Cortical demyelination can be modeled in specific rat models of autoimmune encephalomyelitis and is major histocompatibility complex (MHC) haplotype-related

Proteomic analysis reveals candidate molecules to mediate cortical pathology and identify possible biomarkers in an animal model of multiple sclerosis

Introduction

Multiple Sclerosis (MS) is a complex neurodegenerative disease marked by recurring inflammatory episodes, demyelination, axonal damage, and subsequent loss of function. MS presents a wide range of clinical courses, with the progressive forms leading to irreversible neurological disability. Cortical demyelinating lesions are central to the pathology of these progressive forms, gaining critical importance in recent decades due to their strong correlation with physical disability and cognitive decline. Despite this, the underlying mechanisms driving cortical lesion formation remain poorly understood, and no specific treatments are currently available. A significant challenge lies in the lack of animal models that accurately mirror the key characteristics of these lesions.

Methods

We developed a focal cortical animal model that replicates many features of cortical lesions, including cognitive impairment. This study focuses on conducting proteomic analyses of both the cortical lesions and cerebrospinal fluid (CSF) from these animals, aiming to identify key proteins and biomarkers that could be validated in MS patients.

Results

Proteomic differences between frontal cortex tissue and CSF were observed when comparing experimental animals with controls. Among the identified proteins, some have been previously described in MS patients and animal models, while others represent novel discoveries. Notably, we identified two proteins, S100A8 and orosomucoid-1, that were highly expressed in both regions.

Conclusions

These findings suggest that the prognostic molecules identified in this model could facilitate the discovery of new biomarkers or key molecules relevant to MS, particularly in the cortical lesion that mainly characterized the progressive forms of the disease.

Spatial transcriptomics of meningeal inflammation reveals inflammatory gene signatures in adjacent brain parenchyma

While modern high efficacy disease modifying therapies have revolutionized the treatment of relapsing-remitting multiple sclerosis, they are less effective at controlling progressive forms of the disease. Meningeal inflammation is a recognized risk factor for cortical gray matter pathology which can result in disabling symptoms such as cognitive impairment and depression, but the mechanisms linking meningeal inflammation and gray matter pathology remain unclear. Here, we performed magnetic resonance imaging (MRI)-guided spatial transcriptomics in a mouse model of autoimmune meningeal inflammation to characterize the transcriptional signature in areas of meningeal inflammation and the underlying brain parenchyma. We found broadly increased activity of inflammatory signaling pathways at sites of meningeal inflammation, but only a subset of these pathways active in the adjacent brain parenchyma. Subclustering of regions adjacent to meningeal inflammation revealed the subset of immune programs induced in brain parenchyma, notably complement signaling and antigen processing/presentation. Trajectory gene and gene set modeling analysis confirmed variable penetration of immune signatures originating from meningeal inflammation into the adjacent brain tissue. This work contributes a valuable data resource to the field, provides the first detailed spatial transcriptomic characterization in a model of meningeal inflammation, and highlights several candidate pathways in the pathogenesis of gray matter pathology.

Remyelination in animal models of multiple sclerosis: finding the elusive grail of regeneration

Remyelination biology and the therapeutic potential of restoring myelin sheaths to prevent neurodegeneration and disability in multiple sclerosis (MS) has made considerable gains over the past decade with many regeneration strategies undergoing tested in MS clinical trials. Animal models used to investigate oligodendroglial responses and regeneration of myelin vary considerably in the mechanism of demyelination, involvement of inflammatory cells, neurodegeneration and capacity for remyelination. The investigation of remyelination in the context of aging and an inflammatory environment are of considerable interest for the potential translation to progressive multiple sclerosis. Here we review how remyelination is assessed in mouse models of demyelination, differences and advantages of these models, therapeutic strategies that have emerged and current pro-remyelination clinical trials.

Periventricular magnetisation transfer abnormalities in early multiple sclerosis

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Periventricular-MTR gradients are present from the earliest stage of MS and become steeper in advanced disease.

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Lower MTR in periventricular-NAWM was positively associated with reduced cortical-mean-thickness.

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MTR in periventricular-lesions scaled with cortical-mean-thickness, while non-periventricular lesions were unrelated.

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These findings suggest a common pathophysiologic mechanism between CSF-adjacent cortical and periventricular areas.

Objective

Recent studies suggested that CSF-mediated factors contribute to periventricular (PV) T2-hyperintense lesion formation in multiple sclerosis (MS) and this in turn correlates with cortical damage. We thus investigated if such PV-changes are observable microstructurally in early-MS and if they correlate with cortical damage.

Methods

We assessed the magnetisation transfer ratio (MTR) in PV normal-appearing white matter (NAWM) and in MS lesions in 44 patients with a clinically isolated syndrome (CIS) suggestive of MS and 73 relapsing-remitting MS (RRMS) patients. Band-wise MTR values were related to cortical mean thickness (CMT) and compared with 49 healthy controls (HCs). For each band, MTR changes were assessed relative to the average MTR values of all HCs.

Results

Relative to HCs, PV-MTR was significantly reduced up to 2.63% in CIS and 5.37% in RRMS (p < 0.0001). The MTR decreased towards the lateral ventricles with 0.18%/mm in CIS and 0.31%/mm in RRMS patients, relative to HCs. In RRMS, MTR-values adjacent to the ventricle and in PV-lesions correlated positively with CMT and negatively with EDSS.

Conclusion

PV-MTR gradients are present from the earliest stage of MS, consistent with more pronounced microstructural WM-damage closer to the ventricles. The positive association between reduced CMT and lower MTR in PV-NAWM suggests a common pathophysiologic mechanism. Together, these findings indicate the potential use of multimodal MRI as refined marker for MS-related tissue changes.

CD8+ T Cell-Mediated Mechanisms Contribute to the Progression of Neurocognitive Impairment in Both Multiple Sclerosis and Alzheimer's Disease?

Neurocognitive impairment (NCI) is one of the most relevant clinical manifestations of multiple sclerosis (MS). The profile of NCI and the structural and functional changes in the brain structures relevant for cognition in MS share some similarities to those in Alzheimer's disease (AD), the most common cause of neurocognitive disorders. Additionally, despite clear etiopathological differences between MS and AD, an accumulation of effector/memory CD8+ T cells and CD8+ tissue-resident memory T (Trm) cells in cognitively relevant brain structures of MS/AD patients, and higher frequency of effector/memory CD8+ T cells re-expressing CD45RA (TEMRA) with high capacity to secrete cytotoxic molecules and proinflammatory cytokines in their blood, were found. Thus, an active pathogenetic role of CD8+ T cells in the progression of MS and AD may be assumed. In this mini-review, findings supporting the putative role of CD8+ T cells in the pathogenesis of MS and AD are displayed, and putative mechanisms underlying their pathogenetic action are discussed. A special effort was made to identify the gaps in the current knowledge about the role of CD8+ T cells in the development of NCI to "catalyze" translational research leading to new feasible therapeutic interventions.

