LINGO-1 regulates oligodendrocyte differentiation by inhibiting ErbB2 translocation and activation in lipid rafts

Nogo-A and LINGO-1: Two Important Targets for Remyelination and Regeneration

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) that causes progressive neurological disability in most patients due to neurodegeneration. Activated immune cells infiltrate the CNS, triggering an inflammatory cascade that leads to demyelination and axonal injury. Non-inflammatory mechanisms are also involved in axonal degeneration, although they are not fully elucidated yet. Current therapies focus on immunosuppression; however, no therapies to promote regeneration, myelin repair, or maintenance are currently available. Two different negative regulators of myelination have been proposed as promising targets to induce remyelination and regeneration, namely the Nogo-A and LINGO-1 proteins. Although Nogo-A was first discovered as a potent neurite outgrowth inhibitor in the CNS, it has emerged as a multifunctional protein. It is involved in numerous developmental processes and is necessary for shaping and later maintaining CNS structure and functionality. However, the growth-restricting properties of Nogo-A have negative effects on CNS injury or disease. LINGO-1 is also an inhibitor of neurite outgrowth, axonal regeneration, oligodendrocyte differentiation, and myelin production. Inhibiting the actions of Nogo-A or LINGO-1 promotes remyelination both in vitro and in vivo, while Nogo-A or LINGO-1 antagonists have been suggested as promising therapeutic approaches for demyelinating diseases. In this review, we focus on these two negative regulators of myelination while also providing an overview of the available data on the effects of Nogo-A and LINGO-1 inhibition on oligodendrocyte differentiation and remyelination.

Manipulating oligodendrocyte intrinsic regeneration mechanism to promote remyelination

In demyelinated lesions, astrocytes, activated microglia and infiltrating macrophages secrete several factors regulating oligodendrocyte precursor cells' behaviour. What appears to be the initiation of an intrinsic mechanism of myelin repair is only leading to partial recovery and inefficient remyelination, a process worsening over the course of the disease. This failure is largely due to the concomitant accumulation of inhibitory cues in and around the lesion sites opposing to growth promoting factors. Here starts a complex game of interactions between the signalling pathways controlling oligodendrocytes migration or differentiation. Receptors of positive or negative cues are modulating Ras, PI3K or RhoGTPases pathways acting on oligodendrocyte cytoskeleton remodelling. From the description of this intricate signalling network, this review addresses the extent to which the modulation of the global response to inhibitory cues may pave the route towards novel therapeutic approaches for myelin repair.

The Implication of Reticulons (RTNs) in Neurodegenerative Diseases: From Molecular Mechanisms to Potential Diagnostic and Therapeutic Approaches

Reticulons (RTNs) are crucial regulatory factors in the central nervous system (CNS) as well as immune system and play pleiotropic functions. In CNS, RTNs are transmembrane proteins mediating neuroanatomical plasticity and functional recovery after central nervous system injury or diseases. Moreover, RTNs, particularly RTN4 and RTN3, are involved in neurodegeneration and neuroinflammation processes. The crucial role of RTNs in the development of several neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), or other neurological conditions such as brain injury or spinal cord injury, has attracted scientific interest. Reticulons, particularly RTN-4A (Nogo-A), could provide both an understanding of early pathogenesis of neurodegenerative disorders and be potential therapeutic targets which may offer effective treatment or inhibit disease progression. This review focuses on the molecular mechanisms and functions of RTNs and their potential usefulness in clinical practice as a diagnostic tool or therapeutic strategy.

