Identification of neuroprotective properties of anti-MAG antibody: a novel approach for the treatment of stroke?

Case Report: Presence of Anti-MAG in the CSF Can Be Associated With a Neurodegenerative Process With Frontal Involvement

Background

Autoimmune encephalitis (AIE) is an increasingly broad nosological framework that may clinically mimic neurodegenerative diseases (NDDs).

Cases Reported

We describe here the clinical, radiological, electrophysiological, and biological evolution of three patients. Two women aged 73 and 72 years and a 69-year-old man presented with complex cognitive and focal neurological symptoms and each had a predominant frontal dysexecutive involvement and an unexpectedly high titer of anti-MAG antibodies in the serum and cerebrospinal fluid (CSF). The question of an autoimmune cause was raised. After 2 years of follow-up and, for two of them, without improvement despite immunosuppressive treatments, diagnoses of NDD were eventually retained: post-radiation encephalopathy, progressive supranuclear palsy (PSP), and Alzheimer's disease.

Conclusion

The presence of a high titer of anti-MAG antibodies may be found in NDD. It could reflect cerebral tissue damages, particularly in the case of significant frontal involvement. Atypical presentations may lead to a search for a paraneoplastic neurologic syndrome or AIE. However, the indirect immunofluorescence staining positivity on a monkey cerebellum section linked with anti-MAG antibodies should not lead to those diagnoses being retained.

Myelin-associated glycoprotein activation triggers glutamate uptake by oligodendrocytes in vitro and contributes to ameliorate glutamate-mediated toxicity in vivo

BACKGROUND

Myelin-associated glycoprotein (MAG) is a key molecule involved in the nurturing effect of myelin on ensheathed axons. MAG also inhibits axon outgrowth after injury. In preclinical stroke models, administration of a function-blocking anti-MAG monoclonal antibody (mAb) aimed to improve axon regeneration demonstrated reduced lesion volumes and a rapid clinical improvement, suggesting a mechanism of immediate neuroprotection rather than enhanced axon regeneration. In addition, it has been reported that antibody-mediated crosslinking of MAG can protect oligodendrocytes (OLs) against glutamate (Glu) overload by unknown mechanisms.

PURPOSE

To unravel the molecular mechanisms underlying the protective effect of anti-MAG therapy with a focus on neuroprotection against Glu toxicity.

RESULTS

MAG activation (via antibody crosslinking) triggered the clearance of extracellular Glu by its uptake into OLs via high affinity excitatory amino acid transporters. This resulted not only in protection of OLs but also nearby neurons. MAG activation led to a PKC-dependent activation of factor Nrf2 (nuclear-erythroid related factor-2) leading to antioxidant responses including increased mRNA expression of metabolic enzymes from the glutathione biosynthetic pathway and the regulatory chain of cystine/Glu antiporter system xc^- increasing reduced glutathione (GSH), the main antioxidant in cells. The efficacy of early anti-MAG mAb administration was demonstrated in a preclinical model of excitotoxicity induced by intrastriatal Glu administration and extended to a model of Experimental Autoimmune Encephalitis showing axonal damage secondary to demyelination.

CONCLUSIONS

MAG activation triggers Glu uptake into OLs under conditions of Glu overload and induces a robust protective antioxidant response.

Therapeutic antibodies - natural and pathological barriers and strategies to overcome them

Antibody-based therapeutics have become a major class of therapeutics with over 120 recombinant antibodies approved or under review in the EU or US. This therapeutic class has experienced a remarkable expansion with an expected acceleration in 2021-2022 due to the extraordinary global response to SARS-CoV2 pandemic and the public disclosure of over a hundred anti-SARS-CoV2 antibodies. Mainly delivered intravenously, alternative delivery routes have emerged to improve antibody therapeutic index and patient comfort. A major hurdle for antibody delivery and efficacy as well as the development of alternative administration routes, is to understand the different natural and pathological barriers that antibodies face as soon as they enter the body up to the moment they bind to their target antigen. In this review, we discuss the well-known and more under-investigated extracellular and cellular barriers faced by antibodies. We also discuss some of the strategies developed in the recent years to overcome these barriers and increase antibody delivery to its site of action. A better understanding of the biological barriers that antibodies have to face will allow the optimization of antibody delivery near its target. This opens the way to the development of improved therapy with less systemic side effects and increased patients' adherence to the treatment.

Proof-of-Concept Randomized Trial of the Monoclonal Antibody GSK249320 Versus Placebo in Stroke Patients

Supplemental Digital Content is available in the text.

