Single, high-dose intraspinal injection of chondroitinase reduces glycosaminoglycans in injured spinal cord and promotes corticospinal axonal regrowth after hemisection but not contusion

The Role and Modulation of Spinal Perineuronal Nets in the Healthy and Injured Spinal Cord

Rather than being a stable scaffold, perineuronal nets (PNNs) are a dynamic and specialized extracellular matrix involved in plasticity modulation. They have been extensively studied in the brain and associated with neuroprotection, ionic buffering, and neural maturation. However, their biological function in the spinal cord and the effects of disrupting spinal PNNs remain elusive. The goal of this review is to summarize the current knowledge of spinal PNNs and their potential in pathological conditions such as traumatic spinal cord injury (SCI). We also highlighted interventions that have been used to modulate the extracellular matrix after SCI, targeting the glial scar and spinal PNNs, in an effort to promote regeneration and stabilization of the spinal circuits, respectively. These concepts are discussed in the framework of developmental and neuroplastic changes in PNNs, drawing similarities between immature and denervated neurons after an SCI, which may provide a useful context for future SCI research.

Heparin-Binding Growth-Associated Molecule (Pleiotrophin) Affects Sensory Signaling and Selected Motor Functions in Mouse Model of Anatomically Incomplete Cervical Spinal Cord Injury

Heparin-binding growth-associated molecule (pleiotrophin) is a neurite outgrowth-promoting secretory protein that lines developing fiber tracts in juvenile CNS (central nervous system). Previously, we have shown that heparin-binding growth-associated molecule (HB-GAM) reverses the CSPG (chondroitin sulfate proteoglycan) inhibition on neurite outgrowth in the culture medium of primary CNS neurons and enhances axon growth through the injured spinal cord in mice demonstrated by two-photon imaging. In this study, we have started studies on the possible role of HB-GAM in enhancing functional recovery after incomplete spinal cord injury (SCI) using cervical lateral hemisection and hemicontusion mouse models. In vivo imaging of blood-oxygen-level-dependent (BOLD) signals associated with functional activity in the somatosensory cortex was used to assess the sensory functions during vibrotactile hind paw stimulation. The signal displays an exaggerated response in animals with lateral hemisection that recovers to the level seen in the sham-operated mice by injection of HB-GAM to the trauma site. The effect of HB-GAM treatment on sensory-motor functions was assessed by performance in demanding behavioral tests requiring integration of afferent and efferent signaling with central coordination. Administration of HB-GAM either by direct injection into the trauma site or by intrathecal injection improves the climbing abilities in animals with cervical hemisection and in addition enhances the grip strength in animals with lateral hemicontusion without affecting the spontaneous locomotor activity. Recovery of sensory signaling in the sensorimotor cortex by HB-GAM to the level of sham-operated mice may contribute to the improvement of skilled locomotion requiring integration of spatiotemporal signals in the somatosensory cortex.

Locomotor Behavior Analysis in Spinal Cord Injured Macaca radiata after Predegenerated Peripheral Nerve Grafting-A Preliminary Evidence

INTRODUCTION

Primate animal models are being utilized to explore novel therapies for spinal cord injuries. This study aimed to evaluate the efficiency of the transplantation of predegenerated nerve segments in unilateral spinal cord-hemisected bonnet monkeys' (Macaca radiata) locomotor functions using the complex runways.

MATERIALS AND METHODS

The bonnet monkeys were initially trained to walk in a bipedal motion on grid and staircase runways. In one group of trained monkeys, surgical hemisection was made in the spinal cord at the T12-L1 level. In the other group, hemisection was induced in the spinal cord, and the ulnar nerve was also transected at the same time (transplant group). After one week, the hemisected cavity was reopened and implanted with predegenerated ulnar nerve segments obtained from the same animal of the transplant group.

RESULTS

All the operated monkeys showed significant deficits in locomotion on runways at the early postoperative period. The walking ability of operated monkeys was found to be gradually improved, and they recovered nearer to preoperative level at the fourth postoperative month, and there were no marked differences.

CONCLUSION

The results demonstrate that there were no significant improvements in the locomotion of monkeys on runways after the delayed grafting of nerve segments until one year later. The failure of the predegenerated nerve graft as a possible therapeutic strategy to improve the locomotion of monkeys may be due to a number of factors set in motion by trauma, which could possibly prevent the qualities of regeneration. The exact reason for this ineffectiveness of predegenerated nerve segments and their underlying mechanism is not known.

Acute spinal cord injury: Pathophysiology and pharmacological intervention (Review)

Spinal cord injury (SCI) is one of the most debilitating of all the traumatic conditions that afflict individuals. For a number of years, extensive studies have been conducted to clarify the molecular mechanisms of SCI. Experimental and clinical studies have indicated that two phases, primary damage and secondary damage, are involved in SCI. The initial mechanical damage is caused by local impairment of the spinal cord. In addition, the fundamental mechanisms are associated with hyperflexion, hyperextension, axial loading and rotation. By contrast, secondary injury mechanisms are led by systemic and cellular factors, which may also be initiated by the primary injury. Although significant advances in supportive care have improved clinical outcomes in recent years, a number of studies continue to explore specific pharmacological therapies to minimize SCI. The present review summarized some important pathophysiologic mechanisms that are involved in SCI and focused on several pharmacological and non‑pharmacological therapies, which have either been previously investigated or have a potential in the management of this debilitating injury in the near future.

Substrate Specificity and Biochemical Characteristics of an Engineered Mammalian Chondroitinase ABC

Chondroitin sulfate proteoglycans inhibit regeneration, neuroprotection, and plasticity following spinal cord injury. The development of a second-generation chondroitinase ABC enzyme, capable of being secreted from mammalian cells (mChABC), has facilitated the functional recovery of animals following severe spinal trauma. The genetically modified enzyme has been shown to efficiently break down the inhibitory extracellular matrix surrounding cells at the site of injury, while facilitating cellular integration and axonal growth. However, the activity profile of the enzyme in relation to the original bacterial chondroitinase (bChABC) has not been determined. Here, we characterize the activity profile of mChABC and compare it to bChABC, both enzymes having been maintained under physiologically relevant conditions for the duration of the experiment. We show that this genetically modified enzyme can be secreted reliably and robustly in high yields from a mammalian cell line. The modifications made to the cDNA of the enzyme have not altered the functional activity of mChABC compared to bChABC, ensuring that it has optimal activity on chondroitin sulfate-A, with an optimal pH at 8.0 and temperature at 37 °C. However, mChABC shows superior thermostability compared to bChABC, ensuring that the recombinant enzyme operates with enhanced activity over a variety of physiologically relevant substrates and temperatures compared to the widely used bacterial alternative without substantially altering its kinetic output. The determination that mChABC can function with greater robustness under physiological conditions than bChABC is an important step in the further development of this auspicious treatment strategy toward a clinical application.

