Neural stem cells in the adult spinal cord

Current Options for Cell Therapy in Spinal Cord Injury

Spinal cord injury (SCI) is a complex pathology that evolves after primary acute mechanical injury, causing further damage to the spinal cord tissue that exacerbates clinical outcomes. Based on encouraging results from preclinical experiments, some cell treatments being translated into clinical practice demonstrate promising and effective improvement in sensory/motor function. Combinatorial treatments of cell and drug/biological factors have been demonstrated to be more effective than cell treatments alone. Recent advances have led to the development of biomaterials aiming to promote in situ cell delivery for SCI, together with combinatorial strategies using drugs/biomolecules to achieve a maximized multitarget approach. This review provides an overview of single and combinatorial regenerative cell treatments as well as potential delivery options to treat SCI.

Cetuximab modified collagen scaffold directs neurogenesis of injury-activated endogenous neural stem cells for acute spinal cord injury repair

Studies have shown that endogenous neural stem cells (NSCs) activated by spinal cord injury (SCI) primarily generate astrocytes to form glial scar. The NSCs do not differentiate into neurons because of the adverse microenvironment. In this study, we defined the activation timeline of endogenous NSCs in rats with severe SCI. These injury-activated NSCs then migrated into the lesion site. Cetuximab, an EGFR signaling antagonist, significantly increased neurogenesis in the lesion site. Meanwhile, implanting cetuximab modified linear ordered collagen scaffolds (LOCS) into SCI lesion sites in dogs resulted in neuronal regeneration, including neuronal differentiation, maturation, myelination, and synapse formation. The neuronal regeneration eventually led to a significant locomotion recovery. Furthermore, LOCS implantation could also greatly decrease chondroitin sulfate proteoglycan (CSPG) deposition at the lesion site. These findings suggest that endogenous neurogenesis following acute complete SCI is achievable in species ranging from rodents to large animals via functional scaffold implantation. LOCS-based Cetuximab delivery system has a promising therapeutic effect on activating endogenous neurogenesis, reducing CSPGs deposition and improving motor function recovery.

Spinal cord injuries: how could cell therapy help?

INTRODUCTION

Spinal cord injury (SCI) is a devastating condition, where regenerative failure and cell loss lead to paralysis. The heterogeneous and time-sensitive pathophysiology has made it difficult to target tissue repair. Despite many medical advances, there are no effective regenerative therapies. As stem cells offer multi-targeted and environmentally responsive benefits, cell therapy is a promising treatment approach. Areas covered: This review highlights the cell therapies being investigated for SCI, including Schwann cells, olfactory ensheathing cells, mensenchymal stem/stromal cells, neural precursors, oligodendrocyte progenitors, embryonic stem cells, and induced pluripotent stem cells. Through mechanisms of cell replacement, scaffolding, trophic support and immune modulation, each approach targets unique features of SCI pathology. However, as the injury is multifaceted, it is increasingly recognized that a combinatorial approach will be necessary to treat SCI. Expert opinion: Most preclinical studies, and an increasing number of clinical trials, are finding that single cell therapies have only modest benefits after SCI. These considerations, alongside issues of therapy cost-effectiveness, need to be addressed at the bench. In addition to exploring combinatorial strategies, researchers should consider cell reproducibility and storage parameters when designing animal experiments. Equally important, clinical trials must follow strict regulatory guidelines that will enable transparency of results.

A modified collagen scaffold facilitates endogenous neurogenesis for acute spinal cord injury repair

Due to irreversible neuronal loss and glial scar deposition, spinal cord injury (SCI) ultimately results in permanent neurological dysfunction. Neuronal regeneration of neural stem cells (NSCs) residing in the spinal cord could be an ideal strategy for replenishing the lost neurons and restore function. However, many myelin-associated inhibitors in the SCI microenvironment limit the ability of spinal cord NSCs to regenerate into neurons. Here, a linearly ordered collagen scaffold was used to prevent scar deposition, guide nerve regeneration and carry drugs to neutralize the inhibitory molecules. A collagen-binding EGFR antibody Fab fragment, CBD-Fab, was constructed to neutralize the myelin inhibitory molecules, which was demonstrated to promote neuronal differentiation and neurite outgrowth under myelin in vitro. This fragment could also specifically bind to the collagen and undergo sustained release from collagen scaffold. Then, the scaffolds modified with CBD-Fab were transplanted into an acute rat SCI model. The robust neurogenesis of endogenous injury-activated NSCs was observed, and these NSCs could not only differentiate into neurons but further mature into functional neurons to reconnect the injured gap. The results indicated that the modified collagen scaffold could be an ideal candidate for spinal cord regeneration after acute SCI.

