Published Online
on October 25, 2004

A more recent version of this article appeared on November 2, 2004

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Submitted on March 5, 2004
Revised on May 13, 2004
Accepted on May 21, 2004

Anti-Glycoprotein VI Treatment Severely Compromises Hemostasis in Mice With Reduced ₂₁ Levels or Concomitant Aspirin Therapy

Sabine Grüner MD, Miroslava Prostredna MSc, Barsom Aktas PhD, Alexandra Moers PhD, Valerie Schulte PhD, Thomas Krieg MD, Stefan Offermanns MD, Beate Eckes PhD, and Bernhard Nieswandt PhD^*

From the Rudolf Virchow Center, DFG Research Center for Experimental Biomedicine, University of Würzburg, Würzburg (S.G., M.P., B.A., V.S., B.N.); the Institute of Pharmacology, University of Heidelberg, Heidelberg (A.M., S.O.); and the Department of Dermatology, University of Cologne, Cologne (T.K., B.E.), Germany.

^* To whom correspondence should be addressed. E-mail: bernhard.nieswandt{at}virchow.uni-wuerzburg.de.

Background--Platelet inhibition is a major strategy to prevent arterial thrombosis, but it is frequently associated with increased bleeding because of impaired primary hemostasis. The activating platelet collagen receptor, glycoprotein VI (GP VI), may serve as a powerful antithrombotic target because its inhibition or absence results in profound protection against arterial thrombosis but no major bleeding in mice.

Methods and Results--Mice lacking (-/-) or expressing half-levels (+/-) of the other major platelet collagen receptor, integrin ₂₁, were injected with the anti-GP VI antibody JAQ1 and analyzed on day 5. Anti-GP VI treatment resulted in a marked hemostatic defect in ₂^-/- or ₂^+/- mice, as shown by dramatically prolonged tail bleeding times. Platelet adhesion to collagen was studied in an ex vivo whole-blood perfusion system under high shear conditions. Weak integrin activation by thromboxane A₂ (TxA₂) receptor stimulation restored defective adhesion of anti-GP VI-treated wild-type but not ₂^-/- or ₂^+/- platelets to collagen. This process required the simultaneous activation of the G_q and G₁₃ signaling pathways, as demonstrated by use of the respective knockout strains. Conversely, inhibition of TxA₂ production by aspirin severely compromised hemostasis in anti-GP VI-treated or GP VI/Fc receptor -chain-deficient but not control mice.

Conclusions--Anti-GP VI therapy may result in defective hemostasis in patients with reduced ₂₁ levels or concomitant aspirin therapy. These observations may have important implications for a potential use of anti-GP VI-based therapeutics in the prevention of cardiovascular disease.

Key words: collagen • glycoproteins • receptors • platelets • thrombosis

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