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      Selective Suppression of an Endothelin and Platelet-Derived Growth Factor Containing Vesicular System in Endothelium of Rat Saphenous Vein by Long-Term Orthostasis

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          Abstract

          Electron-dense vesicles were observed in rat vascular endothelium. The purpose of this study was to characterize their content(s), venous-arterial distribution and response to chronic orthostatic stress in extremity vessels. Saphenous and brachial vessels – saphenous vein (SV), saphenous artery (SA), brachial vein, brachial artery – were prepared for electron microscopy to quantitate the vesicle area within the endothelium following immunohistochemical and immunocytochemical identification. The effect of long-term orthostasis was assessed by exposure to head-up tilt for 2 weeks. The vesicular area in relation to the total cross-sectional area of the endothelial cells in the SV and SA of normal and confined control groups was 3.88 ± 0.38 versus 0.89 ± 0.06% (p < 0.05) and 4.92 ± 0.25 versus 1.09 ± 0.47% (p < 0.05), respectively. Head-up tilt suppressed the vesicle content of the SV to 2.26 ± 0.39% (p < 0.05), but it remained low in the SA (1.29 ± 0.45%), brachial vein (0.45 ± 0.12%) and brachial artery (0.59 ± 0.17%). Endothelin and platelet-derived growth factor, but not acidic phosphatase activity or lipid content, could be identified in the vesicles. Plasma endothelin levels were unchanged. We conclude that dense vesicles in the endothelium of extremity vessels are not cell degradation products. They may represent a vesicular secretory or storage system for endothelin and platelet-derived growth factor which participates in regional vascular adaptation to long-term orthostatic load.

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          Most cited references 19

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          Evidence that release of adenosine triphosphate from endothelial cells during increased shear stress is vesicular.

           G Burnstock,  P Bodin (2001)
          In response to increased shear stress, vascular endothelial cells release adenosine triphosphate (ATP) by an unknown mechanism. We have investigated this mechanism using different approaches. First, we discovered that quinacrine, used to locate intracellular stores of ATP bound to peptides, displayed a granular fluorescence, typical of vesicular storage. Second, we found that two inhibitors of vesicular transport (monensin and N-ethylmaleimide) produced a highly significant reduction in the release of ATP from vascular endothelial cells in response to increased shear stress. Preliminary experiments using inhibitors of the cystic fibrosis transmembrane regulator, the sulfonylurea receptor, and the multidrug resistance protein showed no involvement of these ATP-binding cassette transporter proteins (previously characterized in endothelial cells) in the mechanism of release of ATP. We suggest, therefore, that the release of ATP from vascular endothelial cells, like that of nerve cells, is probably by vesicular exocytosis.
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            Biogenesis and exocytosis of Weibel-Palade bodies.

            Vascular endothelial cells contain typical, elongated vesicles, the so-called Weibel-Palade bodies, which serve as a storage compartment for von Willebrand factor (VWF), a plasma protein that plays an essential role in controlling the adhesion and aggregation of platelets at sites of vascular injury. Upon activation of endothelial cells by agonists such as thrombin, epinephrine or histamine, the Weibel-Palade bodies fuse with the plasma membrane and release their contents into the blood circulation. This process provides an adequate means by which endothelial cells can actively participate in controlling the arrest of bleeding upon vascular damage. Besides VWF, Weibel-Palade bodies contain a subset of other proteins, including interleukin-8 (IL-8), P-selectin and endothelin. Similar to VWF, these proteins are transported to the outside of the cell upon stimulation and may control local or systemic biological effects, including inflammatory and vasoactive responses. Apparently, endothelial cells are able to create a storage pool for a variety of bioactive molecules which can be mobilised upon demand. Endothelial cells that are deficient of VWF synthesis are not only unable to form Weibel-Palade bodies, but also lack the ability to store IL-8 or P-selectin or release these proteins in a regulated manner. It thus appears that VWF not only plays a prominent role in controlling primary haemostasis, but also may modulate inflammatory processes through its ability to target inflammatory mediators to the regulated secretion pathway of the endothelium.
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              Signalling mechanisms in the regulation of vascular cell migration.

               H Abedi,  I Zachary (1995)
              The migration of arterial vascular smooth muscle cells (VSMC) is thought to play a central role in atherogenesis and restenosis. The migration of several other cell types, including monocytes, T-lymphocytes and endothelial cells is also involved in the development of the mature atherosclerotic lesion. Several defined growth factors, cytokines and extracellular matrix components which are released at the sites of lesions have been implicated in the regulation of migration of VSMC and other lesion-associated cells. Platelet-derived growth factor BB-homodimer of PDGF (PDGF-BB) is strongly implicated in neo-intima formation in vivo and is the most potent known chemoattractant for VSMC in vitro. Dynamic interactions between cell surface adhesive receptors (integrins) for ECM components, organisation of the actin cytoskeleton and the turnover of focal adhesions are all key processes in cell locomotion and migration. The signal transduction pathways which mediate the chemotactic effects of PDGF-BB and other migration factors on VSMC are unknown, but several classes of cellular components are implicated including components associated with focal adhesions, small GTP-binding proteins of the rho family, and certain substrates of the PDGF beta-receptor. Tyrosine phosphorylation of the novel focal adhesion-associated protein tyrosine kinase, p125 focal adhesion kinase (p125FAK), is regulated by integrins and by several factors which alter actin cytoskeletal organisation. Recent findings suggest that tyrosine phosphorylation of p125FAK and other focal adhesion-associated proteins may be implicated in the chemotactic response of VSMC to PDGF-BB. The migratory response to PDGF-BB may be dependent on both ligand isoform bio-availability and on receptor-isotype expression as well as on down-stream signalling events. Ultimately, cell migration in vivo will be determined by a complex array of diverse extracellular molecules organised in intercellular paracrine/autocrine networks as well as multiple interacting intracellular signal transduction pathways.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2005
                April 2005
                13 April 2005
                : 42
                : 2
                : 157-164
                Affiliations
                aInstitute of Human Physiology and Clinical Experimental Research, bDepartment of Anatomy, Histology and Embryology, and cFirst Department of Pathology and Experimental Cancer Research, and Molecular Pathology Research Group, Joint Research Organization of the Hungarian Academy of Sciences and Semmelweis University, Budapest, Hungary
                Article
                84404 J Vasc Res 2005;42:157–164
                10.1159/000084404
                15767762
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 3, Tables: 1, References: 40, Pages: 8
                Categories
                Research Paper

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