Netrin-4 promotes mural cell adhesion and recruitment to endothelial cells

Increased glycolysis and cellular crosstalk in eosinophilic chronic rhinosinusitis with nasal polyps

Introduction

Chronic rhinosinusitis (CRS) is a chronic inflammatory disease of the sinonasal mucosa with distinct endotypes including type 2 (T2) high eosinophilic CRS with nasal polyps (eCRSwNP), T2 low non-eosinophilic CRS with nasal polyps (neCRSwNP), and CRS without nasal polyps (CRSsNP).

Methods

Given the heterogeneity of disease, we hypothesized that assessment of single cell RNA sequencing (scRNA-seq) across this spectrum of disease would reveal connections between infiltrating and activated immune cells and the epithelial and stromal populations that reside in sinonasal tissue.

Results

Here we find increased expression of genes encoding glycolytic enzymes in epithelial cells (EpCs), stromal cells, and memory T-cell subsets from patients with eCRSwNP, as compared to healthy controls. In basal EpCs, this is associated with a program of cell motility and Rho GTPase effector expression. Across both stromal and immune subsets, glycolytic programming was associated with extracellular matrix interactions, proteoglycan generation, and collagen formation. Furthermore, we report increased cell-cell interactions between EpCs and stromal/immune cells in eCRSwNP compared to healthy control tissue, and we nominate candidate receptor-ligand pairs that may drive tissue remodeling.

Discussion

These findings support a role for glycolytic reprograming in T2-elicited tissue remodeling and implicate increased cellular crosstalk in eCRSwNP.

Hepatic Expression of NTN4 and Its Receptors in Patients with Hepatocellular Carcinoma

BACKGROUND

Angiogenesis contributes to hepatocellular carcinoma (HCC) progression by promoting tumor growth and metastasis. Netrin-4 (NTN4) is a secreted glycoprotein that has been reported to control angiogenesis and preserve endothelial homeostasis. Macrovascular invasion of the portal vein, referred to as portal vein invasion (PVI) is associated with poor prognosis in HCC patients. In this work, we sought to understand more about the systemic and hepatic level expression of NTN4 and its receptors in HCC patients with and without portal vein invasion.

METHODS

A total of 154 patients with HCC, and 90 healthy volunteers were recruited in this case-control study. Patients with HCC were further subdivided into those with portal vein invasion (PVI) (n=68), and those without portal vein invasion (NPVI) (n=86). Clinical characteristics and liver function parameters were recorded among the study subjects PVI and NPVI. The serum levels of NTN4 (pg/ml) were estimated by ELISA. HCC tissues and normal non-tumorous liver tissues (controls) were collected for gene expression analysis of NTN4 and its receptors.

RESULTS

ALT, ALP, and GGT levels were significantly elevated in the serum of HCC patients with PVI compared to NPVI and control subjects. Systemic NTN4 was significantly reduced in both PVI and NPVI patients compared to control subjects. At the tissue level, the hepatic NTN4 followed a similar trend with significantly lower mRNA expression in both patients with PVI and NPVI compared to control subjects.

CONCLUSIONS

Systemic and hepatic NTN4 levels were reduced in both PVI and NPVI subjects. The hepatic expression of NTN4 receptors Neogenin and UNC5B were markedly elevated in patients with HCC with PVI compared to NPVI. Future experimental studies might shed the role of NTN4 and its receptors in the development of PVI in HCC.

