Identification, isolation, and promoter-defined separation of mitotic oligodendrocyte progenitor cells from the adult human subcortical white matter

Young glial progenitor cells competitively replace aged and diseased human glia in the adult chimeric mouse brain

Competition among adult brain cells has not been extensively researched. To investigate whether healthy glia can outcompete diseased human glia in the adult forebrain, we engrafted wild-type (WT) human glial progenitor cells (hGPCs) produced from human embryonic stem cells into the striata of adult mice that had been neonatally chimerized with mutant Huntingtin (mHTT)-expressing hGPCs. The WT hGPCs outcompeted and ultimately eliminated their human Huntington's disease (HD) counterparts, repopulating the host striata with healthy glia. Single-cell RNA sequencing revealed that WT hGPCs acquired a YAP1/MYC/E2F-defined dominant competitor phenotype upon interaction with the host HD glia. WT hGPCs also outcompeted older resident isogenic WT cells that had been transplanted neonatally, suggesting that competitive success depended primarily on the relative ages of competing populations, rather than on the presence of mHTT. These data indicate that aged and diseased human glia may be broadly replaced in adult brain by younger healthy hGPCs, suggesting a therapeutic strategy for the replacement of aged and diseased human glia.

Glial-restricted progenitor cells: a cure for diseased brain?

The central nervous system (CNS) is home to neuronal and glial cells. Traditionally, glia was disregarded as just the structural support across the brain and spinal cord, in striking contrast to neurons, always considered critical players in CNS functioning. In modern times this outdated dogma is continuously repelled by new evidence unravelling the importance of glia in neuronal maintenance and function. Therefore, glia replacement has been considered a potentially powerful therapeutic strategy. Glial progenitors are at the center of this hope, as they are the source of new glial cells. Indeed, sophisticated experimental therapies and exciting clinical trials shed light on the utility of exogenous glia in disease treatment. Therefore, this review article will elaborate on glial-restricted progenitor cells (GRPs), their origin and characteristics, available sources, and adaptation to current therapeutic approaches aimed at various CNS diseases, with particular attention paid to myelin-related disorders with a focus on recent progress and emerging concepts. The landscape of GRP clinical applications is also comprehensively presented, and future perspectives on promising, GRP-based therapeutic strategies for brain and spinal cord diseases are described in detail.

Remyelination in the Central Nervous System

The inability of the mammalian central nervous system (CNS) to undergo spontaneous regeneration has long been regarded as a central tenet of neurobiology. However, while this is largely true of the neuronal elements of the adult mammalian CNS, save for discrete populations of granule neurons, the same is not true of its glial elements. In particular, the loss of oligodendrocytes, which results in demyelination, triggers a spontaneous and often highly efficient regenerative response, remyelination, in which new oligodendrocytes are generated and myelin sheaths are restored to denuded axons. Yet remyelination in humans is not without limitation, and a variety of demyelinating conditions are associated with sustained and disabling myelin loss. In this work, we will (1) review the biology of remyelination, including the cells and signals involved; (2) describe when remyelination occurs and when and why it fails, including the consequences of its failure; and (3) discuss approaches for therapeutically enhancing remyelination in demyelinating diseases of both children and adults, both by stimulating endogenous oligodendrocyte progenitor cells and by transplanting these cells into demyelinated brain.

CD44 correlates with longevity and enhances basal ATF6 activity and ER stress resistance

The naked mole rat (NMR) is the longest-lived rodent, resistant to multiple age-related diseases including neurodegeneration. However, the mechanisms underlying the NMR's resistance to neurodegenerative diseases remain elusive. Here, we isolated oligodendrocyte progenitor cells (OPCs) from NMRs and compared their transcriptome with that of other mammals. Extracellular matrix (ECM) genes best distinguish OPCs of long- and short-lived species. Notably, expression levels of CD44, an ECM-binding protein that has been suggested to contribute to NMR longevity by mediating the effect of hyaluronan (HA), are not only high in OPCs of long-lived species but also positively correlate with longevity in multiple cell types/tissues. We found that CD44 localizes to the endoplasmic reticulum (ER) and enhances basal ATF6 activity. CD44 modifies proteome and membrane properties of the ER and enhances ER stress resistance in a manner dependent on unfolded protein response regulators without the requirement of HA. HA-independent role of CD44 in proteostasis regulation may contribute to mammalian longevity.

Glial progenitor cells of the adult human white and grey matter are contextually distinct

Genomic analyses have revealed heterogeneity among glial progenitor cells (GPCs), but the compartment selectivity of human GPCs (hGPCs) is unclear. Here, we asked if GPCs of human grey and white brain matter are distinct in their architecture and associated gene expression. RNA profiling of NG2-defined hGPCs derived from adult human neocortex and white matter differed in their expression of genes involved in Wnt, NOTCH, BMP and TGFβ signaling, suggesting compartment-selective biases in fate and self-renewal. White matter hGPCs over-expressed the BMP antagonists BAMBI and CHRDL1, suggesting their tonic suppression of astrocytic fate relative to cortical hGPCs, whose relative enrichment of cytoskeletal genes presaged their greater morphological complexity. In human glial chimeric mice, cortical hGPCs assumed larger and more complex morphologies than white matter hGPCs, and both were more complex than their mouse counterparts. These findings suggest that human grey and white matter GPCs comprise context-specific pools with distinct functional biases.

Development of Brain-Derived Bioscaffolds for Neural Progenitor Cell Culture

Biomaterials derived from brain extracellular matrix (ECM) have the potential to promote neural tissue regeneration by providing instructive cues that can direct cell survival, proliferation, and differentiation. This study focused on the development and characterization of microcarriers derived from decellularized brain tissue (DBT) as a platform for neural progenitor cell culture. First, a novel detergent-free decellularization protocol was established that effectively reduced the cellular content of porcine and rat brains, with a >97% decrease in the dsDNA content, while preserving collagens (COLs) and glycosaminoglycans (GAGs). Next, electrospraying methods were applied to generate ECM-derived microcarriers incorporating the porcine DBT that were stable without chemical cross-linking, along with control microcarriers fabricated from commercially sourced bovine tendon COL. The DBT microcarriers were structurally and biomechanically similar to the COL microcarriers, but compositionally distinct, containing a broader range of COL types and higher sulfated GAG content. Finally, we compared the growth, phenotype, and neurotrophic factor gene expression levels of rat brain-derived progenitor cells (BDPCs) cultured on the DBT or COL microcarriers within spinner flask bioreactors over 2 weeks. Both microcarrier types supported BDPC attachment and expansion, with immunofluorescence staining results suggesting that the culture conditions promoted BDPC differentiation toward the oligodendrocyte lineage, which may be favorable for cell therapies targeting remyelination. Overall, our findings support the further investigation of the ECM-derived microcarriers as a platform for neural cell derivation for applications in regenerative medicine.

