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

Adult stem cell therapies for neurological disorders: benefits beyond neuronal replacement?

The modest capacity of endogenous repair processes in the central nervous system (CNS) justifies the broad interest in the development of effective stem cell based therapies for neurodegenerative disorders and other acute or chronic lesions. Motivated by the ambitious expectation to achieve functional neuronal replacement, several studies have already evidenced a potential benefit of stem cell grafts in animal models of human disorders. Nevertheless, growing evidence suggests that the effects orchestrated by stem cells, in most experimental cases, are not necessarily associated with the generation of new neurons. This hypothesis correlates with the versatile properties of adult and embryonic stem cells. When introduced into the lesioned CNS, nondifferentiated stem cells can have a positive influence through intrinsic neuroprotective capacities related to the production of neurotrophic factors, stimulation of endogenous neurogenesis, and modulation of neuroinflammation. Stem cells are also endowed with a multipotent differentiation profile, suggesting that a positive outcome could result from the replacement of nonneuronal cell types, in particular astrocytes and oligodendrocytes. Focusing on adult stem cells, this Review aims at summarizing experimental observations supporting the concept that, in cell-based therapies, stem cells operate not through a unidirectional mechanism (e.g., generating neurons) but rather as cellular mediators of a multitude of biological activities that could provide a favorable outcome for diverse nervous disorders.

Stem cells: comprehensive treatments for amyotrophic lateral sclerosis in conjunction with growth factor delivery

Amyotrophic lateral sclerosis (ALS) is characterized by loss of both upper and lower motor neurons. ALS progression is complex and likely due to cellular dysfunction at multiple levels, including mitochondrial dysfunction, glutamate excitotoxicity, oxidative stress, axonal dysfunction, reactive astrocytosis, and mutant superoxide dismutase expression, therefore, treatment must provide neuronal protection from multiple insults. A significant amount of ALS research focuses on growth factor-based therapies. Growth factors including insulin-like growth factor-I, vascular endothelial growth factor, brain-derived neurotrophic factor, and glial-derived neurotrophic factor exhibit robust neuroprotective effects on motor neurons in ALS models. Issues concerning growth factor delivery, stability and unwanted side effects slow the transfer of these treatments to human ALS patients. Stem cells represent a new therapeutic approach offering both cellular replacement and trophic support for the existing population. Combination therapy consisting of stem cells expressing beneficial growth factors may provide a comprehensive treatment for ALS.

Adult stem cells and their trans-differentiation potential--perspectives and therapeutic applications

Stem cells are self-renewing multipotent progenitors with the broadest developmental potential in a given tissue at a given time. Normal stem cells in the adult organism are responsible for renewal and repair of aged or damaged tissue. Adult stem cells are present in virtually all tissues and during most stages of development. In this review, we introduce the reader to the basic information about the field. We describe selected stem cell isolation techniques and stem cell markers for various stem cell populations. These include makers for endothelial progenitor cells (CD146/MCAM/MUC18/S-endo-1, CD34, CD133/prominin, Tie-2, Flk1/KD/VEGFR2), hematopoietic stem cells (CD34, CD117/c-Kit, Sca1), mesenchymal stem cells (CD146/MCAM/MUC18/S-endo-1, STRO-1, Thy-1), neural stem cells (CD133/prominin, nestin, NCAM), mammary stem cells (CD24, CD29, Sca1), and intestinal stem cells (NCAM, CD34, Thy-1, CD117/c-Kit, Flt-3). Separate section provides a concise summary of recent clinical trials involving stem cells directed towards improvement of a damaged myocardium. In the last part of the review, we reflect on the field and on future developments.

Focal transplantation-based astrocyte replacement is neuroprotective in a model of motor neuron disease

Cellular abnormalities in amyotrophic lateral sclerosis (ALS) are not limited to motor neurons. Astrocyte dysfunction also occurs in human ALS and transgenic rodents expressing mutant human SOD1 protein (SOD1(G93A)). Here we investigated focal enrichment of normal astrocytes using transplantation of lineage-restricted astrocyte precursors, called glial-restricted precursors (GRPs). We transplanted GRPs around cervical spinal cord respiratory motor neuron pools, the principal cells whose dysfunction precipitates death in ALS. GRPs survived in diseased tissue, differentiated efficiently into astrocytes and reduced microgliosis in the cervical spinal cords of SOD1(G93A) rats. GRPs also extended survival and disease duration, attenuated motor neuron loss and slowed declines in forelimb motor and respiratory physiological functions. Neuroprotection was mediated in part by the primary astrocyte glutamate transporter GLT1. These findings indicate the feasibility and efficacy of transplantation-based astrocyte replacement and show that targeted multisegmental cell delivery to the cervical spinal cord is a promising therapeutic strategy for slowing focal motor neuron loss associated with ALS.

A novel cell transplantation protocol and its application to an ALS mouse model

Amyotrophic lateral sclerosis (ALS) is a lethal neurodegenerative disease, which selectively affects motor neurons throughout the central nervous system. The extensive distribution of motor neurons is an obstacle to applying cell transplantation therapy for the treatment of ALS. To overcome this problem, we developed a cell transplantation method via the fourth cerebral ventricle in mice. We used mouse olfactory ensheathing cells (OECs) and rat mesenchymal stem cells (MSCs) as donor cells. OECs are reported to promote regeneration and remyelination in the spinal cord, while MSCs have a capability to differentiate into several types of specific cells including neural cells. Furthermore both types of cells can be relatively easily obtained by biopsy in human. Initially, we confirmed the safety of the operative procedure and broad distribution of grafted cells in the spinal cord using wild-type mice. After transplantation, OECs distributed widely and survived as long as 100 days after transplantation, with a time-dependent depletion of cell number. In ALS model mice, OEC transplantation revealed no adverse effects but no significant differences in clinical evaluation were found between OEC-treated and non-transplanted animals. After MSC transplantation into the ALS model mice, females, but not males, showed a statistically longer disease duration than the non-transplanted controls. We conclude that intrathecal transplantation could be a promising way to deliver donor cells to the central nervous system. Further experiments to elucidate relevant conditions for optimal outcomes are required.

