Hypoxia-inducible factor-dependent induction of netrin-1 dampens inflammation caused by hypoxia

Fluoxetine induces vascular endothelial growth factor/Netrin over-expression via the mediation of hypoxia-inducible factor 1-alpha in SH-SY5Y cells

Fluoxetine has become one of the most promising drugs for improving clinical outcome in patients with cerebral infarction. Although the clinical efficacy of fluoxetine has been preliminarily demonstrated, its mechanism remains unclear. Hypoxia-inducible factor 1-alpha (HIF-1α) is upstream to Netrin and vascular endothelial growth factor (VEGF), and under hypoxia conditions it may induce expression of Netrin-1 and VEGF in vascular endothelial cells. We sought to explore whether it can regulate their expression in hypoxia and mediate the effect of fluoxetine in hypoxia. In this study, the effect of hypoxia on the expression of VEGF and Netrin was observed in vitro by real-time PCR and western blotting in SH-SY5Y cells; the binding sites of HIF-1α in VEGF and Netrin gene promoters were identified by luciferase reporter; the effect of fluoxetine on binding of HIF-1α with Netrin and VEGF promoters in hypoxia was observed by Chromatin Immunoprecipitation (ChIP) Assay. We prove that HIF-1α regulates transcription of both VEGF and Netrin, and that in hypoxia fluoxetine up-regulates VEGF and Netrin expression via mediation of HIF-1α that binds to hypoxia-response element sites of VEGF and Netrin promoters. Our study indicates that HIF-1α may play an important role in the treatment of cerebral infarction through mediating the recovery of neurological function induced by fluoxetine, which provides theoretical basis for the development of gene therapeutic drugs targeting HIF-1α. We show that hypoxia-inducible factor 1-alpha (HIF-1α) regulates transcription of both vascular endothelial growth factor (VEGF) and Netrin. Furthermore, we also show that in hypoxia fluoxetine up-regulates VEGF and Netrin expression via mediation of HIF-1α that binds to hypoxia-response element (HRE) sites of VEGF and Netrin promoters. Our study indicates that HIF-1α may play an important role in the treatment of cerebral infarction through mediating the recovery of neurological function induced by fluoxetine. These findings provide a theoretical basis for development of gene therapeutic drugs targeting HIF-1α.

Semaphorin 7A Aggravates Pulmonary Inflammation during Lung Injury

The extent of pulmonary inflammation during lung injury ultimately determines patient outcome. Pulmonary inflammation is initiated by the migration of neutrophils into the alveolar space. Recent work has demonstrated that the guidance protein semaphorin 7A (SEMA7A) influences the migration of neutrophils into hypoxic tissue sites, yet, its role during lung injury is not well understood. Here, we report that the expression of SEMA7A is induced in vitro through pro-inflammatory cytokines. SEMA7A itself induces the production of pro-inflammatory cytokines in endothelial and epithelial cells, enhancing pulmonary inflammation. The induction of SEMA7A facilitates the transendothelial migration of neutrophils. In vivo, animals with deletion of SEMA7A expression showed reduced signs of pulmonary inflammatory changes following lipopolysaccharide challenge. We define here the role of SEMA7A in the development of lung injury and identify a potential pathway to interfere with these detrimental changes. Future anti-inflammatory strategies for the treatment of lung injury might be based on this finding.

Netrin-1 Protects Hepatocytes Against Cell Death Through Sustained Translation During the Unfolded Protein Response

BACKGROUND & AIMS

Netrin-1, a multifunctional secreted protein, is up-regulated in cancer and inflammation. Netrin-1 blocks apoptosis induced by the prototypical dependence receptors deleted in colorectal carcinoma and uncoordinated phenotype-5. Although the unfolded protein response (UPR) triggers apoptosis on exposure to stress, it first attempts to restore endoplasmic reticulum homeostasis to foster cell survival. Importantly, UPR is implicated in chronic liver conditions including hepatic oncogenesis. Netrin-1's implication in cell survival on UPR in this context is unknown.

METHODS

Isolation of translational complexes, determination of RNA secondary structures by selective 2'-hydroxyl acylation and primer extension/dimethyl sulfate, bicistronic constructs, as well as conventional cell biology and biochemistry approaches were used on in vitro-grown hepatocytic cells, wild-type, and netrin-1 transgenic mice.

RESULTS

HepaRG cells constitute a bona fide model for UPR studies in vitro through adequate activation of the 3 sensors of the UPR (protein kinase RNA-like endoplasmic reticulum kinase (PERK)), inositol requiring enzyme 1α (IRE1α), and activated transcription factor 6 (ATF6). The netrin-1 messenger RNA 5'-end was shown to fold into a complex double pseudoknot and bear E-loop motifs, both of which are representative hallmarks of related internal ribosome entry site regions. Cap-independent translation of netrin 5' untranslated region-driven luciferase was observed on UPR in vitro. Unlike several structurally related oncogenic transcripts (l-myc, c-myc, c-myb), netrin-1 messenger RNA was selected for translation during UPR both in human hepatocytes and in mice livers. Depletion of netrin-1 during UPR induces apoptosis, leading to cell death through an uncoordinated phenotype-5A/C-mediated involvement of protein phosphatase 2A and death-associated protein kinase 1 in vitro and in netrin transgenic mice.

CONCLUSIONS

UPR-resistant, internal ribosome entry site-driven netrin-1 translation leads to the inhibition of uncoordinated phenotype-5/death-associated protein kinase 1-mediated apoptosis in the hepatic context during UPR, a hallmark of chronic liver disease.

Stimulation of gastric acid secretion by rabbit parietal cell A2B adenosine receptor activation

Adenosine modulates different functional activities in many cells of the gastrointestinal tract; some of them are believed to be mediated by interaction with its four G protein-coupled receptors. The renewed interest in the adenosine A2B receptor (A2BR) subtype can be traced by studies in which the introduction of new genetic and chemical tools has widened the pharmacological and structural knowledge of this receptor as well as its potential therapeutic use in cancer and inflammation- or hypoxia-related pathologies. In the acid-secreting parietal cells of the gastric mucosa, the use of various radioligands for adenosine receptors suggested the presence of the A2 adenosine receptor subtype(s) on the cell surface. Recently, we confirmed A2BR expression in native, nontransformed parietal cells at rest by using flow cytometry and confocal microscopy. In this study, we show that A2BR is functional in primary rabbit gastric parietal cells, as indicated by the fact that agonist binding to A2BR increased adenylate cyclase activity and acid production. In addition, both acid production and radioligand binding of adenosine analogs to isolated cell membranes were potently blocked by selective A2BR antagonists, whereas ligands for A1, A2A, and A3 adenosine receptors failed to abolish activation. We conclude that rabbit gastric parietal cells possess functional A2BR proteins that are coupled to Gs and stimulate HCl production upon activation. Whether adenosine- and A2BR-mediated functional responses play a role in human gastric pathophysiology is yet to be elucidated.

