Rho, tyrosine kinase, Ca(2+), and junctions in endothelial hyperpermeability

Protective role of Cav-1 in pneumolysin-induced endothelial barrier dysfunction

Pneumolysin (PLY) is a bacterial pore forming toxin and primary virulence factor of Streptococcus pneumonia, a major cause of pneumonia. PLY binds cholesterol-rich domains of the endothelial cell (EC) plasma membrane resulting in pore assembly and increased intracellular (IC) Ca2+ levels that compromise endothelial barrier integrity. Caveolae are specialized plasmalemma microdomains of ECs enriched in cholesterol. We hypothesized that the abundance of cholesterol-rich domains in EC plasma membranes confers cellular susceptibility to PLY. Contrary to this hypothesis, we found increased PLY-induced IC Ca2+ following membrane cholesterol depletion. Caveolin-1 (Cav-1) is an essential structural protein of caveolae and its regulation by cholesterol levels suggested a possible role in EC barrier function. Indeed, Cav-1 and its scaffolding domain peptide protected the endothelial barrier from PLY-induced disruption. In loss of function experiments, Cav-1 was knocked-out using CRISPR-Cas9 or silenced in human lung microvascular ECs. Loss of Cav-1 significantly enhanced the ability of PLY to disrupt endothelial barrier integrity. Rescue experiments with re-expression of Cav-1 or its scaffolding domain peptide protected the EC barrier against PLY-induced barrier disruption. Dynamin-2 (DNM2) is known to regulate caveolar membrane endocytosis. Inhibition of endocytosis, with dynamin inhibitors or siDNM2 amplified PLY induced EC barrier dysfunction. These results suggest that Cav-1 protects the endothelial barrier against PLY by promoting endocytosis of damaged membrane, thus reducing calcium entry and PLY-dependent signaling.

Effect of ascorbic acid, α-tocopherol and its combination on human umbilical vein endothelial cells permeability exposed to high concentration of glucose

Aim — To evaluate the effect of ascorbic acid, α-tocopherol, and its combination on the permeability of human umbilical vein endothelial cells (HUVEC’S) culture after high glucose concentration exposure. Material and Methods — The study was performed using HUVEC’S culture on transwell polyester filter. The ascorbic acid, α-tocopherol, and its combination (25-200 µM) were concomitantly given with glucose 22 µM to the culture media. After seven days of treatment, endothelial permeability was observed by measuring the concentration of trypan blue-labeled albumin in a luminal compartment with a spectrophotometer (λ=592 nm). The morphology of the cells was observed under an inverted microscope. The data was analyzed using ANOVA test followed by Dunnet test (p<0.05). Results — HUVEC’S culture exposed to high concentration glucose increased endothelial permeability better than those which exposed to normal concentration (p<0.05). The treatment of ascorbic acid 200 µM, α-tocopherol 100 µM and 200 µM were capable to inhibit the increase HUVEC’S permeability exposed to high concentration glucose better than control group (p<0.05). Moreover, two combinations of ascorbic acid and α-tocopherol, respectively 50 and 100 µM, could prevent the increased permeability of HUVEC’S culture better than control (p<0.05). Conclusion — Ascorbic acid, α-tocopherol, and its combination could inhibit the increase of endothelial permeability exposed to a high concentration of glucose.

Dasatinib inhibits actin fiber reorganization and promotes endothelial cell permeability through RhoA-ROCK pathway

Treatment with dasatinib, a tyrosine kinase inhibitor, is associated with edema, pleural effusion, and pulmonary edema. We investigated the effect of dasatinib on the barrier function of human microvascular endothelial cells‐1 (HMEC‐1) in vitro and in vivo. The permeability of HMEC‐1 to fluorescein isothiocyante (FITC)‐dextran increased in Transwell chambers within 5 min following the addition of therapeutic concentrations of dasatinib. The change in permeability was associated with increased activation of RhoA GTPase and its effector Rho‐associated coiled‐coil kinase 1(ROCK1). RhoA inhibitor C3 transferase almost completely inhibited dasatinib‐induced increase in permeability. Under similar conditions, imatinib had no effect on permeability or activation of RhoA. Since integrin‐induced cell spreading suppresses RhoA activation, we examined the effect of dasatinib on cell spreading on fibronectin substrate. Dasatinib impaired endothelial cell spreading in a concentration‐dependent manner and induced disorganization of actin fibers. Tyrosine kinases play an essential role in transmitting signals from integrins to RhoA and we examined tyrosine phosphorylation of several cytoskeletal proteins. Dasatinib markedly inhibited tyrosine phosphorylation of p130 Crk‐associated substrate (p130cas), paxillin and vinculin. These results suggest that the inhibition of tyrosine phosphorylation of the focal adhesion plaque components by dasatinib may alter the assembly of actin fibers resulting in the activation of RhoA/ROCK pathway. Consistent with these findings, dasatinib‐induced increase in the permeability was blocked by ROCK inhibitor y27632. In vivo administration of y27632, significantly inhibited the dasatinib‐induced extravasation of Evans blue in mice and dasatinib‐induced increase in microvascular permeability was attenuated in ROCK1‐deficient mice. These findings suggest that ROCK inhibitors could serve as therapeutic modalities to ameliorate the dasatinib‐induced pulmonary changes.

