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1.  Templated Agarose Scaffolds for the Support of Motor Axon Regeneration Into Sites of Complete Spinal Cord Transection 
Biomaterials  2012;34(5):1529-1536.
Bioengineered scaffolds have the potential to support and guide injured axons after spinal cord injury, contributing to neural repair. In previous studies we have reported that templated agarose scaffolds can be fabricated into precise linear arrays and implanted into the partially injured spinal cord, organizing growth and enhancing the distance over which local spinal cord axons and ascending sensory axons extend into a lesion site. However, most human injuries are severe, sparing only thin rims of spinal cord tissue in the margins of a lesion site. Accordingly, in the present study we examined whether template agarose scaffolds seeded with bone marrow stromal cells secreting Brain-Derived Neurotrophic Factor (BDNF) would support regeneration into severe, complete spinal cord transection sites. Moreover, we tested responses of motor axon populations originating from the brainstem. We find that templated agarose scaffolds support motor axon regeneration into a severe spinal cord injury model and organize axons into fascicles of highly linear configuration. BDNF significantly enhances axonal growth. Collectively, these findings support the feasibility of scaffold implantation for enhancing central regeneration after even severe central nervous system injury.
PMCID: PMC3518618  PMID: 23182350
2.  Development of a tissue-engineered composite implant for treating traumatic paraplegia in rats 
European Spine Journal  2005;15(2):234-245.
This study was designed to assess a new composite implant to induce regeneration of injured spinal cord in paraplegic rats following complete cord transection. Neuronal xenogeneic cells from biopsies of adult nasal olfactory mucosa (NOM) of human origin, or spinal cords of human embryos, were cultured in two consecutive stages: stationary cultures in a viscous semi-solid gel (NVR-N-Gel) and in suspension on positively charged microcarriers (MCs). A tissue-engineered tubular scaffold, containing bundles of parallel nanofibers, was developed. Both the tube and the nanofibers were made of a biodegradable dextran sulphate–gelatin co-precipitate. The suturable scaffold anchored the implant at the site of injury and provided guidance for the regenerating axons. Implants of adult human NOM cells were implanted into eight rats, from which a 4 mm segment of the spinal cord had been completely removed. Another four rats whose spinal cords had also been transected were implanted with a composite implant of cultured human embryonic spinal cord cells. Eight other cord-transected rats served as a control group. Physiological and behavioral analysis, performed 3 months after implantation, revealed partial recovery of function in one or two limbs in three out of eight animals of the NOM implanted group and in all the four rats that were implanted with cultured human embryonic spinal cord cells. Animals of the control group remained completely paralyzed and did not show transmission of stimuli to the brain. The utilization of an innovative composite implant to bridge a gap resulting from the transection and removal of a 4 mm spinal cord segment shows promise, suggesting the feasibility of this approach for partial reconstruction of spinal cord lesions. Such an implant may serve as a vital bridging station in acute and chronic cases of paraplegia.
PMCID: PMC3489403  PMID: 16292587
Olfactory mucosa; Spinal cord; Transection; Transplantation
3.  Neural Stem Cell– and Schwann Cell–Loaded Biodegradable Polymer Scaffolds Support Axonal Regeneration in the Transected Spinal Cord 
Tissue Engineering. Part A  2009;15(7):1797-1805.
Biodegradable polymer scaffolds provide an excellent approach to quantifying critical factors necessary for restoration of function after a transection spinal cord injury. Neural stem cells (NSCs) and Schwann cells (SCs) support axonal regeneration. This study examines the compatibility of NSCs and SCs with the poly-lactic-co-glycolic acid polymer scaffold and quantitatively assesses their potential to promote regeneration after a spinal cord transection injury in rats. NSCs were cultured as neurospheres and characterized by immunostaining for nestin (NSCs), glial fibrillary acidic protein (GFAP) (astrocytes), βIII-tubulin (immature neurons), oligodendrocyte-4 (immature oligodendrocytes), and myelin oligodendrocyte (mature oligodendrocytes), while SCs were characterized by immunostaining for S-100. Rats with transection injuries received scaffold implants containing NSCs (n = 17), SCs (n = 17), and no cells (control) (n = 8). The degree of axonal regeneration was determined by counting neurofilament-stained axons through the scaffold channels 1 month after transplantation. Serial sectioning through the scaffold channels in NSC- and SC-treated groups revealed the presence of nestin, neurofilament, S-100, and βIII tubulin–positive cells. GFAP-positive cells were only seen at the spinal cord–scaffold border. There were significantly more axons in the NSC- and SC- treated groups compared to the control group. In conclusion, biodegradable scaffolds with aligned columns seeded with NSCs or SCs facilitate regeneration across the transected spinal cord. Further, these multichannel biodegradable polymer scaffolds effectively serve as platforms for quantitative analysis of axonal regeneration.
