Transplanted neural progenitor cells expressing mutant NT3 promote myelination and partial hindlimb recovery in the chronic phase after spinal cord injury

Neural stem cell therapies for spinal cord injury repair: an update on recent preclinical and clinical advances

Traumatic spinal cord injury (SCI) is a leading cause of lifelong disabilities. Permanent sensory, motor and autonomic impairments after SCI are substantially attributed to degeneration of spinal cord neurons and axons, and disintegration of neural network. To date, minimal regenerative treatments are available for SCI with an unmet need for new therapies to reconstruct the damaged spinal cord neuron-glia network and restore connectivity with the supraspinal pathways. Multipotent neural precursor cells (NPCs) have a unique capacity to generate neurons, oligodendrocytes and astrocytes. Due to this capacity, NPCs have been an attractive cell source for cellular therapies for SCI. Transplantation of NPCs has been extensively tested in preclinical models of SCI in the past two decades. These studies have identified opportunities and challenges associated with NPC therapies. While NPCs have the potential to promote neuroregeneration through various mechanisms, their low long-term survival and integration within the host injured spinal cord limit the functional benefits of NPC-based therapies for SCI. To address this challenge, combinatorial strategies have been developed to optimize the outcomes of NPC therapies by enriching SCI microenvironment through biomaterials, genetic and pharmacological therapies. In this review, we will provide an in-depth discussion on recent advances in preclinical NPC-based therapies for SCI. We will discuss modes of actions and mechanism by which engrafted NPCs contribute to the repair process and functional recovery. We will also provide an update on current clinical trials and new technologies that have facilitated preparation of medical-grade human NPCs suitable for transplantation in clinical studies.

A Review of Treatment Methods Focusing on Human Induced Pluripotent Stem Cell-Derived Neural Stem/Progenitor Cell Transplantation for Chronic Spinal Cord Injury

Cell transplantation therapy using human induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NS/PCs) has attracted attention as a regenerative therapy for spinal cord injury (SCI), and its efficacy in treating the subacute phase of SCI has been reported in numerous studies. However, few studies have focused on treatment in the chronic phase, which accounts for many patients, suggesting that there are factors that are difficult to overcome in the treatment of chronic SCI. The search for therapeutic strategies that focus on chronic SCI is fraught with challenges, and the combination of different therapies is thought to be the key to a solution. In addition, many issues remain to be addressed, including the investigation of therapeutic approaches for more severe injury models of chronic SCI and the acquisition of practical motor function. This review summarizes the current progress in regenerative therapy for SCI and discusses the prospects for regenerative medicine, particularly in animal models of chronic SCI.

Rehabilitative Training Enhances Therapeutic Effect of Human-iPSC-Derived Neural Stem/Progenitor Cells Transplantation in Chronic Spinal Cord Injury

Cell transplantation therapy using human-induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NS/PCs) is a new therapeutic strategy for spinal cord injury (SCI). Preclinical studies have demonstrated the efficacy of hiPSC-NS/PCs transplantation in the subacute phase of SCI. However, locomotor recovery secondary to hiPSC-NS/PCs transplantation is limited in the chronic phase, suggesting that additional treatment, including rehabilitative training, is required to ensure recovery. The therapeutic potential of hiPSC-NS/PCs that qualify for clinical application is yet to be fully delineated. Therefore, in this study, we investigated the therapeutic effect of the combined therapy of clinical-grade hiPSC-NS/PCs transplantation and rehabilitative training that could produce synergistic effects in a rodent model of chronic SCI. Our findings indicated that rehabilitative training promoted the survival rate and neuronal differentiation of transplanted hiPSC-NS/PCs. The combination therapy was able to enhance the expressions of the BDNF and NT-3 proteins in the spinal cord tissue. Moreover, rehabilitation promoted neuronal activity and increased 5-HT-positive fibers at the lumbar enlargement. Consequently, the combination therapy significantly improved motor functions. The findings of this study suggest that the combined therapy of hiPSC-NS/PCs transplantation and rehabilitative training has the potential to promote functional recovery even when initiated during chronic SCI.

Advances in Neural Stem Cell Therapy for Spinal Cord Injury: Safety, Efficacy, and Future Perspectives

Spinal cord injury (SCI) is a devastating central nervous system injury that leads to severe disabilities in motor and sensory functions, causing significant deterioration in patients' quality of life. Owing to the complexity of SCI pathophysiology, there has been no effective treatment for reversing neural tissue damage and recovering neurological functions. Several novel therapies targeting different stages of pathophysiological mechanisms of SCI have been developed. Among these, treatments using stem cells have great potential for the regeneration of damaged neural tissues. In this review, we have summarized recent preclinical and clinical studies focusing on neural stem cells (NSCs). NSCs are multipotent cells with specific differentiation capabilities for neural lineage. Several preclinical studies have demonstrated the regenerative effects of transplanted NSCs in SCI animal models through both paracrine effects and direct neuronal differentiation, restoring synaptic connectivity and neural networks. Based on the positive results of several preclinical studies, phase I and II clinical trials using NSCs have been performed. Despite several hurdles and issues that need to be addressed in the clinical use of NSCs in patients with SCI, gradual progress in the technical development and therapeutic efficacy of NSCs treatments has enhanced the prospects for cell-based treatments in SCI.

