Nogo-a regulates neural precursor migration in the embryonic mouse cortex

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.

Nogo‑A/NgR signaling regulates stemness in cancer stem‑like cells derived from U87MG glioblastoma cells

Neurite outgrowth inhibitor A (Nogo-A), a member of the reticulon 4 family, is an axon regeneration inhibitor that is negatively associated with the malignancy of oligodendroglial tumors. It has been suggested that the Nogo-A/Nogo Receptor (NgR) pathway plays a promoting effect in regulating cancer stem-like cells (CSCs) derived from glioblastoma, indicating that Nogo-A could exert different roles in CSCs than those in parental cancer cells. In the present study, CSCs were generated from the human Uppsala 87 malignant glioma (U87MG) cell line. These U87MG-CSCs were characterized by the upregulation of CD44 and CD133, which are two markers of stemness. The expression levels of Nogo-A and the differentiation of U87MG-CSCs were investigated. In addition, the proliferation, invasion and colony formation U87MG-CSCs were examined. Using culture in serum-containing medium, U87MG-CSCs were differentiated into neuron-like cells specifically expressing MAP2, β-III-tubulin and nestin. Nogo-A was upregulated in U87MG-CSCs compared with parental cells. Knockdown of Nogo-A and inhibition of the Nogo-A/NgR signaling pathway in U87MG-CSCs markedly decreased cell viability, cell cycle entry, invasion and tumor formation, indicating that Nogo-A could regulate U87MG-CSC function. Moreover, Nogo-A was involved in intracellular ATP synthesis and scavenging of accumulated reactive oxygen species. Nogo-A/NgR pathway exerted protective effects against hypoxia-induced non-apoptotic and apoptotic cell death. These results suggest that Nogo-A plays an important role in regulating U87MG-CSCs via the Nogo-A/NgR signaling pathway. Nogo-A may also different roles in U87MG-CSCs compared with their parental cells.

Single-Cell RNA-Seq Reveals the Cellular Diversity and Developmental Characteristics of the Retinas of an Infant and a Young Child

The human retina, located in the innermost layer of the eye, plays a decisive role in visual perception. Dissecting the heterogeneity of retinal cells is essential for understanding the mechanism of visual development. Here, we performed single-cell RNA-seq to analyze 194,967 cells from the donors of infants and young children, resulting in 17 distinct clusters representing major cell types in the retina: rod photoreceptors (PRs), cone PRs, bipolar cells (BCs), horizontal cells (HCs), amacrine cells (ACs), retinal ganglion cells (RGCs), Müller glial cells (MGs), microglia, and astrocytes (ASTs). Through reclustering, we identified known subtypes of cone PRs as well as additional unreported subpopulations and corresponding markers in BCs. Additionally, we linked inherited retinal diseases (IRDs) to certain cell subtypes or subpopulations through enrichment analysis. We next constructed extensive intercellular communication networks and identified ligand-receptor interactions that play crucial roles in regulating neural cell development and immune homeostasis in the retina. Intriguingly, we found that the status and functions of PRs changed drastically between the young children and adult retina. Overall, our study offers the first retinal cell atlas in infants and young children dissecting the heterogeneity of the retina and identifying the key molecules in the developmental process, which provides an important resource that will pave the way for research on retinal development mechanisms and advancements in regenerative medicine concerning retinal biology.

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.

LINGO-1 shRNA protects the brain against ischemia/reperfusion injury by inhibiting the activation of NF-κB and JAK2/STAT3

LINGO-1 may be involved in the pathogenesis of cerebral ischemia. However, its biological function and underlying molecular mechanism in cerebral ischemia remain to be further defined. In our study, middle cerebral artery occlusion/reperfusion (MACO/R) mice model and HT22 cell oxygen–glucose deprivation/reperfusion (OGD/R) were established to simulate the pathological process of cerebral ischemia in vivo and in vitro and to detect the relevant mechanism. We found that LINGO-1 mRNA and protein were upregulated in mice and cell models. Down-regulation LINGO-1 improved the neurological symptoms and reduced pathological changes and the infarct size of the mice after MACO/R. In addition, LINGO-1 interference alleviated apoptosis and promoted cell proliferation in HT22 of OGD/R. Moreover, down-regulation of LINGO-1 proved to inhibit nuclear translocation of p-NF-κB and reduce the expression level of p-JAK2 and p-STAT3. In conclusion, our data suggest that shLINGO-1 attenuated ischemic injury by negatively regulating NF-KB and JAK2/STAT3 pathways, highlighting a novel therapeutic target for ischemic stroke.

Modulation of Nogo receptor 1 expression orchestrates myelin-associated infiltration of glioblastoma

As the clinical failure of glioblastoma treatment is attributed by multiple components, including myelin-associated infiltration, assessment of the molecular mechanisms underlying such process and identification of the infiltrating cells have been the primary objectives in glioblastoma research. Here, we adopted radiogenomic analysis to screen for functionally relevant genes that orchestrate the process of glioma cell infiltration through myelin and promote glioblastoma aggressiveness. The receptor of the Nogo ligand (NgR1) was selected as the top candidate through Differentially Expressed Genes (DEG) and Gene Ontology (GO) enrichment analysis. Gain and loss of function studies on NgR1 elucidated its underlying molecular importance in suppressing myelin-associated infiltration in vitro and in vivo. The migratory ability of glioblastoma cells on myelin is reversibly modulated by NgR1 during differentiation and dedifferentiation process through deubiquitinating activity of USP1, which inhibits the degradation of ID1 to downregulate NgR1 expression. Furthermore, pimozide, a well-known antipsychotic drug, upregulates NgR1 by post-translational targeting of USP1, which sensitizes glioma stem cells to myelin inhibition and suppresses myelin-associated infiltration in vivo. In primary human glioblastoma, downregulation of NgR1 expression is associated with highly infiltrative characteristics and poor survival. Together, our findings reveal that loss of NgR1 drives myelin-associated infiltration of glioblastoma and suggest that novel therapeutic strategies aimed at reactivating expression of NgR1 will improve the clinical outcome of glioblastoma patients.

