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

Neuroimmune circuits in the plaque and bone marrow regulate atherosclerosis

Atherosclerosis remains the leading cause of death globally. Although its focal pathology is atheroma that develops in arterial walls, atherosclerosis is a systemic disease involving contributions by many organs and tissues. It is now established that the immune system causally contributes to all phases of atherosclerosis. Recent and emerging evidence positions the nervous system as a key modulator of inflammatory processes that underly atherosclerosis. This neuro-immune crosstalk, we are learning, is bidirectional, and immune regulated afferent signaling is becoming increasingly recognized in atherosclerosis. Here, we summarize data and concepts that link the immune and nervous systems in atherosclerosis by focusing on two important sites, the arterial vessel and the bone marrow.

Netrin-1 protects blood-brain barrier (BBB) integrity after cerebral ischemia-reperfusion by activating the Kruppel-like factor 2 (KLF2)/occludin pathway

Ischemia/reperfusion (I/R)-induced neural damage and neuroinflammation have been associated with pathological progression during stroke. Netrin-1 is an important member of the family of laminin-related secreted proteins, which plays an important role in governing axon elongation. However, it is unknown whether Netrin-1 possesses a beneficial role in stroke. Here, we employed the middle cerebral artery occlusion (MCAO) model to study the function of Netrin-1 in alleviating brain injuries. Our results demonstrate that Netrin-1 rescued poststroke neurological deficits and inhibited production of the inflammatory cytokines such as interleukin 6 (IL-6) and endothelial chemokine (C-X-C motif) ligand 1 (Cxcl1). Importantly, Netrin-1 protected against MCAO-induced dysfunction of the blood-brain barrier (BBB) in mice and a reduction in the expression of the tight junction (TJ) protein occludin. Additionally, we report that Netrin-1 could ameliorate oxygen-glucose deprivation/reoxygenation (OGD/R)-induced injury and prevent aggravation in endothelial monolayer permeability in bEnd.3 human brain microvascular endothelial cells (HBMVECs). Mechanistically, Netrin-1 ameliorated OGD/R-induced decrease in occludin and Kruppel-like factor 2 (KLF2) in HBMVECs. Notably, silencing of KLF2 abolished the beneficial effects of Netrin-1 in protecting endothelial permeability and occludin expression, suggesting that these effects are mediated by KLF2. In conclusion, our findings suggest that Netrin-1 could constitute a novel therapeutic strategy for ischemic stroke.

Systemwide effects of ER-intracellular membrane contact site disturbance in primary endothelial cells

Membrane contact sites (MCS) make up a crucial route of inter-organelle non-vesicular transport within the cell. Multiple proteins are involved in this process, which includes the ER-resident proteins vesicle associated membrane protein associated protein A and -B (VAPA/B) that form MCS between the ER and other membrane compartments. Currently most functional data on VAP depleted phenotypes have shown alterations in lipid homeostasis, induction of ER stress, dysfunction of UPR and autophagy, as well as neurodegeneration. Literature on concurrent silencing of VAPA/B is still sparse; therefore, we investigated how it affects the macromolecule pools of primary endothelial cells. Our transcriptomics results showed significant upregulation in genes related to inflammation, ER and Golgi dysfunction, ER stress, cell adhesion, as well as Coat Protein Complex-I and -II (COP-I, COP-II) vesicle transport. Genes related to cellular division were downregulated, as well as key genes of lipid and sterol biosynthesis. Lipidomics analyses revealed reductions in cholesteryl esters, very long chain highly unsaturated and saturated lipids, whereas increases in free cholesterol and relatively short chain unsaturated lipids were evident. Furthermore, the knockdown resulted in an inhibition of angiogenesis in vitro. We speculate that ER MCS depletion has led to multifaceted outcomes, which include elevated ER free cholesterol content and ER stress, alterations in lipid metabolism, ER-Golgi function and vesicle transport, which have led to a reduction in angiogenesis. The silencing also induced an inflammatory response, consistent with upregulation of markers of early atherogenesis. To conclude, ER MCS mediated by VAPA/B play a crucial role in maintaining cholesterol traffic and sustain normal endothelial functions.

Netrin-1 and RGMa: Novel Regulators of Atherosclerosis-Related Diseases

BACKGROUNDS

Neuronal guidance proteins (NGPs) have been demonstrated to guide the elongation of neuronal axonal growth cones in the developing central nervous system. Non-neuronal functions of NGPs have also been described, especially in relation to atherosclerosis.