Chondroitinase improves anatomical and functional outcomes after primate spinal cord injury

Inhibitory extracellular matrices form around mature neurons as perineuronal nets containing chondroitin sulfate proteoglycans (CSPGs) that limit axonal sprouting after CNS injury. The enzyme chondroitinase (Chase) degrades the inhibitory CSPGs and improves axonal sprouting and functional recovery after spinal cord injury (SCI) in rodents. We evaluated the effects of Chase in Rhesus monkeys that had undergone C7 spinal cord hemisection. Four weeks after hemisection, multiple intraparenchymal Chase injections targeted spinal cord circuits controlling hand function below the lesion. Hand function improved significantly in Chase-treated monkeys relative to vehicle-injected controls. Moreover, Chase significantly increased corticospinal axon growth and the number of synapses formed by corticospinal terminals in gray matter caudal to the lesion. No detrimental effects were detected. This approach appears to merit clinical translation in SCI.

Plasticity Induced Recovery of Breathing Occurs at Chronic Stages after Cervical Contusion

Severe midcervical contusion injury causes profound deficits throughout the respiratory motor system that last from acute to chronic time points post-injury. We use chondroitinase ABC (ChABC) to digest chondroitin sulphate proteoglycans within the extracellular matrix (ECM) surrounding the respiratory system at both acute and chronic time points post-injury to explore whether augmentation of plasticity can recover normal motor function. We demonstrate that, regardless of time post-injury or treatment application, the lesion cavity remains consistent, showing little regeneration or neuroprotection within our model. Through electromyography (EMG) recordings of multiple inspiratory muscles, however, we show that application of the enzyme at chronic time points post-injury initiates the recovery of normal breathing in previously paralyzed respiratory muscles. This reduced the need for compensatory activity throughout the motor system. Application of ChABC at acute time points recovered only modest amounts of respiratory function. To further understand this effect, we assessed the anatomical mechanism of this recovery. Increased EMG activity in previously paralyzed muscles was brought about by activation of spared bulbospinal pathways through the site of injury and/or sprouting of spared serotonergic fibers from the contralateral side of the cord. Accordingly, we demonstrate that alterations to the ECM and augmentation of plasticity at chronic time points post-cervical contusion can cause functional recovery of the respiratory motor system and reveal mechanistic evidence of the pathways that govern this effect.

The Biology of Regeneration Failure and Success After Spinal Cord Injury

Since no approved therapies to restore mobility and sensation following spinal cord injury (SCI) currently exist, a better understanding of the cellular and molecular mechanisms following SCI that compromise regeneration or neuroplasticity is needed to develop new strategies to promote axonal regrowth and restore function. Physical trauma to the spinal cord results in vascular disruption that, in turn, causes blood-spinal cord barrier rupture leading to hemorrhage and ischemia, followed by rampant local cell death. As subsequent edema and inflammation occur, neuronal and glial necrosis and apoptosis spread well beyond the initial site of impact, ultimately resolving into a cavity surrounded by glial/fibrotic scarring. The glial scar, which stabilizes the spread of secondary injury, also acts as a chronic, physical, and chemo-entrapping barrier that prevents axonal regeneration. Understanding the formative events in glial scarring helps guide strategies towards the development of potential therapies to enhance axon regeneration and functional recovery at both acute and chronic stages following SCI. This review will also discuss the perineuronal net and how chondroitin sulfate proteoglycans (CSPGs) deposited in both the glial scar and net impede axonal outgrowth at the level of the growth cone. We will end the review with a summary of current CSPG-targeting strategies that help to foster axonal regeneration, neuroplasticity/sprouting, and functional recovery following SCI.

Benefícios da condroitinase abc associada a células-tronco mesenquimais na lesão espinhal aguda em ratos

RESUMO Com o objetivo de estudar o efeito da condroitinase associada às células-tronco mesenquimais na lesão aguda da medula espinhal, utilizaram-se 50 ratos Lewis, distribuídos igualmente nos grupos: controle negativo (CN), tratamento com placebo (PLA), condroitinase (CDN), células-tronco mesenquimais (CTM) e condroitinase mais células-tronco mesenquimais (CDN+CTM). Todos os animais tiveram a medula espinhal exposta por laminectomia, e os grupos PLA, CDT, CTM e CDT+CTM sofreram também trauma medular compressivo. Após sete dias, procedeu-se à reexposição da medula espinhal, quando os grupos PLA e CTM receberam 4µL de líquido cefalorraquidiano artificial via intralesional, e os grupos CDT e CDT+CTM receberam o mesmo líquido contendo 2,2U de condroitinase. Após 14 dias da cirurgia inicial, todos os animais receberam 0,2mL de PBS via endovenosa, contudo, nos grupos CTM e CDT+CTM, esse líquido continha 1x106 CTM. Avaliou-se a capacidade motora até o 28o dia pós-trauma e, posteriormente, as medulas espinhais foram analisadas por RT-PCR, para quantificação da expressão gênica para BDNF, NT-3, VEGF, KDR e PECAM-1, e por imunoistoquímica, para detecção das células-tronco GFP injetadas (anti-GFP), quantificação dos neurônios (anti-NeuN) e da GFAP e vimentina, para avaliação da cicatriz glial. As análises estatísticas foram realizadas com o auxílio do Prism 5 for Windows, com o nível de significância de 5%. Não houve diferença entre os grupos quanto à capacidade motora. O grupo CDT+CTM apresentou maior imunoexpressão de neurônios viáveis do que o placebo. No CTM, houve maior expressão dos fatores neurotróficos BDNF e VEGF. E no CDT, houve menor imunoexpressão de vimentina. Concluiu-se que a associação CDT+CTM favorece a viabilidade neuronal após o trauma, que o tratamento com CTM promove aumento na expressão dos fatores tróficos BDNF e VEGF e que o tratamento com condroitinase é efetivo na redução da cicatriz glial.

Potential risk of clonally expanded amnion mesenchymal stem cell transplants in contused spinal cords

OBJECTIVE

Mesenchymal stem/stromal cells (MSC) promote recovery after spinal cord injury (SCI) using adult bone marrow MSC (BM-MSC). Newborn tissues are a convenient source of MSC that does not involve an invasive procedure for cell collection. In this study the authors tested the effects of rat amnion MSC clone (rAM-MSC) in SCI.

