An inside view: VEGF receptor trafficking and signaling

VEGF as a Key Actor in Recurrent Respiratory Papillomatosis: A Narrative Review

Recurrent respiratory papillomatosis (RRP) is a benign disease of the upper aerodigestive tract caused by human papillomavirus (HPV) types 6 and 11. The clinical course is unpredictable and some patients, especially younger children, experience a high rate of recurrence with a significant impact on their quality of life. The molecular mechanisms of HPV infection in keratinocytes have been extensively studied throughout the years, with particular regard to its role in causing malignant tumors, like cervical cancer and head and neck carcinomas. A minor but not negligible amount of the literature has investigated the molecular landscape of RRP patients, and some papers have studied the role of angiogenesis (the growth of blood vessels from pre-existing vasculature) in this disease. A central role in this process is played by vascular endothelial growth factor (VEGF), which activates different signaling cascades on multiple levels. The increased knowledge has led to the introduction of the VEGF inhibitor bevacizumab in recent years as an adjuvant treatment in some patients, with good results. This review summarizes the current evidence about the role of VEGF in the pathophysiology of RRP, the molecular pathways activated by binding with its receptors, and the current and future roles of anti-angiogenic treatment.

Phosphoproteomic profiling identifies DNMT1 as a key substrate of beta IV spectrin-dependent ERK/MAPK signaling in suppressing angiogenesis

βIV-spectrin is a membrane-associated cytoskeletal protein that maintains the structural stability of cell membranes and integral proteins such as ion channels and transporters. Its biological functions are best characterized in the brain and heart, although recently we discovered a fundamental new role in the vascular system. Using cellular and genetic mouse models, we reported that βIV-spectrin acts as a critical regulator of developmental and tumor-associated angiogenesis. βIV-spectrin was shown to selectively express in proliferating endothelial cells (EC) and suppress VEGF/VEGFR2 signaling by enhancing receptor internalization and degradation. Here we examined how these events impact the downstream kinase signaling cascades and target substrates. Based on quantitative phosphoproteomics, we found that βIV-spectrin significantly affects the phosphorylation of epigenetic regulatory enzymes in the nucleus, among which DNA methyltransferase 1 (DNMT1) was determined as a top substrate. Biochemical and immunofluorescence results showed that βIV-spectrin inhibits DNMT1 function by activating ERK/MAPK, which in turn phosphorylates DNMT1 at S717 to impede its nuclear localization. Given that DNMT1 controls the DNA methylation patterns genome-wide, and is crucial for vascular development, our findings suggest that epigenetic regulation is a key mechanism by which βIV-spectrin suppresses angiogenesis.

Microvesicles derived from dermal myofibroblasts modify the integrity of the blood and lymphatic barriers using distinct endocytosis pathways

Microvesicles (MVs) are a subtype of extracellular vesicles that can transfer biological information from their producer cells to target cells. This communication can in turn affect both normal and pathological processes. Mounting evidence has revealed that dermal wound myofibroblasts (Wmyo) produce MVs, which can transfer biomolecules impacting receptor cells such as human dermal microvascular endothelial cells (HDMECs). While the effects of MVs on HDMECs are generally well described in the literature, little is known about the transport of MVs across the HDMEC barrier, and their potential effect on the barrier integrity remains unknown. Here, we investigated these roles of Wmyo-derived MVs on two sub-populations of HDMECs, blood endothelial cells (BECs) and lymphatic endothelial cells (LECs). Using an in vitro model to mimic the endothelial barrier, we showed that MVs crossed the LEC barrier but not the BEC barrier. In addition, we demonstrated that MVs were able to influence the cell-cell junctions of HDMECs. Specifically, we observed that after internalization via the predominantly caveolin-dependent pathway, MVs induced the opening of junctions in BECs. Conversely, in LECs, MVs mainly use the macropinocytosis pathway and induce closure of these junctions. Moreover, proteins in the MV membrane were responsible for this effect, but not specifically those belonging to the VEGF family. Finally, we found that once the LEC barrier permeability was reduced by MV stimuli, MVs ceased to cross the barrier. Conversely, when the BEC barrier was rendered permeable following stimulation with MVs, they were subsequently able to cross the barrier via the paracellular pathway. Taken together, these results suggest that the study of Wmyo-derived MVs offers valuable insights into their interaction with the HDMEC barrier in the context of wound healing. They highlight the potential significance of these MVs in the overall process.

Endomucin selectively regulates vascular endothelial growth factor receptor-2 endocytosis through its interaction with AP2

The endothelial glycocalyx, located at the luminal surface of the endothelium, plays an important role in the regulation of leukocyte adhesion, vascular permeability, and vascular homeostasis. Endomucin (EMCN), a component of the endothelial glycocalyx, is a mucin-like transmembrane glycoprotein selectively expressed by venous and capillary endothelium. We have previously shown that knockdown of EMCN impairs retinal vascular development in vivo and vascular endothelial growth factor 165 isoform (VEGF165)-induced cell migration, proliferation, and tube formation by human retinal endothelial cells in vitro and that EMCN is essential for VEGF165-stimulated clathrin-mediated endocytosis and signaling of VEGF receptor 2 (VEGFR2). Clathrin-mediated endocytosis is an essential step in receptor signaling and is of paramount importance for a number of receptors for growth factors involved in angiogenesis. In this study, we further investigated the molecular mechanism underlying EMCN's involvement in the regulation of VEGF-induced endocytosis. In addition, we examined the specificity of EMCN's role in angiogenesis-related cell surface receptor tyrosine kinase endocytosis and signaling. We identified that EMCN interacts with AP2 complex, which is essential for clathrin-mediated endocytosis. Lack of EMCN did not affect clathrin recruitment to the AP2 complex following VEGF stimulation, but it is necessary for the interaction between VEGFR2 and the AP2 complex during endocytosis. EMCN does not inhibit VEGFR1 and FGFR1 internalization or their downstream activities since EMCN interacts with VEGFR2 but not VEGFR1 or FGFR1. Additionally, EMCN also regulates VEGF121-induced VEGFR2 phosphorylation and internalization.

Regulation of angiogenesis by endocytic trafficking mediated by cytoplasmic dynein 1 light intermediate chain 1

Dynein cytoplasmic 1 light intermediate chain 1 (LIC1, DYNC1LI1) is a core subunit of the dynein motor complex. The LIC1 subunit also interacts with various cargo adaptors to regulate Rab-mediated endosomal recycling and lysosomal degradation. Defects in this gene are predicted to alter dynein motor function, Rab binding capabilities, and cytoplasmic cargo trafficking. Here, we have identified a dync1li1 zebrafish mutant, harboring a premature stop codon at the exon 12/13 splice acceptor site, that displays increased angiogenesis. In vitro, LIC1-deficient human endothelial cells display increases in cell surface levels of the pro-angiogenic receptor VEGFR2, SRC phosphorylation, and Rab11-mediated endosomal recycling. In vivo, endothelial-specific expression of constitutively active Rab11a leads to excessive angiogenesis, similar to the dync1li1 mutants. Increased angiogenesis is also evident in zebrafish harboring mutations in rilpl1/2, the adaptor proteins that promote Rab docking to Lic1 to mediate lysosomal targeting. These findings suggest that LIC1 and the Rab-adaptor proteins RILPL1 and 2 restrict angiogenesis by promoting degradation of VEGFR2-containing recycling endosomes. Disruption of LIC1- and RILPL1/2-mediated lysosomal targeting increases Rab11-mediated recycling endosome activity, promoting excessive SRC signaling and angiogenesis.

Epsin Endocytic Adaptor Proteins in Angiogenic and Lymphangiogenic Signaling

Circulating vascular endothelial growth factor (VEGF) ligands and receptors are central regulators of vasculogenesis, angiogenesis, and lymphangiogenesis. In response to VEGF ligand binding, VEGF receptor tyrosine kinases initiate the chain of events that transduce extracellular signals into endothelial cell responses such as survival, proliferation, and migration. These events are controlled by intricate cellular processes that include the regulation of gene expression at multiple levels, interactions of numerous proteins, and intracellular trafficking of receptor-ligand complexes. Endocytic uptake and transport of macromolecular complexes through the endosome-lysosome system helps fine-tune endothelial cell responses to VEGF signals. Clathrin-dependent endocytosis remains the best understood means of macromolecular entry into cells, although the importance of non-clathrin-dependent pathways is increasingly recognized. Many of these endocytic events rely on adaptor proteins that coordinate internalization of activated cell-surface receptors. In the endothelium of both blood and lymphatic vessels, epsins 1 and 2 are functionally redundant adaptors involved in receptor endocytosis and intracellular sorting. These proteins are capable of binding both lipids and proteins and are important for promoting curvature of the plasma membrane as well as binding ubiquitinated cargo. Here, we discuss the role of epsin proteins and other endocytic adaptors in governing VEGF signaling in angiogenesis and lymphangiogenesis and discuss their therapeutic potential as molecular targets.

