Endothelium-derived Netrin-4 supports pancreatic epithelial cell adhesion and differentiation through integrins α2β1 and α3β1

NEUROD1 reinforces endocrine cell fate acquisition in pancreatic development

NEUROD1 is a transcription factor that helps maintain a mature phenotype of pancreatic β cells. Disruption of Neurod1 during pancreatic development causes severe neonatal diabetes; however, the exact role of NEUROD1 in the differentiation programs of endocrine cells is unknown. Here, we report a crucial role of the NEUROD1 regulatory network in endocrine lineage commitment and differentiation. Mechanistically, transcriptome and chromatin landscape analyses demonstrate that Neurod1 inactivation triggers a downregulation of endocrine differentiation transcription factors and upregulation of non-endocrine genes within the Neurod1-deficient endocrine cell population, disturbing endocrine identity acquisition. Neurod1 deficiency altered the H3K27me3 histone modification pattern in promoter regions of differentially expressed genes, which resulted in gene regulatory network changes in the differentiation pathway of endocrine cells, compromising endocrine cell potential, differentiation, and functional properties.

Bioactive semaphorin 3A promotes sequential formation of sensory nerve and type H vessels during in situ osteogenesis

Introduction: Sensory nerves and vessels are critical for skeletal development and regeneration, but crosstalk between neurovascular network and mineralization are not clear. The aim of this study was to explore neurovascular changes and identify bioactive regulators during in situ osteogenesis. Method: In situ osteogenesis model was performed in male rats following Achilles tenotomy. At 3, 6 and 9 weeks after surgery, mineralization, blood vessels, sensory innervation, and bioactive regulators expression were evaluated via micro-computed tomography, immunofluorescent staining, histology and reverse transcriptase-polymerase chain reaction analyses. Result: In the process of in situ osteogenesis, the mineral density increased with time, and the locations of minerals, nerves and blood vessels were highly correlated at each time point. The highest density of sensory nerve was observed in the experimental group at the 3rd week, and then gradually decreased with time, but still higher than that in the sham control group. Among many regulatory factors, semaphorin 3A (Sema3A) was highly expressed in experimental model and its expression was temporally sequential and spatially correlated sensory nerve. Conclusion: The present study showes that during in situ osteogenesis, innervation and angiogenesis are highly correlated, and Sema3A is associated with the position and expression of the sensory nerve.

β1-Integrin-A Key Player in Controlling Pancreatic Beta-Cell Insulin Secretion via Interplay With SNARE Proteins

Shortcomings in cell-based therapies for patients with diabetes have been revealed to be, in part, a result of an improper extracellular matrix (ECM) environment. In vivo, pancreatic islets are emersed in a diverse ECM that provides physical support and is crucial for healthy function. β1-Integrin receptors have been determined to be responsible for modulation of beneficial interactions with ECM proteins influencing beta-cell development, proliferation, maturation, and function. β1-Integrin signaling has been demonstrated to augment insulin secretion by impacting the actin cytoskeleton via activation of focal adhesion kinase and downstream signaling pathways. In other secretory cells, evidence of a bidirectional relationship between integrins and exocytotic machinery has been demonstrated, and, thus, this relationship could be present in pancreatic beta cells. In this review, we will discuss the role of ECM-β1-integrin interplay with exocytotic proteins in controlling pancreatic beta-cell insulin secretion through their dynamic and unique signaling pathway.

NTN4 as a prognostic marker and a hallmark for immune infiltration in breast cancer

Netrin-4 (NTN4), a member of neurite guidance factor family, can promote neurite growth and elongation. This study aims to investigate if NTN4 correlates with prognosis and immune infiltration in breast cancer. The prognostic landscape of NTN4 and its relationship with immune infiltration in breast cancer were deciphered with public databases and immunohistochemistry (IHC) in tissue samples. The expression profiling and prognostic value of NTN4 were explored using UALCAN, TIMER, Kaplan-Meier Plotter and Prognoscan databases. Based on TIMER, relationships of NTN4 expression with tumor immune invasion and immune cell surface markers were evaluated. Transcription and survival analyses of NTN4 in breast cancer were investigated with cBioPortal database. The STRING database was explored to identify molecular functions and signaling pathways downstream of NTN4. NTN4 expression was significantly lower in invasive breast carcinoma compared with adjacent non-malignant tissues. Promoter methylation of NTN4 exhibited different patterns in breast cancer. Low expression of NTN4 was associated with poorer survival. NTN4 was significantly positively related to infiltration of CD8⁺ T cells, macrophages and neutrophils, whereas significantly negatively related to B cells and tumor purity. Association patterns varied with different subtypes. Various associations between NTN4 levels and immune cell surface markers were revealed. Different subtypes of breast cancer carried different genetic alterations. Mechanistically, NTN4 was involved in mediating multiple biological processes including morphogenesis and migration.

