Restricted inflammatory reaction in the CNS: a key impediment to axonal regeneration?

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.

Pharmacological, Cell, and Gene Therapy Strategies to Promote Spinal Cord Regeneration

In this review, recent studies using pharmacological treatment, cell transplantation, and gene therapy to promote regeneration of the injured spinal cord in animal models will be summarized. Pharmacological and cell transplantation treatments generally revealed some degree of effect on the regeneration of the injured ascending and descending tracts, but further improvements to achieve a more significant functional recovery are necessary. The use of gene therapy to promote repair of the injured nervous system is a relatively new concept. It is based on the development of methods for delivering therapeutic genes to neurons, glia cells, or nonneural cells. Direct in vivo gene transfer or gene transfer in combination with (neuro)transplantation (ex vivo gene transfer) appeared powerful strategies to promote neuronal survival and axonal regrowth following traumatic injury to the central nervous system. Recent advances in understanding the cellular and molecular mechanisms that govern neuronal survival and neurite outgrowth have enabled the design of experiments aimed at viral vector-mediated transfer of genes encoding neurotrophic factors, growth-associated proteins, cell adhesion molecules, and antiapoptotic genes. Central to the success of these approaches was the development of efficient, nontoxic vectors for gene delivery and the acquirement of the appropriate (genetically modified) cells for neurotransplantation. Direct gene transfer in the nervous system was first achieved with herpes viral and E1-deleted adenoviral vectors. Both vector systems are problematic in that these vectors elicit immunogenic and cytotoxic responses. Adeno-associated viral vectors and lentiviral vectors constitute improved gene delivery systems and are beginning to be applied in neuroregeneration research of the spinal cord. Ex vivo approaches were initially based on the implantation of genetically modified fibroblasts. More recently, transduced Schwann cells, genetically modified pieces of peripheral nerve, and olfactory ensheathing glia have been used as implants into the injured spinal cord.

Immune response in peripheral axons delays disease progression in SOD1G93A mice

Background

Increasing evidence suggests that the immune system has a beneficial role in the progression of amyotrophic lateral sclerosis (ALS) although the mechanism remains unclear. Recently, we demonstrated that motor neurons (MNs) of C57SOD1^G93A mice with slow disease progression activate molecules classically involved in the cross-talk with the immune system. This happens a lot less in 129SvSOD1^G93A mice which, while expressing the same amount of transgene, had faster disease progression and earlier axonal damage. The present study investigated whether and how the immune response is involved in the preservation of motor axons in the mouse model of familial ALS with a more benign disease course.

Methods

First, the extent of axonal damage, Schwann cell proliferation, and neuromuscular junction (NMJ) denervation were compared between the two ALS mouse models at the disease onset. Then, we compared the expression levels of different immune molecules, the morphology of myelin sheaths, and the presence of blood-derived immune cell infiltrates in the sciatic nerve of the two SOD1G93A mouse strains using immunohistochemical, immunoblot, quantitative reverse transcription PCR, and rotating-polarization Coherent Anti-Stokes Raman Scattering techniques.

Results

Muscle denervation, axonal dysregulation, and myelin disruption together with reduced Schwann cell proliferation are prominent in 129SvSOD1^G93A compared to C57SOD1^G93A mice at the disease onset, and this correlates with a faster disease progression in the first strain. On the contrary, a striking increase of immune molecules such as CCL2, MHCI, and C3 was seen in sciatic nerves of slow progressor C57SOD1^G93A mice and this was accompanied by heavy infiltration of CD8⁺ T lymphocytes and macrophages. These phenomena were not detectable in the peripheral nervous system of fast-progressing mice.

Conclusions

These data show for the first time that damaged MNs in SOD1-related ALS actively recruit immune cells in the peripheral nervous system to delay muscle denervation and prolong the lifespan. On the contrary, the lack of this response has a negative impact on the disease course.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0732-2) contains supplementary material, which is available to authorized users.

A Self-Assembling Injectable Biomimetic Microenvironment Encourages Retinal Ganglion Cell Axon Extension in Vitro

Sensory-somatic nervous system neurons, such as retinal ganglion cells (RGCs), are typically thought to be incapable of regenerating. However, it is now known that these cells may be stimulated to regenerate by providing them with a growth permissive environment. We have engineered an injectable microenvironment designed to provide growth-stimulating cues for RGC culture. Upon gelation, this injectable material not only self-assembles into laminar sheets, similar to retinal organization, but also possesses a storage modulus comparable to that of retinal tissue. Primary rat RGCs were grown, stained, and imaged in this three-dimensional scaffold. We were able to show that RGCs grown in this retina-like structure exhibited characteristic long, prominent axons. In addition, RGCs showed a consistent increase in average axon length and neurite-bearing ratio over the 7 day culture period, indicating this scaffold is capable of supporting substantial RGC axon extension.

Acute spinal cord injury: tetraplegia and paraplegia in small animals

Spinal cord injury (SCI) is a common problem in animals for which definitive treatment is lacking, and information gained from its study has benefit for both companion animals and humans in developing new therapeutic approaches. This review provides an overview of the main concepts that are useful for clinicians in assessing companion animals with severe acute SCI. Current available advanced ancillary tests and those in development are reviewed. In addition, the current standard of care for companion animals following SCI and recent advances in the development of new therapies are presented, and new predictors of recovery discussed.

Optic nerve crush induces spatial and temporal gene expression patterns in retina and optic nerve of BALB/cJ mice

Background

Central nervous system (CNS) trauma and neurodegenerative disorders trigger a cascade of cellular and molecular events resulting in neuronal apoptosis and regenerative failure. The pathogenic mechanisms and gene expression changes associated with these detrimental events can be effectively studied using a rodent optic nerve crush (ONC) model. The purpose of this study was to use a mouse ONC model to: (a) evaluate changes in retina and optic nerve (ON) gene expression, (b) identify neurodegenerative pathogenic pathways and (c) discover potential new therapeutic targets.

Results

Only 54% of total neurons survived in the ganglion cell layer (GCL) 28 days post crush. Using Bayesian Estimation of Temporal Regulation (BETR) gene expression analysis, we identified significantly altered expression of 1,723 and 2,110 genes in the retina and ON, respectively. Meta-analysis of altered gene expression (≥1.5, ≤-1.5, p < 0.05) using Partek and DAVID demonstrated 28 up and 20 down-regulated retinal gene clusters and 57 up and 41 down-regulated optic nerve clusters. Regulated gene clusters included regenerative change, synaptic plasticity, axonogenesis, neuron projection, and neuron differentiation. Expression of selected genes (Vsnl1, Syt1, Synpr and Nrn1) from retinal and ON neuronal clusters were quantitatively and qualitatively examined for their relation to axonal neurodegeneration by immunohistochemistry and qRT-PCR.

Conclusion

A number of detrimental gene expression changes occur that contribute to trauma-induced neurodegeneration after injury to ON axons. Nrn1 (synaptic plasticity gene), Synpr and Syt1 (synaptic vesicle fusion genes), and Vsnl1 (neuron differentiation associated gene) were a few of the potentially unique genes identified that were down-regulated spatially and temporally in our rodent ONC model. Bioinformatic meta-analysis identified significant tissue-specific and time-dependent gene clusters associated with regenerative changes, synaptic plasticity, axonogenesis, neuron projection, and neuron differentiation. These ONC induced neuronal loss and regenerative failure associated clusters can be extrapolated to changes occurring in other forms of CNS trauma or in clinical neurodegenerative pathological settings. In conclusion, this study identified potential therapeutic targets to address two key mechanisms of CNS trauma and neurodegeneration: neuronal loss and regenerative failure.