Netrin 1 directs vascular patterning and maturity in the developing kidney

The intricate vascular system of the kidneys supports body fluid and organ homeostasis. However, little is known about how vascular architecture is established during kidney development. More specifically, how signals from the kidney influence vessel maturity and patterning remains poorly understood. Netrin 1 (Ntn1) is a secreted ligand that is crucial for vessel and neuronal guidance. Here, we demonstrate that Ntn1 is expressed by Foxd1+ stromal progenitors in the developing mouse kidney and conditional deletion (Foxd1GC/+;Ntn1fl/fl) results in hypoplastic kidneys with extended nephrogenesis. Wholemount 3D analyses additionally revealed the loss of a predictable vascular pattern in Foxd1GC/+;Ntn1fl/fl kidneys. As vascular patterning has been linked to vessel maturity, we investigated arterialization. Quantification of the CD31+ endothelium at E15.5 revealed no differences in metrics such as the number of branches or branch points, whereas the arterial vascular smooth muscle metrics were significantly reduced at both E15.5 and P0. In support of our observed phenotypes, whole kidney RNA-seq revealed disruptions to genes and programs associated with stromal cells, vasculature and differentiating nephrons. Together, our findings highlight the significance of Ntn1 to proper vascularization and kidney development.

Serum Levels of Netrin-4 and Its Association With Hepatocellular Carcinoma: Results From a Case-Control Study

BACKGROUND

Angiogenesis plays a vital role in the progression of hepatocellular carcinoma (HCC) by contributing to tumor growth and metastasis. Netrin-4 (NTN4) is a secreted glycoprotein that regulates angiogenesis and maintains endothelial homeostasis. There were no studies found focusing on the value of NTN4 as a serum biomarker for the diagnosis and prognosis of HCC. In this study, we aimed to investigate the systemic expression of NTN4 in patients with HCC. We also explore the association of NTN4 with major clinicopathological and biochemical characteristics of HCC.

METHODS

A total of 116 patients with HCC and 44 healthy volunteers were recruited in this case-control study. Clinical characteristics and liver function parameters were recorded among the study subjects. The levels of α-fetoprotein (AFP) were quantified in patients with HCC. The serum levels of NTN4 (pg/ml) were estimated by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The median NTN4 levels were significantly decreased in patients with HCC when compared to control subjects (p < 0.0001). There was no difference between NTN4 levels in AFP-positive patients and AFP-negative patients (p = 0.39). Of note, NTN4 levels were significantly decreased in HCC patients with metastasis (p < 0.02) and portal vein invasion (p < 0.04). Further, NTN4 levels were significantly reduced in HCC patients with Child-Pugh C score (p < 0.05). The receiver operating characteristic curve for serum levels of NTN4 in the HCC group and control group was generated. At a cut-off of 30 pg/ml, the sensitivity and specificity for NTN4 were 80% and 82%, respectively, with an AUC of 0.894.

CONCLUSIONS

Low levels of NTN4 were associated with increased tumor aggressiveness and metastasis in HCC. Estimation of circulating NTN4 has prognostic value as a minimally invasive biomarker in HCC. Future studies might shed the role of NTN4 in the development of HCC.

Netrin-1 directs vascular patterning and maturity in the developing kidney

Blood filtering by the kidney requires the establishment of an intricate vascular system that works to support body fluid and organ homeostasis. Despite these critical roles, little is known about how vascular architecture is established during kidney development. More specifically, how signals from the kidney influence vessel maturity and patterning remains poorly understood. Netrin-1 (Ntn1) is a secreted ligand critical for vessel and neuronal guidance. Here, we demonstrate that Ntn1 is expressed by stromal progenitors in the developing kidney, and conditional deletion of Ntn1 from Foxd1+ stromal progenitors (Foxd1GC/+;Ntn1fl/fl) results in hypoplastic kidneys that display extended nephrogenesis. Despite expression of the netrin-1 receptor Unc5c in the adjacent nephron progenitor niche, Unc5c knockout kidneys develop normally. The netrin-1 receptor Unc5b is expressed by embryonic kidney endothelium and therefore we interrogated the vascular networks of Foxd1GC/+;Ntn1fl/fl kidneys. Wholemount, 3D analyses revealed the loss of a predictable vascular pattern in mutant kidneys. As vascular patterning has been linked to vessel maturity, we investigated arterialization in these mutants. Quantification of the CD31+ endothelium at E15.5 revealed no differences in metrics such as the number of branches or branch points, whereas the arterial vascular smooth muscle metrics were significantly reduced at both E15.5 and P0. In support of these results, whole kidney RNA-seq showed upregulation of angiogenic programs and downregulation of muscle-related programs which included smooth muscle-associated genes. Together, our findings highlight the significance of netrin-1 to proper vascularization and kidney development.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

