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

Purification of immature neuronal cells from neural stem cell progeny

Large-scale proliferation and multi-lineage differentiation capabilities make neural stem cells (NSCs) a promising renewable source of cells for therapeutic applications. However, the practical application for neuronal cell replacement is limited by heterogeneity of NSC progeny, relatively low yield of neurons, predominance of astrocytes, poor survival of donor cells following transplantation and the potential for uncontrolled proliferation of precursor cells. To address these impediments, we have developed a method for the generation of highly enriched immature neurons from murine NSC progeny. Adaptation of the standard differentiation procedure in concert with flow cytometry selection, using scattered light and positive fluorescent light selection based on cell surface antibody binding, provided a near pure (97%) immature neuron population. Using the purified neurons, we screened a panel of growth factors and found that bone morphogenetic protein-4 (BMP-4) demonstrated a strong survival effect on the cells in vitro, and enhanced their functional maturity. This effect was maintained following transplantation into the adult mouse striatum where we observed a 2-fold increase in the survival of the implanted cells and a 3-fold increase in NeuN expression. Additionally, based on the neural-colony forming cell assay (N-CFCA), we noted a 64 fold reduction of the bona fide NSC frequency in neuronal cell population and that implanted donor cells showed no signs of excessive or uncontrolled proliferation. The ability to provide defined neural cell populations from renewable sources such as NSC may find application for cell replacement therapies in the central nervous system.

Study of the efficiency of transplantation of human neural stem cells to rats with spinal trauma: the use of functional load tests and BBB test

Human ensheating neural stem cells of the olfactory epithelium were transplanted to adult male rats immediately after contusion trauma of the spinal cord at T9 level rostrally and caudally to the injury. Voluntary movements (by a 21-point BBB scale), rota-rod performance, and walking along a narrowing beam were monitored weekly over 60 days. In rats receiving cell transplantation, the mean BBB score significantly increased by 11% by the end of the experiment. The mean parameters of load tests also regularly surpassed the corresponding parameters in controls. The efficiency of transplantation (percent of animals with motor function recovery parameters surpassing the corresponding mean values in the control groups) was 62% by the state of voluntary motions, 37% by the rota-rod test, and 32% by the narrowing beam test. Morphometry revealed considerable shrinking of the zone of traumatic damage in the spinal cord and activation of posttraumatic remyelination in animals receiving transplantation of human neural stem cells.

Oligodendrocyte fate after spinal cord injury

Oligodendrocytes (OLs) are particularly susceptible to the toxicity of the acute lesion environment after spinal cord injury (SCI). They undergo both necrosis and apoptosis acutely, with apoptosis continuing at chronic time points. Loss of OLs causes demyelination and impairs axon function and survival. In parallel, a rapid and protracted OL progenitor cell proliferative response occurs, especially at the lesion borders. Proliferating and migrating OL progenitor cells differentiate into myelinating OLs, which remyelinate demyelinated axons starting at 2 weeks post-injury. The progression of OL lineage cells into mature OLs in the adult after injury recapitulates development to some degree, owing to the plethora of factors within the injury milieu. Although robust, this endogenous oligogenic response is insufficient against OL loss and demyelination. First, in this review we analyze the major spatial-temporal mechanisms of OL loss, replacement, and myelination, with the purpose of highlighting potential areas of intervention after SCI. We then discuss studies on OL protection and replacement. Growth factors have been used both to boost the endogenous progenitor response, and in conjunction with progenitor transplantation to facilitate survival and OL fate. Considerable progress has been made with embryonic stem cell-derived cells and adult neural progenitor cells. For therapies targeting oligogenesis to be successful, endogenous responses and the effects of the acute and chronic lesion environment on OL lineage cells must be understood in detail, and in relation, the optimal therapeutic window for such strategies must also be determined.

Induction of human bone marrow mesenchymal stem cells differentiation into neural-like cells using cerebrospinal fluid

To optimize a technique that induces bone marrow mesenchymal stem cells (BMSCs) to differentiation into neural-like cells, using cerebrospinal fluid (CSF) from the patient. In vitro, CSF (Group A) and the cell growth factors EGF and bFGF (Group B) were used to induce BMSCs to differentiate into neural-like cells. Post-induction, presence of neural-like cells was confirmed through the use of light and immunofluorescence microscopy. BMSCs can be induced to differentiate into neural-like cells. The presence of neural-like cells was confirmed via morphological characteristics, phenotype, and biological properties. Induction using CSF can shorten the production time of neural-like cells and the quantity is significantly higher than that obtained by induction with growth factor (P < 0.01). The two induction methods can induce BMSCs to differentiate into neural-like cells. Using CSF induction, 30 ml bone marrow can produce a sufficient number of neural-like cells that totally meet the requirements for clinical treatment.

Optimal location and time for neural stem cell transplantation into transected rat spinal cord

Implanted neural stem cells (NSC) could improve neurological functions following spinal cord injury (SCI), but the optimal conditions for NSC transplantation are largely unknown, especially in transected spinal cord. This study investigated the effect and fate of NSC engrafted into spinal cords at different locations and time points following T(9) spinal cord transection. Engrafted NSC could survive and migrate in host spinal cords. Significant improvement in hindlimb locomotor functions associated with NSC survival was found in rats receiving NSC transplantation in the spinal cords rostral to the transection site at the subacute stage (7 days post operation), compared with those caudal to the transection site at the acute stage (at the time of injury). At 4 weeks post operation, CD68 immunohistochemical staining confirmed that macrophages were less in rostrally transplanted sites and in subacute groups than seen in caudal and acute transplanted rats. The present findings indicated that NSC transplantation into spinal cords rostral to transection site at the subacute stage is an optimal strategy for engrafted NSC survival and host behavioral improvement. It therefore would be available to the usage of NSC for the treatment of SCI in the future clinic trial.

Nestin-GFP transgene reveals neural precursor cells in adult skeletal muscle

BACKGROUND

Therapy for neural lesions or degenerative diseases relies mainly on finding transplantable active precursor cells. Identifying them in peripheral tissues accessible for biopsy, outside the central nervous system, would circumvent the serious immunological and ethical concerns impeding cell therapy.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we isolated neural progenitor cells in cultured adult skeletal muscle from transgenic mice in which nestin regulatory elements control GFP expression. These cells also expressed the early neural marker Tuj1 and light and heavy neurofilament but not S100β, indicating that they express typical neural but not Schwann cell markers. GFP+/Tuj1+ cells were also negative for the endothelial and pericyte markers CD31 and α-smooth muscle actin, respectively. We established their a) functional response to glutamate in patch-clamp recordings; b) interstitial mesenchymal origin; c) replicative capacity; and d) the environment necessary for their survival after fluorescence-activated cell sorting.

