VE-PTP maintains the endothelial barrier via plakoglobin and becomes dissociated from VE-cadherin by leukocytes and by VEGF

We have shown recently that vascular endothelial protein tyrosine phosphatase (VE-PTP), an endothelial-specific membrane protein, associates with vascular endothelial (VE)–cadherin and enhances VE-cadherin function in transfected cells (Nawroth, R., G. Poell, A. Ranft, U. Samulowitz, G. Fachinger, M. Golding, D.T. Shima, U. Deutsch, and D. Vestweber. 2002. EMBO J. 21:4885–4895). We show that VE-PTP is indeed required for endothelial cell contact integrity, because down-regulation of its expression enhanced endothelial cell permeability, augmented leukocyte transmigration, and inhibited VE-cadherin–mediated adhesion. Binding of neutrophils as well as lymphocytes to endothelial cells triggered rapid (5 min) dissociation of VE-PTP from VE-cadherin. This dissociation was only seen with tumor necrosis factor α–activated, but not resting, endothelial cells. Besides leukocytes, vascular endothelial growth factor also rapidly dissociated VE-PTP from VE-cadherin, indicative of a more general role of VE-PTP in the regulation of endothelial cell contacts. Dissociation of VE-PTP and VE-cadherin in endothelial cells was accompanied by tyrosine phoshorylation of VE-cadherin, β-catenin, and plakoglobin. Surprisingly, only plakoglobin but not β-catenin was necessary for VE-PTP to support VE-cadherin adhesion in endothelial cells. In addition, inhibiting the expression of VE-PTP preferentially increased tyrosine phosphorylation of plakoglobin but not β-catenin. In conclusion, leukocytes interacting with endothelial cells rapidly dissociate VE-PTP from VE-cadherin, weakening endothelial cell contacts via a mechanism that requires plakoglobin but not β-catenin.     

Microparticles from apoptotic monocytes enhance nitrosative stress in human endothelial cells

Microparticles are membrane vesicles with procoagulant and proinflammatory properties released during cell activation or apoptosis. Microparticles from monocytes have been implicated in atherosclerosis and vascular inflammation, but their direct effects on endothelial cells are not completely elucidated. The present study was designed to dissect the signaling pathways of monocytic microparticles in endothelial cells with respect to both NO pathway and reactive oxygen species. Microparticles were produced by treatment of human monocytic cell line THP-1 with the apoptotic agent VP-16. Human endothelial cells were treated with monocytic microparticles and then, we studied their effects on nitrosative and oxidative stresses. Incubation of human endothelial cells with microparticles enhanced the production of NO without affecting superoxide anions generation. Microparticles did not affect endothelial NO synthase expression and its phosphorylation. Interestingly, microparticles decreased caveolin-1 expression and increased its phosphorylation. Inhibition of PI-3-kinase or MEK1/2 reversed the effects of microparticles on caveolin-1 expression but not its phosphorylation. Moreover, microparticles increased nitration of several proteins, reflecting peroxynitrite production, which was prevented by blockade of PI-3-kinase pathway. In summary, monocyte microparticles active multiple pathways related to nitrosative stress in endothelial cells including both PI-3-kinase and ERK1/2 in the regulation of caveolin-1 expression. These data underscore the pleiotropic effect of microparticles on endothelial cells and suggest that they probably play a critical role on vascular function.     

Breast cancer chemotherapy induces vascular dysfunction and hypertension through a NOX4-dependent mechanism