Pancreatic Pseudoislets: An Organoid Archetype for Metabolism Research

Pancreatic islets are vital endocrine regulators of systemic metabolism, and recent investigations have increasingly focused on understanding human islet biology. Studies of isolated human islets have advanced understanding of the development, function, and regulation of cells comprising islets, especially pancreatic α- and β-cells. However, the multicellularity of the intact islet has stymied specific experimental approaches-particularly in genetics and cell signaling interrogation. This barrier has been circumvented by the observation that islet cells can survive dispersion and reaggregate to form "pseudoislets," organoids that retain crucial physiological functions, including regulated insulin and glucagon secretion. Recently, exciting advances in the use of pseudoislets for genetics, genomics, islet cell transplantation, and studies of intraislet signaling and islet cell interactions have been reported by investigators worldwide. Here we review molecular and cellular mechanisms thought to promote islet cell reaggregation, summarize methods that optimize pseudoislet development, and detail recent insights about human islet biology from genetic and transplantation-based pseudoislet experiments. Owing to robust, international programs for procuring primary human pancreata, pseudoislets should serve as both a durable paradigm for primary organoid studies and as an engine of discovery for islet biology, diabetes, and metabolism research.

Netrins: Evolutionarily Conserved Regulators of Epithelial Fusion and Closure in Development and Wound Healing

Epithelial remodelling plays a crucial role during development. The ability of epithelial sheets to temporarily lose their integrity as they fuse with other epithelial sheets underpins events such as the closure of the neural tube and palate. During fusion, epithelial cells undergo some degree of epithelial-mesenchymal transition (EMT), whereby cells from opposing sheets dissolve existing cell-cell junctions, degrade the basement membrane, extend motile processes to contact each other, and then re-establish cell-cell junctions as they fuse. Similar events occur when an epithelium is wounded. Cells at the edge of the wound undergo a partial EMT and migrate towards each other to close the gap. In this review, we highlight the emerging role of Netrins in these processes, and provide insights into the possible signalling pathways involved. Netrins are secreted, laminin-like proteins that are evolutionarily conserved throughout the animal kingdom. Although best known as axonal chemotropic guidance molecules, Netrins also regulate epithelial cells. For example, Netrins regulate branching morphogenesis of the lung and mammary gland, and promote EMT during Drosophila wing eversion. Netrins also control epithelial fusion during optic fissure closure and inner ear formation, and are strongly implicated in neural tube closure and secondary palate closure. Netrins are also upregulated in response to organ damage and epithelial wounding, and can protect against ischemia-reperfusion injury and speed wound healing in cornea and skin. Since Netrins also have immunomodulatory properties, and can promote angiogenesis and re-innervation, they hold great promise as potential factors in future wound healing therapies.

Involvement of Netrins and Their Receptors in Neuronal Migration in the Cerebral Cortex

In mammals, excitatory cortical neurons develop from the proliferative epithelium and progenitor cells in the ventricular zone and subventricular zone, and migrate radially to the cortical plate, whereas inhibitory GABAergic interneurons are born in the ganglionic eminence and migrate tangentially. The migration of newly born cortical neurons is tightly regulated by both extracellular and intracellular signaling to ensure proper positioning and projections. Non-cell-autonomous extracellular molecules, such as growth factors, axon guidance molecules, extracellular matrix, and other ligands, play a role in cortical migration, either by acting as attractants or repellents. In this article, we review the guidance molecules that act as cell-cell recognition molecules for the regulation of neuronal migration, with a focus on netrin family proteins, their receptors, and related molecules, including neogenin, repulsive guidance molecules (RGMs), Down syndrome cell adhesion molecule (DSCAM), fibronectin leucine-rich repeat transmembrane proteins (FLRTs), and draxin. Netrin proteins induce attractive and repulsive signals depending on their receptors. For example, binding of netrin-1 to deleted in colorectal cancer (DCC), possibly together with Unc5, repels migrating GABAergic neurons from the ventricular zone of the ganglionic eminence, whereas binding to α3β1 integrin promotes cortical interneuron migration. Human genetic disorders associated with these and related guidance molecules, such as congenital mirror movements, schizophrenia, and bipolar disorder, are also discussed.