PMCID: PMC2792101  PMID: 19191513
4.  Biomaterial Design Strategies for the Treatment of Spinal Cord Injuries 
Journal of Neurotrauma  2010;27(1):1-19.
The highly debilitating nature of spinal cord injuries has provided much inspiration for the design of novel biomaterials that can stimulate cellular regeneration and functional recovery. Many experts agree that the greatest hope for treatment of spinal cord injuries will involve a combinatorial approach that integrates biomaterial scaffolds, cell transplantation, and molecule delivery. This manuscript presents a comprehensive review of biomaterial-scaffold design strategies currently being applied to the development of nerve guidance channels and hydrogels that more effectively stimulate spinal cord tissue regeneration. To enhance the regenerative capacity of these two scaffold types, researchers are focusing on optimizing the mechanical properties, cell-adhesivity, biodegradability, electrical activity, and topography of synthetic and natural materials, and are developing mechanisms to use these scaffolds to deliver cells and biomolecules. Developing scaffolds that address several of these key design parameters will lead to more successful therapies for the regeneration of spinal cord tissue.
PMCID: PMC2924783  PMID: 19698073
biomaterials; peripheral nerve injury; regeneration; spinal cord injury; therapeutic approaches for the treatment of CNS injury
5.  Rigid Fixation of the Spinal Column Improves Scaffold Alignment and Prevents Scoliosis in the Transected Rat Spinal Cord 
Spine  2008;33(24):E914-E919.
Study Design
A controlled study to evaluate a new technique for spinal rod fixation after spinal cord injury in rats. Alignment of implanted tissue-engineered scaffolds was assessed radiographically and by magnetic resonance imaging.
To evaluate the stability of implanted scaffolds and the extent of kyphoscoliotic deformities after spinal fixation.
Summary of Background Data
Biodegradable scaffolds provide an excellent platform for the quantitative assessment of cellular and molecular factors that promote regeneration within the transected cord. Successful delivery of scaffolds to the damaged cord can be hampered by malalignment following transplantation, which in turn, hinders the assessment of neural regeneration.
Radio-opaque barium sulfate-impregnated poly-lactic-co-glycolic acid scaffolds were implanted into spinal transection injuries in adult rats. Spinal fixation was performed in one group of animals using a metal rod fixed to the spinous processes above and below the site of injury, while the control group received no fixation. Radiographic morphometry was performed after 2 and 4 weeks, and 3-dimensional magnetic resonance microscopy analysis 4 weeks after surgery.
Over the course of 4 weeks, progressive scoliosis was evident in the unfixed group, where a Cobb angle of 8.13 ± 2.03° was measured. The fixed group demonstrated significantly less scoliosis, with a Cobb angle measurement of 1.89 ± 0.75° (P = 0.0004). Similarly, a trend for less kyphosis was evident in the fixed group (7.33 ± 1.68°) compared with the unfixed group (10.13 ± 1.46°). Quantitative measurements of the degree of malalignment of the scaffolds were also significantly less in the fixed group (5 ± 1.23°) compared with the unfixed group (11 ± 2.82°) (P = 0.0143).
Radio-opaque barium sulfate allows for visualization of scaffolds in vivo using radiographic analysis. Spinal fixation was shown to prevent scoliosis, reduce kyphosis, and reduce scaffold malalignment within the transected rat spinal cord. Using a highly optimized model will increase the potential for finding a therapy for restoring function to the injured cord.
PMCID: PMC2773001  PMID: 19011531
spine fixation; transection spinal cord injury; scaffold; scoliosis
6.  Effects of Human Mesenchymal Stem Cell Transplantation Combined with Polymer on Functional Recovery Following Spinal Cord Hemisection in Rats 
The spontaneous axon regeneration of damaged neurons is limited after spinal cord injury (SCI). Recently, mesenchymal stem cell (MSC) transplantation was proposed as a potential approach for enhancing nerve regeneration that avoids the ethical issues associated with embryonic stem cell transplantation. As SCI is a complex pathological entity, the treatment of SCI requires a multipronged approach. The purpose of the present study was to investigate the functional recovery and therapeutic potential of human MSCs (hMSCs) and polymer in a spinal cord hemisection injury model. Rats were subjected to hemisection injuries and then divided into three groups. Two groups of rats underwent partial thoracic hemisection injury followed by implantation of either polymer only or polymer with hMSCs. Another hemisection-only group was used as a control. Behavioral, electrophysiological and immunohistochemical studies were performed on all rats. The functional recovery was significantly improved in the polymer with hMSC-transplanted group as compared with control at five weeks after transplantation. The results of electrophysiologic study demonstrated that the latency of somatosensory-evoked potentials (SSEPs) in the polymer with hMSC-transplanted group was significantly shorter than in the hemisection-only control group. In the results of immunohistochemical study, β-gal-positive cells were observed in the injured and adjacent sites after hMSC transplantation. Surviving hMSCs differentiated into various cell types such as neurons, astrocytes and oligodendrocytes. These data suggest that hMSC transplantation with polymer may play an important role in functional recovery and axonal regeneration after SCI, and may be a potential therapeutic strategy for SCI.
