Netrin-1 Alleviates Early Brain Injury by Regulating Ferroptosis via the PPARγ/Nrf2/GPX4 Signaling Pathway Following Subarachnoid Hemorrhage.

Subarachnoid hemorrhage (SAH) is a type of stroke with high morbidity and mortality. Netrin-1 (NTN-1) can alleviate early brain injury (EBI) following SAH by enhancing peroxisome proliferator-activated receptor gamma (PPARγ), which is an important transcriptional factor modulating lipid metabolism. Ferroptosis is a newly discovered type of cell death related to lipid metabolism. However, the specific function of ferroptosis in NTN-1-mediated neuroprotection following SAH is still unclear. This study aimed to evaluate the neuroprotective effects and the possible molecular basis of NTN-1 in SAH-induced EBI by modulating neuronal ferroptosis using the filament perforations model of SAH in mice and the hemin-stimulated neuron injury model in HT22 cells. NTN-1 or a vehicle was administered 2 h following SAH. We examined neuronal death, brain water content, neurological score, and mortality. NTN-1 treatment led to elevated survival probability, greater survival of neurons, and increased neurological score, indicating that NTN-1-inhibited ferroptosis ameliorated neuron death in vivo/in vitro in response to SAH. Furthermore, NTN-1 treatment enhanced the expression of PPARγ, nuclear factor erythroid 2-related factor 2 (Nrf2), and glutathione peroxidase 4 (GPX4), which are essential regulators of ferroptosis in EBI after SAH. The findings show that NTN-1 improves neurological outcomes in mice and protects neurons from death caused by neuronal ferroptosis. Furthermore, the mechanism underlying NTN-1 neuroprotection is correlated with the inhibition of ferroptosis, attenuating cell death via the PPARγ/Nrf2/GPX4 pathway and coenzyme Q10-ferroptosis suppressor protein 1 (CoQ10-FSP1) pathway.

Radioprotective effect of Ginkgolide B on brain: the mediating role of DCC/MST1 signaling.

PURPOSE: The risk of brain exposure to ionizing radiation increases gradually due to the extensive application of nuclear technology in medical, industrial, and aerospace fields. Radiation-induced brain injury (RBI) is highly likely to cause a wide range of neurological complications, including schizophrenia, Alzheimer's disease (AD), depression. Ginkgolide B (GB) is one of the effective active components extracted from ginkgo biloba leaves, exerts protective effects on CNS, which is involved in the regulation of the Hippo signaling pathway. MST1, as one of the core kinases of the Hippo pathway, participated in regulating cell proliferation, differentiation, and apoptosis. However, it remains unclear whether GB attenuates radiation brain injury (RBI) and whether the radioprotective effect of GB refers to MST1 signaling. Hence, our study aimed to explore the radiation protection effect and the potential mechanism of GB. MATERIALS AND METHODS: C57BL/6 mice were stimulated with an X-ray (20 Gy) to establish an RBI model. Then, morris water maze test (MWM) and step-down passive avoidance test (SDPAT) were used to assess the learning and memory function of mice. The open field test (OFT), tail suspension test (TST), and forced swimming test (FST) were used to assess changes in locomotor activity and hopelessness. Besides, X-ray-stimulated SH-SY5Y cells were used to verify the radioprotective effect of GB. Immunofluorescence double staining, Dihydroethidium (DHE), western blot, and flow cytometry were used to explore the role of DCC/MST1 signaling in RBI. RESULTS: In this study, X-ray-treated mice exhibited cognitive impairment and depression-like behavior, which was ameliorated by GB treatment. GB also reduced the ROS production and the number of TUNEL-positive cells in the hippocampus. Moreover, GB increased the protein levels of p-AKT and Bcl2, while decreased the protein levels of MST1, p-p38, p-JNK, cleaved-caspase-3 and Bax both in vivo and in vitro. Additionally, exogenous Netrin-1 alleviated X-ray-induced ROS production and apoptosis, whereas knockout of Netrin-1 receptor DCC abolished the protective effect of GB. CONCLUSION: Oxidative stress and MST1-mediated neuronal apoptosis participated in radiation-induced cognitive impairment and depression-like behaviors, and modulation of DCC by GB was an effective intervention against RBI.

