Postinjury niches induce temporal shifts in progenitor fates to direct lesion repair after spinal cord injury

Extracellular vesicles from UTX-knockout endothelial cells boost neural stem cell differentiation in spinal cord injury

BACKGROUND

Vascular endothelial cells are pivotal in the pathophysiological progression following spinal cord injury (SCI). The UTX (Ubiquitously Transcribed Tetratripeptide Repeat on Chromosome X) serves as a significant regulator of endothelial cell phenotype. The manipulation of endogenous neural stem cells (NSCs) offers a compelling strategy for the amelioration of SCI.

METHODS

Two mouse models were used to investigate SCI: NSCs lineage-traced mice and mice with conditional UTX knockout (UTX KO) in endothelial cells. To study the effects of UTX KO on neural differentiation, we harvested extracellular vesicles (EVs) from both UTX KO spinal cord microvascular endothelial cells (SCMECs) and negative control SCMECs. These EVs were then employed to modulate the differentiation trajectory of endogenous NSCs in the SCI model.

RESULTS

In our NSCs lineage-traced mice model of SCI, a marked decrease in neurogenesis was observed post-injury. Notably, NSCs in UTX KO SCMECs mice showed enhanced neuronal differentiation compared to controls. RNA sequencing and western blot analyses revealed an upregulation of L1 cell adhesion molecule (L1CAM), a gene associated with neurogenesis, in UTX KO SCMECs and their secreted EVs. This aligns with the observed promotion of neurogenesis in UTX KO conditions. In vivo administration of L1CAM-rich EVs from UTX KO SCMECs (KO EVs) to the mice significantly enhanced neural differentiation. Similarly, in vitro exposure of NSCs to KO EVs resulted in increased activation of the Akt signaling pathway, further promoting neural differentiation. Conversely, inhibiting Akt phosphorylation or knocking down L1CAM negated the beneficial effects of KO EVs on NSC neuronal differentiation.

CONCLUSIONS

In conclusion, our findings substantiate that EVs derived from UTX KO SCMECs can act as facilitators of neural differentiation following SCI. This study not only elucidates a novel mechanism but also opens new horizons for therapeutic interventions in the treatment of SCI. Video Abstract.

Understanding the Role of the Glial Scar through the Depletion of Glial Cells after Spinal Cord Injury

Spinal cord injury (SCI) is a condition that affects between 8.8 and 246 people in a million and, unlike many other neurological disorders, it affects mostly young people, causing deficits in sensory, motor, and autonomic functions. Promoting the regrowth of axons is one of the most important goals for the neurological recovery of patients after SCI, but it is also one of the most challenging goals. A key event after SCI is the formation of a glial scar around the lesion core, mainly comprised of astrocytes, NG2⁺-glia, and microglia. Traditionally, the glial scar has been regarded as detrimental to recovery because it may act as a physical barrier to axon regrowth and release various inhibitory factors. However, more and more evidence now suggests that the glial scar is beneficial for the surrounding spared tissue after SCI. Here, we review experimental studies that used genetic and pharmacological approaches to ablate specific populations of glial cells in rodent models of SCI in order to understand their functional role. The studies showed that ablation of either astrocytes, NG2⁺-glia, or microglia might result in disorganization of the glial scar, increased inflammation, extended tissue degeneration, and impaired recovery after SCI. Hence, glial cells and glial scars appear as important beneficial players after SCI.

Glial progenitor heterogeneity and key regulators revealed by single-cell RNA sequencing provide insight to regeneration in spinal cord injury

Recent studies have revealed the heterogeneous nature of astrocytes; however, how diverse constituents of astrocyte-lineage cells are regulated in adult spinal cord after injury and contribute to regeneration remains elusive. We perform single-cell RNA sequencing of GFAP-expressing cells from sub-chronic spinal cord injury models and identify and compare with the subpopulations in acute-stage data. We find subpopulations with distinct functional enrichment and their identities defined by subpopulation-specific transcription factors and regulons. Immunohistochemistry, RNAscope experiments, and quantification by stereology verify the molecular signature, location, and morphology of potential resident neural progenitors or neural stem cells in the adult spinal cord before and after injury and uncover the populations of the intermediate cells enriched in neuronal genes that could potentially transition into other subpopulations. This study has expanded the knowledge of the heterogeneity and cell state transition of glial progenitors in adult spinal cord before and after injury.

Discovery of Hippo signaling as a regulator of CSPG4 expression and as a therapeutic target for Clostridioides difficile disease

The signaling pathways and networks regulating expression of chondroitin sulfate proteoglycan 4 (CSPG4), a cancer-related protein that serves as a receptor for Clostridiodes difficile TcdB, are poorly defined. In this study, TcdB-resistant/CSPG4-negative HeLa cells were generated by exposure to increasing concentrations of the toxin. The cells that emerged (HeLa R5) lost expression of CSPG4 mRNA and were resistant to binding by TcdB. mRNA expression profiles paired with integrated pathway analysis correlated changes in the Hippo and estrogen signaling pathways with a CSPG4 decrease in HeLa R5 cells. Both signaling pathways altered CSPG4 expression when modulated chemically or through CRISPR-mediated deletion of key transcriptional regulators in the Hippo pathway. Based on the in vitro findings, we predicted and experimentally confirmed that a Hippo pathway inactivating drug (XMU-MP-1) provides protection from C. difficile disease in a mouse model. These results provide insights into key regulators of CSPG4 expression and identify a therapeutic for C. difficile disease.

Surgical Considerations to Improve Recovery in Acute Spinal Cord Injury

Acute traumatic spinal cord injury (SCI) can be a devastating and costly event for individuals, their families, and the health system as a whole. Prognosis is heavily dependent on the physical extent of the injury and the severity of neurological dysfunction. If not treated urgently, individuals can suffer exacerbated secondary injury cascades that may increase tissue injury and limit recovery. Initial recognition and rapid treatment of acute SCI are vital to limiting secondary injury, reducing morbidity, and providing the best chance of functional recovery. This article aims to review the pathophysiology of SCI and the most up-to-date management of the acute traumatic SCI, specifically examining the modern approaches to surgical treatments along with the ethical limitations of research in this field.