The Current Challenges for Drug Discovery in CNS Remyelination

The myelin sheath wraps around axons, allowing saltatory currents to be transmitted along neurons. Several genetic, viral, or environmental factors can damage the central nervous system (CNS) myelin sheath during life. Unless the myelin sheath is repaired, these insults will lead to neurodegeneration. Remyelination occurs spontaneously upon myelin injury in healthy individuals but can fail in several demyelination pathologies or as a consequence of aging. Thus, pharmacological intervention that promotes CNS remyelination could have a major impact on patient’s lives by delaying or even preventing neurodegeneration. Drugs promoting CNS remyelination in animal models have been identified recently, mostly as a result of repurposing phenotypical screening campaigns that used novel oligodendrocyte cellular models. Although none of these have as yet arrived in the clinic, promising candidates are on the way. Many questions remain. Among the most relevant is the question if there is a time window when remyelination drugs should be administrated and why adult remyelination fails in many neurodegenerative pathologies. Moreover, a significant challenge in the field is how to reconstitute the oligodendrocyte/axon interaction environment representative of healthy as well as disease microenvironments in drug screening campaigns, so that drugs can be screened in the most appropriate disease-relevant conditions. Here we will provide an overview of how the field of in vitro models developed over recent years and recent biological findings about how oligodendrocytes mature after reactivation of their staminal niche. These data have posed novel questions and opened new views about how the adult brain is repaired after myelin injury and we will discuss how these new findings might change future drug screening campaigns for CNS regenerative drugs.

LINGO family receptors are differentially expressed in the mouse brain and form native multimeric complexes

Leucine-rich repeat and immunoglobin-domain containing (LRRIG) proteins that are commonly involved in protein-protein interactions play important roles in nervous system development and maintenance. LINGO-1, one of this family members, is characterized as a negative regulator of neuronal survival, axonal regeneration, and oligodendrocyte precursor cell (OPC) differentiation into mature myelinating oligodendrocytes. Three LINGO-1 homologs named LINGO-2, LINGO-3, and LINGO-4 have been described. However, their relative expression and functions remain unexplored. Here, we show by in situ hybridization and quantitative polymerase chain reaction that the transcripts of LINGO homologs are differentially expressed in the central nervous system. The immunostaining of brain slices confirmed this observation and showed the co-expression of LINGO-1 with its homologs. Using BRET (bioluminescence resonance energy transfer) analysis, we demonstrate that LINGO proteins can physically interact with each of the other ones with comparable affinities and thus form the oligomeric states. Furthermore, co-immunoprecipitation experiments indicate that LINGO proteins form heterocomplexes in both heterologous systems and cortical neurons. Since LINGO-1 is a promising target for the treatment of demyelinating diseases, its ability to form heteromeric complexes reveals a new level of complexity in its functioning and opens the way for new strategies to achieve diverse and nuanced LINGO-1 regulation.

Lipid rafts and neurodegeneration: structural and functional roles in physiologic aging and neurodegenerative diseases

Lipid rafts are small, dynamic membrane areas characterized by the clustering of selected membrane lipids as the result of the spontaneous separation of glycolipids, sphingolipids, and cholesterol in a liquid-ordered phase. The exact dynamics underlying phase separation of membrane lipids in the complex biological membranes are still not fully understood. Nevertheless, alterations in the membrane lipid composition affect the lateral organization of molecules belonging to lipid rafts. Neural lipid rafts are found in brain cells, including neurons, astrocytes, and microglia, and are characterized by a high enrichment of specific lipids depending on the cell type. These lipid rafts seem to organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating the homeostasis of the brain. The progressive decline of brain performance along with physiological aging is at least in part associated with alterations in the composition and structure of neural lipid rafts. In addition, neurodegenerative conditions, such as lysosomal storage disorders, multiple sclerosis, and Parkinson's, Huntington's, and Alzheimer's diseases, are frequently characterized by dysregulated lipid metabolism, which in turn affects the structure of lipid rafts. Several events underlying the pathogenesis of these diseases appear to depend on the altered composition of lipid rafts. Thus, the structure and function of lipid rafts play a central role in the pathogenesis of many common neurodegenerative diseases.jlr;61/5/636/F1F1f1.

