Axon loss in the spinal cord determines permanent neurological disability in an animal model of multiple sclerosis

CSF1R antagonism results in increased supraspinal infiltration in EAE

BACKGROUND

Colony stimulating factor 1 receptor (CSF1R) signaling is crucial for the maintenance and function of various myeloid subsets. CSF1R antagonism was previously shown to mitigate clinical severity in experimental autoimmune encephalomyelitis (EAE). The associated mechanisms are still not well delineated.

METHODS

To assess the effect of CSF1R signaling, we employed the CSF1R antagonist PLX5622 formulated in chow (PLX5622 diet, PD) and its control chow (control diet, CD). We examined the effect of PD in steady state and EAE by analyzing cells isolated from peripheral immune organs and from the CNS via flow cytometry. We determined CNS infiltration sites and assessed the extent of demyelination using immunohistochemistry of cerebella and spinal cords. Transcripts of genes associated with neuroinflammation were also analyzed in these tissues.

RESULTS

In addition to microglial depletion, PD treatment reduced dendritic cells and macrophages in peripheral immune organs, both during steady state and during EAE. Furthermore, CSF1R antagonism modulated numbers and relative frequencies of T effector cells both in the periphery and in the CNS during the early stages of the disease. Classical neurological symptoms were milder in PD compared to CD mice. Interestingly, a subset of PD mice developed atypical EAE symptoms. Unlike previous studies, we observed that the CNS of PD mice was infiltrated by increased numbers of peripheral immune cells compared to that of CD mice. Immunohistochemical analysis showed that CNS infiltrates in PD mice were mainly localized in the cerebellum while in CD mice infiltrates were primarily localized in the spinal cords during the onset of neurological deficits. Accordingly, during the same timepoint, cerebella of PD but not of CD mice had extensive demyelinating lesions, while spinal cords of CD but not of PD mice were heavily demyelinated.

CONCLUSIONS

Our findings suggest that CSF1R activity modulates the cellular composition of immune cells both in the periphery and within the CNS, and affects lesion localization during the early EAE stages.

Astrocyte interferon-gamma signaling dampens inflammation during chronic central nervous system autoimmunity via PD-L1

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease of the central nervous system (CNS). Infiltrating inflammatory immune cells perpetuate demyelination and axonal damage in the CNS and significantly contribute to pathology and clinical deficits. While the cytokine interferon (IFN)γ is classically described as deleterious in acute CNS autoimmunity, we and others have shown astrocytic IFNγ signaling also has a neuroprotective role. Here, we performed RNA sequencing and ingenuity pathway analysis on IFNγ-treated astrocytes and found that PD-L1 was prominently expressed. Interestingly, PD-1/PD-L1 antagonism reduced apoptosis in leukocytes exposed to IFNγ-treated astrocytes in vitro. To further elucidate the role of astrocytic IFNγ signaling on the PD-1/PD-L1 axis in vivo, we induced the experimental autoimmune encephalomyelitis (EAE) model of MS in Aldh1l1-CreERT2, Ifngr1fl/fl mice. Mice with conditional astrocytic deletion of IFNγ receptor exhibited a reduction in PD-L1 expression which corresponded to increased infiltrating leukocytes, particularly from the myeloid lineage, and exacerbated clinical disease. PD-1 agonism reduced EAE severity and CNS-infiltrating leukocytes. Importantly, PD-1 is expressed by myeloid cells surrounding MS lesions. These data support that IFNγ signaling in astrocytes diminishes inflammation during chronic autoimmunity via upregulation of PD-L1, suggesting potential therapeutic benefit for MS patients.

Changes in serum cytokine profile and deficit severity in patients with relapsing-remitting multiple sclerosis

INTRODUCTION

In experimental autoimmune encephalomyelitis, neurological deficit correlates with axonal loss and the CD8+ T cells are a likely mediator of axonal damage. In relapsing-remitting multiple sclerosis, there is a correlation of the immune inflammatory activity in the lesion foci with the axon transection.

TMEM106B Puncta Is Increased in Multiple Sclerosis Plaques, and Reduced Protein in Mice Results in Delayed Lipid Clearance Following CNS Injury

During inflammatory, demyelinating diseases such as multiple sclerosis (MS), inflammation and axonal damage are prevalent early in the course. Axonal damage includes swelling, defects in transport, and failure to clear damaged intracellular proteins, all of which affect recovery and compromise neuronal integrity. The clearance of damaged cell components is important to maintain normal turnover and restore homeostasis. In this study, we used mass spectrometry to identify insoluble proteins within high-speed/mercaptoethanol/sarcosyl-insoluble pellets from purified white matter plaques isolated from the brains of individuals with relapsing-remitting MS (RRMS). We determined that the transmembrane protein 106B (TMEM106B), normally lysosome-associated, is insoluble in RRMS plaques relative to normal-appearing white matter from individuals with Alzheimer's disease and non-neurologic controls. Relative to wild-type mice, hypomorphic mice with a reduction in TMEM106B have increased axonal damage and lipid droplet accumulation in the spinal cord following myelin-oligodendrocyte-glycoprotein-induced experimental autoimmune encephalomyelitis. Additionally, the corpora callosa from cuprizone-challenged hypomorphic mice fail to clear lipid droplets efficiently during remyelination, suggesting that when TMEM106B is compromised, protein and lipid clearance by the lysosome is delayed. As TMEM106B contains putative lipid- and LC3-binding sites, further exploration of these sites is warranted.

Co-modulation of TNFR1 and TNFR2 in an animal model of multiple sclerosis

BACKGROUND

Tumour necrosis factor (TNF) is a pleiotropic cytokine and master regulator of the immune system. It acts through two receptors resulting in often opposing biological effects, which may explain the lack of therapeutic potential obtained so far in multiple sclerosis (MS) with non-receptor-specific anti-TNF therapeutics. Under neuroinflammatory conditions, such as MS, TNF receptor-1 (TNFR1) is believed to mediate the pro-inflammatory activities associated with TNF, whereas TNF receptor-2 (TNFR2) may instead induce anti-inflammatory effects as well as promote remyelination and neuroprotection. In this study, we have investigated the therapeutic potential of blocking TNFR1 whilst simultaneously stimulating TNFR2 in a mouse model of MS.

METHODS

Experimental autoimmune encephalomyelitis (EAE) was induced with myelin oligodendrocyte glycoprotein (MOG_35-55) in humanized TNFR1 knock-in mice. These were treated with a human-specific TNFR1-selective antagonistic antibody (H398) and a mouse-specific TNFR2 agonist (EHD2-sc-mTNF_R2), both in combination and individually. Histopathological analysis of spinal cords was performed to investigate demyelination and inflammatory infiltration, as well as axonal and neuronal degeneration. Retinas were examined for any protective effects on retinal ganglion cell (RGC) degeneration and neuroprotective signalling pathways analysed by Western blotting.

