Vascular endothelial cell-specific phosphotyrosine phosphatase (VE-PTP) activity is required for blood vessel development

Rare genetic variation in VE-PTP is associated with central serous chorioretinopathy, venous dysfunction and glaucoma

Central serous chorioretinopathy (CSC) is a fluid maculopathy whose etiology is not well understood. Abnormal choroidal veins in CSC patients have been shown to have similarities with varicose veins. To identify potential mechanisms, we analyzed genotype data from 1,477 CSC patients and 455,449 controls in FinnGen. We identified an association for a low-frequency (AF=0.5%) missense variant (rs113791087) in the gene encoding vascular endothelial protein tyrosine phosphatase (VE-PTP) (OR=2.85, P=4.5×10-9). This was confirmed in a meta-analysis of 2,452 CSC patients and 865,767 controls from 4 studies (OR=3.06, P=7.4×10-15). Rs113791087 was associated with a 56% higher prevalence of retinal abnormalities (35.3% vs 22.6%, P=8.0×10-4) in 708 UK Biobank participants and, surprisingly, with varicose veins (OR=1.31, P=2.3×10-11) and glaucoma (OR=0.82, P=6.9×10-9). Predicted loss-of-function variants in VEPTP, though rare in number, were associated with CSC in All of Us (OR=17.10, P=0.018). These findings highlight the significance of VE-PTP in diverse ocular and systemic vascular diseases.

Beyond VEGF: Angiopoietin-Tie Signaling Pathway in Diabetic Retinopathy

Complications from diabetic retinopathy such as diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR) constitute leading causes of preventable vision loss in working-age patients. Since vascular endothelial growth factor (VEGF) plays a major role in the pathogenesis of these complications, VEGF inhibitors have been the cornerstone of their treatment. Anti-VEGF monotherapy is an effective but burdensome treatment for DME. However, due to the intensive and burdensome treatment, most patients in routine clinical practice are undertreated, and therefore, their outcomes are compromised. Even in adequately treated patients, persistent DME is reported anywhere from 30% to 60% depending on the drug used. PDR is currently treated by anti-VEGF, panretinal photocoagulation (PRP) or a combination of both. Similarly, a number of eyes, despite these treatments, continue to progress to tractional retinal detachment and vitreous hemorrhage. Clearly there are other molecular pathways other than VEGF involved in the pathogenesis of DME and PDR. One of these pathways is the angiopoietin-Tie signaling pathway. Angiopoietin 1 (Ang1) plays a major role in maintaining vascular quiescence and stability. It acts as a molecular brake against vascular destabilization and inflammation that is usually promoted by angiopoietin 2 (Ang2). Several pathological conditions including chronic hyperglycemia lead to Ang2 upregulation. Recent regulatory approval of the bi-specific antibody, faricimab, may improve long term outcomes in DME. It targets both the Ang/Tie and VEGF pathways. The YOSEMITE and RHINE were multicenter, double-masked, randomized non-inferiority phase 3 clinical trials that compared faricimab to aflibercept in eyes with center-involved DME. At 12 months of follow-up, faricimab demonstrated non-inferior vision gains, improved anatomic outcomes and a potential for extended dosing when compared to aflibercept. The 2-year results of the YOSEMITE and RHINE trials demonstrated that the anatomic and functional results obtained at the 1 year follow-up were maintained. Short term outcomes of previously treated and treatment-naive eyes with DME that were treated with faricimab during routine clinical practice suggest a beneficial effect of faricimab over other agents. Targeting of Ang2 has been reported by several other means including VE-PTP inhibitors, integrin binding peptide and surrobodies.

Heterogeneity of endothelial VE-PTP downstream polarization, Tie2 activation, junctional claudin-5, and permeability in the aorta and vena cava

Endothelial cells of mammalian blood vessels have multiple levels of heterogeneity along the vascular tree and among different organs. Further heterogeneity results from blood flow turbulence and variations in shear stress. In the aorta, vascular endothelial protein tyrosine phosphatase (VE-PTP), which dephosphorylates tyrosine kinase receptor Tie2 in the plasma membrane, undergoes downstream polarization and endocytosis in endothelial cells exposed to laminar flow and high shear stress. VE-PTP sequestration promotes Tie2 phosphorylation at tyrosine992 and endothelial barrier tightening. The present study characterized the heterogeneity of VE-PTP polarization, Tie2-pY992 and total Tie2, and claudin-5 in anatomically defined regions of endothelial cells in the mouse descending thoracic aorta, where laminar flow is variable and IgG extravasation is patchy. We discovered that VE-PTP and Tie2-pY992 had mosaic patterns, unlike the uniform distribution of total Tie2. Claudin-5 at tight junctions also had a mosaic pattern, whereas VE-cadherin at adherens junctions bordered all endothelial cells. Importantly, the amounts of Tie2-pY992 and claudin-5 in aortic endothelial cells correlated with downstream polarization of VE-PTP. VE-PTP and Tie2-pY992 also had mosaic patterns in the vena cava, but claudin-5 was nearly absent and extravasated IgG was ubiquitous. Correlation of Tie2-pY992 and claudin-5 with VE-PTP polarization supports their collective interaction in the regulation of endothelial barrier function in the aorta, yet differences between the aorta and vena cava indicate additional flow-related determinants of permeability. Together, the results highlight new levels of endothelial cell functional mosaicism in the aorta and vena cava, where blood flow dynamics are well known to be heterogeneous.

Comparative Analysis of Water Extracts from Roselle (Hibiscus sabdariffa L.) Plants and Callus Cells: Constituents, Effects on Human Skin Cells, and Transcriptome Profiles

Roselle (Hibiscus sabdariffa L.) is a plant that has traditionally been used in various food and beverage products. Here, we investigated the potential of water extracts derived from Roselle leaves and callus cells for cosmetic and pharmaceutical purposes. We generated calluses from Roselle leaves and produced two different water extracts through heat extraction, which we named Hibiscus sabdariffa plant extract (HSPE) and Hibiscus sabdariffa callus extract (HSCE). HPLC analysis showed that the two extracts have different components, with nucleic acids and metabolites such as phenylalanine and tryptophan being the most common components in both extracts. In vitro assays demonstrated that HSCE has strong anti-melanogenic effects and functions for skin barrier and antioxidant activity. Transcriptome profiling of human skin cells treated with HSPE and HSCE showed significant differences, with HSPE having more effects on human skin cells. Up-regulated genes by HSPE function in angiogenesis, the oxidation-reduction process, and glycolysis, while up-regulated genes by HSCE encode ribosome proteins and IFI6, functioning in the healing of radiation-injured skin cells. Therefore, we suggest that the two extracts from Roselle should be applied differently for cosmetics and pharmaceutical purposes. Our findings demonstrate the potential of Roselle extracts as a natural source for skincare products.

Activation of Angiopoietin-Tie2 Signaling Protects the Kidney from Ischemic Injury by Modulation of Endothelial-Specific Pathways

SIGNIFICANCE STATEMENT

Ischemia-reperfusion AKI (IR-AKI) is common and causes significant morbidity. Effective treatments are lacking. However, preclinical studies suggest that inhibition of angiopoietin-Tie2 vascular signaling promotes injury, whereas activation of Tie2 is protective. We show that kidney ischemia leads to increased levels of the endothelial-specific phosphatase vascular endothelial protein tyrosine phosphatase (VE-PTP; PTPRB), which inactivates Tie2. Activation of Tie2 through VE-PTP deletion, or delivery of a novel angiopoietin mimetic (Hepta-ANG1), abrogated IR-AKI in mice. Single-cell RNAseq analysis showed Tie2 activation promotes increased Entpd1 expression, downregulation of FOXO1 target genes in the kidney vasculature, and emergence of a new subpopulation of glomerular endothelial cells. Our data provide a molecular basis and identify a candidate therapeutic to improve endothelial integrity and kidney function after IR-AKI.