Injection of Micronized Human Amnion/Chorion Membrane Results in Increased Early Supraspinatus Muscle Regeneration in a Chronic Model of Rotator Cuff Tear

Surgical repair of severe rotator cuff tear often results in retear due to unaddressed muscle degeneration. The objective of this study was to test the regenerative potential of micronized dehydrated Human Amnion/Chorion Membrane (dHACM), in a clinically relevant delayed reattachment model of rotator cuff repair. Micronized dHACM was injected into rat supraspinatus muscle during tendon re-attachment surgery, three weeks after original tendon injury. One week after material injection, inflammatory and mesenchymal stem cell infiltration into supraspinatus muscles was assessed via flow cytometry. Histological methods were utilized to assess structural and regenerative changes in muscle one and three weeks after material injection. Micronized dHACM injection resulted in increased M1-like macrophages (17.1 [Formula: see text] fold change over contralateral controls) and regenerating muscle fibers (4.3% vs 1.7% in saline treated muscles) one week after injection compared to saline treated muscles. Tendon reattachment itself exhibited intrinsic healing in this model, demonstrated by a general return of muscle weight and reduced fibrosis. Our results indicate that injection of micronized dHACM may initiate an inflammatory response in degenerated muscle that promotes early muscle regeneration, and that our animal model may be a suitable platform for studying treatments in muscle at early timepoints, before intrinsic healing occurs.

Netrin-1 in Glioblastoma Neovascularization: The New Partner in Crime?

Glioblastoma (GBM) is the most aggressive and common primary tumor of the central nervous system. It is characterized by having an infiltrating growth and by the presence of an excessive and aberrant vasculature. Some of the mechanisms that promote this neovascularization are angiogenesis and the transdifferentiation of tumor cells into endothelial cells or pericytes. In all these processes, the release of extracellular microvesicles by tumor cells plays an important role. Tumor cell-derived extracellular microvesicles contain pro-angiogenic molecules such as VEGF, which promote the formation of blood vessels and the recruitment of pericytes that reinforce these structures. The present study summarizes and discusses recent data from different investigations suggesting that Netrin-1, a highly versatile protein recently postulated as a non-canonical angiogenic ligand, could participate in the promotion of neovascularization processes in GBM. The relevance of determining the angiogenic signaling pathways associated with the interaction of Netrin-1 with its receptors is posed. Furthermore, we speculate that this molecule could form part of the microvesicles that favor abnormal tumor vasculature. Based on the studies presented, this review proposes Netrin-1 as a novel biomarker for GBM progression and vascularization.

Identification of NEO1 as a prognostic biomarker and its effects on the progression of colorectal cancer

Background

Due to the high morbidity and poor clinical outcomes, early predictive and prognostic biomarker identification is desiderated in colorectal cancer (CRC). As a homologue of the Deleted in Colorectal Cancer (DCC) gene, the role of Neogenin-1 (NEO1) in CRC remained unveiled. This study was designed to probe into the effects and potential function of NEO1 in CRC.

Methods

Online databases, Gene Set Enrichment Analysis (GSEA), quantitative real-time PCR and western blotting were used to evaluate NEO1 expression in colorectal cancer tissues. Survival analysis was performed to predict the prognosis of CRC patients based on NEO1 expression level. Then, cell proliferation was detected by colony formation and Cell Counting Kit 8 (CCK-8) assays. CRC cell migration and invasion were examined by transwell assays. Finally, we utilized the Gene Set Variation Analysis (GSVA) and GSEA to dig the potential mechanisms of NEO1 in CRC.