CONCLUSIONS/SIGNIFICANCE

We propose that the decline in nestin-GFP expression in muscle progenitor cells and its persistence in neural precursor cells in muscle cultures provide an invaluable tool for isolating a population of predifferentiated neural cells with therapeutic potential.

Cellular and paracellular transplants for spinal cord injury: a review of the literature

BACKGROUND

Experimental approaches to limit the spinal cord injury and to promote neurite outgrowth and improved function from a spinal cord injury have exploded in recent decades. Due to the cavitation resulting after a spinal cord injury, newer important treatment strategies have consisted of implanting scaffolds with or without cellular transplants. There are various scaffolds, as well as various different cellular transplants including stem cells at different levels of differentiation, Schwann cells and peripheral nerve implants, that have been reviewed. Also, attention has been given to different re-implantation techniques in avulsion injuries.

METHODS

Using standard search engines, this literature is reviewed.

CONCLUSION

Cellular and paracellular transplantation for application to spinal cord injury offers promising results for those patients with spinal cord pathology.

Neurite outgrowth of neural progenitors in presence of inhibitory proteoglycans

Attempts to promote host regeneration after spinal cord injury (SCI) have often resulted in poor axon extension due to formation of a glial scar, which creates a dense physical barrier around the injury and contains molecules that inhibit regeneration and repair of adult injured axons. Previous studies have shown that, while transplants of multipotent neural stem cells (NSC) integrate poorly in the injury site, the use of neuronal-restricted precursor cells (NRP) together with glial-restricted precursor cells (GRP) allow differentiation and integration of neurons, possibly because NRP are able to overcome chondroitin sulfate proteoglycan (CSPG) inhibition. To investigate this possibility, we grew mixed cultures of NRP/GRP on CSPG at inhibitory concentrations, using embryonic hippocampal cultures as controls. We found that NRP/GRP grown on CSPG survive and differentiate into neurons with no significant changes in neurite length, relative to growth on control polylysine substrate, and in contrast to a significant inhibition of axon growth in hippocampal cultures grown on CSPG-coated substrate. There was, however, a significant decrease in neurite number and branching in both cultures, indicating that CSPG also has important effects on neuronal morphology. These data suggest that embryonic neurons supported by glial cells derived from NRP/GRP transplants are less sensitive to inhibitory effects of CSPG in the glial scar, and are thus an appropriate source for neuronal cell replacement and reconnection of damaged circuits after SCI.

Comparative study of methods for administering neural stem/progenitor cells to treat spinal cord injury in mice

To investigate potential cures for spinal cord injury (SCI), several researchers have transplanted neural stem/progenitor cells (NS/PCs) into the injured spinal cord by different procedures, including intralesional (IL), intrathecal (IT), and intravenous (IV) injection. However, there are no reports quantifying or comparing the number of cells successfully transplanted to the lesion site by each procedure in vivo. The purpose of the present study was to determine the optimal method of cell transplantation to the SCI site in terms of grafted cell survival and safety. For this purpose, we developed mouse NS/PCs that expressed a novel Venus-luciferase fusion protein that enabled us to detect a minimum of 1,000 grafted cells in vivo by bioluminescence imaging (BLI). After inducing contusive SCI at the T10 level in mice, NS/PCs were transplanted into the injured animals three different ways: by IL, IT, or IV injection. Six weeks after the transplantation, BLI analysis showed that in the IL group, the luminescence intensity of the grafted cells had decreased to about 10% of its initial level, and appeared at the site of injury. In the IT group, the luminescence of the grafted cells, which was distributed throughout the entire subarachnoid space immediately after transplantation, was detected at the injured site 1 week later, and by 6 weeks had gradually decreased to about 0.3% of its initial level. In the IV group, no grafted cells were detected at the site of injury, but all of these mice showed luminescence in the bilateral chest, suggesting pulmonary embolism. In addition, one third of these mice died immediately after the IV injection. In terms of grafted cell survival and safety, we conclude that the IL application of NS/PCs is the most effective and feasible method for transplanting NS/PCs into the SCI site.

Embryonic stem cells inhibit expression of erythropoietin in the injured spinal cord

Recent observations have demonstrated neuroprotective role of erythropoietin (Epo) and Epo receptor in the central nervous system. Here we examined Epo function in the murine spinal cord after transplantation of pluripotent mouse embryonic stem (ES) cells pre-differentiated towards neuronal type following spinal cord injury. Expression of Epo was measured at both mRNA and protein levels in the ES cells as well as in the spinal cords after 1 and 7 days. Our data demonstrated that expression of Epo mRNA, as well as its protein content, in ES cells was significantly decreased after differentiation procedure. In the spinal cords, analysis showed that Epo mRNA level was significantly decreased after 1 day of ES cell injections in comparison to media-injected control. Epo protein level detected by Western blot was diminished as well. Examination of Epo production in the injured spinal cords after media or ES cells injections by indirect immunofluorescence showed increased Epo-immunopositive staining after media injections 1 day after injection. In contrast, ES cell transplantation did not induce Epo expression. Seven days after ES cell injections, Epo-immunopositive cells' distribution in the ipsilateral side was not changed, while the intensity of immunostaining on the contralateral side was increased, approaching levels in control media-injected tissues. Our data let us to presume that previously described immediate positive effects of ES cells injected into the injured zone of spinal cord are not based on Epo, but on other factors or hormones, which should be elucidated further.

Tissue-engineered fibrin scaffolds containing neural progenitors enhance functional recovery in a subacute model of SCI

Two recurring problems with stem/neural progenitor cell (NPC) transplantation therapies for spinal cord injury (SCI) are poor cell survival and uncontrolled cell differentiation. The current study evaluated the viability and differentiation of embryonic stem cell-derived neural progenitor cells (ESNPCs) transplanted within fibrin scaffolds containing growth factors (GFs) and a heparin-binding delivery system (HBDS) to enhance cell survival and direct differentiation into neurons. Mouse ESNPCs were generated from mouse embryonic stem cells (ESCs) using a 4-/4+ retinoic acid (RA) induction protocol that resulted in a population of cells that was 70% nestin positive NPCs. The ESNPCs were transplanted directly into a rat subacute dorsal hemisection lesion SCI model. ESNPCs were either encapsulated in a fibrin scaffold; encapsulated in fibrin containing the HBDS, neurotrophin-3 (NT-3) and platelet derived growth factor (PDGF-AA); or encapsulated in fibrin scaffolds with NT-3 and PDGF-AA without the HBDS. We report that the combination of GFs and fibrin scaffold (without HBDS) enhanced the total number of ESNPCs present in the treated spinal cords and increased the number of ESNPC-derived NeuN positive neurons 8 weeks after transplantation. All experimental groups treated with ESNPCs exhibited an increase in behavioral function 4 weeks after transplantation. In a subset of animals, the ESNPCs over-proliferated as evidenced by SSEA-1 positive/Ki67 positive ESCs found at 4 and 8 weeks. These results demonstrate the potential of tissue-engineered fibrin scaffolds to enhance the survival of NPCs and highlight the need to purify cell populations used in therapies for SCI.

