initiated during the early somite stages of development when the embryo begins to exhibit three-dimensional tissue organization. Accordingly, the contractile heart is the first functional organ that develops in both the bird and mammalian embryo. The vertebrate heart is quickly assembled as a simple two-layer tube consisting of an outer myocardium and inner endocardium. During embryogenesis, the heart undergoes substantial growth and remodeling to meet the increased circulatory requirements of an adult organism. Until recently, it was thought that all the cells that comprise the muscle of the mature heart could trace their roots back to two bilaterally distributed mesodermal fields within the early gastrula. It is now known that the cellular components that give rise to the myocardium have multiple ancestries and that de novo addition of cardiac myocytes to the developing heart occurs at various points during embryogenesis. In this article, we review what is presently known about the source of the cells that contribute to the myocardium and explore reasons why multiple myocardial cell sources exist.

Skeletal muscle fiber-specific green autofluorescence: potential for stem cell engraftment artifacts

Adult stem cell research has lately been plagued by controversy regarding the possibility that some adult stem cells can engraft into nonautochthonous tissues. While most reports have observed some level of engraftment, the prevalence has varied in some cases by two orders of magnitude, suggesting that major technical variations may underlie these differences, possibly outweighing the biological basis of the observations. Here we describe bright green autofluorescence in a specific subset of skeletal muscle fibers that strongly resembles emission from green fluorescent protein (GFP). Moreover, we show that oxidative muscle fibers exhibit this autofluorescence, likely due to flavin, associated with NADH dehydrogenase. Finally, we demonstrate that confocal microscopy, in conjunction with spectral scanning, can be used to distinguish between GFP and autofluorescence. We suggest this autofluorescence artifact may account for some of the discrepancies in this field, particularly those describing skeletal muscle engraftment.

Stromal cell-derived factor-1alpha plays a critical role in stem cell recruitment to the heart after myocardial infarction but is not sufficient to induce homing in the absence of injury

BACKGROUND

After myocardial infarction (MI), bone marrow-derived cells (BMDCs) are found within the myocardium. The mechanisms determining BMDC recruitment to the heart remain unclear. We investigated the role of stromal cell-derived factor-1alpha (SDF-1) in this process.

METHODS AND RESULTS

MI produced in mice by coronary ligation induced SDF-1 mRNA and protein expression in the infarct and border zone and decreased serum SDF-1 levels. By quantitative polymerase chain reaction, 48 hours after intravenous infusion of donor-lineage BMDCs, there were 80.5+/-15.6% more BDMCs in infarcted hearts compared with sham-operated controls (P<0.01). Administration of AMD3100, which specifically blocks binding of SDF-1 to its endogenous receptor CXCR4, diminished BMDC recruitment after MI by 64.2+/-5.5% (P<0.05), strongly suggesting a requirement for SDF-1 in BMDC recruitment to the infarcted heart. Forced expression of SDF-1 in the heart by adenoviral gene delivery 48 hours after MI doubled BMDC recruitment over MI alone (P<0.001) but did not enhance recruitment in the absence of MI, suggesting that SDF-1 can augment, but is not singularly sufficient for, BDMC recruitment to the heart. Gene expression analysis after MI revealed increased levels of several genes in addition to SDF-1, including those for vascular endothelial growth factor, matrix metalloproteinase-9, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, which might act in concert with SDF-1 to recruit BMDCs to the injured heart.

CONCLUSIONS

SDF-1/CXCR4 interactions play a crucial role in the recruitment of BMDCs to the heart after MI and can further increase homing in the presence, but not in the absence, of injury.

[Bone marrow cells transplant in the treatment of chronic chagasic cardiomyopathy]

Chronic chagasic cardiomyopathy remains a major cause of death due to heart failure in Latin American countries and for which there is currently no effective treatment. While chagasic patients wait for the development of more efficient and less toxic chemotherapeutics for the elimination of Trypanosoma cruzi, a new strategy has appeared in an attempt to repair or ameliorate the damage caused to the myocardium of patients with chronic chagasic cardiomyopathy. This therapy, involving the transplant of bone marrow cells obtained from the patient to be treated, may lead to improvement in heart function and in life quality of patients with severe chagasic cardiopathy, similar to that obtained with this approach in the treatment of patients with heart failure of ischemic etiology. The possible effects of cell therapies and its applications in chronic chagasic cardiopaths are discussed in the present report.