Retinal ganglion cell expression of cytokine enhances occupancy of NG2 cell-derived astrocytes at the nerve injury site: Implication for axon regeneration

Following injury in the central nervous system, a population of astrocytes occupy the lesion site, form glial bridges and facilitate axon regeneration. These astrocytes originate primarily from resident astrocytes or NG2+ oligodendrocyte progenitor cells. However, the extent to which these cell types give rise to the lesion-filling astrocytes, and whether the astrocytes derived from different cell types contribute similarly to optic nerve regeneration remain unclear. Here we examine the distribution of astrocytes and NG2+ cells in an optic nerve crush model. We show that optic nerve astrocytes partially fill the injury site over time after a crush injury. Viral mediated expression of a growth-promoting factor, ciliary neurotrophic factor (CNTF), in retinal ganglion cells (RGCs) promotes axon regeneration without altering the lesion size or the degree of lesion-filling GFAP+ cells. Strikingly, using inducible NG2CreER driver mice, we found that CNTF overexpression in RGCs increases the occupancy of NG2+ cell-derived astrocytes in the optic nerve lesion. An EdU pulse-chase experiment shows that the increase in NG2 cell-derived astrocytes is not due to an increase in cell proliferation. Lastly, we performed RNA-sequencing on the injured optic nerve and reveal that CNTF overexpression in RGCs results in significant changes in the expression of distinct genes, including those that encode chemokines, growth factor receptors, and immune cell modulators. Even though CNTF-induced axon regeneration has long been recognized, this is the first evidence of this procedure affecting glial cell fate at the optic nerve crush site. We discuss possible implication of these results for axon regeneration.

Recent Advances in Cell and Functional Biomaterial Treatment for Spinal Cord Injury

Spinal cord injury (SCI) is a devastating central nervous system disease caused by accidental events, resulting in loss of sensory and motor function. Considering the multiple effects of primary and secondary injuries after spinal cord injury, including oxidative stress, tissue apoptosis, inflammatory response, and neuronal autophagy, it is crucial to understand the underlying pathophysiological mechanisms, local microenvironment changes, and neural tissue functional recovery for preparing novel treatment strategies. Treatment based on cell transplantation has become the forefront of spinal cord injury therapy. The transplanted cells provide physical and nutritional support for the damaged tissue. At the same time, the implantation of biomaterials with specific biological functions at the site of the SCI has also been proved to improve the local inhibitory microenvironment and promote axonal regeneration, etc. The combined transplantation of cells and functional biomaterials for SCI treatment can result in greater neuroprotective and regenerative effects by regulating cell differentiation, enhancing cell survival, and providing physical and directional support for axon regeneration and neural circuit remodeling. This article reviews the pathophysiology of the spinal cord, changes in the microenvironment after injury, and the mechanisms and strategies for spinal cord regeneration and repair. The article will focus on summarizing and discussing the latest intervention models based on cell and functional biomaterial transplantation and the latest progress in combinational therapies in SCI repair. Finally, we propose the future prospects and challenges of current treatment regimens for SCI repair, to provide references for scientists and clinicians to seek better SCI repair strategies in the future.

The regenerative potential of glial progenitor cells and reactive astrocytes in CNS injuries

Cell therapeutic approaches focusing on the regeneration of damaged tissue have been a popular topic among researchers in recent years. In particular, self-repair scarring from the central nervous system (CNS) can significantly complicate the treatment of an injured patient. In CNS regeneration schemes, either glial progenitor cells or reactive glial cells have key roles to play. In this review, the contribution and underlying mechanisms of these progenitor/reactive glial cells during CNS regeneration are discussed, as well as their role in CNS-related diseases.

Organization of the ventricular zone of the cerebellum

The roof of the fourth ventricle (4V) is located on the ventral part of the cerebellum, a region with abundant vascularization and cell heterogeneity that includes tanycyte-like cells that define a peculiar glial niche known as ventromedial cord. This cord is composed of a group of biciliated cells that run along the midline, contacting the ventricular lumen and the subventricular zone. Although the complex morphology of the glial cells composing the cord resembles to tanycytes, cells which are known for its proliferative capacity, scarce or non-proliferative activity has been evidenced in this area. The subventricular zone of the cerebellum includes astrocytes, oligodendrocytes, and neurons whose function has not been extensively studied. This review describes to some extent the phenotypic, morphological, and functional characteristics of the cells that integrate the roof of the 4V, primarily from rodent brains.

Cellular and Molecular Gradients in the Ventral Horns With Increasing Distance From the Injury Site After Spinal Cord Contusion

To identify cellular and molecular gradients following spinal cord injury (SCI), a rat contusion model of severe SCI was used to investigate the expression of NG2 and molecules that identify astrocytes and axons of the ventral horns (VH) at different distances on 7 and 30 days post-injury (dpi). A gradient of expression of NG2⁺/Olig2⁺ cells was determined, with the highest concentrations focused close to the injury site. A decrease in NG2 mean intensity correlates with a decrease in the number of NG2⁺ cells more distally. Immunoelectron microscopy subsequently revealed the presence of NG2 in connection with the membrane and within the cytoplasm of NG2⁺ glial cells and in large amounts within myelin membranes. Analysis of the astrocyte marker GFAP showed increased expression local to injury site from 7 dpi, this increase in expression spread more distally from the injury site by 30 dpi. Paradoxically, astrocyte perisynaptic processes marker GLT-1 was only increased in expression in areas remote from the epicenter, which was traced both at 7 and 30 dpi. Confocal microscopy showed a significant decrease in the number of 5-HT⁺ axons at a distance from the epicenter in the caudal direction, which is consistent with a decrease in β3-tubulin in these areas. The results indicate significant cellular and molecular reactions not only in the area of the gray matter damage but also in adjacent and remote areas, which is important for assessing the possibility of long-distance axonal growth.

Heat-Shock Proteins Can Potentiate the Therapeutic Ability of Cryopreserved Mesenchymal Stem Cells for the Treatment of Acute Spinal Cord Injury in Dogs

BACKGROUND

Mesenchymal stem cells (MSCs) are applied in the treatment of spinal cord injury (SCI) because of their neural tissue restoring ability. In the clinical setting, intravenous injection of cryopreserved cells is essential for the immediate treatment of SCI, exhibiting the disadvantage of reduced cell properties.

METHODS

In this study, we potentiated the characteristics of cryopreserved MSCs by heat-shock (HS) treatment to induce the expression of HS protein (HSP) HSP70/HSP27 and further improved antioxidant capacity by overexpressing HSP32 (heme oxygenase-1 [HO-1]). We randomly assigned 12 beagle dogs with acute SCI into three groups and transplanted cells intravenously: (i) F-MSCs (MSCs in frozen/thawed conditions); (ii) F-HSP-MSCs (HS-treated MSCs in frozen/thawed conditions); and (iii) F-HSP-HO-MSCs (HO-1-overexpressing and HS-treated MSCs in frozen/thawed conditions).

RESULTS

The potentiated MSCs exhibited increased growth factor-, anti-inflammatory-, antioxidant-, homing- and stemness-related gene expression. In the animal experiments, the HSP-induced groups showed significant improvement in hind-limb locomotion, highly expressed neural markers, less intervened fibrotic changes, and improved myelination. In particular, the HO-1-overexpression group was more prominent, controlling the initial inflammatory response with high antioxidant capabilities, suggesting that antioxidation was important to prevent secondary injury. Accordingly, HSPs not only successfully increased the ability of frozen MSCs but also demonstrated excellent neural protection and regeneration capacity in the case of acute SCI.