Results

Oncomine database and The Cancer Genome Atlas (TCGA) database showed that NEO1 was down-regulated in CRC. Further results validated that NEO1 mRNA and protein expression were both significantly lower in CRC tumor tissues than in the adjacent tissues in our clinical samples. NEO1 expression was decreased with the progression of CRC. Survival and other clinical characteristic analyses exhibited that low NEO1 expression was related with poor prognosis. A gain-of-function study showed that overexpression of NEO1 restrained proliferation, migration and invasion of CRC cells while a loss-of-function showed the opposite effects. Finally, functional pathway enrichment analysis revealed that NEO1 low expression samples were enriched in inflammation-related signaling pathways, EMT and angiogenesis.

Conclusion

A tumor suppressor gene NEO1 was identified and verified to be correlated with the prognosis and progression of CRC, which could serve as a prognostic biomarker for CRC patients.

Polyomavirus Small T Antigen Induces Apoptosis in Mammalian Cells through the UNC5B Pathway in a PP2A-Dependent Manner

UNC5B is a dependence receptor that promotes survival in the presence of its ligand, netrin-1, while inducing cell death in its absence. The receptor has an important role in the development of the nervous and vascular systems. It is also involved in the normal turnover of intestinal epithelium. Netrin-1 and UNC5B are deregulated in multiple cancers, including colorectal, neuroblastoma, and breast tumors. However, the detailed mechanism of UNC5B function is not fully understood. We have utilized the murine polyomavirus small T antigen (PyST) as a tool to study UNC5B-mediated apoptosis. PyST is known to induce mitotic arrest followed by extensive cell death in mammalian cells. Our results show that the expression of PyST increases mRNA levels of UNC5B by approximately 3-fold in osteosarcoma cells (U2OS) and also stabilizes UNC5B at the posttranslational level. Furthermore, UNC5B is upregulated predominantly in those cells that undergo mitotic arrest upon PyST expression. Interestingly, although its expression was previously reported to be regulated by p53, our data show that the increase in UNC5B levels by PyST is p53 independent. The posttranslational stabilization of UNC5B by PyST is regulated by the interaction of PyST with PP2A. We also show that netrin-1 expression, which is known to inhibit UNC5B apoptotic activity, promotes survival of PyST-expressing cells. Our results thus suggest an important role of UNC5B in small-T antigen-induced mitotic catastrophe that also requires PP2A.IMPORTANCE UNC5B, PP2A, and netrin-1 are deregulated in a variety of cancers. UNC5B and PP2A are regarded as tumor suppressors, as they promote apoptosis and are deleted or mutated in many cancers. In contrast, netrin-1 promotes survival by inhibiting dependence receptors, including UNC5B, and is upregulated in many cancers. Here, we show that UNC5B-mediated apoptosis can occur independently of p53 but in a PP2A-dependent manner. A substantial percentage of cancers arise due to p53 mutations and are insensitive to chemotherapeutic treatments that activate p53. Unexpectedly, treatment of cancers having functional p53 with many conventional drugs leads to the upregulation of netrin-1 through activated p53, which is counterintuitive. Therefore, understanding the p53-independent mechanisms of the netrin-UNC5B axis, such as those involving PP2A, assumes greater clinical significance. Anticancer strategies utilizing anti-netrin-1 antibody treatment are already in clinical trials.

Targeting Netrin-1 and -4 as a Novel Diagnostic Parameter and Treatment Option for Diabetic Retinopathy

Diabetic retinopathy (DR) is a retinal vascular disorder associated with both type 1 and type 2 diabetes mellitus (DM). It is characterized by specific loss of pericytes, which leads to an augmented blood vessel permeability, and development of new blood vessels (retinal neovascularization). Moreover, stiffening of eye membrane, inflammation, and apoptosis of endothelial cells also lead to damage of the blood-retinal barrier and blindness in most cases unless it's detected and managed early. Hence, this review was intended to assess the potential roles of Netrin-1 and -4 as new/alternative biomarkers and therapeutic options for DR. Netrin-1 and -4 have been the most known ligands and are well known for their role in neural guidance. DR has both neural and vascular components; therefore, biomarkers used for both neural and vascular retinal tissues are potentially important. According to different experimental and clinical studies, as compared to the normal groups, there was a significant increment in both retinal Netrin-1 and -4 mRNA and protein levels in the retinopathy groups. In addition, exogenous supplementation of these proteins is also used as a therapeutic agent for DR.

