Endothelial Cell-cell Junctions Research Articles

AB035. Vasohibin-1 as a potential therapeutic target for erectile dysfunction

Induction of neovascularization is a promising strategy to treat erectile dysfunction (ED). Here we for the first time report the unexpected role of vasohibin-1, which is previously defined as an anti-angiogenic factor, in the restoration of erectile function by enhancing cavernous (penile) angiogenesis in an animal model of diabetic ED. The cavernous expression of vasohibin-1 was down-regulated in diabetic mice and in patients with diabetic ED; vasohibin-1 was mainly expressed in endothelial cells. Vasohibin-1 knockout mice revealed decrease in cavernous endothelial and pericyte content compared with wild type mice, which resulted in deterioration of erectile function. Local delivery of vasohibin-1 peptide into the corpus cavernosum of diabetic mice induced significant restoration of erectile function, which reached up to 85% of control values at the concentration of 4 µg/20 µL. Vasohibin-1 significantly increased cavernous endothelial cell content and induced eNOS phosphorylation (Ser1177). Vasohibin-1 decreased extravasation of oxidized-LDL by restoring pericytes and endothelial cell-cell junction proteins in the diabetic mice. By using proteome profiler array kit, we found that the induction of angiogenic factors, including angiopoietin-1, vascular endothelial growth factor, and basic fibroblasts growth factor, mainly in fibroblasts is a major molecular mechanism responsible for vasohibin-1-mediated cavernous angiogenesis and subsequent restoration of erectile function. Our findings suggest that vasohibin-1 is proangiogenic in diabetic penis and is a promising therapeutic target for ED from vascular causes.

Altered redox homeostasis and signaling in Cerebral Cavernous Malformation disease: towards a complex but unifying pathogenic mechanism and therapeutic implications

Cerebral Cavernous Malformation (CCM) is a major cerebrovascular disease of genetic origin affecting 0.3-0.5% of the population and still awaiting therapies other than neurosurgery. It is characterized by abnormally enlarged and leaky capillaries, which predispose to seizures, neurological deficits and intracerebral hemorrhage (ICH), and may occur sporadically or is dominantly inherited with incomplete penetrance and variable expressivity. Three disease genes have been identified, KRIT1 (CCM1), CCM2 and PDCD10 (CCM3), whose loss-of-function mutations are major pathogenic determinants, accounting for the main phenotypic hallmarks of CCM disease, including destabilization of endothelial cell-cell junctions and increased vascular permeability [1]. However, accumulating evidence in animal models clearly demonstrate that homozygous loss of CCM genes is not fully sufficient to cause CCM lesion formation and disease progression, suggesting the necessary contribution of additional determinants, including microenvironmental stress events [1]. Indeed, the clinical behavior in individual patients, including development of numerous and large lesions, and risk of ICH, remains highly unpredictable, while novel pharmacological strategies are particularly needed to limit disease progression and severity in susceptible individuals [1]. Useful insights into innovative approaches for CCM disease prevention and treatment are emerging from a growing understanding of the biological functions of the three known CCM proteins. Previously, we found that CCM proteins, including KRIT1, play an important role in maintaining intracellular redox homeostasis through the modulation of master regulators of ROS production/detoxification and cell responses to oxidative stress, thereby limiting altered redox signaling and oxidative damage, and preserving cellular resistance to oxidative stress [1-3]. Consistently, recently we demonstrated that KRIT1 loss-of-function causes upregulation of NADPH oxidase-mediated redox signaling, leading to enhanced endothelial cell sensitivity to oxidative stress and inflammation, and decreased microvessel barrier function, further suggesting that altered redox signaling and oxidative stress contribute to CCM pathogenesis [4]. Moreover, preliminary results indicate that these events involve also carbonyl compounds generated through the lipid peroxidation process, and a sustained upregulation of Nrf2, suggesting a complex but unifying pathogenic mechanism that reconciles both the pleiotropic functions of CCM proteins and the distinct therapeutic approaches proposed so far. In addition, we identified genetic modifiers influencing disease severity, including polymorphisms in genes related to inter-individual variability in susceptibility to oxidative stress [5]. Taken together, our findings point to a major role for altered redox signaling in CCM pathogenesis and indicate that inter-individual variability in cell responses to oxidative stress may impact disease onset, progression and severity, suggesting novel preventive and therapeutic approaches.