STATEMENTS OF SIGNIFICANCE

A linearly ordered collagen scaffold was specifically modified with collagen-binding EGFR antibody, allowed for sustained release of this EGFR neutralizing factor, to block the myelin associated inhibitory molecules and guide spinal cord regeneration along its linear fibers. Dorsal root ganglion neurons and neural stem cells induced by CBD-Fab exhibited enhanced neurite outgrowth and neuronal differentiation rate under myelin in vitro. Transplantation of the modified collagen scaffold with moderate EGFR neutralizing proteins showed greatest advantage on endogenous neurogenesis of injury-activated neural stem cells for acute spinal cord injury repair.

Transplantation of hUC-MSCs seeded collagen scaffolds reduces scar formation and promotes functional recovery in canines with chronic spinal cord injury

Spinal cord injury (SCI) can lead to locomotor deficits, and the repair of chronic SCI is considered one of the most challenging clinical problems. Although extensive studies have evaluated treatments for acute SCI in small animals, comparatively fewer studies have been conducted on large-animal SCI in the chronic phase, which is more clinically relevant. Here, we used a collagen-based biomaterial, named the NeuroRegen scaffold, loaded with human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in a canine chronic SCI model. To generate chronic SCI, the T8 spinal cord segment was removed by complete transection of the spinal cord. Two months later, glial scar tissue was removed and a NeuroRegen scaffold was transplanted into the lesion area. Functionalized NeuroRegen scaffold implantation promoted both locomotor recovery and endogenous neurogenesis in the lesion area. Moreover, some newly generated neurons successfully matured into 5-HT-positive neurons at 1 year post-injury. In addition, many regenerated axon fibers in the lesion area exhibited remyelination and synapse formation at 1 year post-injury in the functionalized NeuroRegen scaffold group. In conclusion, the NeuroRegen scaffold functionalized with hUC-MSCs is a promising potential therapeutic approach to chronic SCI that promotes neuronal regeneration, reduces glial scar formation, and ultimately improves locomotor recovery.

Transspinal direct current stimulation modulates migration and proliferation of adult newly born spinal cells in mice

Direct current electrical fields have been shown to be a major factor in the regulation of cell proliferation, differentiation, migration, and survival, as well as in the maturation of dividing cells during development. During adulthood, spinal cord cells are continuously produced in both animals and humans, and they hold great potential for neural restoration following spinal cord injury. While the effects of direct current electrical fields on adult-born spinal cells cultured ex vivo have recently been reported, the effects of direct current electrical fields on adult-born spinal cells in vivo have not been characterized. Here, we provide convincing findings that a therapeutic form of transspinal direct current stimulation (tsDCS) affects the migration and proliferation of adult-born spinal cells in mice. Specifically, cathodal tsDCS attracted the adult-born spinal cells, while anodal tsDCS repulsed them. In addition, both tsDCS polarities caused a significant increase in cell number. Regarding the potential mechanisms involved, both cathodal and anodal tsDCS caused significant increases in expression of brain-derived neurotrophic factor, while expression of nerve growth factor increased and decreased, respectively. In the spinal cord, both anodal and cathodal tsDCS increased blood flow. Since blood flow and angiogenesis are associated with the proliferation of neural stem cells, increased blood flow may represent a major factor in the modulation of newly born spinal cells by tsDCS. Consequently, we propose that the method and novel findings presented in the current study have the potential to facilitate cellular, molecular, and/or bioengineering strategies to repair injured spinal cords.

NEW & NOTEWORTHY Our results indicate that transspinal direct current stimulation (tsDCS) affects the migratory pattern and proliferation of adult newly born spinal cells, a cell population which has been implicated in learning and memory. In addition, our results suggest a potential mechanism of action regarding the functional effects of applying direct current. Thus tsDCS may represent a novel method by which to manipulate the migration and cell number of adult newly born cells and restore functions following brain or spinal cord injury.

Ependymal cell contribution to scar formation after spinal cord injury is minimal, local and dependent on direct ependymal injury

Ependyma have been proposed as adult neural stem cells that provide the majority of newly proliferated scar-forming astrocytes that protect tissue and function after spinal cord injury (SCI). This proposal was based on small, midline stab SCI. Here, we tested the generality of this proposal by using a genetic knock-in cell fate mapping strategy in different murine SCI models. After large crush injuries across the entire spinal cord, ependyma-derived progeny remained local, did not migrate and contributed few cells of any kind and less than 2%, if any, of the total newly proliferated and molecularly confirmed scar-forming astrocytes. Stab injuries that were near to but did not directly damage ependyma, contained no ependyma-derived cells. Our findings show that ependymal contribution of progeny after SCI is minimal, local and dependent on direct ependymal injury, indicating that ependyma are not a major source of endogenous neural stem cells or neuroprotective astrocytes after SCI.

