Pluripotent stem cells engrafted into the normal or lesioned adult rat spinal cord are restricted to a glial lineage

Bridging defects in chronic spinal cord injury using peripheral nerve grafts combined with a chitosan-laminin scaffold and enhancing regeneration through them by co-transplantation with bone-marrow-derived mesenchymal stem cells: case series of 14 patients

OBJECTIVE

To investigate the effect of bridging defects in chronic spinal cord injury using peripheral nerve grafts combined with a chitosan-laminin scaffold and enhancing regeneration through them by co-transplantation with bone-marrow-derived mesenchymal stem cells.

METHODS

In 14 patients with chronic paraplegia caused by spinal cord injury, cord defects were grafted and stem cells injected into the whole construct and contained using a chitosan-laminin paste. Patients were evaluated using the International Standards for Classification of Spinal Cord Injuries.

RESULTS

Chitosan disintegration leading to post-operative seroma formation was a complication. Motor level improved four levels in 2 cases and two levels in 12 cases. Sensory-level improved six levels in two cases, five levels in five cases, four levels in three cases, and three levels in four cases. A four-level neurological improvement was recorded in 2 cases and a two-level neurological improvement occurred in 12 cases. The American Spinal Impairment Association (ASIA) impairment scale improved from A to C in 12 cases and from A to B in 2 cases. Although motor power improvement was recorded in the abdominal muscles (2 grades), hip flexors (3 grades), hip adductors (3 grades), knee extensors (2-3 grades), ankle dorsiflexors (1-2 grades), long toe extensors (1-2 grades), and plantar flexors (0-2 grades), this improvement was too low to enable them to stand erect and hold their knees extended while walking unaided.

CONCLUSION

Mesenchymal stem cell-derived neural stem cell-like cell transplantation enhances recovery in chronic spinal cord injuries with defects bridged by sural nerve grafts combined with a chitosan-laminin scaffold.

The isolation and cultivation of bone marrow stem cells and evaluation of differences for neural-like cells differentiation under the induction with neurotrophic factors

The bone marrow represents the most common source from which to isolate mesenchymal stem cells (MSCs). They can be obtained directly from patients and successfully induced to form various differentiated cell types. In addition, cell-based transplantation therapies have been proven to be promising strategies for curing disease of the nerve system. Therefore, it was particularly important to establish an easy and feasible method for the isolation, purification, and differentiation of bone marrow stromal cells (BMSCs). The aim of this study was to isolate and characterize putative bone marrow derived MSCs from Sprague-Dawley (SD) rats. Furthermore, differentiation effects were compared between the GDNF-induction group and the BDNF-induction group. Of these, BMSCs were isolated from the SD rats in a traditional manner, and identified based on plastic adherence, morphology, and surface phenotype assays. After induction with GDNF and BDNF, viability of BMSCs was detected by MTT assay and neuronal differentiation of BMSCs was confirmed by using immunofluorescence and Western blotting. Besides, the number of BMSCs that obviously exhibited neuronal morphology was counted and the results were compared between the GDNF-induction group and BDNF-induction groups. Our results indicate that direct adherence was a simple and convenient method for isolation and cultivation of BMSCs. Furthermore, BMSCs can be induced in vitro to differentiate into neuronal cells by using GDNF, which could achieve a more persistent and stable inducing effect than when using BDNF.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

Safety of human neural stem cell transplantation in chronic spinal cord injury

The spinal cord injury (SCI) microenvironment undergoes dynamic changes over time, which could potentially affect survival or differentiation of cells in early versus delayed transplantation study designs. Accordingly, assessment of safety parameters, including cell survival, migration, fate, sensory fiber sprouting, and behavioral measures of pain sensitivity in animals receiving transplants during the chronic postinjury period is required for establishing a potential therapeutic window. The goal of the study was assessment of safety parameters for delayed transplantation of human central nervous system-derived neural stem cells (hCNS-SCns) by comparing hCNS-SCns transplantation in the subacute period, 9 days postinjury (DPI), versus the chronic period, 60 DPI, in contusion-injured athymic nude rats. Although the number of surviving human cells after chronic transplantation was lower, no changes in cell migration were detected between the 9 and 60 DPI cohorts; however, the data suggest chronic transplantation may have enhanced the generation of mature oligodendrocytes. The timing of transplantation did not induce changes in allodynia or hyperalgesia measures. Together, these data support the safety of hCNS-SCns transplantation in the chronic period post-SCI.

New strategies for repairing the injured spinal cord: the role of stem cells

Thanks to advances in the stem cell biology of the central nervous system, the previously unconceivable regeneration of the damaged spinal cord is approaching reality. A number of potential strategies aim to optimize functional recovery after spinal cord injury. They include minimizing the progression of secondary injury, manipulating the inhibitory environment of the spinal cord, replacing lost tissue with transplanted cells or peripheral nerve grafts, remyelinating denuded axons and maximizing the intrinsic regenerative potential of endogenous progenitor cells. We review the application of stem cell transplantation to the spinal cord, emphasizing the use of embryonic stem cells for remyelinating damaged axons. Recent advancements in neural injury and repair, and the progress towards development of neuroprotective and regenerative interventions are discussed.

