PTEN mediates Notch-dependent stalk cell arrest in angiogenesis

Shear stress and pathophysiological PI3K involvement in vascular malformations

Molecular characterization of vascular anomalies has revealed that affected endothelial cells (ECs) harbor gain-of-function (GOF) mutations in the gene encoding the catalytic α subunit of PI3Kα (PIK3CA). These PIK3CA mutations are known to cause solid cancers when occurring in other tissues. PIK3CA-related vascular anomalies, or "PIKopathies," range from simple, i.e., restricted to a particular form of malformation, to complex, i.e., presenting with a range of hyperplasia phenotypes, including the PIK3CA-related overgrowth spectrum. Interestingly, development of PIKopathies is affected by fluid shear stress (FSS), a physiological stimulus caused by blood or lymph flow. These findings implicate PI3K in mediating physiological EC responses to FSS conditions characteristic of lymphatic and capillary vessel beds. Consistent with this hypothesis, increased PI3K signaling also contributes to cerebral cavernous malformations, a vascular disorder that affects low-perfused brain venous capillaries. Because the GOF activity of PI3K and its signaling partners are excellent drug targets, understanding PIK3CA's role in the development of vascular anomalies may inform therapeutic strategies to normalize EC responses in the diseased state. This Review focuses on PIK3CA's role in mediating EC responses to FSS and discusses current understanding of PIK3CA dysregulation in a range of vascular anomalies that particularly affect low-perfused regions of the vasculature. We also discuss recent surprising findings linking increased PI3K signaling to fast-flow arteriovenous malformations in hereditary hemorrhagic telangiectasias.

Comparative analysis of the effect of hypoxia in two different tumor cell models shows the differential involvement of PTEN control of proangiogenic pathways

Hypoxia, low, non-physiological oxygen tension is a key regulator of tumor microenvironment, determining the pathological tumor vascularization. Alleviation of hypoxia through vessel normalization may be a promising therapeutic approach. We aimed to assess the role of low oxygen tension in PTEN-related pathways and proangiogenic response, in vitro, in two different tumor cell lines, focusing on potential therapeutic targets for tumor vessel normalization. Downregulation of PTEN in hypoxia mediates the activation of distinct mechanisms: cytoplasmic pAKT activation in melanoma and pMDM2 modulation in kidney cancer. We show that hypoxia-induced proangiogenic potential was stronger in Renca cells than B16 F10-confirmed by a distinct secretory potential and different ability to affect endothelial cells functions. Therefore, the impact of hypoxia on PTEN-mediated regulation may determine the therapeutic targets and effectiveness of vessel normalization and intrinsic characteristics of cancer cell have to be taken into account when designing treatment.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

PI3K-C2β limits mTORC1 signaling and angiogenic growth

Phosphoinositide 3-kinases (PI3Ks) phosphorylate intracellular inositol lipids to regulate signaling and intracellular vesicular trafficking. Mammals have eight PI3K isoforms, of which class I PI3Kα and class II PI3K-C2α are essential for vascular development. The class II PI3K-C2β is also abundant in endothelial cells. Using in vivo and in vitro approaches, we found that PI3K-C2β was a critical regulator of blood vessel growth by restricting endothelial mTORC1 signaling. Mice expressing a kinase-inactive form of PI3K-C2β displayed enlarged blood vessels without corresponding changes in endothelial cell proliferation or migration. Instead, inactivation of PI3K-C2β resulted in an increase in the size of endothelial cells, particularly in the sprouting zone of angiogenesis. Mechanistically, we showed that the aberrantly large size of PI3K-C2β mutant endothelial cells was caused by mTORC1 activation, which sustained growth in these cells. Consistently, pharmacological inhibition of mTORC1 with rapamycin normalized vascular morphogenesis in PI3K-C2β mutant mice. Together, these results identify PI3K-C2β as a crucial determinant of endothelial signaling and illustrate the importance of mTORC1 regulation during angiogenic growth.

Redox-Mediated Rewiring of Signalling Pathways: The Role of a Cellular Clock in Brain Health and Disease

Metazoan signalling pathways can be rewired to dampen or amplify the rate of events, such as those that occur in development and aging. Given that a linear network topology restricts the capacity to rewire signalling pathways, such scalability of the pace of biological events suggests the existence of programmable non-linear elements in the underlying signalling pathways. Here, we review the network topology of key signalling pathways with a focus on redox-sensitive proteins, including PTEN and Ras GTPase, that reshape the connectivity profile of signalling pathways in response to an altered redox state. While this network-level impact of redox is achieved by the modulation of individual redox-sensitive proteins, it is the population by these proteins of critical nodes in a network topology of signal transduction pathways that amplifies the impact of redox-mediated reprogramming. We propose that redox-mediated rewiring is essential to regulate the rate of transmission of biological signals, giving rise to a programmable cellular clock that orchestrates the pace of biological phenomena such as development and aging. We further review the evidence that an aberrant redox-mediated modulation of output of the cellular clock contributes to the emergence of pathological conditions affecting the human brain.

New molecular targets in canine hemangiosarcoma-Comparative review and future of the precision medicine

Human angiosarcoma and canine hemangiosarcoma reveal similarities not only in their aggressive clinical behaviour, but especially in molecular landscape and genetic alterations involved in tumorigenesis and metastasis formation. Currently, no satisfying treatment that allows for achieving long overall survival or even prolonged time to progression does not exist. Due to the progress that has been made in targeted therapies and precision medicine the basis for a new treatment design is to uncover mutations and their functions as possible targets to provide tailored drugs for individual cases. Whole exome or genome sequencing studies and immunohistochemistry brought in the last few years important discoveries and identified the most common mutations with probably crucial role in this tumour development. Also, despite a lack of mutation in some of the culprit genes, the cancerogenesis cause may be buried in main cellular pathways connected with proteins encoded by those genes and involving, for example, pathological angiogenesis. The aim of this review is to highlight the most promising molecular targets for precision oncology treatment from the veterinary perspective aided by the principles of comparative science. Some of the drugs are only undergoing laboratory in vitro studies and others entered the clinic in the management of other cancer types in humans, but those used in dogs with promising responses have been mentioned as priorities.

Estrogen promotes Epithelial ovarian cancer cells proliferation via down-regulating expression and activating phosphorylation of PTEN

Epithelial ovarian cancer (EOC) is the most common of cancer death among malignant tumors in women, its occurrence and development are strongly linked to estrogen. Having identified the phosphatase and tensin homologue (PTEN) is a potent tumor suppressor regulating cell proliferation, migration, and survival. Meanwhile, there is a correlation between PTEN protein expression and estrogen receptor expression in EOC. However, no study has amplified on the molecular regulatory mechanism and function between estrogen and PTEN in the development of EOC. In this research, we found that PTEN shows a low expression level in EOC tissues and estrogen decreased PTEN expression via the estrogen receptor 1 (ESR1) in EOC cells. Knockdown of PTEN enhanced the proliferation and migration level of EOC cells driven by estrogen. Moreover, PTEN was also phosphorylated by G protein-coupled receptor 30 (GPR30)-Protein kinase C (PKC) signaling pathway upon estrogen stimulation. Inhibiting the phosphorylation of PTEN weakened the proliferation and migration of estrogen induced-EOC cells estrogen and decreased the phosphorylation of Protein kinase B (AKT) and Mammalian target of rapamycin (mTOR). These results indicated that estrogen decreased PTEN expression level via the ESR1 genomic pathway and phosphorylated PTEN via the GPR30-PKC non-genomic pathway to activate the PI3K/AKT/mTOR signaling pathway, thereby determining the fate of EOC cells.

