Spontaneous longitudinally orientated axonal regeneration is associated with the Schwann cell framework within the lesion site following spinal cord compression injury of the rat

Characterization of a Novel Aspect of Tissue Scarring Following Experimental Spinal Cord Injury and the Implantation of Bioengineered Type-I Collagen Scaffolds in the Adult Rat: Involvement of Perineurial-like Cells?

Numerous intervention strategies have been developed to promote functional tissue repair following experimental spinal cord injury (SCI), including the bridging of lesion-induced cystic cavities with bioengineered scaffolds. Integration between such implanted scaffolds and the lesioned host spinal cord is critical for supporting regenerative growth, but only moderate-to-low degrees of success have been reported. Light and electron microscopy were employed to better characterise the fibroadhesive scarring process taking place after implantation of a longitudinally microstructured type-I collagen scaffold into unilateral mid-cervical resection injuries of the adult rat spinal cord. At long survival times (10 weeks post-surgery), sheets of tightly packed cells (of uniform morphology) could be seen lining the inner surface of the repaired dura mater of lesion-only control animals, as well as forming a barrier along the implant–host interface of the scaffold-implanted animals. The highly uniform ultrastructural features of these scarring cells and their anatomical continuity with the local, reactive spinal nerve roots strongly suggest their identity to be perineurial-like cells. This novel aspect of the cellular composition of reactive spinal cord tissue highlights the increasingly complex nature of fibroadhesive scarring involved in traumatic injury, and particularly in response to the implantation of bioengineered collagen scaffolds.

Oligodendrogliogenesis and Axon Remyelination after Traumatic Spinal Cord Injuries in Animal Studies: A Systematic Review

Extensive oligodendrocyte death after acute traumatic spinal cord injuries (TSCI) leads to axon demyelination and subsequently may leave axons vulnerable to degeneration. Despite the present evidence showing spontaneous remyelination after TSCI the cellular origin of new myelin and the time course of the axon ensheathment/remyelination remained controversial issue. In this systematic review the trend of oligodendrocyte death after injury as well as the extent and the cellular origin of oligodendrogliogenesis were comprehensively evaluated. The study design was based on Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-guided systematic review. PubMed and EMBASE were searched with no temporal or linguistic restrictions. Also, hand-search was performed in the bibliographies of relevant articles. Non-interventional animal studies discussing different types of myelinating cells including oligodendrocytes, Schwann cells and oligodendrocyte progenitor cells (OPCs) were evaluated. The extent of oligodendrocyte death, oligodendrocyte differentiation and remyelination were the pathophysiological outcome measures. We found 12,359 studies, 34 of which met the inclusion criteria. The cumulative evidence shows extensive oligodendrocytes cell death during the first week post-injury (pi). OPCs and peripheral invading Schwann cells are the dominant cells contributing in myelin formation. The maximum OPC proliferation was observed at around 2 weeks pi and oligodendrogliogenesis continues at later stages until the number of oligodendrocytes return to normal tissue by one month pi. Taken together, the evidence in animals reveals the potential role for endogenous myelinating cells in the axon ensheathment/remyelination after TSCI and this can be the target of pharmacotherapy to induce oligodendrocyte differentiation and myelin formation post-injury.

Using biomaterials to promote pro-regenerative glial phenotypes after nervous system injuries

Trauma to either the central or peripheral nervous system (PNS) often leads to significant loss of function and disability in patients. This high rate of long-term disability is due to the overall limited regenerative potential of nervous tissue, even though the PNS has more regenerative potential than the central nervous system (CNS). The supporting glial cells in the periphery, Schwann cells, are part of the reason for the improved recovery observed in the PNS. In the CNS, the glial populations, astrocytes and oligodendrocytes (OLs), do not have as much potential to promote regeneration and are at times inhibitory to neuronal growth. In particular, the inhibitory roles astrocytes play following trauma has led to a historical focus on neurons and OLs instead of astrocytes. Recently, this focus has shifted as new, regenerative astrocyte phenotypes have been described. From these observations, glial cells clearly play critical roles in native recovery pathways in both the CNS and PNS. This makes the ability to manipulate both transplanted and native glial cell phenotypes a potentially successful strategy to improve nerve injury outcomes. This review focuses on factors that cause glial cells to adopt repair phenotypes and biomaterials that manipulate and/or harness these glial phenotypes.

Human olfactory mesenchymal stromal cell transplants promote remyelination and earlier improvement in gait co-ordination after spinal cord injury

Autologous cell transplantation is a promising strategy for repair of the injured spinal cord. Here we have studied the repair potential of mesenchymal stromal cells isolated from the human olfactory mucosa after transplantation into a rodent model of incomplete spinal cord injury. Investigation of peripheral type remyelination at the injury site using immunocytochemistry for P0, showed a more extensive distribution in transplanted compared with control animals. In addition to the typical distribution in the dorsal columns (common to all animals), in transplanted animals only, P0 immunolabelling was consistently detected in white matter lateral and ventral to the injury site. Transplanted animals also showed reduced cavitation. Several functional outcome measures including end‐point electrophysiological testing of dorsal column conduction and weekly behavioural testing of BBB, weight bearing and pain, showed no difference between transplanted and control animals. However, gait analysis revealed an earlier recovery of co‐ordination between forelimb and hindlimb stepping in transplanted animals. This improvement in gait may be associated with the enhanced myelination in ventral and lateral white matter, where fibre tracts important for locomotion reside. Autologous transplantation of mesenchymal stromal cells from the olfactory mucosa may therefore be therapeutically beneficial in the treatment of spinal cord injury. GLIA 2017 GLIA 2017;65:639–656

Morphological study of dynamic culture of thermosensitive collagen hydrogel in constructing tissue engineering complex

ABSTACT The purpose of this study is to research the morphologies and functional characteristics of the cell-scaffold complex in vitro constructed under dynamic culture conditions. BMSCs were isolated from the long bones of Fischer344 rats, and performed in vitro amplification to the third generation as seed cells, together with thermosensitive collagen hydrogel (TCH) as cell adhesion matrix, and poly-L-lactic acid (PLLA) as scaffold, to construct cell-scaffold complex. The cell-scaffold complexes in the experiment group and the control group were then performed dynamic culture and static culture. After 7 d of in vitro culture, the complexes in the 2 groups were performed gross observation and SEM; meanwhile, the total DNA content in the complex was detected on D0,1,3, and 7 of culture. After cultured using these 2 ways, collagen could both wrap the PLLA scaffold, forming dense film-like structures on the PLLA surface. The total DNA contents in the cell-scaffold complex of the experiment group on D1,3, and 7 were significantly higher than the control group (P < 0.05). Compared with D0, the total DNA contents on D1,3, and 7 in both groups were gradually increased, but only the total DNA contents on D7 showed statistically significant difference than D0 (P < 0.05). TCH -PLLA fiber joint-constructed complex extracellular matrix had good biocompatibility, and dynamic culture could promote the distribution of BMSCs on the surface and inside the structure, thus promoting cell proliferation, so it could be used for the in vitro construction of tissue engineering complex.