Activation of vascular endothelial cells by synovial fibrosis promotes Netrin-1-induced sensory nerve sprouting and exacerbates pain sensitivity.

Synovial fibrosis is one of the most dominant histopathological changes in osteoarthritis of the knee (KOA), and activation of vascular endothelial cells in synovial fibrosis is both an important factor in mediating pain in KOA and a major contributor to the generation of pain signals. At the same time, angiogenesis and nerve fibres are more likely to underlie the pathology of pain induced by synovial fibrosis. In the present study, we established a co-culture model of human umbilical vein endothelial cells (HUVECs) with dorsal root ganglion (DRG) and detected tissue and cellular Netrin-1, vascular cell adhesion molecule-1 (VCAM-1), intercellular cell adhesion molecule-1 (ICAM-1), growth-associated protein-43 (GAP43), colorectal cancer deleted (DCC), uncoordinated 5 (UNC5), and the related expression of calcitonin gene-related peptide (CGRP), substance P (SP) and nerve growth factor (NGF) in supernatant by ELISA to investigate the intervention of vascular endothelial cell activation on sensory nerve sprouting exacerbating peripheral pain sensitivity and to investigate the effect of Netrin-1 from the perspective of Netrin-1 secretion to illustrate its effector mechanism.

Viral delivery of L1CAM promotes axonal extensions by embryonic cerebral grafts in mouse brain.

Cell replacement therapy is expected as a new and more radical treatment against brain damage. We previously reported that transplanted human cerebral organoids extend their axons along the corticospinal tract in rodent brains. The axons reached the spinal cord but were still sparse. Therefore, this study optimized the host brain environment by the adeno-associated virus (AAV)-mediated expression of axon guidance proteins in mouse brain. Among netrin-1, SEMA3, and L1CAM, only L1CAM significantly promoted the axonal extension of mouse embryonic brain tissue-derived grafts. L1CAM was also expressed by donor neurons, and this promotion was exerted in a haptotactic manner by their homophilic binding. Primary cortical neurons cocultured on L1CAM-expressing HEK-293 cells supported this mechanism. These results suggest that optimizing the host environment by the AAV-mediated expression of axon guidance molecules enhances the effect of cell replacement therapy.

Netrin-1 upregulates GPX4 and prevents ferroptosis after traumatic brain injury via the UNC5B/Nrf2 signaling pathway.

AIM: We aimed to investigate the regulatory role of Netrin-1 (NTN1) in ferroptosis after traumatic brain injury (TBI) in mice. METHODS: We assessed the expression pattern of NTN1 by RT-PCR, western blot, and immunofluorescence after establishing the TBI model in mice. After treatment with NTN1 shRNA or recombinant NTN1, we determined the biochemical and morphological changes associated with ferroptosis and netrin-1-related pathways. We used Nissl staining to assess lesion volume and Morris water maze and beam-walking test to evaluate ethological manifestation. RESULTS: The mRNA and protein levels of NTN1 were upregulated after TBI. The application of NTN1 shRNA increased the number of FJB positive cells, malondialdehyde (MDA), and reactive oxygen species (ROSs) levels. However, the application of NTN1 recombinant had the opposite effect. Furthermore, knockdown or inhibition of GPX4, Nrf2, and UNC5B counteracted the effects of NTN1 recombinant. Intravenous injection of NTN1 recombinant reduced neuronal loss after CCI and improved motor and cognitive function. CONCLUSION: NTN1 had a neuroprotective effect after TBI and inhibited ferroptosis via activating the UNC5B/Nrf2 pathway. These findings may provide potential therapeutic strategies for TBI.

Netrin-1 induces the anti-apoptotic and pro-survival effects of B-ALL cells through the Unc5b-MAPK axis.