The regulation of junctional actin dynamics by cell adhesion receptors.

The formation of cell-cell junctions and the development of stable cell-cell adhesion require the association of actin filaments with the sites of cell-cell adhesion. From the initial formation of cell-cell junctions, which appear as punctate, spot-like junctions, to the formation of a stable actin belt that runs adjacent to cell-cell junctions, the actin cytoskeleton is closely associated with the adhesion apparatus. Importantly, the junctional actin is highly dynamic, even after the maturation of intercellular junctions and the development of apico-basal polarity. Regulators of both branched actin networks and of linear actin cables have been identified at cell-cell junctions, in particular at adherens junctions but also at tight junctions. These regulators of actin dynamics are often directly or indirectly associated with cell adhesion receptors, suggesting a critical role for cell adhesion molecules for the recruitment of regulators of actin dynamics to cell-cell junctions. Here, we review the recent developments on the role of cell adhesion molecules at epithelial and endothelial cell-cell junctions in the regulation of junctional actin dynamics.

325 Preserved erectile function in the hyperhomocysteinaemia transgenic rats harboring human tissue kallikrein 1

To investigate the detailed mechanism of erectile dysfunction (ED) induced by hyperhomocysteinaemia (HHcy) in rats and determine whether the Human Tissue Kallikrein 1 (hKLK1) might improve it, as we have proved the protective role of hKLK1 on erectile function in aged rats. We established a rat model of HHCy through dietary-rich methionine (Met) in male Sprague-Dawley (SD) rats. Male wild-type SD rats (WTR) and transgenic rats harboring the hKLK1 gene (TGR) were fed to 10 weeks of age. Then 24 WTRs were divided into control (n=8), the low-dose (4% Met, n=8), and the high-dose (7% Met, n=8). Another 8 age-matched TGRs with the high-dose formed the TGR+7%Met group. 30 days later, erectile function, level of total homocysteinaemia (tHcy), oxidative stress, endothelial function, cavernous nerve function and fibrosis of all groups were determined. hKLK1 in the TGR+7%Met group could greatly decrease the tHcy levels and improve ED induced by HHcy in rats. For the endothelial function, hKLK1 could preserve the endothelial cell-cell junction, enhance endothelial regeneration and activated the Akt/eNOS signaling pathway. Together with the promotion of hKLK1 on nNOS expression, the NO/cGMP signaling pathway activity was also increased. For the fibrosis, hKLK1 could preserve normal corpus cavernosum structure through inhibiting apoptosis and promoting autophagy on corpus cavernosum smooth muscle cells. In addition, hKLK1 also inhibited the fibrosis-related signaling pathway activity.

Research progress in the structure, assembly and functional regulation of tight junctions

Tight junctions (TJs) are a type of multi-functional complex present in the most apical portion of the lateral plasma membrane of both epithelial and endothelial cell-cell junctions, and are mainly composed of transmembrane and cytoplasmic proteins. As a structural and functional basis, TJs are required to transport material through the paracellular pathway and responsible for maintaining apicobasal polarization. Additionally, TJs are involved in signal transduction bi-directionally. On the one hand, TJs receive signals from the cell interior and regulate assembly and maturation of TJs complex. On the other hand, TJs can also transmit external signals to the cell interior to modulate cell proliferation, migration, survival and differentiation. The present review mainly focuses on the latest research progress on TJs, including TJ’s molecular architecture, assembly and its related regulatory mechanisms, as well as its biological function in tumorigenesis and development, hepatitis C virus infection and hereditary hearing impairment. We hope that the review may provide valuable reference for the future therapeutic strategies of epithelium-related disease by targeting TJs.

