Quetiapine attenuates cognitive impairment and decreases seizure susceptibility possibly through promoting myelin development in a rat model of malformations of cortical development

Developmental delay, cognitive impairment, and refractory epilepsy are the most frequent consequences found in patients suffering from malformations of cortical development (MCD). However, therapeutic options for these psychiatric and neurological comorbidities are currently limited. The development of white matter undergoes dramatic changes during postnatal brain maturation, thus myelination deficits resulting from MCD contribute to its comorbid diseases. Consequently, drugs specifically targeting white matter are a promising therapeutic option for the treatment of MCD. We have used an in utero irradiation rat model of MCD to investigate the effects of postnatal quetiapine treatment on brain myelination as well as neuropsychological and cognitive performances and seizure susceptibility. Fatally irradiated rats were treated with quetiapine (10mg/kg, i.p.) or saline once daily from postnatal day 0 (P0) to P30. We found that postnatal administration of quetiapine attenuated object recognition memory impairment and improved long-term spatial memory in the irradiated rats. Quetiapine treatment also reduced the susceptibility and severity of pentylenetetrazol-induced seizures. Importantly, quetiapine treatment resulted in an inhibition of irradiation-induced myelin breakdown in the cerebral cortex and corpus callosum. These findings suggest that quetiapine may have beneficial, postnatal effects in the irradiated rats, strongly suggesting that improving MCD-derived white matter pathology is a possible underlying mechanism. Collectively, these results indicate that brain myelination represents an encouraging pharmacological target to improve the prognosis of patients with MCD.

Plasmalogen phospholipids protect internodal myelin from oxidative damage

Reactive oxygen species (ROS) are implicated in a range of degenerative conditions, including aging, neurodegenerative diseases, and neurological disorders. Myelin is a lipid-rich multilamellar sheath that facilitates rapid nerve conduction in vertebrates. Given the high energetic demands and low antioxidant capacity of the cells that elaborate the sheaths, myelin is considered intrinsically vulnerable to oxidative damage, raising the question whether additional mechanisms prevent structural damage. We characterized the structural and biochemical basis of ROS-mediated myelin damage in murine tissues from both central nervous system (CNS) and peripheral nervous system (PNS). To determine whether ROS can cause structural damage to the internodal myelin, whole sciatic and optic nerves were incubated ex vivo with a hydroxyl radical-generating system consisting of copper (Cu), hydrogen peroxide (HP), and ortho-phenanthroline (OP). Quantitative assessment of unfixed tissue by X-ray diffraction revealed irreversible compaction of myelin membrane stacking in both sciatic and optic nerves. Incubation in the presence of the hydroxyl radical scavenger sodium formate prevented this damage, implicating hydroxyl radical species. Myelin membranes are particularly enriched in plasmalogens, a class of ether-linked phospholipids proposed to have antioxidant properties. Myelin in sciatic nerve from plasmalogen-deficient (Pex7 knockout) mice was significantly more vulnerable to Cu/OP/HP-mediated ROS-induced compaction than myelin from WT mice. Our results directly support the role of plasmalogens as endogenous antioxidants providing a defense that protects ROS-vulnerable myelin.

Myelin repair in vivo is increased by targeting oligodendrocyte precursor cells with nanoparticles encapsulating leukaemia inhibitory factor (LIF)

Multiple sclerosis (MS) is a progressive demyelinating disease of the central nervous system (CNS). Many nerve axons are insulated by a myelin sheath and their demyelination not only prevents saltatory electrical signal conduction along the axons but also removes their metabolic support leading to irreversible neurodegeneration, which currently is untreatable. There is much interest in potential therapeutics that promote remyelination and here we explore use of leukaemia inhibitory factor (LIF), a cytokine known to play a key regulatory role in self-tolerant immunity and recently identified as a pro-myelination factor. In this study, we tested a nanoparticle-based strategy for targeted delivery of LIF to oligodendrocyte precursor cells (OPC) to promote their differentiation into mature oligodendrocytes able to repair myelin. Poly(lactic-co-glycolic acid)-based nanoparticles of ∼120 nm diameter were constructed with LIF as cargo (LIF-NP) with surface antibodies against NG-2 chondroitin sulfate proteoglycan, expressed on OPC. In vitro, NG2-targeted LIF-NP bound to OPCs, activated pSTAT-3 signalling and induced OPC differentiation into mature oligodendrocytes. In vivo, using a model of focal CNS demyelination, we show that NG2-targeted LIF-NP increased myelin repair, both at the level of increased number of myelinated axons, and increased thickness of myelin per axon. Potency was high: a single NP dose delivering picomolar quantities of LIF is sufficient to increase remyelination. Impact statement Nanotherapy-based delivery of leukaemia inhibitory factor (LIF) directly to OPCs proved to be highly potent in promoting myelin repair in vivo: this delivery strategy introduces a novel approach to delivering drugs or biologics targeted to myelin repair in diseases such as MS.

P2Y6 Receptor-Mediated Microglial Phagocytosis in Radiation-Induced Brain Injury

Microglia are the resident immune cells and the professional phagocytic cells of the CNS, showing a multitude of cellular responses after activation. However, how microglial phagocytosis changes and whether it is involved in radiation-induced brain injury remain unknown. In the current study, we found that microglia were activated and microglial phagocytosis was increased by radiation exposure both in cultured microglia in vitro and in mice in vivo. Radiation increased the protein expression of the purinergic receptor P2Y6 receptor (P2Y6R) located on microglia. The selective P2Y6 receptor antagonist MRS2578 suppressed microglial phagocytosis after radiation exposure. Inhibition of microglial phagocytosis increased inhibitory factor Nogo-A and exacerbated radiation-induced neuronal apoptosis and demyelination. We also found that the levels of protein expression for phosphorylated Ras-related C3 botulinum toxin substrate 1 (Rac1) and myosin light chain kinase (MLCK) were elevated, indicating that radiation exposure activated Rac1 and MLCK. The Rac1 inhibitor NSC23766 suppressed expression of MLCK, indicating that the Rac1-MLCK pathway was involved in microglial phagocytosis. Taken together, these findings suggest that the P2Y6 receptor plays a critical role in mediating microglial phagocytosis in radiation-induced brain injury, which might be a potential strategy for therapeutic intervention to alleviate radiation-induced brain injury.

Oligodendrocyte morphometry and expression of myelin - Related mRNA in ventral prefrontal white matter in major depressive disorder

White matter disturbance in the ventral prefrontal cortex (vPFC) in major depressive disorder (MDD) has been noted with diffusion tensor imaging (DTI). However, the cellular and molecular pathology of prefrontal white matter in MDD and potential influence of antidepressant medications is not fully understood. Oligodendrocyte morphometry and myelin-related mRNA and protein expression was examined in the white matter of the vPFC in MDD. Sections of deep and gyral white matter from the vPFC were collected from 20 subjects with MDD and 16 control subjects. Density and size of CNPase-immunoreactive (-IR) oligodendrocytes were estimated using 3-dimensional cell counting. While neither density nor soma size of oligodendrocytes was significantly affected in deep white matter, soma size was significantly decreased in the gyral white matter in MDD. In rhesus monkeys treated chronically with fluoxetine there was no significant effect on oligodendrocyte morphometry. Using quantitative RT-PCR to measure oligodendrocyte-related mRNA for CNPase, PLP1, MBP, MOG, MOBP, Olig1 and Olig2, in MDD there was a significantly reduced expression of PLP1 mRNA (which positively correlated with smaller sizes) and increased expression of mRNA for CNPase, OLIG1 and MOG. The expression of CNPase protein was significantly decreased in MDD. Altered expression of four myelin genes and CNPase protein suggests a mechanism for the degeneration of cortical axons and dysfunctional maturation of oligodendrocytes in MDD. The change in oligodendrocyte morphology in gyral white matter may parallel altered axonal integrity as revealed by DTI.

