Mechanisms of axon ensheathment and myelin growth

Contactin -Associated protein1 Regulates Autophagy by Modulating the PI3K/AKT/mTOR Signaling Pathway and ATG4B Levels in Vitro and in Vivo

Contactin-associated protein1 (Caspr1) plays an important role in the formation and stability of myelinated axons. In Caspr1 mutant mice, autophagy-related structures accumulate in neurons, causing axonal degeneration; however, the mechanism by which Caspr1 regulates autophagy remains unknown. To illustrate the mechanism of Caspr1 in autophagy process, we demonstrated that Caspr1 knockout in primary neurons from mice along with human cell lines, HEK-293 and HeLa, induced autophagy by downregulating the PI3K/AKT/mTOR signaling pathway to promote the conversion of microtubule-associated protein light chain 3 I (LC3-I) to LC3-II. In contrast, Caspr1 overexpression in cells contributed to the upregulation of this signaling pathway. We also demonstrated that Caspr1 knockout led to increased LC3-I protein expression in mice. In addition, Caspr1 could inhibit the expression of autophagy-related 4B cysteine peptidase (ATG4B) protein by directly binding to ATG4B in overexpressed Caspr1 cells. Intriguingly, we found an accumulation of ATG4B in the Golgi apparatuses of cells overexpressing Caspr1; therefore, we speculate that Caspr1 may restrict ATG4 secretion from the Golgi apparatus to the cytoplasm. Collectively, our results indicate that Caspr1 may regulate autophagy by modulating the PI3K/AKT/mTOR signaling pathway and the levels of ATG4 protein, both in vitro and in vivo. Thus, Caspr1 can be a potential therapeutic target in axonal damage and demyelinating diseases.

Morphological Influence on a Nonionic Bilayer Bending Rigidity and Compression Modulus

The mechanical properties of multilamellar vesicles and their relevance to soft matter physics and material science are of significant interest. The bending rigidity, κ, and compression modulus, B, of three-dimensional (3D) finite nonspontaneous multilamellar vesicles, formed by a nonionic surfactant, are linked to nanoscale bilayer thickness, δ, estimated via small-angle X-ray scattering, and macroscopic elastic modulus measured through small-amplitude oscillatory shear experiments. κ and B significantly differ from the same system in the two-dimensional (2D) infinite nanostructured planar lamellar phase. Particularly, κ3D was found to be much smaller than κ2D, while an opposite behavior was seen for B. The 2D-to-3D morphology transition occurs under a transient mechanical field, resulting in rheopectic behavior. κ scales quadratically with δ, consistent with bilayer membrane theories, and linearly with vesicle radius in the densely packed state. These findings have implications for understanding and designing soft interfaces due to the influence of bending rigidity on transport properties.

Cholesterol-dependent LXR transcription factor activity represses pronociceptive effects of estrogen in sensory neurons and pain induced by myelin basic protein fragments

Background

A bioactive myelin basic protein (MBP) fragment, comprising MBP84-104, is released in sciatic nerve after chronic constriction injury (CCI). Intraneural injection (IN) of MBP84-104 in an intact sciatic nerve is sufficient to induce persistent neuropathic pain-like behavior via robust transcriptional remodeling at the injection site and ipsilateral dorsal root ganglia (DRG) and spinal cord. The sex (female)-specific pronociceptive activity of MBP84-104 associates with sex-specific changes in cholesterol metabolism and activation of estrogen receptor (ESR)1 signaling.

Methods

In male and female normal and post-CCI rat sciatic nerves, we assessed: (i) cholesterol precursor and metabolite levels by lipidomics; (ii) MBP84-104 interactors by mass spectrometry of MBP84-104 pull-down; and (iii) liver X receptor (LXR)α protein expression by immunoblotting. To test the effect of LXRα stimulation on IN MBP84-104-induced mechanical hypersensitivity, the LXRα expression was confirmed along the segmental neuraxis, in DRG and spinal cord, followed by von Frey testing of the effect of intrathecally administered synthetic LXR agonist, GW3965. In cultured male and female rat DRGs exposed to MBP84-104 and/or estrogen treatments, transcriptional effect of LXR stimulation by GW3965 was assessed on downstream cholesterol transporter Abc, interleukin (IL)-6, and pronociceptive Cacna2d1 gene expression.

Results

CCI regulated LXRα ligand and receptor levels in nerves of both sexes, with cholesterol precursors, desmosterol and 7-DHC, and oxysterol elevated in females relative to males. MBP84-104 interacted with nuclear receptor coactivator (Ncoa)1, known to activate LXRα, injury-specific in nerves of both sexes. LXR stimulation suppressed ESR1-induced IL-6 and Cacna2d1 expression in cultured DRGs of both sexes and attenuated MBP84-104-induced pain in females.

Conclusion

The injury-released bioactive MBP fragments induce pronociceptive changes by selective inactivation of nuclear transcription factors, including LXRα. By Ncoa1 sequestration, bioactive MBP fragments render LXRα function to counteract pronociceptive activity of estrogen/ESR1 in sensory neurons. This effect of MBP fragments is prevalent in females due to high circulating estrogen levels in females relative to males. Restoring LXR activity presents a promising therapeutic strategy in management of neuropathic pain induced by bioactive MBP.

The role of glial cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has traditionally been considered a neuron-centric disease. This view is now outdated, with increasing recognition of cell autonomous and non-cell autonomous contributions of central and peripheral nervous system glia to ALS pathomechanisms. With glial research rapidly accelerating, we comprehensively interrogate the roles of astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells and satellite glia in nervous system physiology and ALS-associated pathology. Moreover, we highlight the inter-glial, glial-neuronal and inter-system polylogue which constitutes the healthy nervous system and destabilises in disease. We also propose classification based on function for complex glial reactive phenotypes and discuss the pre-requisite for integrative modelling to advance translation. Given the paucity of life-enhancing therapies currently available for ALS patients, we discuss the promising potential of harnessing glia in driving ALS therapeutic discovery.

Pathophysiology in cortico-amygdala circuits and excessive aversion processing: the role of oligodendrocytes and myelination

Stress-related psychiatric illnesses, such as major depressive disorder, anxiety and post-traumatic stress disorder, present with alterations in emotional processing, including excessive processing of negative/aversive stimuli and events. The bidirectional human/primate brain circuit comprising anterior cingulate cortex and amygdala is of fundamental importance in processing emotional stimuli, and in rodents the medial prefrontal cortex-amygdala circuit is to some extent analogous in structure and function. Here, we assess the comparative evidence for: (i) Anterior cingulate/medial prefrontal cortex<->amygdala bidirectional neural circuits as major contributors to aversive stimulus processing; (ii) Structural and functional changes in anterior cingulate cortex<->amygdala circuit associated with excessive aversion processing in stress-related neuropsychiatric disorders, and in medial prefrontal cortex<->amygdala circuit in rodent models of chronic stress-induced increased aversion reactivity; and (iii) Altered status of oligodendrocytes and their oligodendrocyte lineage cells and myelination in anterior cingulate/medial prefrontal cortex<->amygdala circuits in stress-related neuropsychiatric disorders and stress models. The comparative evidence from humans and rodents is that their respective anterior cingulate/medial prefrontal cortex<->amygdala circuits are integral to adaptive aversion processing. However, at the sub-regional level, the anterior cingulate/medial prefrontal cortex structure-function analogy is incomplete, and differences as well as similarities need to be taken into account. Structure-function imaging studies demonstrate that these neural circuits are altered in both human stress-related neuropsychiatric disorders and rodent models of stress-induced increased aversion processing. In both cases, the changes include altered white matter integrity, albeit the current evidence indicates that this is decreased in humans and increased in rodent models. At the cellular-molecular level, in both humans and rodents, the current evidence is that stress disorders do present with changes in oligodendrocyte lineage, oligodendrocytes and/or myelin in these neural circuits, but these changes are often discordant between and even within species. Nonetheless, by integrating the current comparative evidence, this review provides a timely insight into this field and should function to inform future studies-human, monkey and rodent-to ascertain whether or not the oligodendrocyte lineage and myelination are causally involved in the pathophysiology of stress-related neuropsychiatric disorders.

