LINGO-1 and its role in CNS repair

H2S-RhoA/ROCK Pathway and Glial Cells in Axonal Remyelination After Ischemic Stroke

Ischemic stroke is one of the main reasons of disability and death. Stroke-induced functional deficits are mainly due to the secondary degeneration of the white matter characterized by axonal demyelination and injury of axon-glial integrity. Enhancement of the axonal regeneration and remyelination could promote the neural functional recovery. However, cerebral ischemia-induced activation of RhoA/Rho kinase (ROCK) pathway plays a crucial and harmful role in the process of axonal recovery and regeneration. Inhibition of this pathway could promote the axonal regeneration and remyelination. In addition, hydrogen sulfide (H2S) has the significant neuroprotective role during the recovery of ischemic stroke via inhibiting the inflammatory response and oxidative stress, regulating astrocyte function, promoting the differentiation of endogenous oligodendrocyte precursor cells (OPCs) to mature oligodendrocyte. Among all of these effects, promoting the formation of mature oligodendrocyte is a crucial part of axonal regeneration and remyelination. Furthermore, numerous studies have uncovered the crosstalk between astrocytes and oligodendrocyte, microglial cells and oligodendrocyte in the axonal remyelination following ischemic stroke. The purpose of this review was to discuss the relationship among H2S, RhoA/ROCK pathway, astrocytes, and microglial cells in the axonal remyelination following ischemic stroke to reveal new strategies for preventing and treating this devastating disease.

How does Nogo receptor influence demyelination and remyelination in the context of multiple sclerosis?

Multiple sclerosis (MS) can progress with neurodegeneration as a consequence of chronic inflammatory mechanisms that drive neural cell loss and/or neuroaxonal dystrophy in the central nervous system. Immune-mediated mechanisms can accumulate myelin debris in the disease extracellular milieu during chronic-active demyelination that can limit neurorepair/plasticity and experimental evidence suggests that potentiated removal of myelin debris can promote neurorepair in models of MS. The myelin-associated inhibitory factors (MAIFs) are integral contributors to neurodegenerative processes in models of trauma and experimental MS-like disease that can be targeted to promote neurorepair. This review highlights the molecular and cellular mechanisms that drive neurodegeneration as a consequence of chronic-active inflammation and outlines plausible therapeutic approaches to antagonize the MAIFs during the evolution of neuroinflammatory lesions. Moreover, investigative lines for translation of targeted therapies against these myelin inhibitors are defined with an emphasis on the chief MAIF, Nogo-A, that may demonstrate clinical efficacy of neurorepair during progressive MS.

Signaling mechanisms involved in the regulation of remyelination in multiple sclerosis: a mini review

Multiple sclerosis is an autoimmune neurodegenerative disease of the CNS that causes progressive disabilities, owing to CNS axon degeneration as a late result of demyelination. In the search for the prevention of axonal loss, mitigating inflammatory attacks in the CNS and myelin restoration are two possible approaches. As a result, therapies that target diverse signaling pathways involved in neuroprotection and remyelination have the potential to overcome the challenges in the development of multiple sclerosis treatments. LINGO1 (Leucine rich repeat and Immunoglobulin domain containing, Nogo receptor- interaction protein), AKT/PIP3/mTOR, Notch, Wnt, RXR (Retinoid X receptor gamma), and Nrf2 (nuclear factor erythroid 2-related factor 2) signaling pathways are highlighted in this section. This article reviews the present knowledge regarding numerous signaling pathways and their functions in regulating remyelination in multiple sclerosis pathogenesis. These pathways are potential biomarkers and therapeutic targets in MS.

Myelin repair in Alzheimer's disease: a review of biological pathways and potential therapeutics

This literature review investigates the significant overlap between myelin-repair signaling pathways and pathways known to contribute to hallmark pathologies of Alzheimer's disease (AD). We discuss previously investigated therapeutic targets of amyloid, tau, and ApoE, as well as other potential therapeutic targets that have been empirically shown to contribute to both remyelination and progression of AD. Current evidence shows that there are multiple AD-relevant pathways which overlap significantly with remyelination and myelin repair through the encouragement of oligodendrocyte proliferation, maturation, and myelin production. There is a present need for a single, cohesive model of myelin homeostasis in AD. While determining a causative pathway is beyond the scope of this review, it may be possible to investigate the pathological overlap of myelin repair and AD through therapeutic approaches.

CAQK, a peptide associating with extracellular matrix components targets sites of demyelinating injuries

The destruction of the myelin sheath that encircles axons leads to impairments of nerve conduction and neuronal dysfunctions. A major demyelinating disorder is multiple sclerosis (MS), a progressively disabling disease in which immune cells attack the myelin. To date, there are no therapies to target selectively myelin lesions, repair the myelin or stop MS progression. Small peptides recognizing epitopes selectively exposed at sites of injury show promise for targeting therapeutics in various pathologies. Here we show the selective homing of the four amino acid peptide, cysteine-alanine-lysine glutamine (CAQK), to sites of demyelinating injuries in three different mouse models. Homing was assessed by administering fluorescein amine (FAM)-labeled peptides into the bloodstream of mice and analyzing sites of demyelination in comparison with healthy brain or spinal cord tissue. FAM-CAQK selectively targeted demyelinating areas in all three models and was absent from healthy tissue. At lesion sites, the peptide was primarily associated with the fibrous extracellular matrix (ECM) deposited in interstitial spaces proximal to reactive astrocytes. Association of FAM-CAQK was detected with tenascin-C although tenascin depositions made up only a minor portion of the examined lesion sites. In mice on a 6-week cuprizone diet, FAM-CAQK peptide crossed the nearly intact blood-brain barrier and homed to demyelinating fiber tracts. These results demonstrate the selective targeting of CAQK to demyelinating injuries under multiple conditions and confirm the previously reported association with the ECM. This work sets the stage for further developing CAQK peptide targeting for diagnostic and therapeutic applications aimed at localized myelin repair.

MiR-615 Agomir Encapsulated in Pluronic F-127 Alleviates Neuron Damage and Facilitates Function Recovery After Brachial Plexus Avulsion

Brachial plexus avulsion (BPA) is a devastating traumatic peripheral nerve injury complicated with paralysis of the upper extremity. We previously reported that leucine-rich repeat and immunoglobulin-like domain-containing NOGO receptor-interacting protein 1 (LINGO-1) has a potent role in inhibiting neuron survival and axonal regeneration after the central nervous system (CNS) damage and miR-615 is a potential microRNA (miRNA) negatively regulated LINGO-1. However, the effect of miR-615 in BPA remains to be elucidated. Accumulating evidence indicates that pluronic F-127 (PF-127) hydrogel could serve as a promising vehicle for miRNA encapsulation. Thus, to further explore the potential role of hydrogel-miR-615 in BPA-reimplantation, the present study established the BPA rat model and injected miR-615 agomir encapsulated by PF-127 hydrogel into the reimplantation site using a microsyringe. In this study, results indicated that hydrogel-miR-615 agomir effectively alleviated motoneuron loss by LINGO-1 inhibition, promoted musculocutaneous nerve regeneration and myelination, reduced astrocytes activation, promoted angiogenesis and attenuated peripheral amyotrophy, leading to improved motor functional rehabilitation of the upper extremity. In conclusion, our findings demonstrate that miR-615-loaded PF-127 hydrogel may represent a novel therapeutic strategy for BPA treatment.