BACKGROUND

Ischemia-reperfusion AKI (IR-AKI) is estimated to affect 2%-7% of all hospitalized patients. The significant morbidity and mortality associated with AKI indicates urgent need for effective treatments. Previous studies have shown activation of the vascular angiopoietin-Tie2 tyrosine kinase signaling pathway abrogates ischemia-reperfusion injury (IRI). We extended previous studies to (1) determine the molecular mechanism(s) underlying kidney injury and protection related to decreased or increased activation of Tie2, respectively, and (2) to test the hypothesis that deletion of the Tie2 inhibitory phosphatase vascular endothelial protein tyrosine phosphatase (VE-PTP) or injection of a new angiopoietin mimetic protects the kidney from IRI by common molecular mechanism(s).

METHODS

Bilateral IR-AKI was performed in VE-PTP wild-type or knockout mice and in C57BL/6J mice treated with Hepta-ANG1 or vehicle. Histologic, immunostaining, and single-cell RNA sequencing analyses were performed.

RESULTS

The phosphatase VE-PTP, which negatively regulates the angiopoietin-Tie2 pathway, was upregulated in kidney endothelial cells after IRI, and genetic deletion of VE-PTP in mice protected the kidney from IR-AKI. Injection of Hepta-ANG1 potently activated Tie2 and protected the mouse kidney from IRI. Single-cell RNAseq analysis of kidneys from Hepta-ANG1-treated and vehicle-treated mice identified endothelial-specific gene signatures and emergence of a new glomerular endothelial subpopulation associated with improved kidney function. Overlap was found between endothelial-specific genes upregulated by Hepta-ANG1 treatment and those downregulated in HUVECs with constitutive FOXO1 activation, including Entpd1 / ENTPD1 that modulates purinergic receptor signaling.

CONCLUSIONS

Our data support a key role of the endothelium in the development of IR-AKI, introduce Hepta-ANG1 as a putative new therapeutic biologic, and report a model to explain how IRI reduces Tie2 signaling and how Tie2 activation protects the kidney.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2023_05_23_JSN_Ang_EP23_052323.mp3.

VE-Cadherin in Cancer-Associated Angiogenesis: A Deceptive Strategy of Blood Vessel Formation

Tumor growth depends on the vascular system, either through the expansion of blood vessels or novel adaptation by tumor cells. One of these novel pathways is vasculogenic mimicry (VM), which is defined as a tumor-provided vascular system apart from endothelial cell-lined vessels, and its origin is partly unknown. It involves highly aggressive tumor cells expressing endothelial cell markers that line the tumor irrigation. VM has been correlated with high tumor grade, cancer cell invasion, cancer cell metastasis, and reduced survival of cancer patients. In this review, we summarize the most relevant studies in the field of angiogenesis and cover the various aspects and functionality of aberrant angiogenesis by tumor cells. We also discuss the intracellular signaling mechanisms involved in the abnormal presence of VE-cadherin (CDH5) and its role in VM formation. Finally, we present the implications for the paradigm of tumor angiogenesis and how targeted therapy and individualized studies can be applied in scientific analysis and clinical settings.

The Emerging Role of Protein Phosphatase in Regeneration

Maintaining normal cellular behavior is essential for the survival of organisms. One of the main mechanisms to control cellular behavior is protein phosphorylation. The process of protein phosphorylation is reversible under the regulation of protein kinases and protein phosphatases. The importance of kinases in numerous cellular processes has been well recognized. In recent years, protein phosphatases have also been demonstrated to function actively and specifically in various cellular processes and thus have gained more and more attention from researchers. In the animal kingdom, regeneration frequently occurs to replace or repair damaged or missing tissues. Emerging evidence has revealed that protein phosphatases are crucial for organ regeneration. In this review, after providing a brief overview of the classification of protein phosphatases and their functions in several representative developmental processes, we highlight the critical roles that protein phosphatases play in organ regeneration by summarizing the most recent research on the function and underlying mechanism of protein phosphatase in the regeneration of the liver, bone, neuron, and heart in vertebrates.

Shear stress control of vascular leaks and atheromas through Tie2 activation by VE-PTP sequestration

Vascular endothelial protein tyrosine phosphatase (VE-PTP) influences endothelial barrier function by regulating the activation of tyrosine kinase receptor Tie2. We determined whether this action is linked to the development of atherosclerosis by examining the influence of arterial shear stress on VE-PTP, Tie2 activation, plasma leakage, and atherogenesis. We found that exposure to high average shear stress led to downstream polarization and endocytosis of VE-PTP accompanied by Tie2 activation at cell junctions. In aortic regions with disturbed flow, VE-PTP was not redistributed away from Tie2. Endothelial cells exposed to high shear stress had greater Tie2 activation and less macromolecular permeability than regions with disturbed flow. Deleting endothelial VE-PTP in VE-PTPiECKO mice increased Tie2 activation and reduced plasma leakage in atheroprone regions. ApoE-/- mice bred with VE-PTPiECKO mice had less plasma leakage and fewer atheromas on a high-fat diet. Pharmacologic inhibition of VE-PTP by AKB-9785 had similar anti-atherogenic effects. Together, the findings identify VE-PTP as a novel target for suppression of atherosclerosis.

An agonistic anti-Tie2 antibody suppresses the normal-to-tumor vascular transition in the glioblastoma invasion zone

Tumor progression is intimately associated with the vasculature, as tumor proliferation induces angiogenesis and tumor cells metastasize to distant organs via blood vessels. However, whether tumor invasion is associated with blood vessels remains unknown. As glioblastoma (GBM) is featured by aggressive invasion and vascular abnormalities, we characterized the onset of vascular remodeling in the diffuse tumor infiltrating zone by establishing new spontaneous GBM models with robust invasion capacity. Normal brain vessels underwent a gradual transition to severely impaired tumor vessels at the GBM periphery over several days. Increasing vasodilation from the tumor periphery to the tumor core was also found in human GBM. The levels of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) showed a spatial correlation with the extent of vascular abnormalities spanning the tumor-invading zone. Blockade of VEGFR2 suppressed vascular remodeling at the tumor periphery, confirming the role of VEGF-VEGFR2 signaling in the invasion-associated vascular transition. As angiopoietin-2 (ANGPT2) was expressed in only a portion of the central tumor vessels, we developed a ligand-independent tunica interna endothelial cell kinase 2 (Tie2)-activating antibody that can result in Tie2 phosphorylation in vivo. This agonistic anti-Tie2 antibody effectively normalized the vasculature in both the tumor periphery and tumor center, similar to the effects of VEGFR2 blockade. Mechanistically, this antibody-based Tie2 activation induced VE-PTP-mediated VEGFR2 dephosphorylation in vivo. Thus, our study reveals that the normal-to-tumor vascular transition is spatiotemporally associated with GBM invasion and may be controlled by Tie2 activation via a novel mechanism of action.

Single Cell RNA Sequencing Reveals Deep Homology of Dental Cell Types Across Vertebrates

Like most mammals, humans replace their teeth once throughout their lives and have limited regenerative capabilities. In contrast, mice continually renew tissues lost due to gnawing through a well characterized population of stem cells on the labial surface of the incisor. Most non-mammalian vertebrates replace teeth throughout life; the cellular and molecular mechanisms of successional tooth replacement are largely unknown. Here we use single nuclei RNA sequencing (snRNA-seq) of replacement teeth and adjacent oral lamina in Lake Malawi cichlids, species with lifelong whole–tooth replacement, to make two main discoveries. First, despite hundreds of millions of years of evolution, we demonstrate conservation of cell type gene expression across vertebrate teeth (fish, mouse, human). Second, we used an approach that combines marker gene expression and developmental potential of dental cells to uncover the transcriptional signature of stem-like cells in regenerating teeth. Our work underscores the importance of a comparative framework in the study of vertebrate oral and regenerative biology.

The Effects of Acidosis on eNOS in the Systemic Vasculature: A Focus on Early Postnatal Ontogenesis

The activity of many vasomotor signaling pathways strongly depends on extracellular/intracellular pH. Nitric oxide (NO) is one of the most important vasodilators produced by the endothelium. In this review, we present evidence that in most vascular beds of mature mammalian organisms metabolic or respiratory acidosis increases functional endothelial NO-synthase (eNOS) activity, despite the observation that direct effects of low pH on eNOS enzymatic activity are inhibitory. This can be explained by the fact that acidosis increases the activity of signaling pathways that positively regulate eNOS activity. The role of NO in the regulation of vascular tone is greater in early postnatal ontogenesis compared to adulthood. Importantly, in early postnatal ontogenesis acidosis also augments functional eNOS activity and its contribution to the regulation of arterial contractility. Therefore, the effect of acidosis on total peripheral resistance in neonates may be stronger than in adults and can be one of the reasons for an undesirable decrease in blood pressure during neonatal asphyxia. The latter, however, should be proven in future studies.