METHODS

We tested intra-parenchymal injection of a GFP+ rat rAM-MSC clone derived from E18.5 rats in rat SCI and measured behavioral recovery (BBB scores), histology and X-ray opacity. Expression of aggrecan was measured in culture after treatment with TGFß.

RESULTS

Injection of rAM-MSC after SCI did not improve BBB scores compared to control vehicle injections; rather they reduced scores significantly over 6 weeks. Spinal cords injected with rAM-MSC were hard in regions surrounding the SCI site, which was confirmed by X-ray opacity. Whole mount imaging of these cords showed minimal tissue loss in the SCI site that occurred in SCI controls, and persistence of GFP+ rAM-MSC. Mason's Trichrome staining of tissue sections showed more intense staining for extracellular matrix (ECM) surrounding and extending beyond the SCI site with injections of rAM-MSC but not in controls. In response to TGF-ß treatment in culture, chondrogenic aggrecan was expressed at higher levels in rAM-MSC than in rBM-MSC, suggesting that the upregulation of TGF-ß in SCI sites may promote chondrogenic differentiation.

CONCLUSION

Acute injection after SCI of a clonally expanded rAM-MSC resulted in aberrant differentiation towards a chondrocytic phenotype that disrupts the spinal cord and inhibits behavioral recovery after SCI. It will be critical to ensure that injection of extensively expanded neonatal cells do not differentiate aberrantly in traumatic CNS tissue and disrupt recovery.

Combined delivery of chondroitinase ABC and human induced pluripotent stem cell-derived neuroepithelial cells promote tissue repair in an animal model of spinal cord injury

The lack of tissue regeneration after traumatic spinal cord injury in animal models is largely attributed to the local inhibitory microenvironment. To overcome this inhibitory environment while promoting tissue regeneration, we investigated the combined delivery of chondroitinase ABC (chABC) with human induced pluripotent stem cell-derived neuroepithelial stem cells (NESCs). ChABC was delivered to the injured spinal cord at the site of injury by affinity release from a crosslinked methylcellulose (MC) hydrogel by injection into the intrathecal space. NESCs were distributed in a hydrogel comprised of hyaluronan and MC and injected into the spinal cord tissue both rostral and caudal to the site of injury. Cell transplantation led to reduced cavity formation, but did not improve motor function. While few surviving cells were found 2 weeks post injury, the majority of live cells were neurons, with only few astrocytes, oligodendrocytes, and progenitor cells. At 9 weeks post injury, there were more progenitor cells and a more even distribution of cell types compared to those at 2 weeks post injury, suggesting preferential survival and differentiation. Interestingly, animals that received cells and chABC had more neurons than animals that received cells alone, suggesting that chABC influenced the injury environment such that neuronal differentiation or survival was favoured.

Combinatorial Therapies After Spinal Cord Injury: How Can Biomaterials Help?

Traumatic spinal cord injury (SCI) results in an immediate loss of motor and sensory function below the injury site and is associated with a poor prognosis. The inhibitory environment that develops in response to the injury is mainly due to local expression of inhibitory factors, scarring and the formation of cystic cavitations, all of which limit the regenerative capacity of endogenous or transplanted cells. Strategies that demonstrate promising results induce a change in the microenvironment at- and around the lesion site to promote endogenous cell repair, including axonal regeneration or the integration of transplanted cells. To date, many of these strategies target only a single aspect of SCI; however, the multifaceted nature of SCI suggests that combinatorial strategies will likely be more effective. Biomaterials are a key component of combinatorial strategies, as they have the potential to deliver drugs locally over a prolonged period of time and aid in cell survival, integration and differentiation. Here we summarize the advantages and limitations of widely used strategies to promote recovery after injury and highlight recent research where biomaterials aided combinatorial strategies to overcome some of the barriers of spinal cord regeneration.

Combined chondroitinase and KLF7 expression reduce net retraction of sensory and CST axons from sites of spinal injury

Axon regeneration in the central nervous system is limited both by inhibitory extracellular cues and by an intrinsically low capacity for axon growth in some CNS populations. Chondroitin sulfate proteoglycans (CSPGs) are well-studied inhibitors of axon growth in the CNS, and degradation of CSPGs by chondroitinase has been shown to improve the extension of injured axons. Alternatively, axon growth can be improved by targeting the neuron-intrinsic growth capacity through forced expression of regeneration-associated transcription factors. For example, a transcriptionally active chimera of Krüppel-like Factor 7 (KLF7) and a VP16 domain improves axon growth when expressed in corticospinal tract neurons. Here we tested the hypothesis that combined expression of chondroitinase and VP16-KLF7 would lead to further improvements in axon growth after spinal injury. Chondroitinase was expressed by viral transduction of cells in the spinal cord, while VP16-KLF7 was virally expressed in sensory neurons of the dorsal root ganglia or corticospinal tract (CST) neurons. After transection of the dorsal columns, both chondroitinase and VP16-KLF7 increased the proximity of severed sensory axons to the injury site. Similarly, after complete crush injuries, VP16-KLF7 expression increased the approach of CST axons to the injury site. In neither paradigm however, did single or combined treatment with chondroitinase or VP16-KLF7 enable regenerative growth distal to the injury. These results substantiate a role for CSPG inhibition and low KLF7 activity in determining the net retraction of axons from sites of spinal injury, while suggesting that additional factors act to limit a full regenerative response.

Extracellular vimentin is a novel axonal growth facilitator for functional recovery in spinal cord-injured mice

Vimentin, an intermediate filament protein, is an intracellular protein that is involved in various cellular processes. Several groups have recently reported that vimentin also appears in the extracellular space and shows novel protein activity. We previously reported that denosomin improved motor dysfunction in mice with a contusive spinal cord injury (SCI). At the injured area, astrocytes expressing and secreting vimentin were specifically increased, and axonal growth occurred in a vimentin-dependent manner in denosomin-treated mice. However, the axonal growth that was induced by extracellular vimentin was only investigated in vitro in the previous study. Here, we sought to clarify whether increased extracellular vimentin can promote the axonal extension related to motor improvement after SCI in vivo. Extracellular vimentin treatment in SCI mice significantly ameliorated motor dysfunction. In vimentin-treated mice, 5-HT-positive axons increased significantly at the rostral and central areas of the lesion, and the total axonal densities increased in the central and caudal parts of the lesioned area. This finding suggests that increased axonal density may contribute to motor improvement in vimentin-treated mice. Thus, our in vivo data indicate that extracellular vimentin may be a novel neurotrophic factor that enhances axonal growth activity and motor function recovery after SCI.

