Neuritin affects the activity of neuralized-like 1 by promoting degradation and weakening its affinity for substrate

Neuritin plays a key role in neural development and regeneration by promoting neurite outgrowth and synapse maturation. Our previous research revealed the mechanism by which neuritin inhibits Notch signaling through interaction with neuralized-like 1 (Neurl1) to promote neurite growth. However, how neuritin regulates Notch signaling through Neurl1 has not been elucidated. Here, we first confirm that neuritin is an upstream regulator of Neurl1 and inhibits Notch signaling through Neurl1. Neurl1 is an E3 ubiquitin ligase that can promote ubiquitination and endocytosis of the Notch1 ligand Jagged1. Therefore, we observe the effect of neuritin on the ligase activity of Neurl1. The results indicate that neuritin inhibits Neurl1 activity by reducing the ubiquitination level and endocytosis of the target protein Jagged1. Moreover, we find that decreased activity of Neurl1 results in reduced expression of Notch receptor Notch intracellular domain (NICD) and downstream target gene hairy and enhancer of split-1 ( HES1). Furthermore, we investigate how neuritin affects Neurl1 enzyme activity. The results show that neuritin not only weakens the affinity between Neurl1 and Jagged1 but also promotes the degradation of Neurl1 by the 26S proteasome pathway. Taken together, our results suggest that neuritin negatively regulates Notch signaling by inhibiting the activity of Neurl1, promoting the degradation of Neurl1 and weakening the affinity of Neurl1 for Jagged1. Our study clarifies the molecular mechanisms of neuritin in regulating the Notch signaling pathway and provides new clues about how neuritin mediates neural regeneration and plasticity.

Establishment and Functional Characterization of Murine Monoclonal Antibodies Recognizing Neuritin

Neuritin represents a neurotrophic factor that is not only important in neuronal development and plasticity but also impacts endothelial angiogenesis, cell migration, tumor growth and the production of antibodies by B cells. We established monoclonal mouse anti-mouse neuritin antibodies by immunizing knock-out mice with two different neuritin-derived peptides. Because neuritin is well conserved between species, these new monoclonal antibodies recognize the neuritin of a wide variety of species, including human. Moreover, they not only recognize specifically surface-bound neuritin expressed by murine follicular regulatory T cells but also the block binding of recombinant neuritin to germinal center B cells. This suggests that these newly generated tools will be of great use in studying neuritin expression and function.

Neuritin promotes angiogenesis through inhibition of DLL4/Notch signaling pathway

Neuritin is a member of the neurotrophic factor family, which plays an important role in the promotion and development of the nervous system. Neuritin is also involved in angiogenesis. Neuritin was recently found to be a negative regulatory factor of the Notch 1 signaling pathway. Notch signaling pathway is known as a regulatory pathway of angiogenesis. Thus, neuritin may play a role in angiogenesis through the Notch signaling pathway. In the present study, we investigated the expressions of neuritin and Notch signaling pathway factors in the pulmonary vascular tissue. The results showed that neuritin expression was increased in the paraneoplastic vascular tissue and decreased in the lung cancer vascular tissue. The neuritin expression was increased with the increase of vascular tissue density, and a negative correlation between neuritin expression and delta-like ligand 4 (DLL4) was identified in vascular tissues of lung cancer. Overexpression of neuritin in human umbilical vein endothelial cells (HUVECs) inhibited the expressions of Notch signaling pathway-associated factors, including DLL4, NICD, and Hes-1, and promoted the migration and tubular formation of HUVECs. In conclusion, our results indicated that neuritin is involved in angiogenesis and may play a role in angiogenesis through the Notch signaling pathway. This study provides a theoretical basis for clinical anti-angiogenesis therapy.