Current Concepts of Neural Stem/Progenitor Cell Therapy for Chronic Spinal Cord Injury

Chronic spinal cord injury (SCI) is a devastating condition that results in major neurological deficits and social burden. It continues to be managed symptomatically, and no real therapeutic strategies have been devised for its treatment. Neural stem/neural progenitor cells (NSCs/NPCs) being used for the treatment of chronic SCI in experimental SCI models can not only replace the lost cells and remyelinate axons in the injury site but also support their growth and provide neuroprotective factors. Currently, several clinical studies using NSCs/NPCs are underway worldwide. NSCs/NPCs also have the potential to differentiate into all three neuroglial lineages to regenerate neural circuits, demyelinate denuded axons, and provide trophic support to endogenous cells. This article explains the challenging pathophysiology of chronic SCI and discusses key NSC/NPC-based techniques having the greatest potential for translation over the next decade.

Chronic spinal cord injury functionally repaired by direct implantation of encapsulated hair-follicle-associated pluripotent (HAP) stem cells in a mouse model: Potential for clinical regenerative medicine

Chronic spinal cord injury (SCI) is a highly debilitating and recalcitrant disease with limited treatment options. Although various stem cell types have shown some clinical efficacy for injury repair they have not for SCI. Hair-follicle-associated pluripotent (HAP) stem cells have been shown to differentiate into neurons, Schwan cells, beating cardiomyocytes and many other type of cells, and have effectively regenerated acute spinal cord injury in mouse models. In the present report, HAP stem cells from C57BL/6J mice, encapsulated in polyvinylidene fluoride membranes (PFM), were implanted into the severed thoracic spinal cord of C57BL/6J or athymic nude mice in the early chronic phase. After implantation, HAP stem cells differentiated to neurons, astrocytes and oligodendrocytes in the regenerated thoracic spinal cord of C57BL/6J and nude mice. Quantitative motor function analysis, with the Basso Mouse Scale for Locomotion (BMS) score, demonstrated a significant functional improvement in the HAP-stem-cell-implanted mice, compared to non-implanted mice. HAP stem cells have critical advantages over other stem cells: they do not develop teratomas; do not loose differentiation ability when cryopreserved and thus are bankable; are autologous, readily obtained from anyone; and do not require genetic manipulation. HAP stem cells therefore have greater clinical potential for SCI repair than induced pluripotent stem cells (iPSCs), neuronal stem cells (NSCs)/neural progenitor cells (NPCs) or embryonic stem cells (ESCs). The present report demonstrates future clinical potential of HAP-stem-cell repair of chronic spinal cord injury, currently a recalcitrant disease.

New Therapy for Spinal Cord Injury: Autologous Genetically-Enriched Leucoconcentrate Integrated with Epidural Electrical Stimulation

The contemporary strategy for spinal cord injury (SCI) therapy aims to combine multiple approaches to control pathogenic mechanisms of neurodegeneration and stimulate neuroregeneration. In this study, a novel regenerative approach using an autologous leucoconcentrate enriched with transgenes encoding vascular endothelial growth factor (VEGF), glial cell line-derived neurotrophic factor (GDNF), and neural cell adhesion molecule (NCAM) combined with supra- and sub-lesional epidural electrical stimulation (EES) was tested on mini-pigs similar in morpho-physiological scale to humans. The complex analysis of the spinal cord recovery after a moderate contusion injury in treated mini-pigs compared to control animals revealed: better performance in behavioural and joint kinematics, restoration of electromyography characteristics, and improvement in selected immunohistology features related to cell survivability, synaptic protein expression, and glial reorganization above and below the injury. These results for the first time demonstrate the positive effect of intravenous infusion of autologous genetically-enriched leucoconcentrate producing recombinant molecules stimulating neuroregeneration combined with neuromodulation by translesional multisite EES on the restoration of the post-traumatic spinal cord in mini-pigs and suggest the high translational potential of this novel regenerative therapy for SCI patients.

Dynamics of biomarkers across the stages of traumatic spinal cord injury - implications for neural plasticity and repair

BACKGROUND

Traumatic spinal cord injury (SCI) is a complex medical condition causing significant physical disability and psychological distress. While the adult spinal cord is characterized by poor regenerative potential, some recovery of neurological function is still possible through activation of neural plasticity mechanisms. We still have limited knowledge about the activation of these mechanisms in the different stages after human SCI.

OBJECTIVE

In this review, we discuss the potential role of biomarkers of SCI as indicators of the plasticity mechanisms at work during the different phases of SCI.

