Axonopathy is associated with complex axonal transport defects in a model of multiple sclerosis

How does Nogo-A signalling influence mitochondrial function during multiple sclerosis pathogenesis?

Multiple sclerosis (MS) is a severe neurological disorder that involves inflammation in the brain, spinal cord and optic nerve with key disabling neuropathological outcomes being axonal damage and demyelination. When degeneration of the axo-glial union occurs, a consequence of inflammatory damage to central nervous system (CNS) myelin, dystrophy and death can lead to large membranous structures from dead oligodendrocytes and degenerative myelin deposited in the extracellular milieu. For the first time, this review covers mitochondrial mechanisms that may be operative during MS-related neurodegenerative changes directly activated during accumulating extracellular deposits of myelin associated inhibitory factors (MAIFs), that include the potent inhibitor of neurite outgrowth, Nogo-A. Axonal damage may occur when Nogo-A binds to and signals through its cognate receptor, NgR1, a multimeric complex, to initially stall axonal transport and limit the delivery of important growth-dependent cargo and subcellular organelles such as mitochondria for metabolic efficiency at sites of axo-glial disintegration as a consequence of inflammation. Metabolic efficiency in axons fails during active demyelination and progressive neurodegeneration, preceded by stalled transport of functional mitochondria to fuel axo-glial integrity.

Probing the basis of disease heterogeneity in multiple sclerosis using genetically diverse mice

Multiple sclerosis (MS) is a complex disease with significant heterogeneity in disease course and progression. Genetic studies have identified numerous loci associated with MS risk, but the genetic basis of disease progression remains elusive. To address this, we leveraged the Collaborative Cross (CC), a genetically diverse mouse strain panel, and experimental autoimmune encephalomyelitis (EAE). The thirty-two CC strains studied captured a wide spectrum of EAE severity, trajectory, and presentation, including severe-progressive, monophasic, relapsing remitting, and axial rotary (AR)-EAE, accompanied by distinct immunopathology. Sex differences in EAE severity were observed in six strains. Quantitative trait locus analysis revealed distinct genetic linkage patterns for different EAE phenotypes, including EAE severity and incidence of AR-EAE. Machine learning-based approaches prioritized candidate genes for loci underlying EAE severity ( Abcc4 and Gpc6 ) and AR-EAE ( Yap1 and Dync2h1 ). This work expands the EAE phenotypic repertoire and identifies novel loci controlling unique EAE phenotypes, supporting the hypothesis that heterogeneity in MS disease course is driven by genetic variation.

Summary

The genetic basis of disease heterogeneity in multiple sclerosis (MS) remains elusive. We leveraged the Collaborative Cross to expand the phenotypic repertoire of the experimental autoimmune encephalomyelitis (EAE) model of MS and identify loci controlling EAE severity, trajectory, and presentation.

Shedding light on neurofilament involvement in cognitive decline in obstructive sleep apnea and its possible role as a biomarker

Obstructive sleep apnea is one of the most common sleep disorders with a high estimated global prevalence and a large number of associated comorbidities in general as well as specific neuropsychiatric complications such as cognitive impairment. The complex pathogenesis and effects of the disorder including chronic intermittent hypoxia and sleep fragmentation may lead to enhanced neuronal damage, thereby contributing to neuropsychiatric pathologies. Obstructive sleep apnea has been described as an independent risk factor for several neurodegenerative diseases, including Alzheimer's disease and all-cause dementia. The influence of obstructive sleep apnea on cognitive deficits is still a topic of recent debate, and several mechanisms, including neurodegeneration and depression-related cognitive dysfunction, underlying this correlation are taken into consideration. The differentiation between both pathomechanisms of cognitive impairment in obstructive sleep apnea is a complex clinical issue, requiring the use of multiple and costly diagnostic methods. The studies conducted on neuroprotection biomarkers, such as brain-derived neurotrophic factors and neurofilaments, are recently gaining ground in the topic of cognition assessment in obstructive sleep apnea patients. Neurofilaments as neuron-specific cytoskeletal proteins could be useful non-invasive indicators of brain conditions and neurodegeneration, which already are observed in many neurological diseases leading to cognitive deficits. Additionally, neurofilaments play an important role as a biomarker in other sleep disorders such as insomnia. Thus, this review summarizes the current knowledge on the involvement of neurofilaments in cognitive decline and neurodegeneration in obstructive sleep apnea patients as well as discusses its possible role as a biomarker of these changes.

How does Nogo receptor influence demyelination and remyelination in the context of multiple sclerosis?

Multiple sclerosis (MS) can progress with neurodegeneration as a consequence of chronic inflammatory mechanisms that drive neural cell loss and/or neuroaxonal dystrophy in the central nervous system. Immune-mediated mechanisms can accumulate myelin debris in the disease extracellular milieu during chronic-active demyelination that can limit neurorepair/plasticity and experimental evidence suggests that potentiated removal of myelin debris can promote neurorepair in models of MS. The myelin-associated inhibitory factors (MAIFs) are integral contributors to neurodegenerative processes in models of trauma and experimental MS-like disease that can be targeted to promote neurorepair. This review highlights the molecular and cellular mechanisms that drive neurodegeneration as a consequence of chronic-active inflammation and outlines plausible therapeutic approaches to antagonize the MAIFs during the evolution of neuroinflammatory lesions. Moreover, investigative lines for translation of targeted therapies against these myelin inhibitors are defined with an emphasis on the chief MAIF, Nogo-A, that may demonstrate clinical efficacy of neurorepair during progressive MS.