Essential Tremor - A Cerebellar Driven Disorder?

Abnormal tremors are the most common of all movement disorders. In this review we focus on the role of the cerebellum in Essential Tremor, a highly debilitating but poorly treated movement disorder. We propose a variety of mechanisms driving abnormal burst firing of deep cerebellar nuclei neurons as a key initiator of tremorgenesis in Essential Tremor. Targetting these mechanisms may generate more effective treatments for Essential Tremor.

Epidermal Growth Factor in the CNS: A Beguiling Journey from Integrated Cell Biology to Multiple Sclerosis. An Extensive Translational Overview

This article reviews the wealth of papers dealing with the different effects of epidermal growth factor (EGF) on oligodendrocytes, astrocytes, neurons, and neural stem cells (NSCs). EGF induces the in vitro and in vivo proliferation of NSCs, their migration, and their differentiation towards the neuroglial cell line. It interacts with extracellular matrix components. NSCs are distributed in different CNS areas, serve as a reservoir of multipotent cells, and may be increased during CNS demyelinating diseases. EGF has pleiotropic differentiative and proliferative effects on the main CNS cell types, particularly oligodendrocytes and their precursors, and astrocytes. EGF mediates the in vivo myelinotrophic effect of cobalamin on the CNS, and modulates the synthesis and levels of CNS normal prions (PrP^Cs), both of which are indispensable for myelinogenesis and myelin maintenance. EGF levels are significantly lower in the cerebrospinal fluid and spinal cord of patients with multiple sclerosis (MS), which probably explains remyelination failure, also because of the EGF marginal role in immunology. When repeatedly administered, EGF protects mouse spinal cord from demyelination in various experimental models of autoimmune encephalomyelitis. It would be worth further investigating the role of EGF in the pathogenesis of MS because of its multifarious effects.

Genetic variants and cognitive functions in patients with brain tumors

BACKGROUND

Patients with brain tumors treated with radiotherapy (RT) and chemotherapy (CT) often experience cognitive dysfunction. We reported that single nucleotide polymorphisms (SNPs) in the APOE, COMT, and BDNF genes may influence cognition in brain tumor patients. In this study, we assessed whether genes associated with late-onset Alzheimer's disease (LOAD), inflammation, cholesterol transport, dopamine and myelin regulation, and DNA repair may influence cognitive outcome in this population.

METHODS

One hundred and fifty brain tumor patients treated with RT ± CT or CT alone completed a neurocognitive assessment and provided a blood sample for genotyping. We genotyped genes/SNPs in these pathways: (i) LOAD risk/inflammation/cholesterol transport, (ii) dopamine regulation, (iii) myelin regulation, (iv) DNA repair, (v) blood-brain barrier disruption, (vi) cell cycle regulation, and (vii) response to oxidative stress. White matter (WM) abnormalities were rated on brain MRIs.

RESULTS

Multivariable linear regression analysis with Bayesian shrinkage estimation of SNP effects, adjusting for relevant demographic, disease, and treatment variables, indicated strong associations (posterior association summary [PAS] ≥ 0.95) among tests of attention, executive functions, and memory and 33 SNPs in genes involved in: LOAD/inflammation/cholesterol transport (eg, PDE7A, IL-6), dopamine regulation (eg, DRD1, COMT), myelin repair (eg, TCF4), DNA repair (eg, RAD51), cell cycle regulation (eg, SESN1), and response to oxidative stress (eg, GSTP1). The SNPs were not significantly associated with WM abnormalities.

CONCLUSION

This novel study suggests that polymorphisms in genes involved in aging and inflammation, dopamine, myelin and cell cycle regulation, and DNA repair and response to oxidative stress may be associated with cognitive outcome in patients with brain tumors.

Genetic Risk Factors for Essential Tremor: A Review

Highlights

In the current review, we thoroughly reviewed 74 identified articles regarding genes and genetic loci that confer susceptibility to ET. Over 50 genes/genetic loci have been examined for possible association with ET, but consistent results failed to be reported raising the need for collaborative multiethnic studies.

Background:

Essential tremor (ET) is a common movement disorder, which is mainly characterized by bilateral tremor (postural and/or kinetic) in the upper limbs, with other parts of the body possibly involved. While the pathophysiology of ET is still unclear, there is accumulating evidence indicating that genetic variability may be heavily involved in ET pathogenesis. This review focuses on the role of genetic risk factors in ET susceptibility.

Methods:

The PubMed database was searched for articles written in English, for studies with humans with ET, controls without ET, and genetic variants. The terms “essential tremor” and “polymorphism” (as free words) were used during search. We also performed meta-analyses for the most examined genetic variants.

Results:

Seventy four articles concerning LINGO1, LINGO2, LINGO4, SLC1A2, STK32B, PPARGC1A, CTNNA3, DRD3, ALAD, VDR, HMOX1, HMOX2, LRRK1,LRRK2, GBA, SNCA, MAPT, FUS, CYPsIL17A, IL1B, NOS1, ADH1B, TREM2, RIT2, HNMT, MTHFR, PPP2R2B, GSTP1, PON1, GABA receptors and GABA transporter, HS1BP3, ADH2, hSKCa3 and CACNL1A4 genes, and ETM genetic loci were included in the current review. Results from meta-analyses revealed a marginal association for the STK32B rs10937625 and a marginal trend for association (in sensitivity analysis) for the LINGO1 rs9652490, with ET.

Discussion:

Quite a few variants have been examined for their possible association with ET. LINGO1 rs9652490 and STK32B rs10937625 appear to influence, to some extent, ET susceptibility. However, the conflicting results and the lack of replication for many candidate genes raise the need for collaborative multiethnic studies.