Background and Purpose—

One class of poststroke restorative therapy focuses on promoting axon outgrowth by blocking myelin-based inhibitory proteins such as myelin-associated glycoprotein. The purpose of the current study was to extend preclinical and clinical findings of GSK249320, a humanized monoclonal antibody to myelin-associated glycoprotein with disabled Fc region, to explore effects on motor outcomes poststroke.

Methods—

In this phase IIb double-blind, randomized, placebo-controlled study, patients at 30 centers with ischemic stroke 24 to 72 hours prior and gait deficits were randomized to 2 IV infusions of GSK249320 or placebo. Primary outcome measure was change in gait velocity from baseline to day 90.

Results—

A total of 134 subjects were randomized between May 2013 and July 2014. The 2 groups were overall well matched at baseline. The study was stopped at the prespecified interim analysis because the treatment difference met the predefined futility criteria cutoff; change in gait velocity to day 90 was 0.55±0.46 (mean±SD) in the GSK249320 group and 0.56±0.50 for placebo. Secondary end points including upper extremity function were concordant. The 2 IV infusions of GSK249320 were well tolerated. No neutralizing antibodies to GSK249320 were detected.

Conclusions—

GSK249320, within 72 hours of stroke, demonstrated no improvement on gait velocity compared with placebo. Possible reasons include challenges translating findings into humans and no direct evidence that the therapy reached the biological target. The antibody was well tolerated and showed low immunogenicity, findings potentially useful to future studies aiming to use a monoclonal antibody to modify activity in specific biological pathways to improve recovery from stroke.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01808261.

The Involvement of the Myelin-Associated Inhibitors and Their Receptors in CNS Plasticity and Injury

The limited capacity for the central nervous system (CNS) to repair itself was first described over 100 years ago by Spanish neuroscientist Ramon Y. Cajal. However, the exact mechanisms underlying this failure in neuronal regeneration remain unclear and, as such, no effective therapeutics yet exist. Numerous studies have attempted to elucidate the biochemical and molecular mechanisms that inhibit neuronal repair with increasing evidence suggesting that several inhibitory factors and repulsive guidance cues active during development actually persist into adulthood and may be contributing to the inhibition of repair. For example, in the injured adult CNS, there are various inhibitory factors that impede the outgrowth of neurites from damaged neurons. One of the most potent of these neurite outgrowth inhibitors is the group of proteins known as the myelin-associated inhibitors (MAIs), present mainly on the membranes of oligodendroglia. Several studies have shown that interfering with these proteins can have positive outcomes in CNS injury models by promoting neurite outgrowth and improving functional recovery. As such, the MAIs, their receptors, and downstream effectors are valid drug targets for the treatment of CNS injury. This review will discuss the current literature on MAIs in the context of CNS development, plasticity, and injury. Molecules that interfere with the MAIs and their receptors as potential candidates for the treatment of CNS injury will additionally be introduced in the context of preclinical and clinical trials.

Correlates of Post-Stroke Brain Plasticity, Relationship to Pathophysiological Settings and Implications for Human Proof-of-Concept Studies

The promotion of neurological recovery by enhancing neuroplasticity has recently obtained strong attention in the stroke field. Experimental studies support the hypothesis that stroke recovery can be improved by therapeutic interventions that augment neuronal sprouting. However plasticity responses of neurons are highly complex, involving the growth and differentiation of axons, dendrites, dendritic spines and synapses, which depend on the pathophysiological setting and are tightly controlled by extracellular and intracellular signals. Thorough mechanistic insights are needed into how neuronal plasticity is influenced by plasticity-promoting therapies in order not to risk the success of future clinical proof-of-concept studies.

GSK249320, A Monoclonal Antibody Against the Axon Outgrowth Inhibition Molecule Myelin-Associated Glycoprotein, Improves Outcome of Rodents with Experimental Stroke

