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

A view of the genetic and proteomic profile of extracellular matrix molecules in aging and stroke

Introduction

Modification of the extracellular matrix (ECM) is one of the major processes in the pathology of brain damage following an ischemic stroke. However, our understanding of how age-related ECM alterations may affect stroke pathophysiology and its outcome is still very limited.

Methods

We conducted an ECM-targeted re-analysis of our previously obtained RNA-Seq dataset of aging, ischemic stroke and their interactions in young adult (3-month-old) and aged (18-month-old) mice. The permanent middle cerebral artery occlusion (pMCAo) in rodents was used as a model of ischemic stroke. Altogether 56 genes of interest were chosen for this study.

Results

We identified an increased activation of the genes encoding proteins related to ECM degradation, such as matrix metalloproteinases (MMPs), proteases of a disintegrin and metalloproteinase with the thrombospondin motifs (ADAMTS) family and molecules that regulate their activity, tissue inhibitors of metalloproteinases (TIMPs). Moreover, significant upregulation was also detected in the mRNA of other ECM molecules, such as proteoglycans, syndecans and link proteins. Notably, we identified 8 genes where this upregulation was enhanced in aged mice in comparison with the young ones. Ischemia evoked a significant downregulation in only 6 of our genes of interest, including those encoding proteins associated with the protective function of ECM molecules (e.g., brevican, Hapln4, Sparcl1); downregulation in brevican was more prominent in aged mice. The study was expanded by proteome analysis, where we observed an ischemia-induced overexpression in three proteins, which are associated with neuroinflammation (fibronectin and vitronectin) and neurodegeneration (link protein Hapln2). In fibronectin and Hapln2, this overexpression was more pronounced in aged post-ischemic animals.

Conclusion

Based on these results, we can conclude that the ratio between the protecting and degrading mechanisms in the aged brain is shifted toward degradation and contributes to the aged tissues' increased sensitivity to ischemic insults. Altogether, our data provide fresh perspectives on the processes underlying ischemic injury in the aging brain and serve as a freely accessible resource for upcoming research.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Advanced approaches to regenerate spinal cord injury: The development of cell and tissue engineering therapy and combinational treatments

Spinal cord injury (SCI) is a central nervous system (CNS) devastate event that is commonly caused by traumatic or non-traumatic events. The reinnervation of spinal cord axons is hampered through a myriad of devices counting on the damaged myelin, inflammation, glial scar, and defective inhibitory molecules. Unfortunately, an effective treatment to completely repair SCI and improve functional recovery has not been found. In this regard, strategies such as using cells, biomaterials, biomolecules, and drugs have been reported to be effective for SCI recovery. Furthermore, recent advances in combinatorial treatments, which address various aspects of SCI pathophysiology, provide optimistic outcomes for spinal cord regeneration. According to the global importance of SCI, the goal of this article review is to provide an overview of the pathophysiology of SCI, with an emphasis on the latest modes of intervention and current advanced approaches for the treatment of SCI, in conjunction with an assessment of combinatorial approaches in preclinical and clinical trials. So, this article can give scientists and clinicians' clues to help them better understand how to construct preclinical and clinical studies that could lead to a breakthrough in spinal cord regeneration.

Thermosensitive collagen/fibrinogen gels loaded with decorin suppress lesion site cavitation and promote functional recovery after spinal cord injury

The treatment of spinal cord injury (SCI) is a complex challenge in regenerative medicine, complicated by the low intrinsic capacity of CNS neurons to regenerate their axons and the heterogeneity in size, shape and extent of human injuries. For example, some contusion injuries do not compromise the dura mater and in such cases implantation of preformed scaffolds or drug delivery systems may cause further damage. Injectable in situ thermosensitive scaffolds are therefore a less invasive alternative. In this study, we report the development of a novel, flowable, thermosensitive, injectable drug delivery system comprising bovine collagen (BC) and fibrinogen (FB) that forms a solid BC/FB gel (Gel) immediately upon exposure to physiological conditions and can be used to deliver reparative drugs, such as the naturally occurring anti-inflammatory, anti-scarring agent Decorin, into adult rat spinal cord lesion sites. In dorsal column lesions of adult rats treated with the Gel + Decorin, cavitation was completely suppressed and instead lesion sites became filled with injury-responsive cells and extracellular matrix materials, including collagen and laminin. Decorin increased the intrinsic potential of dorsal root ganglion neurons (DRGN) by increasing their expression of regeneration associated genes (RAGs), enhanced local axon regeneration/sprouting, as evidenced both histologically and by improved electrophysiological, locomotor and sensory function recovery. These results suggest that this drug formulated, injectable hydrogel has the potential to be further studied and translated into the clinic.

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

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

The Molecular Dance of Fibronectin: Conformational Flexibility Leads to Functional Versatility

Fibronectin, a large multimodular protein and one of the major fibrillar components of the extracellular matrix, has been the subject of study for many decades and plays critical roles in embryonic development and tissue homeostasis. Moreover, fibronectin has been implicated in the pathology of many diseases, including cancer, and abnormal depositions of fibronectin have been identified in a number of amyloid and nonamyloid lesions. The ability of fibronectin to carry all these diverse functionalities depends on interactions with a large number of molecules, including adhesive and signaling cell surface receptors, other components of the extracellular matrix, and growth factors and cytokines. The regulation and integration of such large number of interactions depends on the modular architecture of fibronectin, which allows a large number of conformations, exposing or destroying different binding sites. In this Review, we summarize the current knowledge regarding the conformational flexibility of fibronectin, with an emphasis on how it regulates the ability of fibronectin to interact with various signaling molecules and cell-surface receptors and to form supramolecular assemblies and fibrillar structures.