Bone marrow mesenchymal stem cells from healthy donors and sporadic amyotrophic lateral sclerosis patients

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease lacking effective therapies. Cell replacement therapy has been suggested as a promising therapeutic approach for multiple neurodegenerative diseases, including motor neuron disease. We analyzed expanded mesenchymal stem cells (MSCs) isolated from sporadic ALS patients and compared them with MSCs isolated from healthy donors. MSCs were isolated from bone marrow by Percoll gradient and maintained in culture in MSC Medium until the third passage. Growth kinetics, immunophenotype, telomere length, and karyotype were evaluated during in vitro expansion. Osteogenic, adipogenic, chondrogenic, and neurogenic differentiation potential were also evaluated. No morphological differences were observed in the MSCs isolated from donors or patients. The cellular expansion potential of MSCs from donors and patients was slightly different. After three passages, the MSCs isolated from donors reached a cumulative population doubling higher than from patients but the difference was not statistically significant. No significant differences between donors or patients were observed in the immunophenotype analysis. No chromosomal alteration or evidence of cellular senescence was observed in any samples. Both donor and patient MSCs, after exposure to specific conditioning media, differentiated into adipocytes, osteoblasts, chondrocytes, and neuron-like cells. These results suggest that extensive in vitro expansion of patient MSCs does not involve any functional modification of the cells, including chromosomal alterations or cellular senescence. Hence, there is a good chance that MSCs might be used as a cell-based therapy for ALS patients.

Pilot study of granulocyte colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells in amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of upper and lower motor neurons in the brain, brainstem, and spinal cord. It has been proposed that bone marrow (BM)-derived cells might supply motor neurons and other cells with a cellular milieu more conducive to survival in ALS. Direct injection of stem cells in ALS is problematic because of the large expanse of the neuraxis that would need to be injected. We reasoned that transiently increasing the number of circulating hematopoietic stem cells might be a useful therapeutic approach. However, agents stimulating the activation and mobilization of hematopoietic stem cells may have adverse effects such as activation of microglial cells. We conducted a small pilot trial of the collection and reinfusion of granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells (PBSC) in ALS patients and found no adverse effects, paving the way for a properly powered therapeutic trial with an optimized regimen of G-CSF.

Human mesenchymal stem cell transplantation extends survival, improves motor performance and decreases neuroinflammation in mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a lethal disease affecting motoneurons. In familial ALS, patients bear mutations in the superoxide dismutase gene (SOD1). We transplanted human bone marrow mesenchymal stem cells (hMSCs) into the lumbar spinal cord of asymptomatic SOD1(G93A) mice, an experimental model of ALS. hMSCs were found in the spinal cord 10 weeks after, sometimes close to motoneurons and were rarely GFAP- or MAP2-positive. In females, where progression is slower than in males, astrogliosis and microglial activation were reduced and motoneuron counts with the optical fractionator were higher following transplantation. Motor tests (Rotarod, Paw Grip Endurance, neurological examination) were significantly improved in transplanted males. Therefore hMSCs are a good candidate for ALS cell therapy: they can survive and migrate after transplantation in the lumbar spinal cord, where they prevent astrogliosis and microglial activation and delay ALS-related decrease in the number of motoneurons, thus resulting in amelioration of the motor performance.

Activation of bone marrow-derived microglia promotes photoreceptor survival in inherited retinal degeneration

The role of microglia in neurodegeneration is controversial, although microglial activation in the retina has been shown to provide an early response against infection, injury, ischemia, and degeneration. Here we show that endogenous bone marrow (BM)-derived microglia play a protective role in vascular and neural degeneration in the retinitis pigmentosa model of inherited retinal degeneration. BM-derived cells were recruited to the degenerating retina where they differentiated into microglia and subsequently localized to the degenerating vessels and neurons. Inhibition of stromal-derived factor-1 in the retina reduced the number of BM-derived microglia and accelerated the rate of neurovascular degeneration. Systemic depletion of myeloid progenitors also accelerated the degenerative process. Conversely, activation of BM-derived myeloid progenitors by systemic administration of both granulocyte colony-stimulating factor and erythropoietin resulted in the deceleration of retinal degeneration and the promotion of cone cell survival. These data indicate that BM-derived microglia may play a protective role in retinitis pigmentosa. Functional activation of BM-derived myeloid progenitors by cytokine therapy may provide a novel strategy for the treatment of inherited retinal degeneration and other neurodegenerative diseases, regardless of the underlying genetic defect.

In vitro evidence for impaired neuroprotective capacities of adult mesenchymal stem cells derived from a rat model of familial amyotrophic lateral sclerosis (hSOD1(G93A))

Protection of neurons by stem cells is an attractive challenge in the development of efficient therapies of neurodegenerative diseases. When giving preference to autologous grafts, the bone marrow constitutes a valuable source of adult stem cells. Therefore, we herein studied the acquisition of neuroprotective functions by cultured mesenchymal stem cells (MSCs) exposed to growth factors known to promote the differentiation of neural stem cells into astrocytes. In these conditions, MSCs showed increased transcription and expression of the high-affinity glutamate transporter GLT-1 and functional studies revealed increased aspartate uptake activity. In addition, differentiation was shown to endow the cells with the capacity to respond to riluzole which triggers a robust up-regulation of the GDNF production. In parallel, MSCs derived from the bone marrow of a transgenic rat model of familial ALS (hSOD1(G93A)) were also characterised. Unexpectedly, cells from this rat strain submitted to the differentiation protocol showed modest capacity to take up aspartate and did not respond to the riluzole treatments. These data highlight the neuroprotective potential attributable to MSCs, supporting their use as valuable tools for the treatment of neurodegenerative disorders. However, the cells from the transgenic animal model of ALS appeared deficient in their capacity to gain the neuroprotective properties, raising questions regarding the suitability of autologous stem cell grafts in future therapies against familial forms of this disease.

