Myelin-based inhibitors of oligodendrocyte myelination: clues from axonal growth and regeneration.
Ontology highlight
ABSTRACT:
SUBMITTER: Mei F
PROVIDER: S-EPMC5190510 | biostudies-other | 2013 Apr
REPOSITORIES: biostudies-other
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Project description:Oligodendrocytes are essential for the development, function, and health of the vertebrate central nervous system. These cells maintain axon myelination to ensure saltatory propagation of action potentials. Oligodendrocyte develops from neural progenitor cells, in a step-wise process that involves oligodendrocyte precursor specification, proliferation, and differentiation. The lineage progression requires coordination of transcriptional and epigenetic circuits to mediate the stage-specific intricacies of oligodendrocyte development. Epigenetic mechanisms involve DNA methylation, histone modifications, ATP-dependent chromatin remodeling, and non-coding RNA modulation that regulate the chromatin state over regulatory genes, which must be expressed or repressed to establish oligodendrocyte identity and lineage progression. In this review, we will focus on epigenetic programming associated with histone modification enzymes, chromatin remodeling, and non-coding RNAs that regulate oligodendrocyte lineage progression, and discuss how these mechanisms might be harnessed to induce myelin repair for treatment of demyelinating diseases such as multiple sclerosis.
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Project description:The correct targeting of myelin is essential for nervous system formation and function. Oligodendrocytes in the CNS myelinate some axons, but not others, and do not myelinate structures including cell bodies and dendrites [1]. Recent studies indicate that extrinsic signals, such as neuronal activity [2, 3] and cell adhesion molecules [4], can bias myelination toward some axons and away from cell bodies and dendrites, indicating that, in vivo, neuronal and axonal cues regulate myelin targeting. In vitro, however, oligodendrocytes have an intrinsic propensity to myelinate [5-7] and can promiscuously wrap inert synthetic structures resembling neuronal processes [8, 9] or cell bodies [4]. A current therapeutic goal for the treatment of demyelinating diseases is to greatly promote oligodendrogenesis [10-13]; thus, it is important to test how accurately extrinsic signals regulate the oligodendrocyte's intrinsic program of myelination in vivo. Here, we test the hypothesis that neurons regulate myelination with sufficient stringency to always ensure correct targeting. Surprisingly, however, we find that myelin targeting in vivo is not very stringent and that mistargeting occurs readily when oligodendrocyte and myelin supply exceed axonal demand. We find that myelin is mistargeted to neuronal cell bodies in zebrafish mutants with fewer axons and independently in drug-treated zebrafish with increased oligodendrogenesis. Additionally, by increasing myelin production of oligodendrocytes in zebrafish and mice, we find that excess myelin is also inappropriately targeted to cell bodies. Our results suggest that balancing oligodendrocyte-intrinsic programs of myelin supply with axonal demand is essential for correct myelin targeting in vivo and highlight potential liabilities of strongly promoting oligodendrogenesis.
| S-EPMC5912901 | biostudies-literature
Project description:Repair of myelin injury in multiple sclerosis may fail, resulting in chronic demyelination, axonal loss, and disease progression. As cellular pathways regulated by phosphatase and tensin homologue deleted on chromosome 10 (PTEN; eg, phosphatidylinositol-3-kinase [PI-3K]) have been reported to enhance axon regeneration and oligodendrocyte maturation, we investigated potentially beneficial effects of Pten loss of function in the oligodendrocyte lineage on remyelination.We characterized oligodendrocyte numbers and myelin sheath thickness in mice with conditional inactivation of Pten in oligodendrocytes, Olig2-cre, Pten(fl/fl) mice. Using a model of central nervous system demyelination, lysolecithin injection into the spinal cord white matter, we performed short- and long-term lesioning experiments and quantified oligodendrocyte maturation and myelin sheath thickness in remyelinating lesions.During development, we observed dramatic hypermyelination in the corpus callosum and spinal cord. Following white matter injury, however, there was no detectable improvement in remyelination. Moreover, we observed progressive myelin sheath abnormalities and massive axon degeneration in the fasciculus gracilis of mutant animals, as indicated by ultrastructure and expression of SMI-32, amyloid precursor protein, and caspase 6.These studies indicate adverse effects of chronic Pten inactivation (and by extension, activation PI-3K signaling) on myelinating oligodendrocytes and their axonal targets. We conclude that PTEN function in oligodendrocytes is required to regulate myelin thickness and preserve axon integrity. In contrast, PTEN is dispensable during myelin repair, and its inactivation confers no detectable benefit.