Roles of developmentally regulated KIF2A alternative isoforms in cortical neuron migration and differentiation

KIF2A is a kinesin motor protein with essential roles in neural progenitor division and axonal pruning during brain development. However, how different KIF2A alternative isoforms function during development of the cerebral cortex is not known. Here, we focus on three Kif2a isoforms expressed in the developing cortex. We show that Kif2a is essential for dendritic arborization in mice and that the functions of all three isoforms are sufficient for this process. Interestingly, only two of the isoforms can sustain radial migration of cortical neurons; a third isoform, lacking a key N-terminal region, is ineffective. By proximity-based interactome mapping for individual isoforms, we identify previously known KIF2A interactors, proteins localized to the mitotic spindle poles and, unexpectedly, also translation factors, ribonucleoproteins and proteins that are targeted to organelles, prominently to the mitochondria. In addition, we show that a KIF2A mutation, which causes brain malformations in humans, has extensive changes to its proximity-based interactome, with depletion of mitochondrial proteins identified in the wild-type KIF2A interactome. Our data raises new insights about the importance of alternative splice variants during brain development.

Neurite Outgrowth Inhibitor (NogoA) Is Upregulated in White Matter Lesions of Complex Cortical Malformations

Complex cortical malformations (CCMs), such as hemimegalencephaly and polymicrogyria, are associated with drug-resistant epilepsy and developmental impairment. They share certain neuropathological characteristics including mammalian target of rapamycin (mTOR) activation and an atypical number of white matter neurons. To get a better understanding of the pathobiology of the lesion architecture, we investigated the role of neurite outgrowth inhibitor A (NogoA), a known regulator of neuronal migration. Epilepsy surgery specimens from 16 CCM patients were analyzed and compared with sections of focal cortical dysplasia IIB (FCD IIB, n = 22), tuberous sclerosis complex (TSC, n = 8) as well as healthy controls (n = 15). Immunohistochemistry was used to characterize NogoA, myelination, and mTOR signaling. Digital slides were evaluated automatically with ImageJ. NogoA staining showed a significantly higher expression within the white matter of CCM and FCD IIB, whereas cortical tubers presented levels similar to controls. Further analysis of possible associations of NogoA with other factors revealed a positive correlation with mTOR and seizure frequency. To identify the main expressing NogoA cell type, double staining revealed dysmorphic neuronal white matter cells. Increased NogoA expression is associated with profound inhibition of neuritic sprouting and therefore contributes to a decrease in neuronal network complexity in CCM patients.

Dynamic Changes in the Neurogenic Potential in the Ventricular-Subventricular Zone of Common Marmoset during Postnatal Brain Development

Even after birth, neuronal production continues in the ventricular-subventricular zone (V-SVZ) and hippocampus in many mammals. The immature new neurons ("neuroblasts") migrate and then mature at their final destination. In humans, neuroblast production and migration toward the neocortex and the olfactory bulb (OB) occur actively only for a few months after birth and then sharply decline with age. However, the precise spatiotemporal profiles and fates of postnatally born neurons remain unclear due to methodological limitations. We previously found that common marmosets, small nonhuman primates, share many features of V-SVZ organization with humans. Here, using marmosets injected with thymidine analogue(s) during various postnatal periods, we demonstrated spatiotemporal changes in neurogenesis during development. V-SVZ progenitor proliferation and neuroblast migration toward the OB and neocortex sharply decreased by 4 months, most strikingly in a V-SVZ subregion from which neuroblasts migrated toward the neocortex. Postnatally born neurons matured within a few months in the OB and hippocampus but remained immature until 6 months in the neocortex. While neurogenic activity was sustained for a month after birth, the distribution and/or differentiation diversity was more restricted in 1-month-born cells than in the neonatal-born population. These findings shed light on distinctive features of postnatal neurogenesis in primates.

In the line-up: deleted genes associated with DiGeorge/22q11.2 deletion syndrome: are they all suspects?

BACKGROUND

22q11.2 deletion syndrome (22q11DS), a copy number variation (CNV) disorder, occurs in approximately 1:4000 live births due to a heterozygous microdeletion at position 11.2 (proximal) on the q arm of human chromosome 22 (hChr22) (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011). This disorder was known as DiGeorge syndrome, Velo-cardio-facial syndrome (VCFS) or conotruncal anomaly face syndrome (CTAF) based upon diagnostic cardiovascular, pharyngeal, and craniofacial anomalies (McDonald-McGinn and Sullivan, Medicine 90:1-18, 2011; Burn et al., J Med Genet 30:822-4, 1993) before this phenotypic spectrum was associated with 22q11.2 CNVs. Subsequently, 22q11.2 deletion emerged as a major genomic lesion associated with vulnerability for several clinically defined behavioral deficits common to a number of neurodevelopmental disorders (Fernandez et al., Principles of Developmental Genetics, 2015; Robin and Shprintzen, J Pediatr 147:90-6, 2005; Schneider et al., Am J Psychiatry 171:627-39, 2014).

RESULTS

The mechanistic relationships between heterozygously deleted 22q11.2 genes and 22q11DS phenotypes are still unknown. We assembled a comprehensive "line-up" of the 36 protein coding loci in the 1.5 Mb minimal critical deleted region on hChr22q11.2, plus 20 protein coding loci in the distal 1.5 Mb that defines the 3 Mb typical 22q11DS deletion. We categorized candidates based upon apparent primary cell biological functions. We analyzed 41 of these genes that encode known proteins to determine whether haploinsufficiency of any single 22q11.2 gene-a one gene to one phenotype correspondence due to heterozygous deletion restricted to that locus-versus complex multigenic interactions can account for single or multiple 22q11DS phenotypes.

CONCLUSIONS

Our 22q11.2 functional genomic assessment does not support current theories of single gene haploinsufficiency for one or all 22q11DS phenotypes. Shared molecular functions, convergence on fundamental cell biological processes, and related consequences of individual 22q11.2 genes point to a matrix of multigenic interactions due to diminished 22q11.2 gene dosage. These interactions target fundamental cellular mechanisms essential for development, maturation, or homeostasis at subsets of 22q11DS phenotypic sites.