Cell reprogramming for oligodendrocytes: A review of protocols and their applications to disease modeling and cell-based remyelination therapies

Oligodendrocytes are a type of glial cells that produce a lipid-rich membrane called myelin. Myelin assembles into a sheath and lines neuronal axons in the brain and spinal cord to insulate them. This not only increases the speed and efficiency of nerve signal transduction but also protects the axons from damage and degradation, which could trigger neuronal cell death. Demyelination, which is caused by a loss of myelin and oligodendrocytes, is a prominent feature of many neurological conditions, including Multiple sclerosis (MS), spinal cord injuries (SCI), and leukodystrophies. Demyelination is followed by a time of remyelination mediated by the recruitment of endogenous oligodendrocyte precursor cells, their migration to the injury site, and differentiation into myelin-producing oligodendrocytes. Unfortunately, endogenous remyelination is not sufficient to overcome demyelination, which explains why there are to date no regenerative-based treatments for MS, SCI, or leukodystrophies. To better understand the role of oligodendrocytes and develop cell-based remyelination therapies, human oligodendrocytes have been derived from somatic cells using cell reprogramming. This review will detail the different cell reprogramming methods that have been developed to generate human oligodendrocytes and their applications to disease modeling and cell-based remyelination therapies. Recent developments in the field have seen the derivation of brain organoids from pluripotent stem cells, and protocols have been devised to incorporate oligodendrocytes within the organoids, which will also be reviewed.

Modelling the Interplay Between Neuron-Glia Cell Dysfunction and Glial Therapy in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complicated, interpersonally defined, static condition of the underdeveloped brain. Although the aetiology of autism remains unclear, disturbance of neuronglia interactions has lately been proposed as a significant event in the pathophysiology of ASD. In recent years, the contribution of glial cells to autism has been overlooked. In addition to neurons, glial cells play an essential role in mental activities, and a new strategy that emphasises neuron-glia interactions should be applied. Disturbance of neuron-glia connections has lately been proposed as a significant event in the pathophysiology of ASD because aberrant neuronal network formation and dysfunctional neurotransmission are fundamental to the pathology of the condition. In ASD, neuron and glial cell number changes cause brain circuits to malfunction and impact behaviour. A study revealed that reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Recent discoveries also suggest that dysfunction or changes in the ability of microglia to carry out physiological and defensive functions (such as failure in synaptic elimination or aberrant microglial activation) may be crucial for developing brain diseases, especially autism. The cerebellum, white matter, and cortical regions of autistic patients showed significant microglial activation. Reactive glial cells result in the loss of synaptic functioning and induce autism under inflammatory conditions. Replacement of defective glial cells (Cell-replacement treatment), glial progenitor cell-based therapy, and medication therapy (inhibition of microglia activation) are all utilised to treat glial dysfunction. This review discusses the role of glial cells in ASD and the various potential approaches to treating glial cell dysfunction.

Identifying Genes that Affect Differentiation of Human Neural Stem Cells and Myelination of Mature Oligodendrocytes

Human neural stem cells (NSCs) are self-renewing, multipotent cells of the central nervous system (CNS). They are characterized by their ability to differentiate into a range of cells, including oligodendrocytes (OLs), neurons, and astrocytes, depending on exogenous stimuli. An efficient and easy directional differentiation method was developed for obtaining large quantities of high-quality of human OL progenitor cells (OPCs) and OLs from NSCs. RNA sequencing, immunofluorescence staining, flow cytometry, western blot, label-free proteomic sequencing, and qPCR were performed in OL lines differentiated from NSC lines. The changes in the positive rate of typical proteins were analyzed expressed by NSCs, neurons, astrocytes, OPCs, and OLs. We assessed Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of differentially expressed (DE) messenger RNAs (mRNAs) related to the differentiation of NSCs and the maturation of OLs. The percentage of NSCs differentiated into neurons, astrocytes, and OLs was 82.13%, 80.19%, and 90.15%, respectively. We found that nestin, PAX6, Musashi, and vimentin were highly expressed in NSCs; PDGFR-α, A2B5, NG2, OLIG2, SOX10, and NKX2-2 were highly expressed in OPCs; and CNP, GALC, PLP1, and MBP were highly expressed in OLs. RNA sequencing, western blot and qPCR revealed that ERBB4 and SORL1 gradually increased during NSC–OL differentiation. In conclusion, NSCs can differentiate into neurons, astrocytes, and OLs efficiently. PDGFR-α, APC, ID4, PLLP, and other markers were related to NSC differentiation and OL maturation. Moreover, we refined a screening method for ERBB4 and SORL1, which may underlie NSC differentiation and OL maturation.

Graphical Abstract

Potential unreported genes and proteins may regulate differentiation of human neural stem cells into oligodendrocyte lineage. Neural stem cells (NSCs) can differentiate into neurons, astrocytes, and oligodendrocyte (OLs) efficiently. By analyzing the DE mRNAs and proteins of NSCs and OLs lineage, we could identify reported markers and unreported markers of ERBB4 and SORL1 that may underlie regulate NSC differentiation and OL maturation.

A TCF7L2-responsive suppression of both homeostatic and compensatory remyelination in Huntington disease mice

Huntington's disease (HD) is characterized by defective oligodendroglial differentiation and white matter disease. Here, we investigate the role of oligodendrocyte progenitor cell (OPC) dysfunction in adult myelin maintenance in HD. We first note a progressive, age-related loss of myelin in both R6/2 and zQ175 HD mice compared with wild-type controls. Adult R6/2 mice then manifest a significant delay in remyelination following cuprizone demyelination. RNA-sequencing and proteomic analysis of callosal white matter and OPCs isolated from both R6/2 and zQ175 mice reveals a systematic downregulation of genes associated with oligodendrocyte differentiation and myelinogenesis. Gene co-expression and network analysis predicts repressed Tcf7l2 signaling as a major driver of this expression pattern. In vivo Tcf7l2 overexpression restores both myelin gene expression and remyelination in demyelinated R6/2 mice. These data causally link impaired TCF7L2-dependent transcription to the poor development and homeostatic retention of myelin in HD and provide a mechanism for its therapeutic restoration.