Axonal degeneration in dorsal columns of spinal cord does not induce recruitment of hematogenous macrophages

It is generally accepted that there are two populations of macrophages that respond to neural injuries and successful recruitment of hematogenous macrophages has been shown to help the process of nerve repair in the peripheral nervous system (PNS). Meanwhile, the recruitment of circulating macrophages after central nerve system (CNS) injuries is considered mild and delayed. We compared the recruitment of circulating macrophages in the peripheral nerves and spinal cord after dorsal root ganglionectomies, which induce selective and approximately similar extent of sensory fiber degeneration in PNS and CNS, in bone marrow chimeric mice. Our results showed that circulating macrophages were efficiently recruited in PNS but virtually no recruitment in CNS despite degeneration of peripheral and central sensory projections emanating from the same dorsal root ganglion (DRG) neurons. The mechanisms that prevent recruitment of circulating macrophages in CNS after injury remain poorly elucidated.

Effect of an inductive hydrogel composed of urinary bladder matrix upon functional recovery following traumatic brain injury

Traumatic brain injury (TBI) is a major public health problem with no effective clinical treatment. Use of bioactive scaffold materials has been shown to be a promising strategy for tissue regeneration and repair in a number of injury models. Of these scaffold materials, urinary bladder matrix (UBM) derived from porcine bladder tissue, has demonstrated desirable properties for supporting and promoting the growth of neural cells in vitro, suggesting its potential as a scaffold for brain tissue repair in the treatment of TBI. Herein we evaluate the biocompatibility of UBM within brain tissue and the effects of UBM delivery upon functional outcome following TBI. A hydrogel form of UBM was injected into healthy rat brains for 1, 3, and 21 days to examine the tissue response to UBM. Multiple measures of tissue injury, including reactive astrocytosis, microglial activation, and neuron degeneration showed that UBM had no deleterious effects on normal brain. Following TBI, the brains were evaluated histologically and behaviorally between sham-operated controls and UBM- and vehicle-treated groups. Application of UBM reduced lesion volume and attenuated trauma-induced myelin disruption. Importantly, UBM treatment resulted in significant neurobehavioral recovery following TBI as demonstrated by improvements in vestibulomotor function; however, no differences in cognitive recovery were observed between the UBM- and vehicle-treated groups. The present study demonstrated that UBM is not only biocompatible within the brain tissue, but also can exert protective effects upon injured brain.

Macrophage polarization: an opportunity for improved outcomes in biomaterials and regenerative medicine

The host response to biomaterials has been studied for decades. Largely, the interaction of host immune cells, macrophages in particular, with implanted materials has been considered to be a precursor to granulation tissue formation, the classic foreign body reaction, and eventual encapsulation with associated negative impacts upon device functionality. However, more recently, it has been shown that macrophages, depending upon context dependent polarization profiles, are capable of affecting both detrimental and beneficial outcomes in a number of disease processes and in tissue remodeling following injury. Herein, the diverse roles played by macrophages in these processes are discussed in addition to the potential manipulation of macrophage effector mechanisms as a strategy for promoting site-appropriate and constructive tissue remodeling as opposed to deleterious persistent inflammation and scar tissue formation.

Brain regeneration in physiology and pathology: the immune signature driving therapeutic plasticity of neural stem cells

Regenerative processes occurring under physiological (maintenance) and pathological (reparative) conditions are a fundamental part of life and vary greatly among different species, individuals, and tissues. Physiological regeneration occurs naturally as a consequence of normal cell erosion, or as an inevitable outcome of any biological process aiming at the restoration of homeostasis. Reparative regeneration occurs as a consequence of tissue damage. Although the central nervous system (CNS) has been considered for years as a "perennial" tissue, it has recently become clear that both physiological and reparative regeneration occur also within the CNS to sustain tissue homeostasis and repair. Proliferation and differentiation of neural stem/progenitor cells (NPCs) residing within the healthy CNS, or surviving injury, are considered crucial in sustaining these processes. Thus a large number of experimental stem cell-based transplantation systems for CNS repair have recently been established. The results suggest that transplanted NPCs promote tissue repair not only via cell replacement but also through their local contribution to changes in the diseased tissue milieu. This review focuses on the remarkable plasticity of endogenous and exogenous (transplanted) NPCs in promoting repair. Special attention will be given to the cross-talk existing between NPCs and CNS-resident microglia as well as CNS-infiltrating immune cells from the circulation, as a crucial event sustaining NPC-mediated neuroprotection. Finally, we will propose the concept of the context-dependent potency of transplanted NPCs (therapeutic plasticity) to exert multiple therapeutic actions, such as cell replacement, neurotrophic support, and immunomodulation, in CNS repair.

Quantitative iTRAQ analysis of retinal ganglion cell degeneration after optic nerve crush

Retinal ganglion cells (RGCs) are central nervous system (CNS) neurons that transmit visual information from the retina to the brain. Apoptotic RGC degeneration causes visual impairment that can be modeled by optic nerve crush. Neuronal apoptosis is also a salient feature of CNS trauma, ischemia (stroke), and diseases of the CNS such as Alzheimer's, Parkinson's, multiple sclerosis, and amyotrophic lateral sclerosis. Optic nerve crush induces the apoptotic cell death of ∼ 70% of RGCs within the first 14 days after injury. This model is particularly attractive for studying adult neuron apoptosis because the time-course of RGC death is well established and axon regeneration within the myelinated optic nerve can be concurrently evaluated. Here, we performed a large scale iTRAQ proteomic study to identify and quantify proteins of the rat retina at 1, 3, 4, 7, 14, and 21 days after optic nerve crush. In total, 337 proteins were identified, and 110 were differentially regulated after injury. Of these, 58 proteins were upregulated (>1.3 ×), 46 were downregulated (<0.7 ×), and 6 showed both positive and negative regulation over 21 days, relative to normal retinas. Among the differentially expressed proteins, Thymosin-β4 showed an early upregulation at 3 days, the time-point that immediately precedes the induction of RGC apoptosis after injury. We examined the effect of exogenous Thymosin-β4 administration on RGC death after optic nerve injury. Intraocular injections of Thymosin-β4 significantly increased RGC survival by ∼ 3-fold compared to controls and enhanced axon regeneration after crush, demonstrating therapeutic potential for CNS insults. Overall, our study identified numerous proteins that are differentially regulated at key time-points after optic nerve crush, and how the temporal profiles of their expression parallel RGC death. This data will aid in the future development of novel therapeutics to promote neuronal survival and regeneration in the adult CNS.

"Tissue-repairing" blood-derived macrophages are essential for healing of the injured spinal cord: from skin-activated macrophages to infiltrating blood-derived cells?