Screening of integrins localized on the surface of human epidermal melanocytes

In vivo, melanocytes occupy three-dimensional (3D) space. Nevertheless, most experiments involving melanocytes are performed in a two-dimensional microenvironment, resulting in difficulty obtaining accurate results. Therefore, it is necessary to construct an artificial in vivo-like 3D microenvironment. Here, as a step towards engineering a precisely defined acellular 3D microenvironment supporting the maintenance of human epidermal melanocytes (HEMs), we examined the types of integrin heterodimers that are expressed transcriptionally, translationally, and functionally in HEMs. Real-time PCR and fluorescent immunoassay analyses were used to elucidate the expression of integrin α and β subunit genes at the transcriptional and translational levels, respectively. The functionality of the presumed integrin heterodimers was confirmed using attachment and antibody-inhibition assays. Among the genes encoding 12 integrin subunits (α₁, α₂, α₃, α₄, α₅, α₆, α₇, α_V, β₁, β₃, β₅, and β₈) showing significantly higher transcription levels, proteins translated from the integrin α₂, α₄, α₅, β₁, β₃, and β₅ subunit genes were detected on the surface of HEMs. These HEMs showed significantly increased adhesion to collagen I, fibronectin, laminin, and vitronectin, and functional blockade of the integrin α₂ subunits significantly inhibited adhesion to collagen I, fibronectin, and laminin. In addition, there was no significant inhibition of the adhesion to fibronectin or vitronectin in HEMs with functional blockade of the integrin α₄, α₅, or α_V subunits. These results indicate that the active integrin α₂β₁ heterodimer and the inactive integrin α₄, α₅, α_V, β₃, and β₅ subunits are all localized on the surface of HEMs.

A Systematic Review of Emerging Therapeutic Strategies in the Management of Chemical Injuries of the Ocular Surface

OBJECTIVES

To evaluate recent in vivo studies on emerging therapies for managing corneal epithelial injuries.

METHODS

The search was conducted on PubMed for articles published between January 2015 and September 2019 and in English language.

RESULTS

Thirty studies were identified for evaluation, including those on mesenchymal stem cells, amniotic membrane-derived therapies, endogenous peptides and their inhibitors, as well as hydrogel therapies. Intermediate to strong levels of evidence are presented regarding the use of these strategies on chemically injured cornea, including their effects on healing of corneal epithelial defect, anti-inflammatory properties, prevention of corneal neovascularization, as well as restoration of anatomy and functions of the anterior eye, although clinical trials are needed to determine the safety and efficacy of these strategies on humans.

CONCLUSION

Recent advances and understanding in various novel therapeutic methods for corneal epithelial chemical injuries should provide potential alternatives to current standard treatment regimens and help reduce risks of complications, hence improve patient outcomes.

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.

Understanding netrins and semaphorins in mature endothelial cell biology

Netrins and semaphorins are known as neuronal guidance molecules that are important to the facilitate patterning of the nervous system in embryonic development. In recent years, their function has been broadened to guide development in other systems, including the vascular system, where netrins and semaphorins critically contribute to the development of the vascular system. Evidence is accumulating that these guidance cues are also of critical importance in the biology of the mature endothelium by regulating the maintenance of endothelial quiescence. Here we review our current insights into the roles of netrins and semaphorins in endothelial cell survival, self-renewing, barrier function, response to wall shear stress, and control of the vascular tone. We also provide suggestions for future research into the functions of netrins and semaphorins in mature endothelial cell biology.

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.

Identifying and targeting determinants of melanoma cellular invasion

Epithelial-to-mesenchymal transition is a critical process that increases the malignant potential of melanoma by facilitating invasion and dissemination of tumor cells. This study identified genes involved in the regulation of cellular invasion and evaluated whether they can be targeted to inhibit melanoma invasion. We identified Peroxidasin (PXDN), Netrin 4 (NTN4) and GLIS Family Zinc Finger 3 (GLIS3) genes consistently elevated in invasive mesenchymal-like melanoma cells. These genes and proteins were highly expressed in metastatic melanoma tumors, and gene silencing led to reduced melanoma invasion in vitro. Furthermore, migration of PXDN, NTN4 or GLIS3 siRNA transfected melanoma cells was inhibited following transplantation into the embryonic chicken neural tube compared to control siRNA transfected melanoma cells. Our study suggests that PXDN, NTN4 and GLIS3 play a functional role in promoting melanoma cellular invasion, and therapeutic approaches directed toward inhibiting the action of these proteins may reduce the incidence or progression of metastasis in melanoma patients.

Netrin as a Novel Biomarker and Its Therapeutic Implications in Diabetes Mellitus and Diabetes-Associated Complications

Diabetes is a multifactorial metabolic syndrome and is one of the shared long-lasting illnesses globally. It is linked to long-term microvascular and macrovascular complications that contribute to disability, compromised quality of life, and reduction in lifespan, which eventually leads to death. This disease is not only incurring significant economic burden but also adversely affects the patients, caregivers, communities, and the society at large. The interruption of diabetes progress and its complications is a primary focus of scientific communities. In spite of various diagnostic modalities for diabetes, there is a limited marker to investigate the risk and progress of its complications. Netrin has recently received more attention as a biomarker of diabetes and a broader range of long-term complication. Therefore, the impetus of this review is to exhaustively discuss the role of Netrin as a potential biomarker and its therapeutic implication in diabetes and diverse sets of microvascular and macrovascular complications of diabetes. It also discourses the possible mechanisms of Netrin for the said pharmacological effect for a better understanding of the development and progression of diabetes and its complications in relation to this protein. It enables protective measures to be applied at the subclinical stage and the responses to preventive or therapeutic measures to be scrutinized. Besides, it might also facilitate the appraisal of novel therapeutic options for diabetes and various complications through modifying the endogenous Netrin and provide surrogate endpoints for intervention.

