Effect of homocysteine on platelet activation induced by collagen

Objective The present study investigated the effects of homocysteine on platelet activation induced by collagen and the downstream signaling pathways potentially involved in these effects. Methods Washed human platelets were incubated with homocysteine and collagen type I. The effects of homocysteine on platelet aggregation and adhesion and the tyrosine phosphorylation of total platelet proteins, Src kinase, and phospholipase-Cγ2 (PLCγ2) were studied. Results Homocysteine (10 to 100 μM) increased collagen-induced aggregation of washed platelets. Upon homocysteine (50 to 100 μM) treatment, platelet deposition to collagen-coated surface was significantly augmented under the low shear rate model (100/s) but not under the high shear rate model (1600/s). Collagen-stimulated total protein tyrosine phosphorylation in platelets was further enhanced by incubation with homocysteine. This effect was almost abrogated by genistein. Homocysteine potentiated collagen-stimulated tyrosine phosphorylation of the Src kinase and PLCγ2, which was partly decreased by integrin β1 blocking antibody. Conclusion Homocysteine (at 10 to 100 μM) potentiates collagen type I induced-platelet activation through signaling components of glycoprotein VI and integrin α2β1 pathway. Our results suggested that upregulation of tyrosine phosphorylation of proteins such as Src and PLCγ2 is involved in the downstream signaling events of homocysteine stimulation in human platelets.