The contribution of demyelination to axonal loss in multiple sclerosis

Multiple sclerosis

Multiple sclerosis (MS) is a chronic, complex neurological disease with a variable clinical course in which several pathophysiological mechanisms such as axonal/ neuronal damage, demyelination, inflammation, gliosis, remyelination and repair, oxidative injury and excitotoxicity, alteration of the immune system as well as biochemical disturbances and disruption of blood-brain barrier are involved.(1,2) Exacerbations of MS symptoms reflect inflammatory episodes, while the neurodegenerative aspects of gliosis and axonal loss result in the progression of disability. The precise aetiology of MS is not yet known, although epidemiological data indicate that it arises from a complex interactions between genetic susceptibility and environmental factors.(3) In this chapter the brain structures and processes involved in immunopathogenesis of MS are presented. Additionally, clinical phenotypes and biomarkers of MS are showed.

Regional brain axial and radial diffusivity changes during development

The developing human brain shows rapid myelination and axonal changes during childhood, adolescence, and early adulthood, requiring successive evaluations to determine normative values for potential pathological assessment. Fiber characteristics can be examined by axial and radial diffusivity procedures, which measure water diffusion parallel and perpendicular to axons and show primarily axonal status and myelin changes, respectively. Such measures are lacking from widespread sites for the developing brain. Diffusion tensor imaging data were acquired from 30 healthy subjects (age 17.7 ± 4.6 years, range 8-24 years, body mass index 21.5 ± 4.5 kg/m(2), 18 males) using a 3.0-Tesla MRI scanner. Diffusion tensors were calculated, principal eigenvalues determined, and axial and radial diffusivity maps calculated and normalized to a common space. A set of regions of interest was outlined from widespread brain areas within rostral, thalamic, hypothalamic, cerebellar, and pontine regions, and average diffusivity values were calculated using normalized diffusivity maps and these regions of interest masks. Age-related changes were assessed with Pearson's correlations, and gender differences evaluated with Student's t-tests. Axial and radial diffusivity values declined with age in the majority of brain areas, except for midhippocampus, where axial diffusivity values correlated positively with age. Gender differences emerged within putamen, thalamic, hypothalamic, cerebellar, limbic, temporal, and other cortical sites. Documentation of normal axial and radial diffusivity values will help assess disease-related tissue changes. Axial and radial diffusivities change with age,with fiber structure and organization differing between sexes in several brain areas. The findings may underlie gender-based functional characteristics, and mandate partitioning age- and gender-related changes during developmental brain pathology evaluation.

Corpus callosum microstructural changes correlate with cognitive dysfunction in early stages of relapsing-remitting multiple sclerosis: axial and radial diffusivities approach

The corpus callosum is the largest fiber bundle in the central nervous system and it takes part in several cognitive pathways. It can be affected by multiple sclerosis (MS) early in the disease. DTI is capable of infering the microstructural organization of the white matter. The vectorial analysis of the DTI offers the more specific indices of axial diffusivity (AD) and radial diffusivity (RD), which have shown to be useful to discriminate myelin damage from axon loss, respectively. This study presents DTI results (mean diffusivity (MD), fractional anisotropy (FA), RD, and AD) of 23 relapsing-remitting MS patients and its correlation with cognitive performance. There were 47.8% of cognitive impaired patients (MS CI). We found signs of demyelination, reflected by increased RD, and incipient axon loss, reflected by AD increase, which was slightly higher in the MS CI. The cognitive changes correlated with the DTI parameters, suggesting that loss of complexity in CC connections can impair neural conduction. Thus, cognitive impairment can be related to callosal disconnection, and DTI can be a promising tool to evaluate those changes.

A potential link between autoimmunity and neurodegeneration in immune-mediated neurological disease

Multiple sclerosis (MS) patients make antibodies to heterogeneous nuclear ribonuclear protein A1 (hnRNP-A1), a nucleocytoplasmic protein. We hypothesized this autoimmune reaction might contribute to neurodegeneration. Antibodies from MS patients reacted with hnRNP-A1-'M9', its nuclear translocation sequence. Transfection of anti-M9 antibodies into neurons resulted in neuronal injury and changes in transcripts related to hnRNP-A1 function. Importantly, RNA levels for the spinal paraplegia genes (SPGs) decreased. Changes in SPG RNA levels were confirmed in neurons purified from MS brains. Also, we show molecular interactions between spastin (the encoded protein of SPG4) and hnRNP-A1. These data suggest a link between autoimmunity, clinical phenotype and neurodegeneration in MS.

Radial diffusivity predicts demyelination in ex vivo multiple sclerosis spinal cords

OBJECTIVE

Correlation of diffusion tensor imaging (DTI) with histochemical staining for demyelination and axonal damage in multiple sclerosis (MS) ex vivo human cervical spinal cords.

BACKGROUND

In MS, demyelination, axonal degeneration, and inflammation contribute to disease pathogenesis to variable degrees. Based upon in vivo animal studies with acute injury and histopathologic correlation, we hypothesized that DTI can differentiate between axonal and myelin pathologies within humans.

METHODS

DTI was performed at 4.7 T on 9 MS and 5 normal control fixed cervical spinal cord blocks following autopsy. Sections were then stained for Luxol fast blue (LFB), Bielschowsky silver, and hematoxylin and eosin (H&E). Regions of interest (ROIs) were graded semi-quantitatively as normal myelination, mild (<50%) demyelination, or moderate-severe (>50%) demyelination. Corresponding axonal counts were manually determined on Bielschowsky silver. ROIs were mapped to co-registered DTI parameter slices. DTI parameters evaluated included standard quantitative assessments of apparent diffusion coefficient (ADC), relative anisotropy (RA), axial diffusivity and radial diffusivity. Statistical correlations were made between histochemical gradings and DTI parameters using linear mixed models.