BACKGROUND: B-cell acute lymphoblastic leukemia (B-ALL) comprises over 85% of all acute lymphoblastic leukemia (ALL) cases and is the most common childhood malignancy. Although the 5 year overall survival of patients with B-ALL exceeds 90%, patients with relapsed or refractory B-ALL may suffer from poor prognosis and adverse events. The axon guidance factor netrin-1 has been reported to be involved in the tumorigenesis of many types of cancers. However, the impact of netrin-1 on B-ALL remains unknown. METHODS: The expression level of netrin-1 in peripheral blood samples of children with B-ALL and children without neoplasia was measured by enzyme-linked immunosorbent assay (ELISA) kits. Then, CCK-8 cell proliferation assays and flow cytometric analysis were performed to detect the viability and apoptosis of B-ALL cells (Reh and Sup B15) treated with exogenous recombinant netrin-1 at concentrations of 0, 25, 50, and 100 ng/ml. Furthermore, co-immunoprecipitation(co-IP) was performed to detect the receptor of netrin-1. UNC5B expression interference was induced in B-ALL cells with recombinant lentivirus, and then CCK-8 assays, flow cytometry assays and western blotting assays were performed to verify that netrin-1 might act on B-ALL cells via the receptor Unc5b. Finally, western blotting and kinase inhibitor treatment were applied to detect the downstream signaling pathway. RESULTS: Netrin-1 expression was increased in B-ALL, and netrin-1 expression was upregulated in patients with high- and intermediate-risk stratification group of patients. Then, we found that netrin-1 induced an anti-apoptotic effect in B-ALL cells, implying that netrin-1 plays an oncogenic role in B-ALL. co-IP results showed that netrin-1 interacted with the receptor Unc5b in B-ALL cells. Interference with UNC5B was performed in B-ALL cells and abolished the antiapoptotic effects of netrin-1. Further western blotting was applied to detect the phosphorylation levels of key molecules in common signaling transduction pathways in B-ALL cells treated with recombinant netrin-1, and the FAK-MAPK signaling pathway was found to be activated. The anti-apoptotic effect of netrin-1 and FAK-MAPK phosphorylation was abrogated by UNC5B interference. FAK inhibitor treatment and ERK inhibitor treatment were applied and verified that the FAK-MAPK pathway may be downstream of Unc5b. CONCLUSION: Taken together, our findings suggested that netrin-1 induced the anti-apoptotic effect of B-ALL cells through activation of the FAK-MAPK signaling pathway by binding to the receptor Unc5b. Video Abstract.

Spinal TRPA1 Contributes to the Mechanical Hypersensitivity Effect Induced by Netrin-1.

Netrin-1, a chemoattractant expressed by floor plate cells, and one of its receptors (deleted in colorectal cancer) has been associated with pronociceptive actions in a number of pain conditions. Here, we addressed the question of whether spinal TRPC4/C5 or TRPA1 are among the downstream receptors contributing to pronociceptive actions induced by netrin-1. The experiments were performed on rats using a chronic intrathecal catheter for administration of netrin-1 and antagonists of TRPC4/C5 or TRPA1. Pain sensitivity was assessed behaviorally by using mechanical and heat stimuli. Effect on the discharge rate of rostral ventromedial medullary (RVM) pain control neurons was studied in lightly anesthetized animals. Netrin-1, in a dose-related fashion, induced mechanical hypersensitivity that lasted up to three weeks. Netrin-1 had no effect on heat nociception. Mechanical hypersensitivity induced by netrin-1 was attenuated by TRPA1 antagonist Chembridge-5861528 and by the control analgesic compound pregabalin both during the early (first two days) and late (third week) phase of hypersensitivity. TRPC4/C5 antagonist ML-204 had a weak antihypersensitivity effect that was only in the early phase, whereas TRPC4/C5 antagonist HC-070 had no effect on hypersensitivity induced by netrin-1. The discharge rate in pronociceptive ON-like RVM neurons was increased by netrin-1 during the late but not acute phase, whereas netrin-1 had no effect on the discharge rate of antinociceptive RVM OFF-like neurons. The results suggest that spinal TRPA1 receptors and pronociceptive RVM ON-like neurons are involved in the maintenance of submodality-selective pronociceptive actions induced by netrin-1 in the spinal cord.

