Virtual hypoxia and chronic necrosis of demyelinated axons in multiple sclerosis

Absence of R-Ras1 and R-Ras2 causes mitochondrial alterations that trigger axonal degeneration in a hypomyelinating disease model

Fast synaptic transmission in vertebrates is critically dependent on myelin for insulation and metabolic support. Myelin is produced by oligodendrocytes (OLs) that maintain multilayered membrane compartments that wrap around axonal fibers. Alterations in myelination can therefore lead to severe pathologies such as multiple sclerosis. Given that hypomyelination disorders have complex etiologies, reproducing clinical symptoms of myelin diseases from a neurological perspective in animal models has been difficult. We recently reported that R-Ras1^-/- and/or R-Ras2^-/- mice, which lack GTPases essential for OL survival and differentiation processes, present different degrees of hypomyelination in the central nervous system with a compounded hypomyelination in double knockout (DKO) mice. Here, we discovered that the loss of R-Ras1 and/or R-Ras2 function is associated with aberrant myelinated axons with increased numbers of mitochondria, and a disrupted mitochondrial respiration that leads to increased reactive oxygen species levels. Consequently, aberrant myelinated axons are thinner with cytoskeletal phosphorylation patterns typical of axonal degeneration processes, characteristic of myelin diseases. Although we observed different levels of hypomyelination in a single mutant mouse, the combined loss of function in DKO mice lead to a compromised axonal integrity, triggering the loss of visual function. Our findings demonstrate that the loss of R-Ras function reproduces several characteristics of hypomyelinating diseases, and we therefore propose that R-Ras1^-/- and R-Ras2^-/- neurological models are valuable approaches for the study of these myelin pathologies.

Molecular and Therapeutic Aspects of Hyperbaric Oxygen Therapy in Neurological Conditions

In hyperbaric oxygen therapy (HBOT), the subject is placed in a chamber containing 100% oxygen gas at a pressure of more than one atmosphere absolute. This treatment is used to hasten tissue recovery and improve its physiological aspects, by providing an increased supply of oxygen to the damaged tissue. In this review, we discuss the consequences of hypoxia, as well as the molecular and physiological processes that occur in subjects exposed to HBOT. We discuss the efficacy of HBOT in treating neurological conditions and neurodevelopmental disorders in both humans and animal models. We summarize by discussing the challenges in this field, and explore future directions that will allow the scientific community to better understand the molecular aspects and applications of HBOT for a wide variety of neurological conditions.

The Role of Cerebral Hypoperfusion in Multiple Sclerosis (ROCHIMS) Trial in Multiple Sclerosis: Insights From Negative Results

Background: Accumulating evidence indicates that mitochondrial energy failure is involved in the progressive axonal degeneration in multiple sclerosis (MS). In patients with MS, it has been shown that both levels of N-acetylaspartate (NAA), which is a marker of axonal mitochondrial energy, and cerebral blood flow (CBF) are reduced in cerebral normal appearing white matter (NAWM). The latter is likely due to the vasoconstrictive action of endothelin-1 (ET-1) produced by reactive astrocytes, which is triggered by local proinflammatory cytokines. A preliminary study in patients with MS showed that CBF could be restored to normal values after a single dose of 62.5 mg of the ET-1 antagonist bosentan.

Objective: To investigate whether restoring CBF in patients with relapsing remitting MS (RRMS) increases levels of NAA in cerebral NAWM and improves clinical symptoms.

Methods: 27 RRMS patients were included in a 4 weeks proof-of-concept, randomized, double-blind placebo-controlled trial (ROCHIMS) to investigate whether bosentan 62.5 mg twice daily could increase the NAA/creatine (NAA/Cr) ratio in NAWM of the centrum semiovale. Magnetic resonance imaging (MRI) assessing CBF and NAA/Cr, and clinical evaluations were performed at baseline and at end of study. Separately from the clinical trial, 10 healthy controls underwent the same baseline multimodal brain MRI protocol as the MS patients.

Results: Eleven patients in the bosentan arm and thirteen patients in the placebo arm completed the study. Bosentan did not increase CBF. However, we found that CBF in the patients was not different from that of the healthy controls. There were no effects on NAA levels and clinical symptoms.

Conclusions: Our study showed that CBF in RRMS patients is not always decreased and that bosentan has no effect when CBF values are within the normal range. We hypothesize that in our patients there was no significant astrocytic production of ET-1 because they had a mild disease course, with minimal local inflammatory activity. Future studies with bosentan in MS should focus on patients with elevated ET-1 levels in cerebrospinal fluid or blood.

Neuronal mitochondrial calcium uniporter deficiency exacerbates axonal injury and suppresses remyelination in mice subjected to experimental autoimmune encephalomyelitis

High-capacity mitochondrial calcium (Ca²⁺) uptake by the mitochondrial Ca²⁺ uniporter (MCU) is strategically positioned to support the survival and remyelination of axons in multiple sclerosis (MS) by undocking mitochondria, buffering Ca²⁺ and elevating adenosine triphosphate (ATP) synthesis at metabolically stressed sites. Respiratory chain deficits in MS are proposed to metabolically compromise axon survival and remyelination by suppressing MCU activity. In support of this hypothesis, clinical scores, mitochondrial dysfunction, myelin loss, axon damage and inflammation were elevated while remyelination was blocked in neuronal MCU deficient (Thy1-MCU Def) mice relative to Thy1 controls subjected to experimental autoimmune encephalomyelitis (EAE). At the first sign of walking deficits, mitochondria in EAE/Thy1 axons showed signs of activation. By contrast, cytoskeletal damage, fragmented mitochondria and large autophagosomes were seen in EAE/Thy1-MCU Def axons. As EAE severity increased, EAE/Thy1 axons were filled with massively swollen mitochondria with damaged cristae while EAE/Thy1-MCU Def axons were riddled with late autophagosomes. ATP concentrations and mitochondrial gene expression were suppressed while calpain activity, autophagy-related gene mRNA levels and autophagosome marker (LC3) co-localization in Thy1-expressing neurons were elevated in the spinal cords of EAE/Thy1-MCU Def compared to EAE/Thy1 mice. These findings suggest that MCU inhibition contributes to axonal damage that drives MS progression.

Enhanced axonal response of mitochondria to demyelination offers neuroprotection: implications for multiple sclerosis

Axonal loss is the key pathological substrate of neurological disability in demyelinating disorders, including multiple sclerosis (MS). However, the consequences of demyelination on neuronal and axonal biology are poorly understood. The abundance of mitochondria in demyelinated axons in MS raises the possibility that increased mitochondrial content serves as a compensatory response to demyelination. Here, we show that upon demyelination mitochondria move from the neuronal cell body to the demyelinated axon, increasing axonal mitochondrial content, which we term the axonal response of mitochondria to demyelination (ARMD). However, following demyelination axons degenerate before the homeostatic ARMD reaches its peak. Enhancement of ARMD, by targeting mitochondrial biogenesis and mitochondrial transport from the cell body to axon, protects acutely demyelinated axons from degeneration. To determine the relevance of ARMD to disease state, we examined MS autopsy tissue and found a positive correlation between mitochondrial content in demyelinated dorsal column axons and cytochrome c oxidase (complex IV) deficiency in dorsal root ganglia (DRG) neuronal cell bodies. We experimentally demyelinated DRG neuron-specific complex IV deficient mice, as established disease models do not recapitulate complex IV deficiency in neurons, and found that these mice are able to demonstrate ARMD, despite the mitochondrial perturbation. Enhancement of mitochondrial dynamics in complex IV deficient neurons protects the axon upon demyelination. Consequently, increased mobilisation of mitochondria from the neuronal cell body to the axon is a novel neuroprotective strategy for the vulnerable, acutely demyelinated axon. We propose that promoting ARMD is likely to be a crucial preceding step for implementing potential regenerative strategies for demyelinating disorders.

