Nogo Receptor Research Articles

Alterations of p75 neurotrophin receptor and Myelin transcription factor 1 in the hippocampus of perinatal phencyclidine treated rats.

Postnatal administration of phencyclidine (PCP) in rodents causes major disturbances to neurological processes resulting in severe modifications to normal behavioral traits into adulthood. It is routinely used to model psychiatric disorders such as schizophrenia, producing many of the dysfunctional processes in the brain that are present in this devastating disorder, including elevated levels of apoptosis during neurodevelopment and disruptions to myelin and plasticity processes. Lingo-1 (or Leucine-rich repeat and immunoglobulin domain-containing protein) is responsible for negatively regulating neurite outgrowth and the myelination of axons. Recent findings using a postmortem human brain cohort showed that Lingo-1 signaling partners in the Nogo receptor (NgR)/p75/TNF receptor orphan Y (TROY) signaling complex, and downstream signaling partners With No Lysine (K) (WNK1) and Myelin transcription factor 1 (Myt1), play a significant part in schizophrenia pathophysiology. Here we have examined the implication of Lingo-1 and its signaling partners in a neurodevelopmental model of schizophrenia using PCP to determine if these pathways are altered in the hippocampus throughout different stages of neurodevelopment. Male Sprague-Dawley rats were injected subcutaneously with PCP (10mg/kg) or saline solution on postnatal days (PN) 7, 9, and 11. Rats (n=6/group) were sacrificed at PN12, 5weeks, or 14weeks. Relative expression levels of Lingo-1 signaling proteins were examined in the hippocampus of the treated rats. p75 and Myt1 were decreased (0.001≤p≤0.011) in the PCP treated rats at PN12. There were no significant changes in any of the tested proteins at 5weeks (p>0.05). At 14weeks, p75, TROY, and Myt1 were increased in the PCP treated rats (0.014≤p≤0.022). This is the first report of an alteration in Lingo-1 signaling proteins in the rat hippocampus, both directly after PCP treatment in early development and in adulthood. Based on our results, we propose that components of the Lingo-1 signaling pathways may be involved in the acute neurotoxicity induced by perinatal administration of PCP in rats early in development and suggest that this may have implications for the hippocampal deficits seen in schizophrenia.

Metallothionein-I/II Promotes Axonal Regeneration in the Central Nervous System

The adult CNS does not spontaneously regenerate after injury, due in large part to myelin-associated inhibitors such as myelin-associated glycoprotein (MAG), Nogo-A, and oligodendrocyte-myelin glycoprotein. All three inhibitors can interact with either the Nogo receptor complex or paired immunoglobulin-like receptor B. A conditioning lesion of the sciatic nerve allows the central processes of dorsal root ganglion (DRG) neurons to spontaneously regenerate in vivo after a dorsal column lesion. After a conditioning lesion, DRG neurons are no longer inhibited by myelin, and this effect is cyclic AMP (cAMP)- and transcription-dependent. Using a microarray analysis, we identified several genes that are up-regulated both in adult DRGs after a conditioning lesion and in DRG neurons treated with cAMP analogues. One gene that was up-regulated under both conditions is metallothionein (MT)-I. We show here that treatment with two closely related isoforms of MT (MT-I/II) can overcome the inhibitory effects of both myelin and MAG for cortical, hippocampal, and DRG neurons. Intrathecal delivery of MT-I/II to adult DRGs also promotes neurite outgrowth in the presence of MAG. Adult DRGs from MT-I/II-deficient mice extend significantly shorter processes on MAG compared with wild-type DRG neurons, and regeneration of dorsal column axons does not occur after a conditioning lesion in MT-I/II-deficient mice. Furthermore, a single intravitreal injection of MT-I/II after optic nerve crush promotes axonal regeneration. Mechanistically, MT-I/II ability to overcome MAG-mediated inhibition is transcription-dependent, and MT-I/II can block the proteolytic activity of α-secretase and the activation of PKC and Rho in response to soluble MAG.