Organotypic spinal cord slice culture to study neural stem/progenitor cell microenvironment in the injured spinal cord

The molecular microenvironment of the injured spinal cord does not support survival and differentiation of either grafted or endogenous NSCs, restricting the effectiveness of the NSC-based cell replacement strategy. Studying the biology of NSCs in in vivo usually requires a considerable amount of time and cost, and the complexity of the in vivo system makes it difficult to identify individual environmental factors. The present study sought to establish the organotypic spinal cord slice culture that closely mimics the in vivo environment. The cultured spinal cord slices preserved the cytoarchitecture consisting of neurons in the gray matter and interspersed glial cells. The majority of focally applied exogenous NSCs survived up to 4 weeks. Pre-exposure of the cultured slices to a hypoxic chamber markedly reduced the survival of seeded NSCs on the slices. Differentiation into mature neurons was severely limited in this co-culture system. Endogenous neural progenitor cells were marked by BrdU incorporation, and applying an inflammatory cytokine IL-1β significantly increased the extent of endogenous neural progenitors with the oligodendrocytic lineage. The present study shows that the organotypic spinal cord slice culture can be properly utilized to study molecular factors from the post-injury microenvironment affecting NSCs in the injured spinal cord.

Pre-differentiated embryonic stem cells promote neuronal regeneration by cross-coupling of BDNF and IL-6 signaling pathways in the host tissue

The mechanism of embryonic stem (ES) cell therapeutic action remains far from being elucidated. Our recent report has shown that transplantation of ES cells, predifferentiated into neuronal progenitors, prevented appearance of chronic pain behaviors in mice after experimentally induced spinal cord injury. In the current study, we tested the hypothesis that this beneficial effect is mediated by antiapoptotic and regenerative signaling pathways activated in the host tissue by transplanted ES cells. Spinal cord injury was induced by unilateral microinjections of quisqualic acid at spinal levels T12-L2. At 1 week after injury, the pre-differentiated towards neuronal phenotype ES cells were transplanted into the site of injury. Here we show that transplantation of pre-differentiated ES cells activate both brain-derived neurotrophic factor (BDNF) and interleukin-6 (IL-6) signaling pathways in the host tissue, leading to activation of cAMP/PKA, phosporylation of cofilin and synapsin I, and promoting regenerative growth and neuronal survival.

Differentiation of neural precursor cell-derived oligodendrocyte progenitor cells following transplantation into normal and injured spinal cords

Demyelination contributes to the functional deficits after spinal cord injury (SCI). Therefore, remyelination may be an important strategy to facilitate repair after SCI. Oligodendrocyte precursor cells (OPCs) are immature oligodendrocytes and can differentiate into myelin-forming cells of central nervous system under certain conditions. OPC transplantation is an attractive approach for the treatment of demyelinating diseases. In this study, we transplanted OPCs expressing green fluorescent protein (GFP-OPCs) into normal and injured rat spinal cords to evaluate the differentiation of transplanted OPCs in vivo. Unfortunately, the grafted GFP-OPCs, in spinal cord whether normal or injured, were all differentiated into astrocytes, but not oligodendrocytes. Our further study indicated that inflammatory environment might not be the key factor influencing the differentiation of OPCs. Some spinal cord components, such as bone morphogenetic proteins (BMPs), were the major factors that induced OPCs to differentiate into astrocytes. The three types of BMP receptor (BMPRIA, IB and II) could all be detected in OPCs, and the astroglial differentiation of OPCs induced by spinal cord homogenate extract (SCHE) in vitro could be blocked partly by noggin, an antagonist of BMP. These results suggested that the BMPR signal transduction pathway might be one of the key factors which determine the differentiation direction of engrafted OPCs in spinal cord.

The effect of topology of chitosan biomaterials on the differentiation and proliferation of neural stem cells

Neural stem cells (NSCs) are capable of self-renewal and differentiation into three principle central nervous system cell types under specific local microenvironments. Chitosan films (Chi-F), chitosan porous scaffolds (Chi-PS) and chitosan multimicrotubule conduits (Chi-MC) were used to investigate their effects on the differentiation and proliferation of NSCs isolated from the cortices of fetal rats. In the presence of 10% fetal bovine serum most NSCs cultured on Chi-F differentiated into astrocytes, NSCs cultured on Chi-MC showed a significant increase in neuronal differentiation, while Chi-PS somewhat promoted NSCs to differentiate into neurons. However, in serum-free medium with 20 ng ml(-1) basic fibroblast growth factor NSCs cultured on Chi-F showed the greatest proliferation, NSCs cultured on Chi-MC showed moderate cell proliferation, but NSCs cultured on Chi-PS exhibited the least cell proliferation. These observations indicate that chitosan topology can play an important role in regulating differentiation and proliferation of NSCs and raise the possibility of the utilization of chitosan in various structural biomaterials in neural tissue engineering.

Diffusible, membrane-bound, and extracellular matrix factors from olfactory ensheathing cells have different effects on the self-renewing and differentiating properties of neural stem cells

Transplantation of olfactory ensheathing cells (OECs) has been a promising strategy in enhancing central nervous system (CNS) regeneration. However, little is known about the effects of transplanted OECs on the self-renewal, neurogenesis, and oligodendrogenesis of neural stem cells (NSCs), which are known to play a very important role in the repair of damaged CNS tissue. In this study, we investigated the influence of diffusible, membrane-bound, and extracellular matrix factors from OECs on the self-renewal and differentiation properties of NSCs. We found that diffusible factors from cultured OECs promoted self-renewal, whereas the extracellular matrix molecules from OECs increased neurogenesis and oligodendrogenesis of NSCs. Furthermore, we demonstrated that directly coculturing OECs and NSCs inhibited not only self-renewal but also neurogenesis and oligodendrogenesis of NSCs. We propose three models for the interaction between transplanted OECs and endogenous NSCs. Our findings provide new insight into the ability of OECs to promote CNS repair and also indicate potential targets for manipulation of these cells to enhance their restorative ability.