The immunoregulatory and neuroprotective effects of human adipose derived stem cells overexpressing IL-11 and IL-13 in the experimental autoimmune encephalomyelitis mice

Multiple sclerosis (MS) is an inflammatory demyelination disease in the central nervous system (CNS) characterized by incomplete endogenous remyelination in the chronic phase. A shift of the balance between pro and anti-inflammatory cytokines is one of the important markers in the pathogenesis of MS. This study aimed to evaluate the effects of human adipose derived stem cells (hADSCs) overexpressing interleukin 11 and interleukin 13 (IL-11, 13-hADSCs) on the experimental autoimmune encephalomyelitis (EAE), an animal model of MS.12 days after immunization of C57Bl/6 female mice with MOG35-55 and initial clinical symptoms appearance, the IL-11, 13-hADSCs were injected via the tail vein into the EAE mice. Then, the mice were sacrificed at 30 days post-immunization (DPI) and the spinal cords of experimental groups were extracted for histopathological and real-time RT-PCR studies.The results indicated that the clinical scores and mononuclear cells infiltration into the spinal cords of EAE mice were significantly reduced in mice treated with IL-11, 13-hADSCs. Likewise, the remyelination and oligodendrogenesis were significantly enhanced in the mentioned treatment group. Real-time results demonstrated that pro/anti-inflammatory cytokine genes expression was reversed in IL-11, 13-hADSCs treatment group in comparison to the untreated EAE group.Expression of IL-11 as a neurotrophic cytokine and IL-13 as an anti-inflammatory cytokine by hADSCs could increase the immunomodulatory and neuroprotective effects of hADSCs and be a powerful candidate in stem cell therapy for future treatment of MS.

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

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

Kynurenines in the Pathogenesis of Multiple Sclerosis: Therapeutic Perspectives

Over the past years, an increasing amount of evidence has emerged in support of the kynurenine pathway’s (KP) pivotal role in the pathogenesis of several neurodegenerative, psychiatric, vascular and autoimmune diseases. Different neuroactive metabolites of the KP are known to exert opposite effects on neurons, some being neuroprotective (e.g., picolinic acid, kynurenic acid, and the cofactor nicotinamide adenine dinucleotide), while others are toxic to neurons (e.g., 3-hydroxykynurenine, quinolinic acid). Not only the alterations in the levels of the metabolites but also disturbances in their ratio (quinolinic acid/kynurenic acid) have been reported in several diseases. In addition to the metabolites, the enzymes participating in the KP have been unearthed to be involved in modulation of the immune system, the energetic upkeep of neurons and have been shown to influence redox processes and inflammatory cascades, revealing a sophisticated, intertwined system. This review considers various methods through which enzymes and metabolites of the kynurenine pathway influence the immune system, the roles they play in the pathogenesis of neuroinflammatory diseases based on current evidence with a focus on their involvement in multiple sclerosis, as well as therapeutic approaches.

Sarm1 knockout protects against early but not late axonal degeneration in experimental allergic encephalomyelitis

Programmed axonal degeneration, also known as Wallerian degeneration, occurs in immune-mediated central nervous system (CNS) inflammatory disorders such as multiple sclerosis and the animal model experimental allergic encephalomyelitis (EAE). Sterile alpha and TIR domain containing protein 1 (SARM1) functions to promote programmed axonal degeneration. To test the hypothesis that loss of SARM1 will reduce axonal degeneration in immune-mediated CNS inflammatory disorders, the course and pathology of EAE was compared in Sarm1 knockout mice and wild type littermates. The clinical course of EAE was similar in Sarm1 knockout and wild type. Analysis of EAE in mice expressing neuronal yellow fluorescent protein (YFP) showed significantly less axonal degeneration in Sarm1 knockout mice compared to wild type littermates at 14 days post-induction of EAE. At 21 days post-induction, however, difference in axonal degeneration was not significant. At 42 days post-induction, Sarm1 knockout mice were indistinguishable from wild type with respect to markers of axonal injury, and were similar with respect to axonal density in the lumbar cords. There was no significant change in peripheral immune activation or CNS inflammatory cell infiltration associated with EAE in Sarm1 knockout mice. In conclusion, Sarm1 deletion delayed axonal degeneration early in the course of CNS inflammation, but did not confer long-term protection from axonal degeneration in an animal model of immune-mediated CNS inflammation.

Sodium in the Relapsing-Remitting Multiple Sclerosis Spinal Cord: Increased Concentrations and Associations With Microstructural Tissue Anisotropy

BACKGROUND

Associations between brain total sodium concentration, disability, and disease progression have recently been reported in multiple sclerosis. However, such measures in spinal cord have not been reported.

PURPOSE

To measure total sodium concentration (TSC) alterations in the cervical spinal cord of people with relapsing-remitting multiple sclerosis (RRMS) and a control cohort using sodium MR spectroscopy (MRS).

STUDY TYPE

Retrospective cohort.

SUBJECTS

Nineteen people with RRMS and 21 healthy controls.

FIELD STRENGTH/SEQUENCE

3 T sodium MRS, diffusion tensor imaging, and 3D gradient echo.

ASSESSMENT

Quantification of total sodium concentration in the cervical cord using a reference phantom. Measures of spinal cord cross-sectional area, fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity from ¹ H MRI. Clinical assessments of 9-Hole Peg Test, 25-Foot Timed walk test, Paced Auditory Serial Addition Test with 3-second intervals, grip strength, vibration sensitivity, and posturography were performed on the RRMS cohort as well as reporting lesions in the C2/3 area.

STATISTICAL TESTS

Multiple linear regression models were run between sodium and clinical scores, cross-sectional area, and diffusion metrics to establish any correlations.

RESULTS

A significant increase in spinal cord total sodium concentration was found in people with RRMS relative to healthy controls (57.6 ± 18 mmol and 38.0 ± 8.6 mmol, respectively, P < 0.001). Increased TSC correlated with reduced fractional anisotropy (P = 0.034) and clinically with decreased mediolateral stability assessed with posturography (P = 0.045).

DATA CONCLUSION

Total sodium concentration in the cervical spinal cord is elevated in RRMS. This alteration is associated with reduced fractional anisotropy, which may be due to changes in tissue microstructure and, hence, in the integrity of spinal cord tissue.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 2.

BOLD signal within and around white matter lesions distinguishes multiple sclerosis and non-specific white matter disease: a three-dimensional approach

Multiple sclerosis (MS) diagnostic criteria are based upon clinical presentation and presence of white matter hyperintensities on two-dimensional magnetic resonance imaging (MRI) views. Such criteria, however, are prone to false-positive interpretations due to the presence of similar MRI findings in non-specific white matter disease (NSWMD) states such as migraine and microvascular disease. The coexistence of age-related changes has also been recognized in MS patients, and this comorbidity further poses a diagnostic challenge. In this study, we investigated the physiologic profiles within and around MS and NSWMD lesions and their ability to distinguish the two disease states. MS and NSWMD lesions were identified using three-dimensional (3D) T₂-FLAIR images and segmented using geodesic active contouring. A dual-echo functional MRI sequence permitted near-simultaneous measurement of blood-oxygen-level-dependent signal (BOLD) and cerebral blood flow (CBF). BOLD and CBF were calculated within lesions and in 3D concentric layers surrounding each lesion. BOLD slope, an indicator of lesion metabolic capacity, was calculated as the change in BOLD from a lesion through its surrounding perimeters. We observed sequential BOLD signal reductions from the lesion towards the perimeters for MS, while no such decreases were observed for NSWMD lesions. BOLD slope was significantly lower in MS compared to NSWM lesions, suggesting decreased metabolic activity in MS lesions. Furthermore, BOLD signal within and around lesions significantly distinguished MS and NSWMD lesions. These results suggest that this technique shows promise for clinical utility in distinguishing NSWMD or MS disease states and identifying NSWMD lesions occurring in MS patients.

Effects of Biotin on survival, ensheathment, and ATP production by oligodendrocyte lineage cells in vitro

Mechanisms implicated in disease progression in multiple sclerosis include continued oligodendrocyte (OL)/myelin injury and failure of myelin repair. Underlying causes include metabolic stress with resultant energy deficiency. Biotin is a cofactor for carboxylases involved in ATP production that impact myelin production by promoting fatty acid synthesis. Here, we investigate the effects of high dose Biotin (MD1003) on the functional properties of post-natal rat derived oligodendrocyte progenitor cells (OPCs). A2B5 positive OPCs were assessed using an in vitro injury assay, culturing cells in either DFM (DMEM/F12+N1) or “stress media” (no glucose (NG)-DMEM), with Biotin added over a range from 2.5 to 250 μg/ml, and cell viability determined after 24 hrs. Biotin reduced the increase in OPC cell death in the NG condition. In nanofiber myelination assays, biotin increased the percentage of ensheathing cells, the number of ensheathed segments per cell, and length of ensheathed segments. In dispersed cell culture, Biotin also significantly increased ATP production, assessed using a Seahorse bio-analyzer. For most assays, the positive effects of Biotin were observed at the higher end of the dose-response analysis. We conclude that Biotin, in vitro, protects OL lineage cells from metabolic injury, enhances myelin-like ensheathment, and is associated with increased ATP production.

