Neuroprotection and secondary damage following spinal cord injury: concepts and methods

SNHG3 deficiency restrains spinal cord injury-induced inflammation through sponging miR-139-5p and provides a novel biomarker for disease severity

BACKGROUND

MicroRNAs and long non-coding RNAs play pivotal roles in the progression and recovery of spinal cord injury (SCI), which is a serious traumatic disease in central nervous system. The purpose of this study was to investigate the expression and clinical value of SNHG3 in SCI patients and explore the regulatory effects of SNHG3 on SCI-induced inflammatory responses in vitro.

METHODS

The relationship between SNHG3 and miR-139-5p was confirmed using a dual-luciferase reporter assay. A SCI cell model was constructed in SH-SY5Y cells using hypoxia treatment. SNHG3 and miR-139-5p expression was analyzed using qRT-PCR. Effects of SNHG3 and miR-139-5p on cell model viability and inflammatory cytokines were evaluated by CCK-8 assay and ELISA kits, respectively. ROC curves based on serum SNHG3 and miR-139-5p were constructed to evaluate their diagnostic performance.

RESULTS

In SCI patients, serum SNHG3 was upregulated, but miR-139-5p was downregulated (P<0.05), and a negative correlation between the two ncRNAs was found. Both SNHG3 and miR-139-5p showed relatively high discrimination abilities for the screening of SCI and complete SCI (CSCI) patients. SNHG3 was positively correlated with inflammatory cytokines, and miR-139-5p showed opposite results in SCI patients. By in-vitro analysis, SNHG3 knockdown enhanced cell viability but inhibited inflammation by increasing miR-139-5p.

CONCLUSIONS

All the data found that serum upregulated SNHG3 and downregulated miR-139-5p served as biomarkers to diagnose SCI and indicate injury severity. The deficiency of SNHG3 alleviated neuronal injury by restraining inflammatory responses through targeting miR-139-5p. Thus, the SNHG3/miR-139-5p axis may provide novel biomarkers and therapeutic targets for SCI.

Oligodendrocyte-selective deletion of the eIF2α kinase Perk/Eif2ak3 limits functional recovery after spinal cord injury

After spinal cord injury (SCI), re-establishing cellular homeostasis is critical to optimize functional recovery. Central to that response is PERK signaling, which ultimately initiates a pro-apoptotic response if cellular homeostasis cannot be restored. Oligodendrocyte (OL) loss and white matter damage drive functional consequences and determine recovery potential after thoracic contusive SCI. We examined acute (<48 h post-SCI) and chronic (6 weeks post-SCI) effects of conditionally deleting Perk from OLs prior to SCI. While Perk transcript is expressed in many types of cells in the adult spinal cord, its levels are disproportionately high in OL lineage cells. Deletion of OL-Perk prior to SCI resulted in: (1) enhanced acute phosphorylation of eIF2α, a major PERK substrate and the critical mediator of the integrated stress response (ISR), (2) enhanced acute expression of the downstream ISR genes Atf4, Ddit3/Chop, and Tnfrsf10b/Dr5, (3) reduced acute OL lineage-specific Olig2 mRNA, but not neuronal or astrocytic mRNAs, (4) chronically decreased OL content in the spared white matter at the injury epicenter, (5) impaired hindlimb locomotor recovery, and (6) reduced chronic epicenter white matter sparing. Cultured primary OL precursor cells with reduced PERK expression and activated ER stress response showed: (1) unaffected phosphorylation of eIF2α, (2) enhanced ISR gene induction, and (3) increased cytotoxicity. Therefore, OL-Perk deficiency exacerbates ISR signaling and potentiates white matter damage after SCI. The latter effect is likely mediated by increased loss of Perk-/- OLs.

Sexual Dimorphism of Spinal Neural Circuits Controlling the Mouse External Urethral Sphincter With and Without Spinal Cord Injury

Spinal cord injury (SCI) disrupts coordination between the bladder and the external urinary sphincter (EUS), leading to transient or permanent voiding impairment, which is more severe in males. Male versus female differences in spinal circuits related to the EUS as well as post-SCI rewiring are essential for understanding of sex-/gender-specific impairments and possible recovery mechanisms. To quantitatively assess differences between EUS circuits in males versus females and in spinal intact (SI) versus SCI animals, we retrogradely traced and counted EUS-related neurons. In transgenic ChAT-GFP mice, motoneurons (MNs), interneurons (INs), and propriospinal neurons (PPNs) were retrogradely trans-synaptically traced with PRV614-red fluorescent protein (RFP) injected into EUS. EUS-MNs in dorsolateral nucleus (DLN) were separated from other GFP+ MNs by tracing them with FluoroGold (FG). We found two morphologically distinct cell types in DLN: FG+ spindle-shaped bipolar (SB-MNs) and FG- rounded multipolar (RM-MNs) cholinergic cells. Number of MNs of both types in males was twice as large as in females. SCI caused a partial loss of MNs in all spinal nuclei. After SCI, males showed a fourfold rise in the number of RFP-labeled cells in retro-DLN (RDLN) innervating hind limbs. This suggests (a) an existence of direct synaptic interactions between spinal nuclei and (b) a post-SCI increase of non-specific inputs to EUS-MNs from other motor nuclei. Number of INs and PPNs deferred between males and females: In SI males, the numbers of INs and PPNs were ∼10 times larger than in SI females. SCI caused a twofold decrease of INs and PPNs in males but not in females.

Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging

Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo.

Lesion-remote astrocytes govern microglia-mediated white matter repair

Spared regions of the damaged central nervous system undergo dynamic remodeling and exhibit a remarkable potential for therapeutic exploitation. Here, lesion-remote astrocytes (LRAs), which interact with viable neurons, glia and neural circuitry, undergo reactive transformations whose molecular and functional properties are poorly understood. Using multiple transcriptional profiling methods, we interrogated LRAs from spared regions of mouse spinal cord following traumatic spinal cord injury (SCI). We show that LRAs acquire a spectrum of molecularly distinct, neuroanatomically restricted reactivity states that evolve after SCI. We identify transcriptionally unique reactive LRAs in degenerating white matter that direct the specification and function of local microglia that clear lipid-rich myelin debris to promote tissue repair. Fueling this LRA functional adaptation is Ccn1 , which encodes for a secreted matricellular protein. Loss of astrocyte CCN1 leads to excessive, aberrant activation of local microglia with (i) abnormal molecular specification, (ii) dysfunctional myelin debris processing, and (iii) impaired lipid metabolism, culminating in blunted debris clearance and attenuated neurological recovery from SCI. Ccn1 -expressing white matter astrocytes are specifically induced by local myelin damage and generated in diverse demyelinating disorders in mouse and human, pointing to their fundamental, evolutionarily conserved role in white matter repair. Our findings show that LRAs assume regionally divergent reactivity states with functional adaptations that are induced by local context-specific triggers and influence disorder outcome. Astrocytes tile the central nervous system (CNS) where they serve vital roles that uphold healthy nervous system function, including regulation of synapse development, buffering of neurotransmitters and ions, and provision of metabolic substrates 1 . In response to diverse CNS insults, astrocytes exhibit disorder-context specific transformations that are collectively referred to as reactivity 2-5 . The characteristics of regionally and molecularly distinct reactivity states are incompletely understood. The mechanisms through which distinct reactivity states arise, how they evolve or resolve over time, and their consequences for local cell function and CNS disorder progression remain enigmatic. Immediately adjacent to CNS lesions, border-forming astrocytes (BFAs) undergo transcriptional reprogramming and proliferation to form a neuroprotective barrier that restricts inflammation and supports axon regeneration 6-9 . Beyond the lesion, spared but dynamic regions of the injured CNS exhibit varying degrees of synaptic circuit remodeling and progressive cellular responses to secondary damage that have profound consequences for neural repair and recovery 10,11 . Throughout these cytoarchitecturally intact, but injury-reactive regions, lesion-remote astrocytes (LRAs) intermingle with neurons and glia, undergo little to no proliferation, and exhibit varying degrees of cellular hypertrophy 7,12,13 . The molecular and functional properties of LRAs remain grossly undefined. Therapeutically harnessing spared regions of the injured CNS will require a clearer understanding of the accompanying cellular and molecular landscape. Here, we leveraged integrative transcriptional profiling methodologies to identify multiple spatiotemporally resolved, molecularly distinct states of LRA reactivity within the injured spinal cord. Computational modeling of LRA-mediated heterotypic cell interactions, astrocyte-specific conditional gene deletion, and multiple mouse models of acute and chronic CNS white matter degeneration were used to interrogate a newly identified white matter degeneration-reactive astrocyte subtype. We define how this reactivity state is induced and its role in governing the molecular and functional specification of local microglia that clear myelin debris from the degenerating white matter to promote repair.

