Cellular morphology of chronic spinal cord injury in the cat: analysis of myelinated axons by line-sampling

Early intervention for spinal cord injury with human induced pluripotent stem cells oligodendrocyte progenitors

Induced pluripotent stem (iPS) cells are at the forefront of research in regenerative medicine and are envisaged as a source for personalized tissue repair and cell replacement therapy. Here, we demonstrate for the first time that oligodendrocyte progenitors (OPs) can be derived from iPS cells generated using either an episomal, non-integrating plasmid approach or standard integrating retroviruses that survive and differentiate into mature oligodendrocytes after early transplantation into the injured spinal cord. The efficiency of OP differentiation in all 3 lines tested ranged from 40% to 60% of total cells, comparable to those derived from human embryonic stem cells. iPS cell lines derived using episomal vectors or retroviruses generated a similar number of early neural progenitors and glial progenitors while the episomal plasmid-derived iPS line generated more OPs expressing late markers O1 and RIP. Moreover, we discovered that iPS-derived OPs (iPS-OPs) engrafted 24 hours following a moderate contusive spinal cord injury (SCI) in rats survived for approximately two months and that more than 70% of the transplanted cells differentiated into mature oligodendrocytes that expressed myelin associated proteins. Transplanted OPs resulted in a significant increase in the number of myelinated axons in animals that received a transplantation 24 h after injury. In addition, nearly a 5-fold reduction in cavity size and reduced glial scarring was seen in iPS-treated groups compared to the control group, which was injected with heat-killed iPS-OPs. Although further investigation is needed to understand the mechanisms involved, these results provide evidence that patient-specific, iPS-derived OPs can survive for three months and improve behavioral assessment (BBB) after acute transplantation into SCI. This is significant as determining the time in which stem cells are injected after SCI may influence their survival and differentiation capacity.

Acute spinal cord injury: tetraplegia and paraplegia in small animals

Spinal cord injury (SCI) is a common problem in animals for which definitive treatment is lacking, and information gained from its study has benefit for both companion animals and humans in developing new therapeutic approaches. This review provides an overview of the main concepts that are useful for clinicians in assessing companion animals with severe acute SCI. Current available advanced ancillary tests and those in development are reviewed. In addition, the current standard of care for companion animals following SCI and recent advances in the development of new therapies are presented, and new predictors of recovery discussed.

Purine-crosslinked injectable chitosan sponges promote oligodendrocyte progenitor cells' attachment and differentiation

Oligodendrocyte Progenitor Cells (OPCs) reside in the central nervous system (CNS) and are responsible for remyelinating axons after a spinal cord injury (SCI). However, the remyelination process is incomplete and abnormal due to the inability of OPCs to fully differentiate at the site of injury. In this study a newly developed injectable chitosan sponge crosslinked using guanosine 5'-diphosphate (GDP) was used to enhance OPC survival, attachment and differentiation. This purine-based biomaterial is the first of its kind and its inception was based on the growing body of literature concerning the role of purinergic signalling in the CNS. GDP-crosslinked chitosan sponges are rapidly-gelling and can be easily administered in situ using an injection system based on a double-lumen design. The chitosan sponges prompted OPC differentiation even in the presence of mitogens. Moreover, neurotrophin-3 (NT-3) was successfully entrapped in the sponges and a sustained release for up to 30 days was achieved. OPCs were shown to differentiate into mature oligodendrocytes that express myelin basic protein (MBP) when cultured on sponges containing NT-3. These findings, along with the suitable physicochemical and biological properties, make these sponges conducive to use as viable therapeutic agents for enhancing remyelination post-SCI.

In vivo longitudinal Myelin Water Imaging in rat spinal cord following dorsal column transection injury

Longitudinal Myelin Water Imaging was carried out in vivo to characterize white matter damage following dorsal column transection (DC Tx) injury at the lumbar level L1 of rat spinal cords. A transmit-receive implantable coil system was used to acquire multiple spin-echo (MSE) quantitative T2 data from the lumbar spinal cords of 16 rats at one week pre-injury as well as 3 and 8weeks post-injury (117 microns in-plane resolution and 1.5mm slice thickness). In addition, ex vivo MSE and DTI data were acquired from cords fixed and excised at 3 or 8weeks post injury using a solenoid coil. The MSE data were used to generate Myelin Water Fractions (MWFs) as a surrogate measure of myelin content, while DTI data were acquired to study damage to the axons. Myelin damage was assessed histologically with Eriochrome cyanine (EC) and Myelin Basic Protein in degenerated myelin (dgen-MBP) staining, and axonal damage was assessed by neurofilament-H in combination with neuron specific beta-III-tubulin (NF/Tub) staining. These MRI and histological measures of injury were studied in the dorsal column at 5mm cranial and 5mm caudal to injury epicenter. MWF increased significantly at 3weeks post-injury at both the cranial and caudal sites, relative to baseline. The values on the cranial side of injury returned to baseline at 8weeks post-injury but remained elevated on the caudal side. This trend was found in both in vivo and ex vivo data. This MWF increase was likely due to the presence of myelin debris, which were cleared by 8 weeks on the cranial, but not the caudal, side. Both EC and dgen-MBP stains displayed similar trends. MWF showed significant correlation with EC staining (R=0.63, p=0.005 in vivo and R=0.74, p=0.0001 ex vivo). MWF also correlated strongly with the dgen-MBP stain, but only on the cranial side (R=0.64, p=0.05 in vivo; R=0.63, p=0.038 ex vivo). This study demonstrates that longitudinal MWI in vivo can accurately characterize white matter damage in DC Tx model of injury in the rat 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.

Effect of norepinephrine on spinal cord blood flow and parenchymal hemorrhage size in acute-phase experimental spinal cord injury

PURPOSE

In the acute phase of spinal cord injury (SCI), ischemia and parenchymal hemorrhage are believed to worsen the primary lesions induced by mechanical trauma. To minimize ischemia, keeping the mean arterial blood pressure above 85 mmHg for at least 1 week is recommended, and norepinephrine is frequently administered to achieve this goal. However, no experimental study has assessed the effect of norepinephrine on spinal cord blood flow (SCBF) and parenchymal hemorrhage size. We have assessed the effect of norepinephrine on SCBF and parenchymal hemorrhage size within the first hour after experimental SCI.

