The link between excitotoxic oligodendroglial death and demyelinating diseases

Bridging the gap: Prenatal nutrition, myelination, and schizophrenia etiopathogenesis

Schizophrenia (SZ) is a complex mental illness characterized by disturbances in thinking, emotionality, and behavior, significantly impacting the quality of life for individuals affected and those around them. The etiology of SZ involves intricate interactions between genetic and environmental factors, although the precise mechanisms remain incompletely understood. Genetic predisposition, neurotransmitter dysregulation (particularly involving dopamine and serotonin), and structural brain abnormalities, including impaired prefrontal cortex function, have been implicated in SZ development. However, increasing evidence reveals the role of environmental factors, such as nutrition, during critical periods like pregnancy and lactation. Epidemiological studies suggest that early malnutrition significantly increases the risk of SZ symptoms manifesting in late adolescence, a crucial period coinciding with peak myelination and brain maturation. Prenatal undernutrition may disrupt myelin formation, rendering individuals more susceptible to SZ pathology. This review explores the potential relationship between prenatal undernutrition, myelin alterations, and susceptibility to SZ. By delineating the etiopathogenesis, examining genetic and environmental factors associated with SZ, and reviewing the relationship between SZ and myelination disorders, alongside the impact of malnutrition on myelination, we aim to examine how malnutrition might be linked to SZ by altering myelination processes, which contribute to increasing the understanding of SZ etiology and help identify targets for intervention and management.

Neuroprotective effect of GJ-4 against cognitive impairments in vascular dementia by improving white matter damage

BACKGROUND

White matter lesions (WMLs) are increasingly linked to the pathological process of chronic vascular dementia (VaD). An effective crocins fraction extracted from Gardenia Fructus, GJ-4, has been shown to improve cognitive function in several Alzheimer's disease models and VaD models.

OBJECTIVES

To explore the potential mechanisms of GJ-4 on WMLs in a chronic VaD mouse model.

METHODS

The chronic VaD mouse model was established, and WMLs were characterized by cerebral blood flow (CBF), behavioral tests, LFB staining, and immunohistochemistry. The anti-oxidative effect of GJ-4 was validated by examining biochemical parameters (SOD, MDA, and GSH) and the Keap1-Nrf2/HO-1 pathway. The impact of GJ-4 on lipid metabolism in WM was further investigated through lipidomic analysis.

RESULTS

GJ-4 significantly attenuated cognitive impairments and improved the CBF of BCAS (bilateral common carotid artery stenosis)-induced mice. Mechanism research showed that GJ-4 could enhance cognition by promoting the repair of WMLs by inhibiting oxidative stress. Furthermore, GJ-4 treatment significantly reduced chronic cerebral hypoperfusion (CCH)-induced WMLs via improving lipid metabolism disorder in the WM.

CONCLUSION

This research has provided valuable insights into the significance of WMLs in CCH-induced VaD and underscored the potential of GJ-4 as a therapeutic agent for improving cognitive function by targeting WMLs. These findings suggest that GJ-4 is a promising candidate for the treatment of VaD.

Citrullinated isomer of myelin basic protein can induce inflammatory responses in astrocytes

Purpose

During the course of demyelinating inflammatory diseases, myelin-derived proteins, including myelin basic protein(MBP), are secreted into extracellular space. MBP shows extensive post-translational modifications, including deimination/citrullination. Deiminated MBP is structurally less ordered, susceptible to proteolytic attack, and more immunogenic than unmodified MBP. This study investigated the effect of the deiminated/citrullinated isomer of MBP(C8) and the unmodified isomer of MBP(C1) on cultured primary astrocytes.

Methods

MBP charge isomers were isolated/purified from bovine brain. Primary astrocyte cultures were prepared from the 2-day-old Wistar rats. For evaluation of glutamate release/uptake a Fluorimetric glutamate assay was used. Expression of peroxisome proliferator-activated receptor-gamma(PPAR-γ), excitatory amino acid transporter 2(EAAT2), the inhibitor of the nuclear factor kappa-B(ikB) and high mobility group-B1(HMGB1) protein were assayed by Western blot analysis. IL-17A expression was determined in cell medium by ELISA.

Results

We found that MBP(C8) and MBP(C1) acted differently on the uptake/release of glutamate in astrocytes: C1 increased glutamate uptake and did not change its release, whereas C8 decreased glutamate release but did not change its uptake. Both isomers increased the expression of PPAR-γ and EAAT2 to the same degree. Western blots of cell lysates revealed decreased expression of ikB and increased expression of HMGB1 proteins after treatment of astrocytes by C8. Moreover, C8-treated cells released more nitric oxide and proinflammatory IL-17A than C1-treated cells.

Conclusions

These data suggest that the most immunogenic deiminated isomer C8, in parallel to the decreases in glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B(NF-kB).

Summary statement

The most modified-citrullinated myelin basic protein charge isomer decreases glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B in astrocytes.

Testosterone Reduces Myelin Abnormalities in the Wobbler Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motoneuron degenerative disease that is associated with demyelination. The Wobbler (WR) mouse exhibits motoneuron degeneration, gliosis and myelin deterioration in the cervical spinal cord. Since male WRs display low testosterone (T) levels in the nervous system, we investigated if T modified myelin-relative parameters in WRs in the absence or presence of the aromatase inhibitor, anastrozole (A). We studied myelin by using luxol-fast-blue (LFB) staining, semithin sections, electron microscopy and myelin protein expression, density of IBA1+ microglia and mRNA expression of inflammatory factors, and the glutamatergic parameters glutamine synthetase (GS) and the transporter GLT1. Controls and WR + T showed higher LFB, MBP and PLP staining, lower g-ratios and compact myelin than WRs and WR + T + A, and groups showing the rupture of myelin lamellae. WRs showed increased IBA1+ cells and mRNA for CD11b and inflammatory factors (IL-18, TLR4, TNFαR1 and P2Y12R) vs. controls or WR + T. IBA1+ cells, and CD11b were not reduced in WR + T + A, but inflammatory factors' mRNA remained low. A reduction of GS+ cells and GLT-1 immunoreactivity was observed in WRs and WR + T + A vs. controls and WR + T. Clinically, WR + T but not WR + T + A showed enhanced muscle mass, grip strength and reduced paw abnormalities. Therefore, T effects involve myelin protection, a finding of potential clinical translation.

Mechanisms Governing Oligodendrocyte Viability in Multiple Sclerosis and Its Animal Models

Multiple sclerosis (MS) is a chronic autoimmune inflammatory demyelinating disease of the central nervous system (CNS), which is triggered by an autoimmune assault targeting oligodendrocytes and myelin. Recent research indicates that the demise of oligodendrocytes due to an autoimmune attack contributes significantly to the pathogenesis of MS and its animal model experimental autoimmune encephalomyelitis (EAE). A key challenge in MS research lies in comprehending the mechanisms governing oligodendrocyte viability and devising therapeutic approaches to enhance oligodendrocyte survival. Here, we provide an overview of recent findings that highlight the contributions of oligodendrocyte death to the development of MS and EAE and summarize the current literature on the mechanisms governing oligodendrocyte viability in these diseases.

