Effect of nitric oxide to axonal degeneration in multiple sclerosis via downregulating monocarboxylate transporter 1 in oligodendrocytes

Siponimod Modulates the Reaction of Microglial Cells to Pro-Inflammatory Stimulation

Siponimod (Mayzent®), a sphingosine 1-phosphate receptor (S1PR) modulator which prevents lymphocyte egress from lymphoid tissues, is approved for the treatment of relapsing-remitting and active secondary progressive multiple sclerosis. It can cross the blood-brain barrier (BBB) and selectively binds to S1PR1 and S1PR5 expressed by several cell populations of the central nervous system (CNS) including microglia. In multiple sclerosis, microglia are a key CNS cell population moving back and forth in a continuum of beneficial and deleterious states. On the one hand, they can contribute to neurorepair by clearing myelin debris, which is a prerequisite for remyelination and neuroprotection. On the other hand, they also participate in autoimmune inflammation and axonal degeneration by producing pro-inflammatory cytokines and molecules. In this study, we demonstrate that siponimod can modulate the microglial reaction to lipopolysaccharide-induced pro-inflammatory activation.

Autoimmune neuroinflammation triggers mitochondrial oxidation in oligodendrocytes

Oligodendrocytes (ODCs) are myelinating cells of the central nervous system (CNS) supporting neuronal survival. Oxidants and mitochondrial dysfunction have been suggested as the main causes of ODC damage during neuroinflammation as observed in multiple sclerosis (MS). Nonetheless, the dynamics of this process remain unclear, thus hindering the design of neuroprotective therapeutic strategies. To decipher the spatio-temporal pattern of oxidative damage and dysfunction of ODC mitochondria in vivo, we created a novel mouse model in which ODCs selectively express the ratiometric H₂ O₂ biosensor mito-roGFP2-Orp1 allowing for quantification of redox changes in their mitochondria. Using 2-photon imaging of the exposed spinal cord, we observed significant mitochondrial oxidation in ODCs upon induction of the MS model experimental autoimmune encephalomyelitis (EAE). This redox change became already apparent during the preclinical phase of EAE prior to CNS infiltration of inflammatory cells. Upon clinical EAE development, mitochondria oxidation remained detectable and was associated with a significant impairment in organelle density and morphology. These alterations correlated with the proximity of ODCs to inflammatory lesions containing activated microglia/macrophages. During the chronic progression of EAE, ODC mitochondria maintained an altered morphology, but their oxidant levels decreased to levels observed in healthy mice. Taken together, our study implicates oxidative stress in ODC mitochondria as a novel pre-clinical sign of MS-like inflammation and demonstrates that evolving redox and morphological changes in mitochondria accompany ODC dysfunction during neuroinflammation.

The role of SLC transporters for brain health and disease

The brain exchanges nutrients and small molecules with blood via the blood-brain barrier (BBB). Approximately 20% energy intake for the body is consumed by the brain. Glucose is known for its critical roles for energy production and provides substrates for biogenesis in neurons. The brain takes up glucose via glucose transporters GLUT1 and 3, which are expressed in several neural cell types. The brain is also equipped with various transport systems for acquiring amino acids, lactate, ketone bodies, lipids, and cofactors for neuronal functions. Unraveling the mechanisms by which the brain takes up and metabolizes these nutrients will be key in understanding the nutritional requirements in the brain. This could also offer opportunities for therapeutic interventions in several neurological disorders. For instance, emerging evidence suggests a critical role of lactate as an alternative energy source for neurons. Neuronal cells express monocarboxylic transporters to acquire lactate. As such, treatment of GLUT1-deficient patients with ketogenic diets to provide the brain with alternative sources of energy has been shown to improve the health of the patients. Many transporters are present in the brain, but only a small number has been characterized. In this review, we will discuss about the roles of solute carrier (SLC) transporters at the blood brain barrier (BBB) and neural cells, in transport of nutrients and metabolites in the brain.