FINDINGS

Netrin-1 and repulsive guidance molecule a (RGMa) are NGPs that have been shown to regulate endothelial cell adhesion and angiogenesis, macrophage migration and apoptosis, smooth muscle cells (SMCs) phenotypic dedifferentiation and mobility, chemokine activities, and inflammatory responses during atherosclerosis initiation and progression.

PURPOSES

However, mechanistic studies have generated controversy about the specific role of Netrin-1 in atherosclerosis due to the diversity of its structure, receptors and cell sources, and the actions of RGMa in atherosclerosis have not been reported in previous reviews. Therefore, the current work reviews the evidence for roles of Netrin-1 and RGMa in the initiation and progression of atherosclerosis and discusses potential therapeutic targets in the future.

Association of Netrin 1 with hsCRP in Subjects with Obesity and Recent Diagnosis of Type 2 Diabetes

Netrin 1 (Ntn1) is a cell migration protein with an anti-inflammatory effect, which may play a key role in the pathological development of type 2 diabetes (T2D). In this study, we evaluate the relationships between the serum concentrations of Ntn1, glucose, and high-sensitivity C-reactive Protein (hsCRP). We carried out a cross-sectional study including 90 individuals divided into three groups (n = 30): healthy subjects, individuals with obesity without glucose alterations, and individuals with newly diagnosed T2D. Serum concentrations of Ntn1 and hs-CRP were determined by enzyme-linked immunosorbent assay (ELISA). The serum concentration of Ntn1 was higher in individuals with newly diagnosed T2D (0.33 ± 0.22 ng/mL), in comparison to healthy subjects and individuals with obesity (0.13 ± 0.06 and 0.15 ± 0.07 ng/mL, respectively). In addition, we observed a positive association between the levels of Ntn1 and hsCRP (rho = 0.443; p < 0.001) as well as with serum glucose (rho = −0.110; p = 0.05). The serum concentration of Ntn1 was higher in individuals with T2D, in comparison with the other groups in this study, and presented a positive correlation with hsCRP. Therefore, Ntn1 can be considered a promising risk biomarker and a potential therapeutic target for T2D.

Netrin-1 Secreted by Human Osteoarthritic Articular Chondrocytes Promotes Angiogenesis in Vitro

OBJECTIVE

Netrin-1 expression in articular cartilage is correlated with osteoarthritic changes. We aimed to investigate the contribution of Netrin-1 secreted by human osteoarthritic articular chondrocytes to angiogenesis process in vitro.

DESIGN

Human articular chondrocytes were extracted from non-osteoarthritic (n = 10) and osteoarthritic (n = 22) joints obtained from surgical specimens and incubated for 24 hours. Medium conditioned by non-osteoarthritic and osteoarthritic articular chondrocytes were collected. Human umbilical vein endothelial cells (HUVEC) were treated with control and conditioned medium and assessed using assays for cell adherence, migration, and tube formation. Netrin-1 expression and secretion was compared between non-osteoarthritic and osteoarthritic chondrocytes by qPCR, Western blot, and ELISA. The role of chondrocyte-secreted Netrin-1 on HUVEC functions was assessed by immunological neutralization using an anti-Netrin-1 monoclonal antibody.

RESULTS

As compared with medium conditioned by non-osteoarthritic chondrocytes, medium conditioned by osteoarthritic chondrocytes permitted tube formation by HUVEC. Both non-osteoarthritic and osteoarthritic chondrocytes expressed Netrin-1 at the RNA and protein levels. At the RNA level, Netrin-1 expression did not differ between non-osteoarthritic and osteoarthritic chondrocytes. At the protein level, Netrin-1 appeared as a full protein of 64 kDa in non-osteoarthritic chondrocytes and as two cleaved proteins of 55 kDa and 64 kDa in osteoarthritic chondrocytes. Immunological neutralization of endogenous Netrin-1 reduced the pro-angiogenic and pro-inflammatory transcriptional profile of HUVEC treated with the medium conditioned by osteoarthritic chondrocytes, as well as their capacities to form tubes.

CONCLUSIONS

Medium conditioned by osteoarthritic chondrocytes permits tube formation by HUVEC in vitro. This permissive effect is mediated by Netrin-1.

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.