Combination of stromal vascular fraction and Ad-COMP-Ang1 gene therapy improves long-term therapeutic efficacy for diabetes-induced erectile dysfunction

Men with diabetic erectile dysfunction (ED) respond poorly to the currently available oral phosphodiesterase-5 inhibitors. Therefore, functional therapies for diabetic ED are needed. Stromal vascular fraction (SVF) and the adenovirus-mediated cartilage oligomeric matrix angiopoietin-1 (Ad-COMP-Ang1) gene are known to play critical roles in penile erection. We previously reported that SVF and Ad-COMP-Ang1 have only a short-term effect in restoring erectile function. Further improvements to ED therapy are needed for long-lasting effects. In the present study, we aimed to test if the combination of SVF and Ad-COMP-Ang1 could extend the erection effect in diabetic ED. We found that the combination therapy showed a long-term effect in restoring erectile function through enhanced penile endothelial and neural cell regeneration. Combination therapy with SVF and Ad-COMP-Ang1 notably restored cavernous endothelial cell numbers, pericyte numbers, endothelial cell–cell junctions, decreased cavernous endothelial cell permeability, and promoted neural regeneration for at least 4 weeks in diabetic mice. In summary, this is an initial description of the long-term effect of combination therapy with SVF and Ad-COMP-Ang1 in restoring erectile function through a dual effect on endothelial and neural cell regeneration. Such combination therapy may have therapeutic potential for the treatment of diabetic ED.

New microtubulin inhibitor MT189 suppresses angiogenesis via the JNK-VEGF/VEGFR2 signaling axis

The microtubulin inhibitor MT189 possesses anticancer activity and has been shown to overcome multidrug resistance. Here, we report that MT189 also inhibits angiogenesis. MT189 inhibited the proliferation, migration and differentiation of endothelial cells, with or without VEGF stimulation, and suppressed microvessel formation ex vivo and in vivo. MT189 reduced VEGF expression and secretion in both tumor and endothelial cells, under either hypoxic or normoxic conditions. The activation of VEGFR2 and downstream Src was thus abrogated in the MT189-treated endothelial cells. MT189 subsequently stabilized endothelial cell-cell junctions consist of VE-cadherin, β-catenin, vinculin, and actin. MT189 also disrupted endothelial cell-matrix junctions by inhibiting the turnover of focal adhesions containing FAK, paxillin, vinculin, and actin. Inhibition of JNK reversed MT189-mediated inhibition of endothelial migration and differentiation, JNK activation, the reduction of VEGF expression and secretion, and the decrease of Src and FAK phosphorylation. These results indicate that MT189 suppresses angiogenesis by reducing endothelial proliferation, migration, and differentiation via the JNK-VEGF/VEGFR2 signaling axis. Together with our previous report showing that MT189 exhibited anticancer activity via the JNK-MCL-1 pathway, these new findings further support MT189-based drug development for cancer therapy.

Live imaging molecular changes in junctional tension upon VE-cadherin in zebrafish

Forces play diverse roles in vascular development, homeostasis and disease. VE-cadherin at endothelial cell-cell junctions links the contractile acto-myosin cytoskeletons of adjacent cells, serving as a tension-transducer. To explore tensile changes across VE-cadherin in live zebrafish, we tailored an optical biosensor approach, originally established in vitro. We validate localization and function of a VE-cadherin tension sensor (TS) in vivo. Changes in tension across VE-cadherin observed using ratio-metric or lifetime FRET measurements reflect acto-myosin contractility within endothelial cells. Furthermore, we apply the TS to reveal biologically relevant changes in VE-cadherin tension that occur as the dorsal aorta matures and upon genetic and chemical perturbations during embryonic development.