Unraveling the Angiogenic Puzzle: Pre-Treatment sVEGFR1 and sVEGFR2 Levels as Promising Prognostic Indicators in Early-Stage Breast Cancer Patients

Despite the advancements in breast cancer (BrC) diagnosis and treatment, a considerable proportion of patients with early-stage disease still experience local recurrence or metastasis. This study aimed to assess the levels of specific angiogenic parameters in the EDTA plasma of BrC patients before and after treatment and to explore their clinical and prognostic significance. The levels of vascular endothelial growth factor A (VEGF-A), soluble form of vascular endothelial growth factor receptor type 1 (sVEGFR1), and soluble form of vascular endothelial growth factor receptor type 2 (sVEGFR2) were measured in 84 early BrC patients, both prior to surgery and within a median time of nine months post-treatment. Prognostic significance was evaluated using Kaplan-Meier survival and Cox regression analyses. Linear regression models were employed to examine the independent impact of selected angiogenic factors on DFS in breast cancer patients. The results of uni- and multivariate analyses indicated that a pre-treatment concentration of sVEGFR1 above 30.99 pg/mL was associated with improved disease-free survival (DFS) (p < 0.0001 for both analyses), while a pre-treatment concentration of sVEGFR2 above 9475.67 pg/mL was associated with an increased risk of BrC relapse (p < 0.0001 for both analyses). Additionally, a post-treatment concentration of sVEGFR2 above 7361.71 pg/mL was associated with better overall survival (OS) based on the Kaplan-Meier survival analysis (p = 0.0141). Furthermore, linear regression models revealed a significant inverse association between pre-treatment levels of sVEGFR1 and the risk of relapse (standardized β -0.2578, p = 0.0499) and a significant positive association of VEGF-A levels with the risk of recurrence (standardized β 0.2958, p = 0.0308). In conclusion, the findings suggest that both pre- and post-treatment levels of sVEGFR1 and sVEGFR2 may hold promise as potential prognostic markers for BrC patients.

The Multi-Kinase Inhibitor RepSox Enforces Barrier Function in the Face of Both VEGF and Cytokines

The therapeutic benefit provided by anti-vascular endothelial growth factor (VEGF) for patients with vision-threatening conditions such as diabetic retinopathy (DR) demonstrates the important role of VEGF in this affliction. Cytokines, which can be elevated in the vitreous of patients with DR, promote leakage of retinal blood vessels, and may also contribute to pathology, especially in those patients for whom anti-VEGF does not provide adequate benefit. In this in vitro study using primary human retinal endothelial cells, we compared anti-VEGF with the (transforming growth factor beta) TGFβ receptor inhibitor RepSox (RS) for their ability to enforce barrier function in the face of VEGF, cytokines, and the combination of both. RS was superior to anti-VEGF because it prevented permeability in response to VEGF, cytokines, and their combination, whereas anti-VEGF was effective against VEGF alone. The inhibitory effect of RS was associated with suppression of both agonist-induced pore formation and disorganization of adherens junctions. RS-mediated inhibition of the TGFβ pathway and increased expression of claudin-5 did not adequately explain how RS stabilized the endothelial cell barrier. Finally, RS not only prevented barrier relaxation, but also completely or partially reclosed a barrier relaxed with tumor necrosis factor α (TNF α) or VEGF, respectively. These studies demonstrate that RS stabilized the endothelial barrier in the face of both cytokines and VEGF, and thereby identify RS as a therapeutic that has the potential to overcome permeability driven by multiple agonists that play a role in the pathology of DR.

ARL13B promotes angiogenesis and glioma growth by activating VEGFA-VEGFR2 signaling

BACKGROUND

Tumor angiogenesis is essential for solid tumor progression, invasion and metastasis. The aim of this study was to identify potential signaling pathways involved in tumor angiogenesis.

METHODS

Genetically engineered mouse models were used to investigate the effects of endothelial ARL13B(ADP-ribosylation factor-like GTPase 13B) over-expression and deficiency on retinal and cerebral vasculature. An intracranially transplanted glioma model and a subcutaneously implanted melanoma model were employed to examine the effects of ARL13B on tumor growth and angiogenesis. Immunohistochemistry was used to measure ARL13B in glioma tissues, and scRNA-seq was used to analyze glioma and endothelial ARL13B expression. GST-fusion protein-protein interaction and co-immunoprecipitation assays were used to determine the ARL13B-VEGFR2 interaction. Immunobloting, qPCR, dual-luciferase reporter assay and functional experiments were performed to evaluate the effects of ARL13B on VEGFR2 activation.

RESULTS

Endothelial ARL13B regulated vascular development of both the retina and brain in mice. Also, ARL13B in endothelial cells regulated the growth of intracranially transplanted glioma cells and subcutaneously implanted melanoma cells by controlling tumor angiogenesis. Interestingly, this effect was attributed to ARL13B interaction with VEGFR2, through which ARL13B regulated the membrane and ciliary localization of VEGFR2 and consequently activated its downstream signaling in endothelial cells. Consistent with its oncogenic role, ARL13B was highly expressed in human gliomas, which was well correlated with the poor prognosis of glioma patients. Remarkably, ARL13B, transcriptionally regulated by ZEB1, enhanced the expression of VEGFA by activating Hedgehog signaling in glioma cells.

CONCLUSIONS

ARL13B promotes angiogenesis and tumor growth by activating VEGFA-VEGFR2 signaling. Thus, targeting ARL13B might serve as a potential approach for developing an anti-glioma or anti-melanoma therapy.

Arf6 Regulates Endocytosis and Angiogenesis by Promoting Filamentous Actin Assembly

Clathrin-mediated endocytosis (CME) is a process vital to angiogenesis as well as general vascular homeostasis. In pathologies where supraphysiological growth factor signaling underlies disease etiology, such as in diabetic retinopathy and solid tumors, strategies to limit chronic growth factor signaling by way of CME have been shown to have tremendous clinical value. ADP ribosylation factor 6 (Arf6) is a small GTPase that promotes the assembly of actin necessary for CME. In its absence, growth factor signaling is greatly diminished, which has been shown to ameliorate pathological signaling input in diseased vasculature. However, it is less clear if there are bystander effects related to loss of Arf6 on angiogenic behaviors. Our goal was to provide a analysis of Arf6’s function in angiogenic endothelium, focusing on its role in lumenogenesis as well as its relation to actin and CME. We found that Arf6 localized to both filamentous actin and sites of CME in 2-dimensional culture. Loss of Arf6 distorted both apicobasal polarity and reduced the total cellular filamentous actin content, and this may be the primary driver underlying gross dysmorphogenesis during angiogenic sprouting in its absence. Our findings highlight that endothelial Arf6 is a potent mediator of both actin regulation and CME.

VEGF-A enhances the cytotoxic function of CD4+ cytotoxic T cells via the VEGF-receptor 1/VEGF-receptor 2/AKT/mTOR pathway

BACKGROUND

CD4⁺ cytotoxic T cells (CD4 CTLs) are CD4⁺ T cells with major histocompatibility complex-II-restricted cytotoxic function. Under pathologic conditions, CD4 CTLs hasten the development of autoimmune disease or viral infection by enhancing cytotoxicity. However, the regulators of the cytotoxicity of CD4 CTLs are not fully understood.

METHODS

To explore the potential regulators of the cytotoxicity of CD4 CTLs, bulk RNA and single-cell RNA sequencing (scRNA-seq), enzyme-linked immunosorbent assay, flow cytometry, quantitative PCR, and in-vitro stimulation and inhibition assays were performed.

RESULTS

In this study, we found that VEGF-A promoted the cytotoxicity of CD4 CTLs through scRNA-seq and flow cytometry. Regarding the specific VEGF receptor (R) involved, VEGF-R1/R2 signaling was activated in CD4 CTLs with increased cytotoxicity, and the VEGF-A effects were inhibited when anti-VEGF-R1/R2 neutralizing antibodies were applied. Mechanistically, VEGF-A treatment activated the AKT/mTOR pathway in CD4 CTLs, and the increases of cytotoxic molecules induced by VEGF-A were significantly reduced when the AKT/mTOR pathway was inhibited.

CONCLUSION

In conclusion, VEGF-A enhances the cytotoxicity of CD4 CTLs through the VEGF-R1/VEGF-R2/AKT/mTOR pathway, providing insights for the development of novel treatments for disorders associated with CD4 CTLs.

Protein disulfide isomerase A1 as a novel redox sensor in VEGFR2 signaling and angiogenesis

VEGFR2 signaling in endothelial cells (ECs) is regulated by reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria, which plays an important role in postnatal angiogenesis. However, it remains unclear how highly diffusible ROS signal enhances VEGFR2 signaling and reparative angiogenesis. Protein disulfide isomerase A1 (PDIA1) functions as an oxidoreductase depending on the redox environment. We hypothesized that PDIA1 functions as a redox sensor to enhance angiogenesis. Here we showed that PDIA1 co-immunoprecipitated with VEGFR2 or colocalized with either VEGFR2 or an early endosome marker Rab5 at the perinuclear region upon stimulation of human ECs with VEGF. PDIA1 silencing significantly reduced VEGF-induced EC migration, proliferation and spheroid sprouting via inhibiting VEGFR2 signaling. Mechanistically, VEGF stimulation rapidly increased Cys-OH formation of PDIA1 via the NOX4-mitochondrial ROS axis. Overexpression of "redox-dead" mutant PDIA1 with replacement of the active four Cys residues with Ser significantly inhibited VEGF-induced PDIA1-CysOH formation and angiogenic responses via reducing VEGFR2 phosphorylation. Pdia1+/- mice showed impaired angiogenesis in developmental retina and Matrigel plug models as well as ex vivo aortic ring sprouting model. Study using hindlimb ischemia model revealed that PDIA1 expression was markedly increased in angiogenic ECs of ischemic muscles, and that ischemia-induced limb perfusion recovery and neovascularization were impaired in EC-specific Pdia1 conditional knockout mice. These results suggest that PDIA1 can sense VEGF-induced H2O2 signal via CysOH formation to promote VEGFR2 signaling and angiogenesis in ECs, thereby enhancing postnatal angiogenesis. The oxidized PDIA1 is a potential therapeutic target for treatment of ischemic vascular diseases.