Suppression of axonal attractant netrin-1 injured dopaminergic neuronal and motor function of mice during manganese overexposure.

Manganese (Mn) can accumulate in the striatum through the blood-brain barrier and cause neurotoxicity. It is mainly due to the decrease of dopamine (DA) levels in the striatum, which leads to extrapyramidal dysfunction. Netrin-1, as an axon guidance factor, can regulate the normal transmission of DA. However, few people have explored the role of netrin-1 in Mn-induced neurotoxicity. The purpose of the present study is to verify whether overexposure of Mn inhibits the axon attractant netrin-1, thereby damaging dopaminergic neuronal and motor function of mice. Here, we found that excessive Mn exposure reduces the expression of striatum netrin-1, tyrosine hydroxylase, DA receptor D3, and dopamine transporter 1, and the levels of serum netrin-1, and promotes dopaminergic neuronal and striatum injury, leading to DA transmission and motor dysfunction. Notably, recombinant mouse netrin-1 protein significantly antagonized Mn-induced neurotoxicity. These findings suggest that netrin-1 participates in Mn-induced motor dysfunction. Our findings may provide an experimental basis for fully elucidating the effects of Mn-induced neurotoxicity.

A Novel Netrin-1-Derived Peptide Enhances Protection against Neuronal Death and Mitigates of Intracerebral Hemorrhage in Mice.

It has been reported that Netrin-1 is involved in neuroprotection following injury to the central nervous system. However, the minimal functional domain of Netrin-1 which can preserve the neuroprotection but avoid the major side effects of Netrin remains elusive. Here, we investigated the neuroprotective effect of a peptide E1 derived from Netrin-1's EGF3 domain (residues 407-422). We found that it interacts with deleted colorectal carcinoma (DCC) to activate focal adhesion kinase phosphorylation exhibiting neuroprotection. The administration of the peptide E1 was able to improve functional recovery through reduced apoptosis in an experimental murine model of intracerebral hemorrhage (ICH). In summary, we reveal a functional sequence of Netrin-1 that is involved in the recovery process after ICH and identify a candidate peptide for the treatment of ICH.

Netrin-1 protects the SH-SY5Y cells against amyloid beta neurotoxicity through NF-κB/Nrf2 dependent mechanism.

Many evidence confirms that amyloid beta 1-42 fragment (Aß1-42) causes neuroinflammation, oxidative stress, and cell death, which are related to progressive memory loss, cognitive impairments and mental disorders that will lead to Alzheimer's disease (AD) progression. Netrin-1, as a member of the laminins, has been proved to inhibit apoptosis and inflammation outside of nervous system, in addition to having a vital role in morphogenesis and neurogenesis of neural system. This study was designed to assess the protective effects of netrin-1 in SH-SY5Y human neuroblastoma cell line exposed to Aß1-42 and to explore some mechanisms that underlie netrin-1 effects. Cultured SH-SY5Y neuroblast-like cells were treated with netrin-1 prior to Aß1-42 exposure and the effects were assessed by MTT and ELISA assay kits. Netrin- 1 pretreatment of Aß1-42-exposed SH-SY5Y human neuroblastoma cells attenuated Aß1-42 induced toxic effects, increased cell viability and partially restored levels of 3 inflammatory and oxidative stress biomarkers including: nuclear factor erythroid 2-like 2 (Nrf2), tumor necrosis factor alpha (TNFα) and nuclear factor kappa-light chain-enhancer of activated B cells (NF-κB). Based on the findings of this study, netrin-1 represents a promising therapeutic bio agent to abrogate cellular inflammation and reactive oxygen species (ROS) activation induced by Aß1-42 in the SH-SY5Y cell model of AD.

