Axonal loss and gray matter pathology as a direct result of autoimmunity to neurofilaments

Active Induction of a Multiple Sclerosis-Like Disease in Common Laboratory Mouse Strains

Experimental autoimmune encephalomyelitis (EAE) is a neuroinflammatory disease with facets in common with multiple sclerosis (MS). It is induced in susceptible mammalian species, with rodents as the preferred hosts, and has been used for decades as a model to investigate the immunopathogenesis of MS as well as for preclinical evaluation of candidate MS therapeutics. Most commonly, EAE is generated by active immunization with central nervous system (CNS) antigens, such as whole CNS homogenate, myelin proteins, or peptides derived from these proteins. However, EAE actually represents a spectrum of diseases in which specific combinations of host/CNS antigen exhibit defined clinical profiles, each associated with unique immunological and pathological features. Similar to MS, EAE is a complex disease where development and progression are also modulated by environmental factors; therefore, the establishment of any given EAE variant can be challenging and requires careful optimization. Here, we describe protocols for three EAE variants, successfully generated in our laboratory, and provide additional information as to how to maintain their unique features and reproducibility.

Autoimmunity to a ribonucleoprotein drives neuron loss in multiple sclerosis models

Neurodegeneration, the progressive loss or damage to neurons and axons, underlies permanent disability in multiple sclerosis (MS); yet its mechanisms are incompletely understood. Recent data indicates autoimmunity to several intraneuronal antigens, including the RNA binding protein (RBP) heterogenous nuclear ribonucleoprotein A1 (hnRNP A1), as contributors to neurodegeneration. We previously showed that addition of anti-hnRNP A1 antibodies, which target the same immunodominant domain of MS IgG, to mice with experimental autoimmune encephalomyelitis (EAE) worsened disease and resulted in an exacerbation of hnRNP A1 dysfunction including cytoplasmic mislocalization of hnRNP A1, stress granule (SG) formation and neurodegeneration in the chronic stages of disease. Because this previous study focused on a singular timepoint during EAE, it is unclear whether anti-hnRNP A1 antibody induced hnRNP A1 dysfunction caused neurodegeneration or was result of it. In the present study, we analyzed in vivo and in vitro models of anti-hnRNP A1 antibody-mediated autoimmunity for markers of hnRNP A1 dysfunction and neurodegeneration over a time course to gain a better understanding of the connection between hnRNP A1 dysfunction and neurodegeneration. Anti-hnRNP A1 antibody treatment resulted in increased neuronal hnRNP A1 mislocalization and nuclear depletion temporally followed by altered RNA expression and SG formation, and lastly an increase in necroptotic signalling and neuronal cell death. Treatment with necrostatin-1s inhibited necroptosis and partially rescued anti-hnRNP A1 antibody-mediated neurodegeneration while clathrin knockdown specifically inhibited anti-hnRNP A1 antibody uptake into neurons. This data identifies a novel antibody-mediated mechanism of neurodegeneration, which may be targeted to inhibit neurodegeneration and prevent permanent neurological decline in persons living with MS.

Pro-Inflammatory Cytokines and Antibodies Induce hnRNP A1 Dysfunction in Mouse Primary Cortical Neurons

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system with a significant neurodegenerative component. Dysfunctional RNA-binding proteins (RBPs) are causally linked to neuronal damage and are a feature of MS, including the mislocalization of the RBP heterogeneous nuclear ribonucleoprotein A1 (A1). Here, we show that primary neurons exposed to pro-inflammatory cytokines and anti-A1 antibodies, both characteristic of an MS autoimmune response, displayed increased A1 mislocalization, stress granule formation, and decreased neurite length, a marker of neurodegeneration. These findings illustrate a significant relationship between secreted immune factors, A1 dysfunction, and neuronal damage in a disease-relevant model system.

Platelets in Multiple Sclerosis: Early and Central Mediators of Inflammation and Neurodegeneration and Attractive Targets for Molecular Imaging and Site-Directed Therapy

Platelets are clearly central to thrombosis and hemostasis. In addition, more recently, evidence has emerged for non-hemostatic roles of platelets including inflammatory and immune reactions/responses. Platelets express immunologically relevant ligands and receptors, demonstrate adhesive interactions with endothelial cells, monocytes and neutrophils, and toll-like receptor (TLR) mediated responses. These properties make platelets central to innate and adaptive immunity and potential candidate key mediators of autoimmune disorders. Multiple sclerosis (MS) is the most common chronic autoimmune central nervous system (CNS) disease. An association between platelets and MS was first indicated by the increased adhesion of platelets to endothelial cells. This was followed by reports identifying structural and functional changes of platelets, their chronic activation in the peripheral blood of MS patients, platelet presence in MS lesions and the more recent revelation that these structural and functional abnormalities are associated with all MS forms and stages. Investigations based on the murine experimental autoimmune encephalomyelitis (EAE) MS model first revealed a contribution to EAE pathogenesis by exacerbation of CNS inflammation and an early role for platelets in EAE development via platelet-neuron and platelet-astrocyte associations, through sialated gangliosides in lipid rafts. Our own studies refined and extended these findings by identifying the critical timing of platelet accumulation in pre-clinical EAE and establishing an initiating and central rather than merely exacerbating role for platelets in disease development. Furthermore, we demonstrated platelet-neuron associations in EAE, coincident with behavioral changes, but preceding the earliest detectable autoreactive T cell accumulation. In combination, these findings establish a new paradigm by asserting that platelets play a neurodegenerative as well as a neuroinflammatory role in MS and therefore, that these two pathological processes are causally linked. This review will discuss the implications of these findings for our understanding of MS, for future applications for imaging toward early detection of MS, and for novel strategies for platelet-targeted treatment of MS.

Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation

Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.

The Potential Contribution of Dysfunctional RNA-Binding Proteins to the Pathogenesis of Neurodegeneration in Multiple Sclerosis and Relevant Models

Neurodegeneration in multiple sclerosis (MS) is believed to underlie disease progression and permanent disability. Many mechanisms of neurodegeneration in MS have been proposed, such as mitochondrial dysfunction, oxidative stress, neuroinflammation, and RNA-binding protein dysfunction. The purpose of this review is to highlight mechanisms of neurodegeneration in MS and its models, with a focus on RNA-binding protein dysfunction. Studying RNA-binding protein dysfunction addresses a gap in our understanding of the pathogenesis of MS, which will allow for novel therapies to be generated to attenuate neurodegeneration before irreversible central nervous system damage occurs.