Htr2b Promotes M1 Microglia Polarization and Neuroinflammation after Spinal Cord Injury via Inhibition of Neuregulin-1/ErbB Signaling

The secondary injury of spinal cord injury (SCI) is dominated by neuroinflammation, which was caused by microglia M1 polarization. This study aimed to investigate the role and mechanism of Htr2b on neuroinflammation of SCI. The BV2 and HMC3 microglia were treated with lipopolysaccharide (LPS) or interferon (IFN)-γ to simulate in vitro models of SCI. Sprague-Dawley rats were subjected to the T10 laminectomy to induce animal model of SCI. Htr2b mRNA expression was measured by qRT-PCR. The expression of Htr2b and Iba-1 was detected by western blot and immunofluorescence. The expression of inflammatory cytokines in vitro and in vivo was also measured. Kyoto Encyclopedia of Genes and Genomes (KEGG) was employed to analyze Htr2b-regulated signaling pathways. Rat behavior was analyzed by the Basso, Beattie, and Bresnahan (BBB) and inclined plane test. Rat dorsal horn tissues were stained by hematoxylin-eosin (H&E) and Nissl to measure neuron loss. Htr2b was highly expressed in LPS- and IFN-γ-treated microglia and SCI rats. SCI modeling promoted M1 microglia polarization and increased levels of inflammatory cytokines. Inhibition of Htr2b by Htr2b shRNA or RS-127445 reduced the expression of Htr2b, Iba-1, and iNOS and suppressed cytokine levels. KEGG showed that Htr2b inhibited ErbB signaling pathway. Inhibition of Htr2b increased protein expression of neuregulin-1 (Nrg-1) and p-ErbB4. Inhibition of the ErbB signaling pathway markedly reversed the effect of Htr2b shRNA on M1 microglia polarization and inflammatory cytokines. Htr2b promotes M1 microglia polarization and neuroinflammation after SCI by inhibiting Nrg-1/ErbB signaling pathway.

CCL2 Knockdown Attenuates Inflammatory Response After Spinal Cord Injury Through the PI3K/Akt Signaling Pathway: Bioinformatics Analysis and Experimental Validation

Spinal cord injury (SCI) is a common clinical problem in orthopedics with a lack of effective treatments and drug targets. In the present study, we performed bioinformatic analysis of SCI datasets GSE464 and GSE45006 in the Gene Expression Omnibus (GEO) public database and experimentally validated CCL2 expression in an animal model of SCI. This was followed by stimulation of PC-12 cells using hydrogen peroxide to construct a cellular model of SCI. CCL2 expression was knocked down using small interfering RNA (si-CCL2), and PI3K signaling pathway inhibitors and activators were used to validate and observe the changes in downstream inflammation. Through data mining, we found that the inflammatory chemokine CCL2 and PI3K/Akt signaling pathways after SCI expression were significantly increased, and after peroxide stimulation of PC-12 cells with CCL2 knockdown, their downstream cellular inflammatory factor levels were decreased. The PI3K/Akt signaling pathway was blocked by PI3K inhibitors, and the downstream inflammatory response was suppressed. In contrast, when PI3K activators were used, the inflammatory response was enhanced, indicating that the CCL2-PI3K/Akt signaling pathway plays a key role in the regulation of the inflammatory response. This study revealed that the inflammatory chemokine CCL2 can regulate the inflammatory response of PC-12 cells through the PI3K/Akt signaling pathway, and blocking the expression of the inflammatory chemokine CCL2 may be a promising strategy for the treatment of secondary injury after SCI.

The Role of Interleukin-10 in the Pathogenesis and Treatment of a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that often leads to severe and permanent neurological deficits. The complex pathophysiology of an SCI involves a cascade of events, including inflammation, oxidative stress, and secondary injury processes. Among the myriad of molecular players involved, interleukin-10 (IL-10) emerges as a key regulator with the potential to modulate both the inflammatory response and promote neuroprotection. This comprehensive review delves into the intricate interplay of IL-10 in the pathogenesis of an SCI and explores its therapeutic implications in the quest for effective treatments. IL-10 has been found to regulate inflammation, oxidative stress, neuronal apoptosis, and glial scars after an SCI. Its neuroprotective properties have been evaluated in a plethora of animal studies. IL-10 administration, either isolated or in combination with other molecules or biomaterials, has shown neuroprotective effects through a reduction in inflammation, the promotion of tissue repair and regeneration, the modulation of glial scar formation, and improved functional outcomes. In conclusion, IL-10 emerges as a pivotal player in the pathogenesis and treatment of SCIs. Its multifaceted role in modulating inflammation, oxidative stress, neuronal apoptosis, glial scars, and neuroprotection positions IL-10 as a promising therapeutic target. The ongoing research exploring various strategies for harnessing the potential of IL-10 offers hope for the development of effective treatments that could significantly improve outcomes for individuals suffering from spinal cord injuries. As our understanding of IL-10's intricacies deepens, it opens new avenues for innovative and targeted therapeutic interventions, bringing us closer to the goal of alleviating the profound impact of SCIs on patients' lives.

Pharmacological interventions targeting the microcirculation following traumatic spinal cord injury

Traumatic spinal cord injury is a devastating disorder characterized by sensory, motor, and autonomic dysfunction that severely compromises an individual's ability to perform activities of daily living. These adverse outcomes are closely related to the complex mechanism of spinal cord injury, the limited regenerative capacity of central neurons, and the inhibitory environment formed by traumatic injury. Disruption to the microcirculation is an important pathophysiological mechanism of spinal cord injury. A number of therapeutic agents have been shown to improve the injury environment, mitigate secondary damage, and/or promote regeneration and repair. Among them, the spinal cord microcirculation has become an important target for the treatment of spinal cord injury. Drug interventions targeting the microcirculation can improve the microenvironment and promote recovery following spinal cord injury. These drugs target the structure and function of the spinal cord microcirculation and are essential for maintaining the normal function of spinal neurons, axons, and glial cells. This review discusses the pathophysiological role of spinal cord microcirculation in spinal cord injury, including its structure and histopathological changes. Further, it summarizes the progress of drug therapies targeting the spinal cord microcirculation after spinal cord injury.

FGF-18 Protects the Injured Spinal cord in mice by Suppressing Pyroptosis and Promoting Autophagy via the AKT-mTOR-TRPML1 axis

Spinal cord injury (SCI) is a severe medical condition with lasting effects. The efficacy of numerous clinical treatments is hampered by the intricate pathophysiological mechanism of SCI. Fibroblast growth factor 18 (FGF-18) has been found to exert neuroprotective effects after brain ischaemia, but its effect after SCI has not been well explored. The aim of the present study was to explore the therapeutic effect of FGF-18 on SCI and the related mechanism. In the present study, a mouse model of SCI was used, and the results showed that FGF-18 may significantly affect functional recovery. The present findings demonstrated that FGF-18 directly promoted functional recovery by increasing autophagy and decreasing pyroptosis. In addition, FGF-18 increased autophagy, and the well-known autophagy inhibitor 3-methyladenine (3MA) reversed the therapeutic benefits of FGF-18 after SCI, suggesting that autophagy mediates the therapeutic effects of FGF-18 on SCI. A mechanistic study revealed that after stimulation of the protein kinase B (AKT)-transient receptor potential mucolipin 1 (TRPML1)-calcineurin signalling pathway, the FGF-18-induced increase in autophagy was mediated by the dephosphorylation and nuclear translocation of transcription factor E3 (TFE3). Together, these findings indicated that FGF-18 is a robust autophagy modulator capable of accelerating functional recovery after SCI, suggesting that it may be a promising treatment for SCI in the clinic.