Ischemia-induced Netrin-4 promotes neovascularization through endothelial progenitor cell activation via Unc-5 Netrin receptor B

Endothelial progenitor cells (EPCs) promote neovascularization and tissue repair by migrating to vascular injury sites; therefore, factors that enhance EPC homing to damaged tissues are of interest. Here, we provide evidence of the prominent role of the Netrin-4 (NTN4)-Unc-5 Netrin receptor B (UNC5B) axis in EPC-specific promotion of ischemic neovascularization. Our results showed that NTN4 promoted the proliferation, chemotactic migration, and paracrine effects of small EPCs (SEPCs) and significantly increased the incorporation of large EPCs (LEPCs) into tubule networks. Additionally, NTN4 prominently augmented neovascularization in mice with hindlimb ischemia by increasing the homing of exogenously transplanted EPCs to the ischemic limb and incorporating EPCs into vessels. Moreover, silencing of UNC5B, an NTN4 receptor, abrogated the NTN4-induced cellular activities of SEPCs in vitro and blood-flow recovery and neovascularization in vivo in ischemic muscle by reducing EPC homing and incorporation. These findings suggest NTN4 as an EPC-based therapy for treating angiogenesis-dependent diseases.

Identification of differential gene expression in endothelial cells from young and aged mice using RNA-Seq technique

Aging is a complex phenomenon. Endothelial cell senescence is regarded as a vital characteristic of cardiovascular diseases. This study aims to identify differentially expressed genes in vascular endothelial cells (ECs) of different age groups by RNA sequencing (RNA-Seq) technique, and to explore which molecular pathways differentially expressed genes (DEGs) may enrich in. In this study, we used RNA-Seq to analyze DEGs in primary endothelial cells of young and old mice, and further analyzed them by gene ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Our results showed that in total identified 229 of the DEGs, 104 were upregulated and 125 were downregulated in endothelial cells of aged mice compared with young mice. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the involvement of these DEGs in the regulation of morphogenesis of a branching structure, angiogenesis, upregulation of cell proliferation, and extracellular matrix (ECM)-receptor interaction. These results provided a novel insight to understand the molecular mechanisms underlying aortic endothelial cell senescence, and some of the novel candidate genes identified in this study may be valuable in elucidating the molecular mechanisms underlying endothelial cell senescence.

Cellular Recruitment by Podocyte-Derived Pro-migratory Factors in Assembly of the Human Renal Filter

Analysis of kidney disease-causing genes and pathology resulting from systemic diseases highlight the importance of the kidney's filtering system, the renal corpuscles. To elucidate the developmental processes that establish the renal corpuscle, we performed single-nucleus droplet-based sequencing of the human fetal kidney. This enabled the identification of nephron, interstitial, and vascular cell types that together generate the renal corpuscles. Trajectory analysis identified transient developmental gene expression, predicting precursors or mature podocytes express FBLN2, BMP4, or NTN4, in conjunction with recruitment, differentiation, and modeling of vascular and mesangial cell types into a functional filter. In vitro studies provide evidence that these factors exhibit angiogenic or mesangial recruiting and inductive properties consistent with a key organizing role for podocyte precursors in kidney development. Together these studies define a spatiotemporal developmental program for the primary filtration unit of the human kidney and provide novel insights into cell interactions regulating co-assembly of constituent cell types.