Neuro-immune interactions of neural stem cell transplants: from animal disease models to human trials

Stem cell technology is a promising branch of regenerative medicine that is aimed at developing new approaches for the treatment of severely debilitating human diseases, including those affecting the central nervous system (CNS). Despite the increasing understanding of the mechanisms governing their biology, the application of stem cell therapeutics remains challenging. The initial idea that stem cell transplants work in vivo via the replacement of endogenous cells lost or damaged owing to disease has been challenged by accumulating evidence of their therapeutic plasticity. This new concept covers the remarkable immune regulatory and tissue trophic effects that transplanted stem cells exert at the level of the neural microenvironment to promote tissue healing via combination of immune modulatory and tissue protective actions, while retaining predominantly undifferentiated features. Among a number of promising candidate stem cell sources, neural stem/precursor cells (NPCs) are under extensive investigation with regard to their therapeutic plasticity after transplantation. The significant impact in vivo of experimental NPC therapies in animal models of inflammatory CNS diseases has raised great expectations that these stem cells, or the manipulation of the mechanisms behind their therapeutic impact, could soon be translated to human studies. This review aims to provide an update on the most recent evidence of therapeutically-relevant neuro-immune interactions following NPC transplants in animal models of multiple sclerosis, cerebral stroke and traumas of the spinal cord, and consideration of the forthcoming challenges related to the early translation of some of these exciting experimental outcomes into clinical medicines.

Safety of epicenter versus intact parenchyma as a transplantation site for human neural stem cells for spinal cord injury therapy

Neural stem cell transplantation may have the potential to yield repair and recovery of function in central nervous system injury and disease, including spinal cord injury (SCI). Multiple pathological processes are initiated at the epicenter of a traumatic spinal cord injury; these are generally thought to make the epicenter a particularly hostile microenvironment. Conversely, the injury epicenter is an appealing potential site of therapeutic human central nervous system-derived neural stem cell (hCNS-SCns) transplantation because of both its surgical accessibility and the avoidance of spared spinal cord tissue. In this study, we compared hCNS-SCns transplantation into the SCI epicenter (EPI) versus intact rostral/caudal (R/C) parenchyma in contusion-injured athymic nude rats, and assessed the cell survival, differentiation, and migration. Regardless of transplantation site, hCNS-SCns survived and proliferated; however, the total number of hCNS-SCns quantified in the R/C transplant animals was twice that in the EPI animals, demonstrating increased overall engraftment. Migration and fate profile were unaffected by transplantation site. However, although transplantation site did not alter the proportion of human astrocytes, EPI transplantation shifted the localization of these cells and exhibited a correlation with calcitonin gene-related peptide fiber sprouting. Critically, no changes in mechanical allodynia or thermal hyperalgesia were observed. Taken together, these data suggest that the intact parenchyma may be a more favorable transplantation site than the injury epicenter in the subacute period post-SCI.

Cell transplantation for spinal cord injury: a systematic review

Cell transplantation, as a therapeutic intervention for spinal cord injury (SCI), has been extensively studied by researchers in recent years. A number of different kinds of stem cells, neural progenitors, and glial cells have been tested in basic research, and most have been excluded from clinical studies because of a variety of reasons, including safety and efficacy. The signaling pathways, protein interactions, cellular behavior, and the differentiated fates of experimental cells have been studied in vitro in detail. Furthermore, the survival, proliferation, differentiation, and effects on promoting functional recovery of transplanted cells have also been examined in different animal SCI models. However, despite significant progress, a "bench to bedside" gap still exists. In this paper, we comprehensively cover publications in the field from the last years. The most commonly utilized cell lineages were covered in this paper and specific areas covered include survival of grafted cells, axonal regeneration and remyelination, sensory and motor functional recovery, and electrophysiological improvements. Finally we also review the literature on the in vivo tracking techniques for transplanted cells.

Time-dependent changes in the microenvironment of injured spinal cord affects the therapeutic potential of neural stem cell transplantation for spinal cord injury

Background

The transplantation of neural stem/progenitor cells (NS/PCs) at the sub-acute phase of spinal cord injury, but not at the chronic phase, can promote functional recovery. However, the reasons for this difference and whether it involves the survival and/or fate of grafted cells under these two conditions remain unclear. To address this question, NS/PC transplantation was performed after contusive spinal cord injury in adult mice at the sub-acute and chronic phases.

Results

Quantitative analyses using bio-imaging, which can noninvasively detect surviving grafted cells in living animals, revealed no significant difference in the survival rate of grafted cells between the sub-acute and chronic transplantation groups. Additionally, immunohistology revealed no significant difference in the differentiation phenotypes of grafted cells between the two groups. Microarray analysis revealed no significant differences in the expression of genes encoding inflammatory cytokines or growth factors, which affect the survival and/or fate of grafted cells, in the injured spinal cord between the sub-acute and chronic phases. By contrast, the distribution of chronically grafted NS/PCs was restricted compared to NS/PCs grafted at the sub-acute phase because a more prominent glial scar located around the lesion epicenter enclosed the grafted cells. Furthermore, microarray and histological analysis revealed that the infiltration of macrophages, especially M2 macrophages, which have anti-inflammatory role, was significantly higher at the sub-acute phase than the chronic phase. Ultimately, NS/PCs that were transplanted in the sub-acute phase, but not the chronic phase, promoted functional recovery compared with the vehicle control group.

Conclusions

The extent of glial scar formation and the characteristics of inflammation is the most remarkable difference in the injured spinal cord microenvironment between the sub-acute and chronic phases. To achieve functional recovery by NS/PC transplantation in cases at the chronic phase, modification of the microenvironment of the injured spinal cord focusing on glial scar formation and inflammatory phenotype should be considered.