Myelin-associated glycoprotein (MAG) is an inhibitor of axon growth. MAG levels increase after stroke. GSK249320 is a monoclonal antibody that neutralizes MAG-mediated inhibition and so may promote axon outgrowth and improve post-stroke outcomes. The current study tested the hypothesis that GSK249320 initiated 24 hours or 7 days after experimental stroke improves behavioural outcomes. Rats with right middle cerebral artery occlusion for 90 minutes were randomized to receive 6 weeks of intravenous (a) GSK249320 starting 24 hours post-stroke, (b) GSK249320 starting 7 days post-stroke, or (c) vehicle. Behavioral testing was performed over 7 weeks. Serial MRI demonstrated no differences in infarct volume across groups. Animals treated with GSK249320 24 hours post-stroke showed larger increases in Neuroscore (time X group, p = 0.0008) and staircase test (main effect of group, p = 0.0214) as compared to controls, but animals treated 7 days post-stroke showed no significant behavioral benefit. No significant results were found for the sticky tape or cylinder tests. A separate set of animals with experimental stroke received a single intravenous dose of GSK249320 or vehicle at 1 hour, 24 hours, 48 hours or 1 week post-stroke, and immunohistochemistry methods were used to measure GSK249320 distribution; GSK249320 was found in the ipsilesional hemisphere only, the extent of which increased with later times of injection. These data suggest that intravenous GSK249320 penetrates the lesion site and is associated with a small effect on functional outcomes when initiated 24 hours post-stroke and so support the translational potential of this monoclonal antibody as a restorative therapy for patients with stroke.

Therapeutic Targeting of Siglecs using Antibody- and Glycan-Based Approaches

The sialic acid-binding immunoglobulin-like lectins (Siglecs) are a family of immunomodulatory receptors whose functions are regulated by their glycan ligands. Siglecs are attractive therapeutic targets because of their cell type-specific expression pattern, endocytic properties, high expression on certain lymphomas/leukemias, and ability to modulate receptor signaling. Siglec-targeting approaches with therapeutic potential encompass antibody- and glycan-based strategies. Several antibody-based therapies are in clinical trials and continue to be developed for the treatment of lymphoma/leukemia and autoimmune disease, while the therapeutic potential of glycan-based strategies for cargo delivery and immunomodulation is a promising new approach. Here we review these strategies with special emphasis on emerging approaches and disease areas that may benefit from targeting the Siglec family.

Effects of Postinfarct Myelin-Associated Glycoprotein Antibody Treatment on Motor Recovery and Motor Map Plasticity in Squirrel Monkeys

Background and Purpose—

New insights into the brain’s ability to reorganize after injury are beginning to suggest novel restorative therapy targets. Potential therapies include pharmacological agents designed to promote axonal growth. The purpose of this study was to test the efficacy of one such drug, GSK249320, a monoclonal antibody that blocks the axon outgrowth inhibition molecule, myelin-associated glycoprotein, to facilitate recovery of motor skills in a nonhuman primate model of ischemic cortical damage.

Methods—

Using a between-groups repeated-measures design, squirrel monkeys were randomized to 1 of 2 groups: an experimental group received intravenous GSK249320 beginning 24 hours after an ischemic infarct in motor cortex with repeated dosages given at 1-week intervals for 6 weeks and a control group received only the vehicle at matched time periods. The primary end point was a motor performance index based on a distal forelimb reach-and-retrieval task. Neurophysiological mapping techniques were used to determine changes in spared motor representations.

Results—

All monkeys recovered to baseline motor performance levels by postinfarct day 16. Functional recovery in the experimental group was significantly facilitated on the primary end point, albeit using slower movements. At 7 weeks post infarct, motor maps in the spared ventral premotor cortex in the experimental group decreased in area compared with the control group.

Conclusions—

GSK249320, initiated 24 hours after a focal cortical ischemic infarct, facilitated functional recovery. Together with the neurophysiological data, these results suggest that GSK249320 has a substantial biological effect on spared cortical tissue. However, its mechanisms of action may be widespread and not strictly limited to peri-infarct cortex and nearby premotor areas.

Human NgR-Fc decoy protein via lumbar intrathecal bolus administration enhances recovery from rat spinal cord contusion

Axonal growth and neurological recovery after traumatic spinal cord injury (SCI) is limited by the presence of inhibitory proteins in myelin, several of which act via the NgR1 protein in neurons. A truncated soluble ligand-binding fragment of NgR1 serves as a decoy and promotes recovery in acute and chronic rodent SCI models. To develop the translational potential of these observations, we created a human sequence-derived NgR1(310)-Fc protein. This protein is active in vitro. When the human NgR1 decoy is administered by continuous intracerebroventricular infusion to rats with a spinal contusion injury at doses of 0.09-0.53 mg/kg/d, neurological recovery is improved. Effective doses double the percentage of rats able to bear weight on their hindlimbs. Next, we considered the half-life and distribution of NgR1(310)-Fc after bolus delivery to the lumbar intrathecal space. The protein is found throughout the neuraxis and has a tissue half-life of approximately 2 days in the rat, and 5 days in the nonhuman primate. At an intermittent, once every 4 day, lumbar bolus dosing schedule of 0.14 mg/kg/d, NgR1(310)-Fc promoted locomotor rat recovery from spinal cord contusion at least as effectively as continuous infusion in open field and grid walking tasks. Moreover, the intermittent lumbar NgR1(310)-Fc treatment increased the growth of raphespinal axons into the lumbar spinal cord after injury. Thus, human NgR1(310)-Fc provides effective treatment for recovery from traumatic SCI in this preclinical model with a simplified administration regimen that facilitates clinical testing.