The axon-glia unit in white matter stroke: mechanisms of damage and recovery

Approximately one quarter of all strokes in humans occur in white matter, and the progressive nature of white matter lesions often results in severe physical and mental disability. Unlike cortical grey matter stroke, the pathology of white matter stroke revolves around disrupted connectivity and injured axons and glial cells, rather than neuronal cell bodies. Consequently, the mechanisms behind ischemic damage to white matter elements, the regenerative responses of glial cells and their signaling pathways, all differ significantly from those in grey matter. Development of effective therapies for white matter stroke would require an enhanced understanding of the complex cellular and molecular interactions within the white matter, leading to the identification of new therapeutic targets. This review will address the unique properties of the axon-glia unit during white matter stroke, describe the challenging process of promoting effective white matter repair, and discuss recently-identified signaling pathways which may hold potential targets for repair in this disease. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Netrin-1 is highly expressed and required in inflammatory infiltrates in wear particle-induced osteolysis

OBJECTIVE

Netrin-1 is a chemorepulsant and matrix protein expressed during and required for osteoclast differentiation, which also plays a role in inflammation by preventing macrophage egress. Because wear particle-induced osteolysis requires osteoclast-mediated destruction of bone, we hypothesised that blockade of Netrin-1 or Unc5b, a receptor for Netrin-1, may diminish this pathological condition.

METHODS

C57BL/6 mice, 6-8 weeks old, had 3 mg of ultrahigh-molecular-weight polyethylene particles implanted over the calvaria and then received 10 µg of monoclonal antibodies for Netrin-1 or its receptors, Unc5b and deleted in colon cancer (DCC), injected intraperitoneally on a weekly basis. After 2 weeks, micro-computed tomography and histology analysis were performed. Netrin-1 expression was analysed in human tissue obtained following primary prosthesis implantation or after prosthesis revision for peri-implant osteolysis and aseptic implant loosening.

RESULTS

Weekly injection of anti-Netrin-1 or anti-Unc5b-antibodies significantly reduced particle-induced bone pitting in calvaria exposed to wear particles (46±4% and 49±3% of control bone pitting, respectively, p<0.001) but anti-DCC antibody did not affect inflammatory osteolysis (80±7% of control bone pitting, p=ns). Anti-Netrin-1 or anti-Unc5b, but not anti-DCC, antibody treatment markedly reduced the inflammatory infiltrate and the number of tartrate resistance acid phosphatase (TRAP)-positive osteoclasts (7±1, 4±1 and 14±1 cells/high power field (hpf), respectively, vs 12±1 cells/hpf for control, p<0.001), with no significant changes in alkaline phosphatase-positive osteoblasts on bone-forming surfaces in any antibody-treated group. Netrin-1 immunostaining colocalised with CD68 staining for macrophages. The peri-implant tissues of patients undergoing prosthesis revision surgery showed an increase in Netrin-1 expression, whereas there was little Netrin-1 expression in soft tissues removed at the time of primary joint replacement.

CONCLUSIONS

These results demonstrate a unique role for Netrin-1 in osteoclast biology and inflammation and may be a novel target for prevention/treatment of inflammatory osteolysis.

The Regulation of Proresolving Lipid Mediator Profiles in Baboon Pneumonia by Inhaled Carbon Monoxide

Strategies for the treatment of bacterial pneumonia beyond traditional antimicrobial therapy have been limited. The recently discovered novel genus of lipid mediators, coined "specialized proresolving mediators" (SPMs), which orchestrate clearance of recruited leukocytes and restore epithelial barrier integrity, have offered new insight into the resolution of inflammation. We performed lipid mediator (LM) metabololipidomic profiling and identification of LMs on peripheral blood leukocytes and plasma from a baboon model of Streptococcus pneumoniae pneumonia. Leukocytes and plasma were isolated from whole blood of S. pneumoniae-infected (n = 5-6 per time point) and control, uninfected baboons (n = 4 per time point) at 0, 24, 48, and 168 hours. In a subset of baboons with pneumonia (n = 3), we administered inhaled carbon monoxide (CO) at 48 hours (200-300 ppm for 60-90 min). Unstimulated leukocytes from control animals produced a proresolving LM signature with elevated resolvins and lipoxins. In contrast, serum-treated, zymosan-stimulated leukocytes and leukocytes from baboons with S. pneumoniae pneumonia produced a proinflammatory LM signature profile with elevated leukotriene B4 and prostaglandins. Plasma from baboons with S. pneumoniae pneumonia also displayed significantly reduced LM-SPM levels, including eicosapentaenoic acid-derived E-series resolvins (RvE) and lipoxins. CO inhalation increased levels of plasma RvE and lipoxins relative to preexposure levels. These results establish the leukocyte and plasma LM profiles biosynthesized during S. pneumoniae pneumonia in baboons and provide evidence for pneumonia-induced dysregulation of these proresolution programs. Moreover, these SPM profiles are partially restored with inhaled low-dose CO and SPM, which may shorten the time to pneumonia resolution.

Netrin-1 as a novel therapeutic target in cardiovascular disease: to activate or inhibit?

Netrins are a family of laminin-like proteins, which were initially identified for their role in embryonic axonal guidance. Over recent years, it has become apparent that netrin-1 may additionally be involved in the underlying pathology of several multisystem diseases, making it an attractive potential therapeutic target. It is involved in postnatal angiogenesis, particularly in the context of an ischaemic insult, although there are conflicting reports as to whether netrin-1 acts in a pro- or anti-angiogenic capacity. In atherosclerosis, opposing effects have similarly been reported on plaque progression, due to the ability of netrin-1 to inhibit both macrophage egress from and monocyte ingress into lesions. Netrin-1 has also been shown to exert a cardioprotective action in the context of ischaemia-reperfusion injury following myocardial infarction. Moreover, urinary netrin-1 levels rise in response to acute kidney injury and at a faster rate than traditional markers of renal impairment, highlighting a potential clinical role for netrin-1 as a biomarker of renal function. The increased urinary excretion of netrin-1 during kidney disease is paralleled by a down-regulation of its plasma levels, with potential implications at a systemic level. In summary, the role of netrin-1 in cardiovascular disease is an emerging area of research requiring further in-depth study to elucidate its mechanism of action and potential as a therapeutic target, especially in view of its seemingly contradictory actions in certain physiological pathways which serve to highlight its manifold and often opposite effects in numerous physiological and pathophysiological processes.

