Variation in human platelet glycoprotein VI content modulates glycoprotein VI-specific prothrombinase activity

Glycoprotein VI (GPVI) is a platelet-specific receptor for collagen that figures prominently in signal transduction. An addition to binding to type I and III collagens, GPVI is also bound specifically by collagen-related peptide and convulxin (CVX), a snake venom protein. We developed a quantitative assay of platelet GPVI in which biotin-conjugated CVX binds selectively to GPVI in separated total platelet proteins by a ligand blot procedure. Using this approach, we have documented a 5-fold range in platelet GPVI content among 23 normal healthy subjects. In addition, we have determined that CVX-induced or collagen-related peptide-induced prothrombinase activity is directly proportional to the platelet content of GPVI. A statistically significant correlation was observed at 2 CVX concentrations: 14.7 ng/mL (R-2 = 0.854 and P < 0.001, n = 11) and 22 ng/mL (R-2 = 0.776 and P < 0.001, n = 12). In previous studies, we established a similar range of expression of the integrin collagen receptor alpha (2)beta (1) on platelets of normal subjects. Among 15 donors, there is a direct correlation between platelet alpha (2)beta (1) density and GPVI content (R-2 = 0.475 and P = 0.004). In view of the well-documented association of GPVI with platelet procoagulant activity, this study suggests that the variation in GPVI content is a potential risk factor that may predispose individuals to hemorrhagic or thromboembolic disorders.