Finding an optimal rehabilitation paradigm after stroke: enhancing fiber growth and training of the brain at the right moment

After stroke the central nervous system reveals a spectrum of intrinsic capacities to react as a highly dynamic system which can change the properties of its circuits, form new contacts, erase others, and remap related cortical and spinal cord regions. This plasticity can lead to a surprising degree of spontaneous recovery. It includes the activation of neuronal molecular mechanisms of growth and of extrinsic growth promoting factors and guidance signals in the tissue. Rehabilitative training and pharmacological interventions may modify and boost these neuronal processes, but almost nothing is known on the optimal timing of the different processes and therapeutic interventions and on their detailed interactions. Finding optimal rehabilitation paradigms requires an optimal orchestration of the internal processes of re-organization and the therapeutic interventions in accordance with defined plastic time windows. In this review we summarize the mechanisms of spontaneous plasticity after stroke and experimental interventions to enhance growth and plasticity, with an emphasis on anti-Nogo-A immunotherapy. We highlight critical time windows of growth and of rehabilitative training and consider different approaches of combinatorial rehabilitative schedules. Finally, we discuss potential future strategies for designing repair and rehabilitation paradigms by introducing a “3 step model”: determination of the metabolic and plastic status of the brain, pharmacological enhancement of its plastic mechanisms, and stabilization of newly formed functional connections by rehabilitative training.

Microwave & Magnetic (M2) Proteomics of a Mouse Model of Mild Traumatic Brain Injury

Short-term increases in oxidative stress and decreases in motor function, including debilitating effects on balance and motor control, can occur following primary mild traumatic brain injuries (mTBI). However, the long-term effects on motor unit impairment and integrity as well as the molecular mechanisms underlying secondary injuries are poorly understood. We hypothesized that changes in central nervous system-specific protein (CSP) expression might correlate to these long-term effects. To test our hypothesis, we longitudinally assessed a closed-skull mTBI mouse model, vs. sham control, at 1, 7, 30, and 120 days post-injury. Motor impairment was determined by rotarod and grip strength performance measures, while motor unit integrity was determined using electromyography. Relative protein expression was determined by microwave & magnetic (M²) proteomics of ipsilateral brain tissue, as previously described. Isoprostane measurements were performed to confirm a primary oxidative stress response. Decoding the relative expression of 476 ± 56 top-ranked proteins for each specimen revealed statistically significant changes in the expression of two well-known CSPs at 1, 7 and 30 days post-injury: P < 0.001 for myelin basic protein (MBP) and P < 0.05 for myelin associated glycoprotein (MAG). This was confirmed by Western blot. Moreover, MAG, αII-spectrin (SPNA2) and neurofilament light (NEFL) expression at 30 days post-injury were directly related to grip strength (P < 0.05). While higher-powered studies of larger cohorts merit further investigation, this study supports the proof-of-concept that M² proteomics is a rapid method to quantify putative protein biomarkers and therapeutic targets of mTBI and suggests the feasibility of CSP expression correlations to long-term effects on motor impairment.

Therapeutic antibodies in stroke

Immunotherapy represents an active area of biomedical research to treat cancer, autoimmune diseases, and neurodegenerative disorders. In stroke, recanalization therapy is effective in reducing brain tissue damage after acute ischemic stroke. However, the narrow time window restricts its application for the majority of stroke patients. There is an urgent need to develop adjuvant therapies such as immunotherapy, stem cell replacement, and neuroprotective drugs. A number of molecules have been targeted for immunotherapy in stroke management, including myelin-associated proteins and their receptors, N-methyl-d-aspartic acid receptors, cytokines, and cell adhesion molecules. Both active vaccination and passive antibodies were tested in animal models of acute ischemic stroke. However, the mechanisms underlying the efficacy of immunotherapy are different for each target protein. Blocking myelin-associated proteins may enhance neuroplasticity, whereas blocking adhesion molecules may yield neuroprotection by suppressing the immune response after stroke. Although results from animal studies are encouraging, clinical trials using therapeutic antibodies failed to improve stroke outcome due to severe side effects. It remains a challenge to generate specific therapeutic antibodies with minimal side effects on other organs and systems.