METHODS

A total of 38 animals were included in four groups according to whether SCI was induced and norepinephrine injected. SCI was induced at level Th10 by dropping a 10-g weight from a height of 10 cm. Each experiment lasted 60 min. Norepinephrine was started 15 min after the trauma. SCBF was measured in the ischemic penumbra zone surrounding the trauma epicenter using contrast-enhanced ultrasonography. Hemorrhage size was measured repeatedly on parasagittal B-mode ultrasonography slices.

RESULTS

SCI was associated with significant decreases in SCBF (P = 0.0002). Norepinephrine infusion did not significantly modify SCBF. Parenchymal hemorrhage size was significantly greater in the animals given norepinephrine (P = 0.0002).

CONCLUSION

In the rat, after a severe SCI at the Th10 level, injection of norepinephrine 15 min after SCI does not modify SCBF and increases the size of the parenchymal hemorrhage.

Extensive neurological recovery from a complete spinal cord injury: a case report and hypothesis on the role of cortical plasticity

Neurological recovery in patients with severe spinal cord injury (SCI) is extremely rare. We have identified a patient with chronic cervical traumatic SCI, who suffered a complete loss of motor and sensory function below the injury for 6 weeks after the injury, but experienced a progressive neurological recovery that continued for 17 years. The extent of the patient's recovery from the severe trauma-induced paralysis is rare and remarkable. A detailed study of this patient using diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), and resting state fMRI (rs-fMRI) revealed structural and functional changes in the central nervous system that may be associated with the neurological recovery. Sixty-two percent cervical cord white matter atrophy was observed. DTI-derived quantities, more sensitive to axons, demonstrated focal changes, while MTI-derived quantity, more sensitive to myelin, showed a diffuse change. No significant cortical structural changes were observed, while rs-fMRI revealed increased brain functional connectivity between sensorimotor and visual networks. The study provides comprehensive description of the structural and functional changes in the patient using advanced MR imaging technique. This multimodal MR imaging study also shows the potential of rs-fMRI to measure the extent of cortical plasticity.

Systematic Review of Induced Pluripotent Stem Cell Technology as a Potential Clinical Therapy for Spinal Cord Injury

Transplantation therapies aimed at repairing neurodegenerative and neuropathological conditions of the central nervous system (CNS) have utilized and tested a variety of cell candidates, each with its own unique set of advantages and disadvantages. The use and popularity of each cell type is guided by a number of factors including the nature of the experimental model, neuroprotection capacity, the ability to promote plasticity and guided axonal growth, and the cells' myelination capability. The promise of stem cells, with their reported ability to give rise to neuronal lineages to replace lost endogenous cells and myelin, integrate into host tissue, restore functional connectivity, and provide trophic support to enhance and direct intrinsic regenerative ability, has been seen as a most encouraging step forward. The advent of the induced pluripotent stem cell (iPSC), which represents the ability to “reprogram” somatic cells into a pluripotent state, hails the arrival of a new cell transplantation candidate for potential clinical application in therapies designed to promote repair and/or regeneration of the CNS. Since the initial development of iPSC technology, these cells have been extensively characterized in vitro and in a number of pathological conditions and were originally reported to be equivalent to embryonic stem cells (ESCs). This review highlights emerging evidence that suggests iPSCs are not necessarily indistinguishable from ESCs and may occupy a different “state” of pluripotency with differences in gene expression, methylation patterns, and genomic aberrations, which may reflect incomplete reprogramming and may therefore impact on the regenerative potential of these donor cells in therapies. It also highlights the limitations of current technologies used to generate these cells. Moreover, we provide a systematic review of the state of play with regard to the use of iPSCs in the treatment of neurodegenerative and neuropathological conditions. The importance of balancing the promise of this transplantation candidate in the light of these emerging properties is crucial as the potential application in the clinical setting approaches. The first of three sections in this review discusses (A) the pathophysiology of spinal cord injury (SCI) and how stem cell therapies can positively alter the pathology in experimental SCI. Part B summarizes (i) the available technologies to deliver transgenes to generate iPSCs and (ii) recent data comparing iPSCs to ESCs in terms of characteristics and molecular composition. Lastly, in (C) we evaluate iPSC-based therapies as a candidate to treat SCI on the basis of their neurite induction capability compared to embryonic stem cells and provide a summary of available in vivo data of iPSCs used in SCI and other disease models.

Rodent Models and Behavioral Outcomes of Cervical Spinal Cord Injury

Rodent spinal cord injury (SCI) models have been developed to examine functional and physiological deficits after spinal cord injury with the hope that these models will elucidate information about human SCI. Models are needed to examine possible treatments and to understand histopathology after SCI; however, they should be considered carefully and chosen based on the goals of the study being performed. Contusion, compression, transection, and other models exist and have the potential to reveal important information about SCI that may be related to human SCI and the outcomes of treatment and timing of intervention.

Granulocyte colony-stimulating factor (G-CSF) protects oligodendrocyte and promotes hindlimb functional recovery after spinal cord injury in rats

BACKGROUND

Granulocyte colony-stimulating factor (G-CSF) is a protein that stimulates differentiation, proliferation, and survival of cells in the granulocytic lineage. Recently, a neuroprotective effect of G-CSF was reported in a model of cerebral infarction and we previously reported the same effect in studies of murine spinal cord injury (SCI). The aim of the present study was to elucidate the potential therapeutic effect of G-CSF for SCI in rats.

METHODS

Adult female Sprague-Dawley rats were used in the present study. Contusive SCI was introduced using the Infinite Horizon Impactor (magnitude: 200 kilodyne). Recombinant human G-CSF (15.0 µg/kg) was administered by tail vein injection at 1 h after surgery and daily the next four days. The vehicle control rats received equal volumes of normal saline at the same time points.

RESULTS

Using a contusive SCI model to examine the neuroprotective potential of G-CSF, we found that G-CSF suppressed the expression of pro-inflammatory cytokine (IL-1 beta and TNF- alpha) in mRNA and protein levels. Histological assessment with luxol fast blue staining revealed that the area of white matter spared in the injured spinal cord was significantly larger in G-CSF-treated rats. Immunohistochemical analysis showed that G-CSF promoted up-regulation of anti-apoptotic protein Bcl-Xl on oligpodendrocytes and suppressed apoptosis of oligodendrocytes after SCI. Moreover, administration of G-CSF promoted better functional recovery of hind limbs.