Memantine Improves the Disturbed Glutamine and γ-Amino Butyric Acid Homeostasis in the Brain of Rats Subjected to Experimental Autoimmune Encephalomyelitis

Glutamine (Gln), glutamate (Glu), and γ-amino butyric acid (GABA) are essential amino acids for brain metabolism and function. Astrocyte-derived Gln is the precursor for the two most important neurotransmitters in the central nervous system (CNS), which are the excitatory neurotransmitter Glu and the inhibitory neurotransmitter GABA. In addition to their roles in neurotransmission, these amino acids can be used as alternative substrates in brain metabolism that enable metabolic coupling between astrocytes and neurons in the glutamate-glutamine cycle (GGC). The disturbed homeostasis of these amino acids within the tripartite synapse may be involved in the pathogenesis of various neurological diseases. Interactions between astrocytes and neurons in terms of Gln, Glu, and GABA homeostasis were studied in different phases of experimental allergic encephalomyelitis (EAE) in Lewis rats. The results of the study showed a decrease in the transport (uptake and release) of Gln and GABA in both neuronal and astrocyte-derived fractions. These effects were fully or partially reversed when the EAE rats were treated with memantine, a NMDA receptor antagonist. Changes in the expression and activity of selected glutamine/glutamate metabolizing enzymes, such as glutamine synthase (GS) and phosphate-activated glutaminase (PAG), which were affected by memantine, were observed in different phases of EAE. The results suggested perturbed homeostasis of Gln, Glu, and GABA during EAE, which may indicate alterations in neuron-astrocyte coupling and dysfunction of the tripartite synapse. Memantine appears to partially regulate the disturbed relationships between Gln, Glu, and GABA.

Connecting Neurobiological Features with Interregional Dysconnectivity in Social-Cognitive Impairments of Schizophrenia

Schizophrenia (SZ) is a devastating psychiatric disorder affecting about 1% of the world's population. Social-cognitive impairments in SZ prevent positive social interactions and lead to progressive social withdrawal. The neurobiological underpinnings of social-cognitive symptoms remain poorly understood, which hinders the development of novel treatments. At the whole-brain level, an abnormal activation of social brain regions and interregional dysconnectivity within social-cognitive brain networks have been identified as major contributors to these symptoms. At the cellular and subcellular levels, an interplay between oxidative stress, neuroinflammation and N-methyl-D-aspartate receptor hypofunction is thought to underly SZ pathology. However, it is not clear how these molecular processes are linked with interregional dysconnectivity in the genesis of social-cognitive symptoms. Here, we aim to bridge the gap between macroscale (connectivity analyses) and microscale (molecular and cellular mechanistic) knowledge by proposing impaired myelination and the disinhibition of local microcircuits as possible causative biological pathways leading to dysconnectivity and abnormal activity of the social brain. Furthermore, we recommend electroencephalography as a promising translational technique that can foster pre-clinical drug development and discuss attractive drug targets for the treatment of social-cognitive symptoms in SZ.

Epilepsy and Autism Spectrum Disorder (ASD): The Underlying Mechanisms and Therapy Targets Related to Adenosine

Epilepsy and autism spectrum disorder (ASD) are highly mutually comorbid, suggesting potential overlaps in genetic etiology, pathophysiology, and neurodevelopmental abnormalities. Adenosine, an endogenous anticonvulsant and neuroprotective neuromodulator of the brain, has been proved to affect the process of epilepsy and ASD. On the one hand, adenosine plays a crucial role in preventing the progression and development of epilepsy through adenosine receptordependent and -independent ways. On the other hand, adenosine signaling can not only regulate core symptoms but also improve comorbid disorders in ASD. Given the important role of adenosine in epilepsy and ASD, therapeutic strategies related to adenosine, including the ketogenic diet, neuromodulation therapy, and adenosine augmentation therapy, have been suggested for the arrangement of epilepsy and ASD. There are several proposals in this review. Firstly, it is necessary to further discuss the relationship between both diseases based on the comorbid symptoms and mechanisms of epilepsy and ASD. Secondly, it is important to explore the role of adenosine involved in epilepsy and ASD. Lastly, potential therapeutic value and clinical approaches of adenosine-related therapies in treating epilepsy and ASD need to be emphasized.

The biochemical basis of neurodegenerative disease: The role of immunoexcitoxicity and ways to possibly attenuate it

There is growing evidence that inflammation secondary to immune activation is intimately connected to excitotoxicity. We now know that most peripheral tissues contain fully operational glutamate receptors. While most of the available research deals with excitotoxicity in central nervous system (CNS) tissues, this is no longer true. Even plant has been found to contain glutamate receptors. Most of the immune cells, including mask cells, contain glutamate receptors. The receptors are altered by inflammation, both chemokine and cytokines. A host of new diseases have been found that are caused by immunity to certain glutamate receptors, as we see with Rasmussen's encephalitis. In this paper, I try to explain this connection and possible ways to reduce or even stop the reaction.

Insights into White Matter Defect in Huntington's Disease

Huntington's disease (HD) is an autosomal-dominant inherited progressive neurodegenerative disorder. It is caused by a CAG repeat expansion in the Huntingtin gene that is translated to an expanded polyglutamine (PolyQ) repeat in huntingtin protein. HD is characterized by mood swings, involuntary movement, and cognitive decline in the late disease stage. HD patients often die 15-20 years after disease onset. Currently, there is no cure for HD. Due to the striking neuronal loss in HD, most studies focused on the investigation of the predominantly neuronal degeneration in specific brain regions. However, the pathology of the white matter area in the brains of HD patients was also reported by clinical imaging studies, which showed white matter abnormalities even before the clinical onset of HD. Since oligodendrocytes form myelin sheaths around the axons in the brain, white matter lesions are likely attributed to alterations in myelin and oligodendrocyte-associated changes in HD. In this review, we summarized the evidence for white matter, myelin, and oligodendrocytes alterations that were previously observed in HD patients and animal models. We also discussed potential mechanisms for white matter changes and possible treatment to prevent glial dysfunction in HD.

GABA Receptor Agonists Protect From Excitotoxic Damage Induced by AMPA in Oligodendrocytes

Oligodendrocytes are the myelin forming cells of the central nervous system, and their vulnerability to excitotoxicity induced by glutamate contributes to the pathogenesis of neurological disorders including brain ischemia and neurodegenerative diseases, such as multiple sclerosis. In addition to glutamate receptors, oligodendrocytes express GABA receptors (GABAR) that are involved in their survival and differentiation. The interactions between glutamate and GABAergic systems are well documented in neurons, under both physiological and pathological conditions, but this potential crosstalk in oligodendrocytes has not been studied in depth. Here, we evaluated the protective effect of GABAR agonists, baclofen (GABAB) and muscimol (GABAA), against AMPA-induced excitotoxicity in cultured rat oligodendrocytes. First, we observed that both baclofen and muscimol reduced cell death and caspase-3 activation after AMPA insult, proving their oligoprotective potential. Interestingly, analysis of the cell-surface expression of calcium-impermeable GluR2 subunits in oligodendrocytes revealed that GABAergic agonists significantly reverted GluR2 internalization induced by AMPA. We determined that baclofen and muscimol also impaired AMPA-induced intracellular calcium increase and subsequent mitochondrial membrane potential alteration, ROS generation, and calpain activation. However, AMPA-triggered activation of Src, Akt, JNK and CREB was not affected by baclofen or muscimol. Overall, our results suggest that GABAR activation initiates alternative molecular mechanisms that attenuate AMPA-mediated apoptotic excitotoxicity in oligodendrocytes by interfering with expression of GluR subunits in membranes and with calcium-dependent intracellular signaling pathways. Together, these findings provide evidence of GABAR agonists as potential oligodendroglial protectants in central nervous system disorders.

