Neuropilin 1 balances β8 integrin-activated TGFβ signaling to control sprouting angiogenesis in the brain

Interactions between neural cells and blood vessels in central nervous system development

The sophisticated function of the central nervous system (CNS) is largely supported by proper interactions between neural cells and blood vessels. Accumulating evidence has demonstrated that neurons and glial cells support the formation of blood vessels, which in turn, act as migratory scaffolds for these cell types. Neural progenitors are also involved in the regulation of blood vessel formation. This mutual interaction between neural cells and blood vessels is elegantly controlled by several chemokines, growth factors, extracellular matrix, and adhesion molecules such as integrins. Recent research has revealed that newly migrating cell types along blood vessels repel other preexisting migrating cell types, causing them to detach from the blood vessels. In this review, we discuss vascular formation and cell migration, particularly during development. Moreover, we discuss how the crosstalk between blood vessels and neurons and glial cells could be related to neurodevelopmental disorders.

Endothelial Neuropilin-1: a multifaced signal transducer with an emerging role in inflammation and atherosclerosis beyond angiogenesis

Neuropilin-1 (NRP1) is a transmembrane glycoprotein expressed by several cell types including, neurons, endothelial cells (ECs), smooth muscle cells, cardiomyocytes and immune cells comprising macrophages, dendritic cells and T cell subsets. Since NRP1 discovery in 1987 as an adhesion molecule in the frog nervous system, more than 2300 publications on PubMed investigated the function of NRP1 in physiological and pathological contexts. NRP1 has been characterised as a coreceptor for class 3 semaphorins and several members of the vascular endothelial growth factor (VEGF) family. Because the VEGF family is the main regulator of blood and lymphatic vessel growth in addition to promoting neurogenesis, neuronal patterning, neuroprotection and glial growth, the role of NRP1 in these biological processes has been extensively investigated. It is now established that NRP1 promotes the physiological growth of new vessels from pre-existing ones in the process of angiogenesis. Furthermore, several studies have shown that NRP1 mediates signalling pathways regulating pathological vascular growth in ocular neovascular diseases and tumour development. Less defined are the roles of NRP1 in maintaining the function of the quiescent established vasculature in an adult organism. This review will focus on the opposite roles of NRP1 in regulating transforming growth factor β signalling pathways in different cell types, and on the emerging role of endothelial NRP1 as an atheroprotective, anti-inflammatory factor involved in the response of ECs to shear stress.

Exosomal circCOL1A1 promotes angiogenesis via recruiting EIF4A3 protein and activating Smad2/3 pathway in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the third frequently diagnosed cancer with high incidence and mortality rate worldwide. Our previous report has demonstrated that circCOL1A1 (hsa_circ_0044556) functions as an oncogene in CRC, and Gene Ontology (GO) analysis has also revealed the strong association between circCOL1A1 and angiogenesis. However, the mechanism of circCOL1A1 or exosomal circCOL1A1 in CRC angiogenesis remains elusive.

METHODS

Purified exosomes from CRC cells were characterized by nanoparticle tracking analyzing, electron microscopy and western blot. qRT-PCR, immunohistochemistry or western blot were employed to test the expression of circCOL1A1, EIF4A3, Smad pathway and angiogenic markers. Cell proliferation of HUVECs was monitored by CCK-8 assay. The migratory and angiogenic capabilities of HUVECs were detected by wound healing and tube formation assay, respectively. Bioinformatics analysis, RNA immunoprecipitation (RIP), RNA pull-down and FISH assays were used to detect the interactions among circCOL1A1, EIF4A3 and Smad2/3 mRNA. The in vitro findings were verified in xenograft model.

RESULTS

CRC cell-derived exosomal circCOL1A1 promoted angiogenesis of HUVECs via recruiting EIF4A3. EIF4A3 was elevated in CRC tissues, and it stimulated angiogenesis of HUVECs through directly binding and stabilizing Smad2/3 mRNA. Moreover, exosomal circCOL1A1 promoted angiogenesis via inducing Smad2/3 signaling pathway in vitro, and it also accelerated tumor growth and angiogenesis in vivo.

CONCLUSION

CRC cell-derived exosomal circCOL1A1 promoted angiogenesis via recruiting EIF4A3 and activating Smad2/3 signaling.

Endothelial-derived angiocrine factors as instructors of embryonic development

Blood vessels are well-known to play roles in organ development and repair, primarily owing to their fundamental function in delivering oxygen and nutrients to tissues to promote their growth and homeostasis. Endothelial cells however are not merely passive conduits for carrying blood. There is now evidence that endothelial cells of the vasculature actively regulate tissue-specific development, morphogenesis and organ function, as well as playing roles in disease and cancer. Angiocrine factors are growth factors, cytokines, signaling molecules or other regulators produced directly from endothelial cells to instruct a diverse range of signaling outcomes in the cellular microenvironment, and are critical mediators of the vascular control of organ function. The roles of angiocrine signaling are only beginning to be uncovered in diverse fields such as homeostasis, regeneration, organogenesis, stem-cell maintenance, cell differentiation and tumour growth. While in some cases the specific angiocrine factor involved in these processes has been identified, in many cases the molecular identity of the angiocrine factor(s) remain to be discovered, even though the importance of angiocrine signaling has been implicated. In this review, we will specifically focus on roles for endothelial-derived angiocrine signaling in instructing tissue morphogenesis and organogenesis during embryonic and perinatal 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.

The alpha7 integrin subunit in astrocytes promotes endothelial blood-brain barrier integrity

The blood-brain barrier (BBB) is a vascular endothelial cell boundary that partitions the circulation from the central nervous system to promote normal brain health. We have a limited understanding of how the BBB is formed during development and maintained in adulthood. We used quantitative transcriptional profiling to investigate whether specific adhesion molecules are involved in BBB functions, with an emphasis on understanding how astrocytes interact with endothelial cells. Our results reveal a striking enrichment of multiple genes encoding laminin subunits as well as the laminin receptor gene Itga7, which encodes the alpha7 integrin subunit, in astrocytes. Genetic ablation of Itga7 in mice led to aberrant BBB permeability and progressive neurological pathologies. Itga7-/- mice also showed a reduction in laminin protein expression in parenchymal basement membranes. Blood vessels in the Itga7-/- brain showed separation from surrounding astrocytes and had reduced expression of the tight junction proteins claudin 5 and ZO-1. We propose that the alpha7 integrin subunit in astrocytes via adhesion to laminins promotes endothelial cell junction integrity, all of which is required to properly form and maintain a functional BBB.

