Demyelination and remyelination after spinal cord injury

Improvement of motor function in mice after implantation of mononuclear stem cells from human umbilical cord and placenta blood after 3 and 6 weeks of experimental spinal cord injury

STUDY DESIGN

Experimental study utilizing with a standardized model (MASCIS Impactor) of Spinal Cord Injury (SCI) in Balb C mouse model with implantation of mononuclear stem cells derived from the human umbilical cord and placenta blood in the early chronic phase of SCI.

OBJECTIVES

The aim of this study was to evaluate the nerve regeneration and motor functional recovery in Balb C mice with surgically induced paraplegia in response to the use of mononuclear stem cells, in early chronic phase (> 2 weeks and < 6 months), because there is yet potential of neuronal and functional recovery as the neuronal scar is not still completely established.

METHODS

Forty-eight mice were randomly assigned to 6 groups of 8 animals. Group 1 received the stem cells 3 weeks after the trauma, and Group 2 received them six weeks later. In Group 3, saline solution was injected at the site of the lesion 3 weeks after the trauma, and in Group 4, 6 weeks later. Group 5 underwent only spinal cord injury and Group 6 underwent laminectomy only. The scales used for motor assessment were BMS and MFS for 12 weeks.

RESULTS

The intervention groups showed statistically significant motor improvement. In the histopathological analysis, the intervention groups had a lower degree of injury (p < 0.05). Regarding axonal budding, the intervention groups showed increasing in axonal budding in the caudal portion (p < 0.05).

CONCLUSIONS

The use of stem cells in mice in the chronic phase after 3 and 6 weeks of SCI brings functional and histopathological benefits to them.

Progesterone alleviates esketamine-induced hypomyelination via PI3K/Akt signaling pathway in the developing rat brain

The neurodevelopmental toxicity of anesthetics has been confirmed repeatedly, and esketamine is now widely used in pediatric surgeries. Oligodendrocyte precursor cells (OPCs) evolved into mature oligodendrocytes (OLs) and formed myeline sheath during the early brain development. In this study, we investigated whether esketamine exposure interrupted development of OPCs and induced hypomyelination in rats. Further we explored the roles of PI3K/Akt phosphorylation in OPCs development and myelination. Sprague Dawley rats with different ages (postnatal day (P) 1, 3, 7 and 12) were exposed to 40mg/kg esketamine. Progesterone treatment was given (16 mg/kg per day for 3 days) 24 h after esketamine exposure via the intraperitoneal route. Corpus callosum tissues were collected at P8 or P14 for western blot and immunofluorescence analyses. Esketamine exposure at P7 and P12 significantly reduced myelin basic protein (MBP) expression and CC1+ OLs number in corpus callosum. Esketamine exposure at P7 not only aggravated the mature OLs apoptosis, also decreased the OPCs proliferation and differentiation, which was related with dephosphorylation of PI3K/Akt. Progesterone was able to promote OPCs differentiation and ameliorate esketamine-induced hypomyelination by enhancing PI3K/Akt phosphorylation. Stage-dependent abnormality of OPCs/OLs after esketamine leads to the esketamine-induced hypomyelination. Esketamine interrupted OPCs evolution via PI3K/Akt signaling pathway, which can be ameliorated by progesterone.

Modulation of αv integrins by lebecetin, a viper venom-derived molecule, in experimental neuroinflammation and demyelination models

Several neurodegenerative diseases, such as multiple sclerosis and Parkinson's disease, are linked to alterations in myelin content or structure. Transmembrane receptors such as integrins could be involved in these alterations. In the present study, we investigated the role of αv-integrins in experimental models of neuroinflammation and demyelination with the use of lebecetin (LCT), a C-lectin protein purified from Macrovipera lebetina viper venom, as an αv-integrin modulator. In a model of neuroinflammation, LCT inhibited the upregulation of αv, β3, β5, α5, and β1 integrins, as well as the associated release of pro-inflammatory factor IL-6 and chemokine CXCL-10, and decreased the expression of phosphorylated NfκB. The subsequent "indirect culture" between reactive astrocytes and oligodendrocytes showed a down-regulation of αv and β3 integrins versus upregulation of β1 one, accompanied by a reduced expression of myelin basic protein (MBP). Treatment of oligodendrocytes with LCT rectified the changes in integrin and MBP expression. Through Western blot quantification, LCT was shown to upregulate the expression levels of PI3K and p-mTOR while downregulating expression levels of p-AKT in oligodendrocytes, suggesting the neuroprotective and pro-myelinating effects of LCT may be related to the PI3K/mTor/AKT pathway. Concomitantly, we found that LCT promoted remyelination by tracking the increased expression of MBP in the brains of cuprizone-intoxicated mice. These results point to an involvement of integrins in not only neuroinflammation but demyelination as well. Thus, targeting αv integrins could offer potential therapeutic avenues for the treatment of demyelinating diseases.

Imaging demyelinated axons after spinal cord injuries with PET tracer [ 18 F]3F4AP

Spinal cord injuries (SCI) often lead to lifelong disability. Among the various types of injuries, incomplete and discomplete injuries, where some axons remain intact, offer potential for recovery. However, demyelination of these spared axons can worsen disability. Demyelination is a reversible phenomenon, and drugs like 4-aminopyridine (4AP), which target K+ channels in demyelinated axons, show that conduction can be restored. Yet, accurately assessing and monitoring demyelination post-SCI remains challenging due to the lack of suitable imaging methods. In this study, we introduce a novel approach utilizing the positron emission tomography (PET) tracer, [ 18 F]3F4AP, specifically targeting K+ channels in demyelinated axons for SCI imaging. Rats with incomplete contusion injuries were imaged up to one month post-injury, revealing [ 18 F]3F4AP's exceptional sensitivity to injury and its ability to detect temporal changes. Further validation through autoradiography and immunohistochemistry confirmed [ 18 F]3F4AP's targeting of demyelinated axons. In a proof-of-concept study involving human subjects, [ 18 F]3F4AP differentiated between a severe and a largely recovered incomplete injury, indicating axonal loss and demyelination, respectively. Moreover, alterations in tracer delivery were evident on dynamic PET images, suggestive of differences in spinal cord blood flow between the injuries. In conclusion, [ 18 F]3F4AP demonstrates efficacy in detecting incomplete SCI in both animal models and humans. The potential for monitoring post-SCI demyelination changes and response to therapy underscores the utility of [ 18 F]3F4AP in advancing our understanding and management of spinal cord injuries.

The role of myelin in neurodegeneration: implications for drug targets and neuroprotection strategies

Myelination of axons in the central nervous system offers numerous advantages, including decreased energy expenditure for signal transmission and enhanced signal speed. The myelin sheaths surrounding an axon consist of a multi-layered membrane that is formed by oligodendrocytes, while specific glycoproteins and lipids play various roles in this formation process. As beneficial as myelin can be, its dysregulation and degeneration can prove detrimental. Inflammation, oxidative stress, and changes in cellular metabolism and the extracellular matrix can lead to demyelination of these axons. These factors are hallmark characteristics of certain demyelinating diseases including multiple sclerosis. The effects of demyelination are also implicated in primary degeneration in diseases such as glaucoma and Alzheimer's disease, as well as in processes of secondary degeneration. This reveals a relationship between myelin and secondary processes of neurodegeneration, including resultant degeneration following traumatic injury and transsynaptic degeneration. The role of myelin in primary and secondary degeneration is also of interest in the exploration of strategies and targets for remyelination, including the use of anti-inflammatory molecules or nanoparticles to deliver drugs. Although the use of these methods in animal models of diseases have shown to be effective in promoting remyelination, very few clinical trials in patients have met primary end points. This may be due to shortcomings or considerations that are not met while designing a clinical trial that targets remyelination. Potential solutions include diversifying disease targets and requiring concomitant interventions to promote rehabilitation.

The promotive effect of activation of the Akt/mTOR/p70S6K signaling pathway in oligodendrocytes on nerve myelin regeneration in rats with spinal cord injury

PURPOSE

Akt/mTOR/p70S6K signaling pathway promotes motor function recovery after spinal cord injury (SCI) in both neurons and astrocytes. But the role and mechanism of this pathway in oligodendrocytes during nerve repair following SCI has not been researched. This study aimed to investigate the effect and mechanism of this signaling pathway in oligodendrocytes on nerve myelin regeneration and motor function recovery in rats with SCI.