Mitochondrial Dysfunction in EAE Mice Brains and Impact of HIF1-α Induction to Compensate Energy Loss

Background: Mitochondrial dysfunction may be involved in the process of degradation and death of gray matter cells of the central nervous system (CNS) in patients with multiple sclerosis (MS). MS is known as a chronic, progressive demyelinating disease of the CNS. Objectives: Experimental autoimmune encephalomyelitis (EAE) mouse model of MS is the best method for extracting data trend for diagnosing this disorder. The aim of this study was to evaluate the specific activity of the Cytochrome oxidase (COX), ATP, and hypoxia-inducible factor 1 alpha (HIF-1α) in brain tissues of the EAE mice model. Methods: Twenty-one female mice (C57BL/6) were used, 9 for inducing the EAE model and 6 for each of both negative and sham control groups. The specific activity of the COX, ATP, and HIF-1α levels were evaluated in the whole brain of all 3 mice groups. Results: According to the findings, specific COX activity and ATP levels were decreased significantly, which could be due to the mitochondrial dysfunction and neuronal loss in MS lesions, whereas HIF-1α levels increased significantly in the EAE mice group, compared to the sham and negative control groups. The significant increase of HIF-1α levels reinforces the hypothesis that the HIF-1α induction may provide prevention of neuronal death by compensating energy loss under hypoxia-like conditions in EAE mice brains. Conclusions: The results of this study suggest that HIF-1α induction may also be a potential target for controlling the progression of MS, or the development of HIF-1α inducing compounds could be a potential candidate for the management of this disease and provide a rationale to conduct further research in this area.

Effects of EHP-101 on inflammation and remyelination in murine models of Multiple sclerosis

Multiple Sclerosis (MS) is characterized by a combination of inflammatory and neurodegenerative processes in the spinal cord and the brain. Natural and synthetic cannabinoids such as VCE-004.8 have been studied in preclinical models of MS and represent promising candidates for drug development. VCE-004.8 is a multitarget synthetic cannabidiol (CBD) derivative acting as a dual Peroxisome proliferator-activated receptor-gamma/Cannabinoid receptor type 2 (PPARγ/CB₂) ligand agonist that also activates the Hypoxia-inducible factor (HIF) pathway. EHP-101 is an oral lipidic formulation of VCE-004.8 that has shown efficacy in several preclinical models of autoimmune, inflammatory, fibrotic, and neurodegenerative diseases. EHP-101 alleviated clinical symptomatology in EAE and transcriptomic analysis demonstrated that EHP-101 prevented the expression of many inflammatory genes closely associated with MS pathophysiology in the spinal cord. EHP-101 normalized the expression of several genes associated with oligodendrocyte function such as Teneurin 4 (Tenm4) and Gap junction gamma-3 (Gjc3) that were downregulated in EAE. EHP-101 treatment prevented microglia activation and demyelination in both the spinal cord and the brain. Moreover, EAE was associated with a loss in the expression of Oligodendrocyte transcription factor 2 (Olig2) in the corpus callosum, a marker for oligodendrocyte differentiation, which was restored by EHP-101 treatment. In addition, EHP-101 enhanced the expression of glutathione S-transferase pi (GSTpi), a marker for mature oligodendrocytes in the brain. We also found that a diet containing 0.2% cuprizone for six weeks induced a clear loss of myelin in the brain measured by Cryomyelin staining and Myelin basic protein (MBP) expression. Moreover, EHP-101 also prevented cuprizone-induced microglial activation, astrogliosis and reduced axonal damage. Our results provide evidence that EHP-101 showed potent anti-inflammatory activity, prevented demyelination, and enhanced remyelination. Therefore, EHP-101 represents a promising drug candidate for the potential treatment of different forms of MS.

The pathology of central nervous system inflammatory demyelinating disease accompanying myelin oligodendrocyte glycoprotein autoantibody

We sought to define the pathological features of myelin oligodendrocyte glycoprotein (MOG) antibody associated disorders (MOGAD) in an archival autopsy/biopsy cohort. We histopathologically analyzed 2 autopsies and 22 brain biopsies from patients with CNS inflammatory demyelinating diseases seropositive for MOG-antibody by live-cell-based-assay with full length MOG in its conformational form. MOGAD autopsies (ages 52 and 67) demonstrate the full spectrum of histopathological features observed within the 22 brain biopsies (median age, 10 years; range, 1-66; 56% female). Clinical, radiologic, and laboratory characteristics and course (78% relapsing) are consistent with MOGAD. MOGAD pathology is dominated by coexistence of both perivenous and confluent white matter demyelination, with an over-representation of intracortical demyelinated lesions compared to typical MS. Radially expanding confluent slowly expanding smoldering lesions in the white matter as seen in MS, are not present. A CD4+ T-cell dominated inflammatory reaction with granulocytic infiltration predominates. Complement deposition is present in all active white matter lesions, but a preferential loss of MOG is not observed. AQP4 is preserved, with absence of dystrophic astrocytes, and variable oligodendrocyte and axonal destruction. MOGAD is pathologically distinguished from AQP4-IgG seropositive NMOSD, but shares some overlapping features with both MS and ADEM, suggesting a transitional pathology. Complement deposition in the absence of selective MOG protein loss suggest humoral mechanisms are involved, however argue against endocytic internalization of the MOG antigen. Parallels with MOG-EAE suggest MOG may be an amplification factor that augments CNS demyelination, possibly via complement mediated destruction of myelin or ADCC phagocytosis.