TFF3 interacts with LINGO2 to regulate EGFR activation for protection against colitis and gastrointestinal helminths

Intestinal epithelial cells (IEC) have important functions in nutrient absorption, barrier integrity, regeneration, pathogen-sensing, and mucus secretion. Goblet cells are a specialized cell type of IEC that secrete Trefoil factor 3 (TFF3) to regulate mucus viscosity and wound healing, but whether TFF3-responsiveness requires a receptor is unclear. Here, we show that leucine rich repeat receptor and nogo-interacting protein 2 (LINGO2) is essential for TFF3-mediated functions. LINGO2 immunoprecipitates with TFF3, co-localizes with TFF3 on the cell membrane of IEC, and allows TFF3 to block apoptosis. We further show that TFF3-LINGO2 interactions disrupt EGFR-LINGO2 complexes resulting in enhanced EGFR signaling. Excessive basal EGFR activation in Lingo2 deficient mice increases disease severity during colitis and augments immunity against helminth infection. Conversely, TFF3 deficiency reduces helminth immunity. Thus, TFF3-LINGO2 interactions de-repress inhibitory LINGO2-EGFR complexes, allowing TFF3 to drive wound healing and immunity.

Inhibitory milieu at the multiple sclerosis lesion site and the challenges for remyelination

Regeneration of myelin, following injury, can occur within the central nervous system to reinstate proper axonal conductance and provide trophic support. Failure to do so renders the axons vulnerable, leading to eventual degeneration, and neuronal loss. Thus, it is essential to understand the mechanisms by which remyelination or failure to remyelinate occur, particularly in the context of demyelinating and neurodegenerative disorders. In multiple sclerosis, oligodendrocyte progenitor cells (OPCs) migrate to lesion sites to repair myelin. However, during disease progression, the ability of OPCs to participate in remyelination diminishes coincident with worsening of the symptoms. Remyelination is affected by a broad range of cues from intrinsic programming of OPCs and extrinsic local factors to the immune system and other systemic elements including diet and exercise. Here we review the literature on these diverse inhibitory factors and the challenges they pose to remyelination. Results spanning several disciplines from fundamental preclinical studies to knowledge gained in the clinic will be discussed.

A critical role for miR-184 in the fate determination of oligodendrocytes

Background

New insights on cellular and molecular aspects of both oligodendrocyte (OL) differentiation and myelin synthesis pathways are potential avenues for developing a cell-based therapy for demyelinating disorders comprising multiple sclerosis. MicroRNAs (miRNA) have broad implications in all aspects of cell biology including OL differentiation. MiR-184 has been identified as one of the most highly enriched miRNAs in oligodendrocyte progenitor cells (OPCs). However, the exact molecular mechanism of miR-184 in OL differentiation is yet to be elucidated.

Methods and results

Based on immunochemistry assays, qRT-PCR, and western blotting findings, we hypothesized that overexpression of miR-184 in either neural progenitor cells (NPCs) or embryonic mouse cortex stimulated the differentiation of OL lineage efficiently through regulating crucial developmental genes. Luciferase assays demonstrated that miR-184 directly represses positive regulators of neural and astrocyte differentiation, i.e., SOX1 and BCL2L1, respectively, including the negative regulator of myelination, LINGO1. Moreover, blocking the function of miR-184 reduced the number of committed cells to an OL lineage.

Conclusions

Our data highlighted that miR-184 could promote OL differentiation even in the absence of exogenous growth factors and propose a novel strategy to improve the efficacy of OL differentiation, with potential applications in cell therapy for neurodegenerative diseases.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1208-y) contains supplementary material, which is available to authorized users.

Anti-LINGO-1 has no detectable immunomodulatory effects in preclinical and phase 1 studies

Objective:

To evaluate whether the anti-LINGO-1 antibody has immunomodulatory effects.