Nitrosative Stress Molecules in Multiple Sclerosis: A Meta-Analysis

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system of unknown etiology. As it is still a diagnosis of exclusion, there is an urgent need for biomarkers supporting its diagnosis. Increasing evidence suggests that nitrosative stress may play a pivotal role in the pathogenesis of MS. However, previous reports supporting the role of nitrosative stress molecules as disease biomarkers are inconsistent overall. We therefore systematically analyzed the existing literature to compare the serum and cerebrospinal fluid (CSF) levels of nitrite/nitrate in MS patients with those in patients with noninflammatory other neurological diseases (NIOND) and healthy controls (HC), respectively. We searched the PubMed database and included original articles investigating nitrite/nitrate levels in MS patients and NIOND patients or HC based on predefined selection criteria. Effect sizes were estimated by the standardized mean difference using a random effects model. Our results suggest that MS is associated with higher nitrite/nitrate levels within the CSF compared with patients with NIOND (SMD of 1.51; 95% CI: 0.72, 2.30; p = 0.0008). Likewise, nitrite/nitrate in the CSF of MS patients trends towards increased levels compared with those of HC but does not reach statistical significance (SMD of 3.35; 95% CI: −0.48, 7.19; p = 0.07). Measurement of nitrite/nitrate in the CSF might be a valuable tool facilitating the differentiation of MS and NIOND. Further studies with more homogeneous study criteria are needed to corroborate this hypothesis.

Effects of photobiomodulation on interleukin-10 and nitrites in individuals with relapsing-remitting multiple sclerosis - Randomized clinical trial

Objective

Investigate the effects of photobiomodulation (PBM) on the expression of IL-10 and nitrites in individuals with Relapsing-Remitting multiple sclerosis (MS), as these biomarkers play a fundamental role in the physiopathology of the disease. The modulation of IL-10 and nitrites through treatment with PBM may be a novel treatment modality for MS.

Methods

A randomized, uncontrolled, clinical trial was conducted involving 14 individuals with a diagnosis of Relapsing-Remitting MS and a score of up to 6.0 on the Expanded Disability Status Scale (EDSS).

The participants were randomized to two groups

Group 1 –PBM in the sublingual region; Group 2 –PBM over the radial artery. Irradiation was administered with a wavelength of 808 nm and output power of 100 mW for 360 seconds twice a week, totaling 24 sessions. Peripheral blood was analyzed for the determination of serum levels of IL-10 and nitrites.

Results

After treatment with PBM, the expression of IL-10 increased in both the sublingual group (pre-treatment: 2.8 ± 1.4 pg/ml; post-treatment: 8.3 ± 2.4 pg/ml) and the radial artery group (pre-treatment: 2.7 pg/ml ± 1.4; post-treatment: 11.7 ± 3.8 pg/ml). In contrast, nitrite levels were not modulated in the sublingual group (pre-treatment: 65 ± 50 nmol/mg protein; post-treatment: 51 ± 42 nmol/mg protein) or the radial artery group (pre-treatment: 51 ± 16 nmol/mg protein; post-treatment: 42 ± 7 nmol/mg protein).

Conclusion

Treatment with PBM positively modulated the expression of IL-10 but had no effect on nitrite levels. Further studies should be conducted with a larger sample and a control group, as PBM may be a promising complementary treatment for the management of MS.

This trial is registered at ClinicalTrials.gov. Identifier: NCT03360487.

Monocarboxylate Transporter 1 in Brain Diseases and Cancers

Background:

Monocarboxylate Transporter 1 (MCT1), an important membrane transport protein, mediates the translocation of monocarboxylates together with protons across biological membranes. Due to its pathological significance, MCT1 plays an important role in the progression of some diseases, such as brain diseases and cancers.

Methods:

We summarize the general description of MCT1 and provide a comprehensive understanding of the role of MCT1 in brain diseases and cancers. Furthermore, this review discusses the opportunities and challenges of MCT1- targeting drug-delivery systems in the treatment of brain diseases and cancers.