Netrin-1 Promotes Visceral Adipose Tissue Inflammation in Obesity and Is Associated with Insulin Resistance

Netrin (NTN)-1 exhibits pro- and anti-inflammatory roles in different settings, playing important roles in the obesity-associated low-grade chronic inflammation. We aimed to determine the impact of NTN-1 on obesity and obesity-associated type 2 diabetes, as well as its role in visceral adipose tissue (VAT) inflammation. A total of 91 subjects were enrolled in this case-control study. Circulating levels of NTN-1 and its receptor neogenin (NEO)-1 were determined before and after weight loss achieved by caloric restriction and bariatric surgery. mRNA levels of NTN1 and NEO1 were assessed in human VAT, liver, and peripheral blood mononuclear cells. In vitro studies in human visceral adipocytes and human monocytic leukemia cells (THP-1)-derived macrophages were performed to analyze the impact of inflammation-related mediators on the gene expression levels of NTN1 and its receptor NEO1 as well as the effect of NTN-1 on inflammation. Increased (p < 0.001) circulating concentrations of NTN-1 in obesity decreased (p < 0.05) after diet-induced weight loss being also associated with a reduction in glucose (p < 0.01) and insulin levels (p < 0.05). Gene expression levels of NTN1 and NEO1 were upregulated (p < 0.05) in the VAT from patients with obesity with the highest expression in the stromovascular fraction cells compared with mature adipocytes (p < 0.01). NTN1 expression levels were enhanced (p < 0.01) under hypoxia and by inflammatory factors in both adipocytes and macrophages. Adipocyte-conditioned media strongly upregulated (p < 0.001) the mRNA levels of NTN1 in macrophages. The treatment of adipocytes with NTN-1 promoted the upregulation (p < 0.05) of pro-inflammatory and chemotactic molecules as well as its receptor NEO1. Collectively, these findings suggest that NTN-1 regulates VAT chronic inflammation and insulin resistance in obesity.

Metformin Alleviates LPS-Induced Acute Lung Injury by Regulating the SIRT1/NF-κB/NLRP3 Pathway and Inhibiting Endothelial Cell Pyroptosis

Acute respiratory distress syndrome (ARDS), a devastating complication of numerous conditions, is often associated with high mortality. It is well known that endothelial cell (EC) damage and inflammation are vital processes in the pathogenesis of ARDS. Nevertheless, the mechanisms of EC damage are largely unknown. In the present study, we investigated the role of pyroptosis in the initiation of ARDS and demonstrated that endothelial pyroptosis might play a pivotal role in the pathophysiology of ARDS. Metformin, an antidiabetic drug, exhibited a protective effect in lipopolysaccharide (LPS)-induced lung injury, and we hypothesized that metformin alleviated LPS-induced lung injury via inhibiting ECs pyroptosis. In vivo, male ICR mice were intratracheally injected with LPS, and metformin was previously administered intraperitoneally. Morphological properties of lung tissues were detected. We showed that metformin inhibited NLRP3 inflammasome activation and NLRP3-stimulated pyroptosis induction, as shown by decreased levels of cleaved caspase-1, N-terminal fragment of GSDMD, and protein contents of IL-1β in lung tissues of mice exposed to LPS. LPS-induced expression of vascular adhesion molecules was also reduced after the treatment with metformin. In vitro, exposure of pulmonary ECs to LPS resulted in increased expression of NLRP3 and pyroptosis-associated indicators. By inhibiting the expression of NLRP3 with NLRP3 inhibitor MCC950, pyroptosis-related markers and vascular adhesion molecules were ameliorated. Moreover, metformin treatment significantly inhibited the NF-κB signaling pathway and increased the expression of sirtuin 1 (SIRT1) both in LPS-stimulated lung tissues and pulmonary ECs. Administration of the selective SIRT1 inhibitor nicotinamide significantly reversed the protective effect of metformin against endothelial pyroptosis and lung injury in LPS-treated ECs and LPS-induced acute lung injury (ALI). Thus, these findings demonstrated that metformin alleviated LPS-induced ALI by inhibiting NF-κB-NLRP3–mediated ECs pyroptosis, possibly by upregulating the expression of SIRT1.

Plasma Netrin-1 & cardiovascular risk in children with end stage renal disease

Background: Cardiovascular disease (CVD) is the most common cause of mortality and morbidity in children with end stage kidney disease (ESKD) which arises from the interaction of several risk factors. The aim of the study is to assess CV risk of ESKD children and outline the impact of KTX on this CV risk. Also valuate the relation between plasma Netrin-1, chronic inflammatory markers and CV risk. Methods: Sixty ESKD (30 on regular hemodialysis (HD), 30 recipients of kidney transplant (KTX)) were assessed using 24 hour AMBP assessment, laboratory (including lipid profile and markers of chronic inflammation namely N/L and HsCRP) and echocardiographic data. Plasma netrin-1 was assessed by ELISA technique for all patients. Results: showed significant higher prevalence of hypertension, higher number of patients with 24hrs BP> 95th percentile by ABPM, more prevalence of nocturnal non-dipping BP, higher percentage of obese and overweight patients, worse biochemical analysis, higher chance of medical calcification by higher Po4 and Ca X Po4, higher triglyceride level and lower HDL level and higher N/L in HD than KTX group. Significant inverse relation was detected between plasma netrin 1 and Hs CRP and between netrin 1 and N/L (p<0.001).

