Virtual hypoxia and chronic necrosis of demyelinated axons in multiple sclerosis

Persistent sodium currents in neurons: potential mechanisms and pharmacological blockers

Persistent sodium current (INaP) is an important activity-dependent regulator of neuronal excitability. It is involved in a variety of physiological and pathological processes, including pacemaking, prolongation of sensory potentials, neuronal injury, chronic pain and diseases such as epilepsy and amyotrophic lateral sclerosis. Despite its importance, neither the molecular basis nor the regulation of INaP are sufficiently understood. Of particular significance is a solid knowledge and widely accepted consensus about pharmacological tools for analysing the function of INaP and for developing new therapeutic strategies. However, the literature on INaP is heterogeneous, with varying definitions and methodologies used across studies. To address these issues, we provide a systematic review of the current state of knowledge on INaP, with focus on mechanisms and effects of this current in the central nervous system. We provide an overview of the specificity and efficacy of the most widely used INaP blockers: amiodarone, cannabidiol, carbamazepine, cenobamate, eslicarbazepine, ethosuximide, gabapentin, GS967, lacosamide, lamotrigine, lidocaine, NBI-921352, oxcarbazepine, phenytoine, PRAX-562, propofol, ranolazine, riluzole, rufinamide, topiramate, valproaic acid and zonisamide. We conclude that there is strong variance in the pharmacological effects of these drugs, and in the available information. At present, GS967 and riluzole can be regarded bona fide INaP blockers, while phenytoin and lacosamide are blockers that only act on the slowly inactivating component of sodium currents.

Determinants and Biomarkers of Progression Independent of Relapses in Multiple Sclerosis

Clinical, pathological, and imaging evidence in multiple sclerosis (MS) suggests that a smoldering inflammatory activity is present from the earliest stages of the disease and underlies the progression of disability, which proceeds relentlessly and independently of clinical and radiological relapses (PIRA). The complex system of pathological events driving "chronic" worsening is likely linked with the early accumulation of compartmentalized inflammation within the central nervous system as well as insufficient repair phenomena and mitochondrial failure. These mechanisms are partially lesion-independent and differ from those causing clinical relapses and the formation of new focal demyelinating lesions; they lead to neuroaxonal dysfunction and death, myelin loss, glia alterations, and finally, a neuronal network dysfunction outweighing central nervous system (CNS) compensatory mechanisms. This review aims to provide an overview of the state of the art of neuropathological, immunological, and imaging knowledge about the mechanisms underlying the smoldering disease activity, focusing on possible early biomarkers and their translation into clinical practice. ANN NEUROL 2024;96:1-20.

Exploring the Therapeutic Potential: Bioactive Molecules and Dietary Interventions in Multiple Sclerosis Management

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system, the etiology of which is still unclear. Its hallmarks are inflammation and axonal damage. As a disease primarily impacting younger individuals, the social cost of MS is high. It has been proposed that environmental factors, smoking, and dietary habits acting on a genetic susceptibility play a role in MS. Recent studies indicate that diet can significantly influence the onset and progression of MS. This review delves into the impact of natural bioactive molecules on MS development and explores the dietary interventions that hold promise in managing the disease. Dietary patterns, including ketogenic and Mediterranean diets, are discussed. Theories about the potential mechanistic associations beneath the noted effects are also proposed. Several dietary components and patterns demonstrated the potential for a significant impact on MS. However, extensive prospective clinical trials are necessary to fully understand the role of natural bioactive molecules as disease modifiers in MS.

Age-related decline in cerebral oxygen consumption in multiple sclerosis

Cerebral oxygen metabolism is altered in relapsing-remitting multiple sclerosis (RRMS), possibly a result of disease related cerebral atrophy with subsequent decreased oxygen demand. However, MS inflammation can also inhibit brain metabolism. Therefore, we measured cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) using MRI phase contrast mapping and susceptibility-based oximetry in 44 patients with early RRMS and 36 healthy controls. Cerebral atrophy and white matter lesion load were assessed from high-resolution structural MRI. Expanded Disability Status Scale (EDSS) scores were collected from medical records. The CMRO2 was significantly lower in patients (-15%, p = 0.002) and decreased significantly with age in patients relative to the controls (-1.35 µmol/100 g/min/year, p = 0.036). The lower CMRO2 in RRMS was primarily driven by a higher venous oxygen saturation in the sagittal sinus (p = 0.007) and not a reduction in CBF (p = 0.69). There was no difference in cerebral atrophy between the groups, and no correlation between CMRO2 and MS lesion volume or EDSS score. Therefore, the progressive CMRO2 decline observed before the occurrence of significant cerebral atrophy and despite adequate CBF supports emerging evidence of dysfunctional cellular respiration as a potential pathogenic mechanism and therapeutic target in RRMS.

Assessment of Outer Retina and Choroid Using Swept Source Optical Coherence Tomography and Angiography in Patients With Multiple Sclerosis

BACKGROUND

For patients with multiple sclerosis (MS), both structure and microvasculature alterations in the inner retina have been investigated in several studies. However, little is known about the alterations in the outer retina and choroid. Hence, this study aimed to assess the outer retinal and choroidal changes in patients with MS with no history of optic neuritis (ON).

METHODS

Patients with MS and healthy control participants were enrolled in this cross-sectional study. Quantitative analyses were performed using swept source optical coherence tomography and swept source optical coherence tomography angiography images to assess outer retina thickness (ORT) and choroid thickness (CT), vessel density (VD) of choriocapillaris, and choroidal vascularity index (CVI), which were then compared between the groups.

RESULTS

A total of 37 participants with MS (72 eyes) and 74 healthy control participants (148 eyes) were included in this study. Compared with healthy controls, patients with MS with no history of ON showed reduced VD of the choriocapillaris and CVI. There was no significant difference in ORT and CT between 2 groups. Meanwhile, in patients with MS, no correlation between OCTA parameters and expanded disability status scale score were found in this study.

CONCLUSIONS

Our study indicates that patients with MS with no history of optical neuritis have reduced choriocapillaris vessel density and decreased choroidal vascularity index without detectable alteration in outer retina thickness and choroid thickness. The findings complement the outer retinal and choroidal component of MS, providing deeper insight into the pathophysiology of MS.

Reduced oxygen extraction fraction in deep cerebral veins associated with cognitive impairment in multiple sclerosis

Studying the relationship between cerebral oxygen utilization and cognitive impairment is essential to understanding neuronal functional changes in the disease progression of multiple sclerosis (MS). This study explores the potential of using venous susceptibility in internal cerebral veins (ICVs) as an imaging biomarker for cognitive impairment in relapsing-remitting MS (RRMS) patients. Quantitative susceptibility mapping derived from fully flow-compensated MRI phase data was employed to directly measure venous blood oxygen saturation levels (SvO2) in the ICVs. Results revealed a significant reduction in the susceptibility of ICVs (212.4 ± 30.8 ppb vs 239.4 ± 25.9 ppb) and a significant increase of SvO2 (74.5 ± 1.89% vs 72.4 ± 2.23%) in patients with RRMS compared with age- and sex-matched healthy controls. Both the susceptibility of ICVs (r = 0.508, p = 0.031) and the SvO2 (r = -0.498, p = 0.036) exhibited a moderate correlation with cognitive decline in these patients assessed by the Paced Auditory Serial Addition Test, while no significant correlation was observed with clinical disability measured by the Expanded Disability Status Scale. The findings suggest that venous susceptibility in ICVs has the potential to serve as a specific indicator of oxygen metabolism and cognitive function in RRMS. .