Stem cell sources and therapeutic approaches for central nervous system and neural retinal disorders

In the past decades, stem cell biology has made a profound impact on our views of mammalian development as well as opened new avenues in regenerative medicine. The potential of stem cells to differentiate into various cell types of the body is the principal reason they are being explored in treatments for diseases in which there may be dysfunctional cells and/or loss of healthy cells due to disease. In addition, other properties are unique to stem cells; their endogenous trophic support, ability to home to sites of pathological entities, and stability in culture, which allows genetic manipulation, are also being utilized to formulate stem cell-based therapy for central nervous system (CNS) disorders. In this review, the authors will review key characteristics of embryonic and somatic (adult) stem cells, consider therapeutic strategies employed in stem cell therapy, and discuss the recent advances made in stem cell-based therapy for a number of progressive neurodegenerative diseases in the CNS as well as neuronal degeneration secondary to other abnormalities and injuries. Although a great deal of progress has been made in our knowledge of stem cells and their utility in treating CNS disorders, much still needs to be elucidated regarding the biology of the stem cells and the pathogenesis of targeted CNS diseases to maximize therapeutic benefits. Nonetheless, stem cells present tremendous promise in the treatment of a variety of neurodegenerative diseases.

Combining growth factor and stem cell therapy for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease where motor neurons within the brain and spinal cord are lost, leading to paralysis and death. Certain growth factors should, in principle, be able to protect dying motor neurons. However, targeted delivery to the spinal cord or brain has been a constant problem. There is also accumulating evidence that glial cells might play a crucial role in maintaining motor neuron function and survival in ALS. Stem cells isolated and expanded in culture can be modified to release growth factors and generate glial cells following transplantation into the spinal cord or brain. As such, they might be able to both detoxify the local environment around dying motor neurons and deliver trophic factors. Here we examine the feasibility of translating these findings into new treatments for ALS patients.

Shifting the balance: cell-based therapeutics as modifiers of the amyotrophic lateral sclerosis–specific neuronal microenvironment

✓ Recent advances in the laboratory have improved the current understanding of neurobiological mechanisms underlying the initiating events and pathological progression observed in amyotrophic lateral sclerosis (ALS). Whereas initial studies have revealed the late-stage intracellular cascades contributing to neuronal dysfunction and cell death, more recently collected data have begun to elucidate the presence and importance of a “non–cell autonomous” component indicating that affected glial cell subtypes may serve distinct and required roles. Pharmacological interventions for ALS have largely been disappointing likely in part because they have failed to address either the proximate events contributing to neuronal dysfunction and death or the deleterious contributions of non-neuronal cells within the local microenvironment. Alternatively, cell-based therapeutics offer the potential of a multifaceted approach oriented toward the dual ends of protecting remaining viable neurons and attempting to restore neuronal function lost as a manifestation of disease progression. The authors review the evolving knowledge of disease initiation and progression, with specific emphasis on the role of affected glia as crucial contributors to the observed ALS phenotype. This basis is used to underscore the potential roles of cell-based therapeutics as modifiers of the ALS-specific microenvironment.

MyD88-deficient bone marrow cells accelerate onset and reduce survival in a mouse model of amyotrophic lateral sclerosis

Increasing evidence suggests that neurotoxicity of secreted superoxide dismutase 1 (SOD1) mutants is associated with amyotrophic lateral sclerosis (ALS). We show here that mutant SOD1 protein activates microglia via a myeloid differentiation factor 88 (MyD88)–dependent pathway. This inflammatory response is also associated with a marked recruitment of bone marrow–derived microglia (BMDM) in the central nervous system. We then generated chimeric SOD1^G37R and SOD1^G93A mice by transplantation of bone marrow (BM) cells from MyD88-deficient or green fluorescent protein (GFP)–expressing mice. SOD1^G37R mice receiving MyD88^−/− BM cells exhibit a significantly earlier disease onset and shorter lifespan compared with mice transplanted with control GFP cells. This compelling beneficial effect of MyD88-competent BMDM is a previously unrecognized natural innate immune mechanism of neuroprotection in a mouse model of late-onset motor neuron disease.

Stem cell transplantation for neurodegenerative diseases

PURPOSE OF REVIEW

To review recent developments in the application of stem cells for transplantation therapies in neurodegenerative diseases.

RECENT FINDINGS

Stem cell transplantation has the potential to improve function by replacing cells lost to the disease and reconstructing elements of neural circuitry or by providing support for host cells (e.g. by secretion of trophic factors). Other mechanisms, such as modulation of the immune system by bone marrow stem cell transplantation, pertinent to conditions such as multiple sclerosis, are emerging as therapies but will not be discussed here. There have been substantial advances in our understanding of stem cell biology and some recent important advances in controlling their differentiated phenotype. Using stem cells to provide trophic support places less stringent requirements on the cells and this is the area in which many of the first clinical studies are taking place.

SUMMARY

There are real prospects of stem cell technology having a place in clinical management of neurodegenerative conditions, but directing the differentiation of stem cells towards the appropriate neural phenotype remains a challenge. This is a relatively new and rapidly evolving area, and caution should be applied when advising patients.

Human mesenchymal stromal cells ameliorate the phenotype of SOD1-G93A ALS mice

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal, neurodegenerative disease, currently without any effective therapy. Multiple advantages make mesenchymal stromal cells (MSC) a good candidate for cellular therapy in many intractable diseases such as stroke and brain injury. Until now, no irrefutable evidence exists regarding the outcome of MSC transplantation in the mouse model of ALS. The present study was designed to investigate the therapeutic potential of human MSC (hMSC) in the mouse model of ALS (SOD1-G93A mice).

METHODS

hMSC were isolated from iliac crest aspirates from healthy donors and kept in cell cultures. hMSC of the fifth passage were delivered intravenously into irradiated pre-symptomatic SOD1-G93A mice. Therapeutic effects were analyzed by survival analysis, rotarod test, motor neuron count in spinal cord and electrophysiology. The engraftment and in vivo differentiation of hMSC were examined in the brain and spinal cord of hMSC-transplanted mice.

RESULTS

After intravenous injection into irradiated pre-symptomatic SOD1-G93A mice, hMSC survived more than 20 weeks in recipient mice, migrated into the parenchyma of brain and spinal cord and showed neuroglia differentiation. Moreover, hMSC-transplanted mice showed significantly delayed disease onset (14 days), increased lifespan (18 days) and delayed disease progression compared with untreated mice.

DISCUSSION

Our data document the positive effects of hMSC transplantation in the mouse model of ALS. It may signify the potential use of hMSC in treatment of ALS.

