Bridging the transected or contused adult rat spinal cord with Schwann cell and olfactory ensheathing glia transplants

Cellular repair strategies for spinal cord injury

The implantation of exogenous cells or tissues has been a popular and successful strategy to overcome physical discontinuity and support axon growth in experimental models of spinal cord injury (SCI). Cellular therapies exhibit a multifarious potential for SCI restoration, providing not only a supportive substrate upon which axons can traverse the injury site, but also reducing progressive tissue damage and scarring, facilitating remyelination repair, and acting as a source for replacing and re-establishing lost neural tissue and its circuitry. The past two decades of research into cell therapies for SCI repair have seen the progressive evolution from whole tissue strategies, such as peripheral nerve grafts, to the use of specific, purified cell types from a diverse range of sources and, recently, to the employment of stem or neural precursor cell populations that have the potential to form a full complement of neural cell types. Although the progression of cell therapies from laboratory to clinical implementation has been slow, human SCI safety and efficacy trials involving several cell types within the US appear to be close at hand.

Genes associated with adult axon regeneration promoted by olfactory ensheathing cells: a new role for matrix metalloproteinase 2

The molecular mechanisms used by olfactory ensheathing cells (OECs) to promote repair in the damaged adult mammalian CNS remain unknown. Thus, we used microarrays to analyze three OEC populations with different capacities to promote axonal regeneration in cultured rat retinal neurons. Gene expression in "long-term cultured OECs" that do not stimulate adult axonal outgrowth was compared with that of "primary olfactory ensheathing cells" and the immortalized OEC cell line TEG3. In this way, we identified a number of candidate genes that might play a role in promoting adult axonal regeneration. Among these genes, it was striking that both the matrix metalloproteinase 2 (MMP2) and an inhibitor of this protease were represented. The disruption of MMP2 activity in TEG3 cells impaired their capacity to trigger axon regeneration in cultured adult retinal neurons. Furthermore, the MMP2 protein was detected in grafts of OECs that elicited robust axonal regeneration in the injured spinal cord of adult rats in vivo. These data suggest that MMP2 does indeed participate in adult axonal regeneration induced by OECs.

Signaling axis in schwann cell proliferation and differentiation

Recent progress in molecular biology has markedly expanded our knowledge of the molecular mechanism behind the proliferation and differentiation processes of Schwann cells, the myelin-forming cells in peripheral nervous systems. Intracellular signaling molecules participate in integrating various stimuli from cytokines and other humoral factors and control the transcriptional activities of the genes that regulate mitosis or differentiation. This article provides an overview of the roles played by the intracellular pathways regulating Schwann cell functions. In Schwann cell proliferation, cyclic adenosine monophosphate signals and mitogen-activated protein kinase pathways play pivotal roles and may also interact with each other. Regarding differentiation, myelin formation is regulated by various cytokines and extracellular matrix molecules. Specifically, platelet-derived growth factor, neuregulin, and insulin-like growth factor-I all are classified as ligands for receptor-type tyrosine kinase and activate common intracellular signaling cascades, mitogen-activated protein kinase pathways, and phosphatidylinositol-3-kinase pathways. The balance of activities between these two pathways appears crucial in regulating Schwann cell differentiation, in which phosphatidylinositol-3-kinase pathways promote myelin formation. Analysis of these signaling molecules in Schwann cells will enable us not only to understand their physiological development but also to innovate new approaches to treat disorders related to myelination.

Transplantation of Schwann cells to subarachnoid space induces repair in contused rat spinal cord

Schwann cell transplantation is well known to induce repair in the injured spinal cord which disables millions of injured patients throughout the world. An ideal route of delivering the grafted Schwann cells to the spinal cord should neither cause more injury nor reinitiate inflammatory events and also provide a favorable milieu to the grafted cells. In this study, we have utilized subarachnoid route to transplant Schwann cells and evaluated their effects in a contusive model of spinal cord injury. Adult rats weighing 100-140 g were experimentally injured by crushing the spinal cord with a titanium clip and then divided into four groups (Tracing, Control, Medium-treated and Schwann cell-treated). Cultured Schwann cells (5x10(4) cells in 5 microl) or medium were injected to the animals of corresponding groups via subarachnoid space at the injured site 7 days after injury. In tracing group, Schwann cells (labeled with Hoechst) demonstrated their presence within spinal cord 7 days after transplantation. Evaluation of locomotor performance of animals for 60 days after injury showed that animals treated with Schwann cells had significant improvement (P<0.01). Similarly, the axon density at the site of injury was significantly higher. The results indicate the efficacy of subarachnoid route for the transplantation of Schwann cells in inducing repair of the contused spinal cord. We conclude that this route can be useful for the transplantation of Schwann cells and offers a hope for the patients suffering from spinal cord injury.