Blocking the Thrombin Receptor Promotes Repair of Demyelinated Lesions in the Adult Brain

Myelin loss limits neurological recovery and myelin regeneration and is critical for restoration of function. We recently discovered that global knock-out of the thrombin receptor, also known as Protease Activated Receptor 1 (PAR1), accelerates myelin development. Here we demonstrate that knocking out PAR1 also promotes myelin regeneration. Outcomes in two unique models of myelin injury and repair, that is lysolecithin or cuprizone-mediated demyelination, showed that PAR1 knock-out in male mice improves replenishment of myelinating cells and remyelinated nerve fibers and slows early axon damage. Improvements in myelin regeneration in PAR1 knock-out mice occurred in tandem with a skewing of reactive astrocyte signatures toward a prorepair phenotype. In cell culture, the promyelinating effects of PAR1 loss of function are consistent with possible direct effects on the myelinating potential of oligodendrocyte progenitor cells (OPCs), in addition to OPC-indirect effects involving enhanced astrocyte expression of promyelinating factors, such as BDNF. These findings highlight previously unrecognized roles of PAR1 in myelin regeneration, including integrated actions across the oligodendrocyte and astroglial compartments that are at least partially mechanistically linked to the powerful BDNF-TrkB neurotrophic signaling system. Altogether, findings suggest PAR1 may be a therapeutically tractable target for demyelinating disorders of the CNS.SIGNIFICANCE STATEMENT Replacement of oligodendroglia and myelin regeneration holds tremendous potential to improve function across neurological conditions. Here we demonstrate Protease Activated Receptor 1 (PAR1) is an important regulator of the capacity for myelin regeneration across two experimental murine models of myelin injury. PAR1 is a G-protein-coupled receptor densely expressed in the CNS, however there is limited information regarding its physiological roles in health and disease. Using a combination of PAR1 knock-out mice, oligodendrocyte monocultures and oligodendrocyte-astrocyte cocultures, we demonstrate blocking PAR1 improves myelin production by a mechanism related to effects across glial compartments and linked in part to regulatory actions toward growth factors such as BDNF. These findings set the stage for development of new clinically relevant myelin regeneration strategies.

Mechanism of delayed encephalopathy after acute carbon monoxide poisoning

Many hypotheses exist regarding the mechanism underlying delayed encephalopathy after acute carbon monoxide poisoning (DEACMP), including the inflammation and immune-mediated damage hypothesis and the cellular apoptosis and direct neuronal toxicity hypothesis; however, no existing hypothesis provides a satisfactory explanation for the complex clinical processes observed in DEACMP. Leucine-rich repeat and immunoglobulin-like domain-containing protein-1 (LINGO-1) activates the Ras homolog gene family member A (RhoA)/Rho-associated coiled-coil containing protein kinase 2 (ROCK2) signaling pathway, which negatively regulates oligodendrocyte myelination, axonal growth, and neuronal survival, causing myelin damage and participating in the pathophysiological processes associated with many central nervous system diseases. However, whether LINGO-1 is involved in DEACMP remains unclear. A DEACMP model was established in rats by allowing them to inhale 1000 ppm carbon monoxide gas for 40 minutes, followed by 3000 ppm carbon monoxide gas for an additional 20 minutes. The results showed that compared with control rats, DEACMP rats showed significantly increased water maze latency and increased protein and mRNA expression levels of LINGO-1, RhoA, and ROCK2 in the brain. Compared with normal rats, significant increases in injured neurons in the hippocampus and myelin sheath damage in the lateral geniculate body were observed in DEACMP rats. From days 1 to 21 after DEACMP, the intraperitoneal injection of retinoic acid (10 mg/kg), which can inhibit LINGO-1 expression, was able to improve the above changes observed in the DEACMP model. Therefore, the overexpression of LINGO-1 appeared to increase following carbon monoxide poisoning, activating the RhoA/ROCK2 signaling pathway, which may be an important pathophysiological mechanism underlying DEACMP. This study was reviewed and approved by the Medical Ethics Committee of Xiangya Hospital of Central South Hospital (approval No. 201612684) on December 26, 2016.

Advances in identification of genes involved in autosomal recessive intellectual disability: a brief review

Intellectual disability (ID) is a clinically and genetically heterogeneous disorder, affecting 1%-3% of the general population. The number of ID-causing genes is high. Many X-linked genes have been implicated in ID. Autosomal dominant genes have recently been the focus of several large-scale studies. The total number of autosomal recessive ID (ARID) genes is estimated to be very high, and most are still unknown. Although research into the genetic causes of ID has recently gained momentum, identification of pathogenic mutations that cause ARID has lagged behind, predominantly due to non-availability of sizeable families. A commonly used approach to identify genetic loci for recessive disorders in consanguineous families is autozygosity mapping and whole-exome sequencing. Combination of these two approaches has recently led to identification of many genes involved in ID. These genes have diverse function and control various biological processes. In this review, we will present an update regarding genes that have been recently implicated in ID with focus on ARID.

LINGO-1 shRNA Loaded by Pluronic F-127 Promotes Functional Recovery After Ventral Root Avulsion

Spinal root avulsion typically leads to massive motoneuron death and severe functional deficits of the target muscles. Multiple pathological factors such as severe neuron loss, induction of inhibitory molecules, and insufficient regeneration are responsible for the poor functional recovery. Leucine-rich repeat and immunoglobulin-like domain-containing Nogo receptor-interacting protein 1 (LINGO-1), a central nervous system (CNS)-specific transmembrane protein that is selectively expressed on neurons and oligodendrocytes, serves as a potent negative mediator of axonal regeneration and myelination in CNS injuries and diseases. Although accumulating evidence has demonstrated improvement in axonal regeneration and neurological functions by LINGO-1 antagonism in CNS damage, the possible effects of LINGO-1 in spinal root avulsion remain undiscovered. In this study, a LINGO-1 knockdown strategy using lentiviral vectors encoding LINGO-1 short hairpin interfering RNA (shRNA) delivered by the Pluronic F-127 (PF-127) hydrogel was described after brachial plexus avulsion (BPA). We provide evidence that following BPA and immediate reimplantation, transplantation of LINGO-1 shRNA lentiviral vectors encapsulated by PF-127 rescued the injured motoneurons, enhanced axonal outgrowth and myelination, rebuilt motor endplates, facilitated the reinnervation of terminal muscles, improved angiogenesis, and promoted recovery of avulsed forelimbs. Altogether, these data suggest that delivery of LINGO-1 shRNA by a gel scaffold is a potential therapeutic approach for root avulsion. Impact Statement In this study, we attempted transplantation of lentivirus (LV)/leucine-rich repeat and immunoglobulin-like domain-containing Nogo receptor-interacting protein 1 (LINGO-1)-short hairpin interfering RNA (shRNA) encapsulated by the Pluronic F-127 (PF-127) hydrogel into a brachial plexus avulsion (BPA)-reimplantation model. We found that administration of LV/LINGO-1 shRNA facilitates neuron survival and axonal regeneration, attenuates muscle atrophy and motor endplate (MEP) loss, enhances neovascularization, and promotes functional recovery in BPA rats. Co-transplantation of LV/LINGO-1 shRNA and gel reinforces the survival-promoting effect, axonal outgrowth, and angiogenesis in comparison with LV/LINGO-1 shRNA application alone. Our research provides evidence that LV /LINGO-1 shRNA delivered by PF-127 represents a new treatment strategy for BPA repair.

