Schwann cells genetically modified to secrete human BDNF promote enhanced axonal regrowth across transected adult rat spinal cord

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.

Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The axonal growth-restrictive character of traumatic spinal cord injury (SCI) makes finding a therapeutic strategy a very demanding task, due to the postinjury events impeditive to spontaneous axonal outgrowth and regeneration. Considering SCI pathophysiology complexity, it has been suggested that an effective therapy should tackle all the SCI-related aspects and provide sensory and motor improvement to SCI patients. Thus, the current aim of any therapeutic approach for SCI relies in providing neuroprotection and support neuroregeneration. Acknowledging the current SCI treatment paradigm, cell transplantation is one of the most explored approaches for SCI with mesenchymal stem cells (MSCs) being in the forefront of many of these. Studies showing the beneficial effects of MSC transplantation after SCI have been proposing a paracrine action of these cells on the injured tissues, through the secretion of protective and trophic factors, rather than attributing it to the action of cells itself. This manuscript provides detailed information on the most recent data regarding the neuroregenerative effect of the secretome of MSCs as a cell-free based therapy for SCI. The main challenge of any strategy proposed for SCI treatment relies in obtaining robust preclinical evidence from in vitro and in vivo models, before moving to the clinics, so we have specifically focused on the available vertebrate and mammal models of SCI currently used in research and how can SCI field benefit from them.

BDNF-Gene Transfected Schwann Cell-Assisted Axonal Extension and Sprouting on New PLA-PPy Microfiber Substrates

The work here reported analyzes the effect of increased efficiency of brain-derived neurotrophic factor (BDNF) production by electroporated Schwann cells (SCs) on the axonal extension in a coculture system on a biomaterial platform that can be of interest for the treatment of injuries of the nervous system, both central and peripheral. Rat SCs are electrotransfected with a plasmid coding for the BDNF protein in order to achieve an increased expression and release of this protein into the culture medium of the cells, performing the best balance between the level of transfection and the number of living cells. Gene-transfected SCs show an about 100-fold increase in the release of BDNF into the culture medium, compared to nonelectroporated SCs. Cocultivation of electroporated SCs with rat dorsal root ganglia (DRG) is performed on highly aligned substrates of polylactic acid (PLA) microfibers coated with the electroconductive polymer polypyrrol (PPy). The coculture of DRG with electrotransfected SCs increase both the axonal extension and the axonal sprouting from DRG neurons compared to the coculture of DRG with nonelectroporated SCs. Therefore, the use of PLA-PPy highly aligned microfiber substrates preseeded with electrotransfected SCs with an increased BDNF secretion is capable of both guiding and accelerating axonal growth.

Cutaneous Inputs to Dorsal Column Nuclei in Adult Macaque Monkeys Subjected to Unilateral Lesion of the Primary Motor Cortex or of the Cervical Spinal Cord and Treatments Promoting Axonal Growth

The highly interconnected somatosensory and motor systems are subjected to connectivity changes at close or remote locations following a central nervous system injury. What is the impact of unilateral injury of the primary motor cortex (hand area; MCI) or of the cervical cord (hemisection at C7-C8 level; SCI) on the primary somatosensory (cutaneous) inputs to the dorsal column nuclei (DCN) in adult macaque monkeys? The effects of treatments promoting axonal growth were assessed. In the SCI group (n = 4), 1 monkey received a control antibody and 3 monkeys a combination treatment of anti-Nogo-A antibody and brain-derived neurotrophic factor (BDNF). In the MCI group (n = 4), 2 monkeys were untreated and 2 were treated with the anti-Nogo-A antibody. Using trans-ganglionic transport of cholera toxin B subunit injected in the first 2 fingers and toes on both sides, the areas of axonal terminal fields in the cuneate and gracile nuclei were bilaterally compared. Unilateral SCI at C7-C8 level, encroaching partially on the dorsal funiculus, resulted in an ipsilesional lower extent of the inputs from the toes in the gracile nuclei, not modified by the combined treatment. SCI at C7-C8 level did not affect the bilateral balance of primary inputs to the cuneate nuclei, neither in absence nor in presence of the combined treatment. MCI targeted to the hand area did not impact on the primary inputs to the cuneate nuclei in 2 untreated monkeys. After MCI, the administration of anti-Nogo-A antibody resulted in a slight bilateral asymmetrical extent of cutaneous inputs to the cuneate nuclei, with a larger extent ipsilesionally. Overall, remote effects following MCI or SCI have not been observed at the DCN level, except possibly after MCI and anti-Nogo-A antibody treatment.

Schwann Cell-Like Cells: Origin and Usability for Repair and Regeneration of the Peripheral and Central Nervous System

Functional recovery after neurotmesis, a complete transection of the nerve fiber, is often poor and requires a surgical procedure. Especially for longer gaps (>3 mm), end-to-end suturing of the proximal to the distal part is not possible, thus requiring nerve graft implantation. Artificial nerve grafts, i.e., hollow fibers, hydrogels, chitosan, collagen conduits, and decellularized scaffolds hold promise provided that these structures are populated with Schwann cells (SC) that are widely accepted to promote peripheral and spinal cord regeneration. However, these cells must be collected from the healthy peripheral nerves, resulting in significant time delay for treatment and undesired morbidities for the donors. Therefore, there is a clear need to explore the viable source of cells with a regenerative potential similar to SC. For this, we analyzed the literature for the generation of Schwann cell-like cells (SCLC) from stem cells of different origins (i.e., mesenchymal stem cells, pluripotent stem cells, and genetically programmed somatic cells) and compared their biological performance to promote axonal regeneration. Thus, the present review accounts for current developments in the field of SCLC differentiation, their applications in peripheral and central nervous system injury, and provides insights for future strategies.

Method and Apparatus for the Automated Delivery of Continuous Neural Stem Cell Trails Into the Spinal Cord of Small and Large Animals

BACKGROUND

Immature neurons can extend processes after transplantation in adult animals. Neuronal relays can form between injected neural stem cells (NSCs) and surviving neurons, possibly improving recovery after spinal cord injury (SCI). Cell delivery methods of single or multiple bolus injections of concentrated cell suspensions thus far tested in preclinical and clinical experiments are suboptimal for new tract formation. Nonuniform injectate dispersal is often seen due to gravitational cell settling and clumping. Multiple injections have additive risks of hemorrhage, parenchymal damage, and cellular reflux and require additional surgical exposure. The deposition of multiply delivered cells boluses may be uneven and discontinuous.

OBJECTIVE

To develop an injection apparatus and methodology to deliver continuous cellular trails bridging spinal cord lesions.