RESULTS

TNFR modulation successfully ameliorated symptoms of EAE and reduced demyelination, inflammatory infiltration and axonal degeneration. Furthermore, the combinatorial approach of blocking TNFR1 and stimulating TNFR2 signalling increased RGC survival and promoted the phosphorylation of Akt and NF-κB, both known to mediate neuroprotection.

CONCLUSION

These results further support the potential of regulating the balance of TNFR signalling, through the co-modulation of TNFR1 and TNFR2 activity, as a novel therapeutic approach in treating inflammatory demyelinating disease.

Immunomodulatory therapy with glatiramer acetate reduces endoplasmic reticulum stress and mitochondrial dysfunction in experimental autoimmune encephalomyelitis

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are found in lesions of multiple sclerosis (MS) and animal models of MS such as experimental autoimmune encephalomyelitis (EAE), and may contribute to the neuronal loss that underlies permanent impairment. We investigated whether glatiramer acetate (GA) can reduce these changes in the spinal cords of chronic EAE mice by using routine histology, immunostaining, and electron microscopy. EAE spinal cord tissue exhibited increased inflammation, demyelination, mitochondrial dysfunction, ER stress, downregulation of NAD+ dependent pathways, and increased neuronal death. GA reversed these pathological changes, suggesting that immunomodulating therapy can indirectly induce neuroprotective effects in the CNS by mediating ER stress.

Neurodegeneration in multiple sclerosis

Axonal loss in multiple sclerosis (MS) is a key component of disease progression and permanent neurologic disability. MS is a heterogeneous demyelinating and neurodegenerative disease of the central nervous system (CNS) with varying presentation, disease courses, and prognosis. Immunomodulatory therapies reduce the frequency and severity of inflammatory demyelinating events that are a hallmark of MS, but there is minimal therapy to treat progressive disease and there is no cure. Data from patients with MS, post-mortem histological analysis, and animal models of demyelinating disease have elucidated patterns of MS pathogenesis and underlying mechanisms of neurodegeneration. MRI and molecular biomarkers have been proposed to identify predictors of neurodegeneration and risk factors for disease progression. Early signs of axonal dysfunction have come to light including impaired mitochondrial trafficking, structural axonal changes, and synaptic alterations. With sustained inflammation as well as impaired remyelination, axons succumb to degeneration contributing to CNS atrophy and worsening of disease. These studies highlight the role of chronic demyelination in the CNS in perpetuating axonal loss, and the difficulty in promoting remyelination and repair amidst persistent inflammatory insult. Regenerative and neuroprotective strategies are essential to overcome this barrier, with early intervention being critical to rescue axonal integrity and function. The clinical and basic research studies discussed in this review have set the stage for identifying key propagators of neurodegeneration in MS, leading the way for neuroprotective therapeutic development. This article is categorized under: Immune System Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology.

Modulation of Ryanodine Receptors Activity Alters the Course of Experimental Autoimmune Encephalomyelitis in Mice

Ryanodine receptors (RyRs), the intracellular Ca²⁺ release channels, are expressed in T lymphocytes and other types of immune cells. Modulation of RyRs has been shown to affect T cell functions in vitro and immune responses in vivo. The effects of modulation of RyRs on the development of autoimmune diseases have not been investigated. Here we studied how modulation of RyRs through administration of RyR inhibitor dantrolene or introducing a gain-of-function RYR1-p.R163C mutation affects clinical progression of experimental autoimmune encephalomyelitis (EAE) in mice, a T cell-mediated autoimmune neuroinflammatory disease. We found that daily intraperitoneal administration of 5 or 10 mg/kg dantrolene beginning at the time of EAE induction significantly reduced the severity of EAE clinical symptoms and dampened inflammation in the spinal cord. The protective effect of dantrolene on EAE was reversible. Dantrolene administration elicited dose-dependent skeletal muscle weakness: mice that received 10 mg/kg dose developed a waddling gait, while 5 mg/kg dantrolene dose administration produced a reduction in four-limb holding impulse values. Mice bearing the gain-of-function RYR1-p.R163C mutation developed the EAE clinical symptoms faster and more severely than wild-type mice. This study demonstrates that RyRs play a significant role in EAE pathogenesis and suggests that inhibition of RyRs with low doses of dantrolene may have a protective effect against autoimmunity and inflammation in humans.

Dopaminergic Receptors as Neuroimmune Mediators in Experimental Autoimmune Encephalomyelitis

The dopaminergic system plays an essential role in maintaining homeostasis between the central nervous system (CNS) and the immune system. Previous studies have associated imbalances in the dopaminergic system to the pathogenesis of multiple sclerosis (MS). Here, we examined the protein levels of dopaminergic receptors (D1R and D2R) in different phases of the experimental autoimmune encephalomyelitis (EAE) model. We also investigated if the treatment with pramipexole (PPX)-a dopamine D2/D3 receptor-preferring agonist-would be able to prevent EAE-induced motor and mood dysfunction, as well as its underlying mechanisms of action. We report that D2R immunocontent is upregulated in the spinal cord of EAE mice 14 days post-induction. Moreover, D1R and D2R immunocontents in lymph nodes and the oxidative damage in the spinal cord and striatum of EAE animals were significantly increased during the chronic phase. Also, during the pre-symptomatic phase, axonal damage in the spinal cord of EAE mice could already be found. Surprisingly, therapeutic treatment with PPX failed to inhibit the progression of EAE. Of note, PPX treatment inhibited EAE-induced depressive-like while failed to inhibit anhedonic-like behaviors. We observed that PPX treatment downregulated IL-1β levels and increased BNDF content in the spinal cord after EAE induction. Herein, we show that a D2/D3 receptor-preferred agonist mitigated EAE-induced depressive-like behavior, which could serve as a new possibility for further clinical trials on treating depressive symptoms in MS patients. Thus, we infer that D2R participates in the crosstalk between CNS and immune system during autoimmune and neuroinflammatory response induced by EAE, mainly in the acute and chronic phase of the disease.

Flavonoids, the compounds with anti-inflammatory and immunomodulatory properties, as promising tools in multiple sclerosis (MS) therapy: A systematic review of preclinical evidence

Multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS, are diseases resulting in neurological disabilities that are regarded as chronic, inflammatory, and autoimmune diseases of central nervous system (CNS). In this respect, the use of anti-inflammatory compounds including flavonoids, polyphenolic compounds abundantly found in vegetables and fruits, has proposed to combat MS to dampen the inflammation and thereby ameliorating the disease severity. The objective of this study was to clarify the probable therapeutic effect of flavonoids for treatment of MS. Therefore, only English published articles that reported the therapeutic effect of flavonoids alone or in combination with other anti-MS therapeutic agents on MS, were selected by searching scientific electronic databases including PubMed, Scopus and Web of Science. Evaluation of the selected researches (686) showed that a total of 13 studies were suitable to be included in this systematic review. Interestingly, all of the studies (11 studies concerning EAE and 2 studies concerning MS) reported positive outcomes for the therapeutic effect of flavonoids on EAE and MS. All flavonoid compounds which are mentioned herein could successfully decrease the maximum clinical score of EAE, which is particularly connected to the anti-inflammatory property of these compounds. The literature review clearly discloses that flavonoids alone or in combination with other anti-MS therapeutic agents can pave the way for improving MS therapeutic strategies.