Transplantation of human glial-restricted neural precursors into injured spinal cord promotes functional and sensory recovery without causing allodynia

BACKGROUND AIMS

Traumatic injuries of the central nervous system cause damage and degeneration of specific cell populations with subsequent functional loss. Cell transplantation is a strategy to treat such injuries by replacing lost or damaged cell populations. Many kinds of cells are considered candidates for intraspinal transplantation. Human neural precursor cells (hNPC) derived from post-mortem fetal tissue are easy to isolate and expand, and are capable of producing large numbers of neuronal and glial cells. After transplantation into the nervous system, hNPC produce mature neural phenotypes and permit functional improvement in some models of neurodegenerative disease. In this study, we aimed to elucidate the therapeutic effect of different neuronal and glial progenitor populations of hNPC on locomotor and sensory functions of spinal cord-injured (SCI) rats.

METHODS

Different populations of progenitor cells were obtained from hNPC by cell sorting and neural induction, resulting in cell cultures that were NCAM(+) A2B5(+), NCAM(+) A2B5(-) or A2B5(+) NG2(+). These different cell populations were then tested for efficacy in repair of the injured spinal cord by transplantation into rats with SCI.

RESULTS

The A2B5(+) NG2(+) population of hNPC significantly improved locomotor and sensory (hindlimb) functional recovery of SCI rats. Importantly, no abnormal pain responses were observed in the forelimbs following transplantation.

CONCLUSIONS

This treatment approach can improve functional recovery after SCI without causing allodynia. Further studies will be conducted to investigate the ability of A2B5(+) NG2(+) cells to survive, differentiate and integrate in the injured spinal cord.

Cell-mediated neuroprotection in a mouse model of human tauopathy

Tau protein in a hyperphosphorylated state makes up the intracellular inclusions of several neurodegenerative diseases, including Alzheimer's disease and cases of frontotemporal dementia. Mutations in Tau cause familial forms of frontotemporal dementia, establishing that dysfunction of tau protein is sufficient to cause neurodegeneration and dementia. Transgenic mice expressing human mutant tau in neurons exhibit the essential features of tauopathies, including neurodegeneration and abundant filaments composed of hyperphosphorylated tau. Here we show that a previously described mouse line transgenic for human P301S tau exhibits an age-related, layer-specific loss of superficial cortical neurons, similar to what has been observed in human frontotemporal dementias. We also show that focal neural precursor cell implantation, resulting in glial cell differentiation, leads to the sustained rescue of cortical neurons. Together with evidence indicating that astrocyte transplantation may be neuroprotective, our findings suggest a beneficial role for glial cell-based repair in neurodegenerative diseases.

Optimal time point for neuronal generation of transplanted neural progenitor cells in injured spinal cord following root avulsion

Root avulsion of the brachial plexus results in a progressive and pronounced loss of motoneurons. Cell replacement strategies have therapeutic potential in the treatment of motoneuron degenerative neurological disorders. Here, we transplanted spinal cord-derived neural progenitor cells (NPCs) into the cervical ventral horn of adult rats immediately, 2 weeks, or 6 weeks after root avulsion to determine an optimal time scale for the survival and differentiation of grafted cells. We showed that grafted NPCs survived robustly at all three time points and there was no statistical difference in survival rate. Interestingly, however, transplantation at 2 weeks postavulsion significantly increased the neuronal differentiation of transplanted NPCs compared to transplantation immediately or at 6 weeks postavulsion. Moreover, only NPCs transplanted at 2 weeks postavulsion were able to differentiate into choline acetyltransferase (ChAT)-positive neurons. Specific ELISAs and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that expression levels of BDNF and GDNF were significantly upregulated in the ventral cord at 2 weeks postavulsion compared to immediately or at 6 weeks postavulsion. Our study suggests that the cervical ventral horn at 2 weeks postavulsion both supports neuronal differentiation and induces region-specific neuronal generation possibly because of its higher expression of BDNF and GDNF.

Human neural stem cells differentiate and promote locomotor recovery in an early chronic spinal cord injury NOD-scid mouse model

Background

Traumatic spinal cord injury (SCI) results in partial or complete paralysis and is characterized by a loss of neurons and oligodendrocytes, axonal injury, and demyelination/dysmyelination of spared axons. Approximately 1,250,000 individuals have chronic SCI in the U.S.; therefore treatment in the chronic stages is highly clinically relevant. Human neural stem cells (hCNS-SCns) were prospectively isolated based on fluorescence-activated cell sorting for a CD133⁺ and CD24^−/lo population from fetal brain, grown as neurospheres, and lineage restricted to generate neurons, oligodendrocytes and astrocytes. hCNS-SCns have recently been transplanted sub-acutely following spinal cord injury and found to promote improved locomotor recovery. We tested the ability of hCNS-SCns transplanted 30 days post SCI to survive, differentiate, migrate, and promote improved locomotor recovery.

Methods and Findings

hCNS-SCns were transplanted into immunodeficient NOD-scid mice 30 days post spinal cord contusion injury. hCNS-SCns transplanted mice demonstrated significantly improved locomotor recovery compared to vehicle controls using open field locomotor testing and CatWalk gait analysis. Transplanted hCNS-SCns exhibited long-term engraftment, migration, limited proliferation, and differentiation predominantly to oligodendrocytes and neurons. Astrocytic differentiation was rare and mice did not exhibit mechanical allodynia. Furthermore, differentiated hCNS-SCns integrated with the host as demonstrated by co-localization of human cytoplasm with discrete staining for the paranodal marker contactin-associated protein.

Conclusions

The results suggest that hCNS-SCns are capable of surviving, differentiating, and promoting improved locomotor recovery when transplanted into an early chronic injury microenvironment. These data suggest that hCNS-SCns transplantation has efficacy in an early chronic SCI setting and thus expands the “window of opportunity” for intervention.

Nogo-A expresses on neural stem cell surface

Nogo-A, as a myelin-associated molecule to inhibit axon regeneration in the injured adult central nervous system (CNS), has been detected to be enriched in numerous populations of cells in CNS. In this study, we found that Nogo-A was also expressed on the surface of neural stem cells (NSCs). The possible effects of NSCs-expressed Nogo-A on the NSC transplantation for CNS repair were discussed.

Transplantation of galectin-1-expressing human neural stem cells into the injured spinal cord of adult common marmosets

Delayed transplantation of neural stem/progenitor cells (NS/PCs) into the injured spinal cord can promote functional recovery in adult rats and monkeys. To enhance the functional recovery after NS/PC transplantation, we focused on galectin-1, a carbohydrate-binding protein with pleiotropic roles in cell growth, differentiation, apoptosis, and neurite outgrowth. Here, to determine the combined therapeutic effect of NS/PC transplantation and galectin-1 on spinal cord injury (SCI), human NS/PCs were transfected by lentivirus with galectin-1 and green fluorescent protein (GFP), (Gal-NS/PCs) or GFP alone (GFP-NS/PCs), expanded in vitro, and then transplanted into the spinal cord of adult common marmosets, 9 days after contusive cervical SCI. The animals' motor function was evaluated by their spontaneous motor activity, bar grip power, and performance on a treadmill test. Histological analyses revealed that the grafted human NS/PCs survived and differentiated into neurons, astrocytes, and oligodendrocytes. There were significant differences in the myelinated area, corticospinal fibers, and serotonergic fibers among the Gal-NS/PC, GFP-NS/PC, vehicle-control, and sham-operated groups. The Gal-NS/PC-grafted animals showed a better performance on all the behavioral tests compared with the other groups. These findings suggest that Gal-NS/PCs have better therapeutic potential than NS/PCs for SCI in nonhuman primates and that human Gal-NS/PC transplantation might be a feasible treatment for human SCI.