Extensive subpial cortical demyelination is specific to multiple sclerosis

Cortical demyelinated lesions are frequent and widespread in chronic multiple sclerosis (MS) patients, and may contribute to disease progression. Inflammation and related oxidative stress have been proposed as central mediators of cortical damage, yet meningeal and cortical inflammation is not specific to MS, but also occurs in other diseases. The first aim of this study was to test whether cortical demyelination was specific for demyelinating CNS diseases compared to other CNS disorders with prominent meningeal and cortical inflammation. The second aim was to assess whether oxidative tissue damage was associated with the extent of neuroaxonal damage. We studied a large cohort of patients diagnosed with demyelinating CNS diseases and non‐demyelinating diseases of autoimmune, infectious, neoplastic or metabolic origin affecting the meninges and the cortex. Included were patients with MS, acute disseminated encephalomyelitis (ADEM), neuromyelitis optica (NMO), viral and bacterial meningoencephalitis, progressive multifocal leukoencephalopathy (PML), subacute sclerosing panencephalitis (SSPE), carcinomatous and lymphomatous meningitis and metabolic disorders such as extrapontine myelinolysis, thus encompassing a wide range of adaptive and innate cytokine signatures. Using myelin protein immunohistochemistry, we found cortical demyelination in MS, ADEM, PML and extrapontine myelinolysis, whereby each condition showed a disease‐specific histopathological pattern. Remarkably, extensive ribbon‐like subpial demyelination was only observed in MS, thus providing an important pathogenetic and diagnostic cue. Cortical oxidative injury was detected in both demyelinating and non‐demyelinating CNS disorders. Our data demonstrate that meningeal and cortical inflammation alone accompanied by oxidative stress are not sufficient to generate the extensive subpial cortical demyelination found in MS, but require other MS‐specific factors.

Mechanisms for lesion localization in neuromyelitis optica spectrum disorders

Purpose of review

Neuromyelitis optica spectrum disorders (NMOSD) are severe inflammatory diseases of the central nervous system (CNS), with the presence of aquaporin 4 (AQP4)-specific serum antibodies in the vast majority of patients, and with the presence of myelin oligodendrocyte glycoprotein (MOG)-specific antibodies in approximately 40% of all AQP4-antibody negative NMOSD patients. Despite differences in antigen recognition, the preferred sites of lesions are similar in both groups of patients: They localize to the spinal cord and to the anterior visual pathway including retina, optic nerves, chiasm, and optic tracts, and – to lesser extent – also to certain predilection sites in the brain.

Recent findings

The involvement of T cells in the formation of NMOSD lesions has been challenged for quite some time. However, several recent findings demonstrate the key role of T cells for lesion formation and localization. Studies on the evolution of lesions in the spinal cord of NMOSD patients revealed a striking similarity of early NMOSD lesions with those observed in corresponding T-cell-induced animal models, both in lesion formation and in lesion localization. Studies on retinal abnormalities in NMOSD patients and corresponding animals revealed the importance of T cells for the very early stages of retinal lesions which eventually culminate in damage to Müller cells and to the retinal nerve fiber layer. Finally, a study on cerebrospinal fluid (CSF) barrier pathology demonstrated that NMOSD immunopathology extends beyond perivascular astrocytic foot processes to include the pia, the ependyma, and the choroid plexus, and that diffusion of antibodies from the CSF could further influence lesion formation in NMOSD patients.

Summary

The pathological changes observed in AQP4-antibody positive and MOG-antibody positive NMOSD patients are strikingly similar to those found in corresponding animal models, and many mechanisms which determine lesion localization in experimental animals seem to closely reflect the human situation.

The formation of a glial scar does not prohibit remyelination in an animal model of multiple sclerosis

The role of astrocytes in the pathophysiology of multiple sclerosis (MS) is discussed controversially. Especially the formation of the glial scar is often believed to act as a barrier for remyelination. At the same time, astrocytes are known to produce factors that influence oligodendrocyte precursor cell (OPC) survival. To explore these mechanisms, we investigated the astrocytic reaction in an animal model induced by immunization with myelin oligodendrocyte glycoprotein (MOG) in Dark Agouti (DA) rats, which mimics most of the histological features of MS. We correlated the astroglial reaction by immunohistochemistry (IHC) for glial fibrillary acidic protein (GFAP) to the remyelination capacity by in situ hybridization for mRNA of proteolipid protein (PLP), indicative of OPCs, over the full course of the disease. PLP mRNA peaked in early remyelinating lesions while the amount of GFAP positive astrocytes was highest in remyelinated lesions. In shadow plaques, we found at the same time all features of a glial scar and numbers of OPCs and mature oligodendrocytes, which were nearly equal to that in unaffected white matter areas. To assess the plaque environment, we furthermore quantitatively analyzed factors expressed by astrocytes previously suggested to influence remyelination. From our data, we conclude that remyelination occurs despite an abundant glial reaction in this animal model. The different patterns of astrocytic factors and the occurrence of different astrocytic phenotypes during lesion evolution furthermore indicate a finely regulated, balanced astrocytic involvement leading to successful repair.

Pathogenic Mechanisms Associated With Different Clinical Courses of Multiple Sclerosis

In the majority of patients multiple sclerosis starts with a relapsing remitting course (RRMS), which may at later times transform into secondary progressive disease (SPMS). In a minority of patients the relapsing remitting disease is skipped and the patients show progression from the onset (primary progressive MS, PPMS). Evidence obtained so far indicate major differences between RRMS and progressive MS, but no essential differences between SPMS and PPMS, with the exception of a lower incidence in the global load of focal white matter lesions and in particular in the presence of classical active plaques in PPMS. We suggest that in MS patients two types of inflammation occur, which develop in parallel but partially independent from each other. The first is the focal bulk invasion of T- and B-lymphocytes with profound blood brain barrier leakage, which predominately affects the white matter, and which gives rise to classical active demyelinated plaques. The other type of inflammation is a slow accumulation of T-cells and B-cells in the absence of major blood brain barrier damage in the connective tissue spaces of the brain, such as the meninges and the large perivascular Virchow Robin spaces, where they may form aggregates or in most severe cases structures in part resembling tertiary lymph follicles. This type of inflammation is associated with the formation of subpial demyelinated lesions in the cerebral and cerebellar cortex, with slow expansion of pre-existing lesions in the white matter and with diffuse neurodegeneration in the normal appearing white or gray matter. The first type of inflammation dominates in acute and relapsing MS. The second type of inflammation is already present in early stages of MS, but gradually increases with disease duration and patient age. It is suggested that CD8⁺ T-lymphocytes remain in the brain and spinal cord as tissue resident cells, which may focally propagate neuroinflammation, when they re-encounter their cognate antigen. B-lymphocytes may propagate demyelination and neurodegeneration, most likely by producing soluble neurotoxic factors. Whether lymphocytes within the brain tissue of MS lesions have also regulatory functions is presently unknown. Key open questions in MS research are the identification of the target antigen recognized by tissue resident CD8⁺ T-cells and B-cells and the molecular nature of the soluble inflammatory mediators, which may trigger tissue damage.