The role of adropin, salusin-α, netrin-1, and nesfatin-1 in endometriosis and their association with insulin resistance

Objective:

The pathogenesis of endometriosis has not been clearly explained. Inflammatory factors of ectopic implantation and the growth of ectopic endometrial cells have been subjects of major interest. The number of studies evaluating salusin-α and nesfatin-1 markers in patients with endometriosis is limited. No studies have evaluated the levels of anti-inflammatory markers for adropin and netrin-1 in patients with endometriosis. This study investigates how some important inflammatory regulatory markers in the inflammatory process affect the pathogenesis of endometriosis and determines whether any relationship exists between serum levels of these parameters and endometriosis and insulin resistance.

Materials and Methods:

This prospective study included 73 patients with endometriosis diagnosed histopathologically after laparoscopic surgery and 75 healthy controls. Serum adropin, salusin-α, netrin-1, and nesfatin-1 levels and homeostatic model assessment of insulin resistance (HOMA-IR) values of the participants were measured.

Results:

The endometriosis group had significantly lower nesfatin-1 levels than the control group (3.0±0.53 vs 9.5±0.94, p=0.005). Between the patient and control groups, there was no difference regarding serum adropin, salusin-α, and netrin-1 levels (p=0.36, p=0.34, p=0.75, respectively). Nesfatin-1 had a significant positive correlation with adropin, salusin-α, and netrin-1 (r=0.563, p<0.01; r=0.738, p<0.01; r=0.700, p<0.01, respectively), but had a negative correlation with fasting blood glucose (r=−0.343, p<0.05). HOMA-IR values were comparable between both groups.

Conclusion:

The lower nesfatin-1 levels leading to increased inflammatory pathway activity in patients with endometriosis might play a role in endometriosis pathogenesis. Without causing systemic insulin resistance, decreased nesfatin-1 might contribute to endometriosis pathogenesis locally by leading to the reduced insulin susceptibility of endometriosis cells.

Preparation of Fucoidan-Based Electrospun Nanofibers and Their Interaction With Endothelial Cells

Sulfated polysaccharide fucoidan (FD) is widely applied in biomedical applications owing to its outstanding bioactivities. In addition to the biochemical features, the architecture of biomaterials plays a critical role in tissue repair and regeneration. Particularly, nanofibers have elicited great interest due to their extracellular matrix-like structure, high specific surface area, and favorable biological properties. Herein, chitosan-modified FD/ultra-high molecular weight polyethylene oxide (UHMWPEO) nanofibers are developed via green electrospinning and electrostatic interaction for studying their interaction with endothelial cells. The appropriate solvent is screened to dissolve FD. The electrospinnability of FD/UHMWPEO aqueous solutions is greatly dependent on the weight ratios of FD/UHMWPEO. The incorporation of UHMWPEO significantly improves the electrospinnability of solution and thermo-stability of nanofibers. Also, it is found that there is good miscibility or no phase separation in FD/UHMWPEO solutions. In vitro biological experiments show that the chitosan-modified FD/UHMWPEO nanofibers greatly facilitate the adhesion of endothelial cells and inhibit the attachment of monocytes. Thus, the designed FD-based nanofibers are promising bio-scaffolds in building tissue-engineered blood vessels.

Apolipoprotein E receptor 2 deficiency decreases endothelial adhesion of monocytes and protects against autoimmune encephalomyelitis

Under normal conditions, the blood-brain barrier effectively regulates the passage of immune cells into the central nervous system (CNS). However, under pathological conditions such as multiple sclerosis (MS), leukocytes, especially monocytes, infiltrate the CNS where they promote inflammatory demyelination, resulting in paralysis. Therapies targeting the immune cells directly and preventing leukocyte infiltration exist for MS but may compromise the immune system. Here, we explore how apolipoprotein E receptor 2 (ApoER2) regulates vascular adhesion and infiltration of monocytes during inflammation. We induced experimental autoimmune encephalitis in ApoER2 knockout mice and in mice carrying a loss-of-function mutation in the ApoER2 cytoplasmic domain. In both models, paralysis and neuroinflammation were largely abolished as a result of greatly diminished monocyte adherence due to reduced expression of adhesion molecules on the endothelial surface. Our findings expand our mechanistic understanding of the vascular barrier, the regulation of inflammation and vascular permeability, and the therapeutic potential of ApoER2-targeted therapies.

