187,937 research outputs found
Differential cargo mobilisation within Weibel-Palade bodies after transient fusion with the plasma membrane.
No full textInflammatory chemokines can be selectively released from Weibel-Palade bodies (WPBs) during kiss-and-run exocytosis. Such selectivity may arise from molecular size filtering by the fusion pore, however differential intra-WPB cargo re-mobilisation following fusion-induced structural changes within the WPB may also contribute to this process. To determine whether WPB cargo molecules are differentially re-mobilised, we applied FRAP to residual post-fusion WPB structures formed after transient exocytosis in which some or all of the fluorescent cargo was retained. Transient fusion resulted in WPB collapse from a rod to a spheroid shape accompanied by substantial swelling (>2 times by surface area) and membrane mixing between the WPB and plasma membranes. Post-fusion WPBs supported cumulative WPB exocytosis. To quantify diffusion inside rounded organelles we developed a method of FRAP analysis based on image moments. FRAP analysis showed that von Willebrand factor-EGFP (VWF-EGFP) and the VWF-propolypeptide-EGFP (Pro-EGFP) were immobile in post-fusion WPBs. Because Eotaxin-3-EGFP and ssEGFP (small soluble cargo proteins) were largely depleted from post-fusion WPBs, we studied these molecules in cells preincubated in the weak base NH4Cl which caused WPB alkalinisation and rounding similar to that produced by plasma membrane fusion. In these cells we found a dramatic increase in mobilities of Eotaxin-3-EGFP and ssEGFP that exceeded the resolution of our method (∼ 2.4 µm2/s mean). In contrast, the membrane mobilities of EGFP-CD63 and EGFP-Rab27A in post-fusion WPBs were unchanged, while P-selectin-EGFP acquired mobility. Our data suggest that selective re-mobilisation of chemokines during transient fusion contributes to selective chemokine secretion during transient WPB exocytosis. Selective secretion provides a mechanism to regulate intravascular inflammatory processes with reduced risk of thrombosis
Temperature-Dependence of Weibel-Palade Body Exocytosis and Cell Surface Dispersal of von Willebrand Factor and Its Propolypeptide
No full textBackground: Weibel-Palade bodies (WPB) are endothelial cell (EC) specific secretory organelles containing Von Willebrand factor (VWF). The temperature-dependence of Ca2+-driven WPB exocytosis is not known, although indirect evidence suggests that WPB exocytosis may occur at very low temperatures. Here we quantitatively analyse the temperature-dependence of Ca2+-driven WPB exocytosis and release of secreted VWF from the cell surface of ECs using fluorescence microscopy of cultured human ECs containing fluorescent WPBs.
Principal Findings: Ca2+-driven WPB exocytosis occurred at all temperatures studied (7–37°C). The kinetics and extent of WPB exocytosis were strongly temperature-dependent: Delays in exocytosis increased from 0.92 s at 37°C to 134.2 s at 7°C, the maximum rate of WPB fusion decreased from 10.0±2.2 s−1 (37°C) to 0.80±0.14 s−1 (7°C) and the fractional extent of degranulation of WPBs in each cell from 67±3% (37°C) to 3.6±1.3% (7°C). A discrepancy was found between the reduction in Ca2+-driven VWF secretion and WPB exocytosis at reduced temperature; at 17°C VWF secretion was reduced by 95% but WPB exocytosis by 75–80%. This discrepancy arises because VWF dispersal from sites of WPB exocytosis is largely prevented at low temperature. In contrast VWF-propolypeptide (proregion) dispersal from WPBs, although slowed, was complete within 60–120 s. Novel antibodies to the cleaved and processed proregion were characterised and used to show that secreted proregion more accurately reports the secretion of WPBs at sub-physiological temperatures than assay of VWF itself.
