Axonal pathology in myelin disorders

The Node of Ranvier as an Interface for Axo-Glial Interactions: Perturbation of Axo-Glial Interactions in Various Neurological Disorders

The action potential conduction along the axon is highly dependent on the healthy interactions between the axon and myelin-producing glial cells. Myelin, which facilitates action potential, is the protective insulation around the axon formed by Schwann cells and oligodendrocytes in the peripheral (PNS) and central nervous system (CNS), respectively. Myelin is a continuous structure with intermittent gaps called nodes of Ranvier, which are the sites enriched with ion channels, transmembrane, scaffolding, and cytoskeletal proteins. Decades-long extensive research has identified a comprehensive proteome with strictly regularized localization at the node of Ranvier. Concurrently, axon-glia interactions at the node of Ranvier have gathered significant attention as the pathophysiological targets for various neurodegenerative disorders. Numerous studies have shown the alterations in the axon-glia interactions culminating in neurological diseases. In this review, we have provided an update on the molecular composition of the node of Ranvier. Further, we have discussed in detail the consequences of disruption of axon-glia interactions during the pathogenesis of various CNS and PNS disorders.

B cell-directed therapies: a new era in Multiple Sclerosis treatment

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system (CNS) that often progresses to severe disability. Previous studies have highlighted the role of T cells in disease pathophysiology; however, the success of B-cell-targeted therapies has led to an increased interest in how B cells contribute to disease immunopathology. In this review, we summarize evidence of B-cell involvement in MS disease mechanisms, starting with pathology and moving on to review aspects of B cell immunobiology potentially relevant to MS. We describe current theories of critical B cell contributions to the inflammatory CNS milieu in MS, namely (i) production of autoantibodies, (ii) antigen presentation, (iii) production of proinflammatory cytokines (bystander activation), and (iv) EBV involvement. In the second part of the review, we summarize medications that have targeted B cells in patients with MS and their current position in the therapeutic armamentarium based on clinical trials and real-world data. Covered therapeutic strategies include the targeting of surface molecules such as CD20 (rituximab, ocrelizumab, ofatumumab, ublituximab) and CD19 (inebilizumab), and molecules necessary for B-cell activation such as B cell activating factor (BAFF) (belimumab) and Bruton's Tyrosine Kinase (BTK) (evobrutinib). We finally discuss the use of B-cell-targeted therapeutics in pregnancy.

Deuterium double quantum-filtered NMR studies of peripheral and optic nerves

OBJECTIVE

Characterization of the nerve components by deuterium double quantum-filtered magnetization transfer (DQF-MT) NMR.

METHODS

Nerves were equilibrated in deuterated saline and ²H single-pulse and ²H DQF-MT NMR spectra were measured, enabling the separation of the different water compartments, according to their quadrupolar splittings.

RESULTS

Rat sciatic and brachial nerves and porcine optic nerve immersed in deuterated saline yielded ²H DQF spectra composed of three pairs of quadrupolar-split signals assigned to the water in the collagenous compartments and the myelin bilayer and one narrow signal assigned to the axonal water. Stretching of the nerves, application of osmotic stress and incubation in collagenase did not affect the quadrupolar splitting of the myelin water. The signals of myelin and axonal water were shown to decay during Wallerian degeneration and to rise during maturation. The chemical exchange between the myelin and the intra-axonal water was measured for optic nerve during maturation. The quadrupolar splitting of the signal of myelin water was not sensitive to its orientation relative to the magnetic field. This resembles liquid crystalline behavior, but leaves its mechanism open for interpretation.

CONCLUSIONS

²H DQF-MT NMR characterizes the different components of nerves, the water exchange between them and their changes during processes such as nerve maturation and Wallerian degeneration.

Siglec Ligands

A dense and diverse array of glycans on glycoproteins and glycolipids decorate all cell surfaces. In vertebrates, many of these carry sialic acid, in a variety of linkages and glycan contexts, as their outermost sugar moiety. Among their functions, glycans engage complementary glycan binding proteins (lectins) to regulate cell physiology. Among the glycan binding proteins are the Siglecs, sialic acid binding immunoglobulin-like lectins. In humans, there are 14 Siglecs, most of which are expressed on overlapping subsets of immune system cells. Each Siglec engages distinct, endogenous sialylated glycans that initiate signaling programs and regulate cellular responses. Here, we explore the emerging science of Siglec ligands, including endogenous sialoglycoproteins and glycolipids and synthetic sialomimetics. Knowledge in this field promises to reveal new molecular pathways controlling cell physiology and new opportunities for therapeutic intervention.

Clinically detectable structural abnormalities in pediatric-onset multiple sclerosis: A large-scale magnetic resonance imaging analysis

BACKGROUND

Multiple Sclerosis is characterized by neural demyelination. Structural magnetic resonance imaging (MRI) provides soft tissue contrast, which forms the basis of techniques for extracting regional biomarkers across a participant's brain.

OBJECTIVES

To investigate the clinical presentation of multiple sclerosis in a large-scale MRI analysis that includes thorough consideration of extractable structural measurements (average and variability of regional cortical thicknesses, cortical surface measurements, and volumes).

METHODS

We performed a large-scale retrospective analysis of 370 T1 structural volumetric MRIs from 64 participants with multiple sclerosis and compared them with a large cohort of neurotypical participants, consisting of 993 MRIs from 988 participants. Regionally distributed measurements of cortical thickness (average and standard deviation) were extracted along with surface area, surface curvature, and volumetric measurements.

RESULTS

The largest observed finding involved regionally distributed reductions in average cortical thickness, with the parahippocampal region exhibiting the largest effect size, a finding that may be linked with known hippocampal atrophy in multiple sclerosis. Group-wise differences were also observed in terms of distributed volume, surface area, and surface curvature measurements.

CONCLUSIONS

Participants with pediatric-onset multiple sclerosis present clinically with a variety of structural abnormalities, including perirhinal cortex thickness abnormalities not previously reported in the literature.

