Spontaneous and augmented growth of axons in the primate spinal cord: effects of local injury and nerve growth factor-secreting cell grafts

Acute spinal cord injury serum biomarkers in human and rat: a scoping systematic review

STUDY DESIGN

Scoping systematic review.

OBJECTIVES

To summarize the available experimental clinical and animal studies for the identification of all CSF and serum-derived biochemical markers in human and rat SCI models.

SETTING

Tehran, Iran.

METHODS

In this scoping article, we systematically reviewed the electronic databases of PubMed, Scopus, WOS, and CENTRAL to retrieve current literature assessing the levels of different biomarkers in human and rat SCI models.

RESULTS

A total of 19,589 articles were retrieved and 6897 duplicated titles were removed. The remaining 12,692 studies were screened by their title/abstract and 12,636 were removed. The remaining 56 were considered for full-text assessment, and 11 papers did not meet the criteria, and finally, 45 studies were included. 26 studies were human observational studies comprising 1630 patients, and 19 articles studied SCI models in rats, including 832 rats. Upon reviewing the literature, we encountered a remarkable heterogeneity in terms of selected biomarkers, timing, and method of measurement, studied models, extent, and mechanism of injury as well as outcome assessment measures.

CONCLUSIONS

The specific expression and distribution patterns of biomarkers in relation to spinal cord injury (SCI) phases, and their varied concentrations over time, suggest that cerebrospinal fluid (CSF) and blood biomarkers are effective measures for assessing the severity of SCI.

Capacity of astrocytes to promote axon growth in the injured mammalian central nervous system

Understanding the regulation of axon growth after injury to the adult central nervous system (CNS) is crucial to improve neural repair. Following acute focal CNS injury, astrocytes are one cellular component of the scar tissue at the primary lesion that is traditionally associated with inhibition of axon regeneration. Advances in genetic models and experimental approaches have broadened knowledge of the capacity of astrocytes to facilitate injury-induced axon growth. This review summarizes findings that support a positive role of astrocytes in axon regeneration and axon sprouting in the mature mammalian CNS, along with potential underlying mechanisms. It is important to recognize that astrocytic functions, including modulation of axon growth, are context-dependent. Evidence suggests that the local injury environment, neuron-intrinsic regenerative potential, and astrocytes’ reactive states determine the astrocytic capacity to support axon growth. An integrated understanding of these factors will optimize therapeutic potential of astrocyte-targeted strategies for neural repair.

Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The axonal growth-restrictive character of traumatic spinal cord injury (SCI) makes finding a therapeutic strategy a very demanding task, due to the postinjury events impeditive to spontaneous axonal outgrowth and regeneration. Considering SCI pathophysiology complexity, it has been suggested that an effective therapy should tackle all the SCI-related aspects and provide sensory and motor improvement to SCI patients. Thus, the current aim of any therapeutic approach for SCI relies in providing neuroprotection and support neuroregeneration. Acknowledging the current SCI treatment paradigm, cell transplantation is one of the most explored approaches for SCI with mesenchymal stem cells (MSCs) being in the forefront of many of these. Studies showing the beneficial effects of MSC transplantation after SCI have been proposing a paracrine action of these cells on the injured tissues, through the secretion of protective and trophic factors, rather than attributing it to the action of cells itself. This manuscript provides detailed information on the most recent data regarding the neuroregenerative effect of the secretome of MSCs as a cell-free based therapy for SCI. The main challenge of any strategy proposed for SCI treatment relies in obtaining robust preclinical evidence from in vitro and in vivo models, before moving to the clinics, so we have specifically focused on the available vertebrate and mammal models of SCI currently used in research and how can SCI field benefit from them.

Neurotrophic effects of dental pulp stem cells on trigeminal neuronal cells

Evidence indicates that dental pulp stem cells (DPSC) secrete neurotrophic factors which play an important role in neurogenesis, neural maintenance and repair. In this study we investigated the trophic potential of DPSC-derived conditioned medium (CM) to protect and regenerate isolated primary trigeminal ganglion neuronal cells (TGNC). DPSC and TGNC were harvested by enzymatic digestion from Wister-Hann rats. CM was collected from 72 h serum-free DPSC cultures and neurotrophic factors; nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and glial cell line-derived neurotrophic factor (GDNF) were analysed by specific enzyme-linked immunosorbent assays (ELISAs). Primary co-cultures of DPSC and TGNC were established to evaluate the paracrine effects of DPSC. In comparison, NGF was used to evaluate its neurotrophic and neuritogenic effect on TGNC. Immunocytochemistry was performed to detect the neuronal-markers; neuronal nuclei (NeuN), microtubule-associated protein-2 (MAP-2) and βIII-tubulin. Quantitative real time polymerase chain reaction (qRT-PCR) was used to analyse neuronal-associated gene expression of NeuN, MAP-2, βIII-tubulin in addition to growth-associated protein-43 (GAP-43), Synapsin-I and thermo-sensitive transient receptor potential vanilloid channel-1 (TRPV1). DPSC-CM contained significant levels of NGF, BDNF, NT-3 and GDNF. DPSC and DPSC-CM significantly enhanced TGNC survival with extensive neurite outgrowth and branching as evaluated by immunocytochemistry of neuronal markers. DPSC-CM was more effective in stimulating TGNC survival than co-cultures or NGF treated culture. In comparison to controls, DPSC-CM significantly upregulated gene expression of several neuronal markers as well as TRPV1. This study demonstrated that DPSC-derived factors promoted survival and regeneration of isolated TGNC and may be considered as cell-free therapy for TG nerve repair.