Local Delivery of High-Dose Chondroitinase ABC in the Sub-Acute Stage Promotes Axonal Outgrowth and Functional Recovery after Complete Spinal Cord Transection

Chondroitin sulfate proteoglycans (CSPGs) are glial scar-associated molecules considered axonal regeneration inhibitors and can be digested by chondroitinase ABC (ChABC) to promote axonal regeneration after spinal cord injury (SCI). We previously demonstrated that intrathecal delivery of low-dose ChABC (1 U) in the acute stage of SCI promoted axonal regrowth and functional recovery. In this study, high-dose ChABC (50 U) introduced via intrathecal delivery induced subarachnoid hemorrhage and death within 48 h. However, most SCI patients are treated in the sub-acute or chronic stages, when the dense glial scar has formed and is minimally digested by intrathecal delivery of ChABC at the injury site. The present study investigated whether intraparenchymal delivery of ChABC in the sub-acute stage of complete spinal cord transection would promote axonal outgrowth and improve functional recovery. We observed no functional recovery following the low-dose ChABC (1 U or 5 U) treatments. Furthermore, animals treated with high-dose ChABC (50 U or 100 U) showed decreased CSPGs levels. The extent and area of the lesion were also dramatically decreased after ChABC treatment. The outgrowth of the regenerating axons was significantly increased, and some partially crossed the lesion site in the ChABC-treated groups. In addition, retrograde Fluoro-Gold (FG) labeling showed that the outgrowing axons could cross the lesion site and reach several brain stem nuclei involved in sensory and motor functions. The Basso, Beattie and Bresnahan (BBB) open field locomotor scores revealed that the ChABC treatment significantly improved functional recovery compared to the control group at eight weeks after treatment. Our study demonstrates that high-dose ChABC treatment in the sub-acute stage of SCI effectively improves glial scar digestion by reducing the lesion size and increasing axonal regrowth to the related functional nuclei, which promotes locomotor recovery. Thus, our results will aid in the treatment of spinal cord injury.

"GAG-ing with the neuron": The role of glycosaminoglycan patterning in the central nervous system

Proteoglycans (PGs) are a diverse family of proteins that consist of one or more glycosaminoglycan (GAG) chains, covalently linked to a core protein. PGs are major components of the extracellular matrix (ECM) and play critical roles in development, normal function and damage-response of the central nervous system (CNS). GAGs are classified based on their disaccharide subunits, into the following major groups: chondroitin sulfate (CS), heparan sulfate (HS), heparin (HEP), dermatan sulfate (DS), keratan sulfate (KS) and hyaluronic acid (HA). All except HA are modified by sulfation, giving GAG chains specific charged structures and binding properties. While significant neuroscience research has focused on the role of one PG family member, chondroitin sulfate proteoglycan (CSPG), there is ample evidence in support of a role for the other PGs in regulating CNS function in normal and pathological conditions. This review discusses the role of all the identified PG family members (CS, HS, HEP, DS, KS and HA) in normal CNS function and in the context of pathology. Understanding the pleiotropic roles of these molecules in the CNS may open the door to novel therapeutic strategies for a number of neurological conditions.

Chondroitinase gene therapy improves upper limb function following cervical contusion injury

Chondroitin sulphate proteoglycans (CSPGs) are known to be important contributors to the intensely inhibitory environment that prevents tissue repair and regeneration following spinal cord injury. The bacterial enzyme chondroitinase ABC (ChABC) degrades these inhibitory molecules and has repeatedly been shown to promote functional recovery in a number of spinal cord injury models. However, when used to treat more traumatic and clinically relevant spinal contusion injuries, findings with the ChABC enzyme have been inconsistent. We recently demonstrated that delivery of mammalian-compatible ChABC via gene therapy led to sustained and widespread digestion of CSPGs, resulting in significant functional repair of a moderate thoracic contusion injury in adult rats. Here we demonstrate that chondroitinase gene therapy significantly enhances upper limb function following cervical contusion injury, with improved forelimb ladder performance and grip strength as well as increased spinal conduction through the injury site and reduced lesion pathology. This is an important addition to our previous findings as improving upper limb function is a top priority for spinal injured patients. Additionally great importance is placed on replication in the spinal cord injury field. That chondroitinase gene therapy has now been shown to be efficacious in contusion models at either thoracic or cervical level is an important step in the further development of this promising therapeutic strategy towards the clinic.

Expression of hyaluronidase-4 in a rat spinal cord hemisection model

Study Design

Examination of hyaluronidase-4 (Hyal-4) expression in a rat spinal cord hemisection model.

Purpose

To determine the status of Hyal-4 expression after hemisection of the spinal cord, and the relationship between its expression and that of chondroitin sulfate proteoglycans (CSPGs).

Overview of Literature

CSPGs are expressed at the site of spinal cord injury and inhibit axon regeneration. Administration of exogenous chrondroitinase ABC (ChABC), derived from bacteria, digested CSPGs and promoted axonal regrowth. Using a rat hemisection model, we have demonstrated peak CSPGs levels at by 3 weeks after injury but then decreased spontaneously. Could there be an endogenous enzyme similar to ChABC in the spinal cord? It has been suggested that Hyal-4 is involved in CSPG degradation.

Methods

A rat hemisection model was prepared and spinal cord frozen sections were prepared at 4 days and 1, 2, 3, 4, 5, and 6 weeks post-cordotomy and stained for CSPGs and Hyal-4 and subjected to Western blotting.

Results

CSPGs appeared at the injury site at 4 days after hemisection, reached a peak after 3 weeks, and then decreased. Hyal-4 was observed around the injury site from 4 days after cordotomy and increased until after 5-6 weeks. Double staining showed Hyal-4 around CSPGs. Western blotting identified a band corresponding to Hyal-4 from 4 days after hemisection.

Conclusions

Hyal-4 was expressed in a rat hemisection model in areas surrounding CSPGs, and as its peak was delayed compared with that of CSPGs. These results suggest the involvement of Hyal-4 in the digestion of CSPGs.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

Restoring function after spinal cord injury: towards clinical translation of experimental strategies

Spinal cord injury is currently incurable and treatment is limited to minimising secondary complications and maximising residual function by rehabilitation. Improved understanding of the pathophysiology of spinal cord injury and the factors that prevent nerve and tissue repair has fuelled a move towards more ambitious experimental treatments aimed at promoting neuroprotection, axonal regeneration, and neuroplasticity. By necessity, these new options are more invasive. However, in view of recent advances in spinal cord injury research and demand from patients, clinicians, and the scientific community to push promising experimental treatments to the clinic, momentum and optimism exist for the translation of candidate experimental treatments to clinical spinal cord injury. The ability to rescue, reactivate, and rewire spinal systems to restore function after spinal cord injury might soon be within reach.