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Project description:In the central nervous system (CNS), myelin formation and repair are regulated by oligodendrocyte (OL) lineage cells, which sense and integrate signals from their environment, including from other glial cells and the extracellular matrix (ECM). The signaling pathways that coordinate this complex communication, however, remain poorly understood. The adhesion G protein-coupled receptor ADGRG1 (also known as GPR56) is an evolutionarily conserved regulator of OL development in humans, mice, and zebrafish, although its activating ligand for OL lineage cells is unknown. Here, we report that microglia-derived transglutaminase-2 (TG2) signals to ADGRG1 on OL precursor cells (OPCs) in the presence of the ECM protein laminin and that TG2/laminin-dependent activation of ADGRG1 promotes OPC proliferation. Signaling by TG2/laminin to ADGRG1 on OPCs additionally improves remyelination in two murine models of demyelination. These findings identify a novel glia-to-glia signaling pathway that promotes myelin formation and repair, and suggest new strategies to enhance remyelination.
| S-EPMC5980231 | biostudies-literature
Project description:IntroductionStem cell therapy using neural progenitor cells (NPCs) shows promise in mitigating the debilitating effects of spinal cord injury (SCI). Notably, myelin stimulates axonal regeneration from mammalian NPCs. This led us to hypothesize that myelin-associated proteins may contribute to axonal regeneration from NPCs.MethodsWe conducted an R-based bioinformatics analysis to identify key gene(s) that may participate in myelin-associated axonal regeneration from murine NPCs, which identified the serine protease myelin basic protein (Mbp). We employed E12 murine NPCs, E14 rat NPCs, and human iPSC-derived Day 1 NPCs (D1 hNPCs) with or without CRISPR/Cas9-mediated Mbp knockout in combination with rescue L1-70 overexpression, constitutively-active VP16-PPARγ2, or the PPARγ agonist ciglitazone. A murine dorsal column crush model of SCI utilizing porous collagen-based scaffolding (PCS)-seeded murine NPCs with or without stable Mbp overexpression was used to assess locomotive recovery and axonal regeneration in vivo.ResultsMyelin promotes axonal outgrowth from NPCs in an Mbp-dependent manner and that Mbp's stimulatory effects on NPC neurite outgrowth are mediated by Mbp's production of L1-70. Furthermore, we determined that Mbp/L1-70's stimulatory effects on NPC neurite outgrowth are mediated by PPARγ-based repression of neuron differentiation-associated gene expression and PPARγ-based Erk1/2 activation. In vivo, PCS-seeded murine NPCs stably overexpressing Mbp significantly enhanced locomotive recovery and axonal regeneration in post-SCI mice.ConclusionsWe discovered that Mbp supports axonal regeneration from mammalian NPCs through the novel Mbp/L1cam/Pparγ signaling pathway. This study suggests that bioengineered, NPC-based interventions can promote axonal regeneration and functional recovery post-SCI.