The β8 integrin cytoplasmic domain activates extracellular matrix adhesion to promote brain neurovascular development

In the developing mammalian brain, neuroepithelial cells interact with blood vessels to regulate angiogenesis, blood-brain barrier maturation and other key neurovascular functions. Genetic studies in mice have shown that neurovascular development is controlled, in part, by Itgb8, which encodes the neuroepithelial cell-expressed integrin β8 subunit. However, these studies have involved complete loss-of-function Itgb8 mutations, and have not discerned the relative roles for the β8 integrin extracellular matrix (ECM) binding region versus the intracellular signaling tail. Here, Cre/lox strategies have been employed to selectively delete the cytoplasmic tail of murine Itgb8 without perturbing its transmembrane and extracellular domains. We report that the β8 integrin cytoplasmic domain is essential for inside-out modulation of adhesion, including activation of latent-TGFβs in the ECM. Quantitative sequencing of the brain endothelial cell transcriptome identifies TGFβ-regulated genes with putative links to blood vessel morphogenesis, including several genes linked to Wnt/β-catenin signaling. These results reveal that the β8 integrin cytoplasmic domain is essential for the regulation of TGFβ-dependent gene expression in endothelial cells and suggest that cross-talk between TGFβs and Wnt pathways is crucial for neurovascular development.

Neuropilin-1: A Key Protein to Consider in the Progression of Pediatric Brain Tumors

Neuropilins are transmembrane glycoproteins that play important roles in cardiovascular and neuronal development, as well as in immunological system regulations. NRP1 functions as a co-receptor, binding numerous ligands, such as SEMA 3 or VEGF and, by doing so, reinforcing their signaling pathways and can also interface with the cytoplasmic protein synectin. NRP1 is expressed in many cancers, such as brain cancers, and is associated with poor prognosis. The challenge today for patients with pediatric brain tumors is to improve their survival rate while minimizing the toxicity of current treatments. The aim of this review is to highlight the involvement of NRP1 in pediatric brain cancers, focusing essentially on the roles of NRP1 in cancer stem cells and in the regulation of the immune system. For this purpose, recent literature and tumor databases were analyzed to show correlations between NRP1 and CD15 (a stem cancer cells marker), and between NRP1 and PDL1, for various pediatric brain tumors, such as high- and low-grade gliomas, medulloblastomas, and ependymomas. Finally, this review suggests a relevant role for NRP1 in pediatric brain tumors progression and identifies it as a potential diagnostic or therapeutic target to improve survival and life quality of these young patients.

The BMP Pathway in Blood Vessel and Lymphatic Vessel Biology

Bone morphogenetic proteins (BMPs) were originally identified as the active components in bone extracts that can induce ectopic bone formation. In recent decades, their key role has broadly expanded beyond bone physiology and pathology. Nowadays, the BMP pathway is considered an important player in vascular signaling. Indeed, mutations in genes encoding different components of the BMP pathway cause various severe vascular diseases. Their signaling contributes to the morphological, functional and molecular heterogeneity among endothelial cells in different vessel types such as arteries, veins, lymphatic vessels and capillaries within different organs. The BMP pathway is a remarkably fine-tuned pathway. As a result, its signaling output in the vessel wall critically depends on the cellular context, which includes flow hemodynamics, interplay with other vascular signaling cascades and the interaction of endothelial cells with peri-endothelial cells and the surrounding matrix. In this review, the emerging role of BMP signaling in lymphatic vessel biology will be highlighted within the framework of BMP signaling in the circulatory vasculature.

Hippocampal CA3 transcriptional modules associated with granule cell alterations and cognitive impairment in refractory mesial temporal lobe epilepsy patients

In about a third of the patients with epilepsy the seizures are not drug-controlled. The current limitation of the antiepileptic drug therapy derives from an insufficient understanding of epilepsy pathophysiology. In order to overcome this situation, it is necessary to consider epilepsy as a disturbed network of interactions, instead of just looking for changes in single molecular components. Here, we studied CA3 transcriptional signatures and dentate gyrus histopathologic alterations in hippocampal explants surgically obtained from 57 RMTLE patients submitted to corticoamygdalohippocampectomy. By adopting a systems biology approach, integrating clinical, histopathological, and transcriptomic data (weighted gene co-expression network analysis), we were able to identify transcriptional modules highly correlated with age of disease onset, cognitive dysfunctions, and granule cell alterations. The enrichment analysis of transcriptional modules and the functional characterization of the highly connected genes in each trait-correlated module allowed us to unveil the modules’ main biological functions, paving the way for further investigations on their roles in RMTLE pathophysiology. Moreover, we found 15 genes with high gene significance values which have the potential to become novel biomarkers and/or therapeutic targets in RMTLE.

Cerebrovascular development: mechanisms and experimental approaches

The cerebral vasculature plays a central role in human health and disease and possesses several unique anatomic, functional and molecular characteristics. Despite their importance, the mechanisms that determine cerebrovascular development are less well studied than other vascular territories. This is in part due to limitations of existing models and techniques for visualisation and manipulation of the cerebral vasculature. In this review we summarise the experimental approaches used to study the cerebral vessels and the mechanisms that contribute to their development.

Sensing the world and its dangers: An evolutionary perspective in neuroimmunology

Detecting danger is key to the survival and success of all species. Animal nervous and immune systems cooperate to optimize danger detection. Preceding studies have highlighted the benefits of bringing neurons into the defense game, including regulation of immune responses, wound healing, pathogen control, and survival. Here, we summarize the body of knowledge in neuroimmune communication and assert that neuronal participation in the immune response is deeply beneficial in each step of combating infection, from inception to resolution. Despite the documented tight association between the immune and nervous systems in mammals or invertebrate model organisms, interdependence of these two systems is largely unexplored across metazoans. This review brings a phylogenetic perspective of the nervous and immune systems in the context of danger detection and advocates for the use of non-model organisms to diversify the field of neuroimmunology. We identify key taxa that are ripe for investigation due to the emergence of key evolutionary innovations in their immune and nervous systems. This novel perspective will help define the primordial principles that govern neuroimmune communication across taxa.