SENP6-Mediated deSUMOylation of VEGFR2 Enhances Its Cell Membrane Transport in Angiogenesis

Angiogenesis is a significant pathogenic characteristic of diabetic microangiopathy. Advanced glycation end products (AGEs) are considerably elevated in diabetic tissues and can affect vascular endothelial cell shape and function. Regulation of the vascular endothelial growth factor (VEGF)-VEGF receptor 2 (VEGFR2) signaling pathway is a critical mechanism in the regulation of angiogenesis, and VEGFR2 activity can be modified by post-translational changes. However, little research has been conducted on the control of small ubiquitin-related modifier (SUMO)-mediated VEGFR2 alterations. The current study investigated this using human umbilical vein endothelial cells (HUVECs) in conjunction with immunoblotting and immunofluorescence. AGEs increased Nrf2 translocation to the nucleus and promoted VEGFR2 expression. They also increased the expression of sentrin/SUMO-specific protease 6 (SENP6), which de-SUMOylated VEGFR2, and immunofluorescence indicated a reduction in VEGFR2 accumulation in the Golgi and increased VEGFR2 transport from the Golgi to the cell membrane surface via the coatomer protein complex subunit beta 2. VEGFR2 on the cell membrane was linked to VEGF generated by pericytes, triggering the VEGF signaling cascade. In conclusion, this study demonstrates that SENP6 regulates VEGFR2 trafficking from the Golgi to the endothelial cell surface. The SENP6-VEGFR2 pathway plays a critical role in pathological angiogenesis.

Phenotypic and functional characterization of two coelomocyte subsets in Apostichopus japonicus

The hemocytes of invertebrates are composed of different cell subsets with different morphologies and structures. Different cell subsets have different immune functions, which play an important role in innate immune response against pathogens. However, the understanding of the classification of Apostichopus japonicus coelomocytes and the molecular basis of immune function of different cell subsets is very limited. In this study, two coelomocyte subpopulations of A. japonicus were isolated by Percoll density gradient centrifugation. They were identified from their morphological and structural characteristics, namely, spherical cells with a size of 10-12 μm spherical in shape and a large number of small granules inside; lymphocyte-like cells with a size of 4-5 μm spherical or oval in shape, and 1-3 filopodia. Functionally, the phagocytic capacity and lysosomal activity in spherical cells were significantly greater than those in lymphocyte-like cells. The results suggest that spherical cells may play a more critical role in the immune responses. Meanwhile, transcriptome sequencing analysis was performed to further clarify the functional differences between the two cell subsets. The data indicated significantly different gene expression patterns in them. Spherical cells tend to participate in immune defense, whereas lymphocyte-like cells tend to participate in energy metabolism. In addition, lymphocyte-like cells may convert oxidative phosphorylation to glycolysis by changing the manner of energy metabolism to quickly adapt to the energy demand of external stimuli. Spherical cells may respond to LPS stimulation through phagocytosis, and their response time is slower than that of lymphocyte-like cells. The expression of genes involved in endocytosis, phagocytosis, and lysosomal and humoral immunity in spherical cells was significantly higher than that in lymphocyte-like cells. These data provide valuable information for understanding the molecular basis of cellular and humoral immunity in A. japonicus.

Impact of Breaking up of Sitting Time on Anti-inflammatory Response Induced by Extracellular Vesicles

Physical inactivity and sedentary behaviors (SB) have promoted a dramatic increase in the incidence of a host of chronic disorders over the last century. The breaking up of sitting time (i.e., sitting to standing up transition) has been proposed as a promising solution in several epidemiological and clinical studies. In parallel to the large interest it initially created, there is a growing body of evidence indicating that breaking up prolonged sedentary time (i.e., > 7 h in sitting time) could reduce overall mortality risks by normalizing the inflammatory profile and cardiometabolic functions. Recent advances suggest that the latter health benefits, may be mediated through the immunomodulatory properties of extracellular vesicles. Primarily composed of miRNA, lipids, mRNA and proteins, these vesicles would influence metabolism and immune system functions by promoting M1 to M2 macrophage polarization (i.e., from a pro-inflammatory to anti-inflammatory phenotype) and improving endothelial function. The outcomes of interrupting prolonged sitting time may be attributed to molecular mechanisms induced by circulating angiogenic cells. Functionally, circulating angiogenic cells contribute to repair and remodel the vasculature. This effect is proposed to be mediated through the secretion of paracrine factors. The present review article intends to clarify the beneficial contributions of breaking up sitting time on extracellular vesicles formation and macrophage polarization (M1 and M2 phenotypes). Hence, it will highlight key mechanistic information regarding how breaking up sitting time protocols improves endothelial health by promoting antioxidant and anti-inflammatory responses in human organs and tissues.

VEGFR2 insufficiency enhances phosphotoxicity and undermines Klotho's protection against peritubular capillary rarefaction and kidney fibrosis

Vascular endothelial growth factor (VEGF) and its cognate receptor (VEGFR2) system are crucial for cell functions associated with angiogenesis and vasculogenesis. Klotho contributes to vascular health maintenance in the kidney and other organs in mammals, but it is unknown whether renoprotection by Klotho is dependent on VEGF/VEGFR2 signaling. We used heterozygous VEGFR2-haploinsufficient (VEGFR2+/-) mice resulting from heterozygous knockin of green fluorescent protein in the locus of fetal liver kinase 1 encoding VEGFR2 to test the interplay of Klotho, phosphate, and VEGFR2 in kidney function, the vasculature, and fibrosis. VEGFR2+/- mice displayed downregulated VEGF/VEGFR2 signaling in the kidney, lower density of peritubular capillaries, and accelerated kidney fibrosis, all of which were also found in the homozygous Klotho hypomorphic mice. High dietary phosphate induced higher plasma phosphate, greater peritubular capillary rarefaction, and more kidney fibrosis in VEGFR2+/- mice compared with wild-type mice. Genetic overexpression of Klotho significantly attenuated the elevated plasma phosphate, kidney dysfunction, peritubular capillary rarefaction, and kidney fibrosis induced by a high-phosphate diet in wild-type mice but only modestly ameliorated these changes in the VEGFR2+/- background. In cultured endothelial cells, VEGFR2 inhibition reduced free VEGFR2 but enhanced its costaining of an endothelial marker (CD31) and exacerbated phosphotoxicity. Klotho protein maintained VEGFR2 expression and attenuated high phosphate-induced cell injury, which was reduced by VEGFR2 inhibition. In conclusion, normal VEGFR2 function is required for vascular integrity and for Klotho to exert vascular protective and antifibrotic actions in the kidney partially through the regulation of VEGFR2 function.NEW & NOTEWORTHY This research paper studied the interplay of vascular endothelial growth factor receptor type 2 (VEGFR2), high dietary phosphate, and Klotho, an antiaging protein, in peritubular structure and kidney fibrosis. Klotho protein was shown to maintain VEGFR2 expression in the kidney and reduce high phosphate-induced cell injury. However, Klotho cytoprotection was attenuated by VEGFR2 inhibition. Thus, normal VEGFR2 function is required for vascular integrity and Klotho to exert vascular protective and antifibrotic actions in the kidney.

Capturing membrane trafficking events during 3D angiogenic development in vitro

OBJECTIVES

Vesicular trafficking dictates protein localization, functional activity, and half-life, providing a critically important regulatory step in tissue development; however, there is little information detailing endothelial-specific trafficking signatures. This is due, in part, to limitations in visualizing trafficking events in endothelial tissues. Our aim in this investigation was to explore the use of a 3-dimensional (3D) in vitro sprouting model to image endothelial membrane trafficking events.

METHODS

Endothelial cells were challenged to grow sprouts in a fibrin bead assay. Thereafter, spouts were transfected with fluorescent proteins and stained for various cell markers. Sprouts were then imaged for trafficking events using live and fixed-cell microscopy.

RESULTS

Our results demonstrate that fibrin bead sprouts have a strong apicobasal polarity marked by apical localization of proteins moesin and podocalyxin. Comparison of trafficking mediators Rab27a and Rab35 between 3D sprouts and 2D culture showed that vesicular carriers can be imaged at high resolution, exhibiting proper membrane polarity solely in 3D sprouts. Lastly, we imaged exocytic events of von Willebrand Factor and demonstrated a distinct imaging advantage for monitoring secretion events in 3D sprouts as compared with 2D culture.

CONCLUSIONS

Our results establish that the fibrin bead sprouting assay is well-suited for imaging of trafficking events during angiogenic growth.