Linking Plasma Amyloid Beta and Neurofilament Light Chain to Intracortical Myelin Content in Cognitively Normal Older Adults

Evidence suggests that lightly myelinated cortical regions are vulnerable to aging and Alzheimer’s disease (AD). However, it remains unknown whether plasma markers of amyloid and neurodegeneration are related to deficits in intracortical myelin content, and whether this relationship, in turn, is associated with altered patterns of resting-state functional connectivity (rs-FC). To shed light into these questions, plasma levels of amyloid-β fragment 1–42 (Aβ_1–42) and neurofilament light chain (NfL) were measured using ultra-sensitive single-molecule array (Simoa) assays, and the intracortical myelin content was estimated with the ratio T1-weigthed/T2-weighted (T1w/T2w) in 133 cognitively normal older adults. We assessed: (i) whether plasma Aβ_1–42 and/or NfL levels were associated with intracortical myelin content at different cortical depths and (ii) whether cortical regions showing myelin reductions also exhibited altered rs-FC patterns. Surface-based multiple regression analyses revealed that lower plasma Aβ_1–42 and higher plasma NfL were associated with lower myelin content in temporo-parietal-occipital regions and the insular cortex, respectively. Whereas the association with Aβ_1–42 decreased with depth, the NfL-myelin relationship was most evident in the innermost layer. Older individuals with higher plasma NfL levels also exhibited altered rs-FC between the insula and medial orbitofrontal cortex. Together, these findings establish a link between plasma markers of amyloid/neurodegeneration and intracortical myelin content in cognitively normal older adults, and support the role of plasma NfL in boosting aberrant FC patterns of the insular cortex, a central brain hub highly vulnerable to aging and neurodegeneration.

Transdiagnostic role of glutamate and white matter damage in neuropsychiatric disorders: A Systematic Review

Neuropsychiatric disorders including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ) have been considered distinct categories of diseases despite their overlapping characteristics and symptomatology. We aimed to provide an in-depth review elucidating the role of glutamate/Glx and white matter (WM) abnormalities in these disorders from a transdiagnostic perspective. The PubMed online database was searched for studies published between 2010 and 2021. After careful screening, 401 studies were included. The findings point to decreased levels of glutamate in the Anterior Cingulate Cortex in both SZ and BD, whereas Glx is elevated in the Hippocampus in SZ and MDD. With regard to WM abnormalities, the Corpus Callosum and superior Longitudinal Fascicle were the most consistently identified brain regions showing decreased fractional anisotropy (FA) across all the reviewed disorders, except GAD. Additionally, the Uncinate Fasciculus displayed decreased FA in all disorders, except OCD. Decreased FA was also found in the inferior Longitudinal Fasciculus, inferior Fronto-Occipital Fasciculus, Thalamic Radiation, and Corona Radiata in SZ, BD, and MDD. Decreased FA in the Fornix and Corticospinal Tract were found in BD and SZ patients. The Cingulum and Anterior Limb of Internal Capsule exhibited decreased FA in MDD and SZ patients. The results suggest a gradual increase in severity from GAD to SZ defined by the number of brain regions with WM abnormality which may be partially caused by abnormal glutamate levels. WM damage could thus be considered a potential marker of some of the main neuropsychiatric disorders.

An integrated systems-level model of the toxicity of brevetoxin based on high-resolution magic-angle spinning nuclear magnetic resonance (HRMAS NMR) metabolic profiling of zebrafish embryos

Brevetoxins (PbTx) are a well-recognized group of neurotoxins associated with harmful algal blooms, and specifically recurrent "Florida Red Tides," in marine waters that are linked to impacts on both human and ecosystem health including well-documented "fish kills" and marine mammal mortalities in affected coastal waters. Understanding mechanisms and pathways of PbTx toxicity enables identification of relevant biomarkers to better understand these environmental impacts, and improve monitoring efforts, in relation to this toxin. Toward a systems-level understanding of toxicity, and identification of potential biomarkers, high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) was utilized for metabolic profiling of zebrafish (Danio rerio) embryos, as an established toxicological model, exposed to PbTx-2 (the most common congener in marine waters). Metabolomics studies were, furthermore, complemented by an assessment of the toxicity of PbTx-2 in embryonic stages of zebrafish and mahi-mahi (Coryphaena hippurus), the latter representing an ecologically and geographically relevant marine species of fish, which identified acute embryotoxicity at environmentally relevant (i.e., parts-per-billion) concentrations in both species. HRMAS NMR analysis of intact zebrafish embryos exposed to sub-lethal concentrations of PbTx-2 afforded well-resolved spectra, and in turn, identification of 38 metabolites of which 28 were found to be significantly altered, relative to controls. Metabolites altered by PbTx-2 exposure specifically included those associated with (1) neuronal excitotoxicity, as well as associated neural homeostasis, and (2) interrelated pathways of carbohydrate and energy metabolism. Metabolomics studies, thereby, enabled a systems-level model of PbTx toxicity which integrated multiple metabolic, molecular and cellular pathways, in relation to environmentally relevant concentrations of the toxin, providing insight to not only targets and mechanisms, but potential biomarkers pertinent to environmental risk assessment and monitoring strategies.

Histopathological effects of topical coenzyme q 10 + Vit E TPGS in experimental ischemic optic neuropathy

We aimed to create a mechanical optic nerve damage model in rats and to investigate the neuroprotective effects of topical Coenzyme Q10 + Vitamin E TPGS (CoQ10+Vit E) molecule on retinal ganglion cells. In our study, 30 eyes of 20 male Wistar rats were used. Three groups, each consisting of 10 eyes, were formed as control, experimental, and treatment groups. The control group was used to test the formation of optic nerve damage. Topical CoQ10 + Vit E TPGS solution was applied to the rats in the treatment group, one drop twice a day for 3 weeks. On the other hand, physiological drops were applied to the experimental group 2 times a day for 3 weeks. After 3 weeks, the optic nerves of the rats were dissected and examined histopathologically. In electron microscopic examination of the treatment group, it was noted that the myelin sheath in the majority of myelinated nerve fibers and the normal structures of mitochondria, neurotubules, and neurofilaments in the axoplasm were preserved. It was observed that the oligodendrocytes surrounded the myelinated axons. In the experimental group, significant degenerative changes were observed in myelinated nerve fibers in many areas. The number of myelinated axons was significantly increased in the treatment group compared to the experimental group (p = .0028). In the light of the data obtained, the neuroprotective effect of the topically used CoQ10 + Vit E TPGS molecule was found to be histopathologically effective in our experimental study.Abbreviations: NAAION: Nonarteritic anterior ischemic optic neuropathy; CoQ10: Coenzyme q10; CG: Control group; EG: Experimental group; TG: Treatment group.

Cuprizone-induced Demyelination in Mouse Brain is not due to Depletion of Copper

The cuprizone (CPZ) model allows the study of the biochemical processes underlying nonautoimmune-mediated demyelination, remyelination, and chronic white matter disease progression. CPZ is a copper (Cu) chelator that chiefly causes oligodendrocyte apoptosis in the corpus callosum and cerebellum when administered in the mouse diet. While disruption of Cu homeostasis is known to cause neurodegeneration (as is observed in Wilson’s and Menkes disease), no consensus exists to date as to CPZ’s mechanism of action. We sought to determine whether CPZ-induced pathology is due to Cu depletion as is generally believed. Cu supplementation in chow, in stoichiometric excess to the added CPZ, did not reduce CPZ-induced demyelination in C57Bl/6 mice. Moreover, equivalent doses of other known Cu chelators neocuproine and D-penicillamine (D-Pen) failed to induce central nervous system (CNS) demyelination. Since administration of D-Pen in the treatment of Wilson’s disease can induce hypocupremia, we next sought to recreate penicillamine-induced Cu deficiency to compare with purported CPZ-induced Cu deficiency. The resulting clinical phenotype and histopathology were unlike that of CPZ. D-Pen-treated mice exhibited digit paralysis, tail flaccidity, subcutaneous hemorrhaging, and optic and sciatic neuropathy, all of which were prevented with Cu supplementation. No demyelination of the corpus callosum or cerebellum was observed, even with D-Pen doses tenfold higher than CPZ. Intriguingly, addition of D-Pen to the CPZ diet paradoxically prevented demyelination in a dose-dependent manner.