METHODS

We improved the uniformity of cellular trails by formulating NSCs in hyaluronic acid. The TrailmakerTM stereotaxic injection device was automatized to extend a shape memory needle from a single-entry point in the spinal cord longitudinal axis to "pioneer" a new trail space and then retract while depositing an hyaluronic acid-NSC suspension. We conducted testing in a collagen spinal models, and animal testing using human NSCs (hNSCs) in rats and minipigs.

RESULTS

Continuous surviving trails of hNSCs within rat and minipig naive spinal cords were 12 and 40 mm in length. hNSC trails were delivered across semi-acute contusion injuries in rats. Transplanted hNSCs survived and were able to differentiate into neural lineage cells and astrocytes.

CONCLUSION

The TrailmakerTM creates longitudinal cellular trails spanning multiple levels from a single-entry point. This may enhance the ability of therapeutics to promote functional relays after SCI.

Neural crest derived stem cells from dental pulp and tooth-associated stem cells for peripheral nerve regeneration

The peripheral nerve injuries, representing some of the most common types of traumatic lesions affecting the nervous system, are highly invalidating for the patients besides being a huge social burden. Although peripheral nervous system owns a higher regenerative capacity than does central nervous system, mostly depending on Schwann cells intervention in injury repair, several factors determine the extent of functional outcome after healing. Based on the injury type, different therapeutic approaches have been investigated so far. Nerve grafting and Schwann cell transplantation have represented the gold standard treatment for peripheral nerve injuries, however these approaches own limitations, such as scarce donor nerve availability and donor site morbidity. Cell based therapies might provide a suitable tool for peripheral nerve regeneration, in fact, the ability of different stem cell types to differentiate towards Schwann cells in combination with the use of different scaffolds have been widely investigated in animal models of peripheral nerve injuries in the last decade. Dental pulp is a promising cell source for regenerative medicine, because of the ease of isolation procedures, stem cell proliferation and multipotency abilities, which are due to the embryological origin from neural crest. In this article we review the literature concerning the application of tooth derived stem cell populations combined with different conduits to peripheral nerve injuries animal models, highlighting their regenerative contribution exerted through either glial differentiation and neuroprotective/neurotrophic effects on the host tissue.

In situ injectable hydrogels for spinal cord regeneration: advances from the last 10 years

Spinal cord injury (SCI) is a tremendously devastating disorder with no effective therapy. Neuroprotective strategies have been applied aiming to prevent secondary cell death but no successful and robust effects have been observed. Recently, combinatorial approaches using biomaterials with cells and/or growth factors have demonstrated promising therapeutic effects because of the improvement of axonal growth and in vivo functional recovery in model organisms. In situ injectable hydrogels are a particularly attractive neuroregenerative approach to improve spinal cord repair and regeneration since they can be precisely injected into the lesion site filling the space prior to gelification, decrease scarring and promote axon growth due to the hydrogel's soft structure. Important advances regarding the use of hydrogels as potential therapeutic approaches has been reported during the last 10 years. Injectable alginate hydrogel loaded with GDNF, thermoresponsives heparin-poloxamer loaded with NGF and imidazole-poly(organophosphazenes) hydrogels are just three examples of biomaterials that can promote neurite, axon growth and improve functional recovery in hemisected and resected rats. Here we will review the status of in situ injectable hydrogels for spinal cord regeneration with special focus in the advantages of using hydrogel scaffolds, the ideal polymers to be used, the gelification process and the cells or growth factors combined. The in vitro and in vivo results reported for those biomaterials will be presented, compared and discussed.

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Cellular therapies play a critical role in the treatment of spinal cord injury (SCI). Compared with cell-seeded conduits, fully cellular grafts have more similarities with autografts, and thus might result in better regeneration effects. In this study, we fabricated Schwann cell (SC)-neural stem cell (NSC) core–shell alginate hydrogel fibers in a coaxial extrusion manner. The rat SC line RSC96 and mouse NSC line NE-4C were used in this experiment. Fully cellular components were achieved in the core portion and the relative spatial positions of these two cells partially mimic the construction of nerve fibers in vivo. SCs were demonstrated to express more genes of neurotrophic factors in alginate shell. Enhanced proliferation and differentiation tendency of NSCs was observed when they were co-cultured with SCs. This model has strong potential for application in SCI repair.

A Milled Microdevice to Advance Glia-Mediated Therapies in the Adult Nervous System

Neurodegenerative disorders affect millions of adults worldwide. Neuroglia have become recent therapeutic targets due to their reparative abilities in the recycling of exogenous neurotoxins and production of endogenous growth factors for proper functioning of the adult nervous system (NS). Since neuroglia respond effectively to stimuli within in vivo environments on the micron scale, adult glial physiology has remarkable synergy with microscale systems. While clinical studies have begun to explore the reparative action of Müller glia (MG) of the visual system and Schwann Cells (ShC) of the peripheral NS after neural injury, few platforms enable the study of intrinsic neuroglia responses to changes in the local microenvironment. This project developed a low-cost, benchtop-friendly microfluidic system called the glia line system, or gLL, to advance the cellular study needed for emerging glial-based therapies. The gLL was fabricated using elastomeric kits coupled with a metal mold milled via conventional computer numerical controlled (CNC) machines. Experiments used the gLL to measure the viability, adhesion, proliferation, and migration of MG and ShC within scales similar to their respective in vivo microenvironments. Results illustrate differences in neuroglia adhesion patterns and chemotactic behavior significant to advances in regenerative medicine using implants and biomaterials, as well as cell transplantation techniques. Data showed highest survival and proliferation of MG and ShC upon laminin and illustrated a four-fold and two-fold increase of MG migration to dosage-dependent signaling from vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF), respectively, as well as a 20-fold increase of ShC migration toward exogenous brain-derived neurotrophic factor (BDNF), compared to media control. The ability to quantify these biological parameters within the gLL offers an effective and reliable alternative to photolithography study neuroglia in a local environment ranging from the tens to hundreds of microns, using a low-cost and easily fabricated system.

Macrophage depletion and Schwann cell transplantation reduce cyst size after rat contusive spinal cord injury

Schwann cell transplantation is a promising therapy for the treatment of spinal cord injury (SCI) and is currently in clinical trials. In our continuing efforts to improve Schwann cell transplantation strategies, we sought to determine the combined effects of Schwann cell transplantation with macrophage depletion. Since macrophages are major inflammatory contributors to the acute spinal cord injury, and are the major phagocytic cells, we hypothesized that transplanting Schwann cells after macrophage depletion will improve cell survival and integration with host tissue after SCI. To test this hypothesis, rat models of contusive SCI at thoracic level 8 were randomly subjected to macrophage depletion or not. In rat subjected to macrophage depletion, liposomes filled with clodronate were intraperitoneally injected at 1, 3, 6, 11, and 18 days post injury. Rats not subjected to macrophage depletion were intraperitoneally injected with liposomes filled with phosphate buffered saline. Schwann cells were transplanted 1 week post injury in all rats. Biotinylated dextran amine (BDA) was injected at thoracic level 5 to evalute axon regeneration. The Basso, Beattie, and Bresnahan locomotor test, Gridwalk test, and sensory test using von Frey filaments were performed to assess functional recovery. Immunohistochemistry was used to detect glial fibrillary acidic protein, neurofilament, and green fluorescent protein (GFP), and also to visulize BDA-labelled axons. The GFP labeled Schwann cell and cyst and lesion volumes were quantified using stained slides. The numbers of BDA-positive axons were also quantified. At 8 weeks after Schwann cell transplantation, there was a significant reduction in cyst and lesion volumes in the combined treatment group compared to Schwann cell transplantation alone. These changes were not associated, however, with improved Schwann cell survival, axon growth, or locomotor recovery. Although combining Schwann cell transplantation with macrophage depletion does improve histopathology of the injury site, the effect on axon growth and behavioral recovery appears no better than what can be achieved with Schwann cell transplants alone.