Endothelial plasticity across PTEN and Hippo pathways: A complex hormetic rheostat modulated by extracellular vesicles

Vascularization is a multifactorial and spatiotemporally regulated process, essential for cell and tissue survival. Vascular alterations have repercussions on the development and progression of diseases such as cancer, cardiovascular diseases, and diabetes, which are the leading causes of death worldwide. Additionally, vascularization continues to be a challenge for tissue engineering and regenerative medicine. Hence, vascularization is the center of interest for physiology, pathophysiology, and therapeutic processes. Within vascularization, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and Hippo signaling have pivotal roles in the development and homeostasis of the vascular system. Their suppression is related to several pathologies, including developmental defects and cancer. Non-coding RNAs (ncRNAs) are among the regulators of PTEN and/or Hippo pathways during development and disease. The purpose of this paper is to review and discuss the mechanisms by which exosome-derived ncRNAs modulate endothelial cell plasticity during physiological and pathological angiogenesis, through the regulation of PTEN and Hippo pathways, aiming to establish new perspectives on cellular communication during tumoral and regenerative vascularization.

PI(4,5)P2-dependent regulation of endothelial tip cell specification contributes to angiogenesis

Dynamic positioning of endothelial tip and stalk cells, via the interplay between VEGFR2 and NOTCH signaling, is essential for angiogenesis. VEGFR2 activates PI3K, which phosphorylates PI(4,5)P₂ to PI(3,4,5)P₃, activating AKT; however, PI3K/AKT does not direct tip cell specification. We report that PI(4,5)P₂ hydrolysis by the phosphoinositide-5-phosphatase, INPP5K, contributes to angiogenesis. INPP5K ablation disrupted tip cell specification and impaired embryonic angiogenesis associated with enhanced DLL4/NOTCH signaling. INPP5K degraded a pool of PI(4,5)P₂ generated by PIP5K1C phosphorylation of PI(4)P in endothelial cells. INPP5K ablation increased PI(4,5)P₂, thereby releasing β-catenin from the plasma membrane, and concurrently increased PI(3,4,5)P₃-dependent AKT activation, conditions that licensed DLL4/NOTCH transcription. Suppression of PI(4,5)P₂ in INPP5K-siRNA cells by PIP5K1C-siRNA, restored β-catenin membrane localization and normalized AKT signaling. Pharmacological NOTCH or AKT inhibition in vivo or genetic β-catenin attenuation rescued angiogenesis defects in INPP5K-null mice. Therefore, PI(4,5)P₂ is critical for β-catenin/DLL4/NOTCH signaling, which governs tip cell specification during angiogenesis.

Tumour suppressor PTEN activity is differentially inducible by myo-inositol phosphates

Tumour evolution and efficacy of treatments are controlled by the microenvironment, the composition of which is primarily dependent on the angiogenic reaction to hypoxic stress. Tumour angiogenesis normalization is a challenge for adjuvant therapy strategies to chemo-, radio- and immunotherapeutics. Myo-inositol trispyrophosphate (ITPP) appears to provide the means to alleviate hypoxia in the tumour site by a double molecular mechanism. First, it modifies the properties of red blood cells (RBC) to release oxygen (O₂ ) in the hypoxic sites more easily, leading to a rapid and stable increase in the partial pressure of oxygen (pO₂ ). And second, it activates the endothelial phosphatase and tensin homologue deleted on Chromosome 10 (PTEN). The hypothesis that stable normalization of the vascular system is due to the PTEN, a tumour suppressor and phosphatase which controls the proper angiogenic reaction was ascertained. Here, by direct biochemical measurements of PTEN competitive activity in relation to PIP2 production, we show that the kinetics are complex in terms of the activation/inhibition effects of ITPP with an inverted consequence towards the kinase PI3K. The use of the surface plasmon resonance (SPR) technique allowed us to demonstrate that PTEN binds inositol derivatives differently but weakly. This method permitted us to reveal that PTEN is highly sensitive to the local concentration conditions, especially that ITPP increases the PTEN activity towards PIP3, and importantly, that PTEN affinity for ITPP is considerably increased by the presence of PIP3, as occurs in vivo. Our approach demonstrates the validity of using ITPP to activate PTEN for stable vessel normalization strategies.

Notch Signaling in the Vasculature: Angiogenesis and Angiocrine Functions

Formation of a functional blood vessel network is a complex process tightly controlled by pro- and antiangiogenic signals released within the local microenvironment or delivered through the bloodstream. Endothelial cells precisely integrate such temporal and spatial changes in extracellular signals and generate an orchestrated response by modulating signaling transduction, gene expression, and metabolism. A key regulator in vessel formation is Notch signaling, which controls endothelial cell specification, proliferation, migration, adhesion, and arteriovenous differentiation. This review summarizes the molecular biology of endothelial Notch signaling and how it controls angiogenesis and maintenance of the established, quiescent vasculature. In addition, recent progress in the understanding of Notch signaling in endothelial cells for controlling organ homeostasis by transcriptional regulation of angiocrine factors and its relevance to disease will be discussed.

Cyclic AMP response element-binding protein (CREB) transcription factor in astrocytic synaptic communication

Astrocytes are known to actively participate in synaptic communication by forming structures called tripartite synapses. These synapses consist of presynaptic axon terminals, postsynaptic dendritic spines, and astrocytic processes where astrocytes release and receive transmitters. Although the transcription factor cyclic AMP response element (CRE)-binding protein (CREB) has been actively studied as an important factor for mediating synaptic activity-induced responses in neurons, its role in astrocytes is relatively unknown. Synaptic signals are known to activate various downstream pathways in astrocytes, which can activate the CREB transcription factor. Therefore, there is a need to summarize studies on astrocytic intracellular pathways that are induced by synaptic communication resulting in activation of the CREB pathway. In this review, we discuss the various neurotransmitter receptors and intracellular pathways that can induce CREB activation and CREB-induced gene regulation in astrocytes.