RESULTS

Within ROIs in MS subjects, increased radial diffusivity distinguished worsening severities of demyelination. Relative anisotropy was decreased in the setting of moderate-severe demyelination compared to normal areas and areas of mild demyelination. Radial diffusivity, ADC, and RA became increasingly altered within quartiles of worsening axonal counts. Axial diffusivity did not correlate with axonal density (p=0.091).

CONCLUSIONS

Increased radial diffusivity can serve as a surrogate for demyelination. However, radial diffusivity was also altered with axon injury, suggesting that this measure is not pathologically specific within chronic human MS tissue. We propose that radial diffusivity can serve as a marker of overall tissue integrity within chronic MS lesions. This study provides pathologic foundation for on-going in vivo DTI studies in MS.

Phosphorylated neurofilament heavy chain correlations to visual function, optical coherence tomography, and treatment

Objective. To correlate visual and neurologic clinical scores and treatment of optic neuritis and multiple sclerosis (MS) patients with assays of serum phosphorylated neurofilament heavy chain (pNF-H) and optical coherence tomography (OCT) measurements of axonal loss. Design/Methods. The Optic Neuritis Treatment Trial (ONTT) randomized 457 patients with acute optic neuritis to intravenous methylprednisolone (IVMP) followed by oral prednisone, oral prednisone or placebo treatment arms. We quantified serum pNF-H levels in 175 ONTT patients 5 years after study entry. We performed OCT measurements of macular volume and the retinal nerve fiber layer (RNFL) in a subset of 51 patients at year 15. Results. Elevated pNF-H levels at year 5 correlated to poorer visual function at study entry. Lower 15 year macular volumes and RNFL thickness correlated better with follow-up than with baseline visual function measures. With IVMP treatment, 15 year RNFL differences of the fellow eye (FE) minus the affected eye (SE) RNFLFEmSE correlated with five-year pNF-H levels. PNF-H was reduced by half with IVMP relative to placebo or by 40% relative to prednisone. Conclusions/Relevance. Acute optic neuritis patients who have more severe visual loss during initial presentation have a higher incidence of axonal loss that was slightly suppressed with IVMP treatment.

Using diffusion tensor imaging and immunofluorescent assay to evaluate the pathology of multiple sclerosis

PURPOSE

To determine the ability of the principal diffusion tensor imaging (DTI) indices to predict the underlying histopathology evaluated with immunofluorescent assay (IFA).

MATERIALS AND METHODS

Conventional T2 and 3D multishot-diffusion weighted echoplanar imaging (3D ms-DWEPI) was performed on a fixed, ex vivo human cervical spinal cord (CSC) from a patient with a history of multiple sclerosis (MS). In all, 170 regions of interest (ROIs) were selected within the white matter and categorized as a high intensity lesion (HIL), low intensity lesion (LIL), and normal-appearing white matter (NAWM). The longitudinal diffusivity (λl), radial diffusivity (λr), and fractional anisotropy (FA) were obtained from each ROI. The underlying histopathology was then evaluated using immunofluorescent assay with antibodies directed to myelin and neurofilament staining.

RESULTS

The mean values for λl and λr were significantly elevated within HIL relative to NAWM and LIL. IFA analysis of HIL demonstrated significant demyelination, without significant if any axon loss. The FA values were significantly reduced in HIL and LILs. FA values were also reduced in lesions with increased λl and λr values relative to normal.

CONCLUSION

Aberrant λl, λr, and FA relative to normal values are strong indicators of demyelination. DTI indices are not specific for axon loss. IFA analysis is a reliable method to demonstrate myelin and axon pathology within the ex vivo setting.

Axonal loss and neurofilament phosphorylation changes accompany lesion development and clinical progression in multiple sclerosis

Neuroaxonal damage and loss are increasingly recognized as disability determining features in multiple sclerosis (MS) pathology. However, little is known about the long-term sequelae of inflammatory demyelination on neurons and axons. Spinal cord tissue of 31 MS patients was compared to three amyotrophic lateral sclerosis (ALS) and 10 control subjects. MS lesions were staged according to the density of KiM-1P positive macrophages and microglia and the presence of myelin basic protein (MBP) positive phagocytes. T cells were quantified in the parenchyma and meninges. Neuroaxonal changes were studied by immunoreactivity (IR) for amyloid precursor protein (APP) and variably phosphorylated neurofilaments (SMI312, SMI31, SMI32). Little T cell infiltration was still evident in chronic inactive lesions. The loss of SMI32 IR in ventral horn neurons correlated with MS lesion development and disease progression. Similarly, axonal loss in white matter (WM) lesions correlated with disease duration. A selective reduction of axonal phosphorylated neurofilaments (SMI31) was observed in WM lesions. In ALS, the loss of neuronal SMI32 IR was even more pronounced, whereas the relative axonal reduction resembled that found in MS. Progressive neuroaxonal neurofilament alterations in the context of chronic inflammatory demyelination may reflect changes in neuroaxonal metabolism and result in chronic neuroaxonal dysfunction as a putative substrate of clinical progression.

Optical coherence tomography (OCT): imaging the visual pathway as a model for neurodegeneration

Axonal and neuronal degeneration are important features of multiple sclerosis (MS) and other neurologic disorders that affect the anterior visual pathway. Optical coherence tomography (OCT) is a non-invasive technique that allows imaging of the retinal nerve fiber layer (RNFL), a structure which is principally composed of ganglion cell axons that form the optic nerves, chiasm, and optic tracts. Since retinal axons are nonmyelinated until they penetrate the lamina cribrosa, the RNFL is an ideal structure (no other central nervous system tract has this unique arrangement) for visualizing the processes of neurodegeneration, neuroprotection and, potentially, even neuro-repair. OCT is capable of providing high-resolution reconstructions of retinal anatomy in a rapid and reproducible fashion and permits objective analysis of the RNFL (axons) as well as ganglion cells and other neurons in the macula. In a systematic OCT examination of multiple sclerosis (MS) patients, RNFL thickness and macular volumes are reduced when compared to disease-free controls. Conspicuously, these changes, which signify disorganization of retinal structural architecture, occur over time even in the absence of a history of acute demyelinating optic neuritis. RNFL axonal loss in MS is most severe in those eyes with a corresponding reduction in low-contrast letter acuity (a sensitive vision test involving the perception of gray letters on a white background) and in those patients who exhibit the greatest magnitude of brain atrophy, as measured by validated magnetic resonance imaging techniques. These unique structure-function correlations make the anterior visual pathway an ideal model for investigating the effects of standard and novel therapies that target axonal and neuronal degeneration. We provide an overview of the physics of OCT, its unique properties as a non-invasive imaging technique, and its potential applications toward understanding mechanisms of brain tissue injury in MS, other optic neuropathies, and neurologic disorders.