Axonal regeneration of different tracts following transplants of human glial restricted progenitors into the injured spinal cord in rats

The goal of this study was to compare the efficacy of human glial restricted progenitors (hGRPs) in promoting axonal growth of different tracts. We examined the potential of hGRPs grafted into a cervical (C4) dorsal column lesion to test sensory axons, and into a C4 hemisection to test motor tracts. The hGRPs, thawed from frozen stocks, were suspended in a PureCol matrix and grafted acutely into a C4 dorsal column or hemisection lesion. Control rats received PureCol only. Five weeks after transplantation, all transplanted cells survived in rats with the dorsal column lesion but only about half of the grafts in the hemisection. In the dorsal column lesion group, few sensory axons grew short distances into the lesion site of control animals. The presence of hGRPs transplants enhanced axonal growth significantly farther into the transplants. In the hemisection group, coerulospinal axons extended similarly into both control and transplant groups with no enhancement by the presence of hGRPs. Rubrospinal axons did not grow into the lesion even in the presence of hGRPs. However, reticulospinal and raphespinal axons grew for a significantly longer distance into the transplants. These results demonstrate the differential capacity of axonal growth/regeneration of the motor and sensory tracts based on their intrinsic abilities as well as their response to the modified environment induced by the hGRPs transplants. We conclude that hGRP transplants can modify the injury site for axon growth of sensory and some motor tracts, and suggest they could be combined with other interventions to restore connectivity.

Cell therapy for spinal cord injury with olfactory ensheathing glia cells (OECs)

The prospects of achieving regeneration in the central nervous system (CNS) have changed, as most recent findings indicate that several species, including humans, can produce neurons in adulthood. Studies targeting this property may be considered as potential therapeutic strategies to respond to injury or the effects of demyelinating diseases in the CNS. While CNS trauma may interrupt the axonal tracts that connect neurons with their targets, some neurons remain alive, as seen in optic nerve and spinal cord (SC) injuries (SCIs). The devastating consequences of SCIs are due to the immediate and significant disruption of the ascending and descending spinal pathways, which result in varying degrees of motor and sensory impairment. Recent therapeutic studies for SCI have focused on cell transplantation in animal models, using cells capable of inducing axon regeneration like Schwann cells (SchCs), astrocytes, genetically modified fibroblasts and olfactory ensheathing glia cells (OECs). Nevertheless, and despite the improvements in such cell-based therapeutic strategies, there is still little information regarding the mechanisms underlying the success of transplantation and regarding any secondary effects. Therefore, further studies are needed to clarify these issues. In this review, we highlight the properties of OECs that make them suitable to achieve neuroplasticity/neuroregeneration in SCI. OECs can interact with the glial scar, stimulate angiogenesis, axon outgrowth and remyelination, improving functional outcomes following lesion. Furthermore, we present evidence of the utility of cell therapy with OECs to treat SCI, both from animal models and clinical studies performed on SCI patients, providing promising results for future treatments.

Thermosensitive heparin-poloxamer hydrogels enhance the effects of GDNF on neuronal circuit remodeling and neuroprotection after spinal cord injury

Traumatic spinal cord injury (SCI) results in paraplegia or quadriplegia, and currently, therapeutic interventions for axonal regeneration after SCI are not clinically available. Animal studies have revealed that glial cell-derived neurotrophic factor (GDNF) plays multiple beneficial roles in neuroprotection, glial scarring remodeling, axon regeneration and remyelination in SCI. However, the poor physicochemical stability of GDNF, as well as its limited ability to cross the blood-spinal cord barrier, hampers the development of GDNF as an effective therapeutic intervention in clinical practice. In this study, a novel temperature-sensitive heparin-poloxamer (HP) hydrogel with high GDNF-binding affinity was developed. HP hydrogels showed a supporting scaffold for GDNF when it was injected into the lesion epicenter after SCI. GDNF-HP by orthotopic injection on lesioned spinal cord promoted the beneficial effects of GDNF on neural stem cell proliferation, reactive astrogliosis inhibition, axonal regeneration or plasticity, neuroprotection against cell apoptosis, and body functional recovery. Most interestingly, GDNF demonstrated a bidirectional regulation of autophagy, which inhibited cell apoptosis at different stages of SCI. Furthermore, the HP hydrogel promoted the inhibition of autophagy-induced apoptosis by GDNF in SCI. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2816-2829, 2017.

Transdifferentiation of brain-derived neurotrophic factor (BDNF)-secreting mesenchymal stem cells significantly enhance BDNF secretion and Schwann cell marker proteins

The use of genetically modified mesenchymal stem cells (MSCs) is a rapidly growing area of research targeting delivery of therapeutic factors for neuro-repair. Cells can be programmed to hypersecrete various growth/trophic factors such as brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and nerve growth factor (NGF) to promote regenerative neurite outgrowth. In addition to genetic modifications, MSCs can be subjected to transdifferentiation protocols to generate neural cell types to physically and biologically support nerve regeneration. In this study, we have taken a novel approach by combining these two unique strategies and evaluated the impact of transdifferentiating genetically modified MSCs into a Schwann cell-like phenotype. After 8 days in transdifferentiation media, approximately 30-50% of transdifferentiated BDNF-secreting cells immunolabeled for Schwann cell markers such as S100β, S100, and p75^NTR. An enhancement was observed 20 days after inducing transdifferentiation with minimal decreases in expression levels. BDNF production was quantified by ELISA, and its biological activity tested via the PC12-TrkB cell assay. Importantly, the bioactivity of secreted BDNF was verified by the increased neurite outgrowth of PC12-TrkB cells. These findings demonstrate that not only is BDNF actively secreted by the transdifferentiated BDNF-MSCs, but also that it has the capacity to promote neurite sprouting and regeneration. Given the fact that BDNF production remained stable for over 20 days, we believe that these cells have the capacity to produce sustainable, effective, BDNF concentrations over prolonged time periods and should be tested within an in vivo system for future experiments.