Cardiovascular disease is the major cause of morbidity and mortality in breast cancer survivors. Chemotherapy contributes to this risk. We aimed to define the mechanisms of long-term vascular dysfunction caused by neoadjuvant chemotherapy (NACT) and identify novel therapeutic targets. We studied arteries from postmenopausal women who had undergone breast cancer treatment using docetaxel, doxorubicin, and cyclophosphamide (NACT) and from women with no history of such treatment matched for key clinical parameters. We explored mechanisms in WT and Nox4^–/– mice and in human microvascular endothelial cells. Endothelium-dependent, NO-mediated vasodilatation was severely impaired in patients after NACT, while endothelium-independent responses remained normal. This was mimicked by a 24-hour exposure of arteries to NACT agents ex vivo. When applied individually, only docetaxel impaired endothelial function in human vessels. Mechanistic studies showed that NACT increased inhibitory eNOS phosphorylation of threonine 495 in a Rho-associated protein kinase–dependent (ROCK-dependent) manner and augmented vascular superoxide and hydrogen peroxide production and NADPH oxidase activity. Docetaxel increased expression of the NADPH oxidase NOX4 in endothelial and smooth muscle cells and NOX2 in the endothelium. A NOX4 increase in human arteries may be mediated epigenetically by diminished DNA methylation of the NOX4 promoter. Docetaxel induced endothelial dysfunction and hypertension in mice, and these were prevented in Nox4^–/– mice and by pharmacological inhibition of Nox4 or Rock. Commonly used chemotherapeutic agents and, in particular, docetaxel alter vascular function by promoting the inhibitory phosphorylation of eNOS and enhancing ROS production by NADPH oxidases.     

机械牵张对人肺血管内皮细胞通透性的影响及其分子机制

目的观察机械牵张对人肺动脉内皮细胞（HPAEC）和人肺微血管内皮细胞（HPMVEC）通透性的影响及对通透性关键蛋白VE-cadherin、Claudin-5和Caveolin-1表达的调控。 方法采用机械牵张装置Flexcell FX-5000T对HPAEC（ATCC）和HPMVEC（ATCC）施加0.5 Hz频率10%或20%牵张应力。应用qRT-PCR及Western Blot方法检测机械牵张前后内皮通透性关键蛋白VE-cadherin、Claudin-5、Caveolin-1 mRNA和蛋白含量表达变化。采用细胞动态分析仪以及Transwell小室/异硫氰酸荧光素（FITC）-白蛋白法检测机械牵张后的HPAEC细胞和HPMVEC细胞通透性改变。 结果20%机械牵张后，与对照组比较，HPAEC细胞通透性关键蛋白VE-cadherin mRNA和蛋白表达、Claudin-5 mRNA和蛋白表达和Caveolin-1 mRNA表达均下降（P<0.05），而Caveolin-1蛋白水平较对照组无明显变化；HPMVEC细胞通透性关键蛋白VE-cadherin mRNA和蛋白表达，Caveolin-1 mRNA和蛋白表达均下降（P<0.05），而Claudin-5 mRNA和蛋白水平较对照组无明显变化。 结论机械牵张会导致肺血管内皮通透性增高，是通过下调通透性关键蛋白的表达，并且两种细胞的通透性影响机制有差异，HPAEC牵涉紧密连接，HPMVEC牵涉跨内皮细胞途径。     

乌司他丁对炎症状态下血管内皮屏障功能的影响及机制

目的阐明乌司他丁（UTI）对炎症状态下血管内皮屏障功能的影响及具体分子机制。 方法以人脐静脉内皮细胞系EA.hy926为研究对象,建立炎症细胞模型及RhoA过表达细胞模型,分别用UTI和TNF-α处理细胞,采用Transwell法、TEER法检测细胞通透性;Western Blot法及RT-PCR法检测Rho/ROCK信号通路相关关键分子（RhoA、ROCK2、MYPT1、p-MYPT1及VE-cadherin）的表达变化情况。 结果与正常对照组相比,TNF-α作用后EA.hy926细胞电阻值明显降低,细胞通透性显著升高,差异具有统计学意义[（33.67±4.04）Ω/cm² vs（67.17±3.81）Ω/cm²,t=10.435,P<0.01],细胞内RhoA、ROCK2、p-MYPT1的表达量明显增加,差异具有统计学意义（均P<0.05）,VE-cadherin的表达量明显降低,差异具有统计学意义（P<0.05）,而UTI可逆转上述变化情况;与UTI处理组相比,RhoA过表达细胞模型中RhoA、ROCK2及p-MYPT1的表达显著增高,VE-cadherin表达降低,细胞通透性增加,差异具有统计学意义（均P<0.05）,而空载病毒组中上述分子的表达水平以及细胞通透性无明显变化,差异无统计学意义（均P>0.05）。 结论UTI能通过Rho/ROCK信号通路抑制TNF-α引起的血管内皮细胞通透性增加,改善血管内皮屏障功能障碍。     