Brain arteriovenous malformation in hereditary hemorrhagic telangiectasia: Recent advances in cellular and molecular mechanisms

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder characterized by vessel dilatation, such as telangiectasia in skin and mucosa and arteriovenous malformations (AVM) in internal organs such as the gastrointestinal tract, lungs, and brain. AVMs are fragile and tortuous vascular anomalies that directly connect arteries and veins, bypassing healthy capillaries. Mutations in transforming growth factor β (TGFβ) signaling pathway components, such as ENG (ENDOGLIN), ACVRL1 (ALK1), and SMAD4 (SMAD4) genes, account for most of HHT cases. 10-20% of HHT patients develop brain AVMs (bAVMs), which can lead to vessel wall rupture and intracranial hemorrhages. Though the main mutations are known, mechanisms leading to AVM formation are unclear, partially due to lack of animal models. Recent mouse models allowed significant advances in our understanding of AVMs. Endothelial-specific deletion of either Acvrl1, Eng or Smad4 is sufficient to induce AVMs, identifying endothelial cells (ECs) as primary targets of BMP signaling to promote vascular integrity. Loss of ALK1/ENG/SMAD4 signaling is associated with NOTCH signaling defects and abnormal arteriovenous EC differentiation. Moreover, cumulative evidence suggests that AVMs originate from venous ECs with defective flow-migration coupling and excessive proliferation. Mutant ECs show an increase of PI3K/AKT signaling and inhibitors of this signaling pathway rescue AVMs in HHT mouse models, revealing new therapeutic avenues. In this review, we will summarize recent advances and current knowledge of mechanisms controlling the pathogenesis of bAVMs, and discuss unresolved questions.

The roles of metabolic profiles and intracellular signaling pathways of tumor microenvironment cells in angiogenesis of solid tumors

Innate and adaptive immune cells patrol and survey throughout the human body and sometimes reside in the tumor microenvironment (TME) with a variety of cell types and nutrients that may differ from those in which they developed. The metabolic pathways and metabolites of immune cells are rooted in cell physiology, and not only provide nutrients and energy for cell growth and survival but also influencing cell differentiation and effector functions. Nowadays, there is a growing awareness that metabolic processes occurring in cancer cells can affect immune cell function and lead to tumor immune evasion and angiogenesis. In order to safely treat cancer patients and prevent immune checkpoint blockade-induced toxicities and autoimmunity, we suggest using anti-angiogenic drugs solely or combined with Immune checkpoint blockers (ICBs) to boost the safety and effectiveness of cancer therapy. As a consequence, there is significant and escalating attention to discovering techniques that target metabolism as a new method of cancer therapy. In this review, a summary of immune-metabolic processes and their potential role in the stimulation of intracellular signaling in TME cells that lead to tumor angiogenesis, and therapeutic applications is provided. Video abstract.

IL-35 enhances angiogenic effects of small extracellular vesicles in breast cancer

As an indispensable process for breast cancer metastasis, tumour angiogenesis requires a tight interaction between cancer cells and endothelial cells in tumour microenvironment. Here, we explored the participation of small extracellular vesicles (sEVs) derived from breast cancer cells in modulating angiogenesis and investigated the effect of IL-35 in facilitating this process. Firstly, we characterized breast cancer cells-derived sEVs untreated or treated with IL-35 and visualized the internalization of these sEVs by human umbilical vein endothelial cells (HUVECs). Breast cancer cells-derived sEVs promoted endothelial cell proliferation through facilitating cell cycle progression and enhanced capillary-like structures formation and microvessel formation. Subsequent results proved that IL-35 further reinforced the angiogenic effect induced by breast cancer cells-derived sEVs. Moreover, sEVs from breast cancer cells significantly enhanced tumour growth and microvessel density in breast tumour-bearing mice model. Microarray analysis showed that IL-35 might alter the mRNA profiles of sEVs and activate the Ras/Raf/MEK/ERK signalling pathway. These findings demonstrated that IL-35 indirectly promoted angiogenesis in breast cancer through regulating the content of breast cancer cells-derived sEVs, which could be internalized by HUVECs.

Notch Signaling in Vascular Endothelial and Mural Cell Communications

The Notch signaling pathway is a highly versatile and evolutionarily conserved mechanism with an important role in cell fate determination. Notch signaling plays a vital role in vascular development, regulating several fundamental processes such as angiogenesis, arterial/venous differentiation, and mural cell investment. Aberrant Notch signaling can result in severe vascular phenotypes as observed in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and Alagille syndrome. It is known that vascular endothelial cells and mural cells interact to regulate vessel formation, cell maturation, and stability of the vascular network. Defective endothelial-mural cell interactions are a common phenotype in diseases characterized by impaired vascular integrity. Further refinement of the role of Notch signaling in the vascular junctions will be critical to attempts to modulate Notch in the context of human vascular disease. In this review, we aim to consolidate and summarize our current understanding of Notch signaling in the vascular endothelial and mural cells during development and in the adult vasculature.

The anti-angiogenesis mechanism of Geniposide on rheumatoid arthritis is related to the regulation of PTEN

Rheumatoid arthritis (RA) is a systemic immune disease characterized by joint inflammation and pannus. The nascent pannus contributes to synovial hyperplasia, cartilage, and tissue damage in RA. This study aims to explore the therapeutic effect and potential mechanism of Geniposide (GE) on RA angiogenesis, involving the participation of phosphate and tension homology deleted on chromosome ten (PTEN) and downstream pathways. Clinical manifestations, synovial pathomorphology, microvessel density, and the level of angiogenesis-related factors were used to evaluate the therapeutic effect of GE on adjuvant-induced arthritis (AA) rats. The proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) indicate the degree of angiogenesis in vitro. Lentivirus over-expression of PTEN was employed to elucidate the potential mechanism. The results showed that GE improved the degree of arthritis and angiogenesis in AA rats. The expression of PTEN was decreased significantly in vivo and in vitro, and over-expression of PTEN improved the biological function of HUVECs to inhibit angiogenesis. GE inhibited the proliferation, migration, and tubule formation of HUVECs and plays an anti-angiogenesis role in vitro. Mechanism study showed that PTEN expression was increased and p-PI3K and p-Akt expression was decreased with GE treatment. It suggests that GE up-regulated the expression of PTEN and inhibited the activation of PI3K-Akt signal, which plays a role in inhibiting angiogenesis in RA in vivo and in vitro.

A novel peptide inhibitor of Dll4-Notch1 signalling and its pro-angiogenic functions

BACKGROUND AND PURPOSE

The Dll4-Notch1 signalling pathway plays an important role in sprouting angiogenesis, vascular remodelling and arterial or venous specificity. Genetic or pharmacological inhibition of Dll4-Notch1 signalling leads to excessive sprouting angiogenesis. However, transcriptional inhibitors of Dll4-Notch1 signalling have not been described.

EXPERIMENTAL APPROACH

We designed a new peptide targeting Notch signalling, referred to as TAT-ANK, and assessed its effects on angiogenesis. In vitro, tube formation and fibrin gel bead assay were carried out, using human umbilical vein endothelial cells (HUVECs). In vivo, Matrigel plug angiogenesis assay, a developmental retinal model and tumour models in mice were used. The mechanisms underlying TAT-ANK activity were investigated by immunochemistry, western blotting, immunoprecipitation, RT-qPCR and luciferase reporter assays.

KEY RESULTS

The amino acid residues 179-191 in the G-protein-coupled receptor-kinase-interacting protein-1 (GIT1-ankyrin domain) are crucial for GIT1 binding to the Notch transcription repressor, RBP-J. We designed the peptide TAT-ANK, based on residues 179-191 in GIT1. TAT-ANK significantly inhibited Dll4 expression and Notch 1 activation in HUVECs by competing with activated Notch1 to bind to RBP-J. The analyses of biological functions showed that TAT-ANK promoted angiogenesis in vitro and in vivo by inhibiting Dll4-Notch1 signalling.