An injectable hydrogel enhances tissue repair after spinal cord injury by promoting extracellular matrix remodeling

The cystic cavity that develops following injuries to brain or spinal cord is a major obstacle for tissue repair in central nervous system (CNS). Here we report that injection of imidazole-poly(organophosphazenes) (I-5), a hydrogel with thermosensitive sol–gel transition behavior, almost completely eliminates cystic cavities in a clinically relevant rat spinal cord injury model. Cystic cavities are bridged by fibronectin-rich extracellular matrix. The fibrotic extracellular matrix remodeling is mediated by matrix metalloproteinase-9 expressed in macrophages within the fibrotic extracellular matrix. A poly(organophosphazenes) hydrogel lacking the imidazole moiety, which physically interacts with macrophages via histamine receptors, exhibits substantially diminished bridging effects. I-5 injection improves coordinated locomotion, and this functional recovery is accompanied by preservation of myelinated white matter and motor neurons and an increase in axonal reinnervation of the lumbar motor neurons. Our study demonstrates that dynamic interactions between inflammatory cells and injectable biomaterials can induce beneficial extracellular matrix remodeling to stimulate tissue repair following CNS injuries.

The cystic cavity that develops following injuries to brain or spinal cord is a major obstacle. Here the authors show an injection of imidazole poly(organophosphazenes), a hydrogel with thermosensitive sol–gel transition behavior, almost completely eliminates cystic cavities in a clinically relevant rat spinal cord injury model.

Self-assembling peptides optimize the post-traumatic milieu and synergistically enhance the effects of neural stem cell therapy after cervical spinal cord injury

INTRODUCTION

The hostile environment after spinal cord injury (SCI) can compromise effects of regenerative therapies. We hypothesized that optimizing the post-traumatic environment with QL6 self-assembling peptides (SAPs) before neural precursor cell (NPC) transplantation would improve cell survival, differentiation and functional recovery.

METHODS

A total of 90 Wistar rats received a clip-compression SCI at C7. Within each of two study arms, animals were randomized into 5 groups (NPC, SAP, NPC+SAP, vehicle, and sham). SAPs and NPCs were injected into the spinal cord 1day and 14days post-injury, respectively. Animals received growth factors over 7days and were immunosuppressed. Rats were sacrificed at 4weeks and sections of the cervical spinal cord prepared for immunohistochemistry (first study arm). Neurological function was assessed weekly for 8weeks using a battery of behavioral tests. Nine weeks post-SCI, the corticospinal tract was assessed using fiber-tracking (second arm).

RESULTS

SAP-treated animals had significantly more surviving NPCs which showed increased differentiation to neurons and oligodendrocytes compared to controls. SAPs alone or in combination with NPCs resulted in smaller intramedullary cysts and larger volume of preserved tissue compared to other groups. The combined treatment group showed reduced astrogliosis and chondroitin sulfate proteoglycan deposition. Synaptic connectivity was increased in the NPC and combined treatment groups. Corticospinal tract preservation and behavioral outcomes improved with combinatorial treatment.

CONCLUSION

Injecting SAPs after SCI enhances subsequent NPC survival, integration and differentiation and improves functional recovery.

STATEMENT OF SIGNIFICANCE

The hostile environment after spinal cord injury (SCI) can compromise effects of regenerative therapies. We hypothesized that improving this environment with self-assembling peptides (SAPs) before neural precursor cell (NPC) transplantation would support their beneficial effects. SAPs assemble once injected, providing a supportive scaffold for repair and regeneration. We investigated this in a rat model of spinal cord injury. More NPCs survived in SAP-treated animals and these showed increased differentiation compared to controls. SAPS alone or in combination with NPCs resulted in smaller cysts and larger volume of preserved tissue with the combined treatment also reducing scarring and improving behavioral outcomes. Overall, injection of SAPs was shown to improve the efficacy of NPC treatment, a promising finding for those with SCIs.

Cell Transplantation and Neuroengineering Approach for Spinal Cord Injury Treatment: A Summary of Current Laboratory Findings and Review of Literature

Spinal cord injury (SCI) can cause severe traumatic injury to the central nervous system (CNS). Current therapeutic effects achieved for SCI in clinical medicine show that there is still a long way to go to reach the desired goal of full or significant functional recovery. In basic medical research, however, cell transplantation, gene therapy, application of cytokines, and biomaterial scaffolds have been widely used and investigated as treatments for SCI. All of these strategies when used separately would help rebuild, to some extent, the neural circuits in the lesion area of the spinal cord. In light of this, it is generally accepted that a combined treatment may be a more effective strategy. This review focuses primarily on our recent series of work on transplantation of Schwann cells and adult stem cells, and transplantation of stem cell-derived neural network scaffolds with functional synapses. Arising from this, an artificial neural network (an exogenous neuronal relay) has been designed and fabricated by us—a biomaterial scaffold implanted with Schwann cells modified by the neurotrophin-3 (NT-3) gene and adult stem cells modified with the TrkC (receptor of NT-3) gene. More importantly, experimental evidence suggests that the novel artificial network can integrate with the host tissue and serve as an exogenous neuronal relay for signal transfer and functional improvement of SCI.