Comparative profiling of microRNA expression between neural stem cells and motor neurons in embryonic spinal cord in rat

Neural stem cells' transplantation has been proposed as a future therapy for spinal cord injury. The challenge is how to make proportionally more neural stem cells differentiate into spinal motor neurons. Recent reports reveal that microRNAs play an important role in regulating stem cell self-renewal and differentiation. The aim of this study was to compare the profiling of microRNA expression between neural stem cells and motor neurons and to find candidate targets that direct differentiation of neural stem cells into motor neurons. We performed a parallel isolation and purification of motor neurons and neural stem cells from the same rat embryonic spinal cord sample. With the high-throughput TaqMan low-density array platform, 44 differentially expressed microRNAs were identified (22 specially expressed microRNAs in motor neurons and neural stem cells, respectively). Using bioinformatic methods, clustering, transcriptional regulation and target genes of differential microRNAs were analyzed. Furthermore, miR-126 specially expressed in cultured motor neurons identified by TaqMan low-density array was significantly elevated in choline acetyltransferase-positive neurons differentiated from the neural stem cells. These findings suggest that specially expressed microRNAs may contribute to the directed differentiation of neural stem cells into motor neurons and are potential targets for therapeutic interventions following spinal cord injury.

Synergistic effect of neural stem cells and olfactory ensheathing cells on repair of adult rat spinal cord injury

Spinal cord injury (SCI) is a common clinical disease that places a heavy burden on families and society. Cellular therapy provides a method of giving a supplement of cells lost in the injury and promoting functional recovery after SCI. Neural stem cells (NSCs) and olfactory ensheathing cells (OECs) are two most promising cell types. NSCs have the potential of differentiating into neurons and glial cells, and OECs could help the axons of neurons pass through the glial scar to promote functional recovery. NSCs were isolated from the cortices of fetal rats on days 12-14 of embryonic development and OECs were isolated from the olfactory bulbs of adult rats. In vitro coculture studies demonstrated OECs could promote NSCs to differentiate into neurons. Four groups of rats that had been 3/4 spinal cord transectioned at T9 were injected with DMEM/F12 solution, NSCs, OECs, and NSCs + OECs, respectively, 7 days post-SCI. Twelve weeks postoperation, the hindlimb locomotor function of rats in the cotransplantation group was significantly improved compared with that in the other three groups. Histological observation and immunohistochemical staining of NF-200 both showed new nerve fibers across the injured region. Cotransplantation of NSCs and OECs might have a synergistic effect on promoting neural regeneration and improving the recovery of locomotion function. Cotransplantation of NSCs and OECs was better than a single graft of either NSCs or OECs. These findings have provided a new way of thinking in the treatment of SCI.

A systematic review of cellular transplantation therapies for spinal cord injury

Cell transplantation therapies have become a major focus in pre-clinical research as a promising strategy for the treatment of spinal cord injury (SCI). In this article, we systematically review the available pre-clinical literature on the most commonly used cell types in order to assess the body of evidence that may support their translation to human SCI patients. These cell types include Schwann cells, olfactory ensheathing glial cells, embryonic and adult neural stem/progenitor cells, fate-restricted neural/glial precursor cells, and bone-marrow stromal cells. Studies were included for review only if they described the transplantation of the cell substrate into an in-vivo model of traumatic SCI, induced either bluntly or sharply. Using these inclusion criteria, 162 studies were identified and reviewed in detail, emphasizing their behavioral effects (although not limiting the scope of the discussion to behavioral effects alone). Significant differences between cells of the same "type" exist based on the species and age of donor, as well as culture conditions and mode of delivery. Many of these studies used cell transplantations in combination with other strategies. The systematic review makes it very apparent that cells derived from rodent sources have been the most extensively studied, while only 19 studies reported the transplantation of human cells, nine of which utilized bone-marrow stromal cells. Similarly, the vast majority of studies have been conducted in rodent models of injury, and few studies have investigated cell transplantation in larger mammals or primates. With respect to the timing of intervention, nearly all of the studies reviewed were conducted with transplantations occurring subacutely and acutely, while chronic treatments were rare and often failed to yield functional benefits.

The effect of the dosage of NT-3/chitosan carriers on the proliferation and differentiation of neural stem cells

This study aimed to determine the optimal dosage range of NT-3 in the soluble form or loaded with chitosan carriers by using NT-3/chitosan carriers to support the survival and proliferation of neural stem cells (NSCs) and induce them to differentiate into desired phenotypes. NSCs were co-cultured with chitosan carriers loaded with different doses of NT-3. As the control, NSCs were cultured in the defined medium, into which were added different doses of NT-3 in the soluble form every day. The ELISA kit was used to study the NT-3 releasing kinetics, which showed that, in the initial co-culture stage from 1 h to 14 weeks, the chitosan carriers loaded with different doses of NT-3 released NT-3 stably and constantly. The 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was conducted to measure the cell viability, and the immunocytochemical methods were adopted to quantitatively analyze the phenotypes differentiating from the NSCs. Compared to the 100 ng NT-3 daily addition group (1400 ng over 14 days), the 25 ng, 50 ng and 200 ng NT-3 daily addition group showed dramatically shorter processes length and much lower differentiation percentage from NSCs into neurons. By contrast, the NT-3 (25 ng)-chitosan carriers group had not only higher cell viability, but also similar processes length and differentiation percentage from NSCs into neurons to the 100 ng NT-3 daily addition group. The method developed in this study significantly reduced the NT-3 amount required to support the survival, proliferation and differentiation of NSCs in vitro. Meanwhile, the chitosan carriers used here provided an ideal 3-dimensional scaffold for the adhesion, migration, proliferation and differentiation of NSC and the differentiated cells. Therefore, this method may open a new field for the large-scaled culture and amplification of NSCs in vitro to replace the lost neural cells, meanwhile lower the consumption of neurotrophic factors in the cell transplantation therapy of brain and spinal injury.