CONCLUSIONS AND IMPLICATIONS

We synthesized and investigated the biological actions of TAT-ANK peptide, a new inhibitor of Notch signalling. This peptide will be of significant interest to research on Dll4-Notch1 signalling and to clinicians carrying out clinical trials using Notch signalling inhibitors. Furthermore, our findings will have important conceptual and therapeutic implications for angiogenesis-related diseases.

Angiocrine polyamine production regulates adiposity

Reciprocal interactions between endothelial cells (ECs) and adipocytes are fundamental to maintain white adipose tissue (WAT) homeostasis, as illustrated by the activation of angiogenesis upon WAT expansion, a process that is impaired in obesity. However, the molecular mechanisms underlying the crosstalk between ECs and adipocytes remain poorly understood. Here, we show that local production of polyamines in ECs stimulates adipocyte lipolysis and regulates WAT homeostasis in mice. We promote enhanced cell-autonomous angiogenesis by deleting Pten in the murine endothelium. Endothelial Pten loss leads to a WAT-selective phenotype, characterized by reduced body weight and adiposity in pathophysiological conditions. This phenotype stems from enhanced fatty acid β-oxidation in ECs concomitant with a paracrine lipolytic action on adipocytes, accounting for reduced adiposity. Combined analysis of murine models, isolated ECs and human specimens reveals that WAT lipolysis is mediated by mTORC1-dependent production of polyamines by ECs. Our results indicate that angiocrine metabolic signals are important for WAT homeostasis and organismal metabolism.

PI3K-regulated Glycine N-methyltransferase is required for the development of prostate cancer

Glycine N-Methyltransferase (GNMT) is a metabolic enzyme that integrates metabolism and epigenetic regulation. The product of GNMT, sarcosine, has been proposed as a prostate cancer biomarker. This enzyme is predominantly expressed in the liver, brain, pancreas, and prostate tissue, where it exhibits distinct regulation. Whereas genetic alterations in GNMT have been associated to prostate cancer risk, its causal contribution to the development of this disease is limited to cell line-based studies and correlative human analyses. Here we integrate human studies, genetic mouse modeling, and cellular systems to characterize the regulation and function of GNMT in prostate cancer. We report that this enzyme is repressed upon activation of the oncogenic Phosphoinositide-3-kinase (PI3K) pathway, which adds complexity to its reported dependency on androgen signaling. Importantly, we demonstrate that expression of GNMT is required for the onset of invasive prostate cancer in a genetic mouse model. Altogether, our results provide further support of the heavy oncogenic signal-dependent regulation of GNMT in prostate cancer.

A Long Journey before Cycling: Regulation of Quiescence Exit in Adult Muscle Satellite Cells

Skeletal muscle harbors a pool of stem cells called muscle satellite cells (MuSCs) that are mainly responsible for its robust regenerative capacities. Adult satellite cells are mitotically quiescent in uninjured muscles under homeostasis, but they exit quiescence upon injury to re-enter the cell cycle to proliferate. While most of the expanded satellites cells differentiate and fuse to form new myofibers, some undergo self-renewal to replenish the stem cell pool. Specifically, quiescence exit describes the initial transition of MuSCs from quiescence to the first cell cycle, which takes much longer than the time required for subsequent cell cycles and involves drastic changes in cell size, epigenetic and transcriptomic profiles, and metabolic status. It is, therefore, an essential period indispensable for the success of muscle regeneration. Diverse mechanisms exist in MuSCs to regulate quiescence exit. In this review, we summarize key events that occur during quiescence exit in MuSCs and discuss the molecular regulation of this process with an emphasis on multiple levels of intrinsic regulatory mechanisms. A comprehensive understanding of how quiescence exit is regulated will facilitate satellite cell-based muscle regenerative therapies and advance their applications in various disease and aging conditions.

Rethinking growth factors: the case of BMP9 during vessel maturation

Angiogenesis is an essential process for correct development and physiology. This mechanism is tightly regulated by many signals that activate several pathways, which are constantly interacting with each other. There is mounting evidence that BMP9/ALK1 pathway is essential for a correct vessel maturation. Alterations in this pathway lead to the development of hereditary haemorrhagic telangiectasias. However, little was known about the BMP9 signalling cascade until the last years. Recent reports have shown that while BMP9 arrests cell cycle, it promotes the activation of anabolic pathways to enhance endothelial maturation. In light of this evidence, a new criterion for the classification of cytokines is proposed here, based on the physiological objective of the activation of anabolic routes. Whether this activation by a growth factor is needed to sustain mitosis or to promote a specific function such as matrix formation is a critical characteristic that needs to be considered to classify growth factors. Hence, the state-of-the-art of BMP9/ALK1 signalling is reviewed here, as well as its implications in normal and pathogenic angiogenesis.

Three-Dimensional Culture Decreases the Angiogenic Ability of Mouse Macrophages

Macrophages play important roles in angiogenesis; however, previous studies on macrophage angiogenesis have focused on traditional 2D cultures. In this study, we established a 3D culture system for macrophages using collagen microcarriers and assessed the effect of 3D culture on their angiogenic capabilities. Macrophages grown in 3D culture displayed a significantly different morphology and arrangement under electron microscopy compared to those grown in 2D culture. Tube formation assays and chick embryo chorioallantoic membrane assays further revealed that 3D-cultured macrophages were less angiogenic than those in 2D culture. Whole-transcriptome sequencing showed that nearly 40% of genes were significantly differently expressed, including nine important angiogenic factors of which seven had been downregulated. In addition, the expression of almost all genes related to two important angiogenic pathways was decreased in 3D-cultured macrophages, including the two key angiogenic factors, VEGFA and ANG2. Together, the findings of our study improve our understanding of angiogenesis and 3D macrophage culture in tissues, and provide new avenues and methods for future research on macrophages.

Barriers to Immunotherapy in Ovarian Cancer: Metabolic, Genomic, and Immune Perturbations in the Tumour Microenvironment

A lack of explicit early clinical signs and effective screening measures mean that ovarian cancer (OC) often presents as advanced, incurable disease. While conventional treatment combines maximal cytoreductive surgery and platinum-based chemotherapy, patients frequently develop chemoresistance and disease recurrence. The clinical application of immune checkpoint blockade (ICB) aims to restore anti-cancer T-cell function in the tumour microenvironment (TME). Disappointingly, even though tumour infiltrating lymphocytes are associated with superior survival in OC, ICB has offered limited therapeutic benefits. Herein, we discuss specific TME features that prevent ICB from reaching its full potential, focussing in particular on the challenges created by immune, genomic and metabolic alterations. We explore both recent and current therapeutic strategies aiming to overcome these hurdles, including the synergistic effect of combination treatments with immune-based strategies and review the status quo of current clinical trials aiming to maximise the success of immunotherapy in OC.