CONCLUSIONS

G-CSF protects oligodendrocyte from SCI-induced cell death via the suppression of inflammatory cytokines and up-regulation of anti-apoptotic protein. As a result, G-CSF attenuates white matter loss and promotes hindlimb functional recovery.

Cervical spinal demyelination with ethidium bromide impairs respiratory (phrenic) activity and forelimb motor behavior in rats

Although respiratory complications are a major cause of morbidity/mortality in many neural injuries or diseases, little is known concerning mechanisms whereby deficient myelin impairs breathing, or how patients compensate for such changes. Here, we tested the hypothesis that respiratory and forelimb motor functions are impaired in a rat model of focal dorsolateral spinal demyelination (ethidium bromide, EB). Ventilation, phrenic nerve activity and horizontal ladder walking were performed 7-14 days post-C2 injection of EB or vehicle (SHAM). EB caused dorsolateral demyelination at C2-C3 followed by significant spontaneous remyelination at 14 days post-EB. Although ventilation did not differ between groups, ipsilateral integrated phrenic nerve burst amplitude was significantly reduced versus SHAM during chemoreceptor activation at 7 days post-EB but recovered by 14 days. The ratio of ipsi- to contralateral phrenic nerve amplitude correlated with cross-sectional lesion area. This ratio was significantly reduced 7 days post-EB versus SHAM during baseline conditions, and versus SHAM and 14-day groups during chemoreceptor activation. Limb function ipsilateral to EB was impaired 7 days post-EB and partially recovered by 14 days post-EB. EB provides a reversible model of focal, spinal demyelination, and may be a useful model to study mechanisms of functional impairment and recovery via motor plasticity, or the efficacy of new therapeutic interventions to reduce severity or duration of disease.

Real-time and spatial quantification using contrast-enhanced ultrasonography of spinal cord perfusion during experimental spinal cord injury

STUDY DESIGN

Experimental study in male Wistar rats.

OBJECTIVE

To quantify temporal and spatial changes simultaneously in spinal cord blood flow and hemorrhage during the first hour after spinal cord injury (SCI), using contrast-enhanced ultrasonography (CEU).

SUMMARY OF BACKGROUND DATA

Post-traumatic ischemia and hemorrhage worsen the primary lesions induced by SCI. Previous studies did not simultaneously assess temporal and spatial changes in spinal cord blood flow.

METHODS

SCI was induced at Th10 in 12 animals, which were compared with 11 sham-operated controls. Spinal cord blood flow was measured in 7 adjacent regions of interest and in the sum of these 7 regions. Blood flow was quantified using CEU with intravenous microbubble injection. Spinal cord hemorrhage was measured on conventional B-mode sonogram slices.

RESULTS

CEU allowed us to measure the temporal and spatial changes in spinal cord blood flow in both groups. In the SCI group, spinal cord blood flow was significantly decreased in the global region of interest (P = 0.0016), at the impact site (epicenter), and in the 4 regions surrounding the epicenter, compared with the sham group. The blood flow decrease was maximum at the epicenter. No statistically significant differences between the sham groups were found for the most rostral and caudal regions of interest. Hemorrhage size increased significantly with time (P < 0.0001), from 30.3 mm(2) (±2) after 5 minutes to 39.6 mm(2) (±2.3) after 60 minutes.

CONCLUSION

CEU seems reliable for quantifying temporal and spatial changes in spinal cord blood flow. After SCI, bleeding occurs in the spinal cord parenchyma and increases significantly throughout the first hour.

Therapeutic approaches for spinal cord injury

This study reviews the literature concerning possible therapeutic approaches for spinal cord injury. Spinal cord injury is a disabling and irreversible condition that has high economic and social costs. There are both primary and secondary mechanisms of damage to the spinal cord. The primary lesion is the mechanical injury itself. The secondary lesion results from one or more biochemical and cellular processes that are triggered by the primary lesion. The frustration of health professionals in treating a severe spinal cord injury was described in 1700 BC in an Egyptian surgical papyrus that was translated by Edwin Smith; the papyrus reported spinal fractures as a "disease that should not be treated." Over the last biological or pharmacological treatment method. Science is unraveling the mechanisms of cell protection and neuroregeneration, but clinically, we only provide supportive care for patients with spinal cord injuries. By combining these treatments, researchers attempt to enhance the functional recovery of patients with spinal cord injuries. Advances in the last decade have allowed us to encourage the development of experimental studies in the field of spinal cord regeneration. The combination of several therapeutic strategies should, at minimum, allow for partial functional recoveries for these patients, which could improve their quality of life.

Pathological changes in the white matter after spinal contusion injury in the rat

It has been shown previously that after spinal cord injury, the loss of grey matter is relatively faster than loss of white matter suggesting interventions to save white matter tracts offer better therapeutic possibilities. Loss of white matter in and around the injury site is believed to be the main underlying cause for the subsequent loss of neurological functions. In this study we used a series of techniques, including estimations of the number of axons with pathology, immunohistochemistry and mapping of distribution of pathological axons, to better understand the temporal and spatial pathological events in white matter following contusion injury to the rat spinal cord. There was an initial rapid loss of axons with no detectable further loss beyond 1 week after injury. Immunoreactivity for CNPase indicated that changes to oligodendrocytes are rapid, extending to several millimetres away from injury site and preceding much of the axonal loss, giving early prediction of the final volume of white matter that survived. It seems that in juvenile rats the myelination of axons in white matter tracts continues for some time, which has an important bearing on interpretation of our, and previous, studies. The amount of myelin debris and axon pathology progressively decreased with time but could still be observed at 10 weeks after injury, especially at more distant rostral and caudal levels from the injury site. This study provides new methods to assess injuries to spinal cord and indicates that early interventions are needed for the successful sparing of white matter tracts following injury.

Immunological demyelination enhances nerve regeneration after acute transection injury in the adult rat sciatic nerve

INTRODUCTION

Our recent experiments demonstrate that demyelination enhances peripheral nerve regeneration after contusion injury in the adult rat sciatic nerve. The role of demyelination in peripheral nerve regeneration in a sciatic nerve transection model has yet to be elucidated. We hypothesize that (1) axon regeneration within a region of injury increases after experimental, immunologic demyelination, and (2) regenerated axons are partially derived from the proximal motor axons.

METHODS

Sciatic nerves of adult female Sprague-Dawley rats (n = 20) were injected with a demyelinating agent immediately after transection injury. The sciatic nerves were harvested 1 month (n = 5) and 2 months (n = 5) after surgery. In the control groups, the cut nerves were reapproximated without demyelination therapy. The lesion containing length of nerve was cut into 1-mm transverse blocks and processed to preserve orientation. Specimens were evaluated using structural and immunohistochemical analyses.