Heterogeneity in multiple sclerosis: scratching the surface of a complex disease

Multiple Sclerosis (MS) is the most common demyelinating disease of the central nervous system. Although the etiology and the pathogenesis of MS has been extensively investigated, no single pathway, reliable biomarker, diagnostic test, or specific treatment have yet been identified for all MS patients. One of the reasons behind this failure is likely to be the wide heterogeneity observed within the MS population. The clinical course of MS is highly variable and includes several subcategories and variants. Moreover, apart from the well-established association with the HLA-class II DRB1*15:01 allele, other genetic variants have been shown to vary significantly across different populations and individuals. Finally both pathological and immunological studies suggest that different pathways may be active in different MS patients. We conclude that these "MS subtypes" should still be considered as part of the same disease but hypothesize that spatiotemporal effects of genetic and environmental agents differentially influence MS course. These considerations are extremely relevant, as outcome prediction and personalised medicine represent the central aim of modern research.

Meningeal T cells associate with diffuse axonal loss in multiple sclerosis spinal cords

OBJECTIVE

A link between diffuse axonal loss and diffuse inflammation has been established in the brain of patients with progressive multiple sclerosis (MS). In the present paper, we sought to determine whether such a link could be similarly demonstrated in the spinal cord of patients with progressive MS.

METHODS

A neuropathological quantitative assessment of inflammation and axonal loss was performed in the cervical spinal cord of 18 patients with progressive MS and 5 control subjects.

RESULTS

As previously reported, we found a mean 25% decrease of axonal density in the normal-appearing white matter (NAWM) of MS versus control spinal cords. T-cell perivascular infiltrates were rare, but a robust diffuse inflammation was observed in both the normal-appearing parenchyma and the meninges. The extent of diffuse axonal loss in the NAWM correlated with both the density of major histocompatibility complex (MHC) class II(+) microglia in the NAWM and, surprisingly, the density of CD3(+) T cells in the meninges. Interestingly, close interactions between T cells and MHC class II(+) macrophages were observed in the meninges of spinal cords from MS patients.

INTERPRETATION

Recent studies assigned a major role to meningeal B-cell follicles in the pathophysiology of secondary progressive MS. The present work also emphasizes the link between meningeal inflammation and parenchymal lesions and points to a specific role exerted by both meningeal T cells and activated microglia in diffuse axonal loss in the spinal cord.

Demyelination versus remyelination in progressive multiple sclerosis

The causes of incomplete remyelination in progressive multiple sclerosis are unknown, as are the pathological correlates of the different clinical characteristics of patients with primary and secondary progressive disease. We analysed brains and spinal cords from 51 patients with progressive multiple sclerosis by planimetry. Thirteen patients with primary progressive disease were compared with 34 with secondary progressive disease. In patients with secondary progressive multiple sclerosis, we found larger brain plaques, more demyelination in total and higher brain loads of active demyelination compared with patients with primary progressive disease. In addition, the brain density of plaques with high-grade inflammation and active demyelination was highest in secondary progressive multiple sclerosis and remained ~18% higher than in primary progressive multiple sclerosis after adjustments for other plaque types and plaque number (P<0.05). Conversely, the proportion of remyelinated shadow plaques (P<0.05) and the overall remyelination capacity (P<0.01) per brain were higher in primary, compared with secondary, progressive multiple sclerosis. By contrast, there were no group differences in the brain load or frequency of low-grade inflammatory plaques with slowly expanding demyelination. Spinal cord lesion loads and remyelination capacity were also comparable in the two patient groups. Remyelinated areas were more vulnerable than the normal-appearing white matter to new demyelination, including active demyelination in secondary progressive multiple sclerosis. 'Recurrent' slowly expanding demyelination, affecting remyelinated areas, and the load of slowly expanding demyelination correlated with incomplete remyelination in both groups. In turn, incomplete remyelination in the spinal cord correlated with higher disease-related disability (determined retrospectively; r = -0.53; P<0.05 for remyelination capacity versus disease severity). By contrast, such a correlation was not observed in the brain. We propose that regulatory and reparative properties could protect the white matter of the brain in patients with primary progressive multiple sclerosis. These patients may, thereby, be spared symptoms until the spinal cord is affected. By contrast, recurrent active demyelination of repaired myelin could explain why similar symptoms often develop in consecutive relapses in relapsing-remitting/secondary progressive multiple sclerosis. Our data also indicate that slowly expanding demyelination may irreparably destroy normal and repaired myelin, supporting the concept of slowly expanding demyelination as an important pathological correlate of clinical progression.