A metabolic perspective on CSF-mediated neurodegeneration in multiple sclerosis

Multiple sclerosis is an autoimmune demyelinating disorder of the CNS, characterized by inflammatory lesions and an underlying neurodegenerative process, which is more prominent in patients with progressive disease course. It has been proposed that mitochondrial dysfunction underlies neuronal damage, the precise mechanism by which this occurs remains uncertain. To investigate potential mechanisms of neurodegeneration, we conducted a functional screening of mitochondria in neurons exposed to the CSF of multiple sclerosis patients with a relapsing remitting (n = 15) or a progressive (secondary, n = 15 or primary, n = 14) disease course. Live-imaging of CSF-treated neurons, using a fluorescent mitochondrial tracer, identified mitochondrial elongation as a unique effect induced by the CSF from progressive patients. These morphological changes were associated with decreased activity of mitochondrial complexes I, III and IV and correlated with axonal damage. The effect of CSF treatment on the morphology of mitochondria was characterized by phosphorylation of serine 637 on the dynamin-related protein DRP1, a post-translational modification responsible for unopposed mitochondrial fusion in response to low glucose conditions. The effect of neuronal treatment with CSF from progressive patients was heat stable, thereby prompting us to conduct an unbiased exploratory lipidomic study that identified specific ceramide species as differentially abundant in the CSF of progressive patients compared to relapsing remitting multiple sclerosis. Treatment of neurons with medium supplemented with ceramides, induced a time-dependent increase of the transcripts levels of specific glucose and lactate transporters, which functionally resulted in progressively increased glucose uptake from the medium. Thus ceramide levels in the CSF of patients with progressive multiple sclerosis not only impaired mitochondrial respiration but also decreased the bioavailability of glucose by increasing its uptake. Importantly the neurotoxic effect of CSF treatment could be rescued by exogenous supplementation with glucose or lactate, presumably to compensate the inefficient fuel utilization. Together these data suggest a condition of 'virtual hypoglycosis' induced by the CSF of progressive patients in cultured neurons and suggest a critical temporal window of intervention for the rescue of the metabolic impairment of neuronal bioenergetics underlying neurodegeneration in multiple sclerosis patients.

Patterns of retrograde axonal degeneration in the visual system

Conclusive evidence for existence of acquired retrograde axonal degeneration that is truly trans-synaptic (RTD) has not yet been provided for the human visual system. Convincing data rely on experimental data of lesions to the posterior visual pathways. This study aimed to overcome the limitations of previous human studies, namely pathology to the anterior visual pathways and neurodegenerative co-morbidity. In this prospective, longitudinal cohort retinal optical coherence tomography scans were acquired before and after elective partial temporal lobe resection in 25 patients for intractable epilepsy. Newly developed region of interest-specific, retinotopic areas substantially improved on conventional reported early treatment diabetic retinopathy study (ETDRS) grid-based optical coherence tomography data. Significant inner retinal layer atrophy separated patients with normal visual fields from those who developed a visual field defect. Acquired RTD affected the retinal nerve fibre layer, ganglion cell and inner plexiform layer and stopped at the level of the inner nuclear layer. There were significant correlations between the resected brain tissue volume and the ganglion cell layer region of interest (R = -0.78, P < 0.0001) and ganglion cell inner plexiform layer region of interest (R = -0.65, P = 0.0007). In one patient, damage to the anterior visual pathway resulted in occurrence of microcystic macular oedema as recognized from experimental data. In the remaining 24 patients with true RTD, atrophy rates in the first 3 months were strongly correlated with time from surgery for the ganglion cell layer region of interest (R = -0.74, P < 0.0001) and the ganglion cell inner plexiform layer region of interest (R = -0.51, P < 0.0001). The different time course of atrophy rates observed relate to brain tissue volume resection and suggest that three distinct patterns of retrograde axonal degeneration exist: (i) direct retrograde axonal degeneration; (ii) rapid and self-terminating RTD; and (iii) prolonged RTD representing a 'penumbra', which slowly succumbs to molecularly governed spatial cellular stoichiometric relationships. We speculate that the latter could be a promising target for neuroprotection.

Visual Function and Disability Are Associated with Increased Retinal Volumetric Vessel Density in Patients with Multiple Sclerosis

PURPOSE

The goal of this study was to determine the volumetric vessel density (VVD) in the intraretinal layers and its relationship with visual function and disability in patients with multiple sclerosis (MS).

DESIGN

Cross-sectional study.

METHODS

A total of 80 patients with relapsing-remitting MS and 99 age- and sex-matched healthy controls (HC) were recruited. The retinal microvascular network in the macular area was imaged using optical coherence tomography angiography in 123 eyes without a history of optic neuritis (ON) (MSNON) and 36 eyes with a history of ON (MSON). The VVD was calculated as the vessel densities in the retinal vascular network (RVN), superficial vascular plexus (SVP), or deep vascular plexus (DVP) of an annulus (0.6-2.5 mm in diameter), divided by the corresponding tissue volume of the intraretinal layers respectively.

RESULTS

The VVD of RVN and DVP in MSNON were significantly higher than in HC (P < .05). The VVD of RVN, SVP, and DVP in MSON were significantly higher than in MSNON and HC (P < .05). The VVD in both RVN and SVP were positively related to EDSS and disease duration, but negatively related to low-contrast letter acuity (P < .05). The VVD measurements were also negatively and strongly related to the corresponding tissue volumes (P < .05).

CONCLUSIONS

This is the first study to reveal increased retinal VVD in patients with relapsing-remitting MS. The measurements of VVD in the RVN and SVP were related to disability and visual function, which may be developed as image markers for tracking disease progression.

Progressive Multiple Sclerosis Is Associated with Faster and Specific Retinal Layer Atrophy

OBJECTIVE

Therapeutic development in progressive multiple sclerosis (PMS) has been hampered by a lack of reliable biomarkers to monitor neurodegeneration. Optical coherence tomography (OCT)-derived retinal measures have been proposed as promising biomarkers to fulfill this role. However, it is unclear whether retinal atrophy persists in PMS, exceeds normal aging, or can be distinguished from relapsing-remitting multiple sclerosis (RRMS).

METHODS

178 RRMS, 186 PMS, and 66 control participants were followed with serial OCT for a median follow-up of 3.7 years.

RESULTS

The estimated proportion of peripapillary retinal nerve fiber layer (pRNFL) and macular ganglion cell + inner plexiform layer (GCIPL) thinning in multiple sclerosis (MS) attributable to normal aging increased from 42.7% and 16.7% respectively at age 25 years, to 83.7% and 81.1% at age 65 years. However, independent of age, PMS was associated with faster pRNFL (-0.34 ± 0.09%/yr, p < 0.001) and GCIPL (-0.27 ± 0.07%/yr, p < 0.001) thinning, as compared to RRMS. In both MS and controls, higher baseline age was associated with faster inner nuclear layer (INL) and outer nuclear layer (ONL) thinning. INL and ONL thinning were independently faster in PMS, as compared to controls (INL:-0.09 ± 0.04%/yr, p = 0.03; ONL:-0.12 ± 0.06%/yr, p = 0.04), and RRMS (INL:-0.10 ± 0.04%/yr, p = 0.01; ONL:-0.13 ± 0.05%/yr, p = 0.01), whereas they were similar in RRMS and controls. Unlike RRMS, disease-modifying therapies (DMTs) did not impact rates of retinal layer atrophy in PMS.

INTERPRETATION

PMS is associated with faster retinal atrophy independent of age. INL and ONL measures may be novel biomarkers of neurodegeneration in PMS that appear to be unaffected by conventional DMTs. The effects of aging on rates of retinal layer atrophy should be considered in clinical trials incorporating OCT outcomes. ANN NEUROL 2020;87:885-896.

