Combination of engineered Schwann cell grafts to secrete neurotrophin and chondroitinase promotes axonal regeneration and locomotion after spinal cord injury

Coordination function index: A novel indicator for assessing hindlimb locomotor recovery in spinal cord injury rats based on catwalk gait parameters

In preclinical studies of spinal cord injury (SCI), behavioral assessments are crucial for evaluating treatment effectiveness. Commonly used methods include Basso, Beattie, Bresnahan (BBB) score and the Louisville swim scale (LSS), relying on subjective observations. The CatWalk automated gait analysis system is also widely used in SCI studies, providing extensive gait parameters from footprints. However, these parameters are often used independently or combined simply without utilizing the vast amount of data provided by CatWalk. Therefore, it is necessary to develop a novel approach encompassing multiple CatWalk parameters for a comprehensive and objective assessment of locomotor function. In this work, we screened 208 CatWalk XT gait parameters and identified 38 suitable for assessing hindlimb motor function recovery in a rat thoracic contusion SCI model. Exploratory factor analysis was used to reveal structural relationships among these parameters. Weighted scores for Coordination effectively differentiated hindlimb motor function levels, termed as the Coordinated Function Index (CFI). CFI showed high reliability, exhibiting high correlations with BBB scores, LSS, and T2WI lesion area. Finally, we simplified CFI based on factor loadings and correlation analysis, obtaining a streamlined version with reliable assessment efficacy. In conclusion, we developed a systematic assessment indicator utilizing multiple CatWalk parameters to objectively evaluate hindlimb motor function recovery in rats after thoracic contusion SCI.

Anisotropic microtopography surface of chitosan scaffold regulating skin precursor-derived Schwann cells towards repair phenotype promotes neural regeneration

For repairing peripheral nerve and spinal cord defects, biomaterial scaffold-based cell-therapy was emerged as an effective strategy, requiring the positive response of seed cells to biomaterial substrate and environment signals. Previous work highlighted that the imposed surface properties of scaffold could provide important guidance cues to adhered cells for polarization. However, the insufficiency of native Schwann cells and unclear cellular response mechanisms remained to be addressed. Given that, this study aimed to illuminate the micropatterned chitosan-film action on the rat skin precursor-derived Schwann cells (SKP-SCs). Chitosan-film with different ridge/groove size was fabricated and applied for the SKP-SCs induction. Results indicated that SKP-SCs cultured on 30 μm size microgroove surface showed better oriented alignment phenotype. Induced SKP-SCs presented similar genic phenotype as repair Schwann cells, increasing expression of c-Jun, neural cell adhesion molecule, and neurotrophic receptor p75. Moreover, SKP-SC-secretome was subjected to cytokine array GS67 assay, data indicated the regulation of paracrine phenotype, a panel of cytokines was verified up-regulated at secreted level and gene expression level in induced SKP-SCs. These up-regulated cytokines exhibit a series of promotive neural regeneration functions, including cell survival, cell migration, cell proliferation, angiogenesis, axon growth, and cellular organization etc. through bioinformatics analysis. Furthermore, the effectively polarized SKP-SCs-sourced secretome, promoted the proliferation and migration capacity of the primarily cultured native rat Schwann cells, and augmented neurites growth of the cultured motoneurons, as well as boosted axonal regrowth of the axotomy-injured motoneurons. Taken together, SKP-SCs obtained pro-neuroregeneration phenotype in adaptive response to the anisotropic topography surface of chitosan-film, displayed the oriented parallel growth, the transition towards repair Schwann cell genic phenotype, and the enhanced paracrine effect on neural regeneration. This study provided novel insights into the potency of anisotropic microtopography surface to Schwann-like cells phenotype regulation, that facilitating to provide promising engineered cell-scaffold in neural injury therapies.

Chondroitinase as a therapeutic enzyme: Prospects and challenges

The chondroitinases (Chase) are bacterial lyases that specifically digest chondroitin sulfate and/or dermatan sulfate glycosaminoglycans via a β-elimination reaction and generate unsaturated disaccharides. In recent decades, these enzymes have attracted the attention of many researchers due to their potential applications in various aspects of medicine from the treatment of spinal cord injury to use as an analytical tool. In spite of this diverse spectrum, the application of Chase is faced with several limitations and challenges such as thermal instability and lack of a suitable delivery system. In the current review, we address potential therapeutic applications of Chase with emphasis on the challenges ahead. Then, we summarize the latest achievements to overcome the problems by considering the studies carried out in the field of enzyme engineering, drug delivery, and combination-based therapy.

Schwann Cell-Derived Exosomal Vesicles: A Promising Therapy for the Injured Spinal Cord

Exosomes are nanoscale-sized membrane vesicles released by cells into their extracellular milieu. Within these nanovesicles reside a multitude of bioactive molecules, which orchestrate essential biological processes, including cell differentiation, proliferation, and survival, in the recipient cells. These bioactive properties of exosomes render them a promising choice for therapeutic use in the realm of tissue regeneration and repair. Exosomes possess notable positive attributes, including a high bioavailability, inherent safety, and stability, as well as the capacity to be functionalized so that drugs or biological agents can be encapsulated within them or to have their surface modified with ligands and receptors to imbue them with selective cell or tissue targeting. Remarkably, their small size and capacity for receptor-mediated transcytosis enable exosomes to cross the blood-brain barrier (BBB) and access the central nervous system (CNS). Unlike cell-based therapies, exosomes present fewer ethical constraints in their collection and direct use as a therapeutic approach in the human body. These advantageous qualities underscore the vast potential of exosomes as a treatment option for neurological injuries and diseases, setting them apart from other cell-based biological agents. Considering the therapeutic potential of exosomes, the current review seeks to specifically examine an area of investigation that encompasses the development of Schwann cell (SC)-derived exosomal vesicles (SCEVs) as an approach to spinal cord injury (SCI) protection and repair. SCs, the myelinating glia of the peripheral nervous system, have a long history of demonstrated benefit in repair of the injured spinal cord and peripheral nerves when transplanted, including their recent advancement to clinical investigations for feasibility and safety in humans. This review delves into the potential of utilizing SCEVs as a therapy for SCI, explores promising engineering strategies to customize SCEVs for specific actions, and examines how SCEVs may offer unique clinical advantages over SC transplantation for repair of the injured spinal cord.

Axonal growth inhibitors and their receptors in spinal cord injury: from biology to clinical translation

Axonal growth inhibitors are released during traumatic injuries to the adult mammalian central nervous system, including after spinal cord injury. These molecules accumulate at the injury site and form a highly inhibitory environment for axonal regeneration. Among these inhibitory molecules, myelin-associated inhibitors, including neurite outgrowth inhibitor A, oligodendrocyte myelin glycoprotein, myelin-associated glycoprotein, chondroitin sulfate proteoglycans and repulsive guidance molecule A are of particular importance. Due to their inhibitory nature, they represent exciting molecular targets to study axonal inhibition and regeneration after central injuries. These molecules are mainly produced by neurons, oligodendrocytes, and astrocytes within the scar and in its immediate vicinity. They exert their effects by binding to specific receptors, localized in the membranes of neurons. Receptors for these inhibitory cues include Nogo receptor 1, leucine-rich repeat, and Ig domain containing 1 and p75 neurotrophin receptor/tumor necrosis factor receptor superfamily member 19 (that form a receptor complex that binds all myelin-associated inhibitors), and also paired immunoglobulin-like receptor B. Chondroitin sulfate proteoglycans and repulsive guidance molecule A bind to Nogo receptor 1, Nogo receptor 3, receptor protein tyrosine phosphatase σ and leucocyte common antigen related phosphatase, and neogenin, respectively. Once activated, these receptors initiate downstream signaling pathways, the most common amongst them being the RhoA/ROCK signaling pathway. These signaling cascades result in actin depolymerization, neurite outgrowth inhibition, and failure to regenerate after spinal cord injury. Currently, there are no approved pharmacological treatments to overcome spinal cord injuries other than physical rehabilitation and management of the array of symptoms brought on by spinal cord injuries. However, several novel therapies aiming to modulate these inhibitory proteins and/or their receptors are under investigation in ongoing clinical trials. Investigation has also been demonstrating that combinatorial therapies of growth inhibitors with other therapies, such as growth factors or stem-cell therapies, produce stronger results and their potential application in the clinics opens new venues in spinal cord injury treatment.

