Role of Netrin-1 Signaling in Nerve Regeneration

Netrin-1 signaling pathway mechanisms in neurodegenerative diseases

Netrin-1 and its receptors play crucial roles in inducing axonal growth and neuronal migration during neuronal development. Their profound impacts then extend into adulthood to encompass the maintenance of neuronal survival and synaptic function. Increasing amounts of evidence highlight several key points: (1) Diminished Netrin-1 levels exacerbate pathological progression in animal models of Alzheimer's disease and Parkinson's disease, and potentially, similar alterations occur in humans. (2) Genetic mutations of Netrin-1 receptors increase an individuals' susceptibility to neurodegenerative disorders. (3) Therapeutic approaches targeting Netrin-1 and its receptors offer the benefits of enhancing memory and motor function. (4) Netrin-1 and its receptors show genetic and epigenetic alterations in a variety of cancers. These findings provide compelling evidence that Netrin-1 and its receptors are crucial targets in neurodegenerative diseases. Through a comprehensive review of Netrin-1 signaling pathways, our objective is to uncover potential therapeutic avenues for neurodegenerative disorders.

Netrin-1 co-cross-linked hydrogel accelerates diabetic wound healing in situ by modulating macrophage heterogeneity and promoting angiogenesis

Diabetic wounds, characterized by prolonged inflammation and impaired vascularization, are a serious complication of diabetes. This study aimed to design a gelatin methacrylate (GelMA) hydrogel for the sustained release of netrin-1 and evaluate its potential as a scaffold to promote diabetic wound healing. The results showed that netrin-1 was highly expressed during the inflammation and proliferation phases of normal wounds, whereas it synchronously exhibited aberrantly low expression in diabetic wounds. Neutralization of netrin-1 inhibited normal wound healing, and the topical application of netrin-1 accelerated diabetic wound healing. Mechanistic studies demonstrated that netrin-1 regulated macrophage heterogeneity via the A2bR/STAT/PPARγ signaling pathway and promoted the function of endothelial cells, thus accelerating diabetic wound healing. These data suggest that netrin-1 is a potential therapeutic target for diabetic wounds.

Association between plasma Netrin-1 levels and motor and nonmotor symptoms in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by dopaminergic neuron degeneration and diverse motor and nonmotor symptoms. Early diagnosis and intervention are crucial but challenging due to reliance on clinical presentation. Recent research suggests potential biomarkers for early detection, including plasma netrin-1 (NTN-1), a protein implicated in neuronal survival.

METHODS

This cross-sectional study recruited 105 PD patients and 65 healthy controls, assessing plasma NTN-1 levels and correlating them with clinical characteristics. Statistical analyses explored associations between NTN-1 levels and PD symptoms, considering demographic factors.

RESULTS

PD patients exhibited significantly lower plasma NTN-1 levels compared to controls. NTN-1 demonstrated moderate potential as a PD biomarker. Positive correlations were found between NTN-1 levels and motor, depression, and cognitive symptoms. Multiple regression analysis revealed disease duration and NTN-1 levels as key factors influencing symptom severity. Gender also impacted symptom scores.

CONCLUSION

Reduced plasma NTN-1 levels correlate with PD severity, suggesting its potential as a biomarker. However, further research is needed to elucidate the roles of NTN-1 in PD pathophysiology and validate its diagnostic and therapeutic implications. Understanding the involvement of NTN-1 may lead to personalized management strategies for PD.

The Effect of Breast Milk from Different Lactation Stages on in Vitro Wound Healing

Objective: Wound healing is a complex and dynamic process essential for restoring tissue integrity and homeostasis. It is thought that breast milk contributes positively to the wound healing process, thanks to the components it contains. The aim of this study is to compare the effects of breast milk on the wound healing process at different lactation stages and to evaluate the underlying mechanism(s). Materials and Methods: The effects of breast milk from different lactation stages (colostrum, transitional, and mature milk) on wound healing were determined by in vitro scratch assay in L929 fibroblast cells. 2,2-Diphenyl-1-picrylhydrazyl (DPPH), total oxidant, and antioxidant capacity were used to confirm antioxidant effects. The effect of breast milk on netrin-1 levels in L929 cells was elucidated by ELISA. Results: Breast milk at different lactation stages promoted wound healing. While the wound closure percentage was determined as 48.7% in the control group, this rate was determined to be the highest at 81.6% in the mature milk group (p:0.0002). The free radical scavenging capacity of colostrum, transitional, and mature milk with DPPH was determined as 49.69%, 60.64%, and 80.85%, respectively, depending on the lactation stages. Netrin-1 levels detected by ELISA were determined as 490.1 ± 6.5 pg/mL in the control group, while the lowest level was determined as 376.6 ± 4.5 pg/mL in mature milk (p:0.0003). Conclusions: Breast milk, especially mature milk, promoted wound healing on L929 cells by suppressing netrin-1 levels and scavenging free radicals.

Circulating netrin-1 levels are reduced and related to corneal nerve fiber loss in patients with diabetic neuropathy

AIMS/INTRODUCTION

Deficiency of neurotropic factors is implicated in diabetic neuropathy (DN). Netrin-1 is a neurotropic factor, but its association with DN has not been explored. We have assessed the association between serum netrin-1 levels and early diabetic neuropathy assessed by quantifying corneal nerve fiber loss using corneal confocal microscopy.

MATERIALS AND METHODS

A total of 72 participants with type 2 diabetes, without and with corneal nerve fiber loss (DN- n = 42, DN+ n = 30), and 45 healthy controls were studied. Serum netrin-1 levels were measured by enzyme-linked immunosorbent assay, and corneal nerve morphology was assessed using corneal confocal microscopy.

RESULTS

Corneal nerve fiber density, branch density, fiber length and serum netrin-1 levels were significantly lower in the DN- and DN+ groups compared with controls (P < 0.001). Netrin-1 levels correlated with corneal nerve fiber length in the DN+ group (r = 0.51; P < 0.01). A receiver operating characteristic curve analysis showed that a netrin-1 cut-off value of 599.6 (pg/mL) had an area under the curve of 0.85, with a sensitivity of 76% and specificity of 74% (P < 0.001; 95% confidence interval 0.76-0.94) for differentiating patients with and without corneal nerve loss.

CONCLUSIONS

Serum netrin-1 levels show a progressive decline with increasing severity of small nerve fiber damage in patients with diabetes. Netrin-1 could act as a biomarker for small nerve fiber damage in DN.

Netrin-1-engineered endothelial cell exosomes induce the formation of pre-regenerative niche to accelerate peripheral nerve repair

The formation of vascular niche is pivotal during the early stage of peripheral nerve regeneration. Nevertheless, the mechanisms of vascular niche in the regulation of peripheral nerve repair remain unclear. Netrin-1 (NTN1) was found up-regulated in nerve stump after peripheral nerve injury (PNI). Herein, we demonstrated that NTN1-high endothelial cells (NTN1+ECs) were the critical component of vascular niche, fostering angiogenesis, axon regeneration, and repair-related phenotypes. We also found that NTN1+EC-derived exosomes (NTN1 EC-EXO) were involved in the formation of vascular niche as a critical role. Multi-omics analysis further verified that NTN1 EC-EXO carried a low-level expression of let7a-5p and activated key pathways associated with niche formation including focal adhesion, axon guidance, phosphatidylinositol 3-kinase-AKT, and mammalian target of rapamycin signaling pathway. Together, our study suggested that the construction of a pre-regenerative niche induced by NTN1 EC-EXO could establish a beneficial microenvironment for nerve repair and facilitate functional recovery after PNI.

The Role of SLIT3-ROBO4 Signaling in Endoplasmic Reticulum Stress-Induced Delayed Corneal Epithelial and Nerve Regeneration

Purpose

In the present study, we aim to elucidate the underlying molecular mechanism of endoplasmic reticulum (ER) stress induced delayed corneal epithelial wound healing and nerve regeneration.

Methods

Human limbal epithelial cells (HLECs) were treated with thapsigargin to induce excessive ER stress and then RNA sequencing was performed. Immunofluorescence, qPCR, Western blot, and ELISA were used to detect the expression changes of SLIT3 and its receptors ROBO1-4. The role of recombinant SLIT3 protein in corneal epithelial proliferation and migration were assessed by CCK8 and cell scratch assay, respectively. Thapsigargin, exogenous SLIT3 protein, SLIT3-specific siRNA, and ROBO4-specific siRNA was injected subconjunctivally to evaluate the effects of different intervention on corneal epithelial and nerve regeneration. In addition, Ki67 staining was performed to evaluate the proliferation ability of epithelial cells.