Understanding the role of integrins in breast cancer invasion, metastasis, angiogenesis, and drug resistance

Integrins are cell adhesion receptors, which are typically transmembrane glycoproteins that connect to the extracellular matrix (ECM). The function of integrins regulated by biochemical events within the cells. Understanding the mechanisms of cell growth by integrins is important in elucidating their effects on tumor progression. One of the major events in integrin signaling is integrin binding to extracellular ligands. Another event is distant signaling that gathers chemical signals from outside of the cell and transmit the signals upon cell adhesion to the inside of the cell. In normal breast tissue, integrins function as checkpoints to monitor effects on cell proliferation, while in cancer tissue these functions altered. The combination of tumor microenvironment and its associated components determines the cell fate. Hypoxia can increase the expression of several integrins. The exosomal integrins promote the growth of metastatic cells. Expression of certain integrins is associated with increased metastasis and decreased prognosis in cancers. In addition, integrin-binding proteins promote invasion and metastasis in breast cancer. Targeting specific integrins and integrin-binding proteins may provide new therapeutic approaches for breast cancer therapies. This review will examine the current knowledge of integrins' role in breast cancer.

Astrocytes in the regulation of cerebrovascular functions

Astrocytes are the most numerous type of neuroglia in the brain and have a predominant influence on the cerebrovascular system; they control perivascular homeostasis, the integrity of the blood-brain barrier, the dialogue with the peripheral immune system, the transfer of metabolites from the blood, and blood vessel contractility in response to neuronal activity. These regulatory processes occur in a specialized interface composed of perivascular astrocyte extensions that almost completely cover the cerebral blood vessels. Scientists have only recently started to study how this interface is formed and how it influences cerebrovascular functions. Here, we review the literature on the astrocytes' role in the regulation of the cerebrovascular system. We cover the anatomy and development of the gliovascular interface, the known gliovascular functions, and molecular factors, the latter's implication in certain pathophysiological situations, and recent cutting-edge experimental tools developed to examine the astrocytes' role at the vascular interface. Finally, we highlight some open questions in this field of research.

Isolation and transcriptional characterization of mouse perivascular astrocytes

In the post-natal mammalian brain perivascular astrocytes (PAs) ensheath blood vessels to regulate their unique permeability properties known as the blood-brain barrier (BBB). Very little is known about PA-expressed genes and signaling pathways that mediate contact and communication with endothelial cells (ECs) to regulate BBB physiology. This is due, in part, to lack of suitable models to distinguish PAs from other astrocyte sub-populations in the brain. To decipher the unique biology of PAs, we used in vivo gene knock-in technology to fluorescently label these cells in the adult mouse brain followed by fractionation and quantitative single cell RNA sequencing. In addition, PAs and non-PAs were also distinguished with transgenic fluorescent reporters followed by gene expression comparisons using bulk RNA sequencing. These efforts have identified several genes and pathways in PAs with potential roles in contact and communication with brain ECs. These genes encode various extracellular matrix (ECM) proteins and adhesion receptors, secreted growth factors, and intracellular signaling enzymes. Collectively, our experimental data reveal a set of genes that are expressed in PAs with putative roles in BBB physiology.

Reciprocal Interaction between Vascular Filopodia and Neural Stem Cells Shapes Neurogenesis in the Ventral Telencephalon

Angiogenesis and neurogenesis are tightly coupled during embryonic brain development. However, little is known about how these two processes interact. We show that nascent blood vessels actively contact dividing neural stem cells by endothelial filopodia in the ventricular zone (VZ) of the murine ventral telencephalon; this association is conserved in the human ventral VZ. Using mouse mutants with altered vascular filopodia density, we show that this interaction leads to prolonged cell cycle of apical neural progenitors (ANPs) and favors early neuronal differentiation. Interestingly, pharmacological experiments reveal that ANPs induce vascular filopodia formation by upregulating vascular endothelial growth factor (VEGF)-A in a cell-cycle-dependent manner. This mutual relationship between vascular filopodia and ANPs works as a self-regulatory system that senses ANP proliferation rates and rapidly adjusts neuronal production levels. Our findings indicate a function of vascular filopodia in fine-tuning neural stem cell behavior, which is the basis for proper brain development.

The vascular endothelial cell-expressed prion protein doppel promotes angiogenesis and blood-brain barrier development

The central nervous system (CNS) contains a complex network of blood vessels that promote normal tissue development and physiology. Abnormal control of blood vessel morphogenesis and maturation is linked to the pathogenesis of various neurodevelopmental diseases. The CNS-specific genes that regulate blood vessel morphogenesis in development and disease remain largely unknown. Here, we have characterized functions for the gene encoding prion protein 2 (Prnd) in CNS blood vessel development and physiology. Prnd encodes the glycosylphosphatidylinositol (GPI)-linked protein doppel, which is expressed on the surface of angiogenic vascular endothelial cells, but is absent in quiescent endothelial cells of the adult CNS. During CNS vascular development, doppel interacts with receptor tyrosine kinases and activates cytoplasmic signaling pathways involved in endothelial cell survival, metabolism and migration. Analysis of mice genetically null for Prnd revealed impaired CNS blood vessel morphogenesis and associated endothelial cell sprouting defects. Prnd^-/- mice also displayed defects in endothelial barrier integrity. Collectively, these data reveal novel mechanisms underlying doppel control of angiogenesis in the developing CNS, and may provide new insights about dysfunctional pathways that cause vascular-related CNS disorders.

The Roles of TGF-β Signaling in Cerebrovascular Diseases

Cerebrovascular diseases are one of the leading causes of death worldwide, however, little progress has been made in preventing or treating these diseases to date. The transforming growth factor-β (TGF-β) signaling pathway plays crucial and highly complicated roles in cerebrovascular development and homeostasis, and dysregulated TGF-β signaling contributes to cerebrovascular diseases. In this review, we provide an updated overview of the functional role of TGF-β signaling in the cerebrovascular system under physiological and pathological conditions. We discuss the current understanding of TGF-β signaling in cerebral angiogenesis and the maintenance of brain vessel homeostasis. We also review the mechanisms by which disruption of TGF-β signaling triggers or promotes the progression of cerebrovascular diseases. Finally, we briefly discuss the potential of targeting TGF-β signaling to treat cerebrovascular diseases.