Preparation of neural stem cells and progenitors: neuronal production and grafting applications

Neural stem cells (NSC) are not only a valuable tool for the study of neural development and function, but an integral component in the development of transplantation strategies for neural disease. NSC can be used to study how neurons acquire distinct phenotypes and how the reciprocal interactions between neurons and glia in the developing nervous system shape the structure and function of the central nervous system (CNS). In addition, neurons prepared from NSC can be used to elucidate the molecular basis of neurological disorders as well as potential treatments. Although NSC can be derived from different species and many sources, including embryonic stem cells, induced pluripotent stem cells, adult CNS, and direct reprogramming of non-neural cells, isolating primary NSC directly from rat fetal tissue is the most common technique for preparation and study of neurons with a wealth of data available for comparison. Regardless of the source material, similar techniques are used to maintain NSC in culture and to differentiate NSC toward mature neural lineages. This chapter will describe specific methods for isolating multipotent NSC and neural precursor cells (NPC) from embryonic rat CNS tissue (mostly spinal cord). In particular, NPC can be separated into neuronal and glial restricted precursors (NRP and GRP, respectively) and used to reliably produce neurons or glial cells both in vitro and following transplantation into the adult CNS. This chapter will describe in detail the methods required for the isolation, propagation, storage, and differentiation of NSC and NPC isolated from rat spinal cords for subsequent in vitro or in vivo studies.

Transplantation of D15A-expressing glial-restricted-precursor-derived astrocytes improves anatomical and locomotor recovery after spinal cord injury

The transplantation of neural stem/progenitor cells is a promising therapeutic strategy for spinal cord injury (SCI). In this study, we tested whether combination of neurotrophic factors and transplantation of glial-restricted precursor (GRPs)-derived astrocytes (GDAs) could decrease the injury and promote functional recovery after SCI. We developed a protocol to quickly produce a sufficiently large, homogenous population of young astrocytes from GRPs, the earliest arising progenitor cell population restricted to the generation of glia. GDAs expressed the axonal regeneration promoting substrates, laminin and fibronectin, but not the inhibitory chondroitin sulfate proteoglycans (CSPGs). Importantly, GDAs or its conditioned medium promoted the neurite outgrowth of dorsal root ganglion neurons in vitro. GDAs were infected with retroviruses expressing EGFP or multi-neurotrophin D15A and transplanted into the contused adult thoracic spinal cord at 8 days post-injury. Eight weeks after transplantation, the grafted GDAs survived and integrated into the injured spinal cord. Grafted GDAs expressed GFAP, suggesting they remained astrocyte lineage in the injured spinal cord. But it did not express CSPG. Robust axonal regeneration along the grafted GDAs was observed. Furthermore, transplantation of D15A-GDAs significantly increased the spared white matter and decreased the injury size compared to other control groups. More importantly, transplantation of D15A-GDAs significantly improved the locomotion function recovery shown by BBB locomotion scores and Tredscan footprint analyses. However, this combinatorial strategy did not enhance the aberrant synaptic connectivity of pain afferents, nor did it exacerbate posttraumatic neuropathic pain. These results demonstrate that transplantation of D15A-expressing GDAs promotes anatomical and locomotion recovery after SCI, suggesting it may be an effective therapeutic approach for SCI.

Cell transplantation therapies for spinal cord injury focusing on induced pluripotent stem cells

Stimulated by the 2012 Nobel Prize in Physiology or Medicine awarded for Shinya Yamanaka and Sir John Gurdon, there is an increasing interest in the induced pluripotent stem (iPS) cells and reprograming technologies in medical science. While iPS cells are expected to open a new era providing enormous opportunities in biomedical sciences in terms of cell therapies and regenerative medicine, safety-related concerns for iPS cell-based cell therapy should be resolved prior to the clinical application of iPS cells. In this review, the pre-clinical investigations of cell therapy for spinal cord injury (SCI) using neural stem/progenitor cells derived from iPS cells, and their safety issues in vivo, are outlined. We also wish to discuss the strategy for the first human trails of iPS cell-based cell therapy for SCI patients.

Guiding Differentiation of Stem Cells in Vivo by Tetracycline-Controlled Expression of Key Transcription Factors

Transplantation of stem or progenitor cells is an attractive strategy for cell replacement therapy. However, poor long-term survival and insufficiently reproducible differentiation to functionally appropriate cells in vivo still present major obstacles for translation of this methodology to clinical applications. Numerous experimental studies have revealed that the expression of just a few transcription factors can be sufficient to drive stem cell differentiation toward a specific cell type, to transdifferentiate cells from one fate to another, or to dedifferentiate mature cells to pluripotent stem/progenitor cells (iPSCs). We thus propose here to apply the strategy of expressing the relevant key transcription factors to guide the differentiation of transplanted cells to the desired cell fate in vivo. To achieve this requires tools allowing us to control the expression of these genes in the transplant. Here, we describe drug-inducible systems that allow us to sequentially and timely activate gene expression from the outside, with a particular emphasis on the Tet system, which has been widely and successfully used in stem cells. These regulatory systems offer a tool for strictly limiting gene expression to the respective optimal stage after transplantation. This approach will direct the differentiation of the immature stem/progenitor cells in vivo to the desired cell type.