CRISPR-mediated deletion of the PECAM-1 cytoplasmic domain increases receptor lateral mobility and strengthens endothelial cell junctional integrity

AimsPECAM-1 is an abundant endothelial cell surface receptor that becomes highly enriched at endothelial cell-cell junctions, where it functions to mediate leukocyte transendothelial migration, sense changes in shear and flow, and maintain the vascular permeability barrier. Homophilic interactions mediated by the PECAM-1 extracellular domain are known to be required for PECAM-1 to perform these functions; however, much less is understood about the role of its cytoplasmic domain in these processes. Main methodsCRISPR/Cas9 gene editing technology was employed to generate human endothelial cell lines that either lack PECAM-1 entirely, or express mutated PECAM-1 missing the majority of its cytoplasmic domain (∆CD-PECAM-1). The endothelial barrier function was evaluated by Electric Cell-substrate Impedance Sensing, and molecular mobility was assessed by fluorescence recovery after photobleaching. Key findingsWe found that ∆CD-PECAM-1 concentrates normally at endothelial cell junctions, but has the unexpected property of conferring increased baseline barrier resistance, as well as a more rapid rate of recovery of vascular integrity following thrombin-induced disruption of the endothelial barrier. Fluorescence recovery after photobleaching analysis revealed that ∆CD-PECAM-1 exhibits increased mobility within the plane of the plasma membrane, thus allowing it to redistribute more rapidly back to endothelial cell-cell borders to reform the vascular permeability barrier. SignificanceThe PECAM-1 cytoplasmic domain plays a novel role in regulating the rate and extent of vascular permeability following thrombotic or inflammatory challenge.

Non-muscular myosin light chain kinase triggers intermittent hypoxia-induced interleukin-6 release, endothelial dysfunction and permeability

Obstructive sleep apnea is characterized by intermittent hypoxia (IH) which alters endothelial function, induces inflammation and accelerates atherosclerosis-induced cardiovascular diseases. The non-muscular myosin light chain kinase (nmMLCK) isoform contributes to endothelial cell-cell junction opening. Deletion of nmMLCK protects mice from death in septic shock models and prevents atherosclerosis in high-fat diet-fed mice. The aim of the study was to analyze the implication of nmMLCK in IH-induced vascular inflammation. Human aortic endothelial cells were exposed to 6 hours of IH in absence or presence of nmMLCK inhibitors, ML-7 (5 µM) or PIK (150 µM). IH increased reactive oxygen species (ROS) and nitric oxide (NO) production, p65-NFκB activation and IL-6 secretion. While nmMLCK inhibition did not prevent IH-induced ROS production and p65-NFκB activation, it decreased NO production and partially prevented IL-6 secretion. IH-induced IL-6 secretion and vesicle-associated membrane protein-associated vesicles re-organization were inhibited in presence of the inhibitor of protein secretion, brefeldin A, or ML-7. IH increased monocytes transendothelial migration that was partially prevented by ML-7. Finally, IH reduced endothelium-dependent relaxation to acetylcholine of aortas from wild-type but not those taken from nmMLCK-deficient mice. These results suggest that nmMLCK participates to IH-induced endothelial dysfunction resulting from cytokines secretion and endothelial permeability.

Hold Me, but Not Too Tight-Endothelial Cell-Cell Junctions in Angiogenesis.

Endothelial cell-cell junctions must perform seemingly incompatible tasks during vascular development-providing stable connections that prevent leakage, while allowing dynamic cellular rearrangements during sprouting, anastomosis, lumen formation, and functional remodeling of the vascular network. This review aims to highlight recent insights into the molecular mechanisms governing endothelial cell-cell adhesion in the context of vascular development.

Vascular Endothelial (VE)-Cadherin, Endothelial Adherens Junctions, and Vascular Disease.

Endothelial cell-cell adherens junctions (AJs) supervise fundamental vascular functions, such as the control of permeability and transmigration of circulating leukocytes, and the maintenance of existing vessels and formation of new ones. These processes are often dysregulated in pathologies. However, the evidence that links dysfunction of endothelial AJs to human pathologies is mostly correlative. In this review, we present an update of the molecular organization of AJ complexes in endothelial cells (ECs) that is mainly based on observations from experimental models. Furthermore, we report in detail on a human pathology, cerebral cavernous malformation (CCM), which is initiated by loss-of-function mutations in the genes that encode the three cytoplasmic components of AJs (CCM1, CCM2, and CCM3). At present, these represent a unique example of mutations in components of endothelial AJs that cause human disease. We describe also how studies into the defects of AJs in CCM are shedding light on the crucial regulatory mechanisms and signaling activities of these endothelial structures. Although these observations are specific for CCM, they support the concept that dysfunction of endothelial AJs can directly contribute to human pathologies.