Transcriptional Regulation of Notch1 Expression by Nkx6.1 in Neural Stem/Progenitor Cells during Ventral Spinal Cord Development

Notch1 signaling plays a critical role in maintaining and determining neural stem/progenitor cell (NSPC) fate, yet the transcriptional mechanism controlling Notch1 specific expression in NSPCs remains incomplete. Here, we show transcription factor Nkx6.1 interacts with a cis-element (CR2, an evolutionarily conserved non-coding fragment in the second intron of Notch1 locus) and regulates the expression of Notch1 in ventral NSPCs of the developing spinal cord. We show that the Notch1 expression is modulated by the interaction of Nkx6.1 with a 139 bp enhancer sequence within CR2. Knockdown or overexpression of Nkx6.1 leads to down- or up-regulated Notch1 expression, respectively. In CR2-GFP transgenic mouse, GFP expression was found prominent in the ventricular zone and neural progenitor cells from embryonic day 9.5 to postnatal day 7. GFP+ cells were mainly neural progenitors for interneurons and not for motoneurons or glial cells. Moreover, GFP expression persisted in a subset of ependymal cells in the adult spinal cord, suggesting that CR2 is active in both embryonic and adult NSPCs. Together our data reveal a novel mechanism of Notch1 transcriptional regulation in the ventral spinal cord by Nkx6.1 via its binding with Notch1 enhancer CR2 during embryonic development.

Regenerative Potential of Ependymal Cells for Spinal Cord Injuries Over Time

Stem cells have a high therapeutic potential for the treatment of spinal cord injury (SCI). We have shown previously that endogenous stem cell potential is confined to ependymal cells in the adult spinal cord which could be targeted for non-invasive SCI therapy. However, ependymal cells are an understudied cell population. Taking advantage of transgenic lines, we characterize the appearance and potential of ependymal cells during development. We show that spinal cord stem cell potential in vitro is contained within these cells by birth. Moreover, juvenile cultures generate more neurospheres and more oligodendrocytes than adult ones. Interestingly, juvenile ependymal cells in vivo contribute to glial scar formation after severe but not mild SCI, due to a more effective sealing of the lesion by other glial cells. This study highlights the importance of the age-dependent potential of stem cells and post-SCI environment in order to utilize ependymal cell's regenerative potential.

Radially Aligned Electrospun Fibers with Continuous Gradient of SDF1α for the Guidance of Neural Stem Cells

Repair of spinal cord injury will require enhanced recruitment of endogenous neural stem cells (NSCs) from the central canal region to the lesion site to reestablish neural connectivity. The strategy toward this goal is to provide directional cues, e.g., alignment topography and biological gradients from the rostral and caudal ends toward the center. This study demonstrates a facile method for fabrication of continuous gradients of stromal-cell-derived factor-1α (SDF1α) embedded in the radially aligned electrospun collagen/poly (ε-caprolactone) mats. Gradients can be readily produced in a controllable and reproducible fashion by adjusting the collection time and collector size during electrospinning. To get a long-term gradient, the SDF1α is fused with a unique peptide of collagen-binding domain (CBD), which can bind to collagen specifically. Aligned CBD-SDF1α gradients show stable, sustained, and gradual release during 7 d. Further, the effect of aligned CBD-SDF1α gradients on the guidance of NSCs is investigated. It is found that the CBD-SDF1α gradient scaffolds direct and enhance NSC migration from the periphery to the center along the aligned electrospun fibers. Taken together, the tubular conduits based on radially aligned electrospun fibers with continuous SDF1α gradient show great potential for guiding nerve regeneration.

Neural Placode Tissue Derived From Myelomeningocele Repair Serves as a Viable Source of Oligodendrocyte Progenitor Cells

BACKGROUND

The presence, characteristics, and potential clinical relevance of neural progenitor populations within the neural placodes of myelomeningocele patients remain to be studied. Neural stem cells are known to reside adjacent to ependyma-lined surfaces along the central nervous system axis.

OBJECTIVE

Given such neuroanatomic correlation and regenerative capacity in fetal development, we assessed myelomeningocele-derived neural placode tissue as a potentially novel source of neural stem and progenitor cells.

METHODS

Nonfunctional neural placode tissue was harvested from infants during the surgical repair of myelomeningocele and subsequently further analyzed by in vitro studies, flow cytometry, and immunofluorescence. To assess lineage potential, neural placode-derived neurospheres were subjected to differential media conditions. Through assessment of platelet-derived growth factor receptor α (PDGFRα) and CD15 cell marker expression, Sox2+Olig2+ putative oligodendrocyte progenitor cells were successfully isolated.