Until recently, the local inflammation that occurs in response to spinal cord injury has received a negative reputation; overall, it was assumed to be one of the major causes of a vicious neurotoxic cycle that leads to impaired recovery following injury. This local inflammation involves both the activated tissue-resident microglia and monocyte-derived macrophages infiltrating from the blood. Ten years ago, we proposed that the blood-derived macrophages, reminiscent of "alternatively activated" macrophages (also known as tissue repairing, M2), are not spontaneously recruited in sufficient numbers to sites of injured central nervous system (CNS). We further demonstrated that their exogenous administration to the margins of injured spinal cord improved functional outcome. However, our suggestions evoked criticism, claiming that we were adding macrophages to a site that is already overwhelmed with inflammatory cells. Using experimental paradigms that enabled functional distinction between the resident and infiltrating cells, our most recent studies further corroborated our repair perception, showing that (a) infiltrating monocyte-derived macrophages are recruited following injury and localize to the margins of the lesion, unlike the activated resident microglia that are not compartmentalized, and (b) activated resident microglia and infiltrating monocyte-derived macrophages perform distinct roles; recruited blood-derived macrophages display an (IL-10-dependent) anti-inflammatory phenotype when they become co-localized with the glial scar. We further found that post-injury recruitment of blood monocytes is indeed suboptimal. Augmentation of the levels of naïve blood monocytes leads to their increased recruitment to the same zones that are the targets of the infiltrated endogenous monocytes, and they acquire the same anti-inflammatory activity, leading to improved recovery. Thus, boosting the levels of the relevant blood monocytes reinforces the body's own repair mechanisms that, for reasons that are currently under investigation, are not optimally triggered within the critical post-injury period.

Microglia and neuroprotection: from in vitro studies to therapeutic applications

Microglia are the main immune cells in the brain, playing a role in both physiological and pathological conditions. Microglial involvement in neurodegenerative diseases is well-established, being microglial activation and neuroinflammation common features of these neuropathologies. Microglial activation has been considered harmful for neurons, but inflammatory state is not only associated with neurotoxic consequences, but also with neuroprotective effects, such as phagocytosis of dead neurons and clearance of debris. This brought to the idea of protective autoimmunity in the brain and to devise immunomodulatory therapies, aimed to specifically increase neuroprotective aspects of microglia. During the last years, several data supported the intrinsic neuroprotective function of microglia through the release of neuroprotective molecules. These data led to change the traditional view of microglia in neurodegenerative diseases: from the idea that these cells play an detrimental role for neurons due to a gain of their inflammatory function, to the proposal of a loss of microglial neuroprotective function as a causing factor in neuropathologies. This "microglial dysfunction hypothesis" points at the importance of understanding the mechanisms of microglial-mediated neuroprotection to develop new therapies for neurodegenerative diseases. In vitro models are very important to clarify the basic mechanisms of microglial-mediated neuroprotection, mainly for the identification of potentially effective neuroprotective molecules, and to design new approaches in a gene therapy set-up. Microglia could act as both a target and a vehicle for CNS gene delivery of neuroprotective factors, endogenously produced by microglia in physiological conditions, thus strengthening the microglial neuroprotective phenotype, even in a pathological situation.

Activated autologous macrophage implantation in a large-animal model of spinal cord injury

OBJECT

Axonal regeneration may be hindered following spinal cord injury (SCI) by a limited immune response and insufficient macrophage recruitment. This limitation has been partially surmounted in small-mammal models of SCI by implanting activated autologous macrophages (AAMs). The authors sought to replicate these results in a canine model of partial SCI.

METHODS

Six dogs underwent left T-13 spinal cord hemisection. The AAMs were implanted at both ends of the lesion in 4 dogs, and 2 other dogs received sham implantations of cell media. Cortical motor evoked potentials (MEPs) were used to assess electrophysiological recovery. Functional motor recovery was assessed with a modified Tarlov Scale. After 9 months, animals were injected with wheat germ agglutinin-horseradish peroxidase at L-2 and killed for histological assessment.

RESULTS

Three of the 4 dogs that received AAM implants and 1 of the 2 negative control dogs showed clear recovery of MEP response. Behavioral assessment showed no difference in motor function between the AAM-treated and control groups. Histological investigation with an axonal retrograde tracer showed neither local fiber crossing nor significant uptake in the contralateral red nucleus in both implanted and negative control groups.

CONCLUSIONS

In a large-animal model of partial SCI treated with implanted AAMs, the authors saw no morphological or histological evidence of axonal regeneration. Although they observed partial electrophysiological and functional motor recovery in all dogs, this recovery was not enhanced in animals treated with implanted AAMs. Furthermore, there was no morphological or histological evidence of axonal regeneration in animals with implants that accounted for the observed recovery. The explanation for this finding is probably multifactorial, but the authors believe that the AAM implantation does not produce axonal regeneration, and therefore is a technology that requires further investigation before it can be clinically relied on to ameliorate SCI.

Delayed accumulation of activated macrophages and inhibition of remyelination after spinal cord injury in an adult rodent model

OBJECT

Inhibition of remyelination is part of the complex problem of persistent dysfunction after spinal cord injury (SCI), and residual myelin debris may be a factor that inhibits remyelination. Phagocytosis by microglial cells and by macrophages that migrate from blood vessels plays a major role in the clearance of myelin debris. The object of this study was to investigate the mechanisms underlying the failure of significant remyelination after SCI.

METHODS

The authors investigated macrophage recruitment and related factors in rats by comparing a contusion model (representing contusive SCI with residual myelin debris and failure of remyelination) with a model consisting of chemical demyelination by lysophosphatidylcholine (representing multiple sclerosis with early clearance of myelin debris and remyelination). The origin of infiltrating macrophages was investigated using mice transplanted with bone marrow cells from green fluorescent protein-transfected mice. The changes in levels of residual myelin debris and the infiltration of activated macrophages in demyelinated lesions were investigated by immunostaining at 2, 4, and 7 days postinjury. To investigate various factors that might be involved, the authors also investigated gene expression of macrophage chemotactic factors and adhesion factors.

RESULTS

Activated macrophages coexpressing green fluorescent protein constituted the major cell population in the lesions, indicating that the macrophages in both models were mainly derived from the bone marrow, and that very few were derived from the intrinsic microglia. Immunostaining showed that in the contusion model, myelin debris persisted for a long period, and the infiltration of macrophages was significantly delayed. Among the chemotactic factors, the levels of monocyte chemoattractant protein-1 and granulocyte-macrophage colony-stimulating factor were lower in the contusion model at 2 and 4 days postinjury.

CONCLUSIONS

The results suggest that the delayed infiltration of activated macrophages is related to persistence of myelin debris after contusive SCI, resulting in the inhibition of remyelination.

Diffuse axonal damage, myelin impairment, astrocytosis and inflammatory response following microinjections of NMDA into the rat striatum

White matter damage and inflammatory response are important secondary outcomes after acute neural disorders. Nevertheless, a few studies addressed the temporal outcomes of these pathological events using non-traumatic models of acute brain injury. In the present study, we describe acute inflammatory response and white matter neuropathology between 1 and 7 days after acute excitotoxic striatal damage. Twenty micrometer sections were stained by hematoxylin and eosin technique for gross histopathological analysis and immunolabed for neutrophils (anti-mbs-1), activated macrophages/microglia (anti-ed1), astrocytes (anti-gfap), damaged axons (anti-betaapp) and myelin basic protein (MBP). Recruitment peak of neutrophils and macrophages occurred at 1 and 7 days post-nmda injection, respectively. Diffuse damaged axons (beta-app + end-bulbs) were apparent at 7 days, concomitant with progressive myelin impairment and astrocytosis. Further studies using electron microscopy and blockers of inflammatory response and glutamatergic receptors should be performed to confirm and address the mechanisms of white matter damage following an excitotoxic lesion.