Copy number variation of LINGO1 in familial dystonic tremor

Objective

To elucidate the genetic cause of a large 5 generation South Indian family with multiple individuals with predominantly an upper limb postural tremor and posturing in keeping with another form of tremor, namely, dystonic tremor.

Methods

Whole-genome single nucleotide polymorphism (SNP) microarray analysis was undertaken to look for copy number variants in the affected individuals.

Results

Whole-genome SNP microarray studies identified a tandem duplicated genomic segment of chromosome 15q24 present in all affected family members. Whole-genome sequencing demonstrated that it comprised a ∼550-kb tandem duplication encompassing the entire LINGO1 gene.

Conclusions

The identification of a genomic duplication as the likely molecular cause of this condition, resulting in an additional LINGO1 gene copy in affected cases, adds further support for a causal role of this gene in tremor disorders and implicates increased expression levels of LINGO1 as a potential pathogenic mechanism.

Myelin injury induces axonal transport impairment but not AD-like pathology in the hippocampus of cuprizone-fed mice

Both multiple sclerosis (MS) and Alzheimer's disease (AD) are progressive neurological disorders with myelin injury and memory impairment. However, whether myelin impairment could cause AD-like neurological pathology remains unclear. To explore neurological pathology following myelin injury, we assessed cognitive function, the expression of myelin proteins, axonal transport-associated proteins, axonal structural proteins, synapse-associated proteins, tau and beta amyloid and the status of neurons, using the cuprizone mouse model of demyelination. We found the mild impairment of learning ability in cuprizone-fed mice and the decreased expression of myelin basic protein (MBP) in the hippocampus. And anti-LINGO-1 improved learning ability and partly restored MBP level. Furthermore, we also found kinesin light chain (KLC), neurofilament light chain (NFL) and neurofilament heavy chain (NF200) were declined in demyelinated hippocampus, which could be partly improved by treatment with anti-LINGO-1. However, we did not observe the increased expression of beta amyloid, hyperphosphorylation of tau and loss of neurons in demyelinated hippocampus. Our results suggest that demyelination might lead to the impairment of neuronal transport, but not cause increased level of hyperphosphorylated tau and beta amyloid. Our research demonstrates remyelination might be an effective pathway to recover the function of neuronal axons and cognition in MS.

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.

(WNK)ing at death: With-no-lysine (Wnk) kinases in neuropathies and neuronal survival

Members of With-no-lysine (WNK) family of serine-threonine kinase are key regulators of chloride ion transport in diverse cell types, controlling the activity and the surface expression of cation-chloride (Na(+)/K(+)-Cl(-)) co-transporters. Mutations in WNK1 and WNK4 are linked to a hereditary form of hypertension, and WNKs have been extensively investigated pertaining to their roles in renal epithelial ion homeostasis. However, some members of the WNK family and their splice isoforms are also expressed in the mammalian brain, and have been implicated in aspects of hereditary neuropathy as well as neuronal and glial survival. WNK2, which is exclusively enriched in neurons, is well known as an anti-proliferative tumor suppressor. WNK3, on the other hand, appears to promote cell survival as its inhibition enhances neuronal apoptosis. However, loss of WNK3 has been recently shown to reduce ischemia-associated brain damage. In this review, I surveyed the potentially context-dependent roles of WNKs in neurological disorders and neuronal survival.

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

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

LINGO-1 antibody ameliorates myelin impairment and spatial memory deficits in experimental autoimmune encephalomyelitis mice

More than 50% of multiple sclerosis patients develop cognitive impairment. However, the underlying mechanisms are still unclear, and there is no effective treatment. LINGO-1 (LRR and Ig domain containing NOGO receptor interacting protein 1) has been identified as an inhibitor of oligodendrocyte differentiation and myelination. Using the experimental autoimmune encephalomyelitis (EAE) mouse model, we assessed cognitive function at early and late stages of EAE, determined brain expression of myelin basic protein (MBP) and investigated whether the LINGO-1 antibody could restore deficits in learning and memory and ameliorate any loss of MBP. We found that deficits in learning and memory occurred in late EAE and identified decreased expression of MBP in the parahippocampal cortex (PHC) and fimbria-fornix. Moreover, the LINGO-1 antibody significantly improved learning and memory in EAE and partially restored MBP in PHC. Furthermore, the LINGO-1 antibody activated the AKT/mTOR signaling pathway regulating myelin growth. Our results suggest that demyelination in the PHC and fimbria-fornix might contribute to cognitive deficits and the LINGO-1 antibody could ameliorate these deficits by promoting myelin growth in the PHC. Our research demonstrates that LINGO-1 antagonism may be an effective approach to the treatment of the cognitive impairment of multiple sclerosis patients.

Analysis and meta-analysis of five polymorphisms of the LINGO1 and LINGO2 genes in Parkinson's disease and multiple system atrophy in a Chinese population

Whether polymorphisms rs11856808 and rs9652490 of the Leucine-rich repeat and Ig domain containing, Nogo receptor-interacting protein-1 (LINGO1) gene, as well as rs10968280, rs13362909 and rs7033345 of the LINGO2 gene, increase the risk for Parkinson's disease (PD) is controversial. Considering the overlap of the clinical and pathological characteristics among PD and multiple system atrophy (MSA), we explored the associations between these five polymorphisms and PD and MSA in a Chinese population. A total of 1055 PD patients, 320 MSA patients, and 810 healthy controls (HCs) were genotyped for these five polymorphisms in LINGO1 and LINGO 2 using Sequenom iPLEX Assay technology. Moreover, after combining our results with available published data, a meta-analysis was conducted to investigate the associations between LINGO 1 rs11856808 and rs9652490 and the risk of PD. The frequency of the minor alleles "T" of LINGO1 rs11856808 was significantly lower in PD than that in HCs (p = 0.011, OR 0.89, 95 % CI 0.81-0.97), but not in MSA. Moreover, there were no significant differences in the minor allele frequency distributions of the other four polymorphisms between PD and HCs, and between MSA and HCs. The meta-analysis showed a lack of association of rs9652490 and PD, regardless of the genetic model or ethnic origin. However, the rs11856808 allele decreased the risk of PD in patients of Asian origin in a dominant genetic model. Our findings suggest that rs11856808 plays a protective role by decreasing the risk for PD, but not for MSA, in Asian population, the other four polymorphisms do not contribute to the risk for PD and MSA.