Neuritin inhibits astrogliosis to ameliorate diabetic cognitive dysfunction

Earlier, it was shown that reversing the downregulation of neuritin expression in the brain improves central neuropathy in diabetic rats. We investigated the protective mechanism of neuritin in diabetic cognitive dysfunction via astrocytes. Further, the impact of the overexpression of neuritin in the cortex and the hippocampus on diabetic cognitive dysfunction and astrogliosis in type 2 diabetic (db/db) mice was assessed. Antagonists were used to inhibit the JAK2/STAT3 signaling pathway in U-118MG, an astrocyte cell line. Immunofluorescence, Western blotting, and real-time PCR were performed. Neuritin overexpression in the hippocampus of db/db mice significantly ameliorated cognitive dysfunction, hippocampal neuronal impairment, and synaptic plasticity deterioration, and inhibited astrogliosis and the JAK2/STAT3 signaling pathway in the hippocampus. Neuritin suppressed the JAK2/STAT3 signaling pathway to inhibit lipopolysaccharide-induced gliosis in U-118MG cells. It was observed that neuritin regulates the JAK2/STAT3 signaling pathway in astrocytes to inhibit astrogliosis and improve diabetic cognitive dysfunction.

Follicular regulatory T cells produce neuritin to regulate B cells

Regulatory T cells prevent the emergence of autoantibodies and excessive IgE, but the precise mechanisms are unclear. Here, we show that BCL6-expressing Tregs, known as follicular regulatory T (Tfr) cells, produce abundant neuritin protein that targets B cells. Mice lacking Tfr cells or neuritin in Foxp3-expressing cells accumulated early plasma cells in germinal centers (GCs) and developed autoantibodies against histones and tissue-specific self-antigens. Upon immunization, these mice also produced increased plasma IgE and IgG1. We show that neuritin is taken up by B cells, causes phosphorylation of numerous proteins, and dampens IgE class switching. Neuritin reduced differentiation of mouse and human GC B cells into plasma cells, downregulated BLIMP-1, and upregulated BCL6. Administration of neuritin to Tfr-deficient mice prevented the accumulation of early plasma cells in GCs. Production of neuritin by Tfr cells emerges as a central mechanism to suppress B cell-driven autoimmunity and IgE-mediated allergies.

Neuritin-overexpressing transgenic mice demonstrate enhanced neuroregeneration capacity and improved spatial learning and memory recovery after ischemia-reperfusion injury

Acute ischemia-reperfusion (IR)-induced brain injury is further exacerbated by a series of slower secondary pathogenic events, including delayed apoptosis due to neurotrophic factor deficiency. Neuritin, a neurotrophic factor regulating nervous system development and plasticity, is a potential therapeutic target for treatment of IR injury. In this study, Neuritin-overexpressing transgenic (Tg) mice were produced by pronuclear injection and offspring with high overexpression used to generate a line with stable inheritance for testing the neuroprotective capacity of Neuritin against transient global ischemia (TGI). Compared to wild-type mice, transgenic mice demonstrated reduced degradation of the DNA repair factor poly [ADP-ribose] polymerase 1 (PARP 1) in the hippocampus, indicating decreased hippocampal apoptosis rate, and a greater number of surviving hippocampal neurons during the first week post-TGI. In addition, Tg mice showed increased expression of the regeneration markers NF-200, synaptophysin, and GAP-43, and improved recovery of spatial learning and memory. Our findings exhibited that the window of opportunity of neural recovery in Neuritin transgenic mice group had a tendency to move ahead after TGI, which indicated that Neuritin can be used as a potential new therapeutic strategy for improving the outcome of cerebral ischemia injury.

CPG15/Neuritin Mimics Experience in Selecting Excitatory Synapses for Stabilization by Facilitating PSD95 Recruitment

A key feature of brain plasticity is the experience-dependent selection of optimal connections· implemented by a set of activity-regulated genes that dynamically adjust synapse strength and number. The activity-regulated gene cpg15/neuritin has been previously implicated in stabilization and maturation of excitatory synapses. Here· we combine two-photon microscopy with genetic and sensory manipulations to dissect excitatory synapse formation in vivo and examine the role of activity and CPG15 in dendritic spine formation, PSD95 recruitment, and synapse stabilization. We find that neither visual experience nor CPG15 is required for spine formation. However, PSD95 recruitment to nascent spines and their subsequent stabilization requires both. Further, cell-autonomous CPG15 expression is sufficient to replace experience in facilitating PSD95 recruitment and spine stabilization. CPG15 directly interacts with α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors on immature dendritic spines, suggesting a signaling mode for this small extracellular molecule acting as an experience-dependent “selector” for spine stabilization and synapse maturation.