METHODS

After inhibiting or activating this signaling pathway, Western blotting and double immunofluorescence labeling were used to determine the levels of the signaling molecules in this pathway and myelin formation-related proteins in the plane of the thoracic segment of the injured spinal cord. The level of motor function recovery was evaluated and the oligodendrocytes involved in nerve myelin regeneration were studied. Primary oligodendrocytes were isolated and cultured in vitro, then MBP, PLP, and MOG were measured with reverse transcription-quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Akt/mTOR/p70S6K signaling pathway was activated after SCI compared with the sham-operated rats, prominently elevated levels of the pathway components were observed in the SC79-treated group. The activation of the signaling pathway significantly increased the expression levels of myelin formation-related proteins, including MBP, PLP, and MOG, and improved the Basso, Beattie, and Bresnahan (BBB) scores in the injured spinal cord. Conversely, rapamycin suppressed the expression of these signaling molecules and reduced the levels of myelin formation-related proteins.

CONCLUSION

Akt/mTOR/p70S6K signaling pathway activation can contribute to nerve myelin regeneration and has the potential to improve the regenerative environment and motor function, as well as the potential to promote repair of SCI.

Pathogenic mechanisms of human immunodeficiency virus (HIV)-associated pain

Chronic pain is a prevalent neurological complication among individuals living with human immunodeficiency virus (PLHIV) in the post-combination antiretroviral therapy (cART) era. These individuals experience malfunction in various cellular and molecular pathways involved in pain transmission and modulation, including the neuropathology of the peripheral sensory neurons and neurodegeneration and neuroinflammation in the spinal dorsal horn. However, the underlying etiologies and mechanisms leading to pain pathogenesis are complex and not fully understood. In this review, we aim to summarize recent progress in this field. Specifically, we will begin by examining neuropathology in the pain pathways identified in PLHIV and discussing potential causes, including those directly related to HIV-1 infection and comorbidities, such as antiretroviral drug use. We will also explore findings from animal models that may provide insights into the molecular and cellular processes contributing to neuropathology and chronic pain associated with HIV infection. Emerging evidence suggests that viral proteins and/or antiretroviral drugs trigger a complex pathological cascade involving neurons, glia, and potentially non-neural cells, and that interactions between these cells play a critical role in the pathogenesis of HIV-associated pain.

Cortical stimulation leads to shortened myelin sheaths and increased axonal branching in spared axons after cervical spinal cord injury

Neural activity and learning lead to myelin sheath plasticity in the intact central nervous system (CNS), but this plasticity has not been well-studied after CNS injury. In the context of spinal cord injury (SCI), demyelination occurs at the lesion site and natural remyelination of surviving axons can take months. To determine if neural activity modulates myelin and axon plasticity in the injured, adult CNS, we electrically stimulated the contralesional motor cortex at 10 Hz to drive neural activity in the corticospinal tract of rats with sub-chronic spinal contusion injuries. We quantified myelin and axonal characteristics by tracing corticospinal axons rostral to and at the lesion epicenter and identifying nodes of Ranvier by immunohistochemistry. Three weeks of daily stimulation induced very short myelin sheaths, axon branching, and thinner axons outside of the lesion zone, where remodeling has not previously been reported. Surprisingly, remodeling was particularly robust rostral to the injury which suggests that electrical stimulation can promote white matter plasticity even in areas not directly demyelinated by the contusion. Stimulation did not alter myelin or axons at the lesion site, which suggests that neuronal activity does not contribute to myelin remodeling near the injury in the sub-chronic period. These data are the first to demonstrate wide-scale remodeling of nodal and myelin structures of a mature, long-tract motor pathway in response to electrical stimulation. This finding suggests that neuromodulation promotes white matter plasticity in intact regions of pathways after injury and raises intriguing questions regarding the interplay between axonal and myelin plasticity.

Cooperative assembly of a designer peptide and silk fibroin into hybrid nanofiber gels for neural regeneration after spinal cord injury

Local reconstruction of a permissive environment with biomaterials is a promising strategy to treat spinal cord injury (SCI). We reported a hybrid hydrogel fabricated from a small functional self-assembling peptide (F-SAP) and large silk fibroin (SF). The diffusion of SF micelles into F-SAP solution was driven by the dynamic synergy between osmotic pressure and F-SAP/SF electrostatic interactions, resulting in the rearrangement of SF micelles and the formation of rod-like filaments with axes nearly perpendicular to F-SAP nanofibers. Spectroscopy analysis, including circular dichroism, Raman and fluorescence, indicated conformation changes of SF from random coil to β sheet, which contributed to enhanced mechanical properties of the resultant hybrid hydrogel. Furthermore, the F-SAP/SF hybrid hydrogel coupled with controlled release of NT-3 provided a permissive environment for neural regeneration by providing nanofibrous substrates for regenerating axons, inflammatory modulation and remyelination, consequently resulting in improved locomotion and electrophysiological properties. This hydrogel could be used as a long-term stent in vivo for the treatment of SCI.

Therapeutic administration of mouse mast cell protease 6 improves functional recovery after traumatic spinal cord injury in mice by promoting remyelination and reducing glial scar formation

Traumatic spinal cord injury (SCI) most often leads to permanent paralysis due to the inability of axons to regenerate in the adult mammalian central nervous system (CNS). In the past, we have shown that mast cells (MCs) improve the functional outcome after SCI by suppressing scar tissue formation at the lesion site via mouse mast cell protease 6 (mMCP6). In this study, we investigated whether recombinant mMCP6 can be used therapeutically to improve the functional outcome after SCI. Therefore, we applied mMCP6 locally via an intrathecal catheter in the subacute phase after a spinal cord hemisection injury in mice. Our findings showed that hind limb motor function was significantly improved in mice that received recombinant mMCP6 compared with the vehicle-treated group. In contrast to our previous findings in mMCP6 knockout mice, the lesion size and expression levels of the scar components fibronectin, laminin, and axon-growth-inhibitory chondroitin sulfate proteoglycans were not affected by the treatment with recombinant mMCP6. Surprisingly, no difference in infiltration of CD4+ T cells and reactivity of Iba-1+ microglia/macrophages at the lesion site was observed between the mMCP6-treated mice and control mice. Additionally, local protein levels of the pro- and anti-inflammatory mediators IL-1β, IL-2, IL-4, IL-6, IL-10, TNF-α, IFNγ, and MCP-1 were comparable between the two treatment groups, indicating that locally applied mMCP6 did not affect inflammatory processes after injury. However, the increase in locomotor performance in mMCP6-treated mice was accompanied by reduced demyelination and astrogliosis in the perilesional area after SCI. Consistently, we found that TNF-α/IL-1β-astrocyte activation was decreased and that oligodendrocyte precursor cell (OPC) differentiation was increased after recombinant mMCP6 treatment in vitro. Mechanistically, this suggests effects of mMCP6 on reducing astrogliosis and improving (re)myelination in the spinal cord after injury. In conclusion, these data show for the first time that recombinant mMCP6 is therapeutically active in enhancing recovery after SCI.

Segmental motor recovery after cervical spinal cord injury relates to density and integrity of corticospinal tract projections

Cervical spinal cord injury (SCI) causes extensive impairments for individuals which may include dextrous hand function. Although prior work has focused on the recovery at the person-level, the factors determining the recovery of individual muscles are poorly understood. Here, we investigate the muscle-specific recovery after cervical spinal cord injury in a retrospective analysis of 748 individuals from the European Multicenter Study about Spinal Cord Injury (NCT01571531). We show associations between corticospinal tract (CST) sparing and upper extremity recovery in SCI, which improves the prediction of hand muscle strength recovery. Our findings suggest that assessment strategies for muscle-specific motor recovery in acute spinal cord injury are improved by accounting for CST sparing, and complement person-level predictions.

