Integrin α6β1 is the Main Receptor for Vascular Laminins and Plays a Role in Platelet Adhesion, Activation and Arterial Thrombosis
Background—Laminins are major components of basement membranes, well located to interact with platelets upon vascular injury. Laminin-111 (α1β1γ1) is known to support platelet adhesion but is absent from most blood vessels, which contain isoforms with the α2, α4 or α5 chain. Whether vascular laminins support platelet adhesion and activation and the significance of these interactions in hemostasis and thrombosis remains unknown.
Methods and Results—Using an in vitro flow assay, we show that laminin-411 (α4β1γ1), laminin-511 (α5β1γ1) and laminin-521 (α5β2γ1), but not laminin-211 (α2β1γ1), allow efficient platelet adhesion and activation across a wide range of arterial wall shear rates. Adhesion was critically dependent on integrin α6β1 and the glycoprotein Ib-IX complex, which binds to plasmatic von Willebrand factor adsorbed on laminins. Glycoprotein VI did not participate in the adhesive process but mediated platelet activation induced by α5-containing laminins. To address the significance of platelet/laminin interactions in vivo, we developed a platelet-specific knock-out of integrin α6. Platelets from these mice failed to adhere to laminin-411, laminin-511 and laminin-521 but responded normally to a series of agonists. α6β1-deficient mice presented a marked decrease in arterial thrombosis in three models of injury of the carotid, aorta and mesenteric arterioles. The tail bleeding time and blood loss remained unaltered, indicating normal hemostasis.
Conclusions—This study reveals an unsuspected important contribution of laminins to thrombus formation in vivo and suggests that targeting their main receptor, integrin α6β1, could represent an alternative antithrombotic strategy with a potentially low bleeding risk.
- Received December 19, 2012.
- Revision received May 6, 2013.
- Accepted May 30, 2013.