Adherent self-renewable human embryonic stem cell-derived neural stem cell line: functional engraftment in experimental stroke model

Neuroprotection of Stem Cells Against Ischemic Brain Injury: From Bench to Clinic

Neurological injuries can have numerous debilitating effects on functional status including sensorimotor deficits, cognitive impairment, and behavioral symptoms. Despite the disease burden, treatment options remain limited. Current pharmacological interventions are targeted at symptom management but are ineffective in reversing ischemic brain damage. Stem cell therapy for ischemic brain injury has shown promising preclinical and clinical results and has attracted attention as a potential therapeutic option. Various stem cell sources (embryonic, mesenchymal/bone marrow, and neural stem cells) have been investigated. This review provides an overview of the advances made in our understanding of the various types of stem cells and progress made in the use of these stem cells for the treatment of ischemic brain injuries. In particular, the use of stem cell therapy in global cerebral ischemia following cardiac arrest and in focal cerebral ischemia after ischemic stroke are discussed. The proposed mechanisms of stem cells' neuroprotective effects in animal models (rat/mice, pig/swine) and other clinical studies, different routes of administration (intravenous/intra-arterial/intracerebroventricular/intranasal/intraperitoneal/intracranial) and stem cell preconditioning are discussed. Much of the promising data on stem cell therapies after ischemic brain injury remains in the experimental stage and several limitations remain unsettled. Future investigation is needed to further assess the safety and efficacy and to overcome the remaining obstacles.

Stem cell therapy as a promising approach for ischemic stroke treatment

Ischemia as the most common type of stroke is the main cause of death and disability in the world. However, there are few therapeutic approaches to treat ischemic stroke. The common approach to the treatment of ischemia includes surgery-cum-chemical drugs. Surgery and chemical drugs are used to remove blood clots to prevent the deterioration of the nervous system. Given the surgical hazards and the challenges associated with chemical drugs, these cannot be considered safe approaches to the treatment of brain ischemia. Besides surgery-cum-chemical drugs, different types of stem cells including mesenchymal stem cells and neurological stem cells have been considered to treat ischemic stroke. Therapeutic approaches utilizing stem cells to treat strokes are promising because of their neuroprotective and regenerative benefits. However, the mechanisms by which the transplanted stem cells perform their precisely actions are unknown. The purpose of this study is to critically review stem cell-based therapeutic approaches for ischemia along with related challenges.

Combining physical & cognitive training with iPSC-derived dopaminergic neuron transplantation promotes graft integration & better functional outcome in parkinsonian marmosets

Parkinson's disease (PD) is a relentlessly progressive and currently incurable neurodegenerative disease with significant unmet medical needs. Since PD stems from the degeneration of midbrain dopaminergic (DA) neurons in a defined brain location, PD patients are considered optimal candidates for cell replacement therapy. Clinical trials for cell transplantation in PD are beginning to re-emerge worldwide with a new focus on induced pluripotent stem cells (iPSCs) as a source of DA neurons since they can be derived from adult somatic cells and produced in large quantities under current good manufacturing practices. However, for this therapeutic strategy to be realized as a viable clinical option, fundamental translational challenges need to be addressed including the manufacturing process, purity and efficacy of the cells, the method of delivery, the extent of host reinnervation and the impact of patient-centered adjunctive interventions. In this study we report on the impact of physical and cognitive training (PCT) on functional recovery in the nonhuman primate (NHP) model of PD after cell transplantation. We observed that at 6 months post-transplant, the PCT group returned to normal baseline in their daily activity measured by actigraphy, significantly improved in their sensorimotor and cognitive tasks, and showed enhanced synapse formation between grafted cells and host cells. We also describe a robust, simple, efficient, scalable, and cost-effective manufacturing process of engraftable DA neurons derived from iPSCs. This study suggests that integrating PCT with cell transplantation therapy could promote optimal graft functional integration and better outcome for patients with PD.

Critical points for optimizing long-term culture and neural differentiation capacity of rodent and human neural stem cells to facilitate translation into clinical settings

Despite several decades of research on the nature and functional properties of neural stem cells, which brought great advances in regenerative medicine, there is still a plethora of ambiguous protocols and interpretations linked to their applications. Here, we present a whole spectrum of protocol elements that should be standardized in order to obtain viable cell cultures and facilitate their translation into clinical settings. Additionally, this review also presents outstanding limitations and possible problems to be encountered when dealing with protocol optimization. Most importantly, we also outline the critical points that should be considered before starting any experiments utilizing neural stem cells or interpreting their results.

Neural Stem Cells in the Treatment of Alzheimer's Disease: Current Status, Challenges, and Future Prospects

Alzheimer's disease (AD), a progressive dementia, is one of the world's most dangerous and debilitating diseases. Clinical trial results of amyloid-β (Aβ) and tau regulators based on the pretext of straightforward amyloid and tau immunotherapy were disappointing. There are currently no effective strategies for slowing the progression of AD. Further understanding of the mechanisms underlying AD and the development of novel therapeutic options are critical. Neurogenesis is impaired in AD, which contributes to memory deficits. Transplanted neural stem cells (NSCs) can regenerate degraded cholinergic neurons, and new neurons derived from NSCs can form synaptic connections with neighboring neurons. In theory, employing NSCs to replace and restore damaged cholinergic neurons and brain connections may offer new treatment options for AD. However there remain barriers to surmount before NSC-based therapy can be used clinically. The objective of this article is to describe recent advances in the treatment of AD models and clinical trials involving NSCs. In addition, we discuss the challenges and prospects associated with cell transplant therapy for AD.

Electrical modulation of transplanted stem cells improves functional recovery in a rodent model of stroke

Stroke is a leading cause of long-term disability worldwide, intensifying the need for effective recovery therapies. Stem cells are a promising stroke therapeutic, but creating ideal conditions for treatment is essential. Here we developed a conductive polymer system for stem cell delivery and electrical modulation in animals. Using this system, electrical modulation of human stem cell transplants improve functional stroke recovery in rodents. Increased endogenous stem cell production corresponds with improved function. Transcriptome analysis identified stanniocalcin 2 (STC2) as one of the genes most significantly upregulated by electrical stimulation. Lentiviral upregulation and downregulation of STC2 in the transplanted stem cells demonstrate that this glycoprotein is an essential mediator in the functional improvements seen with electrical modulation. Moreover, intraventricular administration of recombinant STC2 post-stroke confers functional benefits. In summation, our conductive polymer system enables electrical modulation of stem cells as a potential method to improve recovery and identify important therapeutic targets.