Promoting Oligodendrocyte Differentiation from Human Induced Pluripotent Stem Cells by Activating Endocannabinoid Signaling for Treating Spinal Cord Injury

Transplantation of oligodendrocyte progenitor cell (OPC) at the injury site is being developed as a potential therapeutic strategy for promoting remyelination and locomotor function recovery after spinal cord injury (SCI). To this end, the development of expandable and functional human OPCs is crucial for testing their efficacy in SCI. In mice and rats, the endocannabinoid signaling system is crucial for the survival, differentiation, and maturation of OPCs. Similar studies in humans are lacking currently. Endocannabinoids and exogenous cannabinoids exert their effects mainly via cannabinoid receptors (CB1R and CB2R). We demonstrated that these receptors were differentially expressed in iPSC-derived human NSCs and OPCs, and they could be activated by WIN55212-2 (WIN), a potent CB1R/CB2R agonist to upregulate the endocannabinoid signaling during glial induction. WIN primed NSCs generated more OLIG2 + glial progenitors and migratory PDGFRα + OPC in a CB1/CB2 dependent manner compared to unprimed NSCs. Furthermore, WIN-induced OPCs (WIN-OPCs) robustly differentiated into functional oligodendrocytes and myelinate in vitro and in vivo in a mouse spinal cord injury model. RNA-Seq revealed that WIN upregulated the biological process of positive regulation of oligodendrocyte differentiation. Mechanistically, WIN could act as a partial smoothed (SMO) inhibitor or activate CB1/CB2 to form heteromeric complexes with SMO leading to the inhibition of GLI1 in the Sonic hedgehog pathway. The partial and temporal inhibition of GLI1 during glial induction is shown to promote OPCs that differentiate faster than control's. Thus, CB1R/CB2R activation results in more efficient generation of OPCs that can mature and efficiently myelinate.

Repair of the Injured Spinal Cord by Schwann Cell Transplantation

Spinal cord injury (SCI) can result in sensorimotor impairments or disability. Studies of the cellular response to SCI have increased our understanding of nerve regenerative failure following spinal cord trauma. Biological, engineering and rehabilitation strategies for repairing the injured spinal cord have shown impressive results in SCI models of both rodents and non-human primates. Cell transplantation, in particular, is becoming a highly promising approach due to the cells’ capacity to provide multiple benefits at the molecular, cellular, and circuit levels. While various cell types have been investigated, we focus on the use of Schwann cells (SCs) to promote SCI repair in this review. Transplantation of SCs promotes functional recovery in animal models and is safe for use in humans with subacute SCI. The rationales for the therapeutic use of SCs for SCI include enhancement of axon regeneration, remyelination of newborn or sparing axons, regulation of the inflammatory response, and maintenance of the survival of damaged tissue. However, little is known about the molecular mechanisms by which transplanted SCs exert a reparative effect on SCI. Moreover, SC-based therapeutic strategies face considerable challenges in preclinical studies. These issues must be clarified to make SC transplantation a feasible clinical option. In this review, we summarize the recent advances in SC transplantation for SCI, and highlight proposed mechanisms and challenges of SC-mediated therapy. The sparse information available on SC clinical application in patients with SCI is also discussed.

Inhibition of CDK1 attenuates neuronal apoptosis and autophagy and confers neuroprotection after chronic spinal cord injury in vivo

Chronic spinal cord injury (CSCI) results from progressive compression of the spinal cord over time. A variety of factors cause CSCI, and its exact pathogenesis is unknown. Cyclin-dependent kinase 1 (CDK1) is closely related to the apoptosis pathway, but no CSCI-related studies on CDK1 have been conducted. In this study, the role of CDK1 in CSCI was explored in a rat model. The CSCI model was established by screw compression using the cervical anterior approach for twelve weeks. The neurological function of the rats was evaluated using the neurological severity scores (NSS) and motor evoked potentials (MEPs). Pathological changes in spinal cord tissue were observed by hematoxylin-eosin (HE) staining, and Nissl staining was performed to assess the survival of motor neurons in the anterior horn of the spinal cord. Changes in autophagy and apoptosis in anterior horn of spinal cord tissue were detected using transmission electron microscopy and the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, respectively. The expression levels of glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor (IBA) and choline acetyltransferase (CHAT) in the anterior horn were determined using immunohistochemistry assays to investigate astrocytes, microglia and motor neurons, respectively, in the anterior horn. Western blot assays were used to detect the expression levels of CDK1, Bcl-2, Bax, Caspase 3, LC3 and Beclin1. Changes in the expression of CDK1, LC3 and Beclin1 were also observed using immunohistochemistry. The results indicated that CSCI resulted in neuronal injury and a decrease in the NSS. In the CSCI model group, anterior horn astrocytes and microglia were activated, and motor neurons were decreased. Neuronal apoptosis was promoted, and the number of autophagic vacuoles was elevated. Rats treated with the CDK1 shRNA lentivirus exhibited better NSS, more surviving motor neurons, and fewer apoptotic neurons than the model rats. The occurrence of autophagy and the expression of proapoptotic and autophagy-related proteins were lower in the CDK1 shRNA group than the model group. In conclusion, CDK1 downregulation suppressed the activation of anterior horn astrocytes and microglia, promoted motor neuron repair, and inhibited neurons apoptosis and autophagy to promote the recovery of motor function after spinal cord injury.

The Unique Properties of Placental Mesenchymal Stromal Cells: A Novel Source of Therapy for Congenital and Acquired Spinal Cord Injury

Spinal cord injury (SCI) is a devasting condition with no reliable treatment. Spina bifida is the most common cause of congenital SCI. Cell-based therapies using mesenchymal stem/stromal cells (MSCS) have been largely utilized in SCI. Several clinical trials for acquired SCI use adult tissue-derived MSC sources, including bone-marrow, adipose, and umbilical cord tissues. The first stem/stromal cell clinical trial for spina bifida is currently underway (NCT04652908). The trial uses early gestational placental-derived mesenchymal stem/stromal cells (PMSCs) during the fetal repair of myelomeningocele. PMSCs have been shown to exhibit unique neuroprotective, angiogenic, and antioxidant properties, all which are promising applications for SCI. This review will summarize the unique properties and current applications of PMSCs and discuss their therapeutic role for acquired SCI.

Therapeutic Effect of BDNF-Overexpressing Human Neural Stem Cells (F3.BDNF) in a Contusion Model of Spinal Cord Injury in Rats

The most common type of spinal cord injury is the contusion of the spinal cord, which causes progressive secondary tissue degeneration. In this study, we applied genetically modified human neural stem cells overexpressing BDNF (brain-derived neurotrophic factor) (F3.BDNF) to determine whether they can promote functional recovery in the spinal cord injury (SCI) model in rats. We transplanted F3.BDNF cells via intrathecal catheter delivery after a contusion of the thoracic spinal cord and found that they were migrated toward the injured spinal cord area by MR imaging. Transplanted F3.BDNF cells expressed neural lineage markers, such as NeuN, MBP, and GFAP and were functionally connected to the host neurons. The F3.BDNF-transplanted rats exhibited significantly improved locomotor functions compared with the sham group. This functional recovery was accompanied by an increased volume of spared myelination and decreased area of cystic cavity in the F3.BDNF group. We also observed that the F3.BDNF-transplanted rats showed reduced numbers of Iba1- and iNOS-positive inflammatory cells as well as GFAP-positive astrocytes. These results strongly suggest the transplantation of F3.BDNF cells can modulate inflammatory cells and glia activation and also improve the hyperalgesia following SCI.

The Comparative Effects of Mesenchymal Stem Cell Transplantation Therapy for Spinal Cord Injury in Humans and Animal Models: A Systematic Review and Meta-Analysis

Animal models have been used in preclinical research to examine potential new treatments for spinal cord injury (SCI), including mesenchymal stem cell (MSC) transplantation. MSC transplants have been studied in early human trials. Whether the animal models represent the human studies is unclear. This systematic review and meta-analysis has examined the effects of MSC transplants in human and animal studies. Following searches of PubMed, Clinical Trials and the Cochrane Library, published papers were screened, and data were extracted and analysed. MSC transplantation was associated with significantly improved motor and sensory function in humans, and significantly increased locomotor function in animals. However, there are discrepancies between the studies of human participants and animal models, including timing of MSC transplant post-injury and source of MSCs. Additionally, difficulty in the comparison of functional outcome measures across species limits the predictive nature of the animal research. These findings have been summarised, and recommendations for further research are discussed to better enable the translation of animal models to MSC-based human clinical therapy.