The dual role of microglia in neuropathic pain after spinal cord injury: Detrimental and protective effects

Spinal cord injury (SCI) is a debilitating condition that is frequently accompanied by neuropathic pain, resulting in significant physical and psychological harm to a vast number of individuals globally. Despite the high prevalence of neuropathic pain following SCI, the precise underlying mechanism remains incompletely understood. Microglia are a type of innate immune cell that are present in the central nervous system (CNS). They have been observed to have a significant impact on neuropathic pain following SCI. This article presents a comprehensive overview of recent advances in understanding the role of microglia in the development of neuropathic pain following SCI. Specifically, the article delves into the detrimental and protective effects of microglia on neuropathic pain following SCI, as well as the mechanisms underlying their interconversion. Furthermore, the article provides a thorough overview of potential avenues for future research in this area.

Vasculature cells control neuroglial co-localization and synaptic connection in a central nervous system tissue mimic system

Despite the development of neural tissue differentiation methods using a wide variety of stem cells and compartments, there is no standardized strategy for establishing synapses. As the neuronal network is developed in parallel with blood vessel angiogenesis in the central nervous system (CNS) from the embryonic period, we examined neuron-astrocyte-vasculature interactions to understand the effect of the vasculature on the development and stabilization of neurological morphogenesis. We generated a cellular co-culture module targeting the CNS that was embedded in a collagen-based extracellular matrix (ECM) gel. Our neuron-astrocyte-vascular complex module identified the neurological co-localization effect by endothelial cells, as well as the pericyte-induced improvement of synaptic connections. Furthermore, it was suggested that the PDGF, BDNF, IGF, and WNT/BMP pathways were upregulated in synaptic connections enhanced conditions, which are composed of neurexin. These results suggest that the integrity of the vasculature cells in the CNS is important for the establishment of neuronal networks and for synapse connection.

Application of Conductive Hydrogels on Spinal Cord Injury Repair: A Review

Spinal cord injury (SCI) causes severe motor or sensory damage that leads to long-term disabilities due to disruption of electrical conduction in neuronal pathways. Despite current clinical therapies being used to limit the propagation of cell or tissue damage, the need for neuroregenerative therapies remains. Conductive hydrogels have been considered a promising neuroregenerative therapy due to their ability to provide a pro-regenerative microenvironment and flexible structure, which conforms to a complex SCI lesion. Furthermore, their conductivity can be utilized for noninvasive electrical signaling in dictating neuronal cell behavior. However, the ability of hydrogels to guide directional axon growth to reach the distal end for complete nerve reconnection remains a critical challenge. In this Review, we highlight recent advances in conductive hydrogels, including the incorporation of conductive materials, fabrication techniques, and cross-linking interactions. We also discuss important characteristics for designing conductive hydrogels for directional growth and regenerative therapy. We propose insights into electrical conductivity properties in a hydrogel that could be implemented as guidance for directional cell growth for SCI applications. Specifically, we highlight the practical implications of recent findings in the field, including the potential for conductive hydrogels to be used in clinical applications. We conclude that conductive hydrogels are a promising neuroregenerative therapy for SCI and that further research is needed to optimize their design and application.

Effect of multifactorial therapeutic approach on axonal regeneration and cell viability in an in-vitro model of spinal-derived neural injury

The highly debilitated nature of spinal cord injuries (SCI) creates an inhibitory repair environment that limits the recovery rate and therefore single interventional treatment has been resulted in incomplete recovery. A multifactorial approach that combines several therapeutic approaches may address diverse aspects of SCI pathology and enhance the recovery rate over single therapy. Accordingly, in this study, we aimed to investigate the effect of combined olfactory ensheathing cells (OECs) (to transport trophic factor, mediate immunomodulation, provide a suitable environment for cell survival), G-CSF (to establish a favorable environment for cell survival) and lipopolysaccharide (LPS) (to boost the protective activity of OEC) therapy on the cell viability after a scratch injury caused by a cataract knife on cells in an in-vitro model of spinal-derived neural injury. In this study, we used mixed neuronal-glial cultures, which are widely used for an in vitro study of neuronal damage. Scratch insult was made on cells using a cataract knife. The cells were divided into 8 groups (two control groups with and without olfactory ensheathing cells (OECs) treatment, injury group, three injury groups with single therapy by using super low dose of LPS (SLD-LPS) (100 pg/ml), OEC group, and G-CSF (100 ng/ml) group, and two injury groups with combined therapy (OEC with SLD-LPS and with all three treatments)). We found a significant decrease in the survival rate of injured cells (p < 0.001) 24 h after scratching insult. Our results indicated morphological alterations in cells in the acute phase (1, 2 and 6 h) after injury, with significant increased gap size at 6 h after induction of injury. Our combined therapy, significantly prevented cell death and decreased the size of the gap over time. We found that combined therapy promoted cell survival following spinal injury by providing a neuroprotective environment for cells. Therefore, our findings provide new insight into the combined therapy, which can be considered for promising preclinical therapeutic strategy for SCI toward clinical trials.

HSPA1A ameliorated spinal cord injury in rats by inhibiting apoptosis to exert neuroprotective effects

Traumatic spinal cord injury (TSCI) is a serious nervous system insult, and apoptosis in secondary injury is an important barrier to recovery from TSCI. Heat shock protein family A member 1A (HSPA1A) is a protective protein whose expression is elevated after stress. However, whether HSPA1A can inhibit apoptosis after spinal cord injury, and the potential mechanism of this inhibition, remain unclear. In this study, we established in vivo and in vitro models of TSCI and induced HSPA1A overexpression and silencing. HSPA1A upregulation promoted the recovery of neurological function and pathological morphology at the injury site, enhanced neurological cell survival, and inhibited apoptosis in rats following TSCI. In the in vitro model, HSPA1A overexpression inhibited H₂O₂-induced apoptosis, indicating that HSPA1A suppressed the expression of Bax, caspase-9, and cleaved-caspase-3, promoted the expression of Bcl-2. Furthermore, inhibition of HSPA1A expression can aggravate H₂O₂-induced apoptosis. We also found that HSPA1A overexpression activated the Wnt/β-catenin signaling pathway, and that inhibition of this pathway attenuated the inhibitory effect of HSPA1A overexpression on apoptosis. Together, these results indicate that HSPA1A has neuroprotective effects against TSCI that may be exerted through activation of the Wnt/β-catenin signaling pathway to inhibit apoptosis.

Improved Locomotor Recovery in a Rat Model of Spinal Cord Injury by BioLuminescent-OptoGenetic (BL-OG) Stimulation with an Enhanced Luminopsin

Irrespective of the many strategies focused on dealing with spinal cord injury (SCI), there is still no way to restore motor function efficiently or an adequate regenerative therapy. One promising method that could potentially prove highly beneficial for rehabilitation in patients is to re-engage specific neuronal populations of the spinal cord following SCI. Targeted activation may maintain and strengthen existing neuronal connections and/or facilitate the reorganization and development of new connections. BioLuminescent-OptoGenetics (BL-OG) presents an avenue to non-invasively and specifically stimulate neurons; genetically targeted neurons express luminopsins (LMOs), light-emitting luciferases tethered to light-sensitive channelrhodopsins that are activated by adding the luciferase substrate coelenterazine (CTZ). This approach employs ion channels for current conduction while activating the channels through treatment with the small molecule CTZ, thus allowing non-invasive stimulation of all targeted neurons. We previously showed the efficacy of this approach for improving locomotor recovery following severe spinal cord contusion injury in rats expressing the excitatory luminopsin 3 (LMO3) under control of a pan-neuronal and motor-neuron-specific promoter with CTZ applied through a lateral ventricle cannula. The goal of the present study was to test a new generation of LMOs based on opsins with higher light sensitivity which will allow for peripheral delivery of the CTZ. In this construct, the slow-burn Gaussia luciferase variant (sbGLuc) is fused to the opsin CheRiff, creating LMO3.2. Taking advantage of the high light sensitivity of this opsin, we stimulated transduced lumbar neurons after thoracic SCI by intraperitoneal application of CTZ, allowing for a less invasive treatment. The efficacy of this non-invasive BioLuminescent-OptoGenetic approach was confirmed by improved locomotor function. This study demonstrates that peripheral delivery of the luciferin CTZ can be used to activate LMOs expressed in spinal cord neurons that employ an opsin with increased light sensitivity.