Neuron-Oligodendrocyte Interactions in the Structure and Integrity of Axons

The myelination of axons by oligodendrocytes is a highly complex cell-to-cell interaction. Oligodendrocytes and axons have a reciprocal signaling relationship in which oligodendrocytes receive cues from axons that direct their myelination, and oligodendrocytes subsequently shape axonal structure and conduction. Oligodendrocytes are necessary for the maturation of excitatory domains on the axon including nodes of Ranvier, help buffer potassium, and support neuronal energy metabolism. Disruption of the oligodendrocyte-axon unit in traumatic injuries, Alzheimer's disease and demyelinating diseases such as multiple sclerosis results in axonal dysfunction and can culminate in neurodegeneration. In this review, we discuss the mechanisms by which demyelination and loss of oligodendrocytes compromise axons. We highlight the intra-axonal cascades initiated by demyelination that can result in irreversible axonal damage. Both the restoration of oligodendrocyte myelination or neuroprotective therapies targeting these intra-axonal cascades are likely to have therapeutic potential in disorders in which oligodendrocyte support of axons is disrupted.

Diffusion Basis Spectrum Imaging Detects Axonal Loss After Transient Dexamethasone Treatment in Optic Neuritis Mice

Optic neuritis is a frequent first symptom of multiple sclerosis (MS) for which corticosteroids are a widely employed treatment option. The Optic Neuritis Treatment Trial (ONTT) reported that corticosteroid treatment does not improve long-term visual acuity, although the evolution of underlying pathologies is unclear. In this study, we employed non-invasive diffusion basis spectrum imaging (DBSI)-derived fiber volume to quantify 11% axonal loss 2 months after corticosteroid treatment (vs. baseline) in experimental autoimmune encephalomyelitis mouse optic nerves affected by optic neuritis. Longitudinal DBSI was performed at baseline (before immunization), after a 2-week corticosteroid treatment period, and 1 and 2 months after treatment, followed by histological validation of neuropathology. Pathological metrics employed to assess the optic nerve revealed axonal protection and anti-inflammatory effects of dexamethasone treatment that were transient. Two months after treatment, axonal injury and loss were indistinguishable between PBS- and dexamethasone-treated optic nerves, similar to results of the human ONTT. Our findings in mice further support that corticosteroid treatment alone is not sufficient to prevent eventual axonal loss in ON, and strongly support the potential of DBSI as an in vivo imaging outcome measure to assess optic nerve pathology.

Small Molecule SARM1 Inhibitors Recapitulate the SARM1-/- Phenotype and Allow Recovery of a Metastable Pool of Axons Fated to Degenerate

Axonal degeneration is responsible for disease progression and accumulation of disability in many neurodegenerative conditions. The axonal degenerative process can generate a metastable pool of damaged axons that remain structurally and functionally viable but fated to degenerate in the absence of external intervention. SARM1, an NADase that depletes axonal energy stores upon activation, is the central driver of an evolutionarily conserved program of axonal degeneration. We identify a potent and selective small molecule isoquinoline inhibitor of SARM1 NADase that recapitulates the SARM1^-/- phenotype and protects axons from degeneration induced by axotomy or mitochondrial dysfunction. SARM1 inhibition post-mitochondrial injury with rotenone allows recovery and rescues axons that already entered the metastable state. We conclude that SARM1 inhibition with small molecules has the potential to treat axonopathies of the central and peripheral nervous systems by preventing axonal degeneration and by allowing functional recovery of a metastable pool of damaged, but viable, axons.

Toward Regulatory Effects of Curcumin on Transforming Growth Factor-Beta Across Different Diseases: A Review

Immune response, proliferation, migration and angiogenesis are juts a few of cellular events that are regulated by transforming growth factor-β (TGF-β) in cells. A number of studies have documented that TGF-β undergoes abnormal expression in different diseases, e.g., diabetes, cancer, fibrosis, asthma, arthritis, among others. This has led to great fascination into this signaling pathway and developing agents with modulatory impact on TGF-β. Curcumin, a natural-based compound, is obtained from rhizome and roots of turmeric plant. It has a number of pharmacological activities including antioxidant, anti-inflammatory, anti-tumor, anti-diabetes and so on. Noteworthy, it has been demonstrated that curcumin affects different molecular signaling pathways such as Wnt/β-catenin, Nrf2, AMPK, mitogen-activated protein kinase and so on. In the present review, we evaluate the potential of curcumin in regulation of TGF-β signaling pathway to corelate it with therapeutic impacts of curcumin. By modulation of TGF-β (both upregulation and down-regulation), curcumin ameliorates fibrosis, neurological disorders, liver disease, diabetes and asthma. Besides, curcumin targets TGF-β signaling pathway which is capable of suppressing proliferation of tumor cells and invading cancer cells.

Interleukin-17 in Chronic Inflammatory Neurological Diseases

A critical role for IL-17, a cytokine produced by T helper 17 (Th17) cells, has been indicated in the pathogenesis of chronic inflammatory and autoimmune diseases. A positive effect of blockade of IL-17 secreted by autoreactive T cells has been shown in various inflammatory diseases. Several cytokines, whose production is affected by environmental factors, control Th17 differentiation and its maintenance in tissues during chronic inflammation. The roles of IL-17 in the pathogenesis of chronic neuroinflammatory conditions, multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE), Alzheimer's disease, and ischemic brain injury are reviewed here. The role of environmental stimuli in Th17 differentiation is also summarized, highlighting the role of viral infection in the regulation of pathogenic T helper cells in EAE.