RESULTS

PDGFRαCD15 cell populations demonstrated the highest rate of self-renewal capacity and multipotency of cell progeny. Immunofluorescence of neural placode-derived neurospheres demonstrated preferential expression of the oligodendrocyte progenitor marker, CNPase, whereas differentiation to neurons and astrocytes was also noted, albeit to a limited degree.

CONCLUSION

Neural placode tissue contains multipotent progenitors that are preferentially biased toward oligodendrocyte progenitor cell differentiation and presents a novel source of such cells for use in the treatment of a variety of pediatric and adult neurological disease, including spinal cord injury, multiple sclerosis, and metabolic leukoencephalopathies.

Chronic administration of AMD3100 increases survival and alleviates pathology in SOD1(G93A) mice model of ALS

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a progressive fatal neurodegenerative disease, involving both upper and lower motor neurons. The disease is induced by multifactorial pathologies, and as such, it requires a multifaceted therapeutic approach. CXCR4, a chemokine receptor widely expressed in neurons and glial cells and its ligand, CXCL12, also known as stromal-cell-derived factor (SDF1), modulate both neuronal function and apoptosis by glutamate release signaling as well as hematopoietic stem and progenitor cells (HSPCs) migration into the blood and their homing towards injured sites. Inhibition approaches towards the CXCR4/CXCL12 signaling may result in preventing neuronal apoptosis and alter the HSPCs migration and homing. Such inhibition can be achieved by means of treatment with AMD3100, an antagonist of the chemokine receptor CXCR4.

METHODS

We chronically treated male and female transgenic mice model of ALS, SOD1(G93A) mice, with AMD3100. Mice body weight and motor function, evaluated by Rotarod test, were recorded once a week. The most effective treatment regimen was repeated for biochemical and histological analyses in female mice.

RESULTS

We found that chronic administration of AMD3100 to SOD1(G93A) mice led to significant extension in mice lifespan and improved motor function and weight loss. In addition, the treatment significantly improved microglial pathology and decreased proinflammatory cytokines in spinal cords of treated female mice. Furthermore, AMD3100 treatment decreased blood-spinal cord barrier (BSCB) permeability by increasing tight junction proteins levels and increased the motor neurons count in the lamina X area of the spinal cord, where adult stem cells are formed.

CONCLUSIONS

These data, relevant to the corresponding disease mechanism in human ALS, suggest that blocking CXCR4 by the small molecule, AMD3100, may provide a novel candidate for ALS therapy with an increased safety.

Control of adult neurogenesis by programmed cell death in the mammalian brain

The presence of neural stem cells (NSCs) and the production of new neurons in the adult brain have received great attention from scientists and the public because of implications to brain plasticity and their potential use for treating currently incurable brain diseases. Adult neurogenesis is controlled at multiple levels, including proliferation, differentiation, migration, and programmed cell death (PCD). Among these, PCD is the last and most prominent process for regulating the final number of mature neurons integrated into neural circuits. PCD can be classified into apoptosis, necrosis, and autophagic cell death and emerging evidence suggests that all three may be important modes of cell death in neural stem/progenitor cells. However, the molecular mechanisms that regulate PCD and thereby impact the intricate balance between self-renewal, proliferation, and differentiation during adult neurogenesis are not well understood. In this comprehensive review, we focus on the extent, mechanism, and biological significance of PCD for the control of adult neurogenesis in the mammalian brain. The role of intrinsic and extrinsic factors in the regulation of PCD at the molecular and systems levels is also discussed. Adult neurogenesis is a dynamic process, and the signals for differentiation, proliferation, and death of neural progenitor/stem cells are closely interrelated. A better understanding of how adult neurogenesis is influenced by PCD will help lead to important insights relevant to brain health and diseases.

The Spinal Ependymal Layer in Health and Disease

Ependymal cells are epithelial support cells that line the central canal and ventricular cavities of the central nervous system, providing the interface between the cerebrospinal fluid and the parenchyma of the brain and spinal cord. The spinal ependymal layer (SEL) is composed of 3 main cell types: tanycytes, ependymocytes, and cerebrospinal fluid-contacting neurons. A fourth cell type, termed the supraependymal cell, is also occasionally described. Cells of the SEL show restricted proliferative capacity in health but display neural stem cell properties both in vitro and in vivo in various disease states. A growing body of literature is devoted to the regenerative roles of the SEL, particularly in the context of spinal cord injury, where mechanical damage to the spinal cord leads to a significant increase in SEL proliferation. SEL-derived cell progeny migrate to sites of injury within the injured spinal cord parenchyma and contribute primarily to glial scar formation. In additional to their role as endogenous neural stem cells, cells of the SEL may be an important source of cytokines and other cell signaling molecules, such as tumor necrosis factor, heat shock proteins, and various growth factors. The SEL has become of recent interest to neuroscience researchers because of its potential to participate in and respond to diseases affecting the spinal cord (eg, traumatic spinal cord injury) and neurodegenerative disease. The intimate association of the SEL with the cerebrospinal fluid makes intrathecal therapies a viable option, and recent studies highlight the potential promise of treatments that augment SEL responses to disease.

