In search of human oligodendroglia for myelin repair

High Dose Pharmaceutical Grade Biotin (MD1003) Accelerates Differentiation of Murine and Grafted Human Oligodendrocyte Progenitor Cells In Vivo

Accumulating evidences suggest a strong correlation between metabolic changes and neurodegeneration in CNS demyelinating diseases such as multiple sclerosis (MS). Biotin, an essential cofactor for five carboxylases, is expressed by oligodendrocytes and involved in fatty acid synthesis and energy production. The metabolic effect of biotin or high-dose-biotin (MD1003) has been reported on rodent oligodendrocytes in vitro, and in neurodegenerative or demyelinating animal models. However, clinical studies, showed mild or no beneficial effect of MD1003 in amyotrophic lateral sclerosis (ALS) or MS. Here, we took advantage of a mouse model of myelin deficiency to study the effects of MD1003 on the behavior of murine and grafted human oligodendrocytes in vivo. We show that MD1003 increases the number and the differentiation potential of endogenous murine oligodendroglia over time. Moreover, the levels of MD1003 are increased in the plasma and brain of pups born to treated mothers, indicating that MD1003 can pass through the mother's milk. The histological analysis of the grafted animals shows that MD1003 increased proliferation and accelerates differentiation of human oligodendroglia, but without enhancing their myelination potential. These findings provide important insights into the role of MD1003 on murine and human oligodendrocyte maturation/myelination that may explain the mitigated outcome of ALS/MS clinical trials.

A primary cilium in oligodendrocytes: a fine structure signal of repairs in thalamic Osmotic Demyelination Syndrome (ODS)

A murine osmotic demyelination syndrome (ODS) model of the central nervous system included the relay thalamic ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei. Morphologic comparisons between treatments have revealed oligodendrocyte changes and, already 12 hours following the osmolality restoration, some heavily contrasted oligodendrocytes formed a unique intracellular primary cilium. This unique structure, found in vivo, in mature CNS oligodendrocytes, could account for a local awakening of some of the developmental proteome as it can be expressed in oligodendrocyte precursor cells. This resilience accompanied the emergence of arl13b protein expression along with restoration of nerve cell body axon hillocks shown in a previous issue of this journal. Additionally, the return of several thalamic oligodendrocyte fine features (nucleus, organelles) was shown 36 h later, including some mitosis. Those cell restorations and recognized translational activities comforted that local repairs could again take place, due to oligodendrocyte resilience after ODS instead or added to a postulated immigration of oligodendrocyte precursor cells distant from the sites of myelinolysis.

Stem cell derived oligodendrocytes to study myelin diseases

Oligodendroglial pathology is central to de- and dysmyelinating, but also contributes to neurodegenerative and psychiatric diseases as well as brain injury. The understanding of oligodendroglial biology in health and disease has been significantly increased during recent years by experimental in vitro and in vivo preclinical studies as well as histological analyses of human tissue samples. However, for many of these diseases the underlying pathology is still not fully understood and treatment options are frequently lacking. This is at least partly caused by the limited access to human oligodendrocytes from patients to perform functional studies and drug screens. The induced pluripotent stem cell technology (iPSC) represents a possibility to circumvent this obstacle and paves new ways to study human disease and to develop new treatment options for so far incurable central nervous system (CNS) diseases. In this review, we summarize the differences between human and rodent oligodendrocytes, provide an overview of the different techniques to generate oligodendrocytes from human progenitor or stem cells and describe the results from studies using iPSC derived oligodendroglial lineage cells. Furthermore, we discuss future perspectives and challenges of the iPSC technology with respect to disease modeling, drug screen, and cell transplantation approaches.

Development of glial restricted human neural stem cells for oligodendrocyte differentiation in vitro and in vivo

In this study, we have developed highly expandable neural stem cells (NSCs) from HESCs and iPSCs that artificially express the oligodendrocyte (OL) specific transcription factor gene Zfp488. This is enough to restrict them to an exclusive oligodendrocyte progenitor cell (OPC) fate during differentiation in vitro and in vivo. During CNS development, Zfp488 is induced during the early stages of OL generation, and then again during terminal differentiation of OLs. Interestingly, the human ortholog Znf488, crucial for OL development in human, has been recently identified to function as a dorsoventral pattering regulator in the ventral spinal cord for the generation of P1, P2/pMN, and P2 neural progenitor domains. Forced expression of Zfp488 gene in human NSCs led to the robust generation of OLs and suppression of neuronal and astrocyte fate in vitro and in vivo. Zfp488 expressing NSC derived oligodendrocytes are functional and can myelinate rat dorsal root ganglion neurons in vitro, and form myelin in Shiverer mice brain in vivo. After transplantation near a site of demyelination, Zfp488 expressing hNSCs migrated to the lesion and differentiated into premyelinating OLs. A certain fraction also homed in the subventricular zone (SVZ). Zfp488-ZsGreen1-hNSC derived OLs formed compact myelin in Shiverer mice brain seen under the electron microscope. Transplanted human neural stem cells (NSC) that have the potential to differentiate into functional oligodendrocytes in response to remyelinating signals can be a powerful therapeutic intervention for disorders where oligodendrocyte (OL) replacement is beneficial.