LINGO-1 Protein Interacts with the p75 Neurotrophin Receptor in Intracellular Membrane Compartments

Axon outgrowth inhibition in response to trauma is thought to be mediated via the binding of myelin-associated inhibitory factors (e.g. Nogo-66, myelin-associated glycoprotein, oligodendrocyte myelin glycoprotein, and myelin basic protein) to a putative tripartite LINGO-1·p75(NTR)·Nogo-66 receptor (NgR) complex at the cell surface. We found that endogenous LINGO-1 expression in neurons in the cortex and cerebellum is intracellular. Mutation or truncation of the highly conserved LINGO-1 C terminus altered this intracellular localization, causing poor intracellular retention and increased plasma membrane expression. p75(NTR) associated predominantly with natively expressed LINGO-1 containing immature N-glycans, characteristic of protein that has not completed trans-Golgi-mediated processing, whereas mutant forms of LINGO-1 with enhanced plasma membrane expression did not associate with p75(NTR). Co-immunoprecipitation experiments demonstrated that LINGO-1 and NgR competed for binding to p75(NTR) in a manner that is difficult to reconcile with the existence of a LINGO-1·p75(NTR)·NgR ternary complex. These findings contradict models postulating functional LINGO-1·p75(NTR)·NgR complexes in the plasma membrane.

Effect of recombinant human granulocyte colony-stimulating factor on Nogo receptor expression in the brain tissues of neonatal rats after hypoxic-ischemic brain damage

Objective To observe the different effects of 2 doses recombinant human granulocyte colony-stimulating factors(rhG-CSF)on Nogo receptor(NgR)expression in the brain tissue of neonatal rats after hypoxic-ischemic brain damage(HIBD)at different times in order to reveal the neuroprotective effects of rhG-CSF. Methods Seven-day neonatal Sprague-Dawley(SD)rats were randomly divided into 4 groups by drawing method: sham operation group, model group, low-dose rhG-CSF group and high-dose rhG-CSF group, 24 rats in each group.Then each group was divided into 4 subgroups(6 rats in each subgroup)and all rats were exterminated at different times after HIBD(1 d, 3 d, 7 d and 14 d). In the low-dose rhG-CSF group and high-dose rhG-CSF group, the rats were given daily doses of rhG-CSF 50 μg/kg, 100 μg/kg respectively for 7 days by subcutaneous injection immediately after the molding(total 7 injections). In model group, rats received an injection of same amount of 9 g/L saline.In sham operation group, rats received no special treatment.Brain tissues of rats from each group were collected at different time points.The expressions of NgR protein and NgR mRNA in the left brain tissue were detected by immunohistochemistry and real-time fluorescent quantitative polymerase chain reaction(PCR). Results Immunohistochemistry: NgR proteins were constitutively expressed in the cerebral cortex in sham operation group at each time point; compared with sham operation group, the expressions of NgR in model group were increased markedly at each time point (135.67±16.63, 173.98±17.82, 234.00±14.70, 319.59±25.22), and the differences were statistically significant(all P<0.01); compared with model group, the expressions of NgR in the cerebral cortex in low-dose rhG-CSF group (134.35±8.89, 109.04±12.62, 75.99±13.39)and high-dose rhG-CSF group (81.38±12.25, 80.14±10.50, 72.58±13.66) on the 3rd, 7th, 14th day were reduced significantly(all P<0.01). Compared with low-dose rhG-CSF group, the protein expressions of NgR in the high-does rhG-CSF group were decreased faster, and had the marked difference on the 3rd, 7th day (P<0.05). Real-time fluorescent quantitative PCR: compared with the sham operation group, the expressions of NgR mRNA increased gradually in the cerebral cortex in the model group (1.34±0.24, 1.88±0.27, 2.88±0.84, 4.26±0.86), the differences in NgR mRNA expression were statistically significant at different times(all P<0.05); compared with model group, the expressions of NgR mRNA in low-dose rhG-CSF group on the 7th (1.08±0.30), 14th day (0.93±0.26) and high-dose rhG-CSF group on the 3rd(0.61±0.10), 7th(0.56±0.28), 14th day (0.47±0.12) were significantly different(all P<0.05). The expressions of low-dose group and high-dose group were reduced gradually.The NgR mRNA expression reduced more quickly in the high-dose group than in the low-dose rhG-CSF group and had substantial difference between two groups in 3 days (P<0.05). Conclusions The findings suggest that rhG-CSF intervention can reduce the expressions of NgR in the brain tissues of neonatal rats after HIBD, and low-dose rhG-CSF also has neuroprotective effect, but it could be weaker than high-dose rhG-CSF. Key words: Recombinant human granulocyte colony-stimulating factor; Hypoxic ischemic brain damage; Nogo receptor