RESULTS

A single epineural injection of complement proteins plus antibodies to galactocerebroside resulted in demyelination followed by Schwann cell remyelination. At 1 month, remyelination was clearly shown throughout the injured sciatic nerve segment. At 2 months, there was a statistically significant increase in peripheral nerve regeneration following demyelination therapy as evidenced by total axon count, axon density, and fiber diameter.

CONCLUSION

This study demonstrates enhanced histomorphologic nerve regeneration in the rat sciatic nerve after local delivery of experimental, immunologic demyelination following transection injury. It highlights the utility of demyelination in peripheral nerve regeneration. This therapy may be applicable for tissue-engineered constructs, cell-based systems, and nerve transfers to improve outcomes in peripheral nervous system injuries.

Silencing of miR20a is crucial for Ngn1-mediated neuroprotection in injured spinal cord

MicroRNAs (miRNAs) compose a relatively new discipline in biomedical research, and many physiological processes in disease have been associated with changes in miRNA expression. Several studies report that miRNAs participate in biological processes such as the control of secondary injury in several disease models. Recently, we identified novel miRNAs that were abnormally up-regulated in a traumatic spinal cord injury (SCI). In the current study, we focused on miR20a, which causes continuing motor neuron degeneration when overexpressed in SCI lesions. Blocking miR20a in SCI animals led to neural cell survival and eventual neurogenesis with rescued expression of the key target gene, neurogenin 1 (Ngn1). Infusion of siNgn1 resulted in functional deficit in the hindlimbs caused by aggressive secondary injury and actively enhanced the inflammation involved in secondary injury progression. The events involving miR20a underlie motor neuron and myelin destruction and pathophysiology and ultimately block regeneration in injured spinal cords. Inhibition of miR20a expression effectively induced definitive motor neuron survival and neurogenesis, and SCI animals showed improved functional deficit. In this study, we showed that abnormal expression of miR20a induces secondary injury, which suggests that miR20a could be a potential target for therapeutic intervention following SCI.

Oligodendrocyte-protection and remyelination post-spinal cord injuries: a review

In the past four decades, the main focus of investigators in the field of spinal cord regeneration has been to devise therapeutic measures that enhance neural regeneration. More recently, emphasis has been placed on enhancing remyelination and providing oligodendrocyte-protection after a spinal cord injury (SCI). Demyelination post-SCI is part of the cascading secondary injury that takes place immediately after the primary insult; therefore, therapeutic measures are needed to reduce oligodendrocyte death and/or enhance remyelination during the acute stage, preserving neurological functions that would be lost otherwise. In this review a thorough investigation of the oligodendrocyte-protective and remyelinative molecular therapies available to date is provided. The advent of new biomaterials shown to promote remyelination post-SCI is discussed mainly in the context of a combinatorial approach where the biomaterial also provides drug delivery capabilities. The aim of these molecular and biomaterial-based therapies is twofold: (1) oligodendrocyte-protective therapy, which involves protecting already existing oligodendrocytes from undergoing apoptosis/necrosis; and (2) inductive remyelination, which involves harnessing the remyelinative capabilities of endogenous oligodendrocyte precursor cells (OPCs) at the lesion site by providing a suitable environment for their migration, survival, proliferation and differentiation. From the evidence reported in the literature, we conclude that the use of a combinatorial approach including biomaterials and molecular therapies would provide advantages such as: (1) sustained release of the therapeutic molecule, (2) local delivery at the lesion site, and (3) an environment at the site of injury that promotes OPC migration, differentiation and remyelination.

Chronic spinal compression model in minipigs: a systematic behavioral, qualitative, and quantitative neuropathological study

The goal of the present study was to develop a porcine spinal cord injury (SCI) model, and to describe the neurological outcome and characterize the corresponding quantitative and qualitative histological changes at 4-9 months after injury. Adult Gottingen-Minnesota minipigs were anesthetized and placed in a spine immobilization frame. The exposed T12 spinal segment was compressed in a dorso-ventral direction using a 5-mm-diameter circular bar with a progressively increasing peak force (1.5, 2.0, or 2.5 kg) at a velocity of 3 cm/sec. During recovery, motor and sensory function were periodically monitored. After survival, the animals were perfusion fixed and the extent of local SCI was analyzed by (1) post-mortem MRI analysis of dissected spinal cords, (2) qualitative and quantitative analysis of axonal survival at the epicenter of injury, and (3) defining the presence of local inflammatory changes, astrocytosis, and schwannosis. Following 2.5-kg spinal cord compression the animals demonstrated a near complete loss of motor and sensory function with no recovery over the next 4-9 months. Those that underwent spinal cord compression with 2 kg force developed an incomplete injury with progressive partial neurological recovery characterized by a restricted ability to stand and walk. Animals injured with a spinal compression force of 1.5 kg showed near normal ambulation 10 days after injury. In fully paralyzed animals (2.5 kg), MRI analysis demonstrated a loss of spinal white matter integrity and extensive septal cavitations. A significant correlation between the magnitude of loss of small and medium-sized myelinated axons in the ventral funiculus and neurological deficits was identified. These data, demonstrating stable neurological deficits in severely injured animals, similarities of spinal pathology to humans, and relatively good post-injury tolerance of this strain of minipigs to spinal trauma, suggest that this model can successfully be used to study therapeutic interventions targeting both acute and chronic stages of SCI.

Spinal cord injury and its treatment: current management and experimental perspectives

Clinical management of spinal cord injury (SCI) has significantly improved its general prognosis. However, to date, traumatic paraplegia and tetraplegia remain incurable, despite massive research efforts. Current management focuses on surgical stabilisation of the spine, intensive neurological rehabilitation, and the prevention and treatment of acute and chronic complications. Prevention remains the most efficient strategy and should be the main focus of public health efforts. Nevertheless, major advances in the understanding of the pathophysiological mechanisms of SCI open promising new therapeutic perspectives. Even if complete recovery remains elusive due to the complexity of spinal cord repair, a strategy combining different approaches may result in some degree of neurological improvement after SCI. Even slight neurological recovery can have high impact on the daily functioning of severely handicapped patients and, thus, result in significant improvements in quality of life.The main investigated strategies are: [1] initial neuroprotection, in order to decrease secondary injury to the spinal cord parenchyma after the initial insult; [2] spinal cord repair, in order to bridge the lesion site and reestablish the connection between the supraspinal centres and the deafferented cord segment below the lesion; and [3] re-training and enhancing plasticity of the central nervous system circuitry that was preserved or rebuilt after the injury.Now and in the future, treatment strategies that have both a convincing rationale and seen their efficacy confirmed reproducibly in the experimental setting must carefully be brought from bench to bedside. In order to obtain clinically significant results, their introduction into clinical research must be guided by scientific rigour, and their coordination must be rationally structured in a long-term perspective.