Isolation and Purification of Self-Renewable Human Neural Stem Cells from iPSCs for Cell Therapy in Experimental Model of Ischemic Stroke

Neural stem cell therapy has been galvanized by the discovery of pluripotent stem cells. The possibility to generate specialized central nervous system-specific differentiated cells using human somatic cells engineered to become induced pluripotent stem cells (iPSCs) was a game changer. This technology has broad applications in the field of regenerative medicine, in vitro disease modeling, targeted drug discovery, and precision medicine. Currently, iPSCs are one of the most promising cell sources amenable for commercialization and off-the-shelf neural stem cell therapy products. iPSCs exhibit a strong self-renewable ability that supports the development of a virtually unlimited source of neural cells for structural repair in neurological disorders. However, along with this strong proliferative capacity of iPSCs comes the tumorigenic potential of these cells after transplantation. Thus, the isolation and purification of a homogeneous population of human neural stem cells (hNSCs) are of paramount importance to ensure consistency in the composition of the cellular product and to avoid tumor formation in the host brain. This chapter describes the isolation, neuralization, and long-term perpetuation of hNSCs derived from iPSCs through the use of specific growth medium and the preparation of hNSCs for transplantation in an experimental model of stroke. Additionally, we will describe methods to analyze the ischemic stroke and size of grafts using magnetic resonance imaging and OsiriX software and neuroanatomical tracing procedures to study axonal remodeling after ischemic stroke and cell transplantation.

Neural stem cell treatment for perinatal brain injury: A systematic review and meta-analysis of preclinical studies

Perinatal brain injury can lead to significant neurological and cognitive deficits and currently no therapies can regenerate the damaged brain. Neural stem cells (NSCs) have the potential to engraft and regenerate damaged brain tissue. The aim of this systematic review was to evaluate the preclinical literature to determine whether NSC administration is more effective than controls in decreasing perinatal brain injury. Controlled interventional studies of NSC therapy using animal models of perinatal brain injury were identified using MEDLINE and Embase. Primary outcomes were brain infarct size, motor, and cognitive function. Data for meta‐analysis were synthesized and expressed as standardized mean difference (SMD) with 95% confidence intervals (CI), using a random effects model. We also reported secondary outcomes including NSC survival, migration, differentiation, and effect on neuroinflammation. Eighteen studies met inclusion criteria. NSC administration decreased infarct size (SMD 1.09; CI: 0.44, 1.74, P = .001; I² = 74%) improved motor function measured via the impaired forelimb preference test (SMD 2.27; CI: 0.85, 3.69, P = .002; I² = 86%) and the rotarod test (SMD 1.88; CI: 0.09, 3.67, P = .04; I² = 95%). Additionally, NSCs improved cognitive function measured via the Morris water maze test (SMD of 2.41; CI: 1.16, 3.66, P = .0002; I² = 81%). Preclinical evidence suggests that NSC therapy is promising for the treatment of perinatal brain injury. We have identified key knowledge gaps, including the lack of large animal studies and uncertainty regarding the necessity of immunosuppression for NSC transplantation in neonates. These knowledge gaps should be addressed before NSC treatment can effectively progress to clinical trial.

A neurovascular-unit-on-a-chip for the evaluation of the restorative potential of stem cell therapies for ischaemic stroke

The therapeutic efficacy of stem cells transplanted into an ischaemic brain depends primarily on the responses of the neurovascular unit. Here, we report the development and applicability of a functional neurovascular unit on a microfluidic chip as a microphysiological model of ischaemic stroke that recapitulates the function of the blood-brain barrier as well as interactions between therapeutic stem cells and host cells (human brain microvascular endothelial cells, pericytes, astrocytes, microglia and neurons). We used the model to track the infiltration of a number of candidate stem cells and to characterize the expression levels of genes associated with post-stroke pathologies. We observed that each type of stem cell showed unique neurorestorative effects, primarily by supporting endogenous recovery rather than through direct cell replacement, and that the recovery of synaptic activities is correlated with the recovery of the structural and functional integrity of the neurovascular unit rather than with the regeneration of neurons.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Insight Into the Mechanisms and the Challenges on Stem Cell-Based Therapies for Cerebral Ischemic Stroke

Strokes are the most common types of cerebrovascular disease and remain a major cause of death and disability worldwide. Cerebral ischemic stroke is caused by a reduction in blood flow to the brain. In this disease, two major zones of injury are identified: the lesion core, in which cells rapidly progress toward death, and the ischemic penumbra (surrounding the lesion core), which is defined as hypoperfusion tissue where cells may remain viable and can be repaired. Two methods that are approved by the Food and Drug Administration (FDA) include intravenous thrombolytic therapy and endovascular thrombectomy, however, the narrow therapeutic window poses a limitation, and therefore a low percentage of stroke patients actually receive these treatments. Developments in stem cell therapy have introduced renewed hope to patients with ischemic stroke due to its potential effect for reversing the neurological sequelae. Over the last few decades, animal tests and clinical trials have been used to treat ischemic stroke experimentally with various types of stem cells. However, several technical and ethical challenges must be overcome before stem cells can become a choice for the treatment of stroke. In this review, we summarize the mechanisms, processes, and challenges of using stem cells in stroke treatment. We also discuss new developing trends in this field.

Cell Therapy for Ischemic Stroke: How to Turn a Promising Preclinical Research into a Successful Clinical Story

Stroke is a major public health issue with limited treatment. The pharmacologically or mechanically removing of the clot is accessible to less than 10% of the patients. Stem cell therapy is a promising alternative strategy since it increases the therapeutic time window but many issues remain unsolved. To avoid a new dramatic failure when translating experimental data on the bedside, this review aims to highlight the indispensable checkpoints to make a successful clinical trial based on the current preclinical literature. The large panel of progenitors/ stem cells at the researcher's disposal is to be used wisely, regarding the type of cells, the source of cells, the route of delivery, the time window, since it will directly affect the outcome. Mechanisms are still incompletely understood, although recent studies have focused on the inflammation modulation of most cells types.

Neural stem cell therapy for neurovascular injury in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by progressive neurodegeneration leading to severe cognitive decline and eventual death. AD pathophysiology is complex, but neurotoxic accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau are believed to be main drivers of neurodegeneration in AD. The formation and deposition of Aβ plaques occurs in the brain parenchyma as well as in the cerebral vasculature. Thus, proper blood-brain barrier (BBB) and cerebrovascular functioning are crucial for clearance of Aβ from the brain, and neurovascular dysfunction may be a critical component of AD development. Further, neuroinflammation and dysfunction of angiogenesis, neurogenesis, and neurorestorative capabilities play a role in AD pathophysiology. Currently, there is no effective treatment to prevent or restore loss of brain tissue and cognitive decline in patients with AD. Based on multifactorial and complex pathophysiological cascades in multiple Alzheimer's disease stages, effective AD therapies need to focus on targeting early AD pathology and preserving cerebrovascular function. Neural stem cells (NSCs) participate extensively in mammalian brain homeostasis and repair and exhibit pleiotropic intrinsic properties that likely make them attractive candidates for the treatment of AD. In the review, we summarize the current advances in knowledge regarding neurovascular aspects of AD-related neurodegeneration and discuss multiple actions of NSCs from preclinical studies of AD to evaluate their potential for future clinical treatment of AD.