In vivo contribution of murine mesenchymal stem cells into multiple cell-types under minimal damage conditions

Murine mesenchymal stem cells are capable of differentiating in vitro into different lineages under stimulation with certain cytokines, growth factors and chemicals. However, the true capacitiy of these cells to contribute to different cell-types in vivo is still unclear, especially under minimal injury conditions. In this study, we describe a method of purifying murine mesenchymal stem cells from bone marrow and efficiently transducing them using a lentivirus vector expressing the eGFP reporter gene. Lentivirus-transduced mesenchymal stem cells retained their in vitro ability to differentiate into adipocytes, osteocytes and chondrocytes as well as into myocyte- and astrocyte-like cells. eGFP-mesenchymal stem cells were delivered systemically into minimally injured syngeneic mice. Tracking and tissue-specific differentiation were determined by PCR and immunohistochemistry, respectively. We found donor-derived hepatocytes, lung epithelial cells, myofibroblasts, myofibers and renal tubular cells in some of the recipient mice. Our data indicate that even in the absence of substantial injury, phenotypically defined murine mesenchymal stem cells could acquire tissue specific morphology and antigen expression and thus contribute to different tissue cell-types in vivo.

Heal Thyself

Acute myocardial infarction results in regional necrotic heart tissue that is considered irreversible. Although angioplasty and thrombolytic therapy can remove the offending atherosclerotic plaque and thrombi, both therapies are dependent upon timely recognition and initiation of treatment and thus have a limited window of opportunity. No currently available therapy has the capability to restore cardiomyocytes or to replace myocardial scar tissue with contractile tissue. In animal models, use of a wide range of cells such as fetal cardiomyocytes, skeletal myoblasts, and bone marrow stem cells have been shown to differentiate into functional cardiomyocytes. In addition, transplantation of adult stem cells directly into the area of infarction has shown clinical promise. This article explores the current data on extramedullary hematopoiesis, stem cell differentiation, and stem cell therapy and its ability to repair injured or ischemic cardiac tissue.

Potential of embryonic and adult stem cells in vitro

Recent developments in the field of stem cell research indicate their enormous potential as a source of tissue for regenerative therapies. The success of such applications will depend on the precise properties and potentials of stem cells isolated either from embryonic, fetal or adult tissues. Embryonic stem cells established from the inner cell mass of early mouse embryos are characterized by nearly unlimited proliferation, and the capacity to differentiate into derivatives of essentially all lineages. The recent isolation and culture of human embryonic stem cell lines presents new opportunities for reconstructive medicine. However, important problems remain; first, the derivation of human embryonic stem cells from in vitro fertilized blastocysts creates ethical problems, and second, the current techniques for the directed differentiation into somatic cell populations yield impure products with tumorigenic potential. Recent studies have also suggested an unexpectedly wide developmental potential of adult tissue-specific stem cells. Here too, many questions remain concerning the nature and status of adult stem cells both in vivo and in vitro and their proliferation and differentiation/transdifferentiation capacity. This review focuses on those issues of embryonic and adult stem cell biology most relevant to their in vitro propagation and differentiation. Questions and problems related to the use of human embryonic and adult stem cells in tissue regeneration and transplantation are discussed.

Gene Therapy Progress and Prospects: Gene therapy for diabetes mellitus

Diabetes mellitus has long been targeted, as yet unsuccessfully, as being curable with gene therapy. The main hurdles have not only been vector-related toxicity but also the lack of physiological regulation of the expressed insulin. Recent advances in understanding the developmental biology of beta-cells and the transcriptional cascade that drives it have enabled both in vivo and ex vivo gene therapy combined with cell therapy to be used in animal models of diabetes with success. The associated developments in the stem cell biology and immunology have opened up further opportunities for gene therapy to be applied to target autoimmune diabetes.

Neural crest stem cells undergo multilineage differentiation in developing peripheral nerves to generate endoneurial fibroblasts in addition to Schwann cells

Neural crest stem cells (NCSCs) persist in peripheral nerves throughout late gestation but their function is unknown. Current models of nerve development only consider the generation of Schwann cells from neural crest, but the presence of NCSCs raises the possibility of multilineage differentiation. We performed Cre-recombinase fate mapping to determine which nerve cells are neural crest derived. Endoneurial fibroblasts, in addition to myelinating and non-myelinating Schwann cells, were neural crest derived, whereas perineurial cells, pericytes and endothelial cells were not. This identified endoneurial fibroblasts as a novel neural crest derivative, and demonstrated that trunk neural crest does give rise to fibroblasts in vivo, consistent with previous studies of trunk NCSCs in culture. The multilineage differentiation of NCSCs into glial and non-glial derivatives in the developing nerve appears to be regulated by neuregulin, notch ligands, and bone morphogenic proteins, as these factors are expressed in the developing nerve, and cause nerve NCSCs to generate Schwann cells and fibroblasts, but not neurons, in culture. Nerve development is thus more complex than was previously thought, involving NCSC self-renewal, lineage commitment and multilineage differentiation.