CONCLUSIONS

The application of HSP-induced cryopreserved MSCs in first-aid treatment for acute SCI is considered to help early neural sparing and further hind-limb motor function restoration.

Heterogeneity and Molecular Markers for CNS Glial Cells Revealed by Single-Cell Transcriptomics

Glial cells, including astrocytes, oligodendrocytes, and microglia, are the major components in the central nervous system (CNS). Studies have revealed the heterogeneity of each glial cell type and that they each may play distinct roles in physiological processes and/or neurological diseases. Single-cell sequencing (scRNA-seq) technology developed in recent years has extended our understanding of glial cell heterogeneity from the perspective of transcriptome profiling. This review summarizes the marker genes of major glial cells in the CNS and reveals their heterogeneity in different species, CNS regions, developmental stages, and pathological states (Alzheimer's disease and spinal cord injury), expanding our knowledge of glial cell heterogeneity on both molecular and functional levels.

Generation of High-Yield, Functional Oligodendrocytes from a c-myc Immortalized Neural Cell Line, Endowed with Staminal Properties

Neural stem cells represent a powerful tool to study molecules involved in pathophysiology of Nervous System and to discover new drugs. Although they can be cultured and expanded in vitro as a primary culture, their use is hampered by their heterogeneity and by the cost and time needed for their preparation. Here we report that mes-c-myc A1 cells (A1), a neural cell line, is endowed with staminal properties. Undifferentiated/proliferating and differentiated/non-proliferating A1 cells are able to generate neurospheres (Ns) in which gene expression parallels the original differentiation status. In fact, Ns derived from undifferentiated A1 cells express higher levels of Nestin, Kruppel-like factor 4 (Klf4) and glial fibrillary protein (GFAP), markers of stemness, while those obtained from differentiated A1 cells show higher levels of the neuronal marker beta III tubulin. Interestingly, Ns differentiation, by Epidermal Growth Factors (EGF) and Fibroblast Growth Factor 2 (bFGF) withdrawal, generates oligodendrocytes at high-yield as shown by the expression of markers, Galactosylceramidase (Gal-C) Neuron-Glial antigen 2 (NG2), Receptor-Interacting Protein (RIP) and Myelin Basic Protein (MBP). Finally, upon co-culture, Ns-A1-derived oligodendrocytes cause a redistribution of contactin-associated protein (Caspr/paranodin) protein on neuronal cells, as primary oligodendrocytes cultures, suggesting that they are able to form compact myelin. Thus, Ns-A1-derived oligodendrocytes may represent a time-saving and low-cost tool to study the pathophysiology of oligodendrocytes and to test new drugs.

Unraveling the adult cell progeny of early postnatal progenitor cells

NG2-glia, also referred to as oligodendrocyte precursor cells or polydendrocytes, represent a large pool of proliferative neural cells in the adult brain that lie outside of the two major adult neurogenic niches. Although their roles are not fully understood, we previously reported significant clonal expansion of adult NG2-cells from embryonic pallial progenitors using the StarTrack lineage-tracing tool. To define the contribution of early postnatal progenitors to the specific NG2-glia lineage, we used NG2-StarTrack. A temporal clonal analysis of single postnatal progenitor cells revealed the production of different glial cell types in distinct areas of the dorsal cortex but not neurons. Moreover, the dispersion and size of the different NG2 derived clonal cell clusters increased with age. Indeed, clonally-related NG2-glia were located throughout the corpus callosum and the deeper layers of the cortex. In summary, our data reveal that postnatally derived NG2-glia are proliferative cells that give rise to NG2-cells and astrocytes but not neurons. These progenitors undergo clonal cell expansion and dispersion throughout the adult dorsal cortex in a manner that was related to aging and cell identity, adding new information about the ontogeny of these cells. Thus, identification of clonally-related cells from specific progenitors is important to reveal the NG2-glia heterogeneity.

Protein Kinase CK2 Regulates Nerve/Glial Antigen (NG)2-Mediated Angiogenic Activity of Human Pericytes

Protein kinase CK2 is a crucial regulator of endothelial cell proliferation, migration and sprouting during angiogenesis. However, it is still unknown whether this kinase additionally affects the angiogenic activity of other vessel-associated cells. In this study, we investigated the effect of CK2 inhibition on primary human pericytes. We found that CK2 inhibition reduces the expression of nerve/glial antigen (NG)2, a crucial factor which is involved in angiogenic processes. Reporter gene assays revealed a 114 bp transcriptional active region of the human NG2 promoter, whose activity was decreased after CK2 inhibition. Functional analyses demonstrated that the pharmacological inhibition of CK2 by CX-4945 suppresses pericyte proliferation, migration, spheroid sprouting and the stabilization of endothelial tubes. Moreover, aortic rings of NG2^−/− mice showed a significantly reduced vascular sprouting when compared to rings of NG2^+/+ mice, indicating that NG2 is an important regulator of the angiogenic activity of pericytes. In vivo, implanted Matrigel plugs containing CX-4945-treated pericytes exhibited a lower microvessel density when compared to controls. These findings demonstrate that CK2 regulates the angiogenic activity of pericytes through NG2 gene expression. Hence, the inhibition of CK2 represents a promising anti-angiogenic strategy, because it does not only target endothelial cells, but also vessel-associated pericytes.

Cell Fate Potential of NG2 Progenitors

Determining the origin of different glial subtypes is crucial to understand glial heterogeneity, and to enhance our knowledge of glial and progenitor cell behavior in embryos and adults. NG2-glia are homogenously distributed in a grid-like manner in both, gray and white matter of the adult brain. While some NG2-glia in the CNS are responsible for the generation of mature oligodendrocytes (OPCs), most of them do not differentiate and they can proliferate outside of adult neurogenic niches. Thus, NG2-glia constitute a heterogeneous population containing different subpopulations with distinct functions. We hypothesized that their diversity emerges from specific progenitors during development, as occurs with other glial cell subtypes. To specifically target NG2-pallial progenitors and to define the NG2-glia lineage, as well as the NG2-progenitor potential, we designed two new StarTrack strategies using the NG2 promoter. These approaches label NG2 expressing progenitor cells, permitting the cell fates of these NG2 progenitors to be tracked in vivo. StarTrack labelled cells producing different neural phenotypes in different regions depending on the age targeted, and the strategy selected. This specific genetic targeting of neural progenitors in vivo has provided new data on the heterogeneous pool of NG2 progenitors at both embryonic and postnatal ages.