A systematic review and meta-analysis of chondroitinase ABC promotes functional recovery in rat models of spinal cord injury

BACKGROUND

To comprehensively assess the neurologic recovery potential of chondroitinase ABC (ChABC) in rats after spinal cord injury (SCI).

METHODS

The PubMed, Embase, ScienceDirect, Web of Science, and China National Knowledge Infrastructure databases were searched for animal experiments that evaluated the use of ChABC in the treatment of SCI up to November 2022. Studies reporting neurological function using the Basso, Beattie, and Bresnahan (BBB) scale, as well as assessments of cavity area, lesion area, and glial fibrillary acidic protein (GFAP) levels, were included in the analysis.

RESULTS

A total of 46 studies were ultimately selected for inclusion. The results of the study showed that rats with SCI that received ChABC therapy exhibited a significant improvement in locomotor function after 7 days compared with controls (32 studies, weighted mean difference (WMD) = 0.58, [0.33, 0.83], p < 0.00001). Furthermore, the benefits of ChABC therapy were maintained for up to 28 days according to BBB scale. The lesion area was reduced by ChABC (5 studies, WMD = -20.94, [-28.42, -13.46], p < 0.00001). Meanwhile, GFAP levels were reduced in the ChABC treatment group (8 studies, WMD = -29.15, [-41.57, -16.72], p < 0.00001). Cavity area is not statistically significant. The subgroup analysis recommended that a single injection of 10 μL (8 studies, WMD = 2.82, [1.99, 3.65], p < 0.00001) or 20 U/mL (4 studies, WMD = 2.21, [0.73, 3.70], p = 0.003) had a better effect on improving the function. The funnel plot of the BBB scale was found to be essentially symmetrical, indicating a low risk of publication bias.

CONCLUSIONS

This systematic review and meta-analysis has indicated that ChABC could improve functional recovery in rats after SCI.

A Novel Magnetic Responsive miR-26a@SPIONs-OECs for Spinal Cord Injury: Triggering Neural Regeneration Program and Orienting Axon Guidance in Inhibitory Astrocytic Environment

Addressing the challenge of promoting directional axonal regeneration in a hostile astrocytic scar, which often impedes recovery following spinal cord injury (SCI), remains a daunting task. Cell transplantation is a promising strategy to facilitate nerve restoration in SCI. In this research, a pro-regeneration system is developed, namely miR-26a@SPIONs-OECs, for olfactory ensheathing cells (OECs), a preferred choice for promoting nerve regeneration in SCI patients. These entities show high responsiveness to external magnetic fields (MF), leading to synergistic multimodal cues to enhance nerve regeneration. First, an MF stimulates miR-26a@SPIONs-OECs to release extracellular vesicles (EVs) rich in miR-26a. This encourages axon growth by inhibiting PTEN and GSK-3β signaling pathways in neurons. Second, miR-26a@SPIONs-OECs exhibit a tendency to migrate and orientate along the direction of the MF, thereby potentially facilitating neuronal reconnection through directional neurite elongation. Third, miR-26a-enriched EVs from miR-26a@SPIONs-OECs can interact with host astrocytes, thereby diminishing inhibitory cues for neurite growth. In a rat model of SCI, the miR-26a@SPIONs-OECs system led to significantly improved morphological and motor function recovery. In summary, the miR-26a@SPIONS-OECs pro-regeneration system offers innovative insights into engineering exogenous cells with multiple additional cues, augmenting their efficacy for stimulating and guiding nerve regeneration within a hostile astrocytic scar in SCI.

Optogenetic spinal stimulation promotes new axonal growth and skilled forelimb recovery in rats with sub-chronic cervical spinal cord injury

Objective.Spinal cord injury (SCI) leads to debilitating sensorimotor deficits that greatly limit quality of life. This work aims to develop a mechanistic understanding of how to best promote functional recovery following SCI. Electrical spinal stimulation is one promising approach that is effective in both animal models and humans with SCI. Optogenetic stimulation is an alternative method of stimulating the spinal cord that allows for cell-type-specific stimulation. The present work investigates the effects of preferentially stimulating neurons within the spinal cord and not glial cells, termed 'neuron-specific' optogenetic spinal stimulation. We examined forelimb recovery, axonal growth, and vasculature after optogenetic or sham stimulation in rats with cervical SCI.Approach.Adult female rats received a moderate cervical hemicontusion followed by the injection of a neuron-specific optogenetic viral vector ipsilateral and caudal to the lesion site. Animals then began rehabilitation on the skilled forelimb reaching task. At four weeks post-injury, rats received a micro-light emitting diode (µLED) implant to optogenetically stimulate the caudal spinal cord. Stimulation began at six weeks post-injury and occurred in conjunction with activities to promote use of the forelimbs. Following six weeks of stimulation, rats were perfused, and tissue stained for GAP-43, laminin, Nissl bodies and myelin. Location of viral transduction and transduced cell types were also assessed.Main Results.Our results demonstrate that neuron-specific optogenetic spinal stimulation significantly enhances recovery of skilled forelimb reaching. We also found significantly more GAP-43 and laminin labeling in the optogenetically stimulated groups indicating stimulation promotes axonal growth and angiogenesis.Significance.These findings indicate that optogenetic stimulation is a robust neuromodulator that could enable future therapies and investigations into the role of specific cell types, pathways, and neuronal populations in supporting recovery after SCI.

Electrospun Piezoelectric Scaffold with External Mechanical Stimulation for Promoting Regeneration of Peripheral Nerve Injury

Safe and efficient provision of electrical stimulation (ES) for nerve repair and regeneration is a problem that needs to be addressed. In this study, a silk fibroin/poly(vinylidene fluoride-co-hexafluoropropylene)/Ti₃C₂T_x (SF/PVDF-HFP/MXene) composite scaffold with piezoelectricity was developed by electrospinning technology. MXene was loaded to the scaffold to enhance the piezoelectric properties (Output voltage reaches up to 100 mV), mechanical properties, and antibacterial activity. Cell experiments demonstrated piezoelectric stimulation under external ultrasonication for promoting the growth and proliferation of Schwann cells (SCs) cultured on this electrospun scaffold. Further in vivo study with rat sciatic nerve injury model revealed that the SF/PVDF-HFP/MXene nerve conduit could induce the proliferation of SCs, enhance the elongation of axon, and promote axonal myelination. Under the piezoelectric effect of this nerve scaffold, the rats with regenerative nerve exhibited a favorable recovery effect of motor and sensory function, indicating a safe and feasible method of using this SF/PVDF-HFP/MXene piezoelectric scaffold for ES provision in vivo.

A Multi-Stage Bioprocess for the Expansion of Rodent Skin-Derived Schwann Cells in Computer-Controlled Bioreactors

Regenerative therapies for the treatment of peripheral nerve and spinal cord injuries can require hundreds of millions of autologous cells. Current treatments involve the harvest of Schwann cells (SCs) from nerves; however, this is an invasive procedure. Therefore, a promising alternative is using skin-derived Schwann cells (Sk-SCs), in which between 3–5 million cells can be harvested from a standard skin biopsy. However, traditional static planar culture is still inefficient at expanding cells to clinically relevant numbers. As a result, bioreactors can be used to develop reproducible bioprocesses for the large-scale expansion of therapeutic cells. Here, we present a proof-of-concept SC manufacturing bioprocess using rat Sk-SCs. With this integrated process, we were able to simulate a feasible bioprocess, taking into consideration the harvest and shipment of cells to a production facility, the generation of the final cell product, and the cryopreservation and shipment of cells back to the clinic and patient. This process started with 3 million cells and inoculated and expanded them to over 200 million cells in 6 days. Following the harvest and post-harvest cryopreservation and thaw, we were able to maintain 150 million viable cells that exhibited a characteristic Schwann cell phenotype throughout each step of the process. This process led to a 50-fold expansion, producing a clinically relevant number of cells in a 500 mL bioreactor in just 1 week, which is a dramatic improvement over current methods of expansion.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Electrospun fiber-mediated delivery of neurotrophin-3 mRNA for neural tissue engineering applications