Experience plays a key role in formation and continuous optimization of brain circuits. Subramanian et al. show that the molecule CPG15/neuritin can replace experience in selecting which nascent contacts between neurons are retained, facilitating the recruitment of proteins that promote synapse maturation and stabilization.

Exogenous neuritin treatment improves survivability and functions of Schwann cells with improved outgrowth of neurons in rat diabetic neuropathy

Pathogenesis and treatment for diabetic neuropathy are still complex. A deficit of neurotrophic factors affecting Schwann cells is a very important cause of diabetic neuropathy. Neuritin is a newly discovered potential neurotrophic factor. In this study, we explored the effect of exogenous neuritin on survivability and functions of diabetic Schwann cells of rats with experimental diabetic neuropathy. Diabetic neuropathy was induced in rats. 12‐week diabetic rats contrasted with non‐diabetic normal rats had decreased levels of serum neuritin and slowed nerve conduction velocities (NCVs). Schwann cells isolated from these diabetic rats and cultured in high glucose showed reduced cell neuritin mRNA and protein and supernatant neuritin protein, increased apoptosis rates, increased caspase‐3 activities and progressively reduced viability. In contrast, exogenous neuritin treatment reduced apoptosis and improved viability, with elevated Bcl‐2 levels (not Bax) and decreased caspase‐3 activities. Co‐cultured with diabetic Schwann cells pre‐treated with exogenous neuritin in high glucose media, and diabetic DRG neurons showed lessened decreased neurite outgrowth and supernatant NGF concentration occurring in co‐culture of diabetic cells. Exogenous neuritin treatment ameliorated survivability and functions of diabetic Schwann cells of rats with diabetic neuropathy. Our study may provide a new mechanism and potential treatment for diabetic neuropathy.

The Biological-Behavioral Effect Of Neuritin On Non-Small Cell Lung Cancer Vascular Endothelial Cells Via VEGFR And Notch1

Purpose

This study aims to elucidate the biological behavior of Neuritin abnormal expression in pulmonary vascular endothelial cells (VECs) of non-small cell lung cancer (NSCLC), and explore its possible underlying mechanisms.

Patients and methods

Primary NSCLC-VECs were isolated from 10 cancer tissues from NSCLC patients, purified and identified by CD34 and Factor VIII staining. Real-time PCR and Western-blot were adopted for detecting the expression levels of Neuritin, Notch1, and VEGFR in NSCLC-VECs and HPMECs. Neuritin-overexpression, Neuritin-knockdown NSCLC-VECs and HPMECs were constructed by transfection of pcDNA3, 1-Neuritin vector, and pBS/U6-Neuritin siRNA. Changes in cell proliferation, migration, cell cycle, and apoptosis were determined by using the MTT assay, scratch assay, transwell migration assay, and flow cytometry, respectively. Post-transfection changes in cell morphology were examined by scanning electron microscopy.

Results

The expression of Neuritin in NSCLC-VECs was significantly higher compared to that in HPMECs (p<0.01). Overexpression of Neuritin increased the expression of VEGFR while it reduced the expression of Notch1 (p<0.01); it also promoted cell proliferation, scratch healing, and in vitro migration (p<0.05) in HPMECs and NSCLC-VECs cells. Additionally, overexpression of Neuritin stimulated cell cycle progression and inhibited apoptosis in HPMECs and NSCLC-VECs (p<0.001). Under electron microscope, the pseudopodium of cell surface was obvious, indicating that the intercellular adhesion was upregulated. However, knockdown of Neuritin in HPMECs and NSCLC-VECs played exactly the opposite roles.

Conclusion

Neuritin was key in the progression of NSCLC through its biological activities, including anti-apoptosis, promoting VEC proliferation, migration, and cell cycle progression. Neuritin may affect its biological activity by positively regulating VEGFR expression and negatively regulating Notch1 signaling. Neuritin may serve as a potential biomarker for NSCLC.

Production of polyclonal antibody against human Neuritin and its application of immunodetection

OBJECTIVE

To date, a commercial antibody to human Neuritin for immunoprecipitation is still limited. In this study, we aimed to develop a specific antibody for further research on the potential function of Neuritin.