Signalling, Metabolic Pathways and Iron Homeostasis in Endothelial Cells in Health, Atherosclerosis and Alzheimer's Disease

Endothelial cells drive the formation of new blood vessels in physiological and pathological contexts such as embryonic development, wound healing, cancer and ocular diseases. Once formed, all vessels of the vasculature system present an endothelial monolayer (the endothelium), lining the luminal wall of the vessels, that regulates gas and nutrient exchange between the circulating blood and tissues, contributing to maintaining tissue and vascular homeostasis. To perform their functions, endothelial cells integrate signalling pathways promoted by growth factors, cytokines, extracellular matrix components and signals from mechanosensory complexes sensing the blood flow. New evidence shows that endothelial cells rely on specific metabolic pathways for distinct cellular functions and that the integration of signalling and metabolic pathways regulates endothelial-dependent processes such as angiogenesis and vascular homeostasis. In this review, we provide an overview of endothelial functions and the recent advances in understanding the role of endothelial signalling and metabolism in physiological processes such as angiogenesis and vascular homeostasis and vascular diseases. Also, we focus on the signalling pathways promoted by the transmembrane protein Neuropilin-1 (NRP1) in endothelial cells, its recently discovered role in regulating mitochondrial function and iron homeostasis and the role of mitochondrial dysfunction and iron in atherosclerosis and neurodegenerative diseases.

αvβ8 integrin adhesion and signaling pathways in development, physiology and disease

Cells must interpret a complex milieu of extracellular cues to modulate intracellular signaling events linked to proliferation, differentiation, migration and other cellular processes. Integrins are heterodimeric transmembrane proteins that link the extracellular matrix (ECM) to the cytoskeleton and control intracellular signaling events. A great deal is known about the structural and functional properties for most integrins; however, the adhesion and signaling pathways controlled by αvβ8 integrin, which was discovered nearly 30 years ago, have only recently been characterized. αvβ8 integrin is a receptor for ECM-bound forms of latent transforming growth factor β (TGFβ) proteins and promotes the activation of TGFβ signaling pathways. Studies of the brain, lung and immune system reveal that the αvβ8 integrin-TGFβ axis mediates cell-cell contact and communication within complex multicellular structures. Perturbing components of this axis results in aberrant cell-cell adhesion and signaling leading to the initiation of various pathologies, including neurodegeneration, fibrosis and cancer. As discussed in this Review, understanding the functions for αvβ8 integrin, its ECM ligands and intracellular effector proteins is not only an important topic in cell biology, but may lead to new therapeutic strategies to treat human pathologies related to integrin dysfunction.

Toxoplasma gondii infection impairs radial glia differentiation and its potential to modulate brain microvascular endothelial cell function in the cerebral cortex

Congenital toxoplasmosis is a parasitic disease that occurs due vertical transmission of the protozoan Toxoplasma gondii (T. gondii) during pregnancy. The parasite crosses the placental barrier and reaches the developing brain, infecting progenitor, glial, neuronal and vascular cell types. Although the role of Radial glia (RG) neural stem cells in the development of the brain vasculature has been recently investigated, the impact of T. gondii infection in these events is not yet understood. Herein, we studied the role of T. gondii infection on RG cell function and its interaction with endothelial cells. By infecting isolated RG cultures with T. gondii tachyzoites, we observed a cytotoxic effect with reduced numbers of RG populations together with decrease neuronal and oligodendrocyte progenitor populations. Conditioned medium (CM) from RG control cultures increased ZO-1 protein levels and organization on endothelial bEnd.3 cells membranes, which was impaired by CM from infected RG, accompanied by decreased trans-endothelial electrical resistance (TEER). ELISA assays revealed reduced levels of anti-inflammatory cytokine TGF-β1 in CM from T. gondii-infected RG cells. Treatment with recombinant TGF-β1 concomitantly with CM from infected RG cultures led to restoration of ZO-1 staining in bEnd.3 cells. Congenital infection in Swiss Webster mice led to abnormalities in the cortical microvasculature in comparison to uninfected embryos. Our results suggest that infection of RG cells by T. gondii negatively modulates cytokine secretion, which might contribute to endothelial loss of barrier properties, thus leading to impairment of neurovascular interaction establishment.

Neuronal and glial regulation of CNS angiogenesis and barriergenesis

Neurovascular pathologies of the central nervous system (CNS), which are associated with barrier dysfunction, are leading causes of death and disability. The roles that neuronal and glial progenitors and mature cells play in CNS angiogenesis and neurovascular barrier maturation have been elucidated in recent years. Yet how neuronal activity influences these processes remains largely unexplored. Here, we discuss our current understanding of how neuronal and glial development affects CNS angiogenesis and barriergenesis, and outline future directions to elucidate how neuronal activity might influence these processes. An understanding of these mechanisms is crucial for developing new interventions to treat neurovascular pathologies.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

CDC42 Deletion Elicits Cerebral Vascular Malformations via Increased MEKK3-Dependent KLF4 Expression

RATIONALE

Aberrant formation of blood vessels precedes a broad spectrum of vascular complications; however, the cellular and molecular events governing vascular malformations are not yet fully understood.

OBJECTIVE

Here, we investigated the role of CDC42 (cell division cycle 42) during vascular morphogenesis and its relative importance for the development of cerebrovascular malformations.

METHODS AND RESULTS

To avoid secondary systemic effects often associated with embryonic gene deletion, we generated an endothelial-specific and inducible knockout approach to study postnatal vascularization of the mouse brain. Postnatal endothelial-specific deletion of Cdc42 elicits cerebrovascular malformations reminiscent of cerebral cavernous malformations (CCMs). At the cellular level, loss of CDC42 function in brain endothelial cells (ECs) impairs their sprouting, branching morphogenesis, axial polarity, and normal dispersion within the brain tissue. Disruption of CDC42 does not alter EC proliferation, but malformations occur where EC proliferation is the most pronounced during brain development-the postnatal cerebellum-indicating that a high, naturally occurring EC proliferation provides a permissive state for the appearance of these malformations. Mechanistically, CDC42 depletion in ECs elicited increased MEKK3 (mitogen-activated protein kinase kinase kinase 3)-MEK5 (mitogen-activated protein kinase kinase 5)-ERK5 (extracellular signal-regulated kinase 5) signaling and consequent detrimental overexpression of KLF (Kruppel-like factor) 2 and KLF4, recapitulating the hallmark mechanism for CCM pathogenesis. Through genetic approaches, we demonstrate that the coinactivation of Klf4 reduces the severity of vascular malformations in Cdc42 mutant mice. Moreover, we show that CDC42 interacts with CCMs and that CCM3 promotes CDC42 activity in ECs.

