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Background: Immune-mediated demyelination and consequent degeneration of oligodendrocytes and axons are hallmark features of multiple sclerosis (MS). Remyelination declines in progressive MS, causing permanent axonal loss and irreversible disabilities. Strategies aimed at enhancing remyelination are critical to attenuate disease progression. Objective: We systematically reviewed recent advances in neuroprotective and regenerative therapies for MS, covering preclinical and clinical studies. Methods: We searched three biomedical databases using defined keywords. Two authors independently reviewed articles for inclusion based on pre-specified criteria. The data were extracted from each study and assessed for risk of bias. Results: Our search identified 7351 studies from 2014 to 2020, of which 221 met the defined criteria. These studies reported 262 interventions, wherein 92% were evaluated in animal models. These interventions comprised protein, RNA, lipid and cellular biologics, small molecules, inorganic compounds, and dietary and physiological interventions. Small molecules were the most highly represented strategy, followed by antibody therapies and stem cell transplantation. Conclusion: While significant strides have been made to develop regenerative treatments for MS, the current evidence illustrates a skewed representation of the types of strategies that advance to clinical trials. Further examination is thus required to address current barriers to implementing experimental treatments in clinical settings.

Traumatic spinal cord injury (SCI) is a leading cause of permanent neurologic disabilities in young adults. Functional impairments after SCI are substantially attributed to the progressive neurodegeneration. However, regeneration of spinal-specific neurons and circuit re-assembly remain challenging in the dysregulated milieu of SCI because of impaired neurogenesis and neuronal maturation by neural precursor cells (NPCs) spontaneously or in cell-based strategies. The extrinsic mechanisms that regulate neuronal differentiation and synaptogenesis in SCI are poorly understood. Here, we perform extensivein vitroandin vivostudies to unravel that SCI-induced upregulation of matrix chondroitin sulfate proteoglycans (CSPGs) impedes neurogenesis of NPCs through co-activation of two receptor protein tyrosine phosphatases, LAR and PTPσ. In adult female rats with SCI, systemic co-inhibition of LAR and PTPσ promotes regeneration of motoneurons and spinal interneurons by engrafted human directly reprogramed caudalized NPCs (drNPC-O2) and fosters their morphologic maturity and synaptic connectivity within the host neural network that culminate in improved recovery of locomotion and sensorimotor integration. Our transcriptomic analysis of engrafted human NPCs in the injured spinal cord confirmed that inhibition of CSPG receptors activates a comprehensive program of gene expression in NPCs that can support neuronal differentiation, maturation, morphologic complexity, signal transmission, synaptic plasticity, and behavioral improvement after SCI. We uncovered that CSPG/LAR/PTPσ axis suppresses neuronal differentiation in part by blocking Wnt/β-Catenin pathway. Taken together, we provide the first evidence that CSPGs/LAR/PTPσ axis restricts neurogenesis and synaptic integration of new neurons in NPC cellular therapies for SCI. We propose targeting LAR and PTPσ receptors offers a promising clinically-feasible adjunct treatment to optimize the efficacy and neurologic benefits of ongoing NPC-based clinical trials for SCI.SIGNIFICANCE STATEMENTTransplantation of neural precursor cells (NPCs) is a promising approach for replacing damaged neurons after spinal cord injury (SCI). However, survival, neuronal differentiation, and synaptic connectivity of transplanted NPCs within remain challenging in SCI. Here, we unravel that activation of chondroitin sulfate proteoglycan (CSPG)/LAR/PTPσ axis after SCI impedes the capacity of transplanted human NPCs for replacing functionally integrated neurons. Co-blockade of LAR and PTPσ is sufficient to promote re-generation of motoneurons and spinal V1 and V3 interneurons by engrafted human caudalized directly reprogramed NPCs (drNPC-O2) and facilitate their synaptic integration within the injured spinal cord. CSPG/LAR/PTPσ axis appears to suppress neuronal differentiation of NPCs by inhibiting Wnt/β-Catenin pathway. These findings identify targeting CSPG/LAR/PTPσ axis as a promising strategy for optimizing neuronal replacement, synaptic re-connectivity, and neurologic recovery in NPC-based strategies.

Astrocytes play essential roles in development, homeostasis, injury, and repair of the central nervous system (CNS). Their development is tightly regulated by distinct spatial and temporal cues during embryogenesis and into adulthood throughout the CNS. Astrocytes have several important responsibilities such as regulating blood flow and permeability of the blood-CNS barrier, glucose metabolism and storage, synapse formation and function, and axon myelination. In CNS pathologies, astrocytes also play critical parts in both injury and repair mechanisms. Upon injury, they undergo a robust phenotypic shift known as "reactive astrogliosis," which results in both constructive and deleterious outcomes. Astrocyte activation and migration at the site of injury provides an early defense mechanism to minimize the extent of injury by enveloping the lesion area. However, astrogliosis also contributes to the inhibitory microenvironment of CNS injury and potentiate secondary injury mechanisms, such as inflammation, oxidative stress, and glutamate excitotoxicity, which facilitate neurodegeneration in CNS pathologies. Intriguingly, reactive astrocytes are increasingly a focus in current therapeutic strategies as their activation can be modulated toward a neuroprotective and reparative phenotype. This review will discuss recent advancements in knowledge regarding the development and role of astrocytes in the healthy and pathological CNS. We will also review how astrocytes have been genetically modified to optimize their reparative potential after injury, and how they may be transdifferentiated into neurons and oligodendrocytes to promote repair after CNS injury and neurodegeneration.

Spinal cord injury (SCI) causes sensorimotor and autonomic impairment that partly reflects extensive, permanent loss of neurons at the epicenter and penumbra of the injury. Strategies aimed at enhancing neuronal protection are critical to attenuate neurodegeneration and improve neurological recovery after SCI. In rat SCI, we previously uncovered that the tissue levels of neuregulin-1beta 1 (Nrg-1β1) are acutely and persistently downregulated in the injured spinal cord. Nrg-1β1 is well-known for its critical roles in the development, maintenance and physiology of neurons and glia in the developing and adult spinal cord. However, despite this pivotal role, Nrg-1β1 specific effects and mechanisms of action on neuronal injury remain largely unknown in SCI. In the present study, using a clinically-relevant model of compressive/contusive SCI in rats and an in vitro model of glutamate toxicity in primary neurons, we demonstrate Nrg-1β1 provides early neuroprotection through attenuation of reactive oxygen species, lipid peroxidation, necrosis and apoptosis in acute and subacute stages of SCI. Mechanistically, availability of Nrg-1β1 following glutamate challenge protects neurons from caspase-dependent and independent cell death that is mediated by modulation of mitochondria associated apoptotic cascades and MAP kinase and AKT signaling pathways. Altogether, our work provides novel insights into the role and mechanisms of Nrg-1β1 in neuronal injury after SCI and introduces its potential as a new neuroprotective target for this debilitating neurological condition.