Large-scale chondroitin sulfate proteoglycan digestion with chondroitinase gene therapy leads to reduced pathology and modulates macrophage phenotype following spinal cord contusion injury

Chondroitin sulfate proteoglycans (CSPGs) inhibit repair following spinal cord injury. Here we use mammalian-compatible engineered chondroitinase ABC (ChABC) delivered via lentiviral vector (LV-ChABC) to explore the consequences of large-scale CSPG digestion for spinal cord repair. We demonstrate significantly reduced secondary injury pathology in adult rats following spinal contusion injury and LV-ChABC treatment, with reduced cavitation and enhanced preservation of spinal neurons and axons at 12 weeks postinjury, compared with control (LV-GFP)-treated animals. To understand these neuroprotective effects, we investigated early inflammatory changes following LV-ChABC treatment. Increased expression of the phagocytic macrophage marker CD68 at 3 d postinjury was followed by increased CD206 expression at 2 weeks, indicating that large-scale CSPG digestion can alter macrophage phenotype to favor alternatively activated M2 macrophages. Accordingly, ChABC treatment in vitro induced a significant increase in CD206 expression in unpolarized monocytes stimulated with conditioned medium from spinal-injured tissue explants. LV-ChABC also promoted the remodelling of specific CSPGs as well as enhanced vascularity, which was closely associated with CD206-positive macrophages. Neuroprotective effects of LV-ChABC corresponded with improved sensorimotor function, evident as early as 1 week postinjury, a time point when increased neuronal survival correlated with reduced apoptosis. Improved function was maintained into chronic injury stages, where improved axonal conduction and increased serotonergic innervation were also observed. Thus, we demonstrate that ChABC gene therapy can modulate secondary injury processes, with neuroprotective effects that lead to long-term improved functional outcome and reveal novel mechanistic evidence that modulation of macrophage phenotype may underlie these effects.

Combination of chondroitinase ABC and AAV-NT3 promotes neural plasticity at descending spinal pathways after thoracic contusion in rats

Transmission through descending pathways to lumbar motoneurons, although important for voluntary walking in humans and rats, has not been fully understood at the cellular level in contusion models. Major descending pathways innervating lumbar motoneurons include those at corticospinal tract (CST) and ventrolateral funiculus (VLF). We examined transmission and plasticity at synaptic pathways from dorsal (d)CST and VLF to individual motoneurons located in ventral horn and interneurons located in dorsomedial gray matter at lumbar segments after thoracic chronic contusion in adult anesthetized rats. To accomplish this, we used intracellular electrophysiological recordings and performed acute focal spinal lesions during the recordings. We directly demonstrate that after thoracic T10 chronic contusion the disrupted dCST axons spontaneously form new synaptic contacts with individual motoneurons, extending around the contusion cavity, through spared ventrolateral white matter. These detour synaptic connections are very weak, and strengthening these connections in order to improve function may be a target for therapeutic interventions after spinal cord injury (SCI). We found that degradation of scar-related chondroitin sulfate proteoglycans with the enzyme chondroitinase ABC (ChABC) combined with adeno-associated viral (AAV) vector-mediated prolonged delivery of neurotrophin NT-3 (AAV-NT3) strengthened these spontaneously formed connections in contused spinal cord. Moreover, ChABC/AAV-NT3 treatment induced the appearance of additional detour synaptic pathways innervating dorsomedial interneurons. Improved transmission in ChABC/AAV-NT3-treated animals was associated with increased immunoreactivity of 5-HT-positive fibers in lumbar dorsal and ventral horns. Improved locomotor function assessed with automated CatWalk highlights the physiological significance of these novel connections.

Targeting the neural extracellular matrix in neurological disorders

The extracellular matrix (ECM) is known to regulate important processes in neuronal cell development, activity and growth. It is associated with the structural stabilization of neuronal processes and synaptic contacts during the maturation of the central nervous system. The remodeling of the ECM during both development and after central nervous system injury has been shown to affect neuronal guidance, synaptic plasticity and their regenerative responses. Particular interest has focused on the inhibitory role of chondroitin sulfate proteoglycans (CSPGs) and their formation into dense lattice-like structures, termed perineuronal nets (PNNs), which enwrap sub-populations of neurons and restrict plasticity. Recent studies in mammalian systems have implicated CSPGs and PNNs in regulating and restricting structural plasticity. The enzymatic degradation of CSPGs or destabilization of PNNs has been shown to enhance neuronal activity and plasticity after central nervous system injury. This review focuses on the role of the ECM, CSPGs and PNNs; and how developmental and pharmacological manipulation of these structures have enhanced neuronal plasticity and aided functional recovery in regeneration, stroke, and amblyopia. In addition to CSPGs, this review also points to the functions and potential therapeutic value of these and several other key ECM molecules in epileptogenesis and dementia.

A contusion model of severe spinal cord injury in rats

The translational potential of novel treatments should be investigated in severe spinal cord injury (SCI) contusion models. A detailed methodology is described to obtain a consistent model of severe SCI. Use of a stereotactic frame and computer controlled impactor allows for creation of reproducible injury. Hypothermia and urinary tract infection pose significant challenges in the post-operative period. Careful monitoring of animals with daily weight recording and bladder expression allows for early detection of post-operative complications. The functional results of this contusion model are equivalent to transection models. The contusion model can be utilized to evaluate the efficacy of both neuroprotective and neuroregenerative approaches.

Arylsulfatase B improves locomotor function after mouse spinal cord injury

Bacterial chondroitinase ABC (ChaseABC) has been used to remove the inhibitory chondroitin sulfate chains from chondroitin sulfate proteoglycans to improve regeneration after rodent spinal cord injury. We hypothesized that the mammalian enzyme arylsulfatase B (ARSB) would also enhance recovery after mouse spinal cord injury. Application of the mammalian enzyme would be an attractive alternative to ChaseABC because of its more robust chemical stability and reduced immunogenicity. A one-time injection of human ARSB into injured mouse spinal cord eliminated immunoreactivity for chondroitin sulfates within five days, and up to 9 weeks after injury. After a moderate spinal cord injury, we observed improvements of locomotor recovery assessed by the Basso Mouse Scale (BMS) in ARSB treated mice, compared to the buffer-treated control group, at 6 weeks after injection. After a severe spinal cord injury, mice injected with equivalent units of ARSB or ChaseABC improved similarly and both groups achieved significantly more locomotor recovery than the buffer-treated control mice. Serotonin and tyrosine hydroxylase immunoreactive axons were more extensively present in mouse spinal cords treated with ARSB and ChaseABC, and the immunoreactive axons penetrated further beyond the injury site in ARSB or ChaseABC treated mice than in control mice. These results indicate that mammalian ARSB improves functional recovery after CNS injury. The structural/molecular mechanisms underlying the observed functional improvement remain to be elucidated.