Cell Therapy From Bench to Bedside Translation in CNS Neurorestoratology Era

Recent advances in cell biology, neural injury and repair, and the progress towards development of neurorestorative interventions are the basis for increased optimism. Based on the complexity of the processes of demyelination and remyelination, degeneration and regeneration, damage and repair, functional loss and recovery, it would be expected that effective therapeutic approaches will require a combination of strategies encompassing neuroplasticity, immunomodulation, neuroprotection, neurorepair, neuroreplacement, and neuromodulation. Cell-based restorative treatment has become a new trend, and increasing data worldwide have strongly proven that it has a pivotal therapeutic value in CNS disease. Moreover, functional neurorestoration has been achieved to a certain extent in the CNS clinically. Up to now, the cells successfully used in preclinical experiments and/or clinical trial/treatment include fetal/embryonic brain and spinal cord tissue, stem cells (embryonic stem cells, neural stem/progenitor cells, hematopoietic stem cells, adipose-derived adult stem/precursor cells, skin-derived precursor, induced pluripotent stem cells), glial cells (Schwann cells, oligodendrocyte, olfactory ensheathing cells, astrocytes, microglia, tanycytes), neuronal cells (various phenotypic neurons and Purkinje cells), mesenchymal stromal cells originating from bone marrow, umbilical cord, and umbilical cord blood, epithelial cells derived from the layer of retina and amnion, menstrual blood-derived stem cells, Sertoli cells, and active macrophages, etc. Proof-of-concept indicates that we have now entered a new era in neurorestoratology.

From birth till death: neurogenesis, cell cycle, and neurodegeneration

Neurogenesis in the embryo involves many signaling pathways and transcriptional programs and an elaborate orchestration of cell cycle exit in differentiating precursors. However, while the neurons differentiate into a plethora of different subtypes and different identities, they also presume a highly polar structure with a particular morphology of the cytoskeleton, thereby making it almost impossible for any differentiated cell to re-enter the cell cycle. It has been observed that dysregulated or forced cell cycle reentry is closely linked to neurodegeneration and apoptosis in neurons, most likely through changes in the neurocytoskeleton. However, proliferative cells still exist within the nervous system, and adult neural stem cells (NSCs) have been identified in the Central Nervous System (CNS) in the past decade, raising a great stir in the neuroscience community. NSCs present a new therapeutic potential, and much effort has since gone into understanding the molecular mechanisms driving differentiation of specific neuronal lineages, such as dopaminergic neurons, for use in regenerative medicine, either through transplanted NSCs or manipulation of existing ones. Nevertheless, differentiation and proliferation are two sides of the same coin, just like tumorigenesis and degeneration. Tumor formation may be regarded as a de-differentiation of tissues, where cell cycle mechanisms are reactivated in differentiated cell types. It is thus important to understand the molecular mechanisms underlying various brain tumors in this perspective. The recent Cancer Stem Cell (CSC) hypothesis also suggests the presence of Brain Tumor Initiating Cells (BTICs) within a tumor population, although the exact origin of these rare and mostly elusive BTICs are yet to be identified. This review attempts to investigate the correlation of neural stem cells/precursors, mature neurons, BTICs and brain tumors with respect to cell cycle regulation and the impact of cell cycle in neurodegeneration.

Transplantation of ciliary neurotrophic factor-expressing adult oligodendrocyte precursor cells promotes remyelination and functional recovery after spinal cord injury

Demyelination contributes to the dysfunction after traumatic spinal cord injury (SCI). We explored whether the combination of neurotrophic factors and transplantation of adult rat spinal cord oligodendrocyte precursor cells (OPCs) could enhance remyelination and functional recovery after SCI. Ciliary neurotrophic factor (CNTF) was the most effective neurotrophic factor to promote oligodendrocyte (OL) differentiation and survival of OPCs in vitro. OPCs were infected with retroviruses expressing enhanced green fluorescent protein (EGFP) or CNTF and transplanted into the contused adult thoracic spinal cord 9 d after injury. Seven weeks after transplantation, the grafted OPCs survived and integrated into the injured spinal cord. The survival of grafted CNTF-OPCs increased fourfold compared with EGFP-OPCs. The grafted OPCs differentiated into adenomatus polyposis coli (APC(+)) OLs, and CNTF significantly increased the percentage of APC(+) OLs from grafted OPCs. Immunofluorescent and immunoelectron microscopic analyses showed that the grafted OPCs formed central myelin sheaths around the axons in the injured spinal cord. The number of OL-remyelinated axons in ventrolateral funiculus (VLF) or lateral funiculus (LF) at the injured epicenter was significantly increased in animals that received CNTF-OPC grafts compared with all other groups. Importantly, 75% of rats receiving CNTF-OPC grafts recovered transcranial magnetic motor-evoked potential and magnetic interenlargement reflex responses, indicating that conduction through the demyelinated axons in VLF or LF, respectively, was partially restored. More importantly, recovery of hindlimb locomotor function was significantly enhanced in animals receiving grafts of CNTF-OPCs. Thus, combined treatment with OPC grafts expressing CNTF can enhance remyelination and facilitate functional recovery after traumatic SCI.

Bridging the Divide between Neuroprosthetic Design, Tissue Engineering and Neurobiology

Neuroprosthetic devices have made a major impact in the treatment of a variety of disorders such as paralysis and stroke. However, a major impediment in the advancement of this technology is the challenge of maintaining device performance during chronic implantation (months to years) due to complex intrinsic host responses such as gliosis or glial scarring. The objective of this review is to bring together research communities in neurobiology, tissue engineering, and neuroprosthetics to address the major obstacles encountered in the translation of neuroprosthetics technology into long-term clinical use. This article draws connections between specific challenges faced by current neuroprosthetics technology and recent advances in the areas of nerve tissue engineering and neurobiology. Within the context of the device-nervous system interface and central nervous system implants, areas of synergistic opportunity are discussed, including platforms to present cells with multiple cues, controlled delivery of bioactive factors, three-dimensional constructs and in vitro models of gliosis and brain injury, nerve regeneration strategies, and neural stem/progenitor cell biology. Finally, recent insights gained from the fields of developmental neurobiology and cancer biology are discussed as examples of exciting new biological knowledge that may provide fresh inspiration toward novel technologies to address the complexities associated with long-term neuroprosthetic device performance.

Transplantation of Von Hippel-Lindau peptide delivered neural stem cells promotes recovery in the injured rat spinal cord

For transplantation of neural stem cells (NSCs) to repair the injured spinal cord, neuronal differentiation of NSCs before transplantation has more satisfactory effect because differentiation grafted NSCs are restricted to the glial lineage. Therefore, we focused on the Von Hippel-Lindau protein (VHL), which has the potential to induce neuronal differentiation of NSCs. Here, we show the transplantation of protein transduction domain-linked VHL peptide-delivered NSCs promotes the repair of the injured spinal cord. Transplantation of protein transduction domain -linked VHL peptide-delivered NSCs more recovered the behaviors of the rats than that of nondelivered NSCs, and engrafted NSCs differentiated to neuronal marker positive cells. Thus, our finding of the neuronal differentiation through VHL-peptide transfer has the great potential to cure the spinal cord injury.