A longitudinal study of MRI-detected atrophy in secondary progressive multiple sclerosis

MRI measures of tissue atrophy within the central nervous system may reflect the neurodegenerative process which underpins the progressive phase of multiple sclerosis (MS). There has been limited longitudinal investigation of MRI-detected atrophy in secondary progressive MS. This study includes 56 subjects with secondary progressive MS. Subjects were followed up for 2 years and MRI analysis was conducted at 12 month intervals using the following measures: (1) whole brain (WB) volume change; (2) grey and white matter (WM) volumes; (3) central brain volume; (4) upper cervical spinal cord (SC) area; (5) T2 lesion volumes. Clinical measures included the Expanded Disability Status Scale and the MS Functional Composite. All volumetric MRI measures were assessed for sensitivity, responsiveness, reliability and correlation with disability. The mean annual atrophy rate of WB was 0.59% per year and this was the most responsive atrophy measure assessed. Grey matter (GM) atrophy (-1.18% per year) was greater and more responsive than WM atrophy (0.12% per year). The SC demonstrated the highest atrophy rate at 1.63% per year. WB, GM and SC atrophy all correlated with change in the Multiple Sclerosis Functional Composite z score (r = 0.35, 0.42, 0.34), and GM atrophy was the only correlate of change in the 9 Hole Peg Test and Paced Auditory Serial Addition Test performance. None of the MRI measures correlated with Expanded Disability Status Score progression. Measures of WB, GM and SC atrophy all have attributes for use as surrogate markers in secondary progressive MS trials and improvement in the reliability of the GM and SC volume measurements may enhance these further.

The natural history of multiple sclerosis: a geographically based study 10: relapses and long-term disability

The relationship of relapses to long-term disability in multiple sclerosis is uncertain. Relapse reduction is a common therapeutic target but clinical trials have shown dissociation between relapse suppression and disability accumulation. We investigated relationships between relapses and disability progression for outcomes of requiring assistance to walk, being bedridden and dying from multiple sclerosis [Disability Status Scale 6, 8, 10] by analysing 28 000 patient-years of evolution in 806-bout onset patients from the London Ontario natural history cohort. Having previously shown no effect of relapse frequency among progressive multiple sclerosis subtypes, here we examined these measures in the pre-progressive or relapsing-remitting phase. Survival was compared among groups stratified by (i) early relapses--number of attacks during the first 2 years of multiple sclerosis; (ii) length of first inter-attack interval; (iii) interval between onset and Disability Status Scale 3 (moderate disability); (iv) number of attacks from the third year of disease up to onset of progression; and (v) during the entire relapsing-remitting phase. Early clinical features can predict hard disability outcomes. Frequent relapses in the first 2 years and shorter first inter-attack intervals predicted shorter times to reach hard disability endpoints. Attack frequencies, in the first 2 years, of 1 versus >or=3, gave differences of 7.6, 12.8 and 20.3 years in times from disease onset to Disability Status Scale 6, 8 and 10, respectively. Time to Disability Status Scale 3 highly and independently predicted time to Disability Status Scale 6, 8 and 10. In contrast, neither total number of relapsing-remitting phase attacks nor of relapses experienced during the relapsing-remitting phase after the second year up to onset of progression showed a deleterious effect on times from disease onset, from progression onset and from Disability Status Scale 3 to these hard endpoints. The failure of a regulatory mechanism tied to neurodegeneration is suggested. Relapse frequency beyond Year 2 does not appear to predict the key outcome of secondary progression or times to Disability Status Scale 6, 8 or 10, highlighting two distinct disease phases related to late outcome. These appear to be separated by a watershed within the relapsing-remitting phase, just a few years after clinical onset. Higher early relapse frequencies and shorter first inter-attack intervals herald more rapid deterioration via interaction with the neurodegeneration characterizing secondary progression. They increase the probability of its occurrence, its latency and influence--to a lesser degree--its slope. The prevention or delay of the progressive phase of the disease is implicated as a key therapeutic target in relapsing-remitting patients.

Longitudinal study of vision and retinal nerve fiber layer thickness in multiple sclerosis

OBJECTIVE

Cross-sectional studies of optical coherence tomography (OCT) show that retinal nerve fiber layer (RNFL) thickness is reduced in multiple sclerosis (MS) and correlates with visual function. We determined how longitudinal changes in RNFL thickness relate to visual loss. We also examined patterns of RNFL thinning over time in MS eyes with and without a prior history of acute optic neuritis (ON).

METHODS

Patients underwent OCT measurement of RNFL thickness at baseline and at 6-month intervals during a mean follow-up of 18 months at 3 centers. Low-contrast letter acuity (2.5%, 1.25% contrast) and visual acuity (VA) were assessed.

RESULTS

Among 299 patients (593 eyes) with >or=6 months follow-up, eyes with visual loss showed greater RNFL thinning compared to eyes with stable vision (low-contrast acuity, 2.5%: p < 0.001; VA: p = 0.005). RNFL thinning increased over time, with average losses of 2.9microm at 2 to 3 years and 6.1microm at 3 to 4.5 years (p < 0.001 vs 0.5-1-year follow-up interval). These patterns were observed for eyes with or without prior history of ON. Proportions of eyes with RNFL loss greater than test-retest variability (>or=6.6microm) increased from 11% at 0 to 1 year to 44% at 3 to 4.5 years (p < 0.001).

INTERPRETATION

Progressive RNFL thinning occurs as a function of time in some patients with MS, even in the absence of ON, and is associated with clinically significant visual loss. These findings are consistent with subclinical axonal loss in the anterior visual pathway in MS, and support the use of OCT and low-contrast acuity as methods to evaluate the effectiveness of putative neuroprotection protocols.

Abnormal tau phosphorylation in primary progressive multiple sclerosis

Although neurodegeneration is the pathological substrate of progression in multiple sclerosis (MS), the underlying mechanisms remain unresolved. Abnormal phosphorylation of tau, implicated in the aetiopathogenesis of a number of classic neurodegenerative disorders, has also recently been described in secondary progressive MS (SPMS). In contrast to SPMS, primary progressive MS (PPMS) represents a significant subset of patients with accumulating neurological disability from onset. The neuropathological relationship between SPMS and PPMS is unknown. Against this background, we investigated tau phosphorylation status in five cases of PPMS using immunohistochemical and biochemical methods. We report widespread abnormal tau hyperphosphorylation of the classic tau phospho-epitopes occurring in multiple cell types but with a clear immunohistochemical glial bias. In addition, biochemical analysis revealed abnormally phosphorylated insoluble tau in all cases. These findings establish a platform for further study of the role of insoluble tau formation, including determining the relevance of glial tau pathology, in the neurodegenerative phase of MS.