Prophylactic exposure to oral riluzole reduces the clinical severity and immune-related biomarkers of experimental autoimmune encephalomyelitis

Glutamate-mediated excitotoxicity and immune cell infiltration are hallmarks of multiple sclerosis. The glutamate release inhibitor, riluzole (RIL), has been shown to attenuate the clinical symptoms of experimental autoimmune encephalomyelitis (EAE) in mice, but an association between glutamate excitotoxicity and the progression of MOG35-55-induced EAE has not been well defined. This study investigated the effects of prophylactic and chronic oral RIL on the clinical severity of EAE. Prophylactic+chronic RIL reduced the presence of inflammatory infiltrates, altered GFAP and Foxp3, and attenuated disease severity. These findings indicate a need to delineate the distinct role of glutamate in EAE symptomatology.

Morroniside protects OLN-93 cells against H2O2-induced injury through the PI3K/Akt pathway-mediated antioxidative stress and antiapoptotic activities

Neurodegenerative disorders, including spinal cord injury (SCI), result in oxidative stress-induced cell damage. Morroniside (MR), a major active ingredient of the Chinese herb Shan Zhu Yu, has been shown to ameliorate oxidative stress and inflammatory response. Our previous study also confirmed that morroniside protects SK-N-SH cell line (human neuroblastoma cells) against oxidative impairment. However, it remains unclear whether MR also plays a protective role for oligodendrocytes that are damaged following SCI. The present study investigated the protective effects of MR against hydrogen peroxide (H₂O₂)-induced cell death in OLN-93 cells. MR protected OLN-93 cells from H₂O₂-induced injury, attenuated H₂O₂-induced increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and blocked the reduction of mitochondrial membrane potential (MMP) induced by H2O2. MR enhanced the activity of the antioxidant enzyme superoxide dismutase (SOD) and suppressed H₂O₂-induced downregulation of the antiapoptotic protein Bcl-2 and activation of the proapoptotic protein caspase-3. Finally, we found that LY294002, a specific inhibitor of the PI3K/Akt pathway, inhibited the protective effect of MR against H₂O₂-induced OLN-93 cell injury in the MTT and TUNEL assays. LY294002 also inhibited the expression of SOD and Bcl-2, and increased the expression of iNOS and c-caspase-3 induced by MR treatment. MR exerts protective effects against H₂O₂-induced OLN-93 cell injury through the PI3K/Akt signaling pathway-mediated antioxidative stress and antiapoptotic activities. MR may provide a potential strategy for SCI treatment or other related neurodegeneration.

Metabolomic Biomarkers of Multiple Sclerosis: A Systematic Review

Background

Magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) analysis, and the McDonald’s clinical criteria are currently utilized tools in diagnosing multiple sclerosis. However, a more conclusive, consistent, and efficient way of diagnosing multiple sclerosis (MS) is yet to be discovered. A potential biomarker, discovered using advances in high-throughput sequencing such as nuclear magnetic resonance (NMR) spectroscopy and other “Omics”-based techniques, may make diagnosis and prognosis more reliable resulting in a more personalized and targeted treatment regime and improved outcomes. The aim of this review was to systematically search the literature for potential biomarkers from any bodily fluid that could consistently and accurately diagnose MS and/or indicate disease progression.

Methods

A systematic literature review of EMBASE, PubMed (MEDLINE), The Cochrane Library, and CINAHL databases produced over a thousand potential studies. Inclusion criteria stated studies with potential biomarker outcomes for people with MS were to be included in the review. Studies were limited to those with human participants who had a clinically defined diagnosis of MS and published in English, with no limit placed on date of publication or the type of bodily fluid sampled.

Results

A total of 1,805 studies were recorded from the literature search. A total of 1,760 studies were removed based on their abstract, with a further 18 removed after considering the full text. A total of 30 studies were considered relevant and had their data retrieved and analyzed. Due to the heterogeneity of focus and results from the refined studies, a narrative synthesis was favored.

Conclusion

Several promising candidate biomarkers suitable for clinical application in MS have been studied. It is recommended follow-up studies with larger sample sizes be completed on several potential biomarkers.

Acute Cellular and Functional Changes With a Combinatorial Treatment of Ion Channel Inhibitors Following Spinal Cord Injury

Reducing the extent of secondary degeneration following spinal cord injury (SCI) is necessary to preserve function, but treatment options have thus far been limited. A combination of the ion channel inhibitors Lomerizine (Lom), YM872 and oxATP, to inhibit voltage-gated Ca²⁺ channels, Ca²⁺ permeable AMPA receptors, and purinergic P2X₇ receptors respectively, effectively limits secondary consequences of injury in in vitro and in vivo models of CNS injury. Here, we investigated the efficacy of these inhibitors in a clinically relevant model of SCI. Fischer (F344) rats were subjected to a moderate (150 kD) contusive SCI at thoracic level T10 and assessed at 2 weeks or 10 weeks post-injury. Lom was delivered orally twice daily and YM872 and oxATP were delivered via osmotic mini-pump implanted at the time of SCI until 2 weeks following injury. Open field locomotion analysis revealed that treatment with the three inhibitors in combination improved the rate of functional recovery of the hind limb (compared to controls) as early as 1-day post-injury, with beneficial effects persisting to 14 days post-injury, while all three inhibitors were present. At 2 weeks following combinatorial treatment, the functional improvement was associated with significantly decreased cyst size, increased immunoreactivity of β-III tubulin^+ve axons, myelin basic protein, and reduced lipid peroxidation by-products, and increased CC1^+ve oligodendrocytes and NG2^+ve/PDGFα^+ve oligodendrocyte progenitor cell densities, compared to vehicle-treated SCI animals. The combination of Lom, oxATP, and YM872 shows preclinical promise for control of secondary degeneration following SCI, and further investigation of long-term sustained treatment is warranted.

Astrocytes Are Required for Oligodendrocyte Survival and Maintenance of Myelin Compaction and Integrity

Astrocytes have been implicated in regulating oligodendrocyte development and myelination in vitro, although their functions in vivo remain less well defined. Using a novel approach to locally ablate GFAP+ astrocytes, we demonstrate that astrocytes are required for normal CNS myelin compaction during development, and for maintaining myelin integrity in the adult. Transient ablation of GFAP+ astrocytes in the mouse spinal cord during the first postnatal week reduced the numbers of mature oligodendrocytes and inhibited myelin formation, while prolonged ablation resulted in myelin that lacked compaction and structural integrity. Ablation of GFAP+ astrocytes in the adult spinal cord resulted in the rapid, local loss of myelin integrity and regional demyelination. The loss of myelin integrity induced by astrocyte ablation was greatly reduced by NMDA receptor antagonists, both in vitro and in vivo, suggesting that myelin stability was affected by elevation of local glutamate levels following astrocyte ablation. Furthermore, targeted delivery of glutamate into adult spinal cord white matter resulted in reduction of myelin basic protein expression and localized disruption of myelin compaction which was also reduced by NMDA receptor blockade. The pathology induced by localized astrocyte loss and elevated exogenous glutamate, supports the concept that astrocytes are critical for maintenance of myelin integrity in the adult CNS and may be primary targets in the initiation of demyelinating diseases of the CNS, such as Neuromyelitis Optica (NMO).