Sialidase, chondroitinase ABC, and combination therapy after spinal cord contusion injury

Axon regeneration in the central nervous system is severely hampered, limiting functional recovery. This is in part because of endogenous axon regeneration inhibitors that accumulate at the injury site. Therapeutic targeting of these inhibitors and their receptors may facilitate axon outgrowth and enhance recovery. A rat model of spinal cord contusion injury was used to test the effects of two bacterial enzyme therapies that target independent axon regeneration inhibitors, sialidase (Vibrio cholerae) and chondroitinase ABC (ChABC, Proteus vulgaris). The two enzymes, individually and in combination, were infused for 2 weeks via implanted osmotic pumps to the site of a moderate thoracic spinal cord contusion injury. Sialidase was completely stable, whereas ChABC retained>30% of its activity in vivo over the 2 week infusion period. Immunohistochemistry revealed that infused sialidase acted robustly throughout the spinal cord gray and white matter, whereas ChABC activity was more intense superficially. Sialidase treatment alone resulted in improved behavioral and anatomical outcomes. Rats treated exclusively with sialidase showed significantly increased hindlimb motor function, evidenced by higher Basso Beattie and Bresnahan (BBB) and BBB subscores, and fewer stepping errors on a horizontal ladder. Sialidase-treated rats also had increased serotonergic axons caudal to the injury. ChABC treatment, in contrast, did not enhance functional recovery or alter axon numbers after moderate spinal cord contusion injury, and dampened the response of sialidase in the dual enzyme treatment group. We conclude that sialidase infusion enhanced recovery from spinal cord contusion injury, and that combining sialidase with ChABC failed to improve outcomes.

Chondroitinase ABC promotes compensatory sprouting of the intact corticospinal tract and recovery of forelimb function following unilateral pyramidotomy in adult mice

Chondroitin sulphate proteoglycans (CSPGs) are extracellular matrix molecules whose inhibitory activity is attenuated by the enzyme chondroitinase ABC (ChABC). Here we assess whether CSPG degradation can promote compensatory sprouting of the intact corticospinal tract (CST) following unilateral injury and restore function to the denervated forelimb. Adult C57BL/6 mice underwent unilateral pyramidotomy and treatment with either ChABC or a vehicle control. Significant impairments in forepaw symmetry were observed following pyramidotomy, with injured mice preferentially using their intact paw during spontaneous vertical exploration of a cylinder. No recovery on this task was observed in vehicle-treated mice. However, ChABC-treated mice showed a marked recovery of function, with forelimb symmetry fully restored by 5 weeks post-injury. Functional recovery was associated with robust sprouting of the uninjured CST, with numerous axons observed crossing the midline in the brainstem and spinal cord and terminating in denervated grey matter. CST fibres in the denervated side of the spinal cord following ChABC treatment were closely associated with the synaptic marker vGlut1. Immunohistochemical assessment of chondroitin-4-sulphate revealed that CSPGs were heavily digested around lamina X, alongside midline crossing axons and in grey matter regions where sprouting axons and reduced peri-neuronal net staining was observed. Thus, we demonstrate that CSPG degradation promotes midline crossing and reinnervation of denervated target regions by intact CST axons and leads to restored function in the denervated forepaw. Enhancing compensatory sprouting using ChABC provides a route to restore function that could be applied to disorders such as spinal cord injury and stroke.

Systemic administration of a deoxyribozyme to xylosyltransferase-1 mRNA promotes recovery after a spinal cord contusion injury

After spinal cord injury, proteoglycans with growth-inhibitory glycosaminoglycan (GAG-) side chains in scar tissue limit spontaneous axonal sprouting/regeneration. Interventions that reduce scar-related inhibition facilitate an axonal growth response and possibly plasticity-based spinal cord repair. Xylosyltransferase-1 (XT-1) is the enzyme that initiates GAG-chain formation. We investigated whether intravenous administration of a deoxyribozyme (DNA enzyme) to XT-1 mRNA (DNAXT-1as) would elicit plasticity after a clinically relevant contusion of the spinal cord in adult rats. Our data showed that systemic DNAXT-1as administration resulted in a significant increase in sensorimotor function and serotonergic axon presence caudal to the injury. DNAXT1as treatment did not cause pathological or toxicological side effects. Importantly, intravenous delivery of DNAXT-1as did not exacerbate contusion-induced neuropathic pain. Collectively, our data demonstrate that DNAXT-1as is a safe neurotherapeutic, which holds promise to become an integral component of therapies that aim to improve the quality of life of persons with spinal cord injury.

Delayed intrathecal delivery of RhoA siRNA to the contused spinal cord inhibits allodynia, preserves white matter, and increases serotonergic fiber growth

RhoA is a key regulator of the actin cytoskeleton that is upregulated after spinal cord injury (SCI). We analyzed different methods for siRNA delivery and developed siRNAs targeting RhoA (siRhoA) for SCI treatment. Cy 3.5-labeled siRNA delivered at the time of SCI yielded fluorescence in several cell types in the injury site. Intraspinal injections of chemically stabilized siRhoA into the spinal cord of injured rats reduced RhoA protein levels after 1 week and improved hindlimb walking over 6 weeks. To explore a less invasive route, we tested intrathecal injection of Cy 3.5-labeled siRNA via lumbar puncture 1 day after SCI, which resulted in robust uptake in the T9-T10 injury site. Lumbar injection of siRhoA 1 day after SCI reduced RhoA mRNA and protein levels 3 days after injection. Although siRhoA treatment did not yield significant improvement in locomotion, it decreased tactile hypersensitivity significantly compared to controls. Histological analysis at 8 weeks showed significant improvement in white matter sparing with siRhoA compared to control siRNA. siRhoA treatment also resulted in less accumulation of ED1+macrophages, increased PKC-γ immunoreactivity in the corticospinal tract rostral to the injury site, and increased serotonergic fiber growth 12 mm caudal to the contusion site. The ability of siRhoA to preserve white matter and promote serotonergic axonal regrowth caudal to the injury site is likely to suppress allodynia. This provides justification for considering clinical development of RhoA inhibitors to treat SCI sub-acutely to reduce allodynia, which occurs frequently in SCI patients.