Stem cells and spinal cord regeneration

Cell-based transplantation strategies are inherently combination therapies, as they may mediate spinal cord repair via trophic or phenotypic mechanisms. The growth factor expression profile and phenotype of transplanted cells are determined by the transplant population as well as by the site into which they are transplanted. Identifying the key pathways involved in transplant survival and differentiation, as well as neuroprotection and regeneration of endogenous tissue, will enable manipulation of both the transplanted cells and the microenvironment to improve transplant efficiency. High purity populations derived from stem cells will serve to better delineate lineage-specific mechanisms of repair, while providing both neurotrophic and phenotypic benefits to the injured spinal cord.

Transplantation-mediated strategies to promote axonal regeneration following spinal cord injury

Devastating central nervous system injuries and diseases continue to occur in spite of the tremendous efforts of various prevention programs. The enormity and annual escalation of healthcare costs due to them require that therapeutic strategies be responsibly developed. The dysfunctions that occur after injury and disease are primarily due to neurotransmission damage. The last two decades of both experimental and clinical research have demonstrated that neural and non-neural tissue and cell transplantation is a viable option for ameliorating dysfunctions to markedly improve quality of life. Moreover, significant progress has been made with tissue and cell transplantation in studies of pathophysiology, plasticity, sprouting, regeneration, and functional recovery. This article will review information about the ability and potential, particularly for traumatic spinal cord injury, that neural and non-neural tissue and cell transplantation has to replace lost neurons and glia, to reconstruct damaged neural circuitry, and to restore neurotransmitters, hormones, neurotrophic factors, and neurotransmission. Donor tissues and cells to be discussed include peripheral nerve, fetal spinal cord and brain, central and peripheral nervous systems' glia, stem cells, those that have been genetically engineered, and non-neural ones. Combinatorial approaches and clinical research are also reviewed.

Critical involvement of Rho GTPase activity in the efficient transplantation of neural stem cells into the injured spinal cord

BACKGROUND

Transplantation of neural stem/progenitor cells is a promising approach toward functional restoration of the damaged neural tissue, but the injured spinal cord has been shown to be an adverse environment for the survival, migration, and differentiation of the donor cells. To improve the efficiency of cell replacement therapy, cell autonomous factors in the donor cells should be optimized. In light of recent findings that Rho family GTPases regulate stem cell functions, genetic manipulation of Rho GTPases can potentially control phenotypes of transplanted cells. Therefore we expressed mutant forms of Rho GTPases, Rac, Rho, and Cdc42, in the neural stem/progenitor cells and examined their survival and migration after transplantation.

RESULTS

Manipulation of the individual Rho GTPases showed differential effects on survival, with little variation in their migratory route and predominant differentiation into the oligodendroglial lineage. Combined suppression of both Rac and Rho activity had a prominent effect on promoting survival, consistent with its highly protective effect on drug-induced apoptosis in culture.

CONCLUSION

Manipulation of Rac and Rho activities fully rescued suppression of cell survival induced by the spinal cord injury. Our results indicate that precise regulation of cell autonomous factors within the donor cells can ameliorate the detrimental environment created by the injury.

Controlled release of neurotrophin-3 and platelet-derived growth factor from fibrin scaffolds containing neural progenitor cells enhances survival and differentiation into neurons in a subacute model of SCI

A consistent problem with stem/neural progenitor cell transplantation following spinal cord injury (SCI) is poor cell survival and uncontrolled differentiation following transplantation. The current study evaluated the feasibility of enhancing embryonic stem cell-derived neural progenitor cell (ESNPC) viability and directing their differentiation into neurons and oligodendrocytes by embedding the ESNPCs in fibrin scaffolds containing growth factors (GF) and a heparin-binding delivery system (HBDS) in a subacute rat model of SCI. Mouse ESNPCs were generated from mouse embryonic stem cells (ESCs) using a 4-/4+ retinoic acid (RA) induction protocol. The ESNPCs were then transplanted as embryoid bodies (EBs, 70% neural progenitor cells) into the subacute model of SCI. ESNPCs (10 EBs per animal) were implanted directly into the SCI lesion, encapsulated in fibrin scaffolds, encapsulated in fibrin scaffolds containing the HBDS, neurotrophin-3 (NT-3), and platelet-derived growth factor (PDGF), or encapsulated in fibrin scaffolds with NT-3 and PDGF with no HBDS. We report here that the combination of the NT-3, PDGF, and fibrin scaffold (with or without HBDS) enhanced the total number of ESNPCs present in the spinal cord lesion 2 weeks after injury. In addition, the inclusion of the HBDS with growth factor resulted in an increase in the number of ESNPC-derived NeuN-positive neurons. These results demonstrate the ability of fibrin scaffolds and the controlled release of growth factors to enhance the survival and differentiation of neural progenitor cells following transplantation into a SCI model.

Neural progenitor cells enhance the survival and axonal regeneration of injured motoneurons after transplantation into the avulsed ventral horn of adult rats

In the present study, we transplanted E13.5 spinal cord-derived neural progenitor cells (NPCs) into the acutely avulsed ventral horn of adult rats. The results showed that NPCs survived and integrated nicely within the host ventral horn at 6 weeks post-grafting. Although the majority of grafted NPCs differentiated into astrocytes and only a small proportion into neuronal cells, interestingly, grafted NPCs in the avulsed ventral horn significantly enhanced the survival of injured motoneurons and promoted their regeneration into a peripheral nerve (PN) graft, as revealed by retrograde FluoroGold (FG) labeling. Specific ELISAs, Western blotting, and quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that NPCs produced nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and glial cell line-derived neutrophilic factor (GDNF), both in vitro and after transplantation in vivo. These results indicate that NPCs have beneficial effects on the survival and axonal regeneration of avulsion-injured motoneurons after transplantation. Such beneficial effects are possibly due to their inherent ability to secrete various trophic factors after transplantation in vivo.

Transplantation of human neural stem cells transduced with Olig2 transcription factor improves locomotor recovery and enhances myelination in the white matter of rat spinal cord following contusive injury

Background

Contusive spinal cord injury is complicated by a delayed loss of oligodendrocytes, resulting in chronic progressive demyelination. Therefore, transplantation strategies to provide oligodendrocyte lineage cells and to enhance the extent of myelination appear to be justified for spinal cord repair. The present study investigated whether transplantation of human neural stem cells (NSCs) genetically modified to express Olig2 transcription factor, an essential regulator of oligodendrocyte development, can improve locomotor recovery and enhance myelination in a rat contusive spinal cord injury model.