Cardioinductive network guiding stem cell differentiation revealed by proteomic cartography of tumor necrosis factor alpha-primed endodermal secretome

In the developing embryo, instructive guidance from the ventral endoderm secures cardiac program induction within the anterolateral mesoderm. Endoderm-guided cardiogenesis, however, has yet to be resolved at the proteome level. Here, through cardiopoietic priming of the endoderm with the reprogramming cytokine tumor necrosis factor alpha (TNFalpha), candidate effectors of embryonic stem cell cardiac differentiation were delineated by comparative proteomics. Differential two-dimensional gel electrophoretic mapping revealed that more than 75% of protein species increased >1.5-fold in the TNFalpha-primed versus unprimed endodermal secretome. Protein spot identification by linear ion trap quadrupole (LTQ) tandem mass spectrometry (MS/MS) and validation by shotgun LTQ-Fourier transform MS/MS following multidimensional chromatography mapped 99 unique proteins from 153 spot assignments. A definitive set of 48 secretome proteins was deduced by iterative bioinformatic screening using algorithms for detection of canonical and noncanonical indices of secretion. Protein-protein interaction analysis, in conjunction with respective expression level changes, revealed a nonstochastic TNFalpha-centric secretome network with a scale-free hierarchical architecture. Cardiovascular development was the primary developmental function of the resolved TNFalpha-anchored network. Functional cooperativity of the derived cardioinductive network was validated through direct application of the TNFalpha-primed secretome on embryonic stem cells, potentiating cardiac commitment and sarcomerogenesis. Conversely, inhibition of primary network hubs negated the procardiogenic effects of TNFalpha priming. Thus, proteomic cartography establishes a systems biology framework for the endodermal secretome network guiding stem cell cardiopoiesis.

Heterogeneity in motoneuron disease

Recently, mutations in several genes have been identified as primary causes for the degeneration of motoneurons and their axons. Strikingly, mutations in the same genes were associated with clinically different motoneuron syndromes. The identity of these genes also shed light on the mechanisms of motoneuron degeneration and revealed that overlapping motoneuron phenotypes might be caused by heterogeneous molecular mechanisms. Overall, these findings have challenged the diagnostic classification system set by clinical judgement and triggered the notion of heterogeneity in motoneuron disease. It will now be especially relevant to identify the mechanisms and principles that motoneuron diseases have in common, as this will allow us to identify the most relevant therapeutic targets. On the other hand, heterogeneity in motoneuron disease also implies that finding a monotherapy cure for motoneuron disease will be challenging and that pre-clinical testing of therapeutic targets should not be limited to a single animal model.

Human stem cells for CNS repair

Although most peripheral tissues have at least a limited ability for self-repair, the central nervous system (CNS) has long been known to be relatively resistant to regeneration. Small numbers of stem cells have been found in the adult brain but do not appear to be able to affect any significant recovery following disease or insult. In the last few decades, the idea of being able to repair the brain by introducing new cells to repair damaged areas has become an accepted potential treatment for neurodegenerative diseases. This review focuses on the suitability of various human stem cell sources for such treatments of both slowly progressing conditions, such as Parkinson's disease, Huntington's disease and multiple sclerosis, and acute insult, such as stroke and spinal cord injury. Despite stem cell transplantation having now moved a step closer to the clinic with the first trials of autologous mesenchymal stem cells, the effects shown are moderate and are not yet at the stage of development that can fulfil the hopes that have been placed on stem cells as a means to replace degenerating cells in the CNS. Success will depend on careful investigation in experimental models to enable us to understand not just the practicalities of stem cell use, but also the underlying biological principles.

REVIEW ARTILCE: Cell therapy and stem cells in animal models of motor neuron disorders

Amyotrophic lateral sclerosis (ALS), spinal bulbar muscular atrophy (or Kennedy's disease), spinal muscular atrophy and spinal muscular atrophy with respiratory distress 1 are neurodegenerative disorders mainly affecting motor neurons and which currently lack effective therapies. Recent studies in animal models as well as primary and embryonic stem cell models of ALS, utilizing over-expression of mutated forms of Cu/Zn superoxide dismutase 1, have shown that motor neuron degeneration in these models is in part a non cell-autonomous event and that by providing genetically non-compromised supporting cells such as microglia or growth factor-excreting cells, onset can be delayed and survival increased. Using models of acute motor neuron injury it has been shown that embryonic stem cell-derived motor neurons implanted into the spinal cord can innervate muscle targets and improve functional recovery. Thus, a rationale exists for the development of cell therapies in motor neuron diseases aimed at either protecting and/or replacing lost motor neurons, interneurons as well as non-neuronal cells. This review evaluates approaches used in animal models of motor neuron disorders and their therapeutic relevance.

Grafted neural stem cells increase the life span and protect motoneurons in pmn mice

In this study, we have grafted neural stem cells (NSCs) into the lumbar spinal cord of a mouse mutant that has a specific loss of motoneurons (progressive motor neuronopathy/pmn). A small number of grafted cells ( approximately 3000) increased the life span of the mice by 56%. The improved survival was accompanied by a rescue of host motoneurons, a stabilization in the weight and an increase in the size of the muscle fibers. The grafted NSCs were small and round and exhibited no neural markers, suggesting that they remained in an undifferentiated state. Thus grafting of NSCs in a mouse model with motoneuron degeneration exerts a neuroprotective effect.

Selective ablation of bone marrow-derived dendritic cells increases amyloid plaques in a mouse Alzheimer's disease model

We have recently shown that the ability of microglia to effectively fight off aggregated beta-amyloid plaque formation and cognitive loss in transgenic mouse models of Alzheimer's disease (Tg-AD), is augmented in response to T-cell-based immunization, using glatiramer acetate (GA). The immunization increases incidence of local CD11c+ dendritic-like cells. It is unclear, however, whether these dendritic cells are derived from resident microglia or from the bone marrow. To determine the origin of this dendritic-cell population, we used chimeric mice whose bone marrow-derived cells express a transgene that allows the cells to be specifically ablated by diphtheria toxin. We show here that T-cell-based immunization of these mice, using GA, induced the recruitment of bone marrow-derived dendritic cells. Depletion of the dendritic cells by systemic injection of diphtheria toxin resulted in significantly increased formation of amyloid plaques. Thus, recruitment of bone marrow-derived dendritic cells evidently plays a role in reducing plaque formation in a mouse model of Alzheimer's disease.