Aligned electrospun fibers provide topographical cues and local therapeutic delivery to facilitate robust peripheral nerve regeneration. mRNA delivery enables transient expression of desired proteins that promote axonal regeneration. However, no prior work delivers mRNA from electrospun fibers for peripheral nerve regeneration applications. Here, we developed the first aligned electrospun fibers to deliver pseudouridine-modified (Ψ) neurotrophin-3 (NT-3) mRNA (ΨNT-3mRNA) to primary Schwann cells and assessed NT-3 secretion and bioactivity. We first electrospun aligned poly(L-lactic acid) (PLLA) fibers and coated them with the anionic substrates dextran sulfate sodium salt (DSS) or poly(3,4-dihydroxy-L-phenylalanine) (pDOPA). Cationic lipoplexes containing ΨNT-3mRNA complexed to JetMESSENGER® were then immobilized to the fibers, resulting in detectable ΨNT-3mRNA release for 28 days from all fiber groups investigated (PLLA+mRNA, 0.5DSS4h+mRNA, and 2pDOPA4h+mRNA). The 2pDOPA4h+mRNA group significantly increased Schwann cell secretion of NT-3 for 21 days compared to control PLLA fibers (p < 0.001-0.05) and, on average, increased Schwann cell secretion of NT-3 by ≥ 2-fold compared to bolus mRNA delivery from the 1µgBolus+mRNA and 3µgBolus+mRNA groups. The 2pDOPA4h+mRNA fibers supported Schwann cell secretion of NT-3 at levels that significantly increased dorsal root ganglia (DRG) neurite extension by 44% (p < 0.0001) and neurite area by 64% (p < 0.001) compared to control PLLA fibers. The data show that the 2pDOPA4h+mRNA fibers enhance the ability of Schwann cells to promote neurite growth from DRG, demonstrating this platform's potential capability to improve peripheral nerve regeneration. STATEMENT OF SIGNIFICANCE: Aligned electrospun fibers enhance axonal regeneration by providing structural support and guidance cues, but further therapeutic stimulation is necessary to improve functional outcomes. mRNA delivery enables the transient expression of therapeutic proteins, yet achieving local, sustained delivery remains challenging. Previous work shows that genetic material delivery from electrospun fibers improves regeneration; however, mRNA delivery has not been explored. Here, we examine mRNA delivery from aligned electrospun fibers to enhance neurite outgrowth. We show that immobilization of NT-3mRNA/JetMESSENGER® lipoplexes to aligned electrospun fibers functionalized with pDOPA enables local, sustained NT-3mRNA delivery to Schwann cells, increasing Schwann cell secretion of NT-3 and enhancing DRG neurite outgrowth. This study displays the potential benefits of electrospun fiber-mediated mRNA delivery platforms for neural tissue engineering.

Chronic muscle recordings reveal recovery of forelimb function in spinal injured female rats after cortical epidural stimulation combined with rehabilitation and chondroitinase ABC

Cervical level spinal cord injury (SCI) can severely impact upper limb muscle function, which is typically assessed in the clinic using electromyography (EMG). Here, we established novel preclinical methodology for EMG assessments of muscle function after SCI in awake freely moving animals. Adult female rats were implanted with EMG recording electrodes in bicep muscles and received bilateral cervical (C7) contusion injuries. Forelimb muscle activity was assessed by recording maximum voluntary contractions during a grip strength task and cortical motor evoked potentials in the biceps. We demonstrate that longitudinal recordings of muscle activity in the same animal are feasible over a chronic post-injury time course and provide a sensitive method for revealing post-injury changes in muscle activity. This methodology was utilized to investigate recovery of muscle function after a novel combination therapy. Cervical contused animals received intraspinal injections of a neuroplasticity-promoting agent (lentiviral-chondroitinase ABC) plus 11 weeks of cortical epidural electrical stimulation (3 h daily, 5 days/week) and behavioral rehabilitation (15 min daily, 5 days/week). Longitudinal monitoring of voluntary and evoked muscle activity revealed significantly increased muscle activity and upper limb dexterity with the combination treatment, compared to a single treatment or no treatment. Retrograde mapping of motor neurons innervating the biceps showed a predominant distribution across spinal segments C5-C8, indicating that treatment effects were likely due to neuroplastic changes in a mixture of intact and injured motor neurons. Thus, longitudinal assessments of muscle function after SCI correlate with skilled reach and grasp performance and reveal functional benefits of a novel combination therapy.

Gene-Modified Stem Cells for Spinal Cord Injury: a Promising Better Alternative Therapy

Stem cell therapy holds great promise for the treatment of spinal cord injury (SCI), which can reverse neurodegeneration and promote tissue regeneration via its pluripotency and ability to secrete neurotrophic factors. Although various stem cell-based approaches have shown certain therapeutic effects when applied to the treatment of SCI, their clinical efficacies have been disappointing. Thus, it is an urgent need to further enhance the neurological benefits of stem cells through bioengineering strategies including genetic engineering. In this review, we summarize the progress of stem cell therapy for SCI and the prospect of genetically modified stem cells, focusing on the genome editing tools and functional molecules involved in SCI repair, trying to provide a deeper understanding of genetically modified stem cell therapy and more applicable clinical strategies for SCI repair.

Growth Factor Gene-Modified Cells in Spinal Cord Injury Recovery; a Systematic Review

BACKGROUND

Numerous pre-clinical studies have been performed in recent years on the effects of growth factor gene-modified cells' administration in spinal cord injury (SCI). However, findings of these studies are contradictory.

OBJECTIVE

The present study aims to conduct a systematic review and meta-analysis on animal studies evaluating the effects of growth factor gene-modified cells' administration on locomotion recovery following SCI.

METHODS

A search of the Medline, Embase, Scopus and Web of Science databases was conducted, including all animal studies until the end of 2020. Two researchers screened search results, summarized relevant studies and assessed risk of bias, independently.

RESULTS

Thirty-three studies were included in the final analysis. Transplantation of growth factor gene-modified cells in the injured spinal cord resulted in a significant improvement in animals' locomotion compared with non-treated animals [standardized mean difference (SMD)=1.86; 95% CI: 1.39-2.33; p<0.0001)] and non-genetically modified cells treated animals (SMD=1.30; 0.80-1.79; p<0.0001). Transplantation efficacy of these cells failed to achieve significance in moderate lesions (p=0.091), when using modified neural stem/progenitor cells (p=0.164), when using synthetic neurotrophins (p=0.086) and when the number of transplanted cells was less than 1.0 × 10⁵ cells per animal (p = 0.119).

CONCLUSION

The result showed that transplantation of growth factor gene-modified cells significantly improved locomotion in SCI animal models. However, there is a major concern regarding the safety of genetically modified cells' transplantation, in terms of overexpressing growth factors. Further studies are needed before any effort to perform a translational and clinical study.

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.

Protease Activated Receptor 1 and Its Ligands as Main Regulators of the Regeneration of Peripheral Nerves

In contrast with the brain and spinal cord, peripheral nerves possess a striking ability to regenerate after damage. This characteristic of the peripheral nervous system is mainly due to a specific population of glial cells, the Schwann cells. Schwann cells promptly activate after nerve injury, dedifferentiate assuming a repair phenotype, and assist axon regrowth. In general, tissue injury determines the release of a variety of proteases which, in parallel with the degradation of their specific targets, also activate plasma membrane receptors known as protease-activated receptors (PARs). PAR1, the prototypical member of the PAR family, is also known as thrombin receptor and is present at the Schwann cell plasma membrane. This receptor is emerging as a possible regulator of the pro-regenerative capacity of Schwann cells. Here, we summarize the most recent literature data describing the possible contribution of PAR1 and PAR1-activating proteases in regulating the regeneration of peripheral nerves.