Neural Progenitor Cells Generate Motoneuron-Like Cells to Form Functional Connections with Target Muscles after Transplantation into the Musculocutaneous Nerve

Neural progenitor cells (NPCs) are suggested to be a valuable source of cell transplant in treatment of various neurological diseases because of their distinct attributes. They can be expanded and induced to differentiate in vitro. However, it remains uncertain whether in vitro expanded NPCs have the capacity to give rise to functional motoneurons after transplantation in vivo. Here, we showed that in vitro expanded NPCs, when transplanted into the musculocutaneous nerve, generated motoneuron-like cells that exhibited typical morphology with large cell bodies, expressed specific molecules, and extended axons to form functional connections with the target muscle. In contrast, transplanted NPCs failed to yield motoneurons in the injured ventral horn of the spinal cord. The results of the study demonstrate that NPCs have the potential to generate functional motoneurons in an appropriate environment. The distinct differentiating fate of NPCs in the musculocutaneous nerve and the injured ventral horn suggests the importance and necessity of modifying the host microenvironment in use of NPCs for cell replacement therapies for motoneuron diseases.

Integration and long distance axonal regeneration in the central nervous system from transplanted primitive neural stem cells

Spinal cord injury (SCI) results in devastating motor and sensory deficits secondary to disrupted neuronal circuits and poor regenerative potential. Efforts to promote regeneration through cell extrinsic and intrinsic manipulations have met with limited success. Stem cells represent an as yet unrealized therapy in SCI. Recently, we identified novel culture methods to induce and maintain primitive neural stem cells (pNSCs) from human embryonic stem cells. We tested whether transplanted human pNSCs can integrate into the CNS of the developing chick neural tube and injured adult rat spinal cord. Following injection of pNSCs into the developing chick CNS, pNSCs integrated into the dorsal aspects of the neural tube, forming cell clusters that spontaneously differentiated into neurons. Furthermore, following transplantation of pNSCs into the lesioned rat spinal cord, grafted pNSCs survived, differentiated into neurons, and extended long distance axons through the scar tissue at the graft-host interface and into the host spinal cord to form terminal-like structures near host spinal neurons. Together, these findings suggest that pNSCs derived from human embryonic stem cells differentiate into neuronal cell types with the potential to extend axons that associate with circuits of the CNS and, more importantly, provide new insights into CNS integration and axonal regeneration, offering hope for repair in SCI.

An update on spinal cord injury research

Spinal cord injury (SCI) can have a range of debilitating effects and permanently alter the capabilities and quality of life of survivors. The first specialized centers of care for SCI were established in 1944 and since then an increasing amount of research has been carried out in this area. Despite this, the present treatment and care levels for SCI are not comparable to those in other areas of medicine. In the clinic, the aim of SCI treatment is primarily to limit secondary damage by reducing compression in trauma spots and stabilizing the spinal column. Currently, no effective strategy for functional recovery is offered. In this review, we focus on research progress on the molecular mechanisms underlying SCI, and assess the treatment outcomes of SCI in animal models, i.e., neurotrophins and stem cells are discussed as pre-clinical therapies in animal models. We also assess the resources available and national research projects carried out on SCI in China in recent years, as well as making recommendations for the future allocation of funds in this area.

Transplantation of GABAergic cells derived from bioreactor-expanded human neural precursor cells restores motor and cognitive behavioral deficits in a rodent model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder that is characterized by progressive dementia, choreiform involuntary movements, and emotional deterioration. Neuropathological features include the progressive degeneration of striatal γ-aminobutyric acid (GABA) neurons. New therapeutic approaches, such as the transplantation of human neural precursor cells (hNPCs) to replace damaged or degenerated cells, are currently being investigated. The aim of this study was to investigate the potential for utilizing telencephalic hNPCs expanded in suspension bioreactors for cell restorative therapy in a rodent model of HD. hNPCs were expanded in a hydrodynamically controlled and homogeneous environment under serum-free conditions. In vitro analysis revealed that the bioreactor-expanded telencephalic (BET)-hNPCs could be differentiated into a highly enriched population of GABAergic neurons. Behavioral assessments of unilateral striatal quinolinic acid-lesioned rodents revealed a significant improvement in motor and memory deficits following transplantation with GABAergic cells differentiated from BET-hNPCs. Immunohistochemical analysis revealed that transplanted BET-hNPCs retained a GABAergic neuronal phenotype without aberrant transdifferentiation or tumor formation, indicating that BET-hNPCs are a safe source of cells for transplantation. This preclinical study has important implications as the transplantation of GABAergic cells derived from predifferentiated BET-hNPCs may be a safe and feasible cell replacement strategy to promote behavioral recovery in HD.

Effect of BDNF-plasma-collagen matrix controlled delivery system on the behavior of adult rats neural stem cells

The neurogenesis amount in central nervous system (CNS) stimulated by the injury or diseases is so small that neural stem cells (NSCs) cannot specifically differentiate into the ideal phenotypes to repair the injured CNS. The transplanted exogenous NSCs also have such problems as poor survival and insufficient neuronal differentiation. In this study, the behavior of NSCs from the spinal cord of adult rats was compared at the neurosphere level after the respective addition of the brain-derived neurotrophic factor (BDNF) daily, the BDNF-loaded plasma-collagen matrix, the plasma-collagen matrix alone, or the defined medium alone. The results suggested that the BDNF, either in the control release form or in the soluble form, initiated NSCs proliferation and differentiation by activating receptors Trk B and p75NTR. BDNF also increased the differentiation percentage of adult NSCs into neurons and supported the long-term cell survival and growth. The BDNF was stably released by the plasma-collagen matrix for up to 21 days. The plasma-collagen matrix alone showed its biocompatibility with cells by facilitating the adhesion, survival, and differentiation of NSCs. The NSCs in the defined medium alone group showed poor survival and a very low level of neuronal differentiation and proliferation abilities than above three groups. This study suggested that the BDNF-loaded plasma-collagen matrix may provide a promising means to resolve either the poor survival and insufficient neuronal differentiation of transplanted exogenous NSCs, or stimulating the intrinsic NSCs to proliferate and differentiate into neurons so as to repair the injured adult CNS.