A2B5 Expression in Central Nervous System and Gliomas

A2B5 IgM recognizes c-series gangliosides with three sialic acids. The aim of this review was to focus on A2B5 expression in the central nervous system and gliomas. In brain development, A2B5+ cells are recorded in areas containing multipotent neural stem cells (NSC). In adults, A2B5+ cells persist in neurogenic areas and in white matter where it identifies oligodendrocyte precursor cells (OPCs) but also cells with NSC properties. Although the expression of A2B5 has been widely studied in culture, where it characterizes bipotential glial progenitor cells, its expression in vivo is less characterized mainly because of technical issues. A new interest was given to the NSCs and OPCs since the discovery of cancer stem cells (CSC) in gliomas. Among other cell surface molecules, A2B5 has been identified as an accurate marker to identify glioma CSCs. We and others have shown that all types of gliomas express A2B5, and that only A2B5+ cells, and not A2B5- cells, can generate a tumor after orthotopic implantation in immunocompromised animals. Moreover, A2B5 epitope expression is positively correlated with stemness and tumor growth. This review highlights that A2B5 is an attractive target to tackle glioma CSCs, and a better characterization of its expression in the developing and adult CNS will benefit to a better understanding of gliomagenesis.

The Relevance of Circadian Clocks to Stem Cell Differentiation and Cancer Progression

The molecular mechanism of circadian clocks depends on transcription-translation feedback loops (TTFLs) that have known effects on key cellular processes. However, the distinct role of circadian TTFLs in mammalian stem cells and other less differentiated cells remains poorly understood. Neural stem cells (NSCs) of the brain generate neurons and glia postnatally but also may become cancer stem cells (CSCs), particularly in astrocytomas. Evidence indicates clock TTFL impairment is needed for tumor growth and progression; although, this issue has been examined primarily in more differentiated cancer cells rather than CSCs. Similarly, few studies have examined circadian rhythms in NSCs. After decades of research, it is now well recognized that tumors consist of CSCs and a range of other cancer cells along with noncancerous stromal cells. The circadian properties of these many contributors to tumor properties and treatment outcome are being widely explored. New molecular tools and ones in development will likely enable greater discrimination of important circadian and non-circadian cells within malignancies at multiple stages of cancer progression and following therapy. Here, we focus on adult NSCs and glioma CSCs to address how cells at different stages of differentiation may harbor unique states of the molecular circadian clock influencing differentiation and cell fate.

Human oligodendrocyte myelination potential; relation to age and differentiation

OBJECTIVE

Myelin regeneration in the human central nervous system relies on progenitor cells within the tissue parenchyma, with possible contribution from previously myelinating oligodendrocytes. In multiple sclerosis, a demyelinating disorder, variables affecting remyelination efficiency include age, severity of initial injury, and progenitor cell properties. Our aim was to investigate the effects of age and differentiation on the myelination potential of human oligodendrocyte lineage cells.

METHODS

We derived viable primary oligodendrocyte lineage cells from surgical resections of pediatric and adult brain tissue. Ensheathment capacity using nanofiber assays and transcriptomic profiles from RNA sequencing were compared between A2B5+ antibody-selected progenitors and mature oligodendrocytes (non-selected cells).

RESULTS

We demonstrate that pediatric progenitor and mature cells ensheathed nanofibers more robustly than did adult progenitor and mature cells respectively. Within both age groups, the percentage of fibers ensheathed and ensheathment length per fiber were greater for A2B5+ progenitors. Gene expression of oligodendrocyte progenitor markers PDGFRA and PTPRZ1 were higher in A2B5+ vs A2B5- cells and in pediatric A2B5+ vs adult A2B5+ cells. p38 MAP kinases and actin cytoskeleton-associated pathways were upregulated in pediatric cells; both have been shown to regulate OL process outgrowth. Significant upregulation of "cell senescence" genes was detected in pediatric samples; this could reflect their role in development and the increased susceptibility of pediatric oligodendrocytes to activating cell death responses to stress.

INTERPRETATION

Our findings identify specific biological pathways relevant to myelination that are differentially enriched in human pediatric and adult oligodendrocyte lineage cells and suggest potential targets for remyelination enhancing therapies. This article is protected by copyright. All rights reserved.

Identifying the functions of two biomarkers in human oligodendrocyte progenitor cell development

BACKGROUND

Human oligodendrocyte precursor cells (hOPCs) are an important source of myelinating cells for cell transplantation to treat demyelinating diseases. Myelin oligodendrocytes develop from migratory and proliferative hOPCs. It is well known that NG2 and A2B5 are important biological markers of hOPCs. However, the functional differences between the cell populations represented by these two biomarkers have not been well studied in depth.

OBJECTIVE

To study the difference between NG2 and A2B5 cells in the development of human oligodendrocyte progenitor cells.

METHODS

Using cell sorting technology, we obtained NG2+/-, A2B5+/- cells. Further research was then conducted via in vitro cell proliferation and migration assays, single-cell sequencing, mRNA sequencing, and cell transplantation into shiverer mice.

RESULTS

The proportion of PDGFR-α + cells in the negative cell population was higher than that in the positive cell population. The migration ability of the NG2+/-, A2B5+/- cells was inversely proportional to their myelination ability. The migration, proliferation, and myelination capacities of the negative cell population were stronger than those of the positive cell population. The ability of cell migration and proliferation of the four groups of cells from high to low was: A2B5- > NG2- > NG2+ > A2B5+. The content of PDGFR-α+ cells and the ability of cell differentiation from high to low was: NG2- > A2B5- > A2B5+ > NG2+.

CONCLUSION

In summary, NG2+  and A2B5+ cells have poor myelination ability due to low levels of PDGFR-α+ cells. Therefore, hOPCs with a higher content of PDGFR-α+ cells may have a better effect in the cell transplantation treatment of demyelinating diseases.

Effect of mesenchymal stem cells transplantation on the changes of oligodendrocyte lineage in rat brain with experimental autoimmune encephalomyelitis

OBJECTIVE

To explore the effect of bone marrow mesenchymal stem cells (BM-MSCs) transplantation on the changes of oligodendrocyte lineage in brain of experimental autoimmune encephalomyelitis (EAE) rats.

METHODS

The animals were divided into normal control group, EAE model group (EAE group), cell culture medium injection treatment group (placebo treatment group), and MSCs treatment group (treatment group). The changes of A2B5-, O4-, and CNPase-positive cells in oligodendrocyte lineage in rat brain were observed after 1, 3, 7, 14, 21, and 28 days.