Non-cell autonomous mechanism of Parkinson's disease pathology caused by G2019S LRRK2 mutation in Ashkenazi Jewish patient: Single cell analysis

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease, characterized by the loss of the midbrain dopaminergic neurons, which leads to impaired motor and cognitive functions. PD is predominantly an idiopathic disease, however about 5% of cases are linked to hereditary mutations. The most common mutation in both familial and sporadic PD is the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2) with high prevalence in Ashkenazi Jewish patients and in North African Berber and Arab patients. It is still not fully understood how this mutation leads to PD pathology. In this study, we derived induced pluripotent stem cells (iPSCs) from an Ashkenazi Jewish patient with G2019S LRRK2 mutation to isolate self-renewable multipotent neural stem cells (NSCs) and to model this form of PD in vitro. To investigate the cellular diversity and disease pathology in the NSCs, we used single cell RNA-seq transcriptomic profiling. The evidence suggests there are three subpopulations within the NSCs: a committed neuronal population, intermediate stage population and undifferentiated stage population. Unbiased single-cell transcriptomic analysis revealed differential expression and dysregulation of genes involved in PD pathology. The significantly affected genes were involved in mitochondrial function, DNA repair, protein degradation, oxidative stress, lysosome biogenesis, ubiquitination, endosome function, autophagy and mitochondrial quality control. The results suggest that G2019S LRRK2 mutation may affect multiple cell types in a non-cell autonomous mechanism of PD pathology and that unbiased single-cell transcriptomics holds promise for personalized medicine.

Aggregation of human mesenchymal stem cells enhances survival and efficacy in stroke treatment

Human mesenchymal stem cells (hMSCs) have been shown to enhance stroke lesion recovery by mediating inflammation and tissue repair through secretion of trophic factors. However, low cell survival and reduced primitive stem cell function of culture-expanded hMSCs are the major challenges limiting hMSC therapeutic efficacy in stroke treatment. In this study, we report the effects of short-term preconditioning of hMSCs via three-dimensional (3D) aggregation on stroke lesion recovery after intra-arterial (IA) transplantation of 3D aggregate-derived hMSCs (Agg-D hMSCs) in a transient middle cerebral artery occlusion (MCAO) stroke model. Compared with two-dimensional (2D) monolayer culture, Agg-D hMSCs exhibited increased resistance to ischemic stress, secretory function and therapeutic outcome. Short-term preconditioning via 3D aggregation reconfigured hMSC energy metabolism and altered redox cycle, which activated the PI3K/AKT pathway and enhanced resistance to in vitro oxidative stress. Analysis of transplanted hMSCs in MCAO rats using ultra-high-field magnetic resonance imaging at 21.1 T showed increased hMSC persistence and stroke lesion reduction by sodium (²³Na) imaging in the Agg-D hMSC group compared with 2D hMSC control. Behavioral analyses further revealed functional improvement in MCAO animal treated with Agg-D hMSCs compared with saline control. Together, the results demonstrated the improved outcome for Agg-D hMSCs in the MCAO model and suggest short-term 3D aggregation as an effective preconditioning strategy for hMSC functional enhancement in stroke treatment.

Pluripotent Stem Cells for Brain Repair: Protocols and Preclinical Applications in Cortical and Hippocampal Pathologies

Brain injuries causing chronic sensory or motor deficit, such as stroke, are among the leading causes of disability worldwide, according to the World Health Organization; furthermore, they carry heavy social and economic burdens due to decreased quality of life and need of assistance. Given the limited effectiveness of rehabilitation, novel therapeutic strategies are required to enhance functional recovery. Since cell-based approaches have emerged as an intriguing and promising strategy to promote brain repair, many efforts have been made to study the functional integration of neurons derived from pluripotent stem cells (PSCs), or fetal neurons, after grafting into the damaged host tissue. PSCs hold great promises for their clinical applications, such as cellular replacement of damaged neural tissues with autologous neurons. They also offer the possibility to create in vitro models to assess the efficacy of drugs and therapies. Notwithstanding these potential applications, PSC-derived transplanted neurons have to match the precise sub-type, positional and functional identity of the lesioned neural tissue. Thus, the requirement of highly specific and efficient differentiation protocols of PSCs in neurons with appropriate neural identity constitutes the main challenge limiting the clinical use of stem cells in the near future. In this Review, we discuss the recent advances in the derivation of telencephalic (cortical and hippocampal) neurons from PSCs, assessing specificity and efficiency of the differentiation protocols, with particular emphasis on the genetic and molecular characterization of PSC-derived neurons. Second, we address the remaining challenges for cellular replacement therapies in cortical brain injuries, focusing on electrophysiological properties, functional integration and therapeutic effects of the transplanted neurons.

Influencing neuroplasticity in stroke treatment with advanced biomaterials-based approaches

Since the early 1990s, we have known that the adult brain is not static and has the capacity to repair itself. The delivery of various therapeutic factors and cells have resulted in some exciting pre-clinical and clinical outcomes in stroke models by targeting post-injury plasticity to enhance recovery. Developing a deeper understanding of the pathways that modulate plasticity will enable us to optimize delivery strategies for therapeutics and achieve more robust effects. Biomaterials are a key tool for the optimization of these potential treatments, owing to their biocompatibility and tunability. In this review, we identify factors and targets that impact plastic processes known to contribute to recovery, discuss the role of biomaterials in enhancing the efficacy of treatment strategies, and suggest combinatorial approaches based on the stage of injury progression.

Generation of Neural Stem Cells from Induced Pluripotent Stem Cells

Neural stem cells (NSCs) are defined by three necessary but not sufficient criteria: (1) self-renewable, (2) ability to generate a large number of progeny, and (3) ability to differentiate into the principal central nervous system (CNS) cell types, neurons, astrocytes, and oligodendrocytes. There are various approaches to derive neural lineages from pluripotent stem cells. It is well recognized that the chosen method of NSC derivation is critical to answering the basic biology question under investigation, to the success rate in drug discovery and to the efficacy of the therapeutic cells intended for repairing the CNS. There are three critical attributes of NSCs: (1) well-defined and stable cellular composition, (2) consistent process of perpetuation that avoids drift in composition, and (3) stable phenotype or therapeutic activity of the NSCs or their differentiated progeny. Over the past decades, we have been continuously developing consistent processes for generating stable, multipotent self-renewable NSCs from various sources. In this chapter, we report a method to generate NSCs from induced pluripotent stem cells.