Dissecting the Dual Role of the Glial Scar and Scar-Forming Astrocytes in Spinal Cord Injury

Recovery from spinal cord injury (SCI) remains an unsolved problem. As a major component of the SCI lesion, the glial scar is primarily composed of scar-forming astrocytes and plays a crucial role in spinal cord regeneration. In recent years, it has become increasingly accepted that the glial scar plays a dual role in SCI recovery. However, the underlying mechanisms of this dual role are complex and need further clarification. This dual role also makes it difficult to manipulate the glial scar for therapeutic purposes. Here, we briefly discuss glial scar formation and some representative components associated with scar-forming astrocytes. Then, we analyze the dual role of the glial scar in a dynamic perspective with special attention to scar-forming astrocytes to explore the underlying mechanisms of this dual role. Finally, taking the dual role of the glial scar into account, we provide several pieces of advice on novel therapeutic strategies targeting the glial scar and scar-forming astrocytes.

Longitudinal assessment of recovery after spinal cord injury with behavioral measures and diffusion, quantitative magnetization transfer and functional magnetic resonance imaging

Spinal cord injuries (SCIs) are a leading cause of disability and can severely impact the quality of life. However, to date, the processes of spontaneous repair of damaged spinal cord remain incompletely understood, partly due to a lack of appropriate longitudinal tracking methods. Noninvasive, multiparametric magnetic resonance imaging (MRI) provides potential biomarkers for the comprehensive evaluation of spontaneous repair after SCI. In this study in rats, a clinically relevant contusion injury was introduced at the lumbar level that impairs both hindlimb motor and sensory functions. Quantitative MRI measurements were acquired at baseline and serially post-SCI for up to 2 wk. The progressions of injury and spontaneous recovery in both white and gray matter were tracked longitudinally using pool-size ratio (PSR) measurements derived from quantitative magnetization transfer (qMT) methods, measurements of water diffusion parameters using diffusion tensor imaging (DTI) and intrasegment functional connectivity derived from resting state functional MRI. Changes in these quantitative imaging measurements were correlated with behavioral readouts. We found (a) a progressive decrease in PSR values within 2 wk post-SCI, indicating a progressive demyelination at the center of the injury that was validated with histological staining, (b) PSR correlated closely with fractional anisotropy and transverse relaxation of free water, but did not show significant correlations with behavioral recovery, and (c) preliminary evidence that SCI induced a decrease in functional connectivity between dorsal horns below the injury site at 24 h. Findings from this study not only confirm the value of qMT and DTI methods for assessing the myelination state of injured spinal cord but indicate that they may also have further implications on whether therapies targeted towards remyelination may be appropriate. Additionally, a better understanding of changes after SCI provides valuable information to guide and assess interventions.

Multiple lineages enable robust development of the neuropil-glia architecture in adult Drosophila

Neural remodeling is essential for the development of a functional nervous system and has been extensively studied in the metamorphosis of Drosophila Despite the crucial roles of glial cells in brain functions, including learning and behavior, little is known of how adult glial cells develop in the context of neural remodeling. Here, we show that the architecture of neuropil-glia in the adult Drosophila brain, which is composed of astrocyte-like glia (ALG) and ensheathing glia (EG), robustly develops from two different populations in the larva: the larval EG and glial cell missing-positive (gcm+ ) cells. Whereas gcm+ cells proliferate and generate adult ALG and EG, larval EG dedifferentiate, proliferate and redifferentiate into the same glial subtypes. Each glial lineage occupies a certain brain area complementary to the other, and together they form the adult neuropil-glia architecture. Both lineages require the FGF receptor Heartless to proliferate, and the homeoprotein Prospero to differentiate into ALG. Lineage-specific inhibition of gliogenesis revealed that each lineage compensates for deficiency in the proliferation of the other. Together, the lineages ensure the robust development of adult neuropil-glia, thereby ensuring a functional brain.

Niche stiffness underlies the ageing of central nervous system progenitor cells

Ageing causes a decline in tissue regeneration owing to a loss of function of adult stem cell and progenitor cell populations1. One example is the deterioration of the regenerative capacity of the widespread and abundant population of central nervous system (CNS) multipotent stem cells known as oligodendrocyte progenitor cells (OPCs)2. A relatively overlooked potential source of this loss of function is the stem cell 'niche'-a set of cell-extrinsic cues that include chemical and mechanical signals3,4. Here we show that the OPC microenvironment stiffens with age, and that this mechanical change is sufficient to cause age-related loss of function of OPCs. Using biological and synthetic scaffolds to mimic the stiffness of young brains, we find that isolated aged OPCs cultured on these scaffolds are molecularly and functionally rejuvenated. When we disrupt mechanical signalling, the proliferation and differentiation rates of OPCs are increased. We identify the mechanoresponsive ion channel PIEZO1 as a key mediator of OPC mechanical signalling. Inhibiting PIEZO1 overrides mechanical signals in vivo and allows OPCs to maintain activity in the ageing CNS. We also show that PIEZO1 is important in regulating cell number during CNS development. Thus we show that tissue stiffness is a crucial regulator of ageing in OPCs, and provide insights into how the function of adult stem and progenitor cells changes with age. Our findings could be important not only for the development of regenerative therapies, but also for understanding the ageing process itself.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury

Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.

Furanodienone overcomes temozolomide resistance in glioblastoma through the downregulation of CSPG4-Akt-ERK signalling by inhibiting EGR1-dependent transcription

Glioblastoma multiforme (GBM) is a highly aggressive type of brain tumour. Patients with GBM respond poorly to chemotherapy and have poor survival outcomes. Neuron-glial antigen 2 (NG2), also known as chondroitin sulphate proteoglycan 4 (CSPG4), has been shown to contribute to critical processes, such as cell survival, proliferation, and chemotherapy resistance, during glioma progression. In this study, we found that furanodienone (FUR), a diene-type sesquiterpene isolated from the rhizomes of Rhizoma curcumae, exhibited a potential cytotoxic effect on temozolomide (TMZ)-resistant GBM cells in vitro by inhibiting CSPG4 and related signalling pathways. Studies investigating the mechanism demonstrated that FUR suppressed CSPG4-Akt-ERK signalling, inflammatory responses, and cytokine levels but activated caspase-dependent pathways and mitochondrial dysfunction. Furthermore, an immunofluorescence assay and a dual-luciferase reporter assay revealed that inhibition of EGR1-mediated transcription might have contributed to the FUR-dependent blockade of CSPG4 signalling and glioma cell survival. These results established a link between FUR-induced CSPG4 inhibition and the suppression of EGR1-dependent transcription. Attenuation of ERK1/2 and cytokine signalling might have generated the EGR1-dependent negative feedback loop of the CSPG4 pathway during FUR-induced apoptosis. These findings suggested that FUR could be a therapeutic candidate for the treatment of malignant glioma via targeting CSPG4 signalling.