Mitochondrial division inhibitor 1 disrupts oligodendrocyte Ca2+ homeostasis and mitochondrial function

Mitochondrial fission mediated by cytosolic dynamin related protein 1 (Drp1) is essential for mitochondrial quality control but may contribute to apoptosis as well. Blockade of Drp1 with mitochondrial division inhibitor 1 (mdivi-1) provides neuroprotection in several models of neurodegeneration and cerebral ischemia and has emerged as a promising therapeutic drug. In oligodendrocytes, overactivation of AMPA-type ionotropic glutamate receptors (AMPARs) induces intracellular Ca²⁺ overload and excitotoxic death that contributes to demyelinating diseases. Mitochondria are key to Ca²⁺ homeostasis, however it is unclear how it is disrupted during oligodendroglial excitotoxicity. In the current study, we have analyzed mitochondrial dynamics during AMPAR activation and the effects of mdivi-1 on excitotoxicity in optic nerve-derived oligodendrocytes. Sublethal AMPAR activation triggered Drp1-dependent mitochondrial fission, whereas toxic AMPAR activation produced Drp1-independent mitochondrial swelling. Accordingly, mdivi-1 efficiently inhibited Drp1-mediated mitochondrial fission and did not prevent oligodendrocyte excitotoxicity. Unexpectedly, mdivi-1 also induced mitochondrial depolarization, ER Ca²⁺ depletion and modulation of AMPA-induced Ca²⁺ signaling. These off-target effects of mdivi-1 sensitized oligodendrocytes to excitotoxicity and ER stress and eventually produced oxidative stress and apoptosis. Interestingly, in cultured astrocytes mdivi-1 induced nondetrimental mitochondrial depolarization and oxidative stress that did not cause toxicity or sensitization to apoptotic stimuli. In summary, our results provide evidence of Drp1-mediated mitochondrial fission during activation of ionotropic glutamate receptors in oligodendrocytes, and uncover a deleterious and Drp1-independent effect of mdivi-1 on mitochondrial and ER function in these cells. These off-target effects of mdivi-1 limit its therapeutic potential and should be taken into account in clinical studies.

Moving past antioxidant supplementation for the dietary treatment of multiple sclerosis

Current research has demonstrated the definitive presence of oxidative stress in multiple sclerosis (MS). This finding has led to clinical trial research which has indicated that specific antioxidants have the ability to effectively reduce markers of oxidative stress. However, few interventions testing antioxidant supplements have shown efficacy for reducing the symptom burden in the disorder. This paper quickly reviews what is currently known about oxidative stress and antioxidants in MS, explains which nutrients are critical for the creation and maintenance of the myelin sheath, describes potential negative effectors in the diet which may be contributing to oxidative stress, and how these aspects of diet, combined with current knowledge on antioxidants, may be able to be combined into a whole food dietary intervention which can be tested for efficacy in MS.

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

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

Multiple sclerosis pathogenesis: missing pieces of an old puzzle

Traditionally, multiple sclerosis (MS) was considered to be a CD4 T cell-mediated CNS autoimmunity, compatible with experimental autoimmune encephalitis model, which can be characterized by focal lesions in the white matter. However, studies of recent decades revealed several missing pieces of MS puzzle and showed that MS pathogenesis is more complex than the traditional view and may include the following: a primary degenerative process (e.g. oligodendroglial pathology), generalized abnormality of normal-appearing brain tissue, pronounced gray matter pathology, involvement of innate immunity, and CD8 T cells and B cells. Here, we review these findings and discuss their implications in MS pathogenesis.

Sirtuins in Multiple Sclerosis: The crossroad of neurodegeneration, autoimmunity and metabolism

Multiple Sclerosis (MS) is a challenging and disabling condition particularly in the secondary progressive (SP) phase of this disease. The available treatments cannot ameliorate or stop disease progression in this phase, and there is an urgent need to focus on effective therapies and the molecular pathways involved SPMS. Given the significant impact of neurodegeneration, autoimmunity and metabolic alterations in MS, focusing on the molecules that target these different pathways could help in finding new treatments. Sirtuins (SIRTs) are NAD⁺ dependent epigenetic and metabolic regulators, which have critical roles in the physiology of central nervous system, immune system and metabolism. Based on these facts, SIRTs are crucial candidates of therapeutic targets in MS and collecting the information related to MS disease for each SIRT individually is noteworthy and highlights the lack of investigation in each part. In this review we summarized the role of different sirtuins as key regulator in neurodegeneration, autoimmunity and metabolism pathways. We also clarify the rationale behind selecting SIRTs as therapeutic targets in MS disease by collecting the researches showing alteration of these proteins in human samples of MS patients and animal model of MS, and also the improvement of modeled animals after SIRT-directed treatments.

Stores, Channels, Glue, and Trees: Active Glial and Active Dendritic Physiology

Glial cells and neuronal dendrites were historically assumed to be passive structures that play only supportive physiological roles, with no active contribution to information processing in the central nervous system. Research spanning the past few decades has clearly established this assumption to be far from physiological realities. Whereas the discovery of active channel conductances and their localized plasticity was the turning point for dendritic structures, the demonstration that glial cells release transmitter molecules and communicate across the neuroglia syncytium through calcium wave propagation constituted path-breaking discoveries for glial cell physiology. An additional commonality between these two structures is the ability of calcium stores within their endoplasmic reticulum (ER) to support active propagation of calcium waves, which play crucial roles in the spatiotemporal integration of information within and across cells. Although there have been several demonstrations of regulatory roles of glial cells and dendritic structures in achieving common physiological goals such as information propagation and adaptability through plasticity, studies assessing physiological interactions between these two active structures have been few and far. This lacuna is especially striking given the strong connectivity that is known to exist between these two structures through several complex and tightly intercoupled mechanisms that also recruit their respective ER structures. In this review, we present brief overviews of the parallel literatures on active dendrites and active glial physiology and make a strong case for future studies to directly assess the strong interactions between these two structures in regulating physiology and pathophysiology of the brain.

Adenosine Actions on Oligodendroglia and Myelination in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is the most commonly diagnosed neurodevelopmental disorder. Independent of neuronal dysfunction, ASD and its associated comorbidities have been linked to hypomyelination and oligodendroglial dysfunction. Additionally, the neuromodulator adenosine has been shown to affect certain ASD comorbidities and symptoms, such as epilepsy, impairment of cognitive function, and anxiety. Adenosine is both directly and indirectly responsible for regulating the development of oligodendroglia and myelination through its interaction with, and modulation of, several neurotransmitters, including glutamate, dopamine, and serotonin. In this review, we will focus on the recent discoveries in adenosine interaction with physiological and pathophysiological activities of oligodendroglia and myelination, as well as ASD-related aspects of adenosine actions on neuroprotection and neuroinflammation. Moreover, we will discuss the potential therapeutic value and clinical approaches of adenosine manipulation against hypomyelination in ASD.