Dynamic behaviors of astrocytes in chemically modified fibrin and collagen hydrogels

Astrocytes play a critical role in supporting the normal physiological function of neurons in the central nervous system (CNS). Astrocyte transplantation can potentially promote axonal regeneration and functional recovery after spinal cord injury (SCI). Fibrin and collagen hydrogels provide growth-permissive substrates and serve as carriers for therapeutic cell transplantation into an injured spinal cord. However, the application of fibrin and collagen hydrogels may be limited due to their relatively rapid degradation rate in vivo. In this study, immature astrocytes isolated from neonatal rats were grown in fibrin hydrogels containing aprotinin and collagen hydrogels crosslinked with poly(ethylene glycol) ether tetrasuccinimidyl glutarate (4S-StarPEG), and the cell behavior in these hydrogels was studied. The cell viability of astrocytes in the hydrogels was tested using the LIVE/DEAD® assay and the AlamarBlue® assay, and this study showed that astrocytes maintained good viability in these hydrogels. The cell migration study showed that astrocytes migrated in the fibrin and collagen hydrogels, and the migration speed is similar in these hydrogels. The crosslinking of collagen hydrogels with 4S-StarPEG did not change the astrocyte migration speed. However, the addition of aprotinin in the fibrin hydrogel inhibited astrocyte migration. The expression of chondroitin sulfate proteoglycan (CSPG), including NG2, neurocan, and versican, by astrocytes grown in the hydrogels was analyzed by quantitative RT-PCR. The expression of NG2, neurocan, and versican by the cells in these hydrogels was not significantly different.

Does the preclinical evidence for functional remyelination following myelinating cell engraftment into the injured spinal cord support progression to clinical trials?

This article reviews all historical literature in which rodent-derived myelinating cells have been engrafted into the contused adult rodent spinal cord. From 2500 initial PubMed citations identified, human cells grafts, bone mesenchymal stem cells, olfactory ensheathing cells, non-myelinating cell grafts, and rodent grafts into hemisection or transection models were excluded, resulting in the 67 studies encompassed in this review. Forty five of those involved central nervous system (CNS)-derived cells, including neural stem progenitor cells (NSPCs), neural restricted precursor cells (NRPs) or oligodendrocyte precursor cells (OPCs), and 22 studies involved Schwann cells (SC). Of the NSPC/NPC/OPC grafts, there was no consistency with respect to the types of cells grafted and/or the additional growth factors or cells co-grafted. Enhanced functional recovery was reported in 31/45 studies, but only 20 of those had appropriate controls making conclusive interpretation of the remaining studies impossible. Of those 20, 19 were properly powered and utilized appropriate statistical analyses. Ten of those 19 studies reported the presence of graft-derived myelin, 3 reported evidence of endogenous remyelination or myelin sparing, and 2 reported both. For the SC grafts, 16/21 reported functional improvement, with 11 having appropriate cellular controls and 9/11 using proper statistical analyses. Of those 9, increased myelin was reported in 6 studies. The lack of consistency and replication among these preclinical studies are discussed with respect to the progression of myelinating cell transplantation therapies into the clinic.

Progress of electrospun fibers as nerve conduits for neural tissue repair

Nerve tissue regeneration approaches have gained much attention in recent years, and nerve conduits (NCs), which facilitate nerve tissue regeneration, have become an attractive alternative to nerve autologous graft. Several methods are proposed to fabricate NCs, including electrospinning, which is a widely used approach for NCs and other tissue scaffolds, and has advantages such as the ability to control the thickness, diameter and porosity of fibers, as well as its simple experimental set up. This article gives an overview of electrospun fibers for nerve conduits utilized in peripheral and central nerve regeneration. Natural and synthetic materials with different mechanical strength, degradation rates and biocompatibility are proposed. Several bioactive proteins that can help the process of nerve regeneration are introduced. Finally, some approaches to control the morphology of electrospun fibers and to deliver bioactive proteins are discussed in detail.

Hydrogels and Cell Based Therapies in Spinal Cord Injury Regeneration

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

Neuroprotective role of fibronectin in neuron-glial extrasynaptic transmission

Most hypotheses concerning the mechanisms underlying Parkinson's disease are based on altered synaptic transmission of the nigrostriatal system. However, extrasynaptic transmission was recently found to affect dopamine neurotransmitter delivery by anisotropic diffusion in the extracellular matrix, which is modulated by various extracellular matrix components such as fibronectin. The present study reviewed the neuroprotective effect of fibronectin in extrasynaptic transmission. Fibronectin can regulate neuroactive substance diffusion and receptor activation, and exert anti- neuroinflammatory, adhesive and neuroprotective roles. Fibronectin can bind to integrin and growth factor receptors to transactivate intracellular signaling events such as the phosphatidylinositol 3-kinase/protein kinase B pathway to regulate or amplify growth factor-like neuroprotective actions. Fibronectin is assembled into a fibrillar network around cells to facilitate cell migration, molecule and ion diffusion, and even drug delivery and treatment. In addition, the present study analyzed the neuroprotective mechanism of fibronectin in the pathogenesis of Parkinson's disease, involving integrin and growth factor receptor interactions, and discussed the possible therapeutic and diagnostic significance of fibronectin in Parkinson's disease.