Cnp Promoter-Driven Sustained ERK1/2 Activation Increases B-Cell Activation and Suppresses Experimental Autoimmune Encephalomyelitis

The ERK1/2 signaling pathway promotes myelin wrapping during development and remyelination, and sustained ERK1/2 activation in the oligodendrocyte (OL) lineage results in hypermyelination of the CNS. We therefore hypothesized that increased ERK1/2 signaling in the OL lineage would 1) protect against immune-mediated demyelination due to increased baseline myelin thickness and/or 2) promote enhanced remyelination and thus functional recovery after experimental autoimmune encephalomyelitis (EAE) induction. Cnp-Cre;Mek1DD-eGFP/+ mice that express a constitutively active form of MEK1 (the upstream activator of ERK1/2) in the OL lineage, exhibited a significant decrease in EAE clinical severity compared to controls. However, experiments using tamoxifen-inducible Plp-CreERT;Mek1DD-eGFP/+ or Pdgfrα-CreERT;Mek1DD-eGFP mice revealed this was not solely due to a protective or reparative effect resulting from MEK1DD expression specifically in the OL lineage. Because EAE is an immune-mediated disease, we examined Cnp-Cre;Mek1DD-eGFP/+ splenic immune cells for recombination. Surprisingly, GFP+ recombined CD19+ B-cells, CD11b+ monocytes, and CD3+ T-cells were noted when Cre expression was driven by the Cnp promoter. While ERK1/2 signaling in monocytes and T-cells is associated with proinflammatory activation, fewer studies have examined ERK1/2 signaling in B-cell populations. After in vitro stimulation, MEK1DD-expressing B-cells exhibited a 3-fold increase in CD138+ plasmablasts and a 5-fold increase in CD5+CD1dhi B-cells compared to controls. Stimulated MEK1DD-expressing B-cells also exhibited an upregulation of IL-10, known to suppress the initiation of EAE when produced by CD5+CD1dhi regulatory B-cells. Taken together, our data support the conclusion that sustained ERK1/2 activation in B-cells suppresses immune-mediated demyelination via increasing activation of regulatory B10 cells.

MicroRNAs as disease progression biomarkers and therapeutic targets in experimental autoimmune encephalomyelitis model of multiple sclerosis

Multiple sclerosis is an autoimmune neurodegenerative disease of the central nervous system characterized by pronounced inflammatory infiltrates entering the brain, spinal cord and optic nerve leading to demyelination. Focal demyelination is associated with relapsing-remitting multiple sclerosis, while progressive forms of the disease show axonal degeneration and neuronal loss. The tests currently used in the clinical diagnosis and management of multiple sclerosis have limitations due to specificity and sensitivity. MicroRNAs (miRNAs) are dysregulated in many diseases and disorders including demyelinating and neuroinflammatory diseases. A review of recent studies with the experimental autoimmune encephalomyelitis animal model (mostly female mice 6–12 weeks of age) has confirmed miRNAs as biomarkers of experimental autoimmune encephalomyelitis disease and importantly at the pre-onset (asymptomatic) stage when assessed in blood plasma and urine exosomes, and spinal cord tissue. The expression of certain miRNAs was also dysregulated at the onset and peak of disease in blood plasma and urine exosomes, brain and spinal cord tissue, and at the post-peak (chronic) stage of experimental autoimmune encephalomyelitis disease in spinal cord tissue. Therapies using miRNA mimics or inhibitors were found to delay the induction and alleviate the severity of experimental autoimmune encephalomyelitis disease. Interestingly, experimental autoimmune encephalomyelitis disease severity was reduced by overexpression of miR-146a, miR-23b, miR-497, miR-26a, and miR-20b, or by suppression of miR-182, miR-181c, miR-223, miR-155, and miR-873. Further studies are warranted on determining more fully miRNA profiles in blood plasma and urine exosomes of experimental autoimmune encephalomyelitis animals since they could serve as biomarkers of asymptomatic multiple sclerosis and disease course. Additionally, studies should be performed with male mice of a similar age, and with aged male and female mice.

Diffusion basis spectrum imaging provides insights into MS pathology

Objective

To use diffusion basis spectrum imaging (DBSI) to assess how damage to normal-appearing white matter (NAWM) in the corpus callosum (CC) influences neurologic impairment in people with MS (pwMS).

Methods

Using standard MRI, the primary pathologies in MS of axonal injury/loss, demyelination, and inflammation are not differentiated well. DBSI has been shown in animal models, phantoms, and in biopsied and autopsied human CNS tissues to distinguish these pathologies. Fifty-five pwMS (22 relapsing-remitting, 17 primary progressive, and 16 secondary progressive) and 13 healthy subjects underwent DBSI analyses of NAWM of the CC, the main WM tract connecting the cerebral hemispheres. Tract-based spatial statistics were used to minimize misalignment. Results were correlated with scores from a battery of clinical tests focused on deficits typical of MS.

Results

Normal-appearing CC in pwMS showed reduced fiber fraction and increased nonrestricted isotropic fraction, with the most extensive abnormalities in secondary progressive MS (SPMS). Reduced DBSI-derived fiber fraction and increased DBSI-derived nonrestricted isotropic fraction of the CC correlated with worse cognitive scores in pwMS. Increased nonrestricted isotropic fraction in the body of the CC correlated with impaired hand function in the SPMS cohort.

Conclusions

DBSI fiber fraction and nonrestricted isotropic fraction were the most useful markers of injury in the NAWM CC. These 2 DBSI measures reflect axon loss in animal models. Because of its ability to reveal axonal loss, as well as demyelination, DBSI may be a useful outcome measure for trials of CNS reparative treatments.

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

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

Changes in spinal cord stiffness in the course of experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a commonly used mouse model of multiple sclerosis, a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination leading to brain and spinal cord malfunctions. We postulate that not only biological but also biomechanical properties play an important role in impairements of CNS function. Atomic force microscopy (AFM) was applied to investigate mechanical properties of spinal cords collected from EAE mice in preonset, onset, peak, and chronic disease phases. Biomechanical changes were compared with histopathological alterations observed in the successive phases. The deformability of gray matter did not change, while rigidity of white matter increased during the onset phase, remained at the same level in the peak phase and decreased in the chronic phase. Inflammatory infiltration and laminin content accompanied the tissue rigidity increase, whereas demyelination and axonal damage showed an opposite effect. The increase in white matter rigidity can be regarded as an early signature of EAE.

Aged hind-limb clasping experimental autoimmune encephalomyelitis models aspects of the neurodegenerative process seen in multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is the most common model of multiple sclerosis (MS). This model has been instrumental in understanding the events that lead to the initiation of central nervous system (CNS) autoimmunity. Though EAE has been an effective screening tool for identifying novel therapies for relapsing-remitting MS, it has proven to be less successful in identifying therapies for progressive forms of this disease. Though axon injury occurs in EAE, it is rapid and acute, making it difficult to intervene for the purpose of evaluating neuroprotective therapies. Here, we describe a variant of spontaneous EAE in the 2D2 T cell receptor transgenic mouse (2D2⁺ mouse) that presents with hind-limb clasping upon tail suspension and is associated with T cell-mediated inflammation in the posterior spinal cord and spinal nerve roots. Due to the mild nature of clinical signs in this model, we were able to maintain cohorts of mice into middle age. Over 9 mo, these mice exhibited a relapsing-remitting course of hind-limb clasping with the development of progressive motor deficits. Using a combined approach of ex vivo magnetic resonance (MR) imaging and histopathological analysis, we observed neurological progression to associate with spinal cord atrophy, synapse degradation, and neuron loss in the gray matter, as well as ongoing axon injury in the white matter of the spinal cord. These findings suggest that mild EAE coupled with natural aging may be a solution to better modeling the neurodegenerative processes seen in MS.