An update on clinical, pathological, diagnostic, and therapeutic perspectives of childhood leukodystrophies

Introduction: Leukodystrophies constitute heterogenous group of rare heritable disorders primarily affecting the white matter of central nervous system. These conditions are often under-appreciated among physicians. The first clinical manifestations of leukodystrophies are often nonspecific and can occur in different ages from neonatal to late adulthood periods. The diagnosis is, therefore, challenging in most cases.Area covered: Herein, the authors discuss different aspects of leukodystrophies. The authors used MEDLINE, EMBASE, and GOOGLE SCHOLAR to provide an extensive update about epidemiology, classifications, pathology, clinical findings, diagnostic tools, and treatments of leukodystrophies. Comprehensive evaluation of clinical findings, brain magnetic resonance imaging, and genetic studies play the key roles in the early diagnosis of individuals with leukodystrophies. No cure is available for most heritable white matter disorders but symptomatic treatments can significantly decrease the burden of events. New genetic methods and stem cell transplantation are also under investigation to further increase the quality and duration of life in affected population.Expert opinion: The improvements in molecular diagnostic tools allow us to identify the meticulous underlying etiology of leukodystrophies and result in higher diagnostic rates, new classifications of leukodystrophies based on genetic information, and replacement of symptomatic managements with more specific targeted therapies.Abbreviations: 4H: Hypomyelination, hypogonadotropic hypogonadism and hypodontia; AAV: Adeno-associated virus; AD: autosomal dominant; AGS: Aicardi-Goutieres syndrome; ALSP: Axonal spheroids and pigmented glia; APGBD: Adult polyglucosan body disease; AR: autosomal recessive; ASO: Antisense oligonucleotide therapy; AxD: Alexander disease; BAEP: Brainstem auditory evoked potentials; CAA: Cerebral amyloid angiopathy; CADASIL: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy; CARASAL: Cathepsin A-related arteriopathy with strokes and leukoencephalopathy; CARASIL: Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy; CGH: Comparative genomic hybridization; ClC2: Chloride Ion Channel 2; CMTX: Charcot-Marie-Tooth disease, X-linked; CMV: Cytomegalovirus; CNS: central nervous system; CRISP/Cas9: Clustered regularly interspaced short palindromic repeat/CRISPR-associated 9; gRNA: Guide RNA; CTX: Cerebrotendinous xanthomatosis; DNA: Deoxyribonucleic acid; DSB: Double strand breaks; DTI: Diffusion tensor imaging; FLAIR: Fluid attenuated inversion recovery; GAN: Giant axonal neuropathy; H-ABC: Hypomyelination with atrophy of basal ganglia and cerebellum; HBSL: Hypomyelination with brainstem and spinal cord involvement and leg spasticity; HCC: Hypomyelination with congenital cataracts; HEMS: Hypomyelination of early myelinated structures; HMG CoA: Hydroxy methylglutaryl CoA; HSCT: Hematopoietic stem cell transplant; iPSC: Induced pluripotent stem cells; KSS: Kearns-Sayre syndrome; L-2-HGA: L-2-hydroxy glutaric aciduria; LBSL: Leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate; LCC: Leukoencephalopathy with calcifications and cysts; LTBL: Leukoencephalopathy with thalamus and brainstem involvement and high lactate; MELAS: Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke; MERRF: Myoclonic epilepsy with ragged red fibers; MLC: Megalencephalic leukoencephalopathy with subcortical cysts; MLD: metachromatic leukodystrophy; MRI: magnetic resonance imaging; NCL: Neuronal ceroid lipofuscinosis; NGS: Next generation sequencing; ODDD: Oculodentodigital dysplasia; PCWH: Peripheral demyelinating neuropathy-central-dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschprung disease; PMD: Pelizaeus-Merzbacher disease; PMDL: Pelizaeus-Merzbacher-like disease; RNA: Ribonucleic acid; TW: T-weighted; VWM: Vanishing white matter; WES: whole exome sequencing; WGS: whole genome sequencing; X-ALD: X-linked adrenoleukodystrophy; XLD: X-linked dominant; XLR: X-linked recessive.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

Evaluation of Diffusional Kurtosis Imaging in Sub-acute Ischemic Stroke: Comparison with Rehabilitation Treatment Effect

Stroke is a serious worldwide medical condition that causes neurological function disability. Diffusional kurtosis imaging, which measures the non-Gaussianity of water diffusion, has been demonstrated to be a sensitive biomarker in many neuro-pathologies. This study explores the relationship between neural function recovery and transformation of the ischemic lesion and/or corticospinal tract during the sub-acute phase after stroke by using diffusional kurtosis imaging. We performed a prospective study of function recovery and K metrics of 43 patients with sub-acute ischemic stroke in the middle cerebral artery territory. The effect of rehabilitation treatment was evaluated using both the Fugl-Meyer motor function score and modified Barthel index score at post-treatment compared with admission, and patients were allocated to two groups: good and poor rehabilitation effect (GRE and PRE). Metrics of diffusional kurtosis imaging within ischemic lesion and along the corticospinal tract were acquired, respectively. All three relative axial diffusional kurtoses (rKas) along the corticospinal tract in the GRE group ( n = 21) were significantly larger than those of the PRE group ( n = 22), including rKa in the posterior limb of internal capsule, rKa in the cerebral peduncle, and rKa in the basal part of the pons ( p = 0.014, 0.005, and 0.021, respectively). This multi-parametric magnetic resonance imaging study showed that diffusional kurtosis imaging has the potential to complement existing stroke imaging techniques and revealed its own advantages in elucidating the possible biophysical mechanism of functional restoration underlying ischemic stroke.

CNS inflammation and neurodegeneration

There is an increasing recognition that inflammation plays a critical role in neurodegenerative diseases of the CNS, including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and the prototypic neuroinflammatory disease multiple sclerosis (MS). Differential immune responses involving the adaptive versus the innate immune system are observed at various stages of neurodegenerative diseases, and may not only drive disease processes but could serve as therapeutic targets. Ongoing investigations into the specific inflammatory mechanisms that play roles in disease causation and progression have revealed lessons about inflammation-driven neurodegeneration that can be applied to other neurodegenerative diseases. An increasing number of immunotherapeutic strategies that have been successful in MS are now being applied to other neurodegenerative diseases. Some approaches suppress CNS immune mechanisms, while others harness the immune system to clear deleterious products and cells. This Review focuses on the mechanisms by which inflammation, mediated either by the peripheral immune response or by endogenous CNS immune mechanisms, can affect CNS neurodegeneration.

Leukodystrophies: a proposed classification system based on pathological changes and pathogenetic mechanisms

Leukodystrophies are genetically determined disorders characterized by the selective involvement of the central nervous system white matter. Onset may be at any age, from prenatal life to senescence. Many leukodystrophies are degenerative in nature, but some only impair white matter function. The clinical course is mostly progressive, but may also be static or even improving with time. Progressive leukodystrophies are often fatal, and no curative treatment is known. The last decade has witnessed a tremendous increase in the number of defined leukodystrophies also owing to a diagnostic approach combining magnetic resonance imaging pattern recognition and next generation sequencing. Knowledge on white matter physiology and pathology has also dramatically built up. This led to the recognition that only few leukodystrophies are due to mutations in myelin- or oligodendrocyte-specific genes, and many are rather caused by defects in other white matter structural components, including astrocytes, microglia, axons and blood vessels. We here propose a novel classification of leukodystrophies that takes into account the primary involvement of any white matter component. Categories in this classification are the myelin disorders due to a primary defect in oligodendrocytes or myelin (hypomyelinating and demyelinating leukodystrophies, leukodystrophies with myelin vacuolization); astrocytopathies; leuko-axonopathies; microgliopathies; and leuko-vasculopathies. Following this classification, we illustrate the neuropathology and disease mechanisms of some leukodystrophies taken as example for each category. Some leukodystrophies fall into more than one category. Given the complex molecular and cellular interplay underlying white matter pathology, recognition of the cellular pathology behind a disease becomes crucial in addressing possible treatment strategies.