Safety, Pharmacokinetics, and Pharmacodynamics of Escalating Repeat Doses of GSK249320 in Patients With Stroke

Background and Purpose—

Restorative therapies have the potential to improve function and reduce disability after stroke with a wide therapeutic window. The current study evaluated GSK249320, a monoclonal antibody that blocks the axon outgrowth inhibition molecule myelin-associated glycoprotein and also protects oligodendrocytes.

Methods—

Patients with mild-moderate stroke were randomized to intravenous GSK249320 (1, 5, or 15 mg/kg per infusion, in escalating cohorts of 8–9 subjects) versus placebo (n=17). Infusion 1 was 24 to 72 hours after stroke; infusion 2 was 9±1 days later. The primary objective evaluated safety and tolerability, and the secondary objectives evaluated immunogenicity, pharmacokinetics, biomarkers, neurophysiology, and motor function.

Results—

Baseline (n=42) characteristics were similar across treatment groups. No safety concerns were found based on adverse events, examination, vital signs, ECG, nerve conduction tests, brain imaging, motor function testing, and laboratory studies. Two of the 25 subjects dosed with GSK249320 developed transient antidrug antibodies after infusion 1. The pharmacokinetics profile was as expected for an IgG1 type monoclonal antibody. Serum levels of the biomarker S100β did not differ between groups. Global outcome measures were similar across groups. Modality-specific end points could be consistently measured in the first few days after stroke, and one of these, gait velocity, demonstrated a trend toward improvement with GSK249320 compared with placebo.

Conclusions—

GSK249320 was generally well tolerated. No major safety issues were identified in this first study of a monoclonal antibody to modulate the neurobiology of brain repair after stroke. Future studies might explore the efficacy of GSK249320 as a restorative therapy for stroke.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique Identifier: NCT00833989.

Modifying expression of EphA4 and its downstream targets improves functional recovery after stroke

Functional recovery after stroke varies greatly between patients, potentially due to differences in gene expression. Several processes like angiogenesis, neurogenesis, axonal reorganization and synaptic plasticity act in concert to restore neurological functions. The ephrin family has known roles in all these processes. EphA4 is the most abundant ephrin receptor in the nervous system. Therefore, we investigated whether EphA4 affects functional recovery from stroke, and evaluated the potential of this receptor as a therapeutic target. Motor recovery after photothrombotic stroke was studied in transgenic mice in which expression of EphA4 was reduced. Furthermore, blocking a downstream target of EphA4, ROCK (Rho-associated kinase), by two different compounds was evaluated in the same model. Motor recovery after photothrombotic stroke was markedly enhanced in transgenic mice with reduced levels of EphA4, whereas infarct sizes were similar compared with non-transgenic controls. Pharmacological inhibition of the EphA4 signaling cascade using two ROCK inhibitors,Y-27632 and fasudil, improved motor function of mice after stroke. Infarct size was comparable in all groups studied, suggesting that the benefit obtained by EphA4 inhibition is not neuroprotective in nature but due to an effect on the mechanisms underlying recovery. Our findings show that reduction of EphA4 improves motor function after experimental stroke and demonstrate that ROCK inhibition is a promising therapeutic strategy to enhance recovery after ischemic stroke.

Intracerebral chondroitinase ABC and heparan sulfate proteoglycan glypican improve outcome from chronic stroke in rats

Physical and chemical constraints imposed by the periinfarct glial scar may contribute to the limited clinical improvement often observed after ischemic brain injury. To investigate the role of some of these mediators in outcome from cerebral ischemia, we treated rats with the growth-inhibitory chondroitin sulfate proteoglycan neurocan, the growth-stimulating heparan sulfate proteoglycan glypican, or the chondroitin sulfate proteoglycan-degrading enzyme chondroitinase ABC. Neurocan, glypican, or chondroitinase ABC was infused directly into the infarct cavity for 7 d, beginning 7 d after middle cerebral artery occlusion. Glypican and chondroitinase ABC reduced glial fibrillary acidic protein immunoreactivity and increased microtubule-associated protein-2 immunoreactivity in the periinfarct region, and glypican- and chondroitinase ABC-treated rats showed behavioral improvement compared with neurocan- or saline-treated rats. Glypican and chondroitinase ABC also increased neurite extension in cortical neuron cultures. Glypican increased fibroblast growth factor-2 expression and chondroitinase ABC increased brain-derived neurotrophic factor expression in these cultures, whereas no such effects were seen following neurocan treatment. Thus, treatment with glypican or enzymatic disruption of neurocan with chondroitinase ABC improves gross anatomical, histological, and functional outcome in the chronic phase of experimental stroke in rats. Changes in growth factor expression and neuritogenesis may help to mediate these effects.