Adenosine regulation of the immune response initiated by ischemia reperfusion injury

It is clinically established that adenosine has negative chronotropic, antiarrhythmic effects and reduces arterial blood pressure. Adenosine addition to cardioplegic solutions used in cardiac operations is clinically well tolerated and has been shown to improve myocardial protection in several studies. However, the mechanism of action remains unclear. Therefore, it is important to define the effect of adenosine on the inflammatory cascade as immune cell activation occurs early during ischemia reperfusion injury. Adenosine appears to mediate the initial steps of the inflammatory cascade via its four G-coupled protein receptors: A1, A2A, A2B, and A3, expressed on neutrophils, lymphocytes and macrophages. The adenosine receptor isotype dictates the immune response. More specifically, the A1 and A3 receptors stimulate a pro-inflammatory immune response whereas the A2A and A2B are immunosuppressive. As the adenosine receptors are important for cardiac pre-conditioning and post-conditioning, adenosine may regulate the inflammatory responses initiated during ischemia-mediated immune injury related to myocardial protection.

Netrin-1 - DCC Signaling Systems and Age-Related Macular Degeneration

We conducted a nested candidate gene study and pathway-based enrichment analysis on data from a multi-national 77,000-person project on the molecular genetics of age-related macular degeneration (AMD) to identify AMD-associated DNA-sequence variants in genes encoding constituents of a netrin-1 (NTN1)-based signaling pathway that converges on DNA-binding transcription complexes through a 3'-5'-cyclic adenosine monophosphate-calcineurin (cAMP-CN)-dependent axis. AMD-associated single nucleotide polymorphisms (SNPs) existed in 9 linkage disequilibrium-independent genomic regions; these included loci overlapping NTN1 (rs9899630, P ≤ 9.48 x 10^-5), DCC (Deleted in Colorectal Cancer)—the gene encoding a primary NTN1 receptor (rs8097127, P ≤ 3.03 x 10^-5), and 6 other netrin-related genes. Analysis of the NTN1-DCC pathway with exact methods demonstrated robust enrichment with AMD-associated SNPs (corrected P-value = 0.038), supporting the idea that processes driven by NTN1-DCC signaling systems operate in advanced AMD. The NTN1-DCC pathway contains targets of FDA-approved drugs and may offer promise for guiding applied clinical research on preventive and therapeutic interventions for AMD.

Netrin-1 is a critical autocrine/paracrine factor for osteoclast differentiation

Bone metabolism is a vital process that involves resorption by osteoclasts and formation by osteoblasts, which is closely regulated by immune cells. The neuronal guidance protein Netrin-1 regulates immune cell migration and inflammatory reactions, but its role in bone metabolism is unknown. During osteoclast differentiation, osteoclast precursors increase expression of Netrin-1 and its receptor Unc5b. Netrin-1 binds, in an autocrine and paracrine manner, to Unc5b to promote osteoclast differentiation in vitro, and absence of Netrin-1 or antibody-mediated blockade of Netrin-1 or Unc5b prevents osteoclast differentiation of both murine and human precursors. We confirmed the functional relationship of Netrin-1 in osteoclast differentiation in vivo using Netrin-1-deficient (Ntn1(-/-) ) or wild-type (WT) bone marrow transplanted mice. Notably, Ntn1(-/-) chimeras have markedly diminished osteoclasts, as well as increased cortical and trabecular bone density and volume compared with WT mice. Mechanistic studies revealed that Netrin-1 regulates osteoclast differentiation by altering cytoskeletal assembly. Netrin-1 increases regulator of Rho-GEF subfamily (LARG) and repulsive guidance molecule (RGMa) association with Unc5b, which increases expression and activation of cytoskeletal regulators RhoA and focal adhesion kinase (FAK). Netrin-1 and its receptor Unc5b likely play a role in fusion of osteoclast precursors because Netrin-1 and DC-STAMP are tightly linked. These results identify Netrin-1 as a key regulator of osteoclast differentiation that may be a new target for bone therapies.

Netrin 1 regulates blood-brain barrier function and neuroinflammation

Blood-brain barrier function is driven by the influence of astrocyte-secreted factors. During neuroinflammatory responses the blood-brain barrier is compromised resulting in central nervous system damage and exacerbated pathology. Here, we identified endothelial netrin 1 induction as a vascular response to astrocyte-derived sonic hedgehog that promotes autocrine barrier properties during homeostasis and increases with inflammation. Netrin 1 supports blood-brain barrier integrity by upregulating endothelial junctional protein expression, while netrin 1 knockout mice display disorganized tight junction protein expression and barrier breakdown. Upon inflammatory conditions, blood-brain barrier endothelial cells significantly upregulated netrin 1 levels in vitro and in situ, which prevented junctional breach and endothelial cell activation. Finally, netrin 1 treatment during experimental autoimmune encephalomyelitis significantly reduced blood-brain barrier disruption and decreased clinical and pathological indices of disease severity. Our results demonstrate that netrin 1 is an important regulator of blood-brain barrier maintenance that protects the central nervous system against inflammatory conditions such as multiple sclerosis and experimental autoimmune encephalomyelitis.

The resolution of inflammation: Principles and challenges

The concept that chemokines, cytokines and pro-inflammatory mediators act in a co-ordinated fashion to drive the initiation of the inflammatory reaction is well understood. The significance of such networks acting during the resolution of inflammation however is poorly appreciated. In recent years, specific pro-resolving mediators were discovered which activate resolution pathways to return tissues to homeostasis. These mediators are diverse in nature, and include specialized lipid mediators (lipoxins, resolvins, protectins and maresins) proteins (annexin A1, galectins) and peptides, gaseous mediators including hydrogen sulphide, a purine (adenosine), as well as neuromodulator release under the control of the vagus nerve. Functionally, they can act to limit further leukocyte recruitment, induce neutrophil apoptosis and enhance efferocytosis by macrophages. They can also switch macrophages from classical to alternatively activated cells, promote the return of non-apoptotic cells to the lymphatics and help initiate tissue repair mechanisms and healing. Within this review we highlight the essential cellular aspects required for successful tissue resolution, briefly discuss the pro-resolution mediators that drive these processes and consider potential challenges faced by researchers in the quest to discover how inflammation resolves and why chronic inflammation persists.

Therapeutic effects of topical netrin-4 in a corneal acute inflammatory model

AIM

To evaluate the therapeutic effect of netrin-4 on the early acute phase of inflammation in the alkali-burned eye.

METHODS

Eye drops containing netrin-4 or phosphate buffered saline (PBS) were administered to a alkali-burn-induced corneal acute inflammatory model four times daily. The clinical evaluations, including fluorescein staining and inflammatory index, were performed on day 1, 4 and 7 using slit lamp microscopy. Global specimens were collected on day 7 and processed for immunofluorescent staining. The levels of inflammatory mediators in the corneas were determined by real-time polymerase chain reaction (PCR).

RESULTS

Exogenous netrin-4 administered on rat ocular surfaces showed more improvements in decreasing fluorescein staining on day 4 and 7, and resolved alkali burn-induced corneal inflammation index on day 7 (P<0.01). The levels of IL-1β, IL-6, intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1) in corneas were decreased in netrin-4-treated groups (P<0.05). In addition, netrin-4 significantly reduced the expression of leukocyte common antigen 45 (CD45) in the alkali-burn cornea (P<0.001).

