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      Lipopolysaccharide-induced caveolin-1 phosphorylation-dependent increase in transcellular permeability precedes the increase in paracellular permeability

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          Abstract

          Background

          Lipopolysaccharide (LPS) was shown to induce an increase in caveolin-1 (Cav-1) expression in endothelial cells; however, the mechanisms regarding this response and the consequences on caveolae-mediated transcellular transport have not been completely investigated. This study aims to investigate the role of LPS-induced Cav-1 phosphorylation in pulmonary microvascular permeability in pulmonary microvascular endothelial cells (PMVECs).

          Methods

          Rat PMVECs were isolated, cultured, and identified. Endocytosis experiments were employed to stain the nuclei by DAPI, and images were obtained with a fluorescence microscope. Permeability of endothelial cultures was measured to analyze the barrier function of endothelial monolayer. Western blot assay was used to examine the expression of Cav-1, pCav-1, triton-insoluble Cav-1, and triton-soluble Cav-1 protein.

          Results

          The LPS treatment induced phosphorylation of Cav-1, but did not alter the total Cav-1 level till 60 min in both rat and human PMVECs. LPS treatment also increased the triton-insoluble Cav-1 level, which peaked 15 min after LPS treatment in both rat and human PMVECs. LPS treatment increases the intercellular cell adhesion molecule-1 expression. Src inhibitors, including PP2, PP1, Saracatinib, and Quercetin, partially inhibited LPS-induced phosphorylation of Cav-1. In addition, both PP2 and caveolae disruptor MβCD inhibited LPS-induced increase of triton-insoluble Cav-1. LPS induces permeability by activating interleukin-8 and vascular endothelial growth factor and targeting other adhesion markers, such as ZO-1 and occludin. LPS treatment also significantly increased the endocytosis of albumin, which could be blocked by PP2 or MβCD. Furthermore, LPS treatment for 15 min significantly elevated Evans Blue-labeled BSA transport in advance of a decrease in transendothelial electrical resistance of PMVEC monolayer at this time point. After LPS treatment for 30 min, transendothelial electrical resistance decreased significantly. Moreover, PP2 and MβCD blocked LPS-induced increase in Evans Blue-labeled BSA level.

          Conclusion

          Our study demonstrates that LPS-induced Cav-1 phosphorylation may lead to the increase of transcellular permeability prior to the increase of paracellular permeability in a Src-dependent manner. Thus, LPS-induced Cav-1 phosphorylation may be a therapeutic target for the treatment of inflammatory lung disease associated with elevated microvascular permeability.

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          Most cited references 27

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          Regulation of endothelial junctional permeability.

          The endothelium is a semi-permeable barrier that regulates the flux of liquid and solutes, including plasma proteins, between the blood and surrounding tissue. The permeability of the vascular barrier can be modified in response to specific stimuli acting on endothelial cells. Transport across the endothelium can occur via two different pathways: through the endothelial cell (transcellular) or between adjacent cells, through interendothelial junctions (paracellular). This review focuses on the regulation of the paracellular pathway. The paracellular pathway is composed of adhesive junctions between endothelial cells, both tight junctions and adherens junctions. The actin cytoskeleton is bound to each junction and controls the integrity of each through actin remodeling. These interendothelial junctions can be disassembled or assembled to either increase or decrease paracellular permeability. Mediators, such as thrombin, TNF-alpha, and LPS, stimulate their respective receptor on endothelial cells to initiate signaling that increases cytosolic Ca2+ and activates myosin light chain kinase (MLCK), as well as monomeric GTPases RhoA, Rac1, and Cdc42. Ca2+ activation of MLCK and RhoA disrupts junctions, whereas Rac1 and Cdc42 promote junctional assembly. Increased endothelial permeability can be reversed with "barrier stabilizing agents," such as sphingosine-1-phosphate and cyclic adenosine monophosphate (cAMP). This review provides an overview of the mechanisms that regulate paracellular permeability.
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            Caveolin-1 regulates NF-kappaB activation and lung inflammatory response to sepsis induced by lipopolysaccharide.