Dysfunctional RNA-binding protein biology and neurodegeneration in experimental autoimmune encephalomyelitis in female mice

Altered stress granule (SG) and RNA-binding protein (RBP) biology have been shown to contribute to the pathogenesis of several neurodegenerative diseases, yet little is known about their role in multiple sclerosis (MS). Pathological features associated with dysfunctional RBPs include RBP mislocalization from its normal nuclear location to the cytoplasm and the formation of chronic SGs. We tested the hypothesis that altered SG and RBP biology might contribute to the neurodegeneration in experimental autoimmune encephalomyelitis (EAE). C57BL/6 female mice were actively immunized with MOG_35-55 to induce EAE. Spinal cords were examined for mislocalization of the RBPs, heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and TAR-DNA binding protein-43 (TDP-43), SGs, neurodegeneration (SMI-32), T cells (CD3), and macrophages (CD68). In contrast to naive mice, mice with EAE showed SG formation (p < 0.0001) and mislocalization of hnRNP A1 (p < 0.05) in neurons of the ventral spinal cord gray matter, which correlated with clinical score (R = 0.8104, p = 0.0253). In these same areas, there was a neuronal loss (p < 0.0001) and increased SMI-32 immunoreactivity (both markers of neurodegeneration) and increased staining for CD3⁺ T cells and IFN-gamma. These findings recapitulate the SG and RBP biology and markers of neurodegeneration in MS tissues and suggest that altered SG and RBP biology contribute to the neurodegeneration in EAE, which might also apply to the pathogenesis of MS.

Does cognitive dysfunction correlate with neurofilament light polypeptide levels in the CSF of patients with multiple sclerosis?

Objective

To investigate whether neurofilament light polypeptide (NfL) level in cerebrospinal fluid (CSF), currently a prognostic biomarker of neurodegeneration in patients with multiple sclerosis (MS), may be a potential biomarker of cognitive dysfunction in MS.

Methods

This observational case–control study included patients with MS. CSF levels of NfL were determined using enzyme-linked immunosorbent assay. Cognitive function was measured with the Brief International Cognitive Assessment for MS (BICAMS) battery and Paced Auditory Serial Addition Test (PASAT3), standardized to the Greek population.

Results

Of 39 patients enrolled (aged 42.7 ± 13.6 years), 36% were classified as cognitively impaired according to BICAMS z-scores (–0.34 ± 1.13). Relapsing MS was significantly better than progressive forms regarding BICAMS z-score (mean difference [MD] 1.39; 95% confidence interval [CI] 0.54, 2.24), Symbol Digit Modality Test score (MD 1.73; 95% CI 0.46, 3.0) and Greek Verbal Learning Test (MD 1.77; 95% CI 0.82, 2.72). An inversely proportional association between CSF NfL levels and BICAMS z-scores was found in progressive forms of MS (r_p = –0.944).

Conclusions

This study provides preliminary evidence for an association between CSF NfL levels and cognition in progressive forms of MS, which requires validation in larger samples.

Neurofilament light as an immune target for pathogenic antibodies

Antibodies to neuronal antigens are associated with many neurological diseases including paraneoplastic neurological disorders, epilepsy, amyotrophic lateral sclerosis and multiple sclerosis. Immunization with neuronal antigens such as neurofilament light (NF-L), a neuronal intermediate filament in axons, has been shown to induce neurological disease and spasticity in mice. Also, although antibodies to NF-L are widely used as surrogate biomarkers of axonal injury in amyotrophic lateral sclerosis and multiple sclerosis, it remains to be elucidated if antibodies to NF-L contribute to neurodegeneration and neurological disease. To address this, we examined the pathogenic role of antibodies directed to NF-L in vitro using spinal cord co-cultures and in vivo in experimental autoimmune encephalomyelitis (EAE) and optic neuritis animal models of multiple sclerosis. Here we show that peripheral injections of antibodies to NF-L augmented clinical signs of neurological disease in acute EAE, increased retinal ganglion cell loss in experimental optic neuritis and induced neurological signs following intracerebral injection into control mice. The pathogenicity of antibodies to NF-L was also observed in spinal cord co-cultures where axonal loss was induced. Taken together, our results reveal that as well as acting as reliable biomarkers of neuronal damage, antibodies to NF-L exacerbate neurological disease, suggesting that antibodies to NF-L generated during disease may also be pathogenic and play a role in the progression of neurodegeneration.

Contribution of the Degeneration of the Neuro-Axonal Unit to the Pathogenesis of Multiple Sclerosis

Multiple sclerosis (MS) is a demyelinating, autoimmune disease of the central nervous system. In recent years, it has become more evident that neurodegeneration, including neuronal damage and axonal injury, underlies permanent disability in MS. This manuscript reviews some of the mechanisms that could be responsible for neurodegeneration and axonal damage in MS and highlights the potential role that dysfunctional heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and antibodies to hnRNP A1 may play in MS pathogenesis.

Multiple sclerosis: experimental models and reality

One of the most frequent statements, provided in different variations in the introduction of experimental studies on multiple sclerosis (MS), is that "Multiple sclerosis is a demyelinating autoimmune disease and experimental autoimmune encephalomyelitis (EAE) is a suitable model to study its pathogenesis". However, so far, no single experimental model covers the entire spectrum of the clinical, pathological, or immunological features of the disease. Many different models are available, which proved to be highly useful for studying different aspects of inflammation, demyelination, remyelination, and neurodegeneration in the central nervous system. However, the relevance of results from such models for MS pathogenesis has to be critically validated. Current EAE models are mainly based on inflammation, induced by auto-reactive CD4+ T-cells, and these models reflect important aspects of MS. However, pathological data and results from clinical trials in MS indicate that CD8+ T-cells and B-lymphocytes may play an important role in propagating inflammation and tissue damage in established MS. Viral models may reflect key features of MS-like inflammatory demyelination, but are difficult to use due to their very complex pathogenesis, involving direct virus-induced and immune-mediated mechanisms. Furthermore, evidence for a role of viruses in MS pathogenesis is indirect and limited, and an MS-specific virus infection has not been identified so far. Toxic models are highly useful to unravel mechanisms of de- and remyelination, but do not reflect other important aspects of MS pathology and pathogenesis. For all these reasons, it is important to select the right experimental model to answer specific questions in MS research.

Autoantibodies to heterogeneous nuclear ribonuclear protein A1 (hnRNPA1) cause altered 'ribostasis' and neurodegeneration; the legacy of HAM/TSP as a model of progressive multiple sclerosis

Several years following its discovery in 1980, infection with human T-lymphotropic virus type 1 (HTLV-1) was shown to cause HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), a disease biologically similar to progressive forms of multiple sclerosis (MS). In this manuscript, we review some of the clinical, pathological, and immunological similarities between HAM/TSP and MS with an emphasis on how autoantibodies to an RNA binding protein, heterogeneous nuclear ribonuclear protein A1 (hnRNP A1), might contribute to neurodegeneration in immune mediated diseases of the central nervous system.