Dissociation of VE-PTP from VE-cadherin is required for leukocyte extravasation and for VEGF-induced vascular permeability in vivo

We have recently shown that vascular endothelial protein tyrosine phosphatase (VE-PTP), an endothelial membrane protein, associates with VE-cadherin and is required for optimal VE-cadherin function and endothelial cell contact integrity. The dissociation of VE-PTP from VE-cadherin is triggered by vascular endothelial growth factor (VEGF) and by the binding of leukocytes to endothelial cells in vitro, suggesting that this dissociation is a prerequisite for the destabilization of endothelial cell contacts. Here, we show that VE-cadherin/VE-PTP dissociation also occurs in vivo in response to LPS stimulation of the lung or systemic VEGF stimulation. To show that this dissociation is indeed necessary in vivo for leukocyte extravasation and VEGF-induced vascular permeability, we generated knock-in mice expressing the fusion proteins VE-cadherin-FK 506 binding protein and VE-PTP-FRB* under the control of the endogenous VE-cadherin promoter, thus replacing endogenous VE-cadherin. The additional domains in both fusion proteins allow the heterodimeric complex to be stabilized by a chemical compound (rapalog). We found that intravenous application of the rapalog strongly inhibited VEGF-induced (skin) and LPS-induced (lung) vascular permeability and inhibited neutrophil extravasation in the IL-1β inflamed cremaster and the LPS-inflamed lung. We conclude that the dissociation of VE-PTP from VE-cadherin is indeed required in vivo for the opening of endothelial cell contacts during induction of vascular permeability and leukocyte extravasation.     

Complement C3a receptor–mediated vascular dysfunction: a complex interplay between aging and neurodegeneration

Vascular dysfunction resulting in compromised blood-brain barrier (BBB) integrity is evident in aging and disease. Although the complement C3a/C3a receptor (C3a/C3aR) axis influences normal brain aging and disease progression, the mechanisms governing endothelial C3aR–mediated neurovascular inflammation and BBB permeability remain unexplored. In this issue of the JCI, Propson et al. investigated endothelial C3a/C3aR signaling in normal, aged, and neurodegenerative mouse models. Endothelial C3aR signaling modulated age-dependent increases in VCAM1, initiated peripheral lymphocyte infiltration, and enhanced microglial activity. Increased calcium release downstream of C3aR signaling disrupted the vascular endothelial cadherin (VE-cadherin) junctions, increased BBB permeability, and degraded vascular structure and function. Mice lacking C3aR (C3ar1^–/–) and mice treated with a C3aR antagonist showed attenuated age-related microglial reactivity and neurodegeneration. These results confirm that complement-mediated signaling impacts vascular health and BBB function in normal aging and neurodegenerative disease, suggesting that complement inhibitors represent a therapeutic option for cerebral microvascular dysfunction.     

VEGFR2 induces c-Src signaling and vascular permeability in vivo via the adaptor protein TSAd

Regulation of vascular endothelial (VE) growth factor (VEGF)-induced permeability is critical in physiological and pathological processes. We show that tyrosine phosphorylation of VEGF receptor 2 (VEGFR2) at Y951 facilitates binding of VEGFR2 to the Rous sarcoma (Src) homology 2-domain of T cell-specific adaptor (TSAd), which in turn regulates VEGF-induced activation of the c-Src tyrosine kinase and vascular permeability. c-Src was activated in vivo and in vitro in a VEGF/TSAd-dependent manner, and was regulated via increased phosphorylation at pY418 and reduced phosphorylation at pY527. Tsad silencing blocked VEGF-induced c-Src activation, but did not affect pathways involving phospholipase Cγ, extracellular regulated kinase, and endothelial nitric oxide. VEGF-induced rearrangement of VE-cadherin-positive junctions in endothelial cells isolated from mouse lungs, or in mouse cremaster vessels, was dependent on TSAd expression, and TSAd formed a complex with VE-cadherin, VEGFR2, and c-Src at endothelial junctions. Vessels in tsad(-/-) mice showed undisturbed flow and pressure, but impaired VEGF-induced permeability, as measured by extravasation of Evans blue, dextran, and microspheres in the skin and the trachea. Histamine-induced extravasation was not affected by TSAd deficiency. We conclude that TSAd is required for VEGF-induced, c-Src-mediated regulation of endothelial cell junctions and for vascular permeability.     