Perspectives in the Cell-Based Therapies of Various Aspects of the Spinal Cord Injury-Associated Pathologies: Lessons from the Animal Models

Traumatic injury of the spinal cord (SCI) is a devastating neurological condition often leading to severe dysfunctions, therefore an improvement in clinical treatment for SCI patients is urgently needed. The potential benefits of transplantation of various cell types into the injured spinal cord have been intensively investigated in preclinical SCI models and clinical trials. Despite the many challenges that are still ahead, cell transplantation alone or in combination with other factors, such as artificial matrices, seems to be the most promising perspective. Here, we reviewed recent advances in cell-based experimental strategies supporting or restoring the function of the injured spinal cord with a particular focus on the regenerative mechanisms that could define their clinical translation.

Newly regenerated axons via scaffolds promote sub-lesional reorganization and motor recovery with epidural electrical stimulation

Here, we report the effect of newly regenerated axons via scaffolds on reorganization of spinal circuitry and restoration of motor functions with epidural electrical stimulation (EES). Motor recovery was evaluated for 7 weeks after spinal transection and following implantation with scaffolds seeded with neurotrophin producing Schwann cell and with rapamycin microspheres. Combined treatment with scaffolds and EES-enabled stepping led to functional improvement compared to groups with scaffold or EES, although, the number of axons across scaffolds was not different between groups. Re-transection through the scaffold at week 6 reduced EES-enabled stepping, still demonstrating better performance compared to the other groups. Greater synaptic reorganization in the presence of regenerated axons was found in group with combined therapy. These findings suggest that newly regenerated axons through cell-containing scaffolds with EES-enabled motor training reorganize the sub-lesional circuitry improving motor recovery, demonstrating that neuroregenerative and neuromodulatory therapies cumulatively enhancing motor function after complete SCI.

Scalable culture techniques to generate large numbers of purified human Schwann cells for clinical trials in human spinal cord and peripheral nerve injuries

OBJECTIVE

Schwann cells (SCs) have been shown to play an essential role in axon regeneration in both peripheral nerve injuries (PNIs) and spinal cord injuries (SCIs). The transplantation of SCs as an adjunctive therapy is currently under investigation in human clinical trials due to their regenerative capacity. Therefore, a reliable method for procuring large quantities of SCs from peripheral nerves is necessary. This paper presents a well-developed, validated, and optimized manufacturing protocol for clinical-grade SCs that are compliant with Current Good Manufacturing Practices (CGMPs).

METHODS

The authors evaluated the SC culture manufacturing data from 18 clinical trial participants who were recruited for autologous SC transplantation due to subacute SCI (n = 7), chronic SCI (n = 8), or PNIs (n = 3). To initiate autologous SC cultures, a mean nerve length of 11.8 ± 3.7 cm was harvested either from the sural nerve alone (n = 17) or with the sciatic nerve (n = 1). The nerves were digested with enzymes and SCs were isolated and further expanded in multiple passages to meet the dose requirements for transplantation.

RESULTS

An average yield of 87.2 ± 89.2 million cells at P2 and 150.9 ± 129.9 million cells at P3 with high viability and purity was produced. Cell counts and rates of expansion increased with each subsequent passage from P0 to P3, with the largest rate of expansion between P2 and P3. Larger harvest nerve lengths correlated significantly with greater yields at P0 and P1 (p < 0.05). In addition, a viability and purity above 90% was sustained throughout all passages in nearly all cell products.

CONCLUSIONS

This study presents reliable CGMP-compliant manufacturing methods for autologous SC products that are suitable for regenerative treatment of patients with SCI, PNI, or other conditions.

Combining cell therapy with human autologous Schwann cell and bone marrow-derived mesenchymal stem cell in patients with subacute complete spinal cord injury: safety considerations and possible outcomes

Background

Cellular transplantations have promising effects on treating spinal cord injury (SCI) patients. Mesenchymal stem cells (MSCs) and Schwann cells (SCs), which have safety alongside their complementary characteristics, are suggested to be the two of the best candidates in SCI treatment. In this study, we assessed the safety and possible outcomes of intrathecal co-transplantation of autologous bone marrow MSC and SC in patients with subacute traumatic complete SCI.

Methods

Eleven patients with complete SCI (American Spinal Injury Association Impairment Scale (AIS); grade A) were enrolled in this study during the subacute period of injury. The patients received an intrathecal autologous combination of MSC and SC and were followed up for 12 months. We assessed the neurological changes by the American Spinal Injury Association’s (ASIA) sensory-motor scale, functional recovery by spinal cord independence measure (SCIM-III), and subjective changes along with adverse events (AE) with our checklist. Furthermore, electromyography (EMG), nerve conduction velocity (NCV), magnetic resonance imaging (MRI), and urodynamic study (UDS) were conducted for all the patients at the baseline, 6 months, and 1 year after the intervention.

Results

Light touch AIS score alterations were approximately the same as the pinprick changes (11.6 ± 13.1 and 12 ± 13, respectively) in 50% of the cervical and 63% of the lumbar-thoracic patients, and both were more than the motor score alterations (9.5 ± 3.3 in 75% of the cervical and 14% of the lumbar-thoracic patients). SCIM III total scores (21.2 ± 13.3) and all its sub-scores (“respiration and sphincter management” (15 ± 9.9), “mobility” (9.5 ± 13.3), and “self-care” (6 ± 1.4)) had statistically significant changes after cell injection. Our findings support that the most remarkable positive, subjective improvements were in trunk movement, equilibrium in standing/sitting position, the sensation of the bladder and rectal filling, and the ability of voluntary voiding. Our safety evaluation revealed no systemic complications, and radiological images showed no neoplastic overgrowth, syringomyelia, or pseudo-meningocele.

Conclusion

The present study showed that autologous SC and bone marrow-derived MSC transplantation at the subacute stage of SCI could reveal statistically significant improvement in sensory and neurological functions among the patients. It appears that using this combination of cells is safe and effective for clinical application to spinal cord regeneration during the subacute period.

Effect of Schwann cell transplantation combined with electroacupuncture on axonal regeneration and remyelination in rats with spinal cord injury

Axonal impairment and demyelination after compressed spinal cord injury lead to serious neurological dysfunction. Increasing studies have suggested that Schwann cells (SCs) transplantation is a reliable, effective, and promising method for treating spinal cord injury. However, single SCs transplantation is insufficient to promote the full recovery of neurological function. Additional approaches are required to support SCs transplantation as a treatment for spinal cord injury. In the study, we investigated whether the combination of electroacupuncture (EA) and SCs transplantation was a reliable intervention for spinal cord injury. We found that rats in the combination group had significantly higher functional locomotor scores than those received single treatment. By immunostaining, we found EA can not only improve survival and proliferation of transplanted SCs but also inhibit SC apoptosis and block the formation of an astrocytic scar. Additionally, EA promoted regenerated axons extending "bullet-shaped" growth cones into the lesion. Remarkably, EA can modify astrogliosis to promote axonal regeneration following SCs transplantation through inducing extension of astrocytic processes in the SCs graft interface. More importantly, the combination of SCs engraftment and EA can enhance corticospinal-tract axonal regeneration and remyelination after spinal cord injury through up-regulating neuregulin 1 type III in SCs and its downstream signaling mediators. Thus, it is concluded that SCs effectively promote axonal recovery after spinal cord injury when combined with EA stimulation. The experimental results have reinforced the theoretical basis of EA for its clinical efficacy in patients with spinal cord injury and merited further investigation for potential clinical application.

An injectable and self-healing hydrogel with controlled release of curcumin to repair spinal cord injury

The harsh local micro-environment following spinal cord injury (SCI) remains a great challenge for neural regeneration. Local reconstitution of a favorable micro-environment by biocompatible scaffolds with desirable functions has thus been an area of concern. Herein, a hybrid hydrogel was developed using Fmoc-grafted chitosan (FC) and Fmoc peptide (FI). Dynamic reversible π-π stacking interactions of the fluorenyl rings enabled the FC/FI hybrid hydrogel to exhibit excellent injectable and self-healing properties, as characterized by visual appearances and rheological tests. Furthermore, the FC/FI hybrid hydrogel showed a slow and persistent release of curcumin (Cur), which was named as FC/FI-Cur hydrogel. In vitro studies confirmed that with the support of FC/FI-Cur hydrogel, neurite outgrowth was promoted, and Schwann cell (SC) migration away from dorsal root ganglia (DRG) spheres with enhanced myelination was substantiated. The FC/FI-Cur hydrogel well reassembled extracellular matrix at the lesion site of rat spinal cord and exerted outstanding effects in modulating local inflammatory reaction by regulating the phenotypes of infiltrated inflammatory cells. In addition, endogenous SCs were recruited in the FC/FI-Cur graft and participated in the remyelination process of the regenerated nerves. These outcomes favored functional recovery, as evidenced by improved hind limbs movement and enhanced electrophysiological properties. Thus, our study not only advanced the development of multifunctional hydrogels but also provided insights into comprehensive approaches for SCI repair.