Promoting Brain Repair and Regeneration After Stroke: a Plea for Cell-Based Therapies

PURPOSE OF REVIEW

After decades of hype, cell-based therapies are emerging into the clinical arena for the purposes of promoting recovery after stroke. In this review, we discuss the most recent science behind the role of cell-based therapies in ischemic stroke and the efforts to translate these therapies into human clinical trials.

RECENT FINDINGS

Preclinical data support numerous beneficial effects of cell-based therapies in both small and large animal models of ischemic stroke. These benefits are driven by multifaceted mechanisms promoting brain repair through immunomodulation, trophic support, circuit reorganization, and cell replacement. Cell-based therapies offer tremendous potential for improving outcomes after stroke through multimodal support of brain repair. Based on recent clinical trials, cell-based therapies appear both feasible and safe in all phases of stroke. Ongoing translational research and clinical trials will further refine these therapies and have the potential to transform the approach to stroke recovery and rehabilitation.

Harnessing stem cells and biomaterials to promote neural repair

With the limited capacity for self-repair in the adult CNS, efforts to stimulate quiescent stem cell populations within discrete brain regions, as well as harness the potential of stem cell transplants, offer significant hope for neural repair. These new cells are capable of providing trophic cues to support residual host populations and/or replace those cells lost to the primary insult. However, issues with low-level adult neurogenesis, cell survival, directed differentiation and inadequate reinnervation of host tissue have impeded the full potential of these therapeutic approaches and their clinical advancement. Biomaterials offer novel approaches to stimulate endogenous neurogenesis, as well as for the delivery and support of neural progenitor transplants, providing a tissue-appropriate physical and trophic milieu for the newly integrating cells. In this review, we will discuss the various approaches by which bioengineered scaffolds may improve stem cell-based therapies for repair of the CNS.

Tracking Neural Progenitor Cell Migration in the Rodent Brain Using Magnetic Resonance Imaging

The study of neurogenesis and neural progenitor cells (NPCs) is important across the biomedical spectrum, from learning about normal brain development and studying disease to engineering new strategies in regenerative medicine. In adult mammals, NPCs proliferate in two main areas of the brain, the subventricular zone (SVZ) and the subgranular zone, and continue to migrate even after neurogenesis has ceased within the rest of the brain. In healthy animals, NPCs migrate along the rostral migratory stream (RMS) from the SVZ to the olfactory bulb, and in diseased animals, NPCs migrate toward lesions such as stroke and tumors. Here we review how MRI-based cell tracking using iron oxide particles can be used to monitor and quantify NPC migration in the intact rodent brain, in a serial and relatively non-invasive fashion. NPCs can either be labeled directly in situ by injecting particles into the lateral ventricle or RMS, where NPCs can take up particles, or cells can be harvested and labeled in vitro, then injected into the brain. For in situ labeling experiments, the particle type, injection site, and image analysis methods have been optimized and cell migration toward stroke and multiple sclerosis lesions has been investigated. Delivery of labeled exogenous NPCs has allowed imaging of cell migration toward more sites of neuropathology, which may enable new diagnostic and therapeutic opportunities for as-of-yet untreatable neurological diseases.

[Cell therapy for ischemic stroke. Stem cell types and results of pre-clinical trials]

The literature review addresses the use of stem cells (SC) in ischemic stroke (IS). Part 1 of the paper overviews the results of experimental animal studies. Characteristics of different SC types and results of their studies in experimental models of IS are presented in the first section, the second section considers pros and cons of the methods of SC injection.

Intraparenchymal Neural Stem/Progenitor Cell Transplantation for Ischemic Stroke Animals: A Meta-Analysis and Systematic Review

Intraparenchymal transplantation of neural stem/progenitor cells (NSPCs) has been extensively investigated in animal models of ischemic stroke. However, the reported therapeutic efficacy was inconsistent among studies. To evaluate this situation, PubMed, Embase, and Web of Science databases were searched for preclinical studies using NSPC intraparenchymal transplantation in ischemic stroke animals. Data of study quality score, neurobehavioral (mNSS, rotarod test, and cylinder test) and histological (infarct volume) outcomes, cell therapy-related serious adverse events, and related cellular mechanisms were extracted for meta-analysis and systematic review. A total of 62 studies containing 73 treatment arms were included according to our criterion, with a mean quality score of 5.10 in 10. Among these studies, almost half of the studies claimed no adverse events of tumorigenesis. The finally pooled effect sizes for neurobehavioral and histological assessments were large (1.27 for mNSS, 1.63 for the rotarod test, 0.71 for the cylinder test, and 1.11 for infarct volume reduction). With further analysis, it was found that the administration time poststroke, NSPC donor species, and transplantation immunogenicity had close correlations with the degree of infarct volume reduction. The NSPC dosage delivered into the brain parenchyma was also negatively correlated with the effect of the cylinder test. Intriguingly, endogenous apoptosis inhibition and axonal regeneration played the most critical role in intraparenchymal NSPC transplantation among the cellular mechanisms. These results indicate that intraparenchymal NSPC transplantation is beneficial for neurobehavioral and histological improvement and is relatively safe for ischemic stroke animals. Therefore, intraparenchymal NSPC transplantation is a promising treatment for stroke patients.

Standards for Deriving Nonhuman Primate-Induced Pluripotent Stem Cells, Neural Stem Cells and Dopaminergic Lineage

Humans and nonhuman primates (NHP) are similar in behavior and in physiology, specifically the structure, function, and complexity of the immune system. Thus, NHP models are desirable for pathophysiology and pharmacology/toxicology studies. Furthermore, NHP-derived induced pluripotent stem cells (iPSCs) may enable transformative developmental, translational, or evolutionary studies in a field of inquiry currently hampered by the limited availability of research specimens. NHP-iPSCs may address specific questions that can be studied back and forth between in vitro cellular assays and in vivo experimentations, an investigational process that in most cases cannot be performed on humans because of safety and ethical issues. The use of NHP model systems and cell specific in vitro models is evolving with iPSC-based three-dimensional (3D) cell culture systems and organoids, which may offer reliable in vitro models and reduce the number of animals used in experimental research. IPSCs have the potential to give rise to defined cell types of any organ of the body. However, standards for deriving defined and validated NHP iPSCs are missing. Standards for deriving high-quality iPSC cell lines promote rigorous and replicable scientific research and likewise, validated cell lines reduce variability and discrepancies in results between laboratories. We have derived and validated NHP iPSC lines by confirming their pluripotency and propensity to differentiate into all three germ layers (ectoderm, mesoderm, and endoderm) according to standards and measurable limits for a set of marker genes. The iPSC lines were characterized for their potential to generate neural stem cells and to differentiate into dopaminergic neurons. These iPSC lines are available to the scientific community. NHP-iPSCs fulfill a unique niche in comparative genomics to understand gene regulatory principles underlying emergence of human traits, in infectious disease pathogenesis, in vaccine development, and in immunological barriers in regenerative medicine.