METHODS

An extensive review of literature related to SCI pathophysiology, neural plasticity and humoral biomarkers was conducted by consulting the PubMed database. Research and review articles from SCI animal models and SCI clinical trials published in English until January 2021 were reviewed. The selection of candidates for humoral biomarkers of plasticity after SCI was based on the following criteria: 1) strong evidence supporting involvement in neural plasticity (mandatory); 2) evidence supporting altered expression after SCI (optional).

RESULTS

Based on selected findings, we identified two main groups of potential humoral biomarkers of neural plasticity after SCI: 1) neurotrophic factors including: Brain derived neurotrophic factor (BDNF), Nerve growth factor (NGF), Neurotrofin-3 (NT-3), and Insulin-like growth factor 1 (IGF-1); 2) other factors including: Tumor necrosis factor-alpha (TNF-α), Matrix Metalloproteinases (MMPs), and MicroRNAs (miRNAs). Plasticity changes associated with these biomarkers often can be both adaptive (promoting functional improvement) and maladaptive. This dual role seems to be influenced by their concentrations and time-window during SCI.

CONCLUSIONS

Further studies of dynamics of biomarkers across the stages of SCI are necessary to elucidate the way in which they reflect the remodeling of neural pathways. A better knowledge about the mechanisms underlying plasticity could guide the selection of more appropriate therapeutic strategies to enhance positive spinal network reorganization.

Treadmill training based on the overload principle promotes locomotor recovery in a mouse model of chronic spinal cord injury

Rehabilitative treatment, including treadmill training, is considered an important strategy for restoring motor function after spinal cord injury (SCI). However, many unexplained problems persist regarding the appropriate rehabilitative method and the mechanism underlying the beneficial effects of rehabilitation. Moreover, only a few preclinical studies have been performed on rehabilitative interventions for chronic SCI, although most patients have chronic injuries. In fact, several preclinical studies reported that rehabilitative training was less effective when applied during the chronic phase than when applied sooner. While numerous studies have examined the effects of treadmill training during the subacute phase, the training conditions vary considerably among preclinical reports. Therefore, establishing a standard training protocol is essential for achieving beneficial rehabilitation effects at the chronic stage. Since the difficulty of applying an appropriate training load hinders training at constant speeds, it is important to adjust the training intensity in accordance with the exercise tolerance of an individual animal to provide further functional recovery benefits. Here, we created a novel quadrupedal treadmill training protocol based on the overload principle for mice with incomplete thoracic SCI. We subjected SCI model mice to rehabilitative training according to the protocol for two consecutive weeks starting at 42 days after injury. We examined the treadmill speeds at which the mice were able to run based on the severity of paresis and investigated the impact of the protocol on functional recovery. Assessment of running speed changes during the treadmill training period revealed faster treadmill speeds for mice with mild paresis than for those with severe paresis. The training parameters, including the speed and distance traveled, were positively correlated with the changes in motor function. These results suggest that the most suitable running speed during treadmill training differs according to the level of motor dysfunction and that running longer distances has a positive impact on motor functional recovery. Based on this established protocol, we compared functional and histological results between the chronic SCI groups with and without rehabilitation. The gait analyses showed significantly better functional improvement in the rehabilitation group than in the nonrehabilitation group. Histological analyses revealed that the BDNF- and VGLUT1-positive areas of lumbar enlargement were significantly increased in the rehabilitation group. These findings implied that rehabilitation promoted not only motor performance but also motor control, including forelimb-hindlimb coordination, even in chronic SCI, resulting in functional improvement by treadmill training alone. Therefore, rehabilitative training based on the overload principle appears to be one of the appropriate treatment options for incomplete thoracic SCI, and evidence of its efficacy exists in actual clinical settings.

Stem Cell Therapy for Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in direct and indirect damage to neural tissues, which results in motor and sensory dysfunction, dystonia, and pathological reflex that ultimately lead to paraplegia or tetraplegia. A loss of cells, axon regeneration failure, and time-sensitive pathophysiology make tissue repair difficult. Despite various medical developments, there are currently no effective regenerative treatments. Stem cell therapy is a promising treatment for SCI due to its multiple targets and reactivity benefits. The present review focuses on SCI stem cell therapy, including bone marrow mesenchymal stem cells, umbilical mesenchymal stem cells, adipose-derived mesenchymal stem cells, neural stem cells, neural progenitor cells, embryonic stem cells, induced pluripotent stem cells, and extracellular vesicles. Each cell type targets certain features of SCI pathology and shows therapeutic effects via cell replacement, nutritional support, scaffolds, and immunomodulation mechanisms. However, many preclinical studies and a growing number of clinical trials found that single-cell treatments had only limited benefits for SCI. SCI damage is multifaceted, and there is a growing consensus that a combined treatment is needed.