Antibodies to the RNA-binding protein hnRNP A1 contribute to neurodegeneration in a model of central nervous system autoimmune inflammatory disease

BACKGROUND

Neurodegeneration is believed to be the primary cause of permanent, long-term disability in patients with multiple sclerosis. The cause of neurodegeneration in multiple sclerosis appears to be multifactorial. One mechanism that has been implicated in the pathogenesis of neurodegeneration in multiple sclerosis is the targeting of neuronal and axonal antigens by autoantibodies. Multiple sclerosis patients develop antibodies to the RNA-binding protein, heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), which is enriched in neurons. We hypothesized that anti-hnRNP A1 antibodies would contribute to neurodegeneration in an animal model of multiple sclerosis.

METHODS

Following induction of experimental autoimmune encephalomyelitis (EAE) by direct immunization with myelin oligodendrocyte glycoprotein, mice were injected with anti-hnRNP A1 or control antibodies. Animals were examined clinically, and the central nervous system (CNS) tissues were tested for neurodegeneration with Fluoro-Jade C, a marker of degenerating neural elements.

RESULTS

Injection of anti-hnRNP A1 antibodies in mice with EAE worsened clinical disease, altered the clinical disease phenotype, and caused neurodegeneration preferentially in the ventral spinocerebellar tract and deep white matter of the cerebellum in the CNS. Neurodegeneration in mice injected with hnRNP A1-M9 antibodies compared to control groups was consistent with "dying back" axonal degeneration.

CONCLUSIONS

These data suggest that antibodies to the RNA-binding protein hnRNP A1 contribute to neurodegeneration in immune-mediated disease of the CNS.

A monoclonal natural human IgM protects axons in the absence of remyelination

BACKGROUND

Whereas demyelination underlies early neurological symptoms in multiple sclerosis (MS), axonal damage is considered critical for permanent chronic deficits. Intracerebral infection of susceptible mouse strains with Theiler's murine encephalomyelitis virus (TMEV) results in chronic induced demyelinating disease (TMEV-IDD) with progressive axonal loss and neurologic dysfunction similar to progressive forms of MS. We previously reported that treatment of chronic TMEV-IDD mice with a neurite outgrowth-promoting natural human antibody, HIgM12, improved brainstem NAA concentrations and preserved functional motor activity. In order to translate this antibody toward clinical trial, we generated a fully human recombinant form of HIgM12, rHIgM12, determined the optimal in vivo dose for functional improvement in TMEV-IDD, and evaluated the functional preservation of descending spinal cord axons by retrograde labeling.

FINDINGS

SJL/J mice at 45 to 90 days post infection (dpi) were studied. A single intraperitoneal dose of 0.25 mg/kg of rHIgM12 per mouse is sufficient to preserve motor function in TMEV-IDD. The optimal dose was 10 mg/kg. rHIgM12 treatment protected the functional transport in spinal cord axons and led to 40 % more Fluoro-Gold-labeled brainstem neurons in retrograde transport studies. This suggests that axons are not only present but also functionally competent. rHIgM12-treated mice also contained more mid-thoracic (T6) spinal cord axons than controls.

CONCLUSIONS

This study confirms that a fully human recombinant neurite outgrowth-promoting monoclonal IgM is therapeutic in a model of progressive MS using multiple reparative readouts. The minimum effective dose is similar to that of a remyelination-promoting monoclonal human IgM discovered by our group that is presently in clinical trials for MS.

Type 1 narcolepsy: a CD8(+) T cell-mediated disease?

Type 1 narcolepsy is a sleep disorder characterized by excessive daytime sleepiness with unintentional sleep attacks and cataplexy. The disorder is caused by a loss of hypocretinergic neurons in the brain. The specific loss of these neurons in narcolepsy is thought to result from an autoimmune attack, and this is supported by evidence of both environmental and genetic factors pointing toward an involvement of the immune system. However, definitive proof of an autoimmune etiology is still missing. Several different immune-mediated disorders targeting neurons are known, and many of these are believed to be caused by autoreactive CD8(+) T cells. In this paper, we review the current knowledge on CD8(+) T cell-mediated neuronal damage on the basis of our understanding of other autoimmune disorders and experimental studies. We identify major histocompatibility complex class I presentation of autoantigens on neurons as a possible mechanism in the development of the disease, and propose T cell-mediated pathogenesis, with cytotoxic CD8(+) T cells targeting the hypocretinergic neurons, as a central element.

A single dose of a neuron-binding human monoclonal antibody improves brainstem NAA concentrations, a biomarker for density of spinal cord axons, in a model of progressive multiple sclerosis

BACKGROUND

Intracerebral infection of susceptible mouse strains with Theiler's murine encephalomyelitis virus (TMEV) results in chronic demyelinating disease with progressive axonal loss and neurologic dysfunction similar to progressive forms of multiple sclerosis (MS). We previously showed that as the disease progresses, a marked decrease in brainstem N-acetyl aspartate (NAA; metabolite associated with neuronal integrity) concentrations, reflecting axon health, is measured. We also demonstrated stimulation of neurite outgrowth by a neuron-binding natural human antibody, IgM12. Treatment with either the serum-derived or recombinant human immunoglobulin M 12 (HIgM12) preserved functional motor activity in the TMEV model. In this study, we examined IgM-mediated changes in brainstem NAA concentrations and central nervous system (CNS) pathology.

FINDINGS

(1)H-magnetic resonance spectroscopy (MRS) showed that treatment with HIgM12 significantly increased brainstem NAA concentrations compared to controls in TMEV-infected mice. Pathologic analysis demonstrated a significant preservation of axons in the spinal cord of animals treated with HIgM12.

CONCLUSIONS

This study links drug efficacy of slowing deficits with axon preservation and NAA concentrations in the brainstem in a model of progressive MS. HIgM12-mediated changes of NAA concentrations in the brainstem are a surrogate marker of axon injury/preservation throughout the spinal cord. This study provides proof-of-concept that a neuron-reactive human IgM can be therapeutic and provides a biomarker for clinical trials.

From classic to spontaneous and humanized models of multiple sclerosis: impact on understanding pathogenesis and drug development

Multiple sclerosis (MS), a demyelinating disease of the central nervous system (CNS), presents as a complex disease with variable clinical and pathological manifestations, involving different pathogenic pathways. Animal models, particularly experimental autoimmune encephalomyelitis (EAE), have been key to deciphering the pathophysiology of MS, although no single model can recapitulate the complexity and diversity of MS, or can, to date, integrate the diverse pathogenic pathways. Since the first EAE model was introduced decades ago, multiple classic (induced), spontaneous, and humanized EAE models have been developed, each recapitulating particular aspects of MS pathogenesis. The advances in technologies of genetic ablation and transgenesis in mice of C57BL/6J background and the development of myelin-oligodendrocyte glycoprotein (MOG)-induced EAE in C57BL/6J mice yielded several spontaneous and humanized EAE models, and resulted in a plethora of EAE models in which the role of specific genes or cell populations could be precisely interrogated, towards modeling specific pathways of MS pathogenesis/regulation in MS. Collectively, the numerous studies on the different EAE models contributed immensely to our basic understanding of cellular and molecular pathways in MS pathogenesis as well as to the development of therapeutic agents: several drugs available today as disease modifying treatments were developed from direct studies on EAE models, and many others were tested or validated in EAE. In this review, we discuss the contribution of major classic, spontaneous, and humanized EAE models to our understanding of MS pathophysiology and to insights leading to devising current and future therapies for this disease.