Review : The Role of Schwann cells in Neural Regeneration

The difference in regenerative capacity between the PNS and the CNS is not due to an intrinsic inability of central neurons to extend fibers. Rather, it is probably related to the environment in the CNS that is either repulsive to axonal outgrowth and/or nonsupportive of axonal elongation. In contrast, the PNS both supports and allows for axonal elongation after injury. The Schwann cell, which is the glial cell of the PNS, is strictly required for peripheral regeneration. Here we discuss recent work describing the biology of Schwann cell- dependent regeneration, discuss what is known of the molecular basis of this phenomenon, and how it might apply to the damaged CNS. NEUROSCIENTIST 5:208-216, 1999

A silver lining of neuroinflammation: Beneficial effects on myelination

Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.

Laser fabricated discontinuous anisotropic microconical substrates as a new model scaffold to control the directionality of neuronal network outgrowth

Patterning of neuronal outgrowth in vitro is important in tissue engineering as well as for the development of neuronal interfaces with desirable characteristics. To date, this has been achieved with the aid of micro- and nanofabrication techniques giving rise to various anisotropic topographies, either in the form of continuous or discontinuous structures. In this study we propose a currently unexplored geometry of a 3D culture substrate for neuronal cell growth comprising discontinuous subcellular microstructures with anisotropic geometrical cross-section. Specifically, using laser precision 3D micro/nano fabrication techniques, silicon substrates comprising arrays of parallel oriented elliptical microcones (MCs) were fabricated to investigate whether a discontinuous geometry comprising anisotropic features at the subcellular level could influence the alignment of peripheral nervous system cell populations. It was shown that both Schwann cells and axons of sympathetic neurons were parallel oriented onto the MCs of elliptical shape, while they exhibited a random orientation onto the MCs of arbitrary shape. Notably, this topography-induced guidance effect was also observed in more complex cell culture systems, such as the organotypic culture whole dorsal root ganglia (DRG) explants. Our results suggest that a discontinuous topographical pattern could promote Schwann cell and axonal alignment, provided that it hosts anisotropic geometrical features, even though the sizes of those range at the subcellular lengthscale. The laser-patterned arrays of MCs presented here could potentially be a useful platform for patterning neurons into artificial networks, allowing the study of neuronal cells interactions under 3D ex-vivo conditions.

Intraspinal Delivery of Polyethylene Glycol-coated Gold Nanoparticles Promotes Functional Recovery After Spinal Cord Injury

Failure of the mammalian central nervous system (CNS) to regenerate effectively after injury leads to mostly irreversible functional impairment. Gold nanoparticles (AuNPs) are promising candidates for drug delivery in combination with tissue-compatible reagents, such as polyethylene glycol (PEG). PEG administration in CNS injury models has received interest for potential therapy, but toxicity and low bioavailability prevents clinical application. Here we show that intraspinal delivery of PEG-functionalized 40-nm-AuNPs at early stages after mouse spinal cord injury is beneficial for recovery. Positive outcome of hind limb motor function was accompanied by attenuated inflammatory response, enhanced motor neuron survival, and increased myelination of spared or regrown/sprouted axons. No adverse effects, such as body weight loss, ill health, or increased mortality were observed. We propose that PEG-AuNPs represent a favorable drug-delivery platform with therapeutic potential that could be further enhanced if PEG-AuNPs are used as carriers of regeneration-promoting molecules.

The neuropathological foundations for the restorative neurology of spinal cord injury

An appreciation of the neuropathology of human spinal cord injury (SCI) is a basic requirement for all concerned with the medical treatment of patients with SCI as well as for the many neuroscientists devoted to finding a "cure". An understanding of the neuropathology of SCI is a necessary guide to those concerned at all levels of treatment, whether they are doctors or other health professionals. The underlying changes in the spinal cord are especially relevant to the restorative neurology (RN) of SCI. The new discipline of RN seeks to enhance the function of residual spinal cord elements which have survived the injury and so improve the patient's rehabilitative status. This is in contrast to the conventional approach in rehabilitation which works around the clinical neurological deficiencies. Following the injury a series of changes take place in the spinal cord and surrounding tissues which continue to evolve throughout the life of the patient. In flexion and extension injuries resulting from motor vehicle trauma, diving and sporting accidents the spinal cord is compressed and disrupted but usually with some continuity remaining in the white matter columns. The brunt of the injury is usually centrally placed where there is bleeding into the disrupted grey matter involving one two segments, usually cervical. The loss of central grey matter is nowhere near as important as is the tearing apart of the white matter tracts in determining the patient's clinical state. The central grey matter supplies one two overlapping segmental myotomes and sensory fields. In contrast loss of continuity in the long white matter tracts is catastrophic because all functions below the level of injury are affected, autonomic or voluntary either by paralysis or anaesthesia, usually both. It is important to determine the exact nature of the injury in every patient as a preliminary to treatment by RN. This assessment is both clinical and neurophysiological with special attention given to any part of the long white matter tracts which may have escaped the initial injury. It is these residual nerve fibres which provide the opportunity to improve the patient's neurological state by being re-activated, modulated and enhanced by stimulation or by other RN methods. The conversion of a clinically complete SCI patient to being incomplete and ambulant is a tremendous improvement in the patient's status. It is the purpose of this article to provide the reader with the essential neuropathology of SCI as a beginning point in planning treatment whether it is medical or ancillary, as well as to inform the neuroscientist about the condition being addressed in his or her research.

Schwann cell transplantation for spinal cord injury repair: its significant therapeutic potential and prospectus

Transplantation of Schwann cells (SCs) is a promising therapeutic strategy for spinal cord repair. The introduction of SCs into the injured spinal cord has been shown to reduce tissue loss, promote axonal regeneration, and facilitate myelination of axons for improved sensorimotor function. The pathology of spinal cord injury (SCI) comprises multiple processes characterized by extensive cell death, development of a milieu inhibitory to growth, and glial scar formation, which together limits axonal regeneration. Many studies have suggested that significant functional recovery following SCI will not be possible with a single therapeutic strategy. The use of additional approaches with SC transplantation may be needed for successful axonal regeneration and sufficient functional recovery after SCI. An example of such a combination strategy with SC transplantation has been the complementary administration of neuroprotective agents/growth factors, which improves the effect of SCs after SCI. Suspension of SCs in bioactive matrices can also enhance transplanted SC survival and increase their capacity for supporting axonal regeneration in the injured spinal cord. Inhibition of glial scar formation produces a more permissive interface between the SC transplant and host spinal cord for axonal growth. Co-transplantation of SCs and other types of cells such as olfactory ensheathing cells, bone marrow mesenchymal stromal cells, and neural stem cells can be a more effective therapy than transplantation of SCs alone following SCI. This article reviews some of the evidence supporting the combination of SC transplantation with additional strategies for SCI repair and presents a prospectus for achieving better outcomes for persons with SCI.