METHODS AND RESULTS

By epitope prediction of recombinant human Neuritin, the active fragment of human Neuritin that could be used as an excellent immunogen. Soluble His-tagged Neuritin was expressed and purified from Pichia pastoris. Polyclonal antibody against Neuritin was obtained by immunizing Sprague-Dawley rats with purified recombinant human Neuritin. Affinity-purified polyclonal antibody against Neuritin was characterized with indirect enzyme-linked immunosorbent assay, immunoblotting, immunoprecipitation, and immunofluorescence. The results demonstrated that the polyclonal antibody against Neuritin had been prepared successfully. The prepared antibody bound to both exogenous and endogenous Neuritin. Importantly, the anti-Neuritin polyclonal antibody could be used in immunoprecipitation assays.

CONCLUSIONS

The prepared polyclonal antibody could be used in immunoprecipitation and provide researchers with a useful tool for further investigating the function and mechanism of Neuritin.

Functions and the related signaling pathways of the neurotrophic factor neuritin

Neuritin is a member of the neurotrophic factor family, which is activated by neural activity and neurotrophins, and promotes neurite growth and branching. It has shown to play an important role in neuronal plasticity and regeneration. It is also involved in other biological processes such as angiogenesis, tumorigenesis and immunomodulation. Thus far, however, the primary mechanisms of neuritin, including whether or not it acts through a receptor or which downstream signals might be activated following binding, are not fully understood. Recent evidence suggests that neuritin may be a potential therapeutic target in several neurodegenerative diseases. This review focuses on the recent advances in studies regarding the newly identified functions of neuritin and the signaling pathways related to these functions. We also discuss current hot topics and difficulties in neuritin research.

Neuritin promotes neurite and spine growth in rat cerebellar granule cells via L-type calcium channel-mediated calcium influx

Neuritin is a neurotrophic factor that is activated by neural activity and neurotrophins. Its major function is to promote neurite growth and branching; however, the underlying mechanisms are not fully understood. To address this issue, this study investigated the effects of neuritin on neurite and spine growth and intracellular Ca²⁺ concentration in rat cerebellar granule neurons (CGNs). Incubation of CGNs for 24 h with neuritin increased neurite length and spine density; this effect was mimicked by insulin and abolished by inhibiting insulin receptor (IR) or mitogen‐activated protein kinase kinase/extracellular signal‐regulated kinase (ERK) activity. Calcium imaging and western blot analysis revealed that neuritin enhanced the increase in intracellular Ca²⁺ level induced by high K⁺, and stimulated the cell surface expression of Ca_V1.2 and Ca_V1.3 α subunits of the L‐type calcium channel, which was suppressed by inhibition of IR or mitogen‐activated protein kinase kinase/ERK. Treatment with inhibitors of L‐type calcium channels, calmodulin, and calcineurin (CaN) abrogated the effects of neuritin on neurite length and spine density. A similar result was obtained by silencing nuclear factor of activated T cells c4, which is known to be activated by neuritin in CGNs. These results indicate that IR and ERK signaling as well as the Ca²⁺/CaN/nuclear factor of activated T cells c4 axis mediate the effects of neuritin on neurite and spine growth in CGNs.

Open Practices

Open Science: This manuscript was awarded with the Open Materials Badge.

For more information see: https://cos.io/our-services/open-science-badges/

Cover Image for this issue: doi: 10.1111/jnc.14195.

Neuritin provides neuroprotection against experimental traumatic brain injury in rats

OBJECTIVES

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Neuritin is a neurotrophic factor that regulates neural growth and development. However, the role of neuritin in alleviating TBI has not been investigated.

METHODS

In this study, Sprague Dawley rats (n = 144) weighing 300 ± 50 g were categorized into control, sham, TBI and TBI + neuritin groups. The neurological scores and the ultrastructure of cortical neurons, apoptotic cells and caspase-3 were measured by using Garcia scoring system, transmission electron microscopy, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, Western blot analysis and real-time RT-PCR at various time points post-TBI.

CONCLUSIONS

Our findings indicated that neuritin plays a protective role in TBI by improving neurological scores, repairing injured neurons and protecting the cortical neurons against apoptosis through inhibition of caspase-3 expression. Further investigation of the molecular mechanisms underlying caspase-3 inhibition by neuritin will provide a research avenue for potential TBI therapeutics.

