Differences and similarities in tyrosine phosphorylation of proteins in platelets from human and pig species.

BACKGROUND: Pigs have been widely used as animal models to study hemostasis. However, there are significant differences when comparing the hemostatic behavior of pig and human platelets.
OBJECTIVE: To investigate signaling through tyrosine-phosphorylation of proteins in pig platelets after activation in suspension or by adhesion under flow conditions, in comparison with human platelets.
METHODS: Activation of platelet suspensions was performed with thrombin (T; 0.1 and 1 U mL(-1)) and type I collagen (Col-I; 20 microg mL(-1)), at two different time points (30 and 90 s). Activation by adhesion was carried out on Col-I-coated coverslips, using citrated whole blood samples perfused through a parallel-plate chamber. RESULTS AND
CONCLUSIONS: Significant differences between pig and human platelets were detected before and after activation. Activation of pig platelets required higher concentrations of thrombin, as well as increased activation times, to achieve similar levels of tyrosine phosphorylation. Proteins p160, p140, p85 and pp62, present in human platelets, were not detected in profiles corresponding to activated pig platelets. A protein of 70 kDa appeared only in pig platelet profiles, p55 was highly phosphorylated, and the phosphorylation levels of some proteins were significantly different from those found in human platelet profiles. In profiles corresponding to adhered pig platelets, p85 and p62 were absent, and p115 appeared highly phosphorylated. As observed in suspension studies, p70 and p55 appeared specifically in adhered pig platelets. Our study shows that the phosphotyrosine proteins involved in the activation of pig platelets are significantly different from those observed in activated human platelets. These findings may help to explain the differing adhesive and cohesive properties of platelets from both species, which should be considered when extrapolating results.