Cell transplantation: stem cells and precursor cells

Stem cells have been used to approach four different therapeutic repair strategies in spinal cord injury (SCI): (1) replacement of lost neurons, (2) replacement of oligodendrocytes to promote remyelination of demyelinated and/or regenerated axons, (3) providing a permissive substrate for axonal regeneration to overcome the intrinsic inhibition of surface molecules, and (4) engendering host repair. The first two strategies involve cell-specific differentiation of engrafted neural cells and the latter two may involve grafted neural or non-neural cells. The preclinical data for all of these approaches is at times contradictory and there is no consensus as to what type of stem cell is optimal to facilitate repair in specific injuries. Remyelination has been the most successful stem cell replacement strategy. Partial lineage restriction and pharmacological and/or genetic manipulation to express additional trophic support or restrict responses to host signals appears necessary for optimal neuronal and oligodendrocytic differentiation. However, these modifications will make their clinical application exceedingly difficult. Effects of grafted stem cells on abrogating host immune responses and engendering intrinsic repair is also a mechanism through which stem cells are likely therapeutically beneficial. While clinical trials with stem cell grafting into the injured spinal cord are ongoing, preclinical studies have yet to define mechanisms of action that can be definitively translated to those clinical approaches.

Frontiers of spinal cord and spine repair: experimental approaches for repair of spinal cord injury

Regeneration of injured CNS neurons was once thought to be an unachievable goal. Most patients with significant damage to the spinal cord suffer from permanently impaired neurological function. A century of research, however, has led to an understanding of multiple factors that limit CNS regeneration and from this knowledge experimental strategies have emerged for enhancing CNS repair. Some of these approaches have undergone human translation. Nevertheless, translating experimental findings to human trials has been more challenging than anticipated. In this chapter, we will review the current state of knowledge regarding central axonal growth failure after injury, and approaches taken to enhance recovery after SCI.

Approaches to repairing the damaged spinal cord: overview

Affecting young people during the most productive period of their lives, spinal cord injury (SCI) is a devastating problem for modern society. In the past, treating SCI seemed frustrating and hopeless because of the tremendous morbidity and mortality, life-shattering impact, and limited therapeutic options associated with the condition. Today, however, an understanding of the underlying pathophysiological mechanisms, the development of neuroprotective interventions, and progress toward regenerative interventions are increasing hope for functional restoration. In this chapter, we provide an overview of various repair strategies for the injured spinal cord. Special attention will be paid to strategies that promote spontaneous regeneration, including functional electrical stimulation, cell replacement, neuroprotection, and remyelination. The concept that limited rebuilding can provide a disproportionate improvement in quality of life is emphasized throughout. New surgical procedures, pharmacological treatments, and functional neuromuscular stimulation methods have evolved over the last decades and can improve functional outcomes after spinal cord injury; however, limiting secondary injury remains the primary goal. Tissue replacement strategies, including the use of embryonic stem cells, become an important tool and can restore function in animal models. Controlled clinical trials are now required to confirm these observations. The ultimate goal is to harness the body's own potential to replace lost central nervous system cells by activation of endogenous progenitor cell repair mechanisms.

Limiting spinal cord injury by pharmacological intervention

The direct primary mechanical trauma to neurons, glia and blood vessels that occurs with spinal cord injury (SCI) is followed by a complex cascade of biochemical and cellular changes which serve to increase the size of the injury site and the extent of cellular and axonal loss. The aim of neuroprotective strategies in SCI is to limit the extent of this secondary cell loss by inhibiting key components of the evolving injury cascade. In this review we will briefly outline the pathophysiological events that occur in SCI, and then review the wide range of neuroprotective agents that have been evaluated in preclinical SCI models. Agents will be considered under the following categories: antioxidants, erythropoietin and derivatives, lipids, riluzole, opioid antagonists, hormones, anti-inflammatory agents, statins, calpain inhibitors, hypothermia, and emerging strategies. Several clinical trials of neuroprotective agents have already taken place and have generally had disappointing results. In attempting to identify promising new treatments, we will therefore highlight agents with (1) low known risks or established clinical use, (2) behavioral data gained in clinically relevant animal models, (3) efficacy when administered after the injury, and (4) robust effects seen in more than one laboratory and/or more than one model of SCI.

Paranodal myelin damage after acute stretch in Guinea pig spinal cord

Mechanical injury causes myelin disruption and subsequent axonal conduction failure in the mammalian spinal cord. However, the underlying mechanism is not well understood. In mammalian myelinated axons, proper paranodal myelin structure is crucial for the generation and propagation of action potentials. The exposure of potassium channels at the juxtaparanodal region due to myelin disruption is thought to induce outward potassium currents and inhibit the genesis of the action potential, leading to conduction failure. Using multimodal imaging techniques, we provided anatomical evidence demonstrating paranodal myelin disruption and consequent exposure and redistribution of potassium channels following mechanical insult in the guinea pig spinal cord. Decompaction of paranodal myelin was also observed. It was shown that paranodal demyelination can result from both an initial physical impact and secondary biochemical reactions that are calcium dependent. 4-Aminopyridine (4-AP), a known potassium channel blocker, can partially restore axonal conduction, which further implicates the role of potassium channels in conduction failure. We provide important evidence of paranodal myelin damage, the role of potassium channels in conduction loss, and the therapeutic value of potassium blockade as an effective intervention to restore function following spinal cord trauma.