Macrophage-mediated vascular permeability via VLA4/VCAM1 pathway dictates ascites development in ovarian cancer

The development of ascites correlates with advanced stage disease and poor prognosis in ovarian cancer. Vascular permeability is the key pathophysiological change involved in ascites development. Previously, we provided evidence that perivascular M2-like macrophages protect the vascular barrier through direct contact with endothelial cells (ECs). Here, we investigated the molecular mechanism and its clinical significance in the ovarian cancer setting. We found that upon direct coculture with the endothelium, M2 macrophages tuned down their VLA4 and reduced the levels of VCAM1 in ECs. On the other hand, ectopically overexpressing VLA4 in macrophages or VCAM1 in ECs induced hyperpermeability. Mechanistically, downregulation of VLA4 or VCAM1 led to reduced levels of RAC1 and ROS, which resulted in decreased phosphorylation of PYK2 (p-PYK2) and VE-cadherin (p–VE-cad), hence enhancing cell adhesion. Furthermore, targeting the VLA4/VCAM1 axis augmented vascular integrity and abrogated ascites formation in vivo. Finally, VLA4 expression on the macrophages isolated from ascites dictated permeability ex vivo. Importantly, VLA4 antibody acted synergistically with bevacizumab to further enhance the vascular barrier. Taking these data together, we reveal here that M2 macrophages regulate the vascular barrier though the VCAM1/RAC1/ROS/p-PYK2/p–VE-cad cascade, which provides specific therapeutic targets for the treatment of malignant ascites.     

Peptide Bβ15-42 Preserves Endothelial Barrier Function in Shock

Loss of vascular barrier function causes leak of fluid and proteins into tissues, extensive leak leads to shock and death. Barriers are largely formed by endothelial cell-cell contacts built up by VE-cadherin and are under the control of RhoGTPases. Here we show that a natural plasmin digest product of fibrin, peptide Bß15-42 (also called FX06), significantly reduces vascular leak and mortality in animal models for Dengue shock syndrome. The ability of Bß15-42 to preserve endothelial barriers is confirmed in rats i.v.-injected with LPS. In endothelial cells, Bß15-42 prevents thrombin-induced stress fiber formation, myosin light chain phosphorylation and RhoA activation. The molecular key for the protective effect of Bß15-42 is the src kinase Fyn, which associates with VE-cadherin-containing junctions. Following exposure to Bß15-42 Fyn dissociates from VE-cadherin and associates with p190RhoGAP, a known antagonists of RhoA activation. The role of Fyn in transducing effects of Bß15-42 is confirmed in Fyn^−/− mice, where the peptide is unable to reduce LPS-induced lung edema, whereas in wild type littermates the peptide significantly reduces leak. Our results demonstrate a novel function for Bß15-42. Formerly mainly considered as a degradation product occurring after fibrin inactivation, it has now to be considered as a signaling molecule. It stabilizes endothelial barriers and thus could be an attractive adjuvant in the treatment of shock.     