Serum netrin-1 as a potential biomarker for functional outcome of traumatic brain injury

BACKGROUND

Decreased serum netrin-1 concentrations have been found after acute brain injury. We investigated the role of serum netrin in prognosis of traumatic brain injury (TBI).

METHODS

In this prospective and observational study, enzyme-linked immunosorbent assay was used to detect serum netrin-1 concentrations in 50 mild TBI patients (Glasgow coma scale (GCS) score, 13-15), 83 moderate TBI patients (GCS score, 9-12), 69 severe TBI patients (GCS score, 3-8) and 50 healthy controls. Glasgow outcome scale score of 1-3 at 6 months after trauma was defined as poor outcome.

RESULTS

Serum netrin-1 concentrations were significantly lower in moderate or severe TBI patients than in controls and in severe TBI patients than in moderate TBI patients, while not in mild TBI patients than in controls. GCS score and Rotterdam computed tomography classification were closely correlated with serum netrin-1 concentrations among TBI patients. Forty-two (20.8%) patients had poor outcome. Receiver operating characteristic curve analysis revealed that serum netrin-1 concentrations could distinguish patients with poor outcome from the other remainders significantly. In addition, serum netrin-1 concentrations were independently associated with poor outcome.

CONCLUSIONS

Serum netrin-1 might serve as a potential biomarker for prognosis of TBI.

Netrin-1 reduces lung ischemia-reperfusion injury by increasing the proportion of regulatory T cells

Objective

Inflammation is the primary mechanism of lung ischemia-reperfusion injury (LIRI) and neurologic factors can regulate inflammatory immune responses. Netrin-1 is an axonal guidance molecule, but whether Netrin-1 plays a role in LIRI remains unclear.

Methods

A mouse model of LIRI was established. Immunohistochemistry was used to detect expression of Netrin-1 and to enumerate macrophages and T cells in lung tissue. The proportion of regulatory T cells (Tregs) was assessed by flow cytometry. Levels of apoptosis were assessed by terminal deoxynucleotidyl transferase dUTP nick end staining.

Results

Numbers of macrophages and T cells in the lung tissues of mice with LIRI were elevated, while expression of netrin-1 was significantly decreased. Flow cytometry showed that the proportion of Tregs in mice with LIRI was significantly decreased. The proportion of Tregs among lymphocytes was positively correlated with netrin-1 expression. In vitro experiments showed that netrin-1 promoted an increase in Treg proportion through the A2b receptor. Animal experiments showed that netrin-1 could inhibit apoptosis and reduce T cell and macrophage infiltration by increasing the proportion of Tregs, ultimately reducing LIRI. Treg depletion using an anti-CD25 monoclonal antibody blocked the effects of netrin-1.

Conclusion

Netrin-1 reduced LIRI by increasing the proportion of Tregs.

Netrin-1 in Atherosclerosis: Relationship between Human Macrophage Intracellular Levels and In Vivo Plaque Morphology

Netrin-1 is a laminin-like protein that plays a pivotal role in cell migration and, according to the site of its release, exerts both pro and anti-atherosclerotic functions. Macrophages, key cells in atherosclerosis, are heterogeneous in morphology and function and different subpopulations may support plaque progression, stabilization, and/or regression. Netrin-1 was evaluated in plasma and, together with its receptor UNC5b, in both spindle and round monocyte-derived macrophages (MDMs) morphotypes from coronary artery disease (CAD) patients and control subjects. In CAD patients, plaque features were detected in vivo by optical coherence tomography. CAD patients had lower plasma Netrin-1 levels and a higher MDMs expression of both protein and its receptor compared to controls. Specifically, a progressive increase in Netrin-1 and UNC5b was evidenced going from controls to stable angina (SA) and acute myocardial infarction (AMI) patients. Of note, spindle MDMs of AMI showed a marked increase of both Netrin-1 and its receptor compared to spindle MDMs of controls. UNC5b expression is always higher in spindle compared to round MDMs, regardless of the subgroup. Finally, CAD patients with higher intracellular Netrin-1 levels showed greater intraplaque macrophage accumulation in vivo. Our findings support the role of Netrin-1 and UNC5b in the atherosclerotic process.

