on May 1, 2008
Published online before print May 1, 2008, doi: 10.1161/ATVBAHA.108.166629
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Submitted on September 10, 2007
Accepted on April 17, 2008
Complete Downmodulation of P-Selectin Glycoprotein Ligand in Monocytes Undergoing Apoptosis
Jan-Julius Stampfuss ;
From the Institut für Pharmakologie und Klinische Pharmakologie (J.-J.S., P.C., J.W.F., G.K., B.H.R., K.F., K.S.), Universitätsklinikum Düsseldorf, Germany; the Institut für Molekulare Medizin (U.T., K.S.-O.), Universitätsklinikum Düsseldorf, Germany; the Institute for Translational Medicine and Therapeutics (T.G.), University of Pennsylvania School of Medicine, Philadelphia; and the Institut für Pharmakologie (M.G., A.-A.W.), Universität Duisburg-Essen, Universitätsklinikum Essen, Germany.
* To whom correspondence should be addressed. E-mail: artur.weber{at}uk-essen.de.
Objectives—Apoptotic monocytes release membrane microparticles which may play a major role in thrombogenicity through a P-selectin glycoprotein ligand (PGSL-1)–mediated mechanism. We have studied systematically the regulation of PSGL-1 expression and function in apoptotic monocytic cells.
Methods and Results—PSGL-1 expression (flow cytometry, immunofluorescence microscopy, immunoblot) was virtually abolished in apoptotic monocytes by proteolytic shedding. This was accompanied by a complete loss of PSGL-1–mediated platelet–leukocyte (flow cytometry) and leukocyte–endothelial cell (parallel plate flow chamber) interactions. Systematic screening of protease inhibitors combined with knock-out and siRNA experiments characterized the PSGL-1-cleaving enzyme as an N-ethylmaleimide-inhibitable metalloproteinase of the ADAM family.
Conclusions—Downmodulation of PGSL-1 in apoptotic monocytes may prevent ectopic cell clearance in the peripheral vasculature to reduce local inflammatory and proliferative responses. Depletion of PSGL-1 expression on apoptotic microparticles may also act as a molecular switch to modulate their thrombogenic activity.
Key words: PSGL-1 • apoptosis • monocytes • platelets • endothelial cells