Fas small interfering RNA reduces motoneuron death in amyotrophic lateral sclerosis mice

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disease characterized by selective motoneuron death. Understanding of the molecular mechanisms that trigger and regulate motoneuron degeneration could be relevant to ALS and other motoneuron disorders. This study investigates the role of Fas-linked motoneuron death in the pathogenesis of ALS.

METHODS

We performed in vitro and in vivo small interfering RNA-mediated interference, by silencing the Fas receptor on motoneurons that carry the superoxide dismutase-1 (SOD1)-G93A mutation.

RESULTS

We observed a significant reduction in Fas expression at messenger RNA (p < 0.001) and protein levels. Treated motoneurons demonstrated an increase in survival and a reduction in cytochrome c release from mitochondria. In vivo, continuous intrathecal administration of Fas small interfering RNA by an osmotic minipump improved motor function and survival in SOD1-G93A mice (mean increase, 18 days; p < 0.0001). Treated mice showed a significant reduction in Fas and Fas mediators p38 mitogen-activated protein kinase, neuronal nitric oxide synthase, and caspase-8.

INTERPRETATION

Fas silencing interferes with motoneuron-specific downstream death pathways and results in increased motoneuron survival and amelioration of the SOD1-G93A phenotype, suggesting new possible strategies for molecular therapy of ALS.

Stem cell treatment in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis is a progressive fatal neurodegenerative disease that targets motor neurons. Its origin is unknown but a main role of reactive astrogliosis and microglia activation in the pathogenesis has been recently demonstrated. Surrounding neurons with healthy adjoining cells completely stops motor neuron death in some cases. Hence stem cell transplantation might represent a promising therapeutic strategy. In this study MSCs were isolated from bone marrow of 9 patients with definite ALS. Growth kinetics, immunophenotype, telomere length and karyotype were evaluated during in vitro expansion. No significant differences between donors or patients were observed. The patients received intraspinal injections of autologous MSCs at the thoracic level and monitored for 4 years. No significant acute or late side effects were evidenced. No modification of the spinal cord volume or other signs of abnormal cell proliferation were observed. Four patients show a significant slowing down of the linear decline of the forced vital capacity and of the ALS-FRS score. Our results seem to demonstrate that MSCs represent a good chance for stem cell cell-based therapy in ALS and that intraspinal injection of MSCs is safe also in the long term. A new phase 1 study is carried out to verify these data in a larger number of patients.

Evaluation of Sca-1 and c-Kit As Selective Markers for Muscle Remodelling by Nonhemopoietic Bone Marrow Cells

Bone marrow (BM)-derived cells (BMCs) have demonstrated a myogenic tissue remodeling capacity. However, because the myoremodeling is limited to approximately 1%-3% of recipient muscle fibers in vivo, there is disagreement regarding the clinical relevance of BM for therapeutic application in myodegenerative conditions. This study sought to determine whether rare selectable cell surface markers (in particular, c-Kit) could be used to identify a BMC population with enhanced myoremodeling capacity. Dystrophic mdx muscle remodeling has been achieved using BMCs sorted by expression of stem cell antigen-1 (Sca-1). The inference that Sca-1 is also a selectable marker associated with myoremodeling capacity by muscle-derived cells prompted this study of relative myoremodeling contributions from BMCs (compared with muscle cells) on the basis of expression or absence of Sca-1. We show that myoremodeling activity does not differ in cells sorted solely on the basis of Sca-1 from either muscle or BM. In addition, further fractionation of BM to a more mesenchymal-like cell population with lineage markers and CD45 subsequently revealed a stronger selectability of myoremodeling capacity with c-Kit/Sca-1 (p < .005) than with Sca-1 alone. These results suggest that c-Kit may provide a useful selectable marker that facilitates selection of cells with an augmented myoremodeling capacity derived from BM and possibly from other nonmuscle tissues. In turn, this may provide a new methodology for rapid isolation of myoremodeling capacities from muscle and nonmuscle tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Intrathecal application of neuroectodermally converted stem cells into a mouse model of ALS: limited intraparenchymal migration and survival narrows therapeutic effects

Stem and progenitor cells provide a promising therapeutic strategy for amyotrophic lateral sclerosis (ALS). To comparatively evaluate the therapeutic potentials of human bone marrow-derived mesodermal stromal cells (hMSCs) and umbilical cord blood cells (hUBCs) in ALS, we transplanted hMSCs and hUBCs and their neuroectodermal derivatives (hMSC-NSCs and hUBC-NSCs) into the ALS mouse model over-expressing the G93A mutant of the human SOD1 gene. We used a standardized protocol similar to clinical studies by performing a power calculation to estimate sample size prior to transplantation, matching the treatment groups for gender and hSOD-G93A gene content, and applying a novel method for directly injecting 100,000 cells into the CSF (the cisterna magna). Ten days after transplantation we found many cells within the subarachnoidal space ranging from frontal basal cisterns back to the cisterna magna, but only a few cells around the spinal cord. hMSCs and hMSC-NSCs were also located within the Purkinje cell layer. Intrathecal cell application did not affect survival times of mice compared to controls. Consistently, time of disease onset and first pareses, death weight, and motor neuron count in lumbar spinal cord did not vary between treatment groups. Interestingly, transplantation of hMSCs led to an increase of pre-symptomatic motor performance compared to controls in female animals. The negative outcome of the present study is most likely due to insufficient cell numbers within the affected brain regions (mainly the spinal cord). Further experiments defining the optimal cell dose, time point and route of application and particularly strategies to improve the homing of transplanted cells towards the CNS region of interest are warranted to define the therapeutic potential of mesodermal stem cells for the treatment of ALS.