Multiple sclerosis is characterized by immune mediated neurodegeneration that results in progressive, life-long neurological and cognitive impairments. Yet, the endogenous mechanisms underlying multiple sclerosis pathophysiology are not fully understood. Here, we provide compelling evidence that associates dysregulation of neuregulin-1 beta 1 (Nrg-1β1) with multiple sclerosis pathogenesis and progression. In the experimental autoimmune encephalomyelitis model of multiple sclerosis, we demonstrate that Nrg-1β1 levels are abated within spinal cord lesions and peripherally in the plasma and spleen during presymptomatic, onset and progressive course of the disease. We demonstrate that plasma levels of Nrg-1β1 are also significantly reduced in individuals with early multiple sclerosis and is positively associated with progression to relapsing-remitting multiple sclerosis. The functional impact of Nrg-1β1 downregulation preceded disease onset and progression, and its systemic restoration was sufficient to delay experimental autoimmune encephalomyelitis symptoms and alleviate disease burden. Intriguingly, Nrg-1β1 therapy exhibited a desirable and extended therapeutic time window of efficacy when administered prophylactically, symptomatically, acutely or chronically. Using in vivo and in vitro assessments, we identified that Nrg-1β1 treatment mediates its beneficial effects in EAE by providing a more balanced immune response. Mechanistically, Nrg-1β1 moderated monocyte infiltration at the blood-CNS interface by attenuating chondroitin sulphate proteoglycans and MMP9. Moreover, Nrg-1β1 fostered a regulatory and reparative phenotype in macrophages, T helper type 1 (Th1) cells and microglia in the spinal cord lesions of EAE mice. Taken together, our new findings in multiple sclerosis and experimental autoimmune encephalomyelitis have uncovered a novel regulatory role for Nrg-1β1 early in the disease course and suggest its potential as a specific therapeutic target to ameliorate disease progression and severity.

The involvement of glutamate in neuronal cell death in neurodegenerative diseases and neurotrauma is mediated through excitotoxicity or oxytosis. The latter process induces oxidative stress via glutamate-mediated inhibition of cysteine transporter xCT, leading to depletion of the cellular glutathione pool. Mitochondrial damage, loss of mitochondrial membrane potential (MMP), and depletion of energy metabolites have been shown in this process. The Voltage-Dependent Anion Channel-1 (VDAC1) is one of the main components of the mitochondrial outer membrane and plays a gatekeeping role in mitochondria-cytoplasm transport of metabolites. In this study, we explored the possible participation of VDAC-1 in the pathophysiology of oxytosis. Administration of glutamate in HT22 cells that lack the glutamate ionotropic receptors induced an upregulation and oligomerization of VDAC1. This was associated with an increase in ROS and loss of cell survival. Glutamate-mediated oxytosis in this model also decreased MMP and promoted ATP depletion, resulting in translocation of cytochrome c (cyt C) and apoptosis inducing factor (AIF) from mitochondria into the cytosol. This was also accompanied by cleavage of AIF to form truncated AIF. Inhibition of VDAC1 oligomerization using 4,4'-Diisothiocyanatostilbene-2,2'-disulfonate (DIDS), significantly improved the cell survival, decreased the ROS levels, improved mitochondrial functions, and decreased the mitochondrial damage. Notably, DIDS also inhibited the mitochondrial fragmentation caused by glutamate, indicating the active role of VDAC1 oligomerization in the process of mitochondrial fragmentation in oxytosis. These results suggest a critical role for VDAC1 in mitochondrial fragmentation and its potential therapeutic value against glutamate-mediated oxidative neurotoxicity.

Following spinal cord injury (SCI), the population of mature oligodendrocytes undergoes substantial cell death; promoting their preservation and replacement is a viable strategy for preserving axonal integrity and white matter repair in the injured spinal cord. Dramatic upregulation of matrix chondroitin sulfate proteoglycans (CSPGs) is shown to pose an obstacle to endogenous repair processes, and targeting CSPGs improves functional recovery after SCI. However, the cellular and molecular mechanisms underlying the inhibitory effects of CSPGs remain largely undefined. Modulation of CSPGs specific signaling receptors, leukocyte common antigen-related (LAR), and protein tyrosine phosphatase-sigma (PTPσ) allows us to uncover the role and mechanisms of CSPGs in regulating oligodendrocytes in SCI. Here, utilizing specific functionally blocking peptides in a clinically relevant model of contusive/compressive SCI in the rat, we demonstrate that inhibition of PTPσ and LAR receptors promotes oligodendrogenesis by endogenous precursor cells, attenuates caspase 3-mediated cell death in mature oligodendrocytes, and preserves myelin. In parallel in vitro systems, we have unraveled that CSPGs directly induce apoptosis in populations of neural precursor cells and oligodendrocyte progenitor cells and limit their ability for oligodendrocyte differentiation, maturation, and myelination. These negative effects of CSPGs are mediated through the activation of both LAR and PTPσ receptors and the downstream Rho/ROCK pathway. Thus, we have identified a novel inhibitory role for PTPσ and LAR in regulating oligodendrocyte differentiation and apoptosis in the injured adult spinal cord and a new feasible therapeutic strategy for optimizing endogenous cell replacement following SCI.

Spinal cord injury (SCI) results in glial activation and neuroinflammation, which play pivotal roles in the secondary injury mechanisms with both pro- and antiregeneration effects. Presently, little is known about the endogenous molecular mechanisms that regulate glial functions in the injured spinal cord. We previously reported that the expression of neuregulin-1 (Nrg-1) is acutely and chronically declined following traumatic SCI. Here, we investigated the potential ramifications of Nrg-1 dysregulation on glial and immune cell reactivity following SCI. Using complementary in vitro approaches and a clinically-relevant model of severe compressive SCI in rats, we demonstrate that immediate delivery of Nrg-1 (500 ng/day) after injury enhances a neuroprotective phenotype in inflammatory cells associated with increased interleukin-10 and arginase-1 expression. We also found a decrease in proinflammatory factors including IL-1β, TNF-α, matrix metalloproteinases (MMP-2 and 9) and nitric oxide after injury. In addition, Nrg-1 modulates astrogliosis and scar formation by reducing inhibitory chondroitin sulfate proteoglycans after SCI. Mechanistically, Nrg-1 effects on activated glia are mediated through ErbB2 tyrosine phosphorylation in an ErbB2/3 heterodimer complex. Furthermore, Nrg-1 exerts its effects through downregulation of MyD88, a downstream adaptor of Toll-like receptors, and increased phosphorylation of Erk1/2 and STAT3. Nrg-1 treatment with the therapeutic dosage of 1.5 μg/day significantly improves tissue preservation and functional recovery following SCI. Our findings for the first time provide novel insights into the role and mechanisms of Nrg-1 in acute SCI and suggest a positive immunomodulatory role for Nrg-1 that can harness the beneficial properties of activated glia and inflammatory cells in recovery following SCI.