Neuronal guidance proteins in cardiovascular inflammation

Cardiovascular pathologies are often induced by inflammation. The associated changes in the inflammatory response influence vascular endothelial biology; they complicate the extent of ischaemia and reperfusion injury, direct the migration of immune competent cells and activate platelets. The initiation and progression of inflammation is regulated by the classical paradigm through the system of cytokines and chemokines. Therapeutic approaches have previously used this knowledge to control the extent of cardiovascular changes with varying degrees of success. Neuronal guidance proteins (NGPs) have emerged in recent years and have been shown to be significantly involved in the control of tissue inflammation and the mechanisms of immune cell activation. Therefore, proteins of this class might be used in the future as targets to control the extent of inflammation in the cardiovascular system. In this review, we describe the role of NGPs during cardiovascular inflammation and highlight potential therapeutic options that could be explored in the future.

Netrin-1: Focus on its role in cardiovascular physiology and atherosclerosis

The netrins form a family of laminin-related proteins which were first described as modulators of cell migration and axonal guidance during fetal development. Netrin-1 is the most extensively studied member of this family and, since its discovery, non-neural roles have been associated with it. Together with its receptors, DCC/neogenin and UNC5, netrin-1 has been shown to be involved in the regulation of angiogenesis, organogenesis, cancer and inflammation. An NF-κB-dependent truncated isoform of netrin-1 has also been shown to be produced in endothelial and some types of cancer cells, which both accumulates in and affects the function of the nucleus. In atherosclerosis, conflicting roles for netrin-1 have been reported on plaque progression via its receptor UNC5b. Whereas endothelial-derived netrin-1 inhibits chemotaxis of leukocytes and reduces the migration of monocytes to the atherosclerotic plaque, netrin-1 expressed by macrophages within the plaque plays a pro-atherogenic role, promoting cell survival, recruiting smooth muscle cells and inhibiting foam cell egress to the lymphatic system. In contrast, there is evidence that netrin-1 promotes macrophage differentiation to an alternative activated phenotype and induces expression of IL-4 and IL-13, while downregulate expression of IL-6 and COX-2. Further work is needed to elucidate the precise roles of the two isoforms of netrin-1 in different cell types in the context of atherosclerosis, and its potential as a putative novel therapeutic target in this disease.

The identification and function of a Netrin-1 mutation in a pedigree with premature atherosclerosis

BACKGROUND AND AIMS

Neuroimmune guidance cues have been shown to play a role in atherosclerosis, but their exact role in human pathophysiology is largely unknown. In the current study, we investigated the role of a c.1769G > T variant in Netrin-1 in (premature) atherosclerosis.

METHODS

To determine the effect of the genetic variation, purified Netrin-1, either wild type (wtNetrin-1) or the patient observed variation (mutNetrin-1), was used for migration, adhesion, endothelial barrier function and bindings assays. Expression of adhesion molecules and transcription proteins was analyzed by RT-PCR, Western blot or ELISA. To further delineate how mutNetrin-1 mediates its effect on cell migration, lenti-viral knockdown of UNC5B or DCC was used.

RESULTS

Bindings assays revealed a decreased binding capacity of mutNetrin-1 to the receptors UNC5B, DCC and β3-integrin and an increased binding capacity to neogenin, heparin and heparan sulfate compared to wtNetrin-1. Exposure of endothelial cells to mutNetrin-1 resulted in enhanced monocyte adhesion and expression of IL-6, CCL2 and ICAM-1 compared to wtNetrin-1. In addition, mutNetrin-1 lacks the inhibitory effect on the NF-κB pathway that is observed for wtNetrin-1. Moreover, the presence of mutNetrin-1 diminished migration of macrophages and smooth muscle cells. Importantly, UNC5B or DCC specific knockdown showed that mutNetrin-1 is unable to act through DCC resulting in enhanced inhibition of migration.

CONCLUSIONS

Our data demonstrates that mutNetrin-1 fails to exert anti-inflammatory effects on endothelial cells and more strongly blocks macrophage migration compared to wtNetrin-1, suggesting that the carriers of this genetic molecular variant may well be at risk for premature atherosclerosis.