Ex Vivo Rat Transected Spinal Cord Slices as a Model to Assess Lentiviral Vector Delivery of Neurotrophin-3 and Short Hairpin RNA against NG2

The failure of the spinal cord to regenerate can be attributed both to a lack of trophic support for regenerating axons and to upregulation of inhibitory factors such as chondroitin sulphate proteoglycans including NG2 following injury. Lentiviral vector-mediated gene therapy is a possible strategy for treating spinal cord injury (SCI). This study investigated the effect of lentiviral vectors expressing Neurotrophin-3 (NT-3) and short-hairpin RNA against NG2 (NG2 sh) to enhance neurite outgrowth in in vitro and ex vivo transection injury models. Conditioned medium from cells transduced with NT-3 or shNG2 lentiviruses caused a significant increase in neurite length of primary dorsal root ganglia neurons compared to the control group in vitro. In an ex vivo organotypic slice culture (OSC) transduction with Lenti-NT-3 promoted axonal growth. Transducing OSCs with a combination of Lenti-NT-3/NG2 sh lead to a further increase in axonal growth but only in injured slices and only within the region adjacent to the site of injury. These findings suggest that the combination of lentiviral NT-3 and NG2 sh reduced NG2 levels and provided a more favourable microenvironment for neuronal regeneration after SCI. This study also shows that OSCs may be a useful platform for studying glial scarring and potential SCI treatments.

NT3P75-2 gene-modified bone mesenchymal stem cells improve neurological function recovery in mouse TBI model

BACKGROUND

The attainment of extensive neurological function recovery remains the key challenge for the treatment of traumatic brain injury (TBI). Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) has been shown to improve neurological function recovery after TBI. However, the survival of BMSCs after transplantation in early-stage TBI is limited, and much is unknown about the mechanisms mediating this neurological function recovery. Secretion of neurotrophic factors, including neurotrophin 3 (NT3), is one of the critical factors mediating BMSC neurological function recovery. Gene mutation of NT3 (NT3^P75-2) has been shown to enhance the biological function of NT3 via the reduction of the activation of the P75 signal pathway. Thus, we investigated whether NT3^P75-2 gene-modified BMSCs could enhance the survival of BMSCs and further improve neurological function recovery after TBI.

METHODS

The ability of NT3^P75-2 induction to improve cell growth rate of NSC-34 and PC12 cells in vitro was first determined. BMSCs were then infected with three different lentiviruses (green fluorescent protein (GFP), GFP-NT3, or GFP-NT3^P75-2), which stably express GFP, GFP-NT3, or GFP-NT3^P75-2. At 24 h post-TBI induction in mice, GFP-labeled BMSCs were locally transplanted into the lesion site. Immunofluorescence and histopathology were performed at 1, 3, and/or 7 days after transplantation to evaluate the survival of BMSCs as well as the lesion volume. A modified neurological severity scoring system and the rotarod test were chosen to evaluate the functional recovery of the mice. Cell growth rate, glial activation, and signaling pathway analyses were performed to determine the potential mechanisms of NT3^P75-2 in functional recovery after TBI.

RESULTS

Overall, NT3^P75-2 improved cell growth rate of NSC-34 and PC12 cells in vitro. In addition, NT3^P75-2 significantly improved the survival of transplanted BMSCs and neurological function recovery after TBI. Overexpression of NT3^P75-2 led to a significant reduction in the activation of glial cells, brain water content, and brain lesion volume after TBI. This was associated with a reduced activation of the p75 neurotrophin receptor (P75NTR) and the c-Jun N-terminal kinase (JNK) signal pathway due to the low affinity of NT3^P75-2 for the receptor.

CONCLUSIONS

Taken together, our results demonstrate that administration of NT3^P75-2 gene-modified BMSCs dramatically improves neurological function recovery after TBI by increasing the survival of BMSCs and ameliorating the inflammatory environment, providing a new promising treatment strategy for TBI.

G-CSF enhances the therapeutic potency of stem cells transplantation in spinal cord-injured rats

Aim: The therapeutic effects of human wisdom teeth-derived neuronal stem cell (tNSC) cotreatment with granulocyte-colony-stimulating factor (G-CSF) were evaluated for contusion-induced spinal cord injury in rats. Materials & methods: 7 days after contusion, tNSCs were transplanted to the injury site and followed by G-CSF cotreatment for 5 days. Behavioral deficits were evaluated by the Basso, Beattie and Bresnahan test. The injury site was collected for immunohistochemistry analysis. Results: The Basso, Beattie and Bresnahan test significantly improved in the cotreated group compared with the tNSCs or G-CSF single treatment groups. However, inflammation indices did not differ among the three groups. In vitro experiment demonstrated that tNSCs express both G-CSF and its relevant receptor. G-CSF enhanced tNSC proliferation and neurotrophins secretion in vitro. Conclusion: This study demonstrated that G-CSF enhances neurotrophins secretion of tNSCs, and might help improving functional recovery from spinal cord injury in rats if they were given together.