Molecular and clinical features of inherited neuropathies due to PMP22 duplication

PMP22 is a transmembrane glycoprotein component of myelin, important for myelin functioning. Mutation of PMP22 gene which encodes for the production of PMP22 glycoprotein is associated with a variety of inherited neuropathies. This literature review sought to review the molecular mechanism and clinical features of inherited neuropathies caused by PMP22 duplication. PMP22 duplication causes CMT1A which accounts for more than half of all CMT cases and about 70% of CMT1 cases. It manifests with muscle weakness, depressed reflexes, impaired distal sensation, hand and foot deformities, slowing of NCV and onion bulbs. With no specific treatment available, it is managed conservatively. Future treatment may be based on the molecular genetics of the disease.

In vivo time-lapse imaging of mitochondria in healthy and diseased peripheral myelin sheath

The myelin sheath that covers a large amount of neurons is critical for their homeostasis, and myelinating glia mitochondria have recently been shown to be essential for neuron survival. However morphological and physiological properties of these organelles remain elusive. Here we report a method to analyze mitochondrial dynamics and morphology in myelinating Schwann cells of living mice using viral transduction and time-lapse multiphoton microscopy. We describe the distribution, shape, size and dynamics of mitochondria in live cells. We also report mitochondrial alterations in Opa1(delTTAG) mutant mice cells at presymptomatic stages, suggesting that mitochondrial defects in myelin contribute to OPA1 related neuropathy and represent a biomarker for the disease.

Of mothers and myelin: Aberrant myelination phenotypes in mouse model of Angelman syndrome are dependent on maternal and dietary influences

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by a number of neurological problems, including developmental delay, movement disorders, and epilepsy. AS results from the loss of UBE3A (an imprinted gene) expressed from the maternal chromosome in neurons. Given the ubiquitous expression of Ube3a and the devastating nature of AS, the role of environmental and maternal effects has been largely ignored. Severe ataxia, anxiety-like behaviors and learning deficits are well-documented in patients and AS mice. More recently, clinical imaging studies of AS patients suggest myelination may be delayed or reduced. Utilizing a mouse model of AS, we found disrupted expression of cortical myelin proteins, the magnitude of which is influenced by maternal status, in that the aberrant myelination in the AS pups of AS affected mothers were more pronounced than those seen in AS pups raised by unaffected (Ube3a (m+/p-)) Carrier mothers. Furthermore, feeding the breeding mothers a higher fat (11% vs 5%) diet normalizes these myelin defects. These effects are not limited to myelin proteins. Since AS mice have abnormal stress responses, including altered glucocorticoid receptor (GR) expression, we measured GR expression in pups from Carrier and affected AS mothers. AS pups had higher GR expression than their WT littermates. However, we also found an effect of maternal status, with reduced GR levels in pups from affected mothers compared to genotypically identical pups raised by unaffected Carrier mothers. Taken together, our findings suggest that the phenotypes observed in AS mice may be modulated by factors independent of Ube3a genotype.

In vitro myelin formation using embryonic stem cells

Myelination in the central nervous system is the process by which oligodendrocytes form myelin sheaths around the axons of neurons. Myelination enables neurons to transmit information more quickly and more efficiently and allows for more complex brain functions; yet, remarkably, the underlying mechanism by which myelination occurs is still not fully understood. A reliable in vitro assay is essential to dissect oligodendrocyte and myelin biology. Hence, we developed a protocol to generate myelinating oligodendrocytes from mouse embryonic stem cells and established a myelin formation assay with embryonic stem cell-derived neurons in microfluidic devices. Myelin formation was quantified using a custom semi-automated method that is suitable for larger scale analysis. Finally, early myelination was followed in real time over several days and the results have led us to propose a new model for myelin formation.

Oligodendroglia and Myelin in Neurodegenerative Diseases: More Than Just Bystanders?

Oligodendrocytes, the myelinating cells of the central nervous system, mediate rapid action potential conduction and provide trophic support for axonal as well as neuronal maintenance. Their progenitor cell population is widely distributed in the adult brain and represents a permanent cellular reservoir for oligodendrocyte replacement and myelin plasticity. The recognition of oligodendrocytes, their progeny, and myelin as contributing factors for the pathogenesis and the progression of neurodegenerative disease has recently evolved shaping our understanding of these disorders. In the present review, we aim to highlight studies on oligodendrocytes and their progenitors in neurodegenerative diseases. We dissect oligodendroglial biology and illustrate evolutionary aspects in regard to their importance for neuronal functionality and maintenance of neuronal circuitries. After covering recent studies on oligodendroglia in different neurodegenerative diseases mainly in view of their function as myelinating cells, we focus on the alpha-synucleinopathy multiple system atrophy, a prototypical disorder with a well-defined oligodendroglial pathology.

The roles of extracellular related-kinases 1 and 2 signaling in CNS myelination

Substantial progress has been made in identifying the intracellular signaling pathways that regulate central nervous system myelination. Recently, the mitogen activated protein kinase pathway, in particular the extracellular signal-related kinase 1 (Erk1) and Erk2, have been identified as critically important in mediating the effects of several growth factors that regulate oligodendroglial development and myelination. Here we will review the recent studies that identify the key role that Erk1/2 signaling plays in regulating oligodendroglial development, myelination and remyelination, discuss the potential mechanisms that Erk1/2 may utilize to influence myelination, and highlight some questions for further research. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Fingolimod induces the transition to a nerve regeneration promoting Schwann cell phenotype

Successful regeneration of injured peripheral nerves is mainly attributed to the plastic behavior of Schwann cells. Upon loss of axons, these cells trans-differentiate into regeneration promoting repair cells which provide trophic support to regrowing axons. Among others, activation of cJun was revealed to be involved in this process, initiating the stereotypic pattern of Schwann cell phenotype alterations during Wallerian degeneration. Nevertheless, the ability of Schwann cells to adapt and therefore the nerve's potential to regenerate can be limited in particular after long term denervation or in neuropathies leading to incomplete regeneration only and thus emphasizing the need for novel therapeutic approaches. Here we stimulated primary neonatal and adult rat Schwann cells with Fingolimod/FTY720P and investigated its impact on the regeneration promoting phenotype. FTY720P activated a number of de-differentiation markers including cJun and interfered with maturation marker and myelin expression. Functionally, FTY720P treated Schwann cells upregulated growth factor expression and these cells enhanced dorsal root ganglion neurite outgrowth on inhibitory substrates. Our results therefore provide strong evidence that FTY720P application supports the generation of a repair promoting cellular phenotype and suggest that Fingolimod could be used as treatment for peripheral nerve injuries and diseases.

Axon diameter and axonal transport: In vivo and in vitro effects of androgens

Testosterone is a sex hormone involved in brain maturation via multiple molecular mechanisms. Previous human studies described age-related changes in the overall volume and structural properties of white matter during male puberty. Based on this work, we have proposed that testosterone may induce a radial growth of the axon and, possibly, modulate axonal transport. In order to determine whether this is the case we have used two different experimental approaches. With electron microscopy, we have evaluated sex differences in the structural properties of axons in the corpus callosum (splenium) of young rats, and tested consequences of castration carried out after weaning. Then we examined in vitro the effect of the non-aromatizable androgen Mibolerone on the structure and bidirectional transport of wheat-germ agglutinin vesicles in the axons of cultured sympathetic neurons. With electron microscopy, we found robust sex differences in axonal diameter (males>females) and g ratio (males>females). Removal of endogenous testosterone by castration was associated with lower axon diameter and lower g ratio in castrated (vs. intact) males. In vitro, Mibolerone influenced the axonal transport in a time- and dose-dependent manner, and increased the axon caliber as compared with vehicle-treated neurons. These findings are consistent with the role of testosterone in shaping the axon by regulating its radial growth, as predicted by the initial human studies.

The effects of white matter hyperintensities and amyloid deposition on Alzheimer dementia

Background and purpose

Elevated levels of amyloid deposition as well as white matter damage are thought to be risk factors for Alzheimer Disease (AD). Here we examined whether qualitative ratings of white matter damage predicted cognitive impairment beyond measures of amyloid.

Materials and methods

The study examined 397 cognitively normal, 51 very mildly demented, and 11 mildly demented individuals aged 42–90 (mean 68.5). Participants obtained a T₂-weighted scan as well as a positron emission tomography scan using ¹¹[C] Pittsburgh Compound B. Periventricular white matter hyperintensities (PVWMHs) and deep white matter hyperintensities (DWMHs) were measured on each T₂ scan using the Fazekas rating scale. The effects of amyloid deposition and white matter damage were assessed using logistic regressions.