Late Protective Effect of Netrin-1 in the Murine Acetaminophen Hepatotoxicity Model.

Acetaminophen (APAP) overdose-induced acute liver failure is an important clinical problem in the United States and the current antidote N-acetylcysteine, has a short early therapeutic window. Since most patients present late to the clinic, there is need for novel late-acting therapeutic options. Though the neuronal guidance cue netrin-1, has been shown to promote hepatic repair and regeneration during liver ischemia/reperfusion injury, its effect in APAP-induced hepatotoxicity is unknown. In the quest for a late-acting therapeutic intervention in APAP-induced liver injury, we examined the role of netrin-1 in a mouse model of APAP overdose. Male C57BL/6J mice were cotreated with exogenous netrin-1 or vehicle control, along with 300 mg/kg APAP and euthanized at 6, 12, and 24 h. Significant elevations in alanine aminotransferase indicative of liver injury were seen in control mice at 6 h and this was not affected by netrin-1 administration. Also, netrin-1 treatment did not influence mitochondrial translocation of phospho-JNK, or peroxynitrite formation indicating that there was no interference with APAP-induced injury processes. Interestingly however, netrin-1 administration attenuated liver injury at 24 h, as seen by alanine aminotransferase levels and histology, at which time significant elevations in the netrin-1 receptor, adenosine A2B receptor (A2BAR) as well as macrophage infiltration was evident. Removal of resident macrophages with clodronate liposomes or treatment with the A2BAR antagonist PSB1115 blocked the protective effects of netrin-1. Thus, our data indicate a previously unrecognized role for netrin-1 in attenuation of APAP hepatotoxicity by enhancing recovery and regeneration, which is mediated through the A2BAR and involves resident liver macrophages.

Netrin-1: A new promising diagnostic marker for muscle invasion in bladder cancer.

BACKGROUND: Bladder cancer is the most common urological malignancy with a high tendency for progression and recurrence. So far, no reliable diagnostic marker is present with 100% sensitivity and specificity. Netrins are related to laminin proteins, and were first discovered to be involved in neural development. After that, they were found in other organs of the body and several studies stated that they have implicated in cancer progression. PURPOSE: This study aimed at investigating the netrin-1 gene expression in bladder cancer tissues, in addition to the possibility of using urinary netrin-1 as a marker for muscle invasion diagnosis in bladder cancer cases. METHODS: Netrin-1 gene expression in bladder cancer tissue was detected in this study by real-time polymerase chain reaction. Moreover, netrin-1 protein was measured in tissue and urinary deposit samples by western blotting. RESULTS: The results of this study revealed that netrin-1 is expressed in bladder cancer and control tissues, with a strong positive correlation between netrin-1 in tissues and urinary netrin-1 (rs = 0.762, P < 0.0005). Receiver operating characteristic curve analysis confirmed the muscle-invasion diagnostic value of urinary netrin-1 with bladder cancer cases, providing an area under the curve equals to 0.758 (95% confidence interval, 0.630-0.886, P < 0.0005), with 96% sensitivity and 67% specificity. Bladder cancer patients had been included to examine risk factors for local recurrence, distant metastasis, and death. Cox regression models showed that netrin-1 gene expression, tumor size, and age are positive predictor markers for local tumor recurrence. Age is a predictor for distant metastasis, and tumor stage is a predictor for death. CONCLUSION: Urinary netrin-1 can be used as a promising biomarker for diagnosis of muscle invasion, which may help in the follow up of non-invasive tumors. In addition, tissue netrin-1 expression may serve as a predictor of local tumor recurrence.

Netrin-1 prolongs skin graft survival by inducing the transformation of mesenchymal stem cells from pro-rejection to immune-tolerant phenotype.