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FC/FI hydrogel exhibited excellent injectable, self-healing properties, and performed well in releasing curcumin (Cur).

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FC/FI-Cur hydrogel promoted neurite outgrowth and myelination in vitro.

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FC/FI-Cur modulated local inflammatory reaction and recruited Schwann cells to repair spinal cord injury.

Comparison of the effects of two therapeutic strategies based on olfactory ensheathing cell transplantation and repetitive magnetic stimulation after spinal cord injury in female mice

Spinal cord injury (SCI) is a debilitating condition, which leads to a permanent loss of functions below the injury site. The events which take place after SCI are characterized by cellular death, release of inhibitory factors, and inflammation. Many therapies have been studied to cure SCI, among them magnetic stimulation aims to reduce the secondary damages in particular by decreasing apoptosis, while, cellular transplantation promotes neuroregeneration by enhancing axonal regrowth. In the present study, we compared individually primary olfactory ensheathing cell (OEC) transplantation and repetitive trans‐spinal magnetic stimulation (rTSMS) and then, we combined these two therapeutic approaches on tissue repair and functional recovery after SCI. To do so, SCIs were performed at Th10 level on female C57BL/6 mice, which were randomized into four groups: SCI, SCI + primary bOECs, SCI + STM, SCI + primary bulbar olfactory ensheathing cells (bOECs) + stimulation (STM). On these animals bioluminescence, immunohistological, and behavioral experiments were performed after SCI. Our results show that rTSMS has beneficial effect on the modulation of spinal scar by reducing fibrosis, demyelination, and microglial cell activation and by increasing the astroglial component of the scar, while, primary bOEC transplantation decreases microglial reactivity. At the opposite, locotronic experiments show that both treatments induce functional recovery. We did not observed any additional effect by combining the two therapeutic approaches. Taken together, the present study indicates that primary bOEC transplantation and rTSMS treatment act through different mechanisms after SCI to induce functional recovery. In our experimental paradigm, the combination of the two therapies does not induce any additional benefit.

Terminal Schwann Cell Aging: Implications for Age-Associated Neuromuscular Dysfunction

Action potential is transmitted to muscle fibers through specialized synaptic interfaces called neuromuscular junctions (NMJs). These structures are capped by terminal Schwann cells (tSCs), which play essential roles during formation and maintenance of the NMJ. tSCs are implicated in the correct communication between nerves and muscles, and in reinnervation upon injury. During aging, loss of muscle mass and strength (sarcopenia and dynapenia) are due, at least in part, to the progressive loss of contacts between muscle fibers and nerves. Despite the important role of tSCs in NMJ function, very little is known on their implication in the NMJ-aging process and in age-associated denervation. This review summarizes the current knowledge about the implication of tSCs in the age-associated degeneration of NMJs. We also speculate on the possible mechanisms underlying the observed phenotypes.

Delivery of chondroitinase by canine mucosal olfactory ensheathing cells alongside rehabilitation enhances recovery after spinal cord injury

Spinal cord injury (SCI) can cause chronic paralysis and incontinence and remains a major worldwide healthcare burden, with no regenerative treatment clinically available. Intraspinal transplantation of olfactory ensheathing cells (OECs) and injection of chondroitinase ABC (chABC) are both promising therapies but limited and unpredictable responses are seen, particularly in canine clinical trials. Sustained delivery of chABC presents a challenge due to its thermal instability; we hypothesised that transplantation of canine olfactory mucosal OECs genetically modified ex vivo by lentiviral transduction to express chABC (cOEC-chABC) would provide novel delivery of chABC and synergistic therapy. Rats were randomly divided into cOEC-chABC, cOEC, or vehicle transplanted groups and received transplant immediately after dorsal column crush corticospinal tract (CST) injury. Rehabilitation for forepaw reaching and blinded behavioural testing was conducted for 8 weeks. We show that cOEC-chABC transplanted animals recover greater forepaw reaching accuracy on Whishaw testing and more normal gait than cOEC transplanted or vehicle control rats. Increased CST axon sprouting cranial to the injury and serotonergic fibres caudal to the injury suggest a mechanism for recovery. We therefore demonstrate that cOECs can deliver sufficient chABC to drive modest functional improvement, and that this genetically engineered cellular and molecular approach is a feasible combination therapy for SCI.

Red-Light (670 nm) Therapy Reduces Mechanical Sensitivity and Neuronal Cell Death, and Alters Glial Responses after Spinal Cord Injury in Rats

Individuals with spinal cord injury (SCI) often develop debilitating neuropathic pain, which may be driven by neuronal damage and neuroinflammation. We have previously demonstrated that treatment using 670 nm (red) light irradiation alters microglia/macrophage responses and alleviates mechanical hypersensitivity at 7 days post-injury (dpi). Here, we investigated the effect of red light on the development of mechanical hypersensitivity, neuronal markers, and glial response in the subacute stage (days 1-7) following SCI. Wistar rats were subjected to a mild hemi-contusion SCI at vertebra T10 or to sham surgery followed by daily red-light treatment (30 min/day; 670 nm LED; 35 mW/cm²) or sham treatment. Mechanical sensitivity of the rat dorsum was assessed from 1 dpi and repeated every second day. Spinal cords were collected at 1, 3, 5, and 7 dpi for analysis of myelination, neurofilament protein NF200 expression, neuronal cell death, reactive astrocytes (glial fibrillary acidic protein [GFAP]⁺ cells), interleukin 1 β (IL-1β) expression, and inducible nitric oxide synthase (iNOS) production in IBA1⁺ microglia/macrophages. Red-light treatment significantly reduced the cumulative mechanical sensitivity and the hypersensitivity incidence following SCI. This effect was accompanied by significantly reduced neuronal cell death, reduced astrocyte activation, and reduced iNOS expression in IBA1⁺ cells at the level of the injury. However, myelin and NF200 immunoreactivity and IL-1β expression in GFAP⁺ and IBA1⁺ cells were not altered by red-light treatment. Thus, red-light therapy may represent a useful non-pharmacological approach for treating pain during the subacute period after SCI by decreasing neuronal loss and modulating the inflammatory glial response.

Intrathecal Delivery of BDNF Into the Lumbar Cistern Re-Engages Locomotor Stepping After Spinal Cord Injury

Delivery of neurotrophins to the spinal injury site via cellular transplants or viral vectors administration has been shown to promote recovery of locomotion in the absence of locomotor training in adult spinalized animals. These delivery methods involved risks of secondary injury to the cord and do not allow for precise and controlled dosing making them unsuitable for clinical applications. The present study was aimed at evaluating the locomotor recovery efficacy and safety of the neurotrophin BDNF delivered intrathecally to the lumbar locomotor centers using an implantable and programmable infusion mini-pump. Results showed that BDNF treated spinal cats recovered weight-bearing plantar stepping at all velocities tested (0.3-0.8 m/s). Spinal cats treated with saline did not recover stepping ability, especially at higher velocities, and dragged their hind paws on the treadmill. Histological evaluation showed minimal catheter associated trauma and tissue inflammation, underlining that intrathecal delivery by an implantable/programmable pump is a safe and effective method for delivery of a controlled BDNF dosage; it poses minimal risks to the cord and is clinically translational.