CONCLUSIONS

We show that endothelial-specific deletion of Cdc42 elicits CCM-like cerebrovascular malformations and that CDC42 is engaged in the CCM signaling network to restrain the MEKK3-MEK5-ERK5-KLF2/4 pathway.

Neuropilin 1 modulates TGF‑β1‑induced epithelial‑mesenchymal transition in non‑small cell lung cancer

Previously, the authors reported that neuropilin-1 (NRP1) was significantly increased and acted as a vital promoter in the metastasis of non-small cell lung cancer (NSCLC). However, the regulatory mechanism of NRP1 in NSCLC cell migration and invasion remained unclear. The present study aimed to explore the regulatory mechanism of NRP1 in the transforming growth factor-β (TGF-β) 1-induced migration and invasion of NSCLC cells. The expression level of NRP1 was determined by RT-qPCR analysis in human tissue samples with or without lymph node metastasis. Transwell assay and wound healing assay were conducted to determine the cell migration. Lentivirus-mediated stable knockdown and overexpression of NRP1 cell lines were constructed. Exogenous TGF-β1 stimulation, SIS3 treatment, western blot analysis and in vivo metastatic model were utilized to clarify the underlying regulatory mechanisms. The results demonstrated that the expression of NRP1 was increased in metastatic NSCLC tissues. NRP1 promoted NSCLC metastasis in vitro and in vivo. The Transwell assays, wound healing assays and western blot analysis revealed that the knockdown of NRP1 significantly inhibited TGF-β1-mediated EMT and migratory and invasive capabilities of NSCLC. Furthermore, the overexpression of NRP1 weakened the inhibitory effect of SIS3 on the NSCLC migration and invasion. Co-IP assay revealed that NRP1 interacted with TGFβRII to induce EMT. On the whole, the findings of this study demonstrated that NRP1 was overexpressed in metastatic NSCLC tissues. NRP1 could contributes to TGF-β1-induced EMT and metastasis in NSCLC by binding with TGFβRII.

Harnessing region-specific neurovascular signaling to promote germinal matrix vessel maturation and hemorrhage prevention

Germinal matrix hemorrhage (GMH), affecting about 1 in 300 births, is a major perinatal disease with lifelong neurological consequences. Yet despite advances in neonatal medicine, there is no effective intervention. GMH is characterized by localized bleeding in the germinal matrix (GM), due to inherent vessel fragility unique to this developing brain region. Studies have shown that reduced TGFβ signaling contributes to this vascular immaturity. We have previously shown that a region-specific G-protein-coupled receptor pathway in GM neural progenitor cells regulates integrin β8, a limiting activator of pro-TGFβ. In this study, we use mice to test whether this regional pathway can be harnessed for GMH intervention. We first examined the endogenous dynamics of this pathway and found that it displays specific patterns of activation. We then investigated the functional effects of altering these dynamics by chemogenetics and found that there is a narrow developmental window during which this pathway is amenable to manipulation. Although high-level activity in this time window interferes with vessel growth, moderate enhancement promotes vessel maturation without compromising growth. Furthermore, we found that enhancing the activity of this pathway in a mouse model rescues all GMH phenotypes. Altogether, these results demonstrate that enhancing neurovascular signaling through pharmacological targeting of this pathway may be a viable approach for tissue-specific GMH intervention. They also demonstrate that timing and level are likely two major factors crucial for success. These findings thus provide critical new insights into both brain neurovascular biology and the intervention of GMH.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

Neurovascular Communication during CNS Development

A precise communication between the nervous and the vascular systems is crucial for proper formation and function of the central nervous system (CNS). Interestingly, this communication does not only occur by neural cells regulating the growth and properties of the vasculature, but new studies show that blood vessels actively control different neurodevelopmental processes. Here, we review the current knowledge on how neurons in particular influence growing blood vessels during CNS development and on how vessels participate in shaping the neural compartment. We also review the identified molecular mechanisms of this bidirectional communication.

Metastatic Brain Tumors Disrupt the Blood-Brain Barrier and Alter Lipid Metabolism by Inhibiting Expression of the Endothelial Cell Fatty Acid Transporter Mfsd2a

Disruption of the blood-brain barrier (BBB) by cancer cells is linked to metastatic tumor initiation and progression; however, the pathways that drive these events remain poorly understood. Here, we have developed novel patient-derived xenograft (PDX) models of brain metastases that recapitulate pathological growth features found in original patient samples, thus allowing for analysis of BBB disruption by tumor cells. We report that the BBB is selectively disrupted in brain metastases, in part, via inhibition of the endothelial cell-expressed docosahexaenoic acid (DHA) transporter, major facilitator superfamily domain 2a (Mfsd2a). Loss of Mfsd2a expression in the tumor endothelium results in enhanced BBB leakage, but reduced DHA transport and altered lipid metabolism within metastases. Mfsd2a expression in normal cerebral endothelial cells is cooperatively regulated by TGFβ and bFGF signaling pathways, and these pathways are pathologically diminished in the brain metastasis endothelium. These results not only reveal a fundamental pathway underlying BBB disruption by metastatic cancer cells, but also suggest that restoring DHA metabolism in the brain tumor microenvironment may be a novel therapeutic strategy to block metastatic cell growth and survival.

PTPN12/PTP-PEST Regulates Phosphorylation-Dependent Ubiquitination and Stability of Focal Adhesion Substrates in Invasive Glioblastoma Cells

Glioblastoma (GBM) is an invasive brain cancer with tumor cells that disperse from the primary mass, escaping surgical resection and invariably giving rise to lethal recurrent lesions. Here we report that PTP-PEST, a cytoplasmic protein tyrosine phosphatase, controls GBM cell invasion by physically bridging the focal adhesion protein Crk-associated substrate (Cas) to valosin-containing protein (Vcp), an ATP-dependent protein segregase that selectively extracts ubiquitinated proteins from multiprotein complexes and targets them for degradation via the ubiquitin proteasome system. Both Cas and Vcp are substrates for PTP-PEST, with the phosphorylation status of tyrosine 805 (Y805) in Vcp impacting affinity for Cas in focal adhesions and controlling ubiquitination levels and protein stability. Perturbing PTP-PEST-mediated phosphorylation of Cas and Vcp led to alterations in GBM cell-invasive growth in vitro and in preclinical mouse models. Collectively, these data reveal a novel regulatory mechanism involving PTP-PEST, Vcp, and Cas that dynamically balances phosphorylation-dependent ubiquitination of key focal proteins involved in GBM cell invasion.Significance: PTP-PEST balances GBM cell growth and invasion by interacting with the ATP-dependent ubiquitin segregase Vcp/p97 and regulating phosphorylation and stability of the focal adhesion protein p130Cas.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/14/3809/F1.large.jpg Cancer Res; 78(14); 3809-22. ©2018 AACR.