Results

Thapsigargin suppressed normal corneal epithelial and nerve regeneration significantly. RNA sequencing genes related to development and regeneration revealed that thapsigargin induced ER stress significantly upregulated the expression of SLIT3 and ROBO4 in corneal epithelial cells. Exogenous SLIT3 inhibited normal corneal epithelial injury repair and nerve regeneration, and significantly suppressed the proliferation and migration ability of cultured mouse corneal epithelial cells. SLIT3 siRNA inhibited ROBO4 expression and promoted epithelial wound healing under thapsigargin treatment. ROBO4 siRNA significantly attenuated the delayed corneal epithelial injury repair and nerve regeneration induced by SLIT3 treatment or thapsigargin treatment.

Conclusions

ER stress inhibits corneal epithelial injury repair and nerve regeneration may be related with the upregulation of SLIT3-ROBO4 pathway.

Circular RNA expression profiles and functional predication after restraint stress in the amygdala of rats

Prolonged or repeated exposure to stress elevates the risk of various psychological diseases, many of which are characterized by central nervous system dysfunction. Recent studies have demonstrated that circular RNAs (circRNAs) are highly abundant in the mammalian brain. Although their precise expression and function remain unknown, they have been hypothesized to regulate transcriptional and post-transcriptional gene expression. In this investigation, we comprehensively analyzed whether restraint stress for 2 days altered the circRNA expression profile in the amygdala of male rats. The impact of restraint stress on behavior was evaluated using an elevated plus maze and open field test. Serum corticosterone levels were measured using an enzyme-linked immunosorbent assay. A total of 10,670 circRNAs were identified using RNA sequencing. Ten circRNAs were validated by reverse transcription and quantitative polymerase chain reaction analysis. Gene ontology and Kyoto encyclopedia of genes and genomes pathway analyzes supported the notion that genes associated with differentially expressed circRNAs are primarily implicated in neuronal activity and neurotransmitter transport. Moreover, the three differentially expressed circRNAs showed high specificity in the amygdala. Overall, these findings indicate that differentially expressed circRNAs are highly enriched in the amygdala and offer a potential direction for further research on restraint stress.

Emerging role of extracellular vesicles and exogenous stimuli in molecular mechanisms of peripheral nerve regeneration

Peripheral nerve injuries lead to significant morbidity and adversely affect quality of life. The peripheral nervous system harbors the unique trait of autonomous regeneration; however, achieving successful regeneration remains uncertain. Research continues to augment and expedite successful peripheral nerve recovery, offering promising strategies for promoting peripheral nerve regeneration (PNR). These include leveraging extracellular vesicle (EV) communication and harnessing cellular activation through electrical and mechanical stimulation. Small extracellular vesicles (sEVs), 30-150 nm in diameter, play a pivotal role in regulating intercellular communication within the regenerative cascade, specifically among nerve cells, Schwann cells, macrophages, and fibroblasts. Furthermore, the utilization of exogenous stimuli, including electrical stimulation (ES), ultrasound stimulation (US), and extracorporeal shock wave therapy (ESWT), offers remarkable advantages in accelerating and augmenting PNR. Moreover, the application of mechanical and electrical stimuli can potentially affect the biogenesis and secretion of sEVs, consequently leading to potential improvements in PNR. In this review article, we comprehensively delve into the intricacies of cell-to-cell communication facilitated by sEVs and the key regulatory signaling pathways governing PNR. Additionally, we investigated the broad-ranging impacts of ES, US, and ESWT on PNR.

Genes in Axonal Regeneration

This review explores the molecular and genetic underpinnings of axonal regeneration and functional recovery post-nerve injury, emphasizing its significance in reversing neurological deficits. It presents a systematic exploration of the roles of various genes in axonal regrowth across peripheral and central nerve injuries. Initially, it highlights genes and gene families critical for axonal growth and guidance, delving into their roles in regeneration. It then examines the regenerative microenvironment, focusing on the role of glial cells in neural repair through dedifferentiation, proliferation, and migration. The concept of "traumatic microenvironments" within the central nervous system (CNS) and peripheral nervous system (PNS) is discussed, noting their impact on regenerative capacities and their importance in therapeutic strategy development. Additionally, the review delves into axonal transport mechanisms essential for accurate growth and reinnervation, integrating insights from proteomics, genome-wide screenings, and gene editing advancements. Conclusively, it synthesizes these insights to offer a comprehensive understanding of axonal regeneration's molecular orchestration, aiming to inform effective nerve injury therapies and contribute to regenerative neuroscience.

Netrin-1 mitigates acute lung injury by preventing the activation of the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) signaling

Acute lung injury (ALI) is one of the most common high-risk diseases associated with a high mortality rate and is still a challenge to treat effectively. Netrin-1 (NT-1) is a novel peptide with a wide range of biological functions, however, its effects on ALI have not been reported before. In this study, an ALI model was constructed using lipopolysaccharide (LPS) and treated with NT-1. Pulmonary function and lung wet to dry weight ratio (W/D) were detected. The expressions of pro-inflammatory cytokines and chemokines interleukin-8 (IL-8), interleukin-1β (IL-1β), and chemokine (C-X-C motif) ligand 2 (CXCL2) were measured using real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). We found that the levels of NT-1 were reduced in the LPS-induced ALI mice model. Administration of NT-1 improved histopathological changes of lung tissues and lung function in LPS-challenged ALI mice. We also report that NT-1 decreased Myeloperoxidase (MPO) activity and ameliorated pulmonary edema. Additionally, treatment with NT-1 reduced the levels of pro-inflammatory cytokines and chemokines such as IL-8, IL-1β, and CXCL2 in lung tissues of LPS-challenged ALI mice. Importantly, NT-1 reduced cell count in BALF and mitigated oxidative stress (OS) by reducing the levels of MDA and increasing the levels of GSH. Mechanistically, it is shown that NT-1 reduced the levels of Toll-like receptor 4 (TLR4) and prevented nuclear translocation of nuclear factor-κB (NF-κB) p65. Our findings indicate that NT-1 is a promising agent for the treatment of ALI through inhibiting TLR4/NF-κB signaling.

Antioxidant and Anti-Inflammatory Effects of Garlic in Ischemic Stroke: Proposal of a New Mechanism of Protection through Regulation of Neuroplasticity

Stroke represents one of the main causes of death and disability in the world; despite this, pharmacological therapies against stroke remain insufficient. Ischemic stroke is the leading etiology of stroke. Different molecular mechanisms, such as excitotoxicity, oxidative stress, and inflammation, participate in cell death and tissue damage. At a preclinical level, different garlic compounds have been evaluated against these mechanisms. Additionally, there is evidence supporting the participation of garlic compounds in other mechanisms that contribute to brain tissue recovery, such as neuroplasticity. After ischemia, neuroplasticity is activated to recover cognitive and motor function. Some garlic-derived compounds and preparations have shown the ability to promote neuroplasticity under physiological conditions and, more importantly, in cerebral damage models. This work describes damage/repair mechanisms and the importance of garlic as a source of antioxidant and anti-inflammatory agents against damage. Moreover, we examine the less-explored neurotrophic properties of garlic, culminating in proposals and observations based on our review of the available information. The aim of the present study is to propose that garlic compounds and preparations could contribute to the treatment of ischemic stroke through their neurotrophic effects.

Exosomes derived from human umbilical cord mesenchymal stem cells loaded with RVG-Lamp2b and Netrin-1 promotes Schwann cell invasion and migration

BACKGROUND

Netrin-1 has a neuroprotective effect by regulating angiogenesis, autophagy, apoptosis, and neuroinflammation. This study investigated the effects of netrin-1 delivery to mouse Schwann cells and vascular endothelial cells using exosomes modified with rabies virus glycoprotein (RVG) peptides.

MATERIALS AND METHODS

RVG-Lamp2b and/or Netrin-1 were overexpressed in human umbilical cord mesenchymal stem cells to obtain exosomes modified with RVG-Lamp2b and/or loaded with Netrin-1. Then, exosomes were labeled with carboxyfluorescein diacetate succinimidyl ester and co-cultured with mouse Schwann cells and endothelial cells. Netrin-1 expression in Schwann cells and endothelial cells was measured using quantitative polymerase chain reaction and immunoblotting. Moreover, methyl thiazolyl tetrazolium assays and Transwell assays were used to detect proliferation, migration, and invasion of Schwann cells and endothelial cells.

RESULTS

Exosomes with RVG-Lamp2b entered Schwann cells more readily compared with the exosomes without RVG-Lamp2b. Meanwhile, this was not the case in endothelial cells. Netrin-1-loaded exosomes significantly promoted Netrin-1 expression, cell proliferation, migration, invasion, and epithelial-mesenchymal transition in Schwann cells and endothelial cells. These effects were further enhanced by Netrin-1-loaded exosomes modified with RVG-Lamp2b in Schwann cells, but not in endothelial cells.

