Plasma fibronectin concentration: a risk factor for arterial thrombosis?

Accumulation and cohesion of platelets at sites of vascular injury are essential for the formation of the hemostatic plug but also result in thrombosis.1,2 Platelet plug or thrombus formation is initiated by interaction of platelet receptors with components of extracellular matrix (ECM) of injured vessels. Fibronectin is both an ECM component and moderately abundant 460-kDa glycoprotein in blood, present at 300 to 400 g/mL (0.6 to 0.9 mol/L) in plasma and 0.5 g per 3 10 platelets in platelet -granules.3–5 Plasma fibronectin is a dimer of nearly identical 230-kDa subunits (Figure) that can multimerize to the insoluble form found in ECM.6 Because it is a ligand of platelet surface receptors and an ECM component, fibronectin has long been suspected of playing a role in platelet biology.4,5 Interestingly, fibronectin and its type I module, of which there are 12 in fibronectin (Figure), are well characterized to date only in vertebrates.7,8 Therefore, fibronectin seems to be a recent addition to the armamentarium of proteins that function in the vertebrate vasculature.