Cross-talk between blood vessels and neural progenitors in the developing brain

The formation of the central nervous system (CNS) involves multiple cellular and molecular interactions between neural progenitor cells (NPCs) and blood vessels to establish extensive and complex neural networks and attract a vascular supply that support their function. In this review, we discuss studies that have performed genetic manipulations of chick, fish and mouse embryos to define the spatiotemporal roles of molecules that mediate the reciprocal regulation of NPCs and blood vessels. These experiments have highlighted core functions of NPC-expressed ligands in initiating vascular growth into and within the neural tube as well as establishing the blood-brain barrier. More recent findings have also revealed indispensable roles of blood vessels in regulating NPC expansion and eventual differentiation, and specific regional differences in the effect of angiocrine signals. Accordingly, NPCs initially stimulate blood vessel growth and maturation to nourish the brain, but blood vessels subsequently also regulate NPC behaviour to promote the formation of a sufficient number and diversity of neural cells. A greater understanding of the molecular cross-talk between NPCs and blood vessels will improve our knowledge of how the vertebrate nervous system forms and likely help in the design of novel therapies aimed at regenerating neurons and neural vasculature following CNS disease or injury.

Neuropilin-1 and platelet-derived growth factor receptors cooperatively regulate intermediate filaments and mesenchymal cell migration during alveolar septation

Generation of secondary alveolar septa occurs primarily after birth in humans and is complete in mice postnatally, when mechanical stresses vary as air space pressure oscillates. Alveolar mesenchymal cells deposit elastic fibers, which limit cell strain; although when the elastic fiber network is incomplete, this function is also served by the intracellular cytoskeleton. Intermediate filament proteins support deformation during cell division and migration, which occur during septal elongation. Because platelet-derived growth factor receptor-α (PDGFRα) signaling is essential for alveolar septation, we hypothesized that neuropilin-1 (NRP1) may link PDGFRα to cytoskeletal deformation. During cell migration, NRP1 links receptor tyrosine kinase signaling to cytoskeletal and focal adhesion remodeling. Therefore, we examined the consequences of nrp1 gene deletion in alveolar mesenchymal cells (myofibroblasts and pericytes). NRP1 depletion reduced the proportion of mesenchymal cells that contain nestin and desmin within the subpopulation that lacked PDGFRα but contained PDGFRβ. Desmin was reduced at alveolar entry rings, air spaces were enlarged, and surface area was reduced after NRP1 depletion. PDGFRα and NRP1 colocalized to membrane lipid rafts, which are known to contain Src kinase. NRP1 depletion reduced alveolar mesenchymal cell migration and PDGF-A-mediated activation of Src kinase, which may limit accumulation of desmin at septal tips (alveolar entry rings). Cooperation between NRP1 and PDGF signaling is required for secondary septation, and manipulation of NRP1 could promote alveolar regeneration without producing fibrosis.

Novel regulatory role of neuropilin-1 in endothelial-to-mesenchymal transition and fibrosis in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by an intense fibrotic reaction termed tumor desmoplasia, which is in part responsible for its aggressiveness. Endothelial cells have been shown to display cellular plasticity in the form of endothelial-to-mesenchymal transition (EndMT) that serves as an important source of fibroblasts in pathological disorders, including cancer. Angiogenic co-receptor, neuropilin-1 (NRP-1) actively binds TGFβ1, the primary mediator of EndMT and is involved in oncogenic processes like epithelial-to-mesenchymal transition (EMT). NRP-1 and TGFβ1 signaling have been shown to be aberrantly up-regulated in PDAC. We report herein a positive correlation between NRP-1 levels, EndMT and fibrosis in human PDAC xenografts. Loss of NRP-1 in HUVECs limited TGFβ1-induced EndMT as demonstrated by gain of endothelial and loss of mesenchymal markers, while maintaining endothelial cell architecture. Knockdown of NRP-1 down-regulated TGFβ canonical signaling (pSMAD2) and associated pro-fibrotic genes. Overexpression of NRP-1 exacerbated TGFβ1-induced EndMT and up-regulated TGFβ signaling and expression of pro-fibrotic genes. In vivo, loss of NRP-1 attenuated tumor perfusion and size, accompanied by reduction in EndMT and fibrosis. This study defines a previously unrecognized role of NRP-1 in regulating TGFβ1-induced EndMT and fibrosis, and advocates NRP-1 as a therapeutic target to reduce tumor fibrosis and PDAC progression.

TGF-β family co-receptor function and signaling

Transforming growth factor-β (TGF-β) family members, which include TGF-βs, activins and bone morphogenetic proteins, are pleiotropic cytokines that elicit cell type-specific effects in a highly context-dependent manner in many different tissues. These secreted protein ligands signal via single-transmembrane Type I and Type II serine/threonine kinase receptors and intracellular SMAD transcription factors. Deregulation in signaling has been implicated in a broad array of diseases, and implicate the need for intricate fine tuning in cellular signaling responses. One important emerging mechanism by which TGF-β family receptor signaling intensity, duration, specificity and diversity are regulated and/or mediated is through cell surface co-receptors. Here, we provide an overview of the co-receptors that have been identified for TGF-β family members. While some appear to be specific to TGF-β family members, others are shared with other pathways and provide possible ways for signal integration. This review focuses on novel functions of TGF-β family co-receptors, which continue to be discovered.

Retinal vasculature development in health and disease

Development of the retinal vasculature is based on highly coordinated signalling between different cell types of the retina, integrating internal metabolic requirements with external influences such as the supply of oxygen and nutrients. The developing mouse retinal vasculature is a useful model system to study these interactions because it is experimentally accessible for intra ocular injections and genetic manipulations, can be easily imaged and develops in a similar fashion to that of humans. Research using this model has provided insights about general principles of angiogenesis as well as pathologies that affect the developing retinal vasculature. In this review, we discuss recent advances in our understanding of the molecular and cellular mechanisms that govern the interactions between neurons, glial and vascular cells in the developing retina. This includes a review of mechanisms that shape the retinal vasculature, such as sprouting angiogenesis, vascular network remodelling and vessel maturation. We also explore how the disruption of these processes in mice can lead to pathology - such as oxygen induced retinopathy - and how this translates to human retinopathy of prematurity.

