Recombinant DNA vaccine encoding multiple domains related to inhibition of neurite outgrowth: a potential strategy for axonal regeneration

A Modern Approach to the Treatment of Traumatic Brain Injury

Background: Traumatic brain injury manifests itself in various forms, ranging from mild impairment of consciousness to severe coma and death. Traumatic brain injury remains one of the leading causes of morbidity and mortality. Currently, there is no therapy to reverse the effects associated with traumatic brain injury. New neuroprotective treatments for severe traumatic brain injury have not achieved significant clinical success. Methods: A literature review was performed to summarize the recent interdisciplinary findings on management of traumatic brain injury from both clinical and experimental perspective. Results: In the present review, we discuss the concepts of traditional and new approaches to treatment of traumatic brain injury. The recent development of different drug delivery approaches to the central nervous system is also discussed. Conclusions: The management of traumatic brain injury could be aimed either at the pathological mechanisms initiating the secondary brain injury or alleviating the symptoms accompanying the injury. In many cases, however, the treatment should be complex and include a variety of medical interventions and combination therapy.

Small Extracellular Vesicles Derived from Altered Peptide Ligand-Loaded Dendritic Cell Act as A Therapeutic Vaccine for Spinal Cord Injury Through Eliciting CD4+ T cell-Mediated Neuroprotective Immunity

The balance among different CD4+ T cell subsets is crucial for repairing the injured spinal cord. Dendritic cell (DC)-derived small extracellular vesicles (DsEVs) effectively activate T-cell immunity. Altered peptide ligands (APLs), derived from myelin basic protein (MBP), have been shown to affect CD4+ T cell subsets and reduce neuroinflammation levels. However, the application of APLs is challenging because of their poor stability and associated side effects. Herein, it is demonstrate that DsEVs can act as carriers for APL MBP87-99 A91 (A91-DsEVs) to induce the activation of 2 helper T (Th2) and regulatory T (Treg) cells for spinal cord injury (SCI) in mice. These stimulated CD4+ T cells can efficiently "home" to the lesion area and establish a beneficial microenvironment through inducing the activation of M2 macrophages/microglia, inhibiting the expression of inflammatory cytokines, and increasing the release of neurotrophic factors. The microenvironment mediated by A91-DsEVs may enhance axon regrowth, protect neurons, and promote remyelination, which may support the recovery of motor function in the SCI model mice. In conclusion, using A91-DsEVs as a therapeutic vaccine may help induce neuroprotective immunity in the treatment of SCI.

Systemic Administration of Allogeneic Cord Blood Mononuclear Cells in Adults with Severe Acute Contusion Spinal Cord Injury: Phase I/IIa Pilot Clinical Study - Safety and Primary Efficacy Evaluation

OBJECTIVES

Current Phase I part of SUBSCI I/IIa study was focused on safety and primary efficacy of multiple systemic infusions of allogeneic unrelated human umbilical cord blood mononuclear cells in patients with severe acute spinal cord contusion having severe neurological deficit. The primary endpoint was safety. The secondary endpoint was the fact of restoration of motor and sensory function in lower limbs within 1-year period.

METHODS

Ten subjects with acute contusion SCI and ASIA A/B deficit were enrolled into Phase I part. Subjects were treated with 4 infusions of group- and rhesus-matched cord blood samples following primary surgery within 3 days post-SCI. All patients were followed-up for 12 months post-SCI. Safety was assessed using adverse events classification depending on severity and relation to cell therapy. Primary efficacy was assessed using dynamics of deficit (ASIA scale).

RESULTS

The overall number of AEs reached 419 in 10 subjects. Only 2 of them were estimated as possibly related to cell therapy, other 417 were definitely unrelated. Both AEs were mild and clinically insignificant. No signs of immunization were found in participants. Analysis of clinical outcomes also demonstrated that cell therapy promotes significant functional restoration of motor function.

CONCLUSIONS

Obtained data suggest that systemic administration of allogenic, non-HLA matched HUCB cells is safe and demonstrates primary efficacy in adults with severe acute contusion SCI and ASIA A/B deficit.

