Evoked potentials as a biomarker of remyelination.

Multiple sclerosis (MS) is a common cause of neurologic disease in young adults that is primarily treated with disease-modifying therapies which target the immune and inflammatory responses. Promotion of remyelination has opened a new therapeutic avenue, but how best to determine efficacy of remyelinating drugs remains unresolved. Although prolongation and then shortening of visual evoked potential (VEP) latencies in optic neuritis in MS may identify demyelination and remyelination, this has not been directly confirmed. We recorded VEPs in a model in which there is complete demyelination of the optic nerve, with subsequent remyelination. We examined the optic nerves microscopically during active disease and recovery, and quantitated both demyelination and remyelination along the length of the nerves. Latencies of the main positive component of the control VEP demonstrated around 2-fold prolongation during active disease. VEP waveforms were nonrecordable in a few subjects or exhibited a broadened profile which precluded peak identification. As animals recovered neurologically, the VEP latencies decreased in association with complete remyelination of the optic nerve but remained prolonged relative to controls. Thus, it has been directly confirmed that VEP latencies reflect the myelin status of the optic nerve and will provide a surrogate marker in future remyelination clinical trials.

Critical role for iron accumulation in the pathogenesis of fibrotic lung disease.

Increased iron levels and dysregulated iron homeostasis, or both, occur in several lung diseases. Here, the effects of iron accumulation on the pathogenesis of pulmonary fibrosis and associated lung function decline was investigated using a combination of murine models of iron overload and bleomycin-induced pulmonary fibrosis, primary human lung fibroblasts treated with iron, and histological samples from patients with or without idiopathic pulmonary fibrosis (IPF). Iron levels are significantly increased in iron overloaded transferrin receptor 2 (Tfr2) mutant mice and homeostatic iron regulator (Hfe) gene-deficient mice and this is associated with increases in airway fibrosis and reduced lung function. Furthermore, fibrosis and lung function decline are associated with pulmonary iron accumulation in bleomycin-induced pulmonary fibrosis. In addition, we show that iron accumulation is increased in lung sections from patients with IPF and that human lung fibroblasts show greater proliferation and cytokine and extracellular matrix responses when exposed to increased iron levels. Significantly, we show that intranasal treatment with the iron chelator, deferoxamine (DFO), from the time when pulmonary iron levels accumulate, prevents airway fibrosis and decline in lung function in experimental pulmonary fibrosis. Pulmonary fibrosis is associated with an increase in Tfr1+ macrophages that display altered phenotype in disease, and DFO treatment modified the abundance of these cells. These experimental and clinical data demonstrate that increased accumulation of pulmonary iron plays a key role in the pathogenesis of pulmonary fibrosis and lung function decline. Furthermore, these data highlight the potential for the therapeutic targeting of increased pulmonary iron in the treatment of fibrotic lung diseases such as IPF. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The adult oligodendrocyte can participate in remyelination.

Endogenous remyelination of the CNS can be robust and restore function, yet in multiple sclerosis it becomes less complete with time. Promoting remyelination is a major therapeutic goal, both to restore function and to protect axons from degeneration. Remyelination is thought to depend on oligodendrocyte progenitor cells, giving rise to nascent remyelinating oligodendrocytes. Surviving, mature oligodendrocytes are largely regarded as being uninvolved. We have examined this question using two large animal models. In the first model, there is extensive demyelination and remyelination of the CNS, yet oligodendrocytes survive, and in recovered animals there is a mix of remyelinated axons interspersed between mature, thick myelin sheaths. Using 2D and 3D light and electron microscopy, we show that many oligodendrocytes are connected to mature and remyelinated myelin sheaths, which we conclude are cells that have reextended processes to contact demyelinated axons while maintaining mature myelin internodes. In the second model in vitamin B12-deficient nonhuman primates, we demonstrate that surviving mature oligodendrocytes extend processes and ensheath demyelinated axons. These data indicate that mature oligodendrocytes can participate in remyelination.

Thin myelin sheaths as the hallmark of remyelination persist over time and preserve axon function.

The presence of thin myelin sheaths in the adult CNS is recognized as a marker of remyelination, although the reason there is not a recovery from demyelination to normal myelin sheath thickness remains unknown. Remyelination is the default pathway after myelin loss in all mammalian species, in both naturally occurring and experimental disease. However, there remains uncertainty about whether these thin sheaths thicken with time and whether they remain viable for extended periods. We provide two lines of evidence here that thin myelin sheaths may persist indefinitely in long-lived animal models. In the first, we have followed thin myelin sheaths in a model of delayed myelination during a period of 13 years that we propose results in the same myelin sheath deficiencies as seen in remyelination; that is, thin myelin sheaths and short internodes. We show that the myelin sheaths remain thin and stable on many axons throughout this period with no detrimental effects on axons. In a second model system, in which there is widespread demyelination of the spinal cord and optic nerves, we also show that thinly remyelinated axons with short internodes persist for over the course of 2 y. These studies confirm the persistence and longevity of thin myelin sheaths and the importance of remyelination to the long-term health and function of the CNS.