Treatment with a Gamma-Secretase Inhibitor Promotes Functional Recovery in Human iPSC- Derived Transplants for Chronic Spinal Cord Injury

Treatment involving regenerative medicine for chronic spinal cord injury (SCI) is difficult due to phase-dependent changes in the intraspinal environment. We previously reported that treatment with a gamma-secretase inhibitor (GSI), which inhibits Notch signaling, promotes the differentiation into mature neurons in human induced pluripotent stem cell-derived neural stem/progenitor cell (hiPSC-NS/PC) transplantation for subacute SCI. Here, we evaluated the efficacy of GSI-treated hiPSC-NS/PC transplantation in treating chronic SCI, which resulted in significantly enhanced axonal regrowth, remyelination, inhibitory synapse formation with the host neural circuitry, and reticulo spinal tract fiber formation. Interestingly, inhibiting Notch signaling with GSI caused phosphorylation of p38 MAPK, which is a key molecule required to promote axonal regeneration. These favorable outcomes contributed to motor function improvement. Therefore, treating cells with GSI provides a beneficial effect after transplantation, even in the chronic phase following SCI.

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GSI-treated hiPSC-NS/PCs induce regenerative axons and extension of RtST fibers

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GSI-treated hiPSC-NS/PCs induce remyelination by host-derived glial cells

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GSI causes phosphorylation of p38 MAPK and promotes axonal regeneration

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Grafts of GSI-treated hiPSC-NS/PCs provide a beneficial effect in the chronic SCI

Concise Review: Laying the Groundwork for a First-In-Human Study of an Induced Pluripotent Stem Cell-Based Intervention for Spinal Cord Injury

There have been numerous attempts to develop stem cell transplantation approaches to promote the regeneration of spinal cord injury (SCI). Our multicenter team is currently planning to launch a first-in-human clinical study of an induced pluripotent stem cell (iPSC)-based cell transplant intervention for subacute SCI. This trial was conducted as class I regenerative medicine protocol as provided for under Japan's Act on the Safety of Regenerative Medicine, using neural stem/progenitor cells derived from a clinical-grade, integration-free human "iPSC stock" generated by the Kyoto University Center for iPS Cell Research and Application. In the present article, we describe how we are preparing to initiate this clinical study, including addressing the issues of safety and tumorigenesis as well as practical problems that must be overcome to enable the development of therapeutic interventions for patients with chronic SCI. Stem Cells 2019;37:6-13.

The Amelioration of Pain-Related Behavior in Mice with Chronic Spinal Cord Injury Treated with Neural Stem/Progenitor Cell Transplantation Combined with Treadmill Training

Progress in regenerative medicine is realizing the possibility of neural regeneration and functional recovery in spinal cord injury (SCI). Recently, rehabilitation has attracted much attention with respect to the synergistic promotion of functional recovery in combination with neural stem/progenitor cell (NS/PC) transplantation, even in the chronic refractory phase of SCI. Nevertheless, sensory disturbance is one of the most prominent sequelae, even though the effects of combination or single therapies have been investigated mostly in the context of motor recovery. To determine how combination therapy with treadmill training (TMT) and NS/PC transplantation affects the manifestation of thermal allodynia and tactile hyperalgesia in chronic phase SCI, four groups of SCI mice were used to assess pain-related behavior and histological changes: combined transplantation and TMT therapy, transplantation only, TMT only, and control groups. Thermal allodynia and coarse touch-pressure hyperalgesia exhibited significant recovery in the combined therapy group in comparison with controls, whereas there were no significant differences with fine touch-pressure hyperalgesia and motor function. Further investigation revealed fewer fibers remaining in the posterior funiculus, which contained the tracts associated with the two modalities showing less recovery; that is, touch-pressure hyperalgesia and motor function. A significant correlation was only observed between these two modalities. Although no remarkable histological recovery was found within the lesion epicenter, changes indicating amelioration of pain were observed in the lumbar enlargement of the combination therapy group. Our results suggest that amelioration of thermal allodynia and tactile hyperalgesia can be brought about by the additive effect of NS/PC transplantation and TMT. The degree of recovery seems dependent on the distribution of damage.

Neurotrophin-3 restores synaptic plasticity in the striatum of a mouse model of Huntington's disease

AIMS

Neurotrophin-3 (NT-3) is expressed in the mouse striatum; however, it is not clear the NT-3 role in striatal physiology. The expression levels of mRNAs and immune localization of the NT-3 protein and its receptor TrkC are altered in the striatum following damage induced by an in vivo treatment with 3-nitropropionic acid (3-NP), a mitochondrial toxin used to mimic the histopathological hallmarks of Huntington's disease (HD). The aim of this study was to evaluate the role of NT-3 on corticostriatal synaptic transmission and its plasticity in both the control and damaged striatum.