PMCID: PMC3526745  PMID: 23269903
Electrophysiology; Mesenchymal stem cells; Polymer; Spinal cord injury
7.  Combining Peripheral Nerve Grafts and Chondroitinase Promotes Functional Axonal Regeneration in the Chronically Injured Spinal Cord 
Because there currently is no treatment for spinal cord injury, most patients are living with long-standing injuries. Therefore, strategies aimed at promoting restoration of function to the chronically injured spinal cord have high therapeutic value. For successful regeneration, long-injured axons must overcome their poor intrinsic growth potential as well as the inhibitory environment of the glial scar established around the lesion site. Acutely injured axons that regenerate into growth-permissive peripheral nerve grafts (PNGs) reenter host tissue to mediate functional recovery if the distal graft– host interface is treated with chondroitinase ABC (ChABC) to cleave inhibitory chondroitin sulfate proteoglycans in the scar matrix. To determine whether a similar strategy is effective for a chronic injury, we combined grafting of a peripheral nerve into a highly relevant, chronic, cervical contusion site with ChABC treatment of the glial scar and glial cell line-derived neurotrophic factor (GDNF) stimulation of long-injured axons. We tested this combination in two grafting paradigms: (1) a peripheral nerve that was grafted to span a chronic injury site or (2) a PNG that bridged a chronic contusion site with a second, more distal injury site. Unlike GDNF–PBS treatment, GDNF–ChABC treatment facilitated axons to exit the PNG into host tissue and promoted some functional recovery. Electrical stimulation of axons in the peripheral nerve bridge induced c-Fos expression in host neurons, indicative of synaptic contact by regenerating fibers. Thus, our data demonstrate, for the first time, that administering ChABC to a distal graft interface allows for functional axonal regeneration by chronically injured neurons.
PMCID: PMC2824589  PMID: 19940184
8.  Concise Review: The Potential of Stromal Cell-Derived Factor 1 and Its Receptors to Promote Stem Cell Functions in Spinal Cord Repair 
Stem Cells Translational Medicine  2012;1(10):732-739.
This report discusses the experimental data available on the role of stromal cell-derived factor 1 (SDF-1) in stem and progenitor cell biology following central nervous system injury and suggests strategies for how manipulation of the SDF-1 system could facilitate stem cell-based therapeutic approaches in spinal cord injury. In addition, it covers challenges such as how to circumvent off-target effects in order to facilitate the transfer of SDF-1 to the clinic.
Transplanted stem cells provide beneficial effects on regeneration/recovery after spinal cord injury (SCI) by the release of growth-promoting factors, increased tissue preservation, and provision of a permissive environment for axon regeneration. A rise in chemokine stromal cell-derived factor 1 (SDF-1/CXCL12) expression levels in central nervous system (CNS) injury sites has been shown to play a central role in recruiting transplanted stem cells. Although technically more challenging, it has been shown that after SCI few endogenous stem cells are recruited via SDF-1/CXCR4 signaling. Evidence is accumulating that increasing SDF-1 levels at the injury site (e.g., by exogenous application or transfection methods) further enhances stem cell recruitment. Moreover, SDF-1 might, in addition to migration, also influence survival, proliferation, differentiation, and cytokine secretion of stem cells. Here, we discuss the experimental data available on the role of SDF-1 in stem and progenitor cell biology following CNS injury and suggest strategies for how manipulation of the SDF-1 system could facilitate stem cell-based therapeutic approaches in SCI. In addition, we discuss challenges such as how to circumvent off-target effects in order to facilitate the transfer of SDF-1 to the clinic.
PMCID: PMC3659654  PMID: 23197665
Stromal derived factor-1 (SDF-1); Stem/progenitor cell; Spinal cord injury; Somatic cell therapy; Mesenchymal stem cells; Neural stem cell; Umbilical cord blood
9.  Combination Therapies in the CNS: Engineering the Environment 
Neuroscience Letters  2012;519(2):115-121.
The inhibitory extracellular environment that develops in response to traumatic brain injury and spinal cord injury hinders axon growth thereby limiting restoration of function. Several strategies have been developed to engineer a more permissive central nervous system (CNS) environment to promote regeneration and functional recovery. The multi-faced inhibitory nature of the CNS lesion suggests that therapies used in combination may be more effective. In this mini-review we summarize the most recent attempts to engineer the CNS extracellular environment after injury using combinatorial strategies. The advantages and limits of various combination therapies utilizing neurotrophin delivery, cell transplantation, and biomaterial scaffolds are discussed. Treatments that reduce the inhibition by chondroitin sulfate proteoglycans, myelin-associated inhibitors, and other barriers to axon regeneration are also reviewed. Based on the current state of the field, future directions are suggested for research on combination therapies in the CNS.