Multiple sclerosis-related white matter microstructural change alters the BOLD hemodynamic response

Multiple sclerosis (MS) results in inflammatory damage to white matter microstructure. Prior research using blood-oxygen-level dependent (BOLD) imaging indicates MS-related alterations to brain function. What is currently unknown is the extent to which white matter microstructural damage influences BOLD signal in MS. Here we assessed changes in parameters of the BOLD hemodynamic response function (HRF) in patients with relapsing-remitting MS compared to healthy controls. We also used diffusion tensor imaging to assess whether MS-related changes to the BOLD-HRF were affected by changes in white matter microstructural integrity. Our results showed MS-related reductions in BOLD-HRF peak amplitude. These MS-related amplitude decreases were influenced by individual differences in white matter microstructural integrity. Other MS-related factors including altered reaction time, limited spatial extent of BOLD activity, elevated lesion burden, or lesion proximity to regions of interest were not mediators of group differences in BOLD-HRF amplitude. Results are discussed in terms of functional hyperemic mechanisms and implications for analysis of BOLD signal differences.

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.

Astrocytes are central in the pathomechanisms of vanishing white matter

Vanishing white matter (VWM) is a fatal leukodystrophy that is caused by mutations in genes encoding subunits of eukaryotic translation initiation factor 2B (eIF2B). Disease onset and severity are codetermined by genotype. White matter astrocytes and oligodendrocytes are almost exclusively affected; however, the mechanisms of VWM development remain unclear. Here, we used VWM mouse models, patients' tissue, and cell cultures to investigate whether astrocytes or oligodendrocytes are the primary affected cell type. We generated 2 mouse models with mutations (Eif2b5Arg191His/Arg191His and Eif2b4Arg484Trp/Arg484Trp) that cause severe VWM in humans and then crossed these strains to develop mice with various mutation combinations. Phenotypic severity was highly variable and dependent on genotype, reproducing the clinical spectrum of human VWM. In all mutant strains, impaired maturation of white matter astrocytes preceded onset and paralleled disease severity and progression. Bergmann glia and retinal Müller cells, nonforebrain astrocytes that have not been associated with VWM, were also affected, and involvement of these cells was confirmed in VWM patients. In coculture, VWM astrocytes secreted factors that inhibited oligodendrocyte maturation, whereas WT astrocytes allowed normal maturation of VWM oligodendrocytes. These studies demonstrate that astrocytes are central in VWM pathomechanisms and constitute potential therapeutic targets. Importantly, astrocytes should also be considered in the pathophysiology of other white matter disorders.

Molecular substrates of schizophrenia: homeostatic signaling to connectivity

Schizophrenia (SZ) is a devastating psychiatric condition affecting numerous brain systems. Recent studies have identified genetic factors that confer an increased risk of SZ and participate in the disease etiopathogenesis. In parallel to such bottom-up approaches, other studies have extensively reported biological changes in patients by brain imaging, neurochemical and pharmacological approaches. This review highlights the molecular substrates identified through studies with SZ patients, namely those using top-down approaches, while also referring to the fruitful outcomes of recent genetic studies. We have subclassified the molecular substrates by system, focusing on elements of neurotransmission, targets in white matter-associated connectivity, immune/inflammatory and oxidative stress-related substrates, and molecules in endocrine and metabolic cascades. We further touch on cross-talk among these systems and comment on the utility of animal models in charting the developmental progression and interaction of these substrates. Based on this comprehensive information, we propose a framework for SZ research based on the hypothesis of an imbalance in homeostatic signaling from immune/inflammatory, oxidative stress, endocrine and metabolic cascades that, at least in part, underlies deficits in neural connectivity relevant to SZ. Thus, this review aims to provide information that is translationally useful and complementary to pathogenic hypotheses that have emerged from genetic studies. Based on such advances in SZ research, it is highly expected that we will discover biomarkers that may help in the early intervention, diagnosis or treatment of SZ.

Central nervous system infiltrates are characterized by features of ongoing B cell-related immune activity in MP4-induced experimental autoimmune encephalomyelitis

In multiple sclerosis (MS) lymphoid follicle-like aggregates have been reported in the meninges of patients. Here we investigated the functional relevance of B cell infiltration into the central nervous system (CNS) in MP4-induced experimental autoimmune encephalomyelitis (EAE), a B cell-dependent mouse model of MS. In chronic EAE, B cell aggregates were characterized by the presence of CXCL13(+) and germinal center CD10(+) B cells. Germline transcripts were expressed in the CNS and particularly related to TH17-associated isotypes. We also observed B cells with restricted VH gene usage that differed from clones found in the spleen. Finally, we detected CNS-restricted spreading of the antigen-specific B cell response towards a myelin and a neuronal autoantigen. These data imply the development of autonomous B cell-mediated autoimmunity in the CNS in EAE - a concept that might also apply to MS itself.

Glial cells as progenitors and stem cells: new roles in the healthy and diseased brain

The diverse functions of glial cells prompt the question to which extent specific subtypes may be devoted to a specific function. We discuss this by reviewing one of the most recently discovered roles of glial cells, their function as neural stem cells (NSCs) and progenitor cells. First we give an overview of glial stem and progenitor cells during development; these are the radial glial cells that act as NSCs and other glial progenitors, highlighting the distinction between the lineage of cells in vivo and their potential when exposed to a different environment, e.g., in vitro. We then proceed to the adult stage and discuss the glial cells that continue to act as NSCs across vertebrates and others that are more lineage-restricted, such as the adult NG2-glia, the most frequent progenitor type in the adult mammalian brain, that remain within the oligodendrocyte lineage. Upon certain injury conditions, a distinct subset of quiescent astrocytes reactivates proliferation and a larger potential, clearly demonstrating the concept of heterogeneity with distinct subtypes of, e.g., astrocytes or NG2-glia performing rather different roles after brain injury. These new insights not only highlight the importance of glial cells for brain repair but also their great potential in various aspects of regeneration.

Differentiation of neurosphere-derived rat neural stem cells into oligodendrocyte-like cells by repressing PDGF-α and Olig2 with triiodothyronine

One of the approaches for treating demyelination diseases is cytotherapy, and adult stem cells are potential sources. In this investigation, we tried to increase the yield of oligodendrocyte-like cells (OLCs) by inducing neural stem cells generated from BMSCs-derived neurospheres, which were used for deriving the neural stem cells (NSCs). The latter were induced into OLCs by heregulin, PDGF-AA, bFGF and triiodothyronine (T3). The BMSCs, NS, NSCs and OLCs were characterized by using immunocytochemistry for fibronectin, CD44, CD90, CD45, Oct-4, O4, Olig2, O1 and MBP markers. PDGF receptor α (PDGFR-α), Olig2 and MOG expression were evaluated by RT-PCR. The BMSCs expressed CD44, CD90, CD106 and Oct-4; the NSCs were immunoreactive to nestin and neurofilament 68. Incubation of the NSCs for 4 days with heregulin, PDGF-AA and bFGF resulted in their induction into oligodendrocyte progenitor-like cells (OPLCs), which immunoreacted to O4, Olig2 and O1, while Olig2 and PDGFR-α were detected by RT-PCR. Replacing heregulin, PDGF-AA and bFGF with T3 for 6 days resulted in repression of O4, O1, Olig2 and PDGFR-α. The OLCs were co-cultured with motoneurons resulted in induction of MOG and MBP, which were expressed in functional OLCs. The latter can be generated from BMSCs-derive NS with high yield.