            Caveolin-1, the principal structural and signaling protein of caveolae, is implicated in NO-mediated cell signaling events, but its precise role in inflammation is not well understood. Using caveolin-1-knockout (Cav-1(-/-)) mice, we addressed the role of caveolin-1 in the lung inflammatory response to sepsis induced by i.p. injection of LPS. LPS-challenged wild-type (WT) lungs exhibited significant increases in neutrophil sequestration (approximately 16-fold), lung microvascular permeability K(f,c) (approximately 5.7-fold), and edema formation (approximately 1.6-fold). Compared with WT, Cav-1(-/-) lungs showed marked attenuation of LPS-induced neutrophil sequestration (approximately 11-fold increase) and inhibition of microvascular barrier breakdown and edema formation. Prevention of lung injury in Cav-1(-/-) mice was associated with decreased mortality in response to LPS challenge. To address the basis of the reduced inflammation and injury in Cav-1(-/-) lungs, we examined the role of NO because its plasma concentration is known to be increased in Cav-1(-/-) mice. Cav-1(-/-) mouse lungs demonstrated a significant increase in endothelial NO synthase (eNOS)-derived NO production relative to WT, which is consistent with the role of caveolin-1 as a negative regulator of eNOS activity. Cav-1(-/-) lungs concurrently showed suppression of NF-kappaB activity and decreased transcription of inducible NO synthase and ICAM-1. Coadministration of LPS with the NO synthase inhibitor nitro-L-arginine in Cav-1(-/-) mice prevented the suppression of NF-kappaB activity and restored lung polymorphonuclear leukocyte sequestration in response to LPS challenge. Thus, caveolin-1, through its ability to regulate eNOS-derived NO production, is a crucial determinant of NF-kappaB activation and the lung inflammatory response to LPS.
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              Acute lung injury review.

              The first report of acute respiratory distress syndrome (ARDS) was published in 1967, and even now acute lung injury (ALI) and ARDS are severe forms of diffuse lung disease that impose a substantial health burden all over the world. Recent estimates indicate approximately 190,000 cases per year of ALI in the United States each year, with an associated 74,500 deaths per year. Common causes of ALI/ARDS are sepsis, pneumonia, trauma, aspiration pneumonia, pancreatitis, and so on. Several pathologic stages of ALI/ARDS have been described: acute inflammation with neutrophil infiltration, fibroproliferative phase with hyaline membranes, with varying degrees of interstitial fibrosis, and resolution phase. There has been intense investigation into the pathophysiologic events relevant to each stage of ALI/ARDS, and much has been learned in the alveolar epithelial, endobronchial homeostasis, and alveolar cell immune responses, especially neutrophils and alveolar macrophages in an animal model. However, these effective results in the animal models are not equally adoptive to those in randomized, controlled trials. The clinical course of ALI/ARDS is variable with the likely pathophysiologic complexity of human ALI/ARDS. In 1994, the definition was recommended by the American-European Consensus Conference Committee, which facilitated easy nomination of patients with ALI/ARDS for a randomized, clinical trial. Here, we review the recent randomized, clinical trials of ALI/ARDS.
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                Author and article information

                Journal
                Drug Des Devel Ther
                Drug Des Devel Ther
                Drug Design, Development and Therapy
                Drug Design, Development and Therapy
                Dove Medical Press
                1177-8881
                2015
                28 August 2015
                : 9
                : 4965-4977
                Affiliations
                [1 ]Department of Respiration, The First Affiliated Hospital of Anhui Medical University, Hefei, People’s Republic of China
                [2 ]Department of Emergency, The First Affiliated Hospital of Anhui Medical University, Hefei, People’s Republic of China
                Author notes
                Correspondence: Gengyun Sun, Department of Respiration, The First Affiliated Hospital of Anhui Medical University, 218 Jixi Road, Hefei 230022, People’s Republic of China, Tel +86 551 6292 3329, Fax +86 551 6292 3421, Email sungengy@ 123456126.com
                Article
                dddt-9-4965
                10.2147/DDDT.S77646
                4560510
                © 2015 Wang et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License

                The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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                Original Research

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