Taking central nervous system regenerative therapies to the clinic: curing rodents versus nonhuman primates versus humans

The central nervous system is known to have limited regenerative capacity. Not only does this halt the human body's reparative processes after central nervous system lesions, but it also impedes the establishment of effective and safe therapeutic options for such patients. Despite the high prevalence of stroke and spinal cord injury in the general population, these conditions remain incurable and place a heavy burden on patients' families and on society more broadly. Neuroregeneration and neural engineering are diverse biomedical fields that attempt reparative treatments, utilizing stem cells-based strategies, biologically active molecules, nanotechnology, exosomes and highly tunable biodegradable systems (e.g., certain hydrogels). Although there are studies demonstrating promising preclinical results, safe clinical translation has not yet been accomplished. A key gap in clinical translation is the absence of an ideal animal or ex vivo model that can perfectly simulate the human microenvironment, and also correspond to all the complex pathophysiological and neuroanatomical factors that affect functional outcomes in humans after central nervous system injury. Such an ideal model does not currently exist, but it seems that the nonhuman primate model is uniquely qualified for this role, given its close resemblance to humans. This review considers some regenerative therapies for central nervous system repair that hold promise for future clinical translation. In addition, it attempts to uncover some of the main reasons why clinical translation might fail without the implementation of nonhuman primate models in the research pipeline.

Therapeutic repair for spinal cord injury: combinatory approaches to address a multifaceted problem

The recent years saw the advent of promising preclinical strategies that combat the devastating effects of a spinal cord injury (SCI) that are progressing towards clinical trials. However, individually, these treatments produce only modest levels of recovery in animal models of SCI that could hamper their implementation into therapeutic strategies in spinal cord injured humans. Combinational strategies have demonstrated greater beneficial outcomes than their individual components alone by addressing multiple aspects of SCI pathology. Clinical trial designs in the future will eventually also need to align with this notion. The scenario will become increasingly complex as this happens and conversations between basic researchers and clinicians are required to ensure accurate study designs and functional readouts.

A First-in-Human, Phase I Study of Neural Stem Cell Transplantation for Chronic Spinal Cord Injury

We tested the feasibility and safety of human-spinal-cord-derived neural stem cell (NSI-566) transplantation for the treatment of chronic spinal cord injury (SCI). In this clinical trial, four subjects with T2-T12 SCI received treatment consisting of removal of spinal instrumentation, laminectomy, and durotomy, followed by six midline bilateral stereotactic injections of NSI-566 cells. All subjects tolerated the procedure well and there have been no serious adverse events to date (18-27 months post-grafting). In two subjects, one to two levels of neurological improvement were detected using ISNCSCI motor and sensory scores. Our results support the safety of NSI-566 transplantation into the SCI site and early signs of potential efficacy in three of the subjects warrant further exploration of NSI-566 cells in dose escalation studies. Despite these encouraging secondary data, we emphasize that this safety trial lacks statistical power or a control group needed to evaluate functional changes resulting from cell grafting.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Exogenous LRRK2G2019S induces parkinsonian-like pathology in a nonhuman primate

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease among the elderly. To understand its pathogenesis and to test therapies, animal models that faithfully reproduce key pathological PD hallmarks are needed. As a prelude to developing a model of PD, we tested the tropism, efficacy, biodistribution, and transcriptional effect of canine adenovirus type 2 (CAV-2) vectors in the brain of Microcebus murinus, a nonhuman primate that naturally develops neurodegenerative lesions. We show that introducing helper-dependent (HD) CAV-2 vectors results in long-term, neuron-specific expression at the injection site and in afferent nuclei. Although HD CAV-2 vector injection induced a modest transcriptional response, no significant adaptive immune response was generated. We then generated and tested HD CAV-2 vectors expressing leucine-rich repeat kinase 2 (LRRK2) and LRRK2 carrying a G2019S mutation (LRRK2G2019S), which is linked to sporadic and familial autosomal dominant forms of PD. We show that HD-LRRK2G2019S expression induced parkinsonian-like motor symptoms and histological features in less than 4 months.

The limited application of stem cells in medicine: a review

The history of stem cell therapies is one of a limited number of clinical applications despite a vast therapeutic potential. Major breakthroughs in stem cell research have not yet enjoyed clinical success—all stem cell therapies bar hematopoietic stem cell transplantations remain experimental. With the increased risk of organ failure and neurodegenerative disease associated with our ability to push the boundaries of life expectancy comes an increased pressure to pioneer novel stem cell-based therapeutic approaches. We conclude that the failure of such therapies to achieve clinical translation stems from the polarising effect of the ethical debate around their use. The intractability of the ethical debate is double edged: legislators not only have placed tighter restrictions on certain stem cell therapies, but do so in favour of less controversial cells which will have worse outcomes for patients. It is by considering this relationship between the politics, ethics and science of stem cells that the reasons for the currently limited clinical significance of stem cell therapies be realised.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Evaluation of the neural function of nonhuman primates with spinal cord injury using an evoked potential-based scoring system

Nonhuman primate models of spinal cord injury (SCI) have been widely used in evaluation of the efficacy and safety of experimental restorative interventions before clinical trials. However, no objective methods are currently available for the evaluation of neural function in nonhuman primates. In our long-term clinical practice, we have used evoked potential (EP) for neural function surveillance during operation and accumulated extensive experience. In the present study, a nonhuman primate model of SCI was established in 6 adult cynomologus monkeys through spinal cord contusion injury at T8-T9. The neural function before SCI and within 6 months after SCI was evaluated based on EP recording. A scoring system including somatosensory evoked potentials (SSEPs) and transcranial electrical stimulation-motor evoked potentials (TES-MEPs) was established for the evaluation of neural function of nonhuman primates with SCI. We compared the motor function scores of nonhuman primates before and after SCI. Our results showed that the EP below the injury level significantly changed during the 6 months after SCI. In addition, a positive correlation was identified between the EP scores and motor function. The EP-based scoring system is a reliable approach for evaluating the motor function changes in nonhuman primates with SCI.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

Interferon-β Delivery via Human Neural Stem Cell Abates Glial Scar Formation in Spinal Cord Injury

Glial scar formation is the major impedance to axonal regrowth after spinal cord injury (SCI), and scar-modulating treatments have become a leading therapeutic goal for SCI treatment. In this study, human neural stem cells (NSCs) encoding interferon-β (INF-β) gene were administered intravenously to mice 1 week after SCI. Animals receiving NSCs encoding IFN-β exhibited significant neurobehavioral improvement, electrophysiological recovery, suppressed glial scar formation, and preservation of nerve fibers in lesioned spinal cord. Systemic evaluation of SCI gliosis lesion site with lesion-specific microdissection, genome-wide microarray, and MetaCore pathway analysis identified upregulation of toll-like receptor 4 (TLR4) in SCI gliosis lesion site, and this led us to focus on TLR4 signaling in reactive astrocytes. Examination of primary astrocytes from TLR4 knockout mice, and in vivo inhibition of TLR4, revealed that the effect of IFN-β on the suppression of glial scar formation in SCI requires TLR4 stimulation. These results suggest that IFN-β delivery via intravenous injection of NSCs following SCI inhibits glial scar formation in spinal cord through stimulation of TLR4 signaling.