Role and impact of the extracellular matrix on integrin-mediated pancreatic β-cell functions

Understanding the organisation and role of the extracellular matrix (ECM) in islets of Langerhans is critical for maintaining pancreatic β-cells, and to recognise and revert the physiopathology of diabetes. Indeed, integrin-mediated adhesion signalling in response to the pancreatic ECM plays crucial roles in β-cell survival and insulin secretion, two major functions, which are affected in diabetes. Here, we would like to present an update on the major components of the pancreatic ECM, their role during integrin-mediated cell-matrix adhesions and how they are affected during diabetes. To treat diabetes, a promising approach consists in replacing β-cells by transplantation. However, efficiency is low, because β-cells suffer of anoikis, due to enzymatic digestion of the pancreatic ECM, which affects the survival of insulin-secreting β-cells. The strategy of adding ECM components during transplantation, to reproduce the pancreatic microenvironment, is a challenging task, as many of the regulatory mechanisms that control ECM deposition and turnover are not sufficiently understood. A better comprehension of the impact of the ECM on the adhesion and integrin-dependent signalling in β-cells is primordial to improve the healthy state of islets to prevent the onset of diabetes as well as for enhancing the efficiency of the islet transplantation therapy.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

The biomechanical properties of an epithelial tissue determine the location of its vasculature

An important question is how growing tissues establish a blood vessel network. Here we study vascular network formation in pancreatic islets, endocrine tissues derived from pancreatic epithelium. We find that depletion of integrin-linked kinase (ILK) in the pancreatic epithelial cells of mice results in glucose intolerance due to a loss of the intra-islet vasculature. In turn, blood vessels accumulate at the islet periphery. Neither alterations in endothelial cell proliferation, apoptosis, morphology, Vegfa expression and VEGF-A secretion nor ‘empty sleeves' of vascular basement membrane are found. Instead, biophysical experiments reveal that the biomechanical properties of pancreatic islet cells, such as their actomyosin-mediated cortex tension and adhesive forces to endothelial cells, are significantly changed. These results suggest that a sorting event is driving the segregation of endothelial and epithelial cells and indicate that the epithelial biomechanical properties determine whether the blood vasculature invades or envelops a growing epithelial tissue.

Vasculature is denser in soft than in stiff tissues. Kragl et al. suggest a mechanistic link between biomechanical tissue properties and vascularization by showing that integrin-linked kinase reduces the contractile forces of the cell cortex in endocrine pancreatic cells, facilitating their adhesion to blood vessels and enabling pancreatic islet vascularization.

Netrin-4 as a biomarker promotes cell proliferation and invasion in gastric cancer

Gastric cancer (GC) is the second most common cause of cancer-related death with limited serum biomarkers for diagnosis and prognosis. Netrin-4 (Ntn4) is a laminin-related secreted molecule found to regulate tumor progression and metastasis. However, it is completely unknown whether Ntn4 has roles in GC development. Here, we first reported Ntn4 knockdown significantly suppressed cell proliferation and motility, while overexpression or addition of exogenous Ntn4 reversed these effects. In addition, Ntn4 receptor, neogenin (Neo) was also found highly expressed in GC cells and mediated the Ntn4-induced cell proliferation and invasion. Moreover, Ntn4 or Neo silencing decreased the phosphorylation of Stat3, ERK, Akt and p38, indicating multi-oncogenic pathways (Jak/Stat, PI3K/Akt, and ERK/MAPK) were involved in Ntn4-induced effects on the GC cells. Importantly, Ntn4 level was significantly increased in 82 tumor tissues (p = 0.001) and 52 serum samples (p < 0.0001) from GC patients and positively correlated with Neo expression (p = 0.003). Ntn4 expression was negatively correlated with the survival period (p = 0.038), and positively associated with the severity of pathological stages of the tumors (p = 0.008). Taken together, Ntn4 promoted the proliferation and motility of GC cells which was mediated by its receptor Neo and through further activation of multi-oncogenic pathways. Elevated Ntn4 was detected in both tumor tissues and serum samples of GC patients and suggested a relatively poor survival, indicating Ntn4 may be used as a potential non-invasive biomarker for diagnosis and prognosis of GC.

Human pancreas development

A wealth of data and comprehensive reviews exist on pancreas development in mammals, primarily mice, and other vertebrates. By contrast, human pancreatic development has been less comprehensively reviewed. Here, we draw together those studies conducted directly in human embryonic and fetal tissue to provide an overview of what is known about human pancreatic development. We discuss the relevance of this work to manufacturing insulin-secreting β-cells from pluripotent stem cells and to different aspects of diabetes, especially permanent neonatal diabetes, and its underlying causes.