The importance of the bi-directional natural killer–dendritic cell crosstalk in coordinating anti-tumour and anti-microbial responses in vivo has been well established. However, physical parameters associated with natural killer–dendritic cell interactions have not been fully elucidated. We have previously used a simple “Y” shaped microfluidic device to study natural killer cell-migratory responses toward chemical gradients from a conditioned medium of dendritic cells. There are, however, limitations of the Y-shaped microfluidic devices that could not support higher throughput analyses and studies of cell–cell interactions. Here, we report two novel microfluidic devices (D3-Chip, T2-Chip) we applied in advanced studies of natural killer-cell migrations and their interactions with dendritic cells in vitro. The D3-Chip is an improved version of the previously published Y-shaped device that supports high-throughput analyses and docking of the cells of interest in the migration assay before they are exposed to a chemical gradient. The T2-Chip is created to support analyses of natural killer–dendritic cell cell–cell interactions without the requirement of promoting a natural killer cell to migrate long distances to find a loaded dendritic cell in the device. Using these two microfluidic platforms, we observe quantitative differences in the abilities of the immature and lipopolysaccharide-activated mature dendritic cells to interact with activated natural killer cells. The contact time between the activated natural killer cells and immature dendritic cells is significantly longer than that of the mature dendritic cells. There is a significantly higher frequency of an immature dendritic cell coming into contact with multiple natural killer cells and/or making multiple simultaneous contacts with multiple natural killer cells. To contrast, an activated natural killer cell has a significantly higher frequency of coming into contact with the mature dendritic cells than immature dendritic cells. Collectively, these differences in natural killer–dendritic cell interactions may underlie the differential maturation of immature dendritic cells by activated natural killer cells. Further applications of these microfluidic devices in studying natural killer–dendritic cell crosstalk under defined microenvironments shall enrich our understanding of the functional regulations of natural killer cells and dendritic cells in the natural killer–dendritic cell crosstalk.

Traumatic spinal cord injury (SCI) elicits a cascade of secondary injury mechanisms that induce profound changes in glia and neurons resulting in their activation, injury or cell death. The resultant imbalanced microenvironment of acute SCI also negatively impacts regenerative processes in the injured spinal cord. Thus, it is imperative to uncover endogenous mechanisms that drive these acute injury events. Here, we demonstrate that the active form of bone morphogenetic protein-4 (BMP4) is robustly and transiently upregulated in acute SCI in rats. BMP4 is a key morphogen in neurodevelopment; however, its role in SCI is not fully defined. Thus, we elucidated the ramification of BMP4 upregulation in a preclinical model of compressive/contusive SCI in the rat by employing noggin, an endogenous antagonist of BMP ligands, and LDN193189, an intracellular inhibitor of BMP signaling. In parallel, we studied cell-specific effects of BMP4 on neural precursor cells (NPCs), oligodendrocyte precursor cells (OPCs), neurons and astrocytes in vitro. We demonstrate that activation of BMP4 inhibits differentiation of spinal cord NPCs and OPCs into mature myelin-expressing oligodendrocytes, and acute blockade of BMPs promotes oligodendrogenesis, oligodendrocyte preservation and remyelination after SCI. Importantly, we report for the first time that BMP4 directly induces caspase-3 mediated apoptosis in neurons and oligodendrocytes in vitro, and noggin and LDN193189 remarkably attenuate caspase-3 activation and lipid peroxidation in acute SCI. BMP4 also enhances the production of inhibitory chondroitin sulfate proteoglycans (CSPGs) in activated astrocytes in vitro and after SCI. Interestingly, our work reveals that despite the beneficial effects of BMP inhibition in acute SCI, neither noggin nor LDN193189 treatment resulted in long-term functional recovery. Collectively, our findings suggest a role for BMP4 in regulating acute secondary injury mechanisms following SCI, and a potential target for combinatorial approaches to improve endogenous cell response and remyelination.

Microglia play diverse roles in homeostasis and pathology of the central nervous system (CNS). Their response to injury or insult is critical for initiating neuroinflammation and tissue damage as well as resolution of inflammation and wound healing. Changes to the microenvironment of microglia appear to be a key determinant of their phenotype and their role in the endogenous repair process in the injured or diseased CNS. Our recent findings have identified a positive role for neuregulin-1 (Nrg-1) in regulating immune response in spinal cord injury and focal demyelinating lesions. We show that increasing the tissue availability of Nrg-1 after injury can promote endogenous repair by modulating neuroinflammation. In the present study, we sought to elucidate the specific role of Nrg-1 in regulating microglial activity and more importantly their influence on the behavior of neural stem/progenitor cells (NPCs). Using injury-relevant in vitro systems, we demonstrate that Nrg-1 attenuates the expression of proinflammatory mediators in activated microglia. Moreover, we provide novel evidence that availability of Nrg-1 can restore the otherwise suppressed phagocytic ability of proinflammatory microglia. Interestingly, the presence of Nrg-1 in the microenvironment of proinflammatory microglia mitigates their inhibitory effects on NPC proliferation. Nrg-1 treated proinflammatory microglia also augment mobilization of NPCs, while they had no influence on their suppressive effects on NPC differentiation. Mechanistically, we show that Nrg-1 enhances the interactions of proinflammatory microglia and NPCs, at least in part, through reduction of TNF-α expression in microglia. These findings provide new insights into the endogenous regulation of microglia-NPC interactions and identify new potential targets for optimizing this important crosstalk during the regenerative process after CNS injury and neuroinflammatory conditions.

White matter degeneration is an important pathophysiological event of the central nervous system that is collectively characterized by demyelination, oligodendrocyte loss, axonal degeneration and parenchymal changes that can result in sensory, motor, autonomic and cognitive impairments. White matter degeneration can occur due to a variety of causes including trauma, neurotoxic exposure, insufficient blood flow, neuroinflammation, and developmental and inherited neuropathies. Regardless of the etiology, the degeneration processes share similar pathologic features. In recent years, a plethora of cellular and molecular mechanisms have been identified for axon and oligodendrocyte degeneration including oxidative damage, calcium overload, neuroinflammatory events, activation of proteases, depletion of adenosine triphosphate and energy supply. Extensive efforts have been also made to develop neuroprotective and neuroregenerative approaches for white matter repair. However, less progress has been achieved in this area mainly due to the complexity and multifactorial nature of the degeneration processes. Here, we will provide a timely review on the current understanding of the cellular and molecular mechanisms of white matter degeneration and will also discuss recent pharmacological and cellular therapeutic approaches for white matter protection as well as axonal regeneration, oligodendrogenesis and remyelination.

Myelin is a proteolipid sheath enwrapping axons in the nervous system that facilitates signal transduction along the axons. In the central nervous system (CNS), oligodendrocytes are specialized glial cells responsible for myelin formation and maintenance. Following spinal cord injury (SCI), oligodendroglia cell death and myelin damage (demyelination) cause chronic axonal damage and irreparable loss of sensory and motor functions. Accumulating evidence shows that replacement of damaged oligodendrocytes and renewal of myelin (remyelination) are promising approaches to prevent axonal degeneration and restore function following SCI. Neural precursor cells (NPCs) and oligodendrocyte progenitor cells (OPCs) are two main resident cell populations in the spinal cord with innate capacities to foster endogenous oligodendrocyte replacement and remyelination. However, due to the hostile microenvironment of SCI, the regenerative capacity of these endogenous precursor cells is conspicuously restricted. Activated resident glia, along with infiltrating immune cells, are among the key modulators of secondary injury mechanisms that create a milieu impermissible to oligodendrocyte differentiation and remyelination. Recent studies have uncovered inhibitory roles for astrocyte-associated molecules such as matrix chondroitin sulfate proteoglycans (CSPGs), and a plethora of pro-inflammatory cytokines and neurotoxic factors produced by activated microglia/macrophages. The quality of axonal remyelination is additionally challenged by dysregulation of the supportive growth factors required for maturation of new oligodendrocytes and axo-oligodendrocyte signalling. Careful understanding of factors that modulate the activity of endogenous precursor cells in the injury microenvironment is a key step in developing efficient repair strategies for remyelination and functional recovery following SCI.