The Proteostasis Network: A Global Therapeutic Target for Neuroprotection after Spinal Cord Injury

Proteostasis (protein homeostasis) is critical for cellular as well as organismal survival. It is strictly regulated by multiple conserved pathways including the ubiquitin-proteasome system, autophagy, the heat shock response, the integrated stress response, and the unfolded protein response. These overlapping proteostasis maintenance modules respond to various forms of cellular stress as well as organismal injury. While proteostasis restoration and ultimately organism survival is the main evolutionary driver of such a regulation, unresolved disruption of proteostasis may engage pro-apoptotic mediators of those pathways to eliminate defective cells. In this review, we discuss proteostasis contributions to the pathogenesis of traumatic spinal cord injury (SCI). Most published reports focused on the role of proteostasis networks in acute/sub-acute tissue damage post-SCI. Those reports reveal a complex picture with cell type- and/or proteostasis mediator-specific effects on loss of neurons and/or glia that often translate into the corresponding modulation of functional recovery. Effects of proteostasis networks on such phenomena as neuro-repair, post-injury plasticity, as well as systemic manifestations of SCI including dysregulation of the immune system, metabolism or cardiovascular function are currently understudied. However, as potential interventions that target the proteostasis networks are expected to impact many cell types across multiple organ systems that are compromised after SCI, such therapies could produce beneficial effects across the wide spectrum of highly variable human SCI.

Small extracellular vesicles derived from mesenchymal stem cell facilitate functional recovery in spinal cord injury by activating neural stem cells via the ERK1/2 pathway

Spinal cord injury (SCI) causes severe neurological dysfunction leading to a devastating disease of the central nervous system that is associated with high rates of disability and mortality. Small extracellular vesicles (sEVs) derived from human umbilical cord mesenchymal stem cells (hucMSC-sEVs) have been explored as a promising strategy for treating SCI. In this study, we investigated the therapeutic effects of the intralesional administration of hucMSC-sEVs after SCI and determined the potential mechanisms of successful repair by hucMSC-sEVs. In vivo, we established the rat model of SCI. The Basso, Beattie, Bresnahan (BBB) scores showed that hucMSC-sEVs dramatically promoted the recovery of spinal cord function. The results of the hematoxylin–eosin (HE) staining, Enzyme-Linked Immunosorbent Assay (ELISA), and immunohistochemistry showed that hucMSC-sEVs inhibited inflammation and the activation of glia, and promoted neurogenesis. Furthermore, we studied the effect of hucMSC-sEVs on neural stem cells(NSCs) in vitro. We found that hucMSC-sEVs did not improve the migration ability of NSCs, but promoted NSCs to proliferate and differentiate via the ERK1/2 signaling pathway. Collectively, these findings suggested that hucMSC-sEVs promoted the functional recovery of SCI by activating neural stem cells via the ERK1/2 pathway and may provide a new perspective and therapeutic strategy for the clinical application of hucMSC-sEVs in SCI treatment.

Biomaterial-Mediated Factor Delivery for Spinal Cord Injury Treatment

Spinal cord injury (SCI) is an injurious process that begins with immediate physical damage to the spinal cord and associated tissues during an acute traumatic event. However, the tissue damage expands in both intensity and volume in the subsequent subacute phase. At this stage, numerous events exacerbate the pathological condition, and therein lies the main cause of post-traumatic neural degeneration, which then ends with the chronic phase. In recent years, therapeutic interventions addressing different neurodegenerative mechanisms have been proposed, but have met with limited success when translated into clinical settings. The underlying reasons for this are that the pathogenesis of SCI is a continued multifactorial disease, and the treatment of only one factor is not sufficient to curb neural degeneration and resulting paralysis. Recent advances have led to the development of biomaterials aiming to promote in situ combinatorial strategies using drugs/biomolecules to achieve a maximized multitarget approach. This review provides an overview of single and combinatorial regenerative-factor-based treatments as well as potential delivery options to treat SCIs.

The PI3K/AKT signalling pathway in inflammation, cell death and glial scar formation after traumatic spinal cord injury: Mechanisms and therapeutic opportunities

Objects

Traumatic spinal cord injury (TSCI) causes neurological dysfunction below the injured segment of the spinal cord, which significantly impacts the quality of life in affected patients. The phosphoinositide 3kinase/serine‐threonine kinase (PI3K/AKT) signaling pathway offers a potential therapeutic target for the inhibition of secondary TSCI. This review summarizes updates concerning the role of the PI3K/AKT pathway in TSCI.

Materials and Methods

By searching articles related to the TSCI field and the PI3K/AKT signaling pathway, we summarized the mechanisms of secondary TSCI and the PI3K/AKT signaling pathway; we also discuss current and potential future treatment methods for TSCI based on the PI3K/AKT signaling pathway.

Results

Early apoptosis and autophagy after TSCI protect the body against injury; a prolonged inflammatory response leads to the accumulation of pro‐inflammatory factors and excessive apoptosis, as well as excessive autophagy in the surrounding normal nerve cells, thus aggravating TSCI in the subacute stage of secondary injury. Initial glial scar formation in the subacute phase is a protective mechanism for TSCI, which limits the spread of damage and inflammation. However, mature scar tissue in the chronic phase hinders axon regeneration and prevents the recovery of nerve function. Activation of PI3K/AKT signaling pathway can inhibit the inflammatory response and apoptosis in the subacute phase after secondary TSCI; inhibiting this pathway in the chronic phase can reduce the formation of glial scar.

Conclusion

The PI3K/AKT signaling pathway has an important role in the recovery of spinal cord function after secondary injury. Inducing the activation of PI3K/AKT signaling pathway in the subacute phase of secondary injury and inhibiting this pathway in the chronic phase may be one of the potential strategies for the treatment of TSCI.

Emerging Roles of Microglia Depletion in the Treatment of Spinal Cord Injury

Microglia, as the resident immune cells and first responder to neurological insults, play an extremely important role in the pathophysiological process of spinal cord injury. On the one hand, microglia respond rapidly and gather around the lesion in the early stage of injury to exert a protective role, but with the continuous stimulation of the injury, the excessive activated microglia secrete a large number of harmful substances, aggravate the injury of spinal cord tissue, and affect functional recovery. The effects of microglia depletion on the repair of spinal cord injury remain unclear, and there is no uniformly accepted paradigm for the removal methods and timing of microglia depletion, but different microglia depletion strategies greatly affect the outcomes after spinal cord injury. Therefore, this review summarizes the physiological and pathological roles of microglia, especially the effects of microglia depletion on spinal cord injury-sustained microglial depletion would aggravate injury and impair functional recovery, while the short-term depletion of microglial population in diseased conditions seems to improve tissue repair and promote functional improvement after spinal cord injury. Furthermore, we discuss the advantages and disadvantages of major strategies and timing of microglia depletion to provide potential strategy for the treatment of spinal cord injury.

An Emerging Frontier in Intercellular Communication: Extracellular Vesicles in Regeneration

Regeneration requires cellular proliferation, differentiation, and other processes that are regulated by secreted cues originating from cells in the local environment. Recent studies suggest that signaling by extracellular vesicles (EVs), another mode of paracrine communication, may also play a significant role in coordinating cellular behaviors during regeneration. EVs are nanoparticles composed of a lipid bilayer enclosing proteins, nucleic acids, lipids, and other metabolites, and are secreted by most cell types. Upon EV uptake by target cells, EV cargo can influence diverse cellular behaviors during regeneration, including cell survival, immune responses, extracellular matrix remodeling, proliferation, migration, and differentiation. In this review, we briefly introduce the history of EV research and EV biogenesis. Then, we review current understanding of how EVs regulate cellular behaviors during regeneration derived from numerous studies of stem cell-derived EVs in mammalian injury models. Finally, we discuss the potential of other established and emerging research organisms to expand our mechanistic knowledge of basic EV biology, how injury modulates EV biogenesis, cellular sources of EVs in vivo, and the roles of EVs in organisms with greater regenerative capacity.