eIF2B Mutations Cause Mitochondrial Malfunction in Oligodendrocytes

Vanishing white matter (VWM) disease (OMIM#306896) is an autosomal recessive neurodegenerative leukodystrophy caused by hypomorphic mutations in any of the five genes encoding the subunits of eukaryotic translation initiation factor 2B (eIF2B). The disease is manifested by loss of cerebral white matter and progressive deterioration upon exposure to environmental and physiological stressors. "Foamy" oligodendrocytes (OLG), increased numbers of oligodendrocytes precursor cells (OPC), and immature defective astrocytes are major neuropathological denominators. Our recent work using Eif2b5^R132H/R132H mice uncovered a fundamental link between eIF2B and mitochondrial function. A decrease in oxidative phosphorylation capacity was observed in mutant astrocytes and fibroblasts. While an adaptive increase in mitochondria abundance corrects the phenotype of mutant fibroblasts, it is not sufficient to compensate for the high-energy demand of astrocytes, explaining their involvement in the disease. To date, astrocytes are marked as central for the disease while eIF2B-mutant OLG are currently assumed to lack a cellular phenotype on their own. Here we show a reduced capacity of eIF2B-mutant OPC isolated from Eif2b5^R132H/R132H mice to conduct oxidative respiration despite the adaptive increase in their mitochondrial abundance. We also show their impaired ability to efficiently complete critical differentiation steps towards mature OLG. The concept that defective differentiation of eIF2B-mutant OPC could be a consequence of mitochondrial malfunction is in agreement with numerous studies indicating high dependency of differentiating OLG on accurate mitochondrial performance and ATP availability.

Ameliorating Effect of Osteopontin on H2O2-Induced Apoptosis of Human Oligodendrocyte Progenitor Cells

Recently our group used oligodendrocyte progenitor cells (OPCs) as appropriate model cells to pinpoint the mechanism of the progress of neurodegenerative disorders. In the present study, we focused on the therapeutic role of osteopontin (OPN), a secreted glycosylated phosphoprotein, involved in a number of physiological events including bone formation and remodeling, immune responses, and tumor progression. Protective role of OPN, as a negative regulator of tumorigenesis, has already been clarified. Human embryonic stem cell-derived OPCs were pretreated with OPN before induction of apoptosis by H₂O₂. Data indicated that OPN prohibited cell death and enhanced OPC viability. This effect is achieved through reduction of apoptosis and induction of anti-apoptosis markers. In addition OPN induces expression of several integrin subunits, responsible for OPN interaction. Notably, our findings showed that expression of αV β1/β3/β5 and β8 integrins increased in response to OPN, while treatment with H₂O₂ down-regulated αV β1/β5 and β8 integrins expression significantly. In conclusion, OPN may act via αV integrin signaling and trigger suppression of P53-dependent apoptotic cascades. Therefore OPN therapy may be considered as a feasible process to prevent progress of neurodegenerative diseases in human.

Purinergic Receptor Expression and Potential Association with Human Embryonic Stem Cell-Derived Oligodendrocyte Progenitor Cell Development

Objective

Due to recent progress in production of human embryonic stem cell-derived oligodendrocyte progenitor cells (hESC-OPCs) for ameliorating myelin disease such as multiple sclerosis (MS) and the role of purinergic signaling in OPCs development, we avaluated the profile of purinergic receptors expression during development of OPCs from hESC.

Materials and Methods

In this experimental study, we used reverse transcription and quantitative polymerase chain reaction (RT-qPCR) to obtain more information about potential roles of purinergic receptors during in vitro production of hESC-OPCs. We first determined the expression level of different subtypes of purinergic receptors in hESCs, embryoid bodies (EBs), and hESC-OPCs. The effects of A1adenosine receptor (A₁AR) activation on hESC-OPCs development were subsequently examined.