Oligodendrogliogenesis and Axon Remyelination after Traumatic Spinal Cord Injuries in Animal Studies: A Systematic Review

Extensive oligodendrocyte death after acute traumatic spinal cord injuries (TSCI) leads to axon demyelination and subsequently may leave axons vulnerable to degeneration. Despite the present evidence showing spontaneous remyelination after TSCI the cellular origin of new myelin and the time course of the axon ensheathment/remyelination remained controversial issue. In this systematic review the trend of oligodendrocyte death after injury as well as the extent and the cellular origin of oligodendrogliogenesis were comprehensively evaluated. The study design was based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-guided systematic review. PubMed and EMBASE were searched with no temporal or linguistic restrictions. Also, hand-search was performed in the bibliographies of relevant articles. Non-interventional animal studies discussing different types of myelinating cells including oligodendrocytes, Schwann cells and oligodendrocyte progenitor cells (OPCs) were evaluated. The extent of oligodendrocyte death, oligodendrocyte differentiation and remyelination were the pathophysiological outcome measures. We found 12,359 studies, 34 of which met the inclusion criteria. The cumulative evidence shows extensive oligodendrocytes cell death during the first week post-injury (pi). OPCs and peripheral invading Schwann cells are the dominant cells contributing in myelin formation. The maximum OPC proliferation was observed at around 2 weeks pi and oligodendrogliogenesis continues at later stages until the number of oligodendrocytes return to normal tissue by one month pi. Taken together, the evidence in animals reveals the potential role for endogenous myelinating cells in the axon ensheathment/remyelination after TSCI and this can be the target of pharmacotherapy to induce oligodendrocyte differentiation and myelin formation post-injury.

Combinatorial lentiviral gene delivery of pro-oligodendrogenic factors for improving myelination of regenerating axons after spinal cord injury

Spinal cord injury (SCI) results in paralysis below the injury and strategies are being developed that support axonal regrowth, yet recovery lags, in part, because many axons are not remyelinated. Herein, we investigated strategies to increase myelination of regenerating axons by overexpression of platelet-derived growth factor (PDGF)-AA and noggin either alone or in combination in a mouse SCI model. Noggin and PDGF-AA have been identified as factors that enhance recruitment and differentiation of endogenous progenitors to promote myelination. Lentivirus encoding for these factors was delivered from a multichannel bridge, which we have previously shown creates a permissive environment and supports robust axonal growth through channels. The combination of noggin+PDGF enhanced total myelination of regenerating axons relative to either factor alone, and importantly, enhanced functional recovery relative to the control condition. The increase in myelination was consistent with an increase in oligodendrocyte-derived myelin, which was also associated with a greater density of cells of an oligodendroglial lineage relative to each factor individually and control conditions. These results suggest enhanced myelination of regenerating axons by noggin+PDGF that act on oligodendrocyte-lineage cells post-SCI, which ultimately led to improved functional outcomes.

NG2 expression in NG2 glia is regulated by binding of SoxE and bHLH transcription factors to a Cspg4 intronic enhancer

NG2 is a type 1 integral membrane glycoprotein encoded by the Cspg4 gene. It is expressed on glial progenitor cells known as NG2 glial cells or oligodendrocyte precursor cells that exist widely throughout the developing and mature central nervous system and vascular mural cells but not on mature oligodendrocytes, astrocytes, microglia, neurons, or neural stem cells. Hence NG2 is widely used as a marker for NG2 glia in the rodent and human. The regulatory elements of the mouse Cspg4 gene and its flanking sequences have been used successfully to target reporter and Cre recombinase to NG2 glia in transgenic mice when used in a large 200 kb bacterial artificial chromosome cassette containing the 38 kb Cspg4 gene in the center. Despite the tightly regulated cell type- and stage-specific expression of NG2 in the brain and spinal cord, the mechanisms that regulate its transcription have remained unknown. Here, we describe a 1.45 kb intronic enhancer of the mouse Cspg4 gene that directed transcription of EGFP reporter to NG2 glia but not to pericytes in vitro and in transgenic mice. The 1.45 kb enhancer contained binding sites for SoxE and basic helix-loop-helix transcription factors, and its enhancer activity was augmented cooperatively by these factors, whose respective binding elements were found in close proximity to each other. Mutations in these binding elements abrogated the enhancer activity when tested in the postnatal mouse brain.

Locomotor recovery following contusive spinal cord injury does not require oligodendrocyte remyelination

Remyelination occurs after spinal cord injury (SCI) but its functional relevance is unclear. We assessed the necessity of myelin regulatory factor (Myrf) in remyelination after contusive SCI by deleting the gene from platelet-derived growth factor receptor alpha positive (PDGFRα-positive) oligodendrocyte progenitor cells (OPCs) in mice prior to SCI. While OPC proliferation and density are not altered by Myrf inducible knockout after SCI, the accumulation of new oligodendrocytes is largely prevented. This greatly inhibits myelin regeneration, resulting in a 44% reduction in myelinated axons at the lesion epicenter. However, spontaneous locomotor recovery after SCI is not altered by remyelination failure. In controls with functional MYRF, locomotor recovery precedes the onset of most oligodendrocyte myelin regeneration. Collectively, these data demonstrate that MYRF expression in PDGFRα-positive cell derived oligodendrocytes is indispensable for myelin regeneration following contusive SCI but that oligodendrocyte remyelination is not required for spontaneous recovery of stepping.

Injury type-dependent differentiation of NG2 glia into heterogeneous astrocytes

The glial scar is comprised of a heterogeneous population of reactive astrocytes. NG2 glial cells (also known as oligodendrocyte progenitor cells or polydendrocytes) may contribute to this heterogeneity by differentiating into astrocytes in the injured CNS, but there have been conflicting reports about whether astrocytes comprise a significant portion of the NG2 cell lineage. By using genetic fate mapping after spinal cord injury (SCI) and experimental autoimmune encephalomyelitis (EAE) in mice, the goal of this study was to confirm and extend upon previous findings, which have shown that NG2 cell plasticity varies across CNS injuries. We generated mice that express tdTomato in NG2 lineage cells and express GFP under the Aldh1l1 or Glt1 promoter so that NG2 glia-derived astrocytes can be detected by their expression of GFAP and/or GFP. We found that astrocytes comprise approximately 25% of the total NG2 cell lineage in the glial scar by 4 weeks after mid-thoracic contusive SCI, but only 9% by the peak of functional deficit after EAE. Interestingly, a subpopulation of astrocytes expressed only GFP without co-expression of GFAP, uncovering their heterogeneity and the possibility of an underestimation of NG2 glia-derived astrocytes in previous studies. Additionally, we used high performance liquid chromatography to measure the level of tamoxifen and its metabolites in the spinal cord and show that genetic labeling of NG2 glia-derived astrocytes is not an artifact of residual tamoxifen. Overall, our data demonstrate that a heterogeneous population of astrocytes are derived from NG2 glia in an injury type-dependent manner.