Apoptosis signal-regulating kinase 1-mediated signaling pathway regulates hydrogen peroxide-induced apoptosis in human pulmonary vascular endothelial cells

OBJECTIVE: Reactive oxygen species initiate pulmonary vascular endothelial cell damage leading to an increase in endothelial permeability resulting in the production of pulmonary edema. Apoptosis signal-regulating kinase (ASK)-1 is a ubiquitously expressed mitogen-activated protein kinase kinase kinase (MAPKKK) that activates the MKK3/MKK6-p38 MAPK and the SEK1-c-Jun N-terminal kinase (JNK) signaling cascade. ASK1 has been implicated in cytokine- and stress-induced apoptosis. However, little is known about the role of ASK1 in apoptosis in hydrogen peroxide (H2O2)-stimulated pulmonary vascular endothelial cells and how ASK1-mediated apoptosis is executed. To clarify this issue, we examined the role of ASK1-p38 MAPK/JNK cascade in apoptosis and caspase-3 activation in H2O2-stimulated pulmonary vascular endothelial cells. DESIGN: Experimental laboratory study. SETTING: University laboratory. SUBJECTS: Normal human pulmonary artery endothelial cells. INTERVENTIONS: Western blot analysis and quantification of apoptosis in cells. MEASUREMENTS AND MAIN RESULTS: The results showed that H2O2 induced ASK1 phosphorylation and concomitantly p38 MAPK and JNK phosphorylation as well as induced caspase-3 activation in pulmonary vascular endothelial cells. To further characterize the role of ASK1 cascade in H2O2-induced apoptosis of pulmonary vascular endothelial cells, the dominant negative form of ASK1-stably transfected porcine artery endothelial cells was used. p38 MAPK and JNK phosphorylation, caspase-3 activation, and apoptosis in the dominant negative form of ASK1-stably transfected porcine artery endothelial cells were depressed compared with those in the parental porcine artery endothelial cells. CONCLUSION: ASK1-p38 MAPK/JNK cascade regulates apoptosis of H2O2-stimulated human pulmonary vascular endothelial cells.     

过氧化氢对金属硫蛋白Ⅰ／Ⅱ敲除小鼠脾细胞的氧化应激

背景：脑缺血再灌注早期,由于脾脏中有大量炎症因子浸润引发氧化应激损伤,导致脑缺血再灌注后脾细胞出现大量凋亡。目的：观察外源性过氧化氢对金属硫蛋白Ⅰ/Ⅱ敲除小鼠脾细胞活力的影响及N-乙酰-L-半胱氨酸对过氧化氢诱导的脾细胞氧化应激损伤的保护作用。方法：制备金属硫蛋白敲除小鼠脾细胞悬液,分别用不同浓度（0．1,0．2,0．5,1,2mmol／L）过氧化氢处理2h后,MTT比色法检测细胞活力。根据MTT结果选择不同浓度过氧化氢（0．5,1mmol／L）诱导脾细胞凋亡,实验分为6组：对照组、N-乙酰-L-半胱氨酸组、0．5mmol／L过氧化氢组、1mmol／L过氧化氢组、N-乙酰-L-半胱氨酸＋O.5mmoI／L过氧化氢组、N-乙酰-L-半胱氨酸＋1mmol／L过氧化氢组,2h后MTT比色法检测细胞活力,酶标仪法检测乳酸脱氢酶活力及紫外分光光度仪检测线粒体通透性转换孔的开放情况。结果与结论：随过氧化氢浓度增加脾细胞活力呈明显下降趋势（P〈0．01）,且0．2,0．5,1,2mmol／L过氧化氢组脾细胞活力下降幅度最大。与对照组相比,N-乙酰-L-半胱氨酸组脾细胞活力明显提高（P〈O．01）,且乳酸脱氢酶活力降低（P〈0．01）,线粒体通透性转换孔开放减少（P〈0．01）;分别于0．5,1mmol／L过氧化氢组相比,N-乙酰-L-半胱氨酸＋O．5mmol／L过氧化氢组、N-乙酰-L-半胱氨酸＋1mmol／L过氧化氢组脾细胞活力也明显提高（P〈0．01）,乳酸脱氢酶活力降低（P〈0．01）,线粒体通透性转换孔开放减少（P〈0．01）。结果表明,金属硫蛋白Ⅰ/Ⅱ敲除小鼠随着过氧化氢浓度的升高,脾细胞活力逐渐下降,呈浓度依赖性,尤其对0．2,0．5,1,2mmol／L过氧化氢刺激最为敏感。N-乙酰-L-半胱氨酸使乳酸脱氢酶释放和线粒体通透性转换孔的开放减少,脾细胞活力增强,以此减轻过氧化氢诱导的金属硫蛋白Ⅰ/Ⅱ敲除鼠脾细胞的氧化应激损伤。     