Axonal loss in multiple sclerosis: causes and mechanisms

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system and the leading cause of non-traumatic neurologic disability in young adults in the United States and Europe. The disease course is variable and starts with reversible episodes of neurologic disability which transforms into continuous and irreversible neurologic decline. It is well established that loss of axons and neurons is the major cause of the progressive neurologic decline that most MS patients endure. Current hypotheses support primary inflammatory demyelination as the underlying cause of axonal loss during earlier stages in MS. The transition to progressive disease course is thought to occur when a threshold of neuronal and axonal loss is reached and the compensatory capacity of the central nervous system is surpassed. Available immunomodulatory therapies are of little benefit to MS after entering this irreversible phase of the disease. Elucidation of mechanisms that are responsible for axonal loss is therefore essential for the development of therapies directed to stop neurologic decline in MS patients. The current chapter reviews existing data on mechanisms of axonal pathology in MS.

Antineuroinflammatory and neurotrophic effects of CNTF and C16 peptide in an acute experimental autoimmune encephalomyelitis rat model

Experimentalallergic encephalomyelitis (EAE) is an animal model for inflammatory demyelinating autoimmune disease, i.e., multiple sclerosis (MS). In the present study, we investigated the antineuroinflammatory/neuroprotective effects of C16, an ανβ3 integrin-binding peptide, and recombinant rat ciliary neurotrophic factor (CNTF), a cytokine that was originally identified as a survival factor for neurons, in an acute rodent EAE model. In this model, C16 peptide was injected intravenously every day for 2 weeks, and CNTF was delivered into the cerebral ventricles with Alzet miniosmotic pumps. Disease severity was assessed weekly using a scale ranging from 0 to 5. Multiple histological and molecular biological assays were employed to assess inflammation, axonal loss, neuronal apoptosis, white matter demyelination, and gliosis in the brain and spinal cord of different groups. Our results showed that the EAE induced rats revealed a significant increase in inflammatory cells infiltration, while C16 treatment could inhibit the infiltration of leukocytes and macrophages down to 2/3–1/3 of vehicle treated EAE control (P < 0.05). The delayed onset of disease, reduced clinical score (P < 0.01) in peak stage and more rapid recovery also were achieved in C16 treated group. Besides impairing inflammation, CNTF treatment also exerted direct neuroprotective effects, decreasing demyelination and axon loss score (P < 0.05 versus vehicle treated EAE control), and reducing the neuronal death from 40 to 50% to 10 to 20% (P < 0.05). Both treatments suppressed the expression of cytokine tumor necrosis factor-α and interferon-γ when compared with the vehicle control (P < 0.05). Combined treatment with C16 and CNTF produced more obvious functional recovery and neuroprotective effects than individually treatment (P < 0.05). These results suggested that combination treatment with C16 and CNTF, which target different neuroprotection pathways, may be an effective therapeutic alternative to traditional therapy.

White matter water diffusion changes in primary Sjögren syndrome

BACKGROUND AND PURPOSE

Histopathologic studies have demonstrated WM damage in primary Sjögren syndrome. The purpose of this study was to evaluate WM microstructural changes by use of DTI-derived parameters in patients with primary Sjögren syndrome.

MATERIALS AND METHODS

DTI was performed in 19 patients with primary Sjögren syndrome (age, 64.73 ± 9.1 years; disease duration, 11.5 ± 7.56 years) and 16 age-matched control subjects. Exclusion criteria were a history of major metabolic, neurologic, or psychiatric disorder and high risk for cardiovascular disease. Data were analyzed by use of tract-based spatial statistics, for which the WM skeleton was created, and a permutation-based inference with 5000 permutations was used with a threshold of P < .01, corrected for multiple comparisons to enable identification of abnormalities in fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity.

RESULTS

Tract-based spatial statistics showed decreased fractional anisotropy in multiple areas in patients with primary Sjögren syndrome compared with control subjects, located mainly in the corticospinal tract, superior longitudinal fasciculus, anterior thalamic radiation, inferior fronto-occipital fasciculus, uncinate fasciculus, and inferior longitudinal fasciculus. Increased mean diffusivity and radial diffusivity and decreased axial diffusivity were observed in most of the fiber tracts of the brain in patients with primary Sjögren syndrome, compared with control subjects.

CONCLUSIONS

Patients with primary Sjögren syndrome show loss of WM microstructural integrity, probably related to both Wallerian degeneration and demyelination.

Risk variant of oligodendrocyte lineage transcription factor 2 is associated with reduced white matter integrity

The oligodendrocyte lineage transcription factor 2 (OLIG2) regulates the genesis of oligodendrocytes, the brain cells responsible for axonal myelination. Although it has been associated with psychiatric and neurological disorders, the impact of this gene on white matter integrity has never been investigated in humans. Using diffusion tensor imaging, we examined the effect of a single nucleotide polymorphism (rs1059004) in OLIG2 previously associated with reduced gene expression, and with psychiatric disorders on fractional anisotropy in 78 healthy subjects. We found that the risk allele (A) was associated with reduced white matter integrity in the corona radiata bilaterally. This is consistent with evidence that it is a schizophrenia susceptibility gene, and suggests that it may confer increased risk through an effect on neuroanatomical connectivity.

Autophagy promotes oligodendrocyte survival and function following dysmyelination in a long-lived myelin mutant

The Long-Evans shaker (les) rat has a mutation in myelin basic protein that results in severe CNS dysmyelination and subsequent demyelination during development. During this time, les oligodendrocytes accumulate cytoplasmic vesicles, including lysosomes and membrane-bound organelles. However, the mechanism and functional relevance behind these oligodendrocyte abnormalities in les have not been investigated. Using high-magnification electron microscopy, we identified the accumulations in les oligodendrocytes as early and late autophagosomes. Additionally, immunohistochemistry and Western blots showed an increase in autophagy markers in les. However, autophagy did not precede the death of les oligodendrocytes. Instead, upregulating autophagy promoted membrane extensions in les oligodendrocytes in vitro. Furthermore, upregulating autophagy in les rats via intermittent fasting increased the proportion of myelinated axons as well as myelin sheath thickness in les and control rats. Overall, this study provides insight into the abnormalities described in les as well as identifying a novel mechanism that promotes the survival and function of oligodendrocytes.