Optimizing the Sunitinib for cardio-toxicity and thyro-toxicity by scaffold hopping approach

Sunitinib is a potent anti-cancer scaffold that acts as a VEGFR-2 inhibitor. Although the scaffold exhibits potent anti-cancer activity, it is cardiotoxic and also induces hypothyroidism. The current research aims to optimize the Sunitinib for cardio-toxicity and thyro-toxicity by scaffold hopping approach using the admetSAR server. The server has optimized the physico-chemical properties of Sunitinib, which were contributing to the cardiotoxicity and thyro-toxicity. The library of the optimized compounds was further screened by the molecular docking studies and results were validated by the MD simulation and DFT analysis for VEGFR-2 inhibition. Compounds 163 and 432 exhibited the highest affinity to VEGFR-2 receptor with minimal cardiotoxicity and thyro-toxicity. These two compounds could be the starting point for the further discovery of angiogenic inhibitors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-022-00125-1.

Gatekeeping role of Nf2/Merlin in vascular tip EC induction through suppression of VEGFR2 internalization

In sprouting angiogenesis, the precise mechanisms underlying how intracellular vascular endothelial growth factor receptor 2 (VEGFR2) signaling is higher in one endothelial cell (EC) compared with its neighbor and acquires the tip EC phenotype under a similar external cue are elusive. Here, we show that Merlin, encoded by the neurofibromatosis type 2 (NF2) gene, suppresses VEGFR2 internalization depending on VE-cadherin density and inhibits tip EC induction. Accordingly, endothelial Nf2 depletion promotes tip EC induction with excessive filopodia by enhancing VEGFR2 internalization in both the growing and matured vessels. Mechanistically, Merlin binds to the VEGFR2-VE-cadherin complex at cell-cell junctions and reduces VEGFR2 internalization-induced downstream signaling during tip EC induction. As a consequence, nonfunctional excessive sprouting occurs during tumor angiogenesis in EC-specific Nf2-deleted mice, leading to delayed tumor growth. Together, Nf2/Merlin is a crucial molecular gatekeeper for tip EC induction, capillary integrity, and proper tumor angiogenesis by suppressing VEGFR2 internalization.

KANK4 Promotes Arteriogenesis by Potentiating VEGFR2 Signaling in a TALIN-1-Dependent Manner

BACKGROUND

Arteriogenesis plays a critical role in maintaining adequate tissue blood supply and is related to a favorable prognosis in arterial occlusive diseases. Strategies aimed at promoting arteriogenesis have thus far not been successful because the factors involved in arteriogenesis remain incompletely understood. Previous studies suggest that evolutionarily conserved KANK4 (KN motif and ankyrin repeat domain-containing proteins 4) might involve in vertebrate vessel development. However, how the KANK4 regulates vessel function remains unknown. We aim to determine the role of endothelial cell-specifically expressed KANK4 in arteriogenesis.

METHODS

The role of KANK4 in regulating arteriogenesis was evaluated using Kank4^-/- and KANK4^iECOE mice. Molecular mechanisms underlying KANK4-potentiated arteriogenesis were investigated by employing RNA transcriptomic profiling and mass spectrometry analysis.

RESULTS

By analyzing Kank4-EGFP reporter mice, we showed that KANK4 was specifically expressed in endothelial cells. In particular, KANK4 displayed a dynamic expression pattern from being ubiquitously expressed in all endothelial cells of the developing vasculature to being explicitly expressed in the endothelial cells of arterioles and arteries in matured vessels. In vitro microfluidic chip-based vascular morphology analysis and in vivo hindlimb ischemia assays using Kank4^-/- and KANK4^iECOE mice demonstrated that deletion of KANK4 impaired collateral artery growth and the recovery of blood perfusion, whereas KANK4 overexpression leads to increased vessel caliber and blood perfusion. Bulk RNA sequencing and Co-immunoprecipitation/mass spectrometry (Co-IP/MS) analysis identified that KANK4 promoted EC proliferation and collateral artery remodeling through coupling VEGFR2 (vascular endothelial growth factor receptor 2) to TALIN-1, which augmented the activation of the VEGFR2 signaling cascade.

CONCLUSIONS

This study reveals a novel role for KANK4 in arteriogenesis in response to ischemia. KANK4 links VEGFR2 to TALIN-1, resulting in enhanced VEGFR2 activation and increased EC proliferation, highlighting that KANK4 is a potential therapeutic target for promoting arteriogenesis for arterial occlusive diseases.

Mediating EGFR-TKI Resistance by VEGF/VEGFR Autocrine Pathway in Non-Small Cell Lung Cancer

Simple Summary

Non-small cell lung cancer (NSCLC) patients acquire resistance to tyrosine kinase inhibitors (TKIs) via EGFR mutations or overexpression of vascular endothelial growth factor receptor-2 (VEGFR-2). In this study, we elucidated the mechanism of EGFR-TKI resistance mediated by VEGF/VEGFR in EGFR-mutated NSCLC cell lines and Erlotinib-resistant cell lines as compared to parental cell lines. Increased expression of VEGF, VEGFR-2, and NP1 was observed in Erlotinib-resistant cell lines. Furthermore, we observed an increased efficacy of Erlotinib in combination with a VEGFR-2 inhibitor in Erlotinib-resistant cell lines. Late-stage NSCLC patients with high expression of VEGFR-2 had shorter survival times compared to patients with low VEGFR-2 expression. These results indicate that VEGFR-2 may play a key role in EGFR-TKI resistance that can be overcome with a combination treatment of Erlotinib and a VEGFR-2 inhibitor, which may serve as an effective treatment option for NSCLC patients with EGFR mutations.

Abstract

NSCLC treatment includes targeting of EGFR with tyrosine kinase inhibitors (TKIs) such as Erlotinib; however, resistance to TKIs is commonly acquired through T790M EGFR mutations or overexpression of vascular endothelial growth factor receptor-2 (VEGFR-2). We investigated the mechanisms of EGFR-TKI resistance in NSCLC cell lines with EGFR mutations or acquired resistance to Erlotinib. These studies showed upregulated gene and protein expression of VEGF, VEGFR-2, and a VEGF co-receptor neuropilin-1 (NP-1) in Erlotinib-resistant (1.4–5.3-fold) and EGFR double-mutant (L858R and T790M; 4.1–8.3-fold) NSCLC cells compared to parental and EGFR single-mutant (L858R) NSCLC cell lines, respectively. Immunofluorescence and FACS analysis revealed increased expression of VEGFR-2 and NP-1 in EGFR-TKI-resistant cell lines compared to TKI-sensitive cell lines. Cell proliferation assays showed that treatment with a VEGFR-2 inhibitor combined with Erlotinib lowered cell survival in EGFR double-mutant NSCLC cells to 9% compared to 72% after treatment with Erlotinib alone. Furthermore, Kaplan–Meier analysis revealed shorter median survival in late-stage NSCLC patients with high vs. low VEGFR-2 expression (14 mos vs. 21 mos). The results indicate that VEGFR-2 may play a key role in EGFR-TKI resistance and that combined treatment of Erlotinib with a VEGFR-2 inhibitor may serve as an effective therapy in NSCLC patients with EGFR mutations.

βIV-spectrin as a stalk cell-intrinsic regulator of VEGF signaling

Defective angiogenesis underlies over 50 malignant, ischemic and inflammatory disorders yet long-term therapeutic applications inevitably fail, thus highlighting the need for greater understanding of the vast crosstalk and compensatory mechanisms. Based on proteomic profiling of angiogenic endothelial components, here we report β_IV-spectrin, a non-erythrocytic cytoskeletal protein, as a critical regulator of sprouting angiogenesis. Early loss of endothelial-specific β_IV-spectrin promotes embryonic lethality in mice due to hypervascularization and hemorrhagic defects whereas neonatal depletion yields higher vascular density and tip cell populations in developing retina. During sprouting, β_IV-spectrin expresses in stalk cells to inhibit their tip cell potential by enhancing VEGFR2 turnover in a manner independent of most cell-fate determining mechanisms. Rather, β_IV-spectrin recruits CaMKII to the plasma membrane to directly phosphorylate VEGFR2 at Ser984, a previously undefined phosphoregulatory site that strongly induces VEGFR2 internalization and degradation. These findings support a distinct spectrin-based mechanism of tip-stalk cell specification during vascular development.

Defective angiogenesis remains a high source of morbidity in multiple disorders. Here they show that β_IV-spectrin, a membrane-associated cytoskeletal protein, is essential for regulation of endothelial tip cell populations and VEGF signaling during sprouting angiogenesis.

