Virtual hypoxia and chronic necrosis of demyelinated axons in multiple sclerosis

TRPM4 cation channel mediates axonal and neuronal degeneration in experimental autoimmune encephalomyelitis and multiple sclerosis

In multiple sclerosis, an inflammatory disease of the central nervous system (CNS), axonal and neuronal loss are major causes for irreversible neurological disability. However, which molecules contribute to axonal and neuronal injury under inflammatory conditions remains largely unknown. Here we show that the transient receptor potential melastatin 4 (TRPM4) cation channel is crucial in this process. TRPM4 is expressed in mouse and human neuronal somata, but it is also expressed in axons in inflammatory CNS lesions in experimental autoimmune encephalomyelitis (EAE) in mice and in human multiple sclerosis tissue. Deficiency or pharmacological inhibition of TRPM4 using the antidiabetic drug glibenclamide resulted in reduced axonal and neuronal degeneration and attenuated clinical disease scores in EAE, but this occurred without altering EAE-relevant immune function. Furthermore, Trpm4(-/-) mouse neurons were protected against inflammatory effector mechanisms such as excitotoxic stress and energy deficiency in vitro. Electrophysiological recordings revealed TRPM4-dependent neuronal ion influx and oncotic cell swelling upon excitotoxic stimulation. Therefore, interference with TRPM4 could translate into a new neuroprotective treatment strategy.

Cortical remyelination: a new target for repair therapies in multiple sclerosis

OBJECTIVE

Generation and differentiation of new oligodendrocytes in demyelinated white matter is the best described repair process in the adult human brain. However, remyelinating capacity falters with age in patients with multiple sclerosis (MS). Because demyelination of cerebral cortex is extensive in brains from MS patients, we investigated the capacity of cortical lesions to remyelinate and directly compared the extent of remyelination in lesions that involve cerebral cortex and adjacent subcortical white matter.

METHODS

Postmortem brain tissue from 22 patients with MS (age 27-77 years) and 6 subjects without brain disease were analyzed. Regions of cerebral cortex with reduced myelin were examined for remyelination, oligodendrocyte progenitor cells, reactive astrocytes, and molecules that inhibit remyelination.

RESULTS

New oligodendrocytes that were actively forming myelin sheaths were identified in 30 of 42 remyelinated subpial cortical lesions, including lesions from 3 patients in their 70s. Oligodendrocyte progenitor cells were not decreased in demyelinated or remyelinated cortices when compared to adjacent normal-appearing cortex or controls. In demyelinated lesions involving cortex and adjacent white matter, the cortex showed greater remyelination, more actively remyelinating oligodendrocytes, and fewer reactive astrocytes. Astrocytes in the white matter, but not in cortical portions of these lesions, significantly upregulate CD44, hyaluronan, and versican, molecules that form complexes that inhibit oligodendrocyte maturation and remyelination.

INTERPRETATION

Endogenous remyelination of the cerebral cortex occurs in individuals with MS regardless of disease duration or chronological age of the patient. Cortical remyelination should be considered as a primary outcome measure in future clinical trials testing remyelination therapies.

Neuroprotection and repair in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease that is considered by many people to have an autoimmune aetiology. In recent years, new data emerging from histopathology, imaging and other studies have expanded our understanding of the disease and may change the way in which it is treated. Conceptual shifts have included: first, an appreciation of the extent to which the neuron and its axon are affected in MS, and second, elucidation of how the neurobiology of axon-glial and, particularly, axon-myelin interaction may influence disease progression. In this article, we review advances in both areas, focusing on the molecular mechanisms underlying axonal loss in acute inflammation and in chronic demyelination, and discussing how the restoration of myelin sheaths via the regenerative process of remyelination might prevent axon degeneration. An understanding of these processes could lead to better strategies for the prevention and treatment of axonal loss, which will ultimately benefit patients with MS.

Susceptibility-weighted imaging in the experimental autoimmune encephalomyelitis model of multiple sclerosis indicates elevated deoxyhemoglobin, iron deposition and demyelination

BACKGROUND

Susceptibility-weighted imaging (SWI) is an iron-sensitive magnetic resonance imaging (MRI) method that has shown iron-related lesions in multiple sclerosis (MS) patients. The contribution of deoxyhemoglobin to the signals seen in SWI has not been well characterized in MS.

OBJECTIVES

To determine if SWI lesions (seen as focal hypointensities) exist in the experimental autoimmune encephalomyelitis (EAE) animal model of MS, and to determine whether the lesions relate to iron deposits, inflammation, demyelination, and/or deoxyhemoglobin in the vasculature.

METHODS

We performed SWI on the lumbar spinal cord and cerebellum of EAE and control mice (both complete Freund's adjuvant/pertussis toxin (CFA/PTX)-immunized and naive). We also performed SWI on mice before and after perfusion (to remove blood from vessels). SWI lesions were counted and their locations were compared to histology for iron, myelin and inflammation.

RESULTS

SWI lesions were found to exist in the EAE model. Many lesions seen by SWI were not present after perfusion, especially at the grey/white matter boundary of the lumbar spinal cord and in the cerebellum, indicating that these lesion signals were associated with deoxyhemoglobin present in the lumen of vessels. We also observed SWI lesions in the white matter of the lumbar spinal cord that corresponded to iron deposition, inflammation and demyelination. In the cerebellum, SWI lesions were present in white matter tracts, where we found histological evidence of inflammatory perivascular cuffs.

CONCLUSIONS

SWI lesions exist in EAE mice. Many lesions seen in SWI were a result of deoxyhemoglobin in the blood, and so may indicate areas of hypoxia. A smaller number of SWI lesions coincided with parenchymal iron, demyelination, and/or inflammation.

Progressive multiple sclerosis: pathology and pathogenesis

Major progress has been made during the past three decades in understanding the inflammatory process and pathogenetic mechanisms in multiple sclerosis (MS). Consequently, effective anti-inflammatory and immunomodulatory treatments are now available for patients in the relapsing-remitting stage of the disease. This Review summarizes studies on the pathology of progressive MS and discusses new data on the mechanisms underlying its pathogenesis. In progressive MS, as in relapsing-remitting MS, active tissue injury is associated with inflammation, but the inflammatory response in the progressive phase occurs at least partly behind the blood-brain barrier, which makes it more difficult to treat. The other mechanisms that drive disease in patients with primary or secondary progressive MS are currently unresolved, although oxidative stress resulting in mitochondrial injury might participate in the induction of demyelination and neurodegeneration in both the relapsing-remitting and progressive stages of MS. Oxidative stress seems to be mainly driven by inflammation and oxidative burst in microglia; however, its effects might be amplified in patients with progressive MS by age-dependent iron accumulation in the brain and by mitochondrial gene deletions, triggered by the chronic inflammatory process.

Pathophysiologic cascades in ischemic stroke

Many advances have been achieved in terms of understanding the molecular and cellular mechanisms of ischemic stroke. But thus far, clinically effective neuroprotectants remain elusive. In this minireview, we summarize the basics of ischemic cascades after stroke, covering neuronal death mechanisms, white matter pathophysiology, and inflammation with an emphasis on microglia. Translating promising mechanistic knowledge into clinically meaningful stroke drugs is very challenging. An integrative approach that encompasses the multimodal and multicell signaling phenomenon of stroke will be required to move forward.