CONCLUSION

HucMSC-derived exosomes loaded with RVG-Lamp2b and Netrin-1 promote proliferation, migration, and invasion of Schwann cells.

Decoding muscle-resident Schwann cell dynamics during neuromuscular junction remodeling

Understanding neuromuscular junction (NMJ) repair mechanisms is essential for addressing degenerative neuromuscular conditions. Here, we focus on the role of muscle-resident Schwann cells in NMJ reinnervation. In young Sod1-/- mice, a model of progressive NMJ degeneration, we identified a clear NMJ 'regenerative window' that allowed us to define regulators of reinnervation and crossing Sod1-/- mice with S100GFP-tg mice permitted visualization and analysis of Schwann cells. High-resolution imaging and single-cell RNA sequencing provide a detailed analysis of Schwann cell number, morphology, and transcriptome revealing multiple subtypes, including a previously unrecognized terminal Schwann cell (tSC) population expressing a synapse promoting signature. We also discovered a novel SPP1-driven cellular interaction between myelin Schwann cells and tSCs and show that it promotes tSC proliferation and reinnervation following nerve injury in wild type mice. Our findings offer important insights into molecular regulators critical in NMJ reinnervation that are mediated through tSCs to maintain NMJ function.

The role of N6-methyladenosine modification in rodent models of neuropathic pain: from the mechanism to therapeutic potential

Neuropathic pain (NP) is a common chronic pain condition resulted from lesions or diseases of somatosensory nervous system, but the pathogenesis remains unclear. A growing body of evidence supports the relationship between pathogenesis and N6-methyladenosine (m6A) modifications of RNA. However, studies on the role of m6A modifications in NP are still at an early stage. Elucidating different etiologies is important for understanding the specific pathogenesis of NP. This article provides a comprehensive review on the role of m6A methylation modifications including methyltransferases ("writers"), demethylases ("erasers"), and m6A binding proteins ("readers") in NP models. Further analysis of the pathogenic mechanism relationship between m6A and NP provided novel theoretical and practical significance for clinical treatment of NP.

Stabilizing the neural barrier - A novel approach in pain therapy

Chronic and neuropathic pain are a widespread burden. Incomplete understanding of underlying pathomechanisms is one crucial factor for insufficient treatment. Recently, impairment of the blood nerve barrier (BNB) has emerged as one key aspect of pain initiation and maintenance. In this narrative review, we discuss several mechanisms and putative targets for novel treatment strategies. Cells such as pericytes, local mediators like netrin-1 and specialized proresolving mediators (SPMs), will be covered as well as circulating factors including the hormones cortisol and oestrogen and microRNAs. They are crucial in either the BNB or similar barriers and associated with pain. While clinical studies are still scarce, these findings might provide valuable insight into mechanisms and nurture development of therapeutic approaches.

Metastatic Infiltration of Nervous Tissue and Periosteal Nerve Sprouting in Multiple Myeloma-Induced Bone Pain in Mice and Human

Multiple myeloma (MM) is a neoplasia of B plasma cells that often induces bone pain. However, the mechanisms underlying myeloma-induced bone pain (MIBP) are mostly unknown. Using a syngeneic MM mouse model, we show that periosteal nerve sprouting of calcitonin gene-related peptide (CGRP+) and growth associated protein 43 (GAP43+) fibers occurs concurrent to the onset of nociception and its blockade provides transient pain relief. MM patient samples also showed increased periosteal innervation. Mechanistically, we investigated MM induced gene expression changes in the dorsal root ganglia (DRG) innervating the MM-bearing bone of male mice and found alterations in pathways associated with cell cycle, immune response and neuronal signaling. The MM transcriptional signature was consistent with metastatic MM infiltration to the DRG, a never-before described feature of the disease that we further demonstrated histologically. In the DRG, MM cells caused loss of vascularization and neuronal injury, which may contribute to late-stage MIBP. Interestingly, the transcriptional signature of a MM patient was consistent with MM cell infiltration to the DRG. Overall, our results suggest that MM induces a plethora of peripheral nervous system alterations that may contribute to the failure of current analgesics and suggest neuroprotective drugs as appropriate strategies to treat early onset MIBP.SIGNIFICANCE STATEMENT Multiple myeloma (MM) is a painful bone marrow cancer that significantly impairs the quality of life of the patients. Analgesic therapies for myeloma-induced bone pain (MIBP) are limited and often ineffective, and the mechanisms of MIBP remain unknown. In this manuscript, we describe cancer-induced periosteal nerve sprouting in a mouse model of MIBP, where we also encounter metastasis to the dorsal root ganglia (DRG), a never-before described feature of the disease. Concomitant to myeloma infiltration, the lumbar DRGs presented blood vessel damage and transcriptional alterations, which may mediate MIBP. Explorative studies on human tissue support our preclinical findings. Understanding the mechanisms of MIBP is crucial to develop targeted analgesic with better efficacy and fewer side effects for this patient population.

Netrin-1 attenuates cerebral ischemia/reperfusion injury by limiting mitochondrial ROS and Ca2+ levels via activation of AKT phosphorylation and mitochondrial m-AAA protease AFG3L2

Cerebral ischemia-reperfusion (I/R) injury as the consequence of revascularization after ischemic stroke is associated with mitochondrial dysfunction, oxidative stress, and neuron loss. In this study, we used a deprivation/reoxygenation (OGD/R) model to determine whether interactions between Netrin-1, AKT, and the mitochondrial AAA protease AFG3L2 could influence mitochondrial function in neurons after I/R. We found that Netrin-1 protects primary cortical neurons from OGD/R-induced cell death and regulates mitochondrial reactive oxygen species (ROS) and Ca²⁺ levels. The accumulation of mitochondrial calcium uniporter (MCU) subunits was monitored in cells by immunoblot analysis. Although the regulatory subunits MICU1 and MICU2 were relatively unaffected, the accumulation of the essential MCU regulator (EMRE) subunit was impaired. In OGD/R-induced cells, the 7 kDa form of EMRE was significantly reduced. Netrin-1 inhibited the accumulation of EMRE and mitochondrial Ca²⁺ levels by upregulating AFG3L2 and AKT activation. Loss of AFG3L2 or inhibition of AKT increased levels of 7 kDa EMRE. Moreover, overexpression of AKT increased the expression of AFG3L2 in Netrin-1-knockdown neurons after OGD/R. Our results demonstrate that Netrin-1 enhanced AFG3L2 protein expression via activation of AKT. We also observed that overexpression of Netrin-1 significantly reduced infarction size in an I/R-induced brain injury model in rats but not when AKT was inhibited. Our data suggest that AFG3L2 is a protein substrate of AKT and indicate that Netrin-1 attenuates cerebral I/R injury by limiting mitochondrial ROS and Ca²⁺ levels through activating AKT phosphorylation and AFG3L2.

Magnetic resonance imaging assessment of the therapeutic effect of combined electroacupuncture and stem cells in acute peripheral nerve injury

Objectives: This study aimed to evaluate the therapeutic effect of a combination of Bone Mesenchymal stem cells (BMSCs) transplantation and Electroacupuncture (EA) for acute sciatic nerve injury in rats using magnetic resonance. Methods: Ninety-two male adult healthy Sprague-Dawley rats were randomly divided into the EA+BMSCs group, EA group, MSCs group, and PBS group (control). Electroacupuncture was performed on a rat receiving EA treatment at Huantiao (GB30) and Zusanli (ST36). T2 values and diffusion tensor imaging (DTI) derived from multiparametric magnetic resonance imaging (MRI), histological assessments, and immunohistochemistry was used to monitor nerve regeneration. Walking track analysis was used to assess nerve functional recovery. Repeated-measures one-way analysis of variance was used to evaluate the significance of T2, DTI, and SFI values among the four groups. One-way analysis of variance was used for comparing the histological characteristics. Bonferroni test was used for multiple pairwise comparisons at each time point. Results: In terms of FA, the EA+BMSCs and EA groups had faster recovery than PBS (control) in all time points after surgery, and the EA+BMSCs group recovered better than the BMSCs group at 3 weeks (P ≤ 0.008). FA values were higher in the EA group than in the BMSCs group at 4 weeks (P ≤ 0.008). In terms of RD, the EA+BMSCs group recovered better than the BMSCs group at 2 and 4 weeks (P ≤ 0.008). Immunofluorescence staining for axon guidance molecule netrin-1 revealed that it was significantly higher in the EA+BMSCs subgroup and EA subgroup than it was in the control (PBS) subgroup at 1-3 weeks (P < 0.001). Immunofluorescence staining for S100 showed the continuity of nerve fibers recovered more quickly in the EA+BMSCs subgroup than in the BMSCs subgroup. Conclusion: Our research revealed that a combination of MSCs and EA can provide both topological and biomolecular guidance to promote axonal extension, myelin regeneration, and functional recovery after PNI. EA not only promotes nerve repair on its own, but also enhanced the beneficial effects of stem cell treatment and the secretion of netrin 1, a guidance regeneration factor, and promotes the orderly growth of nerve fibers. These PNI repairs could be monitored non-invasively and in situ by MRI. The FA and RD values derived from MRI could be sensitive biomarkers to reflect the PNI repair process.