Assembly of protein-based hollow spheres encapsulating a therapeutic factor

Neurotrophins, as important regulators of neural development, function, and survival, have a therapeutic potential to repair damaged neurons. However, a controlled delivery of therapeutic molecules to injured tissue remains one of the greatest challenges facing the translation of novel drug therapeutics field. This study presents the development of an innovative protein-protein delivery technology of nerve growth factor (NGF) by an electrostatically assembled protein-based (collagen) reservoir system that can be directly injected into the injury site and provide long-term release of the therapeutic. A protein-based biomimetic hollow reservoir system was fabricated using a template method. The capability of neurotrophins to localize in these reservoir systems was confirmed by confocal images of fluorescently labeled collagen and NGF. In addition, high loading efficiency of the reservoir system was proven using ELISA. By comparing release profile from microspheres with varying cross-linking, highly cross-linked collagen spheres were chosen as they have the slowest release rate. Finally, biological activity of released NGF was assessed using rat pheochromocytoma (PC12) cell line and primary rat dorsal root ganglion (DRG) cell bioassay where cell treatment with NGF-loaded reservoirs induced significant neuronal outgrowth, similar to that seen in NGF treated controls. Data presented here highlights the potential of a high capacity reservoir-growth factor technology as a promising therapeutic treatment for neuroregenerative applications and other neurodegenerative diseases.

Human Mesenchymal Precursor Cells (Stro-1+) from Spinal Cord Injury Patients Improve Functional Recovery and Tissue Sparing in an Acute Spinal Cord Injury Rat Model

This study aimed to determine the potential of purified (Stro-1+) human mesenchymal precursor cells (hMPCs) to repair the injured spinal cord (SC) after transplantation into T-cell-deficient athymic RNU nude rats following acute moderate contusive spinal cord injury (SCI). hMPCs were isolated from the bone marrow (BM) stroma of SCI patients and transplanted as a suspension graft in medium [with or without immunosuppression using cyclosporin A (CsA)]. Extensive anatomical analysis shows statistically significant improvement in functional recovery, tissue sparing, and cyst reduction. We provide quantitative assessment of supraspinal projections in combination with functional outcomes. hMPC-transplanted animals consistently achieved mean BBB scores of 15 at 8 weeks postinjury. Quantitative histological staining revealed that graft-recipient animals possessed more intact spinal tissue and reduced cyst formation than controls. Fluorogold (FG) retrograde tracing revealed sparing/regeneration of supraspinal and local propriospinal axonal pathways, but no statistical differences were observed compared to controls. Immunohistochemical analysis revealed increased serotonergic (5-HT) and sensory (CGRP) axonal growth within and surrounding transplanted donor hMPCs 2 weeks posttransplantation, but no evidence of hMPC transdifferentiation was seen. Although hMPCs initially survive at 2 weeks posttransplantation, their numbers were dramatically reduced and no cells were detected at 8 weeks posttransplantation using retroviral/lentiviral GFP labeling and a human nuclear antigen (HNA) antibody. Additional immunosuppression with CsA did not improve hMPC survival or their ability to promote tissue sparing or functional recovery. We propose Stro-1+-selected hMPCs provide (i) a reproducible source for stem cell transplantation for SC therapy and (ii) a positive host microenvironment resulting in the promotion of tissue sparing/repair that subsequently improves behavioral outcomes after SCI. Our results provide a new candidate for consideration as a stem cell therapy for the repair of traumatic CNS injury.

WIS-NeuroMath enables versatile high throughput analyses of neuronal processes

Automated analyses of neuronal morphology are important for quantifying connectivity and circuitry in vivo, as well as in high content imaging of primary neuron cultures. The currently available tools for quantification of neuronal morphology either are highly expensive commercial packages or cannot provide automated image quantifications at single cell resolution. Here, we describe a new software package called WIS-NeuroMath, which fills this gap and provides solutions for automated measurement of neuronal processes in both in vivo and in vitro preparations. Diverse image types can be analyzed without any preprocessing, enabling automated and accurate detection of neurites followed by their quantification in a number of application modules. A cell morphology module detects cell bodies and attached neurites, providing information on neurite length, number of branches, cell body area, and other parameters for each cell. A neurite length module provides a solution for images lacking cell bodies, such as tissue sections. Finally, a ganglion explant module quantifies outgrowth by identifying neurites at different distances from the ganglion. Quantification of a diverse series of preparations with WIS-NeuroMath provided data that were well matched with parallel analyses of the same preparations in established software packages such as MetaXpress or NeuronJ. The capabilities of WIS-NeuroMath are demonstrated in a range of applications, including in dissociated and explant cultures and histological analyses on thin and whole-mount sections. WIS-NeuroMath is freely available to academic users, providing a versatile and cost-effective range of solutions for quantifying neurite growth, branching, regeneration, or degeneration under different experimental paradigms.

Animal models of neurologic disorders: a nonhuman primate model of spinal cord injury

Primates are an important and unique animal resource. We have developed a nonhuman primate model of spinal cord injury (SCI) to expand our knowledge of normal primate motor function, to assess the impact of disease and injury on sensory and motor function, and to test candidate therapies before they are applied to human patients. The lesion model consists of a lateral spinal cord hemisection at the C7 spinal level with subsequent examination of behavioral, electrophysiological, and anatomical outcomes. Results to date have revealed significant neuroanatomical and functional differences between rodents and primates that impact the development of candidate therapies. Moreover, these findings suggest the importance of testing some therapeutic approaches in nonhuman primates prior to the use of invasive approaches in human clinical trials. Our primate model is intended to: 1) lend greater positive predictive value to human translatable therapies, 2) develop appropriate methods for human translation, 3) lead to basic discoveries that might not be identified in rodent models and are relevant to human translation, and 4) identify new avenues of basic research to "reverse-translate" important questions back to rodent models.