PMCID: PMC3377780  PMID: 22343313
spinal cord injury; traumatic brain injury; cell transplantation; biomaterials; chondroitin sulfate proteoglycans; myelin-associated inhibitors
10.  Nerve Regeneration Restores Supraspinal Control of Bladder Function after Complete Spinal Cord Injury 
The Journal of Neuroscience  2013;33(26):10591-10606.
A life-threatening disability after complete spinal cord injury is urinary dysfunction, which is attributable to lack of regeneration of supraspinal pathways that control the bladder. Although numerous strategies have been proposed that can promote the regrowth of severed axons in the adult CNS, at present, the approaches by which this can be accomplished after complete cord transection are quite limited. In the present study, we modified a classic peripheral nerve grafting technique with the use of chondroitinase to facilitate the regeneration of axons across and beyond an extensive thoracic spinal cord transection lesion in adult rats. The novel combination treatment allows for remarkably lengthy regeneration of certain subtypes of brainstem and propriospinal axons across the injury site and is followed by markedly improved urinary function. Our studies provide evidence that an enhanced nerve grafting strategy represents a potential regenerative treatment after severe spinal cord injury.
PMCID: PMC3693049  PMID: 23804083
11.  Differential Gene Expression in the EphA4 Knockout Spinal Cord and Analysis of the Inflammatory Response Following Spinal Cord Injury 
PLoS ONE  2012;7(5):e37635.
Mice lacking the axon guidance molecule EphA4 have been shown to exhibit extensive axonal regeneration and functional recovery following spinal cord injury. To assess mechanisms by which EphA4 may modify the response to neural injury a microarray was performed on spinal cord tissue from mice with spinal cord injury and sham injured controls. RNA was purified from spinal cords of adult EphA4 knockout and wild-type mice four days following lumbar spinal cord hemisection or laminectomy only and was hybridised to Affymetrix All-Exon Array 1.0 GeneChips™. While subsequent analyses indicated that several pathways were altered in EphA4 knockout mice, of particular interest was the attenuated expression of a number of inflammatory genes, including Arginase 1, expression of which was lower in injured EphA4 knockout compared to wild-type mice. Immunohistological analyses of different cellular components of the immune response were then performed in injured EphA4 knockout and wildtype spinal cords. While numbers of infiltrating CD3+ T cells were low in the hemisection model, a robust CD11b+ macrophage/microglial response was observed post-injury. There was no difference in the overall number or spread of macrophages/activated microglia in injured EphA4 knockout compared to wild-type spinal cords at 2, 4 or 14 days post-injury, however a lower proportion of Arginase-1 immunoreactive macrophages/activated microglia was observed in EphA4 knockout spinal cords at 4 days post-injury. Subtle alterations in the neuroinflammatory response in injured EphA4 knockout spinal cords may contribute to the regeneration and recovery observed in these mice following injury.
PMCID: PMC3358264  PMID: 22629434
12.  Axon Regeneration through Scaffold into Distal Spinal Cord after Transection 
Journal of neurotrauma  2009;26(10):1759-1771.
We employed Fast Blue (FB) axonal tracing to determine the origin of regenerating axons after thoracic spinal cord transection injury in rats. Schwann cell (SC)-loaded, biodegradable, poly(lactic-co-glycolic acid) (PLGA) scaffolds were implanted after transection. Scaffolds loaded with solubilized basement membrane preparation (without SCs) were used for negative controls, and nontransected cords were positive controls. One or 2 months after injury and scaffold implantation, FB was injected 0–15 mm caudal or about 5 mm rostral to the scaffold. One week later, tissue was harvested and the scaffold and cord sectioned longitudinally (30 μm) on a cryostat. Trans-scaffold labeling of neuron cell bodies was identified with confocal microscopy in all cell-transplanted groups. Large (30–50 μm diameter) neuron cell bodies were predominantly labeled in the ventral horn region. Most labeled neurons were seen 1–10 mm rostral to the scaffold, although some neurons were also labeled in the cervical cord. Axonal growth occurred bidirectionally after cord transection, and axons regenerated up to 14 mm beyond the PLGA scaffolds and into distal cord. The extent of FB labeling was negatively correlated with distance from the injection site to the scaffold. Electron microscopy showed myelinated axons in the transverse sections of the implanted scaffold 2 months after implantation. The pattern of myelination, with extracellular collagen and basal lamina, was characteristic of SC myelination. Our results show that FB labeling is an effective way to measure the origin of regenerating axons.