Results

Levels of amyloid deposition (ps < 0.01), as well as ratings of PVWMH (p < 0.01) and DWMH (p < 0.05) discriminated between cognitively normal and demented individuals.

Conclusions

The amount of amyloid deposition and white matter damage independently predicts cognitive impairment. This suggests a diagnostic utility of qualitative white matter scales in addition to measuring amyloid levels.

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White matter damage was quantified using the Fazekas rating scale.

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Measures of amyloid were measured using positron emission tomography.

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There was a greater severity of damage in demented individuals.

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White matter damage significantly predicted dementia after controlling for amyloid.

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There is a clinical utility to using the Fazekas scale in addition to amyloid levels.

Myelination at a glance

The myelin sheath is a plasma membrane extension that is laid down in regularly spaced segments along axons of the nervous system. This process involves extensive changes in oligodendrocyte cell shape and membrane architecture. In this Cell Science at a Glance article and accompanying poster, we provide a model of how myelin of the central nervous system is wrapped around axons to form a tightly compacted, multilayered membrane structure. This model may not only explain how myelin is generated during brain development, but could also help us to understand myelin remodeling in adult life, which might serve as a form of plasticity for the fine-tuning of neuronal networks.

A clinical approach to the diagnosis of patients with leukodystrophies and genetic leukoencephelopathies

Leukodystrophies (LD) and genetic leukoencephalopathies (gLE) are disorders that result in white matter abnormalities in the central nervous system (CNS). Magnetic resonance (MR) imaging (MRI) has dramatically improved and systematized the diagnosis of LDs and gLEs, and in combination with specific clinical features, such as Addison's disease in Adrenoleukodystrophy or hypodontia in Pol-III related or 4H leukodystrophy, can often resolve a case with a minimum of testing. The diagnostic odyssey for the majority LD and gLE patients, however, remains extensive--many patients will wait nearly a decade for a definitive diagnosis and at least half will remain unresolved. The combination of MRI, careful clinical evaluation and next generation genetic sequencing holds promise for both expediting the diagnostic process and dramatically reducing the number of unresolved cases. Here we present a workflow detailing the Global Leukodystrophy Initiative (GLIA) consensus recommendations for an approach to clinical diagnosis, including salient clinical features suggesting a specific diagnosis, neuroimaging features and molecular genetic testing. We also discuss recommendations on the use of broad-spectrum next-generation sequencing in instances of ambiguous MRI or clinical findings. We conclude with a proposal for systematic trials of genome-wide agnostic testing as a first line diagnostic in LDs and gLEs given the increasing number of genes associated with these disorders.

Case definition and classification of leukodystrophies and leukoencephalopathies

OBJECTIVE

An approved definition of the term leukodystrophy does not currently exist. The lack of a precise case definition hampers efforts to study the epidemiology and the relevance of genetic white matter disorders to public health.

METHOD

Thirteen experts at multiple institutions participated in iterative consensus building surveys to achieve definition and classification of disorders as leukodystrophies using a modified Delphi approach.

RESULTS

A case definition for the leukodystrophies was achieved, and a total of 30 disorders were classified under this definition. In addition, a separate set of disorders with heritable white matter abnormalities but not meeting criteria for leukodystrophy, due to presumed primary neuronal involvement and prominent systemic manifestations, was classified as genetic leukoencephalopathies (gLE).

INTERPRETATION

A case definition of leukodystrophies and classification of heritable white matter disorders will permit more detailed epidemiologic studies of these disorders.

Targeting remyelination treatment for multiple sclerosis

Since disability in multiple sclerosis (MS) is a product of neurodegeneration and deficient remyelination, the ability to enhance neuroregeneration and myelin regeneration in MS is an enticing goal for MS drug development. In particular, remyelination treatments could promote return of neurological function and also prevent further axonal loss and neurodegeneration in MS due to trophic effects of myelin. The study of remyelination has advanced dramatically in the last several years such that a number of pathways inhibiting remyelination have been discovered, including those involving LINGO-1, Notch-1, hyaluronan, retinoid X receptor, and wnt/ß-catenin. Other approaches such as high throughput drug screening for remyelination drugs have caught fire, with identification of dozens of known drugs with oligodendrocyte maturation stimulatory effects. Several drugs identified through screens and other mechanisms are in the process of being further evaluated for remyelination in MS and MS models. We discuss the potential molecular targets and the variety of mechanisms towards drug identification and development in remyelination for MS.

Autoimmune peripheral neuropathies

Peripheral nervous system axons and myelin have unique potential protein, proteolipid, and ganglioside antigenic determinants. Despite the existence of a blood-nerve barrier, both humoral and cellular immunity can be directed against peripheral axons and myelin. Molecular mimicry may be triggered at the systemic level, as was best demonstrated in the case of bacterial oligosaccharides. The classification of immune neuropathy has been expanded to take into account specific syndromes that share unique clinical, electrophysiological, prognostic and serological features. Guillain-Barré syndrome encompasses a classical syndrome of acute demyelinating polyradiculoneuropathy and many variants: axonal motor and sensory, axonal motor, Miller-Fisher, autonomic, and sensory. Similarly, chronic immune neuropathy is composed of classic chronic inflammatory demyelinating polyradiculoneuropathy and variants characterized as multifocal (motor or sensorimotor), sensory, distal symmetric, and syndromes associated with monoclonal gammopathy. Among putative biomarkers, myelin associated glycoprotein and several anti-ganglioside autoantibodies have shown statistically significant associations with specific neuropathic syndromes. Currently, the strongest biomarker associations are those linking Miller-Fisher syndrome with anti-GQ1b, multifocal motor neuropathy with anti-GM1, and distal acquired symmetric neuropathy with anti-MAG antibodies. Many other autoantibody associations have been proposed, but presently lack sufficient specificity and sensitivity to qualify as biomarkers. This field of research has contributed to the antigenic characterization of motor and sensory functional systems, as well as helping to define immune neuropathic syndromes with widely different clinical presentation, prognosis and response to therapy. Serologic biomarkers are likely to become even more relevant with the advent of new targeted forms of immunotherapy, such as monoclonal antibodies.

Magnetization transfer ratio does not correlate to myelin content in the brain in the MOG-EAE mouse model

Magnetization transfer ratio (MTR) is a magnetic resonance imaging (MRI) method which may detect demyelination not detected by conventional MRI in the central nervous system of patients with multiple sclerosis (MS). A decrease in MTR value has previously been shown to correlate to myelin loss in the mouse cuprizone model for demyelination. In this study, we investigated the sensitivity of MTR for demyelination in the myelin oligodendrocyte (MOG) 1-125 induced experimental autoimmune encephalomyelitis (EAE) mouse model. A total of 24 female c57Bl/6 mice were randomized to a control group (N = 6) or EAE (N = 18). MTR images were obtained at a preclinical 7 Tesla Bruker MR-scanner before EAE induction (baseline), 17-19 days (midpoint) and 31-32 days (endpoint) after EAE induction. Mean MTR values were calculated in five regions of the brain and compared to weight, EAE severity score and myelin content assessed by immunostaining for proteolipid protein and luxol fast blue, lymphocyte and monocyte infiltration and iron deposition. Contrary to what was expected, MTR values in the EAE mice were higher than in the control mice at the midpoint and endpoint. No significant difference in myelin content was found according to histo- or immunohistochemistry. Changes in MTR values did not correlate to myelin content, iron content, lymphocyte or monocyte infiltration, weight or EAE severity scores. This suggest that MTR measures of brain tissue can give significant differences between control mice and EAE mice not caused by demyelination, inflammation or iron deposition, and may not be useful surrogate markers for demyelination in the MOG1-125 mouse model.

Reduced integrity of the left arcuate fasciculus is specifically associated with auditory verbal hallucinations in schizophrenia

BACKGROUND

Schizophrenia patients with auditory verbal hallucinations (AVH) have reduced structural integrity in the left arcuate fasciculus (AFL) compared to healthy controls. However, it is neither known whether these changes are specific to AVH, as opposed to hallucinations or schizophrenia per se, nor how radial and/or axial diffusivity are altered. This study aimed to test the hypothesis that reductions to the structural integrity of the AFL are specifically associated with AVH in schizophrenia.