Mechanisms of oxidative damage in multiple sclerosis and neurodegenerative diseases: therapeutic modulation via fumaric acid esters

Oxidative stress plays a crucial role in many neurodegenerative conditions such as Alzheimer’s disease, amyotrophic lateral sclerosis and Parkinson’s as well as Huntington’s disease. Inflammation and oxidative stress are also thought to promote tissue damage in multiple sclerosis (MS). Recent data point at an important role of anti-oxidative pathways for tissue protection in chronic-progressive MS, particularly involving the transcription factor nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2). Thus, novel therapeutics enhancing cellular resistance to free radicals could prove useful for MS treatment. Here, fumaric acid esters (FAE) are a new, orally available treatment option which had already been tested in phase II/III MS trials demonstrating beneficial effects on relapse rates and magnetic resonance imaging markers. In vitro, application of dimethylfumarate (DMF) leads to stabilization of Nrf2, activation of Nrf2-dependent transcriptional activity and abundant synthesis of detoxifying proteins. Furthermore, application of FAE involves direct modification of the inhibitor of Nrf2, Kelch-like ECH-associated protein 1. On cellular levels, the application of FAE enhances neuronal survival and protects astrocytes against oxidative stress. Increased levels of Nrf2 are detected in the central nervous system of DMF treated mice suffering from experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In EAE, DMF ameliorates the disease course and improves preservation of myelin, axons and neurons. Finally, Nrf2 is also up-regulated in the spinal cord of autopsy specimens from untreated patients with MS, probably as part of a naturally occurring anti-oxidative response. In summary, oxidative stress and anti-oxidative pathways are important players in MS pathophysiology and constitute a promising target for future MS therapies like FAE.

Transgenic inhibition of astroglial NF-κB protects from optic nerve damage and retinal ganglion cell loss in experimental optic neuritis

Background

Optic neuritis is an acute, demyelinating neuropathy of the optic nerve often representing the first appreciable symptom of multiple sclerosis. Wallerian degeneration of irreversibly damaged optic nerve axons leads to death of retinal ganglion cells, which is the cause of permanent visual impairment. Although the specific mechanisms responsible for triggering these events are unknown, it has been suggested that a key pathological factor is the activation of immune-inflammatory processes secondary to leukocyte infiltration. However, to date, there is no conclusive evidence to support such a causal role for infiltrating peripheral immune cells in the etiopathology of optic neuritis.

Methods

To dissect the contribution of the peripheral immune-inflammatory response versus the CNS-specific inflammatory response in the development of optic neuritis, we analyzed optic nerve and retinal ganglion cells pathology in wild-type and GFAP-IκBα-dn transgenic mice, where NF-κB is selectively inactivated in astrocytes, following induction of EAE.

Results

We found that, in wild-type mice, axonal demyelination in the optic nerve occurred as early as 8 days post induction of EAE, prior to the earliest signs of leukocyte infiltration (20 days post induction). On the contrary, GFAP-IκBα-dn mice were significantly protected and showed a nearly complete prevention of axonal demyelination, as well as a drastic attenuation in retinal ganglion cell death. This correlated with a decrease in the expression of pro-inflammatory cytokines, chemokines, adhesion molecules, as well as a prevention of NAD(P)H oxidase subunit upregulation.

Conclusions

Our results provide evidence that astrocytes, not infiltrating immune cells, play a key role in the development of optic neuritis and that astrocyte-mediated neurotoxicity is dependent on activation of a transcriptional program regulated by NF-κB. Hence, interventions targeting the NF-κB transcription factor in astroglia may be of therapeutic value in the treatment of optic neuritis associated with multiple sclerosis.

Glutamate gene polymorphisms predict brain volumes in multiple sclerosis

Background:

Several genetic markers have been associated with multiple sclerosis (MS) susceptibility; however, uncovering the genetic aetiology of the complex phenotypic expression of MS has been more difficult so far. The most common approach in imaging genetics is based on mass-univariate linear modelling (MULM), which faces several limitations.

Objective:

Here we apply a novel multivariate statistical model, sparse reduced-rank regression (sRRR), to identify possible associations of glutamate related single nucleotide polymorphisms (SNPs) and multiple MRI-derived phenotypes in MS.

Methods:

Seven phenotypes related to brain and lesion volumes for a total number of 326 relapsing–remitting and secondary-progressive MS patients and a total of 3809 glutamate related and control SNPs were analysed with sRRR, which resulted in a ranking of SNPs in decreasing order of importance (‘selection probability’). Lasso regression and MULM were used as comparative statistical techniques to assess consistency of the most important associations over different statistical models.

Results:

Five SNPs within the NMDA-receptor-2A-subunit (GRIN2A) domain were identified by sRRR in association with normalized brain volume (NBV), normalized grey matter volume and normalized white matter volume (NMWM). The association between GRIN2A and both NBV and NWMV was confirmed in MULM and Lasso analysis.

Conclusions:

Using a novel, multivariate regression model confirmed by two other statistical approaches we show associations between GRIN2A SNPs and phenotypic variation in NBV and NWMV in this first exploratory study. Replications in independent datasets are now necessary to validate these findings.

The role of mitochondria in axonal degeneration and tissue repair in MS

Axonal injury is a key feature of multiple sclerosis (MS) pathology and is currently seen as the main correlate for permanent clinical disability. Although little is known about the pathogenetic mechanisms that drive axonal damage and loss, there is accumulating evidence highlighting the central role of mitochondrial dysfunction in axonal degeneration and associated neurodegeneration. The aim of this topical review is to provide a concise overview on the involvement of mitochondrial dysfunction in axonal damage and destruction in MS. Hereto, we will discuss putative pathological mechanisms leading to mitochondrial dysfunction and recent imaging studies performed in vivo in patients with MS. Moreover, we will focus on molecular mechanisms and novel imaging studies that address the role of mitochondrial metabolism in tissue repair. Finally, we will briefly review therapeutic strategies aimed at improving mitochondrial metabolism and function under neuroinflammatory conditions.

Will the real multiple sclerosis please stand up?

Multiple sclerosis (MS) is considered to be an autoimmune, inflammatory disease of the CNS. In most patients, the disease follows a relapsing-remitting course and is characterized by dynamic inflammatory demyelinating lesions in the CNS. Although on the surface MS may appear consistent with a primary autoimmune disease, questions have been raised as to whether inflammation and/or autoimmunity are really at the root of the disease, and it has been proposed that MS might in fact be a degenerative disorder. We argue that MS may be an 'immunological convolution' between an underlying primary degenerative disorder and the host's aberrant immune response. To better understand this disease, we might need to consider non-inflammatory primary progressive MS as the 'real' MS, with inflammatory forms reflecting secondary, albeit very important, reactions.

Inflammation-mediated memory dysfunction and effects of a ketogenic diet in a murine model of multiple sclerosis

A prominent clinical symptom in multiple sclerosis (MS), a progressive disorder of the central nervous system (CNS) due to heightened neuro-inflammation, is learning and memory dysfunction. Here, we investigated the effects of a ketogenic diet (KD) on memory impairment and CNS-inflammation in a murine model of experimental autoimmune encephalomyelitis (EAE), using electrophysiological, behavioral, biochemical and in vivo imaging approaches. Behavioral spatial learning deficits were associated with motor disability in EAE mice, and were observed concurrently with brain inflammation. The KD improved motor disability in the EAE model, as well as CA1 hippocampal synaptic plasticity (long-term potentiation) and spatial learning and memory (assessed with the Morris Water Maze). Moreover, hippocampal atrophy and periventricular lesions in EAE mice were reversed in KD-treated EAE mice. Finally, we found that the increased expression of inflammatory cytokines and chemokines, as well as the production of reactive oxygen species (ROS), in our EAE model were both suppressed by the KD. Collectively, our findings indicate that brain inflammation in EAE mice is associated with impaired spatial learning and memory function, and that KD treatment can exert protective effects, likely via attenuation of the robust immune response and increased oxidative stress seen in these animals.