Mesenchymal stem cells: clinical applications and biological characterization

Mesenchymal stem cells (MSCs) have been isolated from bone marrow, periosteum, trabecular bone, adipose tissue, synovium, skeletal muscle and deciduous teeth. These cells have the capacity to differentiate into cells of connective tissue lineages, including bone, fat, cartilage and muscle. A great deal has been learned in recent years about the isolation and characterization of MSCs, and control of their differentiation. These cells have generated a great deal of interest because of their potential use in regenerative medicine and tissue engineering and there are some dramatic examples, derived from both pre-clinical and clinical studies, that illustrate their therapeutic value. This review summarizes recent findings regarding the potential clinical use of MSCs in cardiovascular, neural and orthopaedic applications. As new methods are developed, there are several aspects to the implanted cell-host interaction that need to be addressed before we can fully understand the underlying mechanisms. These include the host immune response to implanted cells, the homing mechanisms that guide delivered cells to a site of injury and the differentiation in vivo of implanted cells under the influence of local signals.

Adult stem cell therapy for the heart

The purpose of this review is to summarize current data leading to and arising from recent clinical application of cellular therapy for acute myocardial infarct (heart attack) and congestive heart failure. We specifically focus on use of adult stem cells and compare and contrast bone marrow and adipose tissue; two different sources from which stem cells can be harvested in substantial numbers with limited morbidity. Cellular therapy is the latest in a series of strategies applied in an effort to prevent or mitigate the progressive and otherwise irreversible loss of cardiac function that frequently follows a heart attack. Unlike surgical, pharmacologic, and gene transfer approaches, cellular therapy has the potential to restore cardiac function by providing cells capable of regenerating damaged myocardium and/or myocardial function. Skeletal muscle myoblast expansion and transfer allows delivery of cells with contractile function, albeit without any evidence of cardiomyogenesis or electrical coupling to remaining healthy myocardium. Delivery of endothelial progenitor cells (EPCs) which drive reperfusion of infarct zone tissues is also promising, although this mechanism is directed at halting ongoing degeneration rather than initiating a regenerative process. By contrast, demonstration of the ability of adult stem cells to undergo cardiomyocyte differentiation both in vitro and in vivo suggests a potential for regenerative medicine. This potential is being examined in early clinical studies.

Cardiomyocytes fuse with surrounding noncardiomyocytes and reenter the cell cycle

The concept of the plasticity or transdifferentiation of adult stem cells has been challenged by the phenomenon of cell fusion. In this work, we examined whether neonatal cardiomyocytes fuse with various somatic cells including endothelial cells, cardiac fibroblasts, bone marrow cells, and endothelial progenitor cells spontaneously in vitro. When cardiomyocytes were cocultured with endothelial cells or cardiac fibroblasts, they fused and showed phenotypes of cardiomyocytes. Furthermore, cardiomyocytes reentered the G2-M phase in the cell cycle after fusing with proliferative noncardiomyocytes. Transplanted endothelial cells or skeletal muscle–derived cells fused with adult cardiomyocytes in vivo. In the cryoinjured heart, there were Ki67-positive cells that expressed both cardiac and endothelial lineage marker proteins. These results suggest that cardiomyocytes fuse with other cells and enter the cell cycle by maintaining their phenotypes.

Wild-type bone marrow cells ameliorate the phenotype of SOD1-G93A ALS mice and contribute to CNS, heart and skeletal muscle tissues

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal neurodegenerative disease without any effective therapy. To evaluate the potential of wild-type bone marrow (BM)-derived stem cells to modify the ALS phenotype, we generated BM chimeric Cu/Zn superoxide dismutase (SOD1) mice by transplantation of BM cells derived from mice expressing green fluorescent protein (GFP) in all tissues and from Thy1-YFP mice that express a spectral variant of GFP (yellow fluorescent protein) in neurons only. In the recipient cerebral cortex, we observed rare GFP+ and YFP+ neurons, which were probably generated by cell fusion, as demonstrated by fluorescence in situ hybridization (FISH) analysis, suggesting that this phenomenon is not limited to Purkinje cells. GFP-positive microglial cells were extensively present in both the brain and spinal cord of the affected animals. Completely differentiated and immature GFP+ myofibres were also present in the heart and skeletal muscles of SOD1 mice, confirming that BM cells can participate in striated muscle tissue regeneration. Moreover, wild-type BM chimeric SOD1 mice showed a significantly delayed disease onset and an increased life span, probably due to a positive 'non-neuronal environmental' effect rather than to neuronogenesis. This improvement in SOD1-G93A mouse survival is comparable with that previously obtained using some safer pharmacological agents. BM transplantation-related complications in humans preclude its clinical application for ALS treatment. However, our data suggest that further studies aimed at improving the degree of tissue chimerism by BM-derived cells may provide valuable insights into strategies to slow ALS progression.