Wallerian degeneration: a major component of early axonal pathology in multiple sclerosis

Axonal loss is a major component of the pathology of multiple sclerosis (MS) and the morphological basis of permanent clinical disability. It occurs in demyelinating plaques but also in the so-called normal-appearing white matter (NAWM). However, the contribution of Wallerian degeneration to axonal pathology is not known. Here, we analyzed the extent of Wallerian degeneration and axonal pathology in periplaque white matter (PPWM) and lesions in early multiple sclerosis biopsy tissue from 63 MS patients. Wallerian degeneration was visualized using an antibody against the neuropeptide Y receptor Y1 (NPY-Y1R). The number of SMI-32-positive axons with non-phosphorylated neurofilaments was significantly higher in both PPWM and plaques compared to control white matter. APP-positive, acutely damaged axons were found in significantly higher numbers in plaques compared to PPWM. Strikingly, the number of NPY-Y1R-positive axons undergoing Wallerian degeneration was significantly higher in PPWM and plaques than in control WM. NPY-Y1R-positive axons in PPWM were strongly correlated to those in the lesions. Our results show that Wallerian degeneration is a major component of axonal pathology in the periplaque white matter in early MS. It may contribute to radiological changes observed in early MS and most likely plays a major role in the development of disability.

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.

Brain tissue sodium concentration in multiple sclerosis: a sodium imaging study at 3 tesla

Neuro-axonal degeneration occurs progressively from the onset of multiple sclerosis and is thought to be a significant cause of increasing clinical disability. Several histopathological studies of multiple sclerosis and experimental autoimmune encephalomyelitis have shown that the accumulation of sodium in axons can promote reverse action of the sodium/calcium exchanger that, in turn, leads to a lethal overload in intra-axonal calcium. We hypothesized that sodium magnetic resonance imaging would provide an indicator of cellular and metabolic integrity and ion homeostasis in patients with multiple sclerosis. Using a three-dimensional radial gradient-echo sequence with short echo time, we performed sodium magnetic resonance imaging at 3 T in 17 patients with relapsing-remitting multiple sclerosis and in 13 normal subjects. The absolute total tissue sodium concentration was measured in lesions and in several areas of normal-appearing white and grey matter in patients, and corresponding areas of white and grey matter in controls. A mixed model analysis of covariance was performed to compare regional tissue sodium concentration levels in patients and controls. Spearman correlations were used to determine the association of regional tissue sodium concentration levels in T(2)- and T(1)-weighted lesions with measures of normalized whole brain and grey and white matter volumes, and with expanded disability status scale scores. In patients, tissue sodium concentration levels were found to be elevated in acute and chronic lesions compared to areas of normal-appearing white matter (P < 0.0001). The tissue sodium concentration levels in areas of normal-appearing white matter were significantly higher than those in corresponding white matter regions in healthy controls (P < 0.0001). The tissue sodium concentration value averaged over lesions and over regions of normal-appearing white and grey matter was positively associated with T(2)-weighted (P < or = 0.001 for all) and T(1)-weighted (P < or = 0.006 for all) lesion volumes. In patients, only the tissue sodium concentration value averaged over regions of normal-appearing grey matter was negatively associated with the normalized grey matter volume (P = 0.0009). Finally, the expanded disability status scale score showed a mild, positive association with the mean tissue sodium concentration value in chronic lesions (P = 0.002), in regions of normal-appearing white matter (P = 0.004) and normal-appearing grey matter (P = 0.002). This study shows the feasibility of using in vivo sodium magnetic resonance imaging at 3 T in patients with multiple sclerosis. Our findings suggest that the abnormal values of the tissue sodium concentration in patients with relapsing-remitting multiple sclerosis might reflect changes in cellular composition of the lesions and/or changes in cellular and metabolic integrity. Sodium magnetic resonance imaging has the potential to provide insight into the pathophysiological mechanisms of tissue injury when correlation with histopathology becomes available.

Type 1 diabetes mellitus and multiple sclerosis: common etiological features

Type 1 diabetes mellitus and multiple sclerosis have been largely seen as different, organ-specific diseases, which are managed by different medical specialties. Research studies on these diseases have for the most part followed independent tracks. In this Review, we highlight the latest epidemiological and genetic findings, which have identified many features common to both disorders. Experts consider it increasingly likely that the environment contributes substantially to this overlap. However, although genetic elements that are distinct to each disease probably determine the ultimate form of autoimmunity that is manifested, strikingly broad parallels are seen between the components of genetic risk of type 1 diabetes mellitus and multiple sclerosis. Similarities and differences between these two diseases draw attention to shared disease pathways but insights into each disorder are providing mutual illumination of their pathogenesis.

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.

Update on inflammation, neurodegeneration, and immunoregulation in multiple sclerosis: therapeutic implications

Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system of uncertain etiology. There is consensus that a dysregulated immune system plays a critical role in the pathogenesis of MS; therefore, we aim to summarize current hypotheses concerning the complex cellular and molecular interactions involved in the immunopathology of MS. Although CD4+ T lymphocytes have long been implicated in the immunopathology of MS, the role of other T-cell subtypes has been recognized. CD4+ and CD8+ cells have been isolated from different locations within MS lesions and gamma/delta T cells have been isolated from early MS lesions. The prevalent dogma has been that CD4+ TH1 cells release cytokines and mediators of inflammation that may cause tissue damage, although CD4+ TH2 cells may be involved in modulation of these effects. Recent evidence, however, suggests that additional T-cell subsets play a prominent role in MS immunopathology: TH17 cells, CD8+ effector T cells, and CD4+CD25+ regulatory T cells. In addition, laboratory and clinical data are accumulating on the prominent role of B lymphocytes and antigen-presenting cells in MS pathogenesis. On the basis of these observations, new therapeutic approaches for MS will need to focus on resetting multiple components of the immune system.