Recombinant Nogo-66 via soluble expression with SUMO fusion in Escherichia coli inhibits neurite outgrowth in vitro.

Nogo-66, a hydrophilic loop of 66 amino acids flank two hydrophobic domains of the Nogo-A C terminus, interacts with the Nogo-66 receptor (NgR) to exert numerous functions in the central nervous system (CNS). Nogo-66 has important roles in aspects of neuronal development, including cell migration, axon guidance, fasciculation, and dendritic branching, and in aspects of CNS plasticity, including oligodendrocyte differentiation and myelination. Here, the small ubiquitin-related modifier (SUMO) was fused to the target gene, Nogo-66, and the construct was expressed in Escherichia coli (E. coli). Under the optimal fermentation conditions, the soluble expression level of the fusion protein was 33 % of the total supernatant protein. After cleaving the fusion proteins with SUMO protease and purifying them by Ni-NTA affinity chromatography, the yield and purity of recombinant Nogo-66 obtained by 10-L scale fermentation were 23 ± 1.5 mg/L and greater than 93 %, respectively. The authenticity of the recombinant Nogo-66 was confirmed by an electrospray ionization-mass spectrometry analysis. The functional analyses indicated that the recombinant Nogo-66 was capable of binding the NgR specifically. The immunofluorescence results showed that the recombinant Nogo-66 could significantly inhibit neurite outgrowth of rat pheochromocytoma (PC12) cells stimulated by nerve growth factor and cerebellar granule cells (CGCs). Furthermore, Nogo-66 inhibited neurite outgrowth by increasing the level of phosphorylated Rho-associated coiled-coil-containing protein kinase 2 (ROCK2), collapsin response mediator protein 2 (CRMP2), and myosin light chain (MLC). This study provided a feasible and convenient production method for generating sufficient recombinant Nogo-66 for experimental and clinical applications.

Effects of N-Butylphthalide on the expressions of Nogo/NgR in rat brain tissue after carbon monoxide poisoning

Carbon monoxide (CO) intoxication is one of the most common types of poisoning worldwide, and may result in neuropathologic sequelae, yet its pathogenesis is not clear and there is no optimal management strategy for patients with CO poisoning. In this study, the rat model of CO poisoning was established in a hyperbaric chamber by CO exposure. Rats were administered orally N-Butylphthalide (NBP) at a dose of 1ml/100g. Neuronal apoptosis was assessed by TUNEL stain and flow cytometry. The expressions of neurite outgrowth inhibitor (Nogo), myelin-associated glycoprotein (MAG) and Nogo receptor-1 (NgR1) were observed in rat brain tissue by immunohistochemistry and double immunofluorescence staining. As we expected, CO poisoning could start the mechanism of apoptosis. The number of apoptotic cells and the early neuronal apoptosis percentage (EAR) were significantly increased at 1 day, 3 day after CO exposure. NBP treatment obviously reduce neuronal apoptosis and the EAR (P<0.05). CO poisoning could induce Nogo, MAG and NgR1 expressions. The increased Nogo, MAG and NgR1 proteins were still observed at 4 week after CO poisoning. NBP could significantly reduce the levels of Nogo and NgR1 proteins. Then we suspected that the expressions of Nogo, MAG and NGR1 proteins might be associated with brain injury and demyelination induced by CO poisoning. NBP might inhibit neuronal apoptosis and the EAR, down-regulate the expressions of Nogo and NgR1 proteins (but not MAG), and play a neuro-protective role in brain damage after acute CO poisoning.