Adenoviral mediated gene transfer of PDGF-B enhances wound healing in type I and type II diabetic wounds

We have shown that the genetically diabetic mouse (C57BLKS/J-m+/+Lepr(db)) has a wound healing and neovascularization deficit associated with an inability to recruit endothelial precursor cells (EPCs) to the wound. This may account for a fundamental mechanism in impaired diabetic wound healing. We hypothesized that the adenoviral mediated overexpression of platelet-derived growth factor-B (PDGF-B) would enhance wound healing, improve neovascularization, and recruit EPCs to the epithelial wound in three diabetic mouse models. Eight-mm full-thickness flank wounds were made in db/db, nonobese NOD/Ltj, streptozotocin, and C57BLKS/J mice. Wounds were treated with either 1 x 10(8) PFU Ad-PDGF-B or Ad LacZ or phosphate buffered saline solution. Wounds harvested at seven days were analyzed for epithelial gap, blood vessel density, granulation tissue area, and EPCs per high powered field. All three diabetic models have a significant wound healing and neovascularization defect compared to C57BLKS/J controls. Adenoviral-PDGF-B treatment significantly enhanced epithelial gap closure in db/db, streptozotocin, and nonobese NOD/Ltj mice as compared to diabetic phosphate buffered saline solution or Ad LacZ controls. A similar increase in the formation of granulation tissue and vessel density was also observed. All three models had reduced levels of GATA-2 positive EPCs in the wound bed that was corrected by the adenoviral mediated gene transfer of PDGF. EPC recruitment was positively correlated with neovascularization and wound healing. Three different diabetic models have a wound healing impairment and a decreased ability to recruit EPCs. The vulnerary effect of adenoviral mediated gene therapy with PDGF-B significantly enhanced wound healing and neovascularization in diabetic wounds. The PDGF-B mediated augmentation of EPC recruitment to the wound bed may be a fundamental mechanism of these results.

Induction of glial glutamate transporters in adult mesenchymal stem cells

Adult bone marrow mesenchymal stem cells are multipotent cells that can differentiate into a variety of mesodermal tissues. Recent studies have reported on their ability to also evolve into non-mesodermal cells, especially neural cells. While most of these studies revealed that manipulating these cells triggers the expression of typical neurone markers, less is known about the induction of neuronal- or glial-related physiological properties. The present study focused on the characterisation of glutamate transporters expression and activity in rat mesenchymal stem cells grown in culture conditions favouring their differentiation into astroglial cells. Ten days exposure of the cells to the culture supplement G5 was found to increase the expression of nestin (neuro-epithelial stem cell intermediate filament), an intermediate filament protein expressed by neural stem cells. Simultaneously, a robust induction of the high-affinity glutamate transporter GLT-1 (and GLAST) expression was detected by RT-PCR and immunocytochemistry. This expression was correlated with a highly significant increase in the Na+-dependent [3H]D-aspartate uptake. Finally, while glial fibrillary acidic protein immunoreactivity could not be detected, the induced expression of the astrocytic enzyme glutamine synthetase was demonstrated. These results indicate that in vitro differentiation of adult mesenchymal stem cells in neural precursors coincides with the induction of functional glutamate transport systems. Although the astrocytic nature of these cells remains to be confirmed, this observation gives support to the study of mesenchymal stem cells as a promising tool for the treatment of neurological diseases involving glutamate excitoxicity.

Reflecting on 80 years of excellence

A small group of members of the American Society for Clinical Investigation began chatting in 1916 about the possibility of launching a new biomedical research journal. By October 1924, they managed to make the idea a reality with the publication of the first issue of the Journal of Clinical Investigation. Our 80th birthday seems an appropriate time to reflect on the history of biomedical science as it has been played out on our pages.

The hemangioblast: Cradle to clinic

In the embryo, the mesodermal precursor cell, the hemangioblast, gives rise to blood and blood vessels. During adult life, the hematopoietic stem cell (HSC) also exhibits this bipotential hemangioblast activity, serving as a rich source for circulating endothelial progenitor cells (EPCs). As a result of this finding, many questions have arisen as to whether the adult HSC is involved in the day-to-day maintenance of tissues, what mechanisms influence this adult hemangioblast activity, and whether blood vessels harbor hematopoietic capability. In answering these questions, the power of adult hemangioblast activity could be harnessed to evaluate and treat diseases such as myocardial infarction, stroke, cancer, and blindness. Enumeration of activated EPCs aims to alert the patient as to the severity of their disease, predict response to therapy, and gauge for relapse potential. Identification of hemangioblast stimulatory or inhibitory cues would allow physicians to regulate neovascularization in their patient, augmenting vessel production in situations of hypo-proliferation such as wound healing and inhibiting vessel production in situations of hyper-proliferation such as cancer. Finally, given that EPCs home to sites of new blood vessel growth, genetic engineering of harvested HSC or EPC offers the potential to deliver vasoregulatory factors directly to sites of neovascularization.