Ovalbumin-specific CD4+ and CD8+ T cells contribute to different susceptibility for Theiler's murine encephalomyelitis virus persistence

Theiler's murine encephalomyelitis virus (TMEV) is the causative agent of TMEV-induced demyelinating disease (TMEV-IDD); a well-established animal model for the chronic progressive form of human multiple sclerosis (MS). In susceptible mice with an inadequate immune response, TMEV-IDD is triggered by virus persistence and maintained by a T cell mediated immunopathology. OT-mice are bred on a TMEV-resistant C57BL/6 background and own predominantly chicken ovalbumin (OVA)-specific populations of CD8⁺ T cells (OT-I) or CD4⁺ T cells (OT-II), respectively. It is hypothesized that the lack of antigen specific T cell populations increases susceptibility for a TMEV-infection in OT-mice on a TMEV-resistant C57BL/6 background. OT-I, OT-II, and C57BL/6 control mice were infected intracerebrally with the TMEV-BeAn strain. Mice were scored weekly for clinical disease and after necropsy, histological and immunohistochemical evaluation was performed. OT-I mice started to develop progressive motor dysfunction between 7 and 21 days post infection (dpi), leading up to hind limb paresis and critical weight loss, which resulted in euthanasia for humane reasons between 14 and 35 dpi. OT-I mice displayed a high cerebral virus load, an almost complete absence of CD8⁺ T cells from the central nervous system (CNS) and a significantly diminished CD4⁺ T cell response. Contrarily, only 60% (12 of 20) of infected OT-II mice developed clinical disease characterized by mild ataxia. 25% of clinically affected OT-II mice (3 of 12) made a full recovery. 5 of 12 OT-II mice with clinical disease developed severe motor dysfunction similar to OT-I mice and were euthanized for humane reasons between 13 and 37 dpi. OT-II mice displayed only low virus-immunoreactivity, but clinical disease correlated well with severely reduced infiltration of CD8⁺ T cells and the increased presence of CD4⁺ T cells in the brains of OT-II mice. Though further studies are needed to reveal the underlying pathomechanisms following TMEV infection in OT mice, findings indicate an immunopathological process as a main contributor to clinical disease in OT-II mice, while a direct virus-associated pathology may be the main contributor to clinical disease in TMEV-infected OT-I mice.

Astrocyte depletion alters extracellular matrix composition in the demyelinating phase of Theiler's murine encephalomyelitis

Astrocytes produce extracellular matrix (ECM) glycoproteins contributing to the blood-brain barrier and regulating the immune response in the central nervous system (CNS). The aim of this study was to investigate the impact of astrocyte depletion upon the clinical outcome and the composition of ECM glycoproteins in a virus-induced animal model of demyelination. Glial fibrillary acidic protein (GFAP)-thymidine-kinase transgenic SJL (GFAP-knockout) and wildtype mice were infected with Theiler’s murine encephalomyelitis virus (TMEV). Astrocyte depletion was induced during the progressive, demyelinating disease phase by ganciclovir administration once daily between 56 and 77 days post infection (dpi). At 77 dpi GFAP-knockout mice showed a significant deterioration of clinical signs associated with a reduction of azan and picrosirius red stained ECM-molecules in the thoracic spinal cord. Basement-membrane-associated ECM-molecules including laminin, entactin/nidogen-1 and Kir4.1 as well as non-basement membrane-associated ECM-molecules like collagen I, decorin, tenascin-R and CD44 were significantly reduced in the spinal cord of GFAP-knockout mice. The reduction of the investigated ECM-molecules demonstrates that astrocytes play a key role in the production of ECM-molecules. The present findings indicate that the detected loss of Kir4.1 and CD44 as well as the disruption of the integrity of perineuronal nets led to the deterioration of clinical signs in GFAP-knockout mice.

Association of DYNC1H1 gene SNP/CNV with disease susceptibility, GCs efficacy, HRQOL, anxiety, and depression in Chinese SLE patients

Background

Systemic lupus erythematosus is a heterogeneous autoimmune disease characterized by multi‐system injuries and overproduction of autoantibodies. There are many genetic studies on SLE, but no report has considered the relationship between cytoplasmic dynein and SLE susceptibility.

Objectives

Our study intends to investigate whether DYNC1H1 gene SNP/CNV is related to SLE susceptibility, GCs efficacy, HRQOL, anxiety, and depression in Chinese SLE patients.

Methods

A total of 502 cases and 544 healthy controls were recruited into the case‐control study, and 472 subjects from the case group were followed up for 12 weeks to evaluate GCs efficacy, HRQOL, anxiety, and depression. Multiplex SNaPshot technique was applied to genotype the seven SNPs of DYNC1H1, and AccuCopy^TM method was conducted to quantify the copy number of DYNC1H1. Anxiety and depression were evaluated using HAMA and HAMD‐24 scales, respectively. The SF‐36 scale was used to assess HRQOL.

Results

The significant association between SNP rs1190606 and SLE susceptibility was displayed in the dominant model (P_BH = 0.004) as well as its allele model (P_BH = 0.004). We also found that SNP rs2273440 was related to photosensitization symptom in SLE patients (P_BH = 0.032). In the follow‐up study, SNP rs11160668 was connected with the improvement of BP in male patients (P_BH = 0.011). However, no association of DYNC1H1 gene with GCs efficacy, anxiety, and depression was found. No CNV in DYNC1H1 was detected.

Conclusions

The study suggests that DYNC1H1 gene polymorphisms may have an effect on SLE susceptibility and BP improvement of HRQOL in Chinese SLE patients.