NB-3 expression in endothelial cells contributes to the maintenance of blood brain barrier integrity in a mouse high-altitude cerebral edema model

NB-3, a member of the contactin/F3 subgroup in the immunoglobulin superfamily, plays an important role in neural development and injury recovery. The blood brain barrier (BBB) is typically involved in the pathophysiology of neural disorders, such as hypoxic-ischemic brain injury. Our previous research found that NB-3 protects against brain damage in a mouse stroke model. However, its role in high-altitude disorders caused by hypobaric hypoxia exposure remains unknown. In the present study, we found that NB-3 was expressed in brain microvascular endothelial cells (BMECs) and responded to hypoxia stimulation. Conditional knockout of NB-3 in endothelial cells increased BBB leakage and downregulated tight junction proteins in vivo. NB-3 deficiency promoted the downregulation of tight junction proteins under Lipopolysaccharide (LPS)/hypoxia stimulation. Conversely, overexpression or supplementation with NB-3 alleviated endothelial barrier injuries. Transcriptome sequencing showed that NB-3 regulated various cell attachment genomic changes, including the Notch signaling pathway. Blocking the Notch signaling pathway increased VEGF/VEGFR2 pathway activation induced by LPS/hypoxia. Collectively, we present evidence that NB-3 plays key roles in maintaining BBB integrity under high-altitude cerebral edema conditions.

Nxhl Controls Angiogenesis by Targeting VE-PTP Through Interaction With Nucleolin

Precise regulation of angiogenesis is required for organ development, wound repair, and tumor progression. Here, we identified a novel gene, nxhl (New XingHuo light), that is conserved in vertebrates and that plays a crucial role in vascular integrity and angiogenesis. Bioinformatic analysis uncovered its essential roles in development based on co-expression with several key developmental genes. Knockdown of nxhl in zebrafish causes global and pericardial edema, loss of blood circulation, and vascular defects characterized by both reduced vascularization in intersegmental vessels and decreased sprouting in the caudal vein plexus. The nxhl gene also affects human endothelial cell behavior in vitro. We found that nxhl functions in part by targeting VE-PTP through interaction with NCL (nucleolin). Loss of ptprb (a VE-PTP ortholo) in zebrafish resulted in defects similar to nxhl knockdown. Moreover, nxhl deficiency attenuates tumor invasion and proteins (including VE-PTP and NCL) associated with angiogenesis and EMT. These findings illustrate that nxhl can regulate angiogenesis via a novel nxhl-NCL-VE-PTP axis, providing a new therapeutic target for modulating vascular formation and function, especially for cancer treatment.

Cellular crosstalk regulates the aqueous humor outflow pathway and provides new targets for glaucoma therapies

Primary congenital glaucoma (PCG) is a severe disease characterized by developmental defects in the trabecular meshwork (TM) and Schlemm's canal (SC), comprising the conventional aqueous humor outflow pathway of the eye. Recently, heterozygous loss of function variants in TEK and ANGPT1 or compound variants in TEK/SVEP1 were identified in children with PCG. Moreover, common variants in ANGPT1and SVEP1 have been identified as risk alleles for primary open angle glaucoma (POAG) in GWAS studies. Here, we show tissue-specific deletion of Angpt1 or Svep1 from the TM causes PCG in mice with severe defects in the adjacent SC. Single-cell transcriptomic analysis of normal and glaucomatous Angpt1 deficient eyes allowed us to identify distinct TM and SC cell populations and discover additional TM-SC signaling pathways. Furthermore, confirming the importance of angiopoietin signaling in SC, delivery of a recombinant ANGPT1-mimetic promotes developmental SC expansion in healthy and Angpt1 deficient eyes, blunts intraocular pressure (IOP) elevation and RGC loss in a mouse model of PCG and lowers IOP in healthy adult mice. Our data highlight the central role of ANGPT1-TEK signaling and TM-SC crosstalk in IOP homeostasis and provide new candidates for SC-targeted glaucoma therapy.

Novel Serum Biomarkers of Neurovascular Unit Associated with Cortical Amyloid Deposition

BACKGROUND

Whether blood biomarkers of neurovascular unit are associated with cortical amyloid deposition on positron emission tomography (PET) imaging remains unclear.

OBJECTIVE

To investigate the association between novel serum biomarkers of neurovascular unit, such as protein tyrosine phosphatase receptor type B (PTPRB), gap junction protein alpha-5 (GJA5), adenosine triphosphate-sensitive inward rectifier potassium channel-8 (KCNJ8), and von Willebrand factor (vWF), and cortical amyloid deposition.

METHODS

Between 2012 and 2018, 68 elderly individuals with amnestic mild cognitive impairment (32 men and 36 women; mean age 75.2 years) were enrolled. All participants underwent 11C-Pittsburgh compound-B (PiB)-PET, 18F-fluorodeoxyglucose-PET, and measurement of serum PTPRB, GJA5, KCNJ8, and vWF levels using commercially available human enzyme-linked immunosorbent assay kits. Based on the mean cortical standardized uptake value ratio, the participants were divided into two groups: PiB-negative group and PiB-positive group. Serum levels of PTPRB, GJA5, KCNJ8, and vWF were compared between the two groups. Multiple linear regression analysis was performed to investigate the relationship between serum PTPRB, GJA5, KCNJ8, and vWF levels and cortical amyloid deposition.

RESULTS

PTPRB and GJA5 levels were significantly lower and KCNJ8 and vWF levels were significantly higher in the PiB-positive group than in the PiB-negative group. PTPRB and GJA5 levels inversely correlated with mean PiB uptake, whereas KCNJ8 and vWF levels positively correlated with mean PiB uptake.

CONCLUSION

Serum levels of PTPRB, GJA5, KCNJ8, and vWF correlate with cortical amyloid deposition. These novel blood biomarkers of neurovascular unit are useful for identifying elderly individuals at risk of developing Alzheimer's disease.

Targeting the Angiopoietin/Tie Pathway: Prospects for Treatment of Retinal and Respiratory Disorders

Anti-angiogenic approaches have significantly advanced the treatment of vascular-related pathologies. The ephemeral outcome and known side effects of the current vascular endothelial growth factor (VEGF)-based anti-angiogenic treatments have intensified research on other growth factors. The angiopoietin/Tie (Ang/Tie) family has an established role in vascular physiology and regulates angiogenesis, vascular permeability, and inflammatory responses. The Ang/Tie family consists of angiopoietins 1-4, their receptors, tie1 and 2 and the vascular endothelial-protein tyrosine phosphatase (VE-PTP). Modulation of Tie2 activation has provided a promising outcome in preclinical models and has led to clinical trials of Ang/Tie-targeting drug candidates for retinal disorders. Although less is known about the role of Ang/Tie in pulmonary disorders, several studies have revealed great potential of the Ang/Tie family members as drug targets for pulmonary vascular disorders as well. In this review, we summarize the functions of the Ang/Tie pathway in retinal and pulmonary vascular physiology and relevant disorders and highlight promising drug candidates targeting this pathway currently being or expected to be under clinical evaluation for retinal and pulmonary vascular disorders.

Protein tyrosine phosphatases in cell adhesion

Adhesive structures between cells and with the surrounding matrix are essential for the development of multicellular organisms. In addition to providing mechanical integrity, they are key signalling centres providing feedback on the extracellular environment to the cell interior, and vice versa. During development, mitosis and repair, cell adhesions must undergo extensive remodelling. Post-translational modifications of proteins within these complexes serve as switches for activity. Tyrosine phosphorylation is an important modification in cell adhesion that is dynamically regulated by the protein tyrosine phosphatases (PTPs) and protein tyrosine kinases. Several PTPs are implicated in the assembly and maintenance of cell adhesions, however, their signalling functions remain poorly defined. The PTPs can act by directly dephosphorylating adhesive complex components or function as scaffolds. In this review, we will focus on human PTPs and discuss their individual roles in major adhesion complexes, as well as Hippo signalling. We have collated PTP interactome and cell adhesome datasets, which reveal extensive connections between PTPs and cell adhesions that are relatively unexplored. Finally, we reflect on the dysregulation of PTPs and cell adhesions in disease.