Bioengineered Strategies for Spinal Cord Repair

This article reviews bioengineered strategies for spinal cord repair using tissue engineered scaffolds and drug delivery systems. The pathophysiology of spinal cord injury (SCI) is multifactorial and multiphasic, and therefore, it is likely that effective treatments will require combinations of strategies such as neuroprotection to counteract secondary injury, provision of scaffolds to replace lost tissue, and methods to enhance axonal regrowth, synaptic plasticity, and inhibition of astrocytosis. Biomaterials have major advantages for spinal cord repair because of their structural and chemical versatility. To date, various degradable or non-degradable biomaterial polymers have been tested as guidance channels or delivery systems for cellular and non-cellular neuroprotective or neuroregenerative agents in experimental SCI. There is promise that bioengineering technology utilizing cellular treatment strategies, including Schwann cells, olfactory ensheathing glia, or neural stem cells, can promote repair of the injured spinal cord. This review is divided into three parts: (1) degradable and non-degradable biomaterials; (2) device design; and (3) combination strategies with scaffolds. We will show that bioengineering combinations of cellular and non-cellular strategies have enhanced the potential for experimental SCI repair, although further pre-clinical work is required before this technology can be translated to humans.

Lamina propria and olfactory bulb ensheathing cells exhibit differential integration and migration and promote differential axon sprouting in the lesioned spinal cord

Olfactory bulb-derived (central) ensheathing cell (OB OEC) transplants have shown significant promise in rat models of spinal cord injury, prompting the use of lamina propria-derived (peripheral) olfactory ensheathing cells (LP OECs) in both experimental and clinical trials. Although derived from a common embryonic precursor, both sources of OECs reside in different nervous system compartments postnatally, and their ability to promote regeneration and efficacy after transplantation may differ depending on both their source and mode of transplantation. Here, we have purified green fluorescent protein-expressing LP and OB OECs, assayed their biological differences in vitro, and transplanted them acutely either directly into or rostral and caudal to a dorsolateral funiculus crush. LP and OB OECs exhibit multiple morphological and antigenic similarities in vitro, and, after transplantation, they both attenuate lesion and cavity formation and promote angiogenesis, endogenous Schwann cell infiltration, and axonal sprouting. However, an increased mitotic rate and migratory ability of LP OECs in vitro was reflected in vivo by their superior ability to migrate within the spinal cord, reduce cavity formation and lesion size, and differentially stimulate outgrowth of axonal subpopulations compared with OB OECs. An undesired behavior (autotomy) was also significantly enhanced by LP OEC, over OB OEC, transplantation. These results suggest that LP and OB OECs exhibit intrinsic biological differences that, after transplantation into the lesioned CNS, result in differences in postlesion spinal cord neuropathology and anatomical and behavioral regeneration outcomes that also vary depending on direct versus rostrocaudal transplantation.

Experimental strategies to promote spinal cord regeneration--an integrative perspective

Detailed pathophysiological findings of secondary damage phenomena after spinal cord injury (SCI) as well as the identification of inhibitory and neurotrophic proteins have yielded a plethora of experimental therapeutic approaches. Main targets are (i) to minimize secondary damage progression (neuroprotection), (ii) to foster axon conduction (neurorestoration) and (iii) to supply a permissive environment to promote axonal sprouting (neuroregenerative therapies). Pre-clinical studies have raised hope in functional recovery through the antagonism of growth inhibitors, application of growth factors, cell transplantation, and vaccination strategies. To date, even though based on successful pre-clinical animal studies, results of clinical trials are characterized by dampened effects attributable to difficulties in the study design (patient heterogeneity) and species differences. A combination of complementary therapeutic strategies might be considered pre-requisite for future synergistic approaches. Here, we line out pre-clinical interventions resulting in improved functional neurological outcome after spinal cord injury and track them on their intended way to bedside.