Repair of injured spinal cord using biomaterial scaffolds and stem cells

The loss of neurons and degeneration of axons after spinal cord injury result in the loss of sensory and motor functions. A bridging biomaterial construct that allows the axons to grow through has been investigated for the repair of injured spinal cord. Due to the hostility of the microenvironment in the lesion, multiple conditions need to be fulfilled to achieve improved functional recovery. A scaffold has been applied to bridge the gap of the lesion as contact guidance for axonal growth and to act as a vehicle to deliver stem cells in order to modify the microenvironment. Stem cells may improve functional recovery of the injured spinal cord by providing trophic support or directly replacing neurons and their support cells. Neural stem cells and mesenchymal stem cells have been seeded into biomaterial scaffolds and investigated for spinal cord regeneration. Both natural and synthetic biomaterials have increased stem cell survival in vivo by providing the cells with a controlled microenvironment in which cell growth and differentiation are facilitated. This optimal multi‒disciplinary approach of combining biomaterials, stem cells, and biomolecules offers a promising treatment for the injured spinal cord.

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.

Neural ECM mimetics

The consequence of numerous neurological disorders is the significant loss of neural cells, which further results in multilevel dysfunction or severe functional deficits. The extracellular matrix (ECM) is of tremendous importance for neural regeneration mediating ambivalent functions: ECM serves as a growth-promoting substrate for neurons but, on the other hand, is a major constituent of the inhibitory scar, which results from traumatic injuries of the central nervous system. Therefore, cell and tissue replacement strategies on the basis of ECM mimetics are very promising therapeutic interventions. Numerous synthetic and natural materials have proven effective both in vitro and in vivo. The closer a material's physicochemical and molecular properties are to the original extracellular matrix, the more promising its effectiveness may be. Relevant factors that need to be taken into account when designing such materials for neural repair relate to receptor-mediated cell-matrix interactions, which are dependent on chemical and mechanical sensing. This chapter outlines important characteristics of natural and synthetic ECM materials (scaffolds) and provides an overview of recent advances in design and application of ECM materials for neural regeneration, both in therapeutic applications and in basic biological research.

Long-term characterization of axon regeneration and matrix changes using multiple channel bridges for spinal cord regeneration

Spinal cord injury (SCI) results in loss of sensory and motor function below the level of injury and has limited available therapies. The host response to SCI is typified by limited endogenous repair, and biomaterial bridges offer the potential to alter the microenvironment to promote regeneration. Porous multiple channel bridges implanted into the injury provide stability to limit secondary damage and support cell infiltration that limits cavity formation. At the same time, the channels provide a path that physically directs axon growth across the injury. Using a rat spinal cord hemisection injury model, we investigated the dynamics of axon growth, myelination, and scar formation within and around the bridge in vivo for 6 months, at which time the bridge has fully degraded. Axons grew into and through the channels, and the density increased overtime, resulting in the greatest axon density at 6 months postimplantation, despite complete degradation of the bridge by that time point. Furthermore, the persistence of these axons contrasts with reports of axonal dieback in other models and is consistent with axon stability resulting from some degree of connectivity. Immunostaining of axons revealed both motor and sensory origins of the axons found in the channels of the bridge. Extensive myelination was observed throughout the bridge at 6 months, with centrally located and peripheral channels seemingly myelinated by oligodendrocytes and Schwann cells, respectively. Chondroitin sulfate proteoglycan deposition was restricted to the edges of the bridge, was greatest at 1 week, and significantly decreased by 6 weeks. The dynamics of collagen I and IV, laminin, and fibronectin deposition varied with time. These studies demonstrate that the bridge structure can support substantial long-term axon growth and myelination with limited scar formation.

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.

Host reaction to poly(2-hydroxyethyl methacrylate) scaffolds in a small spinal cord injury model

Tissue engineered scaffolds and matrices have been investigated over the past decade for their potential in spinal cord repair. They provide a 3-D substrate that can be permissive for nerve regeneration yet have other roles including neuroprotection, altering the inflammatory cascade and mechanically stabilizing spinal cord tissue after injury. In this study we investigated very small lesions (approx. 0.25 μL in volume) of the dorsal column into which a phase-separated poly(2-hydroxyethyl methacrylate) hydrogel scaffold is implanted. Using fluorescent immunohistochemistry to quantify glial scarring, the poly(2-hydroxyethyl methacrylate) scaffold group showed reduced intensity compared to lesion controls for GFAP and the chondroitin sulfate proteoglycan neurocan after 6 days. However, the scaffold and tissue was also pushed dorsally after 6 days while the scaffold was not integrated into the spinal cord after 28 days. Overall, this small-lesion spinal cord injury model provided information on the host tissue reaction of a TE scaffold while reducing animal discomfort and care.

Mesenchymal stem cell transplantation reduces glial cyst and improves functional outcome after spinal cord compression

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem cells that have a supportive role in regenerative therapies, especially in the central nervous system, where spontaneous regeneration is limited. MSCs can exert a paracrine activity and modulate the inflammatory response after a central nervous system injury. Spinal cord injury (SCI) leads to permanent neurologic deficits below the injury site, owing to neuronal and axonal damage. Among experimental treatments after SCI, cell transplantation has emerged as a promising approach.

METHODS

Using a compression injury model in the mouse spinal cord, MSCs were acutely transplanted into the lesion cavity; injured mice without the graft served as controls. After 26 days, the survival of MSCs was investigated, and their effect on the formation of glial cyst and on injury-related inflammation was evaluated.