Background Traumatic spinal cord injury (SCI) results in upregulation of chondroitin sulfate proteoglycans (CSPGs) by reactive glia that impedes repair and regeneration in the spinal cord. Degradation of CSPGs is known to be beneficial in promoting endogenous repair mechanisms including axonal sprouting/regeneration, oligodendrocyte replacement, and remyelination, and is associated with improvements in functional outcomes after SCI. Recent evidence suggests that CSPGs may regulate secondary injury mechanisms by modulating neuroinflammation after SCI. To date, the role of CSPGs in SCI neuroinflammation remains largely unexplored. The recent discovery of CSPG-specific receptors, leukocyte common antigen-related (LAR) and protein tyrosine phosphatase-sigma (PTPσ), allows unraveling the cellular and molecular mechanisms of CSPGs in SCI. In the present study, we have employed parallel in vivo and in vitro approaches to dissect the role of CSPGs and their receptors LAR and PTPσ in modulating the inflammatory processes in the acute and subacute phases of SCI. Methods In a clinically relevant model of compressive SCI in female Sprague Dawley rats, we targeted LAR and PTPσ by two intracellular functionally blocking peptides, termed ILP and ISP, respectively. We delivered ILP and ISP treatment intrathecally to the injured spinal cord in a sustainable manner by osmotic mini-pumps for various time-points post-SCI. We employed flow cytometry, Western blotting, and immunohistochemistry in rat SCI, as well as complementary in vitro studies in primary microglia cultures to address our questions. Results We provide novel evidence that signifies a key immunomodulatory role for LAR and PTPσ receptors in SCI. We show that blocking LAR and PTPσ reduces the population of classically activated M1 microglia/macrophages, while promoting alternatively activated M2 microglia/macrophages and T regulatory cells. This shift was associated with a remarkable elevation in pro-regenerative immune mediators, interleukin-10 (IL-10), and Arginase-1. Our parallel in vitro studies in microglia identified that while CSPGs do not induce an M1 phenotype per se, they promote a pro-inflammatory phenotype. Interestingly, inhibiting LAR and PTPσ in M1 and M2 microglia positively modulates their inflammatory response in the presence of CSPGs, and harnesses their ability for phagocytosis and mobilization. Interestingly, our findings indicate that CSPGs regulate microglia, at least in part, through the activation of the Rho/ROCK pathway downstream of LAR and PTPσ. Conclusions We have unveiled a novel role for LAR and PTPσ in regulating neuroinflammation in traumatic SCI. Our findings provide new insights into the mechanisms by which manipulation of CSPG signaling can promote recovery from SCI. More importantly, this work introduces the potential of ILP/ISP as a viable strategy for modulating the immune response following SCI and other neuroinflammatory conditions of the central nervous system. Electronic supplementary material The online version of this article (10.1186/s12974-018-1128-2) contains supplementary material, which is available to authorized users.

Background Spinal cord injury (SCI) triggers a robust neuroinflammatory response that governs secondary injury mechanisms with both degenerative and pro-regenerative effects. Identifying new immunomodulatory therapies to promote the supportive aspect of immune response is critically needed for the treatment of SCI. We previously demonstrated that SCI results in acute and permanent depletion of the neuronally derived Neuregulin-1 (Nrg-1) in the spinal cord. Increasing the dysregulated level of Nrg-1 through acute intrathecal Nrg-1 treatment enhanced endogenous cell replacement and promoted white matter preservation and functional recovery in rat SCI. Moreover, we identified a neuroprotective role for Nrg-1 in moderating the activity of resident astrocytes and microglia following injury. To date, the impact of Nrg-1 on immune response in SCI has not yet been investigated. In this study, we elucidated the effect of systemic Nrg-1 therapy on the recruitment and function of macrophages, T cells, and B cells, three major leukocyte populations involved in neuroinflammatory processes following SCI. Methods We utilized a clinically relevant model of moderately severe compressive SCI in female Sprague-Dawley rats. Nrg-1 (2 μg/day) or saline was delivered subcutaneously through osmotic mini-pumps starting 30 min after SCI. We conducted flow cytometry, quantitative real-time PCR, and immunohistochemistry at acute, subacute, and chronic stages of SCI to investigate the effects of Nrg-1 treatment on systemic and spinal cord immune response as well as cytokine, chemokine, and antibody production. Results We provide novel evidence that Nrg-1 promotes a pro-regenerative immune response after SCI. Bioavailability of Nrg-1 stimulated a regulatory phenotype in T and B cells and augmented the population of M2 macrophages in the spinal cord and blood during the acute and chronic stages of SCI. Importantly, Nrg-1 fostered a more balanced microenvironment in the injured spinal cord by attenuating antibody deposition and expression of pro-inflammatory cytokines and chemokines while upregulating pro-regenerative mediators. Conclusion We provide the first evidence of a significant regulatory role for Nrg-1 in neuroinflammation after SCI. Importantly, the present study establishes the promise of systemic Nrg-1 treatment as a candidate immunotherapy for traumatic SCI and other CNS neuroinflammatory conditions. Electronic supplementary material The online version of this article (10.1186/s12974-018-1093-9) contains supplementary material, which is available to authorized users.

Multipotent adult neural precursor cells (NPCs) have tremendous intrinsic potential to repair the damaged spinal cord. However, evidence shows that the regenerative capabilities of endogenous and transplanted NPCs are limited in the microenvironment of spinal cord injury (SCI). We previously demonstrated that injury-induced upregulation of matrix chondroitin sulfate proteoglycans (CSPGs) restricts the survival, migration, integration, and differentiation of NPCs following SCI. CSPGs are long-lasting components of the astroglial scar that are formed around the lesion. Our recent in vivo studies demonstrated that removing CSPGs from the SCI environment enhances the potential of transplanted and endogenous adult NPCs for spinal cord repair; however, the mechanisms by which CSPGs regulate NPCs remain unclear. In this study, using in vitro models recapitulating the extracellular matrix of SCI, we investigated the direct role of CSPGs in modulating the properties of adult spinal cord NPCs. We show that CSPGs significantly decrease NPCs growth, attachment, survival, proliferation, and oligodendrocytes differentiation. Moreover, using genetic models, we show that CSPGs regulate NPCs by signaling on receptor protein tyrosine phosphate sigma (RPTPσ) and leukocyte common antigen-related phosphatase (LAR). Intracellularly, CSPGs inhibitory effects are mediated through Rho/ROCK pathway and inhibition of Akt and Erk1/2 phosphorylation. Downregulation of RPTPσ and LAR and blockade of ROCK in NPCs attenuates the inhibitory effects of CSPGS. Our work provide novel evidence uncovering how upregulation of CSPGs challenges the response of NPCs in their post-SCI niche and identifies new therapeutic targets for enhancing NPC-based therapies for SCI repair. Stem Cells 2015;33:2550–2563