The scarless heart and the MRL mouse

The ability to regenerate tissues and limbs in its most robust form is seen in many non-mammalian species. The serendipitous discovery that the MRL mouse has a profound capacity for regeneration in some ways rivalling the classic newt and axolotl species raises the possibility that humans, too, may have an innate regenerative ability. The adult MRL mouse regrows cartilage, skin, hair follicles and myocardium with near perfect fidelity and without scarring. This is seen in the ability to close through-and-through ear holes, which are generally used for lifelong identification of mice, and the anatomic and functional recovery of myocardium after a severe cryo-injury. We present histological, biochemical and genetic data indicating that the enhanced breakdown of scar-like tissue may be an underlying factor in the MRL regenerative response. Studies as to the source of the cells in the regenerating MRL tissue are discussed. Such studies appear to support multiple mechanisms for cell replacement.

Autologous stem cell transplantation for myocardial repair

Current therapies for heart failure due to transmural left ventricular (LV) infarction are limited. We have developed a novel patch method for delivering autologous bone marrow stem cells to sites of myocardial infarction for the purpose of improving LV function and preventing LV aneurysm formation. The patch consisted of a fibrin matrix seeded with autologous porcine mesenchymal stem cells labeled with lacZ. We applied this patch to a swine model of postinfarction LV remodeling. Myocardial infarction was produced by using a 60-min occlusion of the left anterior descending coronary artery distal to the first diagonal branch followed by reperfusion. Results were compared between eight pigs with stem cell patch transplantation, six pigs with the patch but no stem cells (P), and six pigs with left anterior descending coronary artery ligation alone (L). Magnetic resonance imaging data collected 19 +/- 1 days after the myocardial infarction indicated a significant increase of LV systolic wall thickening fraction in the infarct zone of transplanted hearts compared with P or L hearts. Blue X-gal staining was observed in the infarcted area of transplanted hearts. PCR amplification of specimens from the X-gal-positive area revealed the Ad5 RSV-lacZ vector fragment DNA sequence. Light microscopy demonstrated that transplanted cells had differentiated into cells with myocyte-like characteristics and a robust increase of neovascularization as evidenced by von Willebrand factor-positive angioblasts and capillaries in transplanted hearts. Thus this patch-based autologous stem cell procedure may serve as a therapeutic modality for myocardial repair.

Increased circulating hematopoietic and endothelial progenitor cells in the early phase of acute myocardial infarction

Endothelial progenitor cell (EPC) mobilization has been reported following tissue damage, whereas no data are available regarding the mobilization of hematopoietic progenitor cells (HPCs). We performed the phenotypic and functional analysis of circulating CD34+ progenitor cells in patients with acute myocardial infarction (AMI), assessed from admission up to 60 days, in patients with stable angina pectoris (SA), and in healthy controls (CTRLs). In patients with AMI at admission (T0), the number of circulating CD34+ cells was higher (P < .001) than in CTRLs and became comparable with CTRLs within 60 days. Both the number of CD34+ cells coexpressing CD33, CD38, or CD117 and the number of HPCs was higher (P < .02 for all) in patients with AMI at T0 than in CTRLs, as was the number of hematopoietic colonies (P < .03). Patients with AMI (T0) had a significantly increased number of CD34+ vascular endothelial growth factor receptor 2-positive (VEGFR-2+) cells (P < .002) with respect to CTRLs, including CD34(+) CD133(+)VEGFR-2+ and CD34+ CD117(+)VEGFR-2+ EPCs. The number of endothelial colonies was higher in patients with AMI (T0) than in CTRLs (P < .05). No significant difference was documented between patients with SA and CTRLs. Spontaneous mobilization of both HPCs and EPCs occurs within a few hours from the onset of AMI and is detectable until 2 months.

Origin and phenotype of lung side population cells

Side population (SP) cells, a rare cell type identified by their ability to efflux the vital dye Hoechst 33342, are highly enriched for stem cell activity. Bone marrow (BM) SP cells uniformly express the pan-hematopoietic marker CD45, whereas tissue SP cells are heterogeneous in CD45 expression. In previous studies, we found that CD45 is expressed on 75% of lung SP cells. By performing whole BM transplantations, we determined that CD45-positive and CD45-negative lung SP cells are marrow derived. Transplantation of 200 highly purified BM SP cells indicated that both lung SP cell subtypes are derived from this marrow cell type. Morphologically, CD45-positive lung and BM SP cells possess similar features. They are small, round, and contain scant cytoplasm. CD45-negative lung SP cells are larger and contain abundant granular cytoplasm. Gene expression patterns for hematopoietic transcription factors GATA-1, GATA-2, and PU.1 further differentiated SP marrow and lung subtypes. By immunostaining for α-smooth muscle actin and cytokeratin, we found significant differences in the relative expression patterns of these markers in lung and marrow SP cell subtypes. In summary, these findings demonstrate that lung SP cells are derived from the BM and that CD45-positive and -negative subtypes can be distinguished by morphological differences and gene expression patterns.