Vascular Endothelial Protein Tyrosine Phosphatase Regulates Endothelial Function

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is a receptor-type PTP (RPTP), predominantly expressed in vascular endothelial cells. It regulates embryonic and tumor angiogenesis and controls vascular permeability and homeostasis in inflammation. Major substrates are the tyrosine kinase receptor Tie-2 and the adhesion molecule VE-cadherin. This review describes how VE-PTP controls vascular functions by its various substrates and the therapeutic potential of VE-PTP in various pathophysiological settings.

Effects of an Environmentally Relevant Mixture of Organophosphate Esters Derived From House Dust on Endochondral Ossification in Murine Limb Bud Cultures

Organophosphate esters (OPEs) are used widely as flame retardants and plasticizers but much remains unknown about their potential toxicity. Previously, we reported that 4 individual OPEs suppress endochondral ossification in murine limb bud cultures. However, real-life exposure is to complex OPE mixtures. In the present study, we tested the hypothesis that a Canadian household dust-based OPE mixture will affect endochondral ossification in gestation day 13 CD1 mouse embryo limb buds expressing fluorescent markers for the major cell populations involved in the process: collagen type II alpha 1-enhanced cyan fluorescent protein (proliferative chondrocytes), collagen type X alpha 1-mCherry (hypertrophic chondrocytes), and collagen type I alpha 1-yellow fluorescent protein (osteoblasts). Limbs were cultured for 6 days in the presence of vehicle or dilutions of the OPE mixture (1/1 000 000, 1/600 000, and 1/300 000). All 3 OPE mixture dilutions affected cartilage template development and the progression of endochondral ossification, as indicated by the fluorescent markers. The expression of Sox9, the master regulator of chondrogenesis, was unchanged, but the expression of Runx2 and Sp7, which drive chondrocyte hypertrophy and osteoblastogenesis, was dilution-dependently suppressed. RNA-seq revealed that exposure to the 1/300 000 dilution of the OPE mixture for 24 h downregulated 153 transcripts and upregulated 48 others by at least 1.5-fold. Downregulated transcripts were enriched for those related to the immune system and bone formation. In contrast, upregulated transcripts were enriched for those with stress response functions known to be regulated by ATF4 activation. Thus, exposure to the mixture of OPEs commonly found in house dust may have adverse effects on bone formation.

Polarized Proteins in Endothelium and Their Contribution to Function

Protein localization in endothelial cells is tightly regulated to create distinct signaling domains within their tight spatial restrictions including luminal membranes, abluminal membranes, and interendothelial junctions, as well as caveolae and calcium signaling domains. Protein localization in endothelial cells is also determined in part by the vascular bed, with differences between arteries and veins and between large and small arteries. Specific protein polarity and localization is essential for endothelial cells in responding to various extracellular stimuli. In this review, we examine protein localization in the endothelium of resistance arteries, with occasional references to other vessels for contrast, and how that polarization contributes to endothelial function and ultimately whole organism physiology. We highlight the protein localization on the luminal surface, discussing important physiological receptors and the glycocalyx. The protein polarization to the abluminal membrane is especially unique in small resistance arteries with the presence of the myoendothelial junction, a signaling microdomain that regulates vasodilation, feedback to smooth muscle cells, and ultimately total peripheral resistance. We also discuss the interendothelial junction, where tight junctions, adherens junctions, and gap junctions all convene and regulate endothelial function. Finally, we address planar cell polarity, or axial polarity, and how this is regulated by mechanosensory signals like blood flow.

Growth Factor Deregulation and Emerging Role of Phosphatases in Diabetic Peripheral Artery Disease

Peripheral artery disease is caused by atherosclerosis of lower extremity arteries leading to the loss of blood perfusion and subsequent critical ischemia. The presence of diabetes mellitus is an important risk factor that greatly increases the incidence, the progression and the severity of the disease. In addition to accelerated disease progression, diabetic patients are also more susceptible to develop serious impairment of their walking abilities through an increased risk of lower limb amputation. Hyperglycemia is known to alter the physiological development of collateral arteries in response to ischemia. Deregulation in the production of several critical pro-angiogenic factors has been reported in diabetes along with vascular cell unresponsiveness in initiating angiogenic processes. Among the multiple molecular mechanisms involved in the angiogenic response, protein tyrosine phosphatases are potent regulators by dephosphorylating pro-angiogenic tyrosine kinase receptors. However, evidence has indicated that diabetes-induced deregulation of phosphatases contributes to the progression of several micro and macrovascular complications. This review provides an overview of growth factor alterations in the context of diabetes and peripheral artery disease, as well as a description of the role of phosphatases in the regulation of angiogenic pathways followed by an analysis of the effects of hyperglycemia on the modulation of protein tyrosine phosphatase expression and activity. Knowledge of the role of phosphatases in diabetic peripheral artery disease will help the development of future therapeutics to locally regulate phosphatases and improve angiogenesis.

A Small Molecule Inhibitor of VE-PTP Activates Tie2 in Schlemm's Canal Increasing Outflow Facility and Reducing Intraocular Pressure

Purpose

Tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (Tie2) activation in Schlemm's canal (SC) endothelium is required for the maintenance of IOP, making the angiopoietin/Tie2 pathway a target for new and potentially disease modifying glaucoma therapies. The goal of the present study was to examine the effects of a Tie2 activator, AKB-9778, on IOP and outflow function.

Methods

AKB-9778 effects on IOP was evaluated in humans, rabbits, and mice. Localization studies of vascular endothelial protein tyrosine phosphatase (VE-PTP), the target of AKB-9778 and a negative regulator of Tie2, were performed in human and mouse eyes. Mechanistic studies were carried out in mice, monitoring AKB-9778 effects on outflow facility, Tie2 phosphorylation, and filtration area of SC.

Results

AKB-9778 lowered IOP in patients treated subcutaneously for diabetic eye disease. In addition to efficacious, dose-dependent IOP lowering in rabbit eyes, topical ocular AKB-9778 increased Tie2 activation in SC endothelium, reduced IOP, and increased outflow facility in mouse eyes. VE-PTP was localized to SC endothelial cells in human and mouse eyes. Mechanistically, AKB-9778 increased the filtration area of SC for aqueous humor efflux in both wild type and in Tie2+/- mice.

Conclusions

This is the first report of IOP lowering in humans with a Tie2 activator and functional demonstration of its action in remodeling SC to increase outflow facility and lower IOP in fully developed mice. Based on these studies, a phase II clinical trial is in progress to advance topical ocular AKB-9778 as a first in class, Tie2 activator for treatment for ocular hypertension and glaucoma.

Generation of a p16 Reporter Mouse and Its Use to Characterize and Target p16high Cells In Vivo

Cell senescence plays a key role in age-associated organ dysfunction, but the in vivo pathogenesis is largely unclear. Here, we generated a p16-Cre^ERT2-tdTomato mouse model to analyze the in vivo characteristics of p16^high cells at a single-cell level. We found tdTomato-positive p16^high cells detectable in all organs, which were enriched with age. We also found that these cells failed to proliferate and had half-lives ranging from 2.6 to 4.2 months, depending on the tissue examined. Single-cell transcriptomics in the liver and kidneys revealed that p16^high cells were present in various cell types, though most dominant in hepatic endothelium and in renal proximal and distal tubule epithelia, and that these cells exhibited heterogeneous senescence-associated phenotypes. Further, elimination of p16^high cells ameliorated nonalcoholic steatohepatitis-related hepatic lipidosis and immune cell infiltration. Our new mouse model and single-cell analysis provide a powerful resource to enable the discovery of previously unidentified senescence functions in vivo.