Oxidative stress involvement in the molecular pathogenesis and progression of multiple sclerosis: a literature review

Multiple sclerosis (MS) is an autoimmune debilitating disease of the central nervous system caused by a mosaic of interactions between genetic predisposition and environmental factors. The pathological hallmarks of MS are chronic inflammation, demyelination, and neurodegeneration. Oxidative stress, a state of imbalance between the production of reactive species and antioxidant defense mechanisms, is considered one of the key contributors in the pathophysiology of MS. This review is a comprehensive overview of the cellular and molecular mechanisms by which oxidant species contribute to the initiation and progression of MS including mitochondrial dysfunction, disruption of various signaling pathways, and autoimmune response activation. The detrimental effects of oxidative stress on neurons, oligodendrocytes, and astrocytes, as well as the role of oxidants in promoting and perpetuating inflammation, demyelination, and axonal damage, are discussed. Finally, this review also points out the therapeutic potential of various synthetic antioxidants that must be evaluated in clinical trials in patients with MS.

CSF1R-mediated myeloid cell depletion shifts the ratio of motor cortical excitatory to inhibitory neurons in a multiple system atrophy model

Motor cortical circuit functions depend on the coordinated fine-tuning of two functionally diverse neuronal populations: glutamatergic pyramidal neurons providing synaptic excitation and GABAergic interneurons adjusting the response of pyramidal neurons through synaptic inhibition. Microglia are brain resident macrophages which dynamically refine cortical circuits by monitoring perineuronal extracellular matrix and remodelling synapses. Previously, we showed that colony-stimulating factor 1 receptor (CSF1R)-mediated myeloid cell depletion extended the lifespan, but impaired motor functions of MBP29 mice, a mouse model for multiple system atrophy. In order to better understand the mechanisms underlying these motor deficits we characterized the microglial involvement in the cortical balance of GABAergic interneurons and glutamatergic pyramidal neurons in 4-months-old MBP29 mice following CSF1R inhibition for 12 weeks. Lack of myeloid cells resulted in a decreased number of COUP TF1 interacting protein 2-positive (CTIP2+) layer V pyramidal neurons, however in a proportional increase of calretinin-positive GABAergic interneurons in MBP29 mice. While myeloid cell depletion did not alter the expression of important presynaptic and postsynaptic proteins, the loss of cortical perineuronal net area was attenuated by CSF1R inhibition in MBP29 mice. These cortical changes may restrict synaptic plasticity and potentially modify parvalbumin-positive perisomatic input. Collectively, this study suggests, that the lack of myeloid cells shifts the neuronal balance toward an increased inhibitory connectivity in the motor cortex of MBP29 mice thereby potentially deteriorating motor functions.

The Time Trajectory of Choroid Plexus Enlargement in Multiple Sclerosis

Choroid plexus (CP) can be seen as a watchtower of the central nervous system (CNS) that actively regulates CNS homeostasis. A growing body of literature suggests that CP alterations are involved in the pathogenesis of multiple sclerosis (MS) but the underlying mechanisms remain elusive. CPs are enlarged and inflamed in relapsing-remitting (RRMS) but also in clinically isolated syndrome (CIS) and radiologically isolated syndrome (RIS) stages, far beyond MS diagnosis. Increases in the choroid plexus/total intracranial volume (CP/TIV) ratio have been robustly associated with increased lesion load, higher translocator protein (TSPO) uptake in normal-appearing white matter (NAWM) and thalami, as well as with higher annual relapse rate and disability progression in highly active RRMS individuals, but not in progressive MS. The CP/TIV ratio has only slightly been correlated with magnetic resonance imaging (MRI) findings (cortical or whole brain atrophy) and clinical outcomes (EDSS score) in progressive MS. Therefore, we suggest that plexus volumetric assessments should be mainly applied to the early disease stages of MS, whereas it should be taken into consideration with caution in progressive MS. In this review, we attempt to clarify the pathological significance of the temporal CP volume (CPV) changes in MS and highlight the pitfalls and limitations of CP volumetric analysis.

The changes of oxygen extraction fraction in different types of lesions in relapsing-remitting multiple sclerosis: A cross-sectional and longitudinal study

OBJECTIVES

To explore the oxygen metabolism level of different types of lesions in relapsing-remitting multiple sclerosis (RRMS) patients by oxygen extraction fraction (OEF) both cross-sectionally and longitudinally.

METHODS

Forty-six RRMS patients and forty-one healthy controls (HC) went MRI examination. The quantitative susceptibility mapping (QSM) and OEF map were reconstructed from a 3D multi-echo gradient echo sequence. MS lesions in white matter were classified as contrast-enhancing lesions (CELs) on post-gadolinium T1-weighted sequence, paramagnetic rim lesions (PRLs), hyperintense lesions and non-hyperintense lesions on QSM, respectively. The susceptibility and OEF of different types of lesions were compared. The susceptibility and OEF values were measured and compared among different types of lesions. Among these RRMS patients, seventeen had follow-up MRI and 232 lesions, and baseline to follow-up longitudinal changes in susceptibility and OEF were measured.

RESULTS

PRLs had higher susceptibility and lower OEF than CELs, hyperintense lesions, and non-hyperintense lesions. The hyperintense lesions had higher susceptibility and lower OEF than non-hyperintense lesions. In longitudinal changes, PRLs had susceptibility increased (P < 0.001) and OEF decreased (P < 0.001). The hyperintense lesions showed significant decreases in susceptibility (P = 0.020), and non-hyperintense lesions showed significant increases in OEF during follow-up (P = 0.005). Notably, hyperintense lesions may convert to PRLs or non-hyperintense lesions as time progresses, accompanied by changes of OEF and susceptibility in the lesions.

CONCLUSION

This study revealed tissue damage and oxygen metabolism level in different types of MS lesions. The OEF may contribute to further understanding the evolution of MS lesions.

The mitochondriogenic but not the immunosuppressant effects of mTOR inhibitors prompt neuroprotection and delay disease evolution in a mouse model of progressive multiple sclerosis

INTRODUCTION

Purportedly, the progression of multiple sclerosis (MS) occurs when neurodegenerative processes due to derangement of axonal bioenergetics take over the autoimmune response. However, a clear picture of the causative interrelationship between autoimmunity and axonal mitochondrial dysfunction in progressive MS (PMS) pathogenesis waits to be provided.

METHODS

In the present study, by adopting the NOD mouse model of PMS, we compared the pharmacological effects of the immunosuppressants dexamethasone and fingolimod with those of mTOR inhibitors rapamycin and everolimus that, in addition to immunosuppression, also regulate mitochondrial functioning. Female Non-Obese Diabetic (NOD) mice were immunized with MOG35-55 and treated with drugs to evaluate functional, immune and mitochondrial parameters during disease evolution.

RESULTS

We found that dexamethasone and fingolimod did not affect the pattern of progression as well as survival. Conversely, mTOR inhibitors rapamycin and everolimus delayed disease progression and robustly extended survival of immunized mice. The same effects were obtained when treatment was delayed by 30 days after immunization. Remarkably, dexamethasone and fingolimod prompted the same degree of immunosuppression of rapamycin within both spleen and spinal cord of mice. However, only rapamycin prompted mitochondriogenesis by increasing mitochondrial content, and expression of several mitochondrial respiratory complex subunits, thereby preventing mtDNA reduction in the spinal cords of immunized mice. These pharmacodynamic effects were not reproduced in healthy NOD mice, suggesting a disease context-dependent pharmacodynamic effect.

DISCUSSION

Data corroborate the key role of mitochondriogenesis to treatment of MS progression, and for the first time disclose the translational potential of mTOR inhibitors in PMS therapy.