Enhanced permeability responses to inflammation in streptozotocin-induced diabetic rat venules: Rho-mediated alterations of actin cytoskeleton and VE-cadherin

Diabetes is a progressive disease that often leads to microvascular complications. This study investigates the impact of diabetes on microvessel permeability under basal and inflammatory conditions. Streptozotocin-induced diabetic rats were used to mimic type 1 diabetes. Parallel experiments were conducted in intact mesenteric venules in normal rats and diabetic rats experiencing hyperglycemia for 2-3 wk. Microvessel permeability was determined by measuring hydraulic conductivity (Lp). The correlated changes in endothelial intracellular Ca(2+) concentration ([Ca(2+)]i), adherens junctions, and cytoskeleton F-actin were examined with fluorescence imaging. Diabetic vessels showed moderately increased basal Lp, but upon platelet-activating factor (PAF) exposure, these vessels showed an ~10-fold higher Lp increase than the normal vessels. Concomitantly, we observed higher increases in endothelial [Ca(2+)]i, enhanced stress fiber formation, vascular endothelial-cadherin separation, and larger gap formation between endothelial cells than those occurring in normal vessels. PAF receptor staining showed no significant difference between normal and diabetic vessels. The application of Rho kinase inhibitor Y27632 did not affect PAF-induced increases in endothelial [Ca(2+)]i but significantly reduced PAF-induced Lp increases by 90% in diabetic vessels. The application of both Y27632 and nitric oxide (NO) synthase inhibitor attenuated PAF-induced Lp increases more than using one inhibitor alone. Our studies indicate that diabetic conditions prime endothelial cells into a phenotype with increased susceptibility to inflammation without altering receptor expression and that the increased Rho activation and NO production play important roles in exaggerated permeability increases when diabetic vessels were exposed to inflammatory mediators, which may account for the exacerbated vascular dysfunction when diabetic patients are exposed to additional inflammation.

Key genes and proteins involved in CTCM-reducing microvascular endothelial cell permeability induced by SLT-IIv using gene chips and DIGE

An Affymetrix mouse genome array and differential in-gel electrophoresis (DIGE) techniques were used to investigate the pharmacological mechanisms of a mixture of herbs, designated CTCM, a compound of traditional Chinese medicine, for the treatment of increased permeability in mouse intestinal microvascular endothelial cells (MIMECs) induced by the Shiga-like toxin type II variant (SLT-IIv). MIMECs were challenged with 10microg/ml SLT-IIv for 12h and then treated with CTCM at a concentration of 200microg/ml for 12h. Total RNA and proteins from each treatment group were extracted from cultured MIMECs for analysis by the Affymetrix GeneChip Mouse Genome 430 2.0 microarray and DIGE. The results obtained demonstrated that there were one genes downregulated and one genes upregulated, one protein downregulated and four proteins upregulated in the SLT-IIv group compared to the control group. In the CTCM group, four genes were upregulated, three genes were downregulated, a single protein was downregulated and a single protein was upregulated when compared to the control group. When the CTCM-treated group was compared to the SLT-IIv group, expression of one gene was found to be increased, and all other genes were decreased, with five proteins downregulated. Analysis of the data suggested that CTCM specifically and effectively reduced microvascular endothelial cell permeability to SLT-IIv in the treatment of pig edema disease. In the CTCM-treated group, hspa9 expression was increased in both gene chip and DIGE analysis, so it may be a key protein in reducing cell permeability and utilized in medical treatments.

Insulin prevents oxidant-induced endothelial cell barrier dysfunction via nitric oxide-dependent pathway

BACKGROUND

The rigorous maintenance of normoglycemia by the administration of insulin is beneficial to critically ill patients. Because insulin induces endothelial nitric oxide (NO) release, and the constitutive release of NO maintains normal microvascular permeability, the authors postulated that insulin would prevent peroxide (H(2)O(2))-induced endothelial barrier dysfunction, an effect dependent on endothelial NO synthase (eNOS) activity.

METHODS

Murine lung microvascular endothelial cells (LMEC) grown to confluence on 8 micro pore polyethylene filters were exposed to media (control), H(2)O(2) (20 to 500 micromol/L), insulin (1 to 1,000 nmol/L) or insulin (100 nmol/L) + H(2)O(2) (10(-4)mol/L). Endothelial monolayer permeability was quantitated by measuring the transendothelial electrical resistance at 15-minute intervals for 120 minutes. Other cells were exposed to H(2)O(2) and insulin after pretreatment with a NO scavenger (PTIO), an eNOS inhibitor (L-NIO), or a phosphoinositol-3-kinase inhibitor (LY-294002).