MicroRNA-223 protects neurons from degeneration in experimental autoimmune encephalomyelitis

Dysregulation of miRNAs has been observed in many neurodegenerative diseases, including multiple sclerosis. Morquette et al. show that overexpression of miR-223-3p prevents accumulation of axonal damage in a rodent model of multiple sclerosis, in part through regulation of glutamate receptor signalling. Manipulation of miRNA levels may have therapeutic potential.

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.

Glial pathology and retinal neurotoxicity in the anterior visual pathway in experimental autoimmune encephalomyelitis

The animal model experimental autoimmune encephalomyelitis (EAE) has been used extensively in the past to test mechanisms that target peripheral immune cells for treatment of multiple sclerosis (MS). While there have been some notable successes in relapsing MS, the development of therapies for progressive multiple sclerosis (MS) has been hampered by lack of an appropriate animal model. Further, the mechanisms underlying CNS inflammation and neuronal injury remain incompletely elucidated. It is known that the MOG _35-55 EAE mouse model does not have insidious behavioral progression as occurs in people with MS, but there is significant neuronal and axonal injury in EAE, as a result of the inflammation. In the present study, we describe the time course of glial activation and retinal neurodegeneration in the EAE model, and highlight the utility of studying the anterior visual pathway for modeling mechanisms of neuronal injury that may recapitulate critical aspects of the pathology described in people with MS following optic neuritis and subclinical optic neuropathy. We show that A1 neurotoxic astrocytes are prevalent in optic nerve tissue and retina, and are associated with subsequent RGC loss in the most commonly used form of the EAE model induced by MOG _35-55 peptide in C57/B6 mice. We developed a semi-automatic method to quantify retinal ganglion cells (RGC) and show that RGCs remain intact at peak EAE (PID 16) but are significantly reduced in late EAE (PID 42). Postsynaptic proteins and neurites were also compromised in the retina of late EAE mice. The retinal pathology manifests weeks after the microglial and astrocyte activation, which were prominent in optic nerve tissues at PID 16. Microglia expressed iNOS and had increased gene expression of C1q, TNF-α, and IL-1α. Astrocytes expressed high levels of complement component 3 and other genes associated with A1 neurotoxic astrocytes. Our data suggest that EAE can be used to study the pathobiology of optic neuropathy and to examine the preclinical neuroprotective effects of drugs that target activation of neurotoxic A1 astrocytes.

Curcumin ameliorates experimental autoimmune encephalomyelitis in a C57BL/6 mouse model

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system. Although the exact etiology of the disease is largely unknown, it is identified that cytokines may play an important role in the pathogenesis of MS. In this study, the effects of curcumin has been investigated on the expression levels of selected cytokine coding genes as well as the extent of demyelination in the corpus callosum of C57BL/6 experimental autoimmune encephalomyelitis (EAE) model of MS. Gene expression analyses revealed that treatment with curcumin could lead to a significant reduction in the expression levels of pro-inflammatory cytokine coding genes including IL-6 (p = 0.001), IL-17 (p = 0.001), tumor necrosis factor (TNF)-α (p = 0.008), and interferon (IFN)-γ (p = 0.033) as well as a significant increase in the expression level of transforming growth factor (TGF)-β (p = 0.006) as an anti-inflammatory cytokine. Moreover, the expression of glutathione peroxidase (GPX)-1 gene and the activity of anti-oxidant enzymes were significantly higher (p < 0.001) in curcumin-treated mice. Luxol fast blue staining also confirmed a significant reduction in the extent of demyelination in the curcumin-treated group (p < 0.001). Our results have confirmed that curcumin is an effective therapeutic agent that could ameliorate the severity of EAE.

Tuftsin Combines With Remyelinating Therapy and Improves Outcomes in Models of CNS Demyelinating Disease

Though promoting remyelination in multiple sclerosis (MS) has emerged as a promising therapeutic strategy, it does not address inflammatory signals that continue to induce neuronal damage and inhibit effectiveness of repair mechanisms. Our lab has previously characterized the immunomodulatory tetrapeptide, tuftsin, which induces an anti-inflammatory shift in microglia and macrophages. This targeted anti-inflammatory agent improves physical deficits in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Here, we sought to determine whether tuftsin is also effective in combination with benztropine, an FDA-approved drug that stimulates remyelination, in both EAE and in the cuprizone model of demyelination. We show that combining these two agents to promote anti-inflammatory and remyelinating mechanisms alleviates symptoms in EAE and lessens pathological hallmarks in both MS models. Importantly, tuftsin is required to transform the inflammatory CNS environment normally present in EAE/MS into one of an anti-inflammatory nature, and benztropine is required in the cuprizone model to improve remyelination. Our data further support tuftsin's beneficial immunomodulatory activity in the context of EAE, and show that when studying remyelination in the absence of an autoimmune insult, tuftsin still activated microglia toward an anti-inflammatory fate, but benztropine was necessary for significant repair of the damaged myelin. Overall, tuftsin effectively combined with benztropine to significantly improve MS-like pathologies in both models.

Nav1.5 in astrocytes plays a sex-specific role in clinical outcomes in a mouse model of multiple sclerosis

Astrogliosis is a hallmark of neuroinflammatory disorders such as multiple sclerosis (MS). A detailed understanding of the underlying molecular mechanisms governing astrogliosis might facilitate the development of therapeutic targets. We investigated whether Nav1.5 expression in astrocytes plays a role in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a murine model of MS. We created a conditional knockout of Nav1.5 in astrocytes and determined whether this affects the clinical course of EAE, focal macrophage and T cell infiltration, and diffuse activation of astrocytes. We show that deletion of Nav1.5 from astrocytes leads to significantly worsened clinical outcomes in EAE, with increased inflammatory infiltrate in both early and late stages of disease, unexpectedly, in a sex-specific manner. Removal of Nav1.5 in astrocytes leads to increased inflammation in female mice with EAE, including increased astroglial response and infiltration of T cells and phagocytic monocytes. These cellular changes are consistent with more severe EAE clinical scores. Additionally, we found evidence suggesting possible dysregulation of the immune response-particularly with regard to infiltrating macrophages and activated microglia-in female Nav1.5 KO mice compared with WT littermate controls. Together, our results show that deletion of Nav1.5 from astrocytes leads to significantly worsened clinical outcomes in EAE, with increased inflammatory infiltrate in both early and late stages of disease, in a sex-specific manner.