Multi-Echo Complex Quantitative Susceptibility Mapping and Quantitative Blood Oxygen Level-Dependent Magnitude (mcQSM + qBOLD or mcQQ) for Oxygen Extraction Fraction (OEF) Mapping

Oxygen extraction fraction (OEF), the fraction of oxygen that tissue extracts from blood, is an essential biomarker used to directly assess tissue viability and function in neurologic disorders. In ischemic stroke, for example, increased OEF can indicate the presence of penumbra-tissue with low perfusion yet intact cellular integrity-making it a primary therapeutic target. However, practical OEF mapping methods are not currently available in clinical settings, owing to the impractical data acquisitions in positron emission tomography (PET) and the limitations of existing MRI techniques. Recently, a novel MRI-based OEF mapping technique, termed QQ, was proposed. It shows high potential for clinical use by utilizing a routine sequence and removing the need for impractical multiple gas inhalations. However, QQ relies on the assumptions of Gaussian noise in susceptibility and multi-echo gradient echo (mGRE) magnitude signals for OEF estimation. This assumption is unreliable in low signal-to-noise ratio (SNR) regions like disease-related lesions, risking inaccurate OEF estimation and potentially impacting clinical decisions. Addressing this, our study presents a novel multi-echo complex QQ (mcQQ) that models realistic Gaussian noise in mGRE complex signals. We implemented mcQQ using a deep learning framework (mcQQ-NET) and compared it with the existing QQ-NET in simulations, ischemic stroke patients, and healthy subjects, using identical training and testing datasets and schemes. In simulations, mcQQ-NET provided more accurate OEF than QQ-NET. In the subacute stroke patients, mcQQ-NET showed a lower average OEF ratio in lesions relative to unaffected contralateral normal tissue than QQ-NET. In the healthy subjects, mcQQ-NET provided uniform OEF maps, similar to QQ-NET, but without unrealistically high OEF outliers in areas of low SNR, such as SNR ≤ 15 (dB). Therefore, mcQQ-NET improves OEF accuracy by more accurately reflecting realistic Gaussian noise in complex mGRE signals. Its enhanced sensitivity to OEF abnormalities, based on more realistic biophysics modeling, suggests that mcQQ-NET has potential for investigating tissue variability in neurologic disorders.

Reduced Oxygen Extraction Fraction in Deep Cerebral Veins Associated with Cognitive Impairment in Multiple Sclerosis

Studying the relationship between cerebral oxygen utilization and cognitive impairment is essential to understanding neuronal functional changes in the disease progression of multiple sclerosis (MS). This study explores the potential of using venous susceptibility in internal cerebral veins (ICVs) as an imaging biomarker for cognitive impairment in relapsing-remitting MS (RRMS) patients. Quantitative susceptibility mapping derived from fully flow-compensated MRI phase data was employed to directly measure venous blood oxygen saturation levels (SvO2) in the ICVs. Results revealed a significant reduction in the susceptibility of ICVs (212.4 ± 30.8 ppb vs 239.4 ± 25.9 ppb) and a significant increase of SvO2 (74.5 ± 1.89 % vs 72.4 ± 2.23 %) in patients with RRMS compared with age- and sex-matched healthy controls. Both the susceptibility of ICVs (r = 0.646, p = 0.004) and the SvO2 (r = -0.603, p = 0.008) exhibited a strong correlation with cognitive decline in these patients assessed by the Paced Auditory Serial Addition Test, while no significant correlation was observed with clinical disability measured by the Expanded Disability Status Scale. The findings suggest that venous susceptibility in ICVs has the potential to serve as a specific indicator of oxygen metabolism and cognitive function in RRMS.

[Optical coherence tomography angiography in the diagnosis of multiple sclerosis]

PURPOSE

This study analyzes the main changes in retinal microcirculation in patients with multiple sclerosis (MS) and their relationship with the type of disease course.

MATERIAL AND METHODS

159 patients (318 eyes) were examined. The groups were formed according to the type of course and duration of MS: group 1 - 37 patients (74 eyes; 23.27%) with relapsing-remitting MS (RRMS) less than 1 year; group 2 - 47 patients (94 eyes; 29.56%) with RRMS from 1 year to 10 years; group 3 - 44 patients (86 eyes; 27.05%) with RRMS >10 years; group 4 - 32 patients (64 eyes; 20.12%) with secondary progressive MS (SPMS). Subgroups A and B were allocated within each group depending on the absence or presence of optic neuritis (ON). Patients underwent standard ophthalmological examination, including optical coherence tomography angiography (OCTA).

RESULTS

A decrease in the vessel density (wiVD) and perfusion density (wiPD) in the macular and peripapillary regions was revealed, progressing with the duration of the disease and with its transition to the progressive type. The minimum values were observed in patients with SPMS (group 4), with the most pronounced in the subgroup with ON (wiVD = 16.06±3.65 mm/mm2, wiPD = 39.38±9.46%, ppwiPD = 44.06±3.09%, ppwiF = 0.41±0.05).

CONCLUSION

OCTA provides the ability to detect subclinical vascular changes and can be considered a comprehensive, reliable method for early diagnosis and monitoring of MS progression.

Changes in brain perfusion with training-related visuomotor improvement in MS

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system. A better understanding of the mechanisms supporting brain plasticity in MS would help to develop targeted interventions to promote recovery. A total of 29 MS patients and 19 healthy volunteers underwent clinical assessment and multi-modal MRI acquisition [fMRI during serial reaction time task (SRT), DWI, T1w structural scans and ASL of resting perfusion] at baseline and after 4-weeks of SRT training. Reduction of functional hyperactivation was observed in MS patients following the training, shown by the stronger reduction of the BOLD response during task execution compared to healthy volunteers. The functional reorganization was accompanied by a positive correlation between improvements in task accuracy and the change in resting perfusion after 4 weeks' training in right angular and supramarginal gyri in MS patients. No longitudinal changes in WM and GM measures and no correlation between task performance improvements and brain structure were observed in MS patients. Our results highlight a potential role for CBF as an early marker of plasticity, in terms of functional (cortical reorganization) and behavioral (performance improvement) changes in MS patients that may help to guide future interventions that exploit preserved plasticity mechanisms.

Microglia-mediated demyelination protects against CD8+ T cell-driven axon degeneration in mice carrying PLP defects

Axon degeneration and functional decline in myelin diseases are often attributed to loss of myelin but their relation is not fully understood. Perturbed myelinating glia can instigate chronic neuroinflammation and contribute to demyelination and axonal damage. Here we study mice with distinct defects in the proteolipid protein 1 gene that develop axonal damage which is driven by cytotoxic T cells targeting myelinating oligodendrocytes. We show that persistent ensheathment with perturbed myelin poses a risk for axon degeneration, neuron loss, and behavioral decline. We demonstrate that CD8+ T cell-driven axonal damage is less likely to progress towards degeneration when axons are efficiently demyelinated by activated microglia. Mechanistically, we show that cytotoxic T cell effector molecules induce cytoskeletal alterations within myelinating glia and aberrant actomyosin constriction of axons at paranodal domains. Our study identifies detrimental axon-glia-immune interactions which promote neurodegeneration and possible therapeutic targets for disorders associated with myelin defects and neuroinflammation.

Remyelination protects neurons from DLK-mediated neurodegeneration

Chronic demyelination is theorized to contribute to neurodegeneration and drive progressive disability in demyelinating diseases like multiple sclerosis. Here, we describe two genetic mouse models of inducible demyelination, one distinguished by effective remyelination, and the other by remyelination failure and persistent demyelination. By comparing these two models, we find that remyelination protects neurons from apoptosis, improves conduction, and promotes functional recovery. Chronic demyelination of neurons leads to activation of the mitogen-associated protein kinase (MAPK) stress pathway downstream of dual leucine zipper kinase (DLK), which ultimately induces the phosphorylation of c-Jun in the nucleus. Both pharmacological inhibition and CRISPR/Cas9-mediated disruption of DLK block c-Jun phosphorylation and the apoptosis of demyelinated neurons. These findings provide direct experimental evidence that remyelination is neuroprotective and identify DLK inhibition as a potential therapeutic strategy to protect chronically demyelinated neurons.