Netrin-5 is highly expressed in neurogenic regions of the adult brain

Mammalian netrin family proteins are involved in targeting of axons, neuronal migration, and angiogenesis and act as repulsive and attractive guidance molecules. Netrin-5 is a new member of the netrin family with homology to the C345C domain of netrin-1. Unlike other netrin proteins, murine netrin-5 consists of two EGF motifs of the laminin V domain (LE) and the C345C domain, but lacks the N-terminal laminin VI domain and one of the three LE motifs. We generated a specific antibody against netrin-5 to investigate its expression pattern in the rodent adult brain. Strong netrin-5 expression was observed in the olfactory bulb (OB), rostral migrate stream (RMS), the subventricular zone (SVZ), and the subgranular zone (SGZ) of the dentate gyrus in the hippocampus, where neurogenesis occurs in the adult brain. In the SVZ and RMS, netrin-5 expression was observed in Mash1-positive transit-amplifying cells and in Doublecortin (DCX)-positive neuroblasts, but not in GFAP-positive astrocytes. In the OB, netrin-5 expression was maintained in neuroblasts, but its level was decreased in NeuN-positive mature neurons. In the hippocampal SGZ, netrin-5 was observed in Mash1-positive cells and in DCX-positive neuroblasts, but not in GFAP-positive astrocytes, suggesting that netrin-5 expression occurs from type 2a to type 3 cells. These data suggest that netrin-5 is produced by both transit-amplifying cells and neuroblasts to control neurogenesis in the adult brain.

Genetic Background is a Key Determinant of Glomerular Extracellular Matrix Composition and Organization

Glomerular disease often features altered histologic patterns of extracellular matrix (ECM). Despite this, the potential complexities of the glomerular ECM in both health and disease are poorly understood. To explore whether genetic background and sex determine glomerular ECM composition, we investigated two mouse strains, FVB and B6, using RNA microarrays of isolated glomeruli combined with proteomic glomerular ECM analyses. These studies, undertaken in healthy young adult animals, revealed unique strain- and sex-dependent glomerular ECM signatures, which correlated with variations in levels of albuminuria and known predisposition to progressive nephropathy. Among the variation, we observed changes in netrin 4, fibroblast growth factor 2, tenascin C, collagen 1, meprin 1-α, and meprin 1-β. Differences in protein abundance were validated by quantitative immunohistochemistry and Western blot analysis, and the collective differences were not explained by mutations in known ECM or glomerular disease genes. Within the distinct signatures, we discovered a core set of structural ECM proteins that form multiple protein-protein interactions and are conserved from mouse to man. Furthermore, we found striking ultrastructural changes in glomerular basement membranes in FVB mice. Pathway analysis of merged transcriptomic and proteomic datasets identified potential ECM regulatory pathways involving inhibition of matrix metalloproteases, liver X receptor/retinoid X receptor, nuclear factor erythroid 2-related factor 2, notch, and cyclin-dependent kinase 5. These pathways may therefore alter ECM and confer susceptibility to disease.

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.

Netrin-4 derived from murine vascular endothelial cells inhibits osteoclast differentiation in vitro and prevents bone loss in vivo

Bone is a highly vascularized organ, thus angiogenesis is a vital process during bone remodeling. However, the role of vascular systems in bone remodeling is not well recognized. Here we show that netrin-4 inhibits osteoclast differentiation in vitro and in vivo. Co-cultures of bone marrow macrophages with vascular endothelial cells markedly inhibited osteoclast differentiation. Adding a neutralizing antibody, or RNA interference against netrin-4, restored in vitro osteoclast differentiation. Administration of netrin-4 prevented bone loss in an osteoporosis mouse model by decreasing the osteoclast number. We propose that vascular endothelial cells interact with bone in suppressing bone through netrin-4.

Gene markers of cellular aging in human multipotent stromal cells in culture

Introduction

Human multipotent stromal cells (MSCs) isolated from bone marrow or other tissue sources have great potential to treat a wide range of injuries and disorders in the field of regenerative medicine and tissue engineering. In particular, MSCs have inherent characteristics to suppress the immune system and are being studied in clinical studies to prevent graft-versus-host disease. MSCs can be expanded in vitro and have potential for differentiation into multiple cell lineages. However, the impact of cell passaging on gene expression and function of the cells has not been determined.

Methods

Commercially available human MSCs derived from bone marrow from six different donors, grown under identical culture conditions and harvested at cell passages 3, 5, and 7, were analyzed with gene-expression profiling by using microarray technology.