Results

hESCs and OPCs had different mRNA expression levels of the AR subtypes. ARs mRNA were expressed in the EB stage, except for A_2AAR. We observed expressions of several P2X (P2X_{1, 2, 3, 4, 5, 7}) and P2Y (P2Y_{1, 2, 4, 6, 11-14}) genes in hESCs. hESC-OPCs expressed different subtypes of P2X (P2X_{1, 2, 3,4,5,7}) and P2Y (P2Y_{1, 2, 4, 6, 11-14}). Except for P2X₁ and P2X₆, all other P2X and P2Y purinergic receptor subtypes expressed in EBs. We also indicate that A₁AR might be involved in modulating gene expression levels of cell cycle regulators in an agonist and/or dose-dependent manner.

Conclusion

Elucidation of the expression pattern of purinergic receptors and the effects of different subtypes of these receptors in hESC-OPCs may have a promising role in future cell-based therapy or drug design for demyelinating disease.

Effect of Fingolimod on Neural Stem Cells: A Novel Mechanism and Broadened Application for Neural Repair

Inflammatory demyelination and axonal damage of the CNS are hallmarks of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Fingolimod (FTY720), the first FDA-approved oral medication for MS, suppresses acute disease but is less effective at the chronic stage, and whether it has a direct effect on neuroregeneration in MS and EAE remains unclear. Here we show that FTY720, at nanomolar concentrations, effectively protected survival of neural stem cells (NSCs) and enhanced their development into mature oligodendrocytes (OLGs) in vitro, primarily through the S1P3 and S1P5 receptors. In vivo, treatment with either FTY720 or NSCs alone had no effect on the secondary progressive stage of remitting-relapsing EAE, but a combination therapy with FTY720 and NSCs promoted significant recovery, including ameliorated clinical signs and CNS inflammatory demyelination, enhanced MBP synthesis and remyelination, inhibited axonal degeneration, and reduced astrogliosis. Moreover, FTY720 significantly improved incorporation and survival of transplanted NSCs in the CNS and drove their differentiation into more OLGs but fewer astrocytes, thus promoting remyelination and CNS repair processes in situ. Our data demonstrate a novel effect of FTY720 on NSC differentiation and remyelination, broadening its possible application to NSC-based therapy in the secondary progressive stage of MS.

Targeting human oligodendrocyte progenitors for myelin repair

Oligodendrocyte development has been studied for several decades, and has served as a model system for both neurodevelopmental and stem/progenitor cell biology. Until recently, the vast majority of studies have been conducted in lower species, especially those focused on rodent development and remyelination. In humans, the process of myelination requires the generation of vastly more myelinating glia, occurring over a period of years rather than weeks. Furthermore, as evidenced by the presence of chronic demyelination in a variety of human neurologic diseases, it appears likely that the mechanisms that regulate development and become dysfunctional in disease may be, in key ways, divergent across species. Improvements in isolation techniques, applied to primary human neural and oligodendrocyte progenitors from both fetal and adult brain, as well as advancements in the derivation of defined progenitors from human pluripotent stem cells, have begun to reveal the extent of both species-conserved signaling pathways and potential key differences at cellular and molecular levels. In this article, we will review the commonalities and differences in myelin development between rodents and man, describing the approaches used to study human oligodendrocyte differentiation and myelination, as well as heterogeneity within targetable progenitor pools, and discuss the advances made in determining which conserved pathways may be both modeled in rodents and translate into viable therapeutic strategies to promote myelin repair.

Pluripotent stem cell-derived radial glia-like cells as stable intermediate for efficient generation of human oligodendrocytes

Neural precursor cells (NPCs) derived from human pluripotent stem cells (hPSCs) represent an attractive tool for the in vitro generation of various neural cell types. However, the developmentally early NPCs emerging during hPSC differentiation typically show a strong propensity for neuronal differentiation, with more limited potential for generating astrocytes and, in particular, for generating oligodendrocytes. This phenomenon corresponds well to the consecutive and protracted generation of neurons and GLIA during normal human development. To obtain a more gliogenic NPC type, we combined growth factor-mediated expansion with pre-exposure to the differentiation-inducing agent retinoic acid and subsequent immunoisolation of CD133-positive cells. This protocol yields an adherent and self-renewing population of hindbrain/spinal cord radial glia (RG)-like neural precursor cells (RGL-NPCs) expressing typical neural stem cell markers such as nestin, ASCL1, SOX2, and PAX6 as well as RG markers BLBP, GLAST, vimentin, and GFAP. While RGL-NPCs maintain the ability for tripotential differentiation into neurons, astrocytes, and oligodendrocytes, they exhibit greatly enhanced propensity for oligodendrocyte generation. Under defined differentiation conditions promoting the expression of the major oligodendrocyte fate-determinants OLIG1/2, NKX6.2, NKX2.2, and SOX10, RGL-NPCs efficiently convert into NG2-positive oligodendroglial progenitor cells (OPCs) and are subsequently capable of in vivo myelination. Representing a stable intermediate between PSCs and OPCs, RGL-NPCs expedite the generation of PSC-derived oligodendrocytes with O4-, 4860-, and myelin basic protein (MBP)-positive cells that already appear within 7 weeks following growth factor withdrawal-induced differentiation. Thus, RGL-NPCs may serve as robust tool for time-efficient generation of human oligodendrocytes from embryonic and induced pluripotent stem cells.