Survival and migration of human and rat olfactory ensheathing cells in intact and injured spinal cord

Increasing evidence indicates the potential of olfactory ensheathing cells (OECs) for treating spinal cord injuries. The present study compared proliferation and migration of adult rat and human OECs transplanted into the spinal cord of athymic (immunodeficient) rats. OECs were purified from the nasal lamina propria and prelabeled with a cytoplasmic dye. After OEC injection into the thoracic spinal cord, animals were perfused 4 hr, 24 hr, and 7 days later. Both rat and human OECs showed similar migration. Cells were seen leaving the injection site after 4 hr, and by 7 days both rat and human OECs had migrated approximately 1 mm rostrally and caudally within the cord (rat: 1,400 +/- 241 microm rostral, 1,134 +/- 262 microm caudal, n = 5; human: 1,337 +/- 192 microm rostral, 1,205 +/- 148 microm caudal, n = 6). Proliferation of transplanted OECs was evident at 4 hr, but most had ceased dividing by 24 hr. In 10 animals, the spinal cord was injured by a contralateral hemisection made 5 mm rostral to the transplantation site at the time of OEC transplantation. After 7 days, macrophages were numerous both around the injury and at the transplantation site. In the injured cord, rat and human OECs migrated for shorter distances, in both rostral and caudal directions (rat: 762 +/- 118 microm rostral, 554 +/- 142 microm caudal, n = 4; human: 430 +/- 55 microm rostral, 399 +/- 161 microm caudal, n = 3). The results show that rat and human OECs rapidly stop dividing after transplantation and have a similar ability to survive and migrate within the spinal cord of immunocompromised hosts. OECs migrated less in animals with a concomitant contralateral hemisection.

G. Heiner Sell memorial lecture: neuronal plasticity after spinal cord injury: significance for present and future treatments

Recent progress in the understanding of movement control allows us to define more precisely the requirements for successful rehabilitation of patients with neurologic deficits after a spinal cord injury (SCI). Load- and hip joint position-related afferent input seems to be of crucial importance for the generation and success of locomotor training. In addition, there is accumulating evidence from animal experiments that axonal regeneration can be induced after a SCI. Consequently, in the near future, new therapeutic approaches will be developed for the treatment of subjects with SCI. Functional training and regeneration represent complimentary approaches. Regenerating spinal tract fibers needs functional training to make the appropriate connections, and training effects will be enhanced by regenerating fibers. A clinical basis for monitoring the effects of novel interventional therapies is needed. Refined and combined clinical and neurophysiologic measures are needed for a precise qualitative and quantitative assessment of spinal cord function in patients with SCI at an early stage. This is a basic requirement for predicting functional outcome, as well as for recognizing any improvement in the recovery of function caused by a new treatment. To this aim, 14 European spinal cord injury centers involved in the rehabilitation of patients with acute SCI have built a close clinical collaboration using a standardized protocol for the assessment of the outcome after SCI and the extent of recovery achieved by actually applied therapies in a larger population of patients with SCI.

Alginate hydrogel and matrigel as potential cell carriers for neurotransplantation

Development of biosynthetic conduits carrying extracellular matrix molecules and cell lines expressing neurotrophic growth factors represents a novel and promising strategy for spinal cord and peripheral nerve repair. In the present in vitro study, the compatibility and growth-promoting effects of (i) alginate hydrogel, (ii) alginate hydrogel complemented with fibronectin, and (iii) matrigel were compared between olfactory ensheathing cells (OECs), Schwann cells (SCs), and bone marrow stromal cells (BMSCs). Neurite outgrowth from embryonic dorsal root ganglia (DRG) neurons was used to assess the efficacy of the hydrogels alone or in combination with cultured cells to promote axonal regeneration. The result showed that alginate hydrogel transformed OECs, SCs, and BMSCs into atypical cells with spherical shape and inhibited their metabolic activity. Combination of alginate hydrogel with fibronectin promoted only OECs proliferation. Alginate hydrogel also inhibited outgrowth of DRG neurites, although this effect was attenuated by addition of fibronectin, SCs, or BMSCs. In contrast, matrigel stimulated cell proliferation, preserved the typical morphological features of the cultured cells and induced massive sprouting of DRG neurites. Addition of cultured cells to matrigel did not further improve DRG neurite outgrowth. The present findings suggest that addition of extracellular matrix should be considered when engineering biosynthetic scaffolds on the basis of alginate hydrogels.