Current Insights Into the Pathology of Canine Intervertebral Disc Extrusion-Induced Spinal Cord Injury

Spinal cord injury (SCI) in dogs is commonly attributed to intervertebral disc extrusion (IVDE). Over the last years substantial progress was made in the elucidation of factors contributing to the pathogenesis of this common canine disease. A detailed understanding of the underlying histopathological and molecular alterations in the lesioned spinal cord represents a prerequisite to translate knowledge on the time course of secondary injury processes into the clinical setting. This review summarizes the current state of knowledge of the underlying pathology of canine IVDE-related SCI. Pathological alterations in the spinal cord of dogs affected by IVDE-related SCI include early and persisting axonal damage and glial responses, dominated by phagocytic microglia/macrophages. These processes are paralleled by a pro-inflammatory microenvironment with dysregulation of cytokines and matrix metalloproteinases within the spinal cord. These data mirror findings from a clinical and therapeutic perspective and can be used to identify biomarkers that are able to more precisely predict the clinical outcome. The pathogenesis of progressive myelomalacia, a devastating complication of SCI in dogs, is not understood in detail so far; however, a fulminant and exaggerating secondary injury response with massive reactive oxygen species formation seems to be involved in this unique neuropathological entity. There are substantial gaps in the knowledge of pathological changes in IVDE with respect to more advanced and chronic lesions and the potential involvement of demyelination. Moreover, the role of microglia/macrophage polarization in IVDE-related SCI still remains to be investigated. A close collaboration of clinical neurologists and veterinary pathologists will help to facilitate an integrative approach to a more detailed understanding of the molecular pathogenesis of canine IVDE and thus to identify therapeutic targets.

Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human GM1-Gangliosidosis

G_M1-gangliosidosis is caused by a reduced activity of β-galactosidase (Glb1), resulting in intralysosomal accumulations of G_M1. The aim of this study was to reveal the pathogenic mechanisms of G_M1-gangliosidosis in a new Glb1 knockout mouse model. Glb1^−/− mice were analyzed clinically, histologically, immunohistochemically, electrophysiologically and biochemically. Morphological lesions in the central nervous system were already observed in two-month-old mice, whereas functional deficits, including ataxia and tremor, did not start before 3.5-months of age. This was most likely due to a reduced membrane resistance as a compensatory mechanism. Swollen neurons exhibited intralysosomal storage of lipids extending into axons and amyloid precursor protein positive spheroids. Additionally, axons showed a higher kinesin and lower dynein immunoreactivity compared to wildtype controls. Glb1^−/− mice also demonstrated loss of phosphorylated neurofilament positive axons and a mild increase in non-phosphorylated neurofilament positive axons. Moreover, marked astrogliosis and microgliosis were found, but no demyelination. In addition to the main storage material G_M1, G_A1, sphingomyelin, phosphatidylcholine and phosphatidylserine were elevated in the brain. In summary, the current Glb1^−/− mice exhibit a so far undescribed axonopathy and a reduced membrane resistance to compensate the functional effects of structural changes. They can be used for detailed examinations of axon–glial interactions and therapy trials of lysosomal storage diseases.

Neurotrophic effects of GM1 ganglioside, NGF, and FGF2 on canine dorsal root ganglia neurons in vitro

Dogs share many chronic morbidities with humans and thus represent a powerful model for translational research. In comparison to rodents, the canine ganglioside metabolism more closely resembles the human one. Gangliosides are components of the cell plasma membrane playing a role in neuronal development, intercellular communication and cellular differentiation. The present in vitro study aimed to characterize structural and functional changes induced by G_M1 ganglioside (G_M1) in canine dorsal root ganglia (DRG) neurons and interactions of G_M1 with nerve growth factor (NGF) and fibroblast growth factor (FGF2) using immunofluorescence for several cellular proteins including neurofilaments, synaptophysin, and cleaved caspase 3, transmission electron microscopy, and electrophysiology. G_M1 supplementation resulted in increased neurite outgrowth and neuronal survival. This was also observed in DRG neurons challenged with hypoxia mimicking neurodegenerative conditions due to disruptions of energy homeostasis. Immunofluorescence indicated an impact of G_M1 on neurofilament phosphorylation, axonal transport, and synaptogenesis. An increased number of multivesicular bodies in G_M1 treated neurons suggested metabolic changes. Electrophysiological changes induced by G_M1 indicated an increased neuronal excitability. Summarized, G_M1 has neurotrophic and neuroprotective effects on canine DRG neurons and induces functional changes. However, further studies are needed to clarify the therapeutic value of gangliosides in neurodegenerative diseases.

Comparison of Theiler's Murine Encephalomyelitis Virus Induced Spinal Cord and Peripheral Nerve Lesions Following Intracerebral and Intraspinal Infection

Hallmarks of Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) include spinal cord (SC) inflammation, demyelination and axonal damage occurring approximately 5-8 weeks after classical intracerebral (i.c.) infection. The aim of this study was to elucidate the consequences of intraspinal (i.s.) TMEV infection and a direct comparison of classical i.c. and intraspinal infection. Swiss Jim Lambert (SJL)-mice were i.s. infected with the BeAn strain of TMEV. Clinical investigations including a scoring system and rotarod analysis were performed on a regular basis. Necropsies were performed at 3, 7, 14, 28 and 63 days post infection (dpi) following i.s. and at 4, 7, 14, 28, 56, 98, 147 and 196 dpi following i.c. infection. Serial sections of formalin-fixed, paraffin-embedded SC and peripheral nerves (PN) were investigated using hematoxylin and eosin (HE) and immunohistochemistry. I.s. infected mice developed clinical signs and a deterioration of motor coordination approximately 12 weeks earlier than i.c. infected animals. SC inflammation, demyelination and axonal damage occurred approximately 6 weeks earlier in i.s. infected animals. Interestingly, i.s. infected mice developed PN lesions, characterized by vacuolation, inflammation, demyelination and axonal damage, which was not seen following i.c. infection. The i.s. infection model offers the advantage of a significantly earlier onset of clinical signs, inflammatory and demyelinating SC lesions and additionally enables the investigation of virus-mediated PN lesions.