RESULTS

H(2)O(2) caused a concentration- and time-dependent reduction in electrical resistance consistent with an increase in monolayer permeability. This effect was prevented by insulin. Inhibiting NO release (L-NIO, LY-294002) or scavenging NO (PTIO) abolished this protective effect.

CONCLUSIONS

These data suggest that insulin may modulate endothelial barrier function during oxidant stress by inducing the release of NO.

The vascular endothelial growth factor-induced disruption of gap junctions is relayed by an autocrine communication via ATP release in coronary capillary endothelium

Little is known concerning how the coordination of Ca(2+) signaling aids in capillary endothelial cell (CEC) functions, such as microvascular permeability and angiogenesis. Previous reports support the major involvement of gap junction (GJ) channels. However, the cell-to-cell communication may not be straightforward, especially if we consider the participation of active molecules released by CEC. In this study, short-term effects of vascular endothelial growth factor (VEGF-165) were compared with those of bradykinin (BK) on gap junction coupling (GJC) and remodeling of connexin-43 (Cx43) and then analyzed for intercellular Ca(2+) signal in primary cultures of coronary CEC. Dye-coupling experiments revealed that BK or VEGF completely blocked GJC. These effects correlated with the rapid internalization of Cx43 and its tyrosine phosphorylation in part via the phosphatidylinositol 3-kinase/Akt pathway. GJC slowly recovered with BK but not with VEGF in the following hour. In control conditions, mechanical stimulation of a single cell within a confluent monolayer triggered an intercellular Ca(2+) wave that was partially inhibited by GJC blockers or purinergic inhibitors. No wave propagation was observed after blockage of both GJC and purinergic receptors. Cell treatment with VEGF also reduced propagation of the Ca(2+) wave, which was totally prevented by applying a purinergic receptor antagonist but not with a GJC blocker. That excludes purine efflux through Cx hemichannels. We conclude that VEGF-induced disruption of GJC via Cx43 remodeling is relayed by an autocrine communication via secretion of ATP to preserve intercellular Ca(2+) signaling in capillary endothelium.

Rho/Rho kinase and phosphoinositide 3-kinase are parallel pathways in the development of spontaneous arterial tone in deoxycorticosterone acetate-salt hypertension

Hypertension is characterized by abnormal vascular contractility and function. Arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats develop spontaneous tone that is not observed in arteries from normotensive rats. Inhibition of phosphoinositide 3-kinase (PI3-kinase) by 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) reduces spontaneous tone development. The Rho/Rho-kinase pathway has been suggested to play a role in hypertension and may be dependent on PI3-kinase activity. We hypothesized that Rhokinase is involved in spontaneous tone development and that Rho/Rho-kinase is a downstream effector of PI3-kinase. Using endothelium-denuded aortic strips in isolated tissue bath, we demonstrated that (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) (Y27632) (1 microM), a Rho-kinase inhibitor, significantly reduced spontaneous tone in the DOCA aorta but that it did not affect sham aorta basal tone (DOCA 63.5 +/- 15.9 versus sham 1.2 +/- 0.4 total change in percentage of phenylephrine contraction). We examined the interaction between the PI3-kinase and Rho pathways by observing the effects of LY294002 on a Rhokinase effector, myosin phosphatase (MYPT), and Y27632 on a PI3-kinase effector, Akt, using Western blot analysis. Inhibition of PI3-kinase reduced spontaneous tone, but it had no effect on the phosphorylation status of MYPT, indicating that PI3-kinase is not a downstream effector of Rho/Rho-kinase. These data indicate that there is little interaction between the Rho/Rhokinase and PI3-kinase pathways in the DOCA-salt aorta, and the two pathways seem to operate in parallel in supporting spontaneous arterial tone. These data reflect spontaneous tone only and do not rule out the possibility of interaction between these pathways in agonist-stimulated tone.