RESULTS

The number of A2B5-positive cells in rat brain of the treatment group at each time point was significantly more than that of the EAE and placebo treatment groups, and most obvious at 14 days. The O4-positive cells number at each time point in the treatment group was significantly increased compared with the EAE and placebo treatment groups, and most obvious at 14 days. The CNPase-positive cells number at each time point in the treatment group was significantly increased compared with the EAE and placebo treatment groups, and most obvious at 14 days.

CONCLUSIONS

MSCs treatment can increase cells expression in oligodendrocyte lineage, which laying a solid foundation for myelin regeneration.

Glial progenitor cell-based repair of the dysmyelinated brain: Progression to the clinic

Demyelinating disorders of the central white matter are among the most prevalent and disabling conditions in neurology. Since myelin-producing oligodendrocytes comprise the principal cell type deficient or lost in these conditions, their replacement by new cells generated from transplanted bipotential oligodendrocyte-astrocyte progenitor cells has emerged as a therapeutic strategy for a variety of primary dysmyelinating diseases. In this review, we summarize the research and clinical considerations supporting current efforts to bring this treatment approach to patients.

Human stem cell-derived oligodendrocytes: From humanized animal models to cell therapy in myelin diseases

Oligodendrocytes are main targets in demyelinating and dysmyelinating diseases of the central nervous system (CNS), but are also involved in accidental, neurodegenerative and psychiatric disorders. The underlying pathology of these diseases is not fully understood and treatments are still lacking. The recent discovery of the induced pluripotent stem cell (iPSC) technology has open the possibility to address the biology of human oligodendroglial cells both in the dish and in vivo via engraftment in animal models, and paves the way for the development of treatment for myelin disorders. In this review, we make a short overview of the different sources human oligodendroglial cells, and animal models available for pre-clinical cell therapy. We discuss the anatomical and functional benefit of grafted iPSC-progenitors over their brain counterparts, their use in disease modeling and the missing gaps that still prevent to study their biology in the most integrated way, and to translate iPSC-stem cell based therapy to the clinic.

Glial restricted precursor cells in central nervous system disorders: Current applications and future perspectives

The crosstalk between glial cells and neurons represents an exceptional feature for maintaining the normal function of the central nervous system (CNS). Increasing evidence has revealed the importance of glial progenitor cells in adult neurogenesis, reestablishment of cellular pools, neuroregeneration, and axonal (re)myelination. Several types of glial progenitors have been described, as well as their potentialities for recovering the CNS from certain traumas or pathologies. Among these precursors, glial-restricted precursor cells (GRPs) are considered the earliest glial progenitors and exhibit tripotency for both Type I/II astrocytes and oligodendrocytes. GRPs have been derived from embryos and embryonic stem cells in animal models and have maintained their capacity for self-renewal. Despite the relatively limited knowledge regarding the isolation, characterization, and function of these progenitors, GRPs are promising candidates for transplantation therapy and reestablishment/repair of CNS functions in neurodegenerative and neuropsychiatric disorders, as well as in traumatic injuries. Herein, we review the definition, isolation, characterization and potentialities of GRPs as cell-based therapies in different neurological conditions. We briefly discuss the implications of using GRPs in CNS regenerative medicine and their possible application in a clinical setting. MAIN POINTS: GRPs are progenitors present in the CNS with differentiation potential restricted to the glial lineage. These cells have been employed in the treatment of a myriad of neurodegenerative and traumatic pathologies, accompanied by promising results, herein reviewed.

From cells to tissue: How cell scale heterogeneity impacts glioblastoma growth and treatment response

Glioblastomas are aggressive primary brain tumors known for their inter- and intratumor heterogeneity. This disease is uniformly fatal, with intratumor heterogeneity the major reason for treatment failure and recurrence. Just like the nature vs nurture debate, heterogeneity can arise from intrinsic or environmental influences. Whilst it is impossible to clinically separate observed behavior of cells from their environmental context, using a mathematical framework combined with multiscale data gives us insight into the relative roles of variation from different sources. To better understand the implications of intratumor heterogeneity on therapeutic outcomes, we created a hybrid agent-based mathematical model that captures both the overall tumor kinetics and the individual cellular behavior. We track single cells as agents, cell density on a coarser scale, and growth factor diffusion and dynamics on a finer scale over time and space. Our model parameters were fit utilizing serial MRI imaging and cell tracking data from ex vivo tissue slices acquired from a growth-factor driven glioblastoma murine model. When fitting our model to serial imaging only, there was a spectrum of equally-good parameter fits corresponding to a wide range of phenotypic behaviors. When fitting our model using imaging and cell scale data, we determined that environmental heterogeneity alone is insufficient to match the single cell data, and intrinsic heterogeneity is required to fully capture the migration behavior. The wide spectrum of in silico tumors also had a wide variety of responses to an application of an anti-proliferative treatment. Recurrent tumors were generally less proliferative than pre-treatment tumors as measured via the model simulations and validated from human GBM patient histology. Further, we found that all tumors continued to grow with an anti-migratory treatment alone, but the anti-proliferative/anti-migratory combination generally showed improvement over an anti-proliferative treatment alone. Together our results emphasize the need to better understand the underlying phenotypes and tumor heterogeneity present in a tumor when designing therapeutic regimens.

Use of human pluripotent stem cell-derived cells for neurodegenerative disease modeling and drug screening platform

Most neurodegenerative diseases are characterized by a complex and mostly still unresolved pathology. This fact, together with the lack of reliable disease models, has precluded the development of effective therapies counteracting the disease progression. The advent of human pluripotent stem cells has revolutionized the field allowing the generation of disease-relevant neural cell types that can be used for disease modeling, drug screening and, possibly, cell transplantation purposes. In this Review, we discuss the applications of human pluripotent stem cells, the development of efficient protocols for the derivation of the different neural cells and their applicability for robust in vitro disease modeling and drug screening platforms for most common neurodegenerative conditions.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.