Increased migration of olfactory ensheathing cells secreting the Nogo receptor ectodomain over inhibitory substrates and lesioned spinal cord.

Olfactory ensheathing cell (OEC) transplantation emerged some years ago as a promising therapeutic strategy to repair injured spinal cord. However, inhibitory molecules are present for long periods of time in lesioned spinal cord, inhibiting both OEC migration and axonal regrowth. Two families of these molecules, chondroitin sulphate proteoglycans (CSPG) and myelin-derived inhibitors (MAIs), are able to trigger inhibitory responses in lesioned axons. Mounting evidence suggests that OEC migration is inhibited by myelin. Here we demonstrate that OEC migration is largely inhibited by CSPGs and that inhibition can be overcome by the bacterial enzyme Chondroitinase ABC. In parallel, we have generated a stable OEC cell line overexpressing the Nogo receptor (NgR) ectodomain to reduce MAI-associated inhibition in vitro and in vivo. Results indicate that engineered cells migrate longer distances than unmodified OECs over myelin or oligodendrocyte-myelin glycoprotein (OMgp)-coated substrates. In addition, they also show improved migration in lesioned spinal cord. Our results provide new insights toward the improvement of the mechanisms of action and optimization of OEC-based cell therapy for spinal cord lesion.

Nogo Receptor 1 Limits Ocular Dominance Plasticity but not Turnover of Axonal Boutons in a Model of Amblyopia.

The formation and stability of dendritic spines on excitatory cortical neurons are correlated with adult visual plasticity, yet how the formation, loss, and stability of postsynaptic spines register with that of presynaptic axonal varicosities is unknown. Monocular deprivation has been demonstrated to increase the rate of formation of dendritic spines in visual cortex. However, we find that monocular deprivation does not alter the dynamics of intracortical axonal boutons in visual cortex of either adult wild-type (WT) mice or adult NgR1 mutant (ngr1-/-) mice that retain critical period visual plasticity. Restoring normal vision for a week following long-term monocular deprivation (LTMD), a model of amblyopia, partially restores ocular dominance (OD) in WT and ngr1-/- mice but does not alter the formation or stability of axonal boutons. Both WT and ngr1-/- mice displayed a rapid return of normal OD within 8 days after LTMD as measured with optical imaging of intrinsic signals. In contrast, single-unit recordings revealed that ngr1-/- exhibited greater recovery of OD by 8 days post-LTMD. Our findings support a model of structural plasticity in which changes in synaptic connectivity are largely postsynaptic. In contrast, axonal boutons appear to be stable during changes in cortical circuit function.

Intravitreal delivery of human NgR-Fc decoy protein regenerates axons after optic nerve crush and protects ganglion cells in glaucoma models.

Glaucoma is a major cause of vision loss due to retinal ganglion cell (RGC) degeneration. Therapeutic intervention controls increased IOP, but neuroprotection is unavailable. NogoReceptor1 (NgR1) limits adult central nervous system (CNS) axonal sprouting and regeneration. We examined NgR1 blocking decoy as a potential therapy by defining the pharmacokinetics of intravitreal NgR(310)-Fc, its promotion of RGC axonal regeneration following nerve crush, and its neuroprotective effect in a microbead glaucoma model. Human NgR1(310)-Fc was administered intravitreally, and levels were monitored in rat vitreal humor and retina. Axonal regeneration after optic nerve crush was assessed by cholera toxin β anterograde labeling. In a microbead model of glaucoma with increased IOP, the number of surviving and actively transporting RGCs was determined after 4 weeks by retrograde tracing with Fluro-Gold (FG) from the superior colliculus. After intravitreal bolus administration, the terminal half-life of NgR1(310)-Fc between 1 and 7 days was approximately 24 hours. Injection of 5 μg protein once per week after optic nerve crush injury significantly increased RGCs with regenerating axons. Microbeads delivered to the anterior chamber increased pressure, and caused 15% reduction in FG-labeled RGCs of control rats, with a 40% reduction in large diameter RGCs. Intravitreal treatment with NgR1(310)-Fc did not reduce IOP, but maintained large diameter RGC density at control levels. Human NgR1(310)-Fc has favorable pharmacokinetics in the vitreal space and rescues large diameter RGC counts from increased IOP. Thus, the NgR1 blocking decoy protein may have efficacy as a disease-modifying therapy for glaucoma.