Clemastine effects in rat models of a myelination disorder.

BackgroundPelizaeus Merzbacher disease (PMD) is a dysmyelinating disorder of the central nervous system caused by impaired differentiation of oligodendrocytes. This study was prompted by findings that antimuscarinic compounds enhance oligodendrocyte differentiation and remyelination in vitro. One of these compounds, clemastine fumarate, is licensed for treatment of allergic conditions. We tested whether clemastine fumarate can promote myelination in two rodent PMD models, the myelin-deficient and the PLP transgenic rat.MethodsPups were treated with daily injections of clemastine (10-30 mg/kg/day) on postnatal days 1-21. Neurologic phenotypes and myelination patterns in the brain, optic nerves, and spinal cords were assessed using histological techniques.ResultsNo changes in neurological phenotype or survival were observed even at the highest dose of clemastine. Postmortem staining with Luxol fast blue and myelin basic protein immunohistochemistry revealed no evidence for improved myelination in the CNS of treated rats compared to vehicle-treated littermates. Populations of mature oligodendrocytes were unaffected by the treatment.ConclusionThese results demonstrate lack of therapeutic effect of clemastine in two rat PMD models. Both models have rapid disease progression consistent with the connatal form of the disease. Further studies are necessary to determine whether clemastine bears a therapeutic potential in milder forms of PMD.

Gene co-expression networks shed light into diseases of brain iron accumulation.

Aberrant brain iron deposition is observed in both common and rare neurodegenerative disorders, including those categorized as Neurodegeneration with Brain Iron Accumulation (NBIA), which are characterized by focal iron accumulation in the basal ganglia. Two NBIA genes are directly involved in iron metabolism, but whether other NBIA-related genes also regulate iron homeostasis in the human brain, and whether aberrant iron deposition contributes to neurodegenerative processes remains largely unknown. This study aims to expand our understanding of these iron overload diseases and identify relationships between known NBIA genes and their main interacting partners by using a systems biology approach. We used whole-transcriptome gene expression data from human brain samples originating from 101 neuropathologically normal individuals (10 brain regions) to generate weighted gene co-expression networks and cluster the 10 known NBIA genes in an unsupervised manner. We investigated NBIA-enriched networks for relevant cell types and pathways, and whether they are disrupted by iron loading in NBIA diseased tissue and in an in vivo mouse model. We identified two basal ganglia gene co-expression modules significantly enriched for NBIA genes, which resemble neuronal and oligodendrocytic signatures. These NBIA gene networks are enriched for iron-related genes, and implicate synapse and lipid metabolism related pathways. Our data also indicates that these networks are disrupted by excessive brain iron loading. We identified multiple cell types in the origin of NBIA disorders. We also found unforeseen links between NBIA networks and iron-related processes, and demonstrate convergent pathways connecting NBIAs and phenotypically overlapping diseases. Our results are of further relevance for these diseases by providing candidates for new causative genes and possible points for therapeutic intervention.

Variation in SNPs of the IL7Ra gene is associated with multiple sclerosis in the Iranian population.

Interleukin-7 receptor-alpha gene (IL7Ra) is a member of the type I cytokine receptor family located on 5p13 human chromosome. Some evidence associates multiple sclerosis and single nucleotide polymorphisms in the promoter and exonic region of IL7Ra gene. In an attempt to clarify this association, the frequency of 3 SNPs located in the promoter and 1 SNP located in the 6th exon of IL7Ra gene were analyzed in a population of 100 Iranian MS patients as well as 100 controls. Restriction enzyme digestion and a designed mismatch PCR-RFLP strategy were used for the SNP genotyping of our study groups. Considering allele, genotype and haplotype frequencies, no significant association was observed between MS and IL7Ra polymorphisms. Meanwhile, a significant difference was detected between control and primary progressive MS patients considering promoter SNPrs11567685 marker frequency. Also, a significant difference was detected considering exonic SNPrs6897932 for secondary progressive MS patients. Our analysis indicates that GCAC and GTAT haplotypes are less common in SP and PP MS groups, respectively. These differences support the concept that clinical phenotypes may have different etiologies and, therefore, require different therapy strategies.

Feline irradiated diet-induced demyelination; a model of the neuropathology of sub-acute combined degeneration?