Functionalized collagen scaffold implantation and cAMP administration collectively facilitate spinal cord regeneration

Previous studies have demonstrated that several mechanisms, including numerous inhibitory molecules, weak neurotrophic stimulation and deficient intrinsic regenerative responses, collectively contribute to the failure of mature spinal cord axon regeneration. Thus, combinatorial therapies targeting multiple mechanisms have attracted much attention. In the present study, a porous collagen scaffold was used to support neuronal attachment and bridge axonal regeneration. The scaffold was specifically functionalized using neutralizing proteins (CBD-EphA4LBD, CBD-PlexinB1LBD and NEP1-40) and collagen-binding neurotrophic factors (CBD-BDNF and CBD-NT3) to simultaneously antagonize myelin inhibitory molecules (ephrinB3, Sema4D and Nogo) and exert neurotrophic protection and stimulation. Cerebellar granular neurons cultured on the functionalized collagen scaffold promoted neurite outgrowth in the presence of myelin. Furthermore, a full combinatorial treatment comprising functionalized scaffold implantation and cAMP administration was developed to evaluate the synergistic repair ability in a rat T10 complete removal spinal cord injury model. The results showed that full combinatorial therapy exhibited the greatest advantage in reducing the volume of cavitation, facilitating axonal regeneration, and promoting neuronal generation. The newborn neurons generated in the lesion area could form the neuronal relay and enhance the locomotion recovery after severe spinal cord injury.

STATEMENT OF SIGNIFICANCE

A porous collagen scaffold was specifically functionalized with neutralizing proteins and neurotrophic factors to antagonize the myelin inhibitory molecules and exert neurotrophic protection and stimulation for spinal cord regeneration. Cerebellar granular neurons seeded on the functionalized collagen scaffold showed enhanced neurite outgrowth ability in vitro. The functionalized scaffold implantation combined with cAMP administration exhibited synergistic repair ability for rat T10 complete spinal cord transection injury.

Applications of the Keap1-Nrf2 system for gene and cell therapy

Oxidative stress has been implicated to play a role in a number of acute and chronic diseases including acute injuries of the central nervous system, neurodegenerative and cardiovascular diseases, and cancer. The redox-activated transcription factor Nrf2 has been shown to protect many different cell types and organs from a variety of toxic insults, whereas in many cancers, unchecked Nrf2 activity increases the expression of cytoprotective genes and, consequently, provides growth advantage to cancerous cells. Herein, we discuss current preclinical gene therapy approaches to either increase or decrease Nrf2 activity with a special reference to neurological diseases and cancer. In addition, we discuss the role of Nrf2 in stem cell therapy for neurological disorders.

The Granulocyte-colony stimulating factor has a dual role in neuronal and vascular plasticity

Granulocyte-colony stimulating factor (G-CSF) is a growth factor that has originally been identified several decades ago as a hematopoietic factor required mainly for the generation of neutrophilic granulocytes, and is in clinical use for that. More recently, it has been discovered that G-CSF also plays a role in the brain as a growth factor for neurons and neural stem cells, and as a factor involved in the plasticity of the vasculature. We review and discuss these dual properties in view of the neuroregenerative potential of this growth factor.

The ependymal region of the adult human spinal cord differs from other species and shows ependymoma-like features

Several laboratories have described the existence of undifferentiated precursor cells that may act like stem cells in the ependyma of the rodent spinal cord. However, there are reports showing that this region is occluded and disassembled in humans after the second decade of life, although this has been largely ignored or interpreted as a post-mortem artefact. To gain insight into the patency, actual structure, and molecular properties of the adult human spinal cord ependymal region, we followed three approaches: (i) with MRI, we estimated the central canal patency in 59 control subjects, 99 patients with traumatic spinal cord injury, and 26 patients with non-traumatic spinal cord injuries. We observed that the central canal is absent from the vast majority of individuals beyond the age of 18 years, gender-independently, throughout the entire length of the spinal cord, both in healthy controls and after injury; (ii) with histology and immunohistochemistry, we describe morphological properties of the non-lesioned ependymal region, which showed the presence of perivascular pseudorosettes, a common feature of ependymoma; and (iii) with laser capture microdissection, followed by TaqMan® low density arrays, we studied the gene expression profile of the ependymal region and found that it is mainly enriched in genes compatible with a low grade or quiescent ependymoma (53 genes); this region is enriched only in 14 genes related to neurogenic niches. In summary, we demonstrate here that the central canal is mainly absent in the adult human spinal cord and is replaced by a structure morphologically and molecularly different from that described for rodents and other primates. The presented data suggest that the ependymal region is more likely to be reminiscent of a low-grade ependymoma. Therefore, a direct translation to adult human patients of an eventual therapeutic potential of this region based on animal models should be approached with caution.