Aligned Fingolimod-Releasing Electrospun Fibers Increase Dorsal Root Ganglia Neurite Extension and Decrease Schwann Cell Expression of Promyelinating Factors

Researchers are investigating the use of biomaterials with aligned guidance cues, like those provided by aligned electrospun fibers, to facilitate axonal growth across critical-length peripheral nerve defects. To enhance the regenerative outcomes further, these aligned fibers can be designed to provide local, sustained release of therapeutics. The drug fingolimod improved peripheral nerve regeneration in preclinical rodent models by stimulating a pro-regenerative Schwann cell phenotype and axonal growth. However, the systemic delivery of fingolimod for nerve repair can lead to adverse effects, so it is necessary to develop a means of providing sustained delivery of fingolimod local to the injury. Here we created aligned fingolimod-releasing electrospun fibers that provide directional guidance cues in combination with the local, sustained release of fingolimod to enhance neurite outgrowth and stimulate a pro-regenerative Schwann cell phenotype. Electrospun fiber scaffolds were created by blending fingolimod into poly(lactic-co-glycolic acid) (PLGA) at a w/w% (drug/polymer) of 0.0004, 0.02, or 0.04%. We examined the effectiveness of these scaffolds to stimulate neurite extension in vitro by measuring neurite outgrowth from whole and dissociated dorsal root ganglia (DRG). Subsequently, we characterized Schwann cell migration and gene expression in vitro. The results show that drug-loaded PLGA fibers released fingolimod for 28 days, which is the longest reported release of fingolimod from electrospun fibers. Furthermore, the 0.02% fingolimod-loaded fibers enhanced neurite outgrowth from whole and dissociated DRG neurons, increased Schwann cell migration, and reduced the Schwann cell expression of promyelinating factors. The in vitro findings show the potential of the aligned fingolimod-releasing electrospun fibers to enhance peripheral nerve regeneration and serve as a basis for future in vivo studies.

Schwann Cell Cultures: Biology, Technology and Therapeutics

Schwann cell (SC) cultures from experimental animals and human donors can be prepared using nearly any type of nerve at any stage of maturation to render stage- and patient-specific populations. Methods to isolate, purify, expand in number, and differentiate SCs from adult, postnatal and embryonic sources are efficient and reproducible as these have resulted from accumulated refinements introduced over many decades of work. Albeit some exceptions, SCs can be passaged extensively while maintaining their normal proliferation and differentiation controls. Due to their lineage commitment and strong resistance to tumorigenic transformation, SCs are safe for use in therapeutic approaches in the peripheral and central nervous systems. This review summarizes the evolution of work that led to the robust technologies used today in SC culturing along with the main features of the primary and expanded SCs that make them irreplaceable models to understand SC biology in health and disease. Traditional and emerging approaches in SC culture are discussed in light of their prospective applications. Lastly, some basic assumptions in vitro SC models are identified in an attempt to uncover the combined value of old and new trends in culture protocols and the cellular products that are derived.

Secretion of a mammalian chondroitinase ABC aids glial integration at PNS/CNS boundaries

Schwann cell grafts support axonal growth following spinal cord injury, but a boundary forms between the implanted cells and host astrocytes. Axons are reluctant to exit the graft tissue in large part due to the surrounding inhibitory environment containing chondroitin sulphate proteoglycans (CSPGs). We use a lentiviral chondroitinase ABC, capable of being secreted from mammalian cells (mChABC), to examine the repercussions of CSPG digestion upon Schwann cell behaviour in vitro. We show that mChABC transduced Schwann cells robustly secrete substantial quantities of the enzyme causing large-scale CSPG digestion, facilitating the migration and adhesion of Schwann cells on inhibitory aggrecan and astrocytic substrates. Importantly, we show that secretion of the engineered enzyme can aid the intermingling of cells at the Schwann cell-astrocyte boundary, enabling growth of neurites over the putative graft/host interface. These data were echoed in vivo. This study demonstrates the profound effect of the enzyme on cellular motility, growth and migration. This provides a cellular mechanism for mChABC induced functional and behavioural recovery shown in in vivo studies. Importantly, we provide in vitro evidence that mChABC gene therapy is equally or more effective at producing these effects as a one-time application of commercially available ChABC.

Protective effect of brain-derived neurotrophic factor and neurotrophin-3 overexpression by adipose-derived stem cells combined with silk fibroin/chitosan scaffold in spinal cord injury

Objectives: Spinal cord injury (SCI) is a most debilitating traumatic injury, and cytotherapy is a promising alternative treatment strategy. Here we investigated the effect and mechanism of adipose-derived stem/stromal cells (ASCs) with overexpressing brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) (BDNF-NT3) in combination with silk fibroin/chitosan scaffold (SFCS) in SCI.Methods: Female Sprague-Dawley rats were used as an SCI model. SFCS,SFCS and ASCs, or ASCs overexpressing NT3, BDNF, and BDNF-NT3 were implanted into SCI rats. Basso, Beattie, and Bresnahan score, pathological changes, and spinal cord tissue and nerve fiber morphology were observed and assayed. GAP-43, GFAP, and caspase-3 expression was determined using immunohistochemistry and western blotting.Results: Smoother spinal cords, less scar tissue, and lower inflammatory activity were found in the SFCS, SFCS and ASCs, ASCs with NT3, BDNF, and BDNF-NT3 overexpression treatment than in the untreated SCI rat groups. Increasing formation of nerve fibers was observed in the above groups in order. GAP-43 expression significantly increased, while GFAP and caspase-3 expression significantly decreased. These results indicated obvious alleviation in pathological changes and BDNF-NT3 overexpression in ASCs combined with SFCS treatment in SCI rats.Conclusion: Thus, BDNF-NT3 overexpression from ASCs with SFCS had synergistic neuroprotective effects on SCI and may be a treatment option for SCI.

Low-energy extracorporeal shock wave therapy promotes BDNF expression and improves functional recovery after spinal cord injury in rats

Low-energy extracorporeal shock wave therapy (ESWT) has been used to treat various human diseases. Previous studies have shown that low-energy ESWT promotes the release of various cell growth factors and trophic factors from the cells surrounding the target lesion. The aim of the current study was to determine whether the application of low-energy ESWT upregulates the expression of brain-derived neurotrophic factor (BDNF) and reduces neural tissue damage and functional impairment using a rat model of thoracic spinal cord contusion injury. We found that low-energy ESWT promoted BDNF expression in the damaged neural tissue. The expression of BDNF was increased in various neural cells at the lesion. Additionally, low-energy ESWT increased the area of spared white matter and the number of oligodendrocytes in the injured spinal cord compared with untreated control animals. There were more axonal fibers around the injured site after the application of low-energy ESWT than control. Importantly, low-energy ESWT improved the locomotor functions evaluated by both the BBB scale and ladder rung walking test in addition to the sensory function measured using a von Frey test. Moreover, the electrophysiological assessment confirmed that the conductivity of the central motor pathway in the injured spinal cord was restored by low-energy ESWT. These findings indicate that low-energy ESWT promotes BDNF expression at the lesion site and reduces the neural tissue damage and functional impairment following spinal cord injury. Our results support the potential application of low-energy ESWT as a novel therapeutic strategy for treating spinal cord injury.

Magnetic Field Promotes Migration of Schwann Cells with Chondroitinase ABC (ChABC)-Loaded Superparamagnetic Nanoparticles Across Astrocyte Boundary in vitro

PURPOSE

The clinical outcome of spinal cord injury is usually poor due to the lack of axonal regeneration and glia scar formation. As one of the most classical supporting cells in neural regeneration, Schwann cells (SCs) provide bioactive substrates for axonal migration and release molecules that regulate axonal growth. However, the effect of SC transplantation is limited by their poor migration capacity in the astrocyte-rich central nervous system.

METHODS

In this study, we first magnetofected SCs with chondroitinase ABC-polyethylenimine functionalized superparamagnetic iron oxide nanoparticles (ChABC/PEI-SPIONs) to induce overexpression of ChABC for the removal of chondroitin sulfate proteoglycans. These are inhibitory factors and forming a dense scar that acts as a barrier to the regenerating axons. In vitro, we observed the migration of SCs in the region of astrocytes after the application of a stable external magnetic field.

RESULTS

We found that magnetofection with ChABC/PEI-SPIONs significantly up-regulated the expression of ChABC in SCs. Under the driven effect of the directional magnetic field (MF), the migration of magnetofected SCs was enhanced in the direction of the magnetic force. The number of SCs with ChABC/PEI-SPIONs migrated and the distance of migration into the astrocyte region was significantly increased. The number of SCs with ChABC/PEI-SPIONs that migrated into the astrocyte region was 11.6- and 4.6-fold higher than those observed for the intact control and non-MF groups, respectively. Furthermore, it was found that SCs with ChABC/PEI-SPIONs were in close contact with astrocytes and no longer formed boundaries in the presence of MF.