The protective effects of inosine against chemical hypoxia on cultured rat oligodendrocytes

Inosine is a purine nucleoside and is considered protective to neural cells including neurons and astrocytes against hypoxic injury. However, whether oligodendrocytes (OLs) could also be protected from hypoxia by inosine is not known. Here we investigated the effects of inosine on primarily cultured rat OLs injured by rotenone-mediated chemical hypoxia, and the mechanisms of the effects using ATP assay, MTT assay, PI-Hoechst staining, TUNEL, and immunocytochemistry. Results showed that rotenone exposure for 24 h caused cell death and impaired viability in both immature and mature OLs, while pretreatment of 10 mM inosine 30 min before rotenone administration significantly reduced cell death and improved the viability of OLs. The same concentration of inosine given 120 min after rotenone exposure also improved viability of injured mature OLs. Immunocytochemistry for nitrotyrosine and cellular ATP content examination indicated that inosine may protect OLs by providing ATP and scavenging peroxynitrite for cells. In addition, immature OLs were more susceptible to hypoxia than mature OLs; and at the similar degree of injury, inosine protected immature and mature OLs differently. Quantitative real-time PCR revealed that expression of adenosine receptors was different between these two stages of OLs. These data suggest that inosine protect OLs from hypoxic injury as an antioxidant and ATP provider, and the protective effects of inosine on OLs vary with cell differentiation, possibly due to the adenosine receptors expression profile. As OLs form myelin in the central nervous system, inosine could be used as a promising drug to treat demyelination-involved disorders.

Platelet-derived growth factor-responsive neural precursors give rise to myelinating oligodendrocytes after transplantation into the spinal cords of contused rats and dysmyelinated mice

Spinal cord injury (SCI) results in substantial oligodendrocyte death and subsequent demyelination leading to white-matter defects. Cell replacement strategies to promote remyelination are under intense investigation; however, the optimal cell for transplantation remains to be determined. We previously isolated a platelet-derived growth factor (PDGF)-responsive neural precursor (PRP) from the ventral forebrain of fetal mice that primarily generates oligodendrocytes, but also astrocytes and neurons. Importantly, human PRPs were found to possess a greater capacity for oligodendrogenesis than human epidermal growth factor- and/or fibroblast growth factor-responsive neural stem cells. Therefore, we tested the potential of PRPs isolated from green fluorescent protein (GFP)-expressing transgenic mice to remyelinate axons in the injured rat spinal cord. PRPs were transplanted 1 week after a moderate thoracic (T9) spinal cord contusion in adult male rats. After initial losses, PRP numbers remained stable from 2 weeks posttransplantation onward and those surviving cells integrated into host tissue. Approximately one-third of the surviving cells developed the typical branched phenotype of mature oligodendrocytes, expressing the marker APC-CC1. The close association of GFP cells with myelin basic protein as well as with Kv1.2 and Caspr in the paranodal and juxtaparanodal regions of nodes of Ranvier indicated that the transplanted cells successfully formed mature myelin sheaths. Transplantation of PRPs into dysmyelinated Shiverer mice confirmed the ability of PRP-derived cells to produce compact myelin sheaths with normal periodicity. These findings indicate that PRPs are a novel candidate for CNS myelin repair, although PRP-derived myelinating oligodendrocytes were insufficient to produce behavioral improvements in our model of SCI.

Emerging concepts in myeloid cell biology after spinal cord injury

Traumatic spinal cord injury (SCI) affects the activation, migration, and function of microglia, neutrophils and monocyte/macrophages. Because these myeloid cells can positively and negatively affect survival of neurons and glia, they are among the most commonly studied immune cells. However, the mechanisms that regulate myeloid cell activation and recruitment after SCI have not been adequately defined. In general, the dynamics and composition of myeloid cell recruitment to the injured spinal cord are consistent between mammalian species; only the onset, duration, and magnitude of the response vary. Emerging data, mostly from rat and mouse SCI models, indicate that resident and recruited myeloid cells are derived from multiple sources, including the yolk sac during development and the bone marrow and spleen in adulthood. After SCI, a complex array of chemokines and cytokines regulate myelopoiesis and intraspinal trafficking of myeloid cells. As these cells accumulate in the injured spinal cord, the collective actions of diverse cues in the lesion environment help to create an inflammatory response marked by tremendous phenotypic and functional heterogeneity. Indeed, it is difficult to attribute specific reparative or injurious functions to one or more myeloid cells because of convergence of cell function and difficulties in using specific molecular markers to distinguish between subsets of myeloid cell populations. Here we review each of these concepts and include a discussion of future challenges that will need to be overcome to develop newer and improved immune modulatory therapies for the injured brain or spinal cord.

High doses of 4-aminopyridine improve functionality in chronic complete spinal cord injury patients with MRI evidence of cord continuity

BACKGROUND AND AIMS

Many patients with complete spinal cord injury (SCI) exhibit demyelinated and poorly myelinated nerve fibers traversing the lesion site. Conventional doses of 4-aminopyridine (4-AP, 30 mg/day) have shown to provide no or minor functional improvement in these patients. We undertook this study to test the functional effect of high doses of 4-AP on patients with chronic complete SCI with cord continuity at the site of injury demonstrated by magnetic resonance imaging.

METHODS

Fourteen patients were included in a double-blind, randomized, placebo-controlled trial followed by an open label long-term follow-up. Initially, patients received 4-AP or placebo orally, with 4-AP being increased gradually (5 mg/week) to reach 30 mg/day. For long-term treatment, 4-AP was increased 10 mg periodically according to negative electroencephalogram and blood test abnormalities and minor adverse reactions. Pre-treatment, 12 and 24 weeks of the controlled trial, and 6 and 12 months of open trial evaluations, or with the highest doses reached were obtained.

RESULTS

Three of 12 patients were able to walk with the assistance of orthopedic devices, 1/12 became incomplete (AIS B), 7/12 improved their somatosensory evoked potentials, 5/12 had sensation and control of bladder and anal sphincters, and 4/9 male patients had psychogenic erection.

CONCLUSIONS

Positive changes were seen mainly in patients with cyst (4/5) or atrophy (3/5) of the injury site. Two patients withdrew from the study: one had seizures and one had intolerant adverse reactions. We conclude that high doses of 4-AP in the studied population produced several functional benefits not observed using lower doses.

Naturally occurring disk herniation in dogs: an opportunity for pre-clinical spinal cord injury research

Traumatic spinal cord injuries represent a significant source of morbidity in humans. Despite decades of research using experimental models of spinal cord injury to identify candidate therapeutics, there has been only limited progress toward translating beneficial findings to human spinal cord injury. Thoracolumbar intervertebral disk herniation is a naturally occurring disease that affects dogs and results in compressive/contusive spinal cord injury. Here we discuss aspects of this disease that are analogous to human spinal cord injury, including injury mechanisms, pathology, and metrics for determining outcomes. We address both the strengths and weaknesses of conducting pre-clinical research in these dogs, and include a review of studies that have utilized these animals to assess efficacy of candidate therapeutics. Finally, we consider a two-species approach to pre-clinical data acquisition, beginning with a reproducible model of spinal cord injury in the rodent as a tool for discovery with validation in pet dogs with intervertebral disk herniation.