During Development NG2 Glial Cells of the Spinal Cord are Restricted to the Oligodendrocyte Lineage, but Generate Astrocytes upon Acute Injury

NG2 glia are self-renewal cells widely populating the entire central nervous system (CNS). The differentiation potential of NG2 glia in the brain has been systematically studied. However, the fate of NG2 glia in the spinal cord during development and after injury is still unclear. Here, we took advantage of faithful expression of Cre in NG2-CreERT2 knock-in mice to demonstrate that spinal NG2 glia remain committed to the oligodendrocyte (OL) lineage and generate OLs, but not astrocytes or neurons, during development. However, we found significant age- and region dependent differences in differentiation into OLs. Embryonic or neonatal NG2 glia generated more than 90% of the white matter OLs, but only 50% (embryonic) or 75% (neonatal) of gray matter OLs. Such differences disappeared after myelin completion coinciding with a decrease in the differentiation rate. While we never detected the generation of astrocytes from NG2 glia during spinal cord development, we found a small portion of NG2 glia could generate astrocytes in adult spinal cord upon acute traumatic injury.

To Be or Not to Be: Environmental Factors that Drive Myelin Formation during Development and after CNS Trauma

Oligodendrocytes are specialized glial cells that myelinate central nervous system (CNS) axons. Historically, it was believed that the primary role of myelin was to compactly ensheath axons, providing the insulation necessary for rapid signal conduction. However, mounting evidence demonstrates the dynamic importance of myelin and oligodendrocytes, including providing metabolic support to neurons and regulating axon protein distribution. As such, the development and maintenance of oligodendrocytes and myelin are integral to preserving CNS homeostasis and supporting proper functioning of widespread neural networks. Environmental signals are critical for proper oligodendrocyte lineage cell progression and their capacity to form functional compact myelin; these signals are markedly disturbed by injury to the CNS, which may compromise endogenous myelin repair capabilities. This review outlines some key environmental factors that drive myelin formation during development and compares that to the primary factors that define a CNS injury milieu. We aim to identify developmental factors disrupted after CNS trauma as well as pathogenic factors that negatively impact oligodendrocyte lineage cells, as these are potential therapeutic targets to promote myelin repair after injury or disease.

FM19G11 and Ependymal Progenitor/Stem Cell Combinatory Treatment Enhances Neuronal Preservation and Oligodendrogenesis after Severe Spinal Cord Injury

Spinal cord injury (SCI) suffers from a lack of effective therapeutic strategies. We have previously shown that individual therapeutic strategies, transplantation of ependymal stem/progenitor cells of the spinal cord after injury (epSPCi) or FM19G11 pharmacological treatment, induce moderate functional recovery after SCI. Here, the combination of treatments has been assayed for functional and histological analysis. Immediately after severe SCI, one million epSPCi were intramedullary injected, and the FM19G11 compound or dimethyl sulfoxide (DMSO) (as the vehicle control) was administrated via intrathecal catheterization. The combination of treatments, epSPCi and FM19G11, improves locomotor tasks compared to the control group, but did not significantly improve the Basso, Beattie, Bresnahan (BBB) scores for locomotor analysis in comparison with the individual treatments. However, the histological analysis of the spinal cord tissues, two months after SCI and treatments, demonstrated that when we treat the animals with both epSPCi and FM19G11, an improved environment for neuronal preservation was generated by reduction of the glial scar extension. The combinatorial treatment also contributes to enhancing the oligodendrocyte precursor cells by inducing the expression of Olig1 in vivo. These results suggest that a combination of therapies may be an exciting new therapeutic treatment for more efficient neuronal activity recovery after severe SCI.

Engineering new neurons: in vivo reprogramming in mammalian brain and spinal cord

Neurons are postmitotic. Once lost because of injury or degeneration, they do not regenerate in most regions of the mammalian central nervous system. Recent advancements nevertheless clearly reveal that new neurons can be reprogrammed from non-neuronal cells, especially glial cells, in the adult mammalian brain and spinal cord. Here, we give a brief overview concerning cell fate reprogramming in vivo and then focus on the underlying molecular and cellular mechanisms. Specifically, we critically review the cellular sources and the reprogramming factors for in vivo neuronal conversion. Influences of environmental cues and the challenges ahead are also discussed. The ability of inducing new neurons from an abundant and broadly distributed non-neuronal cell source brings new perspectives regarding regeneration-based therapies for traumatic brain and spinal cord injuries and degenerative diseases.

The p53 Pathway Controls SOX2-Mediated Reprogramming in the Adult Mouse Spinal Cord

Although the adult mammalian spinal cord lacks intrinsic neurogenic capacity, glial cells can be reprogrammed in vivo to generate neurons after spinal cord injury (SCI). How this reprogramming process is molecularly regulated, however, is not clear. Through a series of in vivo screens, we show here that the p53-dependent pathway constitutes a critical checkpoint for SOX2-mediated reprogramming of resident glial cells in the adult mouse spinal cord. While it has no effect on the reprogramming efficiency, the p53 pathway promotes cell-cycle exit of SOX2-induced adult neuroblasts (iANBs). As such, silencing of either p53 or p21 markedly boosts the overall production of iANBs. A neurotrophic milieu supported by BDNF and NOG can robustly enhance maturation of these iANBs into diverse but predominantly glutamatergic neurons. Together, these findings have uncovered critical molecular and cellular checkpoints that may be manipulated to boost neuron regeneration after SCI.

Myelinogenic Plasticity of Oligodendrocyte Precursor Cells following Spinal Cord Contusion Injury

Spontaneous remyelination occurs after spinal cord injury (SCI), but the extent of myelin repair and identity of the cells responsible remain incompletely understood and contentious. We assessed the cellular origin of new myelin by fate mapping platelet-derived growth factor receptor α (PDGFRα), Olig2+, and P0+ cells following contusion SCI in mice. Oligodendrocyte precursor cells (OPCs; PDGFRα+) produced oligodendrocytes responsible for de novo ensheathment of ∼30% of myelinated spinal axons at injury epicenter 3 months after SCI, demonstrating that these resident cells are a major contributor to oligodendrocyte regeneration. OPCs also produced the majority of myelinating Schwann cells in the injured spinal cord; invasion of peripheral myelinating (P0+) Schwann cells made only a limited contribution. These findings reveal that PDGFRα+ cells perform diverse roles in CNS repair, as multipotential progenitors that generate both classes of myelinating cells. This endogenous repair might be exploited as a therapeutic target for CNS trauma and disease.SIGNIFICANCE STATEMENT Spinal cord injury (SCI) leads to profound functional deficits, though substantial numbers of axons often survive. One possible explanation for these deficits is loss of myelin, creating conduction block at the site of injury. SCI leads to oligodendrocyte death and demyelination, and clinical trials have tested glial transplants to promote myelin repair. However, the degree and duration of myelin loss, and the extent and mechanisms of endogenous repair, have been contentious issues. Here, we use genetic fate mapping to demonstrate that spontaneous myelin repair by endogenous oligodendrocyte precursors is much more robust than previously recognized. These findings are relevant to many types of CNS pathology, raising the possibility that CNS precursors could be manipulated to repair myelin in lieu of glial transplantation.