Survival, integration, and axon growth support of glia transplanted into the chronically contused spinal cord

Due to an ever-growing population of individuals with chronic spinal cord injury, there is a need for experimental models to translate efficacious regenerative and reparative acute therapies to chronic injury application. The present study assessed the ability of fluid grafts of either Schwann cells (SCs) or olfactory ensheathing glia (OEG) to facilitate the growth of supraspinal and afferent axons and promote restitution of hind limb function after transplantation into a 2-month-old, moderate, thoracic (T8) contusion in the rat. The use of cultured glial cells, transduced with lentiviral vectors encoding enhanced green fluorescent protein (EGFP), permitted long-term tracking of the cells following spinal cord transplantation to examine their survival, migration, and axonal association. At 3 months following grafting of 2 million SCs or OEG in 6 microl of DMEM/F12 medium into the injury site, stereological quantification of the three-dimensional reconstructed spinal cords revealed that an average of 17.1 +/- 6.8% of the SCs and 2.3 +/- 1.4% of the OEG survived from the number transplanted. In the OEG grafted spinal cord, a limited number of glia were unable to prevent central cavitation and were found in patches around the cavity rim. The transplanted SCs, however, formed a substantive graft within the injury site capable of supporting the ingrowth of numerous, densely packed neurofilament-positive axons. The SC grafts were able to support growth of both ascending calcitonin gene-related peptide (CGRP)-positive and supraspinal serotonergic axons and, although no biotinylated dextran amine (BDA)-traced corticospinal axons were present within the center of the grafts, the SC transplants significantly increased corticospinal axon numbers immediately rostral to the injury-graft site compared with injury-only controls. Moreover, SC grafted animals demonstrated modest, though significant, improvements in open field locomotion and exhibited less foot position errors (base of support and foot rotation). Whereas these results demonstrate that SC grafts survive, support axon growth, and can improve functional outcome after chronic contusive spinal cord injury, further development of OEG grafting procedures in this model and putative combination strategies with SC grafts need to be further explored to produce substantial improvements in axon growth and function.

Superparamagnetic iron oxide-labeled Schwann cells and olfactory ensheathing cells can be traced in vivo by magnetic resonance imaging and retain functional properties after transplantation into the CNS

Schwann cell (SC) and olfactory ensheathing cell (OEC) transplantation has been shown experimentally to promote CNS axonal regeneration and remyelination. To advance this technique into a clinical setting it is important to be able to follow the fates of transplanted cells by noninvasive imaging. Previous studies, using complex modification processes to enable uptake of contrast agents, have shown that cells labeled in vitro with paramagnetic contrast agents transplanted into rodent CNS can be visualized using magnetic resonance imaging (MRI). Here we show that SCs and OECs efficiently internalize dextran-coated superparamagnetic iron oxide (SPIO) from the culture medium by fluid phase pinocytosis. After transplantation into focal areas of demyelination in adult rat spinal cord both transplanted SPIO-labeled SCs and OECs produce a signal reduction using T(2)-weighted MRI in anesthetized rats that persists for up to 4 weeks. Although signal reduction was discernable after transplantation of unlabelled cells, this is nevertheless distinguishable from that produced by transplanted labeled cells. The region of signal reduction in SPIO-labeled cell recipients correlates closely with areas of remyelination. Because the retention of functional integrity by labeled cells is paramount, we also show that SPIO-labeled SCs and OECs are able to myelinate normally after transplantation into focal areas of demyelination. These studies demonstrate the feasibility of noninvasive imaging of transplanted SCs and OECs and represent a significant step toward the clinical application of promising experimental approaches.

Defining the role of olfactory ensheathing cells in facilitating axon remyelination following damage to the spinal cord

Olfactory ensheathing cells (OECs) are unique cells that are responsible for the successful regeneration of olfactory axons throughout the life of adult mammals. More than a decade of research has shown that implantation of OECs may be a promising therapy for damage to the nervous system, including spinal cord injury. Based on this research, several clinical trials worldwide have been initiated that use autologous transplantation of olfactory tissue containing OECs into the damaged spinal cord of humans. However, research from several laboratories has challenged the widely held belief that OECs are directly responsible for myelinating axons and promoting axon regeneration. The purpose of this review is to provide a working hypothesis that integrates several current ideas regarding the mechanisms of the beneficial effects of OECs. Specifically, OECs promote axon regeneration and functional recovery indirectly by augmenting the endogenous capacity of host Schwann cells to invade the damaged spinal cord. Together with Schwann cells, OECs create a 3-dimensional matrix that provides a permissive microenvironment for successful axon regeneration in the adult mammalian central nervous system.