CONCLUSION

Topical netrin-4 accelerated wound healing and reduced the inflammation on alkali-burn rat model, suggesting a potential as an anti-inflammatory agent in the clinical to treat the acute inflammation.

Deletion of UNC5B in Kidney Epithelium Exacerbates Diabetic Nephropathy in Mice

BACKGROUND

Guidance cue netrin-1 was shown to have protective effects in diabetic nephropathy. However, the role of its receptor UNC5B in diabetic kidney disease is unknown. Moreover, whether netrin-1 is protective against diabetic kidney disease in a genetic model of nephropathy and in the nephropathy prone DBA background is also unknown. The aim of this study was to determine the significance of UNC5B in tubular epithelial cells in chronic kidney disease due to diabetes and evaluate whether netrin-1 is also protective in the case of a nephropathy-prone mouse.

METHODS

Proximal tubular epithelium-specific UNC5B knockout mice as well as heterozygous UNC5B knockout mice were used to determine the roles of UNC5B in nephropathy. Diabetes was induced in these tissue-specific knockout, heterozygous and WT mice, and albuminuria was then monitored.

RESULTS

WT and heterozygous diabetic mice developed significant albuminuria at 8 weeks after induction of diabetes as compared to buffer-treated control mice. However, albuminuria was significantly more pronounced in mice with proximal tubule specific deletion of UNC5B. Transgenic overexpression of netrin-1 in proximal tubules in the DBA background and administration of recombinant netrin-1 to Ins2Akita mice also significantly reduced diabetes-induced albuminuria and suppressed glomerular and interstitial lesions.

CONCLUSION

Our data suggested that netrin-1 signaling in proximal tubular epithelium may play a critical role in the protection of kidney against diabetic kidney disease.

Innate and adaptive immune responses subsequent to ischemia-reperfusion injury in the kidney

Understanding innate immune responses and their correlation to alloimmunity after solid organ transplantation is key to optimizing long term graft outcome. While Ischemia/Reperfusion injury (IRI) has been well studied, new insight into central mechanisms of innate immune activation, i.e. chemokine mediated cell trafficking and the role of Toll-like receptors have evolved recently. The mechanistic implications of Neutrophils, Macrophages/Monocytes, NK-cells, Dendritic cells in renal IRI has been proven by selective depletion of these cell types, thereby offering novel therapeutic interventions. At the same time, the multi-faceted role of different T-cell subsets in IRI has gained interest, highlighting the dichotomous effects of differentiated T-cells and suggesting more selective therapeutic approaches. Targeting innate immune cells and their activation and migration pathways, respectively, has been promising in experimental models holding translational potential. This review will summarize the effects of innate immune activation and potential strategies to interfere with the immunological cascade following renal IRI.

Myeloid HIFs are dispensable for resolution of inflammation during skeletal muscle regeneration

Besides their role in cellular responses to hypoxia, hypoxia-inducible factors (HIFs) are involved in innate immunity and also have anti-inflammatory (M2) functions, such as resolution of inflammation preceding healing. Whereas the first steps of the inflammatory response are associated with proinflammatory (M1) macrophages (MPs), resolution of inflammation is associated with anti-inflammatory MPs exhibiting an M2 phenotype. This M1 to M2 sequence is observed during postinjury muscle regeneration, which provides an excellent paradigm to study the resolution of sterile inflammation. In this study, using in vitro and in vivo approaches in murine models, we demonstrated that deletion of hif1a or hif2a in MPs has no impact on the acquisition of an M2 phenotype. Furthermore, using a multiscale methodological approach, we showed that muscles did not require macrophagic hif1a or hif2a to regenerate. These results indicate that macrophagic HIFs do not play a crucial role during skeletal muscle regeneration induced by sterile tissue damage.

Netrin-1 attenuates cardiac ischemia reperfusion injury and generates alternatively activated macrophages

Ischemia reperfusion (IR) injury is a major issue in cardiac transplantation and inflammatory processes play a major role in myocardial IR injury. Netrin-1 is a laminin-related protein identified as a neuronal guidance cue and netrin-1 expressed outside the nervous system inhibits migration of leukocytes in vitro and in vivo and attenuates inflammation-mediated tissue injury. In our study, hearts of C57BL/6 mice were flushed and stored in cold Bretschneider solution for 8 h and then transplanted into syngeneic recipient. We found that netrin-1 decreased cardiomyocyte apoptosis and recruitment of neutrophils and macrophages. Troponin T (TnT) production on 24 h after myocardial IR injury was reduced by netrin-1 administration. Cardiac output at 60 mmHg of afterload pressure was significantly increased in hearts with netrin-1 administration (IR + Netrin-1: 59.9 ± 5.78 ml/min; IR: 26.2 ± 4.3 ml/min; P < 0.05). Netrin-1 treatment increased expression of the alternatively activated macrophage (AAM) markers arginase-1 (Arg-1) and mannose receptor (MR) and promoted proliferator-activated receptor γ (PPARγ) expression in cardiac allograft. Furthermore, decreased TnT expression and reduced allograft infiltration of neutrophils and monocytes/macrophages by netrin-1 was abolished with addition of PPARγ antagonist. In conclusion, netrin-1 attenuates cardiac IR injury and generates AAM which contributes to the protective effect of netrin-1.

Amelioration of hypoxia and LPS-induced intestinal epithelial barrier dysfunction by emodin through the suppression of the NF-κB and HIF-1α signaling pathways

Intestinal barrier dysfunction occurs in critical illnesses and involves the inflammatory and hypoxic injury of intestinal epithelial cells. Researchers are still defining the underlying mechanisms and evaluating therapeutic strategies for restoring intestinal barrier function. The anti-inflammatory drug, emodin, has been shown to exert a protective effect on intestinal barrier function; however, its mechanisms of action remain unknown. In this study, we investigated the protective effects of emodin on intestinal barrier function and the underlying mechanisms in intestinal epithelial cells challenged with lipopolysaccharide (LPS) and hypoxia/reoxygenation (HR). To induce barrier dysfunction, Caco-2 monolayers were subjected to HR with or without LPS treatment. Transepithelial electrical resistance and paracellular permeability were measured to evaluate barrier function. The expression of the tight junction (TJ) proteins, zonula occludens (ZO)-1, occludin, and claudin-1, as well as that of hypoxia-inducible factor (HIF)-1α, phosphor-IκB-α, phosphor-nuclear factor (NF)-κB p65 and cyclooxygenase (COX)-2 was determined by western blot analysis. The results revealed that emodin markedly attenuated the decrease in transepithelial electrical resistance and the increase in paracellular permeability in the Caco-2 monolayers treated with LPS and subjected to HR. Emodin also markedly alleviated the damage caused by LPS and HR (manifested by a decrease in the expression of the TJ protein, ZO-1), and inhibited the expression of HIF-1α, IκB-α, NF-κB and COX-2 in a dose-dependent manner. In conclusion, our data suggest that emodin attenuates LPS- and HR-induced intestinal epithelial barrier dysfunction by inhibiting the HIF-1α and NF-κB signaling pathways and preventing the damage caused to the TJ barrier (shown by the decrease in the expression of ZO-1).