A Biomimetic Microfluidic Tumor Microenvironment Platform Mimicking the EPR Effect for Rapid Screening of Drug Delivery Systems

Real-time monitoring of tumor drug delivery in vivo is a daunting challenge due to the heterogeneity and complexity of the tumor microenvironment. In this study, we developed a biomimetic microfluidic tumor microenvironment (bMTM) comprising co-culture of tumor and endothelial cells in a 3D environment. The platform consists of a vascular compartment featuring a network of vessels cultured with endothelial cells forming a complete lumen under shear flow in communication with 3D solid tumors cultured in a tumor compartment. Endothelial cell permeability to both small dye molecules and large liposomal drug carriers were quantified using fluorescence microscopy. Endothelial cell intercellular junction formation was characterized by immunostaining. Endothelial cell permeability significantly increased in the presence of either tumor cell conditioned media (TCM) or tumor cells. The magnitude of this increase in permeability was significantly higher in the presence of metastatic breast tumor cells as compared to non-metastatic ones. Immunostaining revealed impaired endothelial cell-cell junctions in the presence of either metastatic TCM or metastatic tumor cells. Our findings indicate that the bMTM platform mimics the tumor microenvironment including the EPR effect. This platform has a significant potential in applications such as cell-cell/cell-drug carrier interaction studies and rapid screening of cancer drug therapeutics/carriers.

VE-Cadherin Phosphorylation Regulates Endothelial Fluid Shear Stress Responses through the Polarity Protein LGN

Fluid shear stress due to blood flow on the vascular endothelium regulates blood vessel development, remodeling, physiology, and pathology [1, 2]. Acomplex consisting of PECAM-1, VE-cadherin, andvascular endothelial growth factor receptors (VEGFRs) that resides at endothelial cell-cell junctions transduces signals important for flow-dependent vasodilation, blood vessel remodeling, and atherosclerosis. PECAM-1 transduces forces to activate src family kinases (SFKs), which phosphorylate and transactivate VEGFRs [3-5]. By contrast, VE-cadherin functions as an adaptor that interacts with VEGFRs through their respective cytoplasmic domains and promotes VEGFR activation in flow [6]. Indeed, shear stress triggers rapid increases in force across PECAM-1 but decreases the force across VE-cadherin, in close association with downstream signaling [5]. Interestingly, VE-cadherin cytoplasmic tyrosine Y658 can be phosphorylated by SFKs [7], which is maximally induced by low shear stress invitro and invivo [8]. These considerations prompted us to address the involvement of VE-cadherin cytoplasmic tyrosines in flow sensing. We found that phosphorylation of a small pool of VE-cadherin on Y658 is essential for flow sensing through the junctional complex. Y658 phosphorylation induces dissociation of p120ctn, which allows binding of the polarity protein LGN. LGN is then required for multiple flow responses invitro and invivo, including activation of inflammatory signaling at regions of disturbed flow, and flow-dependent vascular remodeling. Thus, endothelial flow mechanotransduction through the junctional complex is mediated by a specific pool of VE-cadherin that is phosphorylated on Y658 and bound to LGN.

Magnetic forces enable controlled drug delivery by disrupting endothelial cell-cell junctions

The vascular endothelium presents a major transport barrier to drug delivery by only allowing selective extravasation of solutes and small molecules. Therefore, enhancing drug transport across the endothelial barrier has to rely on leaky vessels arising from disease states such as pathological angiogenesis and inflammatory response. Here we show that the permeability of vascular endothelium can be increased using an external magnetic field to temporarily disrupt endothelial adherens junctions through internalized iron oxide nanoparticles, activating the paracellular transport pathway and facilitating the local extravasation of circulating substances. This approach provides a physically controlled drug delivery method harnessing the biology of endothelial adherens junction and opens a new avenue for drug delivery in a broad range of biomedical research and therapeutic applications.