Multiple sclerosis and the major histocompatibility complex

PURPOSE OF REVIEW

Multiple sclerosis (MS) is the most common neurological disease affecting young adults. The cause is unknown, but detailed epidemiological and genetic studies have shown a clear inherited component. We review here some of the recent findings of MS genetics with a particular focus on genes of the major histocompatibility complex (MHC).

RECENT FINDINGS

Recent studies add further complexity to the role of the MHC in MS. Reported MHC associations are complex, involving haplotypes rather than single alleles and may involve epigenetic mechanisms and other modulators of gene expression. MHC class II haplotypes display a hierarchy of risks, including protective effects and epistatic interactions, which together dwarf any non-MHC genetic effect. Genes in the MHC region have been shown to influence disease severity, display parent-of-origin effects and interact with a major environmental candidate for MS, vitamin D.

SUMMARY

The MHC class II association with MS is not as straightforward as previously thought. A complete understanding of the epistatic interactions and epigenetic features of this region will be important to understand disease pathogenesis and likely aid the discovery of new therapeutics.

Quantification of myelin and axon pathology during relapsing progressive experimental autoimmune encephalomyelitis in the Biozzi ABH mouse

Multiple sclerosis is an immune-mediated demyelinating disease, with axonal loss underlying long-term progressive disability. In this study, we have analyzed axonal and myelin pathology in a chronic relapsing-remitting experimental autoimmune encephalomyelitis model in Biozzi ABH mice induced by immunization with a syngeneic spinal cord homogenate. The animals were followed for3 months; inflammation, T-cell infiltration, demyelination, and axonal loss were examined at various time points throughout the disease course. We found that macrophage infiltration and microglia activation preceded detectable T-cell infiltration. Axonal loss was first evident at the acute phase of disease before demyelination was detected. Demyelination and axonal loss occurred after each relapse and correlated with increasing residual motor deficits in remission. The resulting lesions displayed evidence of demyelination, remyelination, axonal degeneration, and axon loss. After a series of 3 relapses, animals entered a chronic progressive phase with permanent paralysis and a relative absence of inflammation. Axonal loss continued in this phase, although demyelinated axons persisted. These findings indicate that experimental autoimmune encephalomyelitis in Biozzi ABH mice has important similarities to multiple sclerosis with a relapsing-remitting disease course followed by a secondary progressive phase; it is thus a suitable model in which to explore remyelination and neuroprotective therapies for multiple sclerosis.

The relation between inflammation and neurodegeneration in multiple sclerosis brains

Some recent studies suggest that in progressive multiple sclerosis, neurodegeneration may occur independently from inflammation. The aim of our study was to analyse the interdependence of inflammation, neurodegeneration and disease progression in various multiple sclerosis stages in relation to lesional activity and clinical course, with a particular focus on progressive multiple sclerosis. The study is based on detailed quantification of different inflammatory cells in relation to axonal injury in 67 multiple sclerosis autopsies from different disease stages and 28 controls without neurological disease or brain lesions. We found that pronounced inflammation in the brain is not only present in acute and relapsing multiple sclerosis but also in the secondary and primary progressive disease. T- and B-cell infiltrates correlated with the activity of demyelinating lesions, while plasma cell infiltrates were most pronounced in patients with secondary progressive multiple sclerosis (SPMS) and primary progressive multiple sclerosis (PPMS) and even persisted, when T- and B-cell infiltrates declined to levels seen in age matched controls. A highly significant association between inflammation and axonal injury was seen in the global multiple sclerosis population as well as in progressive multiple sclerosis alone. In older patients (median 76 years) with long-disease duration (median 372 months), inflammatory infiltrates declined to levels similar to those found in age-matched controls and the extent of axonal injury, too, was comparable with that in age-matched controls. Ongoing neurodegeneration in these patients, which exceeded the extent found in normal controls, could be attributed to confounding pathologies such as Alzheimer's or vascular disease. Our study suggests a close association between inflammation and neurodegeneration in all lesions and disease stages of multiple sclerosis. It further indicates that the disease processes of multiple sclerosis may die out in aged patients with long-standing disease.

Diffusion tensor imaging of ex vivo cervical spinal cord specimens: the immediate and long-term effects of fixation on diffusivity

Diffusion tensor imaging (DTI) is an emerging noninvasive method for evaluating tissue microstructure, but is highly susceptible to in vivo motion artifact. Ex vivo experiments on fixed tissues are needed to improve DTI techniques, which require fixed tissue specimens. Several efforts have been made to study the effect of fixation on both human and mouse tissue, with varying results. Four human cervical cords and three segments of pig cervical spinal cord specimens were imaged both before and after tissue fixation using 3D multishot diffusion weighted imaging (ms-DWEPI). Fixation caused a significant decrease in the longitudinal diffusivity whereas the relative anisotropy (RA) and radial diffusivity remained unaffected. Additionally, once adequately preserved, the diffusivity parameters of fixed tissue remain constant over time. Fixation has important effects on the diffusivity of tissue specimens. These findings have important implications for the determination of tissue microstructure and function using DTI technologies.

Axonal loss and myelin in early ON loss in postacute optic neuritis

OBJECTIVE

To investigate the relation between retinal nerve fiber layer (RNFL) thickness and latency and amplitude of multifocal visual-evoked potentials (mfVEPs) in the postacute stage of optic neuritis in patients with early or possible multiple sclerosis.

METHOD

Thirty-two patients with clinical diagnosis of unilateral optic neuritis and magnetic resonance imaging lesions typical of demyelination and 25 control subjects underwent mfVEP and optical coherence tomography imaging.

RESULTS

Although there was significant reduction of RNFL thickness in the affected eyes (18.7%), a considerably larger decrease was observed for the amplitude of the mfVEPs (39.8%). Latency of the mfVEPs was also significantly delayed in optic neuritis eyes. In fellow eyes, the amplitude of mfVEPs was significantly reduced and the latency prolonged, but RNFL thickness remained unaltered. RNFL thickness correlated highly with the mfVEP amplitude (r = 0.90). There was also strong correlation between optical coherence tomography measure of axonal loss and mfVEP latency (r = -0.66).