Notch activation promotes endothelial quiescence by repressing MYC expression via miR-218

After angiogenesis-activated embryonic and early postnatal vascularization, endothelial cells (ECs) in most tissues enter a quiescent state necessary for proper tissue perfusion and EC functions. Notch signaling is essential for maintaining EC quiescence, but the mechanisms of action remain elusive. Here, we show that microRNA-218 (miR-218) is a downstream effector of Notch in quiescent ECs. Notch activation upregulated, while Notch blockade downregulated, miR-218 and its host gene Slit2, likely via transactivation of the Slit2 promoter. Overexpressing miR-218 in human umbilical vein ECs (HUVECs) significantly repressed cell proliferation and sprouting in vitro. Transcriptomics showed that miR-218 overexpression attenuated the MYC proto-oncogene, bHLH transcription factor (MYC, also known as c-myc) signature. MYC overexpression rescued miR-218-mediated proliferation and sprouting defects in HUVECs. MYC was repressed by miR-218 via multiple mechanisms, including reduction of MYC mRNA, repression of MYC translation by targeting heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), and promoting MYC degradation by targeting EYA3. Inhibition of miR-218 partially reversed Notch-induced repression of HUVEC proliferation and sprouting. In vivo, intravitreal injection of miR-218 reduced retinal EC proliferation accompanied by MYC repression, attenuated pathological choroidal neovascularization, and rescued retinal EC hyper-sprouting induced by Notch blockade. In summary, miR-218 mediates the effect of Notch activation of EC quiescence via MYC and is a potential treatment for angiogenesis-related diseases.

From remodeling to quiescence: The transformation of the vascular network

The vascular system is essential for embryogenesis, healing, and homeostasis. Dysfunction or deregulated blood vessel function contributes to multiple diseases, including diabetic retinopathy, cancer, hypertension, or vascular malformations. A balance between the formation of new blood vessels, vascular remodeling, and vessel quiescence is fundamental for tissue growth and function. Whilst the major mechanisms contributing to the formation of new blood vessels have been well explored in recent years, vascular remodeling and quiescence remain poorly understood. In this review, we highlight the cellular and molecular mechanisms responsible for vessel remodeling and quiescence during angiogenesis. We further underline how impaired remodeling and/or destabilization of vessel networks can contribute to vascular pathologies. Finally, we speculate how addressing the molecular mechanisms of vascular remodeling and stabilization could help to treat vascular-related disorders.

Role of PTEN-less in cardiac injury, hypertrophy and regeneration

Cardiovascular diseases are the leading cause of death worldwide. Cardiomyocytes are capable of coordinated contractions, which are mainly responsible for pumping blood. When cardiac stress occurs, cardiomyocytes undergo transition from physiological homeostasis to hypertrophic growth, proliferation, or apoptosis. During these processes, many cellular factors and signaling pathways participate. PTEN is a ubiquitous dual-specificity phosphatase and functions by dephosphorylating target proteins or lipids, such as PIP3, a second messenger in the PI3K/AKT signaling pathway. Downregulation of PTEN expression or inhibiting its biologic activity improves heart function, promotes cardiomyocytes proliferation, reduces cardiac fibrosis as well as dilation, and inhibits apoptosis following ischemic stress such as myocardial infarction. Inactivation of PTEN exhibits a potentially beneficial therapeutic effects against cardiac diseases. In this review, we summarize various strategies for PTEN inactivation and highlight the roles of PTEN-less in regulating cardiomyocytes during cardiac development and stress responses.

Role of Notch in endothelial biology

The Notch signalling pathway is one of the main regulators of endothelial biology. In the last 20 years the critical function of Notch has been uncovered in the context of angiogenesis, participating in tip-stalk specification, arterial-venous differentiation, vessel stabilization, and maturation processes. Importantly, pharmacological compounds targeting distinct members of the Notch signalling pathway have been used in the clinics for cancer therapy. However, the underlying mechanisms that support the variety of outcomes triggered by Notch in apparently opposite contexts such as angiogenesis and vascular homeostasis remain unknown. In recent years, advances in -omics technologies together with mosaic analysis and high molecular, cellular and temporal resolution studies have allowed a better understanding of the mechanisms driven by the Notch signalling pathway in different endothelial contexts. In this review we will focus on the main findings that revisit the role of Notch signalling in vascular biology. We will also discuss potential future directions and technologies that will shed light on the puzzling role of Notch during endothelial growth and homeostasis. Addressing these open questions may allow the improvement and development of therapeutic strategies based on modulation of the Notch signalling pathway.

Role of receptor tyrosine kinases mediated signal transduction pathways in tumor growth and angiogenesis-New insight and futuristic vision

In the past two decades, significant progress has been made in the past two decades towards the understanding of the basic mechanisms underlying cancer growth and angiogenesis. In this context, receptor tyrosine kinases (RTKs) play a pivotal role in cell proliferation, differentiation, growth, motility, invasion, and angiogenesis, all of which contribute to tumor growth and progression. Mutations in RTKs lead to abnormal signal transductions in several pathways such as Ras-Raf, MEK-MAPK, PI3K-AKT and mTOR pathways, affecting a wide range of biological functions including cell proliferation, survival, migration and vascular permeability. Increasing evidence demonstrates that multiple kinases are involved in angiogenesis including RTKs such as vascular endothelial growth factor, platelet derived growth factor, epidermal growth factor, insulin-like growth factor-1, macrophage colony-stimulating factor, nerve growth factor, fibroblast growth factor, Hepatocyte Growth factor, Tie 1 & 2, Tek, Flt-3, Flt-4 and Eph receptors. Overactivation of RTKs and its downstream regulation is implicated in tumor initiation and angiogenesis, representing one of the hallmarks of cancer. This review discusses the role of RTKs, PI3K, and mTOR, their involvement, and their implication in pro-oncogenic cellular processes and angiogenesis with effective approaches and newly approved drugs to inhibit their unrestrained action.

NOTCH and EZH2 collaborate to repress PTEN expression in breast cancer

Downregulation of the PTEN tumor suppressor transcript is frequent in breast cancer and associates with poor prognosis and triple-negative breast cancer (TNBC) when comparing breast cancers to one another. Here we show that in almost all cases, when comparing breast tumors to adjacent normal ducts, PTEN expression is decreased and the PRC2-associated methyltransferase EZH2 is increased. We further find that when comparing breast cancer cases in large cohorts, EZH2 inversely correlates with PTEN expression. Within the highest EZH2 expressing group, NOTCH alterations are frequent, and also associate with decreased PTEN expression. We show that repression of PTEN occurs through the combined action of NOTCH (NOTCH1 or NOTCH2) and EZH2 alterations in a subset of breast cancers. In fact, in cases harboring NOTCH1 mutation or a NOTCH2 fusion gene, NOTCH drives EZH2, HES-1, and HEY-1 expression to repress PTEN transcription at the promoter, which may contribute to poor prognosis in this subgroup. Restoration of PTEN expression can be achieved with an EZH2 inhibitor (UNC1999), a γ-secretase inhibitor (Compound E), or knockdown of EZH2 or NOTCH. These findings elucidate a mechanism of transcriptional repression of PTEN induced by NOTCH1 or NOTCH2 alterations, and identifies actionable signaling pathways responsible for driving a large subset of poor-prognosis breast cancers.