Mechanoregulation of Vascular Endothelial Growth Factor Receptor 2 in Angiogenesis

The endothelial cells that compose the vascular system in the body display a wide range of mechanotransductive behaviors and responses to biomechanical stimuli, which act in concert to control overall blood vessel structure and function. Such mechanosensitive activities allow blood vessels to constrict, dilate, grow, or remodel as needed during development as well as normal physiological functions, and the same processes can be dysregulated in various disease states. Mechanotransduction represents cellular responses to mechanical forces, translating such factors into chemical or electrical signals which alter the activation of various cell signaling pathways. Understanding how biomechanical forces drive vascular growth in healthy and diseased tissues could create new therapeutic strategies that would either enhance or halt these processes to assist with treatments of different diseases. In the cardiovascular system, new blood vessel formation from preexisting vasculature, in a process known as angiogenesis, is driven by vascular endothelial growth factor (VEGF) binding to VEGF receptor 2 (VEGFR-2) which promotes blood vessel development. However, physical forces such as shear stress, matrix stiffness, and interstitial flow are also major drivers and effectors of angiogenesis, and new research suggests that mechanical forces may regulate VEGFR-2 phosphorylation. In fact, VEGFR-2 activation has been linked to known mechanobiological agents including ERK/MAPK, c-Src, Rho/ROCK, and YAP/TAZ. In vascular disease states, endothelial cells can be subjected to altered mechanical stimuli which affect the pathways that control angiogenesis. Both normalizing and arresting angiogenesis associated with tumor growth have been strategies for anti-cancer treatments. In the field of regenerative medicine, harnessing biomechanical regulation of angiogenesis could enhance vascularization strategies for treating a variety of cardiovascular diseases, including ischemia or permit development of novel tissue engineering scaffolds. This review will focus on the impact of VEGFR-2 mechanosignaling in endothelial cells (ECs) and its interaction with other mechanotransductive pathways, as well as presenting a discussion on the relationship between VEGFR-2 activation and biomechanical forces in the extracellular matrix (ECM) that can help treat diseases with dysfunctional vascular growth.

Cysteine oxidation of copper transporter CTR1 drives VEGFR2 signalling and angiogenesis

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) is essential for developmental and reparative angiogenesis. Reactive oxygen species (ROS) and copper (Cu) are also involved.in these processes. However, their inter-relationship is poorly understood. The role of endothelial Cu importer CTR1 in VEGFR2 signaling and angiogenesis in vivo is hitherto unknown. Here we show that CTR1 functions as a previously unrecognized redox sensor to promote angiogenesis in ECs. CTR1-depleted ECs showed reduced VEGF-induced VEGFR2 signaling and angiogenic responses. Mechanistically, CTR1 was rapidly sulfenylated at Cys189 in cytosolic C-terminus upon VEGF stimulation, which induced CTR1-VEGFR2 disulfide bond formation and their co-internalization to early endosomes, driving sustained VEGFR2 signaling. In vivo, EC-specific Ctr1-deficient mice or CRISPR/Cas9-generated “redox-dead” Cys to Ala Ctr1 knock-in mutant mice had impaired developmental and reparative angiogenesis. Thus, oxidation of CTR1 at Cys189 promotes VEGFR2 internalization and signaling to enhance angiogenesis. Our study uncovers an important mechanism for ROS sensing through CTR1 to drive neovascularization.

Defective Flow-Migration Coupling Causes Arteriovenous Malformations in Hereditary Hemorrhagic Telangiectasia

BACKGROUND

Activin receptor-like kinase 1 (ALK1) is an endothelial transmembrane serine threonine kinase receptor for BMP family ligands that plays a critical role in cardiovascular development and pathology. Loss-of-function mutations in the ALK1 gene cause type 2 hereditary hemorrhagic telangiectasia, a devastating disorder that leads to arteriovenous malformations. Here, we show that ALK1 controls endothelial cell polarization against the direction of blood flow and flow-induced endothelial migration from veins through capillaries into arterioles.

METHODS

Using Cre lines that recombine in different subsets of arterial, capillary-venous, or endothelial tip cells, we show that capillary-venous Alk1 deletion was sufficient to induce arteriovenous malformation formation in the postnatal retina.

RESULTS

ALK1 deletion impaired capillary-venous endothelial cell polarization against the direction of blood flow in vivo and in vitro. Mechanistically, ALK1-deficient cells exhibited increased integrin signaling interaction with vascular endothelial growth factor receptor 2, which enhanced downstream YAP/TAZ nuclear translocation. Pharmacologic inhibition of integrin or YAP/TAZ signaling rescued flow migration coupling and prevented vascular malformations in Alk1-deficient mice.

CONCLUSIONS

Our study reveals ALK1 as an essential driver of flow-induced endothelial cell migration and identifies loss of flow-migration coupling as a driver of arteriovenous malformation formation in hereditary hemorrhagic telangiectasia disease. Integrin-YAP/TAZ signaling blockers are new potential targets to prevent vascular malformations in patients with hereditary hemorrhagic telangiectasia.

Spatial and temporal VEGF receptor intracellular trafficking in microvascular and macrovascular endothelial cells

The vascular endothelial growth factor receptors (VEGFRs) can shape the neovascular phenotype of vascular endothelial cells when translocated to the nucleus, however the spatial and temporal changes in the intracellular distribution and translocation of VEGFRs to the nucleus and the organelles involved in this process is unclear. This study reports the effect of exogenous VEGF on translocation of VEGFRs and organelles in micro- and macrovascular endothelial cells. We showed that VEGF is responsible for: a rapid and substantial nuclear translocation of VEGFRs; VEGFR1 and VEGFR2 exhibit distinct spatial, temporal and structural translocation characteristics both in vitro and in vivo and this determines the nuclear VEGFR1:VEGFR2 ratio which differs between microvascular and macrovascular cells; VEGFR2 nuclear translocation is associated with the endosomal pathway transporting the receptor from Golgi in microvascular endothelial cells; and an increase in the volume of intracellular organelles. In conclusion, the nuclear translocation of VEGFRs is both receptor and vessel (macro versus micro) dependent and the endosomal pathway plays a key role in the translocation of VEGFRs to the nucleus and the subsequent export to the lysosomal system. Modulating VEGF-mediated VEGFR1 and VEGFR2 intracellular transmigration pathways may offer an alternative for the development of new anti-angiogenic therapies.

FcγR engagement reprograms neutrophils into antigen cross-presenting cells that elicit acquired anti-tumor immunity

Classical dendritic cells (cDC) are professional antigen-presenting cells (APC) that regulate immunity and tolerance. Neutrophil-derived cells with properties of DCs (nAPC) are observed in human diseases and after culture of neutrophils with cytokines. Here we show that FcγR-mediated endocytosis of antibody-antigen complexes or an anti-FcγRIIIB-antigen conjugate converts neutrophils into nAPCs that, in contrast to those generated with cytokines alone, activate T cells to levels observed with cDCs and elicit CD8+ T cell-dependent anti-tumor immunity in mice. Single cell transcript analyses and validation studies implicate the transcription factor PU.1 in neutrophil to nAPC conversion. In humans, blood nAPC frequency in lupus patients correlates with disease. Moreover, anti-FcγRIIIB-antigen conjugate treatment induces nAPCs that can activate autologous T cells when using neutrophils from individuals with myeloid neoplasms that harbor neoantigens or those vaccinated against bacterial toxins. Thus, anti-FcγRIIIB-antigen conjugate-induced conversion of neutrophils to immunogenic nAPCs may represent a possible immunotherapy for cancer and infectious diseases.

Endothelial Insulin Receptors Promote VEGF-A Signaling via ERK1/2 and Sprouting Angiogenesis

Endothelial insulin receptors (Insr) promote sprouting angiogenesis, although the underpinning cellular and molecular mechanisms are unknown. Comparing mice with whole-body insulin receptor haploinsufficiency (Insr+/-) against littermate controls, we found impaired limb perfusion and muscle capillary density after inducing hind-limb ischemia; this was in spite of increased expression of the proangiogenic growth factor Vegfa. Insr+/- neonatal retinas exhibited reduced tip cell number and branching complexity during developmental angiogenesis, which was also found in separate studies of mice with endothelium-restricted Insr haploinsufficiency. Functional responses to vascular endothelial growth factor A (VEGF-A), including in vitro angiogenesis, were also impaired in aortic rings and pulmonary endothelial cells from Insr+/- mice. Human umbilical vein endothelial cells with shRNA-mediated knockdown of Insr also demonstrated impaired functional angiogenic responses to VEGF-A. VEGF-A signaling to Akt and endothelial nitric oxide synthase was intact, but downstream signaling to extracellular signal-reduced kinase 1/2 (ERK1/2) was impaired, as was VEGF receptor-2 (VEGFR-2) internalization, which is required specifically for signaling to ERK1/2. Hence, endothelial insulin receptors facilitate the functional response to VEGF-A during angiogenic sprouting and are required for appropriate signal transduction from VEGFR-2 to ERK1/2.

VEGFR2 Trafficking by KIF13B Is a Novel Therapeutic Target for Wet Age-Related Macular Degeneration

Purpose

Vascular endothelial growth factor (VEGF) and its receptor VEGFR2 are promising therapeutic targets for wet age-related macular degeneration (AMD). As a topically applicable option, we developed the peptide KAI to selectively interfere with VEGFR2 trafficking to the cell surface where it receives VEGF. This study sought to determine the efficacy of KAI in the mouse model of choroidal neovascularization (CNV).

Methods

The specificity of KAI was tested by surface plasmon resonance. The drug delivery was analyzed by cryosection and the ELISA after treatment of KAI eyedrop to the mouse eyes. For the laser-induced CNV model, mice with laser-induced ruptures in Bruch's membrane received daily treatment of KAI eyedrop or control peptide. The other groups of mice received intravitreal injection of anti-VEGF or IgG control. After two weeks, CNV was quantified and compared.

Results

First, we showed the specificity and high affinity of KAI to VEGFR2. Next, biodistribution revealed successful delivery of KAI eyedrop to the back of the mouse eyes. KAI significantly reduced the disease progression in laser-induced CNV. The comparison with current therapy suggests that KAI eyedrop is as effective as current therapy to prevent CNV in wet AMD. Moreover, the genetic deletion of a kinesin KIF13B, which mediates VEGFR2 trafficking to the cell surface, confirmed the pivotal role of KIF13B in disease progression of wet AMD and neovascularization from choroidal vessels.