| S-EPMC8082623 | biostudies-literature
Project description:Recovery of neurological function after traumatic injury of the adult mammalian central nervous system is limited by lack of axonal growth. Myelin-derived inhibitors contribute to axonal growth restriction, with ephrinB3 being a developmentally important axonal guidance cue whose expression in mature oligodendrocytes suggests a role in regeneration. Here we explored the in vivo regeneration role of ephrinB3 using mice lacking a functional ephrinB3 gene. We confirm that ephrinB3 accounts for a substantial portion of detergent-resistant myelin-derived inhibition in vitro. To assess in vivo regeneration, we crushed the optic nerve and examined retinal ganglion fibers extending past the crush site. Significantly increased axonal regeneration is detected in ephrinB3(-/-) mice. Studies of spinal cord injury in ephrinB3(-/-) mice must take into account altered spinal cord development and an abnormal hopping gait before injury. In a near-total thoracic transection model, ephrinB3(-/-) mice show greater spasticity than wild-type mice for 2 mo, with slightly greater hindlimb function at later time points, but no evidence for axonal regeneration. After a dorsal hemisection injury, increased corticospinal and raphespinal growth in the caudal spinal cord are detected by 6 wk. This increased axonal growth is accompanied by improved locomotor performance measured in the open field and by kinematic analysis. Thus, ephrinB3 contributes to myelin-derived axonal growth inhibition and limits recovery from adult CNS trauma.
| S-EPMC3323955 | biostudies-literature
Project description:Oligodendrocyte myelination depends on actin cytoskeleton rearrangement. Neural Wiskott-Aldrich syndrome protein(N-Wasp) is an actin nucleation factor that promotes polymerization of branched actin filaments. N-Wasp activity is essential for myelin membrane wrapping by Schwann cells, but its role in oligodendrocytes and CNS myelination remains unknown. Here we report that oligodendrocytes-specific deletion of N-Wasp in mice of both sexes resulted in hypomyelination (i.e., reduced number of myelinated axons and thinner myelin profiles), as well as substantial focal hypermyelination reflected by the formation of remarkably long myelin outfolds. These myelin outfolds surrounded unmyelinated axons, neuronal cell bodies, and other myelin profiles. The latter configuration resulted in pseudo-multimyelin profiles that were often associated with axonal detachment and degeneration throughout the CNS, including in the optic nerve, corpus callosum, and the spinal cord. Furthermore, developmental analysis revealed that myelin abnormalities were already observed during the onset of myelination, suggesting that they are formed by aberrant and misguided elongation of the oligodendrocyte inner lip membrane. Our results demonstrate that N-Wasp is required for the formation of normal myelin in the CNS. They also reveal that N-Wasp plays a distinct role in oligodendrocytes compared with Schwann cells, highlighting a difference in the regulation of actin dynamics during CNS and PNS myelination.SIGNIFICANCE STATEMENT Myelin is critical for the normal function of the nervous system by facilitating fast conduction of action potentials. During the process of myelination in the CNS, oligodendrocytes undergo extensive morphological changes that involve cellular process extension and retraction, axonal ensheathment, and myelin membrane wrapping. Here we present evidence that N-Wasp, a protein regulating actin filament assembly through Arp2/3 complex-dependent actin nucleation, plays a critical role in CNS myelination, and its absence leads to several myelin abnormalities. Our data provide an important step into the understanding of the molecular mechanisms underlying CNS myelination.
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Project description:Recently, several in vitro studies have shown that the golli-myelin basic proteins regulate Ca2+ homoeostasis in OPCs (oligodendrocyte precursor cells) and immature OLs (oligodendrocytes), and that a number of the functions of these cells are affected by cellular levels of the golli proteins. To determine the influence of golli in vivo on OL development and myelination, a transgenic mouse was generated in which the golli isoform J37 was overexpressed specifically within OLs and OPCs. The mouse, called JOE (J37-overexpressing), is severely hypomyelinated between birth and postnatal day 50. During this time, it exhibits severe intention tremors that gradually abate at later ages. After postnatal day 50, ultrastructural studies and Northern and Western blot analyses indicate that myelin accumulates in the brain, but never reaches normal levels. Several factors appear to underlie the extensive hypomyelination. In vitro and in vivo experiments indicate that golli overexpression causes a significant delay in OL maturation, with accumulation of significantly greater numbers of pre-myelinating OLs that fail to myelinate axons during the normal myelinating period. Immunohistochemical studies with cell death and myelin markers indicate that JOE OLs undergo a heightened and extended period of cell death and are unable to effectively myelinate until 2 months after birth. The results indicate that increased levels of golli in OPC/OLs delays myelination, causing significant cell death of OLs particularly in white matter tracts. The results provide in vivo evidence for a significant role of the golli proteins in the regulation of maturation of OLs and normal myelination.