Remyelination and multiple sclerosis: therapeutic approaches and challenges

Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system. After acute inflammatory mediated demyelination, some remyelination often occurs, but in chronic demyelinated MS plaques, remyelination frequently fails. Chronically demyelinated axons cause a variety of symptoms and probably are more likely to degenerate, leading to irreversible clinical disability. Oligodendrocyte precursor cells (OPCs) present in the adult brain can proliferate and differentiate to remyelinate lesions. Failure of remyelination in the majority of MS patients is secondary to arrest in OPC differentiation. Many therapies have been developed to modulate the immune response in MS, but no neuroprotective or remyelinating therapies are available. Promoting remyelination is a promising avenue for protecting axons, reversing neurologic disability and preventing progressive disease in MS. This review will begin with an overview of remyelination and remyelination failure, consequences of demyelination, and available animal disease models. In addition, preclinical and clinical studies on the most promising potential therapies for inducing remyelination will be described.

Isolation and long-term expansion of functional, myelinating oligodendrocyte progenitor cells from neonatal rat brain

Oligodendrocytes are the myelinating cells of the central nervous system (CNS). The isolation of purified oligodendrocyte progenitor cells (OPCs) in large numbers has been sought after as a source of cells for repair following CNS-demyelinating diseases and injuries, such as multiple sclerosis (MS) and spinal cord injury (SCI). Methods for isolation of OPCs from rodent neonatal brains are well established and have formed the basis for research in myelin repair within the CNS for many years. However, long-term maintenance of OPCs has been a challenge owing to small cellular yields per animal and spontaneous differentiation within a short period of time. Much effort has been devoted to achieving long-term culture and maintenance of OPCs, but little progress has been made. Here, protocols are presented for preparation of highly enriched rat OPC populations and for their long-term maintenance as oligospheres using mixed-glial-conditioned medium. Functional myelinating oligodendrocytes can be achieved from such protocols, when co-cultured with primary neurons. This approach is an extension of our normal shaking method for isolating OPCs, and incorporates some adaptations from previous OPC culture methods.

Differentiation of neurosphere-derived rat neural stem cells into oligodendrocyte-like cells by repressing PDGF-α and Olig2 with triiodothyronine

One of the approaches for treating demyelination diseases is cytotherapy, and adult stem cells are potential sources. In this investigation, we tried to increase the yield of oligodendrocyte-like cells (OLCs) by inducing neural stem cells generated from BMSCs-derived neurospheres, which were used for deriving the neural stem cells (NSCs). The latter were induced into OLCs by heregulin, PDGF-AA, bFGF and triiodothyronine (T3). The BMSCs, NS, NSCs and OLCs were characterized by using immunocytochemistry for fibronectin, CD44, CD90, CD45, Oct-4, O4, Olig2, O1 and MBP markers. PDGF receptor α (PDGFR-α), Olig2 and MOG expression were evaluated by RT-PCR. The BMSCs expressed CD44, CD90, CD106 and Oct-4; the NSCs were immunoreactive to nestin and neurofilament 68. Incubation of the NSCs for 4 days with heregulin, PDGF-AA and bFGF resulted in their induction into oligodendrocyte progenitor-like cells (OPLCs), which immunoreacted to O4, Olig2 and O1, while Olig2 and PDGFR-α were detected by RT-PCR. Replacing heregulin, PDGF-AA and bFGF with T3 for 6 days resulted in repression of O4, O1, Olig2 and PDGFR-α. The OLCs were co-cultured with motoneurons resulted in induction of MOG and MBP, which were expressed in functional OLCs. The latter can be generated from BMSCs-derive NS with high yield.

Magnetic nanoparticles for oligodendrocyte precursor cell transplantation therapies: progress and challenges

Oligodendrocyte precursor cells (OPCs) have shown high promise as a transplant population to promote regeneration in the central nervous system, specifically, for the production of myelin - the protective sheath around nerve fibers. While clinical trials for these cells have commenced in some areas, there are currently key barriers to the translation of neural cell therapies. These include the ability to (a) image transplant populations in vivo; (b) genetically engineer transplant cells to augment their repair potential; and (c) safely target cells to sites of pathology. Here, we review the evidence that magnetic nanoparticles (MNPs) are a 'multifunctional nanoplatform' that can aid in safely addressing these translational challenges in neural cell/OPC therapy: by facilitating real-time and post-mortem assessment of transplant cell biodistribution, and biomolecule delivery to transplant cells, as well as non-invasive 'magnetic cell targeting' to injury sites by application of high gradient fields. We identify key issues relating to the standardization and reporting of physicochemical and biological data in the field; we consider that it will be essential to systematically address these issues in order to fully evaluate the utility of the MNP platform for neural cell transplantation, and to develop efficacious neurocompatible particles for translational applications.