Nogo-A promotes inflammatory heat hyperalgesia by maintaining TRPV-1 function in the rat dorsal root ganglion neuron

Nogo-A is a key inhibitory molecule of axon regeneration in oligodendrocytes. However, little is known about its role in adult neurons. In this study, we showed an important function of Nogo-A on regulation of inflammatory pain in dorsal root ganglion (DRG) neurons. In adult rats with complete Freund's adjuvant (CFA) hind paw inflammation, DRG neurons showed a significant increase in Nogo-A expression. Disruption of Nogo-A signaling with Nogo-66 receptor antagonist peptide, Nogo-A blocking antibody, Nogo-A short hairpin RNA, or Nogo-A gene knockout attenuated CFA-induced inflammatory heat hyperalgesia. Moreover, disruption of Nogo-A signaling suppressed the function and expression in DRG neurons of the transient receptor potential vanilloid subfamily member (TRPV)-1 channel, which is known to be the endogenous transducer of noxious heat during inflammation. These effects were accompanied with a reduction in LIM domain kinase (LIMK)/cofilin phosphorylation and actin polymerization. Similar disruption of actin filament architecture by direct action of Latrunculin A reduced the TRPV-1 activity and up-regulation of TRPV-1 protein caused by CFA. We conclude that Nogo-A plays an essential role in the development of inflammatory heat hyperalgesia, partly through maintaining TRPV-1 function via activation of the LIMK/cofilin pathway, which regulates actin filament dynamics. These findings support a therapeutic potential of modulating Nogo-A signaling in pain management.-Hu, F., Liu, H.-C., Su, D.-Q., Chen, H.-J., Chan, S.-O., Wang, Y., Wang, J. Nogo-A promotes inflammatory heat hyperalgesia by maintaining TRPV-1 function in the rat dorsal root ganglion neuron.

Nogo-66 Restricts Synaptic Strengthening via Lingo1 and the ROCK2-Cofilin Pathway to Control Actin Dynamics

Nogo-A restricts long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway in the adult hippocampus via 2 extracellular domains: Nogo-A-Δ20 and Nogo-66. Nogo-66 signals via Nogo Receptor 1 (NgR1) to regulate synaptic function. Whether the NgR1 coreceptors Lingo1 and p75NTR are involved in the signaling in this context is still not known. Moreover, the intracellular cascade mediating the activity of Nogo-66 in restricting LTP is unexplored. We combine electrophysiology and biochemistry in acute hippocampal slices and demonstrate that a loss of function for Lingo1 results in a significant increase in LTP levels at the Schaffer collateral-CA1 pathway, and that Lingo1 is the NgR1 coreceptor mediating the role of Nogo-66 in restricting LTP. Our data show that p75NTR is not involved in mediating the Nogo-66 effect on LTP. Moreover, loss of function for p75NTR and NgR1 equally attenuate LTD, suggesting that p75NTR might mediate the NgR1-dependent regulation of LTD, independently of Nogo-66. Finally, our results indicate that Nogo-66 signaling limits LTP via the ROCK2-Cofilin pathway to control the dynamics of the actin cytoskeleton. The present results elucidate the signaling pathway activated by Nogo-66 to control LTP and contribute to the understanding of how Nogo-A stabilizes the neural circuits to limit activity-dependent plasticity events in the mature hippocampus.

Quantitative Phosphoproteomics Reveals a Role for Collapsin Response Mediator Protein 2 in PDGF-Induced Cell Migration

The Platelet Derived Growth Factor (PDGF) family of ligands have well established functions in the induction of cell proliferation and migration during development, tissue homeostasis and interactions between tumours and stroma. However, the mechanisms by which these actions are executed are incompletely understood. Here we report a differential phosphoproteomics study, using a SILAC approach, of PDGF-stimulated mouse embryonic fibroblasts (MEFs). 116 phospho-sites were identified as up-regulated and 45 down-regulated in response to PDGF stimulation. These encompass proteins involved in cell adhesion, cytoskeleton regulation and vesicle-mediated transport, significantly expanding the range of proteins implicated in PDGF signalling pathways. Included in the down-regulated class was the microtubule bundling protein Collapsin Response Mediator Protein 2 (CRMP2). In response to stimulation with PDGF, CRMP2 was dephosphorylated on Thr514, an event known to increase CRMP2 activity. This was reversed in the presence of micromolar concentrations of the protein phosphatase inhibitor okadaic acid, implicating PDGF-induced activation of protein phosphatase 1 (PP1) in CRMP2 regulation. Depletion of CRMP2 resulted in impairment of PDGF-mediated cell migration in an in vitro wound healing assay. These results show that CRMP2 is required for PDGF-directed cell migration in vitro.

Myelin-Associated Glycoprotein Inhibits Schwann Cell Migration and Induces Their Death

Remyelination of CNS axons by Schwann cells (SCs) is not efficient, in part due to the poor migration of SCs into the adult CNS. Although it is known that migrating SCs avoid white matter tracts, the molecular mechanisms underlying this exclusion have never been elucidated. We now demonstrate that myelin-associated glycoprotein (MAG), a well known inhibitor of neurite outgrowth, inhibits rat SC migration and induces their death via γ-secretase-dependent regulated intramembrane proteolysis of the p75 neurotrophin receptor (also known as p75 cleavage). Blocking p75 cleavage using inhibitor X (Inh X), a compound that inhibits γ-secretase activity before exposing to MAG or CNS myelin improves SC migration and survival in vitro Furthermore, mouse SCs pretreated with Inh X migrate extensively in the demyelinated mouse spinal cord and remyelinate axons. These results suggest a novel role for MAG/myelin in poor SC-myelin interaction and identify p75 cleavage as a mechanism that can be therapeutically targeted to enhance SC-mediated axon remyelination in the adult CNS.SIGNIFICANCE STATEMENT Numerous studies have used Schwann cells, the myelin-making cells of the peripheral nervous system to remyelinate adult CNS axons. Indeed, these transplanted cells successfully remyelinate axons, but unfortunately they do not migrate far and so remyelinate only a few axons in the vicinity of the transplant site. It is believed that if Schwann cells could be induced to migrate further and survive better, they may represent a valid therapy for remyelination. We show that myelin-associated glycoprotein or CNS myelin, in general, inhibit rodent Schwann cell migration and induce their death via cleavage of the neurotrophin receptor p75. Blockade of p75 cleavage using a specific inhibitor significantly improves migration and survival of the transplanted Schwann cells in vivo.