Neuroprotection induced by dexpramipexole delays disease progression in a mouse model of progressive multiple sclerosis

BACKGROUND AND PURPOSE

Drugs able to counteract progressive multiple sclerosis (MS) represent a largely unmet therapeutic need. Even though the pathogenesis of disease evolution is still obscure, accumulating evidence indicates that mitochondrial dysfunction plays a causative role in neurodegeneration and axonopathy in progressive MS patients. Here, we investigated the effects of dexpramipexole, a compound with a good safety profile in humans and able to sustain mitochondria functioning and energy production, in a mouse model of progressive MS.

EXPERIMENTAL APPROACH

Female non-obese diabetic mice were immunized with MOG_35-55 . Functional, immune and neuropathological parameters were analysed during disease evolution in animals treated or not with dexpramipexole. The compound's effects on bioenergetics and neuroprotection were also evaluated in vitro.

KEY RESULTS

We found that oral treatment with dexpramipexole at a dose consistent with that well tolerated in humans delayed disability progression, extended survival, counteracted reduction of spinal cord mitochondrial DNA content and reduced spinal cord axonal loss of mice. Accordingly, the drug sustained in vitro bioenergetics of mouse optic nerve and dorsal root ganglia and counteracted neurodegeneration of organotypic mouse cortical cultures exposed to the adenosine triphosphate-depleting agents oligomycin or veratridine. Dexpramipexole, however, was unable to affect the adaptive and innate immune responses both in vivo and in vitro.

CONCLUSION AND IMPLICATION

The present findings corroborate the hypothesis that neuroprotective agents may be of relevance to counteract MS progression and disclose the translational potential of dexpramipexole to treatment of progressive MS patients as a stand-alone or adjunctive therapy.

The Cuprizone Model: Dos and Do Nots

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Various pre-clinical models with different specific features of the disease are available to study MS pathogenesis and to develop new therapeutic options. During the last decade, the model of toxic demyelination induced by cuprizone has become more and more popular, and it has contributed substantially to our understanding of distinct yet important aspects of the MS pathology. Here, we aim to provide a practical guide on how to use the cuprizone model and which pitfalls should be avoided.

Cluster analysis of time evolution (CAT) for quantitative susceptibility mapping (QSM) and quantitative blood oxygen level-dependent magnitude (qBOLD)-based oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2 ) mapping

PURPOSE

To improve the accuracy of QSM plus quantitative blood oxygen level-dependent magnitude (QSM + qBOLD or QQ)-based mapping of the oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2 ) using cluster analysis of time evolution (CAT).

METHODS

3D multi-echo gradient echo and arterial spin labeling images were acquired in 11 healthy subjects and 5 ischemic stroke patients. DWI was also carried out on patients. CAT was developed for analyzing signal evolution over TE. QQ-based OEF and CMRO2 were reconstructed with and without CAT, and results were compared using region of interest analysis and a paired t-test.

RESULTS

Simulations demonstrated that CAT substantially reduced noise error in QQ-based OEF. In healthy subjects, QQ-based OEF appeared less noisy and more uniform with CAT than without CAT; average OEF with and without CAT in cortical gray matter was 32.7 ± 4.0% and 37.9 ± 4.5%, with corresponding CMRO2 of 148.4 ± 23.8 and 171.4 ± 22.4 μmol/100 g/min, respectively. In patients, regions of low OEF were confined within the ischemic lesions defined on DWI when using CAT, which was not observed without CAT.

CONCLUSION

The cluster analysis of time evolution (CAT) significantly improves the robustness of QQ-based OEF against noise.

Blood neurofilament light levels segregate treatment effects in multiple sclerosis

Objective

To determine factors (including the role of specific disease modulatory treatments [DMTs]) associated with (1) baseline, (2) on-treatment, and (3) change (from treatment start to on-treatment assessment) in plasma neurofilament light chain (pNfL) concentrations in relapsing-remitting multiple sclerosis (RRMS).

Methods

Data including blood samples analyses and long-term clinical follow-up information for 1,261 Swedish patients with RRMS starting novel DMTs were analyzed using linear regressions to model pNfL and changes in pNfL concentrations as a function of clinical variables and DMTs (alemtuzumab, dimethyl fumarate, fingolimod, natalizumab, rituximab, and teriflunomide).

Results

The baseline pNfL concentration was positively associated with relapse rate, Expanded Disability Status Scale score, Age-Related MS Severity Score, and MS Impact Score (MSIS-29), and negatively associated with Symbol Digit Modalities Test performance and the number of previously used DMTs. All analyses, which used inverse propensity score weighting to correct for differences in baseline factors at DMT start, highlighted that both the reduction in pNfL concentration from baseline to on-treatment measurement and the on-treatment pNfL level differed across DMTs. Patients starting alemtuzumab displayed the highest reduction in pNfL concentration and lowest on-treatment pNfL concentrations, while those starting teriflunomide had the smallest decrease and highest on-treatment levels, but also starting from lower values. Both on-treatment pNfL and decrease in pNfL concentrations were highly dependent on baseline concentrations.

Conclusion

Choice of DMT in RRMS is significantly associated with degree of reduction in pNfL, which supports a role for pNfL as a drug response marker.

High-dose biotin in progressive multiple sclerosis: A prospective study of 178 patients in routine clinical practice

Background:

A recent controlled trial suggested that high-dose biotin supplementation reverses disability progression in patients with progressive multiple sclerosis.

Objective:

To analyze the impact of high-dose biotin in routine clinical practice on disability progression at 12 months.

Methods:

Progressive multiple sclerosis patients who started high-dose biotin at Nantes or Rennes Hospital between 3 June 2015 and 15 September 2017 were included in this prospective study. Disability outcome measures, patient-reported outcome measures, relapses, magnetic resonance imaging (MRI) data, and adverse events were collected at baseline, 6, and 12 months.

Results:

A total of 178 patients were included. At baseline, patients were 52.0 ± 9.4 years old, mean Expanded Disability Status Scale (EDSS) score was 6.1 ± 1.3, mean disease duration was 16.9 ± 9.5 years. At 12 months, 3.8% of the patients had an improved EDSS score. Regarding the other disability scales, scores either remained stable or increased significantly. In total, 47.4% of the patients described stability, 27.6% felt an improvement, and 25% described a worsening. Four patients (2.2%) had a relapse. Of the 74 patients (41.6%) who underwent an MRI, 20 (27.0%) had new T2 lesions, 8 (10.8%) had gadolinium-enhancing lesions. Twenty-five (14%) reported adverse event.

Conclusion:

In this study, high-dose biotin did not seem to be associated with a clear improvement in disability.

The role of glial-neuronal metabolic cooperation in modulating progression of multiple sclerosis and neuropathic pain

While the etiology of multiple sclerosis (MS) remains unclear, research from the clinic and preclinical models identified the essential role of inflammation and demyelination in the pathogenesis of MS. Current treatments focused on anti-inflammatory processes are effective against acute episodes and relapsing-remitting MS, but patients still move on to develop secondary progressive MS. MS progression is associated with activation of microglia and astrocytes, and importantly, metabolic dysfunction leading to neuronal death. Neuronal death also contributes to chronic neuropathic pain. Metabolic support of neurons by glia may play central roles in preventing progression of MS and chronic neuropathic pain. Here, we review mechanisms of metabolic cooperation between glia and neurons and outline future perspectives exploring metabolic support of neurons by glia.

Recent advances in understanding multiple sclerosis

Emerging data point to important contributions of both autoimmune inflammation and progressive degeneration in the pathophysiology of multiple sclerosis (MS). Unfortunately, after decades of intensive investigation, the fundamental cause remains unknown. A large body of research on the immunobiology of MS has resulted in a variety of anti-inflammatory therapies that are highly effective at reducing brain inflammation and clinical/radiological relapses. However, despite potent suppression of inflammation, benefit in the more important and disabling progressive phase is extremely limited; thus, progressive MS has emerged as the greatest challenge for the MS research and clinical communities. Data obtained over the years point to a complex interplay between environment (e.g., the near-absolute requirement of Epstein-Barr virus exposure), immunogenetics (strong associations with a large number of immune genes), and an ever more convincing role of an underlying degenerative process resulting in demyelination (in both white and grey matter regions), axonal and neuro-synaptic injury, and a persistent innate inflammatory response with a seemingly diminishing role of T cell-mediated autoimmunity as the disease progresses. Together, these observations point toward a primary degenerative process, one whose cause remains unknown but one that entrains a nearly ubiquitous secondary autoimmune response, as a likely sequence of events underpinning this disease. Here, we briefly review what is known about the potential pathophysiological mechanisms, focus on progressive MS, and discuss the two main hypotheses of MS pathogenesis that are the topic of vigorous debate in the field: whether primary autoimmunity or degeneration lies at the foundation. Unravelling this controversy will be critically important for developing effective new therapies for the most disabling later phases of this disease.