Co-representation of Functional Brain Networks Is Shaped by Cortical Myeloarchitecture and Reveals Individual Behavioral Ability

Large-scale functional networks are spatially distributed in the human brain. Despite recent progress in differentiating their functional roles, how the brain navigates the spatial coordination among them and the biological relevance of this coordination is still not fully understood. Capitalizing on canonical individualized networks derived from functional MRI data, we proposed a new concept, that is, co-representation of functional brain networks, to delineate the spatial coordination among them. To further quantify the co-representation pattern, we defined two indexes, that is, the co-representation specificity (CoRS) and intensity (CoRI), for separately measuring the extent of specific and average expression of functional networks at each brain location by using the data from both sexes. We found that the identified pattern of co-representation was anchored by cortical regions with three types of cytoarchitectural classes along a sensory-fugal axis, including, at the first end, primary (idiotypic) regions showing high CoRS, at the second end, heteromodal regions showing low CoRS and high CoRI, at the third end, paralimbic regions showing low CoRI. Importantly, we demonstrated the critical role of myeloarchitecture in sculpting the spatial distribution of co-representation by assessing the association with the myelin-related neuroanatomical and transcriptomic profiles. Furthermore, the significance of manifesting the co-representation was revealed in its prediction of individual behavioral ability. Our findings indicated that the spatial coordination among functional networks was built upon an anatomically configured blueprint to facilitate neural information processing, while advancing our understanding of the topographical organization of the brain by emphasizing the assembly of functional networks.

Glia trigger endocytic clearance of axonal proteins to promote rodent myelination

Axons undergo striking changes in their content and distribution of cell adhesion molecules (CAMs) and ion channels during myelination that underlies the switch from continuous to saltatory conduction. These changes include the removal of a large cohort of uniformly distributed CAMs that mediate initial axon-Schwann cell interactions and their replacement by a subset of CAMs that mediate domain-specific interactions of myelinated fibers. Here, using rodent models, we examine the mechanisms and significance of this removal of axonal CAMs. We show that Schwann cells just prior to myelination locally activate clathrin-mediated endocytosis (CME) in axons, thereby driving clearance of a broad array of axonal CAMs. CAMs engineered to resist endocytosis are persistently expressed along the axon and delay both PNS and CNS myelination. Thus, glia non-autonomously activate CME in axons to downregulate axonal CAMs and presumptively axo-glial adhesion. This promotes the transition from ensheathment to myelination while simultaneously sculpting the formation of axonal domains.

Oligodendrocyte development and myelin sheath formation are regulated by the antagonistic interaction between the Rag-Ragulator complex and TFEB

Myelination by oligodendrocytes is critical for fast axonal conduction and for the support and survival of neurons in the central nervous system. Recent studies have emphasized that myelination is plastic and that new myelin is formed throughout life. Nonetheless, the mechanisms that regulate the number, length, and location of myelin sheaths formed by individual oligodendrocytes are incompletely understood. Previous work showed that the lysosomal transcription factor TFEB represses myelination by oligodendrocytes and that the RagA GTPase inhibits TFEB, but the step or steps of myelination in which TFEB plays a role have remained unclear. Here, we show that TFEB regulates oligodendrocyte differentiation and also controls the length of myelin sheaths formed by individual oligodendrocytes. In the dorsal spinal cord of tfeb mutants, individual oligodendrocytes produce myelin sheaths that are longer than those produced by wildtype cells. Transmission electron microscopy shows that there are more myelinated axons in the dorsal spinal cord of tfeb mutants than in wildtype animals, but no significant change in axon diameter. In contrast to tfeb mutants, oligodendrocytes in rraga mutants produce shorter myelin sheaths. The sheath length in rraga; tfeb double mutants is not significantly different from wildtype, consistent with the antagonistic interaction between RagA and TFEB. Finally, we find that the GTPase activating protein Flcn and the RagCa and RagCb GTPases are also necessary for myelination by oligodendrocytes. These findings demonstrate that TFEB coordinates myelin sheath length and number during myelin formation in the central nervous system.

ENGEP: advancing spatial transcriptomics with accurate unmeasured gene expression prediction

Imaging-based spatial transcriptomics techniques provide valuable spatial and gene expression information at single-cell resolution. However, their current capability is restricted to profiling a limited number of genes per sample, resulting in most of the transcriptome remaining unmeasured. To overcome this challenge, we develop ENGEP, an ensemble learning-based tool that predicts unmeasured gene expression in spatial transcriptomics data by using multiple single-cell RNA sequencing datasets as references. ENGEP outperforms current state-of-the-art tools and brings biological insight by accurately predicting unmeasured genes. ENGEP has exceptional efficiency in terms of runtime and memory usage, making it scalable for analyzing large datasets.

Innervation of an Ultrasound-Mediated PVDF-TrFE Scaffold for Skin-Tissue Engineering

In this work, electrospun polyvinylidene-trifluoroethylene (PVDF-TrFE) was utilized for its biocompatibility, mechanics, and piezoelectric properties to promote Schwann cell (SC) elongation and sensory neuron (SN) extension. PVDF-TrFE electrospun scaffolds were characterized over a variety of electrospinning parameters (1, 2, and 3 h aligned and unaligned electrospun fibers) to determine ideal thickness, porosity, and tensile strength for use as an engineered skin tissue. PVDF-TrFE was electrically activated through mechanical deformation using low-intensity pulsed ultrasound (LIPUS) waves as a non-invasive means to trigger piezoelectric properties of the scaffold and deliver electric potential to cells. Using this therapeutic modality, neurite integration in tissue-engineered skin substitutes (TESSs) was quantified including neurite alignment, elongation, and vertical perforation into PVDF-TrFE scaffolds. Results show LIPUS stimulation promoted cell alignment on aligned scaffolds. Further, stimulation significantly increased SC elongation and SN extension separately and in coculture on aligned scaffolds but significantly decreased elongation and extension on unaligned scaffolds. This was also seen in cell perforation depth analysis into scaffolds which indicated LIPUS enhanced perforation of SCs, SNs, and cocultures on scaffolds. Taken together, this work demonstrates the immense potential for non-invasive electric stimulation of an in vitro tissue-engineered-skin model.

Brain cholesterol homeostasis and its association with neurodegenerative diseases

The brain is the most cholesterol-rich organ in mammals. However, cholesterol metabolism in the brain is completely independent of other tissues due to the presence of the blood-brain barrier (BBB). Neurons, astrocytes and oligodendrocytes are the main cells responsible for cholesterol synthesis in the brain. The cholesterol content in the brain is maintained at a relatively constant level under strict regulation of synthesis, transport, and turnover, that is, brain cholesterol homeostasis. Once this balance is disrupted, neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD) ensue. This review summarizes the processes controlling cholesterol homeostasis with respect to the synthesis, transport and turnover of cholesterol in the brain. We further focus on how cholesterol imbalance contributes to neurodegenerative diseases to explore the possibilities to modulate the key steps involved, which will provide clues for the development of therapies for the treatment of central nervous system (CNS) diseases.