Pro-myelinating clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over the chronic implantation period. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

Measuring Pathology in Patients with Multiple Sclerosis Using Positron Emission Tomography

PURPOSE OF REVIEW

Multiple sclerosis is characterized by a diverse and complex pathology. Clinical relapses, the hallmark of the disease, are accompanied by focal white matter lesions with intense inflammatory and demyelinating activity. Prevention of these relapses has been the major focus of pharmaceutical development, and it is now possible to dramatically reduce this inflammatory activity. Unfortunately, disability accumulation persists for many people living with multiple sclerosis owing to ongoing damage within existing lesions, pathology outside of discrete lesions, and other yet unknown factors. Understanding this complex pathological cascade will be critical to stopping progressive multiple sclerosis. Positron emission tomography uses biochemically specific radioligands to quantitatively measure pathological processes with molecular specificity. This review examines recent advances in the understanding of multiple sclerosis facilitated by positron emission tomography and identifies future avenues to expand understanding and treatment options.

RECENT FINDINGS

An increasing number of radiotracers allow for the quantitative measurement of inflammatory abnormalities, de- and re-myelination, and metabolic disruption associated with multiple sclerosis. The studies have identified contributions of ongoing, smoldering inflammation to accumulating tissue injury and clinical worsening. Myelin studies have quantified the dynamics of myelin loss and recovery. Lastly, metabolic changes have been found to contribute to symptom worsening. The molecular specificity facilitated by positron emission tomography in people living with multiple sclerosis will critically inform efforts to modulate the pathology leading to progressive disability accumulation. Existing studies show the power of this approach applied to multiple sclerosis. This armamentarium of radioligands allows for new understanding of how the brain and spinal cord of people is impacted by multiple sclerosis.

Oligodendroglia Confer Neuroprotection to NSC-34 Motor Neuronal Cells Against the Toxic Insults of Cerebrospinal Fluid from Sporadic Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disorder with multifactorial pathomechanisms affecting not only motor neurons but also glia. Both astrocytes and microglia get activated and contribute significantly to neurodegeneration. The role of oligodendroglia in such a situation remains obscure, especially in the sporadic form of ALS (SALS), which contributes to 90% of cases. Here, we have investigated the role of oligodendroglia in SALS pathophysiology using a human oligodendroglial cell line, MO3.13, by exposing the cells to cerebrospinal fluid from SALS patients (ALS-CSF; 10% v/v for 48 h). ALS-CSF significantly reduced the viability of MO3.13 cells and down-regulated the expression of oligodendroglia-specific proteins, namely, CNPase and Olig2. Furthermore, to investigate the effect of the observed oligodendroglial changes on motor neurons, NSC-34 motor neuronal cells were co-cultured/supplemented with conditioned/spent medium of MO3.13 cells upon exposure to ALS-CSF. Live cell imaging experiments revealed protection to NSC-34 cells against ALS-CSF toxicity upon co-culture with MO3.13 cells. This was evidenced by the absence of neuronal cytoplasmic vacuolation and beading of neurites, which instead resulted in better neuronal differentiation. Enhanced lactate levels and increased expression of its transporter, MCT-1, with sustained expression of trophic factors, namely, GDNF and BDNF, by MO3.13 cells hint towards metabolic and trophic support provided by the surviving oligodendroglia. Similar metabolic changes were seen in the lumbar spinal cord oligodendroglia of rat neonates intrathecally injected with ALS-CSF. The findings indicate that oligodendroglia are indeed rescuer to the degenerating motor neurons when the astrocytes and microglia turn topsy-turvy.

Alterations of Oligodendrocyte and Myelin Energy Metabolism in Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system (CNS), characterized by demyelination and neurodegeneration. Oligodendrocytes play a vital role in maintaining the integrity of myelin, the protective sheath around nerve fibres essential for efficient signal transmission. However, in MS, oligodendrocytes become dysfunctional, leading to myelin damage and axonal degeneration. Emerging evidence suggests that metabolic changes, including mitochondrial dysfunction and alterations in glucose and lipid metabolism, contribute significantly to the pathogenesis of MS. Mitochondrial dysfunction is observed in both immune cells and oligodendrocytes within the CNS of MS patients. Impaired mitochondrial function leads to energy deficits, affecting crucial processes such as impulse transmission and axonal transport, ultimately contributing to neurodegeneration. Moreover, mitochondrial dysfunction is linked to the generation of reactive oxygen species (ROS), exacerbating myelin damage and inflammation. Altered glucose metabolism affects the energy supply required for oligodendrocyte function and myelin synthesis. Dysregulated lipid metabolism results in changes to the composition of myelin, affecting its stability and integrity. Importantly, low levels of polyunsaturated fatty acids in MS are associated with upregulated lipid metabolism and enhanced glucose catabolism. Understanding the intricate relationship between these mechanisms is crucial for developing targeted therapies to preserve myelin and promote neurological recovery in individuals with MS. Addressing these metabolic aspects may offer new insights into potential therapeutic strategies to halt disease progression and improve the quality of life for MS patients.

Targeting the TCA cycle can ameliorate widespread axonal energy deficiency in neuroinflammatory lesions

Inflammation in the central nervous system can impair the function of neuronal mitochondria and contributes to axon degeneration in the common neuroinflammatory disease multiple sclerosis (MS). Here we combine cell-type-specific mitochondrial proteomics with in vivo biosensor imaging to dissect how inflammation alters the molecular composition and functional capacity of neuronal mitochondria. We show that neuroinflammatory lesions in the mouse spinal cord cause widespread and persisting axonal ATP deficiency, which precedes mitochondrial oxidation and calcium overload. This axonal energy deficiency is associated with impaired electron transport chain function, but also an upstream imbalance of tricarboxylic acid (TCA) cycle enzymes, with several, including key rate-limiting, enzymes being depleted in neuronal mitochondria in experimental models and in MS lesions. Notably, viral overexpression of individual TCA enzymes can ameliorate the axonal energy deficits in neuroinflammatory lesions, suggesting that TCA cycle dysfunction in MS may be amendable to therapy.

Acute intermittent hypoxia alters disease course and promotes CNS repair including resolution of inflammation and remyelination in the experimental autoimmune encephalomyelitis model of MS

Remyelination and neurodegeneration prevention mitigate disability in Multiple Sclerosis (MS). We have shown acute intermittent hypoxia (AIH) is a novel, non-invasive and effective therapy for peripheral nerve repair, including remyelination. Thus, we posited AIH would improve repair following CNS demyelination and address the paucity of MS repair treatments. AIH's capacity to enhance intrinsic repair, functional recovery and alter disease course in the experimental autoimmune encephalomyelitis (EAE) model of MS was assessed. EAE was induced by MOG35-55 immunization in C57BL/6 female mice. EAE mice received either AIH (10 cycles-5 min 11% oxygen alternating with 5 min 21% oxygen) or Normoxia (control; 21% oxygen for same duration) once daily for 7d beginning at near peak EAE disease score of 2.5. Mice were followed post-treatment for an additional 7d before assessing histopathology or 14d to examine maintenance of AIH effects. Alterations in histopathological correlates of multiple repair indices were analyzed quantitatively in focally demyelinated ventral lumbar spinal cord areas to assess AIH impacts. AIH begun at near peak disease significantly improved daily clinical scores/functional recovery and associated histopathology relative to Normoxia controls and the former were maintained for at least 14d post-treatment. AIH enhanced correlates of myelination, axon protection and oligodendrocyte precursor cell recruitment to demyelinated areas. AIH also effected a dramatic reduction in inflammation, while polarizing remaining macrophages/microglia toward a pro-repair state. Collectively, this supports a role for AIH as a novel non-invasive therapy to enhance CNS repair and alter disease course following demyelination and holds promise as a neuroregenerative MS strategy.