Methods:

Human peripheral blood mononuclear cells (hPBMCs), rat splenocytes, and rat CD4⁺ T cells were assessed to determine whether LINGO-1 was expressed and was inducible. Anti-LINGO-1 Li81 (0.1–30 μg/mL) effect on proliferation/cytokine production was assessed in purified rat CD4⁺ T cells and hPBMCs stimulated with antibodies to CD3 +/– CD28. In humans, the effect of 2 opicinumab (anti-LINGO-1/BIIB033; 30, 60, and 100 mg/kg) or placebo IV administrations was evaluated in RNA from blood and CSF samples taken before and after administration in phase 1 clinical trials; paired samples were assessed for differentially expressed genes by microarray. RNA from human CSF cell pellets was analyzed by quantitative real-time PCR for changes in transcripts representative of cell types, activation markers, and soluble proteins of the adaptive/innate immune systems. ELISA quantitated the levels of CXCL13 protein in human CSF supernatants.

Results:

LINGO-1 is not expressed in hPBMCs, rat splenocytes, or rat CD4⁺ T cells; LINGO-1 blockade with Li81 did not affect T-cell proliferation or cytokine production from purified rat CD4⁺ T cells or hPBMCs. LINGO-1 blockade with opicinumab resulted in neither significant changes in immune system gene expression in blood and CSF, nor changes in CXCL13 CSF protein levels (clinical studies).

Conclusions:

These data support the hypothesis that LINGO-1 blockade does not affect immune function.

Classification of evidence:

This study provides Class II evidence that in patients with MS, opicinumab does not have immunomodulatory effects detected by changes in immune gene transcript expression.

Recruitment of endogenous CNS stem cells for regeneration in demyelinating disease

Demyelinating diseases, such as multiple sclerosis (MS), are responsible for a significant portion of the neurological disability burden worldwide, especially in young adults. Demyelination can be followed by a spontaneous regenerative process called remyelination, in which new myelin sheaths are restored to denuded axons. However, in chronic demyelinating disease such as MS, this process becomes progressively less efficient. This chapter reviews the biology of remyelination and the rationale and strategies by which it can be enhanced therapeutically in acquired demyelinating disease.

LINGO-1 Regulates Oligodendrocyte Differentiation through the Cytoplasmic Gelsolin Signaling Pathway

Differentiation and maturation of oligodendrocyte progenitor cells (OPCs) involve the assembly and disassembly of actin microfilaments. However, how actin dynamics are regulated during this process remains poorly understood. Leucine-rich repeat and Ig-like domain-containing Nogo receptor interacting protein 1 (LINGO-1) is a negative regulator of OPC differentiation. We discovered that anti-LINGO-1 antibody-promoted OPC differentiation was accompanied by upregulation of cytoplasmic gelsolin (cGSN), an abundant actin-severing protein involved in the depolymerization of actin filaments. Treating rat OPCs with cGSN siRNA reduced OPC differentiation, whereas overexpression of cGSN promoted OPC differentiation in vitro and remyelination in vivo Furthermore, coexpression of cGSN and LINGO-1 blocked the inhibitory effect of LINGO-1. Our study demonstrates that cGSN works downstream of LINGO-1 signaling pathway, which enhances actin dynamics and is essential for OPC morphogenesis and differentiation. This finding may lead to novel therapeutic approaches for the treatment of demyelinating diseases such as multiple sclerosis (MS).SIGNIFICANCE STATEMENT Myelin loss and subsequent axon degeneration contributes to a variety of neurological diseases, such as multiple sclerosis (MS). Understanding the regulation of myelination by oligodendrocytes is therefore critical for developing therapies for the treatment of MS. We previously demonstrated that leucine-rich repeat and Ig-like domain-containing Nogo receptor interacting protein 1 (LINGO-1) is a negative regulator of oligodendrocyte differentiation and that anti-LINGO-1 promotes remyelination in preclinical animal models for MS and in a phase II acute optic neuritis clinical trial (RENEW). The mechanism by which LINGO-1 regulates oligodendrocyte differentiation is unknown. Here, we demonstrate that LINGO-1 regulates oligodendrocyte differentiation and maturation through the cytoplasmic gelsolin signaling pathway, providing new drug targets for the treatment of demyelination diseases.