Curcumin Protects against White Matter Injury through NF-κB and Nrf2 Cross Talk

Inflammation and oxidative stress play a central role in the pathogenesis of white matter injury (WMI). Curcumin (Cur), a polyphenolic compound, exhibits anti-inflammatory and anti-oxidant effects on several conditions. The objective of this study was to investigate neuroprotective effects of Cur on WMI and explore its underlying mechanisms of action. Sprague-Dawley rats were subjected to the removal of white matter from the dorsal column of the spinal cord. Dorsal columns were randomly divided into three groups: Sham (Ringer's solution bubbled with 95% O₂ and 5% CO₂), hypoxia (Hyp; Ringer's solution bubbled with 95% N₂ and 5% CO₂ for 1 h), and Cur-treated (Hyp+Cur; Ringer's solution bubbled with 95% N₂ and 5% CO₂ for 1 h in the presence of 50 μM Cur). For NF-κB inhibition experiments, dorsal columns were incubated with 50 μM BAY 11-7082 (BAY) for 30 min in 95% O₂ and 5% CO₂ prior to 1-h incubation with 50 μM Cur in 95% N₂ and 5% CO₂. Our data show that Cur inhibited hypoxia-induced HIF1-α expression and tissue damage by demonstrating the improved morphology of astrocytes and remarkable reduction in vacuolation. Cur also inhibited the hypoxia-induced upregulation of glial fibrillary acidic protein (GFAP) and neurofilament-H (NF-H) after hypoxia and downregulated the expression of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin 1 (IL-1). Terminal dexynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-assay analysis showed that Cur effectively attenuated apoptosis in white matter. In addition, we demonstrated that Cur exerted its neuroprotective effect through cross talk between nuclear factor kappa-light-chain-enhancer of activated B (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathways. In conclusion, our results indicate that treatment with Cur inhibited the hypoxia, inflammation and apoptosis associated with WMI. Further, the Nrf-2 pathway inhibits NF-κB activation by preventing IkB degradation and increasing HO-1 expression, which in turn reduces reactive oxygen species (ROS) and as a result NF-κB activation is suppressed. Similarly, NF-κB-mediated transcription reduces Nrf2 activation by reducing anti-oxidant response element (ARE) gene and free CREB binding protein by competing with Nrf2 for CBP thus inhibiting the Nrf-2 activation.

Neuroprotective potential of Spirulina platensis on lesioned spinal cord corticospinal tract under experimental conditions in rat models

Spinal cord injury (SCI) results from penetrating or compressive traumatic injury to the spine in humans or by the surgical compression of the spinal cord in experimental animals. In this study, the neuroprotective potential of Spirulina platensis was investigated on ultrastructural and functional recovery of the spinal cord following surgical-induced injury. Twenty-four Sprague-Dawley rats were divided into three groups; sham group, control (trauma) group, and experimental (S. platensis) group (180 mg/kg) of eight rats each. For each group, the rats were then subdivided into two groups to allow measurement at two different timepoints (day 14 and 28) for the microscopic analysis. Rats in the control and experimental S. platensis groups were subjected to partial crush injury at the level of T12 with Inox number 2 modified forceps by compressing on the spinal cord for 30 s. Pairwise comparisons of ultrastructural grading mean scores difference between the control and experimental S. platensis groups reveals that there were significant differences on the axonal ultrastructure, myelin sheath and BBB Score on Day 28; these correlate with the functional locomotor recovery at this timepoint. The results suggest that supplementation with S. platensis induces functional recovery and effective preservation of the spinal cord ultrastructure after SCI. These findings will open new potential avenue for further research into the mechanism of S. platensis-mediated spinal cord repair.

Quercetin prevents necroptosis of oligodendrocytes by inhibiting macrophages/microglia polarization to M1 phenotype after spinal cord injury in rats

Background

Oligodendrocytes (OLs) death after spinal cord injury (SCI) contributes to demyelination, even leading to a permanent neurological deficit. Besides apoptosis, our previous study demonstrated that OLs underwent receptor-interacting serine-threonine kinase 3(RIP3)/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis. Considering that necroptosis is always accompanied with pro-inflammatory response and quercetin has long been used as anti-inflammatory agent, in the present study we investigated whether quercetin could inhibit necroptosis of OLs and suppress the M1 macrophages/microglia-mediated immune response after SCI as well as the possible mechanism.

Methods

In this study, we applied quercetin, an important flavonoid component of various herbs, to treat rats with SCI and rats injected with saline were employed as the control group. Locomotor functional recovery was evaluated using Basso-Beattie-Bresnahan (BBB) scoring and rump-height Index (RHI) assay. In vivo, the necroptosis, apoptosis, and regeneration of OLs were detected by immunohistochemistry, 5′-bromo-2′-deoxyuridine (BrdU) incorporation. The loss of myelin and axons after SCI were evaluated by Luxol fast blue (LFB) staining, immunohistochemistry, and electron microscopic study. The polarization of macrophages/microglia after SCI and the underlying mechanisms were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemistry. In vitro, the ATP and reactive oxygen species (ROS) level examination, propidium iodide (PI) labeling, and Western blotting were used to analyze the necroptosis of cultured OLs, while the signaling pathways-mediated polarization of cultured macrophages/microglia was detected by qRT-PCR and Western blotting.

Results

We demonstrated that quercetin treatment improved functional recovery in rats after SCI. We then found that quercetin significantly reduced necroptosis of OLs after SCI without influencing apoptosis and regeneration of OLs. Meanwhile, myelin loss and axon loss were also significantly reduced in quercetin-treated rats, as compared to SCI + saline control. Further, we revealed that quercetin could suppress macrophages/microglia polarized to M1 phenotype through inhibition of STAT1 and NF-κB pathway in vivo and in vitro, which contributes to the decreased necroptosis of OLs.

Conclusions

Quercetin treatment alleviated necroptosis of OLs partially by inhibiting M1 macrophages/microglia polarization after SCI. Our findings suggest that necroptosis of OLs may be a potential therapeutic target for clinical SCI.

Neurofilament Immunohistochemistry Followed by Luxol Fast Blue, for Staining Axons and Myelin in the Same Paraffin Section of Spinal Cord

Many disorders of the central nervous system are characterized by both axonal pathology and demyelination. In assessing this concurrent pathology, techniques for staining axons or myelin are frequently used separately. Here we report the development of a combined immunohistochemical and tinctorial staining technique in which we have modified the Luxol fast blue myelin stain to be used in conjunction with a diaminobenzidine-based immunohistochemical stain for high molecular weight neurofilament (SMI-31). This modification of staining will have utility in experimental neuropathology laboratories investigating demyelination and axonal damage in human tissue and animal models.

High-Dose Neural Stem/Progenitor Cell Transplantation Increases Engraftment and Neuronal Distribution and Promotes Functional Recovery in Rats after Acutely Severe Spinal Cord Injury

Severe spinal cord injury (SCI) leads to permanent, complete paraplegia and places considerable mental and economic burdens on patients, compared with mild to moderate SCI. However, the dose-related effects of the neural stem/precursor cell (NSPC) transplantation on the injury microenvironment, NSPC survival, axonal growth, neuronal distribution, the composition of neurons, oligodendrocytes, and astrocytes in the lesion area and functional recovery have not yet been quantitatively evaluated in the context of severe SCI. In our study, we acutely transplanted 2.5 × 10⁴ or 1.5 × 10⁵ NSPCs/μl into the site of transection SCI. We found that high-dose NSPC transplantation exerted immunomodulatory and neuroprotective effects in the acute phase of severe SCI. In addition, one week later, a remarkable positive relationship was observed between the transplantation dose and the number of surviving NSPCs in severe SCI. At 8 weeks postgrafting, subjects that received the higher cell dose exhibited abundant nerve regeneration, extensive neuronal distribution, increased proportions of neurons and oligodendrocytes, and nascent functional neural network formation in the lesion area. Notably, a significant functional recovery was also observed. Our data suggest that it is important to consider potential dose-related effects on donor cell survival, neuronal distribution, and locomotor recovery in the development of preclinical NSPC transplantation therapy for severe SCI.