Dynamic culture of a thermosensitive collagen hydrogel as an extracellular matrix improves the construction of tissue-engineered peripheral nerve

Tissue engineering technologies offer new treatment strategies for the repair of peripheral nerve injury, but cell loss between seeding and adhesion to the scaffold remains inevitable. A thermosensitive collagen hydrogel was used as an extracellular matrix in this study and combined with bone marrow mesenchymal stem cells to construct tissue-engineered peripheral nerve composites in vitro. Dynamic culture was performed at an oscillating frequency of 0.5 Hz and 35° swing angle above and below the horizontal plane. The results demonstrated that bone marrow mesenchymal stem cells formed membrane-like structures around the poly-L-lactic acid scaffolds and exhibited regular alignment on the composite surface. Collagen was used to fill in the pores, and seeded cells adhered onto the poly-L-lactic acid fibers. The DNA content of the bone marrow mesenchymal stem cells was higher in the composites constructed with a thermosensitive collagen hydrogel compared with that in collagen I scaffold controls. The cellular DNA content was also higher in the thermosensitive collagen hydrogel composites constructed with the thermosensitive collagen hydrogel in dynamic culture than that in static culture. These results indicate that tissue-engineered composites formed with thermosensitive collagen hydrogel in dynamic culture can maintain larger numbers of seeded cells by avoiding cell loss during the initial adhesion stage. Moreover, seeded cells were distributed throughout the material.

Functional improvement following implantation of a microstructured, type-I collagen scaffold into experimental injuries of the adult rat spinal cord

The formation of cystic cavitation following severe spinal cord injury (SCI) constitutes one of the major barriers to successful axonal regeneration and tissue repair. The development of bioengineered scaffolds that assist in the bridging of such lesion-induced gaps may contribute to the formulation of combination strategies aimed at promoting functional tissue repair. Our previous in vitro investigations have demonstrated the directed axon regeneration and glial migration supporting properties of microstructured collagen scaffold that had been engineered to possess mechanical properties similar to those of spinal cord tissues. Here, the effect of implanting the longitudinally orientated scaffold into unilateral resection injuries (2mm long) of the mid-cervical lateral funiculus of adult rats has been investigated using behavioural and correlative morphological techniques. The resection injuries caused an immediate and long lasting (up to 12 weeks post injury) deficit of food pellet retrieval by the ipsilateral forepaw. Implantation of the orientated collagen scaffold promoted a significant improvement in pellet retrieval by the ipsilateral forepaw at 6 weeks which continued to improve up to 12 weeks post injury. In contrast, implantation of a non-orientated gelatine scaffold did not result in significant functional improvement. Surprisingly, the improved motor performance was not correlated with the regeneration of lesioned axons through the implanted scaffold. This observation supports the notion that biomaterials may support functional recovery by mechanisms other than simple bridging of the lesion site, such as the local sprouting of injured, or even non-injured fibres.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Tissue sparing, behavioral recovery, supraspinal axonal sparing/regeneration following sub-acute glial transplantation in a model of spinal cord contusion

Background

It has been shown that olfactory ensheathing glia (OEG) and Schwann cell (SCs) transplantation are beneficial as cellular treatments for spinal cord injury (SCI), especially acute and sub-acute time points. In this study, we transplanted DsRED transduced adult OEG and SCs sub-acutely (14 days) following a T10 moderate spinal cord contusion injury in the rat. Behaviour was measured by open field (BBB) and horizontal ladder walking tests to ascertain improvements in locomotor function. Fluorogold staining was injected into the distal spinal cord to determine the extent of supraspinal and propriospinal axonal sparing/regeneration at 4 months post injection time point. The purpose of this study was to investigate if OEG and SCs cells injected sub acutely (14 days after injury) could: (i) improve behavioral outcomes, (ii) induce sparing/regeneration of propriospinal and supraspinal projections, and (iii) reduce tissue loss.

Results

OEG and SCs transplanted rats showed significant increased locomotion when compared to control injury only in the open field tests (BBB). However, the ladder walk test did not show statistically significant differences between treatment and control groups. Fluorogold retrograde tracing showed a statistically significant increase in the number of supraspinal nuclei projecting into the distal spinal cord in both OEG and SCs transplanted rats. These included the raphe, reticular and vestibular systems. Further pairwise multiple comparison tests also showed a statistically significant increase in raphe projecting neurons in OEG transplanted rats when compared to SCs transplanted animals. Immunohistochemistry of spinal cord sections short term (2 weeks) and long term (4 months) showed differences in host glial activity, migration and proteoglycan deposits between the two cell types. Histochemical staining revealed that the volume of tissue remaining at the lesion site had increased in all OEG and SCs treated groups. Significant tissue sparing was observed at both time points following glial SCs transplantation. In addition, OEG transplants showed significantly decreased chondroitin proteoglycan synthesis in the lesion site, suggesting a more CNS tolerant graft.

Conclusions

These results show that transplantation of OEG and SCs in a sub-acute phase can improve anatomical outcomes after a contusion injury to the spinal cord, by increasing the number of spared/regenerated supraspinal fibers, reducing cavitation and enhancing tissue integrity. This provides important information on the time window of glial transplantation for the repair of the spinal cord.

Scaffolds to promote spinal cord regeneration

Substantial research effort in the spinal cord injury (SCI) field is directed towards reduction of secondary injury changes and enhancement of tissue sparing. However, pathway repair after complete transections, large lesions, or after chronic injury may require the implantation of some form of oriented bridging structure to restore tissue continuity across a trauma zone. These matrices or scaffolds should be biocompatible and create an environment that facilitates tissue growth and vascularization, and allow axons to regenerate through and beyond the implant in order to reconnect with "normal" tissue distal to the injury. The myelination of regrown axons is another important requirement. In this chapter, we describe recent advances in biomaterial technology designed to provide a terrain for regenerating axons to grow across the site of injury and/or create an environment for endogenous repair. Many different types of scaffold are under investigation; they can be biodegradable or nondegradable, natural or synthetic. Scaffolds can be designed to incorporate immobilized signaling molecules and/or used as devices for controlled release of therapeutic agents, including growth factors. These bridging structures can also be infiltrated with specific cell types deemed suitable for spinal cord repair.