Cofea: correlation-based feature selection for single-cell chromatin accessibility data

Single-cell chromatin accessibility sequencing (scCAS) technologies have enabled characterizing the epigenomic heterogeneity of individual cells. However, the identification of features of scCAS data that are relevant to underlying biological processes remains a significant gap. Here, we introduce a novel method Cofea, to fill this gap. Through comprehensive experiments on 5 simulated and 54 real datasets, Cofea demonstrates its superiority in capturing cellular heterogeneity and facilitating downstream analysis. Applying this method to identification of cell type-specific peaks and candidate enhancers, as well as pathway enrichment analysis and partitioned heritability analysis, we illustrate the potential of Cofea to uncover functional biological process.

Thirty years of BDNF study in central myelination: From biology to therapy

Being the highest expressed neurotrophin in the mammalian brain, the brain-derived neurotrophic factor (BDNF) is essential to neural development and plasticity in both health and diseases. Following the discovery of BDNF by Yves-Alain Barde in 1982, the main feature of BDNF's activity in myelination was first described by Cellerino et al. in 1997. Since then, genetic manipulation of the BDNF-encoding gene and its receptors in murine models has revealed the contribution of BDNF to the myelinating process in the central nervous system (CNS). The series of BDNF or receptor mouse mutants as well as the BDNF polymorphism in humans have provided new insights into the roles that BDNF signaling plays in myelination in a complex manner. 2024 marks the 30th year of BDNF's research in myelination. Here, we share our perspective on the 30-year history of BDNF in the field of CNS myelination from phenotyping to therapeutic development, focusing on genetic evidence regarding the mechanism by which BDNF regulates myelin formation and repair in the CNS. This review also discusses the current hypotheses of BDNF's action on CNS myelination: axonal- and oligodendroglial-driven mechanisms, which may be ultimately activity-dependent. Last, this review raises the challenges and opportunities of developing BDNF-based therapies for neurodegenerative diseases, opening unanswered questions for future investigation.

Mechanical Responses of a Single Myelin Layer: A Molecular Simulation Study

The myelin sheath provides insulation to the brain's neuron cells, which aids in signal transmission and communication with the body. Degenerated myelin hampers the connection between the glial cells, which are the front row responders during traumatic brain injury mitigation. Thus, the structural integrity of the myelin layer is critical for protecting the brain tissue from traumatic injury. At the molecular level, myelin consists of a lipid bilayer, myelin basic proteins (MBP), proteolipid proteins (PLP), water and ions. Structurally, the myelin sheath is formed by repeatedly wrapping forty or more myelin layers around an axon. Here, we have used molecular dynamic simulations to model and capture the tensile response of a single myelin layer. An openly available molecular dynamic solver, LAMMPS, was used to conduct the simulations. The interatomic potentials for the interacting atoms and molecules were defined using CHARMM force fields. Following a standard equilibration process, the molecular model was stretched uniaxially at a deformation rate of 5 Å/ps. We observed that, at around 10% applied strain, the myelin started to cohesively fail via flaw formation inside the bilayers. Further stretching led to a continued expansion of the defect inside the bilayer, both radially and transversely. This study provides the cellular-level mechanisms of myelin damage due to mechanical load.

Development and preclinical evaluation of bioactive nerve conduits for peripheral nerve regeneration: A comparative study

In severe peripheral nerve injuries, nerve conduits (NCs) are good alternatives to autografts/allografts; however, the results the available devices guarantee for are still not fully satisfactory. Herein, differently bioactivated NCs based on the new polymer oxidized polyvinyl alcohol (OxPVA) are compared in a rat model of sciatic nerve neurotmesis (gap: 5 mm; end point: 6 weeks). Thirty Sprague Dawley rats are randomized to 6 groups: Reverse Autograft (RA); Reaxon®; OxPVA; OxPVA + EAK (self-assembling peptide, mechanical incorporation); OxPVA + EAK-YIGSR (mechanical incorporation); OxPVA + Nerve Growth Factor (NGF) (adsorption). Preliminarily, all OxPVA-based devices are comparable with Reaxon® in Sciatic Functional Index score and gait analysis; moreover, all conduits sustain nerve regeneration (S100, β-tubulin) without showing substantial inflammation (CD3, F4/80) evidences. Following morphometric analyses, OxPVA confirms its potential in PNI repair (comparable with Reaxon®) whereas OxPVA + EAK-YIGSR stands out for its myelinated axons total number and density, revealing promising in injury recovery and for future application in clinical practice.

Type III NRG-1 plays a regulatory role in the regeneration process of nerves from the beginning of transplantation

The present study investigated the effect of type III Neuregulin-1 (NRG-1) on changes in the myelin sheath and the recovery of nerve function during the regeneration process following autologous nerve transplantation. Seventy-two Sprague-Dawley rats were divided into a Blank, Model and (antisense oligonucleotide, ASON) group. The Model and ASON groups of SD rats were subjected to autologous nerve transplantation, and the Blank group only had the sciatic nerve exposed. The Model and ASON groups were given local injections of 2 ml PBS buffer solution and 2 ml ASON of Type III NRG-1, respectively, the NRG-1 type III was inhibited by ASON. Changes in the sciatic nerve functional index (SFI) and conduction velocities were observed at different 6 time points. Regeneration of the myelin sheath was observed using transmission electron microscopy. Type III NRG-1 protein was detected using Western blotting and immunohistochemistry, and NRG-1 mRNA was detected using PCR. The SFI of the ASON group was lower than the Model group after transplantation. The conduction velocities of the ASON group on the 14th and 21st days after autologous nerve transplantation were lower than the Model group (P < 0.01). The protein and mRNA expression of type III NRG-1 in the ASON group was lower than the Model group at all 6 time points. The area of medullated nerve fibres was significantly different between the ASON group and the Model group on the 3rd day (P < 0.05), as was the number of medullated nerve fibres per unit area (P < 0.01). The diameter of axons was obviously different between the two groups (P < 0.01). Type III NRG-1 played an important regulatory role in the regeneration process of the nerve from the beginning of transplantation to the 28th day.

A new perspective on HIV: effects of HIV on brain-heart axis

The human immunodeficiency virus (HIV) infection can cause damage to multiple systems within the body, and the interaction among these various organ systems means that pathological changes in one system can have repercussions on the functions of other systems. However, the current focus of treatment and research on HIV predominantly centers around individual systems without considering the comprehensive relationship among them. The central nervous system (CNS) and cardiovascular system play crucial roles in supporting human life, and their functions are closely intertwined. In this review, we examine the effects of HIV on the CNS, the resulting impact on the cardiovascular system, and the direct damage caused by HIV to the cardiovascular system to provide new perspectives on HIV treatment.