Oligodendroglial cell death and demyelination are hallmarks of neurotrauma and multiple sclerosis that cause axonal damage and functional impairments. Remyelination remains a challenge as the ability of endogenous precursor cells for oligodendrocyte replacement is hindered in the unfavorable milieu of demyelinating conditions. Here, in a rat model of lysolecithin lysophosphatidyl-choline (LPC)-induced focal demyelination, we report that Neuregulin-1 (Nrg-1), an important factor for oligodendrocytes and myelination, is dysregulated in demyelinating lesions and its bio-availability can promote oligodendrogenesis and remyelination. We delivered recombinant human Nrg-1β1 (rhNrg-1β1) intraspinally in the vicinity of LPC demyelinating lesion in a sustained manner using poly lactic-co-glycolic acid microcarriers. Availability of Nrg-1 promoted generation and maturation of new oligodendrocytes, and accelerated endogenous remyelination by both oligodendrocyte and Schwann cell populations in demyelinating foci. Importantly, Nrg-1 enhanced myelin thickness in newly remyelinated spinal cord axons. Our complementary in vitro studies also provided direct evidence that Nrg-1 significantly promotes maturation of new oligodendrocytes and facilitates their transition to a myelinating phenotype. Nrg-1 therapy remarkably attenuated the upregulated expression chondroitin sulfate proteoglycans (CSPGs) specific glycosaminoglycans in the extracellular matrix of demyelinating foci and promoted interleukin-10 (IL-10) production by immune cells. CSPGs and IL-10 are known to negatively and positively regulate remyelination, respectively. We found that Nrg-1 effects are mediated through ErbB2 and ErbB4 receptor activation. Our work provides novel evidence that dysregulated levels of Nrg-1 in demyelinating lesions of the spinal cord pose a challenge to endogenous remyelination, and appear to be an underlying cause of myelin thinning in newly remyelinated axons.

Neuregulin-1 (Nrg-1) is a member of the Neuregulin family of growth factors with essential roles in the developing and adult nervous system. Six different types of Nrg-1 (Nrg-1 type I-VI) and over 30 isoforms have been discovered; however, their specific roles are not fully determined. Nrg-1 signals through a complex network of protein-tyrosine kinase receptors, ErbB2, ErbB3, ErbB4 and multiple intracellular pathways. Genetic and pharmacological studies of Nrg-1 and ErbB receptors have identified a critical role for Nrg-1/ErbB network in neurodevelopment including neuronal migration, neural differentiation, myelination as well as formation of synapses and neuromuscular junctions. Nrg-1 signaling is best known for its characterized role in development and repair of the peripheral nervous system (PNS) due to its essential role in Schwann cell development, survival and myelination. However, our knowledge of the impact of Nrg-1/ErbB on the central nervous system (CNS) has emerged in recent years. Ongoing efforts have uncovered a multi-faceted role for Nrg-1 in regulating CNS injury and repair processes. In this review, we provide a timely overview of the most recent updates on Nrg-1 signaling and its role in nervous system injury and diseases. We will specifically highlight the emerging role of Nrg-1 in modulating the glial and immune responses and its capacity to foster neuroprotection and remyelination in CNS injury. Nrg-1/ErbB network is a key regulatory pathway in the developing nervous system; therefore, unraveling its role in neuropathology and repair can aid in development of new therapeutic approaches for nervous system injuries and associated disorders.

Spinal cord injury (SCI) results in degeneration of oligodendrocytes that leads to demyelination and axonal dysfunction. Replacement of oligodendrocytes is impaired after SCI, owing to the improper endogenous differentiation and maturation of myelinating oligodendrocytes. Here, we report that SCI-induced dysregulation of neuregulin-1 (Nrg-1)-ErbB signaling may underlie the poor replacement of oligodendrocytes. Nrg-1 and its receptors, ErbB-2, ErbB-3, and ErbB-4, play essential roles in several aspects of oligodendrocyte development and physiology. In rats with SCI, we demonstrate that the Nrg-1 level is dramatically reduced at 1 day after injury, with no restoration at later time-points. Our characterisation shows that Nrg-1 is mainly expressed by neurons, axons and oligodendrocytes in the adult spinal cord, and the robust and lasting decrease in its level following SCI reflects the permanent loss of these cells. Neural precursor cells (NPCs) residing in the spinal cord ependyma express ErbB receptors, suggesting that they are responsive to Nrg-1 availability. In vitro, exogenous Nrg-1 enhanced the proliferation and differentiation of spinal NPCs into oligodendrocytes while reducing astrocyte differentiation. In rats with SCI, recombinant human Nrg-1β1 treatment resulted in a significant increase in the number of new oligodendrocytes and the preservation of existing ones after injury. Nrg-1β1 administration also enhanced axonal preservation and attenuated astrogliosis, tumor necrosis factor-α release and tissue degeneration after SCI. The positive effects of Nrg-1β1 treatment were reversed by inhibiting its receptors. Collectively, our data provide strong evidence to suggest an impact of Nrg-1-ErbB signaling on endogenous oligodendrocyte replacement and maintenance in the adult injured spinal cord, and its potential as a therapeutic target for SCI.

After spinal cord injury (SCI), precise assessment of motor recovery is essential to evaluate the outcome of new therapeutic approaches. Very little is known on the recovery of kinematic parameters after clinically-relevant severe compressive/contusive incomplete spinal cord lesions in experimental animal models. In the present study we evaluated the time-course of kinematic parameters during a 6-week period in rats walking on a treadmill after a severe thoracic clip compression SCI. The effect of daily treadmill training was also assessed. During the recovery period, a significant amount of spontaneous locomotor recovery occurred in 80% of the rats with a return of well-defined locomotor hindlimb pattern, regular plantar stepping, toe clearance and homologous hindlimb coupling. However, substantial residual abnormalities persisted up to 6 weeks after SCI including postural deficits, a bias of the hindlimb locomotor cycle toward the back of the animals with overextension at the swing/stance transition, loss of lateral balance and impairment of weight bearing. Although rats never recovered the antero-posterior (i.e. homolateral) coupling, different levels of decoupling between the fore and hindlimbs were measured. We also showed that treadmill training increased the swing duration variability during locomotion suggesting an activity-dependent compensatory mechanism of the motor control system. However, no effect of training was observed on the main locomotor parameters probably due to a ceiling effect of self-training in the cage. These findings constitute a kinematic baseline of locomotor recovery after clinically relevant SCI in rats and should be taken into account when evaluating various therapeutic strategies aimed at improving locomotor function.

Changes in intracellular Ca(2+) play a key role in regulating gene expression and developmental changes in oligodendroglial precursor cells (OPCs). However, the mechanisms by which Ca(2+) influx in OPCs is controlled remains incompletely understood. Although there are several mechanisms that modulate Ca(2+) influx, in many systems the large-conductance, voltage- and Ca(2+) -activated K(+) channel (BK channel) plays an important role in regulating both membrane excitability and intracellular Ca(2+) levels. To date, the role of the BK channel in the regulation of intracellular Ca(2+) in oligodendroglial lineage cells is unknown. Here we investigated whether cells of the oligodendroglial lineage express BK channels and what potential role they play in regulation of Ca(2+) influx in these cells. In oligodendrocytes derived from differentiated adult neural precursor cells (NPCs, obtained from C57bl6 mice) we observed outward currents that were sensitive to the BK channel blocker iberiotoxin (IbTx). Further confirmation of the expression of the BK channel was obtained utilizing other blockers of the BK channel and by confocal immunofluoresence labelling of the BK channel on oligodendroglia. Using Fura-2AM to monitor intracellular Ca(2+) , it was observed that inhibition of the BK channel during glutamate-induced depolarization led to an additive increase in intracellular Ca(2+) levels. Electrophysiological difference currents demonstrated that the expression levels of the BK channel decrease with developmental age. This latter finding was further corroborated via RT-PCR and Western blot analysis. We conclude that the BK channel is involved in regulating Ca(2+) influx in OPCs, and may potentially play a role during differentiation of oligodendroglial lineage cells.