Neuritin Inhibits Notch Signaling through Interacted with Neuralized to Promote the Neurite Growth

Neuritin plays a key role in neural development and regeneration by promoting neurite outgrowth and synapse maturation. However, the mechanism of neuritin in modulating neurite growth has not been elucidated. Here, using yeast two-hybrid we screened and discovered the interaction of neuritin and neuralized (NEURL1), which is an important regulator that can activate Notch signaling through promoting endocytosis of Notch ligand. And then we identified the interaction of neuritin and neuralized by co-immunoprecipitation (IP) assays, and clarified that neuritin and NEURL1 were co-localized on the cell membrane of SH-SY5Y cells. Moreover, neuritin significantly suppressed Notch ligand Jagged1 (JAG1) endocytosis promoted by NEURL1, and then inhibited the activation of Notch receptor Notch intracellular domain (NICD) and decreased the expression of downstream gene hairy and enhancer of split-1 (HES1). Importantly, the effect of neuritin on inhibiting Notch signaling was rescued by NEURL1, which indicated that neuritin is an upstream and negative regulator of NEURL1 to inhibit Notch signaling through interaction with NEURL1. Notably, recombinant neuritin restored the retraction of neurites caused by activation of Notch, and neurite growth stimulated by neuritin was partially blocked by NEURL1. These findings establish neuritin as an upstream and negative regulator of NEURL1 that inhibits Notch signaling to promote neurite growth. This mechanism connects neuritin with Notch signaling, and provides a valuable foundation for further investigation of neuritin's role in neurodevelopment and neural plasticity.

Corrigendum: Recombinant hNeuritin Promotes Structural and Functional Recovery of Sciatic Nerve Injury in Rats

[This corrects the article on p. 589 in vol. 10, PMID: 28066172.].

Transcript levels of plastin 3 and neuritin 1 modifier genes in spinal muscular atrophy siblings

BACKGROUND

In single gene disorders, patients with the same genotype may have variations in severity. One of the main factors affecting disease severity is modifier genes. Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by degeneration of alpha motor neurons. Plastin 3 (PLS3) is a phenotypic modifier of SMA, and neuritin 1 (NRN1) has also been suggested as a possible modifier gene. The aim of the present study was therefore to analyze PLS3 and NRN1 expression in SMA siblings in four families.

METHODS

The study group consisted of four SMA families with seven with discordant phenotype and two affected siblings. Total RNA was isolated from whole blood. PLS3 and NRN1 expression was analyzed on quantitative real-time polymerase chain reaction.

RESULTS

In family 1 only NRN1 expression was increased in the mildly affected sister. In family 2 only PLS3 had a modifier effect. Family 3, which had type III siblings with identical clinical phenotypes, had similar PLS3 expression between the siblings but no NRN1 expression. In family 4, neither PLS3 nor NRN1 had any correlation with severity.

CONCLUSION

On analysis of the expression of NRN1 in SMA patients for the first time, NRN1 could be a potential modifier gene. PLS3 expression does not always modify SMA phenotype. In patients with no modifier effect of known genes, genome sequencing and transcriptome analysis are promising for the identification of novel modifiers and understanding of SMA pathophysiology.

Recombinant hNeuritin Promotes Structural and Functional Recovery of Sciatic Nerve Injury in Rats

Neuritin is a new neurotropic factor implicated in nervous system development and plasticity. Studies have shown that Neuritin is upregulated in injured nerves, suggesting that it is involved in nerve repair. To test this hypothesis, we investigated whether recombinant human Neuritin could restore nerve structure and function in a rat model of sciatic nerve injury. Neuritin treatment had a dose-dependent effect on functional recovery 4 weeks after injury, as determined by the walking-track test. Similar trends were observed for gastrocnemius muscular strength and nerve conduction velocity. Additionally, sciatic nerve fiber density and organization as well as degree of remyelination were increased, while growth-associated protein 43 and neurofilament 200 expression was upregulated upon treatment with Neuritin. These findings demonstrate that Neuritin stimulates nerve regeneration and functional recovery and thus promotes the repair of injured sciatic nerves.