The Involvement of the Myelin-Associated Inhibitors and Their Receptors in CNS Plasticity and Injury

The limited capacity for the central nervous system (CNS) to repair itself was first described over 100 years ago by Spanish neuroscientist Ramon Y. Cajal. However, the exact mechanisms underlying this failure in neuronal regeneration remain unclear and, as such, no effective therapeutics yet exist. Numerous studies have attempted to elucidate the biochemical and molecular mechanisms that inhibit neuronal repair with increasing evidence suggesting that several inhibitory factors and repulsive guidance cues active during development actually persist into adulthood and may be contributing to the inhibition of repair. For example, in the injured adult CNS, there are various inhibitory factors that impede the outgrowth of neurites from damaged neurons. One of the most potent of these neurite outgrowth inhibitors is the group of proteins known as the myelin-associated inhibitors (MAIs), present mainly on the membranes of oligodendroglia. Several studies have shown that interfering with these proteins can have positive outcomes in CNS injury models by promoting neurite outgrowth and improving functional recovery. As such, the MAIs, their receptors, and downstream effectors are valid drug targets for the treatment of CNS injury. This review will discuss the current literature on MAIs in the context of CNS development, plasticity, and injury. Molecules that interfere with the MAIs and their receptors as potential candidates for the treatment of CNS injury will additionally be introduced in the context of preclinical and clinical trials.

TAT-PEP Enhanced Neurobehavioral Functional Recovery by Facilitating Axonal Regeneration and Corticospinal Tract Projection After Stroke

Paired immunoglobulin-like receptor B (PirB) has been identified as a new receptor for myelin-associated inhibitory (MAI) proteins, which may play important role in axonal regeneration and corticospinal tract (CST) projection associated with neurobehavioral function recovery after stroke. Here, we found that the expression of PirB was increased in the cortical penumbra from 1 to 28 days after transient focal cerebral ischemic reperfusion of rats. Then, transactivator of transcription-PirB extracellular peptide (TAT-PEP) was generated that might block the interactions between MAIs and PirB. The results showed that TAT-PEP displayed high affinity for MAIs and ameliorated their inhibitory effect on neurite growth. Furthermore, TAT-PEP can widely distribute in the penumbra after intraperitoneal injection. Then, we found that TAT-PEP enhanced neurite growth and alleviated growth cone collapse after oxygen glucose deprivation (OGD) injury. In addition, TAT-PEP promoted long-term neurobehavioral functional recovery through enhancing axonal regeneration and CST projection. Finally, the observations demonstrated that POSH/RhoA/growth-associated protein 43 (GAP43) as PirB-associated downstream signaling molecules played important role in neurobehavioral functional recovery after stroke. Moreover, the underlying mechanism associated with TAT-PEP-mediated promoting axonal regeneration and CST projection was by intervening in the expression of POSH, RhoA, and GAP43. These studies suggest that TAT-PEP may represent an attractive therapeutic strategy against stroke.

Anti-Nogo-A Immunotherapy Does Not Alter Hippocampal Neurogenesis after Stroke in Adult Rats

Ischemic stroke is a leading cause of adult disability, including cognitive impairment. Our laboratory has previously shown that treatment with function-blocking antibodies against the neurite growth inhibitory protein Nogo-A promotes functional recovery after stroke in adult and aged rats, including enhancing spatial memory performance, for which the hippocampus is critically important. Since spatial memory has been linked to hippocampal neurogenesis, we investigated whether anti-Nogo-A treatment increases hippocampal neurogenesis after stroke. Adult rats were subject to permanent middle cerebral artery occlusion followed 1 week later by 2 weeks of antibody treatment. Cellular proliferation in the dentate gyrus was quantified at the end of treatment, and the number of newborn neurons was determined at 8 weeks post-stroke. Treatment with both anti-Nogo-A and control antibodies stimulated the accumulation of new microglia/macrophages in the dentate granule cell layer, but neither treatment increased cellular proliferation or the number of newborn neurons above stroke-only levels. These results suggest that anti-Nogo-A immunotherapy does not increase post-stroke hippocampal neurogenesis.

Expression of Nogo receptor 1 in microglia during development and following traumatic brain injury

As the receptor of myelin associated inhibitory factors Nogo receptor 1 (NgR1) plays an important role in central nervous system (CNS) injury and regeneration. It is found that NgR1 complex acts in neurons to transduce the signals intracelluarly including induction of growth cone collapse, inhibition of axonal regeneration and regulation of nerve inflammation. In recent studies, NgR1 has also been found to be expressed in the microglia. However, NgR1 expressed in microglia in the developing nervous systems and following CNS injury have not been widely investigated. In this study, we detected the expression and cellular localization of NgR1 in microglia during development and following traumatic brain injury (TBI) in mice. The results showed that NgR1 was mainly expressed in microglia during embryonic and postnatal periods. The expression levels peaked at P4 and decreased thereafter into adulthood, while increased significantly with aging representatively at 17 mo. On the other hand, there was no significant difference in the number of double positive NgR1(+)Iba1(+) cells between normal and TBI group. In summary, we first detected the expression of NgR1 in microglia during development and found that NgR1 protein expression increased significantly in microglia with aging. These findings will contribute to make a foundation for subsequent study about the role of NgR1 expressed in microglia on the CNS disorders.

Non-canonical actions of Nogo-A and its receptors

Nogo-A is a myelin associated protein and one of the most potent neurite growth inhibitors in the central nervous system. Interference with Nogo-A signaling has thus been investigated as therapeutic target to promote functional recovery in CNS injuries. Still, the finding that Nogo-A presents a fairly ubiquitous expression in many types of neurons in different brain regions, in the eye and even in the inner ear suggests for further functions besides the neurite growth repression. Indeed, a growing number of studies identified a variety of functions including regulation of neuronal stem cells, modulation of microglial activity, inhibition of angiogenesis and interference with memory formation. Aim of the present commentary is to draw attention on these less well-known and sometimes controversial roles of Nogo-A. Furthermore, we are addressing the role of Nogo-A in neuropathological conditions such as ischemic stroke, schizophrenia and neurodegenerative diseases.

New Insights into the Roles of Nogo-A in CNS Biology and Diseases

Nogos have become a hot topic for its well-known number Nogo-A's big role in clinical matters. It has been recognized that the expression of Nogo-A and the receptor NgR1 inhibit the neuron's growth after CNS injuries or the onset of the MS. The piling evidence supports the notion that the Nogo-A is also involved in the synaptic plasticity, which was shown to negatively regulate the strength of synaptic transmission. The occurrence of significant schizophrenia-like behavioral phenotypes in Nogo-A KO rats also added strong proof to this conclusion. This review mainly focuses on the structure of Nogo-A and its corresponding receptor-NgR1, its intra- and extra-cellular signaling, together with its major physiological functions such as regulation of migration and distribution and its related diseases like stroke, AD, ALS and so on.