METHODS

Corticostriatal population spikes were electrophysiologically recorded and striatal synaptic plasticity was induced by high-frequency stimulation. Further, the phosphorylation status of Trk receptors was tested under conditions that imitated electrophysiological experiments.

RESULTS

NT-3 modulates both synaptic transmission and plasticity in the striatum; nonetheless, synaptic plasticity was modified by the 3-NP treatment, where instead of producing striatal long-term depression (LTD), long-term potentiation (LTP) was obtained. Moreover, the administration of NT-3 in the recording bath restored the plasticity observed under control conditions (LTD) in this model of striatal degeneration.

CONCLUSION

NT-3 modulates corticostriatal transmission through TrkB stimulation and restores striatal LTD by signaling through its TrkC receptor.

Combining NT3-overexpressing MSCs and PLGA microcarriers for brain tissue engineering: A potential tool for treatment of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that characterized by destruction of substantia nigrostriatal pathway due to the loss of dopaminergic (DA) neurons. Regardless of substantial efforts for treatment of PD in recent years, an effective therapeutic strategy is still missing. In a multidisciplinary approach, bone marrow derived mesenchymal stem cells (BMSCs) are genetically engineered to overexpress neurotrophin-3 (nt-3 gene) that protect central nervous system tissues and stimulates neuronal-like differentiation of BMSCs. Poly(lactic-co-glycolic acid) (PLGA) microcarriers are designed as an injectable scaffold and synthesized via double emulsion method. The surface of PLGA microcarriers are functionalized by collagen as a bioadhesive agent for improved cell attachment. The results demonstrate effective overexpression of NT-3. The expression of tyrosine hydroxylase (TH) in transfected BMSCs reveal that NT-3 promotes the intracellular signaling pathway of DA neuron differentiation. It is also shown that transfected BMSCs are successfully attached to the surface of microcarriers. The presence of dopamine in peripheral media of cell/microcarrier complex reveals that BMSCs are successfully differentiated into dopaminergic neuron. Our approach that sustains presence of growth factor can be suggested as a novel complementary therapeutic strategy for treatment of Parkinson disease.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Exercise Training Promotes Functional Recovery after Spinal Cord Injury

The exercise training is an effective therapy for spinal cord injury which has been applied to clinic. Traditionally, the exercise training has been considered to improve spinal cord function only through enhancement, compensation, and replacement of the remaining function of nerve and muscle. Recently, accumulating evidences indicated that exercise training can improve the function in different levels from end-effector organ such as skeletal muscle to cerebral cortex through reshaping skeletal muscle structure and muscle fiber type, regulating physiological and metabolic function of motor neurons in the spinal cord and remodeling function of the cerebral cortex. We compiled published data collected in different animal models and clinical studies into a succinct review of the current state of knowledge.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Functional Recovery from Neural Stem/Progenitor Cell Transplantation Combined with Treadmill Training in Mice with Chronic Spinal Cord Injury

Most studies targeting chronic spinal cord injury (SCI) have concluded that neural stem/progenitor cell (NS/PC) transplantation exerts only a subclinical recovery; this in contrast to its remarkable effect on acute and subacute SCI. To determine whether the addition of rehabilitative intervention enhances the effect of NS/PC transplantation for chronic SCI, we used thoracic SCI mouse models to compare manifestations secondary to both transplantation and treadmill training, and the two therapies combined, with a control group. Significant locomotor recovery in comparison with the control group was only achieved in the combined therapy group. Further investigation revealed that NS/PC transplantation improved spinal conductivity and central pattern generator activity, and that treadmill training promoted the appropriate inhibitory motor control. The combined therapy enhanced these independent effects of each single therapy, and facilitated neuronal differentiation of transplanted cells and maturation of central pattern generator activity synergistically. Our data suggest that rehabilitative treatment represents a therapeutic option for locomotor recovery after NS/PC transplantation, even in chronic SCI.

Gene delivery strategies to promote spinal cord repair

Gene therapies hold great promise for the treatment of many neurodegenerative disorders and traumatic injuries in the central nervous system. However, development of effective methods to deliver such therapies in a controlled manner to the spinal cord is a necessity for their translation to the clinic. Although essential progress has been made to improve efficiency of transgene delivery and reduce the immunogenicity of genetic vectors, there is still much work to be done to achieve clinical strategies capable of reversing neurodegeneration and mediating tissue regeneration. In particular, strategies to achieve localized, robust expression of therapeutic transgenes by target cell types, at controlled levels over defined time periods, will be necessary to fully regenerate functional spinal cord tissues. This review summarizes the progress over the last decade toward the development of effective gene therapies in the spinal cord, including identification of appropriate target genes, improvements to design of genetic vectors, advances in delivery methods, and strategies for delivery of multiple transgenes with synergistic actions. The potential of biomaterials to mediate gene delivery while simultaneously providing inductive scaffolding to facilitate tissue regeneration is also discussed.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

Hypoxia modulates the differentiation potential of stem cells of the apical papilla

INTRODUCTION

Stem cells from the apical papilla (SCAP) are a population of mesenchymal stem cells likely involved in regenerative endodontic procedures and have potential use as therapeutic agents in other tissues. In these situations, SCAP are exposed to hypoxic conditions either within a root canal devoid of an adequate blood supply or in a scaffold material immediately after implantation. However, the effect of hypoxia on SCAP proliferation and differentiation is largely unknown. Therefore, the objective of this study was to evaluate the effect of hypoxia on the fate of SCAP.