Differences in topological progression profile among neurodegenerative diseases from imaging data

The spatial distribution of atrophy in neurodegenerative diseases suggests that brain connectivity mediates disease propagation. Different descriptors of the connectivity graph potentially relate to different underlying mechanisms of propagation. Previous approaches for evaluating the influence of connectivity on neurodegeneration consider each descriptor in isolation and match predictions against late-stage atrophy patterns. We introduce the notion of a topological profile - a characteristic combination of topological descriptors that best describes the propagation of pathology in a particular disease. By drawing on recent advances in disease progression modeling, we estimate topological profiles from the full course of pathology accumulation, at both cohort and individual levels. Experimental results comparing topological profiles for Alzheimer's disease, multiple sclerosis and normal ageing show that topological profiles explain the observed data better than single descriptors. Within each condition, most individual profiles cluster around the cohort-level profile, and individuals whose profiles align more closely with other cohort-level profiles show features of that cohort. The cohort-level profiles suggest new insights into the biological mechanisms underlying pathology propagation in each disease.

Detecting neurodegenerative pathology in multiple sclerosis before irreversible brain tissue loss sets in

Background

Multiple sclerosis (MS) is a complex chronic inflammatory and degenerative disorder of the central nervous system. Accelerated brain volume loss, or also termed atrophy, is currently emerging as a popular imaging marker of neurodegeneration in affected patients, but, unfortunately, can only be reliably interpreted at the time when irreversible tissue damage likely has already occurred. Timing of treatment decisions based on brain atrophy may therefore be viewed as suboptimal.

Main body

This Narrative Review focuses on alternative techniques with the potential of detecting neurodegenerative events in the brain of subjects with MS prior to the atrophic stage. First, metabolic and molecular imaging provide the opportunity to identify early subcellular changes associated with energy dysfunction, which is an assumed core mechanism of axonal degeneration in MS. Second, cerebral hypoperfusion has been observed throughout the entire clinical spectrum of the disorder but it remains an open question whether this serves as an alternative marker of reduced metabolic activity, or exists as an independent contributing process, mediated by endothelin-1 hyperexpression. Third, both metabolic and perfusion alterations may lead to repercussions at the level of network performance and structural connectivity, respectively assessable by functional and diffusion tensor imaging. Fourth and finally, elevated body fluid levels of neurofilaments are gaining interest as a biochemical mirror of axonal damage in a wide range of neurological conditions, with early rises in patients with MS appearing to be predictive of future brain atrophy.

Conclusions

Recent findings from the fields of advanced neuroradiology and neurochemistry provide the promising prospect of demonstrating degenerative brain pathology in patients with MS before atrophy has installed. Although the overall level of evidence on the presented topic is still preliminary, this Review may pave the way for further longitudinal and multimodal studies exploring the relationships between the abovementioned measures, possibly leading to novel insights in early disease mechanisms and therapeutic intervention strategies.

Oligodendrocyte dysfunction and regeneration failure: A novel hypothesis of delayed encephalopathy after carbon monoxide poisoning

Carbon monoxide (CO) poisoning usually causes brain lesions and delayed encephalopathy, also known as delayed neurological sequelae (DNS). Demyelination of white matter (WM) is one of the most common sites of abnormalities in patients with DNS, but its mechanisms remain unclear. Oligodendrocytes (OLs) are myelinated cells that ensure the rapid conduction of neuronal axon signals and provide the nutritional factors necessary for maintaining nerve integrity in the central nervous system (CNS). OLs readily regenerate and replace damaged myelin membranes around axons in the adult mammalian CNS following demyelination. The ability to regenerate OLs depends on the availability of precursor cells (OPCs) in the CNS of adults. Multiple injury-related signals can induce OPC expansion followed by OL differentiation, axonal contact and myelin regeneration (remyelination). Therefore, OL dysfunction and regeneration failure in the deep WM of the brain are the key pathophysiological mechanisms leading to delayed brain injury after CO poisoning. CO-induced toxicity may interfere with OL function and render OPCs unable to regenerate OLs through some unclear mechanisms, leading to progressive demyelinating damage and resulting in DNS. In the future, combination therapies to reduce OL damage and promote OPC differentiation and remyelination may be important for the prevention and treatmentof DNS after CO poisoning.

Roads to Formation of Normal Myelin Structure and Pathological Myelin Structure

Demyelination and axonal damage are responsible for neurological deficits in demyelinating diseases including multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system. However, the pathology of demyelination and axonal damage in MS is not fully understood. While immunologists have accumulated evidence, which is involved in many immunological events in these diseases, neuroscientists and anatomists have also investigated morphological changes of myelin in these diseases. In this chapter, a new concept of demyelination will be described.

The Na+/Ca2+ exchangers in demyelinating diseases

Intracellular [Na⁺]_i and [Ca²⁺]_i imbalance significantly contribute to neuro-axonal dysfunctions and maladaptive myelin repair or remyelination failure in chronic inflammatory demyelinating diseases such as multiple sclerosis. Progress in recent years has led to significant advances in understanding how [Ca²⁺]_i signaling network drive degeneration or remyelination of demyelinated axons. The Na⁺/Ca²⁺ exchangers (NCXs), a transmembrane protein family including three members encoded by ncx1, ncx2, and ncx3 genes, are emerging important regulators of [Na⁺]_i and [Ca²⁺]_i both in neurons and glial cells. Here we review recent advance highlighting the role of NCX exchangers in axons and myelin-forming cells, i.e. oligodendrocytes, which represent the major targets of the aberrant inflammatory attack in multiple sclerosis. The contribution of NCX subtypes to axonal pathology and myelin synthesis will be discussed. Although a definitive understanding of mechanisms regulating axonal pathology and remyelination failure in chronic demyelinating diseases is still lacking and requires further investigation, current knowledge suggest that NCX activity plays a crucial role in these processes. Defining the relative contributions of each NCX transporter in axon pathology and myelinating glia will constitute not only a major advance in understanding in detail the intricate mechanism of neurodegeneration and remyelination failure in demyelinating diseases but also will help to identify neuroprotective or remyelinating strategies targeting selective NCX exchangers as a means of treating MS.

Laquinimod Supports Remyelination in Non-Supportive Environments

Inflammatory demyelination, which is a characteristic of multiple sclerosis lesions, leads to acute functional deficits and, in the long term, to progressive axonal degeneration. While remyelination is believed to protect axons, the endogenous-regenerative processes are often incomplete or even completely fail in many multiple sclerosis patients. Although it is currently unknown why remyelination fails, recurrent demyelination of previously demyelinated white matter areas is one contributing factor. In this study, we investigated whether laquinimod, which has demonstrated protective effects in active multiple sclerosis patients, protects against recurrent demyelination. To address this, male mice were intoxicated with cuprizone for up to eight weeks and treated with either a vehicle solution or laquinimod at the beginning of week 5, where remyelination was ongoing. The brains were harvested and analyzed by immunohistochemistry. At the time-point of laquinimod treatment initiation, oligodendrocyte progenitor cells proliferated and maturated despite ongoing demyelination activity. In the following weeks, myelination recovered in the laquinimod- but not vehicle-treated mice, despite continued cuprizone intoxication. Myelin recovery was paralleled by less severe microgliosis and acute axonal injury. In this study, we were able to demonstrate that laquinimod, which has previously been shown to protect against cuprizone-induced oligodendrocyte degeneration, exerts protective effects during oligodendrocyte progenitor differentiation as well. By this mechanism, laquinimod allows remyelination in non-supportive environments. These results should encourage further clinical studies in progressive multiple sclerosis patients.