Magnetic nanoparticles for oligodendrocyte precursor cell transplantation therapies: progress and challenges

Oligodendrocyte precursor cells (OPCs) have shown high promise as a transplant population to promote regeneration in the central nervous system, specifically, for the production of myelin – the protective sheath around nerve fibers. While clinical trials for these cells have commenced in some areas, there are currently key barriers to the translation of neural cell therapies. These include the ability to (a) image transplant populations in vivo; (b) genetically engineer transplant cells to augment their repair potential; and (c) safely target cells to sites of pathology. Here, we review the evidence that magnetic nanoparticles (MNPs) are a ‘multifunctional nanoplatform’ that can aid in safely addressing these translational challenges in neural cell/OPC therapy: by facilitating real-time and post-mortem assessment of transplant cell biodistribution, and biomolecule delivery to transplant cells, as well as non-invasive ‘magnetic cell targeting’ to injury sites by application of high gradient fields. We identify key issues relating to the standardization and reporting of physicochemical and biological data in the field; we consider that it will be essential to systematically address these issues in order to fully evaluate the utility of the MNP platform for neural cell transplantation, and to develop efficacious neurocompatible particles for translational applications.

Intraventricularly injected Olig2-NSCs attenuate established relapsing-remitting EAE in mice

In multiple sclerosis (MS), a chronic inflammatory relapsing demyelinating disease, failure to control or repair damage leads to progressive neurological dysfunction and neurodegeneration. Implantation of neural stem cells (NSCs) has been shown to promote repair and functional recovery in the acute experimental autoimmune encephalomyelitis (EAE) animal model for MS; the major therapeutic mechanism of these NSCs appeared to be immune regulation. In the present study, we examined the efficacy of intraventricularly injected NSCs in chronic relapsing experimental autoimmune encephalomyelitis (CREAE), the animal disease model that is widely accepted to mimic most closely recurrent inflammatory demyelination lesions as observed in relapsing-remitting MS. In addition, we assessed whether priming these NSCs to become oligodendrocyte precursor cells (OPCs) by transient overexpression of Olig2 would further promote functional recovery, for example, by contributing to actual remyelination. Upon injection at the onset of the acute phase or the relapse phase of CREAE, NSCs as well as Olig2-NSCs directly migrated toward active lesions in the spinal cord as visualized by in vivo bioluminescence and biofluorescence imaging, and once in the spinal cord, the majority of Olig2-NSCs, in contrast to NSCs, differentiated into OPCs. The survival of Olig2-NSCs was significantly higher than that of injected control NSCs, which remained undifferentiated. Nevertheless, both Olig2-NSCs and NSC significantly reduced the clinical signs of acute and relapsing disease and, in case of Olig2-NSCs, even completely abrogated relapsing disease when administered early after onset of acute disease. We provide the first evidence that NSCs and in particular NSC-derived OPCs (Olig2-NSCs) ameliorate established chronic relapsing EAE in mice. Our experimental data in established neurological disease in mice indicate that such therapy may be effective in relapsing-remitting MS preventing chronic progressive disease.

In vivo evidence that TRAF4 is required for central nervous system myelin homeostasis

Tumor Necrosis Factor Receptor-Associated Factors (TRAFs) are major signal transducers for the TNF and interleukin-1/Toll-like receptor superfamilies. However, TRAF4 does not fit the paradigm of TRAF function in immune and inflammatory responses. Its physiological and molecular functions remain poorly understood. Behavorial analyses show that TRAF4-deficient mice (TRAF4-KO) exhibit altered locomotion coordination typical of ataxia. TRAF4-KO central nervous system (CNS) ultrastructure shows strong myelin perturbation including disorganized layers and disturbances in paranode organization. TRAF4 was previously reported to be expressed by CNS neurons. Using primary cell culture, we now show that TRAF4 is also expressed by oligodendrocytes, at all stages of their differentiation. Moreover, histology and electron microscopy show degeneration of a high number of Purkinje cells in TRAF4-KO mice, that was confirmed by increased expression of the Bax pro-apoptotic marker (immunofluorescence), TUNEL analysis, and caspase-3 activation and PARP1 cleavage (western blotting). Consistent with this phenotype, MAG and NogoA, two myelin-induced neurite outgrowth inhibitors, and their neuron partners, NgR and p75NTR were overexpressed (Q-RT-PCR and western blotting). The strong increased phosphorylation of Rock2, a RhoA downstream target, indicated that the NgR/p75NTR/RhoA signaling pathway, known to induce actin cytoskeleton rearrangement that favors axon regeneration inhibition and neuron apoptosis, is activated in the absence of TRAF4 (western blotting). Altogether, these results provide conclusive evidence for the pivotal contribution of TRAF4 to myelination and to cerebellar homeostasis, and link the loss of TRAF4 function to demyelinating or neurodegenerative diseases.