The Properties of Cytokines in Multiple Sclerosis: Pros and Cons

Multiple sclerosis (MS) is a chronic autoimmune disease that affects the central nervous system and is characterized by demyelination, axonal loss, gliosis and inflammation. The last plays a major role in the onset and propagation of the disease. MS presents with heterogeneous lesions containing a broad range of cells and soluble mediators of the immune system such as T cells, B cells, macrophages, microglia, cytokines, chemokines, antibodies, complement and other toxic substances. This review outlines, analyzes and discusses the different immune mechanisms of MS that are responsible for the initiation and propagation of active lesions, demyelination, axonal injury, remyelination and cell loss as well as the role of cytokines in the disease process. Proinflammatory cytokines such as interleukin-17 (IL-17), IL-22, tumor necrosis factor-α, IL-1, IL-12 and interferon-γ may cause MS through several signaling pathways. Conversely, anti-inflammatory circulating cytokines such as IL-4 and IL-10 are reduced and theoretically can exert a direct protective effect in this condition. Future studies are necessary to develop effective, safe and long-lasting strategies to reduce the abnormal cytokine cascades and to treat MS.

Nogo-A antibodies enhance axonal repair and remyelination in neuro-inflammatory and demyelinating pathology

Two hallmarks of chronic multiple sclerosis lesions are the absence of significant spontaneous remyelination and primary as well as secondary neurodegeneration. Both characteristics may be influenced by the presence of inhibitory factors preventing myelin and neuronal repair. We investigated the potential of antibodies against Nogo-A, a well-known inhibitory protein for neuronal growth and plasticity, to enhance neuronal regeneration and remyelination in two animal models of multiple sclerosis. We induced a targeted experimental autoimmune encephalomyelitis (EAE) lesion in the dorsal funiculus of the cervical spinal cord of adult rats resulting in a large drop of skilled forelimb motor functions. We subsequently observed improved recovery of forelimb function after anti-Nogo-A treatment. Anterograde tracing of the corticospinal tract revealed enhanced axonal sprouting and arborisation within the spinal cord gray matter preferentially targeting pre-motor and motor spinal cord laminae on lesion level and above in the anti-Nogo-A-treated animals. An important additional effect of Nogo-A-neutralization was enhanced remyelination observed after lysolecithin-induced demyelination of spinal tracts. Whereas remyelinated fiber numbers in the lesion site were increased several fold, no effect of Nogo-A-inhibition was observed on oligodendrocyte precursor proliferation, migration, or differentiation. Enhancing remyelination and promoting axonal regeneration and plasticity represent important unmet medical needs in multiple sclerosis. Anti-Nogo-A antibodies hold promise as a potential new therapy for multiple sclerosis, in particular during the chronic phase of the disease when neurodegeneration and remyelination failure determine disability evolution.

Oligodendrocyte regeneration: Its significance in myelin replacement and neuroprotection in multiple sclerosis

Oligodendrocytes readily regenerate and replace myelin membranes around axons in the adult mammalian central nervous system (CNS) following injury. The ability to regenerate oligodendrocytes depends on the availability of neural progenitors called oligodendrocyte precursor cells (OPCs) in the adult CNS that respond to injury-associated signals to induce OPC expansion followed by oligodendrocyte differentiation, axonal contact and myelin regeneration (remyelination). Remyelination ensures the maintenance of axonal conduction, and the oligodendrocytes themselves provide metabolic factors that are necessary to maintain neuronal integrity. Recent advances in oligodendrocyte regeneration research are beginning to shed light on critical intrinsic signals, as well as extrinsic, environmental factors that regulate the distinct steps of oligodendrocyte lineage progression and myelin replacement under CNS injury. These studies may offer novel pharmacological targets for regenerative medicine in inflammatory demyelinating disorders in the CNS such as multiple sclerosis. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Influenza virus infection exacerbates experimental autoimmune encephalomyelitis disease by promoting type I T cells infiltration into central nervous system

Multiple sclerosis starts with increased migration of auto-reactive lymphocytes across the blood-brain barrier, resulting in persistent neurodegeneration. Clinical and epidemiological studies indicated upper respiratory viral infections are associated with clinical exacerbation of multiple sclerosis. However, so far there is no any direct evidence to support it. Using the experimental autoimmune encephalomyelitis mice as the model for multiple sclerosis, we demonstrated that mice experienced with influenza virus infection were unable to recover from experimental autoimmune encephalomyelitis with a long-term exacerbation. The exacerbated disease was due to more type I T cells, such as CD45^highCD4⁺CD44^high, CD45^highCD4⁺CCR5⁺, CD45^high IFNγ⁺CD4⁺, MOG_35-55-specific IFNγ⁺CD4⁺ and influenza virus-specific IFNγ⁺CD4⁺ T cells, infiltrating central nervous system in mice with prior influenza virus infection. Influenza virus infection created a notable inflammatory environment in lung and mediastinal lymph node after influenza virus inoculation, suggesting the lung may constitute an inflammatory niche in which auto-aggressive T cells gain the capacity to enter CNS. Indeed, the early stage of EAE disease was accompanied by increased CCR5⁺CD4⁺, CXCR3⁺CD4⁺ T cell and MOG_35-55 specific CD4⁺ T cells localized in the lung in influenza virus-infected mice. CCL5/CCR5 might mediate the infiltration of type I T cells into CNS during the disease development after influenza infection. Administration of CCR5 antagonist could significantly attenuate the exacerbated disease. Our study provided the evidence that the prior influenza virus infection may promote the type I T cells infiltration into the CNS, and subsequently cause a long-term exacerbation of experimental autoimmune encephalomyelitis.

Antibody-Mediated Oligodendrocyte Remyelination Promotes Axon Health in Progressive Demyelinating Disease

Demyelination underlies early neurological symptoms in multiple sclerosis (MS); however, axonal damage is considered critical for permanent chronic deficits. The precise mechanisms by which axonal injury occurs in MS are unclear; one hypothesis is the absence or failure of remyelination, suggesting that promoting remyelination may protect axons from death. This report provides direct evidence that promoting oligodendrocyte remyelination protects axons and maintains transport function. Persistent Theiler's virus infection of Swiss Jim Lambert (SJL)/J mice was used as a model of MS to assess the effects of remyelination on axonal injury following demyelination in the spinal cord. Remyelination was induced using an oligodendrocyte/myelin-specific recombinant human monoclonal IgM, rHIgM22. The antibody is endowed with strong anti-apoptotic and pro-proliferative effects on oligodendrocyte progenitor cells. We used (1)H-magnetic resonance spectroscopy (MRS) at the brainstem to measure N-acetyl-aspartate (NAA) as a surrogate of neuronal health and spinal cord integrity. We found increased brainstem NAA concentrations at 5 weeks post-treatment with rHIgM22, which remained stable out to 10 weeks. Detailed spinal cord morphology studies revealed enhanced remyelination in the rHIgM22-treated group but not in the isotype control antibody- or saline-treated groups. Importantly, we found rHIgM22-mediated remyelination protected small- and medium-caliber mid-thoracic spinal cord axons from damage despite similar demyelination and inflammation across all experimental groups. The most direct confirmation of remyelination-mediated protection of descending neurons was an improvement in retrograde transport. Treatment with rHIgM22 significantly increased the number of retrograde-labeled neurons in the brainstem, indicating that preserved axons are functionally competent. This is direct validation that remyelination preserves spinal cord axons and protects functional axon integrity.