LINGO-1 and AMIGO3, potential therapeutic targets for neurological and dysmyelinating disorders?

Leucine rich repeat proteins have gained considerable interest as therapeutic targets due to their expression and biological activity within the central nervous system. LINGO-1 has received particular attention since it inhibits axonal regeneration after spinal cord injury in a RhoA dependent manner while inhibiting leucine rich repeat and immunoglobulin-like domain-containing protein 1 (LINGO-1) disinhibits neuron outgrowth. Furthermore, LINGO-1 suppresses oligodendrocyte precursor cell maturation and myelin production. Inhibiting the action of LINGO-1 encourages remyelination both in vitro and in vivo. Accordingly, LINGO-1 antagonists show promise as therapies for demyelinating diseases. An analogous protein to LINGO-1, amphoterin-induced gene and open reading frame-3 (AMIGO3), exerts the same inhibitory effect on the axonal outgrowth of central nervous system neurons, as well as interacting with the same receptors as LINGO-1. However, AMIGO3 is upregulated more rapidly after spinal cord injury than LINGO-1. We speculate that AMIGO3 has a similar inhibitory effect on oligodendrocyte precursor cell maturation and myelin production as with axogenesis. Therefore, inhibiting AMIGO3 will likely encourage central nervous system axonal regeneration as well as the production of myelin from local oligodendrocyte precursor cell, thus providing a promising therapeutic target and an area for future investigation.

Emerging strategies in the management of essential tremor

Currently available therapies for essential tremor (ET) provide sufficient control only for less than a half of patients and many unmet needs exist. This is in part due to the empiric nature of existing treatment options and persisting uncertainties about the pathogenesis of ET. The emerging concept of ET as a possible neurodegenerative disorder, better understanding of associated biochemical changes, including alterations in the γ-aminobutyric acid (GABA)-ergic system and gap junctions, and the identification of the role of the leucine-rich repeat and immunoglobulin-like domain-containing 1 (LINGO-1) gene in ET pathogenesis suggest new avenues for more targeted therapies. Here we review the most promising new approaches to treating ET, including allosteric modulation of GABA receptors and modifications of the LINGO-1 pathway. Medically refractory tremor can be successfully treated by high-frequency deep brain stimulation (DBS) of the ventral intermediate nucleus, but surgical therapies are also fraught with limitations due to adverse effects of stimulation and the loss of therapeutic response. The selection of additional thalamic and extrathalamic targets for electrode placements and the development of a closed-loop DBS system enabling automatic adjustment of stimulation parameters in response to changes in electrophysiologic brain activity are also reviewed. Tremor cancellation methods using exoskeleton and external hand-held devices are also briefly discussed.

Mechanisms and Medicines for Remyelination

Demyelination of central nervous system axons, associated with traumatic injury and demyelinating diseases such as multiple sclerosis, causes impaired neural transmission and ultimately axon degeneration. Consequently, extensive research has focused on signaling systems that promote myelinating activity of oligodendrocytes or promote production of new oligodendrocytes from oligodendrocyte progenitor cells. Many receptor systems, notably including growth factor receptors and G protein-coupled receptors, control myelination. A number of recent clinical trials target these receptor signaling pathways.

Oligodendrocyte regeneration: Its significance in myelin replacement and neuroprotection in multiple sclerosis

Oligodendrocytes readily regenerate and replace myelin membranes around axons in the adult mammalian central nervous system (CNS) following injury. The ability to regenerate oligodendrocytes depends on the availability of neural progenitors called oligodendrocyte precursor cells (OPCs) in the adult CNS that respond to injury-associated signals to induce OPC expansion followed by oligodendrocyte differentiation, axonal contact and myelin regeneration (remyelination). Remyelination ensures the maintenance of axonal conduction, and the oligodendrocytes themselves provide metabolic factors that are necessary to maintain neuronal integrity. Recent advances in oligodendrocyte regeneration research are beginning to shed light on critical intrinsic signals, as well as extrinsic, environmental factors that regulate the distinct steps of oligodendrocyte lineage progression and myelin replacement under CNS injury. These studies may offer novel pharmacological targets for regenerative medicine in inflammatory demyelinating disorders in the CNS such as multiple sclerosis. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Extracellular cues influencing oligodendrocyte differentiation and (re)myelination