Using human pluripotent stem cells to study post-transcriptional mechanisms of neurodegenerative diseases

Post-transcriptional regulation plays a major role in the generation of cell type diversity. In particular, alternative splicing increases diversification of transcriptome between tissues, in different cell types within a tissue, and even in different compartments of the same cell. The complexity of alternative splicing has increased during evolution. With increasing sophistication, however, comes greater potential for malfunction of these intricate processes. Indeed, recent years have uncovered a wealth of disease-causing mutations affecting RNA-binding proteins and non-coding regions on RNAs, highlighting the importance of studying disease mechanisms that act at the level of RNA processing. For instance, mutations in TARDBP and FUS, or a repeat expansion in the intronic region of the C9ORF72 gene, can all cause amyotrophic lateral sclerosis. We discuss how interspecies differences highlight the necessity for human model systems to complement existing non-human approaches to study neurodegenerative disorders. We conclude by discussing the improvements that could further increase the promise of human pluripotent stem for cell-based disease modeling. This article is part of a Special Issue entitled "RNA-Binding Proteins".

Increased encapsulated cell biodelivery of nerve growth factor in the brain by transposon-mediated gene transfer

Nerve growth factor (NGF) is a potential therapeutic agent for Alzheimer's disease (AD) as it has positive effects on the basal forebrain cholinergic neurons whose degeneration correlates with the cognitive decline in AD. We have previously described an encapsulated cell biodelivery device, NsG0202, capable of local delivery of NGF by a genetically modified human cell line, NGC-0295. The NsG0202 devices have shown promising safety and therapeutic results in a small phase 1b clinical study. However, results also show that the NGF dose could advantageously be increased. We have used the sleeping beauty transposon expression technology to establish a new clinical grade cell line, NGC0211, with at least 10 times higher NGF production than that of NGC-0295. To test whether encapsulation of this cell line provides a relevant dose escalation step in delivering NGF for treatment of the cognitive decline in AD patients, we have validated the bioactivity of devices with NGC0211 and NGC-0295 cells in normal rat striatum as well as in the quinolinic acid striatal lesion model. These preclinical animal studies show that implantation of devices with NGC0211 cells lead to significantly higher NGF output, which in both cases correlate with highly improved potency.

Analysis of Dosing Regimen and Reproducibility of Intraspinal Grafting of Human Spinal Stem Cells in Immunosuppressed Minipigs

In recent studies using a rat aortic balloon occlusion model, we have demonstrated that spinal grafting of rat or human neuronal precursors or human postmitotic hNT neurons leads to progressive amelioration of spasticity and rigidity and corresponding improvement in ambulatory function. In the present study, we characterized the optimal dosing regimen and safety profile of human spinal stem cells (HSSC) when grafted into the lumbar spinal cord segments of naive immunosuppressed minipigs. Gottingen-Minnesota minipigs (18–23 kg) were anesthetized with halothane, mounted into a spine-immobilization apparatus, and received five bilateral injections of HSSC delivered in 2, 4, 6, 8, or 10 μl of media targeted into L2-L5 central gray matter (lamina VII). The total number of delivered cells ranged between 2,500 and 100,000 per injection. Animals were immunosuppressed with Prograf® for the duration of study. After cell grafting, ambulatory function was monitored daily using a Tarlov's score. Sensory functions were assessed by mechanically evoked skin twitch test. Animals survived for 6–7 weeks. Three days before sacrifice animals received daily injections of bromodeoxyuridine (100 mg/kg; IV) and were then transcardially perfused with 4% paraformaldehyde. Th12-L6 spinal column was then dissected; the spinal cord was removed and scanned with MRI. Lumbar transverse spinal cord sections were then cut and stained with a combination of human-specific (hNUMA, hMOC, hNSE, hSYN) or nonspecific (DCX, MAP2, GABA, CHAT) antibodies. The total number of surviving cells was estimated using stereological quantification. During the first 12–24 h after cell grafting, a modest motor weakness was observed in three of eight animals but was no longer present at 4 days to 7 weeks. No sensory dysfunction was seen at any time point. Postmortem MRI scans revealed the presence of the individual grafts in the targeted spinal cord areas. Histological examination of spinal cord sections revealed the presence of hNUMA-immunoreactive grafted cells distributed between the base of the dorsal horn and the ventral horn. In all grafts intense hMOC, DCX, and hSYN immunoreactivity in grafted cells was seen. In addition, a rich axodendritic network of DCX-positive processes was identified extending 300–700 μm from the grafts. On average, 45% of hNUMA-positive neurons were GABA immunoreactive. Stereological analysis of hNUMA-positive cells showed an average of 2.5- to 3-fold increase in number of surviving cells compared with the number of injected cells. Analysis of spinal structural morphology showed that in animals injected with more than 50,000 cells/injection or volumes of injectate higher than 6 μl/injection there was tissue expansion and disruption of the local axodendritic network. Based on these data the safe total number of injected cells and volume of injectate were determined to be 30,000 cells delivered in ≤6 μl of media. These data demonstrate that highly reproducible delivery of a potential cell therapeutic candidate into spinal parenchyma can be achieved across a wide range of cell doses by direct intraspinal injections. The resulting grafts uniformly showed robust cell survival and progressive neuronal maturation.

Local and remote growth factor effects after primate spinal cord injury

Primate models of spinal cord injury differ from rodent models in several respects, including the relative size and functional neuroanatomy of spinal projections. Fundamental differences in scale raise the possibility that retrograde injury signals, and treatments applied at the level of the spinal cord that exhibit efficacy in rodents, may fail to influence neurons at the far greater distances of primate systems. Thus, we examined both local and remote neuronal responses to neurotrophic factor-secreting cell grafts placed within sites of right C7 hemisection lesions in the rhesus macaque. Six months after gene delivery of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) into C7 lesion sites, we found both local effects of growth factors on axonal growth, and remote effects of growth factors reflected in significant reductions in axotomy-induced atrophy of large pyramidal neurons within the primary motor cortex. Additional examination in a rodent model suggested that BDNF, rather than NT-3, mediated remote protection of corticospinal neurons in the brain. Thus, injured neural systems retain the ability to respond to growth signals over the extended distances of the primate CNS, promoting local axonal growth and preventing lesion-induced neuronal degeneration at a distance. Remote cortical effects of spinally administered growth factors could "prime" the neuron to respond to experimental therapies that promote axonal plasticity or regeneration.