NADPH oxidase expression in active multiple sclerosis lesions in relation to oxidative tissue damage and mitochondrial injury

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, associated with demyelination and neurodegeneration. The mechanisms of tissue injury are poorly understood, but recent data suggest that mitochondrial injury may play an important role in this process. Mitochondrial injury can be triggered by reactive oxygen and nitric oxide species, and we recently provided evidence for oxidative damage of oligodendrocytes and dystrophic axons in early stages of active multiple sclerosis lesions. In this study, we identified potential sources of reactive oxygen and nitrogen species through gene expression in carefully staged and dissected lesion areas and by immunohistochemical analysis of protein expression. Genome-wide microarrays confirmed mitochondrial injury in active multiple sclerosis lesions, which may serve as an important source of reactive oxygen species. In addition, we found differences in the gene expression levels of various nicotinamide adenine dinucleotide phosphate oxidase subunits between initial multiple sclerosis lesions and control white matter. These results were confirmed at the protein level by means of immunohistochemistry, showing upregulation of the subunits gp91phox, p22phox, p47phox, nicotinamide adenine dinucleotide phosphate oxidase 1 and nicotinamide adenine dinucleotide phosphate oxidase organizer 1 in activated microglia in classical active as well as slowly expanding lesions. The subunits gp91phox and p22phox were constitutively expressed in microglia and were upregulated in the initial lesion. In contrast, p47phox, nicotinamide adenine dinucleotide phosphate oxidase 1 and nicotinamide adenine dinucleotide phosphate oxidase organizer 1 expression were more restricted to the zone of initial damage or to lesions from patients with acute or early relapsing/remitting multiple sclerosis. Double labelling showed co-expression of the nicotinamide adenine dinucleotide phosphate oxidase subunits in activated microglia and infiltrated macrophages, suggesting the assembly of functional complexes. Our data suggest that the inflammation-associated oxidative burst in activated microglia and macrophages plays an important role in demyelination and free radical-mediated tissue injury in the pathogenesis of multiple sclerosis.

Mitofusin2 mutations disrupt axonal mitochondrial positioning and promote axon degeneration

Alterations in mitochondrial dynamics (fission, fusion, and movement) are implicated in many neurodegenerative diseases, from rare genetic disorders such as Charcot-Marie-Tooth disease, to common conditions including Alzheimer's disease. However, the relationship between altered mitochondrial dynamics and neurodegeneration is incompletely understood. Here we show that disease associated MFN2 proteins suppressed both mitochondrial fusion and transport, and produced classic features of segmental axonal degeneration without cell body death, including neurofilament filled swellings, loss of calcium homeostasis, and accumulation of reactive oxygen species. By contrast, depletion of Opa1 suppressed mitochondrial fusion while sparing transport, and did not induce axonal degeneration. Axon degeneration induced by mutant MFN2 proteins correlated with the disruption of the proper mitochondrial positioning within axons, rather than loss of overall mitochondrial movement, or global mitochondrial dysfunction. We also found that augmenting expression of MFN1 rescued the axonal degeneration caused by MFN2 mutants, suggesting a possible therapeutic strategy for Charcot-Marie-Tooth disease. These experiments provide evidence that the ability of mitochondria to sense energy requirements and localize properly within axons is key to maintaining axonal integrity, and may be a common pathway by which disruptions in axonal transport contribute to neurodegeneration.

Stimulation of the neurotrophin receptor TrkB on astrocytes drives nitric oxide production and neurodegeneration

Neurotrophin growth factors support neuronal survival and function. In this study, we show that the expression of the neurotrophin receptor TrkB is induced on astrocytes in white matter lesions in multiple sclerosis (MS) patients and mice with experimental autoimmune encephalomyelitis (EAE). Surprisingly, mice lacking TrkB specifically in astrocytes were protected from EAE-induced neurodegeneration. In an in vitro assay, astrocytes stimulated with the TrkB agonist brain-derived neurotrophic factor (BDNF) released nitric oxide (NO), and conditioned medium from activated astrocytes had detrimental effects on the morphology and survival of neurons. This neurodegenerative process was amplified by NO produced by neurons. NO synthesis in the central nervous system during EAE depended on astrocyte TrkB. Together, these findings suggest that TrkB expression on astrocytes may represent a new target for neuroprotective therapies in MS.

White-matter astrocytes, axonal energy metabolism, and axonal degeneration in multiple sclerosis

In patients with multiple sclerosis (MS), a diffuse axonal degeneration occurring throughout the white matter of the central nervous system causes progressive neurologic disability. The underlying mechanism is unclear. This review describes a number of pathways by which dysfunctional astrocytes in MS might lead to axonal degeneration. White-matter astrocytes in MS show a reduced metabolism of adenosine triphosphate-generating phosphocreatine, which may impair the astrocytic sodium potassium pump and lead to a reduced sodium-dependent glutamate uptake. Astrocytes in MS white matter appear to be deficient in β(2) adrenergic receptors, which are involved in stimulating glycogenolysis and suppressing inducible nitric oxide synthase (NOS2). Glutamate toxicity, reduced astrocytic glycogenolysis leading to reduced lactate and glutamine production, and enhanced nitric oxide (NO) levels may all impair axonal mitochondrial metabolism, leading to axonal degeneration. In addition, glutamate-mediated oligodendrocyte damage and impaired myelination caused by a decreased production of N-acetylaspartate by axonal mitochondria might also contribute to axonal loss. White-matter astrocytes may be considered as a potential target for neuroprotective MS therapies.

Characterizing brain oxygen metabolism in patients with multiple sclerosis with T2-relaxation-under-spin-tagging MRI

In this study, venous oxygen saturation and oxygen metabolic changes in multiple sclerosis (MS) patients were assessed using a recently developed T2-relaxation-under-spin-tagging (TRUST) magnetic resonance imaging (MRI), which measures the superior sagittal venous sinus blood oxygenation (Yv) and cerebral metabolic rate of oxygen (CMRO(2)), an index of global oxygen consumption. Thirty patients with relapsing-remitting MS and 30 age-matched healthy controls were studied using TRUST at 3 T MR. The mean expanded disability status scale (EDSS) of the patients was 2.3 (range, 0 to 5.5). We found significantly increased Yv (P<0.0001) and decreased CMRO(2) (P=0.003) in MS patients (mean±s.d.: 65.9%±5.1% and 138.8±35.4 μmol per 100 g per minute) as compared with healthy control subjects (60.2%±4.0% and 180.2±24.8 μmol per 100 g per minute, respectively), implying decrease of oxygen consumption in MS. There was a significant positive correlation between Yv and EDSS and between Yv and lesion load in MS patients (n=30); on the contrary, there was a significant negative correlation between CMRO(2) and EDSS and between CMRO(2) and lesion load (n=12). There was no correlation between Yv and brain atrophy measures. This study showed preliminary evidence of the potential utility of TRUST in global oxygen metabolism. Our results of significant underutilization of oxygen in MS raise important questions regarding mitochondrial respiratory dysfunction and neurodegeneration of the disease.