HIF prolyl hydroxylase 2/3 deletion disrupts astrocytic integrity and exacerbates neuroinflammation

Astrocytes constitute the parenchymal border of the blood-brain barrier (BBB), modulate the exchange of soluble and cellular elements, and are essential for neuronal metabolic support. Thus, astrocytes critically influence neuronal network integrity. In hypoxia, astrocytes upregulate a transcriptional program that has been shown to boost neuroprotection in several models of neurological diseases. We investigated transgenic mice with astrocyte-specific activation of the hypoxia-response program by deleting the oxygen sensors, HIF prolyl-hydroxylase domains 2 and 3 (Phd2/3). We induced astrocytic Phd2/3 deletion after onset of clinical signs in experimental autoimmune encephalomyelitis (EAE) that led to an exacerbation of the disease mediated by massive immune cell infiltration. We found that Phd2/3-ko astrocytes, though expressing a neuroprotective signature, exhibited a gradual loss of gap-junctional Connexin-43 (Cx43), which was induced by vascular endothelial growth factor-alpha (Vegf-a) expression. These results provide mechanistic insights into astrocyte biology, their critical role in hypoxic states, and in chronic inflammatory CNS diseases.

More extensive white matter disruptions present in untreated obstructive sleep apnea than we thought: A large sample diffusion imaging study

Obstructive sleep apnea (OSA) may lead to white mater (WM) disruptions and cognitive deficits. However, no studies have investigated the full extent of the brain WM, and its associations with cognitive deficits in OSA remain unclear. We thus applied diffusion tensor imaging (DTI) tractography with multi-fiber models and used atlas-based bundle-specific approach to investigate the WM abnormalities for various tracts of the cerebral cortex, thalamus, brainstem, and cerebellum in patients with untreated OSA. We enrolled 100 OSA patients and 63 healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) values mapped on 33 regions of interest including WM tracts of cortex, thalamus, brainstem, and cerebellum were obtained from tractography-based reconstructions. We compared FA/MD values between groups and correlated FA/MD with clinical data in the OSA group after controlling for age and body mass index. OSA patients showed significantly lower FA values in multiple WM fibers including corpus callosum, inferior fronto-occipital fasciculus, middle/superior longitudinal fasciculi, thalamic radiations, and uncinate (FDR <0.05). Higher FA values were found in medial lemniscus of patients compared to controls (FDR <0.05). Lower FA values of rostrum of corpus callosum correlated with lower visual memory performance in OSA group (p < .005). Our quantitative DTI analysis demonstrated that untreated OSA could negatively impact the integrity of pathways more broadly, including brainstem structures such as medial lemniscus, in comparison to previous findings. Fiber tract abnormalities of the rostral corpus callosum were associated with impaired visual memory in untreated OSA may provide insights into the related pathomechanism.

Pro-myelinating Clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over chronic implantation. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

Abstract Figure

Potential biological contributers to the sex difference in multiple sclerosis progression

Multiple sclerosis (MS) is an immune-mediated disease that targets the myelin sheath of central nervous system (CNS) neurons leading to axon injury, neuronal death, and neurological progression. Though women are more highly susceptible to developing MS, men that develop this disease exhibit greater cognitive impairment and accumulate disability more rapidly than women. Magnetic resonance imaging and pathology studies have revealed that the greater neurological progression seen in males correlates with chronic immune activation and increased iron accumulation at the rims of chronic white matter lesions as well as more intensive whole brain and grey matter atrophy and axon loss. Studies in humans and in animal models of MS suggest that male aged microglia do not have a higher propensity for inflammation, but may become more re-active at the rim of white matter lesions as a result of the presence of pro-inflammatory T cells, greater astrocyte activation or iron release from oligodendrocytes in the males. There is also evidence that remyelination is more efficient in aged female than aged male rodents and that male neurons are more susceptible to oxidative and nitrosative stress. Both sex chromosome complement and sex hormones contribute to these sex differences in biology.

Brain region dependent molecular signatures and myelin repair following chronic demyelination

Multiple sclerosis (MS) is the most prevalent demyelinating disease of the central nervous system, characterized by myelin destruction, axonal degeneration, and progressive loss of neurological functions. Remyelination is considered an axonal protection strategy and may enable functional recovery, but the mechanisms of myelin repair, especially after chronic demyelination, remain poorly understood. Here, we used the cuprizone demyelination mouse model to investigate spatiotemporal characteristics of acute and chronic de- and remyelination and motor functional recovery following chronic demyelination. Extensive remyelination occurred after both the acute and chronic insults, but with less robust glial responses and slower myelin recovery in the chronic phase. Axonal damage was found at the ultrastructural level in the chronically demyelinated corpus callosum and in remyelinated axons in the somatosensory cortex. Unexpectedly, we observed the development of functional motor deficits after chronic remyelination. RNA sequencing of isolated brain regions revealed significantly altered transcripts across the corpus callosum, cortex and hippocampus. Pathway analysis identified selective upregulation of extracellular matrix/collagen pathways and synaptic signaling in the chronically de/remyelinating white matter. Our study demonstrates regional differences of intrinsic reparative mechanisms after a chronic demyelinating insult and suggests a potential link between long-term motor function alterations and continued axonal damage during chronic remyelination. Moreover, the transcriptome dataset of three brain regions and over an extended de/remyelination period provides a valuable platform for a better understanding of the mechanisms of myelin repair as well as the identification of potential targets for effective remyelination and neuroprotection for progressive MS.

Cis-p-tau plays crucial role in lysolecithin-induced demyelination and subsequent axonopathy in mouse optic chiasm

Multiple sclerosis (MS) is an autoimmune demyelinating disease that leads to axon degeneration as the major cause of everlasting neurological disability. The cis-phosphorylated tau (cis-p-tau) is an isoform of tau phosphorylated on threonine 231 and causes tau fails to bind micro-tubules and promotes assembly. It gains toxic function and forms tangles in the cell which finally leads to cell death. An antibody raised against cis- p-tau (cis mAb) detects this isoform and induces its clearance. Here, we investigated the formation of cis-p-tau in a lysophosphatidylcholine (LPC)-induced prolonged demyelination model as well as the beneficial effects of its clearance using cis mAb. Cis -p-tau was increased in the lesion site, especially in axons and microglia. Behavioral and functional studies were performed using visual cliff test, visual placing test, and visual evoked potential recording. Cis-p-tau clearance resulted in decreased gliosis, protected myelin and reduced axon degeneration. Analysis of behavioral and electrophysiological data showed that clearance of cis-p-tau by cis mAb treatment improved the visual acuity along with the integrity of the optic pathway. Our results highlight the opportunity of using cis mAb as a new therapy for protecting myelin and axons in patients suffering from MS.

Reduced brain oxygen metabolism in patients with multiple sclerosis: Evidence from dual-calibrated functional MRI

Cerebral energy deficiency is increasingly recognised as an important feature of multiple sclerosis (MS). Until now, we have lacked non-invasive imaging methods to quantify energy utilisation and mitochondrial function in the human brain. Here, we used novel dual-calibrated functional magnetic resonance imaging (dc-fMRI) to map grey-matter (GM) deoxy-haemoglobin sensitive cerebral blood volume (CBVdHb), cerebral blood flow (CBF), oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen consumption (CMRO2) in patients with MS (PwMS) and age/sex matched controls. By integrating a flow-diffusion model of oxygen transport, we evaluated the effective oxygen diffusivity of the capillary network (DC) and the partial pressure of oxygen at the mitochondria (PmO2). Significant between-group differences were observed as decreased CBF (p = 0.010), CMRO2 (p < 0.001) and DC (p = 0.002), and increased PmO2 (p = 0.043) in patients compared to controls. No significant differences were observed for CBVdHb (p = 0.389), OEF (p = 0.358), or GM volume (p = 0.302). Regional analysis showed widespread reductions in CMRO2 and DC for PwMS. Our findings may be indicative of reduced oxygen demand or utilisation in the MS brain and mitochondrial dysfunction. Our results suggest changes in brain physiology may precede MRI-detectable GM loss and may contribute to disease progression and neurodegeneration.

Chronic oligodendrocyte injury in central nervous system pathologies

Myelin, the membrane surrounding neuronal axons, is critical for central nervous system (CNS) function. Injury to myelin-forming oligodendrocytes (OL) in chronic neurological diseases (e.g. multiple sclerosis) ranges from sublethal to lethal, leading to OL dysfunction and myelin pathology, and consequent deleterious impacts on axonal health that drive clinical impairments. This is regulated by intrinsic factors such as heterogeneity and age, and extrinsic cellular and molecular interactions. Here, we discuss the responses of OLs to injury, and perspectives for therapeutic targeting. We put forward that targeting mature OL health in neurological disease is a promising therapeutic strategy to support CNS function.