Possible Strategies to Optimize a Biomarker Discovery Approach to Correlate with Neurological Outcome in Patients with Spinal Cord Injury: A Pilot Study

The lack of reliable diagnostic and prognostic markers for spinal cord injured (SCI) patients is a severe obstacle in development and testing of new therapies, and it also impairs appropriate rehabilitation care. The sparse available data on the biochemical composition of cerebrospinal fluid (CSF) during the acute and/or chronic phase of the lesion provide, up until now, inconsistent results. In this pilot study, we then explored the possibility of combining a multi-parametric and bioinformatic analysis of CSF for its biological properties tested on different cells types, suitable for investigating inflammation and re-myelination. The patient enrollment was based on stringent inclusion criteria; that is, cervical and thoracic SCI trauma, CSF collection within 24 h of trauma, type of surgical approach for spine stabilization, and absence of steroid therapy before CSF collection. Eleven SCI patients and four healthy controls were included, and in three patients, CSF was also collected at 3 months after lesion. We identified 19 proteins among the 60 investigated cytokines, chemokines, growth factors, and structural biomarkers, which are transiently regulated 24 h after SCI. A bioinformatic analysis indicated that interleukin (IL)-6 and IL-10 are in the core of the interconnected net of activated proteins. Cell-based experiments indicate that CSF from SCI patients stimulates astroglia derivation from neural precursor cells, and an inverse correlation between IL-8 CSF level and oligodendrocyte precursor cells generated from neural stem cells was also observed. Results from this pilot study suggest that using a combined bioanalytic and biological approach to analyze SCI CSF at different times after injury could be a useful approach for identifying reliable diagnostic and prognostic markers in SCI.

Elucidating the Inability of Functionalized Nanoparticles to Cross the Blood-Brain Barrier and Target Specific Cells in Vivo

The adsorption of serum proteins on the surface of nanoparticles (NPs) delivered into a biological environment has been known to alter NP surface properties and consequently their targeting efficiency. In this paper, we use random copolymer (p(HEMA- ran-GMA))-based NPs synthesized using 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA). We show that serum proteins bind to the NP and that functionalization with antibodies and peptides designed to facilitate NP passage across the blood-brain barrier (BBB) to bind specific cell types is ineffective. In particular, we use systematic in vitro and in vivo analyses to demonstrate that p(HEMA- ran-GMA) NPs functionalized with HIV-1 trans-activating transcriptor peptide (known to cross the BBB) and α neural/glial antigen 2 (NG2) (known for targeting oligodendrocyte precursor cells (OPCs)), individually and in combination, do not specifically target OPCs and are unable to cross the BBB, likely due to the serum protein binding to the NPs.

Regulation of Myelination by Exosome Associated Retinoic Acid Release from NG2-Positive Cells

In the CNS, oligodendrocytes are responsible for myelin formation and maintenance. Following spinal cord injury, oligodendrocyte loss and an inhibitory milieu compromise remyelination and recovery. Here, we explored the role of retinoic acid receptor-beta (RARβ) signaling in remyelination. Using a male Sprague Dawley rat model of PNS-CNS injury, we show that oral treatment with a novel drug like RARβ agonist, C286, induces neuronal expression of the proteoglycan decorin and promotes myelination and differentiation of oligodendrocyte precursor cells (NG2⁺ cells) in a decorin-mediated neuron–glia cross talk. Decorin promoted the activation of RARα in NG2⁺ cells by increasing the availability of the endogenous ligand RA. NG2⁺ cells synthesize RA, which is released in association with exosomes. We found that decorin prevents this secretion through regulation of the EGFR–calcium pathway. Using functional and pharmacological studies, we further show that RARα signaling is both required and sufficient for oligodendrocyte differentiation. These findings illustrate that RARβ and RARα are important regulators of oligodendrocyte differentiation, providing new targets for myelination.

SIGNIFICANCE STATEMENT This study identifies novel therapeutic targets for remyelination after PNS-CNS injury. Pharmacological and knock-down experiments show that the retinoic acid (RA) signaling promotes differentiation of oligodendrocyte precursor cells (OPCs) and remyelination in a cross talk between neuronal RA receptor-beta (RARβ) and RARα in NG2⁺ cells. We show that stimulation of RARα is required for the differentiation of OPCs and we describe for the first time how oral treatment with a RARβ agonist (C286, currently being tested in a Phase 1 trial, ISRCTN12424734) leads to the endogenous synthesis of RA through retinaldehyde dehydrogenase 2 (Raldh2) in NG2 cells and controls exosome-associated-RA intracellular levels through a decorin–Ca²⁺ pathway. Although RARβ has been implicated in distinct aspects of CNS regeneration, this study identifies a novel function for both RARβ and RARα in remyelination.

Axonal degeneration and demyelination following traumatic spinal cord injury: A systematic review and meta-analysis

The pathophysiology of spinal cord injury (SCI) related processes of axonal degeneration and demyelination are poorly understood. The present systematic review and meta-analysis were performed such to establish quantitative results of animal studies regarding the role of injury severity, SCI models and level of injury on the pathophysiology of axon and myelin sheath degeneration. 39 related articles were included in the analysis. The compiled data showed that the total number of axons, number of myelinated axons, myelin sheath thickness, axonal conduction velocity, and internode length steadily decreased as time elapsed from the injury (P_{for trend}<0.0001). The rate of axonal retrograde degeneration was affected by SCI model and severity of the injury. Axonal degeneration was higher in injuries of the thoracic region. The SCI model and the site of the injury also affected axonal retrograde degeneration. The number of myelinated axons in the caudal region of the injury was significantly higher than the lesion site and the rostral region. The findings of the present meta-analysis show that the pathophysiology of axons and myelin sheath differ in various phases of SCI and are affected by multiple factors related to the injury.

ErbB receptor signaling directly controls oligodendrocyte progenitor cell transformation and spontaneous remyelination after spinal cord injury

We recently discovered a novel role for neuregulin‐1 (Nrg1) signaling in mediating spontaneous regenerative processes and functional repair after spinal cord injury (SCI). We revealed that Nrg1 is the molecular signal responsible for spontaneous functional remyelination of dorsal column axons by peripheral nervous system (PNS)‐like Schwann cells after SCI. Here, we investigate whether Nrg1/ErbB signaling controls the unusual transformation of centrally derived progenitor cells into these functional myelinating Schwann cells after SCI using a fate‐mapping/lineage tracing approach. Specific ablation of Nrg1‐ErbB receptors in central platelet‐derived growth factor receptor alpha (PDGFRα)‐derived lineage cells (using PDGFRαCreERT2/Tomato‐red reporter mice crossed with ErbB3fl/fl/ErbB4fl/fl mice) led to a dramatic reduction in P0‐positive remyelination in the dorsal columns following spinal contusion injury. Central myelination, assessed by Olig2 and proteolipid protein expression, was unchanged. Loss of ErbB signaling in PDGFRα lineage cells also significantly impacted the degree of spontaneous locomotor recovery after SCI, particularly in tests dependent on proprioception. These data have important implications, namely (a) cells from the PDGFRα‐expressing progenitor lineage (which are presumably oligodendrocyte progenitor cells, OPCs) can differentiate into remyelinating PNS‐like Schwann cells after traumatic SCI, (b) this process is controlled by ErbB tyrosine kinase signaling, and (c) this endogenous repair mechanism has significant consequences for functional recovery after SCI. Thus, ErbB tyrosine kinase receptor signaling directly controls the transformation of OPCs from the PDGFRα‐expressing lineage into PNS‐like functional remyelinating Schwann cells after SCI.