Review: the architecture of inflammatory demyelinating lesions: implications for studies on pathogenesis

Recent technological advances provided the chance to analyse the molecular events involved in the pathogenesis of lesions in human disease. A major prerequisite for such studies is, however, that the pathological material used is exactly defined and characterized. In multiple sclerosis (MS), this is difficult, as several types of active lesions exist, depending upon the stage of the disease, the age and location of these lesions and the inter-individual differences between patients. In addition, within an active lesion, different closely adjacent zones are present reflecting initial tissue injury, debris removal or repair. Here evidence is reviewed, showing that distinct subareas of active MS lesions reflect different pathological hallmarks of lesion evolution. These data provide the basis for our understanding of the pathogenesis of tissue injury in MS and imply that studies on MS pathogenesis have to rely on a clear definition of the lesions analysed and have to focus on specific lesion areas, isolated by microdissection. In addition, these data also imply that molecules, identified in these studies, must be confirmed and validated in the correct context of lesion initiation and/or progression.

In vivo evidence that TRAF4 is required for central nervous system myelin homeostasis

Tumor Necrosis Factor Receptor-Associated Factors (TRAFs) are major signal transducers for the TNF and interleukin-1/Toll-like receptor superfamilies. However, TRAF4 does not fit the paradigm of TRAF function in immune and inflammatory responses. Its physiological and molecular functions remain poorly understood. Behavorial analyses show that TRAF4-deficient mice (TRAF4-KO) exhibit altered locomotion coordination typical of ataxia. TRAF4-KO central nervous system (CNS) ultrastructure shows strong myelin perturbation including disorganized layers and disturbances in paranode organization. TRAF4 was previously reported to be expressed by CNS neurons. Using primary cell culture, we now show that TRAF4 is also expressed by oligodendrocytes, at all stages of their differentiation. Moreover, histology and electron microscopy show degeneration of a high number of Purkinje cells in TRAF4-KO mice, that was confirmed by increased expression of the Bax pro-apoptotic marker (immunofluorescence), TUNEL analysis, and caspase-3 activation and PARP1 cleavage (western blotting). Consistent with this phenotype, MAG and NogoA, two myelin-induced neurite outgrowth inhibitors, and their neuron partners, NgR and p75NTR were overexpressed (Q-RT-PCR and western blotting). The strong increased phosphorylation of Rock2, a RhoA downstream target, indicated that the NgR/p75NTR/RhoA signaling pathway, known to induce actin cytoskeleton rearrangement that favors axon regeneration inhibition and neuron apoptosis, is activated in the absence of TRAF4 (western blotting). Altogether, these results provide conclusive evidence for the pivotal contribution of TRAF4 to myelination and to cerebellar homeostasis, and link the loss of TRAF4 function to demyelinating or neurodegenerative diseases.

Rapid disruption of axon-glial integrity in response to mild cerebral hypoperfusion

Myelinated axons have a distinct protein architecture essential for action potential propagation, neuronal communication, and maintaining cognitive function. Damage to myelinated axons, associated with cerebral hypoperfusion, contributes to age-related cognitive decline. We sought to determine early alterations in the protein architecture of myelinated axons and potential mechanisms after hypoperfusion. Using a mouse model of hypoperfusion, we assessed changes in proteins critical to the maintenance of paranodes, nodes of Ranvier, axon-glial integrity, axons, and myelin by confocal laser scanning microscopy. As early as 3 d after hypoperfusion, the paranodal septate-like junctions were damaged. This was marked by a progressive reduction of paranodal Neurofascin signal and a loss of septate-like junctions. Concurrent with paranodal disruption, there was a significant increase in nodal length, identified by Nav1.6 staining, with hypoperfusion. Disruption of axon-glial integrity was also determined after hypoperfusion by changes in the spatial distribution of myelin-associated glycoprotein staining. These nodal/paranodal changes were more pronounced after 1 month of hypoperfusion. In contrast, the nodal anchoring proteins AnkyrinG and Neurofascin 186 were unchanged and there were no overt changes in axonal and myelin integrity with hypoperfusion. A microarray analysis of white matter samples indicated that there were significant alterations in 129 genes. Subsequent analysis indicated alterations in biological pathways, including inflammatory responses, cytokine-cytokine receptor interactions, blood vessel development, and cell proliferation processes. Our results demonstrate that hypoperfusion leads to a rapid disruption of key proteins critical to the stability of the axon-glial connection that is mediated by a diversity of molecular events.

IFN-gamma signaling in the central nervous system controls the course of experimental autoimmune encephalomyelitis independently of the localization and composition of inflammatory foci

Background

Murine experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, presents typically as ascending paralysis. However, in mice in which interferon-gamma (IFNγ) signaling is disrupted by genetic deletion, limb paralysis is accompanied by atypical deficits, including head tilt, postural imbalance, and circling, consistent with cerebellar/vestibular dysfunction. This was previously attributed to intense cerebellar and brainstem infiltration by peripheral immune cells and formation of neutrophil-rich foci within the CNS. However, the exact mechanism by which IFNγ signaling prohibits the development of vestibular deficits, and whether the distribution and composition of inflammatory foci within the CNS affects the course of atypical EAE remains elusive.

Methods

We induced EAE in IFNγ-/- mice and bone marrow chimeric mice in which IFNγR is not expressed in the CNS but is intact in the periphery (IFNγR^CNSKO) and vice versa (IFNγR^periKO). Blood-brain barrier permeability was determined by Evans blue intravenous administration at disease onset. Populations of immune cell subsets in the periphery and the CNS were quantified by flow cytometry. CNS tissues isolated at various time points after EAE induction, were analyzed by immunohistochemistry for composition of inflammatory foci and patterns of axonal degeneration.

Results

Incidence and severity of atypical EAE were more pronounced in IFNγR^CNSKO as compared to IFNγR^periKO mice. Contrary to what we anticipated, cerebella/brainstems of IFNγR^CNSKO mice were only minimally infiltrated, while the same areas of IFNγR^periKO mice were extensively populated by peripheral immune cells. Furthermore, the CNS of IFNγR^periKO mice was characterized by persistent neutrophil-rich foci as compared to IFNγR^CNSKO. Immunohistochemical analysis of the CNS of IFNγ-/- and IFNγR chimeric mice revealed that IFNγ protective actions are exerted through microglial STAT1.

Conclusions

Alterations in distribution and composition of CNS inflammatory foci are not sufficient for the onset of atypical EAE. IFNγ dictates the course of neuroinflammatory disorders mainly through actions exerted within the CNS. This study provides strong evidence that link microglial STAT1 inactivation to vestibular dysfunction.

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.

Current status of myelin replacement therapies in multiple sclerosis

Multiple sclerosis is an autoimmune disease of the human central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths. There are two aspects to the treatment of MS-first, the prevention of damage by suppressing the maladaptive immune system, and second, the long-term preservation of axons by the promotion of remyelination, a regenerative process in which new axons are restored to demyelinated axons. Medicine has made significant progress in the first of these in recent years-there is an increasing number of ever more effective disease-modifying immunomodulatory interventions. However, there are currently no widely used regenerative therapies in MS. Conceptually, there are two approaches to remyelination therapy-transplantation of myelinogenic cells and promotion of endogenous remyelination mediated by myelinogenic cells present within the diseased tissue. In this chapter, in addition to describing why remyelination therapies are important, we review both these approaches, outlining their current status and future developments.

Gene expression profiling in multiple sclerosis brain

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system and the leading cause of non-traumatic neurological disability in young adults in the United States and Europe. The clinical disease course is variable and starts with reversible episodes of neurological disability in the third or fourth decade of life. Microarray-based comparative gene profiling provides a snapshot of genes underlying a particular condition. Several large scale microarray studies have been conducted using brain tissue from MS patients. In this review, we summarize existing data from different gene expression profiling studies and how they relate to understand the pathogenesis of MS.