Purinergic receptors in ocular inflammation

Inflammation is a complex process that implies the interaction between cells and molecular mediators, which, when not properly “tuned,” can lead to disease. When inflammation affects the eye, it can produce severe disorders affecting the superficial and internal parts of the visual organ. The nucleoside adenosine and nucleotides including adenine mononucleotides like ADP and ATP and dinucleotides such as P¹,P⁴-diadenosine tetraphosphate (Ap₄A), and P¹,P⁵-diadenosine pentaphosphate (Ap₅A) are present in different ocular locations and therefore they may contribute/modulate inflammatory processes. Adenosine receptors, in particular A_2A adenosine receptors, present anti-inflammatory action in acute and chronic retinal inflammation. Regarding the A₃ receptor, selective agonists like N⁶-(3-iodobenzyl)-5′-N-methylcarboxamidoadenosine (CF101) have been used for the treatment of inflammatory ophthalmic diseases such as dry eye and uveoretinitis. Sideways, diverse stimuli (sensory stimulation, large intraocular pressure increases) can produce a release of ATP from ocular sensory innervation or after injury to ocular tissues. Then, ATP will activate purinergic P2 receptors present in sensory nerve endings, the iris, the ciliary body, or other tissues surrounding the anterior chamber of the eye to produce uveitis/endophthalmitis. In summary, adenosine and nucleotides can activate receptors in ocular structures susceptible to suffer from inflammatory processes. This involvement suggests the possible use of purinergic agonists and antagonists as therapeutic targets for ocular inflammation.

Crucial role of Plexin C1 for pulmonary inflammation and survival during lung injury

Acute pulmonary inflammation during lung injury is initiated by the migration of neutrophils into the alveolar space. The severity of these inflammatory changes within the pulmonary tissue determines the severity of lung injury and ultimately patient outcome. Recent work has demonstrated that the guidance protein Semaphorin 7A propagates the infiltration of neutrophils into an hypoxic tissue site, yet the role of its target receptor Plexin C1 (PLXNC1) during lung injury is to date unknown. We demonstrate here that PLXNC1(+) neutrophils are present within the alveolar space and that PLXNC1 is induced in vitro and in vivo during lung injury. In a model of high-pressure ventilation PLXNC1(-/-) animals show decreased signs of alveolar inflammation and improved survival compared with wild-type controls. Studies employing chimeric animals identified the hematopoietic expression of PLXNC1 to be of crucial importance for the observed results. Functional inhibition of PLXNC1 resulted in improved survival and ameliorated the signs of inflammation within the lung. Furthermore, the injection of a peptide binding to PLXNC1 resulted in improved survival and attenuated pulmonary inflammation. As such we demonstrate here, that previously unknown PLXNC1 holds significant importance for degree of pulmonary inflammation and determines outcome during experimental lung injury.

Effects of hypoxia-inducible factor-1α and matrix metalloproteinase-9 on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury

The aim of this study was to investigate the effects of hypoxia-inducible factor-1α (HIF-1α) and matrix metalloproteinase-9 (MMP-9) on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury (PALI). A total of 40 male Sprague-Dawley rats were randomly divided into a sham surgery group (n=10) and three PALI groups, in which acute pancreatitis was induced by the retrograde infusion of 5% sodium taurocholate (1 ml/kg). The PALI groups were as follows: i) Untreated PALI group (n=10); ii) 2-methoxyestradiol (2ME2) group (5 mg/kg body mass; n=10); and iii) 2ME2 group (15 mg/kg body mass; n=10). In the two 2ME2 groups, the HIF-1α inhibitor 2ME2 was administered intraperitoneally 1 h after the induction of AP. The severity of the pancreatitis was evaluated by the serum amylase levels and pathology. The severity of the lung injury was evaluated by the wet/dry ratio, blood gas analysis and pathology. The alveolar-capillary barrier disruption was assessed by Evans blue dye extravasation. The protein and mRNA expression levels of HIF-1α and MMP-9 were studied using enzyme-linked immunosorbent assays (ELISAs), western blot analysis and reverse transcription-polymerase chain reaction. The active tumor necrosis factor-α levels were measured using an ELISA. The HIF-1α inhibitor 2ME2 attenuated the severity of the pancreatitis and PALI, while the lung edema and alveolar-capillary barrier disruption were significantly ameliorated compared with those in the untreated PALI group. Administration of the higher dose of 2ME2 significantly suppressed the protein expression of MMP-9 in the lung tissues. The results indicate that HIF-1α has a major function in alveolar-capillary barrier disruption and lung edema in PALI via a molecular pathway cascade involving MMP-9. Inhibition of HIF-1α by 2ME2 attenuates alveolar-capillary barrier disruption and lung edema. Pharmacological blockade of this pathway in patients with PALI may provide a novel therapeutic strategy.

DNA hypermethylation of the serotonin receptor type-2A gene is associated with a worse response to a weight loss intervention in subjects with metabolic syndrome

Understanding the regulation of gene activities depending on DNA methylation has been the subject of much recent study. However, although polymorphisms of the HTR2A gene have been associated with both obesity and psychiatric disorders, the role of HTR2A gene methylation in these illnesses remains uncertain. The aim of this study was to evaluate the association of HTR2A gene promoter methylation levels in white blood cells (WBC) with obesity traits and depressive symptoms in individuals with metabolic syndrome (MetS) enrolled in a behavioural weight loss programme. Analyses were based on 41 volunteers (mean age 49 ± 1 year) recruited within the RESMENA study. Depressive symptoms (as determined using the Beck Depression Inventory), anthropometric and biochemical measurements were analysed at the beginning and after six months of weight loss treatment. At baseline, DNA from WBC was isolated and cytosine methylation in the HTR2A gene promoter was quantified by a microarray approach. In the whole-study sample, a positive association of HTR2A gene methylation with waist circumference and insulin levels was detected at baseline. Obesity measures significantly improved after six months of dietary treatment, where a lower mean HTR2A gene methylation at baseline was associated with major reductions in body weight, BMI and fat mass after the treatment. Moreover, mean HTR2A gene methylation at baseline significantly predicted the decrease in depressive symptoms after the weight loss treatment. In conclusion, this study provides newer evidence that hypermethylation of the HTR2A gene in WBC at baseline is significantly associated with a worse response to a weight-loss intervention and with a lower decrease in depressive symptoms after the dietary treatment in subjects with MetS.