RESULTS

Grafted MSCs remained permanently undifferentiated. The lesion volume was reduced by 31.6% compared with control mice despite the fact that astroglial and microglial activation was not altered by the graft. Sensory and motor tests showed that MSC cell therapy results in improvement on a battery of behavioral tests compared with control mice: MSC-treated mice versus control mice scored 0.00 versus 0.50 in the posture test, 0.00 versus 1.50 in the hindlimb flexion test, 3.00 versus 2.25 in the sensory test, and 7.50 mistakes versus 15.83 mistakes in the foot-fault test.

CONCLUSIONS

These results underscore the therapeutic potential of MSCs, making them promising treatments for central nervous system pathologies.

Engineering an integrated cellular interface in three-dimensional hydrogel cultures permits monitoring of reciprocal astrocyte and neuronal responses

This study reports a new type of three-dimensional (3D) tissue model for studying interactions between cell types in collagen hydrogels. The aim was to create a 3D cell culture model containing separate cell populations in close proximity without the presence of a mechanical barrier, and demonstrate its relevance to modeling the axon growth-inhibitory cellular interfaces that develop in the central nervous system (CNS) in response to damage. This provides a powerful new tool to determine which aspects of the astroglial scar response and subsequent neuronal regeneration inhibition are determined by the presence of the other cell types. Astrocytes (CNS glia) and dissociated dorsal root ganglia (DRG; containing neurons and peripheral nervous system [PNS] glia) were seeded within collagen solution at 4 °C in adjacent chambers of a stainless steel mould, using cells cultured from wild-type or green fluorescent protein expressing rats, to track specific populations. The divider between the chambers was removed using a protocol that allowed the gels to integrate without mixing of the cell populations. Following setting of the gels, they were maintained in culture for up to 15 days. Reciprocal astrocyte and neuronal responses were monitored using confocal microscopy and 3D image analysis. At DRG:astrocyte interfaces, by 5 days there was an increase in the number of astrocytes at the interface followed by hypertrophy and increased glial fibrillary acidic protein expression at 10 and 15 days, indicative of reactive gliosis. Neurons avoided crossing DRG:astrocyte interfaces, and neuronal growth was restricted to the DRG part of the gel. By contrast, neurons were able to grow freely across DRG:DRG interfaces, demonstrating the absence of a mechanical barrier. These results show that in a precisely controlled 3D environment, an interface between DRG and astrocyte cultures is sufficient to trigger reactive gliosis and inhibition of neuronal regeneration across the interface. Different aspects of the astrocyte response could be independently monitored, providing an insight into the formation of a glial scar. This technology has wide potential for researchers wishing to maintain and monitor interactions between adjacent cell populations in 3D culture.

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

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

Transforming growth factor α transforms astrocytes to a growth-supportive phenotype after spinal cord injury

Astrocytes are both detrimental and beneficial for repair and recovery after spinal cord injury (SCI). These dynamic cells are primary contributors to the growth-inhibitory glial scar, yet they are also neuroprotective and can form growth-supportive bridges on which axons traverse. We have shown that intrathecal administration of transforming growth factor α (TGFα) to the contused mouse spinal cord can enhance astrocyte infiltration and axonal growth within the injury site, but the mechanisms of these effects are not well understood. The present studies demonstrate that the epidermal growth factor receptor (EGFR) is upregulated primarily by astrocytes and glial progenitors early after SCI. TGFα directly activates the EGFR on these cells in vitro, inducing their proliferation, migration, and transformation to a phenotype that supports robust neurite outgrowth. Overexpression of TGFα in vivo by intraparenchymal adeno-associated virus injection adjacent to the injury site enhances cell proliferation, alters astrocyte distribution, and facilitates increased axonal penetration at the rostral lesion border. To determine whether endogenous EGFR activation is required after injury, SCI was also performed on Velvet (C57BL/6J-Egfr(Vel)/J) mice, a mutant strain with defective EGFR activity. The affected mice exhibited malformed glial borders, larger lesions, and impaired recovery of function, indicating that intrinsic EGFR activation is necessary for neuroprotection and normal glial scar formation after SCI. By further stimulating precursor proliferation and modifying glial activation to promote a growth-permissive environment, controlled stimulation of EGFR at the lesion border may be considered in the context of future strategies to enhance endogenous cellular repair after injury.

Multifunctional, multichannel bridges that deliver neurotrophin encoding lentivirus for regeneration following spinal cord injury

Therapeutic strategies following spinal cord injury must address the multiple barriers that limit regeneration. Multiple channel bridges have been developed that stabilize the injury following implantation and provide physical guidance for regenerating axons. These bridges have now been employed as a vehicle for localized delivery of lentivirus. Implantation of lentivirus loaded multiple channel bridges produced transgene expression that persisted for at least 4 weeks. Expression was maximal at the implant at the earliest time point, and decreased with increasing time of implantation, as well as rostral and caudal to the bridge. Immunohistochemical staining indicated transduction of macrophages, Schwann cells, fibroblasts, and astrocytes within the bridge and adjacent tissue. Subsequently, the delivery of lentivirus encoding the neurotrophic factors NT-3 or BDNF significantly increased the extent of axonal growth into the bridge relative to empty scaffolds. In addition to promoting axon growth, the induced expression of neurotrophic factors led to myelination of axons within the channels of the bridge, where the number of myelinated axons was significantly enhanced relative to control. Combining gene delivery with biomaterials to provide physical guidance and create a permissive environment can provide a platform to enhance axonal growth and promote regeneration.