On the Viability and Potential Value of Stem Cells for Repair and Treatment of Central Neurotrauma: Overview and Speculations

Central neurotrauma, such as spinal cord injury or traumatic brain injury, can damage critical axonal pathways and neurons and lead to partial to complete loss of neural function that is difficult to address in the mature central nervous system. Improvement and innovation in the development, manufacture, and delivery of stem-cell based therapies, as well as the continued exploration of newer forms of stem cells, have allowed the professional and public spheres to resolve technical and ethical questions that previously hindered stem cell research for central nervous system injury. Recent in vitro and in vivo models have demonstrated the potential that reprogrammed autologous stem cells, in particular, have to restore functionality and induce regeneration-while potentially mitigating technical issues of immunogenicity, rejection, and ethical issues of embryonic derivation. These newer stem-cell based approaches are not, however, without concerns and problems of safety, efficacy, use and distribution. This review is an assessment of the current state of the science, the potential solutions that have been and are currently being explored, and the problems and questions that arise from what appears to be a promising way forward (i.e., autologous stem cell-based therapies)-for the purpose of advancing the research for much-needed therapeutic interventions for central neurotrauma.

Neural stem cell therapy for subacute and chronic ischemic stroke

Neural stem cells (NSCs) play vital roles in brain homeostasis and exhibit a broad repertoire of potentially therapeutic actions following neurovascular injury. One such injury is stroke, a worldwide leading cause of death and disability. Clinically, extensive injury from ischemic stroke results from ischemia-reperfusion (IR), which is accompanied by inflammation, blood-brain barrier (BBB) damage, neural cell death, and extensive tissue loss. Tissue plasminogen activator (tPA) is still the only US Food and Drug Administration-approved clot-lysing agent. Whereas the thrombolytic role of tPA within the vasculature is beneficial, the effects of tPA (in a non-thrombolytic role) within the brain parenchyma have been reported as harmful. Thus, new therapies are needed to reduce the deleterious side effects of tPA and quickly facilitate vascular repair following stroke. The Stroke Treatment Academic Industry Roundtable (STAIR) recommends that stroke therapies "focus on drugs/devices/treatments with multiple mechanisms of action and that target multiple pathways". Thus, based on multifactorial ischemic cascades in various stroke stages, effective stroke therapies need to focus on targeting and ameliorating early IR injury as well as facilitating angiogenesis, neurogenesis, and neurorestorative mechanisms following stroke. This review will discuss the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury and will emphasize both the subacute and chronic phase of ischemic stroke.

Neural stem cell therapies and hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury is a significant cause of morbidity and mortality in the adult as well as in the neonate. Extensive pre-clinical studies have shown promising therapeutic effects of neural stem cell-based treatments for hypoxic-ischemic brain injury. There are two major strategies of neural stem cell-based therapies: transplanting exogenous neural stem cells and boosting self-repair of endogenous neural stem cells. Neural stem cell transplantation has been proved to improve functional recovery after brain injury through multiple by-stander mechanisms (e.g., neuroprotection, immunomodulation), rather than simple cell-replacement. Endogenous neural stem cells reside in certain neurogenic niches of the brain and response to brain injury. Many molecules (e.g., neurotrophic factors) can stimulate or enhance proliferation and differentiation of endogenous neural stem cells after injury. In this review, we first present an overview of neural stem cells during normal brain development and the effect of hypoxic-ischemic injury on the activation and function of endogenous neural stem cells in the brain. We then summarize and discuss the current knowledge of strategies and mechanisms for neural stem cell-based therapies on brain hypoxic-ischemic injury, including neonatal hypoxic-ischemic brain injury and adult ischemic stroke.

Peptide-Based Scaffolds Support Human Cortical Progenitor Graft Integration to Reduce Atrophy and Promote Functional Repair in a Model of Stroke

Stem cell transplants offer significant hope for brain repair following ischemic damage. Pre-clinical work suggests that therapeutic mechanisms may be multi-faceted, incorporating bone-fide circuit reconstruction by transplanted neurons, but also protection/regeneration of host circuitry. Here, we engineered hydrogel scaffolds to form "bio-bridges" within the necrotic lesion cavity, providing physical and trophic support to transplanted human embryonic stem cell-derived cortical progenitors, as well as residual host neurons. Scaffolds were fabricated by the self-assembly of peptides for a laminin-derived epitope (IKVAV), thereby mimicking the brain's major extracellular protein. Following focal ischemia in rats, scaffold-supported cell transplants induced progressive motor improvements over 9 months, compared to cell- or scaffold-only implants. These grafts were larger, exhibited greater neuronal differentiation, and showed enhanced electrophysiological properties reflective of mature, integrated neurons. Varying graft timing post-injury enabled us to attribute repair to both neuroprotection and circuit replacement. These findings highlight strategies to improve the efficiency of stem cell grafts for brain repair.

Human Neural Stem Cells for Ischemic Stroke Treatment

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. It takes place when the brain does not receive sufficient blood supply due to the blood clot in the vessels or narrowing of vessels' inner space due to accumulation of fat products. Apart from thrombolysis (dissolving of blood clot) and thrombectomy (surgical removal of blood clot or widening of vessel inner area) during the first hours after an ischemic stroke, no effective treatment to improve functional recovery exists in the post-ischemic phase. Due to their narrow therapeutic time window, thrombolysis and thrombectomy are unavailable to more than 80% of stroke patients.Many experimental studies carried out in animal models of stroke have demonstrated that stem cell transplantation may become a new therapeutic strategy in stroke. Transplantation of stem cells of different origin and stage of development has been shown to lead to improvement in experimental models of stroke through several mechanisms including neuronal replacement, modulation of cellular and synaptic plasticity and inflammation, neuroprotection and stimulation of angiogenesis. Several clinical studies and trials based on stem cell delivery in stroke patients are in progress with goal of improvements of functional recovery through mechanisms other than neuronal replacement. These approaches may provide therapeutic benefit, but generation of specific neurons for reconstruction of stroke-injured neural circuitry remains ultimate challenge. For this purpose, neural stem cells could be developed from multiple sources and fated to adopt required neuronal phenotype.

Getting Closer to an Effective Intervention of Ischemic Stroke: The Big Promise of Stem Cell

Stem cell therapy for ischemic stroke has widely been explored. Results from both preclinical and clinical studies have immensely supported the judicious use of stem cells as therapy. These provide an attractive means for preserving and replacing the damaged brain tissues following an ischemic attack. Since the past few years, researchers have used various types of stem cells to replenish insulted neuronal and glial cells in neurological disorders. In the present review, we discuss different types of stem cells employed for the treatment of ischemic stroke and mechanisms and challenges these cells face once introduced into the living system. Further, we also present different ways to maneuver and overcome challenges to translate the advances made at the preclinical level to clinics.