Lesion Dynamics Under Varying Paracrine PDGF Signaling in Brain Tissue

Paracrine PDGF signaling is involved in many processes in the body, both normal and pathological, including embryonic development, angiogenesis, and wound healing as well as liver fibrosis, atherosclerosis, and cancers. We explored this seemingly dual (normal and pathological) role of PDGF mathematically by modeling the release of PDGF in brain tissue and then varying the dynamics of this release. Resulting simulations show that by varying the dynamics of a PDGF source, our model predicts three possible outcomes for PDGF-driven cellular recruitment and lesion growth: (1) localized, short duration of growth, (2) localized, chronic growth, and (3) widespread chronic growth. Further, our model predicts that the type of response is much more sensitive to the duration of PDGF exposure than the maximum level of that exposure. This suggests that extended duration of paracrine PDGF signal during otherwise normal processes could potentially lead to lesions having a phenotype consistent with pathologic conditions.

Human Glial Chimeric Mice to Define the Role of Glial Pathology in Human Disease

Human glial progenitor cells (hGPCs) can engraft, expand, and differentiate into functional oligodendrocytes and astrocytes when transplanted neonatally into murine hosts, in which they outcompete the host glial pool to ultimately colonize and dominate the recipient brains. When congenitally hypomyelinated mutants are used as hosts, the donor hGPCs generate myelinogenic oligodendrocytes as well as astrocytes, so that the recipient mice develop a largely humanized white matter, with entirely human-derived myelin. In addition, by neonatally engrafting hGPCs derived from patient- and disease-specific pluripotent stem cells, glial chimeric mice may be produced in which large proportions of all macroglial cells are not only human but also patient and disease specific. Human glial chimeric mice thus provide intriguing preparations by which to investigate the species-specific contributions of human glia to both cognition and human-selective neurodegenerative and neuropsychiatric diseases, as well as the potential for therapeutic glial cell replacement in these disorders. This review presents an overview of the uses, characteristics, and limitations of the human glial chimeric brain model, while providing a step-by-step protocol for the establishment of these mice.

Innate Immune Responses and Viral-Induced Neurologic Disease

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by chronic neuroinflammation, axonal damage, and demyelination. Cellular components of the adaptive immune response are viewed as important in initiating formation of demyelinating lesions in MS patients. This notion is supported by preclinical animal models, genome-wide association studies (GWAS), as well as approved disease modifying therapies (DMTs) that suppress clinical relapse and are designed to impede infiltration of activated lymphocytes into the CNS. Nonetheless, emerging evidence demonstrates that the innate immune response e.g., neutrophils can amplify white matter damage through a variety of different mechanisms. Indeed, using a model of coronavirus-induced neurologic disease, we have demonstrated that sustained neutrophil infiltration into the CNS of infected animals correlates with increased demyelination. This brief review highlights recent evidence arguing that targeting the innate immune response may offer new therapeutic avenues for treatment of demyelinating disease including MS.

Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc.

Emerging Cellular and Molecular Strategies for Enhancing Central Nervous System (CNS) Remyelination

Myelination is critical for the normal functioning of the central nervous system (CNS) in vertebrates. Conditions in which the development of myelin is perturbed result in severely compromised individuals often with shorter lifespans, while loss of myelin in the adult results in a variety of functional deficits. Although some form of spontaneous remyelination often takes place, the repair process as a whole often fails. Several lines of evidence suggest it is feasible to develop strategies that enhance the capacity of the CNS to undergo remyelination and potentially reverse functional deficits. Such strategies include cellular therapies using either neural or mesenchymal stem cells as well as molecular regulators of oligodendrocyte development and differentiation. Given the prevalence of demyelinating diseases and their effects on the quality of life for affected individuals it is imperative that effective therapies are developed. Here we discuss some of the new approaches to CNS myelin repair that hold promise for reducing the burden of diseases characterized by myelin loss.

Clinical implications of myelin regeneration in the central nervous system

INTRODUCTION

Amongst strategies to repair the brain, myelin repair offers genuine cause for optimism. Myelin, which sheaths most axons in the central nervous system (CNS), is vital for normal neurological function, as demonstrated by the functional deficits that accrue when it is absent in a range of debilitating myelin diseases. Following demyelination, post-mortem and imaging studies have shown that extensive regeneration of myelin is possible in the human brain. Over recent decades preclinical research has given us a strong understanding of the biology of myelin regeneration, opening up several exciting therapeutic opportunities that are on the cusp of clinical translation. Areas covered: This review discusses diseases that compromise the function of myelin, the endogenous capacity of the CNS to regenerate myelin, and why this sometimes fails. We then outline the extensive progress that has been made towards therapies that promote the regeneration of myelin. Expert commentary: Finally, a commentary on the first examples of these therapies to reach human patients and the evidence base that supports them, giving our opinion on where attention should be focused going forward is provided.

The Updated World Health Organization Glioma Classification: Cellular and Molecular Origins of Adult Infiltrating Gliomas

CONTEXT

- In the recently updated World Health Organization (WHO) classification of central nervous system tumors, our concept of infiltrating gliomas as a molecular dichotomy between oligodendroglial and astrocytic tumors has been codified. Advances in animal models of glioma and a wealth of sophisticated molecular analyses of human glioma tissue have led to a greater understanding of some of the biologic underpinnings of gliomagenesis.

OBJECTIVE

- To review our understanding of gliomagenesis in the setting of the recently updated WHO classification of central nervous system tumors. Topics addressed include a summary of an updated diagnostic schema for infiltrating gliomas, the crucial importance of isocitrate dehydrogenase mutations, candidate cells of origin for gliomas, environmental and other posited contributing factors to gliomagenesis, and the possible role of chromatin topology in setting the stage for gliomagenesis.

DATA SOURCES

- We conducted a primary literature search using PubMed.

CONCLUSIONS

- With multidimensional molecular data sets spanning increasingly larger numbers of patients with infiltrating gliomas, our understanding of the disease at the point of surgical resection has improved dramatically and this understanding is reflected in the updated WHO classification. Animal models have demonstrated a diversity of candidates for glioma cells of origin, but crucial questions remain, including the role of neural stem cells, more differentiated progenitor cells, and glioma stem cells. At this stage the increase in data generated from human samples will hopefully inform the creation of newer animal models that will recapitulate more accurately the diversity of gliomas and provide novel insights into the biologic mechanisms underlying tumor initiation and progression.