Remyelination of spinal cord axons by olfactory ensheathing cells and Schwann cells derived from a transgenic rat expressing alkaline phosphatase marker gene

Transplantation of cell suspensions containing olfactory ensheathing cells (OECs) has been reported to remyelinate demyelinated axons in the spinal cord with a Schwann cell (SC)-like pattern of myelination. However, questions have been raised recently as to whether OECs can form SC-like myelin. To address this issue we prepared SCs and OECs from transgenic rats in which a marker gene, human placental alkaline phosphatase (hPAP), is linked to the ubiquitously active promoter of the R26 gene. SCs were prepared from the sciatic nerve and OECs from the outer nerve-fiber layer of the olfactory bulb. Positive S100 and p75 immunostaining indicated that >95% of cells in culture displayed either SC or OEC phenotypes. Suspensions of either SCs or OECs were transplanted into an X-irradiation/ethidium bromide demyelinating lesion in the spinal cord. We observed extensive SC-like remyelination following either SC or OEC transplantation 3 weeks after injection of the cells. Alkaline phosphatase (ALP) chromagen reaction product was associated clearly with the myelin-forming cells. Thus, cell suspensions that are enriched in either SCs or OECs result in peripheral-like myelin when transplanted in vivo.

Realizing the maximum potential of Schwann cells to promote recovery from spinal cord injury

Transplantation of Schwann cells (SCs) has been extensively investigated as a therapeutic intervention in rodent models of spinal cord injury (SCI). Here we review both strengths and weaknesses of this approach and discuss additional strategies for maximizing the potential of SCs to repair the injured spinal cord. With no additional treatments, SCs were consistently shown to provide a bridge across the lesion site, supporting the ingrowth of sensory and propriospinal axons, to myelinate axons and to decrease the size of cavities formed after injury. Supraspinal axons did not, however, grow onto the bridge, axons failed to traverse the caudal SC-host cord interface and transplanted SC survival was poor. More recent studies have shown that the potential of SC transplantation as a therapeutic approach can be strongly enhanced by combining additional strategies . For example, combining SC transplantation with elevation of cAMP levels resulted in growth of brainstem axons into the SC graft and caudal to the lesion and in significant improvements in locomotion. Axon growth (and functional improvement) have been increased by strategies to raise neurotrophin levels, either by injection or by genetic modification of the SCs before transplantation. A major problem in maximizing SC potential in injured cord has been in achieving good integration of the transplanted cells with the adjacent cord parenchyma. Several previous studies suggested an ability of SCs to migrate extensively in CNS tissue when astroctyes were absent and to myelinate CNS axons. Furthermore, in some cases involving very limited injury, SCs migrated and integrated well even in the presence of host astrocytes. Consistent with these observations, treatments with an enzyme, chondroitinase, to modify the SC-astrocyte interface surrounding the graft, have shown much promise. Very new studies have shown that SCs derived from SC precursors show a higher ability to survive, integrate well with host tissue and support brainstem axon growth into and beyond the graft, confirming the innate promise of SCs in spinal cord repair. We review one clinical trial already underway in Iran testing SC transplantation in patients with SCI. Finally, we briefly describe a protocol, adaptable to the principles of good manufacturing practice, for generating large numbers of human SCs. Overall, the available evidence suggests that SCs, especially when used in combination with other treatments, offer one of the best hopes we have today of devising an effective treatment for spinal cord repair.

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.

Inducing alignment in astrocyte tissue constructs by surface ligands patterned on biomaterials

Planar substrates with patterned ligands were used to induce astrocyte alignment whereas substrates with uniform fields of ligand were used to produce random cell orientation. DRG neurons plated on top of oriented astrocyte monolayers exhibited directional outgrowth along aligned astrocytes, demonstrating that purely biological cues provided by the oriented astrocytes were sufficient to provide guidance cues. Antibody blocking studies demonstrated that astrocyte associated FN played a major mechanistic role in directing engineered neurite extension. Our results show that nanometer level surface cues are sufficient to direct nerve outgrowth through an intervening organized astrocyte cell layer. In other studies, we showed that patterned ligands were able to transmit organization cues through multiple cell layers to control the overall alignment of an astrocyte tissue construct, demonstrating how natural scar tissue may develop in situ into potent barriers. In such constructs the spatial organization of astrocyte derived FN maintained its organizational anisotropy throughout the thickness of multilayered astrocyte constructs. These in vitro studies suggest possible roles for such constructs as bridging substrates for neuroregenerative applications.

Altered T cell responses in children with autism

Autism spectrum disorders (ASD) are characterized by impairment in social interactions, communication deficits, and restricted repetitive interests and behaviors. A potential etiologic role for immune dysfunction in ASD has been suggested. Dynamic adaptive cellular immune function was investigated in 66 children with a confirmed diagnosis of ASD and 73 confirmed typically developing (TD) controls 2-5 years-of-age. In vitro stimulation of peripheral blood mononuclear cells with PHA and tetanus was used to compare group-associated cellular responses. The production of GM-CSF, TNFα, and IL-13 were significantly increased whereas IL-12p40 was decreased following PHA stimulation in ASD relative to TD controls. Induced cytokine production was associated with altered behaviors in ASD children such that increased pro-inflammatory or T(H)1 cytokines were associated with greater impairments in core features of ASD as well as aberrant behaviors. In contrast, production of GM-CSF and T(H)2 cytokines were associated with better cognitive and adaptive function. Following stimulation, the frequency of CD3(+), CD4(+) and CD8(+) T cells expressing activation markers CD134 and CD25 but not CD69, HLA-DR or CD137 were significantly reduced in ASD, and suggests an altered activation profile for T cells in ASD. Overall these data indicate significantly altered adaptive cellular immune function in children with ASD that may reflect dysfunctional immune activation, along with evidence that these perturbations may be linked to disturbances in behavior and developmental functioning. Further longitudinal analyzes of cellular immunity profiles would delineate the relationship between immune dysfunction and the progression of behavioral and developmental changes throughout the course of this disorder.