Results

The phenotype of these cells did not change as reported previously; however, a statistical analysis revealed a set of 78 significant genes that were distinguishable in expression between passages 3 and 7. None of these significant genes corresponded to the markers established by the International Society for Cellular Therapy (ISCT) for MSC identification. When the significant gene lists were analyzed through pathway analysis, these genes were involved in the top-scoring networks of cellular growth and proliferation and cellular development. A meta-analysis of the literature for significant genes revealed that the MSCs seem to be undergoing differentiation into a senescent cell type when cultured extensively. Consistent with the differences in gene expression at passage 3 and 7, MSCs exhibited a significantly greater potential for cell division at passage 3 in comparison to passage 7.

Conclusions

Our results identified specific gene markers that distinguish aging MSCs grown in cell culture. Confirmatory studies are needed to correlate these molecular markers with biologic attributes that may facilitate the development of assays to test the quality of MSCs before clinical use.

Genome-wide identification of AR-regulated genes translated in Sertoli cells in vivo using the RiboTag approach

An understanding of the molecular mechanisms by which androgens drive spermatogenesis has been thwarted by the fact that few consistent androgen receptor (AR) target genes have been identified. Here, we addressed this issue using next-generation sequencing coupled with the RiboTag approach, which purifies translated mRNAs expressed in cells that express cyclic recombinase (CRE). Using RiboTag mice expressing CRE in Sertoli cells (SCs), we identified genes expressed specifically in SCs in both prepubertal and adult mice. Unexpectedly, this analysis revealed that the SC-specific gene program is already largely defined at the initiation of spermatogenesis despite the subsequent dramatic maturational changes known to occur in SCs. To identify AR-regulated genes, we generated triple-mutant mice in which the SCs express the RiboTag but lack ARs. RNA sequencing analysis revealed hundreds of SC-expressed AR-regulated genes that had previously gone unnoticed, including suppressed genes involved in ovarian development. Comparison of the SC-enriched dataset with that from the whole testes allowed us to classify genes in terms of their degree of expression in SCs. This revealed that a greater fraction of AR-up-regulated genes than AR-down-regulated genes were expressed predominantly in SCs. Our results also revealed that AR signaling in SCs causes a large number of genes not detectably expressed in SCs to undergo altered expression, thereby providing genome-wide evidence for wide-scale communication between SCs and other cells. Taken together, our results identified novel classes of genes expressed in a hormone-dependent manner in different testicular cell subsets and highlight a new approach to analyze cell type-specific gene regulation.

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

Netrins are secreted molecules involved in axon guidance and angiogenesis. We previously showed that Netrin-4 acts as an anti-angiogenic factor by inhibiting endothelial cell (EC) functions. In this study, we investigated the effects of Netrin-4 on vascular smooth muscle cell (VSMC) activity in vitro and in vivo. We show that exogenous Netrin-4 stimulated VSMC adhesion and migration, and increased their coverage on EC tubes (grown on a Matrigel substrate). siRNA knock-down of endogenous Netrin-4 expression in VSMC decreased their recruitment to EC tubes. VSMC expressed Netrin-4 and three of the six Netrin-1 cognate receptors: DCC, Neogenin, and Unc5B. Silencing of these receptors reduced Netrin-4 adhesion to VSMC, strongly suggesting that these receptors were involved in the recruitment process. We previously showed that Netrin-4 overexpression in PC3 cancer cells delayed tumor growth in a model of subcutaneous xenograft by reducing tumor vessel density. Here, we show that Netrin-4 overexpression improved tumor blood vessel structure and increased VSMC coverage. Thus, Netrin-4 induced mural cell recruitment may play a role in the inhibition of tumor growth. Our data suggest that Netrin-4 is important for blood vessel normalization through the regulation of both endothelial and perivascular cells.

α2β1 Integrin

The α2β1 integrin, also known as VLA-2, GPIa-IIa, CD49b, was first identified as an extracellular matrix receptor for collagens and/or laminins [55, 56]. It is now recognized that the α2β1 integrin serves as a receptor for many matrix and nonmatrix molecules [35, 79, 128]. Extensive analyses have clearly elucidated the α2 I domain structural motifs required for ligand binding, and also defined distinct conformations that lead to inactive, partially active or highly active ligand binding [3, 37, 66, 123, 136, 137, 140]. The mechanisms by which the α2β1 integrin plays a critical role in platelet function and homeostasis have been carefully defined via in vitro and in vivo experiments [76, 104, 117, 125]. Genetic and epidemiologic studies have confirmed human physiology and disease states mediated by this receptor in immunity, cancer, and development [6, 20, 21, 32, 43, 90]. The role of the α2β1 integrin in these multiple complex biologic processes will be discussed in the chapter.