Axonal degeneration in multiple sclerosis: can we predict and prevent permanent disability?

Axonal degeneration is a major determinant of permanent neurological impairment during multiple sclerosis (MS). Due to the variable course of clinical disease and the heterogeneity of MS lesions, the mechanisms governing axonal degeneration may differ between disease stages. While the etiology of MS remains elusive, there now exist potential prognostic biomarkers that can predict the conversion to clinically definite MS. Specialized imaging techniques identifying axonal injury and drop-out are becoming established in clinical practice as a predictive measure of MS progression, such as optical coherence tomography (OCT) or diffusion tensor imaging (DTI). However, these imaging techniques are still being debated as predictive biomarkers since controversy surrounds their lesion-specific association with expanded disability status scale (EDSS). A more promising diagnostic measure of axonal degeneration has been argued for the detection of reduced N-acetyl aspartate (NAA) and Creatine ratios via magnetic resonance spectroscopic (MRS) imaging, but again fail with its specificity for predicting actual axonal degeneration. Greater accuracy of predictive biomarkers is therefore warranted and may include CSF neurofilament light chain (NF-L) and neurofilament heavy chain (NF-H) levels, for progressive MS. Furthermore, defining the molecular mechanisms that occur during the neurodegenerative changes in the various subgroups of MS may in fact prove vital for the future development of efficacious neuroprotective therapies. The clinical translation of a combined Na⁺ and Ca²⁺ channel blocker may lead to the establishment of a bona fide neuroprotective agent for the treatment of progressive MS. However, more specific therapeutic targets to limit axonal damage in MS need investigation and may include such integral axonal proteins such as the collapsin response mediator protein-2 (CRMP-2), a molecule which upon post-translational modification may propagate axonal degeneration in MS. In this review, we discuss the current clinical determinants of axonal damage in MS and consider the cellular and molecular mechanisms that may initiate these neurodegenerative changes. In particular we highlight the therapeutic candidates that may formulate novel therapeutic strategies to limit axonal degeneration and EDSS during progressive MS.

Inflammation in neurodegenerative diseases--an update

Neurodegeneration, the progressive dysfunction and loss of neurons in the central nervous system (CNS), is the major cause of cognitive and motor dysfunction. While neuronal degeneration is well-known in Alzheimer's and Parkinson's diseases, it is also observed in neurotrophic infections, traumatic brain and spinal cord injury, stroke, neoplastic disorders, prion diseases, multiple sclerosis and amyotrophic lateral sclerosis, as well as neuropsychiatric disorders and genetic disorders. A common link between these diseases is chronic activation of innate immune responses including those mediated by microglia, the resident CNS macrophages. Such activation can trigger neurotoxic pathways leading to progressive degeneration. Yet, microglia are also crucial for controlling inflammatory processes, and repair and regeneration. The adaptive immune response is implicated in neurodegenerative diseases contributing to tissue damage, but also plays important roles in resolving inflammation and mediating neuroprotection and repair. The growing awareness that the immune system is inextricably involved in mediating damage as well as regeneration and repair in neurodegenerative disorders, has prompted novel approaches to modulate the immune system, although it remains whether these approaches can be used in humans. Additional factors in humans include ageing and exposure to environmental factors such as systemic infections that provide additional clues that may be human specific and therefore difficult to translate from animal models. Nevertheless, a better understanding of how immune responses are involved in neuronal damage and regeneration, as reviewed here, will be essential to develop effective therapies to improve quality of life, and mitigate the personal, economic and social impact of these diseases.

The experimental autoimmune encephalomyelitis (EAE) model of MS: utility for understanding disease pathophysiology and treatment

While no single model can exactly recapitulate all aspects of multiple sclerosis (MS), animal models are essential in understanding the induction and pathogenesis of the disease and to develop therapeutic strategies that limit disease progression and eventually lead to effective treatments for the human disease. Several different models of MS exist, but by far the best understood and most commonly used is the rodent model of experimental autoimmune encephalomyelitis (EAE). This model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4+ T lymphocytes. Mouse models are most frequently used because of the inbred genotype of laboratory mice, their rapid breeding capacity, the ease of genetic manipulation, and availability of transgenic and knockout mice to facilitate mechanistic studies. Although not all therapeutic strategies for MS have been developed in EAE, all of the current US Food and Drug Administration (FDA)-approved immunomodulatory drugs are effective to some degree in treating EAE, a strong indicator that EAE is an extremely useful model to study potential treatments for MS. Several therapies, such as glatiramer acetate (GA: Copaxone), and natalizumab (Tysabri), were tested first in the mouse model of EAE and then went on to clinical trials. Here we discuss the usefulness of the EAE model in understanding basic disease pathophysiology and developing treatments for MS as well as the potential drawbacks of this model.

Antineuroinflammatory and neurotrophic effects of CNTF and C16 peptide in an acute experimental autoimmune encephalomyelitis rat model

Experimentalallergic encephalomyelitis (EAE) is an animal model for inflammatory demyelinating autoimmune disease, i.e., multiple sclerosis (MS). In the present study, we investigated the antineuroinflammatory/neuroprotective effects of C16, an ανβ3 integrin-binding peptide, and recombinant rat ciliary neurotrophic factor (CNTF), a cytokine that was originally identified as a survival factor for neurons, in an acute rodent EAE model. In this model, C16 peptide was injected intravenously every day for 2 weeks, and CNTF was delivered into the cerebral ventricles with Alzet miniosmotic pumps. Disease severity was assessed weekly using a scale ranging from 0 to 5. Multiple histological and molecular biological assays were employed to assess inflammation, axonal loss, neuronal apoptosis, white matter demyelination, and gliosis in the brain and spinal cord of different groups. Our results showed that the EAE induced rats revealed a significant increase in inflammatory cells infiltration, while C16 treatment could inhibit the infiltration of leukocytes and macrophages down to 2/3–1/3 of vehicle treated EAE control (P < 0.05). The delayed onset of disease, reduced clinical score (P < 0.01) in peak stage and more rapid recovery also were achieved in C16 treated group. Besides impairing inflammation, CNTF treatment also exerted direct neuroprotective effects, decreasing demyelination and axon loss score (P < 0.05 versus vehicle treated EAE control), and reducing the neuronal death from 40 to 50% to 10 to 20% (P < 0.05). Both treatments suppressed the expression of cytokine tumor necrosis factor-α and interferon-γ when compared with the vehicle control (P < 0.05). Combined treatment with C16 and CNTF produced more obvious functional recovery and neuroprotective effects than individually treatment (P < 0.05). These results suggested that combination treatment with C16 and CNTF, which target different neuroprotection pathways, may be an effective therapeutic alternative to traditional therapy.