Association of cerebrospinal fluid levels of lateral olfactory tract usher substance (LOTUS) with disease activity in multiple sclerosis.

Although multiple sclerosis (MS) is generally considered an autoimmune demyelinating disorder of the central nervous system, axonal degeneration through Nogo receptor-1 signaling was recently recognized as an important pathological feature. Our previous identification of lateral olfactory tract usher substance (LOTUS), an endogenous Nogo receptor-1 antagonist, prompted us to analyze the relationship between LOTUS levels of cerebrospinal fluid and the clinical course of MS to evaluate whether LOTUS could be a useful biomarker for MS. To examine variations in LOTUS concentrations in the cerebrospinal fluid of patients with MS in accordance with their clinical course. Cerebrospinal fluid samples were obtained retrospectively from normal controls (NCs; n = 27) and patients with MS (n = 40), amyotrophic lateral sclerosis (n = 22), and multiple system atrophy (n = 10) between January 1, 2008, and January 1, 2014. Patients with MS were divided into relapsing-remitting MS (RRMS; n = 30) and secondary progressive MS (n = 10). Patients with RRMS were further divided into relapse and remission groups. The LOTUS concentration in cerebropsinal fluid was quantitatively detected by immunoblotting using a specific LOTUS antibody and the concentrations compared in accordance with the patients' clinical course, such as remission and relapse groups in RRMS and secondary progressive MS. The mean (SD) cerebrospinal fluid LOTUS concentration in the relapse group of RRMS (9.3 [3.6] µg/dL) was lower than that of NCs (19.2 [4.7] µg/dL; P < .001) whereas the level in the remission group of RRMS (19.6 [5.8] µg/dL) was similar to that of NCs. The LOTUS concentration in SPMS (6.7 [1.4] µg/dL; P < .001) was lower than that of NCs and the remission group of RRMS. The LOTUS levels in other neurodegenerative diseases, such as amyotrophic lateral sclerosis and multiple system atrophy, were normal. Variations in LOTUS concentrations were correlated with disease activity in MS. Therefore, LOTUS concentration may be useful as a possible biomarker for MS. Low LOTUS concentrations may be possibly involved in Nogo receptor-1 signaling, which may induce axonal degeneration in the relapse phase of RRMS and secondary progressive MS.

Plasticity of intact rubral projections mediates spontaneous recovery of function after corticospinal tract injury.

Axons in the adult CNS fail to regenerate after injury, and therefore recovery from spinal cord injury (SCI) is limited. Although full recovery is rare, a modest degree of spontaneous recovery is observed consistently in a broad range of clinical and nonclinical situations. To define the mechanisms mediating spontaneous recovery of function after incomplete SCI, we created bilaterally complete medullary corticospinal tract lesions in adult mice, eliminating a crucial pathway for voluntary skilled movement. Anatomic and pharmacogenetic tools were used to identify the pathways driving spontaneous functional recovery in wild-type and plasticity-sensitized mice lacking Nogo receptor 1. We found that plasticity-sensitized mice recovered 50% of normal skilled locomotor function within 5 weeks of lesion. This significant, yet incomplete, spontaneous recovery was accompanied by extensive sprouting of intact rubrofugal and rubrospinal projections with the emergence of a de novo circuit between the red nucleus and the nucleus raphe magnus. Transient silencing of this rubro-raphe circuit in vivo via activation of the inhibitory DREADD (designer receptor exclusively activated by designer drugs) receptor hM4di abrogated spontaneous functional recovery. These data highlight the pivotal role of uninjured motor circuit plasticity in supporting functional recovery after trauma, and support a focus of experimental strategies on enhancing intact circuit rearrangement to promote functional recovery after SCI.