PMCID: PMC2763055  PMID: 19413501
axonal tracing; biodegradable polymers; Fast Blue; Schwann cells; spinal cord injury
13.  Axon Regeneration through Scaffold into Distal Spinal Cord after Transection 
Journal of Neurotrauma  2009;26(10):1759-1771.
We employed Fast Blue (FB) axonal tracing to determine the origin of regenerating axons after thoracic spinal cord transection injury in rats. Schwann cell (SC)-loaded, biodegradable, poly(lactic-co-glycolic acid) (PLGA) scaffolds were implanted after transection. Scaffolds loaded with solubilized basement membrane preparation (without SCs) were used for negative controls, and nontransected cords were positive controls. One or 2 months after injury and scaffold implantation, FB was injected 0–15 mm caudal or about 5 mm rostral to the scaffold. One week later, tissue was harvested and the scaffold and cord sectioned longitudinally (30 μm) on a cryostat. Trans-scaffold labeling of neuron cell bodies was identified with confocal microscopy in all cell-transplanted groups. Large (30–50 μm diameter) neuron cell bodies were predominantly labeled in the ventral horn region. Most labeled neurons were seen 1–10 mm rostral to the scaffold, although some neurons were also labeled in the cervical cord. Axonal growth occurred bidirectionally after cord transection, and axons regenerated up to 14 mm beyond the PLGA scaffolds and into distal cord. The extent of FB labeling was negatively correlated with distance from the injection site to the scaffold. Electron microscopy showed myelinated axons in the transverse sections of the implanted scaffold 2 months after implantation. The pattern of myelination, with extracellular collagen and basal lamina, was characteristic of SC myelination. Our results show that FB labeling is an effective way to measure the origin of regenerating axons.
PMCID: PMC2763055  PMID: 19413501
axonal tracing; biodegradable polymers; Fast Blue; Schwann cells; spinal cord injury
14.  Transection method for shortening the rat spine and spinal cord 
Previous studies have presented evidence which indicates that the regeneration of axons in the spinal cord occurs following spinal cord transection in young rats. However, in a transection-regeneration model, the completeness of the transection is often a matter of dispute. We established a method for shortening the rat spine and spinal cord to provide a spinal cord injury (SCI) model in which there was no doubt about whether the axonal transection was complete. In the future, this model may be applied to the chronic period of complete paralysis following SCI. Adult, female Wistar rats (220–250g) were used in the study. The spinal cord was exposed and a 4-mm-long segment of the spinal cord was removed at Th8. Subsequently, the Th7/8 and Th8/9 discs were cut between the stumps of the spinal cord to remove the Th8 vertebra. The stitches which had been passed through the 7th and 9th ribs bilaterally were tied gradually to bring together the stumps of the spinal cord. Almost all the rats survived until the end of the experiment. Uncoordinated movements of the hind limbs in locomotion were observed at 4 weeks after surgery. However coordinated movements of the hind limbs in locomotion were not observed until the end of the experiment. After 12 weeks, an intracardiac perfusion was performed to remove the thoracic spine and the spinal cord. There were no signs of infection. The bone fusion of the Th7 and Th9 vertebrae was observed to be complete in all specimens and the alignment of the thoracic spine was maintained. The spinal canal was also correctly reconstituted. The stumps of the spinal cord were connected. Light microscopy of the cord showed that scar tissue intervened at the connection site. Cavitation inhibiting the axonal regeneration was also observed. This model was also made on the assumption that glial scar tissue inhibits axonal regeneration in chronic SCI. Axonal regeneration was not observed across the transected spinal cord in this model. Attempts should be made to minimize the damage to the spinal cord and the surgery time for successful axonal regeneration to occur. The model developed in this study may be useful in the study of axonal regeneration in SCI.
PMCID: PMC3570119  PMID: 23403404
spinal cord injury; animal model; rat
15.  Axon repair: surgical application at a subcellular scale 
Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.
PMCID: PMC3150872  PMID: 20101712
16.  Intrinsic control of axon regeneration 
Spinal cord injury disrupts the connections between the brain and spinal cord, often resulting in the loss of sensory and motor function below the lesion site. The most important reason for such permanent functional deficits is the failure of injured axons to regenerate after injury. In principle, the functional recovery could be achieved by two forms of axonal regrowth: the regeneration of lesioned axons which will reconnect with their original targets and the sprouting of spared axons that form new circuits and compensate for the lost function. Our recent studies reveal the activity of the mammalian target of rapamycin (mTOR) pathway, a major regulator of new protein synthesis, as a critical determinant of axon regrowth in the adult retinal ganglion neurons[1]. In this review, I summarize current understanding of the cellular and molecular mechanisms that control the intrinsic regenerative ability of mature neurons.