Axonal degeneration in multiple sclerosis: defining therapeutic targets by identifying the causes of pathology

Current therapeutics in multiple sclerosis (MS) target the putative inflammation and immune attack on CNS myelin. Despite their effectiveness in blunting the relapse rate in MS patients, such therapeutics do not prevent MS disease progression. Importantly, specific clinical dilemma arises through inability to predict MS progression and thereby therapeutically target axonal injury during MS, limiting permanent disability. The current review identifies immune and neurobiological principles that govern the sequelae of axonal degeneration during MS disease progression. Defining the specific disease arbiters, inflammatory and autoimmune, oligodendrocyte dystrophy and degenerative myelin, we discuss a basis for a molecular mechanism in axons that may be targeted therapeutically, in spatial and temporal manner to limit axonal degeneration and thereby halt progression of MS.

Inhibition of Gli1 mobilizes endogenous neural stem cells for remyelination

Enhancing repair of myelin is an important, but still elusive therapeutic goal in many neurological disorders¹. In Multiple Sclerosis (MS), an inflammatory demyelinating disease, endogenous remyelination does occur but is frequently insufficient to restore function. Both parenchymal oligodendrocyte progenitor cells (OPCs) and endogenous adult neural stem cells (NSCs) resident within the subventricular zone (SVZ) are known sources of remyelinating cells². Here, we characterize the contribution to remyelination of a subset of adult NSCs, identified by their expression of Gli1, a transcriptional effector of the Sonic Hedgehog (Shh) pathway. We show that these cells are recruited from the SVZ to populate demyelinated lesions in the forebrain but never enter healthy, white matter tracts. Unexpectedly, recruitment of this pool of NSCs, and their differentiation into oligodendrocytes, is significantly enhanced by genetic or pharmacological inhibition of Gli1. Importantly, complete inhibition of canonical hedgehog signaling was ineffective indicating that Gli1’s role in both augmenting hedgehog signaling and retarding myelination is specialized. Indeed, inhibition of Gli1 improves the functional outcome in a relapsing/remitting model of experimental autoimmune encephalomyelitis (RR-EAE) and is neuroprotective. Thus, endogenous NSCs can be mobilized for the repair of demyelinated lesions by inhibiting Gli1, identifying a new therapeutic avenue for the treatment of demyelinating disorders.

Transfer of myelin-reactive th17 cells impairs endogenous remyelination in the central nervous system of cuprizone-fed mice

Multiple sclerosis (MS) is a demyelinating disease of the CNS characterized by inflammation and neurodegeneration. Animal models that enable the study of remyelination in the context of ongoing inflammation are greatly needed for the development of novel therapies that target the pathological inhibitory cues inherent to the MS plaque microenvironment. We report the development of an innovative animal model combining cuprizone-mediated demyelination with transfer of myelin-reactive CD4(+) T cells. Characterization of this model reveals both Th1 and Th17 CD4(+) T cells infiltrate the CNS of cuprizone-fed mice, with infiltration of Th17 cells being more efficient. Infiltration correlates with impaired spontaneous remyelination as evidenced by myelin protein expression, immunostaining, and ultrastructural analysis. Electron microscopic analysis further reveals that demyelinated axons are preserved but reduced in caliber. Examination of the immune response contributing to impaired remyelination highlights a role for peripheral monocytes with an M1 phenotype. This study demonstrates the development of a novel animal model that recapitulates elements of the microenvironment of the MS plaque and reveals an important role for T cells and peripheral monocytes in impairing endogenous remyelination in vivo. This model could be useful for testing putative MS therapies designed to enhance remyelination in the setting of active inflammation, and may also facilitate modeling the pathophysiology of denuded axons, which has been a challenge in rodents because they typically remyelinate very quickly.

Preferential Recruitment of Neutrophils into the Cerebellum and Brainstem Contributes to the Atypical Experimental Autoimmune Encephalomyelitis Phenotype

The JAK/STAT pathway is critical for development, regulation, and termination of immune responses, and dysregulation of the JAK/STAT pathway, that is, hyperactivation, has pathological implications in autoimmune and neuroinflammatory diseases. Suppressor of cytokine signaling 3 (SOCS3) regulates STAT3 activation in response to cytokines that play important roles in the pathogenesis of neuroinflammatory diseases, including IL-6 and IL-23. We previously demonstrated that myeloid lineage-specific deletion of SOCS3 resulted in a severe, nonresolving atypical form of experimental autoimmune encephalomyelitis (EAE), characterized by lesions, inflammatory infiltrates, elevated STAT activation, and elevated cytokine and chemokine expression in the cerebellum. Clinically, these mice exhibit ataxia and tremors. In this study, we provide a detailed analysis of this model, demonstrating that the atypical EAE observed in LysMCre-SOCS3(fl/fl) mice is characterized by extensive neutrophil infiltration into the cerebellum and brainstem, increased inducible NO synthase levels in the cerebellum and brainstem, and prominent axonal damage. Importantly, infiltrating SOCS3-deficient neutrophils produce high levels of CXCL2, CCL2, CXCL10, NO, TNF-α, and IL-1β. Kinetic studies demonstrate that neutrophil infiltration into the cerebellum and brainstem of LysMCre-SOCS3(fl/fl) mice closely correlates with atypical EAE clinical symptoms. Ab-mediated depletion of neutrophils converts the atypical phenotype to the classical EAE phenotype and, in some cases, a mixed atypical/classical phenotype. Blocking CXCR2 signaling ameliorates atypical EAE development by reducing neutrophil infiltration into the cerebellum/brainstem. Thus, neutrophils lacking SOCS3 display elevated STAT3 activation and expression of proinflammatory mediators and play a critical role in the development of atypical EAE.