Pappas et al. show that the combination of NOTCH and EZH2 alterations drive transcriptional repression of PTEN through reversible epigenetic modification of the PTEN promoter. These results suggest an actionable target for treating poor-prognosis breast cancer.

Tumour angiogenesis normalized by myo-inositol trispyrophosphate alleviates hypoxia in the microenvironment and promotes antitumor immune response

Pathologic angiogenesis directly responds to tumour hypoxia and controls the molecular/cellular composition of the tumour microenvironment, increasing both immune tolerance and stromal cooperation with tumour growth. Myo-inositol-trispyrophosphate (ITPP) provides a means to achieve stable normalization of angiogenesis. ITPP increases intratumour oxygen tension (pO₂ ) and stabilizes vessel normalization through activation of endothelial Phosphatase-and-Tensin-homologue (PTEN). Here, we show that the tumour reduction due to the ITPP-induced modification of the tumour microenvironment by elevating pO₂ affects the phenotype and properties of the immune infiltrate. Our main observations are as follows: a relative change in the M1 and M2 macrophage-type proportions, increased proportions of NK and CD8⁺ T cells, and a reduction in Tregs and Th2 cells. We also found, in vivo and in vitro, that the impaired access of PD1⁺ NK cells to tumour cells is due to their adhesion to PD-L1⁺ /PD-L2⁺ endothelial cells in hypoxia. ITPP treatment strongly reduced PD-L1/PD-L2 expression on CD45+/CD31+ cells, and PD1⁺ cells were more numerous in the tumour mass. CTLA-4⁺ cell numbers were stable, but level of expression decreased. Similarly, CD47⁺ cells and expression were reduced. Consequently, angiogenesis normalization induced by ITPP is the mean to revert immunosuppression into an antitumor immune response. This brings a key adjuvant effect to improve the efficacy of chemo/radio/immunotherapeutic strategies for cancer treatment.

Tumor Hypoxia Regulates Immune Escape/Invasion: Influence on Angiogenesis and Potential Impact of Hypoxic Biomarkers on Cancer Therapies

The environmental and metabolic pressures in the tumor microenvironment (TME) play a key role in molding tumor development by impacting the stromal and immune cell fractions, TME composition and activation. Hypoxia triggers a cascade of events that promote tumor growth, enhance resistance to the anti-tumor immune response and instigate tumor angiogenesis. During growth, the developing angiogenesis is pathological and gives rise to a haphazardly shaped and leaky tumor vasculature with abnormal properties. Accordingly, aberrantly vascularized TME induces immunosuppression and maintains a continuous hypoxic state. Normalizing the tumor vasculature to restore its vascular integrity, should hence enhance tumor perfusion, relieving hypoxia, and reshaping anti-tumor immunity. Emerging vascular normalization strategies have a great potential in achieving a stable normalization, resulting in mature and functional blood vessels that alleviate tumor hypoxia. Biomarkers enabling the detection and monitoring of tumor hypoxia could be highly advantageous in aiding the translation of novel normalization strategies to clinical application, alone, or in combination with other treatment modalities, such as immunotherapy.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

Endothelial sprouting, proliferation, or senescence: tipping the balance from physiology to pathology

Therapeutic modulation of vascular cell proliferation and migration is essential for the effective inhibition of angiogenesis in cancer or its induction in cardiovascular disease. The general view is that an increase in vascular growth factor levels or mitogenic stimulation is beneficial for angiogenesis, since it leads to an increase in both endothelial proliferation and sprouting. However, several recent studies showed that an increase in mitogenic stimuli can also lead to the arrest of angiogenesis. This is due to the existence of intrinsic signaling feedback loops and cell cycle checkpoints that work in synchrony to maintain a balance between endothelial proliferation and sprouting. This balance is tightly and effectively regulated during tissue growth and is often deregulated or impaired in disease. Most therapeutic strategies used so far to promote vascular growth simply increase mitogenic stimuli, without taking into account its deleterious effects on this balance and on vascular cells. Here, we review the main findings on the mechanisms controlling physiological vascular sprouting, proliferation, and senescence and how those mechanisms are often deregulated in acquired or congenital cardiovascular disease leading to a diverse range of pathologies. We also discuss alternative approaches to increase the effectiveness of pro-angiogenic therapies in cardiovascular regenerative medicine.

Apelin signaling drives vascular endothelial cells toward a pro-angiogenic state

To form new blood vessels (angiogenesis), endothelial cells (ECs) must be activated and acquire highly migratory and proliferative phenotypes. However, the molecular mechanisms that govern these processes are incompletely understood. Here, we show that Apelin signaling functions to drive ECs into such an angiogenic state. Zebrafish lacking Apelin signaling exhibit defects in endothelial tip cell morphology and sprouting. Using transplantation experiments, we find that in mosaic vessels, wild-type ECs leave the dorsal aorta (DA) and form new vessels while neighboring ECs defective in Apelin signaling remain in the DA. Mechanistically, Apelin signaling enhances glycolytic activity in ECs at least in part by increasing levels of the growth-promoting transcription factor c-Myc. Moreover, APELIN expression is regulated by Notch signaling in human ECs, and its function is required for the hypersprouting phenotype in Delta-like 4 (Dll4) knockdown zebrafish embryos. These data provide new insights into fundamental principles of blood vessel formation and Apelin signaling, enabling a better understanding of vascular growth in health and disease.

Phosphoinositide 3-Kinase-Regulated Pericyte Maturation Governs Vascular Remodeling

BACKGROUND

Pericytes regulate vessel stabilization and function, and their loss is associated with diseases such as diabetic retinopathy or cancer. Despite their physiological importance, pericyte function and molecular regulation during angiogenesis remain poorly understood.

METHODS

To decipher the transcriptomic programs of pericytes during angiogenesis, we crossed Pdgfrb(BAC)-CreER^T2 mice into RiboTag^flox/flox mice. Pericyte morphological changes were assessed in mural cell-specific R26-mTmG reporter mice, in which low doses of tamoxifen allowed labeling of single-cell pericytes at high resolution. To study the role of phosphoinositide 3-kinase (PI3K) signaling in pericyte biology during angiogenesis, we used genetic mouse models that allow selective inactivation of PI3Kα and PI3Kβ isoforms and their negative regulator phosphate and tensin homolog deleted on chromosome 10 (PTEN) in mural cells.

RESULTS

At the onset of angiogenesis, pericytes exhibit molecular traits of cell proliferation and activated PI3K signaling, whereas during vascular remodeling, pericytes upregulate genes involved in mature pericyte cell function, together with a remarkable decrease in PI3K signaling. Immature pericytes showed stellate shape and high proliferation, and mature pericytes were quiescent and elongated. Unexpectedly, we demonstrate that PI3Kβ, but not PI3Kα, regulates pericyte proliferation and maturation during vessel formation. Genetic PI3Kβ inactivation in pericytes triggered early pericyte maturation. Conversely, unleashing PI3K signaling by means of PTEN deletion delayed pericyte maturation. Pericyte maturation was necessary to undergo vessel remodeling during angiogenesis.