Neurotrophin 3 transduction augments remyelinating and immunomodulatory capacity of neural stem cells

Neural stem cells (NSCs) have therapeutic potential in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS); however, to date, their use has resulted in only limited clinical and pathological improvement. To enhance their therapeutic capacity, in the present study, we transduced bone marrow-derived NSCs (BM-NSCs) with neurotrophin 3 (NT-3), a potent neurotrophic factor that is both neuroprotective and immunomodulatory. We found that BM-NSCs transduced with NT-3 reduced central nervous system (CNS) inflammation and neurological deficits in ongoing EAE significantly more than conventional NSC therapy, and, in addition, had the following advantages: (i) enhanced BM-NSC proliferation and differentiation into oligodendrocytes and neurons, as well as inhibited differentiation into astrocytes, thus promoting remyelination and neuronal repopulation, and reducing astrogliosis; (ii) enhanced anti-inflammatory capacity of BM-NSCs, thus more effectively suppressing CNS inflammation and accelerating remyelination; (iii) the easy accessibility of BM-NSCs provides another advantage over brain-derived NSCs for MS therapy; and (iv) a novel Tet-on system we used enables efficient control of NT-3 expression. Thus, our study provides a novel approach to break the vicious inflammation-demyelination cycle, and could pave the way to an easily accessible and highly effective therapy for CNS inflammatory demyelination.

Characterization of immune response to neurofilament light in experimental autoimmune encephalomyelitis

BACKGROUND

Autoimmunity to neuronal proteins occurs in several neurological syndromes, where cellular and humoral responses are directed to surface as well as intracellular antigens. Similar to myelin autoimmunity, pathogenic immune response to neuroaxonal components such as neurofilaments may contribute to neurodegeneration in multiple sclerosis.

METHODS

We studied the immune response to the axonal protein neurofilament light (NF-L) in the experimental autoimmune encephalomyelitis animal model of multiple sclerosis. To examine the association between T cells and axonal damage, pathology studies were performed on NF-L immunized mice. The interaction of T cells and axons was analyzed by confocal microscopy of central nervous system tissues and T-cell and antibody responses to immunodominant epitopes identified in ABH (H2-Ag7) and SJL/J (H2-As) mice. These epitopes, algorithm-predicted peptides and encephalitogenic motifs within NF-L were screened for encephalitogenicity.

RESULTS

Confocal microscopy revealed both CD4+ and CD8+ T cells alongside damaged axons in the lesions of NF-L immunized mice. CD4+ T cells dominated the areas of axonal injury in the dorsal column of spastic mice in which the expression of granzyme B and perforin was detected. Identified NF-L epitopes induced mild neurological signs similar to the observed with the NF-L protein, yet distinct from those characteristic of neurological disease induced with myelin oligodendrocyte glycoprotein.

CONCLUSIONS

Our data suggest that CD4+ T cells are associated with spasticity, axonal damage and neurodegeneration in NF-L immunized mice. In addition, defined T-cell epitopes in the NF-L protein might be involved in the pathogenesis of the disease.

Autoantibodies to Non-myelin Antigens as Contributors to the Pathogenesis of Multiple Sclerosis

For years, investigators have sought to prove that myelin antigens are the primary targets of autoimmunity in multiple sclerosis (MS). Recent experiments have begun to challenge this assumption, particularly when studying the neurodegenerative phase of MS. T-lymphocyte responses to myelin antigens have been extensively studied, and are likely early contributors to the pathogenesis of MS. Antibodies to myelin antigens have a much more inconstant association with the pathogenesis of MS. Recent studies indicate that antibodies to non-myelin antigens such as neurofilaments, neurofascin, RNA binding proteins and potassium channels may contribute to the pathogenesis of MS. The purpose of this review is to analyze recent studies that examine the role that autoantibodies to non-myelin antigens might play in the pathogenesis of MS.

Functional and molecular evidence of myelin- and neuroprotection by thyroid hormone administration in experimental allergic encephalomyelitis

AIMS

Recent data in mouse and rat demyelination models indicate that administration of thyroid hormone (TH) has a positive effect on the demyelination/remyelination balance. As axonal pathology has been recognized as an early neuropathological event in multiple sclerosis, and remyelination is considered a pre-eminent neuroprotective strategy, in this study we investigated whether TH administration improves nerve impulse propagation and protects axons.

METHODS

We followed up the somatosensory evoked potentials (SEPs) in triiodothyronine (T3)-treated and untreated experimental allergic encephalomyelitis (EAE) Dark-Agouti female rats during the electrical stimulation of the tail nerve. T3 treatment started on the 10th day post immunization (DPI) and a pulse administration was continued until the end of the study (33 DPI). SEPs were recorded at baseline (8 DPI) and the day after each hormone/ vehicle administration.

RESULTS

T3 treatment was associated with better outcome of clinical and neurophysiological parameters. SEPs latencies of the two groups behaved differently, being briefer and closer to control values (=faster impulse propagation) in T3-treated animals. The effect was evident on 24 DPI. In the same groups of animals, we also investigated axonal proteins, showing that T3 administration normalizes neurofilament immunoreactivity in the fasciculus gracilis and tau hyperphosphorylation in the lumbar spinal cord of EAE animals. No sign of plasma hyperthyroidism was found; moreover, the dysregulation of TH nuclear receptor expression observed in the spinal cord of EAE animals was corrected by T3 treatment.

CONCLUSIONS

T3 supplementation results in myelin sheath protection, nerve conduction preservation and axon protection in this animal model of multiple sclerosis.