Delayed Astrogliosis Associated with Reduced M1 Microglia Activation in Matrix Metalloproteinase 12 Knockout Mice during Theiler's Murine Encephalomyelitis

Theiler’s murine encephalomyelitis (TME) represents a versatile animal model for studying the pathogenesis of demyelinating diseases such as multiple sclerosis. Hallmarks of TME are demyelination, astrogliosis, as well as inflammation. Previous studies showed that matrix metalloproteinase 12 knockout (Mmp12^−/−) mice display an ameliorated clinical course associated with reduced demyelination. The present study aims to elucidate the impact of MMP12 deficiency in TME with special emphasis on astrogliosis, macrophages infiltrating the central nervous system (CNS), and the phenotype of microglia/macrophages (M1 or M2). SJL wild-type and Mmp12^−/− mice were infected with TME virus (TMEV) or vehicle (mock) and euthanized at 28 and 98 days post infection (dpi). Immunohistochemistry or immunofluorescence of cervical and thoracic spinal cord for detecting glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1), chemokine receptor 2 (CCR2), CD107b, CD16/32, and arginase I was performed and quantitatively evaluated. Statistical analyses included the Kruskal–Wallis test followed by Mann–Whitney U post hoc tests. TMEV-infected Mmp12^−/− mice showed transiently reduced astrogliosis in association with a strong trend (p = 0.051) for a reduced density of activated/reactive microglia/macrophages compared with wild-type mice at 28 dpi. As astrocytes are an important source of cytokine production, including proinflammatory cytokines triggering or activating phagocytes, the origin of intralesional microglia/macrophages as well as their phenotype were determined. Only few phagocytes in wild-type and Mmp12^−/− mice expressed CCR2, indicating that the majority of phagocytes are represented by microglia. In parallel to the reduced density of activated/reactive microglia at 98 dpi, TMEV-infected Mmp12^−/− showed a trend (p = 0.073) for a reduced density of M1 (CD16/32- and CD107b-positive) microglia, while no difference regarding the density of M2 (arginase I- and CD107b-positive) cells was observed. However, a dominance of M1 cells was detected in the spinal cord of TMEV-infected mice at all time points. Reduced astrogliosis in Mmp12^−/− mice was associated with a reduced density of activated/reactive microglia and a trend for a reduced density of M1 cells. This indicates that MMP12 plays an important role in microglia activation, polarization, and migration as well as astrogliosis and microglia/astrocyte interaction.

Facets of Theiler's Murine Encephalomyelitis Virus-Induced Diseases: An Update

Theiler’s murine encephalomyelitis virus (TMEV), a naturally occurring, enteric pathogen of mice is a Cardiovirus of the Picornaviridae family. Low neurovirulent TMEV strains such as BeAn cause a severe demyelinating disease in susceptible SJL mice following intracerebral infection. Furthermore, TMEV infections of C57BL/6 mice cause acute polioencephalitis initiating a process of epileptogenesis that results in spontaneous recurrent epileptic seizures in approximately 50% of affected mice. Moreover, C3H mice develop cardiac lesions after an intraperitoneal high-dose application of TMEV. Consequently, TMEV-induced diseases are widely used as animal models for multiple sclerosis, epilepsy, and myocarditis. The present review summarizes morphological lesions and pathogenic mechanisms triggered by TMEV with a special focus on the development of hippocampal degeneration and seizures in C57BL/6 mice as well as demyelination in the spinal cord in SJL mice. Furthermore, a detailed description of innate and adaptive immune responses is given. TMEV studies provide novel insights into the complexity of organ- and mouse strain-specific immunopathology and help to identify factors critical for virus persistence.

Increasing Agrin Function Antagonizes Muscle Atrophy and Motor Impairment in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a pediatric genetic disease, characterized by motor neuron (MN) death, leading to progressive muscle weakness, respiratory failure, and, in the most severe cases, to death. Abnormalities at the neuromuscular junction (NMJ) have been reported in SMA, including neurofilament (NF) accumulation at presynaptic terminals, immature and smaller than normal endplates, reduced transmitter release, and, finally, muscle denervation. Here we have studied the role of agrin in SMAΔ7 mice, the experimental model of SMAII. We observed a 50% reduction in agrin expression levels in quadriceps of P10 SMA mice compared to age-matched WT controls. To counteract such condition, we treated SMA mice from birth onwards with therapeutic agrin biological NT-1654, an active splice variant of agrin retaining synaptogenic properties, which is also resistant to proteolytic cleavage by neurotrypsin. Mice were analyzed for behavior, muscle and NMJ histology, and survival. Motor behavior was significantly improved and survival was extended by treatment of SMA mice with NT-1654. At P10, H/E-stained sections of the quadriceps, a proximal muscle early involved in SMA, showed that NT-1654 treatment strongly prevented the size decrease of muscle fibers. Studies of NMJ morphology on whole-mount diaphragm preparations revealed that NT-1654-treated SMA mice had more mature NMJs and reduced NF accumulation, compared to vehicle-treated SMA mice. We conclude that increasing agrin function in SMA has beneficial outcomes on muscle fibers and NMJs as the agrin biological NT-1654 restores the crosstalk between muscle and MNs, delaying muscular atrophy, improving motor performance and extending survival.

Microarray-Based Gene Expression Analysis for Veterinary Pathologists: A Review

High-throughput, genome-wide transcriptome analysis is now commonly used in all fields of life science research and is on the cusp of medical and veterinary diagnostic application. Transcriptomic methods such as microarrays and next-generation sequencing generate enormous amounts of data. The pathogenetic expertise acquired from understanding of general pathology provides veterinary pathologists with a profound background, which is essential in translating transcriptomic data into meaningful biological knowledge, thereby leading to a better understanding of underlying disease mechanisms. The scientific literature concerning high-throughput data-mining techniques usually addresses mathematicians or computer scientists as the target audience. In contrast, the present review provides the reader with a clear and systematic basis from a veterinary pathologist's perspective. Therefore, the aims are (1) to introduce the reader to the necessary methodological background; (2) to introduce the sequential steps commonly performed in a microarray analysis including quality control, annotation, normalization, selection of differentially expressed genes, clustering, gene ontology and pathway analysis, analysis of manually selected genes, and biomarker discovery; and (3) to provide references to publically available and user-friendly software suites. In summary, the data analysis methods presented within this review will enable veterinary pathologists to analyze high-throughput transcriptome data obtained from their own experiments, supplemental data that accompany scientific publications, or public repositories in order to obtain a more in-depth insight into underlying disease mechanisms.