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.

Two Useful Umbilical Biomarkers for Therapeutic Hypothermia Decision in Patients with Hypoxic İschemic Encephalopathy with Perinatal Asphyxia: Netrin-1 and Neuron Specific Enolase

Hypoxic-ischemic encephalopathy (HIE) has a high risk of mortality in addition to serious neurological damage. In this study, we investigated the values of umbilical cord netrin-1 (NT-1) and neuron specific enolase (NSE) levels in the early diagnosis of HIE stage II/III induced by neonatal asphyxia. In the study group, infants with gestational age ≥ 36 weeks who were diagnosed with HIE II/III were included. NT-1 and NSE levels were measured from the umbilical cord immediately after birth. Results were compared between HIE II/III and the healthy control group. Cutoff values for serum NT-1 and NSE were determined with receiver-operating characteristics curves and the area under the curve (AUC) was used to determine the diagnostic value of NT-1 and NSE levels in infants diagnosed with HIE II/III. NT-1 (358.3 ± 108.3 pg/mL) and NSE (52.97 ± 17.8 ng/mL) levels in the cord blood in the HIE group were significantly higher (p = .030, p = .001, respectively) than cord blood values in the control group (NT-1 (275.1 ± 84.6 pg/mL) and NSE (28.7 ± 16.3 ng/mL)). NT-1 cutoff value for HIE was 292.3 pg/mL and 34.7 ng/mL for NSE (AUC: 990, sensitivity: 94%, specificity 100% and AUC: 1.0, sensitivity: 100% vs. specificity 100%, respectively). NT-1 and NSE represent candidate biomarkers with high reliability in the prediction in newborns with moderate-to-severe HIE.

Relationship between circulating netrin-1 levels, obesity, prediabetes and newly diagnosed type 2 diabetes

BACKGROUND

Netrin-1 is presumed to have regenerative, angiogenic and anti-inflammatory properties, thus it could play a substantial role in the development of insulin resistance and T2DM.

OBJECTIVE

The aim of this study was to evaluate the relationship between serum netrin-1 levels and carbohydrate disturbances in patients with obesity.

METHODS

Sample size consisted of 163 patients, divided into four groups: obesity without carbohydrate disturbances prediabetes and diabetes and healthy controls Netrin-1 level was determined using ELISA method.

RESULTS

Circulating serum Netrin-1 was significantly lower in patients only with obesity, as well as with those with prediabetes and diabetes in comparison to the control group. Correlation analysis revealed that netrin-1 correlates negatively with BMI, waist, WSR, LDL and positive with sudomotor function. Netrin-1 ≤ 0.17 ng/ml has about 3 fold higher risk for carbohydrate disturbances (OR 3.06, 95% CI 1.48-6.34, p = .003).

CONCLUSION

Netrin-1 is associated with an increased risk for glycaemic disorders in patients with obesity.

Single Nuclei Analyses Reveal Transcriptional Profiles and Marker Genes for Diverse Supraspinal Populations

The mammalian brain contains numerous neurons distributed across forebrain, midbrain, and hindbrain that project axons to the lower spinal cord and work in concert to control movement and achieve homeostasis. Extensive work has mapped the anatomic location of supraspinal cell types and continues to establish specific physiological functions. The patterns of gene expression that typify and distinguish these disparate populations, however, are mostly unknown. Here, using adult mice of mixed sex, we combined retrograde labeling of supraspinal cell nuclei with fluorescence-activated nuclei sorting and single-nuclei RNA sequencing analyses to transcriptionally profile neurons that project axons from the brain to lumbar spinal cord. We identified 14 transcriptionally distinct cell types and used a combination of established and newly identified marker genes to assign an anatomic location to each. To validate the putative marker genes, we visualized selected transcripts and confirmed selective expression within lumbar-projecting neurons in discrete supraspinal regions. Finally, we illustrate the potential utility of these data by examining the expression of transcription factors that distinguish different supraspinal cell types and by surveying the expression of receptors for growth and guidance cues that may be present in the spinal cord. Collectively, these data establish transcriptional differences between anatomically defined supraspinal populations, identify a new set of marker genes of use in future experiments, and provide insight into potential differences in cellular and physiological activity across the supraspinal connectome.SIGNIFICANCE STATEMENT The brain communicates with the body through a wide variety of neuronal populations with distinct functions and differential sensitivity to damage and disease. We have used single-nuclei RNA sequencing technology to distinguish patterns of gene expression within a diverse set of neurons that project axons from the mouse brain to the lumbar spinal cord. The results reveal transcriptional differences between populations previously defined on the basis of anatomy, provide new marker genes to facilitate rapid identification of cell type in future work, and suggest distinct responsiveness of different supraspinal populations to external growth and guidance cues.

Pyroptosis and Intervertebral Disc Degeneration: Mechanistic Insights and Therapeutic Implications

Low back pain (LBP) is a common problem worldwide, resulting in great patient suffering and great challenges for the social health system. Intervertebral disc (IVD) degeneration (IVDD) is widely acknowledged as one of the key causes of LBP. Accumulating evidence suggests that aberrant pyroptosis of IVD cells is involved in the pathogenesis of IVDD progression, however, the comprehensive roles of pyroptosis in IVDD have not been fully established, leaving attempts to treat IVDD with anti-pyroptosis approaches questionable. In this review, we summarize the characteristics of pyroptosis and emphasize the effects of IVD cell pyroptosis on the pathological progression of IVDD, including secretion of cytokines, nucleus pulposus cell apoptosis and autophagy, accelerated extracellular matrix degradation, annulus fibrosus rupture, cartilage endplate calcification, vascularization, sensory and sympathetic fiber neoinnervation, and infiltrating lymphatic vessels. Finally, we discuss several interventions used to treat IVDD by targeting pyroptosis. This review provides novel insights into the crucial role of IVD cell pyroptosis in IVDD pathogenesis, and could be informative for developing novel therapeutic approaches for IVDD and LBP.

Placental Therapeutic Targets and Nanodelivery Systems

Pregnancy complications affect millions of women each year. Some of these diseases have high morbidity and mortality such as preeclampsia. At present, there is no safe and effective treatment for pregnancy complications, so it is still a difficult clinical problem. As many pregnancy complications are closely related to placental dysplasia, placenta-specific therapy, as an important method, is expected to be a safe, effective, and specific therapeutic strategy. This review explains in detail the placenta physiological structure, characteristics, and action mechanism of some biomolecules and signaling pathways that play roles in normal development and disorders of the development of the placenta, and how to use these biomolecules as therapeutic targets when the placenta disorder causes disease, combining the latest progress in the field of nanodelivery systems, so as to lay a foundation for the development of placenta-specific therapy of pregnancy complications.

NetrinG1+ cancer-associated fibroblasts generate unique extracellular vesicles that support the survival of pancreatic cancer cells under nutritional stress

It is projected that in 5 years, pancreatic cancer will become the second deadliest cancer in the United States. A unique aspect of pancreatic ductal adenocarcinoma (PDAC) is its stroma; rich in cancer-associated fibroblasts (CAFs) and a dense CAF-generated extracellular matrix (ECM). These pathogenic stroma CAF/ECM units cause the collapse of local blood vessels rendering the tumor microenvironment nutrient-poor. PDAC cells are able to survive this state of nutrient stress via support from CAF-secreted material, which includes small extracellular vesicles (sEVs). The tumor-supportive CAFs possess a distinct phenotypic profile, compared to normal-like fibroblasts, expressing NetrinG1 (NetG1) at the plasma membrane, and active Integrin α₅β₁ localized to the multivesicular bodies; traits indicative of poor patient survival. We herein report that NetG1⁺ CAFs secrete sEVs that stimulate Akt-mediated survival in nutrient-deprived PDAC cells, protecting them from undergoing apoptosis. Further, we show that NetG1 expression in CAFs is required for the pro-survival properties of sEVs. Additionally, we report that the above-mentioned CAF markers are secreted in distinct subpopulations of EVs; with NetG1 being enriched in exomeres, and Integrin α₅β₁ being enriched in exosomes. Finally, we found that NetG1 and Integrin α₅β₁ were detected in sEVs collected from plasma of PDAC patients, while their levels were significantly lower in plasma-derived sEVs of sex/age-matched healthy donors. The discovery of these tumor-supporting CAF-EVs elucidates novel avenues in tumor-stroma interactions and pathogenic stroma detection.