The challenges of axon survival: introduction to the special issue on axonal degeneration

Early axon loss is a common feature of many neurodegenerative disorders. It renders neurons functionally inactive, or less active if axon branches are lost, in a manner that is often irreversible. In the CNS, there is no long-range axon regeneration and even peripheral nerve axons are unlikely to reinnervate their targets while the cause of the problem persists. In most disorders, axon degeneration precedes cell death so it is not simply a consequence of it, and it is now clear that axons have at least one degeneration mechanism that differs from that of the soma. It is important to understand these degeneration mechanisms and their contribution to axon loss in neurodegenerative disorders. In this way, it should become possible to prevent axon loss as well as cell death. This special edition considers the roles and mechanisms of axon degeneration in amyotrophic lateral sclerosis, Charcot-Marie-Tooth disease, hereditary spastic paraplegia, ischemic injury, traumatic brain injury, Alzheimer's disease, glaucoma, Huntington's disease and Parkinson's disease. Using examples from these and other disorders, this introduction considers some of the reasons for axon vulnerability. It also illustrates how molecular genetics and studies of Wallerian degeneration have contributed to our understanding of axon degeneration mechanisms.

Remyelination reporter reveals prolonged refinement of spontaneously regenerated myelin

Neurological diseases and trauma often cause demyelination, resulting in the disruption of axonal function and integrity. Endogenous remyelination promotes recovery, but the process is not well understood because no method exists to definitively distinguish regenerated from preexisting myelin. To date, remyelinated segments have been defined as anything abnormally short and thin, without empirical data to corroborate these morphological assumptions. To definitively identify regenerated myelin, we used a transgenic mouse with an inducible membrane-bound reporter and targeted Cre recombinase expression to a subset of glial progenitor cells after spinal cord injury, yielding remarkably clear visualization of spontaneously regenerated myelin in vivo. Early after injury, the mean length of sheaths regenerated by Schwann cells and oligodendrocytes (OLs) was significantly shorter than control, uninjured myelin, confirming past assumptions. However, OL-regenerated sheaths elongated progressively over 6 mo to approach control values. Moreover, OL-regenerated myelin thickness was not significantly different from control myelin at most time points after injury. Thus, many newly formed OL sheaths were neither thinner nor shorter than control myelin, vitiating accepted dogmas of what constitutes regenerated myelin. We conclude that remyelination, once thought to be static, is dynamic and elongates independently of axonal growth, in contrast to stretch-based mechanisms proposed in development. Further, without clear identification, past assessments have underestimated the extent and quality of regenerated myelin.

Alteration in genes expression patterns during in vitro differentiation of mouse spermatogonial cells into neuroepithelial-like cells

Pluripotent stem cells derived from testis is a new, natural, and unlimited source for cell therapy in regenerative medicine and represent a possible alternative to replacing of all cells in the body. Here, we designed a simple co-culture system of spermatogonia cells with Sertoli cells for the generation of embryonic stem-like cells from mouse testis. The importance of our simple method will be clear when we compared it with other complex and time-consuming methods. Embryonic stem-like colonies with sharp border confirmed by real-time PCR, immunocytochemistry and flow cytometry assessments. Embryonic stem-like colonies were immunopositive for pluripotency markers. Transition of spermatogonia cells to embryonic stem-like cells was accompanied by extensive changes in gene expression. These changes included significant increase in pluripotency genes expression and significant decrease in germ cell-specific genes expression. Also, we proved the differentiation capacity of embryonic stem-like cells to neuroepithelial-like cells which were immunoreactive to Nestin and Neurofilament 68. Evaluation of genes expression during in vitro differentiation into neuroepithelial-like cells showed high-level expression of Nestin whether this gene approximately has no expression in undifferentiated embryonic stem-like cells. Also, expression of pluripotency genes has significantly decreased in neuroepithelial-like cells compared with embryonic stem-like cells. This study shows that embryonic stem-like cells derived from testis are capable to differentiate into neuroepithelial-like cells that may provide a cellular reservoir usable for neurodegenerative disorders.

Cytoskeletal transition at the paranodes: the Achilles' heel of myelinated axons

Myelination organizes axons into distinct domains that allow nerve impulses to propagate in a saltatory manner. The edges of the myelin sheath are sealed at the paranodes by axon-glial junctions that have a crucial role in organizing the axonal cytoskeleton. Here we propose a model in which the myelinated axons depend on the axon-glial junctions to stabilize the cytoskeletal transition at the paranodes. Thus paranodal regions are likely to be particularly susceptible to damage induced by demyelinating diseases such as multiple sclerosis.

Axonal thinning and extensive remyelination without chronic demyelination in spinal injured rats

Remyelination following spinal cord injury (SCI) is thought to be incomplete; demyelination is reported to persist chronically and is proposed as a compelling therapeutic target. Yet most reports do not distinguish between the myelin status of intact axons and injury-severed axons whose proximal stumps persist but provide no meaningful function. We previously found full remyelination of spared, intact rubrospinal axons caudal to the lesion in chronic mouse SCI. However, the clinical concept of chronically demyelinated spared axons remains controversial. Since mouse models may have limitations in clinical translation, we asked whether the capacity for full remyelination is conserved in clinically relevant chronic rat SCI. We determined myelin status by examining paranodal protein distribution on anterogradely labeled, intact corticospinal and rubrospinal axons throughout the extent of the lesion. Demyelination was evident on proximal stumps of severed axons, but not on intact axons. For the first time, we demonstrate that a majority of intact axons exhibit remyelination (at least one abnormally short internode, <100 μm). Remarkably, shortened internodes were significantly concentrated at the lesion epicenter and individual axons were thinned by 23% compared with their rostral and caudal zones. Mathematical modeling predicted a 25% decrease in conduction velocity at the lesion epicenter due to short internodes and axonal thinning. In conclusion, we do not find a large chronically demyelinated population to target with remyelination therapies. Interventions may be better focused on correcting structural or molecular abnormalities of regenerated myelin.

Increased axonal expression of nectin-1 in multiple sclerosis plaques

Nectin-1 is a cell adhesion molecule that plays a role in interneuronal synapse formation, in axonal guidance during development and possibly in neuron-glia interactions. To better understand axonal changes in MS, nectin-1 expression was determined by immunohistochemistry in normal adult human cerebral white matter (n = 4) and in six MS plaques (three active and three inactive). The intensity of axonal nectin-1 expression was scored on a scale of 0 to 4+. In normal adult cerebral white matter, axons showed weak nectin-1 expression with a score of 1.25 ± 0.50. Axonal nectin-1 expression was significantly stronger within both active (score = 3.33 ± 0.289, p = 0.001) and inactive (score = 2.16 ± 0.29, p = 0.038) MS plaques than in normal white matter. Axons in white matter adjacent to MS plaques showed nectin-1 expression (score = 1.5 ± 0.50) that was not statistically different from normal controls (p = 0.542). These findings raise the possibility that increased expression of nectin-1 in MS lesions plays a role in the pathogenesis of MS through participation in axonal responses to injury and mediation of altered neuron-glia interactions relevant to myelination.