PMCID: PMC3596529  PMID: 23554605
17.  Meningeal cells and glia establish a permissive environment for axon regeneration after spinal cord injury in newts 
Neural Development  2011;6:1.
Newts have the remarkable ability to regenerate their spinal cords as adults. Their spinal cords regenerate with the regenerating tail after tail amputation, as well as after a gap-inducing spinal cord injury (SCI), such as a complete transection. While most studies on newt spinal cord regeneration have focused on events occurring after tail amputation, less attention has been given to events occurring after an SCI, a context that is more relevant to human SCI. Our goal was to use modern labeling and imaging techniques to observe axons regenerating across a complete transection injury and determine how cells and the extracellular matrix in the injury site might contribute to the regenerative process.
We identify stages of axon regeneration following a spinal cord transection and find that axon regrowth across the lesion appears to be enabled, in part, because meningeal cells and glia form a permissive environment for axon regeneration. Meningeal and endothelial cells regenerate into the lesion first and are associated with a loose extracellular matrix that allows axon growth cone migration. This matrix, paradoxically, consists of both permissive and inhibitory proteins. Axons grow into the injury site next and are closely associated with meningeal cells and glial processes extending from cell bodies surrounding the central canal. Later, ependymal tubes lined with glia extend into the lesion as well. Finally, the meningeal cells, axons, and glia move as a unit to close the gap in the spinal cord. After crossing the injury site, axons travel through white matter to reach synaptic targets, and though ascending axons regenerate, sensory axons do not appear to be among them. This entire regenerative process occurs even in the presence of an inflammatory response.
These data reveal, in detail, the cellular and extracellular events that occur during newt spinal cord regeneration after a transection injury and uncover an important role for meningeal and glial cells in facilitating axon regeneration. Given that these cell types interact to form inhibitory barriers in mammals, identifying the mechanisms underlying their permissive behaviors in the newt will provide new insights for improving spinal cord regeneration in mammals.
PMCID: PMC3025934  PMID: 21205291
18.  Allografts of the Acellular Sciatic Nerve and Brain-Derived Neurotrophic Factor Repair Spinal Cord Injury in Adult Rats 
PLoS ONE  2012;7(8):e42813.
We aimed to investigate whether an innovative growth factor-laden scaffold composed of acellular sciatic nerve (ASN) and brain-derived neurotrophic factor (BDNF) could promote axonal regeneration and functional recovery after spinal cord injury (SCI).
Following complete transection at the thoracic level (T9), we immediately transplanted the grafts between the stumps of the severed spinal cords. We evaluated the functional recovery of the hindlimbs of the operated rats using the BBB locomotor rating scale system every week. Eight weeks after surgery, axonal regeneration was examined using the fluorogold (FG) retrograde tracing method. Electrophysiological analysis was carried out to evaluate the improvement in the neuronal circuits. Immunohistochemistry was employed to identify local injuries and recovery.
The results of the Basso-Beattie-Bresnahan (BBB) scale indicated that there was no significant difference between the individual groups. The FG retrograde tracing and electrophysiological analyses indicated that the transplantation of ASN-BDNF provided a permissive environment to support neuron regeneration.
The ASN-BDNF transplantation provided a promising therapeutic approach to promote axonal regeneration and recovery after SCI, and can be used as part of a combinatory treatment strategy for SCI management.
PMCID: PMC3429476  PMID: 22952613
19.  Axon regeneration and exercise-dependent plasticity after spinal cord injury 
Current dogma is that meaningful recovery of function after spinal cord injury (SCI) likely will require a combination of therapeutic interventions comprised of regenerative/neuroprotective transplants, addition of neurotrophic factors, elimination of inhibitory molecules, functional sensorimotor training, and/or stimulation of paralyzed muscles or spinal circuits. We routinely use: (1) peripheral nerve grafts to support and direct axonal regeneration across an incomplete cervical or a complete thoracic transection injury, (2) matrix modulation with chondroitinase (ChABC) to facilitate axonal extension beyond the distal graft-spinal cord interface and (3) exercise, such as forced wheel walking, bicycling or step training on a treadmill. We (and others) have demonstrated an increase in spinal cord levels of endogenous neurotrophic factors with exercise, which may be useful in facilitating elongation and/or synaptic activity of regenerating axons and plasticity of spinal neurons below the level of injury
PMCID: PMC3616327  PMID: 23531013
rehabilitation; neurotrophic factors; neurotransplantation; cFos
20.  Nanofibrous Collagen Nerve Conduits for Spinal Cord Repair 
Tissue Engineering. Part A  2012;18(9-10):1057-1066.