Netrin-1 and the Grade of Atherosclerosis Are Inversely Correlated in Humans

OBJECTIVE

Netrin-1 has been shown to play a role in the initiation of atherosclerosis in mice models. However, little is known about the role of Netrin-1 in humans. We set out to study whether Netrin-1 is associated with different stages of atherosclerosis. Approach and Results: Plasma Netrin-1 levels were measured in different patient cohorts: (1) 22 patients with high cardiovascular risk who underwent arterial wall inflammation assessment using positron-emission tomography / computed tomography, (2) 168 patients with a positive family history of premature atherosclerosis in whom coronary artery calcium scores were obtained, and (3) 104 patients with chest pain who underwent coronary computed tomography angiography imaging to evaluate plaque vulnerability and burden. Netrin-1 plasma levels were negatively correlated with arterial wall inflammation (β, -0.01 [95% CI, 0.02 to -0.01] R², 0.61; P<0.0001), and concentrations of Netrin-1 were significantly lower when atherosclerosis was present compared with individuals without atherosclerosis (28.01 versus 10.51 ng/mL, P<0.001). There was no difference in Netrin-1 plasma concentrations between patients with stable versus unstable plaques (11.17 versus 11.74 ng/mL, P=0.511). However, Netrin-1 plasma levels were negatively correlated to total plaque volume (β, -0.09 [95% CI, -0.11 to -0.08] R², 0.57, P<0.0001), calcified plaque volumes (β, -0.10 [95% CI, -0.12 to -0.08] R², 0.53; P<0.0001), and noncalcified plaque volumes (β, -0.08 [95% CI, -0.10 to -0.06] R², 0.41; P<0.0001). Treatment of inflammatory stimulated endothelial cells with plasma with high Netrin-1 level resulted in reduced endothelial inflammation and consequently, less monocyte adhesion.

CONCLUSIONS

Netrin-1 plasma levels are lower in patients with subclinical atherosclerosis and in patients with arterial wall inflammation. Netrin-1 is not associated with plaque vulnerability; however, it is negatively correlated to plaque burden, suggesting that Netrin-1 is involved in some, but not all, stages of atherosclerosis.

Netrin-1 and its receptor Unc5b as markers of periodontal disease

OBJECTIVES

The aim of this present study was to evaluate the levels of Netrin-1 and Unc5b in periodontal health and disease.

BACKGROUND

Netrin-1, acting via its receptor UNC5b, regulates the inflammatory response and takes apart in bone destructive diseases.

METHODS

Samples of gingival crevicular fluid (GCF), whole saliva, and serum were taken from systemically healthy, nonsmoking 20 periodontitis , 20 gingivitis patients, and 20 periodontally healthy subjects at baseline and 4 weeks after nonsurgical periodontal treatment (NSPT). Whole-mouth and site-specific clinical periodontal parameters were recorded. Netrin-1 and Unc5b levels were measured by enzyme-linked immunosorbent assay. Data were analyzed by nonparametric tests.

RESULTS

Total amount of Netrin-1 in GCF was significantly higher in periodontitis than the others, and the levels were significantly reduced after NSPT. Salivary and serum concentrations of Netrin-1 were significantly different among the study groups (P = .000), and NSPT significantly increased the concentration levels of both salivary and serum Netrin-1 (P < .05). Healthy subjects had significantly lower GCF (P = .001) and conversely, higher salivary and serum levels of Unc5b than the other groups (P = .002). The GCF levels of Unc5b were significantly reduced (P < .01), and conversely, serum concentrations were significantly increased after NSPT (P < .05). GCF Netrin-1 and Unc5b total amounts were positively correlated with clinical parameters (P < .01 and P < .05) whereas salivary Netrin-1 and Unc5b concentrations were negatively correlated with clinical parameters (P < .01 and P < .05).

CONCLUSIONS

The results of this study indicate that Netrin-1 and its receptor Unc5b may have essential roles in periodontal inflammation and those can be assumed as useful therapeutic agent to control inflammation and periodontal breakdown.