Nogo-A and its functions beyond axonal inhibition: the controversial role of Nogo-A in Parkinson's disease.

Nogo-A belongs to the reticulon family (RTN4) and is generally assumed to be one of the most potent myelin associated neurite outgrowth inhibitors in the central nervous system (CNS). Together with other inhibitors such as the myelin associated glycoprotein (MAG), oligodendrocyte myelin glycoprotein (OMgp), several semaphorins and ephrins as well as chondriotin sulphate proteoglycans, Nogo-A contributes to a nonpermissive environment in the brain and spinal cord. Based on their seminal observation that neurons grown in close proximity to CNS derived oligodendrocytes showed a robust decrease in neurite outgrowth and number of processes, Schwab and Caroni (1988) postulated for nonpermissive substrate properties present in the CNS myelin. In further studies, they identified a high molecular weight component from the CNS myelin called NI-250 which was later renamed Nogo-A. In the course it could be demonstrated that Nogo-A is expressed on the surface of oligodendrocytes and is responsible for the inhibition of axonal sprouting. Since the nonpermissive environment plays a very important role in brain injuries and neurodegenerative diseases, Nogo-A and its receptors were extensively studied.

LOTUS, a potent blocker of Nogo receptor-1 causing inhibition of axonal growth.

Glia-derived axonal growth inhibitory proteins limit functional repair following damage to the adult central nervous system (CNS). Nogo proteins, myelin-associated glycoprotein (MAG), oligodendrocyte myelin glycoprotein (OMgp) and B lymphocyte stimulator (BLyS), are 4 inhibitors that commonly interact with the neuronal receptor, Nogo receptor-1 (NgR1), leading to inhibition of axonal growth. Here, we demonstrate that lateral olfactory tract usher substance (LOTUS) binds to NgR1 and blocks the binding of all four ligands to NgR1, resulting in the suppression of axonal growth inhibition induced by these NgR1 ligands. LOTUS allows neurons to overcome NgR1-mediated axonal growth inhibition, raising the possibility that LOTUS may be useful in future therapeutic approaches as an endogenous potent inhibitor of NgR1 for promoting neuronal regeneration.

Axon regeneration impediment: the role of paired immunoglobulin-like receptor B.

Regenerative capacity is weak after central nervous system injury because of the absence of an enhancing microenvironment and presence of an inhibitory microenvironment for neuronal and axonal repair. In addition to the Nogo receptor (NgR), the paired immunoglobulin-like receptor B (PirB) is a recently discovered coreceptor of Nogo, myelin-associated glycoprotein, and myelin oligodendrocyte glycoprotein. Concurrent blocking of NgR and PirB almost completely eliminates the inhibitory effect of myelin-associated inhibitory molecules on axonal regeneration. PirB participates in a key pathological process of the nervous system, specifically axonal regeneration inhibition. PirB is an inhibitory receptor similar to NgR, but their effects are not identical. This study summarizes the structure, distribution, relationship with common nervous system diseases, and known mechanisms of PirB, and concludes that PirB is also distributed in cells of the immune and hematopoietic systems. Further investigations are needed to determine if immunomodulation and blood cell migration involve inhibition of axonal regeneration.

NgR1 Expressed in P19 Embryonal Carcinoma Cells Differentiated by Retinoic Acid Can Activate STAT3.