The next-generation sphingosine-1 receptor modulator BAF312 (siponimod) improves cortical network functionality in focal autoimmune encephalomyelitis

Autoimmune diseases of the central nervous system (CNS) like multiple sclerosis (MS) are characterized by inflammation and demyelinated lesions in white and grey matter regions. While inflammation is present at all stages of MS, it is more pronounced in the relapsing forms of the disease, whereas progressive MS (PMS) shows significant neuroaxonal damage and grey and white matter atrophy. Hence, disease-modifying treatments beneficial in patients with relapsing MS have limited success in PMS. BAF312 (siponimod) is a novel sphingosine-1-phosphate receptor modulator shown to delay progression in PMS. Besides reducing inflammation by sequestering lymphocytes in lymphoid tissues, BAF312 crosses the blood-brain barrier and binds its receptors on neurons, astrocytes and oligodendrocytes. To evaluate potential direct neuroprotective effects, BAF312 was systemically or locally administered in the CNS of experimental autoimmune encephalomyelitis mice with distinct grey- and white-matter lesions (focal experimental autoimmune encephalomyelitis using an osmotic mini-pump). Ex-vivo flow cytometry revealed that systemic but not local BAF312 administration lowered immune cell infiltration in animals with both grey and white matter lesions. Ex-vivo voltage-sensitive dye imaging of acute brain slices revealed an altered spatio-temporal pattern of activation in the lesioned cortex compared to controls in response to electrical stimulation of incoming white-matter fiber tracts. Here, BAF312 administration showed partial restore of cortical neuronal circuit function. The data suggest that BAF312 exerts a neuroprotective effect after crossing the blood-brain barrier independently of peripheral effects on immune cells. Experiments were carried out in accordance with German and EU animal protection law and approved by local authorities (Landesamt für Natur, Umwelt und Verbraucherschutz Nordrhein-Westfalen; 87-51.04.2010.A331) on December 28, 2010.

Multiple Sclerosis Pathology

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS), which gives rise to focal lesions in the gray and white matter and to diffuse neurodegeneration in the entire brain. In this review, the spectrum of MS lesions and their relation to the inflammatory process is described. Pathology suggests that inflammation drives tissue injury at all stages of the disease. Focal inflammatory infiltrates in the meninges and the perivascular spaces appear to produce soluble factors, which induce demyelination or neurodegeneration either directly or indirectly through microglia activation. The nature of these soluble factors, which are responsible for demyelinating activity in sera and cerebrospinal fluid of the patients, is currently undefined. Demyelination and neurodegeneration is finally accomplished by oxidative injury and mitochondrial damage leading to a state of "virtual hypoxia."

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

A B Cell-Driven Autoimmune Pathway Leading to Pathological Hallmarks of Progressive Multiple Sclerosis in the Marmoset Experimental Autoimmune Encephalomyelitis Model

The absence of pathological hallmarks of progressive multiple sclerosis (MS) in commonly used rodent models of experimental autoimmune encephalomyelitis (EAE) hinders the development of adequate treatments for progressive disease. Work reviewed here shows that such hallmarks are present in the EAE model in marmoset monkeys (Callithrix jacchus). The minimal requirement for induction of progressive MS pathology is immunization with a synthetic peptide representing residues 34–56 from human myelin oligodendrocyte glycoprotein (MOG) formulated with a mineral oil [incomplete Freund’s adjuvant (IFA)]. Pathological aspects include demyelination of cortical gray matter with microglia activation, oxidative stress, and redistribution of iron. When the peptide is formulated in complete Freund’s adjuvant, which contains mycobacteria that relay strong activation signals to myeloid cells, oxidative damage pathways are strongly boosted leading to more intensive pathology. The proven absence of immune potentiating danger signals in the MOG34–56/IFA formulation implies that a narrow population of antigen-experienced T cells present in the monkey’s immune repertoire is activated. This novel pathway involves the interplay of lymphocryptovirus-infected B cells with MHC class Ib/Caja-E restricted CD8+ CD56+ cytotoxic T lymphocytes.

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.

The topograpy of demyelination and neurodegeneration in the multiple sclerosis brain

Multiple sclerosis is a chronic inflammatory disease with primary demyelination and neurodegeneration in the central nervous system. In our study we analysed demyelination and neurodegeneration in a large series of multiple sclerosis brains and provide a map that displays the frequency of different brain areas to be affected by these processes. Demyelination in the cerebral cortex was related to inflammatory infiltrates in the meninges, which was pronounced in invaginations of the brain surface (sulci) and possibly promoted by low flow of the cerebrospinal fluid in these areas. Focal demyelinated lesions in the white matter occurred at sites with high venous density and additionally accumulated in watershed areas of low arterial blood supply. Two different patterns of neurodegeneration in the cortex were identified: oxidative injury of cortical neurons and retrograde neurodegeneration due to axonal injury in the white matter. While oxidative injury was related to the inflammatory process in the meninges and pronounced in actively demyelinating cortical lesions, retrograde degeneration was mainly related to demyelinated lesions and axonal loss in the white matter. Our data show that accumulation of lesions and neurodegeneration in the multiple sclerosis brain does not affect all brain regions equally and provides the pathological basis for the selection of brain areas for monitoring regional injury and atrophy development in future magnetic resonance imaging studies.

Periventricular lesions correlate with cortical thinning in multiple sclerosis

OBJECTIVE

It has been suggested recently that cortical pathology in multiple sclerosis (MS) may, at least partly, be caused by factors in cerebrospinal fluid (CSF). We thus hypothesized that MS-related tissue changes in compartments close to the CSF, such as periventricular lesions, might correlate with cortical pathology.

METHODS

We investigated a cohort of 160 patients, comprising 91 with a clinically isolated syndrome (CIS) and 69 with relapsing-remitting MS (RRMS; mean age: CIS: 31.4 ± 9.0; RRMS: 33.0 ± 8.7 years; mean disease duration: CIS: 7.2 ± 15 months; RRMS: 8.0 ± 6.5 years, Expanded Disability Status Scale (median, min-max): CIS: 1, 0-3.5; RRMS: 1.25, 0-4) with 3.0T magnetic resonance imaging. MS lesions were segmented semiautomatically on fluid-attenuated inversion recovery images. To quantify periventricular lesion load (PV-LL), we generated ventricle masks and dilated them by a voxel factor of 3. Lesions within the dilated ventricle margin were classified as periventricular. Cortical thinning was assessed by cortical mean thickness (CMT) and compared to data from 58 healthy controls (HCs; mean age: 29.1 ± 7.4 years).

RESULTS

Compared to HC, CIS and (even more so) RRMS patients demonstrated significantly reduced CMT. Even after controlling for ventricular volume and total lesion load, increased periventricular lesion occupancy (percentage of PV-LL) significantly correlated with decreased CMT in RRMS (r = -0.295; p = 0.015), but not in CIS (r = 0.032; p = 0.768) patients.