Conclusions : We report the first quantitative analysis of the temperature-dependence of WPB exocytosis. We provide evidence; by comparison of biochemical data for VWF or proregion secretion with direct analysis of WPB exocytosis at reduced temperature, that proregion is a more reliable marker for WPB exocytosis at reduced temperature, where VWF-EC adhesion is increased
Successfull Blossom Thinning and Crop Load Regulation for Organic Apple Growing with Potassium-bi-carbonate (Armicarb(R)): Results of Field Experiments over 3 Years and with 11 Cultivars
No full textWith field trials over 3 years in a commercial organic orchard in Switzerland we have tested the efficacy of Armicarb® (potassium-bi-carbonate) for flower thinning in organic apple production. Over time, Armicarb was tested on 11 cultivars, at different application periods, in different concentrations, and always in comparison to other agents that are already allowed for thinning in organic fruit production in the European Union as e.g. lime sulphur, molasses, mechanical rope-thinner or combinations of methods. Armicarb proved to be an efficient and reliable thinning agent with an efficacy similar to the now recommended methods with rope device, molasses or lime sulphur but has the advantage to be an environmentally very friendly product. On the other hand, the risk for fruit russeting is comparably elevated especially with cultivars ‘Elstar’, ‘Golden Del.’ ’and ‘Gala’. Finally, we have elaborated cultivar-specific recommendations for the use of Armicarb for thinning purposes, which were the basis for the Swiss Federal approval to use Armicarb for thinning in conventional and organic apple production in 2011/2012
Weibel instability (1D-2V)
No full textWeibel instability in one spatial dimension and two velocity dimensions.</p
Weibel-Palade bodies : an exciting way out!
No full textWeibel-Palade bodies are specialized secretory granules found in endothelial cells. These vesicles are able to store a variety of proteins with different biological functions such as the multimeric glycoprotein von Willebrand factor (VWF) that is required for normal haemostasis, the leukocyte adhesion receptor P-selectin, and the chemokine interleukin-8 (IL-8). Correct delivery of these proteins to the cell membrane or to the circulation is essential for the biological role of these proteins. Indeed, regulated exocytosis of Weibel-Palade bodies serves several physiological functions including inflammatory and haemostatic responses. However, the mechanisms such as sorting of proteins to Weibel-Palade bodies, Weibel-Palade body trafficking in the cell and secretion of their content into the circulation, are far of being understood. In this thesis, I tried to get more insight into the life cycle of Weibel-Palade bodies and the extracellular function of one of their constituents.
The first step of the life cycle of Weibel-Palade bodies is the sorting process of proteins into these storage organelles. Chapter 2 indicates that VWF plays an active role in sequestering IL-8 into Weibel-Palade bodies.
Chapter 3 describes the existence of different pools of Weibel-Palade bodies: some vesicles barely moved as if they were tethered, others seemed to travel in a stochastic manner. Upon arrival at the plasma membrane, tethered Weibel-Palade bodies are trapped in the actin cortex of endothelial cells awaiting a trigger for release. Upon stimulation of endothelial cells, either with Ca2+- or cAMP-raising agonists, we observed fusion of individual vesicles with the plasma membrane, gradual release and diffusion of Weibel-Palade body content into the extracellular compartment. As a result of slow exocytosis, endothelial cells may present at their surface focal sites with high concentrations VWF, IL-8 and P-selectin which, in turn, may play a role in focal adhesion of blood constituents to the endothelium upon vascular injury. In addition to exocytosis, cAMP-raising agonists induce clustering of a subset of Weibel-Palade bodies in the perinuclear region of the cell. This may be a mechanism to prevent excessive exocytosis of Weibel-Palade bodies.
Chapter 4 indicates that RalA, a small GTP-binding protein shown to be associated with Weibel-Palade bodies, is involved in the regulated exocytosis of these vesicles. RalA may interact with a putative exocyst leading to docking of Weibel-Palade bodies at the plasma membrane.
VWF-propeptide, a Weibel-Palade constituent, was used as a marker for endothelial cell perturbation in Chapter 6 to determine whether endothelial cell activation is the primary event in the pathogenesis of thrombotic thrombocytopenic purpura (TTP). We concluded that endothelial cell activation is not the primary event leading to TTP. Vascular perturbation seems a consequence rather than a cause of the disease.
In Chapter 7 the potential role of the VWF-propeptide as an inflammatory mediator was investigated. Neutrophil adhesion induced by IL-8 increased significantly upon co-stimulation with VWF-propeptide suggesting that the propeptide acts synergistically with IL-8 upon appropriate stimulation of the endothelium.
Taken together, biogenesis and exocytosis of Weibel-Palade bodies are essential in the processes underlying hemostatic, thrombotic and inflammatory response
Le Savoir et le corps, essai sur P. Bayle, de Luc Weibel
No full textBlanchard Gérard. Le Savoir et le corps, essai sur P. Bayle, de Luc Weibel. In: Communication et langages, n°29, 1976. pp. 115-117
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