Rapid repair of rat sciatic nerve injury using a nanosilver-embedded collagen scaffold coated with laminin and fibronectin

AIM

Scaffold with micro-channels has shown great promise in facilitating axonal regeneration after peripheral nerve injury. Significant research has focused on mimicking, in terms of composition and function, the ability of the basement membrane of Schwann cells to both promote and guide axonal regeneration. We aim to investigate the ability of a tissue-engineered scaffold with nanosilver and collagen to adsorb laminin and fibronectin, and the usefulness of this scaffold for repairing and regenerating a 10-mm peripheral nerve gap in rats.

METHODS

In this study, nanosilver-embedded collagen scaffolds were prepared and coated with laminin (LN) or LN plus fibronectin (FN). Scanning electron microscopy of the transverse and longitudinal sections of the scaffold revealed axially oriented microtubules ranging from 20 to 80 µm in diameter, and the internal surface of microtubules was found to be evenly coated with LN and FN. Energy dispersive spectrometry also confirmed an even distribution of nanosilver particles within the scaffold. To test its effectiveness in restoring neuronal connection, the scaffold was used in order to bridge 10 mm gaps in the severed sciatic nerve of rats. The rats were divided into an experimental group (receiving scaffold coated with LN and FN), a control group (receiving scaffold coated with LN only) and an autologous graft group. The functional recovery 40 days after surgery was examined by electrophysiology and sciatic nerve functional index (SFI) evaluation. FluoroGold™ (FG) retrograde tracing, toluidine blue staining and transmission electron microscopy were also used to examine the regenerated nerve fibers and to establish their myelination status.

RESULTS

The experimental group displayed partially restored nerve function. The recovery was comparable to the effect of autologous nerve graft and was better than that observed in the control group. A better functional recovery correlated with more FG-labeled neurons, higher density of toluidine blue stained nerve fibers and thicker myelin sheath.

CONCLUSION

Our results demonstrated that nanosilver-embedded collagen scaffolds with LN and FN coating is effective in aiding axonal regeneration, and recovery is comparable to the effect of an autologous nerve graft.

Evaluation of early and late effects into the acute spinal cord injury of an injectable functionalized self-assembling scaffold

The complex physiopathological events occurring after spinal cord injury (SCI) make this devastating trauma still incurable. Self-assembling peptides (SAPs) are nanomaterials displaying some appealing properties for application in regenerative medicine because they mimic the structure of the extra-cellular matrix (ECM), are reabsorbable, allow biofunctionalizations and can be injected directly into the lesion. In this study we evaluated the putative neurorigenerative properties of RADA16-4G-BMHP1 SAP, proved to enhance in vitro neural stem cells survival and differentiation. This SAP (RADA16-I) has been functionalized with a bone marrow homing motif (BMHP1) and optimized via the insertion of a 4-glycine-spacer that ameliorates scaffold stability and exposure of the biomotifs. We injected the scaffold immediately after contusion in the rat spinal cord, then we evaluated the early effects by semi-quantitative RT-PCR and the late effects by histological analysis. Locomotor recovery over 8 weeks was assessed using Basso, Beattie, Bresnahan (BBB) test. Gene expression analysis showed that at 7 days after lesion the functionalized SAP induced a general upregulation of GAP-43, trophic factors and ECM remodelling proteins, whereas 3 days after SCI no remarkable changes were observed. Hystological analysis revealed that 8 weeks after SCI our scaffold increased cellular infiltration, basement membrane deposition and axon regeneration/sprouting within the cyst. Moreover the functionalized SAP showed to be compatible with the surrounding nervous tissue and to at least partially fill the cavities. Finally SAP injection resulted in a statistically significant improvement of both hindlimbs' motor performance and forelimbs-hindlimbs coordination. Altogether, these results indicate that RADA16-4G-BMHP1 induced favourable reparative processes, such as matrix remodelling, and provided a physical and trophic support to nervous tissue ingrowth. Thus this biomaterial, eventually combined with cells and growth factors, may constitute a promising biomimetic scaffold for regenerative applications in the injured central nervous system.

Bone marrow mesenchymal stem cells in a three-dimensional gelatin sponge scaffold attenuate inflammation, promote angiogenesis, and reduce cavity formation in experimental spinal cord injury

Three-dimensional (3D) gelatin sponge (GS) scaffolds were constructed by ensheathing GS with a thin film of poly-(lactide-co-glycolide) (PLGA). Rat bone marrow-derived mesenchymal stem cells (MSCs) were isolated, cultured, and then seeded to the scaffolds. Distribution of cells and cell growth, survival, and proliferation within the scaffolds were then determined. Immunofluorescence and Western blot analysis were employed to detect the deposition of fibronectin to the scaffolds on day 3 and day 7 of culture. Scaffolds with or without MSCs were then transplanted into the transected rat spinal cord. One or 8 weeks following transplantation, cavity areas, activated macrophages/microglia, expression of TNF-α and IL-1β, and neovascularization within the grafts were examined and quantified. Deposition of fibronectin (FN) and expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) as potential inducing factors for angiogenesis were also examined. Results showed that 3D GS scaffolds allowed MSCs to adhere, survive, and proliferate and also FN to deposit. In vivo transplantation experiments demonstrated that these scaffolds were biocompatible, and MSCs seeded to the scaffolds played an important role in attenuating inflammation, promoting angiogenesis, and reducing cavity formation. Therefore, the GS scaffolds with MSCs may serve as promising supporting transplants for repairing spinal cord injury.