Molinate induces organ defects by promoting apoptosis, inflammation, and endoplasmic reticulum stress during the developmental stage of zebrafish

Molinate is classified as a thiocarbamate herbicide and is mainly used in paddy fields to culture rice. However, the toxic effects of molinate and the associated mechanisms in the process of development have not been completely elucidated. Therefore, in the present study, we demonstrated that molinate reduced the viability of zebrafish larvae and the probability of successful hatching using zebrafish (Danio rerio), one of the remarkable in vivo models for testing the toxicity of chemicals. In addition, molinate treatment triggered the occurrence of apoptosis, inflammation, and endoplasmic reticulum (ER) stress response in zebrafish larvae. Furthermore, we identified that an abnormal cardiovascular phenotype through wild type zebrafish, neuronal defects through transgenic olig2:dsRed zebrafish, and developmental toxicity in the liver through transgenic lfabp:dsRed zebrafish. Collectively, these results provide evidence of the hazardous effects of molinate on the developmental stage of non-target organisms by elucidating the toxic mechanisms of molinate in developing zebrafish.

Synthesis and bioactivity evaluation of a myelin-specific contrast agent for magnetic resonance imaging of myelination in central nervous system

Demyelination exists in many neurological diseases of nervous system, such as stroke. Currently, magnetic resonance imaging (MRI) has been the main tool for diagnosing and monitoring the myelin related diseases. However, the conventional MRI unable to distinguish demyelinating lesions from other inflammatory lesions. To address this problem, we have designed and prepared a myelin specific magnetic resonance contrast agent, Gd-DTDAS, which was based myelin specific moiety MeDAS^g and Gd-DTPA^h. In this work, we verified the specificity and sensitivity of Gd-DTDAS to myelin. Moreover, we investigated the specific binding ability of Gd-DTDAS to myelin sheath in the MCAO miceⁱ models. The in vivo imaging results showed that Gd-DTDAS can bind to the undamaged myelin sheath in the BBB disruption areas, and in turn reduce the relaxation time. The fluorescence images also showed significant fluorescence in the brain right infarct area of the MCAO model mice with administration of Gd-DTDAS. The above results confirmed that Gd-DTDAS could be preferentially distributed in areas with high myelination and can detect focally induced demyelination.

Emerging mitochondrial-mediated mechanisms involved in oligodendrocyte development

Oligodendrocytes are the myelinating glia of the central nervous system and are generated after oligodendrocyte progenitor cells (OPCs) transition into pre-oligodendrocytes and then into myelinating oligodendrocytes. Myelin is essential for proper signal transmission within the nervous system and axonal metabolic support. Although the intrinsic and extrinsic factors that support the differentiation, survival, integration, and subsequent myelination of appropriate axons have been well investigated, little is known about how mitochondria-related pathways such as mitochondrial dynamics, bioenergetics, and apoptosis finely tune these developmental events. Previous findings suggest that changes to mitochondrial morphology act as an upstream regulatory mechanism of neural stem cell (NSC) fate decisions. Whether a similar mechanism is engaged during OPC differentiation has yet to be elucidated. Maintenance of mitochondrial dynamics is vital for regulating cellular bioenergetics, functional mitochondrial networks, and the ability of cells to distribute mitochondria to subcellular locations, such as the growing processes of oligodendrocytes. Myelination is an energy-consuming event, thus, understanding the interplay between mitochondrial dynamics, metabolism, and apoptosis will provide further insight into mechanisms that mediate oligodendrocyte development in healthy and disease states. Here we will provide a concise overview of oligodendrocyte development and discuss the potential contribution of mitochondrial mitochondrial-mediated mechanisms to oligodendrocyte bioenergetics and development.

Higher throughput workflow with sensitive, reliable and automatic quantification of myelination in vitro suitable for drug screening

Multiple sclerosis (MS) is the most common demyelinating autoimmune disease of the central nervous system (CNS). Immune-mediated myelin and axonal damage that is accompanied by chronic axonal loss causing destruction of the myelin sheaths are hallmarks of MS. While great strides have been made in understanding the molecular underpinnings of re-/myelination, currently no remyelination therapy is available for MS. As myelination is a complex process that is not fully understood, we sought to develop a systematic, reliable, automated and quantitative higher throughput screening method. We aimed to quantitate myelin sheaths in vitro with high sensitivity at the single cell level suitable for testing small compound libraries. To this end, we miniaturised in vitro retinal ganglion cell-oligodendrocyte precursor cell (RGC-OPC) co-cultures into a multi-well plate format. This allowed us to maintain the reciprocal interaction of live axons and oligodendrocytes (OLs) to ensure compact myelin formation. To quantify our co-cultures, we developed a novel computer vision algorithm to precisely measure myelination. We demonstrated efficacy of our system with known pro-differentiating compounds BQ3020 and XAV939 which exhibited robust, efficient, and dose dependent effects on myelination. Through this combination of experimental and technical advances, we have developed a method allowing systematic and reliable testing of remyelinating compound efficacy.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

Schwann cell functions in peripheral nerve development and repair

The glial cell of the peripheral nervous system (PNS), the Schwann cell (SC), counts among the most multifaceted cells of the body. During development, SCs secure neuronal survival and participate in axonal path finding. Simultaneously, they orchestrate the architectural set up of the developing nerves, including the blood vessels and the endo-, peri- and epineurial layers. Perinatally, in rodents, SCs radially sort and subsequently myelinate individual axons larger than 1 μm in diameter, while small calibre axons become organised in non-myelinating Remak bundles. SCs have a vital role in maintaining axonal health throughout life and several specialized SC types perform essential functions at specific locations, such as terminal SC at the neuromuscular junction (NMJ) or SC within cutaneous sensory end organs. In addition, neural crest derived satellite glia maintain a tight communication with the soma of sensory, sympathetic, and parasympathetic neurons and neural crest derivatives are furthermore an indispensable part of the enteric nervous system. The remarkable plasticity of SCs becomes evident in the context of a nerve injury, where SC transdifferentiate into intriguing repair cells, which orchestrate a regenerative response that promotes nerve repair. Indeed, the multiple adaptations of SCs are captivating, but remain often ill-resolved on the molecular level. Here, we summarize and discuss the knowns and unknowns of the vast array of functions that this single cell type can cover in peripheral nervous system development, maintenance, and repair.

Inverted human umbilical artery as a 3D scaffold for sciatic nerve regeneration in rats

Treatment of peripheral nerve injuries (PNIs) remains a challenge. Interposing a graft delivers better regenerative outcomes. Autografts present major drawbacks which have given rise to the development of alternatives such as artificial scaffolds, some of which are very promising. This study was designed to investigate the potential use of an inverted human umbilical cord artery (iHUA) as a 3D scaffold nerve chamber, for nerve regeneration after transection of the sciatic nerve (SN) in rats. Rats underwent surgical SN transection in their right hindlimb, followed by suture of the device at the resected stumps. Local tolerance, insert biodegradability and nerve reconstruction over time were thoroughly studied by histopathological and morphometric analysis, completed by functional test assessment of sensitivity and motricity recovery. We have demonstrated that nerve reconstruction in the presence of an iHUA insert is effective. The device is well tolerated and highly biodegraded. Although the regenerated nerve is still immature at the end of our study, signs of sensitivity and partial functional recovery were witnessed, confirming our histological findings. Our results support the potential clinical use of iHUA as a 3D scaffold to bridge nerve discontinuity and guide axonal regrowth in selected cases of PNIs.