Inhaled budesonide protects against chronic asthma-induced neuroinflammation in mouse brain

Chronic asthma is one of the most common respiratory diseases, characterized by airway inflammation. However, little is known whether asthma-induced airway inflammation might influence the brain. We found that chronic asthma not only resulted in peripheral inflammation, but also induced neuroinflammation which was characterized by microglial activations and increased levels of TNFα and IL-1β in the hippocampus and prefrontal cortex. Simultaneously, we found that there was significant neuronal loss in the asthmatic mouse brain. Inhaled budesonide, the classic therapeutic drug for chronic asthma, could inhibit asthma-induced microglial activation, down-regulate TNFα and IL-1β but up-regulate TGFβ and IL-10 of mouse brain, and thereby attenuate neuronal loss. Further study showed that chronic asthma increased the expressions of TLR4 and p65/NFκB in the brain, which could be reversed by budesonide treatment. Therefore, the present study reveals that inhaled budesonide protects against asthma-induced neuroinflammation in mouse brain, which might be contributed to attenuate neuronal loss.

Netrin-1 ameliorates myocardial infarction-induced myocardial injury: mechanisms of action in rats and diabetic mice

Netrin-1 is typically known as a neuronal guidance factor. Studies have reported the proangiogenic, antiapoptotic, and antiinflammatory properties of Netrin-1. A critical role for Netrin-1 in ischemic organ damage, myocardial infarction (MI) in particular, has also been demonstrated, making Netrin-1 a potential therapeutic target for the treatment of cardiovascular diseases (CVDs). Mesenchymal stem cells (MSCs) have shown promising therapeutic efficacy in preclinical studies. However, limited clinical success was observed, mainly due to poor MSC survival. Given the reported beneficial impact of Netrin-1 in tissue repair and cell survival, we examined the effects of Netrin-1 in MSC therapy against MI-induced ischemic cardiac injury in rats and type 2 diabetic (T2D) mice. MSCs were isolated and Netrin-1-expressing MSCs were obtained by transduction with a Netrin-1-encoding retroviral vector. The Netrin-1-MSCs were then delivered intramyocardially to the infarct sites of rats and T2D mice with MI. Thirty days after MSC implantation, changes at the infarct area, level of collagen deposition, and cardiac hypertrophy were assessed. Molecular mechanisms underlying the effects of Netrin-1 were also investigated. Attenuated MI-induced myocardial dysfunction was observed after Netrin-1-MSC treatment. Protective effects of the Netrin-1-MSCs were attributable primarily to better MSC survival and migration, which is mediated by Netrin-1-induced phosphorylation of p44/42 mitogen-activated protein kinase. Netrin-1-stimulated nitric oxide production was also responsible, which could promote neovessel formation and progenitor cell mobilization in vivo. We report a protective role for Netrin-1 against MI-induced ischemic injuries, reinstating its promising potential as a therapeutic target for CVDs and, more importantly, for patients with CVD with coexisting diabetes.

Guidance cue netrin-1 and the regulation of inflammation in acute and chronic kidney disease

Acute kidney injury (AKI) is a common problem in the hospital setting and intensive care unit. Despite improved understanding, there are no effective therapies available to treat AKI. A large body of evidence strongly suggests that ischemia reperfusion injury is an inflammatory disease mediated by both adaptive and innate immune systems. Cell migration also plays an important role in embryonic development and inflammation, and this process is highly regulated to ensure tissue homeostasis. One such paradigm exists in the developing nervous system, where neuronal migration is mediated by a balance between chemoattractive and chemorepulsive signals. The ability of the guidance molecule netrin-1 to repulse or abolish attraction of neuronal cells expressing the UNC5B receptor makes it an attractive candidate for the regulation of inflammatory cell migration. Recent identification of netrin-1 as regulators of immune cell migration has led to a large number of studies looking into how netrin-1 controls inflammation and inflammatory cell migration. This review will focus on recent advances in understanding netrin-1 mediated regulation of inflammation during acute and chronic kidney disease and whether netrin-1 and its receptor activation can be used to treat acute and chronic kidney disease.

Vagus nerve controls resolution and pro-resolving mediators of inflammation

Axonal guidance molecule netrin-1 promotes resolution of inflammation, with netrin-1 and resolvin D1 mutually inducing each other’s expression.

Resolution of inflammation is now recognized as a biosynthetically active process involving pro-resolving mediators. Here, we show in zymosan-initiated peritoneal inflammation that the vagus nerve regulates local expression of netrin-1, an axonal guidance molecule that activates resolution, and that vagotomy reduced local pro-resolving mediators, thereby delaying resolution. In netrin-1^+/− mice, resolvin D1 (RvD1) was less effective in reducing neutrophil influx promoting resolution of peritonitis compared with Ntn1^+/+. Netrin-1 shortened the resolution interval, decreasing exudate neutrophils, reducing proinflammatory mediators, and stimulating the production of resolvins, protectins, and lipoxins. Human monocytes incubated with netrin-1 produced proresolving mediators, including resolvins and lipoxins. Netrin-1 and RvD1 displayed bidirectional activation in that they stimulated each other’s expression and enhanced efferocytosis. These results indicate that the vagus nerve regulates both netrin-1 and pro-resolving lipid mediators, which act in a bidirectional fashion to stimulate resolution, and provide evidence for a novel mechanism for local neuronal control of resolution.

Hypoxic condition promotes differentiation and mineralization of dental pulp cells in vivo

AIM

To investigate the behaviour of dental pulp cells under hypoxic conditions in vivo using an experimental animal model.

METHODOLOGY

A mini-screw was inserted into the inferior dental nerve canal of rats to arrest the blood supply, which resulted in a reduced oxygen level in the dental pulps of molar teeth used for the experimental group. The decrease in blood supply was evaluated by injected India ink in transparent specimens. The hypoxia marker hypoxyprobe-1 was investigated by immunohistochemical staining. The mRNA expressions of ATP-binding cassette transporter (ABC) G2 (ABCG2) which is a marker for the capacity to excrete metabolites and for stem-like cells as well as dentine sialophosphoprotein (DSPP) and osteocalcin (OCN) which are markers for mineralization were evaluated by RT-PCR. Protein was evaluated by immunohistochemical staining using ABCG2, dentine sialoprotein (DSP) and OCN.

RESULTS

The evaluation of India ink indicated a decreased blood supply in the transparent specimens, and hypoxyprobe-1 immunohistochemical staining showed positive expression. ABCG2, DSPP and OCN mRNA expressions increased at 7 and 14 days. Immunohistochemically, ABCG2, DSP and OCN-positive cells were localized in the odontoblastic layer.

CONCLUSIONS

Hypoxic conditions promoted mineralization and differentiation of dental pulp cells of the odontoblastic layer.