Neural stem cells LewisX+ CXCR4+ modify disease progression in an amyotrophic lateral sclerosis model

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease characterized by the degeneration of the motor neurons. We tested whether treatment of superoxide dismutase (SOD1)-G93A transgenic mouse, a model of ALS, with a neural stem cell subpopulation double positive for Lewis X and the chemokine receptor CXCR4 (LeX+CXCR4+) can modify the disease's progression. In vitro, after exposure to morphogenetic stimuli, LeX+CXCR4+ cells generate cholinergic motor neuron-like cells upon differentiation. LeX+CXCR4+ cells deriving from mice expressing Green Fluorescent Protein in all tissues or only in motor neurons, after a period of priming in vitro, were grafted into spinal cord of SOD1-G93A mice. Transplanted transgenic mice exhibited a delayed disease onset and progression, and survived significantly longer than non-treated animals by 23 days. Examination of the spinal cord revealed integration of donor-derived cells that differentiated mostly in neurons and in a lower proportion in motor neuron-like cells. Quantification of motor neurons of the spinal cord suggests a significant neuroprotection by LeX+CXCR4+ cells. Both VEGF- and IGF1-dependent pathways were significantly modulated in transplanted animals compared to controls, suggesting a role of these neurotrophins in MN protection. Our results support the therapeutic potential of neural stem cell fractions through both neurogenesis and growth factors release in motor neuron disorders.

Mutant SOD1G93A in bone marrow-derived cells exacerbates 3-nitropropionic acid induced striatal damage in mice

3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, produces selective lesions in striatal neurons that resemble those observed in Huntington's disease neuropathology. In this study, we evaluated the role of peripheral bone marrow-derived cells (BMDCs) in the 3-NP-induced striatal damage by transplanting bone marrow cells with human SOD1 G93A mutation (mSOD1(G93A)) which induces amyotrophic lateral sclerosis through an unknown gain of toxicity and mitochondrial dysfunction. We assessed striatal damage after 3-NP treatment in the recipient C57BL/6 wild-type (WT) mice that received bone marrow cells from WT or mSOD1(G93A) transgenic donor mice (WT-->WT or mSOD(G93A)-->WT). After intraperitoneal injection of 3-NP, six of the eight mSOD1(G93A)-->WT mice had bilateral striatal lesions while only one out of eight WT-->WT mice had a striatal lesion. The lesion volume was significantly higher in the mSOD1(G93A)-->WT mice than in the WT-->WT mice. However, following an intrastriatal injection of 3-NP, there was no significant difference in the lesion volumes between the WT-->WT mice and mSOD1(G93A)-->WT mice. Thus, the exacerbation of 3-NP-induced striatal damage in mSOD(G93A)-->WT mice was only seen after systemic administration of 3-NP, but not after intrastriatal injection. These results demonstrate that altered SOD1 activity (mSOD(G93A)) in BMDCs affects striatal damage probably through a mechanism involving a systemic factor.

Bone marrow-derived stem cells in neurological diseases: stones or masons?

In spite of the commonly held belief that ‘the brain does not regenerate’, it is now accepted that postnatal neurogenesis does occur. Thus, one wonders whether cellular-replacement therapy might be used to heal the brain in diseases caused by neuronal cell loss. The existence of neural stem cells has been demonstrated by many scientists and is now generally accepted. The exact role of these cells, how their numbers are regulated and how they participate in CNS and spinal cord regeneration in postnatal life are still not well known. There are many reviews summarizing work on these cells; consequently, I will focus instead on other cells that may participate in postnatal neurogenesis: bone marrow-derived stem cells. The possibility that bone marrow-derived stem cells populate the CNS and differentiate into various neural elements is certainly not universally accepted.

ALS: a disease of motor neurons and their nonneuronal neighbors

Amyotrophic lateral sclerosis is a late-onset progressive neurodegenerative disease affecting motor neurons. The etiology of most ALS cases remains unknown, but 2% of instances are due to mutations in Cu/Zn superoxide dismutase (SOD1). Since sporadic and familial ALS affects the same neurons with similar pathology, it is hoped that therapies effective in mutant SOD1 models will translate to sporadic ALS. Mutant SOD1 induces non-cell-autonomous motor neuron killing by an unknown gain of toxicity. Selective vulnerability of motor neurons likely arises from a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, excitotoxicity, insufficient growth factor signaling, and inflammation. Damage within motor neurons is enhanced by damage incurred by nonneuronal neighboring cells, via an inflammatory response that accelerates disease progression. These findings validate therapeutic approaches aimed at nonneuronal cells.

Wild-type microglia extend survival in PU.1 knockout mice with familial amyotrophic lateral sclerosis

The most common inherited form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motoneurons, is caused by dominant mutations in the ubiquitously expressed Cu(2+)/Zn(2+) superoxide dismutase (SOD1). Recent studies suggest that glia may contribute to motoneuron injury in animal models of familial ALS. To determine whether the expression of mutant SOD1 (mSOD1(G93A)) in CNS microglia contributes to motoneuron injury, PU.1(-/-) mice that are unable to develop myeloid and lymphoid cells received bone marrow transplants resulting in donor-derived microglia. Donor-derived microglia from mice overexpressing mSOD1(G93A), an animal model of familial ALS, transplanted into PU.1(-/-) mice could not induce weakness, motoneuron injury, or an ALS-like disease. To determine whether expression of mSOD1(G93A) in motoneurons and astroglia, as well as microglia, was required to produce motoneuron disease, PU.1(-/-) mice were bred with mSOD1(G93A) mice. In mSOD1(G93A)/PU.1(-/-) mice, wild-type donor-derived microglia slowed motoneuron loss and prolonged disease duration and survival when compared with mice receiving mSOD1(G93A) expressing cells or mSOD1(G93A) mice. In vitro studies confirmed that wild-type microglia were less neurotoxic than similarly cultured mSOD1(G93A) microglia. Compared with wild-type microglia, mSOD1(G93A) microglia produced and released more superoxide and nitrite+nitrate, and induced more neuronal death. These data demonstrate that the expression of mSOD1(G93A) results in activated and neurotoxic microglia, and suggests that the lack of mSOD1(G93A) expression in microglia may contribute to motoneuron protection. This study confirms the importance of microglia as a double-edged sword, and focuses on the importance of targeting microglia to minimize cytotoxicity and maximize neuroprotection in neurodegenerative diseases.