Restoration of spinal cord injury: From endogenous repairing process to cellular therapy

Spinal cord injury (SCI) disrupts neurological pathways and impacts sensory, motor, and autonomic nerve function. There is no effective treatment for SCI currently. Numerous endogenous cells, including astrocytes, macrophages/microglia, and oligodendrocyte, are involved in the histological healing process following SCI. By interfering with cells during the SCI repair process, some advancements in the therapy of SCI have been realized. Nevertheless, the endogenous cell types engaged in SCI repair and the current difficulties these cells confront in the therapy of SCI are poorly defined, and the mechanisms underlying them are little understood. In order to better understand SCI and create new therapeutic strategies and enhance the clinical translation of SCI repair, we have comprehensively listed the endogenous cells involved in SCI repair and summarized the six most common mechanisms involved in SCI repair, including limiting the inflammatory response, protecting the spared spinal cord, enhancing myelination, facilitating neovascularization, producing neurotrophic factors, and differentiating into neural/colloidal cell lines.

Accelerating Neurite Growth and Directing Neuronal Connections Constrained by 3D Porous Microtubes

Investigation of neural growth and connection is crucial in the field of neural tissue engineering. Here, using a femtosecond laser direct writing (fs-DLW) technique, we propose a directionally aligned porous microtube array as a culture system for accelerating the growth of neurons and directing the connection of neurites. These microtubes exhibited an unprecedented guidance effect toward the outgrowth of primary embryonic rat hippocampal neurons, with a wrap resembling the myelin sheaths of neurons. The speed of neurite growth inside these microtubes was significantly faster than that outside these microtubes. We also achieved selective/directing connection of neural networks inside the magnetic microtubes via precise microtube delivery to a gap between two neural clusters. This work not only proposes a powerful microtube platform for accelerated growth of neurons but also offers a new idea for constructing biological neural circuits by arranging the size, location, and pattern of microtubes.

Nerve Density and Neuronal Biomarkers in Cancer

Simple Summary

Researchers have shown that tumor biomarkers and increased nerve density are important clinical tools for determining cancer prognosis and developing effective treatments. The aims of our review were to synthesize these findings by detailing the histology of peripheral nerves, discuss the use of various neuronal biomarkers in cancer, and assess the impact of increased nerve density on tumorigenesis. This review demonstrates that specific neuronal markers may have an important role in tumorigenesis and may serve as diagnostic and prognostic factors for various cancers. Moreover, increased nerve density may be associated with worse prognosis in different cancers, and cancer therapies that decrease nerve density may offer benefit to patients.

Abstract

Certain histologic characteristics of neurons, novel neuronal biomarkers, and nerve density are emerging as important diagnostic and prognostic tools in several cancers. The tumor microenvironment has long been known to promote tumor development via promoting angiogenesis and cellular proliferation, but new evidence has shown that neural proliferation and invasion in the tumor microenvironment may also enable tumor growth. Specific neuronal components in peripheral nerves and their localization in certain tumor sites have been identified and associated with tumor aggressiveness. In addition, dense neural innervation has been shown to promote tumorigenesis. In this review, we will summarize the histological components of a nerve, explore the neuronal biomarkers found in tumor sites, and discuss clinical correlates between tumor neurobiology and patient prognosis.

Timely Schwann cell division drives peripheral myelination in vivo via the laminin/cAMP pathway

Schwann cells (SCs) migrate along peripheral axons and divide intensively to generate the right number of cells prior to axonal ensheathment; however, little is known regarding the temporal and molecular control of their division and its impact on myelination. We report that Sil, a spindle pole protein associated with autosomal recessive primary microcephaly, is required for temporal mitotic exit of SCs. In sil-deficient cassiopeia (csp−/−) mutants, SCs fail to radially sort and myelinate peripheral axons. Elevation of cAMP, but not Rac1 activity, in csp−/− restores myelin ensheathment. Most importantly, we show a significant decrease in laminin expression within csp−/− posterior lateral line nerve and that forcing Laminin 2 expression in csp−/− fully restores the ability of SCs to myelinate. Thus, we demonstrate an essential role for timely SC division in mediating laminin expression to orchestrate radial sorting and peripheral myelination in vivo.

A novel mouse model of CMT1B identifies hyperglycosylation as a new pathogenetic mechanism

Mutations in the Myelin Protein Zero gene (MPZ), encoding P0, the major structural glycoprotein of peripheral nerve myelin, are the cause of Charcot-Marie-Tooth (CMT) type 1B neuropathy, and most P0 mutations appear to act through gain-of-function mechanisms. Here, we investigated how misglycosylation, a pathomechanism encompassing several genetic disorders, may affect P0 function. Using in vitro assays, we showed that gain of glycosylation is more damaging for P0 trafficking and functionality as compared with a loss of glycosylation. Hence, we generated, via CRISPR/Cas9, a mouse model carrying the MPZD61N mutation, predicted to generate a new N-glycosylation site in P0. In humans, MPZD61N causes a severe early-onset form of CMT1B, suggesting that hyperglycosylation may interfere with myelin formation, leading to pathology. We show here that MPZD61N/+ mice develop a tremor as early as P15 which worsens with age and correlates with a significant motor impairment, reduced muscular strength and substantial alterations in neurophysiology. The pathological analysis confirmed a dysmyelinating phenotype characterized by diffuse hypomyelination and focal hypermyelination. We find that the mutant P0D61N does not cause significant endoplasmic reticulum stress, a common pathomechanism in CMT1B, but is properly trafficked to myelin where it causes myelin uncompaction. Finally, we show that myelinating dorsal root ganglia cultures from MPZD61N mice replicate some of the abnormalities seen in vivo, suggesting that they may represent a valuable tool to investigate therapeutic approaches. Collectively, our data indicate that the MPZD61N/+ mouse represents an authentic model of severe CMT1B affirming gain-of-glycosylation in P0 as a novel pathomechanism of disease.

Coherent Anti-Stokes Raman Spectroscopy (CARS) Application for Imaging Myelination in Brain Slices

Coherent anti-Stokes Raman spectroscopy (CARS) is a technique classically employed by chemists and physicists to produce a coherent signal of signature vibrations of molecules. However, these vibrational signatures are also characteristic of molecules within anatomical tissue such as the brain, making it increasingly useful and applicable for Neuroscience applications. For example, CARS can measure lipids by specifically exciting chemical bonds within these molecules, allowing for quantification of different aspects of tissue, such as myelin involved in neurotransmission. In addition, compared to other techniques typically used to quantify myelin, CARS can also be set up to be compatible with immunofluorescent techniques, allowing for co-labeling with other markers such as sodium channels or other components of synaptic transmission. Myelination changes are an inherently important mechanism in demyelinating diseases such as multiple sclerosis or other neurological conditions such as Fragile X Syndrome or autism spectrum disorders is an emerging area of research. In conclusion, CARS can be utilized in innovative ways to answer pressing questions in Neuroscience and provide evidence for underlying mechanisms related to many different neurological conditions.

Traumatic and Diabetic Schwann Cell Demyelination Is Triggered by a Transient Mitochondrial Calcium Release through Voltage Dependent Anion Channel 1

A large number of peripheral neuropathies, among which are traumatic and diabetic peripheral neuropathies, result from the degeneration of the myelin sheath, a process called demyelination. Demyelination does not result from Schwann cell death but from Schwann cell dedifferentiation, which includes reprograming and several catabolic and anabolic events. Starting around 4 h after nerve injury, activation of MAPK/cJun pathways is the earliest characterized step of this dedifferentiation program. Here we show, using real-time in vivo imaging, that Schwann cell mitochondrial pH, motility and calcium content are altered as soon as one hour after nerve injury. Mitochondrial calcium release occurred through the VDAC outer membrane channel and mPTP inner membrane channel. This calcium influx in the cytoplasm induced Schwann-cell demyelination via MAPK/c-Jun activation. Blocking calcium release through VDAC silencing or VDAC inhibitor TRO19622 prevented demyelination. We found that the kinetics of mitochondrial calcium release upon nerve injury were altered in the Schwann cells of diabetic mice suggesting a permanent leak of mitochondrial calcium in the cytoplasm. TRO19622 treatment alleviated peripheral nerve defects and motor deficit in diabetic mice. Together, these data indicate that mitochondrial calcium homeostasis is instrumental in the Schwann cell demyelination program and that blocking VDAC constitutes a molecular basis for developing anti-demyelinating drugs for diabetic peripheral neuropathy.