Locally Triggered Release of the Chemokine CCL21 Promotes Dendritic Cell Transmigration across Lymphatic Endothelia

SummaryTrafficking cells frequently transmigrate through epithelial and endothelial monolayers. How monolayers cooperate with the penetrating cells to support their transit is poorly understood. We studied dendritic cell (DC) entry into lymphatic capillaries as a model system for transendothelial migration. We find that the chemokine CCL21, which is the decisive guidance cue for intravasation, mainly localizes in the trans-Golgi network and intracellular vesicles of lymphatic endothelial cells. Upon DC transmigration, these Golgi deposits disperse and CCL21 becomes extracellularly enriched at the sites of endothelial cell-cell junctions. When we reconstitute the transmigration process in vitro, we find that secretion of CCL21-positive vesicles is triggered by a DC contact-induced calcium signal, and selective calcium chelation in lymphatic endothelium attenuates transmigration. Altogether, our data demonstrate a chemokine-mediated feedback between DCs and lymphatic endothelium, which facilitates transendothelial migration.

VEGFR3 Modulates Vascular Permeability by Controlling VEGF/VEGFR2 Signaling.

Vascular endothelial growth factor (VEGF) is the main driver of angiogenesis and vascular permeability via VEGF receptor 2 (VEGFR2), whereas lymphangiogenesis signals are transduced by VEGFC/D via VEGFR3. VEGFR3 also regulates sprouting angiogenesis and blood vessel growth, but to what extent VEGFR3 signaling controls blood vessel permeability remains unknown. To investigate the role of VEGFR3 in the regulation of VEGF-induced vascular permeability. Long-term global Vegfr3 gene deletion in adult mice resulted in increased fibrinogen deposition in lungs and kidneys, indicating enhanced vascular leakage at the steady state. Short-term deletion of Vegfr3 in blood vascular endothelial cells increased baseline leakage in various tissues, as well as in tumors, and exacerbated vascular permeability in response to VEGF, administered via intradermal adenoviral delivery or through systemic injection of recombinant protein. VEGFR3 gene silencing upregulated VEGFR2 protein levels and phosphorylation in cultured endothelial cells. Consistent with elevated VEGFR2 activity, vascular endothelial cadherin showed reduced localization at endothelial cell-cell junctions in postnatal retinas after Vegfr3 deletion, or after VEGFR3 silencing in cultured endothelial cells. Furthermore, concurrent deletion of Vegfr2 prevented VEGF-induced excessive vascular leakage in mice lacking Vegfr3. VEGFR3 limits VEGFR2 expression and VEGF/VEGFR2 pathway activity in quiescent and angiogenic blood vascular endothelial cells, thereby preventing excessive vascular permeability.

PDZRN3 destabilizes endothelial cell-cell junctions through a PKCζ-containing polarity complex to increase vascular permeability.

Endothelial cells serve as a barrier between blood and tissues. Maintenance of the endothelial cell barrier depends on the integrity of intercellular junctions, which is regulated by a polarity complex that includes the ζ isoform of atypical protein kinase C (PKCζ) and partitioning defective 3 (PAR3). We revealed that the E3 ubiquitin ligase PDZ domain-containing ring finger 3 (PDZRN3) regulated endothelial intercellular junction integrity. Endothelial cell-specific overexpression of Pdzrn3 led to early embryonic lethality with severe hemorrhaging and altered organization of endothelial intercellular junctions. Conversely, endothelial-specific loss of Pdzrn3 prevented vascular leakage in a mouse model of transient ischemic stroke, an effect that was mimicked by pharmacological inhibition of PKCζ. PDZRN3 regulated Wnt signaling and associated with a complex containing PAR3, PKCζ, and the multi-PDZ domain protein MUPP1 (Discs Lost-multi-PDZ domain protein 1) and targeted MUPP1 for proteasomal degradation in transfected cells. Transient ischemic stroke increased the ubiquitination of MUPP1, and deficiency of MUPP1 in endothelial cells was associated with decreased localization of PKCζ and PAR3 at intercellular junctions. In endothelial cells, Pdzrn3 overexpression increased permeability through a PKCζ-dependent pathway. In contrast, Pdzrn3 depletion enhanced PKCζ accumulation at cell-cell contacts and reinforced the cortical actin cytoskeleton under stress conditions. These findings reveal how PDZRN3 regulates vascular permeability through a PKCζ-containing complex.

