Cytoskeleton protein composition upon platelet stimulation with thrombin in essential thrombocythemia

Structural and functional platelet alterations are present in essential thrombocythemia (E.T.). Platelet aggregation patterns are highly variable; moreover, structural, biochemical and metabolic platelet defects have also been shown. In this study, data on function and structure of platelets from a group of patients affected with E.T. are reported. Since cytoskeleton proteins are involved in activation and aggregation mechanisms, we investigated the cytoskeleton protein composition of resting, activated and aggregated platelets using electrophoretic analysis.

Studies were performed on 13 patients affected with E.T. On the basis of their functional behavior in response to thrombin, patients were divided into two groups: T1 (5 patients) and T2 (8 patients). A group of 11 healthy subjects was examined as control. Washed platelets were stimulated with 0.05 or 0.25 U/mL thrombin in the presence or the absence of EGTA in order to obtain activated or aggregated platelets. Triton-insoluble residues of activated and aggregated platelets were electrophoresed on 4.5-15% linear gradient SDS polyacrylamide gel, visualized by Coomassie blue stain and scanned with a densitometer.

On the basis of the response to thrombin, group T1 was composed of subjects showing completely normal functional behaviour, while group T2 included patients who were more active than controls in response to low thrombin concentrations. By comparing the densitometric data of the two groups of patients it is possible to show that cytoskeleton structures in the T2 group have a significantly higher protein content than normals and than group T1. Platelet treatment with high thrombin concentrations cancels every difference between the two groups of patients with the exceptions of a 33-Kd protein and actin, which remain higher in group T2.

Abnormal platelet function and quantitative cytoskeleton protein content can be correlated in patients affected with E.T. In the platelets of those patients who display higher responsiveness to thrombin, either altered calcium homeostasis or changes in membrane viscosity leading to altered thrombin receptor expression, or both these events, could be present.