Schwann cell plasticity after spinal cord injury shown by neural crest lineage tracing

After spinal cord injury (SCI), various cell types are recruited to the lesion site, including Schwann cells, which originate in the neural crest and normally myelinate axons in the peripheral nervous system. Here, we investigated the differentiation states, migration patterns, and roles of neural crest derivatives following SCI, using two transgenic mouse lines carrying neural crest-specific reporters, P0-Cre/Floxed-EGFP and Wnt1-Cre/Floxed-EGFP. In these mice, EGFP is expressed only in the neural crest cell lineage. Immunohistochemical analysis revealed that most of the EGFP(+) cells that infiltrated the lesion site after SCI were Schwann cells. Seven days after SCI, the P0-positive, mature Schwann cells residing at the nerve roots had dedifferentiated into P0(-)/p75(+) immature Schwann cells, which proliferated and began migrating into the lesion site. The dedifferentiation of the Schwann cells was corroborated by their expression of phosphorylated c-Jun, which promotes dedifferentiation and inhibits the expression of myelin-associated genes in the peripheral nerves. Thereafter, the number of EGFP(+)/p75(+) immature Schwann cells decreased and that of EGFP(+)/P0(+) mature cells increased gradually, indicating that the cells redifferentiated into mature Schwann cells within the lesion site. This study draws on the advantages offered by transgenic mouse lines bearing a genetic cell-lineage marker and extends previous work by describing the origins and behavior of the neural crest-derived cells that contribute to endogenous repair after SCI. This process, involving Schwann cell plasticity, is a novel repair mechanism for the lesioned mammalian spinal cord.

Olprinone attenuates the acute inflammatory response and apoptosis after spinal cord trauma in mice

Background

Olprinone hydrochloride is a newly developed compound that selectively inhibits PDE type III and is characterized by several properties, including positive inotropic effects, peripheral vasodilatory effects, and a bronchodilator effect. In clinical settings, olprinone is commonly used to treat congestive cardiac failure, due to its inotropic and vasodilating effects. The mechanism of these cardiac effects is attributed to increased cellular concentrations of cAMP. The aim of the present study was to evaluate the pharmacological action of olprinone on the secondary damage in experimental spinal cord injury (SCI) in mice.

Methodology/Principal Findings

Traumatic SCI is characterized by an immediate, irreversible loss of tissue at the lesion site, as well as a secondary expansion of tissue damage over time. Although secondary injury should be preventable, no effective treatment options currently exist for patients with SCI. Spinal cord trauma was induced in mice by the application of vascular clips (force of 24 g) to the dura via a four-level T5–T8 laminectomy. SCI in mice resulted in severe trauma characterized by edema, neutrophil infiltration, and production of inflammatory mediators, tissue damage, apoptosis, and locomotor disturbance. Olprinone treatment (0.2 mg/kg, i.p.) 1 and 6 h after the SCI significantly reduced: (1) the degree of spinal cord inflammation and tissue injury (histological score), (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation, (4) pro-inflammatory cytokines, (5) NF-κB expression, (6) p-ERK1/2 and p38 expression and (7) apoptosis (TUNEL staining, FAS ligand, Bax and Bcl-2 expression). Moreover, olprinone significantly ameliorated the recovery of hind-limb function (evaluated by motor recovery score).

Conclusions/Significance

Taken together, our results clearly demonstrate that olprinone treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma.

Axon growth-promoting properties of human bone marrow mesenchymal stromal cells

Mesenchymal stromal cells are promising candidate donor cells for promoting functional tissue repair following traumatic spinal cord injury (SCI), however, the mechanism(s) of action remain poorly defined. Here, we describe an in vitro study of the axon growth-promoting properties of highly enriched populations of adult human mesenchymal stromal cells (hMSC). A random, non-oriented pattern of neuritic outgrowth was observed from dissociated adult rat DRG neurons seeded onto confluent A431 cells and PLL/laminin positive control substrata. Confluent hMSC formed arrays of similarly orientated cell bodies and processes which supported the regeneration of significantly more primary neurites but a slightly lower overall neuritic length than was observed over the PLL/laminin control substrate. The hMSC exerted a strong influence on the direction of neuritic outgrowth, with many regenerating processes following the orientation of underlying hMSC. The production of extracellular matrix appeared to be responsible for neuritic directionality, but the release of growth factors was a significant promoter for DRG neuritic outgrowth. This suggests that further investigations into the properties of hMSC may be of particular interest in the development of transplant-mediated strategies intending to promote functional axonal regeneration after SCI.

Granulocyte-macrophage colony-stimulating factor antibody suppresses microglial activity: implications for anti-inflammatory effects in Alzheimer's disease and multiple sclerosis

The objective of our study was to determine granulocyte-macrophage colony-stimulating factor (GM-CSF) activity in the brain following GM-CSF induction. We injected recombinant mouse GM-CSF into the brains of 8-month-old C57BL6 mice via intracerebroventricular injections and studied the activities of microglia, astrocytes, and neurons. We also sought to determine whether an anti-GM-CSF antibody could suppress endogenous microglial activity in the C57BL6 mice and could also suppress microglial activity induced by the recombinant mouse GM-CSF in another group of C57BL6 mice. Using quantitative real-time RT-PCR, we assessed microglial, astrocytic, and neuronal activity by measuring mRNA expression of pro-inflammatory cytokines, GFAP, and the neuronal marker NeuN in the cerebral cortex tissues from C57BL6 mice. We performed immunoblotting and immunohistochemistry of activated microglia in different regions of the brains from control (phosphate-buffered saline-injected C57BL6 mice) and experimental mice (recombinant GM-CSF-injected C57BL6 mice, GM-CSF antibody-injected C57BL6 mice, and recombinant mouse GM-CSF plus anti-GM-CSF antibody-injected C57BL6 mice). We found increased mRNA expression of CD40 (9.75-fold), tumor necrosis factor-alpha (2.1-fold), CD45 (1.73-fold), and CD11c (1.70-fold) in the cerebral cortex of C57BL6 mice that were induced with recombinant GM-CSF, compared with control mice. Further, the anti-GM-CSF antibody suppressed microglia in mice that were induced with recombinant GM-CSF. Our immunoblotting and immunohistochemistry findings of GM-CSF-associated cytokines in C57BL6 mice induced with recombinant GM-CSF, in C57BL6 mice injected with the anti-GM-CSF antibody, and in C57BL6 mice injected with recombinant mouse GM-CSF plus anti-GM-CSF antibody concurred with our real-time RT-PCR findings. These findings suggest that GM-CSF is critical for microglial activation and that anti-GM-CSF antibody suppresses microglial activity in the CNS. The findings from this study may have implications for anti-inflammatory effects of Alzheimer's disease and experimental autoimmune encephalomyelitis mice (a multiple sclerosis mouse model).