Cytotoxic CD8+ T cell ablation enhances the capacity of regulatory T cells to delay viral elimination in Theiler's murine encephalomyelitis

Theiler's murine encephalomyelitis (TME) of susceptible mouse strains is a commonly used infectious animal model for multiple sclerosis. The study aim was to test the hypothesis whether cytotoxic T cell responses account for the limited impact of regulatory T cells on antiviral immunity in TME virus-induced demyelinating disease (TMEV-IDD) resistant C57BL/6 mice. TME virus-infected C57BL/6 mice were treated with (i) interleukin-2/-anti-interleukin-2-antibody-complexes to expand regulatory T cells ("Treg-expansion"), (ii) anti-CD8-antibodies to deplete cytotoxic T cells ("CD8-depletion") or (iii) with a combination of Treg-expansion and CD8-depletion ("combined treatment") prior to infection. Results showed that "combined treatment", but neither sole "Treg-expansion" nor "CD8-depletion," leads to sustained hippocampal infection and virus spread to the spinal cord in C57BL/6 mice. Prolonged infection reduces myelin basic protein expression in the spinal cord together with increased accumulation of β-amyloid precursor protein in axons, characteristic of myelin loss and axonal damage, respectively. Chronic spinal cord infection upon "combined treatment" was also associated with increased T and B cell recruitment, accumulation of CD107b⁺ microglia/macrophages and enhanced mRNA expression of interleukin (IL)-1α, IL-10 and tumor necrosis factor α. In conclusion, data revealed that the suppressive capacity of Treg on viral elimination is efficiently boosted by CD8-depletion, which renders C57BL/6 mice susceptible to develop chronic neuroinfection and TMEV-IDD.

Synaptophysin Is a Reliable Marker for Axonal Damage

Synaptophysin is an abundant membrane protein of synaptic vesicles. The objective of this study was to determine the utility of identifying synaptophysin accumulations (spheroids/ovoids/bulbs) in CNS white matter as an immunohistochemical marker of axonal damage in demyelinating and neuroinflammatory conditions. We studied the cuprizone toxicity and Theiler’s murine encephalomyelitis virus (TMEV) infection models of demyelination and analyzed CNS tissue from patients with multiple sclerosis (MS). Synaptophysin colocalized with the amyloid precursor protein (APP), a well-known marker of axonal damage. In the cuprizone model, numerous pathological synaptophysin/APP-positive spheroids/ovoids were identified in the corpus callosum at the onset of demyelination; the extent of synaptophysin/APP-positive vesicle aggregates correlated with identified reactive microglia; during late and chronic demyelination, the majority of synaptophysin/APP-positive spheroids/ovoids resolved but a few remained, indicating persistent axonal damage; in the remyelination phase, scattered large synaptophysin/APP-positive bulbs persisted. In the TMEV model, only a few large- to medium-sized synaptophysin/APP-positive bulbs were found in demyelinated areas. In MS patient tissue samples, the bulbs appeared exclusively at the inflammatory edges of lesions. In conclusion, our data suggest that synaptophysin as a reliable marker of axonal damage in the CNS in inflammatory/demyelinating conditions.

Viral Infection of the Central Nervous System Exacerbates Interleukin-10 Receptor Deficiency-Mediated Colitis in SJL Mice

Theiler´s murine encephalomyelitis virus (TMEV)-infection is a widely used animal model for studying demyelinating disorders, including multiple sclerosis (MS). The immunosuppressive cytokine Interleukin (IL)-10 counteracts hyperactive immune responses and critically controls immune homeostasis in infectious and autoimmune disorders. In order to investigate the effect of signaling via Interleukin-10 receptor (IL-10R) in infectious neurological diseases, TMEV-infected SJL mice were treated with IL-10R blocking antibody (Ab) in the acute and chronic phase of the disease. The findings demonstrate that (i) Ab-mediated IL-10 neutralization leads to progressive colitis with a reduction in Foxp3+ regulatory T cells and increased numbers of CD8+CD44+ memory T cells as well as activated CD4+CD69+ and CD8+CD69+ T cells in uninfected mice. (ii) Concurrent acute TMEV-infection worsened enteric disease-mediated by IL-10R neutralization. Virus-triggered effects were associated with an enhanced activation of CD4+ T helper cells and CD8+ cytotoxic T lymphocytes and augmented cytokine expression. By contrast, (iii) IL-10R neutralization during chronic TMEV-infection was not associated with enhanced peripheral immunopathology but an increased CD3+ T cell influx in the spinal cord. IL-10R neutralization causes a breakdown in peripheral immune tolerance in genetically predisposed mice, which leads to immune-mediated colitis, resembling inflammatory bowel disease. Hyperactive immune state following IL-10R blockade is enhanced by central nervous system-restricted viral infection in a disease phase-dependent manner.

Axonopathy in the Central Nervous System Is the Hallmark of Mice with a Novel Intragenic Null Mutation of Dystonin

Dystonia musculorum is a neurodegenerative disorder caused by a mutation in the dystonin gene. It has been described in mice and humans where it is called hereditary sensory autonomic neuropathy. Mutated mice show severe movement disorders and die at the age of 3-4 weeks. This study describes the discovery and molecular, clinical, as well as pathological characterization of a new spontaneously occurring mutation in the dystonin gene in C57BL/6N mice. The mutation represents a 40-kb intragenic deletion allele of the dystonin gene on chromosome 1 with exactly defined deletion borders. It was demonstrated by Western blot, mass spectrometry, and immunohistology that mice with a homozygous mutation were entirely devoid of the dystonin protein. Pathomorphological lesions were restricted to the brain stem and spinal cord and consisted of swollen, argyrophilic axons and dilated myelin sheaths in the white matter and, less frequently, total chromatolysis of neurons in the gray matter. Axonal damage was detected by amyloid precursor protein and nonphosphorylated neurofilament immunohistology. Axonopathy in the central nervous system (CNS) represents the hallmark of this disease. Mice with the dystonin mutation also showed suppurative inflammation in the respiratory tract, presumably due to brain stem lesion-associated food aspiration, whereas skeletal muscles showed no pathomorphological changes. This study describes a novel mutation in the dystonin gene in mice leading to axonopathy in the CNS. In further studies, this model may provide new insights into the pathogenesis of neurodegenerative diseases and may elucidate the complex interactions of dystonin with various other cellular proteins especially in the CNS.