Neuroimaging Assessment of Spasticity Developed after Acquired Brain Injuries and Multiple Sclerosis

This study evaluated whether different imaging techniques correlate with specific variables routinely used to grade the types and complexities of patient conditions in neurorehabilitation services and their clinical outcomes, and if there are radiological patterns, topography or distribution of the lesions correlated to spasticity. The cohort studied included 75 patients, 38 patients with multiple sclerosis (MS) and 37 patients with acquired brain injuries (ABI) referred to the neurorehabilitation department from April 2009 to March 2010. Data included age, gender, diagnoses, complications, spasticity, length of stay, Rehabilitation Complexity Scale (RCS) and Northwick Park Dependency (NPDS) scores on admission and discharge. Forward stepwise multiple regressions were performed considering Spasticity as dependent and considering NPDS, RCS on admission and discharge, age, gender and length of stay as independent variables. Standardized intra-axial lesions in those with spasticity were fused with standardized axial DTIs from normal controls obtained under 3 T and 1.5 T MRI scanners. Spasticity was present in 36 patients. Regression was found between spasticity and all the other variables with r = 0.42, r2 = 0.17, adjr2 = 0.12r, F(4,66) = 3.53, p < 0.01. Residuals were acceptable. If the same is calculated excluding MS patients the results are higher with: r = 0.59, r2 = 0.35, adjr2 = 0.30, F(2,27) = 7.1885, p < 0.003. In MS subjects, spasticity appeared if lesions affected pyramidal tracts, callosal radiations extensively or brainstem. Those with ABI did develop spasticity if the lesion involved the internal capsules, pericommissural areas, optochiasmatic cistern or brainstem. Findings suggest that NPDSa and discharge and RCSd are higher in those developing spasticity. No obvious correlation between spasticity and RCSa was found. Subjects with MS are more likely to develop spasticity especially if the lesions are numerous and affect the corticospinal tracts, callosal radiations extensively or brainstem. In patients with ABI lesions affecting pyramidal tracts, pericommissural areas and optochiasmatic cisterns seem more likely to develop spasticity.

Phagocytosis of neuronal debris by microglia is associated with neuronal damage in multiple sclerosis

Neuroaxonal degeneration is a pathological hallmark of multiple sclerosis (MS) contributing to irreversible neurological disability. Pathological mechanisms leading to axonal damage include autoimmunity to neuronal antigens. In actively demyelinating lesions, myelin is phagocytosed by microglia and blood-borne macrophages, whereas the fate of degenerating or damaged axons is unclear. Phagocytosis is essential for clearing neuronal debris to allow repair and regeneration. However, phagocytosis may lead to antigen presentation and autoimmunity, as has been described for neuroaxonal antigens. Despite this notion, it is unknown whether phagocytosis of neuronal antigens occurs in MS. Here, we show using novel, well-characterized antibodies to axonal antigens, that axonal damage is associated with HLA-DR expressing microglia/macrophages engulfing axonal bulbs, indicative of axonal damage. Neuronal proteins were frequently observed inside HLA-DR(+) cells in areas of axonal damage. In vitro, phagocytosis of neurofilament light (NF-L), present in white and gray matter, was observed in human microglia. The number of NF-L or myelin basic protein (MBP) positive cells was quantified using the mouse macrophage cell line J774.2. Intracellular colocalization of NF-L with the lysosomal membrane protein LAMP1 was observed using confocal microscopy confirming that NF-L is taken up and degraded by the cell. In vivo, NF-L and MBP was observed in cerebrospinal fluid cells from patients with MS, suggesting neuronal debris is drained by this route after axonal damage. In summary, neuroaxonal debris is engulfed, phagocytosed, and degraded by HLA-DR(+) cells. Although uptake is essential for clearing neuronal debris, phagocytic cells could also play a role in augmenting autoimmunity to neuronal antigens.

Cortical injury in multiple sclerosis; the role of the immune system

The easily identifiable, ubiquitous demyelination and neuronal damage that occurs within the cerebral white matter of patients with multiple sclerosis (MS) has been the subject of extensive study. Accordingly, MS has historically been described as a disease of the white matter. Recently, the cerebral cortex (gray matter) of patients with MS has been recognized as an additional and major site of disease pathogenesis. This acknowledgement of cortical tissue damage is due, in part, to more powerful MRI that allows detection of such injury and to focused neuropathology-based investigations. Cortical tissue damage has been associated with inflammation that is less pronounced to that which is associated with damage in the white matter. There is, however, emerging evidence that suggests cortical damage can be closely associated with robust inflammation not only in the parenchyma, but also in the neighboring meninges. This manuscript will highlight the current knowledge of inflammation associated with cortical tissue injury. Historical literature along with contemporary work that focuses on both the absence and presence of inflammation in the cerebral cortex and in the cerebral meninges will be reviewed.

Macroglial plasticity and the origins of reactive astroglia in experimental autoimmune encephalomyelitis

Accumulations of hypertrophic, intensely glial fibrillary acidic protein-positive (GFAP(+)) astroglia, which also express immunoreactive nestin and vimentin, are prominent features of multiple sclerosis lesions. The issues of the cellular origin of hypertrophic GFAP(+)/vimentin(+)/nestin(+) "reactive" astroglia and also the plasticities and lineage relationships among three macroglial progenitor populations-oligodendrocyte progenitor cells (OPCs), astrocytes and ependymal cells-during multiple sclerosis and other CNS diseases remain controversial. We used genetic fate-mappings with a battery of inducible Cre drivers (Olig2-Cre-ER(T2), GFAP-Cre-ER(T2), FoxJ1-Cre-ER(T2) and Nestin-Cre-ER(T2)) to explore these issues in adult mice with myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis (EAE). The proliferative rate of spinal cord OPCs rose fivefold above control levels during EAE, and numbers of oligodendroglia increased as well, but astrogenesis from OPCs was rare. Spinal cord ependymal cells, previously reported to be multipotent, did not augment their low proliferative rate, nor give rise to astroglia or OPCs. Instead, the hypertrophic, vimentin(+)/nestin(+), reactive astroglia that accumulated in spinal cord in this multiple sclerosis model were derived by proliferation and phenotypic transformation of fibrous astroglia in white matter, and solely by phenotypic transformation of protoplasmic astroglia in gray matter. This comprehensive analysis of macroglial plasticity in EAE helps to clarify the origins of astrogliosis in CNS inflammatory demyelinative disorders.

Experimental in vivo and in vitro models of multiple sclerosis: EAE and beyond

Although the primary cause of multiple sclerosis (MS) is unknown, the widely accepted view is that aberrant (auto)immune responses possibly arising following infection(s) are responsible for the destructive inflammatory demyelination and neurodegeneration in the central nervous system (CNS). This notion, and the limited access of human brain tissue early in the course of MS, has led to the development of autoimmune, viral and toxin-induced demyelination animal models as well as the development of human CNS cell and organotypic brain slice cultures in an attempt to understand events in MS. The autoimmune models, collectively known as experimental autoimmune encephalomyelitis (EAE), and viral models have shaped ideas of how environmental factors may trigger inflammation, demyelination and neurodegeneration in the CNS. Understandably, these models have also heavily influenced the development of therapies targeting the inflammatory aspect of MS. Demyelination and remyelination in the absence of overt inflammation are better studied in toxin-induced demyelination models using cuprizone and lysolecithin. The paradigm shift of MS as an autoimmune disease of myelin to a neurodegenerative disease has required more appropriate models reflecting the axonal and neuronal damage. Thus, secondary progressive EAE and spastic models have been crucial to develop neuroprotective approaches. In this review the current in vivo and in vitro experimental models to examine pathological mechanisms involved in inflammation, demyelination and neuronal degeneration, as well as remyelination and repair in MS are discussed. Since this knowledge is the basis for the development of new therapeutic approaches for MS, we particularly address whether the currently available models truly reflect the human disease, and discuss perspectives to further optimise and develop more suitable experimental models to study MS.

