Inflammatory mediators increase vascular permeability primarily by formation of intercellular gaps between endothelial cells of post-capillary venules. Under these conditions, endothelial cell-cell contacts such as adherens and tight junctions open to allow paracellular fluid passage. Small guanosine triphosphatases (GTPases) from the ras superfamily, primarily Rho GTPases (RhoA, Rac1, Cdc42) or Rap1 are known to regulate cell adhesion, in part by reorganization of the junction-associated cortical actin cytoskeleton. In this review, we will discuss the role of small GTPases for the maintenance of microvascular barrier functions under resting conditions as well as under conditions of increased permeability and their involvement in signalling pathways downstream of both barrier-stabilizing and inflammatory mediators. Rac1 and Cdc42 are the main GTPases required for barrier maintenance and stabilization, whereas RhoA negatively regulates barrier properties under both resting and inflammatory conditions. For Rac1 and RhoA, contrary functions under certain conditions have also been described. However, Rac1-mediated barrier destabilization in microvascular endothelium appears to be largely restricted to conditions of enhanced endothelial cell migration and thus to be more closely related to angiogenesis rather than to inflammation. Recent studies revealed that cAMP signalling, which is well known to be barrier protective, enhances barrier functions in part via Rap1-mediated activation of Rac1 and Cdc42 as well as by inhibition of RhoA. Moreover, barrier-stabilizing mediators directly activate Rac1 and Cdc42 or increase cAMP levels. On the other hand, several barrier-disruptive components appear to increase permeability by reduced formation of cAMP, leading to both inactivation of Rac1 and activation of RhoA.
"Hoelzle and Svitkina for example showed that endothelial cells use lamellipodia as the initial contact and then transform these into filopodia-like bridges that develop into nascent VE-cadherin-based junctions (Hoelzle and Svitkina, 2012). Moreover, Rac1 is reported to be required for barrier maintenance, but also needed for VE-cadherin endocytosis and reactive oxygen species (ROS)-mediated loss of VE-cadherin-mediated cell-cell contacts (Gavard and Gutkind, 2006; Spindler et al., 2010; van Wetering et al., 2002). Thus, Rac1 controls signaling mechanisms that have opposing effects on endothelial cell-cell junctions, suggesting a need for finebalanced spatial and temporal regulation of its activity. "
"e l s e v i e r . c o m / l o c a t e / a n t i v i r a l membrane localization and activation, the small GTPases, Rac1 and CDC42, stabilize VE-cadherin-mediated cell adhesion by crosslinking VE-cadherin and its binding partners with actin polymers, thereby conferring a stable vasculature (Fukata and Kaibuchi, 2001; Kouklis et al., 2004; Broman et al., 2006; Spindler et al., 2010). In contrast, activation of RhoA, through its downstream binding, ROCK, is associated with increased trans-endothelial permeability through enhanced cell contraction and junction protein remodeling (Fig. 1) (Breslin and Yuan, 2004; Gorovoy et al., 2007; van Nieuw Amerongen and van Hinsbergh, 2007). "
[Show abstract][Hide abstract] ABSTRACT: Activation of the RhoA/Rho-kinase (ROCK) pathway induces endothelial barrier dysfunction and increased vascular permeability, which is a hallmark of various life- threatening vascular pathologies. Therapeutic approaches aimed at inhibiting the RhoA/ROCK pathway have proven effective in the attenuation of vascular leakage observed in animal models of endotoxin-induced lung injury/sepsis, edema, autoimmune disorders, and stroke. These findings suggest that treatments targeting the ROCK pathway might be of benefit in the management of the Ebola virus disease (EVD), which is characterized by severe vascular leak, likely involving pro-inflammatory cytokines, such as tumor necrosis factor-alpha, released from virus-infected macrophages. In this paper, we review evidence from in vivo and in vitro models of vascular leakage, suggesting that the RhoA/ROCK pathway is an important therapeutic target for the reversal of the vascular permeability defects associated with EVD. Future studies should explore the efficacy of pharmacological inhibition of RhoA/ROCK pathway on reversing the endothelial barrier dysfunction in animal models of EVD and other hemorrhagic fever virus infections as part of an adjunctive therapy. Such experimental studies should focus, in particular, on the small molecule fasudil (HA-1077), a derivative of isoquinoline, which is a safe and clinically approved inhibitor of ROCK, making it an excellent candidate in this context.
Antiviral Research 12/2014; 114. DOI:10.1016/j.antiviral.2014.12.005 · 3.94 Impact Factor
"Endothelial barrier functions are dependent on the organization of junctional complex and the actin cytoskeleton . Therefore, possible alterations of these structures accompanying the TAT-Ahx-AKAPis-induced decrease in TER were investigated by immunofluorescence studies in HDMEC. "
[Show abstract][Hide abstract] ABSTRACT: cAMP-mediated PKA signaling is the main known pathway involved in maintenance of the endothelial barrier. Tight regulation of PKA function can be achieved by discrete compartmentalization of the enzyme via physical interaction with A-kinase anchoring proteins (AKAPs). Here, we investigated the role of AKAPs 220 and 12 in endothelial barrier regulation. Analysis of human and mouse microvascular endothelial cells as well as isolated rat mesenteric microvessels was performed using TAT-Ahx-AKAPis peptide, designed to competitively inhibit PKA-AKAP interaction. In vivo microvessel hydraulic conductivity and in vitro transendothelial electrical resistance measurements showed that this peptide destabilized endothelial barrier properties, and dampened the cAMP-mediated endothelial barrier stabilization induced by forskolin and rolipram. Immunofluorescence analysis revealed that TAT-Ahx-AKAPis led to both adherens junctions and actin cytoskeleton reorganization. Those effects were paralleled by redistribution of PKA and Rac1 from endothelial junctions and by Rac1 inactivation. Similarly, membrane localization of AKAP220 was also reduced. In addition, depletion of either AKAP12 or AKAP220 significantly impaired endothelial barrier function and AKAP12 was also shown to interfere with cAMP-mediated barrier enhancement. Furthermore, immunoprecipitation analysis demonstrated that AKAP220 interacts not only with PKA but also with VE-cadherin and ß-catenin. Taken together, these results indicate that AKAP-mediated PKA subcellular compartmentalization is involved in endothelial barrier regulation. More specifically, AKAP220 and AKAP12 contribute to endothelial barrier function and AKAP12 is required for cAMP-mediated barrier stabilization.
PLoS ONE 09/2014; 9(9):e106733. DOI:10.1371/journal.pone.0106733 · 3.23 Impact Factor
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