Current progress in the derivation and therapeutic application of neural stem cells

Neural stem cells (NSCs) have a unique role in neural regeneration. Cell therapy based on NSC transplantation is a promising tool for the treatment of nervous system diseases. However, there are still many issues and controversies associated with the derivation and therapeutic application of these cells. In this review, we summarize the different sources of NSCs and their derivation methods, including direct isolation from primary tissues, differentiation from pluripotent stem cells and transdifferentiation from somatic cells. We also review the current progress in NSC implantation for the treatment of various neural defects and injuries in animal models and clinical trials. Finally, we discuss potential optimization strategies for NSC derivation and propose urgent challenges to the clinical translation of NSC-based therapies in the near future.

Stem cell transplantation therapy for multifaceted therapeutic benefits after stroke

One of the exciting advances in modern medicine and life science is cell-based neurovascular regeneration of damaged brain tissues and repair of neuronal structures. The progress in stem cell biology and creation of adult induced pluripotent stem (iPS) cells has significantly improved basic and pre-clinical research in disease mechanisms and generated enthusiasm for potential applications in the treatment of central nervous system (CNS) diseases including stroke. Endogenous neural stem cells and cultured stem cells are capable of self-renewal and give rise to virtually all types of cells essential for the makeup of neuronal structures. Meanwhile, stem cells and neural progenitor cells are well-known for their potential for trophic support after transplantation into the ischemic brain. Thus, stem cell-based therapies provide an attractive future for protecting and repairing damaged brain tissues after injury and in various disease states. Moreover, basic research on naïve and differentiated stem cells including iPS cells has markedly improved our understanding of cellular and molecular mechanisms of neurological disorders, and provides a platform for the discovery of novel drug targets. The latest advances indicate that combinatorial approaches using cell based therapy with additional treatments such as protective reagents, preconditioning strategies and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the characteristics of cell therapy in different ischemic models and the application of stem cells and progenitor cells as regenerative medicine for the treatment of stroke.

Potential Therapeutic Mechanisms and Tracking of Transplanted Stem Cells: Implications for Stroke Treatment

Stem cell therapy is a promising potential therapeutic strategy to treat cerebral ischemia in preclinical and clinical trials. Currently proposed treatments for stroke employing stem cells include the replacement of lost neurons and integration into the existing host circuitry, the release of growth factors to support and promote endogenous repair processes, and the secretion of extracellular vesicles containing proteins, noncoding RNA, or DNA to regulate gene expression in recipient cells and achieve immunomodulation. Progress has been made to elucidate the precise mechanisms underlying stem cell therapy and the homing, migration, distribution, and differentiation of transplanted stem cells in vivo using various imaging modalities. Noninvasive and safe tracer agents with high sensitivity and image resolution must be combined with long-term monitoring using imaging technology to determine the optimal therapy for stroke in terms of administration route, dosage, and timing. This review discusses potential therapeutic mechanisms of stem cell transplantation for the treatment of stroke and the limitations of current therapies. Methods to label transplanted cells and existing imaging systems for stem cell labeling and in vivo tracking will also be discussed.

Electrical preconditioning of stem cells with a conductive polymer scaffold enhances stroke recovery

Exogenous human neural progenitor cells (hNPCs) are promising stroke therapeutics, but optimal delivery conditions and exact recovery mechanisms remain elusive. To further elucidate repair processes and improve stroke outcomes, we developed an electrically conductive, polymer scaffold for hNPC delivery. Electrical stimulation of hNPCs alters their transcriptome including changes to the VEGF-A pathway and genes involved in cell survival, inflammatory response, and synaptic remodeling. In our experiments, exogenous hNPCs were electrically stimulated (electrically preconditioned) via the scaffold 1 day prior to implantation. After in vitro stimulation, hNPCs on the scaffold are transplanted intracranially in a distal middle cerebral artery occlusion rat model. Electrically preconditioned hNPCs improved functional outcomes compared to unstimulated hNPCs or hNPCs where VEGF-A was blocked during in vitro electrical preconditioning. The ability to manipulate hNPCs via a conductive scaffold creates a new approach to optimize stem cell-based therapy and determine which factors (such as VEGF-A) are essential for stroke recovery.

Comparison of Nutech Functional Score with European Stroke Scale for Patients with Cerebrovascular Accident Treated with Human Embryonic Stem Cells: NFS for CVA Patients Treated with hESCs

PURPOSE

Stem cell therapy is a promising modality for treatment of patients with chronic cerebrovascular accident (CVA) in whom treatment other than physiotherapy or occupational therapy does not address the repair or recovery of the lost function. In this study, the author aimed at evaluating CVA patients treated with human embryonic stem cell (hESC) therapy and comparing their study outcomes with globally accepted European Stroke Scale (ESS) to that with novel scoring system, Nutech functional score (NFS), a 21-point positional and directional scoring system for assessing patients with CVA.

MATERIALS AND METHODS

Patients diagnosed with CVA were assessed with NFS and ESS before and after hESC therapy. NFS assessed the patients in the direction of 1-5 (bad to good), where 5 was considered as the highest possible grade (HPG). The findings were obtained for the patients who scored HPG, and had shown improvement by at least one grade.

RESULTS

Overall, 66.7% of patients scored HPG level on the NFS scale and about 62.5% of the patients scored HPG according to the ESS scale. Approximately, 52.2% patients showed an improvement of 100% (by at least one grade) on NFS scale. None of the patients showed 100% improvement in the alteration of the score by at least one grade when scored with ESS.

CONCLUSION

NFS and ESS scores show that a large population of CVA patients was benefitted with hESC therapy. NFS was found to give more convincing results than ESS, and overcomes the shortcomings of ESS.