A ready-to-use fluorescence probe of Pd2+ in water: novel tricyclic heterocyclic base on 1,3,4-oxadiazole

A ready-to-use hetero-tricyclic compound, 5,5'-(furan-2,5-diyl) bis (1,3,4- oxadiazol-2-amine) (5), was synthesized with a good yield; it has an suitable fluorescence characteristic and research founded that it can respond to trace Pd²⁺ in water at a normal pH range. A fluorescence titration revealed the detection limit for Pd²⁺ was as low as 3.97 × 10^-9  M. Density-functional theory calculation using Guassian09 implied that the breakage of conjugation and coplanarity of compound 5 led to fluorescence quenching. Compound 5 could be applied as a chemical probe to detect trace amounts of Pd²⁺ with good accuracy, fast response time, excellent selectivity, and high sensitivity. FT-IR, NMR, and MS were used to characterize the chemical structure of compound 5.

An in vitro study of peptide-loaded alginate nanospheres for antagonizing the inhibitory effect of Nogo-A protein on axonal growth

The adult mammalian central nervous system has limited ability to regenerate after injury. This is due, in part, to the presence of myelin-associated axon growth inhibitory proteins such as Nogo-A that bind and activate the Nogo receptor, leading to profound inhibition of actin-based motility within the growing axon tip. This paper presents an in vitro study of the use of a Nogo receptor-blocking peptide to antagonize the inhibitory effect of Nogo-A on axon growth. Alginate nanospheres were fabricated using an emulsion technique and loaded with Nogo receptor-blocking peptide, or with other model proteins. Protein release profiles were studied, and retention of the bioactivity of released proteins was verified. Primary dorsal root ganglion neurons were cultured and their ability to grow neurites was challenged with Nogo-A chimeric protein in the absence or presence of Nogo receptor antagonist peptide-loaded alginate nanospheres. Our results demonstrate that peptide released from alginate nanospheres could overcome the growth inhibitory effect of Nogo-A, suggesting that a similar peptide delivery strategy using alginate nanospheres might be used to improve axon regeneration within the injured central nervous system.

Meta analysis of olfactory ensheathing cell transplantation promoting functional recovery of motor nerves in rats with complete spinal cord transection

OBJECTIVE:

To evaluate the effects of olfactory ensheathing cell transplantation on functional recovery of rats with complete spinal cord transection.

DATA SOURCES:

A computer-based online search of Medline (1989–2013), Embase (1989–2013), Cochrane library (1989–2013), Chinese Biomedical Literature Database (1989–2013), China National Knowledge Infrastructure (1989–2013), VIP (1989–2013), Wanfang databases (1989–2013) and Chinese Clinical Trial Register was conducted to collect randomized controlled trial data regarding olfactory ensheathing cell transplantation for the treatment of complete spinal cord transection in rats.

SELECTION CRITERIA:

Randomized controlled trials investigating olfactory ensheathing cell transplantation and other transplantation methods for promoting neurological functional recovery of rats with complete spinal cord transection were included in the analysis. Meta analysis was conducted using RevMan 4.2.2 software.

MAIN OUTCOME MEASURES:

Basso, Beattie and Bresnahan scores of rats with complete spinal cord transection were evaluated in this study.

RESULTS:

Six randomized controlled trials with high quality methodology were included. Meta analysis showed that Basso, Beattie and Bresnahan scores were significantly higher in the olfactory ensheathing cell transplantation group compared with the control group (WMD = 3.16, 95% CI (1.68, 4.65); P < 0.00001).

CONCLUSION:

Experimental studies have shown that olfactory ensheathing cell transplantation can promote the functional recovery of motor nerves in rats with complete spinal cord transection.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