VEGFR2 signaling drives meningeal vascular regeneration upon head injury

Upon severe head injury (HI), blood vessels of the meninges and brain parenchyma are inevitably damaged. While limited vascular regeneration of the injured brain has been studied extensively, our understanding of meningeal vascular regeneration following head injury is quite limited. Here, we identify key pathways governing meningeal vascular regeneration following HI. Rapid and complete vascular regeneration in the meninges is predominantly driven by VEGFR2 signaling. Substantial increase of VEGFR2 is observed in both human patients and mouse models of HI, and endothelial cell-specific deletion of Vegfr2 in the latter inhibits meningeal vascular regeneration. We further identify the facilitating, stabilizing and arresting roles of Tie2, PDGFRβ and Dll4 signaling, respectively, in meningeal vascular regeneration. Prolonged inhibition of this angiogenic process following HI compromises immunological and stromal integrity of the injured meninges. These findings establish a molecular framework for meningeal vascular regeneration after HI, and may guide development of wound healing therapeutics.

Severe head injury results in critical damage of blood vessels of the meninges and brain parenchyma. Here, the authors describe key pathways governing meningeal vascular regeneration following head injury, characterizing the differential roles of VEGFR2, Tie2, Dll4 and PDGFRβ signaling.

The VE-PTP Inhibitor AKB-9778 Improves Antitumor Activity and Diminishes the Toxicity of Interleukin 2 (IL-2) Administration

Administration of interleukin (IL)-2 has led to a durable response in patients with advanced renal cancer and melanoma but is restricted for clinical application because of adverse effects, including the vascular leak syndrome (VLS). VLS is associated with increased circulating levels of the Tie2 antagonist ligand, angiopoietin 2, and decreased Tie2 receptor phosphorylation and downstream signaling in endothelial cells (ECs). Given that vascular endothelial protein tyrosine phosphatase (VE-PTP) is a specific membrane phosphatase in ECs that dephosphorylates Tie2, the effects of targeting VE-PTP by a selective inhibitor AKB-9778 (AKB) in terms of VLS and antitumor efficacy were examined in this study. The authors found, by targeting VE-PTP, that the antitumor effects induced by IL-2 were augmented [tumor-free 44% (IL-2 alone) vs. 87.5% (IL-2+AKB)], associated with enhanced immune cell infiltrate (90% increase for CD8 T cells and natural killer cells). In addition, the side effects of IL-2 therapy were lessened, as demonstrated by diminished lung weight (less vascular leakage) as well as reduced cytokine levels (serum HMGB1 from 137.04±2.69 to 43.86±3.65 pg/mL; interferon-γ from 590.52±90.52 to 31.37±1.14 pg/mL). The authors further sought to determine the potential mechanism of the action of AKB-9778. The findings suggest that AKB-9778 may function through reducing serum angiopoietin 2 level and regulating EC viability. These findings provide insights into the targeting VE-PTP to improve tolerance and efficacy of IL-2 therapy and highlight the clinical potential of AKB-9778 for treating patients with VLS and cancer.

miR-624-5p promoted tumorigenesis and metastasis by suppressing hippo signaling through targeting PTPRB in osteosarcoma cells

Background

Accumulating evidence indicates that aberrant microRNA (miRNA) expression contributes to osteosarcoma progression. This study aimed to elucidate the association between miR-624-5p expression and osteosarcoma (OS) development and to investigate its underlying mechanism.

Methods

We analyzed GSE65071 from the GEO database and found miR-624-5p was the most upregulated miRNA. The expression of miR-624-5p and its specific target gene were determined in human OS specimens and cell lines by RT-PCR and western blot. The effects of miR-624-5p depletion or ectopic expression on OS proliferation, migration and invasion were evaluated in vitro using CCK-8 proliferation assay, colony formation assay, transwell assay, would-healing assay and 3D spheroid BME cell invasion assay respectively. We investigated in vivo effects of miR-624-5p using a mouse tumorigenicity model. Besides, luciferase reporter assays were employed to identify interactions between miR-624-5p and its specific target gene.

Results

miR-624-5p expression was upregulated in OS cells and tissues, and overexpressing miR-624-5p led to a higher malignant level of OS, including cell proliferation, migration and invasion in vitro and in vivo. Protein tyrosine phosphatase receptor type B (PTPRB) was negatively correlated with miR-624-5p expression in OS tissues. Using the luciferase reporter assay and Western blotting, PTPRB was confirmed as a downstream target of miR-624-5p. PTPRB restored the effects of miR-624-5p on OS migration and invasion. The Hippo signaling pathway was identified as being involved in the miR-624-5p/PTPRB axis.

Conclusions

In conclusion, our results suggest that miR-624-5p is a negative regulator of PTPRB and a risk factor for tumor metastasis in OS progression.

Fabrication of core-shell spheroids as building blocks for engineering 3D complex vascularized tissue

Cell spheroids as building blocks for engineering micro-tissue should be able to mimic the complex structure of natural tissue. However, control of the distribution of multiple cell populations within cell spheroids is difficult to achieve with current spheroid-harvest methods such as hanging-drop and with the use of microwell plates. In this study, we report the fabrication of core-shell spheroids with the ultimate goal to form 3D complex micro-tissue. We used endothelial cells and two types of stem cells (human turbinate mesenchymal stem cells (hTMSCs)/adipose-derived stem cells (ADSCs)). The stem cells and endothelial cells formed layered micro-sized cell sheets (µCSs) on polydopamine micro-patterned temperature-responsive hydrogel surfaces by a sequential seeding method, and these layered µCSs self-assembled to form core-shell spheroids by expansion of the hydrogels. The co-cultured spheroids formed a core-shell structure irrespective of stem cell type. In addition, the size of the core-shell spheroids was controlled from 90 ± 1 to 144 ± 3 µm by changing pattern sizes (200, 300, and 400 µm). The shell thickness gradually increased from 12 ± 3 to 30 ± 6 µm by adjusting the endothelial cell seeding density. Finally, we fabricated the micro-tissue by fusion of the co-cultured spheroids, and the spheroids with the core-shell structure rapidly induced in vitro vessel-like network in 3 days. Thus, the position of endothelial cells in co-cultured spheroids may be an important factor for the modulation of the vascularization process, which can be useful for the production of 3D complex micro-tissues using spheroids as building blocks. STATEMENT OF SIGNIFICANCE: This manuscript describes our work on the fabrication of core-shell spheroids as building blocks to form 3D complex vascularized micro-tissue. Stem cells (human turbinate mesenchymal stem cells (hTMSCs) or adipose-derived stem cells (ADSCs)) and endothelial cells formed layered micro-sized cell sheets (µCSs) on micro-patterned temperature-responsive hydrogel surfaces by a sequential seeding method, and these layered µCSs self-assembled to form core-shell spheroids (core - stem cells, shell - endothelial cells), irrespective of stem cell type. In addition, the size and shell thickness of the core-shell spheroids were controlled by modifying pattern size and endothelial cell seeding density. We fabricated the vascularized micro-tissue by fusion of the spheroids and demonstrated that the spheroids with a core-shell structure rapidly induced vessel-like network.

Targeting the vascular-specific phosphatase PTPRB protects against retinal ganglion cell loss in a pre-clinical model of glaucoma

Elevated intraocular pressure (IOP) due to insufficient aqueous humor outflow through the trabecular meshwork and Schlemm’s canal (SC) is the most important risk factor for glaucoma, a leading cause of blindness worldwide. We previously reported loss of function mutations in the receptor tyrosine kinase TEK or its ligand ANGPT1 cause primary congenital glaucoma in humans and mice due to failure of SC development. Here, we describe a novel approach to enhance canal formation in these animals by deleting a single allele of the gene encoding the phosphatase PTPRB during development. Compared to Tek haploinsufficient mice, which exhibit elevated IOP and loss of retinal ganglion cells, Tek^+/-;Ptprb^+/- mice have elevated TEK phosphorylation, which allows normal SC development and prevents ocular hypertension and RGC loss. These studies provide evidence that PTPRB is an important regulator of TEK signaling in the aqueous humor outflow pathway and identify a new therapeutic target for treatment of glaucoma.