Potential role of stem cells in severe spinal cord injury: current perspectives and clinical data

Stem cell transplantation for spinal cord injury (SCI) along with new pharmacotherapy research offers the potential to restore function and ease the associated social and economic burden in the years ahead. Various sources of stem cells have been used in the treatment of SCI, but the most convincing results have been obtained with neural progenitor cells in preclinical models. Although the use of cell-based transplantation strategies for the repair of chronic SCI remains the long sought after holy grail, these approaches have been to date the most successful when applied in the subacute phase of injury. Application of cell-based strategies for the repair and regeneration of the chronically injured spinal cord will require a combinational strategy that may need to include approaches to overcome the effects of the glial scar, inhibitory molecules, and use of tissue engineering strategies to bridge the lesion. Nonetheless, cell transplantation strategies are promising, and it is anticipated that the Phase I clinical trials of some form of neural stem cell-based approach in SCI will commence very soon.

Bench to bedside of neural stem cell in traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of major disability and death worldwide. Neural stem cells (NSCs) have recently been shown to contribute to the cellular remodelling that occurs following TBI and attention has been drawn to the area of neural stem cell as possible therapy for TBI. The NSCs may play an important role in the treatment of TBI by replacing the damaged cells and eventual remyelination. This paper summarized a critical assessment of recent data and developed a view comprising of six points to possible quality translation of NSCs in TBI.

Functional multipotency of stem cells: a conceptual review of neurotrophic factor-based evidence and its role in translational research

We here propose an updated concept of stem cells (SCs), with an emphasis on neural stem cells (NSCs). The conventional view, which has touched principally on the essential property of lineage multipotency (e.g., the ability of NSCs to differentiate into all neural cells), should be broadened to include the emerging recognition of biofunctional multipotency of SCs to mediate systemic homeostasis, evidenced in NSCs in particular by the secretion of neurotrophic factors. Under this new conceptual context and taking the NSC as a leading example, one may begin to appreciate and seek the “logic” behind the wide range of molecular tactics the NSC appears to serve at successive developmental stages as it integrates into and prepares, modifies, and guides the surrounding CNS micro- and macro-environment towards the formation and self-maintenance of a functioning adult nervous system. We suggest that embracing this view of the “multipotency” of the SCs is pivotal for correctly, efficiently, and optimally exploiting stem cell biology for therapeutic applications, including reconstitution of a dysfunctional CNS.

Differential effects of distinct central nervous system regions on cell migration and axonal extension of neural precursor transplants

Transplantation of neural precursor cells (NPCs) is a promising therapeutic strategy in CNS injury. However, the adult CNS lacks instructive signals present during development and, depending on the region and type of transplant, may be inhibitory for neuron generation and axonal growth. We examined the effects of the white matter in different regions of the adult CNS on the properties of NPC transplants with respect to cell survival, differentiation, migration, and axonal growth. NPCs were prepared from day 13.5 embryonic spinal cord of transgenic rats that express the human placental alkaline phosphatase (AP) reporter. These NPCs were injected unilaterally into the cervical spinal cord white matter and into the corpus callosum of adult rats and were analyzed immunohistochemically 2 weeks later. NPCs survived in both regions and differentiated into astrocytes, oligodendrocytes, and neurons, with no apparent differences in survival or phenotypic composition. However, in the spinal cord white matter, graft-derived cells, identified as precursors and glial cells, migrated from the injection site rostrally and caudally, whereas, in the corpus callosum, graft-derived cells did not migrate and remained at the injection site. Importantly, graft-derived neurons extended axons from the grafting site along the corpus callosum past the midline, entering into the contralateral side of the corpus callosum. These results demonstrate dramatic differences between white matter regions in the spinal cord and brain with respect to cell migration and axonal growth and underscore the importance of considering the effects of the local CNS environment in the design of effective transplantation strategies.

Current challenges for the advancement of neural stem cell biology and transplantation research

Transplantation of neural stem cells (NSC) is hoped to become a promising primary or secondary therapy for the treatment of various neurodegenerative disorders of the central nervous system (CNS), as demonstrated by multiple pre-clinical animal studies in which functional recovery has already been demonstrated. However, for NSC therapy to be successful, the first challenge will be to define a transplantable cell population. In the first part of this review, we will briefly discuss the main features of ex vivo culture and characterisation of NSC. Next, NSC grafting itself may not only result in the regeneration of lost tissue, but more importantly has the potential to improve functional outcome through many bystander mechanisms. In the second part of this review, we will briefly discuss several pre-clinical studies that contributed to a better understanding of the therapeutic potential of NSC grafts in vivo. However, while many pre-clinical animal studies mainly report on the clinical benefit of NSC grafting, little is known about the actual in vivo fate of grafted NSC. Therefore, the third part of this review will focus on non-invasive imaging techniques for monitoring cellular grafts in the brain under in vivo conditions. Finally, as NSC transplantation research has evolved during the past decade, it has become clear that the host micro-environment itself, either in healthy or injured condition, is an important player in defining success of NSC grafting. The final part of this review will focus on the host environmental influence on survival, migration and differentiation of grafted NSC.