Long-term delivery of nerve growth factor by encapsulated cell biodelivery in the Göttingen minipig basal forebrain

Nerve growth factor (NGF) prevents cholinergic degeneration in Alzheimer's disease (AD) and improves memory in AD animal models. In humans, the safe delivery of therapeutic doses of NGF is challenging. For clinical use, we have therefore developed an encapsulated cell (EC) biodelivery device, capable of local delivery of NGF. The clinical device, named NsG0202, houses an NGF-secreting cell line (NGC-0295), which is derived from a human retinal pigment epithelial (RPE) cell line, stably genetically modified to secrete NGF. Bioactivity and correct processing of NGF was confirmed in vitro. NsG0202 devices were implanted in the basal forebrain of Göttingen minipigs and the function and retrievability were evaluated after 7 weeks, 6 and 12 months. All devices were implanted and retrieved without associated complications. They were physically intact and contained a high number of viable and NGF-producing NGC-0295 cells after explantation. Increased NGF levels were detected in tissue surrounding the devices. The implants were well tolerated as determined by histopathological brain tissue analysis, blood analysis, and general health status of the pigs. The NsG0202 device represents a promising approach for treating the cognitive decline in AD patients.

FK1706, a novel non-immunosuppressant neurophilin ligand, ameliorates motor dysfunction following spinal cord injury through its neuroregenerative action

Injured spinal cord axons fail to regenerate in part due to a lack of trophic support. While various methods for replacing neurotrophins have been pursued, clinical uses of these methods face significant barriers. FK1706, a non-immunosuppressant neurophilin ligand, potentiates nerve growth factor signaling, suggesting therapeutic potential for functional deficits following spinal cord injury. Here, we demonstrate that FK1706 significantly improves behavioral outcomes in animal models of spinal cord hemisection and contusion injuries in rats. Furthermore, we show that FK1706 is effective even if administration is delayed until 1 week after injury, suggesting that FK1706 has a reasonable therapeutic time-window. Morphological analysis of injured axons in the dorsal corticospinal tract showed an increase in the radius and perimeter of stained axons, which were reduced by FK1706 treatment, suggesting that axonal swelling and retraction balls observed in injured spinal cord were improved by the neurotrophic effect of FK1706. Taken together, FK1706 improves both behavioral motor function and the underlying morphological changes, suggesting that FK1706 may have therapeutic potential in meeting the significant unmet needs in spinal cord injury.

Cell therapy for spinal cord regeneration

This review presents a summary of the various types of cellular therapy used to treat spinal cord injury. The inhibitory environment and loss of axonal connections after spinal cord injury pose many obstacles to regenerating the lost tissue. Cellular therapy provides a means of restoring the cells lost to the injury and could potentially promote functional recovery after such injuries. A wide range of cell types have been investigated for such uses and the advantages and disadvantages of each cell type are discussed along with the research studying each cell type. Additionally, methods of delivering cells to the injury site are evaluated. Based on the current research, suggestions are given for future investigation of cellular therapies for spinal cord regeneration.

Axon growth across a lesion site along a preformed guidance pathway in the brain

Our previous studies showed that axonal outgrowth from dorsal root ganglia (DRG) transplants in the adult rat brain could be directed toward a specific target location using a preformed growth-supportive pathway. This pathway induced axon growth within the corpus callosum across the midline to the opposite hemisphere. In this study, we examined whether such pathways would also support axon growth either through or around a lesion of the corpus callosum. Pathways expressing GFP, NGF, or FGF2/NGF were set up by multiple injections of adenovirus along the corpus callosum. Each pathway included the transplantation site in the left corpus callosum, 2.8 mm away from the midline, and a target site in the right corpus callosum, 2.5 mm from the midline. At the same time, a 1 mm lesion was made through the corpus callosum at the midline in an anteroposterior direction. A group of control animals received lesions and Ad-NGF injections only at the transplant and target sites, without a bridging pathway. DRG cell suspensions from postnatal day 1 or 2 rats were injected at the transplantation site three to four days later. Two weeks after transplantation, brain sections were stained using an anti-CGRP antibody. The CGRP+ axons were counted at 0.5 mm and 1.5 mm from the lesion site in both hemispheres. Few axons grew past the lesion in animals with control pathways, but there was robust axon growth across the lesion site in the FGF2/NGF and NGF-expressing pathways. This study indicated that preformed NGF and combination guidance pathways support more axon growth past a lesion in the adult mammalian brain.

In vivo tracing of neural tracts in the intact and injured spinal cord of marmosets by diffusion tensor tractography

In spinal cord injury, axonal disruption results in motor and sensory function impairment. The evaluation of axonal fibers is essential to assess the severity of injury and efficacy of any treatment protocol, but conventional methods such as tracer injection in brain parenchyma are highly invasive and require histological evaluation, precluding clinical applications. Previous advances in magnetic resonance imaging technology have led to the development of diffusion tensor tractography (DTT) as a potential modality to perform in vivo tracing of axonal fibers. The properties and clinical applications of DTT in the brain have been reported, but technical difficulties have limited DTT studies of the spinal cord. In this study, we report the effective use of DTT to visualize both intact and surgically disrupted spinal long tracts in adult common marmosets. To verify the feasibility of spinal cord DTT, we first performed DTT of postmortem marmosets. DTT clearly illustrated spinal projections such as the corticospinal tract and afferent fibers in control animals, and depicted the severed long tracts in the injured animals. Histology of the spinal cords in both control and injured groups were consistent with DTT findings, verifying the accuracy of DTT. We also conducted DTT in live marmosets and demonstrated that DTT can be performed in live animals to reveal in vivo nerve fiber tracing images, providing an essential tool to evaluate axonal conditions in the injured spinal cord. Taken together, these findings demonstrate the feasibility of applying DTT to preclinical and clinical studies of spinal cord injury.