Netrin-1 guides inflammatory cell migration to control mucosal immune responses during intestinal inflammation

The intestinal epithelium is a dynamic barrier playing an active role in intestinal homeostasis and inflammation. Intestinal barrier function is dysregulated during inflammatory bowel disease (IBD), with epithelial cells playing a significant part in generating an inflammatory milieu through the release of signals that attract leukocytes to the intestinal lamina propria. However, it is increasingly appreciated that the intestinal epithelium mediates a counterbalancing response to drive resolution. Drawing analogies with neuronal development, where the balance of chemoattractive and chemorepellent signals is key to directed neuronal movement it has been postulated that such secreted cues play a role in leukocyte migration. Netrin-1 is one of the best-described neuronal guidance molecules, which has been shown to play a significant role in directed migration of leukocytes. Prior to our study the potential role of netrin-1 in IBD was poorly characterized. We defined netrin-1 as an intestinal epithelial-derived protein capable of limiting neutrophil recruitment to attenuate acute colitis. Our study highlights that the intestinal epithelium releases factors during acute inflammation that are responsible for fine-tuning the immune response. Exploration of these epithelial-mediated protective mechanisms will shed light on the complexity of the intestinal epithelial barrier in health and disease.

Netrin-1 promotes epithelial sodium channel-mediated alveolar fluid clearance via activation of the adenosine 2B receptor in lipopolysaccharide-induced acute lung injury

BACKGROUND

The epithelial sodium channel (ENaC) is the driving force for pulmonary edema absorption in acute lung injury (ALI). Netrin-1 is a newly found anti-inflammatory factor that works by activating the adenosine 2B receptor (A2BAR). Meanwhile, activated A2BAR has the potential to enhance ENaC-dependent alveolar fluid clearance (AFC). However, whether netrin-1 can increase ENaC-mediated AFC by activating A2BAR remains unclear.

OBJECTIVES

To investigate the effect of netrin-1 on AFC in ALI and clarify the pathway via which netrin-1 regulates the expression of ENaC in vivo and in vitro.

METHODS

An ALI model was established by intratracheal instillation of lipopolysaccharide (LPS; 5 mg/kg) in C57BL/J mice, followed by netrin-1 with or without pretreatment with PSB1115, via the caudal vein. Twenty-four hours later, the lungs were isolated for determination of the bronchoalveolar lavage fluid, the lung wet/dry weight (W/D) ratio, AFC, the expressions of α-, β-, and γ-ENaC, and cyclic adenosine monophosphate (cAMP) levels. LPS-stimulated MLE-12 cells were incubated with netrin-1 with or without preincubation with PSB1115. Twenty-four hours later, the expressions of α-, β-, and γ-ENaC were detected.

RESULTS

In vivo, netrin-1 expression was significantly decreased during ALI. Substituted netrin-1 significantly dampened the lung injury, decreased the W/D ratio, and enhanced AFC, the expressions of α-, β-, and γ-ENaC, and cAMP levels in ALI, which were abolished by specific A2BAR inhibitor PSB1115. In vitro, netrin-1 increased the expressions of α-, β-, and γ-ENaC, which were prevented by PSB1115.

CONCLUSION

These results indicate that netrin-1 dampens pulmonary inflammation and increases ENaC-mediated AFC to alleviate pulmonary edema in LPS-induced ALI by enhancing cAMP levels through the activation of A2BAR.

Role of Pannexin-1 hemichannels and purinergic receptors in the pathogenesis of human diseases

In the last decade several groups have determined the key role of hemichannels formed by pannexins or connexins, extracellular ATP and purinergic receptors in physiological and pathological conditions. Our work and the work of others, indicate that the opening of Pannexin-1 hemichannels and activation of purinergic receptors by extracellular ATP is essential for HIV infection, cellular migration, inflammation, atherosclerosis, stroke, and apoptosis. Thus, this review discusses the importance of purinergic receptors, Panx-1 hemichannels and extracellular ATP in the pathogenesis of several human diseases and their potential use to design novel therapeutic approaches.

Netrin-1 promotes adipose tissue macrophage retention and insulin resistance in obesity

During obesity, macrophage accumulation in adipose tissue propagates the chronic inflammation and insulin resistance associated with type 2 diabetes. The factors, however, that regulate the accrual of macrophages in adipose tissue are not well understood. Here we show that the neuroimmune guidance cue netrin-1 is highly expressed in obese but not lean adipose tissue of humans and mice, where it directs the retention of macrophages. Netrin-1, whose expression is induced in macrophages by the saturated fatty acid palmitate, acts via its receptor Unc5b to block their migration. In a mouse model of diet-induced obesity, we show that adipose tissue macrophages exhibit reduced migratory capacity, which can be restored by blocking netrin-1. Furthermore, hematopoietic deletion of Ntn1 facilitates adipose tissue macrophage emigration, reduces inflammation and improves insulin sensitivity. Collectively, these findings identify netrin-1 as a macrophage retention signal in adipose tissue during obesity that promotes chronic inflammation and insulin resistance.

High altitude journeys and flights are associated with an increased risk of flares in inflammatory bowel disease patients

BACKGROUND AND AIMS

Hypoxia can induce inflammation in the gastrointestinal tract. However, the impact of hypoxia on the course of inflammatory bowel disease (IBD) is poorly understood. We aimed to evaluate whether flights and/or journeys to regions lying at an altitude of >2000 m above the sea level are associated with flare-ups within 4 weeks of the trip.

METHODS

IBD patients with at least one flare-up during a 12-month observation period were compared to a group of patients in remission. Both groups completed a questionnaire.

RESULTS

A total of 103 IBD patients were included (43 with Crohn's disease (CD): mean age 39.3 ± 14.6 years; 60 with ulcerative colitis (UC): mean age 40.4 ± 15.1 years). Fifty-two patients with flare-ups were matched to 51 patients in remission. IBD patients experiencing flare-ups had more frequently undertaken flights and/or journeys to regions >2000 m above sea level within four weeks of the flare-up when compared to patients in remission (21/52 [40.4%] vs. 8/51 [15.7%], p=0.005).

CONCLUSIONS

Journeys to high altitude regions and/or flights are a risk factor for IBD flare-ups occurring within 4 weeks of travel.

Identification of hypoxia-inducible factor HIF-1A as transcriptional regulator of the A2B adenosine receptor during acute lung injury

Although acute lung injury (ALI) contributes significantly to critical illness, resolution often occurs spontaneously through endogenous pathways. We recently found that mechanical ventilation increases levels of pulmonary adenosine, a signaling molecule known to attenuate lung inflammation. In this study, we hypothesized a contribution of transcriptionally controlled pathways to pulmonary adenosine receptor (ADOR) signaling during ALI. We gained initial insight from microarray analysis of pulmonary epithelia exposed to conditions of cyclic mechanical stretch, a mimic for ventilation-induced lung disease. Surprisingly, these studies revealed a selective induction of the ADORA2B. Using real-time RT-PCR and Western blotting, we confirmed an up to 9-fold induction of the ADORA2B following cyclic mechanical stretch (A549, Calu-3, or human primary alveolar epithelial cells). Studies using ADORA2B promoter constructs identified a prominent region within the ADORA2B promoter conveying stretch responsiveness. This region of the promoter contained a binding site for the transcription factor hypoxia-inducible factor (HIF)-1. Additional studies using site-directed mutagenesis or transcription factor binding assays demonstrated a functional role for HIF-1 in stretch-induced increases of ADORA2B expression. Moreover, studies of ventilator-induced lung injury revealed induction of the ADORA2B during ALI in vivo that was abolished following HIF inhibition or genetic deletion of Hif1a. Together, these studies implicate HIF in the transcriptional control of pulmonary adenosine signaling during ALI.