Enhanced regenerative axon growth of multiple fibre populations in traumatic spinal cord injury following scar-suppressing treatment

We analysed the effect of scar-suppressing treatment (anti-scarring treatment; AST) on augmenting axonal regeneration of various neuronal populations following spinal cord injury (SCI) in adult rat. AST included local iron chelator (2,2'-dipyridine-5,5'-dicarboxylic acid) injection and 8-bromo-cyclic adenosine monophosphate application to the lesion core. In previous studies, this treatment promoted long-distance regeneration of cut corticospinal tract axons, neuroprotection of projecting cortical neurons and functional improvement of treated rats [N. Klapka et al. (2005)Eur. J. Neurosci., 22, 3047-3058]. Treatment yielded significantly enhanced regrowth of descending serotonergic (5-HT), catecholaminergic (tyrosine hydroxylase; TH), corticospinal and rubrospinal axons into the lesion zone, as assessed by anterograde tracing and immunohistochemistry followed by quantification of axon profiles at 5 and 12 weeks post-injury. In addition, the determination of axons crossing the proximal borderline from uninjured tissue into fibrous scar area revealed a significant AST-promoted increase of intersecting fibres for 5-HT, TH and calcitonin gene-related peptide containing ascending sensory fibres. For a prolonged time period after lesion, the delayed (secondary) scar developing in treated rats is significantly more permeable for all analysed axon tracts than the initial (primary) scar forming in injured control animals lacking treatment. Furthermore, enhanced outgrowth of descending axons from fibrous scar into distal healthy spinal tissue was achieved in treated animals, and is in line with previous functional studies [S. Hermanns et al. (2001) Restor. Neurol. Neurosci., 19,139-148; N. Klapka et al. (2005)Eur. J. Neurosci., 22, 3047-3058]. Our findings indicate that AST exerts a prolonged beneficial effect on fibrous scarring allowing enhanced axonal regrowth of different fibre tracts in SCI regardless of their distinct regenerative demands.

NG2 and phosphacan are present in the astroglial scar after human traumatic spinal cord injury

BACKGROUND

A major class of axon growth-repulsive molecules associated with CNS scar tissue is the family of chondroitin sulphate proteoglycans (CSPGs). Experimental spinal cord injury (SCI) has demonstrated rapid re-expression of CSPGs at and around the lesion site. The pharmacological digestion of CSPGs in such lesion models results in substantially enhanced axonal regeneration and a significant functional recovery. The potential therapeutic relevance of interfering with CSPG expression or function following experimental injuries seems clear, however, the spatio-temporal pattern of expression of individual members of the CSPG family following human spinal cord injury is only poorly defined. In the present correlative investigation, the expression pattern of CSPG family members NG2, neurocan, versican and phosphacan was studied in the human spinal cord.

METHODS

An immunohistochemical investigation in post mortem samples of control and lesioned human spinal cords was performed. All patients with traumatic SCI had been clinically diagnosed as having "complete" injuries and presented lesions of the maceration type.

RESULTS

In sections from control spinal cord, NG2 immunoreactivity was restricted to stellate-shaped cells corresponding to oligodendrocyte precursor cells. The distribution patterns of phosphacan, neurocan and versican in control human spinal cord parenchyma were similar, with a fine reticular pattern being observed in white matter (but also located in gray matter for phosphacan). Neurocan staining was also associated with blood vessel walls. Furthermore, phosphacan, neurocan and versican were present in the myelin sheaths of ventral and dorsal nerve roots axons. After human SCI, NG2 and phosphacan were both detected in the evolving astroglial scar. Neurocan and versican were detected exclusively in the lesion epicentre, being associated with infiltrating Schwann cells in the myelin sheaths of invading peripheral nerve fibres from lesioned dorsal roots.

CONCLUSION

NG2 and phosphacan were both present in the evolving astroglial scar and, therefore, might play an important role in the blockade of successful CNS regeneration. Neurocan and versican, however, were located at the lesion epicentre, associated with Schwann cell myelin on regenerating peripheral nerve fibres, a distribution that was unlikely to contribute to failed CNS axon regeneration. The present data points to the importance of such correlative investigations for demonstrating the clinical relevance of experimental data.

Acute rolipram/thalidomide treatment improves tissue sparing and locomotion after experimental spinal cord injury

Traumatic spinal cord injury (SCI) causes severe and permanent functional deficits due to the primary mechanical insult followed by secondary tissue degeneration. The cascade of secondary degenerative events constitutes a range of therapeutic targets which, if successfully treated, could significantly ameliorate functional loss after traumatic SCI. During the early hours after injury, potent pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) are synthesized and released, playing key roles in secondary tissue degeneration. In the present investigation, the ability of rolipram and thalidomide (FDA approved drugs) to reduce secondary tissue degeneration and improve motor function was assessed in an experimental model of spinal cord contusion injury. The combined acute single intraperitoneal administration of both drugs attenuated TNF-alpha and IL-1beta production and improved white matter sparing at the lesion epicenter. This was accompanied by a significant (2.6 point) improvement in the BBB locomotor score by 6 weeks. There is, at present, no widely accepted intervention strategy that is appropriate for the early treatment of human SCI. The present data suggest that clinical trials for the acute combined application of rolipram and thalidomide may be warranted. The use of such "established drugs" could facilitate the early initiation of trials.

Pharmacological modification of the extracellular matrix to promote regeneration of the injured brain and spinal cord

This chapter focuses on the role of the fibrous lesion scar as a major impediment for axonal regeneration in the injured central nervous system (CNS). We describe the appearance and complementary distribution of the glial and fibrous scar components in spinal cord lesions focusing on the morphology as well as on axon growth inhibitory molecular components accumulating in the collagenous and basement membrane-rich fibrous scar. We further report on the differential responses to fibrous scar of distinct fiber tracts in the injured spinal cord including the rubrospinal and corticospinal tracts as well as serotonergic, dopaminergic, and calcitonin gene-related peptide (CGRP) systems. Finally, we discuss therapeutic strategies to suppress fibrous scarring in traumatic CNS injury with particular emphasis on a unique pharmacological treatment using iron chelators and cyclic adenosine monophosphate (cAMP) to inhibit collagen biosynthesis. The latter treatment has been shown to promote long-distance axon growth, retrograde protection of injured neurons, and significant functional improvement.

A graded forceps crush spinal cord injury model in mice

Given the rising availability and use of genetically modified animals in basic science research, it has become increasingly important to develop clinically relevant models for spinal cord injury (SCI) for use in mice. We developed a graded forceps crush model of SCI in mice that uses three different forceps with spacers of 0.25, 0.4, and 0.55 mm, to produce severe, moderate, and mild injuries, respectively. Briefly, each mouse was subjected to laminectomy of T5-T7, 15-second spinal cord crush using one of those forceps, behavioral assessments, and post-mortem neuroanatomical analyses. There were significant differences among the three injury severity groups on behavioral measures (Basso Mouse Score, footprint, and ladder analyses), demonstrating an increase in neurological deficits for groups with greater injury severity. Quantitative analysis of the lesion demonstrated that as injury severity increased, lesion size and GFAP negative area increased, and spared tissue, spinal cord cross-sectional area, spared grey matter and spared white matter decreased. These measures strongly correlated with the behavioral outcomes. Similar to other studies of SCI in mice, we report a dense laminin and fibronectin positive extracellular matrix in the lesion sites of injured mice, but unlike those previous studies, we also report the presence of numerous p75 positive Schwann cells in and around the lesion epicenter. These results provide evidence that the graded forceps crush model is an attractive alternative for the study of SCI and related therapeutic interventions. Because of its demonstrated consistency, ease of use, low cost, and clinical relevance, this graded forceps crush is an attractive alternative to the other mouse models of SCI currently available.