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Single-nuclear RNA-seq analysis of human fetal kidney development

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Co-ordinated programs of podocyte-driven glomerular development

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Secreted podocyte factors act on endothelial and interstitial cells

EGF/EGFR upregulates and cooperates with Netrin-4 to protect glioblastoma cells from DNA damage-induced senescence

BACKGROUND

Glioblastoma multiforme (GBM) is the most malignant central nervous system tumor. Alkylating agent, temozolomide (TMZ), is currently the first-line chemotherapeutic agent for GBM. However, the sensitivity of GBM cells to TMZ is affected by many factors. And, several clinic trials, including co-administration of TMZ with other drugs, have failed in successful treatment of GBM. We have previously reported that Netrin-4 (NTN4), a laminin-like axon guidance protein, plays a protective role in GBM cell senescence upon TMZ-triggered DNA damage. However, the master regulator of NTN4 needs further elucidation. Epidermal growth factor/Epidermal growth factor receptor (EGF/EGFR) can modulate the expression of various extracellular matrix related molecules, and prevent DNA damage in GBM cells. In this study, we investigated the relationship between EGF/EGFR signaling and NTN4, and explored their effect on therapeutic efficacy in GBM cells upon TMZ treatment.

METHODS

Co-expression analysis were performed by using the RNA sequencing data from NIH 934 cell lines and from single cell RNA sequencing data of GBM tumor. The co-expressing genes were used for GO enrichment and signaling pathway enrichment. mRNA expression of the target genes were quantified by qPCR, and cell senescence were investigated by Senescence-Associated Beta-Galactosidase Staining. Protein phosphorylation were observed and analyzed by immunoblotting. The RNA sequencing data and clinical information of TMZ treated patients were extracted from TCGA-glioblastoma project, and then used for Kaplan-Meier survival analysis.

RESULTS

Analysis of RNA sequencing data revealed a potential co-expression relationship between NTN4 and EGFR. GO enrichment of EGFR-correlated genes indicated that EGFR regulates GBM cells in a manner similar to that in central nervous system development and neural cell differentiation. Pathway analysis suggested that EGFR and its related genes contribute to cell adhesion, extracellular matrix (ECM) organization and caspase related signaling. We also show that EGF stimulates NTN4 expression in GBM cells and cooperates with NTN4 to attenuate GBM cell senescence induced by DNA damage, possibly via AKT and ERK. Clinical analysis showed that co-expression of EGFR and NTN4 significantly predicts poor survival in TMZ-treated GBM patients.

CONCLUSIONS

This study indicates that EGF/EGFR regulates and cooperates with NTN4 in DNA damage resistance in GBM. Therefore, our findings provide a potential therapeutic target for GBM.

Guidance Molecules in Vascular Smooth Muscle

Several highly conserved families of guidance molecules, including ephrins, Semaphorins, Netrins, and Slits, play conserved and distinct roles in tissue remodeling during tissue patterning and disease pathogenesis. Primarily, these guidance molecules function as either secreted or surface-bound ligands that interact with their receptors to activate a variety of downstream effects, including cell contractility, migration, adhesion, proliferation, and inflammation. Vascular smooth muscle cells, contractile cells comprising the medial layer of the vessel wall and deriving from the mural population, regulate vascular tone and blood pressure. While capillaries lack a medial layer of vascular smooth muscle, mural-derived pericytes contribute similarly to capillary tone to regulate blood flow in various tissues. Furthermore, pericyte coverage is critical in vascular development, as perturbations disrupt vascular permeability and viability. During cardiovascular disease, smooth muscle cells play a more dynamic role in which suppression of contractile markers, enhanced proliferation, and migration lead to the progression of aberrant vascular remodeling. Since many types of guidance molecules are expressed in vascular smooth muscle and pericytes, these may contribute to blood vessel formation and aberrant remodeling during vascular disease. While vascular development is a large focus of the existing literature, studies emerged to address post-developmental roles for guidance molecules in pathology and are of interest as novel therapeutic targets. In this review, we will discuss the roles of guidance molecules in vascular smooth muscle and pericyte function in development and disease.