Fibrin-based tissue engineering scaffolds enhance neural fiber sprouting and delay the accumulation of reactive astrocytes at the lesion in a subacute model of spinal cord injury

The purpose of this study was to evaluate the effects of fibrin scaffolds on subacute rat spinal cord injury (SCI). Long-Evans rats were anesthetized and underwent a dorsal hemisection injury; two weeks later, the injury site was re-exposed, scar tissue was removed, and a fibrin scaffold was implanted into the wound site. An effective method for fibrin scaffold implantation following subacute SCI was investigated based on the presence of fibrin within the lesion site and morphological analysis 1 week after implantation. Prepolymerized fibrin scaffolds were found to be present within the lesion site 1 week after treatment and were used for the remainder of the study. Fibrin scaffolds were then implanted for 2 and 4 weeks, after which spinal cords were harvested and evaluated using markers for neurons, astrocytes, and chondroitin sulfate proteoglycans. Compared with untreated control, the fibrin-treated group had significantly higher levels of neural fiber staining in the lesion site at 2 and 4 weeks after treatment, and the accumulation of glial fibrillary acidic protein (GFAP) positive reactive astrocytes surrounding the lesion was delayed. These results show that fibrin is conducive to regeneration and cellular migration and illustrate the advantage of using fibrin as a scaffold for drug delivery and cell-based therapies for SCI.

Multiple channel bridges for spinal cord injury: cellular characterization of host response

Bridges for treatment of the injured spinal cord must stabilize the injury site to prevent secondary damage and create a permissive environment that promotes regeneration. The host response to the bridge is central to creating a permissive environment, as the cell types that respond to the injury have the potential to secrete both stimulatory and inhibitory factors. We investigated multiple channel bridges for spinal cord regeneration and correlated the bridge structure to cell infiltration and axonal elongation. Poly(lactide-co-glycolide) bridges were fabricated by a gas foaming/particulate leaching process. Channels within the bridge had diameters of 150 or 250 microm, and the main body of the bridge was highly porous with a controllable pore size. Upon implantation in a rat spinal cord hemisection site, cells infiltrated into the bridge pores and channels, with the pore size influencing the rate of infiltration. The pores had significant cell infiltration, including fibroblasts, macrophages, S-100beta-positive cells, and endothelial cells. The channels of the bridge were completely infiltrated with cells, which had aligned axially, and consisted primarily of fibroblasts, S-100beta-positive cells, and endothelial cells. Reactive astrocytes were observed primarily outside of the bridge, and staining for chondroitin sulfate proteoglycans was decreased in the region surrounding the bridge relative to studies without bridges. Neurofilament staining revealed a preferential growth of the neural fibers within the bridge channels relative to the pores. Multiple channel bridges capable of supporting cellular infiltration, creating a permissive environment, and directing the growth of neural fibers have potential for promoting and directing spinal cord regeneration.

Cytocompatibility of a novel, longitudinally microstructured collagen scaffold intended for nerve tissue repair

Traumatic injury to the nervous system induces functional deficits as a result of axonal destruction and the formation of scar tissue, cystic cavitation, and physical gaps. Bioengineering bridging materials should ideally act as cell carriers for the implantation of axon growth-promoting glia, as well as supporting integration with host cell types. Here, we describe the cytocompatibility of a novel, micro-structured porcine collagen scaffold containing densely packed and highly orientated channels that, in three-dimensional (3D) tissue culture, supports attachment, proliferation, aligned process extension, and directed migration by populations of glial cells (olfactory nerve ensheathing cells and astrocytes) and orientated axonal growth by neurons (differentiated human SH-SY5Y neuroblastoma cell line). The seeded glia required several weeks to penetrate deeply into the highly porous scaffold, where they adopted an orientated morphology similar to that displayed in simple 2D cultures. The direct interaction between SH-SY5Y-derived nerve fibers and the collagen scaffold also resulted in highly orientated axonal growth. It is likely that biocompatible scaffolds that are capable of promoting glial cell attachment, migration, and highly orientated process outgrowth will be important for future repair strategies for traumatically injured nervous tissues.

Local gene delivery from ECM-coated poly(lactide-co-glycolide) multiple channel bridges after spinal cord injury

Tissue engineering scaffolds with complex geometries can provide an architecture that directs tissue formation. Drug delivery from these scaffolds to promote regeneration is often challenging due to the complex fabrication processes. Surface-mediated DNA delivery from multiple channel bridges was applied to deliver lipoplexes in vivo to the injured spinal cord. The surface properties of the polymer, DNA deposition with or without drying, and the presence of ECM components were investigated. In vitro studies revealed that fibronectin produced greater expression levels and immobilization efficiencies compared with collagen, laminin, and no coating. In addition, lipoplex incubation on ECM-coated PLG increased expression relative to either of the drying methods. Additionally, the incubation method had more homogeneously distributed lipoplexes and a higher number of transfected cells relative to the dried conditions. Translation to three-dimensional bridges led to high levels of transgene expression in vitro. In vivo, lipoplexes immobilized to the bridge produced transgene expression levels in a rat spinal cord hemisection model that were 2-fold greater than naked plasmid. Additionally, expression with lipoplexes persisted for at least three weeks. Surface-mediated delivery can be applied to scaffolds with complex geometries to promote transgene expression in vivo.