Schwann Cell Transplantation Improves Reticulospinal Axon Growth and Forelimb Strength after Severe Cervical Spinal Cord Contusion

Schwann cell (SC) implantation alone has been shown to promote the growth of propriospinal and sensory axons, but not long-tract descending axons, after thoracic spinal cord injury (SCI). In the current study, we examined if an axotomy close to the cell body of origin (so as to enhance the intrinsic growth response) could permit supraspinal axons to grow onto SC grafts. Adult female Fischer rats received a severe (C5) cervical contusion (1.1 mm displacement, 3 KDyn). At 1 week postinjury, 2 million SCs ex vivo transduced with lentiviral vector encoding enhanced green fluorescent protein (EGFP) were implanted within media into the injury epicenter; injury-only animals served as controls. Animals were tested weekly using the BBB score for 7 weeks postimplantation and received at end point tests for upper body strength: self-supported forelimb hanging, forearm grip force, and the incline plane. Following behavioral assessment, animals were anterogradely traced bilaterally from the reticular formation using BDA-Texas Red. Stereological quantification revealed a twofold increase in the numbers of preserved NeuN+ neurons rostral and caudal to the injury/graft site in SC implanted animals, corroborating previous reports of their neuroprotective efficacy. Examination of labeled reticulospinal axon growth revealed that while rarely an axon was present within the lesion site of injury-only controls, numerous reticulospinal axons had penetrated the SC implant/lesion milieu. This has not been observed following implantation of SCs alone into the injured thoracic spinal cord. Significant behavioral improvements over injury-only controls in upper limb strength, including an enhanced grip strength (a 296% increase) and an increased self-supported forelimb hanging, accompanied SC-mediated neuroprotection and reticulospinal axon growth. The current study further supports the neuroprotective efficacy of SC implants after SCI and demonstrates that SCs alone are capable of supporting modest supraspinal axon growth when the site of axon injury is closer to the cell body of the axotomized neuron.

The Proliferation Enhancing Effects of Salidroside on Schwann Cells In Vitro

Derived from Rhodiola rosea L., which is a popular plant in Eastern Europe and Asia, salidroside has pharmacological properties including antiviral, anticancer, hepatoprotective, antidiabetic, and antioxidative effects. Recent studies show that salidroside has neurotrophic and neuroprotective effects. However, the effect of salidroside on Schwann cells (SCs) and the underlying mechanisms of the salidroside-induced neurotrophin secretion have seldom been studied. In this study, the effect of salidroside on the survival, proliferation, and gene expression of Schwann cells lineage (RSC96) was studied through the examinations of the cell viability, proliferation, morphology, and expression of neurotrophic factor related genes including BDNF, GDNF, and CDNF at 2, 4, and 6 days, respectively. These results showed that salidroside significantly enhanced survival and proliferation of SCs. The underlying mechanism might involve that salidroside affected SCs growth through the modulation of several neurotrophic factors including BDNF, GDNF, and CDNF. As for the concentration, 0.4 mM, 0.2 mM, and 0.1 mM of salidroside were recommended, especially 0.2 mM. This investigation indicates that salidroside is capable of enhancing SCs survival and function in vitro, which highlights the possibility that salidroside as a drug agent to promote nerve regeneration in cellular nerve scaffold through salidroside-induced neurotrophin secretion in SCs.

Low-Intensity Extracorporeal Shock Wave Therapy Enhances Brain-Derived Neurotrophic Factor Expression through PERK/ATF4 Signaling Pathway

Low-intensity extracorporeal shock wave therapy (Li-ESWT) is used in the treatment of erectile dysfunction, but its mechanisms are not well understood. Previously, we found that Li-ESWT increased the expression of brain-derived neurotrophic factor (BDNF). Here we assessed the underlying signaling pathways in Schwann cells in vitro and in penis tissue in vivo after nerve injury. The result indicated that BDNF were significantly increased by the Li-ESWT after nerve injury, as well as the expression of BDNF in Schwann cells (SCs, RT4-D6P2T) in vitro. Li-ESWT activated the protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK) pathway by increasing the phosphorylation levels of PERK and eukaryotic initiation factor 2a (eIF2α), and enhanced activating transcription factor 4 (ATF4) in an energy-dependent manner. In addition, GSK2656157—an inhibitor of PERK—effectively inhibited the effect of Li-ESWT on the phosphorylation of PERK, eIF2α, and the expression of ATF4. Furthermore, silencing ATF4 dramatically attenuated the effect of Li-ESWT on the expression of BDNF, but had no effect on hypoxia-inducible factor (HIF)1α or glial cell-derived neurotrophic factor (GDNF) in Schwann cells. In conclusion, our findings shed new light on the underlying mechanisms by which Li-ESWT may stimulate the expression of BDNF through activation of PERK/ATF4 signaling pathway. This information may help to refine the use of Li-ESWT to further improve its clinical efficacy.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Spinal Plasticity and Behavior: BDNF-Induced Neuromodulation in Uninjured and Injured Spinal Cord

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophic factor family of signaling molecules. Since its discovery over three decades ago, BDNF has been identified as an important regulator of neuronal development, synaptic transmission, and cellular and synaptic plasticity and has been shown to function in the formation and maintenance of certain forms of memory. Neural plasticity that underlies learning and memory in the hippocampus shares distinct characteristics with spinal cord nociceptive plasticity. Research examining the role BDNF plays in spinal nociception and pain overwhelmingly suggests that BDNF promotes pronociceptive effects. BDNF induces synaptic facilitation and engages central sensitization-like mechanisms. Also, peripheral injury-induced neuropathic pain is often accompanied with increased spinal expression of BDNF. Research has extended to examine how spinal cord injury (SCI) influences BDNF plasticity and the effects BDNF has on sensory and motor functions after SCI. Functional recovery and adaptive plasticity after SCI are typically associated with upregulation of BDNF. Although neuropathic pain is a common consequence of SCI, the relation between BDNF and pain after SCI remains elusive. This article reviews recent literature and discusses the diverse actions of BDNF. We also highlight similarities and differences in BDNF-induced nociceptive plasticity in naïve and SCI conditions.