In vitro differentiation of bone marrow stromal cells into oligodendrocyte-like cells using triiodothyronine as inducer

An in vitro technique was devised to induced autologous adult stem cells into oligodendrocyte-like cells. In this study, a protocol was developed for the induction of bone marrow stromal cells (BMSCs) into oligodendrocyte-like cells. BMSCs were incubated in one of these three pre-inducers: dimethyl sulfoxide (DMSO), β-mercaptoethanol (βME) or biotylated hydroxyanisol (BHA), each followed by retinoic acid (RA) treatment. The percentage of viable cells in BHA-RA preinduced cells was significantly lower than the others. The results showed that the preinduced cells were immunoreactive for nestin and NF-68; among the mentioned protocols, the immunoreactivity yielded by following the DMSO-RA protocol was significantly higher than the others. Moreover, no significant immunoreactivity was observed for preinduced cells to O4, O1, MBP (myelin basic protein), S100, and GFAP (glial fibrillary acidic protein). The cells were immunoreactive to oligo-2. Two phases of induction were done: the first was a combination of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and heregulin (HRG), followed by either triiodothyronine (T3) or Forskolin (FSK) as the second phase. The conclusion is that the trans-differentiation of BMSCs by DMSO followed by RA (preinduction stage) then bFGF-PDGF-HRG followed by T3 (10 ng/ml) (induction stage) can be a potential source for oligodendrocyte-like cells preparation.

Cell therapy for multiple sclerosis

The spontaneous recovery observed in the early stages of multiple sclerosis (MS) is substituted with a later progressive course and failure of endogenous processes of repair and remyelination. Although this is the basic rationale for cell therapy, it is not clear yet to what degree the MS brain is amenable for repair and whether cell therapy has an advantage in comparison to other strategies to enhance endogenous remyelination. Central to the promise of stem cell therapy is the therapeutic plasticity, by which neural precursors can replace damaged oligodendrocytes and myelin, and also effectively attenuate the autoimmune process in a local, nonsystemic manner to protect brain cells from further injury, as well as facilitate the intrinsic capacity of the brain for recovery. These fundamental immunomodulatory and neurotrophic properties are shared by stem cells of different sources. By using different routes of delivery, cells may target both affected white matter tracts and the perivascular niche where the trafficking of immune cells occur. It is unclear yet whether the therapeutic properties of transplanted cells are maintained with the duration of time. The application of neural stem cell therapy (derived from fetal brain or from human embryonic stem cells) will be realized once their purification, mass generation, and safety are guaranteed. However, previous clinical experience with bone marrow stromal (mesenchymal) stem cells and the relative easy expansion of autologous cells have opened the way to their experimental application in MS. An initial clinical trial has established the probable safety of their intravenous and intrathecal delivery. Short-term follow-up observed immunomodulatory effects and clinical benefit justifying further clinical trials.

Peripheral neuropathy in the Twitcher mouse involves the activation of axonal caspase 3

Infantile Krabbe disease results in the accumulation of lipid-raft-associated galactosylsphingosine (psychosine), demyelination, neurodegeneration and premature death. Recently, axonopathy has been depicted as a contributing factor in the progression of neurodegeneration in the Twitcher mouse, a bona fide mouse model of Krabbe disease. Analysis of the temporal-expression profile of MBP (myelin basic protein) isoforms showed unexpected increases of the 14, 17 and 18.5 kDa isoforms in the sciatic nerve of 1-week-old Twitcher mice, suggesting an abnormal regulation of the myelination process during early postnatal life in this mutant. Our studies showed an elevated activation of the pro-apoptotic protease caspase 3 in sciatic nerves of 15- and 30-day-old Twitcher mice, in parallel with increasing demyelination. Interestingly, while active caspase 3 was clearly contained in peripheral axons at all ages, we found no evidence of caspase accumulation in the soma of corresponding mutant spinal cord motor neurons. Furthermore, active caspase 3 was found not only in unmyelinated axons, but also in myelinated axons of the mutant sciatic nerve. These results suggest that axonal caspase activation occurs before demyelination and following a dying-back pattern. Finally, we showed that psychosine was sufficient to activate caspase 3 in motor neuronal cells in vitro in the absence of myelinating glia. Taken together, these findings indicate that degenerating mechanisms actively and specifically mediate axonal dysfunction in Krabbe disease and support the idea that psychosine is a pathogenic sphingolipid sufficient to cause axonal defects independently of demyelination.

P0 (protein zero) mutation S34C underlies instability of internodal myelin in S63C mice

P0 constitutes 50-60% of protein in peripheral nerve myelin and is essential for its structure and stability. Mutations within the P0 gene (MPZ) underlie a variety of hereditary neuropathies. MpzS63C transgenic mice encode a P0 with a serine to cysteine substitution at position 34 in the extracellular domain of mature P0 (P0S34C), associated with the hypomyelinating Déjérine-Sottas syndrome in human. S63C mice develop a dysmyelinating neuropathy, with packing defects in peripheral myelin. Here, we used x-ray diffraction to examine time-dependent packing defects in unfixed myelin. At ∼7 h post-dissection, WT and S63C(+/+) myelin showed native periods (175 Å) with the latter developing at most a few percent swollen myelin, whereas up to ∼50% of S63C(+/-) (mutant P0 on heterozygous P0 null background) or P0(+/-) myelin swelled to periods of ∼205 Å. In the same time frame, S63C(-/-) myelin was stable, remaining swollen at ∼210 Å. Surprisingly, treatment of whole S63C(-/-) nerves with a reducing agent completely reverted swollen arrays to native spacing and also normalized the swollen arrays that had formed in S63C(+/-) myelin, the genotype most closely related to the human disorder. Western blot revealed P0-positive bands at ∼27 and ∼50 kDa, and MALDI-TOF mass spectrometry showed these bands consisted of Ser(34)-containing peptides or P0 dimers having oxidized Cys(34) residues. We propose that P0S34C forms ectopic disulfide bonds in trans between apposed Cys(34) side chains that retard wrapping during myelin formation causing hypomyelination. Moreover, the new bonds create a packing defect by stabilizing swollen membrane arrays that leads to demyelination.

Docosahexaenoic acid prevents white matter damage after spinal cord injury

We have previously shown that the omega-3 fatty acid docosahexaenoic acid (DHA) significantly improves several histological and behavioral measures after spinal cord injury (SCI). White matter damage plays a key role in neurological outcome following SCI. Therefore, we examined the effects of the acute intravenous (IV) administration of DHA (250 nmol/kg) 30 min after thoracic compression SCI in rats, alone or in combination with a DHA-enriched diet (400 mg/kg/d, administered for 6 weeks post-injury), on white matter pathology. By 1 week post-injury, the acute IV DHA injection led to significantly reduced axonal dysfunction, as indicated by accumulation of β-amyloid precursor protein (-55% compared to vehicle-injected controls) in the dorsal columns. The loss of cytoskeletal proteins following SCI was also significantly reduced. There were 43% and 73% more axons immunoreactive for non-phosphorylated 200-kD neurofilament in the ventral white matter and ventrolateral white matter, respectively, in animals receiving DHA injections than vehicle-injected rats. The acute DHA treatment also led to a significant improvement in microtubule-associated protein-2 immunoreactivity. By 6 weeks, damage to myelin and serotonergic fibers was also reduced. For some of the parameters measured, the combination of DHA injection and DHA-enriched diet led to greater neuroprotection than DHA injection alone. These findings demonstrate the therapeutic potential of DHA in SCI, and clearly indicate that this fatty acid confers significant protection to the white matter.