Aspiration of a cervical spinal contusion injury in preparation for delayed peripheral nerve grafting does not impair forelimb behavior or axon regeneration

A peripheral nerve graft model was used to examine axonal growth after a unilateral cervical (C) contusion injury in adult rats and to determine if manipulation of an injury site prior to transplantation affects spontaneous behavioral recovery. After a short delay (7 d) the epicenter of a C4 contusion was exposed and aspirated without harming the cavity walls followed by apposition with one end of a pre-degenerated tibial nerve to the rostral cavity wall. After a longer delay (28 d) the aspirated cavity was treated with GDNF to promote regeneration by chronically injured neurons. In both groups forelimb and hindlimb locomotor scores decreased significantly 2 d after lesion site manipulation, but by 7 d, the forelimb score was not different from the pre-manipulation score. There was no significant difference in grid walking or grip strength scores for the affected forelimb in either group 7 d after contusion vs. 7 d after manipulation. Over 1500 brain stem and propriospinal neurons grew axons into the graft with either delay. These results demonstrate that a contusion injury site can be manipulated prior to transplantation without causing long-lasting forelimb or hindlimb behavioral deficits and that peripheral nerve grafts support axonal growth after acute or chronic contusion injury.

Erythropoietin and carbamylated erythropoietin are neuroprotective following spinal cord hemisection in the rat

The cytokine erythropoietin (EPO) has been shown to be neuroprotective in a variety of models of central and peripheral nervous system injury. Derivatives of EPO that lack its erythropoietic effects have recently been developed, and the initial reports suggest that they have a neuroprotective potential comparable to that of EPO. One such derivative is carbamylated EPO (CEPO). In the current study we compared the effects of treatment with EPO and CEPO on some of the early neurodegenerative events that occur following spinal cord injury (SCI) induced by hemisection. Adult male Wistar rats received a unilateral hemisection of the spinal cord. Thirty minutes and 24 h following injury, animals received an intraperitoneal injection of saline, EPO (40 microg/kg) or CEPO (40 microg/kg). Results indicated that 3 days post-injury, both CEPO and EPO decreased to a similar extent the size of the lesion compared with control animals. Both compounds also decreased the number of terminal transferase-mediated dUTP nick-end labelling (TUNEL)-labelled apopotic nuclei around the lesion site, as well as the number of axons expressing the injury marker beta-amyloid precursor protein. EPO and CEPO also increased Schwann cell infiltration into the lesion site, although neither compound had any effect on macrophage infiltration either within the lesion site itself or in the surrounding intact tissue. In addition, immunohistochemistry showed an increased expression of both the EPO receptor and the beta common receptor subunit, the components of the receptor complex proposed to mediate the neuroprotective effects of EPO and CEPO in neurons near the site of the injury. The results show that not only does CEPO have an efficacy comparable to that of EPO in its neuroprotective potential following injury, but also that changes in the receptors for these compounds following SCI may underlie their neuroprotective efficacy.

Mice lacking L1 have reduced CGRP fibre in-growth into spinal transection lesions

Repair strategies for spinal cord injury often focus on promoting regeneration of injured axons and stimulating subsequent functional recovery. Although many of these strategies have proven their merits, less is known about potential unwanted side-effects, such as sprouting of nociceptive CGRP immunoreactive axons, which may bring about pain-related behavior. Sprouting of CGRP axons into lesion sites spontaneously occurs after spinal cord injury (SCI). Using L1-deficient mice we show a reduction of such CGRP growth response. This reduction was specific for CGRP axons since the overall neurofilament positive fibre in-growth into the spinal lesion site was not affected. Our results may have important implications on the development and assessment of repair strategies that should not only stimulate functional recovery, but also prevent the development of pain or autonomic dysreflexia.

Transplantation of Schwann cells and/or olfactory ensheathing glia into the contused spinal cord: Survival, migration, axon association, and functional recovery

Schwann cells (SCs) and olfactory ensheathing glia (OEG) have shown promise for spinal cord injury repair. We sought their in vivo identification following transplantation into the contused adult rat spinal cord at 1 week post-injury by: (i) DNA in situ hybridization (ISH) with a Y-chromosome specific probe to identify male transplants in female rats and (ii) lentiviral vector-mediated expression of EGFP. Survival, migration, and axon-glia association were quantified from 3 days to 9 weeks post-transplantation. At 3 weeks after transplantation into the lesion, a 60-90% loss of grafted cells was observed. OEG-only grafts survived very poorly within the lesion (<5%); injection outside the lesion led to a 60% survival rate, implying that the injury milieu was hostile to transplanted cells and or prevented their proliferation. At later times post-grafting, p75(+)/EGFP(-) cells in the lesion outnumbered EGFP(+) cells in all paradigms, evidence of significant host SC infiltration. SCs and OEG injected into the injury failed to migrate from the lesion. Injection of OEG outside of the injury resulted in their migration into the SC-injected injury site, not via normal-appearing host tissue but along the pia or via the central canal. In all paradigms, host axons were seen in association with or ensheathed by transplanted glia. Numerous myelinated axons were found within regions of grafted SCs but not OEG. The current study details the temporal survival, migration, axon association of SCs and OEG, and functional recovery after grafting into the contused spinal cord, research previously complicated due to a lack of quality, long-term markers for cell tracking in vivo.

Remyelination of the injured spinal cord

Contusive spinal cord injury (SCI) can result in necrosis of the spinal cord, but often long white matter tracts outside of the central necrotic core are demyelinated. One experimental strategy to improve functional outcome following SCI is to transplant myelin-forming cells to remyelinate these axons and improve conduction. This review focuses on transplantation studies using olfactory ensheathing cell (OEC) to improve functional outcome in experimental models of SCI and demyelination. The biology of the OEC, and recent experimental research and clinical studies using OECs as a potential cell therapy candidate are discussed.