Curiosity and cure: translational research strategies for neural repair-mediated rehabilitation

Clinicians who seek interventions for neural repair in patients with paralysis and other impairments may extrapolate the results of cell culture and rodent experiments into the framework of a preclinical study. These experiments, however, must be interpreted within the context of the model and the highly constrained hypothesis and manipulation being tested. Rodent models of repair for stroke and spinal cord injury offer examples of potential pitfalls in the interpretation of results from developmental gene activation, transgenic mice, endogeneous neurogenesis, cellular transplantation, axon regeneration and remyelination, dendritic proliferation, activity-dependent adaptations, skills learning, and behavioral testing. Preclinical experiments that inform the design of human trials ideally include a lesion of etiology, volume and location that reflects the human disease; examine changes induced by injury and by repair procedures both near and remote from the lesion; distinguish between reactive molecular and histologic changes versus changes critical to repair cascades; employ explicit training paradigms for the reacquisition of testable skills; correlate morphologic and physiologic measures of repair with behavioral measures of task reacquisition; reproduce key results in more than one laboratory, in different strains or species of rodent, and in a larger mammal; and generalize the results across several disease models, such as axonal regeneration in a stroke and spinal cord injury platform. Collaborations between basic and clinical scientists in the development of translational animal models of injury and repair can propel experiments for ethical bench-to-bedside therapies to augment the rehabilitation of disabled patients.

Behavioral, Temporal, and Spatial Targets for Cellular Transplants as Adjuncts to Rehabilitation for Stroke

Stem cell and more differentiated neural cell transplantation strategies are an intriguing approach for neural repair to augment rehabilitation interventions after stroke. In the cortex, exogenous cells could create, augment, or extend in time endogenous peri-infarct and remote molecular signals, such as those for neurogenesis, cell differentiation, axonal and dendritic sprouting, network connectivity, and long-term potentiation, as well as deliver engineered genes and provide replacement cells in a network. If demyelinated axons exist in the periphery of an infarct, they could be targets for remyelination to reestablish conductivity. Much is unknown, however, about the mechanisms by which pluripotent embryonic and multipotent neural stem cells serve as agents of therapeutic plasticity. The robustness of their effects on neuromodulation, reorganization, regeneration, and behavioral recovery is a work in progress. Invasive interventions may have adverse effects not appreciated in preclinical testing. These should initially be offered only to patients with specific profound impairments after it is clinically certain that major disabilities will not improve. If a cellular strategy is very safe, it may be offered to subjects with moderate impairments when they are no longer likely to make further functional gains. Clinical trial designs are suggested that take into account the optimal timing after stroke and specific targets for cellular therapies to foster repair, remapping, and modulation of neural circuits. Cell-mediated rehabilitation would then use task-specific therapies in an optimal dose to maximize training-induced reorganization and learning and, most important, reduce unwanted disability.

Implantation of BM mesenchymal stem cells into injured spinal cord elicits de novo neurogenesis and functional recovery: evidence from a study in rhesus monkeys

BACKGROUND

Transplantation of mesenchymal stem cells (MSC) in rodent models has proved to be an effective therapeutic approach for spinal cord injury (SCI). However, further studies in primate models are still needed before clinical application of MSC to patients.

METHODS

MSC were isolated from rhesus monkey BM and induced ex vivo to differentiate into neural lineage cells. Induced cells were labeled with Hoechst 33342 and injected into the injured sites of rhesus SCI models. Function of the injured spinal cord was assessed using Tarlov behavior assessment, sensory responses and electrophysiologic tests of cortical somatosensory-evoked potential (CSEP) and motor-evoked potential (MEP). In vivo differentiation of the implanted cells was demonstrated by the presence of neural cell markers in Hoechst 33342-labeled cells. The re-establishment of the axonal pathway was demonstrated using a true blue (TB) chloride retrograde tracing study.

RESULTS

Monkeys achieved Tarlov grades 2-3 and nearly normal sensory responses 3 months after cell transplantation. Both CSEP and MEP showed recovery features. The presence of the neural cell markers neurofilament (NF), neuro-specific enolase (NSE) and glial fibrillary acidic protein (GFAP) was observed in approximately 10% of Hoechst 33342-labeled cells. TB, originally injected at the caudal side of injured sites, was traceable in the rostral thoracic spinal cord, red nucleus and sensory motor cortex.

DISCUSSION

Our results suggest that the implantation of MSC-derived cells elicits de novo neurogenesis and functional recovery in a non-human primate SCI model and should harness the clinical application of BM MSC in SCI patients.

[Role of gene therapy in trauma and orthopedic surgery]

Mit Hilfe molekularbiologischer und gentechnologischer Methoden kann durch den Transfer von spezifischen Genen das Erbgut einer Zelle verändert werden. Hierdurch werden die Zellfunktionen so moduliert, dass die Zelle, die durch das implantierte Gen verschlüsselte Funktionen erhält, Proteine synthetisiert, die sie normalerweise nicht oder nur in geringen Mengen produziert.

Wie erste tierexperimentelle Studien zeigen, kann die Gentherapie die Heilungs- und Regenerationsfähigkeit der Haut, von Sehnen, Knorpel und Knochen unterstützen und beschleunigen. In jüngster Zeit werden in Tierversuchen neue Vektoren mit einer geringeren Immunogenität und verbesserten Steuerbarkeit sowie einer erhöhten Transfersicherheit getestet. Es ist zu erwarten, dass die Gentherapie in den nächsten Jahrzehnten bei der Frakturheilung, der Sanierung von Knorpelschäden und für die Behandlung von Infektionen einen bedeutenden Stellenwert einnehmen wird.