Nasal and frontal sinus mucosa of the adult dog contain numerous olfactory sensory neurons and ensheathing glia

Olfactory glial cells have been the focus of much recent research interest because of their possible future use as cellular transplants in repair of spinal cord injury. Although olfactory glial cells can be collected from the olfactory bulb for in vitro culture, alternative sites would be preferable for safer surgical access. This study was designed to investigate the distribution of olfactory sensory neurons and olfactory glial cells within the canine peripheral olfactory system. Using immunohistochemistry and electron microscopy on perfused tissue we demonstrate that olfactory sensory neurons are found in both the caudal nasal and the frontal sinus epithelia. Olfactory ensheathing glia were found in the mucosa at both these sites implying that surgical access for harvesting cells for transplantation would be straightforward.

Opposing extracellular signal-regulated kinase and Akt pathways control Schwann cell myelination

Schwann cells are the myelinating glia of the peripheral nervous system, and their development is regulated by various growth factors, such as neuregulin, platelet-derived growth factor (PDGF), and insulin-like growth factor-I (IGF-I). However, the mechanism of intracellular signaling pathways following these ligand stimuli in Schwann cell differentiation remains elusive. Here, we demonstrate that in cultured Schwann cells, neuregulin and PDGF suppressed the expression of myelin-associated protein markers, whereas IGF-I promoted it. Although these ligands activated common downstream signaling pathways [i.e., extracellular signal-regulated kinase (Erk) and phosphatidylinositol-3-kinase (PI3K)-Akt pathways], the profiles of activation varied among ligands. To elucidate the function of these pathways and the mechanisms underlying Schwann cell differentiation, we used adenoviral vectors to selectively activate or inactivate these pathways. We found that the selective activation of Erk pathways suppressed Schwann cell differentiation, whereas that of PI3K pathways promoted it. Furthermore, lithium chloride, a modulator of glycogen synthase kinase-3beta (GSK-3beta) promoted Schwann cell differentiation, suggesting the involvement of GSK-3beta as a downstream molecule of PI3K-Akt pathways. Selective activation of PI3K pathways in Schwann cells by gene transfer also demonstrated increased myelination in in vitro Schwann cell-DRG neuron cocultures and in vivo allogenic nerve graft experiments. We conclude that signals mediated by PI3K-Akt are crucial for initiation of myelination and that the effects of growth factors are primarily dependent on the balance between Erk and PI3K-Akt activation. Our results also propose the possibility of augmenting Schwann cell functions by modulating intracellular signals in light of future cell therapies.

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

Here we review mechanisms and molecules that necessitate protection and oppose axonal growth in the injured spinal cord, representing not only a cast of villains but also a company of therapeutic targets, many of which have yet to be fully exploited. We next discuss recent progress in the fields of bridging, overcoming conduction block and rehabilitation after spinal cord injury (SCI), where several treatments in each category have entered the spotlight, and some are being tested clinically. Finally, studies that combine treatments targeting different aspects of SCI are reviewed. Although experiments applying some treatments in combination have been completed, auditions for each part in the much-sought combination therapy are ongoing, and performers must demonstrate robust anatomical regeneration and/or significant return of function in animal models before being considered for a lead role.

Minimally invasive delivery of stem cells for spinal cord injury: advantages of the lumbar puncture technique

Object. Stem cell therapy has been shown to have considerable therapeutic potential for spinal cord injuries (SCIs); however, most experiments in animals have been performed by injecting cells directly into the injured parenchyma. This invasive technique compromises the injured spinal cord, although it delivers cells into the hostile environment of the acutely injured cord. In this study, the authors tested the possibility of delivering stem cells to injured spinal cord by using three different minimally invasive techniques.

Methods. Bone marrow stromal cells (BMSCs) are clinically attractive because they have shown therapeutic potential in SCI and can be obtained in patients at the bedside, raising the possibility of autologous transplantation. In this study transgenically labeled cells were used for transplantation, facilitating posttransplantation tracking. Inbred Fisher-344 rats received partial cervical hemisection injury, and 2 × 106 BMSCs were intravenously, intraventricularly, or intrathecally transplanted 24 hours later via lumbar puncture (LP). The animals were killed 3, 10, or 14 days posttransplantation, and tissue samples were submitted to histochemical and immunofluorescence analyses. For additional comparison and validation, lineage restricted neural precursor (LRNP) cells obtained from E13.5 rat embryos were transplanted via LP, and these findings were also analyzed.