Complexity of astrocyte-motor neuron interactions in amyotrophic lateral sclerosis

Neurons and surrounding glial cells compose a highly specialized functional unit. In amyotrophic lateral sclerosis (ALS) astrocytes interact with motor neurons in a complex manner to modulate neuronal survival. Experiments using chimeric mice expressing ALS-linked mutations to Cu,Zn superoxide dismutase (SOD-1) suggest a critical modulation exerted by neighboring non-neuronal cell types on disease phenotype. When perturbed by primary neuronal damage, e.g. expression of SOD-1 mutations, neurons can signal astrocytes to proliferate and become reactive. Fibroblast growth factor-1 (FGF-1) can be released by motor neurons in response to damage to induce astrocyte activation by signaling through the receptor FGFR1. FGF-1 stimulates nerve growth factor (NGF) expression and secretion, as well as activity of the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor. Nrf2 leads to the expression of antioxidant and cytoprotective enzymes such as heme oxygenase-1 and a group of enzymes involved in glutathione metabolism that prevent motor neuron degeneration. However, prolonged stimulation with FGF-1 or SOD-mediated oxidative stress in astrocytes may disrupt the normal neuron-glia interactions and lead to progressive neuronal degeneration. The re-expression of p75 neurotrophin receptor and neuronal NOS in motor neurons in parallel with increased NGF secretion by reactive astrocytes may be a mechanism to eliminate critically damaged neurons. Consequently, astrocyte activation in ALS may have a complex pathogenic role.

Autologous mesenchymal stem cells: clinical applications in amyotrophic lateral sclerosis

OBJECTIVES

Our study was aimed to evaluate the feasibility and safety of intraspinal cord implantation of autologous mesenchymal stem cells (MSCs) in a few well-monitored amyotrophic lateral sclerosis (ALS) patients.

METHODS

Seven patients affected by definite ALS were enrolled in the study and two patients were treated for compassionate use and monitored for at least 3 years. Bone marrow was collected from the posterior iliac crest according to the standard procedure and MSCs were expanded ex vivo according to Pittenger's protocol. The cells were suspended in 2 ml autologous cerebrospinal fluid and transplanted into the spinal cord by a micrometric pump injector.

RESULTS

The in vitro expanded MSCs did not show any bacterial o fungal contamination, hemopoietic cell contamination, chromosomic alterations and early cellular senescence. No patient manifested major adverse events such as respiratory failure or death. Minor adverse events were intercostal pain irradiation and leg sensory dysesthesia, both reversible after a mean period of 6 weeks. No modification of the spinal cord volume or other signs of abnormal cell proliferation were observed. A significant slowing down of the linear decline of the forced vital capacity was evident in four patients 36 months after MSCs transplantation.

CONCLUSIONS

Our results demonstrate that direct injection of autologous expanded MSCs into the spinal cord of ALS patients is safe, with no significant acute or late toxicity, and well tolerated. The clinical results seem to be encouraging.

Relevance of motoneuron specification and programmed cell death in embryos to therapy of ALS

The molecular cues that generate spinal motoneurons in early embryonic development are well defined. Motoneurons are generated in excess and consequently undergo a natural period of programmed cell death. Although it is not known exactly how motoneurons compete for survival in embryonic development, it is hypothesized that they rely on the ability to access limited amounts of trophic factors from peripheral tissues, a process that is tightly regulated by skeletal muscle activity. Attempts to elucidate the molecular mechanisms that underlie motoneuron generation and programmed cell death in embryos have led to various effective strategies for treating injury and disease in animal models. Such studies provide great hope for the amelioration of human amyotrophic lateral sclerosis (ALS), a devastating progressive motoneuron degenerative disease. Here we review the clinical relevance of studying motoneuron specification and death during embryonic development.

Origin and distribution of bone marrow-derived cells in the central nervous system in a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is associated with increased numbers of microglia within the central nervous system (CNS). However, it is unknown whether the microgliosis results from proliferation of CNS resident microglia, or recruitment of bone marrow (BM)-derived microglial precursors. Here we assess the distribution and number of BM-derived cells in spinal cord using transplantation of green fluorescent protein (GFP)-labeled BM cells into myelo-ablated mice over-expressing human mutant superoxide dismutase 1 (mSOD), a murine model of ALS. Transplantation of GFP+ BM did not affect the rate of disease progression in mSOD mice. Mean numbers of microglia and GFP+ cells in spinal cords of control mice were not significantly different from those in asymptomatic mSOD mice and showed no change with animal age. The number of GFP+ cells and microglia (F4/80+ and CD11b+ cells) within the spinal cord of mSOD mice increased compared to age-matched controls at a time when mSOD mice exhibited disease symptoms, continuing up to disease end-stage. Although we observed an increase in the number of GFP+ cells in spinal cords of mSOD mice with disease symptoms, mean numbers of GFP+ F4/80+ cells comprised less than 20% of all F4/80+ cells and did not increase with disease progression. Furthermore, the relative rates of proliferation in CD45+GFP- and CD45+GFP+ cells were comparable. Thus, we demonstrate that the microgliosis present in spinal cord tissue of mSOD mice is primarily due to an expansion of resident microglia and not to the recruitment of microglial precursors from the circulation.

Transplanted ALDHhiSSClo neural stem cells generate motor neurons and delay disease progression of nmd mice, an animal model of SMARD1

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is an infantile autosomal-recessive motor neuron disease caused by mutations in the immunoglobulin micro-binding protein 2. We investigated the potential of a spinal cord neural stem cell population isolated on the basis of aldehyde dehydrogenase (ALDH) activity to modify disease progression of nmd mice, an animal model of SMARD1. ALDH(hi)SSC(lo) stem cells are self-renewing and multipotent and when intrathecally transplanted in nmd mice generate motor neurons properly localized in the spinal cord ventral horns. Transplanted nmd animals presented delayed disease progression, sparing of motor neurons and ventral root axons and increased lifespan. To further investigate the molecular events responsible for these differences, microarray and real-time reverse transcription-polymerase chain reaction analyses of wild-type, mutated and transplanted nmd spinal cord were undertaken. We demonstrated a down-regulation of genes involved in excitatory amino acid toxicity and oxidative stress handling, as well as an up-regulation of genes related to the chromatin organization in nmd compared with wild-type mice, suggesting that they may play a role in SMARD1 pathogenesis. Spinal cord of nmd-transplanted mice expressed high transcript levels for genes related to neurogenesis such as doublecortin (DCX), LIS1 and drebrin. The presence of DCX-expressing cells in adult nmd spinal cord suggests that both exogenous and endogenous neurogeneses may contribute to the observed nmd phenotype amelioration.