Ca2+ sensitivity of smooth muscle and nonmuscle myosin II: modulated by G proteins, kinases, and myosin phosphatase

Ca2+ sensitivity of smooth muscle and nonmuscle myosin II reflects the ratio of activities of myosin light-chain kinase (MLCK) to myosin light-chain phosphatase (MLCP) and is a major, regulated determinant of numerous cellular processes. We conclude that the majority of phenotypes attributed to the monomeric G protein RhoA and mediated by its effector, Rho-kinase (ROK), reflect Ca2+ sensitization: inhibition of myosin II dephosphorylation in the presence of basal (Ca2+ dependent or independent) or increased MLCK activity. We outline the pathway from receptors through trimeric G proteins (Galphaq, Galpha12, Galpha13) to activation, by guanine nucleotide exchange factors (GEFs), from GDP. RhoA. GDI to GTP. RhoA and hence to ROK through a mechanism involving association of GEF, RhoA, and ROK in multimolecular complexes at the lipid cell membrane. Specific domains of GEFs interact with trimeric G proteins, and some GEFs are activated by Tyr kinases whose inhibition can inhibit Rho signaling. Inhibition of MLCP, directly by ROK or by phosphorylation of the phosphatase inhibitor CPI-17, increases phosphorylation of the myosin II regulatory light chain and thus the activity of smooth muscle and nonmuscle actomyosin ATPase and motility. We summarize relevant effects of p21-activated kinase, LIM-kinase, and focal adhesion kinase. Mechanisms of Ca2+ desensitization are outlined with emphasis on the antagonism between cGMP-activated kinase and the RhoA/ROK pathway. We suggest that the RhoA/ROK pathway is constitutively active in a number of organs under physiological conditions; its aberrations play major roles in several disease states, particularly impacting on Ca2+ sensitization of smooth muscle in hypertension and possibly asthma and on cancer neoangiogenesis and cancer progression. It is a potentially important therapeutic target and a subject for translational research.

Shear stress-induced c-fos activation is mediated by Rho in a calcium-dependent manner

We aimed at elucidating the molecular basis of c-fos promoter activation in vascular endothelial cells (ECs) in response to shear stress, with emphases on Rho family GTPases (Rho, Cdc42, and Rac) and intracellular calcium. Dominant-negative and constitutively activated mutants of these GTPases were used to block the action of upstream signals and to activate the downstream pathways, respectively. The role of intracellular calcium was assessed with intracellular calcium chelators. Only Rho, but not Cdc42 or Rac, is involved in the shear stress induction of c-fos. This Rho-mediated shear-induction of c-fos is dependent on intracellular calcium, but not on the Rho effector p160ROCK or actin filaments. While the inhibition of p160ROCK and its ensuing disruption of actin filaments decreased the basal c-fos activity in static ECs (no flow), it did not affect the shear-inductive effect. The calcium chelator BAPTA-AM inhibits the shear-induction, as well as the static level, of c-fos activity.

Extracellular matrix, junctional integrity and matrix metalloproteinase interactions in endothelial permeability regulation

Vascular endothelial permeability is maintained by the regulated apposition of adherens and tight junctional proteins whose organization is controlled by several pharmacological and physiological mediators. Endothelial permeability changes are associated with: (1) the spatial redistribution of surface cadherins and occludin, (2) stabilization of focal adhesive bonds and (3) the progressive activation of matrix metalloproteinases (MMPs). In response to peroxide, histamine and EDTA, endothelial cells sequester VE-cadherin and alter its cytoskeletal binding. Simultaneously, these mediators enhance focal adhesion to the substratum. Oxidants, cytokines and pharmacological mediators also trigger the activation of matrix metalloproteinases (MMPs) in a cytoskeleton and tyrosine phosphorylation dependent manner to degrade occludin, a well-characterized tight junction element. These related in vitro phenomena appear to co-operate during inflammation, to increase endothelial permeability, structurally stabilize cells while also remodelling cell junctions and substratum.

Rapid transactivation of the vascular endothelial growth factor receptor KDR/Flk-1 by the bradykinin B2 receptor contributes to endothelial nitric-oxide synthase activation in cardiac capillary endothelial cells

Bradykinin (BK) and vascular endothelial growth factor (VEGF)-165 stimulate vasodilatation, microvascular permeability, and angiogenesis via the activation of the B2-type and KDR/Flk-1 receptors. To delineate the signal transduction pathways distal to the receptor activation in microvascular permeability, we compared their effects on two downstream targets, i.e. endothelial nitric-oxide (NO) synthase (eNOS) and F-actin, in primary cultures of cardiac capillary endothelial cells. The two mediators induced a similar cytoskeletal reorganization and both the translocation and activation of eNOS, leading to NO release within the first minutes of cell exposure. At the same time, BK produced the tyrosine phosphorylation and internalization of KDR/Flk-1 as did VEGF itself. This transactivation was blocked by the selective inhibitor of VEGF receptor tyrosine kinase activity but not by inhibitors of epidermal growth factor receptor or protein kinase C activity. The selective inhibitor of VEGF receptor tyrosine kinase activity totally prevented the effects of VEGF but only partially inhibited NO release induced by BK without affecting the concomitant cytoskeletal reorganization. Thus, BK transactivated KDR/Flk-1 through an intrinsic kinase activity of KDR/Flk-1, resulting in a further eNOS activation in endothelial cells. This represents a novel mechanism whereby a G protein-coupled receptor activates a receptor tyrosine kinase to generate biological response.