The effect of dipyridamole on vascular cell-derived reactive oxygen species

Platelet and vascular stimulation leads to release of reactive oxygen species (ROS) that are known to influence vascular reactivity and thrombosis. Dipyridamole is a vasodilator and platelet inhibitor that has previously been shown to have direct antioxidant properties. The antioxidant effects of dipyridamole on vascular cell-derived ROS are not known; therefore, dipyridamole was incubated with endothelial cells and platelets and cellular redox status and release of endogenous ROS were assessed. Dipyridamole decreased intracellular basal ROS generation from endothelial cells as measured by DCFDA (2',7'-dichlorodihydrofluorescein diacetate) oxidation. Incubation of endothelial cells with dipyridamole also attenuated t-butylhydroperoxide-induced oxidative stress. Using a redox-sensitive fluorescent dye, dipyridamole improved cellular activity after treatment with t-butylhydroperoxide. Incubation with dipyridamole did not alter platelet release of nitric oxide or hydrogen peroxide but significantly attenuated superoxide release. Using flow cytometry and confocal microscopy, dipyridamole decreased platelet ROS generation. Dipyridamole also suppressed platelet-soluble CD40 ligand release. In summary, at therapeutically relevant concentrations, dipyridamole suppresses the formation of ROS in platelets and endothelial cells and improves cellular redox status. These data suggest that the redox-dependent properties of dipyridamole have a direct effect on vascular cells.     

Interfering with VE-PTP stabilizes endothelial junctions in vivo via Tie-2 in the absence of VE-cadherin