NgR1, a Nogo receptor, is involved in inhibition of neurite outgrowth and axonal regeneration and regulation of synaptic plasticity. P19 embryonal carcinoma cells were induced to differentiate into neuron-like cells using all trans-retinoic acid and the presence and/or function of cellular molecules, such as NgR1, NMDA receptors and STAT3, were examined. Neuronally differentiated P19 cells expressed the mRNA and protein of NgR1, which could stimulate the phosphorylation of STAT3 when activated by Nogo-P4 peptide, an active segment of Nogo-66. During the whole period of differentiation, mRNAs of all of the NMDA receptor subtypes tested (NR1, NR2A-2D) were consistently expressed, which meant that neuronally differentiated P19 cells maintained some characteristics of neurons, especially central nervous system neurons. Our results suggests that neuronally differentiated P19 cells expressing NgR1 may be an efficient and convenient in vitro model for studying the molecular mechanism of cellular events that involve NgR1 and its binding partners, and for screening compounds that activate or inhibit NgR1.

The p75 neurotrophin receptor: at the crossroad of neural repair and death

The strong repair and pro-survival functions of neurotrophins at their primary receptors, TrkA, TrkB and TrkC, have made them attractive candidates for treatment of nervous system injury and disease. However, difficulties with the clinical implementation of neurotrophin therapies have prompted the search for treatments that are stable, easier to deliver and allow more precise regulation of neurotrophin actions. Recently, the p75 neurotrophin receptor (p75NTR) has emerged as a potential target for pharmacological control of neurotrophin activity, supported in part by studies demonstrating 1) regulation of neural plasticity in the mature nervous system, 2) promotion of adult neurogenesis and 3) increased expression in neurons, macrophages, microglia, astrocytes and/or Schwann cells in response to injury and neurodegenerative diseases. Although the receptor has no intrinsic catalytic activity it interacts with and modulates the function of TrkA, TrkB, and TrkC, as well as sortilin and the Nogo receptor. This provides substantial cellular and molecular diversity for regulation of neuron survival, neurogenesis, immune responses and processes that support neural function. Upregulation of the p75NTR under pathological conditions places the receptor in a key position to control numerous processes necessary for nervous system recovery. Support for this possibility has come from recent studies showing that small, non-peptide p75NTR ligands can selectively modify pro-survival and repair functions. While a great deal remains to be discovered about the wide ranging functions of the p75NTR, studies summarized in this review highlight the immense potential for development of novel neuroprotective and neurorestorative therapies.

Co-culture of oligodendrocytes and neurons can be used to assess drugs for axon regeneration in the central nervous system.

We present a novel in vitro model in which to investigate the efficacy of experimental drugs for the promotion of axon regeneration in the central nervous system. We co-cultured rat hippocampal neurons and cerebral cortical oligodendrocytes, and tested the co-culture system using a Nogo-66 receptor antagonist peptide (NEP1–40), which promotes axonal growth. Primary cultured oligodendrocytes suppressed axonal growth in the rat hippocampus, but NEP1–40 stimulated axonal growth in the co-culture system. Our results confirm the validity of the neuron-oligodendrocyte co-culture system as an assay for the evaluation of drugs for axon regeneration in the central nervous system.

Genetic variants in Nogo receptor signaling pathways may be associated with early life adversity in schizophrenia susceptibility