Recombinant DNA vaccine against neurite outgrowth inhibitors attenuates behavioral deficits and decreases Abeta in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a chronic neurodegenerative disease that causes a progressive loss in learning and memory capabilities and eventually results in dementia. The non-renewable nature of neurons in the central nervous system leads to the basic pathological changes that are related to the various behavioral and psychological symptoms of AD. Oligodendrocyte- and myelin-related neurite outgrowth inhibitors (NOIs) tend to hinder the regeneration of neurons. We designed a recombinant DNA vaccine composed of multiple specific inhibitory domains of NOIs. Vaccination induced effective antibodies against the specific domains in the sera of mice treated with a DNA primed-vaccinia virus boost regimen. The vaccine attenuated neuronal degeneration in the mouse brain and protected the model mice from behavioral deficits. Vaccination also decreased the formation of soluble Aβ oligomer and amyloid plaques in the co-transgenic mice brain. What's more, astrocytosis in brains of APP/PS1 co-transgenic mice was also relieved. The results suggested that immunotherapy with multiple specific domains of myelin- and oligodendrocyte-related NOIs may be a promising approach for Alzheimer's disease and other degenerative central nervous system diseases.

Passive immunization with tenascin-R (TN-R) polyclonal antibody promotes axonal regeneration and functional recovery after spinal cord injury in rats

Tenascin-R (TN-R) is a neural specific protein and an important molecule involved in inhibition of axonal regeneration after spinal cord injury (SCI). Here we report on rabbit-derived TN-R polyclonal antibody, which acts as a TN-R antagonist with high titer and high specificity, promoted neurite outgrowth and sprouting of rat cortical neurons cultured on the inhibitory TN-R substrate in vitro. When locally administered into the lesion sites of rats received spinal cord dorsal hemisection, these TN-R antibodies could significantly decrease RhoA activation and improve functional recovery from corticospinal tract (CST) transection. Thus, passive immunotherapy with specific TN-R antagonist may represent a promising repair strategy following acute SCI.

Therapeutic DNA vaccination as a repair strategy following spinal cord injury

Myelin-derived proteins, such as tenascin-R (TN-R), myelin associate glycoprotein (MAG), oligodendrocyte-myelin glycoprotein (OMgp), and Nogo-A, inhibit the central nervous system regeneration. In this study, the DNA vaccine encoding for oligodendrocyte and myelin-related antigens was employed to attenuate the axonal growth inhibitory properties of myelin in the setting of spinal cord injury. Using a rat spinal cord dorsal hemisection model, the vaccine directed against the inhibitory epitopes of Nogo-A, MAG, OMgp, and TN-R was administered intramuscularly once a week following spinal cord injury, supplemented with local application of specific anti-sera against the four antigens. Anterograde labeling of dorsal column fibers showed active axonal regeneration through the lesion site at the eighth week following the treatment in experimental group but not in control groups. Light microscopic and ultrastructural analysis revealed that vaccination with these myelin-related antigens did not lead to demyelinating disease. OMgp and TN-R levels were down-regulated at the lesion site together with a parallel increase in growth-associated protein 43 levels in the treatment groups. This study reveals the effective approach of a DNA vaccine strategy by attaining the special antibody to direct neutralization of the myelin inhibitors during spinal cord injury.

Receptors for myelin inhibitors: Structures and therapeutic opportunities

Many studies have indicated that the inability of adult mammalian central nervous system (CNS) to regenerate after injury is partly due to the existence of growth-inhibitory molecules associated with CNS myelin. Studies over the years have led to the identification of multiple myelin-associated inhibitors, among which Nogo, myelin-associated glycoprotein (MAG) and oligodendrocyte-myelin glycoprotein (Omgp) represent potentially major contributors to CNS axon regeneration failure. Here we review in vitro and in vivo investigations into these inhibitory ligands and their functional mechanisms, focusing particularly on the neuronal receptors that mediate the inhibitory signals from these myelin molecules. A better understanding of the receptors for myelin-associated inhibitors could provide opportunities to decipher the mechanism of restriction in CNS regeneration, and lead to the development of potential therapeutic targets in neurodegenerative diseases and neurological injury. We will discuss the structures of the receptors and therapeutic opportunities that might arise based on this information.