Purinergic receptors in multiple sclerosis pathogenesis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system, characterized by the presence of focal lesions in white and grey matter with peripheral immune cells infiltration. Purinergic receptors control immune cell function as well as neuronal and oligodendroglial survival, and the activation of astrocytes and microglia, the endogenous brain immune cells. In particular, ionotropic purinergic receptors P2X4 and P2X7 and metabotropic receptor P2Y12 are differently expressed along the disease and their activation or blockage modifies the course of texperimental autoimmune encephalomyelitis (EAE), the dominant animal model of MS. In this review, we will summarize emerging evidence of the role of these three receptor types as potential MS biomarkers and therapeutic targets.

Glutamate receptors and white matter stroke

White matter (WM) damage during ischemia occurs at multiple sites including myelin, oligodendrocytes, astrocytes and axons. A major driver of WM demise is excitoxicity as a consequence of excessive glutamate release by vesicular and non-vesicular mechanisms from axons and glial cells. This results in over-activation of ionotropic glutamate receptors (GluRs) profusely expressed by all cell compartments in WM. Thus, blocking excitotoxicity in WM with selective antagonists of those receptors has a potential therapeutic value. The significance of WM GluR expression for WM stroke injury is the focus of this review, and we will examine the role of GluRs in injury to myelin, oligodendrocytes, astrocytes and the axon cylinder.

Oligodendroglia Are Particularly Vulnerable to Oxidative Damage After Neurotrauma In Vivo

In the paper “Oligodendroglia are particularly vulnerable to oxidative damage after neurotrauma in vivo,” we determined the extent of oxidative damage to specific cellular subpopulations and structures within regions vulnerable to secondary degeneration and assessed the effect this had on oligodendroglial function. Comparative assessment of oxidative damage demonstrated selective vulnerability of oligodendroglia, specifically oligodendrocyte progenitor cells (OPCs) to DNA oxidation in vivo. Immunohistochemical fate mapping along the oligodendroglial lineage showed a transient susceptibility of these cells to DNA oxidation, protein nitration, and lipid peroxidation, with mature oligodendrocytes derived immediately after injury more vulnerable to DNA oxidation than their counterparts existing at the time of injury or later derived. In situ hybridization demonstrated a reduction in myelin regulatory factor (MyRF) messenger RNA (mRNA) fluorescence in newly derived mature oligodendrocytes, suggesting a compromise in the production and maintenance of the myelin sheath in these cells. The data imply a deficit in the normal differentiation of OPCs to myelinating oligodendrocytes, associated with a transient increase in oxidative damage, which may contribute to the dysmyelinating phenotype seen at chronic time points after injury. Identifying and understanding the sources of this oxidative damage is integral for the development of therapeutic interventions for neurotrauma.

Blockade of IL-6 signaling in neuromyelitis optica

Neuromyelitis optica (NMO) and neuromyelitis optica spectrum disorder (NMOSD) are autoimmune diseases associated with a disease-specific autoantibody directed against the water channel protein aquaporin-4. Standard immunotherapy, immunosuppressive agents, and corticosteroids can prevent acute attacks and maintain remission in most patients with NMOSD. However, there is a strong need for additional options for patients who are refractory to standard treatments. Emerging therapies targeting specific molecules related to the pathogenicity of NMOSD are currently being developed. The review focuses on improving preventive treatments for NMOSD, including ongoing randomized clinical trials using biological drugs targeting CD19 and CD20 on B cells, interleukin-6, and complement protein C5. The anti-IL-6 receptor monoclonal antibody tocilizumab (TCZ), which can block IL-6 signaling, was shown to be highly effective for refractory patients with NMOSD. Notably, TCZ has marked effects on chronic neuropathic pain and general fatigue in patients refractory to standard medications. TCZ is a promising drug for preventing acute attacks in patients with NMOSD.

Inhibition of Casein Kinase 2 Protects Oligodendrocytes From Excitotoxicity by Attenuating JNK/p53 Signaling Cascade

Oligodendrocytes are highly vulnerable to glutamate excitotoxicity, a central mechanism involved in tissue damage in Multiple Sclerosis (MS). Sustained activation of AMPA receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, increase of reactive oxygen species, and activation of intracelular pathways resulting in apoptotic cell death. Although many signals driven by excitotoxicity have been identified, some of the key players are still under investigation. Casein kinase 2 (CK2) is a serine/threonine kinase, constitutively expressed in all eukaryotic tissues, involved in cell proliferation, malignant transformation and apoptosis. In this study, we identify CK2 as a critical regulator of oligodendrocytic death pathways and elucidate its role as a signal inductor following excitotoxic insults. We provide evidence that CK2 activity is up-regulated in AMPA-treated oligodendrocytes and CK2 inhibition significantly diminished AMPA receptor-induced oligodendroglial death. In addition, we analyzed mitogen-activated protein kinase (MAPK) signaling after excitotoxic insult. We observed that AMPA receptor activation induced a rapid increase in c-Jun N-terminal kinase (JNK) and p38 phosphorylation that was reduced after CK2 inhibition. Moreover, blocking their phosphorylation, we enhanced oligodendrocyte survival after excitotoxic insult. Finally, we observed that the tumor suppressor p53 is activated during AMPA receptor-induced cell death and, interestingly, down-regulated by JNK or CK2 inhibition. Together, these data indicate that the increase in CK2 activity induced by excitotoxic insults regulates MAPKs, triggers p53 activation and mediates subsequent oligodendroglial loss. Therefore, targeting CK2 may be a useful strategy to prevent oligodendrocyte death in MS and other diseases involving central nervous system (CNS) white matter.

Chlorogenic Acid Prevents AMPA-Mediated Excitotoxicity in Optic Nerve Oligodendrocytes Through a PKC and Caspase-Dependent Pathways

In the CNS, including the optic nerve, oligodendrocytes play a critical role in the myelination of axons. Oligodendrocytes are exceptionally sensitive to insults to the CNS, such as injury, ischemia, or inflammation, which result in the loss of oligodendrocytes and myelin and eventually secondary axon degeneration. Oligodendrocytes are sensitive to excitotoxic insults mediated by overactivation of their AMPA ionotropic glutamate receptors. Phenolic compounds, which are widely distributed in fruits and vegetables, received the great attention of scientists due to their antioxidant activities and free radical scavenging abilities. Chlorogenic acid (CGA) has been demonstrated to possess potent neuroprotective activities against oxidative stress in various cellular models and pathological conditions. Hence, CGA protect against oxidative stress and excitotoxic insults mediated by AMPA receptors and that the protective mechanisms involve free radical scavenging, Ca²⁺ handling in the cytosol, and modulating antioxidant enzyme system. CGA was associated with the protein kinase A (PKC) signaling pathways transduction. Caspases and calpains have been studied as apoptotic mediators and cell death in this model of AMPA toxicity. Inhibitors of caspases initiators, caspases 1, 8, and 9, the upstream of caspase 3 effectors, have totally abrogated the protective activity of CGA. Inhibitors of calpains also totally abrogated the protective activity of CGA. In addition, a potential role for the CGA in inhibiting Bax in oligodendrocyte cell model undergoing AMPA is inducing excitotoxic death. Our results indicate that CGA exhibits a protective potential via antioxidant and apoptosis caspases and calpains dependent against AMPA-mediated excitotoxicity, and these finding indicate that CGA is able to be a good candidate for preventive approach for neurodegenerative disorders associated with loss and damage in oligodendrocytes and AMPA-mediated excitotoxicity.

Culture of Neonatal Rodent Microglia, Astrocytes, and Oligodendrocytes from the Cortex, Spinal Cord, and Cerebellum

The protocol described in this chapter covers the preparation and culture of enriched populations of microglia, astrocytes, and oligodendrocytes from the cortex and spinal cord of neonatal rat and mouse. The procedure is based on enzymatic digestion of the tissue, followed by the culture of a mixed glial cell population which is then utilized as the starting point for the isolation, via differential attachment, of the different cell types.