Overexpression of neuritin in gastric cancer

The aim of the present study was to investigate the expression of neuritin in gastric cancer tissues, in order to explore the association between the expression of neuritin and the occurrence and development of gastric cancer. Tissue specimens were collected from 58 patients with gastric cancer. Immunohistochemistry, western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine the expression of neuritin in the gastric cancer and corresponding adjacent normal gastric tissues. The expression rate of neuritin in gastric cancer tissues was 96.55% (56/58), demonstrating no statistically significant difference from the expression rate in the adjacent normal tissues (94.83%) (P>0.05). However, the rate of strong neuritin expression in gastric cancer tissues (82.76%) was significantly increased compared with the rate in the adjacent normal tissues (15.52%) (P<0.05). Neuritin expression exhibited no correlation with the gender or age of patients, tumor-node-metastasis staging, tumor depth, presence of lymph node metastasis, histological or pathological type of the tumor or presence of distant metastasis (P>0.05). As determined by RT-PCR and western blot analysis, the mRNA expression of neuritin in gastric cancer tissues was markedly increased compared with the expression in the adjacent normal tissues. In conclusion, neuritin is highly expressed in gastric cancer tissues, suggesting that neuritin may act as a novel potential target for the treatment of gastric cancer.

Supraphysiological doses of performance enhancing anabolic-androgenic steroids exert direct toxic effects on neuron-like cells

Anabolic-androgenic steroids (AAS) are lipophilic hormones often taken in excessive quantities by athletes and bodybuilders to enhance performance and increase muscle mass. AAS exert well known toxic effects on specific cell and tissue types and organ systems. The attention that androgen abuse has received lately should be used as an opportunity to educate both athletes and the general population regarding their adverse effects. Among numerous commercially available steroid hormones, very few have been specifically tested for direct neurotoxicity. We evaluated the effects of supraphysiological doses of methandienone and 17-α-methyltestosterone on sympathetic-like neuron cells. Vitality and apoptotic effects were analyzed, and immunofluorescence staining and western blot performed. In this study, we demonstrate that exposure of supraphysiological doses of methandienone and 17-α-methyltestosterone are toxic to the neuron-like differentiated pheochromocytoma cell line PC12, as confirmed by toxicity on neurite networks responding to nerve growth factor and the modulation of the survival and apoptosis-related proteins ERK, caspase-3, poly (ADP-ribose) polymerase and heat-shock protein 90. We observe, in contrast to some previous reports but in accordance with others, expression of the androgen receptor (AR) in neuron-like cells, which when inhibited mitigated the toxic effects of AAS tested, suggesting that the AR could be binding these steroid hormones to induce genomic effects. We also note elevated transcription of neuritin in treated cells, a neurotropic factor likely expressed in an attempt to resist neurotoxicity. Taken together, these results demonstrate that supraphysiological exposure to the AAS methandienone and 17-α-methyltestosterone exert neurotoxic effects by an increase in the activity of the intrinsic apoptotic pathway and alterations in neurite networks.

Developmental regulation of CPG15 expression in Xenopus

Mechanisms controlling dendritic arbor formation affect the establishment of neuronal circuits. Candidate plasticity gene 15 (CPG15) is a glycosylphosphatidyl inositol (GPI)-linked activity-induced protein that has been shown to function as an intercellular signaling molecule that can promote the morphological and physiological development of the Xenopus retinotectal system. A thorough understanding of CPG15 function requires knowledge of the spatiotemporal expression of the endogenous protein. We therefore cloned Xenopus cpg15 and used RNA in situ hybridization and immunohistochemistry to determine the pattern of CPG15 expression. cpg15 mRNA and CPG15 protein are first detectable in the developing spinal cord and become widespread as development proceeds. CPG15 is expressed in sensory regions of the brain, including the visual, auditory, and olfactory systems. Within the retina, CPG15 is only expressed in retinal ganglion cells. CPG15 protein is concentrated in axon tracts, including retinal axons. These data support a model in which CPG15 expressed in retinal ganglion cells is trafficked to retinal axons, where it modulates postsynaptic dendritic arbor elaboration, and synaptic maturation.