OCAM regulates embryonic spinal cord stem cell proliferation by modulating ErbB2 receptor

The proliferation and differentiation of neural stem cells are tightly controlled by intrinsic and extrinsic cues. Cell adhesion molecules are increasingly recognized as regulators of these processes. Here we report the expression of the olfactory cell adhesion molecule (OCAM/NCAM2/RNCAM) during mouse spinal cord development and in neural stem cells cultured as neurospheres. OCAM is also weakly expressed in the dormant adult stem cell niche around the central canal and is overexpressed after spinal cord injury. Both transmembrane (TM) and glycosylphosphatidylinositol (GPI)-linked isoforms are present in neurospheres. Electron microscopy and internalisation experiments revealed a dynamic trafficking of OCAM between the membrane and intracellular compartments. After differentiation, OCAM remains in neurons and oligodendrocytes whereas no expression is detected in astrocytes. Using OCAM knockout (KO) mice, we found that mutant spinal cord stem cells showed an increased proliferation and self-renewal rates although no effect on differentiation was observed. This effect was reversed by lentivirus-mediated re-introduction of OCAM. Mechanistically, we identified the ErbB2/Neu/HER2 protein as being implicated in the enhanced proliferation of mutant cells. ErbB2 protein expression and phosphorylation level were significantly increased in KO cells whereas no difference was observed at the mRNA level. Overexpression of ErbB2 in wild-type and mutant cells also increased their growth while reintroduction of OCAM in mutant cells reduced the level of phosphorylated ErbB2. These results indicate that OCAM exerts a posttranscriptional control on the ErbB2 signalling in spinal cord stem cells. This study adds further support for considering cell adhesion molecules as regulators of the ErbB signalling.

Lin41/Trim71 is essential for mouse development and specifically expressed in postnatal ependymal cells of the brain

Lin41/Trim71 is a heterochronic gene encoding a member of the Trim-NHL protein family, and is the original, genetically defined target of the microRNA let-7 in C. elegans. Both the LIN41 protein and multiple regulatory microRNA binding sites in the 3′ UTR of the mRNA are highly conserved from nematodes to humans. Functional studies have described essential roles for mouse LIN41 in embryonic stem cells, cellular reprogramming and the timing of embryonic neurogenesis. We have used a new gene trap mouse line deficient in Lin41 to characterize Lin41 expression during embryonic development and in the postnatal central nervous system (CNS). In the embryo, Lin41 is required for embryonic viability and neural tube closure. Nevertheless, neurosphere assays suggest that Lin41 is not required for adult neurogenesis. Instead, we show that Lin41 promoter activity and protein expression in the postnatal CNS is restricted to ependymal cells lining the walls of the four ventricles. We use ependymal cell culture to confirm reestablishment of Lin41 expression during differentiation of ependymal progenitors to post-mitotic cells possessing motile cilia. Our results reveal that terminally differentiated ependymal cells express Lin41, a gene to date associated with self-renewing stem cells.

Neurogenic potential of spinal cord organotypic culture

There are several neurogenic niches in the adult mammalian central nervous system. In the central nervous system, neural stem cells (NSC) localize not only to the periventricular area, but are also diffusely distributed in the parenchyma. Here, we assessed neurogenic potential of organotypic cultures prepared from adult mouse spinal cord. Slices were placed on Millipore inserts for organotypic culture and incubated in neurobasal media supplemented with B27 and N2 for up to 9 weeks. After 3-4 weeks, the cell's aggregates formed in the slices. The aggregate's cells were BrdU-uptake, nestin and alkaline phosphatase positive. At the later stage of incubation, we observed Oct3/4 in the inner mass of the neurospheres as well as expression of Dppa1, which is an Oct-4 downstream target gene and a marker for pluripotency. To check differentiation, the formed neurospheres were isolated and cultured for several days in differentiation media. The obtained data demonstrated the cells from isolated neurospheres differentiate into astrocytes and MAP2-positive neurons. Immunostaining for HB9 and Lim2 revealed subsequent differentiation of MAP2-positive cells into motor neurons and interneurons, respectively. We hypothesized neuronal loss and/or long-term culturing of spinal cord slices may trigger a reset of the internal cell program and promote proliferation and further differentiation of NSC.