Nanoscale laminin coating modulates cortical scarring response around implanted silicon microelectrode arrays

Neural electrodes could significantly enhance the quality of life for patients with sensory and/or motor deficits as well as improve our understanding of brain functions. However, long-term electrical connectivity between neural tissue and recording sites is compromised by the development of astroglial scar around the recording probes. In this study we investigate the effect of a nanoscale laminin (LN) coating on Si-based neural probes on chronic cortical tissue reaction in a rat model. Tissue reaction was evaluated after 1 day, 1 week, and 4 weeks post-implant for coated and uncoated probes using immunohistochemical techniques to evaluate activated microglia/macrophages (ED-1), astrocytes (GFAP) and neurons (NeuN). The coating did not have an observable effect on neuronal density or proximity to the electrode surface. However, the response of microglia/macrophages and astrocytes was altered by the coating. One day post-implant, we observed an approximately 60% increase in ED-1 expression near LN-coated probe sites compared with control uncoated probe sites. Four weeks post-implant, we observed an approximately 20% reduction in ED-1 expression along with an approximately 50% reduction in GFAP expression at coated relative to uncoated probe sites. These results suggest that LN has a stimulatory effect on early microglia activation, accelerating the phagocytic function of these cells. This hypothesis is further supported by the increased mRNA expression of several pro-inflammatory cytokines (TNF-alpha, IL-1 and IL-6) in cultured microglia on LN-bound Si substrates. LN immunostaining of coated probes immediately after insertion and retrieval demonstrates that the coating integrity is not compromised by the shear force during insertion. We speculate, based on these encouraging results, that LN coating of Si neural probes could potentially improve chronic neural recordings through dispersion of the astroglial scar.

Failed central nervous system regeneration: a downside of immune privilege?

Immunity is required to eliminate dangerous or degenerated material and to support regeneration, but also causes significant parenchymal damage. In the eye and the brain, in which cornea and lens poorly regenerate and neurons are hardly replaceable, early transplantation experiments demonstrated remarkable tolerance to various grafts. This "immunologically privileged status" (Billingham and Boswell, 1953) may reflect evolutionary pressure to downmodulate certain actions of immune cells within particularly vulnerable tissues. As an example, tolerating certain "neurotrophic" viruses may often be a more successful strategy for survival than the elimination of all infected neurons. While several constitutive and inducible signals maintaining or re-establishing immune tolerance within the brain have been identified, it has also become evident that the resulting anti-inflammatory environment limits certain beneficial effects of neuroinflammation such as neurotrophin secretion or glutamate buffering by T-cells and the clearance of growth-inhibiting myelin or amyloid. Following spinal cord injury, the costs and benefits of neuroinflammation seem to come close because enhancing as well as suppressing innate or adaptive immunity caused amelioration and aggravation of functional regeneration in similar experiments. Evaluating such balances has also begun in (animal models of) Alzheimer's disease, central nervous system trauma, and stroke, and the appreciation of the beneficial side of neuroinflammation has caused a rethinking of the ill-defined use of immune suppressants. As dual roles for individual molecules have been recognized (Merrill and Benveniste, 1996), we are uncovering an already fine-tuned system, but the challenge remains to further support beneficial immune cascades without causing additional damage, and vice versa.

Macrophages and neurons are targets of retinoic acid signaling after spinal cord contusion injury

The physiological reactions after spinal cord injury are accompanied by local synthesis of the transcriptional activator retinoic acid (RA). RA exerts its effects by binding to retinoic acid receptors (RAR) which heterodimerize with retinoid X receptors (RXR) and then act as ligand-activated transcription factors. To identify possible cellular targets of RA we investigated protein levels and cellular distribution of retinoid receptors in the rat spinal cord at 4, 7, 14 and 21 days after a contusion injury. In the nonlesioned spinal cord, immunoreactivity for RARalpha, RXRalpha, RXRbeta and RXRgamma was localized in the cytosol of neurons, that of RXRalpha and RXRbeta in astrocytes and that of RARalpha, RXRalpha and RXRgamma in some oligodendrocytes. After contusion injury RARalpha and all RXRs appeared in the cell nuclei of reactive microglia and macrophages. This nuclear staining began at 4 days, was most prominent at 7 and 14 days and had decreased at 21 days after injury. A similar nuclear translocation was also observed for the RARalpha, RXRalpha and RXRbeta staining in neurons situated around the border of the contusion. These observations suggest that RA participates as a signal for the physiological responses of microglia and neurons after CNS injury.

Systematic analysis of axonal damage and inflammatory response in different white matter tracts of acutely injured rat spinal cord

The mechanisms of white matter (WM) damage during secondary degeneration are a fundamental issue in the pathophysiology of central nervous system (CNS) diseases. Our main goal was to describe the pattern of an acute inflammatory response and secondary damage to axons in different WM tracts of acutely injured rat spinal cord. Adult rats were deeply anesthetized and injected with 20 nmol of NMDA into the spinal cord ventral horn on T7. Animals were perfused after survival times of 1 day, 3 days and 7 days. Ten micrometer sections were submitted to immunocytochemical analysis for activated macrophages/microglia, neutrophils and damaged axons. There were inflammatory response and progressive tissue destruction of ventral WM (VWM) with formation of microcysts in both VWM and lateral WM (LWM). In the VWM, the number of beta-amyloid precursor protein (beta-APP) end-bulbs increased from 1 day with a peak at 3 days, decreasing by 7 days following the injection. APP end-bulbs were present in the dorsal WM (DWM) at 3 days survival time but were not in the LWM. Electron microscopic analysis revealed different degrees of myelin disruption and axonal pathology in the vacuolated WM up to 14 mm along the rostrocaudal axis. Quantitative analysis revealed a significant loss of medium and large axons (P < 0.05), but not of small axons (P > 0.05). Our results suggest that bystander axonal damage and myelin vacuolation are important secondary component of the pathology of WM tracts following rat SCI. Further studies are needed to understand the mechanisms of these pathological events.

Current status of clinical trials for acute spinal cord injury

Acute spinal cord injury (ASCI) occurs as a result of physical disruption of spinal cord axons through the epicenter of injury leading to deficits in motor, sensory, and autonomic function. This is a debilitating neurological disorder common in young adults that often requires life-long therapy and rehabilitative care, placing a significant burden on our healthcare system. While no cure exists, research has identified various pharmacological compounds that specifically antagonize primary and secondary mechanisms contributing to the etiology of ASCI. Several compounds including methylprednisolone (MPSS), GM-1 ganglio-side, thyrotropin releasing hormone (TRH), nimodipine, and gacyclidine have been tested in prospective randomized clinical trials of ASCI. MPSS and GM-1 ganglioside have shown evidence of modest benefits. Clearly trials of improved neuroprotective agents are required. Promising potential therapies for ASCI include riluzole, minocycline, erythropoietin, and the fusogen polyethylene glycol, as well as mild hypothermia.