Immunohistochemical and transcriptome analyses indicate complex breakdown of axonal transport mechanisms in canine distemper leukoencephalitis

INTRODUCTION

CDV-DL (Canine distemper virus-induced demyelinating leukoencephalitis) represents a spontaneously occurring animal model for demyelinating disorders. Axonopathy represents a key pathomechanism in this disease; however, its underlying pathogenesis has not been addressed in detail so far. This study aimed at the characterization of axonal cytoskeletal, transport, and potential regenerative changes with a parallel focus upon Schwann cell remyelination.

METHODS

Immunohistochemistry of canine cerebellar tissue as well as a comparative analysis of genes from an independent microarray study were performed.

RESULTS

Increased axonal immunoreactivity for nonphosphorylated neurofilament was followed by loss of cytoskeletal and motor proteins. Interestingly, a subset of genes encoding for neurofilament subunits and motor proteins was up-regulated in the chronic stage compared to dogs with subacute CDV-DL. However, immunohistochemically, hints for axonal regeneration were restricted to up-regulated axonal positivity of hypoxia-inducible factor 1 alpha, while growth-associated protein 43, erythropoietin and its receptor were not or even down-regulated. Periaxin-positive structures, indicative of Schwann cell remyelination, were only detected within few advanced lesions.

CONCLUSIONS

The present findings demonstrate a complex sequence of axonal cytoskeletal breakdown mechanisms. Moreover, though sparse, this is the first report of Schwann cell remyelination in CDV-DL. Facilitation of these very limited endogenous regenerative responses represents an important topic for future research.

Neuromuscular Junctions as Key Contributors and Therapeutic Targets in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a recessive autosomal neuromuscular disease, representing the most common fatal pediatric pathology. Even though, classically and in a simplistic way, it is categorized as a motor neuron (MN) disease, there is an increasing general consensus that its pathogenesis is more complex than expected. In particular, neuromuscular junctions (NMJs) are affected by dramatic alterations, including immaturity, denervation and neurofilament accumulation, associated to impaired synaptic functions: these abnormalities may in turn have a detrimental effect on MN survival. Here, we provide a description of NMJ development/maintenance/maturation in physiological conditions and in SMA, focusing on pivotal molecules and on the time-course of pathological events. Moreover, since NMJs could represent an important target to be exploited for counteracting the pathology progression, we also describe several therapeutic strategies that, directly or indirectly, aim at NMJs.

Interferon-stimulated genes-essential antiviral effectors implicated in resistance to Theiler's virus-induced demyelinating disease

Background

Experimental infection of mice with Theiler’s murine encephalomyelitis virus (TMEV) is used as an animal model of human multiple sclerosis. TMEV persists in susceptible mouse strains and causes a biphasic disease consisting of acute polioencephalomyelitis and chronic demyelinating leukomyelitis. In contrast, resistant mice eliminate the virus within 2 to 4 weeks, which seems to be based on a strong antiviral innate immune response including the activation of the type I interferon (IFN) pathway. Several interferon-stimulated genes (ISGs) such as IFN-stimulated protein of 15 kDa (ISG15), protein kinase R (PKR), and 2′5′-oligoadenylate synthetase (OAS) function as antiviral effectors and might contribute to virus elimination. Nevertheless, detailed investigations of the type I IFN pathway during TMEV-induced demyelinating disease (TMEV-IDD) are lacking.

Methods

The present study evaluated microarray data of the spinal cord obtained from susceptible SJL/J mice after TMEV infection focusing on IFN-related genes. Moreover, ISG gene and protein expression was determined in mock- and TMEV-infected SJL/J mice and compared to its expression in resistant C57BL/6 mice using real- time PCR, immunohistochemistry, and immunofluorescence.

Results

Interestingly, despite of increased ISG gene expression during TMEV-IDD, ISG protein expression was impaired in SJL/J mice and mainly restricted to demyelinated lesions. In contrast, high ISG protein levels were found in spinal cord gray and white matter of C57BL/6 compared to SJL/J mice in the acute and chronic phase of TMEV-IDD. In both mouse strains, ISG15 was mainly found in astrocytes and endothelial cells, whereas PKR was predominantly expressed by microglia/macrophages, oligodendrocytes, and neurons. Only few cells were immunopositive for OAS proteins.

Conclusions

High levels of antiviral ISG15 and PKR proteins in the spinal cord of C57BL/6 mice might block virus replication and play an important role in the resistance to TMEV-IDD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0462-x) contains supplementary material, which is available to authorized users.

Reductions in kinesin expression are associated with nitric oxide-induced axonal damage

Axonal injury is often characterized by axonal transport defects and abnormal accumulation of intra-axonal components. Nitric oxide (NO) has a key role in mediating inflammatory axonopathy in many neurodegenerative diseases, but little is known about how nitrosative/oxidative stress affects axonal transport or whether reductions in kinesin superfamily protein (KIF) expression correlate with axon pathology. KIFs are molecular motors that have a key role in axonal and dendritic transport, and impairment of these mechanisms has been associated with a number of neurological disorders. This study shows that rat cortical neurons exposed to NO display both a time-dependent decrease in KIF gene/protein expression and neurofilament phosphorylation in addition to a reduction in axonal length and neuronal survival. Because mesenchymal stem cells (MSCs) represent a promising therapeutic candidate for neuronal/axonal repair, this study analyzes the capacity of MSCs to protect neurons and axonal transport mechanisms from NO damage. Results show that coculture of MSCs with NO-exposed neurons results in the preservation of KIF expression, axonal length, and neuronal survival. Altogether, these results suggest a potential mechanism involved in the disruption of axonal transport and abnormal accumulation of proteins in axons during nitrosative insult. We hypothesize that impaired axonal transport contributes, per se, to progression of injury and provide further evidence of the therapeutic potential of MSCs for neurodegenerative disorders. © 2015 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Dynamic Changes of Microglia/Macrophage M1 and M2 Polarization in Theiler's Murine Encephalomyelitis