Role of Extracellular Vesicles in Glia-Neuron Intercellular Communication

Cross talk between glia and neurons is crucial for a variety of biological functions, ranging from nervous system development, axonal conduction, synaptic transmission, neural circuit maturation, to homeostasis maintenance. Extracellular vesicles (EVs), which were initially described as cellular debris and were devoid of biological function, are now recognized as key components in cell-cell communication and play a critical role in glia-neuron communication. EVs transport the proteins, lipids, and nucleic acid cargo in intercellular communication, which alters target cells structurally and functionally. A better understanding of the roles of EVs in glia-neuron communication, both in physiological and pathological conditions, can aid in the discovery of novel therapeutic targets and the development of new biomarkers. This review aims to demonstrate that different types of glia and neuronal cells secrete various types of EVs, resulting in specific functions in intercellular communications.

Newly Identified Deficiencies in the Multiple Sclerosis Central Nervous System and Their Impact on the Remyelination Failure

The pathogenesis of multiple sclerosis (MS) remains enigmatic and controversial. Myelin sheaths in the central nervous system (CNS) insulate axons and allow saltatory nerve conduction. MS brings about the destruction of myelin sheaths and the myelin-producing oligodendrocytes (ODCs). The conundrum of remyelination failure is, therefore, crucial in MS. In this review, the roles of epidermal growth factor (EGF), normal prions, and cobalamin in CNS myelinogenesis are briefly summarized. Thereafter, some findings of other authors and ourselves on MS and MS-like models are recapitulated, because they have shown that: (a) EGF is significantly decreased in the CNS of living or deceased MS patients; (b) its repeated administration to mice in various MS-models prevents demyelination and inflammatory reaction; (c) as was the case for EGF, normal prion levels are decreased in the MS CNS, with a strong correspondence between liquid and tissue levels; and (d) MS cobalamin levels are increased in the cerebrospinal fluid, but decreased in the spinal cord. In fact, no remyelination can occur in MS if these molecules (essential for any form of CNS myelination) are lacking. Lastly, other non-immunological MS abnormalities are reviewed. Together, these results have led to a critical reassessment of MS pathogenesis, partly because EGF has little or no role in immunology.

Clusters of neuronal neurofascin prefigure the position of a subset of nodes of Ranvier along individual central nervous system axons in vivo

The spacing of nodes of Ranvier crucially affects conduction properties along myelinated axons. It is assumed that node position is primarily driven by growing myelin sheaths. Here, we reveal an additional mechanism of node positioning that is driven by the axon. Through longitudinal live imaging of node formation dynamics in the zebrafish central nervous system, we show that stable clusters of the cell adhesion molecule neurofascin a can accumulate at specific sites along axons prior to myelination. While some of these clusters are pushed into future node position by extending myelin sheaths, others are not and thus prefigure the position of where a mature node forms. Animals that lack full-length neurofascin a show increased internodal distances and less regular nodal spacing along single axons. Together, our data reveal the existence of an axonal mechanism to position nodes of Ranvier that does not depend on regulation by myelin sheath growth.

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Stable clusters of neuronal neurofascin can form along axons prior to myelination

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Some clusters are pushed in place by developing myelin sheaths

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Other clusters restrict sheath growth and thus prefigure node position

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Animals lacking axonal neurofascin have longer and less regular internodal spacing

An electroceutical approach enhances myelination via upregulation of lipid biosynthesis in the dorsal root ganglion

As the myelin sheath is crucial for neuronal saltatory conduction, loss of myelin in the peripheral nervous system (PNS) leads to demyelinating neuropathies causing muscular atrophy, numbness, foot deformities and paralysis. Unfortunately, few interventions are available for such neuropathies, because previous pharmaceuticals have shown severe side effects and failed in clinical trials. Therefore, exploring new strategies to enhance PNS myelination is critical to provide solution for such intractable diseases. This study aimed to investigate the effectiveness of electrical stimulation (ES) to enhance myelination in the mouse dorsal root ganglion (DRG) - an ex vivo model of the PNS. Mouse embryonic DRGs were extracted at E13 and seeded onto Matrigel-coated surfaces. After sufficient growth and differentiation, screening was carried out by applying ES in the 1-100 Hz range at the beginning of the myelination process. DRG myelination was evaluated via immunostaining at the intermediate (19 DIV) and mature (30 DIV) stages. Further biochemical analyses were carried out by utilizing RNA sequencing, qPCR and biochemical assays at both intermediate and mature myelination stages. Imaging of DRG myelin lipids was carried out via time-of-flight secondary ion mass spectrometry (ToF-SIMS). With screening ES conditions, optimal condition was identified at 20 Hz, which enhanced the percentage of myelinated neurons and average myelin length not only at intermediate (129% and 61%) but also at mature (72% and 17%) myelination stages. Further biochemical analyses elucidated that ES promoted lipid biosynthesis in the DRG. ToF-SIMS imaging showed higher abundance of the structural lipids, cholesterol and sphingomyelin, in the myelin membrane. Therefore, promotion of lipid biosynthesis and higher abundance of myelin lipids led to ES-mediated myelination enhancement. Given that myelin lipid deficiency is culpable for most demyelinating PNS neuropathies, the results might pave a new way to treat such diseases via electroceuticals.

Insights Into Central Nervous System Glial Cell Formation and Function From Zebrafish

The term glia describes a heterogenous collection of distinct cell types that make up a large proportion of our nervous system. Although once considered the glue of the nervous system, the study of glial cells has evolved significantly in recent years, with a large body of literature now highlighting their complex and diverse roles in development and throughout life. This progress is due, in part, to advances in animal models in which the molecular and cellular mechanisms of glial cell development and function as well as neuron-glial cell interactions can be directly studied in vivo in real time, in intact neural circuits. In this review we highlight the instrumental role that zebrafish have played as a vertebrate model system for the study of glial cells, and discuss how the experimental advantages of the zebrafish lend themselves to investigate glial cell interactions and diversity. We focus in particular on recent studies that have provided insight into the formation and function of the major glial cell types in the central nervous system in zebrafish.

Myelin Biology

Myelin is a key evolutionary specialization and adaptation of vertebrates formed by the plasma membrane of glial cells, which insulate axons in the nervous system. Myelination not only allows rapid and efficient transmission of electric impulses in the axon by decreasing capacitance and increasing resistance but also influences axonal metabolism and the plasticity of neural circuits. In this review, we will focus on Schwann cells, the glial cells which form myelin in the peripheral nervous system. Here, we will describe the main extrinsic and intrinsic signals inducing Schwann cell differentiation and myelination and how myelin biogenesis is achieved. Finally, we will also discuss how the study of human disorders in which molecules and pathways relevant for myelination are altered has enormously contributed to the current knowledge on myelin biology.