The regulatory mechanisms of NG2/CSPG4 expression

Neuron-glial antigen 2 (NG2), also known as chondroitin sulphate proteoglycan 4 (CSPG4), is a surface type I transmembrane core proteoglycan that is crucially involved in cell survival, migration and angiogenesis. NG2 is frequently used as a marker for the identification and characterization of certain cell types, but little is known about the mechanisms regulating its expression. In this review, we provide evidence that the regulation of NG2 expression underlies inflammation and hypoxia and is mediated by methyltransferases, transcription factors, including Sp1, paired box (Pax) 3 and Egr-1, and the microRNA miR129-2. These regulatory factors crucially determine NG2-mediated cellular processes such as glial scar formation in the central nervous system (CNS) or tumor growth and metastasis. Therefore, they are potential targets for the establishment of novel NG2-based therapeutic strategies in the treatment of CNS injuries, cancer and other conditions of these types.

MMP9-sensitive polymers mediate environmentally-responsive bivalirudin release and thrombin inhibition

MMP9-responsive bivalirudin-HPMA copolymers were synthesized for direct, local administration in rat spinal cord contusion injury models. Polymer-conjugated bivalirudin peptides maintained activity while demonstrating enzyme-mediated release upon MMP9 exposure and prolonged release from hyaluronic acid/methylcellulose (HAMC) hydrogels compared to free bivalirudin peptide. Localized administration of bivalirudin copolymers in vivo at the site of rat spinal cord injury decreased cellular proliferation and astrogliosis, suggesting the bivalirudin copolymer and HAMC hydrogel system are a promising therapeutic intervention for reducing immediate inflammatory responses and long term scarring.

Understanding the NG2 Glial Scar after Spinal Cord Injury

NG2 cells, also known as oligodendrocyte progenitor cells, are located throughout the central nervous system and serve as a pool of progenitors to differentiate into oligodendrocytes. In response to spinal cord injury (SCI), NG2 cells increase their proliferation and differentiation into remyelinating oligodendrocytes. While astrocytes are typically associated with being the major cell type in the glial scar, many NG2 cells also accumulate within the glial scar but their function remains poorly understood. Similar to astrocytes, these cells hypertrophy, upregulate expression of chondroitin sulfate proteoglycans, inhibit axon regeneration, contribute to the glial-fibrotic scar border, and some even differentiate into astrocytes. Whether NG2 cells also have a role in other astrocyte functions, such as preventing the spread of infiltrating leukocytes and expression of inflammatory cytokines, is not yet known. Thus, NG2 cells are not only important for remyelination after SCI but are also a major component of the glial scar with functions that overlap with astrocytes in this region. In this review, we describe the signaling pathways important for the proliferation and differentiation of NG2 cells, as well as the role of NG2 cells in scar formation and tissue repair.

Physiological, pathological, and engineered cell identity reprogramming in the central nervous system

Multipotent neural stem cells persist in restricted regions of the adult mammalian central nervous system. These proliferative cells differentiate into diverse neuron subtypes to maintain neural homeostasis. This endogenous process can be reprogrammed as a compensatory response to physiological cues, traumatic injury, and neurodegeneration. In addition to innate neurogenesis, recent research has demonstrated that new neurons can be engineered via cell identity reprogramming in non-neurogenic regions of the adult central nervous system. A comprehensive understanding of these reprogramming mechanisms will be essential to the development of therapeutic neural regeneration strategies that aim to improve functional recovery after injury and neurodegeneration. WIREs Dev Biol 2016, 5:499-517. doi: 10.1002/wdev.234 For further resources related to this article, please visit the WIREs website.

Intraventricular injections of mesenchymal stem cells activate endogenous functional remyelination in a chronic demyelinating murine model

Current treatments for demyelinating diseases are generally only capable of ameliorating the symptoms, with little to no effect in decreasing myelin loss nor promoting functional recovery. Mesenchymal stem cells (MSCs) have been shown by many researchers to be a potential therapeutic tool in treating various neurodegenerative diseases, including demyelinating disorders. However, in the majority of the cases, the effect was only observed locally, in the area surrounding the graft. Thus, in order to achieve general remyelination in various brain structures simultaneously, bone marrow-derived MSCs were transplanted into the lateral ventricles (LVs) of the cuprizone murine model. In this manner, the cells may secrete soluble factors into the cerebrospinal fluid (CSF) and boost the endogenous oligodendrogenic potential of the subventricular zone (SVZ). As a result, oligodendrocyte progenitor cells (OPCs) were recruited within the corpus callosum (CC) over time, correlating with an increased myelin content. Electrophysiological studies, together with electron microscopy (EM) analysis, indicated that the newly formed myelin correctly enveloped the demyelinated axons and increased signal transduction through the CC. Moreover, increased neural stem progenitor cell (NSPC) proliferation was observed in the SVZ, possibly due to the tropic factors released by the MSCs. In conclusion, the findings of this study revealed that intraventricular injections of MSCs is a feasible method to elicit a paracrine effect in the oligodendrogenic niche of the SVZ, which is prone to respond to the factors secreted into the CSF and therefore promoting oligodendrogenesis and functional remyelination.

STAT3 and SOCS3 regulate NG2 cell proliferation and differentiation after contusive spinal cord injury

NG2 cells, also known as oligodendrocyte progenitors or polydendrocytes, are a major component of the glial scar that forms after spinal cord injury. NG2 cells react to injury by proliferating around the lesion site and differentiating into oligodendrocytes and astrocytes, but the molecular mechanism is poorly understood. In this study, we tested the role of the transcription factor STAT3, and its suppressor SOCS3, in NG2 cell proliferation and differentiation after spinal cord injury. Using knockout mice in which STAT3 or SOCS3 are genetically deleted specifically in NG2 cells, we found that deletion of STAT3 led to a reduction in oligodendrogenesis, while deletion of SOCS3 led to enhanced proliferation of NG2 cells within the glial scar after spinal cord injury. Additionally, STAT3 and SOCS3 were not required for astrogliogenesis from NG2 cells after spinal cord injury. Interestingly, genetic deletion of STAT3 and SOCS3 did not have opposing effects, suggesting that SOCS3 may have targets other than the STAT3 pathway in NG2 cells after spinal cord injury. Altogether, our data show that both STAT3 and SOCS3 play important, yet unexpected, roles in NG2 cell proliferation and differentiation after spinal cord injury.