Effect of retinoic acid on expression of LINGO-1 and neural regeneration after cerebral ischemia

The purpose of this study was to observe the expression of LINGO-1 after cerebral ischemia, investigate the effects of retinoic acid (RA) on the expression of LINGO-1 and GAP-43, and the number of synapses, and to emplore the repressive effect of LINGO-1 on neural regeneration after cerebral ischemia. The model of permanent focal cerebral ischemia was established by the modified suture method of middle cerebral artery occlusion (MCAO) in Sprague-Dawley (SD) rats. The expression of LINGO-1 was detected by Western blotting and that of GAP-43 by immunohistochemistry. The number of synapses was observed by transmission electron microscopy. The SD rats were divided into three groups: sham operation (sham) group, cerebral ischemia (CI) group and RA treatment (RA) group. The results showed that the expression level of LINGO-1 at 7th day after MCAO in sham, CI and RA groups was 0.266 ± 0.019, 1.215 ± 0.063 and 0.702 ± 0.081, respectively (P<0.01). The number of Gap-43-positive nerve cells at 7th day after MCAO in sham, CI and RA group was 0, 59.08 ± 1.76 and 76.20 ± 3.12 per high power field, respectively (P<0.05). The number of synapses at 7th day after MCAO was 8.42 ± 0.13, 1.74 ± 0.37 and 5.39 ± 0.26 per μm², respectively (P<0.05). It is concluded that LINGO-1 expression is up-regulated after cerebral ischemia, and RA inhibits the expression of LINGO-1, promotes the expression of GAP-43 and increases the number of synapses. It suggests that LINGO-1 may be involved in the pathogenesis of cerebral ischemia, which may provide an experimenal basis for LINGO-1 antogonist, RA, for the treatment of cerebral ischemia.

Targeting the cis-dimerization of LINGO-1 with low MW compounds affects its downstream signalling

BACKGROUND AND PURPOSE

The transmembrane protein LINGO-1 is a negative regulator in the nervous system mainly affecting axonal regeneration, neuronal survival, oligodendrocyte differentiation and myelination. However, the molecular mechanisms regulating its functions are poorly understood. In the present study, we investigated the formation and the role of LINGO-1 cis-dimers in the regulation of its biological activity.

EXPERIMENTAL APPROACH

LINGO-1 homodimers were identified in both HEK293 and SH-SY5Y cells using co-immunoprecipitation experiments and BRET saturation analysis. We performed a hypothesis-driven screen for identification of small-molecule protein-protein interaction modulators of LINGO-1 using a BRET-based assay, adapted for screening. The compound identified was further assessed for effects on LINGO-1 downstream signalling pathways using Western blotting analysis and AlphaScreen technology.

KEY RESULTS

LINGO-1 was present as homodimers in primary neuronal cultures. LINGO-1 interacted homotypically in cis-orientation and LINGO-1 cis-dimers were formed early during LINGO-1 biosynthesis. A BRET-based assay allowed us to identify phenoxybenzamine as the first conformational modulator of LINGO-1 dimers. In HEK-293 cells, phenoxybenzamine was a positive modulator of LINGO-1 function, increasing the LINGO-1-mediated inhibition of EGF receptor signalling and Erk phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that LINGO-1 forms constitutive cis-dimers at the plasma membrane and that low MW compounds affecting the conformational state of these dimers can regulate LINGO-1 downstream signalling pathways. We propose that targeting the LINGO-1 dimerization interface opens a new pharmacological approach to the modulation of its function and provides a new strategy for drug discovery.

Cyclin-dependent kinase 5 mediates adult OPC maturation and myelin repair through modulation of Akt and GsK-3β signaling

Failure of remyelination in diseases, such as multiple sclerosis (MS), leads to permanent axonal damage and irreversible functional loss. The mechanisms controlling remyelination are currently poorly understood. Recent studies implicate the cyclin-dependent kinase 5 (Cdk5) in regulating oligodendrocyte (OL) development and myelination in CNS. In this study, we show that Cdk5 is also an important regulator of remyelination. Pharmacological inhibition of Cdk5 inhibits repair of lysolecithin lesions. This inhibition is a consequence of Cdk5 disruption in neural cells because remyelination in slice cultures is blocked by Cdk5 inhibitors, whereas specific deletion of Cdk5 in OLs inhibits myelin repair. In CNP-Cre;Cdk5(fl/fl) conditional knock-out mouse (Cdk5 cKO), myelin repair was delayed significantly in response to focal demyelinating lesions compared with wild-type animals. The lack of myelin repair was reflected in decreased expression of MBP and proteolipid protein and a reduction in the total number of myelinated axons in the lesion. The number of CC1(+) cells in the lesion sites was significantly reduced in Cdk5 cKO compared with wild-type animals although the total number of oligodendrocyte lineage cells (Olig2(+) cells) was increased, suggesting that Cdk5 loss perturbs the transition of early OL lineage cell into mature OL and subsequent remyelination. The failure of remyelination in Cdk5 cKO animals was associated with a reduction in signaling through the Akt pathway and an enhancement of Gsk-3β signaling pathways. Together, these data suggest that Cdk5 is critical in regulating the transition of adult oligodendrocyte precursor cells to mature OLs that is essential for myelin repair in adult CNS.

Lingo-1 inhibited by RNA interference promotes functional recovery of experimental autoimmune encephalomyelitis

Lingo-1 is a negative regulator of myelination. Repairment of demyelinating diseases, such as multiple sclerosis (MS)/experimental autoimmune encephalomyelitis (EAE), requires activation of the myelination program. In this study, we observed the effect of RNA interference on Lingo-1 expression, and the impact of Lingo-1 suppression on functional recovery and myelination/remyelination in EAE mice. Lentiviral vectors encoding Lingo-1 short hairpin RNA (LV/Lingo-1-shRNA) were constructed to inhibit Lingo-1 expression. LV/Lingo-1-shRNA of different titers were transferred into myelin oligodendrocyte glycoprotein-induced EAE mice by intracerebroventricular (ICV) injection. Meanwhile, lentiviral vectors carrying nonsense gene sequence (LVCON053) were used as negative control. The Lingo-1 expression was detected and locomotor function was evaluated at different time points (on days 1,3,7,14,21, and 30 after ICV injection). Myelination was investigated by luxol fast blue (LFB) staining.LV/Lingo-1-shRNA administration via ICV injection could efficiently down-regulate the Lingo-1 mRNA and protein expression in EAE mice on days 7,14,21, and 30 (P < 0.01), especially in the 5 × 10(8) TU/mL and 5 × 10(9) TU/mL LV/Lingo-1-shRNA groups. The locomotor function score in the LV/Lingo-1-shRNA treated groups were significantly lower than the untreated or LVCON053 group from day 7 on. The 5 × 10(8) TU/mL LV/Lingo-1-shRNA group achieved the best functional improvement (0.87 ± 0.11 vs. 3.05 ± 0.13, P < 0.001). Enhanced myelination/remyelination was observed in the 5 × 10(7) , 5 × 10(8) , 5 × 10(9) TU/mL LV/Lingo-1-shRNA groups by LFB staining (P < 0.05, P < 0.01, and P < 0.05).The data showed that administering LV/Lingo-1-shRNA by ICV injection could efficiently knockdown Lingo-1 expression in vivo, improve functional recovery and enhance myelination/remyelination. Antagonism of Lingo-1 by RNA interference is, therefore, a promising approach for the treatment of demyelinating diseases, such as MS/EAE.