Protective autoimmunity and neuroprotection in inflammatory and noninflammatory neurodegenerative diseases

Autoimmune diseases are traditionally viewed as an outcome of a malfunctioning of the immune system, in which an individual's immune system reacts against the body's own proteins. In multiple sclerosis (MS), a disease of the white matter of the central nervous system (CNS), the attack is directed against myelin proteins. In this article we summarize a paradigm shift proposed by us in the perception of autoimmune disease. Observations by our group indicating that an autoimmune response is the body's mechanism for coping with CNS damage led us to suggest that all individuals are apparently endowed with a purposeful autoimmune response to CNS injuries, but have only limited inherent ability to control this response so that its effect will be beneficial. In animals susceptible to autoimmune diseases, the same autoimmune T cells are responsible both for neuroprotection and for disease development; the timing and strength of their activity will determine which of these effects is expressed. Individuals with non-inflammatory neurodegenerative diseases need a heightened autoimmunity. We discovered that autoimmunity could be boosted without risk of disease induction, even in susceptible strains, by the use of Copolymer-1 (Copaxone(R)), a weak agonist of a wide range of self-reactive T cells. Here we summarize the basic findings that led us to formulate the concept of protective autoimmunity, the mechanisms underlying its constitutive presence and its on/off regulation, and its therapeutic implications. We also offer an explanation for the commonly observed presence of cells and antibodies directed against self-components in healthy individuals.

Nicotine Attenuates Morphological Deficits in a Contusion Model of Spinal Cord Injury

Protection against the progression of secondary injury appears to be an effective therapeutic strategy in spinal cord injury (SCI). Evidence indicates that nicotine can induce potent neuroprotective effects against injury to spinal cord neurons. Therefore, the present study was focused on the effects of nicotine on the behavioral and morphological recovery associated with SCI. Adult male Long-Evans rats were subjected to a moderate contusion model of SCI and received subcutaneous injections of nicotine for 14 days at the dose of 0.35 or 7 mg/kg/day. The rats were examined using the BBB locomotor rating scale for 6 weeks. At the end of the BBB recording, spinal cords were examined for the volumetric tissue sparing of gray and white matters. All SCI rats demonstrated a loss of hindlimb function followed by a recovery phase that peaked at 2-3 weeks after the trauma. Compared to untreated SCI rats, chronic nicotine administration appeared to improve the recovery of the locomotor functions. Indeed, nicotine-treated animals scored consistently higher on the BBB scale indicating that the treatment altered animal behavior. However, when taking under consideration correction factors for multiple comparisons, these data did not reach significance at overall experimental levels of significance 0.05. Nevertheless, nicotine administration was effective in sparing tissue at injury epicenter and a lower dose of nicotine also resulted in significant sparing of white matter of the injured spinal cord. These results suggest that agonists of neuronal nicotinic receptors can be attractive candidates for SCI therapy.

Accumulation of Ym1/2 protein in the mouse olfactory epithelium during regeneration and aging

A unique feature of the olfactory system is its efficiency to produce new neurons in the adult. Thus, destruction of the olfactory receptor neurons (ORNs) using chemical (intranasal perfusion with ZnSO4) or surgical (axotomy or bulbectomy) methods, leads to an enhanced rate of proliferation of their progenitors and to complete ORNs regeneration. The aim of our study was to identify new factors implied in this regenerative process. Using an electrophoretic method, we observed the accumulation of a 42 kDa protein after axotomy in the olfactory mucosa, but not in the olfactory bulb. Its expression started after a few days following injury and increased massively during the phase of ORN regeneration. The purification and the sequence characterization revealed that this protein was Ym1/2, recently identified in activated macrophages present in various tissues during inflammation. Western blotting analysis of Ym1/2 confirmed the accumulation of this protein in the regenerating olfactory mucosa consecutively to olfactory axotomy or bulbectomy but also after ZnSO4 irrigation of the nasal cavity. In the olfactory mucosa of control mice, Ym1/2 was hardly detectable in young animals and became more and more abundant with increasing age. In injured and aged mice, Ym1/2 mainly accumulates in the cytoplasm of supporting cells as well as in other cells located throughout the olfactory epithelium. Our results suggest that Ym1/2 is involved in olfactory epithelium remodeling following several kinds of lesions of the adult olfactory mucosa and support the view of a critical role of inflammatory cues in neurodegeneration and aging.

Stem cells and nervous tissue repair: from in vitro to in vivo

Recent development in stem cell biology has indicated a new possible approach for the treatment of neurological diseases. However, in spite of tremendous hope generated, we are still on the way to understand if the use of stem cells to repair mature brain and spinal cord is a reliable possibility. In particular, we know very little on the in situ regulation of adult neural stem, and this also negatively impact on cell transplant possibilities. In this chapter we will discuss issues concerning the role and function of stem cells in neurological diseases, with regard to the impact of features of degenerating neurons and glial cells on in situ stem cells. Stem cell location and biology in the adult brain, brain host reaction to transplantation, neural stem cell reaction to experimental injuries and possibilities for exogenous regulation are the main topics discussed.

Features of skin-coincubated macrophages that promote recovery from spinal cord injury

Uncontrolled inflammation is considered to exacerbate the neuronal loss that follows spinal cord trauma. However, controlled inflammation response appears to be beneficial. Skin-coincubated macrophages injected into contused spinal cord of rats resulted in improved motor recovery and reduced spinal cyst formation. The macrophages express elevated levels of cell-surface molecules CD80, CD86, CD54 and MHC-II, markers characteristic of antigen presenting cells (APCs). Additionally, skin-coincubation elevates secretion of interleukin-1 beta (IL-1 beta) and Brain-Derived Neurotrophic Factor (BDNF), and reduces secretion of tumor necrosis factor alpha (TNF-alpha). We propose that macrophages activated by skin-coincubation bolster neuroprotective immune activity in the spinal cord, making the environment less cytotoxic and less hostile to axonal regeneration.

Reciprocal interactions between microglia and neurons: from survival to neuropathology

Microglia represent a major cellular component of the brain, where they constitute a widely distributed network of immunoprotective cells. During the last decades, it has become clear that the functions traditionally ascribed to microglia, i.e. to dispose of dead cells and debris and to mediate brain inflammatory states, are only a fraction of a much wider repertoire of functions spanning from brain development to aging and neuropathology. The aim of the present survey is to critically discuss some of these functions, focusing in particular on the reciprocal microglia-neuron interactions and on the complex signaling systems subserving them. We consider first some of the functional interactions dealing with invasion, proliferation and migration of microglia as well as with the establishment of the initial blueprint of neural circuits in the developing brain. The signals related to the suppression of immunological properties of microglia by neurons in the healthy brain, and the derangement from this physiological equilibrium in aging and diseases, are then examined. Finally, we make a closer examination of the reciprocal signaling between damaged neurons and microglia and, on these bases, we propose that microglial activation, consequent to neuronal injury, is primarily aimed at neuroprotection. The loss of specific communication between damaged neurons and microglia is viewed as responsible for the turning of microglia to a hyperactivated state, which allows them to escape neuronal control and to give rise to persistent inflammation, resulting in exacerbation of neuropathology. The data surveyed here point at microglial-neuron interactions as the basis of a complex network of signals conveying messages with high information content and regulating the most important aspects of brain function. This network shares similar features with some fundamental principles governing the activity of brain circuits: it is provided with memory and it continuously evolves in relation to the flow of time and information.

Manipulating neuroinflammatory reactions in the injured spinal cord: back to basics

Recruitment of inflammatory leukocytes to the injured spinal cord is a physiological response that is associated with the production of cytokines and proteinases that are involved in host defense and wound repair. Cells in the spinal cord are mainly post-mitotic and tissue regeneration is poor; thus, these inflammatory mediators can exacerbate the damage to spared tissue and thereby impair spontaneous functional recovery. Although several aspects of immune function might benefit the CNS, experimental studies indicate that acute neuroinflammation aggravates tissue injury. Until the timing and nature of the molecular signals that govern leukocyte recruitment and activation after spinal injury are defined, clinical therapies designed to boost immune cell function should be avoided.