METHOD

Diffusion tensor imaging scans and clinical data were obtained from the Australian Schizophrenia Research Bank for 39 schizophrenia patients with lifetime AVH (18 current, 21 remitted), 74 schizophrenia patients with no lifetime AVH (40 with lifetime hallucinations in other modalities, 34 no lifetime hallucinations) and 40 healthy controls.

RESULTS

Fractional anisotropy was significantly reduced in the AFL of patients with lifetime AVH compared to both healthy controls (Cohen's d=1.24) and patients without lifetime AVH (d=.72), including compared to the specific subsets of patients without AVH who either had hallucinations in other modalities (d=.69) or no history of any hallucinations (d=.73). Radial, but not axial, diffusivity was significantly increased in patients with lifetime AVH compared to both healthy controls (d=.89) and patients without lifetime AVH (d=.39). Evidence was found for a non-linear relation between fractional anisotropy in the AFL and state AVH.

CONCLUSION

Reduced integrity of the AFL is specifically associated with AVH, as opposed to schizophrenia in general or hallucinations in other modalities. Increased radial diffusivity suggests dysmyelination or demyelination of the AFL may play a role in AVH.

Fast quantitative susceptibility mapping using 3D EPI and total generalized variation

Quantitative susceptibility mapping (QSM) allows new insights into tissue composition and organization by assessing its magnetic property. Previous QSM studies have already demonstrated that magnetic susceptibility is highly sensitive to myelin density and fiber orientation as well as to para- and diamagnetic trace elements. Image resolution in QSM with current approaches is limited by the long acquisition time of 3D scans and the need for high signal to noise ratio (SNR) to solve the dipole inversion problem. We here propose a new total-generalized-variation (TGV) based method for QSM reconstruction, which incorporates individual steps of phase unwrapping, background field removal and dipole inversion in a single iteration, thus yielding a robust solution to the reconstruction problem. This approach has beneficial characteristics for low SNR data, allowing for phase data to be rapidly acquired with a 3D echo planar imaging (EPI) sequence. The proposed method was evaluated with a numerical phantom and in vivo at 3 and 7 T. Compared to total variation (TV), TGV-QSM enforced higher order smoothness which yielded solutions closer to the ground truth and prevented stair-casing artifacts. The acquisition time for images with 1mm isotropic resolution and whole brain coverage was 10s on a clinical 3 Tesla scanner. In conclusion, 3D EPI acquisition combined with single-step TGV reconstruction yields reliable QSM images of the entire brain with 1mm isotropic resolution in seconds. The short acquisition time combined with the robust reconstruction may enable new QSM applications in less compliant populations, clinical susceptibility tensor imaging, and functional resting state examinations.

Cholesterol in myelin biogenesis and hypomyelinating disorders

The largest pool of free cholesterol in mammals resides in myelin membranes. Myelin facilitates rapid saltatory impulse propagation by electrical insulation of axons. This function is achieved by ensheathing axons with a tightly compacted stack of membranes. Cholesterol influences myelination at many steps, from the differentiation of myelinating glial cells, over the process of myelin membrane biogenesis, to the functionality of mature myelin. Cholesterol emerged as the only integral myelin component that is essential and rate-limiting for the development of myelin in the central and peripheral nervous system. Moreover, disorders that interfere with sterol synthesis or intracellular trafficking of cholesterol and other lipids cause hypomyelination and neurodegeneration. This review summarizes recent results on the roles of cholesterol in CNS myelin biogenesis in normal development and under different pathological conditions. This article is part of a Special Issue entitled Brain Lipids.

The axon-glia unit in white matter stroke: mechanisms of damage and recovery

Approximately one quarter of all strokes in humans occur in white matter, and the progressive nature of white matter lesions often results in severe physical and mental disability. Unlike cortical grey matter stroke, the pathology of white matter stroke revolves around disrupted connectivity and injured axons and glial cells, rather than neuronal cell bodies. Consequently, the mechanisms behind ischemic damage to white matter elements, the regenerative responses of glial cells and their signaling pathways, all differ significantly from those in grey matter. Development of effective therapies for white matter stroke would require an enhanced understanding of the complex cellular and molecular interactions within the white matter, leading to the identification of new therapeutic targets. This review will address the unique properties of the axon-glia unit during white matter stroke, describe the challenging process of promoting effective white matter repair, and discuss recently-identified signaling pathways which may hold potential targets for repair in this disease. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Transcriptional upregulation of myelin components in spontaneous myelin basic protein-deficient mice

Myelin is essential for efficient signal transduction in the nervous system comprising of multiple proteins. The intricacies of the regulation of the formation of myelin, and its components, are not fully understood. Here, we describe the characterization of a novel myelin basic protein (Mbp) mutant mouse, mbp(jive), which spontaneously occurred in our mouse colony. These mice displayed the onset of a shaking gait before 3 weeks of age and seizure onset before 2 months of age. Due to a progressive increase of seizure intensity, mbp(jive) mice experienced premature lethality at around 3 months of age. Mbp mRNA transcript or protein was undetectable and, accordingly, genetic analysis demonstrated a homozygous loss of exons 3 to 6 of Mbp. Peripheral nerve conductance was mostly unimpaired. Additionally, we observed grave structural changes in white matter predominant structures were detected by T1, T2 and diffusion weighted magnetic resonance imaging. We additionally observed that Mbp-deficiency results in an upregulation of Qkl, Mag and Cnp, suggestive of a regulatory feedback mechanism whereby compensatory increases in Qkl have downstream effects on Mag and Cnp. Further research will clarify the role and specifications of this myelin feedback loop, as well as determine its potential role in therapeutic strategies for demyelinating disorders.

Propofol inhibits SIRT2 deacetylase through a conformation-specific, allosteric site

meta-Azi-propofol (AziPm) is a photoactive analog of the general anesthetic propofol. We photolabeled a myelin-enriched fraction from rat brain with [(3)H]AziPm and identified the sirtuin deacetylase SIRT2 as a target of the anesthetic. AziPm photolabeled three SIRT2 residues (Tyr(139), Phe(190), and Met(206)) that are located in a single allosteric protein site, and propofol inhibited [(3)H]AziPm photolabeling of this site in myelin SIRT2. Structural modeling and in vitro experiments with recombinant human SIRT2 determined that propofol and [(3)H]AziPm only bind specifically and competitively to the enzyme when co-equilibrated with other substrates, which suggests that the anesthetic site is either created or stabilized in enzymatic conformations that are induced by substrate binding. In contrast to SIRT2, specific binding of [(3)H]AziPm or propofol to recombinant human SIRT1 was not observed. Residues that line the propofol binding site on SIRT2 contact the sirtuin co-substrate NAD(+) during enzymatic catalysis, and assays that measured SIRT2 deacetylation of acetylated α-tubulin revealed that propofol inhibits enzymatic function. We conclude that propofol inhibits the mammalian deacetylase SIRT2 through a conformation-specific, allosteric protein site that is unique from the previously described binding sites of other inhibitors. This suggests that propofol might influence cellular events that are regulated by protein acetylation state.

Spreading depression transiently disrupts myelin via interferon-gamma signaling

Multiple sclerosis and migraine with aura are clinically correlated and both show imaging changes suggestive of myelin disruption. Furthermore, cortical myelin loss in the cuprizone animal model of multiple sclerosis enhances susceptibility to spreading depression, the likely underlying cause of migraine with aura. Since multiple sclerosis pathology involves inflammatory T cell lymphocyte production of interferon-gamma and a resulting increase in oxidative stress, we tested the hypothesis that spreading depression disrupts myelin through similar signaling pathways. Rat hippocampal slice cultures were initially used to explore myelin loss in spreading depression, since they contain T cells, and allow for controlled tissue microenvironment. These experiments were then translated to the in vivo condition in neocortex. Spreading depression in slice cultures induced significant loss of myelin integrity and myelin basic protein one day later, with gradual recovery by seven days. Myelin basic protein loss was abrogated by T cell depletion, neutralization of interferon-gamma, and pharmacological inhibition of neutral sphingomyelinase-2. Conversely, one day after exposure to interferon-gamma, significant reductions in spreading depression threshold, increases in oxidative stress, and reduced levels of glutathione, an endogenous neutral sphingomyelinase-2 inhibitor, emerged. Similarly, spreading depression triggered significant T cell accumulation, sphingomyelinase activation, increased oxidative stress, and reduction of gray and white matter myelin in vivo. Myelin disruption is involved in spreading depression, thereby providing pathophysiological links between multiple sclerosis and migraine with aura. Myelin disruption may promote spreading depression by enhancing aberrant excitability. Thus, preservation of myelin integrity may provide novel therapeutic targets for migraine with aura.