Oligodendrogenesis in the normal and pathological central nervous system

Oligodendrocytes (OLGs) are generated late in development and myelination is thus a tardive event in the brain developmental process. It is however maintained whole life long at lower rate, and myelin sheath is crucial for proper signal transmission and neuronal survival. Unfortunately, OLGs present a high susceptibility to oxidative stress, thus demyelination often takes place secondary to diverse brain lesions or pathologies. OLGs can also be the target of immune attacks, leading to primary demyelination lesions. Following oligodendrocytic death, spontaneous remyelination may occur to a certain extent. In this review, we will mainly focus on the adult brain and on the two main sources of progenitor cells that contribute to oligodendrogenesis: parenchymal oligodendrocyte precursor cells (OPCs) and subventricular zone (SVZ)-derived progenitors. We will shortly come back on the main steps of oligodendrogenesis in the postnatal and adult brain, and summarize the key factors involved in the determination of oligodendrocytic fate. We will then shed light on the main causes of demyelination in the adult brain and present the animal models that have been developed to get insight on the demyelination/remyelination process. Finally, we will synthetize the results of studies searching for factors able to modulate spontaneous myelin repair.

Quercetin promotes proliferation and differentiation of oligodendrocyte precursor cells after oxygen/glucose deprivation-induced injury

The aim of this study was to investigate quercetin's (Qu) ability to promote proliferation and differentiation of oligodendrocyte precursor cells (OPCs) under oxygen/glucose deprivation (OGD)-induced injury in vitro. The results showed that after OGD, OPCs survival rate was significantly increased by Qu as measured by Cell Counting Kit-8. Furthermore, Qu treatment reduced apoptosis of OPCs surveyed by Hoechst 33258 nuclear staining. Qu at 9 and 27 μM promoted the proliferation of OPCs the most by Brdu and Olig2 immunocytochemical staining after OGD 3 days. Also, Qu treatment for 8 days after OGD, the differentiation of OPCs to oligodendrocyte was detected by immunofluorescence staining showing that O4, Olig2, and myelin basic protein (MBP) positive cells were significantly increased compared to control group. Additionally, the protein levels of Olig2 and MBP of OPCs were quantified using western blot and mRNA levels of Olig2 and Inhibitor of DNA binding 2 (Id2) were measured by RT-PCR. Western blot showed a significant increase in Olig2 and MBP expression levels compared with controls after OGD and Qu treatment with a linear does-response curve from 3 to 81 μM. After treatment with Qu compared to its control group, Olig2 mRNA level was significantly up-regulated, whereas Id2 mRNA level was down-regulated. In conclusion, Qu at 3-27 μM can promote the proliferation and differentiation of OPCs after OGD injury and may regulate the activity of Olig2 and Id2.

Increased LINGO1 in the cerebellum of essential tremor patients

Essential tremor (ET) is the most prevalent adult-onset movement disorder. Despite its health burden, no clear pathognomonic sign has been identified to date because of the rarity of clinicopathological studies. Moreover, treatment options are still scarce and have not significantly changed in the last 30 years, underscoring the urgent need to develop new treatment avenues. In the recent years, leucine-rich repeat (LRR) and immunoglobulin (Ig) domain-containing Nogo receptor-interacting proteins 1 and 2 (LINGO1 and LINGO2, respectively) have been increasingly regarded as possible ET modulators due to emerging genetic association studies linking LINGO with ET. We have investigated LINGO protein and messenger RNA (mRNA) expression in the cerebellum of patients with ET, patients with Parkinson's disease (PD), and a control group using Western immunoblotting and in situ hybridization. Protein levels of LINGO1, but not LINGO2, were significantly increased in the cerebellar cortex of ET patients compared with controls, particularly in individuals with longer disease duration. Compared with controls, LINGO1 protein levels were increased in the cerebellar white matter of PD and ET patients but, for the latter, only when disease duration exceeded 20 years. However, no alteration in LINGO1 mRNA was observed between groups in either the cerebellar cortex or the white matter. We observed alterations in LINGO expression in diseased brain that seemed to progress along with the disease, being initiated in the cerebellar cortex before reaching the white matter. Because LINGO up-regulation has been identified as a potential pathological response to ongoing neurodegenerative processes, the present data suggest that LINGO1 is a potential drug target for ET.

Neural cell adhesion molecules belonging to the family of leucine-rich repeat proteins

Leucine-rich repeats (LRRs) are motifs that form protein-ligand interaction domains. There are approximately 140 human genes encoding proteins with extracellular LRRs. These encode cell adhesion molecules (CAMs), proteoglycans, G-protein-coupled receptors, and other types of receptors. Here we give a brief description of 36 proteins with extracellular LRRs that all can be characterized as CAMs or putative CAMs expressed in the nervous system. The proteins are involved in multiple biological processes in the nervous system including the proliferation and survival of cells, neuritogenesis, axon guidance, fasciculation, myelination, and the formation and maintenance of synapses. Moreover, the proteins are functionally implicated in multiple diseases including cancer, hearing impairment, glaucoma, Alzheimer's disease, multiple sclerosis, Parkinson's disease, autism spectrum disorders, schizophrenia, and obsessive-compulsive disorders. Thus, LRR-containing CAMs constitute a large group of proteins of pivotal importance for the development, maintenance, and regeneration of the nervous system.

Knockdown of Lingo1b protein promotes myelination and oligodendrocyte differentiation in zebrafish

Demyelinating diseases include multiple sclerosis, which is a neurodegenerative disease characterized by immune attacks on the central nervous system (CNS), resulting in myelin sheath damage and axonal loss. Leucine-rich repeat and immunoglobulin domain-containing neurite outgrowth inhibitory protein (Nogo) receptor-interacting protein-1 (LINGO-1) have been identified as a negative regulator of oligodendrocytes differentiation. Targeted LINGO-1 inhibition promotes neuron survival, axon regeneration, oligodendrocyte differentiation, and remyelination in diverse animal models. Although studies in rodent models have extended our understanding of LINGO-1, its roles in neural development and myelination in zebrafish (Danio rerio) are not yet clear. In this study, we cloned the zebrafish homolog of the human LINGO-1 and found that lingo1b regulated myelination and oligodendrocyte differentiation. The expression of lingo1b started 1 (mRNA) and 2 (protein) days post-fertilization (dpf) in the CNS. Morpholino oligonucleotide knockdown of lingo1b resulted in developmental abnormalities, including less dark pigment, small eyes, and a curly spinal cord. The lack of lingo1b enhanced myelination and oligodendrocyte differentiation during embryogenesis. Furthermore, immunohistochemistry and movement analysis showed that lingo1b was involved in the axon development of primary motor neurons. These results suggested that Lingo1b protein functions as a negative regulator of myelination and oligodendrocyte differentiation during zebrafish development.