Efficacy of Schwann cell transplantation for spinal cord repair is improved with combinatorial strategies

When cells (including Schwann cells; SCs) of the peripheral nervous system (PNS) could be purified and expanded in number in tissue culture, Richard Bunge in 1975 envisioned that the SCs could be introduced to repair the central nervous system (CNS), as SCs enable axons to regenerate after PNS injury. Importantly, autologous human SCs could be transplanted into injured human spinal cord. Availability of the new culture systems to study interactions between sensory neurons, SCs and fibroblasts increased our knowledge of SC biology in the 1970s and '80s. Joining the Miami Project to Cure Paralysis in 1989 brought the opportunity to use this knowledge to initiate spinal cord repair studies. Development of a rat complete spinal cord transection/SC bridge model allowed the demonstration that axons regenerate into the SC bridge. Together with study of contused rat spinal cord, it was concluded that implanted SCs reduce cavitation, protect tissue around the lesion, support axon regeneration and form myelin. SC transplantation efficacy was improved when combined with neurotrophins, elevation of cyclic AMP levels, olfactory ensheathing cells, a steroid or chondroitinase. Increased efficacy meant higher numbers of axons, particularly from the brainstem, and more SC-myelinated axons in the implants and improvement in hindlimb movements. Human SCs support axon regeneration as do rat SCs. Astrocytes at the SC bridge-host spinal cord interfaces play a key role in determining whether axons enter the SC milieu. The SC work described here contributed to gaining approval from the FDA for an initial autologous human SC clinical trial (at the Miami Project) that has been completed and found to be safe.

Gene-activated fat grafts for the repair of spinal cord injury: a pilot study

BACKGROUND

Spinal cord injury (SCI) is a complex disease requiring a concerted multi-target approach. The most appropriate combination of therapeutic gene, cellular vehicle, and space filling scaffold still has to be determined. We present an approach that employs syngeneic adipose tissue serving as a three-dimensional biological implant, source of progenitor cells, and delivery system for therapeutic genes. In this pilot experiment, we evaluated the feasibility and short-term effects using gene-activated autologous fat grafts after SCI.

METHODS

An experimental SCI model was established in syngeneic Fischer 344 rats by a T9-T10 hemimyelonectomy. Fat tissue was harvested from two donor rats. Animals were divided into four groups and treated with either (i) fat grafts activated by an adenoviral vector carrying the human NT-3 cDNA, (ii) or BDNF, (iii) or with untreated fat grafts or (iv) remained untreated. Animals were euthanized either 7 or 21 days after surgery, and spinal cord tissue was investigated by histological and immunohistochemical methods.

RESULTS

NT-3 and BDNF were produced by gene-activated fat grafts for at least 21 days in vitro and in vivo. Fat tissue grafts remained stable at the site of implantation at 7 days and at 21 days. Neither BDNF-activated nor NT-3-activated fat graft had a detectable limiting effect on the neuronal degeneration. BDNF recruited microglia to perilesional site and attenuated their inflammatory response.

CONCLUSIONS

Gene-activated syngeneic fat tissue serves as a three-dimensional biological material delivering therapeutic molecules to the site of SCI over an extended period of time. The BDNF-fat graft attenuated the inflammatory response. Whether these findings translate into functional recovery will require extended observation times.

Localized and sustained release of brain-derived neurotrophic factor from injectable hydrogel/microparticle composites fosters spinal learning after spinal cord injury

Injectable hydrogel allows for sustained delivery of growth factor resulting in spinal mediated learning after injury.

Using NGF heparin-poloxamer thermosensitive hydrogels to enhance the nerve regeneration for spinal cord injury

OBJECTIVE

Nerve growth factor (NGF) has potential in spinal cord injury (SCI) therapy, but limited by the poor physicochemical stability and low ability to cross the blood spinal cord barrier. Novel heparin-poloxamer (HP) thermo-sensitive hydrogel was constructed to enhance the NGF regeneration on SCI.

METHOD

NGF-HP thermo-sensitive hydrogel was prepared and related characteristics including gelation temperature, rheological behavior and micromorphology were measured. Local NGF delivery to the injured spinal cord was achieved by in situ injection in the injured space. The cellular uptake of NGF-HP hydrogel was evaluated with PC12 cells in vitro. Pathologic characteristics and neuron regeneration effects on the SCI rats were studied to evaluate the enhanced therapy of NGF-HP hydrogel. Endoplasmic reticulum (ER) stress-induced apoptosis was analyzed to explore the related mechanism in SCI regeneration.

RESULTS

NGF-HP hydrogel showed good morphology and stable bioactivity of NGF in vitro. NGF-HP hydrogel combined treatment significantly enhanced the efficiency of NGF cellular uptake (P<0.05) without obvious cytotoxicity. Significant improvements in both neuron functions and tissue morphology on the SCI rats were observed in NGF-HP hydrogel group. Compared with free HP hydrogel and NGF treatment groups, NGF-HP hydrogel group showed significant inhibition on the formation of glial scars in the extreme crushed rat SCI model. The neuroprotective effects of NGF-HP were related to the inhibition of chronic ER stress-induced apoptosis.

CONCLUSIONS

HP hydrogel combined with orthotopic injection technique might be an effective method to deliver NGF into the injured site, which will provide an effective strategy for SCI regeneration.

STATEMENT OF SIGNIFICANCE

Spinal cord injury (SCI) is a devastating condition that can lead to sudden loss of sensory and autonomic function. Current treatment includes decompression surgery, injury stabilization, secondary complications prevention and rehabilitation. However, neurological recovery is limited. Nerve growth factor (NGF) has potential in SCI therapy, but limited by the poor physicochemical stability and low ability to cross the blood spinal cord barrier. Hydrogels have good affinity and compatibility to biological tissue. In this study, we developed a novel heparin-poloxamer (HP) thermo-sensitive hydrogel to enhance the spinal cord regeneration of NGF. From SCI rat experiment, HP hydrogel combined with orthotopic injection technique showed best neuroprotective effects among experimental groups. This novel combined technique will provide an effective strategy for SCI regeneration.

Combination therapy of stem cell derived neural progenitors and drug delivery of anti-inhibitory molecules for spinal cord injury

Regeneration of lost synaptic connections following spinal cord injury (SCI) is limited by local ischemia, cell death, and an excitotoxic environment, which leads to the development of an inhibitory glial scar surrounding a cystic cavity. While a variety of single therapy interventions provide incremental improvements to functional recovery after SCI, they are limited; a multifactorial approach that combines several single therapies may provide a better chance of overcoming the multitude of obstacles to recovery. To this end, fibrin scaffolds were modified to provide sustained delivery of neurotrophic factors and anti-inhibitory molecules, as well as encapsulation of embryonic stem cell-derived progenitor motor neurons (pMNs). In vitro characterization of this combination scaffold confirmed that pMN viability was unaffected by culture alongside sustained delivery systems. When transplanted into a rat sub-acute SCI model, fibrin scaffolds containing growth factors (GFs), anti-inhibitory molecules without pMNs, or pMNs with GFs had lower chondroitin sulfate proteoglycan levels compared to scaffolds containing anti-inhibitory molecules with pMNs. Scaffolds containing pMNs, but not anti-inhibitory molecules, showed survival, differentiation into neuronal cell types, axonal extension in the transplant area, and the ability to integrate into host tissue. However, the combination of pMNs with sustained-delivery of anti-inhibitory molecules led to reduced cell survival and increased macrophage infiltration. While combination therapies retain potential for effective treatment of SCI, further work is needed to improve cell survival and to limit inflammation.