Decrease in Cavity Size and Oligodendrocyte Cell Death Using Neurosphere-Derived Oligodendrocyte-Like Cells in Spinal Cord Contusion Model

Background

Oligodendrocyte cell death is among the important features of spinal cord injury, which appears within 15 min and occurs intensely for 4 h after injury, in the rat spinal contusion model. Accordingly, the number of oligodendrocytes progressively reduced within 24 h after injury. Administration of oligodendrocyte-like cells (OLCs) into the lesion area is one of the approaches to counterbalance this condition.

Methods

Bone marrow stromal cells were transdifferentiated into neurospheres and then into neural stem cells and later were differentiated into OLCs using triiodothyronine and transplanted into the spinal cord contusion rats. The post-injury functional recovery was explored and compared with the control group using Basso-Beattie-Bresnahan and narrow beam behavioral tests. At the end of 12th week, spinal cord segments T12-L1 were histomorphologically studied by immunohistochemistry.

Results

Motor improvement was more obvious during 2nd to 4th weeks and got less prominent during 4th to 12th weeks. Histomorphometric findings indicated that cavity formation decreased in epicenter of transplantation area in experimental groups in comparison with the control groups.

Conclusion

The findings obtained in the present study showed that OLC therapy is a potential approach in the treatment of spinal cord traumatic injuries.

Organotypic cultures of cerebellar slices as a model to investigate demyelinating disorders

INTRODUCTION

Demyelinating disorders, characterized by a chronic or episodic destruction of the myelin sheath, are a leading cause of neurological disability in young adults in western countries. Studying the complex mechanisms involved in axon myelination, demyelination and remyelination requires an experimental model preserving the neuronal networks and neuro-glial interactions. Organotypic cerebellar slice cultures appear to be the best alternative to in vivo experiments and the most commonly used model for investigating etiology or novel therapeutic strategies in multiple sclerosis. Areas covered: This review gives an overview of slice culture techniques and focuses on the use of organotypic cerebellar slice cultures on semi-permeable membranes for studying many aspects of axon myelination and cerebellar functions. Expert opinion: Cerebellar slice cultures are probably the easiest way to faithfully reproduce all stages of axon myelination/demyelination/remyelination in a three-dimensional neuronal network. However, in the cerebellum, neurological disability in multiple sclerosis also results from channelopathies which induce changes in Purkinje cell excitability. Cerebellar cultures offer easy access to electrophysiological approaches which are largely untapped and we believe that these cultures might be of great interest when studying changes in neuronal excitability, axonal conduction or synaptic properties that likely occur during multiple sclerosis.

Glial cells as key elements in the pathophysiology and treatment of bipolar disorder

OBJECTIVE

The exact pathophysiology of bipolar disorder (BD) is not yet fully understood, and there are many questions in this area which should be answered. This review aims to discuss the roles of glial cells in the pathophysiology of BD and their contribution to the mechanism of action of mood-stabilising drugs.

METHODS

We critically reviewed the most recent advances regarding glial cell roles in the pathophysiology and treatment of BD and the neuroprotective and neurotrophic effects of these cells.

RESULTS

Postmortem studies revealed a decrease in the glial cell number or density in the specific layers of prefrontal and anterior cingulate cortex in the patients with BD, whereas there was no difference in other brain regions, such as entorhinal cortex, amygdala and hippocampus. Astrocytes and oligodendrocytes were the most important glial types that were responsible for the glial reduction, but microglia activation rather than loss may be implicated in BD. The decreased number or density of glial cells may contribute to the pathological changes observed in neurons in the patients with BD. Alteration of specific neurotrophic factors such as glial cell line-derived neurotrophic factor and S100B may be an important feature of BD. Glial cells mediate the therapeutic effects of mood-stabilising agents in the treatment of BD.

CONCLUSION

Recent studies provide important evidence on the impairment of glial cells in the pathophysiology and treatment of BD. However, future controlled studies are necessary to elucidate different aspects of glial cells contribution to BD, and the mechanism of action of mood-stabilising drugs.

Glutamate, T cells and multiple sclerosis

Glutamate is the major excitatory neurotransmitter in the nervous system, where it induces multiple beneficial and essential effects. Yet, excess glutamate, evident in a kaleidoscope of acute and chronic pathologies, is absolutely catastrophic, since it induces excitotoxicity and massive loss of brain function. Both the beneficial and the detrimental effects of glutamate are mediated by a large family of glutamate receptors (GluRs): the ionotropic glutamate receptors (iGluRs) and the metabotropic glutamate receptors (mGluRs), expressed by most/all cells of the nervous system, and also by many non-neural cells in various peripheral organs and tissues. T cells express on their cell surface several types of functional GluRs, and so do few other immune cells. Furthermore, glutamate by itself activates resting normal human T cells, and induces/elevates key T cell functions, among them: T cell adhesion, chemotactic migration, cytokine secretion, gene expression and more. Glutamate has also potent effects on antigen/mitogen/cytokine-activated T cells. Furthermore, T cells can even produce and release glutamate, and affect other cells and themselves via their own glutamate. Multiple sclerosis (MS) and its animal model Experimental Autoimmune Encephalomyelitis (EAE) are mediated by autoimmune T cells. In MS and EAE, there are excess glutamate levels, and multiple abnormalities in glutamate degrading enzymes, glutamate transporters, glutamate receptors and glutamate signaling. Some GluR antagonists block EAE. Enhancer of mGluR4 protects from EAE via regulatory T cells (Tregs), while mGluR4 deficiency exacerbates EAE. The protective effect of mGluR4 on EAE calls for testing GluR4 enhancers in MS patients. Oral MS therapeutics, namely Fingolimod, dimethyl fumarate and their respective metabolites Fingolimod-phosphate and monomethyl fumarate, can protect neurons against acute glutamatergic excitotoxic damage. Furthermore, Fingolimod reduce glutamate-mediated intracortical excitability in relapsing-remitting MS. Glatiramer acetate -COPAXONE®, an immunomodulator drug for MS, reverses TNF-α-induced alterations of striatal glutamate-mediated excitatory postsynaptic currents in EAE-afflicted mice. With regard to T cells of MS patients: (1) The cell surface expression of a specific GluR: the AMPA GluR3 is elevated in T cells of MS patients during relapse and with active disease, (2) Glutamate and AMPA (a selective agonist for glutamate/AMPA iGluRs) augment chemotactic migration of T cells of MS patients, (3) Glutamate augments proliferation of T cells of MS patients in response to myelin-derived proteins: MBP and MOG, (4) T cells of MS patients respond abnormally to glutamate, (5) Significantly higher proliferation values in response to glutamate were found in MS patients assessed during relapse, and in those with gadolinium (Gd)+ enhancing lesions on MRI. Furthermore, glutamate released from autoreactive T cells induces excitotoxic cell death of neurons. Taken together, the evidences accumulated thus far indicate that abnormal glutamate levels and signaling in the nervous system, direct activation of T cells by glutamate, and glutamate release by T cells, can all contribute to MS. This may be true also to other neurological diseases. It is postulated herein that the detrimental activation of autoimmune T cells by glutamate in MS could lead to: (1) Cytotoxicity in the CNS: T cell-mediated killing of neurons and glia cells, which would subsequently increase the extracellular glutamate levels, and by doing so increase the excitotoxicity mediated by excess glutamate, (2) Release of proinflammatory cytokines, e.g., TNFα and IFNγ that increase neuroinflammation. Finally, if excess glutamate, abnormal neuronal signaling, glutamate-induced activation of T cells, and glutamate release by T cells are indeed all playing a key detrimental role in MS, then optional therapeutic tolls include GluR antagonists, although these may have various side effects. In addition, an especially attractive therapeutic strategy is the novel and entirely different therapeutic approach to minimize excess glutamate and excitotoxicity, titled: 'brain to blood glutamate scavenging', designed to lower excess glutamate levels in the CNS by 'pumping it out' from the brain to the blood. The glutamate scavanging is achieved by lowering glutamate levels in the blood by intravenous injection of the blood enzyme glutamate oxaloacetate transaminase (GOT). The glutamate-scavenging technology, which is still experimental, validated so far for other brain pathologies, but not tested on MS or EAE yet, may be beneficial for MS too, since it could decrease both the deleterious effects of excess glutamate on neural cells, and the activation of autoimmune T cells by glutamate in the brain. The topic of glutamate scavenging, and also its potential benefit for MS, are discussed towards the end of the review, and call for research in this direction.