Tissue engineered regeneration of completely transected spinal cord using human mesenchymal stem cells

The present study employed a combinatorial strategy using poly(D,L-lactide-co-glycolide) (PLGA) scaffolds seeded with human mesenchymal stem cells (hMSCs) to promote cell survival, differentiation, and neurological function in a completely transected spinal cord injury (SCI) model. The SCI model was prepared by complete removal of a 2-mm length of spinal cord in the eighth-to-ninth spinal vertebra, a procedure that resulted in bilateral hindlimb paralysis. PLGA scaffolds 2 mm in length without hMSCs (control) or with different numbers of hMSCs (1 × 10(5), 2 × 10(4), and 4 × 10(3)) were fitted into the completely transected spinal cord. Rats implanted with hMSCs received Basso-Beattie-Bresnahan scores for hindlimb locomotion of about 5, compared with ~2 for animals in the control group. The amplitude of motor-evoked potentials (MEPs) averaged 200-300 μV in all hMSC-implanted SCR model rats. In contrast, the amplitude of MEPs in control group animals averaged 135 μV at 4 weeks and then declined to 100 μV at 8 weeks. These results demonstrate functional recovery in a completely transected SCI model under conditions that exclude self-recovery. hMSCs were detected at the implanted site 4 and 8 weeks after transplantation, indicating in vivo survival of implanted hMSCs. Immunohistochemical staining revealed differentiation of implanted hMSCs into nerve cells, and immunostained images showed clear evidence for axonal regeneration only in hMSC-seeded PLGA scaffolds. Collectively, our results indicate that hMSC-seeded PLGA scaffolds induced nerve regeneration in a completely transected SCI model, a finding that should have significant implications for the feasibility of therapeutic and clinical hMSC-delivery using three-dimensional scaffolds, especially in the context of complete spinal cord transection.

Biodegradable biomatrices and bridging the injured spinal cord: the corticospinal tract as a proof of principle

Important advances in the development of smart biodegradable implants for axonal regeneration after spinal cord injury have recently been reported. These advances are evaluated in this review with special emphasis on the regeneration of the corticospinal tract. The corticospinal tract is often considered the ultimate challenge in demonstrating whether a repair strategy has been successful in the regeneration of the injured mammalian spinal cord. The extensive know-how of factors and cells involved in the development of the corticospinal tract, and the advances made in material science and tissue engineering technology, have provided the foundations for the optimization of the biomatrices needed for repair. Based on the findings summarized in this review, the future development of smart biodegradable bridges for CST regrowth and regeneration in the injured spinal cord is discussed.

Translational spinal cord injury research: preclinical guidelines and challenges

Advances in the neurobiology of spinal cord injury (SCI) have prompted increasing attention to opportunities for moving experimental strategies towards clinical applications. Preclinical studies are the centerpiece of the translational process. A major challenge is to establish strategies for achieving optimal translational progression while minimizing potential repetition of previous disappointments associated with clinical trials. This chapter reviews and expands upon views pertaining to preclinical design reported in recently published opinion surveys. Subsequent discussion addresses other preclinical considerations more specifically related to current and potentially imminent cellular and pharmacological approaches to acute/subacute and chronic SCI. Lastly, a retrospective and prospective analysis examines how guidelines currently under discussion relate to select examples of past, current, and future clinical translations. Although achieving definition of the "perfect" preclinical scenario is difficult to envision, this review identifies therapeutic robustness and independent replication of promising experimental findings as absolutely critical prerequisites for clinical translation. Unfortunately, neither has been fully embraced thus far. Accordingly, this review challenges the notion "everything works in animals and nothing in humans", since more rigor must first be incorporated into the bench-to-bedside translational process by all concerned, whether in academia, clinical medicine, or corporate circles.

Chondroitinase combined with rehabilitation promotes recovery of forelimb function in rats with chronic spinal cord injury

Chondroitinase ABC (ChABC) in combination with rehabilitation has been shown to promote functional recovery in acute spinal cord injury. For clinical use, the optimal treatment window is concurrent with the beginning of rehabilitation, usually 2-4 weeks after injury. We show that ChABC is effective when given 4 weeks after injury combined with rehabilitation. After C4 dorsal spinal cord injury, rats received no treatment for 4 weeks. They then received either ChABC or penicillinase control treatment followed by hour-long daily rehabilitation specific for skilled paw reaching. Animals that received both ChABC and task-specific rehabilitation showed the greatest recovery in skilled paw reaching, approaching similar levels to animals that were treated at the time of injury. There was also a modest increase in skilled paw reaching ability in animals receiving task-specific rehabilitation alone. Animals treated with ChABC and task-specific rehabilitation also showed improvement in ladder and beam walking. ChABC increased sprouting of the corticospinal tract, and these sprouts had more vGlut1(+ve) presynaptic boutons than controls. Animals that received rehabilitation showed an increase in perineuronal net number and staining intensity. Our results indicate that ChABC treatment opens a window of opportunity in chronic spinal cord lesions, allowing rehabilitation to improve functional recovery.

Plasticity after spinal cord injury: relevance to recovery and approaches to facilitate it

Motor, sensory, and autonomic functions can spontaneously return or recover to varying extents in both humans and animals, regardless of the traumatic spinal cord injury (SCI) level and whether it was complete or incomplete. In parallel, adverse and painful functions can appear. The underlying mechanisms for all of these diverse functional changes are summarized under the term plasticity. Our review will describe what is known regarding this phenomenon after traumatic SCI and focus on its relevance to motor and sensory recovery. Although it is still somewhat speculative, plasticity can be found throughout the neuraxis and includes various changes ranging from alterations in the properties of spared neuronal circuitries, intact or lesioned axon collateral sprouting, and synaptic rearrangements. Furthermore, we will discuss a selection of potential approaches for facilitating plasticity as possible SCI treatments. Because a mechanism underlying spontaneous plasticity and recovery might be motor activity and the related neuronal activity, activity-based therapies are being used and investigated both clinically and experimentally. Additional pharmacological and gene-delivery approaches, based on plasticity being dependent on the delicate balance between growth inhibition and promotion as well as the basic intrinsic growth ability of the neurons themselves, have been found to be effective alone and in combination with activity-based therapies. The positive results have to be tempered with the reality that not all plasticity is beneficial. Therefore, a tremendous number of questions still need to be addressed. Ultimately, answers to these questions will enhance plasticity's potential for improving the quality of life for persons with SCI.