What is regenerative medicine? Emergence of applied stem cell and developmental biology

Regenerative medicine is an emerging, but still poorly defined, field of biomedicine. The ongoing 'regenerative medicine revolution' is based on a series of new exciting breakthrough discoveries in the field of stem cell biology and developmental biology. The main problem of regenerative medicine is not so much stem cell differentiation, isolation and lineage diversity, although these are very important issues, but rather stem cell mobilisation, recruitment and integration into functional tissues. The key issue in enhancing tissue and organ regeneration is how to mobilise circulating stem and progenitor cells and how to provide an appropriate environment ('niche') for their tissue and organo-specific recruitment, 'homing' and complete functional integration. We need to know more about basic tissue biology, tissue regeneration and the cellular and molecular mechanisms of tissue turnover (both cellular and extracellular components) at different periods of human life and in different diseases. Systematic in silico, in vitro and in vivo research is a foundation for further progress in regenerative medicine. Regenerative medicine is a rapidly advancing field that opens new and exciting opportunities for completely revolutionary therapeutic modalities and technologies. Regenerative medicine is, at its essence, an emergence of applied stem cell and developmental biology.

Transplanted BM and BM side population cells contribute progeny to the lung and liver in irradiated mice

BACKGROUND

BM cells have been shown to give rise to progeny of various cell lineages, including cells in lung and liver. This investigation evaluated whether purified BM mononuclear cells and side population (SP) cells that have hematopoietic stem-cell activity also had this property; whether a TBI preparative regimen was necessary for engraftment; and where BM-derived cells were engrafted.

METHODS

Either 1-3 million BM mononuclear cells or 2000 BM SP cells from transgenic enhanced green fluorescent protein-expressing (EGFP) mice were transplanted i.v. to unirradiated or 7-9.5 Gy irradiated recipients.

RESULTS

Flow cytometric analysis showed that lung cells (mean 45%, range 4-70%) and liver cells (mean 4%, range 0.4-8.3%) from irradiated, but not unirradiated recipients, were EGFP donor-derived. Similar results were obtained transplanting BM mononuclear cells or SP cells. Morphologically, donor-derived cells in the lung were primarily monocytes and macrophages. Additionally, lung fibroblasts and Type I, but not Type II, alveolar cells and rare cells in the bronchial epithelium were donor BM derived. In the liver, Kupffer cells, inflammatory cells and small clusters of hepatocytes, but not bile duct cells, were donor-derived.

DISCUSSION

BM mononuclear and SP cells generated progeny in some compartments of the lung and liver, but only in TBI recipients. Stem cells in BM can contribute to repair of tissue injury in some compartments, but not to the same extent in the lung and liver.

Mesenchymal stem cells from adult human bone marrow differentiate into a cardiomyocyte phenotype in vitro

A method for isolating adult human bone marrow mesenchymal stem cells (MSCs) was established, and the ability of human MSCs to differentiate into cells with characteristics of cardiomyocytes in vitro was investigated. Selected MSC surface antigens were analyzed by flow cytometry. The MSCs at Passage 2 were treated with 5-azacytidine to investigate their differentiation into cardiomyocytes. Characteristics of the putative myogenic cells were determined by immunohistochemistry and transmission electron and confocal microscopies. The expression of myogenic specific genes was detected by reverse transcriptase-polymerase chain reaction (RT-PCR), real-time quantitative PCR, and DNA sequencing. The MSCs were spindle-shaped with irregular processes and were respectively positive for CD(13), CD(29), CD(44), CD(71) and negative for CD(3), CD(14), CD(15), CD(33), CD(34), CD(38), CD(45), and HLA-DR. The myogenic cells differentiated from MSCs were positive for beta-myosin heavy chain (beta-MHC), desmin, and alpha-cardiac actin. When the myogenic cells were stimulated with low concentration of K(+) (5.0 mM), an increase in intracellular calcium fluorescence was observed. Myofilament-like structures were observed in electron micrographs of the differentiated myogenic cells. The mRNAs of beta-MHC, desmin, alpha-cardiac actin, and cardiac troponin T were highly expressed in the myogenic cells. These results indicate that 5-azacytidine can induce human MSCs to differentiate in vitro into cells with characteristics commonly attributed to cardiomyocytes. Cardiomyocytes cultured from bone marrow sources are potentially valuable for repairing injured myocardium.

Adult stem cells

Development of a multicellular organism is accomplished through a series of events that are preprogrammed in the genome. These events encompass cellular proliferation, lineage commitment, lineage progression, lineage expression, cellular inhibition, and regulated apoptosis. The sequential progression of cells through these events results in the formation of the differentiated cells, tissues, and organs that constitute an individual. Although most cells progress through this sequence during development, a few cells leave the developmental continuum to become reserve precursor cells. The reserve precursor cells are involved in the continual maintenance and repair of the tissues and organs throughout the life span of the individual. Until recently it was generally assumed that the precursor cells in postnatal individuals were limited to lineage-committed progenitor cells specific for various tissues. However, studies by Young, his colleagues, and others have demonstrated the presence of two categories of precursor cells that reside within the organs and tissues of postnatal animals. These two categories of precursor cells are lineage-committed (multipotent, tripotent, bipotent, and unipotent) progenitor cells and lineage-uncommitted pluripotent (epiblastic-like, ectodermal, mesodermal, and endodermal) stem cells. These reserve precursor cells provide for the continual maintenance and repair of the organism after birth.

