title: Differentially regulated GPVI ectodomain shedding by multiple platelet-expressed proteinases.
abstract: Glycoprotein VI (GPVI) mediates platelet activation on exposed subendothelial collagens at sites of vascular injury and thereby contributes to normal hemostasis, but also to the occlusion of diseased vessels in the setting of myocardial infarction or stroke. GPVI is an attractive target for antithrombotic therapy, particularly because previous studies have shown that anti-GPVI antibodies induce irreversible down-regulation of the receptor in circulating platelets by internalization and/or ectodomain shedding. Metalloproteinases of the a disintegrin and metalloproteinase (ADAM) family have been proposed to mediate this ectodomain shedding, but direct evidence for this is lacking. Here, we studied GPVI shedding in vitro and in vivo in newly generated mice with a megakaryocyte-specific ADAM10 deficiency and in Adam17(ex/ex) mice, which lack functional ADAM17. We demonstrate that GPVI cleavage in vitro can occur independently through either ADAM10 or ADAM17 in response to distinct stimuli. In contrast, antibody (JAQ1)-induced GPVI shedding in vivo occurred in mice lacking both ADAM10/ADAM17 in their platelets, suggesting the existence of a third GPVI cleaving platelet enzyme. This was supported by in vitro studies on ADAM10/ADAM17 double-deficient platelets. These results reveal that ectodomain shedding of GPVI can be mediated through multiple differentially regulated platelet-expressed proteinases with obvious therapeutic implications.
authors.affiliation: Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Josef-Schneider-Strasse 2, Würzburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Bender
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hofmann
authors.forename: David
authors.initials: D
authors.lastname: Stegner
authors.forename: Athena
authors.initials: A
authors.lastname: Chalaris
authors.forename: Michael
authors.initials: M
authors.lastname: Bösl
authors.forename: Attila
authors.initials: A
authors.lastname: Braun
authors.forename: Jürgen
authors.initials: J
authors.lastname: Scheller
authors.forename: Stefan
authors.initials: S
authors.lastname: Rose-John
authors.forename: Bernhard
authors.initials: B
authors.lastname: Nieswandt
mesh_terms: D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism*; D000072197:ADAM10 Protein; D000072198:ADAM17 Protein; D053829:Amyloid Precursor Protein Secretases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D017353:Gene Deletion; D008533:Megakaryocytes / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology; D009154:Mutation; D010447:Peptide Hydrolases / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D053829:Amyloid Precursor Protein Secretases; D010447:Peptide Hydrolases; D051722:ADAM Proteins; D000072197:ADAM10 Protein; C491234:Adam10 protein, mouse; D000072198:ADAM17 Protein; C000606463:Adam17 protein, mouse