There is an increasing number of neurologic disorders found to be associated with loss and/or dysfunction of the CNS myelin sheath, ranging from the classic demyelinating disease, multiple sclerosis, through CNS injury, to neuropsychiatric diseases. The disabling burden of these diseases has sparked a growing interest in gaining a better understanding of the molecular mechanisms regulating the differentiation of the myelinating cells of the CNS, oligodendrocytes (OLGs), and the process of (re)myelination. In this context, the importance of the extracellular milieu is becoming increasingly recognized. Under pathological conditions, changes in inhibitory as well as permissive/promotional cues are thought to lead to an overall extracellular environment that is obstructive for the regeneration of the myelin sheath. Given the general view that remyelination is, even though limited in human, a natural response to demyelination, targeting pathologically 'dysregulated' extracellular cues and their downstream pathways is regarded as a promising approach toward the enhancement of remyelination by endogenous (or if necessary transplanted) OLG progenitor cells. In this review, we will introduce the extracellular cues that have been implicated in the modulation of (re)myelination. These cues can be soluble, part of the extracellular matrix (ECM) or mediators of cell-cell interactions. Their inhibitory and permissive/promotional roles with regard to remyelination as well as their potential for therapeutic intervention will be discussed.

Regulating Axonal Responses to Injury: The Intersection between Signaling Pathways Involved in Axon Myelination and The Inhibition of Axon Regeneration

Following spinal cord injury (SCI), a multitude of intrinsic and extrinsic factors adversely affect the gene programs that govern the expression of regeneration-associated genes (RAGs) and the production of a diversity of extracellular matrix molecules (ECM). Insufficient RAG expression in the injured neuron and the presence of inhibitory ECM at the lesion, leads to structural alterations in the axon that perturb the growth machinery, or form an extraneous barrier to axonal regeneration, respectively. Here, the role of myelin, both intact and debris, in antagonizing axon regeneration has been the focus of numerous investigations. These studies have employed antagonizing antibodies and knockout animals to examine how the growth cone of the re-growing axon responds to the presence of myelin and myelin-associated inhibitors (MAIs) within the lesion environment and caudal spinal cord. However, less attention has been placed on how the myelination of the axon after SCI, whether by endogenous glia or exogenously implanted glia, may alter axon regeneration. Here, we examine the intersection between intracellular signaling pathways in neurons and glia that are involved in axon myelination and axon growth, to provide greater insight into how interrogating this complex network of molecular interactions may lead to new therapeutics targeting SCI.

How to make an oligodendrocyte

Oligodendrocytes produce myelin, an insulating sheath required for the saltatory conduction of electrical impulses along axons. Oligodendrocyte loss results in demyelination, which leads to impaired neurological function in a broad array of diseases ranging from pediatric leukodystrophies and cerebral palsy, to multiple sclerosis and white matter stroke. Accordingly, replacing lost oligodendrocytes, whether by transplanting oligodendrocyte progenitor cells (OPCs) or by mobilizing endogenous progenitors, holds great promise as a therapeutic strategy for the diseases of central white matter. In this Primer, we describe the molecular events regulating oligodendrocyte development and how our understanding of this process has led to the establishment of methods for producing OPCs and oligodendrocytes from embryonic stem cells and induced pluripotent stem cells, as well as directly from somatic cells. In addition, we will discuss the safety of engrafted stem cell-derived OPCs, as well as approaches by which to modulate their differentiation and myelinogenesis in vivo following transplantation.