Cotransplantation of Human Embryonic Stem Cell-Derived Neural Progenitors and Schwann Cells in a Rat Spinal Cord Contusion Injury Model Elicits a Distinct Neurogenesis and Functional Recovery

Cotransplantation of neural progenitors (NPs) with Schwann cells (SCs) might be a way to overcome low rate of neuronal differentiation of NPs following transplantation in spinal cord injury (SCI) and the improvement of locomotor recovery. In this study, we initially generated NPs from human embryonic stem cells (hESCs) and investigated their potential for neuronal differentiation and functional recovery when cocultured with SCs in vitro and cotransplanted in a rat acute model of contused SCI. Cocultivation results revealed that the presence of SCs provided a consistent status for hESC-NPs and recharged their neural differentiation toward a predominantly neuronal fate. Following transplantation, a significant functional recovery was observed in all engrafted groups (NPs, SCs, NPs + SCs) relative to the vehicle and control groups. We also observed that animals receiving cotransplants established a better state as assessed with the BBB functional test. Immunohistofluorescence evaluation 5 weeks after transplantation showed invigorated neuronal differentiation and limited proliferation in the cotransplanted group when compared to the individual hESC-NP-grafted group. These findings have demonstrated that the cotransplantation of SCs with hESC-NPs could offer a synergistic effect, promoting neuronal differentiation and functional recovery.

Recent therapeutic strategies for spinal cord injury treatment: possible role of stem cells

Spinal cord injury (SCI) often results in significant dysfunction and disability. A series of treatments have been proposed to prevent and overcome the formation of the glial scar and inhibitory factors to axon regrowth. In the last decade, cell therapy has emerged as a new tool for several diseases of the nervous system. Stem cells act as minipumps providing trophic and immunomodulatory factors to enhance axonal growth, to modulate the environment, and to reduce neuroinflammation. This capability can be boosted by genetical manipulation to deliver trophic molecules. Different types of stem cells have been tested, according to their properties and the therapeutic aims. They differ from each other for origin, developmental stage, stage of differentiation, and fate lineage. Related to this, stem cells differentiating into neurons could be used for cell replacement, even though the feasibility that stem cells after transplantation in the adult lesioned spinal cord can differentiate into neurons, integrate within neural circuits, and emit axons reaching the muscle is quite remote. The timing of cell therapy has been variable, and may be summarized in the acute and chronic phases of disease, when stem cells interact with a completely different environment. Even though further experimental studies are needed to elucidate the mechanisms of action, the therapeutic, and the side effects of cell therapy, several clinical protocols have been tested or are under trial. Here, we report the state-of-the-art of cell therapy in SCI, in terms of feasibility, outcome, and side effects.

TISSUE ENGINEERING FOR NERVE REPAIR

Nerve regeneration is a complex biological phenomenon. Once the nervous system is impaired, its recovery is difficult and malfunctions in other parts of the body may occur because mature neurons don't undergo cell division. To increase the prospects of axonal regeneration and functional recovery, researches have focused on designing “nerve guidance channels” or “nerve conduits”. For developing tissue engineered nerve conduits, four components come to mind, including a scaffold for axonal proliferation, supporting cells such as Schwann cells, growth factors, and extracelluar matrix. This article reviews the nervous system physiology, the factors that are critical for nerve repair, and the advanced technologies that are explored to fabricate nerve conduits. Furthermore, we also introduce a new method we developed to create longitudinally oriented channels within biodegradable polymers, Chitosan and PLGA, using a combined lyophilizing and wire-heating process. This innovative method using Ni-Cr wires as mandrels to create nerve guidance channels. The process is easy, straightforward, highly reproducible, and could easily be tailored to other polymer and solvent systems. These scaffolds could be useful for guided regeneration after transection injury in either the peripheral nerve or spinal cord.

Advanced cell therapies with and without scaffolds

Tissue engineering and regenerative medicine aim to produce tissue substitutes to restore lost functions of tissues and organs. This includes cell therapies, induction of tissue/organ regeneration by biologically active molecules, or transplantation of in vitro grown tissues. This review article discusses advanced cell therapies that make use of scaffolds and scaffold-free approaches. The first part of this article covers the basic characteristics of scaffolds, including characteristics of scaffold material, fabrication and surface functionalization, and their applications in the construction of hard (bone and cartilage) and soft (nerve, skin, blood vessel, heart muscle) tissue substitutes. In addition, cell sources as well as bioreactive agents, such as growth factors, that guide cell functions are presented. The second part in turn, examines scaffold-free applications, with a focus on the recently discovered cell sheet engineering. This article serves as a good reference for all applications of advanced cell therapies and as well as advantages and limitations of scaffold-based and scaffold-free strategies.

Effects of Olig2-overexpressing neural stem cells and myelin basic protein-activated T cells on recovery from spinal cord injury