Myelin in the Central Nervous System: Structure, Function, and Pathology

Oligodendrocytes generate multiple layers of myelin membrane around axons of the central nervous system to enable fast and efficient nerve conduction. Until recently, saltatory nerve conduction was considered the only purpose of myelin, but it is now clear that myelin has more functions. In fact, myelinating oligodendrocytes are embedded in a vast network of interconnected glial and neuronal cells, and increasing evidence supports an active role of oligodendrocytes within this assembly, for example, by providing metabolic support to neurons, by regulating ion and water homeostasis, and by adapting to activity-dependent neuronal signals. The molecular complexity governing these interactions requires an in-depth molecular understanding of how oligodendrocytes and axons interact and how they generate, maintain, and remodel their myelin sheaths. This review deals with the biology of myelin, the expanded relationship of myelin with its underlying axons and the neighboring cells, and its disturbances in various diseases such as multiple sclerosis, acute disseminated encephalomyelitis, and neuromyelitis optica spectrum disorders. Furthermore, we will highlight how specific interactions between astrocytes, oligodendrocytes, and microglia contribute to demyelination in hereditary white matter pathologies.

Neuroimmunological characterization of a mouse model of primary progressive experimental autoimmune encephalomyelitis and effects of immunosuppressive or neuroprotective strategies on disease evolution

Progressive multiple sclerosis (PMS) is a devastating disorder sustained by neuroimmune interactions still wait to be identified. Recently, immune-independent, neural bioenergetic derangements have been hypothesized as causative of neurodegeneration in PMS patients. To gather information on the immune and neurodegenerative components during PMS, in the present study we investigated the molecular and cellular events occurring in a Non-obese diabetic (NOD) mouse model of experimental autoimmune encephalomyelitis (EAE). In these mice, we also evaluated the effects of clinically-relevant immunosuppressive (dexamethasone) or bioenergetic drugs (bezafibrate and biotin) on functional, immune and neuropathological parameters. We found that immunized NOD mice progressively accumulated disability and severe neurodegeneration in the spinal cord. Unexpectedly, although CD4 and CD8 lymphocytes but not B or NK cells infiltrate the spinal cord linearly with time, their suppression by different dexamethasone treatment schedules did not affect disease progression. Also, the spreading of the autoimmune response towards additional immunogenic myelin antigen occurred neither in the periphery nor in the CNS of EAE mice. Conversely, we found that altered mitochondrial morphology, reduced contents of mtDNA and decreased transcript levels for respiratory complex subunits occurred at early disease stages and preceded axonal degeneration within spinal cord columns. However, the mitochondria boosting drugs, bezafibrate and biotin, were unable to reduce disability progression. Data suggest that EAE NOD mice recapitulate some features of PMS. Also, by showing that bezafibrate or biotin do not affect progression in NOD mice, our study suggests that this model can be harnessed to anticipate experimental information of relevance to innovative treatments of PMS.

Experimental autoimmune encephalomyelitis accelerates remyelination after lysophosphatidylcholine-induced demyelination in the corpus callosum

Experimental autoimmune encephalomyelitis (EAE) and lysophosphatidylcholine (LPC)-induced demyelination were combined to study remyelination in a pro-inflammatory context. Two groups of female C57BL/6 mice were subjected either to EAE (EAE mice) or injected with just complete Freund's adjuvant (CFA) and pertussis toxin (PTX) followed by bilateral LPC and phosphate buffered saline injections in the corpus callosum on day 7 (CFA controls). Relative to CFA controls, EAE accelerated remyelination and increased innate immune cell activation, lymphocyte infiltration and cytokine gene expression in the LPC lesions. However, compared to CFA mice, remyelination was reduced (day 14) suggesting this aggressive immune response also compromised myelin repair in EAE mice.

Myelin Disturbances Produced by Sub-Toxic Concentration of Heavy Metals: The Role of Oligodendrocyte Dysfunction

Evidence has been accumulated demonstrating that heavy metals may accumulate in various organs, leading to tissue damage and toxic effects in mammals. In particular, the Central Nervous System (CNS) seems to be particularly vulnerable to cumulative concentrations of heavy metals, though the pathophysiological mechanisms is still to be clarified. In particular, the potential role of oligodendrocyte dysfunction and myelin production after exposure to subtoxic concentration I confirmed. It is ok of heavy metals is to be better assessed. Here we investigated on the effect of sub-toxic concentration of several essential (Cu^{2 +}, Cr^{3 +}, Ni^{2 +}, Co²⁺) and non-essential (Pb^{2 +}, Cd²⁺, Al³⁺) heavy metals on human oligodendrocyte MO3.13 and human neuronal SHSY5Y cell lines (grown individually or in co-culture). MO3.13 cells are an immortal human–human hybrid cell line with the phenotypic characteristics of primary oligodendrocytes but following the differentiation assume the morphological and biochemical features of mature oligodendrocytes. For this reason, we decided to use differentiated MO3.13 cell line. In particular, exposure of both cell lines to heavy metals produced a reduced cell viability of co-cultured cell lines compared to cells grown separately. This effect was more pronounced in neurons that were more sensitive to metals than oligodendrocytes when the cells were grown in co-culture. On the other hand, a significant reduction of lipid component in cells occurred after their exposure to heavy metals, an effect accompanied by substantial reduction of the main protein that makes up myelin (MBP) in co-cultured cells. Finally, the effect of heavy metals in oligodendrocytes were associated to imbalanced intracellular calcium ion concentration as measured through the fluorescent Rhod-2 probe, thus confirming that heavy metals, even used at subtoxic concentrations, lead to dysfunctional oligodendrocytes. In conclusion, our data show, for the first time, that sub-toxic concentrations of several heavy metals lead to dysfunctional oligodendrocytes, an effect highlighted when these cells are co-cultured with neurons. The pathophysiological mechanism(s) underlying this effect is to be better clarified. However, imbalanced intracellular calcium ion regulation, altered lipid formation and, finally, imbalanced myelin formation seem to play a major role in early stages of heavy metal-related oligodendrocyte dysfunction.

Gray matter microglial activation in relapsing vs progressive MS: A [F-18]PBR06-PET study

Objective

To determine the value of [F-18]PBR06-PET for assessment of microglial activation in the cerebral gray matter in patients with MS.

Methods

Twelve patients with MS (7 relapsing-remitting and 5 secondary progressive [SP]) and 5 healthy controls (HCs) had standardized uptake value (SUV) PET maps coregistered to 3T MRI and segmented into cortical and subcortical gray matter regions. SUV ratios (SUVRs) were global brain normalized. Voxel-by-voxel analysis was performed using statistical parametric mapping (SPM). Normalized brain parenchymal volumes (BPVs) were determined from MRI using SIENAX.

Results

Cortical SUVRs were higher in the hippocampus, amygdala, midcingulate, posterior cingulate, and rolandic operculum and lower in the medial-superior frontal gyrus and cuneus in the MS vs HC group (all p < 0.05). Subcortical gray matter SUVR was higher in SPMS vs RRMS (+10.8%, p = 0.002) and HC (+11.3%, p = 0.055) groups. In the MS group, subcortical gray matter SUVR correlated with the Expanded Disability Status Scale (EDSS) score (r = 0.75, p = 0.005) and timed 25-foot walk (T25FW) (r = 0.70, p = 0.01). Thalamic SUVRs increased with increasing EDSS scores (r = 0.83, p = 0.0008) and T25FW (r = 0.65, p = 0.02) and with decreasing BPV (r = -0.63, p = 0.03). Putaminal SUVRs increased with increasing EDSS scores (0.71, p = 0.009) and with decreasing BPV (r = -0.67, p = 0.01). On SPM analysis, peak correlations of thalamic voxels with BPV were seen in the pulvinar and with the EDSS score and T25FW in the dorsomedial thalamic nuclei.

Conclusions

This study suggests that [F-18]PBR06-PET detects widespread abnormal microglial activation in the cerebral gray matter in MS. Increased translocator protein binding in subcortical gray matter regions is associated with brain atrophy and may link to progressive MS.