Vascular endothelial (VE)–protein tyrosine phosphatase (PTP) associates with VE-cadherin, thereby supporting its adhesive activity and endothelial junction integrity. VE-PTP also associates with Tie-2, dampening the tyrosine kinase activity of this receptor that can support stabilization of endothelial junctions. Here, we have analyzed how interference with VE-PTP affects the stability of endothelial junctions in vivo. Blocking VE-PTP by antibodies, a specific pharmacological inhibitor (AKB-9778), and gene ablation counteracted vascular leak induction by inflammatory mediators. In addition, leukocyte transmigration through the endothelial barrier was attenuated. Interference with Tie-2 expression in vivo reversed junction-stabilizing effects of AKB-9778 into junction-destabilizing effects. Furthermore, lack of Tie-2 was sufficient to weaken the vessel barrier. Mechanistically, inhibition of VE-PTP stabilized endothelial junctions via Tie-2, which triggered activation of Rap1, which then caused the dissolution of radial stress fibers via Rac1 and suppression of nonmuscle myosin II. Remarkably, VE-cadherin gene ablation did not abolish the junction-stabilizing effect of the VE-PTP inhibitor. Collectively, we conclude that inhibition of VE-PTP stabilizes challenged endothelial junctions in vivo via Tie-2 by a VE-cadherin–independent mechanism. In the absence of Tie-2, however, VE-PTP inhibition destabilizes endothelial barrier integrity in agreement with the VE-cadherin–supportive effect of VE-PTP.The endothelium of the blood vessel wall forms a barrier for blood solutes and for leukocytes. The entry of molecules and cells of the immune system into inflamed tissue is mainly regulated via endothelial junctions. Vascular endothelial (VE)–cadherin is a central component of these junctions, and it is generally considered one of the major adhesive mechanisms that controls the stability and barrier function of the endothelium (Dejana and Vestweber, 2013). Antibodies against VE-cadherin can destabilize endothelial junctions in vitro and in vivo (Breviario et al., 1995; Gotsch et al., 1997; Corada et al., 1999). In agreement with this, enhancing the adhesive function of VE-cadherin by directly fusing it to α-catenin blocks the induction of vascular permeability in the skin of the respective knock-in mice and strongly reduces leukocyte extravasation in various tissues (Schulte et al., 2011).The VE–protein tyrosine phosphatase (PTP) was shown to associate with VE-cadherin and thereby enhance the adhesive function of VE-cadherin (Nawroth et al., 2002; Nottebaum et al., 2008). Permeability-inducing mediators such as VE growth factor (VEGF) and the attachment of leukocytes to endothelial cells (ECs) both stimulate a signaling pathway that triggers the dissociation of VE-PTP from VE-cadherin (Nottebaum et al., 2008; Vockel and Vestweber, 2013). This dissociation is necessary for the induction of vascular permeability and for leukocyte extravasation in vivo. Evidence for this has been based on the analysis of knock-in mice where modified forms of VE-cadherin and VE-PTP, each containing a different binding site for a small molecular weight compound, had been knocked into the VE-cadherin locus (Broermann et al., 2011). In these mice, administration of the appropriate compound inhibited the dissociation of VE-PTP from VE-cadherin and thereby attenuated the induction of vascular permeability and leukocyte extravasation, demonstrating the importance of VE-cadherin–associated VE-PTP for the control of endothelial junction stability in vivo. Moreover, HIF2α was recently reported to enhance endothelial barrier integrity, in part through induced VE-PTP expression (Gong et al., 2015). In line with these findings, tyrosine phosphorylation of VE-cadherin has been demonstrated to be involved in the regulation of EC contacts in vitro (Allingham et al., 2007; Turowski et al., 2008; Monaghan-Benson and Burridge, 2009) and in vivo (Orsenigo et al., 2012; Wessel et al., 2014).VE-PTP also associates with Tie-2 (Fachinger et al., 1999), an endothelial tyrosine kinase receptor that regulates angiogenesis and can support the integrity of endothelial junctions. VE-PTP gene ablation causes embryonic lethality at embryonic day (E) 9.5 (Bäumer et al., 2006; Dominguez et al., 2007). This is caused by a defect in blood vessel remodeling leading to enlarged and fused vessel structures. Antibodies against VE-PTP caused similar defects when incubated with explant cultures of allantois from WT mice, but not if the tissue originated from Tie-2 gene–deficient mice (Winderlich et al., 2009). In addition, these antibodies against the extracellular part of VE-PTP dissociated the phosphatase from Tie-2 and caused phosphorylation of this receptor and signaling (Winderlich et al., 2009).We have recently shown that a specific pharmacological inhibitor of VE-PTP catalytic activity, AKB-9778, activated Tie-2 in the mouse, and this correlated with suppression of ocular neovascularization and blocking of VEGF-induced vascular leak (Shen et al., 2014). Although direct evidence for the relevance of Tie-2 is still missing, these results are in line with studies reporting that the Tie-2 ligand Angiopoietin-1 (Ang1) protects the vasculature against plasma leakage (Gamble et al., 2000; Thurston et al., 2000; Mammoto et al., 2007; Gavard et al., 2008). In a mouse breast cancer model, AKB-9778 normalized tumor vessels and delayed tumor growth (Goel et al., 2013). VE-PTP was also found to associate with VEGF receptor-2 (VEGFR-2; Mellberg et al., 2009), and this interaction was suggested to affect VEGFR-2 activity in endothelial sprouts of mouse embryoid bodies (Hayashi et al., 2013).Here we have analyzed how interference with VE-PTP activity influences endothelial junctions in adult mice and how this relates to the functions of Tie-2 and VE-cadherin. We found that conditional gene ablation of VE-PTP, as well as interference with antibodies or administering the inhibitor AKB-9778 each stabilized challenged endothelial junctions, thereby preventing enhanced permeability and leukocyte extravasation induced by inflammatory mediators. These effects required the expression of Tie-2 because blocking its expression in vivo reversed the effect of the VE-PTP inhibitor on endothelial junction integrity. Thus, VE-PTP inhibition stabilizes challenged endothelial junctions via Tie-2 and destabilizes them in the absence of Tie-2. Remarkably, the junction-stabilizing effect was even observed in mice conditionally gene deficient for VE-cadherin. Inhibition of leak formation was accompanied by activation of Rap1 and cytoskeletal remodeling and reduced radial stress fiber formation. Our results reveal that inhibition of VE-PTP in vivo has opposing effects on endothelial junctions as the result of its different effects on VE-cadherin and on Tie-2. Activation of Tie-2 via inhibition of VE-PTP protects endothelial junctions against inflammation-induced destabilization and overrides the negative effect of VE-PTP inhibition on the adhesive function of VE-cadherin.     