Recombinant DNA vaccine against inhibition of neurite outgrowth promotes functional recovery associated with endogeous NGF expression in spinal cord hemisected adult rats

Axonal regeneration across the site of spinal cord lesion is often aborted in adult mammalian species. The use of DNA vaccine to nullify the inhibitory molecules has been shown to be effective in promoting axonal regeneration in injured spinal cord. The possible molecular mechanisms, however, remain to be elucidated. The present study showed that the administration of recombinant DNA vaccine encoding multiple domains, Nogo-66, Nogo-N, TnR, and MAG, significantly improved hindlimb locomotor functions in rats subjected to ablation of the dorsal halves of the cord. Western blot analysis demonstrated that nerve growth factor (NGF) levels in the spinal cord of immunized rats were significantly upregulated than those of control rats. Immunohistochemistry as well as in situ hybridization confirmed that NGF was expressed in neurons of the spinal cord. These findings indicated that functional recovery in immunized rats could be correlated with endogeous NGF expression in hemisected rat spinal cords.

Role of extracellular factors in axon regeneration in the CNS: implications for therapy

The glial scar that forms after an injury to the CNS contains molecules that are inhibitory to axon growth. Understanding of the mechanisms of inhibition has allowed the development of therapeutic strategies aimed at promoting axon regeneration. Promising results have been obtained in animal models, and some therapies are undergoing clinical trials. This offers great hope for achievement of functional recovery after CNS injury.

Immunization with recombinant Nogo-66 receptor (NgR) promotes axonal regeneration and recovery of function after spinal cord injury in rats

Nogo-66 receptor (NgR), a common receptor for the three known myelin-associated inhibitors, i.e., Nogo-A, myelin-associated glycoprotein (MAG), and oligodendrocyte myelin glycoprotein (OMgp), plays a key role in the failure of axonal regeneration in the adult mammalian central nervous system (CNS). Here we report a novel vaccine approach that stimulates the production of anti-NgR antibody to overcome NgR-mediated growth inhibition after spinal cord injury (SCI). We showed that adult rats immunized with recombinant NgR produced high titers of the anti-NgR antibody and that antisera obtained from the immunized rats promoted neurite outgrowth of rat cerebellar neurons on the inhibitory MAG substrate in vitro. In a spinal cord dorsal hemisection model, NgR immunization promoted regeneration of lesioned corticospinal tract (CST) axons, anterogradely labeled with biotin dextran amine (BDA), beyond the lesion site. In a contusive SCI model, NgR immunization markedly reduced the total lesion volume and improved Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and grid walking performance. Thus, the NgR vaccine approach may represent a promising repair strategy to promote structural and functional recovery following SCI.

Can the immune system be harnessed to repair the CNS?

Experimental and clinical data have demonstrated that activating the immune system in the CNS can be destructive. However, other studies have shown that enhancing an immune response can be therapeutic, and several clinical trials have been initiated with the aim of boosting immune responses in the CNS of individuals with spinal cord injury, multiple sclerosis and Alzheimer's disease. Here, we evaluate the controversies in the field and discuss the remaining scientific challenges that are associated with enhancing immune function in the CNS to treat neurological diseases.

Vaccines for multiple sclerosis: progress to date

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS, characterized pathologically by a perivascular infiltrate consisting predominantly of T cells and macrophages. Although its aetiology remains unknown, several lines of evidence support the hypothesis that autoimmune mechanisms play a major role in the development of the disease. Several widely used disease-modifying agents are approved for the treatment of MS. However, these agents are only partially effective and their ability to attenuate the more progressive phases of the disease is not clear at this time. Therefore, there is a need to develop improved treatment options for MS. This article reviews the role of several novel, selective vaccine strategies that are currently under investigation, including: (i) T-cell vaccination (TCV); (ii) T-cell receptor (TCR) peptide vaccination; (iii) DNA vaccination; and (iv) altered peptide ligand (APL) vaccination. The administration of attenuated autoreactive T cells induces regulatory networks to specifically suppress pathogenic T cells in MS, a strategy named TCV. The concept of TCV was based on the experience of vaccination against aetiological agents of infectious diseases in which individuals are purposely exposed to an attenuated microbial pathogen, which then instructs the immune system to recognize and neutralize it in its virulent form. In regard to TCV, attenuated, pathogenic T cells are similarly used to instruct the immune system to recognize and neutralize disease-inducing T cells. In experimental allergic encephalomyelitis (EAE), an animal model for MS, pathogenic T cells use a strikingly limited number of variable-region elements (V region) to form TCR specific for defined autoantigens. Thus, vaccination with peptides directed against these TCR structures may induce immunoregulatory mechanisms, thereby preventing EAE. However, unlike EAE, myelin-reactive T cells derived from MS patients utilize a broad range of different V regions, challenging the clinical utility of this approach. Subsequently, the demonstration that injection of plasmid DNA encoding a reporter gene into skeletal muscle results in expression of the encoded proteins, as well as in the induction of immune responses in animal models of autoimmunity, was explored as another strategy to re-establish self-tolerance. This approach has promise for the treatment of MS and, therefore, warrants further investigation. APLs are molecules in which the native encephalitogenic peptides are modified by substitution(s) of one or a few amino acids critical for contact with the TCR. Depending on the substitution(s) at the TCR contact residues of the cognate peptide, an APL can induce immune responses that can protect against or reverse EAE. However, the heterogeneity of the immune response in MS patients requires further study to determine which patients are most likely to benefit from APL therapy. Other potential approaches for vaccines in MS include vaccination against axonal growth inhibitors associated with myelin, use of dendritic cells pulsed with specific antigens, and active vaccination against proinflammatory cytokines. Overall, vaccines for MS represent promising approaches for the treatment of this devastating disease, as well as other autoimmune diseases.