Docosahexaenoic acid prevents white matter damage after spinal cord injury

We have previously shown that the omega-3 fatty acid docosahexaenoic acid (DHA) significantly improves several histological and behavioral measures after spinal cord injury (SCI). White matter damage plays a key role in neurological outcome following SCI. Therefore, we examined the effects of the acute intravenous (IV) administration of DHA (250 nmol/kg) 30 min after thoracic compression SCI in rats, alone or in combination with a DHA-enriched diet (400 mg/kg/d, administered for 6 weeks post-injury), on white matter pathology. By 1 week post-injury, the acute IV DHA injection led to significantly reduced axonal dysfunction, as indicated by accumulation of β-amyloid precursor protein (-55% compared to vehicle-injected controls) in the dorsal columns. The loss of cytoskeletal proteins following SCI was also significantly reduced. There were 43% and 73% more axons immunoreactive for non-phosphorylated 200-kD neurofilament in the ventral white matter and ventrolateral white matter, respectively, in animals receiving DHA injections than vehicle-injected rats. The acute DHA treatment also led to a significant improvement in microtubule-associated protein-2 immunoreactivity. By 6 weeks, damage to myelin and serotonergic fibers was also reduced. For some of the parameters measured, the combination of DHA injection and DHA-enriched diet led to greater neuroprotection than DHA injection alone. These findings demonstrate the therapeutic potential of DHA in SCI, and clearly indicate that this fatty acid confers significant protection to the white matter.

The acute administration of eicosapentaenoic acid is neuroprotective after spinal cord compression injury in rats

The aim of the present study was to investigate the effects of treatment with eicosapentaenoic acid (EPA) after spinal cord compression injury in adult rats. Saline or EPA (250 nmol/kg) was administered intravenously 30 min after compression injury. Locomotor recovery was assessed daily using the BBB open-field locomotor score. One week after injury, animals were sacrificed and the spinal cord tissue containing the compression epicenter, and the adjacent rostral and caudal segments, was immunostained using specific markers for neurons, oligodendrocytes, axonal injury, and macrophages/microglia. Administration of EPA resulted in decreased axonal injury and increased neuronal and oligodendrocyte survival, in the lesion epicenter and adjacent tissue. The behavioural assessment mirrored the neuroprotective effects and showed a significantly improved functional recovery in animals treated with EPA compared to the saline-treated controls over the 7-day period. These observations suggest that EPA has neuroprotective properties when administered after spinal cord trauma.

Human embryonic stem cell-derived oligodendrocyte progenitor cell transplants improve recovery after cervical spinal cord injury

Evidence that cell transplants can improve recovery outcomes in spinal cord injury (SCI) models substantiates treatment strategies involving cell replacement for humans with SCI. Most pre-clinical studies of cell replacement in SCI examine thoracic injury models. However, as most human injuries occur at the cervical level, it is critical to assess potential treatments in cervical injury models and examine their effectiveness using at-level histological and functional measures. To directly address cervical SCI, we used a C5 midline contusion injury model and assessed the efficacy of a candidate therapeutic for thoracic SCI in this cervical model. The contusion generates reproducible, bilateral movement and histological deficits, although a number of injury parameters such as acute severity of injury, affected gray-to-white matter ratio, extent of endogenous remyelination, and at-level locomotion deficits do not correspond with these parameters in thoracic SCI. On the basis of reported benefits in thoracic SCI, we transplanted human embryonic stem cell (hESC)-derived oligodendrocyte progenitor cells (OPCs) into this cervical model. hESC-derived OPC transplants attenuated lesion pathogenesis and improved recovery of forelimb function. Histological effects of transplantation included robust white and gray matter sparing at the injury epicenter and, in particular, preservation of motor neurons that correlated with movement recovery. These findings further our understanding of the histopathology and functional outcomes of cervical SCI, define potential therapeutic targets, and support the use of these cells as a treatment for cervical SCI.

Involvement of ERK2 in traumatic spinal cord injury

Activation of extracellular signal-regulated protein kinase 1/2 (ERK1/2) are implicated in the pathophysiology of spinal cord injury (SCI). However, the specific functions of individual ERK isoforms in neurodegeneration are largely unknown. We investigated the hypothesis that ERK2 activation may contribute to pathological and functional deficits following SCI and that ERK2 knockdown using RNA interference may provide a novel therapeutic strategy for SCI. Lentiviral ERK2 shRNA and siRNA were utilized to knockdown ERK2 expression in the spinal cord following SCI. Pre-injury intrathecal administration of ERK2 siRNA significantly reduced excitotoxic injury-induced activation of ERK2 (p < 0.001) and caspase 3 (p < 0.01) in spinal cord. Intraspinal administration of lentiviral ERK2 shRNA significantly reduced ERK2 expression in the spinal cord (p < 0.05), but did not alter ERK1 expression. Administration of the lentiviral ERK2 shRNA vector 1 week prior to severe spinal cord contusion injury resulted in a significant improvement in locomotor function (p < 0.05), total tissue sparing (p < 0.05), white matter sparing (p < 0.05), and gray matter sparing (p < 0.05) 6 weeks following severe contusive SCI. Our results suggest that ERK2 signaling is a novel target associated with the deleterious consequences of spinal injury.

Novel Potassium Channel Blocker, 4-AP-3-MeOH, Inhibits Fast Potassium Channels and Restores Axonal Conduction in Injured Guinea Pig Spinal Cord White Matter

We have demonstrated that 4-aminopyridine-3-methanol (4-AP-3-MeOH), a 4-aminopyridine derivative, significantly restores axonal conduction in stretched spinal cord white-matter strips and shows no preference in restoring large and small axons. This compound is 10 times more potent when compared with 4-AP and other derivatives in restoring axonal conduction. Unlike 4-AP, 4-AP-3-MeOH can restore axonal conduction without changing axonal electrophysiological properties. In addition, we also have confirmed that 4-AP-3-MeOH is indeed an effective blocker of IA based on patch-clamp studies using guinea pig dorsal root ganglia cells. Furthermore, we have also provided the critical evidence to confirm the unmasking of potassium channels following mechanical injury. Taken together, our data further supports and implicates the role of potassium channels in conduction loss and its therapeutic value as an effective target for intervention to restore function in spinal cord trauma. Furthermore, due to its high potency and possible low side effect of impacting electrophysiological properties, 4-AP-3-MeOH is perhaps the optimal choice in reversing conduction block in spinal cord injury compared with other derivatives previously reported from this group.