Actualities on molecular pathogenesis and repairing processes of cerebral damage in perinatal hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is the most important cause of cerebral damage and long-term neurological sequelae in the perinatal period both in term and preterm infant.

Hypoxic-ischemic (H-I) injuries develop in two phases: the ischemic phase, dominated by necrotic processes, and the reperfusion phase, dominated by apoptotic processes extending beyond ischemic areas. Due to selective ischemic vulnerability, cerebral damage affects gray matter in term newborns and white matter in preterm newborns with the typical neuropathological aspects of laminar cortical necrosis in the former and periventricular leukomalacia in the latter.

This article summarises the principal physiopathological and biochemical processes leading to necrosis and/or apoptosis of neuronal and glial cells and reports recent insights into some endogenous and exogenous cellular and molecular mechanisms aimed at repairing H-I cerebral damage.

In vivo diffusion tensor magnetic resonance imaging and fiber tracking of the mouse brain

Until very recently, the study of neural architecture using fixed tissue has been a major scientific focus of neurologists and neuroanatomists. A non-invasive detailed insight into the brain's axonal connectivity in vivo has only become possible since the development of diffusion tensor magnetic resonance imaging (DT-MRI). This unique approach of analyzing axonal projections in the living brain was used in the present study to describe major white matter fiber tracts of the mouse brain and also to identify for the first time non-invasively the rich connectivity between the amygdala and different target regions. To overcome the difficulties associated with high spatially and temporally resolved DT-MRI measurements a 4-shot diffusion weighted spin echo (SE) echo planar imaging (EPI) protocol was adapted to mouse brain imaging at 9.4T. Diffusion tensor was calculated from data sets acquired by using 30 diffusion gradient directions while keeping the acquisition time at 91 min. Two fiber tracking algorithms were employed. A deterministic approach (fiber assignment by continuous tracking - FACT algorithm) allowed us to identify and generate the 3D representations of various neural pathways. A probabilistic approach was further used for the generation of probability maps of connectivity with which it was possible to investigate - in a statistical sense - all possible connecting pathways between selected seed points. We show here applications to determine the connection probability between regions belonging to the visual or limbic systems. This method does not require a priori knowledge about the projections' trajectories and is shown to be efficient even if the investigated pathway is long or three-dimensionally complex. Additionally, high resolution images of rotational invariant parameters of the diffusion tensor, such as fractional anisotropy, volume ratio or main eigenvalues allowed quantitative comparisons in-between regions of interest (ROIs) and showed significant differences between various white matter regions.

FLT-3 expression and function on microglia in multiple sclerosis

Inflammatory cell infiltration and resident microglial activation within the central nervous system (CNS) are pathological events in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). While MS therapies target the peripheral immune system, no treatment is currently known to also modulate microglia. FMS-like tyrosine-3 (FLT-3) is expressed on hematopoietic and dendritic cells. We reported that FLT-3 inhibition ameliorates early actively induced EAE by predominantly modulating dendritic cell function as compared to microglia. We demonstrate in this report that FLT-3 is expressed in perivascular cuffs, brain parenchyma and in non-lesioned gray and white matter within MS brain but not in these regions within control brain. Furthermore, we demonstrate that FLT-3 is expressed on two populations of cells within MS brain; one which expresses the dendritic cell marker CD209, and the other which does not, suggesting that FLT-3 within MS brain is expressed on infiltrating dendritic cells and a non-dendritic cell such as microglia. Additionally, we report that FLT-3 inhibition in murine microglia blocks, in a dose-dependent manner, IFN-γ-induced expression of MHC class II and CD86, and LPS-induced secretion of IL-6. These data suggest that FLT-3 is involved in microglial cells' capacity to respond to environmental cues to function as antigen presenting cells and mediate CNS inflammation. Furthermore these data suggest that FLT-3 may be a therapeutic target on microglia to mitigate CNS inflammation.

Hypoxia during pregnancy in rats leads to the changes of the cerebral white matter in adult offspring

The aim of the present study is to evaluate the effect of reduced fetal oxygen supply on cerebral white matter in the adult offspring and further assess its susceptibility to postnatal hypoxia and high-fat diet. Based on a 3 x 2 full factorial design consisting of three factors of maternal hypoxia, postnatal high-fat diet, and postnatal hypoxia, the ultrastructure of myelin, axon and capillaries were observed, and the expression of myelin basic protein (MBP), neurofilament-H+L(NF-H+L), and glial fibrillary acidic protein (GFAP) was analyzed in periventricular white matter of 16-month-old offspring. Demyelination, injured axon and damaged microvasculars were observed in maternal hypoxia offspring. The main effect of maternal hypoxia lead to decreased expression of MBP or NF-H+L, and increased expression of GFAP (all P<0.05). Moreover, there was positive three-way interaction among maternal hypoxia, high-fat diet and postnatal hypoxia on MBP, NF-H+L or GFAP expression (all P<0.05). In summary, our results indicated that maternal hypoxia during pregnancy in rats lead to changes of periventricular white matter in adult offspring, including demyelination, damaged axon and proliferated astroglia. This effect was amplified by high-fat diet and postnatal hypoxia.

Axonal damage in leukodystrophies

Recent advances in radioimaging and immunocytological techniques have enhanced investigations of neurometabolites and axons, giving rise to renewed interest in human white-matter disorders. A strong correlation between axonal loss and disability in some demyelination diseases (e.g., multiple sclerosis) led to several studies examining the mechanisms of axonal damage. We review the relationship between demyelination, axon loss, and neurologic progression, and the role of advanced neuroimaging in children with different types of leukodystrophies, i.e., X-linked adrenoleukodystrophy, metachromatic leukodysrtophy, Krabbe's disease, Pelizaeus-Merzbacher disease, and Alexander's disease.

Myelin-associated glycoprotein and its axonal receptors

Myelin-associated glycoprotein (MAG) is expressed on the innermost myelin membrane wrap, directly apposed to the axon surface. Although it is not required for myelination, MAG enhances long-term axon-myelin stability, helps to structure nodes of Ranvier, and regulates the axon cytoskeleton. In addition to its role in axon-myelin stabilization, MAG inhibits axon regeneration after injury; MAG and a discrete set of other molecules on residual myelin membranes at injury sites actively signal axons to halt elongation. Both the stabilizing and the axon outgrowth inhibitory effects of MAG are mediated by complementary MAG receptors on the axon surface. Two MAG receptor families have been described, sialoglycans (specifically gangliosides GD1a and GT1b) and Nogo receptors (NgRs). Controversies remain about which receptor(s) mediates which of MAG's biological effects. Here we review the findings and challenges in associating MAG's biological effects with specific receptors.