DNA vaccination efficiently induces antibodies to Nogo-A and does not exacerbate experimental autoimmune encephalomyelitis

Antibodies against the neurite outgrowth inhibitor Nogo-A enhance axonal regeneration following spinal cord injury. However, antibodies directed against myelin components can also enhance CNS inflammation. The present study was designed to assess the efficacy of DNA vaccination for generating antibodies against Nogo-A and to study their pathogenic potential in a mouse model for multiple sclerosis. Mice were immunized by a single i.m. injection of a plasmid expression vector encoding either full length membrane-integral Nogo-A equipped with a signal peptide or two versions of its large N-terminal extramembrane region. The presence of serum antibodies to Nogo-A was measured 4 weeks after injection by ELISA, Western blotting and immunohistochemistry. DNA vaccination efficiently induced production of Nogo-A-specific antibodies that recognized recombinant, intracellular Nogo-A in cell culture but also stained native Nogo-A on the oligodendrocyte surface. Experimental autoimmune encephalomyelitis was induced in DNA-vaccinated mice by immunization with proteolipid peptide (a.a. 139-154). In contrast to vaccination with DNA encoding myelin oligodendrocyte glycoprotein that exacerbates this disease, Nogo-A DNA vaccination did not enhance clinical severity of disease. In summary, DNA vaccination is a simple and efficient method for generating an antibody response to Nogo-A. No pathogenicity was observed even during a full-blown inflammatory response of the central nervous system.

A re-assessment of the effects of a Nogo-66 receptor antagonist on regenerative growth of axons and locomotor recovery after spinal cord injury in mice

This study was undertaken as part of the NIH "Facilities of Research-Spinal Cord Injury" project to support independent replication of published studies. Here, we repeated a study reporting that treatment with the NgR antagonist peptide NEP1-40 results in enhanced growth of corticospinal and serotonergic axons and enhanced locomotor recovery after thoracic spinal cord injury. Mice received dorsal hemisection injuries at T8 and then received either NEP1-40, Vehicle, or a Control Peptide beginning 4-5 h (early treatment) or 7 days (delayed treatment) post-injury. CST axons were traced by injecting BDA into the sensorimotor cortex. Serotonergic axons were assessed by immunocytochemistry. Hindlimb motor function was assessed using the BBB and BMS scales, kinematic and footprint analyses, and a grid climbing task. There were no significant differences between groups in the density of CST axon arbors in the gray matter rostral to the injury or in the density of serotonergic axons caudal to the injury. Tract tracing revealed that a small number of CST axons extended past the lesion in the ventral column in some mice in all treatment groups. The proportion of mice with such axons was higher in the NEP1-40 groups that received early treatment. In one experiment, mice treated with either NEP1-40 or a Control Peptide (reverse sequence) had higher BBB and BMS scores than Vehicle-treated controls at the early post-injury testing intervals, but scores converged at later intervals. There were no statistically significant differences between groups on other functional outcome measures. In a second experiment comparing NEP-treated and Vehicle controls, there were no statistically significant differences on any of the functional outcome measures. Together, our results suggest that treatment with NEP1-40 created a situation that was slightly more conducive to axon regeneration or sprouting. Enhanced functional recovery was not seen consistently with the different functional assessments, however.