CONCLUSIONS

Our results identify new molecular and morphological traits associated with pericyte maturation and uncover PI3Kβ activity as a checkpoint to ensure appropriate vessel formation. In turn, our results may open new therapeutic opportunities to regulate angiogenesis in pathological processes through the manipulation of pericyte PI3Kβ activity.

miR-136-3p targets PTEN to regulate vascularization and bone formation and ameliorates alcohol-induced osteopenia

Alcohol consumption is regarded as one of the leading risk factors for secondary osteopenia. Coupled angiogenesis and osteogenesis via distinct type-H vessels orchestrates subtle biological processes of bone homeostasis. The dysfunction of angiogenesis and osteogenesis contributes to decreased bone mass during the development of osteopenia. Herein, we identified microRNA-136-3p was remarkedly downregulated in the mouse model of alcohol-induced osteopenia. Following the alcohol administration, downregulated microRNA-136-3p significantly suppressed vascularization and osteogenic differentiation in human umbilical vein endothelial cells (HUVECs) and bone mesenchymal stem cells (BMSCs), respectively. Furthermore, microRNA-136-3p could target phosphatase and tensin homolog deleted on chromosome ten (PTEN) in both HUVECs and BMSCs, thus substantially modulating the capacity of vessel formation and osteogenic differentiation. In the mouse model, microRNA-136-3p Agomir ameliorated alcohol-induced osteopenia, with the concomitant restoration of bone mass and type-H vessel formation. For the first time, this study demonstrated the pivotal role of microRNA-136-3p/PTEN axis in regulations of vascularization and bone formation, which might become the potential therapeutic target of alcohol-induced bone loss.

Is there a causal link between PTEN deficient tumors and immunosuppressive tumor microenvironment?

The PTEN tumor suppressor is the second most commonly inactivated gene across cancer types. While it's role in PI3K/AKT and DNA damage pathways are clear, increasing evidences suggest that PTEN may also promote anti-tumor immunity. PTEN-deficient tumors are characterized by (i) reduced levels of cytotoxic T cells, helper T cells and NK cells, (ii) elevated pro-oncogenic inflammatory cytokines like CCL2 and (iii) increased levels of immunosuppressive cells such as MDSCs and Tregs. An intriguing possibility is that link between PTEN and anti-tumor immunity is mediated by the interferon signaling pathway. In this review, we summarize the evidences for the mechanistic link between PTEN deficiency and immunosuppressive tumor microenvironment and the interferon signaling pathway. We further discuss how the link between these pathways can be exploited for development of personalized immunotherapy for patients with PTEN deficient tumors.

ΜicroRNA-221 participates in cerebral ischemic stroke by modulating endothelial cell function by regulating the PTEN/PI3K/AKT pathway

An effective method to improve the blood supply of brain tissue is by angiogenesis, which is crucial for the prognosis of patients with cerebral ischemic stroke (CIS). Therefore, angiogenesis has been a focus of CIS research in recent years. The present study aimed to investigate the expression of microRNA (miR)-221 in patients with CIS and to explore the effect of miR-221 on endothelial cell function. The level of miR-221 was detected using reverse transcription-quantitative PCR (RT-qPCR). The relationship between miR-221 and phosphatase and tensin homolog (PTEN) was predicted and confirmed by bioinformatics and dual luciferase reporter assay. Cell viability, migration and invasion, and cell apoptosis were determined using MTT assay, Transwell assay and flow cytometry respectively. Tube formation in human umbilical vein endothelial cells (HUVECs) was determined by performing the tube formation assay. In addition, protein levels were measured using western blot analysis. The results of the current study indicated that miR-221 levels were significantly decreased in the peripheral blood of patients with CIS. PTEN was confirmed to be a direct target of miR-221. Downregulation of miR-221 significantly inhibited the function of HUVECs as evidenced by the decreased cell viability, migration and invasion with increased cell apoptosis and tube formation inhibition. miR-221 upregulation produced the reverse effects, whilst all the effects of miR-221 upregulation on HUVECs were reversed by PTEN overexpression. The PI3K/AKT pathway was identified to be involved in the regulation of miR-221 on HUVECs. In conclusion, miR-221 was downregulated in CIS patients, and it promoted the function of HUVECs by regulating the PTEN/PI3K/AKT pathway in vitro, suggesting the ability to promote angiogenesis. Therefore, miR-221 may be a novel and promising therapeutic target for CIS treatment.

Revisiting PI3-kinase signalling in angiogenesis

PI3Ks belong to a family of lipid kinases that comprises eight isoforms. They phosphorylate the third position of the inositol ring present in phosphatidylinositol lipids and, in turn, activate a broad range of proteins. The PI3K pathway regulates primal cellular responses, including proliferation, migration, metabolism and vesicular traffic. These processes are fundamental for endothelial cell function during sprouting angiogenesis, the most common type of blood vessel formation. Research in animal models has revealed key functions of PI3K family members and downstream effectors in angiogenesis. In addition, perturbations in PI3K signalling have been associated with aberrant vascular growth including tumour angiogenesis and vascular malformations. Together, this highlights that endothelial cells are uniquely sensitive to fluctuations in PI3K signalling. Here, we aim to update the current view on this important signalling cue in physiological and pathological blood vessel growth.

Activation of the STAT3/microRNA-21 pathway participates in angiotensin II-induced angiogenesis

Angiotensin II (AngII) facilitates angiogenesis that is associated with the continuous progression of atherosclerotic plaques, but the underlying mechanisms are still not fully understood. Several microRNAs (miRNAs) have been shown to promote angiogenesis; however, whether miRNAs play a crucial role in AngII-induced angiogenesis remains unclear. This study evaluated the functional involvement of miRNA-21 (miR-21) in the AngII-mediated proangiogenic response in human microvascular endothelial cells (HMECs). We found that AngII exerted a proangiogenic role, indicated by the promotion of proliferation, migration, and tube formation in HMECs. Next, miR-21 was found to be upregulated in AngII-treated HMECs, and its specific inhibitor potently blocked the proangiogenic effects of AngII. Subsequently, we focused on the constitutive activation of STAT3 in the AngII-mediated proangiogenic process. Bioinformatic analysis indicated that STAT3 acted as a transcription factor initiating miR-21 expression, which was verified by ChIP-PCR. A reporter assay further identified three functional binding sites of STAT3 in the miR-21 promoter region. Moreover, phosphatase and tensin homolog (PTEN) was recognized as a target of miR-21, and STAT3 inhibition restored AngII-induced reduction in PTEN. Similarly, the STAT3/miR-21 axis was shown to mediate AngII-provoked angiogenesis in vivo, which was demonstrated by using the appropriate inhibitors. Our data suggest that AngII was involved in proangiogenic responses through miR-21 upregulation and reduced PTEN expression, which was, at least in part, linked to STAT3 signaling. The present study provides novel insights into AngII-induced angiogenesis and suggests potential treatment strategies for attenuating the progression of atherosclerotic lesions and preventing atherosclerosis complications.