Irradiation of food at 50-55 kGy results in a profound, chronic demyelinating-remyelinating disease of the entire central nervous system (CNS) in cats, named Feline Irradiated Diet-Induced Demyelination (FIDID). This study examines the early stages of demyelination and long-term consequences of demyelination and remyelination on axon survival or loss. Myelin vacuolation is the primary defect leading to myelin breakdown, demyelination then prompt remyelination in the spinal cord and brain. There is no evidence of oligodendrocyte death. The spinal cord dorsal column is initially spared yet eventually becomes severely demyelinated with subsequent loss of axons in the core and then surface of the fasciculus gracilis. However remyelination of the sub-pial axons in the dorsal column results in their protection. While there was a lack of biochemical evidence of Vitamin B12 deficiency, the pathological similarities of FIDID with sub-acute combined degeneration (SCD) led us to explore treatment with Vitamin B12. Treatment led to recovery or improvement in some cats and neurologic relapse on cessation of B12 therapy. While the reason that irradiated food is myelinotoxic in the cat remains unresolved, nonetheless the neuropathological changes match exactly what is seen in SCD and its models and provide an ideal model to study the cellular and molecular basis of remyelination.

Advantages of Array-Based Technologies for Pre-Emptive Pharmacogenomics Testing.

As recognised by the National Institutes of Health (NIH) Precision Medicine Initiative (PMI), microarray technology currently provides a rapid, inexpensive means of identifying large numbers of known genomic variants or gene transcripts in experimental and clinical settings. However new generation sequencing techniques are now being introduced in many clinical genetic contexts, particularly where novel mutations are involved. While these methods can be valuable for screening a restricted set of genes for known or novel mutations, implementation of whole genome sequencing in clinical practice continues to present challenges. Even very accurate high-throughput methods with small error rates can generate large numbers of false negative or false positive errors due to the high numbers of simultaneous readings. Additional validation is likely to be required for safe use of any such methods in clinical settings. Custom-designed arrays can offer advantages for screening for common, known mutations and, in this context, may currently be better suited for accredited, quality-controlled clinical genetic screening services, as illustrated by their successful application in several large-scale pre-emptive pharmacogenomics programs now underway. Excessive, inappropriate use of next-generation sequencing may waste scarce research funds and other resources. Microarrays presently remain the technology of choice in applications that require fast, cost-effective genome-wide screening of variants of known importance, particularly for large sample sizes. This commentary considers some of the applications where microarrays continue to offer advantages over next-generation sequencing technologies.

Pathological relationships involving iron and myelin may constitute a shared mechanism linking various rare and common brain diseases.

We previously demonstrated elevated brain iron levels in myelinated structures and associated cells in a hemochromatosis Hfe (-/-) xTfr2 (mut) mouse model. This was accompanied by altered expression of a group of myelin-related genes, including a suite of genes causatively linked to the rare disease family 'neurodegeneration with brain iron accumulation' (NBIA). Expanded data mining and ontological analyses have now identified additional myelin-related transcriptome changes in response to brain iron loading. Concordance between the mouse transcriptome changes and human myelin-related gene expression networks in normal and NBIA basal ganglia testifies to potential clinical relevance. These analyses implicate, among others, genes linked to various rare central hypomyelinating leukodystrophies and peripheral neuropathies including Pelizaeus-Merzbacher-like disease and Charcot-Marie-Tooth disease as well as genes linked to other rare neurological diseases such as Niemann-Pick disease. The findings may help understand interrelationships of iron and myelin in more common conditions such as hemochromatosis, multiple sclerosis and various psychiatric disorders.

Evaluation of Different Normalization and Analysis Procedures for Illumina Gene Expression Microarray Data Involving Small Changes.

While Illumina microarrays can be used successfully for detecting small gene expression changes due to their high degree of technical replicability, there is little information on how different normalization and differential expression analysis strategies affect outcomes. To evaluate this, we assessed concordance across gene lists generated by applying different combinations of normalization strategy and analytical approach to two Illumina datasets with modest expression changes. In addition to using traditional statistical approaches, we also tested an approach based on combinatorial optimization. We found that the choice of both normalization strategy and analytical approach considerably affected outcomes, in some cases leading to substantial differences in gene lists and subsequent pathway analysis results. Our findings suggest that important biological phenomena may be overlooked when there is a routine practice of using only one approach to investigate all microarray datasets. Analytical artefacts of this kind are likely to be especially relevant for datasets involving small fold changes, where inherent technical variation-if not adequately minimized by effective normalization-may overshadow true biological variation. This report provides some basic guidelines for optimizing outcomes when working with Illumina datasets involving small expression changes.