History, genetic, and recent advances on Krabbe disease

Krabbe disease or globoid cell leukodystrophy is one of the classic genetic lysosomal storage diseases with autosomal recessive inheritance that affects both central and peripheral nervous systems in several species including humans, rhesus macaques, dogs, mice, and sheep. Since its identification in 1916, lots of scientific investigations were made to define the cause, to evaluate the molecular mechanisms of the damage and to develop more efficient therapies inducing clinical benefit and ameliorating the patients' quality of life. This manuscript gives a historical overview and summarizes the new recent findings about Krabbe disease. Human symptoms and phenotypes, gene encoding for β-galactocerebrosidase and encoded protein were described. Indications about the classical mutations were reported and some specific mutations in restricted geographical area, like the north of Catania City (Italy), were added. Briefly, here we present a mix of past and present investigations on Krabbe disease in order to update the knowledge on its genetic history and molecular mechanisms and to move new scientific investigations.

Transferrin and thyroid hormone converge in the control of myelinogenesis

Myelination is a concerted mechanism tightly regulated in the brain. Although several factors are known to participate during this process, the complete sequence of events is far from being fully elucidated. Separate effects of apotransferrin (aTf) and thyroid hormone (TH) are well documented on rat myelin formation. TH promotes the maturation of oligodendrocyte progenitors (OPCs) into myelinating oligodendrocytes (OLGs), while aTf is able to induce the commitment of neural stem cells (NSCs) toward the oligodendroglial linage and favors OLG maturation. We have also demonstrated that Tf mRNA exhibited a seven-fold increase in hyperthyroid animals. These observations have led us to hypothesize that both factors may interplay during oligodendrogenesis. To assess the combined effects of aTf and TH on proper myelination in the rat brain, Tf expression and oligodendroglial maturation were evaluated at postnatal days 10 (P10) and 20 (P20) in several experimental groups. At P10, an up-regulation of both Tf mRNA and protein, as well as myelination, was found in hyperthyroid animals, while a decrease in Tf mRNA levels and myelin formation was detected in the hypothyroid group. At P20, no differences were found either in Tf mRNA or protein levels between hyperthyroid and control (Ctrol) rats, although differences in OLG differentiation remained. Also at P20, hypothyroid animals showed decreased Tf mRNA and protein levels accompanied with a less mature myelinating phenotype. Moreover, TH and aTf differentially regulate the expression of KLF9 transcription factor as well as TRα and TRβ at P10 and P20. Our results suggest that TH is necessary early in OLG development for aTf action, as exogenous aTf administration was unable to counteract the effect of low TH levels in the hypothyroid state in all the time points analyzed. Furthermore, the fact that hyperthyroidism induced an increase in Tf expression and aTf-dependent regulation of TRα strongly suggests that Tf could be involved in some of TH later effects on OLG maturation. Here we describe the possible relationship between TH and aTf and its implication in oligodendrogenesis.

Abnormal morphology of myelin and axon pathology in murine models of multiple sclerosis

Demyelination and axonal damage are responsible for neurological deficits in multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system. However, the pathology of axonal damage in MS is not fully understood. In this study, histological analysis of morphological changes of axonal organelles during demyelination in murine models was investigated by scanning electron microscopy (SEM) using an osmium-maceration method. In cuprizone-induced demyelination, SEM showed typical morphology of demyelination in the corpus callosum of mouse brain. In contrast, SEM displayed variations in ultrastructural abnormalities of myelin structures and axonal organelles in spinal cord white matter of experimental autoimmune encephalomyelitis (EAE) mice, an animal model of MS. Myelin detachment and excessive myelin formation were observed as typical morphological myelin abnormalities in EAE. In addition, well-developed axoplasmic reticulum-like structures and accumulated mitochondria were observed in tortuous degenerating/degenerated axons and the length of mitochondria in axons of EAE spinal cord was shorter compared with naïve spinal cord. Immunohistochemistry also revealed dysfunction of mitochondrial fusion/fission machinery in EAE spinal cord axons. Moreover, the number of Y-shaped mitochondria was significantly increased in axons of the EAE spinal cord. Axonal morphologies in myelin basic protein-deficient shiverer mice were similar to those in EAE. However, shiverer mice had "tortuous" (S-curve shaped mitochondria) and larger mitochondria compared with wild-type and EAE mice. Lastly, analysis of human MS patient autopsied brains also demonstrated abnormal myelin structures in demyelinating lesions. These results indicate that morphological abnormalities of myelin and axonal organelles play important role on the pathogenesis of axonal injury in demyelinating diseases.

Myelin, myelin-related disorders, and psychosis

The neuropathological basis of schizophrenia and related psychoses remains elusive despite intensive scientific investigation. Symptoms of psychosis have been reported in a number of conditions where normal myelin development is interrupted. The nature, location, and timing of white matter pathology seem to be key factors in the development of psychosis, especially during the critical adolescent period of association area myelination. Numerous lines of evidence implicate myelin and oligodendrocyte function as critical processes that could affect neuronal connectivity, which has been implicated as a central abnormality in schizophrenia. Phenocopies of schizophrenia with a known pathological basis involving demyelination or dysmyelination may offer insights into the biology of schizophrenia itself. This article reviews the pathological changes in white matter of patients with schizophrenia, as well as demyelinating diseases associated with psychosis. In an attempt to understand the potential role of dysmyelination in schizophrenia, we outline the evidence from a number of both clinically-based and post-mortem studies that provide evidence that OMR genes are genetically associated with increased risk for schizophrenia. To further understand the implication of white matter dysfunction and dysmyelination in schizophrenia, we examine diffusion tensor imaging (DTI), which has shown volumetric and microstructural white matter differences in patients with schizophrenia. While classical clinical-neuropathological correlations have established that disruption in myelination can produce a high fidelity phenocopy of psychosis similar to schizophrenia, the role of dysmyelination in schizophrenia remains controversial.

Metabolism and functions of lipids in myelin

Rapid conduction of nerve impulses requires coating of axons by myelin sheaths, which are lipid-rich and multilamellar membrane stacks. The lipid composition of myelin varies significantly from other biological membranes. Studies in mutant mice targeting various lipid biosynthesis pathways have shown that myelinating glia have a remarkable capacity to compensate the lack of individual lipids. However, compensation fails when it comes to maintaining long-term stability of myelin. Here, we summarize how lipids function in myelin biogenesis, axon-glia communication and in supporting long-term maintenance of myelin. We postulate that change in myelin lipid composition might be relevant for our understanding of aging and demyelinating diseases. This article is part of a Special Issue titled Brain Lipids.

The olfactomedin domain from gliomedin is a β-propeller with unique structural properties

All members of the olfactomedin (OLF) family have a conserved extracellular OLF domain, for which a structure has not been available. We present here the crystal structure of the OLF domain from gliomedin. Gliomedin is a protein expressed by Schwann cells in peripheral nerves, important for the formation of the nodes of Ranvier. Gliomedin interacts with neuronal cell adhesion molecules, such as neurofascin, but the structural details of the interaction are not known. The structure of the OLF domain presents a five-bladed β-propeller fold with unusual geometric properties. The symmetry of the structure is not 5-fold, but rather reveals a twisted arrangement. The conserved top face of the gliomedin OLF domain is likely to be important for binding to neuronal ligands. Our results provide a structural basis for the functions of gliomedin in Schwann cells, enable the understanding of the role of the gliomedin OLF domain in autoimmune neuropathies, and unravel the locations of human disease-causing mutations in other OLF family members, including myocilin.