Morphological characterization of NG2 glia and their association with neuroglial cells in the 3-nitropropionic acid-lesioned striatum of rat

Our aim was to examine the spatiotemporal profiles and phenotypic characteristics of neuron-glia antigen 2 (NG2) glia and their associations with neuroglial cells in striatal lesions due to the mitochondrial toxin 3-nitropropionic acid (3-NP). In control striatum, weak NG2 immunoreactivity was restricted to resting NG2 glia with thin processes, but prominent NG2 expression was noted on activated microglia/macrophages, and reactive NG2 glia in the lesion core after 3-NP injection. Activation of NG2 glia, including enhanced proliferation and morphological changes, had a close spatiotemporal relationship with infiltration of activated microglia into the lesion core. Thick and highly branched processes of reactive NG2 glia formed a cellular network in the astrocyte-free lesion core and primarily surrounded developing cavities 2–4 weeks post-lesion. NG2 glia became associated with astrocytes in the lesion core and the border of cavities over the chronic interval of 4–8 weeks. Immunoelectron microscopy indicated that reactive NG2 glia had large euchromatic nuclei with prominent nucleoli and thick and branched processes that ramified distally. Thus, our data provide detailed information regarding the morphologies of NG2 glia in the lesion core, and support the link between transformation of NG2 glia to the reactive form and microglial activation/recruitment in response to brain insults.

Parallel Evaluation of Two Potassium Channel Blockers in Restoring Conduction in Mechanical Spinal Cord Injury in Rat

Myelin damage is a hallmark of spinal cord injury (SCI), and potassium channel blocker (PCB) is proven effective to restore axonal conduction and regain neurological function. Aiming to improve this therapy beyond the U.S. Food and Drug Administration-approved 4-aminopyridine (4-AP), we have developed multiple new PCBs, with 4-aminopyridine-3-methanol (4-AP-3-MeOH) being the most potent and effective. The current study evaluated two PCBs, 4-AP-3-MeOH and 4-AP, in parallel in both ex vivo and in vivo rat mechanical SCI models. Specifically, 4-AP-3-MeOH induced significantly greater augmentation of axonal conduction than 4-AP in both acute and chronic injury. 4-AP-3-MeOH had no negative influence on the electrical responsiveness of rescued axons whereas 4-AP-recruited axons displayed a reduced ability to follow multiple stimuli. In addition, 4-AP-3-MeOH can be applied intraperitoneally at a dose that is at least 5 times higher (5 mg/kg) than that of 4-AP (1 mg/kg) in vivo. Further, 5 mg/kg of 4-AP-3-MeOH significantly improved motor function whereas both 4-AP-3-MeOH (1 and 5 mg/kg) and, to a lesser degree, 4-AP (1 mg/kg) alleviated neuropathic pain-like behavior when applied in rats 2 weeks post-SCI. Based on these and other findings, we conclude that 4-AP-3-MeOH appears to be more advantageous over 4-AP in restoring axonal conduction because of the combination of its higher efficacy in enhancing the amplitude of compound action potential, lesser negative effect on axonal responsiveness to multiple stimuli, and wider therapeutic range in both ex vivo and in vivo application. As a result, 4-AP-3-MeOH has emerged as a strong alternative to 4-AP that can complement the effectiveness, and even partially overcome the shortcomings, of 4-AP in the treatment of neurotrauma and degenerative diseases where myelin damage is implicated.

Stem Cell-Based Cell Therapy for Spinal Cord Injury

Traumatic injuries to the spinal cord lead to severe and permanent neurological deficits. Although no effective therapeutic option is currently available, recent animal studies have shown that cellular transplantation strategies hold promise to enhance functional recovery after spinal cord injury (SCI). This review is to analyze the experiments where transplantation of stem/progenitor cells produced successful functional outcome in animal models of SCI. There is no consensus yet on what kind of stem/progenitor cells is an ideal source for cellular grafts. Three kinds of stem/progenitor cells have been utilized in cell therapy in animal models of SCI: embryonic stem cells, bone marrow mesenchymal stem cells, and neural stem cells. Neural stem cells or fate-restricted neuronal or glial progenitor cells were preferably used because they have clear capacity to become neurons or glial cells after transplantation into the injured spinal cord. At least a part of functional deficits after SCI is attributable to chronic progressive demyelination. Therefore, several studies transplanted glial-restricted progenitors or oligodendrocyte precursors to target the demyelination process. Directed differentiation of stem/progenitor cells to oligodendrocyte lineage prior to transplantation or modulation of microenvironment in the injured spinal cord to promote oligodendroglial differentiation seems to be an effective strategy to increase the extent of remyelination. Transplanted stem/progenitor cells can also contribute to promoting axonal regeneration by functioning as cellular scaffolds for growing axons. Combinatorial approaches using polymer scaffolds to fill the lesion cavity or introducing regeneration-promoting genes will greatly increase the efficacy of cellular transplantation strategies for SCI.

Local injection of Lenti-Olig2 at lesion site promotes functional recovery of spinal cord injury in rats

AIMS

Olig2 is one of the most critical factors during CNS development, which belongs to b-HLH transcription factor family. Previous reports have shown that Olig2 regulates the remyelination processes in CNS demyelination diseases models. However, the role of Olig2 in contusion spinal cord injury (SCI) and the possible therapeutic effects remain obscure. This study aims to investigate the effects of overexpression Olig2 by lentivirus on adult spinal cord injury rats.

METHODS

Lenti-Olig2 expression and control Lenti-eGFP vectors were prepared, and virus in a total of 5 μL (10⁸ TU/mL) was locally injected into the injured spinal cord 1.5 mm rostral and caudal near the epicenter. Immunostaining, Western blot, electron microscopy, and CatWalk analyzes were employed to investigate the effects of Olig2 on spinal cord tissue repair and functional recovery.

RESULTS

Injection of Lenti-Olig2 significantly increased the number of oligodendrocytes lineage cells and enhanced myelination after SCI. More importantly, the introduction of Olig2 greatly improved hindlimb locomotor performances. Other oligodendrocyte-related transcription factors, which were downregulated or upregulated after injury, were reversed by Olig2 induction.

CONCLUSIONS

Our findings provided the evidence that overexpression Olig2 promotes myelination and locomotor recovery of contusion SCI, which gives us more understanding of Olig2 on spinal cord injury treatment.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Aescin reduces oxidative stress and provides neuroprotection in experimental traumatic spinal cord injury

Aescin has many physiological functions that are highly relevant to spinal cord injury (SCI), including anti-inflammation, anti-oxidation, anti-oedema, and enhancing vascular tone. The present study investigated the putative therapeutic value of aescin in SCI, with a focus on its neuroprotective, anti-inflammatory, and anti-oxidative properties. Sodium aescinate (1.0mg/kg body weight) or equivalent volume of saline was administered 30min after injury by intravenous injection, with an additional dose daily for seven consecutive days after moderate SCI in rats. After contusion injury of the 8th thoracic (T8) spinal cord, aescin-treated rats developed less severe hind limb weakness than saline controls, as assayed by the Basso-Beattie-Bresnahan scale, the beam walking test, and a footprint analysis. The improved locomotor outcomes in aescin-treated rats corresponded to markedly decreased immune response, oxidative stress, neuronal loss, axon demyelination, spinal cord swelling, and cell apoptosis, measured around T8 after impact. Our data suggest aescin treatment as a novel, early, neuroprotective approach in SCI. Given the known safety of aescin in clinical applications, the results of this study suggest that it is a good candidate for SCI treatment in humans.

Inhibition of Epidermal Growth Factor Receptor Improves Myelination and Attenuates Tissue Damage of Spinal Cord Injury

Preventing demyelination and promoting remyelination of denuded axons are promising therapeutic strategies for spinal cord injury (SCI). Epidermal growth factor receptor (EGFR) inhibition was reported to benefit the neural functional recovery and the axon regeneration after SCI. However, its role in de- and remyelination of axons in injured spinal cord is unclear. In the present study, we evaluated the effects of EGFR inhibitor, PD168393 (PD), on the myelination in mouse contusive SCI model. We found that expression of myelin basic protein (MBP) in the injured spinal cords of PD treated mice was remarkably elevated. The density of glial precursor cells and oligodendrocytes (OLs) was increased and the cell apoptosis in lesions was attenuated after PD168393 treatment. Moreover, PD168393 treatment reduced both the numbers of OX42 + microglial cells and glial fibrillary acidic protein + astrocytes in damaged area of spinal cords. We thus conclude that the therapeutic effects of EGFR inhibition after SCI involves facilitating remyelination of the injured spinal cord, increasing of oligodendrocyte precursor cells and OLs, as well as suppressing the activation of astrocytes and microglia/macrophages.