Simulating PDGF-Driven Glioma Growth and Invasion in an Anatomically Accurate Brain Domain

Gliomas are the most common of all primary brain tumors. They are characterized by their diffuse infiltration of the brain tissue and are uniformly fatal, with glioblastoma being the most aggressive form of the disease. In recent years, the over-expression of platelet-derived growth factor (PDGF) has been shown to produce tumors in experimental rodent models that closely resemble this human disease, specifically the proneural subtype of glioblastoma. We have previously modeled this system, focusing on the key attribute of these experimental tumors-the "recruitment" of oligodendroglial progenitor cells (OPCs) to participate in tumor formation by PDGF-expressing retrovirally transduced cells-in one dimension, with spherical symmetry. However, it has been observed that these recruitable progenitor cells are not uniformly distributed throughout the brain and that tumor cells migrate at different rates depending on the material properties in different regions of the brain. Here we model the differential diffusion of PDGF-expressing and recruited cell populations via a system of partial differential equations with spatially variable diffusion coefficients and solve the equations in two spatial dimensions on a mouse brain atlas using a flux-differencing numerical approach. Simulations of our in silico model demonstrate qualitative agreement with the observed tumor distribution in the experimental animal system. Additionally, we show that while there are higher concentrations of OPCs in white matter, the level of recruitment of these plays little role in the appearance of "white matter disease," where the tumor shows a preponderance for white matter. Instead, simulations show that this is largely driven by the ratio of the diffusion rate in white matter as compared to gray. However, this ratio has less effect on the speed of tumor growth than does the degree of OPC recruitment in the tumor. It was observed that tumor simulations with greater degrees of recruitment grow faster and develop more nodular tumors than if there is no recruitment at all, similar to our prior results from implementing our model in one dimension. Combined, these results show that recruitment remains an important consideration in understanding and slowing glioma growth.

Geminin Participates in Differentiation Decisions of Adult Neural Stem Cells Transplanted in the Hemiparkinsonian Mouse Brain

Neural stem cells have been considered as a source of stem cells that can be used for cell replacement therapies in neurodegenerative diseases, as they can be isolated and expanded in vitro and can be used for autologous grafting. However, due to low percentages of survival and varying patterns of differentiation, strategies that will enhance the efficacy of transplantation are under scrutiny. In this article, we have examined whether alterations in Geminin's expression, a protein that coordinates the balance between self-renewal and differentiation, can improve the properties of stem cells transplanted in 6-OHDA hemiparkinsonian mouse model. Our results indicate that, in the absence of Geminin, grafted cells differentiating into dopaminergic neurons were decreased, while an increased number of oligodendrocytes were detected. The number of proliferating multipotent cells was not modified by the absence of Geminin. These findings encourage research related to the impact of Geminin on transplantations for neurodegenerative disorders, as an important molecule in influencing differentiation decisions of the cells composing the graft.

Progenitor cell-based treatment of glial disease

Diseases of glia, including astrocytes and oligodendrocytes, are among the most prevalent and disabling, yet least appreciated, conditions in neurology. In recent years, it has become clear that besides the overtly glial disorders of oligodendrocyte loss and myelin failure, such as the leukodystrophies and inflammatory demyelinations, a number of neurodegenerative and psychiatric disorders may also be causally linked to glial dysfunction and derive from astrocytic as well as oligodendrocytic pathology. The relative contribution of glial dysfunction to many of these disorders may be so great as to allow their treatment by the delivery of allogeneic glial progenitor cells, the precursors to both astroglia and myelin-producing oligodendrocytes. Given the development of new methods for producing and isolating these cells from pluripotent stem cells, both the myelin disorders and appropriate glial-based neurodegenerative conditions may now be compelling targets for cell-based therapy. As such, glial cell-based therapies may offer potential benefit to a broader range of diseases than ever before contemplated, including disorders such as Huntington's disease and the motor neuron degeneration of amyotrophic lateral sclerosis, which have traditionally been considered neuronal in nature.

Stem and Progenitor Cell-Based Therapy of the Central Nervous System: Hopes, Hype, and Wishful Thinking

A variety of neurological disorders are attractive targets for stem and progenitor cell-based therapy. Yet many conditions are not, whether by virtue of an inhospitable disease environment, poorly understood pathophysiology, or poor alignment of donor cell capabilities with patient needs. Moreover, some disorders may be medically feasible targets but are not practicable, in light of already available treatments, poor risk-benefit and cost-benefit profiles, or resource limitations. This Perspective seeks to define those neurological conditions most appropriate for cell replacement therapy by considering its potential efficacy and clinical feasibility in those disorders, as well as potential impediments to its application.

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.

How to make an oligodendrocyte

Oligodendrocytes produce myelin, an insulating sheath required for the saltatory conduction of electrical impulses along axons. Oligodendrocyte loss results in demyelination, which leads to impaired neurological function in a broad array of diseases ranging from pediatric leukodystrophies and cerebral palsy, to multiple sclerosis and white matter stroke. Accordingly, replacing lost oligodendrocytes, whether by transplanting oligodendrocyte progenitor cells (OPCs) or by mobilizing endogenous progenitors, holds great promise as a therapeutic strategy for the diseases of central white matter. In this Primer, we describe the molecular events regulating oligodendrocyte development and how our understanding of this process has led to the establishment of methods for producing OPCs and oligodendrocytes from embryonic stem cells and induced pluripotent stem cells, as well as directly from somatic cells. In addition, we will discuss the safety of engrafted stem cell-derived OPCs, as well as approaches by which to modulate their differentiation and myelinogenesis in vivo following transplantation.

Glial progenitor cell-based treatment of the childhood leukodystrophies

The childhood leukodystrophies comprise a group of hereditary disorders characterized by the absence, malformation or destruction of myelin. These disorders share common clinical, radiological and pathological features, despite their diverse molecular and genetic etiologies. Oligodendrocytes and astrocytes are the major affected cell populations, and are either structurally impaired or metabolically compromised through cell-intrinsic pathology, or are the victims of mis-accumulated toxic byproducts of metabolic derangement. In either case, glial cell replacement using implanted tissue or pluripotent stem cell-derived human neural or glial progenitor cells may comprise a promising strategy for both structural remyelination and metabolic rescue. A broad variety of pediatric white matter disorders, including the primary hypomyelinating disorders, the lysosomal storage disorders, and the broader group of non-lysosomal metabolic leukodystrophies, may all be appropriate candidates for glial progenitor cell-based treatment. Nonetheless, a variety of specific challenges remain before this therapeutic strategy can be applied to children. These include timely diagnosis, before irreparable neuronal injury has ensued; understanding the natural history of the targeted disease; defining the optimal cell phenotype for each disorder; achieving safe and scalable cellular compositions; designing age-appropriate controlled clinical trials; and for autologous therapy of genetic disorders, achieving the safe genetic editing of pluripotent stem cells. Yet these challenges notwithstanding, the promise of glial progenitor cell-based treatment of the childhood myelin disorders offers hope to the many victims of this otherwise largely untreatable class of disease.