Conclusions

Taken together, pharmacologic inhibition and genetic deletion complementarily suggest the therapeutic possibility of targeting VEGFR2 trafficking to inhibit pathological angiogenesis in wet AMD.

Early Imaging and Molecular Changes with Neoadjuvant Bevacizumab in Stage II/III Breast Cancer

This prospective, phase II study evaluated novel biomarkers as predictors of response to bevacizumab in patients with breast cancer (BC), using serial imaging methods and gene expression analysis. Patients with primary stage II/III BC received bevacizumab 15 mg/kg (cycle 1; C1), then four cycles of neoadjuvant docetaxel doxorubicin, and bevacizumab every 3 weeks (C2-C5). Tumour proliferation and hypoxic status were evaluated using 18F-fluoro-3'-deoxy-3'-L-fluorothymidine (FLT)- and 18F-fluoromisonidazole (FMISO)-positron emission tomography (PET) at baseline, and during C1 and C5. Pre- and post-bevacizumab vascular changes were evaluated using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Molecular biomarkers were assessed using microarray analysis. A total of 70 patients were assessed for treatment efficacy. Significant decreases from baseline in tumour proliferation (FLT-PET), vascularity, and perfusion (DCE-MRI) were observed during C1 (p ≤ 0.001), independent of tumour subtype. Bevacizumab treatment did not affect hypoxic tumour status (FMISO-PET). Significant changes in the expression of 28 genes were observed after C1. Changes in vascular endothelial growth factor receptor (VEGFR)-2p levels were observed in 65 patients, with a > 20% decrease in VEGFR-2p observed in 13/65. Serial imaging techniques and molecular gene profiling identified several potentially predictive biomarkers that may predict response to neoadjuvant bevacizumab therapy in BC patients.

The physiological and pathological functions of VEGFR3 in cardiac and lymphatic development and related diseases

Vascular endothelial growth factor receptors (VEGFRs) are part of the evolutionarily conserved VEGF signalling pathways that regulate the development and maintenance of the body's cardiovascular and lymphovascular systems. VEGFR3, encoded by the FLT4 gene, has an indispensable and well-characterized function in development and establishment of the lymphatic system. Autosomal dominant VEGFR3 mutations, that prevent the receptor functioning as a homodimer, cause one of the major forms of hereditary primary lymphoedema; Milroy disease. Recently, we and others have shown that FLT4 variants, distinct to those observed in Milroy disease cases, predispose individuals to Tetralogy of Fallot, the most common cyanotic congenital heart disease, demonstrating a novel function for VEGFR3 in early cardiac development. Here, we examine the familiar and emerging roles of VEGFR3 in the development of both lymphovascular and cardiovascular systems, respectively, compare how distinct genetic variants in FLT4 lead to two disparate human conditions, and highlight the research still required to fully understand this multifaceted receptor.

The P-type ATPase transporter ATP7A promotes angiogenesis by limiting autophagic degradation of VEGFR2

VEGFR2 (KDR/Flk1) signaling in endothelial cells (ECs) plays a central role in angiogenesis. The P-type ATPase transporter ATP7A regulates copper homeostasis, and its role in VEGFR2 signaling and angiogenesis is entirely unknown. Here, we describe the unexpected crosstalk between the Copper transporter ATP7A, autophagy, and VEGFR2 degradation. The functional significance of this Copper transporter was demonstrated by the finding that inducible EC-specific ATP7A deficient mice or ATP7A-dysfunctional ATP7Amut mice showed impaired post-ischemic neovascularization. In ECs, loss of ATP7A inhibited VEGF-induced VEGFR2 signaling and angiogenic responses, in part by promoting ligand-induced VEGFR2 protein degradation. Mechanistically, VEGF stimulated ATP7A translocation from the trans-Golgi network to the plasma membrane where it bound to VEGFR2, which prevented autophagy-mediated lysosomal VEGFR2 degradation by inhibiting autophagic cargo/adapter p62/SQSTM1 binding to ubiquitinated VEGFR2. Enhanced autophagy flux due to ATP7A dysfunction in vivo was confirmed by autophagy reporter CAG-ATP7Amut -RFP-EGFP-LC3 transgenic mice. In summary, our study uncovers a novel function of ATP7A to limit autophagy-mediated degradation of VEGFR2, thereby promoting VEGFR2 signaling and angiogenesis, which restores perfusion recovery and neovascularization. Thus, endothelial ATP7A is identified as a potential therapeutic target for treatment of ischemic cardiovascular diseases.

Exploring the Intracrine Functions of VEGF-A

Vascular endothelial growth factor A (VEGF-A or VEGF) is a highly conserved secreted signalling protein best known for its roles in vascular development and angiogenesis. Many non-endothelial roles for VEGF are now established, with the discovery that VEGF and its receptors VEGFR1 and VEGFR2 are expressed in many non-vascular cell-types, as well as various cancers. In addition to secreted VEGF binding to its receptors in the extracellular space at the cell membrane (i.e., in a paracrine or autocrine mode), intracellularly localised VEGF is emerging as an important signalling molecule regulating cell growth, survival, and metabolism. This intracellular mode of signalling has been termed “intracrine”, and refers to the direct action of a signalling molecule within the cell without being secreted. In this review, we describe examples of intracrine VEGF signalling in regulating cell growth, differentiation and survival, both in normal cell homeostasis and development, as well as in cancer. We further discuss emerging evidence for the molecular mechanisms underpinning VEGF intracrine function, as well as the implications this intracellular mode of VEGF signalling may have for use and design of anti-VEGF cancer therapeutics.

RIPK3 modulates growth factor receptor expression in endothelial cells to support angiogenesis

Receptor-interacting protein kinase 3 (RIPK3) is a multifunctional intracellular protein that was first recognized as an important component of the necroptosis programmed cell death pathway. RIPK3 is also highly expressed in non-necroptotic murine embryonic endothelial cells (ECs) during vascular development, indicating its potential contribution to angiogenesis. To test this hypothesis, we generated mice lacking endothelial RIPK3 and found non-lethal embryonic and perinatal angiogenesis defects in multiple vascular beds. Our in vitro data indicate that RIPK3 supports angiogenesis by regulating growth factor receptor degradation in ECs. We found that RIPK3 interacted with the membrane trafficking protein myoferlin to sustain expression of vascular endothelial growth factor receptor 2 (VEGFR2) in cultured ECs following vascular endothelial growth factor A (VEGFA) stimulation. Restoration of myoferlin, which was diminished after RIPK3 knockdown, rescued decreased VEGFR2 expression and vascular sprouting in RIPK3-deficient ECs after VEGFA treatment. In addition, we found that RIPK3 modulated expression of genes involved in endothelial identity by inhibiting ERK signaling independently of growth factor receptor turnover. Altogether, our data reveal unexpected non-necroptotic roles for RIPK3 in ECs and evidence that RIPK3 promotes developmental angiogenesis in vivo.

Tumor microenvironment responsive VEGF-antibody functionalized pH sensitive liposomes of docetaxel for augmented breast cancer therapy

The present work exploits the tumor microenvironment which differs significantly from normal cellular environment in terms of both, having lower extracellular pH and increased angiogenesis capacity. To reduce systemic toxicity of docetaxel (DTX) and increase its therapeutic potential, VEGF antibody functionalized PEGylated pH sensitive liposomes (VEGF-PEG-pH-Lipo-DTX) were developed. The liposomes prepared by thin film hydration technique were later conjugated with VEGF antibody on liposomal surface by standard carbodiimide chemistry and using DSPE-PEG-COOH as linker. The VEGF-PEG-pH-Lipo-DTX displayed particle size of ~206 nm with an entrapment efficiency of ~62%. The transmission electron microscopy images revealed spherical shape of liposomes and corroborated the particle size obtained from zetasizer. The in vitro release study revealed biphasic release pattern of DTX from VEGF-PEG-pH-Lipo-DTX. The % drug released was also significantly higher at pH 5.5 which guarantees rapid endosomal escape and faster intracellular drug release. In case of VEGF-PEG-pH-Lipo-DTX the cellular uptake in MCF-7 cell line was augmented ~3.17-fold as compared to free DTX probably due to the VEGF-positive nature of MCF-7 cell (increased affinity for VEGF). Further, it was evident from the cytotoxicity assay that VEGF-PEG-pH-Lipo-DTX showed higher cytotoxicity in MCF-7 cells and ~5.78-fold reduction in IC₅₀ value as compared to free DTX. The apoptotic index observed in case of VEGF-PEG-pH-Lipo-DTX was ~1.70-fold higher than free DTX. The VEGF-PEG-pH-Lipo-DTX inhibited the proliferation of HUVECs stimulated by VEGF, warranting its anti-angiogenic potential. Furthermore, pharmacokinetic profile of VEGF-PEG-pH-Lipo-DTX revealed a ~2.94-fold increase in t_1/2 and a ~1.25-fold higher AUC _(0→∞) as compared to marketed formulation Taxotere®. Similarly, mean residence time was also increased ~2.50-fold as compared to Taxotere®. Finally, treatment with VEGF-PEG-pH-Lipo-DTX demonstrated significant reduction in % tumor burden (~35%) as compared to Taxotere® (~75%). Thus, the combined approach of using PEGylated pH sensitive liposomes along with VEGF antibody functionalization for efficient targeting can improve current standards of DTX therapy for treatment of breast cancer.