Vascular Endothelial Receptor Tyrosine Phosphatase: Identification of Novel Substrates Related to Junctions and a Ternary Complex with EPHB4 and TIE2

Vascular endothelial protein tyrosine phosphatase (VE-PTP, PTPRB) is a receptor type phosphatase that is crucial for the regulation of endothelial junctions and blood vessel development. We and others have shown recently that VE-PTP regulates vascular integrity by dephosphorylating substrates that are key players in endothelial junction stability, such as the angiopoietin receptor TIE2, the endothelial adherens junction protein VE-cadherin and the vascular endothelial growth factor receptor VEGFR2. Here, we have systematically searched for novel substrates of VE-PTP in endothelial cells by utilizing two approaches. First, we studied changes in the endothelial phosphoproteome on exposing cells to a highly VE-PTP-specific phosphatase inhibitor followed by affinity isolation and mass-spectrometric analysis of phosphorylated proteins by phosphotyrosine-specific antibodies. Second, we used a substrate trapping mutant of VE-PTP to pull down phosphorylated substrates in combination with SILAC-based quantitative mass spectrometry measurements. We identified a set of substrate candidates of VE-PTP, of which a remarkably large fraction (29%) is related to cell junctions. Several of those were found in both screens and displayed very high connectivity in predicted functional interaction networks. The receptor protein tyrosine kinase EPHB4 was the most prominently phosphorylated protein on VE-PTP inhibition among those VE-PTP targets that were identified by both proteomic approaches. Further analysis revealed that EPHB4 forms a ternary complex with VE-PTP and TIE2 in endothelial cells. VE-PTP controls the phosphorylation of each of these two tyrosine kinase receptors. Despite their simultaneous presence in a ternary complex, stimulating each of the receptors with their own specific ligand did not cross-activate the respective partner receptor. Our systematic approach has led to the identification of novel substrates of VE-PTP, of which many are relevant for the control of cellular junctions further promoting the importance of VE-PTP as a key player of junctional signaling.

Vasculogenic Mimicry: Become an Endothelial Cell "But Not So Much"

Blood vessels supply all body tissues with nutrients and oxygen, take away waste products and allow the arrival of immune cells and other cells (pericytes, smooth muscle cells) that form part of these vessels around the principal endothelial cells. Vasculogenic mimicry (VM) is a tumor blood supply system that takes place independently of angiogenesis or endothelial cells, and is associated with poor survival in cancer patients. Aberrant expression of VE-cadherin has been strongly associated with VM. Even more, VE-cadherin has constitutively high phosphorylation levels on the residue of Y658 in human malignant melanoma cells. In this review we focus on non-endothelial VE-cadherin and its post-translational modifications as a crucial component in the development of tumor VM, highlighting the signaling pathways that lead to their pseudo-endothelial and stem-like phenotype and the role of tumor microenvironment. We discuss the importance of the tumor microenvironment in VM acquisition, and describe the most recent therapeutic targets that have been proposed for the repression of VM.

VE-PTP inhibition stabilizes endothelial junctions by activating FGD5

Inhibition of VE-PTP, an endothelial receptor-type tyrosine phosphatase, triggers phosphorylation of the tyrosine kinase receptor Tie-2, which leads to the suppression of inflammation-induced vascular permeability. Analyzing the underlying mechanism, we show here that inhibition of VE-PTP and activation of Tie-2 induce tyrosine phosphorylation of FGD5, a GTPase exchange factor (GEF) for Cdc42, and stimulate its translocation to cell contacts. Interfering with the expression of FGD5 blocks the junction-stabilizing effect of VE-PTP inhibition in vitro and in vivo. Likewise, FGD5 is required for strengthening cortical actin bundles and inhibiting radial stress fiber formation, which are each stimulated by VE-PTP inhibition. We identify Y820 of FGD5 as the direct substrate for VE-PTP. The phosphorylation of FGD5-Y820 is required for the stabilization of endothelial junctions and for the activation of Cdc42 by VE-PTP inhibition but is dispensable for the recruitment of FGD5 to endothelial cell contacts. Thus, activation of FGD5 is a two-step process that comprises membrane recruitment and phosphorylation of Y820. These steps are necessary for the junction-stabilizing effect stimulated by VE-PTP inhibition and Tie-2 activation.

Akt in cancer: Mediator and more

Akt is a serine/threonine kinase and it participates in the key role of the PI3K signaling pathway. The Akt can be activated by a wide range of growth signals and the biochemical mechanisms leading to Akt activation are well defined. Once activated, Akt modulates the function of many downstream proteins involved in cellular survival, proliferation, migration, metabolism, and angiogenesis. The Akt is a central node of many signaling pathways and it is frequently deregulated in many types of human cancers. In this review, we provide an overview of Akt function and its role in the hallmarks of human cancer. We also discussed various mechanisms of Akt dysregulation in cancers, including epigenetic modifications like methylation, post-transcriptional non-coding RNAs-mediated regulation, and the overexpression and mutation.

Targeting VE-PTP phosphatase protects the kidney from diabetic injury

Diabetic nephropathy is a leading cause of kidney failure. VE-PTP phosphatase expression is increased in the endothelium of rodents with diabetes and hypertension. Genetic deletion of VE-PTP reduces kidney injury in diabetic mice, suggesting it may be a therapeutic target.

Diabetic nephropathy is a leading cause of end-stage kidney failure. Reduced angiopoietin-TIE2 receptor tyrosine kinase signaling in the vasculature leads to increased vascular permeability, inflammation, and endothelial cell loss and is associated with the development of diabetic complications. Here, we identified a mechanism to explain how TIE2 signaling is attenuated in diabetic animals. Expression of vascular endothelial protein tyrosine phosphatase VE-PTP (also known as PTPRB), which dephosphorylates TIE2, is robustly up-regulated in the renal microvasculature of diabetic rodents, thereby reducing TIE2 activity. Increased VE-PTP expression was dependent on hypoxia-inducible factor transcriptional activity in vivo. Genetic deletion of VE-PTP restored TIE2 activity independent of ligand availability and protected kidney structure and function in a mouse model of severe diabetic nephropathy. Mechanistically, inhibition of VE-PTP activated endothelial nitric oxide synthase and led to nuclear exclusion of the FOXO1 transcription factor, reducing expression of pro-inflammatory and pro-fibrotic gene targets. In sum, we identify inhibition of VE-PTP as a promising therapeutic target to protect the kidney from diabetic injury.

Exome sequencing in families with chronic central serous chorioretinopathy

BACKGROUND

Central serous chorioretinopathy (CSC) is a chorioretinal disease characterized by fluid accumulation between the neuroretina and retinal pigment epithelium with unknown etiology. Family studies have suggested a heritable component for CSC with an autosomal dominant inheritance pattern. Therefore, exome sequencing was performed on familial cCSC to indentify the genetic components contributing to familial cCSC.

METHODS

Exome sequencing was performed on 72 individuals of 18 families with CSC. In these families, we determined whether rare genetic variants (minor allele frequency < 1%) were segregated with CSC and also performed familial gene-burden analysis.

RESULTS

In total, 11 variants segregated in two out of 18 families. One of these variants, c.4145C>T; p.T1382I (rs61758735) in the PTPRB gene, was also associated with CSC in a large case-control cohort sequenced previously (p = 0.009). Additionally, in 28 genes two or more different heterozygous variants segregated in two or more families, but no gene showed consistent associations in both the family gene-burden results and gene-burden analysis in the case-control cohort.

CONCLUSION

We identified potential candidate genes for familial CSC and managed to exclude Mendelian inheritance of variants in one or a limited number of genes. Instead, familial CSC may be a heterogeneous Mendelian disease caused by variants in many different genes, or alternatively CSC may represent a complex disease to which both environmental factors and genetics contribute.