Cerebrovascular reactivity in multiple sclerosis is restored with reduced inflammation during immunomodulation

Cerebrovascular reactivity (CVR) reflects the capacity of the brain’s vasculature to increase blood flow following a vasodilatory stimulus. Reactivity is an essential property of the brain’s blood vessels that maintains nutrient supplies in the face of changing demand. In Multiple Sclerosis (MS), CVR may be diminished with brain inflammation and this may contribute to neurodegeneration. We test the hypothesis that CVR is altered with MS neuroinflammation and that it is restored when inflammation is reduced. Using a breath-hold task during functional Magnetic Resonance Imaging (MRI), we mapped grey matter and white matter CVRs (CVR_GM and CVR_WM, respectively) in 23 young MS patients, eligible for disease modifying therapy, before and during Interferon beta treatment. Inflammatory activity was inferred from the presence of Gadolinium enhancing lesions at MRI. Eighteen age and gender-matched healthy controls (HC) were also assessed. Enhancing lesions were observed in 12 patients at the start of the study and in 3 patients during treatment. Patients had lower pre-treatment CVR_GM (p = 0.04) and CVR_WM (p = 0.02) compared to HC. In patients, a lower pre-treatment CVR_GM was associated with a lower GM volume (r = 0.60, p = 0.003). On-treatment, there was an increase in CVR_GM (p = 0.02) and CVR_WM (p = 0.03) that negatively correlated with pre-treatment CVR (GM: r = − 0.58, p = 0.005; WM: r = − 0.60, p = 0.003). CVR increased when enhancing lesions reduced in number (GM: r = − 0.48, p = 0.02, WM: r = − 0.62, p = 0.003). Resolution of inflammation may restore altered cerebrovascular function limiting neurodegeneration in MS. Imaging of cerebrovascular function may thereby inform tissue physiology and improve treatment monitoring.

Progressive Multiple Sclerosis

PURPOSE OF REVIEW

This article provides an update on progressive forms of multiple sclerosis (MS) commonly referred to as primary progressive MS and secondary progressive MS. It discusses the importance of diagnosing and detecting progression early, the similarities between progressive forms, challenges in detecting progression, factors that could augment progression, and the importance of disease-modifying therapies in patients with evidence of active progressive MS. It also discusses the overall care of progressive MS.

RECENT FINDINGS

The pathogenesis of primary progressive MS and secondary progressive MS is overlapping, and in both presentations, patients with relapses or focal MRI activity are classified as having active, progressive MS. All currently approved disease-modifying therapies are indicated for active secondary progressive MS. The therapeutic opportunity of anti-inflammatory drugs for the treatment of progressive MS is enhanced in those who are younger and have a shorter disease duration. Vascular comorbidities may contribute to progression in MS.

SUMMARY

Several challenges remain in the diagnosis, follow-up, and treatment of progressive MS. Early identification of active progressive MS is needed to maximize treatment benefit. The advantages of optimal comorbidity management (eg, hypertension, hyperlipidemia) in delaying progression are uncertain. Clinical care guidelines for advanced, severe MS are lacking.

Basal metabolic rate and risk of multiple sclerosis: a Mendelian randomization study

To determine the relationship between basal metabolic rate (BMR) and multiple sclerosis (MS) susceptibility, we analyzed genome-wide association study (GWAS) summary statistics data from the International Multiple Sclerosis Genetics Consortium on a total of 115,803 participants of European descent, including 47,429 patients with MS and 68,374 controls. We selected 378 independent genetic variants strongly associated with BMR in a GWAS involving 454,874 participants as instrumental variables to examine a potential causal relationship between BMR and MS. A genetically predicted higher BMR was associated with a greater risk of MS (odds ratio [OR]: 1.283 per one standard deviation increase in BMR, 95% confidence interval [CI]: 1.108-1.486, P = 0.001). Moreover, we used the lasso method to eliminate heterogeneity (Q statistic = 384.58, P = 0.370). There was no pleiotropy in our study and no bias was found in the sensitivity analysis using the leave-one-out test. We provide novel evidence that a higher BMR is an independent causal risk factor in the development of MS. Further work is warranted to elucidate the potential mechanisms.

Targeting Fibronectin to Overcome Remyelination Failure in Multiple Sclerosis: The Need for Brain- and Lesion-Targeted Drug Delivery

Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease with unknown etiology that can be characterized by the presence of demyelinated lesions. Prevailing treatment protocols in MS rely on the modulation of the inflammatory process but do not impact disease progression. Remyelination is an essential factor for both axonal survival and functional neurological recovery but is often insufficient. The extracellular matrix protein fibronectin contributes to the inhibitory environment created in MS lesions and likely plays a causative role in remyelination failure. The presence of the blood–brain barrier (BBB) hinders the delivery of remyelination therapeutics to lesions. Therefore, therapeutic interventions to normalize the pathogenic MS lesion environment need to be able to cross the BBB. In this review, we outline the multifaceted roles of fibronectin in MS pathogenesis and discuss promising therapeutic targets and agents to overcome fibronectin-mediated inhibition of remyelination. In addition, to pave the way for clinical use, we reflect on opportunities to deliver MS therapeutics to lesions through the utilization of nanomedicine and discuss strategies to deliver fibronectin-directed therapeutics across the BBB. The use of well-designed nanocarriers with appropriate surface functionalization to cross the BBB and target the lesion sites is recommended.

Clinical, Radiological and Pathological Characteristics Between Cerebral Small Vessel Disease and Multiple Sclerosis: A Review

Cerebral small vessel disease (CSVD) and multiple sclerosis (MS) are a group of diseases associated with small vessel lesions, the former often resulting from the vascular lesion itself, while the latter originating from demyelinating which can damage the cerebral small veins. Clinically, CSVD and MS do not have specific signs and symptoms, and it is often difficult to distinguish between the two from the aspects of the pathology and imaging. Therefore, failure to correctly identify and diagnose the two diseases will delay early intervention, which in turn will affect the long-term functional activity for patients and even increase their burden of life. This review has summarized recent studies regarding their similarities and difference of the clinical manifestations, pathological features and imaging changes in CSVD and MS, which could provide a reliable basis for the diagnosis and differentiation of the two diseases in the future.

Cerebrovascular Reactivity and Neurovascular Coupling in Multiple Sclerosis-A Systematic Review

The inflammatory processes observed in the central nervous system in multiple sclerosis (MS) could damage the endothelium of the cerebral vessels and lead to a dysfunctional regulation of vessel tonus and recruitment, potentially impairing cerebrovascular reactivity (CVR) and neurovascular coupling (NVC). Impaired CVR or NVC correlates with declining brain health and potentially plays a causal role in the development of neurodegenerative disease. Therefore, we examined studies on CVR or NVC in MS patients to evaluate the evidence for impaired cerebrovascular function as a contributing disease mechanism in MS. Twenty-three studies were included (12 examined CVR and 11 examined NVC). Six studies found no difference in CVR response between MS patients and healthy controls. Five studies observed reduced CVR in patients. This discrepancy can be because CVR is mainly affected after a long disease duration and therefore is not observed in all patients. All studies used CO₂ as a vasodilating stimulus. The studies on NVC demonstrated diverse results; hence a conclusion that describes all the published observations is difficult to find. Future studies using quantitative techniques and larger study samples are needed to elucidate the discrepancies in the reported results.