The epicardium and epicardially derived cells (EPDCs) as cardiac stem cells

After its initial formation the epicardium forms the outermost cell layer of the heart. As a result of an epithelial-to-mesenchymal transformation (EMT) individual cells delaminate from this primitive epicardial epithelium and migrate into the subepicardial space (Pérez-Pomares et al., Dev Dyn 1997; 210:96-105; Histochem J 1998a;30:627-634). Several studies have demonstrated that these epicardially derived cells (EPDCs) subsequently invade myocardial and valvuloseptal tissues (Mikawa and Fischman, Proc Natl Acad Sci USA 1992;89:9504-9508; Mikawa and Gourdie, Dev Biol 1996;174:221-232; Dettman et al., Dev Biol 1998;193:169-181; Gittenberger de Groot et al., Circ Res 1998;82:1043-1052; Manner, Anat Rec 1999;255:212-226; Pérez-Pomares et al., Dev. Biol. 2002b;247:307-326). A subset of EPDCs continue to differentiate in a variety of different cell types (including coronary endothelium, coronary smooth muscle cells (CoSMCs), interstitial fibroblasts, and atrioventricular cushion mesenchymal cells), whereas other EPDCs remain in a more or less undifferentiated state. Based on its specific characteristics, we consider the EPDC as the ultimate 'cardiac stem cell'. In this review we briefly summarize what is known about events that relate to EPDC development and differentiation while at the same time identifying some of the directions where EPDC-related research might lead us in the near future.

Efficient generation of neural stem cell-like cells from adult human bone marrow stromal cells

Clonogenic neural stem cells (NSCs) are self-renewing cells that maintain the capacity to differentiate into brain-specific cell types, and may also replace or repair diseased brain tissue. NSCs can be directly isolated from fetal or adult nervous tissue, or derived from embryonic stem cells. Here, we describe the efficient conversion of human adult bone marrow stromal cells (hMSC) into a neural stem cell-like population (hmNSC, for human marrow-derived NSC-like cells). These cells grow in neurosphere-like structures, express high levels of early neuroectodermal markers, such as the proneural genes NeuroD1, Neurog2, MSl1 as well as otx1 and nestin, but lose the characteristics of mesodermal stromal cells. In the presence of selected growth factors, hmNSCs can be differentiated into the three main neural phenotypes: astroglia, oligodendroglia and neurons. Clonal analysis demonstrates that individual hmNSCs are multipotent and retain the capacity to generate both glia and neurons. Our cell culture system provides a powerful tool for investigating the molecular mechanisms of neural differentiation in adult human NSCs. hmNSCs may therefore ultimately help to treat acute and chronic neurodegenerative diseases.

Angiogenesis and vasculogenesis are impaired in the precocious-aging klotho mouse

BACKGROUND

The effects of aging on angiogenesis (vascular sprouting) and vasculogenesis (endothelial precursor cell [EPC] incorporation into vessels) are not well known. We examined whether ischemia-induced angiogenesis/vasculogenesis is altered in klotho (kl) mutant mice, an animal model of typical aging.

METHODS AND RESULTS

After unilateral hindlimb ischemia, laser Doppler blood-flow (LDBF) analysis revealed a decreased ischemic-normal LDBF ratio in kl mice. Tissue capillary density was also suppressed in kl mice (+/+>+/kl>kl/kl). Aortic-ring culture assay showed impaired angiogenesis in kl/kl mice, accompanied by reduced endothelium-derived nitric oxide release. Moreover, the rate of transplanted homologous bone marrow cells incorporated into capillaries in ischemic tissues (vasculogenesis) was lower in kl/kl mice than in wild-type (+/+) mice, which was associated with a decrease in the number of c-Kit+CD31+ EPC-like mononuclear cells in bone marrow and in peripheral blood. Finally, the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor cerivastatin restored the impaired neovascularization in kl/kl mice, accompanied by an increase in c-Kit+CD31+ cells in bone marrow and peripheral blood, and enhanced angiogenesis in the aortic-ring culture.

CONCLUSIONS

Angiogenesis and vasculogenesis are impaired in kl mutant mice, a model of typical aging. Moreover, the age-associated impairment of neovascularization might be a new target of statin therapy.