Diseases Involving Myelin

This chapter focuses on multiple sclerosis and the acquired and inherited peripheral neuropathies. The integrity of myelin sheaths is dependent upon the normal functioning of the myelin-forming oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS) as well as on the viability of the axons that they ensheath. Neuronal death inevitably leads to degeneration of axons and secondary degeneration of the myelin surrounding them. Failure of synthesis of normal myelin proteins or lipids is referred to as hypomyelination or dysmyelination. Primary demyelination involves the destruction of myelin with relative sparing of axons, whereas secondary demy­elination includes those disorders in which myelin is involved only after damage to neurons and axons occurs. The integrity of myelin sheaths is dependent upon the normal functioning of myelin-forming oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS) as well as on the viability of the axons that they ensheath.

Pathogenesis of multiple sclerosis: what can we learn from the cuprizone model

Multiple sclerosis is an inflammatory demyelinating and neurodegenerative disorder of the central nervous system (CNS). The primary cause of the disease remains unknown, but an altered immune regulation with features of autoimmunity has generally been considered to play a critical role in the pathogenesis. Historically, lesion development has been attributed to activation of CD4 and CD8 T lymphocytes, B lymphocytes, and monocytes in the peripheral circulation and the migration of these cells through the blood-brain barrier to exert direct or indirect cytotoxic effects on myelin, oligodendrocytes and neuronal processes in the CNS. This broadly accepted concept was significantly influenced by the experimental autoimmune encephalitis (EAE) model, in which either immunization with myelin antigens or injection of a myelin antigen-specific T cell line into a recipient results in inflammatory demyelination in the CNS. More recent studies reveal that the loss of oligodendrocytes and neurons begins in the earliest stages of the disease and may not always be associated with blood-derived inflammatory cells. The pathology affects both the white and the gray matters and the clinical disability best correlates with the overall neurodegenerative process. These newer observations prompted several revisions of the classical concept of MS and facilitated a shift from using EAE to using other model systems. This chapter summarizes the classical and more contemporary concepts of MS, and provides methodologies for employing the cuprizone model for further explorations of the pathogenesis and treatment of the disease.

Pathogenic implications of iron accumulation in multiple sclerosis

Iron, an essential element used for a multitude of biochemical reactions, abnormally accumulates in the CNS of patients with multiple sclerosis (MS). The mechanisms of abnormal iron deposition in MS are not fully understood, nor do we know whether these deposits have adverse consequences, that is, contribute to pathogenesis. With some exceptions, excess levels of iron are represented concomitantly in multiple deep gray matter structures often with bilateral representation, whereas in white matter, pathological iron deposits are usually located at sites of inflammation that are associated with veins. These distinct spatial patterns suggest disparate mechanisms of iron accumulation between these regions. Iron has been postulated to promote disease activity in MS by various means: (i) iron can amplify the activated state of microglia resulting in the increased production of proinflammatory mediators; (ii) excess intracellular iron deposits could promote mitochondria dysfunction; and (iii) improperly managed iron could catalyze the production of damaging reactive oxygen species (ROS). The pathological consequences of abnormal iron deposits may be dependent on the affected brain region and/or accumulation process. Here, we review putative mechanisms of enhanced iron uptake in MS and address the likely roles of iron in the pathogenesis of this disease.

Decreased brain venous vasculature visibility on susceptibility-weighted imaging venography in patients with multiple sclerosis is related to chronic cerebrospinal venous insufficiency

Background

The potential pathogenesis between the presence and severity of chronic cerebrospinal venous insufficiency (CCSVI) and its relation to clinical and imaging outcomes in brain parenchyma of multiple sclerosis (MS) patients has not yet been elucidated. The aim of the study was to investigate the relationship between CCSVI, and altered brain parenchyma venous vasculature visibility (VVV) on susceptibility-weighted imaging (SWI) in patients with MS and in sex- and age-matched healthy controls (HC).

Methods

59 MS patients, 41 relapsing-remitting and 18 secondary-progressive, and 33 HC were imaged on a 3T GE scanner using pre- and post-contrast SWI venography. The presence and severity of CCSVI was determined using extra-cranial and trans-cranial Doppler criteria. Apparent total venous volume (ATVV), venous intracranial fraction (VIF) and average distance-from-vein (DFV) were calculated for various vein mean diameter categories: < .3 mm, .3-.6 mm, .6-.9 mm and > .9 mm.

Results

CCSVI criteria were fulfilled in 79.7% of MS patients and 18.2% of HC (p < .0001). Patients with MS showed decreased overall ATVV, ATVV of veins with a diameter < .3 mm, and increased DFV compared to HC (all p < .0001). Subjects diagnosed with CCSVI had significantly increased DFV (p < .0001), decreased overall ATVV and ATVV of veins with a diameter < .3 mm (p < .003) compared to subjects without CCSVI. The severity of CCSVI was significantly related to decreased VVV in MS (p < .0001) on pre- and post-contrast SWI, but not in HC.

Conclusions

MS patients with higher number of venous stenoses, indicative of CCSVI severity, showed significantly decreased venous vasculature in the brain parenchyma. The pathogenesis of these findings has to be further investigated, but they suggest that reduced metabolism and morphological changes of venous vasculature may be taking place in patients with MS.

A physics link between venous stenosis and multiple sclerosis

This paper hypothesizes that a stenosis or obstruction at a lower extremity of an internal jugular vein (IJV) would, in accordance with the physics of fluid dynamics, cause a standing pressure wave within the vein. This pressure wave would possess regions of large pressure fluctuations and other regions of relatively little fluctuation which also have substantially lower peak pressure values. If the wavelength of the hypothesized pressure wave is comparable to the distance from the obstruction to the venule end of the capillary bed, then a region of high pressure fluctuation would exist at the venules. Depending on the degree of obstruction, the pressure fluctuations at the venules of the capillary bed would be substantially greater than those that would exist in a healthy unobstructed vein. This increase in blood pressure fluctuation located at the venule end of the capillary bed, which would be equivalent to local hypertension, is predicted to reduce the pressure drop across the bed which, in turn, would reduce blood flow through the bed in accordance with Darcy's Law. Such a reduction in blood flow through the bed would be accompanied by a reduction in the transfer of oxygen, glucose and other nutrients into the brain tissue in accordance with Fick's Principle. The reduction in oxygen levels in the brain tissue (i.e. hypoxia), would, in turn, be associated with increased fatigue and decreased mental acuity in the subject patient. Also the deprivation of oxygen in the brain tissue may result in the death of oligodendrocyte cells, which, in turn would result in the deterioration of the myelin surrounding the brain's neural axons. In addition, the paper also predicts that, in cases of extreme obstruction, the predicted localized hypertension at the venule end of the capillary bed may be sufficiently high to cause a localized disruption in the blood-brain barrier. Such a disruption of the blood-brain barrier could then allow the migration of leukocytes (auto-immune attack cells), from the blood into the brain tissue, enabling them to attack myelin, which has degenerated or deteriorated from the reduction in repair function normally provided by oligodendrocyte cells. Such leukocyte attack on myelin has long been associated with multiple sclerosis.