The Netrin-4/Laminin γ1/Neogenin-1 complex mediates migration in SK-N-SH neuroblastoma cells

Neuroblastoma (NB) is the most common pediatric extracranial solid tumor. It arises during development of the sympathetic nervous system. Netrin-4 (NTN4), a laminin-related protein, has been proposed as a key factor to target NB metastasis, although there is controversy about its function. Here, we show that NTN4 is broadly expressed in tumor, stroma and blood vessels of NB patient samples. Furthermore, NTN4 was shown to act as a cell adhesion molecule required for the migration induced by Neogenin-1 (NEO1) in SK-N-SH neuroblastoma cells. Therefore, we propose that NTN4, by forming a ternary complex with Laminin γ1 (LMγ1) and NEO1, acts as an essential extracellular matrix component, which induces the migration of SK-N-SH cells.

A network map of netrin receptor UNC5B-mediated signaling

UNC-5 Homolog B (UNC5B) is a member of the dependence receptor family. This family of receptors can induce two opposite intracellular signaling cascades depending on the presence or absence of the ligand and is thus capable of driving two opposing processes. UNC5B signaling has been implicated in several cancers, where it induces cell death in the absence of its ligand Netrin-1 and promotes cell survival in its presence. In addition, inhibition of Netrin-1 ligand has been reported to decrease invasiveness and angiogenesis in tumors. UNC5B signaling pathway has also been reported to be involved in several processes such as neural development, developmental angiogenesis and inflammatory processes. However, literature pertaining to UNC5B signaling is scarce and scattered. Considering the importance of UNC5B signaling, we developed a resource of signaling events mediated by UNC5B. Using data mined from published literature, we compiled an integrated pathway map consisting of 88 UNC5B-mediated signaling events and 55 proteins. These signaling events include 27 protein-protein interaction events, 33 catalytic events involving various post-translational modifications, 9 events of UNC5B-mediated protein activation/inhibition, 27 gene regulation events and 2 events of translocation. This pathway resource has been made available to the research community through NetPath ( http://www.netpath.org /), a manually curated resource of signaling pathways (Database URL: http://www.netpath.org/pathways?path_id=NetPath_172 ). The current resource provides a foundation for the understanding of UNC5B-mediated cellular responses. The development of resource will serve researchers to explore the mechanisms of UNC-5B signaling in cancers.

Expression of the Atypical Chemokine Receptor ACKR4 Identifies a Novel Population of Intestinal Submucosal Fibroblasts That Preferentially Expresses Endothelial Cell Regulators

Atypical chemokine receptors (ACKRs) are expressed by discrete populations of stromal cells at specific anatomical locations where they control leukocyte migration by scavenging or transporting chemokines. ACKR4 is an atypical receptor for CCL19, CCL21, and CCL25. In skin, ACKR4 plays indispensable roles in regulating CCR7-dependent APC migration, and there is a paucity of migratory APCs in the skin-draining lymph nodes of Ackr4-deficient mice under steady-state and inflammatory conditions. This is caused by loss of ACKR4-mediated CCL19/21 scavenging by keratinocytes and lymphatic endothelial cells. In contrast, we show in this study that Ackr4 deficiency does not affect dendritic cell abundance in the small intestine and mesenteric lymph nodes, at steady state or after R848-induced mobilization. Moreover, Ackr4 expression is largely restricted to mesenchymal cells in the intestine, where it identifies a previously uncharacterized population of fibroblasts residing exclusively in the submucosa. Compared with related Ackr4^- mesenchymal cells, these Ackr4⁺ fibroblasts have elevated expression of genes encoding endothelial cell regulators and lie in close proximity to submucosal blood and lymphatic vessels. We also provide evidence that Ackr4⁺ fibroblasts form physical interactions with lymphatic endothelial cells, and engage in molecular interactions with these cells via the VEGFD/VEGFR3 and CCL21/ACKR4 pathways. Thus, intestinal submucosal fibroblasts in mice are a distinct population of intestinal mesenchymal cells that can be identified by their expression of Ackr4 and have transcriptional and anatomical properties that strongly suggest roles in endothelial cell regulation.