INTERPRETATION

Although our findings demonstrate strong associations between structural and functional measures of optic nerve integrity, the functional loss was more marked. This fact, together with amplitude and latency changes of the mfVEPs observed in clinically normal fellow eyes, may indicate greater sensitivity of mfVEPs in detecting optic nerve abnormality or the presence of widespread inflammation in the central nervous system, or both. The significant correlation of the mfVEP latency with RNFL thickness suggests a role for demyelination in promoting axonal loss.

Multiple sclerosis: immunopathogenesis and controversies in defining the cause

PURPOSE OF REVIEW

Multiple sclerosis is a major cause of neurological disability in Western societies. The most important reason for the limited success obtained in the treatment and prevention so far is most likely related to the limited knowledge about its cause and pathogenesis. This paper discusses recent progress and controversies in the understanding of the pathogenesis and cause of multiple sclerosis.

RECENT FINDINGS

Both T helper cells type 1 (Th1 cells), Th17 cells, cytotoxic T cells, B cells and regulatory T cells are involved in the inflammatory process. Axonal loss seems to be driven by inflammation during the early stages of disease but may become independent of inflammation at later stages. The target antigen of the immune response has not been identified. Weak genetic association has been established in two cytokine receptors, whereas increasing female: male ratio support the importance of environmental risk factors. A substantial proportion of intrathecal B cells are infected with Epstein-Barr virus.

SUMMARY

Multiple sclerosis is a complex disease and calls for integrated efforts from immunology, epidemiology, neuroscience and genetics. In particular, the immunological implications of environmental risk factors such as vitamin D desufficiency, smoking and Epstein-Barr virus infection need to be explored.

Transient 5-(4-phenylbutoxy)psoralen (PAP-1) treatment dissociates developing pathologies in autoimmune optic neuritis into two distinct pathology profiles

Discovery of treatments to protect axonal function of neurons and prevent permanent disability associated with progressive multiple sclerosis (MS) has faced the uphill challenge of assessing relatively small changes in accumulated axon damage within a background environment that is disorganized by CNS inflammation. We hypothesized that transient immunosuppression after initiation of MS-like autoimmune mechanisms would disassociate development of MS-like myelinated axon pathology from development of CNS inflammation in a rat model of autoimmune optic neuritis (AON). A rat model of myelin oligodendrocyte glycoprotein peptide-induced AON was transiently treated (on days 3-7 after antigen exposure) with 5-(4-phenylbutoxy)psoralen (PAP-1), an immunomodulatory drug previously shown specifically to suppress proliferation of effector memory T-cells and immunoglobulin class-switched B-cells. Thirteen days after antigen exposure, optic nerves were harvested for quantitative assessment of 12 MS-associated pathologies using microfluorimetry. With one exception, the immunoreactivities (-ir) for eight markers of MS-like neuroinflammation and immune infiltration were significantly reduced (P < 0.05) by transient PAP-1 treatment, often to levels significantly below those detected in normal control rat optic nerves. With one exception, four immunoreactive markers of MS-like myelinated axon pathology were detected at levels indicating increased axon/myelin pathology compared with vehicle-treated rats with AON (P < 0.05). These data suggest the conclusion that early causative mechanisms in CNS autoimmunity initiate signaling mechanisms that diverge into two separate pathways, one that is strongly associated with inflammatory responses and one that is associated predominantly with disturbed axon-myelin interactions and impaired fast axonal transport.

No effect of preterm birth on the risk of multiple sclerosis: a population based study

Background

Genetic and environmental factors have important roles in multiple sclerosis (MS) susceptibility. A clear parent of origin effect has been shown in several populations, perhaps resulting from factors operating during gestation. Preterm birth (birth at less than 37 weeks gestational age) has been shown to result in long-term health problems, including impaired neurological development. Here, in a population-based cohort, we investigate whether preterm birth increases the risk to subsequently develop MS.

Methods

We identified 6585 MS index cases and 2509 spousal controls with preterm birth information from the Canadian Collaborative Project on Genetic Susceptibility to MS. Rates of individuals born preterm were compared for index cases and controls.

Results

There were no significant differences between cases and controls with respect to preterm births. 370 (5.6%) MS index cases and 130 (5.2%) spousal controls were born preterm, p = 0.41.

Conclusion

Preterm birth does not appear to contribute to MS aetiology. Other factors involved in foetal and early development need to be explored to elucidate the mechanism of the increased risk conferred by the apparent maternal effect.

Protecting axons in multiple sclerosis

Typically patients with multiple sclerosis (MS) experience acute episodes of neurological dysfunction, which recover followed, at a later stage, by slow and insidious accumulation of disability (disease progression). Disease progression reflects axon damage and loss within the central nervous system. However, the precise mechanism of axon injury in MS is not clear. Inflammation occurring during acute relapses undoubtedly causes some degree of acute axon damage, but epidemiological data and treatment studies have suggested that inflammation alone is not the sole cause of axonopathy. Indeed, there appears to be dissociation between inflammation and disease progression once a certain level of clinical disability has been reached because immune suppression in patients who have established disease progression does not halt the slow decrease of function. The slow and insidious loss of neurological function that occurs during the progressive phase of the disease implies a degenerative process. Whether axon drop-out occurs at these later stages because of previous inflammatory damage to axons; because of low grade inflammation causing damage to already vulnerable demyelinated axons; because of loss of trophic environment for axons to survive; or as part of a completely independent neurodegenerative process is not clear. Understanding disease mechanisms involved in the axonopathy of MS allows for the development of rational therapies for disease progression.