| S-EPMC2785512 | biostudies-literature
Project description:BackgroundMyelin sheath is a crucial accessory to the functional nerve-fiber unit, its disruption or loss can lead to axonal degeneration and subsequent neurodegenerative diseases (NDs). Notwithstanding of substantial progress in possible molecular mechanisms underlying myelination, there is no therapeutics that prevent demyelination in NDs. Therefore, it is crucial to seek for potential intervention targets. Here, we focused on the transcriptional factor, signal transducer and activator of transcription 1 (Stat1), to explore its effects on myelination and its potential as a drug target.MethodsBy analyzing the transcriptome data obtained from Schwann cells (SCs) at different stages of myelination, it was found that Stat1 might be involved in myelination. To test this, we used the following experiments: (1) In vivo, the effect of Stat1 on remyelination was observed in an in vivo myelination mode with Stat1 knockdown in sciatic nerves or specific knockdown in SCs. (2) In vitro, the RNA interference combined with cell proliferation assay, scratch assay, SC aggregate sphere migration assay, and a SC differentiation model, were used to assess the effects of Stat1 on SC proliferation, migration and differentiation. Chromatin immunoprecipitation sequencing (ChIP-Seq), RNA-Seq, ChIP-qPCR and luciferase activity reporter assay were performed to investigate the possible mechanisms of Stat1 regulating myelination.ResultsStat1 is important for myelination. Stat1 knockdown in nerve or in SCs reduces the axonal remyelination in the injured sciatic nerve of rats. Deletion of Stat1 in SCs blocks SC differentiation thereby inhibiting the myelination program. Stat1 interacts with the promoter of Rab11-family interacting protein 1 (Rab11fip1) to initiate SC differentiation.ConclusionOur findings demonstrate that Stat1 regulates SC differentiation to control myelinogenic programs and repair, uncover a novel function of Stat1, providing a candidate molecule for clinical intervention in demyelinating diseases.
| S-EPMC10291779 | biostudies-literature
Project description:Myelination of axons by oligodendrocytes enables fast saltatory conduction. Oligodendrocytes are responsive to neuronal activity, which has been shown to induce changes to myelin sheaths, potentially to optimize conduction and neural circuit function. However, the cellular bases of activity-regulated myelination in vivo are unclear, partly due to the difficulty of analyzing individual myelinated axons over time. Activity-regulated myelination occurs in specific neuronal subtypes and can be mediated by synaptic vesicle fusion, but several questions remain: it is unclear whether vesicular fusion occurs stochastically along axons or in discrete hotspots during myelination and whether vesicular fusion regulates myelin targeting, formation, and/or growth. It is also unclear why some neurons, but not others, exhibit activity-regulated myelination. Here, we imaged synaptic vesicle fusion in individual neurons in living zebrafish and documented robust vesicular fusion along axons during myelination. Surprisingly, we found that axonal vesicular fusion increased upon and required myelination. We found that axonal vesicular fusion was enriched in hotspots, namely the heminodal non-myelinated domains into which sheaths grew. Blocking vesicular fusion reduced the stable formation and growth of myelin sheaths, and chemogenetically stimulating neuronal activity promoted sheath growth. Finally, we observed high levels of axonal vesicular fusion only in neuronal subtypes that exhibit activity-regulated myelination. Our results identify a novel "feedforward" mechanism whereby the process of myelination promotes the neuronal activity-regulated signal, vesicular fusion that, in turn, consolidates sheath growth along specific axons selected for myelination.
| S-EPMC8445327 | biostudies-literature