Microglia and macrophages play a central role for demyelination in Theiler's murine encephalomyelitis (TME) virus infection, a commonly used infectious model for chronic-progressive multiple sclerosis. In order to determine the dynamic changes of microglia/macrophage polarization in TME, the spinal cord of Swiss Jim Lambert (SJL) mice was investigated by gene expression profiling and immunofluorescence. Virus persistence and demyelinating leukomyelitis were confirmed by immunohistochemistry and histology. Electron microscopy revealed continuous myelin loss together with abortive myelin repair during the late chronic infection phase indicative of incomplete remyelination. A total of 59 genes out of 151 M1- and M2-related genes were differentially expressed in TME virus-infected mice over the study period. The onset of virus-induced demyelination was associated with a dominating M1 polarization, while mounting M2 polarization of macrophages/microglia together with sustained prominent M1-related gene expression was present during the chronic-progressive phase. Molecular results were confirmed by immunofluorescence, showing an increased spinal cord accumulation of CD16/32(+) M1-, arginase-1(+) M2- and Ym1(+) M2-type cells associated with progressive demyelination. The present study provides a comprehensive database of M1-/M2-related gene expression involved in the initiation and progression of demyelination supporting the hypothesis that perpetuating interaction between virus and macrophages/microglia induces a vicious circle with persistent inflammation and impaired myelin repair in TME.

Feminized behavior and brain gene expression in a novel mouse model of Klinefelter Syndrome

Klinefelter Syndrome (KS) is the most common sex chromosome aneuploidy in men and is characterized by the presence of an additional X chromosome (XXY). In some Klinefelter males, certain traits may be feminized or shifted from the male-typical pattern towards a more female-typical one. Among them might be partner choice, one of the most sexually dimorphic traits in the animal kingdom. We investigated the extent of feminization in XXY male mice (XXYM) in partner preference and gene expression in the bed nucleus of the stria terminalis/preoptic area and the striatum in mice from the Sex Chromosome Trisomy model. We tested for partner preference using a three-chambered apparatus in which the test mouse was free to choose between stimulus animals of either sex. We found that partner preference in XXYM was feminized. These differences were likely due to interactions of the additional X chromosome with the Y. We also discovered genes that differed in expression in XXYM versus XYM. Some of these genes are feminized in their expression pattern. Lastly, we also identified genes that differed only between XXYM versus XYM and not XXM versus XYM. Genes that are both feminized and unique to XXYM versus XYM represent strong candidates for dissecting the molecular pathways responsible for phenotypes present in KS/XXYM but not XXM. In sum, our results demonstrated that investigating behavioral and molecular feminization in XXY males can provide crucial information about the pathophysiology of KS and may aid our understanding of sex differences in brain and behavior.

New aspects of the pathogenesis of canine distemper leukoencephalitis

Canine distemper virus (CDV) is a member of the genus morbillivirus, which is known to cause a variety of disorders in dogs including demyelinating leukoencephalitis (CDV-DL). In recent years, substantial progress in understanding the pathogenetic mechanisms of CDV-DL has been made. In vivo and in vitro investigations provided new insights into its pathogenesis with special emphasis on axon-myelin-glia interaction, potential endogenous mechanisms of regeneration, and astroglial plasticity. CDV-DL is characterized by lesions with a variable degree of demyelination and mononuclear inflammation accompanied by a dysregulated orchestration of cytokines as well as matrix metalloproteinases and their inhibitors. Despite decades of research, several new aspects of the neuropathogenesis of CDV-DL have been described only recently. Early axonal damage seems to represent an initial and progressive lesion in CDV-DL, which interestingly precedes demyelination. Axonopathy may, thus, function as a potential trigger for subsequent disturbed axon-myelin-glia interactions. In particular, the detection of early axonal damage suggests that demyelination is at least in part a secondary event in CDV-DL, thus challenging the dogma of CDV as a purely primary demyelinating disease. Another unexpected finding refers to the appearance of p75 neurotrophin (NTR)-positive bipolar cells during CDV-DL. As p75NTR is a prototype marker for immature Schwann cells, this finding suggests that Schwann cell remyelination might represent a so far underestimated endogenous mechanism of regeneration, though this hypothesis still remains to be proven. Although it is well known that astrocytes represent the major target of CDV infection in CDV-DL, the detection of infected vimentin-positive astrocytes in chronic lesions indicates a crucial role of this cell population in nervous distemper. While glial fibrillary acidic protein represents the characteristic intermediate filament of mature astrocytes, expression of vimentin is generally restricted to immature or reactive astrocytes. Thus, vimentin-positive astrocytes might constitute an important cell population for CDV persistence and spread, as well as lesion progression. In vitro models, such as dissociated glial cell cultures, as well as organotypic brain slice cultures have contributed to a better insight into mechanisms of infection and certain morphological and molecular aspects of CDV-DL. Summarized, recent in vivo and in vitro studies revealed remarkable new aspects of nervous distemper. These new perceptions substantially improved our understanding of the pathogenesis of CDV-DL and might represent new starting points to develop novel treatment strategies.