SEL1L regulates adhesion, proliferation and secretion of insulin by affecting integrin signaling

SEL1L, a component of the endoplasmic reticulum associated degradation (ERAD) pathway, has been reported to regulate the (i) differentiation of the pancreatic endocrine and exocrine tissue during the second transition of mouse embryonic development, (ii) neural stem cell self-renewal and lineage commitment and (iii) cell cycle progression through regulation of genes related to cell-matrix interaction. Here we show that in the pancreas the expression of SEL1L is developmentally regulated, such that it is readily detected in developing islet cells and in nascent acinar clusters adjacent to basement membranes, and becomes progressively restricted to the islets of Langherans in post-natal life. This peculiar expression pattern and the presence of two inverse RGD motifs in the fibronectin type II domain of SEL1L protein indicate a possible interaction with cell adhesion molecules to regulate islets architecture. Co-immunoprecipitation studies revealed SEL1L and ß1-integrin interaction and, down-modulation of SEL1L in pancreatic ß-cells, negatively influences both cell adhesion on selected matrix components and cell proliferation likely due to altered ERK signaling. Furthermore, the absence of SEL1L protein strongly inhibits glucose-stimulated insulin secretion in isolated mouse pancreatic islets unveiling an important role of SEL1L in insulin trafficking. This phenotype can be rescued by the ectopic expression of the ß1-integrin subunit confirming the close interaction of these two proteins in regulating the cross-talk between extracellular matrix and insulin signalling to create a favourable micro-environment for ß-cell development and function.

β1 integrin is a crucial regulator of pancreatic β-cell expansion

Development of the endocrine compartment of the pancreas, as represented by the islets of Langerhans, occurs through a series of highly regulated events encompassing branching of the pancreatic epithelium, delamination and differentiation of islet progenitors from ductal domains, followed by expansion and three-dimensional organization into islet clusters. Cellular interactions with the extracellular matrix (ECM) mediated by receptors of the integrin family are postulated to regulate key functions in these processes. Yet, specific events regulated by these receptors in the developing pancreas remain unknown. Here, we show that ablation of the β1 integrin gene in developing pancreatic β-cells reduces their ability to expand during embryonic life, during the first week of postnatal life, and thereafter. Mice lacking β1 integrin in insulin-producing cells exhibit a dramatic reduction of the number of β-cells to only ∼18% of wild-type levels. Despite the significant reduction in β-cell mass, these mutant mice are not diabetic. A thorough phenotypic analysis of β-cells lacking β1 integrin revealed a normal expression repertoire of β-cell markers, normal architectural organization within islet clusters, and a normal ultrastructure. Global gene expression analysis revealed that ablation of this ECM receptor in β-cells inhibits the expression of genes regulating cell cycle progression. Collectively, our results demonstrate that β1 integrin receptors function as crucial positive regulators of β-cell expansion.

Dynamic chromatin remodeling mediated by polycomb proteins orchestrates pancreatic differentiation of human embryonic stem cells

Embryonic development is characterized by dynamic changes in gene expression, yet the role of chromatin remodeling in these cellular transitions remains elusive. To address this question, we profiled the transcriptome and select chromatin modifications at defined stages during pancreatic endocrine differentiation of human embryonic stem cells. We identify removal of Polycomb group (PcG)-mediated repression on stage-specific genes as a key mechanism for the induction of developmental regulators. Furthermore, we discover that silencing of transitory genes during lineage progression associates with reinstatement of PcG-dependent repression. Significantly, in vivo- but not in vitro-differentiated endocrine cells exhibit close similarity to primary human islets in regard to transcriptome and chromatin structure. We further demonstrate that endocrine cells produced in vitro do not fully eliminate PcG-mediated repression on endocrine-specific genes, probably contributing to their malfunction. These studies reveal dynamic chromatin remodeling during developmental lineage progression and identify possible strategies for improving cell differentiation in culture.

Understanding vascular development

The vasculature of an organism has the daunting task of connecting all the organ systems to nourish tissue and sustain life. This complex network of vessels and associated cells must maintain blood flow, but constantly adapt to acute and chronic changes within tissues. While the vasculature has been studied for over a century, we are just beginning to understand the processes that regulate its formation and how genetic hierarchies are influenced by mechanical and metabolic cues to refine vessel structure and optimize efficiency. As we gain insights into the developmental mechanisms, it is clear that the processes that regulate blood vessel development can also enable the adult to adapt to changes in tissues that can be elicited by exercise, aging, injury, or pathology. Thus, research in vessel development has provided tremendous insights into therapies for vascular diseases and disorders, cancer interventions, wound repair and tissue engineering, and in turn, these models have clearly impacted our understanding of development. Here we provide an overview of the development of the vascular system, highlighting several areas of active investigation and key questions that remain to be answered.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Netrin-4 promotes glioblastoma cell proliferation through integrin β4 signaling