Potential treatment strategies for enhancing neuroplasticity and regeneration after ischemic stroke

Strokes are a major cause of death and result in a drastic reduction in quality of life. Novel therapeutic strategies for patients suffering from stroke are thus required. Two possible strategies can be proposed for treating ischemic stroke: enhancing neuroplasticity, allowing the surviving neuronal cells to compensate for stroke-related impairment through brain reorganization, sprouting and rewiring of neuronal cells, or regeneration of neuronal cells, including enhancement of intrinsic neurogenesis and stem cell transplantation therapy with neural stem cells, embryonic stem cells or induced pluripotent stem cells. Endogenous neurogenesis or transplanted neural stem cells, embryonic stem cells or induced pluripotent stem cell-derived cells are able to not only supply newborn neurons integrated into a damaged neuronal network, but also produce growth factors into the recovering brains. These secretory factors enhance sprouting and angiogenesis and may be important in neuroplasticity and recovery in the poststroke brain.

The Injured and Regenerating Nervous System

Understanding restricted functional recovery and designing efficient treatments to alleviate dysfunction after injury of the nervous system remain major challenges in neuroscience and medicine. Numerous molecules of potential significance in neural repair have been identified in vitro, but only few of these have proved to be of major importance in vivo up to now. Among the molecules involved in regeneration are several members of the immunoglobulin superfamily, most notably the neural cell adhesion molecules L1, its close homologue CHL1, and NCAM and, in particular, its polysialic acid glycan moiety. Sufficient evidence is now available to justify the statement that these molecules are major players not only in nervous system development but also in the adult during neural repair and synaptic plasticity. Importantly, insights into the functions of these molecules in promoting or inhibiting functional recovery have allowed the design and assessment of therapeutic approaches in animal models of central nervous system injury that could prove to be applicable in clinical settings.

Myelin-associated glycoprotein protects neurons from excitotoxicity

In addition to supporting rapid nerve conduction, myelination nurtures and stabilizes axons and protects them from acute toxic insults. One myelin molecule that protects and sustains axons is myelin-associated glycoprotein (MAG). MAG is expressed on the innermost wrap of myelin, apposed to the axon surface, where it interacts with axonal receptors that reside in lateral membrane domains including gangliosides, the glycosylphosphatidylinositol-anchored Nogo receptors, and β1-integrin. We report here that MAG protection extends beyond the axon to the neurons from which those axons emanate, protecting them from excitotoxicity. Compared to wild type mice, Mag-null mice displayed markedly increased seizure activity in response to intraperitoneal injection of kainic acid, an excitotoxic glutamate receptor agonist. Mag-null mice also had larger lesion volumes in response to intrastriatal injection of the excitotoxin NMDA. Prior injection of a soluble form of MAG partially protected Mag-null mice from NMDA-induced lesions. Hippocampal neurons plated on proteins extracted from wild-type rat or mouse myelin were resistant to kainic acid-induced excitotoxicity, whereas neurons plated on proteins from Mag-null myelin were not. Protection was reversed by anti-MAG antibody and replicated by addition of soluble MAG. MAG-mediated protection from excitotoxicity was dependent on Nogo receptors and β1-integrin. We conclude that MAG engages membrane-domain resident neuronal receptors to protect neurons from excitotoxicity, and that soluble MAG mitigates excitotoxic damage in vivo.

Physical exercise and cognitive recovery in acquired brain injury: a review of the literature

OBJECTIVE

Physical exercise has been shown to play an ever-broadening role in the maintenance of overall health and has been implicated in the preservation of cognitive function in both healthy elderly and demented populations. Animal and human studies of acquired brain injury (ABI) from trauma or vascular causes also suggest a possible role for physical exercise in enhancing cognitive recovery.

DATA SOURCES

A review of the literature was conducted to explore the current understanding of how physical exercise impacts the molecular, functional, and neuroanatomic status of both intact and brain-injured animals and humans.

STUDY SELECTION

Searches of the MEDLINE, CINHAL, and PsychInfo databases yielded an extensive collection of animal studies of physical exercise in ABI. Animal studies strongly tie physical exercise to the upregulation of multiple neural growth factor pathways in brain-injured animals, resulting in both hippocampal neurogenesis and functional improvements in memory.

DATA EXTRACTION

A search of the same databases for publications involving physical exercise in human subjects with ABI yielded 24 prospective and retrospective studies.