The Neural Stem Cell Microenvironment: Focusing on Axon Guidance Molecules and Myelin-Associated Factors

Neural stem cells (NSCs) could produce various cell phenotypes in the subventricular zone (SVZ) and dentate gyrus of the hippocampus in the central nervous system (CNS), where neurogenesis has been determined to occur. The extracellular microenvironment also influences the behaviors of NSCs during development and at CNS injury sites. Our previous study indicates that myelin, a component of the CNS, could regulate the differentiation of NSCs in vitro. Recent reports have implicated three myelin-derived inhibitors, NogoA, myelin-associated glycoprotein (MAG), and oligodendrocyte-myelin glycoprotein (OMgp), as well as several axon guidance molecules as regulators of NSC survival, proliferation, migration, and differentiation. However, the molecular mechanisms underlying the behavior of NSCs are not fully understood. In this study, we summarize the current literature on the effects of different extrinsic factors on NSCs and discuss possible mechanisms, as well as future possible clinical applications.

NogoR1 and PirB signaling stimulates neural stem cell survival and proliferation

Neural stem cells (NSCs) and neural progenitors (NPs) in the mammalian neocortex give rise to the main cell types of the nervous system. The biological behavior of these NSCs and NPs is regulated by extracellular niche derived autocrine-paracrine signaling factors on a developmental timeline. Our previous reports [Plos One 2010;5:e15341; J Neurochem 2011;117:565-578] have shown that chondroitin sulfate proteoglycan and ApolipoproteinE are autocrine-paracrine survival factors for NSCs. NogoA, a myelin related protein, is expressed in the cortical ventricular zones where NSCs reside. However, the functional role of Nogo signaling proteins in NSC behavior is not completely understood. In this study, we show that NogoA receptors, NogoR1 and PirB, are expressed in the ventricular zone where NSCs reside between E10.5 and 14.5 but not at E15.5. Nogo ligands stimulate NSC survival and proliferation in a dosage-dependent manner in vitro. NogoR1 and PirB are low and high affinity Nogo receptors, respectively and are responsible for the effects of Nogo ligands on NSC behavior. Inhibition of autocrine-paracrine Nogo signaling blocks NSC survival and proliferation. In NSCs, NogoR1 functions through Rho whereas PirB uses Shp1/2 signaling pathways to control NSC behavior. Taken together, this work suggests that Nogo signaling is an important pathway for survival of NSCs.

Tetraspanin-3 is an organizer of the multi-subunit Nogo-A signaling complex

To ensure precision and specificity of ligand – receptor induced signaling, co-receptors and modulatory factors play important roles. The membrane bound ligand Nogo-A induces inhibition of neurite outgrowth, cell spreading, adhesion and migration via multi-subunit receptor complexes. Here, we identified the 4-transmembrane-spanning protein tetraspanin-3 (TSPAN3) as a new modulatory co-receptor for the Nogo-A inhibitory domain Nogo-A-Δ20. Single-molecule-tracking showed that TSPAN3 molecules in the cell membrane reacted with elevated mobility to Nogo-A binding, followed by association with the signal transducing Nogo-A receptor sphingosine-1-phosphate receptor 2 (S1PR2). Subsequently, TSPAN3 was co-internalized as part of the Nogo-A ligand – receptor complex into early endosomes, where it subsequently separated from Nogo-A and S1PR2 to be recycled to the cell surface. The functional importance of the Nogo-A – TSPAN3 interaction is shown by the fact that knockdown of TSPAN3 strongly reduced the Nogo-A-induced S1PR2 clustering, RhoA activation and cell spreading and neurite outgrowth inhibition. In addition to the modulatory functions of TSPAN3 on Nogo-A-S1PR2 signaling, these results illustrate the very dynamic spatiotemporal reorganizations of membrane proteins during ligand-induced receptor complex organizations.

Cell type-specific Nogo-A gene ablation promotes axonal regeneration in the injured adult optic nerve

Nogo-A is a well-known myelin-enriched inhibitory protein for axonal growth and regeneration in the central nervous system (CNS). Besides oligodendrocytes, our previous data revealed that Nogo-A is also expressed in subpopulations of neurons including retinal ganglion cells, in which it can have a positive role in the neuronal growth response after injury, through an unclear mechanism. In the present study, we analyzed the opposite roles of glial versus neuronal Nogo-A in the injured visual system. To this aim, we created oligodendrocyte (Cnp-Cre(+/-)xRtn4/Nogo-A(flox/flox)) and neuron-specific (Thy1-Cre(tg+)xRtn4(flox/flox)) conditional Nogo-A knock-out (KO) mouse lines. Following complete intraorbital optic nerve crush, both spontaneous and inflammation-mediated axonal outgrowth was increased in the optic nerves of the glia-specific Nogo-A KO mice. In contrast, neuron-specific deletion of Nogo-A in a KO mouse line or after acute gene recombination in retinal ganglion cells mediated by adeno-associated virus serotype 2.Cre virus injection in Rtn4(flox/flox) animals decreased axon sprouting in the injured optic nerve. These results therefore show that selective ablation of Nogo-A in oligodendrocytes and myelin in the optic nerve is more effective at enhancing regrowth of injured axons than what has previously been observed in conventional, complete Nogo-A KO mice. Our data also suggest that neuronal Nogo-A in retinal ganglion cells could participate in enhancing axonal sprouting, possibly by cis-interaction with Nogo receptors at the cell membrane that may counteract trans-Nogo-A signaling. We propose that inactivating Nogo-A in glia while preserving neuronal Nogo-A expression may be a successful strategy to promote axonal regeneration in the CNS.

Nogo receptor inhibition enhances functional recovery following lysolecithin-induced demyelination in mouse optic chiasm

BACKGROUND

Inhibitory factors have been implicated in the failure of remyelination in demyelinating diseases. Myelin associated inhibitors act through a common receptor called Nogo receptor (NgR) that plays critical inhibitory roles in CNS plasticity. Here we investigated the effects of abrogating NgR inhibition in a non-immune model of focal demyelination in adult mouse optic chiasm.