Therapeutic vaccination for central nervous system repair

1. Vaccination against infectious agents has been heralded as a triumph in modern medicine and, more recently, cancer vaccines have risen in prominence. The present review looks towards the use of vaccine therapy to attenuate damage after injury to the central nervous system (CNS). 2. Significant debility is associated with brain injury, most commonly occurring as a result of physical trauma or stroke. This end result reflects the inability of neurons and axons to regenerate following injury to the CNS. This unconductive environment is due, in large part, to the presence of myelin and oligodendrocyte-related inhibitors of neurite outgrowth. 3. We review how a vaccine-based approach has been variably used to circumvent this issue and promote axonal regeneration and repair following traumatic injury and other neurodegenerative disorders. In addition, emerging evidence suggests that the immune response to injury in the CNS may be manipulated so as to reduce cellular damage. Vaccine-directed approaches using this concept are also outlined.

DNA vaccine against NgR promotes functional recovery after spinal cord injury in adult rats

NgR is a common receptor for three myelin-associated inhibitors and mediates their inhibitory activities on neurite outgrowth. In the present study, we investigated whether a DNA vaccine targeting NgR could play a beneficial role in improving recovery from spinal cord injury (SCI). We demonstrated that a DNA vaccine against NgR was successfully constructed and expressed efficiently in vitro and in vivo. After immunization with anti-NgR DNA vaccine, a low level of antibody response and a T cell-mediated immune response were induced in the vaccinated rats. And the antisera taken from the anti-NgR DNA vaccinated rats could partly reverse the inhibition of MAG on neurite outgrowth. When the rats were subjected to a contusive SCI, the vaccinated rats showed much better functional recovery than the controls. In those vaccinated rats that induced a T cell response and generated antibodies against NgR, functional improvements were even better. Histological assessments by three-dimensional reconstruction further demonstrated that the total lesion volume in the vaccinated rats was reduced by 30.8% compared to the controls. These results collectively suggest that DNA vaccine against NgR can significantly improve functional recovery in rats that received contusive SCI and that the vaccination approach may provide a promising strategy for promoting SCI repair.

Spinal cord injury--scientific challenges for the unknown future

The history of spinal cord injuries starts with the ancient Egyptian medical papyrus known as the Edwin Smith Surgical Papyrus. The papyrus written about 2500 B.C.by the physician and architect of the Sakkara pyramids Imhotep, describes "crushed vertebra in his neck" as well as symptoms of neurological deterioration. An ailment not to be treated was the massage to the patients at that time. This fatalistic attitude remained until the end of World War II when the first rehabilitation centre focused on the rehabilitation of spinal cord injured patients was opened. Our knowledge of the pathophysiological processes, both the primary as well as the secondary, has increased tremendously. However, all this knowledge has only led to improved medical care but not to any therapeutic method to restore, even partially, the neurological function. Neuroprotection is defined as measures to counteract secondary injury mechanisms and/or limit the extent of damage caused by self-destructive cellular and tissue processes. The co-existence of several distinctly different injury mechanisms after trauma has provided opportunities to explore a large number of potentially neuroprotective agents in animal experiments such as methylprednisolone sodium succinate. The results of this research have been very discouraging and pharmacological neuroprotection for patients with spinal cord injury has fallen short of the expectations created by the extensive research and promising observations in animal experiments. The focus of research has now, instead, been transformed to the field of neural regeneration. This field includes the discovery of regenerating obstacles in the nerve cell and/or environmental factors but also various regeneration strategies such as bridging the gap at the site of injury as well as transplantation of foetal tissue and stem cells. The purpose of this review is to highlight selected experimental and clinical studies that form the basis for undertaking future challenges in the research field of spinal cord injury. We will focus our discussion on methods either preventing the consequences of secondary injury in the acute period (neuroprotection) and/or various techniques of neural regeneration in the sub-acute and chronic phase and finally expose some thoughts about future avenues within this scientific field.