碱性成纤维细胞生长因子荧光真核表达载体构建及对过氧化氢诱导血管内皮细胞凋亡的影响

背景:已证实外源性碱性成纤维细胞生长因子(basic fibroblast growth factor,bFGF)可抑制血管内皮细胞凋亡。目的:构建表达bFGF的荧光真核表达载体,探讨其对过氧化氢(H2O2)诱导的血管内皮细胞凋亡和凋亡相关蛋白的影响。方法:通过基因亚克隆构建荧光真核表达载体pcDNA3.1-bFGF-GFP,利用脂质体介导将bFGF基因导入人脐静脉内皮细胞内,通过荧光观察和RT-PCR检测基因的表达。实验分为3组,对照组(转染pcDNA3.1)、过氧化氢组(转染pcDNA3.1+H2O2)和bFGF转染+过氧化氢组(转染pcDNA3.1-bFGF-GFP+H2O2),流式细胞术测定细胞凋亡率,Western blot检测caspase-3 P17活性亚单位和Bax蛋白表达。结果与结论:成功构建荧光真核表达载体pcDNA3.1-bFGF-GFP,该载体转染人脐静脉内皮细胞后,bFGF mRNA显著增加,并可观察到绿色荧光。与对照组相比,过氧化氢组细胞凋亡率和caspase-3 P17活性亚单位、Bax蛋白的表达量都明显增加(P<0.01),而bFGF转染+过氧化氢组的细胞凋亡率和caspase-3 P17活性亚单位、Bax蛋白的表达量则比过氧化氢组显著降低(P<0.01)。证实bFGF基因转染能抑制过氧化氢诱导的血管内皮细胞凋亡,其作用机制可能与调控Bax蛋白表达和caspase-3活性有关。     

Soluble fms-like tyrosine kinase 1 promotes angiotensin II sensitivity in preeclampsia

Preeclampsia is a hypertensive disorder of pregnancy in which patients develop profound sensitivity to vasopressors, such as angiotensin II, and is associated with substantial morbidity for the mother and fetus. Enhanced vasoconstrictor sensitivity and elevations in soluble fms-like tyrosine kinase 1 (sFLT1), a circulating antiangiogenic protein, precede clinical signs and symptoms of preeclampsia. Here, we report that overexpression of sFlt1 in pregnant mice induced angiotensin II sensitivity and hypertension by impairing endothelial nitric oxide synthase (eNOS) phosphorylation and promoting oxidative stress in the vasculature. Administration of the NOS inhibitor l-NAME to pregnant mice recapitulated the angiotensin sensitivity and oxidative stress observed with sFlt1 overexpression. Sildenafil, an FDA-approved phosphodiesterase 5 inhibitor that enhances NO signaling, reversed sFlt1-induced hypertension and angiotensin II sensitivity in the preeclampsia mouse model. Sildenafil treatment also improved uterine blood flow, decreased uterine vascular resistance, and improved fetal weights in comparison with untreated sFlt1-expressing mice. Finally, sFLT1 protein expression inversely correlated with reductions in eNOS phosphorylation in placental tissue of human preeclampsia patients. These data support the concept that endothelial dysfunction due to high circulating sFLT1 may be the primary event leading to enhanced vasoconstrictor sensitivity that is characteristic of preeclampsia and suggest that targeting sFLT1-induced pathways may be an avenue for treating preeclampsia and improving fetal outcomes.