Anti-angiogenic Targets: Angiopoietin and Angiopoietin Receptors

Tumor blood vessel formation (angiogenesis) is essential for tumor growth and metastasis. Two main endothelial ligand–receptor pathways regulating angiogenesis are vascular endothelial growth factor (VEGF) receptor and angiopoietin-TIE receptor pathways. The angiopoietin-TIE pathway is required for the remodeling and maturation of the blood and lymphatic vessels during embryonic development after VEGF and VEGF-C mediated development of the primary vascular plexus. Angiopoietin-1 (ANGPT1) stabilizes the vasculature after angiogenic processes, via tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (TIE2) activation. In contrast, ANGPT2 is upregulated at sites of vascular remodeling. ANGPT2 is secreted by activated endothelial cells in inflammation, promoting vascular destabilization. ANGPT2 has been found to be expressed in many human cancers. Intriguingly, in preclinical models inhibition of ANGPT2 has provided promising results in preventing tumor angiogenesis, tumor growth, and metastasis, making it an attractive candidate to target in tumors. However, until now the first ANGPT2 targeting therapies have been less effective in clinical trials than in experimental models. Additionally, in preclinical models combined therapy against ANGPT2 and VEGF or immune checkpoint inhibitors has been superior to monotherapies, and these pathways are also targeted in early clinical trials. In order to improve current anti-angiogenic therapies and successfully exploit ANGPT2 as a target for cancer treatment, the biology of the angiopoietin-TIE pathway needs to be profoundly clarified.

Synthesis and biological evaluation of (3'-amino-[1,1'-biphenyl]-4-yl) sulfamic acid derivatives as novel HPTPβ inhibitors

A series of novel (3'-amino-[1,1'-biphenyl]-4-yl) sulfamic acid derivatives were designed as nonphosphonate-based phosphotyrosy (pTyr) mimetics, synthesized and screened for use as HPTPβ inhibitors. Compounds C22 and C2 showed favorable HPTPβ inhibitory activity and better selectivity for HPTPβ than for PTP1B and SHP2. Docking results suggested that compounds C2 and C22 could not only efficiently fit into the catalytic site of the HPTPβ enzyme but also interact with the Lys1807, Arg1809 and Lys1811 residues of the secondary binding site, which was next to the catalytic center of the enzyme. The mode of interaction of the synthesized compound with the protein was different from the one found in a complex crystal of small molecules with HPTPβ (2I4H), in which the inhibitory molecule formed hydrogen bonds with the Gln1948 and Asn1735 residues of the secondary binding site.

Collagen regulates the ability of endothelial progenitor cells to protect hypoxic myocardium through a mechanism involving miR-377/VE-PTP axis

The possibility to employ stem/progenitor cells in the cardiovascular remodelling after myocardial infarction is one of the main queries of regenerative medicine. To investigate whether endothelial progenitor cells (EPCs) participate in the restoration of hypoxia-affected myocardium, we used a co-culture model that allowed the intimate interaction between EPCs and myocardial slices, mimicking stem cell transplantation into the ischaemic heart. On this model, we showed that EPCs engrafted to some extent and only transiently survived into the host tissue, yet produced visible protective effects, in terms of angiogenesis and protection against apoptosis and identified miR-377-VE-PTP axis as being involved in the protective effects of EPCs in hypoxic myocardium. We also showed that collagen, the main component of the myocardial scar, was important for these protective effects by preserving VE-PTP levels, which were otherwise diminished by miR-377. By this, a good face of the scar is revealed, which was so far perceived as having only detrimental impact on the exogenously delivered stem/progenitor cells by affecting not only the engraftment, but also the general protective effects of stem cells.

Atorvastatin enhances endothelial adherens junctions through promoting VE-PTP gene transcription and reducing VE-cadherin-Y731 phosphorylation

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is essential for endothelial cells (ECs) adherens junction and vascular homeostasis; however, the regulatory mechanism of VE-PTP transcription is unknown, and a drug able to promote VE-PTP expression in ECs has not yet been reported in the literature. In this study, we used human ECs as a model to explore small molecule compounds able to promote VE-PTP expression, and found that atorvastatin, a HMG-CoA reductase inhibitor widely used in the clinic to treat hypercholesterolemia-related cardiovascular diseases, strongly promoted VE-PTP transcription in ECs through activating the VE-PTP promoter and upregulating the expression of the transcription factor, specificity protein 1 (SP1). Additionally, atorvastatin markedly reduced VE-cadherin-Y731 phosphorylation induced by cigarette smoke extract and significantly enhanced stability of endothelial adherens junctions. Together, our findings reveal that atorvastatin up-regulates VE-PTP expression, increases VE-cadherin protein levels, and decreases VE-cadherin-Y731 phosphorylation to strengthen EC adherens junctions and maintain vascular cell monolayer integrity, offering a new mechanism of atorvastatin against CSE-induced disruption of vascular integrity and relevant cardio-cerebrovascular disease.

Context-dependent functions of angiopoietin 2 are determined by the endothelial phosphatase VEPTP

The angiopoietin (ANGPT)-TIE2/TEK signaling pathway is essential for blood and lymphatic vascular homeostasis. ANGPT1 is a potent TIE2 activator, whereas ANGPT2 functions as a context-dependent agonist/antagonist. In disease, ANGPT2-mediated inhibition of TIE2 in blood vessels is linked to vascular leak, inflammation, and metastasis. Using conditional knockout studies in mice, we show TIE2 is predominantly activated by ANGPT1 in the cardiovascular system and by ANGPT2 in the lymphatic vasculature. Mechanisms underlying opposing actions of ANGPT2 in blood vs. lymphatic endothelium are poorly understood. Here we show the endothelial-specific phosphatase VEPTP (vascular endothelial protein tyrosine phosphatase) determines TIE2 response to ANGPT2. VEPTP is absent from lymphatic endothelium in mouse in vivo, permitting ANGPT2/TIE2-mediated lymphangiogenesis. Inhibition of VEPTP converts ANGPT2 into a potent TIE2 activator in blood endothelium. Our data support a model whereby VEPTP functions as a rheostat to modulate ANGPT2 ligand effect on TIE2.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

The receptor protein tyrosine phosphatase PTPRB negatively regulates FGF2-dependent branching morphogenesis

PTPRB is a transmembrane protein tyrosine phosphatase known to regulate blood vessel remodelling and angiogenesis. Here, we demonstrate that PTPRB negatively regulates branching morphogenesis in the mouse mammary epithelium. We show that Ptprb is highly expressed in adult mammary stem cells and also, although at lower levels, in oestrogen receptor-positive luminal cells. During mammary development, Ptprb expression is downregulated during puberty, a period of extensive ductal outgrowth and branching. In vivo shRNA knockdown of Ptprb in the cleared mammary fat pad transplant assay resulted in smaller epithelial outgrowths with an increased branching density and also increased branching in an in vitro organoid assay. Organoid branching was dependent on stimulation by FGF2, and Ptprb knockdown in mammary epithelial cells resulted in a higher level of fibroblast growth factor receptor (FGFR) activation and ERK1/2 phosphorylation, both at baseline and following FGF2 stimulation. Therefore, PTPRB regulates branching morphogenesis in the mammary epithelium by modulating the response of the FGFR signalling pathway to FGF stimulation. Considering the importance of branching morphogenesis in multiple taxa, our findings have general importance outside mammary developmental biology.

Recent advances in understanding the role of protein-tyrosine phosphatases in development and disease

Protein-tyrosine phosphatases (PTPs) remove phosphate groups from tyrosine residues, and thereby propagate or inhibit signal transduction, and hence influence cellular processes such as cell proliferation and differentiation. The importance of tightly controlled PTP activity is reflected by the numerous mechanisms employed by the cell to control PTP activity, including a variety of post-translational modifications, and restricted subcellular localization. This review highlights the strides made in the last decade and discusses the important role of PTPs in key aspects of embryonic development: the regulation of stem cell self-renewal and differentiation, gastrulation and somitogenesis during early embryonic development, osteogenesis, and angiogenesis. The tentative importance of PTPs in these processes is highlighted by the diseases that present upon aberrant activity.