Multiple sclerosis as a by-product of the failure to sustain protective autoimmunity: a paradigm shift

Autoimmune diseases are traditionally viewed as an outcome of a chaotic situation in which an individual's immune system reacts against the body's own proteins. In multiple sclerosis, a disease of the white matter of the central nervous system (CNS), the immune attack is directed against myelin proteins. In this article, the authors propose a paradigm shift in the perception of autoimmune disease. They suggest that an autoimmune disease may be viewed as a by-product of the malfunctioning of a physiological autoimmune response whose purpose is protective. The proposed view is based on observations by their group suggesting that an autoimmune response is the body's own mechanism for coping with CNS damage. According to this view, all individuals are endowed with the potential ability to evoke an autoimmune response to CNS injuries. However, the inherent ability to control this response so that its beneficial effect will be expressed is limited and is correlated with the individual's inherent ability to resist autoimmune disease induction. The same autoimmune T cells are responsible for neuroprotection and for disease development. In patients with CNS trauma or neurodegenerative disorders, it might be possible to gain maximal autoimmune protection and avoid autoimmune disease induction by boosting the immune response, using myelin-associated peptides that are nonpathogenic or antigens that simulate the activities of such peptides. In patients with multiple sclerosis and other neurodegenerative diseases, where the aim is to block the autoimmune disorder while deriving the potential benefit of the autoimmune response, the effect of treatment should be immunomodulatory rather than immunosuppressive. In this article, the authors present a novel concept of protective autoimmunity and propose that autoimmune disease is a by-product of failure to sustain it. They summarize the basic findings that led them to formulate the new concept and offer an explanation for the commonly observed presence of cells and antibodies directed against self-components in healthy individuals. The therapeutic implications of the new concept and their experimental findings are discussed.

Cytokines regulate microglial adhesion to laminin and astrocyte extracellular matrix via protein kinase C-dependent activation of the alpha6beta1 integrin

Microglia are highly plastic cells that participate in inflammatory and injury responses within the CNS and that can migrate extensively after activation. Because astrocytes and their extracellular matrix (ECM) form a large part of the CNS parenchyma, we undertook to study the adhesive interactions between microglia and these substrates in vitro. In contrast to oligodendrocyte precursor cells, microglia formed only weak interactions with astrocytes and their ECM. On specific ECM substrates the microglia adhered strongly to fibronectin, vitronectin, and plastic but only weakly to laminin. Microglial adhesion to laminin was increased significantly by the proinflammatory cytokines TNF, IFN-alpha, and IFN-gamma but was decreased by TGF-beta1, with the TGF-beta1 effect being dominant over the other cytokines. Fluorescence-activated cell sorting (FACS) analysis and immunoprecipitation showed that microglia constitutively express the alpha6beta1 integrin, a well characterized laminin receptor, and that alpha6beta1 expression levels did not change after cytokine treatment. Function-blocking studies showed that microglial adhesion to laminin is mediated entirely by the alpha6beta1 integrin, strongly suggesting that the cytokine regulation of adhesion to laminin is mediated by changes in the activation state of alpha6beta1. Analysis of signaling pathways revealed that activation of alpha6beta1 is mediated by a PKC-dependent mechanism. In light of the evidence that laminin expression is upregulated after CNS injury, the findings suggest that cytokine regulation of microglial adhesion to laminin may play a fundamental role in determining the extent of microglial infiltration into and retention at the site of injury.

Experimental modelling of human spinal cord injury: a model that crosses the species barrier and mimics the spectrum of human cytopathology

STUDY DESIGN

Literature review and presentation of an experimental model of human spinal cord injury, (SCI).

OBJECTIVES

Experimental designs seek to mimic and model the physical processes by which human SCI occurs and replicate the variety of chronic pathologies that characterize its long term effects. The variations in biological processes that are present between species have contributed to recent difficulties in generalizing experimental findings to the human condition. In this review, one finds: (1) a discourse on the pathological nature of the chronic human lesion, (2) a consideration of how the physical properties of soft tissue injury result in acute and chronic changes in the spinal substance, (3) a description of a device (ESCID) that is able to replicate and dynamically monitor physical indices of SCI as they take place in experimental models, and (4) a summary of how use of this device in different species has allowed the biomechanical descriptors of such injuries to be easily compared even in murine models.

SETTING

Ohio State University, Ohio, USA.

RESULTS

Careful attention to the details of injury device design has finally allowed a direct comparison of contusion-type injury models in the rat and mouse. Biomechanical outcomes with predictive capabilities have evolved that allow the investigator to create the range of pathologies seen in the human lesion even in these small vertebrates. The predictive cytopathology and our ability to manipulate the mouse genome will allow the testing of specific hypotheses related to cause and effect in experimental spinal cord injuries. Since the biomechanics, pathology, and chronic outcomes appear to be similar to those seen in the human, these animal models should facilitate rapid progress in the design of human therapeutics.

CONCLUSIONS

Biomechanics of certain elements of experimental spinal injury are surprisingly accurate descriptors of acute and chronic pathologies in the spinal cord. This tenet applies across species and has often allowed more accurate design of clinical trials in the past few decades. As molecular approaches to this problem evolve, the use of species with known genomes appear warranted. Models that take advantage of these approaches are likely to produce innovations that quicken the pace of human trial strategies.

Central and peripheral nerve regeneration by transplantation of Schwann cells and transdifferentiated bone marrow stromal cells

In contrast to the peripheral nervous system (PNS), little structural and functional regeneration of the central nervous system (CNS) occurs spontaneously following injury in adult mammals. The inability of the CNS to regenerate is mainly attributed to its own inhibitorial environment such as glial scar formation and the myelin sheath of oligodendrocytes. Therefore, one of the strategies to promote axonal regeneration of the CNS is to experimentally modify the environment to be similar to that of the PNS. Schwann cells are the myelinating glial cells in the PNS, and are known to play a key role in Wallerian degeneration and subsequent regeneration. Central nervous system regeneration can be elicited by Schwann cell transplantation, which provides a suitable environment for regeneration. The underlying cellular mechanism of regeneration is based upon the cooperative interactions between axons and Schwann cells involving the production of neurotrophic factors and other related molecules. Furthermore, tight and gap junctional contact between the axon and Schwann cell also mediates the molecular interaction and linking. In this review, the role of the Schwann cell during the regeneration of the sciatic (representing the PNS) and optic (representing the CNS) nerves is explained. In addition, the possibility of optic nerve reconstruction by an artificial graft of Schwann cells is also described. Finally, the application of cells not of neuronal lineage, such as bone marrow stromal cells (MSCs), in nerve regeneration is proposed. Marrow stromal cells are known as multipotential stem cells that, under specific conditions, differentiate into several kinds of cells. The strategy to transdifferentiate MSCs into the cells with a Schwann cell phenotype and the induction of sciatic and optic nerve regeneration are described.

Protective autoimmunity as a T-cell response to central nervous system trauma: prospects for therapeutic vaccines

Immune activity in general, and autoimmunity in particular, have long been considered as harmful in the context of central nervous system (CNS) trauma. Increasing evidence suggests, however, that the injured CNS can benefit from autoimmune manipulations. Active or passive immunization with CNS-associated self antigens was shown to promote recovery from a CNS insult. It is now also evident that this beneficial 'autoimmunity' is not solely an outcome of immune manipulation but is also a physiological response, evoked by a non-pathogenic insult and apparently designed to counteract the insult-related toxicity which is induced in part by essential physiological compounds present in excess of their normal levels. It appears that when the buffering capacity of constitutive local mechanisms (transporters, enzymes, etc.) that normally regulate these compounds is exceeded, assistance is recruited from the immune system. Like the overactive physiological compounds themselves, the immune system needs to be rigorously regulated in order to produce adequate phagocytic activity and the required quantity of cytokines and growth factors at the right time and place. Boosting of this autoimmune response is potentially a powerful strategy for neuroprotective therapy.