Lamin B1 Accumulation's Effects on Autosomal Dominant Leukodystrophy (ADLD): Induction of Reactivity in the Astrocytes

Autosomal dominant leukodystrophy (ADLD) is an extremely rare and fatal neurodegenerative disease due to the overexpression of the nuclear lamina component Lamin B1. Many aspects of the pathology still remain unrevealed. This work highlights the effect of Lamin B1 accumulation on different cellular functions in an ADLD astrocytic in vitro model. Lamin B1 overexpression induces alterations in cell survival signaling pathways with GSK3β inactivation, but not the upregulation of β-catenin targets, therefore resulting in a reduction in astrocyte survival. Moreover, Lamin B1 build up affects proliferation and cell cycle progression with an increase of PPARγ and p27 and a decrease of Cyclin D1. These events are also associated to a reduction in cell viability and an induction of apoptosis. Interestingly, ADLD astrocytes trigger a tentative activation of survival pathways that are ineffective. Finally, astrocytes overexpressing Lamin B1 show increased immunoreactivity for both GFAP and vimentin together with NF-kB phosphorylation and c-Fos increase, suggesting astrocytes reactivity and substantial cellular activation. These data demonstrate that Lamin B1 accumulation is correlated to biochemical, metabolic, and morphologic remodeling, probably related to the induction of a reactive astrocytes phenotype that could be strictly associated to ADLD pathological mechanisms.

The Multiple Roles of Sphingomyelin in Parkinson's Disease

Advances over the past decade have improved our understanding of the role of sphingolipid in the onset and progression of Parkinson's disease. Much attention has been paid to ceramide derived molecules, especially glucocerebroside, and little on sphingomyelin, a critical molecule for brain physiopathology. Sphingomyelin has been proposed to be involved in PD due to its presence in the myelin sheath and for its role in nerve impulse transmission, in presynaptic plasticity, and in neurotransmitter receptor localization. The analysis of sphingomyelin-metabolizing enzymes, the development of specific inhibitors, and advanced mass spectrometry have all provided insight into the signaling mechanisms of sphingomyelin and its implications in Parkinson's disease. This review describes in vitro and in vivo studies with often conflicting results. We focus on the synthesis and degradation enzymes of sphingomyelin, highlighting the genetic risks and the molecular alterations associated with Parkinson's disease.

Fluroxypyr-1-methylheptyl ester interferes with the normal embryogenesis of zebrafish by inducing apoptosis, inflammation, and neurovascular toxicity

Fluroxypyr-1-methylheptyl ester (FPMH) is a synthetic auxin herbicide used to regulate the growth of post-emergence broad-leaved weeds. Although acute exposure to FPMH increases the mortality of several fish species in the juvenile stage, the developmental toxicity of FPMH in aquatic vertebrates has not yet been investigated. In the present study, we assessed the developmental toxicity of FPMH using zebrafish models that offer many advantages for studying toxicology. During embryogenesis, survival rates gradually decreased with increasing FPMH concentrations and exposure times. At 120 h post-fertilization, FPMH-exposed zebrafish larvae showed various abnormalities such as small eye size, heart defects, enlarged yolk sac, and shortened body length. The study results confirmed the induction of apoptosis in the anterior body of zebrafish and upregulation of inflammatory gene expression. Further, defects in vascular networks, especially the loss of central arteries and abnormal aortic arch structures, were seen in the fli1:eGFP transgenic zebrafish model. Neurotoxicity of FPMH was examined using mbp:eGFP zebrafish and which displayed compromised myelination following FPMH administration. Our study has demonstrated the mechanisms underlying FPMH toxicity in developing zebrafish that is a representative model of vertebrates.

Metachromatic Leukodystrophy: Diagnosis and Treatment Challenges

Metachromatic leukodystrophy is a neurological disease of the lysosomal deposit that has a significant impact given the implications for the neurodegenerative deterioration of the patient. Currently, there is no treatment available that reverses the development of characteristic neurological and systemic symptoms. Objective. Carry out an updated bibliographic search on the most critical advances in the treatment and diagnosis for LDM. A retrospective topic review published in English and Spanish in the Orphanet and Pubmed databases. Current treatment options, such as enzyme replacement therapy and hematopoietic stem cell transplantation aimed at decreasing the rapid progression of the disease, improving patient survival; however, these are costly. The pathophysiological events of intracellular signaling related to the deficiency of the enzyme Arylsulfatase A and subsequent accumulation of sulphatides and glycosylated ceramides have not yet been established. Recently, the accumulation of C16 sulphatides has been shown to inhibit glycolysis and insulin secretion in pancreatic cells. The significant advance in technology has allowed timely diagnosis in patients suffering from LDM; however, they still do not have an effective treatment.

MyelTracer: A Semi-Automated Software for Myelin g-Ratio Quantification

In the central and peripheral nervous systems, the myelin sheath promotes neuronal signal transduction. The thickness of the myelin sheath changes during development and in disease conditions like multiple sclerosis. Such changes are routinely detected using electron microscopy through g-ratio quantification. While g-ratio is one of the most critical measurements in myelin studies, a major drawback is that g-ratio quantification is extremely laborious and time-consuming. Here, we report the development and validation of MyelTracer, an installable, stand-alone software for semi-automated g-ratio quantification based on the Open Computer Vision Library (OpenCV). Compared with manual g-ratio quantification, using MyelTracer produces consistent results across multiple tissues and animal ages, as well as in remyelination after optic nerve crush, and reduces total quantification time by 40-60%. With g-ratio measurements via MyelTracer, a known hypomyelination phenotype can be detected in a Williams syndrome mouse model. MyelTracer is easy to use and freely available for Windows and Mac OS X (https://github.com/HarrisonAllen/MyelTracer).

Dicer Deletion in Astrocytes Inhibits Oligodendroglial Differentiation and Myelination

Increasing evidence has shown that astrocytes are implicated in regulating oligodendrocyte myelination, but the underlying mechanisms remain largely unknown. To understand whether microRNAs in astrocytes function in regulating oligodendroglial differentiation and myelination in the developing and adult CNS, we generated inducible astrocyte-specific Dicer conditional knockout mice (hGFAP-CreERT; Dicer fl/fl). By using a reporter mouse line (mT/mG), we confirmed that hGFAP-CreERT drives an efficient and astrocyte-specific recombination in the developing CNS, upon tamoxifen treatment from postnatal day 3 (P3) to P7. The Dicer deletion in astrocytes resulted in inhibited oligodendroglial differentiation and myelination in the developing CNS of Dicer cKO mice at P10 and P14, and did not alter the densities of neurons or axons, indicating that Dicer in astrocytes is required for oligodendrocyte myelination. Consequently, the Dicer deletion in astrocytes at P3 resulted in impaired spatial memory and motor coordination at the age of 9 weeks. To understand whether Dicer in astrocytes is also required for remyelination, we induced Dicer deletion in 3-month-old mice and then injected lysolecithin into the corpus callosum to induce demyelination. The Dicer deletion in astrocytes blocked remyelination in the corpus callosum 14 days after induced demyelination. Together, our results indicate that Dicer in astrocytes is required for oligodendroglia myelination in both the developing and adult CNS.