Allosteric modulators of human A2B adenosine receptor

BACKGROUND

Among adenosine receptors (ARs) the A2B subtype exhibits low affinity for the endogenous agonist compared with the A1, A2A, and A3 subtypes and is therefore activated when concentrations of adenosine increase to a large extent following tissue damages (e.g. ischemia, inflammation). For this reason, A2B AR represents an important pharmacological target.

METHODS

We evaluated seven 1-benzyl-3-ketoindole derivatives (7-9) for their ability to act as positive or negative allosteric modulators of human A2B AR through binding and functional assays using CHO cells expressing human A1, A2A, A2B, and A3 ARs.

RESULTS

The investigated compounds behaved as specific positive or negative allosteric modulators of human A2B AR depending on small differences in their structures. The positive allosteric modulators 7a,b and 8a increased agonist efficacy without any effect on agonist potency. The negative allosteric modulators 8b,c and 9a,b reduced agonist potency and efficacy.

CONCLUSIONS

A number of 1-benzyl-3-ketoindole derivatives were pharmacologically characterized as selective positive (7a,b) or negative (8c, 9a,b) allosteric modulators of human A2B AR.

GENERAL SIGNIFICANCE

The 1-benzyl-3-ketoindole derivatives 7-9 acting as positive or negative allosteric modulators of human A2B AR represent new pharmacological tools useful for the development of therapeutic agents to treat pathological conditions related to an altered functionality of A2B AR.

Association of Neuroimmune Guidance Cue Netrin-1 and Its Chemorepulsive Receptor UNC5B With Atherosclerotic Plaque Expression Signatures and Stability in Human(s)

Background—

Macrophage (MΦ) infiltration and smooth muscle cell (SMC) proliferation are hallmarks of atherosclerosis and unstable plaques. Neuroimmune guidance cue 1 (netrin-1 [NTN1]) plays a critical role controlling MΦ trafficking and SMC activation. Characterization of expression of NTN1 and its receptors and their association with plaque stability in human(s) is lacking.

Methods and Results—

The expression of NTN1 and its receptors did not differ in either whole blood or circulating monocytes from patients with coronary artery disease (n=55) compared with healthy controls (n=45). However, NTN1 was downregulated (−2.9-fold; P <0.0001) and UNC5B upregulated (2.2-fold; P <0.0001) in atherosclerotic plaques (n=68), whereas there were no differences in other NTN1 receptors compared with histologically normal controls (n=28). Increased UNC5B expression is associated with histologically more stable plaques ( P =0.011). NTN1 expression correlated positively with SMC markers and signatures and negatively with inflammatory markers and M1 and especially M2 signatures in the atherosclerotic plaques. UNC5B clustering correlated positively with inflammatory and MΦ markers. NTN1 protein colocalized with CD68-positive cells of monocytic origin and muscle-actin-specific-antibody (HHF3)-positive cells indicative of SMCs in the plaques and only with SMCs in the control samples. NTN1 protein was highly expressed in the intimal layer of the control vessels.

Conclusions—

Present findings provide support for the hypothesis that dysregulation of expression of NTN1 in SMCs and its chemorepulsive receptor UNC5B in macrophages are involved in the development of atherosclerosis and unstable plaques.

Netrin-1 overexpression promotes white matter repairing and remodeling after focal cerebral ischemia in mice

Damage of oligodendrocytes after ischemia has negative impact on white matter integrity and neuronal function. In this work, we explore whether Netrin-1 (NT-1) overexpression facilitates white matter repairing and remodeling. Adult CD-1 mice received stereotactic injection of adeno-associated virus carrying NT-1 gene (AAV-NT-1). One week after gene transfer, mice underwent 60 minutes of middle cerebral artery occlusion. The effect of NT-1 on neural function was evaluated by neurobehavioral tests. Proliferated oligodendrocyte progenitor cells (OPCs), newly matured oligodendrocytes, and remyelination were semi-quantified by immunohistochemistry. The role of NT-1 in oligodendrogenesis was further explored by examining specific NT-1 receptors and their function. Netrin-1 overexpression was detected in neurons and astrocytes 2 weeks after AAV-NT-1 gene transfer and significantly improved the neurobehavioral outcomes compared with the control (P<0.05). In comparison with the control, proliferated OPCs, newly matured oligodendrocytes, and remyelination were greatly increased in the ipsilateral hemisphere of AAV-NT-1-transduced mice. Furthermore, both NT-1 receptors deleted in colorectal carcinoma and UNC5H2 were expressed on OPCs whereas only UNC5H2 was expressed in myelinated axons. Our study indicated that NT-1 promoted OPC proliferation, differentiation, and increased remyelination, suggesting that NT-1 is a promising factor for white matter repairing and remodeling after ischemia.

The expression of netrin-1 in the thymus and its effects on thymocyte adhesion and migration

Netrin-1, a known axon guidance molecule, being a secreted laminin-related molecule, has been suggested to be involved in multiple physiological and pathological conditions, such as organogenesis, angiogenesis, tumorigenesis, and inflammation-mediated tissue injury. However, its function in thymocyte development is still unknown. Here, we demonstrate that Netrin-1 is expressed in mouse thymus tissue and is primarily expressed in thymic stromal cells, and the expression of Netrin-1 in thymocytes can be induced by anti-CD3 antibody or IL-7 treatment. Importantly, Netrin-1 mediates the adhesion of thymocytes, and this effect is comparable to or greater than that of fibronectin. Furthermore, Netrin-1 specifically promotes the chemotaxis of CXCL12. These suggest that Netrin-1 may play an important role in thymocyte development.

The neuroimmune guidance cue netrin-1: a new therapeutic target in cardiovascular disease

Netrins are a family of proteins involved in cell migration and axon guidance during embryogenesis. The different functions and mechanisms of action of this family of proteins have been better characterized with the study of netrin-1. They are chemotropic and act as a bifunctional regulator of neuron migration. Apart from its role in the central nervous system, researchers have proven that netrin-1 plays a role in the development and formation of non-neural tissue; netrin-1 is thereby involved in regulation of cancers, cardiovascular diseases, kidney diseases, and other diseases. Concerning the cardiovascular realm, netrin-1 promotes angiogenesis and accelerates atherosclerosis, protects the heart against ischemia-reperfusion injury, and reduces the infarct size. These findings make the neuroimmune guidance cue netrin-1 an important therapeutic target. This work seeks to review the subject based on studies that have been conducted over the past decade to identify the perspectives and extent of the research on this protein in the field of cardiology.