A new form of axonal pathology in a spinal model of neuromyelitis optica

Neuromyelitis optica is a chronic neuroinflammatory disease, which primarily targets astrocytes and often results in severe axon injury of unknown mechanism. Neuromyelitis optica patients harbour autoantibodies against the astrocytic water channel protein, aquaporin-4 (AQP4-IgG), which induce complement-mediated astrocyte lysis and subsequent axon damage. Using spinal in vivo imaging in a mouse model of such astrocytopathic lesions, we explored the mechanism underlying neuromyelitis optica-related axon injury. Many axons showed a swift and morphologically distinct 'pearls-on-string' transformation also readily detectable in human neuromyelitis optica lesions, which especially affected small calibre axons independently of myelination. Functional imaging revealed that calcium homeostasis was initially preserved in this 'acute axonal beading' state, ruling out disruption of the axonal membrane, which sets this form of axon injury apart from previously described forms of traumatic and inflammatory axon damage. Morphological, pharmacological and genetic analyses showed that AQP4-IgG-induced axon injury involved osmotic stress and ionic overload, but does not appear to use canonical pathways of Wallerian-like degeneration. Subcellular analysis demonstrated remodelling of the axonal cytoskeleton in beaded axons, especially local loss of microtubules. Treatment with the microtubule stabilizer epothilone, a putative therapy approach for traumatic and degenerative axonopathies, prevented axonal beading, while destabilizing microtubules sensitized axons for beading. Our results reveal a distinct form of immune-mediated axon pathology in neuromyelitis optica that mechanistically differs from known cascades of post-traumatic and inflammatory axon loss, and suggest a new strategy for neuroprotection in neuromyelitis optica and related diseases.

A Narrative Review on Axonal Neuroprotection in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in demyelination and neurodegeneration. The therapeutic strategy is now largely based on reducing inflammation with immunosuppressive drugs. Unfortunately, when disease progression is observed, no drug offers neuroprotection apart from its anti-inflammatory effect. In this review, we explore current knowledge on the assessment of neurodegeneration in MS and look at putative targets that might prove useful in protecting the axon from degeneration. Among them, Bruton's tyrosine kinase inhibitors, anti-apoptotic and antioxidant agents, sex hormones, statins, channel blockers, growth factors, and molecules preventing glutamate excitotoxicity have already been studied. Some of them have reached phase III clinical trials and carry a great message of hope for our patients with MS.

A tractometry principal component analysis of white matter tract network structure and relationships with cognitive function in relapsing-remitting multiple sclerosis

Understanding the brain changes underlying cognitive dysfunction is a key priority in multiple sclerosis (MS) to improve monitoring and treatment of this debilitating symptom. Functional connectivity network changes are associated with cognitive dysfunction, but it is less well understood how changes in normal appearing white matter relate to cognitive symptoms. If white matter tracts have network structure it would be expected that tracts within a network share susceptibility to MS pathology. In the present study, we used a tractometry approach to explore patterns of variance in white matter metrics across white matter (WM) tracts, and assessed how such patterns relate to neuropsychological test performance across cognitive domains. A sample of 102 relapsing-remitting MS patients and 27 healthy controls underwent MRI and neuropsychological testing. Tractography was performed on diffusion MRI data to extract 40 WM tracts and microstructural measures were extracted from each tract. Principal component analysis (PCA) was used to decompose metrics from all tracts to assess the presence of any co-variance structure among the tracts. Similarly, PCA was applied to cognitive test scores to identify the main cognitive domains. Finally, we assessed the ability of tract co-variance patterns to predict test performance across cognitive domains. We found that a single co-variance pattern which captured microstructure across all tracts explained the most variance (65% variance explained) and that there was little evidence for separate, smaller network patterns of pathology. Variance in this pattern was explained by effects related to lesions, but one main co-variance pattern persisted after this effect was regressed out. This main WM tract co-variance pattern contributed to explaining a modest degree of variance in one of our four cognitive domains in MS. These findings highlight the need to investigate the relationship between the normal appearing white matter and cognitive impairment further and on a more granular level, to improve the understanding of the network structure of the brain in MS.

Proteomics in Multiple Sclerosis: The Perspective of the Clinician

Multiple sclerosis (MS) is the inflammatory demyelinating and neurodegenerative disease of the central nervous system (CNS) that affects approximately 2.8 million people worldwide. In the last decade, a new era was heralded in by a new phenotypic classification, a new diagnostic protocol and the first ever therapeutic guideline, making personalized medicine the aim of MS management. However, despite this great evolution, there are still many aspects of the disease that are unknown and need to be further researched. A hallmark of these research are molecular biomarkers that could help in the diagnosis, differential diagnosis, therapy and prognosis of the disease. Proteomics, a rapidly evolving discipline of molecular biology may fulfill this dire need for the discovery of molecular biomarkers. In this review, we aimed to give a comprehensive summary on the utility of proteomics in the field of MS research. We reviewed the published results of the method in case of the pathogenesis of the disease and for biomarkers of diagnosis, differential diagnosis, conversion of disease courses, disease activity, progression and immunological therapy. We found proteomics to be a highly effective emerging tool that has been providing important findings in the research of MS.

Lower cerebral arterial blood flow is associated with greater serum neurofilament light chain levels in multiple sclerosis patients

BACKGROUND

Hypoperfusion, vascular pathology, and cardiovascular risk factors are associated with disease severity in multiple sclerosis (MS). We aimed to assess relationships between cerebral arterial blood flow (CABF) and serum neurofilament light chain (sNfL), as neuronal damage biomarker.

METHODS AND MATERIALS

Total CABF was measured in 137 patients (86 clinically isolated syndrome (CIS)/relapsing-remitting (RR) and 51 progressive MS (PMS)) and 48 healthy controls (HCs) using Doppler ultrasound. sNfL was quantitated using single molecule assay (Simoa). 3.0T MRI examination allowed quantification of T2 lesion and whole-brain volume (WBV). Multiple linear regression models determined the sNfL associated with CABF after correction for demographic and MRI-derived variables.

RESULTS

After adjustment for age, sex and BMI, total CABF remained statistically significant and model comparisons showed that CABF explained additional 2.6% of the sNfL variance (β=-0.167, p=0.044). CABF also remained significant in a step-wise regression model (β=0.18, p=0.034) upon the inclusion of T2 lesion burden and WBV effects. Patients in the lowest CABF quartile (CABF≤761mL/min) had significantly higher sNfL (34.6pg/mL versus 23.9pg/mL, adjusted-p=0.042) when compared to the highest quartile (CABF≥1130mL/min).

CONCLUSION

Lower CABF is associated with increased sNfL in MS patients, highlighting the relationship between cerebral hypoperfusion and axonal pathology.

PDK4 Inhibition Ameliorates Melatonin Therapy by Modulating Cerebral Metabolism and Remyelination in an EAE Demyelinating Mouse Model of Multiple Sclerosis

We recently showed that melatonin ameliorates the severity of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. However, efficiency of melatonin therapy was associated with side effects, manifested by slowing down of remyelination, through increasing the inhibitory effects of brain pyruvate dehydrogenase kinase-4 (PDK-4) on pyruvate dehydrogenase complex (PDC), a key enzyme in fatty acid (FA) synthesis during remyelination. In this study, we investigated the metabolic profile of FA synthesis using combination therapy of melatonin and diisopropylamine dichloroacetate (DADA), a PDK4 inhibitor, in EAE mice. Disease progression was monitored by recording the disability scores. Immunological, oligodendrogenesis and metabolic factors were also evaluated. Results showed that combination therapy of melatonin and DADA significantly reduced EAE disability scores, compared to melatonin, whereas DADA alone did not have any effect. In addition, co-therapy inhibited pro-inflammatory while increasing anti-inflammatory cytokines, significantly better than melatonin alone. Moreover, administration of combination drugs recovered the declined expression of oligodendrocytic markers in EAE, more potently than melatonin. Furthermore, co-therapy affected cerebral energy metabolism by significantly reducing lactate levels while increasing N-acetylaspartate (NAA) and 3-hydroxy-3-methyl-glutaryl-coenzyme-A reductase (HMGCR) levels. Finally, while melatonin increased lactate and PDK4 expression levels and greatly reduced PDC activity, co-therapy significantly restored PDC function while reducing the lactate levels. In summary, administration of melatonin with DADA increased the efficiency of melatonin treatment by eliminating the inhibitory effects of PDK4 on PDC’s function, a critical step for proper FA synthesis during remyelination.