The transplantation of neural stem/progenitor cells (NPCs) is a promising therapeutic strategy for spinal cord injury (SCI). However, to date NPC transplantation has exhibited only limited success in the treatment of chronic SCI. Here, we show that chondroitin sulfate proteoglycans (CSPGs) in the glial scar around the site of chronic SCI negatively influence the long-term survival and integration of transplanted NPCs and their therapeutic potential for promoting functional repair and plasticity. We targeted CSPGs in the chronically injured spinal cord by sustained infusion of chondroitinase ABC (ChABC). One week later, the same rats were treated with transplants of NPCs and transient infusion of growth factors, EGF, bFGF, and PDGF-AA. We demonstrate that perturbing CSPGs dramatically optimizes NPC transplantation in chronic SCI. Engrafted NPCs successfully integrate and extensively migrate within the host spinal cord and principally differentiate into oligodendrocytes. Furthermore, this combined strategy promoted the axonal integrity and plasticity of the corticospinal tract and enhanced the plasticity of descending serotonergic pathways. These neuroanatomical changes were also associated with significantly improved neurobehavioral recovery after chronic SCI. Importantly, this strategy did not enhance the aberrant synaptic connectivity of pain afferents, nor did it exacerbate posttraumatic neuropathic pain. For the first time, we demonstrate key biological and functional benefits for the combined use of ChABC, growth factors, and NPCs to repair the chronically injured spinal cord. These findings could potentially bring us closer to the application of NPCs for patients suffering from chronic SCI or other conditions characterized by the formation of a glial scar.

Injury to the central nervous system (CNS) results in oligodendrocyte cell death and progressive demyelination. Demyelinated axons undergo considerable physiological changes and molecular reorganizations that collectively result in axonal dysfunction, degeneration and loss of sensory and motor functions. Endogenous adult oligodendrocyte precursor cells and neural stem/progenitor cells contribute to the replacement of oligodendrocytes, however, the extent and quality of endogenous remyelination is suboptimal. Emerging evidence indicates that optimal remyelination is restricted by multiple factors including (i) low levels of factors that promote oligodendrogenesis; (ii) cell death among newly generated oligodendrocytes, (iii) inhibitory factors in the post-injury milieu that impede remyelination, and (iv) deficient expression of key growth factors essential for proper re-construction of a highly organized myelin sheath. Considering these challenges, over the past several years, a number of cell-based strategies have been developed to optimize remyelination therapeutically. Outcomes of these basic and preclinical discoveries are promising and signify the importance of remyelination as a mechanism for improving functions in CNS injuries. In this review, we provide an overview on: (1) the precise organization of myelinated axons and the reciprocal axo-myelin interactions that warrant properly balanced physiological activities within the CNS; (2) underlying cause of demyelination and the structural and functional consequences of demyelination in axons following injury and disease; (3) the endogenous mechanisms of oligodendrocyte replacement; (4) the modulatory role of reactive astrocytes and inflammatory cells in remyelination; and (5) the current status of cell-based therapies for promoting remyelination. Careful elucidation of the cellular and molecular mechanisms of demyelination in the pathologic CNS is a key to better understanding the impact of remyelination for CNS repair.

Spinal cord injury (SCI) results in loss of oligodendrocytes demyelination of surviving axons and severe functional impairment. Spontaneous remyelination is limited. Thus, cell replacement therapy is an attractive approach for myelin repair. In this study, we transplanted adult brain-derived neural precursor cells (NPCs) isolated from yellow fluorescent protein-expressing transgenic mice into the injured spinal cord of adult rats at 2 and 8 weeks after injury, which represents the subacute and chronic phases of SCI. A combination of growth factors, the anti-inflammatory drug minocycline, and cyclosporine A immunosuppression was used to enhance the survival of transplanted adult NPCs. Our results show the presence of a substantial number of surviving NPCs in the injured spinal cord up to 10 weeks after transplantation at the subacute stage of SCI. In contrast, cell survival was poor after transplantation into chronic lesions. After subacute transplantation, grafted cells migrated >5 mm rostrally and caudally. The surviving NPCs integrated principally along white-matter tracts and displayed close contact with the host axons and glial cells. Approximately 50% of grafted cells formed either oligodendroglial precursor cells or mature oligodendrocytes. NPC-derived oligodendrocytes expressed myelin basic protein and ensheathed the axons. We also observed that injured rats receiving NPC transplants had improved functional recovery as assessed by the Basso, Beattie, and Bresnahan Locomotor Rating Scale and grid-walk and footprint analyses. Our data provide strong evidence in support of the feasibility of adult NPCs for cell-based remyelination after SCI.

Abnormal formation or loss of myelin is a distinguishing feature of many neurological disorders and contributes to the pathobiology of neurotrauma. In this study we characterize the functional and molecular changes in CNS white matter in Long Evans Shaker (LES) rats. These rats have a spontaneous mutation of the gene encoding myelin basic protein which results in severe dysmyelination of the central nervous system (CNS), providing a unique model for demyelinating/dysmyelinating disorders. To date, the functional and molecular changes in CNS white matter in this model are not well understood. We have used in vivo somatosensory evoked potential (SSEP), in vitro compound action potential (CAP) recording in isolated dorsal columns, confocal immunohistochemistry, Western blotting and real-time PCR to examine the electrophysiological, molecular and cellular changes in spinal cord white matter in LES rats. We observed that dysmyelination is associated with dispersed labeling of Kv1.1 and Kv1.2 K+ channel subunits, as well as Caspr, a protein normally confined to paranodes, along the LES rat spinal cord axons. Abnormal electrophysiological properties including attenuation of CAP amplitude and conduction velocity, high frequency conduction failure and enhanced sensitivity to K+ channel blockers 4-aminopyridine and dendrotoxin-I were observed in spinal cord axons from LES rats. Our results in LES rats clarify some of the key molecular, cellular and functional consequences of dysmyelination and myelin–axon interactions. Further understanding of these issues in this model could provide critical insights for neurological disorders characterized by demyelination.