Results

HB1.F3 (F3) immortalized human NSC line was transduced with a retroviral vector encoding Olig2, an essential regulator of oligodendrocyte development. Overexpression of Olig2 in human NSCs (F3.Olig2) induced activation of NKX2.2 and directed differentiation of NSCs into oligodendrocyte lineage cells in vitro. Introduction of Olig2 conferred higher proliferative activity, and a much larger number of F3.Olig2 NSCs were detected by 7 weeks after transplantation into contused spinal cord than that of parental F3 NSCs. F3.Olig2 NSCs exhibited frequent migration towards the white matter, whereas F3 NSCs were mostly confined to the gray matter or around the lesion cavities. Most of F3.Olig2 NSCs occupying the spared white matter differentiated into mature oligodendrocytes. Transplantation of F3.Olig2 NSCs increased the volume of spared white matter and reduced the cavity volume. Moreover, F3.Olig2 grafts significantly increased the thickness of myelin sheath around the axons in the spared white matter. Finally, animals with F3.Olig2 grafts showed an improvement in the quality of hindlimbs locomotion.

Conclusion

Transplantation of NSCs genetically modified to differentiate into an oligodendrocytic lineage may be an effective strategy to improve functional outcomes following spinal cord trauma. The present study suggests that molecular factors governing cell fate decisions can be manipulated to enhance reparative potential of the cell-based therapy.

Neural stem cell- and Schwann cell-loaded biodegradable polymer scaffolds support axonal regeneration in the transected spinal cord

Biodegradable polymer scaffolds provide an excellent approach to quantifying critical factors necessary for restoration of function after a transection spinal cord injury. Neural stem cells (NSCs) and Schwann cells (SCs) support axonal regeneration. This study examines the compatibility of NSCs and SCs with the poly-lactic-co-glycolic acid polymer scaffold and quantitatively assesses their potential to promote regeneration after a spinal cord transection injury in rats. NSCs were cultured as neurospheres and characterized by immunostaining for nestin (NSCs), glial fibrillary acidic protein (GFAP) (astrocytes), betaIII-tubulin (immature neurons), oligodendrocyte-4 (immature oligodendrocytes), and myelin oligodendrocyte (mature oligodendrocytes), while SCs were characterized by immunostaining for S-100. Rats with transection injuries received scaffold implants containing NSCs (n=17), SCs (n=17), and no cells (control) (n=8). The degree of axonal regeneration was determined by counting neurofilament-stained axons through the scaffold channels 1 month after transplantation. Serial sectioning through the scaffold channels in NSC- and SC-treated groups revealed the presence of nestin, neurofilament, S-100, and betaIII tubulin-positive cells. GFAP-positive cells were only seen at the spinal cord-scaffold border. There were significantly more axons in the NSC- and SC- treated groups compared to the control group. In conclusion, biodegradable scaffolds with aligned columns seeded with NSCs or SCs facilitate regeneration across the transected spinal cord. Further, these multichannel biodegradable polymer scaffolds effectively serve as platforms for quantitative analysis of axonal regeneration.

Current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury using polymer scaffolds

This review highlights current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury. The concept of developing 3-dimensional polymer scaffolds for placement into a spinal cord transection model has recently been more extensively explored as a solution for restoring neurologic function after injury. Given the patient morbidity associated with respiratory compromise, the discrete tracts in the spinal cord conveying innervation for breathing represent an important and achievable therapeutic target. The aim is to derive new neuronal tissue from the surrounding, healthy cord that will be guided by the polymer implant through the injured area to make functional reconnections. A variety of naturally derived and synthetic biomaterial polymers have been developed for placement in the injured spinal cord. Axonal growth is supported by inherent properties of the selected polymer, the architecture of the scaffold, permissive microstructures such as pores, grooves or polymer fibres, and surface modifications to provide improved adherence and growth directionality. Structural support of axonal regeneration is combined with integrated polymeric and cellular delivery systems for therapeutic drugs and for neurotrophic molecules to regionalize growth of specific nerve populations.

Stem cell-based therapies for spinal cord injury

Spinal cord injury (SCI) results in loss of nervous tissue and consequently loss of motor and sensory function. There is no treatment available that restores the injury-induced loss of function to a degree that an independent life can be guaranteed. Transplantation of stem cells or progenitors may support spinal cord repair. Stem cells are characterized by self-renewal and their ability to become any cell in an organism. Promising results have been obtained in experimental models of SCI. Stem cells can be directed to differentiate into neurons or glia in vitro, which can be used for replacement of neural cells lost after SCI. Neuroprotective and axon regeneration-promoting effects have also been credited to transplanted stem cells. There are still issues related to stem cell transplantation that need to be resolved, including ethical concerns. This paper reviews the current status of stem cell application for spinal cord repair.

Combined extrinsic and intrinsic manipulations exert complementary neuronal enrichment in embryonic rat neural precursor cultures: an in vitro and in vivo analysis

Numerous central nervous system (CNS) disorders share a common pathology in dysregulation of gamma-aminobutyric acid (GABA) inhibitory signaling. Transplantation of GABA-releasing cells at the site of disinhibition holds promise for alleviating disease symptoms with fewer side effects than traditional drug therapies. We manipulated fibroblast growth factor (FGF)-2 deprivation and mammalian achaete-scute homolog (MASH)1 transcription factor levels in an attempt to amplify the default GABAergic neuronal fate in cultured rat embryonic neural precursor cells (NPCs) for use in transplantation studies. Naïve and MASH1 lentivirus-transduced NPCs were maintained in FGF-2 or deprived of FGF-2 for varying lengths of time. Immunostaining and quantitative analysis showed that GABA- and beta-III-tubulin-immunoreactive cells generally decreased through successive passages, suggesting a loss of neurogenic potential in rat neurospheres expanded in vitro. However, FGF-2 deprivation resulted in a small, but significantly increased population of GABAergic cells derived from passaged neurospheres. In contrast to naïve and GFP lentivirus-transduced clones, MASH1 transduction resulted in increased bromodeoxyuridine (BrdU) incorporation and clonal colony size. Western blotting showed that MASH1 overexpression and FGF-2 deprivation additively increased beta-III-tubulin and decreased cyclic nucleotide phosphodiesterase (CNPase) expression, whereas FGF-2 deprivation alone attenuated glial fibrillary acidic protein (GFAP) expression. These results suggest that low FGF-2 signaling and MASH1 activity can operate in concert to enrich NPC cultures for a GABA neuronal phenotype. When transplanted into the adult rat spinal cord, this combination also yielded GABAergic neurons. These findings indicate that, even for successful utilization of the default GABAergic neuronal precursor fate, a combination of both extrinsic and intrinsic manipulations will likely be necessary to realize the full potential of NSC grafts in restoring function.