Atrophy in white matter fiber tracts in multiple sclerosis is not dependent on tract length or local white matter lesions

The pathogenesis of tissue injury outside the white matter (WM) plaques of multiple sclerosis (MS) has not yet been clearly defined. To better understand the pathogenesis of this injury and the associated atrophy, we investigated volume loss over time in 20 WM fiber tracts. We defined two main aims: (1) to examine whether certain fiber tracts were more prone to atrophy, and to test the possible relation of tract atrophy to tract length and selected MS-specific variables; and (2) to investigate the possible relation of atrophy to lesion load (whole brain and in the specific tract). Local volume change was assessed between two distant time points for each MS patient studied. Fiber tracts were segmented automatically using a tractography-based atlas. Results demonstrate volume loss in all fiber tracts. The uncinate fasciculus and anterior-thalamic radiation had the greatest yearly percentage atrophy. Disease type, duration, median expanded disability status scale, total lesion load, and gender exhibited significant effects on atrophy in at least one tract. Together, these data are more consistent with a pathogenesis for the degeneration related to diffuse inflammation rather than the secondary effects of focal lesions.

Astrocytes--friends or foes in multiple sclerosis?

In multiple sclerosis (MS), the presence of demyelinating plaques has concentrated researchers' minds on the role of the oligodendrocyte in its pathophysiology. Recently, with the rediscovery of early and widespread loss of axons in the disease, new emphasis has been put on the role of axons and axon-oligodendrocyte interactions in MS. Despite the fact that, in 1904, Müller claimed that MS was a disease of astrocytes, more recently, astrocytes have taken a back seat, except as the cells that form the final glial scar after all hope of demyelination is over. However, perhaps it is time for the return of the astrocyte to popularity in the pathogenesis of MS, with recent reports on the dual role of astrocytes in aiding degeneration and demyelination, by promoting inflammation, damage of oligodendrocytes and axons, and glial scarring, but also in creating a permissive environment for remyelination by their action on oligodendrocyte precursor migration, oligodendrocyte proliferation, and differentiation. We review these findings to try to provide a cogent view of astrocytes in the pathology of MS.

Multiple sclerosis findings in the spinal cord

The spinal cord is commonly affected by acute demyelinating lesions, chronic tissue loss and atrophy in multiple sclerosis, and is a clinically eloquent site. Historically, however, more attention has been focussed on the analysis and contribution of brain lesions. In this review, we discuss some of the key findings from MRI analysis and histopathological examination of the spinal cord, and how they relate to the clinical characteristics of this common and disabling disease.

Neurofascin as a novel target for autoantibody-mediated axonal injury

Axonal injury is considered the major cause of disability in patients with multiple sclerosis (MS), but the underlying effector mechanisms are poorly understood. Starting with a proteomics-based approach, we identified neurofascin-specific autoantibodies in patients with MS. These autoantibodies recognize the native form of the extracellular domains of both neurofascin 186 (NF186), a neuronal protein concentrated in myelinated fibers at nodes of Ranvier, and NF155, the oligodendrocyte-specific isoform of neurofascin. Our in vitro studies with hippocampal slice cultures indicate that neurofascin antibodies inhibit axonal conduction in a complement-dependent manner. To evaluate whether circulating antineurofascin antibodies mediate a pathogenic effect in vivo, we cotransferred these antibodies with myelin oligodendrocyte glycoprotein-specific encephalitogenic T cells to mimic the inflammatory pathology of MS and breach the blood-brain barrier. In this animal model, antibodies to neurofascin selectively targeted nodes of Ranvier, resulting in deposition of complement, axonal injury, and disease exacerbation. Collectively, these results identify a novel mechanism of immune-mediated axonal injury that can contribute to axonal pathology in MS.

Microfluorimetry defines early axonal damage in a rat model of optic neuritis: a novel method targeting early CNS autoimmunity

Autoimmune optic neuritis is a common early manifestation of multiple sclerosis (MS), yet early therapeutic interventions for MS often have high ocular toxicity associated with increased risks for glaucoma, cataract, or retinopathy. This need to discover better early treatment options prompted our development of a sensitive and reliable means to quantify the broad range of pathologies that potentially develop very early in autoimmune optic neuritis. Tissue microfluorimetry was used to measure seven established markers for human MS pathology in normal and autoimmune optic nerves 13 days after antigen exposure, in a Brown Norway rat model of myelin oligodendrocyte glycoprotein (MOG) peptide (35-55)-induced autoimmune optic neuritis. Optic neuritis rats demonstrated early and significant pathologic changes in five established indices for neuroinflammation, immune infiltration, and demyelination that accurately modeled pathologies characteristic of MS. Two indices of MS-like axon damage advanced significantly within 13 days of antigen exposure. Fluorimetrically measured immunoreactivity (-ir) was significantly decreased for paranodin (PN, the requisite axonal paranodal junction protein) and significantly increased for amyloid precursor protein (APP), indicating loss of paranodal junctions and impaired fast axonal transport, respectively. Measurements showing decreased PN-ir with increased APP-ir quantitatively defined a pattern of early axonal damage in autoimmune optic neuritis.

Sodium channels and multiple sclerosis: roles in symptom production, damage and therapy

Our understanding of the potential role of sodium channels in multiple sclerosis (MS) has grown substantially in recent years. The channels have long had a recognized role in the symptomatology of the disease, but now also have suspected roles in causing permanent axonal destruction, and a potential role in modulating the intensity of immune activity. Sodium channels might also provide an avenue to achieve axonal and neuronal protection in MS, thereby impeding the otherwise relentless advance of permanent neurological deficit. The symptoms of MS are largely determined by the conduction properties of axons and these, in turn, are largely determined by sodium channels. The number, subtype and distribution of the sodium channels are all important, together with the way that channel function is modified by local factors, such as those resulting from inflammation (eg, nitric oxide). Suspicion is growing that sodium channels may also contribute to the axonal degeneration primarily responsible for permanent neurological deficits. The proposed mechanism involves intra-axonal sodium accumulation which promotes reverse action of the sodium/calcium exchanger and thereby a lethal rise in intra-axonal calcium. Partial blockade of sodium channels protects axons from degeneration in experimental models of MS, and therapy based on this approach is currently under investigation in clinical trials. Some recent findings suggest that such systemic inhibition of sodium channels may also promote axonal protection by suppressing inflammation within the brain.