STATEMENT OF SIGNIFICANCE

Spinal cord injury (SCI) creates a highly complex inhibitory environment with a multitude of obstacles that limit recovery. Many therapeutic options have been developed to overcome single obstacles, but single therapies typically only lead to limited functional improvement. Therefore combination therapies may improve recovery by targeting several inhibitory obstacles simultaneously. The present study used biomaterial scaffolds to combine the sustained release of anti-inhibitory molecules and growth factors with cell transplantation of highly purified progenitor motor neurons. This expands upon previously established biomaterial scaffolds by supporting surviving cells, limiting inhibition from the extracellular environment, and replenishing lost cell populations. We show that while promising, certain combinations may exacerbate negative side-effects instead of augmenting positive features.

Cell-seeded alginate hydrogel scaffolds promote directed linear axonal regeneration in the injured rat spinal cord

Despite recent progress in enhancing axonal growth in the injured spinal cord, the guidance of regenerating axons across an extended lesion site remains a major challenge. To determine whether regenerating axons can be guided in rostrocaudal direction, we implanted 2mm long alginate-based anisotropic capillary hydrogels seeded with bone marrow stromal cells (BMSCs) expressing brain-derived neurotrophic factor (BDNF) or green fluorescent protein (GFP) as control into a C5 hemisection lesion of the rat spinal cord. Four weeks post-lesion, numerous BMSCs survived inside the scaffold channels, accompanied by macrophages, Schwann cells and blood vessels. Quantification of axons growing into channels demonstrated 3-4 times more axons in hydrogels seeded with BMSCs expressing BDNF (BMSC-BDNF) compared to control cells. The number of anterogradely traced axons extending through the entire length of the scaffold was also significantly higher in scaffolds with BMSC-BDNF. Increasing the channel diameters from 41μm to 64μm did not lead to significant differences in the number of regenerating axons. Lesions filled with BMSC-BDNF without hydrogels exhibited a random axon orientation, whereas axons were oriented parallel to the hydrogel channel walls. Thus, alginate-based scaffolds with an anisotropic capillary structure are able to physically guide regenerating axons.

STATEMENT OF SIGNIFICANCE

After injury, regenerating axons have to extend across the lesion site in the injured spinal cord to reestablish lost neuronal connections. While cell grafting and growth factor delivery can promote growth of injured axons, without proper guidance, axons rarely extend across the lesion site. Here, we show that alginate biomaterials with linear channels that are filled with cells expressing the growth-promoting neurotrophin BDNF promote linear axon extension throughout the channels after transplantation to the injured rat spinal cord. Animals that received the same cells but no alginate guidance structure did not show linear axonal growth and axons did not cross the lesion site. Thus, alginate-based scaffolds with a capillary structure are able to physically guide regenerating axons.

Hydrogels and Cell Based Therapies in Spinal Cord Injury Regeneration

Spinal cord injury (SCI) is a central nervous system- (CNS-) related disorder for which there is yet no successful treatment. Within the past several years, cell-based therapies have been explored for SCI repair, including the use of pluripotent human stem cells, and a number of adult-derived stem and mature cells such as mesenchymal stem cells, olfactory ensheathing cells, and Schwann cells. Although promising, cell transplantation is often overturned by the poor cell survival in the treatment of spinal cord injuries. Alternatively, the therapeutic role of different cells has been used in tissue engineering approaches by engrafting cells with biomaterials. The latter have the advantages of physically mimicking the CNS tissue, while promoting a more permissive environment for cell survival, growth, and differentiation. The roles of both cell- and biomaterial-based therapies as single therapeutic approaches for SCI repair will be discussed in this review. Moreover, as the multifactorial inhibitory environment of a SCI suggests that combinatorial approaches would be more effective, the importance of using biomaterials as cell carriers will be herein highlighted, as well as the recent advances and achievements of these promising tools for neural tissue regeneration.

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

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

The role of the serotonergic system in locomotor recovery after spinal cord injury

Serotonin (5-HT), a monoamine neurotransmitter synthesized in various populations of brainstem neurons, plays an important role in modulating the activity of spinal networks involved in vertebrate locomotion. Following spinal cord injury (SCI) there is a disruption of descending serotonergic projections to spinal motor areas, which results in a subsequent depletion in 5-HT, the dysregulation of 5-HT transporters as well as the elevated expression, super-sensitivity and/or constitutive auto-activation of specific 5-HT receptors. These changes in the serotonergic system can produce varying degrees of locomotor dysfunction through to paralysis. To date, various approaches targeting the different components of the serotonergic system have been employed to restore limb coordination and improve locomotor function in experimental models of SCI. These strategies have included pharmacological modulation of serotonergic receptors, through the administration of specific 5-HT receptor agonists, or by elevating the 5-HT precursor 5-hydroxytryptophan, which produces a global activation of all classes of 5-HT receptors. Stimulation of these receptors leads to the activation of the locomotor central pattern generator (CPG) below the site of injury to facilitate or improve the quality and frequency of movements, particularly when used in concert with the activation of other monoaminergic systems or coupled with electrical stimulation. Another approach has been to employ cell therapeutics to replace the loss of descending serotonergic input to the CPG, either through transplanted fetal brainstem 5-HT neurons at the site of injury that can supply 5-HT to below the level of the lesion or by other cell types to provide a substrate at the injury site for encouraging serotonergic axon regrowth across the lesion to the caudal spinal cord for restoring locomotion.

Intraspinal Transplantation of hNT Neurons in the Lesioned Adult Rat Spinal Cord

Background:

The role of neural transplantation as a restorative strategy for spinal cord injury continues to be intensely investigated. Ideally, the tissue source for transplantation must be readily available, free of disease and able to survive and mature following implantation into the adverse environment created by the injury. We have studied the use of a commercially available cell line of cultured human neurons (hNT neurons) as a tissue source for neural transplantation in spinal cord injury.

Methods:

Following a left lateral thoracic hemisection, 54 immunosuppressed, female Wistar rats were randomly allocated into different treatment groups; hemisection only or hemisection and hNT cell transplantation (via a bridge, double or triple graft). Grafting occurred three days after spinal cord injury. After thirteen weeks the animals were sacrificed and tissue sections were stained with human neuron specific enolase and human specific neural cell adhesion molecule.

Results:

Immunohistochemical evidence of graft survival was displayed in 66.7% of the surviving, grafted animals. Fibre outgrowth, greatest in the bridge and triple grafts, was observed in both rostral and caudal directions essentially bridging the lesion. Double grafts were smaller, displaying less fibre outgrowth, which did not cross the lesion. Long fibre outgrowth was evident up to 2 cm from the graft as assessed by tracing and immunohistochemical studies.

