C1qTNF-related protein-1 (CTRP-1): a vascular wall protein that inhibits collagen-induced platelet aggregation by blocking VWF binding to collagen.

CTRP-1 is a novel member of the C1qTNF-related protein family containing family characteristic collagen and TNF-like domains and shows marked expression in vascular wall tissue. We observed that recombinant human CTRP-1 specifically bound to fibrillar collagen and blocked collagen-induced platelet aggregation. CTRP-1 completely or partially prevented VWF and GPVI-Fc4 binding to collagen, respectively. However, GPVI-Fc4 failed to compete for the binding of CTRP-1 to collagen. CTRP-1 had no effects on alpha(2)beta(1) integrin I-domain binding to collagen. Using whole human blood under flow at low and high shear rates, CTRP-1 prevented platelets from accumulating on a collagen-coated surface but had no effects on "platelet-rolling" on a surface coated with VWF. These data suggest that CTRP-1 prevents collagen-induced platelet aggregation by specific blockade of VWF binding to collagen. By using the Folts vascular injury model in nonhuman primates (Macaca fascicularis), we were able to demonstrate that CTRP-1 can prevent platelet thrombosis in vivo. This effect was achieved in the absence of changes in activated-clotting time (ACT) and template cut bleeding times, suggesting that CTRP-1 has promising antiplatelet thrombotic activity and most likely acts by pacifying the thrombogenic site of vascular injury.