Genistein Protects against Spinal Cord Injury in Mice by Inhibiting Neuroinflammation via TLR4-Mediated Microglial Polarization

Objective

The present study was designed to study the effect of genistein on spinal cord injury (SCI) in mice and to explore its underlying mechanisms.

Methods

We established SCI mouse model, and genistein was administered for treatment. We used the Basso, Beattie, and Bresnahan (BBB) exercise rating scale to evaluate exercise recovery, and the detection of spinal cord edema was done using the wet/dry weight method. Apoptosis was determined by TUNEL staining, and inflammation was evaluated by measuring inflammatory factors by an ELISA kit. The expression of M1 and M2 macrophage markers was determined using flow cytometry, and the expression of proteins was detected using immunoblotting.

Results

Genistein treatment not only improved the BBB score but also reduced spinal cord edema in SCI mice. Genistein treatment reduced apoptosis by increasing Bcl2 protein expression and decreasing Bax and caspase 3 protein expression. It also reduced the expression of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8) in the SCI area of SCI mice. Flow cytometry analysis indicated that genistein treatment significantly decreased the ratio of M1 macrophages (CD45+/Gr-1-/CD11b+/iNOS+) and increased the ratio of M2 macrophages (CD45+/Gr-1-/CD11b+/Arginase 1+) in the SCI area of SCI mice on the 28th day after being treated with genistein. We also found that genistein treatment significantly decreased the expression of TLR4, MyD88, and TRAF6 protein in the SCI area of SCI mice on 28th day after being treated with genistein.

Conclusion

Our findings suggested that genistein exerted neuroprotective action by inhibiting neuroinflammation by promoting the activation of M2 macrophages, and its underlying mechanisms might be related to the inhibition of the TLR4-mediated MyD88-dependent signaling pathway.

Effects of the Notch Signaling Pathway on Secondary Brain Changes Caused by Spinal Cord Injury in Mice

Spinal cord injury (SCI) can cause secondary brain changes, leading to hypomyelination in the dorsolateral prefrontal cortex (dlPFC). Some studies have shown that notch signaling pathway activation can regulate oligodendrocyte maturation and myelination. The aim of this study was to investigate whether inhibition of the Notch signaling pathway can alleviate hypomyelination in the dlPFC caused by SCI. Moreover, we further investigated whether the changes in myelination in the dlPFC are associated with neuropathic pain following SCI. We established a mouse model of SCI and observed the changes in mechanical and thermal hyperalgesia. Western blotting and immunofluorescence were used to analyze the changes in myelination in the dlPFC. The results indicated the existence of a relationship between activation of the Notch signaling pathway and hypomyelination in the dlPFC and confirmed the existence of a relationship between hypomyelination in the dlPFC and decreases in mechanical and thermal hyperalgesia thresholds. In conclusion, these results suggested that the Notch signaling pathway is activated after SCI, leading to hypomyelination in the dlPFC, and that DAPT can inhibit the Notch signaling pathway and improve mechanical and thermal hyperalgesia thresholds. Our findings provide a new target for the treatment of neuropathic pain caused by SCI.

Hyperbaric oxygen therapy after mid-cervical spinal contusion injury

Hyperbaric oxygen (HBO) therapy is frequently used to treat peripheral wounds or decompression sickness. Evidence suggests that HBO therapy can provide neuroprotection and has an anti-inflammatory impact after neurological injury, including spinal cord injury (SCI). Our primary purpose was to conduct a genome-wide screening of mRNA expression changes in the injured spinal cord after HBO therapy. An mRNA gene array was used to evaluate samples taken from the contused region of the spinal cord following a lateralized mid-cervical contusion injury in adult female rats. HBO therapy consisted of daily, 1-h sessions (3.0 ATA, 100% O₂) initiated on the day of SCI and continued for 10 days. Gene set enrichment analyses indicated that HBO upregulated genes in pathways associated with electron transport, mitochondrial function, and oxidative phosphorylation, and downregulated genes in pathways associated with inflammation (including cytokines and nuclear factor kappa B [NF-κB]) and apoptotic signaling. In a separate cohort, spinal cord histology was performed to verify whether the HBO treatment impacted neuronal cell counts or inflammatory markers. Compared with untreated rats, there were increased NeuN positive cells in the spinal cord of HBO-treated rats (p = 0.004). We conclude that HBO therapy, initiated shortly after SCI and continued for 10 days, can alter the molecular signature of the lesioned spinal cord in a manner consistent with a neuroprotective impact.

Hippo-Yap/Taz signalling in zebrafish regeneration

The extent of tissue regeneration varies widely between species. Mammals have a limited regenerative capacity whilst lower vertebrates such as the zebrafish (Danio rerio), a freshwater teleost, can robustly regenerate a range of tissues, including the spinal cord, heart, and fin. The molecular and cellular basis of this altered response is one of intense investigation. In this review, we summarise the current understanding of the association between zebrafish regeneration and Hippo pathway function, a phosphorylation cascade that regulates cell proliferation, mechanotransduction, stem cell fate, and tumorigenesis, amongst others. We also compare this function to Hippo pathway activity in the regenerative response of other species. We find that the Hippo pathway effectors Yap/Taz facilitate zebrafish regeneration and that this appears to be latent in mammals, suggesting that therapeutically promoting precise and temporal YAP/TAZ signalling in humans may enhance regeneration and hence reduce morbidity.

Clemastine Enhances Myelination, Delays Axonal Loss and Promotes Functional Recovery in Spinal Cord Injury

Recent evidence has shown that demyelination occurs along with axonal degeneration in spinal cord injury (SCI) during the secondary injury phase. Oligodendrocyte precursor cells (OPC) are present in the lesions but fail to differentiate into mature oligodendrocytes and form new myelin. Given the limited recovery of neuronal functions after SCI in adults without effective treatment available so far, it remains unknown whether enhancing OPC differentiation and myelination could benefit the recovery of SCI. To show the significance of myelin regeneration after SCI, the injury was treated with clemastine in the rat model. Clemastine is an FDA-approved drug that is potent in promoting oligodendrocyte differentiation and myelination in vivo, for four weeks following SCI. Motor function was assessed using sloping boards and grid walking tests and scored according to the Basso, Beattie, and Bresnahan protocol. The myelin integrity and protein expression were evaluated using transmission electron microscopy and immunofluorescence, respectively. The results indicated that clemastine treatment preserves myelin integrity, decreases loss of axons and improves functional recovery in the rat SCI model. The presented data suggest that myelination-enhancing strategies may serve as a potential therapeutic approach for the functional recovery in SCI.

Numerical Investigation of Spinal Cord Injury After Flexion-Distraction Injuries At the Cervical Spine

Flexion-distraction injuries frequently cause traumatic cervical spinal cord injury (SCI). Post-traumatic instability can cause aggravation of the secondary SCI during patient's care. However, there is little information on how the pattern of disco-ligamentous injury affects the SCI severity and mechanism. This study objective was to analyze how different flexion-distraction disco-ligamentous injuries affect the SCI mechanisms during post-traumatic flexion and extension. A cervical spine finite element model including the spinal cord was used and different combinations of partial or complete intervertebral disc (IVD) rupture and disruption of various posterior ligaments were modeled at C4-C5, C5-C6 or C6-C7. In flexion, complete IVD rupture combined with posterior ligamentous complex rupture was the most severe injury leading to the most extreme von Mises stress (47 to 66 kPa), principal strains p1 (0.32 to 0.41 in white matter) and p3 (-0.78 to -0.96 in white matter) in the spinal cord and to the most important spinal cord compression (35 to 48 %). The main post-trauma SCI mechanism was identified as compression of the anterior white matter at the injured level combined with distraction of the posterior spinal cord during flexion. There was also a concentration of the maximum stresses in the gray matter after injury. Finally, in extension, the injuries tested had little impact on the spinal cord. The capsular ligament was the most important structure in protecting the spinal cord. Its status should be carefully examined during patient's management.