Epsins in vascular development, function and disease

Epsins are a family of adaptor proteins involved in clathrin-dependent endocytosis. In the vasculature, epsins 1 and 2 are functionally redundant members of this family that are expressed in the endothelial cells of blood vessels and the lymphatic system throughout development and adulthood. These proteins contain a number of peptide motifs that allow them to interact with lipid moieties and a variety of proteins. These interactions facilitate the regulation of a wide range of cell signaling pathways. In this review, we focus on the involvement of epsins 1 and 2 in controlling vascular endothelial growth factor receptor signaling in angiogenesis and lymphangiogenesis. We also discuss the therapeutic implications of understanding the molecular mechanisms of epsin-mediated regulation in diseases such as atherosclerosis and diabetes.

Cross-Talk between NADPH Oxidase and Mitochondria: Role in ROS Signaling and Angiogenesis

Angiogenesis, a new vessel formation from the pre-existing ones, is essential for embryonic development, wound repair and treatment of ischemic heart and limb diseases. However, dysregulated angiogenesis contributes to various pathologies such as diabetic retinopathy, atherosclerosis and cancer. Reactive oxygen species (ROS) derived from NADPH oxidase (NOX) as well as mitochondria play an important role in promoting the angiogenic switch from quiescent endothelial cells (ECs). However, how highly diffusible ROS produced from different sources and location can communicate with each other to regulate angiogenesis remains unclear. To detect a localized ROS signal in distinct subcellular compartments in real time in situ, compartment-specific genetically encoded redox-sensitive fluorescence biosensors have been developed. Recently, the intercellular communication, “cross-talk”, between ROS derived from NOX and mitochondria, termed “ROS-induced ROS release”, has been proposed as a mechanism for ROS amplification at distinct subcellular compartments, which are essential for activation of redox signaling. This “ROS-induced ROS release” may represent a feed-forward mechanism of localized ROS production to maintain sustained signaling, which can be targeted under pathological conditions with oxidative stress or enhanced to promote therapeutic angiogenesis. In this review, we summarize the recent knowledge regarding the role of the cross-talk between NOX and mitochondria organizing the sustained ROS signaling involved in VEGF signaling, neovascularization and tissue repair.

Polymorphisms in the Angiogenesis-Related Genes EFNB2, MMP2 and JAG1 Are Associated with Survival of Colorectal Cancer Patients

An individual's inherited genetic variation may contribute to the 'angiogenic switch', which is essential for blood supply and tumor growth of microscopic and macroscopic tumors. Polymorphisms in angiogenesis-related genes potentially predispose to colorectal cancer (CRC) or affect the survival of CRC patients. We investigated the association of 392 single nucleotide polymorphisms (SNPs) in 33 angiogenesis-related genes with CRC risk and survival of CRC patients in 1754 CRC cases and 1781 healthy controls within DACHS (Darmkrebs: Chancen der Verhütung durch Screening), a German population-based case-control study. Odds ratios and 95% confidence intervals (CI) were estimated from unconditional logistic regression to test for genetic associations with CRC risk. The Cox proportional hazard model was used to estimate hazard ratios (HR) and 95% CIs for survival. Multiple testing was adjusted for by a false discovery rate. No variant was associated with CRC risk. Variants in EFNB2, MMP2 and JAG1 were significantly associated with overall survival. The association of the EFNB2 tagging SNP rs9520090 (p < 0.0001) was confirmed in two validation datasets (p-values: 0.01 and 0.05). The associations of the tagging SNPs rs6040062 in JAG1 (p-value 0.0003) and rs2241145 in MMP2 (p-value 0.0005) showed the same direction of association with overall survival in the first and second validation sets, respectively, although they did not reach significance (p-values: 0.09 and 0.25, respectively). EFNB2, MMP2 and JAG1 are known for their functional role in angiogenesis and the present study points to novel evidence for the impact of angiogenesis-related genetic variants on the CRC outcome.

Systems Biology Will Direct Vascular-Targeted Therapy for Obesity

Healthy adipose tissue expansion and metabolism during weight gain require coordinated angiogenesis and lymphangiogenesis. These vascular growth processes rely on the vascular endothelial growth factor (VEGF) family of ligands and receptors (VEGFRs). Several studies have shown that controlling vascular growth by regulating VEGF:VEGFR signaling can be beneficial for treating obesity; however, dysregulated angiogenesis and lymphangiogenesis are associated with several chronic tissue inflammation symptoms, including hypoxia, immune cell accumulation, and fibrosis, leading to obesity-related metabolic disorders. An ideal obesity treatment should minimize adipose tissue expansion and the advent of adverse metabolic consequences, which could be achieved by normalizing VEGF:VEGFR signaling. Toward this goal, a systematic investigation of the interdependency of vascular and metabolic systems in obesity and tools to predict personalized treatment ranges are necessary to improve patient outcomes through vascular-targeted therapies. Systems biology can identify the critical VEGF:VEGFR signaling mechanisms that can be targeted to regress adipose tissue expansion and can predict the metabolic consequences of different vascular-targeted approaches. Establishing a predictive, biologically faithful platform requires appropriate computational models and quantitative tissue-specific data. Here, we discuss the involvement of VEGF:VEGFR signaling in angiogenesis, lymphangiogenesis, adipogenesis, and macrophage specification – key mechanisms that regulate adipose tissue expansion and metabolism. We then provide useful computational approaches for simulating these mechanisms, and detail quantitative techniques for acquiring tissue-specific parameters. Systems biology, through computational models and quantitative data, will enable an accurate representation of obese adipose tissue that can be used to direct the development of vascular-targeted therapies for obesity and associated metabolic disorders.

Liposomal Delivery of Mycophenolic Acid With Quercetin for Improved Breast Cancer Therapy in SD Rats

The present study explores the influence of mycophenolic acid (MPA) in combination therapy with quercetin (QC) (impeding MPA metabolic rate) delivered using the liposomal nanoparticles (LNPs). Mycophenolic acid liposome nanoparticles (MPA-LNPs) and quercetin liposome nanoparticles (QC-LNPs) were individually prepared and comprehensively characterized. The size of prepared MPA-LNPs and QC-LNPs were found to be 183 ± 13 and 157 ± 09.8, respectively. The in vitro studies revealed the higher cellular uptake and cytotoxicity of combined therapy (MPA-LNPs + QC-LNPs) compared to individual ones. Moreover pharmacokinetics studies in female SD-rat shown higher T 1 / 2 value (1.94 fold) of combined therapy compared to MPA. Furthermore, in vivo anticancer activity in combination of MPA-LNPs and QC-LNPs was also significantly higher related to other treatments groups. The combination therapy of liposomes revealed the new therapeutic approach for the treatment of breast cancer.

Team-Based Approach to Management of Hypertension Associated with Angiogenesis Inhibitors

Angiogenesis inhibitors, also known as vascular endothelial growth factor (VEGF) or vascular signaling pathway (VSP) inhibitors, have improved care of neoplastic diseases over the past decade. However, cardiovascular toxicities associated with these agents, such as hypertension and less commonly left ventricular systolic dysfunction and heart failure, have often been a limiting factor for continued use. Balancing the benefits of these agents with the associated toxicities is critical to ensure these therapies do not negatively impact oncological outcomes. The care of cancer patients with cardiovascular risks is challenging due to the heterogeneity of cardiovascular complications, paucity of evidence-based guidelines, and lack of channels for collaboration among healthcare providers. Herein, we provide a team-based approach for treatment of angiogenesis inhibitor-induced hypertension along with recommendations on monitoring and appropriate selection of anti-hypertensive agents.

Raftlin is recruited by neuropilin-1 to the activated VEGFR2 complex to control proangiogenic signaling

Background

VEGFR2 (vascular endothelial growth factor receptor 2) is the major pro-angiogenic receptor in endothelial cells. Compared to other members of the receptor tyrosine kinase family, we know relatively few VEGFR2 signaling partners. Our objective was to use mass spectrometry-based proteomics to identify novel binding partners of activated VEGFR2.

Methods

We created an endothelial cell line stably expressing GFP-tagged VEGFR2 and isolated activated receptor complexes. Analysis by mass spectrometry identified raftlin as a novel binding partner of VEGFR2.

Results

We found that raftlin is recruited to the activated VEGFR2 complex via the co-receptor Nrp1 (neuropilin-1). We show that raftlin regulates the surface levels of Nrp1 in endothelial cells, controlling the availability of Nrp1 for VEGFR2 interaction. Raftlin stabilizes active VEGFR2 at the cell surface by inhibiting endocytosis of the activated receptor. Raftlin also promotes recycling of internalized VEGFR2 to the cell surface. Raftlin alters the signaling outcomes of VEGFR2 activation, inhibiting the activation of p38 and FAK (focal adhesion kinases) specifically. Both pathways are linked to cell migration in endothelial cells, and raftlin inhibits endothelial cell migration in response to VEGF.

Conclusion

Nrp1 is an important co-receptor for VEGFR2; however, its functions are still only partially understood. We show that raftlin works with Nrp1 in endothelial cells to control intracellular trafficking of the activated VEGFR2. This modulates the response to VEGF and controls endothelial cell migration.