INTERPRETATION

The correlation between increased periventricular lesion burden and decreased CMT indicative of subpial cortical pathology supports the concept that common CSF-mediated factors might play a role in the accumulation of damage to gray and white matter in MS.

Prophylactic Effect of BIO-1211 Small-Molecule Antagonist of VLA-4 in the EAE Mouse Model of Multiple Sclerosis

BACKGROUND AND PURPOSE

Some functional limitations and economic burden of therapeutic antibodies indicated that introducing of alternative therapeutic compounds with same or different mechanism of action could be worthwhile. In this regard small-molecule antagonists can have a wide range of impacts, so in this research, we examine the prophylactic effects of BIO-1211 [Very Late Antigen-4 (VLA4) blocker], in experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis in comparison with commercial available medicine, Natalizumab (NTZ)].

METHODS

EAE was induced by subcutaneous immunization of myelin oligodendrocyte glycoprotein (MOG35-55) in 8-week-old C57BL/6 mice. During EAE induction, mice were separated to distinct groups and provided either BIO-1211 (5 and 10 mg/kg) or NTZ (5 mg/kg) and co-administration of these two compounds. After 21 days, neuro-inflammatory responses were analyzed using qRT-PCR, western blot, and ELISA methods. Pervade of immune cells to brain was examined by Evans blue staining and immunohistochemistry (IHC) analysis of specific markers of microglia/monocytes (CD11b) and leukocytes (CD45).

RESULTS

Targeted disruption of VLA4/VCAM1 interactions, by BIO-1211 agonist in mice, results in reduced cytokines expression, leukocyte trafficking, and inhibition of inflammatory responses in EAE (p < 0.01) in a dose-independent manner (data not shown). Mice treated with both BIO-1211 and NTZ exhibited a considerable depletion in the EAE clinical score, which correlated with decreased expression of TNF-α, IL-17, IFN-γ and pervade of CD11b(+) and CD45(+) cells into the cerebral cortex.

CONCLUSION

Our results indicated that BIO12-11 compound would be an useful tool to further understand the biological roles of VLA4/VCAM1 interactions, and could also be considered as EAE-suppressing agent.

Autoimmune disease in the brain--how to spot the culprits and how to keep them in check

Current concepts attribute an early and central role for auto-aggressive, myelin-specific T-lymphocytes in the pathogenesis of multiple sclerosis. This view emerged from immunological and pathological findings in experimental autoimmune encephalitis, an animal model characterised by pathological lesions closely resembling the ones found in multiple sclerosis. Furthermore, therapeutic strategies targeting the functions of these encephalitogenic T cells which attenuate their pathogenicity such as glatiramer acetate or anti-VLA4 antibody treatments represent proven approaches in multiple sclerosis. Nonetheless, all therapies evaluated to date either insufficiently dampen down inflammation or completely block immune processes. For this reason, there is a need to identify new therapeutic targets. We have employed live intravital two-photon microscopy to learn more about the behaviour of T cells during the preclinical phase of EAE, when T cells acquire the properties required to invade their target organ. Furthermore, we were able to identify an unexpected locomotive behaviour of T cells at the blood-brain barrier, which occurs immediately before diapedesis and the induction of paralytic disease. Such studies might open new avenues for the treatment of CNS autoimmune diseases. Multiple sclerosis is considered to be an autoimmune disease in which self-reactive T cells enter the central nervous system (CNS) and create an inflammatory milieu that destroys myelin and neurons. Immunomodulatory strategies for the treatment of multiple sclerosis target this process by attempting to inactivate these auto-aggressive T cells. However, so far, these strategies have failed to extinguish disease activity completely. For this reason, there is a need to understand in more detail the mechanisms by which T cells become encephalitogenic, how they enter the nervous system, and what the signals are that guide them along this path. If these processes could be better understood, it may be possible to design more effective and specific therapies for multiple sclerosis. This article will give a brief overview about our recent findings obtained using intravital imaging of autoaggressive effector T cells in an experimental model of multiple sclerosis. This new technological approach might help to fill some gaps in the understanding of autoimmune pathogenesis of multiple sclerosis.

Increased Meningeal T and Plasma Cell Infiltration is Associated with Early Subpial Cortical Demyelination in Common Marmosets with Experimental Autoimmune Encephalomyelitis

Subpial cortical demyelination (SCD) accounts for the greatest proportion of demyelinated cortex in multiple sclerosis (MS). SCD is already found in biopsy cases with early MS and in marmosets with experimental autoimmune encephalomyelitis (EAE), but the pathogenesis of SCD is not well understood. The objective of this study was to investigate whether and, if so, which meningeal inflammatory cells were associated with early SCD in marmosets with EAE. Immunohistochemistry was performed to analyze brain samples from eight control animals and eight marmosets immunized with myelin oligodendrocyte glycoprotein. Meningeal T, B and plasma cells were quantified adjacent to SCD, normal-appearing EAE cortex (NAC) and control marmoset cortex. SCD areas appeared mostly hypocellular with low-grade microglial activation. In marmosets with EAE, meninges adjacent to SCD showed significantly increased T cells paralleled by elevated plasma cells, but unaltered B cell numbers compared with NAC. The elevation of meningeal T and plasma cells was a specific finding topographically associated with SCD, as the meninges overlying NAC displayed similarly low T, B and plasma cell numbers as control cortex. These findings suggest that local meningeal T and plasma cell infiltration contributes to the pathogenesis of SCD in marmosets with EAE.

Actively Induced Experimental Autoimmune Encephalomyelitis in Rats

The rat and especially a number of inbred rat strains are very well suited for modeling multiple sclerosis (MS). Experimental autoimmune encephalomyelitis (EAE), the model of MS, can be induced by active or passive immunization. Active immunization can be performed with different myelin proteins or peptides thereof. Passive immunization is performed by transfer of myelin-specific T cells. Most known is EAE induced with myelin basic protein (MBP) in LEW (RT1(l)) rats that results in monophasic disease and EAE induced with myelin oligodendrocyte glycoprotein (MOG) in DA (RT1(av1)) rats that leads to relapsing remitting or chronic disease. Depending on the selected inbred rat strain, the immunogen and adjuvant used, different disease courses and pathologies can be induced that mimic different aspects of MS.

Interleukin-1β and interleukin-1 receptor antagonist appear in grey matter additionally to white matter lesions during experimental multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) has been mainly attributed to white matter (WM) pathology. However, recent evidence indicated the presence of grey matter (GM) lesions. One of the principal mediators of inflammatory processes is interleukin-1β (IL-1β), which is known to play a role in MS pathogenesis. It is unknown whether IL-1β is solely present in WM or also in GM lesions. Using an experimental MS model, we questioned whether IL-1β and the IL-1 receptor antagonist (IL-1ra) are present in GM in addition to affected WM regions.