An Overview of Mesenchymal Stem Cell-based Therapy Mediated by Noncoding RNAs in the Treatment of Neurodegenerative Diseases

Mesenchymal stem cells (MSCs) have become a promising tool for neurorestorative therapy of neurodegenerative diseases (NDDs), which are mainly characterized by the progressive and irreversible loss of neuronal structure and function in the central or peripheral nervous system. Recently, studies have reported that genetic manipulation mediated by noncoding RNAs (ncRNAs) can increase survival and neural regeneration of transplanted MSCs, offering a new strategy for clinical translation. In this review, we summarize the potential role and regulatory mechanism of two major types of ncRNAs, including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), during the neurogenesis of MSCs with gene expression profile analyses. We also overview the realization of MSC-based therapy mediated by ncRNAs in the treatment of spinal cord injury, stroke, Alzheimer's disease and peripheral nerve injury. It is expected that ncRNAs will become promising therapeutic targets for NDD on stem cells, while the underlying mechanisms require further exploration.

Diversity of Reactive Astrogliosis in CNS Pathology: Heterogeneity or Plasticity?

Astrocytes are essential for the development and homeostatic maintenance of the central nervous system (CNS). They are also critical players in the CNS injury response during which they undergo a process referred to as "reactive astrogliosis." Diversity in astrocyte morphology and gene expression, as revealed by transcriptional analysis, is well-recognized and has been reported in several CNS pathologies, including ischemic stroke, CNS demyelination, and traumatic injury. This diversity appears unique to the specific pathology, with significant variance across temporal, topographical, age, and sex-specific variables. Despite this, there is limited functional data corroborating this diversity. Furthermore, as reactive astrocytes display significant environmental-dependent plasticity and fate-mapping data on astrocyte subsets in the adult CNS is limited, it remains unclear whether this diversity represents heterogeneity or plasticity. As astrocytes are important for neuronal survival and CNS function post-injury, establishing to what extent this diversity reflects distinct established heterogeneous astrocyte subpopulations vs. environmentally dependent plasticity within established astrocyte subsets will be critical for guiding therapeutic development. To that end, we review the current state of knowledge on astrocyte diversity in the context of three representative CNS pathologies: ischemic stroke, demyelination, and traumatic injury, with the goal of identifying key limitations in our current knowledge and suggesting future areas of research needed to address them. We suggest that the majority of identified astrocyte diversity in CNS pathologies to date represents plasticity in response to dynamically changing post-injury environments as opposed to heterogeneity, an important consideration for the understanding of disease pathogenesis and the development of therapeutic interventions.

Ginsenoside Rb1 attenuates microglia activation to improve spinal cord injury via microRNA-130b-5p/TLR4/NF-κB axis

Ginsenoside Rb1 (GRb1), a major ingredient of ginseng, has been found to be a potential protective agent in spinal cord injury (SCI) and in activated microglia-induced neuronal injury. This study discovered that GRb1 could facilitate miR-130b-5p expression in SCI rats and Toll-like receptor 4 (TLR4; a crucial player in inflammation) was a potential target of miR-130b-5p. Hence, we further investigated whether GRb1 could relieve SCI by reducing microglia-mediated inflammatory responses and neuronal injury via miR-130b-5p/TLR4 pathways. The results showed that GRb1 alleviated SCI through inhibiting neuronal apoptosis and proinflammatory factor expression via increasing miR-130b-5p.GRb1 weakened the damage of activated microglia to neurons through upregulating miR-130b-5p. miR-130b-5p attenuated activated microglia-induced neuron injury via targeting TLR4. GRb1 inactivated TLR4/nuclear factor-κB (NF-κB) activation and inhibited proinflammatory cytokine secretion by increasing miR-130b-5p in activated microglia. As a conclusion, GRb1 alleviated SCI through reducing activated microglia-induced neuronal injury via miR-130b-5p/TLR4/NF-κB axis, providing a deep insight into the molecular basis of GRb1 in the treatment of SCI.

Ketogenic regimens for acute neurotraumatic events

Dietary modification would be the most translatable, cost-efficient, and, likely, the safest approach available that can reduce the reliance on pharmaceutical treatments for treating acute or chronic neurological disorders. A wide variety of evidence suggests that the ketogenic diet (KD) could have beneficial effects in acute traumatic events, such as spinal cord injury and traumatic brain injury. Review of existing human and animal studies revealed that KD can improve motor neuro-recovery, gray matter sparing, pain thresholds, and neuroinflammation and decrease depression. Although the exact mechanism by which the KD provides neuroprotection is not fully understood, its effects on cellular energetics, mitochondria function and inflammation are likely to have a role.

Neuroprotective effect of immunomodulatory peptides in rats with traumatic spinal cord injury

Several therapies have shown obvious effects on structural conservation contributing to motor functional recovery after spinal cord injury (SCI). Nevertheless, neither strategy has achieved a convincing effect. We purposed a combined therapy of immunomodulatory peptides that individually have shown significant effects on motor functional recovery in rats with SCI. The objective of this study was to investigate the effects of the combined therapy of monocyte locomotion inhibitor factor (MLIF), A91 peptide, and glutathione monoethyl ester (GSH-MEE) on chronic-stage spinal cord injury. Female Sprague-Dawley rats underwent a laminectomy of the T9 vertebra and a moderate contusion. Six groups were included: sham, PBS, MLIF + A91, MLIF + GSH-MEE, A91 + GSH-MEE, and MLIF + A91 + GSH-MEE. Two months after injury, motor functional recovery was evaluated using the open field test. Parenchyma and white matter preservation was evaluated using hematoxylin & eosin staining and Luxol Fast Blue staining, respectively. The number of motoneurons in the ventral horn and the number of axonal fibers were determined using hematoxylin & eosin staining and immunohistochemistry, respectively. Collagen deposition was evaluated using Masson's trichrome staining. The combined therapy of MLIF, A91, and GSH-MEE greatly contributed to motor functional recovery and preservation of the medullary parenchyma, white matter, motoneurons, and axonal fibres, and reduced the deposition of collagen in the lesioned area. The combined therapy of MLIF, A91, and GSH-MEE preserved spinal cord tissue integrity and promoted motor functional recovery of rats after SCI. This study was approved by the National Commission for Scientific Research on Bioethics and Biosafety of the Instituto Mexicano del Seguro Social under registration number R-2015-785-116 (approval date November 30, 2015) and R-2017-3603-33 (approval date June 5, 2017).

CCL3 contributes to secondary damage after spinal cord injury

Background

Secondary damage after spinal cord injury (SCI) is characterized by a cascade of events including hemorrhage, apoptosis, oxidative stress, and inflammation which increase the lesion size which can influence the functional impairment. Thus, identifying specific mechanisms attributed to secondary injury is critical in minimizing tissue damage and improving neurological outcome. In this work, we are investigating the role of CCL3 (macrophage inflammatory protein 1-α, MIP-1α), a chemokine involved in the recruitment of inflammatory cells, which plays an important role in inflammatory conditions of the central and peripheral nervous system.

Methods

A mouse model of lower thoracic (T11) spinal cord contusion injury was used. We assessed expression levels of CCL3 and its receptors on the mRNA and protein level and analyzed changes in locomotor recovery and the inflammatory response in the injured spinal cord of wild-type and CCL3^−/− mice.

Results

The expression of CCL3 and its receptors was increased after thoracic contusion SCI in mice. We then examined the role of CCL3 after SCI and its direct influence on the inflammatory response, locomotor recovery and lesion size using CCL3^−/− mice. CCL3^−/− mice showed mild but significant improvement of locomotor recovery, a smaller lesion size and reduced neuronal damage compared to wild-type controls. In addition, neutrophil numbers as well as the pro-inflammatory cytokines and chemokines, known to play a deleterious role after SCI, were markedly reduced in the absence of CCL3.

Conclusion

We have identified CCL3 as a potential target to modulate the inflammatory response and secondary damage after SCI. Collectively, this study shows that CCL3 contributes to progressive tissue damage and functional impairment during secondary injury after SCI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02037-3.