Human induced pluripotent stem cells differentiation into oligodendrocyte progenitors and transplantation in a rat model of optic chiasm demyelination

Background

This study aims to differentiate human induced pluripotent stem cells (hiPSCs) into oligodendrocyte precursors and assess their recovery potential in a demyelinated optic chiasm model in rats.

Methodology/Principal Findings

We generated a cell population of oligodendrocyte progenitors from hiPSCs by using embryoid body formation in a defined medium supplemented with a combination of factors, positive selection and mechanical enrichment. Real-time polymerase chain reaction and immunofluorescence analyses showed that stage-specific markers, Olig2, Sox10, NG2, PDGFRα, O4, A2B5, GalC, and MBP were expressed following the differentiation procedure, and enrichment of the oligodendrocyte lineage. These results are comparable with the expression of stage-specific markers in human embryonic stem cell-derived oligodendrocyte lineage cells. Transplantation of hiPSC-derived oligodendrocyte progenitors into the lysolecithin-induced demyelinated optic chiasm of the rat model resulted in recovery from symptoms, and integration and differentiation into oligodendrocytes were detected by immunohistofluorescence staining against PLP and MBP, and measurements of the visual evoked potentials.

Conclusions/Significance

These results showed that oligodendrocyte progenitors generated efficiently from hiPSCs can be used in future biomedical studies once safety issues have been overcome.

The myelin mutants as models to study myelin repair in the leukodystrophies

The leukodystrophies are rare and serious genetic disorders of the central nervous system that primarily affect children who frequently die early in life or have significantly delayed motor and mental milestones that result in long-term disability. Although with some of these disorders, early intervention with bone marrow or cord blood transplantation has been proven useful, it has not yet been determined that such therapies promote myelin repair of the central nervous system. Research on experimental therapies aimed at myelin repair is aided by the ability to test cell replacement strategies in genetic models in which the mutations and neuropathology match the human disorder. Thus, models exist of Pelizaeus-Merzbacher disease and the lysosomal storage disorder, Krabbe disease, which reflect the clinical and pathological course of the human disorders. Collectively, animals with mutations in myelin genes are called the myelin mutants, and they include rodent models such as the shiverer mouse that have been extensively used to study myelination by exogenous cell transplantation. These studies have encompassed many permutations of the age of the recipient, type of transplanted cell, site of engraftment, and so forth, and they offer hope that the scaling up of myelin produced by transplanted cells will have clinical significance in treating patients. Here we review these models and discuss their relative importance and use in such translational approaches. We discuss how grafts are identified and functional outcomes are measured. Finally, we briefly discuss the cells that have been successfully transplanted, which may be used in future clinical trials.

Magnetic nanoparticle-mediated gene transfer to oligodendrocyte precursor cell transplant populations is enhanced by magnetofection strategies

This study has tested the feasibility of using physical delivery methods, employing static and oscillating field "magnetofection" techniques, to enhance magnetic nanoparticle-mediated gene transfer to rat oligodendrocyte precursor cells derived for transplantation therapies. These cells are a major transplant population to mediate repair of damage as occurs in spinal cord injury and neurological diseases such as multiple sclerosis. We show for the first time that magnetic nanoparticles mediate effective transfer of reporter and therapeutic genes to oligodendrocyte precursors; transfection efficacy was significantly enhanced by applied static or oscillating magnetic fields, the latter using an oscillating array employing high-gradient NdFeB magnets. The effects of oscillating fields were frequency-dependent, with 4 Hz yielding optimal results. Transfection efficacies obtained using magnetofection methods were highly competitive with or better than current widely used nonviral transfection methods (e.g., electroporation and lipofection) with the additional critical advantage of high cell viability. No adverse effects were found on the cells' ability to divide or give rise to their daughter cells, the oligodendrocytes-key properties that underpin their regeneration-promoting effects. The transplantation potential of transfected cells was tested in three-dimensional tissue engineering models utilizing brain slices as the host tissue; modified transplanted cells were found to migrate, divide, give rise to daughter cells, and integrate within host tissue, further evidencing the safety of the protocols used. Our findings strongly support the concept that magnetic nanoparticle vectors in conjunction with state-of-the-art magnetofection strategies provide a technically simple and effective alternative to current methods for gene transfer to oligodendrocyte precursor cells.