Axonal damage in multiple sclerosis

Multiple sclerosis is a debilitating disease of the central nervous system that has been characteristically classified as an immune-mediated destruction of myelin, the protective coating on nerve fibers. Although the mechanisms responsible for the immune attack to central nervous system myelin have been the subject of intense investigation, more recent studies have focused on the neurodegenerative component, which is cause of clinical disability in young adults and appears to be only partially controlled by immunomodulatory therapies. Here, we review distinct, but not mutually exclusive, mechanisms of pathogenesis of axonal damage in multiple sclerosis patients that are either consequent to long-term demyelination or independent from it. We propose that the complexity of axonal degeneration and the heterogeneity of the underlying pathogenetic mechanisms should be taken into consideration for the design of targeted therapeutic intervention.

Distinct pathological patterns in relapsing-remitting and chronic models of experimental autoimmune enchephalomyelitis and the neuroprotective effect of glatiramer acetate

The respective roles of inflammatory and neurodegenerative processes in the pathology of multiple sclerosis (MS) and in its animal model experimental autoimmune encephalomyelitis (EAE) are controversial. Novel treatment strategies aim to operate within the CNS to induce neuroprotection and repair processes in addition to their anti-inflammatory properties. In this study we analyzed and compared the in situ pathological manifestations of EAE utilizing two different models, namely the relapsing-remitting PLP-induced and the chronic MOG-induced diseases. To characterize pathological changes, both transmission electron microscopy (TEM) and immunohistochemistry were employed. The effect of the approved MS drug glatiramer acetate (GA, Copaxone) on myelin damage/repair and on motor neuron loss/preservation was studied in both EAE models. Ultrastructural spinal cord analysis revealed multiple white matter damage foci, with different patterns in the two EAE models. Thus, the relapsing-remitting model was characterized mainly by widespread myelin damage and by remyelinating fibers, whereas in the chronic model axonal degeneration was more prevalent. Loss of lower motor neurons was manifested only in mice with chronic MOG-induced disease. In the GA-treated mice, smaller lesions, increased axonal density and higher prevalence of normal appearing axons were observed, as well as decreased demyelination and degeneration. Furthermore, quantitative analysis of the relative remyelination versus demyelination, provides for the first time evidence of significant augmentation of remyelination after GA treatment. The loss of motor neurons in GA-treated mice was also reduced in comparison to that of EAE untreated mice. These effects were obtained even when GA treatment was applied in a therapeutic schedule, namely after the appearance of clinical symptoms. Hence, the remyelination and neuronal preservation induced by GA are in support of the neuroprotective consequences of this treatment.

Theiler's virus infection: Pathophysiology of demyelination and neurodegeneration

Multiple sclerosis (MS) has been suggested to be an autoimmune demyelinating disease of the central nervous system (CNS), whose primary target is either myelin itself, or myelin-forming cells, the oligodendrocytes. Although axonal damage occurs in MS, it is regarded as a secondary event to the myelin damage. Here, the lesion develops from the myelin (outside) to the axons (inside) "Outside-In model". The Outside-In model has been supported by an autoimmune model for MS, experimental autoimmune (allergic) encephalomyelitis (EAE). However, recently, (1) EAE-like disease has also been shown to be induced by immune responses against axons, and (2) immune responses against axons and neurons as well as neurodegeneration independent of inflammatory demyelination have been reported in MS, which can not be explained by the Outside-In model. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a viral model for MS. In TMEV infection, axonal injury precedes demyelination, where the lesion develops from the axons (inside) to the myelin (outside) "Inside-Out model". The initial axonal damage could result in the release of neuroantigens, inducing autoimmune responses against myelin antigens, which potentially attack the myelin from outside the nerve fiber. Thus, the Inside-Out and Outside-In models can make a "vicious" immunological cycle or initiate an immune cascade.

Cerebrospinal fluid and blood biomarkers of neuroaxonal damage in multiple sclerosis

Following emerging evidence that neurodegenerative processes in multiple sclerosis (MS) are present from its early stages, an intensive scientific interest has been directed to biomarkers of neuro-axonal damage in body fluids of MS patients. Recent research has introduced new candidate biomarkers but also elucidated pathogenetic and clinical relevance of the well-known ones. This paper reviews the existing data on blood and cerebrospinal fluid biomarkers of neuroaxonal damage in MS and highlights their relation to clinical parameters, as well as their potential predictive value to estimate future disease course, disability, and treatment response. Strategies for future research in this field are suggested.

Understanding the roles of the kynurenine pathway in multiple sclerosis progression

The kynurenine pathway (KP) is a major degradative pathway of tryptophan ultimately leading to the production of nicotinamide adenine dinucleotide (NAD⁺) and is also one of the major regulatory mechanisms of the immune response. The KP is known to be involved in several neuroinflammatory disorders including Alzheimer’s disease, amyotrophic lateral sclerosis, AIDS dementia complex, Parkinson’s disease, schizophrenia, Huntington’s disease and brain tumours. However, the KP remains a relatively new topic for the field of multiple sclerosis (MS). Over the last 2–3 years, some evidence has progressively emerged suggesting that the KP is likely to be involved in the pathogenesis of autoimmune diseases especially MS. Some KP modulators are already in clinical trials for other inflammatory diseases and would potentially provide a new and important therapeutic strategy for MS patients. This review summarizes the known relationships between the KP and MS.

Inflammation in neurodegenerative diseases

Neurodegeneration, the slow and progressive dysfunction and loss of neurons and axons in the central nervous system, is the primary pathological feature of acute and chronic neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease, neurotropic viral infections, stroke, paraneoplastic disorders, traumatic brain injury and multiple sclerosis. Despite different triggering events, a common feature is chronic immune activation, in particular of microglia, the resident macrophages of the central nervous system. Apart from the pathogenic role of immune responses, emerging evidence indicates that immune responses are also critical for neuroregeneration. Here, we review the impact of innate and adaptive immune responses on the central nervous system in autoimmune, viral and other neurodegenerative disorders, and discuss their contribution to either damage or repair. We also discuss potential therapies aimed at the immune responses within the central nervous system. A better understanding of the interaction between the immune and nervous systems will be crucial to either target pathogenic responses, or augment the beneficial effects of immune responses as a strategy to intervene in chronic neurodegenerative diseases.