Time course of spinal doublecortin expression in developing rat and porcine spinal cord: implication in in vivo neural precursor grafting studies

Expression of doublecortin (DCX), a 43-53 kDa microtubule binding protein, is frequently used as (i) an early neuronal marker to identify the stage of neuronal maturation of in vivo grafted neuronal precursors (NSCs), and (ii) a neuronal fate marker transiently expressed by immature neurons during development. Reliable identification of the origin of DCX-immunoreactive cells (i.e., host vs. graft) requires detailed spatial and temporal mapping of endogenous DCX expression at graft-targeted brain or spinal cord regions. Accordingly, in the present study, we analyzed (i) the time course of DCX expression in pre- and postnatal rat and porcine spinal cord, and (ii) the DCX expression in spinally grafted porcine-induced pluripotent stem cells (iPS)-derived NSCs and human embryonic stem cell (ES)-derived NSCs. In addition, complementary temporospatial GFAP expression study in porcine spinal cord was also performed. In 21-day-old rat fetuses, an intense DCX immunoreactivity distributed between the dorsal horn (DH) and ventral horn was seen and was still present in the DH neurons on postnatal day 20. In animals older than 8 weeks, no DCX immunoreactivity was seen at any spinal cord laminae. In contrast to rat, in porcine spinal cord (gestational period 113-114 days), DCX was only expressed during the pre-natal period (up to 100 days) but was no longer present in newborn piglets or in adult animals. Immunohistochemical analysis was confirmed with a comparable expression profile by western blot analysis. Contrary, the expression of porcine GFAP started within 70-80 days of the pre-natal period. Spinally grafted porcine iPS-NSCs and human ES-NSCs showed clear DCX expression at 3-4 weeks postgrafting. These data indicate that in spinal grafting studies which employ postnatal or adult porcine models, the expression of DCX can be used as a reliable marker of grafted neurons. In contrast, if grafted neurons are to be analyzed during the first 4 postnatal weeks in the rat spinal cord, additional markers or grafted cell-specific labeling techniques need to be employed to reliably identify grafted early postmitotic neurons and to differentiate the DCX expression from the neurons of the host.

Central nervous system regenerative failure: role of oligodendrocytes, astrocytes, and microglia

Animal studies are now showing the exciting potential to achieve significant functional recovery following central nervous system (CNS) injury by manipulating both the inefficient intracellular growth machinery in neurons, as well as the extracellular barriers, which further limit their regenerative potential. In this review, we have focused on the three major glial cell types: oligodendrocytes, astrocytes, and microglia/macrophages, in addition to some of their precursors, which form major extrinsic barriers to regrowth in the injured CNS. Although axotomized neurons in the CNS have, at best, a limited capacity to regenerate or sprout, there is accumulating evidence that even in the adult and, especially after boosting their growth motor, neurons possess the capacity for considerable circuit reorganization and even lengthy regeneration when these glial obstacles to neuronal regrowth are modified, eliminated, or overcome.

Finding degrees of separation: experimental approaches for astroglial and oligodendroglial cell isolation and genetic targeting

The study of CNS glial cell function requires experimental methods to detect, purify, and manipulate each cell population with fidelity and specificity. With the identification and cloning of cell- and stage-specific markers, glial cell analysis techniques have grown beyond physical methods of tissue dissociation and cell culture, and become highly specific with immunoselection of cell cultures in vitro and genetic targeting in vivo. The unique plasticity of glial cells offers the potential for cell replacement therapies in neurological disease that utilize neural cells derived from transplanted neural stem and progenitor cells. In this mini-review, we outline general physical and genetic approaches for macroglial cell generation. We summarize cell culture methods to obtain astrocytes and oligodendrocytes and their precursors, from developing and adult tissue, as well as approaches to obtain human neural progenitor cells through the establishment of stem cells. We discuss popular targeting rodent strains designed for cell-specific detection, selection and manipulation of neuroglial cell progenitors and their committed progeny. Based on shared markers between astrocytes and stem cells, we discuss genetically modified mouse strains with overlapping expression, and highlight SOX-expressing strains available for targeting of stem and progenitor cell populations. We also include recently established mouse strains for detection, and tag-assisted RNA and miRNA analysis. This discussion aims to provide a brief overview of the rapidly expanding collection of experimental approaches and genetic resources for the isolation and targeting of macroglial cells, their sources, progeny and gene products to facilitate our understanding of their properties and potential application in pathology.