Safety of intramedullary Schwann cell transplantation for postrehabilitation spinal cord injuries: 2-year follow-up of 33 cases

OBJECT

Many experimental studies on spinal cord injuries (SCIs) support behavioral improvement after Schwann cell treatment. This study was conducted to evaluate safety issues 2 years after intramedullary Schwann cell transplantation in 33 consecutively selected patients with SCI.

METHODS

Of 356 patients with SCIs who had completed at least 6 months of a conventional rehabilitation program and who were screened for the study criteria, 33 were enrolled. After giving their informed consent, they volunteered for participation. They underwent sural nerve harvesting and intramedullary injection of a processed Schwann cell solution. Outcome assessments included a general health questionnaire, neurological examination, and functional recordings in terms of American Spinal Injury Association (ASIA) and Functional Independence Measure scoring, which were documented by independent observers. There were 24 patients with thoracic and 9 with cervical injuries. Sixteen patients were categorized in ASIA Grade A, and the 17 remaining participants had ASIA Grade B.

RESULTS

There were no cases of deep infection, and the follow-up MR imaging studies obtained at 2 years did not reveal any deformity related to the procedure. There was no case of permanent neurological worsening or any infectious or viral complications. No new increment in syrinx size or abnormal tissue and/or tumor formation were observed on contrast-enhanced MR imaging studies performed 2 years after the treatment.

CONCLUSIONS

Preliminary results, especially in terms of safety, seem to be promising, paving the way for future cell therapy trials.

Overexpression of basic helix-loop-helix transcription factors enhances neuronal differentiation of fetal human neural progenitor cells in various ways

In a perspective of regenerative medicine, multipotent human neural progenitor cells (hNPCs) offer a therapeutic advantage over pluripotent stem cells in that they are already invariantly "neurally committed" and lack tumorigenicity. However, some of their intrinsic properties, such as slow differentiation and uncontrolled multipotency, remain among the obstacles to their routine use for transplantation. Although rodent NPCs have been genetically modified in vitro to overcome some of these limitations, the translation of this strategy to human cells remains in its early stages. In the present study, we compare the actions of 4 basic helix-loop-helix transcription factors on the proliferation, specification, and terminal differentiation of hNPCs isolated from the fetal dorsal telencephalon. Consistent with their proneural activity, Ngn1, Ngn2, Ngn3, and Mash1 prompted rapid commitment of the cells. The Ngns induced a decrease in proliferation, whereas Mash1 maintained committed progenitors in a proliferative state. As opposed to Ngn1 and Ngn3, which had no effect on glial differentiation, Ngn2 induced an increase in astrocytes in addition to neurons, whereas Mash1 led to both neuronal and oligodendroglial specification. GABAergic, cholinergic, and motor neuron differentiations were considerably increased by overexpression of Ngn2 and, to a lesser extent, of Ngn3 and Mash1. Thus, we provide evidence that hNPCs can be efficiently, rapidly, and safely expanded in vitro as well as rapidly differentiated toward mature neural (typically neuronal) lineages by the overexpression of select proneural genes.

Human neural progenitors from different foetal forebrain regions remyelinate the adult mouse spinal cord

Improving oligodendroglial differentiation from human foetal neural progenitor cells remains a primordial issue to accomplish successful cell-based therapies in myelin diseases. Here, we combined in situ, in vitro and in vivo approaches to assess the oligodendrogenic potential of different human foetal forebrain regions during the first trimester of gestation. We show for the first time that the initial wave of oligodendrocyte progenitor emergence in the ventral telencephalon onsets as early as 7.5 weeks into gestation. Interestingly, in vitro, isolation of ganglionic eminences yielded oligodendrocyte progenitor-enriched cultures, as compared with cortex and thalamus. Most importantly, single injection of human neural progenitors into rodent models of focal gliotoxic demyelination revealed the great capacity of these cells to survive, extensively migrate and successfully remyelinate the spinal cord, irrespective of their origin. Thus, our study brings novel insights into the biology of early human foetal neural progenitor cells and offers new support for the development of cellular therapeutics for myelin disorders.