Transcription Profiling of a Revealed the Potential Molecular Mechanism of Governor Vessel Electroacupuncture for Spinal Cord Injury in Rats

OBJECTIVE

This study aimed to identify differentially expressed genes (DEGs) by transcriptome analysis to elucidate a potential mechanism by which governor vessel electroacupuncture (GV-EA) promotes neuronal survival, axonal regeneration, and functional recovery after complete transection spinal cord injury (SCI).

METHODS

Sham, control, or GV-EA group adult female Sprague Dawley rats underwent a complete transection SCI protocol. SCI area RNA-seq investigated the DEGs of coding and noncoding RNAs 7 days post-SCI. Gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses were used to classify DEGs functions, to explain a possible molecular mechanism. Immunofluorescence and BBB (Basso, Beattie, and Bresnahan) score were used to verify a GV-EA treatment effect following SCI.

RESULTS

GV-EA treatment could regulate the expression of 173 mRNA, 260 lncRNA, and 153 circRNA genes among these DEGs resulted by SCI. GO enrichment analysis showed that the DEGs were most enriched in membrane, actin binding, and regulation of Toll-like receptor signaling pathway. KEGG pathway analysis showed enriched pathways (e.g. , Toll-like receptors, MAPK, Hippo signaling). According to the ceRNA network, miR-144-3p played a regulatory role by interacting with lncRNA and circRNA. GV-EA also promoted the injured spinal cord neuron survival, axonal regeneration, and functional improvement of hind limb locomotion.

CONCLUSION

Results of our RNA-seq suggest that post-SCI GV-EA may regulate characteristic changes in transcriptome gene expression, potential critical genes, and signaling pathways, providing clear directions for further investigation into the mechanism of GV-EA in subacute SCI treatment. Moreover, we found that GV-EA promotes neuronal survival, nerve fiber extension, and motor function recovery in subacute SCI.

Exosomal lncRNA PCAT1 Promotes Tumor Circulating Cell-Mediated Colorectal Cancer Liver Metastasis by Regulating the Activity of the miR-329-3p/Netrin-1-CD146 Complex

Objective

This study explored the colorectal cancer exosome lncRNA prostate cancer associated transcript 1– (PCAT1) mediated circulating tumors and the mechanism of cell colorectal cancer liver metastasis.

Methods

Exosomes were extracted from the primary colorectal cancer (CRC) cell lines HCT116 and SW480 and cultured with T84 and human umbilical vein endothelial (HUVE) cells. The expression of PCAT1 and miR-329-3p was detected by real-time quantitative polymerase chain reaction (RT-qPCR), the expression of Netrin-1, CD146, and epithelial mesenchymal transition (EMT) related proteins was detected by Western blot, the proliferation activity of T84 cells was detected by cell counting kit 8 (CCK-8), and cell migration was detected by Transwell. The expression of the F-actin signal was detected by immunofluorescence after coculture of exosomes with human umbilical vein endothelial cells (HUVECs). Changes in subcutaneous tumor and liver nodule size after PCAT1 deletion were observed in a mouse model of liver metastasis from rectal cancer.

Results

PCAT1 expression was upregulated in primary cell lines and their exosomes. After exosomes were cocultured with colorectal cancer tumor circulating T84 cells, the expression of Netrin-1 and CD146 was upregulated, the expression of miR-329-3p was downregulated, the proliferation and migration ability of T84 cells were enhanced, and EMT occurred. After knocking down PCAT1, the above phenomenon was reversed. Similarly, after exosomes were cocultured with HUVECs, the expression of the F-actin signal increased, and after PCAT1 was knocked down, the F-actin signal also decreased. PCAT1 regulates miR-329-3p/Netrin-1 and affects the biological behavior of T84 and F-actin signal expression in HUVECs. In a mouse model of colorectal cancer liver metastasis, knocking down PCAT1 significantly reduced the nodules formed by liver metastasis in mice.

Conclusions

LncRNA PCAT1 derived from colorectal cancer exosomes regulates the activity of the Netrin-1-CD146 complex in circulating tumor cells (CTCs) to promote the occurrence of colorectal cancer EMT and liver metastasis and provides new molecular targets for the treatment of colorectal cancer liver metastasis.

Conductive Hydrogel Conduits with Growth Factor Gradients for Peripheral Nerve Repair in Diabetics with Non-Suture Tape

Diabetic patients suffer from peripheral nerve injury with slow and incomplete regeneration owing to hyperglycemia and microvascular complications. This study develops a graphene-based nerve guidance conduit by incorporating natural double network hydrogel and a neurotrophic concentration gradient with non-invasive treatment for diabetics. GelMA/silk fibroin double network hydrogel plays quadruple roles for rapid setting/curing, suitable mechanical supporting, good biocompatibility, and sustainable growth factor delivery. Meanwhile, graphene mesh can improve the toughness of conduit and enhance conductivity of conduit for regeneration. Here, novel silk tapes show quick and tough adhesion of wet tissue by dual mechanism to replace suture step. The in vivo results demonstrate that gradient concentration of netrin-1 in conduit have better performance than uniform concentration caused by chemotaxis phenomenon for axon extension, remyelination, and angiogenesis. Altogether, GelMA/silk graphene conduit with gradient netrin-1 and dry double-sided adhesive tape can significantly promote repairing of peripheral nerve injury and inhibit the atrophy of muscles for diabetics.

Effect of Recombinant Netrin-1 Protein Combined with Peripheral Blood Mesenchymal Stem Cells on Angiogenesis in Rats with Arteriosclerosis Obliterans

This work was aimed to explore the effect of recombinant netrin-1 protein and peripheral blood mesenchymal stem cells (MSCs) on the angiogenesis ability of atherosclerosis. 28 Sprague Dawley (SD) rats were taken as research models. The arterial occlusion models were created by surgery and then divided into the saline control group (n =7), netrin-1 treatment group (n =7), MSCs treatment group (n =7), and netrin-1 + MSCs combined treatment group (n =7). The peripheral blood MSCs were extracted from the peritoneal cavity of diseased SD rats and cultured alone or in combination with netrin-1. The individually cultured MSCs and netrin-1 were locally injected into the ischemic tissues of SD rats. The Tarlov scoring was performed at the first, second, and third week of treatment, respectively. The expression of vascular endothelial growth factor (VEGF) was also measured by quantitative real-time polymerase chain reaction (qRT-PCR), and the capillary density was measured by immunofluorescence staining. The mean maximum contractility of the gastrocnemius muscle in each group was determined in the third week after treatment. The Tarlov score of the netrin-1 + MSCs group was significantly higher than that of the control group (P < 0.05) at the second week. To the 4th week of treatment, the Tarlov score of the netrin-1 + MSCs group was highly increased compared to the netrin-1 group and the MSCs group (P < 0.05). The expression of VEGF in the treatment groups was greatly increased each week compared to the control group (P < 0.05). Compared with the netrin-1 and the MSCs groups, the VEGF was also notably increased in the netrin-1 + MSCs group (P <0.05). The capillary densities of the treatment groups were observably greater than that of the control group in the second and third weeks (P <0.05), while the capillary density in the netrin-1 + MSCs group was also significantly increased than those in the netrin-1 group and the MSCs group (P < 0.05). The mean maximum contractility of the netrin-1 + MSCs group was remarkably higher than that of the other groups (P < 0.05). The netrin-1 + MSCs group achieved the higher Tarlov score, higher VEGF expression, higher capillary density, and better muscle recovery than netrin-1 and MSCs treatments.

Peripheral nerves in the tibial subchondral bone : the role of pain and homeostasis in osteoarthritis

Osteoarthritis (OA) is a highly prevalent degenerative joint disorder characterized by joint pain and physical disability. Aberrant subchondral bone induces pathological changes and is a major source of pain in OA. In the subchondral bone, which is highly innervated, nerves have dual roles in pain sensation and bone homeostasis regulation. The interaction between peripheral nerves and target cells in the subchondral bone, and the interplay between the sensory and sympathetic nervous systems, allow peripheral nerves to regulate subchondral bone homeostasis. Alterations in peripheral innervation and local transmitters are closely related to changes in nociception and subchondral bone homeostasis, and affect the progression of OA. Recent literature has substantially expanded our understanding of the physiological and pathological distribution and function of specific subtypes of neurones in bone. This review summarizes the types and distribution of nerves detected in the tibial subchondral bone, their cellular and molecular interactions with bone cells that regulate subchondral bone homeostasis, and their role in OA pain. A comprehensive understanding and further investigation of the functions of peripheral innervation in the subchondral bone will help to develop novel therapeutic approaches to effectively prevent OA, and alleviate OA pain.