Plasmid releasing multiple channel bridges for transgene expression after spinal cord injury

The regeneration of tissues with complex architectures requires strategies that promote the appropriate cellular processes, and can direct their organization. Plasmid-loaded multiple channel bridges were engineered for spinal cord regeneration with the ability to support and direct cellular processes and promote gene transfer at the injury site. The bridges were manufactured with a gas foaming technique, and had multiple channels with controllable diameter and encapsulated plasmid. Initial studies investigating bridge implantation subcutaneously (SC) indicated transgene expression in vivo for 44 days, with gene expression dependent upon the pore size of the bridge. In the rat spinal cord, bridges implanted into a lateral hemisection supported substantial cell infiltration, aligned cells within the channels, axon growth across the channels, and high levels of transgene expression at the implant site with decreasing levels rostral and caudal. Immunohistochemistry revealed that the transfected cells at the implant site were present in both the pores and channels of the bridge and were mainly identified as Schwann cells, fibroblasts, and macrophages, in descending order of transfection. This synergy between gene delivery and the scaffold architecture may enable the engineering of tissues with complex architectures.

The role of biodegradable engineered scaffolds seeded with Schwann cells for spinal cord regeneration

Spinal cord injury is very complicated, as there are factors in the body that inhibit its repair. Although regeneration of the mammalian central nervous system (CNS) was once thought to be impossible, studies over the past two decades have shown that axonal growth after spinal cord injury can occur when provided with the correct substratum. Traditionally, tissue transplantation or peripheral nerve grafting are used to repair damaged or diseased regions of the CNS, but donor shortage and immunological problems associated with infectious disease are often encountered. Fortunately, recent advances in neuroscience, cell culture, and biomaterials provide optimistic future using new treatments for nerve injuries. Biomaterial scaffold creates substrate within which cells are instructed to form a tissue or an organ in a highly controlled way. The principal function of a scaffold is to direct cell behavior such as migration, proliferation, differentiation, maintenance of phenotype, and apoptosis by facilitating sensing and responding to the environment via cell-matrix and cell-cell communications. Therefore, having such abilities provides scaffolds seeded with a special type of cell as an important part of tissue engineering and regenerative medicine which spinal cord regeneration is an example of. Nevertheless, the vast number of biodegradable synthetic and natural biopolymers makes choosing the right one very difficult. In this review article, it was tried to provide an inclusive survey of biopolymers seeded with Schwann cells (SCs) to be used for axonal regeneration in the nervous system.

Bone marrow-derived mesenchymal stromal cells for the repair of central nervous system injury

Transplantation of bone marrow-derived mesenchymal stromal cells (MSCs) into the injured brain or spinal cord may provide therapeutic benefit. Several models of central nervous system (CNS) injury have been examined, including that of ischemic stroke, traumatic brain injury and traumatic spinal cord injury in rodent, primate and, more recently, human trials. Although it has been suggested that differentiation of MSCs into cells of neural lineage may occur both in vitro and in vivo, this is unlikely to be a major factor in functional recovery after brain or spinal cord injury. Other mechanisms of recovery that may play a role include neuroprotection, creation of a favorable environment for regeneration, expression of growth factors or cytokines, vascular effects or remyelination. These mechanisms are not mutually exclusive, and it is likely that more than one contribute to functional recovery. In light of the uncertainty surrounding the fate and mechanism of action of MSCs transplanted into the CNS, further preclinical studies with appropriate animal models are urgently needed to better inform the design of new clinical trials.

Approaches to neural tissue engineering using scaffolds for drug delivery

This review seeks to give an overview of the current approaches to drug delivery from scaffolds for neural tissue engineering applications. The challenges presented by attempting to replicate the three types of nervous tissue (brain, spinal cord, and peripheral nerve) are summarized. Potential scaffold materials (both synthetic and natural) and target drugs are discussed with the benefits and drawbacks given. Finally, common methods of drug delivery, including degradable/diffusion-based delivery systems, affinity-based delivery systems, immobilized drug delivery systems, and electrically controlled drug delivery systems, are examined and critiqued. Based on the current body of work, suggestions for future directions of research in the field of neural tissue engineering are presented.

An overview of tissue engineering approaches for management of spinal cord injuries

Severe spinal cord injury (SCI) leads to devastating neurological deficits and disabilities, which necessitates spending a great deal of health budget for psychological and healthcare problems of these patients and their relatives. This justifies the cost of research into the new modalities for treatment of spinal cord injuries, even in developing countries. Apart from surgical management and nerve grafting, several other approaches have been adopted for management of this condition including pharmacologic and gene therapy, cell therapy, and use of different cell-free or cell-seeded bioscaffolds. In current paper, the recent developments for therapeutic delivery of stem and non-stem cells to the site of injury, and application of cell-free and cell-seeded natural and synthetic scaffolds have been reviewed.

Cell responses to biomimetic protein scaffolds used in tissue repair and engineering

Basic science research in tissue engineering and regenerative medicine aims to investigate and understand the deposition, growth, and remodeling of tissues by drawing together approaches from a range of disciplines. This review discusses approaches that use biomimetic proteins and cellular therapies, both in the development of clinical products and of model platforms for scientific investigation. Current clinical approaches to repairing skin, bone, nerve, heart valves, blood vessels, ligaments, and tendons are described and their limitations identified. Opportunities and key questions for achieving clinical goals are discussed through commonly used examples of biomimetic scaffolds: collagen, fibrin, fibronectin, and silk. The key questions addressed by three-dimensional culture models, biomimetic materials, surface chemistry, topography, and their interaction with cells in terms of durotaxis, mechano-regulation, and complex spatial cueing are reviewed to give context to future strategies for biomimetic technology.

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.