DATA SYNTHESIS

Four of these evaluated cognitive outcomes in persons with ABI who were involved in physical exercise. Three studies cited a positive association between exercise and improvements in cognitive function, whereas one observed no effect. Human exercise interventions varied greatly in duration, intensity, and level of subject supervision, and tools for assessing neurocognitive changes were inconsistent.

CONCLUSIONS

There is strong evidence in animal ABI models that physical exercise facilitates neurocognitive recovery. Physical exercise interventions are safe in the subacute and rehabilitative phases of recovery for humans with ABI. In light of strong evidence of positive effects in animal studies, more controlled, prospective human interventions are warranted to better explore the neurocognitive effects of physical exercise on persons with ABI.

The development of stroke therapeutics: promising mechanisms and translational challenges

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. Intravenous thrombolysis with rt-PA remains the only available acute therapy in patients who present within 3h of stroke onset other than the recently approved mechanical MERCI device, substantiating the high unmet need in available stroke therapeutics. The development of successful therapeutic strategies remains challenging, as evidenced by the continued failures of new therapies in clinical trials. However, significant lessons have been learned and this knowledge is currently being incorporated into improved pre-clinical and clinical design. Furthermore, advancements in imaging technologies and continued progress in understanding biological pathways have established a prolonged presence of salvageable penumbral brain tissue and have begun to elucidate the natural repair response initiated by ischemic insult. We review important past and current approaches to drug development with an emphasis on implementing principles of translational research to achieve a rigorous conversion of knowledge from bench to bedside. We highlight current strategies to protect and repair brain tissue with the promise to provide longer therapeutic windows, preservation of multiple tissue compartments and improved clinical success.

Intra-peritoneal injection of polyclonal anti-interferon alpha antibodies cross the blood brain barrier and neutralize interferon alpha

The central nervous system (CNS) is known to be an immunologically privileged organ in the body largely because the blood brain barrier (BBB) prevents the flow of large molecules, proteins, and cells from crossing into the CNS from the periphery. These restrictive properties of the BBB have made it difficult to treat CNS diseases. In this study, mice were infected intracranially (i.c.) with Sindbis virus (SV) and then treated either i.c. or intraperitoneally (i.p.) with neutralizing antibodies against interferon alpha (IFNalpha). SV infected control mice received i.p. saline. Antibodies against mouse IFNalpha were detected in the brain tissue of mice that received i.p. and i.c. injections of the antibody. ELISA analysis showed that both i.c. and i.p. antibody treated mice had significantly decreased levels of IFNalpha in the brain tissue. Also, mice that received IFNalpha neutralizing antibodies showed decreased presence of protein kinase R (PKR) measured by immunohistochemical densitometry, indicating the antibody successfully inhibited IFNalpha. The data shows that antibodies are capable of crossing the BBB and inhibiting IFNalpha, indicating that it is possible to target molecules of interest in the CNS with peripheral antibody treatment.

Neuronal plasticity and functional recovery after ischemic stroke

Ischemic stroke affects many new patients each year. The sequelae of brain ischemia can include lasting sensorimotor and cognitive deficits, which negatively impact quality of life. Currently, treatment options for improving poststroke deficits are limited, and the development of new clinical alternatives to improve functional recovery after stroke is actively under investigation. Anti-Nogo-A immunotherapy to reduce the central nervous system inhibitory environment, cell transplantation strategies, pharmacological agents, and movement-based therapies represent emerging treatments of poststroke deficits through enhancement of neuroanatomical plasticity.

Myelin-associated glycoprotein-mediated signaling in central nervous system pathophysiology

The myelin-associated glycoprotein (MAG) is a type I membrane-spanning protein expressed exclusively in oligodendrocytes and Schwann cells. It has two generally known pathophysiological roles in the central nervous system (CNS): maintenance of myelin integrity and inhibition of CNS axonal regeneration. The subtle CNS phenotype resulting from genetic ablation of MAG expression has made mechanistic analysis of its functional role in these difficult. However, the past few years have brought some major revelations, particularly in terms of mechanisms of MAG signaling through the Nogo-66 receptor (NgR) complex. Although apparently converging through NgR, a readily noticeable fact is that the neuronal growth inhibitory effect of MAG differs from that of Nogo-66. This may result from the influence of coreceptors in the form of gangliosides or from MAG-specific neuronal receptors such as NgR2. MAG has several other neuronal binding partners, and some of these may modulate its interaction with the NgR complex or downstream signaling. This article discusses new findings in MAG-forward and -reverse signaling and its role in CNS pathophysiology.