METHODOLOGY/PRINCIPAL FINDINGS

A focal area of demyelination was induced in adult mouse optic chiasm by microinjection of lysolecithin. To knock down NgR levels, siRNAs against NgR were intracerebroventricularly administered via a permanent cannula over 14 days, Functional changes were monitored by electrophysiological recording of latency of visual evoked potentials (VEPs). Histological analysis was carried out 3, 7 and 14 days post demyelination lesion. To assess the effect of NgR inhibition on precursor cell repopulation, BrdU was administered to the animals prior to the demyelination induction. Inhibition of NgR significantly restored VEPs responses following optic chiasm demyelination. These findings were confirmed histologically by myelin specific staining. siNgR application resulted in a smaller lesion size compared to control. NgR inhibition significantly increased the numbers of BrdU+/Olig2+ progenitor cells in the lesioned area and in the neurogenic zone of the third ventricle. These progenitor cells (Olig2+ or GFAP+) migrated away from this area as a function of time.

CONCLUSIONS/SIGNIFICANCE

Our results show that inhibition of NgR facilitate myelin repair in the demyelinated chiasm, with enhanced recruitment of proliferating cells to the lesion site. Thus, antagonizing NgR function could have therapeutic potential for demyelinating disorders such as Multiple Sclerosis.

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.

Essential roles of zebrafish rtn4/Nogo paralogues in embryonic development

Background

As a consequence of gene/genome duplication, the RTN4/Nogo gene has two counterparts in zebrafish: rtn4a and rtn4b. The shared presence of four specific amino acid motifs—M1 to M4—in the N-terminal region of mammalian RTN4, and zebrafish Rtn4b suggests that Rtn4b is the closest homologue of mammalian Nogo-A.

Results

To explore their combined roles in zebrafish development, we characterized the expression patterns of rtn4a and rtn4b in a comparative manner and performed morpholino-mediated knockdowns. Although both genes were coexpressed in the neural tube and developing brain at early stages, they progressively acquired distinct expression domains such as the spinal cord (rtn4b) and somites (rtn4a). Downregulation of rtn4a and rtn4b caused severe brain abnormalities, with rtn4b knockdown severely affecting the spinal cord and leading to immobility. In addition, the retinotectal projection was severely affected in both morphants, as the retina and optic tectum appeared smaller and only few retinal axons reached the abnormally reduced tectal neuropil. The neuronal defects were more persistent in rtn4b morphants. Moreover, the latter often lacked pectoral fins and lower jaws and had malformed branchial arches. Notably, these defects led to larval death in rtn4b, but not in rtn4a morphants.

Conclusions

In contrast to mammalian Nogo-A, its zebrafish homologues, rtn4a and particularly rtn4b, are essential for embryonic development and patterning of the nervous system.

Two monoclonal antibodies recognising aa 634-668 and aa 1026-1055 of NogoA enhance axon extension and branching in cultured neurons

In a previous study, we generated two monoclonal antibodies (mAbs) in mice, aNogoA-N and aNogo-66 mAb, which were raised against recombinant N-terminal fragments of rat NogoA and Nogo-66, respectively. When compared with the commercial rabbit anti-rat NogoA polyclonal antibody (pAb), which can specifically recognise NogoA, the two mAbs were also specific for the NogoA antigen in immunofluorescence histochemical (IHC) staining and Western blot (WB) analysis. Serial truncations of NogoA covering the N-terminal region of NogoA (aa 570–691) and Nogo-66 (aa 1026–1091) were expressed in E. coli. The epitopes recognised by aNogoA-N and aNogo-66 are located in the aa 634–668 and aa 1026–1055 regions of NogoA, respectively. Both mAbs remarkably enhanced the axon growth and branching of cultured hippocampal neurons in vitro. These results suggest that the antibodies that bind to aa 634–668 and aa 1026–1055 of NogoA may have stimulatory effects on axon growth and branching. Additionally, the two mAbs that we generated are specific for NogoA and significantly block NogoA function. In conclusion, two sites in NogoA located within aa 634–668 and aa 1026–1055 are recognised by our two antibodies and are novel and potentially promising targets for repair after central nervous system (CNS) injury.

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.

Intracellular Nogo-A facilitates initiation of neurite formation in mouse midbrain neurons in vitro

Nogo-A is a transmembrane protein originally discovered in myelin, produced by postnatal CNS oligodendrocytes. Nogo-A induces growth cone collapse and inhibition of axonal growth in the injured adult CNS. In the intact CNS, Nogo-A functions as a negative regulator of growth and plasticity. Nogo-A is also expressed by certain neurons. Neuronal Nogo-A depresses long-term potentiation in the hippocampus and modulates neurite adhesion and fasciculation during development in mice. Here we show that Nogo-A is present in neurons derived from human midbrain (Lund human mesencephalic (LUHMES) cell line), as well as in embryonic and postnatal mouse midbrain (dopaminergic) neurons. In LUHMES cells, Nogo-A was upregulated threefold upon differentiation and neurite extension. Nogo-A was localized intracellularly in differentiated LUHMES cells. Cultured midbrain (dopaminergic) neurons from Nogo-A knock-out mice exhibited decreased numbers of neurites and branches when compared with neurons from wild-type (WT) mice. However, this phenotype was not observed when the cultures from WT mice were treated with an antibody neutralizing plasma membrane Nogo-A. In vivo, neither the regeneration of nigrostriatal tyrosine hydroxylase fibers, nor the survival of nigral dopaminergic neurons after partial 6-hydroxydopamine lesions was affected by Nogo-A deletion. These results indicate that during maturation of cultured midbrain (dopaminergic) neurons, intracellular Nogo-A supports neurite growth initiation and branch formation.

An open source based high content screening method for cell biology laboratories investigating cell spreading and adhesion

BACKGROUND

Adhesion dependent mechanisms are increasingly recognized to be important for a wide range of biological processes, diseases and therapeutics. This has led to a rising demand of pharmaceutical modulators. However, most currently available adhesion assays are time consuming and/or lack sensitivity and reproducibility or depend on specialized and expensive equipment often only available at screening facilities. Thus, rapid and economical high-content screening approaches are urgently needed.