[Progress and prospects of metabolic therapy in multiple sclerosis]

Side-effects and incomplete response to standard therapy of patients with multiple sclerosis (MS) stimulate the development of an alternative therapy, that influences, in particular, metabolic functions of MS patients. Metabolic therapy (vitamins, antioxidants and others) have been used for a long time in neurologic practice for the treatment of MS on the basis of pathophysiological mechanisms, positive clinical experience, low rate of side-effects and practical availability. Recent objective scientific data explain the necessity of correction of the disturbed metabolic profile (metabolome) in MS, and the first evidence of the efficacy of several metabolic agents, particularly, biotin and vitamin D, was shown. Taking into account the mechanisms of action and clinical experience, the authors consider the prospects of using the combined medicine cytoflavin, that contains succinate, nicotinamide, riboflavin and inosine, in metabolic therapy of MS.

The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury

Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.

Diagnosis and Management of Progressive Multiple Sclerosis

Multiple sclerosis is a chronic autoimmune disease of the central nervous system that results in varying degrees of disability. Progressive multiple sclerosis, characterized by a steady increase in neurological disability independently of relapses, can occur from onset (primary progressive) or after a relapsing-remitting course (secondary progressive). As opposed to active inflammation seen in the relapsing-remitting phases of the disease, the gradual worsening of disability in progressive multiple sclerosis results from complex immune mechanisms and neurodegeneration. A few anti-inflammatory disease-modifying therapies with a modest but significant effect on measures of disease progression have been approved for the treatment of progressive multiple sclerosis. The treatment effect of anti-inflammatory agents is particularly observed in the subgroup of patients with younger age and evidence of disease activity. For this reason, a significant effort is underway to develop molecules with the potential to induce myelin repair or halt the degenerative process. Appropriate trial methodology and the development of clinically meaningful disability outcome measures along with imaging and biological biomarkers of progression have a significant impact on the ability to measure the efficacy of potential medications that may reverse disease progression. In this issue, we will review current evidence on the physiopathology, diagnosis, measurement of disability, and treatment of progressive multiple sclerosis.

New Ways of "Seeing" the Mechanistic Heterogeneity of Multiple Sclerosis Plaque Pathogenesis

BACKGROUND

Over the past few decades, we have witnessed a transformation with respect to the principles and pathobiological underpinnings of multiple sclerosis (MS). From the traditional rubric of MS as an inflammatory and demyelinating disorder restricted to central nervous system (CNS) white matter, our contemporary view has evolved to encompass a broader understanding of the variable mechanisms that contribute to tissue injury, in a disorder now recognized to affect white and grey matter compartments.

EVIDENCE ACQUISITION

A constellation of inflammation, ion channel derangements, bioenergetic supply: demand mismatches within the intra-axonal compartment, and alterations in the dynamics and oximetry of blood flow in CNS tissue compartments are observed in MS. These findings have raised questions regarding how histopathologic heterogeneity may influence the diverse clinical spectrum of MS; and, accordingly, how individual treatment needs vary from 1 patient to the next.

RESULTS

We are now on new scaffolding in MS; one that promises to translate key clinical and laboratory observations to the application of emerging patient-centered therapies.

CONCLUSIONS

This review highlights our current knowledge of the underlying disease mechanisms in MS, explores the inflammatory and neurodegenerative consequences of tissue damage, and examines physiologic factors that contribute to bioenergetic homeostasis within the CNS of affected patients.

Progression of regional grey matter atrophy in multiple sclerosis

See Stankoff and Louapre (doi:10.1093/brain/awy114) for a scientific commentary on this article.

Grey matter atrophy is present from the earliest stages of multiple sclerosis, but its temporal ordering is poorly understood. We aimed to determine the sequence in which grey matter regions become atrophic in multiple sclerosis and its association with disability accumulation. In this longitudinal study, we included 1417 subjects: 253 with clinically isolated syndrome, 708 with relapsing-remitting multiple sclerosis, 128 with secondary-progressive multiple sclerosis, 125 with primary-progressive multiple sclerosis, and 203 healthy control subjects from seven European centres. Subjects underwent repeated MRI (total number of scans 3604); the mean follow-up for patients was 2.41 years (standard deviation = 1.97). Disability was scored using the Expanded Disability Status Scale. We calculated the volume of brain grey matter regions and brainstem using an unbiased within-subject template and used an established data-driven event-based model to determine the sequence of occurrence of atrophy and its uncertainty. We assigned each subject to a specific event-based model stage, based on the number of their atrophic regions. Linear mixed-effects models were used to explore associations between the rate of increase in event-based model stages, and T₂ lesion load, disease-modifying treatments, comorbidity, disease duration and disability accumulation. The first regions to become atrophic in patients with clinically isolated syndrome and relapse-onset multiple sclerosis were the posterior cingulate cortex and precuneus, followed by the middle cingulate cortex, brainstem and thalamus. A similar sequence of atrophy was detected in primary-progressive multiple sclerosis with the involvement of the thalamus, cuneus, precuneus, and pallidum, followed by the brainstem and posterior cingulate cortex. The cerebellum, caudate and putamen showed early atrophy in relapse-onset multiple sclerosis and late atrophy in primary-progressive multiple sclerosis. Patients with secondary-progressive multiple sclerosis showed the highest event-based model stage (the highest number of atrophic regions, P < 0.001) at the study entry. All multiple sclerosis phenotypes, but clinically isolated syndrome, showed a faster rate of increase in the event-based model stage than healthy controls. T₂ lesion load and disease duration in all patients were associated with increased event-based model stage, but no effects of disease-modifying treatments and comorbidity on event-based model stage were observed. The annualized rate of event-based model stage was associated with the disability accumulation in relapsing-remitting multiple sclerosis, independent of disease duration (P < 0.0001). The data-driven staging of atrophy progression in a large multiple sclerosis sample demonstrates that grey matter atrophy spreads to involve more regions over time. The sequence in which regions become atrophic is reasonably consistent across multiple sclerosis phenotypes. The spread of atrophy was associated with disease duration and with disability accumulation over time in relapsing-remitting multiple sclerosis.

Learning from other autoimmunities to understand targeting of B cells to control multiple sclerosis

Although many suspected autoimmune diseases are thought to be T cell-mediated, the response to therapy indicates that depletion of B cells consistently inhibits disease activity. In multiple sclerosis, it appears that disease suppression is associated with the long-term reduction of memory B cells, which serves as a biomarker for disease activity in many other CD20+ B cell depletion-sensitive, autoimmune diseases. Following B cell depletion, the rapid repopulation by transitional (immature) and naïve (mature) B cells from the bone marrow masks the marked depletion and slow repopulation of lymphoid tissue-derived, memory B cells. This can provide long-term protection from a short treatment cycle. It seems that memory B cells, possibly via T cell stimulation, drive relapsing disease. However, their sequestration in ectopic follicles and the chronic activity of B cells and plasma cells in the central nervous system may drive progressive neurodegeneration directly via antigen-specific mechanisms or indirectly via glial-dependent mechanisms. While unproven, Epstein-Barr virus may be an aetiological trigger of multiple sclerosis. This infects mature B cells, drives the production of memory B cells and possibly provides co-stimulatory signals promoting T cell-independent activation that breaks immune tolerance to generate autoreactivity. Thus, a memory B cell centric mechanism can integrate: potential aetiology, genetics, pathology and response to therapy in multiple sclerosis and other autoimmune conditions with ectopic B cell activation that are responsive to memory B cell-depleting strategies.

Structural adaption of axons during de- and remyelination in the Cuprizone mouse model

Multiple Sclerosis is an autoimmune disorder causing neurodegeneration mostly in young adults. Thereby, myelin is lost in the inflammatory lesions leaving unmyelinated axons at a high risk to degenerate. Oligodendrocyte precursor cells maintain their regenerative capacity into adulthood and are able to remyelinate axons if they are properly activated and differentiate. Neuronal activity influences the success of myelination indicating a close interplay between neurons and oligodendroglia. The myelination profile determines the distribution of voltage-gated ion channels along the axon. Here, we analyze the distribution of the sodium channel subunit Nav1.6 and the ultrastructure of axons after cuprizone-induced demyelination in transgenic mice expressing GFP in oligodendroglial cells. Using this mouse model, we found an increased number of GFP-expressing oligodendroglial cells compared to untreated mice. Analyzing the axons, we found an increase in the number of nodes of Ranvier in mice that had received cuprizone. Furthermore, we found an enhanced portion of unmyelinated axons showing vesicles in the cytoplasm. These vesicles were labeled with VGlut1, indicating that they are involved in axonal signaling. Our results highlight the flexibility of axons towards changes in the glial compartment and depict the structural changes they undergo upon myelin removal. These findings might be considered if searching for new neuroprotective therapies that aim at blocking neuronal activity in order to avoid interfering with the process of remyelination.