NG2 colocalizes with axons and is expressed by a mixed cell population in spinal cord lesions

The NG2 proteoglycan is of general interest after spinal cord injury because it is expressed by oligodendrocyte progenitors (OPCs), which contribute to central nervous system remyelination; however, NG2 may inhibit axon regeneration. We and others have examined the spatiotemporal expression of NG2 after spinal cord injury (SCI). Here, we extend those observations and provide a comprehensive analysis of the distribution, phenotype, and colocalization of NG2 cells with axons in a clinically relevant model of spinal contusion. Because contusion models mimic the majority of human SCI, this information is important for understanding endogenous processes that promote and/or prevent repair. The data demonstrate that NG2 levels rise significantly between 3 and 7 days postinjury (dpi) and remain elevated chronically throughout the lesions. NG2 within the lesions could be derived from an array of infiltrating cells; thus, a panel of antibodies was used to investigate NG2 cell phenotypes. First, platelet-derived growth factor-alpha receptor (PDGFalphaR) colocalization was examined because OPCs normally express both markers. PDGFalphaR cells were present in lesions at all times examined. However, only 37% of NG2 cells coexpressed PDGFalphaR at 14 dpi, which dropped to <1% by 70 dpi. This contrasts with the nearly complete overlap in spared tissue surrounding the lesion. In contrast, 40% to 60% of NG2 cells expressed p75 and approximately 84% expressed Sox10, suggesting that many NG2 cells were nonmyelinating Schwann cells. Despite rising levels of NG2, we noted robust and sustained axon growth into the lesions, many of which were located along NG2 profiles. Thus, spinal contusion produces an NG2-rich environment into which axons grow and in which the source of NG2 appears considerably different from that in surrounding spared tissue.

Delayed GM‐CSF treatment stimulates axonal regeneration and functional recovery in paraplegic rats via an increased BDNF expression by endogenous macrophages

Macrophages (monocytes/microglia) could play a critical role in central nervous system repair. We have previously found a synchronism between the regression of spontaneous axonal regeneration and the deactivation of macrophages 3-4 wk after a compression-injury of rat spinal cord. To explore whether reactivation of endogenous macrophages might be beneficial for spinal cord repair, we have studied the effects of granulocyte-macrophage colony stimulating factor (GM-CSF) in the same paraplegia model and in cell cultures. There was a significant, though transient, improvement of locomotor recovery after a single delayed intraperitoneal injection of 2 microg GM-CSF, which also increased significantly the expression of Cr3 and brain-derived neurotrophic factor (BDNF) by macrophages at the lesion site. At longer survival delays, axonal regeneration was significantly enhanced in GM-CSF-treated rats. In vitro, BV2 microglial cells expressed higher levels of BDNF in the presence of GM-CSF and neurons cocultured with microglial cells activated by GM-CSF generated more neurites, an effect blocked by a BDNF antibody. These experiments suggest that GM-CSF could be an interesting treatment option for spinal cord injury and that its beneficial effects might be mediated by BDNF.

Chondroitinase ABC combined with neural stem/progenitor cell transplantation enhances graft cell migration and outgrowth of growth-associated protein-43-positive fibers after rat spinal cord injury

We previously reported that the transplantation of neural stem/progenitor cells (NSPCs) can contribute to the repair of injured spinal cord in adult rats and monkeys. In some cases, however, most of the transplanted cells adhered to the cavity wall and failed to migrate and integrate into the host spinal cord. In this study we focused on chondroitin sulfate proteoglycan (CSPG), a known constituent of glial scars that is strongly expressed after spinal cord injury (SCI), as a putative inhibitor of NSPC migration in vivo. We hypothesized that the digestion of CSPG by chondroitinase ABC (C-ABC) might promote the migration of transplanted cells and neurite outgrowth after SCI. An in vitro study revealed that the migration of NSPC-derived cells was inhibited by CSPG and that this inhibitory effect was attenuated by C-ABC pre-treatment. Consistently, an in vivo study of C-ABC treatment combined with NSPC transplantation into injured spinal cord revealed that C-ABC pre-treatment promoted the migration of the transplanted cells, whereas CSPG-immunopositive scar tissue around the lesion cavity prevented their migration into the host spinal cord in the absence of C-ABC pre-treatment. Furthermore, this combined treatment significantly induced the outgrowth of a greater number of growth-associated protein-43-positive fibers at the lesion epicentre, compared with NSPC transplantation alone. These findings suggested that the application of C-ABC enhanced the benefits of NSPC transplantation for SCI by reducing the inhibitory effects of the glial scar, indicating that this combined treatment may be a promising strategy for the regeneration of injured spinal cord.

Neurite Outgrowth Is Directed by Schwann Cell Alignment in the Absence of Other Guidance Cues

Schwann cells enhance axonal regeneration following nerve injury in vivo and provide a favorable substrate for neurite outgrowth in vitro. However, much remains unknown about the nature of interactions that occur between Schwann cells and growing neurites. In this paper, we describe direct evidence of the ability of Schwann cell alignment alone to direct neurite outgrowth. Previously, we reported that laminin micro-patterns can be used to align Schwann cells and thus create oriented Schwann cell monolayers. In the current study, dissociated rat spinal neurons were seeded onto oriented Schwann cell monolayers, whose alignment provided the only directional cue for growing neurites, and neurite alignment with the underlying Schwann cells was analyzed. The orientation of neurite outgrowth mimicked that of the Schwann cells. Associations observed between neurites and Schwann cells suggest that Schwann cells may guide neurite outgrowth through both topographical and molecular mechanisms. This work demonstrates that Schwann cell alignment can direct neurite outgrowth in the absence of other directional cues, and provides a new method for examining neuronal-Schwann cell interactions in vitro.

Characterization of non-neuronal elements within fibronectin mats implanted into the damaged adult rat spinal cord

Previous studies have shown that mats made from fibronectin (FN) integrate well into spinal cord lesion sites and support extensive axonal growth. Using immunohistochemistry, we have investigated the non-neuronal factors that contribute to these properties. Extensive vascularization was observed in FN mats by 1 week along with heavy macrophage infiltration by 3 days post-implantation. By 1 week post-implantation, laminin tubules had formed and were associated with axons and p75 immunoreactive Schwann cells. By 4 weeks post-implantation, most axons were associated with Schwann cell derived myelin. Few oligodendrocytes were present within the mat, even with an increase in the number of oligodendrocyte precursors around the implant site by 7 days post-implantation. Astrocyte proliferation also occurred in the intact tissue, with a prominent glial scar forming around the implant within 4 weeks. However, by 2 months post-implantation astrocytes were present in the FN implant site and were intermingled with the axons. Axonal ingrowth and integration of the FN mats is probably due to the ability of FN mats to support and organize infiltration of Schwann cells and deposition of laminin. At later time points, myelinated axons remain in the implant site, even after other elements (e.g. macrophages and laminin) have disappeared. Both of these properties are likely to be important in the design of biomaterial bridges for CNS regeneration.