Slitrk gene duplication and expression in the developing zebrafish nervous system

BACKGROUND

The Slitrk family of leucine-rich repeat (LRR) transmembrane proteins bears structural similarity to the Slits and the Trk receptor families, which exert well-established roles in directing nervous system development. Slitrks are less well understood, although they are highly expressed in the developing vertebrate nervous system. Moreover, slitrk variants are associated with several sensory and neuropsychiatric disorders, including myopia, deafness, obsessive-compulsive disorder (OCD), schizophrenia, and Tourette syndrome. Loss-of-function studies in mice show that Slitrks modulate neurite outgrowth and inhibitory synapse formation, although the molecular mechanisms of Slitrk function remain poorly characterized.

RESULTS

As a prelude to examining the functional roles of Slitrks, we identified eight slitrk orthologs in zebrafish and observed that seven of the eight orthologs were actively transcribed in the nervous system at embryonic, larval, and adult stages. Similar to previous findings in mice and humans, zebrafish slitrks exhibited unique but overlapping spatial and temporal expression patterns in the developing brain, retina, and spinal cord.

CONCLUSIONS

Zebrafish express Slitrks in the developing central nervous system at times and locations important to neuronal morphogenesis and synaptogenesis. Future studies will use zebrafish as a convenient, cost-effective model organism to characterize the functional roles of Slitrks in nervous system development.

Local injection of lentivirus encoding LINGO-1-shRNA promotes functional recovery in rats with complete spinal cord transection

STUDY DESIGN

We used a complete spinal cord transection model and locomotor function, histological, and immunohistochemical examinations to evaluate the effects of local injection of lentivirus/LINGO-1-short hairpin RNA (VL) on rats with spinal cord injury (SCI).

OBJECTIVE

To demonstrate the neuroregenerative and neuroprotective effects of LINGO-1 RNAi on complete transection SCI rats.

SUMMARY OF BACKGROUND DATA

LINGO-1 has been reported as a negative regulator of axonal sprouting and its antagonist was determined to improve functional outcomes in SCI rats. However, it has not been assessed whether blockade of LINGO-1 mediated by lentivirus vectors could stimulate neural recovery after SCI.

METHODS

Complete spinal cord transection was made at T10 level. Suspension of lentivirus vectors encoding LINGO-1-short hairpin RNA was injected into the lesion gap. Controls received control vectors in the same manner and the sham group was subjected to laminectomy only. The Basso-Beattie-Bresnahan scale and surface righting reflex test were used to evaluate functional outcomes. Finally, the spinal cords were harvested for histological and immunohistochemical analysis.

RESULTS

The treatment with VL improved Basso-Beattie-Bresnahan scores and surface righting reflex after SCI. Tissue repair was facilitated and the cavity area was significantly decreased in VL-treated animals. More sprouting and myelinated nerve fibers were detected within the injured site in the VL group as compared with the control. In addition, the number of survival neurons and oligodendrocytes around the epicenter was notably higher under the VL condition.

CONCLUSION

Local injection of lentivirus/LINGO-1-short hairpin RNA after complete transection of spinal cord resulted in meaningful histological and functional outcomes in rats. The mechanism of VL protection may be related to its promotion of axonal sprouting, remyelination, and cell survival.

Nogo/RTN4 isoforms and RTN3 expression protect SH-SY5Y cells against multiple death insults

Among the members of the reticulon (RTN) family, Nogo-A/RTN4A, a prominent myelin-associated neurite growth inhibitory protein, and RTN3 are highly expressed in neurons. However, neuronal cell-autonomous functions of Nogo-A, as well as other members of the RTN family, are unclear. We show here that SH-SY5Y neuroblastoma cells stably over-expressing either two of the three major isoforms of Nogo/RTN4 (Nogo-A and Nogo-B) or a major isoform of RTN3 were protected against cell death induced by a battery of apoptosis-inducing agents (including serum deprivation, staurosporine, etoposide, and H2O2) compared to vector-transfected control cells. Nogo-A, -B, and RTN3 are particularly effective in terms of protection against H2O2-induced increase in intracellular reactive oxygen species levels and ensuing apoptotic and autophagic cell death. Expression of these RTNs upregulated basal levels of Bax, activated Bax, and activated caspase 3, but did not exhibit an enhanced ER stress response. The protective effect of RTNs is also not dependent on classical survival-promoting signaling pathways such as Akt and Erk kinase pathways. Neuron-enriched Nogo-A/Rtn4A and RTN3 may, therefore, exert a protective effect on neuronal cells against death stimuli, and elevation of their levels during injury may have a cell-autonomous survival-promoting function.

Blocking LINGO-1 as a therapy to promote CNS repair: from concept to the clinic

LINGO-1 is a leucine-rich repeat and Ig domain-containing, Nogo receptor interacting protein, selectively expressed in the CNS on both oligodendrocytes and neurons. Its expression is developmentally regulated, and is upregulated in CNS diseases and injury. In animal models, LINGO-1 expression is upregulated in rat spinal cord injury, experimental autoimmune encephalomyelitis, 6-hydroxydopamine neurotoxic lesions and glaucoma models. In humans, LINGO-1 expression is increased in oligodendrocyte progenitor cells from demyelinated white matter of multiple sclerosis post-mortem samples, and in dopaminergic neurons from Parkinson's disease brains. LINGO-1 negatively regulates oligodendrocyte differentiation and myelination, neuronal survival and axonal regeneration by activating ras homolog gene family member A (RhoA) and inhibiting protein kinase B (Akt) phosphorylation signalling pathways. Across diverse animal CNS disease models, targeted LINGO-1 inhibition promotes neuron and oligodendrocyte survival, axon regeneration, oligodendrocyte differentiation, remyelination and functional recovery. The targeted inhibition of LINGO-1 function presents a novel therapeutic approach for the treatment of CNS diseases.