Fatty Acid Binding Protein 5 Modulates Docosahexaenoic Acid-Induced Recovery in Rats Undergoing Spinal Cord Injury

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) promote functional recovery in rats undergoing spinal cord injury (SCI). However, the precise molecular mechanism coupling n-3 PUFAs to neurorestorative responses is not well understood. The aim of the present study was to determine the spatiotemporal expression of fatty acid binding protein 5 (FABP5) after contusive SCI and to investigate whether this protein plays a role in n-3 PUFA-mediated functional recovery post-SCI. We found that SCI resulted in a robust spinal cord up-regulation in FABP5 mRNA levels (556 ± 187%) and protein expression (518 ± 195%), when compared to sham-operated rats, at 7 days post-injury (dpi). This upregulation coincided with significant alterations in the metabolism of fatty acids in the injured spinal cord, as revealed by metabolomics-based lipid analyses. In particular, we found increased levels of the n-3 series PUFAs, particularly docosahexaenoic acid (DHA; 22:6 n-3) and eicosapentaenoic acid (EPA; 20:5 n-3) at 7 dpi. Animals consuming a diet rich in DHA and EPA exhibited a significant upregulation in FABP5 mRNA levels at 7 dpi. Immunofluorescence showed low basal FABP5 immunoreactivity in spinal cord ventral gray matter NeuN(+) neurons of sham-operated rats. SCI resulted in a robust induction of FABP5 in glial (GFAP(+), APC(+), and NG2(+)) and precursor cells (DCX(+), nestin(+)). We found that continuous intrathecal administration of FABP5 silencing with small interfering RNA (2 μg) impaired spontaneous open-field locomotion post-SCI. Further, FABP5 siRNA administration hindered the beneficial effects of DHA to ameliorate functional recovery at 7 dpi. Altogether, our findings suggest that FABP5 may be an important player in the promotion of cellular uptake, transport, and/or metabolism of DHA post-SCI. Given the beneficial roles of n-3 PUFAs in ameliorating functional recovery, we propose that FABP5 is an important contributor to basic repair mechanisms in the injured spinal cord.

The Role of NG2 Proteoglycan in Glioma

Neuron glia antigen-2 ((NG2), also known as chondroitin sulphate proteoglycan 4, or melanoma-associated chondroitin sulfate proteoglycan) is a type-1 membrane protein expressed by many central nervous system (CNS) cells during development and differentiation and plays a critical role in proliferation and angiogenesis. ‘NG2’ often references either the protein itself or the highly proliferative and undifferentiated glial cells expressing high levels of NG2 protein. NG2 glia represent the fourth major type of neuroglia in the mammalian nervous system and are classified as oligodendrocyte progenitor cells by virtue of their committed oligodendrocyte generation in developing and adult brain. Here, we discuss NG2 glial cells as well as NG2 protein and its expression and role with regards to CNS neoplasms as well as its potential as a therapeutic target for treating childhood CNS cancers.

Pushing Forward: Remyelination as the New Frontier in CNS Diseases

The evolutionary acquisition of myelin sheaths around large caliber axons in the central nervous system (CNS) represented a milestone in the development of vertebrate higher brain function. Myelin ensheathment of axons enabled saltatory conduction and thus accelerated information processing. However, a number of CNS diseases harm or destroy myelin and oligodendrocytes (myelin-producing cells), ultimately resulting in demyelination. In the adult CNS, new oligodendrocytes can be generated from a quiescent pool of precursor cells, which - upon differentiation - can replace lost myelin sheaths. The efficiency of this spontaneous regeneration is limited, which leads to incomplete remyelination and residual clinical symptoms. Here, we discuss CNS pathologies characterized by white matter degeneration and regeneration and highlight drugs that could potentially serve as remyelination therapies.

Age-Dependent Netrin-1 Signaling Regulates NG2+ Glial Cell Spatial Homeostasis in Normal Adult Gray Matter

Neuron-glial antigen 2-positive (NG2(+)) glial cells are the most proliferative glia type in the adult CNS, and their tile-like arrangement in adult gray matter is under tight regulation. However, little is known about the cues that govern this unique distribution. To this end, using a NG2(+) glial cell ablation model in mice, we examined the repopulation dynamics of NG2(+) glial cells in the mature and aged mice gray matter. We found that some resident NG2(+) glial cells that escaped depletion rapidly enter the cell cycle to repopulate the cortex with altered spatial distribution. We reveal that netrin-1 signaling is involved in the NG2(+) glial cell early proliferative, late repopulation, and distribution response after ablation in the gray matter. However, ablation of NG2(+) glial cell in older animals failed to stimulate a similar repopulation response, possibly because of a decrease in the sensitivity to netrin-1. Our findings indicate that endogenous netrin-1 plays a role in NG2(+) glial cell homeostasis that is distinct from its role in myelination.

Chronic oligodendrogenesis and remyelination after spinal cord injury in mice and rats

Adult progenitor cells proliferate in the acutely injured spinal cord and their progeny differentiate into new oligodendrocytes (OLs) that remyelinate spared axons. Whether this endogenous repair continues beyond the first week postinjury (wpi), however, is unknown. Identifying the duration of this response is essential for guiding therapies targeting improved recovery from spinal cord injury (SCI) by enhancing OL survival and/or remyelination. Here, we used two PDGFRα-reporter mouse lines and rats injected with a GFP-retrovirus to assess progenitor fate through 80 d after injury. Surprisingly, new OLs were generated as late as 3 months after injury and their processes ensheathed axons near and distal to the lesion, colocalized with MBP, and abutted Caspr+ profiles, suggesting newly formed myelin. Semithin sections confirmed stereotypical thin OL remyelination and few bare axons at 10 wpi, indicating that demyelination is relatively rare. Astrocytes in chronic tissue expressed the pro-OL differentiation and survival factors CNTF and FGF-2. In addition, pSTAT3+ NG2 cells were present through at least 5 wpi, revealing active signaling of the Jak/STAT pathway in these cells. The progenitor cell fate genes Sox11, Hes5, Id2, Id4, BMP2, and BMP4 were dynamically regulated for at least 4 wpi. Collectively, these data verify that the chronically injured spinal cord is highly dynamic. Endogenous repair, including oligodendrogenesis and remyelination, continues for several months after SCI, potentially in response to growth factors and/or transcription factor changes. Identifying and understanding spontaneous repair processes such as these is important so that beneficial plasticity is not inadvertently interrupted and effort is not exerted to needlessly duplicate ongoing spontaneous repair.

Electroacupuncture promotes the proliferation of endogenous neural stem cells and oligodendrocytes in the injured spinal cord of adult rats

A contusive model of spinal cord injury at spinal segment T_8-9 was established in rats. Huantiao (GB30) and Huatuojiaji (Ex-B05) were punctured with needles, and endogenous neural stem cells were labeled with 5-bromo-2’-deoxyuridine (BrdU) and NG2. Double immunofluorescence staining showed that electroacupuncture markedly increased the numbers of BrdU⁺/NG2⁺ cells at spinal cord tissue 15 mm away from the injury center in the rostral and caudal directions. The results suggest that electroacupuncture promotes the proliferation of endogenous neural stem cells and oligodendrocytes in rats with spinal cord injury.