Integrins in Vascular Development and Pathology

During vascular development, endothelial cells (ECs) and neighboring stromal cells interact and communicate through autocrine and paracrine signaling mechanisms involving extracellular matrix (ECM) proteins and their cell surface integrin adhesion receptors. Integrin-mediated adhesion and signaling pathways are crucial for normal vascular development and physiology, and alterations in integrin expression and/or function drive several vascular-related pathologies including thrombosis, autoimmune disorders, and cancer. The purpose of this chapter is to discuss integrin adhesion and signaling pathways important for EC growth, survival, and migration. Integrin-mediated paracrine links between ECs and surrounding stromal cells in the organ microenvironment will also be discussed. Lastly, we will review roles for integrins in vascular pathologies and discuss possible targets for therapeutic intervention.

VEGF-A and neuropilin 1 (NRP1) shape axon projections in the developing CNS via dual roles in neurons and blood vessels

Visual information is relayed from the eye to the brain via retinal ganglion cell (RGC) axons. Mice lacking NRP1 or NRP1-binding VEGF-A isoforms have defective RGC axon organisation alongside brain vascular defects. It is not known whether axonal defects are caused exclusively by defective VEGF-A signalling in RGCs or are exacerbated by abnormal vascular morphology. Targeted NRP1 ablation in RGCs with a Brn3b^Cre knock-in allele reduced axonal midline crossing at the optic chiasm and optic tract fasciculation. In contrast, Tie2-Cre-mediated endothelial NRP1 ablation induced axon exclusion zones in the optic tracts without impairing axon crossing. Similar defects were observed in Vegfa^120/120 and Vegfa^188/188 mice, which have vascular defects as a result of their expression of single VEGF-A isoforms. Ectopic midline vascularisation in endothelial Nrp1 and Vegfa^188/188 mutants caused additional axonal exclusion zones within the chiasm. As in vitro and in vivo assays demonstrated that vessels do not repel axons, abnormally large or ectopically positioned vessels are likely to present physical obstacles to axon growth. We conclude that proper axonal wiring during brain development depends on the precise molecular control of neurovascular co-patterning.

Summary: NRP1 plays a dual role in retinal ganglion cells and in vascular endothelial cells to organise axons along the optic pathway between the mouse retina and diencephalon.

Neuropilin-1 modulates TGFβ signaling to drive glioblastoma growth and recurrence after anti-angiogenic therapy

Glioblastoma (GBM) is a rapidly progressive brain cancer that exploits the neural microenvironment, and particularly blood vessels, for selective growth and survival. Anti-angiogenic agents such as the vascular endothelial growth factor-A (VEGF-A) blocking antibody bevacizumab yield short-term benefits to patients due to blood vessel regression and stabilization of vascular permeability. However, tumor recurrence is common, and this is associated with acquired resistance to bevacizumab. The mechanisms that drive acquired resistance and tumor recurrence in response to anti-angiogenic therapy remain largely unknown. Here, we report that Neuropilin-1 (Nrp1) regulates GBM growth and invasion by balancing tumor cell responses to VEGF-A and transforming growth factor βs (TGFβs). Nrp1 is expressed in GBM cells where it promotes TGFβ receptor internalization and signaling via Smad transcription factors. GBM that recur after bevacizumab treatment show down-regulation of Nrp1 expression, indicating that altering the balance between VEGF-A and TGFβ signaling is one mechanism that promotes resistance to anti-angiogenic agents. Collectively, these data reveal that Nrp1 plays a critical role in balancing responsiveness to VEGF-A versus TGFβ to regulate GBM growth, progression, and recurrence after anti-vascular therapy.

Glioblastoma stem cells exploit the αvβ8 integrin-TGFβ1 signaling axis to drive tumor initiation and progression

Glioblastoma (GBM) is a primary brain cancer that contains populations of stem-like cancer cells (GSCs) that home to specialized perivascular niches. GSC interactions with their niche influence self-renewal, differentiation and drug resistance, although the pathways underlying these events remain largely unknown. Here, we report that the integrin αvβ8 and its latent transforming growth factor β1 (TGFβ1) protein ligand have central roles in promoting niche co-option and GBM initiation. αvβ8 integrin is highly expressed in GSCs and is essential for self-renewal and lineage commitment in vitro. Fractionation of β8^high cells from freshly resected human GBM samples also reveals a requirement for this integrin in tumorigenesis in vivo. Whole-transcriptome sequencing reveals that αvβ8 integrin regulates tumor development, in part, by driving TGFβ1-induced DNA replication and mitotic checkpoint progression. Collectively, these data identify the αvβ8 integrin-TGFβ1 signaling axis as crucial for exploitation of the perivascular niche and identify potential therapeutic targets for inhibiting tumor growth and progression in patients with GBM.

RICE CRISPR: Rapidly increased cut ends by an exonuclease Cas9 fusion in zebrafish

Application of CRISPR-Cas9 technology in diverse organisms has resulted in an explosion of genome modification efforts. To expand the toolbox of applications, we have created an E. coli Exonuclease I (sbcB)-Cas9 fusion that has altered enzymatic activity in zebrafish embryos. This Cas9 variant has increased mutation efficiency and favors longer deletions relative to wild-type Cas9. We anticipate that this variant will allow for more efficient screening for F0 phenotypes and mutation of a larger spectrum of genomic targets including deletion of regulatory regions and creating loss of function mutations in transcription units with poor sequence conservation such as lncRNAs where larger deletions may be required for loss of function.

Radial Glia Cells Control Angiogenesis in the Developing Cerebral Cortex Through TGF-β1 Signaling

Neuroangiogenesis in the developing central nervous system is controlled by interactions between endothelial cells (ECs) and radial glia (RG) neural stem cells, although RG-derived molecules implicated in these events are not fully known. Here, we investigated the role of RG-secreted TGF-β1, in angiogenesis in the developing cerebral cortex. By isolation of murine microcapillary brain endothelial cells (MBECs), we demonstrate that conditioned medium from RG cultures (RG-CM) promoted MBEC migration and formation of vessel-like structures in vitro, in a TGF-β1-dependent manner. These events were followed by endothelial regulation of GPR124 and BAI-1 gene expression by RG-CM. Proteome profile of RG-CM identified angiogenesis-related molecules IGFBP2/3, osteopontin, endostatin, SDF1, fractalkine, TIMP1/4, Ang-1, pentraxin3, and Cyr61, some of them modulated by TGF-β1 induction. In vivo gain and loss of function assays targeting RG cells demonstrates a specific TGF-β1-dependent control of blood vessels branching in the cerebral cortex. Together, our results point to TGF-β1 signaling pathway as a potential mediator of the RG-EC interactions and shed light to the key role of RG in paving the brain vascular network.