Netrin-4 Promotes Differentiation and Migration of Osteoblasts

BACKGROUND/AIM

While netrin-4 plays a vital role in the vascular system, the role of netrin-1 in osteoblast differentiation is not well understood. In this study we explored whether netrin-4 has functional roles in osteoblasts.

MATERIALS AND METHODS

Quantitative reverse-transcriptase polymerase chain reaction (PCR), RNA interference, the generation of plasmids, transfections, measurement of alkaline phosphatase activity, a mineralization assay, a migration assay and a cell proliferation assay were performed.

RESULTS

Netrin-4 expression was up-regulated during osteoblast differentiation and an RNA interference experiment showed that small interfering RNA used to silence netrin-4 inhibited osteoblast differentiation. Recombinant mouse netrin-4 promoted alkaline phosphatase (ALP) activity of osteoblasts and enhancement of calcium deposits. Moreover, we constructed a vector containing the netrin-4 gene on the basis of the plasmid pcDNA3.1/V5-His. Overexpression of netrin-4 enhanced differentiation of osteoblasts. Finally, recombinant mouse netrin-4 promoted cell migration of osteoblasts.

CONCLUSION

Netrin-4 promotes differentiation and migration of osteoblasts.

The Netrin-4/ Neogenin-1 axis promotes neuroblastoma cell survival and migration

Neogenin-1 (NEO1) is a transmembrane receptor involved in axonal guidance, angiogenesis, neuronal cell migration and cell death, during both embryonic development and adult homeostasis. It has been described as a dependence receptor, because it promotes cell death in the absence of its ligands (Netrin and Repulsive Guidance Molecule (RGM) families) and cell survival when they are present. Although NEO1 and its ligands are involved in tumor progression, their precise role in tumor cell survival and migration remain unclear. Public databases contain extensive information regarding the expression of NEO1 and its ligands Netrin-1 (NTN1) and Netrin-4 (NTN4) in primary neuroblastoma (NB) tumors. Analysis of this data revealed that patients with high expression levels of both NEO1 and NTN4 have a poor survival rate. Accordingly, our analyses in NB cell lines with different genetic backgrounds revealed that knocking-down NEO1 reduces cell migration, whereas silencing of endogenous NTN4 induced cell death. Conversely, overexpression of NEO1 resulted in higher cell migration in the presence of NTN4, and increased apoptosis in the absence of ligand. Increased apoptosis was prevented when utilizing physiological concentrations of exogenous Netrin-4. Likewise, cell death induced after NTN4 knock-down was rescued when NEO1 was transiently silenced, thus revealing an important role for NEO1 in NB cell survival. In vivo analysis, using the chicken embryo chorioallantoic membrane (CAM) model, showed that NEO1 and endogenous NTN4 are involved in tumor extravasation and metastasis. Our data collectively demonstrate that endogenous NTN4/NEO1 maintain NB growth via both pro-survival and pro-migratory molecular signaling.

Netrins and their roles in placental angiogenesis

Netrins, a family of laminin-related proteins, were originally identified as axonal guidance molecules. Subsequently, netrins were found to modulate various biological processes including morphogenesis, tumorogenesis, adhesion, and, recently, angiogenesis. In human placenta, the most vascularized organ, the presence of netrins has also been reported. Recent studies demonstrated the involvement of netrins in the regulation of placental angiogenesis. In this review we focused on the role of netrins in human placental angiogenesis. Among all netrins examined, netrin-4 and netrin-1 have been found to be either pro- or antiangiogenic factors. These opposite effects appear to be related to the endothelial cell phenotype studied and seem also to depend on the receptor type to which netrin binds, that is, the canonical receptor member of the DCC family, the members of the UNC5 family, or the noncanonical receptor members of the integrin family or DSCAM.