Electronic supplementary material

The online version of this article (10.1007/s10456-020-09715-z) contains supplementary material, which is available to authorized users.

The in vitro effect of VEGF receptor inhibition on primary alveolar osteoblast nodule formation

BACKGROUND

Vascular endothelial growth factor (VEGF) is a master regulator and is required for the effective coupling of angiogenesis and osteogenesis supporting both skeletal development and postnatal bone repair. A direct role for VEGF in intramembranous-derived osteoblast growth and differentiation is not clear. We investigated the expression of primary alveolar osteoblast VEGF receptors and the subsequent effects on mineralization and nodule formation in vitro following VEGFR inhibition.

METHODS

Primary human alveolar osteoblasts (HAOBs) were cultured in the presence of VEGF receptor inhibitors, exogenous VEGF or the bisphosphonate, zoledronic acid. VEGF, VEGFR1 and VEGFR2 mRNA expression and nodule formation following 21 days of culture. VEGFR1 protein expression was examined using immunofluorescence after 48 h.

RESULTS

The HAOBs expressed high levels of VEGF and VEGFR1 protein but VEGFR2 was not detected. The VEGFR1/2 inhibitors, ZM306416 and KRN633, lead to a dose-dependent decrease in mineralization. Treatment with zoledronic acid showed no difference in HAOB VEGF receptor expression.

CONCLUSION

VEGF/VEGFR1 pathway appears to be important for intramembranous-derived osteoblast differentiation and maturation in vitro.

Protein kinase D up-regulates transcription of VEGF receptor-2 in endothelial cells by suppressing nuclear localization of the transcription factor AP2β

Vascular endothelial growth factor A (VEGF) signals primarily through its cognate receptor VEGF receptor-2 (VEGFR-2) to control vasculogenesis and angiogenesis, key physiological processes in cardiovascular disease and cancer. In human umbilical vein endothelial cells (HUVECs), knockdown of protein kinase D-1 (PKD1) or PKD2 down-regulates VEGFR-2 expression and inhibits VEGF-induced cell proliferation and migration. However, how PKD regulates VEGF signaling is unclear. Previous bioinformatics analyses have identified binding sites for the transcription factor activating enhancer-binding protein 2 (AP2) in the VEGFR-2 promoter. Using ChIP analyses, here we found that PKD knockdown in HUVECs increases binding of AP2β to the VEGFR-2 promoter. Luciferase reporter assays with serial deletions of AP2-binding sites within the VEGFR-2 promoter revealed that its transcriptional activity negatively correlates with the number of these sites. Next we demonstrated that AP2β up-regulation decreases VEGFR-2 expression and that loss of AP2β enhances VEGFR-2 expression in HUVECs. In vivo experiments confirmed increased VEGFR-2 immunostaining in the spinal cord of AP2β knockout mouse embryos. Mechanistically, we observed that PKD phosphorylates AP2β at Ser258 and Ser277 and suppresses its nuclear accumulation. Inhibition of PKD activity with a pan-PKD inhibitor increased AP2β nuclear localization, and overexpression of both WT and constitutively active PKD1 or PKD2 reduced AP2β nuclear localization through a Ser258- and Ser277-dependent mechanism. Furthermore, substitution of Ser277 in AP2β increased its binding to the VEGFR-2 promoter. Our findings uncover evidence of a molecular pathway that regulates VEGFR-2 expression, insights that may shed light on the etiology of diseases associated with aberrant VEGF/VEGFR signaling.

Eriocalyxin B Biological Activity: A Review on Its Mechanism of Action

Natural products, a rich source of bioactive chemical compounds, have served humans as a safer drug of choice since times. Eriocalyxin B, an ent-Kaurene diterpenoid, has been extracted from a traditional Chinese herb Isodon eriocalyx. Experimental data support the anticancer and anti-inflammatory activities of EriB. This natural entity exhibits anticancer effects against breast, pancreatic, leukemia, ovarian, lung, bladder, and colorectal cancer. EriB has capability to inhibit the proliferation of cancer cells by prompting apoptosis, arresting cell cycle, and modulating cell signaling pathways. The regulation of signaling pathways in cancerous cells by EriB involves the modulation of various apoptosis-related factors (Bak, Bax, caspases, XIAP, survivin, and Beclin-1), transcriptional factors (nuclear factor kappa B [NF-κB], STAT3, Janus-activated kinase 2, Notch, AP-1, and lκBα), enzymes (cyclooxygenase 2, matrix metalloproteinase 2 [MMP-2], MMP-9, and poly (ADP-ribose) polymerase), cytokines, and protein kinases (mitogen-activated protein kinase and ERK1/2). This review proposes that EriB supplies a novel opportunity for the cure of cancer but supplementary investigations along with preclinical trials are obligatory to effectively figure out its biological and pharmacological applications.

Uptake of Ranibizumab but Not Bevacizumab into Uveal Melanoma Cells Correlates with a Sustained Decline in VEGF-A Levels and Metastatic Activities

Despite the implication of vascular endothelial growth factor-A (VEGF-A) in the pathophysiology of uveal melanoma (UM), the anti-VEGF-A antibody bevacizumab yielded conflicting results on UM growth. Here, we evaluated whether bevacizumab and ranibizumab, a humanized Fab-fragment against VEGF-A, can enter UM cells and induce a sustained physiological response. The primary and metastatic UM cell lines Mel-270 and OMM-2.5 were exposed to bevacizumab or ranibizumab for one day and were maintained further in untreated medium for a total of three days. Both antibodies significantly reduced the levels of extracellular VEGF-A and the angiogenic potential of the conditioned medium after one day. These inhibitory effects of bevacizumab diminished by day three. Ranibizumab suppressed the metabolic activity, proliferation, and intracellular VEGF-A levels in a cell-type and concentration-dependent manner, whereas bevacizumab exerted no effect. Both drugs were detected inside early endosomes within the UM cells, with the stronger and sustained colocalization of ranibizumab. Our results therefore demonstrated the more potent and persistent suppressive activity of ranibizumab on the UM cells, possibly due to its higher level of uptake and prolonged intracellular retention. Further research on the endosome dynamics in UM cells might provide valuable insight into the response of these heterogenous tumors to therapeutic antibodies.

SU5416 does not attenuate early RV angiogenesis in the murine chronic hypoxia PH model

BACKGROUND

Right ventricular (RV) angiogenesis has been associated with adaptive myocardial remodeling in pulmonary hypertension (PH), though molecular regulators are poorly defined. Endothelial cell VEGFR-2 is considered a "master regulator" of angiogenesis in other models, and the small molecule VEGF receptor tyrosine kinase inhibitor SU5416 is commonly used to generate PH in rodents. We hypothesized that SU5416, through direct effects on cardiac endothelial cell VEGFR-2, would attenuate RV angiogenesis in a murine model of PH.

METHODS

C57 BL/6 mice were exposed to chronic hypoxia (CH-PH) to generate PH and stimulate RV angiogenesis. SU5416 (20 mg/kg) or vehicle were administered at the start of the CH exposure, and weekly thereafter. Angiogenesis was measured after one week of CH-PH using a combination of unbiased stereological measurements and flow cytometry-based quantification of myocardial endothelial cell proliferation. In complementary experiments, primary cardiac endothelial cells from C57 BL/6 mice were exposed to recombinant VEGF (50 ng/mL) or grown on Matrigel in the presence of SU5416 (5 μM) or vehicle.

RESULT

SU5416 directly inhibited VEGF-mediated ERK phosphorylation, cell proliferation, and Kdr transcription, but not Matrigel tube formation in primary murine cardiac endothelial cells in vitro. SU5416 did not inhibit CH-PH induced RV angiogenesis, endothelial cell proliferation, or RV hypertrophy in vivo, despite significantly altering the expression profile of genes involved in angiogenesis.

CONCLUSIONS

These findings demonstrate that SU5416 directly inhibited VEGF-induced proliferation of murine cardiac endothelial cells but does not attenuate CH-PH induced RV angiogenesis or myocardial remodeling in vivo.

Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity

We have previously shown that knockdown of endomucin (EMCN), an integral membrane glycocalyx glycoprotein, prevents VEGF-induced proliferation, migration, and tube formation in vitro and angiogenesis in vivo. In the endothelium, VEGF mediates most of its angiogenic effects through VEGF receptor 2 (VEGFR2). To understand the role of EMCN, we examined the effect of EMCN depletion on VEGFR2 endocytosis and activation. Results showed that although VEGF stimulation promoted VEGFR2 internalization in control endothelial cells (ECs), loss of EMCN prevented VEGFR2 endocytosis. Cell surface analysis revealed a decrease in VEGFR2 following VEGF stimulation in control but not siRNA directed against EMCN-transfected ECs. EMCN depletion resulted in heightened phosphorylation following VEGF stimulation with an increase in total VEGFR2 protein. These results indicate that EMCN modulates VEGFR2 endocytosis and activity and point to EMCN as a potential therapeutic target.-LeBlanc, M. E., Saez-Torres, K. L., Cano, I., Hu, Z., Saint-Geniez, M., Ng, Y.-S., D'Amore, P. A. Glycocalyx regulation of vascular endothelial growth factor receptor 2 activity.