OBJECTIVE: Mesenchymal stem cells (MSCs) induce allograft immune tolerance, but low efficacy severely limits their wide application. In this work, Netrin-1 was used to maintain MSC function in an IR environment to study its role in the immune tolerance induction of the allograft. MATERIALS AND METHODS: The experiments were divided into three groups: the control group, the IR group and the Netrin-1 group (Netrin-1 was added to MSC medium and then cultured for 48 h). After digestion, MSCs were mixed with TLR4 and TLR3 antibodies (BD), incubated for 20 min, and washed with Phosphate-Buffered Saline (PBS) three times. The mean fluorescence intensity (MFI) of TLR4 and TLR3 was detected by flow cytometry. Isolated lymphocytes were divided into four groups: the control group (no treatment), the MSC group (lymphocytes were co-cultured with MSCs in the control group), the rejection group (lymphocytes were co-cultured with MSCs in the IR group), and the Netrin-1 group (MSCs in the IR group) was stimulated by Netrin-1 for 48h. RESULTS: Our study found that compared with control mice, toll-like receptor (TLR3) expression in bone marrow MSCs decreased as the expression of TLR4 increased, the secretion of transforming growth factor-ß (TGF-ß) and interleukin-10 (IL-10) was reduced, while the secretion of IL-6 significantly increased in immune rejection (IR) mice. MSCs in IR mice promoted T-cell proliferation and reduced the ratio of Treg cells. Netrin-1 inhibited the pro-rejection effect of these MSCs, further inhibited T-cell proliferation and facilitated an increase in the ratio of Treg cells. The animal experiment results showed that MSC transplantation in the rejection group would shorten the mean survival time of the skin graft and induce the infiltration of lymphocytes. Netrin-1 prolonged the mean survival time of the skin graft by enhancing MSC function. The immunohistochemistry results showed that, compared with the rejection group, the T cell number in the skin graft significantly decreased in the Netrin-1 group. CONCLUSIONS: MSC can be divided into immune-tolerant and pro-rejection types in organ transplantation and Netrin-1 can induce the transformation of MSC from the pro-rejection to immune-tolerant type and markedly prolong the skin graft survival time.

Effect of Netrin-1 Anti-Inflammatory Factor on Acute Lung Injury in Sepsis Rats.

BACKGROUND Acute lung injury (ALI) often occurs early and seriously in the progress of sepsis. Netrin-1 is demonstrated to be an effective anti-inflammatory agent. However, whether netrin-1 can relieve sepsis-induced ALI remains unknown. MATERIAL AND METHODS The sepsis rat model was built with the method of cecal ligation and puncture (CLP). The lung tissue changes were represented as the results of hematoxylin-eosin (HE) staining, wet-to-dry (W/D) ratio, Western blot analysis, and immunohistochemistry. An in vitro lung injury model was simulated with LPS-induced BEAS-2B cells. The cell transfection effects were evaluated by Western blot analysis and RT-qPCR analysis. TNF-alpha, IL-1ß, and IL-6 levels were detected by Western blot analysis in LPS-induced BEAS-2B cells. RESULTS Obvious inflammation caused by sepsis appeared in lung tissues with the increase of the W/D ratio and expression of inflammatory cytokines. Netrin-1 and its receptor UNC5B were reduced in sepsis. However, upregulation of netrin-1 alleviated the levels of inflammation and increased the UNC5B levels in BEAS-2B cells. CONCLUSIONS Netrin-1 protects against ALI in sepsis rats through its anti-inflammation effect and may provide a novel treatment to prevent lung injury caused by sepsis.

Netrin-1 Dampens Hypobaric Hypoxia-Induced Lung Injury in Mice.