CONCLUSION

The mobility of the SCs with ChABC/PEI-SPIONs was enhanced along the axis of MF, holding the potential to promote nerve regeneration by providing a bioactive microenvironment and relieving glial obstruction to axonal regeneration in the treatment of spinal cord injury.

[Identification of biomarkers and new therapies for taxane-induced peripheral neuropathy]

Chemotherapy-induced peripheral neuropathy (CIPN) is a side effect frequently caused by taxanes. Because the mechanisms underlying CIPN pathogenesis remain to be fully elucidated, there is no indicator for objective diagnosis like a biomarker. In addition, treatment options for CIPN is still unsatisfactory. We have previously demonstrated that paclitaxel preferentially impair myelin-forming Schwann cells, and consequently induce dedifferentiation and demyelination of Schwann cells. Recently, in a paclitaxel CIPN model mouse, we found that an inflammatory factor is released from dedifferentiated Schwann cells in the mouse sciatic nerve into the blood, highly correlated with the on-set of mechanical hypersensitivity. On the other hand, considering our previous findings, it seems that some drugs, which supply newly formed mature Schwann cells at the sites of demyelinated lesions, may be a new beneficial therapy for taxane-induced peripheral neuropathy. In this review, we will introduce our findings about new therapeutic drug candidate for taxane-related CIPN based on this concept, and plasma biomarker to detect CIPN on-set and progression.

Catecholaminergic axons in the neocortex of adult mice regrow following brain injury

Serotonin axons in the adult rodent brain can regrow and recover their function following several forms of injury including controlled cortical impact (CCI), a neocortical stab wound, or systemic amphetamine toxicity. To assess whether this capacity for regrowth is unique to serotonergic fibers, we used CCI and stab injury models to assess whether fibers from other neuromodulatory systems can also regrow following injury. Using tyrosine-hydoxylase (TH) immunohistochemistry we measured the density of catecholaminergic axons before and at various time points after injury. One week after CCI injury we observed a pronounced loss, across cortical layers, of TH+ axons posterior to the site of injury. One month after CCI injury the same was true of TH+ axons both anterior and posterior to the site of injury. This loss was followed by significant recovery of TH+ fiber density across cortical layers, both anterior and posterior to the site of injury, measured three months after injury. TH+ axon loss and recovery over weeks to months was also observed throughout cortical layers using the stab injury model. Double label immunohistochemistry revealed that nearly all TH+ axons in neocortical layer 1/2 are also dopamine-beta-hyroxylase+ (DBH+; presumed norepinephrine), while TH+ axons in layer 5 are a mixture of DBH+ and dopamine transporter+ types. This suggests that noradrenergic axons can regrow following CCI or stab injury in the adult mouse neocortex and leaves open the question of whether dopaminergic axons can do the same.

Cell Therapeutic Strategies for Spinal Cord Injury

Significance: Spinal cord injury (SCI) is a neurological disorder that resulted from destroyed long axis of spinal cord, affecting thousands of people every year. With the occurrence of SCI, the lesions can form cystic cavities and produce glial scar, myelin inhibitor, and inflammation that negatively impact repair of spinal cord. Therefore, SCI remains a difficult problem to overcome with present therapeutics. This review of cell therapeutics in SCI provides a systematic review of combinatory therapeutics of SCI and helps the realization of regeneration of spinal cord in the future. Recent Advances: With major breakthroughs in neurobiology in recent years, present therapeutic strategies for SCI mainly aim at nerve regeneration or neuroprotection. For nerve regeneration, the application approaches are tissue engineering and cell transplantation, while drug therapeutics is applied for neuroprotection. Cell therapeutics is a new approach that treats SCI by cell transplantation. Cell therapeutics possesses advantages of neuroprotection, immune regulation, axonal regeneration, neuron relay formation, and remyelination. Critical Issues: Neurons cannot regenerate at the site of injury. Therefore, it is essential to find a repair strategy for remyelination, axon regeneration, and functional recovery. Cell therapeutics is emerging as the most promising approach for treating SCI. Future Directions: The future application of SCI therapy in clinical practice may require a combination of multiple strategies. A comprehensive treatment of injury of spinal cord is the focus of the present research. With the combination of different cell therapy strategies, future experiments will achieve more dramatic success in spinal cord repair.

Recent advances in the therapeutic uses of chondroitinase ABC

Many studies, using pre-clinical models of SCI, have demonstrated the efficacy of chondroitinase ABC as a treatment for spinal cord injury and this has been confirmed in laboratories worldwide and in several animal models. The aim of this review is report the current state of research in the field and to compare the relative efficacies of these new interventions to improve outcomes in both acute and chronic models of SCI. We also report new methods of chondroitinase delivery and the outcomes of two clinical trials using the enzyme to treat spinal cord injury in dogs and disc herniation in human patients. Recent studies have assessed the outcomes of combining chondroitinase with other strategies known to promote recovery following spinal cord injury and new approaches. Evidence is emerging that one of the most powerful combinations is that of chondroitinase with cell transplants. The particular benefits of each of the different cell types used for these transplant experiments are discussed. Combining chondroitinase with rehabilitation also improves outcomes. Gene therapy is an efficient method of enzyme delivery to the injured spinal cord and circumvents the issue of the enzyme's thermo-instability. Other methods of delivery, such as via nanoparticles or synthetic scaffolds, have shown promise; however, the outcomes from these experiments suggest that these methods of delivery require further optimization to achieve similar levels of efficacy to that obtained by a gene therapy approach. Pre-clinical models have also shown chondroitinase is efficacious in the treatment of other conditions, such as peripheral nerve injury, stroke, coronary reperfusion, Parkinson's disease and certain types of cancer. The wide range of conditions where the benefits of chondroitinase treatment have been demonstrated reflects the complex roles that chondroitin sulphate proteoglycans (its substrate) play in health and disease and warrants the enzyme's further development as a therapy.

Moving beyond the glial scar for spinal cord repair

Traumatic spinal cord injury results in severe and irreversible loss of function. The injury triggers a complex cascade of inflammatory and pathological processes, culminating in formation of a scar. While traditionally referred to as a glial scar, the spinal injury scar in fact comprises multiple cellular and extracellular components. This multidimensional nature should be considered when aiming to understand the role of scarring in limiting tissue repair and recovery. In this Review we discuss recent advances in understanding the composition and phenotypic characteristics of the spinal injury scar, the oversimplification of defining the scar in binary terms as good or bad, and the development of therapeutic approaches to target scar components to enable improved functional outcome after spinal cord injury.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Stem cell/cellular interventions in human spinal cord injury: Is it time to move from guidelines to regulations and legislations? Literature review and Spinal Cord Society position statement

PURPOSE

In preclinical studies, many stem cell/cellular interventions demonstrated robust regeneration and/or repair in case of SCI and were considered a promising therapeutic candidate. However, data from clinical studies are not robust. Despite lack of substantial evidence for the efficacy of these interventions in spinal cord injury (SCI), many clinics around the world offer them as "therapy." These "clinics" claim efficacy through patient testimonials and self-advertisement without any scientific evidence to validate their claims. Thus, SCS established a panel of experts to review published preclinical studies, clinical studies and current global guidelines/regulations on usage of cellular transplants and make recommendations for their clinical use.

METHODS

The literature review and draft position statement was compiled and circulated among the panel and relevant suggestions incorporated to reach consensus. This was discussed and finalized in an open forum during the SCS Annual Meeting, ISSICON.

RESULTS

Preclinical evidence suggests safety and clinical potency of cellular interventions after SCI. However, evidence from clinical studies consisted of mostly case reports or uncontrolled case series/studies. Data from animal studies cannot be generalized to human SCI with regard to toxicity prediction after auto/allograft transplantation.