Oligodendrocyte Secreted Factors Shape Hippocampal GABAergic Neuron Transcriptome and Physiology

Oligodendrocytes form myelin for central nervous system axons and release factors which signal to neurons during myelination. Here, we ask how oligodendroglial factors influence hippocampal GABAergic neuron physiology. In mixed hippocampal cultures, GABAergic neurons fired action potentials (APs) of short duration and received high frequencies of excitatory synaptic events. In purified neuronal cultures without glial cells, GABAergic neuron excitability increased and the frequency of synaptic events decreased. These effects were largely reversed by adding oligodendrocyte conditioned medium (OCM). We compared the transcriptomic signature with the electrophysiological phenotype of single neurons in these three culture conditions. Genes expressed by single pyramidal or GABAergic neurons largely conformed to expected cell-type specific patterns. Multiple genes of GABAergic neurons were significantly downregulated by the transition from mixed cultures containing glial cells to purified neuronal cultures. Levels of these genes were restored by the addition of OCM to purified cultures. Clustering genes with similar changes in expression between different culture conditions revealed processes affected by oligodendroglial factors. Enriched genes are linked to roles in synapse assembly, AP generation, and transmembrane ion transport, including of zinc. These results provide new insight into the molecular targets by which oligodendrocytes influence neuron excitability and synaptic function.

Calcineurin Activity Is Increased in Charcot-Marie-Tooth 1B Demyelinating Neuropathy

Schwann cells produce a considerable amount of lipids and proteins to form myelin in the PNS. For this reason, the quality control of myelin proteins is crucial to ensure proper myelin synthesis. Deletion of serine 63 from P0 (P0S63del) protein in myelin forming Schwann cells causes Charcot-Marie-Tooth type 1B neuropathy in humans and mice. Misfolded P0S63del accumulates in the ER of Schwann cells where it elicits the unfolded protein response (UPR). PERK is the UPR transducer that attenuates global translation and reduces ER stress by phosphorylating the translation initiation factor eIF2alpha. Paradoxically, Perk ablation in P0S63del Schwann cells (S63del/PerkSCKO ) reduced the level of P-eIF2alpha, leaving UPR markers upregulated, yet unexpectedly improved S63del myelin defects in vivo We therefore investigated the hypothesis that PERK may interfere with signals outside of the UPR and specifically with calcineurin/NFATc4 pro-myelinating pathway. Using mouse genetics including females and males in our experimental setting, we show that PERK and calcineurin interact in P0S63del nerves and that calcineurin activity and NFATc4 nuclear localization are increased in S63del Schwann cells, without altering EGR2/KROX20 expression. Moreover, genetic manipulation of the calcineurin subunits appears to be either protective or toxic in S63del in a context-dependent manner, suggesting that Schwann cells are highly sensitive to alterations of calcineurin activity.SIGNIFICANCE STATEMENT Our work shows a novel activity and function for calcineurin in Schwann cells in the context of ER stress. Schwann cells expressing the S63del mutation in P0 protein induce the unfolded protein response and upregulate calcineurin activity. Calcineurin interacts with the ER stress transducer PERK, but the relationship between the UPR and calcineurin in Schwann cells is unclear. Here we propose a protective role for calcineurin in S63del neuropathy, although Schwann cells appear to be very sensitive to its regulation. The paper uncovers a new important role for calcineurin in a demyelinating diseases.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

Lipid Rafts from Olfactory Ensheathing Cells: Molecular Composition and Possible Roles

Olfactory ensheathing cells (OECs) are specialized glial cells of the olfactory system, believed to play a role in the continuous production of olfactory neurons and ensheathment of their axons. Although OECs are used in therapeutic applications, little is known about the cellular mechanisms underlying their migratory behavior. Recently, we showed that OEC migration is sensitive to ganglioside blockage through A2B5 and Jones antibody in OEC culture. Gangliosides are common components of lipid rafts, where they participate in several cellular mechanisms, including cell migration. Here, we characterized OEC lipid rafts, analyzing the presence of specific proteins and gangliosides that are commonly expressed in motile neural cells, such as young neurons, oligodendrocyte progenitors, and glioma cells. Our results showed that lipid rafts isolated from OECs were enriched in cholesterol, sphingolipids, phosphatidylcholine, caveolin-1, flotillin-1, gangliosides GM1 and 9-O-acetyl GD3, A2B5-recognized gangliosides, CNPase, α-actinin, and β1-integrin. Analysis of the actin cytoskeleton of OECs revealed stress fibers, membrane spikes, ruffled membranes and lamellipodia during cell migration, as well as the distribution of α-actinin in membrane projections. This is the first description of α-actinin and flotillin-1 in lipid rafts isolated from OECs and suggests that, together with β1-integrin and gangliosides, membrane lipid rafts play a role during OEC migration. This study provides new information on the molecular composition of OEC membrane microdomains that can impact on our understanding of the role of OEC lipid rafts under physiological and pathological conditions of the nervous system, including inflammation, hypoxia, aging, neurodegenerative diseases, head trauma, brain tumor, and infection.

Bu Shen Yi Sui Capsule Alleviates Neuroinflammation and Demyelination by Promoting Microglia toward M2 Polarization, Which Correlates with Changes in miR-124 and miR-155 in Experimental Autoimmune Encephalomyelitis

BACKGROUND

Bu Shen Yi Sui capsule (BSYS) is a traditional Chinese medicine prescription that has shown antineuroinflammatory and neuroprotective effects in treating multiple sclerosis (MS) and its animal model of experimental autoimmune encephalomyelitis (EAE). Microglia play an important role in neuroinflammation. The M1 phenotype of microglia is involved in the proinflammatory process of the disease, while the M2 phenotype plays an anti-inflammatory role. Promoting the polarization of microglia to M2 in MS/EAE is a promising therapeutic strategy. This study is aimed at exploring the effects of BSYS on microglial polarization in mice with EAE.

METHODS

The EAE model was established by the intraperitoneal injection of pertussis toxin and subcutaneous injection of myelin oligodendrocyte glycoprotein (MOG)35-55 in C57BL/6J mice. The mice were treated with BSYS (3.02 g/kg), FTY720 (0.3 mg/kg), or distilled water by intragastric administration. H&E and LFB staining, transmission electron microscopy, qRT-PCR, immunofluorescence, ELISA, fluorescence in situ hybridization, and western blotting were used to detect the histological changes in myelin, microglial M1/M2 polarization markers, and the expression of key genes involved in EAE. Results and Conclusions. BSYS treatment of EAE mice increased the body weight, decreased the clinical score, and reduced demyelination induced by inflammatory infiltration. BSYS also inhibited the mRNA expression of M1 microglial markers while increasing the mRNA level of M2 markers. Additionally, BSYS led to a marked decrease in the ratio of M1 microglia (iNOS+/Iba1+) and an obvious increase in the number of M2 microglia (Arg1+/Iba1+). In the EAE mouse model, miR-124 expression was decreased, and miR-155 expression was increased, while BSYS treatment significantly reversed this effect and modulated the levels of C/EBP α, PU.1, and SOCS1 (target genes of miR-124 and miR-155). Therefore, the neuroprotective effect of BSYS against MS/EAE was related to promoting microglia toward M2 polarization, which may be correlated with changes in miR-124 and miR-155 in vivo.

Neuron-Oligodendrocyte Communication in Myelination of Cortical GABAergic Cells

Axonal myelination by oligodendrocytes increases the speed and reliability of action potential propagation, and so plays a pivotal role in cortical information processing. The extent and profile of myelination vary between different cortical layers and groups of neurons. Two subtypes of cortical GABAergic neurons are myelinated: fast-spiking parvalbumin-expressing cells and somatostatin-containing cells. The expression of pre-nodes on the axon of these inhibitory cells before myelination illuminates communication between oligodendrocytes and neurons. We explore the consequences of myelination for action potential propagation, for patterns of neuronal connectivity and for the expression of behavioral plasticity.