HDAC6 is a target for protection and regeneration following injury in the nervous system

Central nervous system (CNS) trauma can result in tissue disruption, neuronal and axonal degeneration, and neurological dysfunction. The limited spontaneous CNS repair in adulthood and aging is often insufficient to overcome disability. Several investigations have demonstrated that targeting HDAC activity can protect neurons and glia and improve outcomes in CNS injury and disease models. However, the enthusiasm for pan-HDAC inhibition in treating neurological conditions is tempered by their toxicity toward a host of CNS cell types -a biological extension of their anticancer properties. Identification of the HDAC isoform, or isoforms, that specifically mediate the beneficial effects of pan-HDAC inhibition could overcome this concern. Here, we show that pan-HDAC inhibition not only promotes neuronal protection against oxidative stress, a common mediator of injury in many neurological conditions, but also promotes neurite growth on myelin-associated glycoprotein and chondroitin sulfate proteoglycan substrates. Real-time PCR revealed a robust and selective increase in HDAC6 expression due to injury in neurons. Accordingly, we have used pharmacological and genetic approaches to demonstrate that inhibition of HDAC6 can promote survival and regeneration of neurons. Consistent with a cytoplasmic localization, the biological effects of HDAC6 inhibition appear transcription-independent. Notably, we find that selective inhibition of HDAC6 avoids cell death associated with pan-HDAC inhibition. Together, these findings define HDAC6 as a potential nontoxic therapeutic target for ameliorating CNS injury characterized by oxidative stress-induced neurodegeneration and insufficient axonal regeneration.

Anatomical and functional outcomes following a precise, graded, dorsal laceration spinal cord injury in C57BL/6 mice

To study the pathophysiology of spinal cord injury (SCI), we used the LISA-Vibraknife to generate a precise and reproducible dorsal laceration SCI in the mouse. The surgical procedure involved a T9 laminectomy, dural resection, and a spinal cord laceration to a precisely controlled depth. Four dorsal hemisection injuries with lesion depths of 0.5, 0.8, 1.1, and 1.4 mm, as well as normal, sham (laminectomy and dural removal only), and transection controls were examined. Assessments including the Basso Mouse Scale (BMS), footprint analysis, beam walk, toe spread reflex, Hargreaves' test, and transcranial magnetic motor-evoked potential (tcMMEP) analysis were performed to assess motor, sensorimotor, and sensory function. These outcome measures demonstrated significant increases in functional deficits as the depth of the lesion increased, and significant behavioral recovery was observed in the groups over time. Quantitative histological examination showed significant differences between the injury groups and insignificant lesion depth variance within each of the groups. Statistically significant differences were additionally found in the amount of ventral spared tissue at the lesion site between the injury groups. This novel, graded, reproducible laceration SCI model can be used in future studies to look more closely at underlying mechanisms that lead to functional deficits following SCI, as well as to determine the efficacy of therapeutic intervention strategies in the injury and recovery processes following SCI.

The P2Y-like receptor GPR17 as a sensor of damage and a new potential target in spinal cord injury

Upon central nervous system injury, the extracellular concentrations of nucleotides and cysteinyl-leukotrienes, two unrelated families of endogenous signalling molecules, are markedly increased at the site of damage, suggesting that they may act as 'danger signals' to alert responses to tissue damage and start repair. Here we show that, in non-injured spinal cord parenchyma, GPR17, a P2Y-like receptor responding to both uracil nucleotides (e.g. UDP-glucose) and cysteinyl-leukotrienes (e.g. LTD4 and LTC4), is present on a subset of neurons and of oligodendrocytes at different stages of maturation, whereas it is not expressed by astrocytes. GPR17 immunoreactivity was also found on ependymal cells lining the central canal that still retain some of the characteristics of stem/progenitor cells during adulthood. Induction of spinal cord injury (SCI) by acute compression resulted in marked cell death of GPR17+ neurons and oligodendrocytes inside the lesion followed by the appearance of proliferating GPR17+ microglia/macrophages migrating to and infiltrating into the lesioned area. Moreover, 72 h after SCI, GPR17+ ependymal cells started to proliferate and to express GFAP, suggesting their activation and 'de-differentiation' to pluripotent progenitor cells. The in vivo knock down of GPR17 by an antisense oligonucleotide strategy during SCI induction markedly reduced tissue damage and related histological and motor deficits, thus confirming the crucial role played by this receptor in the early phases of tissue damage development. Taken together, our findings suggest a dual and spatiotemporal-dependent role for GPR17 in SCI. At very early times after injury, GPR17 mediates neuronal and oligodendrocyte death inside the lesioned area. At later times, GPR17+ microglia/macrophages are recruited from distal parenchymal areas and move toward the lesioned zone, to suggest a role in orchestrating local remodelling responses. At the same time, the induction of the stem cell marker GFAP in GPR17+ ependymal cells suggests initiation of repair mechanisms. Thus, GPR17 may act as a 'sensor' of damage that is activated by nucleotides and cysteinyl-leukotrienes released in the lesioned area, and could also participate in post-injury responses. Moreover, its presence on spinal cord pre-oligodendrocytes and precursor-like cells suggests GPR17 as a novel target for therapeutic manipulation to foster remyelination and functional repair in SCI.

Endogenous remyelination is induced by transplant rejection in a viral model of multiple sclerosis

Human embryonic stem cell-derived oligodendrocyte progenitors (OPCs) were transplanted into mice persistently infected with the neurotropic JHM strain of mouse hepatitis virus with established demyelination. Engrafted cells did not survive past 2 weeks following transplantation despite treatment with high dose cyclosporine A. While T cell infiltration into the CNS was dampened, elevated numbers of macrophage/microglia and endogenous OPCs were evident surrounding the implantation site and this was associated with increased remyelination. These data suggest that remyelination was initiated by the local response to xenograft transplantation. These findings illustrate the complexities of OPC transplantation into areas of robust immune-mediated pathology.