Long-Distance Axonal Growth and Protracted Functional Maturation of Neurons Derived from Human Induced Pluripotent Stem Cells After Intracerebral Transplantation

The capacity for induced pluripotent stem (iPS) cells to be differentiated into a wide range of neural cell types makes them an attractive donor source for autologous neural transplantation therapies aimed at brain repair. Translation to the in vivo setting has been difficult, however, with mixed results in a wide variety of preclinical models of brain injury and limited information on the basic in vivo properties of neural grafts generated from human iPS cells. Here we have generated a human iPS cell line constitutively expressing green fluorescent protein as a basis to identify and characterize grafts resulting from transplantation of neural progenitors into the adult rat brain. The results show that the grafts contain a mix of neural cell types, at various stages of differentiation, including neurons that establish extensive patterns of axonal growth and progressively develop functional properties over the course of 1 year after implantation. These findings form an important basis for the design and interpretation of preclinical studies using human stem cells for functional circuit re‐construction in animal models of brain injury. Stem Cells Translational Medicine2017;6:1547–1556

Spontaneous Recovery of Upper Extremity Motor Impairment After Ischemic Stroke: Implications for Stem Cell-Based Therapeutic Approaches

Preclinical studies suggest that stem cell therapy (SCT) may improve sensorimotor recovery after stroke. Upper extremity motor impairment (UEMI) is common after stroke, often entailing substantial disability. To evaluate the feasibility of post-stroke UEMI as a target for SCT, we examined a selected sample of stroke patients potentially suitable for SCT, aiming to assess the frequency and recovery of UEMI, as well as its relation to activity limitations and participation restrictions. Patients aged 20–75 years with first-ever ischemic stroke, and National Institutes of Health Stroke Scale (NIHSS) scores 1–18, underwent brain diffusion-weighted MRI within 4 days of stroke onset (n = 108). Survivors were followed up after 3–5 years, including assessment with NIHSS, Fugl-Meyer assessment of upper extremity (FMA-UE), modified Rankin Scale (mRS), and Stroke Impact Scale (SIS). UEMI was defined as NIHSS arm/hand score ≥1. UEMI recovery was evaluated with change in NIHSS arm/hand scores between baseline and follow-up. Of 97 survivors, 84 were available to follow-up. Among 76 subjects (of 84) without recurrent stroke, 41 had UEMI at baseline of which 10 had residual UEMI at follow-up. The FMA-UE showed moderate-severe impairment in seven of 10 survivors with residual UEMI. UEMI was correlated to mRS (r_s = 0.49, p < 0.001) and the SIS social participation domain (r_s = −0.38, p = 0.001). Nearly 25% of the subjects with UEMI at baseline had residual impairment after 3–5 years, whereas about 75% showed complete recovery. Most of the subjects with residual UEMI had moderate-severe impairment, which correlated strongly to dependency in daily activities and social participation restrictions. Our findings suggest that SCT targeting post-stroke UEMI may be clinically valuable with significant meaningful benefits for patients but also emphasize the need of early prognostication to detect patients that will have residual impairment in order to optimize patient selection for SCT.

Ellagic acid improves endogenous neural stem cells proliferation and neurorestoration through Wnt/β-catenin signaling in vivo and in vitro

SCOPE

The aim of this study is to research the effects of the polyphenol ellagic acid (EA) on brain cells and to explore its mechanism of action, and to evaluate whether EA can be safely utilized by humans as a functional food or therapeutic agent.

METHODS AND RESULTS

A photothrombosis-induced model of brain injury in rats was created, and EA was administered intragastrically to rats on 7 consecutive days post-venous ischemia. An oxygen-glucose deprivation and re-perfusion model was established in neural stem cells in order to research the effects on proliferation after 2 days of EA treatment in vitro. The administration of EA improved the rats' nerve-related abilities, remedied infarct volumes and morphological changes in the brain, and enhanced the content of nestin protein in the brain semidarkness zone. The proliferation of NSCs and the expression of β-catenin and Cyclin D1 genes were also increased in primary cultured NSCs.

CONCLUSIONS

EA administration can improve brain injury outcomes and increase the proliferation of NSCs through the Wnt/β-catenin signaling pathway. The presented results represent new insights on the mechanisms of the brain cell protective activity of EA. Thus, EA may be used in functional foods or medicines to help treat nerve dysfunction, neurodegenerative disease and aging.

Enhancement of human neural stem cell self-renewal in 3D hypoxic culture

The pathology of neurological disorders is associated with the loss of neuronal and glial cells that results in functional impairments. Human neural stem cells (hNSCs), due to their self-renewing and multipotent characteristics, possess enormous tissue-specific regenerative potential. However, the efficacy of clinical applications is restricted due to the lack of standardized in vitro cell production methods with the capability of generating hNSC populations with well-defined cellular compositions. At any point, a population of hNSCs may include undifferentiated stem cells, intermediate and terminally differentiated progenies, and dead cells. Due to the plasticity of hNSCs, environmental cues play crucial roles in determining the cellular composition of hNSC cultures over time. Here, we investigated the independent and synergistic effect of three important environmental factors (i.e., culture dimensionality, oxygen concentration, and growth factors) on the survival, renewal potential, and differentiation of hNSCs. Our experimental design included two dimensional (2D) versus three dimensional (3D) cultures and normoxic (21% O₂ ) versus hypoxic (3% O₂ ) conditions in the presence and absence of epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2). Additionally, we discuss the feasibility of mathematical models that predict hNSC growth and differentiation under these culture conditions by adopting a negative feedback regulatory term. Our results indicate that the synergistic effect of culture dimensionality and hypoxic oxygen concentration in the presence of growth factors enhances the proliferation of viable, undifferentiated hNSCs. Moreover, the same synergistic effect in the absence of growth factors promotes the differentiation of hNSCs. Biotechnol. Bioeng. 2017;114: 1096-1106. © 2016 Wiley Periodicals, Inc.

Magnetic Resonance Imaging-Guided Delivery of Neural Stem Cells into the Basal Ganglia of Nonhuman Primates Reveals a Pulsatile Mode of Cell Dispersion

Optimal stem cell delivery procedures are critical to the success of the cell therapy approach. Variables such as flow rate, suspension solution, needle diameter, cell density, and tissue mechanics affect tissue penetration, backflow along the needle, and the dispersion and survival of injected cells during delivery. Most cell transplantation centers engaged in human clinical trials use custom‐designed cannula needles, syringes, or catheters, sometimes precluding the use of magnetic resonance imaging (MRI)‐guided delivery to target tissue. As a result, stem cell therapies may be hampered because more than 80% of grafted cells do not survive the delivery—for example, to the heart, liver/pancreas, and brain—which translates to poor patient outcomes. We developed a minimally invasive interventional MRI (iMRI) approach for intraoperatively imaging neural stem cell (NSC) delivery procedures. We used NSCs prelabeled with a contrast agent and real‐time magnetic resonance imaging to guide the injection cannula to the target and to track the delivery of the cells into the putamen of baboons. We provide evidence that cell injection into the brain parenchyma follows a novel pulsatile mode of cellular discharge from the delivery catheter despite a constant infusion flow rate. The rate of cell infusion significantly affects the dispersion and viability of grafted cells. We report on our investigational use of a frameless navigation system for image‐guided NSC transplantation using a straight cannula. Through submillimeter accuracy and real‐time imaging, iMRI approaches may improve the safety and efficacy of neural cell transplantation therapies. Stem Cells Translational Medicine2017;6:877–885

Optogenetic modulation in stroke recovery

Stroke is one of the leading contributors to morbidity, mortality, and health care costs in the United States. Although several preclinical strategies have shown promise in the laboratory, few have succeeded in the clinical setting. Optogenetics represents a promising molecular tool, which enables highly specific circuit-level neuromodulation. Here, the conceptual background and preclinical body of evidence for optogenetics are reviewed, and translational considerations in stroke recovery are discussed.