1 H-31 P magnetic resonance spectroscopy: effect of biotin in multiple sclerosis

Biotin is thought to improve functional impairment in progressive multiple sclerosis (MS) by upregulating bioenergetic metabolism. We enrolled 19 patients suffering from progressive MS (5 primary and 14 secondary Progressive-MS). Using cerebral multinuclear magnetic resonance spectroscopy (MMRS) and clinical evaluation before and after 6 months of biotin cure, we showed significant modifications of: PME/PDE, ATP, and lactate resonances; an improvement of EDSS Neuroscore. Our results are consistent with metabolic pathways concerned with biotin action and could suggest the usefulness of MMRS for monitoring.

Retinal Tissue Perfusion in Patients with Multiple Sclerosis

Purpose: The goal of this work was to determine whether the retinal tissue perfusion (RTP) is impaired in patients with multiple sclerosis (MS). Methods: Seventy-four patients [66 relapsing-remitting MS (RRMS) and 8 clinically isolated syndrome (CIS)] and 74 age- and gender-matched healthy controls were recruited. RTP was calculated as the retinal blood flow (measured using retinal function imager) supplying the macular area divided by the corresponding tissue volume of the inner retina from the inner limiting membrane to the outer plexiform layer, as measured by ultrahigh-resolution optical coherence tomography. Results: The RTP in the MS group was 2.37 ± 0.59 nl/s/mm³ (mean ± standard deviation), which was significantly lower than the control group (4.06 ± 0.89 nl/s/mm³, P < .001), reflecting a decrease of 42%. The blood flow volume was 2.50 ± 0.50 nl/s in MS, which was 45% lower than in the control group (4.56 ± 0.91 nl/s, P < .001). In addition, the tissue volume of the inner retina was significantly lower than in the control group (P < .05). The RTP in patients with MS was significantly correlated with the retinal blood flow volume (r = 0.84, P < .001) and retinal tissue volume (r = -0.56, P < .001). However, the retinal blood flow in patients with MS was not related to the tissue volume (r = -0.06, P = .59). Conclusions: Impaired retinal tissue perfusion occurred in patients with MS, which could be developed as a possible biomarker in monitoring disease progression in MS.

Mitochondrial Dysfunction and Multiple Sclerosis

In recent years, several studies have examined the potential associations between mitochondrial dysfunction and neurodegenerative diseases such as multiple sclerosis (MS), Parkinson’s disease and Alzheimer’s disease. In MS, neurological disability results from inflammation, demyelination, and ultimately, axonal damage within the central nervous system. The sustained inflammatory phase of the disease leads to ion channel changes and chronic oxidative stress. Several independent investigations have demonstrated mitochondrial respiratory chain deficiency in MS, as well as abnormalities in mitochondrial transport. These processes create an energy imbalance and contribute to a parallel process of progressive neurodegeneration and irreversible disability. The potential roles of mitochondria in neurodegeneration are reviewed. An overview of mitochondrial diseases that may overlap with MS are also discussed, as well as possible therapeutic targets for the treatment of MS and other neurodegenerative conditions.

Unique RNA signature of different lesion types in the brain white matter in progressive multiple sclerosis

The heterogeneity of multiple sclerosis is reflected by dynamic changes of different lesion types in the brain white matter (WM). To identify potential drivers of this process, we RNA-sequenced 73 WM areas from patients with progressive MS (PMS) and 25 control WM. Lesion endophenotypes were described by a computational systems medicine analysis combined with RNAscope, immunohistochemistry, and immunofluorescence. The signature of the normal-appearing WM (NAWM) was more similar to control WM than to lesions: one of the six upregulated genes in NAWM was CD26/DPP4 expressed by microglia. Chronic active lesions that become prominent in PMS had a signature that were different from all other lesion types, and were differentiated from them by two clusters of 62 differentially expressed genes (DEGs). An upcoming MS biomarker, CHI3L1 was among the top ten upregulated genes in chronic active lesions expressed by astrocytes in the rim. TGFβ-R2 was the central hub in a remyelination-related protein interaction network, and was expressed there by astrocytes. We used de novo networks enriched by unique DEGs to determine lesion-specific pathway regulation, i.e. cellular trafficking and activation in active lesions; healing and immune responses in remyelinating lesions characterized by the most heterogeneous immunoglobulin gene expression; coagulation and ion balance in inactive lesions; and metabolic changes in chronic active lesions. Because we found inverse differential regulation of particular genes among different lesion types, our data emphasize that omics related to MS lesions should be interpreted in the context of lesion pathology. Our data indicate that the impact of molecular pathways is substantially changing as different lesions develop. This was also reflected by the high number of unique DEGs that were more common than shared signatures. A special microglia subset characterized by CD26 may play a role in early lesion development, while astrocyte-derived TGFβ-R2 and TGFβ pathways may be drivers of repair in contrast to chronic tissue damage. The highly specific mechanistic signature of chronic active lesions indicates that as these lesions develop in PMS, the molecular changes are substantially skewed: the unique mitochondrial/metabolic changes and specific downregulation of molecules involved in tissue repair may reflect a stage of exhaustion.

Preserved canonicality of the BOLD hemodynamic response reflects healthy cognition: Insights into the healthy brain through the window of Multiple Sclerosis

The hemodynamic response function (HRF), a model of brain blood-flow changes in response to neural activity, reflects communication between neurons and the vasculature that supplies these neurons in part by means of glial cell intermediaries (e.g., astrocytes). Intact neural-vascular communication might play a central role in optimal cognitive performance. This hypothesis can be tested by comparing healthy individuals to those with known white-matter damage and impaired performance, as seen in Multiple Sclerosis (MS). Glial cell intermediaries facilitate the ability of neurons to adequately convey metabolic needs to cerebral vasculature for sufficient oxygen and nutrient perfusion. In this study, we isolated measurements of the HRF that could quantify the extent to which white-matter affects neural-vascular coupling and cognitive performance. HRFs were modeled from multiple brain regions during multiple cognitive tasks using piecewise cubic spline functions, an approach that minimized assumptions regarding HRF shape that may not be valid for diseased populations, and were characterized using two shape metrics (peak amplitude and time-to-peak). Peak amplitude was reduced, and time-to-peak was longer, in MS patients relative to healthy controls. Faster time-to-peak was predicted by faster reaction time, suggesting an important role for vasodilatory speed in the physiology underlying processing speed. These results support the hypothesis that intact neural-glial-vascular communication underlies optimal neural and cognitive functioning.

Comparing MRI metrics to quantify white matter microstructural damage in multiple sclerosis

Quantifying white matter damage in vivo is becoming increasingly important for investigating the effects of neuroprotective and repair strategies in multiple sclerosis (MS). While various approaches are available, the relationship between MRI‐based metrics of white matter microstructure in the disease, that is, to what extent the metrics provide complementary versus redundant information, remains largely unexplored. We obtained four microstructural metrics from 123 MS patients: fractional anisotropy (FA), radial diffusivity (RD), myelin water fraction (MWF), and magnetisation transfer ratio (MTR). Coregistration of maps of these four indices allowed quantification of microstructural damage through voxel‐wise damage scores relative to healthy tissue, as assessed in a group of 27 controls. We considered three white matter tissue‐states, which were expected to vary in microstructural damage: normal appearing white matter (NAWM), T2‐weighted hyperintense lesional tissue without T1‐weighted hypointensity (T2L), and T1‐weighted hypointense lesional tissue with corresponding T2‐weighted hyperintensity (T1L). All MRI indices suggested significant damage in all three tissue‐states, the greatest damage being in T1L. The correlations between indices ranged from r = 0.18 to r = 0.87. MWF was most sensitive when differentiating T2L from NAWM, while MTR was most sensitive when differentiating T1L from NAWM and from T2L. Combining the four metrics into one, through a principal component analysis, did not yield a measure more sensitive to damage than any single measure. Our findings suggest that the metrics are (at least partially) correlated with each other, but sensitive to the different aspects of pathology. Leveraging these differences could be beneficial in clinical trials testing the effects of therapeutic interventions.