Cells enriched in markers of neural tissue-committed stem cells reside in the bone marrow and are mobilized into the peripheral blood following stroke

The concept that bone marrow (BM)-derived cells participate in neural regeneration remains highly controversial and the identity of the specific cell type(s) involved remains unknown. We recently reported that the BM contains a highly mobile population of CXCR4+ cells that express mRNA for various markers of early tissue-committed stem cells (TCSCs), including neural TCSCs. Here, we report that these cells not only express neural lineage markers (beta-III-tubulin, Nestin, NeuN, and GFAP), but more importantly form neurospheres in vitro. These neural TCSCs are present in significant amounts in BM harvested from young mice but their abundance and responsiveness to gradients of motomorphogens, such as SDF-1, HGF, and LIF, decreases with age. FACS analysis, combined with analysis of neural markers at the mRNA and protein levels, revealed that these cells reside in the nonhematopoietic CXCR4+/Sca-1+/lin-/CD45 BM mononuclear cell fraction. Neural TCSCs are mobilized into the peripheral-blood following stroke and chemoattracted to the damaged neural tissue in an SDF-1-CXCR4-, HGF-c-Met-, and LIF-LIF-R-dependent manner. Based on these data, we hypothesize that the postnatal BM harbors a nonhematopoietic population of cells that express markers of neural TCSCs that may account for the beneficial effects of BM-derived cells in neural regeneration.

Cardiac stem cells and mechanisms of myocardial regeneration

This review discusses current understanding of the role that endogenous and exogenous progenitor cells may have in the treatment of the diseased heart. In the last several years, a major effort has been made in an attempt to identify immature cells capable of differentiating into cell lineages different from the organ of origin to be employed for the regeneration of the damaged heart. Embryonic stem cells (ESCs) and bone marrow-derived cells (BMCs) have been extensively studied and characterized, and dramatic advances have been made in the clinical application of BMCs in heart failure of ischemic and nonischemic origin. However, a controversy exists concerning the ability of BMCs to acquire cardiac cell lineages and reconstitute the myocardium lost after infarction. The recognition that the adult heart possesses a stem cell compartment that can regenerate myocytes and coronary vessels has raised the unique possibility to rebuild dead myocardium after infarction, to repopulate the hypertrophic decompensated heart with new better functioning myocytes and vascular structures, and, perhaps, to reverse ventricular dilation and wall thinning. Cardiac stem cells may become the most important cell for cardiac repair.

Multipotentiality, homing properties, and pyramidal neurogenesis of CNS‐derived LeX(ssea‐1) + /CXCR4 + stem cells

Achieving efficient distribution of neural stem cells throughout the central nervous system (CNS) and robust generation of specific neurons is a major challenge for the development of cell-mediated therapy for neurodegenerative diseases. We isolated a primitive neural stem cell subset, double positive for LeX(Le) and CXCR4(CX) antigens that possesses CNS homing potential and extensive neuronal repopulating capacity. Le+CX+ cells are multipotential and can generate neurons as well as myogenic and endothelial cells. In vivo Le+CX+ cells displayed widespread incorporation and differentiated into cortical and hippocampal pyramidal neurons. Since intravenous delivery could be a less invasive route of transplantation, we investigated whether Le+CX+ cells could migrate across endothelial monolayers. Intracerebral coadministration of SDF enabled migration of intravenously injected Le+CX+ cells into the CNS and a small, yet significant, number of donor cells differentiated into neurons. The isolation of a specific neural stem cell population could offer major advantages to neuronal replacement strategies.

Trafficking of normal stem cells and metastasis of cancer stem cells involve similar mechanisms: pivotal role of the SDF-1-CXCR4 axis

The alpha-chemokine stromal-derived factor (SDF)-1 and the G-protein-coupled seven-span transmembrane receptor CXCR4 axis regulates the trafficking of various cell types. In this review, we present the concept that the SDF-1-CXCR4 axis is a master regulator of trafficking of both normal and cancer stem cells. Supporting this is growing evidence that SDF-1 plays a pivotal role in the regulation of trafficking of normal hematopoietic stem cells (HSCs) and their homing/retention in bone marrow. Moreover, functional CXCR4 is also expressed on nonhematopoietic tissue-committed stem/progenitor cells (TCSCs); hence, the SDF-1-CXCR4 axis emerges as a pivotal regulator of trafficking of various types of stem cells in the body. Furthermore, because most if not all malignancies originate in the stem/progenitor cell compartment, cancer stem cells also express CXCR4 on their surface and, as a result, the SDF-1-CXCR4 axis is also involved in directing their trafficking/metastasis to organs that highly express SDF-1 (e.g., lymph nodes, lungs, liver, and bones). Hence, we postulate that the metastasis of cancer stem cells and trafficking of normal stem cells involve similar mechanisms, and we discuss here the common molecular mechanisms involved in these processes. Finally, the responsiveness of CXCR4+ normal and malignant stem cells to an SDF-1 gradient may be regulated positively/primed by several small molecules related to inflammation which enhance incorporation of CXCR4 into membrane lipid rafts, or may be inhibited/blocked by small CXCR4 antagonist peptides. Consequently, strategies aimed at modulating the SDF-1-CXCR4 axis could have important clinical applications both in regenerative medicine to deliver normal stem cells to the tissues/organs and in clinical hematology/oncology to inhibit metastasis of cancer stem cells.

Unchain my heart: the scientific foundations of cardiac repair

In humans, the biological limitations to cardiac regenerative growth create both a clinical imperative--to offset cell death in acute ischemic injury and chronic heart failure--and a clinical opportunity; that is, for using cells, genes, and proteins to rescue cardiac muscle cell number or in other ways promote more efficacious cardiac repair. Recent experimental studies and early-phase clinical trials lend credence to the visionary goal of enhancing cardiac repair as an achievable therapeutic target.