Antigen-specific suppression of experimental autoimmune encephalomyelitis by a novel bifunctional peptide inhibitor: structure optimization and pharmacokinetics

The objective of this study was to optimize the in vivo activity of proteolipid protein (PLP)-bifunctional peptide inhibitor (BPI) molecule to suppress experimental autoimmune encephalomyelitis (EAE) in SJL/J mice and evaluate pharmacokinetic profiles of PLP-BPI. PLP-BPI is constructed via conjugation of myelin PLP(139-151) with CD11a(237-246)-derived peptide (LABL) via a spacer. The hypothesis is that PLP-BPI binds simultaneously to major histocompatibility complex-II and intercellular adhesion molecule-1 on the antigen-presenting cell (APC) and inhibits the formation of the immunological synapse during T-cell and APC interactions. In this study, the structure of BPI was modified by varying the spacer and was evaluated in the EAE model. Intravenous injections of BPI derivatives inhibited the onset, severity, and incidence of EAE more effectively and induced a lower incidence of anaphylaxis than that produced by unmodified PLP-BPI. As anticipated, production of interleukin-17, a proinflammatory cytokine commonly found in elevated levels among multiple sclerosis (MS) patients, was significantly lower in Ac-PLP-BPI-PEG6- or Ac-PLP-BPI-NH(2)-2-treated mice than in phosphate-buffered saline-treated mice. These results suggest that BPI-type molecules can be modified to achieve more efficient and better tolerated BPI-based derivatives for the treatment of MS.

Adult neural stem cells expressing IL-10 confer potent immunomodulation and remyelination in experimental autoimmune encephalitis

Adult neural stem cells (aNSCs) derived from the subventricular zone of the brain show therapeutic effects in EAE, an animal model of the chronic inflammatory neurodegenerative disease MS; however, the beneficial effects are modest. One critical weakness of aNSC therapy may be an insufficient antiinflammatory effect. Here, we demonstrate that i.v. or i.c.v. injection of aNSCs engineered to secrete IL-10 (IL-10-aNSCs), a potent immunoregulatory cytokine, induced more profound functional and pathological recovery from ongoing EAE than that with control aNSCs. IL-10-aNSCs exhibited enhanced antiinflammatory effects in the periphery and inflammatory foci in the CNS compared with control aNSCs, more effectively reducing myelin damage, a hallmark of MS. When compared with mice treated with control aNSCs, those treated with IL-10-aNSCs demonstrated differentiation of transplanted cells into greater numbers of oligodendrocytes and neurons but fewer astrocytes, thus enhancing exogenous remyelination and neuron/axonal growth. Finally, IL-10-aNSCs converted a hostile environment to one supportive of neurons/oligodendrocytes, thereby promoting endogenous remyelination. Thus, aNSCs engineered to express IL-10 show enhanced ability to induce immune suppression, remyelination, and neuronal repair and may represent a novel approach that can substantially improve the efficacy of neural stem cell-based therapy in EAE/MS.

Axonal and neuronal pathology in multiple sclerosis: what have we learnt from animal models

Axonal and neuronal injury and loss are of critical importance for permanent clinical disability in multiple sclerosis patients. Axonal injury occurs already early during the disease and accumulates with disease progression. It is not restricted to focal demyelinated lesions in the white matter, but also affects the normal appearing white matter and the grey matter. Experimental studies show that many different immunological mechanisms may lead to axonal and neuronal injury, including antigen-specific destruction by specific T-cells and auto-antibodies as well as injury induced by products of activated macrophages and microglia. They all appear to be relevant for multiple sclerosis pathogensis in different patients and at different stages of the disease. However, in MS lesions a major mechanism of axonal and neuronal damage appears to be related to the action of reactive oxygen and nitrogen species, which may induce neuronal injury through impairment of mitochondrial function and subsequent energy failure.

The myelin-associated oligodendrocytic basic protein (MOBP) as a relevant primary target autoantigen in multiple sclerosis

Multiple sclerosis (MS) is a disease of the human CNS, characterized by perivascular inflammation, demyelination and axonal damage. Although the etiology of MS is unknown, it is believed that the disease results from destructive autoimmune mechanisms, presumably initiated by abnormal activation of potentially pathogenic autoimmune T-cells recognizing CNS components. The myelin-associated oligodendrocyte basic protein (MOBP), a relatively abundant CNS-specific myelin protein, which plays a role in stabilizing the myelin sheath in the CNS, has recently been implicated in the pathogenesis of MS. Here we review studies showing that MOBP is as an important candidate target antigen in MS as the other widely studied target antigens, myelin basic protein (MBP), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG). The studies summarized below indicate that T-cell autoimmunity against MOBP can be detected in MS patients; T-cells reactive against MOBP can be pathogenic in several mouse strains as well as in the "humanized" HLA-DR15-Tg mice; and, that the HLA-DQ6-restricted, but not HLA-DR15-restricted, MOBP-reactive T-cells cause in HLA-DR15-Tg mice MS-like clinical disease associated with perivascular and parenchymal infiltration, demyelination, axonal loss, and optic neuritis. Accordingly, the MOBP should be considered a bona fide primary target antigen in MS, in addition to MBP, PLP, and MOG.

Contactin-2/TAG-1-directed autoimmunity is identified in multiple sclerosis patients and mediates gray matter pathology in animals

Gray matter pathology is increasingly recognized as an important feature of multiple sclerosis (MS), but the nature of the immune response that targets the gray matter is poorly understood. Starting with a proteomics approach, we identified contactin-2/transiently expressed axonal glycoprotein 1 (TAG-1) as a candidate autoantigen recognized by both autoantibodies and T helper (Th) 1/Th17 T cells in MS patients. Contactin-2 and its rat homologue, TAG-1, are expressed by various neuronal populations and sequestered in the juxtaparanodal domain of myelinated axons both at the axonal and myelin sides. The pathogenic significance of these autoimmune responses was then explored in experimental autoimmune encephalitis models in the rat. Adoptive transfer of TAG-1-specific T cells induced encephalitis characterized by a preferential inflammation of gray matter of the spinal cord and cortex. Cotransfer of TAG-1-specific T cells with a myelin oligodendrocyte glycoprotein-specific mAb generated focal perivascular demyelinating lesions in the cortex and extensive demyelination in spinal cord gray and white matter. This study identifies contactin-2 as an autoantigen targeted by T cells and autoantibodies in MS. Our findings suggest that a contactin-2-specific T-cell response contributes to the development of gray matter pathology.

Gray matter pathology in (chronic) MS: modern views on an early observation

Involvement of the gray matter (GM) in the pathology of multiple sclerosis (MS) was already recognized in the early days of MS research, but the detection of (cortical) GM lesions under the microscope and with magnetic resonance imaging (MRI) techniques was initially suboptimal and could only recently be enhanced. The visualization of GM lesions in vivo opens new doors for studies focusing on clinical, especially cognitive, effects of GM pathology, as well as for monitoring of neuroprotective treatment. However, so far little is known about what causes GM pathology. In this review, several pathogenetic mechanisms will be discussed, affecting the MS brain both from the 'outside-in' and from the 'inside-out'. Also, the use and reliability of MRI atrophy measures as a monitoring tool for GM damage in the therapeutic setting will be reviewed.