ERK1/2 pathway-mediated differentiation of IGF-1-transfected spinal cord-derived neural stem cells into oligodendrocytes

Spinal cord injury (SCI) is a devastating event that causes substantial morbidity and mortality, for which no fully restorative treatments are available. Stem cells transplantation offers some promise in the restoration of neurological function but with limitations. Insulin-like growth factor 1 (IGF-1) is a well-appreciated neuroprotective factor that is involved with various aspects of neural cells. Herein, the IGF-1 gene was introduced into spinal cord-derived neural stem cells (NSCs) and expressed steadily. The IGF-1-transfected NSCs exhibited higher viability and were promoted to differentiate into oligodendrocytes. Moreover, the most possible underlying mechanism, through which IGF-1 exerted its neuroprotective effects, was investigated. The result revealed that the differentiation was mediated by the IGF-1 activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and its downstream pathway. These findings provide the evidence for revealing the therapeutic merits of IGF-1-modified NSCs for SCI.

Plastic changes in the spinal cord in motor neuron disease

In the present paper, we analyze the cell number within lamina X at the end stage of disease in a G93A mouse model of ALS; the effects induced by lithium; the stem-cell like phenotype of lamina X cells during ALS; the differentiation of these cells towards either a glial or neuronal phenotype. In summary we found that G93A mouse model of ALS produces an increase in lamina X cells which is further augmented by lithium administration. In the absence of lithium these nestin positive stem-like cells preferentially differentiate into glia (GFAP positive), while in the presence of lithium these cells differentiate towards a neuron-like phenotype (βIII-tubulin, NeuN, and calbindin-D28K positive). These effects of lithium are observed concomitantly with attenuation in disease progression and are reminiscent of neurogenetic effects induced by lithium in the subependymal ventricular zone of the hippocampus.

Central canal ependymal cells proliferate extensively in response to traumatic spinal cord injury but not demyelinating lesions

The adult mammalian spinal cord has limited regenerative capacity in settings such as spinal cord injury (SCI) and multiple sclerosis (MS). Recent studies have revealed that ependymal cells lining the central canal possess latent neural stem cell potential, undergoing proliferation and multi-lineage differentiation following experimental SCI. To determine whether reactive ependymal cells are a realistic endogenous cell population to target in order to promote spinal cord repair, we assessed the spatiotemporal dynamics of ependymal cell proliferation for up to 35 days in three models of spinal pathologies: contusion SCI using the Infinite Horizon impactor, focal demyelination by intraspinal injection of lysophosphatidylcholine (LPC), and autoimmune-mediated multi-focal demyelination using the active experimental autoimmune encephalomyelitis (EAE) model of MS. Contusion SCI at the T9-10 thoracic level stimulated a robust, long-lasting and long-distance wave of ependymal proliferation that peaked at 3 days in the lesion segment, 14 days in the rostral segment, and was still detectable at the cervical level, where it peaked at 21 days. This proliferative wave was suppressed distal to the contusion. Unlike SCI, neither chemical- nor autoimmune-mediated demyelination triggered ependymal cell proliferation at any time point, despite the occurrence of demyelination (LPC and EAE), remyelination (LPC) and significant locomotor defects (EAE). Thus, traumatic SCI induces widespread and enduring activation of reactive ependymal cells, identifying them as a robust cell population to target for therapeutic manipulation after contusion; conversely, neither demyelination, remyelination nor autoimmunity appears sufficient to trigger proliferation of quiescent ependymal cells in models of MS-like demyelinating diseases.

Retinal stem cells and regeneration of vision system

The vertebrate retina is a well-characterized model for studying neurogenesis. Retinal neurons and glia are generated in a conserved order from a pool of mutlipotent progenitor cells. During retinal development, retinal stem/progenitor cells (RPC) change their competency over time under the influence of intrinsic (such as transcriptional factors) and extrinsic factors (such as growth factors). In this review, we summarize the roles of these factors, together with the understanding of the signaling pathways that regulate eye development. The information about the interactions between intrinsic and extrinsic factors for retinal cell fate specification is useful to regenerate specific retinal neurons from RPCs. Recent studies have identified RPCs in the retina, which may have important implications in health and disease. Despite the recent advances in stem cell biology, our understanding of many aspects of RPCs in the eye remains limited. PRCs are present in the developing eye of all vertebrates and remain active in lower vertebrates throughout life. In mammals, however, PRCs are quiescent and exhibit very little activity and thus have low capacity for retinal regeneration. A number of different cellular sources of RPCs have been identified in the vertebrate retina. These include PRCs at the retinal margin, pigmented cells in the ciliary body, iris, and retinal pigment epithelium, and Müller cells within the retina. Because PRCs can be isolated and expanded from immature and mature eyes, it is possible now to study these cells in culture and after transplantation in the degenerated retinal tissue. We also examine current knowledge of intrinsic RPCs, and human embryonic stems and induced pluripotent stem cells as potential sources for cell transplant therapy to regenerate the diseased retina.