Late onset neuropathy with spontaneous clinical remission in mice lacking the POZ domain of the transcription factor Myc-interacting zinc finger protein 1 (Miz1) in Schwann cells

The transcription factor Miz1 (Myc-interacting zinc finger 1) is a known regulator of the cell cycle but also has cell cycle-independent functions. Here we analyzed the role of Miz1 in the peripheral nervous system, using an early embryonic conditional knock-out model in which the Miz1 POZ domain is ablated in Schwann cells. Although the development of myelinated nerve fibers was not impaired, Miz1ΔPOZ mice acquired behavioral signs of a peripheral neuropathy at the age of 3 months. At this time, ultrastructural analysis of the sciatic nerve showed de- and dysmyelination of fibers, with massive outfoldings and a focal infiltration of macrophages. Although the expression of genes encoding structural myelin proteins, such as periaxin, myelin basic protein, and myelin protein zero, was decreased, genes associated with a negative regulation of myelination, including c-Jun, Sox2, and Id2, were up-regulated in Miz1ΔPOZ mice compared with controls. In animals older than 4 months, the motor disabilities vanished, and the ultrastructure of the sciatic nerve exhibited numerous tomacula and remyelinated fibers, as indicated by thinner myelin. No second acute attack was observed up to the age of 1 year. Thus, the deletion of the Miz1 POZ domain in Schwann cells induces an acute neuropathy with a subsequent regeneration in which there is ongoing balancing between de- and remyelination. Miz1ΔPOZ mice are impaired in the maintenance of myelinated fibers and are a promising model for studying remyelination in adult peripheral nerves.

Gray matter myelination of 1555 human brains using partial volume corrected MRI images

The myelin content of the cortex changes over the human lifetime and aberrant cortical myelination is associated with diseases such as schizophrenia and multiple sclerosis. Recently magnetic resonance imaging (MRI) techniques have shown potential in differentiating between myeloarchitectonically distinct cortical regions in vivo. Here we introduce a new algorithm for correcting partial volume effects present in mm-scale MRI images which was used to investigate the myelination pattern of the cerebral cortex in 1555 clinically normal subjects using the ratio of T1-weighted (T1w) and T2-weighted (T2w) MRI images. A significant linear cross-sectional age increase in T1w/T2w estimated myelin was detected across an 18 to 35 year age span (highest value of ~ 1%/year compared to mean T1w/T2w myelin value at 18 years). The cortex was divided at mid-thickness and the value of T1w/T2w myelin calculated for the inner and outer layers separately. The increase in T1w/T2w estimated myelin occurs predominantly in the inner layer for most cortical regions. The ratio of the inner and outer layer T1w/T2w myelin was further validated using high-resolution in vivo MRI scans and also a high-resolution MRI scan of a postmortem brain. Additionally, the relationships between cortical thickness, curvature and T1w/T2w estimated myelin were found to be significant, although the relationships varied across the cortex. We discuss these observations as well as limitations of using the T1w/T2w ratio as an estimate of cortical myelin.

In vitro study of the direct effect of extracellular hemoglobin on myelin components

There is a relationship between cerebral vasculature and multiple sclerosis (MS) lesions: abnormal accumulations of iron have been found in the walls of dilated veins in MS plaques. The sources of this iron can be varied, but capillary and venous hemorrhages leading to blood extravasation have been recorded, and could result in the release of hemoglobin extracellularly. Extracellular hemoglobin oxidizes quickly and is known to become a reactive molecule that triggers low-density lipoprotein oxidation and plays a pivotal role in atherogenesis. In MS, it could lead to local oxidative stress, inflammation, and tissue damage. Here, we investigated whether extracellular hemoglobin and its breakdown products can cause direct oxidative damage to myelin components in a peroxidative environment such as occurs in inflamed tissue. Oxidation of lipids was assessed by the formation of fluorescent peroxidized lipid-protein covalent adducts, by the increase in conjugated diene and malondialdehyde. Oxidation of proteins was analyzed by the change in protein mass. The results suggest that the globin radical could be a trigger of myelin basic protein oxidative cross-linking, and that heme transferred to the lipids is involved in lipid peroxidation. This study provides new insight into the mechanism by which hemoglobin exerts its pathological oxidative activity towards myelin components. This work supports further research into the vascular pathology in MS, to gain insight into the origin and role of iron deposits in disease pathogenesis, or in stimulation of different comorbidities such as cardiovascular disease.

Neuropathic pain-induced depressive-like behavior and hippocampal neurogenesis and plasticity are dependent on TNFR1 signaling

Patients suffering from neuropathic pain have a higher incidence of mood disorders such as depression. Increased expression of tumor necrosis factor (TNF) has been reported in neuropathic pain and depressive-like conditions and most of the pro-inflammatory effects of TNF are mediated by the TNF receptor 1 (TNFR1). Here we sought to investigate: (1) the occurrence of depressive-like behavior in chronic neuropathic pain and the associated forms of hippocampal plasticity, and (2) the involvement of TNFR1-mediated TNF signaling as a possible regulator of such events. Neuropathic pain was induced by chronic constriction injury of the sciatic nerve in wild-type and TNFR1(-/-) mice. Anhedonia, weight loss and physical state were measured as symptoms of depression. Hippocampal neurogenesis, neuroplasticity, myelin remodeling and TNF/TNFRs expression were analyzed by immunohistochemical analysis and western blot assay. We found that neuropathic pain resulted in the development of depressive symptoms in a time dependent manner and was associated with profound hippocampal alterations such as impaired neurogenesis, reduced expression of neuroplasticity markers and myelin proteins. The onset of depressive-like behavior also coincided with increased hippocampal levels of TNF, and decreased expression of TNF receptor 2 (TNFR2), which were all fully restored after mice spontaneously recovered from pain. Notably, TNFR1(-/-) mice did not develop depressive-like symptoms after injury, nor were there changes in hippocampal neurogenesis and plasticity. Our data show that neuropathic pain induces a cluster of depressive-like symptoms and profound hippocampal plasticity that are dependent on TNF signaling through TNFR1.

History, genetic, and recent advances on Krabbe disease

Krabbe disease or globoid cell leukodystrophy is one of the classic genetic lysosomal storage diseases with autosomal recessive inheritance that affects both central and peripheral nervous systems in several species including humans, rhesus macaques, dogs, mice, and sheep. Since its identification in 1916, lots of scientific investigations were made to define the cause, to evaluate the molecular mechanisms of the damage and to develop more efficient therapies inducing clinical benefit and ameliorating the patients' quality of life. This manuscript gives a historical overview and summarizes the new recent findings about Krabbe disease. Human symptoms and phenotypes, gene encoding for β-galactocerebrosidase and encoded protein were described. Indications about the classical mutations were reported and some specific mutations in restricted geographical area, like the north of Catania City (Italy), were added. Briefly, here we present a mix of past and present investigations on Krabbe disease in order to update the knowledge on its genetic history and molecular mechanisms and to move new scientific investigations.

Loss of lysophosphatidic acid receptor LPA1 alters oligodendrocyte differentiation and myelination in the mouse cerebral cortex

Lysophosphatidic acid (LPA) is an intercellular signaling lipid that regulates multiple cellular functions, acting through specific G-protein coupled receptors (LPA(1-6)). Our previous studies using viable Malaga variant maLPA1-null mice demonstrated the requirement of the LPA1 receptor for normal proliferation, differentiation, and survival of the neuronal precursors. In the cerebral cortex LPA1 is expressed extensively in differentiating oligodendrocytes, in parallel with myelination. Although exogenous LPA-induced effects have been investigated in myelinating cells, the in vivo contribution of LPA1 to normal myelination remains to be demonstrated. This study identified a relevant in vivo role for LPA1 as a regulator of cortical myelination. Immunochemical analysis in adult maLPA1-null mice demonstrated a reduction in the steady-state levels of the myelin proteins MBP, PLP/DM20, and CNPase in the cerebral cortex. The myelin defects were confirmed using magnetic resonance spectroscopy and electron microscopy. Stereological analysis limited the defects to adult differentiating oligodendrocytes, without variation in the NG2+ precursor cells. Finally, a possible mechanism involving oligodendrocyte survival was demonstrated by the impaired intracellular transport of the PLP/DM20 myelin protein which was accompanied by cellular loss, suggesting stress-induced apoptosis. These findings describe a previously uncharacterized in vivo functional role for LPA1 in the regulation of oligodendrocyte differentiation and myelination in the CNS, underlining the importance of the maLPA1-null mouse as a model for the study of demyelinating diseases.