The encephalopathy of prematurity--brain injury and impaired brain development inextricably intertwined

The field of neonatal neurology, and specifically its focus on the premature infant, had its inception in neuropathologic studies. Since then, the development of advanced imaging techniques has guided our developing understanding of the etiology and nature of neonatal brain injury. This review promotes the concept that neonatal brain injury has serious and diverse effects on subsequent brain development, and that these effects likely are more important than simple tissue loss in determining neurologic outcome. Brain injury in the premature infant is best illustrative of this concept. This "encephalopathy of prematurity" is reviewed in the context of the remarkable array of developmental events actively proceeding during the last 16-20 weeks of human gestation. Recent insights into the brain abnormalities in survivors of preterm birth obtained by both advanced magnetic resonance imaging and neuropathologic techniques suggest that this encephalopathy is a complex amalgam of destructive and developmental disturbances. The interrelations between destructive and developmental mechanisms in the genesis of the encephalopathy are emphasized. In the future, advances in neonatal neurology will likely reiterate the dependence of this field on neuropathologic studies, including new cellular and molecular approaches in developmental neurobiology.

Shifting the paradigm toward earlier treatment of multiple sclerosis with interferon beta

BACKGROUND

Axonal damage occurs early in the course of multiple sclerosis (MS). Among untreated patients, 85% to 94% with a first clinically isolated syndrome (CIS) suggestive of MS and positive findings on magnetic resonance imaging (MRI) are at risk for developing MS.

OBJECTIVES

This article reviews the current literature concerning early diagnosis of MS, the rationale for early immunomodulatory treatment of patients with a CIS and MRI evidence of central nervous system lesions, and the efficacy of early treatment with interferon beta (IFN-beta).

METHODS

MEDLINE was searched from 1990 through the end of 2008 for papers published in English concerning the treatment of MS. Search terms included IFN-beta, early treatment, CIS, and multiple sclerosis, and limits were set to return results related to human clinical trials in adults.

RESULTS

Three pivotal randomized controlled trials were identified, 2 involving IFN-beta-1a (30 microg IM once weekly and 22 microg SC once weekly) and 1 involving IFN-beta-1b (250 microg SC qod). In these trials, treatment with IFN-beta effectively reduced the risk of developing MS by up to 50% in patients with a CIS. Furthermore, compared with delayed treatment, early treatment was associated with a reduced risk of disease progression: a 40% reduction in risk for confirmed disability progression at 3 years and a 41% reduction in risk of MS at 3 years.

CONCLUSIONS

The evidence that axonal damage begins in the early stages of MS, before symptoms are evident, provides a rationale for early intervention with immunomodulatory agents. In 3 pivotal clinical trials, IFN-beta effectively reduced the risk of developing clinically definite MS in CIS patients with a first demyelinating event and positive brain MRI.

Diffusion tensor magnetic resonance imaging of Wallerian degeneration in rat spinal cord after dorsal root axotomy

Diffusion tensor imaging (DTI) and immunohistochemistry were used to examine axon injury in the rat spinal cord after unilateral L(2)-L(4) dorsal root axotomy at multiple time points (from 16 h to 30 d after surgery). Three days after axotomy, DTI revealed a lesion in the ipsilateral dorsal column extending from the lumbar to the cervical cord. The lesion showed significantly reduced parallel diffusivity and increased perpendicular diffusivity at day 3 compared with the contralateral unlesioned dorsal column. These findings coincided with loss of phosphorylated neurofilaments, accumulation of nonphosphorylated neurofilaments, swollen axons and formation of myelin ovoids, and no clear loss of myelin (stained by Luxol fast blue and 2'-3'-cyclic nucleotide 3'-phosphodiesterase). At day 30, DTI of the lesion continued to show significantly decreased parallel diffusivity. There was a slow but significant increase in perpendicular diffusivity between day 3 and day 30, which correlated with gradual clearance of myelin without further significant changes in neurofilament levels. These results show that parallel diffusivity can detect axon degeneration within 3 d after injury. The clearance of myelin at later stages may contribute to the late increase in perpendicular diffusivity, whereas the cause of its early increase at day 3 may be related to changes associated with primary axon injury. These data suggest that there is an early imaging signature associated with axon transections that could be used in a variety of neurological disease processes.

Brain injury in premature infants: a complex amalgam of destructive and developmental disturbances

Brain injury in premature infants is of enormous public health importance because of the large number of such infants who survive with serious neurodevelopmental disability, including major cognitive deficits and motor disability. This type of brain injury is generally thought to consist primarily of periventricular leukomalacia (PVL), a distinctive form of cerebral white matter injury. Important new work shows that PVL is frequently accompanied by neuronal/axonal disease, affecting the cerebral white matter, thalamus, basal ganglia, cerebral cortex, brain stem, and cerebellum. This constellation of PVL and neuronal/axonal disease is sufficiently distinctive to be termed "encephalopathy of prematurity". The thesis of this Review is that the encephalopathy of prematurity is a complex amalgam of primary destructive disease and secondary maturational and trophic disturbances. This Review integrates the fascinating confluence of new insights into both brain injury and brain development during the human premature period.

Derivation of high-purity oligodendroglial progenitors

Oligodendrocytes are a type of glial cells that play a critical role in supporting the central nervous system (CNS), in particular insulating axons within the CNS by wrapping them with a myelin sheath, thereby enabling saltatory conduction. They are lost, and myelin damaged - demyelination - in a wide variety of neurological disorders. Replacing depleted cell types within demyelinated areas, however, has been shown experimentally to achieve remyelination and so help restore function. One method to produce oligodendrocytes for cellular replacement therapies is through the use of progenitor or stem cells. The ability to differentiate progenitor or stem cells into high-purity fates not only permits the generation of specific cells for transplantation therapies, but also provides powerful tools for studying cellular mechanisms of development. This chapter outlines methods of generating high-purity OPCs from multipotent neonatal progenitor or human embryonic stem cells.

Prospects of cell therapy for disorders of myelin

Recent advances in stem cell biology have raised expectations that both diseases of, and injuries to, the central nervous system may be ameliorated by cell transplantation. In particular, cell therapy has been studied for inducing efficient remyelination in disorders of myelin, including both the largely pediatric disorders of myelin formation and maintenance and the acquired demyelinations of both children and adults. Potential cell-based treatments of two major groups of disorders include both delivery of myelinogenic replacements and mobilization of residual oligodendrocyte progenitor cells as a means of stimulating endogenous repair; the choice of modality is then predicated upon the disease target. In this review we consider the potential application of cell-based therapeutic strategies to disorders of myelin, highlighting the promises as well as the problems and potential perils of this treatment approach.