METHODS

The expression of IL-1β and IL-1ra in chronic-relapsing EAE (cr-EAE) rats was examined using in situ hybridization, immunohistochemistry and real-time PCR. Rats were sacrificed at the peak of the first disease phase, the trough of the remission phase, and at the peak of the relapse. Histopathological characteristics of CNS lesions were studied using immunohistochemistry for PLP, CD68 and CD3 and Oil-Red O histochemistry.

RESULTS

IL-1β and IL-ra expression appears to a similar extent in affected GM and WM regions in the brain and spinal cord of cr-EAE rats, particularly in perivascular and periventricular locations. IL-1β and IL-1ra expression was dedicated to macrophages and/or activated microglial cells, at sites of starting demyelination. The time-dependent expression of IL-1β and IL-1ra revealed that within the spinal cord IL-1β and IL-1ra mRNA remained present throughout the disease, whereas in the brain their expression disappeared during the relapse.

CONCLUSIONS

The appearance of IL-1β expressing cells in GM within the CNS during cr-EAE may explain the occurrence of several clinical deficits present in EAE and MS which cannot be attributed solely to the presence of IL-1β in WM. Endogenously produced IL-1ra seems not capable to counteract IL-1β-induced effects. We put forward that IL-1β may behold promise as a target to address GM, in addition to WM, related pathology in MS.

Blood-brain barrier alterations in the cerebral cortex in experimental autoimmune encephalomyelitis

The pathophysiology of cerebral cortical lesions in multiple sclerosis (MS) is not understood. We investigated cerebral cortex microvessels during immune-mediated demyelination in the MS model chronic murine experimental autoimmune encephalomyelitis (EAE) by immunolocalization of the endothelial cell tight junction (TJ) integral proteins claudin-5 and occludin, a structural protein of caveolae, caveolin-1, and the blood-brain barrier-specific endothelial transporter, Glut 1. In EAE-affected mice, there were areas of extensive subpial demyelination and well-demarcated lesions that extended to deeper cortical layers. Activation of microglia and absence of perivascular inflammatory infiltrates were common in these areas. Microvascular endothelial cells showed increased expression of caveolin-1 and a coincident loss of both claudin-5 and occludin normal junctional staining patterns. At a very early disease stage, claudin-5 molecules tended to cluster and form vacuoles that were also Glut 1 positive; the initially preserved occludin pattern became diffusely cytoplasmic at more advanced stages. Possible internalization of claudin-5 on TJ dismantling was suggested by its coexpression with the autophagosomal marker MAP1LC3A. Loss of TJ integrity was confirmed by fluorescein isothiocyanate-dextran experiments that showed leakage of the tracer into the perivascular neuropil. These observations indicate that, in the cerebral cortex of EAE-affected mice, there is a microvascular disease that differentially targets claudin-5 and occludin during ongoing demyelination despite only minimal inflammation.

Cortical Pathology in RRMS: Taking a Cue from Four Sisters

Background. Although grey matter pathology is a relevant aspect of multiple sclerosis (MS) both with physical and cognitive rebounds, its pathogenesis is still under investigation. To what extent the familial and sporadic cases of MS differ in cortical pathology has not been elucidated yet. Here we present a multiple case report of four sisters affected by MS, all of them having a very high burden of cortical pathology. Methods. The clinical and grey matter MRI parameters of the patients were compared with those of twenty-five-aged matched healthy women and 25 women affected by sporadic MS (matched for age, disease duration, EDSS, and white matter lesion load). Results. Despite their short disease duration (<5 years), the four sisters showed a significant cortical thinning compared to healthy controls (P = 0.003) and sporadic MS (P = 0.041) and higher CLs number (P < 0.001) and volume (P < 0.001) compared to sporadic MS. Discussion. Although limited to a single family, our observation is worth of interest since it suggests that familial factors may account for a peculiar involvement of the cortex in MS pathology. This hypothesis should be further evaluated in a large number of multiplex MS families.

Re-expression of N-cadherin in remyelinating lesions of experimental inflammatory demyelination

The cell adhesion molecule N-cadherin is involved in several processes during central nervous system development, but also in certain pathologic conditions in the adult brain, including tumorigenesis and Alzheimer's disease. N-cadherin function in inflammatory demyelinating disease has so far not been investigated. In vitro studies suggest a role of N-cadherin in myelination; on the other hand N-cadherin has been implicated in the formation of the glial scar, which is believed to impede remyelination. The aim of our study was to investigate the expression pattern of N-cadherin immunoreactivity in experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein (MOG-EAE), an animal model closely mimicking multiple sclerosis. It allows a detailed evaluation of all stages of de- and remyelination during lesion development. Immunopathological evaluation was performed on paraffin-embedded CNS sections sampled at days 20 to 120 post immunization. We found a predominant expression of N-cadherin on oligodendrocytes in early remyelinating lesions, while in fully remyelinated shadow plaques there was no detectable immunoreactivity for N-cadherin. This expression pattern indicates a role of N-cadherin in the initiation of remyelination, most likely by providing a guidance between myelin lamellae and oligodendrocytes. Once the initial contact is made N-cadherin is then rapidly downregulated and virtually absent after completion of the repair process, analog to its known role in developmental myelination. Our results show that N-cadherin plays an important role in creating a remyelination-facilitating environment.

Cuprizone-induced demyelination in the rat cerebral cortex and thyroid hormone effects on cortical remyelination

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the Central Nervous System which is characterized by multifocal demyelinated lesions dispersed throughout the brain. Although white matter lesions have been the most extensively studied, cortical demyelinaton lesions are also detected in MS brains. Cuprizone (CPZ)-induced demyelination in rodents has been widely used as a model for MS. Most of these studies focus on oligodendrocyte-rich structures, such as the corpus callosum (CC) and the cerebellar peduncles. However, it has been recently described that CPZ administration in mice also produces cortical demyelination, resembling some of the lesions found in MS patients. In this work we used CPZ-demyelinating model in Wistar rats to study demyelination in cortical forebrain areas. At the ultrastructural level, demyelination in the cortex was observed before detectable myelin loss in the subcortical white matter. During the course of CPZ intoxication Myelin Basic Protein immunodetection was decreased in cortical layers I-III due to a reduction in the number of cortical oligodendrocytes (OL). Oligodendroglial loss in CPZ-intoxicated rats correlated with an increase in the number of Glial Fibrillary Acidic Protein positive astrocytes and a shift in the location of Carbonic Anhydrase II from OL to astrocytes. After removal of CPZ from the diet, we evaluate intranasal Thyroid hormone (TH) effects on the progression of cortical lesions. As previously reported in the CC, TH treatment also accelerates remyelination rate in the cortex compared to rats undergoing spontaneous remyelination. Our results suggest that manipulation of TH levels could be considered as a strategy to promote remyelination process in the cortex and to prevent neuronal irreversible damage in patients suffering from MS.