Neural stem cell (NSC) transplantation is a major focus of current research for treatment of spinal cord injury (SCI). However, it is very important to promote the survival and differentiation of NSCs into myelinating oligodendrocytes (OLs). In this study, myelin basic protein-activated T (MBP-T) cells were passively immunized to improve the SCI microenvironment. Olig2-overexpressing NSCs were infected with a lentivirus carrying the enhanced green fluorescent protein (GFP) reporter gene to generate Olig2-GFP-NSCs that were transplanted into the injured site to differentiate into OLs. Transferred MBP-T cells infiltrated the injured spinal cord, produced neurotrophic factors, and induced the differentiation of resident microglia and/or infiltrating blood monocytes into an "alternatively activated" anti-inflammatory macrophage phenotype by producing interleukin-13. As a result, the survival of transplanted NSCs increased fivefold in MBP-T cell-transferred rats compared with that of the vehicle-treated control. In addition, the differentiation of MBP-positive OLs increased 12-fold in Olig2-GFP-NSC-transplanted rats compared with that of GFP-NSC-transplanted controls. In the MBP-T cell and Olig2-GFP-NSC combined group, the number of OL-remyelinated axons significantly increased compared with those of all other groups. However, a significant decrease in spinal cord lesion volume and an increase in spared myelin and behavioral recovery were observed in Olig2-NSC- and NSC-transplanted MBP-T cell groups. Collectively, these results suggest that MBP-T cell adoptive immunotherapy combined with NSC transplantation has a synergistic effect on histological and behavioral improvement after traumatic SCI. Although Olig2 overexpression enhances OL differentiation and myelination, the effect on functional recovery may be surpassed by MBP-T cells.

The Nogo-66 receptor family in the intact and diseased CNS

The Nogo-66 receptor family (NgR) consists in three glycophosphatidylinositol (GPI)-anchored receptors (NgR1, NgR2 and NgR3), which are primarily expressed by neurons in the central and peripheral mammalian nervous system. NgR1 was identified as serving as a high affinity binding protein for the three classical myelin-associated inhibitors (MAIs) Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), which limit axon regeneration and sprouting in the injured brain. Recent studies suggest that NgR signaling may also play an essential role in the intact adult CNS in restricting axonal and synaptic plasticity and are involved in neurodegenerative diseases, particularly in Alzheimer's disease pathology through modulation of β-secretase cleavage. Here, we outline the biochemical properties of NgRs and their functional roles in the intact and diseased CNS.

Cell transplantation: stem cells and precursor cells

Stem cells have been used to approach four different therapeutic repair strategies in spinal cord injury (SCI): (1) replacement of lost neurons, (2) replacement of oligodendrocytes to promote remyelination of demyelinated and/or regenerated axons, (3) providing a permissive substrate for axonal regeneration to overcome the intrinsic inhibition of surface molecules, and (4) engendering host repair. The first two strategies involve cell-specific differentiation of engrafted neural cells and the latter two may involve grafted neural or non-neural cells. The preclinical data for all of these approaches is at times contradictory and there is no consensus as to what type of stem cell is optimal to facilitate repair in specific injuries. Remyelination has been the most successful stem cell replacement strategy. Partial lineage restriction and pharmacological and/or genetic manipulation to express additional trophic support or restrict responses to host signals appears necessary for optimal neuronal and oligodendrocytic differentiation. However, these modifications will make their clinical application exceedingly difficult. Effects of grafted stem cells on abrogating host immune responses and engendering intrinsic repair is also a mechanism through which stem cells are likely therapeutically beneficial. While clinical trials with stem cell grafting into the injured spinal cord are ongoing, preclinical studies have yet to define mechanisms of action that can be definitively translated to those clinical approaches.

Approaches to repairing the damaged spinal cord: overview

Affecting young people during the most productive period of their lives, spinal cord injury (SCI) is a devastating problem for modern society. In the past, treating SCI seemed frustrating and hopeless because of the tremendous morbidity and mortality, life-shattering impact, and limited therapeutic options associated with the condition. Today, however, an understanding of the underlying pathophysiological mechanisms, the development of neuroprotective interventions, and progress toward regenerative interventions are increasing hope for functional restoration. In this chapter, we provide an overview of various repair strategies for the injured spinal cord. Special attention will be paid to strategies that promote spontaneous regeneration, including functional electrical stimulation, cell replacement, neuroprotection, and remyelination. The concept that limited rebuilding can provide a disproportionate improvement in quality of life is emphasized throughout. New surgical procedures, pharmacological treatments, and functional neuromuscular stimulation methods have evolved over the last decades and can improve functional outcomes after spinal cord injury; however, limiting secondary injury remains the primary goal. Tissue replacement strategies, including the use of embryonic stem cells, become an important tool and can restore function in animal models. Controlled clinical trials are now required to confirm these observations. The ultimate goal is to harness the body's own potential to replace lost central nervous system cells by activation of endogenous progenitor cell repair mechanisms.

Clinical translation of stem cell therapy in traumatic brain injury: the potential of encapsulated mesenchymal cell biodelivery of glucagon-like peptide-1

Traumatic brain injury remains a major cause of death and disability; it is estimated that annually 10 million people are affected. Preclinical studies have shown the potential therapeutic value of stem cell therapies. Neuroprotective as well as regenerative properties of stem cells have been suggested to be the mechanism of action in preclinical studies. However, up to now stem cell therapy has not been studied extensively in clinical trials. This article summarizes the current experimental evidence and points out hurdles for clinical application. Focusing on a cell therapy in the acute stage of head injury, the potential of encapsulated cell biodelivery as a novel cell-therapeutic approach will also be discussed.