Targeting progressive neuroaxonal injury: lessons from multiple sclerosis

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), are characterized by progressive neuroaxonal injury, suggesting a common pathophysiological pathway. Identification and development of neuroprotective therapies for such diseases has proven a major challenge, particularly because of an already substantial neuroaxonal compromise at the time of initial onset of clinical symptoms. Methods for early identification of neurodegeneration are therefore vital to ensure that neuroprotective therapies are applied as early as possible. Recent investigations have enhanced our understanding of the role of neuroaxonal injury in multiple sclerosis (MS). As MS generally manifests earlier in life and can be diagnosed much earlier in the course of the disease than the above-mentioned 'classic' neurodegenerative diseases, it is possible that MS could be used as a model disease to study degeneration and regeneration of the CNS. The mechanism of neuroaxonal injury in MS is believed to be inflammation-led neurodegeneration; however, the reverse may also be true (i.e. neuroaxonal degeneration may precede inflammation). Animal models of PD, AD and ALS have shown that it is likely that most cases of disease are due to initial inflammation, followed by a degenerative process, providing a parallel between MS and the classic neurodegenerative diseases. Other common factors between MS and the neurodegenerative diseases include iron and mitochondrial dysregulation, abnormalities in α-synuclein and tau protein, and a number of immune mediators. Conventional MRI techniques, using markers such as T2-weighted lesions, gadolinium-enhancing lesions and T1-weighted hypointensities, are readily available and routinely used in clinical practice; however, the utility of these MRI measures to predict disease progression in MS is limited. More recently, MRI techniques that provide more pathology-specific data have been applied in MS studies, including magnetic resonance spectroscopy, magnetization transfer ratio and myelin water imaging. Optical coherence tomography (OCT) is a non-MRI technique that quantifies optic nerve integrity and retinal ganglion cell loss as markers of neuroaxonal injury; more research is needed to evaluate whether information obtained from OCT is a reliable marker of axonal injury and long-term disability in MS. Using these advanced techniques, it may become possible to follow degeneration and regeneration longitudinally in patients with MS and to better differentiate the effects of drugs under investigation. Currently available immune-directed therapies that are approved by the US FDA for the first-line treatment of MS (interferon-β and glatiramer acetate) have been shown to decelerate the inflammatory process in MS; however, such therapy is less effective in preventing the progression of the disease and neuroaxonal injury. The use of MS as a clinical model to study modulation of neuroaxonal injury in the brain could have direct implications for the development of treatment strategies in neurodegenerative diseases such as AD, PD and ALS.

Vascular contributions to cognitive impairment and dementia: a statement for healthcare professionals from the american heart association/american stroke association

BACKGROUND AND PURPOSE

This scientific statement provides an overview of the evidence on vascular contributions to cognitive impairment and dementia. Vascular contributions to cognitive impairment and dementia of later life are common. Definitions of vascular cognitive impairment (VCI), neuropathology, basic science and pathophysiological aspects, role of neuroimaging and vascular and other associated risk factors, and potential opportunities for prevention and treatment are reviewed. This statement serves as an overall guide for practitioners to gain a better understanding of VCI and dementia, prevention, and treatment.

METHODS

Writing group members were nominated by the writing group co-chairs on the basis of their previous work in relevant topic areas and were approved by the American Heart Association Stroke Council Scientific Statement Oversight Committee, the Council on Epidemiology and Prevention, and the Manuscript Oversight Committee. The writing group used systematic literature reviews (primarily covering publications from 1990 to May 1, 2010), previously published guidelines, personal files, and expert opinion to summarize existing evidence, indicate gaps in current knowledge, and, when appropriate, formulate recommendations using standard American Heart Association criteria. All members of the writing group had the opportunity to comment on the recommendations and approved the final version of this document. After peer review by the American Heart Association, as well as review by the Stroke Council leadership, Council on Epidemiology and Prevention Council, and Scientific Statements Oversight Committee, the statement was approved by the American Heart Association Science Advisory and Coordinating Committee.

RESULTS

The construct of VCI has been introduced to capture the entire spectrum of cognitive disorders associated with all forms of cerebral vascular brain injury-not solely stroke-ranging from mild cognitive impairment through fully developed dementia. Dysfunction of the neurovascular unit and mechanisms regulating cerebral blood flow are likely to be important components of the pathophysiological processes underlying VCI. Cerebral amyloid angiopathy is emerging as an important marker of risk for Alzheimer disease, microinfarction, microhemorrhage and macrohemorrhage of the brain, and VCI. The neuropathology of cognitive impairment in later life is often a mixture of Alzheimer disease and microvascular brain damage, which may overlap and synergize to heighten the risk of cognitive impairment. In this regard, magnetic resonance imaging and other neuroimaging techniques play an important role in the definition and detection of VCI and provide evidence that subcortical forms of VCI with white matter hyperintensities and small deep infarcts are common. In many cases, risk markers for VCI are the same as traditional risk factors for stroke. These risks may include but are not limited to atrial fibrillation, hypertension, diabetes mellitus, and hypercholesterolemia. Furthermore, these same vascular risk factors may be risk markers for Alzheimer disease. Carotid intimal-medial thickness and arterial stiffness are emerging as markers of arterial aging and may serve as risk markers for VCI. Currently, no specific treatments for VCI have been approved by the US Food and Drug Administration. However, detection and control of the traditional risk factors for stroke and cardiovascular disease may be effective in the prevention of VCI, even in older people.

CONCLUSIONS

Vascular contributions to cognitive impairment and dementia are important. Understanding of VCI has evolved substantially in recent years, based on preclinical, neuropathologic, neuroimaging, physiological, and epidemiological studies. Transdisciplinary, translational, and transactional approaches are recommended to further our understanding of this entity and to better characterize its neuropsychological profile. There is a need for prospective, quantitative, clinical-pathological-neuroimaging studies to improve knowledge of the pathological basis of neuroimaging change and the complex interplay between vascular and Alzheimer disease pathologies in the evolution of clinical VCI and Alzheimer disease. Long-term vascular risk marker interventional studies beginning as early as midlife may be required to prevent or postpone the onset of VCI and Alzheimer disease. Studies of intensive reduction of vascular risk factors in high-risk groups are another important avenue of research.

Tissue inhibitor of metalloproteinases-3 mediates the death of immature oligodendrocytes via TNF-α/TACE in focal cerebral ischemia in mice

Background and Purpose

Oligodendrocyte (OL) death is important in focal cerebral ischemia. TIMP-3 promotes apoptosis in ischemic neurons by inhibiting proteolysis of TNF-α superfamily of death receptors. Since OLs undergo apoptosis during ischemia, we hypothesized that TIMP-3 contributes to OL death.

Methods

Middle cerebral artery occlusion (MCAO) was induced in Timp-3 knockout (KO) and wild type (WT) mice with 24 or 72 h of reperfusion. Cell death in white matter was investigated by stereology and TUNEL. Mature or immature OLs were identified using antibodies against glutathione S-transferase-π (GST-π) and galactocerebroside (GalC), respectively. Expression and level of proteins were examined using immunohistochemistry and immunoblotting. Protein activities were determined using a FRET peptide.

Results

Loss of OL-like cells was detected at 72 h only in WT ischemic white matter where TUNEL showed greater cell death. TIMP-3 expression was increased in WT reactive astrocytes. GST-π was reduced in ischemic white matter of WT mice compared with WT shams with no difference between KO and WT at 72 h. GalC level was significantly increased in both KO and WT ischemic white matter at 72 h. However, the increase in GalC in KO mice was significantly higher than WT; most TUNEL-positive cells in ischemic white matter expressed GalC, suggesting TIMP-3 deficiency protects the immature OLs from apoptosis. There were significantly higher levels of cleaved caspase-3 at 72 h in WT white matter than in KO. Greater expression of MMP-3 and -9 was seen in reactive astrocytes and/or microglia/macrophages in WT at 72 h. We found more microglia/macrophages in WT than in KO, which were the predominant source of increased TNF-α detected in the ischemic white matter. TACE activity was significantly increased in ischemic WT white matter, which was expressed in active microglia/macrophages and OLs.