Background: This study aimed to explore the effects of netrin-1 on hypobaric hypoxia-induced lung injury in mice. Methods: We exposed 6-8-week-old C57BL/6 mice to hypobaric stress at 340 mmHg for 30 minutes followed by 260 mmHg for different periods (6, 12, 18, and 24 hours) to observe the severity of lung injury (O2 concentration, 21%; 54.6 mmHg). The wet/dry weight ratio and protein leakage from the mouse lung were used to determine the suitable exposure time. Netrin-1 was injected into the tail vein of mice before 18-hour decompression. Inflammatory cytokines, lung injury scores, and activity of nuclear factor κB were evaluated. The expression of apoptosis-related proteins was also examined. Results: Protein concentration in the bronchoalveolar lavage fluid was significantly higher in the 18-hour group (p < 0.05). Pulmonary pathology revealed neutrophil infiltration, alveolar septum thickening, and tissue edema. Injury score and macrophage inflammatory protein 2 levels were also increased. Intrinsic apoptosis pathway was activated. Hypoxia decreased the expression of Bcl2 protein, the number of active caspase-3-stained cells, and UNC5HB receptors. Pretreatment with netrin-1 reduced protein leakage, inhibited neutrophil migration, lowered the injury score, attenuated apoptosis, and increased UNC5HB receptor expression. Conclusion: Netrin-1 dampens hypobaric hypoxia-induced lung injury by inhibiting neutrophil migration and attenuating apoptosis.

Netrin-1 plays a critical role in regulating capacities of epidermal stem cells upon ultraviolet-B (UV-B) irradiation.

Loss of the capacities of epidermal stem cells (ESCs) induced by ultraviolet-B (UV-B) irradiation has been widely associated with various skin diseases. Netrin-1, a member of the axonal guidance protein family, has displayed diverse biological functions in different types of cells and tissues, mediated by its specific receptor UNC-5 homolog B (UNC5b). In this study, we examined the physiological functions of netrin-1 and UNC5b in ESCs upon UV-B exposure. Our results indicate that UNC5b is expressed in ESCs, and its expression is upregulated in response to UV-B radiation. We found that treatment with netrin-1 prevented UV-B radiation-induced oxidative stress by reducing the generation of reactive oxygen species (ROS) and expression of NADPH oxidase 4 (NOX-4). Additionally, treatment with netrin-1 improved UV-B radiation-induced mitochondrial dysfunction by increasing mitochondrial membrane potential (MMP) levels and adenosine triphosphate (ATP) production. The presence of netrin-1 attenuated UV-B radiation-induced lactic dehydrogenase (LDH) release. UV-B exposure resulted in the loss of the capacities of ESCs by reducing the expressions of integrin ß1 and Krt19, the two major ESC markers. Importantly, this process was prevented by netrin-1. Silencing of UNC5b abolished the effects of netrin-1 on the expression of integrin ß1 and Krt19, suggesting that the effects of netrin-1 in maintaining the capacities of ESCs are dependent on UNC5b. Mechanistically, we found that the Wnt/ß-catenin signalling may be involved. Our findings suggest that netrin-1 may serve as a therapeutic agent for the treatment of skin diseases.

Netrin-1 alleviates subarachnoid haemorrhage-induced brain injury via the PPARγ/NF-KB signalling pathway.

Netrin-1 (NTN-1) is a novel drug to alleviate early brain injury following subarachnoid haemorrhage (SAH). However the molecular mechanism of NTN-1-mediated protection against early brain injury following SAH remains largely elusive. This study aims to evaluate the effects and mechanisms of NTN-1 in protecting SAH-induced early brain injury. The endovascular perforation SAH model was constructed using male C57BL/6J mice, and recombinant NTN-1 was administrated intravenously. Mortality rates, SAH grade, brain water content, neurological score and neuronal apoptosis were evaluated. The expression of PPARγ, Bcl-2, Bax and nuclear factor-kappa B (NF-κB) were detected by Western blot. Small interfering RNA specific to NTN-1 receptor, UNC5B, and a selective PPARγ antagonist, bisphenol A diglycidyl ether (BADGE), were applied in combination with NTN-1. The results suggested that NTN-1 improved the neurological deficits, reduced the brain water content and alleviated neuronal apoptosis. In addition, NTN-1 enhanced PPARγ and Bcl-2 expression and decreased the levels of Bax and NF-κB. However, the neuroprotection of NTN-1 was abolished by UNC5B and BADGE. In conclusion, our results demonstrated that NTN-1 attenuates early brain injury following SAH via the UNC5B PPARγ/NF-κB signalling pathway.