METHODS

SCAP were cultured under normoxia (21% O2) or hypoxia (1% O2) in basal or differentiation media. Cellular proliferation, gene expression, differentiation, and protein secretion were analyzed by live imaging, quantitative reverse-transcriptase polymerase chain reaction, cellular staining, and enzyme-linked immunosorbent assay, respectively.

RESULTS

Hypoxia had no effect on SCAP proliferation, but it evoked the up-regulation of genes specific for osteogenic differentiation (runt-related transcription factor 2, alkaline phosphatase, and transforming growth factor-β1), neuronal differentiation ( 2'-3'-cyclic nucleotide 3' phosphodiesterase, SNAIL, neuronspecific enolase, glial cell-derived neurotrophic factor and neurotrophin 3), and angiogenesis (vascular endothelial growth factor A and B). Hypoxia also increased the sustained production of VEGFa by SCAP. Moreover, hypoxia augmented the neuronal differentiation of SCAP in the presence of differentiation exogenous factors as detected by the up-regulation of NSE, VEGFB, and GDNF and the expression of neuronal markers (PanF and NeuN).

CONCLUSIONS

This study shows that hypoxia induces spontaneous differentiation of SCAP into osteogenic and neurogenic lineages while maintaining the release of the proangiogenic factor VEGFa. This highlights the potential of SCAP to promote pulp-dentin regeneration. Moreover, SCAP may represent potential therapeutic agents for neurodegenerative conditions because of their robust differentiation potential.

Molecular imaging in stem cell therapy for spinal cord injury

Spinal cord injury (SCI) is a serious disease of the center nervous system (CNS). It is a devastating injury with sudden loss of motor, sensory, and autonomic function distal to the level of trauma and produces great personal and societal costs. Currently, there are no remarkable effective therapies for the treatment of SCI. Compared to traditional treatment methods, stem cell transplantation therapy holds potential for repair and functional plasticity after SCI. However, the mechanism of stem cell therapy for SCI remains largely unknown and obscure partly due to the lack of efficient stem cell trafficking methods. Molecular imaging technology including positron emission tomography (PET), magnetic resonance imaging (MRI), optical imaging (i.e., bioluminescence imaging (BLI)) gives the hope to complete the knowledge concerning basic stem cell biology survival, migration, differentiation, and integration in real time when transplanted into damaged spinal cord. In this paper, we mainly review the molecular imaging technology in stem cell therapy for SCI.

Graft of a tissue-engineered neural scaffold serves as a promising strategy to restore myelination after rat spinal cord transection

Remyelination remains a challenging issue in spinal cord injury (SCI). In the present study, we cocultured Schwann cells (SCs) and neural stem cells (NSCs) with overexpression of neurotrophin-3 (NT-3) and its high affinity receptor tyrosine kinase receptor type 3 (TrkC), respectively, in a gelatin sponge (GS) scaffold. This was aimed to generate a tissue-engineered neural scaffold and to investigate whether it could enhance myelination after a complete T10 spinal cord transection in adult rats. Indeed, many NT-3 overexpressing SCs (NT-3-SCs) in the GS scaffold assumed the formation of myelin. More strikingly, a higher incidence of NSCs overexpressing TrkC differentiating toward myelinating cells was induced by NT-3-SCs. By transmission electron microscopy, the myelin sheath showed distinct multilayered lamellae formed by the seeded cells. Eighth week after the scaffold was transplanted, some myelin basic protein (MBP)-positive processes were observed within the transplantation area. Remarkably, certain segments of myelin derived from NSC-derived myelinating cells and NT-3-SCs were found to ensheath axons. In conclusion, we show here that transplantation of the GS scaffold promotes exogenous NSC-derived myelinating cells and SCs to form myelins in the injury/transplantation area of spinal cord. These findings thus provide a neurohistological basis for the future application or transplantation using GS neural scaffold to repair SCI.