Cite this article: Bone Joint Res 2022;11(7):439–452.

The Prognostic Value of Deleted in Colorectal Cancer (DCC) Receptor and Serum Netrin-1 in Severe Traumatic Brain Injury

Traumatic brain injury (TBI) is a common neurological disease. Netrin-1 and deleted in colorectal cancer (DCC) receptor are potential biomarkers associated with nerve regeneration and immune regulation. We aimed to investigate the ability of the DCC receptor and Netrin-1 to predict a high ICP level after operation in severe traumatic brain injury and their prognostic significance. This study is a prospective observational study. We selected 23 patients with traumatic brain injury who had undergone surgical operations as subjects. Immunohistochemical staining was performed on the contusion tissue that was removed by the operation to determine the expression of DCC receptor. At the same time, enzyme-linked immunosorbent assay (ELISA) kits were used to detect the serum Netrin-1 content. Determination of intracranial pressure (ICP) value was measured by intraventricular catheter. The Glasgow Outcome Scale (GOS) score at six months after trauma was defined as the main study endpoint. The results showed that serum Netrin-1 concentrations of patients in the critical TBI group (GCS 3–5 points) was significantly lower than that in the severe TBI group (GCS 6–8 points). The ICP peak and average mannitol consumption in the high Netrin-1 group were significantly lower than those in the low Netrin-1 group. DCC receptor-positive patients had a significantly lower ICP peak. There was no significant difference in six month-GOS scores between patients in the high and low Netrin-1 groups, while DCC receptor concentrations below 3.82 ng/mL predicted poor prognosis (GOS 1–3 points). In conclusion, the expression level of the DCC receptor can better evaluate the postoperative high ICP level and prognosis than the level of serum Netrin-1 in severe traumatic brain injury.

UNC5B Overexpression Alleviates Peripheral Neuropathic Pain by Stimulating Netrin-1-Dependent Autophagic Flux in Schwann Cells

Lesions or diseases of the somatosensory system can cause neuropathic pain (NP). Schwann cell (SC) autophagy plays an important role in NP. Uncoordinated gene 5 homolog B (UNC5B), the canonical dependent receptor of netrin-1, is known to be exclusively expressed in SCs and involved in NP; however, the underlying mechanisms were unclear. A rat model of sciatic nerve chronic constriction injury (CCI) was used to induce peripheral neuropathic pain. Adeno-associated virus (AAV) overexpressing UNC5B was applied to the injured nerve, and an autophagy inhibitor, 3-mechyladenine (3-MA), was intraperitoneally injected in some animals. Behavioral tests were performed to evaluate NP, the morphology of the injured nerves was analyzed, and autophagy-related proteins were detected. A rat SC line (RSC96) undergoing oxygen and glucose deprivation (OGD) was used to mimic an ischemic setting to examine the role of UNC5B in autophagy. Local UNC5B overexpression alleviated CCI-induced NP and rescued myelin degeneration. Meanwhile, UNC5B overexpression improved CCI-induced impairment of autophagic flux, while the autophagy inhibitor 3-MA reversed the analgesic effect of UNC5B. In cultured SCs, UNC5B helped recruit netrin-1 to the cell membrane. UNC5B overexpression promoted autophagic flux while inhibiting apoptosis, which was further augmented with exogenous netrin-1 and reversed by netrin-1 knockdown. The enhanced phosphorylation of AMP-activated protein kinase (AMPK) and Unc51-like autophagy activating kinase 1 (ULK1) by UNC5B overexpression was also correlated with netrin-1. Our results suggest that UNC5B facilitates autophagic flux in SCs via phosphorylation of AMPK and ULK1, dependent on its ligand netrin-1, protecting myelin and partly preventing injury-induced NP.

Netrin-1: A Serum Marker Predicting Cognitive Impairment after Spinal Cord Injury

Objective

Although cognitive impairment has received more attention in recent years as a result of spinal cord injury (SCI), the pathogenic process that causes it is still unknown. The neuroprotective effects of Netrin as a family of laminin-related secreted proteins were discovered. The purpose of this study was to determine the changes of serum Netrin-1 after SCI and its relationship with cognitive impairment.

Methods

96 SCI patients and 60 controls were included in our study. We collected baseline data from all participants, measured their serum Netrin-1 levels, and followed up their cognitive levels 3 months later.

Results

The clinical baseline values between the control and SCI groups were not significantly different (p > 0.05). However, the serum Netrin-1 level in the SCI group was significantly lower than that in the control group (528.4 ± 88.3 pg/ml vs. 673.5 ± 97.2 pg/ml, p < 0.05). According to the quartile level of serum Netrin-1 level in the SCI group, we found that with the increase of serum Netrin-1 level, the MoCA score also increased significantly (p < 0.001), indicating that the serum Netrin-1 level was positively correlated with the MoCA score after SCI. After controlling for baseline data, multiple regression analysis revealed that Netrin-1 remained an independent risk factor for cognitive impairment after SCI (=0.274, p = 0.036).

Conclusions

Netrin-1 may be a neuroprotective factor for cognitive impairment, which may serve as a serum marker to predict cognitive impairment after SCI.

Gene Expression Profile of Mycobacterium leprae Contribution in the Pathology of Leprosy Neuropathy

Peripheral neuropathy is the main cause of physical disability in leprosy patients. Importantly, the extension and pattern of peripheral damage has been linked to how the host cell will respond against Mycobacterium leprae (M. leprae) infection, in particular, how the pathogen will establish infection in Schwann cells. Interestingly, viable and dead M. leprae have been linked to neuropathology of leprosy by distinct mechanisms. While viable M. leprae promotes transcriptional modifications that allow the bacteria to survive through the use of the host cell's internal machinery and the subvert of host metabolites, components of the dead bacteria are associated with the generation of a harmful nerve microenvironment. Therefore, understanding the pathognomonic characteristics mediated by viable and dead M. leprae are essential for elucidating leprosy disease and its associated reactional episodes. Moreover, the impact of the viable and dead bacteria in Schwann cells is largely unknown and their gene signature profiling has, as yet, been poorly explored. In this study, we analyzed the early differences in the expression profile of genes involved in peripheral neuropathy, dedifferentiation and plasticity, neural regeneration, and inflammation in human Schwann cells challenged with viable and dead M. leprae. We substantiated our findings by analyzing this genetic profiling in human nerve biopsies of leprosy and non-leprosy patients, with accompanied histopathological analysis. We observed that viable and dead bacteria distinctly modulate Schwann cell genes, with emphasis to viable bacilli upregulating transcripts related to glial cell plasticity, dedifferentiation and anti-inflammatory profile, while dead bacteria affected genes involved in neuropathy and pro-inflammatory response. In addition, dead bacteria also upregulated genes associated with nerve support, which expression profile was similar to those obtained from leprosy nerve biopsies. These findings suggest that early exposure to viable and dead bacteria may provoke Schwann cells to behave differentially, with far-reaching implications for the ongoing neuropathy seen in leprosy patients, where a mixture of active and non-active bacteria are found in the nerve microenvironment.

Evaluation of Platelet-Rich Plasma Therapy for Peripheral Nerve Regeneration: A Critical Review of Literature

Peripheral nerve injury (PNI) is a common disease in clinic, and the regeneration process of peripheral nerve tissue is slow, and patients with PNI often suffer from the loss of nerve function. At present, related research on the mechanism of peripheral nerve regeneration has become a hot spot, and scholars are also seeking a method that can accelerate the regeneration of peripheral nerve. Platelet-rich plasma (PRP) is a platelet concentrate extracted from autologous blood by centrifugation, which is a kind of bioactive substance. High concentration of platelets can release a variety of growth factors after activation, and can promote the proliferation and differentiation of tissue cells, which can accelerate the process of tissue regeneration. The application of PRP comes from the body, there is no immune rejection reaction, it can promote tissue regeneration with less cost, it is,therefore, widely used in various clinical fields. At present, there are relatively few studies on the application of PRP to peripheral nerve regeneration. This article summarizes the literature in recent years to illustrate the effect of PRP on peripheral nerve regeneration from mechanism to clinical application, and prospects for the application of PRP to peripheral nerve.