Autophagy modulation in multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS), a white matter demyelinating disease of the central nervous system (CNS), is characterized by neuroinflammatory and neurodegenerative. Experimental autoimmune encephalomyelitis (EAE) is a commonly used animal model for investigating pathogenic mechanisms of MS, representing the destruction of the blood-brain barrier (BBB), the activation of T cells, and the infiltration of myeloid cells. An increasing number of studies have documented that autophagy plays a critical role in the pathogenesis of both MS and EAE. Autophagy maintains CNS homeostasis by degrading the damaged organelles and abnormal proteins. Furthermore, autophagy is involved in inflammatory responses by regulating the activation of immune cells and the secretion of inflammatory factors. However, the specific mechanisms of autophagy involved in MS and EAE are not completely understood. In this review, we will summarize the complex mechanisms of autophagy in MS and EAE, providing potential therapeutic approaches for the management of MS.

Characterizing the time course of cerebrovascular reactivity in multiple sclerosis

BACKGROUND AND PURPOSE

Changes in cerebral perfusion occur early in relapsing and progressive multiple sclerosis (MS) patients, though whether cerebral blood flow (CBF) can be altered by therapy is unknown. We sought to characterize the time course of change in CBF (cerebral vascular reactivity [CVR]), following intravenous (IV) acetazolamide (ACZ) in whole brain and within various gray and white matter brain regions in MS patients.

METHODS

We enrolled five relapsing MS patients on injectable therapies. Participants received a 1000 mg IV bolus of ACZ and CBF was measured using pseudocontinuous arterial spin labeling MRI. To quantify differences in time course between patients, we calculated the numerical integration of CVR over time using the trapezoidal rule to estimate area under the curve (AUC_(CVR) ).

RESULTS

A change in whole brain CBF of 30%-65% was seen in all participants at 15 minutes after ACZ challenge. CBF increases >20% above baseline were sustained for 90 minutes within whole-brain, normal-appearing white matter and total T2-hyperintense lesioned tissue. AUC_(CVR) values for both gray (cortical and deep gray matter) and white (normal-appearing and T2-lesioned) matter regions were similar between patients.

CONCLUSION

Our findings show a prolonged time course in vascular reactivity after ACZ stimulus in MS patients with a similar time course for both gray and white matter brain regions, including in previously injured tissue. Our preliminary results suggest that blood flow can be augmented in the established MS lesion suggesting that even previously injured tissue might be responsive to treatment.

Smouldering multiple sclerosis: the ‘real MS’

Using a philosophical approach or deductive reasoning, we challenge the dominant clinico-radiological worldview that defines multiple sclerosis (MS) as a focal inflammatory disease of the central nervous system (CNS). We provide a range of evidence to argue that the ‘real MS’ is in fact driven primarily by a smouldering pathological disease process. In natural history studies and clinical trials, relapses and focal activity revealed by magnetic resonance imaging (MRI) in MS patients on placebo or on disease-modifying therapies (DMTs) were found to be poor predictors of long-term disease evolution and were dissociated from disability outcomes. In addition, the progressive accumulation of disability in MS can occur independently of relapse activity from early in the disease course. This scenario is underpinned by a more diffuse smouldering pathological process that may affect the entire CNS. Many putative pathological drivers of smouldering MS can be potentially modified by specific therapeutic strategies, an approach that may have major implications for the management of MS patients. We hypothesise that therapeutically targeting a state of ‘no evident inflammatory disease activity’ (NEIDA) cannot sufficiently prevent disability accumulation in MS, meaning that treatment should also focus on other brain and spinal cord pathological processes contributing to the slow loss of neurological function. This should also be complemented with a holistic approach to the management of other systemic disease processes that have been shown to worsen MS outcomes.

Abnormal Oxidative Metabolism in the Cuprizone Mouse Model of Demyelination: an in vivo NIRS-MRI Study

Disruptions in oxidative metabolism may occur in multiple sclerosis and other demyelinating neurological diseases. The impact of demyelination on metabolic rate is also not understood. It is possible that mitochondrial damage may be associated with many such neurological disorders. To study oxidative metabolism with one model of demyelination, we implemented a novel multimodal imaging technique combining Near-Infrared Spectroscopy (NIRS) and MRI to cuprizone mouse model. The cuprizone model is used to study demyelination and may be associated with inhibition of mitochondrial function. Cuprizone mice showed reduced oxygen extraction fraction (-39.1%, p≤0.001), increased tissue oxygenation (6.4%, p≤0.001), and reduced cerebral metabolic rate of oxygen in cortical gray matter (-62.1%, p≤0.001). These changes resolved after the cessation of cuprizone exposure and partial remyelination. A decrease in hemoglobin concentration (-34.4%, p≤0.001), but no change in cerebral blood flow were also observed during demyelination. The oxidized state of the mitochondrial enzyme, Cytochrome C Oxidase (CCO) increased (46.3%, p≤0.001) while the reduced state decreased (-34.4%, p≤0.05) significantly in cuprizone mice. The total amount of CCO did not change significantly during cuprizone exposure. Total CCO did decline after recovery both in control (-23.1%, p≤0.01) and cuprizone (-28.8%, p≤0.001) groups which may relate to age. A reduction in the magnetization transfer ratio, indicating demyelination, was found in the cuprizone group in the cerebral cortex (-3.2%, p≤0.01) and corpus callosum (-5.5%, p≤0.001). In summary, we were able to detect evidence of altered CCO metabolism during cuprizone exposure, consistent with a mitochondrial defect. We observed increased oxygenation and reduced metabolic rate associated with reduced myelination in the gray and white matter. The novel multimodal imaging technique applied here shows promise for noninvasively assessing parameters associated with oxidative metabolism in both mouse models of neurological disease and for translation to study oxidative metabolism in the human brain.

Multiple Sclerosis and related disorders

Multiple Sclerosis (MS) is a common neuroinflammatory disorder which is associated with disabling clinical consequences. The MS disease process may involve neural centers implicated in the control of breathing, leading to ventilatory disturbances during both wakefulness and sleep. In this chapter, a brief overview of MS disease mechanisms and clinical sequelae including sleep disorders is provided. The chapter then focuses on obstructive sleep apnea-hypopnea (OSAH) which is the most prevalent respiratory control abnormality encountered in ambulatory MS patients. The diagnosis, prevalence, and clinical consequences as well as data on effects of OSAH treatment in MS patients are discussed, including the impact on the disabling symptom of fatigue and other clinical sequelae. We also review pathophysiologic mechanisms contributing to OSAH in MS, and in turn mechanisms by which OSAH may impact on the MS disease process, resulting in a bidirectional relationship between these two conditions. We then discuss central sleep apnea, other respiratory control disturbances, and the pathogenesis and management of respiratory muscle weakness and chronic hypoventilation in MS. We also provide a brief overview of Neuromyelitis Optica Spectrum Disorders and review current data on respiratory control disturbances and sleep-disordered breathing in that condition.

Regulated cell death: discovery, features and implications for neurodegenerative diseases

Regulated cell death (RCD) is a ubiquitous process in living organisms that is essential for tissue homeostasis or to restore biological balance under stress. Over the decades, various forms of RCD have been reported and are increasingly being found to involve in human pathologies and clinical outcomes. We focus on five high-profile forms of RCD, including apoptosis, pyroptosis, autophagy-dependent cell death, necroptosis and ferroptosis. Cumulative evidence supports that not only they have different features and various pathways, but also there are extensive cross-talks between modes of cell death. As the understanding of RCD pathway in evolution, development, physiology and disease continues to improve. Here we review an updated classification of RCD on the discovery and features of processes. The prominent focus will be placed on key mechanisms of RCD and its critical role in neurodegenerative disease. Video abstract.