(-)-Epicatechin metabolites promote vascular health through epigenetic reprogramming of endothelial-immune cell signaling and reversing systemic low-grade inflammation

Ingestion of (-)-epicatechin flavanols reverses endothelial dysfunction by increasing flow mediated dilation and by reducing vascular inflammation and oxidative stress, monocyte-endothelial cell adhesion and transendothelial monocyte migration in vitro and in vivo. This involves multiple changes in gene expression and epigenetic DNA methylation by poorly understood mechanisms. By in silico docking and molecular modeling we demonstrate favorable binding of different glucuronidated, sulfated or methylated (-)-epicatechin metabolites to different DNA methyltransferases (DNMT1/DNMT3A). In favor of this model, genome-wide DNA methylation profiling of endothelial cells treated with TNF and different (-)-epicatechin metabolites revealed specific DNA methylation changes in gene networks controlling cell adhesion-extravasation endothelial hyperpermeability as well as gamma-aminobutyric acid, renin-angiotensin and nitric oxide hypertension pathways. Remarkably, blood epigenetic profiles of an 8 weeks intervention with monomeric and oligomeric flavanols (MOF) including (-)-epicatechin in male smokers revealed individual epigenetic gene changes targeting similar pathways as the in vitro exposure experiments in endothelial cells. Furthermore, epigenetic changes following MOF diet intervention oppose atherosclerosis associated epigenetic changes. In line with biological data, the individual epigenetic response to a MOF diet is associated with different vascular health parameters (glutathione peroxidase 1 and endothelin-1 expression, acetylcholine-mediated microvascular response), in part involving systemic shifts in blood immune cell types which reduce the neutrophil-lymphocyte ratio (NLR). Altogether, our study suggests that different (-)-epicatechin metabolites promote vascular health in part via epigenetic reprogramming of endothelial-immune cell signaling and reversing systemic low-grade inflammation.

Lack of netrin-4 alters vascular remodeling in the retina

PURPOSE

Netrin-4 (NTN4) is a protein that plays an important role in the regulation of angiogenesis in the pathological retina. Some evidences show that it can also have a role in inflammation and vascular stability. We will explore these questions in vivo in the mature mouse retina.

METHODS

We created a NTN4 knockout that expresses EGFP in mononuclear phagocytes (CSFR1-positive cells) to track inflammation in vivo in the retina by scanning laser ophthalmoscopy (SLO). Fundus angiography permitted to study blood vessels. Retinal function was assessed with electroretinography (ERG).

RESULTS

Lack of NTN4 leads to an increased amount of amoeboid mononuclear phagocytes in the adult retina, and blood vessels displayed increased tortuosity when compared with the wildtype. Inner retina function also seemed affected in NTN4 null. Lack of NTN4 resulted in a higher persistence of hyaloid artery and spontaneous leakage in the adult retina. No differences were found regarding vessel bifurcation, vessel width, or vein/artery ratio.

CONCLUSIONS

These in vivo data show for the first time that lack of NTN4 induces changes in the retinal vascular phenotype in a non-pathological scenario. This evidence widens the role of NTN4 as a guidance cue in vascular remodeling.

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 β1 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 β1 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/β-catenin signalling may be involved. Our findings suggest that netrin-1 may serve as a therapeutic agent for the treatment of skin diseases.

Magic roundabout is an endothelial-specific ohnolog of ROBO1 which neo-functionalized to an essential new role in angiogenesis

BACKGROUND

Magic roundabout (ROBO4) is an unusual endothelial-specific paralog of the family of neuronally-expressed axon guidance receptors called roundabouts. Endothelial cells (ECs), whose uninterrupted sheet delimits the lumen of all vertebrate blood vessels and which are absent from invertebrate species, are a vertebrate-specific evolutionary novelty.

RESULTS

Herein, the evolutionary mechanism of the duplication, retention and divergence of ROBO4 was investigated for the first time. Phylogenetic analyses carried out suggested that ROBO4 is a fast-evolving paralog of ROBO1 formed at the base of vertebrates. The ancestral expression pattern was neuronal. ROBO4 dramatically shifted its expression and became exceptionally specific to ECs. The data-mining of FANTOM5 and ENCODE reveals that ROBO4's endothelial expression arises from a single transcription start site (TSS), conserved in mouse, controlled by a proximal promoter with a complex architecture suggestive of regulatory neo-functionalization. (An analysis of promoter probabilities suggested the architecture was not due to a chance arrangement of TFBSes). Further evidence for the neo-functionalization of ROBO4 comes from the analysis of its protein interactions, the rates of protein evolution, and of positively selected sites.

CONCLUSIONS

The neo-functionalization model explains why ROBO4 protein acquired new context-specific biological functions in the control of angiogenesis. This endothelial-specific roundabout receptor is an illustrative example of the emergence of an essential vertebrate molecular novelty and an endothelial-specific signaling sub-network through 2R-WGD. The emergence of novel cell types, such as ECs, might be a neglected evolutionary force contributing to the high rate of retention of duplicates post-2R-WGD. Crucially, expression neo-functionalization to evolutionarily novel sites of expression conceptually extends the classical model of neo-functionalization.