Neurotrophin-3 gradients established by lentiviral gene delivery promote short-distance axonal bridging beyond cellular grafts in the injured spinal cord

Neurotrophic factor delivery to sites of spinal cord injury (SCI) promotes axon growth into but not beyond lesion sites. We tested the hypothesis that sustained growth factor gradients beyond regions of SCI will promote significant axonal bridging into and beyond lesions. Adult rats underwent C3 lesions to transect ascending dorsal column sensory axons, and autologous bone marrow stromal cells were grafted into the lesion to provide a cellular bridge for growth into the injured region. Concurrently, lentiviral vectors expressing neurotrophin-3 (NT-3) or green fluorescent protein (GFP) (controls) were injected into the host cord rostral to the lesion to promote axon extension beyond the graft/lesion. Four weeks later, NT-3 gradients beyond the lesion were detectable by ELISA in animals that received NT-3-expressing lentiviral vectors, with highest average NT-3 levels located near the rostral vector injection site. Significantly more ascending sensory axons extended into tissue rostral to the lesion site in animals injected with NT-3 vectors compared with GFP vectors, but only if the zone of NT-3 vector transduction extended continuously from the injection site to the graft; any "gap" in NT-3 expression from the graft to rostral tissue resulted in axon bridging failure. Despite axon bridging beyond the lesion, regenerating axons did not continue to grow over very long distances, even in the presence of a continuing growth factor gradient beyond the lesion. These findings indicate that a localized and continuous gradient of NT-3 can achieve axonal bridging beyond the glial scar, but growth for longer distances is not sustainable simply with a trophic stimulus.

Matrix-mediated gene transfer to brain cortex and dorsal root ganglion neurones by retrograde axonal transport after dorsal column lesion

BACKGROUND

In previous studies, we showed that the immobilisation of DNAs encoding basic fibroblast growth factor, neurotrophin-3 and brain-derived neurotrophic factor in a gene-activated matrix (GAM) promotes sustained survival of axotomised retinal ganglion cells after optic nerve injury. Here, we evaluated if the immobilisation of DNAs in a GAM could be an effective approach to deliver genes to axotomised dorsal root ganglion (DRG) neurones after spinal cord injury and if the matrix component of the GAM would modulate the deposition of a dense scar at the injury site.

METHODS

We evaluated the expression of the thymidine kinase (TK) reporter gene in brain cortex and DRG after a bilateral T8 dorsal column (DC) lesion using PCR, RT-PCR and in situ hybridisation analyses. Collagen-based GAMs were implanted at the lesion site and the cellular response to the GAM was assessed using cell-specific markers.

RESULTS

At 1 week post-injury, PCR analyses confirmed that DNATK was retrogradely transported from the DC lesion where the GAM was implanted to the brain cortex and to caudal DRG neurones, and RT-PCR analyses showed expression of mRNATK. At 7 weeks post-injury, DNATK was still be detected in the GAM and DRG. In situ hybridisation localised DNATK and mRNATK within fibroblasts, glia, endothelial and inflammatory cells invading the GAM and in DRG neurones. Interestingly, the presence of a GAM also reduced secondary cavitation and scar deposition at the lesion site.

CONCLUSIONS

These results establish that GAMs act as bridging scaffolds in DC lesions limiting cavitation and scarring and delivering genes both locally to injury-reactive cells and distally to the cerebral cortex and to DRG neuronal somata through retrograde axonal transport.

Therapeutic interventions after spinal cord injury

Spinal cord injury (SCI) can lead to paraplegia or quadriplegia. Although there are no fully restorative treatments for SCI, various rehabilitative, cellular and molecular therapies have been tested in animal models. Many of these have reached, or are approaching, clinical trials. Here, we review these potential therapies, with an emphasis on the need for reproducible evidence of safety and efficacy. Individual therapies are unlikely to provide a panacea. Rather, we predict that combinations of strategies will lead to improvements in outcome after SCI. Basic scientific research should provide a rational basis for tailoring specific combinations of clinical therapies to different types of SCI.

Clinical trials in spinal cord injury

Progress in promoting axonal plasticity and regeneration in animal models of spinal cord injury (SCI) has led to novel prospects for the initiation of human clinical trials in the near future. This review discusses a number of considerations in the path to translating a preclinical candidate from the laboratory to clinical testing. We will also briefly discuss issues associated with the design, performance, analysis, and reporting of human clinical trials in SCI. It is important, for both the medical community and the spinal cord injured community, that objective scientific and medical standards are adopted in the clinical translation of potentially promising, but as yet unproven, therapies for SCI.

Euroconference on tissue repair and ulcer/wound healing: molecular mechanisms, therapeutic targets and future directions

The meeting was part of the Euroconference series organised at the Pasteur Institute in Paris. Comprising delegates from both academia and industry, it drew on expertise from many aspects of tissue repair in a wide range of human disease. The principal component of this report concerns progress with the therapeutic application of biological agents in promoting tissue repair, as gene therapeutics, monoclonal antibodies and therapeutic proteins. In addition, the effect of pioglitazone on the rate and quality of wound healing in diabetic rats is also reported.

Long-Term Care of Paraplegic Laboratory Mammals

Repair of spinal cord injuries (SCIs) is still a major clinical challenge. Several attempts have been made to find a cure for this condition in experimental animals that could be extrapolated to humans. A key for success seems the availability of optimum animal models for testing different therapies. Complete spinal cord lesion in mammals is considered the most accurate injury model. In addition, long-term survival of animals seems more appropriate, as this increases the efficacy of the repair strategies. However, paraplegic animals require special care and treatment for proper longterm maintenance, and to date, there are no published protocols. This lack of available information has discouraged scientists from working with this injury model. Over the past 7 years, we have tested the repair efficacy of olfactory ensheathing glia in paraplegic rats for survival periods of more than 8 months. To keep these animals healthy for this long time, we adapted and administered treatments used in people with paraplegia. These same protocols (developed for rodents in our group) are being applied to paraplegic monkeys. In this review, we provide an overview of the proper handling and care of paraplegic adult laboratory mammals for long periods. This information might help other groups to optimize the outcome obtained and to better evaluate the prospect of a given experimental repair strategy. In addition, the use of human treatments in paraplegic animals provides a more realistic model for a later transfer to the clinical arena.

Olfactory glia transplantation into cervical spinal cord contusion injuries

Object. The results of olfactory ensheathing cell (OEC) transplantation have raised great expectations as a potential treatment for spinal cord injury (SCI). Its capacity to promote functional neural repair, however, remains unclear. The authors studied axonal growth and locomotor recovery after C-7 contusion injury and OEC transplantation in adult rats.