Nerve regeneration in an injured spinal cord is often restricted, contributing to the devastating outcome of neurologic impairment below the site of injury. Although implantation of tissue-engineered scaffolds has evolved as a potential treatment method, the outcomes remain sub-optimal. One possible reason may be the lack of topographical signals from these constructs to provide contact guidance to invading cells or regrowing axons. Nanofibers mimic the natural extracellular matrix architecturally and may therefore promote physiologically relevant cellular phenotypes. In this study, the potential application of electrospun collagen nanofibers (diameter=208.2±90.4 nm) for spinal cord injury (SCI) treatment was evaluated in vitro and in vivo. Primary rat astrocytes and dorsal root ganglias (DRGs) were seeded on collagen-coated glass cover slips (two-dimensional [2D] substrate controls), and randomly oriented or aligned collagen fibers to evaluate scaffold topographical effects on astrocyte behavior and neurite outgrowth, respectively. When cultured on collagen nanofibers, astrocyte proliferation and expression of glial fibrillary acidic protein (GFAP) were suppressed as compared to cells on 2D controls at days 3 (p<0.05) and 7 (p<0.01). Aligned fibers resulted in elongated astrocytes (elongation factor >4, p<0.01) and directed the orientation of neurite outgrowth from DRGs along fiber axes. In the contrast, neurites emanated radially on randomly oriented collagen fibers. By forming collagen scaffolds into spiral tubular structures, we demonstrated the feasibility of using electrospun nanofibers for the treatment of acute SCI using a rat hemi-section model. At days 10 and 30 postimplantation, extensive cellular penetration into the constructs was observed regardless of fiber orientation. However, scaffolds with aligned fibers appeared more structurally intact at day 30. ED1 immunofluorescent staining revealed macrophage invasion by day 10, which decreased significantly by day 30. Neural fiber sprouting as evaluated by neurofilament staining was observed as early as day 10. In addition, GFAP immunostained astrocytes were found only at the boundary of the lesion site, and no astrocyte accumulation was observed in the implantation area at any time point. These findings indicate the feasibility of fabricating 3D spiral constructs using electrospun collagen fibers and demonstrated the potential of these scaffolds for SCI repair.
PMCID: PMC3338103  PMID: 22220714
21.  Nanofibrous Patches for Spinal Cord Regeneration 
Advanced functional materials  2010;20(9):1433-1440.
The difficulty in spinal cord regeneration is related to the inhibitory factors for axon growth and the lack of appropriate axon guidance in the lesion region. Here we developed scaffolds with aligned nanofibers for nerve guidance and drug delivery in spinal cord. Blended polymers including Poly (l-lactic acid) (PLLA) and Poly (lactide-co-glycolide) (PLGA) were used to electrospin nanofibrous scaffolds with two-layer structure: aligned nanofibers in the inner layer and random nanofibers in the outer layer. Rolipram, a small molecule that can enhance cAMP activity in neurons and suppress inflammatory responses, was immobilized onto nanofibers. To test the therapeutic effects of nanofibrous scaffolds, the nanofibrous scaffolds loaded with rolipram were used to bridge the hemisection lesion in 8-week old athymic rats. The scaffolds with rolipram increased axon growth through the scaffolds and in the lesion, promoted angiogenesis through the scaffold, and decreased the population of astrocytes and chondroitin sulfate proteoglycans in the lesion. Locomotor scale rating analysis showed that the scaffolds with rolipram significantly improved hindlimb function after 3 weeks. This study demonstrated that nanofibrous scaffolds offered a valuable platform for drug delivery for spinal cord regeneration.
PMCID: PMC3558949  PMID: 23378825
Nanofibers; spinal cord; drug delivery; regeneration
22.  Poly(Trimethylene Carbonate-co-ε-Caprolactone) Promotes Axonal Growth 
PLoS ONE  2014;9(2):e88593.
Mammalian central nervous system (CNS) neurons do not regenerate after injury due to the inhibitory environment formed by the glial scar, largely constituted by myelin debris. The use of biomaterials to bridge the lesion area and the creation of an environment favoring axonal regeneration is an appealing approach, currently under investigation. This work aimed at assessing the suitability of three candidate polymers – poly(ε-caprolactone), poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) (11∶89 mol%) and poly(trimethylene carbonate) - with the final goal of using these materials in the development of conduits to promote spinal cord regeneration. Poly(L-lysine) (PLL) coated polymeric films were tested for neuronal cell adhesion and neurite outgrowth. At similar PLL film area coverage conditions, neuronal polarization and axonal elongation was significantly higher on P(TMC-CL) films. Furthermore, cortical neurons cultured on P(TMC-CL) were able to extend neurites even when seeded onto myelin. This effect was found to be mediated by the glycogen synthase kinase 3β (GSK3β) signaling pathway with impact on the collapsin response mediator protein 4 (CRMP4), suggesting that besides surface topography, nanomechanical properties were implicated in this process. The obtained results indicate P(TMC-CL) as a promising material for CNS regenerative applications as it promotes axonal growth, overcoming myelin inhibition.
