Patients with inflammatory cardiovascular disease have an increased number of circulating activated platelets and platelet-leukocyte aggregates (PLAs), both of which play a central role in the initiation and progression of disease. Activated platelets can activate the complement system on their surface, with potential consequences in vascular inflammation and thrombosis. Properdin, a positive regulator of the alternative pathway (AP) of complement, is produced mainly by stimulated leukocytes. The mechanisms by which properdin participates in complement activation on platelets and in PLA formation remain unknown. We have shown that the physiological forms of human properdin bind directly to activated, but not resting, platelets. The binding of properdin promotes AP complement activation on activated platelets, as measured by C3b and C9 deposition on their surface, by forming novel C3 convertases on the platelet [C3(H2O),Bb]. Removal of surface proteins by treating platelets with a low dose of proteinase K, leads to reduced properdin binding to activated platelets. On the other hand, chondroitin sulfate-A (a glycosaminoglycan that is released by platelets upon activation) increases the binding of properdin to activated platelets by ~4 fold. These results suggest that interaction of properdin with activated platelets may depend on a protein receptor as well as glycosaminoglycans (i.e. proteoglycans). We have also determined that properdin released by PMA-stimulated neutrophils binds to activated platelets. Since activated neutrophils and platelets directly interact with one another in pro-inflammatory microenvironments, the fresh properdin produced by neutrophils would be available to platelets at high concentrations. Using ex-vivo whole blood assays, we show that properdin leads to an increase in PLA formation in TRAP (thrombin receptor activating peptide)-stimulated whole blood and inhibition of properdin leads to decrease in PLA formation. Our data also show that properdin-mediated PLA formation is controlled by complement regulatory protein factor H. Altogether, the results support a role for properdin in the cellular microenvironment, contributing to complement activation on activated platelets and PLA formation, with potential consequences in inflammation pathophysiology.
|Advisor:||Ferreira, Viviana P.|
|Commitee:||Pan, Kevin, Stepkowski, Stanislaw, Vazquez, Guillermo, Wooten, Mark|
|School:||The University of Toledo|
|Department:||College of Medicine|
|School Location:||United States -- Ohio|
|Source:||DAI-B 76/01(E), Dissertation Abstracts International|
|Keywords:||Alternative pathway, Complement, Factor h, Platelet-leukocyte aggregates, Platelets, Properdin|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be