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

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

Characterization of Proliferating Neural Progenitors after Spinal Cord Injury in Adult Zebrafish

Zebrafish can repair their injured brain and spinal cord after injury unlike adult mammalian central nervous system. Any injury to zebrafish spinal cord would lead to increased proliferation and neurogenesis. There are presences of proliferating progenitors from which both neuronal and glial loss can be reversed by appropriately generating new neurons and glia. We have demonstrated the presence of multiple progenitors, which are different types of proliferating populations like Sox2⁺ neural progenitor, A2B5⁺ astrocyte/ glial progenitor, NG2⁺ oligodendrocyte progenitor, radial glia and Schwann cell like progenitor. We analyzed the expression levels of two common markers of dedifferentiation like msx-b and vimentin during regeneration along with some of the pluripotency associated factors to explore the possible role of these two processes. Among the several key factors related to pluripotency, pou5f1 and sox2 are upregulated during regeneration and associated with activation of neural progenitor cells. Uncovering the molecular mechanism for endogenous regeneration of adult zebrafish spinal cord would give us more clues on important targets for future therapeutic approach in mammalian spinal cord repair and regeneration.

Promoting remyelination: utilizing a viral model of demyelination to assess cell-based therapies

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS. While a broad range of therapeutics effectively reduce the incidence of focal white matter inflammation and plaque formation for patients with relapse-remitting forms of MS, a challenge within the field is to develop therapies that allow for axonal protection and remyelination. In the last decade, growing interest has focused on utilizing neural precursor cells (NPCs) to promote remyelination. To understand how NPCs function in chronic demyelinating environments, several excellent pre-clinical mouse models have been developed. One well accepted model is infection of susceptible mice with neurotropic variants of mouse hepatitis virus (MHV) that undergo chronic demyelination exhibiting clinical and histopathologic similarities to MS patients. Combined with the possibility that an environmental agent such as a virus could trigger MS, the MHV model of demyelination presents a relevant mouse model to assess the therapeutic potential of NPCs transplanted into an environment in which inflammatory-mediated demyelination is established.

NG2-glia and their functions in the central nervous system

In the central nervous system, NG2-glia represent a neural cell population that is distinct from neurons, astrocytes, and oligodendrocytes. While in the past the main role ascribed to these cells was that of progenitors for oligodendrocytes, in the last years it has become more obvious that they have further functions in the brain. Here, we will discuss some of the most current and highly debated issues regarding NG2-glia: Do these cells represent a heterogeneous population? Can they give rise to different progenies, and does this change under pathological conditions? How do they respond to injury or pathology? What is the role of neurotransmitter signaling between neurons and NG2-glia? We will first give an overview on the developmental origin of NG2-glia, and then discuss whether their distinct properties in different brain regions are the result of environmental influences, or due to intrinsic differences. We will then review and discuss their in vitro differentiation potential and in vivo lineage under physiological and pathological conditions, together with their electrophysiological properties in distinct brain regions and at different developmental stages. Finally, we will focus on their potential to be used as therapeutic targets in demyelinating and neurodegenerative diseases. Therefore, this review article will highlight the importance of NG2-glia not only in the healthy, but also in the diseased brain.

Modeling cognition and disease using human glial chimeric mice

As new methods for producing and isolating human glial progenitor cells (hGPCs) have been developed, the disorders of myelin have become especially compelling targets for cell-based therapy. Yet as animal modeling of glial progenitor cell-based therapies has progressed, it has become clear that transplanted hGPCs not only engraft and expand within murine hosts, but dynamically outcompete the resident progenitors so as to ultimately dominate the host brain. The engrafted human progenitor cells proceed to generate parenchymal astrocytes, and when faced with a hypomyelinated environment, oligodendrocytes as well. As a result, the recipient brains may become inexorably humanized with regards to their resident glial populations, yielding human glial chimeric mouse brains. These brains provide us a fundamentally new tool by which to assess the species-specific attributes of glia in modulating human cognition and information processing. In addition, the cellular humanization of these brains permits their use in studying glial infectious and inflammatory disorders unique to humans, and the effects of those disorders on the glial contributions to cognition. Perhaps most intriguingly, by pairing our ability to construct human glial chimeras with the production of patient-specific hGPCs derived from pluripotential stem cells, we may now establish mice in which a substantial proportion of resident glia are both human and disease-derived. These mice in particular may provide us new opportunities for studying the human-specific contributions of glia to psychopathology, as well as to higher cognition. As such, the assessment of human glial chimeric mice may provide us new insight into the species-specific contributions of glia to human cognitive evolution, as well as to the pathogenesis of human neurological and neuropsychiatric disease.

Mesenchymal stem cells and induced pluripotent stem cells as therapies for multiple sclerosis

Multiple sclerosis (MS) is a chronic, autoimmune, inflammatory demyelinating disorder of the central nervous system that leads to permanent neurological deficits. Current MS treatment regimens are insufficient to treat the irreversible neurological disabilities. Tremendous progress in the experimental and clinical applications of cell-based therapies has recognized stem cells as potential candidates for regenerative therapy for many neurodegenerative disorders including MS. Mesenchymal stem cells (MSC) and induced pluripotent stem cell (iPSCs) derived precursor cells can modulate the autoimmune response in the central nervous system (CNS) and promote endogenous remyelination and repair process in animal models. This review highlights studies involving the immunomodulatory and regenerative effects of mesenchymal stem cells and iPSCs derived cells in animal models, and their translation into immunomodulatory and neuroregenerative treatment strategies for MS.

From demyelination to remyelination: the road toward therapies for spinal cord injury

Myelin integrity is crucial for central nervous system (CNS) physiology while its preservation and regeneration after spinal cord injury (SCI) is key to functional restoration. Disturbance of nodal organization acutely after SCI exposes the axon and triggers conduction block in the absence of overt demyelination. Oligodendrocyte (OL) loss and myelin degradation follow as a consequence of secondary damage. Here, we provide an overview of the major biological events and underlying mechanisms leading to OL death and demyelination and discuss strategies to restrain these processes. Another aspect which is critical for SCI repair is the enhancement of endogenously occurring spontaneous remyelination. Recent findings have unveiled the complex roles of innate and adaptive immune responses in remyelination and the immunoregulatory potential of the glial scar. Moreover, the intimate crosstalk between neuronal activity, oligodendrogenesis and myelination emphasizes the contribution of rehabilitation to functional recovery. With a view toward clinical applications, several therapeutic strategies have been devised to target SCI pathology, including genetic manipulation, administration of small therapeutic molecules, immunomodulation, manipulation of the glial scar and cell transplantation. The implementation of new tools such as cellular reprogramming for conversion of one somatic cell type to another or the use of nanotechnology and tissue engineering products provides additional opportunities for SCI repair. Given the complexity of the spinal cord tissue after injury, it is becoming apparent that combinatorial strategies are needed to rescue OLs and myelin at early stages after SCI and support remyelination, paving the way toward clinical translation.