Transcriptional Analysis-Based Alterations Affecting Neuritogenesis of the Peripheral Nervous System in Psoriasis

An increasing amount of evidence indicates the critical role of the cutaneous nervous system in the initiation and maintenance of psoriatic skin lesions by neurogenic inflammation. However, molecular mechanisms affecting cutaneous neurons are largely uncharacterized. Therefore, we reanalyzed a psoriatic RNA sequencing dataset from published transcriptome experiments of nearly 300 individuals. Using the Ingenuity Pathway Analysis software, we associated several hundreds of differentially expressed transcripts (DETs) to nervous system development and functions. Since neuronal projections were previously reported to be affected in psoriasis, we performed an in-depth analysis of neurite formation-related process. Our in silico analysis suggests that SEMA-PLXN and ROBO-DCC-UNC5 regulating axonal growth and repulsion are differentially affected in non-lesional and lesional skin samples. We identified opposing expressional alterations in secreted ligands for axonal guidance signaling (RTN4/NOGOA, NTNs, SEMAs, SLITs) and non-conventional axon guidance regulating ligands, including WNT5A and their receptors, modulating axon formation. These differences in neuritogenesis may explain the abnormal cutaneous nerve filament formation described in psoriatic skin. The processes also influence T-cell activation and infiltration, thus highlighting an additional angle of the crosstalk between the cutaneous nervous system and the immune responses in psoriasis pathogenesis, in addition to the known neurogenic pro-inflammatory mediators.

Myelinating Schwann cells and Netrin-1 control intra-nervous vascularization of the developing mouse sciatic nerve

Peripheral nerves are vascularized by a dense network of blood vessels to guarantee their complex function. Despite the crucial role of vascularization to ensure nerve homeostasis and regeneration, the mechanisms governing nerve invasion by blood vessels remain poorly understood. We found, in mice, that the sciatic nerve invasion by blood vessels begins around embryonic day 16 and continues until birth. Interestingly, intra-nervous blood vessel density significantly decreases during post-natal period, starting from P10. We show that, while the axon guidance molecule Netrin-1 promotes nerve invasion by blood vessels via the endothelial receptor UNC5B during embryogenesis, myelinated Schwann cells negatively control intra-nervous vascularization during post-natal period.

Netrin-1 promotes liver regeneration possibly by facilitating vagal nerve repair after partial hepatectomy in mice

Hepatic regeneration after hepatectomy is a great concern in clinical practice. Recently, the neuronal guidance protein netrin-1 has been reported to enhance regeneration after nerve injury. The goal of this study was to preliminarily investigate whether netrin-1 stimulates vagus nerve regeneration to promote liver regeneration after partial hepatectomy in mice. The expression of netrin-1 in murine remnant livers after partial hepatectomy (PHx) was evaluated in initial studies. C57BL/6 mice that received exogenous netrin-1 after PHx were used to examine liver regeneration. PHx was performed in wild-type mice after adeno-associated virus injection (Ntn1 gene silencing) to detect the impact of endogenous netrin-1. After PHx and hepatic branch vagotomy (HV), the mice were injected with or without netrin-1 to evaluate the effects on hepatic regeneration and vagal nerve recovery. Significant reductions in netrin-1 at the transcript and protein levels in murine liver tissue after hepatectomy were observed. Subsequent studies of netrin-1 administration revealed the promotion of hepatocyte proliferation and specific growth factors contributing to liver repair and a decrease in hepatic-specific injury enzymes. Furthermore, the opposite results were observed in the netrin-1 knockdown group. HV delayed liver regeneration after PHx. However, this retardation was reversed by exogenous netrin-1 supplementation. In addition, the results of nerve growth and vagal nerve repair in the remnant liver suggested that netrin-1 promoted vagal nerve regeneration after hepatectomy. Netrin-1 accelerates liver regeneration after partial hepatectomy in mice, and the potential mechanism is related to the promotion of vagus nerve repair and regeneration.

New Frontiers in Peripheral Nerve Regeneration: Concerns and Remedies

Topical advances in studying molecular and cellular mechanisms responsible for regeneration in the peripheral nervous system have highlighted the ability of the nervous system to repair itself. Still, serious injuries represent a challenge for the morphological and functional regeneration of peripheral nerves, calling for new treatment strategies that maximize nerve regeneration and recovery. This review presents the canonical view of the basic mechanisms of nerve regeneration and novel data on the role of exosomes and their transferred microRNAs in intracellular communication, regulation of axonal growth, Schwann cell migration and proliferation, and stromal cell functioning. An integrated comprehensive understanding of the current mechanistic underpinnings will open the venue for developing new clinical strategies to ensure full regeneration in the peripheral nervous system.

Curcumin enhances the proliferation and myelinization of Schwann cells through Runx2 to repair sciatic nerve injury

BACKGROUND

RUNX Family Transcription Factor 2 (Runx2) promotes neurite outgrowth after sciatic nerve injury, and Curcumin can promote the expression of Runx2. It is worthwhile to explore whether curcumin's repair effect on sciatic nerve injury is related to Runx2.

OBJECTIVE

To investigate the repair effect of curcumin on sciatic nerve injury and its possible mechanism.

RESULTS

Curcumin improved the sciatic functional index (SFI) and toe spread index (TSI) of rats with sciatic nerve injury and increased the number and diameter of myelinated axons in the sciatic nerve. Curcumin promoted the myelination of SCs (Schwann cells) by increasing the expression of peripheral myelin protein 22 (PMP22), fibrin, S100, and proliferating cell nuclear antige (PCNA). Curcumin treatment increased the proliferation of SCs and the expression of Runx2. Cell experiments further confirmed that curcumin promoted Schwann cell proliferation and myelination through Runx2.

CONCLUSION

Curcumin promotes SCs proliferation and myelination through Runx2 and improves sciatic nerve repair.

CD146 mediates the anti-apoptotic role of Netrin-1 in endothelial progenitor cells under hypoxic conditions

Modulating the biological status of endothelial progenitor cells (EPCs), such as function and survival, is essential for therapeutic angiogenesis in ischemic vascular disease environments. This study aimed to explore the role and molecular mechanisms underlying Netrin-1 in the viability and angiogenic function of EPCs. EPCs were isolated from the bone barrow of adult C57/BL6 mice. The apoptosis and various functions of EPCs were analyzed in vitro by manipulating the expression of Netrin-1. The TUNEL assay was performed to detect apoptotic EPCs. Cell migration and tube formation assays were performed to detect EPC function. Trypan blue staining was performed to detect cell viability. Western blot analysis was performed to detect the protein expression levels of Netrin-1, CD146 and apoptotic factors. Quantitative PCR analysis was performed to detect the expression levels of Netrin-1 receptors. The results demonstrated that treatment with exogenous Netrin-1 promoted EPC migration and tube formation, whereas transfection with small interfering (si)RNA targeting Netrin-1 exhibited the opposite effects. Exogenous Netrin-1 protected EPCs from hypoxia-induced apoptosis, whereas the interruption of endogenous Netrin-1 enhancement under hypoxia by Netrin-1-siRNA exacerbated the apoptosis of EPCs. Furthermore, CD146, one of the immunoglobulin receptors activated by Netrin-1, was screened for in the present study. Results demonstrated that CD146 did not participate in Netrin-1-promoted EPC function, but mediated the anti-apoptotic effects of Netrin-1 in EPCs. In conclusion, Netrin-1 enhanced the angiogenic function of EPCs and alleviated hypoxia-induced apoptosis, which was mediated by CD146. This biological function of Netrin-1 may provide a potential therapeutic option to promote EPCs for the treatment of ischemic vascular diseases.

Netrin-1 as a Multitarget Barrier Stabilizer in the Peripheral Nerve after Injury

The blood–nerve barrier and myelin barrier normally shield peripheral nerves from potentially harmful insults. They are broken down during nerve injury, which contributes to neuronal damage. Netrin-1 is a neuronal guidance protein with various established functions in the peripheral and central nervous systems; however, its role in regulating barrier integrity and pain processing after nerve injury is poorly understood. Here, we show that chronic constriction injury (CCI) in Wistar rats reduced netrin-1 protein and the netrin-1 receptor neogenin-1 (Neo1) in the sciatic nerve. Replacement of netrin-1 via systemic or local administration of the recombinant protein rescued injury-induced nociceptive hypersensitivity. This was prevented by siRNA-mediated knockdown of Neo1 in the sciatic nerve. Mechanistically, netrin-1 restored endothelial and myelin, but not perineural, barrier function as measured by fluorescent dye or fibrinogen penetration. Netrin-1 also reversed the decline in the tight junction proteins claudin-5 and claudin-19 in the sciatic nerve caused by CCI. Our findings emphasize the role of the endothelial and myelin barriers in pain processing after nerve damage and reveal that exogenous netrin-1 restores their function to mitigate CCI-induced hypersensitivity via Neo1. The netrin-1-neogenin-1 signaling pathway may thus represent a multi-target barrier protector for the treatment of neuropathic pain.