Real time imaging of human progenitor neurogenesis

Human neural progenitors are increasingly being employed in drug screens and emerging cell therapies targeted towards neurological disorders where neurogenesis is thought to play a key role including developmental disorders, Alzheimer’s disease, and depression. Key to the success of these applications is understanding the mechanisms by which neurons arise. Our understanding of development can provide some guidance but since little is known about the specifics of human neural development and the requirement that cultures be expanded in vitro prior to use, it is unclear whether neural progenitors obey the same developmental mechanisms that exist in vivo. In previous studies we have shown that progenitors derived from fetal cortex can be cultured for many weeks in vitro as undifferentiated neurospheres and then induced to undergo neurogenesis by removing mitogens and exposing them to supportive substrates. Here we use live time lapse imaging and immunocytochemical analysis to show that neural progenitors use developmental mechanisms to generate neurons. Cells with morphologies and marker profiles consistent with radial glia and recently described outer radial glia divide asymmetrically and symmetrically to generate multipolar intermediate progenitors, a portion of which express ASCL1. These multipolar intermediate progenitors subsequently divide symmetrically to produce CTIP2⁺ neurons. This 3-cell neurogenic scheme echoes observations in rodents in vivo and in human fetal slice cultures in vitro, providing evidence that hNPCs represent a renewable and robust in vitro assay system to explore mechanisms of human neurogenesis without the continual need for fresh primary human fetal tissue. Knowledge provided by this and future explorations of human neural progenitor neurogenesis will help maximize the safety and efficacy of new stem cell therapies by providing an understanding of how to generate physiologically-relevant cell types that maintain their identities when placed in diagnostic or transplantation environments.

Robust generation of oligodendrocyte progenitors from human neural stem cells and engraftment in experimental demyelination models in mice

BACKGROUND

Cell-based therapy holds great promises for demyelinating diseases. Human-derived fetal and adult oligodendrocyte progenitors (OPC) gave encouraging results in experimental models of dysmyelination but their limited proliferation in vitro and their potential immunogenicity might restrict their use in clinical applications. Virtually unlimited numbers of oligodendroglial cells could be generated from long-term self-renewing human (h)-derived neural stem cells (hNSC). However, robust oligodendrocyte production from hNSC has not been reported so far, indicating the need for improved understanding of the molecular and environmental signals controlling hNSC progression through the oligodendroglial lineage. The aim of this work was to obtain enriched and renewable cultures of hNSC-derived oligodendroglial cells by means of epigenetic manipulation.

METHODOLOGY/PRINCIPAL FINDINGS

We report here the generation of large numbers of hNSC-derived oligodendroglial cells by concurrent/sequential in vitro exposure to combinations of growth factors (FGF2, PDGF-AA), neurotrophins (NT3) and hormones (T3). In particular, the combination FGF2+NT3+PDGF-AA resulted in the maintenance and enrichment of an oligodendroglial cell population displaying immature phenotype (i.e., proliferation capacity and expression of PDGFRalpha, Olig1 and Sox10), limited self-renewal and increased migratory activity in vitro. These cells generate large numbers of oligodendroglial progeny at the early stages of maturation, both in vitro and after transplantation in models of CNS demyelination.

CONCLUSIONS/SIGNIFICANCE

We describe a reliable method to generate large numbers of oligodendrocytes from a renewable source of somatic, non-immortalized NSC from the human foetal brain. We also provide insights on the mechanisms underlying the pro-oligodendrogenic effect of the treatments in vitro and discuss potential issues responsible for the limited myelinating capacity shown by hNSC-derived oligodendrocytes in vivo.

Directing human neural stem/precursor cells into oligodendrocytes by overexpression of Olig2 transcription factor

Multipotential neural stem/precursor cells of the central nervous system were extensively studied for their properties of generating myelinating oligodendrocytes both in vitro and in vivo upon engraftment in animal models of myelin disorders, such as leucodystrophy and multiple sclerosis. These studies provided proof-of-principle that efficient myelination can be achieved by cell transplantation. However, one major drawback of cell-based therapy of myelin diseases is the difficulty in generating oligodendrocytes efficiently from human fetal neural stem/precursor cells (hNPC). Here we explored whether overexpression of the basic helix-loop-helix (bHLH) transcription factor Olig2 in fetal hNPC could enhance the generation of oligodendrocytes both in vitro and in vivo. We report that transduction of hNPC with Olig2-encoding lentiviral vectors enhances their commitment toward an oligodendroglial fate. Moreover, Olig2-transduced hNPC, grafted into the dysmyelinated shiverer mouse brain, survived up to 9 weeks, migrated extensively, and differentiated into MBP(+) myelinating oligodendrocytes. In contrast, control hNPC remained at a less mature stage and generated very few myelinating oligodendrocytes. Our study indicates that bHLH transcription factors, such as Olig2, are interesting targets for directing hNPC into myelinating oligodendrocytes.