TNF-\u03b1 regulates the proteolytic degradation of ST6Gal-1 and endothelial cell-cell junctions through upregulating expression of BACE1

Endothelial dysfunction and monocyte adhesion to vascular endothelial cells are two critical steps in atherosclerosis development, and emerging evidence suggests that protein sialylation is involved in these processes. However, the mechanism underlying this phenomenon remains incompletely elucidated. In this study, we demonstrated that treatment with the proinflammatory cytokine TNF-α disrupted vascular endothelial cell-cell tight junctions and promoted monocyte endothelial cell adhesion. Western blotting and Sambucus nigra lectin (SNA) blotting analyses revealed that TNF-α treatment decreased α-2, 6-sialic acid transferase 1 (ST6Gal-I) levels and downregulated VE-Cadherin α-2, 6 sialylation. Further analysis demonstrated that TNF-α treatment upregulated β-site amyloid precursor protein enzyme 1 (BACE1) expression, thus resulting in sequential ST6Gal-I proteolytic degradation. Furthermore, our results revealed that PKC signaling cascades were involved in TNF-α-induced BACE1 upregulation. Together, these results indicated that the proinflammatory cytokine TNF-α impairs endothelial tight junctions and promotes monocyte-endothelial cell adhesion by upregulating BACE1 expression through activating PKC signaling and sequentially cleaving ST6Gal-I. Thus, inhibition of BACE1 expression may be a new approach for treating atherosclerosis.

Dynamic Regulation of Vascular Permeability by Vascular Endothelial Cadherin-Mediated Endothelial Cell-Cell Junctions.

Endothelial cells lining blood vessels regulate vascular barrier function, which controls the passage of plasma proteins and circulating cells across the endothelium. In most normal adult tissues, endothelial cells preserve basal vascular permeability at a low level, while they increase permeability in response to inflammation. Therefore, vascular permeability is tightly controlled by a number of extracellular stimuli and mediators to maintain tissue homeostasis. Accordingly, impaired regulation of endothelial permeability causes various diseases, including chronic inflammation, asthma, edema, sepsis, acute respiratory distress syndrome, anaphylaxis, tumor angiogenesis, and diabetic retinopathy. Vascular endothelial (VE)-cadherin, a member of the classical cadherin superfamily, is a component of cell-to-cell adherens junctions in endothelial cells and plays an important role in regulating vascular permeability. VE-cadherin mediates intercellular adhesion through trans-interactions formed by its extracellular domain, while its cytoplasmic domain is anchored to the actin cytoskeleton via α- and β-catenins, leading to stabilization of VE-cadherin at cell-cell junctions. VE-cadherin-mediated cell adhesions are dynamically, but tightly, controlled by mechanisms that involve protein phosphorylation and reorganization of the actomyosin cytoskeleton. Phosphorylation of VE-cadherin, and its associated-catenins, results in dissociation of the VE-cadherin/catenin complex and internalization of VE-cadherin, leading to increased vascular permeability. Furthermore, reorganization of the actomyosin cytoskeleton by Rap1, a small GTPase that belongs to the Ras subfamily, and Rho family small GTPases, regulates VE-cadherin-mediated cell adhesions to control vascular permeability. In this review, we describe recent progress in understanding the signaling mechanisms that enable dynamic regulation of VE-cadherin adhesions and vascular permeability. In addition, we discuss the possibility of novel therapeutic approaches targeting the signaling pathways controlling VE-cadherin-mediated cell adhesion in diseases associated with vascular hyper-permeability.