Results:

In the brain, loss of MCT1 function is associated with pathologies of degeneration and injury of the nervous system. In tumors, MCT1 regulates the activity of signaling pathways and controls the exchange of monocarboxylates in aerobic glycolysis to affect tumor metabolism, proliferation and invasion. Meanwhile, MCT1 also acts as a good biomarker for the prediction and diagnosis of cancer progressions.

Conclusion:

MCT1 is an attractive transporter in brain diseases and cancers. Moreover, the development of MCT1- based small molecule drugs and MCT1 inhibitors in the clinic is promising. This review systematically summarizes the basic characteristics of MCT1 and its role in brain diseases and cancers, laying the foundation for further research on MCT1.

Astrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis: Star-shaped cells illuminating the darkness of CNS autoimmunity

Neuropathology in the human autoimmune disease multiple sclerosis (MS) is considered to be mediated by autoreactive leukocytes, such as T cells, B cells, and macrophages. However, the inflammation and tissue damage in MS and its animal model experimental autoimmune encephalomyelitis (EAE) is also critically regulated by astrocytes, the most abundant cell population in the central nervous system (CNS). Under physiological conditions, astrocytes are integral to the development and function of the CNS, whereas in CNS autoimmunity, astrocytes influence the pathogenesis, progression, and recovery of the diseases. In this review, we summarize recent advances in astrocytic functions in the context of MS and EAE, which are categorized into two opposite aspects, one being detrimental and the other beneficial. Inhibition of the detrimental functions and/or enhancement of the beneficial functions of astrocytes might be favorable for the treatment of MS.

Nitric oxide might be an inducing factor in cognitive impairment in Alzheimer's disease via downregulating the monocarboxylate transporter 1

Alzheimer's disease (AD) is a typical neurodegenerative disease in central nervous system (CNS). Generally speaking, patients with severe AD are often accompanied with cognitive impairment. Oligodendrocytes (OLs) are myelin-forming cells in CNS, and myelin injury potentially has something to do with the cognitive impairment in AD. Based on the previous experimental studies, it has been recognized that nitric oxide (NO), as a signaling molecule, might have an influence on the axon and myelin by affecting the energy transport mechanism of OLs through monocarboxylate transporter 1 (MCT1). Interestingly, a novel model of cell signaling----axo-myelinic synapse (AMS) has been put forward. In the context of this model, chances are that a new way is established in which NO can influence the pathogenesis of AD by down-regulating the expression of MCT1. As a consequence, it may provide attractive prospective and underlying drug targeting effects for the treatment of AD.

Eyes are mirror of the brain: comparison of multiple sclerosis patients and healthy controls using OCT

Objective: To evaluate the thickness of choroid and retinal nerve fiber layer (RNFL) in multiple sclerosis (MS) patients with and without optic neuritis using enhanced depth imaging optical coherence tomography (EDI-OCT). Methods: In this cross-sectional study, both eyes of 52 MS patients [n = 104 eyes; 62 eyes of MS patients without optic neuritis (MS-NON) and 42 eyes of MS patients with optic neuritis (MS-ON)] and only one eye of 36 healthy control subjects (n = 36 eyes) were evaluated. Complete ophthalmologic examination and EDI-OCT scanning were completed for all participants. Choroidal thickness measurements were executed at three different points. Results: Choroidal thickness measurements were similar between MS patients and healthy control subjects. However, the mean subfoveal choroidal thickness was increased significantly in MS-ON group (399.13 ± 82.91 μm) compared to MS-NON group (342.71 ± 82.46 μm; p = 0.004). Mean RNFL thickness was significantly reduced in MS patients (90.42 ± 13.31 μm) compared to healthy controls (101.18 ± 10.75 μm; p < 0.001). Moreover, temporal RNFL thickness was significantly thinner in MS-ON group (54 ± 14.50 μm) than MS-NON group (62.15 ± 15.88 μm; p = 0.01). In MS patients, temporal RNFL thickness was correlated with both Expanded Disability Status Score (r = 0.383; p < 0.001) and longer disease duration (r=-0.202; p = 0.04). Conclusion: The results of the present study suggest that RNFL thickness can be used as an important parameter while following up with MS patients. However, more studies using EDI-OCT are required with larger MS patient groups and automated method.