Key mechanisms underlying netrin-1 prevention of impaired spatial and object memory in Aß1-42 CA1-injected rats.

Alzheimer's disease (AD) is a neurodegenerative disorder with an incompletely defined aetiology that is associated with memory and cognitive impairment. Currently available therapeutics only provide temporary assistance with symptoms. In spite of plentiful research in the field and the generation of thousands of studies, much is still to be clarified on precise mechanisms of pathobiology, prevention modalities, disease course and cure. Netrin-1, a laminin family protein, is said to have anti-inflammatory and anti-apoptotic effects and has a key role in neurogenesis and morphogenesis of neural structures. Accordingly, this study was designed to investigate protective effects of bilateral intrahippocampal fissure microinjections of netrin-1 on memory impairment in rat model of AD. Concomitant administration of netrin-1 with amyloid beta 1-42 (Aß1-42 ) improved cognitive dysfunction in novel object recognition task (NOR), ameliorated impaired spatial memory in Morris water maze (MWM) setting, increased neuronal density and reduced amyloid aggregation in rat AD model. Netrin-1 was also seen to prevent Aß1-42 -induced caspase-3, caspase-7 and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation. Therefore, based on the data reported here, netrin-1 may be a promising biologic therapeutic that addresses the memory and neuronal loss associated with AD.

High-throughput three-dimensional chemotactic assays reveal steepness-dependent complexity in neuronal sensation to molecular gradients.

Many cellular programs of neural development are under combinatorial regulation by different chemoattractive or chemorepulsive factors. Here, we describe a microfluidic platform that utilizes well-controlled three-dimensional (3D) diffusion to generate molecular gradients of varied steepness in a large array of hydrogel cylinders, allowing high-throughput 3D chemotactic assays for mechanistic dissection of steepness-dependent neuronal chemotaxis. Using this platform, we examine neuronal sensitivity to the steepness of gradient composed of netrin-1, nerve growth factor, or semaphorin3A (Sema3A) proteins, and reveal dramatic diversity and complexity in the associated chemotactic regulation of neuronal development. Particularly for Sema3A, we find that serine/threonine kinase-11 and glycogen synthase kinase-3 signaling pathways are differentially involved in steepness-dependent chemotactic regulation of coordinated neurite repellence and neuronal migration. These results provide insights to the critical role of gradient steepness in neuronal chemotaxis, and also prove the technique as an expandable platform for studying other chemoresponsive cellular systems.

Netrin-1 prevents the attachment of monocytes to endothelial cells via an anti-inflammatory effect.

Netrin-1 is best known for its function guiding axon growth and migration. Netrin-1 has been shown to be involved in regulating cardiovascular function. In this study, we aimed to understand the biological role of Netrin-1 and its receptor Unc5b in endothelial cells. Our results demonstrate that Unc5b was moderately expressed in human aortic endothelial cells (HAECs) and TNF-α had a dose-dependent inhibitory effect on Unc5b level. Netrin-1 potently suppressed TNF-α-induced vascular adhesion molecules VCAM-1, ICAM-1, E-selectin and blocked the adhesion of monocytes to endothelial cells. Netrin-1 also suppressed TNF-α-induced production of cytokines including MCP-1, IL-1ß, and IL-6. Importantly, Netrin-1 suppressed toll like receptor 4 (TLR4) expression and prevented NF-κB activation. Mechanistically, Netrin-1 reduced TNF-α-induced IKK and IκBα activation and prevented degradation of IκBα. Netrin-1 reduced nuclear accumulation of p65 and strongly suppressed NF-κB promoter activation. Collectively, our data demonstrated that signaling of Netrin-1 and its receptor Unc5b had an anti-inflammatory effect in endothelial cells. Netrin-1 signaling could be imperative for normal endothelial function.