Conclusions. Both BMSCs and LRNP cells home toward injured spinal cord tissues. The use of LP and intraventricular routes allows more efficient delivery of cells to the injured cord compared with the intravenous route. Stem cells delivered via LP for treatment of SCI may potentially be applicable in humans after optimal protocols and safety profiles are established in further studies.

cAMP and Schwann cells promote axonal growth and functional recovery after spinal cord injury

Central neurons regenerate axons if a permissive environment is provided; after spinal cord injury, however, inhibitory molecules are present that make the local environment nonpermissive. A promising new strategy for inducing neurons to overcome inhibitory signals is to activate cAMP signaling. Here we show that cAMP levels fall in the rostral spinal cord, sensorimotor cortex and brainstem after spinal cord contusion. Inhibition of cAMP hydrolysis by the phosphodiesterase IV inhibitor rolipram prevents this decrease and when combined with Schwann cell grafts promotes significant supraspinal and proprioceptive axon sparing and myelination. Furthermore, combining rolipram with an injection of db-cAMP near the graft not only prevents the drop in cAMP levels but increases them above those in uninjured controls. This further enhances axonal sparing and myelination, promotes growth of serotonergic fibers into and beyond grafts, and significantly improves locomotion. These findings show that cAMP levels are key for protection, growth and myelination of injured CNS axons in vivo and recovery of function.

Repair of the Injured Spinal Cord and the Potential of Embryonic Stem Cell Transplantation

Traditionally, treatment of spinal cord injury seemed frustrating and hopeless because of the remarkable morbidity and mortality, and restricted therapeutic options. Recent advances in neural injury and repair, and the progress towards development of neuroprotective and regenerative interventions are basis for increased optimism. Neural stem cells have opened a new arena of discovery for the field of regenerative science and medicine. Embryonic stem (ES) cells can give rise to all neural progenitors and they represent an important scientific tool for approaching neural repair. The growing number of dedicated regeneration centers worldwide exemplifies the changing perception towards the do-ability of spinal cord repair and this review was born from a presentation at one such leading center, the Kentucky Spinal Cord Injury Research Center. Current concepts of the pathophysiology, repair, and restoration of function in the damaged spinal cord are presented with an overlay of how neural stem cells, particularly ES cells, fit into the picture as important scientific tools and therapeutic targets. We focus on the use of genetically tagged and selectable ES cell lines for neural induction and transplantation. Unique features of ES cells, including indefinite replication, pluripotency, and genetic flexibility, provide strong tools to address questions of neural repair. Selective marker expression in transplanted ES cell derived neural cells is providing new insights into transplantation and repair not possible previously. These features of ES cells will produce a predictable and explosive growth in scientific tools that will translate into discoveries and rapid progress in neural repair.

Stem and Precursor Cells in the Nervous System

The early-formed neural tube consists of proliferating, morphologically homogeneous cells, termed "neuroepithelial (NEP) stem cells" which generate neurons, astrocytes, and oligodenrocytes through a series of intermediate precursor cells. In addition to NEP cells, a second class of stem cells-the neurosphere-forming cell-can be isolated at later stages of development. NEP cells can differentiate into neural crest stem cells, which in turn generate PNS derivatives. NEP cells and neurosphereforming stem cells and more restricted precursors express a characteristic spectrum of markers that can be used to characterize them. Each of these cell types can be isolated from embryonic stem (ES) cell cultures, and their behavior appears similar to cells isolated at later developmental ages. The relative advantages and disadvantages of these cells for cell replacement therapy are discussed.

Rodent models for treatment of spinal cord injury: research trends and progress toward useful repair

PURPOSE OF REVIEW

In this review, we have documented some current research trends in rodent models of spinal cord injury. We have also catalogued the treatments used in studies published between October 2002 and November 2003, with special attention given to studies in which treatments were delayed for at least 4 days after injury.

RECENT FINDINGS

Most spinal cord injury studies are performed with one of three general injury models: transection, compression, or contusion. Although most treatments are begun immediately after injury, a growing number of studies have used delayed interventions. Mice and the genetic tools they offer are gaining in popularity. Some researchers are setting their sights beyond locomotion, to issues more pressing for people with spinal cord injury (especially bladder function and pain).