RESULTS

We established a fully open source high-content screening method for identifying modulators of adhesion. We successfully used this method to detect small molecules that are able to influence cell adhesion and cell spreading of Swiss-3T3 fibroblasts in general and/or specifically counteract Nogo-A-Δ20-induced inhibition of adhesion and cell spreading. The tricyclic anti-depressant clomipramine hydrochloride was shown to not only inhibit Nogo-A-Δ20-induced cell spreading inhibition in 3T3 fibroblasts but also to promote growth and counteract neurite outgrowth inhibition in highly purified primary neurons isolated from rat cerebellum.

CONCLUSIONS

We have developed and validated a high content screening approach that can be used in any ordinarily equipped cell biology laboratory employing exclusively freely available open-source software in order to find novel modulators of adhesion and cell spreading. The versatility and adjustability of the whole screening method will enable not only centers specialized in high-throughput screens but most importantly also labs not routinely employing screens in their daily work routine to investigate the effects of a wide range of different compounds or siRNAs on adhesion and adhesion-modulating molecules.

N-Methyl-d-Aspartate Receptor - Nitric Oxide Synthase Pathway in the Cortex of Nogo-A-Deficient Rats in Relation to Brain Laterality and Schizophrenia

It has been suggested that Nogo-A, a myelin-associated protein, could play a role in the pathogenesis of schizophrenia and that Nogo-A-deficient rodents could serve as an animal model for schizophrenic symptoms. Since changes in brain laterality are typical of schizophrenia, we investigated whether Nogo-A-deficient rats showed any signs of disturbed asymmetry in cortical N-methyl-d-aspartate (NMDA) receptor–nitric oxide synthase (NOS) pathway, which is reported as dysfunctional in schizophrenia. In particular, we measured separately in the right and left hemisphere of young and old Nogo-A-deficient male rats the expression of NMDA receptor subunits (NR1, NR2A, and NR2B in the frontal cortex) and activities of NOS isoforms [neuronal (nNOS), endothelial (eNOS), and inducible (iNOS) in the parietal cortex]. In young controls, we observed right/left asymmetry of iNOS activity and three positive correlations (between NR1 in the left and NR2B laterality, between NR2B in the right and left sides, and between NR1 in the right side and nNOS laterality). In old controls, we found bilateral decreases in NR1, an increase in NR2B in the right side, and two changes in correlations in the NR1–nNOS pathway. In young Nogo-A-deficient rats, we observed an increase in iNOS activity in the left hemisphere and two changes in correlations in NR1–nNOS and NR2A–eNOS, compared to young controls. Finally, we revealed in old Nogo-A-deficient animals, bilateral decreases in NR1 and one change in correlation between eNOS–iNOS, compared to old controls. Although some findings from schizophrenic brains did not manifest in Nogo-A-deficient rats (e.g., no alterations in NR2B), others did (e.g., alterations demonstrating accelerated aging in young but not old animals, those occurring exclusively in the right hemisphere in young and old animals and those suggesting abnormal frontoparietal cortical interactions in young animals).

Nogo-A Represses Anatomical and Synaptic Plasticity in the Central Nervous System

Nogo-A was initially discovered as a myelin-associated growth inhibitory protein limiting axonal regeneration after central nervous system (CNS) injury. This review summarizes current knowledge on how myelin and neuronal Nogo-A and its receptors exert physiological functions ranging from the regulation of growth suppression to synaptic plasticity in the developing and adult intact CNS.

Nogo-A is a negative regulator of CNS angiogenesis

Nogo-A is an important axonal growth inhibitor in the adult and developing CNS. In vitro, Nogo-A has been shown to inhibit migration and cell spreading of neuronal and nonneuronal cell types. Here, we studied in vivo and in vitro effects of Nogo-A on vascular endothelial cells during angiogenesis of the early postnatal brain and retina in which Nogo-A is expressed by many types of neurons. Genetic ablation or virus-mediated knock down of Nogo-A or neutralization of Nogo-A with an antibody caused a marked increase in the blood vessel density in vivo. In culture, Nogo-A inhibited spreading, migration, and sprouting of primary brain microvascular endothelial cells (MVECs) in a dose-dependent manner and induced the retraction of MVEC lamellipodia and filopodia. Mechanistically, we show that only the Nogo-A-specific Delta 20 domain exerts inhibitory effects on MVECs, but the Nogo-66 fragment, an inhibitory domain common to Nogo-A, -B, and -C, does not. Furthermore, the action of Nogo-A Delta 20 on MVECs required the intracellular activation of the Ras homolog gene family, member A (Rho-A)-associated, coiled-coil containing protein kinase (ROCK)-Myosin II pathway. The inhibitory effects of early postnatal brain membranes or cultured neurons on MVECs were relieved significantly by anti-Nogo-A antibodies. These findings identify Nogo-A as an important negative regulator of developmental angiogenesis in the CNS. They may have important implications in CNS pathologies involving angiogenesis such as stroke, brain tumors, and retinopathies.

Distinct roles of Nogo-a and Nogo receptor 1 in the homeostatic regulation of adult neural stem cell function and neuroblast migration

In the adult mammalian subventricular zone (SVZ), GFAP-positive neural stem cells (NSCs) generate neuroblasts that migrate tangentially along the rostral migratory stream (RMS) toward the olfactory bulb (OB). In the mouse brain, we found that the plasticity inhibitors Nogo-A and Nogo receptor 1 (NgR1) are differentially expressed in the SVZ-OB system, in which Nogo-A identifies immature neuroblasts and NgR1 germinal astrocytes. We therefore examined the role of Nogo-A and NgR1 in the regulation of neurogenesis. Pharmacological experiments show that Nogo-66/NgR1 interaction reduces the proliferation of NSCs. This is consistent with a negative-feedback loop, in which newly generated neurons modulate cell division of SVZ stem cells. Moreover, the Nogo-A-Δ20 domain promotes neuroblast migration toward the OB through activation of the Rho/ROCK (Rho-associated, coiled-coil containing protein kinase) pathway, without the participation of NgR1. Our findings reveal a new unprecedented function for Nogo-A and NgR1 in the homeostatic regulation of the pace of neurogenesis in the adult mouse SVZ and in the migration of neuroblasts along the RMS.