Endothelial cells promote cardiac myocyte survival and spatial reorganization: implications for cardiac regeneration

BACKGROUND

Endothelial-cardiac myocyte (CM) interactions play a key role in regulating cardiac function, but the role of these interactions in CM survival is unknown. This study tested the hypothesis that endothelial cells (ECs) promote CM survival and enhance spatial organization in a 3-dimensional configuration.

METHODS AND RESULTS

Microvascular ECs and neonatal CMs were seeded on peptide hydrogels in 1 of 3 experimental configurations: CMs alone, CMs mixed with ECs (coculture), or CMs seeded on preformed EC networks (prevascularized). Capillary-like networks formed by ECs promoted marked CM reorganization along the EC structures, in contrast to limited organization of CMs cultured alone. The presence of ECs markedly inhibited CM apoptosis and necrosis at all time points. In addition, CMs on preformed EC networks resulted in significantly less CM apoptosis and necrosis compared with simultaneous EC-CM seeding (P<0.01, ANOVA). Furthermore, ECs promoted synchronized contraction of CMs as well as connexin 43 expression.

CONCLUSIONS

These results provide direct evidence for a novel role of endothelium in survival and organization of nearby CMs. Successful strategies for cardiac regeneration may therefore depend on establishing functional CM-endothelium interactions.

Nonhematopoietic mesenchymal stem cells can be mobilized and differentiate into cardiomyocytes after myocardial infarction

Bone marrow (BM) cells are reported to contribute to the process of regeneration following myocardial infarction. However, the responsible BM cells have not been fully identified. Here, we used 2 independent clonal studies to determine the origin of bone marrow (BM)-derived cardiomyocytes. First, we transplanted single CD34(-) c-kit(+)Sca-1(+) lineage(-) side population (CD34(-)KSL-SP) cells or whole BM cells from mice ubiquitously expressing enhanced green fluorescent protein (EGFP) into lethally irradiated mice, induced myocardial infarction (MI), and treated the animals with granulocyte colony-stimulating factor (G-CSF) to mobilize stem cells to the damaged myocardium. At 8 weeks after MI, from 100 specimens we counted only 3 EGFP(+) actinin(+) cells in myocardium of CD34(-) KSL-SP cells in mice that received transplants, but more than 5000 EGFP(+) actinin(+) cells in whole BM cell in mice that received transplants, suggesting that most of EGFP(+) actinin(+) cells were derived from nonhematopoietic BM cells. Next, clonally purified nonhematopoietic mesenchymal stem cells (MSCs), cardiomyogenic (CMG) cells, that expressed EGFP in the cardiomyocyte-specific manner were transplanted directly into BM of lethally irradiated mice, MI was induced, and they were treated with G-CSF. EGFP(+) actinin(+) cells were observed in the ischemic myocardium, indicating that CMG cells had been mobilized and differentiated into cardiomyocytes. Together, these results suggest that the origin of the vast majority of BM-derived cardiomyocytes is MSCs.

Stem cells, embryos, and the environment: a context for both science and ethics

Debate on the potential and uses of human stem cells tends to be conducted by two constituencies-ethicists and scientists. On many occasions there is little communication between the two, with the result that ethical debate is not informed as well as it might be by scientific insights. The aim of this paper is to highlight those scientific insights that may be of relevance for ethical debate. Environmental factors play a significant role in identifying stem cells and their various subtypes. Research related to the role of the microenvironment has led to emphasis upon "plasticity", which denotes the ability of one type of stem cell to undergo a transition to cells from other lineages. This could increase the value given to adult stem cells, in comparison with embryonic stem cell research. Any such conclusion should be treated with caution, however, since optimism of this order is not borne out by current research. The role of the environment is also important in distinguishing between the terms totipotency and pluripotency. We argue that blastocysts (early embryos) and embryonic stem cells are only totipotent if they can develop within an appropriate environment. In the absence of this, they are merely pluripotent. Hence, blastocysts in the laboratory are potentially totipotent, in contrast to their counterparts within the human body which are actually totipotent. This may have implications for ethical debate, suggesting as it does that arguments based on potential for life may be of limited relevance.

Generation of Neuroprogenitor-like Cells from Adult Mammalian Bone Marrow Stromal Cells In Vitro

Recently, it has been proposed that bone marrow stromal cells (BMSCs) have a broader capacity for differentiation than previously contemplated. In vitro studies have indicated that BMSCs may have the capacity to differentiate into neuroectodermal-like cells in response to various growth conditions, including those commonly used to maintain and differentiate cultures of primary neural stem cells (NSCs). Interpreting the wealth of data on this subject has been difficult because of variation in the starting cell population and the differences between the methods used to induce their differentiation. Here we evaluate how cultures of expanded BMSCs with a consistent immunophenotype respond to a variety of growth conditions and induction agents and review their ability to form neural-like derivatives. In addition, we report on some modifications to previously published techniques for the generation of neural-like cells from BMSCs in vitro.