MicroRNA-219 Inhibits Proliferation and Induces Differentiation of Oligodendrocyte Precursor Cells after Contusion Spinal Cord Injury in Rats

MicroRNA-219 (miR-219) regulates the proliferation and differentiation of oligodendrocyte precursor cells (OPCs) during central nervous system (CNS) development. OPCs only differentiate into oligodendrocytes (OLs) in the healthy CNS, but can generate astrocytes (As) after injury. We hypothesized that miR-219 may modulate OPC proliferation and differentiation in a cervical C5 contusion spinal cord injury (SCI) model. After injury, we observed a decrease in the miR-219 level and quantity of OLs and an increase in the number of OPCs and As. Silencing of miR-219 by its antagomir in vivo produced similar results, but of greater magnitude. Overexpression of miR-219 by its agomir in vivo increased the number of OLs and suppressed generation of OPCs and As. Luxol fast blue staining confirmed that SCI caused demyelination and that the extent of demyelination was attenuated by miR-219 overexpression, but aggravated by miR-219 reduction. Monocarboxylate transporter 1 (MCT-1) may be implicated in the regulation of OPC proliferation and differentiation mediated by miR-219 following contusion SCI. Collectively, our data suggest that miR-219 may mediate SCI-induced OPC proliferation and differentiation, and MCT-1 may participate in this process as a target of miR-219.

Can We Design a Nogo Receptor-Dependent Cellular Therapy to Target MS?

The current landscape of therapeutics designed to treat multiple sclerosis (MS) and its pathological sequelae is saturated with drugs that modify disease course and limit relapse rates. While these small molecules and biologicals are producing profound benefits to patients with reductions in annualized relapse rates, the repair or reversal of demyelinated lesions with or without axonal damage, remains the principle unmet need for progressive forms of the disease. Targeting the extracellular pathological milieu and the signaling mechanisms that drive neurodegeneration are potential means to achieve neuroprotection and/or repair in the central nervous system of progressive MS patients. The Nogo-A receptor-dependent signaling mechanism has raised considerable interest in neurological disease paradigms since it can promulgate axonal transport deficits, further demyelination, and extant axonal dystrophy, thereby limiting remyelination. If specific therapeutic regimes could be devised to directly clear the Nogo-A-enriched myelin debris in an expedited manner, it may provide the necessary CNS environment for neurorepair to become a clinical reality. The current review outlines novel means to achieve neurorepair with biologicals that may be directed to sites of active demyelination.

Insights in pathogenesis of multiple sclerosis: nitric oxide may induce mitochondrial dysfunction of oligodendrocytes

Demyelinating diseases, such as multiple sclerosis (MS), are kinds of common diseases in the central nervous system (CNS), and originated from myelin loss and axonal damage. Oligodendrocyte dysfunction is the direct reason of demyelinating lesions in the CNS. Nitric oxide (NO) plays an important role in the pathological process of demyelinating diseases. Although the neurotoxicity of NO is more likely mediated by peroxynitrite rather than NO itself, NO can impair oligodendrocyte energy metabolism through mediating the damaging of mitochondrial DNA, mitochondrial membrane and mitochondrial respiratory chain complexes. In the progression of MS, NO can mainly mediate demyelination, axonal degeneration and cell death. Hence, in this review, we extensively discuss endangerments of NO in oligodendrocytes (OLs), which is suggested to be the main mediator in demyelinating diseases, e.g. MS. We hypothesize that NO takes part in MS through impairing the function of monocarboxylate transporter 1, especially causing axonal degeneration. Then, it further provides a new insight that NO for OLs may be a reliable therapeutic target to ameliorate the course of demyelinating diseases.