SUMMARY

Delayed treatment protocols may extend the window of opportunity for treatment of spinal cord injury, whereas continued progress in the prevention of secondary cell death will reduce the severity of new cases. The use of mice will hopefully accelerate progress towards useful regeneration in humans. Researchers must improve cross-study comparability to allow balanced decisions about potentially useful treatments.

Confocal imaging of changes in glial calcium dynamics and homeostasis after mechanical injury in rat spinal cord white matter

Periaxonal glia play an important role in maintaining axonal function in white matter. However, little is known about the changes that occur in glial cells in situ immediately after traumatic injury. We used fluo-3 and confocal microscopy to examine the effects of localized (<0.5 mm) mechanical trauma on intracellular calcium (Ca(i)(2+)) levels in glial cells in a mature rat spinal cord white matter preparation in vitro. At the injury site, the glial Ca(i)(2+) signal increased by 300-400% within 5 min and then irreversibly declined indicating cell lysis and death. In glial cells at sites adjacent to the injury (1.5-2 mm from epicenter), Ca(i)(2+) levels peaked at 10-15 min, and thereafter declined but remained significantly above rest levels. At distal sites (6-9 mm), Ca(i)(2+) levels rose and declined even slower, peaking at 80-90 min. Injury in zero calcium dampened Ca(i)(2+) responses, indicating a role for calcium influx in the generation and propagation of the injury-induced Ca(i)(2+) signal. By 50-80 min post-injury, surviving glial cells demonstrated an enhanced ability to withstand supraphysiological Ca(i)(2+) loads induced by the calcium ionophore A-23187. Glial fibrillary acidic protein (GFAP) and CNPase immunolabeling determined that the glial cells imaged with fluo-3 included both astrocytes and oligodendrocytes. These data provide the first direct evidence that the effects of localized mechanical trauma include a glial calcium signal that can spread along white matter tracts for up to 9 mm within less than 3 h. The results further show that trauma can enhance calcium regulation in surviving glial cells in the acute post-injury period.

Peripheral olfactory ensheathing cells reduce scar and cavity formation and promote regeneration after spinal cord injury

Bridging of a lesion site and minimizing local damage to create an environment permissive for regeneration are both primary components of a successful strategy to repair spinal cord injury (SCI). Olfactory ensheathing cells (OECs) are prime candidates for autologous transplantation to bridge this gap, but little is known currently about their mechanism of action. In addition, OECs from the accessible lamina propria (LP) of the olfactory mucosa are a more viable source in humans but have yet to be tested for their ability to promote regeneration in established SCI models. Here, mouse LP-OECs expressing green fluorescent protein (GFP) transplanted directly into both rat and mouse dorsolateral spinal cord lesion sites demonstrate limited migration but interact with host astrocytes to develop a new transitional zone at the lesion border. LP-OECs also promote extensive migration of host Schwann cells into the central nervous system repair zone and stimulate angiogenesis to provide a biological scaffold for repair. This novel environment created by transplanted and host glia within the spinal cord inhibits cavity and scar formation and promotes extensive sprouting of multiple sensory and motor axons into and through the lesion site. Sixty days after rat SCI, serotonin- and tyrosine hydroxylase-positive axons sprouted across the lesion into the distal cord, although axotomized rubrospinal axons did not. Thus, even in a xenotransplant paradigm, LP-OECs work collaboratively with host glial cells to create an environment to ameliorate local damage and simultaneously promote a regenerative response in multiple axonal populations.

Spinal cord injury: promising interventions and realistic goals

Long regarded as impossible, spinal cord repair is approaching the realm of reality as efforts to bridge the gap between bench and bedside point to novel approaches to treatment. It is important to recognize that the research playing field is rapidly changing and that new mechanisms of resource development are required to effectively make the transition from basic science discoveries to effective clinical treatments. This article reviews recent laboratory studies and phase 1 clinical trials in neural and nonneural cell transplantation, stressing that the transition from basic science to clinical applications requires a parallel rather than serial approach, with continuous, two-way feedback to most efficiently translate basic science findings, through evaluation and optimization, to clinical treatments. An example of mobilizing endogenous stem cells for repair is reviewed, with emphasis on the rapid application of basic science to clinical therapy. Successful and efficient transition from basic science to clinical applications requires (1) a parallel rather than a serial approach; (2) development of centers that integrate three spheres of science, translational, transitional, and clinical trials; and (3) development of novel resources to fund the most critically limited step of transitional to clinical trials.