Delayed treatment with chondroitinase ABC reverses chronic atrophy of rubrospinal neurons following spinal cord injury

Degradation of extracellular matrix chondroitin sulphate proteoglycans (CSPGs) using Chondroitinase ABC (ChABC) is a promising strategy for the treatment of spinal cord injury, with potent effects on promoting functional recovery and anatomical repair in spinal injured animals. We have previously demonstrated that ChABC treatment prevents atrophy of corticospinal projection neurons following spinal injury in adult YFP-H mice. Here, we investigate whether ChABC-mediated repair of the cell body extends to rubrospinal projection neurons (RSNs), whether neuroprotective effects can be sustained long-term and importantly, whether delayed treatment with ChABC can reverse chronic atrophy. Adult YFP-H mice underwent unilateral rubrospinal tract transection and were treated with ChABC or a control enzyme, delivered either acutely post-injury or after a one month delay. Eight weeks following injury and control treatment, RSNs in the injured red nucleus, identified by YFP label and NeuN immunoreactivity, showed severe atrophy, with ~40% loss of mean cell area compared to uninjured neurons in the contralateral red nucleus. Both acute and delayed treatment with ChABC promoted a significant rescue of injured RSNs, restoring cell area to ~80% and ~70%, respectively, of that in uninjured neurons. Thus, we demonstrate for the first time that CSPG degradation in the injured spinal cord not only promotes sustained rescue of cell atrophy when delivered acutely but can also reverse chronic atrophy in descending projection neurons. Thus, modulation of the extracellular matrix can mediate neuroprotective effects both early and late after spinal cord injury.

Role of chondroitin sulfate proteoglycans in axonal conduction in Mammalian spinal cord

Chronic unilateral hemisection (HX) of the adult rat spinal cord diminishes conduction through intact fibers in the ventrolateral funiculus (VLF) contralateral to HX. This is associated with a partial loss of myelination from fibers in the VLF (Arvanian et al., 2009). Here, we again measured conduction through the VLF using electrical stimulation while recording the resulting volley and synaptic potentials in target motoneurons. We found that intraspinal injection of chondroitinase-ABC, known to digest chondroitin sulfate proteoglycans (CSPGs), prevented the decline of axonal conduction through intact VLF fibers across from chronic T10 HX. Chondroitinase treatment was also associated with behavior suggestive of an improvement of locomotor function after chronic HX. To further study the role of CSPGs in axonal conduction, we injected three purified CSPGs, NG2 and neurocan, which increase in the vicinity of a spinal injury, and aggrecan, which decreases, into the lateral column of the uninjured cord at T10 in separate experiments. Intraspinal injection of NG2 acutely depressed axonal conduction through the injected region in a dose-dependent manner. Similar injections of saline, aggrecan, or neurocan had no significant effect. Immunofluorescence staining experiments revealed the presence of endogenous and exogenous NG2 at some nodes of Ranvier. These results identify a novel acute action of CSPGs on axonal conduction in the spinal cord and suggest that antagonism of proteoglycans reverses or prevents the decline of axonal conduction, in addition to stimulating axonal growth.

Manipulating the glial scar: chondroitinase ABC as a therapy for spinal cord injury

Chondroitin sulphate proteoglycans (CSPGs) are potent inhibitors of growth in the adult CNS. Use of the enzyme chondroitinase ABC (ChABC) as a strategy to reduce CSPG inhibition in experimental models of spinal cord injury has led to observations of a remarkable capacity for repair. Here we review the evidence that treatment with ChABC, either as an individual therapy or in combination with other strategies, can have multiple beneficial effects on promoting repair following spinal cord injury. These include promoting regeneration of injured axons, plasticity of uninjured pathways and neuroprotection of injured projection neurons. More importantly, ChABC therapy has been demonstrated to promote significant recovery of function to spinal injured animals. Thus, there is robust pre-clinical evidence demonstrating beneficial effects of ChABC treatment following spinal cord injury. Furthermore, these effects have been replicated in a number of different injury models, with independent confirmation by different laboratories, providing an important validation of ChABC as a promising therapeutic strategy. We discuss putative mechanisms underlying ChABC-mediated repair as well as potential issues and considerations in translating ChABC treatment into a clinical therapy for spinal cord injury.

A systematic review of directly applied biologic therapies for acute spinal cord injury

An increasing number of therapies for spinal cord injury (SCI) are emerging from the laboratory and seeking translation into human clinical trials. Many of these are administered as soon as possible after injury with the hope of attenuating secondary damage and maximizing the extent of spared neurologic tissue. In this article, we systematically reviewed the available preclinical research on such neuroprotective therapies that are administered in a non-invasive manner for acute SCI. Specifically, we reviewed treatments that have a relatively high potential for translation due to the fact that they are already used in human clinical applications or are available in a form that could be administered to humans. These included: erythropoietin, NSAIDs, anti-CD11d antibodies, minocycline, progesterone, estrogen, magnesium, riluzole, polyethylene glycol, atorvastatin, inosine, and pioglitazone. The literature was systematically reviewed to examine studies in which an in vivo animal model was utilized to assess the efficacy of the therapy in a traumatic spinal cord injury paradigm. Using these criteria, 122 studies were identified and reviewed in detail. Wide variations exist in the animal species, injury models, and experimental designs reported in the preclinical literature on the therapies reviewed. The review highlights the extent of investigation that has occurred in these specific therapies, and points out gaps in our knowledge that would be potentially valuable prior to human translation.

Sustained delivery of thermostabilized chABC enhances axonal sprouting and functional recovery after spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs) are a major class of axon growth inhibitors that are up-regulated after spinal cord injury (SCI) and contribute to regenerative failure. Chondroitinase ABC (chABC) digests glycosaminoglycan chains on CSPGs and can thereby overcome CSPG-mediated inhibition. But chABC loses its enzymatic activity rapidly at 37 degrees C, necessitating the use of repeated injections or local infusions for a period of days to weeks. These infusion systems are invasive, infection-prone, and clinically problematic. To overcome this limitation, we have thermostabilized chABC and developed a system for its sustained local delivery in vivo, obviating the need for chronically implanted catheters and pumps. Thermostabilized chABC remained active at 37 degrees C in vitro for up to 4 weeks. CSPG levels remained low in vivo up to 6 weeks post-SCI when thermostabilized chABC was delivered by a hydrogel-microtube scaffold system. Axonal growth and functional recovery following the sustained local release of thermostabilized chABC versus a single treatment of unstabilized chABC demonstrated significant differences in CSPG digestion. Animals treated with thermostabilized chABC in combination with sustained neurotrophin-3 delivery showed significant improvement in locomotor function and enhanced growth of cholera toxin B subunit-positive sensory axons and sprouting of serotonergic fibers. Therefore, improving chABC thermostability facilitates minimally invasive, sustained, local delivery of chABC that is potentially effective in overcoming CSPG-mediated regenerative failure. Combination therapy with thermostabilized chABC with neurotrophic factors enhances axonal regrowth, sprouting, and functional recovery after SCI.