The acute chest syndrome is initiated by lung inflammation that induces increased adhesion of sickled redblood cells to pulmonary microvascular endothelium. Emerging evidence indicates the interaction betweenred blood cells and endothelium is dynamic. While in the non-inflamed state perfusion is facilitated by antiadhesiveproteins expressed on the endothelial surface, in the inflamed state vaso-occlusion is partly causedby upregulation of adhesive proteins such as P-selectin and release of von Willebrand factor (vWf) frommicrovascular endothelium. The secretory organelle in endothelium is the endothelial cell specific organellecalled Weibel-Palade body. In the inflamed circulation thrombin and other Gq-linked neurohumoralinflammatory mediators increase endothelial cell cytosolic calcium, and this rise in cytosolic calcium issufficient to cause rapid translocation of Weibel-Palade bodies to the plasmalemma for vWf secretion and P-selectinup-regulation. Specific calcium entry pathways that stimulate vWf secretion and P-selectin upregulationremain incompletely understood, particularly in microvascular endothelial cells obtained from theprominent site of vaso-occlusion. Preliminary studies suggest that lung microvascular endothelial cellsexpess T-type, voltage-activated calcium channels which promote a pro-coagulant endothelial phenotypeduring inflammation. In this proposal, we will test the overall HYPOTHESIS that calcium entry through T-typecalcium channels is an important amplification step in release of vWf and up-regulation of P-selectin fromlung microvascular endothelium that promotes the retention of sickled red blood cells. The hypothesis will beexplored using lung microvascular endothelial cells in culture and an isolated rat lung model, in which therole of the T channel to red blood cell retention can be assessed under flow conditions.
The SPECIFIC AIMS test the hypotheses that: [1] Lung microvascular endothelial cells express a T-type calcium channel that isactivated by Gq-linked neurohumoral inflammatory mediators, and [2] Activation of T-type calcium channelspromotes the release of vWf and up-regulation of P-selectin from lung microvascular endothelial cellsimportant for vaso-occlusion. It is hoped completion of these studies will improve our understanding ofmechanisms that regulate erythrocyte-endothelial adherence so that effective therapies can be developed fortreatment of sickle cell anemia, as well as other vascular thrombosis disorders.
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