PMCID: PMC3937290  PMID: 24586346
23.  Delivery of Neurotrophin-3 from Fibrin Enhances Neuronal Fiber Sprouting After Spinal Cord Injury 
Neurotrophins have been shown to promote axonal growth and regeneration after spinal cord injury. The therapeutic utility of neurotrophins may be enhanced by using a controlled delivery system to increase the duration of neurotrophin availability following injury. Such a delivery system can be incorporated into a bioactive scaffold to serve as a physical bridge for regeneration. This study assessed the effect of controlled delivery of neurotrophin-3 (NT-3) from fibrin scaffolds implanted in spinal cord lesions immediately following 2-mm ablation injury in adult rats. Nine days after injury, fibrin scaffolds containing the delivery system and NT-3 (1000 ng/mL) elicited more robust neuronal fiber growth into the lesion than did control scaffolds or saline (1.5- to 3-fold increase). Implantation of fibrin scaffolds resulted in a dramatic reduction of glial scar formation at the white matter border of the lesion. Hindlimb motor function of treated animals did not improve relative to controls at 12 weeks post-injury. Thus, controlled delivery of NT-3 from fibrin scaffolds enhanced the initial regenerative response by increasing neuronal fiber sprouting and cell migration into the lesion, while functional motor recovery was not observed in this model.
PMCID: PMC1615967  PMID: 16797770
controlled release; growth factor; nerve regeneration
24.  Astrocytes derived from glial-restricted precursors promote spinal cord repair 
Journal of Biology  2006;5(3):7.
Transplantation of embryonic stem or neural progenitor cells is an attractive strategy for repair of the injured central nervous system. Transplantation of these cells alone to acute spinal cord injuries has not, however, resulted in robust axon regeneration beyond the sites of injury. This may be due to progenitors differentiating to cell types that support axon growth poorly and/or their inability to modify the inhibitory environment of adult central nervous system (CNS) injuries. We reasoned therefore that pre-differentiation of embryonic neural precursors to astrocytes, which are thought to support axon growth in the injured immature CNS, would be more beneficial for CNS repair.
Transplantation of astrocytes derived from embryonic glial-restricted precursors (GRPs) promoted robust axon growth and restoration of locomotor function after acute transection injuries of the adult rat spinal cord. Transplantation of GRP-derived astrocytes (GDAs) into dorsal column injuries promoted growth of over 60% of ascending dorsal column axons into the centers of the lesions, with 66% of these axons extending beyond the injury sites. Grid-walk analysis of GDA-transplanted rats with rubrospinal tract injuries revealed significant improvements in locomotor function. GDA transplantation also induced a striking realignment of injured tissue, suppressed initial scarring and rescued axotomized CNS neurons with cut axons from atrophy. In sharp contrast, undifferentiated GRPs failed to suppress scar formation or support axon growth and locomotor recovery.
Pre-differentiation of glial precursors into GDAs before transplantation into spinal cord injuries leads to significantly improved outcomes over precursor cell transplantation, providing both a novel strategy and a highly effective new cell type for repairing CNS injuries.
PMCID: PMC1561531  PMID: 16643674
Experimental neurology  2009;222(1):59-69.
Transplantation of olfactory bulb-derived olfactory ensheathing glia (OEG) combined with step training improves hindlimb locomotion in adult rats with a complete spinal cord transection. Spinal cord injury studies use the presence of noradrenergic (NA) axons caudal to the injury site as evidence of axonal regeneration and we previously found more NA axons just caudal to the transection in OEG- than media-injected spinal rats. We therefore hypothesized that OEG transplantation promotes descending coeruleospinal regeneration that contributes to the recovery of hindlimb locomotion. Now we report that NA axons are present throughout the caudal stump of both media- and OEG-injected spinal rats and they enter the spinal cord from the periphery via dorsal and ventral roots and along large penetrating blood vessels. These results indicate that the presence of NA fibers in the caudal spinal cord is not a reliable indicator of coeruleospinal regeneration. We then asked if NA axons appose cholinergic neurons associated with motor functions, i.e., central canal cluster and partition cells (active during fictive locomotion) and somatic motor neurons (SMNs). We found more NA varicosities adjacent to central canal cluster cells, partition cells, and SMNs in the lumbar enlargement of OEG- than media-injected rats. As non-synaptic release of NA is common in the spinal cord, more associations between NA varicosities and motor-associated cholinergic neurons in the lumbar spinal cord may contribute to the improved treadmill stepping observed in OEG-injected spinal rats. This effect could be mediated through direct association with SMNs and/or indirectly via cholinergic interneurons.
PMCID: PMC2838922  PMID: 20025875
OEC; spinal cord injury; norepinephrine; ChAT; cholinergic neurons; locomotion

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