Diabetic Schwann cells suffer from nerve growth factor and neurotrophin-3 underproduction and poor associability with axons

Schwann cells (SCs) are integral to peripheral nerve biology, contributing to saltatory conduction along axons, nerve and axon development, and axonal regeneration. SCs also provide a microenvironment favoring neural regeneration partially due to production of several neurotrophic factors. Dysfunction of SCs may also play an important role in the pathogenesis of peripheral nerve diseases such as diabetic peripheral neuropathy where hyperglycemia is often considered pathogenic. In order to study the impact of diabetes mellitus (DM) upon the regenerative capacity of adult SCs, we investigated the differential production of the neurotrophic factors nerve growth factor (NGF) and neurotrophin-3 (NT3) by SCs harvested from the sciatic nerves of murine models of type 1 DM (streptozotocin treated C57BL/6J mice) and type 2 DM (LepR(-/-) or db/db mice) or non-diabetic cohorts. In vitro, SCs from diabetic and control mice were maintained under similar hyperglycemic and euglycemic conditions respectively. Mature SCs from diabetic mice produced lower levels of NGF and NT3 under hyperglycemic conditions when compared to SCs in euglycemia. In addition, SCs from both DM and non-DM mice appear to be incapable of insulin production, but responded to exogenous insulin with greater proliferation and heightened myelination potentiation. Moreover, SCs from diabetic animals showed poorer association with co-cultured axons. Hyperglycemia had significant impact upon SCs, potentially contributing to the pathogenesis of diabetic peripheral neuropathy.

Neurotrophin treatment to promote regeneration after traumatic CNS injury

Neurotrophins are a family of growth factors that have been found to be central for the development and functional maintenance of the nervous system, participating in neurogenesis, neuronal survival, axonal growth, synaptogenesis and activity-dependent forms of synaptic plasticity. Trauma in the adult nervous system can disrupt the functional circuitry of neurons and result in severe functional deficits. The limitation of intrinsic growth capacity of adult nervous system and the presence of an inhospitable environment are the major hurdles for axonal regeneration of lesioned adult neurons. Neurotrophic factors have been shown to be excellent candidates in mediating neuronal repair and establishing functional circuitry via activating several growth signaling mechanisms including neuron-intrinsic regenerative programs. Here, we will review the effects of various neurotrophins in mediating recovery after injury to the adult spinal cord.

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.

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.

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.

Functional assessment of the acute local and distal transplantation of human neural stem cells after spinal cord injury

BACKGROUND CONTEXT

Spinal cord injury can lead to severe functional impairments secondary to axonal damage, neuronal loss, and demyelination. The injured spinal cord has limited regrowth of damaged axons. Treatment remains controversial, given inconsistent functional improvement. Previous studies demonstrated functional recovery of rats with spinal cord contusion after transplantation of rat fetal neural stem cells.

PURPOSE

We hypothesized that acute transplantation of human fetal neural stem cells (hNSCs) both locally at the injury site as well as distally via intrathecal injection would lead to improved functional recovery compared with controls.

STUDY DESIGN/SETTING

Twenty-four adult female Long-Evans hooded rats were randomized into four groups with six animals in each group: two experimental and two control. Functional assessment was measured after injury and then weekly for 6 weeks using the Basso, Beattie, and Bresnahan Locomotor Rating Score. Data were analyzed using two-sample t test and linear mixed-effects model analysis.

METHODS

Posterior exposure and laminectomy at T10 level was used. Moderate spinal cord contusion was induced by the Multicenter Animal Spinal Cord Injury Study Impactor with 10-g weight dropped from a height of 25 mm. Experimental subjects received either a subdural injection of hNSCs locally at the injury site or intrathecal injection of hNSCs through a separate distal laminotomy. Controls received control media injection either locally or distally.

RESULTS

Statistically significant functional improvement was observed in local or distal hNSCs subjects versus controls (p=.034 and 0.016, respectively). No significant difference was seen between local or distal hNSC subjects (p=.66).

CONCLUSIONS

Acute local and distal transplantation of hNSCs into the contused spinal cord led to significant functional recovery in the rat model. No statistical difference was found between the two techniques.

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.

New perspectives of tissue remodelling with neural stem and progenitor cell-based therapies

Compelling evidence exists that neural stem cell-based therapies protect the central nervous system (CNS) from chronic inflammatory degeneration, such as that occurring in experimental autoimmune encephalomyelitis and stroke. It was first assumed that stem cells directly replace lost cells but it is now becoming clearer that they might be able to protect the nervous system through mechanisms other than cell replacement. In immune-mediated experimental demyelination and stroke, transplanted neural stem/precursor cells (NPCs) are able to mediate efficient bystander myelin repair and axonal rescue. This is dependent on multiple capacities that transplanted NPCs exhibit within specific microenvironments after transplantation. However, a comprehensive understanding of the mechanisms by which NPCs exert their therapeutic impact is lacking. Here we will review some of the most recent evidence--and discuss some of the likely mechanisms--that support the remarkable capacity of NPCs to cross-talk with endogenous cells and to remodel the injured nervous system when applied as novel therapeutic regimes. We foresee that the exploitation of the innate mechanisms regulating these modalities of cell-to-cell communication has realistic chances of revolutionizing most of the actual understanding of stem cell biology and its application to regenerative medicine and CNS repair.