Transplantation of Neural Stem Cells Cultured in Alginate Scaffold for Spinal Cord Injury in Rats

Study Design

This study investigated the effects of transplantation of alginate encapsulated neural stem cells (NSCs) on spinal cord injury in Sprague-Dawley male rats. The neurological functions were assessed for 6 weeks after transplantation along with a histological study and measurement of caspase-3 levels.

Purpose

The aim of this study was to discover whether NSCs cultured in alginate transplantation improve recovery from spinal cord injury.

Overview of Literature

Spinal cord injury is one of the leading causes of disability and it has no effective treatment. Spinal cord injury can also cause sensory impairment. With an impetus on using stem cells therapy in various central nervous system settings, there is an interest in using stem cells for addressing spinal cord injury. Neural stem cell is one type of stem cells that is able to differentiate to all three neural lineages and it shows promise in spinal injury treatment. Furthermore, a number of studies have shown that culturing NSCs in three-dimensional (3D) scaffolds like alginate could enhance neural differentiation.

Methods

The NSCs were isolated from 14-day-old rat embryos. The isolated NSCs were cultured in growth media containing basic fibroblast growth factor and endothelial growth factor. The cells were characterized by differentiating to three neural lineages and they were cultured in an alginate scaffold. After 7 days the cells were encapsulated and transplanted in a rat model of spinal cord injury.

Results

Our data showed that culturing in an alginate 3D scaffold and transplantation of the NSCs could improve neurological outcome in a rat model of spinal cord injury. The inflammation scores and lesion sizes and also the activity of caspase-3 (for apoptosis evaluation) were less in encapsulated neural stem cell transplantation cases.

Conclusions

Transplantation of NSCs that were cultured in an alginate scaffold led to a better clinical and histological outcome for recovery from spinal cord injury in a rat model.

Cell Transplantation and Neuroengineering Approach for Spinal Cord Injury Treatment: A Summary of Current Laboratory Findings and Review of Literature

Spinal cord injury (SCI) can cause severe traumatic injury to the central nervous system (CNS). Current therapeutic effects achieved for SCI in clinical medicine show that there is still a long way to go to reach the desired goal of full or significant functional recovery. In basic medical research, however, cell transplantation, gene therapy, application of cytokines, and biomaterial scaffolds have been widely used and investigated as treatments for SCI. All of these strategies when used separately would help rebuild, to some extent, the neural circuits in the lesion area of the spinal cord. In light of this, it is generally accepted that a combined treatment may be a more effective strategy. This review focuses primarily on our recent series of work on transplantation of Schwann cells and adult stem cells, and transplantation of stem cell-derived neural network scaffolds with functional synapses. Arising from this, an artificial neural network (an exogenous neuronal relay) has been designed and fabricated by us—a biomaterial scaffold implanted with Schwann cells modified by the neurotrophin-3 (NT-3) gene and adult stem cells modified with the TrkC (receptor of NT-3) gene. More importantly, experimental evidence suggests that the novel artificial network can integrate with the host tissue and serve as an exogenous neuronal relay for signal transfer and functional improvement of SCI.

Neural Placode Tissue Derived From Myelomeningocele Repair Serves as a Viable Source of Oligodendrocyte Progenitor Cells

BACKGROUND

The presence, characteristics, and potential clinical relevance of neural progenitor populations within the neural placodes of myelomeningocele patients remain to be studied. Neural stem cells are known to reside adjacent to ependyma-lined surfaces along the central nervous system axis.

OBJECTIVE

Given such neuroanatomic correlation and regenerative capacity in fetal development, we assessed myelomeningocele-derived neural placode tissue as a potentially novel source of neural stem and progenitor cells.

METHODS

Nonfunctional neural placode tissue was harvested from infants during the surgical repair of myelomeningocele and subsequently further analyzed by in vitro studies, flow cytometry, and immunofluorescence. To assess lineage potential, neural placode-derived neurospheres were subjected to differential media conditions. Through assessment of platelet-derived growth factor receptor α (PDGFRα) and CD15 cell marker expression, Sox2+Olig2+ putative oligodendrocyte progenitor cells were successfully isolated.

RESULTS

PDGFRαCD15 cell populations demonstrated the highest rate of self-renewal capacity and multipotency of cell progeny. Immunofluorescence of neural placode-derived neurospheres demonstrated preferential expression of the oligodendrocyte progenitor marker, CNPase, whereas differentiation to neurons and astrocytes was also noted, albeit to a limited degree.

CONCLUSION

Neural placode tissue contains multipotent progenitors that are preferentially biased toward oligodendrocyte progenitor cell differentiation and presents a novel source of such cells for use in the treatment of a variety of pediatric and adult neurological disease, including spinal cord injury, multiple sclerosis, and metabolic leukoencephalopathies.

EXPRESS: Oligodendrocytes in HIV-associated pain pathogenesis

Background

Although the contributions of microglia and astrocytes to chronic pain pathogenesis have been a focal point of investigation in recent years, the potential role of oligodendrocytes, another major type of glial cells in the CNS that generates myelin, remains largely unknown.

Results

We report here that cell markers of the oligodendrocyte lineage, including NG2, PDGFRα, and Olig2, are significantly increased in the spinal dorsal horn of HIV patients who developed chronic pain. The levels of myelin proteins myelin basic protein and proteolipid protein are also aberrant in the spinal dorsal horn of “pain-positive” HIV patients. Similarly, the oligodendrocyte and myelin markers are up-regulated in the spinal dorsal horn of a mouse model of HIV-1 gp120-induced pain. Surprisingly, the expression of gp120-induced mechanical allodynia appears intact up to 4 h after myelin basic protein is knocked down or knocked out.

Conclusion

These findings suggest that oligodendrocytes are reactive during the pathogenesis of HIV-associated pain. However, interfering with myelination does not alter the induction of gp120-induced pain.

Neuregulin-1 controls an endogenous repair mechanism after spinal cord injury

Spontaneous remyelination after spinal cord injury is mediated largely by Schwann cells of unknown origin. Bartus et al. show that neuregulin-1 promotes differentiation of spinal cord-resident precursor cells into PNS-like Schwann cells, which remyelinate central axons and promote functional recovery. Targeting the neuregulin-1 system could enhance endogenous regenerative processes.

Following traumatic spinal cord injury, acute demyelination of spinal axons is followed by a period of spontaneous remyelination. However, this endogenous repair response is suboptimal and may account for the persistently compromised function of surviving axons. Spontaneous remyelination is largely mediated by Schwann cells, where demyelinated central axons, particularly in the dorsal columns, become associated with peripheral myelin. The molecular control, functional role and origin of these central remyelinating Schwann cells is currently unknown. The growth factor neuregulin-1 (Nrg1, encoded by NRG1) is a key signalling factor controlling myelination in the peripheral nervous system, via signalling through ErbB tyrosine kinase receptors. Here we examined whether Nrg1 is required for Schwann cell-mediated remyelination of central dorsal column axons and whether Nrg1 ablation influences the degree of spontaneous remyelination and functional recovery following spinal cord injury. In contused adult mice with conditional ablation of Nrg1, we found an absence of Schwann cells within the spinal cord and profound demyelination of dorsal column axons. There was no compensatory increase in oligodendrocyte remyelination. Removal of peripheral input to the spinal cord and proliferation studies demonstrated that the majority of remyelinating Schwann cells originated within the injured spinal cord. We also examined the role of specific Nrg1 isoforms, using mutant mice in which only the immunoglobulin-containing isoforms of Nrg1 (types I and II) were conditionally ablated, leaving the type III Nrg1 intact. We found that the immunoglobulin Nrg1 isoforms were dispensable for Schwann cell-mediated remyelination of central axons after spinal cord injury. When functional effects were examined, both global Nrg1 and immunoglobulin-specific Nrg1 mutants demonstrated reduced spontaneous locomotor recovery compared to injured controls, although global Nrg1 mutants were more impaired in tests requiring co-ordination, balance and proprioception. Furthermore, electrophysiological assessments revealed severely impaired axonal conduction in the dorsal columns of global Nrg1 mutants (where Schwann cell-mediated remyelination is prevented), but not immunoglobulin-specific mutants (where Schwann cell-mediated remyelination remains intact), providing robust evidence that the profound demyelinating phenotype observed in the dorsal columns of Nrg1 mutant mice is related to conduction failure. Our data provide novel mechanistic insight into endogenous regenerative processes after spinal cord injury, demonstrating that Nrg1 signalling regulates central axon remyelination and functional repair and drives the trans-differentiation of central precursor cells into peripheral nervous system-like Schwann cells that remyelinate spinal axons after injury. Manipulation of the Nrg1 system could therefore be exploited to enhance spontaneous repair after spinal cord injury and other central nervous system disorders with a demyelinating pathology.