Relationships between cobalamin, epidermal growth factor, and normal prions in the myelin maintenance of central nervous system

Cobalamin (Cbl), epidermal growth factor (EGF), and prions (PrPs) are key molecules for myelin maintenance in the central and peripheral nervous systems. Cbl and EGF increase normal prion (PrP(C)) synthesis and PrP(C) levels in rat spinal cord (SC) and elsewhere. Cbl deficiency increases PrP(C) levels in rat SC and cerebrospinal fluid (CSF), and decreases PrP(C)-mRNA levels in rat SC. The administration of anti-octapeptide repeat PrP(C) region antibodies (Abs) to Cbl-deficient (Cbl-D) rats prevents SC myelin lesions and a local increase in tumor necrosis factor (TNF)-α levels, whereas anti-TNF-α Abs prevent SC myelin lesions and the increase in SC and CSF PrP(C) levels. As it is known that both Cbl and EGF regulate SC PrP(C) synthesis independently, and that Cbl regulates SC EGF synthesis, EGF may play both Cbl-independent and Cbl-dependent roles. When Cbl-D rats undergo Cbl replacement therapy, SC PrP(C) levels are similar to those observed in Cbl-D rats. In rat frontal cortex (which is marginally affected by Cbl deficiency in histological terms), Cbl deficiency decreases PrP(C) levels and the increase induced by Cbl replacement leads to their normalization. Increased nerve PrP(C) levels are detected in the myelin lesions of the peripheral neuropathy of Cbl-D rats, and CSF PrP(C) levels are also increased in Cbl-D patients (but not in patients with Cbl-unrelated neurological diseases). Various common steps in the downstream signaling pathway of Cbl, EGF, and PrP(C) underlines the close relationship between the three molecules in keeping myelin normal.

Acute treatment with valproic acid and l-thyroxine ameliorates clinical signs of experimental autoimmune encephalomyelitis and prevents brain pathology in DA rats

Multiple sclerosis (MS) is the most common chronic inflammatory demyelinating disease of the central nervous system (CNS) in young adults. Chronic treatments with histone deacetylase inhibitors (HDACis) have been reported to ameliorate experimental autoimmune encephalomyelitis (EAE), a rodent model of MS, by targeting immune responses. We have recently shown that the HDAC inhibition/knockdown in the presence of thyroid hormone (T3) can also promote oligodendrocyte (OL) differentiation and expression of myelin genes in neural stem cells (NSCs) and oligodendrocyte precursors (OPCs). In this study, we found that treatment with an HDACi, valproic acid (VPA), and T3, alone or in combination, directly affects encephalitogenic CD4+ T cells. VPA, but not T3, compromised their proliferation, while both molecules reduced the frequency of IL-17-producing cells. Transfer of T3, VPA and VPA/T3 treated encephalitogenic CD4+ T cells into naïve rats induced less severe EAE, indicating that the effects of these molecules are persistent and do not require their maintenance after the initial stimuli. Thus, we investigated the effect of acute treatment with VPA and l-thyroxine (T4), a precursor of T3, on myelin oligodendrocyte glycoprotein-induced EAE in Dark Agouti rats, a close mimic of MS. We found that a brief treatment after disease onset led to sustained amelioration of EAE and prevention of inflammatory demyelination in the CNS accompanied with a higher expression of myelin-related genes in the brain. Furthermore, the treatment modulated immune responses, reduced the number of CD4+ T cells and affected the Th1 differentiation program in the brain. Our data indicate that an acute treatment with VPA and T4 after the onset of EAE can produce persistent clinically relevant therapeutic effects by limiting the pathogenic immune reactions while promoting myelin gene expression.

Combinatorial actions of Tgfβ and Activin ligands promote oligodendrocyte development and CNS myelination

In the embryonic CNS, development of myelin-forming oligodendrocytes is limited by bone morphogenetic proteins, which constitute one arm of the transforming growth factor-β (Tgfβ) family and signal canonically via Smads 1/5/8. Tgfβ ligands and Activins comprise the other arm and signal via Smads 2/3, but their roles in oligodendrocyte development are incompletely characterized. Here, we report that Tgfβ ligands and activin B (ActB) act in concert in the mammalian spinal cord to promote oligodendrocyte generation and myelination. In mouse neural tube, newly specified oligodendrocyte progenitors (OLPs) are first exposed to Tgfβ ligands in isolation, then later in combination with ActB during maturation. In primary OLP cultures, Tgfβ1 and ActB differentially activate canonical Smad3 and non-canonical MAP kinase signaling. Both ligands enhance viability, and Tgfβ1 promotes proliferation while ActB supports maturation. Importantly, co-treatment strongly activates both signaling pathways, producing an additive effect on viability and enhancing both proliferation and differentiation such that mature oligodendrocyte numbers are substantially increased. Co-treatment promotes myelination in OLP-neuron co-cultures, and maturing oligodendrocytes in spinal cord white matter display strong Smad3 and MAP kinase activation. In spinal cords of ActB-deficient Inhbb(-/-) embryos, apoptosis in the oligodendrocyte lineage is increased and OLP numbers transiently reduced, but numbers, maturation and myelination recover during the first postnatal week. Smad3(-/-) mice display a more severe phenotype, including diminished viability and proliferation, persistently reduced mature and immature cell numbers, and delayed myelination. Collectively, these findings suggest that, in mammalian spinal cord, Tgfβ ligands and ActB together support oligodendrocyte development and myelin formation.

Hereditary motor and sensory neuropathies: Understanding molecular pathogenesis could lead to future treatment strategies

Inherited peripheral neuropathies, like many other degenerative disorders, have been challenging to treat. At this point, there is little specific therapy for the inherited neuropathies other than genetic counseling as well as symptomatic treatment and rehabilitation. In the past, ascorbic acid, progesterone antagonists, and subcutaneous neurotrophin-3 (NT3) injections have demonstrated improvement in animal models of CMT 1A, the most common inherited neuropathy, but have failed to translate any effect in humans. Given the difficulty in treatment, it is important to understand the molecular pathogenesis of hereditary neuropathies in order to strategize potential future therapies. The hereditary neuropathies are in an era of molecular insight and over the past 20 years, more than 78 subtypes of Charcot Marie Tooth disease (CMT) have been identified and extensively studied to understand the biological pathways in greater detail. Next generation molecular sequencing has also improved the diagnosis as well as the understanding of CMT. A greater understanding of the molecular pathways will help pave the way to future therapeutics of CMT. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Nonenzymatic oxygenated metabolites of α-linolenic acid B1- and L1-phytoprostanes protect immature neurons from oxidant injury and promote differentiation of oligodendrocyte progenitors through PPAR-γ activation

Phytoprostanes (PhytoP's) are formed in higher plants from α-linolenic acid via a nonenzymatic free radical-catalyzed pathway and act as endogenous mediators capable of protecting cells from damage under various conditions related to oxidative stress. Humans are exposed to PhytoP's, as they are present in relevant quantities in vegetable food and pollen. The uptake of PhytoP's through the olfactory epithelium of the nasal mucosa, upon pollen grain inhalation, is of interest as the intranasal pathway is regarded as a direct route of communication between the environment and the brain. On this basis, we sought to investigate the potential activities of PhytoP's on immature cells of the central nervous system, which are particularly susceptible to oxidative stress. In neuroblastoma SH-SY5Y cells, used as a model for undifferentiated neurons, B1-PhytoP's, but not F1-PhytoP's, increased cell metabolic activity and protected them from oxidant damage caused by H2O2. Moreover, B1-PhytoP's induced a moderate depolarization of the mitochondrial inner membrane potential. These effects were prevented by the PPAR-γ antagonist GW9662. When SH-SY5Y cells were induced to differentiate toward a more mature phenotype, they became resistant to B1-PhytoP activities. B1-PhytoP's also influenced immature cells of an oligodendroglial line, as they increased the metabolic activity of oligodendrocyte progenitors and strongly accelerated their differentiation to immature oligodendrocytes, through mechanisms at least partially dependent on PPAR-γ activity. However, B1-PhytoP's did not protect oligodendrocyte progenitors against oxidant injury. Taken together, these data suggest that B1-PhytoP's, through novel mechanisms involving PPAR-γ, can specifically affect immature brain cells, such as neuroblasts and oligodendrocyte progenitors, thereby conferring neuroprotection against oxidant injury and promoting myelination.