The potential of LINGO-1 as a therapeutic target for essential tremor

INTRODUCTION

LINGO-1 is a negative regulator of neuronal survival, oligodendrocyte differentiation and axonal outgrowth and regeneration, because it interacts with diverse growth factor receptors blocking or inhibiting their action. Consistent findings obtained in vitro and in animal models suggest that anti-LINGO-1 therapy may be useful in neurodegenerative disorders such as multiple sclerosis (MS), Parkinson's disease or essential tremor (ET). Moreover, genetic and pathological evidence provide a robust link between LINGO-1 and ET.

AREAS COVERED

In this review, we present an overview of current knowledge on findings linking LINGO-1 and ET, with a special focus on genetic linkage, we include an overview of LINGO1 gene variations according to the 1000 genomes catalog, and we identify potential gene areas where common changes occur because, as well as the risk developing ET, LINGO1 genetic changes may influence the response to anti-LINGO-1 therapy.

EXPERT OPINION

The goal of anti-LINGO-1 therapy in neurodegenerative diseases is to ease the brakes of neuronal growth and recovery. An anti-LINGO-1 antibody is under clinical trials for MS patients. Before planning trials with ET patients, refinement on the genetic link between LINGO1 and ET, and a detailed genetic and phenotypic assessment of ET patients to be enrolled, should be carried out.

WNK1 is involved in Nogo66 inhibition of OPC differentiation

LINGO-1 is a transmembrane receptor expressed primarily in the central nervous system (CNS) and plays an important role in myelination. Recent studies have indicated that it is also involved in oligodendrocyte precursor cell (OPC) survival and differentiation; however, the downstream signaling pathway underlying OPC development is unknown. In our previous study, we found that LINGO-1 is associated with WNK1 in mediating Nogo-induced neurite extension inhibition by RhoA activation. In an effort to identify the role of LINGO-1-WNK1 in OPCs, we first confirmed that WNK1 is also expressed in OPCs and co-localized with LINGO-1, which suppresses WNK1 expression by RNA interference-attenuated Nogo66-induced inhibition of OPC differentiation. Furthermore, we mapped the WNK1 kinase domain using several fragmented peptides to identify the key region of interaction with LINGO-1. We found that a sequence corresponding to the D6 peptide is necessary for the interaction. Finally, we found that using the TAT-D6 peptide to introduce D6 peptide into primary cultured OPC inhibits the association between LINGO-1 and WNK1 and significantly attenuates Nogo66-induced inhibition of OPC differentiation. Taken together, our results show that WNK1, via a specific region on WNK1 kinase domain, interacts with LINGO-1, thus mediating Nogo66-inhibited OPC differentiation.

Inhibition of LINGO-1 promotes functional recovery after experimental spinal cord demyelination

Blocking LINGO-1 has been shown to enhance remyelination in the rat lysolecithin-induced focal spinal cord demyelination model. We used transcranial magnetic motor-evoked potentials (tcMMEPs) to assess the effect of blocking LINGO-1 on recovery of axonal function in a mouse lysolecithin model at 1, 2 and 4weeks after injury. The role of LINGO-1 was assessed using LINGO-1 knockout (KO) mice and in wild-type mice after intraperitoneal administration of anti-LINGO-1 antagonist monoclonal antibody (mAb3B5). Response rates (at 2 and 4weeks) and amplitudes (at 4weeks) were significantly increased in LINGO-1 KO and mAb3B5-treated mice compared with matched controls. The latency of potentials at 4weeks was significantly shorter in mAb3B5-treated mice compared with controls. Lesion areas in LINGO-1 KO and mAb3B5-treated mice were reduced significantly compared with matched controls. The number of remyelinated axons within the lesions was increased and the G-ratios of the axons were decreased in both LINGO-1 KO and mAb3B5-treated mice compared with matched controls. These data provide morphometric and functional evidence of enhancement of remyelination associated with antagonism of LINGO-1.