Recent Advances in the Regenerative Approaches for Traumatic Spinal Cord Injury: Materials Perspective

Spinal cord injury (SCI) is a devastating health condition that may lead to permanent disabilities and death. Understanding the pathophysiological perspectives of traumatic SCI is essential to define mechanisms that can help in designing recovery strategies. Since central nervous system tissues are notorious for their deficient ability to heal, efforts have been made to identify solutions to aid in restoration of the spinal cord tissues and thus its function. The two main approaches proposed to address this issue are neuroprotection and neuro-regeneration. Neuroprotection involves administering drugs to restore the injured microenvironment to normal after SCI. As for the neuro-regeneration approach, it focuses on axonal sprouting for functional recovery of the injured neural tissues and damaged axons. Despite the progress made in the field, neural regeneration treatment after SCI is still unsatisfactory owing to the disorganized way of axonal growth and extension. Nanomedicine and tissue engineering are considered promising therapeutic approaches that enhance axonal growth and directionality through implanting or injecting of the biomaterial scaffolds. One of these recent approaches is nanofibrous scaffolds that are used to provide physical support to maintain directional axonal growth in the lesion site. Furthermore, these preferable tissue-engineered substrates can afford axonal regeneration by mimicking the extracellular matrix of the neural tissues in terms of biological, chemical, and architectural characteristics. In this review, we discuss the regenerative approach using nanofibrous scaffolds with a focus on their fabrication methods and their properties that define their functionality performed to heal the neural tissue efficiently.

A New Therapeutic Strategy Targeting Protein Deacetylation for Spinal Cord Injury

Lysine acetylation is a post-translational modification that regulates a diversity of biological processes. However, its implication in spinal cord injury (SCI) remains unclear. Here we investigated the acetylation events in injured spinal cords on a proteomic scale for the first time. Additionally, whether promoting acetylation could mitigate SCI was evaluated. A total of 268 differentially acetylated peptides were identified. Among them, 2 peptides were up-acetylated and 141 peptides were down-acetylated in the injured spinal cord tissues (Fold change >2 and P < 0.05). There were also 116 unique acetylated peptides in the sham group and 9 unique acetylated peptides in the SCI group. Functional enrichment analysis revealed that differently acetylated proteins were involved in multiple cellular processes and metabolic processes. Kyoto Encyclopaedia of Genes and Genomes analysis showed that several pathways, including cGMP-PKG signaling pathway and hypoxia-inducible factor-1 (HIF-1) signaling pathway, were predominantly presented. Moreover, promoting acetylation using glycerol triacetate (GTA) showed a therapeutic effect on SCI, with improved Basso-Beattie-Bresnahan scores and histologic morphology, and decreased neuronal apoptosis and inflammation. In conclusion, our data indicated that protein deacetylation might play crucial roles in the development of secondary injury of SCI, and promoting acetylation by GTA effectively mitigated SCI. Our data not only enhance our understanding on acetylproteome dataset in the spinal cord tissues, but also provide novel insights for the treatment of SCI.

IP3R-mediated intra-axonal Ca2+ release contributes to secondary axonal degeneration following contusive spinal cord injury

Secondary axonal loss contributes to the persistent functional disability following trauma. Consequently, preserving axons following spinal cord injury (SCI) is a major therapeutic goal to improve neurological outcome; however, the complex molecular mechanisms that mediate secondary axonal degeneration remain unclear. We previously showed that IP₃R-mediated Ca²⁺ release contributes to axonal dieback and axonal loss following an ex vivo laser-induced SCI. Nevertheless, targeting IP₃R in a clinically relevant in vivo model of SCI and determining its contribution to secondary axonal degeneration has yet to be explored. Here we used intravital two-photon excitation microscopy to assess the role of IP₃R in secondary axonal degeneration in real-time after a contusive-SCI in vivo. To visualize Ca²⁺ changes specifically in spinal axons over time, adult 6-8 week-old triple transgenic Avil-Cre:Ai9:Ai95 (sensory neuron-specific expression of tdTomato and the genetic calcium indicator GCaMP6f) mice were subjected to a mild (30 kdyn) T12 contusive-SCI and received delayed treatment with the IP₃R blocker 2-APB (100 μM, intrathecal delivery at 3, and 24 h following injury) or vehicle control. To determine the IP₃R subtype involved, we knocked-down IP₃R3 using capped phosphodiester oligonucleotides. Delayed treatment with 2-APB significantly reduced axonal spheroids, increased axonal survival, and reduced intra-axonal Ca²⁺ accumulation within dorsal column axons at 24 h following SCI in vivo. Additionally, knockdown of IP₃R3 yielded increased axon survival 24 h post-SCI. These results suggest that IP₃R-mediated Ca²⁺ release contributes to secondary axonal degeneration in vivo following SCI.

Transplanting neural progenitor cells to restore connectivity after spinal cord injury

Spinal cord injury remains a scientific and therapeutic challenge with great cost to individuals and society. The goal of research in this field is to find a means of restoring lost function. Recently we have seen considerable progress in understanding the injury process and the capacity of CNS neurons to regenerate, as well as innovations in stem cell biology. This presents an opportunity to develop effective transplantation strategies to provide new neural cells to promote the formation of new neuronal networks and functional connectivity. Past and ongoing clinical studies have demonstrated the safety of cell therapy, and preclinical research has used models of spinal cord injury to better elucidate the underlying mechanisms through which donor cells interact with the host and thus increase long-term efficacy. While a variety of cell therapies have been explored, we focus here on the use of neural progenitor cells obtained or derived from different sources to promote connectivity in sensory, motor and autonomic systems.

Strategies and prospects of effective neural circuits reconstruction after spinal cord injury

Due to the disconnection of surviving neural elements after spinal cord injury (SCI), such patients had to suffer irreversible loss of motor or sensory function, and thereafter enormous economic and emotional burdens were brought to society and family. Despite many strategies being dealing with SCI, there is still no effective regenerative therapy. To date, significant progress has been made in studies of SCI repair strategies, including gene regulation of neural regeneration, cell or cell-derived exosomes and growth factors transplantation, repair of biomaterials, and neural signal stimulation. The pathophysiology of SCI is complex and multifaceted, and its mechanisms and processes are incompletely understood. Thus, combinatorial therapies have been demonstrated to be more effective, and lead to better neural circuits reconstruction and functional recovery. Combinations of biomaterials, stem cells, growth factors, drugs, and exosomes have been widely developed. However, simply achieving axon regeneration will not spontaneously lead to meaningful functional recovery. Therefore, the formation and remodeling of functional neural circuits also depend on rehabilitation exercises, such as exercise training, electrical stimulation (ES) and Brain-Computer Interfaces (BCIs). In this review, we summarize the recent progress in biological and engineering strategies for reconstructing neural circuits and promoting functional recovery after SCI, and emphasize current challenges and future directions.

Neuroprotection of netrin-1 on neurological recovery via Wnt/β-catenin signaling pathway after spinal cord injury

The neuroprotective effects of netrin-1 after spinal cord injury and its specific molecular mechanisms have not been elucidated. In our study, Western blot, transferase UTP nick end labeling staining and immunofluorescence staining first showed that netrin-1 significantly decreased the expression levels of caspase-3, caspase-9, transferase UTP nick end labeling-positive neurons, nuclear factor kappa-B, and tumor necrosis factor-α after spinal cord injury, which inhibited neuronal apoptosis and inflammatory response. Using Nissl and HE staining, we also found that netrin-1 significantly increased the number of Nissl bodies in the anterior horn of spinal cord and promoted the recovery of injured tissue after spinal cord injury, consequently providing a good microenvironment for recovery of motor function. Finally, the results of Basso, Beattie, and Bresnahan score further confirmed that netrin-1 promoted the recovery of neurological function after spinal cord injury. Furthermore, netrin-1 significantly promoted the expression of β-catenin and inhibited the expression of glycogen synthase kinase-3β, which activated Wnt/β-catenin signaling pathway after spinal cord injury. However, XAV939 inhibited Wnt/β-catenin signaling pathway, which significantly inhibited the regulatory effect of netrin-1 on apoptosis, inflammation, Nissl bodies, damaged tissues, and neuroprotection. These results demonstrate for the first time the correlation between netrin-1 and Wnt/β-catenin signaling pathway after spinal cord injury and show that netrin-1 exerts its neuroprotective effect by activating this signaling pathway after spinal cord injury.