Longitudinal study on diffusion tensor imaging and diffusion tensor tractography following spinal cord contusion injury in rats

INTRODUCTION

Diffusion tensor imaging (DTI) as a potential technology has been used in spinal cord injury (SCI) studies, but the longitudinal evaluation of DTI parameters after SCI, and the correlation between DTI parameters and locomotor outcomes need to be defined.

METHODS

Adult Wistar rats (n = 6) underwent traumatic thoracic cord contusion by an NYU impactor. DTI and Basso-Beattie-Bresnahan datasets were collected pre-SCI and 1, 3, 7, 14, and 84 days post-SCI. Diffusion tensor tractography (DTT) of the spinal cord was also generated. Fractional anisotropy (FA) and connection rate of fibers at the injury epicenter and at 5 mm rostral/caudal to the epicenter were calculated. The variations of these parameters after SCI were observed by one-way analysis of variance and the correlations between these parameters and motor function were explored by Pearson's correlation.

RESULTS

FA at the epicenter decreased most remarkably on day 1 post-SCI (from 0.780 ± 0.012 to 0.330 ± 0.015), and continued to decrease slightly by day 3 post-SCI (0.313 ± 0.015), while other parameters decreased significantly over the first 3 days after SCI. DTT showed residual fibers concentrated on ventral and ventrolateral sides of the cord. Moreover, FA at the epicenter exhibited the strongest correlation (r = 0.887, p = 0.000) with the locomotion performance.

CONCLUSION

FA was sensitive to degeneration in white matter and DTT could directly reflect the distribution of the residual white matter. Moreover, days 1 to 3 post-SCI may be the optimal time window for SCI examination and therapy.

Topographical effects on fiber-mediated microRNA delivery to control oligodendroglial precursor cells development

Effective remyelination in the central nervous system (CNS) facilitates the reversal of disability in patients with demyelinating diseases such as multiple sclerosis. Unfortunately until now, effective strategies of controlling oligodendrocyte (OL) differentiation and maturation remain limited. It is well known that topographical and biochemical signals play crucial roles in modulating cell fate commitment. Therefore, in this study, we explored the combined effects of scaffold topography and sustained gene silencing on oligodendroglial precursor cell (OPC) development. Specifically, microRNAs (miRs) were incorporated onto electrospun polycaprolactone (PCL) fiber scaffolds with different fiber diameters and orientations. Regardless of fiber diameter and orientation, efficient knockdown of differentiation inhibitory factors were achieved by either topography alone (up to 70%) or fibers integrated with miR-219 and miR-338 (up to 80%, p < 0.05). Small fiber promoted OPC differentiation by inducing more RIP(+) cells (p < 0.05) while large fiber promoted OL maturation by inducing more MBP(+) cells (p < 0.05). Random fiber enhanced more RIP(+) cells than aligned fibers (p < 0.05), regardless of fiber diameter. Upon miR-219/miR-338 incorporation, 2 μm aligned fibers supported the most MBP(+) cells (∼17%). These findings indicated that the coupling of substrate topographic cues with efficient gene silencing by sustained microRNA delivery is a promising way for directing OPC maturation in neural tissue engineering and controlling remyelination in the CNS.

NG2-glia and their functions in the central nervous system

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

Molecular mechanisms of acrolein-mediated myelin destruction in CNS trauma and disease

Myelin is a critical component of the nervous system facilitating efficient propagation of electrical signals and thus communication between the central and peripheral nervous systems and the organ systems that they innervate throughout the body. In instances of neurotrauma and neurodegenerative disease, injury to myelin is a prominent pathological feature responsible for conduction deficits, and leaves axons vulnerable to damage from noxious compounds. Although the pathological mechanisms underlying myelin loss have yet to be fully characterized, oxidative stress (OS) appears to play a prominent role. Specifically, acrolein, a neurotoxic aldehyde that is both a product and an instigator of OS, has been observed in studies to elicit demyelination through calcium-independent and -dependent mechanisms and also by affecting glutamate uptake and promoting excitotoxicity. Furthermore, pharmacological scavenging of acrolein has demonstrated a neuroprotective effect in animal disease models, by conserving myelin's structural integrity and alleviating functional deficits. This evidence indicates that acrolein may be a key culprit of myelin damage while acrolein scavenging could potentially be a promising therapeutic approach for patients suffering from nervous system trauma and disease.

Translating mechanisms of neuroprotection, regeneration, and repair to treatment of spinal cord injury

One of the big challenges in neuroscience that remains to be understood is why the central nervous system is not able to regenerate to the extent that the peripheral nervous system does. This is especially problematic after traumatic injuries, like spinal cord injury (SCI), since the lack of regeneration leads to lifelong deficits and paralysis. Treatment of SCI has improved during the last several decades due to standardized protocols for emergency medical response teams and improved medical, surgical, and rehabilitative treatments. However, SCI continues to result in profound impairments for the individual. There are many processes that lead to the pathophysiology of SCI, such as ischemia, vascular disruption, neuroinflammation, oxidative stress, excitotoxicity, demyelination, and cell death. Current treatments include surgical decompression, hemodynamic control, and methylprednisolone. However, these early treatments are associated with modest functional recovery. Some treatments currently being investigated for use in SCI target neuroprotective (riluzole, minocycline, G-CSF, FGF-2, and polyethylene glycol) or neuroregenerative (chondroitinase ABC, self-assembling peptides, and rho inhibition) strategies, while many cell therapies (embryonic stem cells, neural stem cells, induced pluripotent stem cells, mesenchymal stromal cells, Schwann cells, olfactory ensheathing cells, and macrophages) have also shown promise. However, since SCI has multiple factors that determine the progress of the injury, a combinatorial therapeutic approach will most likely be required for the most effective treatment of SCI.

Nanofiber-mediated microRNA delivery to enhance differentiation and maturation of oligodendroglial precursor cells

Remyelination in the central nervous system (CNS) is critical in the treatment of many neural pathological conditions. Unfortunately, the ability to direct and enhance oligodendrocyte (OL) differentiation and maturation remains limited. It is known that microenvironmental signals, such as substrate topography and biochemical signaling, regulate cell fate commitment. Therefore, in this study, we developed a nanofiber-mediated microRNA (miR) delivery method to control oligodendroglial precursor cell (OPC) differentiation through a combination of fiber topography and gene silencing. Using poly(ε-caprolactone) nanofibers, efficient knockdown of OL differentiation inhibitory regulators were achieved by either nanofiber alone (20-40%, p<0.05) or the synergistic integration with miR-219 and miR-338 (up to 60%, p<0.05). As compared to two-dimensional culture, nanofiber topography enhanced OPC differentiation by inducing 2-fold increase in RIP(+) cells (p<0.01) while the presence of miRs further enhanced the result to 3-fold (p<0.001). In addition, nanofiber-mediated delivery of miR-219 and miR-338 promoted OL maturation by increasing the number of MBP(+) cells significantly (p<0.01). Taken together, the results demonstrate the efficacy of nanofibers in providing topographical cues and microRNA reverse transfection to direct OPC differentiation. Such scaffolds may find useful applications in directing oligodendrocyte differentiation and myelination for treatment of CNS pathological conditions that require remyelination.

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.