The cuprizone model: regional heterogeneity of pathology

The cuprizone model is a model of de- and remyelination secondary to oligodendrocyte death, likely to be mediated by an inhibition of mitochondrial function. The aim of this study was to characterize histopathological changes associated with de/remyelination in grey and white matter at different disease stages in C57Bl/6 mice after per oral administration of cuprizone. Oligodendrocyte loss, astrocytosis and complement activation was detected in areas of demyelination. Demyelination, astrocytosis and complement activation occurred earlier in the cerebral cortex than in the corpus callosum. There was no perivascular lymphocyte infiltration. Microglia- and macrophage activation was observed in the corpus callosum, but not in the cerebral cortex. After cuprizone exposure was stopped, remyelination was extensive in the corpus callosum, but scarce in the cortex. In conclusion, cortical demyelination and oligodendrocyte loss in the cuprizone model may be due to a direct effect on oligodendrocyte mitochondrial function, as it occurs in the absence of microglial activation. The histopathology of de/remyelination in the cuprizone treated mice show regional heterogeneities which suggest differences in the underlying pathophysiology. Cuprizone-induced demyelination is a relevant model for the study of regional heterogeneity of demyelination and lesion pathology in multiple sclerosis.

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.

Outbred ICR/CD1 mice display more severe neuroinflammation mediated by microglial TLR4/CD14 activation than inbred C57Bl/6 mice

Neuroinflammation mediated by microglia is a pathological hallmark of many CNS disorders. Cell lines derived from inbred C57Bl/6 and outbred ICR/CD1 mice (BV-2 and N9 respectively), are often used to study microglial inflammatory activities. Although many studies demonstrate different responses of these cell lines to the same stimulus, no comparisons have been done in vivo. Because inbreeding reduces resistance to pathogens and parasites, we hypothesized that microglia from outbred ICR/CD1 mice would have a stronger response to centrally administered LPS than microglia from inbred C57Bl/6 mice. The evaluation of gene expression in freshly isolated CD11b+ cells from brain revealed that microglia from ICR/CD1 mice were more pro-inflammatory than those from C57Bl/6 mice, although these differences did not appear to result from alterations in the expression levels of the LPS receptors TLR4 or CD14. Notably, the timing of inflammatory gene expression did not correlate with CD11b+ cell proliferation/infiltration. The highest expression of TNFα, IL-6 and iNOS occurred 3 h after LPS injection when the number of CD11b+ cells was not changed. Whereas the expression of these pro-inflammatory genes had returned to basal by 48 h when the highest number of CD11b+ cells in the brain was found, the expression of the anti-inflammatory cytokine IL-10 was still significantly up-regulated. This is important because the increased presence of CD11b+ cells in the CNS is often used as an indicator of neuroinflammation. While LPS did not affect the expression of the growth factors VEGF or BDNF, we observed that mechanical injury (caused by intraparenchymal injection) induced distinct patterns of microglial activation characterized by increased expression of VEGF and down-regulation of BDNF. It remains to be determined which type of microglia is more beneficial/detrimental to the CNS, but our data suggest that genetic traits determining microglial properties may have profound effect on many CNS pathologies.

Cerebral cortex demyelination and oligodendrocyte precursor response to experimental autoimmune encephalomyelitis

Experimentally induced autoimmune encephalomyelitis (EAE) in mice provides an animal model that shares many features with human demyelinating diseases such as multiple sclerosis (MS). To what extent the cerebral cortex is affected by the process of demyelination and how the corollary response of the oligodendrocyte lineage is explicated are still not completely known aspects of EAE. By performing a detailed in situ analysis of expression of myelin and oligodendrocyte markers we have identified areas of subpial demyelination in the cerebral cortex of animals with conventionally induced EAE conditions. On EAE-affected cerebral cortices, the distribution and relative abundance of cells of the oligodendrocyte lineage were assessed and compared with control mouse brains. The analysis demonstrated that A2B5(+) glial restricted progenitors (GRPs) and NG2(+)/PDGFR-α(+) oligodendrocyte precursor cells (OPCs) were increased in number during "early" disease, 20 days post MOG immunization, whereas in the "late" disease, 39 days post-immunization, they were strongly diminished, and there was an accompanying reduction in NG2(+)/O4(+) pre-oligodendrocytes and GST-π mature oligodendrocytes. These results, together with the observed steady-state amount of NG2(-)/O4(+) pre-myelinating oligodendrocytes, suggested that oligodendroglial precursors attempted to compensate for the progressive loss of myelin, although these cells appeared to fail to complete the last step of their differentiation program. Our findings confirm that this chronic model of EAE reproduces the features of neocortex pathology in progressive MS and suggest that, despite the proliferative response of the oligodendroglial precursors, the failure to accomplish final differentiation may be a key contributing factor to the impaired remyelination that characterizes these demyelinating conditions.

EAE: imperfect but useful models of multiple sclerosis

The high failure rate of immunotherapies in multiple sclerosis (MS) clinical trials demonstrates problems in translating new treatment concepts from animal models to the patient. One main reason for this 'immunotherapy gap' is the usage of immunologically immature, microbiologically clean and genetically homogeneous rodent strains. Another reason is the artificial nature of the experimental autoimmune encephalomyelitis model, which favors CD4+ T cell driven autoimmune mechanisms, whereas CD8+ T cells are prevalent in MS lesions. In this paper, we discuss preclinical models in humanized rodents and non-human primates that are genetically closer to MS. We also discuss models that best reproduce specific aspects of MS pathology and how these can potentially improve preclinical selection of promising therapies from the discovery pipeline.

An animal model of cortical and callosal pathology in multiple sclerosis

The pathological and radiological hallmarks of multiple sclerosis (MS) include multiple demyelinated lesions disseminated throughout the white matter of the central nervous system (CNS). More recently, the cerebral cortex has been shown to be affected in MS, but the elucidation of events causing cortical demyelination has been hampered by the lack of animal models reflecting such human cortical pathology. In this report, we have described the presence of cortical gray matter and callosal white matter demyelinating lesions in the chronic experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Similar to the pathological lesions of MS patients, EAE lesions have been classified as type I-leukocortical, type II-intracortical and type III-subpial. All of these lesions had varying degrees of demyelination, inflammatory cells and reactive astrocytes. Similar to MS, cortical layers during EAE showed demyelination, microglia activation, synaptic protein alterations and apoptotic cells. In addition, the callosal white matter during EAE had many inflammatory demyelinating lesions and axon degeneration. Functional electrophysiological conduction analysis showed deficits in both myelinated and unmyelinated callosal axons during early and late EAE. The chronic EAE mouse model has features that mimic cortical and callosal pathology of MS, and can be potentially used to screen agents to prevent these features of disease.