Lingo-1 expression is increased in essential tremor cerebellum and is present in the basket cell pinceau

The Lingo-1 sequence variant has been associated with essential tremor (ET) in several genome-wide association studies. However, the role that Lingo-1 might play in pathogenesis of ET is not understood. Since Lingo-1 protein is a negative regulator of axonal regeneration and neurite outgrowth, it could contribute to Purkinje cell (PC) or basket cell axonal pathology observed in postmortem studies of ET brains. In this study, we used Western blotting and immunohistochemistry to examine Lingo-1 protein in ET vs. control brains. In Western blots, Lingo-1 protein expression level was significantly increased in cerebellar cortex (1.56 ± 0.46 in ET cases vs. 0.99 ± 0.20 in controls, p = 0.002), but was similar in the occipital cortex (p = 1.00) of ET cases vs. controls. Lingo-1 immunohistochemistry in cerebellum revealed that Lingo-1 was enriched in the distal axonal processes of basket cells, which formed a "pinceau" structure around the PC axon initial segment (AIS). We found that some Lingo-1-positive pinceau had abnormally elongated processes, targeting PC axon segments distal to the AIS. In ET cases, the percentage of Lingo-1-positive pinceau that were ≥30 or ≥40 μm in length was increased 2.4- to 4.1-fold, respectively, vs. pinceau seen in control brains (p < 0.0001). Elongated Lingo-1-positive pinceau strongly correlated with number of PC axonal torpedoes and a rating of basket cell axonal pathology. The increased cerebellar Lingo-1 expression and elongated Lingo-1-positive pinceau processes could contribute to the abnormal PC and basket cell axonal pathology and cerebellar dysfunction observed in ET.

Systematic evaluation of candidate ligands regulating ectodomain shedding of amyloid precursor protein

Despite intense interest in the proteolysis of the β-Amyloid Precursor Protein (APP) in Alzheimer's disease, how the normal processing of this type I receptor-like glycoprotein is physiologically regulated remains ill-defined. In recent years, several candidate protein ligands for APP, including F-spondin, Reelin, β1 Integrin, Contactins, Lingo-1, and Pancortin, have been reported. However, a cognate ligand for APP that regulates its processing by α- or β-secretase has yet to be widely confirmed in multiple laboratories. Here, we developed new assays in an effort to confirm a role for one or more of these candidate ligands in regulating APP ectodomain shedding in a biologically relevant context. A comprehensive quantification of APPsα and APPsβ, the immediate products of secretase processing, in both non-neuronal cell lines and primary neuronal cultures expressing endogenous APP yielded no evidence that any of these published candidate ligands stimulate ectodomain shedding. Rather, Reelin, Lingo-1, and Pancortin-1 emerged as the most consistent ligands for significantly inhibiting ectodomain shedding. These findings led us to conduct further detailed analyses of the interactions of Reelin and Lingo-1 with APP.

Cyclin dependent kinase 5 is required for the normal development of oligodendrocytes and myelin formation

The development of oligodendrocytes, the myelinating cells of the vertebrate CNS, is regulated by a cohort of growth factors and transcription factors. Less is known about the signaling pathways that integrate extracellular signals with intracellular transcriptional regulators to control oligodendrocyte development. Cyclin dependent kinase 5 (Cdk5) and its co-activators play critical roles in the regulation of neuronal differentiation, cortical lamination, neuronal cell migration and axon outgrowth. Here we demonstrate a previously unrecognized function of Cdk5 in regulating oligodendrocyte maturation and myelination. During late embryonic development Cdk5 null animals displayed a reduction in the number of MBP+ cells in the spinal cord, but no difference in the number of OPCs. To determine whether the reduction of oligodendrocytes reflected a cell-intrinsic loss of Cdk5, it was selectively deleted from Olig1+ oligodendrocyte lineage cells. In Olig1(Cre/+); Cdk5(fl/fl) conditional mutants, reduced levels of expression of MBP and PLP mRNA were observed throughout the CNS and ultrastructural analyses demonstrated a significant reduction in the proportion of myelinated axons in the optic nerve and spinal cord. Pharmacological inhibition or RNAi knockdown of Cdk5 in vitro resulted in the reduction in oligodendrocyte maturation, but had no effect on OPC cell proliferation. Conversely, over-expression of Cdk5 promoted oligodendrocyte maturation and enhanced process outgrowth. Consistent with this data, Cdk5(-/-) oligodendrocytes developed significantly fewer primary processes and branches than control cells. Together, these findings suggest that Cdk5 function as a signaling integrator to regulate oligodendrocyte maturation and myelination.

Myelin-based inhibitors of oligodendrocyte myelination: clues from axonal growth and regeneration

The differentiation of and myelination by oligodendrocytes (OLs) are exquisitely regulated by a series of intrinsic and extrinsic mechanisms. As each OL can make differing numbers of myelin segments with variable lengths along similar axon tracts, myelination can be viewed as a graded process shaped by inhibitory/inductive cues during development. Myelination by OLs is a prime example of an adaptive process determined by the microenvironment and architecture of the central nervous system (CNS). in this review, we discuss how myelin formation by OLs may be controlled by the heterogeneous microenvironment of the CNS. Then we address recent findings demonstrating that neighboring OLs may compete for available axon space, and highlight our current understanding of myelin-based inhibitors of axonal regeneration that are potentially responsible for the reciprocal dialogue between OLs and determine the numbers and lengths of myelin internodes. Understanding the mechanisms that control the spatiotemporal regulation of myelinogenic potential during development may provide valuable insight into therapeutic strategies for promoting remyelination in an inhibitory microenvironment.

The promotion of functional recovery and nerve regeneration after spinal cord injury by lentiviral vectors encoding Lingo-1 shRNA delivered by Pluronic F-127

Lingo-1 is selectively expressed on both oligodendrocytes and neurons in the central nervous system (CNS) and serves as a key negative regulator of nerve regeneration, implying a therapeutic target for spinal cord injury (SCI). Here we described a strategy to knock-down Lingo-1 expression in vivo using lentiviral vectors encoding Lingo-1 short harpin interfering RNA (shRNA) delivered by Pluronic F-127 (PF-127) gel, a non-cytotoxic scaffold and gene delivery carrier, after the complete transection of the T10 spinal cord in adult rats. We showed administration of PF-127 encapsulating Lingo-1 shRNA lentiviral vectors efficiently down-regulated the expression of Lingo-1, and exhibited transduction efficiency comparable to using vectors alone in oligodendrocyte culture in vitro. Furthermore, similar silencing effects and higher transfection efficiency were observed in vivo when Lingo-1 shRNA was co-delivered to the injured site by PF-127 gel with lower viral concentrations. Cografting of gel and Lingo-1 RNAi significantly promoted functional recovery and nerve regeneration, enhanced neurite outgrowth and synapses formation, preserved myelinated axons, and induced the proliferation of glial cells. In addition, the combined implantation also improved neuronal survival and inhibited cell apoptosis, which may be associated with the attenuation of endoplasmic reticulum (ER) stress after SCI. Together, our data indicated that delivering Lingo-1 shRNA by gel scaffold was a valuable treatment approach to SCI and PF-127 delivery of viral vectors to the spinal cord may provide strategy to study and develop therapies for SCI.