Netrin-4 is a laminin-related secreted molecule originally found to have roles in neuronal axon migration. Recent studies have indicated that netrin-4 also participates in the development of nonneural tissues and modulates tumor cell proliferation and tumor metastasis. Here we have explored the functions and molecular mechanisms of netrin-4 in glioblastoma multiforme. The suppression of netrin-4 expression in glioblastoma cell lines significantly reduced cell proliferation and motility and increased serum deprivation-induced apoptosis. Using tandem affinity purification combined with protein identification by mass spectrometry, we found that integrin β(4) interacts with netrin-4 and that it mediates mitogenic effects as well as AKT and mammalian target of rapamycin phosphorylation induced by netrin-4. Interestingly, netrin-4 acted as an inhibitor of cell proliferation in integrin β(4)-silenced glioblastoma cells, and high concentrations of netrin-4 reduced cell proliferation. The negative effects of netrin-4 on proliferation were mediated by UNC5B. Analysis of more than 400 primary tumors from The Cancer Genome Atlas repository revealed that the expression of netrin-4 is significantly downregulated in glioblastoma and that the reduced expression is linked to poor patient survival time. The expression of integrin β(4) is increased in glioblastoma, and it predicts poor patient survival time. Current results illustrate a novel mechanism for glioma progression, where glioma cells reduce netrin-4 expression to decrease its inhibitory effects. In parallel, the expression of integrin β(4) is upregulated to sensitize the cells to low concentrations of netrin-4 for maintaining cell proliferation.

Repeated evolution of identical domain architecture in metazoan netrin domain-containing proteins

The majority of proteins in eukaryotes are composed of multiple domains, and the number and order of these domains is an important determinant of protein function. Although multidomain proteins with a particular domain architecture were initially considered to have a common evolutionary origin, recent comparative studies of protein families or whole genomes have reported that a minority of multidomain proteins could have appeared multiple times independently. Here, we test this scenario in detail for the signaling molecules netrin and secreted frizzled-related proteins (sFRPs), two groups of netrin domain-containing proteins with essential roles in animal development. Our primary phylogenetic analyses suggest that the particular domain architectures of each of these proteins were present in the eumetazoan ancestor and evolved a second time independently within the metazoan lineage from laminin and frizzled proteins, respectively. Using an array of phylogenetic methods, statistical tests, and character sorting analyses, we show that the polyphyly of netrin and sFRP is well supported and cannot be explained by classical phylogenetic reconstruction artifacts. Despite their independent origins, the two groups of netrins and of sFRPs have the same protein interaction partners (Deleted in Colorectal Cancer/neogenin and Unc5 for netrins and Wnts for sFRPs) and similar developmental functions. Thus, these cases of convergent evolution emphasize the importance of domain architecture for protein function by uncoupling shared domain architecture from shared evolutionary history. Therefore, we propose the terms merology to describe the repeated evolution of proteins with similar domain architecture and discuss the potential of merologous proteins to help understanding protein evolution.

Tissue engineering 2.0: guiding self-organization during pluripotent stem cell differentiation

Human pluripotent stem cell (hPSC) differentiation aims to mimic development using growth factors or small molecules in a time-dependent and dose-dependent manner. However, the cell types produced using this approach are predominantly fetal-like in phenotype and function, limiting their use in regenerative medicine. This is particularly true in current efforts to produce pancreatic beta cells, wherein robust pancreatic progenitor maturation can only be accomplished upon transplantation into mice. Recent studies have suggested that hPSC-derived cells are capable of self-organizing in vitro, revealing a new paradigm for creating mature cells and tissues. Tissue engineering strategies that provide subtle and dynamic signals to developmentally naïve cells may be applied to mimic in vitro the self-organization aspects of pancreatic development.

Netrin-4 acts as a pro-angiogenic factor during zebrafish development

Netrins form a heterogeneous family of laminin-related molecules with multifunctional activities. Netrin-4, the most distant member of this family, is related to the laminin β chain and has recently been proposed to play an important role in embryonic and pathological angiogenesis. However, the data reported so far lead to the apparently contradictory conclusions supporting Netrin-4 as either a pro- or an anti-angiogenic factor. To elucidate this controversy, Netrin-4 was analyzed for a vascular activity in both cell-based models (human umbilical vein endothelial cells and human umbilical artery endothelial cells) and two zebrafish models: the wild-type AB/Tü strain and the transgenic Tg(fli1a:EGFP)(y1) strain. We show that Netrin-4 is expressed in endothelial cells and in the zebrafish vascular system. We also show evidence that Netrin-4 activates various kinases and induces various biological effects directly linked to angiogenesis in vitro. Using a morpholinos strategy, we demonstrate that Netrin-4 expression is crucial for zebrafish vessel formation and that a blood vessel formation defect induced by netrin-4 morpholinos can be partially rescued through drug delivery leading to protein kinase activation. Together these data underscore the crucial role of Netrin-4 in blood vessel formation and the involvement of protein kinases activation in Netrin-4-induced biological effects related to vascular development.