Neuropilin 1 Involvement in Choroidal and Retinal Neovascularisation

PURPOSE

Inhibiting VEGF is the gold standard treatment for neovascular age-related macular degeneration (AMD). It is also effective in preventing retinal oedema and neovascularisation (NV) in diabetic retinopathy (DR) and retinal vein occlusions (RVO). Neuropilin 1 (Nrp1) is a co-receptor for VEGF and many other growth factors, and therefore a possible alternative drug target in intra ocular neovascular disease. Here we assessed choroidal and retinal NV in an inducible, endothelial specific knock out model for Nrp1.

METHODS

Crossing Nrp1 floxed mice with Pdgfb-CreERT2 mice produced tamoxifen-inducible, endothelial specific Nrp1 knock out mice (Nrp1ΔEC) and Cre-negative, control littermates. Cre-recombinase activity was confirmed in the Ai3(RCL-EYFP) reporter strain. Animals were subjected to laser-induced CNV (532 nm) and spectral domain-optical coherence tomography (SD-OCT) was performed immediately after laser and at day 7. Fluorescein angiography (FA) evaluated leakage and postmortem lectin staining in flat mounted RPE/choroid complexes was also used to measure CNV. Furthermore, retinal neovascularisation in the oxygen induced retinopathy (OIR) model was assessed by immunohistochemistry in retinal flatmounts.

RESULTS

In vivo FA, OCT and post-mortem lectin staining showed a statistically significant reduction in leakage (p<0.05), CNV volume (p<0.05) and CNV area (p<0.05) in the Nrp1ΔEC mice compared to their Cre-negative littermates. Also the OIR model showed reduced retinal NV in the mutant animals compared to wild types (p<0.001).

CONCLUSION

We have demonstrated reduced choroidal and retinal NV in animals that lack endothelial Nrp1, confirming a role of Nrp1 in those processes. Therefore, Nrp1 may be a promising drug target for neovascular diseases in the eye.

The expanding role of neuropilin: regulation of transforming growth factor-β and platelet-derived growth factor signaling in the vasculature

PURPOSE OF REVIEW

Long recognized for its role in regulation of vascular endothelial growth factor signaling, neuropilin (Nrp)1 has emerged as a modulator of additional signaling pathways critical for vascular development and function. Here we review two novel functions of Nrp1 in blood vessels: regulation of transforming growth factor-β (TGFβ) signaling in endothelial cells and regulation of platelet-derived growth factor (PDGF) signaling in vascular smooth muscle cells.

RECENT FINDINGS

Novel mouse models demonstrate that Nrp1 fulfills vascular functions independent of vascular endothelial growth factor signaling. These include modulation of TGFβ-dependent inhibition of endothelial sprouting during developmental angiogenesis and PDGF signaling in vascular smooth muscle cells during development and disease.

SUMMARY

Broadening our understanding of how and where Nrp1 functions in the vasculature is critical for the development of targeted therapeutics for cancer and vascular diseases such as atherosclerosis and retinopathies.

Sema3d controls collective endothelial cell migration by distinct mechanisms via Nrp1 and PlxnD1

Semaphorins regulate guidance during cell migration. In addition to repelling endothelial cells, Hamm et al. identify a novel mechanism by which Semaphorin3d/Neuropilin1 regulates collective endothelial cell migration through activating a kinase cascade, which regulates Actin network organization and cell–cell contacts.

During cardiovascular development, tight spatiotemporal regulation of molecular cues is essential for controlling endothelial cell (EC) migration. Secreted class III Semaphorins play an important role in guidance of neuronal cell migration and were lately linked to regulating cardiovascular development. Recently, SEMA3D gene disruptions were associated with cardiovascular defects in patients; however, the mechanisms of action were not revealed. Here we show for the first time that Sema3d regulates collective EC migration in zebrafish through two separate mechanisms. Mesenchymal Sema3d guides outgrowth of the common cardinal vein via repulsion and signals through PlexinD1. Additionally, within the same ECs, we identified a novel function of autocrine Sema3d signaling in regulating Actin network organization and EC morphology. We show that this new function requires Sema3d signaling through Neuropilin1, which then regulates Actin network organization through RhoA upstream of Rock, stabilizing the EC sheet. Our findings are highly relevant for understanding EC migration and the mechanisms of collective migration in other contexts.

Mechanisms and regulation of endothelial VEGF receptor signalling. Nat Rev Mol Cell Biol. 2016;17:611-625. [PMID: 27461391 DOI: 10.1038/nrm.2016.87]

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are uniquely required to balance the formation of new blood vessels with the maintenance and remodelling of existing ones, during development and in adult tissues. Recent advances have greatly expanded our understanding of the tight and multi-level regulation of VEGFR2 signalling, which is the primary focus of this Review. Important insights have been gained into the regulatory roles of VEGFR-interacting proteins (such as neuropilins, proteoglycans, integrins and protein tyrosine phosphatases); the dynamics of VEGFR2 endocytosis, trafficking and signalling; and the crosstalk between VEGF-induced signalling and other endothelial signalling cascades. A clear understanding of this multifaceted signalling web is key to successful therapeutic suppression or stimulation of vascular growth.

NRP1 function and targeting in neurovascular development and eye disease

Neuropilin 1 (NRP1) is expressed by neurons, blood vessels, immune cells and many other cell types in the mammalian body and binds a range of structurally and functionally diverse extracellular ligands to modulate organ development and function. In recent years, several types of mouse knockout models have been developed that have provided useful tools for experimental investigation of NRP1 function, and a multitude of therapeutics targeting NRP1 have been designed, mostly with the view to explore them for cancer treatment. This review provides a general overview of current knowledge of the signalling pathways that are modulated by NRP1, with particular focus on neuronal and vascular roles in the brain and retina. This review will also discuss the potential of NRP1 inhibitors for the treatment for neovascular eye diseases.