Conclusions

Our results suggested that focal ischemia leads to proliferation of immature OLs in white matter and that TIMP-3 contributes to a caspase-3-dependent immature OL death via TNF-α-mediated neuroinflammation. Future studies will be needed to delineate the role of MMP-3 and MMP-9 that were increased in the Timp-3 wild type.

Increased mitochondrial content in remyelinated axons: implications for multiple sclerosis

Mitochondrial content within axons increases following demyelination in the central nervous system, presumably as a response to the changes in energy needs of axons imposed by redistribution of sodium channels. Myelin sheaths can be restored in demyelinated axons and remyelination in some multiple sclerosis lesions is extensive, while in others it is incomplete or absent. The effects of remyelination on axonal mitochondrial content in multiple sclerosis, particularly whether remyelination completely reverses the mitochondrial changes that follow demyelination, are currently unknown. In this study, we analysed axonal mitochondria within demyelinated, remyelinated and myelinated axons in post-mortem tissue from patients with multiple sclerosis and controls, as well as in experimental models of demyelination and remyelination, in vivo and in vitro. Immunofluorescent labelling of mitochondria (porin, a voltage-dependent anion channel expressed on all mitochondria) and axons (neurofilament), and ultrastructural imaging showed that in both multiple sclerosis and experimental demyelination, mitochondrial content within remyelinated axons was significantly less than in acutely and chronically demyelinated axons but more numerous than in myelinated axons. The greater mitochondrial content within remyelinated, compared with myelinated, axons was due to an increase in density of porin elements whereas increase in size accounted for the change observed in demyelinated axons. The increase in mitochondrial content in remyelinated axons was associated with an increase in mitochondrial respiratory chain complex IV activity. In vitro studies showed a significant increase in the number of stationary mitochondria in remyelinated compared with myelinated and demyelinated axons. The number of mobile mitochondria in remyelinated axons did not significantly differ from myelinated axons, although significantly greater than in demyelinated axons. Our neuropathological data and findings in experimental demyelination and remyelination in vivo and in vitro are consistent with a partial amelioration of the supposed increase in energy demand of demyelinated axons by remyelination.

Sphingosine kinase 1 and sphingosine 1-phosphate receptor 3 are functionally upregulated on astrocytes under pro-inflammatory conditions

BACKGROUND

Reactive astrocytes are implicated in the development and maintenance of neuroinflammation in the demyelinating disease multiple sclerosis (MS). The sphingosine kinase 1 (SphK1)/sphingosine1-phosphate (S1P) receptor signaling pathway is involved in modulation of the inflammatory response in many cell types, but the role of S1P receptor subtype 3 (S1P(3)) signaling and SphK1 in activated rat astrocytes has not been defined.

METHODOLOGY/PRINCIPAL FINDINGS

Using immunohistochemistry we observed the upregulation of S1P(3) and SphK1 expression on reactive astrocytes and SphK1 on macrophages in MS lesions. Increased mRNA and protein expression of S1P(3) and SphK1, as measured by qPCR and Western blotting respectively, was observed after treatment of rat primary astrocyte cultures with the pro-inflammatory stimulus lipopolysaccharide (LPS). Activation of SphK by LPS stimulation was confirmed by SphK activity assay and was blocked by the use of the SphK inhibitor SKI (2-(p-hydroxyanilino)-4-(p-chlorphenyl) thiazole. Treatment of astrocytes with a selective S1P(3) agonist led to increased phosphorylation of extracellular signal-regulated kinase (ERK)-1/2), which was further elevated with a LPS pre-challenge, suggesting that S1P(3) upregulation can lead to increased functionality. Moreover, astrocyte migration in a scratch assay was induced by S1P and LPS and this LPS-induced migration was sensitive to inhibition of SphK1, and independent of cell proliferation. In addition, S1P induced secretion of the potentially neuroprotective chemokine CXCL1, which was increased when astrocytes were pre-challenged with LPS. A more prominent role of S1P(3) signaling compared to S1P(1) signaling was demonstrated by the use of selective S1P(3) or S1P(1) agonists.

CONCLUSION/SIGNIFICANCE

In summary, our data demonstrate that the SphK1/S1P(3) signaling axis is upregulated when astrocytes are activated by LPS. This signaling pathway appears to play a role in the establishment and maintenance of astrocyte activation. Upregulation of the pathway in MS may be detrimental, e.g. through enhancing astrogliosis, or beneficial through increased remyelination via CXCL1.

The molecular basis of neurodegeneration in multiple sclerosis

Studies aimed to elucidate the pathogenesis of the disease and to find new therapeutic options for multiple sclerosis (MS) patients heavily rely on experimental autoimmune encephalomyelitis (EAE) as a suitable experimental model. This strategy has been highly successful for the inflammatory component of the disease, but had so far little success in the development of neuroprotective therapies, which are also effective in the progressive stage of the disease. Here we discuss opportunities and limitations of EAE models for MS research and provide an overview on the complex mechanisms leading to demyelination and neurodegeneration in this disease. We suggest that the underlying mechanisms involve adaptive and innate immunity. However, mitochondrial injury, resulting in energy failure, is a key element of neurodegeneration in MS and is apparently driven by radical production in activated microglia.

Myelination and axonal electrical activity modulate the distribution and motility of mitochondria at CNS nodes of Ranvier

Energy production presents a formidable challenge to axons as their mitochondria are synthesized and degraded in neuronal cell bodies. To meet the energy demands of nerve conduction, small mitochondria are transported to and enriched at mitochondrial stationary sites located throughout the axon. In this study, we investigated whether size and motility of mitochondria in small myelinated CNS axons are differentially regulated at nodes, and whether mitochondrial distribution and motility are modulated by axonal electrical activity. The size/volume of mitochondrial stationary sites was significantly larger in juxtaparanodal/internodal axoplasm than in nodal/paranodal axoplasm. With three-dimensional electron microscopy, we observed that axonal mitochondrial stationary sites were composed of multiple mitochondria of varying length, except at nodes where mitochondria were uniformly short and frequently absent altogether. Mitochondrial transport speed was significantly reduced in nodal axoplasm compared with internodal axoplasm. Increased axonal electrical activity decreased mitochondrial transport and increased the size of mitochondrial stationary sites in nodal/paranodal axoplasm. Decreased axonal electrical activity had the opposite effect. In cerebellar axons of the myelin-deficient rat, which contain voltage-gated Na(+) channel clusters but lack paranodal specializations, axonal mitochondrial motility and stationary site size were similar at Na(+) channel clusters and other axonal regions. These results demonstrate juxtaparanodal/internodal enrichment of stationary mitochondria and neuronal activity-dependent dynamic modulation of mitochondrial distribution and transport in nodal axoplasm. In addition, the modulation of mitochondrial distribution and motility requires oligodendrocyte-axon interactions at paranodal specializations.