Characterization of the microglial response to cerebral ischemia in the stroke-prone spontaneously hypertensive rat

Stroke-prone spontaneously hypertensive rats (SHRSP) sustain more ischemic damage after middle cerebral artery occlusion than do their reference strain, the Wistar-Kyoto rat (WKY). The cause of increased stroke sensitivity is still under investigation. In general, SHRSP display a greater response to inflammatory stimuli than do WKY. Because inflammatory cells may influence the extent of damage in experimental stroke, this study has investigated the acute inflammatory response to focal ischemia in SHRSP and WKY. Adult male SHRSP (n=5) and WKY (n=5) were anesthetized and underwent distal middle cerebral artery occlusion. After 24 hours of recovery, infarct volume, neutrophil counts, and activated microglia counts were performed. SHRSP displayed more ischemic damage than did WKY (135+/-4.7 versus 102+/-4.7 mm(3) [mean+/-SEM], P<0.005). Brain neutrophil counts were extremely low in both strains. SHRSP displayed significantly more activated microglia than did WKY in the ipsilateral hemisphere (respective SHRSP versus WKY values [mean+/-SEM] were 88+/-3.6 versus 51+/-3.4 per mm(2) for the cortical peri-infarct region [P<0.005] and 183+/-7.9 versus 156+/-3.7 per mm(2) for the infarct core [P<0.05]) and in the contralateral hemisphere (eg, respective SHRSP versus WKY values were 102+/-3.2 versus 50+/-3.1 per mm(2) for the sensorimotor cortex [P<0.0001]). No neutrophils and very few activated microglia were found within the brains of naive rats. However naive SHRSP possessed more microglia (resting and activated) than did naive WKY. This study demonstrates a more pronounced microglial response to focal ischemia in SHRSP compared with WKY and provides evidence of a potential role for inflammatory processes in response to ischemic damage.

Beneficial immune activity after CNS injury: prospects for vaccination

A recent study in our laboratory showed, against all expectations, that macrophages and a particular type of T cell, by promoting regrowth and reducing the post-traumatic spread of damage in the injured rat optic nerve or spinal cord, have a beneficial effect on the injured CNS. Macrophages in the CNS have long been thought to have predominantly destructive effects. Autoimmunity in general, and in the CNS in particular, has never been documented as a purposeful physiological response of benign character. Our results suggest that after traumatic injury to the central nervous system (CNS), both of these immune cell types potentially have beneficial effects: macrophages can promote repair and T cells of a particular specificity can reduce the spread of damage. However, possibly because of the immune-privileged character of the CNS, the spontaneously evoked physiological activities of both macrophages and T cells in the CNS are restricted, and appear to need well-controlled boosting in order to be effective. It thus appears that (i) a stress signal transmitted from the traumatized tissue (in this case the CNS) for recruitment of the adaptive immune system does not have to be pathogen-related in order to evoke a response, (ii) a response to self is not necessarily a quirk of nature, and (iii) an autoimmune response, provided that it is well-regulated, helps the individual to cope with stress signals from the traumatized CNS, and thus plays a role in maintenance of the injured tissue without posing a threat to the organism.

Neurons reduce glial responses to lipopolysaccharide (LPS) and prevent injury of microglial cells from over-activation by LPS

The microenvironment of the CNS has been considered to tonically inhibit glial activities. It has been shown that glia become activated where neuronal death occurs in the aging brain. We have previously demonstrated that neurons tonically inhibit glial activities including their responses to the bacterial endotoxin lipopolysaccharide (LPS). It is not clear whether activation of glia, especially microglia in the aging brain, is the consequence of disinhibition due to neuronal death. This study was designed to determine if glia regain their responsiveness to LPS once the neurons have died in aged cultures. When cultured alone, glia from postnatal day one rat mesencephalons stimulated with LPS (0.1-1000 ng/mL) produced both nitric oxide (NO) and tumor necrosis factor alpha (TNFalpha), yielding a sigmoid and a bell-shaped curve, respectively. When neuron-containing cultures were prepared from embryonic day 14/15 mesencephalons, the shape of the dose-response curve for NO was monotonic and the bell-shaped curve for TNFalpha production was shifted to the right. After 1 month of culture under conditions where neurons die, the production curves for NO and TNFalpha in LPS-stimulated glia shifted back to the left compared to mixed neuron-glia cultures. Immunostaining of rat microglia for the marker CR3 (the receptor for complement component C3) demonstrated that high concentrations of LPS (1 microg/mL) reduced the number of microglia in mixed-glial cultures. In contrast, reduction of CR3 immunostaining was not observed in LPS-stimulated mixed neuron-glia cultures. Taken together, the results demonstrate that disinhibition of the glial response to LPS occurs after neurons die in aged cultures. Once neurons have died, the responsiveness of glia to LPS is restored. Neurons prevented injury to microglia by reducing their responsiveness to LPS. This study broadens our understanding of the ways in which the CNS microenvironment affects cerebral inflammation.

Bridging the gap: from discovery to clinical trials in spinal cord injury

Recently, the Kent Waldrep National Paralysis Foundation initiated a think tank intended to bridge several gaps and achieve several goals in regard to spinal cord injury (SCI) research and funding. Affiliated with the need to bridge a pathophysiological gap in spinal parenchyma and/or reorganize remaining circuitry after injury is a need to bridge resource gaps for timely funding for translational research, gaps in knowledge between researchers, and between researchers/clinicians and SCI patients. The epistemology of cure was examined and redefined to include transitional recoveries and advances. Modes and mechanisms of funding have been evaluated and where deficits were perceived, suggestions have been made to expedite and increase the number and breadth of funding opportunities. Innovative infrastructure changes are submitted. We discuss the progression of clinical trials as well as offer suggestions to facilitate benchtop-to-bedsite translation of valuable research to the customer. Highlights of recently completed, in progress, and future trials are detailed. Finally, we submit five essential processes required to promote advances to the SCI patient population: discovery, development, clinical trials, evaluation, and rehabilitation. These ideas are intended to facilitate entry of serious dialogue and to ultimately improve the lives of patients living with SCI.

Advances in secondary spinal cord injury: role of apoptosis

The outcome of spinal cord injury depends on the extent of secondary damage produced by a series of cellular and molecular events initiated by the primary trauma. This article reviews the evidence that secondary spinal cord injury involves the apoptotic as well as necrotic death of neurons and glial cells. Also discussed are the major factors that can contribute to cell death, such as glutamatergic excitotoxicity, free radical damage, cytokines, and inflammation. The development of innovative therapeutic strategies to reduce secondary spinal cord injury depends on an increased understanding of secondary injury mechanisms at the molecular and biochemical level. Such therapeutic interventions may include the use of antiapoptotic drugs, free radical scavengers, and anti-inflammatory agents. These could be targeted to block key reactions on cellular and molecular injury cascades, thus reducing secondary tissue damage, minimizing side effects, and improving functional recovery.