CNS Schwann cells display oligodendrocyte precursor-like potassium channel activation and antigenic expression in vitro

Central nervous system (CNS) injury triggers production of myelinating Schwann cells from endogenous oligodendrocyte precursors (OLPs). These CNS Schwann cells may be attractive candidates for novel therapeutic strategies aiming to promote endogenous CNS repair. However, CNS Schwann cells have been so far mainly characterized in situ regarding morphology and marker expression, and it has remained enigmatic whether they display functional properties distinct from peripheral nervous system (PNS) Schwann cells. Potassium channels (K+) have been implicated in progenitor and glial cell proliferation after injury and may, therefore, represent a suitable pharmacological target. In the present study, we focused on the function and expression of voltage-gated K+ channels Kv(1-12) and accessory β-subunits in purified adult canine CNS and PNS Schwann cell cultures using electrophysiology and microarray analysis and characterized their antigenic phenotype. We show here that K+ channels differed significantly in both cell types. While CNS Schwann cells displayed prominent K D-mediated K+ currents, PNS Schwann cells elicited K(D-) and K(A-type) K+ currents. Inhibition of K+ currents by TEA and Ba2+ was more effective in CNS Schwann cells. These functional differences were not paralleled by differential mRNA expression of Kv(1-12) and accessory β-subunits. However, O4/A2B5 and GFAP expressions were significantly higher and lower, respectively, in CNS than in PNS Schwann cells. Taken together, this is the first evidence that CNS Schwann cells display specific properties not shared by their peripheral counterpart. Both Kv currents and increased O4/A2B5 expression were reminiscent of OLPs suggesting that CNS Schwann cells retain OLP features during maturation.

Reduced axonal motor protein expression in non-lesional grey matter in multiple sclerosis

Background:

Multiple sclerosis (MS) is a neurological disease characterised by central nervous system inflammation, demyelination, axonal degeneration and neuronal injury. Preventing neuronal and axon damage is of paramount importance in attempts to prevent disease progression. Intact axonal transport mechanisms are crucial to axonal integrity and evidence suggests these mechanisms are disrupted in MS. Anterograde axonal transport is mediated to a large extent through the kinesin superfamily proteins. Recently, certain kinesin superfamily proteins (KIF5A, KIF1B and KIF21B) were implicated in MS pathology.

Objectives:

To investigate the expression of KIF5A, KIF21B and KIF1B in MS and control post-mortem grey matter.

Methods:

Using both quantitative real-time polymerase chain reaction (PCR) and Immunodot-blots assays, we analysed the expression of kinesin superfamily proteins in 27 MS cases and 13 control cases not linked to neurological disease.

Results:

We have shown significant reductions in KIF5A, KIF21B and KIF1B messenger ribonucleic acid (mRNA) expression and also KIF5A protein expression in MS grey matter, as compared to control grey matter.

Conclusion:

We have shown significant reductions in mRNA and protein levels of axonal motor proteins in the grey matter of MS cases, which may have important implications for the pathogenesis of neuronal/axonal injury in the disease.

Immunophenotyping of inflammatory cells associated with Schmallenberg virus infection of the central nervous system of ruminants

Schmallenberg virus (SBV) is a recently discovered Bunyavirus associated mainly with abortions, stillbirths and malformations of the skeletal and central nervous system (CNS) in newborn ruminants. In this study, a detailed immunophenotyping of the inflammatory cells of the CNS of affected animals was carried out in order to increase our understanding of SBV pathogenesis. A total of 82 SBV-polymerase chain reaction (PCR) positive neonatal ruminants (46 sheep lambs, 34 calves and 2 goat kids) were investigated for the presence of inflammation in the brain and spinal cord. The study focused on 15 out of 82 animals (18.3%) showing inflammation in the CNS. All 15 neonates displayed lymphohistiocytic meningoencephalomyelitis affecting most frequently the mesencephalon and the parietal and temporal lobes. The majority of infiltrating cells were CD3-positive T cells, followed by CD79α-positive B cells and CD68-positive microglia/macrophages. Malformations like por- and hydranencephaly, frequently found in the temporal lobe, showed associated demyelination and axonal loss. SBV antigen was detected in 37 out of 82 (45.1%) neonatal brains by immunohistochemistry. In particular, SBV antigen was found in 93.3% (14 out of 15 ruminants) and 32.8% (22 out of 67 ruminants) of animals with and without encephalitis, respectively. Highest amounts of virus-protein expression levels were found in the temporal lobe. Our findings suggest that: (i) different brain regions display differential susceptibility to SBV infection; (ii) inflammatory cells in the CNS are found only in a minority of virus infected animals; (iii) malformations occur in association with and without inflammation in the CNS; and (iv) viral antigen is strongly associated with the presence of inflammation in naturally infected animals. Further studies are required to explore the cell tropism and pathogenesis of SBV infection in ruminants.

Spatio-temporal development of axonopathy in canine intervertebral disc disease as a translational large animal model for nonexperimental spinal cord injury

Spinal cord injury (SCI) represents a devastating central nervous system disease that still lacks sufficient therapies. Here, dogs are increasingly recognized as a preclinical animal model for the development of future therapies. The aim of this study was a detailed characterization of axonopathy in canine intervertebral disc disease, which produces a mixed contusive and compressive injury and functions as a spontaneous translational animal model for human SCI. The results revealed an early occurrence of ultrastructurally distinct axonal swelling. Immunohistochemically, enhanced axonal expression of β-amyloid precursor protein, non-phosphorylated neurofilament (n-NF) and growth-associated protein-43 was detected in the epicenter during acute canine SCI. Indicative of a progressive axonopathy, these changes showed a cranial and caudally accentuated spatial progression in the subacute disease phase. In canine spinal cord slice cultures, immunoreactivity of axons was confined to n-NF. Real-time quantitative polymerase chain reaction of naturally traumatized tissue and slice cultures revealed a temporally distinct dysregulation of the matrix metalloproteinases (MMP)-2 and MMP-9 with a dominating expression of the latter. Contrasting to early axonopathy, diminished myelin basic protein immunoreactivity and phagocytosis were delayed. The results present a basis for assessing new therapies in the canine animal model for translational research that might allow partial extrapolation to human SCI.