After spinal cord injury (SCI), surviving white matter axons display axonal dysfunction associated with demyelination and altered K+ channel activity. To clarify the molecular basis of posttraumatic axonal pathophysiology after SCI, we investigated the changes in expression and distribution of the axonal K+ channel subunits Kv1.1 and Kv1.2 in spinal cord white matter after in vivo SCI in the rat. Using Western blot analysis, we found an increased expression of Kv1.1 and Kv1.2 at 2 and 6 weeks after SCI. By real-time PCR we observed an increase in Kv1.1 and Kv1.2 mRNA levels 1 day after SCI, which persisted until 6 weeks. Confocal immunohistochemistry showed a markedly dispersed labelling of Kv1.1 and Kv1.2 along the injured axons, in contrast to the tight localization of these channels to the juxtaparanodes of noninjured axons. This redistribution of Kv1.1 and Kv1.2 occurred as early as 1 h postinjury along some injured axons, and persisted at 6 weeks postinjury. In parallel with the redistribution of Kv1.1 and 1.2, contactin-associated protein (Caspr), which is normally confined to a paranodal location, also displayed a more diffuse distribution along the injured spinal cord axons. Our results suggest that the increased expression of Kv1.1 and Kv1.2 proteins is transcriptionally regulated. In contrast, the redistribution of the axonal K+ channel subunits occurs very early postinjury and probably reflects a disruption of the juxtaparanodal axonal region due to physical trauma, as shown by altered localization of Caspr.

Chondroitin Sulfate Proteoglycans (CSPGs) are a major component of the extracellular matrix in the central nervous system (CNS) and play critical role in the development and pathophysiology of the brain and spinal cord. Developmentally, CSPGs provide guidance cues for growth cones and contribute to the formation of neuronal boundaries in the developing CNS. Their presence in perineuronal nets plays a crucial role in the maturation of synapses and closure of critical periods by limiting synaptic plasticity. Following injury to the CNS, CSPGs are dramatically upregulated by reactive glia which form a glial scar around the lesion site. Increased level of CSPGs is a hallmark of all CNS injuries and has been shown to limit axonal plasticity, regeneration, remyelination, and conduction after injury. Additionally, CSPGs create a non-permissive milieu for cell replacement activities by limiting cell migration, survival and differentiation. Mounting evidence is currently shedding light on the potential benefits of manipulating CSPGs in combination with other therapeutic strategies to promote spinal cord repair and regeneration. Moreover, the recent discovery of multiple receptors for CSPGs provides new therapeutic targets for targeted interventions in blocking the inhibitory properties of CSPGs following injury. Here, we will provide an in depth discussion on the impact of CSPGs in normal and pathological CNS. We will also review the recent preclinical therapies that have been developed to target CSPGs in the injured CNS.

Contusive spinal cord injury leads to a variety of disabilities owing to limited neuronal regeneration and functional plasticity. It is well established that an upregulation of glial-derived chondroitin sulphate proteoglycans (CSPGs) within the glial scar and perineuronal net creates a barrier to axonal regrowth and sprouting. Protein tyrosine phosphatase σ (PTPσ), along with its sister phosphatase leukocyte common antigen-related (LAR) and the nogo receptors 1 and 3 (NgR), have recently been identified as receptors for the inhibitory glycosylated side chains of CSPGs. Here we find in rats that PTPσ has a critical role in converting growth cones into a dystrophic state by tightly stabilizing them within CSPG-rich substrates. We generated a membrane-permeable peptide mimetic of the PTPσ wedge domain that binds to PTPσ and relieves CSPG-mediated inhibition. Systemic delivery of this peptide over weeks restored substantial serotonergic innervation to the spinal cord below the level of injury and facilitated functional recovery of both locomotor and urinary systems. Our results add a new layer of understanding to the critical role of PTPσ in mediating the growth-inhibited state of neurons due to CSPGs within the injured adult spinal cord.

While several cellular and pharmacological treatments have been evaluated following spinal cord injury (SCI) in animal models, it is increasingly recognized that approaches to address the glial scar, including the use of chondroitinase ABC (ChABC), can facilitate neuroanatomical plasticity. Moreover, increasing evidence suggests that combinatorial strategies are key to unlocking the plasticity that is enabled by ChABC. Given this, we evaluated the anatomical and functional consequences of ChABC in a combinatorial approach that also included growth factor (EGF, FGF2 and PDGF-AA) treatments and daily treadmill training on the recovery of hindlimb locomotion in rats with mid thoracic clip compression SCI. Using quantitative neuroanatomical and kinematic assessments, we demonstrate that the combined therapy significantly enhanced the neuroanatomical plasticity of major descending spinal tracts such as corticospinal and serotonergic-spinal pathways. Additionally, the pharmacological treatment attenuated chronic astrogliosis and inflammation at and adjacent to the lesion with the modest synergistic effects of treadmill training. We also observed a trend for earlier recovery of locomotion accompanied by an improvement of the overall angular excursions in rats treated with ChABC and growth factors in the first 4 weeks after SCI. At the end of the 7-week recovery period, rats from all groups exhibited an impressive spontaneous recovery of the kinematic parameters during locomotion on treadmill. However, although the combinatorial treatment led to clear chronic neuroanatomical plasticity, these structural changes did not translate to an additional long-term improvement of locomotor parameters studied including hindlimb-forelimb coupling. These findings demonstrate the beneficial effects of combined ChABC, growth factors and locomotor training on the plasticity of the injured spinal cord and the potential to induce earlier neurobehavioral recovery. However, additional approaches such as stem cell therapies or a more adapted treadmill training protocol may be required to optimize this repair strategy in order to induce sustained functional locomotor improvement.

Background The aneurysm clip impact-compression model of spinal cord injury (SCI) is a standard injury model in animals that closely mimics the primary mechanism of most human injuries: acute impact and persisting compression. Its histo-pathological and behavioural outcomes are extensively similar to human SCI. To understand the distinct molecular events underlying this injury model we analyzed global mRNA abundance changes during the acute, subacute and chronic stages of a moderate to severe injury to the rat spinal cord. Results Time-series expression analyses resulted in clustering of the majority of deregulated transcripts into eight statistically significant expression profiles. Systematic application of Gene Ontology (GO) enrichment pathway analysis allowed inference of biological processes participating in SCI pathology. Temporal analysis identified events specific to and common between acute, subacute and chronic time-points. Processes common to all phases of injury include blood coagulation, cellular extravasation, leukocyte cell-cell adhesion, the integrin-mediated signaling pathway, cytokine production and secretion, neutrophil chemotaxis, phagocytosis, response to hypoxia and reactive oxygen species, angiogenesis, apoptosis, inflammatory processes and ossification. Importantly, various elements of adaptive and induced innate immune responses span, not only the acute and subacute phases, but also persist throughout the chronic phase of SCI. Induced innate responses, such as Toll-like receptor signaling, are more active during the acute phase but persist throughout the chronic phase. However, adaptive immune response processes such as B and T cell activation, proliferation, and migration, T cell differentiation, B and T cell receptor-mediated signaling, and B cell- and immunoglobulin-mediated immune response become more significant during the chronic phase. Conclusions This analysis showed that, surprisingly, the diverse series of molecular events that occur in the acute and subacute stages persist into the chronic stage of SCI. The strong agreement between our results and previous findings suggest that our analytical approach will be useful in revealing other biological processes and genes contributing to SCI pathology.