High-Resolution Microfluidic Single-Cell Transcriptional Profiling Reveals Clinically Relevant Subtypes among Human Stem Cell Populations Commonly Utilized in Cell-Based Therapies

Stem cell therapies can promote neural repair and regeneration, yet controversy regarding optimal cell source and mechanism of action has slowed clinical translation, potentially due to undefined cellular heterogeneity. Single-cell resolution is needed to identify clinically relevant subpopulations with the highest therapeutic relevance. We combine single-cell microfluidic analysis with advanced computational modeling to study for the first time two common sources for cell-based therapies, human NSCs and MSCs. This methodology has the potential to logically inform cell source decisions for any clinical application.

Generation of diverse neural cell types through direct conversion

A characteristic of neurological disorders is the loss of critical populations of cells that the body is unable to replace, thus there has been much interest in identifying methods of generating clinically relevant numbers of cells to replace those that have been damaged or lost. The process of neural direct conversion, in which cells of one lineage are converted into cells of a neural lineage without first inducing pluripotency, shows great potential, with evidence of the generation of a range of functional neural cell types both in vitro and in vivo, through viral and non-viral delivery of exogenous factors, as well as chemical induction methods. Induced neural cells have been proposed as an attractive alternative to neural cells derived from embryonic or induced pluripotent stem cells, with prospective roles in the investigation of neurological disorders, including neurodegenerative disease modelling, drug screening, and cellular replacement for regenerative medicine applications, however further investigations into improving the efficacy and safety of these methods need to be performed before neural direct conversion becomes a clinically viable option. In this review, we describe the generation of diverse neural cell types via direct conversion of somatic cells, with comparison against stem cell-based approaches, as well as discussion of their potential research and clinical applications.

The effect of hypoxia and laminin-rich substrates on the proliferative behavior of human neural stem cells

Human neural stem cells cultured on laminin and Matrigel under hypoxia significantly increase both the stem cell density and the percentage of activity proliferating cells.

Mechanisms and Functional Significance of Stroke-Induced Neurogenesis

Stroke affects one in every six people worldwide, and is the leading cause of adult disability. After stroke, some limited spontaneous recovery occurs, the mechanisms of which remain largely unknown. Multiple, parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. For years, clinical studies have tried to use exogenous cell therapy as a means of brain repair, with varying success. Since the rediscovery of adult neurogenesis and the identification of adult neural stem cells in the late nineties, one promising field of investigation is focused upon triggering and stimulating this self-repair system to replace the neurons lost following brain injury. For instance, it is has been demonstrated that the adult brain has the capacity to produce large numbers of new neurons in response to stroke. The purpose of this review is to provide an updated overview of stroke-induced adult neurogenesis, from a cellular and molecular perspective, to its impact on brain repair and functional recovery.

Optogenetic Stimulation of Neural Grafts Enhances Neurotransmission and Downregulates the Inflammatory Response in Experimental Stroke Model

Compelling evidence suggests that transplantation of neural stem cells (NSCs) from multiple sources ameliorates motor deficits after stroke. However, it is currently unknown to what extent the electrophysiological activity of grafted NSC progeny participates in the improvement of motor deficits and whether excitatory phenotypes of the grafted cells are beneficial or deleterious to sensorimotor performances. To address this question, we used optogenetic tools to drive the excitatory outputs of the grafted NSCs and assess the impact on local circuitry and sensorimotor performance. We genetically engineered NSCs to express the Channelrhodopsin-2 (ChR2), a light-gated cation channel that evokes neuronal depolarization and initiation of action potentials with precise temporal control to light stimulation. To test the function of these cells in a stroke model, rats were subjected to an ischemic stroke and grafted with ChR2-NSCs. The grafted NSCs identified with a human-specific nuclear marker survived in the peri-infarct tissue and coexpressed the ChR2 transgene with the neuronal markers TuJ1 and NeuN. Gene expression analysis in stimulated versus vehicle-treated animals showed a differential upregulation of transcripts involved in neurotransmission, neuronal differentiation, regeneration, axonal guidance, and synaptic plasticity. Interestingly, genes involved in the inflammatory response were significantly downregulated. Behavioral analysis demonstrated that chronic optogenetic stimulation of the ChR2-NSCs enhanced forelimb use on the stroke-affected side and motor activity in an open field test. Together these data suggest that excitatory stimulation of grafted NSCs elicits beneficial effects in experimental stroke model through cell replacement and non-cell replacement, anti-inflammatory/neurotrophic effects.

Reconstruction of brain circuitry by neural transplants generated from pluripotent stem cells

Pluripotent stem cells (embryonic stem cells, ESCs, and induced pluripotent stem cells, iPSCs) have the capacity to generate neural progenitors that are intrinsically patterned to undergo differentiation into specific neuronal subtypes and express in vivo properties that match the ones formed during normal embryonic development. Remarkable progress has been made in this field during recent years thanks to the development of more refined protocols for the generation of transplantable neuronal progenitors from pluripotent stem cells, and the access to new tools for tracing of neuronal connectivity and assessment of integration and function of grafted neurons. Recent studies in brains of neonatal mice or rats, as well as in rodent models of brain or spinal cord damage, have shown that ESC- or iPSC-derived neural progenitors can be made to survive and differentiate after transplantation, and that they possess a remarkable capacity to extend axons over long distances and become functionally integrated into host neural circuitry. Here, we summarize these recent developments in the perspective of earlier studies using intracerebral and intraspinal transplants of primary neurons derived from fetal brain, with special focus on the ability of human ESC- and iPSC-derived progenitors to reconstruct damaged neural circuitry in cortex, hippocampus, the nigrostriatal system and the spinal cord, and we discuss the intrinsic and extrinsic factors that determine the growth properties of the grafted neurons and their capacity to establish target-specific long-distance axonal connections in the damaged host brain.

Opportunities and challenges: stem cell-based therapy for the treatment of ischemic stroke

Stem cell-based therapy for ischemic stroke has been widely explored in animal models and provides strong evidence of benefits. In this review, we summarize the types of stem cells, various delivery routes, and tracking tools for stem cell therapy of ischemic stroke. MSCs, EPCs, and NSCs are the most explored cell types for ischemic stroke treatment. Although the mechanisms of stem cell-based therapies are not fully understood, the most possible functions of the transplanted cells are releasing growth factors and regulating microenvironment through paracrine mechanism. Clinical application of stem cell-based therapy is still in its infancy. The next decade of stem cell research in stroke field needs to focus on combining different stem cells and different imaging modalities to fully explore the potential of this therapeutic avenue: from bench to bedside and vice versa.