Evolving expectations around early management of multiple sclerosis

Multiple sclerosis is a progressive inflammatory disease of the central nervous system. With prevention or at least delay of disease progression as a key target in the management of multiple sclerosis, current opinion on treatment encourages early intervention with well-tolerated disease-modifying treatments in order to optimize long-term clinical outcomes. Patients presenting with a clinically isolated syndrome (CIS) may progress to clinically definite multiple sclerosis, and clinical trials have demonstrated that early treatment with interferon beta can reduce the conversion rate. Cognitive impairment may already be present in patients with CISs. Today there is evolving evidence that cognitive impairment may be relevant for prognosis and that early treatment with interferon beta may also have a protective effect on the cognitive function. As an accumulation of neuronal loss is now considered to underlie the development of persistent disability in multiple sclerosis, it is crucial that treatment can protect against neuronal damage. In addition to its anti-inflammatory activity, interferon beta may have direct and indirect neuroprotective effects, and several studies have explored the role of interferon beta in regulating neuroprotective factors. With over 15 years of clinical experience as evidence, the long-term safety and efficacy of interferon beta treatment is unquestionable. Results from the CIS studies have demonstrated the high percentage of patients converting to clinically definite multiple sclerosis without treatment and the short- and long-term benefits of an early use of disease-modifying treatments. These findings support starting disease-modifying treatment as soon as the diagnosis of MS is reasonably formulated.

Oxidative damage in multiple sclerosis lesions

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, associated with demyelination and neurodegeneration. The mechanisms of tissue injury are currently poorly understood, but recent data suggest that mitochondrial injury may play an important role in this process. Since mitochondrial injury can be triggered by reactive oxygen and nitric oxide species, we analysed by immunocytochemistry the presence and cellular location of oxidized lipids and oxidized DNA in lesions and in normal-appearing white matter of 30 patients with multiple sclerosis and 24 control patients without neurological disease or brain lesions. As reported before in biochemical studies, oxidized lipids and DNA were highly enriched in active multiple sclerosis plaques, predominantly in areas that are defined as initial or ‘prephagocytic’ lesions. Oxidized DNA was mainly seen in oligodendrocyte nuclei, which in part showed signs of apoptosis. In addition, a small number of reactive astrocytes revealed nuclear expression of 8-hydroxy-d-guanosine. Similarly, lipid peroxidation-derived structures (malondialdehyde and oxidized phospholipid epitopes) were seen in the cytoplasm of oligodendrocytes and some astrocytes. In addition, oxidized phospholipids were massively accumulated in a fraction of axonal spheroids with disturbed fast axonal transport as well as in neurons within grey matter lesions. Neurons stained for oxidized phospholipids frequently revealed signs of degeneration with fragmentation of their dendritic processes. The extent of lipid and DNA oxidation correlated significantly with inflammation, determined by the number of CD3 positive T cells and human leucocyte antigen-D expressing macrophages and microglia in the lesions. Our data suggest profound oxidative injury of oligodendrocytes and neurons to be associated with active demyelination and axonal or neuronal injury in multiple sclerosis.

Matching mitochondria to metabolic needs at nodes of Ranvier

Myelinated axons conduct nerve impulses at high speed using a unique mode of excitation, referred to as saltatory conduction, which is enabled structurally by the narrowing of the site of action potentials to a tiny gap in the axon called the node of Ranvier. With this structural specialization comes an interesting metabolic matching problem. How do mitochondria find and supply energy to these tiny nodes of Ranvier distributed sparsely along a myelinated axon? Does the intense Na(+) influx at the node, which is produced by the highest known sodium channel density in all excitable membranes, help guide where mitochondria stop? Evidence suggests that during excitation in the peripheral nervous system, Na(+) influx recruits mitochondria to the node by triggering Ca(2+) elevation and activating Na(+) pumps. Intriguingly, indirect evidence suggests that in the central nervous system, activity recruits mitochondria to the internode (myelin-covered portion of the axon). Metabolic dysfunction thus might produce spatially distinct lesions in PNS and CNS myelinated fibers. Future dissection of regional variation in mitochondrial biology in myelinated axons using live imaging will likely yield surprises about sites of vulnerability in demyelinating diseases and clues for therapeutic intervention strategy.

Reduced axonopathy and enhanced remyelination after chronic demyelination in fibroblast growth factor 2 (Fgf2)-null mice: differential detection with diffusion tensor imaging

Chronic central nervous system demyelinating diseases result in long-term disability because of limited remyelination capacity and cumulative damage to axons. Corpus callosum demyelination in mice fed cuprizone provides a reproducible model of chronic demyelination in which the demyelinating agent can be removed to test modifications that promote recovery and to develop noninvasive neuroimaging techniques for monitoring changes in myelin and axons. We used the cuprizone model in mice with genetic deletion of fibroblast growth factor 2 (Fgf2) to determine the impact of FGF2 on axon pathology and remyelination after chronic demyelination. We also evaluated the ability of quantitative magnetic resonance diffusion tensor imaging (DTI) to distinguish the corresponding pathological changes in axons and myelin during the progression of demyelination and remyelination. During the recovery period after chronic demyelination, Fgf2-null mice exhibited enhanced remyelination that was detected using DTI measures of radial diffusivity and confirmed by electron microscopic analysis of the proportion of remyelinated axons. Ultrastructural analysis also demonstrated reduced axonal atrophy in chronically demyelinated Fgf2-null versus wild-type mice. This difference in axon atrophy was further demonstrated as reduced immunohistochemical detection of neurofilament dephosphorylation in Fgf2-null mice. Diffusion tensor imaging axial and radial diffusivity measures did not differentiate Fgf2-null mice from wild-type mice to correlate with changes in axonal atrophy during chronic demyelination. Overall, these findings demonstrate that attenuation of FGF2 signaling promotes neuroprotection of axons and remyelination, suggesting that FGF2 is an important negative regulator of recovery after chronic demyelination.

Blood and CSF Biomarker Dynamics in Multiple Sclerosis: Implications for Data Interpretation

Background. Disability in multiple sclerosis (MS) is related to neuroaxonal degeneration. A reliable blood biomarker for neuroaxonal degeneration is needed. Objectives. To explore the relationship between cerebrospinal fluid (CSF) and serum concentrations of a protein biomarker for neuroaxonal degeneration, the neurofilaments heavy chain (NfH). Methods. An exploratory cross-sectional (n = 51) and longitudinal (n = 34) study on cerebrospinal fluid (CSF) and serum NfH phosphoform levels in patients with MS. The expanded disability status scale (EDSS), CSF, and serum levels of NfH-SMI34 and NfH-SMI35 were quantified at baseline. Disability progression was assessed at 3-year followup. Results. At baseline, patients with primary progressive MS (PPMS, EDSS 6) and secondary progressive MS (SPMS, EDSS 6) were more disabled compared to patients with relapsing remitting MS (RRMS, EDSS 2, P < .0001). Serum and CSF NfH phosphoform levels were not correlated. Baseline serum levels of the NfH-SMI34 were significantly (P < .05) higher in patients with PPMS (2.05 ng/mL) compared to SPMS (0.03 ng/mL) and RRMS (1.56 ng/mL). In SPMS higher serum than CSF NfH-SMI34 levels predicted disability progression from baseline (ΔEDSS 2, P < .05). In RRMS higher CSF than serum NfH-SMI35 levels predicted disability progression (ΔEDSS 2, P < .05). Conclusion. Serum and CSF NfH-SMI34 and NfH-SMI35 levels did not correlate with each other in MS. The quantitative relationship of CSF and serum NfH levels suggests that neuroaxonal degeneration of the central nervous system is the likely cause for disability progression in RRMS. In more severely disabled patients with PP/SPMS, subtle pathology of the peripheral nervous system cannot be excluded as an alternative source for blood NfH levels. Therefore, the interpretation of blood protein biomarker data in diseases of the central nervous system (CNS) should consider the possibility that pathology of the peripheral nervous system (PNS) may influence the results.