IP3 receptor signaling and endothelial barrier function

The endothelium, a monolayer of endothelial cells lining vessel walls, maintains tissue-fluid homeostasis by restricting the passage of the plasma proteins and blood cells into the interstitium. The ion Ca²⁺, a ubiquitous secondary messenger, initiates signal transduction events in endothelial cells that is critical to control of vascular tone and endothelial permeability. The ion Ca²⁺ is stored inside the intracellular organelles and released into the cytosol in response to environmental cues. The inositol 1,4,5-trisphosphate (IP₃) messenger facilitates Ca²⁺ release through IP₃ receptors which are Ca²⁺-selective intracellular channels located within the membrane of the endoplasmic reticulum. Binding of IP₃ to the IP₃Rs initiates assembly of IP₃R clusters, a key event responsible for amplification of Ca²⁺ signals in endothelial cells. This review discusses emerging concepts related to architecture and dynamics of IP₃R clusters, and their specific role in propagation of Ca²⁺ signals in endothelial cells.

Expression of receptor-type protein tyrosine phosphatase in developing and adult renal vasculature

Renal vascular development is a coordinated process that requires ordered endothelial cell proliferation, migration, intercellular adhesion, and morphogenesis. In recent decades, studies have defined the pivotal role of endothelial receptor tyrosine kinases (RPTKs) in the development and maintenance of renal vasculature. However, the expression and the role of receptor tyrosine phosphatases (RPTPs) in renal endothelium are poorly understood, though coupled and counterbalancing roles of RPTKs and RPTPs are well defined in other systems. In this study, we evaluated the promoter activity and immunolocalization of two endothelial RPTPs, VE-PTP and PTPμ, in developing and adult renal vasculature using the heterozygous LacZ knock-in mice and specific antibodies. In adult kidneys, both VE-PTP and PTPμ were expressed in the endothelium of arterial, glomerular, and medullary vessels, while their expression was highly limited in peritubular capillaries and venous endothelium. VE-PTP and PTPμ promoter activity was also observed in medullary tubular segments in adult kidneys. In embryonic (E12.5, E13.5, E15.5, E17.5) and postnatal (P0, P3, P7) kidneys, these RPTPs were expressed in ingrowing renal arteries, developing glomerular microvasculature (as early as the S-shaped stage), and medullary vessels. Their expression became more evident as the vasculatures matured. Peritubular capillary expression of VE-PTP was also noted in embryonic and postnatal kidneys. Compared to VE-PTP, PTPμ immunoreactivity was relatively limited in embryonic and neonatal renal vasculature and evident immunoreactivity was observed from the P3 stage. These findings indicate 1) VE-PTP and PTPμ are expressed in endothelium of arterial, glomerular, and medullary renal vasculature, 2) their expression increases as renal vascular development proceeds, suggesting that these RPTPs play a role in maturation and maintenance of these vasculatures, and 3) peritubular capillary VE-PTP expression is down-regulated in adult kidneys, suggesting a role of VE-PTP in the development of peritubular capillaries.

Resolvin D1 via prevention of ROS-mediated SHP2 inactivation protects endothelial adherens junction integrity and barrier function

Resolvins are a novel class of lipid mediators that play an important role in the resolution of inflammation, although the underlying mechanisms are not very clear. To explore the anti-inflammatory mechanisms of resolvins, we have studied the effects of resolvin D1 (RvD1) on lipopolysaccharide (LPS)-induced endothelial barrier disruption as it is linked to propagation of inflammation. We found that LPS induces endothelial cell (EC) barrier disruption via xanthine oxidase (XO)-mediated reactive oxygen species (ROS) production, protein tyrosine phosphatase SHP2 inactivation and Fyn-related kinase (Frk) activation leading to tyrosine phosphorylation of α-catenin and VE-cadherin and their dissociation from each other affecting adherens junction (AJ) integrity and thereby increasing endothelial barrier permeability. RvD1 attenuated LPS-induced AJ disassembly and endothelial barrier permeability by arresting tyrosine phosphorylation of α-catenin and VE-cadherin and their dislocation from AJ via blockade of XO-mediated ROS production and thereby suppression of SHP2 inhibition and Frk activation. We have also found that the protective effects of RvD1 on EC barrier function involve ALX/FPR2 and GPR32 as inhibition or neutralization of these receptors negates its protective effects. LPS also increased XO activity, SHP2 cysteine oxidation and its inactivation, Frk activation, α-catenin and VE-cadherin tyrosine phosphorylation and their dissociation from each other leading to AJ disruption with increased vascular permeability in mice arteries and RvD1 blocked all these effects. Thus, RvD1 protects endothelial AJ and its barrier function from disruption by inflammatory mediators such as LPS via a mechanism involving the suppression of XO-mediated ROS production and blocking SHP2 inactivation.

Dual roles of protein tyrosine phosphatase kappa in coordinating angiogenesis induced by pro-angiogenic factors

A potential role may be played by receptor-type protein tyrosine phosphatase kappa (PTPRK) in angiogenesis due to its critical function in coordinating intracellular signal transduction from various receptors reliant on tyrosine phosphorylation. In the present study, we investigated the involvement of PTPRK in the cellular functions of vascular endothelial cells (HECV) and its role in angiogenesis using in vitro assays and a PTPRK knockdown vascular endothelial cell model. PTPRK knockdown in HECV cells (HECV^PTPRKkd) resulted in a decrease of cell proliferation and cell-matrix adhesion; however, increased cell spreading and motility were seen. Reduced focal adhesion kinase (FAK) and paxillin protein levels were seen in the PTPRK knockdown cells which may contribute to the inhibitory effect on adhesion. HECV^PTPRKkd cells were more responsive to the treatment of fibroblast growth factor (FGF) in their migration compared with the untreated control and cells treated with VEGF. Moreover, elevated c-Src and Akt1 were seen in the PTPRK knockdown cells. The FGF-promoted cell migration was remarkably suppressed by an addition of PLCγ inhibitor compared with other small inhibitors. Knockdown of PTPRK suppressed the ability of HECV cells to form tubules and also impaired the tubule formation that was induced by FGF and conditioned medium of cancer cells. Taken together, it suggests that PTPRK plays dual roles in coordinating angiogenesis. It plays a positive role in cell proliferation, adhesion and tubule formation, but suppresses cell migration, in particular, the FGF-promoted migration. PTPRK bears potential to be targeted for the prevention of tumour associated angiogenesis.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Mechanisms and regulation of endothelial VEGF receptor signalling

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

New Insights into VacA Intoxication Mediated through Its Cell Surface Receptors

Helicobacter pylori (H. pylori), a major cause of gastroduodenal diseases, produces VacA, a vacuolating cytotoxin associated with gastric inflammation and ulceration. The C-terminal domain of VacA plays a crucial role in receptor recognition on target cells. We have previously identified three proteins (i.e., RPTPα, RPTPβ, and LRP1) that serve as VacA receptors. These receptors contribute to the internalization of VacA into epithelial cells, activate signal transduction pathways, and contribute to cell death and gastric ulceration. In addition, other factors (e.g., CD18, sphingomyelin) have also been identified as cell-surface, VacA-binding proteins. Since we believe that, following interactions with its host cell receptors, VacA participates in events leading to disease, a better understanding of the cellular function of VacA receptors may provide valuable information regarding the mechanisms underlying the pleiotropic actions of VacA and the pathogenesis of H. pylori-mediated disease. In this review, we focus on VacA receptors and their role in events leading to cell damage.

Factors controlling permeability of the blood-brain barrier

As the primary protective barrier for neurons in the brain, the blood-brain barrier (BBB) exists between the blood microcirculation system and the brain parenchyma. The normal BBB integrity is essential in protecting the brain from systemic toxins and maintaining the necessary level of nutrients and ions for neuronal function. This integrity is mediated by structural BBB components, such as tight junction proteins, integrins, annexins, and agrin, of a multicellular system including endothelial cells, astrocytes, pericytes, etc. BBB dysfunction is a significant contributor to the pathogeneses of a variety of brain disorders. Many signaling factors have been identified to be able to control BBB permeability through regulating the structural components. Among those signaling factors are inflammatory mediators, free radicals, vascular endothelial growth factor, matrix metalloproteinases, microRNAs, etc. In this review, we provide a summary of recent progress regarding these structural components and signaling factors, relating to their roles in various brain disorders. Attention is also devoted to recent research regarding impact of pharmacological agents such as isoflurane on BBB permeability and how iron ion passes across BBB. Hopefully, a better understanding of the factors controlling BBB permeability helps develop novel pharmacological interventions of BBB hyperpermeability under pathological conditions.