ZNF774 is a potent suppressor of hepatocarcinogenesis through dampening the NOTCH2 signaling

Discerning oncogenic drivers from passengers remain a major effort in understanding of the essence of the initiation and development of hepatocellular carcinoma (HCC), which is the most common primary liver malignancy and the third leading cause of cancer mortality worldwide. Here we report that ZNF774, a novel zinc-finger protein, inhibits the proliferation and invasion of HCC cells. Molecular characterization of this protein indicated that ZNF774 acts as a transcription repressor, and interrogation of ZNF774 interactome by affinity purification-coupled mass spectrometry revealed that ZNF774 is physically associated with the Mi-2/nucleosome remodeling and deacetylase (NuRD) complex in cells. Genome-wide identification of the transcriptional targets of the ZNF774/NuRD complex by ChIP-seq indicated that ZNF774 represses a cohort of genes including NOTCH2 that are critically involved in the growth and mobility of HCC. We demonstrated that the ZNF774/NuRD complex inhibits the proliferation and invasion of HCC cells in vitro and suppresses HCC growth and metastasis in vivo. Importantly, the expression of ZNF774 is significantly downregulated in HCC, and low ZNF774 expression strongly correlated with high NOTCH2 expression, advanced pathological stages, and poor overall survival of the patients. Together, these results uncover a key role for the ZNF774/NuRD-NOTCH2 axis in hepatocarcinogenesis.

Notch pathway: a bistable inducer of biological noise?

Notch signalling pathway is central to development of metazoans. The pathway codes a binary fate switch. Upon activation, downstream signals contribute to resolution of fate dichotomies such as proliferation/differentiation or sub-lineage differentiation outcome. There is, however, an interesting paradox in the Notch signalling pathway. Despite remarkable predictability of fate outcomes instructed by the Notch pathway, the associated transcriptome is versatile and plastic. This inconsistency suggests the presence of an interface that compiles input from the plastic transcriptome of the Notch pathway but communicates only a binary output in biological decisions. Herein, we address the interface that determines fate outcomes. We provide an alternative hypothesis for the Notch pathway as a biological master switch that operates by induction of genetic noise and bistability in order to facilitate resolution of dichotomous fate outcomes in development.

PKM2 regulates endothelial cell junction dynamics and angiogenesis via ATP production

Angiogenesis, the formation of new blood vessels from pre-existing ones, occurs in pathophysiological contexts such as wound healing, cancer, and chronic inflammatory disease. During sprouting angiogenesis, endothelial tip and stalk cells coordinately remodel their cell-cell junctions to allow collective migration and extension of the sprout while maintaining barrier integrity. All these processes require energy, and the predominant ATP generation route in endothelial cells is glycolysis. However, it remains unclear how ATP reaches the plasma membrane and intercellular junctions. In this study, we demonstrate that the glycolytic enzyme pyruvate kinase 2 (PKM2) is required for sprouting angiogenesis in vitro and in vivo through the regulation of endothelial cell-junction dynamics and collective migration. We show that PKM2-silencing decreases ATP required for proper VE-cadherin internalization/traffic at endothelial cell-cell junctions. Our study provides fresh insight into the role of ATP subcellular compartmentalization in endothelial cells during angiogenesis. Since manipulation of EC glycolysis constitutes a potential therapeutic intervention route, particularly in tumors and chronic inflammatory disease, these findings may help to refine the targeting of endothelial glycolytic activity in disease.

Multifaceted Regulation of PTEN Subcellular Distributions and Biological Functions

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor gene frequently found to be inactivated in over 30% of human cancers. PTEN encodes a 54-kDa lipid phosphatase that serves as a gatekeeper of the phosphoinositide 3-kinase pathway involved in the promotion of multiple pro-tumorigenic phenotypes. Although the PTEN protein plays a pivotal role in carcinogenesis, cumulative evidence has implicated it as a key signaling molecule in several other diseases as well, such as diabetes, Alzheimer's disease, and autism spectrum disorders. This finding suggests that diverse cell types, especially differentiated cells, express PTEN. At the cellular level, PTEN is widely distributed in all subcellular compartments and organelles. Surprisingly, the cytoplasmic compartment, not the plasma membrane, is the predominant subcellular location of PTEN. More recently, the finding of a secreted 'long' isoform of PTEN and the presence of PTEN in the cell nucleus further revealed unexpected biological functions of this multifaceted molecule. At the regulatory level, PTEN activity, stability, and subcellular distribution are modulated by a fascinating array of post-translational modification events, including phosphorylation, ubiquitination, and sumoylation. Dysregulation of these regulatory mechanisms has been observed in various human diseases. In this review, we provide an up-to-date overview of the knowledge gained in the last decade on how different functional domains of PTEN regulate its biological functions, with special emphasis on its subcellular distribution. This review also highlights the findings of published studies that have reported how mutational alterations in specific PTEN domains can lead to pathogenesis in humans.

High mitogenic stimulation arrests angiogenesis

Appropriate therapeutic modulation of endothelial proliferation and sprouting is essential for the effective inhibition of angiogenesis in cancer or its induction in cardiovascular disease. The current view is that an increase in growth factor concentration, and the resulting mitogenic activity, increases both endothelial proliferation and sprouting. Here, we modulate mitogenic stimuli in different vascular contexts by interfering with the function of the VEGF and Notch signalling pathways at high spatiotemporal resolution in vivo. Contrary to the prevailing view, our results indicate that high mitogenic stimulation induced by VEGF, or Notch inhibition, arrests the proliferation of angiogenic vessels. This is due to the existence of a bell-shaped dose-response to VEGF and MAPK activity that is counteracted by Notch and p21, determining whether endothelial cells sprout, proliferate, or become quiescent. The identified mechanism should be considered to achieve optimal therapeutic modulation of angiogenesis.

High mitogenic stimuli have been suggested to promote endothelial cell proliferation and sprouting during angiogenesis. Here Pontes-Quero et al., by interfering with levels of VEGF and Notch signalling in single endothelial cells in vivo, find that high mitogenic stimuli instead arrest angiogenesis due to a bell-shaped dose-response to VEGF and MAPK activity that is counteracted by Notch and p21.

Vascular leakage caused by loss of Akt1 is associated with impaired mural cell coverage

Angiogenesis plays a critical role in embryo development, tissue repair, tumor growth and wound healing. In the present study, we investigated the role of the serine/threonine kinase Akt in angiogenesis. Silencing of Akt1 in human umbilical vein endothelial cells significantly inhibited vascular endothelial growth factor (VEGF)-induced capillary-like tube formation. Mice lacking Akt1 exhibited impaired retinal angiogenesis with delayed endothelial cell (EC) proliferation. In addition, VEGF-induced corneal angiogenesis and tumor development were significantly inhibited in mice lacking Akt1. Loss of Akt1 resulted in reduced angiogenic sprouting, as well as the proliferation of ECs and mural cells. Addition of culture supernatant of vascular smooth muscle cells (VSMCs) in which Akt1 was silenced suppressed tube formation, the stability of preformed tubes and the proliferation of ECs. In addition, attachment of VSMCs to ECs was significantly reduced in cells in which Akt1 was silenced. Mural cell coverage of retinal vasculature was reduced in mice lacking Akt1. Finally, mice lacking Akt1 showed severe retinal hemorrhage compared to the wild-type. These results suggest that the regulation of EC function and mural cell coverage by Akt1 is important for blood vessel maturation during angiogenesis.