Positive or negative involvement of heat shock proteins in multiple sclerosis pathogenesis: an overview

Multiple sclerosis (MS) is the most diffuse chronic inflammatory disease of the central nervous system. Both immune-mediated and neurodegenerative processes apparently play roles in the pathogenesis of this disease. Heat shock proteins (HSPs) are a family of highly evolutionarily conserved proteins; their expression in the nervous system is induced in a variety of pathologic states, including cerebral ischemia, neurodegenerative diseases, epilepsy, and trauma. To date, investigators have observed protective effects of HSPs in a variety of brain disease models (e.g. of Alzheimer disease and Parkinson disease). In contrast, unequivocal data have been obtained for their roles in MS that depend on the HSP family and particularly on their localization (i.e. intracellular or extracellular). This article reviews our current understanding of the involvement of the principal HSP families in MS.

Glial cells as progenitors and stem cells: new roles in the healthy and diseased brain

The diverse functions of glial cells prompt the question to which extent specific subtypes may be devoted to a specific function. We discuss this by reviewing one of the most recently discovered roles of glial cells, their function as neural stem cells (NSCs) and progenitor cells. First we give an overview of glial stem and progenitor cells during development; these are the radial glial cells that act as NSCs and other glial progenitors, highlighting the distinction between the lineage of cells in vivo and their potential when exposed to a different environment, e.g., in vitro. We then proceed to the adult stage and discuss the glial cells that continue to act as NSCs across vertebrates and others that are more lineage-restricted, such as the adult NG2-glia, the most frequent progenitor type in the adult mammalian brain, that remain within the oligodendrocyte lineage. Upon certain injury conditions, a distinct subset of quiescent astrocytes reactivates proliferation and a larger potential, clearly demonstrating the concept of heterogeneity with distinct subtypes of, e.g., astrocytes or NG2-glia performing rather different roles after brain injury. These new insights not only highlight the importance of glial cells for brain repair but also their great potential in various aspects of regeneration.

AAV-mediated targeting of gene expression to the peri-infarct region in rat cortical stroke model

BACKGROUND

For stroke patients the recovery of cognitive and behavioral functions is often incomplete. Functional recovery is thought to be mediated largely by connectivity rearrangements in the peri-infarct region. A method for manipulating gene expression in this region would be useful for identifying new recovery-enhancing treatments.

NEW METHOD

We have characterized a way of targeting adeno-associated virus (AAV) vectors to the peri-infarct region of cortical ischemic lesion in rats 2days after middle cerebral artery occlusion (MCAo).

RESULTS

We used magnetic resonance imaging (MRI) to show that the altered properties of post-ischemic brain tissue facilitate the spreading of intrastriatally injected nanoparticles toward the infarct. We show that subcortical injection of green fluorescent protein-encoding dsAAV7-GFP resulted in transduction of cells in and around the white matter tract underlying the lesion, and in the cortex proximal to the lesion. A similar result was achieved with dsAAV7 vector encoding the cerebral dopamine neurotrophic factor (CDNF), a protein with therapeutic potential.

COMPARISON WITH EXISTING METHODS

Viral vector-mediated intracerebral gene delivery has been used before in rodent models of ischemic injury. However, the method of targeting gene expression to the peri-infarct region, after the initial phase of ischemic cell death, has not been described before.

CONCLUSIONS

We demonstrate a straightforward and robust way to target AAV vector-mediated over-expression of genes to the peri-infarct region in a rat stroke model. This method will be useful for studying the action of specific proteins in peri-infarct region during the recovery process.

NG2 cells (polydendrocytes) in brain physiology and repair

NG2 cells, also referred to as oligodendrocyte precursor cells (OPCs) or polydendrocytes, represent a major resident glial cell population that is distinct from mature astrocytes, oligodendrocytes, microglia, and neural stem cells and exist throughout the gray and white matter of the developing and mature central nervous system (CNS). While their most established fate is the oligodendrocyte, they retain lineage plasticity in an age- and region-specific manner. During development, they contribute to 36% of protoplasmic astrocytes in the ventral forebrain. Despite intense investigation on the neuronal fate of NG2 cells, there is no definitive evidence that they contribute substantially to the neuronal population. NG2 cells have attributes that suggest that they have functions other than to generate oligodendrocytes, but their exact role in the neural network remains unknown. Under pathological states, NG2 cells not only contribute to myelin repair, but they become activated in response to a wide variety of insults and could play a primary role in pathogenesis.

SOX2+ cell population from normal human brain white matter is able to generate mature oligodendrocytes

OBJECTIVES

A number of neurodegenerative diseases progress with a loss of myelin, which makes them candidate diseases for the development of cell-replacement therapies based on mobilisation or isolation of the endogenous neural/glial progenitor cells, in vitro expansion, and further implantation. Cells expressing A2B5 or PDGFRA/CNP have been isolated within the pool of glial progenitor cells in the subcortical white matter of the normal adult human brain, all of which demonstrate glial progenitor features. However, the heterogeneity and differentiation potential of this pool of cells is not yet well established.

METHODS

We used diffusion tensor images, histopathology, and immunostaining analysis to demonstrate normal cytoarchitecture and the absence of abnormalities in human temporal lobe samples from patients with mesial temporal sclerosis. These samples were used to isolate and enrich glial progenitor cells in vitro, and later to detect such cells in vivo.

RESULTS

We have identified a subpopulation of SOX2+ cells, most of them co-localising with OLIG2, in the white matter of the normal adult human brain in vivo. These cells can be isolated and enriched in vitro, where they proliferate and generate immature (O4+) and mature (MBP+) oligodendrocytes and, to a lesser extent, astrocytes (GFAP+).

CONCLUSION

Our results demonstrate the existence of a new glial progenitor cell subpopulation that expresses SOX2 in the white matter of the normal adult human brain. These cells might be of use for tissue regeneration procedures.