Therapeutic repair for spinal cord injury: combinatory approaches to address a multifaceted problem

The recent years saw the advent of promising preclinical strategies that combat the devastating effects of a spinal cord injury (SCI) that are progressing towards clinical trials. However, individually, these treatments produce only modest levels of recovery in animal models of SCI that could hamper their implementation into therapeutic strategies in spinal cord injured humans. Combinational strategies have demonstrated greater beneficial outcomes than their individual components alone by addressing multiple aspects of SCI pathology. Clinical trial designs in the future will eventually also need to align with this notion. The scenario will become increasingly complex as this happens and conversations between basic researchers and clinicians are required to ensure accurate study designs and functional readouts.

Repeat intravital imaging of the murine spinal cord reveals degenerative and reparative responses of spinal axons in real-time following a contusive SCI

Spinal cord injury (SCI) induces a secondary degenerative response that causes the loss of spared axons and worsens neurological outcome. The complex molecular mechanisms that mediate secondary axonal degeneration remain poorly understood. To further our understanding of secondary axonal degeneration following SCI, we assessed the spatiotemporal dynamics of axonal spheroid and terminal bulb formation following a contusive SCI in real-time in vivo. Adult 6-8 week old Thy1YFP transgenic mice underwent a T12 laminectomy for acute imaging sessions or were implanted with a custom spinal cord imaging chamber for chronic imaging of the spinal cord. Two-photon excitation time-lapse microscopy was performed prior to a mild contusion SCI (30 kilodyne, IH Impactor) and at 1-4 h and 1-14 days post-SCI. We quantified the number of axonal spheroids, their size and distribution, the number of endbulbs, and axonal survival from 1 h to 14 days post-SCI. Our data reveal that the majority of axons underwent swelling and axonal spheroid formation acutely after SCI resulting in the loss of ~70% of axons by 1 day after injury. In agreement, the number of axonal spheroids rapidly increased at 1 h after SCI and remained significantly elevated up to 14 days after SCI. Furthermore, the distribution of axonal spheroids spread mediolaterally over time indicative of delayed secondary degenerative processes. In contrast, axonal endbulbs were relatively sparse and their numbers peaked at 1 day after injury. Intriguingly, axonal survival significantly increased at 7 and 14 days compared to 3 days after SCI revealing a potential endogenous axonal repair process that mirrors the known spontaneous functional recovery after SCI. In support, ~43% of tracked axonal spheroids resolved over the course of observation revealing their dynamic nature. Furthermore, axonal spheroids and endbulbs accumulated mitochondria and excessive tubulin polyglutamylation suggestive of disrupted axonal transport as a shared mechanism. Collectively, this study provides important insight into both degenerative and recoverable responses of axons following contusive SCI in real-time. Understanding how axons spontaneously recover after SCI will be an important avenue for future SCI research and may help guide future clinical trials.

Neuroprotective effects of a ketogenic diet in combination with exogenous ketone salts following acute spinal cord injury

We have previously shown that induction of ketosis by ketogenic diet (KD) conveyed neuroprotection following spinal cord injury in rodent models, however, clinical translation may be limited by the slow raise of ketone levels when applying KD in the acute post-injury period. Thus we investigated the use of exogenous ketone supplementation (ketone sodium, KS) combined with ketogenic diet as a means rapidly inducing a metabolic state of ketosis following spinal cord injury in adult rats. In uninjured rats, ketone levels increased more rapidly than those in rats with KD alone and peaked at higher levels than we previously demonstrated for the KD in models of spinal cord injury. However, ketone levels in KD + KS treated rats with SCI did not exceed the previously observed levels in rats treated with KD alone. We still demonstrated neuroprotective effects of KD + KS treatment that extend our previous neuroprotective observations with KD only. The results showed increased neuronal and axonal sparing in the dorsal corticospinal tract. Also, better performance of forelimb motor abilities were observed on the Montoya staircase (for testing food pellets reaching) at 4 and 6 weeks post-injury and rearing in a cylinder (for testing forelimb usage) at 6 and 8 weeks post-injury. Taken together, the findings of this study add to the growing body of work demonstrating the potential benefits of inducing ketosis following neurotrauma. Ketone salt combined with a ketogenic diet gavage in rats with acute spinal cord injury can rapidly increase ketone body levels in the blood and promote motor function recovery. This study was approved by the Animal Care Committee of the University of British Columbia (protocol No. A14-350) on August 31, 2015.

Combination Therapy With Hyperbaric Oxygen and Erythropoietin Inhibits Neuronal Apoptosis and Improves Recovery in Rats With Spinal Cord Injury

BACKGROUND

Apoptosis plays an important role in various diseases, including spinal cord injury (SCI). Hyperbaric oxygen (HBO) and erythropoietin (EPO) promote the recovery from SCI, but the relationship between apoptosis and the combination therapeutic effect is not completely clear.

OBJECTIVE

The purpose of this study was to investigate the effects of HBO and EPO on SCI and the mechanisms that underlie their therapeutic benefits.

DESIGN

The study was designed to explore the effects of HBO and EPO on SCI through a randomized controlled trial.

METHODS

Sixty young developing female Sprague-Dawley rats were randomly divided into groups of 12 rats receiving sham, SCI, HBO, EPO, or HBO plus EPO. The SCI model was modified with the Allen method to better control consistency. HBO was performed for 1 hour per day for a total of 21 days, and EPO was given once per week for a total of 3 weeks. Both methods were performed 2 hours after SCI. Locomotor function was evaluated with the 21-point Basso-Beattie-Bresnahan Locomotor Rating Scale, an inclined-plane test, and a footprint analysis. All genes were detected by Western blotting and immunohistochemistry. The level of cell apoptosis was determined by Hoechst staining.

RESULTS

The results showed that HBO and EPO promoted the recovery of locomotor function in the hind limbs of rats by inhibiting the apoptosis of neurons. During this period, the expression of B-cell lymphoma/leukemia 2 protein (Bcl-2) increased significantly, whereas the expression of Bcl-2-associated X protein (Bax) and cleaved caspase 3 decreased significantly, indicating the inhibition of apoptosis. Meanwhile, the expression of G protein-coupled receptor 17 decreased, and that of myelin basic protein increased, suggesting that there may be a potential connection between demyelination and neuronal apoptosis.

LIMITATIONS

The limitations of the study include deviations in the preparation of SCI models; lack of reverse validation of molecular mechanisms; absence of in vitro cell experiments; and only one time point after SCI was studied.

CONCLUSIONS

HBO and EPO treatments are beneficial for SCI, especially when the 2 therapies are combined.

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

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

Intraspinal administration of interleukin-7 promotes neuronal apoptosis and limits functional recovery through JAK/STAT5 pathway following spinal cord injury

It has been previously reported that the blockade of interleukin-7 receptor (IL-7R) promotes functional recovery following spinal cord injury (SCI), however, the direct function and molecular mechanism of IL-7 involved in this pathogenic process are unclear. Here, we report that, contrary to IL-7R blockade, the intraspinal administration of IL-7 limits functional recovery following SCI. In addition, IL-7 treatment promotes neuronal apoptosis in spinal cord lesions, which may be attributed to exacerbated focal inflammatory response, as shown by increased accumulation of activated microglia/macrophage and production of proinflammatory mediators. Moreover, IL-7 treatment activates JAK/STAT5 pathway following SCI. At last, more importantly, the pharmacological inhibition of STAT5 abrogates the effects of IL-7 treatment on functional recovery, neuronal apoptosis and focal inflammatory response, suggesting that the effects of IL-7 treatment following SCI are dependent on activating the JAK/STAT5 pathway. Overall, this study reveals the JAK/STAT5 pathway-dependent detrimental role of IL-7 following SCI, and also implies that targeting the IL-7/JAK/STAT5 axis may represent a potential therapeutic approach for SCI treatment.