Conclusion:

Bridge and triple grafts displayed greater growth and enabled the hNT graft to essentially bridge the lesion. This suggests that hNT neurons have the potential to structurally reconnect the proximal and distal spinal cord across the region of injury.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

Electrical stimulation of schwann cells promotes sustained increases in neurite outgrowth

Endogenous electric fields are instructive during embryogenesis by acting to direct cell migration, and postnatally, they can promote axonal growth after injury (McCaig 1991, Al-Majed 2000). However, the mechanisms for these changes are not well understood. Application of an appropriate electrical stimulus may increase the rate and success of nerve repair by directly promoting axonal growth. Previously, DC electrical stimulation at 50 mV/mm (1 mA, 8 h duration) was shown to promote neurite outgrowth and a more pronounced effect was observed if both peripheral glia (Schwann cells) and neurons were co-stimulated. If electrical stimulation is delivered to an injury site, both the neurons and all resident non-neuronal cells [e.g., Schwann cells, endothelial cells, fibroblasts] will be treated and this biophysical stimuli can influence axonal growth directly or indirectly via changes to the resident, non-neuronal cells. In this work, non-neuronal cells were electrically stimulated, and changes in morphology and neuro-supportive cells were evaluated. Schwann cell response (morphology and orientation) was examined after an 8 h stimulation over a range of DC fields (0-200 mV/mm, DC 1 mA), and changes in orientation were observed. Electrically prestimulating Schwann cells (50 mV/mm) promoted 30% more neurite outgrowth relative to co-stimulating both Schwann cells with neurons, suggesting that electrical stimulation modifies Schwann cell phenotype. Conditioned medium from the electrically prestimulated Schwann cells promoted a 20% increase in total neurite outgrowth and was sustained for 72 h poststimulation. An 11-fold increase in nerve growth factor but not brain-derived neurotrophic factor or glial-derived growth factor was found in the electrically prestimulated Schwann cell-conditioned medium. No significant changes in fibroblast or endothelial morphology and neuro-supportive behavior were observed poststimulation. Electrical stimulation is widely used in clinical settings; however, the rational application of this cue may directly impact and enhance neuro-supportive behavior, improving nerve repair.

Neurotrophic factors in spinal cord injury

A major challenge in repairing the injured spinal cord is to assure survival of damaged cells and to encourage regrowth of severed axons. Because neurotrophins are known to affect these processes during development, many experimental approaches to improving function of the injured spinal cord have made use of these agents, particularly Brain derived neurotrophic factor (BDNF) and Neurotrophin-3 (NT-3). More recently, neurotrophins have also been shown to affect the physiology of cells and synapses in the spinal cord. The effect of neurotrophins on circuit performance adds an important dimension to their consideration as agents for repairing the injured spinal cord. In this chapter we discuss the role of neurotrophins in promoting recovery after spinal cord injury from both a structural and functional perspective.

Combined treatment with platelet-rich plasma and brain-derived neurotrophic factor-overexpressing bone marrow stromal cells supports axonal remyelination in a rat spinal cord hemi-section model

BACKGROUND AIMS

Combining biologic matrices is becoming a better choice to advance stem cell-based therapies. Platelet-rich plasma (PRP) is a biologic product of concentrated platelets and has been used to promote regeneration of peripheral nerves after injury. We examined whether PRP could induce rat bone marrow stromal cells (BMSCs) differentiation in vitro and whether a combination of BMSCs, PRP and brain-derived neurotrophic factor (BDNF) could provide additive therapeutic benefits in vivo after spinal cord injury (SCI).

METHODS

BMSCs and BDNF-secreting BMSCs (BDNF-BMSCs) were cultured with PRP for 7 days and 21 days, respectively, and neurofilament (NF)-200, glial fibrillary acidic protein (GFAP), microtubule-associated protein 2 (MAP2) and ribosomal protein S6 kinase (p70S6K) gene levels were assessed. After T10 hemi-section in 102 rats, 15-μL scaffolds (PRP alone, BMSCs, PRP/BMSCs, BDNF-BMSCs or PRP/BDNF-BMSCs) were transplanted into the lesion area, and real-time polymerase chain reaction, Western blot, immunohistochemistry and ultrastructural studies were performed.

RESULTS

The messenger RNA expression of NF-200, GFAP, MAP2 and p70S6K was promoted in BMSCs and BDNF-BMSCs after culture with PRP in vitro. BDNF levels were significantly higher in the injured spinal cord after implantation of BDNF-BMSCs. In the PRP/BDNF-BMSCs group at 8 weeks postoperatively, more GFAP was observed, with less accumulation of astrocytes at the graft-host interface. Rats that received PRP and BDNF-BMSC implants showed enhanced hind limb locomotor performance at 8 weeks postoperatively compared with control animals, with more axonal remyelination.

CONCLUSIONS

A combined treatment comprising PRP and BDNF-overexpressing BMSCs produced beneficial effects in rats with regard to functional recovery after SCI through enhancing migration of astrocytes into the transplants and axonal remyelination.

Combining Neurotrophin-Transduced Schwann Cells and Rolipram to Promote Functional Recovery from Subacute Spinal Cord Injury

Following spinal cord injury (SCI), both an inhibitory environment and lack of intrinsic growth capacity impede axonal regeneration. In a previous study, prevention of cyclic adenosine monophosphate (AMP) hydrolysis by the phosphodiesterase-4 inhibitor rolipram, in combination with Schwann cell (SC) grafts, promoted significant supraspinal and proprioceptive fiber growth and/or sparing and improved locomotion. In another study, transplanted SCs transduced to generate a bifunctional neurotrophin (D15A) led to significant increases in graft SCs and axons, including supraspinal and myelinated axons. Here we studied the growth and myelination of local and supraspinal axons and functional outcome following the combination of rolipram administration and neurotrophin-transduced SC implantation after SCI. Rolipram was administered subcutaneously for 4 weeks immediately after contusion at vertebral T8 (25.0-mm weight drop, MASCIS impactor). GFP or GFP-D15A-transduced SCs were injected into the injury epicenter 1 week after SCI. GFP-D15A SC grafts and GFP SC grafts with rolipram contained significantly more serotonergic fibers compared to GFP SCs. SC myelinated axons were increased significantly in GFP SC with rolipram-treated animals compared to animals receiving SCI alone. Rolipram administered with either GFP or GFP-D15A SCs significantly increased numbers of brain stem-derived axons below the lesion/implant area and improved hindlimb function. Compared to the single treatments, the combination led to the largest SC grafts, the highest numbers of serotonergic fibers in the grafts, and increased numbers of axons from the reticular formation below the lesion/implant area and provided the greatest improvement in hindlimb function. These findings demonstrate the therapeutic potential for a combination therapy involving the maintenance of cyclic AMP levels and neurotrophin-transduced SCs to repair the subacutely injured spinal cord.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

New strategies for repairing the injured spinal cord: the role of stem cells

Thanks to advances in the stem cell biology of the central nervous system, the previously unconceivable regeneration of the damaged spinal cord is approaching reality. A number of potential strategies aim to optimize functional recovery after spinal cord injury. They include minimizing the progression of secondary injury, manipulating the inhibitory environment of the spinal cord, replacing lost tissue with transplanted cells or peripheral nerve grafts, remyelinating denuded axons and maximizing the intrinsic regenerative potential of endogenous progenitor cells. We review the application of stem cell transplantation to the spinal cord, emphasizing the use of embryonic stem cells for remyelinating damaged axons. Recent advancements in neural injury and repair, and the progress towards development of neuroprotective and regenerative interventions are discussed.