Autoimmunity can benefit self-maintenance

Autoimmunity is usually considered only as a cause of disease; nevertheless, human T-cell repertoires are filled naturally with autoimmune lymphocytes. Here, we review evidence that autoimmune T cells can help heal damaged tissues, indicating that natural autoimmunity could also be a cause of health.

Association of tenascin-R with murine brain myelin membranes: involvement of divalent cations

In the central nervous system (CNS), tenascin-R (TN-R) is mainly expressed by oligodendrocytes and in white matter tracts. Here, we have examined the molecular association of TN-R with CNS myelin by incubation of myelin membranes (MM) purified from adult mouse brain under different ionic conditions. By Western blot analysis, the 160 kDa isoform was the main TN-R component detectable in MM as a dimer which became degraded to monomers of 160 kDa and major fragments of 125 and 80 kDa in the absence of protease inhibitors. In the presence of chelating agents, TN-R was completely extracted from MM. Calcium ions promoted the dissociation of TN-R while zinc or copper blocked it. TN-R release from MM was sensitive to heat suggesting the involvement of calcium-dependent myelin protease(s) in this process. In addition, 1,10-phenanthroline (a metalloprotease blocker) partially inhibited TN-R release in the presence of calcium ions. We conclude that divalent metal ions stabilize the association of TN-R with CNS myelin and upon damage, the protein can be released and degraded by endogenous proteases, suggesting the implication of myelin-derived TN-R in axon growth inhibition and demyelinating diseases.

Role of Schwann cells in retinal ganglion cell axon regeneration

It is a well known fact that the injured PNS can successfully regenerate, on the other hand, the CNS such as retinal ganglion cell (RGC) axons of adult mammals is incapable of regeneration. After injury, RGC axons rapidly degenerate and most cell bodies go through the process of cell death, while glial cells at the site of injury undergo a series of responses which underlie the so-called glial scar formation. However, it has become apparent that RGCs do have an intrinsic capacity to regenerate which can be elicited by experimental replacement of the inhibitory glial environment with a permissive peripheral nerve milieu. Schwann cells are a major component of the PNS and play a role in regeneration, by producing various kinds of functional substances such as diffusible neurotrophic factors, extracellular matrix and cell adhesion molecules. RGC regeneration can be induced by cooperation of these substances. The contact of RGC axons to Schwann cells based upon the structural and molecular linkages seems to be indispensable for the stable and successful regeneration. In addition to cell adhesion molecules such as NCAM and L1, data from our laboratory show that Schwann cells utilize short focal tight junctions to provide morphological stabilization of the contact with the elongating axon, as well as a small scale of gap junctions to facilitate traffic of substances between them. Moreover, our results show that modifications of functional properties in neighboring glial cells of optic nerve are induced by transplantation of Schwann cells. Astrocytes usually considered to form a glial scar guide the regenerating axons in cooperation with Schwann cells. A decrease of the oligodendrocyte marker O4 and migration of ED-1 positive macrophages is observed within the optic nerve stump. Accordingly, RGC regeneration is not a simple phenomenon of axonal elongation on the Schwann cell membrane, but is based on direct and dynamic communication between the axon and the Schwann cell, and is also accompanied by changes and responses among the glial cell populations, which may be partly associated with the mechanisms of optic nerve regeneration.

'Axogenic' and 'somagenic' neurodegenerative diseases: definitions and therapeutic implications

Neurodegenerative diseases are characterized by a relentless loss of specific groups of neuronal subtypes. Many of these diseases share similar molecular mechanisms and extracellular mediators of neuronal loss. We now suggest that neurodegeneration originating in the neuronal cell bodies (e.g. in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis) should be distinguished from that originating in the axons (e.g. in glaucoma, certain peripheral neuropathies and spinal stenosis). We propose that the former group of diseases be defined as 'somagenic' and the latter as 'axogenic'. Although axogenic disorders may share common symptoms and mediators of toxicity with somagenic disorders, they have distinct temporal, subcellular and signal-transduction features. We further suggest that, by adopting this classification of disorders based on pathophysiological processes, we will come to recognize additional diseases (in particular, those defined as axogenic) as being neurodegenerative and therefore possibly amenable to neuroprotective therapy.

Depletion of hematogenous macrophages promotes partial hindlimb recovery and neuroanatomical repair after experimental spinal cord injury

Traumatic injury to the spinal cord initiates a series of destructive cellular processes which accentuate tissue damage at and beyond the original site of trauma. The cellular inflammatory response has been implicated as one mechanism of secondary degeneration. Of the various leukocytes present in the spinal cord after injury, macrophages predominate. Through the release of chemicals and enzymes involved in host defense, macrophages can damage neurons and glia. However, macrophages are also essential for the reconstruction of injured tissues. This apparent dichotomy in macrophage function is further complicated by the overlapping influences of resident microglial-derived macrophages and those phagocytes that are derived from peripheral sources. To clarify the role macrophages play in posttraumatic secondary degeneration, we selectively depleted peripheral macrophages in spinal-injured rats during a time when inflammation has been shown to be maximal. Standardized behavioral and neuropathological analyses (open-field locomotor function, morphometric analysis of the injured spinal cord) were used to evaluate the efficacy of this treatment. Beginning 24 h after injury and then again at days 3 and 6 postinjury, spinal cord-injured rats received intravenous injections of liposome-encapsulated clodronate to deplete peripheral macrophages. Within the spinal cords of rats treated in this fashion, macrophage infiltration was significantly reduced at the site of impact. These animals showed marked improvement in hindlimb usage during overground locomotion. Behavioral recovery was paralleled by a significant preservation of myelinated axons, decreased cavitation in the rostrocaudal axis of the spinal cord, and enhanced sprouting and/or regeneration of axons at the site of injury. These data implicate hematogenous (blood-derived) macrophages as effectors of acute secondary injury. Furthermore, given the selective nature of the depletion regimen and its proven efficacy when administered after injury, cell-specific immunomodulation may prove useful as an adjunct therapy after spinal cord injury.

Inflammatory mediators and stroke: new opportunities for novel therapeutics

Contrary to previous dogmas, it is now well established that brain cells can produce cytokines and chemokines, and can express adhesion molecules that enable an in situ inflammatory reaction. The accumulation of neutrophils early after brain injury is believed to contribute to the degree of brain tissue loss. Support for this hypothesis has been drawn from many studies where neutrophil-depletion blockade of endothelial-leukocyte interactions has been achieved by various techniques. The inflammation reaction is an attractive pharmacologic opportunity, considering its rapid initiation and progression over many hours after stroke and its contribution to evolution of tissue injury. While the expression of inflammatory cytokines that may contribute to ischemic injury has been repeatedly demonstrated, cytokines may also provide "neuroprotection" in certain conditions by promoting growth, repair, and ultimately, enhanced functional recovery. Significant additional basic work is required to understand the dynamic, complex, and time-dependent destructive and protective processes associated with inflammation mediators produced after brain injury. The realization that brain ischemia and trauma elicit robust inflammation in the brain provides fertile ground for discovery of novel therapeutic agents for stroke and neurotrauma. Inhibition of the mitogen-activated protein kinase (MAPK) cascade via cytokine suppressive anti-inflammatory drugs, which block p38 MAPK and hence the production of interleukin-1 and tumor necrosis factor-alpha, are most promising new opportunities. However, spatial and temporal considerations need to be exercised to elucidate the best opportunities for selective inhibitors for specific inflammatory mediators.