Methods. Twenty-four male Wistar rats underwent a mild C-7 contusion injury that completely disrupted the dorsal corticospinal tract (DCST). In 14 rats OECs were transplanted into the lesion, and 10 were used as controls. At 3 months postcontusion, the kinematics of locomotion were assessed, and the CST was traced by injecting dextran tetramethylrhodamine bilaterally into the cerebral cortex. The animals were killed 2 weeks after tracer injection, and their spinal cords were studied immunohistochemically.

Although the survival of transplanted cells varied, they were present in all cases. The authors observed neither OEC migration nor DCST axon regeneration in any of the cell transplant—treated rats. Corticospinal axons ended in retraction bulbs at the proximal edge of the lesion or, exceptionally, a few micrometers inside the transplant. The results of neurofilament immunohistochemical analysis provided evidence of neurites from systems other than the DCST growing into the transplant, but in some cases these neurites formed loops of pathological appearance. Contusion injury of C-7 caused chronic locomotor deficits that did not improve after OEC transplants.

Conclusions. The findings in this study indicate that OEC transplants alone are not sufficient for neural repair and functional recovery after SCI. In addition, OECs can induce abnormal axonal growth, making further studies necessary before considering their clinical use.

Performance of locomotion and foot grasping following a unilateral thoracic corticospinal tract lesion in monkeys (Macaca mulatta)

Six adult monkeys (Macaca mulatta) received a unilateral lesion of the lateral corticospinal tract (CST) in the thoracic spinal cord. Prior to surgery, the animals were trained to perform quadrupedal stepping on a treadmill, and item retrieval with the foot. Whole body kinematics and electromyogram (EMG) recordings were made prior to, and at regular intervals over a period of 12 weeks after the CST lesion. After 1 week of recovery, all monkeys were able to walk unaided quadrupedally on the treadmill. The animals, however, dragged the hindpaw ipsilateral to the lesion along the treadmill belt during the swing phase and showed a significant reorganization of the spatiotemporal pattern of hindlimb (HL) and forelimb (FL) displacements. The inability to appropriately trigger the swing phase resulted in an increase in the cycle duration and stride length of both HLs. The stance duration decreased in the ipsilateral HL, and increased in the contralateral HL and both FLs. Consequently, there was a dramatic disruption of interlimb and intralimb coupling that was reflected in the limb kinematic and EMG patterns. The CST lesion completely abolished the ability of the monkeys to retrieve items with the foot ipsilateral to the lesion and significantly disrupted the level of performance of the contralateral HL during the first 2 weeks post-lesion. Interestingly, selected HL muscles remained almost quiescent when the monkeys attempted to retrieve items, but were unsuccessful with the affected foot at 1 week post-lesion, whereas the capacity to activate the same muscles was preserved, although reduced, during stepping. Spatial and temporal parameters of gait, kinematics, and EMG patterns recorded during locomotion generally converged toward control values over time, but significant differences persisted up to 12 weeks post-lesion. Although some control was recovered over the distal foot musculature, fine foot grasping remained significantly impaired at the end of the testing period. These findings demonstrate that the CST pathway from the brain normally makes an important contribution to interlimb and intralimb coordination during basic locomotion, and to muscle activation to produce dexterous foot digit movements in the monkey. Furthermore, the present study indicates that the primate has the ability to rapidly accommodate locomotor performance, and to a lesser degree fine foot motor skills, to a reduction in supraspinal control. Identification of the neural substrates mediating the rapid recovery of motor function following injury to the primate spinal cord could provide insight into developing repair strategies to augment functional recovery from neuromotor impairments.

Safely slowing down the decline in Alzheimer’s disease: gene therapy shows potential

The role of nerve growth factor in stimulating cholinergic function, loss of which is a cardinal feature in Alzheimer's disease, has been documented for many years from preclinical animal model studies. This anabolic growth factor has been delivered into the forebrain of patients with mild Alzheimer's disease using transfer of autologous fibroblasts engineered to produce nerve growth factor. A Phase I clinical study shows that fibroblast transfer and growth factor expression is well tolerated and the rate of cognitive decline in patients is improved, correlating with an increase in metabolic activity detected in the cortex.

Optimising plasticity: environmental and training associated factors in transplant-mediated brain repair

With progressively ageing populations, degeneration of nerve cells of the brain, due to accident or disease, represents one of the major problems for health and welfare in the developed world. The molecular environment in the adult brain promotes stability limiting its ability to regenerate or to repair itself following injury. Cell transplantation aims to repair the nervous system by introducing new cells that can replace the function of the compromised or lost cells. Alternatives to primary embryonic tissue are actively being sought but this is at present the only source that has been shown reliably to survive grafting into the adult brain and spinal cord, connect with the host nervous system, and influence behaviour. Based on animal studies, several clinical trials have now shown that embryonic tissue grafts can partially alleviate symptoms in Parkinson's disease, and related strategies are under evaluation for Huntington's disease, spinal cord injury, stroke and other CNS disorders. The adult brain is at its most plastic in the period following injury, offering a window of opportunity for therapeutic intervention. Enriched environment, behavioural experience and grafting can each separately influence neuronal plasticity and recovery of function after brain damage, but the extent to which these factors interact is at present unknown. To improve the outcome following brain damage, transplantation must make use of the endogenous potential for plasticity of both the host and the graft and optimise the external circumstances associated with graft-mediated recovery. Our understanding of mechanisms of brain plasticity subsequent to brain damage needs to be associated with what we know about enhancing intrinsic recovery processes in order to improve neurobiological and surgical strategies for repair at the clinical level. With the proof of principle beginning to emerge from clinical trials, a rich area for innovative research with profound therapeutic application, even broader than the specific context of transplantation, is now opening for investigation.

From Animal Models to Humans

There are currently no fully restorative therapies for human spinal cord injury (SCI). Here,we briefly review the different types of human SCI pathology as well as the most commonly used rodent and nonhuman primate models of SCI that are used to simulate these pathologies and to test potential therapies. We then discuss various high profile (sometimes controversial) experimental strategies that have reported CNS axon regeneration and functional recovery of limb movement using these animal models of SCI. We particularly focus upon strategies that have been tested both in rodents and in nonhuman primates, and highlight those which are currently transitioning to clinical tests or trials in humans. Finally we discuss ways in which animal studies might be improved and what the future may hold for physical therapists involved in rehabilitation of humans with SCI.