Excitotoxins, Mitochondrial and Redox Disturbances in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). There is increasing evidence that MS is not only characterized by immune mediated inflammatory reactions, but also by neurodegenerative processes. There is cumulating evidence that neurodegenerative processes, for example mitochondrial dysfunction, oxidative stress, and glutamate (Glu) excitotoxicity, seem to play an important role in the pathogenesis of MS. The alteration of mitochondrial homeostasis leads to the formation of excitotoxins and redox disturbances. Mitochondrial dysfunction (energy disposal failure, apoptosis, etc.), redox disturbances (oxidative stress and enhanced reactive oxygen and nitrogen species production), and excitotoxicity (Glu mediated toxicity) may play an important role in the progression of the disease, causing axonal and neuronal damage. This review focuses on the mechanisms of mitochondrial dysfunction (including mitochondrial DNA (mtDNA) defects and mitochondrial structural/functional changes), oxidative stress (including reactive oxygen and nitric species), and excitotoxicity that are involved in MS and also discusses the potential targets and tools for therapeutic approaches in the future.

Exosomes, an Unmasked Culprit in Neurodegenerative Diseases

Exosomes are extracellular nanovesicles (30–100 nm) generated from endosomal membranes and known to be released by all cell lineages of the Central Nervous System (CNS). They constitute important vesicles for the secretion and transport of multilevel information, including signaling, toxic, and regulatory molecules. Initially thought to have a function merely in waste disposal, the involvement of exosomes in neuronal development, maintenance, and regeneration through its paracrine and endocrine signaling functions has drawn particular attention in recent years. These vesicles, being involved in the clearance and cell-to-cell spreading of toxic molecules, have been naturally implicated in aging, and in several neurodegenerative diseases associated with pathological conversion of proteins, as well as in the transport of other disease-associated molecules, such as nucleic acids or pro-inflammatory cytokines. Our understanding of such unique form of communication may provide not only answers about (patho)physiological processes in the brain, but can also offer means to exploit these vesicles as vehicles for the delivery of biologically relevant molecules or as tools to monitor brain diseases in a non-invasive way. A promising field in expansion, the study of exosomes and related extracellular vesicles has just commenced to unveil their potential as therapeutic tools for brain disorders as well as biomarkers of disease state.

Role of metabolism in neurodegenerative disorders

Along with the increase in life expectancy over the last century, the prevalence of age-related disorders, such as neurodegenerative diseases continues to rise. This is the case of Alzheimer's, Parkinson's, Huntington's diseases and Multiple sclerosis, which are chronic disorders characterized by neuronal loss in motor, sensory or cognitive systems. Accumulating evidence has suggested the presence of a strong correlation between metabolic changes and neurodegeneration. Indeed epidemiologic studies have shown strong associations between obesity, metabolic dysfunction, and neurodegeneration, while animal models have provided insights into the complex relationships between these conditions. In this context, hormones such as leptin, ghrelin, insulin and IGF-1 seem to play a key role in the regulation of neuronal damage, toxic insults and several other neurodegenerative processes. This review aims to presenting the most recent evidence supporting the crosstalk linking energy metabolism and neurodegeneration, and will focus on metabolic manipulation as a possible therapeutic tool in the prevention and treatment of neurodegenerative diseases.

Current Evidence for a Role of the Kynurenine Pathway of Tryptophan Metabolism in Multiple Sclerosis

The kynurenine pathway (KP) is the major metabolic pathway of the essential amino acid tryptophan (TRP). Stimulation by inflammatory molecules, such as interferon-γ (IFN-γ), is the trigger for induction of the KP, driving a complex cascade of production of both neuroprotective and neurotoxic metabolites, and in turn, regulation of the immune response and responses of brain cells to the KP metabolites. Consequently, substantial evidence has accumulated over the past couple of decades that dysregulation of the KP and the production of neurotoxic metabolites are associated with many neuroinflammatory and neurodegenerative diseases, including Parkinson’s disease, AIDS-related dementia, motor neurone disease, schizophrenia, Huntington’s disease, and brain cancers. In the past decade, evidence of the link between the KP and multiple sclerosis (MS) has rapidly grown and has implicated the KP in MS pathogenesis. KP enzymes, indoleamine 2,3-dioxygenase (IDO-1) and tryptophan dioxygenase (highest expression in hepatic cells), are the principal enzymes triggering activation of the KP to produce kynurenine from TRP. This is in preference to other routes such as serotonin and melatonin production. In neurological disease, degradation of the blood–brain barrier, even if transient, allows the entry of blood monocytes into the brain parenchyma. Similar to microglia and macrophages, these cells are highly responsive to IFN-γ, which upregulates the expression of enzymes, including IDO-1, producing neurotoxic KP metabolites such as quinolinic acid. These metabolites circulate systemically or are released locally in the brain and can contribute to the excitotoxic death of oligodendrocytes and neurons in neurological disease principally by virtue of their agonist activity at N-methyl-d-aspartic acid receptors. The latest evidence is presented and discussed. The enzymes that control the checkpoints in the KP represent an attractive therapeutic target, and consequently several KP inhibitors are currently in clinical trials for other neurological diseases, and hence may make suitable candidates for MS patients. Underpinning these drug discovery endeavors, in recent years, several advances have been made in how KP metabolites are assayed in various biological fluids, and tremendous advancements have been made in how specimens are imaged to determine disease progression and involvement of various cell types and molecules in MS.

Myelin Basic Protein Citrullination in Multiple Sclerosis: A Potential Therapeutic Target for the Pathology

Multiple sclerosis (MS) is a multifactorial demyelinating disease characterized by neurodegenerative events and autoimmune response against myelin component. Citrullination or deimination, a post-translational modification of protein-bound arginine into citrulline, catalyzed by Ca(2+) dependent peptidylarginine deiminase enzyme (PAD), plays an essential role in physiological processes include gene expression regulation, apoptosis and the plasticity of the central nervous system, while aberrant citrullination can generate new epitopes, thus involving in the initiation and/or progression of autoimmune disorder like MS. Myelin basic protein (MBP) is the major myelin protein and is generally considered to maintain the stability of the myelin sheath. This review describes the MBP citrullination and its consequence, as well as offering further support for the "inside-out" hypothesis that MS is primarily a neurodegenerative disease with secondary inflammatory demyelination. In addition, it discusses the role of MBP citrullination in the immune inflammation and explores the potential of inhibition of PAD enzymes as a therapeutic strategy for the disease.