Inflammation, demyelination, and degeneration - recent insights from MS pathology

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system which responds to anti-inflammatory treatments in the early disease phase. However, the pathogenesis of the progressive disease phase is less well understood, and inflammatory as well as neurodegenerative mechanisms of tissue damage are currently being discussed. This review summarizes current knowledge on the interrelation between inflammation, demyelination, and neurodegeneration derived from the study of human autopsy and biopsy brain tissue and experimental models of MS.

Clinical findings and treatment of non-infectious meningoencephalomyelitis in dogs: a systematic review of 457 published cases from 1962 to 2008

Non-infectious meningoencephalomyelitis (NIME) presents clinicians with diagnostic problems because specific diagnosis requires histopathological examination of central nervous system (CNS) tissue. In the absence of a precise diagnosis, clinicians refer instead to 'meningoencephalomyelitis of unknown origin' (MUO). This article compares published data on histopathologically diagnosed disease (granulomatous meningoencephalomyelitis and necrotising encephalitis) with information available on the clinically-defined category of MUO. Small, middle-aged female dogs are most commonly affected by all types of NIME, but there is considerable overlap in diagnostic parameters of these diseases. Future clinical trials must aim to compare prospectively two or more randomly allocated treatments and to include pre-trial power calculations. This article provides the necessary background information to permit rational patient selection on clinical presentation alone, rather than requiring CNS biopsy, thus maximising patient recruitment whilst minimising heterogeneity.

Necrotizing meningoencephalitis of Pug dogs associates with dog leukocyte antigen class II and resembles acute variant forms of multiple sclerosis

Necrotizing meningoencephalitis (NME) is a disorder of Pug Dogs that appears to have an immune etiology and high heritability based on population studies. The present study was undertaken to identify a genetic basis for the disease. A genome-wide association scan with single tandem repeat (STR) markers showed a single strong association near the dog leukocyte antigen (DLA) complex on CFA12. Fine resolution mapping with 27 STR markers on CFA12 further narrowed association to the region containing DLA-DRB1, -DQA1 and, -DQB1 genes. Sequencing confirmed that affected dogs were more likely to be homozygous for specific alleles at each locus and that these alleles were linked, forming a single high risk haplotype. The strong DLA class II association of NME in Pug Dogs resembles that of human multiple sclerosis (MS). Like MS, NME appears to have an autoimmune basis, involves genetic and nongenetic factors, has a relatively low incidence, is more frequent in females than males, and is associated with a vascularly orientated nonsuppurative inflammation. However, NME of Pug Dogs is more aggressive in disease course than classical human MS, appears to be relatively earlier in onset, and involves necrosis rather than demyelination as the central pathobiologic feature. Thus, Pug Dog encephalitis (PDE) shares clinical features with the less common acute variant forms of MS. Accordingly, NME of Pug Dogs may represent a naturally occurring canine model of certain idiopathic inflammatory disorders of the human central nervous system.

Progressive multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system, which starts in the majority of patients with a relapsing/remitting MS (RRMS) course , which after several years of disease duration converts into a progressive disease. Since anti-inflammatory therapies and immune modulation exert a beneficial effect at the relapsing/remitting stage of the disease, but not in the progressive stage, the question was raised whether inflammation drives tissue damage in progressive MS at all. We show here that also in progressive MS, inflammation is the driving force for brain injury and that the discrepancy between inflammation-driven tissue injury and response to immunomodulatory therapies can be explained by different pathomechanisms acting in RRMS and progressive MS.

Focal and diffuse cortical degenerative changes in a marmoset model of multiple sclerosis

BACKGROUND

Degenerative features, such as neuronal, glial, synaptic and axonal loss, have been identified in neocortical and other grey matter structures in patients with multiple sclerosis, but mechanisms for neurodegeneration are unclear. Cortical demyelinating lesions are a potential cause of this degeneration, but the pathological and clinical significance of these lesions is uncertain as they remain difficult to identify and study in vivo. In this study we aimed to describe and quantify cellular and subcellular pathology in the cortex of myelin oligodendrocyte glycoprotein-induced marmoset experimental autoimmune encephalomyelitis using quantitative immunohistochemical methods.

RESULTS

We found evidence of diffuse axonal damage occurring throughout cortical grey matter with evidence for synaptic loss and gliosis and a 13.6% decrease in neuronal size and occurring in deep cortical layers. Evidence of additional axonal damage and a 29.6-36.5% loss of oligodendrocytes was found in demyelinated cortical lesions. Leucocortical lesions also showed neuronal loss of 22.2% and a 15.8% increase in oligodendrocyte size.

CONCLUSIONS

The marmoset experimental autoimmune encephalomyelitis model, therefore, shows both focal and generalized neurodegeneration. The generalized changes cannot be directly related to focal lesions, suggesting that they are either a consequence of diffusible inflammatory factors or secondary to remote lesions acting through trans-synaptic or retrograde degeneration.

Models of autoimmune demyelination in the central nervous system: on the way to translational medicine

Multiple sclerosis (MS) is the most common neurologic disease of young adults. In the recent years, our understanding on disease pathomechanisms has considerably improved and new therapies have emerged. Yet a cure for this devastating disorder is still a far cry away and human resources on ex vivo specimens are limited. More than 70 years after its first description, experimental autoimmune encephalomyelitis (EAE) remains an important tool to understand concepts of T cell mediated autoimmunity as well as the roles of the innate and the humoral immune systems. Some EAE models also well reflect mechanisms of tissue damage including demyelination, axonal injury and also cortical changes. A limitation of the classical EAE model is a neglect of CD8 T cell mediated immune mechanisms. Moreover, well characterized models for primary progressive MS or demyelination patterns involving primary oligodendrocyte dystrophy are still not available. Yet many current therapeutic concepts including glatiramer acetate or natalizumab stem from their successful first application in EAE models. New strategies include the widespread use of conditional knockout mice to understand the cell-type specific function of single genes, innovative approaches to establish models on the roles of B cells and CD8 T cells as well as on the relation of inflammation to primary degeneration. In summary, EAE models continue to play an important role in neuroimmunology thereby also stimulating research in other fields of the neurosciences and immunobiology.

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.