Pharmaceutical integrated stress response enhancement protects oligodendrocytes and provides a potential multiple sclerosis therapeutic

Oligodendrocyte death contributes to the pathogenesis of the inflammatory demyelinating disease multiple sclerosis (MS). Nevertheless, current MS therapies are mainly immunomodulatory and have demonstrated limited ability to inhibit MS progression. Protection of oligodendrocytes is therefore a desirable strategy for alleviating disease. Here we demonstrate that enhancement of the integrated stress response using the FDA-approved drug guanabenz increases oligodendrocyte survival in culture and prevents hypomyelination in cerebellar explants in the presence of interferon-γ, a pro-inflammatory cytokine implicated in MS pathogenesis. In vivo, guanabenz treatment protects against oligodendrocyte loss caused by CNS-specific expression of interferon-γ. In a mouse model of MS, experimental autoimmune encephalomyelitis, guanabenz alleviates clinical symptoms, which correlates with increased oligodendrocyte survival and diminished CNS CD4+ T cell accumulation. Moreover, guanabenz ameliorates relapse in relapsing-remitting experimental autoimmune encephalomyelitis. Our results provide support for a MS therapy that enhances the integrated stress response to protect oligodendrocytes against the inflammatory CNS environment.

Current multiple sclerosis treatments focus on prevention of immune attack on oligodendrocytes and myelin. Here the authors show a different strategy to ameliorate disease in several mouse models, protecting oligodendrocytes from inflammation-induced death with an FDA-approved drug, guanabenz.

Pathological mechanisms in progressive multiple sclerosis

A better understanding of the pathological mechanisms that drive neurodegeneration in individuals with multiple sclerosis is needed to develop therapies that will effectively treat patients in the primary and secondary progressive stages of the disease. We propose that the inflammatory demyelinating disease process in early multiple sclerosis triggers a cascade of events that lead to neurodegeneration and are amplified by pathogenic mechanisms related to brain ageing and accumulated disease burden. Key elements driving neurodegeneration include microglia activation, chronic oxidative injury, accumulation of mitochondrial damage in axons, and age-related iron accumulation in the human brain. Altered mitochondrial function in axons might be of particular importance. This process leads to chronic cell stress and imbalance of ionic homoeostasis, resulting in axonal and neuronal death. The evidence suggests that treatment of progressive multiple sclerosis should be based on a combination of anti-inflammatory, regenerative, and neuroprotective strategies.

Challenges in multiple sclerosis; how to define occurence of progression

The challenges in MS are related to number of controversies in various aspects of disease but the relationship between relapses and disability progression, or aspects of MS as an inflammatory and/or neurodegenerative disease are extremely important because of its implications on prognosis and therapy of MS. MS was classically regarded as white matter inflammatory disease, while disability progression, brain and spinal cord atrophy were regarded as a consequence of global inflammation of NAWM and secondary involvement of grey matter. More recent histopathology studies, but also new, modern MRI techniques changed this view in MS as a prominent grey and white matter disease. Inflammatory demyelination of grey matter occurs early in MS sometimes even before occurrence of white matter lesions. Inspite of early therapy of MS with immunomodulatory drugs disability progression and neurodegeneration are still important and common part of MS pathogenesis. This indicate that treatment is not adequate to the predicted severity of MS, or perhaps to the basic pathogenetic mechanisms in MS. Beside acute clinical symptoms, conclusions about the severity of the disease are reflection of MRI sensitivity to detect focal WM lesions and insensitivity to detect grey matter lesions which correlate better with clinical symptoms. All presented studies and evaluations point to the necessity of changing the established diagnostic evaluation and treatment in MS. At the earliest stage of MS as well as in follow up of disease it would be necessary to apply a new MRI techniques more available for clinical practice such as DIR brain MR imaging at 3T because of their sensitivity to detect grey matter lesions. In patient with present cortical lesions even in earliest stages of MS depending on severity of grey matter involvement more efficacious therapy like second or even third line therapy should start.

Bringing CLARITY to gray matter atrophy

Gray matter atrophy has been shown to be a strong correlate to clinical disability in multiple sclerosis (MS) and its most commonly used animal model, experimental autoimmune encephalomyelitis (EAE). However, the relationship between gray mater atrophy and the spinal cord pathology often observed in EAE has never been established. Here EAE was induced in Thy1.1-YFP mice and their brains imaged using in vivo magnetic resonance imaging (MRI). The brains and spinal cords were subsequently optically cleared using Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging-compatible Tissue-hYdrogel (CLARITY). Axons were followed 5mm longitudinally in three dimensions in intact spinal cords revealing that 61% of the axons exhibited a mean of 22 axonal ovoids and 8% of the axons terminating in axonal end bulbs. In the cerebral cortex, we observed a decrease in the mean number of layer V pyramidal neurons and a decrease in the mean length of the apical dendrites of the remaining neurons, compared to healthy controls. MRI analysis demonstrated decreased cortical volumes in EAE. Cross-modality correlations revealed a direct relationship between cortical volume loss and axonal end bulb number in the spinal cord, but not ovoid number. This is the first report of the use of CLARITY in an animal model of disease and the first report of the use of both CLARITY and MRI.

Astrocyte CCL2 sustains immune cell infiltration in chronic experimental autoimmune encephalomyelitis

Chemokine (C-C motif) ligand 2 (CCL2), initially identified as monocyte chemoattractant protein-1 (MCP-1), recruits immune cells to the central nervous system (CNS) during autoimmune inflammation. CCL2 can be expressed by multiple cell types, but which cells are responsible for CCL2 function during acute and chronic phases of autoimmune disease is not known. We determined the role of CCL2 in astrocytes in vivo during experimental autoimmune encephalomyelitis (EAE) by using Cre-loxP gene deletion. Mice with a conditional gene deletion of CCL2 from astrocytes had less severe EAE late in disease while having a similar incidence and severity of disease at onset as compared to wild type (WT) control littermates. EAE mice devoid of CCL2 in astrocytes had less macrophage and T cell inflammation in the white matter of the spinal cord and less diffuse activation of astrocytes and microglia in both white and gray matter as well as less axonal loss and demyelination, compared to WT littermates. These findings demonstrate that CCL2 in astrocytes plays an important role in the continued recruitment of immune cells and activation of glial cells in the CNS during chronic EAE, thereby suggesting a novel cell specific target for neuroprotective treatments of chronic neuroinflammatory diseases.

Statistical physics approach to quantifying differences in myelinated nerve fibers

We present a new method to quantify differences in myelinated nerve fibers. These differences range from morphologic characteristics of individual fibers to differences in macroscopic properties of collections of fibers. Our method uses statistical physics tools to improve on traditional measures, such as fiber size and packing density. As a case study, we analyze cross–sectional electron micrographs from the fornix of young and old rhesus monkeys using a semi-automatic detection algorithm to identify and characterize myelinated axons. We then apply a feature selection approach to identify the features that best distinguish between the young and old age groups, achieving a maximum accuracy of 94% when assigning samples to their age groups. This analysis shows that the best discrimination is obtained using the combination of two features: the fraction of occupied axon area and the effective local density. The latter is a modified calculation of axon density, which reflects how closely axons are packed. Our feature analysis approach can be applied to characterize differences that result from biological processes such as aging, damage from trauma or disease or developmental differences, as well as differences between anatomical regions such as the fornix and the cingulum bundle or corpus callosum.