Nutritional influences on early white matter development: response to Anderson and Burggren

Does breastfeeding alter early brain development? In a recent retrospective study, our group examined the cross-sectional relationship between early infant feeding practice and white matter maturation and cognitive development. In groups matched for child and mother age, gestation duration, birth weight, gender distribution, and socio-economic status; we observed that children who were breastfed exclusively for at least 3 months showed, on average, increased white matter myelin development compared to children who either were exclusively formula-fed, or received a mixture of breast milk and formula. In secondary analysis on sub-sets of these children, again matched for important confounding variables, we found improved cognitive test scores of receptive language in the exclusively breast-fed children compared to formula or formula+breast-fed children; and that prolonged breastfeeding was associated with increased motor, language, and visual functioning in exclusively breast-fed children. In response to this work, Anderson and Burggren have questioned our methodology and, by association, our findings. Further, they use their critique as a platform for advancing an alternative interpretation of our findings: that observed results were not associated with prolonged breast-feeding, but rather delayed the introduction of cow's milk. In this response, we address and clarify some of the misconceptions presented by Anderson and Burggren.

Different mechanisms regulate expression of zebrafish myelin protein zero (P0) in myelinating oligodendrocytes and its induction following axonal injury

Zebrafish CNS axons regenerate robustly following injury; it is thought that CNS oligodendrocytes contribute to this response by expressing growth-promoting molecules. We characterized the mpz gene, which encodes myelin protein zero and is up-regulated in oligodendroglia following axonal injury. The 2.5-kb mpz mRNA is expressed from a single TATA box promoter. Four independent Tg(mpz:egfp) transgenic zebrafish lines, in which GFP was expressed under the mpz promoter and 10 kb of genomic 5'-flanking sequence, showed transgene expression in CNS oligodendrocytes from larval development through adulthood. Following optic nerve crush injury, the mpz:egfp transgene was strongly up-regulated in oligodendrocytes along the regenerating retinotectal projection, mirroring up-regulation of endogenous mpz mRNA. GFP-expressing oligodendroglia were significantly more abundant in the regenerating optic pathway, resulting from both transgene induction in oligodendroglial precursors and the birth of new cells. Up-regulation of the mpz:egfp transgene was not dependent on axonal regeneration, suggesting that the primary signal may be axonal loss, debris, or microglial infiltration. Deletion experiments indicated that an oligodendroglial enhancer located in the region from -6 to -10 kb with respect to the mpz transcriptional start site is dissociable from the cis-regulatory element mediating the mpz transcriptional response to axonal injury, which is located between -1 and -4 kb. These data show that different mechanisms regulate expression of zebrafish mpz in myelinating oligodendrocytes and its induction following axonal injury. The underlying molecular events could potentially be exploited to enhance axonal repair following mammalian CNS injury. The transgenic lines and cis-regulatory constructs reported here will facilitate identification of the relevant signaling pathways.

Rapamycin improves peripheral nerve myelination while it fails to benefit neuromuscular performance in neuropathic mice

Charcot--Marie-Tooth disease type 1A (CMT1A) is a hereditary peripheral neuropathy characterized by progressive demyelination and distal muscle weakness. Abnormal expression of peripheral myelin protein 22 (PMP22) has been linked to CMT1A and is modeled by Trembler J (TrJ) mice, which carry the same leucine to proline substitution in PMP22 as affected pedigrees. Pharmacologic modulation of autophagy by rapamycin in neuron-Schwann cell explant cultures from neuropathic mice reduced PMP22 aggregate formation and improved myelination. Here we asked whether rapamycin administration by food supplementation, or intraperitoneal injection, could alleviate the neuropathic phenotype of affected mice and improve neuromuscular performance. Cohorts of male and female wild type (Wt) and TrJ mice were assigned to placebo or rapamycin treatment starting at 2 or 4months of age and tested monthly on the rotarod. While neither long-term feeding (8 or 10months) on rapamycin-enriched diet, or short-term injection (2months) of rapamycin improved locomotor performance of the neuropathic mice, both regimen benefited peripheral nerve myelination. Together, these results indicate that while treatment with rapamycin benefits the myelination capacity of neuropathic Schwann cells, this intervention does not improve neuromuscular function. The observed outcome might be the result of the differential response of nerve and skeletal muscle tissue to rapamycin.

A hypothesis-driven pathway analysis reveals myelin-related pathways that contribute to the risk of schizophrenia and bipolar disorder

Schizophrenia (SZ) and bipolar disorder (BD) are both severe neuropsychiatric disorders with a strong and potential overlapping genetic background. Multiple lines of evidence, including genetic studies, gene expression studies and neuroimaging studies, have suggested that both disorders are closely related to myelin and oligodendrocyte dysfunctions. In the current study, we hypothesized that the holistic effect of the myelin-related pathway contributes to the genetic susceptibility to both SZ and BD. We extracted pathway data from the canonical pathway database, Gene Ontology (GO), and selected a 'compiled' pathway based on previous literature. We then performed hypothesis-driven pathway analysis on GWAS data from the Psychiatric Genomics Consortium (PGC). As a result, we identified three myelin-related pathways with a joint effect significantly associated with both disorders: 'Myelin sheath' pathway (P(SZ) = 2.45E-7, P(BD) = 1.22E-3), 'Myelination' pathway (P(SZ) = 2.10E-4, P(BD) = 2.53E-24), and 'Compiled' pathway (P(SZ) = 4.57E-8, P(BD) = 2.61E-9). In comparing the SNPs and genes in these three pathways across the two diseases, we identified a substantial overlap in nominally associated SNPs and genes, which could be susceptibility SNPs and genes for both disorders. From these observations, we propose that myelin-related pathways may be involved in the etiologies of both SZ and BD.

Myelin paucity of the superior cerebellar peduncle in individuals with Friedreich ataxia: an MRI magnetization transfer imaging study

The dentate nucleus (DN) is the major relay station for neural connection between the cerebellum and cerebrum via the thalamus, and is a significant component of the neuropathological profile of Friedreich ataxia (FRDA). We have previously shown that the size of the superior cerebellar peduncle (SCP), which links the DN to cortical and subcortical structures via the thalamus, is significantly reduced in individuals with FRDA compared to control participants. This study used magnetization transfer imaging (MTI) to examine and contrast the integrity of white matter (WM) in the SCP and the corpus callosum (CC) (control region) in ten individuals with FRDA and ten controls. Individuals with FRDA demonstrated a significant reduction in the magnetization transfer ratio (MTR) in the SCP compared to control participants. However, there was no significant difference between groups in MTR in the CC. When comparing regions within groups, there was a significant reduction in MTR in the SCP compared to CC in participants with FRDA only. We suggest that the reduction in MTR in the SCP may be indicative of lack of myelin secondary to axonal loss and oligodendroglial dysfunction in WM tracts in individuals with FRDA.

In vivo architectonics: a cortico-centric perspective

Recent advances in noninvasive structural imaging have opened up new approaches to cortical parcellation, many of which are described in this special issue on In Vivo Brodmann Mapping. In this introductory article, we focus on the emergence of cortical myelin maps as a valuable way to assess cortical organization in humans and nonhuman primates. We demonstrate how myelin maps are useful in three general domains: (i) as a way to identify cortical areas and functionally specialized regions in individuals and group averages; (ii) as a substrate for improved intersubject registration; and (iii) as a basis for interspecies comparisons. We also discuss how myelin-based cortical parcellation is complementary in important ways to connectivity-based parcellation using functional MRI or diffusion imaging and tractography. These observations and perspectives provide a useful background and context for other articles in this special issue.