Reactive astrogliosis is a pathologic hallmark of spinal cord injury (SCI). It is characterised by profound morphological, molecular, and functional changes in astrocytes that occur within hours of SCI and evolves as time elapses after injury. Astrogliosis is a defense mechanism to minimize and repair the initial damage but eventually leads to some detrimental effects. Reactive astrocytes secrete a plethora of both growth promoting and inhibitory factors after SCI. However, the production of inhibitory components surpasses the growth stimulating factors, thus, causing inhibitory effects. In severe cases of injury, astrogliosis results in the formation of irreversible glial scarring that acts as regeneration barrier due to the expression of inhibitory components such as chondroitin sulfate proteoglycans. Scar formation was therefore recognized from a negative perspective for many years. Accumulating evidence from pharmacological and genetic studies now signifies the importance of astrogliosis and its timing for spinal cord repair. These studies have advanced our knowledge regarding signaling pathways and molecular mediators, which trigger and modulate reactive astrocytes and scar formation. In this review, we discuss the recent advances in this field. We also review therapeutic strategies that have been developed to target astrocytes reactivity and glial scaring in the environment of SCI. Astrocytes play pivotal roles in governing SCI mechanisms, and it is therefore crucial to understand how their activities can be targeted efficiently to harness their potential for repair and regeneration after SCI.

Spinal cord injury (SCI) has remained a challenging area for scientists and clinicians due to the adverse and complex nature of its pathobiology. To date, clinical therapies for debilitating SCI are largely ineffective. However, emerging research evidence suggests that repair of SCI can be promoted by stem cell-based therapies in regenerative medicine. Over the past decade, therapeutic potential of different types of stem cells for the treatment of SCI have been investigated in preclinical models. These studies have revealed multiple beneficial roles by which stem cells can improve the outcomes of SCI. This chapter will summarize the recent advances in the application of stem cells in regenerative medicine for the repair of SCI.

Changes in intracellular Ca(2+) play a key role in regulating gene expression and developmental changes in oligodendroglial precursor cells (OPCs). However, the mechanisms by which Ca(2+) influx in OPCs is controlled remains incompletely understood. Although there are several mechanisms that modulate Ca(2+) influx, in many systems the large-conductance, voltage- and Ca(2+) -activated K(+) channel (BK channel) plays an important role in regulating both membrane excitability and intracellular Ca(2+) levels. To date, the role of the BK channel in the regulation of intracellular Ca(2+) in oligodendroglial lineage cells is unknown. Here we investigated whether cells of the oligodendroglial lineage express BK channels and what potential role they play in regulation of Ca(2+) influx in these cells. In oligodendrocytes derived from differentiated adult neural precursor cells (NPCs, obtained from C57bl6 mice) we observed outward currents that were sensitive to the BK channel blocker iberiotoxin (IbTx). Further confirmation of the expression of the BK channel was obtained utilizing other blockers of the BK channel and by confocal immunofluoresence labelling of the BK channel on oligodendroglia. Using Fura-2AM to monitor intracellular Ca(2+) , it was observed that inhibition of the BK channel during glutamate-induced depolarization led to an additive increase in intracellular Ca(2+) levels. Electrophysiological difference currents demonstrated that the expression levels of the BK channel decrease with developmental age. This latter finding was further corroborated via RT-PCR and Western blot analysis. We conclude that the BK channel is involved in regulating Ca(2+) influx in OPCs, and may potentially play a role during differentiation of oligodendroglial lineage cells.

✓ Despite advances in medical and surgical care, the current clinical therapies for spinal cord injury (SCI) are largely ineffective. During the last 2 decades, the search for new therapies has been revolutionized by the discovery of stem cells, which has inspired scientists and clinicians to search for a stem cell–based reparative approaches to many diseases, including neurotrauma. In the present study, the authors briefly summarize current knowledge related to the pathophysiology of SCI, including the concepts of primary and secondary injury and the importance of posttraumatic demyelination. Key inhibitory obstacles that impede axonal regeneration include the glial scar and a number of myelin inhibitory molecules including Nogo. Recent advancements in cell replacement therapy as a therapeutic strategy for SCI are summarized. The strategies include the use of pluripotent human stem cells, embryonic stem cells, and a number of adult-derived stem and progenitor cells such as mesenchymal stem cells, Schwann cells, olfactory ensheathing cells, and adult-derived neural precursor cells. Although current strategies to repair the subacutely injured cord appear promising, many obstacles continue to render the treatment of chronic injuries challenging. Nonetheless, the future for stem cell–based reparative strategies for treating SCI appears bright.

Emerging evidence suggests that cell-based remyelination strategies may be a feasible therapeutic approach for CNS diseases characterized by myelin deficiency as a result of trauma, congenital anomalies, or diseases. Although experimental demyelination models targeted at the transient elimination of oligodendrocytes have suggested that transplantation-based remyelination can partially restore axonal molecular structure and function, it is not clear whether such therapeutic approaches can be used to achieve functional remyelination in models associated with long-term, irreversible myelin deficiency. In this study, we transplanted adult neural precursor cells (aNPCs) from the brain of adult transgenic mice into the spinal cords of adultShiverer(shi/shi) mice, which lack compact CNS myelin. Six weeks after transplantation, the transplanted aNPCs expressed oligodendrocyte markers, including MBP, migrated extensively along the white matter tracts of the spinal cord, and formed compact myelin. Conventional and three-dimensional confocal and electron microscopy revealed axonal ensheathment, establishment of paranodal junctional complexes leading tode novoformation of nodes of Ranvier, and partial reconstruction of the juxtaparanodal and paranodal molecular regions of axons based on Kv1.2 and Caspr (contactin-associated protein) expression by the transplanted aNPCs. Electrophysiological recordings revealed improved axonal conduction along the transplanted segments of spinal cords. We conclude that myelination of congenitally dysmyelinated adult CNS axons by grafted aNPCs results in the formation of compact myelin, reconstruction of nodes of Ranvier, and enhanced axonal conduction. These data suggest the therapeutic potential of aNPCs to promote functionally significant myelination in CNS disorders characterized by longstanding myelin deficiency.

Axonal dysfunction after spinal cord injury (SCI) and other types of neurotrauma is associated with demyelination and exposure of juxtaparanodal K+channels. In this study, sucrose gap electrophysiology using selective and nonselective K+channel blockers, confocal immunohistochemistry, and Western blotting were used to study the role of Kv1.1 and Kv1.2 K+channel subunits in dysmyelination-induced spinal cord axonal dysfunction in s hiverer mice, which lack the gene encoding myelin basic protein (MBP) and exhibit incomplete myelin sheath formation on CNS axons. The s hiverer spinal cord axons exhibited smaller amplitude of compound action potentials (CAPs), reduced conduction velocity, reduced excitability, and greater degree of high-frequency conduction failure. The “fast” K+channel blocker 4-aminopyridine, the toxin DTX-I, which targets the Kv1.1 and Kv1.2, but not DTX- K, which has higher selectivity for Kv1.1, increased the amplitude and area of CAPs of shiverer mice spinal cord axons but had insignificant effects in wild-type mice. Confocal immunohistochemistry showed that, unlike wild-type mice, which have a precise juxtaparanodal localization of the Kv1.l and Kv1.2 K+channel subunits, shiverer mouse axons displayed a dispersed distribution of these subunits along the internodes. In contrast, the Kv1.l and Kv1.2 subunits, Na+channels remained highly localized to the nodal regions. Western blotting showed an increased expression of Kv 1.1 and 1.2 in the shiverer mouse spinal cord. These results provide evidence that the neurological deficits associated with myelin deficiency reflect the altered distribution and expression of the K+channel subunits Kv1.l and Kv1.2 along the internodes of spinal cord axons associated with the biophysical consequences caused by alterations in the myelin sheaths.