CONCLUSIONS

Currently, cellular/stem cell transplantation for human SCI is experimental and needs to be tested through a valid clinical trial program. It is not ethical to provide unproven transplantation as therapy with commercial implications. To stop the malpractice of marketing such "unproven therapies" to a vulnerable population, it is crucial that all countries unite to form common, well-defined regulations/legislation on their use in SCI. These slides can be retrieved from Electronic Supplementary Material.

Serotonergic mechanisms in spinal cord injury

Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.

Spinal cord injury: pathophysiology, treatment strategies, associated challenges, and future implications

Axonal regeneration and formation of tripartite (axo-glial) junctions at damaged sites is a prerequisite for early repair of injured spinal cord. Transplantation of stem cells at such sites of damage which can generate both neuronal and glial population has gained impact in terms of recuperation upon infliction with spinal cord injury. In spite of the fact that a copious number of pre-clinical studies using different stem/progenitor cells have shown promising results at acute and subacute stages, at the chronic stages of injury their recovery rates have shown a drastic decline. Therefore, developing novel therapeutic strategies are the need of the hour in order to assuage secondary morbidity and effectuate improvement of the spinal cord injury (SCI)-afflicted patients' quality of life. The present review aims at providing an overview of the current treatment strategies and also gives an insight into the potential cell-based therapies for the treatment of SCI.

The protection of acute spinal cord injury by subarachnoid space injection of Danshen in animal models

CONTEXT/OBJECTIVE

Following acute spinal cord injury (ASCI) in rabbits, subarachnoid space injection of Danshen was performed to protect the neurological damage. In this study, we established rabbit models of spinal cord injury using a modified Allen's method.

DESIGN

After the operation introducing the injuries, the rabbits were randomized into two different groups, control group (normal saline, NS) and Danshen, a component extracted from Chinese herb, treatment group. Each rabbit was supplied with either the drug or placebo at 0.3 ml/kg each day through subarachnoid cavity.

SETTING

Rabbit model of acute spinal cord injury were used for the response to Danshen treatment.

PARTICIPANTS

Total 48 Chinese rabbits aged four∼ five months old provided by Experimental Animal Center of Hubei Province were used for this study.

INTERVENTIONS

Danshen drug or placebo was administered via a silicon tube embedded under the spinal dura mater to administer the drugs into subarachnoid cavity.

OUTCOME MEASURES

After the treatment, damage indicators including cell apoptosis, morphological changes and oxidative damages were assessed.

RESULTS

We found out that cell apoptosis was decreased after Danshen injection as determined by downregulation of apoptosis index (AI) by TUNEL analysis as well as propidium iodide (PI) percentage by FACS analysis. In the meanwhile, we observed cells after the treatment have increased numbers of BCL-2 positive cells, this indicated the antiapoptotic gene expression is increased after Danshen treatment. When we check the oxidative damage indicators, we found superoxide dismutase (SOD) was increased and malondiadehyde (MDA) levels were decreased after the treatment.

CONCLUSION

Danshen can protect ASCI through inhibition of oxidative damage in the injured cells and thus reduce the subsequent cell apoptosis in the spinal.

Proteomics analysis of Schwann cell-derived exosomes: a novel therapeutic strategy for central nervous system injury

Exosomes are nanometer-sized vesicles involved in intercellular communication, and they are released by various cell types. To learn about exosomes produced by Schwann cells (SCs) and to explore their potential function in repairing the central nervous system (CNS), we isolated exosomes from supernatants of SCs by ultracentrifugation, characterized them by electron microscopy and immunoblotting and determined their protein profile using proteomic analysis. The results demonstrated that Schwann cell-derived exosomes (SCDEs) were, on average, 106.5 nm in diameter, round, and had cup-like concavity and expressed exosome markers CD9 and Alix but not tumor susceptibility gene (TSG) 101. We identified a total of 433 proteins, among which 398 proteins overlapped with the ExoCarta database. According to their specific functions, we identified 12 proteins that are closely related to CNS repair and classified them by different potential mechanisms, such as axon regeneration and inflammation inhibition. Gene Oncology analysis indicated that SCDEs are mainly involved in signal transduction and cell communication. Biological pathway analysis showed that pathways are mostly involved in exosome biogenesis, formation, uptake and axon regeneration. Among the pathways, the neurotrophin, PI3K-Akt and cAMP signaling pathways played important roles in CNS repair. Our study isolated SCDEs, unveiled their contents, presented potential neurorestorative proteins and pathways and provided a rich proteomics data resource that will be valuable for future studies of the functions of individual proteins in neurodegenerative diseases.

Plasticity Induced Recovery of Breathing Occurs at Chronic Stages after Cervical Contusion

Severe midcervical contusion injury causes profound deficits throughout the respiratory motor system that last from acute to chronic time points post-injury. We use chondroitinase ABC (ChABC) to digest chondroitin sulphate proteoglycans within the extracellular matrix (ECM) surrounding the respiratory system at both acute and chronic time points post-injury to explore whether augmentation of plasticity can recover normal motor function. We demonstrate that, regardless of time post-injury or treatment application, the lesion cavity remains consistent, showing little regeneration or neuroprotection within our model. Through electromyography (EMG) recordings of multiple inspiratory muscles, however, we show that application of the enzyme at chronic time points post-injury initiates the recovery of normal breathing in previously paralyzed respiratory muscles. This reduced the need for compensatory activity throughout the motor system. Application of ChABC at acute time points recovered only modest amounts of respiratory function. To further understand this effect, we assessed the anatomical mechanism of this recovery. Increased EMG activity in previously paralyzed muscles was brought about by activation of spared bulbospinal pathways through the site of injury and/or sprouting of spared serotonergic fibers from the contralateral side of the cord. Accordingly, we demonstrate that alterations to the ECM and augmentation of plasticity at chronic time points post-cervical contusion can cause functional recovery of the respiratory motor system and reveal mechanistic evidence of the pathways that govern this effect.

Rapid and robust restoration of breathing long after spinal cord injury

There exists an abundance of barriers that hinder functional recovery following spinal cord injury, especially at chronic stages. Here, we examine the rescue of breathing up to 1.5 years following cervical hemisection in the rat. In spite of complete hemidiaphragm paralysis, a single injection of chondroitinase ABC in the phrenic motor pool restored robust and persistent diaphragm function while improving neuromuscular junction anatomy. This treatment strategy was more effective when applied chronically than when assessed acutely after injury. The addition of intermittent hypoxia conditioning further strengthened the ventilatory response. However, in a sub-population of animals, this combination treatment caused excess serotonergic (5HT) axon sprouting leading to aberrant tonic activity in the diaphragm that could be mitigated via 5HT2 receptor blockade. Through unmasking of the continuing neuroplasticity that develops after injury, our treatment strategy ensured rapid and robust patterned respiratory recovery after a near lifetime of paralysis.

Respiratory failure is one of the leading causes of death following spinal cord injury and it is unclear if normal respiratory motor activity can be recovered after chronic injury-induced paralysis. Here, authors show that treatment with chondroitinase ABC induces robust rescue of breathing up to 1.5 years following complete hemidiaphragm paralysis.

CXCL12 has therapeutic value in facial nerve injury and promotes Schwann cells autophagy and migration via PI3K-AKT-mTOR signal pathway

Facial nerve injury is a clinically common disease accompanied by demyelination of damaged nerves. The remyelination of damaged nerves and the unsatisfactory function recovery are problems that have been plaguing people for a long time. The role that CXCL12 plays after facial nerve injury remains unknown. Our experiments found that the expression of CXCL12 was up-regulated in the early stage of facial nerve injury and decreased after two weeks. Further research found that CXCL12 had no effect on Schwann cells proliferation, apoptosis and cell cycle, while significantly promoted Schwann cells migration. Treatment with CXCL12 decreased the phosphorylation of PI3K, AKT and mTOR, but increased autophagy marker LC3II/I. The CXCL12-induced Schwann cells migration was significantly attenuated by inhibition of autophagy and activation of PI3K pathway through pretreatment with 3-MA and IGF-1 respectively, and this effect was enhanced by PI3K pathway inhibitor LY294002. Animal experiment also confirmed that CXCL12 could improve facial nerve function and myelin regeneration. The findings of this study indicate that CXCL12 can promote the migration of Schwann cells and potentially become a key molecule in the repair of facial nerve injury.