The protective effects of resveratrol on Schwann cells with toxicity induced by ethanol in vitro

Schwann cells (SCs) are the myelin forming cells in the peripheral nervous system, they play a key role in the pathology of various polyneuropathies and provide trophic support to axons via expression of various neurotrophic factors, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). Ethanol (EtOH) adversely affected both SCs proliferation and myelin formation in culture. Resveratrol (Res) has been shown to regulate many cellular processes and to display multiple protective and therapeutic effects. Whether Res has protective effects on SCs with EtOH-induced toxicity is still unclear. The protective efficacy of Res on EtOH-treated SCs in vitro was investigated in the present study. Res improved cell viability of the EtOH-treated SCs. Hoechst 33342 staining and terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling analysis showed that the EtOH-induced apoptosis was inhibited by Res. The effects of Res were blocked by the 5'-adenosine monophosphate-activated protein kinase inhibitor Compound C and the silencing information regulator T1 inhibitor nicotinamide. Res could increase the mRNA and protein levels of BDNF and GDNF in the EtOH-treated SCs. However, the EtOH-induced increase of NGF in the SCs is inhibited by Res. The data from the present study indicate that Res protects SCs from EtOH-induced cell death and regulates the expression of neurotrophicfactors. Res and its derivative may be effective for the treatment of neuropathic diseases induced by EtOH.

Dissociated predegenerated peripheral nerve transplants for spinal cord injury repair: a comprehensive assessment of their effects on regeneration and functional recovery compared to Schwann cell transplants

Several recent studies suggest that predegenerated nerves (PDNs) or dissociated PDNs (dPDNs) can improve behavioral and histological outcomes following transplantation into the injured rat spinal cord. In the current study we tested the efficacy of dPDN transplantation by grafting cells isolated from the sciatic nerve 7 days after crush. We did not replicate one study, but rather assessed what appeared, based on five published reports, to be a reported robust effect of dPDN grafts on corticospinal tract (CST) regeneration and locomotor recovery. Using a standardized rodent spinal cord injury model (200 kD IH contusion) and transplantation procedure (injection of GFP⁺ cells 7 days post-SCI), we demonstrate that dPDN grafts survive within the injured spinal cord and promote the ingrowth of axons to a similar extent as purified Schwann cell (SC) grafts. We also demonstrate for the first time that while both dPDN and SC grafts promote the ingrowth of CGRP axons, neither graft results in mechanical or thermal hyperalgesia. Unlike previous studies, dPDN grafts did not promote long-distance axonal growth of CST axons, brainstem spinal axons, or ascending dorsal column sensory axons. Moreover, using a battery of locomotor tests (Basso Beattie Bresnahan [BBB] score, BBB subscore, inked footprint, Catwalk, and ladderwalk), we failed to detect any beneficial effects of dPDN transplantation on the recovery of locomotor function after SCI. We conclude that dPDN transplants are not sufficient to promote CST regeneration or locomotor recovery after SCI.

Endogenous proliferation after spinal cord injury in animal models

Spinal cord injury (SCI) results in motor and sensory deficits, the severity of which depends on the level and extent of the injury. Animal models for SCI research include transection, contusion, and compression mouse models. In this paper we will discuss the endogenous stem cell response to SCI in animal models. All SCI animal models experience a similar peak of cell proliferation three days after injury; however, each specific type of injury promotes a specific and distinct stem cell response. For example, the transection model results in a strong and localized initial increase of proliferation, while in contusion and compression models, the initial level of proliferation is lower but encompasses the entire rostrocaudal extent of the spinal cord. All injury types result in an increased ependymal proliferation, but only in contusion and compression models is there a significant level of proliferation in the lateral regions of the spinal cord. Finally, the fate of newly generated cells varies from a mainly oligodendrocyte fate in contusion and compression to a mostly astrocyte fate in the transection model. Here we will discuss the potential of endogenous stem/progenitor cell manipulation as a therapeutic tool to treat SCI.

Injury-induced accumulation of glial cell line-derived neurotrophic factor in the rostral part of the injured rat spinal cord

The spinal cord of a 7-week-old female Wistar rat was hemi-transected at thoracic position 10 with a razor blade, and changes in glial cell line-derived neurotrophic factor (GDNF) protein and mRNA expression levels in the spinal cord were examined. GDNF protein and mRNA expression levels were evaluated by enzyme immunoassay and reverse transcription polymerase chain reaction, respectively. Although GDNF is distributed in the healthy spinal cord from 150 to 400 pg/g tissue in a regionally dependent manner, hemi-transection (left side) of the spinal cord caused a rapid increase in GDNF content in the ipsilateral rostral but not in the caudal part of the spinal cord. On the other hand, injury-induced GDNF mRNA was distributed limitedly in both rostral and caudal stumps. These observations suggest the possibility that increased GDNF in the rostral part is responsible for the accumulation of GDNF that may be constitutively transported from the rostral to caudal side within the spinal cord. Although such local increase of endogenous GDNF protein may not be sufficient for nerve regeneration and locomotor improvement, it may play a physiological role in supporting spinal neurons including motoneurons.

BDNF: the career of a multifaceted neurotrophin in spinal cord injury

Brain-derived neurotrophic factor (BDNF) has been identified as a potent promoter of neurite growth, a finding that has led to an ongoing exploration of this neurotrophin as a potential treatment for spinal cord injury. BDNF's many effects in the nervous system make it an excellent candidate for neuroprotective strategies as well as for promoting axonal regeneration, plasticity and re-myelination. In addition, neuronal activity and physical exercise can modulate the expression of BDNF, suggesting that non-invasive means to increase BDNF levels might exist. Nonetheless, depending on the location, amount and duration of BDNF delivery, this potent neurotrophin can also have adverse effects, such as modulation of nociceptive pathways or contribution to spasticity. Taken together, the benefits and possible risks require careful assessment when considering this multifaceted neurotrophin as a treatment option for spinal cord injury.