Tissue sparing and functional recovery following experimental traumatic brain injury is provided by treatment with an anti-myelin-associated glycoprotein antibody

Axonal injury is a hallmark of traumatic brain injury (TBI) and is associated with a poor clinical outcome. Following central nervous system injury, axons regenerate poorly, in part due to the presence of molecules associated with myelin that inhibit axonal outgrowth, including myelin-associated glycoprotein (MAG). The involvement of MAG in neurobehavioral deficits and tissue loss following experimental TBI remains unexplored and was evaluated in the current study using an MAG-specific monoclonal antibody (mAb). Anesthetized rats (n=102) were subjected to either lateral fluid percussion brain injury (n=59) or sham injury (n=43). In surviving animals, beginning at 1 h post-injury, 8.64 microg anti-MAG mAb (n=33 injured, n=21 sham) or control IgG (n=26 injured, n=22 sham) was infused intracerebroventricularly for 72 h. One group of these rats (n=14 sham, n=11 injured) was killed at 72 h post-injury for verification of drug diffusion and MAG immunohistochemistry. All other animals were evaluated up to 8 weeks post-injury using tests for neurologic motor, sensory and cognitive function. Hemispheric tissue loss was also evaluated at 8 weeks post-injury. At 72 h post-injury, increased immunoreactivity for MAG was seen in the ipsilateral cortex, thalamus and hippocampus of brain-injured animals, and anti-MAG mAb was detectable in the hippocampus, fimbria and ventricles. Brain-injured animals receiving anti-MAG mAb showed significantly improved recovery of sensorimotor function at 6 and 8 weeks (P<0.01) post-injury when compared with brain-injured IgG-treated animals. Additionally, at 8 weeks post-injury, the anti-MAG mAb-treated brain-injured animals demonstrated significantly improved cognitive function and reduced hemispheric tissue loss (P<0.05) when compared with their brain-injured controls. These results indicate that MAG may contribute to the pathophysiology of experimental TBI and treatment strategies that target MAG may be suitable for further evaluation.

Myelin-associated glycoprotein (MAG): past, present and beyond

The myelin-associated glycoprotein (MAG) is a type I transmembrane glycoprotein localized in periaxonal Schwann cell and oligodendroglial membranes of myelin sheaths where it functions in glia-axon interactions. It contains five immunoglobulin (Ig)-like domains and is in the sialic acid-binding subgroup of the Ig superfamily. It appears to function both as a ligand for an axonal receptor that is needed for the maintenance of myelinated axons and as a receptor for an axonal signal that promotes the differentiation, maintenance and survival of oligodendrocytes. Its function in the maintenance of myelinated axons may be related to its role as one of the white matter inhibitors of neurite outgrowth acting through a receptor complex involving the Nogo receptor and/or gangliosides containing 2,3-linked sialic acid. MAG is expressed as two developmentally regulated isoforms with different cytoplasmic domains that may activate different signal transduction pathways in myelin-forming cells. MAG contains a carbohydrate epitope shared with other glycoconjugates that is a target antigen in autoimmune peripheral neuropathy associated with IgM gammopathy and has been implicated in a dying back oligodendrogliopathy in multiple sclerosis.

Role of matrix metalloproteinases in delayed cortical responses after stroke

Matrix metalloproteinases (MMPs) are zinc-endopeptidases with multifactorial actions in central nervous system (CNS) physiology and pathology. Accumulating data suggest that MMPs have a deleterious role in stroke. By degrading neurovascular matrix, MMPs promote injury of the blood-brain barrier, edema and hemorrhage. By disrupting cell-matrix signaling and homeostasis, MMPs trigger brain cell death. Hence, there is a movement toward the development of MMP inhibitors for acute stroke therapy. But MMPs may have a different role during delayed phases after stroke. Because MMPs modulate brain matrix, they may mediate beneficial plasticity and remodeling during stroke recovery. Here, we show that MMPs participate in delayed cortical responses after focal cerebral ischemia in rats. MMP-9 is upregulated in peri-infarct cortex at 7-14 days after stroke and is colocalized with markers of neurovascular remodeling. Treatment with MMP inhibitors at 7 days after stroke suppresses neurovascular remodeling, increases ischemic brain injury and impairs functional recovery at 14 days. MMP processing of bioavailable VEGF may be involved because inhibition of MMPs reduces endogenous VEGF signals, whereas additional treatment with exogenous VEGF prevents MMP inhibitor-induced worsening of infarction. These data suggest that, contrary to MMP inhibitor therapies for acute stroke, strategies that modulate MMPs may be needed for promoting stroke recovery.