Nogo in multiple sclerosis: Growing roles of a growth inhibitor

In recent years, knowledge about the physiological functions of the Nogo-A protein has grown considerably, and this molecule has evolved from being one of the most important axonal regrowth inhibitors present in central nervous system (CNS) myelin, to several other potentially important roles in different areas such as nervous system development, epilepsy, vascular physiology, muscle pathology and CNS tumors. Therapeutically, targeting the Nogo-A protein by means of the immune response has been tried in an attempt to block neurite growth inhibition and promote regeneration in spinal cord injury models; the immune response to Nogo-A, however, has not been extensively studied. We propose to review recent evidence that Nogo-A may also play an important role in autoimmune demyelinating diseases such as experimental autoimmune encephalomyelitis and multiple sclerosis, including that Nogo-66 derived epitopes are encephalitogenic antigens in susceptible mouse strains, and that the immune response to Nogo-66 antigens includes both strong T cell and B cell activation, with epitope spreading of the antibody response to other myelin molecules. In CNS immunotherapy, careful targeting of neural self-antigens is a prerequisite in order to avoid unexpected deleterious effects, and increasing knowledge about the immune response to Nogo-A may provide a safe basis for the development of relevant therapeutic alternatives for several neurological conditions.

A re-assessment of the consequences of delayed transplantation of olfactory lamina propria following complete spinal cord transection in rats

This study is part of the NIH "Facilities of Research-Spinal Cord Injury" contract to support independent replication of published studies. We repeated a study reporting that delayed transplantation of olfactory lamina propria (OLP) into the site of a complete spinal cord transection led to significant improvement in hindlimb motor function and induced axon regeneration. Adult female rats received complete spinal cord transections at T10. Thirty days post-injury, pieces of OLP, which contains olfactory ensheathing cells (OECs), or respiratory lamina propria (RLP), which should not contain OECs, were placed into the transection site. Hindlimb motor function was tested using the BBB scale from day 1 post-injury through 10 weeks following transplantation. To assess axonal regeneration across the transection site, Fluorogold was injected into the distal segment, and the distribution of 5HT-containing axons was assessed using immunostaining. BBB analyses revealed no significant recovery after OLP transplantation and no significant differences between OLP vs. RLP transplant groups. Fluorogold injections into caudal segments did not lead to retrograde labeling in any animals. Immunostaining for 5HT revealed that a few 5HT-labeled axons extended into both RLP and OLP transplants and a few 5HT-labeled axons were present in sections caudal to the injury in 2 animals that received OLP transplants and 1 animal that received RLP transplants. Our results indicate that, although OLP transplants may stimulate regeneration under some circumstances, the effect is not so robust as to reliably overcome the hostile setting created by a complete transection paradigm.

Why do Nogo/Nogo-66 receptor gene knockouts result in inferior regeneration compared to treatment with neutralizing agents?

IN-1, the monoclonal antibody against the exon 3-encoded N-terminal domain of Nogo-A, and the Nogo-66 receptor (NgR) antagonist NEP1-40 have both shown efficacy in promoting regeneration in animal spinal cord injury models, the latter even when administered subcutaneously 1 week after injury. These results are supportive of the hypothesis that the Nogo-NgR axis is a major path for inhibition of spinal cord axonal regeneration and uphold the promises of these neutralizing agents in clinical applications. However, mice with targeted disruption of Nogo and NgR have, surprisingly, only modest regenerative capacity (if any) compared with treatment with IN-1 or NEP1-40. Disruption of the Nogo gene by various groups yielded results ranging from significant regenerative improvement in young mice to no improvement. Likewise, knockout of NgR produced some improvement in raphespinal and rubrospinal axonal regeneration, but not that of corticospinal neurons. Other than invoking possible differences in genetic background, we suggest here some possible and testable explanations for the above phenomena. These possibilities include effects of IN-1 and NEP1-40 on the CNS beyond neutralization of Nogo and NgR functions, and the latter's possible role in the CNS beyond that of neuronal growth inhibition.