Transcriptome profiling implicated in beneficiary actions of kimchi extracts against Helicobacter pylori infection

Dietary intervention to prevent Helicobacter pylori (H. pylori)-gastric cancer might be ideal because of no risk of bacterial resistance, safety, and rejuvenating action of atrophic gastritis. We have published data about the potential of fermented kimchi as nutritional approach for H. pylori. Hence recent advances in RNAseq analysis lead us to investigate the transcriptome analysis to explain these beneficiary actions of kimchi. gastric cells were infected with either H. pylori or H. pylori plus kimchi. 943 genes were identified as significantly increased or decreased genes according to H. pylori infection and 68 genes as significantly changed between H. pylori infection and H. pylori plus kimchi (p<0.05). Gene classification and Medline database showed DLL4, FGF18, PTPRN, SLC7A11, CHAC1, FGF21, ASAN, CTH, and CREBRF were identified as significantly increased after H. pylori, but significantly decreased with kimchi and NEO1, CLDN8, KLRG1, and IGFBP1 were identified as significantly decreased after H. pylori, but increased with kimchi. After KEGG and STRING-GO analysis, oxidative stress, ER stress, cell adhesion, and apoptosis genes were up-regulated with H. pylori infection but down-regulated with kimchi, whereas tissue regeneration, cellular anti-oxidative response, and anti-inflammation genes were reversely regulated with kimchi (p<0.01). Conclusively, transcriptomes of H. pylori plus kimchi showed significant biological actions.

The expression of Netrin-1 in the MIA-induced osteoarthritic temporomandibular joint in mice

Subchondral bone degeneration is the main pathological change during temporomandibular joint (TMJ) osteoarthritis (OA) development. Netrin-1, an axon-guiding factor, might play roles in OA development and pain. The purpose of this study was to investigate the expression of Netrin-1 in TMJ OA and its possible role in the progression of TMJ OA and pain. The synovial fluids of temporomandibular joint disorders (TMDs) patients were collected for Netrin-1 by enzyme linked immunosorbent assay (ELISA). TMJ OA model was built by MIA joint injection, and then the von Frey test, hematoxylin & eosin (H&E) staining, toluidine blue (TB) staining, immunohistochemical (IHC) staining and micro-CT were performed. After induction of osteoclast differentiation of raw264.7 cells, immunofluorescence (IF) was used to detect the Netrin-1 and its receptors on osteoclast membrane. The concentration of Netrin-1 increased in the synovial fluid of TMJ OA patients. After MIA injection to TMJ, the head withdrawal threshold (HWT) was significantly decreased. Microscopically, the structural disorder of subchondral bone was the most obvious at the 2nd week after MIA injection. In addition, Netrin-1 expression increased in the subchondral bone at the 2nd week after MIA injection. In vitro, the expressions of Netrin-1 and its receptor Unc5B were upregulated on the osteoclast membrane. Netrin-1 might be an important regulator during bone degeneration and pain in the process of TMJ OA.

Unraveling Axon Guidance during Axotomy and Regeneration

During neuronal development and regeneration axons extend a cytoskeletal-rich structure known as the growth cone, which detects and integrates signals to reach its final destination. The guidance cues “signals” bind their receptors, activating signaling cascades that result in the regulation of the growth cone cytoskeleton, defining growth cone advance, pausing, turning, or collapse. Even though much is known about guidance cues and their isolated mechanisms during nervous system development, there is still a gap in the understanding of the crosstalk between them, and about what happens after nervous system injuries. After neuronal injuries in mammals, only axons in the peripheral nervous system are able to regenerate, while the ones from the central nervous system fail to do so. Therefore, untangling the guidance cues mechanisms, as well as their behavior and characterization after axotomy and regeneration, are of special interest for understanding and treating neuronal injuries. In this review, we present findings on growth cone guidance and canonical guidance cues mechanisms, followed by a description and comparison of growth cone pathfinding mechanisms after axotomy, in regenerative and non-regenerative animal models.

Epitranscriptomic Analysis of m6A Methylome After Peripheral Nerve Injury

N6-methyladenosine (m6A) is one of the most plentiful internal RNA modifications, especially in eukaryotic messenger RNA (mRNA), which plays pivotal roles in the regulation of mRNA life cycle and nerve development. However, the mRNA m6A methylation pattern in peripheral nervous injury (PNI) has not been investigated. In this study, sciatic nerve samples were collected from 7 days after sciatic nerve injury (SNI) and control rats. Quantitative real-time PCR demonstrated that m6A-related methyltransferase/demethylase genes were remarkably upregulated in SNI group compared with control group. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) was performed to reveal the m6A methylation landscape. The results showed that 4,014 m6A peaks were significantly altered, including 2,144 upregulated and 1,870 downregulated m6A peaks, which were corresponded to 1,858 genes. Moreover, 919 differentially expressed genes were identified by the conjoint analysis of MeRIP-seq and RNA-seq. GO and KEGG pathway analyses were performed to determine the biological functions and signaling pathways of the m6A-modified genes. Notably, these genes were mainly related to the immune system process, cell activation, and nervous system development in GO analysis. KEGG pathway analysis revealed that these genes were involved in the cell cycle, B cell receptor signaling pathway, axon guidance pathway, and calcium signaling pathway. Furthermore, the m6A methylation and protein expression levels of autophagy-related gene (Atg7) were increased, together with the activation of autophagy. These findings shed some light on the epigenetic regulation of gene expression, which may provide a new opinion to promote functional recovery after PNI.

Roles and Mechanisms of Axon-Guidance Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive memory decline and cognitive dysfunctions. Although the causes of AD have not yet been established, many mechanisms have been proposed. Axon-guidance molecules play the roles in the occurrence and development of AD by participating in different mechanisms. Therefore, what roles do axon-guidance molecules play in AD? This study aimed at elucidating how axon-guidance molecules Netrins, Slits, Semaphorins, and Ephrins regulate the levels of Aβ, hyperphosphorylation of tau protein, Reelin, and other ways through different signaling pathways, in order to show the roles of axon-guidance molecules in the occurrence and development of AD. And it is hoped that this study can provide a theoretical basis and new perspectives in the search for new therapeutic targets for AD.

Regulation of UNC-40/DCC and UNC-6/Netrin by DAF-16 promotes functional rewiring of the injured axon

The adult nervous system has a limited capacity to regenerate after accidental damage. Post-injury functional restoration requires proper targeting of the injured axon to its postsynaptic cell. Although the initial response to axonal injury has been studied in great detail, it is rather unclear what controls the re-establishment of a functional connection. Using the posterior lateral microtubule neuron in Caenorhabditis elegans, we found that after axotomy, the regrowth from the proximal stump towards the ventral side and accumulation of presynaptic machinery along the ventral nerve cord correlated to the functional recovery. We found that the loss of insulin receptor DAF-2 promoted 'ventral targeting' in a DAF-16-dependent manner. We further showed that coordinated activities of DAF-16 in neuron and muscle promoted 'ventral targeting'. In response to axotomy, expression of the Netrin receptor UNC-40 was upregulated in the injured neuron in a DAF-16-dependent manner. In contrast, the DAF-2-DAF-16 axis contributed to the age-related decline in Netrin expression in muscle. Therefore, our study revealed an important role for insulin signaling in regulating the axon guidance molecules during the functional rewiring process.

Functionalizing biomaterials to promote neurovascular regeneration following skeletal muscle injury

During embryogenesis, blood vessels and nerves develop with similar branching structure in response to shared signaling pathways guiding network growth. With both systems integral to physiological homeostasis, dual targeting of blood vessels and nerves to promote neurovascular regeneration following injury is an emerging therapeutic approach in biomedical engineering. A limitation to this strategy is that the nature of cross talk between emergent vessels and nerves during regeneration in an adult is poorly understood. Following peripheral nerve transection, intraneural vascular cells infiltrate the site of injury to provide a migratory pathway for mobilized Schwann cells of regenerating axons. As Schwann cells demyelinate, they secrete vascular endothelial growth factor, which promotes angiogenesis. Recent advances point to concomitant restoration of neurovascular architecture and function through simultaneous targeting of growth factors and guidance cues shared by both systems during regeneration. In the context of traumatic injury associated with volumetric muscle loss, we consider the nature of biomaterials used to engineer three-dimensional scaffolds, functionalization of scaffolds with molecular signals that guide and promote neurovascular growth, and seeding scaffolds with progenitor cells. Physiological success is defined by each tissue component of the bioconstruct (nerve, vessel, muscle) becoming integrated with that of the host. Advances in microfabrication, cell culture techniques, and progenitor cell biology hold great promise for engineering bioconstructs able to restore organ function after volumetric muscle loss.