BackgroundSchizophrenia is a severe neuropsychiatric disorder thought to result from abnormal brain development. Nogo, an oligodendrocyte bound molecule, signals by binding to the Nogo receptor (NgR) located on axonal membranes. The NgR co-receptors include p75 neurotrophin receptor or TNF receptor orphan Y (TROY). Nogo signaling is responsible for central nervous system myelin regulation and neurite outgrowth during neurodevelopment, and plasticity in the mature brain. MethodsWe examined single nucleotide polymorphisms (SNPs) in NgR, p75, and TROY receptor genes and downstream signaling partner With No Lysine (K) (WNK1) and Myelin transcription factor 1-like (Myt1l) genes in an Australian case–control schizophrenia cohort (n=268/group). High-throughput SNP genotyping was performed using the MassARRAY® genotyping assay. ResultsAnalysis revealed a significant association between the Myt1l SNP rs2304008 and female schizophrenia subjects. The WNK1 SNP rs1468326 and the Myt1l SNP rs3748988 showed significant associations with schizophrenia in subjects with a maternal mental history and in subjects who experienced childhood trauma respectively. Following Bonferroni correction, all significance was lost. ConclusionsDespite the lack of positive findings in our population after correction for multiple testing, previous gene expression and association studies in schizophrenia suggest the implication of NgR signaling pathway genes in the etiology of schizophrenia remains topical and timely. General significanceFurther investigations will be necessary to fully assess the role of these genes in the pathophysiology of schizophrenia. However these genes may prove useful in further understanding the mechanism by which negative experiences early in life can affect myelin-related processes in the context of schizophrenia.

Modulation of the proteoglycan receptor PTPσ promotes recovery after spinal cord injury.

SummaryContusive spinal cord injury (SCI) leads to a variety of disabilities due to limited neuronal regeneration and functional plasticity. It is well established that an upregulation of glial derived chondroitin sulfate proteoglycans (CSPGs) within the glial scar and perineuronal net (PNN) creates a barrier to axonal regrowth and sprouting1–5.Protein Tyrosine Phosphatase σ (PTPσ), along with its sister phosphatase Leukocyte common Antigen-Related (LAR), and the Nogo Receptors 1 and 3 (NgR) have recently been identified as receptors for the inhibitory glycosylated side chains of CSPGs6–8. We found that PTPσ plays a critical role in converting growth cones into a dystrophic state by tightly stabilizing them within CSPG-rich substrates. We generated a membrane-permeable peptide mimetic of the PTPσ wedge domain that binds to PTPσ and relieves CSPG-mediated inhibition. Systemic delivery of this peptide over weeks restored substantial serotonergic innervation to the spinal cord below the level of injury and facilitated functional recovery of both locomotor and urinary systems. Our results add a new layer of understanding to the critical role of PTPσ in mediating the growth-inhibited state of neurons due to CSPGs within the injured adult spinal cord.

Ameliorative Effects of p75NTR-ED-Fc on Axonal Regeneration and Functional Recovery in Spinal Cord-Injured Rats.

As a co-receptor of Nogo-66 receptor (NgR) and a critical receptor for paired immunoglobulin-like receptor (PirB), p75 neurotrophin receptor (p75NTR) mediates the inhibitory effects of myelin-associated inhibitors on axonal regeneration after spinal cord injury. Therefore, the p75NTR antagonist, such as recombinant p75NTR protein or its homogenates may block the inhibitory effects of myelin and promote the axonal regeneration and functional recovery. The purposes of this study are to subclone and express the extracellular domain gene of human p75NTR with IgG-Fc (hp75NTR-ED-Fc) in prokaryotic expression system and investigate the effects of the recombinant protein on axonal regeneration and functional recovery in spinal cord-injured rats. The hp75NTR-ED-Fc coding sequence was amplified from pcDNA-hp75NTR-ED-Fc by polymerase chain reaction (PCR) and subcloned into vector pET32a (+), then the effects of the purified recombinant protein on neurite outgrowth of dorsal root ganglion (DRG) neurons cultured with myelin-associated glycoprotein (MAG) were determined, and the effects of the fusion protein on axonal regeneration, functional recovery, and its possible mechanisms in spinal cord-injured rats were further investigated. The results indicated that the purified infusion protein could promote neurite outgrowth of DRG neurons, promote axonal regeneration and functional recovery, and decrease RhoA activation in spinal cord-injured rats. Taken together, the findings revealed that p75NTR still may be a potential and novel target for therapeutic intervention for spinal cord injury and that the hp75NTR-ED-Fc fusion protein treatment enhances functional recovery by limiting tissue loss and stimulating axonal growth in spinal cord-injured rats, which may result from decreasing the activation of RhoA.