Identification of a NEP1-35 recognizing peptide that neutralizes CNS myelin inhibition using phage display library

Nogo-A has been identified as an inhibitory molecule to neurite outgrowth after injury in adult mammalian central nervous system (CNS). The C-terminal fragment of Nogo-A, Nogo-66, inhibits axonal regrowth through NgR1 signaling. Residues 1-32 of Nogo-66 cover two regions that contribute most affinity of Nogo-66 to NgR1. It is unclear whether blocking the two regions with specific small ligands could neutralize the inhibition of Nogo-66. Therefore in this study we explored two phage display peptide libraries to screen small peptides that might bind Nogo-66. NEP1-35 containing 1-33 residues of Nogo-66 was taken as the target for panning. We found that phage-borne peptides with stronger affinity to NEP1-35 contained a relatively conserved motif, RRXXXXXXXRRX. Afterwards one identified peptide, NH(2)-RRQTLSHQMRRP-COOH was synthesized and tested in neurite outgrowth assay, in which this small molecule showed moderate ability to neutralize CNS myelin inhibition in vitro. Our results demonstrated that short peptides could act as adaptors to Nogo-66 and neutralize CNS myelin inhibition in vitro. Additionally, the results also suggested that phage display could help to discover novel small molecules with high affinity to CNS regrowth inhibitors, which might be able to promote CNS regeneration with fewer side effects since they could block only the corresponding regions of inhibitors.

Nogo and Nogo receptor: relevance to schizophrenia?

The membrane protein Nogo-A and its receptor NgR have been extensively characterized for their role in restricting axonal growth, regeneration, and plasticity in the central nervous system. Recent evidence suggests that Nogo and NgR might constitute candidate genes for schizophrenia susceptibility. In this article, we critically review the possibility that dysfunctions related to Nogo-A and NgR might contribute to increased risk for schizophrenia. To this end, we consider the most important insights that have emerged from human genetic and pathological studies and from experimental animal work. Furthermore, we discuss potential mechanisms of Nogo/NgR involvement in neural circuit development and stability, and how mutations or changes in expression levels of these proteins could be developmental risk factors contributing to schizophrenia.

Dibutyryl cyclic AMP inhibits the progression of experimental autoimmune encephalomyelitis and potentiates recruitment of endogenous neural stem cells

Multiple sclerosis is a chronic inflammatory demyelinating disease of the central nervous system. Cyclic AMP and its analogs enhance regeneration of adult mammalian central nervous system (CNS). Endogenous neural stem cells (NSCs) play a pivotal role in CNS regeneration, producing new neuron and glial cells. Here, we examined the effect of dibutyryl cyclic AMP (dbcAMP) on experimental autoimmune encephalomyelitis (EAE) symptoms, endogenous remyelination, and recruitment of NSCs. EAE was induced by immunizing mice using myelin oligodendrocyte glycoprotein peptide and pertussis toxin. Proliferative cells within CNS were labeled using repetitive systemic injections of 5-bromo-2-deoxyuridine (BrdU) before EAE induction. Myelin staining was performed using Luxol fast blue. The number of nestin(+) and BrdU(+) cells in subventricular zone (SVZ) and olfactory bulb (OB) was evaluated using immunohistochemistry. dbcAMP suppressed EAE progression and decreased the extent of demyelinated plaques in the lumbar spinal cord. EAE induction reduced the number of proliferative cells in SVZ and increased their population in OB. EAE also increased the number of nestin(+) cells in OB. We also found that dbcAMP increased the recruitment of NSCs into the OB and brain parenchyma of EAE mice. Our results suggest dbcAMP as a potential therapy for inducing myelin repair in the context of demyelinating diseases like multiple sclerosis. Its positive effect seems to be mediated, at least partially, by endogenous neural stem cells and their increased recruitment.

Time course and spatial profile of Nogo-A expression in experimental autoimmune encephalomyelitis in C57BL/6 mice

Inhibition of the myelin-associated neurite outgrowth inhibitor Nogo-A has been found to be beneficial in experimental autoimmune encephalomyelitis (EAE), but there are little data on its expression dynamics during the disease course. We analyzed Nogo-A mRNA and protein during the course of EAE in 27 C57BL/6 mice and in 8 controls. Histopathologic and molecular analyses were performed on Day 0 (naive), preclinical (Day 10), acute (Days 18-22) and chronic (Day 50) time points. In situ hybridization and real-time polymerase chain reaction analyses revealed reduced Nogo-A mRNA expression at preclinical (p < 0.0001) and acute phases (p < 0.0001), followed by upregulation during the chronic phase (p < 0.0001). Nogo-A mRNA was expressed in neurons and oligodendrocytes. By immunohistochemistry and Western blot, there was increased Nogo-A protein expression (p < 0.001) in the chronic phase. Moreover, spatial differences were observed within EAE lesions. The pattern of Nogo-A protein expression inversely correlated with axonal regeneration growth-associated protein 43-positive axons (60% of which were Nogo-A contact-free during the acute phase) and axonal injury (β-amyloid precursor protein-positive axons). Cortical Nogo-66 receptor protein and mRNA levels increased during the chronic phase. The results indicate that Nogo-A and Nogo receptor are actively regulated in EAE lesions; this may indicate a specific time window for localized axonal regeneration in the acute phase of EAE.

Dopaminergic neurons modulate GABA neuron migration in the embryonic midbrain

Neuronal migration, a key event during brain development, remains largely unexplored in the mesencephalon, where dopaminergic (DA) and GABA neurons constitute two major neuronal populations. Here we study the migrational trajectories of DA and GABA neurons and show that they occupy ventral mesencephalic territory in a temporally and spatially specific manner. Our results from the Pitx3-deficient aphakia mouse suggest that pre-existing DA neurons modulate GABA neuronal migration to their final destination, providing novel insights and fresh perspectives concerning neuronal migration and connectivity in the mesencephalon in normal as well as diseased brains.

The Nogo-66 receptor family in the intact and diseased CNS

The Nogo-66 receptor family (NgR) consists in three glycophosphatidylinositol (GPI)-anchored receptors (NgR1, NgR2 and NgR3), which are primarily expressed by neurons in the central and peripheral mammalian nervous system. NgR1 was identified as serving as a high affinity binding protein for the three classical myelin-associated inhibitors (MAIs) Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), which limit axon regeneration and sprouting in the injured brain. Recent studies suggest that NgR signaling may also play an essential role in the intact adult CNS in restricting axonal and synaptic plasticity and are involved in neurodegenerative diseases, particularly in Alzheimer's disease pathology through modulation of β-secretase cleavage. Here, we outline the biochemical properties of NgRs and their functional roles in the intact and diseased CNS.