Combination of Multifaceted Strategies to Maximize the Therapeutic Benefits of Neural Stem Cell Transplantation for Spinal Cord Repair

Neural stem cells (NSCs) possess therapeutic potentials to reverse complex pathological processes following spinal cord injury (SCI), but many obstacles remain that could not be fully overcome by NSC transplantation alone. Combining complementary strategies might be required to advance NSC-based treatments to the clinical stage. The present study was undertaken to examine whether combination of NSCs, polymer scaffolds, neurotrophin-3 (NT3), and chondroitinase, which cleaves chondroitin sulfate proteoglycans at the interface between spinal cord and implanted scaffold, could provide additive therapeutic benefits. In a rat hemisection model, poly(e-caprolactone) (PCL) was used as a bridging scaffold and as a vehicle for NSC delivery. The PCL scaffolds seeded with F3 NSCs or NT3 overexpressing F3 cells (F3.NT3) were implanted into hemisected cavities. F3.NT3 showed better survival and migration, and more frequently differentiated into neurons and oligodendrocytes than F3 cells. Animals with PCL scaffold containing F3.NT3 cells showed the best locomotor recovery, and motor evoked potentials (MEPs) following transcranial magnetic stimulation were recorded only in PCL-F3.NT3 group in contralateral, but not ipsilateral, hindlimbs. Implantation of PCL scaffold with F3.NT3 cells increased NT3 levels, promoted neuroplasticity, and enhanced remyelination of contralateral white matter. Combining chondroitinase treatment after PCL-F3.NT3 implantation further enhanced cell migration and promoted axonal remodeling, and this was accompanied by augmented locomotor recovery and restoration of MEPs in ipsilateral hindlimbs. We demonstrate that combining multifaceted strategies can maximize the therapeutic benefits of NSC transplantation for SCI. Our results may have important clinical implications for the design of future NSC-based strategies.

Lithium suppresses astrogliogenesis by neural stem and progenitor cells by inhibiting STAT3 pathway independently of glycogen synthase kinase 3 beta

Transplanted neural stem and progenitor cells (NSCs) produce mostly astrocytes in injured spinal cords. Lithium stimulates neurogenesis by inhibiting GSK3b (glycogen synthetase kinase 3-beta) and increasing WNT/beta catenin. Lithium suppresses astrogliogenesis but the mechanisms were unclear. We cultured NSCs from subventricular zone of neonatal rats and showed that lithium reduced NSC production of astrocytes as well as proliferation of glia restricted progenitor (GRP) cells. Lithium strongly inhibited STAT3 (signal transducer and activator of transcription 3) activation, a messenger system known to promote astrogliogenesis and cancer. Lithium abolished STAT3 activation and astrogliogenesis induced by a STAT3 agonist AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), suggesting that lithium suppresses astrogliogenesis by inhibiting STAT3. GSK3β inhibition either by a specific GSK3β inhibitor SB216763 or overexpression of GID5-6 (GSK3β Interaction Domain aa380 to 404) did not suppress astrogliogenesis and GRP proliferation. GSK3β inhibition also did not suppress STAT3 activation. Together, these results indicate that lithium inhibits astrogliogenesis through non-GSK3β-mediated inhibition of STAT. Lithium may increase efficacy of NSC transplants by increasing neurogenesis and reducing astrogliogenesis. Our results also may explain the strong safety record of lithium treatment of manic depression. Millions of people take high-dose (>1 gram/day) lithium carbonate for a lifetime. GSK3b inhibition increases WNT/beta catenin, associated with colon and other cancers. STAT3 inhibition may reduce risk for cancer.

Platelet-derived growth factor-responsive neural precursors give rise to myelinating oligodendrocytes after transplantation into the spinal cords of contused rats and dysmyelinated mice

Spinal cord injury (SCI) results in substantial oligodendrocyte death and subsequent demyelination leading to white-matter defects. Cell replacement strategies to promote remyelination are under intense investigation; however, the optimal cell for transplantation remains to be determined. We previously isolated a platelet-derived growth factor (PDGF)-responsive neural precursor (PRP) from the ventral forebrain of fetal mice that primarily generates oligodendrocytes, but also astrocytes and neurons. Importantly, human PRPs were found to possess a greater capacity for oligodendrogenesis than human epidermal growth factor- and/or fibroblast growth factor-responsive neural stem cells. Therefore, we tested the potential of PRPs isolated from green fluorescent protein (GFP)-expressing transgenic mice to remyelinate axons in the injured rat spinal cord. PRPs were transplanted 1 week after a moderate thoracic (T9) spinal cord contusion in adult male rats. After initial losses, PRP numbers remained stable from 2 weeks posttransplantation onward and those surviving cells integrated into host tissue. Approximately one-third of the surviving cells developed the typical branched phenotype of mature oligodendrocytes, expressing the marker APC-CC1. The close association of GFP cells with myelin basic protein as well as with Kv1.2 and Caspr in the paranodal and juxtaparanodal regions of nodes of Ranvier indicated that the transplanted cells successfully formed mature myelin sheaths. Transplantation of PRPs into dysmyelinated Shiverer mice confirmed the ability of PRP-derived cells to produce compact myelin sheaths with normal periodicity. These findings indicate that PRPs are a novel candidate for CNS myelin repair, although PRP-derived myelinating oligodendrocytes were insufficient to produce behavioral improvements in our model of SCI.

Mesenchymal stem cells for treatment of CNS injury

Brain and spinal cord injuries present significant therapeutic challenges. The treatments available for these conditions are largely ineffective, partly due to limitations in directly targeting the therapeutic agents to sites of pathology within the central nervous system (CNS). The use of stem cells to treat these conditions presents a novel therapeutic strategy. A variety of stem cell treatments have been examined in animal models of CNS trauma. Many of these studies have used stem cells as a cell-replacement strategy. These investigations have also highlighted the significant limitations of this approach. Another potential strategy for stem cell therapy utilises stem cells as a delivery mechanism for therapeutic molecules. This review surveys the literature relevant to the potential of mesenchymal stem cells for delivery of therapeutic agents in CNS trauma in humans.